U.S. patent application number 14/015363 was filed with the patent office on 2014-06-19 for nanoparticulate probe for in vivo monitoring of tissue oxygenation.
This patent application is currently assigned to The Ohio State University Research Foundation. The applicant listed for this patent is The Ohio State University Research Foundation. Invention is credited to Periannan Kuppusamy, Ramasamy P. Pandian, Narasimham L. Parinandi, Jay L. Zweier.
Application Number | 20140170073 14/015363 |
Document ID | / |
Family ID | 34272988 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140170073 |
Kind Code |
A1 |
Kuppusamy; Periannan ; et
al. |
June 19, 2014 |
NANOPARTICULATE PROBE FOR IN VIVO MONITORING OF TISSUE
OXYGENATION
Abstract
A new class of micro- and nano-particulate paramagnetic spin
probes especially useful for magnetic resonance imaging techniques,
including electron paramagnetic resonance (EPR) and magnetic
resonance imaging (MRI). The probes are lithium phthalocyanine
derivative compounds. Also provided are suspensions and emulsions
comprising lithium phthalocyanine derivative probes. Also provided
are noninvasive methods for measuring noninvasive methods of
measuring oxygen concentration, oxygen partial pressure, oxygen
metabolism, and nitric oxide concentration in a specific tissue,
organ, or cell in vivo or in vitro.
Inventors: |
Kuppusamy; Periannan; (New
Albany, OH) ; Pandian; Ramasamy P.; (Columbus,
OH) ; Parinandi; Narasimham L.; (Upper Arlington,
OH) ; Zweier; Jay L.; (Blacklick, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Ohio State University Research Foundation |
Columbus |
OH |
US |
|
|
Assignee: |
The Ohio State University Research
Foundation
Columbus
OH
|
Family ID: |
34272988 |
Appl. No.: |
14/015363 |
Filed: |
August 30, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12688767 |
Jan 15, 2010 |
8568694 |
|
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14015363 |
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|
10935297 |
Sep 7, 2004 |
7662362 |
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12688767 |
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60500714 |
Sep 5, 2003 |
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Current U.S.
Class: |
424/9.3 ;
540/139 |
Current CPC
Class: |
A61K 49/0036 20130101;
A61K 49/20 20130101; B82Y 5/00 20130101; A61K 49/1818 20130101;
G01R 33/62 20130101; G01R 33/60 20130101; A61K 49/10 20130101; G01R
33/5601 20130101; C07F 1/02 20130101 |
Class at
Publication: |
424/9.3 ;
540/139 |
International
Class: |
A61K 49/10 20060101
A61K049/10; C07F 1/02 20060101 C07F001/02 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was funded at least in part by the National
Institutes of Health, grant CA78886. The government may have
certain rights in this invention.
Claims
1. A particulate probe comprising a lithium phthalocyanine
derivative or a radical thereof selected from the group consisting
of: ##STR00019## ##STR00020## wherein R is selected from the group
consisting of O(CH.sub.2).sub.nCH.sub.3, S(CH.sub.2).sub.nCH.sub.3,
O(CH.sub.2).sub.nCH.sub.2OH, O(CH.sub.2).sub.nCH.sub.2NH.sub.2,
O(CH.sub.2).sub.nCH.sub.2SH, and combinations thereof; and, wherein
n is from 1 to 6.
2. The particulate probe of claim 1, wherein the particulate probe
has a size of up to 10 microns.
3. The particulate probe of claim 2, wherein the particulate probe
has a size of less than 0.22 microns.
4. The particulate probe of claim 1, wherein the particulate probe
has been derivatized to be a magnetic resonance imaging (MRI)
probe, an electron spin resonance (ESR) probe, an electron
paramagnetic resonance (EPR) probe, an electron paramagnetic
resonance imaging (EPRI) probe, or a proton electron double
resonance imaging (PEDRI) probe.
5. The particulate probe of claim 1, wherein the probe comprises a
compound of Formula 1 or a radical thereof: ##STR00021## wherein R
is selected from the group consisting of O(CH.sub.2).sub.nCH.sub.3,
S(CH.sub.2).sub.nCH.sub.3, O(CH.sub.2).sub.nCH.sub.2OH,
O(CH.sub.2).sub.nCH.sub.2NH.sub.2, O(CH.sub.2).sub.nCH.sub.2 SH,
and combinations thereof; and, wherein n is from 1 to 6.
6. The particulate probe of claim 1, wherein the probe comprises a
compound of Formula 2 or a radical thereof: ##STR00022## wherein R
is selected from the group consisting of O(CH.sub.2).sub.nCH.sub.3,
S(CH.sub.2)nCH.sub.3, O(CH.sub.2).sub.nCH.sub.2OH,
O(CH.sub.2).sub.nCH.sub.2NH.sub.2, O(CH.sub.2).sub.nCH.sub.2SH, and
combinations thereof; and, wherein n is from 1 to 6.
7. The particulate probe of claim 1, wherein the probe comprises a
compound of Formula 5 or a radical thereof: ##STR00023## wherein R
is selected from the group consisting of O(CH.sub.2).sub.nCH.sub.3,
S(CH.sub.2).sub.nCH.sub.3, O(CH.sub.2).sub.nCH.sub.20H,
O(CH.sub.2).sub.nCH.sub.2NH.sub.2, O(CH.sub.2).sub.nCH.sub.2SH, and
combinations thereof; and, wherein n is from 1 to 6.
8. The particulate probe of claim 1, wherein the probe comprises a
compound of Formula 6 or a radical thereof: ##STR00024## wherein R
is selected from the group consisting of O(CH.sub.2).sub.nCH.sub.3,
S(CH.sub.2).sub.nCH.sub.3, O(CH.sub.2).sub.nCH.sub.20H,
O(CH.sub.2).sub.nCH.sub.2NH.sub.2, O(CH.sub.2).sub.nCH.sub.2SH, and
combinations thereof; and, wherein n is from 1 to 6.
9. A suspension comprising a particulate probe for MR imaging, the
probe having oxygen active centers, wherein the probe is a radical
of a lithium phthalocyanine derivative, and wherein the suspension
is in a medium selected from the group consisting of
nonphysiological media, physiological media, buffers, and
combinations thereof.
10. The suspension of claim 9, wherein the particulate probe is
selected from the group consisting of: ##STR00025## ##STR00026##
wherein R is selected from the group consisting of
O(CH.sub.2).sub.nCH.sub.3, S(CH.sub.2).sub.nCH.sub.3,
O(CH.sub.2).sub.nCH.sub.2OH, O(CH.sub.2).sub.nCH.sub.2NH.sub.2,
O(CH.sub.2).sub.nCH.sub.2SH, and combinations thereof; and, wherein
n is from 1 to 6.
11. The suspension of claim 9, further comprising a stabilizing
agent, wherein the stabilizing agent is selected from the group
consisting of amino acids, synthetic peptides, peptides of natural
origin, proteins, sugars, carbohydrates, nucleic acid homopolymers,
amino acid homopolymers, DNA, RNA, and combinations thereof; and
wherein the stabilizing agent adheres to the radical probe without
blocking the oxygen active centers.
12. The suspension of claim 9, further comprising a stabilizing
medium, wherein the stabilizing medium is selected from the group
consisting of emulsions containing saturated fatty acids; emulsions
containing unsaturated fatty acids; emulsions containing saturated
and unsaturated fatty acids; salts of emulsions containing
saturated fatty acids; salts of emulsions containing unsaturated
fatty acids; salts of emulsions containing saturated and
unsaturated fatty acids; diglycerides; triglycerides; bile salts;
and combinations thereof.
13. The suspension of claim 9, further comprising a phospholipid,
wherein the phospholipid encapsulates the radical probe without
blocking the oxygen active centers.
14. The suspension of claim 13, wherein the phospholipid forms
phospholipid liposomes which encapsulate the radical probe without
blocking the oxygen active centers.
15. The suspension of claim 14, wherein the phospholipid is
selected from the group consisting of cholesterol, phosphatidyl
choline, phosphatidylethanolamine, phosphatidylserine, cardiolipin,
and combinations thereof; and wherein the phospholipid is in the
form of unilamellar or multilamellar liposomes or vesicles.
16. A method of measuring oxygen concentration, oxygen partial
pressure, or oxygen metabolism in a specific tissue or organ in a
subject, the method comprising the steps of: (a) administering at
least one particulate probe according to claim 1 to the subject;
and (b) applying a magnetic resonance (MR) spectroscopy or imaging
technique for measuring O.sub.2 concentration in tissues or organs
of the subject.
17. The method of claim 16, wherein the MR technique is selected
from the group consisting of MRI, ESR, EPR, ERPI, and PEDRI.
18. The method of claim 16, wherein the particulate probe or
radical thereof remains in the subject for at least 180 days.
19. The method of claim 16, wherein the subject is a human
subject.
20. A method of measuring nitric oxide (NO), separately or in
combination with oxygen, in a specific tissue or organ of a
subject, the method comprising the steps of: (a) administering at
least one particulate probe according to claim 1 to the subject;
and (b) applying a magnetic resonance (MR) spectroscopy technique
for measuring NO concentration in tissues or organs of the subject.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of copending application
Ser. No. 12/688,767, filed Jan. 15, 2010, which is a continuation
of application Ser. No. 10/935,297, filed Sep. 7, 2004, now U.S.
Pat. No. 7,662,362, which claims the benefit of U.S. Provisional
Application No. 60/500,714, filed Sep. 5, 2003, the disclosure of
each of which is expressly incorporated by reference herein.
BACKGROUND OF THE INVENTION
Technical Field
[0003] Over the last decade, it has become clear that cigarette
smoking induces lung cancer and vascular disease. It is a major
risk factor in the occurrence of heart attack and stroke. Vascular
disease leads to tissue damage including heart attack and stroke
and is by far the leading cause of morbidity and mortality in the
United States. Tobacco use leads to tissue injury in the lungs,
heart and vasculature and is implicated in approximately 20% of all
deaths in the United States. Tobacco induced peripheral vascular
disease results in a broad range of medical complications including
vascular insufficiency, claudication, stasis ulcers, wound
formation, impaired wound healing and chronic wounds.
[0004] Cigarette smoke has a very high content of free radicals,
molecules with unpaired electron spin, that are highly reactive and
once present in cells and tissues induce lipid, protein and DNA
damage. These free radicals as well as secondary oxygen and
nitrogen centered radicals are the key radical species that trigger
tobacco-induced carcinogenesis, as well as cardiovascular and lung
injury. Oxygen radicals can trigger an inflammatory response
through leukocyte chemotaxis and activation that in turn results in
a vicious cycle of further oxidant formation and inflammation.
Investigators of this program have demonstrated that oxygen
radicals induce cellular proliferation, a key process in the
pathogenesis of cancer and atherosclerosis [5].
[0005] In just over two decades the advent of magnetic resonance
imaging (MRI) has revolutionized the practice of medicine. At an
ever-accelerating rate MRI has achieved breakthroughs first in
enabling high-resolution anatomical imaging of tissue abnormalities
in disease and more recently alterations in organ function. With
the advent of molecular medicine and targeted therapeutics as well
as the breakthroughs in the sequencing of the human genome, it has
been realized that potentially the next even more powerful horizon
for magnetic resonance imaging is in the imaging of molecular and
gene expression that will enable the early detection or prevention
of disease as well as facilitate the treatment and cure of existing
illness.
[0006] Electron paramagnetic resonance (EPR) has advantages over
proton NMR in that it is inherently over 1,000 times more sensitive
on a spin basis and furthermore, for a given frequency,
measurements may be performed at much lower magnetic fields
enabling the use of low-cost magnet systems. Over the last several
years, it has been shown that the electron spin-based technique of
EPR imaging (EPRI) can provide high sensitivity and high resolution
images of paramagnetic materials. For example at 1200 MHz it was
shown that concentrations as low as 10 nM could be detected for a
typical nitroxide spin label and this sensitivity is at least two
orders of magnitude above that achievable even with ultra
high-field proton MRI [1]. In addition, it was shown that
high-resolution 3D images may be obtained with submillimeter
resolution. In addition to direct EPR detection of paramagnetic
spin probes, the hybrid EPR/NMR technique of Proton Electron Double
Resonance Imaging (PEDRI) can also detect paramagnetic probes by
the marked Overhauser enhancement observed in proton MRI signal
seen upon irradiation of the electron spin. Enhancements of over
100 fold may be achieved. These enhancements translate into
markedly improved image quality, contrast and resolution in
biological tissues. With this marked enhancement, proton
magnetization and image quality even at relatively low fields can
exceed that of the highest field MRI systems. For example, in
principle, PEDRI image quality at 0.2 T could exceed that at 20 T,
if indeed such an ultra high-field system could be built.
[0007] With recent technological advances, it has become possible
to image these critical free radical mediators of disease using
novel magnetic resonance imaging techniques. Advances in the
magnetic resonance imaging techniques of in vivo Electron
Paramagnetic Resonance Imaging (EPRI) and Proton Electron Double
Resonance Imaging (PEDRI) have enabled the imaging of these
critical mediators of disease and the redox stress they cause in
living animals and most recently in man [2, 3, 6, 7]. These MR
techniques along with new types of spin probes and spin traps as
well as innovative nanoparticulate probes have enabled the imaging
of free radicals, oxygen and nitric oxide [1, 8-13]. These
breakthroughs have the potential to revolutionize the diagnosis and
treatment of human disease. Beyond their diagnostic power, spin
traps have great potential for the treatment of disease since they
can trap or scavenge free radicals preventing radical-induced
molecular and cellular damage. Free radicals, both extrinsic as
from cigarette smoke, or intrinsic, from inflammatory stress, are
central in the pathogenesis of human disease including: heart
attack, stroke, cancer, neurodegenerative diseases,
emphysema/obstructive pulmonary disease as well as the process of
aging. The ability to trap and scavenge these critical mediators of
disease has the potential to revolutionize current medical
diagnosis and treatment and provide the long-awaited cures to a
variety of the diseases that have plagued mankind.
[0008] While a great wealth of information may be obtained from the
imaging of intrinsic protons, to achieve MR-based imaging of
molecular and gene expression, there is a critical need for new
imaging agents that may be designed or targeted to visualize
specific molecular targets. There is also a need for probes that
can be tagged to proteins or DNA, enabling generalized biomolecular
and gene imaging. There is further a need, in addition to detecting
these materials through their effects on proton relaxation, for the
ability to directly detect paramagnetic materials using the MR
technique of Electron Paramagnetic Resonance (EPR) or other MR
techniques. Additionally, there is a need for new particulate
probes that may be used to accurately determine oxygen
concentration in cells.
BRIEF SUMMARY OF THE INVENTION
[0009] The present invention provides a new class of particulate
probes that are especially useful for magnetic resonance imaging
techniques. The particulate probes are nanoparticulate and
microparticulate probes comprising paramagnetic spin probes that
are especially suitable for use with magnetic resonance (MR)
techniques, particularly, but not limited to, electron paramagnetic
resonance (EPR) and magnetic resonance imaging (MRI). The
nanoparticulate and microparticulate probes comprise radicals of
lithium phthalocyanine derivative compounds, which include lithium
phthalocyanine derivatives, lithium naphthalocyanine derivatives,
and lithium anthraphthalocyanine derivatives.
[0010] The probes preferably have a size of 10 microns or less,
more preferably from 0.22 to 10 microns, and for intravenous
applications, even more preferably less than 0.22 microns. The
probes may be used with a variety of MR spectroscopy and MR imaging
techniques, including but not limited to magnetic resonance imaging
(MRI); electron spin resonance (ESR); electron paramagnetic
resonance (EPR); electron paramagnetic resonance imaging (EPRI);
and proton electron double resonance imaging (PEDRI).
[0011] The probes of the present invention comprise ligands,
dilithium complexes, and lithium radicals. Some preferred dilithium
complexes are shown as compounds 1-6:
##STR00001## ##STR00002##
wherein R is selected from the group consisting of
O(CH.sub.2).sub.nCH.sub.3, S(CH.sub.2).sub.nCH.sub.3,
O(CH.sub.2).sub.nCH.sub.2OH, O(CH.sub.2).sub.nCH.sub.2NH.sub.2,
O(CH.sub.2).sub.nCH.sub.2SH, and combinations thereof; wherein n is
1-6. Preferred lithium radicals are obtained from these dilithium
complexes by electrochemical or chemical oxidation.
[0012] Also provided are suspensions and emulsions comprising
lithium phthalocyanine derivative radicals, which have an oxygen
center, making them useful for various in vivo and in vitro
measurements. The suspensions of the present invention are in a
media selected nonphysiological media, physiological media,
buffers, and combinations thereof. The particulate probes are
selected from the group consisting of:
##STR00003## ##STR00004##
wherein R is selected from the group consisting of
O(CH.sub.2).sub.nCH.sub.3, S(CH.sub.2).sub.nCH.sub.3,
O(CH.sub.2).sub.nCH.sub.2OH, O(CH.sub.2).sub.nCH.sub.2NH.sub.2,
O(CH.sub.2).sub.nCH.sub.2SH, and combinations thereof; and wherein
n is 1-6; and combinations thereof.
[0013] The suspensions of the present invention further comprise a
stabilizing agent and/or a stabilizing media. Some preferred
stabilizing agents are selected from, but not limited to amino
acids, synthetic peptides, peptides of natural origin, proteins,
sugars, carbohydrates, nucleic acid homopolymers, amino acid
homopolymers, DNA, RNA, other bipolymers, and combinations thereof.
The stabilizing agents adhere to the radical probe without blocking
the oxygen active centers. Some preferred stabilizing media
include, but are not limited to emulsions containing saturated
fatty acids; emulsions containing unsaturated fatty acids;
emulsions containing saturated and unsaturated fatty acids; salts
of emulsions containing saturated fatty acids; salts of emulsions
containing unsaturated fatty acids; salts of emulsions containing
saturated and unsaturated fatty acids; diglycerides; triglycerides;
bile salts; and combinations thereof.
[0014] The suspensions of the present invention may further contain
phospholipid, wherein the phospholipid encapsulates the radical
probe without blocking the oxygen active centers. The phosholipid
may form phospholipid liposomes which encapsulate the radical probe
without blocking the oxygen active centers. Some preferred
phospholipids include, but are not limited to cholesterol,
phosphatidyl choline, phosphatidylethanolamine, phosphatidylserine,
cardiolipin, and combinations thereof; and wherein the phospholipid
is in the form of unilamellar or multilamellar liposomes or
vesicles.
[0015] Further provided are noninvasive methods of measuring oxygen
concentration, oxygen partial pressure, or oxygen metabolism in a
specific tissue or organ in a subject, the method comprising the
steps of: (a) administering a lithium phthalocyanine derivative
radical probe to the subject; and (b) applying a magnetic resonance
(MR) spectroscopy technique capable of measuring O.sub.2
concentration in tissues or organs of the subject. Additionally,
the probes of the present invention may be used to measure nitric
oxide (NO) concentration, separate from or along with oxygen
concentration, using the same method.
[0016] Preferred lithium phthalocyanine derivative radical probes
include, but are not limited to:
##STR00005## ##STR00006##
wherein R is selected from the group consisting of
O(CH.sub.2).sub.nCH.sub.3, S(CH.sub.2).sub.nCH.sub.3,
O(CH.sub.2).sub.nCH.sub.2OH, O(CH.sub.2).sub.nCH.sub.2NH.sub.2,
O(CH.sub.2)nCH.sub.2SH, and combinations thereof; wherein n is 1-6;
and combinations thereof.
[0017] The lithium phthalocyanine derivative radical probes are
useful for MR spectroscopy and MR imaging, particularly, but not
limited to MRI, ESR, EPR, ERPI, and PEDRI. The probes may be
delivered to a subject intravenously or may be implanted into
tissue. The probes are useful for studying tissues, organs or
cells. When the radical probe is delivered to the subject
intravenously, it may be delivered as a suspension or emulsion. The
probe may also be delivered directly to the tissue or organ of
interest. When injected into the tissue of interest, the radical
probes may remain active in a subject for up to 12 months, and
preferably remain active for more than 180 days, allowing study of
the same tissue or organ over an extended period of time.
[0018] The radical probes may be attached to a peptide or
glycoconjugate that has specific affinity for cell surface markers,
wherein the radical probe acts as a cell migration marker. The
radical probes may also to an antibody, wherein the antibody has an
affinity to cell surface proteins that lead as markers of cell
migration, cell division, and cell death. The radical probes may
also be internalized in live cells, either in vivo or in vitro for
the study of intracellular oxygenation, cellular hypoxia, cellular
hyperoxia, cell division, cellular migration, or metastatis. The
radical probes may also be utilized to study the kinetics of
enzymes that involve oxygen consumption and release in organs,
tissues, or cells, in vivo or in vitro. The subjects may be any
subject of interest. Preferably, the subject is a human subject.
The methods of the present invention may also be used to study
microbial oxygen metabolism.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1: Molecular structure of lithium
octa-n-butoxynaphthalocyanine (LiNc-BuO) radical. The neutral
radical is paramagnetic and prepared as a microcrystalline
solid.
[0020] FIG. 2: EPR spectrum of LiNc-BuO nanocrystalline powder
suspended in PBS. The spectrum (A) was measured at X-band (9.78
GHz) from a 10 .mu.L of the suspension equilibrated with 10%
(pO.sub.2: 76 mmHg) oxygen at room temperature. The instrumental
settings were: microwave power, 1 mW; modulation amplitude, 63 mG;
modulation frequency, 100 kHz; receiver time constant, 82 msec;
acquisition time, 60 sec (4.times.15 sec scans); A single sharp
peak is observed with peak-to-peak width (Ab.sub.pp) of 852 mG.
Also superimposed on this spectrum is a computer fit that was
calculated assuming Lorentzian line-shape. The difference between
the measured spectrum and the Lorentzian fit is shown in (B) at
4.times. magnification. The difference curve shows only noise
suggesting that the line-shape is 100% Lorentzian (R2=0.9999).
[0021] FIG. 3: Effect or oxygen concentration (pO.sub.2) on the
peak-to-peak EPR line-width (Ab.sub.pp) of LiNc-BuO particulates.
The particulates were suspended in PBS equilibrated with mixtures
of oxygen/nitrogen gases. The spectra were acquired as described in
FIG. 2. The line-width increases linearly with pO.sub.2 in the
range 0 to 760 mmHg (corresponding to 0-100% oxygen at I
atmospheric pressure) with an anoxic at 0% oxygen) line-width of
210 mG and slope (oxygen sensitivity) of 850 mG/mmHg. The effect or
oxygen on the line-width was highly reversible and reproducible
under a variety of conditions.
[0022] FIG. 4: Long-term stability and response to oxygen, in vivo.
The stability of LiNc-BuO particulates implanted in the
gastrocnemius muscle (upper hind leg) of C3H mice was studied up to
180 days. The plot shows repeated measurements of pO.sub.2 from a
single mouse. The response of particulates to oxygen was checked by
temporarily constricting blood-flow to the leg. The data shows that
the particulates are stable and responsive in the live tissues up
to 6 months. The spectra shown above were from a mouse on day 180
after implantation of the particulate. The spectra were acquired as
described in FIG. 2.
[0023] FIG. 5: In vivo measurements of pO.sub.2 from tumor and
normal gastrocnemius muscle tissues in mice as a function of tumor
growth in mice with RIF-1 tumor. LiNc-BuO particulates were
unplanned in the tumor (RIF-1) on right leg and normal muscle on
left leg and the tissue. pO.sub.2 values were repeatedly measured
on the same animals up to 8 days after implantation of the
particulates. Mean values of pO.sub.2 (A) and tumor volume (B)
recorded repetitively from 7 mice are shown. The tumor pO.sub.2
decreased continuously to .about.2 mmHg on day 8 after
implantation, while the normal muscle pO.sub.2 remained almost
constant (17.6.+-.25 mmHg) during the same period.
[0024] FIG. 6: Internalization of the LiNc-BuO particulates in
cells. The particulates (<2 .mu.m) were coincubated with the
human arterial smooth muscle cells for 72 h followed by repeated
washings as described in the Detailed Description of the Invention.
The cells were photographed under an inverted microscope while
still adherent to the substratum of the 35 mm dish. The LiNc-BuO
particulates are seen as dark green crystals inside cells.
[0025] FIG. 7: EPR spectra of LiNc-BuO microcrystalline powder
suspended in saline at various partial pressures of molecular
oxygen. The spectra were measured at X-band (9.78 GHIz) from a 20
.mu.L of the suspension equilibrated with 0% (pO.sub.2 mmHg) and
20.9% (pO.sub.2: 159 mmHg) oxygen at room temperature. The
instrumental settings were: microwave power, 1 mW, modulation
amplitude, 63 mG, modulation frequency 100 kHz, receiver time
constant 82 msec; acquisition time 60 sec (4.times.15 sec scans). A
single sharp peak is observed with a peak-to-peak width
(.DELTA.B.sub.pp) of 210 mG at 0% oxygen and 1550 mG at 20.9%
oxygen.
[0026] FIG. 8: Time dependence of pO.sub.2 in mouse aortic
endothelial cell suspensions exposed to various agents and
treatments. The pO.sub.2 measurements were performed on 20,000
cells taken in a 20 .mu.L capillary tube (id: .times..mu.m; cell
density: 1.times.10.sup.6 cells mL) by EPR spectroscopy utilizing
LiNc-BuO oximetry probe. The capillary tube was sealed at both ends
and pO.sub.2 measurements were performed continuously for up to 20
min. (a) Control (b) KCN (100 .mu.M), (c) rotenone (100 .mu.M), (d)
DPI (100 .mu.M), (e) menadione (50 .mu.M), (f) LPS (10 .mu.g/ml).
Values at each time point are expressed as mean.+-.SD of 4-5
independent experiments. The solid lines through each data set show
the linear variation of pO.sub.2, which suggests constancy in
oxygen consumption as a function of time.
[0027] FIG. 9: Effect of menadione on the rate of oxygen
consumption by mouse aortic endothelial cells. The measurements
were performed as described in the Detailed Description and oxygen
consumption rates are calculated from the slope of change of
pO.sub.2 with time. Cells were treated with 10, 50, 100 and 200
.mu.M concentration of menadione and the measurements were started
immediately after adding menadione. Values are .+-.SD of 5
experiments. *p<0.001 versus control; **p<0.001 versus
control.
[0028] FIG. 10: Effect of lipopolysaccharide (LPS) on the rate of
oxygen consumption by MAECs. The measurements were performed as in
FIG. 2 and oxygen consumption rates were calculated from the slope
of change of pO.sub.2 with time. Cells (1.times.10.sup.6 Cells/ml)
were treated with 10 or 20 .mu.g/ml concentration of LPS and
measured either immediately after mixing or after 2 h or incubation
of the mixture under aerobic conditions. Values are mean.+-.SD of 5
experiments. *p<0.05 versus control.
[0029] FIG. 11: Oxygen consumption rates in mouse aortic
endothelial cell suspensions exposed to various agents and
treatments. Cells (1.times.10.sup.6 Cells/ml) were treated with
menadione (50 .mu.M), LPS (10 .mu.g/ml), KCN (100 .mu.M), rotenone
(100 .mu.M) and DPI treatment. Values are mean.+-.SD of 5
experiments. *p<0.001 versus control; **p<0.01 versus
control.
[0030] FIG. 12: EPR spectrum of a suspension of LiNc-BuO and TAM
(10 .mu.M) in PBS (pH 7.4) equilibrated with room air (20.9%
oxygen). The original spectrum (top) is a composite of two
components: a sharp peak from TAM (g+2.0030) and a broad peak from
KiNc-BuO (g+2.0024). The additional peaks indicated by * on both
sides of the spectrum are due to 13 C hyperfine from TAM (35). EPR
data acquisition parameters were: modulation amplitude, 100 mG;
microwave power 1 mW; time constant, 8-msec, scan time, 15 s. The
computer fit (middle) shows the decomposition of the original
spectrum into two components, that the LiNc-BuO and TAM. The
computer fit (sum of the two components) is superimposed onto the
original spectrum. The residual (bottom) curve shows the difference
between the original and computer fit (R.sup.2=0.9977).
[0031] FIG. 13: Photomicrograph of bovine lung microvascular
endothelial cells showing internalization of the LiNc-BuO
microparticulates. The LiNc-BuO particulates are seen as dark green
crystals inside the cells.
[0032] FIG. 14: Effect of oxygen concentration (pO.sub.2) on the
peak-to-peak EPR line-width (.DELTA.Bpp) of LiNc-BuO and TAM.
Measurements were made independently of LiNc-BuO microcrystalline
particulates suspended in saline and TAM (10 .mu.M) in PBS
equilibrated with mixtures of oxygen/nitrogen gases. The spectra
were acquired as describe din FIG. 1. The line-width increases
linearity of pO.sub.2 in the range of 0 to 160 mmHg) with an anoxic
(0% oxygen) line-width of 210 mG and slope (sensitivity) of 8.5
mG/mmHg for LiNc-BuO and an anoxic line-width of 148 mG and slope
(sensitivity) of 0.36 mG/mmHg for TAM.
[0033] FIG. 15: Extracellular and intracellular measurement of
pO.sub.2 in bovine lunch microvascular endothelial cells (BLMVECs).
Intracellular pO.sub.2 was measured using internalized LiNC-BuO
particulated in BLMECs. The extracellular pO.sub.2 was measured
simultaneously using 10 .mu.M TAM. Measurements were made at room
air (20.9% or pO.sub.2: 159 mmHG) and at 7.5% (pO.sub.2: 57 mmHG)
oxygen. Values are mean.+-.SD of 5 experiments. *p<0.001 versus
extracellular pO.sub.2.
[0034] FIG. 16: Effect of menadione and cyanide on intracellular
and extracellular pO.sub.2 in BLMVECs. The pO.sub.2 measurements
were made in cells treated with menadione (50 .mu.M) and potassium
cyanide (100 .mu.M). The measurements were performed as in FIG. 4.
Values are mean.+-.SD of 5 experiments.
[0035] FIG. 17: Simplified molecular structure of Li(OBu).sub.8Nc
used for the DASH analysis. Eighty eight hydrogens and one lithium
were removed from the original molecule. The side lengths of the
naphthalocyanine rings are 17.9.about.18.0 .ANG. in NiNc, CuNc, and
ZnNc.
[0036] FIG. 18: Positional parameters obtained from initial DASH
trial runs where no constraints were used. Black open circles are
from trials using Li(OBu).sub.8Nc (20 results with lowest
.chi..sub.pro.sup.2, out of 45 trials) and open triangles are form
the trials using Li(OBu).sub.8Nc (reproducibility, 10/10),
Li(OMe).sub.8Nc (8/10), Li(OEt).sub.8Nc (9/10), and Li(OPr).sub.8Nc
(6/10). For the groups marked as I and II, average and deviations
of the coordinates are (0.051.+-.0.021, 0.026.+-.0.019,
0.368.+-.0.031) and (0.443.+-.0.019, 0.024.+-.0.023,
0.151.+-.0.023), respectively.
[0037] FIG. 19: Simulated annealing refinement profile of the XRPD
patter for Li(OBu).sub.8Nc. Calculated (solid line) and observed
(cross) data are overlapped. Bragg reflection positions and the
difference pattern are shown below.
[0038] FIG. 20: Stacking patter of Li(OBu).sub.8Nc as determined
from the DASH analysis, viewed along (a) a-, (b) b-, and (c)
c-axes. The rectangles represent the cross sections of infinite
channels propagating in the viewing direction (their sizes are
mentioned in text).
[0039] FIG. 21: (Top) LeBail and (bottom) Pawley fits to the XRPD
pattern of Li(BuO).sub.8Nc. Observed (cross) and calculated data
(solid line) are overlapped, and the difference pattern and
expected peak positions are shown. In the LeBail fit, background is
also shown.
[0040] FIG. 22: Simulated annealing refinement profile of the XRPD
pattern for Li(OBu).sub.8Nc, between 3.2-32.degree.. Calculated
(solid line) and observed (cross) data are overlapped. Bragg
reflection positions and the difference pattern are shown
below.
DETAILED DESCRIPTION OF THE INVENTION
[0041] NMR-based magnetic resonance imaging, MRI, enables
visualization of the distribution of nuclear spins, mostly protons,
in tissues. It has become a `gold standard` for noninvasive
diagnosis of tissue abnormalities. Electron paramagnetic resonance
imaging (EPRI) is a parallel technology, which enables
visualization of the distribution of electron spins (free radicals)
in tissues. EPR is inherently about 3 orders of magnitude more
sensitive than NMR. It can directly detect and image relatively
stable free radicals as well as labile radicals such as
oxygen-derived superoxide and hydroxyl free radicals that are
implicated in the pathogenesis of oxidant injury [14-21]. Recently,
EPR methods have also been developed to enable detection of nitric
oxide [22-24]. In addition, spin probes may be used to image
cellular radical metabolism and redox state, membrane structure and
fluidity, oxygen, pH, temperature, protein structure, and cell
death. With spin labeling of molecules and cells, noninvasive
mapping of their localization in tissues may be performed [8, 9,
12, 25-34]. Recent advances in magnetic resonance instrumentation
and probe design have enabled integration of these two modalities
into a new technology, proton electron double resonance imaging
(PEDRI) which is capable of co-imaging free radicals and protons
[4, 7, 35].
[0042] A major power of EPR technology is its ability to precisely
measure O.sub.2 in tissues [6, 9, 31, 36-40]. This `EPR oximetry`
technique uses spin probes whose EPR line-widths are highly
sensitive to O.sub.2 concentration. It enables precise and accurate
measurements of O.sub.2 concentrations in tissues, noninvasively
and repeatedly over periods of weeks from the same site. This
approach uses fine crystals (nanoprobes) of phthalocyanine-based
radical molecules that are stacked producing a very strongly
exchanged-narrowed EPR line-shape, that is highly sensitive to
local O.sub.2 concentration [9, 40, 41]. These nanoprobes are
biocompatible and stable in tissues. They may be implanted at the
desired site or with a suitable coating may be infused into the
vasculature for targeted delivery to tissues. In addition, we
recently demonstrated that these nanoprobes may be internalized in
cells enabling measurement of intracellular pO.sub.2 with milliTorr
accuracy.
[0043] Cellular redox measurements are performed using
redox-sensitive nitroxyl molecules that are soluble spin probes
[36]. A variety of nitroxyl molecules capable of reporting cellular
redox levels including total redox, thiols, and glutathione may be
used. These molecules are nontoxic and are converted to nonradical
species and cleared from the system within hours after
infusion.
[0044] Overall, the novel in vivo MR techniques of EPRI and PEDRI
can provide important information about tissue radical generation,
oxygenation, nitric oxide production, metabolism and injury as well
as therapeutic delivery. With the recognized importance of free
radicals, oxygen and NO in disease this information is of crucial
importance. These techniques also can enable high sensitivity
measurement of molecular expression, gene expression, cell therapy
and the delivery of a broad range of molecular therapeutics. These
major advances in molecular and genetic imaging have the potential
to revolutionize medical diagnosis and treatment.
ABBREVIATIONS
[0045] The following abbreviations are used herein:
AAPH--2,2'-azobis(2-amindinopropane)dihydrochloride;
CRISP--Crystalline internal spin probe; DMEM--Dulbecco's modified
Eagle medium; EPR--Electron paramagnetic resonance; FBS--Fetal
bovine serum; HASMC--Human arterial smooth muscle cells;
LiNc--Lithium naphthalocyanine; LiNc-BuO--Lithium
5,9,14,18,23,27,32,36-octa-n-butoxy-2,3-naphthalocyanine;
LiPc--Lithium phthalocyanine; MEM--Minimal essential medium;
Nc-BuO--5,9,14,18,23,27,32,36-octa-n-butoxy-2,3-naphthalocyanine;
PBS--Phosphate-buffered saline; pO.sub.2--Partial pressure of
oxygen; RIF-1--Radiation-induced fibrosarcoma-I;
SNAP--S-nitroso-N-acetyl-penicillamine; and TAM--Triarylmethyl.
[0046] The probes of the present invention are lithium
phthalocyanine derivatives. As used throughout the specification
and claims, "Lithium phthalocyanine derivatives" includes, but is
not limited to lithium phthalocyanine derivatives and radicals
thereof; lithium naphthalocyanine derivatives and radicals thereof;
and lithium anthraphthalocyanine derivatives and radicals thereof.
The probes of the present invention are designed or targeted to
visualize specific molecular targets. These probes may also be
tagged to proteins or DNA enabling generalized biomolecular and
gene imaging. The probes may be implanted at a desired site or
coated with a suitable coating formulation may be infused into the
vasculature for targeted delivery to tissues to facilitate study of
a tissue of interest. The probes of the present invention may also
encapsulated in phospholipid liposomes (e.g. phosphatidylcholine
and cholesterol) to facilitate rapid uptake into the cells, which
are delivered into cells engineered for tissue or wound repair.
[0047] The lithium phthalocyanine derivatives are particulate, and
have low solubility in aqueous solutions as well as in common
organic solvents, making them particularly suitable for the
following applications: (i) as an oxygen-sensing EPR probe for
accurate determination of concentration of oxygen and (ii) as a
molecular and cellular imaging probe for EPR/MRI methods. The
probes also have applications in the field of biomedical research
and clinical studies, including, but not limited to: (1)
determination of oxygen concentration in tissues; (2) determination
of oxygen concentration in cells; (3) determination of oxygen
consumption by cells; (4) targeted intracellular delivery of
particulate oximetry probes; and (5) DNA or protein-targeted spin
probes. Additional applications of the nanoparticulate probes of
the present invention include cell-tagging and cell-tracking
applications; studying cancer metastasis in experimental models;
tissue engineering (stem cell research); tagging antibody; MRI
contrast agent; implantable oxygen-sensor in peripheral vascular
disease; oxygen-sensor in wound healing applications; and
implantable oxygen-sensor in cancer therapy.
[0048] Synthesis of Micro and Nanoparticulate Oximetry Spin Probes
Based on Phthalocyanine Macrocycles:
[0049] Mono-lithiated phthalocyanine and naphthalocyanine
derivatives are synthesized using chemical or electrochemical
procedures as we reported previously [11, 42]. The synthesis is set
forth in the following synthetic schemes:
##STR00007##
##STR00008##
##STR00009##
##STR00010##
##STR00011##
##STR00012##
##STR00013##
##STR00014##
##STR00015##
##STR00016##
##STR00017##
##STR00018##
The spin probes are prepared as microcrystalline particles and
characterized using X-ray diffraction and magnetic susceptibility
techniques. The particles are suspended in complete medium
containing 10% serum and sonicated with a probe sonicator.
Alternatively the particles may be sonicated in presence of 1 mg/ml
dioleoylphosphatidylcholine or lecithin to entrap the particles in
liposomes and filtered through 0.22-10 micron filters to separate
them according to the size. The EPR properties including oxygen
sensitivity of the suspension are verified for each batch.
[0050] Several approaches known to those skilled in the art are
used to further develop stable nanoprobe suspensions for iv or
other systemic use. The following are taken into consideration in
the development: biocompatibility (non-toxicity), preservation of
oxygen sensitivity, and long-term shelf- and tissue stability in
solutions of high ionic strength. In general, the suspension
formulation requires a stabilizing agent, which adheres to the
surface of the particle probe without blocking the oxygen active
centers, which are responsible for the oxygen adsorption. The
conformation and surface distribution of the agent or additive that
is used to stabilize the suspension is taken into consideration.
Fabrication of fine suspensions then requires milling of the probe
particle using a ball mill and a homogenizer. Conventional methods
of preparation of water-based colloidal dispersions using
water-soluble stabilizers (low molecular weight surfactants like
heparin and Tween; water-soluble polymers like pluriol), similar to
described by Gallez et al. [43, 44], may be used. Alternatively,
dispersions may be prepared using organic solvent-based systems
with water-insoluble stabilizers, and subsequently transforming
them to aqueous system by adding water and removing the organic
solvent. Another approach is to synthesize submicrometer-sized
silica oxide suspension (silica gel) in the presence of the probe
particles. This can produce coaggregates of the probe and silica
dioxide. Smaller particles of silica gel can form an
oxygen-permeable shell and thus protect the probe particles from
forming bigger aggregates. Submicron <0.22 micron) particulates
with biocompatible coating formulations will be developed for iv
infusion.
[0051] Targeted Intracellular Delivery of Particulate Oximetry
Probes:
[0052] Specially synthesized particulate oximetry nanoprobes,
encapsulated in phospholipid liposomes (phosphatidylcholine and
cholesterol) to facilitate rapid uptake into the cells, may be
delivered into cells engineered for tissue or wound repair.
Ligand-targeted liposomes and lipoplexes are highly useful as
cargoes to deliver the nanoprobes to designated cell types in vivo
[45-51]. Different types of ligands, such as receptors, peptides,
vitamins, oligonucleotides or carbohydrates may be positioned onto
the liposomal surface which will enhance the binding affinity
[52-55]. The nanoprobe containing cells are characterized using
optical confocal microscopy and EPR spectroscopy. Internalization
techniques may be developed for the different stem or other cells
to promote wound repair and used to image intracellular oxygen
concentration, cell migration and proliferation of the targeted
cell therapy.
[0053] DNA or Protein-Targeted Spin Probes:
[0054] As per the approach of Kursa et al. [56], novel shielded
transferrin-polyethylene glycol-polyethylenimine DNA or protein
complexes ligated with EPR probes (redox, NO, pH and O.sub.2
probes) may be developed and used to study gene or peptide/protein
delivery and concomitant localized oxygen and radical metabolic
events. The use and ability of nonviral DNA complexes to deliver
genes to cells and tissues in vivo offers a potential for delivery
of DNA specific EPR probes [51, 57, 58]. Cell replication and cell
cycle-specific gene expression in concert with oxygen and radical
metabolism may be studied by delivering complexes that will be
generated by mixing plasmid DNA, linear polyethylenimine, PEG and
transferrin that provides a ligand for receptor-mediated cell
uptake [57]. Cells in culture or in situ may be loaded with these
complexes with a specific therapeutic gene (DNA) of interest and
the oxidative and redox metabolism mapped.
[0055] Toxicology and Pharmacokinetic Evaluations as Required for
IND and FDA Approval:
[0056] Many of the paramagnetic molecules under development in this
program have been extensively tested in animals and some even in
human studies. Even at very-high applied concentrations of up to
150 mM no toxicity has been seen. With carbon-based micro and
nanoparticulates there is a history of human application as in the
marking of surgical fields with India ink. The naphthalocyanine
particulates of the present invention have been chronically studied
in small animals and no adverse effect or toxicity has been seen
acutely or up to 3 months. We recognize the need for
pharmacokinetic and toxicological testing particularly for systemic
formulations.
[0057] Derivatives of Phthalocyanines:
[0058] Phthalocyanine is planar macro cycles that contain four
isoindole units and present 18 pi electrons cloud delocalized over
an arrangement of alternating carbon and nitrogen atoms. The unique
property of phthalocyanine comes from the electron delocalization,
which can be easily modified by introducing a variety of structural
alterations.
[0059] In addition to the prototype probe (LiNc-BuO) the present
invention encompasses a series of substituted derivatives (R
groups) and benzo-annulated derivatives (phthalo, naphthalo, and
anthraphthalo) as illustrated in structures 1-18. In general, the
derivatives of the present invention include: (i) Four different R
groups: O--(CH2)n-CH.sub.3, where n=1-6;
O--(CH.sub.2).sub.n--CH.sub.2OH, where n=1-6;
O--(CH.sub.2).sub.n--CH.sub.2NH.sub.2, where n=1-6;
O--(CH.sub.2).sub.n--CH.sub.2SH, where n=1-6; and combinations
thereof; (ii) two different attachments/positions: Para and Ortho,
and (iii) three different benzo-annulations: phthalocyanine,
naphthalocyanine, and anthraphthalocyanine.
[0060] The compounds may be synthesized using any appropriate
chemical or electrochemical procedures. The synthetic procedures
will be optimized for each specific case. Syntheses for compounds
1-18 are shown, and suitable modifications can easily be made by
those skilled in the art.
[0061] The Design of Lithium Phthalocyanine Derivatives as
Oxygen-Sensors:
[0062] Lithium metal has high mobility and smaller size compared to
other alkali metals such as Na or K. This enables the metal ion to
site in the center of the macro cycle allowing very tight stacking
of the molecules in the crystal. This close packing results in
highly exchange-coupled system with extremely narrow EPR lineshape.
The benzo-annulations extend the delocalization of the unpaired
electron in the molecule, which may reduce dipole-dipole
interactions between the unpaired electrons in the stacked
molecules. The absence or minimization of dipole-dipole interaction
is highly preferred to obtain pure Lorentzian lineshapes. The
substituents (R groups) are used as handles (i) to modulate the
molecule-molecule distance in the crystal enabling different
lineshape sensitivities to oxygen, (ii) to impart hydrophobicity to
the particulate so that the material can be internalized or
stabilized in biological tissues, (iii) to vary the inter-stack
bore size in the crystal enabling desired molecules such as oxygen
to freely diffuse into the crystal lattice and (iv) to establish
anchor points to attach specific molecules to the crystal. Thus the
probes may be used for a range of biological applications as
discussed below.
[0063] The lithium phthalocyanine derivatives, have low solubility
in aqueous and common organic solvents. Unsubstituted annulated
phthalocyanines are practically insoluble in organic solvents and
are hard to purify and recrystallize. In order to have their
functionality most effective, the lithium phthalocyanine
derivatives with increasing solubility in organic solvents is
planned. The insolubility of metal phthalocyanine derivatives
results from their molecular stacking, which gives rise to strong
intramolecular interaction between the macrocycles in
phthalocyanine molecules. The introduction of long substituents in
the macro cycle increases the solubility of the metal
phthalocyanine derivatives.
[0064] Calculations of the electronic properties of annulated
phthalocyanines show that linear annulations of benzene rings
produces a continuous destabilization of the HOMO level and
narrowing of the HOMO-LUMO energy gap. One-dimensional stacks of
the linearly annulated phthalocyanines are calculated to have lower
oxidation potentials and narrower gap than angularly annulated
systems. These theoretical results are confirmed by studies on
1,2-naphthalocyanine, 9,10-phenanthrenocyanine and
2,3-naphthalocyanine and the corresponding bridged stacked systems.
Benzoannulation with electron-releasing groups such as alkoxy group
of lithium phthalocyanine increases the electron delocalization,
and increase in spin electron intensity in the macrocycles.
[0065] In accordance with the present invention, the phthalocyanine
or annulated phthalocyanine moieties may also be functionalized
with groups such as hydroxyl, thiol or amino group. This
phthalocyanine moiety may then be tagged with many biologically
important molecules for detection by EPR spectroscopy and
imaging.
[0066] The particulates are paramagnetic spin probes with very high
spin density. The particulates are especially suitable for the
following applications: (i) as an oxygen-sensing EPR probe for
accurate determination of concentration of oxygen and (ii) as a
molecular and cellular imaging probe for EPR/MRI methods. The
probes may be used for many different applications in the field of
biomedical research and clinical studies as set forth in the next
several paragraphs.
[0067] (1) Determination of Oxygen Concentration in Tissues:
[0068] Electron paramagnetic resonance (EPR)-based oxygen
measurements (oximetry) coupled with particulate probes have some
unique advantages over the other methods. The particulate EPR
probes for oximetry have the following advantages: (i) they report
pO.sub.2, which is a better parameter in a heterogeneous cellular
system (ii) they do not consume oxygen (iii) they provide higher
resolution at lower pO.sub.2 and (iv) they are stable in cells and
tissues for repeated measurements of oxygen tensions without
reintroduction of the probe. The probe may be implanted in the
desired location of the tissue and repeated measurements of tissue
oxygenation may be performed over a period of several months. The
measurements are accurate, reliable and noninvasive.
[0069] (2) Determination of Oxygen Concentration in Cells:
[0070] In view of the importance of critical oxygen concentration
in cells for operation of normal cellular events, methods capable
of determining the oxygen concentration in cells and tissues are
highly crucial. Although many methods are available to measure
oxygen concentration in cells, each method has its advantages and
disadvantages, and no single method is completely satisfactory for
cellular studies The pththalocyanine micro/nano crystals can be
easily internalized in cells by endocytosis. This will enable
determination of oxygen concentration in cells. The high spin
density of the particulates can enable measurements in a single
cell.
[0071] (3) Determination of Oxygen Consumption by Cells:
[0072] Cellular oxygenation and oxygen consumption rate (OCR) are
important physiological and metabolic indicators of cellular
function. Normal cellular function and homeostasis require a
critical level of oxygen concentration (measured as oxygen tension,
pO.sub.2) in the cells to provide an adequate supply of oxygen for
the mitochondrial oxidative phosphorylation process.
[0073] We have previously demonstrated that the octa-n-butoxy
derivative of naphthalocyanine neutral radical (LiNc-BuO) enables
accurate, precise and reproducible measurements of pO.sub.2 in
cellular suspensions. In the current study, we carried out
measurements to provide an accurate determination of pO.sub.2 in
small volume with less number of cells (20,000 cells) that has not
been possible with other techniques. This study clearly
demonstrated the utilization of EPR spectrometry with LiNc-BuO
probe for determination of oxygen concentration in cultured
cells.
[0074] Additional applications include, but are not limited to:
cell-tagging and cell-tracking applications; studying cancer
metastasis in experimental models; tissue engineering (stem cell
research); tagging antibody; MRI contrast agent; implantable
oxygen-sensor in peripheral vascular disease; oxygen-sensor in
wound healing applications; and implantable oxygen-sensor in cancer
therapy.
[0075] NMR-based magnetic resonance imaging, MRI, enables
visualization of the distribution of nuclear spins, mostly protons,
in tissues. It has become a `gold standard` for noninvasive
diagnosis of tissue abnormalities. Electron paramagnetic resonance
imaging (EPRI) is a parallel technology, which enables
visualization of the distribution of electron spins (free radicals)
in tissues. EPR is inherently about 3 orders of magnitude more
sensitive than NMR. It can directly detect and image relatively
stable free radicals as well as labile radicals such as
oxygen-derived superoxide and hydroxyl free radicals that are
implicated in the pathogenesis of oxidant injury. With spin
labelling of molecules and cells, noninvasive mapping of their
localization in tissues may be performed [59-62].
[0076] A major power of EPR technology is its ability to precisely
measure molecular oxygen in tissues [61]. This `EPR oximetry`
technique uses spin probes whose EPR line-widths are highly
sensitive to O.sub.2 concentration. It enables precise and accurate
measurements of O.sub.2 in tissues, noninvasively and repeatedly
over periods of weeks from the same site. The approach uses fine
crystals (nano/microparticulates) of phthalocyanine-based radical
molecules that are stacked to produce a very strongly
exchanged-narrowed EPR line-shape that is highly sensitive to local
O.sub.2 concentration. The EPR line-shape of these nanoprobes is
highly O.sub.2 sensitive, and they are biocompatible and stable in
tissues. They may be implanted at the desired site or with a
suitable coating formulation can be infused into the vasculature
for targeted delivery to tissues. In addition, we recently
demonstrated that these nanoprobes can be internalized in cells
enabling measurement of intracellular pO.sub.2 with milliTorr
accuracy
[0077] The newly developed nanoparticulate EPR imaging technology
is especially useful (i) to visualize and track the migration of
endothelial progenitor cells and (ii) to simultaneously measure
intracellular oxygenation. This is done by internalizing the
paramagnetic nanoparticles (size <200 nm) by derivatizing with
Tat protein-derived peptide sequences as reported by Lewin et al.
[63]. The internalized cells may be characterized using optical
confocal microscopy and EPR spectroscopy. The lithium
naphthalocyanine (LiNc-BuO) spin probe, which has very high EPR
spin density and is readily internalized in cells, is used. Imaging
of the distribution of particles is performed in vivo using
low-frequency (1.2 GHz) EPR imager. Measurement and mapping of
intracellular oxygen concentration will be performed as we reported
previously [64].
[0078] Additionally, the inventive particulates are suitable for
the following applications for targeted intracellular delivery of
particulate oximetry probes, and as DNA or protein-targeted spin
probes, as discussed above.
[0079] Novel Particulate Spin Probe for Targeted Determination of
Oxygen in Cells and Tissues:
[0080] The synthesis and characterization of a new lithium
octa-n-butoxy-substituted naphthalocyanine radical probe (LiNc-BuO)
and its use in the determination of concentration of oxygen
(oximetry) by electron paramagnetic resonance (EPR) spectroscopy
are reported. The probe is synthesized as a needle-shaped
microcrystalline particulate. The particulate shows a single-line
EPR spectrum that is highly exchange-narrowed with a line-width of
210 mG. The EPR line-width is sensitive to molecular oxygen showing
a linear relationship between the line-width and concentration of
oxygen (pO.sub.2) with a sensitivity of 8.5 mG/mmHg. We studied a
variety of physicochemical and biological properties of LiNc-BuO
particulates to evaluate the suitability of the probe for in vivo
oximetry. The probe is unaffected by biological oxidoreductants,
stable in tissues for several months, and can be successfully
internalized in cells. We used this probe to monitor changes in
concentration of oxygen in the normal muscle and RIF-1 tumor tissue
of mice as a function of tumor growth. The data showed a rapid
decrease in the tumor pO.sub.2 with increase of tumor volume. Human
arterial smooth muscle cells, upon internalization of the LiNc-BuO
probe, showed a marked oxygen gradient across the cell membrane. In
summary, the newly synthesized octa-n-butoxy derivative of lithium
naphthalocyanine has unique properties that are useful for
determining oxygen concentration in chemical and biological systems
by EPR spectroscopy and also for magnetic tagging of cells.
[0081] Aerobic life relies on oxygen for respiration and
bioenergetic metabolism. In animals, especially mammals, under
normal physiological conditions, oxygen delivery by blood to the
tissues and tissue oxygenation are tightly regulated to maintain a
balance [65], which is altered during many pathophysiological
states. Therefore, an accurate and a reliable method to determine
its concentration in biological systems is highly critical.
Although several existing methods are utilized to measure oxygen
concentration in absolute units or in some related parameter, a
suitable technique for noninvasive and repeated measurements of
oxygen in the same tissue or cells on a temporal scale is
warranted. While electrode techniques have evolved as the standard
methods for measurement of oxygen, they generate analytical
artifacts during assay procedures at the freshly probed sites [66].
Near-infrared and magnetic resonance techniques such as nuclear
magnetic resonance, blood oxygen level-dependent magnetic resonance
imaging, Overhauser-enhanced magnetic resonance imaging, etc, on
the other hand, are noninvasive methods, but they do not report
usually the absolute values of oxygen concentration and lack the
resolution of oxygen measurements [67-75]. Electron paramagnetic
resonance (EPR), closely related to the aforementioned magnetic
resonance techniques, enables reliable and accurate measurements of
concentrations of oxygen [76]. The EPR technique requires the
incorporation of an `oxygen-sensing` paramagnetic spin probe into
the system of interest. Two types of probes are used: (i) soluble
probes that report the concentration of dissolved oxygen and (ii)
particulate probes that measure partial pressure of oxygen
(pO.sub.2) in the milieu. Considerable progress has been made in
the development and use of both types of probes [77-80]. The
advantages in using the particulate probe are higher resolution and
their suitability for repeated measurements in vivo without
reintroduction of the probe into the tissue. Both the naturally
occurring and synthetic materials have been useful for EPR oximetry
[78, 79, 81-83].
[0082] Earlier, alkali metal derivatives of phthalocyanines such as
lithium phthalocyanine (LiPc) [77, 81, 84-86] and lithium
naphthalocyanine (LiNc) [78, 87] were synthesized and their
properties were studied in detail. The materials were characterized
as crystalline solids composed of stacks of neutral free radical
molecules [88]. The crystalline solids exhibit a highly
exchange-narrowed single line EPR spectrum, whose width is
sensitive to the partial pressure of molecular oxygen in the
environment. Our interest in the utilization of oxygensensing
radical probes for biological applications has lead to the
synthesis and development of novel crystalline particulate
materials with remarkable oxygen sensitivity and biocompatibility
[77, 78, 85-87]. While we have identified that these materials
enable us to perform accurate and repeated measurements of oxygen
concentration in tissues, we realize that these particulate probes
can very well be used in other physiological and biochemical
studies that involve oxygen metabolism. The unique stability and
paramagnetic property of these particulates can be exploited by
internalizing them into cells and in specific tissues to visualize
cell proliferation, migration and trafficking, as it is studied
using superparamagnetic particulates in magnetic resonance imaging
technology [89-91]. The EPR technique is advantageous in offering
high sensitivity and direct detection of the particulates and
reporting the absolute value of oxygen concentration in the
environment. We envision that this creates a multitude of
applications in cell-based therapies and tissue engineering [92,
93].
[0083] In order to qualify as an ideal spin probe for targeted
measurements in cells and tissues, a paramagnetic particulate has
to satisfy the following criteria: (i) high spin density with a
simple EPR absorption peak, preferably a single and sharp line (ii)
long-term stability in cells and tissues, maintaining its
line-shape and oxygen sensitivity (iii) non-toxicity to the host
cell or tissue (iv) ability to prepare particulates of various
sizes, and (v) ability to encapsulate in shells or coating to
enable attachment of other probes such as fluorescent labels.
Although a variety of paramagnetic spin particulates, including
natural [82, 94] and semisynthetic [83, 95, 96] has been reported
to be useful as oximetry probes, they do not satisfy most of the
above requirements. Hence, we focused our efforts on synthetic
molecular crystalline particulates, whose properties can be
controlled and systematically altered by appropriate molecular
designs [77, 78, 85-87]. In this manuscript, we report the
synthesis, characterization and application of a new paramagnetic
particulate spin probe. The probe is a lithiated form of
octa-n-butoxynaphthalocyanine neutral radical (FIG. 1) which is
obtained in a microcrystalline form. The preliminary results
indicate that the probe is useful for determining oxygen
concentration in chemical and biological systems by EPR
spectroscopy and that it may significantly expand the capability of
EPR oximetry.
[0084] Materials and Methods:
[0085] Lithium granules,
5,9,14,18,23,27,32,36-octa-n-butoxy-2,3-naphthalocyanine (Nc-BuO),
n-pentanol, n-hexane, tetrahydrofuran and tert-butyl methyl ether
were obtained from Aldrich Chemical Co (St. Louis, Mo.). Minimal
essential medium (MEM), Dulbecco's modified Eagle medium (DMEM),
fetal bovine serum (FBS), glutamate and antibiotic
(penicillin-streptomycin) were purchased from Invitrogen, San
Diego, Calif. Alamar Blue solution was purchased from Biosource
International (Camarillo, Calif.).
[0086] Synthesis of Lithium
5,9,14,18,23,27,32,36-Octa-n-butoxy-2,3-naphthalocyanine (LiNc-BuO)
Radical
[0087] Lithium granules (0.0053 g, 0.774 mmol) were added to
n-pentanol (15 ml) and refluxed for 30 min under nitrogen
atmosphere. The mixture was cooled down to room temperature and
Nc-BuO (0.1 g, 0.0774 mmol) was added and refluxed gently for 2.5 h
under nitrogen atmosphere. After cooling down to room temperature,
300 ml of tert-butyl methyl ether was added and filtered through a
small silica gel plug. The solvent was evaporated under reduced
pressure to 3 ml of solution. The concentrate was dissolved in 100
ml of n-hexane. The greenish solution was slowly evaporated under
reduced pressure to yield shiny crystals of lithium
5,9,14,18,23,27,32,36-octa-n-butoxy-2,3-naphthalocyanine. The
crystals were washed with methanol and dried under vacuum. The
yield was 81%. Microanalysis of the product was in good agreement
with the formula C80H88N808Li (Calculated: C, 74.1; H, 6.84; N,
8.6; Li, 0.53 Found: C, 73.9; H, 7.12; N, 7.89; Li, 0.55).
[0088] Physicochemical Characterizations:
[0089] Electronic absorption spectra were measured in
tetrahydrofuran solvent using a Cary 300 BIO UV-Visible
Spectrophotometer. X-ray diffraction measurements were performed
using a Bruker D8 Advance model X-ray diffractometer operating at
40 kV and 50 mA with Cu K1 a radiation (e=1.5406 .ANG.) using a
Braun position-sensitive detector.
[0090] EPR Measurements:
[0091] EPR measurements were performed using a Bruker ER-300
spectrometer operating at X-band (9.78 GHz). The spectral
acquisitions were carried out using custom-developed software
(SPEX). Unless mentioned otherwise, the EPR line-widths reported
are peak-topeak width (.Bpp) of the first derivative spectra. The
EPR line-width versus partial pressure of oxygen calibration curve
was constructed from X- and L-band EPR measurements on LiNc-BuO
equilibrated with oxygen/nitrogen gas mixture as reported
previously [78].
[0092] Animal Studies:
[0093] Female C3H mice were used in the present work. The mice were
supplied through the Frederick Cancer Research Center Animal
Production, Frederick, Md. The animals were received at 6 weeks of
age and housed five per cage in climate-controlled rooms and
allowed food and acidified water ad lib. The animals were on
average 50 days old at the time of experimentation and weighed
25.+-.3 g. Experiments were conducted according to the principles
outlined in the Guide for the Care and Use of Laboratory Animals
prepared by the Institute of Laboratory Animal Resources, National
Research Council.
[0094] RIF-I Tumor Growth:
[0095] Radiation-induced fibrosarcoma (RIF-1) tumor cells, grown in
mono layered culture, were injected subcutaneously in the right
hind leg with a single cell suspension of 106 cells in 0.1 ml PBS.
The animals were observed closely and the tumors became palpable
approximately 5 days after injection.
[0096] Implantation of LiNc-BuO in Tumor and Gastrocnemius Muscle
of Mice:
[0097] Mice were anesthetized with breathing of isoflurane
(1.5%)-air mixture delivered through a nose cone. About 10 .mu.g of
LiNc-BuO in the form of microcrystalline powder (particulate size
5-20 .mu.m) was implanted in the tumor (right leg) or gastrocnemius
muscle of normal leg (left), using a 21-gauge needle loaded with
the particulate in the tip, and a wire stylus. The material was
deposited at desired locations of the tissue by inserting the
needle and then pulling it back, but keeping the wire stylus
stationary and then removing the stylus from the tissue. In the
case of tumors, the material was carefully implanted at the center
of the tumor at about 3 mm depth. The site of the probe insertion
was marked with a permanent marker for convenient preparation of
the animal for repeated measurements. All the in vivo EPR
measurements of LiNc-BuO in mice were made at least 24 h after the
implantation.
[0098] In Vivo EPR Measurements in Mice:
[0099] The EPR measurements were carried out on anesthetized mice
using L-band (1.32 GHz) spectrometer and a topical (surface loop)
resonator as described [33]. A plastic bedplate with a circular
observation window (20 mm diameter) was used to rest the animal on
the resonator. The animal was placed on the bedplate so that the
observation spot was centered at the slot. The animal was secured
to the bedplate with adhesive tape and placed on top of the
resonator so that the tumor or the normal muscle was in direct
contact with the active surface of the resonator. Anesthesia was
maintained during the measurements with continuous delivery of 1.5%
isoflurane mixed with air using a veterinary anesthesia system
(Vasco Anesthesia, Pro Tech Medical Inc., Hazel Crest, Ill.). The
flow rate of the breathing gas mixture was maintained at 2 L/min.
The gas and anesthesia were delivered to the animal through a nose
cone and the excess air was removed through proper ventilation
maintaining the atmospheric pressure (760 mmHg). A thermistor
rectal probe was used to monitor body temperature. The body
temperature was maintained at 37.+-.1.degree. C. using an infrared
lamp.
[0100] Culture of Smooth Muscle Cells:
[0101] Human arterial smooth muscle cells (HASMCs) were obtained
from Clonetics, San Diego, Calif. at passage 4. Cells were cultured
and passed in Ham's medium containing 225 ml of DMEM, 225 ml of
F-12 medium, 50 ml of FBS (10%), 5 ml of glutamate and 5 ml of
antibiotics in a final volume of 500 ml. Cell cultures were
maintained at 37.degree. C. under 95% air/5% CO2 environment in 35
mm dishes. HASMCs up to passage 11 were used in the current
study.
[0102] Preparation of Particulates for Cell Culture Studies:
[0103] Fine crystals of freshly synthesized LiNc-BuO were suspended
in Ham's medium (10 mg/0.5 ml) and sonicated ten times for 30 sec
on ice with a probe sonicator at a setting of 5. The particulate
mixture was cooled on ice for 1 min between two successive 30 sec
burst of sonication. At the end of the final round of sonication,
the suspension was placed on ice for exactly 2 min to allow the
heavier particulates to settle down at the bottom of the tube and
the decanted liquid was transferred to a separate tube, which
contained fine particulates of LiNc-BuO for intracellular delivery.
The size of the particulates for intracellular delivery was <2
.mu.m as determined by optical microscopy.
[0104] Internalization of Particulates into Smooth Muscle
Cells:
[0105] HMSMCs, at 70% confluence (104 cells/dish), in 1 ml Ham's
medium were treated with 50 .mu.m of LiNc-BuO particulate
suspension that contained particulates of <2 .mu.m prepared by
the procedure as mentioned before. The cells were maintained at
37.degree. C. under 95% air/5% CO2 environment. At 6 h intervals,
for 72 h, cells were examined under light microscope for
internalization of LiNc-BuO particulates. Upon confirming the
particulate uptake by all the cells in a given dish, the cells were
washed 12 times with ice-cold DMEM to remove unincorporated and
extraneous particulates by gentle swirling and aspiration, scrapped
in 1 ml of DMEM, and centrifuged at 1000.times.g in a microfuge for
10 min. The resulting cell pellet was gently resuspended in DMEM
containing glucose (0.5 g/500 mL) for EPR analysis. Cells after
LiNc-BuO internalization and repeated washings were photographed
under an inverted microscope while still adherent to the substratum
of the 35 mm dish. Cell viability was assessed by light microscopy
and Alamar Blue assay according to the manufacturer's
recommendations.
[0106] Results:
[0107] Physicochemical Characterization LiNc-BuO was synthesized as
dark-green needle-shaped crystals of varying sizes, typically with
1-5 .mu.m diameter and 5-50 .mu.m length. The crystals were
insoluble in water, but soluble in chloroform, dichloromethane,
tetrahydrofuran, toluene, benzene and xylenes giving rise to
green-colored solution. The crystals were stable in air at ambient
conditions. The UV-visible absorption spectrum of LiNc-BuO solution
in tetrahydrofuran showed strong Q-bands at 857 and 705 nm and a
weak split Soret band at 449 nm, while the Nc-BuO (the macro cyclic
ligand without Li) showed a strong Q-band at 865 nm. X-ray
diffraction pattern showed strong diffraction peaks suggestive of a
high degree of crystallinity. A thorough investigation of the
optical, magnetic, and structural property of LiNc-BuO will be
published elsewhere [34]. Most of the studies were performed on
fine crystals of LiNc-BuO, with <2 .mu.m in size, obtained by
sonication of the originally synthesized material in PBS or Ham's
medium containing 10% fetal bovine serum. This was done to achieve
particulates of uniform size for internalization in cells and
tissues. We used the term `particulates` to refer to these crystals
throughout the manuscript.
[0108] EPR Properties
[0109] The LiNc-BuO particulates exhibit a single-line EPR spectrum
at room temperature (FIG. 2). The peak-to-peak width of the
spectrum was highly dependent on the oxygen concentration of
environment: 210 mG under anoxic (0% oxygen) conditions, 1550 mG in
room air (20.9% oxygen or 159 mmHg) and 6675 mG in 100% oxygen at 1
atmospheric pressure (760 mmHg). The shape of the spectrum was 100%
Lorentzian. This is evidenced from the very good agreement between
the experimental and simulated spectra in FIG. 2A and the random
noise in the difference spectrum (FIG. 2B). The spin density,
measured in comparison with diphenylpicrylhydrazyl (DPPH) radical,
was 7.2.times.1020 spins/g. Microwave power saturation studies of
LiNc-BuO were performed to establish the useable range of power
levels. It was observed that spectrum was not saturable for up to
25 mW at the X-band frequency. This shows that up to 25 mW
microwave power can be applied to enhance the signal intensity
without compromising the oxygen sensitivity. Both the line-width
and lineshape of the particulates were not affected in aqueous
dispersion media (water, PBS, cell culture media). However, no EPR
spectrum was observed in organic solvents, in which the compound is
freely soluble, suggesting that the radical is not stable in the
molecular form.
[0110] Effect of Molecular Oxygen:
[0111] The peak-to-peak width of the EPR spectrum of LiNc-BuO
particulates was sensitive to oxygen concentration of the
environment. The spectrum was broadened and its amplitude decreased
in presence of oxygen. The oxygen-dependent broadening of the EPR
spectrum has been observed with LiPc, LiNc and several other
paramagnetic solids [77-79, 85-87, 99-101]. It is generally
considered that the broadening in presence of molecular oxygen is
due to the Heisenberg spin exchange between the radical and
molecular oxygen and results in shortening of the spin-spin
relaxation time T2. A plot of line-width measured as a function of
oxygen partial pressure is shown in FIG. 3. It is observed that the
line-width increases linearly with pO.sub.2 in the range 0 to 760
mmHg suggesting that the spin exchange increases linearly with
pO.sub.2. The slope of the line-width versus pO.sub.2 curve, which
reflects the oxygen sensitivity of the probe line-width, is 8.5
mG/mmHg.
[0112] Effect of Biological Oxidoreductants, pH, Temperature, and
Radiation:
[0113] Since our goal was to use the newly synthesized particulate
material for biological applications, we thoroughly investigated
the EPR stability (paramagnetism) as well as sensitivity of the EPR
line-width to molecular oxygen in presence of a variety of
biological oxidants, reductants, pH and radiation. The particulates
when exposed to superoxide (generated by 0.2 mM xanthine+0.01 D/ml
xanthine oxidase), hydroxyl (generated by 0.1 mM Fe2++1 mM
H.sub.2O.sub.2), hydrogen peroxide (1 mM), singlet oxygen
(generated by 1 mM Rose Bengal+light), alkylperoxyl (generated by
aerobic decomposition of 10 mM AAPH at 37.degree. C.), and nitric
oxide (generated by 1 mM SNAP), GSH (10 mM) and ascorbate (5 mM)
for 30 min did not show any effect on the EPR spectrum or oxygen
response. We also observed that pH of the medium in the range 2-10
had no effect on their EPR sensitivity to oxygen. We also treated
the particulates with 15.5 Gy of Cobalt-60 a-ray irradiation for 10
min and found no effect on the EPR properties of the particulates.
These results suggest that the LiNc-BuO particulates are usable in
a variety of extreme biological environments without any adverse
effect on the integrity of data.
[0114] Stability in Tissues:
[0115] In order to evaluate the long-term stability of these
particulates in tissues, we implanted the particulates in the
gastrocnemius muscle tissue of mice and performed repeated
measurements of pO.sub.2 in the same animals over a period of time.
About 10 .mu.g of LiNc-BuO microcrystalline powder was implanted in
the gastrocnemius muscle of the right leg of C3H mice (N=6). The
EPR spectrum of the particulate in the leg was recorded
periodically up to 180 days following the implantation of
particulate (FIG. 4). In order to verify the response of the
particulate to oxygen, blood flow to the leg was constricted by
gentle tying down of the upper leg for 10 min with an elastic band
and the EPR measurement was repeated. Sharpening of the EPR
spectral width during interruption of blood flow to the leg was
used as an indication of reduced tissue oxygenation and
responsiveness of the particulate to changes in tissue pO.sub.2.
The pO.sub.2 of the tissue under normal blood flow conditions was
19.6.+-.2.1 mmHg, while that of constricted tissue was 3.5.+-.0.9
mmHg during the 180 day period. The non-zero pO.sub.2 values in the
flow-constricted tissue suggest that the constrictions were not
totally effective. This was due to our efforts to make the
measurements for at least 6 months and so deliberately avoided
inflicting any permanent injury to the tissue while constriction.
Mice were periodically sacrificed through the 180 day study period
and tissue pO.sub.2 values were assessed to verify the registration
of anoxic pO.sub.2 in the dead tissue. The pO.sub.2 values in the
dead tissues were close to zero. We also observed that the oxygen
sensitivity of the recovered particulates from the dead tissue was
not changed and was similar to that of the original unimplanted
particulate.
[0116] Time-Response to Changes in Oxygenation:
[0117] The response time and reproducibility of the effect of
O.sub.2 in successive measurements were evaluated. The response of
probe was measured from the change in the EPR amplitudes to cycles
of rapid switching of the equilibrating gases between nitrogen and
room air as described previously [78]. It was observed that the
response was reasonably quick with oxygenation occurring at
.about.1 sec, while deoxygenation at .about.20 sec. Similar values
of response time and amplitude were observed on successive cycles
of switching of gas. Thus, the experiments not only confirm that
the probe responds quickly to oxygen and offers steady
reproducibility, but also that oxygen is not irreversibly adsorbed
and that the absorption/desorption process is very rapid and
reversible. Thus, the probe apparently is capable of responding to
changes in oxygen concentration almost instantaneously. A similar
observation has also been reported in the case of LiPc and LiNc
crystals [78].
[0118] Measurement of Tumor pO.sub.2 as a Function of Tumor
Growth:
[0119] The LiNc-BuO particulate was implanted in the tumor on day 5
after inoculation with tumor cells. The average tumor size at the
time of implantation of the particulate was 6 mm in diameter. A
similar implantation of the particulate, as a control, was
performed in the normal muscle on the left leg of the same
tumor-bearing mice. Tissue pO.sub.2 measurements were taken 24 h
following implantation to avoid artifacts associated with trauma
and tissue injury caused by the particulate implantation procedure.
Measurements were performed in the tumor on the right leg and in
the normal muscle on the left leg of each animal daily for the
following 8 days. The mean pO.sub.2 values from the tumor and
muscle tissue in 7 tumor-bearing mice are shown in FIG. 5. It was
observed that while the pO.sub.2 in the muscle tissue (control) of
the RIF-1 tumor-bearing mice remained constant during the study
period (17.6.+-.2.5 mmHg), the tumor pO.sub.2 showed a continuous
decrease towards hypoxia (<4 mmHg). It was also observed that
the RIF-1 tumor showed an accelerated growth during the same period
suggesting that the decrease in tumor oxygenation may be related to
tumor progression. The measurements were discontinued beyond day 8
as the tumors were too big (>20 mm in diameter) and continued to
be hypoxic with pO.sub.2 levels <4 mmHg.
[0120] Intracellular Internalization of Particulates:
[0121] The light microscopy clearly showed that within 18 h of
treatment of HASMCs with LiNc-BuO particulates (<2 .mu.m) in
Ham's medium, almost all the cells in the 35 mm dish internalized
the particulates. There was no apparent cytotoxicity of the
particulates up to 72 h following their internalization as revealed
by the light microscopy and Alamar Blue cytotoxicity assay (data
not shown).
[0122] Measurement of Intracellular pO.sub.2 in Smooth Muscle
Cells:
[0123] The particulates obtained by sonication of the LiNc-BuO
crystals in Ham's complete medium containing 10% fetal bovine serum
were internalized into cells. The extracellular uninternalized
particulates were removed by repeated washings with medium. FIG. 6
shows a photograph of cells internalized with the particulates. The
intracellular oxygen concentration, measured from the internalized
particulates, was 142.+-.2 mmHg, while the extracellular pO.sub.2
was measured to be 158.+-.3 mmHg using unsonicated particulates
that were added to control cells (without internalized
particulates) prior to measurement. The data show that the
particulates are capable of reporting exclusively intracellular
pO.sub.2 when internalized into the cells.
[0124] Discussion:
[0125] The LiNc-BuO belongs to a new class of crystalline internal
spin probe (CRISP) that has several advantages over the previously
reported particulate probes, namely lithium phthalocyanine [77, 81]
and lithium naphthalocyanine [78]. Although LiNc-BuO is a
derivative of the other two, closely similar in molecular
structure, its properties are very different from its predecessors.
Some of the distinct and advantageous features of LiNc-BuO
paramagnetic spin particulates are: (i) their ability to give rise
to a single, sharp and isotropic EPR spectrum characterized by 100%
Lorentzian shape obtained from crystalline powder (ii) their
relatively very high spin density compared to LiPc or LiNc (iii)
they exhibit a linear variation of line-width with pO.sub.2 that is
independent of particulate size (iv) their long term stability in
tissues and (v) their ability to internalize in cells. In addition
the LiNc-BuO particulates also show typical auto-fluorescence
properties which are under investigation. A complete
three-dimensional X-ray structure elucidation of the crystals is in
progress.
[0126] The anoxic line-width of LiNc-BuO is 210 mG. This is larger
when compared to that of LiPc, which we have reported to be <20
mG [77, 81]. However, the value is smaller than that of LiNc (510
mG) though the LiNc is structurally closer to the LiNc-BuO [78].
This difference in the anoxic line-width of LiNc-BuO may be
attributed to changes in the exchange interaction caused by the
introduction of alkoxy substituents to the naphthalocyanine
macrocycle. On the other hand, the oxygen sensitivity of LiNc-BuO
(8.5 mG/mmHg) is much closer to that of LiPc (8.9 mG/mmHg) than
that of LiNc (28.5 mg/mmHg). These differences in properties among
the particulates suggest that even a small change in the structure
can result in substantial change in the electron exchange and
oximetry properties.
[0127] The apparent spin density of LiNc-BuO (7.2.times.1020
spins/g), measured in comparison with diphenylpicrylhydrazyl (DPPH)
radical, is seven-fold higher than that of LiPc and comparable to
that of LiNc (6.8.times.1020 spins/g). The observed spin density of
LiNc-BuO, only a relative value, is determined by comparing the
intensities of the EPR spectra of LiNc-BuO with DPPH measured under
identical experimental conditions. However, the nature of spin
dynamics could affect the absolute value of spin density in the
system as discussed for LiNc [78].
[0128] The oxygen-dependent broadening of the EPR spectrum has been
observed with LiPc, LiNc and several other paramagnetic solids
[77-79, 85-87, 99-101]. The broadening in presence of molecular
oxygen is generally attributed to the Heisenberg spin exchange
between the radical and molecular oxygen and results in shortening
of the spin-spin relaxation time T2 [102]. Alternatively, as per
the mechanism proposed recently for LiPc microcrystalline powders
[86], the O.sub.2 can trap the self-exchanging or diffusing spins
resulting in broad EPR lines. The latter mechanism is more probable
especially for the solid spin probes with self-interacting
spins.
[0129] An important drawback with many particulate oximetry probes
was the instability of the probe in live tissues for prolonged
periods of time. The most widely used LiPc particulate is stable in
the gastrocnemius muscle tissue of mice for only about 3 weeks,
beyond which the probe apparently looses its sensitivity to oxygen.
Though the LiNc probe has several other advantages over LiPc, its
stability in tissue was limited to only a few days. There were
intense efforts to enhance their tissue stability over longer
periods of time, but however, there has been no significant success
to date [99, 103, 104]. Thus, it is important to note that LiNc-BuO
has tissue stability for 6 months, and appears to last longer.
[0130] We have demonstrated the usefulness of the probe for making
repeated and noninvasive measurements in a RIF-1 murine tumor
model. The data show that the pO.sub.2 levels in the normal
(nontumor-bearing) leg muscle are more or less constant while the
values in the tumor of the same set of animals progressively
decreased to hypoxic levels during the measurement period. It is
particularly important to note that there are relatively small
variations in the pO.sub.2 between the tumors as seen from the data
analysis. This observation suggests that the oxygen concentration
in the RIF-1 tumor decreases as a function of tumor growth.
[0131] Though the implantation of the particulates into the tissue
is invasive, it differs from other routine invasive techniques in
many ways. For example, in the case of the commonly used Eppendorf
electrode technique, the electrode is inserted at each sampling
time during the measurement causing local tissue injury and the
pO.sub.2 readings are obtained each time from the freshly injured
site. Although in the case of particulate probes, the implantation
procedure is invasive, the measurements are performed for days
following the implantation of the particulate probe at the tissue
sites where wound healing occurs after preparative surgery.
Furthermore, the implanted probe can be used repeatedly, as long as
the probe is stable and responsive to oxygen, without repeated
insertions and surgery. Thus, the EPR oximetry technique is
minimally invasive in terms of the requirement of one time
implantation and surgery and thus enables subsequent noninvasive
measurement of concentration oxygen from the same location.
[0132] The advantage of LiNc-BuO is the ability to make
particulates of nanometer size without compromising its EPR and
oxygen-sensing abilities. The smaller particulates can be
internalized in a variety of cells for different applications. For
example, intracellular pO.sub.2 can be measured from single cells.
It is also possible to tag cells with the EPR particulate probes
and study their migration, infiltration and proliferation over a
period of time using EPR or MRI technologies, in vivo. This will be
similar to the capabilities of ultra small superparamagnetic
particulates of iron oxide (USPIO) that have been actively pursued
as contrast agents in magnetic resonance imaging [105-107]. The
crystalline internal spin probe (CRISP) technology has biomedical
applications including tissue repair, wound healing and oximetry,
where in vivo EPR spectroscopy and imaging can be used. The EPR
spectroscopy has the advantage of direct detection of these
particulates, compared to the contrast-based detection by MRI, as
well as the capability of measuring absolute concentration of
oxygen concentration in cells and tissues.
[0133] Summary and Conclusions:
[0134] A new butoxy-substituted naphthalocyanine-based radical
probe, LiNc-BuO, with striking EPR properties was synthesized as
fine crystals and characterized with significantly high spin
density. The probe showed a highly exchange-narrowed single line
EPR spectrum that was sensitive to the surrounding oxygen
concentration. The effect of molecular oxygen on the EPR line width
was linear for up to 760 mmHg and highly reproducible on successive
applications, suggesting that it can be used as a probe for
EPR-based oximetry application. The probe has definitive advantages
over other EPR oximetry probes reported earlier. The EPR spectrum
is nonsatuarable up to 25 mW microwave power levels, and hence the
signal to noise ratio can be substantially improved by increasing
microwave power during measurements. The sensitivity of the EPR
line-width to molecular oxygen is 8.5 mG/mmHg which suggests that
changes in pO.sub.2 can be measured with reasonable resolution
(.about.0.2 mmHg) using this probe under the experimental
conditions described in this work. The probe shows a linear
response of its line-width to pO.sub.2 up to 100% molecular oxygen
(760 mmHg), thereby enabling the measurement of the pO.sub.2 even
in the higher range while maintaining the sensitivity. The probe is
stable against a variety of biological oxidoreductants, stable in
tissues for more than 6 months, and can be readily internalized in
cells. Thus the new octa-nbutoxy derivative of LiNc has unique
properties that may be useful for determining oxygen concentration
in chemical/biological systems and for magnetic tagging of
cells.
[0135] Measurement of Oxygen Consumption in Mouse Aortic
Endothelial Cells Using a Microparticulate Oximetry Probe:
[0136] The purpose of this study was to determine the rate of
oxygen consumption in mouse aortic endothelial cells (MAECs) and to
determine the effect of a variety of inhibitors and stimulators of
oxygen consumption measured by electron paramagnetic resonance
(EPR) spectroscopy utilizing a new particulate oximetry probe. We
have previously demonstrated that the octa-n-butoxy derivative of
naphthalocyanine neutral radical (LiNc-BuO) enables accurate,
precise and reproducible measurements of pO.sub.2 in cellular
suspensions. In the current study, we carried out measurements to
provide an accurate determination of pO.sub.2 in small volume with
less number of cells (20,000 cells) that has not been possible with
other techniques. In order to establish the reliability of this
method, agents such as menadione, lipopolysaccharide (LPS),
potassium cyanide, rotenone and diphenyleneiodonium chloride (DPI)
were used to modulate the oxygen consumption rate in the cells. We
observed an increase in oxygen consumption by the cells upon
treatment with menadione and LPS, whereas treatment with cyanide,
rotenone and DPI inhibited oxygen consumption. This study clearly
demonstrated the utilization of EPR spectrometry with LiNc-BuO
probe for determination of oxygen concentration in cultured
cells.
[0137] Introduction:
[0138] Cellular oxygenation and oxygen consumption rate (OCR) are
important physiological and metabolic indicators of cellular
function. Normal cellular function and homeostasis require a
critical level of oxygen concentration (measured as oxygen tension,
pO.sub.2) in the cells to provide an adequate supply of oxygen for
the mitochondrial oxidative phosphorylation process [108, 109].
However, when the cellular oxygen level is altered from the
critical level, the cellular homeostasis is disrupted leading to
abnormalities in cell growth, differentiation and survival. It is
established that too little of oxygen (hypoxia) can lead to the
activation of certain enzymes such as NAD(P)H oxidase, which
results in the generation of reactive oxygen species (ROS) [110].
It is further shown that too much of oxygen (hyperoxia) may also
lead to the generation of ROS from the mitochondrial electron
transport chain and other sources [111]. The ROS cause oxidative
stress by oxidizing the cellular components and by ultimately
altering their structure and function. Although cells have evolved
numerous antioxidant defense mechanisms against ROS-induced
oxidative stress, for example, using superoxide dismutase,
catalase, glutathione peroxidase, and vitamin E, the concentration
of oxygen in cells must be carefully controlled by maintaining a
balance between the ROS and antioxidants. In fact, the
concentrations of oxygen must be regulated such that the energy
needs of the cell via oxidative phosphorylation are adequately met
without a large excess of oxygen.
[0139] In view of the importance of critical oxygen concentration
in cells for operation of normal cellular events, methods capable
of determining the oxygen concentration in cells and tissues are
highly crucial. Although many methods are available to measure
oxygen concentration in cells, each method has its advantages and
disadvantages, and no single method is completely satisfactory for
cellular studies [112]. Electron paramagnetic resonance (EPR)-based
oxygen measurements (oximetry) coupled with particulate probes
[113-118] have some unique advantages over the other methods. The
particulate EPR probes for oximetry have the following advantages:
(i) they report pO.sub.2, which is a better parameter in a
heterogeneous cellular system (ii) they do not consume oxygen (iii)
they provide higher resolution at lower pO.sub.2 and (iv) they are
stable in cells and tissues for repeated measurements of oxygen
tensions without reintroduction of the probe. A variety of
particulate probes possess many of these desirable properties and
thus are useful for several in vitro and in vivo clinical
applications [113-118]. Particularly, lithiated macro cycles of
phthalocyanine and naphthalocyanine have been extensively
investigated [113, 114]. Recently, we synthesized and characterized
octa-n-butoxy derivative of naphthalocyanine neutral radical
(LiNc-BuO), an analog of phthalocyanine with extended
benzoannulation [119]. The LiNc-BuO neutral radical (oximetry
probe), as opposed to LiPc [113], fusinite [117], glucose char
[118] etc., offers marked advantages, especially with regards to
low microwave power saturation, linear response to concentration of
oxygen, dynamic measurement range and higher spin density.
Recently, we demonstrated the utilization of this material to
measure oxygen concentration in intact cells and in vivo biological
systems with greater stability (>6 months in the gastrocnemius
muscle of mice) and reproducibility in aqueous and physiological
environments [119]. Our earlier studies demonstrated that the
LiNc-BuO microcrystalline powder can provide accurate and
repetitive measurements of oxygen concentrations in intact cells
and tissues.
[0140] In order to demonstrate the accuracy and reliability of the
EPR oximetry utilizing the LiNc-BuO probe, we studied the pO.sub.2
and oxygen consumption rate (OCR) in mouse aortic endothelial cells
(MAECs). These cells can be cultured easily and considered as an
established model for endothelial cells that are widely used [120].
The reported OCRs in endothelial cells range from 0.13 nmol/min/106
cells [121] to 87.5 nmol/min/106 cells [122]. The disparity in
results, however, may be due to several factors including
differences in the cell type, experimental conditions and choice of
method. It should be noted that cellular metabolism can vary
profoundly depending on the conditions of incubation, presence and
absence of serum, growth factors and hormones and type of cell line
used in the study.
[0141] The purpose of this study was to determine the basal OCR in
MAECs of low cell density by EPR spectroscopy utilizing the
LiNc-BuO particulate oximetry probe that is capable of providing
accurate and reliable measurements of pO.sub.2 in cellular
suspensions. We demonstrated such measurements in a small volume
(20 .mu.l) with as few as 20,000 cells. We also investigated the
reliability of the method by studying the effect of several
stimulators and inhibitors of cellular oxygen consumption.
Menadione, and lipopolysaccharides (LPS) were chosen as stimulators
of cellular respiration. Cyanide, rotenone and diphenyleneiodonium
(DPI) were chosen as inhibitors of cellular respiration. Here, we
clearly demonstrated that oxygen consumption by endothelial cells
can be measured accurately by EPR oximetry utilizing LiNc-BuO. The
reliability of the method was established by examining the
sensitivity of oxygen consumption by MAECs to various metabolic
stimulators and inhibitors.
[0142] Materials and Methods--Reagents:
[0143] Lithium
5,9,14,18,23,27,32,36-octa-n-butoxy-2,3-naphthalocyanine (LiNc-BuO)
was used as a probe for measuring oxygen concentration in cellular
suspensions using EPR spectroscopy. LiNc-BuO belongs to the class
of crystalline internal spin probe (CRISP) particulates that we
have recently synthesized for measuring oxygen concentration in
cellular suspensions and tissues [119]. Menadione, DPI, LPS
(Escherichia coli O128:B12), rotenone and potassium cyanide were
purchased from Sigma Chemical Company (St. Louis, Mo.). Stock
solutions (1 mM) of menadione, DPI, and rotenone were freshly
prepared in dimethyl sulfoxide (DMSO) and used immediately. LPS was
prepared as 1 mg/ml of sterile phosphate buffered saline (PBS) and
stored at -20.degree. C. until use. KCN was prepared in distilled
water and used immediately.
[0144] Endothelial Cells:
[0145] MAECs used in this study were provided by Dr. Robert
Auerbach at the University of Wisconsin, Madison, Wis. MAECs were
cultured in DMEM containing 5% fetal bovine serum and antibiotics
(penicillin-streptomycin) and maintained at 37.degree. C. in a
humidified atmosphere of 5% CO2/95% air. MAECs were grown to 90%
confluence in T-75 flasks [120]. Cells from the flasks were
detached by gentle scrapping with a Teflon cell scrapper along with
the medium, cell density was determined, centrifuged at
1000.times.g at 4.degree. C. for 10 minutes, and resuspended in a
desired volume of PBS supplemented with glucose (0.1%) by gentle
mixing for oximetry studies. Cell separation by trypsinization was
avoided to keep the cell morphology and function in tact. Cells
were cultured up to 6 passages and used in all the studies.
[0146] Cell suspensions were then treated immediately with various
oxygen-modulating agents such as menadione, LPS, KCN, DPI and
rotenone in aerobic conditions. After the addition of .about.5
.mu.g of the oximetry probe (LiNc-BuO), cell suspensions were drawn
into capillary tubes (20 .mu.l), which was then sealed at both ends
using Critoseal.RTM.. Care was taken to avoid entrapment of any air
bubbles in side the capillary. Cell viability was assessed before
and after the EPR measurements by Trypan blue exclusion method and
found to be >95%.
[0147] EPR Measurements:
[0148] The EPR measurements were carried out using a Bruker X-band
(9.8 GHz) spectrometer (Bruker Instruments, Karlshrue, Germany)
equipped with TM110 cavity. The cavity was rotated 90.degree. so
that the capillary tube filled with the cell suspension could be
kept horizontally to avoid settling down of the cells. EPR spectra
were acquired using custom-developed data acquisition software
(SPEX). Unless mentioned otherwise, the EPR line-widths reported
are peak-to-peak widths (.Bpp) of the first derivative spectra.
[0149] Calibration of LiNc-BuO Oximetry:
[0150] The LiNc-BuO crystals were calibrated for EPR oximetry as
follows: A small amount (.about.10 .mu.g) of the probe was
encapsulated in a 0.8 mm diameter gas-permeable Teflon tube (Zeus
Industrial Products, Orangeburg, S.C., USA), both ends of the tube
were sealed and the tube was inserted into a 3 mm quartz EPR tube
with both the ends open. The EPR tube was placed into the TM110
microwave cavity (X-band) at the center of the active volume of the
resonator. Premixed oxygen and nitrogen gases of known composition
were flown through the EPR tube attached to a gas flow meter
(Cole-Parmer, Vernon Hills, Ill., USA) and gas impermeable silicon
tubing (NOX, Wilmad Lab Glasses, Buena, N.J.). All measurements
were carried out after equilibrating the sample with the gas
mixture 5 min. The flow rate of the gas mixture was maintained at 2
L/min. The total pressure inside the EPR tube was maintained at 760
mmHg (atmospheric pressure) by exposing the other end of the tube
to the ambient atmosphere. A linear variation of line-width was
observed as a function of partial pressure of oxygen (pO.sub.2) as
shown in FIG. 7.
[0151] Oxygen Consumption Measurements:
[0152] The OCRs were determined from pO.sub.2 data as a function of
time obtained from cell suspensions in a sealed capillary tube. The
following expression was used to calculate the OCR and expressed as
nmol/min/1.times.106 cells: OCR=m.a, where m is the slope of the
pO.sub.2 curve (in mmHg/min) and a is the solubility of oxygen in
water (1.59 nmol/mmHg at 22.degree. C.). OCR was expressed as
nanomoles of oxygen/min/106 cells.
[0153] Data Analysis:
[0154] All values are expressed as means.+-.SD of 4 to 6
independent experiments. ANOVA and student's t-test were used for
statistical analysis. Differences between groups were considered to
be significant at P<0.05.
[0155] Results--Effect of Molecular Oxygen on the EPR Spectrum of
LiNc-BuO:
[0156] The effect of molecular oxygen (O.sub.2) on the EPR spectrum
of LiNc-BuO is shown in FIG. 7. The LiNc-BuO exhibited a single EPR
peak with peak-to-peak width of 210 mG under anoxic condition. The
spectrum was broadened with a concomitant decrease in amplitude in
presence of oxygen. FIG. 7 shows the width of the probe as a
function of partial pressure of oxygen (pO.sub.2). It was observed
that the width increased linearly with pO.sub.2 in the range 0-160
mmHg. The slope of the curve, which reflected the oxygen
sensitivity of the probe to oxygen, was 8.5 mG/mmHg. Thus the probe
apparently was capable of measuring oxygen tension to .about.0.1
mmHg resolution in the physiological range.
[0157] Oxygen Consumption Measurements:
[0158] Typical time course data of pO.sub.2 measured in suspensions
of MAECs that were treated with various agents are shown in FIG. 8.
The measurements were performed routinely up to 20 min in a closed
volume of 20 .mu.l of suspension containing 20,000 cells. The data
showed a linear decrease of pO.sub.2 over time in all cases. The
OCR in untreated control cells was 3.07.+-.0.48 nmol/min/106 cells.
Cells treated with menadione and LPS showed increased rates of
oxygen consumption while cells treated with DPI, KCN and rotenone
showed complete inhibition of oxygen consumption.
[0159] Effect of Menadione:
[0160] Menadione is a redox-cycler that uncouples oxidative
phosphorylation. The effect of menadione on the oxygen consumption
by MAECs was investigated in the dose range of 10-200 .mu.M. The
results are shown in FIG. 9. A significant increase in the OCR was
observed when MAECs were treated with menadione (10 and 50 .mu.M)
whereas a decrease in the OCR was observed upon treatment of cells
with higher concentration of menadione (100 and 200 .mu.M). A
decrease in the OCR at the higher concentration of menadione might
be due to enhanced production of oxygen radicals, which apparently
inhibited the mitochondrial respiration. An increase in the OCR
when MAECs were treated with the lower concentrations of menadione
might be due to its redox-cycling activity and uncoupling of
oxidative phosphorylation.
[0161] Effect of Lipopolysaccharide:
[0162] The effect of LPS (an endotoxin of bacterial origin) on the
OCR in MAECs was studied (FIG. 10). Oxygen consumption by MAECs was
measured immediately after treatment with LPS (10 and 20 .mu.g/ml).
As seen in FIG. 10, an increase in the OCR was observed in cells
treated with 10 and 20 .mu.g/ml of LPS. On the other hand, cells
incubated for 2 h at 37.degree. C. in presence of 10 and 20
.mu.g/ml of LPS showed a decrease in the OCR which was not
statistically significant compared to untreated cells. Thus, it
appears that the effect of LPS on the oxygen consumption by MAECs
was both dose- and time-dependent.
[0163] Effect of Stimulators and Inhibitors on the Oxygen
Consumption Rates:
[0164] FIG. 11 shows a comparison of the OCRs in MAECs with several
stimulators and inhibitors of cellular respiration. As shown in the
figure, menadione and LPS increased the OCRs. Measurements
performed in presence of inhibitors of mitochondrial respiration,
namely, KCN (100 .mu.M), rotenone (100 .mu.M) and DPI (a
flavoprotein inhibitor, 100 .mu.M) indicated that there was a
complete inhibition of the OCR in MAECs.
[0165] Discussion:
[0166] The results showed that the OCRs in MAECs can be measured
accurately by EPR oximetry in a small volume suspension containing
20,000 cells. This was feasible by the utilization of LiNc-BuO
particulate oximetry probe which has high sensitivity and higher
resolution for the determination of oxygen concentration. The high
sensitivity of the EPR line-width of LiNc-BuO (8.5 mG/mmHg) is
particularly important for two reasons: (i) the oxygen consumption
measurements in cell suspensions can be performed in a relatively
shorter period (usually 10 min) as opposed to the electrode or
optical techniques which require several hours [123] (ii)
measurements can be performed in small volumes (10-20 .mu.L) and
with less number of cells, as has been demonstrated in the present
work. Thus, any alterations in the OCR due to higher cell densities
or to exposure of cells to varying concentration of oxygen for
prolonged periods of time can be eliminated by this method.
[0167] The OCR of untreated control MAECs measured at 22.degree. C.
was 3.07 nmol/min/10.sup.6 cells. While this value is in the range
of values reported for similar cells by other techniques, there are
some marked differences. For example, James et al. [121] used
15N-PDT, a soluble EPR oximetry probe that measures average
dissolved oxygen concentration in intra- and extracellular space of
the porcine aortic ECs, and reported an OCR of 0.13 nmol/min/106
cells. A higher OCR (1.45 nmol/min/106 cells) was reported by
Kjellstorm et al. [124] in the rat pulmonary arterial endothelial
cells using an oxyhemoglobin-based microrespirometric method. They
also observed comparable values in ECs from the human umbilical
cord veins, but a significantly lower value in the bovine aortic
ECs (0.3 nmol/min/106 cells). Motterlini et al. [123] reported a
value of 1.00 nmol/min/106 cells in the cultured vascular ECs
(0.5.times.106 cells/ml) obtained from the porcine thoracic aorta
using an optical method based on the oxygen-dependent quenching of
a phosphorescent probe. The disparity in the results might be due
to several factors such as the differences in the origin of the
cells, conditions of the incubation, as well as the presence or
absence of serum, growth factors and hormones. Further, the
differences in the detection techniques might also contribute to
the measured values.
[0168] The rate of respiration in cells in suspension may depend on
the ratio of oxygen to the cell density. Several studies have shown
changes in cellular metabolism parallel to changes in the oxygen
concentration in the suspension or to changes in the cell density
[125]. The dependence of the OCR on oxygen concentration in the
medium is usually evidenced by nonlinearity in the oxygen versus
time curve. Absence of any departure from linearity in the oxygen
consumption curve (FIG. 8) suggested that the cellular respiration
by the MAECs, at the cell density used, was not altered due to
depletion of oxygen in the medium. Motterlini et al. [123] observed
that the OCR of the porcine aortic ECs was dependent on the cell
density, with the rate decreasing from 1.0 to 0.6 nmol/min/106
cells when cell density was increased from 0.5-4.times.10.sup.6
cells/ml. However, we did not observe any significant change in the
OCR of MAECs in the range of 0.5-4.times.10.sup.6 cells/ml (data
not shown), suggesting that the respiration rate was not affected
by cell density in this range.
[0169] Endothelial cells are generally characterized with lower OCR
when compared to other cells, e.g., smooth muscle cells, myocytes
or Chinese hamster ovary cells. The lower consumption rate of the
endothelial cells is attributed to the presence of fewer number of
mitochondria in these cells [126]. The observation that cyanide (an
inhibitor of complex I) of the electron transport chain) and
rotenone (an inhibitor of complex I) completely inhibited the
consumption of oxygen suggested that the observed oxygen
utilization in the untreated cells was primarily due to
mitochondrial respiration. This is further confirmed by the
inhibitory effect of DPI, which is a blocker of flavoprotein
complex of NADPH oxidase and complex I of mitochondrial
respiration.
[0170] Menadione is a redox cycler that uncouples oxidative
phosphorylation in the mitochondria leading to increased oxygen
consumption. It is also known to induce oxidative stress in cells
by generating superoxide and other downstream oxidants in the
mitochondria. This causes both structural and functional damage to
mitochondria and membranes in cells. While the pro-oxidant activity
of menadione may strongly depend on the intracellular oxygen
availability, the deleterious effect of the oxidants leading to
mitochondrial injury may impair cellular respiration. The results
of the present study clearly established the involvement of the OCR
on the concentration of menadione. At lower concentrations of
menadione an increase in the consumption of oxygen was observed. A
two-fold increase in the OCR was measured at 50 .mu.M concentration
of menadione. Since the measurements were performed immediately
after the addition of the quinone, the increase in consumption
might be attributed to the increased generation or induction of
reactive oxygen species in addition to the enhancement of oxidative
phosphorylation in the mitochondria. At concentrations higher than
50 .mu.M, however, the OCRs were significantly less compared to the
control values, suggesting that the normal mitochondrial
respiration might be impaired due to damage caused by higher
concentrations of the drug.
[0171] Endotoxemic sepsis is associated with inadequate tissue
oxygenation and altered distribution of oxygen in different organs
[127]. Dysfunction of vascular endothelium and consequent damage to
vascular tissues are attributed to be the major determinants in
organ dysfunction mediated by endotoxin. Several studies which
investigated the possible impairment of oxygen utilization in
vascular cells treated with endotoxin showed conflicting results. A
recent study by James et al. [121] showed that the influence of
endotoxin on the rate of oxygen utilization is very much dependent
on the cell type. While the CHO and kidney cortex cells showed
markedly decreased oxygen consumption after treatment with LPS, ECs
did not show any response to LPS. However, more recently Motterlini
et al. [123] showed a 46% decrease in the rate of oxygen
consumption in the porcine aortic ECs that were exposed to 1
.mu.g/ml LPS. Our results in MAECs, measured immediately after
treatment with 10 .mu.g/ml LPS, indicated a 34% increase in oxygen
consumption. However, cells treated with similar concentration of
LPS but measured after 2 h of incubation showed a 16% decrease in
the OCR compared to untreated cells. The increase in consumption of
oxygen during the first 20 min after treatment with LPS might be
attributed to the oxidative burst of vascular NADPH oxidase. Recent
studies have suggested that a phagocyte-type NADPH oxidase is a
significant source of intracellular ROS in cardiovascular cells
[128]. Pro inflammatory mediators such as TNF-a are known to
stimulate NADPH oxidase in endothelial cells [129]. The oxygen
consumption was completely blocked by DPI, a known inhibitor of
NADPH oxidase suggesting the LPS-induced oxidative burst in the
ECs. We found a decrease in the rate of oxygen consumption after 2
h of incubation with LPS. This might be due to the inhibition of
mitochondrial respiration by nitric oxide. LPS is known to simulate
NO from iNOS [130]. The time required for the endogenous
stimulation of iNOS is usually 2-4 h. Nitric oxide can potentially
regulate cellular oxygen consumption by binding to the oxygen
binding site of cytochrome oxidase, resulting in reversible
inhibition of mitochondrial respiration [131]. Higher
concentrations of NO or its derivatives like peroxynitrite can also
cause irreversible inhibition of respiration at multiple sites
within mitochondria [132-134].
[0172] Summary and Conclusions:
[0173] Oxygen consumption rates of MAECs in suspension were
determined using EPR oximetry. The method utilized a
microparticulate spin probe (LiNc-BuO) with a high sensitivity for
oxygen, enabling accurate measurement of pO.sub.2 in solution. We
determined the effect of metabolic stimulators and inhibitors such
as menadione, LPS, cyanide, rotenone, and DPI on the OCR. The
measurements were performed in a volume of 20 .mu.L containing
20,000 cells (cell density: 1.times.106 cells/ml) contained in a
closed capillary tube. A linear decrease in pO.sub.2 was observed
as a function of time suggesting that the cellular respiration was
independent of oxygen concentration in the medium. We observed an
increase in oxygen consumption when MAECs were treated with
menadione and LPS, whereas cyanide, rotenone and DPI inhibited
oxygen consumption. In summary, we demonstrated that accurate
measurements of cellular oxygen consumption can be performed in
small volumes of cellular suspensions using microparticulate-based
EPR oximetry.
[0174] Simultaneous Measurement of Oxygenation in Intracellular and
Extracellular Compartments of Lung Microvascular Endothelial
Cells:
[0175] A new technique is described for simultaneous determination
of intra- and extracellular oxygen concentrations (pO.sub.2) in
bovine lung microvascular endothelial cells (BLMVECs) using
electron paramagnetic resonance (EPR) oximetry. The method utilizes
dual spin probes, one exclusively internalized in cells and the
other placed extracellularly which are capable of reporting
oxygenation simultaneously from the two distinct regions. The
measurements were performed in BLMVEC suspensions of 20 .mu.L
volume containing 4,000 cells. The extracellular pO.sub.2 was
measured using a trityl EPR probe (TAM, 10 .mu.M), a tricarboxylate
anion, that stays exclusively in the extracellular space. The
intracellular oxygen was measured using a pre-internalized
particulate spin probe, lithium octa-n-butoxynaphthalocyanine
(LiNc-BuO), which enables highly accurate and precise measurements
of intracellular pO.sub.2. Because there is a wide discrepancy in
the reported values of cellular oxygenation by and large due to
differences in the methods employed, we utilized the dual EPR probe
technique to measure the oxygen gradient that apparently exists
across the cell membrane. The intra- and extracellular pO.sub.2
were 139.+-.2.5 and 157.+-.3.6 mmHg, respectively, for cells
exposed to room air (pO.sub.2: 159 mmHg). A fairly smaller gradient
of oxygen was observed in cells exposed to 7.5% oxygen (pO.sub.2:
57 mmHg). There was no significant difference in the intra- and
extracellular pO.sub.2) when cells were treated with either
menadione (50 .mu.M) or cyanide (100 .mu.M). In conclusion, this
study confirms the feasibility of simultaneous and accurate
measurements of intra-extracellular pO.sub.2 using LiNc-BuO and TAM
EPR oximetry probes.
[0176] Oxygen is an important modulator of cellular functions in
both normal physiology and disease states. Cells respond to oxygen
over a wide range of concentrations from anoxia to hyperoxia.
Baseline metabolism and function typically occur in normoxic
environments (30-90 mmHg of O.sub.2) and can modulate
differentiated cell functions [149]. Hyperoxic conditions often
result in the generation of reactive oxygen species (ROS) that have
been implicated in cell injury via lipid peroxidation and cytokine
expression [139]. In lieu of such diversity in cellular responses
to oxygen, the dynamics of tissue oxygenation, including the
transport of oxygen and possible existence of oxygen gradient
across the cell membrane needs to be measured accurately. Various
methods such as manometry, photometry, mass spectrometry and
polarography (Clark-type electrochemical) have been described to
measure concentration and uptake of cellular oxygen [137, 138, 153,
159, 165]. The microelectrode technique, despite being used widely,
has disadvantages as it consumes oxygen during measurement,
apparently causes systematic error under very low oxygen
concentrations, requires insertion into the tissues, disturbs the
local environment and causes tissue damage [166, 167].
[0177] Although the determination of extracellular oxygen
concentration in cell suspensions is straightforward, the
measurement of intracellular pO.sub.2 is complicated. There are a
few methods available to accomplish this, for example, by insertion
of an intracellular oxygen electrode into a single cell [167, 168]
or by fluorescence quenching by O.sub.2 following the cellular
uptake of fluorescent probe, pyrenebutyric or 2-nitroimidazole
(EF5) [136, 151]. Electron paramagnetic resonance (EPR)
spectroscopy, coupled with the use of oxygen-sensitive spin probes,
has become a potential technique for accurate and precise
determination of oxygen concentrations in a variety of biological
samples, including tissues and cells [141, 147, 154, 161, 170]. The
technique, referred to as `EPR oximetry`, uses soluble molecular
spin probes for the determination of dissolved oxygen concentration
and particulate spin probes for targeted determination of local
oxygen tension (partial pressure of oxygen, pO.sub.2) in tissues
and cells [144]. The particulate probes have unique advantages over
the other EPR oximetry probes: (i) they report pO.sub.2, which is a
better parameter in a heterogeneous cellular system (ii) they do
not consume oxygen (iii) they provide higher resolution at lower
pO.sub.2 and (iv) they possess greater stability in cells and
tissues, so that, repeated measurements of oxygen tensions can be
made for months without reintroduction of the probe. Hence, the
particulate oximetry probe-coupled EPR spectroscopic determination
of oxygen has advantages over the other methods of determination of
oxygen in biological samples [137, 153, 159, 165]. A variety of
particulate probes that possess many of these desirable properties
are useful in studies in vitro to in vivo [144, 152]. Recently, we
synthesized and characterized octa-n-butoxy-substituted
naphthalocyanine neutral radical (LiNc-BuO), which exhibits marked
advantages, especially with respect microwave power saturation,
linear response to concentration of oxygen, dynamic measurement
range and higher spin density [156]. We have demonstrated the
application of this material by successfully internalizing into the
lung microvascular endothelial cells in culture for measuring
intracellular pO.sub.2. The probe is capable of providing reliable
measurements of intracellular pO.sub.2 with 0.1 mmHg resolution and
the measurements can be made in a single cell.
[0178] The aim of the present study was to demonstrate the accuracy
and reliability of the EPR oximetry method for simultaneous
measurement of intracellular pO.sub.2 in bovine lung microvascular
endothelial cells (BLMVECs) utilizing internalized particulates of
LiNc-BuO and extracellular pO.sub.2 using TAM. We have also
measured the intracellular and extracellular pO.sub.2 in these
cells in presence of metabolic inhibitors such as menadione (50
.mu.M) and potassium cyanide (100 .mu.M). As we have previously
demonstrated that the LiNc-BuO enables very accurate and reliable
measurement of pO.sub.2 in cellular suspensions, we envisioned that
the measurements will provide accurate values of intracellular
pO.sub.2 that have not been possible with the other techniques.
Further, we extended such measurements to smaller sample volume (20
.mu.l) with 4,000 cells. We observed an intracellular pO.sub.2 of
139 mmHg and extracellular pO.sub.2 of 157 mmHg with an oxygen
gradient of 18 mmHg under aerobic conditions. A gradient of 9 mmHg
of oxygen (extra and intracellular pO.sub.2 were 64 and 55 mmHg
respectively) was observed when the cells were exposed to 7.5%
oxygen. Menadione and potassium cyanide did not affect
significantly the intra- and extracellular pO.sub.2 levels.
[0179] Materials and Methods--Reagents:
[0180] Lithium
5,9,14,18,23,27,32,36-octa-n-butoxy-2,3-naphthalocyanine (LiNc-BuO)
was used as a probe for measuring intracellular oxygen
concentration by EPR spectroscopy. LiNc-BuO belongs to the class of
crystalline internal spin probe (CRISP) particulates that we have
recently reported for measuring oxygen concentration in cellular
suspensions and tissues [156]. TAM was a gift from Nycomed
Innovations (Malmo, Sweden). The EPR properties of TAM have been
well characterized (1). Menadione and potassium cyanide were
purchased from the Sigma Chemical Company (St. Louis, Mo.). Stock
solutions (1 mM) of menadione and KCN were prepared freshly in
dimethylsulfoxide and distilled water, respectively and used
immediately. Minimum essential medium (MEM), fetal bovine serum and
antibiotics were obtained from GIBCO-Invitrogen, Calif.
[0181] Bovine Lung Microvasular Endothelial Cells (BLMVECs)
Culture:
[0182] The BLMVECs used in this study were obtained from the VEC
Technologies, Inc, New York. BLMVECs cultured in MEM were
maintained in 75 mm flasks at 37.degree. C. in a humidified
atmosphere of 5% CO.sub.2/95% air and grown to contact-inhibited
mono layers with a typical cobblestone morphology [157]. Cells from
each primary flask were detached with 0.05% trypsin, resuspended in
fresh medium, and cultured in complete medium to 70% confluency for
other studies. Cells from passages 10-14 were used in all the
experiments.
[0183] Preparation of Particulates for Cell Culture Studies:
[0184] Microcrystalline particulates of LiNc-BuO were suspended in
complete MEM medium (10 mg/0.5 ml) and sonicated for 30 sec pulse
for ten times on ice with a probe sonicator at a setting of 5. The
particulate suspension was cooled for 1 min between two successive
30 sec bursts of sonication. At the end of sonication, the
suspension was placed on ice for exactly 2 min to allow the heavier
particulates to settle down at the bottom of the tube and the
supernatant liquid was transferred to a separate tube for
intracellular delivery. The solution contained fine particulates of
LiNc-BuO with a particulate size <2 .mu.m. All the preparations
were carried out under sterile conditions.
[0185] Internalization of Particulates into Endothelial Cells:
[0186] BLMVECs, at 70% confluence (104 cells/35 mm dish), in 1 ml
complete MEM were treated with 50 .mu.l of LiNc-BuO particulate
suspension that contained particulates of <2 .mu.m prepared by
procedure as described under Materials and Methods. The cells were
maintained at 37.degree. C. under 95% air/5% CO.sub.2 environment.
At 6 h intervals, for 72 h, cells were examined under light
microscope for internalization of LiNc-BuO particulates. Upon
confirming the particulate uptake by all the cells in a given dish
after 48 h of exposure to particulates, the cells were washed 12
times with ice-cold MEM to remove unincorporated and extraneous
particulates by gentle swirling and aspiration, scrapped in 1 ml of
MEM, and centrifuged at 1000.times.g in a microcentrifuge for 10
min. The cell pellet was resuspended in MEM containing glucose (0.5
g per 500 ml), at a density of 2.times.105 cells/ml and used for
EPR analysis. Cells after LiNc-BuO internalization and repeated
washings were photographed under an inverted microscope while still
adherent to the substratum of the 35 mm dish. Cell viability was
assessed by light microscopy and Alamar Blue assay according to the
manufacturer's recommendations. Cell separation by trypsinization
was avoided to keep the cell morphology and function in tact.
[0187] A 20 .mu.L volume of the cell suspension containing 4,000
cells and 10 .mu.M TAM was drawn into a gas-permeable Teflon tube
and subjected to EPR spectroscopy as described below. The
measurements were also carried out with Menadione (50 .mu.M) and
KCN (100 .mu.M). Cell viability was assessed before and after the
EPR measurements by Trypan blue exclusion method and found to be
>95%.
[0188] EPR Measurements:
[0189] The EPR measurements were carried out using a Bruker X-band
(9.8 GHz) spectrometer (Bruker Instruments, Karlshrue, Germany)
equipped with TM110 cavity. EPR spectral acquisitions were
performed using custom-developed data acquisition software (SPEX)
that was capable of fully automated data acquisition and
processing. Unless otherwise mentioned, the EPR line-widths
reported are peak-to-peak widths (.Bpp) of the first derivative
spectra.
[0190] Calibration of LiN-BuO and TAM Oximetry:
[0191] The LiNc-BuO crystals were calibrated for EPR oximetry as
described earlier [156]. Measurements of the line width of LiNc-BuO
after equilibration with a series of oxygen and nitrogen gas
mixtures were performed. Calibration was performed over the oxygen
concentration range (0-21%) with oxygen/nitrogen mixtures. A linear
variation of line-width was observed as a function of partial
pressure of oxygen (pO.sub.2) in the entire range of 0-160 mmHg.
Similarly, the calibration of TAM (10 .mu.M) was also performed
using different oxygen concentrations (0-21%). The oxygen-induced
line-broadening (change in peak-peak width) of the signal was used
to measure extracellular oxygen concentration. The line shape of
the EPR signal was precisely simulated using a Lorentzian functions
and the Lorentzian width was used to establish the calibration
curve.
[0192] Simultaneous Measurements of LiNc-BuO and TAM
Line-Shapes:
[0193] LiNc-BuO and TAM were used as site specific oximetry probes
to measure intra- and extracellular oxygen concentration,
respectively. Both LiNc-BuO and TAM give a single-line EPR
spectrum, whose amplitude (intensity) and width depend on the
amount/concentration of the probe and oxygen, respectively. Since
the g-factor of LiNc-BuO (g=2.0024) and TAM (g=2.0030) are slightly
different, their spectra do not overlap completely and show a
composite feature where the two peaks can be separated by
computer-simulation (FIG. 12).
[0194] The LiNc-BuO absorption profile is characterized by 100%
Lorentzian [156], while the TAM signal can be approximated to be
Lorentzian under conditions of oxygen-induced broadening. Thus, the
deconvolution requires a simple two-component Lorentzian fitting to
the measured spectrum. We validated the faithfulness of the
deconvolution by performing the simulation under different
combination of oxygen broadening to the probes. The reproducibility
was very good (R2>0.99) for non-zero oxygen concentrations. The
line-shape of TAM was non-Lorentzian under anoxic conditions.
[0195] It should also be noted that there was no effect of TAM on
the EPR spectrum of LiNc-BuO and vice versa, when the two probes
were suspended in the same medium having physical contact. This
suggests that the two probes can be used together. However, in our
experiments the probes were distributed in different regions
(intra- and extracellular) and hence, such a contact did not exist.
The components were separated using PEAK FIT (SPSS, Chicago, Ill.)
software and the intracellular and extracellular pO.sub.2 were
determined from the calibration curves of LiNc-BuO and TAM.
[0196] Data Analysis:
[0197] All values are expressed as mean.+-.SD of 4 to 6 independent
experiments. ANOVA and student's t-test were used for statistical
analysis. Differences between groups were considered to be
significant at P<0.05.
[0198] Results--Internalization of LiNc-BuO Crystals into
BLMVECs:
[0199] The light microscopy, as shown in FIG. 13, clearly showed
within 18 h of BLMVECs treatment with LiNc-BuO particulates (<2
.mu.m) in complete MEM, nearly 95% of the cells internalized the
particulates in a 35 mm dish. The internalized particulates show no
cytotoxicity up to 72 h as evidenced by the light microscopy and
Alamar Blue cytotoxicity assay. At the time of measurements, the
viability of the cells that internalized LiNc-BuO was >95% as
studied with 0.4% Trypan blue exclusion method.
[0200] The mean spin density of the LiNc-BuO particulates
internalized in a single cell was calculated in comparison with a
standard solution of TAM to be 6.times.10.sup.11 spins/cell. This
sensitivity is greater than that offered by the X-band EPR
spectrometer, which is typically better than 1.times.10.sup.10
spins. Thus, one can measure EPR spectrum from a single cell that
is internalized with the LiNc-BuO particulates.
[0201] Effect of Molecular Oxygen on the EPR Spectrum of LiNc-BuO
and TAM:
[0202] FIG. 14 shows the width of the probe as a function of
partial pressure of oxygen (pO.sub.2) in the range 0 to 158 mmHg.
It is observed that the width increases linearly with pO.sub.2 in
the range 0-160 mmHg. The slope of the curve, which reflects the
oxygen sensitivity of the probe to oxygen, is 8.5 mG/mmHg. Thus the
probe is capable of measuring oxygen tension to .about.0.1 mmHg
resolution in the physiological range. Similarly, TAM exhibits a
peak-to-peak width of 146 mG under the anoxic condition and the
spectrum is broadened in the presence of oxygen. The oxygen
sensitivity of this radical is 0.36 mG/mmHg. The line shape of the
EPR signal obtained with simultaneous use of intracellular LiNc-BuO
and extracellular TAM was simulated precisely using two Lorentzian
functions and the Lorentzian width was used to measure pO.sub.2
from the calibration curve.
[0203] Intra- and Extracellular Oxygen Concentrations
[0204] The internalized BLMVECs (4,000 cells) mixed with TAM (10
.mu.M) in a 20 .mu.L volume of aerated solution, showed an oxygen
gradient of 18 mmHg with an intracellular pO.sub.2 of 139 mmHg and
extracellular pO.sub.2 of 157 mmHg (FIG. 15). A gradient of 9 mmHg
of oxygen was observed when cells were exposed to 7.5% oxygen.
Internalization of LiNc-BuO particulates into BLMVECs and the
feasibility of accurate measurement of intracellular pO.sub.2 were
confirmed in cell lysates prepared by brief sonication (5.times.10
sec) at 4.degree. C. The pO.sub.2 measured in the lysate was 158
mmHg. This observation clearly indicated the internalization of
particulate probe into BLMVECs and the existence of oxygen gradient
between intra- and extracellular compartments. There was no
significant change in pO.sub.2 and oxygen gradient in cells treated
with menadione (50 .mu.M) or cyanide (100 .mu.M) (FIG. 16).
[0205] Discussion:
[0206] Oxygen gradient in physiological systems plays an important
role in both maintaining homeostasis and inducing cellular
responses. Therefore, an accurate and a reliable method to
determine its concentrations in cells and tissues is highly
critical. Values of oxygen gradient in cells measured by various
methods reported so far in the literature vary widely range from 1
to 40 .mu.M [140, 142, 148, 160, 162-164]. This broad discrepancy
apparently is due to technical difficulty associated with accurate
measurement of intracellular oxygen concentration under
physiological conditions. Using nitroxides and other agents,
several new methods based on EPR oximetry technique have been
developed to measure intracellular oxygen concentrations in cells
[143, 145-147, 158]. The particulate probe-based EPR oximetry, used
in the present study has many advantages over the other oximetry
probe-based EPR spectroscopy and other widely used methods to
measure intracellular pO.sub.2. Some of the distinct and
advantageous features of LiNc-BuO paramagnetic spin particulates
are; their ability to give rise to single sharp and isotropic EPR
spectrum characteristic with 100% Lorentzian shape, linear
variation of line-width with pO.sub.2, that is independent of
particulate size and most importantly their ability to internalize
in cells. We have taken advantage of these favorable
characteristics of LiNc-BuO particulates, successfully internalized
them into in BLMVECs and measured intracellular pO.sub.2 using EPR
spectroscopy.
[0207] The intra- and extracellular pO.sub.2 measured by this
technique in BLMVECs were 139 mmHg and 157 mmHg, respectively at
room air with a gradient of 18 mmHg. This technique also revealed
the existence of a small oxygen gradient of 9 mmHg at 7.5%
(pO.sub.2: 57 mmHg) oxygen (extra and intracellular pO.sub.2 were
64 and 55 mmHg respectively). Similar finding was also observed by
others [150]. This suggest that the cells possess different
gradients when exposed to different oxygen concentration and a
smaller gradient exist at lower oxygen concentrations. Santini et
al. [158] used fusinite as an EPR oximetry probe to measure
intracellular molecular oxygen in K56 (an erythroleukemic cell
line) and A 431 (an epidermal carcinoma cell line) and demonstrated
that menadione (200 .mu.M) increased both intra- and extracellular
pO.sub.2 by 10-15%. But in our study, menadione (50 .mu.M) did not
alter intra and extracellular pO.sub.2 in BLMVECs. This may be due
to different experimental conditions, dose and different cell types
used. Khan et al. [150] measured intra- and extracellular oxygen
concentrations in CHO cells by EPR oximetry using 15N-PDT and LiPc
as intra- and extracellular probes, respectively. The extra- and
intracellular oxygen concentrations observed in this study were 162
mmHg (1 .mu.M of oxygen is equal to 0.714 mmHg in aqueous solution)
and 129 mmHg at 150 mmHg and 38.5 and 34.2 mmHg at 35 mmHg of
pO.sub.2. Using this technique, they demonstrated that plasma
membrane cholesterol is an important barrier in regulating the
oxygen gradient across the cell membrane.
[0208] In our recent study, we used LiNc-BuO particulate probe and
measured the rate of oxygen consumption in mouse aortic endothelial
cells in presence of various stimulants and inhibitors of
respiration [155] and also measured the pO.sub.2 in normal and
tumor tissues [156]. In comparison with other oximetry probes, the
unique advantage of LiNc-BuO is to prepare particulates of
nanometer size without compromising its EPR behavior and
oxygen-sensing abilities. The smaller particulates can be
internalized in a variety of cells for different applications. It
is possible to measure the pO.sub.2 from a single cells
internalized with LiNc-BuO.
[0209] The intracellular molecular oxygen is critical in
determining the cytoplasmic chemical/physical environment of the
cell. The use of highly sensitive EPR probe like LiNc-BuO, capable
of measuring intracellular pO.sub.2 with a greater sensitivity
offers advantages in biological EPR oximetry. The data presented in
this study demonstrated that this novel EPR probe can be
successfully employed for direct and efficient measurement of
intracellular oxygen concentration with a sensitivity of 0.1 mmHg
in all cell types. The cells internalized with LiNc-BuO can be used
as an important tool to monitor oxidative cellular functions and to
study the cellular responses under pathophysiological and
toxicological conditions.
[0210] Summary and Conclusions:
[0211] The intracellular oxygen concentration in BLMVECs was
measured by internalizing oxygen sensitive microparticulate spin
probe (LiNc-BuO) using electron paramagnetic resonance oximetry.
The method utilized a microparticulate spin probe (LiNc-BuO) with a
high sensitivity for oxygen, enabling accurate measurement of
intracellular pO.sub.2 in BLMVECs. We also determined the
extracellular oxygen concentration using another oxygen sensitive
oximetry probe, TAM, simultaneously. The effect of agents which can
alter oxygen concentration such as menadione and potassium cyanide
on oxygen gradient was also studied. The measurements were
performed in a volume of 20 .mu.L containing 4000 cells
(2.times.105 cells/mL) in a gas permeable Teflon tube at room air
and at 7.5% oxygen. The intracellular oxygen concentration in
BLMVECs measured at room air by this technique was 194 .mu.M and
extracellular oxygen concentration was 220 .mu.M with a gradient of
26 .mu.M and an oxygen gradient of 16 .mu.M was seen in cells
exposed 7.5% oxygen. There was no significant difference in extra-
and intracellular oxygen concentration during treatment with
menadione and potassium cyanide. In summary, we demonstrated that
the measurements of intracellular oxygen concentration and oxygen
gradient can be successfully performed using microparticulate-based
EPR oximetry with a fewer number of cells.
[0212] Crystal Structure of Li(BuO).sub.8Nc
[0213] The crystal structure of Li(BuO).sub.8Nc was studied by
X-ray powder diffraction (XRPD) analysis using a Bruker D8
diffractometer equipped with a Cu Ka (.lamda.=1.5406 .ANG.)
radiation tube, an incident beam Ge monochromator, and a Braun
linear position sensitive detector (PSD). The XRPD patterns were
collected at room temperature varying the powder mounting
conditions, angular step size, and counting time. Data were
collected using a conventional flat plate sample holder, a
zero-background silicon single crystal sample holder, and a
spinning thin walled capillary. The various data sets were all
fairly similar, suggesting that preferred orientation effects are
not a significant problem. In the capillary mode a noticeable
background was observed over 28 range 15-30.degree. due to the
amorphous nature of the glass capillary, whereas in the flat plate
mode the peak intensities fell off rapidly with (sin
.theta.)/.lamda.. Taking into account resolution and
signal-to-noise, we elected to use a data set collected using a 1
mm diameter capillary for detailed analysis. This scan covered the
28 range 2--40.degree. using a step size of 0.014347.degree. and a
counting time of 10 sec per step.
[0214] In order to determine the crystal symmetry and unit cell
dimensions of Li(BuO).sub.8Nc, the auto indexing software package
CRYSFIRE [171] was used. Peak positions of first 24 reflections
were fitted using the program XFIT [172] and exported to CRYSFIRE
suite. Among the separate subroutines included in CRYSFIRE, ITO12
[173] identified two triclinic structures of very similar cell
dimensions, with figures of merit (M), [174] 22 and 19. The space
group was assumed to be the centric system P-1 rather than P1, in
light of the pronounced preference for the former space group among
existing structures. Using the approximate cell parameters
suggested by ITOI2, peak intensities were extracted by the whole
pattern fitting approach based on LeBail method [175] as
implemented in the GSAS software suite [176]. The LeBail fit gave a
X2 value of 5.16, an R.sub.wp value of 0.0290, and refined cell
parameters of a=17.087(1) .ANG., b=18.792(1) .ANG., c=14.191(1)
.ANG., a=113.577(6.degree., B=109.771(5).degree.,
y=73.517(6).degree., and volume=3871.5(5) .ANG..sup.3. The number
of formula units per unit cell could be determined as Z=2
(LiC.sub.80H.sub.88N.sub.8O.sub.8, f.w. 1296.54, p=1.113
g/cm.sup.3) from packing considerations.
[0215] Following the autoindexing and whole pattern fitting stages,
the molecular packing of Li(BuO).sub.8Nc was further studied by a
global optimization approach implemented within DASH, [177] the
details of which are described elsewhere [178]. The peak
intensities were extracted using the Pawley method [179]
implemented in DASH, although the lattice parameters were fixed at
values determined in GSAS. Pawley refinement gave a profile X2
(Xpro2) value of 3.67 and a R.sub.wp value of 0.0776. The LeBail
and Pawley fits are shown in the supplementary information.
Structure determination proceeded by means of the simulated
annealing algorithm provided in DASH using a starting model
structure of Li(BuO).sub.8Nc molecule constructed using the 3D
Sketcher included in Material Studio [180]. The internal geometry
of Li(BuO).sub.8Nc molecule did not undergo further optimization,
but the C--C or C--N bond lengths and the size of naphthalocyanine
ring were examined and found to be very similar to those in metal
naphthalocyaninates of nickel, copper, or zinc [181]. Since the
number of atoms in the asymmetric unit, 185, exceeds the default
values of DASH, which can handle up to 150 atoms in an asymmetric
unit, the input structure was modified by removing all hydrogen
atoms. The resulting molecular fragment consists of 96 atoms but
still retains 93% mass of the original Li(BuO).sub.8Nc molecule
(see FIG. 17).
[0216] Using the rigidity of the molecule as a chemical constraint,
the crystal structure of Li(BuO).sub.8Nc molecule can be described
by 3 positional variables and 3 independent rotational parameters.
In addition, each of the eight n-butoxy chains has 4 conformational
degrees of freedom, for a total of 32 unknown torsion angles. In a
single simulated annealing run of DASH, 107 movements were made
adjusting the above 38 variables to generate a theoretical pattern
that best matches the experimental data. The initial 45 trial runs,
in which no constraints were imposed, did not lead to a
straightforward solution possibly because the structure has too
many flexible bonds, the combinations of which cannot be thoroughly
examined. However a careful examination of output structures
revealed two favored regions for the position (center of mass) of
the molecule, as shown in the plot of positional parameters from 20
output results with lowest .chi.pro.sup.2 (see FIG. 18). Within
both convergent groups, the orientations of naphthalocyanine rings
differed only slightly among trials. The reproducible location and
orientation of the naphthalocyanine ring suggests that the crystal
structure adopts one of these two molecular packing arrangements;
referred to as type-I for the group centered at (0.05, 0.03, 0.37)
and type-II for the group centered at (0.44, 0.02, 0.15).
[0217] The results of the DASH structure solution attempts
described in the preceding paragraph indicate that given the
complexity of the molecule in question and the limited resolution
of the X-ray diffraction data it is not possible to obtain a
complete structure solution. However, there is a strong indication
we can determine the approximate location and orientation of the
napthalocyanine ring. To further investigate this assumption we
attempted structure solution using simpler model structures in
which the --OBu groups are replaced by --OC.sub.nH.sub.2n+l (n=0,
1, 2, 3). Omission of all or part of the alkyl chains leaves 65%
(--OH), 74% (--OMe), 83% (--OEt), and 91% (--OPr) of the total mass
of the actual compound. While it is possible that this omission may
mislead the structure solution process, we felt that omission of
atoms that cannot be reliably located in the structure solution
process may help to avoid falling into false minima with regard to
the location and orientation of the napthalocyanine ring. It was
observed that reducing the total number of conformational variables
in this manner, leads to a significant improvement in the
reproducibility of the simulated annealing process. It is
noteworthy that the solutions from all four cases agreed well both
in the position and orientation of the naphthalocyanine ring, with
the type-II solution. The .chi..sub.pro.sup.2 values gradually
increased with the decrease of the number of carbon atoms in the
side chains: --OPr, .about.170, --OEt, .about.230, --OMe,
.about.260, and --OH, .about.290. These results strongly suggest
that the type-II model describes the molecular packing of the
naphthalocyanine rings, and also that the alkoxy chains provide
non-negligible contributions to the diffraction pattern.
[0218] In the subsequent step, we decided to fine-tune the stacking
structure of Li(OBu).sub.8Nc by imposing constraints on the
external degrees of freedom as obtained from above exploratory
trials. The center of mass of Li(OBu).sub.8Nc was confined to a
volume defined by 0.35.ltoreq..times..ltoreq.0.5,
0.ltoreq.y.ltoreq.0.15, 0.05.ltoreq.z.ltoreq.0.2, and the
quarternians, Q.sub.i (i=0, 1, 2, 3; -1.ltoreq.Q.sub.i.ltoreq.1),
[182] were limited to have a width of 0.4, while the thirty two
torsion angles were allowed to vary freely. From 10 trials under
the above controlled condition, solutions were obtained with
X.sub.pro.sup.2 values of 128.5.about.147.2. The positions and
orientations of the rigid ring part were almost invariant according
to the constraints, but the conformations of eight butoxy chains
were rather featureless. Consequently, a meaningful pattern could
not be ascertained. The various and irregular conformations of the
butoxy chains must be responsible for the high and dispersed
X.sub.pro.sup.2 values. The refinement profile for the best-fit
result obtained with a X.sub.pro.sup.2 value of 128.5, is given in
supplementary information.
[0219] At this stage it is instructive to consider the quality of
the data and the solution, in a manner similar to that used in
protein crystallography. The useful information in the diffraction
data begins to die off at .about.26.degree. 2.theta. (see
Supplementary information), which corresponds to a d-spacing of 3.4
A. Consequently, it is futile to hope for a structure solution from
this diffraction data that accurately reproduces the crystal
structure with atomic resolution. A more realistic expectation
would be to attempt to extract the molecular packing diagram of the
planar naphthalocyanine rings. That would entail accurately fitting
the diffraction pattern out to a d-spacing corresponding to the
intermolecular spacing. In many metal naphthalocyaninates, the
shortest interplanar distances are .about.3.3 .ANG. [181] but in
the Li(OBu).sub.8Nc the butoxy chains are likely to increase the
intermolecular spacing. Our results (described in more detail
below) suggest that the napthalocyanine molecules are roughly 5
.ANG. apart. Therefore, the information that we can hope to
reliably extract from the diffraction pattern is contained in the
2.theta. range 3.2-18.60 (d>4.8 .ANG.). Building on this premise
we proceeded to analyze this low angle region of the diffraction
pattern using the simulated annealing algorithms in DASH. The
solution obtained possesses a very low X.sub.pro.sup.2 value of 24,
and once again the type II model for the location and orientation
of the naphthalocyanine ring was obtained. The refinement profile
for 3.2-18.60 range is shown in FIG. 19. This result combined with
the results using truncated alkoxy chains give compelling proof
that the approximate molecular packing diagram corresponds to the
type-II solution, while the type-I solution represents a false
minimum that results from the failure to accurately determine the
orientations of the n-butoxy chains. The high X.sub.pro.sup.2 value
that is obtained from analysis of the entire pattern can be traced
to the poor fit at higher 2.theta. region, where the coherence
related to the orientation of the butoxy chains becomes
increasingly important. Clearly there is some degree of order in
the orientation of these chains, but the vast number of
conformations that could be adopted prevents us from extracting
this information. To obtain this information single crystal studies
are probably necessary. Alternatively, energy minimization
algorithms may be able to find the most favorable conformation
given the dimensions of the unit cell and the approximate location
of the napthalocyanine ring.
[0220] FIG. 20 shows the obtained crystal structure of
Li(OBu).sub.8Nc viewed along the three crystallographic axes. It
can be noted that the molecules are arranged to form infinite
channels along a- and c-axes. These channels interpenetrate each
other at an angle of 109.8.degree., which is nearly the same as the
lattice angle, B. While the exact dimensions will be sensitive to
the conformation of the n-butoxy groups, the cross-sectional
dimensions of the channels are not smaller than 8.1.times.9 .ANG.
and 4.6.times.5.7 .ANG. along a- and c-axes, respectively. The
presence of large and interconnected voids in the crystal structure
could allow facile diffusion of O.sub.2 molecules, whose
approximate size is 2.8.times.3.9 .ANG.. This structural motif is
likely to be crucial to the sensor activity of Li(OBu).sub.8Nc. The
view along the b-axis (FIG. 20b) shows that the planar rings of the
Li(OBu)8Nc molecules are almost parallel to b-axis. Furthermore, it
illustrates the columnar stacking of the molecules in a- and
c-directions, which is responsible for the creation of channels.
Within the columnar arrangements in both the directions, a dimer
unit of Li(OBu).sub.8Nc molecules is formed. The molecules in the
dimer are slightly glided away from the eclipsed conformation to
have an interplanar distance of .about.4.8 .ANG. and a Li--Li
distance of 5.0 .ANG.. Along the a-direction, the closest
Li(OBu).sub.8Nc molecules from two neighboring dimers are separated
by an interplanar distance of 9.4 .ANG. and a Li--Li distance of
13.5 .ANG.. On the other hand, in the c-direction, the planar
spacing between the dimers is almost identical to the intra-dimer
spacing of .about.4.8 .ANG., and the adjacent dimers are glided
from each other to have a Li--Li distance of 11.4 .ANG..
* * * * *