U.S. patent application number 12/575596 was filed with the patent office on 2010-02-11 for use of one or more of the elements from the group yttrium, neodymium and zirconium, and pharmaceutical compositions which contain those elements.
This patent application is currently assigned to BIOTRONIK VI PATENT AG. Invention is credited to Claus Harder, Bernd Heublein, Christoph Heublein, Eva Heublein, Nora Heublein.
Application Number | 20100034899 12/575596 |
Document ID | / |
Family ID | 32115564 |
Filed Date | 2010-02-11 |
United States Patent
Application |
20100034899 |
Kind Code |
A1 |
Harder; Claus ; et
al. |
February 11, 2010 |
USE OF ONE OR MORE OF THE ELEMENTS FROM THE GROUP YTTRIUM,
NEODYMIUM AND ZIRCONIUM, AND PHARMACEUTICAL COMPOSITIONS WHICH
CONTAIN THOSE ELEMENTS
Abstract
A method of treating a patient includes the medical use of one
or more of the elements from the group yttrium, neodymium and
zirconium, pharmaceutical formulations which contain said elements
and implants which are at least region-wise made up of such
formulations. It has been found inter alia that a formulation
containing one or more of the elements has an action of inhibiting
the proliferation of human smooth muscle cells.
Inventors: |
Harder; Claus; (Uttenreuth,
DE) ; Heublein; Bernd; (Hannover, DE) ;
Heublein; Eva; (Hannover, DE) ; Heublein; Nora;
(Koln, DE) ; Heublein; Christoph; (Hannover,
DE) |
Correspondence
Address: |
HAHN LOESER & PARKS, LLP
One GOJO Plaza, Suite 300
AKRON
OH
44311-1076
US
|
Assignee: |
BIOTRONIK VI PATENT AG
Baar
CH
|
Family ID: |
32115564 |
Appl. No.: |
12/575596 |
Filed: |
October 8, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10535084 |
Jun 8, 2006 |
|
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PCT/EP03/12532 |
Oct 11, 2003 |
|
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12575596 |
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Current U.S.
Class: |
424/617 |
Current CPC
Class: |
A61L 31/022 20130101;
A61F 2/91 20130101; A61F 2002/9155 20130101; A61L 31/148 20130101;
A61P 35/00 20180101; A61F 2/915 20130101 |
Class at
Publication: |
424/617 |
International
Class: |
A61K 33/24 20060101
A61K033/24; A61P 35/00 20060101 A61P035/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 13, 2002 |
DE |
102 53 634.1 |
Claims
1. A method of treating a patient comprising use of one or more of
the elements from the group yttrium (Y), neodymium (Nd) or
zirconium (Zr) for the production of a pharmaceutical formulation
for inhibiting the proliferation of human smooth muscle cells.
2. The method according to claim 1, wherein the inhibition of the
proliferation of human smooth muscle cells is directed to the
region of an atherosclerotic lesion.
3. The method according to claim 2 comprising local restenosis
prophylaxis after stent implantation.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of copending U.S.
application Ser. No. 10/535,084, filed Jun. 8, 2006, which is a
national stage entry of international application PCT/EP03/12532,
filed on Oct. 11, 2003.
BACKGROUND OF THE INVENTION
[0002] The invention concerns the medical use of one or more of the
elements from the group consisting of yttrium, neodymium and
zirconium, pharmaceutical formulations which contain those elements
and implants which are at least region-wise made up of such
formulations.
[0003] Inflammation is used to denote the reaction of the organism,
borne by the connective tissue and the blood vessels, to an
external or internally triggered inflammation stimulus with the aim
of eliminating or inactivating same and repairing the
stimulus-induced tissue damage. A triggering action is effected by
mechanical stimuli (foreign bodies, pressure, injury) and other
physical factors (ionizing rays, UV-light, heat, cold), chemical
substances (lyes, acids, heavy metals, bacterial toxins, allergens
and immune complexes) as well as pathogens (micro-organisms, worms,
insects) or diseased metabolic products (out-of-control enzymes,
malignant tumors). The microbiological processes which are complex
due to the specified triggering factors, generally involve the
liberation of so-called growth factors such as FGF, PDGF and EGF
which stimulate proliferation, that is to say the increase in
tissue due to rampant growth or reproduction.
[0004] It will be noted that under certain medical indications
proliferation should be at least temporarily inhibited. In order to
oppose the reproductive activity of the cells or organisms, it is
known for example to use mitosis poisons, ionizing rays or
interferons for anti-viral action.
[0005] Particular requirements are involved in the treatment of
coronary heart diseases. Coronary heart diseases, in particular
acute myocardial infarctions, represent one of the most frequent
causes of death in Western Europe and North America. In more than
80% of cases, the cause of the myocardial infarction is thrombotic
closure of a coronary artery due to rupture of an atheromatous
plaque with pre-existing stenosing atheromatosis. Decisive factors
for the long-term prognosis after acute myocardial infarction are
as follows: [0006] effective and long-lasting re-dilation of the
infarct artery, [0007] the duration of the thrombotic vessel
closure, [0008] the prevention of greater myocardial loss and
ventricular remodeling, and [0009] the mastery of rhythmogenic
complications.
[0010] The specified factors determine not only cardiovascular
mortality but also the quality of life after the infarction.
[0011] Non-operative methods of stenosis treatment have been
established for more than 20 years, in which inter alia, the
constricted or closed blood vessel is dilated again by balloon
dilation (PTCA--percutaneous transluminal coronary angioplasty).
That procedure has proven its worth in particular in terms of
therapy for acute myocardial infarction. It will be noted however
that, with dilation of the blood vessel, very minor injuries,
fissures and dissections occur in the vessel wall, which admittedly
frequently heal up without any problem but which in about a third
of the cases result in proliferation due to triggered cell growth,
which ultimately result in renewed vessel constriction
(restenosis). Dilation also does not eliminate the causes of the
stenosis, that is to say, the molecular-pathological changes in the
wall of the vessel. A further cause of restenosis is the elasticity
of the expanded blood vessel. After removal of the balloon, the
blood vessel constricts excessively so that the vessel
cross-section is reduced (obstruction, referred to as negative
remodeling). The latter effect can only be avoided by the placement
of a stent.
[0012] In terms of interventional therapy for stable and unstable
angina pectoris in the case of coronary heart disease, the
insertion of stents has resulted in a marked reduction in the rate
of restenosis situations and thus better long-term results. That
applies both in regard to primary stenosis and also recidivist
stenosis. The higher level of primary lumen gain is the cause for
using stent implantation.
[0013] An optimum vessel cross-section can admittedly be achieved
by the use of stents, but it will be noted that the use of stents
also results in very minor injuries which can induce proliferation
and which thus can ultimately trigger restenosis. In addition, the
presence of such a foreign body initiates a cascade of cellular
molecular processes which can result in progressive blockage of the
stent.
[0014] In the meantime, extensive knowledge has been acquired
relating to the cell-biological mechanism involved and the
triggering factors in stenosis and restenosis. As already
explained, restenosis occurs as a reaction on the part of the
vessel wall to the local injury as a consequence of expansion of
the atherosclerotic plaque. By way of complex operative mechanisms,
lumen-directed migration and proliferation of the smooth muscle
cells of the media and the adventitia is induced (neointimal
hyperplasia). Under the influence of various growth factors, the
smooth muscle cells produce a cover layer of neointimal smooth
muscle cells and matrix proteins (elastin, collagen and
proteoglycans) whose uncontrolled growth can gradually result in
constriction of the lumen. Systemic drug therapy uses provide inter
alia the oral administration of calcium antagonists, ACE
inhibitors, anticoagulants, antiaggregants, fish oils,
antiproliferative substances, antiinflammatory substances and
serotonin antagonists, but hitherto significant reductions in the
kinds of restenosis have not been achieved in that way. A possible
explanation for the disappointing results of all previous attempts
of systemic application of the most widely varying substances is
that systemic application cannot take the substance in an adequate
level of concentration to the location of the vessel injury.
[0015] For some years now, attempts have been made to reduce the
risk of restenosis upon the implantation of stents by applying
special coating systems. In part, the coating systems serve as
carriers, in which one or more pharmacologically effective
substances are embedded (local drug delivery or LDD). Local
application makes it possible to achieve a higher tissue level, in
which case systemic substance discharge remains low and thus
systemic toxicity is reduced. The coating systems generally cover
at least one peripheral wall of the endovascular implant, which is
towards the vessel wall. Hitherto, numerous preparations have been
proposed as active substances or active substance combinations for
LDD systems, for example Paclitaxel, Actinomycin, Sirolimus,
Tacrolimus, Everolimus and Dexamethasone.
[0016] The carriers of coating systems of that kind comprise a
biocompatible material which either is of natural origin or which
can be produced synthetically. Particularly good compatibility and
the possibility of influencing the elution characteristic of the
embedded drug are afforded by biodegradable coating materials.
Examples for the use of biodegradable polymers are cellulose,
collagen, albumin, casein, polysaccharides (PSAC), polylactide
(PLA), poly-L-lactide (PLLA), polyglycol (PGA),
poly-D,L-lactide-co-glycolide (PDLLA/PGA), polyhydroxybutyric acid
(PHB), polyhydroxyvaleric acid (PHV), polyalkylcarbonates,
polyorthoesters, polyethyleneterephthalate (PET), polymalonic acid
(PML), polyanhydrides, polyphosphazenes, polyamino acids and their
copolymers as well as hyaluronic acid and its derivatives.
[0017] At the present time, 80% of all stents are manufactured from
medical steel (316L). In the course of time, it has been found
however that the material used is admittedly biocompatible but over
medium and long periods of time it promoted in part thrombosis
formation and in part adhesion of biomolecules to its surface. A
further limitation in terms of biocompatibility of permanent stents
is ongoing mechanical stimulus of the vessel wall. A starting point
for resolving those problems is stents comprising a biodegradable
material. The term biodegradation is used to denote hydrolytic,
enzymatic and other metabolism-induced decomposition processes in
the living organism, which result in a gradual dissolution of at
least large parts of the implant. The term biocorrosion is
frequently used synonymously. The notion of bioresorption
additionally includes the subsequent resorption of the
decomposition products. Thus for example, a large number of plastic
materials have been proposed as the stent material, which
admittedly exhibited good degradation behaviour but which by virtue
of their mechanical properties are at most limitedly useful for
medical application and--thus at least in the case of synthetic
polymers based on PU and LDA derivatives--also cause a severe
inflammatory reaction and stimulate neointima proliferation.
[0018] To overcome the above-indicated disadvantage, the use of
special biodegradable metal alloys has recently been proposed, as
are described in particular in DE 197 31 021 and DE 199 45 049. The
metal alloys include special biodegradable iron, tungsten and
magnesium alloys.
[0019] U.S. Pat. No. 6,264,595 discloses a stent which inter alia,
can contain radioactive yttrium isotopes, in which case the
radiation produced upon disintegration of the isotopes is intended
to prevent restenosis after stent implantation. U.S. Pat. No.
4,610,241 describes a method of treating atherosclerosis with
ferro-, dia- or paramagnetic particles which, after placement at
the location of the lesion, are heated up by alternating
electromagnetic fields. The particles are to include inter alia
given yttrium salts.
[0020] Zirconium is a constituent part of numerous ceramic
biomaterials. Hitherto, in vivo and in vitro investigations on
special zirconium-bearing ceramics have not provided any pointers
to a pharmacological effect in connection with smooth human muscle
cells (Piconi, C, Maccauro G, (1999) Biomaterials 20, 1-25).
BRIEF SUMMARY OF THE INVENTION
[0021] The object of the present invention is inter alia, to
provide agents for inhibiting the proliferation of human smooth
muscle cells and pharmaceutical formulations, which are suitable in
particular for use in endovascular implants such as stents.
[0022] In accordance with a first aspect of the invention, that
object is attained by the use of one or more of the elements from
the group yttrium (Y), neodymium (Nd) or zirconium (Zr) for the
production of a pharmaceutical formulation for inhibiting the
proliferation of human smooth muscle cells.
[0023] It has now surprisingly been found that the proliferation of
human smooth muscle cells, in particular arterial muscle cells, is
markedly inhibited in the presence of yttrium, neodymium and/or
zirconium. In particular, the use of those elements means that
neointimal hyperplasia after balloon dilation can be reduced or
even entirely prevented. The use of one or more of the elements
from the group consisting of yttrium, neodymium or zirconium
appears to be particularly suitable for the treatment of sclerotic,
preferably atherosclerotic lesions. In the case of the
pathophysiological processes which form the basis for restenosis,
proliferation of smooth muscle cells which have previously migrated
out of the media plays a crucial part. Inhibition of cell growth
over a given period of time until the growth-stimulating factors
are decomposed for the major part or completely can therefore
effectively obviate restenosis. The elements yttrium, neodymium
and/or zirconium are thus suitable in particular for restenosis
prophylaxis after stent implantation. The reasons for the
surprising pharmaceutical action of the elements yttrium, zirconium
and/or neodymium on human arterial smooth muscle cells have not yet
been completely clarified. Presumably the redox processes which
take place in the cell medium with participation of the metals play
an essential part.
[0024] Previous in vivo and in vitro investigations on mammals and
fish in respect of the toxic and possibly pharmaceutical action of
yttrium trichloride (YCl.sub.3) have not provided any indications
about the particular pharmaceutical action of yttrium on arterial
human smooth muscle cells. [0025] With an intravenous
administration of 1 mg YCl.sub.3/107 g rat an increase in the
aspartate and glutamate-pyruvate-transaminase activity was measured
in the blood plasma 20 hours after administration, which points to
liver damage (Hirano, S, Kodama, N, Shibata, K, and Suzuki, K T
(1993) Toxicol Appl Pharmacol 121(2), 224-232).
[0026] Intratracheally applied YCl.sub.3 led to activation of the
immune response in the lungs (Hirano, S, Kodama, N, Shibata, K, and
Suzuki, K T (1993) Toxicol Appl Pharmacol 104(2), 301-311) and a
rise in inflammatory markers (.beta.-glucuronidase, lactate
dehydrogenase (LDH) and alkaline phosphatase) in the
bronchoalveolar lavage fluid (BALF) (Suzuki, K T, Kobayashi, E,
Ito, Y, Ozawa, H and Suzuki, E (1992) Toxicology (76(2), 141-152;
Murubashi, K, Hirano, S, and Suzuki, K T (1998) Toxicol Lett 99(1),
45-51). [0027] A concentration of 15 .mu.M YCl.sub.3 in water leads
to a reduction in the level of superoxide-dismutase activity in
goldfish liver while catalase activity is only slightly impaired
(Chen, Y, Cao, X D, Lu, Y and Wang, X R (2000) Bull Environ Contam
Toxicol 65(3), 357-365).
[0028] The `isolated organ technique` demonstrated that YCl.sub.3
reduces the amplitude of the peristaltic activity of rat intestine
(Cunat, L, Membre, H, Marchal, L, Chaussidon, M and Burnel, D
(1998) Biol Trace Elem Res 64(1-3), 43-59). [0029] In vitro a
genotoxic action of YCl.sub.3 on human lymphocytes was demonstrated
(Yang, H, Ji, Q, and Zhang, X (1998) Zonghua Yu Fang Yi Xue Za Zhi
32(3), 156-158). [0030] YCl.sub.3 blocks Ca.sup.2+ channels in
vitro (Beedle, A M, Hamid, J, and Zamponi, G W (2002) J Membr Biol
187(3), 225-238; Minar, B, and Enyeart, J J (1993) J Physiol 469,
639-652).
[0031] There are also studies about the influence of yttrium on the
proliferation of bacteria. Investigations were conducted into
Tetrahymena shanghaiensis (Wang, Y, Zhang, M and Wang, X (2000)
Biol Trace Elem Res 75(1-3), 265-275), Klebsiella pneumoniae strain
204 and K9 (Aleksakhina, N N, Miriasova, L V and Basnak'ian, I A
(2002) Zh Mikrobiol Epidemiol Immunobiol (6), 13-18) and also
Pseudomonas fluorescens (Appanna, V D, Hamel, R D, Pankar, E and
Puiseux-Dao, S (2001) Microbios 106(4-13), 19-29). In that case
there was found to be increased proliferation for T. shanghaiensis
and P. fluorescens at low levels of yttrium concentration and an
antiproliferative action at high levels of concentration. For K.
pneumoniae a comparative high level of concentration (142 mM
Y(OH).sub.3) was tested, which resulted in increased
proliferation.
[0032] A second aspect of the invention concerns pharmaceutical
formulations containing one or more of the elements from the group
yttrium, neodymium or zirconium.
[0033] An advantageous adaptation of the pharmaceutical formulation
provides that the formulation includes an at least very
substantially biodegradable carrier which is broken down in vivo
with a predetermined degradation performance. The term `degradation
performance` is used to denote the breakdown of the carrier in the
living organism, which takes place over time, due to chemical,
thermal, oxidative, mechanical or biological processes. This aspect
of the invention is of significance, in particular when the
formulation is to be suited for intravascular liberation after
implantation in a vascular vessel. In particular, local application
of the active substances is to be effected in the region of the
lesion to be treated. Such procedures can be summarised by the term
`local drug delivery` (LDD).
[0034] In accordance with a preferred variant, the biodegradable
carrier is an alloy, in particular a magnesium, iron or tungsten
alloy. Metal alloys of that kind are known for example from DE 197
31 021 and DE 199 45 049. A further, particularly suitable
formulation based on a magnesium alloy is of the following
composition:
[0035] Magnesium: >90%
[0036] Yttrium: 3.7% to 5.5%
[0037] Rare earths (without yttrium): 1.5% to 4.4%
[0038] Balance: <1%.
[0039] Preferably, the formulation further includes a magnesium
alloy with a content of yttrium in the range of between 3.7 and
5.5% by weight, a content of neodymium in the range of between 1.8
and 2.7% by weight and a content of zirconium in the range of
between 0.2 and 1.2% by weight. In a particularly preferable
feature, the formulation corresponds to the commercially available
magnesium alloy WE43 (W-25 EP 5M). The above-mentioned materials
and details relating to the composition are distinguished by their
good workability and favourable liberation performance for yttrium,
neodymium and zirconium upon in vivo breakdown of the carrier. The
literature includes inter alia, a study relating to the degradation
performance of a magnesium alloy under physiological conditions,
which provides indications as to which factors and measures are to
be observed when optimising active substance liberation (Levesque,
J, Dube, D, Fiset, M and Mantovani, D (2003) Material Science Forum
Vols 426-432 pp, 225-238).
[0040] In accordance with a further variant of the formulation
according to the invention, the carrier is a biodegradable polymer
and one or more of the elements from the group yttrium, neodymium
or zirconium is embedded in the form of powders or microparticles
in the polymer. Due to the gradual breakdown of the polymer in
vivo, the powder or the microparticles is or are slowly liberated
and can deploy their pharmacological action after bioresorption.
The polymer carrier can be in particular hyaluronic acid,
poly-L-lactide or a derivative of the polymers.
[0041] It is further preferred if the formulation contains yttrium
in a quantitative proportion of between 0.1 and 10% by weight,
neodymium in a quantitative proportion of between 0.1 and 5% by
weight and/or zirconium in a quantitative proportion of between 0.1
and 3% by weight, in each case with respect to the total weight of
the formulation.
[0042] It is known from cell culture tests that the elements of the
group yttrium, neodymium and zirconium, in certain ranges of
concentration, exhibit an antiproliferative behaviour on arterial
human smooth muscle cells. The formulation according to the
invention, insofar as it includes yttrium, is therefore so adapted
that an yttrium concentration in the region of the human smooth
muscle cells to be treated is between 200 .mu.M and 2 mM, in
particular between 800 and 1 mM. If the composition contains
neodymium, then the formulation is preferably so adapted that there
is a neodymium concentration in the region of the human smooth
muscle cells to be treated of between 600 .mu.M and 2 mM, in
particular between 800 .mu.M and 1 mM. If zirconium is a
constituent of the formulation, a zirconium concentration in the
region of the human smooth muscle cells to be treated is preferably
to be predetermined by targeted adaptation of the formulation at
between 200 .mu.M and 2 mM, in particular between 200 .mu.M and 1
mM. In the case of a formulation which contains yttrium, neodymium
and zirconium, it is particularly preferable for the formulation to
be so adapted that there is an yttrium concentration at between 350
and 550 .mu.M, a neodymium concentration at between 100 and 200
.mu.M and a zirconium concentration at between 10 and 30 .mu.M in
the region of the human smooth muscle cells to be treated. The
specified concentration ranges appear to be particularly suitable
for restenosis prophylaxis after stent implantation as the systemic
substance discharge is very slight and therefore at most a low
level of systemic toxicity has to be reckoned with.
[0043] The actual levels of concentration in the living organism
are dependent on the degradation performance of the formulation,
which in turn depends on the specific composition of the
formulation and the diffusion performance of the decomposition
products in the tissue. Theoretical predictions can only be made
with difficulty here and suitable measurements frequently suffer
from major measurement errors. So that the above-indicated
concentration ranges occur in the environment of the human smooth
muscle cells to be treated, experimental studies relating to
bioresorption of the selected formulation are therefore generally
also necessary.
[0044] The applicants' own experiments demonstrate inter alia a
statistically significant reduction in neointima formation in pigs
when using the alloy WE43 and the resulting degradation performance
(substantial biodegradation within 2 months). The coronary stents
used there were of a weight of 3 mg and contained 123 .mu.g of
yttrium (4.1% by weight), 66 .mu.g of neodymium (2.2% by weight)
and 15 .mu.g of zirconium (0.5% by weight).
[0045] A third aspect of the invention concerns implants which have
an at least region-wise coating consisting of the above-mentioned
formulation according to the invention or which in parts
structurally comprise said formulation. Such an implant can
preferably be in the form of an endovascular support device
(stent).
[0046] Distribution and mass of the formulation in a stent is
preferably predetermined with respect to the length of the stent in
such a way that there is between about 5 and 30 .mu.g/mm, in
particular between 10 and 20 .mu.g/mm, of yttrium. For neodymium
that is preferably fixed at between about 2 and 20 .mu.g/mm, in
particular between 3 and 10 .mu.g/mm, while for zirconium it is
preferably at between about 0.05 and 10 .mu.g/mm, in particular
between 0.5 and 6 .mu.g/mm. The stated limits of the ranges permit
pharmacodynamically favourable local application of the active
substances.
[0047] A fourth aspect of the invention concerns the already known
elements or combinations of elements from the group of yttrium,
neodymium or zirconium, with which no therapeutic action was yet
associated, as therapeutic agents. In particular, this aspect
concerns alloys which contain one or more elements from the group
yttrium, neodymium or zirconium. According to the applicants' own
knowledge hitherto a therapeutic action was not associated with any
of the elements/alloys. Indications in regard to the
antiproliferative action of one or more of the elements from the
group yttrium, neodymium and zirconium, their alloys or their use
in pharmaceutical formulations are not to be found in the state of
the art.
BRIEF SUMMARY OF THE SEVERAL VIEWS OF THE DRAWINGS
[0048] The invention is described in greater detail hereinafter by
means of embodiments and with reference to accompanying drawings in
which:
[0049] FIG. 1 shows a diagrammatic view of an endoprosthesis in the
form of a stent,
[0050] FIG. 2 is a view of a support portion 14.
[0051] FIG. 3 is a cross-sectional view across line A-A of FIG.
2,
[0052] FIG. 4 shows a typical section through a main coronary
vessel of a pig after implantation of a conventional stent, and
[0053] FIG. 5 shows a typical section through a main coronary
vessel of a pig after implantation of a stent comprising the
material WE43.
DETAILED DESCRIPTION OF THE INVENTION
Testing of Yttrium Chloride (YCl.sub.3), Zirconium Chloride
(ZrCl.sub.4) and Neodymium Chloride (NdCl.sub.3) in Cell
Culture
[0054] Test series on arterial human smooth muscle cells with a
concentration in the range of between 1 mM and 1 .mu.M, for
yttrium, neodymium and zirconium respectively were carried out as
follows:
[0055] The action of YCl.sub.3x6H.sub.2O, ZrCl.sub.4 and NdCl.sub.3
on the vitality and proliferation of human arterial smooth muscle
cells (SMC) was investigated. It is to be assumed that the elements
are oxidised in a physiological environment and bioresorption of
the rare earth ions Y.sup.3+, Zr.sup.4+ and Nd.sup.3+ takes place.
The tests were conducted in concentration ranges of between 1 mM
and 1 .mu.M, in each case with respect to the content of rare
earths. Lower levels of concentration exhibited no effects.
[0056] The substances were dissolved in water or ethanol
(ZrCl.sub.4) respectively (strain solution 0.1 M, in each case in
relation to the concentration of rare earths). Upon dilution in
cell culture medium, at higher levels of concentration, deposits
are formed, which could be reduced by ultrasonic treatment but not
completely eliminated. The eluates produced were incubated with
primary cell cultures of human arterial smooth muscle cells (SMC)
(3 days, 37.degree. C.). The cell vitality (MTS test) and cell
proliferation (BrdU test) were investigated. For that purpose tests
were performed similarly to a cytotoxicity testing procedure in
accordance with DIN EN 30993-5.
[0057] The vitality of arterial human smooth muscle cells rose in
the concentration range of between 1 .mu.m and 100 .mu.m. Levels of
concentration of >800 .mu.M of neodymium and zirconium resulted
in a drop in vitality.
[0058] The proliferation of arterial human smooth muscle cells was
increasingly greatly inhibited with levels of neodymium
concentration >800 .mu.M. Proliferation inhibition which was
already extensive was to be found with levels of yttrium
concentration of >800 .mu.M. With levels of zirconium
concentration of between 200 .mu.M and 1 mM the proliferation was
on average 44%. Accordingly, yttrium and neodymium at higher levels
of concentration exhibited a great action on the proliferation of
smooth muscle cells. Zirconium had a moderate antiproliferative
action.
Testing of WE43 Eluates in a Cell Culture
[0059] Sterilised sample bodies of the alloy WE43 weighing about 1
mg were eluted with 2 ml cell culture medium at 37.degree. C. in a
cell culture cabinet for 13 days, in which case the sample body is
only incompletely dissolved. Primary cell cultures of human
arterial smooth muscle cells (SMC) were then incubated with 1 ml of
the eluate and 1 ml of fresh cell culture medium (4 days,
37.degree. C.). Cell activity (MTS test) and cell proliferation
(BrdU test) were investigated. For that purpose tests were
performed similarly to a cytotoxicity testing procedure in
accordance with DIN EN 30993-5.
[0060] The proliferation of smooth muscle cells was 91% inhibited
upon incubation with eluates of the alloy WE43 in comparison with
control cells (SMC+medium). The cell activity of the smooth muscle
cells for the alloy WE43 was 95%.
Animal Tests on Pig
[0061] FIGS. 1-3 show a vascular endoprosthesis in the form of a
tubular stent 10 whose basic structure is composed of a plurality
of individual legs 12. The basic structure of the stent 10 can be
divided in the longitudinal direction into individual support
portions 14 which are each composed of legs 12 folded in a zig-zag
or meander configuration and which extend in the peripheral
direction. The basic structure of the stent 10 is formed by a
plurality of such support portions 14 which occur in succession in
the longitudinal direction. The support portions 14 are connected
together by way of connecting legs 16. Each two connecting legs 16
which are mutually adjacent in the peripheral direction and the
sub-portions of the support portions 14, which are disposed in
mutually opposite relationship between those connecting legs 16,
define a mesh 18 of the stent 10. Such a mesh 18 is shown
emphasised in FIG. 1. Each mesh 18 surrounds a radial opening of
the peripheral wall or the basic structure of the stent 10.
[0062] Each support portion 14 has for example between three and
six connecting legs 16 which are equally distributed over the
periphery of the stent 10 and which respectively connect a support
portion 14 to the adjacent support portion 14. Accordingly the
stent 10 has between three and six meshes in each case in the
peripheral direction between two support portions 14.
[0063] By virtue of the folding of the legs 12, the stent 10 is
expandable in the peripheral direction. That is effected for
example with a per se known balloon catheter (not shown here) which
at its distal end has a balloon which is expandable by means of a
fluid. The stent 10 is crimped in the compressed condition on to
the deflated balloon. Upon expansion of the balloon, both the
balloon and also the stent 10 are enlarged. The balloon can then be
deflated again and the stent 10 comes loose from the balloon. In
that way the catheter can serve simultaneously for insertion of the
stent 10 into a blood vessel and in particular into a constricted
coronary vessel and also for expansion of the stent at that
location.
[0064] The basic structure of the stent 10 shown in FIG. 1
comprises the biodegradable magnesium alloy WE43 of the following
formulation:
[0065] Zirconium: 0.53% by weight
[0066] Yttrium: 4.1% by weight
[0067] Neodymium: 2.2% by weight
[0068] Others: <0.4% by weight
[0069] Magnesium: balance to 100% by weight.
[0070] If a weight of 3 mg is assumed for a 10 mm long stent of
WE43, it contains about 123 .mu.g/1.384 .mu.M yttrium (4.1% by
weight), about 66 .mu.g/458 .mu.M neodymium (2.2% by weight) and
about 15 .mu.g/164 .mu.M zirconium (0.5% by weight). Per mm of
stent length, there is a maximum liberation of 12.3 .mu.g/138.4
.mu.M yttrium, 6.6 .mu.g/45.8 .mu.M neodymium and 1.5 .mu.g/16.4
.mu.M zirconium.
[0071] In animal tests on pigs, stents of the above-mentioned
magnesium alloy were compared with conventional silicon
carbide-coated stents by means of coronary angiography and
morphometric evaluation of histological section preparations. For
that purpose, conventional stents of medical high-grade steel with
a passive silicon carbide coating and stents of WE43 were implanted
in all three coronaries of pigs. A quantitative control angiography
(QCA) was effected in each case after four and eight weeks, in
which case breakdown in the case of the biodegradable stent in the
pig was very substantially concluded after about 8 weeks. In
addition cardiac preparations of the animals were produced after 8
weeks for histological processing.
[0072] The results of the coronary angiography and histological
section preparations demonstrate a marked trend towards a reduction
in surface stenosis when using WE43. The histology exhibited a
substantially uniform image in relation to neointima formation
after eight weeks. In that respect, the magnesium implants were
found to be less proliferative than the control implants. Thus an
average neointima surface formation of 1.23 mm.sup.2 was found when
using WE43, in comparison with 2.9 mm in the case of a conventional
implant.
[0073] FIG. 4 shows a typical section through a coronary vessel of
a pig upon implantation of a conventional stent with silicon
carbide coating after eight weeks while FIG. 5 shows a
corresponding histological section for a WE43-based implant. It
will be clear that neointima formation which can be estimated by
the morphometric cross-section of the neointima surfaces after
eight weeks is reduced approximately by a factor of 2 when using
WE43. The effect appears to be caused essentially by the residues
which are liberated upon degradation of the stent into the
surrounding tissue and which in turn contain yttrium, neodymium and
zirconium.
* * * * *