© 1997 American Heart Association, Inc.
Articles |
Dose-Dependent Suppression of Transplant Arteriosclerosis in Aorta-Allografted, Cholesterol-Clamped Rabbits
Suppression Not Eliminated by the Cholesterol-Raising Effect of Cyclosporine
From the Departments of Thoracic Surgery (H.O.A.) and Clinical Biochemistry (H.O.A., P.H.), Rigshospitalet, Hellerup; the Clinical Institute, University of Odense (S.S.), Odense; the Department of Pathology, Hvidovre Hospital (B.F.H.), Hvidovre; and the Department of Clinical Biochemistry, Herlev Hospital (B.G.N.), Herlev, Denmark.
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Abstract Cyclosporine may suppress transplant arteriosclerosis; however, it also raises plasma cholesterol, which could promote the disease. Our aim was to test these hypotheses experimentally. In experiment 1 (n=34), cholesterol was clamped at a human level of 5 to 7 mmol/L, and rabbits were given either saline or cyclosporine in a low, medium, or high dose. In experiment 2 (n=15), in which dietary cholesterol was fixed at 0.05 g·kg-1·d-1, and experiment 3 (n=16), in which no dietary cholesterol was added to the chow, rabbits were given either medium-dose cyclosporine, saline, or vehicle. The duration of each experiment was 5 weeks. In experiment 1, cyclosporine attenuated the development of transplant arteriosclerosis dose dependently (trend test: P<.0001). Cyclosporine also suppressed, in a dose-dependent manner, the activation of the immune system (trend test: P<.05) and the presence of T lymphocytes (trend test: P<.0001) and macrophages in the intima (trend test: P<.01). Despite a higher plasma cholesterol level in cyclosporine-treated rabbits compared with saline-treated rabbits in both experiment 2 (4.9 versus 2.9 mmol/L) and experiment 3 (1.6 versus 0.8 mmol/L), transplant arteriosclerosis was significantly reduced by cyclosporine (Mann-Whitney U test: P<.05 and P<.05). These results suggest that cyclosporine suppresses experimental transplant arteriosclerosis dose dependently. Accordingly, in the assessment of the optimal cyclosporine dose to heart-transplanted patients, it should be taken into account that a dose reduction may promote transplant arteriosclerosis.
Key Words: transplantation • arteriosclerosis • rabbits • cyclosporine • cholesterol •
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Introduction |
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Transplant arteriosclerosis constitutes a major limit to long-term survival after heart transplantation.1 2 In conventional atherosclerosis, lesions are focal and asymmetric whereas in transplant arteriosclerosis, lesions are concentric and affect the entire length of the transplanted vessels. The lesions in transplanted arteries include intimal proliferation of smooth muscle cells and accumulation of activated T-lymphocytes, both of which are assumed to be triggered by an immunological mechanism,3 4 5 as well as foam cells that seem to be induced by suitable elevated plasma cholesterol levels.6 7 8 In conventional atherosclerosis foam cells, smooth muscle cells and activated T-lymphocytes are also found.9 The progression and relative importance of the different cells for the two types of lesions may, however, be quite different.
Cyclosporine suppresses T-lymphocyte proliferation10 and is widely used in immunosuppressive regimens for heart-transplanted patients. The effect of cyclosporine on transplant arteriosclerosis is, however, controversial.1 11 12 Nevertheless, results from some recent studies in heart-13 14 15 and kidney-transplanted16 17 patients suggest that cyclosporine blood levels less than a certain value may promote the development of transplant arteriosclerosis, and cyclosporine blood levels greater than a certain value attenuate the development of transplant arteriosclerosis. However, cyclosporine has also been reported to increase plasma cholesterol levels,18 19 which in contrast may promote transplant arteriosclerosis.6 20 21 22 Furthermore, cyclosporine is tightly bound to low density lipoproteins in the blood and is probably taken up by lymphocytes23 and other cells24 as an LDL-cyclosporine complex. Effects of cyclosporine on the immune system may therefore be influenced by plasma lipoprotein concentrations.24 25
Most previous studies of experimental transplant arteriosclerosis have examined the effect of cyclosporine in the rat, ie, when plasma cholesterol was between 0.5 and 2 mmol/L,26 27 28 29 30 31 32 33 34 35 36 which is far below that seen in humans in the Western world. One study has examined the short-term effect of cyclosporine on transplant arteriosclerosis in cholesterol-fed, heart-transplanted rabbits.37 In that study, however, no information about plasma cholesterol concentrations was given. We have previously reported that cyclosporine suppresses transplant arteriosclerosis in the aorta-transplanted rabbit with plasma cholesterol clamped at human levels (5 to 7 mmol/L).38 However, in the experimental setting with plasma cholesterol in the human range, it is not known whether the effect of cyclosporine on transplant arteriosclerosis is dose dependent or whether this effect can be eliminated by the cholesterol-raising effect of cyclosporine.
In the present study, we examined at human levels of plasma cholesterol whether the inhibiting effect of cyclosporine on transplant arteriosclerosis is dose dependent (experiment 1) and whether it can be eliminated by the cholesterol-raising effect of cyclosporine (experiments 2 and 3). In experiment 2, the plasma cholesterol levels in the control groups were in the lower human range of 3 to 5 mmol/L, and in experiment 3, 0.5 to 1 mmol/L, the normal range for rabbits and rats. To test these hypothesises, we measured the severity of transplant arteriosclerosis and activation of the immune system as well as the cellular composition of the lesions.
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Methods |
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Animals
Three independent experiments were performed, all with a study period of 5 weeks. Experimental protocols were in accordance with the Danish regulations for experiments on animals. Outbred male white rabbits of the Danish Country Strain (Statens Seruminstitut, Copenhagen, Denmark), with recipients and donors belonging to separate litters, were anesthetized with repeated small doses of intravenous pentobarbital, the total dosage averaging 50 mg/kg. The surgical maneuvers have been described in detail previously.38 39 Briefly, a segment of the abdominal aorta below the origin of the renal arteries was exposed in the recipient animal, and approximately 3 cm of the descending thoracic aorta from the donor rabbit was implanted in the recipient rabbit as an abdominal aortic bypass graft within 1 hour. To direct the entire aortic blood flow through the graft, the abdominal aorta of the recipient rabbit was ligated between the two anastomoses. All surgical procedures were performed under sterile conditions.
Cyclosporine Treatment
Cyclosporine (10 mg/kg) (Sandimmun, Sandoz,
Copenhagen, Denmark), an equivalent volume of saline, or an equivalent
volume of the cyclosporine vehicle
(cremofor:ethanol%=66:33) was administered intramuscularly at the end
of the transplantation and subsequently once a day. In all experiments,
blood cyclosporine trough levels were determined once a
week (Emit Cyclosporine Assay, Syva Company, Palo Alto,
Calif). Additionally, in the dose-response experiment, blood
cyclosporine concentrations were followed for a period of
24 hours in nine rabbits, three from each of the three different
cyclosporine treatment groups.
Study Design
Experiment 1: Dose-Response Effect of Cyclosporine
When Plasma Cholesterol Is Clamped at a Human
Level
Two sets of each 17 rabbits (ie, n=34) were randomized and after
transplantation allocated to one of the following treatments: (1)
saline; (2) low-dose cyclosporine, ie, approximately
one-seventh the dose given to the medium-dose cyclosporine
group; (3) medium-dose cyclosporine; or (4) high-dose
cyclosporine, ie, two to three times the dose given to the
medium-dose cyclosporine group (Fig 1
). By this regimen, blood trough levels
of cyclosporine were held at either very low (low-dose),
lower (medium-dose), or upper (high-dose) levels of the human
therapeutic range, respectively. The medium dose was similar to that
used in our former study.38 After a recovery period of 2
weeks after transplantation, during which time the rabbits were allowed
free access to standard rabbit pellets (Altromin 2113, Lage, Germany),
the rabbits were fed a cholesterol-enriched chow for a
period of 3 weeks; corn oil (Mecobenzon, Copenhagen, Denmark) (9 to
10% in chow) was heated to dissolve the desired amount of
cholesterol (CH-USP, Sigma Chemical Co., St. Louis, Mo),
which was subsequently mixed with the standard pellets. The daily
amount of cholesterol fed to each rabbit was adjusted based
on regular determinations of plasma cholesterol levels to
achieve a mean plasma cholesterol concentration in the
human range of 5 to 7 mmol/L. In the first set of rabbits
in this experiment, plasma creatinine (HiCo
Creatinine, BM/Hitachi system 717, Boehringer
Mannheim, Mannheim, Germany) was determined once a week during the
study period, and plasma alkaline phosphatase (HiCo Alkaline
Phosphatase opt, BM/Hitachi System 717, Boehringer Mannheim)
and plasma bilirubin (calorimetric test for total bilirubin, Kodak,
Ektachem, Rochester, NY) were determined at the end of the study.
Values for intimal thickness and area from eight of the 34 rabbits in
this experiment have been reported previously.38
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Experiment 2: Effect of Medium-Dose Cyclosporine
When Dietary Intake of Cholesterol Is Fixed
Fifteen aorta-transplanted rabbits were randomized into three
groups as follows: (1) medium-dose cyclosporine, (2)
vehicle, or (3) saline group. After the 2-week recovery period, rabbits
from all three groups were fed a fixed daily amount of
cholesterol added to the chow (0.05 g/kg/day,
prepared with corn oil as described above) during the remaining 3
weeks; the amount of 0.05 g/kg/day was chosen because in
experiment 1, the medium-dose cyclosporine group was given
0.04 g/kg/day to clamp plasma cholesterol
between 5 and 7 mmol/L (Fig 1
).
In an earlier study,38 we reported that rabbits treated with cyclosporine were less active than saline-treated controls, ie, it could not be excluded that cyclosporine-treated rabbits were hypothyroid. Since hypercholesterolemia is frequent in patients with hypothyroidism, a hypothyroid state for cyclosporine-treated rabbits could explain the cholesterol-raising effect of cyclosporine. For these reasons, we measured thyroid parameters in plasma, ie, total triiodothyronine, free triiodothyronine, total thyroxine, free thyroxine and thyroid-stimulating hormone (IMx, Abbot Laboratories, Ill) at the start and end of the cholesterol feeding period.
Experiment 3: Effect of Medium-Dose Cyclosporine
When No Dietary Cholesterol Is Given
This experiment was analogous to experiment 2 except that no
cholesterol was added to the chow at any time (Fig 1).
Triiodothyronine and thyroid-stimulating hormone in plasma were
determined at days 0 and 14 and at the end of the study.
Lipoproteins
Plasma and lipoprotein cholesterol concentrations
were measured with an enzymatic kit (CHOD-PAP, Boehringer
Mannheim). Cholesterol content was determined in HDL
(d>1.063 g/mL), LDL (1.063<d<1.019
g/mL), intermediate density lipoprotein
(1.019<d<1.006 g/mL), and very low density
lipoprotein (d<1.006 g/mL) using
ultracentrifugation as described
previously.40
Transplant Arteriosclerosis
Five weeks after transplantation, the transplanted thoracic
aorta and the rabbits' own corresponding thoracic aorta were removed.
A specimen of unopened aorta, 3 to 5 mm long, was taken from the
central part of the graft as well as from the native aorta. After
fixation in neutral buffered formalin, the specimens were imbedded in
paraffin, and serial sections for histological
examinations were stained with elastic-van Gieson and
elastic-hematoxylin and eosine, respectively. Another 3- to 5-mm-long
specimen from the native and grafted aorta was immediately frozen in
isopentane cooled with dry ice, which was kept at -80°C until
further processing. Of the remaining graft and native aorta, the
luminal surface areas were outlined, and the tissues were divided into
an intima-inner media layer and an outer media layer. Each of these
parts was weighed and the tissues were stored at -20°C until further
processing. Total, free, and esterified cholesterol content
was determined as described earlier.40 Histomorphometric
studies as well as qualitative morphological evaluations were performed
blindly by one investigator (H.O.A.). Severity of transplant
arteriosclerosis was evaluated as the intimal area
divided by the medial area, quantified by point-counting as described
previously.41
Immunohistochemistry
Immunohistochemical demonstration of macrophages,
T-lymphocytes, and smooth muscle cells was performed by the
Avidin-Biotin method on formalin-fixed, paraffin-embedded aortic tissue
using the following monoclonal mouse-antirabbit antibodies:
RAM11 (DAKO Corporation, Carpinterie), which recognizes an
uncharacterized cytoplasmic antigen expressed by rabbit alveolar
macrophages,42 L11/135 (Serotec, Oxford, England),
a pan-T-lymphocyte marker, which recognizes rabbit T-lymphocytes in
blood and tissues but does not cross-react with other leucocytes, or
any other cell type,43 and HHF35 (DAKO A/S, Glostrup,
Denmark), which is a specific marker for smooth muscle cell-specific
actin in rabbits.43 As a marker of inflammation with
activation of the immune system, the 2C4 monoclonal mouse-antirabbit
antibody (Serotec, Oxford, England), which binds to the rabbit
homologue of the class II major histocompatibility complex (MHC)
antigen, was used in cryostat sections of aortic
allografts.43 Staining in the three experiments was as
follows: experiment 1: set 1: RAM 11, L11/35, and HHF35; set 2: same as
set 1 plus 2C4 on cryostat sections; experiments 2 and 3: RAM11,
L11/35, and HHF35.
In a representative field (magnificationx400) of the intima, media and adventitia, respectively, the number of antibody-positive cells (RAM11, L11/35, or HHF35; stainings were performed on three consecutive sections) were expressed as a percentage of the total number of cells in the intima, media, and adventitia, respectively. For 2C4, the intensity of staining was graded numerically on a scale from 0 to 5 as follows: grade 0, no staining; grade 1, patchy and weak staining; grade 2, uniform and weak staining; grade 3, patchy and moderate staining; grade 4, uniform and moderate staining; grade 5, uniform and intense staining.44
Statistics
All results are given as mean±SEM. Wilcoxon's test for
paired samples was used to evaluate the change in body weight during
the experiment. For comparison between three or more groups of rabbits,
the Kruskal-Wallis analysis of variance45 was
used. In case of a significant analysis of variance, and since
the analysis of variance does not test which specific groups of
rabbits differ from which other groups but only tests whether the
dependent variables overall differ between the different groups of
rabbits, post hoc analysis was performed with the Mann-Whitney
U-test to examine which specific groups of rabbit differ from the other
groups. The Wilcoxon-type trend test45 was used to
test for linear trends. Spearman's rank correlation coefficient,
calculated as Pearson's r value, was used to examine the
correlation between different sets of variables.45 A
P value of less than .05 was considered statistically
significant.
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Results |
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All rabbits lost weight immediately after the transplantation; however, rabbits from all groups subsequently gained weight with the exception of rabbits from the high-dose cyclosporine group in experiment 1 (Table 1
).
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Experiment 1: Dose-Response Effect of Cyclosporine
When Plasma Cholesterol Is Clamped at a Human
Level
Peak values of blood cyclosporine on 0.42, 0.98, and
1.37 µmol/L were reached at 1, 2, and 4 hours after
administration in rabbits treated with low (1-mg/kg), medium
(8-mg/kg), and high (18-mg/kg) doses of
cyclosporine, respectively (Fig 2). Mean trough levels of
cyclosporine, ie, 24 hours after injection, for the medium-
and high-dose cyclosporine groups were within the human
therapeutic range of 0.08 to 0.33 µmol/L (Table 1). As
judged from plasma creatinine levels carried out throughout
the entire study, renal function was unaffected by
cyclosporine and was similar in all groups at the end of
the study: 0.11±0.00, 0.10±0.00, 0.11±0.01, and 0.10±0.01
mmol/L in saline, low-dose, medium-dose, and high-dose
cyclosporine groups, respectively. The plasma alkaline
phosphatase values decreased with increasing doses of
cyclosporine (Wilcoxon-type trend test,
P<.0001); values at the end of the study in rabbits treated
with saline, low-dose, medium-dose, and high-dose
cyclosporine 228±26, 191±19, 165±5, and 91±12 U/L,
respectively. No difference was demonstrated in plasma bilirubin
concentrations between the groups (data not shown).
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Plasma cholesterol concentrations were similar in all four
groups throughout the study period (Fig 1). The amount of dietary
cholesterol needed to clamp plasma cholesterol
at similar levels during the cholesterol feeding period in
the four groups was inversely-correlated with mean trough levels of
cyclosporine (Table 1 and Fig 1) (Pearson's
r=-.703, P<.0001, n=34). This is in accordance
with a dose-dependent hypercholesterolemic effect of
cyclosporine.
The accumulation of cholesterol in the aortic grafts was
inversely associated with the dose of cyclosporine
(Wilcoxon-type trend test, P<.0001) (Fig 1).
Cholesterol accumulation in grafts from all four groups was
significantly greater than that in native aortas (Fig 1). Transplant
arteriosclerosis in aortic allografts (ratio of
intimal area/media area) was reduced dose dependently
(Wilcoxon-type trend test, P<.0001) (Fig 1). No
significant difference could be demonstrated between grafts from
saline- and low-dose cyclosporine-treated rabbits
(Fig 1).
MHCII expression was present in the intima, media, and adventitia
of aortic allografts from rabbits treated with either saline, low-dose
cyclosporine, or medium-dose cyclosporine but
was absent in allografts from rabbits treated with high-dose
cyclosporine (Figs 3 and 4) (Wilcoxon-type trend test for
all arterial layers (P<.05,
n=1.
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Medial smooth muscle cell necrosis was seen in all allografts from
untreated rabbits and in most rabbits treated with low-dose
cyclosporine, but in none of the allografts from rabbits
treated with medium- or high-dose cyclosporine (Figs 4 and 5). A number of allografts from the two
former but not the two latter groups exhibited smooth muscle cell
proliferation in intima and adventitia (Fig 4).
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T-lymphocytes were not demonstrated in any of the three layers of
aortic allografts from rabbits treated with high doses of
cyclosporine, whereas an increasing occurrence of
T-lymphocyte infiltration was demonstrated in all three layers of the
aorta with decreasing doses of cyclosporine (Figs 4 and 5)
(Wilcoxon-type trend test for T-lymphocytes in intima, n=34,
P<.0001).
Macrophage infiltration was not observed in allografts from
rabbits treated with high-dose cyclosporine. However, a
significant infiltration was found in allografts from rabbits treated
with saline and/or low doses of cyclosporine, whereas
allografts from the medium-dose cyclosporine group had
intermediate infiltration in the intima (Figs 4 and 5)
(Wilcoxon-type trend test for macrophages in intima,
P<.01).
Experiment 2: Effect of Medium-Dose Cyclosporine
When Dietary Intake of Cholesterol Is Fixed
Plasma cholesterol was significantly greater in
cyclosporine-treated rabbits than in saline- or
vehicle-treated rabbits throughout the 5-week study period (Fig 1).
Nevertheless, cholesterol accumulation as well as the
development of transplant arteriosclerosis (intimal
area/medial area) was significantly lower in aortic allografts from
cyclosporine-treated rabbits than from saline- or
vehicle-treated rabbits.
A substantial medial necrosis was observed in the grafts from
saline- and vehicle-treated rabbits but not in grafts from
cyclosporine-treated rabbits (Figs 4 and 5).
T-lymphocytes and macrophages were seen in all layers of grafts
from saline- and vehicle-treated rabbits, whereas these cells were seen
only rarely in grafts from cyclosporine-treated
rabbits, and then only in the adventitia.
Plasma levels of total T3 were significantly lower in cyclosporine-treated than in saline-treated rabbits. However, no difference was observed in free triiodothyronine, total thyroxine, or thyroid-stimulating hormone between groups (data not shown).
Experiment 3: Effect of Medium-Dose Cyclosporine
When No Dietary Cholesterol Is Given
Despite a significantly higher plasma cholesterol
level in cyclosporine-treated rabbits compared with
saline- or vehicle-treated rabbits (Fig 1), cholesterol
accumulation was similar in grafts from all three groups. Transplant
arteriosclerosis (intimal area/medial area)
developed in grafts from saline- and vehicle-treated rabbits
but not in grafts from cyclosporine-treated
rabbits. Immunohistochemical findings in this experiment were similar
to those in experiment 2 (Figs 4 and 5).
Total triiodothyronine was significantly lower in cyclosporine-treated rabbits than in saline- and vehicle-treated rabbits, whereas no difference in thyroid-stimulating hormone levels was demonstrated between groups (data not shown).
Experiments I, II, and III
The accumulation of total and esterfied cholesterol in
the aortic allografts was highly correlated with the
histological quantification of transplant
arteriosclerosis (intimal area/medial area) in
experiments 1 and 2, but not in experiment 3 (Table 2).
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Discussion |
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Cyclosporine and Transplant Arteriosclerosis
In the present study, using aorta-transplanted rabbits clamped at a human level of plasma cholesterol, cyclosporine inhibited the development of transplant arteriosclerosis dose dependently. The present dose-response study (experiment 1) could not completely exclude that the reduction in transplant arteriosclerosis was not caused by the lesser amount of dietary cholesterol or maybe cholesterol oxides given to the animals in the medium- and high-dose cyclosporine groups. However, in experiment 2 when dietary cholesterol (and thereby also cholesterol oxides) were identical in all rabbits, cyclosporine also attenuated the development of transplant arteriosclerosis. A dose-dependent inhibitory effect of transplant arteriosclerosis by cyclosporine has also been demonstrated in the rat, but at a plasma cholesterol level much lower than that seen in humans.32 33 In humans, no dose-response studies have been performed, but results from some recent studies in heart-13 14 15 and kidney-transplanted16 17 patients supported a correlation between the development of transplant arteriosclerosis and the daily cyclosporin dose.
The mechanism behind an inhibitory effect of cyclosporine on transplant arteriosclerosis is at present not clear. However, a tentative explanation is that cyclosporine reduces episodes of acute rejection and thereby also the development of transplant arteriosclerosis. That episodes of acute rejection accelerate the development of transplant arteriosclerosis has been demonstrated in rabbit heart46 and rat kidney allografts47 and has also been suggested by findings in heart transplanted patients.48 49 50 The present demonstration of a dose-dependent reduction in immune activation (MHCII expression), T-lymphocytes, macrophages, and smooth muscle cells in the intima of transplanted vessels, parallel to the dose-dependent reduction in transplant arteriosclerosis, further suggests that even smaller reductions in the cyclosporine dose without precipitating episodes of acute rejection can be important in leading to an increased development of transplant arteriosclerosis.
Interferon-gamma is a cytokine secreted from activated T-lymphocytes4 at an increased rate in experimental transplant arteriosclerosis.51 52 Interferon-gamma activates macrophages,4 promotes up-regulation of endothelial MHCII expression4 and of intercellular adhesion molecule-1,53 which promotes adherence of monocytes to the endothelial cells.53 In heart-transplanted rabbits treated with cyclosporine, however, up-regulation of intercellular adhesion molecule-1 was inhibited5 37 as well as the development of transplant arteriosclerosis.37 Thus, a direct54 or indirect (ie, via reduction in the number of T-lymphocytes) dose-dependent inhibitory effect of cyclosporine on the secretion of interferon-gamma would lead to a dose-dependent reduction in the number of macrophages, in MHCII expression, and in transplant arteriosclerosis, all of which was seen in the present study.
Vascular changes in the media are also observed in human allografts, but these changes consist only of medial thinning55 and focal myocyte necrosis.56 This may be due to the use of cyclosporine. In the present study, cyclosporine mediated protection against medial smooth muscle cell necrosis, which has also been described in rat aorta allografts.26 33 The mechanism behind this protection may be a reduction in an otherwise significant immunological injury, mediated through different cytokines: interferon-gamma, tumor necrosis factor-alpha, and interleukin-1-beta, all supposed to be present at an increased level in transplant arteriosclerosis4 and in different combinations that have been shown to trigger death of vascular smooth muscle cells.57
Cyclosporine-Induced Hypercholesterolemia
A hypercholesterolemic effect of
cyclosporine, which has been reported earlier in
rabbits38 58 59 and humans,18 19 was also a
consistent feature in all cyclosporine-treated
groups in the present study. In experiment 1, it appeared that this
effect was dose dependent, as assessed by the reciprocal association
between the dose of cyclosporine and the amount of daily
dietary cholesterol necessary to clamp the plasma
cholesterol in the four groups. The
hypercholesterolemic effect of cyclosporine
was not related to the vehicle58 since saline- and
vehicle-treated rabbits had similar plasma cholesterol
levels (experiments 2 and 3). In the present study, the beneficial
effect of cyclosporine on transplant
arteriosclerosis by far exceeded the potential
deleterious effects of the elevated plasma cholesterol
levels; cyclosporine-treated rabbits with a higher
plasma cholesterol level had less transplant
arteriosclerosis than saline- or vehicle-treated
groups with a lower plasma cholesterol level. This
conclusion was identical irrespective of whether the plasma
cholesterol level in saline- or vehicle-treated groups was
in the human (experiment 2) or rabbit (experiment 3) range.
Transplant Arteriosclerosis and
Arterial Cholesterol Accumulation
McManus et al22 found a significant correlation
between histological and biochemical evaluation of
transplant arteriosclerosis in aortic and
coronary artery tissue from heart-transplanted patients.
Similarly, we found a significant association between the
histomorphometric quantitation of transplant
arteriosclerosis and aortic cholesterol
accumulation in experiments 1 and 2, in which cholesterol
was added to the diet, but not in experiment 3, in which no dietary
cholesterol was administered. This suggests that only when
plasma cholesterol is greater than 2 to 3
mmol/L will aortic cholesterol accumulation reflect
the degree of transplant arteriosclerosis in aortic
allografts from rabbits. Thus, in species with plasma
cholesterol levels of 0.5 to 2 mmol/L, aortic
cholesterol content may not be useful as a measure of
transplant arteriosclerosis.
Conclusion
At present, the standard cyclosporine treatment in
heart-transplanted patients is a high initial dose that is tapered with
time. This is a rational approach, taking into account the toxic side
effects of cyclosporine. However, it seems that from the
present and other experimental studies,32 33 although
certain doses of cyclosporine may be high enough to prevent
episodes of acute rejection, these same doses may not necessarily be
high enough to prevent immune activation in the intima, thereby
promoting rather than attenuating the development of transplant
arteriosclerosis. Recent findings from studies in
heart-13 14 15 and kidney-transplanted16 17
patients suggest that such a relationship may also exist in humans.
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Acknowledgments |
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We thank technicians Kurt Svarre Jensen, Hanne Damm, and Lone Christensen for their help during the study.
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Footnotes |
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Reprint requests to Dr. Henrik Ørbaek Andersen, Department of Thoracic Surgery R, Gentofte University Hospital, Niels Andersens Vej 65, 2900 Hellerup, Denmark.
Received November 5, 1996; accepted February 24, 1997.
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