© 1998 American Heart Association, Inc.
Original Contributions |
Oxidized Low Density Lipoproteins in Patients With Transplant-Associated Coronary Artery Disease
From the Center for Molecular and Vascular Biology (P.H., J.-M.S., D.C.) and the Department of Cardiology (J.V.C., J.V.), University of Leuven, Belgium.
Correspondence to Dr P. Holvoet, Center for Molecular and Vascular Biology, University of Leuven, Campus Gasthuisberg, O & N Herestraat 49, B-3000 Leuven, Belgium. E-mail paul.holvoet{at}med.kuleuven.ac.be
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Abstract |
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Abstract—The monoclonal antibody 4E6–based ELISA was used to quantify levels of oxidized LDL in plasma of 65 control subjects, 47 patients transplanted for dilated cardiomyopathy (DCM), and 60 patients transplanted for coronary artery disease (CAD). Levels of oxidized LDL were 0.68±0.039 mg/dL (mean±SEM), 1.27±0.14 mg/dL (P<.001 versus control), and 1.73±0.13 mg/dL (P<.001 versus control and <0.01 versus DCM), respectively. Levels of oxidized LDL were significantly lower in transplanted patients with angiographically normal coronary arteries (grade 0, 1.16±0.053 mg/dL; n=79) than in patients with mild (grade 1, 2.13±0.30 mg/dL; n=18; P<.001 versus grade 0) or severe (grade 2, 3.18±0.45 mg/dL; n=10; P<.001 versus grade 0 and P<.05 versus grade 1) coronary artery stenosis. Logistic regression analysis identified three parameters that were significantly and independently correlated with posttransplant CAD: plasma levels of oxidized LDL (P=.0001), length of follow-up (P=.0008), and donor age (P=.047). Thus, the present study demonstrates that plasma levels of oxidized LDL correlate with the extent of CAD in heart transplant patients and suggests that elevated levels of oxidized LDL may be a marker for CAD.
Key Words: oxidized LDL 
coronary artery disease transplantation
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Introduction |
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The development of CAD after cardiac transplantation is a leading cause of graft failure in recipients who survive the first year after surgery.1 2 This posttransplant arteriopathy is characterized by rapid development,3 4 concentric narrowing of smaller coronary arteries,5 6 and the lack of correlation with known atherogenic risk factors.1 2 3 4 5 6 Understanding the etiology of accelerated atherosclerosis might allow identification of patients at risk for this complication.
It has been suggested that ischemic injury of the heart during the peritransplant period significantly contributes to the development of accelerated atherosclerosis in heart transplant patients.7 A correlation between LDL oxidation and atherogenesis was first suggested by experiments showing that oxidized LDL mediated injury to endothelial cells (reviewed in Reference 88 ) and was further supported by studies showing a protective effect of antioxidants against progression of atherosclerosis.9 The study of the correlation between oxidized LDL and atherosclerosis has, however, been hampered by the lack of a sensitive and specific assay for oxidized LDL in plasma. In the present study we have used an ELISA that is highly specific for oxidized LDL.10 The ELISA was used to study the association between plasma levels of oxidized LDL and CAD.
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Methods |
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Patients
The posttransplant study group contained 47 patients transplanted for DCM and 60 patients treated for CAD. The clinical characteristics of these patients are summarized in Table 1
. At the time of blood sampling, between
12 and 84 months after surgery, all patients were in a stable cardiac
condition without evidence of acute rejection. Adequate information
about the smoking habits was available for 92 of the 107 patients (16
smokers and 76 nonsmokers). There was no adequate information about
smoking habits of donors. Rejection was graded by the histopathologic
classification of the International Society for Heart and Lung
Transplantation. Rejections 
grade 3A were treated.
Maintenance immunosuppression consisted of triple-drug therapy
including cyclosporin, azathioprine, and prednisone. Rejection episodes
were treated with high-dose intravenous
corticosteroids and steroid-resistant rejection
with a course of OKT3, a murine anti-CD3 mAb.11
Cytomegalovirus infection was defined as seroconversion of a
seronegative recipient or a fourfold rise in titer postoperatively in a
previously cytomegalovirus-positive recipient.
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Blood samples of 65 nonsmoking control subjects (31 men/34 women; age, 52±1.3 years) without a history of atherosclerotic cardiovascular disease were obtained. The control subjects were matched for age and levels of LDL cholesterol. They were selected from the laboratory and clinical staff (n=27; age, 54±2.0 years; 15 men/12 women) and from a hospital control population without a history of atherosclerotic cardiovascular disease (n=38; age, 52±2.2 years; 16 men/22 women).
Coronary Angiography
Routine annual coronary angiograms were available for
all posttransplant patients at the time of blood sampling. CAD was
assessed by two angiographers (J.V.C. and J.V.H.) who where unaware of
the oxidized LDL levels and was visually graded as follows: grade 0,
normal coronary arteries; grade 1, minor abnormalities with
<50% stenosis of primary or secondary branches and normal
left ventricular function; and grade 2, 50%
stenosis of primary or secondary branches, or distal
involvement with impaired left ventricular function. It is
well known that angiography systematically underestimates the extent of
coronary intimal thickening in cardiac transplant
recipients.12 This study therefore does not
attempt to accurately quantify the extent of coronary artery
stenosis. Rather the subdivision in groups defined above relies
on angiographic data that are easily distinguishable and that have been
shown to correlate with histopathologic findings and
prognosis.13 14 The study was approved by the
Institutional Review Board, and the study subjects provided informed
consent.
Blood Sampling
Venous blood samples from fasting patients and control subjects
were collected on 0.1 vol of 1 mol/L citrate, containing 1 mmol/L
EDTA, 20 µmol/L vitamin E, 10 µmol/L BHT, 20
µmol/L dipyridamole, and 15 mmol/L theophylline
to prevent in vitro LDL oxidation and platelet activation. Blood
samples were centrifuged at 3000g for 15 minutes at
room temperature within 1 hour of collection and stored at -20°C
until the assays were performed.10
Lipoproteins: Isolation and Modification
LDLs were isolated from pooled plasma of fasting normolipidemic
donors by density gradient
ultracentrifugation.15 Standard
preparations of MDA-modified and copper-oxidized LDL were prepared as
described elsewhere16 17 and were used as assay
control subjects.10 Characterization of modified
LDL involved measurement of thiobarbituric acid–reactive substances,
determination of electrophoretic mobility on 1% agarose gels,
quantification of cholesterol and fatty acids by
high-performance liquid chromatography on a
Nova-Pak C18 reversed-phase column (Waters Associates), and
quantification of proteins by Lowry assay and of phospholipids by
enzymatic assay (Biomérieux).18 Oxidized
LDLs were isolated from the purified LDL fractions of patients by fast
flow chromatography on a mono-Q-Sepharose
column.18 The apo B-100 molecules of in vitro
MDA-modified LDL and of copper-oxidized LDL contained on average 244
and 210 substituted lysines (from a total of 356),
respectively.17 18 19 Whereas the extent of lysine
substitution in in vitro MDA-modified LDL and copper-oxidized LDL is
very similar, the lipid moiety in in vitro MDA-modified LDL is not
oxidized. We have demonstrated that the specificity of the mAb E6
depends on the extent of protein modification
only.10 All lipoprotein concentrations were
therefore expressed in terms of protein.
Assays
An mAb 4E6–based ELISA was used for the quantification of
oxidized LDL in plasma.10 Standard oxidized LDL
and plasma samples were diluted in PBS containing antioxidants and
antiplatelet agents as described above. Equal volumes of diluted,
purified mAb 4E6 solution (final concentration, 7.5 ng/mL) and of
diluted standard solution (copper-oxidized LDL added as a competing
ligand at a final concentration ranging between 50 and 500 ng/mL) were
mixed and incubated for 30 minutes at room temperature. Then 200-µL
aliquots of the mixtures were added to coated wells. Samples were
incubated for 2 hours at room temperature. After they were washed, the
wells were incubated for 1 hour with horseradish peroxidase conjugated
rabbit IgG raised against mouse immunoglobulins and washed again. The
peroxidase reaction was performed as described
earlier,12 and the absorbance (A) was read at 492
nm. Control subjects without competing ligand and blanks without
antibody were included routinely. The percentage inhibition of binding
of mAb 4E6 to the immobilized ligand was calculated as
(A492nm control-A492nm
sample)/(A492nm
control-A492nm blank), and standard curves were
obtained by plotting the percentage inhibition versus the concentration
of competing ligand.
The C50 values, ie, concentrations that are required to obtain 50% of antibody binding, were 25 mg/dL for native and acetylated LDL; 1, 0.1, and 0.025 mg/dL for MDA-modified LDL with 60, 90, and at least 120 aldehyde-substituted lysines per apo B-100 molecule, respectively; and 0.025 mg/dL for copper-oxidized LDL. A 50-fold higher molar concentration of aldehyde-substituted lysines in MDA-modified albumin was required to obtain a similar extent of inhibition of antibody binding compared with MDA-modified LDL, whereas up to 1000-fold higher molar concentrations of MDA-modified lysine did not affect antibody binding. The lower limit of detection was 0.020 mg/dL of standard preparations of MDA-modified and in vitro oxidized LDL in undiluted human plasma. When copper-oxidized LDLs were added to human plasma at a final concentration of 0.25 and 2 mg/dL, respectively, recoveries were 95 and 105%, respectively.
Titers of autoimmune antibodies against oxidized LDL were measured as described earlier.10 18 Immobilized antigens for this assay included native LDL prepared from pooled human plasma (protected against in vitro oxidation as described above), copper-oxidized and MDA-modified LDL, and human serum albumin. The plasma samples were diluted 40-fold and incubated for 2 hours at room temperature in the coated microtiter plates. The wells were then washed and incubated for 1 hour with horseradish peroxidase–conjugated goat IgG raised against human immunoglobulins (both IgG and IgM) and washed again. The peroxidase reaction was then performed as described above. The antibody titers for native LDL were expressed as the ratios of the absorbance in wells coated with native LDL versus wells coated with serum albumin. The antibody titers for copper-oxidized LDL and for MDA-modified LDL were expressed as the ratios of the absorbance in wells coated with copper-oxidized LDL and MDA-modified LDL, respectively, versus wells coated with native LDL.
Cholesterol and triglycerides were measured by enzymatic methods (Boehringer Mannheim). Typing of HLA-B and HLA-DR antigens was performed by the microlymphocytotoxicity technique.
Statistical Analysis
Control subjects and patients were compared by ANOVA followed by
the nonparametric Mann-Whitney U test or
Dunnett's multiple comparison test on logarithmically transformed
values, with the Instat V2.05a statistical program (GraphPad Software).
Nonquantitative parameters were compared by
2 analysis. Oxidized LDL levels
measured in three plasma samples obtained from the same patient on 3
consecutive days as well as levels measured in three aliquots of the
same plasma sample on 3 different days were compared in the Friedman
nonparametric repeated measures test. Logistic regression
analysis, using SAS software (SAS Institute, Inc.), was
performed to evaluate the correlation between angiographically assessed
coronary artery stenosis (as the dependent
variable) and plasma levels of oxidized LDL; age and sex of
recipients; age and sex of donors; pretransplant history of
ischemic heart disease or DCM; duration of ischemia;
length of follow-up; number of rejections; number of HLA mismatches;
frequency of cytomegalovirus infection, hypertension (antihypertensive
treatment), or diabetes; treatment with lipid-lowering drugs (statins
or fibrates); and serum levels of LDL cholesterol, HDL
cholesterol and triglycerides as independent
variables. Values of P<.05 were considered to indicate
statistical significance.
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Results |
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The association between oxidized LDL and coronary artery stenosis was evaluated in 47 patients transplanted for DCM and in 60 patients treated for CAD. Analysis of clinical data for the two groups of heart transplant patients (Table 1
) revealed no
significant differences in age and sex of the recipients, age and sex
of donors, duration of ischemia of the donor heart, number of
rejection episodes, number of HLA mismatches, frequency of
cytomegalovirus infections, hypertension, or diabetes, and grade of
coronary artery stenosis. Patients transplanted for CAD
were followed up longer and more frequently received lipid-lowering
drugs (Table 1). Analysis of the laboratory data (Table 2) revealed no significant differences in
serum levels of LDL cholesterol, HDL
cholesterol, and triglycerides between groups
of patients or between patients and control subjects. However,
significant differences in levels of oxidized LDL were observed. Mean
plasma levels of oxidized LDL were 0.68±0.039 mg/dL in control
subjects, 1.27±0.14 mg/dL in DCM patients (P<.001 versus
control subjects), and 1.73±0.13 mg/dL in CAD patients
(P<.001 versus control subjects and <0.01 versus DCM
patients) (Table 2).
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Blood samples were stored for <1 week before oxidized LDL analysis. Levels of oxidized LDL were not different in samples that were stored for 24 hours to 10 months after collection, and up to four thawing and freezing cycles did not cause an increase of oxidized LDL levels. These findings indicated that the addition of EDTA, antioxidants, and antiplatelet agents adequately prevented the in vitro oxidation of LDL. In a subset of 87 consecutive plasma samples, levels of oxidized LDL were measured in three separate aliquots on 3 different days. The levels were 1.38±0.074, 1.48±0.101, and 1.46±0.090 mg/dL, respectively. Friedman nonparametric repeated measures test revealed no significant differences between levels measured in different aliquots of the same sample. The interassay coefficient of variation was 9.6%.
The day-to-day variability of the oxidized LDL levels has been investigated in an independent study group of 33 nontransplanted ischemic heart disease patients with recurrent acute myocardial infarction. Levels of oxidized LDL in plasma samples obtained on 3 consecutive days were 2.84±0.30, 3.04±0.28, and 3.2±0.30 mg/dL, respectively. Friedman nonparametric repeated measures test revealed no significant differences between levels measured in subsequent plasma samples.
Mean oxidized LDL levels were 1.16±0.053 mg/dL (n=79) in
posttransplant samples of patients with angiographically normal
coronary arteries (grade 0), 2.13±0.30 mg/dL in patients with
grade 1 coronary artery stenosis (n=18;
P<.001 versus grade 0), and 3.18±0.45 mg/dL in patients
with grade 2 coronary artery stenosis (n=10;
P<.001 versus grade 0 and P<.05 versus grade 1)
(Table 3). The Figure
represents scatter and box and whisker graphs illustrating
individual oxidized LDL values and the distribution of oxidized LDL
levels in control subjects and patients with grade 0, grade 1, and
grade 2 posttransplant coronary artery stenosis. Serum
levels of LDL cholesterol, triglycerides, and
HDL cholesterol were very similar in patients with higher
grade of coronary artery stenosis (Table 3), and
oxidized LDL levels did not correlate with LDL cholesterol
levels (data not shown). Levels of oxidized LDL in plasma samples of
patients transplanted for DCM or CAD, with the same grade of
coronary artery stenosis, were similar: 1.00±0.066 and
1.32±0.073 mg/dL for grade 0 patients and 2.63±0.60 and 2.53±0.29
mg/dL for patients with higher grade of coronary artery
stenosis. The number of patients with elevated levels of
oxidized LDL (ie, >mean levels of control subjects+2 SD) were 43 (of
60) in the subpopulation of transplanted CAD patients and 21 (of 47) in
the subpopulation of transplanted DCM patients (P=.0057). Of
79 patients with angiographically normal coronary arteries, 42
had elevated levels of oxidized LDL. Elevated levels were detected in
12 (of 18) patients with grade 1 and in all patients with grade 2
stenosis (P=.0046 for trend).
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Titers of autoimmune antibodies reacting with native LDL were 
1.
Titers of autoimmune antibodies reacting with oxidized LDL were
8.30±0.23 in control subjects, 7.81±0.38 in patients with
angiographically normal coronary arteries, and 7.88±0.88 in
patients with grade 1 and grade 2 stenosis. Titers of
autoimmune antibodies reacting with MDA-modified LDL were very similar.
Those data suggested that the higher levels of oxidized LDL in the
transplantation patients did not result from lower antibody titers.
Logistic regression analysis (Table 4) identified 3 parameters
that were significantly and independently correlated with
posttransplant coronary artery stenosis: levels of
oxidized LDL, length of follow-up, and donor age. In contrast,
pretransplant history of DCM or of ischemic heart disease; age
and sex of recipients; sex of donors; duration of ischemia of
the donor heart; extent of HLA mismatch; frequency of rejection,
hypertension, or diabetes; and serum levels of LDL
cholesterol, HDL cholesterol, and
triglycerides in recipients did not significantly
contribute to the individual variations in extent of coronary
artery stenosis (Table 4). Serum levels of LDL
cholesterol, HDL cholesterol, and
triglycerides in patients were similar to those in control
subjects (Table 2), so that higher grade of coronary artery
stenosis was unlikely to depend on those variables in this
study group. Of 107 transplant patients, 56 received lipid lowering
drugs (46 with statins and 10 with fibrates) (Table 2), but the
treatment with these drugs was not correlated with the incidence of
angiographic graft vasculopathy (Table 4). Of 107 patients, 75 were
treated with calcium channel blockers. The plasma levels of oxidized
LDL in those patients (1.53±0.11 mg/dL) were very similar to those in
nontreated patients (1.74±0.14 mg/dL), and treatment with these drugs
was not correlated with the extent of coronary artery
stenosis.
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LDL fractions were isolated from the plasma of 10 patients with the highest extent of coronary artery stenosis by gel filtration on a Superose 6HR 10/30 column, as described previously.19 Of the immunoreactive material, 80±4% (mean±SD) was recovered in the LDL fractions. No immunoreactive material migrated in the serum albumin position. The inhibition curves obtained with the respective LDL fractions were parallel to those obtained with in vitro copper-oxidized or MDA-modified standard LDL preparations. Oxidized LDL was isolated from isolated LDL fractions of those patients by ion-exchange chromatography on a mono-Q-Sepharose column19 with a recovery of 75%. The oxidized LDL fraction isolated from the plasma of those patients was characterized by a 1.3-fold higher electrophoretic mobility on agarose gels, a 75% reduction of the arachidonic levels, and a 80% reduction of the linoleic acid levels. The fraction of aldehyde-substitution of lysine residues was 37% of that in standard preparations of MDA-modified LDL, indicating that about 90 lysine residues in the apo B-100 moiety of the isolated oxidized LDL were substituted. The inhibition curves obtained with oxidized LDL isolated from the plasma of the patients were parallel to these obtained with oxidized LDL that was obtained by in vitro oxidation of LDL that had been isolated from the plasma of control subjects.
A subset of 46 heart transplant patients had a normal coronary
angiogram 3 years before the present study. In 12 of those
patients, CAD had developed during the 3-year follow-up period. There
were no differences in age and sex of recipients; age and sex of
donors; duration of ischemia; extent of HLA mismatch; frequency
of cytomegalovirus infections, hypertension, and diabetes (Table 5); nor serum levels of
triglycerides, HDL cholesterol, and LDL
cholesterol (Table 5) between patients who had developed
CAD and those who had not. However, levels of oxidized LDL were
significantly elevated in patients with development of CAD (Table 5).
Logistic regression analysis revealed that plasma levels of
oxidized LDL (2 value=7.1; P=.0076)
and age of donor (2 value=4.4;
P=.035) correlated with the development of CAD in those
patients.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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The present study demonstrates that plasma levels of oxidized LDL are significantly elevated in ischemic heart disease patients and in heart transplant patients, both in patients transplanted for DCM and those treated for ischemic heart disease, and that plasma levels of oxidized LDL are significantly higher in patients who develop posttransplant coronary artery stenosis. The finding that plasma levels of oxidized LDL correlated with the extent of coronary artery stenosis and also with its development suggests that oxidized LDL may be a marker for patients at increased risk of posttransplant CAD.
It has been suggested that posttransplant atherosclerosis results from a "response to injury" of the endothelium.20 The extent of ischemic injury in endomyocardial biopsies was indeed found to be a strong predictor of the development of accelerated atherosclerosis.7 Endothelial injury may be induced by cellular delayed-type hypersensitivity immune responses elicited by class II histocompatibility (HLA) antigens on coronary artery endothelium,21 22 23 24 25 by cytomegalovirus infection,26 27 by cyclosporin,28 and by oxidized LDL29 that may act synergistically with cyclosporin.30 In the present study, the extent of histoincompatibility between pairs of donors and recipients, and the number of episodes of rejection or cytomegalovirus infection did not correlate with the grade of coronary artery stenosis, whereas oxidized LDL levels were significantly and independently correlated with posttransplant CAD. The observed association between the age of the donor and the occurrence of CAD is in agreement with previous findings that coronary atherosclerosis in the donor heart predisposes to accelerated posttransplant coronary artery stenosis.31
In vitro data suggest that oxidized LDL may be linked to atherogenesis by a sequence of events (reviewed in References 3232 to 34). Endothelial cells exposed to oxidized LDL secrete adhesion molecules, chemoattractant proteins, and colony-stimulating factors that enhance the infiltration, proliferation, and accumulation of monocytes/macrophages in the arterial wall. Uptake of oxidized LDL by infiltrated macrophages may result in the generation of foam cells that produce oxygen radicals and thus further contribute to the oxidation of LDL. It has been demonstrated that oxidized LDL inhibits the migration of aortic endothelial cells in vitro, suggesting that oxidized LDL may limit the healing response of the endothelium after injury, and that basic fibroblast growth factor reverses the atherosclerosis associated impairment of human coronary angiogenesis-like responses in vitro.35 36 Oxidized LDL may also contribute to rapidly progressing coronary atherosclerosis by inducing platelet adhesion, by decreasing the anticoagulant and fibrinolytic capacities of activated endothelium, and by impairing vasodilation and inducing shear stress.32 33 34
Increased intracellular levels of ferritin37 or
of 
-tocopherol analogues38
decreased the extent of endothelial injury elicited by
oxidized LDL in vitro, whereas antioxidants protect against progression
of atherosclerosis in experimental animals (reviewed in
Reference 99 ). These observations suggest that inhibition of oxidation
of LDL or of the effects of oxidized LDL on arterial cells
may reduce the risk for rapidly progressing
atherosclerosis in heart transplant patients, but such
effects would need to be confirmed in prospective clinical trials. It
has been suggested that in the general population, trials with
antioxidants may require very long observation periods (>5 years) for
a beneficial effect to become apparent.9 The
heart transplant population may provide us more rapidly with an answer
as to the value of antioxidant therapy, inasmuch as posttransplant
coronary artery stenosis could serve as a paradigm for
an accelerated form of CAD in general. In a preliminary study we found
that levels of oxidized LDL were very similar in patients with
ischemic heart disease, as evidenced by recurrent acute
myocardial infarction, and in patients with posttransplant CAD,
suggesting that oxidized LDL may indeed be a marker for CAD.
Previously it has been demonstrated that after injection of small amounts of radiolabeled, extensively oxidized LDL in rats it was cleared rapidly by means of scavenger receptors on Kupffer cells.39 On the basis of those data, it was hypothesized that oxidized LDL would not circulate in human blood. However, it has recently been demonstrated that the half-life of Tc99m-labeled, extensively oxidized LDL in humans was only one third shorter than that of native LDL.40 Those data are in agreement with the hypothesis that small amounts of oxidized LDL could circulate in human blood. The moderate extent of lysine substitution, on average 90 lysine residues per apo B-100 molecule, in oxidized LDL in the plasma of transplant patients may result in a delayed clearance compared with that of extensively oxidized LDL. The high affinity of mAb 4E6 for apo B-100 with at least 60 aldehyde-substituted lysines per molecule leads to a very high sensitivity of the ELISA, allowing the detection of amounts of oxidized apo B-100 that represent only 0.03% of the total amounts of apo B-100 (typically 80 mg/dL) and thus of the detection of oxidized LDL in human plasma. The finding that plasma levels of oxidized LDL were also elevated in nontransplanted ischemic heart disease patients suggests that elevated levels of oxidized LDL in transplant patients are not solely due to impaired clearance of oxidized LDL in association with transplantation.
It is difficult to identify the source of the oxidized LDL in these patients. Recently we have demonstrated that the progression of coronary atherosclerosis in hypercholesterolemic rabbits is associated with increased accumulation of oxidized LDL both in the coronary lesions and in the plasma. It was concluded that the significant correlation between plasma levels of LDL and the amounts of oxidized LDL in the plasma and the lesions of those rabbits may indicate (1) that the oxidized LDLs in the lesions are directly derived from the plasma oxidized LDL that infiltrate in the arterial wall, or (2) that both the lesion amounts and the plasma levels of oxidized LDL reflect similar oxidative stresses in both the arterial wall and plasma, or (3) that there is backdiffusion of oxidized LDL generated in the arterial wall in the blood.41 Previously we have demonstrated that acute myocardial infarction is associated with an increase of plasma levels of MDA-modified LDL, suggesting that leakage from arterial lesions may be a source of oxidatively modified LDL in the plasma.18 The finding that the oxidized LDL levels in the patients did not correlate with the plasma LDL cholesterol levels further suggests that the oxidation of the LDL does not occur in the blood but rather in the arterial wall. The present data are thus in agreement with a continuous release of moderately oxidized LDL in the blood that is not cleared very rapidly from the circulation.
Thus, results of the present study demonstrate that plasma levels of oxidized LDL correlate with the extent of coronary artery stenosis in heart transplant patients and suggest that elevated levels of oxidized LDL may be a marker for CAD. Prospective studies are required to establish a causal role of oxidized LDL in the development of CAD.
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Selected Abbreviations and Acronyms |
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Acknowledgments |
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This study was supported in part by a grant from the Nationaal Fonds voor Geneeskundig Wetenschappelijk Onderzoek (Project 3.0103.92) and by the Interuniversitaire Attractiepolen (Program 4/34). Johan Vanhaecke is holder of the Michael Ondetti Chair in Cardiology. The authors are grateful to W. Daenen, W. Flameng, and P. Sergeant for providing coronary arteries of the cardiac explants; to H. Bernar and M. Landeloos for technical assistance; and to E. Lesaffre of the Biostatistical Center for Clinical Trials, University of Leuven, for statistical analysis.
Received July 11, 1997; accepted September 25, 1997.
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References |
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