(Hypertension. 2001;37:851.)
© 2001 American Heart Association, Inc.
Scientific Contributions |
ACE D/I Polymorphism and Incidence of Post-PTCA Restenosis
A Prospective, Angiography-Based Evaluation
From the Endocrine-Hypertension Division (R.Y.L.Z., K.L.), Department of Medicine, Brigham and Women’s Hospital, and the Department of Cardiology (K.L.), Children’s Hospital, Harvard Medical School, Boston, Mass; Hospital Universitario San Carlos (A.F-Z., C.M., E.P., A.F-Z.), Ciudad Universitaria, Madrid, Spain; and the Max Delbruck Centre for Molecular Medicine (K.L.), Berlin, Germany.
Correspondence to Robert Y.L. Zee, PhD, Endocrine-Hypertension Division, Room 209, Longwood Medical Research Center, Brigham and Women’s Hospital, 221 Longwood Ave, Boston, MA, 02115. E-mail rylz{at}calvin.bwh.harvard.edu
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Abstract |
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Early restenosis is the major complication of percutaneous transluminal coronary angioplasty (PTCA), occurring in
30% of all initially successful procedures.
The D/I polymorphism of the
ACE gene, which has variably
been reported to represent a risk factor for manifestations of
ischemic heart disease, has recently been implicated in the
pathophysiology of restenosis after PTCA by some investigators
but not by others. All studies conducted thus far involved relatively
small sample sizes. We investigated the possible association of
ACE D/I genotype and
post-PTCA restenosis in a large, prospective sample of patients
followed by quantitative coronary angiography. The
ACE
D/I gene polymorphism was
characterized in a cohort of 779 patients, of whom 342 (cases) had
developed restenosis (as defined by >50% loss of lumen
compared with immediate postprocedure results) at repeat quantitative
coronary angiography at 6 months after PTCA. Allele
frequencies for the ACE D and
I alleles were 0.58 and
0.42 in cases and 0.58 and 0.42 in control subjects. All observed
genotype frequencies were in Hardy-Weinberg equilibrium. There
was no evidence for an association between genotype and
restenosis or degree of lumen loss. The data from this largest
study of its kind conducted so far provide no evidence for an
association of the ACE D/I
allelic polymorphism with incidence of restenosis after
PTCA. On the basis of the power of this study, we conclude that in a
general population, the ACE D/I
polymorphism is not a useful marker to assess risk of post-PTCA
restenosis.
Key Words: angiotensin-converting enzyme • angioplasty • polymorphism • genetics • risk factors
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Introduction |
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The utility of percutaneous transluminal coronary angioplasty (PTCA) is limited by a high incidence of restenosis.1 Experimental and clinical studies have implicated vessel remodeling in restenosis after PTCA.2 Although a number of factors potentially promoting remodeling are being discussed, the exact molecular and cellular mechanisms of post-PTCA remodeling in humans remain, however, largely unknown. None of a large number of known risk factors for atherosclerosis or ischemic cardiovascular disease except for diabetes mellitus3 has been found to be associated with the occurrence of this complication. Genetic factors are believed to be an important reason for interindividual differences in treatment response. Thus, studies correlating such factors with the incidence of this complication might shed new light on its pathogenesis; such information, in turn, would provide us with tools for prediction and possibly suggest novel therapeutic/preventive approaches.
ACE, with its demonstrated growth-stimulating effects on vascular smooth muscle cells, represents a possible candidate that may contribute to restenosis. An insertion/deletion polymorphism in the gene encoding ACE has consistently been found associated with differential plasma ACE levels and has attracted widespread interest in recent years, based on conflicting reports of association with various cardiovascular disease states.4 Among them, post-PTCA restenosis has been linked to this marker in some5 6 7 8 9 10 but not other studies.11 12 13 All of these studies were of moderate size only, with numbers of cases ranging as low as 17,6 most without quantitative coronary angiography (QCA) assessment,5 7 9 10 13 and commonly based on retrospectively assembled cohorts.5 6 9 11 12 Given the limited power of each of these studies and their individual shortcomings, a more conclusive assessment and a resolution of the contradictory answers they provided has so far not been possible.
We recently had the opportunity to conduct a study in post-PTCA patients that not only avoided the limitations mentioned by being prospective and based on QCA measurements at baseline and 6 months after PTCA but that also used a sample >3 times as large as in the largest study heretofore reported.12
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Methods |
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Study Design
Between March 1995 and March 1997, we obtained permission of consecutive patients who had undergone successful PTCA at the Hospital San Carlos, Universidad Complutense in Madrid, Spain, to perform an angiographic follow-up examination 6 months later, by having an appropriate, comprehensive informed consent form signed. QCA was performed before PTCA, immediately after PTCA (demonstrating the effect of the procedure), and at follow-up cardiac catheterization 6 months later. Ultimately, 779 patients with complete clinical and angiographic follow-up were enrolled, for whom blood samples were available for the present investigation. With a >50% reduction in the luminal diameter at the site of previous PTCA as compared with the immediate postangioplasty angiographic record as the criterion to define restenosis, there were 342 cases (with a total of 378 restenotic lesions).
QCA analysis was carried out off-line independently by 2 experienced operators who were blinded to patients’ clinical or procedural characteristics, using a commercially available, previously validated, interactive automatic edge-detection computer program (ARTREK, Quantim 2001, QCS Inc, ImageComm System Inc).14 15 Disagreements (<1%) were resolved by a further joint reading. Two orthogonal, nonforeshortened angiographic views that optimized separation of the lesion and its proximal coronary segment were selected for analysis. The angioplasty-treated coronary segment was always documented before PTCA, immediately after PTCA, and at 6-month follow-up, with the same views. All analyses were performed on images taken after the administration of intracoronary nitroglycerin.
ACE D/I
Genotype Determination
A detailed description of the protocol used to
determine ACE D/I
genotype has previously been
published.16 In brief, the
D and
I alleles were identified
on the basis of polymerase chain reaction (PCR) amplification of the
respective fragments from intron 16 of
ACE and by subsequent
electrophoretic size fractionation and visualization after staining
with ethidium bromide. Because the
D allele tends to be
preferentially amplified in heterozygotes, all samples determined to be
DD were subjected to a second
independent PCR amplification with a primer pair that recognizes an
insertion-specific sequence to ensure accurate genotyping. To confirm
genotype assignment, the PCR procedure was performed on all
samples on 2 separate occasions. PCR results were scored blinded as to
case-control status.
Statistical Analysis
Alleles and genotype frequencies among
cases and control subjects were counted and compared with
Hardy-Weinberg predictions by 
2
analysis. Crude quantitative data on fractional
restenosis were evaluated by analysis for trend
(additive model, DD versus
DI versus
II) or
2 analysis (dominant and
recessive models, respectively). In addition,
multivariate logistic (with dichotomous dependent
variables) and linear (parameters: acute gain, ie, the
difference between obstruction diameter after and before angioplasty;
late loss, ie, the difference between obstruction diameter after
angioplasty and at follow-up; net gain, ie, the difference between
acute gain and late loss; loss index, ie, the ratio of late loss to
acute gain) regression analyses were performed, adjusting for
age, gender, body mass index (BMI), blood pressure, total serum
cholesterol, smoking habit, diagnosis of diabetes mellitus,
angiographic and occlusion characteristics, and family history of
myocardial infarction (MI). Odds ratios were calculated as a measure of
the association of the ACE
genotype with the phenotype of restenosis, with
the effects of the D allele
assumed to be additive (with scores of 0, 1, and 2 assigned for
II,
DI, and
DD, respectively), dominant
(with scores of 0 for II and 1
for DI and
DD combined), or recessive
(with scores of 0 for II and
DI combined, and 1 for
DD). For each odds ratio, we
calculated 95% confidence intervals. A 2-tailed probability value of
0.05 was considered to represent a statistically significant
result.
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Results |
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Characteristics of the Study Population
Baseline characteristics of the study population are shown in Table 1.17 There were no significant differences among the cases (restenosis) and the control subjects (no restenosis) with regard to age, blood pressure status, plasma lipid profile, smoking status, or family history of coronary heart disease. As expected, cases were more likely to have diabetes (
22df=6.66,
P=0.011).
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Alleles and Genotype
Frequencies
Allele frequencies for
D and
I alleles were 0.58 and
0.42 in case subjects and 0.58 and 0.42 in control subjects,
respectively. The observed genotype frequencies
(Table 2) did not deviate significantly from the
Hardy-Weinberg equilibrium in control subjects
(21df=0.28,
P=0.65), cases
(21df=0.059,
P=0.85) or the whole study
group (21df=0.14,
P=0.80). No overall difference
in genotype distribution was seen among cases and control
subjects
(22df=0.23,
P=0.89).
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Genotype-Restenosis
Association
Analysis of the crude unadjusted data by
categorical assignment of case status to subjects showing >50% lumen
loss in the previously dilated coronary artery segment(s)
failed to reveal an association between
ACE genotype and
phenotype, regardless of whether an additive
(DD versus
DI versus
II; analysis for
trend), dominant (DD and
DI versus
II), or recessive
(DD versus
DI and
II) mode of inheritance was
assumed (data not shown).
Likewise, logistic regression analysis with adjustment for several covariates, such as age, gender, BMI, blood pressure, total serum cholesterol, smoking habit, presence of diabetes mellitus, angiographic and occlusion characteristics, and family history of MI, failed to demonstrate a correlation between genotype and clinical outcome (data not shown).
Finally, linear regression analysis, adjusted for the same covariates, showed no significant correlation between genotype and the degree of loss of lumen at 6-month follow-up examination (Table 3).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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This study represents, to our knowledge, the largest sample so far examined for a possible association of the ACE D/I polymorphism with the outcome after PTCA. A substantial number of preexisting publications had investigated this question, with inconsistent results. Our results support those earlier studies that failed to find such an association.
The initial report of an association of the ACE D/I polymorphism and restenosis after angioplasty was based on a rather small sample of only 82 Japanese patients.5 These findings were not reconfirmed by subsequent, somewhat larger studies,11 12 13 although others reported results more in line with the original publication.6 7 8 9 10 A review of these studies failed to disclose clear reasons for the discordant results, although in several of these studies allele frequencies showed substantial deviations from those encountered in independent, larger samples from the same ethnic background. Because of the limited size of all these studies, the actual contribution, if any, of the ACE D/I marker to the risk to developing post-PTCA restenosis remains difficult to assess.
A somewhat compelling line of reasoning has frequently been advanced to interpret and support an association of the ACE D allele with increased incidence of restenosis, as observed by some: There is little doubt, based on the consistent results from a large number of investigations in a diverse ethnic groups, that the D allele is associated with significantly higher plasma converting enzyme levels and activities than the I allele, and there is somewhat less well-established evidence that the same is true for tissular enzyme activity, at least in the heart. Considering the well-documented growth-stimulating effects of Angiotensin II, carriers of the DD genotype would, therefore, the argument goes, be more prone to proliferative vascular lesions, as post-PTCA restenosis has commonly been regarded. Further support for the notion that the renin-angiotensin system may play a pivotal role in restenosis is based on experimental models of vascular injury in which ACE inhibitors had been found effective in retarding, preventing, or reversing restenosis.18 However, we have since come to understand that the intimal hyperplasia characteristic of these models (to which smooth muscle cell proliferation appears to contribute importantly) differs markedly from the pathophysiology characteristic of post-PTCA restenosis in humans: In the latter, elastic recoil and smooth muscle cell migration rather than proliferation appear to be the main mechanisms responsible for recurrent lumen loss.19 The dramatic failure of 2 large-scale, randomized trials aimed at demonstrating beneficial effects of ACE inhibition on the occurrence of post PTCA-restenosis20 21 is consistent with this view and indicates that growth-promoting actions of the renin-angiotensin system are probably of little consequence to the natural history of post-PTCA restenosis. This much more tangible evidence renders the above-described reasoning for an association of the ACE genotype with restenosis much less compelling. Intriguingly, this may differ from the present situation with in-stent restenosis, a clinical problem of increasing magnitude. Smooth muscle cell proliferation has been reported to be a distinctly more prominent feature in in-stent as compared with post-PTCA restenosis,22 23 24 and the ACE D/I polymorphism has been found associated with the former25 26 but not the latter11 by the same group of investigators.11 25 This observation highlights the need for careful accounting of a large variety of nongenetic variables—many of them likely much less obvious than the difference between stented and nonstented coronary revascularization—that may critically affect the results of such association studies.27
It is always critical for their proper interpretation of
"negative" studies to measure the power they provide to reject the
alternate hypothesis. Given the number of cases and control subjects
and the respective allele frequencies found, the current study
provides 80% power to detect, at an 
-error of 0.05, a risk ratio of
1.38 associated with the D
allele in an additive model. Our study was conducted in a Castilian
cohort, so the data should be extrapolated to other ethnic groups with
the appropriate degree of caution. It is also important to recognize
that association studies like the present one only examine the
possible association between phenotype and the actually tested
polymorphism; such studies cannot exclude that examination of a
different polymorphism—not in linkage disequilibrium with the
D/I marker—might lead to
different results.
Conclusions
This large, prospective study provides good power to
exclude a clinically significant association of
ACE D/I allele carrier
status with the risk of developing post-PTCA restenosis in
white individuals. The present data do not address the possible
association of the polymorphism with in-stent restenosis
and cannot exclude the possibility that other mutations of
ACE may contribute to the risk
of post-PTCA restenosis. Our results indicate, however, that
the ACE D/I polymorphism is
not a useful marker for assessing the risk of restenosis after
coronary
angioplasty.
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Acknowledgments |
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This work was supported by a Research Development Award (K04-HL-03138-01) from the National Heart, Lung, and Blood Institute to Dr Klaus Lindpaintner.
Received February 16, 2000; first decision March 20, 2000; accepted August 30, 2000.
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