Association of cytochrome P450 2C19 genotype with the antiplatelet effect and clinical efficacy of clopidogrel therapy

Abstract

Context: Clopidogrel therapy improves cardiovascular outcomes in patients with acute coronary syndromes and following percutaneous coronary intervention by inhibiting adenosine diphosphate (ADP)-dependent platelet activation. However, nonresponsiveness is widely recognized and is related to recurrent ischemic events.

Objective: To identify gene variants that influence clopidogrel response.

Design, setting, and participants: In the Pharmacogenomics of Antiplatelet Intervention (PAPI) Study (2006-2008), we administered clopidogrel for 7 days to 429 healthy Amish persons and measured response by ex vivo platelet aggregometry. A genome-wide association study was performed followed by genotyping the loss-of-function cytochrome P450 (CYP) 2C19*2 variant (rs4244285). Findings in the PAPI Study were extended by examining the relation of CYP2C19*2 genotype to platelet function and cardiovascular outcomes in an independent sample of 227 patients undergoing percutaneous coronary intervention.

Main outcome measure: ADP-stimulated platelet aggregation in response to clopidogrel treatment and cardiovascular events.

Results: Platelet response to clopidogrel was highly heritable (h(2) = 0.73; P < .001). Thirteen single-nucleotide polymorphisms on chromosome 10q24 within the CYP2C18-CYP2C19-CYP2C9-CYP2C8 cluster were associated with diminished clopidogrel response, with a high degree of statistical significance (P = 1.5 x 10(-13) for rs12777823, additive model). The rs12777823 polymorphism was in strong linkage disequilibrium with the CYP2C19*2 variant, and was associated with diminished clopidogrel response, accounting for 12% of the variation in platelet aggregation to ADP (P = 4.3 x 10(-11)). The relation between CYP2C19*2 genotype and platelet aggregation was replicated in clopidogrel-treated patients undergoing coronary intervention (P = .02). Furthermore, patients with the CYP2C19*2 variant were more likely (20.9% vs 10.0%) to have a cardiovascular ischemic event or death during 1 year of follow-up (hazard ratio, 2.42; 95% confidence interval, 1.18-4.99; P = .02).

Conclusion: CYP2C19*2 genotype was associated with diminished platelet response to clopidogrel treatment and poorer cardiovascular outcomes.

Trial registration: ClinicalTrials.gov NCT00370045 NCT00799396.

Figure 1. Distribution of Adenosine Diphosphate (ADP)–Stimulated (20 μmol/L) Platelet Aggregation Before and After 7 Days of Clopidogrel Administration in 429 Members of the Amish Pharmacogenomics of Anti-Platelet Intervention (PAPI) Study

Class intervals include data greater than the lower limit and equal to the upper limit of each interval.

Figure 2. Genome-Wide Association Study of Adenosine Diphosphate–Stimulated Platelet Aggregation in Response to Clopidogrel

A, Association (plotted as −log P value) of individual single-nucleotide polymorphisms distributed across the 22 autosomes. Horizontal dotted line indicates P=1.0 × 10⁻⁷. B, Enlargement of 1.5-megabase region on chromosome 10q24. Genes encoded in the region are shown below the plot. C, Linkage disequilibrium (r²) among the 13 single-nucleotide polymorphisms showing genome-wide significance with clopidogrel response. Increasing shades of gray represent increasing linkage disequilibrium, from white (r²=0) to black (r²=1).

Figure 3

Association of CYP2C19*2 (rs4244285) Loss-of-Function Variant With Adenosine Diphosphate–Stimulated Platelet Aggregation Before and After Clopidogrel Administration in Participants in the Amish Pharmacogenomics of Antiplatelet Intervention (PAPI) Study and Sinai Hospital of Baltimore Study The horizontal line in the middle of each box indicates the median; the top and bottom borders of each box indicate the interquartile range (IQR). The whiskers above and below the box indicate plus/minus 1.5 IQRs, respectively; the points beyond the whiskers indicate outliers beyond 1.5 IQRs, except for those carrying 2 alleles in which all data points are plotted.

Figure 4. Event-Free Survival Over 1 Year of Follow-up in Sinai Hospital of Baltimore Patients Treated With Clopidogrel Following Percutaneous Coronary Intervention, Stratified by CYP2C19*2 Genotype

Postdischarge ischemic events were defined as myocardial infarction (the occurrence of ischemic symptoms and a troponin I value greater than upper limits of normal), ischemic stroke, stent thrombosis (definite stent thrombosis according to the Academic Research Consortium criteria), unplanned target vessel revascularization (revascularization of vessel treated at time of study enrollment), unplanned nontarget vessel revascularization (revascularization of a vessel different from that treated at time of study enrollment), hospitalization for coronary ischemia without revascularization (hospitalization for chest pain with evidence of ischemia on electrocardiogram and no evidence of myocardial infarction as measured by troponin I value), and death secondary to any cardiovascular cause. Patients were further stratified into those who were taking clopidogrel when the event occurred or at 1 year of follow-up and those who were not. All analyses adjusted for age, sex, and race. For all patients, hazard ratio (HR)=2.42 (95% confidence interval [CI], 1.18-4.99; P=.02); for patients taking clopidogrel at time of event, HR=3.40 (95% CI, 1.36-8.46; P=.004); for patients not taking clopidogrel at time of event, HR=1.39 (95% CI, 0.39-4.88; P=.60).