Correspondence

Cytochrome P-450 Polymorphisms and Response to Clopidogrel

N Engl J Med 2009; 360:2249-2251May 21, 2009

Article

To the Editor:

On the basis of the results of a genetic association study (Jan. 22 issue),1 Mega et al. conclude that reduced-function variants of the CYP2C19 allele are responsible for lower plasma levels of the active metabolite of clopidogrel; these lower levels lead to decreased platelet inhibition and thereby increase cardiovascular risk. However, no direct evidence of the causal involvement of the cytochrome P-450 enzyme CYP2C19 in the biotransformation of clopidogrel to its active metabolite is presented.

To test the hypothesis of Mega et al., we incubated clopidogrel, the inactive metabolic intermediate 2-oxo-clopidogrel,2 and the known CYP2C19 substrate omeprazole3 with human microsome preparations expressing CYP2C19 (Figure 1Figure 1Results of Tests for the CYP2C19-Dependent Biotransformation of Clopidogrel, 2-Oxo-Clopidogrel, and Omeprazole into Metabolites.). Although omeprazole was transformed into 5-hydroxy-omeprazole, no significant biotransformation of clopidogrel into 2-oxo-clopidogrel and active metabolite or of 2-oxo-clopidogrel into active metabolite was observed. Hence, CYP2C19 does not appear to contribute to the biotransformation of clopidogrel.

It is possible that the CYP2C19 polymorphisms represent only tags for the true causal gene variant involved in clopidogrel activation. Moreover, the CYP2C19 polymorphisms may directly affect the risk of cardiovascular events. Genomewide association studies may help resolve these discrepancies.

Dirk Taubert, M.D., Ph.D.
University Hospital of Cologne, 50931 Cologne, Germany
dirk.taubert@medizin.uni-koeln.de

Heleen J. Bouman, M.Sc.
Jochem W. van Werkum, M.D., Ph.D.
St. Antonius Hospital, 3435 CM Nieuwegein, the Netherlands

3 References

1. 1

   Mega JL, Close SL, Wiviott SD, et al. Cytochrome P-450 polymorphisms and response to clopidogrel. N Engl J Med 2009;360:354-362
   Full Text | Web of Science | Medline

2. 2

   Pereillo JM, Maftouh M, Andrieu A, et al. Structure and stereochemistry of the active metabolite of clopidogrel. Drug Metab Dispos 2002;30:1288-1295
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   Kanazawa H, Okada A, Higaki M, Yokota H, Mashige F, Nakahara K. Stereospecific analysis of omeprazole in human plasma as a probe for CYP2C19 phenotype. J Pharm Biomed Anal 2003;30:1817-1824
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To the Editor:

Simon and colleagues (Jan. 22 issue)1 assessed the relation between allelic variants of genes modulating clopidogrel and the risk of adverse events, and they found a significantly higher event rate among carriers of CYP2C19 loss-of-function alleles than among noncarriers. They also found a modestly increased rate of events among carriers of the ABCB1 variant. The authors genotyped multiple known functional variants, including ABCB1, CYP2C19, CYP3A5, P2RY12, and ITGB3, but some functional genetic variants such as CYP3A4 (modulating the metabolic activation of clopidogrel)2 and ITGA2 (modulating expression of platelet glycoprotein Ia/IIa receptor) were not assessed.3,4 Since variations in these genes may also have an effect on the responsiveness to clopidogrel associated with ischemic events,2-4 the study cannot rule out the possibility of the influence of these genetic factors on the response to clopidogrel and the events.

In addition, although the relationship between single-gene polymorphisms and events was analyzed, the role of coexisting polymorphisms in ischemic events remains unclear. Analysis of patients carrying different genetic variants may help us to better understand the complex nature of the genetic cause of outcomes in patients who are receiving clopidogrel treatment.5

Jianting Miao, M.D.
Rui Liu, M.D., Ph.D.
Zhuyi Li, M.D., Ph.D.
Fourth Military Medical University, Xi'an City 710038, China

5 References

1. 1

   Simon T, Verstuyft C, Mary-Krause M, et al. Genetic determinants of response to clopidogrel and cardiovascular events. N Engl J Med 2009;360:363-375
   Full Text | Web of Science | Medline

2. 2

   Savi P, Pereillo JM, Uzabiaga MF, et al. Identification and biological activity of the active metabolite of clopidogrel. Thromb Haemost 2000;84:891-896
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   Giusti B, Gori AM, Marcucci R, et al. Role of glycoprotein Ia gene polymorphisms in determining platelet function in myocardial infarction patients undergoing percutaneous coronary intervention on dual antiplatelet treatment. Atherosclerosis 2008;196:341-348
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   Angiolillo DJ, Fernandez-Ortiz A, Bernardo E, et al. 807 C/T polymorphism of the glycoprotein Ia gene and pharmacogenetic modulation of platelet response to dual antiplatelet treatment. Blood Coagul Fibrinolysis 2004;15:427-433
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   Malek LA, Kisiel B, Spiewak M, et al. Coexisting polymorphisms of P2Y12 and CYP2C19 genes as a risk factor for persistent platelet activation with clopidogrel. Circ J 2008;72:1165-1169
   CrossRef | Web of Science | Medline

Author/Editor Response

We agree with Taubert and colleagues that our genetic association study cannot rule out the possibility that variants in CYP2C19 were in linkage disequilibrium with other causal variants. However, the evaluated CYP2C19 variants are known to have functional consequences. Moreover, other in vitro studies have shown that CYP2C19 does convert clopidogrel to its active metabolite.1 It may be that the active metabolite was not detected by Taubert et al. because the incubation conditions were suboptimal for clopidogrel, the active metabolite was not stabilized,2 or clopidogrel was largely metabolized to inactive, unmeasured metabolites by esterases present in microsomes.3,4 It would have been helpful to have seen evidence that their approach involving in vitro microsomal preparation and liquid chromatography–tandem mass spectrometry can generate and detect the active metabolite of clopidogrel. Finally, it is unlikely that CYP2C19 directly affects cardiovascular risk, since that would not explain the differences in the active metabolite of clopidogrel and platelet inhibition; moreover, we have shown that variants in this gene are not associated with outcomes in patients treated with prasugrel.5

Jessica L. Mega, M.D., M.P.H.
Stephen D. Wiviott, M.D.
Marc S. Sabatine, M.D., M.P.H.
Brigham and Women's Hospital, Boston, MA 02115
jmega@partners.org

5 References

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   Kurihara A, Hagihara K, Kazui M, Ozeki T, Farid NA, Ikeda T. In vitro metabolism of antiplatelet agent clopidogrel: cytochrome P450 isoforms responsible for two oxidation steps involved in the active metabolite formation. Drug Metab Rev 2005;37:Suppl 2:99-99
   

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   Takahashi M, Pang H, Kawabata K, Farid NA, Kurihara A. Quantitative determination of clopidogrel active metabolite in human plasma by LC-MS/MS. J Pharm Biomed Anal 2008;48:1219-1224
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   Imai T. Human carboxylesterase isozymes: catalytic properties and rational drug design. Drug Metab Pharmacokinet 2006;21:173-185
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   Mullangi R, Srinivas NR. Clopidogrel: review of bioanalytical methods, pharmacokinetics/pharmacodynamics, and update on recent trends in drug-drug interaction studies. Biomed Chromatogr 2009;23:26-41
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5. 5

   Mega JL, Close SL, Wiviott SD, et al. Cytochrome P450 genetic polymorphisms and the response to prasugrel: relationship to pharmacokinetic, pharmacodynamic, and clinical outcomes. Circulation (in press).
   

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   F Sofi, B Giusti, R Marcucci, A M Gori, R Abbate, G F Gensini. (2011) Cytochrome P450 2C19*2 polymorphism and cardiovascular recurrences in patients taking clopidogrel: a meta-analysis. The Pharmacogenomics Journal 11:3, 199-206
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   Tracey Baas. (2011) Once a PON-1 an enzyme. Science-Business eXchange 4:4,
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