Relationship between paraoxonase Q192R gene polymorphism and on-clopidogrel platelet reactivity over time in patients treated with percutaneous coronary intervention.

Abstract

Recently, paraoxonase-1 (PON1) has been identified as the crucial enzyme for clopidogrel bioactivation, with its common Q192R polymorphism determining the rate of active metabolite formation [1]. In a first report, PON1 QQ homozygous individuals showed considerably lower platelet inhibition by clopidogrel and a higher risk of stent thrombosis than RR homozygous individuals [1]. This finding was not confirmed in a subsequent study [2]. In the current analysis, we investigated the relationship between PON1 Q192R polymorphism and on-clopidogrel platelet reactivity (PR) at different time points. We also compared its incidence with that of other common gene polymorphisms [3], and we discuss how it is related to clinical outcome. For this purpose, 300 patients undergoing percutaneous coronary intervention (PCI) for ischemic heart disease (with the exception of ST-segment elevation myocardial infarction) were recruited. This study population has been previously investigated [3]. The main aim of the study was to evaluate whether clopidogrel response varied over time [3]. Also, the relationship between on-clopidogrel PR variation, genotype and clinical outcomewas investigated. Briefly, all patients were treated with aspirin and clopidogrel (600 mg as a loading dose at least 12 h before PCI). Blood samples were drawn just before PCI, and at 1 and 6 months after PCI. To evaluate on-clopidogrel PR, we used VerifyNow P2Y12 (Accumetrics, San Diego, CA, USA). The results were expressed in P2Y12 reaction units (PRUs). A poor clopidogrel response was defined as a PRU value ‡ 235. The occurrence of death, myocardial infarction, stroke, stent thrombosis (definite and probable) and bleeds (Thrombolysis in Myocardial Infarction [TIMI] criteria) was assessed. In the present substudy, we integrated the previous data with that of PON1 Q192R gene polymorphism (rs662, genotyped with the TaqMan allelic discrimination assay; Applied Biosystems, Foster City, CA, USA). Our present aim was to assess the relationship of on-clopidogrel PR at different time points with PON1 Q192R gene polymorphism, as compared with other common gene polymorphisms. This study was approved by the local Ethics Committee, and all patients gave written informed consent. Continuous data are presented as mean ± standard deviation and were compared by t-test and one-way ANOVA. It is of note that PRU values are normally distributed (P = 0.7 with the Kolmogorov–Smirnov test). A linear mixed model was used to quantify changes in on-clopidogrel PR over time while integrating the roles of baseline, genetic and procedural characteristics. Also, a multivariable linear regression model was used to assess clinical, procedural and genetic determinants of on-clopidogrel PR. Categorical variables were summarized in terms of numbers and percentages, and were compared by the use of two-sided Fisher s exact test. A two-sided P-value of < 0.05 was considered to be significant. All analyses were performed with STATISTICA 8 (Statsoft, Tulsa, Okla, USA) and R (R Foundation, Vienna, Austria). As previously reported [3], we observed a significant decrease in on-clopidogrel PR from pre-PCI samples to follow-up samples (Table 1; P < 0.01). Of all the clinical and procedural variables listed in Table 1, only age, diabetes, creatinine clearance and hospital admission for acute coronary syndrome (ACS) emerged as independent predictors of on-clopidogrel PR variation over time. Regarding the on-clopidogrel PR evaluation before PCI, age, creatinine clearance and ACS at presentation were the strongest clinical predictors. Regarding PON1 Q192R gene polymorphism, we found 127 (42%) QQ homozygotes, 146 (49%) QR heterozygotes, and 27 (9%) RR homozygotes (Table 1). The on-clopidogrel PR decrease from pre-PCI to 1 month was consistent across all of the different PON1 Q192R genotypes. Regarding the pre-PCI value, PON1 Q192R polymorphism did not show any influence. In contrast, RR homozygotes showed lower on-clopidogrel PR than the other genotypes at 1 month and at 6 months (P = 0.03) (Table 1). Regarding the number of poor responder patients at different time points, no differences were observed after stratification by Q192R genotype. Considering the overall PR Correspondence: Gianluca Campo, Cardiovascular Institute, Azienda Ospedaliero-Universitaria S. Anna, Corso Giovecca, 203, Ferrara 44121, Italy. Tel.: +39 532 202143; fax: +39 532 241885. E-mail: cmpglc@unife.it