ABCB1 hypomethylation is associated with decreased antiplatelet effects of clopidogrel in Chinese ischemic stroke patients

Current predictive models including the CYP2C19 polymorphism and clinical factors still explain only about 12% of variability of clopidogrel responsiveness. Up until recently, the precise mechanism of clopidogrel resistance remains unclear. P-glycoprotein (P-gp) encoded by ABCB1, a transmembrane calcium-dependent efflux pump for clopidogrel, implicated a role in clopidogrel resistance. In this present study, we investigated the methylation status of ABCB1 gene promoter in relation to ABCB1 mRNA expressions and the antiplatelet effects of clopidogrel. This study was a prospective cohort analysis of eligible stroke patients (n = 183, aged 18∼75 years) who received clopidogrel (75 mg/day) for at least 5 days before discharge. A final subcohort of 87 patients with CYP2C19*1/*1 genotype were enrolled in the study population. Patients were grouped in quartiles of maximum platelet aggregation (MPA values (Q1, Q2, Q3 and Q4, MPAQ1 < 14.1%, MPAQ4 > 35.4%). The methylation status of the ABCB1 promoter was 1.8 times in the Q1 MPA group (10.1±2.4%) than in the Q4 MPA group (5.5±2.1%) (P < 0.001). ABCB1 methylation correlated inversely with MPA (R = - 0.764, P < 0.001) and mRNA expression (R = - 0.839, P < 0.001). Results of a multivariate linear regression model demonstrated that ABCB1 methylation was independently associated with MPA (βcoef ficient = –4.71, P < 0.001). ABCB1 expression was 0.62 times in the Q1 MPA group (5.3 ± 1.4‰) than in the Q4 MPA (8.5±2.5 ‰), and the expression of ABCB1 correlated positively with ADP-induced MPA (R = 0.791, P < 0.001). ABCB1 promoter methylation status in whole blood appears to be inversely associated with ABCB1 mRNA expressions and MPA. In conclusions, hypomethylation of ABCB1 promoter is associated with a decreased response to clopidogrel in ischemic stroke patients via increased ABCB1 mRNA expression.