Association between genetic polymorphisms of cytochrome P450 2C19 and the risk of cerebral ischemic stroke in Chinese

The occurrence of cerebral ischemic stroke is influenced by eating habits, environment, genetic factors and so on. Fundamentally, genetic factors involve in a series of key enzymes and receptors on many metabolic pathways. Therefore, the study of the genetic risk factor for cerebral ischemic stroke has become a hot spot currently.

Cytochrome P450(CYP) 2C19 is a very important drug metabolizing enzyme, which involves in approximately 2% of the clinical drug metabolism. The activity of CYP2C19 enzyme not only exhibits a significant ethnic heterogeneity, but also has an obvious differences between individuals. It is believed that the differences are mainly caused by genetic variations. Many researchers have investigated the molecular mechanism of CYP2C19 enzyme polymorphisms, which include the wild-type CYP2C19*1, CYP2C19*2, CYP2C19*3, CYP2C19*4, CYP2C19*5, CYP2C19*6, CYP2C19*7, CYP2C19*8, etc. CYP2C19*2 and CYP2C19*3 are the main variants in CYP2C19, while others are relatively rare in humans.

Studies have shown that the single nucleotide polymorphisms (SNPs) of CYP2C19*2(CYP2C19 G681A, rs4244285) and CYP2C19*3(CYP2C19 G636A, rs4986893) may increase the incidence of cardiovascular events [1‐3]. Whereas there are less research about the relationship between SNPs in CYP2C19 and cerebral ischemic stroke. So we carried out a case-control study to investigate the relationship between the distribution of G681A and G636A polymorphisms in CYP2C19 gene and cerebral ischemic stroke in Chinese Han population.

A total of 299 patients were enrolled in this study, including 177 cases of male, 122 cases of female, the first onset group were 185 cases, the recurrent stroke group were 114 cases, the mean ages were (67.86 ± 11.472) years. And a total of 295 controls were enrolled, including 159 males, 136 females, the mean ages were (66.45 ± 12.972) years.

CYP2C19 is located within a cluster of cytochrome P450 genes on chromosome 10q24, which contains nine exons and eight introns. The gene encodes a 490-aa long protein of approximately 56kDa, which is a member of the cytochrome P450 superfamily of enzymes. This protein localizes to the endoplasmic reticulum and is known to metabolize many xenobiotics, including the anticonvulsive drug mephenytoin, omeprazole, diazepam and some barbiturates. Polymorphism within this gene is associated with variable ability to metabolize mephenytoin, known as the poor metabolizer and extensive metabolizer phenotypes. CYP2C19*2 has been shown to be a G → A transition at 681bp in exon 5 of wild-type CYP2C19*1. This variant results in an aberrant splice site and shifts the reading frame, thereby producing an early-stop codon and a truncated protein [9]. The CYP2C19*3 involves a G → A variant at 636bp in exon 4, that also creates a premature stop codon and a truncated protein [10]. The CYP2C19*2 is the main genetic defect allele of CYP2C19, which accounts for 75% ~ 85% of poor metabolizers (PM) in both white and Oriental populations [11]. The second variant accounts for the remaining defective alleles in Oriental populations PM, but appears to be extremely rare in white persons [12].

Yin et al. [13] found that the allele frequencies of CYP2C19*2 were respectively 29.7%, 32.4% and 18.2% in Han, Hui and Mongolian, the allele frequencies of CYP2C19*3 were respectively 7.9%, 10.2% and 11.2% in Han, Hui and Mongolian. Other literatures [14, 15] reported that the allele frequencies of CYP2C19*2 were 11.1% for Western Africa, 14.0% for Western Europe and 16.3% for Northern Europe respectively, and the allele frequencies of CYP2C19*3 were 0% for Western Africa, 0.2% for Western Europe and 0.2% for Northern Europe respectively. In our study, the allele frequencies of CYP2C19*2 and CYP2C19*3 were 25.9% and 9.4% separately. Our result is close with that in Yin’s report.

Studies have shown that the poor metabolizer gene of CYP2C19 was related to the occurrence of coronary heart disease and stroke. Through the research of 654 patients with coronary heart disease, Mao Chen et al. [16] found that the homozygous CYP2C19*2/*2 genotype was an independent determinant of adverse vascular events in Chinese patients with coronary artery disease (CAD). Mega et al. [17] reported that carriers of a reduced-function CYP2C19 allele had a higher rate of major adverse cardiovascular events than did noncarriers. Actually our research also found that CYP2C19 681AA genotype, CYP2C19 636AA and CYP2C19 636AG genotype were related with cerebral ischemic stroke. Multivariate logistic regression analysis showed that the CYP2C19 681AA genotype may be an independent risk factor for cerebral ischemic stroke. We postulate that the weak metabolic gene of CYP2C19 may be related to the formation of cerebral artery atherosclerosis, thereby causing the incidence of cerebral ischemic stroke.

Clopidogrel is a prodrug requiring metabolism by CYP2C19 enzyme, in order to be active, which can play the role of anti-platelet aggregation. Clopidogrel is widely used in the secondary prevention of cerebral ischemic stroke, but its clinical efficacy has individual differences. Many studies have shown that CYP2C19 polymorphism is associated with reduced clopidogrel response [18‐23]. Our study suggested that the CYP2C19 681AA genotype was an independent risk factor for recurrent stroke, since carriers of a reduced-function CYP2C19 allele had a two-fold risk with recurrent stroke than did noncarriers.

In summary, the AA genotype and A allele of CYP2C19 G681A may be associated with the occurrence and recurrence of cerebral ischemic stroke. In addition, we find that the genotypes of CYP2C19 G681A and G636A have nothing to do with the severity of cerebral ischemic stroke. Since our study has limited sample size, further studies in a large population are needed to confirm these findings.