Functional characterization of the defective CYP2C9 variant CYP2C9*18

Identification and drug metabolic characterization of four new CYP2C9 variants CYP2C9*72-*75 in the Chinese Han population

Cytochrome 2C9 (CYP2C9), one of the most important drug metabolic enzymes in the human hepatic P450 superfamily, is required for the metabolism of 15% of clinical drugs. Similar to other CYP2C family members, CYP2C9 gene has a high genetic polymorphism which can cause significant racial and inter-individual differences in drug metabolic activity. To better understand the genetic distribution pattern of CYP2C9 in the Chinese Han population, 931 individuals were recruited and used for the genotyping in this study. As a result, seven synonymous and 14 non-synonymous variations were identified, of which 4 missense variants were designated as new alleles CYP2C9*72, *73, *74 and *75, resulting in the amino acid substitutions of A149V, R150C, Q214H and N418T, respectively. When expressed in insect cell microsomes, all four variants exhibited comparable protein expression levels to that of the wild-type CYP2C9 enzyme. However, drug metabolic activity analysis revealed that these variants exhibited significantly decreased catalytic activities toward three CYP2C9 specific probe drugs, as compared with that of the wild-type enzyme. These data indicate that the amino acid substitution in newly designated variants can cause reduced function of the enzyme and its clinical significance still needs further investigation in the future.

Polymorphisms of genes related to phase-I metabolic enzymes affecting the clinical efficacy and safety of clopidogrel treatment

Introduction: Clopidogrel is an antiplatelet medication described as a prodrug, which cannot exert the antiplatelet effect until being biotransformed to the active metabolite. It is commonly used to reduce the risk of blood coagulation in patients diagnosed with acute coronary syndrome, or ischemic stroke.Area covered: We reviewed published articles in PubMed and Google Scholar that focused on the mutations of CYP2C19, CYP3A4, CYP2C9, CYP2B6, and CYP1A2 genes related to clopidogrel clinical efficacy and safety.Expert opinion: Based on current pharmacogenetic studies, patients carrying CYP2C19*2, CYP2C19*3, CYP2C9*3, and CYP2B6*5 alleles may not respond to clopidogrel due to poor platelet inhibition efficacy revealed among them. In contrast, carriers of CYP2C19*17, CYP3A4*1G, and CYP1A2*1C alleles showed a more significant antiplatelet effect in clopidogrel users and expected to have a protective role as a genetic factor against cardiovascular events. Genotyping for either CYP2C19, CYP3A4, CYP2C9, CYP2B6, or CYP1A2 variants is not recommended when considering clopidogrel treatment for patients, as some trials showed specific non-genetic factors (e.g. age and diabetes) that could affect clopidogrel responsiveness. Instead, platelets inhibition tests could be used as predictors of the clinical efficacy of clopidogrel treatment. Other P2Y12 receptor inhibitors should be considered as alternative medications.