Influence of CYP2C9 Polymorphisms on Plasma Concentration of Warfarin and 7-Hydroxy Warfarin in South Indian Patients.

BACKGROUND: Warfarin is primarily metabolized by cytochrome P450 2C9 (CYP2C9) enzyme, which is encoded by the CYP2C9 gene. CYP2C9*2 and CYP2C9*3 variants significantly influence warfarin metabolism and subsequently the required dose of warfarin. OBJECTIVES: The current retrospective study was aimed to determine the influence of CYP2C9 variants on warfarin metabolic ratio (MR, warfarin/7-hydroxy warfarin) and warfarin maintenance therapy in 210 patients (mean age 44.6±11.6 (SD) years; male to female ratio 81:129). METHODS: High-performance liquid chromatography (HPLC) with UV detector was used to measure plasma concentrations of warfarin and 7-hydroxy warfarin. Plasma samples were collected 12 h after the previous dose of warfarin was administered. CYP2C9 variants (rs1799853 and rs1057910) were identified using real-time polymerase chain reaction allele-discrimination method. RESULTS: The mean daily maintenance dose of warfarin was 4.6±1.8 (SD) mg. The mean plasma warfarin and 7-hydroxy warfarin concentrations were 3.7±1.6 (SD) µg/mL and 1.1±0.54 (SD) µg/mL, respectively. Patients carrying other CYP2C9 variants required 39% lower warfarin maintenance dose 3.3±1.2(SD)mg than CYP2C9*1*1 carrier 4.9±1.8(SD)mg, (p<0.0001). MRs differed significantly between CYP2C9 variant carriers (8.1±5.1) and normal genotype carriers (4.8±3.9) (p<0.0001). Probit analysis identified an MR value of 7.6 as the anti-mode (sensitivity of 84% and specificity of 55%) to differentiate poor and intermediate metabolizers (carriers of any CYP2C9*2 or CYP2C9*3 variants) from normal metabolizers (CYP2C9*1*1 genotype). CONCLUSION: The present study results provide, insights on the effect of CYP2C9 genetic polymorphisms on inter-individual variability in warfarin metabolism and emphasizes utility of phenotyping in a setting of genotype-guided dosing of warfarin in South Indian population.

Distribution of genetic polymorphisms of genes encoding drug metabolizing enzymes & drug transporters - a review with Indian perspective.

Phase I and II drug metabolizing enzymes (DME) and drug transporters are involved in the absorption, distribution, metabolism as well as elimination of many therapeutic agents, toxins and various pollutants. Presence of genetic polymorphisms in genes encoding these proteins has been associated with marked inter-individual variability in their activity that could result in variation in drug response, toxicity as well as in disease predisposition. The emergent field pharmacogenetics and pharmacogenomics (PGx) is a promising discipline, as it predicts disease risk, selection of proper medication with regard to response and toxicity, and appropriate drug dosage guidance based on an individual's genetic make-up. Consequently, genetic variations are essential to understand the ethnic differences in disease occurrence, development, prognosis, therapeutic response and toxicity. For that reason, it is necessary to establish the normative frequency of these genes in a particular population before unraveling the genotype-phenotype associations. Although a fair amount of allele frequency data are available in Indian populations, the existing pharmacogenetic data have not been compiled into a database. This review was intended to compile the normative frequency distribution of the variants of genes encoding DMEs (CYP450s, TPMT, GSTs, COMT, SULT1A1, NAT2 and UGTs) and transporter proteins (MDR1, OCT1 and SLCO1B1) with Indian perspective.

Inter and intra ethnic variation of vitamin K epoxide reductase complex and cytochrome P450 4F2 genetic polymorphisms and their prevalence in South Indian population.

BACKGROUND: Genetic variation in the vitamin K epoxide reductase complex (VKORC1) and cytochrome P450 4F2 (CYP4F2) genes were found to be strongly associated with the oral anticoagulant (OA) dose requirement. The distribution of genetic variation in these two genes was found to show large inter- and intra-ethnic difference. MATERIALS AND METHODS: A total of 470 unrelated, healthy volunteers of South Indians of either sex (age: 18-60 years) were enrolled for the study. A 5 ml of venous blood was collected and the genomic deoxyribonucleic acid (DNA) was extracted by using phenol-chloroform extraction method. Real-time quantitative polymerase chain reaction (RT-PCR) method was used for genotyping. RESULTS: The variant allele frequencies of VKORC1 rs2359612 (T), rs8050894 (C), rs9934438 (T) and rs9923231 (A) were found to be 11.0%, 11.8%, 11.7% and 12.0%, respectively. The variant allele VKORC1 rs7294 was (80.1%) more frequent and the variant allele CYP4F2 * 3 was found to be 41.8% in South Indians. The allele, genotype and haplotype frequencies of VKORC1 and CYP4F2 gene were distinct from other compared HapMap populations (P < 0.0001). CONCLUSION: The findings of our study provide the basic genetic information for further pharmacogenetic based investigation of OA therapy in the population.

Genetic variation and haplotype structure of the gene Vitamin K epoxide reductase complex, subunit 1 in the Tamilian population.

OBJECTIVE: To study the genetic variation and haplotype structure of Vitamin K epoxide reductase complex, subunit 1 (VKORC1) gene in the Tamilian population. MATERIALS AND METHODS: The study was performed on 210 unrelated, healthy volunteers of the Tamilian population, of either sex between the age group of 18-60 years. Five ml of venous blood sample was collected using sodium ethylene diamine tetra acetic acid (EDTA) as anticoagulant. DNA was extracted using phenol-chloroform extraction method. Eight single nucleotide polymorphisms (SNPs) VKORC1 rs9923231 (G), rs7196161 (T), rs2884737 (T), rs17708472 (C), rs9934438 (C), rs8050894 (G), rs23596121 (C), and rs7294 (A) were studied using real-time quantitative Polymerase Chain Reaction (qPCR) method and they were included for constructing five-major haplotype blocks of VKORC1 gene. RESULTS: The major alleles of VKORC1 rs9923231 (G), rs7196161 (T), rs2884737 (T), rs17708472 (C), rs9934438 (C), rs8050894 (G), and rs23596121 (C), were found to be at frequencies of 90.0%, 89.2%, 90.9%, 94.1%, 90.7%, 89.5% and 91.2%, respectively. The variant allele of VKORC1 rs7294 (A) was more frequent (83.6%) in the Tamilian population. The frequencies of haplotypes HAP1 (GTTCCGCA), HAP2 (ACGCTCTG), HAP3 (GTTTCGCG), HAP4 (GTTCCGCG) and HAP5 (GCTCCCCG) were found to be 80.0%, 7.4%, 4.7%, 1.5% and 1.1%, respectively. CONCLUSION: In the present study the allele- frequency distributions, genotype and haplotype frequencies of the VKORC1 gene was considered. The findings of this study provide the genetic information required for learning the association of VKORC1 genetic variation and oral anticoagulant dose variability among patients receiving oral anticoagulants in the Tamilian population.