Short Communication CYP3A5 GENETIC POLYMORPHISMS IN DIFFERENT ETHNIC POPULATIONS

Cyp3A5 activity varies within any given ethnic population, suggesting that genetic variation within the Cyp3A5 gene may be the most important contributor to interindividual and interracial differences in Cyp3A-dependent drug clearance and response. The full extent of Cyp3A5 polymorphism in a white and an indigenous African population was analyzed using DNA direct sequencing procedures. The presence of 10 and 12 single nucleotide polymorphisms was detected in the white and African samples, respectively. Thirteen novel mutations occurring at low frequencies were identified in these populations. Significant differences were observed in the distribution of Cyp3A5*3, Cyp3A5*6, and Cyp3A5*7 alleles among white and African populations. The frequency of Cyp3A5*3 allele in white Canadians ( 93%) is higher than in Zimbabweans (77.6%) (p < 0.001). In contrast, Cyp3A5*6 and Cyp3A5*7 alleles are relatively frequent in African subjects (10–22%) but absent in white subjects (p < 0.001). These differences may reflect evolutionary pressures generated by environmental factors in geographically distinct regions. However, the genetic polymorphism of Cyp3A5 alone does not explain the interindividual differences in Cyp3Amediated metabolism. Cytochromes in the P4503A family are estimated to participate in the metabolism of 40 to 60% of all clinically administered drugs. Specifically, they catalyze the oxidative, peroxidative, and reductive metabolism of many endogenous substrates and xenobiotics (Vazquez, 1997). The Cyp3A family is composed of four enzymes: Cyp3A4, the major isoform, Cyp3A43, Cyp3A5, and Cyp3A7. Cyp3A43 is expressed at very low levels in adult livers, accounting for only 0.1 to 0.2% of Cyp3A4 transcripts (Westlind et al., 2001). Cyp3A7 is primarily expressed in the fetal liver but can also be present in small amounts in some adult livers (Schuetz et al., 1994). The contribution of Cyp3A43 and Cyp3A7 to the metabolism of Cyp3A substrates in adults is therefore thought to be negligible. Cyp3A4 and Cyp3A5 are expressed primarily in adult human liver and the mucosa of the intestine, and account for the majority of the catalytic activity of this enzyme subfamily (Wrighton et al., 1990; Kuehl et al., 2001). Substantial interindividual differences in Cyp3A enzyme expression contribute to variation in oral bioavailability and systemic clearance of Cyp3A substrates. The Cyp3A5 contribution to drug metabolism has been reported to vary from 6 to 99% of the total Cyp3A activity in different populations (Wrighton et al., 1990; Kuehl et al., 2001). Cyp3A5 is reported in detectable amounts in only 10 to 30% of adult white people and Asians (Lee et al., 2003), whereas 60% of African Americans express the protein (Kuehl et al., 2001). These variations may be due, on the one hand, to the modulation of Cyp3A expression through a wide array of environmental factors and drugdrug interactions or, on the other hand, to genetic variations. Therefore, Cyp3A5 may be an important genetic contributor to interindividual and interracial differences in Cyp3A-dependent drug clearance and response. To date, most studies on Cyp3A5 polymorphism have been conducted in populations from industrialized countries. The distribution of Cyp3A5 genetic variants in people living in developing countries may differ from that of people living in industrialized countries due to the selection pressure exerted on specific alleles by different environmental factors present in these geographic areas. The objective of our study was to analyze the full extent of Cyp3A5 polymorphism in white Canadian and indigenous African populations. To our knowledge, this is the first study to systematically examine the nucleotide sequence diversity of Cyp3A5 gene in a large number of samples collected from indigenous Africans. Materials and Methods Our samples consisted of stored DNA extracts from 100 unrelated Zimbabweans of the Shona ethnic group recruited in the ZVITAMBO project and 77 unrelated whites from Quebec, Canada. The use of theses samples for the present study was approved by ethics committees. DNA was extracted from whole peripheral blood using standard phenol-chloroform extraction procedures. The nucleotide sequence variants in the promoter region and the 13 exons of Cyp3A5 gene were determined by the direct sequencing method using 50 randomly selected samples of each population. The primers for PCR amplification of the promoter region and exon-specific fragments were designed from the wild-type Cyp3A5 sequence (GenBank accession number AC005020). The primers were designed to cover the entire promoter region and each exon, as well as sequences at the exon-intron boundaries that are important for messenger RNA (mRNA) splicing. Details regarding primer sequences and annealing temperatures for amplifying Cyp3A5 DNA fragments for sequencing are shown in Table 1. Amplification reactions contained 200 ng This work was supported by a grant from the Réseau Sida et maladies infectieuses du Fonds de la Recherche en Santé du Québec (FRSQ). M. Roger is supported by a career award from FRSQ. The ZVITAMBO project is supported by the Canadian International Development Agency (R/C Project 690/M3688), Cooperative Agreement DAN 0045-A-005094-00 between the U.S. Agency for International Development and The Johns Hopkins University School of Hygiene and Public Health, and the Rockefeller Foundation. It is a collaborative project of The University of Zimbabwe, The Harare City Health Department, The Johns Hopkins University School of Hygiene and Public Health, and the Montreal General Hospital Research Institute, McGill University. Article, publication date, and citation information can be found at http://dmd.aspetjournals.org. doi:10.1124/dmd.105.003822. ABBREVIATIONS: PCR, polymerase chain reaction; A-RFLP, amplified restriction fragment length polymorphism; SNP, single nucleotide polymorphism. 0090-9556/05/3307-884–887$20.00 DRUG METABOLISM AND DISPOSITION Vol. 33, No. 7 Copyright © 2005 by The American Society for Pharmacology and Experimental Therapeutics 3822/3038847 DMD 33:884–887, 2005 Printed in U.S.A. 884 at A PE T Jornals on A ril 0, 2017 dm d.aspurnals.org D ow nladed from