TY - JOUR T1 - CHARACTERIZATION OF NOVEL <em>CYP2A6</em> POLYMORPHIC ALLELES (<em>CYP2A6<sup>*</sup>18</em> AND <em>CYP2A6<sup>*</sup>19</em>) THAT AFFECT ENZYMATIC ACTIVITY JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 1202 LP - 1210 DO - 10.1124/dmd.105.004994 VL - 33 IS - 8 AU - Tatsuki Fukami AU - Miki Nakajima AU - Eriko Higashi AU - Hiroyuki Yamanaka AU - Haruko Sakai AU - Howard L. McLeod AU - Tsuyoshi Yokoi Y1 - 2005/08/01 UR - http://dmd.aspetjournals.org/content/33/8/1202.abstract N2 - Genetic polymorphisms of CYP2A6 gene are known as a causal factor of the interindividual differences in nicotine metabolism. We found three novel CYP2A6 alleles. The CYP2A6*18A allele has a single nucleotide polymorphism (SNP) of A5668T (A1175T, Y392F) in exon 8. The CYP2A6*18B allele has synonymous SNPs of G51A (G51A), T5684C (T1191C), and T5702C (T1209C) in addition to A5668T (A1175T, Y392F). The CYP2A6*19 allele has the SNPs of A5668T (A1175T, Y392F), T6354C (intron 8), and T6558C (T1412C, I471T) as well as the conversion with the CYP2A7 sequence in the 3′-untranslated region, in which the latter two changes correspond to CYP2A6*7. Ethnic differences in the frequencies of these alleles were observed between whites, African-Americans, Japanese, and Koreans. Wild or variant CYP2A6 (CYP2A6*18, CYP2A6*19, and CYP2A6*7) were expressed in Escherichia coli. For coumarin 7-hydroxylation and 5-fluorouracil formation from tegafur, the Km values were increased, and Vmax values were decreased in CYP2A6.18 compared with those in CYP2A6.1, resulting in decreased clearance to 50 and 35% of that of the wild type, respectively. The Km and Vmax values for nicotine C-oxidation were both increased, resulting in no change of clearance. In CYP2A6.19, the effects on the coumarin 7-hydroxylation and 5-fluorouracil formation (increased Km and decreased Vmax) were prominent, resulting in decreased clearance to 8% of those of the wild type. For nicotine C-oxidation, the Km and Vmax values were both decreased, resulting in decreased clearance to 30% of that of the wild type. The changes of the kinetics in CYP2A6.19 were similar to those in CYP2A6.7. In vivo nicotine metabolism was evaluated in whites (n = 56) and Koreans (n = 40). Although the CYP2A6*18 and CYP2A6*19 alleles were found only heterozygously, a subject with CYP2A6*7/CYP2A6*19 showed a lower cotinine/nicotine ratio of the plasma concentration compared with homozygotes of the CYP2A6*1A, supporting the in vitro results that the CYP2A6*19 allele leads to decreased enzymatic activity. The American Society for Pharmacology and Experimental Therapeutics ER -