title: Characterization of novel CYP2A6 polymorphic alleles (CYP2A6*18 and CYP2A6*19) that affect enzymatic activity.
abstract: 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 K(m) values were increased, and V(max) 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 K(m) and V(max) 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 K(m) and decreased V(max)) were prominent, resulting in decreased clearance to 8% of those of the wild type. For nicotine C-oxidation, the K(m) and V(max) 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.
authors.affiliation: Drug Metabolism and Toxicology, Division of Pharmaceutical Sciences, Graduate School of Medical Science, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan.
authors.forename: Tatsuki
authors.initials: T
authors.lastname: Fukami
authors.forename: Miki
authors.initials: M
authors.lastname: Nakajima
authors.forename: Eriko
authors.initials: E
authors.lastname: Higashi
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Yamanaka
authors.forename: Haruko
authors.initials: H
authors.lastname: Sakai
authors.forename: Howard L
authors.initials: HL
authors.lastname: McLeod
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Yokoi
mesh_terms: D001741:Black or African American / Q000235:genetics; D000483:Alleles; D001189:Aryl Hydrocarbon Hydroxylases / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D044466:Asian People / Q000235:genetics; D003367:Cotinine / Q000097:blood; D065637:Cytochrome P-450 CYP2A6; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D005787:Gene Frequency; D005838:Genotype; D006801:Humans; D007700:Kinetics; D006899:Mixed Function Oxygenases / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D009538:Nicotine / Q000097:blood / Q000378:metabolism* / Q000493:pharmacokinetics; D020641:Polymorphism, Single Nucleotide; D013379:Substrate Specificity; D005641:Tegafur / Q000378:metabolism; D014169:Transformation, Bacterial; D044465:White People / Q000235:genetics
chemical_list: D005641:Tegafur; D009538:Nicotine; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6; D003367:Cotinine