CHARACTERIZATION OF NOVEL CYP2A6 POLYMORPHIC ALLELES (CYP2A618 AND CYP2A619) THAT AFFECT ENZYMATIC ACTIVITY

• Published in: Drug metabolism and disposition Vol. 33; no. 8; pp. 1202 - 1210
• Main Authors: Fukami, Tatsuki, Nakajima, Miki, Higashi, Eriko, Yamanaka, Hiroyuki, Sakai, Haruko, McLeod, Howard L., Yokoi, Tsuyoshi
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 01.08.2005; American Society for Pharmacology and Experimental Therapeutics
• Subjects: Alleles; Aryl Hydrocarbon Hydroxylases - biosynthesis; Aryl Hydrocarbon Hydroxylases - genetics; Aryl Hydrocarbon Hydroxylases - metabolism; Asian People - genetics; Biological and medical sciences; Black or African American - genetics; Cotinine - blood; Cytochrome P-450 CYP2A6; Escherichia coli - genetics; Escherichia coli - metabolism; Gene Frequency; Genotype; Humans; Kinetics; Medical sciences; Mixed Function Oxygenases - biosynthesis; Mixed Function Oxygenases - genetics; Mixed Function Oxygenases - metabolism; Nicotine - blood; Nicotine - metabolism; Nicotine - pharmacokinetics; Pharmacology. Drug treatments; Polymorphism, Single Nucleotide; Substrate Specificity; Tegafur - metabolism; Transformation, Bacterial; White People - genetics; Characterization; Enzymatic activity; Enzyme; Cytochrome P450
• ISSN: 0090-9556; 1521-009X
• DOI: 10.1124/dmd.105.004994

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.