title: Metabolic effects of CYP2A6 and CYP2A13 on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced gene mutation--a mammalian cell-based mutagenesis approach.
abstract: Both cytochrome P450 2A6 (CYP2A6) and cytochrome P450 2A13 (CYP2A13) are involved in metabolic activation of tobacco-specific nitrosamines and may play important roles in cigarette smoking-induced lung cancer. Unlike CYP2A6, effects of CYP2A13 on the tobacco-specific nitrosamine-induced mutagenesis in lung cells remain unclear. This study uses a supF mutagenesis assay to examine the relative effects of CYP2A6 and CYP2A13 on metabolic activation of a tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and its resulting mutagenesis in human lung cells. A recombinant adenovirus-mediated CYP2A6/CYP2A13 expression system was established to specifically address the relative effects of these two CYPs. Mutagenesis results revealed that both CYP2A6 and CYP2A13 significantly enhanced the NNK-induced supF mutation and that the mutagenic effect of CYP2A13 was markedly higher than that of CYP2A6. Analysis of NNK metabolism indicated that ≥70% of NNK was detoxified to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), either with or without CYP2A6/CYP2A13 expression. Both CYP2A6 and CYP2A13 significantly enhanced the α-hydroxylation of NNK; and the α-hydroxylation activity of CYP2A13 was significantly higher than that of CYP2A6. Analysis of the NNK-related DNA adduct formation indicated that, in the presence of CYP2A13, NNK treatments caused marked increases in O(6)-methylguanine (O(6)-MeG). The present results provide the first direct in vitro evidence demonstrating the predominant roles of CYP2A13 in NNK-induced mutagenesis, possibly via metabolic activation of NNK α-hydroxylation.
authors.affiliation: Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan.
authors.forename: Huai-Chih
authors.initials: HC
authors.lastname: Chiang
authors.forename: Chin-Ying
authors.initials: CY
authors.lastname: Wang
authors.forename: Hui-Ling
authors.initials: HL
authors.lastname: Lee
authors.forename: Tsui-Chun
authors.initials: TC
authors.lastname: Tsou
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics / Q000502:physiology*; D001711:Biotransformation; D002273:Carcinogens / Q000378:metabolism*; D065637:Cytochrome P-450 CYP2A6; D018736:DNA Adducts / Q000378:metabolism; D006801:Humans; D016296:Mutagenesis; D009154:Mutation; D009602:Nitrosamines / Q000378:metabolism*
chemical_list: D002273:Carcinogens; D018736:DNA Adducts; D009602:Nitrosamines; C016583:4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone; D001189:Aryl Hydrocarbon Hydroxylases; C414206:CYP2A13 protein, human; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6