title: Role of human cytochrome P450 (CYP) in the metabolic activation of nitrosamine derivatives: application of genetically engineered Salmonella expressing human CYP.
abstract: The role of human cytochrome P450 (CYP) in the metabolic activation of tobacco-related N-nitrosamines was examined by Salmonella mutation test using a series of genetically engineered Salmonella typhimurium YG7108 strains each co-expressing a form of CYP (CYP1A1, CYP1A2, CYP1B1, CYP2A6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4, and CYP3A5) together with human NADPH-cytochrome P450 reductase. Seven tobacco-related N-nitrosamines such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, N-nitrosodiethylamine, N-nitrosopyrrolidine, N-nitrosopiperidine, N-nitrosonornicotine, N-nitrosoanabasine, and N-nitrosoanatabine were used. The CYP2A6 was found to be responsible for the mutagenic activation of essentially all tobacco-related N-nitrosamines examined. On the basis of the evidence, genetic polymorphism of the CYP2A6 gene appeared to be one of the factors determining cancer susceptibility caused by smoking. Previously, we found the whole deletion of the CYP2A6 gene (CYP2A6*4C) as a type of genetic polymorphism in Japanese. We hypothesized that individuals possessing the gene homozygous for CYP2A6*4C were incapable of activating tobacco-related N-nitrosamines and showed lower susceptibility to lung cancer induced by tobacco smoke. Thus, the relationship between the CYP2A6*4C and the susceptibility to the lung cancer was evaluated. The frequency of the CYP2A6*4C was significantly lower in the lung cancer patients than healthy volunteers, suggesting that the subjects carrying the CYP2A6*4C alleles are resistant to carcinogenesis caused by N-nitrosamines because of the poor metabolic activation capacity. Taking these results into account, CYP2A6 is an enzyme enhancing lung cancer risk.
authors.affiliation: Laboratory of Drug Metabolism, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan. kamataki@pharm.hokudai.ac.jp
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Kamataki
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Fujita
authors.forename: Kazuo
authors.initials: K
authors.lastname: Nakayama
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Yamazaki
authors.forename: Masami
authors.initials: M
authors.lastname: Miyamoto
authors.forename: Noritaka
authors.initials: N
authors.lastname: Ariyoshi
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics* / Q000378:metabolism*; D065637:Cytochrome P-450 CYP2A6; D005786:Gene Expression Regulation; D005818:Genetic Engineering; D020022:Genetic Predisposition to Disease; D006801:Humans; D007564:Japan; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000235:genetics* / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000235:genetics / Q000378:metabolism; D009602:Nitrosamines / Q000737:chemistry / Q000378:metabolism*; D011110:Polymorphism, Genetic; D012307:Risk Factors; D012486:Salmonella typhimurium / Q000235:genetics*; D014026:Nicotiana
chemical_list: D009602:Nitrosamines; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6; D009251:NADPH-Ferrihemoprotein Reductase