ROLE OF HUMAN CYTOCHROME P450 (CYP) IN THE METABOLIC ACTIVATION OF NITROSAMINE DERIVATIVES: APPLICATION OF GENETICALLY ENGINEEREDSALMONELLAEXPRESSING 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.

Genetic polymorphism of cytochrome P450 (CYP) 1A1, CYP1A2, and CYP2E1 genes modulate susceptibility to gastric cancer in patients with Helicobacter pylori infection

“…Presence of the 96-bp insert in the CYP2E1 gene is known to be associated with increased enzyme activity [19]. The CYP2E1 enzyme is mainly involved in metabolic activation of N-nitrosamines (a well-defined factor for gastric carcinogenesis) [35]. Therefore, the CYP2E1 genotype frequency observed in the present study is in accordance with this hypothesis.…”

Protective effects of isothiocyanates alone or in combination with vitamin C towards N‐nitrosodibutylamine or N‐nitrosopiperidine‐induced oxidative DNA damage in the single‐cell gel electrophoresis (SCGE)/HepG2 assay

“…Each CYP form shows some substrate specificity for activating promutagens to their mutagenic intermediates (Vermeulen, 1996). CYP2E1 is responsible for α-hydroxylation of N-alkylnitrosamines with a short alkyl chain (Bellec et al, 1996) whereas cyclic N-nitrosamines, such as NPIP and NPYR, are primarily activated by CYP2A6, and to lesser extent by CYP2E1 (Kamataki et al, 2002). Finally CYP1A1 is a molecular form of CYP playing a major role in the metabolic activation of NDBA (Fujita and Kamataki, 2001).…”

Cytochrome P450 2E1/2A6-Selective Inhibition by Halogenated Anilines on Metabolic Activation of Dimethylnitrosamine in Human Liver Microsomes

“…The result confirmed that CYP2E1 is the principal enzyme responsible for the metabolic activation of DMN in human liver microsomes as shown in the previous studies. [4][5][6][7][8] Nine halogenated anilines, 3,5-diF-A, 3,4,5-triF-A, 2,6-diCl-A, 3,4-diCl-A, 3,5-diCl-A, 2,3,4-triCl-A, 2,4,6-triCl-A, 3,4,5-triCl-A, and 2,6-diBr-A, were subjected to analysis of their inhibitory effects on metabolic activation of DMN in human liver microsome (HG56) to evaluate their CYP2E1/2A6-selective inhibition. The inhibitory activities (IC 50 ) of these anilines on human recombinant CYP2E1, CYP1A2, and CYP2A6 activities are shown in Table 2.…”

“…[1][2][3] It is well-known that CYP2E1 and CYP2A6 are responsible for activation of carcinogenic nitrosamines, and CYP2E1 may be the major enzymes catalyzing the metabolic N-demethylation of DMN in human liver microsomes. [4][5][6][7][8] Our previous study indicated that 3,4-dichloroaniline (3,4-diCl-A) and 3,5-diCl-A showed potent inhibition of recombinant human CYP2E1 (IC 50 = 8.0 and 9.2 µM, respectively) and no inhibition of CYP1A2 (IC 50 > 200 µM). 9) Moreover, the inhibitory effects of the anilines on CYP2E1 were widely affected by the substituted halogen species, number, and positions.…”