Metabolic activation of N-alkylnitrosamines in genetically engineered Salmonella typhimurium expressing CYP2E1 or CYP2A6 together with human NADPH-cytochrome P450 reductase

A Salmonella typhimurium tester strain YG7108 2E1/OR co-expressing human CY P2E1 together with human NADPH-cytochrome P450 reductase (OR) was establish ed. The mutagen-activating capacity of human CYP2E1 for N-alkylnitrosamines was compared with that of CYP2A6 using the YG7108 2E1/OR and the YG7108 2A 6/OR strains of Salmonella. Salmonella YG7108 2A6/OR is a derivative of YG7 108 co-expressing CYP2A6 together with OR. Eight N-alkylnitrosamines, inclu ding N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitroso dipropylamine (NDPA), N-nitrosodibutylamine (NDBA), N-nitrosomethylphenylam ine (NMPhA), N-nitrosopyrrolidine (NPYR), N-nitrosonornicotine (NNN) and 4- (methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were examined. CYP2E1 ex pressed in the YG7108 2E1/OR cells showed mutagen-activating capacity, as i ndicated by induced revertants/min/pmol cytochrome P450, for NDMA, NDEA, ND PA, NDBA, NPYR and NNK, but not NMPhA and NNN. CYP2A6 activated NDMA, NDEA, NDPA, NDBA, NMPhA, NPYR, NNN and NNK. The ratio of the mutagen-activating capacity seen with CYP2A6 to that seen with CYP2E1 was calculated for each N-alkylnitrosamine. In the case of NDMA, NPYR and NDEA, the ratio was under 1.0, while the ratio was over 1.0 with NDPA, NDBA, NNK, NMPhA and NNN. We conclude that human CYP2E1 is mainly responsible for the metabolic activati on of N-nitrosamines with a relatively short alkyl chain(s), whereas CYP2A6 was predominantly responsible for the metabolic activation of N-alkylnitro samines possessing a relatively bulky alkyl chain(s).