Mechanism of appearance of mutagenicity of N-nitrosodiphenylamine with norharman.

The mutagenicity of the carcinogen N-nitrosodiphenylamine (NDPhA) to Salmonella typhimurium TA98 was demonstrated only when norharman, a comutagen, was added to the incubation mixture with S9 mix. N,N-Diphenylamine (DPhA), a denitrosated derivative of NDPhA, was also mutagenic to S. typhimurium TA98 when norharman was present. Twice as many revertants were induced by DPhA with norharman as by NDPhA with norharman. The comutagenic effect of norharman was also observed with N-nitroso-methylphenylamine (NMPhA), N-nitrosoethylphenylamine (NEPhA) and N-nitrosophenylbenzylamine (NPhBeA) and their denitrosated derivatives. NDPhA was converted metabolically to DPhA by S9 mix. Stoichiometric studies indicated that the mutagenicity of NDPhA in the presence of norharman was exerted through DPhA. The denitrosation eyzme activity of NDPhA was mainly recovered in the microsomal fraction, and the enzyme seemed to be a cytochrome P-450 monooxygenase system. Denitrosation reactions of NMPhA, NEPhA and NPhBeA were also demonstrated. The mutagenicities of these compounds with norharman are therefore suggested to be due to a mechanism similar to that of NDPhA with norharman.