In vitro metabolic activation of N,N-dibutylnitrosamine in mutagenesis

Enzymatic alpha-hydroxylation is believed to be the initial step in the metabolic activation of mutagenic and carcinogenic nitrosamines. Oxidative in vitro metabolism of N,N-dibutylnitrosamine (DBN) by hepatic microsomal fractions prepared from rats treated with phenobarbital and polychlorinated biphenyl (PCB) was investigated. Following incubation of DBN with the microsomal fractions, N-butyl-N-(3-hydroxybutyl)nitrosamine was identified by gas-liquid chromatography as the principal metabolite with the N-nitroso moiety, and butyraldehyde and/or two isomeric butyl alcohols (n- and sec-) were also identified and determined by gas-liquid chromatography and high-pressure liquid chromatography. The latter compounds originate from the unstable alpha-hydroxylated intermediate, N-butyl-N-(1-hydroxybutyl)nitrosamine, by spontaneous decomposition. An increased production of butyraldehyde with a concomitant enhancement of the mutagenicity of DBN toward Salmonella typhimurium TA1535 was observed when microsomes prepared from phenobarbital- and PCB-treated rats were used. SKF 525-A not only inhibited the mutagenic activation of DBN by microsomes from rats treated with the inducers but also selectively inhibited the formation of butyraldehyde and butyl alcohols from DBN. These results indicate that among the four initial hydroxylations (alpha, omega-2, omega-1, and omega) of the butyl chain demonstrated in the metabolism of DBN, alpha-hydroxylation is primarily involved in the mutagenic activation.