Mutagenic activity of possible metabolites of 4-nitrobiphenyl ether

A series of possible metabolites--4-nitrosobiphenyl ether (4-NO), 4-hydroxylaminobiphenyl ether (4-NHOH), 4-aminobiphenyl ether (4-NH2), 4-hydroxyacetylaminobiphenyl ether (4-N(OH)Ac), 4-acetoxyacetylaminobiphenyl ether (4-N(OAc)Ac)involved in the toxic effects of 4-nitrobiphenyl ether (4-NO2) was synthesized and tested for mutagenic activity toward Salmonella typhimurium TA100 strain in the presence and the absence of liver homogenates of guinea pig treated with Kaneclor-500. 4-NO2, 4-NO and 4-NHOH showed direct-acting mutagenicity. 4-NO and 4-NHOH showed high mutagenic activity, while the mutagenic activity of 4-NO2 was very weak compared to 4-NO and 4-NHOH. 4-NO showed antimicrobial action at high concentrations. The other three compounds tested induced no mutation. Upon addition of NAD(P)H, the mutagenic activities of 4-NO and 4-NHOH were slightly enhanced, but no enhancement was observed by addition of NAD(P)+. Metabolic activation with guinea pig liver homogenates enhanced the mutagenic activities of 4-NO2 and 4-NO, and converted 4-NH2, 4-N(OH)Ac and 4-N(OAc)Ac to the product(s) responsible for the mutagenic activity. Addition of bis(p-nitrophenyl)phosphate, a deacetylase inhibitor, inhibited the mutagenic activities of 4-N(OH)Ac and 4-N(OAc)Ac by about 70% in the presence of NADPH and about 77% in the absence of NADPH. High performance liquid chromatography (HPLC) analysis of non-enzymatic conversion-products of 4-NHOH and 4-BO with and without NADPH indicated that 4-NHOH disappeared after 30 min of incubation and was converted completely to 4-NO without NADPH, while with NADPH, 4-NHOH disappeared very slowly and was detected even after 4 h of incubation. In the case of 4-NO, no decrease of 4-NO was observed without NADPH, while with NADPH 4-NO decreased quickly and a significant amount of 4-NHOH appeared. The mechanism of the NAD(P)H-dependent increase in mutagenicity is also discussed.