Synthesis and mutagenicity of 1-nitropyrene 4,5-oxide and 1-nitropyrene 9,10-oxide, microsomal metabolites of...

[4,5,9,10-(3)H]1-Nitropyrene was incubated with liver microsomes prepared from guinea pigs treated with Aroclor 1254 and the products were examined by h.p.l.c. The previously reported metabolites, 1-nitropyrene trans-4,5-dihydrodiol, 1-nitropyrene trans-9,10-dihydrodiol, and 3-, 6-, and 8-hydroxy-1-nitropyrene were detected. In addition, h.p.l.c., nuclear magnetic resonance and mass spectral analyses indicated the presence of 1-nitropyrene 4,5-oxide and 1-nitropyrene 9,10-oxide. The epoxide hydrase inhibitor, 1,2-epoxy-3,3,3-trichloropropane, decreased the concentration of the 4,5- and 9,10-dihydrodiols in the microsomal incubations and increased the concentration of their corresponding oxides. Reaction of 1-nitropyrene with m-chloroperoxybenzoic acid gave a mixture of 1-nitropyrene 4,5-oxide and 1-nitropyrene 9,10-oxide, which was separated by chromatography. The mutagenicity of the oxides was determined in Salmonella typhimurium strains TA98, TA98NR, and TA98/1,8-DNP6, both with and without exogenous activation by a rat liver homogenate fraction (S9). In the absence of S9, both oxides showed maximum activity in TA98, slightly decreased mutagenicity in the acetylase-deficient strain TA98/1,8-DNP6, and much reduced activity in the nitroreductase-deficient strain, TA98NR. When assayed in the presence of S9, 1-nitropyrene 4,5-oxide had maximum mutagenicity in TA98, and was 50 and 95% less mutagenic in TA98NR and TA98/1,8-DNP6, respectively. 1-Nitropyrene 9,10-oxide had a similar strain sensitivity, except that its total mutagenicity was lower. Since 1-nitropyrene is metabolized by oxidative pathways in vivo, these K-region oxides may contribute to the toxicities elicited by this compound.