MUTAGENICITY OF OXIDIZED MICROSOMAL METABOLITES OF 1-NITROPYRENE IN CHINESE HAMSTER OVARY CELLS

1-Nitropyrene, a tumorigenic environmental pollutant, is mutagenic in Chinese hamster ovary (CHO) cells in the presence of a liver homogenate 9000 g supernatant fraction (S9). The metabolic pathways involved in this response were studied by comparing the mutagenicities at the hypo-xanthine-guanine phosphoribosyl transferase locus of 1-nitropyrene, some oxidized microsomal metabolites of 1-nitropyrene, and related compounds. In the absence of S9, pyrene 4, 5-oxide and 6-hydroxy-1-nitropyrene displayed the highest mutagenicities, followed by 1-nitropyrene 9, 10-oxide and 1-nitropyrene 4, 5-oxide; 3- and 8-hydroxy-1-nitropyrene were weaker mutagens, while pyrene and 1-nitropyrene were essentially without activity. With S9, the order of mutagenic potency was 1-nitropyrene 4,5-oxide > 6-hydroxy-1-nitropyrene -1-nitropyrene 9,10-oxide > 1-nitropyrene %3-hydroxy-1-nitropyrene % 8-hydroxy-1-nitropyrene > pyrene % pyrene 4, 5-oxide, with the latter two compounds being essentially inactive. Inclusion of the epoxide hydrolase inhibitor 1, 2-epoxy-3, 3, 3-trichloropropane during the S9-mediated treatment of CHO cells with 1-nitropyrene increased mutation induction 5-fold. Also, liver microsomes prepared from guinea-pigs treated with Aroclor 1254 mediated a stronger mutagenic response with 1-nitropyrene than microsomes from Aroclor-treated rats. 1-Nitropyrene was essentially non-mutagenic in the presence of microsomes from untreated and phenobarbital-treated rats. Examination of the 1-nitropyrene metabolites produced during the microsomal incubations indicated that Aroclor-induced guinea-pig microsomes yielded substantial amounts of 1-nitropyrene 4, 5-dihydrodiol, while Aroclor-induced rat microsomes produced 6-fold more 6- and 8-hydroxy-1-nitropyrene than phenobarbital microsomes. These findings indicate that the 4, 5- and 9, 10-oxides of 1-nitropyrene, along with 6-hydroxy-1-nitropyrene, are the microsomal metabolites most likely responsible for the S9-mediated mutagenicity of 1-nitropyrene in CHO cells. © 1990 Oxford University Press.