ROLE OF O-ACETYLTRANSFERASE IN ACTIVATION OF OXIDIZED METABOLITES OF THE GENOTOXIC ENVIRONMENTAL-POLLUTANT 1-NITROPYRENE

The genotoxic environmental contaminant l-nitropyrene is metabolised i n mammalian systems by pathways more complex than the straightforward nitroreduction which accounts for most of its biological activity in b acteria. In order to evaluate the role of O-acetyltransferase (OAT) ac tivity in generation of genotoxic intermediates from 1-nitropyrene, th e mutagenicity of the major primary oxidised metabolites of 1-nitropyr ene was characterised in the Ames Salmonella typhimurium plate incorpo ration assay with strain TA98, and with variants of TA98 deficient (TA 98/1,8-DNP6) or enhanced (YG1024) in O-acetyltransferase. 1-Nitropyren -3-ol was more mutagenic in the absence than in the presence of S9, wh ile 1-nitropyren-4-ol, 1-nitropyren-6-ol and 1-nitropyren-8-ol require d S9 for maximum expression of mutagenicity. 1-Nitropyren-4-ol (176 re v/nmol without S9, 467 rev/nmol with S9 in TA98) and 1-nitropyren-6-ol (13 rev/nmol without S9, 266 rev/nmol with S9 in TA98) were overall t he most potent nitropyrenol isomers assayed. 1-Acetamidopyren-8-ol and 2-acetamidopyrene 4,5-quinone were only minimally active. 1-Acetamido pyren-3-ol exhibited direct-acting mutagenicity. 1-Acetamidopyren-6-ol , previously shown to be a major contributor to mutagenicity in the ur ines of rats dosed with l-nitropyrene (Ball et al., 1984b), was confir med as a potent (359 rev/nmol) S9-dependent mutagen. Both the direct-a cting and the S9-dependent mutagenicity of all the compounds studied w as enhanced in the OAT-overproducing strain and much diminished (thoug h not always entirely lost) in the OAT-deficient strain, showing that OAT amplifies expression of the genotoxicity of these compounds. 1-Ace tamidopyren-6-ol required both 89 and OAT activity in order to exhibit any mutagenicity; this finding strongly implicates N-hydroxylation fo llowed by O-esterification, as opposed to further S9-catalyzed ring ox idation, as a major route of activation for urinary metabolites of 1-n itropyrene.