Characterization of DNA adducts in Chinese hamster ovary cells treated with mutagenic doses of 1- and 3-nitrosobenzo[ a]pyrene and the trans-7,8-diol- anti-9,10-epoxides of 1- and 3-nitrobenzo[ a]pyrene

Abstract

The environmental contaminants 1- and 3-nitrobenzo[ a]pyrene (1- and 3-nitro-BaP) are mutagens in Chinese hamster ovary (CHO) cells with exogenous metabolic activation. Previous studies demonstrated the potent direct-acting mutagenicity of the oxidized metabolites, trans-7,8-dihydroxy- anti-9,10-epoxy-7,8,9,10-tetrahydro-1-nitrobenzo[ a]pyrene (1-NBaPDE) and trans-7,8-dihydroxy- anti-9,10-epoxy-7,8,9,10-tetrahydro-3-nitrobenzo[ a]pyrene (3-NBaPDE), and the partially nitroreduced metabolites, 1- and 3-nitrosobenzo[ a]pyrene (1- and 3-NO-BaP). In this study, we have identified the major adduct formed by incubation of calf thymus DNA with 1-NBaPDE and used this standard in conjunction with other adduct standards to characterize the 32P-postlabeled DNA adducts produced by 1- and 3-nitro-BaP metabolites in CHO cultures. The major adduct from 1-NBaPDE exposure was 10-(deoxyguanosin- N 2-yl)-7,8,9-trihydroxy-7,8,9,10-tetrahydro-1-nitrobenzo[ a]pyrene; from 3-NBaPDE, 10-(deoxyguanosin- N 2-yl)-7,8,9-trihydroxy-7,8,9,10-tetrahydro-3-nitrobenzo[ a]pyrene; from 1-NO-BaP, 6-(deoxyguanosin- N 2-yl)-1-aminobenzo[ a]pyrene; and from 3-NO-BaP, 6-(deoxyguanosin- N 2-yl)-3-aminobenzo[ a]pyrene. For comparison, the adducts formed by trans-7,8-dihydroxy- anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[ a]pyrene and the related nitroreduced derivative 6-nitrosobenzo[ a]pyrene were also examined. The nitrobenzo[ a]pyrene DNA adducts described in this study are proposed to be involved in the mutagenicity of 1- and 3-nitro-BaP upon either oxidative or reductive metabolism.