1-Nitropyrene is an environmental contaminant that is mutagenic in many prokaryotic and eukaryotic systems, including the
hypoxanthine-
guanosine phosphoribosyl transferase (
HGPRT) locus in the human
hepatoma cell line HepG2. Metabolism and
DNA adduct formation of [3H]1-nitropyrene in the HepG2 were quantified to understand the role of nitroreduction and/or
cytochrome P450-mediated C-oxidation of
1-nitropyrene in
DNA adduct formation and mutagenicity. In uninduced HepG2 cells, 10 microM [3H]1-nitropyrene was metabolized principally by nitroreduction to
1-aminopyrene (516 pmol/24 hr/10(6) cells), and by
cytochrome P450-mediated C-oxidation to K-region trans-dihydrodiols (37 pmol/24 hr/10(6) cells), 1-nitropyren-3-ol (51 pmol/24 hr/10(6) cells), and 1-nitropyren-6-ol and 1-nitropyren-8-ol (77 pmol/24 hr/10(6) cells). Pretreatment of the HepG2 cells for 24 hr with 5 nM
2,3,7,8-tetrachlorodibenzo-p-dioxin (
TCDD) resulted in a complete change in the metabolism of [3H]1-nitropyrene, with 1-nitropyren-6-ol and 1-nitropyren-8-ol formation (449 pmol/24 hr/10(6) cells) being 80-fold greater than
1-aminopyrene formation (6 pmol/24 hr/10(6) cells). This increase in C-oxidation of
1-nitropyrene was consistent with increased levels of
cytochrome P450 1A. The only
DNA adduct detected using the 32P-postlabeling assay in the HepG2 cells administered
1-nitropyrene was N-(2'-deoxyguanosin-8-yl)-1-aminopyrene (dG-C8-AP). Induction of C-oxidative metabolism through
TCDD treatment resulted in a concomitant decrease in dG-C8-AP formation.
DNA adducts for oxidized
1-nitropyrene metabolites were not detected in the
TCDD-treated HepG2 cells administered
1-nitropyrene, which indicates that
cytochrome P450-mediated C-oxidative pathways are detoxification pathways in HepG2 cells.