Covalent binding of (+) 7S-trans-7,8-dihydrobenzo [a]pyrene-7,8-diol to trout DNA: P-450- and peroxidation-dependent pathways

Bioactivation in vivo of pure (+) 7S-trans-7,8-dihydrobenzo[a]pyrene-7,8-diol ((+) BP-7,8-DHD) was investigated in rainbow trout. Embryos, microinjected with 0.01-1.0 μg of [³H]-(-)-7S-trans-7,8-dihydrobenzo[a]-pyrene-7,8-diol-anti-9,10-epoxide ((-) anti-BPDE), exhibited a dose-dependent increase in DNA adduction. Subsequently, microinjection of trout embryos with [¹⁴C] (+) BP-7,8-DHD also demonstrated a dose-dependent increase in DNA adduction. To determine the relative contribution of P-450-dependent versus peroxidation-dependent epoxygenation of (+)-BP-7,8-DHD, trout embryos were co-injected with [¹⁴C]-(+)-BP-7,8-DHD and either β-naphthoflavone (BNF) (CYP1A1 inducer) or carbon tetrachloride (CCl₄) (lipid peroxidation enhancer). Co-injection with BNF tended to enhance covalent binding to DNA, which was consistent with rapid induction of CYP1A1. Co-injection with CCl₄, significantly increased covalent binding of [¹⁴C]-(+)-BP-7,8-DHD to DNA, suggesting a contribution from non-enzymic cooxidation. ³²P-Postlabeling analysis of liver DNA adducts following i.p. injections of (+) BP-7,8-DHD did not detect appreciable amounts of (-) anti-BPDE-dG from juvenile trout fed control diets or diets containing hydrogen peroxide or BNF. On the contrary, BNF pre-feeding markedly enhanced the levels of an adduct which co-chromatographed with authentic (+) syn-BPDE-dG. These results confirm that trout are capable of metabolically activating BP-DHD to the ultimate carcinogen BPDE and that BNF stimulates CYP1A1-dependent epoxygenation, but peroxidation-dependent activation may not contribute significantly to the bioactivation of BP-7,8-DHD in vivo.