COVALENT BINDING OF (-TRANS-7,8-DIHYDROBENZO[A]PYRENE7,8-DIOL TO TROUT DNA - P-450- AND PEROXIDATION-DEPENDENT PATHWAYS() 7S)

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, m icroinjected with 0.01-1.0 mu g of [H-3] -dihydrobenzo[a]-pyrene-7,8-d iol-anti-9,10-epoxide ((-) anti-BPDE), exhibited a dose-dependent incr ease in DNA adduction. Subsequently, microinjection of trout embryos w ith [C-14] (+) BP-7,8-DHD also demonstrated a dose-dependent increase in DNA adduction. To determine the relative contribution of P-450-depe ndent versus peroxidation-dependent epoxygenation of (+)-BP-7,8-DHD, t rout embryos were co-injected with [C-14]-(+)-BP-7,8-DHD and either be ta-naphthoflavone (BNF) (CYP1A1 inducer) or carbon tetrachloride (CCl4 ) (lipid peroxidation enhancer). Co-injection with BNF tended to enhan ce covalent binding to DNA, which was consistent with rapid induction of CYP1A1. Co-injection with CCl4, significantly increased covalent bi nding of [C-14]-(+)-BP-7,8-DHD to DNA, suggesting a contribution from non-enzymic cooxidation. P-32-Postlabeling analysis of liver DNA adduc ts following i.p. injections of (+) BP-7,8-DHD did not detect apprecia ble 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-chromatogr aphed with authentic (+) syn-BPDE-dG. These results confirm that trout are capable of metabolically activating BP-DHD to the ultimate carcin ogen 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.