HEPATIC CYP1A IN BROWN BULLHEAD CATALYZES THE BINDING OF 2-AMINOANTHRACENE TO DNA IN-VIVO AND IN-VITRO

Brown bullhead were injected i.p. with vehicle or beta-naphthoflavone (beta NF), followed 2 days later with vehicle or ring-tritiated 2-amin oanthracene ([H-3]-AA), such that four treatments were obtained: (1) v ehicle only; (2) beta NF only; [H-3]-AA only; beta NF/[H-3]-AA. Ethoxy resorufin-O-deethylase (EROD) activity in beta NF-treated fish was 15- fold greater than in vehicle-treated fish at day 0 and was also signif icantly greater than vehicle-treated fish at day 1. Western blot analy sis revealed marked induction of hepatic CYPIA in fish treated with PN F and minor induction in fish treated with [H-3]-AA compared with vehi cle-treated fish. Hepatic DNA adducts, as measured by tritium-associat ed DNA, ranged from 1.47 to 2.57 pmol mg(-1) DNA in fish injected only with [H-3]-AA, but ranged from 5.70 to 7.82 pmol mg(-1) DNA in fish i njected with PNF prior to injection with [H-3]-AA. Thus, beta NF pretr eatment significantly increased binding of [H-3]-AA to hepatic DNA in vivo at all time points (P < 0.05). In vitro, hepatic microsomes from beta NF-treated bullhead catalyzed the binding of [H-3]-AA to DNA at a low but measurable level which was significantly inhibited (P < 0.05) by alpha-naphthoflavone and tetrachlorobiphenyl. Collectively, these data indicate that CYP1A activates AA to a DNA-binding metabolite(s), and that CYP1A induction in bullhead results in greater DNA adduct for mation in AA-exposed fish. Comparisons were made between this study an d a parallel study using the same experimental design but conducted wi th a related Ictalurid catfish, the channel catfish.