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 β-naphthoflavone (βNF), followed 2 days later with vehicle erring-tritiated 2-aminoanthracene ([3H]-AA), such that four treatments were obtained: (1) vehicle only; (2) βNF only; [3H]-AA only; βNF/[3H]-AA. Ethoxyresorufin-O-deethylase (EROD) activity in βNF-treated fish was 15-fold greater than in vehicle-treated fish at day O and was also significantly greater than vehicle-treated fish at day 1. Western blot analysis revealed marked induction of hepatic CYP1A in fish treated with βNF and minor induction in fish treated with [3H]-AA compared with vehicle-treated fish. Hepatic DNA adducts, as measured by tritium-associated DNA, ranged from 1.47 to 2.57 pmol mg-1 DNA in fish injected only with [3H-AA, but ranged from 5.70 to 7.82 pmol mg-1 DNA in fish injected with βNF prior to injection with [3H]-AA. Thus, βNF pretreatment significantly increased binding of [3H]-AA to hepatic DNA in vivo at all time points (P < 0.05). In vitro hepatic microsomes from βNF-treated bullhead catalyzed the binding of [3H]-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 formation in AA-exposed fish, Comparisons were made between this study and a parallel study using the same experimental design but conducted with a related Ictalurid catfish, the channel catfish.

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Author Richard T. Di Giulio Environmental Sciences and Policy