INDUCTION OF HEPATIC CYP1A IN CHANNEL CATFISH INCREASES BINDING OF 2-AMINOANTHRACENE TO DNA IN-VITRO AND IN-VIVO

Data are presented from in vitro and in vivo studies that indicate cyt ochrome P4501A (CYP1A) in channel catfish (Ictalurus punctatus) hepati c tissue activates 2-aminoanthracene (AA) to a reactive metabolite tha t binds to DNA, Channel catfish were injected i.p. with vehicle or 10 mg/kg beta-naphthoflavone (beta NF) on two consecutive days. Two days after the final injection of vehicle or beta NF, vehicle or [H-3]AA wa s injected i.p. at 10 mg/kg, creating four different treatments: vehic le only, beta NF only, [H-3]AA only, and beta NF/[H-3]AA, Hepatic tiss ue was examined for CYP1A-associated ethoxyresorufin-O-de-ethylase (ER OD) activity, and for DNA adducts at 1, 2, 4 and 7 days following admi nistration of vehicle or [H-3]AA. Hepatic EROD activity in beta NF-tre ated fish was 17-fold higher at day 0 and remained significantly great er than untreated animals for the 7-day experiment. Hepatic DNA adduct s, as measured by tritium-associated DNA, ranged from 4.8 to 8.6 pmol/ mg DNA in vehicle-pretreated fish injected with [H-3]AA, but ranged fr om 12.6 to 22.7 pmol/mg DNA in beta NF-pretreated fish injected with [ H-3]AA, Thus, pretreatment with beta NF significantly increased bindin g of [H-3]AA to hepatic DNA in vivo at all four times. Analysis by P-3 2-post-labeling and thin layer chromatography of hepatic DNA from chan nel catfish treated with AA revealed two major and several minor spots , which are indicative of DNA adduct formation. Hepatic microsomes fro m beta NF-pretreated fish were more effective at catalysing the bindin g of [H-3]AA to DNA in vitro than were microsomes from non-treated fis h, In addition, binding was decreased by the CYP1A inhibitor 3,3',4,4' -tetrachlorobiphenyl. Collectively, these data demonstrate that CYP1A is involved in the activation of AA in channel catfish.