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Carcinogenesis, Vol 19, 1495-1501, Copyright © 1998 by Oxford University Press

ARTICLES

Induction of hepatic CYP1A in channel catfish increases binding of 2- aminoanthracene to DNA in vitro and in vivo

DE Watson, W Reichert and RT Di Giulio
Ecotoxicology Laboratory, Nicholas School of the Environment, Duke University, Durham, NC 27708-0328, USA. watson2@niehs.nih.gov

Data are presented from in vitro and in vivo studies that indicate cytochrome P4501A (CYP1A) in channel catfish (Ictalurus punctatus) hepatic tissue activates 2-amino-anthracene (AA) to a reactive metabolite that binds to DNA. Channel catfish were injected i.p. with vehicle or 10 mg/kg beta-naphthoflavone (betaNF) on two consecutive days. Two days after the final injection of vehicle or betaNF, vehicle or [3H]AA was injected i.p. at 10 mg/kg, creating four different treatments: vehicle only, betaNF only, [3H]AA only, and betaNF/[3H]AA. Hepatic tissue was examined for CYP1A-associated ethoxyresorufin-O-de- ethylase (EROD) activity, and for DNA adducts at 1, 2, 4 and 7 days following administration of vehicle or [3H]AA. Hepatic EROD activity in betaNF-treated fish was 17-fold higher at day 0 and remained significantly greater than untreated animals for the 7-day experiment. Hepatic DNA adducts, as measured by tritium-associated DNA, ranged from 4.8 to 8.6 pmol/mg DNA in vehicle-pretreated fish injected with [3H]AA, but ranged from 12.6 to 22.7 pmol/mg DNA in betaNF-pretreated fish injected with [3H]AA. Thus, pretreatment with betaNF significantly increased binding of [3H]AA to hepatic DNA in vivo at all four times. Analysis by 32P-post-labeling and thin layer chromatography of hepatic DNA from channel catfish treated with AA revealed two major and several minor spots, which are indicative of DNA adduct formation. Hepatic microsomes from betaNF-pretreated fish were more effective at catalysing the binding of [3H]AA to DNA in vitro than were microsomes from non-treated fish. 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.
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