Comparative in vitro and in vivo benzo[a]pyrene-DNA adduct formation and its relationship to CYP1A activity in two species of ictalurid catfish.
We have measured the formation and persistence of benzo[a]pyrene (BaP)-DNA adducts in the liver of two closely related species of fish, the brown bullhead (Ameriurus nebulosus) and the channel catfish (Ictalurus punctatus) using the 32P-postlabeling method. Liver microsomal ethoxyresorufin-O-deethylase (EROD) activity, arylhydrocarbon hydroxylase (AHH) activity, and in vitro microsome-mediated DNA binding were all significantly higher in the channel catfish. In an in vivo time-course experiment, fish were either induced with beta NF followed by a single BaP i.p. injection (20 mg/kg) or treated with corn oil. BaP-DNA adducts and EROD activity in liver were analyzed 1, 3, 7, 14, and 45 days after the BaP dosage. As in the in vitro experiments, EROD activities in channel catfish were significantly higher at most time points than in bullhead liver (p < 0.05). However, in contrast to the in vitro data, the BaP-DNA adduct profile revealed significantly higher levels of adducts in the bullhead than the channel catfish throughout the time course (p < 0.05). Prior induction with beta NF did not significantly affect the level or type of adduct binding to DNA in either species. Further characterization of the major adduct by HPLC confirmed it to be the anti-BPDE-dGuo adduct. Analysis of tissue distribution of [14C]BaP in the two species suggested similar absorption and initial distribution, but slower elimination from the liver of bullhead than the catfish. The BaP-adduct profiles were consistent with the relative species susceptibility to polycyclic aromatic hydrocarbon-induced liver neoplasia. EROD activities, however, were negatively associated with adduct levels following in vivo exposure.
Ploch, SA; King, LC; Kohan, MJ; Di Giulio, RT
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