Comparative time-course of benzo[a]pyrene-DNA adduct formation, and its relationship to CYP1A activity in two species of catfish

Studies have demonstrated differences between the brown bullhead (Ameriurus nebulosus) (BB) and a closely related species of catfish, the channel catfish (Ictalurus punctatus) (CC) in activity of important liver enzymes that may affect their ability to activate or detoxify certain procarcinogens. We have measured the formation and persistence of benzof[a]pyrene-DNA adducts in the liver of these two species using the 32P-postlabeling (PPL) method, along with the effect of prior induction by β-naphthoflavone (βNF). In this time-course study, a total of 80 fish from each species were used. Half were induced with βNF (i.p. injections of 10 mgkg−1 at day 3 and 2) followed by a single benzo[a]pyrene (BaP) i.p. injection (20 mg kg−1). Liver DNA and microsomes were sampled on day 1, 3, 7, 14 and 45 after the BaP dosage—adducts and ethoxyresorufin-O-deethylase (EROD) activity were analyzed. EROD activity in CC was significantly higher at most time points than in BB. In contrast, the BaP-DNA adduct profile revealed a significantly higher level of adducts in the BB than the CC. Adduct levels at most time points were significantly higher in the BB than in the CC at p < 0.05. Further characterization of the major adduct by HPLC confirmed it to be the anti-BPDE-dG adduct. The adduct profiles of BaP are in contrast to what has been observed for adducts of 2-aminoanthracene in these species, although it is consistent with the relative species susceptibility to PAH induced liver neoplasia.