Influences of chronic cholangiohepatitis and cholestasis on hepatic metabolism of benzo[a]pyrene in white suckers (Catostomus commersoni) from industrially polluted areas of Lake Ontario.
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White suckers from polluted regions of western Lake Ontario have an increased prevalence of cholangiocellular and hepatocellular and hepatocellular neoplasms associated with an idiopathic chronic cholangiohepatitis. We examined the hypothesis that bile duct obstructions and cholestasis in these fish might increase the susceptibility of liver to administered benzo[a]pyrene (B[a]P). Cytosolic glutathione S-transferase (GST) activity (CDNB) was reduced in obstructed liver to 45% of activity in adjacent unobstructed liver. At micromolar concentrations, chenodeoxycholic acid, deoxycholic acid, bilirubin and haematin each inhibited GST activity of hepatic cytosolic and S-hexylglutatione-affinity-purified GST preparations from unobstructed liver. Liver cytosol and affinity-purified hepatic GSTs from normal white sucker liver reduced DNA binding of 3H-benzo[a]-pyrene-7,8-diol-9,10-epoxide (3H-BPDE) after preincubation in vitro in the presence of 5 mM GSH. Under these conditions, cytosol from adjacent unobstructed liver had a moderately stronger protective activity against DNA binding by BPDE (16.4 +/- 1.3 pmol BPDE/mg DNA) than did cytosol from obstructed liver (20.6 +/- 1.6 pmol BPDE/mg DNA). Suckers with obstructed livers identified by laparotomy were orally administered 3H-benzo[a]pyrene (3H-B[a]P) (0.2 mmol/kg) or unlabelled B[a]P (2.0 mg/kg) and the level of B[a]P macromolecular binding was analyzed in liver tissue by liquid scintillation counting and by immunohistochemistry with antibodies to BPDE-DNA adducts. Covalent binding of 3H-B[a]P to hepatic protein was 30% less in adjacent unobstructed liver compared to obstructed liver; however, there was no significant difference in the levels of 3H-B[a]P bound to DNA in the obstructed lobes compared with non-obstructed adjacent liver. These studies demonstrate that some endogenous non-substrate ligands that accumulate during cholestasis can reduce hepatic GST activity in white suckers. While these changes are insufficient to influence total 3H-B[a]P-DNA adducts in obstructed liver, the preferential localization of BPDE-DNA adducts in GST-deficient hyperplastic biliary tracts suggests that cholangiohepatitis might increase susceptibility to cholangiolar neoplasia in fish exposed to genotoxic polycyclic aromatic hydrocarbons.
