Effect of exposure to benzo[ a]pyrene on SODs, CYP1A1/1A2- and CYP2E1 immunopositive proteins in the blood clam Scapharca inaequivalvis

The effects of water-borne exposure to benzo[ a]pyrene (36 h; celite-bound 0.44 mg L −1 B[ a]P) on cytochrome P450 (CYP) and superoxide dismutases (SODs) were examined in digestive gland of the blood clam, Scapharca inaequivalvis. B[ a]P accumulation and elimination were rapid, with maximum whole-body concentrations of 1.78 ng g −1 wet wt after 12 h of treatment, followed by a progressive decline to 0.89 ng g −1 at 36 h. The presence of B[ a]P resulted in an increase in total CYP of digestive gland microsomes from 54 ± 14 to 108 ± 21 pmol/mg protein (mean ± SD; p < 0.05, 24 h). Increases were also seen in microsomal CYP1A1/1A2-immunopositive protein (50.5 kDa app. mol. wt; p < 0.05), but not CYP2E1-immunopositive protein (49 kDa app. mol. wt.), indicating a specific response of the former isoform. Exposure to B[ a]P produced a steady increase in Mn-SOD digestive gland activity ( p < 0.01; p < 0.05) but no significant change in Cu/Zn-SOD activity. The respective proteins, measured by western blotting, were not significant induced after B[ a]P exposure. Cu/Zn-SOD and Mn-SOD activities were correlated with total CYP levels ( r = 0.96 and 0.63, respectively), indicating a role for CYP in reactive oxygen species (ROS) production during exposure. Both ‘NADPH-independent’ and NADPH-dependent metabolism of B[ a]P by digestive gland microsomes was seen, producing mainly 1,6-, 3,6- and 6,12-diones, with some phenols and 7,8-dihydrodiol; putative protein adducts were also formed. Redox cycling of the diones may also have contributed to ROS production, leading to the increased SOD activities.