Effects of tributyltin, benzo[a]pyrene, and their mixture on antioxidant defense systems in Sebastiscus marmoratus

It has been reported that there is a metabolic interaction between tributyltin (TBT), an organometal used as an antifouling biocide, and benzo[a]pyrene (BaP), a widespread carcinogenic polycyclic aromatic hydrocarbon. This study was therefore designed to examine the potential in vivo influence of TBT, BaP, and their mixture on hepatic antioxidant defense systems of Sebastiscus marmoratus, which were given a single ip injection of TBT (0.5, 1, 5, and 10 mg/kg), BaP (0.5, 1, 5, and 10 mg/kg), or both in combination (0.5, 1, 5, and 10 mg/kg); control fish received olive oil vehicle only. Samples were collected for biochemical analysis after injection for 7 days. Cotreatment with BaP caused a significant inhibition of TBT-mediated malondialdehyde contents elevation. Cotreatment with TBT decreased BaP-mediated glutathione peroxidase activity induction. Cotreatment with TBT and BaP did not significantly alter the reduced glutathione levels, which were significantly induced by TBT or BaP alone. TBT-induced suppression of BaP bioactivation or BaP-induced stimulation of the phase II metabolism of TBT and its biliary excretion, both of which have been reported previously, could explain the observed antagonism. The results suggest that combined exposure of TBT and BaP increases the vulnerability of the fish to oxidative stress. BaP cotreatment decreased the induction of glutathione S-transferase (GST) activity by the lower dose of TBT, while cotreatment with TBT and BaP at the highest dose (10 mg/kg) resulted in inhibition of the GST activity by 4.8-fold. The results suggest that these biomarkers should be interpreted with caution in biomonitoring studies. Combined effects of TBT and BaP exposure at environmental levels on these biomarkers should be further researched.