In-vitro metabolism of benzo(a)pyrene in the blood of the gulf toadfish, Opsanus beta

Abstract

Other studies have suggested that the blood of fish may be capable of metabolizing xenobiotic compounds. In this study, whole blood from fish acclimated to 18 or 28°C was incubated with benzo(a)pyrene (BaP) at 18, 23 and 28°C in vitro to directly examine its metabolic capacity and the effects of temperature on metabolism. Toadfish blood metabolized BaP to a variety of Phase I and Phase II metabolites, although at substantially lower rates than toadfish hepatocytes (approximately 1%). However, like hepatocytes, the production of all metabolites showed a relative temperature independence at low substrate concentrations, and a marked temperature dependence at the nearly saturating concentration of 100 μm BaP. At saturating concentrations, fish acclimated to 28°C metabolized BaP at a greater rate than fish acclimated to 18°C even when measured at common temperatures. We detected low but measurable activities of common enzymes of BaP metabolism (glutathione-S-transferase, UDP-glucuronosyl transferase, sulfotransferase, epoxide hydrolase, aryl hydrocarbon hydroxylase) in toadfish red blood cells, but no significant differences were found between fish acclimated to 18 or 28°C. Taken together with prior studies, our results indicate that the contribution of ‘extrahepatic’ tissues such as blood in the biotransformation of xenobiotics may be important, at least in a qualitative sense, with regard to potential damage and adduct formation in blood cells.