Effects of Temperature on Metabolism of Benzo[a]pyrene by Toadfish (Opsanus beta) Hepatocytes

Abstract

Prior in vivo studies of the effects of temperature on uptake, metabolism and excretion of benzo[a]pyrene (BaP) by the gulf toadfish (Opsanus beta) suggested that metabolism of BaP may be partially temperature insensitive under certain conditions. In the present study, hepatocytes were isolated from toadfish acclimated to 18 or 28 °C, and then cells were exposed to BaP at 18, 23, and 28 °C in vitro to more directly examine the effects of temperature on metabolism. Toadfish hepatocytes metabolized BaP to a variety of Phase I and Phase II metabolites in similar proportions to toadfish in vivo, with the exception that fewer Phase I metabolites were detected. A marked temperature dependence of metabolism of BaP to Phase II metabolites was noted between 18 and 28 °C at near saturating concentration of BaP (13 μg∙mL−1). Warm-acclimated toadfish displayed a lower temperature sensitivity than cold-acclimated toadfish (Q10, the ratio of the rate at T + 10 °C: rate at T = 1.85 and 2.65, respectively). However, at a lower, subsaturating concentration of BaP (5 μg∙mL−1), production of all metabolites showed a marked temperature independence. We speculate that this independence is the result of temperature effects on the kinetic properties of the enzymes of xenobiotic metabolism.