Interaction of cadmium and benzo[a]pyrene in mummichog (Fundulus heteroclitus): Biotransformation in isolated hepatocytes

Exposure of mummichog (Fundulus heteroclitus), a common estuarine fish species, to simultaneous doses of cadmium (Cd) and benzo[a]pyrene (BP) has been shown to alter the acute toxicity of BP. In this study the effects of in vivo exposure to Cd and BP on the biotransformation of BP by isolated hepatocytes were investigated. Fish were injected intraperitoneally with sublethal doses of BP and Cd, and hepatocytes from these fish were isolated on days 3, 7 and 14. Hepatocytes were then co-incubated with radiolabeled BP. BP breakdown, and the formation of aqueous and organic solvent-extractable metabolites were quantified using HPLC. After three days there was a significant increase in metabolism in the BP exposed fish. The same increase was still noticeable on day 7, but started to return to baseline values on day 14. In the combined BP/Cd treated fish, BP metabolism was not significantly induced on day 3, but full induction was reached on day 7, and was still at this level on day 14. Analysis of the nonconjugated metabolites showed that hepatocytes produced predominantly BP-9,10-diol, BP-7,8-diol, BP-4,5-diol, and 9-hydroxy-BP. The results of this study suggest that Cd does not influence the profile of generated BP metabolites. However, the initial rate of BP breakdown is significantly decreased by pre-exposure to cadmium.