Effect of the fungicide clotrimazole on the bioconcentration of benzo[a]pyrene in gizzard shad (Dorosoma cepedianum): In vivo and in vitro inhibition of cytochrome P4501A activity

Clotrimazole was found to inhibit in vivo and in vitro hepatic microsomal ethoxyresorufin O-deethylase (EROD) activity in gizzard shad (Dorosoma cepedianum). Gizzard shad pretreated with 50 mg clotrimazole/kg and then exposed for 1 or 3 d to benzo[a]pyrene (BaP) (0.86 mu g/L) had significantly lower EROD activity compared to fish that were exposed to BaP alone. Following 1 and 3 d of BaP exposure, groups pretreated with clotrimazole had a 14- and 4-fold decrease in EROD activity and had bioconcentrated 8 and 11 times more parent BaP, respectively, compared to groups exposed to BaP alone. Addition of clotrimazole to BaP-induced microsomes produced a type II binding spectrum and was an effective in vitro inhibitor of EROD activity. The median inhibitory concentration for EROD activity was 0.51 mu M clotrimazole. Kinetic and spectral experiment, suggest that the mechanism of inhibition by clotrimazole is noncompetitive. Reduction in the rate of oxidative BaP metabolism is hypothesized to result from noncompetitive inhibition of cytochrome P4501A and other P450 enzymes that metabolize BaP.