In vivo and in vitro effects of deltamethrin on cytochrome P450 monooxygenase activity in carp (Cyprinus carpio L) liver

The in vivo and in vitro effects of the insecticide deltamethrin (DM) on hepatic cytochrome P450 (Cyt P450) monooxygenase were examined in adult carp. The in vivo experiments were carried out with 0.2 mu g/l DM at 20 degrees C. The changes in the hepatic microsomal Cyt P450 content and the Cyt P450-dependent monooxygenase activities were studied in DM-treated fish. Although there were no changes in the Cyt P450 content during the exposure time, after treatment for 24 h all the investigated isoenzyme activities (para-nitrophenetole-O-deethylase, p-NPOD; aminopyrene-N-demethylase, APND; ethylmorphine-N-demethylase, EMND; 7-ethoxycoumarin-O-deethylase, ECOD; and ethoxyresorufin-O-deethylase, EROD) were significantly inhibited. After 72 h, all the activities were still lower than in the control animals. In vitro incubation of liver microsomes with DM led to a concentration-dependent decrease in total microsomal Cyt P450 content. A complete loss of Cyt P450 occurred after a 5-min incubation with 60 mu M DM. The maximum in the difference spectra of microsomes was shifted to higher wavelength, showing the strong interaction of DM with Cyt P450, EROD and ECOD activities were inhibited by DM. The in vitro kinetic results on ECOD revealed that the inhibition was of non-competitive type, with K-i = 9.8 +/- 2.3 mu M This study indicates important biochemical effects of DM in fish liver, and suggests that exposure to DM may cause loss of the Cyt P450-dependent metabolism in fish.