Stereoselective Species-specific CYP450 Biotransformation Of Three Chiral Pesticides

Background:Widespread application of chiral pesticides results in their occurrence in various environmental systems. Chiral pesticides can accumulate in organisms via different pathways, and cause toxic effect. In general, the enantiomers of chiral pesticides lead to different outcomes in enantioselective behavior, biological activities and ecotoxicity due to their different biochemical properties. However, chiral pesticides have been treated as racemic mixtures in environmental fate and ecotoxicity for a long time. In recent years, the stereoselectivity and environmental safety of chiral pesticides have become a popular focus of attention. In addition, some researchers have noted that the residual concentrations and enantiomeric ratio (ER) of some chiral compounds were different among species, which may result from stereoselective and species-specific biotransformation. But the reasons have so far received limited research.Methods:In this study, the high vertebrate hepatic cell lines, including human hepatic HepG 2 cells, rat hepatic H4IIE cells, chicken hepatic LMH cells and grass carp hepatic L8824 cells, were used to characterize the effects of fipronil, diclofop and metalaxyl on CYP450 enzymes so as to check whether there is a difference in the responses of CYP450 enzymes among the cells. In addition, we used specific inhibitors of several CYP450 to verify the observation. After that, metalaxyl was chosed as a model chemical and detected for the residual concentrations and enantiomeric ratio (ER) in medium with UPLC-MS/MS after exposure, to explore the stereoselective species-specific biotransformation.Results:In the study of enzyme activity, different chiral pesticides induced different CYP450 enzymes in the same cell line. Meanwhile, the same chiral pesticide also induced different CYP450 enzymes in different cells. In addition, the induction of CYP450 was inhibited by their corresponding inhibitors. The removal of metalaxyl was detected in the medium at the end of exposure and was withdrawn after addition of the inhibitors of CYP450. Furthermore, HepG2, H4IIE and LMH cells were inclined to metabolize S-metalaxyl, while L8824 cells were inclined to metabolize R-metalaxyl.Conclusion:This study shows that there are obvious differences in the stereoselective species-specific metabolism of chiral pesticides by various organisms, causing different enantiomeric ratio of chiral pesticides. Besides, the CYP450-specific induction was found to be related to the discrepancy. The stereoselective species-specific biotransformation of chiral pesticides resulted in different ER among species, which in turn could lead to different degrees of toxicity in these organisms, and increase uncertainty of ecological risk assessment.