The function of two P450s, CYP9 M10 and CYP6AA7, in the permethrin resistance of Culex quinquefasciatus.
Cytochrome P450 monooxygenases play a critical role in insecticide resistance by allowing resistant insects to metabolize insecticides. Previous studies revealed that two P450 genes, CYP9 M10 and CYP6AA7, are not only up-regulated but also induced in resistant Culex mosquitoes. In this study, CYP9 M10 and CYP6AA7 were separately co-expressed with cytochrome P450 reductase (CPR) in insect Spodoptera frugiperda (Sf9) cells using a baculovirus-mediated expression system and the enzymatic activity and metabolic ability of CYP9 M10/CPR and CYP6AA7/CPR to permethrin and its metabolites, including 3-phenoxybenzoic alcohol (PBOH) and 3-phenoxybenzaldehyde (PBCHO), characterized. PBOH and PBCHO, both of which are toxic to Culex mosquito larvae, can be further metabolized by CYP9 M10/CPR and CYP6AA7/CPR, with the ultimate metabolite identified here as PBCOOH, which is considerably less toxic to mosquito larvae. A cell-based MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) cytotoxicity assay revealed that Sf9 cells expressing CYP9 M10/CPR or CYP6AA7/CPR increased the cell line's tolerance to permethrin, PBOH, and PBCHO. This study confirms the important role played by CYP9 M10 and CYP6AA7 in the detoxification of permethrin and its metabolites PBOH and PBCHO.