The role of cytochrome P450 lpr in deltamethrin metabolism by pyrethroid-resistant and susceptible strains of house flies

Abstract

The LPR strain of house fly is highly resistant to pyrethroid insecticides and this resistance is associated with high levels of monooxygenase activity and total cytochromes P450. To evaluate the role of P450 lpr (the major P450 in LPR house flies) in pyrethroid resistance, an antiserum specific for house fly cytochrome P450 lpr was tested for its ability to inhibit cytochrome P450 monooxygenase-dependent metabolism of the pyrethroid insecticide deltamethrin. Treatment of microsomes from pyrethroid resistant LPR house flies with anti-P450 lpr antiserum resulted in 97% of the radiolabel being recovered as deltamethrin compared to 76% in the normal serum control. There was no significant difference in the amount of deltamethrin recovered from microsomes of susceptible (S+) flies treated with normal serum or anti-P450 lpr antiserum compared to the carbon monoxide-inhibited control. However, there was statistically significant inhibition of specific metabolite production in both strains. Using LPR microsomes, seven NADPH-dependent products of [ 14C]deltamethrin metabolism could be identified by thin-layer chromatography, designated as B, C, D, E, F, G, and H (origin). Metabolites B, C, D, and H were the major metabolites. Formation of metabolites B, C, and H was inhibited by anti-P450 lpr while D was increased. In S+ microsomes, only metabolites C, D, and E were consistently detected and anti-P450 lpr inhibited formation of C and D while E was unchanged. The primary metabolites inhibited by the antiserum in LPR appear to be modifications of the acid portion of the deltamethrin molecule, and the major metabolites increased by antiserum treatment were oxidations on the alcohol portion of the molecule, suggesting that P450 lpr preferentially attacks the gem-dimethyl group of deltamethrin. Pyrethroid-resistant LPR flies, topically dosed with a sublethal dose of deltamethrin, rapidly metabolized and excreted polar metabolic products. Similarly, microsomes from LPR house flies exhibited rapid cytochrome P450-dependent metabolism of deltamethrin. This study indicates that P450 lpr contributes to monooxygenase-dependent deltamethrin resistance in LPR house flies.