The role of glutathione in the detoxification of the insecticides methyl parathion and azinphos-methyl in the mouse

Abstract

The dimethyl-substituted organothiophosphate insecticides methyl parathion and azinphos-methyl are thought to undergo glutathione-mediated detoxification in mammals. In the present study, depletion of hepatic glutathione in the mouse by pretreatment with diethyl maleate potentiated the acute toxicities of methyl parathion and azinphos-methyl, whereas depletion of hepatic glutathione by pretreatment with buthionine sulfoximine did not. Furthermore incubation of 50 μ m methyl parathion with mouse hepatic microsomes for 5 min in the presence of 1 m m diethyl maleate led to significantly greater ( p < 0.05) production of methyl paraoxon, compared to incubations in the absence of diethyl maleate. Conversely, 1 m m diethyl maleate had no effect on metabolic activation of azinphos-methyl by mouse hepatic microsomes, while 10 m m inhibited slightly production of azinphos-methyl oxon from azinphos-methyl. These results suggest normal levels of hepatic glutathione are not required for detoxification of methyl parathion or azinphos-methyl in the mouse. Moreover the potentiation of the acute toxicity of methyl parathion following diethyl maleate pretreatment could result, at least in part, from enhanced production of methyl paraoxon. However, diethyl maleate likely acts through another mechanism(s) as well since it did not enhance the metabolic activation of azinphos-methyl in vitro. These data raise serious doubts about the participation of glutathione in the detoxification of methyl parathion and azinphos-methyl in vivo in the mouse.