Studies on the metabolism of vamidothion and its thioanalog in insecticide-resistant and susceptible house fly strains |
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| Institution: | 1. Department of Preventive Medicine, Faculty of Public Health, University of Debrecen, Debrecen, Hungary;2. Environmental Carcinogenesis Unit, Ospedale Policlinico San Martino IRCCS, Genoa, Italy;2. Program in Biomolecular Science and Engineering, University of California Santa Barbara, Santa Barbara, CA, United States;3. University of California Santa Barbara, Santa Barbara, CA, United States;4. College of Creative Studies, University of California Santa Barbara, Santa Barbara, CA, United States |
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| Abstract: | The in vivo and in vitro metabolism of vamidothion O,O-dimethyl S-2-(1-methylcarbamoyl)-ethylthio] ethylphosphorothiolate] as well as the in vitro metabolism of thiovamidothion O,O-dimethyl S-2-(1-methylcarbamoyl)ethylthio] ethylphosphorodithioate] was investigated in insecticide-resistant and susceptible house fly strains. Vamidothion was converted in vivo to the sulfoxide, the principle metabolite, and subsequently to the sulfone at a slower rate. Vamidothion and vamidothion sulfoxide were hydrolyzed at the PS and SC bond. The resulting primary alcohol metabolite was further oxidized to a carboxylic acid followed by decarboxylation. No metabolism of vamidothion or thiovamidothion occurred in vitro without the addition of NADPH. The addition of NADPH resulted in rapid conversion of vamidothion to the sulfoxide, and thiovamidothion was oxidatively metabolized to six metabolic products. No qualitative differences were found between resistant and susceptible strains, but there were signficant quantitative differences. The metabolism was highest in the Rutgers strain followed by Cornell-R, Hirokawa, and then CSMA strain. The route of vamidothion and thiovamidothion metabolism was via the cytochrome P-450-dependent monooxygenase system, and none of the resistant strains showed glutathione S-transferase activity toward vamidothion or thiovamidothion. No further oxidation of vamidothion sulfoxide to the sulfone was observed and also no hydrolysis products were formed, in vitro. |
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