Effect of thiourea on microsomal oxidation alcohols and associated microsomal functions

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Abstract
Thiourea and diethylthiourea, 2 compounds which react with hydroxyl radicals, inhibited NADPH-dependent [rat] microsomal oxidation of ethanol and 1-butanol. Inhibition by both compounds was more effective in the presence of the catalase inhibitor, azide. Inhibition by thiourea was noncompetitive with respect to ethanol in the absence of azide but was competitive in the presence of azide. Urea, a compound which does not react with hydroxyl radicals or H2O2, was without effect. Thiourea had no effect on NADH- and NADPH-cytochrome c reductase, NADPH oxidase and NADH- and NADPH-dependent O2 uptake. Thiourea inhibited the activities of aniline hydroxylase and aminopyrine demethylase. Thiourea, but not other hydroxyl radical scavengers, e.g., dimethyl sulfoxide, mannitol and benzoate, reacted directly with H2O2 and decreased H2O2 accumulation in the presence of azide. The actions of thiourea are complex because it can react with both hydroxyl radicals and H2O2. Differences between the actions of thiourea and those previously reported for dimethyl sulfoxide, mannitol and benzoate, e.g., effects on drug metabolism, effectiveness of inhibition in the absence of azide or kinetics of the inhibition, probably reflect the fact that thiourea reacts directly with H2O2 whereas the other agents do not. The current results remain consistent with the concept that microsomal oxidation of alcohols involves interactions of the alcohols with hydroxyl radicals generated from microsomal electron transfer.

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