Inhibition of the microsomal oxidation of ethanol and 1-butanol by the free-radical, spin-trapping agent 5,5-dimethyl-1-pyrroline-1-oxide

The free-radical, spin-trapping agent, 5,5-dimethyl-1-pyrroline-1-oxide (DMPO), inhibited the microsomal oxidation of ethanol and 1-butanol as well as the metabolism of 2-keto-4-thiomethylbutyrate. DMPO also blocked the stimulation of ethanol oxidation caused by the addition of iron-EDTA to microsomes. Previous electron spin resonance studies with DMPO by others had shown that the free radical produced by rat liver microsomes and augmented by iron-EDTA was the hydroxyl radical. In the current study, DMPO had no effect on microsomal oxygen consumption with NADPH as substrate, nor on NADPH-cytochrome c reductase activity, nor on the demethylation of aminopyrine or the hydroxylation of aniline. Therefore, a general toxic action of DMPO on microsomes is excluded. DMPO also failed to inhibit the catalase-dependent pathway of ethanol oxidation by microsomes. Experiments with Chelex 100 resin and the chelating agent, diethylenetri-aminepentaacetic acid, rule out any major role for contaminating iron in the reagents. These results tend to identify the free radical responsible for microsomal metabolism of ethanol, 1-butanol, and 2-keto-4-thiomethylbutyrate as the radical trapped by DMPO, namely the hydroxyl radical.