Lactate-stimulated ethanol oxidation: Revisiting an old hypothesis.

Liver slices from starved rats and incubated without other substrates oxidized ethanol at a rate of 4.1 µmols • h • g. Addition of 10 mmols • L lactate increased this rate 2-fold. 4-methylpyrazole (4-MP), an alcohol dehydrogenase (ADH) inhibitor, drastically decreased the rate of ethanol oxidation, but did not inhibit the stimulation due to lactate. In the same context, liver acetaldehyde production, as the main by-product of ethanol oxidation, appeared to be much less inhibited by 4-MP in the presence of lactate. Aminotriazole (a catalase inhibitor), however, completely inhibited the stimulation. Furthermore, 2-hydroxybut-3-ynoate, an alpha-hydroxy acid oxidase inhibitor, completely abolished the stimulated ethanol oxidation promoted by lactate. Moreover, to determine the origin of the HO produced, we did liver subcellular fractionation and then analyzed their content in peroxisomes, mitochondria and catalase. We observed that cytoplasm and peroxisomes appears to be the main producers of HO, and that the acceleration of ethanol oxidation by lactate is completely dependent on catalase. In conclusion, the HO necessary to boost the catalase-dependent oxidation of ethanol appears to come from cytoplasm and peroxisomes, and is produced by the enzyme lactate oxidase.