Brain ethanol metabolism and mitochondria

Alcohol abuse and dependence in humans causes an extreme shift in metabolism for which the human brain is not evolutionarily prepared. Oxidation of ethanol and acetaldehyde are not regulated, making ethanol a dominating metabolic substrate that prevents the activity of enzymes from oxidizing their usual endogenous substrates. The enzymes required to oxidize ethanol across the variety of affected tissues all produce acetaldehyde which is then converted to acetate by aldehyde dehydrogenases (ALDHs). ALDHs are NAD+-dependent enzymes, and mitochondrial ALDH2 is likely the primary contributor to ethanol-derived acetaldehyde clearance in cells. Metabolism of alcohol has several adverse effects on mitochondria including increased free radical levels, hyperacetylation of mitochondrial proteins, and excessive mitochondrial fragmentation. This review discusses the role of astrocytic and neuronal mitochondria in ethanol metabolism that contributes to the acute and chronic changes in mitochondrial function and morphology, that might promote tolerance, dependence and withdrawal. We also propose potential modes of therapeutic intervention to reduce the toxicity of chronic alcohol consumption.