Ethanol metabolism in humans occurs mainly in the liver, though degradation has also been shown in gastric, pancreatic, and lung tissue. Ethanol degradation occurs via four pathways, three of which are oxidative pathways and are depicted here. The fourth is a nonoxidative pathway which is less well studied but known to produce fatty acid ethyl esters. Each of the three oxidative pathways is differentiated by the mechanism utilized to oxidize ethanol to acetaldehyde in the first step. In the alcohol dehydrogenase mediated ethanol degradation pathway (I), cytoplasmic alcohol dehydrogenase produces the acetaldehyde from the ethanol. In the MEOS mediated ethanol degradation pathway (II), the ethanol enters the endoplasmic reticulum, where the Microsomal Ethanol Oxidising System (MEOS), also know as also known as cytochrome P-450 2E1, does the oxidizing and returns the acetaldehyde to the cytoplasm. In the catalase mediated ethanol degradation pathway (III), the oxidation occurs in the peroxisome via peroxisomal catalase, with the resulting acetaldehyde being released to the cytoplasm. In each of the three oxidative pathways the cytosolic acetaldehyde then enters the mitochondrial compartment, where it is converted to acetate by mitochondrial aldehyde dehydrogenase. The acetate leaves the mitochondria and moves to extra-hepatic tissues for further metabolism. In extra-hepatic cells the acetate is converted to acetyl-CoA via either cytoplasmic or mitochondrial acetyl-CoA synthetase. The alcohol dehydrogenase mediated ethanol degradation pathway (I) is the predominant mechanism of catabolism under conditions of acute alcohol consumption. However, under conditions of chronic ethanol consumption the MEOS mediated ethanol degradation pathway (II) and nonoxidative pathway are induced to assist with ethanol degradation.

Ethanol Degradation References