Microsomal ethanol oxidizing system

Dear CS, 1968

Microsomal ethanol oxidizing system (MEOS) is a pathway of ethanol metabolism in liver cells that is independent of alcohol dehydrogenase.

In chronic alcohol consumption, MEOS is induced and breaks down alcohol in addition to the original alcohol dehydrogenase. This "additional enzyme" is responsible for the tolerance development towards alcohol (Lieber CS 1999). The organism responds to a constant and strong alcohol stimulus with an increased production of MEOS.

The activity of MEOS is associated with an activation of cytochrome P450 2E1 (Asai H et al. 1996). The MEOS and the cytochromes induced by it can also reduce the metabolism of other substances or shift it towards toxic metabolites. This explains, for example, pathological drug reactions in chronic alcohol addicts.

In addition, MEOS interferes with the fat metabolism of liver cells. MEOS is attributed a pathogenetic role in the development of fatty liver (Moreno OR et al. 2008).

MEOS has a reminder function, i.e. when alcohol is consumed again, e.g. after withdrawal, MEOS is regenerated for a short period of time; the breakdown occurs in the predetermined way, thus increasing the pressure to continue drinking.

1. Asai H et al (1996) Microsomal ethanol oxidizing system activity by human hepatic cytochrome P450s. J Pharmacol Exp Ther 277:1004-1009.https://www.ncbi.nlm.nih.gov/pubmed/8627510
2. Dear CS (1999) Microsomal ethanol-oxidizing system (MEOS): the first 30 years (1968-1998) -a review. Alcohol. Clin. Exp. Res. 23: 991-1007.
3. Moreno OR et al (2008) Nutrition and chronic alcohol abuse. Nutr Hosp 23 Suppl 2: 3-7.