Microsomal ethanol oxidizing system (MEOS): current status of its characterization and its role

Role of hydroxyl radicals in microsomal oxidation of alcohols

A series of hydroxyl radical (.OH) scavenging agents competitively inhibited microsomal oxidation of ethanol and 1-butanol. The inhibition by the scavengers was specific since these agents had no effect on catalase-dependent oxidation of ethanol, microsomal drug metabolism or microsomal electron transfer. Chemical evidence for production of .OH during microsomal electron transfer was provided by the generation of appropriate products from .OH scavenging agents. H2O2 was shown to play a role as a precursor of .OH. Fe-EDTA increased microsomal oxidation of ethanol without affecting drug metabolism. A role for cytochrome P-450 in catalyzing . OH generation remains to be evaluated. These results suggest that the molecular mechanism underlying the oxidation of ethanol by liver microsomes reflects the ability of ethanol to interact with .OH generated from microsomal electron transfer.

Alterations of hepatic alcohol metabolizing enzyme activities due to thyroid hormones

In order to achieve a hyperthyroid state, rats were treated for 7 days with thyroxine (150 microgram/100 g BW) or triiodothyronine (10 microgram/100 g BW). This regimen resulted in an enhanced activity of the microsomal ethanol oxidizing system. In addition, a decrease of hepatic alcohol dehydrogenase activity was observed under these experimental conditions, whereas hepatic catalase activity remained unchanged. These findings suggest that if chronic ethanol consumption simulates a functional "hyperthyroid hepatic state", increased rates of ethanol metabolism observed following prolonged alcohol intake might therefore be attributed at least in part to an induced activity of the microsomal ethanol oxidizing system in the liver.

Influence of chronic ethanol vapor inhalation on hepatic parenchymal and Kupffer cell function

This report evaluates the influence of chronic ethanol vapor inhalation on various facets of liver function as well as induction of hepatic and pulmonary pathology in rats. Chronic ethanol inhalation is associated with minimal hepatic dysfunction, but pronounced induction of metabolic tolerance.

Ethanol metabolism in Drosophila melanogaster

A quantitative study of the transformation of ethanol into acetaldehyde shows that, in Drosophila melanogaster, the mitochondrial ethanol oxidizing system is not very active but that the part played by catalase appears more important than expected. For a strain without alcoholdehydrogenase, ethanol is highly toxic. The presence of acetaldehyde in the culture medium is toxic for all the strains studied. But, since even a strain without any aldehydeoxidase lives normally, the metabolic production of acetaldehyde does not seem dangerous.

Alcoholic liver damage is provoked by 4-methylpyrazole, which prolongs the influence of ethanol but reduces acetaldehyde levels

Rats chronically fed ethanol developed liver injury only if they also received low doses of the alcohol dehydrogenase inhibitor, 4-methylpyrazole, suggesting that the consistency of the influence of ethanol and its metabolism, rather than the level of acetaldehyde or the degree of the metabolic effects, contributes to the pathogenesis of alcoholic liver damage.

Alcohol-oxidizing enzymes from various organisms

1. Enzymes that catalyse the oxidation of aliphatic alcohols to aldehydes are reviewed. 2. Special attention is given to phenazine methosulphate-linked alcohol dehydrogenases from bacteria and to flavin-containing alcohol oxidases from yeasts, moulds and higher plants. 3. Some properties of the microsomal ethanol-oxidative system of rat liver are discussed.