Ethanol Metabolism in the Liver, the Induction of Oxidant Stress, and the Antioxidant Defense System.

The liver metabolizes ethanol through three enzymatic pathways: alcohol dehydrogenase (ADH), cytochrome p450 (also called MEOS), and catalase. Alcohol dehydrogenase class I (ADH1) is considered the most important enzyme for the metabolism of ethanol, MEOS and catalase (CAT) are considered minor alternative pathways. However, contradicting experiments suggest that the non-ADH1 pathway may have a greater relevance for the metabolism of ethanol than previously thought. In some conditions, ethanol is predominately metabolized to acetaldehyde via cytochrome P450 family 2 (CYP2E1), which is involved in the generation of reactive oxygen species (ROS), mainly through electron leakage to oxygen to form the superoxide (O 2 •- ) radical or in catalyzed lipid peroxidation. The CAT activity can also participate in the ethanol metabolism that produces ROS via ethanol directly reacting with the CAT-H 2 O 2 complex, producing acetaldehyde and water and depending on the H 2 O 2 availability, which is the rate-limiting component in ethanol peroxidation. We have shown that CAT actively participates in lactate-stimulated liver ethanol oxidation, where the addition of lactate generates H 2 O 2 , which is used by CAT to oxidize ethanol to acetaldehyde. Therefore, besides its known role as a catalytic antioxidant component, the primary role of CAT could be to function in the metabolism of xenobiotics in the liver.