Also, it appears that overproduction of ROS by the damaged mitochondria could play a salient role. Factors that may be involved in the precipitation of alcoholic hepatitis are briefly discussed later. Only about 2–10% of the absorbed alcohol H 89 is eliminated via the lungs and kidneys; the remaining 90% is metabolized mainly by oxidative pathways in the liver and by nonoxidative pathways in extrahepatic tissues. Oxidative metabolism in the liver results in extensive displacement of the liver’s normal metabolic substrates, the production of acetaldehyde and ROS, and an increase in the NADH/NAD+ ratio (Fig. 2). The major pathway of oxidative metabolism of ethanol in the

liver involves multiple isoforms of cytosolic ADH, which results in the production of acetaldehyde. Accumulation of this highly reactive and toxic molecule contributes to liver damage. The oxidation of ethanol is accompanied by the reduction of NAD+ to NADH and, thereby, generates a highly check details reduced cytosolic environment in hepatocytes. The cytochrome P450 isozymes, including CYP2E1, 1A2, and 3A4, which are predominantly localized to the ER, also contribute to ethanol’s oxidation to acetaldehyde in the liver. CYP2E1 is induced by chronic ethanol consumption and assumes an important role in metabolizing ethanol to acetaldehyde at elevated alcohol concentration. It also produces ROS, including hydroxyethyl, superoxide anion, and hydroxyl radicals.

Acetaldehyde, produced by ethanol oxidation, is rapidly metabolized mainly by mitochondrial ALDH2 to form acetate and NADH. Mitochondrial NADH is reoxidized by the electron transport chain (ETC). Most of the acetate resulting from ethanol metabolism escapes the liver to the blood and is eventually metabolized to CO2 by way of the tricarboxylic acid cycle in tissues such as heart, skeletal muscle, and brain, where mitochondria are

capable of converting acetate to the intermediate acetyl coenzyme A. a)  Acetaldehyde generation/adduct formation: if accumulated to high concentrations, acetaldehyde can form adducts with DNA and RNA, and decrease DNA repair. It also has the capacity to react with lysine residues on proteins including enzymes, microsomal proteins, microtubules, and affect their function. selleck chemicals llc Formation of protein adducts in hepatocytes may contribute to impaired protein secretion, resulting in hepatomegaly. In addition, acetaldehyde and malondialdehyde (a by-product of lipid peroxidation) can combine and react with lysine residues on proteins, giving rise to stable malondialdehyde-acetaldehyde-protein adducts that are immunogenic and, thus, can contribute to immune-mediated liver damage. Nitric oxide (NO), an RNS critical for hepatocyte biology, can interact with peroxides to generate peroxynitrite, which could be detrimental to the liver depending on the amount and duration. NO is produced by inducible nitric oxide synthase which is expressed in all liver cells (i.e.