allopurinol and Liver-Diseases--Alcoholic

Xanthine oxidoreductase (XOR) is a widely distributed enzyme, involved in the metabolism of purines, which generates superoxide and is thought to be involved in free radical-generated tissue injury. It is present at high concentrations in the liver, from where it may be released during liver injury into the circulation, binding to vascular endothelium and causing vascular dysfunction. The cellular localization of the enzyme, essential to understanding its function, is, however, still debated. The present study has used a highly specific mouse monoclonal antibody to define the cellular distribution of XOR in normal and cirrhotic human liver. As shown previously, XOR is present in hepatocytes. However, the novel finding of this study is that XOR is present in bile duct epithelial cells, where it is concentrated toward the luminal surface. Moreover, in liver disease, proliferating bile ducts are also strongly positive for XOR. These findings suggest that the enzyme is secreted into bile, and this was confirmed by analysis of human and rat bile. Xanthine oxidase activity was 10 to 20-fold higher in liver tissue obtained from patients with liver disease, than in healthy liver. We conclude that XOR is expressed primarily in hepatocytes, but is also present in bile duct epithelial cells and is secreted into bile. Its role in bile is unknown but it may be involved in innate immunity of the bowel muscosa.

Topics: Animals; Antibodies, Monoclonal; Bile; Bile Ducts; Blotting, Western; Cell Polarity; Cholangitis, Sclerosing; Electrophoresis, Polyacrylamide Gel; Epithelial Cells; Hepatitis C; Hepatocytes; Humans; Hyperoxaluria, Primary; Immunoenzyme Techniques; Liver Cirrhosis; Liver Cirrhosis, Alcoholic; Liver Cirrhosis, Biliary; Liver Diseases; Liver Diseases, Alcoholic; Mice; Mice, Inbred BALB C; Microscopy, Confocal; Rats; Rats, Sprague-Dawley; Xanthine Oxidase

Free radical formation caused by chronic ethanol administration could activate transcription factors such as nuclear factor-kappaB (NF-kappaB), which regulates production of inflammatory cytokines. Xanthine oxidase is one potential source of reactive oxygen species. Therefore, the purpose of this study is to determine whether allopurinol, a xanthine oxidase inhibitor and scavenger of free radicals, would affect free radical formation, NF-kappaB activation, and early alcohol-induced liver injury in rats. Male Wistar rats were fed a high-fat diet with or without ethanol (10-16 g/kg/day) continuously for up to 4 weeks with the Tsukamoto-French enteral protocol. Either allopurinol or saline vehicle was administered daily. Allopurinol had no effect on body weight or the cyclic pattern of ethanol in urine. Mean urine ethanol concentrations were 271 +/- 38 and 252 +/- 33 mg/dl in ethanol- and ethanol + allopurinol-treated rats, respectively. In the control group, serum aspartate aminotransferase and alanine aminotransferase levels were approximately 40 I.U./l and 25 U/l, respectively. Administration of enteral ethanol for 4 weeks increased serum transaminases approximately 5-fold. Allopurinol blunted these increases significantly by approximately 50%. Ethanol treatment also caused severe fatty infiltration, mild inflammation, and necrosis. These pathological changes also were blunted significantly by allopurinol. Furthermore, enteral ethanol caused free radical adduct formation, values that were reduced by approximately 40% by allopurinol. NF-kappaB binding was minimal in the control group but was increased significantly nearly 2.5-fold by ethanol. This increase was blunted to similar values as control by allopurinol. These results indicate that allopurinol prevents early alcohol-induced liver injury, most likely by preventing oxidant-dependent activation of NF-kappaB.

Topics: Alanine Transaminase; Allopurinol; Animals; Aspartate Aminotransferases; Bile; Body Weight; Central Nervous System Depressants; Diet; Electrophoresis; Enzyme Inhibitors; Ethanol; Free Radical Scavengers; Liver; Liver Diseases, Alcoholic; Male; NF-kappa B; Nuclear Proteins; Rats; Rats, Wistar; Xanthine Oxidase

Free radical generation and catalytic iron have been implicated in the pathogenesis of alcohol-induced liver injury but the source of free radicals is a subject of controversy. The mechanism of ethanol-induced liver injury was investigated in isolated hepatocytes from a rodent model of iron loading in which free radical generation was measured by the determination of alkane production (ethane and pentane). Iron loading (125 mg/kg i.p.) increased hepatic non-heme iron 3-fold, increased the prooxidant activity of cytosolic ultrafiltrates 2-fold and doubled ethanol-induced alkane production. The addition of desferrioxamine (20 microM), a tight chelator of iron, completely abolished alkane production indicating the importance of catalytic iron. The role of cellular oxidases as a source of ethanol induced free radicals was studied through the use of selective inhibitors. In both the presence and absence of iron loading, selective inhibition of xanthine oxidase with oxipurinol(20 microM) diminished ethanol-induced alkane production 0-40%, inhibition of aldehyde oxidase with menadione (20 microM) diminished alkane production 36-75%, while the inhibition of aldehyde and xanthine oxidase by feeding tungstate (100 mg/kg/day) virtually abolished alkane production. Addition of acetaldehyde(50 microM) to hepatocytes generated alkanes at rates comparable to those achieved with ethanol indicating the importance of acetaldehyde metabolism in free radical generation. The cellular oxidases (aldehyde and xanthine oxidase) along with catalytic iron play a fundamental role in the pathogenesis of free radical injury due to ethanol.

Topics: Aldehyde Oxidase; Aldehyde Oxidoreductases; Animals; Deferoxamine; Free Radicals; Iron-Dextran Complex; Lipid Peroxidation; Liver; Liver Diseases, Alcoholic; Male; Rats; Rats, Inbred Strains; Xanthine Oxidase

The ability of acetaldehyde to generate free radicals is often ascribed to its oxidation by xanthine oxidase, with the subsequent production of reactive oxygen intermediates. Chemiluminescence associated with the oxidation of acetaldehyde by xanthine oxidase was inhibited by superoxide dismutase, catalase, or several hydroxyl radical scavenging agents, and was stimulated by the addition of EDTA or ferric-EDTA. This suggests that the light emission is primarily due to the production of hydroxyl radicals via an iron-catalyzed Haber-Weiss type of reaction. Chemiluminescence with hypoxanthine as substrate for xanthine oxidase was much lower than that found with acetaldehyde, yet rates of hydroxyl radical production were greater with hypoxanthine. Acetaldehyde increased light emission in the presence of hypoxanthine by a greater than additive effect. These results suggest a complex role for acetaldehyde in catalyzing xanthine oxidase-dependent chemiluminescence. It appears that besides being a substrate for xanthine oxidase, acetaldehyde also reacts with the generated hydroxyl radical to produce acetaldehyde radicals, which yield chemiluminescence upon their decay. Further studies will be required to evaluate whether the production of such species contributes to or plays a role in the generation of reactive oxygen intermediates and toxicity associated with acetaldehyde metabolism.

Topics: Acetaldehyde; Catalase; Humans; Hydroxides; Hydroxyl Radical; Liver; Liver Diseases, Alcoholic; Luminescent Measurements; Superoxide Dismutase; Xanthine Oxidase

A case of hereditary xanthinuria in a 68-year-old man with congestive heart failure and alcoholic liver disease is presented. Urolithiasis and muscular symptoms were absent, and the metabolic error was revealed by hypouricemia, hypouricosuria and excess of xanthine and hypoxanthine excretion in urine. Xanthine oxidase (EC 1.2.3.2) activity in liver tissue was absent, confirming the diagnosis of xanthinuria.

Topics: Aged; Biopsy, Needle; Heart Failure; Humans; Hypoxanthines; Liver; Liver Diseases, Alcoholic; Male; Purine-Pyrimidine Metabolism, Inborn Errors; Uric Acid; Xanthine Oxidase; Xanthines

Evidence in alcoholics as well as in experimental models support the role of hepatic lipid peroxidation in the pathogenesis of alcohol-induced liver injury, but the mechanism of this injury is not fully delineated. Previous studies of the metabolism of ethanol by alcohol dehydrogenase revealed iron mobilization from ferritin that was markedly stimulated by superoxide radical generation by xanthine oxidase. Peroxidation of hepatic lipid membranes (assessed as malondialdehyde production) was studied during in vitro alcohol metabolism by alcohol dehydrogenase. Peroxidation was initiated by acetaldehyde-xanthine oxidase, stimulated by ferritin, and inhibited by superoxide dismutase or chelation or iron with desferrioxamine. In conclusion, lipid peroxidation may be initiated during the metabolism of ethanol by alcohol dehydrogenase by an iron-dependent acetaldehyde-xanthine oxidase mechanism.

Topics: Acetaldehyde; Alcohol Dehydrogenase; Animals; Ethanol; Ferritins; In Vitro Techniques; Lipid Peroxides; Liver; Liver Diseases, Alcoholic; Male; Rats; Rats, Inbred Strains; Superoxides; Xanthine Oxidase

The hypothesis is presented that lipid peroxidation is responsible for the damage in skeletal and cardiac muscle of chronic alcoholic subjects. The enhanced lipid peroxidation is caused by the accumulation of oxygen radicals. Both excessive production and decreased disposal of oxygen radicals can arise from the acetaldehyde formed in the oxidation of ethanol. Although acetaldehyde from hepatic sources may contribute, muscle itself can generate significant amounts of acetaldehyde through the action of muscle catalase. The effects of alcohol on other tissues, and its known long-term effects on membranes lend support to this hypothesis. The ultrastructural features of the alcoholic myopathies provide further support. The resemblance between vitamin E-deficiency myopathy and the alcoholic myopathies is strong additional evidence in favor of this hypothesis.

Topics: Acetaldehyde; Alcohol Oxidoreductases; Alcoholism; Animals; Cardiomyopathy, Alcoholic; Catalase; Ethanol; Free Radicals; Glutathione Peroxidase; Humans; Lipid Peroxides; Liver; Liver Diseases, Alcoholic; Muscles; Muscular Diseases; Oxygen; Superoxide Dismutase; Xanthine Oxidase

Topics: Acetaldehyde; Humans; Lipid Metabolism; Liver; Liver Cirrhosis, Alcoholic; Liver Diseases, Alcoholic; Models, Chemical; Oxidation-Reduction; Oxygen; Superoxides; Xanthine Oxidase