allopurinol and Hepatitis-C

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

An assay for human plasma xanthine oxidase activity was developed with pterin as the substrate and the separation of product (isoxanthopterin) by high-performance liquid chromatography with a fluorescence detector. The reaction mixture consists of 60 microliters of plasma and 240 microliters of 0.2 M Tris-HCl buffer (pH 9.0) containing 113 microM pterin. With this assay, the activity of plasma xanthine oxidase could be easily determined despite its low activity. As a result, it could be demonstrated that the intravenous administration of heparin or the oral administration of ethanol did not increase plasma xanthine oxidase activity in normal subjects, and also that plasma xanthine oxidase activity was higher in patients with hepatitis C virus infection than in healthy subjects or patients with gout. In addition, a single patient with von Gierke's disease showed a marked increase in the plasma activity of this enzyme, relative to that apparent in normal subjects.

Topics: Chromatography, High Pressure Liquid; Ethanol; Glycogen Storage Disease Type I; Gout; Heparin; Hepatitis C; Humans; Hydrogen-Ion Concentration; Hypoxanthine; Pterins; Spectrometry, Fluorescence; Uric Acid; Xanthine; Xanthine Oxidase; Xanthines; Xanthopterin