Plasma Superoxide Radical in Jaundiced Patients and Role of Xanthine Oxidase

Abstract

In the experimental setting, obstructive jaundice induces oxidative stress in several extrahepatic tissues (systemic phenomenon), which is at least partly attributed to activation of the enzyme xathine oxidase. Very little is known on this important issue in patients with cholestasis. The present study was designed to (a) assess directly oxidative stress in the blood of patients with obstructive jaundice by measuring superoxide radical, and (b) investigate ex vivo whether xanthine oxidase (XO) is the source of this radical. Twelve patients with malignant obstructive jaundice and no signs of cholangitis, 12 nonjaundiced disease-controls with a localized gastrointestinal malignancy, and 12 healthy-controls were enrolled in the study. Superoxide radical levels were measured in the whole blood (plasma and cells) and in plasma previously separated. These measurements were also done in blood samples in the presence of the specific XO inhibitor allopurinol. Superoxide radical levels were significantly increased in the plasma fraction of whole blood in jaundiced patients when compared with disease-controls (P < 0.001) and healthy-controls (P < 0.001), whereas disease-control patients presented significantly increased superoxide radical levels when compared with healthy-controls (P < 0.001). No differences in superoxide radical levels in the blood cells were detected between jaundiced patients and disease-controls. In jaundiced patients, superoxide radical levels in the plasma fraction of whole blood were positively correlated with the degree of cholestasis. The addition of allopurinol to whole blood samples decreased superoxide radical in the plasma fraction of jaundiced patients to the disease-control level (P < 0.001), whereas it had no effect on superoxide radical levels in the cell fraction. No superoxide radical was detected in fractionated plasma in all cases. These data show that increased superoxide radical in the plasma of jaundiced patients is possibly formed from a source in the cytoplasmic membrane of blood cells and secreted into plasma. The reversal of this phenomenon by allopurinol, ex vivo, indicates that a blood cell membranous XO might be the source of increased plasma superoxide radical in patients with extrahepatic cholestasis.