Deficiency in glutathione synthesis and reduction contributes to the pathogenesis of colitis-related liver injury

Abstract

Objectives: Liver disease is the most common extra-intestinal manifestation of ulcerative colitis (UC), but the underlying pathogenesis is still not clarified. It is well accepted that the occurrence of UC-related liver disease has close correlation with immune activation, intestinal bacterial liver translocation, inflammatory cytokine storm, and the disturbance of bile acid circulation. The occurrence of UC-related liver disease makes the therapy difficult, therefor study on the pathogenesis of UC-related liver injury is of great significance for its prevention and treatment. Glutathione (GSH) shows multiple physiological activities, such as free radical scavenging, detoxification metabolism and immune defense. The synthesis and the oxidation-reduction all contribute to GSH antioxidant function. It is reported that the deficiency in hepatic GSH antioxidant function participates in multiple liver diseases, but whether it participates in the pathogenesis of UC-related liver injury is still not clear. This study aims to investigate the feature and underlying mechanism of GSH synthesis and oxidation-reduction function during the development of UC, which will provide useful information for the pathogenesis study on UC-related liver injury.

Methods: UC model was induced by 2,4,6-trinitrobenzenesulfonic acid (TNBS)-ethanol solution (5 mg/0.8 mL per rat, 50% ethanol) via intra-colonic administration in rats, and the samples of serum, liver, and colon tissue of rats were collected at the 3rd, 5th, and 7th days post TNBS. The severity degree of colitis was evaluated by measuring the disease activity index, colonic myeloperoxidase activity, and histopathological score, and the degree of liver injury was evaluated by histopathological score and the serum content of alanine aminotransferase. Spearman correlation analysis was also conducted between the degree of colonic lesions and index of hepatic histopathological score as well as serum aspartate aminotransferase level to clarify the correlation between liver injury and colitis. To evaluate the hepatic antioxidant function of GSH in UC rats, hepatic GSH content, enzyme activity of GSH peroxidase (GSH-Px), and GSH reductase (GR) were determined in rats at the 3rd, 5th, and 7th days post TNBS, and the protein expressions of glutamine cysteine ligase (GCL), GSH synthase, GSH-Px, and GR in the liver of UC rats were also examined by Western blotting.

Results: Compared with the control, the disease activity index, colonic myeloperoxidase activity, and histopathological score were all significantly increased at the 3rd, 5th, and 7th days post TNBS (all P<0.01), the serum aspartate aminotransferase level and hepatic histopathologic score were also obviously elevated at the 7th day post TNBS (all P<0.05). There was a significant positive correlation between the degree of liver injury and the severity of colonic lesions (P=0.000 1). Moreover, compared with the control, hepatic GSH content and the activity of GSH-Px and GR were all significantly decreased at the 3rd and 5th days post TNBS (P<0.05 or P<0.01), and the protein expressions of GCL, GSH-Px, and GR were all obviously down-regulated at the 3rd, 5th, and 7th days post TNBS (P<0.05 or P<0.01).

Conclusions: There is a significant positive correlation between the degree of liver injury and the severity of colonic lesions, and the occurrence of reduced hepatic GSH synthesis and decreased GSH reduction function is obviously earlier than that of the liver injury in UC rats. The reduced hepatic expression of enzymes that responsible for GSH synthesis and reduction may contribute to the deficiency of GSH synthesis and oxidation-reduction function, indicating that the deficiency in GSH antioxidant function may participate in the pathogenesis of UC related liver injury.

Keywords: antioxidant; glutathione; liver injury; ulcerative colitis.

图1

UC大鼠肝脏病理组织学改变(HE) Figure 1 Pathological changes in the liver of UC rats (HE) Blue arrows indicate ballooning degeneration of hepatocytes and black arrows indicate eosinophilic changes and karyopyknosis of hepatocytes.

图2

溃疡性结肠炎大鼠结肠病变与肝病变的相关性(n=12) Figure 2 Correlation between colonic lesions and liver alteration in ulcerative colitis rats (n=12)

图3

UC大鼠肝组织GCL及GS蛋白质表达变化(n=3) Figure 3 Alteration in the protein expression of GCL and GSS in the liver tissues of colitis rats (n=3) UC: Ulcerative colitis; GCL: Glutamine cysteine ligase; GS: Glutathione synthetase. **P<0.001 vs the normal group; †P<0.05 vs the UC-7 d group.

图4

UC大鼠肝脏GSH-Px与GR蛋白质表达变化(n=3) Figure 4 Alteration in the protein expression of GSH-Px and GR in the liver of colitis rats (n=3) UC: Ulcerative colitis; GSH-Px: Glutathione peroxidase; GR: Glutathione reductases. **P<0.001 vsthe normal group; †P<0.05 vs the UC-7 d group.