| Chronic hepatitis C virus (HCV) causes increased oxidative activity in the liver as a result of viral infection. Because hepatic antioxidant enzymes provide an important line of defense against oxidative injury, we evaluated liver biopsies for changes in antioxidant enzymes during chronic HCV infection. Analysis of HCV-infected vs control biopsy samples showed no differences in the expression of superoxide dismutase (MnSOD and CuZnSOD) and catalase immunoreactive proteins or specific mRNAs. However, there was a greater than 4-fold decrease in heme oxygenase-1 (HO-1) protein and mRNA in HCV-infected as compared to control liver. Using a new antigen retrieval method for paraffin-embedded sections, the decrease in HO-1 expression was confirmed by confocal immunohistochemical microscopy to be due to decreased hepatocyte expression of HO-1. Reduced expression of hepatocyte HO-1 was not a generalized response to hepatic inflammation as liver biopsy samples from patients with autoimmune hepatitis showed increased hepatocyte HO-1 compared to control liver. In hepatocyte cell lines that expressed HCV-core protein in vitro, expression of HCV-core protein led to increased oxidative stress, as determined by a decrease in reduced glutathione (GSH) and reduced thioredoxin levels and an increase in oxidized glutathione and DCFH2 fluorescence. Moreover, and consistent with our finding in HCV infected liver tissue, expression of HO-1 mRNA and protein was also reduced, suggesting that the product of the HCV-core gene alone is capable of inducing oxidative stress and regulating HO-1 expression. To the contrary, over expression of HCV-non-structural proteins upregulated antioxidant enzymes (MnSOD and catalase), HO-1 and GSH, indicating a different mechanism of action than HCV-core. Our findings show that HCV infection modulates and down regulates important hepatocyte antioxidant defense enzymes. This might contribute to the oxidative stress associated with HCV infection and play a role in hepatocellular injury. |
