Expression of iNOS during development of liver fibrosis in rats

Increased expression of the enzyme inducible Nitric Oxide Synthase (iNOS) has been observed in models of acute liver inflammation. Since in recent reports an influence of Nitric Oxide radicals (NO) on fibrosis was proposed, we studied the hepatic expression of iNOS after bile duct ligation, a model of chronic liver inflammation leading to fibrosis. Using a polyclonal antibody against iNOS, we investigated iNOS expression with Western blot analysis and immunohistochemical methods. Using Western Blot analysis, we demonstrated the induction of iNOS in the first and second week after ligation. Immunohistochemistry confirmed these results. One day after ligation of the bile duct, the inflammatory cells in the portal areas of the liver started to express iNOS. Four days after ligation, groups of hepatocytes became also iNOS positive. In addition, a typical pattern of MOS staining was found in these fibrotic livers. Cells around necrotic areas showed a clear expression and were identified as hepatocytes and inflammatory cells. After seven days the expression of iNOS gradually declined and virtually no staining was observed after two weeks. In conclusion, the enzyme iNOS is expressed in hepatocytes and inflammatory cells of bile duct ligated livers, especially in the early stage of fibrosis. In the later stages of the fibrotic process, when collagen accumulation increases, the expression of the enzyme disappeared.