Effects of Heme Oxygenase–1 Overexpression on Liver Injury after Bile Duct Ligation in Rats

Abstract

Aims: Chronic cholestasis leads to liver injury and will finally progress to portal fibrosis, cirrhosis and end-stage liver disease necessitating liver transplantation. Heme oxygenases are the rate-limiting enzymes that catalyze the conversion of heme into biliverdin, CO and iron. Recently, there were several reports about protective effects of heme oxygenase–1 (HO–1) against oxidant-induced injury. AIM: Accordingly, this study investigated if cobalt protoporphyrin (CoPP), a HO–1 inducer, would reduce hepatic fibrosis caused by bile duct ligation (BDL). Methods: Either CoPP or saline were injected intraperitoneally into male SD-rats. Three days later, BDL or sham-operations were performed. Rats were sacrificed 3 weeks after BDL and livers were harvested for histology. Fibrosis was evaluated by sirius red staining and image analysis. Alpha-smooth muscular actin, which indicates activation of hepatic stellate cells, was detected by immunohistochemical staining, and cytokine and collagen-Iα (Col-Iα) mRNA was detected using RNase protection assays. Results: As expected, serum alanine transaminase increased about 10-fold one day after BDL. Surprisingly, enzyme release was not reduced in rats receiving CoPP. Liver fibrosis was evaluated 3 weeks after BDL and the sirius red-positive area was found to be increased to about 8.7%. However, in livers from bile duct ligated rats pretreated with CoPP sirius red-positive areas were increased to about 11.7%. Col-Iα mRNA was increased significantly about 20-fold by BDL, consistent with increases in collagen synthesis. Again, this effect was increased by HO–1 overexpression. Transforming growth factor-β and tumor necrosis factor-α were increased significantly after BDL but no difference was observed between the CoPP or saline pretreated rats. Conclusions: Taken together, it is concluded that hepatic fibrosis due to BDL is not reduced by the HO–1 inducer CoPP. In contrast, our data indicate that HO–1 overexpression increases liver injury in rats under conditions of experimental chronic cholestasis.