Objective: To investigate the protective role of heme oxygenase-1 and its reaction product, carbon monoxide against acute liver injury induced by carbon tetrachloride in rats.
Methods: Thirty male Sprague-Dawley rats were randomly divided into six groups with five in each. The control group received a single dose of corn oil injection. Carbon tetrachloride was injected intraperitoneally (i.p) to establish acute liver injury models in rats. Hemin(50 micromol/kg) was administered i.p. 12 hours before CCl(4) treatment, with an aim to induce HO-1 protein expression in the liver of rats. Carbon monoxide was injected i.p. 12 hours prior to CCl(4) injection, resulting in about 8%-12% carboxyhemoglobin concentration in vivo. The expression of HO-1 in the liver of hemin-treated rats was determined by western blot method at different time points. At 24 h after carbon tetrachloride administration, all rats were sacrificed to collect blood samples for the examination of ALT, AST levels and to remove liver tissues for analysis of MDA concentration, SOD activity and caspase-3 activity as well as TNF-alpha contents. In addition, histopathological changes were investigated and hepatocyte apoptosis was detected by TUNEL method.
Results: The administration of carbon tetrachloride to rats caused a marked hepatic damage, characterized by significant elevation of serum ALT, AST levels(2 136.3+/-163.4 U, 1 422.7+/-221.7 U) and liver MDA content(5.28+/-0.93 micromol/g), caspase-3 activity (optical density value 4.69+/-1.02) and TNF-alpha level(256.3+/-27.3 ng/L) combined with a remarkable reduction in liver SOD activity (45.9+/-14.8 U/mg) as compared with the control rats. Histopathological observations revealed severe damage in the liver and prominent hepatocyte apoptosis took place in CCl(4) -treated rats. However, pretreatment with hemin could induce high expression of HO-1 protein and exert potent protective effects against liver injury, as demonstrated by a significant decrease in ALT, AST levels(287.1+/-24.3 U, 246.2+/- 21.7 U) and MDA concentration(3.27+/-1.34 micromol/g), reduction in caspase-3 activity(optical density value 2.49+/-1.47) and TNF-alpha level(132.6+/-19.5 ng/L), as compared with the CCl(4) -treated rats. Moreover, hepatocyte apoptosis and liver injury were both attenuated remarkably in the liver of rats pretreated with hemin. In contrast to hemin administration, single injection of exogenous CO produced the same protective effects, as indicated by the remarkable reduction of ALT, AST levels and caspase-3 activity and TNF-alpha levels.
Conclusion: The above results suggest that HO-1/CO system has a potent protective effect on acute liver injury induced by carbon tetrachloride in rats. Induction of HO-1 expression and low concentration of CO can inhibit the progress of hepatic damage, which might be due to the alleviation of lipid peroxidation and reduction of caspase-3 activity or inhibition of TNF-alpha level.