| Backgrounds Liver fibrosis is an essential pathological process of chronic liver disease,which involves numerous cellular and molecular events. Recent studies showed that liver fibrosis is a dynamic process and can be reversed after appropriate treatment. At present, researches have demonstrated the important role of oxidative stress and the activation of hepatic stellate cell(HSCs) in the fibrogenesis and the development of liver fibrosis. Melatonin(N-acetyl-5-metyoxytryptamine) is a hormone, which is mainly produced by the pinecone gland in brain and has a strong capacity of anti-oxidative stress. Studies showed that melatonin could attenuate a variety of acute and chronic liver injuries. Furthermore, our previous studies showed that melatonin could ameliorate liver fibrosis and the mechanism may be related to the anti-oxidation effects of melatonin. The activation of HSCs plays a key role in the process of liver fibrosis.During the process of activation HSCs, transforming growth factor β1(TGF-β1) is the most important cytokine and TGF-β1 promotes liver fibrosis mainly through intracellular Smad proteins. Studies have proved that the inhibition of the expression of TGF-β1/Smad pathway in liver could attenuate liver fibrosis. However, the mechanisms of the anti-fibrotic effect of melatonin are still unclear. The aims of this study includes three aspects as follows: investigating the anti-fibrotic effect of melatonin on liver fibrosis induced by carbon tetrachloride(CCl4) in rats, investigating the relationship between melatonin and oxidative stress and investigating the relationship between melatonin and the expression of TGF-β1/Smad signaling pathway.Methods 75 male Sprague–Dawley(SD) rats were divided randomly into the normal group, the model group and melatonin-treated groups(2.5mg/kg, 5.0mg/kg, 10.0mg/kg)(n=15 per group). The model of liver fibrosis was induced by the subcutaneous injection of CCl4 for 6 weeks continuously. Aspartate aminotransferase(AST) and alanine aminotransferase(ALT) activities and albumin(ALB) levels in serum were detected by biochemistry. Malondialdehyde(MDA) levels, glutathione peroxidase(GPx) activities and hydroxyproline(Hyp) levels in liver were measured by spectrophotometry. The liver pathology changes were detected using hematoxylin and eosin(HE) staining and Van Gieson(VG) staining. The evaluation of the expression of TGF-β1/Smad pathway in liver was made by immunohistochemistry and Western blot analysis.Results To compared with the model group, activities of ALT and AST in serum and the levels of Hyp in liver of melatonin-treated groups(2.5mg/kg, 5.0mg/kg, 10.0mg/kg)were decreased significantly(P<0.01). Levels of ALB in serum of melatonin-treated group(10.0mg/kg) were increased significantly compared with those in the model group(P<0.05). When compared with the model group, MDA levels in liver homogenates were reduced remarkably(P<0.01) whereas GPx activities in liver homogenates were elevated(P<0.05) in melatonin-treated groups(2.5mg/kg, 5.0mg/kg,10.0mg/kg). The pathologic grading of liver fibrosis of melatonin-treated group(10.0mg/kg) was decreased markedly when compared to the model group(P<0.05).The expressions of TGF-β1, Smad2/3 and p-Smad2/3 in liver were increased notably in the model group compared with those in the normal group(P<0.01). The expressions of TGF-β1, Smad2/3 and p-Smad2/3 were decrease notably in melatonin-treated groups((2.5mg/kg, 5.0mg/kg, 10.0mg/kg) compared with those in the model group(P<0.01)..The expressions of Smad7 in liver were decreased significantly in the model group compared to those in the normal group(P<0.01). However, the expressions of Smad7 in liver were increased in melatonin-treated groups((2.5mg/kg, 5.0mg/kg, 10.0mg/kg)compared with those in the model group(P<0.01).Conclusions 1)Melatonin protected liver fibrosis induced by CCl4 in a certain extent.2)Melatonin exerted its anti-oxidation effects, which may be related to the anti-fibrotic effects of melatonin. 3) Melatonin inhibited the expression of TGF-β1/Smad signaling pathway in liver fibrosis induced by CCl4, which may be related to the anti-fibrotic effects of melatonin. |
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