Protective Effect of Melatonin on Carbon Tetrachloride - induced Hepatic Fibrogenesis in Rats

Abstract

Background: Liver cirrhosis is a critical stage of chronic liver diseases that canproduce liver failure, portal hypertension and hepatic carcinoma. Sustained oxidativestress plays a key role in cell damage and fibrosis induced during liver cirrhosis. Aimof the work: The aim of the present study was to examine the potential protectiveeffect of exogenous melatonin co-treatment on liver tissue injury and oxidative stressprocesses during induction of early phase of liver fibrosis by carbon tetrachloride(CCl4) injection in rats. Methods: Hepatic fibrogenesis model was induced in thisstudy by subcutaneous injection of rats by carbon tetrachloride (CCl4). Eighteenadult, female albino rats were randomly divided into 3 groups (n = 6): control group(group I), carbon tetrachloride treated group (group II) and CCl4 + melatonin cotreatedgroup (group III). Rats in CCl4 treated group were injected subcutaneouslywith sterile CCl4 (2 ml/kg of body weight) in a ratio of 1:1 with olive oil twice a weekfor 8 weeks. Rats of group III (melatonin co-treated group) were injected with CCl4 inthe same manner as in group II and received intraperitoneal melatonin injection in adose of 20 mg/kg twice a week for 8 weeks, starting from the beginning of CCl4injection. Rats in normal control group were injected subcutaneously with olive oil atthe same dose and frequency as those in CCl4 treated group. At the end of theexperiment, rats were sacrificed, blood samples were collected for biochemical assay.Liver from each animal was removed for histopathological examination.Measurement of oxidative stress markers in serum was done by chemical estimationof serum levels of free radicals: lipid peroxides (LPO) and nitric oxide (NO).Antioxidant enzymes were estimated by chemical measurement of glutathioneperoxidase (GSH-Px) and superoxide dismutase (SOD) in the serum. Liver injury wasassessed by evaluation of serum levels of liver enzymes (alanine aminotransferase(ALT), and aspartate aminotransferase (AST)). Determination of development ofearly phase of hepatic fibrogenesis was done by chemical measurement of serum levelof hyaluronic acid (HA) using enzyme immunoassay (ELISA), and byhistopathological examinations of hepatic tissues to detect early fibrotic changes aswell as other histological damage of hepatic tissue caused by CCl4 injection with orwithout melatonin administration. Results: Results of the present study showed thatCCl4 treatment to rats of group II caused highly significant increase in serum levelsof oxidative stress markers (lipid peroxides and nitric oxide), decrease in serum levelsof antioxidant markers (glutathione peroxidase and superoxide dismutase), increaseof serum levels of hepatic enzymes (ALT and AST) as well as increased serum level ofhyaluronic acid (HA) 8 weeks after CCl4 injections when compared with controlgroup. Melatonin co-treatment to animals of group III caused significant reduction in serum levels of lipid peroxides (LPS) and nitric oxide (NO), significant increase inplasma levels of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD),significant reduction in serum levels of liver enzymes (ALT and AST) as well assignificant decrease in serum level of hyaluronic acid (HA) 8 weeks after CCl4injections when compared with group II. Histopathological study of liver tissue ofanimals of CCl4 treated group showed various manifestation of hepatic cell damageand early phase of fibrogenesis as necrosis, degeneration, collagen deposition andfew fibrous threads extending into the hepatic lobules. Histopathological study ofhepatic tissue of melatonin co-treated group showed that melatonin caused markedamelioration of histological manifestations of hepatic cell degeneration and absenceof any sign of fibrogenesis with nearly normalization of the histological appearanceof the hepatic tissue. Compared with CCl4 treated group (group II), histologicalappearance of hepatic tissue of rats in melatonin co-treated group (group III) showedsignificant improvement. Conclusion: Results of this study suggest that melatonin hasa substantial hepatoprotective effect in a rat hepatic fibrosis model induced by an 8-weeks’ CCl4 regimen. The protective effect of melatonin may be due to both its directradical scavenging properties and indirect effect as a regulator of antioxidantsystems. Therefore, the study proposes that melatonin may be a valuable drug forinhibition of unwanted fibrosis in patients exposed to different hepatotoxic agents.