| Objectives(1)To establish rat model of NAFLD induced with high-fat diet in order to observe liver pERK1/2 expression on NAFLD in rats,to study the effects of MEK inhibitor PD98059 on NAFLD in rats and its possible mechanism.(2)To investigate the effects of astragalus membranaceus extraction (AME) on NAFLD in rats and its possible mechanism.Methods(1) The rat NAFLD model was duplicated with high-fat diet. Thirty-two male Wister rats were randomly divided into normal control group(group N),PD98059 and common diet group (group P), high-fat model group(group M)and PD98059 and high-fat diet group(group PM) with 8 for each group. At the end of 4,6,8 weeks, the rats were given a tail vein injection of either PD98059 (0.3mg/kg , group P and group PM) or the relative solvent (group N and group M). The serum alanine aminotransferase (ALT),aspartate aminotransferase(AST),triglycerides(TG),total cholesterol (TC),very low density lipoprotein (VLDL) and the level of liver tissue homogenates TG, TC, malondialdehyde (MDA),superoxide dismutase(SOD) were measured by biochemical methods . Histopathological change in liver was observed.The expression of phosphorylated extracellular-regulated kinase1/2 (pERK1/2) in liver was detected by immunohistochemical method. (2) Forty male Wister rats were randomly divided into normal control group(group A), model group(group B),low dose of AME-treated group(group C), moderate dose of AME-treated group(group D)and high dose of AME-treated group( group E)with 8 for each group.Besides fed with high fat diet, the rats in treatment group were respectively intervened by intragastric administration of different dose of AME every day. After Ten weeks, all the rats were sacrificed .The serum alanine aminotransferase (ALT),aspartate aminotransferase(,AST),triglycerides(TG),total cholesterol (TC), the low density lipoprotein (LDL) , fasting blood glucose (FBG) and the level of liver tissue homogenates TG ,TC ,malondialdehyde (MDA),superoxide dismutase (SOD) were measured .The pathological changes in rat liver were observed. The expression of phosphorylated extracellular-regulated kinase1/2(pERK1/2) and cytochrome P450E1 (CYP2E1) in liver were detected by immunohistochemical method.Results(1) There were no significant differences between group N and group P in all above-mentioned indexs. Compared with group N , the group M developed over 50% steatosis ,different degree of inflammation cell infiltration and necrosis with markedly increase on the serum ALT, AST, TC,VLDL ,the level of liver tissue homogenates TC,TG, MDA and the expression of pERK1/2 in liver, simultaneously with significantly decrease on liver tissue homogenates SOD (P<0.01, P<0.05). Compared with group M, the expression of pERK1/2 ,the serum ALT and the level of liver tissue homogenates TG,TC ,MDA were decreased in group PM, while the level of liver tissue homogenates SOD was increased (P<0.01 , P<0.05). Histopathological change in liver of group PM was ameliorated (P<0.05).(2) Compared with normal control group, the serum ALT, AST, TC, LDL,FBG and the level of liver tissue homogenates TG,TC ,MDA in model group were markedly higher, while the hepatic SOD was significantly lower. The model group presented with steatosis ,inflammation or necroinflammation .Simultaneously,over-expression of pERK1/2 and CYP2E1 existed in rats liver in model group. Compared with the model group, the serum ALT, AST, TC, LDL, FBG and the level of liver tissue homogenates TG, TC, MDA decreased ,while the hepatic SOD increased in liver were improved in AME-treated groups(P<0.01 ,P<0.05),expression of pERK1/2 and CYP2E1 in liver of rats ,hepatic steatosis and integration of histological activity index treated with moderate or high dose of AME were decreased ( P<0.05).Conclusions(1) Expression of pERK1/2 in rat liver of NAFLD induced by chronic feeding of an high fat diet incresed.(2) PD98059 may ameliorate NAFLD in rats by inhibiting expression of pERK1/2.(3) AME exerts protective effects against NAFLD in rats induced by high fat diet possibly through decreasing blood glucose and serum lipid ,increasing antioxidant actions and inhibiting expression of CYP2E1 and pERK1/2.in liver .
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