Improvement And Mechanism On Insulin Resistance Of P. Alkekengi Fruit Saponins In Type ? Diabetic Mellitus Mice

[Objective]The hypoglycemic effect and mechanism of improving insulin resistance of different dose of P.alkekengi fruit saponins(TSP)on type ? diabetic mice were investigated,which may provide a theoretical basis for alleviating insulin resistance.[Methods]60 male SPF ICR mice were randomly divided into 2 groups after 7 days of adaptive feeding,normal control group(n=10)and model group(n=50),respectively.The normal control group which was given normal diet,and the model group which was given high fat and high sugar diet were feeded for the initial of 4 weeks.Then,animals were allowed to fast 12h and were injected intraperitoneally(i.p.)with ice cold streptozotocin(STZ)at a dose of 60 mg/kg body weight.After 3 days,animals were injected again at a dose of 60 mg/kg body weight.Fasting blood glucose levels were measured,and the animals with marked hyperglycemia(fasting blood glucose concentration level above 11.1 mmol/L)were considered diabetic models and selected for further pharmacological studies.The mice(n=10 per group)were divided into six groups.normal control group(NC),normal mice treated with vehicle(normal saline)alone;diabetic model group(DM),diabetic mice treated with vehicle alone;positive control group(PC),diabetic mice treated with Metformin(250 mg/kg body weight);low dose group(TSP-L),diabetic mice treated with P.alkekengi fruit saponins(125 mg/kg body weight);middle dose group(TSP-M),diabetic mice treated with P.alkekengi fruit saponins(250 mg/kg body weight);high dose group(TSP-H),diabetic mice treated with P.alkekengi fruit saponins(250 mg/kg body weight).Body weight and fasting blood glucose were measured every week,during the test.After 4 weeks intragastric administration,oral glucose tolerance test was performed.After the test,the contents of triglycerides(TC),total cholesterol(TG),high density lipoprotein cholesterol(HDL-C),low density lipoprotein cholesterol(LDL-C),aspartate aminotransferase(AST),alanine aminotransferase(ALT)and fasting insulin(FIns)in serum and superoxide dismutase(SOD),glutathione peroxidase(GSH-Px),catalase(CAT)and malondialdehyde(MDA)were determination by ELISA Kit;the morphological changes in liver,kidney and pancreas tissue were observed by HE staining;the relative expression of mRNA of insulin receptor(IR),insulin receptor substrate-2(IRS-2),phosphatidylinositol 3 kinase(PI3K),3-phosphoinositide dependent protein kinase-1(PDK-1),protein kinase B(Akt-2)and forkhead transcription factor(FoxO1)in liver were determined by real-time fluorescent quantitative PCR.[Results](1)Compared with the DM group,the weight and fasting blood glucose of the mice in each dose group of TSP were higher than that of the DM group,while the difference between the TSP-M group and TSP-H group was very significant(P<0.01),and the difference in the TSP-L group was not significant.Compared with the DM group,the levels of serum insulin and HOMA-IR in each dose group of TSP were significantly decreased(P<0.01).AUC in TSP-M group and TSP-H group was significantly lower than that in DM group(P<0.01),and there was no significant difference between TSP-L group and DM group.Compared with the DM group,the content of TC,TG,LDL-C and HDL-C in the TSP-L group was not significantly different,and the TC content in the TSP-M group decreased significantly(P<0.01),and the HDL-C content in the TSP-M group was significantly higher(P<0.01).The contents of TC and LDL-C were significantly decreased(P<0.01),HDL-C content was significantly increased(P<0.01),and TG content was not significantly different in the TSP-H group.Compared with the DM group,there was no significant difference in activity of ALT and AST in the TSP-L group,ALT activity in the TSP-M group decreased significantly(P<0.01),AST activity in the TSP-M group was not significant,ALT and AST activity in TSP-H group decreased significantly(P<0.01).(2)TSP dose groups can reduce the MDA content and increase the activities of SOD,GSH-Px and CAT in liver of T2DM mice.Compared with DM group,there was no significant difference in MDA content,SOD,GSH-Px and CAT activities in TSP-L group,and MDA content was significantly decreased(P<0.01),SOD,GSH-Px,and CAT activities were increased significantly in TSP-M and TSP-H groups.(3)TSP has a certain repair effect on the tissue damage of liver,kidney and pancreas in T2DM mice caused by STZ,and the repair effect of TSP-H and PC groups is significant.Compared with the DM group,the cytoplasm of the hepatocytes was homogeneous,the fat vacuoles were less,the cells arranged more closely,and the morphology was regular and complete,and the steatosis of the renal tubular epithelial cells was alleviated,and the cells arranged neatly in the TSP intervention groups and the PC group.The number of islets and the number of endocrine cells in the TSP-M,TSP-H and PC groups were more,and the vacuolar degeneration was less.(4)Compared with the DM group,the expression of IR mRNA was increased significantly(P<0.01)in TSP-L group,TSP-M group and TSP-H group;there was no significant difference in the expression of PDK-1 and Akt-2 mRNA between TSP-L group and TSP-M group,and the expression of PDK-1 and Akt-2 mRNA was significantly increased(P<0.01)in TSP-H group;there was no significant difference in the expression of PDK-1 and Akt-2 mRNA between TSP-L group and TSP-M group,and the expression of PDK-1 and Akt-2 mRNA was significantly increased(P<0.01)in TSP-H group.[Conclusion]TSP can improve the weight loss of T2DM mice,reduce the level of fasting blood glucose and serum insulin,improve the oral glucose tolerance,reduce the level of blood lipid,reduce the activity of AST and ALT,and improve the liver function damage.TSP intervention can reduce the content of MDA and improve the activity of SOD,GSH-Px and CAT in the liver of T2DM mice.It could relieve the oxidative stress of liver.The mechanism of TSP intervention to improve insulin resistance in T2DM mice may be increasing the expression of IR and IRS-2,activating the PI3K/Akt pathway,inhibiting the expression of FoxO1,inhibiting the liver ISO pathway and alleviating the oxidative stress in the tissues,thus improving the insulin resistance in T2DM mice.