Study On Effects Of Ecdysterone On Insulin Sensitivity And Its Mechanism

I: Study on Glucose-Lowering Effect of Ecdysterone in Vitro Objective: To investigate whether ecdysterone is able to exert glucose-lowering effect on hepatocytes or stimulate the secretion of insulin. Methods: For glucose consumption studies,the amounts of glucose disappeared from the culture medium of HepG2 cells within 24 hours were determined. βTC3 cells were also used to monitor insulin secretion. Results: The glucose concentrations decreased significantly by ecdysterone 1 × 10-6¹0-4M,while glucose consumption increased by 44⁷7% with ecdysterone. It declined as glucose concentrations increased independently on insulin. βTC3 cells were not stimulated by ecdysterone. Conclusion: Ecdysterone is able to exert the glucose-lowering effect on hepatocytes which is insulin independent , but has no effect on insulin secretion. II: Establishment and Evaluation of Insulin-resistant HepG2 Cell Model Induced by High Concentration of Insulin Objective: To establish insulin resistant HepG2 cell model induced by high concentration of insulin in vitro culture. Methods: HepG2 cells were incubated with 5×10-7mol/L insulin for 16 hours,washed with DMEM and finally with pre-cold PBS.The residual 125I-insulin binding and the insulin-stimulated 3H-D-glucose incorporation were determined. Results: It was demonstrated that the residual 125I-insulin binding and incorporation rate of 3H-D-glucose in insulin-resistant HepG2 cells were decreased significantly than that in control cells.Insulin-resistant HepG2 cells were free from stimulation for 60 hours by insulin, but the incorporation rate of 3H-D-glucose were remaining lower than that in control cells. Conclusion: HepG2 cells exposed to 5×10-7mol/L insulin for 16 hours were able to induce a state of insulin resistance and reproduce a insulin-resistant cell model. The state of insulin resistance could be maintained for 60 hours. The method is simple ,practicable and reliable. III: Effects of Ecdysterone on Insulin Sensitivity and Glucose Metabolism in Insulin-resistant Cell ModelObjective: To investigate the effects of ecdysterone on insulin sensitivity and glucose metabolism in the insulin resistant HepG2 cell model induced by high concentration of insulin. Methods: The insulin-stimulated glucose incorporation rate was determined with 3H-D-glucose uptake test which was used to estimate insulin sensitivity of HepG2 cell, and glucose consumption, the amounts of glucose disappeared from the culture medium of HepG2 cells within 24 hours were determined. Results: The incubation of insulin resistance cells with ecdysterone 1×10^-610^-4M could significantly increase the glucose uptake and glucose consumption of the cells compared with that of control cells(P<0.01). The glucose uptake and glucose consumption of insulin resistance cells were not of difference in the insulin resistance cells with ecdysterone and pioglitazone(P>0.05). Conclusion: Ecdysterone could improve the insulin sensitivity in the cell model and might attenuate the aggression of insulin resistance. The effect to improve the insulin sensitivity with ecdysterone was similar to that with pioglitazone. IV: Effect of Ecdysterone on Insulin Signaling Proteins InsR, IRS-1, IRS-2 and GLUT-4 in IR HepG2 Cells Objective: To investigate the effect of ecdysterone on insulin signaling proteins InsR, IRS-1, IRS-2 and GLUT-4 in IR HepG2 cells. Methods: After establishment the insulin resistant HepG2 cell model induced by high concentration of insulin, and the HepG2 cells were incubated with ecdysterone for 24h, Western blotting was used to assess thelevels of InsR and GLUT-4, therefore, IRS-1 and IRS-2 was determinated by immunocytochemistry Assay Results: The protein contents of InsR, IRS-1, IRS-2 and GLUT-4 were significantly increased compared with model control. The levels of IRS-2 raised as ecdysterone concentrations increased by ecdysterone 1 ×10-6¹0-4M. Conclusion: Ecdysterone enhance insuin activity and glucose metabolism in IR HepG2 cells probably by upregulating the expres...