The Mechanism Of Dexamethasone And Intervention By Pioglitazone On Glucose Metabolism In Hepatic Cells

Background and ObjectiveCorticosteroids are widely used in allergy and autoimmune diseases,and also used in organ transplantation aspects, but which also brings the side effect like high blood pressure, obesis, and osteoporosis. And steroid diabetes,which is common in clinic, is also one of the side effect caused by Corticosteroids, but its exact pathogenesis is not clear. Corticosteroids can reduce the uptake and use of glucose in peripheral tissue through many ways:promoting the glycogenesis in liver,and inhibiting the union between insulin and its receptor,and inhibiting glucose transporter-4 to approaches or anchor to the cell membranes.Recent research further reveals glucocorticoids may also damage the function of islet. In addition, the insulin release by glucose stimulation can be inhibited when much corticosteroids is existed. But we found in clinic that insulin secretion did not decrease when corticosteroids was incerased, implicated that more complex mechanism involved in the happen of steroid diabetes.Peroxisome proliferation activated receptor (PPARs) belong to the super family of typeⅡnuclear receptor. Pioglitazone and Rosglitazone which belong to TZDs are the molding ligand to PPAR gamma receptor, which can increase insulin sensitivity of liver and muscles through this way, so TZDs may be used in the treatment of steroids diabetes. Armando research team found the anti-inflammatory effect of PPARs agonists can be blocked by RU486 in animal experiments level, and further found the anti-inflammatory effect can be activated by nuclear inversion not through PPARs way. Lemberger's research showed that RU486 can block the stimulating effect of glucocorticoids on PPAR alpha gene expression, and PPAR alpha also played an important role on lipid metabolism,and the crosstalk between PPAR and GR both on anti-inflammatory and adipocyte differentiation had been proven on many studies. PPAR gamma and GR both belong to nuclear receptor family, But whether TZDs can also block the effect of glucocorticoid on glucose metabolism is unknown.This study used liver cells that cultured by Dexamethasone and Pioglitazone, to observe the the biological effect of dexamethasone on hepatic glucose metaboliam, and the intervention of pioglitazone,further to clarify more molecules mechanism in this course,which can offer the theoretical basis on the prevention and treatment of steroid diabetes in clinic.Methods1. Cells were divided into two groups, The control group and Dexamethasone group,and set paralled groups expectively,then incubated for 24h,36h,48h expectively, observe the most effective time of dexamethasone on inhibiting glucose metabolism through the glucose concentration of each group by GOD-POD method.2. Cells were divided into five groups:The control group,Dexamethasone group, Dexamethasone+Insulin group,Dexamethasone+Pioglitazone group, Dexamethasone+Pioglitazone+Insulin group, cells were incubated by dexamethasone for the most effective time ascertained above,then incubated together for 24h,GOD-POD method, anthrone method, BCA protein assay kit,lactate kit,pyruvate kinase kit were used to observe the glucose concentation and glucose metabolism indicators through glucogen synthesis,gluconegenesis,glycolysis.3. Cells were devided into four groups:the control group,Dexamethasone group, RU486 group, Dexamethasone+RU486 group, and paralleled group of each group above were setted,and the joint action time of each paralleled group is 24h and 48h respectively, GOD-POD method was used to observe the most effective time that RU486 can block the effect of GR. based on this, then HepG2 cells were devided into six groups:the control group, Dexamethasone group, Pioglitazone group, RU486 group,RU486+Dexamethasone group, RU486+ Pioglitazone group, GOD-POD method was used to observe glucose concentration to make sure whether there is a cross talk between PPAR gamma and GR in glucose metabolism of liver cells.Results1. The most effective concentration and action time of dexamethasone (1μmol/L) to inhibit the the glucose consumption of HepG2 cells is 48 hours.2. Among five (Ⅰ～Ⅴ) groups above, the indicators of glycogen synthesis and gluconeogenesis between pioglitazone group and dexamethasone group have significantly difference (P<0.05), but the indicators of glycolysis have no statistically significant difference (P>0.05). when insulin is existed at the same time, insulin and pioglitazone have the co-effect on promoting glucose synthesis, glycolysis and inhibiting gluconeogenesis (P< 0.05)3. Among the four groups above,the glucose concentration have no statistically significant difference when the action time is 24h(P>0.05),when the action is 48h, the glucose concentration among the control group, RU486 group and RU486+ Dexamethasone group have no statistically significant difference (P> 0.05). but the glucose concentration of RU486+ Dexamethasone group is lower than Dexamethasone group (P<0.05).Under this condition, the glucose concentration of the RU486+ Pioglitazone group is higher than Pioglitazone group (P<0.05)Conclusions1. Dexamethasone decrease glucose consumption in HepG2 cells.2. The intervention of pioglitazone on improving insulin resistence mainly through the the promotion of glucogen synthesis and inhibition of gluconeogenesis way,and pioglitazone can also act as Insulin radiosensitizing agent when insulin is existed at the same time. 3. The cross talk between PPAR-y and GR may exist on hepatic glucose metabolism:the function of Dexamethasone may not through PPAR-y way on hepatic glucose metabolism and the part hypoglycemic effect of Pioglitazone which through GR was blocked when the effect of GR had been blocked by RU486.