The Anti-diabetic Effects And Its Mechanism Of GCP-02, A PPARα/γ Dual Agonist

Background and Objective Diabetes mellitus has become one of the main threats to human health in the 21 st century.The diabetes epidemic relates particularly to type 2 diabetes mellitus(T2DM),which accounts for 90%of cases globally.T2DM pathophysiologically arises from two defects:impaired insulin action and impairedβ-cell function/insulin secretion.Impaired insulin action,or insulin resistance,is not only the pathophysiologic basis for T2DM,but also associated closely with cardiovascular diseases.Insulin resistance often exsits together with obesity, dyslipidemia and hypertension,that are called insulin resistance syndrome.Fibrates PPARαagonists are hypolipidemic drugs by promoting fatty acid oxidation and can reduce lipid accumulation and body weight,but are not effective in blood glucose control.Thiazolidinediones(TZDs) PPARγagonists are a new class of anti-diabetic drugs with insulin-sensitizing properties.In addition to lowering blood glucose,TZDs may also benefit cardiovascular parameters,such as lipids,blood pressure, inflammatory biomarkers,endothelial function,and fibrinolytic status.However,side effects such as edema and weight gain restrict the use of TZDs in some patients.Then it's of interest to develop substances with combined PPARα/γeffects that could maintain the beneficial effects on insulin resistance and its associated atherogenic dyslipidemia while reducing the side effects.GCP-02,anα-ethoxy-phenyl-propionic acid derivative synthesized by the synthesis division of Institute of Materia Medica, Chinese Academy of Medical Sciences,has been identified by in vitro transactivation studies as a potent,selective dual activator of both PPARαand PPARγ.Here we report the primary study on the anti-diabetic effects and its mechanism of action of this compound.Methods The research includes three parts.1.Monosodium glutamate-induced insulin resistant obese mice(MSG mice) were used to examine the action of GCP-02 in vivo.MSG mice were divided into four groups:MSG mice control group(Con), rosiglitazone group(7μmol·kg^-1,RSG),high dose of GCP-02 group(7μmol·kg^-1, GCP-02-H) and low dose of GCP-02 group(3.5μmol·kg^-1,GCP-02-L).Agents were given orally once daily for 19 consecutive days,during which insulin tolerance test, oral glucose tolerance test and gluconeogenesis test were performed and in each test serum cholesterol(Chol),triglyceride(TG) and free fatty acids(FFA) were monitored. On day 19,mice were decapitated.Body length and body weight were measured. Serum was collected for the determination of insulin,alanine aminotransferase (ALT),and aspartate aminotransferase(AST).Intraperitoneal adipose,heart,liver were weighed.Liver,soleus muscle and myocardium were assayed for glycogen, Chol,TG and FFA contents.Myocardium superoxide dismutase(SOD) and malonaldehyde(MDA) were determined.The mRNA expressions of insulin receptor (IR),insulin receptor substrate 1 and -2(IRS-1,IRS-2),glucose transportor 1 and -2 (GLUT-1,GLUT-2),PPARαand PPARγ,in liver were analysed by reverse-transcription PCR.To further investigate the mechanism of action of GCP-02, 2.HepG2,HIRc-B and WB-F344 cells were used to test the effects of GCP-02 on glucose transportation,consumption and cell viability.3T3-L1 cells were used to test the effect of GCP-02 on adipocyte differentiation.3.Human umbilical vein endothelial cells(HUVEC) were cultured to test the effects of GCP-02 on NO and ET-1 secretion.The effect of GCP-02 on artery contractility was performed in rat aortic rings.Results 1.In insulin resistant and obese MSG mice,GCP-02 improved insulin sensitivity,insulin tolerance and glucose tolerance,suppressed gluconeogenesis,the effects were more potent than RSG.2.GCP-02 prodeced more potent,rapid and stable effects than RSG in lowering serum Chol,TG and FFA.3.GCP-02 reduced body weight of MSG mice.4.GCP-02 significantly decreased glycogen,TG and FFA contents of liver,slightly decreased glycogen content of soleus muscle,reduced TG content of myocardium and increased myocardial SOD activity.5.The expression of IRS-2 mRNA in the liver was down-regulated in MSG mice and was up-regulated by GCP-02.6.GCP-02 promoted glucose consumption in both HepG2 and HIRc-B cells. 7.GCP-02 elicited similar promoting effect as RSG on 3T3-L1 cell differentiation.8. GCP-02 didn't affect NO and ET-1 production significantly in HUVEC after 24 hours of treatment.9.GCP-02 caused dose-dependent reduction of norepinephrine-induced aortic contraction by mechanisms independent of NO and PGs.Conclusion 1.The effects on insulin sensitivity,insulin tolerance,glucose tolerance,blood glucose and gluconeogenesis indicate the activation of PPARγby GCP-02;the effects on serum Chol,TG,FFA and body weight indicate the activation of PPARαby GCP-02.2.PPARα/γdual agonist GCP-02 is more potent than PPARγagonist rosiglitazone in insulin sensitizing and in blood glucose,blood lipids controlling.3.The mechanism of GCP-02 action correlates possibly to the up-regulation of mRNA expression of IRS-2 in liver and the promotion of glucose consumption and pre-adipocyte differentiation.4.GCP-02 reduced norepinephrineinduced rat aortic contractilion by mechanisms independent of NO and PGs.