肉桂对糖尿病大鼠肠促胰素效应的调节作用

Cinnamomi Cortex Regulates Incretin Effect in Diabetic Rats

目的:探讨通过建立链脲佐菌素(STZ)诱导的糖尿病(DM)大鼠模型,观察肉桂对DM大鼠肠促胰素效应的药效学作用,并基于胰高血糖素样肽-1(GLP-1)、二肽基肽酶-4(DPP-4)蛋白探讨其作用机制。方法:40只SD大鼠随机分为空白组、模型组、西格列汀组(0.1 g·kg^(-1))、肉桂低、高剂量组(0.45、0.9 g·kg^(-1)),除空白组外采用高脂饲料喂养联合腹腔注射STZ(40 mg·kg^(-1))建立DM大鼠模型。给药干预时间为8周,观察大鼠状态、体质量、饮水量、摄食量、空腹血糖(FBG)等情况,采用苏木素-伊红(HE)染色观察大鼠胰腺病理变化,采用免疫组化法检测DM大鼠胰腺中胰高血糖素蛋白表达,生化法检测大鼠血清脂代谢指标总胆固醇(TC)、甘油三酯(TG)、低密度脂蛋白(LDL)及高密度脂蛋白(HDL)水平。酶联免疫吸附测定法(ELISA)检测大鼠血清中糖化血红蛋白、胰岛素、胰高血糖素、GLP-1、葡萄糖依赖性促胰岛素多肽(GIP)含量。采用蛋白免疫印迹法(Western blot)检测DM大鼠胰腺中GLP-1、DPP-4的蛋白表达。结果:各组干预8周后,与正常组比较,模型组大鼠体质量、空腹血糖、TC、TG、LDL、糖化血红蛋白、胰高血糖素、胰岛素、胰岛素抵抗指数显著升高(P<0.01),HDL、GLP-1、GIP明显降低(P<0.05,P<0.01);与模型组比较,肉桂各剂量组大鼠体质量、空腹血糖、TC、TG、LDL、糖化血红蛋白、胰高血糖素、胰岛素、胰岛素抵抗指数明显降低(P<0.05,P<0.01),HDL、GLP-1、GIP明显升高(P<0.05,P<0.01)。HE染色结果显示,肉桂各剂量组胰岛细胞形态明显好转,未出现细胞核密集现象。免疫组化结果显示,与模型组比较,肉桂各剂量组胰高血糖素蛋白在胰岛细胞中央明显减少,含量下降。Western blot结果显示,与正常组比较,模型组大鼠DPP-4的蛋白表达水平显著升高(P<0.01),GLP-1的蛋白表达水平显著降低(P<0.01);与模型组比较,肉桂高剂量组DPP-4的蛋白表达水平明显降低(P<0.05),GLP-1的蛋白表达水平表达明显升高(P<0.05)。结论:肉桂可有效降低DM大鼠血糖,改善肠促胰素效应,进而发挥降糖作用,作用机制可能是通过激活调控DPP-4和GLP-1蛋白来实现。

Objective:To observe the pharmacodynamic effects of Cinnamomi Cortex on the incretin effect in the rat model of diabetes mellites (DM) induced by streptozotocin (STZ) and explore the underlying mechanism from glucagon-like peptide-1 (GLP-1) and dipeptidyl peptidase-4 (DPP-4).Method:Forty SD rats were randomly assigned into blank,model,sitagliptin (0.1 g·kg^(-1)),and low-and high-dose Cinnamomi Cortex(0.45 and 0.9 g·kg^(-1),respectively) groups.The DM rat model was established by a high-fat diet combined with intraperitoneal injection of 40 mg·kg^(-1) STZ in other groups except the blank group.The intervention lasted for 8weeks.The status,body weight,water intake,food intake,and fasting blood glucose (FBG) of the rats were observed and determined.Hematoxylin-eosin staining was employed to reveal the pathological changes of the pancreas,and immunohistochemistry to detect the expression of glucagon in the pancreas.Biochemical assay was employed to measure the serum levels of lipid metabolism indexes such as total cholesterol (TC),triglyceride (TG),low-density lipoprotein (LDL),and high-density lipoprotein (HDL).Enzyme-linked immunosorbent assay was employed to determine the levels of glycosylated hemoglobin,insulin,glucagon,GLP-1,and glucose-dependent insulinotropic polypeptide (GIP) in rat serum,and Western blot to determine the protein levels of GLP-1 and DPP-4 in the pancreas.Result:After 8 weeks of intervention,the model group showed higher body weight,FBG,TC,TG,LDL,glycosylated hemoglobin,glucagon,insulin,and insulin resistance index and lower HDL,GLP-1,and GIP than the blank group (P<0.05,P<0.01).The Cinnamomi Cortex groups showed lower body weight,FBG,TC,TG,LDL,glycosylated hemoglobin,glucagon,insulin,and insulin resistance index and higher HDL,GLP-1,and GIP than the model group (P<0.05,P<0.01).The Cinnamomi Cortex groups showed recovered morphology of islet cells and no nucleus aggregation.Compared with the model group,the Cinnamomi Cortex groups showed declined levels of glucagon in the center of islet cells.Compared with the blank group,the model group showed up-regulated protein level of DPP-4 and downregulated protein level of GLP-1 (P<0.01).Compared with the model group,the high-dose Cinnamomi Cortex groups showed down-regulated protein level of DPP-4 and up-regulated protein level of GLP-1 (P<0.05).Conclusion:Cinnamomi Cortex may reduce blood glucose and improve incretin effect to lower the blood glucose level by regulating DPP-4 and GLP-1 in DM rats.