基于甜味受体信号通路探讨玉竹多糖的降血糖作用

Antihyperglycemic mechanism of Polygonatum odoratum polysaccharides based on sweet taste receptor signaling pathway

目的基于甜味受体信号通路探讨玉竹多糖的降血糖作用。方法高脂高糖饮食联合链脲佐菌素诱导建立大鼠糖尿病模型,造模成功后将大鼠随机分为模型组、二甲双胍组(200 mg/kg)和玉竹多糖低、中、高剂量组(100、200、400 mg/kg),另取8只正常大鼠为正常组。分别于给药前及给药2、4、6、8周末,尾静脉取血测空腹血糖;给药7周后进行口服葡萄糖耐量实验,同时采用ELISA法检测血清GLP-1、胰岛素水平;给药8周后检测大鼠血脂水平,观察胰腺、肝脏的形态,RT-qPCR法检测回肠组织T1R2、T1R3、α-gustducin、TRPM5、SGLT-1、GLUT-2 mRNA表达。以HuTu-80细胞为模型,加玉竹多糖溶液处理,ELISA法检测细胞cAMP、GLP-1水平,激光共聚焦法检测细胞Ca^(2+)荧光强度,RT-qPCR法检测细胞甜味受体mRNA表达。结果动物实验结果显示,与模型组比较,玉竹多糖中、高剂量组大鼠空腹血糖、时间-血糖曲线下面积(AUC)和血清TG、TC、LDL-C水平降低(P<0.05),血清GLP-1、胰岛素水平和回肠组织T1R3、TRPM 5 mRNA表达升高(P<0.05),且高剂量组血清HDL-C水平和回肠组织T1R2、α-gustducin mRNA表达升高(P<0.05)。细胞实验结果显示,与正常组比较,玉竹多糖可增加细胞cAMP、GLP-1、Ca^(2+)水平(P<0.05),增强甜味受体T1R2、T1R 3 mRNA表达(P<0.05)。结论玉竹多糖可能通过上调甜味受体信号分子的表达,从而增强甜味受体信号强度,促进GLP-1分泌,发挥降血糖作用。

AIM To explore the antihyperglycemic mechanism of Polygonatum odoratum polysaccharides based on sweet taste receptor signaling pathway.METHODS After the successful diabetic modeling by high-fat and high-sugar diet combined with streptozotocin,the rats were randomly divided into the model group,the metformin group(200 mg/kg)and the low,medium and high dose P.odoratum polysaccharides groups(100,200 and 400 mg/kg),in contrast to the control group with 8 normal rats.The rats had measurement of their fasting blood glucose level from tail vein blood before the intervention and 2,4,6 and 8 weeks after the corresponding administration;detection of their serum GLP-1 and insulin levels by ELISA,and their oral glucose tolerance test after 7 weeks;detection of their blood lipid level,observation of their morphology of pancreas and liver,and detection of their mRNA expressions of T1R2,T1R3,α-gustducin,TRPM5,SGLT-1 and GLUT-2 in ileum by RT-qPCR after 8 weeks.HuTu-80 cells treated with P.odoratum polysaccharides solution had their the levels of cAMP and GLP-1 detected by ELISA;their fluorescence intensity of Ca^(2+)detected by laser confocal method;and the expression of sweet taste receptor mRNA detected by RT-qPCR.RESULTS The result of animal experiments showed that the groups intervened with middle or high dose of P.odoratum polysaccharides displayed decreased levels of fasting blood glucose,area under the time-blood glucose curve(AUC)and the levels of serum TG,TC and LDL-C(P<0.05),increased levels of serum GLP-1 and insulin and the mRNA expressions of T1R 2 and TRPM 5 in ileum(P<0.05),in contrast to the model group,in addition to the increased serum HDL-C level and mRNA expressions of T1R2,α-gustducin in ileum tissue in the high dose group.The result of cell experiment showed that P.odoratum polysaccharides increased the levels of cAMP,GLP-1 and Ca^(2+)in cells(P<0.05),and enhanced the mRNA expressions of sweet taste receptors T1R 2 and T1R3(P<0.05).CONCLUSION P.odoratum polysaccharides may contribute antihyperglycemic effects through GLP-1 secretion promotion via activation of the sweet taste receptor signaling pathway due to its efficacy in up-regulating expression of molecules.