The Effect Of Polygonatum Cyrtonema Hua Polysaccharides (PCP) On The Expression And Secretion Of GLP-1 And Its Molecular Mechanism

In order to provide the basis and direction for the development of anti-diabetic drugs and functional foods from Polygonatum cyrtonema Hua,the effect of polysaccharide(PCP)isolated from P.cyrtonema rhizome on the expression and secretion of gutglucagon-like peptide-1(GLP-1)and its molercular mechanism were studied in vivo and vitro.The results obtained are as follows:(1)The PCP was a homogeneous polysaccharide fraction.The monosaccharide composition analysis by the p-AMBA derivatization method indicated that PCP was mainly composed of fructose and glucose with the molar ratio of 28.12 : 1.With fluorescent end-labeling method and HPLC,orally administrated PCP was found to remain stable in the gastrointestinal tract of mice.(2)In situ experiment of PCP directly acting on the rat jejunum or ileum of rats showed that PCP could significantly increase the content of hepatic portal vein plasma GLP-1,which reached the peak at 60 min.The effect of PCP on ileum was higher than that on jejunum and a single-dose and continuous administration of PCP could significantly increase the level of plasma GLP-1,thereby improving glucose tolerance in rats.(3)In vitro experiments confirmed that PCP significantly up-regulated the expression of the proglucagon and PC3 genes,enhanced the activity of pro-hormone converting enzyme PC3,increased the intracellular GLP-1 level,and promoted the secretion of GLP-1 in NCI-H716 cells.(4)The specific binding of PCP to NCI-H716 cells was confirmed by flow cytometry.Using the polysaccharide affinity beads,the PCP-binding protein was obtained from NCI-H716 cell membrane proteins,and proved by affinity electrophoresis.SDS-PAGE and western blot were used to identify the receptor types using anti-T1R2 and anti-T1R3 antibody,which indicated that the target protein may be sweet taste receptor.Further,sweet taste receptor inhibitors as well as anti-T1R2 and anti-T1R3 antibodies were employed to inhibit PCP-induced GLP-1 secretion in NCI-H716 cells,suggesting that PCP may activate the coupled G protein by binding to the sweet taste receptor,then triggering a series of downstream signaling pathways.