The Regulation Mechanism Of Polygonatum Sibiricum Saponin On Blood Glucose And Intestinal Flora In T2DM Mice

Polygonatum sibiricum is a plant of the genus Polygonatum in the lily family and has been used as a traditional Chinese medicine for over a thousand years in China.Polygonatum sibiricum saponin(PSS)is an important active ingredient in Polygonatum sibiricum and has a variety of pharmacological activities.In recent years,PSS has been found to have hypoglycemic effect,but the specific mechanism is not clear.Therefore,the purpose of this study is to illustrate the hypoglycemic effect of PSS on type 2 diabetes mellitus(T2DM)mice induced by high-sugar and high-fat diet and combined with streptozotocin(STZ).On this basis,an in-depth investigation was conducted to determine whether PSS could exert its anti-diabetic effects by affecting hepatic glucose metabolic pathways and improving intestinal function,as well as to investigate the mechanism of action of PSS in improving diabetes based on intestinal flora.The main research work is as follows:(1)Effect of PSS on physiological indicators and blood lipids in T2 DM mice.T2 DM mouse models were constructed using a high-sugar,high-fat diet fed for four weeks followed by three days of continuous injection of STZ.Forty diabetic mice were randomly divided into five groups: T2 DM group,low-dose group,medium-dose group,high-dose group and positive group,and mice not involved in the modelling were normal group.The mice were administered continuously by gavage for four weeks to explore the recovery of diabetic mice by physiological and serum indices.After four weeks,the blood glucose in each intervention group decreased to 14.28 mmol/L,15.22 mmol/L,19.67 mmol/L and 12.84 mmol/L,respectively,and there were also reductions in food intake,water intake,body weight and organ index.Serum index results showed that total cholesterol(TCHO),total triglyceride(TG),low-density lipoprotein(LDL-C),lipopolysaccharide(LPS),glycated serum protein(Hb A1c)levels and serum insulin levels in diabetic mice were significantly reduced by PSS,and highdensity lipoprotein(HDL-C)levels in the high-dose and positive groups were increased by40.04% and 51.48%.PSS also improved glucose tolerance as well as insulin tolerance in diabetic mice.(2)The effect of PSS on reducing liver damage and improving hepatic glucose metabolism was investigated by HE-stained and Western blot assays.In diabetic mice,alanine aminotransferase(ALT)and aspartate aminotransferase(AST)were 13.69-fold and 3.35-fold higher,respectively,than in the normal group,but were significantly reduced after PSS intervention.HE staining showed that PSS had a beneficial effect on repairing damaged liver tissues,while Western blot results demonstrated that PSS increased the levels of key enzymes in glycogen synthesis,glycolysis,gluconeogenesis and cholesterol metabolism pathways,promoting hepatic glucose metabolism and glycogen synthesis in the liver.It also reduces the level of inflammatory factors in the liver and prevents liver damage.(3)The effects of PSS on intestinal barrier,intestinal flora and short-chain fatty acids(SCFAs)produced by metabolism were investigated by plate coating and real-time fluorescence quantitative PCR experiments.The results showed that PSS beneficially changed the damaged intestinal flora of diabetic mice,increasing the abundance of Bifidobacterium,Lactobacillus and Bacteroides fragilis and decreasing the abundance of Enterococcus,Enterobacter and Clostridium difficile.Meanwhile total SCFAs content increased by 33.03%,141.79%,174.75% and 256.81%,respectively.The expression of three proteins,Claudin-1,ZO-1 and Occludin,was reduced by 31.03%,27.69% and 36.30%,respectively,in diabetic mice.PSS increased their expression and reduced intestinal permeability.(4)The effect of PSS on intestinal flora was verified by fecal transplantation test(FMT).The faeces of mice after faecal transplantation were examined using 16 S r RNA highthroughput sequencing.Alpha diversity and Beta diversity analysis revealed a reasonable sample size,reduced abundance and diversity of intestinal flora in diabetic mice,and showed species differences between groups.The number of Firmicutes increased by 46.6% and Bacteroidetes decreased by 30.85% in diabetic mice compared to normal mice.The PSS intervention reversed this trend and beneficially regulated the composition of intestinal flora.The results of the heatmap and LSFe analysis showed that the FNC group was positively correlated with Muribaculaceae,Lactobacillus,Bifidobacterium,Alistipes,Romboutsia and Odoribacter,and the main marker species were Muribaculaceae,Alistipes,Romboutsia and Odoribacte.The FTC group was positively correlated with the Lachnospiraceae＿NK4A136＿group,and the main marker species were Firmicutes and Lachnospiraceae＿NK4A136＿group.These results demonstrate the accuracy of the real-time fluorescence quantitative PCR results and suggest that PSS has an important role in regulating the composition of intestinal flora and the changes of key bacteria.In summary,the beneficial effects of PSS on hepatic insulin resistance and hepatic glucose metabolism in T2 DM mice,as well as the ameliorative effects on the damaged intestinal microbiota,were investigated to reveal the mechanisms by which PSS exerts hypoglycaemic and antidiabetic effects.The findings provide a potential therapeutic approach for T2 DM and its associated metabolic disorders,as well as new ideas for the development of new drugs for the treatment of diabetes.