Action Mechanisms Of Wuyuan Green Tea Polysaccharides On Type 2 Diabetes Mellitus

In recent decades,there is increasing number of patients with diabetes,which brings serious damage to human health.Ninety percent of the disease is type 2 diabetes mellitus(T2DM),which is also known as non-insulin-dependent diabetes mellitus.It has been suggested that T2DM is caused by ?-cell dysfunction that resulted from disordered lipid metabolism,a factor contributing to insulin resistance.Meanwhile,hyperglycemia and hyperinsulinemia can lead to the deterioratsion of insulin resistance.Complications caused by diabetes increase the hazards of this disease,such as blindness,renal failure,lower limb amputation,heart disease,nephropathy,and liver diseases.Lower-grade green tea has long been considered as anti-diabetic agent in East Asia,especially in Japan.Research on the anti-diabetic molecules has traditionally been focused on tea polyphenols,such as catechins.Polysaccharides are also one of the antidiabetic constitutes of tea,and have been proved to exhibit various biological functions,such as immune regulation,antioxidant,antitumour and anti-diabetes.In the present study,we assessed the potential of green tea polysaccharides(at dose of 100-400 mg/kg body weight of rats)or a control diets to influence blood glucose and lipids,gut microbiota dysbiosis and liver complication in the high-fat-diet/streptozotocin-induced diabetic rats.The main contents and conclusions are summarized as follows:1)Effects of tea polysaccharides on blood glucose and lipids in T2DM rats.The fasting blood glucose(FBG)levels,weight,food intake,water intake and serum lipid of rats were measured weekly.Oral glucose tolerance test(OGTT)was performed at week 3.The serum levels of free fatty acid(FFA),serum insulin,adiponectin(ADP)and glucagon-like peptide 1(GLP-1)were measured after gavage for 3 weeks.Homeostasis model assessment-insulin resistance(HOMA-IR)and quantitative insulin sensitivity check index(QUICKI)were calculated to quantify the insulin sensitivity of rats.We observed a modification of weight,food intake and water intake by tea polysaccharides in comparison with the diabetes control group.Meanwhile,tea polysaccharides treatment provided a therapeutic and dose-dependent reduction in FBG,ADP,GLP-1 and insulin resistance in comparison with diabetes control group,and insulin sensitivity and glucose intolerance were significantly improved by tea polysaccharides treatment when compared with diabetes control group.In addition,serum TC,TG,LDL-C and FFA levels in tea polysaccharides-treatments groups were improved,whereas serum HDL-C level were decreased compared with diabetes control group.In summary,the results suggest that tea polysaccharides could improve the metabolism of blood glucose and blood lipid.2)Effect of tea polysaccharides on pancreas in T2DM rats.Histopathological changes in the pancreas of T2DM rats were visualized using an optical microscopy.The pancreas tissue samples collected for histology were subjected to immunohistochemical analysis to determine the expression of Bax and Bcl-2 proteins.We observed the improved morphology of islet cells and pancreas in rats receiving tea polysaccharides diets compared with rats in the diabetes control group.The expression of Bax protein in rats treated with tea polysaccharides were significantly lower than that of non-treated rats,whereas the expression of Bcl-2 protein were significantly increased by tea polysaccharides treatment.In conclusion,tea polysaccharide mediated pancreatic apoptosis to reduced pancreatic damage in T2DM rats and in turn improved insulin resistant to reduce FBG.3)Effect of tea polysaccharide on gut microbiota and intestine metabolism in T2DM rats.Colonic contents were used for analysis,and short-chain fatty acids(SCFAs),pH,moisture and abundance of colonic microbiota were determined in experimental rats.The results shown the tea polysaccharides promoted the development of beneficial bacteria in gut of T2DM rats,such as butyrate-producing bacteria(Flintibacter butyricus),Bacteroidetes bacteria(Bacteroides sartorii)and Prevotella bacteria(Prevotella dentasini).In addition,total SCFAs,the major SCFAs(acetic acid,propionic acid,butyric acid)and moisture content were significantly increased by tea polysaccharides treatment,and the pH was significantly reduced,when compared with the diabetes control group.In summary,the present study has shown that tea polysaccharides could improve the intestine microbial structure and intestinal metabolism to improve the dyslipidemia,insulin resistant and insulin sensitivity in T2DM rats.4)Effect of tea polysaccharides on liver complication of T2DM rats.Liver function indices of serum glutamic-pyruvic transaminase(ALT)and serum glutamic oxalacetic transaminase(AST)were measured weekly.Liver function index were determined at week 3.Histopathological changes in the livers of T2DM rats were visualized using an optical microscopy.Antioxidantr enzyme activities in liver of experimental rats were detected by antioxidant kit.We observed the improved morphology of livers by tea polysaccharides in T2DM rats.Concentrations of ALT and AST in T2DM rats with tea polysaccharides treatment were significantly reduced compared with the diabetes control group.Furthermore,acitivity of superoxide dismutase(SOD),catalase(CAT)and total antioxidant capacity(T-AOC)in the livers of T2DM rats were significantly improved by tea polysaccharides,meanwhile,the concentration of malondialdehyde(MDA)in T2DM rats were significantly decreased by tea polysaccharides.In conclusion,tea polysaccharides mediates hepatic oxidation resistance to reduced hepatic damage in T2DM rats.In summary,the results suggest that tea polysaccharides could improve the metabolism of blood glucose and blood lipid,pancreas damage,hepatic damage in T2DM rats.At the same time,the present study has shown that tea polysaccharides could improve the intestine microbial structure and intestinal metabolism.