Preparation,Physicochemical Properties And Hypoglycemic Activities Of Polysaccharides From Hericium Erinaceus

Diabetes mellitus?DM?,known as“Xiaoke disease”in traditional Chinese medicine?TCM?,is an endocrine and metabolic disease,which lead to a variety of complications.At present,DM has become one of the global focus problems that seriously endanger people's health.Hericium erinaceus?H.erinaceus?,as a precious edible fungus,has been widely used as a TCM and tonic for its health benefits.Polysaccharides,as one of the main active components of H.erinaceus,have multiple physiological activities and health effects,such as immunoregulation,anti-tumor,antioxidant,hypoglycemic and hypolipidemic,and liver protection.In the present study,therefore,H.erinaceus polysaccharides?HEPs?were obtained through different extraction solvents from the fruit body of cultivated H.erinaceus.Physicochemical properties,functional characteristics,in vitro antioxidant and hypoglycemic activities of the HEPs were comparatively studied,and the highly bioactive HEP was established.On this basis,the in vivo hypoglycemic activity and mechanism of action of the HEP were evaluated through a diabetic rat model.The main results are as follows:?1?HEPs?HEP-W,HEP-S,HEP-C,and HEP-A?were extracted from the fruit body of H.erinaceus by using four different extraction solvents,i.e.,distilled water,0.9%NaCl,citric acid?pH 3.0?,and 1.25 M NaOH/0.05%NaBH₄ aqueous solutions.Results showed that HEP-A extracted with alkaline solution had the highest extraction yield?11.60%?,protein content?8.31%?and?-1,3-glucan content?23.21%?,but HEP-C extracted with citric aicd solution had the highest total sugar content?81.51%?.The four HEPs were acidic heteropolysaccharides,which composed of glucose,rhamnose,arabinose,mannose and galactose with different molecular molar ratios,together with similar chemical structures and different molecular weights and molecular weight distributions.Amongst of them,HEP-C and HEP-A showed lower molecular weights and intrinsic viscosities,and exhibited obvious non-Newtonian pseudoplastic fluid behaviors at higher concentrations and lower shear rates.Scanning electron microscope observation revealed that extraction solvents had important impacts on surface morphologies and molecular sizes of the HEPs.?2?In vitro antioxidant and hypoglycemic activities of the HEPs were comparatively evaluated.Results demonstrated that the four HEPs possessed prominent free radical scavenging abilities and antioxidant activities in dose-dependent manners,and the antioxidant capacities of the HEP-C were higher than the other three HEPs.Meanwhile,the four HEPs showed obvious inhibitory effects against?-glucosidase and?-amylase,and the highest inhibitory activities were found in the HEP-C within the determined concentrations of the HEPs.Therefore,HEP-C exhibited better antioxidant and hypoglycemic activities in vitro.?3?In vivo hypoglycemic activity of the HEP-C was investigated by using a streptozotoxin?STZ?-induced diabetic rat model.Results showed that compared with the model control?MC?group,the supplements with HEP-C?150 and 300 mg/kg body weight[BW]?could not only significantly and dose-dependently reduce fasting blood glucose and ameliorate glucose tolerance,BW loss and organ injures,but also alleviate hepatic function and serum lipid metabolism,elevate antioxidant enzyme activities and suppress lipid peroxidation,which contributed to its hypoglycemic benefit.?4?The underlying mechanism and signal pathway of hypoglycemic activity of the HEP-C in vivo were preliminarily revealed.Liver histopathological observation demonstrated that the HEP-C,especially at the high dose of 300 mg/kg BW,could effectively attenuate the deteriorated hepatic lesions in STZ-induced diabetic rats,which was almost similar to that of normal hepatic architecture.Specifically,compared with the MC group,different doses of HEP-C could significantly and dose-dependentlyup-regulatetheexpressionsof phosphatidylinositol-3-hydroxykinase?PI3K?,protein kinase?Akt?,phosphorylated Akt?p-Akt?and glycogen synthase?GS?,down-regulate the expression of glycogen synthase kinase?GSK-3??,activate the PI3K/Akt signal transduction pathway,promote glucose transport activity in STZ-induced diabetic rats and mediate the balance of blood glucose in diabetic rats,which further contributed to its hypoglycemic activity in vivo.