Optimizing extraction, structural characterization, and in vitro hypoglycemic activity of a novel polysaccharide component from Lentinus edodes

The extraction, structural characterization, and hypoglycemic activity of L. edodes polysaccharides should be evaluated comprehensively, as the extraction process would affect their hypoglycemic activity by destroying the natural structure. In the current study, based on response surface analysis, the optimum extraction conditions for crude L. edodes polysaccharides were obtained as follows: extraction time of 120 min, the liquid-solid ratio of 30: 1 (mL: g), and ultrasonic time of 20 min. Under these conditions, the yield of polysaccharides was 1.68 ± 0.28%. The structural characterization suggested that the polysaccharide component LNT was a β-pyranose conformation with a three-stranded helical structure, and its molecular weight was 3.95 × 105 Da. The LNT consisted of D-glucose (Glc), D-galactose (Gal), D-mannose (Man), and D-arabinose (Ara) in a molar ratio of 10.20: 3.03: 1.15: 0.39. The in vitro hypoglycemic activity of LNT was positively correlated with its concentration. When the concentration of LNT was 1.0 mg/mL, the inhibition rates of α-glucosidase and α-amylase were 53.92% and 94.85% of the positive control acarbose, respectively. In addition, The LNT could promote glucose consumption in IR-HepG2 cells and reduce the apoptosis rate. The glucose consumption in the LNT-M (800 μg/mL) group was 0.44 ± 0.04 mmol/L, nearly 1.3-fold higher than that in the insulin resistance model group (IR-HepG2 model). Preliminary conclusions indicated that the LNT improved insulin resistance by regulating the expression of PI3K and P-AKT proteins in the PI3K/AKT signaling pathway. This current study provides a possibility and theoretical foundation for applying L. edodes polysaccharide as a hypoglycemic food.