Separation, Purification, Structural Characterization, and In Vitro Hypoglycemic Activity of Polysaccharides from Panax notoginseng Leaves

This study optimized the extraction process of crude polysaccharides from Panax notoginseng leaves (PNLP) using the ultrasonic-assisted dual-enzyme method through a single-factor combined with response surface experiment. The crude polysaccharides were subsequently purified and isolated with DEAE-Cellulose 52, followed by structural analysis, evaluation of antioxidant activity, and examination of digestive enzyme inhibition. The hypoglycemic effects of the purified components were further clarified. The results indicated that the optimized crude polysaccharide had an extraction yield of 17.13 ± 0.29%. The purified fraction PNLP-3 (eluted with 0.3 M NaCl) was obtained through DEAE-Cellulose 52 chromatography, exhibiting a total sugar content of 81.2% and a molecular weight of 16.57 kDa. PNLP is primarily composed of arabinose, galactose, and galacturonic acid, with molar percentages of 20.24%, 33.54%, and 24.27%, respectively. PNLP-3 is mainly composed of arabinose and galactose, with molar percentages of 29.97% and 49.35%, respectively. In this study of hypoglycemic activity, the IC₅₀ values of PNLP-3 for α-glucosidase and α-amylase inhibition were 1.045 mg/mL and 9.53 mg/mL, respectively. Molecular docking results confirmed that PNLP-3 exhibits better inhibitory activity against α-glucosidase. Furthermore, PNLP-3 alleviated hyperglycemia in insulin-resistant HepG2 cells by enhancing glucose consumption and glycogen synthesis. The antioxidant activity of PNLP-3 exhibited a positive correlation with its concentration, potentially contributing to its hypoglycemic effects by reducing oxidative stress. These findings underscore the therapeutic potential of Panax notoginseng leaf polysaccharides in managing type 2 diabetes and offer new perspectives on the use of natural polysaccharides for regulating blood glucose.