Structural characterization and hypoglycemic effect of polysaccharides of Polygonatum sibiricum

Polygonatum sibiricum polysaccharide (PSP) was extracted and purified from raw material obtained from P. sibiricum. The structural features of PSP were investigated by Congo red, circular dichroism spectrum, high-performance gel permeation chromatography, scanning electron microscope, atomic force microscope, ultraviolet spectroscopy, and Fourier transform infrared spectroscopy analysis. In vitro simulations were conducted to investigate the kinetics of PSP enzyme inhibition. Moreover, a type II diabetes mouse model (T2DM) with streptozotocin-induced insulin resistance was established, and the indexes of lipid quadruple, insulin resistance index, oral glucose tolerance (OGTT), organ index, and pancreatic morphology of model mice were measured. The results showed that PSP mainly consists of monosaccharides, such as mannose, glucose, galactose, xylose, and arabinose. It also has a beta-glycosidic bond of a pyranose ring and an irregular reticulated aggregated structure with a triple helix. In vitro enzyme inhibition assays revealed that PSP acts as a reversible competitive inhibitor of alpha-glucosidase and alpha-amylase. Furthermore, PSP was found to reduce insulin resistance index, increase OGTT and serum insulin levels, decrease free fatty acid content to improve lipid metabolism, and lower glycated serum protein content to enhance glucose metabolism in T2DM mice, thereby leading to a reduction in blood glucose concentration. Additionally, PSP exhibited reparative effects on the damaged liver tissue cells and pancreatic tissue in T2DM mice. The experiment results provide a preliminary basis for the therapeutic mechanism of PSP about type II diabetes and a theoretical reference for application in food and pharmaceutical development.