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Sufalted modification of Grifola frondosa polysaccharide (GFP) was performed using the chlorosulfonic acid-pyridine (CSA-Pyr) method. The chemical structure and α-glucosidase inhibitory activity of sulfated Grifola frondosa polysaccharide (S-GFP) were investigated. FT-IR and NMR spectra both revealed C-6 as the main substituted position owing to steric hindrance. Molecular weight (Mw) analysis indicated that sulfation and degradation could exist concurrently during the sulfation reaction given that the Mw of S-GFP was different from that of natural GFP. Inhibition test of α-glucosidase activity implied that S-GFP is a noncompetitive inhibitor of α-glucosidase. S-GFP effectively inhibited the activity of α-glucosidase with an IC50 value of 3.353 µg mL−1. The results of inhibitory mechanism indicated that S-GFP quenched the endogenous fluorescence of α-glucosidase and changed the backbone structure of the protein. Circular dichroism (CD) analysis showed that treatment with S-GFP changed the conformation of α-glucosidase, increased the content of the α-helix structure, and destroyed the hydrogen bond system of the enzyme. This experiment aims to elucidate the potential α-glucosidase inhibitory activity of sulfated polysaccharides and to provide new insights into the targets of their bioactivities.

Type 2 diabetes mellitus (T2DM) is becoming an expanding global health concern, closely linked to the islet dysfunction. This study aimed to investigate the protective effects of Angelica sinensis polysaccharide (ASP), derived from the roots of Angelica sinensis (Oliv.) Diels, on pancreatic islets of T2DM mice. Our research showed that ASP could ameliorate hyperglycemia, restore lipid profile changes and protect against liver injury. ASP increased the Bcl-2/Bax ratio to block caspase-9-caspase-3 cascade in islet β-cells. Simultaneously, the suppression of a caspase-8-driven extrinsic apoptotic pathway further inhibited the activation of subsequent substrate proteins, such as PARP. Results of immunohistochemistry and immunocytochemistry indicated that ASP could increase cell insulin stores. Additionally, ASP could promote the secretion of insulin to attenuate the glucotoxicity by stimulating the insulin gene expression. Taken together, this study suggested that ASP might be applied as a functional food or additive to treat diabetes.