Synthesis, structural characterization, antioxidant activity, and α-glycosidase inhibitory effects of carboxymethylated Houttuynia cordata polysaccharide

The present study investigates the effect of carboxymethylation modification on the physiochemical properties, structure characterization and biological properties of Houttuynia cordata polysaccharide (HCP). The successful synthesis of carboxymethylated HCP (C-HCP) was confirmed by the degree of substitution, FTIR and NMR results. The carbohydrate content and uronic acid of C-HCP were decreased compared with native HCP, while C-HCP exhibited higher water solubility and lower viscosity. The molecular weights of HCP and C-HCP were 5.123 × 10 5  Da and 2.581 × 10 5  Da, respectively. Both polysaccharides were contained the same monosaccharide composition with a slight change in the molar ratio. C-HCP exhibited a greater thermal stability than native HCP. SEM and AFM microscopic observation confirmed the changes on the polysaccharide chain after carboxymethylation. C-HCP demonstrated stronger hydroxyl radical scavenging activity than HCP. Both HCP and C-HCP inhibited α-glucosidase . However, C-HCP showed substantially higher activity, with inhibition rates of 84.66 ± 0.44%, compared with 53.68 ± 2.40% for native HCP at a concentration of 10 mg/mL. Furthermore, kinetic analyses revealed that both HCP and C-HCP inhibited α-glycosidase via a mixed-type mechanism. Fluorescence quenching and molecular docking studies further demonstrated that C-HCP exhibited a higher binding affinity toward α-glycosidase compared with native HCP. Overall, carboxymethylation effectively enhanced the function and hypoglycemic activity of HCP, suggesting that, C-HCP may serve as a potential therapeutic agent or as functional food to control hypoglycemic.