A novel polysaccharide of Undaria pinnatifida: Structural characterization, carboxymethylation and hypoglycemic activity in vivo

A new polysaccharide (UPP) was isolated and purified from Undaria pinnatifida with a low molecular weight of 8.34 kDa. The UPP was modified to obtain carboxymethylated polysaccharide (CM-UPP). UPP and CM-UPP were characterized by FT-IR, Ion chromatography, Congo red, DSC, SEM and NMR, and their hypoglycemic activity in vivo was investigated using the STZ-induced diabetes mice model. UPP mainly contained Ara, Gal, Glc and Man at a molar ratio of 0.18: 0.13: 2.06: 1, and CM-UPP added two alduronic acids including GalA and GlcA. CM-UPP had been prepared successfully and the carboxymethylation reaction might occur partially at the C-2 and C-4 position. There were no triple helix structures in both UPP and CM-UPP. In vivo hypoglycemic activity studies showed that both UPP and CM-UPP could alleviate symptoms of high blood glucose, improve blood lipid level, oxidative stress state and liver glycolytic enzyme activity in diabetic mice. Under the same dose, CM-UPP showed a more significant effect than UPP. These results indicated that carboxymethylation was an effective way to enhance the hypoglycemic activitiy of polysaccharide. UPP and CM-UPP could be potential therapeutic agents of T2DM.