Structure and in vitro hypoglycemic activity of a homogenous polysaccharide purified from Sargassum pallidum

This study aimed at investigating the structure, hypoglycemic activity and the underlying mechanism of a homogeneous polysaccharide (PSP-2) purified from Sargassum pallidum. Structural characterization revealed that PSP-2 with a molecular weight of 144.8 kDa was composed of fucose (21.6%), arabinose (2.5%), galactose (22.4%), glucose (2.2%), xylose (18.8%), mannose (1.2%), glucuronic acid (7.7%) and galacturonic acid (23.6%). The backbone chain of PSP-2 was composed of →1)-β-d-Xylp-(3→, →1,3)-β-l-Fucp-(4→, →1)-α-d-Galp-(6→, and →1)-α-d-GlcpNAc-(2→, and the side chains were composed of →1,3,6)-α-d-Galp-(2→, →3)-β-l-Fucp-(1,4→, β-d-GalpNAc-(1→, and α-d-Manp-(1→. In vitro hypoglycemic assays indicated that PSP-2 could significantly enhance glucose consumption, glycogen synthesis, and pyruvate kinase (PK) and hexokinase (HK) activities of insulin-resistant HepG2 cells. Furthermore, the underlying mechanistic studies revealed that PSP-2 could ameliorate insulin resistance by up-regulating the expression levels of insulin receptor substrate-1 (IRS-1), glycogen synthase (GS), phosphoinositide-3-kinase (PI3K) and glucose transporter-4 (GLUT4). These results suggested that PSP-2 may be a potential candidate for the prevention and treatment of Type 2 diabetes mellitus.