Structural characterization and hypoglycemic activity of a polysaccharide from Imperatae Rhizoma

In this study, high-temperature high-pressure ultrasound-assisted extraction method was used to extract polysaccharides from Imperatae Rhizoma (IRP). The yield of IRP was 14.79 ± 0.12 % under the optimal extraction conditions. IRP was purified by a DEAE-52 cellulose column and a Sephadex G-100 chromatography column to obtain two homogeneous fractions: IRP-0 and IRP-1. IRP-1 showed better inhibitory activity than IRP-0 in α-glucosidase inhibition assay. The chemical structure of IRP-1 was further characterized using molecular weight distribution, monosaccharide composition, infrared spectroscopy, methylation analysis, and nuclear magnetic resonance. The results indicated that IRP-1 (29.79 kDa) was a heteropolysaccharide composed of rhamnose, arabinose, galactose, glucose, xylose, mannose, and glucuronic acid, with a molar ratio of 2.48:11.76:20.08:50.92:10.25:2.08:2.12. The backbone of IRP-1 consisted of →6)-β-D-Glcp-(1→, →3,6)-α-D-Galp-(1→, →4)-β-L-Xylp-(1→, and →5)-Araf-(1→. The results of the in vitro hypoglycemic experiments showed that IRP-1 effectively improved glucose consumption and glycogen synthesis, pyruvate kinase (PK), and hexokinase (HK) activities in insulin-resistant HepG2 (IR-HepG2) cells. Additionally, IRP-1 significantly increased the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), and the levels of glutathione (GSH), while reducing the levels of malondialdehyde (MDA) and reactive oxygen species (ROS), demonstrating its significant hypoglycemic activity. The findings provide a scientific foundation for the development and utilization of polysaccharides from Imperatae Rhizoma, suggesting their potential application in the treatment of diabetes.