Structural characterization, evaluation of lipid-lowering activity, and the structure-activity relationship of a pectic polysaccharide from the whole herb of Euphorbia humifusa

Abstract

This study aimed to purify and characterize a polysaccharide from Euphorbia humifusa herb, which was identified for its lipid-lowering potential among 48 plant-derived polysaccharides, and to investigate its structure–activity relationship (SAR) using an oleic acid (OA)-induced L02 cell model. EPS-2B, a pectin with a molecular weight of 67.0 kDa, was isolated from the whole herb of E. humifusa. EPS-2B was comprised of rhamnose, galactose, arabinose, and galacturonic acid in a molar ratio of 29.73:24.96:13.75:31.56. The structural analysis of EPS-2B revealed rhamnogalacturonan-I (RG-I) and homogalacturonan (HG) domains. The RG-I backbone consisted of →4)-α-D-GalpA-(1→2)-α-L-Rhap-(1→, with branches of 1,3-Galp, 1,6-Galp, 1,3,6-Galp, T-Araf, 1,5-Araf, and T-Rhap attached to the C-4 of 1,2-α-Rhap. EPS-2B dose-dependently alleviated OA-induced lipid accumulation and oxidative stress in L02 cells, including reductions in total cholesterol, triglyceride, malondialdehyde, aspartate aminotransferase, and alanine aminotransferase levels, as well as an increase in superoxide dismutase activity. A high dose of EPS-2B (400 μg/mL) reduced total cholesterol levels by 45.4 % and triglyceride levels by 18.0 %. SAR studies indicated that GalA was the active switch for lowering lipids and that a higher galactose content, an appropriate molecular weight, and arabinose removal favored lipid lowering. This work indicates that EPS-2B holds promise as a lipid-lowering drug.