A polysaccharide from Lycium barbarum L.: Structure and protective effects against oxidative stress and high-glucose-induced apoptosis in ARPE-19 cells

Lycium barbarum polysaccharides (LBPs) are beneficial for vision; however, relevant research has mainly focused on entire crude polysaccharides, with the basis and exact structure of the polysaccharide rarely explored. In this study, LICP009-3F-2a, a novel polysaccharide from Lycium barbarum L., was separated and then purified using anion-exchange and size-exclusion chromatography. Structural characteristics were investigated using chemical and spectroscopic methods, which revealed that LICP009-3F-2a has an Mw of 13720 Da and is an acidic heteropolysaccharide composed of rhamnose (39.1%), arabinose (7.4%), galactose (22.5%), glucose (8.3%), galacturonic acid (13.7%), and glucuronic acid (4.0%). Linkage and NMR data revealed that LICP009-3F-2a has the following backbone: →2)-α-L-Rha-(1 → 2,4)-α-L-Rha-(1 → 4)-α-D-GalAp-(1 → 3,6)-β-D-Galp-(1 → 3,6)-β-D-Galp-(1 → 6)-β-D-Galp-(1→, with three main branches, including: α-L-Araf-(1 → 5)-α-L-Araf-(1 → 6)-β-D-Glcp-(1 → 2,4)-α-L-Rha-(1→, β-D-Glcp-(1 → 4)-β-D-Glcp-(1 → 3,6)-β-D-Galp-(1→, and β-D-Galp-(1 → 3)-β-D-Galp-(1 → 3,6)-β-D-Galp-(1 → . Differential scanning colorimetry and thermogravimetric analysis showed that LICP009-3F-2a is thermally stable, while X-ray diffractometry showed that LICP009-3F-2a has a semi-crystalline structure. In addition, LICP009-3F-2a protects ARPE-19 cells from H2O2-induced oxidative damage by regulating the expression of antioxidant SOD1 and CAT enzymes and down-regulating MMP2 expression. Moreover, LICP009-3F-2a promotes the proliferation of ARPE-19 cells in a concentration-dependent manner, and protects ARPE-19 cells from hyperglycemia by inhibiting apoptosis.