Preparation, characterization, antioxidant activity and protective effect against cellular oxidative stress of polysaccharide from Cynanchum auriculatum Royle ex Wight.

In the present study, a novel polysaccharide fraction (CAP2-1) from Cynanchum auriculatum Royle ex Wight was obtained by hot water extraction, ethanol precipitation and sequential purification through anion-exchange and size-exclusion chromatography. CAP2-1 was a homogeneous heteropolysaccharide composed of mannose, rhamnose, glucuronic acid, galacturonic acid, galactose and arabinose, with an average molecular weight of 830.93 kDa. FT-IR and NMR spectra of CAP2-1 exhibited typical characteristic signals of polysaccharide. For antioxidant activity evaluation in vitro, CAP2-1 showed effective scavenging capacities against ABTS, DPPH and superoxide anion radical in a dose-dependent manner, with IC50 values at 0.1232, 0.5543 and 0.5881 mg/mL, respectively. At cellular level, CAP2-1 provided a significant protective effect against hydrogen peroxide-induced oxidative stress in HepG2 cells by a compositive oxidation defense mechanism. CAP2-1 could reduce oxidative stress by significantly enhancing the contents of antioxidant enzyme SOD and non-enzymatic antioxidant GSH in oxidative damaged cells, in addition to scavenging ROS directly and improving cell viability and membrane integrity, consequently achieving the intracellular antioxidant activity. The results unveiled that CAP2-1 could be explored as a promising natural antioxidant for application in functional foods.