Polysaccharides isolated from Lycium barbarum L. by integrated tandem hybrid membrane technology exert antioxidant activities in mitochondria

Variations in the molecular weight (MW) of polysaccharides may lead to different pharmacological functions. Hierarchical alcohol precipitation is presently the most popular method of separating polysaccharides. However, as polysaccharide molecules in solution becomes dehydrated in ethanol, the conformation transforms and becomes assembled via intramolecular hydrogen bonding, which can complicate studies on the biological activities of polysaccharides. This work developed an integrated tandem hybrid membrane technology (ITHMT) to separate polysaccharides extracted from Lycium barbarum L. into fractions. The polysaccharide fractions LBP1, LBP2, LBP3, and LBP4 were separated using ITHMT. Preliminary structural analysis including homogeneity, molecular weight, monosaccharide composition, scanning electron microscopy and thermogravimetric analysis were investigated. Both LBP3 and LBP4 had symmetrical single peaks and were considered as one homogeneous polysaccharide. A lower MW cut-off for membrane elements was associated with increased polysaccharide homogeneity. LBP1∼LBP4 were found to be heteropolysaccharides and comprised rhamnose, galactose, glucose, mannose, and galacturonic acid with different molar ratios and MW. The MW of LBP1∼LBP4 were 225.6 kDa, 140.2 kDa, 65.0 kDa, and 38.3 kDa, respectively. Four polysaccharide fractions had unique morphologies, good thermal stabilities and different antioxidant effects. The LBP4 fraction exerted significant antioxidant effects against superoxide anion radicals and ferric-reducing antioxidant effect in vitro, as well as superoxide anion radicals in vivo, indicated L. barbarum polysaccharides with different molecular weight did had different antioxidant activity. All polysaccharides reduced the levels of superoxide anions in mitochondria but could not scavenge cytoplasmic H2O2, indicating that the antioxidant capacity of L. barbarum polysaccharides is achieved through the removal of superoxide anions from intracellular mitochondria.