Sulfated modification, structures, antioxidant activities and mechanism of Cyclocarya paliurus polysaccharides protecting dendritic cells against oxidant stress

Abstract In this study, Cyclocarya paliurus polysaccharides purified by DEAE-cellulose columns (CPP0.05) were modified with chlorosulfonic acid–pyridine (CSA–Pyr) method to obtain the sulfation derivative (S-CPP0.05), whose structures were characterized by methylation and NMR analysis. The backbone of S-CPP0.05 was composed of →3)-β-D-Galp-(1→4)-α-D-Glcp-(1→ substituted by α-L-Araf-(1→, →4, 6)-β-D-Galp-(1→ and α-D-Glcp-(1→ at O-4/5/6 position, terminated with α-L-Araf-(1→ and occasionally by α-D-Glcp-(1→. Sulfate groups were substituted at C6 of →4)-α-D-Glcp-(1→. CPP0.05 and S-CPP0.05 had the potential to scavenge DPPH, ABTS, hydroxyl and radical showing reducing power in vitro. CPP0.05 and S-CPP0.05 were found to suppress oxidant stress by improving the enzyme activities of SOD and CAT in dendritic cells (DCs) in the presence of H2O2. Results indicated that S-CPP0.05 showed stronger antioxidant activity compared with CPP0.05. Meanwhile, we found that Nrf2 proteins were significantly increased by the stimulus of polysaccharides with Keap1 decreasing which proved that the antioxidant effect was possibly performed via the Keap1-Nrf2 pathway. The results confirmed that C6 of Cyclocarya paliurus polysaccharides is an effective substitution site for sulfate groups.