Purification, structural characterization and antioxidant mechanism of Noni polysaccharide based on Nrf2/HO-1/NQO1 signaling pathway

The homogeneous Noni polysaccharide was obtained by ultrasonic-assisted hot water extraction, sevage method deproteinization, dialysis, ethanol precipitation, DEAE-52, Sephadex G-200. Noni polysaccharide were mainly composed of Rha, Ara, Gal, Gal-AU and Glc-AU, and its content mole ratio were 1.28%: 5.87%: 8.66%: 83.44%: 0.75%. The chemical structure shows that Noni polysaccharide mainly by →4)-α-D-GalpA-6-OMe-(1→ , and had small →3, 4)-β-D-Galp-(1→ connected form the main chain. Branched chain was mainly composed of α-D-GalpA-6-OMe-(1→ connected to the sugar residues →3, 4)-β-D-Galp-(1→ O-3 position. In vitro antioxidant experiment result showed that max scavenge rates for Noni polysaccharide on ABTS+ , hydroxyl free radical and DPPH free radical were 96.5%, 95.3% and 95.6%, respectively. In vivo antioxidant experiment result showed that the Noni polysaccharide could effectively increase content for SOD in serum and reduce activity for MDA in liver tissue. In addition, preliminary antioxidant mechanism results showed that Noni polysaccharide had significant regulatory effects on the down-regulation of Nrf2, HO-1, NQO1 proteins and genes related to oxidative stress signaling pathways in RAW264.7 cells. It can effectively improve oxidative stress damage of RAW264.7 cells induced by H₂O₂ and inhibit abnormal decrease of level for CAT, SOD, GSH-Px, and the abnormal increase for MDA.