Polysaccharides from steam‐processed Polygonatum cyrtonema Hua protect against d‐galactose‐induced oxidative damage in mice by activation of Nrf2/HO‐1 signaling

Polygonatum cyrtonema Hua is cultivated for its edible and medical value. The steam-processed rhizome of P. cyrtonema is the main form for daily consumption and it has been used traditionally in tonics for treating various age-related disorders. The aim of our study was to compare the physicochemical properties and antioxidant activity of polysaccharides respectively extracted from crude P. Cyrtonema (PCPC), and steam-processed P. cyrtonema (PCPS), and to explore a possible underlying antioxidant mechanism.The PCPC with a molecular weight of 4.35 × 103 Da mainly consisted of fructose and trace amounts of glucose, whereas PCPS with 4.24 × 104 Da was composed of fructose, arabinose, glucose, xylose, mannose, galacturonic acid and glucuronic acid. The PCPC had a triple-helical conformation whereas PCPS was a random coil. Both exhibited free radicals- scavenging activity in vitro. In a mouse model of oxidative damage, PCPC or PCPS treatment significantly reversed histopathological alterations, reactive oxygen species (ROS) accumulation and the reduction of antioxidant enzyme activity. They both also promoted Nrf2 nuclear transport by decreasing Keap-1 expression and increasing HO-1 expression. Both in vitro and in vivo, PCPS exhibited more potent antioxidant activity than PCPC.Overall, the results suggest that PCPS has a stronger effect on the prevention of oxidative damage by activating Nrf2/HO-1 antioxidant signaling. This study demonstrates the role of steam-processed P. cyrtonema rhizome and provides valuable perspective for PCPS as a functional agent. © 2022 Society of Chemical Industry.