Abstract: Ganoderma lucidum polysaccharides (GLPs), one of the most important bioactive substances in Ganoderma lucidum, have excellent health benefits and therefore attract great research interest. The purpose of this study was to explore the extraction and purification of GLPs derived from Ganoderma lucidum strain G055 and to evaluate the mechanism underlying the protective effect of GLPs against oxidative stress injury in human skin fibroblast (HSF) cells. The crude polysaccharides were deproteinated by the Sevag method and separated into two fractions named GLP I and GLP II by DEAE-52 ion exchange chromatography. Using an orthogonal array design, the optimal extraction conditions were determined as 1:35 (m/V), 65 ℃ and 1.5 h for solid-to-solvent ratio, extraction temperature and time, respectively. Experiments performed under these conditions gave GLP extraction yield of (47.70 ± 0.50)% with good reproducibility. The protective effect of the crude GLPs as well as GLP I and GLP II on H2O2-induced oxidative stress injury in HSF cells was evaluated and the underlying mechanism was studied from the perspective of the antioxidant enzyme system and the Keap1 (Kelch-like ECH-associated protein-1)-Nrf2 (NF-E2-related factor 2)/ARE (antioxidant response element) signaling pathway. In the experiments evaluating their effects on preventing and repairing oxidative stress injury in HSF cells, we found that all three polysaccharides could significantly improve the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) (P < 0.05), and decrease the levels of reactive oxygen species (ROS) and malondialdehyde (MDA), a product of lipid peroxidation, in cells. Furthermore, they could activate the key regulatory factor Nrf2 in the Keap1-Nrf2/ARE signaling pathway and inhibit the negative regulatory factor Keap1 thereby promoting the expression of downstream antioxidant enzyme genes (NQO1 and HO-1). Therefore, the protective and repairing effect of GLPs may be closely related to regulating the levels of antioxidant enzymes and activating the Keap1-Nrf2/ARE signaling pathway.

Key words: Ganoderma lucidum polysaccharides, extraction and purification, protection, oxidative stress damage, Kelch-like ECH-associated protein-1-nuclear factor-erythroid 2-related factor 2/antioxidant response element signaling pathway