Structural Characterization and Immunobiological Activity of Polysaccharides from Astragalus Oyster Mushroom

When added to mushroom growing substrates, edible and medicinal herbs affect the mushrooms’ nutritional and medicinal value. In this study, polysaccharides (P(0)OP-I and P(15)OP-I) were extracted and purified from oyster mushrooms grown on substrates supplemented with 0% and 15% Astragalus roots (P(0) and P(15)), respectively, and their chemical structure and immunobiological activities were compared. P(15)OP-I and P(0)OP-I were extracted using ultrasound-assisted hot water and deproteinized with the Sevage method, depigmented with 30% H(2)O(2), desalted with dialysis, and purified using DEAE-52 cellulose and Sephadex G-100 dextran column chromatography. The molecular weight of P(0)OP-I and P(15)OP-I was 21,706.96 and 20,172.65 Da, respectively. Both were composed of monosaccharides D-mannose, galacturonic acid, D-glucose, D-galactose, and L-arabinose but in different molar ratios, and both were connected by a pyranoside linkage. P(15)OP-I consisted of higher contents of mannose, glucose, galactose and arabinose and lower content of galacturonic acid as compared to P(0)OP-I. Both P(0)OP-I and P(15)OP-I induced NO and TNF-α production but did not show cytotoxic effect or induce ROS generation in RAW264.7 cells. P(15)OP-I showed a stronger ability to promote NO and TNF-α production relative to P(0)OP-I. In vitro experiments showed that the immunomodulatory activity of P(0)OP-I and P(15)OP-I in RAW264.7 macrophages were mediated by the JNK/MAPK, Erk/MAPK, and NF-κB signaling pathways. The results would be helpful for elucidation of the health promoting mechanism of Astragalus oyster mushrooms as a source of neutraceuticals.