Anti-tumor and macrophage activation induced by alkali-extracted polysaccharide from Pleurotus ostreatus

Pleurotus ostreatus is popularly consumed as traditional medicine and health food for enhancing immune function in China. Polysaccharides from mushroom have been demonstrated to possess a wide range of health beneficial properties. This study was carried out to elucidate the immunomodulating effects and molecular mechanism involved in the in vivo and in vitro anti-tumor activities of alkali-extracted polysaccharide (WPOP-N1) from the fruiting bodies of P. ostreatus. The results showed that WPOP-N1 significantly inhibited the tumor growth of Sarcoma 180 tumor-bearing mice, and markedly increased the secretion level of TNF-α in serum. In addition, WPOP-N1 enhanced the phagocytic capability of peritoneal macrophages in vitro. Furthermore, the secretion of TNF-α and NO and the amount of TNF-α and iNOS transcript were increased significantly when the peritoneal macrophages were exposed to WPOP-N1. Meanwhile, Western blot analysis revealed that the stimulation of peritoneal macrophages by WPOP-N1 induced the phosphorylation of p65 and a marked decrease of IκB expression. These results suggest that WPOP-N1 could activate macrophages through NF-κB signaling pathway, and the anti-tumor effects of WPOP-N1 can be achieved by its immunostimulating property.