Structure characterization and antitumor activity of a polysaccharide from the alkaline extract of king oyster mushroom

• One polysaccharide (KOMAP) is successfully from the king oyster mushroom.
• KOMAP markedly inhibits the growth of implanted Renca tumor in mice.
• KOMAP enhances the immune functions of mice implanted with Renca tumor.

A water-soluble polysaccharide, designated as KOMAP, was isolated and purified from the alkaline extract of king oyster mushroom, which was composed of glucose (Glc), mannose (Man) and arabinose (Ara) in a molar ratio of 6.2:2.1:2.0. It had an average molecular weight of 2.1 × 104 Da. GC–MS analysis revealed that KOMAP was a linear structure of the polymer with a backbone composed of β-1,4-linked glucopyranosyl and β-1,3,6-linked mannopyranosyl units, which was terminated with α-1-linked arabinofuranosyl unit at C-6 position of β-1,3,6-linked mannopyranosyl residue along the main chain in the ratio of 3.1:1. The results in the animal experiment showed that 50, 100 and 200 mg/mL of KOMAP not only inhibited the tumor growth, but also increased relative thymus and spleen indices, LPS- or ConA-induced lymphocytes proliferation, and serum cytokine IL-2, TNF-α, and IFN-γ levels, as well as the activities of NK cells and CTLs in spleen of Renca tumor-bearing mice. In summary, our data indicate that the KOMAP exerts effective immunoregulatory and anti-tumor activities in vivo.