Review Mushrooms: A Source of Immunomodulating and Antitumor Polysaccharides

Abstract

The number of mushrooms on Earth is estimated at 1,40,000 of which may be only 10% are known. Meanwhile, of those ~ 14,000 species that we known today, about 50% are considered to possess varying degrees of edibility, more than 2,000 are safe and about 700 species are known to possess. In modern medicine, they represent a source of polysaccharides with antitumor and immunostimulating properties.These polysaccharides are present mostly as glucans with different types of glycosidic linkages, such as (1→3),(1→6)-β-glucan, (1→3)-α-glucans, and some are true heteroglycans. Different chemical modification is often carried out to improve the antitumor activity of polysaccharides, clinical qualities and water solubility. Two main procedures for chemical improvement are: modification of mushroom polysaccharides by Smith degradation (oxydo-reductohydrolysis) and activation by the method of formolysis. Carboxymethylation is another chemical method that transforms β-glucans into a water-soluble form. The commercial polysaccharides Lentinan, Schizophyllan and PSK (krestin) are widely used as antitumor material. Human clinical studies proved the beneficial activity of treatment with some other medicinal mushroom species also. These polysaccharides prevent oncogenesis, show direct antitumor activity against various allogeneic and syngeneic tumors and prevent tumor metastasis. Polysaccharides from mushrooms do not attack cancer cell directly, but produce their anti-tumor effects by stimulating macrophages such as natural Killer cells (NK-cell), T-cell, B-cell and macrophage-dependent immune system responses. The present review analyses the different chemical composition, structural correlations, chemical modifications and mode of actions as antitumor polysaccharides derived from fruit bodies and cultured mycelium in selected examples of medicinal mushrooms.