Antitumor Activity and Structural Characterization of Glucans Extracted from Cultured Fruit Bodies of Grifola frondosa

Abstract

Polysaccharides in the cultured fruit body of Grifola frondosa were extracted successively with hot water, aqueous zinc chloride, and cold and hot aqueous sodium hydroxide containing urea. The antitumor effect and structural features of the extracted compounds were examined. The above extraction gave water-soluble glucan fractions together with water-insoluble heteroglycan fractions. The heteroglycan fractions were composed of glucose, xylose and mannose. The zinc chloride extraction gave only a small quantity of polysaccharide. The structural characteristics of these polysaccharides were deduced from the results of gel filtration, methylation, enzymic degradation, and ¹³C-nuclear magnetic resonance (NMR) spectroscopy. The hot water extract contained a large amount of α-1, 4-glycosidic linkages (about 50%) digestable by α-amylase, and also contained α-1, 6-, β-1, 6-, and β-1, 3-linkages. The water-soluble glucan fractions extracted with cold and hot sodium hydroxide contained more 6-branched glucosyl unit in every three 3-substituted β-glucosyl units. All of these water-soluble and insoluble fractions showed potent antitumor activity against the solid form of Sarcoma 180 tumor in ICR mice. The activity of the hot sodium hydroxide extractable, water-soluble fraction was the strongest. The antitumor activity was positively correlated with the content of 6-branched β-1, 3-glucan in these water-soluble fractions.