Abstract

Though it has been reported that β-glucans or protein-binding hetero-glucans isolated from mushrooms have antitumor activity, the antitumor and antimetastatic actions of purified, structurally defined polysaccharides (such as β-glucans) have not been proven yet. A new low molecular weight (approximately 100 kDa) β-glucan was isolated from Aureobasidium pullulans black yeast, and was found to have low viscosity and to be water-soluble. The industrial production of this β-glucan was achieved from the culture media of A. pullulans. The effects of water-soluble low-molecular-weight (LMW) β-(1→3) and 50-80% branched β-(1→6) glucan isolated from A. pullulans on tumor growth and metastasis to the liver were examined in mice intrasplenically with implanted colon 26 tumor cells. In addition, to clarify the antitumor and antimetastatic actions of LMW β-(1,3-1,6) glucan, the effects on immune functions in the small intestine were also examined. The intraperitoneal (5 and 15 mg/kg) and oral (50 mg/kg) administration of LMW β-(1,3-1,6) glucan inhibited the tumor growth and liver metastasis in mice intrasplenically implanted with colon 26 cells. The numbers of natural killer (NK)- and interferon (IFN)-γ-positive cells in the small intestine of colon 26-bearing mice were lower than those in normal mice. The intraperitoneally and orally administered LMW β-(1,3-1,6) glucan prevented the reduction of the number of NK- and IFN-γ-positive cells induced by the tumor growth after implantation of colon 26 cells. These findings suggest that the antitumor and antimetastatic actions of LMW β-(1,3-1,6) glucan may involve the enhancement of intestinal immune functions through increases in NK- and IFN-γ- positive cell numbers.