Studies on an antitumor polysaccharide RBS derived from rice bran. I. Preparation, physico-chemical properties, and biological activities of RBS

Abstract

An antitumor polysaccharide, RBS (rice bran saccharide), has been prepared from rice bran with hot water extraction. Potent antitumor activities against sarcoma-180 solid tumors were observed not only by intraperitoneal administration but also by oral administration of purified RBS (RBS30F1). Physico-chemical properties of RBS30 are follows: (1) it is a white powder and soluble in water, (2) pH of the aqueous solution is neutral, (3) it is a glucan constructed by glucose as a sole sugar component, (4) it has α-1→6-glucosidic bond as a main frame including a small amount of α-1→4-glucosidic bond, (5) it contains a small amount of protein and minerals connected to the polysaccharide, and (6) its molecular weight is over one million. Since it is hardly known that α-glucan has potent antitumor activities, the fact mentioned above would be of interest in the relationship between structure and biological activities of polysaccharides. Antitumor activities of RBS30F1 are thought to be a kind of host mediated action that stimulates the immunological activities of the host, because the substance had no cytocidal activity against an animal cell line in vitro. No acute toxicity against rats was observed in the case of oral administration of crude RBS (RBS30).