Structure And Bioactivities Of Polysaccharides From Sclerotium Of Poria Cocos And Their Derivatives

Recently, fungal polysaccharides have been discovered to exhibit many bioactivities, such as antiviral, anti-flammatory, hypoglycemic, hypocholesterolemic and hypotensive. They are good immunomodulators to inhibit the tumor/cancer cells growth without any damage to the normal cells. However, many polysaccharides are water-insoluble, which limits their applications in the medicine field. The chemical modification can improve water solubility of natural polysaccharides to enhance bioactivities, and even give new bioactivities. It has been reported mat the molecular size and chain conformation of polysaccharides in solution affect strongly on their bioactivities. The determination of the structure and chain conformation of the polysaccharides in solution is essential for the understanding of the bioactivity mechanism and the correlation of the structure to bioactivities. Poria cocos is a traditional medicine in China. However, there are few reports on the chain conformation and the molecular size of Poria cocos polysaccharides (the main component of Poria cocos), and some discrepancies among the literature results of molecular weight. In this thesis, several polysaccharides were extracted and purified from Poria cocos sclerotium, and their derivatives were prepared. The chemical structure, weight-average molecular weight (Mw), chain conformation, and antitumor activities of the polysaccharides and their derivatives were studied. The cellular mechanism, as well as the correlation of structure to antitumor bioactivities was investigated. Therefore, this work is in a cross field of polymer chemistry, polymer physics, biochemistry and medicine, and one of the frontiers of polymer science.The innovative points in this work are as the follows. (1) For the first time, the chemical structure and Mw of six polysaccharides extracted from fresh Poria cocos sclerotium were clarified. (2) Five derivatives from water-insoluble (1-3)-B-D-glucan were successfully synthesized, and their structures were reliably determined by two-dimensional NMR spectroscopy (2D NMR). (3) The antitumor bioactivities of sulfated polysaccharides of Poria cocos against gastric carcinoma cells in vitro and in vivo were firstly revealed. (4) It was proved that derivatives from water-insoluble (1-3)-B-D-glucan of Poria cocos possessed good water-solubility and antitumor activities. (S) Based on the modern theory of polymer solution, the chain conformation of the sulfated and carboxymethylated derivatives of (1-3)-B-D-glucan in 0.2 M NaOH solution was determined by light scattering (LS) and viscometry to be expanded flexible chains. Moreover, the chain of the sulfated derivative was more flexible than mat of the carboxymethylated one in the solution. (6) It has been firstly revealed that the sulfated derivatives of (1-3)-B-D-glucan exhibited good antitumor activities against Sarcoma 180(S-180), gastric carcinoma cell strains (MKN-45 and SGC-7901) both in vivo and in vitro, but not damaged the normal cells. (7) It was conformed for the first time that the cellular mechanism of sulfated (1-3)-B-D-glucan against gastric carcinoma tumor cells was to inhibit the proliferation of tumor cells through inducing apoptosis of the cell.The main contents and conclusions in this thesis are divided into the following. Six polysaccharides were extracted sequentially from the fresh sclerotium of Poria cocos cultivated in China using 0.9% NaCl (PCS1), hot water (PCS2), 0.5 M NaOH (PCS3-I and PCS3-II), and 88% formic acid (PCS4-I and PCS4-II). Their chemical and physical characteristics were determined by infrared spectroscopy (IR), gas chromatography (GC), GC-MS methylation analysis, 13C NMR spectroscopy, elementary analysis (EA), protein analysis, size exclusion chromatography combined with laser light scattering (SEC-LLS), light scattering and viscometry. The results indicated that the polysaccharides PCS1, PCS2 and PCS3-I were heteropolysaccharides containing D-glucose, D-galactose, D-mannose, D-fucose and D-xylose; the predominant monosaccharide was D-glucose exc...