Structural Characterization And Functional Evaluation Of Hepatoprotective Polysacchairde Rfom Dendrobium Huoshanense

Dendrobium huoshanense is a precious medicinal plant in China, and its stem (named as Shihu) has been used as a nutritious and healthy beverage. Polysaccharide is one of the most important components in D. huoshanense, which possesses antioxidative activity, immunomodulation and other bioactivities. In this study, several polysaccharide components were obtained from D. huoshanense via hot water extraction, anion-exchange and sephadex gel chromatography, and the structural features of these polysaccharides were analyzed by chemical and spectral methods. Moreover, the hepatoprotective effects of the polysaccharides were evaluated via the liver injury model caused by carbon tetrachloride (CCl4), which aimed to clarify the relationship between structure and hepatoprotective effect of these polysaccharides. The results were listed as follows:1. Crude D. huoshanense polysaccharide (DHP) was fractionated into four components by DEAE-cellulose anion exchange resin. Among them, DHP1was proved to be neutral polysaccharide with the relative molecular weight of10KDa, consisting of glucose, galactose and a little of mannose. The other three polysaccharides were acidic polysaccharides with the larger molecular weight (more than5000KDa). DHP2and DHP3were mainly composed of galactose, glucose and arabinose, while DHP4was mainly composed of galactose, arabinose, rhamnose and glucose; As compared with the three acidic polysaccharides, the scavenging effects of DHP1on DPPH radical and hydroxyl radical were better, and the inhibitory effect of this polysaccharide on lipid peroxidation was higher, suggesting that DHP1was the main antioxidative polysaccharide component in DHP;2. Hepatopratective effects of the different polysaccharide components from D. huoshanense were evaluated by the liver injury model caused by CCl4in mice. The results showed that DHP1pretreatment could enhance the liver resistance against CCl4toxicity, lower the serum levels of alanine aminotransferase (ALT) and aspertate aminotransferase (AST), inhibit the over-expression of malondialdehyde (MDA) in the liver tissue and restore the activities of superoxide dismutase (SOD) and catalase (CAT), suggesting the good prevent effect on liver injury;3. DHP1was further fractionated into two polysaccharide fractions DHP1A and DHP1B by Sephadex G-100gel chromatography. DHP1A was mainly composed of glucose and mannose with a molecular weight of6.7KDa. Methylation and nuclear magnetic resonance (NMR) analysis indicated that the backbone of DHP1A mainly consisted of1→4linked a-glucose and1→4linked mannose; DHP1B was composed of glucose with a molecular weight of3.51KDa, and its backbone was mainly composed of1→4and1→4,6linked glucose. In vitro antioxidative assays indicated the antioxidative activity of DHP1A was higher than that of DHP1B, demonstrated by the higher scavenging effects the DPPH and hydroxyl radicals, as well as the inhibition effect of DHP1A on the lipid peroxidation;4. Hepatoprotective effect of DHP1A was further evaluated. The results showed that DHP1A ingestion attenuated the liver injury caused by CCUin mice, which decreased the expressions of MDA and8-OHdG; Furthermore, DHP1A exerted the regulating effect on the expression of various inflammatory molecules, including tumor necrosis factor (TNF)-α、interleukin (IL)-1β、monocyte chemotactic protein (MCP)-1、 macrophage inflammatory protein (MIP)-2and CD68antigen. The further investigation implied that the hepatoprotection of DHP1A was possibly related to the disturbance effect on the activation of nuclear factor (NF)-κB in the process of CCl4liver toxicity.