| Dendrobium nobile Lindl.(DNL),Orchidaceae,is a well-known herbal medicine.It has been identified to possess multi-functions in terms of adjusting immunity,regulating blood pressure,promoting the secretion of body fluid and reducing peripheral vascular obstruction.The pharmacological effects of DNL might be attributed to its chemical constituents and bioactive ingredients,including polysaccharides,phenanthrene,coumarin,flavone,cinnamate,sesquiterpene,alkaloids,etc.Among them,polysaccharides have been demonstrated to exhibit a wide range of bioactivities,such as antioxidant,immune-enhancing,hypoglycemic and antitumor effects.In the thesis,the main objectives of this study were to extact,purify and characterize the detailed chemical structure a purified fraction of polysaccharides from DNL,and further investigate the conformational properties and computer modeling to partially establish the structure and conformation relationships.The ethanol-induced gastric ulcer protective effect of polysaccharides from DNL and the related mechanisms was employed by rat model.Nowadays,traditional water extraction(TWE)is the most commonly used method to extract polysaccharides.However,longer extraction time,higher temperature and lower extraction yield are drawbacks of TWE,resulting in the degradation of polysaccharides.Comparing above,PEG as a kind of green solvent is easy and cheap to use with low flammability,nonvolatility,completely non-halogenated,low toxicity and biodegradability.In order to achieve higher yield of extraction,response surface methodology(RSM)has been used increasingly to optimize processing parameters.Highest JCP yield 15.23 ± 0.57%that agreed closely with the predicted yield 15.57%were obtained under the optimal condition as follow:extraction temperature,600C;ultrasound power,195 w and the concentration of polyethylene glycol-200(PEG-200)solution,45%.FT-IR analysis revealed the general characteristic absorption peaks of both polysaccharides with water extraction and PEG-200 solvent extraction(JCPp).Thermal analysis of both polysaccharides was done with Thermal Gravimetric Analyzer(TGA)and Differential Scanning Calorimeter(DSC).Antioxidant activities of two polysaccharides were also compared with no significant differences between them in vitro.A water-soluble polysaccharide(JCP-40)from Dendrobium nobile Lindl.was extracted and purified.Based on HPSEC analysis,average molecular weight of JCP-40 was 67.46 kDa.Combined with&monosaccharide composition analysis,methylation analysis,1D/2D NMR spectroscopy,the structural features of JCP-40 was proposed as follows:the major sugar residues of JCP-40 were consisted of→4)-β-D-Manp-(1→(74.6%)and→4)-β-D-Glep-(1→(25.4%).Acetyl groups were found attached to the 0-2 or O-3 positions on mannosyl residues based on NMR results.(?)It is difficult to analysis the structure of polysaccharide,moreover,the relationship of structure of Dendrobium nobile Lindl.polysaccharide and conformational information was limited to establish.In order to analysis the relationship,computer simulation of molecules was used to allowed for the visualization of the structure and conformation of polymers has played a profound role evaluating the conformational properties.The modeling of GMs with different repeat unit number possessed a rigid conformation.For both Cn and Lp,a significantly increasing trend was observed at the initial stage(the repeat unit number from 30 to 120),then almost remained constant when the repeat unit number from 120 to 240,showing that the influence of molecule weight could not significantly affect chain flexibility in this range.The Rg value of JCP-40 derived from modelling simulation was 18.98 nm,which was higher than that from HPSEC(12.32 nm).The conformational parameters(derived from Rg vs Mw and[η]vs Mw)from HPSEC and molecular modeling both suggested a random coil conformation of JCP-40.Ethanol is one of the aggressive factors that increase the risk of gastriculcer formation.Purified polysaccharide(JCP)where protein and starch was removed was used to protect the ethanol-induced gastric ulcer.H-JCP pretreated could effectively prevent the formation of ethanol-induced gastric ulcer according to histological examination analysis,JCP treatment showed clear evidence of fewer inflammatory cells and less hemorrhage in comparison with those from the vehicle group.H-JCP had antioxidant effects on ulcer healing,accelerated for the EGF and PGE content in rats,effectively inhibit the phosphorylation of ERK and JNK.On the other hand,the increased expression of MMP-2 and MMP-9 in ethanol-treated rats is substantially reduced to control level and even less than that by JCP pretreatment.JCP-40 considerably reduced the level of gastric tissue damage in vivo.Compared with histological examination of haematoxylin and eosin(H&E)stained stomach tissues of vehicle group,JCP-40 treatment showed clear evidence of fewer inflammatory cells and less hemorrhage.Moreover,H-JCP-40(200 mg/kg,b.w)could inhibit the ethanol-induced TNF-a production to prevent the gastric ulcer by ethanol and significant reduced IL-1β content. |
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