| Mushrooms have been treasured as a natural way to support health for thousands of years; they are a very popular food in Asia. Moreover, it has been demonstrated that many kinds of mushrooms, have medicinal or functional properties in remedies for diseases, including Lentinus edodes, Ganderma lucidum, Trametes versicolor,Schizophyllum commune, and flammulina velutipes, etc. Over the past decade, the polysaccharides from edible mushrooms have received increasing attention and been extensively used for preventing or attenuating human diseases, such as cancers,inflammatory diseases, hyperlipidemia and diabetes et al. As mentioned in Chinese traditional medicinal book, the edible mushroom-Pleurotus eryngii which belongs to Pleurotus, Pleurotaceae, Agaricales, Basidiomycetes, may have potential biological functions. However, little are known about what are the bioactive components in P.eryngii and what is the mechanism behind for their biological functions. In this study,we have investigated the comprehensive functions of polysaccharides in P.eryngii and clarified the mechanism of inhibition of lipid accumulation. The results can be summaried as following:1. Firstly, we investigated the function of water-soluble polysaccharide form the fruinting bodies of P.eryngii (PEPE) using in vivo mouse models and in vitro biochemistry analysis. The results showed PEPE significantly removed the free radicals, and increased the activities of antioxidant enzymes in a liver-injury mouse model. Furthermore, in a high-fat-load mouse model, PEPE not only remarkably decreased the lipid levels of total cholesterol, total triglyceride, and low-density lipoprotein cholesterol, but also resulted in an increase of high-density lipoprotein cholesterol. Histopathological observations also indicated that PEPE could effectively prevent excessive lipid formation in liver tissue. All results indicated PEPE can be used as a valuable functional food additive for antioxidant and hypolipidemic treatment.2. HPLC results indicated that PEPE was composed of 5-7 different components.To further investigate which substance is responsible for its biological effect, PEPE was purified using anion exchange column and Sephadex gel column. Meanwhile, to quickly identify the bioactive component, we established the macrophage-derived foam cell model which induced by oxidized low density lipoprotein (oxLDL) in vitro.The results showed PEPE significantly reduced lipid content in foam cell in dose-dependent manner. Furthermore,the single component PEPE-A1 and A2, which obtained through fractionation of DEAE-52 and Sephadex G-100 both significantly inhibited the lipid accumulation in foam cell. At the 200 μg/ml concentration of PEPE-A1 and PEPE-A2, the lipid content were reduced to 20.71 ±6.00% and 18.49 ±1.59% of the control group induced by oxLDL, respectively.3. The excreted polysaccharides from submerged culture have received more and more attentions mainly due to their rapid completion by fermentation. Most importantly, since excreted polysaccharides can be extracted efficiently and easily, it makes the industrialized production feasible. Thus, we also extracted the excreted polysaccharide (EP) from submersion culture of P. eryngii and obtained its purified fraction (EP-1). Most excitingly, we found EP and EP-1 were both able to significantly reduce the amount of lipid droplets in a dose-dependent manner.4. By the analysis of IR,GC,and HPLC,the purified polysaccharides (PEPE-A1,PEPE-A2 and EP-1) were estimated to be 30-38 kDa for the average molecular weight with the monosaccharide composition mainly composed of D-types of mannose, glucose and galactose. The main glycosidic linkage was β (1→3)-glucan branched at O-6 by α-D-glucose, on average, every 1.7 residues of the backbone.They shared nearly the same structural features including molecular weight,monosaccharide composition, configuration and position of glycosidic linkages,which indicated PEPE-A1, PEPE-A2 and EP-1 are identical.5. All above results showed the bioactive polysaccharides in the fruiting bodies or submerged submersion culture of P. eryngii have effects on lipid content in foam cell. However, little is known about how they possess the inhibitory effect of lipid deposition on foam cells. The homeostasis of intracellular lipid was determined by the balance of cholesterol uptake and efflux. Here, SR-A and CD36 are responsible for the uptake of oxLDL, and the ATP-binding cassette transporter A1 and G1 are related with the cholesterol efflux. As the upstream of the transcriptional factors, LXRα,RXRα. PPARγ regulated these progresses. Here, we investigated the effect of polysaccharide on the expressions of these lipid-metabolism-related candidate genes.The results showed EP is able to cause the down-regulation of CD36 (i.e., a scavenger receptor) on both transcription and protein levels. Therefore, the bioactive polysaccharides may lower lipid accumulation in foam cells by decreasing the uptake of oxLDL.6. Since EP can be obtained by fermentation in a mass-production and can be purified easier, the optimization condition of submerged culture for EP production was investigated. The results suggest the optimal recipe as 3.5% galactose, 0.3%KH2PO4, 0.5% peptone and at pH 6.0. As a result, under these optimal culture conditions, maximum EP content reached 5.92 g/1, which is about 2.55 times higher than that in the basal medium.Collectively, the findings presented in this report provide direct evidence that links the purified polysaccharide moiety with its biological function of lipid deposition in a foam cell model. |
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