The Structure Of Sulfated Polysaccharides From Sea Cucumbers And Their Mechanism On Regulating Metabolic Diseases Caused By Overnutrition

Metabolic syndrome involves a group of risk factors,including obesity,insulin resistance,impaired glucose tolerance,dyslipidaemia and hypertension,which increase the risk of metabolic diseases,such as type 2 diabetes mellitus,nonalcoholic steatohepatitis,and cardiovascular disease.Nowadays,metabolic disease has become a major threat to human health.Although genetic factors can determine the propensity of an individual to develop metabolic syndromes,the sharply increasing morbidity of related diseases in recent decades reflect environmental and lifestyle changes,where dietary change represents a major contributor.Functional foods from natural sources are potential choices for addressing metabolic diseases as they provide many health benefits with a low level of adverse side effects.Sulfated polysaccharides from sea cucumbers have aroused the interest researchers because of their well-repeated structure and significant bioactivities.In recent years,more and more studies indicated that sulfated polysaccharides from sea cucumbers can alliveate metabolic diseases caused by over nutrition,which decided by their structure.Excessive food intake(espcialy high-fat diet,HFD)has been a major risk for public health,increasing the likelihood of chronic metabolic disorders,particularly obesity,hyperlipidaemia,insulin resistance,low-grade inflammation,cardiovascular disease,fatty liver disease,and hypercholesterolemia.Based on the former research of our group,we used four well-defined sulfated polysaccharides from sea cucumbers for research objects.NMR,MS,AFM and SEC-MALLS were used here to identify their structures.Meanwhile,the effect of sulfated polysaccharide on metabolic diseases and possible mechanism were investigated in the medol of rodent fed on HFD.The main content are as following:1.The characterization of structure of fucoidan in the sea cucumber P.graeffei.by ES-CID-MS/MS and NMR.The carbohydrate sequence of fucoidan was determined by negative-ion electrospray tandem mass spectrometry(ES-MS)with collision-induced dissociation of the oligosaccharide fragments,which was obtained by mild acid hydrolysis.The structure determinations were completed by NMR for assignment of the anomeric conformation and the linkage,and it was unambiguously identified as a tetrasaccharide repeating unit with a backbone of[→3Fuc(2S,4S)α1→3Fucα1→3Fuc(4S)al→3Fucα1→]n.The glycosidic bonds between the non-sulfated and 2,4-O-disulfated fucose residues were selectively cleaved,and highly ordered oligosaccharide fragments with a tetrasaccharide repeating unit were obtained.The highly 4-0-and 2,4-0-sulfated groups of the polysaccharide deserve further developments for Pharmacia use.2.Macromolecular properties and hypolipidemic effects of four sulfated polysaccharides from sea cucumbers.The chain conformation,determined by a combination of AFM and SEC-MALLS-RI,indicate that fucosylated chondroitin sulfate(fCS)from Pearsonothuria graeffei(fCS-Pg)and Isostichopus badionotus(fCS-Ib),and fucoidan from P.graeffei(fuc-Pg)were assigned as a random coil conformation with polysaccharide chain outstretched,while I.badionotus(fuc-Ib)was assigned as a spherical conformation and exhibited high viscosity.Fuc-Pg and fuc-Ib with higher molecular weights had a greater impact in inhibiting pancreatic lipase activity in vitro.However,fCS-Pg,fCS-Ib and fuc-Pg with random linear conformation exhibited excellent hypolipidemic activity in Sprague-Dawley rats(SD rats)fed on high-fat diet,whereas fuc-Ib showed only a modest effect.Our results indicate that structural characteristics,including side branch and sulfation pattern can affect the chain conformation of polysaccharides,which determine their physicochemical properties and hypolipidemic activity.3.The effect of fCS-Ib and its oligosaccharide(DfCS-Ib)on metabolic diseases caused by over nutrition.Both fCS-Ib and DfCS-Ib showed multi-function on metabolic syndromes in C57BL/6 mice fed on HFD.Both of them can inhibit obesity by reducing weight gains,liver,kidney,and fat tissue weight with on effect on food intake.Meanwhile,they can reduce TG,TC,LDL-C,glucose,TNF-a,and IL-6 levels,while improve HDL-C level in serum.They can also maintain normal histomorphology of liver and fat tissue.In addition,fCS-Ib and DfCS-Ib adjust the abnormal expression of PPARγ,leptin,aP2,and F4/80 in fat tissue to maintain the normal function of fat tissue,promote the normal secretion of adipokine,and allivate inflammation cased by HFD.4.FCS-Ib and DfCS-Ib reshaped gut microbiota in HFD-fed mice.Bacterial diversity and richness was not changed by HFD.Treatments with fCS-Ib and DfCS-Ib exerted almost no influence on bacterial diversity but increased richness.Especially for fCS-Ib,the richness was much improved.FCS-Ib and DfCS-Ib exerted different influence on bacterial composition in HFD-fed mice.HFD caused Firmicutes and Bacteroidetes(F/B)from 0.37 to 1.18.Both the fCS-Ib and DfCS-Ib could reverse the ratio of Firmicutes and Bacteroidetes(F/B).Remarkably,fCS-Ib reverse the ratio of F/B to 0.28,even lower than the control group.DfCS-Ib alleviated the ration of F/B to 0.94.The effect of DfCS-/Ib was not powerful as that of fCS-/Ib.At the genus level,both fCS-Ib and DfCS-Ib increased the proportion of Barnesiella.Notably,the populations of Bacteroides was much higher in the fCS-Ib group than that of other three groups.While,a dramatic increase in Allobaculum was found in the DfCS-Ib group.The fCS-Ib group was composed of Bacteroidaceae,Bacteroidales,Bacteroides,and Alistipes,belonging to Bacteroidetes.The DfCS-Ib group was dominated by Erysipelotrichales,Erysipelotrichaceae,and Allobaculum,belong to Firmicutes.5.FCS-Ib and DfCS-Ib restored energy metabolism in the liver of HFD-fed mice.HFD changed the mRNA expression of liver metabolism,especially in lipid and carbohydrate metabolism.Under excessive fat and sucrose for six weeks,we found that over nutrition activated lipid synthesis,reduced lipid degradation,increased lipid trafficking,and disturbed glycolysis/gluconeogenesis metabolism.Many of these gene are critical for energy balance and associated with metabolic diseases.Both fCS-Ib and DfCS-Ib could restore the liver gene expression profiling.Especially,DfCS-Ib could alleviate most genes involving in lipid/carbohydrate metabolism.