Regulating Lipid Metabolism Effect And Modulation On Intestinal Microfloras Of Polysaccharide Extracted From Gracilaria Lemaneiformis

Gracilaria Lemaneiformis was a traditionally edible seaweed and became one of the four commercial seaweed in China in recent years which contained abundant polysaccharide,vitamin,mineral substance and low fat.It was widespread that Gracilaria Lemaneiformis was benefit for weight control and blood fat adjusting around folks.Polysaccharide is one of its major bioactive compounds,and previous studies have proven that polysaccharide extracted by acid from Gracilaria Lemaneiformis possessing excellent immunoregulatory,hyperglycemic and glucolipid metabolism regulating activities.In the present study,a critic acid extraction was used to prepare the Gracilaria Lemaneiformis polysaccharide,and the basic chemical composition,primary structure and in vitro and in vivo digestibility of Gracilaria Lemaneiformis polysaccharide were determined.The regulating lipid metabolism effect and its mechanism and modulation on intestinal microfloras of Gracilaria Lemaneiformis polysaccharide were carried out,setting the theoretical foundation of the R&D from Gracilaria Lemaneiformis polysaccharide to health food.Main results of the study were listed as follows:?1?The GLP was prepared by critic acid,and its basic chemical composition and primary structure were measured subsequently.The extraction yield of GLP was 22.75 ± 0.45% with a molecular weight of 31.5 kDa.The contents of total carbohydrate,sulfate,uronic acid,ash,moisture and protein were 59.01 ± 0.91%,22.85 ± 0.80%,10.41 ± 0.28%,17.83 ± 0.43%,7.52 ± 0.28%,1.57 ± 0.37%,respectively,while reducing sugar and phenols were not detected.GLP was composed of galactose,glucose,fucose and mannose with a molar ratio of 9.16 : 6.57 : 1.00 : 0.61.Results of methylation analysis showed that the main linkage form of GLP was?1?6?-linked glycosidic bonds,besides,there were a few glycosidic bonds such as?1??-linked,?1?3?-linked and?1?4?-linked in GLP.There was no three helix conformations in GLP.?2?We illustrated the in vitro and in vivo digestive characteristics of GLP.The results presented that GLP was lightly degraded from 31.63 ± 0.20 kDa to 30.57 ± 0.23 kDa during stimulated gastrointestinal digestion.When GLP was given into mice's gastrointestinal by gavage,a slight fluctuation was observed in the blood glucose level.In addition,the glycemic index?GI?of GLP was 38.39,while that of glucose was 100.Results above presented that GLP was a low-GI food helping body maintaing health condition.?3?We demonstrated the modulation on normal mice cecum microfloras of GLP by high-throughput sequencing technology.The results indicated that GLP increased the SCFA contents as well as the moisture of normal mice fecal and promoted the growth of SCFA producer such as Peptococcus,Roseburia,Butyricicoccus,Coprococcus₁ and uncultured_bacterium_fRuminococcaceae.However,the diversity of mice cecum microfloras was not improved significantly.Thus,GLP contributed to keeping the gut in good health.?4?40-day-high-fat-diet induced hyperlipidemia mice were used to evaluate the regulating lipid metabolism effect of GLP.The results showed that 42-day-GLP-intervention contributing to significantly lower the serum total cholesterol,triglyceride and free fatty acid levels as well as the alanine transaminase and glutamic oxalacetic transaminase activity of high-fat-diet mice,indicating that GLP regulated the lipid metabolism,suppressed liver injury and promoted the immunoregulatory.Moreover,GLP could effectively alleviate the accumulation of fat induced by high-fat diet on the premise of not affecting the food or water intake of the high-fat-diet mice.?5?The mechanisms of regulating lipid metabolism of GLP and alleviating liver injury were explored by animal experiment,RT-qPCR,UPLC-MS and 16 s rDNA sequencing technology.And the results elucidated that GLP facilitated fatty acid oxidation by promoting the expression of PPAR?,ACS and CPT1 a indirectly,and accelerated the conversion of cholesterol to bile acids by promoting the expression of LxR? and CYP7A1 followed by exhausting the secondary bile acids such as TLCA,GDCA,GUDCA and TUDCA in fecal.In addition,results of high-throughput sequencing showed that GLP might reduce the level of hydrophobic bile acids DCA and CDCA by promoting the relative abundances of Coprococcus₁,Alistipes,Prevotellaceae_UCG-001,and increase the level of hydrophilic bile acids UDCA and TUDCA by promoting the relative abundances of Roseburia of high-fat-diet mice cecum simultaneously,which might be devoted to suppressing liver injury induced by high-fat diet.