Hypolipidemic Activity And Its Mechanism Of Porphyra Haitanensis Polysaccharides

In recent years,hyperlipidemia has become a global public health problem,and has seriously affected people’s physical and mental health and quality of their life.At present,statins are widely used in the treatment of hyperlipidemia.The long-term use of these hypolipidemic drugs will lead to gastrointestinal discomfort,rash,myalgia and high side effects of liver transaminase.Therefore,the intervention of food nutritional components in diet induced hyperlipidemia has become a new research hotspot in this field of food nutrition.Porphyra haitanensis is an important economic seaweed cultivated on a large scale in Fujian Province.Polysaccharides are one of the main components of Porphyra haitanensis.Studies have shown that Porphyra haitanensis polysaccharides have hypolipidemic activity and significantly reduce serum total cholesterol(TC),triglyceride(TG)and low-density lipoprotein(LDLC)in mice.However,the relationship between the hypolipidemic activity of Porphyra haitanensis crude polysaccharides(PHP)and its structure,and the hypolipidemic mechanism of the"gut-liver"axis of PHP have not been reported.Therefore,the PHP was taken as material.The relationship between the structure of PHP and the hypolipidemic effect was investigated.Its preventive effect on hyperlipidemia in Mesocricetus auratus through dietary intervention,and the relationship between PHP,intestinal flora,hepatic lipid metabolite and liver gene based on the"gut-liver"axis were contrasted.The molecular mechanism of PHP on reducing blood lipid in Mesocricetus auratus fed with a high-fat diet was revealed.The results were as follows:(1)Polysaccharides was extracted from Porphyra haitanensis.The polysaccharide was separated and purified by DEAE Sepharose FF,Sephacryl S-400 HR column and ultrafiltration.The components obtained after separation and purification were characterized by FT-IR,SEC-MALLS-RI,GC-MS,1D NMR and 2D NMR.The result showed that PHP was composed of two components(PHP0.5-1-UF and PHP1.0-1-UF).PHP0.5-1-UF was composed of galactose with a weighted average molecular weight of 6.68×10~6(±3.17%)g/mol,sulfated content was6.93±0.05%,which was sulfated-galactan,and its possible structural unit was→3)G4Sβ(1→3)G(1→6)G4Sα(1→4)LA(1→6)G4Sα(1→.PHP1.0-1-UF was composed of mannose,glucose and galactose,with a weighted average molecular weight of 1.14×10~6(±3.44%)g/mol,sulfated content of 5.07±0.04%,and characterized as a sulfated glucogalactan,with a hypothetical backbone structure of→4)Gα(1→6)G4Sβ(1→4)Glc(1→and with a side chain Man(1→6)Glc.(2)The effects of PHP on blood lipid index,organ index and liver histopathological characteristics of Mesocricetus auratus fed with a high-fat diet were investigated.The results showed that the PHP significantly prevented the increase of TG,TC and LDLC in serum in a dose-dependent manner.PHP significantly inhibited the increase of body weight,liver and kidney index in a high-fat diet Mesocricetus auratus.The results of histopathological observation showed that PHP alleviated the damage of liver cells induced by a high-fat diet in Mesocricetus auratus,especially in middle-dose PHP(MPHP)and high-dose PHP(HPHP)groups.Pearson correlation analysis showed that serum TC and LDLC were negatively correlated with total sugar,sulfated radical,mannose,glucose and galactose.The contents of sulfate,mannose,glucose and galactose of PHP were closely related to the hyperlipidemic effects.(3)The effects of PHP on the diversity and structural composition of colonic flora of Mesocricetus auratus were investigated by 16S r RNA sequencing technology.The results showed that MPHP and HPHP improved the richness and diversity of colonic flora.Firmicutes,Bacteroidota,Actinobacteriota and Desulfobacterota were the main flora at the phylum level.MPHP promoted the proliferation of butyric acid-producing bacteria(Blautia and norank＿f＿Christensenellaceae).HPHP promoted the butyric acid-producing bacteria(Faecalibaculum)and hypolipidemic correlated bacteria(Rikenelaceae＿RC9＿gut＿group).The contents of butyric acid in MPHP and HPHP groups were significantly higher than that in the MC group.MPHP and HPHP might reduce blood lipid through butyric acid pathway.(4)The changes of the lipid metabolites in liver were measured by non-target lipidomics,and the relationships between serum lipid and liver lipid metabolites,intestinal flora and lipid metabolites,SCFAs and lipid metabolites were investigated.The results showed that the main lipid metabolites were sphingolipids,glycerolipids and glycerophospholipids.There were a large number of triglyceride metabolites in low-dose PHP(LPHP)group.The expression of phosphatidylcholine metabolites in MPHP group was affected by colonic butyric acid.MPHP reduced the accumulation of triglycerides in the liver by up-regulating phosphatidylcholine metabolites.The expression of triglyceride metabolites in HPHP group was affected by butyric acid.HPHP reduced the accumulation of triglycerides in the liver by down-regulating triglyceride metabolites.MPHP and HPHP effectively inhibited the accumulation of hepatic lipid triglyceride metabolites.(5)The effects of PHP on the liver gene expression of Mesocricetus auratus and the changes of hepatic SCFAs were investigated.The results showed that compared with the MC group,the liver adipocyte differentiation gene(Plin1)was down-regulated in LPHP group.Fat degradation(Abhd5),adipogenesis(Me1),fatty acid transport(Fabp5),fatty acid synthesis(Fasn and Pnpla3),fatty acid chain elongation(Elovl6)and gluconeogenesis regulation(Pklr)genes were down-regulated in MPHP group.Abhd5 and fatty acid transport(Lpl)genes were down-regulated in HPHP group,and gluconeogenesis regulate(Pck1)gene was up-regulated.The content of n-butyric acid in the liver in the MPHP and HPHP groups was significantly higher than that in the MC group.The molecular mechanism of MPHP on the"gut-liver"axis of the hyperlipidemic effect was as follows.Firstly,MPHP was degraded by Blautia and norank＿f＿Christensenellaceae to promote the production of butyric acid in the colon.Secondly,the butyric acid entered the liver through the peripheral circulation.The hepatic AMPK＿PPAR signaling pathway were activated by butyric acid.The expressions of Fabp5,Fasn,Me1 and Elovl6 genes were down-regulated and the expression of liver phosphatidylcholine metabolites was up-regulated.Finally,the liver TG and blood lipids was down-regulated.Whereas the"gut-liver"axis molecular mechanism of the hyperlipidemic effect of HPHP was as follows.Firstly,HPHP was used by the Rikenellaceae＿RC9＿gut＿group and Faecalibaculum to promote the production of butyric acid.Secondly,the butyric acid entered the liver through the peripheral circulation.Thirdly,butyrate acid activated the hepatic PPAR signaling pathway,inhibited the expression of fatty acid transport gene(Lpl).And the expression of liver triglyceride metabolites was down-regulated.Finally,the hepatic TG and blood lipids was down-regulated.