Structure And Bioactivities Of A Polysaccharide From Lachnum Sp.based On Molecular Modification

In present study,purification and structural charachterization of a exopolysaccharide LEP from Lachnum YM240 were investigated.Carboxymethylated and sulfated modifications of LEP were respectively performed,and their antioxidant and hypoglycemic activities in vitro and hypoglycemic and hypolipidemic activities in vivo before and after modifications were also assessed.An exopolysaccharide was obtained from Lachnum YM240 fermentation broth by ethanol precipitation,depigmentation and deproteinization,then separated and purified by DEAE-cellulose 52 and Sephadex G-100 chromatographic column to obtain the single component LEP.HPLC,GC–MS,methylation analysis,FT-IR and 1D/2D NMR analysis demonstrated that LEP was composed of mannose(Man)and galactose(Gal)at the ratio of 16.3:1.0 with a molecular weight of 1.68×103kDa.The backbone of LEP was composed of(1?3)-?-D-Manp,(1?3,4)-?-D-Manp and(1?3)-?-D-Galp.LEP was substituted mainly at C-4 of Manp by the branch chain which was mainly composed of ?-D-Manp-(1?2)-?-D-Manp-(1?3)-?-D-Manp-(1-trisaccharides unit.Carboxymethylated polysaccharide CLEP with a degree of substitution(DS)of 0.360 and sulfated polysaccharide SLEP with a DS of 0.144 were obtained after LEP was chemically modified.It was proved by FT-IR spectra that the carboxymethylation and sulfation modifications were successful.Analysis of the NMR spectra suggested that carboxymethyl group-CH2 COOH was substituted at C-3 of(1?2)-?-D-Manp,C-4 of(1?3)-?-D-Manp and C-6 of(1?)-?-D-Manp,while sulfate group-SO3 H was mainly at C-4 of(1?2)-?-D-Manp and C-6 of(1?3)-?-D-Galp.Antioxidant activity assay in vitro showed that CLEP and SLEP more significantly increased scavenging effects of the polysaccharide on DPPH radical and hydroxyl radical and reducing power than LEP.Via the hypoglycemic activity in vitro,it was discovered that inhibiting effects of CLEP and SLEP were highlyer enhanced on ?-glucosidase,?-amylase and diffusion of glucose than LEP.Different contents of LEP,CLEP and SLEP were used to treat the type II diabetic mice(T2DM)induced by streptozotocin(STZ)and high fat diet.Compared with LEP,CLEP and SLEP significantly increased body weight,organ index,liver glycogen and the oral glucose tolerance.LEP,CLEP and SLEP showed a marked reduce fast blood glucose(FBG)level,fasting serum insulin(FINS),glycosylated hemoglobulin A1c(HbA1c),as well as serum triglycerides(TG),cholesterol(TC)and free fatty acid(FFA).In addition,Compared with LEP,CLEP and SLEP significantly upregulated expression of glucokinase(GK)and adenosine monophosphate activated protein kinase(AMPK)in liver,AMPK and glucose transporter 4(GLUT4)in skeletal muscle and peroxysome proliferator-activated receptor(PPAR-?)in adipose tissue,but downregulated expression of glucose-6-phosphatase(G6P)in liver.Therefore,LEP and its derivatives possess significant hypoglycemic and hypolipidemic effects and CLEP improved the hypoglycemic and hypolipidemic effects more effectively than SLEP.