Studies On Extraction And Separation Of Polysaccharides From Apocynum And Their Anti-Galectins Effects

Apocynum venetum,a valuable plant of Apocynaceae family,is a specialty in northern China.The leaves of this plant have long been used as traditional medicines for the treatment of neurasthenia,heart palpitation,insomnia,and hypertonia,besides it is also used as functional food materials to make tea drinks for its bioactivities.Here four novel polysaccharides,ALSP,ALFP,ALLP and ALTP were isolated from stems,flowers,leaves and tea of Apocynum venetum,then they were both separated into three fractions(-N,-A1and-A2)by electric charge and their chemical characteristics and galectin inhibitory capacities were determined using HPLC,HPGPC,FTIR,G3 H and G8 H.The extraction rates of ALSP,ALFP,ALLP and ALTP were 3.5%,15.8%,12%and 15.0%,respectively,containing eight monosaccharides,Man,GlcA,Rha,GalA,Glc,Gal,Ara,Xyl.These four kinds of Apocynum polysaccharide possed sugar content of 20-41%,uronic acid content of 12-32%.Apocynum venetum is salt tolerant plants,so the Apocynum polysaccharides possed high ash content,50-85%.Therefore,the series of Apocynum polysaccharides were further purified.Then by DEAE-cellulose ion-exchange chromatography separation of four Apocynum polysaccharides respectively,the neutral fraction was obtained by water elution,and two acidic sugar fractions(A1 and A2)were obtained by elution of 0.5 M NaCl and 1M NaCl.The sugar content,protein content,sugar composition,molecular weight and degree of esterification of four kinds of polysaccharides were compared.Results showed that neutral fractions were mainly composed of 4monosaccharides: Man,Glc,Gal and Ara.The molecular weight of four neutral sugars was less than 10 KDa.Acidic sugar(-A1)fractions contain a large number of GalA(>60%).The content of Ara was 11%-12%,and the content of other monosaccharide was significantly different.There were obvious differences in molecular weight and charge distribution between the four kinds of A1 fractions.In the A2 fractions,there were plenty of GlcA and GalA according to the monosaccharide composition analysis,and the results of molecular weight distribution show that the four kinds of polysaccharides with different degree of polymerization are mixed.Generally,polysaccaride fractions could agonize galectin-8-mediated hemagglutinationant more obviously than galectin-3-mediated hemagglutinationant.ALFP and ALTP showed inhibitory effect on galectin-3 and galectin-8 significantly,but ALSP and ALLP were not.In the series of neutral fractions,they had no inhibition to galectin-3,however,ALSP-N and ALFP-N had strong inhibitory effects on galectin-8.In the series of acidic A1 fractions,four kinds of A1 fractions could not inhibit galectin-3;ALFP-A1 and ALTP-A1 had obvious inhibitory effect on galectin-8.In the series of acidic polysaccharide A2,ALLP-A2 and ALFP-A2 could be combined with galectin-3;ALSP-A2,ALLP-A2 and ALTP-A2 were combined with galectin-8,ALTP-A2 showed the strongest inhibition effect.