Separation, Characterization And α-glucosidase Inhibitory Activity Of Polysaccharides From Leaves Of Gynura Davaricata(L.) DC

Gynura davaricata(L.) DC. is a valuble medicinal and edible plant which has beenwidely used in the treatment of hypertension, hyperlipidemia, and diabetes in public.Gynura davaricata polysaccharides (GDPs) are a group of hypoglycemic components,which has been confirmed by animal experiments in mice. But current research aboutGDPs mainly concentrated on extraction of crude GDPs and mice hypoglycemic activityexperiments, the structure characterization of GDPs and their hypoglycemic activity onmolecular level are seldomly reported. This paper focused on the extraction, separationand purification, structural characterization, and α-glucosidase inhibitory activity ofGDPs. The main contents are as follows:1. The GDPs was extracted by water from spray-dried powder of Gynura davaricatapressed juice. The conditions are as follows: solid-liquid ratio of1:9, temperature of90℃,time of2hours, extraction times of twice; Then the crude GDPs was obtained bydeproteinization, decolorization, and ethanol precipitation. Under these conditions, thecrude polysaccharide extraction rate was9.01%, the polysaccharide content of21.78%.2. Two neutral polysaccharides GDPs-1, GDPs-2and one acidic polysaccharide GDPs-3were separated and purified through D315resin column and Sephadex G-25gel columnchromatography from the crude GDPs. GPC analysis showed that the weight-averagemolecular weights of GDPs-1, GDPs-2and GDPs-3were1.06×10~4,4.17×10~3and3.74×10~3Da with the purity of94.08%,92.3%and99.8%and polydispersity1.43,1.65and1.27respectively.3. GC analysis showed GDPs-1was composed of D-Fru,L-Rha,L-Ara,D-Xyl, D-Man,D-Glu and D-Gal with a molar ratio of0.2:0.4:1:1:1:2:7and GDPs-2composed of L-Ara,D-Man,D-Glu and D-Gal with a molar ratio of0.4:2:2:0.1. IR and1H-NMR showed that allthe three polysaccharides contained only α-configuration. Periodate oxidation reaction,smith reaction, partially acid hydrolysis and13C-NMR suggested GDPs-1had a backboneof α-(1â†'2)-linked galactose residues, the branches were composed of α-(1â†'3)-linked-Xyl,α-(1â†'2)-linked-Glu,α-(1â†'3)-linked-Man and Me-α-Araf,; GDPs-2had a backbone ofα-(1â†'3)-linked mannose residues, the branches were composed of α-(1â†'2)-linked-Gluand α-(1â†'6)-Glu.4. Congo red test suggest that there was stable three-ply spiral structure in GDPs-2;X-ray diffraction showed both the two polysaccharides were weak molecule structured. 5. The in-vitro α-glucosidase inhibitory activity assay was applied to study thehypoglycemic activity of crude GDPs, GDPs-1and GDPs-2, using acarbose tablets aspositive control. The polysaccharides all showed extremely low inhibitory activities onα-glucosidas compared to acarbose tablets, which suggest it was not the mechanism forGDPs to regulate glucose level.The systemic separation and structrue characterization of GDPs, as well as itspreliminary α-glucosidase inhibitory activity were firstly reported in this paper, whichprovided a substancial basis for futher hypoglycemic mechanism study of Gynuradavaricata(L.) DC.