Polysaccharides from Lycium barbarum leaves: isolation, characterization and splenocyte proliferation activity

The polysaccharides from the fruits of Lycium barbarum have received considerable attention in previous publication, but the polysaccharides from the leaves were rarely reported. In the present work, four water-soluble polysaccharide fractions: LBP-I, LBP-II, LBP-III and LBP-IV isolated from L. barbarum leaves were purified through DEAE-Sephadex A-25. LBP-II and LBP-IV respectively showed one symmetrical peak on HPGPC with average molecular weight of 9.39 × 10⁴ Da and 4.18 × 10⁵ Da. UV and IR analysis of the two fractions showed the characteristics of acidic polysaccharides combined with polypeptides or proteins. GC analysis showed LBP-IV was mainly composed of rhamnose, arabinose, xylose, glucose and galactose with molar ratio of 1.61:3.82:3.44:7.54:1.00, and the uronic acid content was 47.68% (w/w) determined by sulfuric acid-carbazole method. ¹H and ¹³C NMR spectra of LBP-IV also showed the presence of carboxyl carbon and five anomeric carbons, and suggested there may be both α- and β-anomeric configurations in this fraction. Moreover, splenocyte proliferation activity assay showed that LBP-IV significantly enhanced the proliferation of splenocyte stimulated by ConA or LPS, indicating the fraction has the beneficial effect on immunostimulating activity.