Structural features of an immunostimulating and antioxidant acidic polysaccharide from the seeds of Cuscuta chinensis

Three crude polysaccharide fractions, named CS-A, CS-B and CS-C, were prepared from the seeds of Cuscuta chinensis by hot water extraction and diluted alkali extraction subsequently, then EtOH precipitation, and tested for lymphocyte proliferation activity. CS-A showed a stimulating effect on concanavalin A or lipopolysaccharide induced mitogenic activity of lymphocytes. An acidic polysaccharide (CS-A-3beta) was purified from CS-A by anion exchange and gel filtration chromatography. The polysaccharide showed potent stimulating effects on lymphocyte proliferation and antibody production, but did not significantly influence the serum IgG level. Its structural features were elucidated by methylation analysis, partial acid hydrolysis, 1 D and 2D NMR and ESI-mass spectroscopy. The data obtained indicated that CS-A-3beta had a backbone consisting of alpha-D-1,4-linked GalpA residues and beta-L-1,2-linked Rhap residues with branches at C-4 of Rhap residues and C-3 of GalpA residues, composed of arabinogalactan and glucobiose. This structure is typical for a pectic polysaccharide of the rhamnogalacturonan type. In addition, the effect of CS-A, CS-B, CS-C and CS-A-3beta on hydrogen peroxide induced cell lesion in rat pheochromocytoma line PC 12 was investigated. The results indicated that, besides its immunostimulating activity, CS-A-3beta had a protective effect against free radical-induced cell toxicity.