Characterization and antitumor activity of a polysaccharide from Strongylocentrotus nudus eggs

A water-soluble polysaccharide named as SEP was isolated from the eggs of Dalian purple sea urchin Strongylocentrotus nudus by hot water extraction, anion-exchange and gel-permeation chromatography and tested for its antitumor activity. Its structural characteristics were investigated by FTIR, HPLC, NMR spectroscopy, GLC–MS, methylation analysis, Periodate oxidation and Smith degradation. Based on the data obtained, SEP was found to be an α-(1 → 4)-d-glucan, with a single α-d-glucose at the C-6 position every nine residue, on average, along the main chain. The glucan has a weight-average molecular weight of about 1.95 × 106 Da. Pharmacological studies revealed SEP could inhibit the growth of Sarcoma 180 tumor remarkably in vivo. SEP also stimulated the spleen lymphocyte proliferation in S180-bearing mice, indicating its antitumor effect may be related to immunomodulation.