Water-soluble polysaccharides from the brown alga Eisenia bicyclis: Structural characteristics and antitumor activity

Water-soluble polysaccharides were isolated from the brown alga Eisenia bicyclis , which was collected near the coast of the Republic of Korea. The structures of laminaran and fucoidan were investigated. Laminaran from E. bicyclis was determined to be a glucan with β-(1 → 6) side chains linked to a β-(1 → 3) backbone with relatively few branch points. Based on nuclear magnetic resonance (NMR) data, the ratio of the β-(1 → 3) and β-(1 → 6) linkages was estimated as 2.6:1. Fucoidan from E. bicyclis was found to contain 1,3-linked fucose residues, some 1,6-, 1,2,6-, 1,4,6-linked galactose residues and traces of mannose and xylose. In addition, the amount of sulfate in fucoidan was 13.2%. Those polysaccharides were non-cytotoxic to human melanoma SK-MEL-28 and colon cancer DLD-1 cells. Laminaran and fucoidan from E. bicyclis inhibited the colony formation of those cells. Therefore, they may have potential as antitumor agents.