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.

► We isolate and investigate laminaran and fucoidan from the brown alga E. bicyclis. ► We estimate the ratio of the β-(1 → 3) and b-(1 → 6)-linkages in laminaran as 2.6 : 1. ► Purified fucoidan was galactofucan with traces of mannose and xylose residues. ► Those polysaccharides show inhibitory effect against investigated cancer cells.