Molecular characteristics of sulfated polysaccharides from Monostroma nitidum and their in vitro anticancer and immunomodulatory activities

We investigated water-soluble sulfated polysaccharides isolated from Monostroma nitidum using ion-exchange chromatography to determine their molecular characteristics and biological activities. The crude and fractionated polysaccharides (F1, F2, and F3) consisted mostly of carbohydrates (58.3–91.9%), uronic acids (0–21.8%) and sulfates (1.8–17.7%) as well as varying amounts of proteins (1.6–9.4%). Their monosaccharide levels were significantly different including rhamnose (0–95.7%) and glucose (0–98.6%) content with small amounts of xylose (0.8–4.3%). These polysaccharides contained one or two subfractions with average molecular weights (Mw) ranging from 94.4 to 1387 × 103 g/mol. The in vitro inhibitory activity (≤75%) of the polysaccharides on a human cancer cell line (AGS) suggested that the polysaccharides had direct cytotoxic effects on the cancer cells. In addition, these hetero-polysaccharides (from the crude and F1 and F2 fractions) stimulated a macrophage cell line, Raw 264.7 cells, inducing considerable NO and PGE2, production, which suggested that they could be strong immunomodulators.