Structure and Biological Activities of an Alginate from Sargassum Fusiforme, and Its Sulfated Derivative

An alginate fraction, 04S2P, was isolated from the brown seaweed Sargassum fusiforme and was structurally characterized by the ratio (M/G) of β-d-mannuronic acid residues (M) to α-l-guluronic acid residues (G) via (1)H and (13)C NMR spectroscopy. When compared to commercial alginate (Alg) and alginates from other brown algae, 04S2P has a higher M/G ratio of 9.0:1.0 as determined by a modified high-performance liquid chromatography method after pre-column derivatization with PMP. Furthermore, the sulfated polysaccharides 04S2P-S and Alg-S were prepared by the chlorosulfonic acid-pyridine method. Both C-2 and/or C-3 of M and G residues of 04S2P-S were substituted by sulfate groups, with C-3 of M residues preferentially substituted. Their effects on tube formation of HMEC-1 cells were examined, and the results indicated that the sulfated Alg, Alg-S, exhibited a strong anti-angiogenic effect on HMEC-1 cells. The anti-tumor activity of native and sulfated alginates was tested on five different tumor cell lines. Alg-S demonstrated significant anti-tumor effects on the Bel7402, SMMC7721, and HT-29 cell lines, whereas 04S2P-S showed a distinct anti-tumor effect only on the Bel7402 cell line.