Structure and anticancer activity in vitro of sulfated galactofucan from brown alga Alaria angusta

Laminaran and three fractions of fucoidan were isolated from brown alga Alaria angusta. The laminaran AaL was characterized as a typical 1,3;1,6-β-D-glucan (ratio of bonds 1,3:1,6 = 10:1). Fucoidans AaF1 and AaF2 are sulfated heteropolysaccharides, containing fucose, galactose, mannose and xylose. The fraction AaF3 is sulfated and acetylated galactofucan with the main chain represented by a repeating unit →3)-α-L-Fucp-(2,4-SO3−)-(1→. According the data of methylation analysis, AaF3 contains mainly 1,3-linked fucose, less 1,4-linked and 1,4,6-linked galactose residues. The autohydrolysis (37 °C) of fucoidan AaF3 allowed to obtain selectively 2-desulfaled polysaccharide fraction, built up of fucose only, and low molecular weight (LMW) fraction. The negative-ion tandem mass spectrometry of LMW fraction, further hydrolyzed by acid hydrolysis identified the following fragments: Gal-2-SO3−-(1 → 4)-Gal, Gal-4-SO3−-(1 → 4)-Gal, Gal-(1 → 2)-Gal-4-SO3−, Fuc-2-SO3−-(1 → 4)-Gal, Gal-2-SO3−-(1 → 3)-Fuc-(1 → 3)-Fuc, Fuc-2-SO3−-(1 → 3)-Fuc-(1 → 4)-Gal. The laminaran AaL and the fucoidan AaF3 exhibited no cytotoxicity in vitro for HT 29, T-47D, and SK-MEL-28 cell lines. The AaF3 fraction suppressed colony formation of HT 29 and T-47D cells, AaL-only HT 29 cells.