Purification, molecular properties, structural characterization, and immunomodulatory activities of water soluble polysaccharides from Sargassum angustifolium

Sulfated polysaccharides isolated from Sargassum angustifolium and purified to determine their structural characteristics and biological activities. Crude polysaccharides and fractions (F1 and F2) were chiefly composed of neutral sugars (49.4–68.5%) and sulfates (12.5–23.0%) along with small amounts of uronic acids (1.3–13.6%) and proteins (4.1–4.7%). Polysaccharides were mainly constructed of different levels of fucose (23.9–69.9%) and galactose (22.5–29.8%) sugars. Subfractions with molecular weights ranging from 157.2 to 790.8 × 103 g/mol were identified for isolated polysaccharides. Polysaccharides induced RAW264.7 macrophage cells to release noticeable amounts of nitric oxide and cytokines including IL-1β, TNF-α, IL-6, IL-10 and IL-12 through NF-κB and MAPKs signaling pathways. Sulfate esters of fraction F2 were necessary to its bioactivity and they were located on carbons 2, 4 and 6 of the major sugars. Fraction F2 was formed of (1 → 4)- and (1 → 3)-linked fucose residues branched at C-2 and C-4 as well as (1 → 6)-linked galactose residues branched at C-3.