Isolation and chemical characterization of a novel immunostimulating galactofucan from freshwater Azolla filiculoides

Water-soluble polysaccharides were isolated from Azolla filiculoides to determine their chemical and structural characteristics as well as anticancer and immunostimulatory activities. Crude and fractions (F1 and F2) were mainly composed of neutral sugars (70.0-80.1%), proteins (2.1-14.2%) and uronic acids (1.2-10.8%). The polysaccharides were mostly formed of different levels of fucose (23.8-61.2%), galactose (28.5-38.7%), mannose (7.5-16.7%), xylose (13.3-13.6%), glucose (12.7-13.3%), arabinose (5.5-11.6%) and rhamnose (8.0-9.5%) units. The polysaccharide molecules contained one or more sub-fractions with average molecular weight ranging from 992 to 2162 × 103 g/mol. Crude and fractionated polysaccharides induced RAW264.7 macrophages to release pro-inflammatory mediators and cytokines including nitric oxide, IL-1β, TNF-α, IL-6, IL-10 and IL-12 through NF-κB and MAPKs signaling pathways as confirmed by the presence of p-NK-κB, p-JNK, p-ERK and p-38 proteins in the cell cytoplasm. The most immunostimulating polysaccharide, F2, consisted of alternating →3)-Fuc-(1→ and →4)-Fuc-(1 → residues.