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

Abstract

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.

Keywords: Azolla filiculoides; Chemical structure; Fucose-containing polysaccharide; Immunostimulatory; NF-κB and MAPKs pathways.