Structural properties and immune‐enhancing activities of galactan isolated from red seaweed Grateloupia filicina

Abstract

AbstractA water‐soluble polysaccharide (GFP) was isolated from Grateloupia filicina and fractionated using a DEAE Sepharose Fast Flow column to evaluate immunostimulatory activity. Carbohydrates (62.0%–68.4%) and sulfates (29.3%–34.3%) were the major components of GFP and its fractions (GFP‐1 and GFP‐2), with relatively lower levels of proteins (4.5%–15.4%) and uronic acid (1.4%–3.9%). The average molecular weight (Mw) for GFP and its fractions was calculated between 98.2%–243.7 kDa. The polysaccharides were composed of galactose (62.1%–87.2%), glucose (4.5%–33.2%), xylose (3.1%–5.3%), mannose (1.4%–2.2%), rhamnose (1.2%–2.0%), and arabinose (0.9%–1.7%) units connected through →3)‐Galp‐(1→, →4)‐Galp‐(1→, →2)‐Galp‐(1→, →6)‐Galp‐(1→, →3,4)‐Galp ‐(1→, →3,6)‐Galp‐(1→, →4,6)‐Galp‐(1→, →3,4,6)‐Galp‐(1→, →2,3)‐Galp‐(1→, →2,4)‐Galp‐(1→, →4)‐Glcp‐(1→, →6)‐Glcp‐(1→ and →4,6)‐Glcp‐(1→residues. The isolated polysaccharides effectively induced RAW264.7 murine macrophages by releasing nitric oxide (NO) and various cytokines via nuclear factor kappa light chain enhancer of activated B cells (NF‐κB) and mitogen‐activated protein kinase (MAPK) signaling pathways. Further, the expression of toll‐like receptor‐2 (TLR‐2) and TLR‐4 in RAW264.7 cells indicated their activation through TLR‐2 and TLR‐4 binding receptors. Among the polysaccharides, GFP‐1 highly stimulated the activation of RAW264.7 cells, which was mainly constituted of (→1) terminal‐D‐galactopyranosyl, (1→3)‐linked‐ᴅ‐galactopyranosyl, (1→4)‐linked‐ᴅ‐galactopyranosyl and (1→3,4) ‐linked‐ᴅ‐galactopyranosyl residues. These findings demonstrate that GFP‐1 from G. filicina are effective at stimulating the immune system and this warrants further investigation to determine potential biomedical applications.