Chlorella vulgaris α-L-arabino-α-L-rhamno-α,β-D-galactan structure and mechanisms of its anti-inflammatory and anti-remodelling effects.

Microalgal exopolysaccharides (EPSs) are given great attention due to their potential biotechnology applications. Purified C. vulgaris EPS was subjected to compositional and sugar linkage analyses, and partial acid hydrolysis. Hydrolysate separation by gel chromatography afforded oligosaccharide fractions. Both, EPS and oligomers were studied by NMR spectroscopy. Data suggest very complex highly branched α-L-arabino-α-L-rhamno-α,β-D-galactan structure. Backbone repeating unit is formed by →2)-α-L-Rha (1 → 3)-α-L-Rha(1 → sequence, highly branched by long 1,6-linked α-D-Galp side chains, further branched at C2, C3 or C4 by α-L-Araf, α-D-Galf and β-D-Galf residues. α-L-Araf form longer 1,2-linked chains branched at C3, C4 or C5. Galf residues are localized as terminal units predominantly in the β configuration, while α-D-Galp and α-L-Araf may be partially O-methylated. Ex vivo biological assays showed increased interleukin-12 (IL-12) and interferon-gamma (INF-γ) levels corresponding to transforming growth factor beta (TGF-β) decrease in guinea pig model experimental asthma. These facts point to the anti-remodelling effect of Chlorella EPS and suggest its possible application in the treatment of asthma and chronic obstructive pulmonary disorder.