Chemical composition and anti-inflammatory activity of pectic polysaccharide isolated from celery stalks

A pectic polysaccharide called apiuman was isolated from fresh celery stalks by extraction with an aqueous ammonium oxalate followed by ultrafiltration, and was shown to consist of d-galacturonic acid (GalA, 81.0%), l-rhamnose (Rha, 2.6%), l-arabinose (Ara, 2.5%), and d-galactose (Gal, 3.6%) residues. Apiuman was found to be digestible with α-1,4-d-galacturonase to yield d-GalA, thus confirming that apiuman represents a pectic polysaccharide. The purified apiuman (AG) obtained was subjected to ion exchange chromatography on DEAE-cellulose to produce two polysaccharide fractions, AG-1 and AG-2, which had similar sugar compositions. Partial acid hydrolysis of apiuman, AG, revealed galacturonan to be at the core of the macromolecule. Nuclear magnetic resonance (NMR) spectra indicated that the backbone of apiuman appeared to represent α-1,4-d-galacturonan, with considerable amounts of l-Rha residues involved by α-1,2-linkages in the linear chain of the macromolecule core. The side chains were found to consist of Ara and Gal attached at the 4-position of the Rha residues.Furthermore, apiuman, AG, was found to improve the survival of mice subjected to a lethal dose of lipopolysaccharide (LPS), and the anti-endotoxemic effect of apiuman, AG, was shown to be mediated by decreased interleukin-1β (IL-1β and increased interleukin-10 (IL-10) production. Apiuman was also shown to diminish the amount of neutrophils migrating to the peritoneal cavity after LPS injection.