Beta-D-(1→4)-galactan-containing side chains in RG-I regions of pectic polysaccharides from Biophytum petersianum Klotzsch. contribute to expression of immunomodulating activity against intestinal Peyer's patch cells and macrophages

Abstract

The aerial parts of the medicinal plant Biophytum petersianum have a long tradition for being used in Mali and other West-African countries against various ailments such as wound healing and malaria. Previous studies on polysaccharides from water extracts of the aerial parts showed the presence of pectic like polymers with an effect on the human complement system as well as the ability to activate macrophages and dendritic cells. The present study shows that pectic polysaccharide fragments (BPII.1 and BPII.2) as well as the original pectic polysaccharide (BPII) expressed immunomodulating activity against Peyer's patch immunocompetent cells. Exo-β-D-(1→3)-galactanase digestion succeeded to decrease IL-6 production enhancing activity against Peyer's patch cells of BPII.2, but the activity of BPII.1 did not decrease. Endo-β-D-(1→4)-galactanase digestion reduced the activities of both BPII.1 and BPII.2. BPII.1 and BPII.2 also stimulated IL-6 production enhancing activity against macrophages, and the activities of both pectic fragments were significantly decreased by either enzymic digestion with exo-β-D-(1→3)-galactanase or endo-β-D-(1→4)-galactanase. Trimming of terminal GlcA by exo-β-D-glucuronidase digestion did not affect IL-6 production enhancing activity against macrophages of both pectic fragments. Methylation analyses of endo-β-D-(1→4)-galactanase digestion products showed the characteristic decrement of 4-linked Gal residues in the pectic fragments. These results suggest that β-D-(1→4)-galactan-containing side chains in BPII.1 and BPII.2 play an important role for expression of immunomodulating activity against both Peyer's patch immunocompetent cells and macrophages in addition to β-D-(1→3,6)-galactan chains.