Identification of the core active structure of a Dendrobium officinale polysaccharide and its protective effect against dextran sulfate sodium-induced colitis via alleviating gut microbiota dysbiosis

It has been claimed that Dendrobium officinale applied as a functional food in China for centuries derived from the excellent anti-inflammatory activities. Herein, we aim to investigate the core structure of a Dendrobium officinale polysaccharide (DOP) based on the linear structural features by a specific endo-β-1,4-mannanase which was required for the protective effect against dextran sulfate sodium (DSS)-induced colitis in mice. Structure characterization revealed that enzymatic fragment contained the core domain (EDOP) which was composed of glucose and mannose in the molar ratio of 1.00:4.76, and consisted of (1 → 4)-β-D-Glcp and (1 → 4)-β-D-Manp with some attached 2-O-acetylated groups. In colitis mice, both DOP and EDOP could dramatically attenuate the clinical signs via blocking pro-inflammatory cytokines (TNF-α, IL-6, IL-1β, and their related mRNA), restoring the levels of short-chain fatty acids (SCFAs), activating the G-protein coupled receptors (GPRs) and modulating the gut microbiota. Gut microbiota dysbiosis is currently considered to be an important factor affecting colitis. The treatment of DOP and EDOP could recall the diversity of gut microbiota and modulate the abundance of the gut microbiota, including increasing the abundance of Bacteroides, Lactobacillus and Ruminococcaceae and reducing the abundance of Proteobacteria. Our findings have suggested that EDOP, as a core domain of DOP, retained similar structural features together with anti-inflammatory activity with DOP, and they could be potentially applied as natural candidates in the treatment of inflammatory bowel disease (IBD).