O-acetylated glucomannan from Dendrobium officinale alleviates DSS-induced colitis through dual immune-oxidative regulation and gut-microbiota modulation.

Plant-derived polysaccharides are promising phytotherapeutics for mucosal inflammation. We purified an O-acetylated glucomannan (DOP-a) from Dendrobium officinale and investigated its protective effects against dextran sulfate sodium (DSS)-induced colitis and the underlying immune and oxidative-stress mechanisms. DOP-a was purified and structurally characterized, and its monosaccharide composition, molecular weight, and O-acetylation/branching patterns were determined. In a chronic DSS mouse model, disease activity, colon length, histopathology, tight-junction proteins, and inflammatory cytokines were evaluated. Colonic TLR4/MyD88/NF-κB and Nrf2/HO-1 signaling were examined at the protein and transcript levels. Gut microbiota changes were profiled by 16S rRNA sequencing, and serum metabolomics was used to explore associated metabolic alterations. DOP-a significantly attenuated body weight loss, prevented colon shortening, and mitigated histological injury. It improved tight-junction-related markers (ZO-1, occludin, claudin-1) and reduced pro-inflammatory cytokines (TNF-α, IL-6, IL-1β) in serum and colon. Mechanistically, DOP-a downregulated TLR4 and MyD88 expression, inhibited NF-κB p65 phosphorylation, and activated Nrf2/HO-1, thereby limiting inflammatory and oxidative damage. DOP-a also partially reversed DSS-induced dysbiosis, enriching beneficial taxa and rebalancing lipid- and amino acid-related metabolites consistent with anti-inflammatory activity. Together, these findings indicate that DOP-a acts as a natural immunomodulatory polysaccharide that protects against experimental colitis by jointly targeting TLR4/NF-κB and Nrf2/HO-1 pathways, with adjunct modulation of the gut microbiota-metabolite axis. Structurally defined D. officinale polysaccharides therefore represent promising phytotherapeutic candidates for inflammation-related intestinal disorders.