Anti-Inflammatory and Antioxidant Mechanisms of Dendrobium moschatum Polysaccharide in Intestinal Epithelial Cells via TLR4-NF-κB and Nrf2 Signaling Pathways

<i>Dendrobium moschatum</i> neutral polysaccharide (DMP-NP) was isolated using a water extraction-ethanol precipitation method, followed by purification with DEAE-cellulose anion-exchange resin and a dextran gel column. The resulting DMP-NP1 exhibited a weight-average molecular weight of 16.23 kDa. The molar ratio of monosaccharides was as follows: glucose-mannose-galactose-fucose-rhamnose = 78.54:19.11:1.59:0.53:0.23, with a glucose-to-mannose ratio of 4.1:1. Infrared spectroscopic analysis revealed characteristic carbohydrate absorption peaks and confirmed the presence of pyranosidic linkages. NMR analysis revealed that DMP-NP1 possesses a backbone mainly formed by 1→4 glycosidic linkages, a small number of 1→6 branches, and O-acetyl substitutions at the C2 and C3 positions of mannose residues. In vitro experiments demonstrated that treatment with 0-20 μg/mL (0-1.23 μM) DMP-NP significantly enhanced the activities of catalase (CAT) and superoxide dismutase (SOD) in IPEC-J2 cells, along with upregulation of the corresponding antioxidant genes. Concurrently, DMP-NP reduced the secretion of key pro-inflammatory cytokines, including TNF-α, IL-1β, and IL-6, and downregulated the expression of genes associated with both antioxidant and inflammatory signaling pathways. Collectively, these findings indicate that DMP-NP not only prevents but also ameliorates LPS-induced inflammatory injury in intestinal epithelial cells, thereby providing a basis for the application of DMP-NP in intestinal inflammation mitigation.