A Paeoniae Radix Alba Polysaccharide Fraction BP-1 Restores Intestinal Barrier Function and Gut Microbiota–Metabolic Homeostasis in Collagen-Induced Arthritis Rats

Abstract Paeoniae Radix Alba (PRA) polysaccharides are promising food-derived bioactives, yet their gut-mediated effects on rheumatoid arthritis (RA) remain unclear. Here, BP-1 was purified, structurally characterized, and evaluated in collagen-induced arthritis (CIA) rats and lipopolysaccharide (LPS)-injured Caco-2 cells. BP-1 was a 14.124 kDa neutral polysaccharide mainly composed of glucose and mannose. NMR analysis identified →4)-α-D-Glcp-(1→, →4,6)-α-D-Glcp-(1→, α-T-D-Glcp-(1→, →4,6)-β-D-Manp-(1→, and α-T-D-Galp-(1→ residues. BP-1 alleviated arthritis severity, joint pathology, systemic inflammation, and colonic injury, while improving intestinal barrier integrity in vivo and in vitro. These effects were potentially associated with suppression of TLR4/MyD88/NF-κB signaling, restoration of immune homeostasis, and modulation of gut microbiota and fecal metabolites. These findings support BP-1 as a potential functional food ingredient for inflammation-associated intestinal and immune disorders.