Abstract：Inflammatory bowel disease (IBD), particularly ulcerative colitis, remains a major global health burden, highlighting the need for novel therapeutic approaches. This study explored the protective role of Larimichthys crocea isinglass polysaccharide (CIP) against dextran sulfate sodium (DSS)-induced colitis. CIP, a 3.97 kDa polysaccharide composed of mannose, rhamnose, glucuronic acid, galacturonic acid, xylose, and fucose, exhibited remarkable potential in restoring intestinal homeostasis. In DSS-treated mice, CIP administration markedly alleviated weight loss, colon shortening, and histological injury. Mechanistically, CIP suppressed the TLR4/MyD88/NF-κB signaling cascade, resulting in downregulation of TNF-α, IL-6, and IL-1β, and upregulation of the anti-inflammatory cytokine IL-10. It also reduced oxidative stress by inhibiting inducible nitric oxide synthase (iNOS).

Beyond its anti-inflammatory and antioxidant actions, CIP strengthened the intestinal barrier by upregulating tight junction proteins (ZO-1, occludin, claudin-1) and mucin MUC2, and enhanced production of short-chain fatty acids (SCFAs), crucial for mucosal energy metabolism. Importantly, CIP modulated gut microbiota composition, enriching beneficial Ligilactobacillus species while suppressing potentially harmful taxa such as Bacteroidota and Campylobacter. Notably, extracellular vesicles derived from Ligilactobacillus isolated from CIP-treated mice significantly attenuated colitis symptoms and mucosal damage, revealing a microbiota-mediated mechanism underlying CIP’s therapeutic effects.

Overall, CIP exerts multifaceted protection against colitis by integrating anti-inflammatory, antioxidant, barrier-enhancing, and microbiota-modulating activities. These findings identify CIP as a promising natural polysaccharide with potential as a functional food ingredient or adjuvant for maintaining intestinal health and preventing IBD progression