Marine-Derived Polysaccharides Against Ulcerative Colitis: Sources, Structures, and Multi-Target Mechanisms

Marine-derived polysaccharides have emerged as promising bioactive candidates for alleviating ulcerative colitis (UC), a chronic inflammatory bowel disease with limited therapeutic options. This review systematically summarizes recent advances in the sources, preparation methods, structural features, and multi-target mechanisms of these polysaccharides from seaweeds, marine animals, and microorganisms. Key physicochemical parameters, including molecular weight, monosaccharide composition, glycosidic linkages, and sulfation patterns, critically influence their anti-colitis efficacy. Mechanistically, these macromolecules synergistically restore gut microbiota homeostasis (e.g., promoting short-chain fatty acids and secondary bile acids), suppress inflammatory pathways (NF-κB, MAPK, and NLRP3), regulate immune responses (inhibiting dendritic cell and Th1/Th17 activation), alleviate oxidative stress via the Nrf2/HO-1 pathway, and reinforce intestinal epithelial barrier integrity (upregulating tight junction proteins and mucins). Although systematic toxicological characterization remains limited, the generally favorable safety profiles reported in preclinical studies, together with their multi-target nature, suggest that marine polysaccharides hold great potential as functional foods or adjunctive therapies for UC. However, challenges remain in structural heterogeneity, batch-to-batch consistency, and limited clinical validation. Future efforts should prioritize structure–activity relationship elucidation, advanced analytical characterization, bioavailability and gastrointestinal fate studies, standardization and quality control, comparative evaluation against conventional therapies and other natural products, and well-designed clinical trials to facilitate translation from bench to bedside.