Eisenia bicyclis Extract Ameliorates Colitis in In Vitro and In Vivo Models Through Modulation of mTOR Axis and Gut Microbiota Composition

Ulcerative colitis (UC) is a chronic inflammatory disease of the colon that is associated with dysbiosis in the gut microbiota. <i>Eisenia bicyclis</i>, a marine alga, is known for its anti-inflammatory, antioxidant, and gut microbiota-modulating properties. This study explored the mechanisms by which a 70% ethanol extract of <i>E. bicyclis</i> may alleviate UC, through both in vitro and in vivo experiments. LC-MS/MS analysis revealed eckol, 7-phloroeckol, dieckol, phlorofucofuroeckol A, and fucofuroeckol as key phenolic compounds present in the extract. The administration of <i>E. bicyclis</i> significantly improved symptoms in a dextran sulfate sodium (DSS)-induced colitis mouse model by reducing intestinal shortening, splenomegaly, and histological scores. Both cell and animal studies demonstrated that <i>E. bicyclis</i> suppressed the release of inflammatory cytokines, downregulated the mRNA expression of genes related to the mTOR pathway, and reduced the p-mTOR/mTOR ratio. Microbiota analysis revealed that, while the Firmicutes/Bacteroidetes ratio was elevated in UC mice, <i>E. bicyclis</i> administration normalized this imbalance, with a notable increase in the abundance of beneficial probiotics such as <i>Bifidobacterium bifidum</i>. In conclusion, a phenolic-rich extract of <i>E. bicyclis</i> demonstrates significant potential as a dietary supplement to prevent and mitigate UC by modulating both the mTOR signaling pathway and gut microbiota composition.