Isoalantolactone ameliorates ulcerative colitis via gut microbiota-mediated modulation of intestinal barrier, T cell homeostasis, and metabolite reprogramming.

Ulcerative colitis (UC) is a chronic inflammatory bowel disease characterized by immune dysregulation, epithelial barrier dysfunction, and gut microbiota imbalance. This study examined the therapeutic potential of isoalantolactone (IAL), a bioactive sesquiterpene lactone naturally occurring in Inula helenium L., using a dextran sulfate sodium-induced murine colitis model. Treatment with IAL significantly mitigated weight loss, improved the disease activity index, preserved colon length, and alleviated goblet cell depletion. Mechanistically, IAL enhanced intestinal barrier integrity by upregulating tight-junction proteins zonula occludens-1, occludin, and mucin 2 and suppressing proinflammatory cytokines interleukin (IL)-6, tumor necrosis factor-α, and IL-1β. Moreover, IAL rebalanced CD4+/CD8+ T cell ratios in the colon, mesenteric lymph nodes, and spleen. Gut microbiota analysis revealed increased diversity, enrichment of beneficial taxa (Muribaculaceae, Prevotellaceae_UCG-001), and a reduced Firmicutes-to-Bacteroidetes ratio. Metabolomic profiling identified 130 differentially abundant metabolites, including increased levels of anti-inflammatory compounds (e.g., hydroferulic acid) and decreased levels of proinflammatory lipids (e.g., linoleoylcarnitine). Correlation analysis demonstrated an association between gut microbiota and faecal metabolites. In addition, faecal microbiota transplantation confirmed that IAL-modulated microbiota ameliorated colitis, with pseudo-germ-free recipients exhibiting improved barrier function and immune homeostasis. These findings highlight the importance of IAL as a novel therapeutic candidate for UC by modulating host-microbiota interactions; however, clinical validation is warranted.