l -Arginine Ameliorates IBS-D by Modulating the Ligilactobacillus murinus –LCA–FXR/eNOS Signaling Axis

Abstract l-Arginine is a semiessential amino acid with diverse metabolic functions and has been implicated in gastrointestinal health through interactions with the gut microbiota; however, its therapeutic potential in diarrhea-predominant irritable bowel syndrome (IBS-D) remains unclear. Here, an IBS-D mouse model was established in C57BL/6J mice, and multiomics analyses combined with in vivo and in vitro validation were performed to investigate the mechanisms underlying l-arginine-mediated protection. l-Arginine supplementation significantly alleviated IBS-D-like symptoms and improved intestinal barrier function. Transcriptomic analysis revealed the activation of the FXR/PI3K/AKT/eNOS signaling pathway, which was associated with enhanced nitric oxide production. Integrated metagenomic and transcriptomic analyses identified Ligilactobacillus murinus (L. murinus) as a key microbiota component associated with bile acid metabolism and eNOS expression. Furthermore, L. murinus transplantation reproduced the beneficial effects of l-arginine, and metabolomic analysis identified lithocholic acid (LCA) as a microbiota-derived metabolite involved in this process. In vitro experiments demonstrated that LCA alleviated lipopolysaccharide-induced epithelial inflammation and barrier dysfunction via FXR/eNOS activation. Collectively, these findings reveal that l-arginine ameliorates IBS-D through microbiota remodeling, LCA-mediated bile acid regulation, and activation of the colonic FXR/PI3K/AKT/eNOS axis, highlighting its potential as a microbiota-targeted therapeutic strategy.