2873-LB: Gut Microbiota–Driven GLP-1 Signaling Defects Underlie Metformin Nonresponsiveness and Are Reversible with Probiotic Therapy

Introduction and Objective: Metformin is first-line therapy for type 2 diabetes (T2D), yet a subset of patients shows inadequate glycemic response. The mechanisms underlying non-responsiveness remain unclear. We hypothesized that gut microbiota dysbiosis impairs GLP-1 signaling, mediating host variability to metformin. Methods: C57BL/6J mice were fed a high-fat diet for 12 weeks followed by metformin with or without probiotic therapy. Responders (Res) and non-responders (nRes) were defined by fasting glucose and glucose tolerance. Microbiome profiling, fecal microbiota transplantation (FMT), intestinal gene expression, GLP-1 quantification, and L-cell histology were performed. Glp1r knockout mice, organoids, GLUTag cells, and untargeted metabolomics were used to define mechanisms. Results: Metformin induced distinct Res and nRes phenotypes. nRes mice exhibited a unique microbiome signature transferable by FMT, demonstrating causality. Transplantation of nRes microbiota impaired glycemic response in recipients. nRes intestine showed reduced GLP-1 signaling, decreased Glp1r expression, and lower circulating GLP-1. Glp1r knockout mice phenocopied non-responsiveness. nRes mice and FMT recipients displayed reduced L-cell density. Fecal-conditioned media from nRes mice induced L-cell death and impaired GLP-1 production. Metabolomics identified microbiota-derived metabolites enriched in nRes mice that disrupted GLP-1 signaling and reduced L-cell viability. Probiotic therapy restored microbial composition, normalized GLP-1 signaling, and rescued metformin efficacy. Conclusion: Gut microbiota-mediated suppression of GLP-1 signaling drives metformin non-responsiveness. Microbiota-derived metabolites impair L-cell integrity, disrupting the metformin-GLP-1 axis. Targeted probiotic modulation restores incretin signaling and glycemic control in T2D. Disclosure S.P. Mishra: None.