Gut microbiome and bile acid metabolism in liver disease: Mechanisms, clinical implications, and therapeutic opportunities.

The intricate interplay between the gut microbiome and bile acid metabolism via the gut-liver axis is fundamental to hepatic homeostasis. Perturbations in this axis are increasingly implicated in the pathogenesis of diverse liver diseases, including metabolic dysfunction-associated steatotic liver disease, alcohol-associated liver disease, cholestatic liver diseases, and hepatocellular carcinoma. This review integrates current understanding of hepatic bile acid synthesis, enterohepatic circulation, and gut microbial bile acid transformations, detailing how bile acids function as signaling molecules through nuclear receptors including farnesoid X receptor, pregnane X receptor, vitamin D receptor, constitutive androstane receptor, and G-protein-coupled receptors; G protein-coupled bile acid receptor 1 (also known as Takeda G protein-coupled receptor 5), and sphingosine-1-phosphate receptor 2. We explore disease-specific alterations in gut microbiota composition and bile acid profiles in metabolic dysfunction-associated steatotic liver disease, alcohol-associated liver disease, cholestatic liver diseases, and liver cancers, focusing on mechanisms linking gut dysbiosis, impaired intestinal barrier function, altered bile acid signaling, inflammation, and immune modulation to liver injury and progression. Furthermore, we discuss the clinical implications, highlighting the potential of microbiome signatures and bile acid profiles as diagnostic and prognostic biomarkers. Therapeutic strategies targeting the gut-liver axis, including probiotics, fecal microbiota transplantation, farnesoid X receptor agonists, and fibroblast growth factor 19 analogs, are reviewed. Finally, we address current challenges and future directions, emphasizing the need for multiomics integration, functional studies, and personalized medicine approaches to leverage the gut-liver axis for improved liver disease management. SIGNIFICANCE STATEMENT: Disruption of the gut microbiome-bile acid-liver axis is now recognized as a unifying mechanism driving multiple liver diseases, including metabolic dysfunction-associated steatotic liver disease, alcohol-associated liver disease, cholestatic liver diseases, and hepatocellular carcinoma. Unraveling the molecular and microbial interactions within this axis offers fundamental insights into disease pathogenesis and reveals novel therapeutic opportunities. Integrating multiomics technologies with artificial intelligence-based analytics will accelerate the discovery of predictive biomarkers and personalized interventions, advancing the field toward precision-based liver disease treatment protocols.