Diet-conditioned microbiota enhances fecal microbiota transplantation efficacy in alcoholic liver disease through caproic acid-PPARα signaling

Abstract Background and Aim Fecal microbiota transplantation (FMT) in Alcohol-related liver disease (ALD) has shown therapeutic potential, with variable efficacy and unclear mechanism. Because dietary protein influences gut microbiota composition, we hypothesized that donor dietary preconditioning could enhance FMT efficacy. We therefore examined in a murine ALD model if high-protein donor diet improves FMT outcome. Methods ALD was induced in C57BL/6N mice using a Lieber–DeCarli ethanol diet combined with thioacetamide administration for 12 weeks. FMT was performed using stool from diet-modulated donors, and recovery was assessed on day7 post-FMT. Multi-omics analysis using 16s rRNA and mass spectroscopy was performed for Gut microbiota composition, plasma- and stool-metabolome, and hepatic proteomes. Multi-omics outcomes were validated in ALD animal and Huh7 hepatocytes. Results Both protein-based FMTs improved ALD recovery; Veg-FMT demonstrated superior efficacy, significantly reducing hepatic injury (AST 1.2-fold, p=0.002; bilirubin 1.2-fold, p=0.03; steatosis 1.7-fold,p=0.01) and restoring gut barrier integrity (occludin 1.5-fold,p=0.04; mucin 2 2.2-fold, p=002; and plasma endotoxin 1.7-fold, p=0.02). A significant 2-fold increase was observed in Lachnospiraceae NK4A136, Coriobacteriaceae UCG-002, and short-chain fatty acids, particularly caproic acid. Functional validation confirmed that caproic acid promoted hepatic fatty acid β-oxidation through PPARα-dependent mechanisms, reducing triglyceride accumulation and lipogenesis in both cellular and animal models. Conclusion Donor preconditioning with a plant-protein enriched diet enhances FMT efficacy in ALD by gut microbiota modulation with increased metabolites like caproic acid. These findings highlight a microbiota-metabolite-host axis through which diet-modulated FMT improves hepatic lipid metabolism and injury, and identifies a pathway via which FMT imparts its effect. Significance This study identifies a mechanistic basis for improving fecal microbiota transplantation (FMT) efficacy in alcohol-related liver disease (ALD) by demonstrating that dietary preconditioning of donor microbiota improves therapeutic outcomes. We show that plant protein–modulated donor microbiota supplements abstinence-associated recovery through increased production of the microbial metabolite caproic acid, which promotes hepatic fatty acid β-oxidation via PPARα signaling. These findings highlight donor dietary conditioning and microbiota-derived metabolites, rather than microbial composition alone, as important determinants of FMT efficacy. The results suggest that microbial metabolites such as caproic acid may represent potential therapeutic targets or biomarkers to enhance and standardize microbiota-based interventions in ALD. Although the current work is based on a murine model, the identified microbiota–metabolite–host metabolic axis provides a framework for future translational studies aimed at optimizing FMT strategies in liver disease.