The gut microbiota metabolite isovalerate enhances the epithelial barrier function in cell monolayers derived from porcine ileum organoids

The gut microbiota produces numerous metabolites that influence the epithelial barrier function. Bacterial catabolism of amino acids produces a wide variety of metabolites whose effects on the intestinal epithelium remain to be identified. In this study, we investigated the effects of amino acid derived metabolites (isovalerate, isobutyrate, 2-methylbutyrate, 5-aminovalerate, cadaverine, putrescine, and tryptamine) in cell monolayers derived from porcine ileum organoids. Our results show that the branched-chain fatty acid (BCFA) isovalerate improved the epithelial barrier function, as assessed by transepithelial electrical resistance measurement and paracellular permeability assay. Isovalerate upregulated the expression of genes involved in innate immunity, markers of absorptive and enteroendocrine cells while reducing the expression of stem cells and mucus related genes. Most of the effects of isovalerate on epithelial cells were also observed with the butyrate, an inhibitor of the epigenetic enzymes histone deacetylases (HDAC). We found that isovalerate also inhibited HDAC, although to a lesser extent than butyrate. Furthermore, the structurally unrelated HDAC inhibitor trichostatin A improved epithelial barrier function and upregulated SLPI and IL10RA gene expression, as observed with isovalerate and butyrate. Interestingly, the other two BCFAs isobutyrate and 2-methylbutyrate did not replicate the effects of isovalerate. Overall, our in vitro results suggest that targeting the bacterial production of isovalerate may be useful to promote gut health. In this perspective, we performed an in silico analysis that identified species belonging to dominant gut microbiota genera such as Prevotella, Blautia, Christensenella, Clostridium, and Ruminococcus, as potential producers of BCFAs through the POR enzymatic pathway.