Abstract: Hypothesis/Objectives – Human and rodent studies implicate microbial indole catabolites of tryptophan (MICT) in the regulation of intestinal mucosal barrier function and inflammatory responses. We hypothesized that two MICTs, indolepropionate (IPA) and indolealdehyde (IAld), would ameliorate epithelial barrier dysfunction and pro-inflammatory responses induced by TNFα. Animals – In-vitro investigation using colonic epithelial organoids from a healthy dog (colonoids). Methods – Colonoids were pre-incubated with IPA (1 mM) or IAld (1 mM), then exposed to TNFα (0.3 nM). Mucosal barrier function was assessed using transepithelial electrical resistance (TEER) and mRNA sequencing was used to compare gene expression responses. Results – TEER (mean ± SD) was significantly decreased following exposure to TNFα (1898.4 ± 340.9 Ω x cm2) compared to pre-exposure baseline (3035.3 ± 265.5 Ω x cm2; p<0.001). TEER was significantly higher in colonoids exposed to IPA+TNFα (2838.9 ± 213.6 Ω x cm2; p<0.001) and IAld+TNFα (2979.2 ± 290.2 Ω x cm2; p=0.001) compared to colonoids exposed to TNFα alone (1898.4 ± 340.9 Ω x cm2). Relative expression of genes regulating inflammatory responses and tight junction integrity were significantly altered by stimulation with TNFα. IPA and IAld ameliorated changes in expression of pro-inflammatory genes induced by TNFα. Conclusions and Clinical Importance – IPA and IAld regulate intestinal permeability and pro-inflammatory gene expression, thereby ameliorating barrier dysfunction and inflammatory responses induced by TNFα in canine colonoids. These observations provide mechanistic insights to enteric microbiome-host interactions, their influence on intestinal homeostasis, and novel therapeutic strategies in dogs with chronic enteropathies.
