Altered tryptophan metabolism and AhR-associated epithelial barrier dysfunction in diet-induced obese mice with...

Obesity may modify intestinal inflammation through altered microbial metabolism and epithelial barrier regulation. We combined acute and chronic dextran sulffate sodium (DSS) colitis model in high-fat diet (HFD)-induced obese mice with fecal microbiota sequencing, fecal and colonic metabolomic profiling, pharmacological intervention and Caco-2 barrier assays with aryl hydrocarbon receptor (AhR) knockdown. Obese mice developed more severe colitis accompanied by alterations in gut microbiota composition and tryptophan metabolism and reduced colonic AhR, CYP1A1, and ZO-1 levels. Fecal tryptamine levels were positively correlated with Ligilactobacillus abundance, while colonic tryptophan metabolite profiles were also altered. In Caco-2 cells, palmitic acid (300 μM) and oleic acid (150 μM), combined with tumor necrosis factor-α and interferon-γ, impaired barrier function. Tryptamine (100 μM) and 6-formylindolo[3,2-b]carbazole (FICZ; 50 nM) increased nuclear AhR abundance and CYP1A1 protein levels. Both treatments partially ameliorated barrier dysfunction, increasing transepithelial electrical resistance, reducing FITC-dextran permeability, and enhancing ZO-1 staining, without restoring claudin-3. Following AhR knockdown, tryptamine treatment was associated with a lower mean basolateral FITC-dextran concentration but no significant restoration of CYP1A1 or ZO-1; FICZ did not significantly improve permeability. FICZ also attenuated colonic mucosal injury in both acute and chronic colitis models. These findings extend the evidence for AhR-mediated barrier regulation to obesity-associated colitis and provide a basis for further investigation of potential causal links between altered microbial metabolism and epithelial barrier dysfunction.