Indole-3-Acetic Acid Improves Intestinal Inflammation and Intestinal Barrier Dysfunction In Vitro via the AHR/NF-κB Signaling Pathway

Impairment of intestinal barrier function is intricately linked to intestinal inflammation. Emerging evidence highlights that tryptophan-derived metabolites from the intestinal microbiota play a crucial role in maintaining the homeostasis of intestinal barrier function. In this study, a Caco-2/HT29 co-culture model was applied to evaluate the effects of indole-3-acetic acid (IAA) on the intestinal barrier and explore its underlying mechanism of action. Results demonstrated that lipopolysaccharide (LPS) caused the transepithelial resistance to drop to 387.5 ± 30.41 Ω·cm 2 , while IAA was able to increase it to 542 ± 31.11 Ω·cm 2 . At the same time, it reduced the paracellular permeability and restored the FITC-Dextran 4 (FD-4) permeability to 108.01%. This phenomenon was accompanied by an upregulation in the expression of tight junction (TJ) proteins. Concurrently, after IAA intervention, aryl hydrocarbon receptor (AHR) pathway was activated, while nuclear factor kappa-B (NF-κB) pathway was significantly inhibited. Furthermore, IAA exerted an inhibitory effect on the LPS-triggered upregulation of inflammatory factors (TNF-α, IL-6, IL-8) in RAW264.7 cells. These findings provide novel insights into the enhancement of intestinal barrier function and the in vitro anti-inflammatory properties of gut microbiota-derived metabolites.