Indole‑3‑propionic acid alleviates intestinal epithelial cell injury via regulation of the TLR4/NF‑κB pathway to improve intestinal barrier function.

Indole‑3‑propionic acid (IPA), a product of metabolism, has been shown to improve intestinal barrier function. In the present study, in vitro experiments using NCM460 human colonic epithelial cells were performed to investigate how IPA alleviates lipopolysaccharide (LPS)‑induced intestinal epithelial cell injury, with the aim of improving intestinal barrier function. In addition, the underlying mechanism was explored. NCM460 cell viability and apoptosis were measured using the Cell Counting Kit‑8 assay and flow cytometry, respectively. The integrity of the intestinal epithelial barrier was evaluated by measuring transepithelial electrical resistance (TEER). The underlying molecular mechanism was explored using western blotting, immunofluorescence staining, a dual luciferase reporter gene assay and quantitative PCR. The results showed that 10 µg/ml LPS induced the most prominent decrease in cell viability after 24 h of treatment. By contrast, IPA effectively inhibited LPS‑induced apoptosis in the intestinal epithelial cells. Additionally, >0.5 mM IPA improved intestinal barrier function by increasing TEER and upregulating the expression of tight junction proteins (zonula occludens‑1, claudin‑1 and occludin). Furthermore, IPA inhibited the release of pro‑inflammatory cytokines (IL‑1β, IL‑6 and TNF‑α) in a dose‑dependent manner and this was achieved via regulation of the Toll‑like receptor 4 (TLR4)/myeloid differentiation factor 88/NF‑κB and TLR4/TRIF/NF‑κB pathways. In conclusion, IPA may alleviate LPS‑induced inflammatory injury in human colonic epithelial cells. Taken together, these results suggest that IPA may be a potential therapeutic approach for the management of diseases characterized by LPS‑induced intestinal epithelial cell injury and intestinal barrier dysfunction.