IDDF2024-ABS-0418 A study on the mechanism and effects of tryptophan and its metabolites on intestinal epithelial cell models in anti-inflammation

Background

Tryptophan (Trp) is an essential amino acid in the human body with a complex metabolic pathway. Recently, tryptophan metabolites have been proposed to influence intestinal ecological balance and intestinal inflammation by acting on intestinal immune cells to sustain intestinal immunological homeostasis via the aromatic hydrocarbon receptor (AHR). Nonetheless, the mechanism of action of these metabolites on intestinal epithelial cells is yet to be determined.

Methods

An intestinal epithelial cell inflammation model was established by applying lipopolysaccharide (LPS) for 24 hours on the Caco2 cell line derived from human colon carcinoma and the NCM460 cell line generated from normal human colon epithelial cells. Subsequently, L-tryptophan and its three metabolites (tryptamine, indole-3-carboxaldehyde, and L-kynurenine) were treated independently, and CH223191 (an aromatic hydrocarbon receptor antagonist) was added to explore the mechanism of action. Using an enzyme-linked immunosorbent assay (ELISA), we assessed the concentrations of TNF-α, IL-1β, IL-6 and IL-10 in the cell supernatant and the mRNA and protein expression of major regulator of intestinal permeability (Occludin, Claudin-1, ZO-1), Ahr and NF-κB were detected by real-time quantitative transcription polymerase chain reaction (RT-qPCR) and western blot.

Results

Compared with the inflammation model group, the addition of tryptophan, tryptamine, indole-3-carboxaldehyde, and L-kynurenine at a concentration of 10μmol/L resulted in a significant decrease in TNF-α, IL-1β, and IL-6 levels (P<0.05) and an elevated level in IL-10 (P<0.05), as well as a marked up-regulation (P<0.05) of the expressions of Occludin, Claudin-1, ZO-1 and Ahr protein and mRNA expressions (P<0.05) and a widespread down-regulation of NF-KB mRNA expression (P<0.05) in comparison to the experimental control group. Even so, the impact of the aforementioned medications was reversed upon the addition of CH223191, and all data was returned.

Conclusions

L-Tryptophan and its three metabolites (tryptamine, indole-3-carboxaldehyde, and L-kynurenine) upregulate aryl hydrocarbon receptors and inhibit the NF-KB signaling pathway, alleviate intestinal epithelial cell inflammation, and enhance intestinal epithelial cell tight junctions.