Original articleEffects of tryptophan, kynurenine and kynurenic acid exerted on human reconstructed corneal epithelium in vitro

BackgroundTryptophan metabolites formed along kynurenine pathway may affect cell proliferation and tissue function. This pathway presents potential sites for drug discovery. Tryptophan and its metabolites kynurenine and kynurenic acid may be involved in the physiology and pathology of the ocular surface. The purpose of this work is to investigate the effect exerted by tryptophan, kynurenine and kynurenic acid upon corneal epithelium.MethodsA SkinEthic™ HCE human reconstructed corneal epithelium model was used. WST-1 test was used to examine cell proliferation and viability, and the Griess reaction for nitric oxide determination. The levels of IL-6 and IL-10 were measured by means of ELISA assay. All analyses were carried out after the cells were exposed to tryptophan, kynurenine and kynurenic acid at concentrations of 5, 50 or 100 μM for 0-24 h and 24-48 h.ResultsTryptophan (100 μM), kynurenine (100 μM) and kynurenic acid (5-100 μM) slightly increased the viability and proliferation of corneal epithelium. All of the tested compounds decreased cellular NO release. Kynurenine (50-100 μM) and tryptophan (50-100 μM) decreased while tryptophan (5 μM) and kynurenic acid (100 μM) increased the release of IL-6. All of the tested substances increased the level of IL-10 and decreased the IL-6 to IL-10 ratio.ConclusionsTryptophan, kynurenine and kynurenic acid affect physiological processes in corneal epithelium and therefore may play a significant role in the physiology and pathology of the ocular surface. Our results indicate that the use of these compounds may be considered in the treatment of ocular surface diseases.