OCLN and colitis: Three tryptophan metabolites (indole-3-ethanol at 600 mg/kg mice, indole-3-pyruvate at 2,900 mg/kg mice, and indole-3-aldehyde at 1,000 mg/kg mice) administration increased gene expression levels of occludin and ZO-1, thereby enhancing adhesive forces between adjacent epithelial cells in order to seal the weakened intestinal barrier of colitis mice induced by dextran sodium sulfate (36).