L-Kynurenine-d₄is intended for use as an internal standard for the quantification of kynurenine by GC- or LC-MS. L-Kynurenine is an active metabolite of tryptophan .¹It is formed from tryptophanviatryptophan 2,3-dioxygenase (TDO) or indoleamine 2,3-dioxygenase (IDO). L-Kynurenine binds to the aryl hydrocarbon receptor (AhR; Kd =^~4 µM) and increases the activity of ethoxyresorufin-O-deethylase (EROD) in H-4-II-E rat hepatoma cells (EC₅₀= 12.3 µM).²It decreases intracellular concentrations of NAD⁺in, and increases lactate dehydrogenase (LDH) activity in the supernatant of, primary human astrocytes and neurons in a concentration-dependent manner.³L-Kynurenine in combination with IFN-γ reduces lung injury induced byA. fumigatusinfection in thep47^phox-/-mouse model of chronic granulomatous disease.⁴

1.Stone, T.W., Forrest, C.M., and Darlington, L.G.Kynurenine pathway inhibition as a therapeutic strategy for neuroprotectionFEBS J.279(8)1386-1397(2012) 2.Opitz, C.A., Litzenburger, U.M., Sahm, F., et al.An endogenous tumour-promoting ligand of the human aryl hydrocarbon receptorNature478(7368)197-203(2011) 3.Braidy, N., Grant, R., Brew, B.J., et al.Effects of kynurenine pathway metabolites on intracellular NAD+ synthesis and cell death in human primary astrocytes and neuronsInt. J. Tryptophan Res.261-69(2009) 4.Romani, L., Fallarino, F., De Luca, A., et al.Defective tryptophan catabolism underlies inflammation in mouse chronic granulomatous diseaseNature451(7175)211-215(2008)