Simultaneous measurement of tryptophan and related compounds by liquid chromatography/electrospray ionization tandem mass spectrometry

We have expanded a liquid chromatographic–tandem mass spectrometric method that measures 3-hydroxykynurenine and 3-hydroxyanthranilic acid in addition to tryptophan and kynurenine both intra- and extracellularly. After reversed phase HPLC separation, the compounds were detected in the MS positive multiple reaction monitoring mode. We found a good linear response for each tryptophan metabolite. The lower limit of quantification for each compound ranged from 0.01 to 0.1 μM. The extraction efficiencies from spiked cell samples and culture medium ranged between 83 and 111% and the overall coefficient of variation of analyses was less than 7%. Using our method, we found tryptophan metabolites in the cells and the culture medium of LN229 human glioma cells were stimulated by interferon-γ, a known inducer of indoleamine 2,3-dioxygenase. The intracellular concentrations of kynurenine, 3-hydroxykynurenine and 3-hydroxyanthranilic acid were higher than those in the medium. This is the first report of a method for the simultaneous determination of tryptophan and its metabolic products both intra- and extracellularly.