Determination of kynurenic acid in human serum and its correlation with the concentration of certain amino acids

BackgroundKynurenic acid (KYNA)—a tryptophan metabolite—elicits antagonistic activity against glutaminergic and cholinergic receptors; it has been suggested to have some relationship with neurological disorders. Considering this, serum KYNA may be an important marker in clinical diagnosis. We determined serum KYNA concentration and elucidate its correlation with several amino acids in human serum.MethodsKYNA and amino acids concentrations in human serum of healthy subjects [n = 35 (21 males and 14 females)] were determined by HPLC with fluorescence detection; thus, the correlation between KYNA concentration and that of several amino acids was examined in these subjects.ResultsOf the amino acids examined in this study, a significant negative correlation was observed between KYNA and glutamine (Gln) concentrations (r = − 0.452, p < 0.01) in the healthy subjects, particularly males (r = − 0.687, p < 0.01), and age-related changes were not observed. In addition to Gln, Gly and Ala concentrations showed a significant negative correlation with KYNA concentration in the serum of male subjects (r = − 0.440 and − 0.456, respectively, p < 0.05).ConclusionThe significant correlation between KYNA and Gln concentrations in vivo may support the previous finding that kynurenine aminotransferase I (KAT I), responsible for the biosynthesis of KYNA, was identical to Gln transaminase K (GTK), which catalyses the transamination of Gln to 2-oxoglutamic acid. Both KYNA and Gln concentrations in vivo might be influenced due to altered KAT I/GTK activity.