Increased Levels of Kynurenine and Kynurenic Acid in the CSF of Patients With Schizophrenia

The kynurenic acid (KYNA) hypothesis for schizophrenia is partly based on studies showing increased brain levels of KYNA in patients. KYNA is an endogenous metabolite of tryptophan (TRP) produced in astrocytes and antagonizes N-methyl-D-aspartate and α7* nicotinic receptors. The formation of KYNA is determined by the availability of substrate, and hence, we analyzed KYNA and its precursors, kynurenine (KYN) and TRP, in the cerebrospinal fluid (CSF) of patients with schizophrenia. CSF from male patients with schizophrenia on olanzapine treatment (n = 16) was compared with healthy male volunteers (n = 29). KYN and KYNA concentrations were higher in patients with schizophrenia (60.7 ± 4.37nM and 2.03 ± 0.23nM, respectively) compared with healthy volunteers (28.6 ± 1.44nM and 1.36 ± 0.08nM, respectively), whereas TRP did not differ between the groups. In all subjects, KYN positively correlated to KYNA. Our results demonstrate increased levels of CSF KYN and KYNA in patients with schizophrenia and further support the hypothesis that KYNA is involved in the pathophysiology of schizophrenia.