Increased plasma level of kynurenic acid in drug-free patients with first-episode schizophrenia compared to patients with chronic schizophrenia and healthy controls: preliminary data

Kynurenic acid (KYNA) is a metabolite of tryptophan (TRP). KYNA levels have been reported with controversial findings in patients with schizophrenia.This study aimed to investigate the probable effects of medication and illness chronicity on peripheral KYNA levels in schizophrenia.We assessed peripheral (plasma) TRP metabolite levels in 38 drug-free patients with first-episode schizophrenia (FES), 65 patients with chronic schizophrenia (CHS), and 70 healthy controls by using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). The symptom severity of patients was evaluated by using the Positive and Negative Syndrome Scale (PANSS). Finally, we analyzed the association of TRP metabolites with symptom severity.We found significantly higher KYNA levels in FES patients than in both healthy controls (p < 0.01) and CHS patients (p < 0.05). No significant association was observed between plasma TRP metabolite levels and PANSS scores in either FES or CHS patients.In conclusion, elevated plasma KYNA levels may be a promising biomarker in FES patients. Medication and illness chronicity may affect peripheral KYNA levels with a currently unknown mechanism.