Plasma levels of quinolinic acid and kynurenic acid in patients with major mental illnesses

Clarifying antipsychotic effects on kynurenine-pathway metabolites may improve understanding of their role in major mental illnesses. Therefore, this study aimed to assess plasma quinolinic and kynurenic acid levels in patients with major mental illnesses. 85 adults comprising 55 treatment-experienced patients with major mental illnesses; schizophrenia, bipolar and depression, and 30 controls were enrolled into this study. The plasma levels of quinolinic acid and kynurenic acid were determined using Enzyme Linked Immunosorbent Assay. Plasma quinolinic acid level was significantly lower in patients with major mental illnesses (14.52 (7.16-48.24) mg/mL) compared with the controls (157.79 (68.64-464.05) mg/mL). In contrast, plasma kynurenic acid level was higher in patients with major mental illnesses (243.96 (210.65-283.05) μmol/L) compared with the controls (215.36 (185.67-243.65) μmol/L). After stratification into groups, patients with schizophrenia (22.86 (7.62-53.14) mg/mL), bipolar (15.34 (8.37-48.21) mg/mL) and depression (6.18 (2.66-43.05) mg/mL) had significantly lower quinolinic acid levels compared with the controls (157.79 (68.64-464.05) mg/mL). However, kynurenic acid levels were only significantly elevated in patients with schizophrenia (247.0 (208.34-290.22 μmol/L) and bipolar (243.20 (212.85-291.12) μmol/L) compared with the controls (215.36 (185.67-243.65) μmol/L). The plasma levels of quinolinic acid and kynurenic acid did not differ significantly among patients with schizophrenia, bipolar disorder, and depression. Treated patients with major mental illnesses exhibited a kynurenine metabolite profile indicative of reduced neurotoxicity and enhanced neuroprotection. These metabolites may serve as potential biomarkers for monitoring treatment effects Received: 27.12.2025 | Revised: 16.04.2026 | Accepted: 26.05.2026