Reduced plasma nitric oxide metabolites before and after antipsychotic treatment in patients with schizophrenia compared to controls

Background: Nitric oxide (NO) is believed to have a role in the pathophysiology of schizophrenia. We examined plasma levels of NO metabolites in patients with schizophrenia and normal controls. We also determined the impact of 6-week risperidone treatment on circulating NO metabolites in patients with schizophrenia. Method: Plasma NO metabolite (NO_x) levels were measured in 55 schizophrenia patients before and after 6-week treatment with risperidone and in 55 normal controls. Severity of schizophrenia and response to treatment were assessed with the positive and negative syndrome scale (PANSS) for schizophrenia. NO_x levels were estimated by the Griess method. Results: Pre-treatment plasma NO_x levels in schizophrenia patients (8.97 ± 6.74 μmol/L) were lower than those of normal controls (14.51 ± 6.30 μmol/L) (p < 0.01). Schizophrenia patients had lower post-treatment NO_x levels (10.99 ± 8.31 μmol/L) than those of normal controls (p < 0.01). There was marginal significant change between plasma NO_x levels before and after 6-week treatment (p = 0.056). Moreover, in 37 treatment responders (≥ 30% improvement in PANSS score), post-treatment plasma NO_x significantly increased in comparison to pre-treatment NO_x (p = 0.028). Conclusions: Plasma levels of NO_x in patients with schizophrenia were significantly lower than normal controls both before and after the treatment. Our findings suggest that the improvement of psychiatric symptoms can lead to partially normalize a deficiency of NO after treatment in schizophrenia patients. Our findings support the hypothesis that the NO system is dampened in schizophrenia.