Human plasma glutathione peroxidase and symptom severity in schizophrenia

Background: Previous studies have shown impaired antioxidant defense system in schizophrenia, including alterations in glutathione peroxidase (GSH-Px) activity in erythrocytes. There exists a related enzyme, human plasma GSH-Px (hpGSH-Px), that has not been previously examined in schizophrenia. Methods: An enzyme-linked immunoassay was used to determine hpGSH-Px levels in male schizophrenic patients (n = 39), using a within-subject, on–off haloperidol (HD) treatment design, compared with age- and gender-matched normal control subjects (n = 37). Results: hpGSH-Px was not significantly different between normal control subjects and patients, consistent with our previous findings in erythrocyte GSH-Px. There were no significant treatment effects. hpGSH-Px was significantly and positively correlated with psychosis rating scores in patients both on and off HD treatment. Conclusions: Although not different from normal controls, hpGSH-Px levels in patients may reflect oxidative stress associated with greater psychosis severity. The present findings thus suggest that schizophrenic patients, without obvious increase of endogenous antioxidant enzymes (e.g., hpGSH-Px), may be at risk for oxidative damage.