Oxidative/nitrative modifications of plasma proteins and thiols from patients with schizophrenia.

OBJECTIVE: The level of various specific biomarkers of oxidative stress in plasma from schizophrenic patients, as well as biomarkers (the level of isoprostanes) in urine in schizophrenic patients was described. The aim of our present study was to evaluate biomarkers of oxidative stress by oxidative/nitrative modifications of plasma proteins (by measuring the level of carbonyl groups and 3-nitrotyrosine in proteins) from patients with schizophrenic disorders and from control group. We also investigated the level of low-molecular-weight thiols [glutathione (GSH), cysteine (CSH), cysteinylglycine (CGSH) and homocysteine] in plasma obtained from schizophrenic patients and from healthy volunteers. Patients hospitalized in the 1st and 2nd Psychiatric Department of the Medical University in Lodz, Poland were interviewed with a special questionnaire (treatment, course of diseases, dyskinesis and other extrapyramidal syndromes). According to DSM-IV criteria, all patients had a diagnosis of paranoid type. They were treated with antipsychotic drugs (clozapine, risperidone, olanzapine). The mean duration of schizophrenia was about 5 years. METHODS: Levels of carbonyl groups and 3-nitrotyrosine residues in plasma proteins were measured by ELISA and a competition ELISA, respectively. High-performance liquid chromatography was used to analyze free thiols in plasma. RESULTS: We observed a statistically increased level of biomarkers of oxidative/nitrative stress such as carbonyl groups or 3-nitrotyrosine in plasma proteins from schizophrenic patients. In schizophrenic patients the amount of homocysteine in plasma was higher compared with the control group; the level of GSH, CSH and CGSH was decreased. This indicates that reactive oxygen species and reactive nitrogen species may stimulate oxidative/nitrative modifications of plasma proteins in schizophrenic patients. CONCLUSION: Considering the data presented in this study, we suggest that the amount of carbonyl groups and 3-nitrotyrosine in plasma proteins may be important indicators of protein damage in vivo in schizophrenia.