The key results of the present study were: (1) the levels of GSHt and GSHr significantly decreased in the drug-naïve FESP in comparison with the control subjects. (2) the group of FESP revealed an increased activity of GPx and a decreased activity of CAT in RBCs. (3) a positive correlation exists between the score of SAPS and the levels of GSHt and GSHr. The findings of this study indicate that some FESP may be poorly equipped to deal with oxidative stress due to impaired antioxidant defenses. Moreover, oxidative stress might play a role in the brain's developmental and maturational processes in the pathogenic cascade of schizophrenia. The findings reported above suggest such a possibility and call for more systematic research on the role of oxidative stress in schizophrenia.
The detailed neurochemical mechanisms underlying the pathophysiology of schizophrenia are not clearly understood. There has been accumulating evidence supporting the involvement of oxidative stress in the pathophysiology of this disease [2
]. Prabakaran et al. [38
] reported that transcript, protein and metabolite alterations are associated with the mitochondrial function and oxidative stress in the cortex, the liver and the RBCs of schizophrenic patients. The antioxidant system eliminates reactive oxygen species to maintain a reduced environment in cells through enzymatic or non-enzymatic approaches. The most studied antioxidants are the SOD, GPx and CAT enzymes. Notably, CAT and SOD, acting in concert with GPx, constitute the major defense or primary antioxidant enzymes against superoxide radicals [39
]. However, it is important to underline the contradictions and the controversial outcomes found in the literature. In fact, these differences can be due to several variables among which are inclusion and exclusion criteria for patient selection, analytical methodologies, testing materials (blood cells vs. plasma or serum), exposure to medication (naïve vs
. drug withdrawal vs
. medicated), stages of the disease (acute vs
. chronic or active vs
. remission phase), lifestyle or dietary pattern, and the patient's origin. The main reason for the difference between the current study and those previously reported [3
], is likely to be the early stage of illness of our patient sample. Also, our study focused on drug-naïve FESP to show whether the oxidative disturbances which occur during the course of the disease can be related to the degenerative process linked to the symptoms and/or treatment, or rather related to schizophrenia and appear at an early stage of the disease. Studies comparing first-episode and chronic schizophrenic patients would be necessary to further investigate a stage-specific change in AODS in schizophrenia.
In our research, we tried to explore the activities of SOD, GPx and CAT in the RBCs of our collected samples of patients and controls. In the present study, we found that the activity of SOD, a key enzyme in the endogenous antioxidant defense pathways, did not differ between the FESP and controls. Similarly, Mico et al. [41
] found no significant difference in SOD activity between early-onset first-psychosis group and the control group. Other studies have reported lower SOD activity in neuroleptic-naïve FESP [3
]. High levels of blood SOD were reported in neuroleptic-naive schizophrenic patients [8
] and higher activities of SOD in neuroleptic-free schizophrenic patients in comparison with the schizophrenic patients treated with haloperidol [13
]. However, in our study, the levels of GPx were significantly higher in the FESP than those in control subjects. The same result observed in the early-onset first-episode psychosis by Mico et al [41
]. Yao et al. [13
] showed also a significant increase in GPx activity in drug-free schizophrenic patients compared to treated ones. In this case, increased GPx antioxidant activity may reflect a preceding cellular oxidative stress or serve as a compensatory mechanism. Interestingly, the CAT activity was significantly lower in the RBCs of drug-naïve FESP than that in control group. Other studies [3
] showed no significant difference in CAT activity between early-onset first-psychosis patients and the control subjects. Raffa et al. [28
] found a significant decrease of CAT activity in neuroleptic-free schizophrenic patients.
On the other hand, it is likely that oxidative stress injury was due to an impaired antioxidant defense in early stage of schizophrenia. Furthermore, because of their impaired antioxidant defense, some patients might be vulnerable to oxidative injury in spite of their normal oxyradical production [42
]. In recent decades, biochemical studies have increasingly more often focused on the role of free radicals in the pathogenic of neuropsychiatric diseases such as schizophrenia [43
]. In addition to the impaired antioxidant enzyme activities, we also found a decreased plasma GSHt and GSHr levels in the drug-naïve FESP. Previous studies recorded a significant decrease in the RBC levels of GSHt [26
] or of GSHr [27
] in schizophrenic patients in comparison with the controls. Plasmatic GSH level was significantly lower in the FESP [41
], magnetic resonance spectroscopy studies have shown that levels of GSH were reduced by 52% in the prefrontal cortex and by 27% in the cerebrospinal fluid of drug-naïve schizophrenic patients [24
]. However, a spectroscopy study showed that patients with first-episode psychosis had a higher concentration of GSH in the medial temporal lobe than control group [23
]. Anomalies in GSH metabolism were also supported by the low expression of the gene of the key GSH-synthesizing enzyme, glutamate cysteine ligase modifier subunit, in patient fibroblasts [30
]. The GSH deficit found in this study and in previous reports [18
] may be involved in membrane peroxidation and microlesions related to dopamine, which seem to be increased in psychosis, and suggest that GSH may be a possible indirect indicator of damage in neuronal membranes [47
]. This study of the drug-naïve FESP also suggests that the deficit in GSH may underlie the pathophysiology of the disease and is not a consequence of treatment. The converging data in literature, in agreement with our results in FESP, indicate that psychosis is associated with an important brain glutathione deficit. In fact, it could be hypothesized that different etiological mechanisms converge into precipitating a first psychotic episode in individuals with a limited GSH synthesis capacity, after which the psychotic episode develops into a degenerating condition that we call schizophrenia. This could be tested by analyzing glutathione in high-risk populations that are subsequently followed up.
In our patient group, using the SAPS, the presence of positive symptoms was associated with higher levels of GSHt and GSHr. Positive symptoms are associated with subcortical dopamine hyperactivity in schizophrenia [49
]. Several studies have revealed that catecholamines, especially dopamine, are associated with free radical generation [47
]. As suggested in the present study, this may serve as a compensatory or protective mechanism employed to neutralize oxidative stress produced from presumably supra-physiological prefrontal dopamine. Therefore, the hyperdopaminergic state in schizophrenia, induced by still unknown mechanisms, may explain the positive association between positive symptoms and GSH levels in the present study. Although, we should be cautious, our findings support the possibility of using peripheral markers of oxidative and antioxidative system in FESP, taking into account the special sensitivity of the brain to oxidative damage [50
This study has some limitations. Diagnostic groups were relatively small, and it was difficult to establish in advance a sample size to perform the data analyses because of the paucity of studies with similar design characteristics. A second limitation was the used samples were limited to blood ones. Because the data presents changes in peripheral blood, further work is needed to determine if such changes adequately reflect changes in the brain. Although, recent findings have identified a genetic origin of GSH deficit, which results in the impairment of the GSH synthesis in patients diagnosed with schizophrenia [51
]. The decreased levels of GSH and/or the activities of antioxidant enzymes in the peripheral blood of the patients may indicate the occurrence of a systematic reaction that may cause oxidative stress in the brain of schizophrenic patients as is the case in other disorders of the central nervous system [52
]. The strengths of the study are the uniformity in age with first-episode and drug-naïve of schizophrenic patients, and the existence of a control group.