Biomarkers of oxidative stress in models of schizophrenia.

Increasing evidence indicates that oxidative injury exists in schizophrenia. Although it may not be the main cause, oxidative damage has been suggested to contribute to the pathophysiology and may account for deteriorating course and poor outcome in schizophrenia. There is increasing interest in the neuroprotective efficacy of antioxidants in modulating such processes, with at least one polyphenolic being tested as a prophylactic in Alzheimers disease. Beneficial effects have been reported for adjunctive omega-3 (n-3 series) polyunsaturated fatty acids, with combined intakes of vitamin C and E on both the positive and negative symptoms of schizophrenia. Robust in vitro systems are desirable, enabling a mechanistic investigation of the molecular mechanisms underpinning such effects as well as identification of additional potentially efficacious nutraceuticals. This thesis undertook comparative studies using a lymphoblastoid cell line of schizophrenic origin, a neuroblastoma IMR-32 cell line and the lymphoma U937 cell line. For the three cell lines, the study assessed the cytoprotective effects of phenolic antioxidants and essential fatty acids in affording protection to cellular DNA, protein and lipids from an oxidative challenge. In addition, two human studies were undertaken. The first study utilised the non-invasive technique of breath hydrocarbon analysis. The lipid peroxidation products were compared between a population of schizophrenic patients and a population of apparently-healthy, aged-matched control subjects. The second study investigated possible differences in biomarkers of DNA, lipid and protein oxidation in schizophrenic and control subjects. Plasma vitamin C levels were also compared in both groups. In terms of the cell culture studies, the thesis found that pre-treatment of peripheral and neuronal cells with antioxidant or omega-3 fatty acids followed by an oxidative challenge significantly reduced the levels of DNA damage. Treatment with H2O2 alone and following pre-treatment with EPA or DHA had no effect on the levels of protein carbonyls in U937 cells. However, DHA supplementation did appear to reduce endogenous and H2O2-induced protein carbonylation. Marked differences were found in the uptake of fatty acids by the cell types and the IMR-32 cell line was found to be most susceptible to the oxidant challenge. Hydroxytyrosol gave significant cytoprotection in all three cell lines and this possible neuroprotective efficacy warrants further investigation, both in vitro and in vivo. Treatment of the three cell lines with a high concentration of H2O2 for 30min or 4 hours did not induce a significant increase in MDA. U937 cells were supplemented for 24 hours with fatty acids followed by a 4 hour oxidative stress. Both EPA and DHA treatment appeared to reduce LOOH levels in the U937 cells, but not significantly. Cytoplasmic PLA2 activity in the three human cell lines was examined, and the basal level of cPLA2 activity was found to be comparable in the lymphoblastoid and IMR-32 cells, but significantly lower than that measured in the U937 cells. Supplementation of the U937 cell line with EPA caused a significant decrease (p < 0.05) in cPLA2 activity relative to the vehicle-treated control, but neither EPA nor DHA supplementation appeared to have any significant effect on either total PLA2 or cPLA2 activity in IMR-32 or lymphoblastoid cell lines. In terms of the human studies, no significant difference was found between the levels of ethane and pentane in the breath from the schizophrenic patients and control samples. In addition, no significant difference in the levels of plasma MDA between the two groups was detected. Ethane levels and MDA levels were higher in the male schizophrenic samples than in the female schizophrenic samples, but the results were not statistically significant. The pentane levels were higher in the female schizophrenic samples when compared to the male schizophrenia samples, but again these were not significantly greater. Finally, results of study 2 revealed that cellular DNA damage and plasma protein carbonyl levels were increased in the schizophrenic group compared to control subjects, but not significantly. However, DNA damage in lymphocytes from the male schizophrenic group was significantly higher than the female group. Biomarkers of lipid peroxidation and plasma vitamin C levels also revealed no significant difference between the two groups under investigation, although a significant elevation in plasma vitamin C was observed in the female control group when compared to the male groups. Treatment of cells with EPA, DHA and hydroxytyrosol to reduce levels of oxidative damage warrants further investigation. Ultimately, it is important to investigate a range of biomarkers to determine whether the measurement of oxidative damage to lipids, proteins and DNA has clinical significance. This will enable better understanding of the disease and allow these biomarkers to become potentially useful clinical tools.