The Role of Oxidative Stress in Depressive Disorders

Studies of the World Health Organization suggest that in the year 2020, depressive disorder will be the illness with the highest burden of disease. Especially unipolar depression is the psychiatric disorder with the highest prevalence and incidence, it is cost-intensive and has a relatively high morbidity. Lately, the biological process involved in the aetiology of depression has been the focus of research. Since its emergence, the monoamine hypothesis has been adjusted and extended considerably. An increasing body of evidence points to alterations not only in brain function, but also in neuronal plasticity. The clinical presentations demonstrate these dysfunctions by accompanying cognitive symptoms such as problems with memory and concentration. Modern imaging techniques show volume reduction of the hippocampus and the frontal cortex. These findings are in line with post-mortem studies of patients with depressive disorder and they point to a significant decrease of neuronal and glial cells in cortico-limbic regions which can be seen as a consequence of alterations in neuronal plasticity in this disorder. This could be triggered by an increase of free radicals which in turn eventually leads to cell death and consequently atrophy of vulnerable neuronal and glial cell population in these regions. Therefore, research on increased oxidative stress in unipolar depressive disorder, mediated by elevated concentrations of free radicals, has been undertaken. This review gives a comprehensive overview over the current literature discussing the involvement of oxidative stress and free radicals in depression. Methods: We have carried out a medline search "oxidative stress depression", "oxidative stress affective disorders", "free radicals and depression", "free radicals and affective disorders" "antidepressants oxidative stress" "antidepressants and free radicals". We found numerous reports elaborating depressive disorder and oxidative stress. Most of the previous studies concentrated on investigating antioxidants in human blood as well as in animal models. However, few of these reports were able to show correlations of reduced oxidative stress with antidepressant treatment and clinical outcome measures. Fewer studies elaborated the concentrations of antioxidants in the human brain and some pro-oxidative enzymes in depression. However, more studies are needed to elucidate the complex role of oxidative stress in the aetiology of depression.