The role of oxidative stress in the pathomechanism of major mood disorders: a narrative review with a special focus on uric acid.

Major mood disorder (i.e. major depressive disorder [MDD] and bipolar disorders [BPDs]) are among the most prevalent and disabling mental illnesses. Several, frequently intertwining theories (such as the monoamine, neuroinflammatory and neurotrophic theories) exist to explain the etiopathogenic background of mood disorders. A lesser-known hypothesis addresses the role of oxidative stress (OS; i.e. the overproduction and accumulation of free radicals) in the pathogenesis of these mental disorders. Free radicals are capable of damaging phospholipids, polyunsaturated fatty acids, proteins and nucleic acids. In the brain, OS impairs inter alia synaptic signalling and neuroplasticity. In the current paper, in addition to a brief description of the aforementioned pathophysiological processes involved in mood disorders (with a special focus on OS), we discuss in detail the results of studies on changes in non-enzymatic antioxidant uric acid (UA) levels in major mood disorders. Findings to date indicate that UA - a routinely measured laboratory parameter - may be a candidate biomarker to distinguish between MDD and BPD. Since the diagnostic criteria are identical for major depressive episodes regardless of whether the episode occurs in the context of MDD or BPD and also bearing in mind that the treatment for those two disorders is different, we may conclude that the identification of biomarkers to enable MDD to be distinguished from BPD would be of great clinical relevance.