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.
