Targeting neuroinflammation by polyphenols: A promising therapeutic approach against inflammation-associated depression

Depression is the most prevalent and debilitating mental disorder that affects a substantial number of people globally, hindering all aspects of their lives and leading to a high number of suicides each year. Despite the availability of an array of antidepressant medications, taking these medications does not relieve depressive symptoms in a considerable number of patients, implying that an incomplete understanding of the pathomechanisms involved in the development of depression. Besides that, a subset of those non-responsive patients exhibits an increased systemic and central inflammatory response, which has collectively led to the evolvement of the inflammatory theory of depression. Indeed, peripherally generated inflammatory mediators, as well as insults within the brain, can activate the brain's resident immune cells, resulting in a neuroinflammatory response that interferes with the multitude of neurobiological domains implicated in the pathogenesis of depression. Polyphenols, a group of plant-derived bioactive molecules, have been shown to exert neuroprotective functions on the brain by influencing an array of neuropathological mechanisms, including neuroinflammation. From these perspectives, this review mechanistically provides an overview of the neuropathological roles of sustained neuroinflammatory response in the development of depression and elucidates the therapeutic potential of flavonoid and nonflavonoid polyphenols in modulating inflammatory mediators and signaling cascades as well as promoting other neurophysiological and neuroprotective functions underlying inflammation-associated depressive symptoms. Therefore, given their significant anti-neuroinflammatory effects, polyphenols could be a promising and effective adjunctive therapy for the treatment of neuropsychiatric symptoms associated with