Melatonin as a Potential Regulator of Oxidative Stress, and Neuroinflammation: Mechanisms and Implications for the Management of Brain Injury-Induced Neurodegeneration

Muhammad Ikram,1,* Hyun Young Park,2,3,* Tahir Ali,1 Myeong Ok Kim1,4 1Division of Life Science and Applied Life Science (BK21 Four), College of Natural Sciences, Gyeongsang National University, Jinju, 52828, Republic of Korea; 2Department of Pediatrics, Maastricht University Medical Center, Maastricht, 6202 AZ, the Netherlands; 3School for Mental Health and Neuroscience (MHeNS), Maastricht Medical Center, Maastricht, 6229 ER, the Netherlands; 4Alz-Dementia Korea Co., Jinju, 52828, Republic of Korea*These authors contributed equally to this workCorrespondence: Myeong Ok Kim Tel +82-55-772-1345, 2655(Sec.)Fax +82-55-772-2656Email mokim@gnu.ac.krAbstract: This review covers the preclinical and clinical literature supporting the role of melatonin in the management of brain injury-induced oxidative stress, neuroinflammation, and neurodegeneration, and reviews the past and current therapeutic strategies. Traumatic brain injury (TBI) is a neurodegenerative condition, unpredictably and potentially progressing into chronic neurodegeneration, with permanent cognitive, neurologic, and motor dysfunction, having no standard therapies. Due to its complex and multi-faceted nature, the TBI has highly heterogeneous pathophysiology, characterized by the highest mortality and disability worldwide. Mounting evidence suggests that the TBI induces oxidative and nitrosative stress, which is involved in the progression of chronic and acute neurodegenerative diseases. Defenses against such conditions are mostly dependent on the usage of antioxidant compounds, the majority of whom are ingested as nutraceuticals or as dietary supplements. A large amount of literature is available regarding the efficacy of antioxidant compounds to counteract the TBI-associated damage in animal and cellular models of the TBI and several clinical studies. Collectively, the studies have suggested that TBI induces oxidative stress, by suppressing the endogenous antioxidant system, such as nuclear factor erythroid 2–related factor-2 (Nrf-2) increasing the lipid peroxidation and elevation of oxidative damage. Moreover, elevated oxidative stress may induce neuroinflammation by activating the microglial cells, releasing and activating the inflammatory cytokines and inflammatory mediators, and energy dyshomeostasis. Thus, melatonin has shown regulatory effects against the TBI-induced autophagic dysfunction, regulation of mitogen-activated protein kinases, such as ERK, activation of the NLRP-3 inflammasome, and release of the inflammatory cytokines. The collective findings strongly suggest that melatonin may regulate TBI-induced neurodegeneration, although further studies should be conducted to better facilitate future therapeutic windows.Keywords: melatonin, antioxidants, brain injury, oxidative and nitrosative stress, neurodegeneratio