Melatonin: A potential therapeutic agent against COVID-19

Coronaviruses (CoVs) are RNA viruses that cause infections of the respiratory, gastrointestinal, and central nervous systems, among others. The pathological symptoms of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) include excessive inflammation, elevated oxidative stress, and an exaggerated immune response, ultimately leading to a cytokine storm and  subsequent progression to acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) and often, death. Melatonin is a multifunctional and highly significant biomolecule that has anti-inflammatory, anti-oxidative, anti-apoptotic, and neuroprotective actions with no serious undesired side effects, even when administered in high doses. In this review, we present a brief account of the origin of coronaviruses, their characteristic features, infections, transmission, and the causes of coronavirus disease 2019 (COVID-19). We discuss their structure, genome organization, and mechanisms of cellular entry, as well as the pathogenicity of severe acute respiratory syndrome (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), and SARS-CoV-2. Furthermore, we provide an account of the typical characteristic features of melatonin, such as its antioxidant, anti-inflammatory, immunomodulatory, and ameliorative effects on various virus-induced infections. Additionally, we identify the rationale for using melatonin as both a prospective adjuvant with vaccine therapy, and as an antiviral immune stimulator. Finally, we provide a perspective on the use of melatonin as a treatment against COVID-19.