Melatonin synthesized in the lungs acts as a barrier against SARS-CoV-2, preventing expression of genes that encode proteins in cells such as resident macrophages in the nose and pulmonary alveoli, and epithelial cells lining the alveoli, all of which are entry points for the virus. The hormone, therefore, prevents infection of these cells by the virus and inhibits the immune response so that the virus remains in the respiratory tract for a few days, eventually leaving to find another host.
The discovery by researchers at the University of São Paulo (USP), in Brazil, helps understand why some people are not infected or do not manifest symptoms of COVID-19 even when reliably diagnosed as carriers of the virus by RT-PCR. In addition, it offers the prospect of nasal administration of melatonin, in drops or as a spray, to prevent disease from developing in pre-symptomatic patients.
Pre-clinical and clinical trials will be needed to prove the therapeutic efficacy of melatonin against the virus, the researchers stress in an article on the study published in the journal Melatonin Research.