Potential value of circulating endothelial cells for the diagnosis and treatment of COVID-19.

The ongoing severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic has been a formidable global challenge. As yet, there are very few drugs to treat this infection and no vaccine is currently available. It has gradually become apparant that coronavirus disease 2019 (COVID-19) is not a simple disease involving a single organ; rather, many vital organs and systems are affected. The endothelium is one target of SARS-CoV-2. Damaged endothelial cells, which break away from organs and enter the bloodstream to form circulating endothelial cells, were recently reported as putative biomarkers for COVID-19. Modulation of the expression level of sphingosine-1 phosphate via sphingosine kinase activation can control endothelial cell proliferation and apoptosis. As such, it may be possible to obtain a sensitive and specific diagnosis of the severity of COVID-19 by assessing the absolute number and the viable/apoptotic ratio of circulating endothelial cells. Furthermore, a focus on the endothelium could help to develop a strategy for COVID-19 treatment from the perspective of endothelial protection and repair.