GDF15 and endothelial dysfunction: Considering the speculated mechanism of GDF-15’s interaction with SARS-CoV-2 and endothelial tissue, further studies should concentrate on the association between GDF-15 and other inflammatory markers elevated in endothelial dysfunction, such as platelet factor 4 (PF-4, CXCL4) [34,35], which has recently been studied in COVID-19 patients [36,37].