These in vitro findings are consistent with clinical studies indicating that arginine metabolism is altered in COVID-19: a recent study found that COVID-19 patients with ARDS exhibit lower levels of soluble eNOS compared to COVID-19 non-ARDS patients [18]; the activity of arginase has been reported, instead, to be upregulated in patients with COVID-19, where it favors the production of ornithine and its metabolites from arginine over the synthesis of NO [17,33,34]. This evidence concerns the gene NOS3 and acute respiratory distress syndrome.