Quercetin Phytosome® as a potential candidate for managing COVID-19.

When looking for new antiviral compounds aimed to counteract the COVID-19, a disease caused by the recently identified novel Coronavirus (SARS-CoV-2), the knowledge of the main viral proteins is fundamental. The major druggable targets of SARS-CoV-2 include 3-chymotrypsin-like protease (3CLpro), papain-like protease (PLpro), RNA-dependent RNA polymerase, and spike (S) protein. Molecular docking studies have highlighted that quercetin, a natural polyphenol belonging to the flavonol class, inhibits 3CLpro, PLpro and S proteins. Biophysical technics have then very recently confirmed that quercetin is reasonably a potent inhibitor of 3CLpro. The likely antiviral properties of quercetin are anyway challenged by its very poor oral bioavailability profile and any attempt to overcome this limit should be welcome. A phospholipid delivery form of quercetin (Quercetin Phytosome®) has been recently tested in humans to evaluate a possible improvement in oral bioavailability. After hydrolysis of the conjugated form (mainly glucuronide) of quercetin found in human plasma, the pharmacokinetics results have demonstrated an increased bioavailability rate by about 20-fold for total quercetin. It has been also observed that the presence of specific glucuronidase could yield free systemic quercetin in human body. Taking also into considerations its anti-inflammatory and thrombin-inhibitory actions, a bioavailable form of quercetin, like Quercetin Phytosome®, should be considered a possible candidate to clinically face COVID-19.