Flavonoids as Complementary Medicines for Therapy and Prevention of COVID-19: Part I. Experimental and Clinical Applications

The first part of this review is devoted to an analysis of the beneficial effect of flavonoids on the prevention, course, and outcomes of COVID-19. In addition to the well-known antioxidant, anti-inflammatory, immunomodulatory, antithrombotic, and antitumor effects, flavonoids, secondary metabolites of many plants, exhibit antiviral activity and low cytotoxicity. The basic stages of SARS-CoV-2 replication and COVID-19 pathogenesis are considered to identify possible targets for flavonoids. The effect of these polyphenolic compounds on SARS-CoV-2 both in in vitro systems and in animal models that adequately reproduce COVID-19 symptoms have been analyzed. The results of the first clinical trials on the prevention of this disease and the feasibility of using flavonoids, mainly quercetin, as adjuvant therapy are discussed.