Flavonoids and other polyphenols against SARS-CoV-2

Phytonutrients (plant chemicals) called flavonoids may be detected in almost all fruits and vegetables. They are responsible for the brilliant colors of fruits and vegetables, together with carotenoids. Flavonoids, like other phytonutrients, are potent antioxidants with antiinflammatory and immune-enhancing characteristics. Polyphenols may diminish severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) viral infection by linking to the angiotensin-converting enzyme 2 (ACE-2) linking site and limiting viral entrance, as well as regulating the severity of COVID-19 lung destruction by controlling ACE-2 expression. A new potential relationship between SARS-CoV-2 and the co-receptor dipeptidyl peptidase 4 (DPP4) may induce the expansion of newer COVID-19 treatment methods, in addition to ACE-2. After glycosylation, flavonoids' solubility in water is significantly enhanced, which increases their pharmacological actions. Antioxidant and antiinflammatory effects have been discovered in resveratrol (RSV). Quercetin was discovered to have a possible repressing consequence against SARS-CoV-2 in a computer simulation. Main protease (Mpro) had a significant preference for quercetin. According to a computer study, the flavonoids icariin, myricitrin, naringin, quercitrin, and neohesperidin have a significant interaction potential for transmembrane protease serine 2 (TMPRSS2). The bioavailability improvement of quercetin has also been shown in vivo. The novel nanovesicles exhibited extended drug durability and significant therapeutic impact compared to uncoated ones due to chitosan resistance to stomach acid. This chapter aims to explain the use of flavonoids and other polyphenols against SARS-CoV-2.