Quercetin for the Experimental Treatment of COVID-19

Introduction

The COVID-19 Pandemic which is caused by the SARS CoV-2 virus has engulfed the whole world and destroyed the economies of many countries. Therefore, in search of treatment and prophylaxis of COVID 19 Quercetin which is a flavonoid obtained from plants and various sources like grapes, onion, tomatoes, apple, etc (Lakhanpal, 2007) and has different properties like anti-inflammatory property, cardioprotective and neuroprotective properties is reviewed for its anti-viral properties so that it can be considered as one of the adjuvant treatments along with the Pharmacological treatments like Remdesivir and convalescent plasma therapy. A review of the antiviral property of Quercetin from reputed published articles suggests that Quercetin has a strong antiviral activity towards SARS C0V-2 and other upper respiratory tract viruses. Quercetin helps in inhibiting the viral infection by different mechanisms such as blocking the entry of the virus, interfering with the DNA and RNA polymerases, and inhibiting reverse transcriptase enzyme (Colunga 2020). Therefore, it is suggested to consider the use of quercetin in high-risk populations for COVID-19 in combination with other pharmacological therapies. Quercetin was found economical to use and did not show severe side effects. Severe Acute Respiratory syndrome also known as SARS CoV-2 has become one of the deadliest pandemic mankind has ever seen. It is not only destroying human life but also the economies of the country. Till 13^th September 2020 the recorded cases worldwide are 299,110,980 out of which 926, 925 patients have died. Therefore, the need of the hour is to develop a pharmacology-based treatment for the COVID-19 disease. A flavonoid is known as Quercetin which has been proved to have very good Antiviral properties can be safely and economically used to fight COVID-19. For high-risk populations, this drug can be an excellent choice of treatment. Here we are providing evidence for the use of Quercetin in association with Pharmacological Treatments like Remdesivir or convalescent plasma therapy (Figure 1).

Figure 1.

Natural sources of quercetin and its biological effects

Background

Natural products were known for their beneficial properties for wellbeing sometime before flavonoids were identified and isolated. More than 4000 assortments of flavonoids have been recognized, a large number of which are liable for their appealing shades of blossoms, leaves, and fruits. In nature, flavonoids are available as methylated derivatives, glycosides, and aglycones. In a six-membered ring, a benzene ring is condensed in flavonoid aglycone whereas a substituent in the second position phenyl ring is present. Based on the molecular structure, flavonoids are differentiated into various classes such as flavone, flavonol, flavanone, flavanol, isoflavone, and anthocyanidin mainly as given in Figure 1 (Lakhanpal and Rai, 2007). A dihydro derivative of pyrone or pyrone itself is attached to the six-membered ring. Classification of flavonoids into isoflavonoids and flavonoids is based on the position of the benzenoid substituent. The difference between flavanones and flavonols is because of the double bond at C2 and C3 position and hydroxyl group which is at the third position (Havsteen, 1983). Quercetin is Widely found in Vegetables, leaves, grains, and seeds the plant flavonoid quercetin which is also known as 3,3′,4′5,7-pentahydroxyflavone forms quercetin glycosides by conjugating with residual sugars (Li et al., 2016). It is very much evident from various studies that quercetin has antiviral, anti-inflammatory (Uchide and Toyoda, 2011), antioxidant (Robaszkiewicz et al., 2007), and immunoprotective effects (Nair et al., 2002). Because of the Polymerase inhibiting the activity of quercetin studies have been conducted on various models of viral infections in inhibiting polymerases (Shinozuka et al., 1988), reverse transcriptase (Spedding et al., 1989), proteases (Bachmetov et al., 2012), binding viral capsid proteins, and suppressing DNA gyrase (Debiaggi et al., 1990; Cushnie and Lamb, 2005). (Figure 2)