The Therapeutic and Prophylactic Potential of Quercetin against COVID-19: An Outlook on the Clinical Studies, Inventive Compositions, and Patent Literature

Abstract

Quercetin is a phenolic flavonol compound with established antioxidant, anti-inflammatory, and immuno-stimulant properties. Recent studies demonstrate the potential of quercetin against COVID-19. This article highlighted the prophylactic/therapeutic potential of quercetin against COVID-19 in view of its clinical studies, inventions, and patents. The literature for the subject matter was collected utilizing different databases, including PubMed, Sci-Finder, Espacenet, Patentscope, and USPTO. Clinical studies expose the potential of quercetin monotherapy, and also its combination therapy with other compounds, including zinc, vitamin C, curcumin, vitamin D3, masitinib, hydroxychloroquine, azithromycin, and ivermectin. The patent literature also examines claims that quercetin containing nutraceuticals, pharmaceuticals, and dietary supplements, alone or in combination with other drugs/compounds, including favipiravir, remdesivir, molnupiravir, navitoclax, dasatinib, disulfiram, rucaparib, tamarixin, iota-carrageenan, and various herbal extracts (aloe, poria, rosemary, and sphagnum) has potential for use against COVID-19. The literature reveals that quercetin exhibits anti-COVID-19 activity because of its inhibitory effect on the expression of the human ACE2 receptors and the enzymes of SARS-CoV-2 (MPro, PLPro, and RdRp). The USFDA designated quercetin as a “Generally Recognized as Safe” substance for use in the food and beverage industries. It is also an inexpensive and readily available compound. These facts increase the possibility and foreseeability of making novel and economical drug combinations containing quercetin to prevent/treat COVID-19. Quercetin is an acidic compound and shows metabolic interaction with some antivirals, antibiotics, and anti-inflammatory agents. Therefore, the physicochemical and metabolic drug interactions between quercetin and the combined drugs/compounds must be better understood before developing new compositions.

Selenium and COVID-19: A spotlight on the clinical trials, inventive compositions, and patent literature

“…The infection with SARS-CoV-2 (a RNA virus) causes contagious COVID-19, which has disastrously impacted the world’s demography [1] . The first case of COVID-19 emerged in December 2019, whereas the World Health Organization (WHO) announced it as a pandemic in March 2020 [1] , [2] , [3] . SARS-CoV-2 is transmitted through the respiratory droplets of the infected person and virus-contaminated surfaces/items [1] .…”

“…SARS-CoV-2 is transmitted through the respiratory droplets of the infected person and virus-contaminated surfaces/items [1] . The general symptoms of COVID-19 include fever, cough, sore throat, nasal congestion, headache, fatigue, pain in muscles/joints, loss of smell/taste, diarrhea, and breathlessness [1] , [2] , [3] , [4] . Most of the COVID-19 patients (about 80%) recover without hospitalization, about 15% get serious symptoms, and about 5% require intensive care [1] , [2] .…”

“…Other possible treatments have also been explored, including lopinavir/ritonavir combination, ivermectin, convalescent plasma, REGN-COV2, sotrovimab, tocilizumab, baricitinib, ruxolitinib, tofacitinib, and ibrutinib [1] , [6] , [7] , [8] , [9] , [10] , [11] . However, the efficacy of the available/explored COVID-19 treatment and vaccines against the emerging and highly transmittable variants of SARS-CoV-2 like Omicron (B.1.1.529), Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Delta (B.1.617.2), Mu (B.1.621), Lambda (C.37), Kappa (B.1.617.1), Iota (B.1.526), Theta (P.3), Eta (B.1.525), Zeta (P.2), and Epsilon (B.1.429 & B.1.427) is not fully established [1] , [3] , [12] . Many countries have also reported the emergence of second and third waves of COVID-19 despite implementing vaccination programs [1] .…”

“…Many countries have also reported the emergence of second and third waves of COVID-19 despite implementing vaccination programs [1] . Some existing COVID-19 treatments/prophylactics are not patient-compliant (injectable remdesivir and vaccines) and may also cause serious side effects (teratogenic effect of molnupiravir) [1] , [3] , [12] . Further, the available vaccines are not 100% effective for all COVID-19 patients [1] .…”

Are Nutraceuticals Effective in COVID-19 and Post-COVID Prevention and Treatment?

“…Additionally, quercetin suppresses inflammation through interference in various signaling pathways, especially NF-κB [ 176 ]. With regard to human studies, the interim results from one RCT that demonstrated that quercetin supplementation improved viral clearance and partially lowered symptoms severity [ 177 ]. In another RCT, the therapeutic efficacy of quercetin was evaluated in combination with antiviral drugs in hospitalized COVID-19 patients, showing that it diminished the hospitalization period.…”