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Quercetin inhibits SARS-CoV-2 infection and prevents syncytium formation by cells co-expressing the viral spike protein and human ACE2

Roy et al., Virology Journal, doi:10.1186/s12985-024-02299-w
Jan 2024  
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Quercetin for COVID-19
24th treatment shown to reduce risk in July 2021
*, now known with p = 0.0031 from 11 studies.
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3,800+ studies for 60+ treatments.
In Vitro study showing inhibition of SARS-CoV-2 infection and syncytium formation by quercetin in Vero E6 and Caco-2 cells at 100-400μM concentrations. Authors found that quercetin prevented the proteolytic processing of the SARS-CoV-2 spike protein required for cell fusion, potentially by inhibiting the furin protease responsible for this cleavage. Quercetin also directly inhibited furin activity. The results suggest that sufficiently bioavailable formulations of quercetin may impair viral propagation mechanisms and be a potential COVID-19 treatment.
In Silico studies predict inhibition of SARS-CoV-2, or minimization of side effects, with quercetin or metabolites via binding to the spike Note A, Alavi, Azmi (B), Chandran, Kandeil, Mandal, Moschovou, Nguyen, Pan, Thapa (B), Şimşek, Mpro Note B, Akinwumi, Alanzi, Ibeh, Kandeil, Mandal, Moschovou, Nguyen, Qin, Rehman, Sekiou (B), Singh, Thapa (B), Wang, Zhang, RNA-dependent RNA polymerase Note C, Corbo, PLpro Note D, Ibeh, Zhang, ACE2 Note E, Chandran, Ibeh, Qin, Thapa (B), Şimşek, Alkafaas, TMPRSS2 Note F, Chandran, helicase Note G, Alanzi, Singh (B), endoribonuclease Note H, Alavi, cathepsin L Note I, Ahmed, Wnt-3 Note J, Chandran, FZD Note K, Chandran, LRP6 Note L, Chandran, ezrin Note M, Chellasamy, ADRP Note N, Nguyen, NRP1 Note O, Şimşek, PTGS2 Note P, Qin, HSP90AA1 Note Q, Qin, matrix metalloproteinase 9 Note R, Sai Ramesh, IL-6 Note S, Yang, Yang (B), IL-10 Note T, Yang, VEGFA Note U, Yang (B), and RELA Note V, Yang (B) proteins. In Vitro studies demonstrate efficacy in Calu-3 Note W, DiGuilio, A549 Note X, Yang, HEK293-ACE2+ Note Y, Singh (C), Huh-7 Note Z, Pan, Caco-2 Note AA, Roy, Vero E6 Note AB, Kandeil, El-Megharbel, Roy, mTEC Note AC, Wu, and RAW264.7 Note AD, Wu cells. Animal studies demonstrate efficacy in K18-hACE2 mice Note AE, Aguado, rats El-Megharbel (B), and db/db mice Note AF, Wu, Wu (B).
Roy et al., 25 Jan 2024, peer-reviewed, 7 authors. Contact:
In Vitro studies are an important part of preclinical research, however results may be very different in vivo.
This PaperQuercetinAll
Quercetin inhibits SARS-CoV-2 infection and prevents syncytium formation by cells co-expressing the viral spike protein and human ACE2
Annie V Roy, Michael Chan, Logan Banadyga, Shihua He, Wenjun Zhu, Michel Chrétien, Majambu Mbikay
Virology Journal, doi:10.1186/s12985-024-02299-w
Background Several in silico studies have determined that quercetin, a plant flavonol, could bind with strong affinity and low free energy to SARS-CoV-2 proteins involved in viral entry and replication, suggesting it could block infection of human cells by the virus. In the present study, we examined the ex vivo ability of quercetin to inhibit of SARS-CoV-2 replication and explored the mechanisms of this inhibition. Methods Green monkey kidney Vero E6 cells and in human colon carcinoma Caco-2 cells were infected with SARS-CoV-2 and incubated in presence of quercetin; the amount of replicated viral RNA was measured in spent media by RT-qPCR. Since the formation of syncytia is a mechanism of SARS-CoV-2 propagation, a syncytialization model was set up using human embryonic kidney HEK293 co-expressing SARS-CoV-2 Spike (S) protein and human angiotensin converting enzyme 2 (ACE2), [HEK293(S + ACE2) cells], to assess the effect of quercetin on this cytopathic event by microscopic imaging and protein immunoblotting. Results Quercetin inhibited SARS-CoV-2 replication in Vero E6 cells and Caco-2 cells in a concentration-dependent manner with a half inhibitory concentration (IC 50 ) of 166.6 and 145.2 µM, respectively. It also inhibited syncytialization of HEK293(S + ACE2) cells with an IC 50 of 156.7 µM. Spike and ACE2 co-expression was associated with decreased expression, increased proteolytic processing of the S protein, and diminished production of the fusogenic S2' fragment of S. Furin, a proposed protease for this processing, was inhibited by quercetin in vitro with an IC 50 of 116 µM. Conclusion These findings suggest that at low 3-digit micromolar concentrations of quercetin could impair SARS-CoV-2 infection of human cells partly by blocking the fusion process that promotes its propagation.
Abbreviations Supplementary Information The online version contains supplementary material available at https://doi. org/10.1186/s12985-024-02299-w. Supplementary Material 1: Supplementary Figure S1 . Confirmation of S protein bands. Cells were transfected with the indicated expression vectors and their extracts analyzed as described for Fig. 3 . Immunoblotting of S protein and its fragments was performed using antibodies from Abcam (cat# ab272504) and Sino Biological (cat# 40592-T62). The Spike-Linker-GFP gene is expressed as a fusion S-GFP protein whereas with the Spike-P2A-GFP gene, the S protein and GFP are expressed as two separate molecules, hence the size difference in immunoreactive S bands produced par the two vectors. Supplementary Material 2: Supplementary Figure S2 . Pull-down of ACE2 by S protein. HEK293(S+ACE2) cell extracts were subjected to immunoprecipitation with GFP-trap beads. The precipitates were analyzed by immunoblotting for ACE-2 and GFP; the densities of immunoreactive bands were determined. A. A representative blot. B&C. The S/ACE2 and S2/ACE density ratios were computed. The values (means ± SD of 3 independent experiments) of quercetin-treated cells were expressed relative to those of DMSO treated control cells. Supplementary Material 3: Supplementary Figure S3 . Effect of isoquercetin on HEK293(S+ACE2) syncytialization. The experiment was conducted as described in Fig. 1 . Isoquercetin did not inhibit the formation de syncytia...
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