Both Baicalein and Gallocatechin Gallate Effectively Inhibit SARS-CoV-2 Replication by Targeting Mpro and Sepsis in Mice

Abstract

The emergence of severe acute syndrome coronavirus 2 (SARS-CoV-2) in December 2019 has led to the global COVID-19 pandemic. Although the symptoms of most COVID-19 patients are mild or self-curable, most of severe patients have sepsis caused by cytokine storms, which greatly increases the case fatality rate. Moreover, there is no effective drug that can limit the novel coronavirus thus far, so it is more needed to develop antiviral drugs for the SARS-CoV-2. In our research, we employed the techniques of molecular docking to screen 35 flavonoid compounds among which 29 compounds have Z-scores lower than - 6. Then, ( -)-gallocatechin gallate, ( +)-gallocatechin and baicalein were identified to have potent inhibitory activity against SARS-CoV-2 M^pro with IC₅₀ values of 5.774 ± 0.805 μM, 13.14 ± 2.081 μM and 5.158 ± 0.928 μM respectively by FRET assay. Molecular docking results also showed that ( -)-gallocatechin gallate, ( +)-gallocatechin and baicalein can non-covalently bind to M^pro through π-π stacking and hydrogen bonds in the Cys145 catalytic site. We further evaluated the effect of ( -)-gallocatechin gallate and baicalein on cytokine storms using a mouse model of sepsis. ( -)-Gallocatechin gallate and baicalein significantly reduced sepsis of mouse models on weight, murine sepsis score, and survival rate and reduced the inflammatory factor levels, such as TNF-α, IL-1α, IL-4, and IL-10. Overall, ( -)-gallocatechin gallate and baicalein show certain potential of treatment against COVID-19.

Keywords: Mpro protease; SARS-CoV-2; cytokine storm; flavonoids; sepsis.

Fig. 1

Screening of 29 flavonoids, docking score lower than -6, against SARS-CoV-2 M^pro using the FRET assay. A 40-μM compound (final concentration 20 μM) was pre-incubated with 0.3 μM SARS-CoV-2 M pro at 30 °C for 10 min, and then 200 μM FRET substrate was added to the reaction mixture to initiate the reaction. The excitation wavelength is 340 nm, and the emission wavelength is 490 nm for fluorescence measurement. Results: Inhibition rate (%) = (RFU100% enzyme activity control-RFU sample) / (RFU100% enzyme activity control-RFU blank control) × 100%. The results are average ± standard deviation of three repeats. B The inhibitory assay of ( −)-gallocatechin gallate, ( +)-gallocatechin, and baicalein show efficient inhibition for M^pro. Error bars: mean ± S.D. of three independent replicates.

Fig. 2

Docked conformations of ( −)-gallocatechin gallate, ( +)-gallocatechin, and baicalein in SARS-CoV-2 M^pro. A–C 3D binding interactions of the compounds with surrounding amino acids. D–F 2D binding interactions of the compounds with surrounding amino acids.

Fig. 3

Effect of ( −)-gallocatechin gallate and baicalein on fecal dilution-induced sepsis in mice. A Experimental scheme of mice sepsis induced by fecal diluent. B Changes in body weight in different groups of mice in review (control, model, 100 mg/kg cefpirome sulfate, 50 mg/kg ( −)-gallocatechin gallate, and 100 mg/kg ( −)-gallocatechin gallate, 100 mg/kg baicalein, and 200 mg/kg baicalein). C The effect of ( −)-gallocatechin gallate and baicalein on murine sepsis score (MSS) of the different groups of mice described above. D The effect of ( −)-gallocatechin gallate and baicalein on the survival time of the different groups of mice described above. E Serum IL-1α, TNF-α, IL-4, and IL-10 were detected by ELISA. Values are presented as the mean ± SEM (n = 5), ##P < 0.01; ####P < 0.0001,significantly different from control group; *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001, significantly different from model groups.

Fig. 4

Effect of ( −)-gallocatechin gallate and baicalein on serum proinflammatory cytokine expression. HE staining was used to evaluate the effect of ( −)-gallocatechin gallate and baicalein on fecal dilution-induced pathological changes (20 × magnification).