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

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 Mpro 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 Mpro 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.

Effect of dihydromyricetin on SARS-CoV-2 viral replication and pulmonary inflammation and fibrosis.

BACKGROUND: COVID-19 (Coronavirus Disease-2019) has spread widely around the world and impacted human health for millions. The lack of effective targeted drugs and vaccines forces scientific world to search for new effective antiviral therapeutic drugs. It has reported that flavonoids have potential inhibitory activity on SARS-CoV-2 Mpro and anti-inflammatory properties. Dihydromyricetin, as a flavonol, also has antiviral and anti-inflammatory potential. However, the inhibition of dihydromyricetin on SARS-CoV-2 Mpro and the protective effect of dihydromyricetin on pulmonary inflammation and fibrosis have not been proved and explained. PURPOSE: The coronavirus main protease (Mpro) is essential for SARS-CoV-2 replication and to be recognized as an attractive drug target, we expect to find the inhibitor of Mpro. Novel coronavirus infection can cause severe inflammation and even sequelae of pulmonary fibrosis in critically ill patients. We hope to find a drug that can not only inhibit virus replication but also alleviate inflammation and pulmonary fibrosis in patients. METHODS: FRET-based enzymatic assay was used to evaluate the inhibit activity of dihydromyricetin on SARS-CoV-2 Mpro. Molecular docking was used to identify the binding pose of dihydromyricetin with SARS-CoV-2 Mpro. The protective effects of dihydromyricetin against BLM-induced pulmonary inflammation and fibrosis were investigated in C57BL6 mice. BALF and lung tissue were collected for inflammation cells count, ELISA, masson and HE staining, western blotting and immunohistochemistry to analyze the effects of dihydromyricetin on pulmonary inflammation and fibrosis. MTT, western blotting, reverse transcription-polymerase chain reaction (RT-PCR) and wound healing were used to analyze the effects of dihydromyricetin on lung fibrosis mechanisms in Mlg cells. RESULTS: In this study, we found that dihydromyricetin is a potent inhibitor targeting the SARS-CoV-2 Mpro with a half-maximum inhibitory concentration (IC50) of 1.716 ± 0.419 µM, using molecular docking and the FRET-based enzymatic assay. The binding pose of dihydromyricetin with SARS-CoV-2 Mpro was identified using molecular docking method. In the binding pocket of SARS-CoV-2 Mpro, the dihydrochromone ring of dihydromyricetin interact with the imidazole side chain of His163 through π-π stacking. The 1-oxygen of dihydromyricetin forms a hydrogen bond with the backbone nitrogen of Glu166. The 3-, 7-, 3'- and 4'-hydroxyl of dihydromyricetin interact with Gln189, Leu141, Arg188 and Thr190 through hydrogen bonds. Moreover, our results showed that dihydromyricetin can significantly alleviate BLM-induced pulmonary inflammation by inhibiting the infiltration of inflammation cells and the secretion of inflammation factors in the early process and also ameliorate pulmonary fibrosis by improving pulmonary function and down-regulate the expression of α-SMA and fibronectin in vivo. Our results also showed that dihydromyricetin inhibits the migration and activation of myofibroblasts and extracellular matrix production via transforming growth factor (TGF)-ß1/Smad signaling pathways. CONCLUSION: Dihydromyricetin is an effective inhibitor for SARS-CoV-2 Mpro and it prevents BLM-induced pulmonary inflammation and fibrosis in mice. Dihydromyricetin will be a potential medicine for the treatment of COVID-19 and its sequelae.

Myricetin Inhibits SARS-CoV-2 Viral Replication by Targeting Mpro and Ameliorates Pulmonary Inflammation.

The coronavirus disease 2019 (COVID-19) has spread widely around the world and has seriously affected the human health of tens of millions of people. In view of lacking anti-virus drugs target to SARS-CoV-2, there is an urgent need to develop effective new drugs. In this study, we reported our discovery of SARS-CoV-2 Mpro inhibitors. We selected 15 natural compounds, including 7 flavonoids, 3 coumarins, 2 terpenoids, one henolic, one aldehyde and one steroid compound for molecular docking and enzymatic screening. Myricetin were identified to have potent inhibit activity with IC50 3.684 ± 0.076 µM in the enzyme assay. The binding pose of Myricetin with SARS-CoV-2 Mpro was identified using molecular docking method. In the binding pocket of SARS-CoV-2 Mpro, the chromone ring of Myricetin interacts with His41 through π-π stacking, and the 3'-, 4'- and 7-hydroxyl of Myricetin interact with Phe140, Glu166and Asp187 through hydrogen bonds. Significantly, our results showed that Myricetin has potent effect on bleomycin-induced pulmonary inflammation by inhibiting the infiltration of inflammatory cells and the secretion of inflammatory cytokines IL-6, IL-1α, TNF-α and IFN-γ. Overall, Myricetin may be a potential drug for anti-virus and symptomatic treatment of COVID-19.