Comparative evaluation of flavonoids reveals the superiority and promising inhibition activity of silibinin against SARS-CoV-2.

Flavonoids are phenolic compounds naturally found in plants and commonly consumed in diets. Herein, flavonoids were sequentially evaluated by a comparative in silico study associated with systematic literature search. This was followed by an in vitro study and enzyme inhibition assays against vital SARS-CoV-2 proteins including spike (S) protein, main protease (Mpro ), RNA-dependent RNA-polymerase (RdRp), and human transmembrane serine protease (TMPRSS2). The results obtained revealed 10 flavonoids with potential antiviral activity. Out of them, silibinin showed promising selectivity index against SARS-CoV-2 in vitro. Screening against S protein discloses the highest inhibition activity of silibinin. Mapping the activity of silibinin indicated its excellent binding inhibition activity against SARS-CoV-2 S protein, Mpro and RdRP at IC50 0.029, 0.021, and 0.042 µM, respectively, while it showed no inhibition activity against TMPRSS2 at its IC50(SARS-CoV-2) . Silibinin was tested safe on human mammalian cells at >7-fold its IC50(SARS-CoV-2) . Additionally, silibinin exhibited >90% virucidal activity at 0.031 µM. Comparative molecular docking (MD) showed that silibinin possesses the highest binding affinity to S protein and RdRP at -7.78 and -7.15 kcal/mol, respectively. MDs showed that silibinin exhibited stable interaction with key amino acids of SARS-CoV-2 targets. Collectively, silibinin, an FDA-approved drug, can significantly interfere with SARS-CoV-2 entry and replication through multi-targeting activity.

Silibinin as potential tool against SARS-Cov-2: In silico spike receptor-binding domain and main protease molecular docking analysis, and in vitro endothelial protective effects.

The spread of SARS-CoV-2, along with the lack of targeted medicaments, encouraged research of existing drugs for repurposing. The rapid response to SARS-CoV-2 infection comprises a complex interaction of cytokine storm, endothelial dysfunction, inflammation, and pathologic coagulation. Thus, active molecules targeting multiple steps in SARS-CoV-2 lifecycle are highly wanted. Herein we explored the in silico capability of silibinin from Silybum marianum to interact with the SARS-CoV-2 main target proteins, and the in vitro effects against cytokine-induced-inflammation and dysfunction in human umbilical vein endothelial cells (HUVECs). Computational analysis revealed that silibinin forms a stable complex with SARS-CoV-2 spike protein RBD, has good negative binding affinity with Mpro, and interacts with many residues on the active site of Mpro, thus supporting its potentiality in inhibiting viral entry and replication. Moreover, HUVECs pretreatment with silibinin reduced TNF-α-induced gene expression of the proinflammatory genes IL-6 and MCP-1, as well as of PAI-1, a critical factor in coagulopathy and thrombosis, and of ET-1, a peptide involved in hemostatic vasoconstriction. Then, due to endothelium antiinflammatory and anticoagulant properties of silibinin and its capability to interact with SARS-CoV-2 main target proteins demonstrated herein, silibinin could be a strong candidate for COVID-19 management from a multitarget perspective.