Investigating the Potential Anti-SARS-CoV-2 and Anti-MERS-CoV Activities of Yellow Necklacepod among Three Selected Medicinal Plants: Extraction, Isolation, Identification, In Vitro, Modes of Action, and Molecular Docking Studies

Abstract

The anti-MERS-CoV activities of three medicinal plants (Azadirachta indica, Artemisia judaica, and Sophora tomentosa) were evaluated. The highest viral inhibition percentage (96%) was recorded for S. tomentosa. Moreover, the mode of action for both S. tomentosa and A. judaica showed 99.5% and 92% inhibition, respectively, with virucidal as the main mode of action. Furthermore, the anti-MERS-CoV and anti-SARS-CoV-2 activities of S. tomentosa were measured. Notably, the anti-SARS-CoV-2 activity of S. tomentosa was very high (100%) and anti-MERS-CoV inhibition was slightly lower (96%). Therefore, the phytochemical investigation of the very promising S. tomentosa L. led to the isolation and structural identification of nine compounds (1−9). Then, both the CC50 and IC50 values for the isolated compounds against SARS-CoV-2 were measured. Compound 4 (genistein 4’-methyl ether) achieved superior anti-SARS-CoV-2 activity with an IC50 value of 2.13 µm. Interestingly, the mode of action of S. tomentosa against SARS-CoV-2 showed that both virucidal and adsorption mechanisms were very effective. Additionally, the IC50 values of S. tomentosa against SARS-CoV-2 and MERS-CoV were found to be 1.01 and 3.11 µg/mL, respectively. In addition, all the isolated compounds were subjected to two separate molecular docking studies against the spike (S) and main protease (Mpr°) receptors of SARS-CoV-2.

Keywords: Sophora tomentosa; anti-MERS-CoV; anti-SARS-CoV-2; coronavirus; extraction; isolation; mode of action; molecular docking.

Figure 1

The isolated compounds from S. tomentosa L. leaves. 4-O-methyl sorbitol (1), 5,8-dimethoxypsoralen (2), formononetin (3), genistein 4’-methyl ether (4), 4’,5-dihydroxy-7-methoxygenistein (5), 8-methoxy daidzin (6), 5,7,4’-trihydroxy-3,6-dimethoxy flavone (7), 6-methoxy-7-O-β-D-glucoside apigenin (8), and daucosterol (9).

Figure 2

Cytotoxicity percentage and the concentration which exhibited 50% cytotoxic concentration (CC₅₀) of A. indica (neem), A. judaica (shih-Balady), and S. tomentosa extracts by MTT assay which was used with CC₅₀ of 22.52, 31.63, and 20.86 µg/mL, respectively.

Figure 3

Mode of action for the two promising medicinal plants: S. tomentosa (Crude) and A. judaica (known shih-Balady), with different safe concentrations against MERS-CoV isolates (NRCE-HKU270 (Accession Number: KJ477103.2)). The virucidal effect was the main mode of action for the two extracts but has less effect on viral adsorption and a very low effect on viral replication.

Figure 4

CC₅₀ and IC₅₀ of the isolated and identified compounds from S. tomentosa against SARS-CoV-2. 5,8-Dimethoxypsoralen (2), formononetin (3), genistein 4’-methyl ether (4), 4’,5-dihydroxy-7-methoxygenistein (5), 5,7,4’-trihydroxy-3,6-dimethoxy flavone (7), 6-methoxy-7-O-β-D-glucoside apigenin (8), and daucosterol (9).

Figure 5

Mode of action for the most promising medicinal plant S. tomentosa (crude) with different safe concentrations against SARS-CoV-2 isolate (hCoV-19/Egypt/NRC-3/2020). S. tomentosa had a promising effect (>99%) against SARS-CoV-2 by two mechanisms of action (virucidal and adsorption) with 12.50 and 6.25 µg/mL. On the other hand, its efficacy by adsorption decreased when decreasing the concentration but was still high (>99%) with a virucidal mechanism at 3.125 and 1.562 µg/mL.

Figure 6

CC₅₀ and IC₅₀ antiviral activity of S. tomentosa against SARS-CoV-2 and MERS-CoV. The IC₅₀ of each test was calculated using nonlinear regression analysis in triplicate for each concentration used. The best-fitting line was drawn between log concentrations and viral inhibition % using GraphPad Prism software.

Figure 7

Superimposition of the redocked O6K inhibitor (green) over its native one (red).