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. 2007 May;74(2):92-101.
doi: 10.1016/j.antiviral.2006.04.014. Epub 2006 May 15.

Emodin Blocks the SARS Coronavirus Spike Protein and Angiotensin-Converting Enzyme 2 Interaction

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Free PMC article

Emodin Blocks the SARS Coronavirus Spike Protein and Angiotensin-Converting Enzyme 2 Interaction

Tin-Yun Ho et al. Antiviral Res. .
Free PMC article

Abstract

Severe acute respiratory syndrome (SARS) is an emerging infectious disease caused by a novel coronavirus (SARS-CoV). SARS-CoV spike (S) protein, a type I membrane-bound protein, is essential for the viral attachment to the host cell receptor angiotensin-converting enzyme 2 (ACE2). By screening 312 controlled Chinese medicinal herbs supervised by Committee on Chinese Medicine and Pharmacy at Taiwan, we identified that three widely used Chinese medicinal herbs of the family Polygonaceae inhibited the interaction of SARS-CoV S protein and ACE2. The IC(50) values for Radix et Rhizoma Rhei (the root tubers of Rheum officinale Baill.), Radix Polygoni multiflori (the root tubers of Polygonum multiflorum Thunb.), and Caulis Polygoni multiflori (the vines of P. multiflorum Thunb.) ranged from 1 to 10 microg/ml. Emodin, an anthraquinone compound derived from genus Rheum and Polygonum, significantly blocked the S protein and ACE2 interaction in a dose-dependent manner. It also inhibited the infectivity of S protein-pseudotyped retrovirus to Vero E6 cells. These findings suggested that emodin may be considered as a potential lead therapeutic agent in the treatment of SARS.

Figures

Fig. 1
Fig. 1
Analysis of SARS-CoV S protein and ACE2 interaction. (A) SDS-PAGE analysis of recombinant SARS-CoV S protein. The preparations of uninduced E. coli (lane 2), induced E. coli (lane 3), and purified recombinant S protein (lane 4) were analyzed by 10% SDS-PAGE and stained by Coomassie brilliant blue. The molecular masses of protein standard (lane 1) are shown at the left. The location of the 138-kDa recombinant S protein is indicated by the arrow. (B) The binding ability of SARS-CoV S protein to ACE2 by biotinylated ELISA. The wells were coated with 1 ng of ACE2 and challenged with various amounts of biotin-labeled S protein. Following three washes, peroxidase-conjugated avidin and chromatic substrate were sequentially added. The absorbance was read at 405 nm in an ELISA plate reader. Values are mean ± standard error of three independent assays.
Fig. 2
Fig. 2
Inhibitory effects of Chinese medicinal herbs on the interaction between SARS-CoV S protein and ACE2. Biotin-labeled S protein (0.05 μg) was mixed with 1 μg of aqueous extracts of herbs, and the mixtures were added to wells, which were coated with 1 ng of ACE2. The biotinylated ELISA was performed as described in Section 2. Results are expressed as inhibition (%) described in Section 2. Numbers in the brackets are the sum of herb species in the family. Values are mean ± standard error of three independent assays. *p < 0.05, **p < 0.01, ***p < 0.001, compared with BSA.
Fig. 3
Fig. 3
Inhibitory effects of Radix et Rhizoma Rhei, Radix Polygoni multiflori, and Caulis Polygoni multiflori on the SARS-CoV S protein and ACE2 interaction. Biotin-labeled S protein (0.05 μg) was mixed with various amounts of aqueous extracts from Radix et Rhizoma Rhei (A), Radix Polygoni multiflori (B) or Caulis Polygoni multiflori (C), and the mixtures were added to wells, which were coated with 1 ng of ACE2. The biotinylated ELISA was performed as described in Section 2. Results are expressed as inhibition (%) described in Section 2. Values are mean ± standard error of six independent assays.
Fig. 4
Fig. 4
Chemical structures of compounds used in this study.
Fig. 5
Fig. 5
Inhibitory effects of emodin, rhein, and chrysin on the interaction between SARS-CoV S protein and ACE2. Biotin-labeled S protein (0.05 μg) was mixed with various amounts of emodin (A), rhein (B) or chrysin (C), and the mixtures were added to wells, which were coated with 1 ng of ACE2. The biotinylated ELISA was performed as described in Section 2. Results are expressed as inhibition (%) described in Section 2. Values are mean ± standard error of six independent assays.
Fig. 6
Fig. 6
Inhibitory effects of emodin and emodin-like compounds on the SARS-CoV S protein and ACE2 interaction. Biotin-labeled S protein (0.05 μg) was mixed with various amounts of emodin, promazine, anthraquinone or 1,4-bis-(1-anthraquinonylamino)-anthraquinone, and the mixtures were added to wells, which were coated with 1 ng of ACE2. The biotinylated ELISA was performed as described in Section 2. Results are expressed as inhibition (%) described in Section 2. Values are mean ± standard error of six independent assays.
Fig. 7
Fig. 7
Inhibitory effects of emodin and promazine on the interaction between SARS-CoV S protein and Vero E6 cells. Vero E6 cells were cultured on glass coverslips and treated with biotin-labeled S protein in the presence of various amounts of compounds. Recombinant S protein was purified from E. coli (A) or baculovirus (B). After a 16-h incubation at 4 °C, cells were stained with fluorescence-conjugated streptavidin and evaluated under a confocal microscope. Magnification, 400×.
Fig. 8
Fig. 8
Inhibitory effects of emodin and promazine on the SARS-CoV S protein-pseudotyped retrovirus infectivity. S protein-pseudotyped retroviruses were mixed with various amounts of emodin and promazine, and then incubated at 37 °C with shaking. After a 2-h incubation, the mixtures were inoculated with Vero E6 cells transfected with the plasmid encoding ACE2. The luciferase activity of cell lysate was assayed 2 days postinfection. The cell viability was determined after a 24-h treatment with emodin or promazine. The bars and lines represent the relative infectivity and cell viability (%), respectively, described in Section 2. Values are mean ± standard error of three independent assays. *p < 0.05, **p < 0.01, compared with untreated cells.

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