The preclinical potential of an herb used in traditional Chinese medicine for the treatment of COVID-19

Danshen is an herb used in traditional Chinese medicine for many different ailments, primarily for blood vessel and heart health. It is the dry extract of the organism Salvia miltiorrhizaand early scientific research suggests strong evidence for its use.

Study: Salvia miltiorrhiza Bunge as a potential natural compound against COVID-19. Image Credit: HelloRF Zcool/Shutterstock

About the study

In a study published in cells, researchers studied the effects of this extract for use against coronavirus disease 2019 (COVID-19). They wanted to assess the effects of the extract at two levels. First, they aimed to find out if the extract could reduce the ability of the S1 subunit of the spike protein to bind to angiotensin-converting enzyme 2 (ACE2) – the method by which the virus enters in the cell. They also wanted to understand whether the extract could affect disease symptoms by ameliorating the pro-inflammatory phenotype infection induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Results

Ultra-high performance liquid chromatography (UHPLC) was used to analyze the content of active compounds in the S. Miltiorrhiza root powder extract including salvianic acid, rosmarinic acid, salvianolic acid A, salvianolic acid B, ursolic acid, tanshinone I, tanshinone IIA, tanshinone IIB, tanshinone VI , dihydrotanshinone I, cryptotanshinone and tetrahydrotanshinone. These represented 12.8% of the total dry matter of the extract. The compound most present was cryptotanshinone, at 77.59 mg/g, followed by dihydrotanshinone I (15.35) and tanshinone IIA/IIB, at 10.8/10.22 mg/g respectively. Tanshinone VI was present at 5.53 mg/g and tetrahydrotanshinone at 3.61. All other compounds were present, although at much lower concentrations.

The ability of the extract to inhibit the SARS-CoV-2-ACE2 interaction was then monitored at the single molecule level using atomic force microscopy (AFM). The S1 subunit of the SARS-CoV-2 spike protein was grafted onto the AFM. tip, and the surfaces were coated with purified ACE2 receptors.

Single-molecule force spectroscopy (SMFS) experiments have recorded curves of force versus distance. Specific unbinding events corresponding to the breaking of the S1-ACE2 bond occurred. The binding frequency was extracted and compared to the ratio of the number of force-distance curves showing that specific adhesion event. These experiments revealed a strong decrease in the probability of binding in the presence of this extract at concentrations greater than 1 ug/mL, reaching 50% inhibition at 100 ug/mL.

To further explore this effect while adapting to more physiological conditions, the influence of the extract on the binding of inactivated virions was evaluated. This revealed even more impressive inhibitory potential, with binding frequency reduced by 50% at 10 µg/mL.

Following this, a in vitro system was established using R8d8 from peripheral blood monocytes (PBMC) from healthy blood donors, leading to the release of pro-inflammatory cytokines to study the modulation of inflammatory responses. Once established, this system was used to assess the ability of the extract to regulate the response of PBMCs to the activation of inflammatory factors TLR7/8.

After incubation with the extract for three hours, IL-1Beta, TNF and IL-6 were significantly inhibited at concentrations between 5 and 10 µg/mL. No significant effect was observed on IL-8 or CXCL8 secretion. Yet, IFN-alpha release was completely suppressed at 5 µg/mL – showing a stronger inhibitory response than 1 µM dexamethasone, the current gold standard treatment for COVID-19.

The NFkB pathway was the researchers’ next research target, as it was thought that the mechanism by which the extract suppressed cytokine responses may be related. Phosphorylation of NFkB p65 was observed after thirty minutes of incubation with R848, without alteration of the acetylated form. A significant inhibition of p65 phosphorylation could be observed at 10 µg/mL when the extract was included for thirty minutes of preincubation.

The conclusion

Study reveals compounds found in S. miltiorrhiza extract and the proportions in which they exist as a percentage of dry matter. It reveals that the extract has a strong inhibitory potential when trying to prevent the binding of S1 subunit ACE2 receptors. The inhibitory potential appeared even more impressive when the experiment was repeated using inactivated virions.

In addition to this, the authors successfully developed and applied a method to study any other effect against SARS-CoV-2 infection in vitro, revealing the suppression of inflammatory factors through the NFkB pathway. These results indicate that S. miltiorrhiza the extract may provide some use against disease and support further study to isolate compounds that can be used for clinical trials.