Plant extracts found to be active against SARS-CoV-2

German scientists have shown in laboratory studies that aqueous and ethanolic extracts of specially bred sweet wormwood plants (A. annua) are active against SARS-Cov-2, the coronavirus that causes COVID-19.

Herbal medicines have been used for millennia to treat infectious diseases, with extracts of A. annua plants having been successfully employed to treat febrile diseases including malaria. Artemisinin is extracted from this plant and is the basis for the WHO-recommended anti-malaria combination therapies used in millions of adults and children each year with few, if any, side effects. The use of A. annua teas is meanwhile promoted as a natural combination therapy against malaria infections, although the WHO discourages their use amid concerns about the development of malaria drug resistance.

Chemists at the Max Planck Institute of Colloids and Interfaces, in close collaboration with virologists at Freie Universität Berlin, set out to determine whether A. annua extracts — pure artemisinin and related derivatives, and mixtures thereof — may be active against SARS-Cov-2. These drugs would be attractive candidates for repurposing considering they have excellent safety profiles and are readily available, rapidly scalable and relatively inexpensive.

“Having worked with compounds derived from A. annua plants, I was familiar with the interesting activities of the plants against many different diseases, including a range of viruses,” said Professor Peter H Seeberger, Director of the Max Planck Institute of Colloids and Interfaces, who initiated to the study. “Therefore, we felt that exploring the activity of this plant against COVID-19 was worth the undertaking.”

A. annua leaves from a cultivated seed line grown by ArtemiLife in Kentucky, when extracted with absolute ethanol or distilled water, provided the best antiviral activity. The addition of either ethanolic or aqueous A. annua extracts prior to virus addition resulted in significantly reduced plaque formation. The ethanolic extract of both A. annua and coffee was found to be most active, while artemisinin alone did not present much antiviral activity.

“I was surprised to find that A. annua extracts worked significantly better than pure artemisinin derivatives and that the addition of coffee further enhanced the activity,” said Professor Klaus Osterrieder from Freie Universität Berlin, who conducted all activity assays.

To test the activity of A. annua extracts, COVID-19 human clinical trials with teas and coffees containing A. annua leaves provided by ArtemiLife are about to begin at the University of Kentucky’s academic medical centre. An artemisinin derivative used to treat malaria, known as artesunate, will be used in a Phase 1/2 clinical trial as well.

Image caption: A flask containing ethanolic A. annua plant extract. Image credit: ©Dr K Gilmore.

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