Researchers have discovered that extracts from two different wild plants can each interfere with the ability of SARS-CoV-2, the virus that causes COVID-19, to infect cells. These findings, which utilized a cell culture model, come from a massive assessment of different botanical extracts. In this effort 1,800 extracts and 18 compounds were screened for efficacy against SARS-CoV-2. Flowers from tall goldenrod (Solidago altissima) plants and the stems of the eagle fern (Pteridium aquilinum) were each able to block SARS-CoV-2 from entering human cells. The work has been published in Scientific Reports.
The study authors stressed that plants only contain miniscule amounts of the effective extracts, so it would be ineffective and possibly dangerous for people to attempt to self-medicate with the plants. They caution that eagle fern is known to be toxic.
This work is promising, but it's at the very early stages. The scientists are trying to find the molecules within the extracts that work against the virus. Once they are isolated, they will be tested to see if they are safe and can work against an actual infection, noted senior study author Cassandra Quave, an associate professor at Emory University.
A rapid screening method was created for this study. SARS-CoV-2 uses its spike protein to latch onto ACE2 receptors on human cells and cause infection. The researchers engineered virus-like particles (VLPs) that mimicked the cell entry method of the pathogenic virus, but could not cause illness. Cells that had been engineered to express higher than usual levels of ACE2 receptors were exposed to these VLPs. If VLPs infected these cells, a green fluorescent protein signal was activated so the researchers could easily see how many cells were being infected.
Plant extracts in Quave's natural product library were introduced to the system to see which ones prevented infection. Tall goldenrod and eagle fern, which are native to North America and have been known as Native American traditional medicines, were found to have the highest activity against SARS-CoV-2 infection. These extracts were effective against the alpha, theta, delta and gamma variants of VLPs.
The researchers also took the test a step further once the effective extracts were identified. With colleagues who have the biosecurity rating to work with infectious pathogens in the lab of study co-author and Emory professor Raymond Schinazi, the plant extracts were tested against the actual SARS-CoV-2 virus. This confirmed that tall goldenrod and eagle fern extracts can inhibit SARS-CoV-2 infection.
"Our results set the stage for the future use of natural product libraries to find new tools or therapies against infectious diseases," added Quave.
Now the researchers want to figure out how the plant extracts are blocking the spike protein from binding to ACE2 receptors.
Sources: Emory University, Scientific Reports