Botanical brawn: Extracts from two wild plants inhibit COVID-19 virus, study finds

14 Feb 2023 --- Extracts from two common wild plants can inhibit the virus that causes COVID-19 to infect living cells, according to a paper published in Scientific Reports. The authors screened 18 compounds and 1,867 extracts from 660 species from the Quave Natural Products Library (QNPL) of plant extracts for viral entry inhibition.

Extracts of the flowers of tall goldenrod (Solidago altissima) and the rhizomes of the eagle fern (Pteridium aquilinum) both had potent antiviral activities, according to the study. Both are native to North America and used by native Americans for traditional medicinal uses.

NutritionInsight spoke with one of the study’s authors, Cassandra Quave, associate professor of dermatology and human health at Emory University in Georgia, the US. “Our lab is most passionate about finding solutions to deadly, antimicrobial-resistant infections.” 

“This study represents the first step in our drug discovery process. After sorting through over 1,800 extracts, we have now homed in on two promising plants for further study.” 

“Science is an iterative process, and the true impact of this study is that of a launchpad to the next level of deeper investigation into these plants,” according to Quave. 

What’s next? The study found that two plant extracts inhibit the virus that causes COVID-19 to infect living cells. 
The authors warn against consumers treating themselves with the two plant extracts, as this would be ineffective and potentially dangerous. The active compounds are only present in minuscule quantities. Moreover, the eagle fern is known to be toxic. 

The research team has already begun the next steps of working toward the isolation of the most bioactive molecules from these two plant species. 

Quave explains: “Each plant extract contains thousands of molecules and, like searching for a needle in a haystack, we are getting very close to finding the ‘needles’ of individual active molecules.”

“Once we have isolated these in sufficient quantities, we will perform extensive chemical analyses to determine their chemical structure and subject them to study with infectious virus.”

 “We will also study the mechanism of action to determine how these molecules work at the cellular, or even protein, level.”

She adds that the researchers are not yet ready for commercial development but hopes they can come closer to that target over the next year. 

Three of the authors have applied for a provisional patent. This patent is based on the research outcomes, specifically the antiviral potential of extracts and natural product compounds derived from species exhibiting bioactivity. 

Over 1,800 extracts tested
The authors developed a method for rapidly testing plant extracts from the QNPL. 

The COVID-19 virus has a spike protein that binds to the angiotensin-converting enzyme 2 (ACE2) on host cells, after which the virus enters the cell, explain the researchers. They programmed virus-like particles to activate a fluorescent green protein instead of infecting a cell with the virus. 

Next, the researchers added plant extracts to human cells, after which they introduced the reprogrammed viral particles. By shining a fluorescent light on the cells, they could determine if the virus had entered the cells and activated the green protein. 

The rapid test results were confirmed by testing the tall goldenrod and eagle fern extracts against the virus. The researchers tested 1,867 extracts from 660 plant species and 18 compounds. 

Additional testing determined that the plant extracts worked across four virus variants: alpha, theta, delta and gamma. 

Limitations of the study 
Plant extracts contain complex mixtures that can produce variable results depending on when and where it is collected, the health of the plant and the extraction methods. To address this limitation, the researchers collected fresh samples in the same season with a similar maturity. 

Moreover, the researchers could not test biological replicates due to cost constraints. These are biologically distinct samples that show natural variation, for example, two plants that grow in similar conditions. 

It was also beyond the scope of the research to determine a mechanism of action. As the ACE2 tested is also involved in different processes in the body, this may have influenced the results found. 

Science behind plants 
During the COVID-19 pandemic, consumer demand for supplements grew to prevent getting ill, a trend that has continued post-pandemic. 

However, the authors of the study state that the science to support the use of botanicals to prevent infection still needs to be completed. They add that this research is the first extensive investigation of botanicals used in traditional food and medicine systems for their efficacy in inhibiting the COVID-19 virus. 

Quave notes that there are more than 34,000 species of medicinal plants used by humans on Earth, of which the majority grows in the wild. She adds that “wild plants require more extensive chemical defenses than cultivated plants.”

Many of the extracts included in the QNPL are created from wild-harvested plants. 

“We find that often the same molecules produced to defend the plant are also responsible for the pharmacological properties we find useful as humans,” says Quave.

Hopes for the future The next step is to isolate the most bioactive molecules from these two plant species. 
“We’ve shown that our natural products library is a powerful tool to help search for potential therapeutics for an emerging disease,” says the paper’s first author, Caitlin Risener, a Ph.D. candidate at Emory University’s Center for the Study of Human Health. 

She adds that “other researchers can adapt the study’s screening method to search for other novel compounds within plants and fungi that may lead to new drugs to treat a range of pathogens.”

“Plants have such chemical complexity that humans probably couldn’t dream up all the botanical compounds waiting to be discovered.” Risener adds that “the vast medicinal potential of plants highlights the importance of preserving ecosystems.”

Quave concludes: “We will continue to leverage the QNPL in the search for novel antibiotics from nature.” 

By Jolanda van Hal