A new study from Finland suggests that willow bark extract, which has been used as a traditional medicine for centuries, could be an effective broad-spectrum antiviral agent against a range of virus, including coronaviruses.
The Main Findings
The study, published in Frontiers in Microbiology, was led by researchers at the University of Jyväskylä. They found that an extract made from the bark of the willow tree (Salix species) inhibited the replication of two strains of enterovirus and two coronaviruses in cell culture experiments.
The enteroviruses tested were Coxsackievirus A and B, which can cause hand, foot and mouth disease, pericarditis, myocarditis, and meningitis. The coronaviruses were a seasonal coronavirus and SARS-CoV-2, the virus that causes COVID-19.
Against enteroviruses, the extract appeared to prevent the virus from releasing its genome into host cells and replicating. With coronaviruses, viral replication inside cells was blocked after the viruses had entered.
Senior author Varpu Marjomäki said the extract showed different mechanisms against enveloped and non-enveloped viruses but was equally effective against both types. Enveloped viruses like coronaviruses have an outer lipid membrane, while non-enveloped viruses such as enteroviruses do not.
“We need broadly acting and efficient tools to combat the virus load in our everyday life,” Marjomäki said. “Vaccinations are important, but they cannot deal with many of the newly emerging serotypes early enough to be effective on their own.”
Willow Bark’s Long History as a Remedy
The bark of the willow tree has been used for medical purposes since ancient times. Historical records suggest it was valued by early civilizations in Mesopotamia, Egypt and Greece for alleviating pain and fever.
Willow bark contains salicin, which the body metabolizes into salicylic acid. In 1828, salicin was isolated from willow bark and used to develop aspirin, one of the world’s most widely used pain relievers and fever reducers.
The current study adds to evidence that willow bark may have other therapeutic properties beyond pain relief.
How the Study Was Conducted
The researchers made the extract by harvesting bark from commercially grown willow branches. The bark was cut into small pieces, frozen, ground up, and extracted in hot water.
In cell culture experiments, the extract was added to human cell samples infected with different viruses. The researchers tested its effects on virus binding, entry into cells, genome release, and replication. They also experimented with timing of administration.
In addition to the whole willow bark extract, the team also tested salixin, a commercial willow bark derivative, and salixin powder. Of these, only salixin extract showed antiviral effects. This suggests the properties of the bark extract result from interactions between multiple compounds rather than a single substance.
Ongoing Efforts to Identify Active Compounds
While the extract clearly inhibited viral replication through different mechanisms, the active antiviral compounds have not yet been pinpointed.
Marjomäki noted her team is continuing to fractionate and identify bioactive molecules in the bark extract. This should isolate individual compounds that can then be studied further.
The researchers also plan to test the purified components against a greater number of viruses, which will provide more insights into the mechanisms of action.
Potential as an Antiviral Therapy
The study authors say the extract’s broad antiviral activity and apparent safety make it a promising candidate for antiviral therapy. Further research is needed, but willow bark extract may one day play a role in fighting viral infections and outbreaks.
Marjomäki highlighted the extract’s potential to help combat emerging viral threats. “Vaccinations are important, but they cannot deal with many of the newly emerging serotypes early enough to be effective on their own,” she said.
The researchers noted the extract could be a beneficial addition to our arsenal of antiviral tools, used either alone or with other treatments. They plan further preclinical studies to evaluate its therapeutic potential.
If the extract successfully moves through clinical trials in humans, it could provide a novel antiviral treatment option derived from ancient medicine.
More Cautions Needed Before Use
While the study shows promise, experts caution that more research is needed before willow bark extracts should be used as an antiviral therapy.
“These early cell culture findings are interesting, but require further validation,” said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University.
He noted that many compounds show antiviral effects in vitro but fail to work when tested in animals or humans. Safety is also a key concern.
“We have to determine optimal dosing, confirm the extract is safe for use in people, and rigorously test its efficacy in clinical trials before considering this as an antiviral treatment,” Schaffner emphasized.
Some side effects have been reported with use of willow bark, including nausea, upset stomach, and increased risk of bleeding when combined with other drugs. The bark contains a compound called salicin which may cause problems in some individuals.
Additionally, the safety and efficacy of standardized bark extracts needs to be evaluated, as plant-based compounds can vary depending on growing conditions and extraction methods.
While interesting as an area for further antiviral research, experts agree willow bark extract is not ready for use as a COVID or flu remedy. Extensive clinical work is required first to validate both its effectiveness and safety.
Traditional Remedies Need Rigorous Study
The discovery of aspirin was a breakthrough stemming from traditional plant medicine. Some scientists hope other natural remedies may yield new therapeutic compounds.
“Traditional medicines can guide drug discovery, but meticulous science is imperative to avoid harms,” said pharmacologist Dr. Clara Davis of Oxford University.
“We must isolate the active agents, determine their mechanisms, test rigourously for safety and efficacy before these plant extracts become clinical reality.”
While traditional use provides clues where to look, Davis said, “We have to put these leads through the same rigorous wringer we do for any drug.”
Marjomäki and her team hope further investigation of willow bark extract will lead to new antiviral therapies. But experts agree years of careful study are still needed to properly evaluate its therapeutic potential and safety.
The research provides hope that willow bark’s long history may lead to new treatments, but only thorough clinical testing will reveal whether it can effectively and safely help combat viruses.