Beyond aspirin: Willow bark also found to be a broad-spectrum antiviral
A new study has found that an extract made from willow bark, the precursor to aspirin, possesses effective broad-spectrum antiviral properties. The discovery may mean we will soon have a new way of fighting viral infections, from stomach bugs to seasonal colds and flu.
The bark of the willow tree is thought to have been used for centuries as a traditional medicine to relieve pain. Its active ingredient, salicin, was discovered in 1828 and used to create salicylic acid 10 years later. Then, in 1899, scientists at the drug firm Bayer modified salicylic acid to create acetylsalicylic acid, otherwise known as aspirin.
Now, a Finnish study led by researchers at the University of Jyväskylä has found that willow bark extract might also be an effective, broad-spectrum antiviral agent.
“We need broadly acting and efficient tools to combat the virus load in our everyday life,” said Varpu Marjomäki, corresponding author of the study. “Vaccinations are important, but they cannot deal with many of the newly emerging serotypes early enough to be effective on their own.”
In a previous study, the researchers had tested willow bark (Salix) extract on non-enteroviruses, a group of RNA viruses such as those that cause polio and hepatitis A, and found it to be very effective and non-toxic. In the current study, they tested the extract on other kinds of viruses to see if it was effective and to try and understand its mechanism of action.
The extract was made by harvesting bark from commercially grown willow branches, which the researchers cut up, froze, ground, and extracted using hot water. The researchers then tested it on cell samples with two strains of enteroviruses, Coxsackievirus A (CVA) and B (CVB), and two coronaviruses, a seasonal coronavirus and SARS-CoV-2, which causes COVID-19.
Viruses can be enveloped or non-enveloped, meaning they either have or don’t have an outer lipid membrane. Non-enveloped viruses, such as enteroviruses, are typically more virulent than enveloped viruses like coronaviruses. CVA can cause hand, foot and mouth disease, and CVB infection can lead to pericarditis and myocarditis. Both CVA and CVB can cause meningitis. Seasonal coronaviruses generally cause cold symptoms and mild upper respiratory tract illness; COVID-19 needs no further introduction.
The researchers found that the Salix extract exhibited different mechanisms of action on different virus types. Enteroviruses couldn’t enter cells after they’d been treated with the extract; in the SARS-CoV-2 samples, the virus could enter the treated cells, but it couldn’t reproduce once inside. Viewed under a microscope, it appeared that the coronaviruses had been broken down, whereas the enteroviruses were intact but prevented from releasing their genome and reproducing.
When the researchers experimented with the timing of adding the extract, they found that it appeared to act on the virus’ surface rather than at a particular stage of its replication cycle.
“The extracts acted through distinct mechanisms against different viruses,” said Marjomäki. “But the extracts were equally effective in inhibiting the enveloped as well as non-enveloped viruses.”
The researchers also tested compounds derived from willow bark, including commercially prepared salixin extract and salixin powder. Only the salixin extract showed antiviral activity, suggesting that the properties of the researchers’ Salix extract could result from the interaction of different bioactive compounds.
As yet, the researchers have been unable to ascertain which compounds in the extract produce the antiviral effect, so further research will be needed.
“We are presently continuing fractionations and bioactive molecule identification from willow bark extracts,” Marjomärki said. “This will give us a number of identified pure molecules which we can study in further detail. Also, we will study a larger number of viruses with purified components. Purified components will give us better opportunities to study their mechanisms of action.”
The study was published in the journal Frontiers in Microbiology.
Source: Frontiers Science News