"Cat's claw" extract inhibits replication of SARS-CoV-2 in vitro

Researchers in Columbia and Peru have shown that Uncaria tomentosa – a woody vine native to South America known of as "Cat's claw" – exerts in vitro antiviral activity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the agent that causes coronavirus disease 2019 (COVID-19).

The study found that the hydroalcoholic extract of Uncaria tomentosa inhibited SARS-CoV-2 viral replication and reduced its cytopathic effect on Vero E6 cells.

The researchers say U. tomentosa has already been widely used as an immunomodulatory agent and that previous studies have shown the extract has a range of effects on several viruses.

However, the team – from the University of Antioquia-UdeA in Medellín, Columbia and the National University of San Marcos in Lima, Peru – say this is the first study to test the effects of U. tomentosa on SARS-CoV-2.

Now, Wildeman Zapata and colleagues report that U. tomentosa reduced the viral titer and cytopathic effect of SARS-CoV-2 in the Vero E6 cell line after just 48 hours of treatment.

"Based on our results, U. tomentosa is a promising medicinal herb to combat COVID-19, but it is necessary to continue with animal models followed by clinical trials to validate our results in the context of COVID-19 patients," writes the team.

A pre-print version of the paper is available on the server bioRxiv*, while the article undergoes peer review.

No effective vaccines or antivirals are available

Since SARS-CoV-2 was first identified in Wuhan, China, late last year (2019), COVID-19 has become a global pandemic, posing a serious threat to public health and the economy as the virus continues to spread at an unprecedented rate.

Although some candidate vaccines are being evaluated in clinical trials, no preventive treatments or antiviral agents are currently available.

However, "nowadays, the World Health Organization (WHO) recognizes that traditional, complementary, and alternative medicine has many benefits. Several candidates with possible antiviral effects have been explored from medicinal plants in the preclinical phase," say the researchers.

"Herbal medicines could become a promising option to tackle the ongoing pandemic caused by COVID19," they suggest.

More about "Cat’s claw”

Also known of as “Cat’s claw,” U. tomentosa is a woody vine, native to Peru, that belongs to the Rubiaceae family.

The research team says that certain alkaloids found in this species have been recognized as having pharmacological activities and that U. tomentosa has previously been shown to exert an antiviral effect on human monocytes infected with dengue virus 2 and herpes simplex virus type 1.

Furthermore, a previous in silico analysis the team conducted showed that components present in U. tomentosa inhibited the SARS-CoV-2 enzyme 3CLpro, which is essential for replication of the virus.

The researchers say that given the results of other studies and their own in silico findings, they decided to investigate the antiviral potential of U. tomentosa against SARS-CoV-2 in vitro.

The preclinical evaluation of natural compounds that might inhibit SARS-CoV-2 could lead to the discovery of new antiviral drugs and a better understanding of the viral life cycle, suggests the team.

What did the researchers do?

Zapata and colleagues assessed the antiviral activity of the hydroalcoholic extract of U. tomentosa stem bark in Vero E6 cells using a plaque reduction assay and a test of cytopathic effect (CPE).

Just 48 hours following treatment, the plaque reduction assay showed that U. tomentosa extract had inhibited the number of infectious SARS-CoV-2 particles by 92.7% at a dose of 25.0 µg/mL.

Treatment with the extract also reduced the CPE by 98.6% at 25 µg/mL and 92.7% at 12.5 µg/mL.

The study shows that U. tomentosa exerts antiviral activity against SARS-CoV-2 in Vero E6 cells, as demonstrated by a reduction in viral titer and CPE just 48 hours following treatment, say the researchers.

“A promising medicinal herb to combat COVID-19”

The team says this study is the first to demonstrate the antiviral effect of U. tomentosa on the novel coronavirus.

“Based on our results, U. tomentosa is a promising medicinal herb to combat COVID-19,” write Zapata and colleagues. “However, further specific in vitro assays combined with in vivo studies need to be carried out to validate this in-vitro finding.”

The researchers say they hope the findings will support the continued investigation of U. tomentosa and ultimately lead to validation of its clinical use in medical trials.

*Important Notice

bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Sally Robertson

Written by

Sally Robertson

Sally first developed an interest in medical communications when she took on the role of Journal Development Editor for BioMed Central (BMC), after having graduated with a degree in biomedical science from Greenwich University.


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