Natural products and herbal medicines show promise in the fight against COVID-19

Researchers in China and the United States have called for further research on the potential prophylactic effects of natural products and herbal medicines on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and subsequent coronavirus disease. 2019 (COVID-19).

In an article recently published in the journal Frontiers in pharmacology, the team discussed natural products that showed an inhibitory effect on SARS-CoV-2 and herbal medicines that were tested as potential therapies for COVID-19.

“In this review, we aimed to provide a new perspective regarding the prevention of COVID-19,” writes Jia-xu Chen of Jinan University in Guangzhou, and colleagues at the University of Houston and the University of California.

Researchers suggest that as the world awaits effective treatments and a commercially available vaccine, reusing natural products and herbal medicines as condoms holds a promising approach to at least slow the transmission of SARS-CoV-2.

“In the interest of public health, this will give health officials better control over the current pandemic,” they say.

There are no effective vaccines or therapies available

Since the start of the COVID-19 outbreak in Wuhan, China, at the end of last year (2019), the pandemic has swept the globe, devastating public health and the world economy.

COVID-19 is caused by the SARS-CoV-2 betacoronavirus, which initiates infection using a surface structure called a spike protein that binds and fuses with target host cells.

Although several candidate vaccines are being evaluated in clinical trials, their use has not yet been approved and their long-term efficacy is uncertain.

In addition to vaccine development, intense efforts have also been focused on finding effective condoms against COVID-19 among high-risk populations. However, few studies have provided satisfactory evidence of results, Chen and colleagues say.

“Since the results of current therapies in severe / critical COVID-19 patients are still questionable, prevention rather than treatment becomes more important in curbing this pandemic,” the team writes.

“Blocking the entry of SARS-CoV-2 and suppressing the infection early on is considered a more practical strategy.”

Historically, natural products and medicinal herbs have been used for the prevention of viral infections and generally show favorable efficacy and acceptable toxicity, the researchers say.

The potential effects of natural products and medicinal herbs

Now, Chen and the team have published a review summarizing some recent findings regarding the potential effectiveness of natural products and herbal medicines in inhibiting SARS-CoV-2 infection.

For example, they discuss compounds derived from natural products that may be effective against cellular receptor A5 heat shock protein (HSPA5).

Some studies have reported that HSPA5 is recognized by the SARS-CoV-2 spike protein, and a 2020 study showed that the phytoestrogens daidzein, genistein, formononetin and biocanin A have binding affinity to HSPA5.

Researchers say these plant-based medicinal compounds can disrupt SARS-CoV-2 attachment to host cells (through the spike), although their antiviral bioactivity requires further investigation.

Host cell enzyme transmembrane protease serine 2 (TMPRSS2) facilitates the entry of SARS-CoV-2 into host cells. Inhibition of this enzyme blocks the ability of the spike protein to fuse with host cell receptor angiotensin converting enzyme 2 (ACE2).

Using molecular docking and molecular dynamics simulations, a study conducted earlier this year showed that withanone, a compound that can be isolated from Ashwagandha leaves (Withania somnifera) could bind to the catalytic site of TMPRSS2.

Withania somnifera, commonly known as ashwagandha, Indian ginseng, poisonous gooseberry or winter cherry, is a plant from the nightshade or nightshade family. Image Credit: H from Hem Stock / Shutterstock

The study also confirmed that witanone significantly downregulated TMPRSS2 in the MCF-7 breast cancer cell line, thus indicating its potential to dampen the function of this enzyme.

Many studies are preliminary, but some compounds have entered clinical trials

The researchers say many of these studies are still in the preliminary stages and more pre-clinical studies are needed to examine the antiviral effects of the compounds.

“Meanwhile, a large number of clinical trials have been registered to study the potential of the natural product to halt the progression of the disease,” the team says.

One such study is investigating the immunomodulatory and antiviral activity of Nigella sativa seed oil among adult patients hospitalized with COVID-19. Another study is currently recruiting participants to study the effectiveness of vitamin C in reducing mortality among patients.

Nigella sativa. Image Credit: theapflueger / Shutterstock

What do the authors conclude?

“It is undeniable that herbal medicine is still a promising resource for drug discovery, and its acceptable toxicity makes it a potential COVID-19 prophylactic candidate,” Chen and colleagues write.

Faced with this global health crisis, the team says exploring herbal medicine-derived condoms is likely a promising and practical approach to containing the pandemic.

Natural products and herbal medicine have a long track record in treating respiratory infections, and many have been approved as over-the-counter medications or food additives, the researchers say.

“Moderate dosage of these bioactive compounds can prevent or at least slow down the SARS-CoV-2 infection process,” they conclude.