Rosemary compound may block Covid-19 infection

A compound found in the medicinal and culinary herb rosemary may potentially block the SARS-CoV-2 virus, and prevent inflammation caused by Covid-19, a preliminary study suggests.

The research, published in the journal Antioxidants, found that the compound, carnosic acid, can block the interaction between the SARS-CoV-2 spike protein and the receptor protein ACE2.

Spike protein is used by the SARS-CoV-2 virus to infect the cells, while ACE2 acts as a gateway to enter the cells.

The researchers also reviewed evidence from prior studies that carnosic acid has a separate effect in inhibiting a powerful inflammatory pathway that is active in severe Covid-19 as well as in other diseases including Alzheimer’s.

“We think that carnosic acid, or some optimised derivative, is worth investigating as a potentially cheap, safe, and effective treatment for Covid-19 and some other inflammation-related disorders,” said study senior author Stuart Lipton, a professor at Scripps Research, US

Rosemary is an economically important plant species that is widely distributed due to its culinary, medicinal, and cosmetic uses.

In a 2016 study, Lipton and colleagues showed that carnosic acid found in rosemary activates an anti-inflammatory, antioxidant signalling pathway called the Nrf2.

They found evidence that this pathway reduces Alzheimer’s-like signs in mouse models of that disease, which is known to feature brain inflammation.

For the new study, Lipton and colleagues from the Tokyo University of Technology, Japan, described their further studies of this anti-inflammatory effect on the immune cells that drive inflammation in Covid-19 and Alzheimer’s.

The researchers proposed that this effect could be beneficial against the inflammation observed in Covid-19 and in some cases of the post-Covid syndrome known as long Covid.

Long Covid is characterised by symptoms such as cognitive difficulties often described as “brain fog.”
Using a standard infectivity assay, the researchers showed that carnosic acid can directly block SARS-CoV-2’s ability to infect cells, with progressively greater infection-blocking activity at higher doses.

While the finding is preliminary, the researchers propose that carnosic acid has this antiviral effect, despite being a safe and relatively unreactive compound, because it is converted to its active form by the inflammation and oxidation found at sites of infection.

In that active form, they suggest, the compound modifies the ACE2 receptor for SARS-CoV-2—making the receptor impregnable to the virus and thereby blocking infection.

“Carnosic acid represents a ‘pathologically activated therapeutic’ in preclinical models of disease—inactive and innocuous in its normal state, but converted to an active form where it needs to be active,” Lipton said.

The researchers are working to synthesise and test more potent derivatives of carnosic acid with improved drug characteristics for potential use in inflammation-related disorders.