Researchers at the Rutgers School of Dental Medicine have recently found evidence demonstrating that two types of mouthrinses disrupt coronavirus disease (COVID-19) transmission.
The study found that Listerine and the prescription mouthwash chlorhexidine gluconate were able to block the virus infection in tissue cultures, or pieces of tissue that are taken to be studied in an artificial environment, said Theresa Chang, co-author and associate professor in the Department of Microbiology, Biochemistry and Molecular Genetics.
The researchers also tested Colgate Peroxyl and the topical antiseptic povidone-iodine, but found that even though the mouthrinses inhibited viral activity, they were also found to have a strong toxic effect on cells, known as cytotoxicity, she said.
Daniel Fine, senior author of the study and chairman of the Department of Oral Biology, said that there are several different ways in which mouthwashes can interfere with viral activity.
“In some cases, (mouthrinses) can interfere with the spike protein on (the) surface (of a COVID-19 virus particle), changing its configuration and making it difficult for the protein to interact with its human skin cell receptor,” he said. “In other cases, mouthrinses have agents that can affect the viral cell envelope.”
The spike protein and cell envelope are what enable many viruses to bind to host cells, so if a mouthwash can affect the shape and interaction of these mechanisms, it can reduce the amount of virus in an infected person's blood, also known as viral load, and further reduce transmission, Fine said.
He and Chang said that the researchers’ primary purpose was to determine the antiviral potential of the studied mouthrinses. They did this by first determining the effect of each substance on cell viability, or the number of healthy cells in a sample, which is significant for both viral replication and human immunity.
“Viruses require live cells to replicate. If tested agents kill cells (cytotoxicity), viruses cannot replicate,” Chang said. “It is important to avoid mouthrinses that kill cells because they may disrupt the surface barrier in the mouth, which can let pathogens into our system.”
Fine said that the researchers determined the concentration of mouthrinse that caused minimal cell death, then tested how the mouthrinse affected viral activity at that concentration. He said the team specifically wanted to understand how each of the mouthrinses performed after minimal contact time because contact with viruses and oral microbes typically happens quickly.
“Understanding that this was an in vitro (test tube) study, our goal was to try to replicate, as close as possible, oral conditions so that we could select from those mouthrinses the best of the group that could show potential in real-life (in vivo) studies,” Fine said.
To do this, the researchers diluted the mouthwashes to concentrations that would mimic actual use, according to an article from Rutgers Today. They then accounted for agent-associated cytotoxicity by developing an assay, or an analysis procedure, to remove excess mouth rinses from the viruses before adding the treated viruses to cells, Chang said.
The researchers tested the effect of mouthwashes on virus replication and ensured there would be no toxic effect, she said, which is useful in determining the actions that people can take to prevent virus spread by reducing viruses in the mouth.
This study differs from previous research, Chang said, because the researchers distinguished between virus-induced cytotoxicity and agent-induced cytotoxicity. In doing so, the team was able to determine the effect of the mouthrinses on viruses and cells.
Fine said that the team cannot make a real-world determination as to how effective the mouthrinses are in humans at the moment, but with further research, they hope to find if the mouthrinse works in the real world, the extent to which the mouthrinse reduces the number of virus particles and how it reduces the potential for infection.
Chang said that this study was important due to potential applications in places such as dentist offices.
“Dentists want to know how to protect their patients and themselves when mask wearing for patients is not optimal,” she said.