Study shows effective light-induced inactivation of SARS-CoV-2 with conjugated oligomers and polymers

A new pilot study by US researchers demonstrates an alternative approach to long-lasting disinfection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by using cationic phenylene ethynylene polymers and oligomers (i.e., conjugated electrolytes). The paper is currently available on medRxiv* preprint server.

The ongoing coronavirus disease (COVID-19) pandemic, caused by the highly contagious SARS-CoV-2, is exceptionally difficult to control or prevent. At the moment, there are only a handful of treatment options, while a safe and effective vaccine and its widespread implementation is still over the horizon.

Furthermore, there are very few long-lasting disinfectants that are available to prevent the spread of the virus. Several conventional ones are shown to be active against the SARS-CoV-2, and the most commonly used among them are hydrogen peroxide, bleach, and alcohol solution.

However, in the last decade, many research groups revealed the effectiveness of cationic phenylene ethynylene polymers, oligomers (conjugated electrolytes), and derivative materials against bacteria, viruses, and fungi. Their antimicrobial activity includes both light-activated and dark-active pathways, with relatively low toxicity against the human skin.

This paper, authored by researchers from the University of New Mexico and the University of Texas at San Antonio in the US, reports a pilot study of five phenylene ethynylene materials and compounds as inactivators of SARS-CoV-2 in aqueous suspensions.

Crystal violet stain of a Vero E6 cell monolayer 3 days post SARS-CoV-2 infection. A viral plaque, which appears as white circular features in the image, begins when a virus infects a cell within the cell monolayer. The virus infected cell subsequently lyses and spreads the infection to adjacent cells where the infection-to-lysis cycle is repeated. The infected cell area creates a plaque, an area of dead cells surrounded by uninfected, live cells, which can be seen by adding a crystal violet solution that colors the cytoplasm of healthy cells.
Crystal violet stain of a Vero E6 cell monolayer 3 days post SARS-CoV-2 infection. A viral plaque, which appears as white circular features in the image, begins when a virus infects a cell within the cell monolayer. The virus infected cell subsequently lyses and spreads the infection to adjacent cells where the infection-to-lysis cycle is repeated. The infected cell area creates a plaque, an area of dead cells surrounded by uninfected, live cells, which can be seen by adding a crystal violet solution that colors the cytoplasm of healthy cells.

The appraisal of SARS-CoV-2 inactivators

The researchers have tested five representative conjugated oligomers and polymers as inactivators of SARS-CoV-2, which were selected from the group of phenylene ethynylene-based cationic and anionic conjugated materials.

More specifically, the aforementioned five materials were chosen as salient examples of a much larger assemblage of polymeric and oligomeric conjugated electrolytes, previously shown to be highly active against various microorganisms.

Samples of each material in solution have been incubated with a suspension of SARS-CoV-2 dissolved in water. In addition, the samples were incubated in the dark and under UV-visible light irradiation in a photoreactor. Following the incubation period for increasing amounts of time, all the samples were analyzed in detail for virus activity.

Antiviral activity under irradiation with light

The most significant result of this study was that all five materials tested demonstrated antiviral activity against SARS-CoV-2 under irradiation with light absorbed by the specific material. More specifically, moderate to very strong inactivation of the virus has been seen on irradiation with near-UV or visible light.

"With both the oligomers and polymers, we can reach several logs of inactivation with relatively short irradiation times", study authors further emphasize their findings in this exciting medRxiv paper.

Such pronounced antiviral activity likely arises due to the binding of the compounds to viral proteins and moving them really close to the virus, which is followed by light-activated singlet oxygen and the generation of reactive oxygen species with damaging effects to the virus.

Nonetheless, although the oligomers and polymers are active under irradiation, they cannot inactivate the virus in the dark. Three oligomers are active when irradiated with near ultraviolet light, while the two polymers are active under both visible and near-UV irradiation.

Practical applications

This study opens the door towards practical applications of these materials. Their use is feasible in the prevention of COVID-19 and a myriad of other virus-based diseases, but also for future virus threats.

In their previous research endeavors, this group of scientists has shown that similar materials prepared can be readily incorporated into surface coatings to achieve broad-spectrum antimicrobial properties. One notable example is textile with compounds either covalently attached via electrospinning or non-covalently incorporated by adsorption.

"Our results suggest several applications involving the incorporation of these materials in wipes, sprays, masks and clothing and other personal protection equipment that can be useful in preventing infections and the spreading of this deadly virus and future outbreaks from similar viruses", accentuate study authors.

On top of that, it seems likely that warfare fighters, clothing for athletes, as well as paints and coatings may provide lasting disinfection of hard surfaces in rooms, outdoor/indoor spaces, and vehicles.

The potential clinical utility has been corroborated by other studies, which have shown that these materials are not hazardous to the environment from their degradation byproducts, and also not harmful to human skin (or other types of mammalian cells for that matter). In any case, further research may bring this concept from bench to bedside much sooner than we expect.

*Important Notice

medRxiv 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:
Dr. Tomislav Meštrović

Written by

Dr. Tomislav Meštrović

Dr. Tomislav Meštrović is a medical doctor (MD) with a Ph.D. in biomedical and health sciences, specialist in the field of clinical microbiology, and an Assistant Professor at Croatia's youngest university - University North. In addition to his interest in clinical, research and lecturing activities, his immense passion for medical writing and scientific communication goes back to his student days. He enjoys contributing back to the community. In his spare time, Tomislav is a movie buff and an avid traveler.

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