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Review 2: "Differential effects of antiseptic mouth rinses on SARS-CoV-2 infectivity in vitro"

This potentially informative in-vitro study finds that some commercially available mouth-rinses have different anti-viral activity/cytotoxicity. Additional animal models and clinical trials are needed to generalize the study’s findings.

Published onJan 30, 2021
Review 2: "Differential effects of antiseptic mouth rinses on SARS-CoV-2 infectivity in vitro"
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Differential effects of antiseptic mouth rinses on SARS-CoV-2 infectivity in vitro
Description

AbstractSARS-CoV-2 is detectable in saliva from asymptomatic individuals, suggesting a potential benefit from the use of mouth rinses to suppress viral load and reduce virus spread. Published studies on reduction of SARS-CoV-2-induced cytotoxic effects by antiseptics do not exclude antiseptic-associated cytotoxicity. Here, we determined the effect of commercially available mouth rinses and antiseptic povidone-iodine on the infectivity of SARS-CoV-2 virus and of a non-pathogenic, recombinant, SARS-CoV-2 infection vector (pseudotyped SARS-CoV-2 virus). We first determined the effect of mouth rinses on cell viability to ensure that antiviral activity was not a consequence of mouth rinse-induced cytotoxicity. Colgate Peroxyl (hydrogen peroxide) exhibited the most cytotoxicity, followed by povidone-iodine, chlorhexidine gluconate (CHG), and Listerine (essential oils and alcohol). Potent anti-viral activities of povidone iodine and Colgate peroxyl mouth rinses was the consequence of rinse-mediated cellular damage. The potency of CHG was greater when the product was not washed off after virus attachment, suggesting that the prolonged effect of mouth rinses on cells impacts anti-viral activity. To minimalize mouth rinse-associated cytotoxicity, mouth rinse was largely removed from treated-viruses by centrifugation prior to infection of cells. A 5% (v/v) dilution of Colgate Peroxyl or povidone-iodine completely blocked viral infectivity. A similar 5% (v/v) dilution of Listerine or CHG had a moderate suppressive effect on the virus, but a 50% (v/v) dilution of Listerine or CHG blocked viral infectivity completely. Prolonged incubation of virus with mouth rinses was not required for viral inactivation. Our results indicate that mouth rinses can significantly reduce virus infectivity, suggesting a potential benefit for reducing SARS-CoV-2 spread.ImportanceSARS-CoV-2 is detectable in saliva from asymptomatic individuals, suggesting the potential necessity for the use of mouth rinses to suppress viral load to reduce virus spread. Published studies on anti-SARS-CoV-2 activities of antiseptics determined by virus-induced cytotoxic effects cannot exclude antiseptic-associated cytotoxicity. We found that all mouth rinses tested inactivated SARS-CoV-2 viruses. Listerine and CHG were less cytotoxic than Colgate Peroxyl or povidone-iodine and were active against the virus. When mouth rinses were present in the cell culture during the infection, the potent anti-viral effect of mouth rinses were in part due to the mouth rinse-associated cytotoxicity. Our results suggest that assessing anti-viral candidates including mouth rinses with minimal potential disruption of cells may help identify active agents that can reduce SARS-CoV-2 spread.

RR:C19 Evidence Scale rating by reviewer:

  • Potentially informative. The main claims made are not strongly justified by the methods and data, but may yield some insight. The results and conclusions of the study may resemble those from the hypothetical ideal study, but there is substantial room for doubt. Decision-makers should consider this evidence only with a thorough understanding of its weaknesses, alongside other evidence and theory. Decision-makers should not consider this actionable, unless the weaknesses are clearly understood and there is other theory and evidence to further support it.

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Review:

This in-vitro study set out to investigate whether the efficacy of various commercially available mouth-rinses is due to cytotoxicity or true anti-viral activity. Considering the laboratory nature of the study, the scientific method to investigate this objective is appropriate. The manuscript is novel, and sheds light on an area not previously investigated. However, there are various limitations which should be highlighted before extrapolating the findings to clinical settings. According to the in vitro results, Colgate peroxyl and Povidone-Iodine have shown to possess a higher cytotoxicity than Listerine and chlorhexidine gluconate (CHG). However, Colgate peroxyl and Povidone-Iodine-based mouth-rinses have been safely used in dental and oral applications for decades. If repurposing of these mouth-rinses in COVID-19 patients can help decrease the SARS Co-V2 viral load through oral route, cytotoxicity-induced antiviral effect can be overruled. Even though the authors have tried to minimize the mouth rinse-associated cytotoxicity by experimental handling, in a real-life scenario the cytotoxicity is expected to be much more reduced as the oral cavity is bathed continuously in saliva and food. Moreover, application of mouth-rinses in real-life is limited to a very short duration (e.g. 30 seconds) compared to the laboratory settings. Therefore, it is not possible to conclude that Listerine and CHG to be better mouth-rinse products for SARS Co-V2 infection. Further tissue-level experiments with animal models as well as clinical trials in patients are needed for firm conclusions. Mouth-rinses may have a potential application in reducing the salivary SARS CoV-2 level under certain conditions. In this regard, the current study provides valuable insight and data for future work on this area.

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