Honeysuckle extracts as a potential inhibitor of SARS-CoV-2 infection

Background In the current era of coronavirus disease 2019 (COVID-19), we were interested in searching for medications other than the currently available antiviral drugs Paxlovid and Molnupiravir that cause minimal side effects and do not harm the human body. Honeysuckle extract (HSE) is a traditional Chinese medicine (TCM) that has been shown to exert antiviral effects in other studies. However, no studies have indicated whether HSE has an inhibitory effect on SARS-CoV-2. Methods We prepared HSEs from dried honeysuckle flowers. We performed a cell viability assay, median tissue culture infection dose (TCID 50 ) assay, and qRT‒PCR, and calculated the virus titers using the Reed-Muench method to evaluate the inhibitory effects of aqueous and alcohol HSEs on SARS‒CoV‒2 and explore the possible underlying mechanisms. Results In this study, post-treatment with HSE resulted in dose-dependent decreases in both the RNA levels and TCID 50 of SARS-CoV-2 in Vero E6 cells; treatment with 50 μg/ml and 100 μg/ml alcohol HSEs achieved up to 95.323% and 92.587% inhibition, respectively. Moreover, pre-treatment with aqueous HSEs effectively reduced the RNA levels, and TCID 50 of SARS-CoV-2 by up to 99.684%, and alcohol HSEs achieved up to 99.921% inhibition; both of these effects occurred in a dose-dependent manner. Conclusion The results suggest that HSEs may have the potential to prevent SARS-CoV-2 infection.