Abstract
Except for specific vaccines and monoclonal antibodies, effective prophylactic or post-exposure therapeutic treatments are currently limited for COVID-19. Propolis, a honeybee’s product, has been suggested as a potential candidate for treatment of COVID-19 for its immunomodulatory properties and for its powerful activity against various types of viruses, including common coronaviruses. However, direct evidence regarding the antiviral activities of this product still remains poorly documented. VERO E6 and CALU3 cell lines were infected with SARS-CoV-2 and cultured in the presence of 12.5 or 25 μg/ml of a standardized Hydroalcoholic Extract acronym (sHEP) of Eurasian poplar type propolis and analyzed for viral RNA transcription, for cell damage by optical and electron microscopy, and for virus infectivity by viral titration at 2, 24, 48, and 72 h post-infection. The three main components of sHEP, caffeic acid phenethyl ester, galangin, and pinocembrin, were tested for the antiviral power, either alone or in combination. On both cell lines, sHEP showed significant effects mainly on CALU3 up to 48 h, i.e., some protection from cytopathic effects and consistent reduction of infected cell number, fewer viral particles inside cellular vesicles, reduction of viral titration in supernatants, dramatic drop of N gene negative sense RNA synthesis, and lower concentration of E gene RNA in cell extracts. Interestingly, pre-treatment of cells with sHEP before virus inoculation induced these same effects described previously and was not able to block virus entry. When used in combination, the three main constituents of sHEP showed antiviral activity at the same levels of sHEP. sHEP has a remarkable ability to hinder the replication of SARS-CoV-2, to limit new cycles of infection, and to protect host cells against the cytopathic effect, albeit with rather variable results. However, sHEP do not block the virus entry into the cells. The antiviral activity observed with the three main components of sHEP used in combination highlights that the mechanism underlying the antiviral activity of sHEP is probably the result of a synergistic effect. These data add further emphasis on the possible therapeutic role of this special honeybee’s product as an adjuvant to official treatments of COVID-19 patients for its direct antiviral activity.
Highlights
Coronavirus Disease 2019 (COVID-19) has been declared a pandemic on March 11, 2020 by WHO, (2020),1 and globally, as of January 25, 2022, there have been 349,641,119 confirmed cases of COVID-19, including 5,592,266 deaths reported in the WHO regions. various SARS-CoV-2 specific vaccines are available with high rate of efficacy, the absence of inhibitors specific for this virus remains a serious problem in counteracting the spread of the infection
Our study evaluated the ability of a standardized hydroalcoholic extract of poplar type propolis to inhibit SARS-CoV-2 infection in vitro, by analyzing the viral transcription by RT-PCR, the infectivity by viral titration, and the cytopathic effects (CPE) by optical and electron microscopy
It was decided to use a dose of standardized hydroalcoholic extract of poplar type propolis (sHEP) lower to the concentration 50% (CC50) value, which had been well tolerated by both cell lines during the experiments, namely 25 μg/ml of sHEP
Summary
Various SARS-CoV-2 specific vaccines are available with high rate of efficacy, the absence of inhibitors specific for this virus remains a serious problem in counteracting the spread of the infection. Except for remdesivir (Teoh et al, 2020; Kokic et al, 2021), for the monoclonal antibodies (Deb et al, 2021), and for an investigational antiviral molnupiravir indicated for adults with increased risk of progressing to severe COVID-19,2 no alternative specific treatment exists for SARS-CoV-2. Among candidate treatment options for COVID-19, the honeybees’ products (i.e., honey, propolis, bee venom, royal jelly) have been considered an attractive potential therapeutic adjuvant. The significant interest comes from numerous evidence related to the well-known immunoregulatory and anti-inflammatory activities (Sforcin, 2007; Machado et al, 2012; Hori et al, 2013; Governa et al, 2019) and from some experimental data pointing to its therapeutic potential against a variety of viruses such as influenza, HIV, HSV, adenovirus, rotavirus, papilloma virus, and other human coronaviruses (Ito et al, 2001; Shimizu et al, 2008; Maruta, 2014; Huynh et al, 2017)
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