Strikingly, the steroid compounds β-sitosterol and β-sitosterol-O-glucoside clearly exerted highly promising antiviral activities against the tested A/H1N1 virus, with IC50 values of 0.975 and 0.719 µg/mL, respectively.
The phytoestrogen β-sitosterol and its derivative β-sitosterol-O-glucoside are structurally similar to estradiol, which is an estrogen steroid hormone and the major female sex hormone. The structural similarity between β-sitosterol and estradiol and the observed male-biased mortality in sex-disaggregated data of influenza deaths recommended the testing of the anti-influenza activity of estradiol. Interestingly, estradiol has high safety at a wide range of concentrations (CC50 > 5 mg/mL), with robust antiviral activity against seasonal influenza A/H1N1 virus (IC50 = 7.1 µg/mL). Conclusively, estradiol showed antiviral activity against the influenza A/H1N1 virus in vitro but with a lower IC50 value, when compared with β-sitosterol.
During the COVID-19 pandemic, several studies have discussed the male-biased mortality in sex-disaggregated data of COVID-19, suggesting that the female sex hormone estrogen is likely to contribute to partially protecting and alleviating disease severity or progression. Similarly, by analyzing the distribution of the differential significance between numbers of influenza cases and deaths within three influenza seasons in Europe, we also found male-biased mortality in sex-disaggregated data of influenza viruses with significant differences towards males during the 2019 influenza season. Interestingly, phytoestrogens, including β-sitosterol, are structurally similar to endogenous estrogens such as estradiol. This structural similarity may explain the ability of both estrogens to control IAV replication via similar mechanisms.
It is worth mentioning that the phytoestrogen β-sitosterol has more potent antiviral activity when compared with the active form of the female endogenous estrogen, but with fewer expected side effects and high biological side benefits.
Conclusions
Conclusively, our study provides a proof-of-principle demonstration that β-sitosterol (Phytosterol) and β-sitosterol-O-glucoside (Sitogluside) significantly have high in vitro antiviral potential against avian and human IAVs. Molecular docking studies were performed and suggested that β-sitosterol and β-sitosterol-O-glucoside exerted viricidal activities by binding to hemagglutinin protein. The β-sitosterol could also inhibit viral replication via interfering with viral neuraminidase and M2 proteins of IAV. This study also highlighted the possible estrogen-like effect of β-sitosterol due to the structural similarities between the two molecules and proved the anti-influenza activity of estradiol as the most active form of estrogen.
Influenza is a contagious infection in humans that is caused frequently by low pathogenic seasonal influenza viruses and occasionally by pathogenic avian influenza viruses (AIV) of H5, H7, and H9 subtypes. Recently, the clinical sector in poultry and humans has been confronted with many...
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