Stigmasterol elicits antiviral activity against influenza viruses through virucidal and entry inhibition activity in...

Influenza viruses pose a significant global public health threat, leading to recurrent seasonal epidemics and occasional pandemics. The rising prevalence of drug-resistant strains highlights the urgent need for new antiviral agents with alternative mechanisms of action. Plant-derived natural products have emerged as promising antiviral resources due to their chemical diversity and wide range of biological activities. Stigmasterol, a naturally occurring phytosterol found in various plants, is recognized for its anti-inflammatory and antioxidant properties; however, its antiviral potential against influenza viruses has not been clearly established. In this study, we systematically assessed the antiviral activity of stigmasterol against influenza A and B viruses in vitro. Stigmasterol demonstrated significant virucidal activity against both virus types at non-cytotoxic concentrations and effectively interfered with the functions of the viral surface proteins hemagglutinin and neuraminidase. Using GFP-expressing reporter viruses and cytopathic effect reduction assays, we showed that stigmasterol robustly suppressed viral infection under pre-, co-, and post-treatment conditions. Importantly, stigmasterol inhibited viral entry through a mechanism independent of hemagglutinin inhibition. These findings provide the first evidence that stigmasterol has broad anti-influenza activity and support its potential as a plant-derived lead compound for developing novel therapeutic strategies against influenza infection.