Antiviral Potential of Onosma bracteata Against Chikungunya Virus: Experimental Validation and Computational Mechanistic Study

Chikungunya fever caused by chikungunya virus (CHIKV) is a mosquito transmitted disease that leads to high fever, rashes, and severe joint pain, that lasts for months. There is still no approved drug or specific treatment available for this infection, which makes the search for new therapeutic options very important. Medicinal plants are often explored as a natural source of antiviral compounds, and Onosma bracteata is one such plant that has been traditionally used in different remedies. Extracts of O. bracteata were tested, and the ethyl acetate fraction showed significant two log reduction and one log reduction in viral titer at 15.62 µg/mL concentration in pre- and post-treatment assays respectively. This suggests that the plant compounds may act at different stages of the viral cycle. Since several phytochemicals are reported from this plant, computational analysis was carried out to understand which molecules might be responsible for the activity. Molecular docking studies indicated that Pulmonarioside C and few other compounds had strong binding with three important viral proteins: nsP2 protease (-6.9 kcal/mol), nsP3 macro domain (-8.7 kcal/mol), and the E2 envelope protein (-9.1 kcal/mol). Molecular dynamics simulations over 100 ns for Pulmonarioside C supported the stable interaction of this compound with the proteins, and MM/PBSA calculations further showed favorable binding energies, strengthening the prediction of its antiviral role. However, it is important to note that Pulmonarioside C has not been isolated from the tested OBEE fraction nor experimentally validated in vitro, and therefore its direct contribution to the observed antiviral activity remains to be established. Thus, in vitro and in silico experiments suggest that O. bracteata contains potential anti-CHIKV compounds, with Pulmonarioside C representing a computationally prioritized candidate for future investigation.