Antiviral Activity of Essential Oil from Populus balsamifera L. Buds and Its Major Compounds Against Betacoronavirus HCoV-OC43 Using a Sensitive Cytoprotection Assay

Plant-derived products, particularly essential oils, represent a promising source of antiviral scaffolds. Although Populus balsamifera L. has been traditionally used to manage respiratory ailments and infections, the antiviral potential of its bud essential oil remains unexplored. In this study, we evaluated the in vitro antiviral cytoprotective activity of P. balsamifera bud essential oil and its major constituents against HCoV-OC43, a human betacoronavirus associated with seasonal respiratory infections, using a cell-based cytoprotection assay. The assay reliably detected the activity of reference antivirals, including chloroquine (EC50 = 0.11 ± 0.01 µg/mL), molnupiravir, and fluvoxamine, supporting its suitability for antiviral screening. Under these conditions, P. balsamifera bud essential oil exhibited strong cytoprotective activity, with an EC50 of 3.3 ± 0.5 µg/mL. Chemical analysis revealed a sesquiterpene-rich composition. Two major constituents, α-bisabolol and nerolidol, also showed marked cytoprotection, with EC50 values of 2.7 ± 0.3 µg/mL and 2.6 ± 0.4 µg/mL, respectively, supporting their contribution to the overall activity of the oil. To our knowledge, this study provides the first experimental evidence of antiviral cytoprotective activity of P. balsamifera bud essential oil against a human coronavirus and identifies α-bisabolol and nerolidol as active compounds in this model.