Antiviral activity of bark extracts from boreal tree species

The discovery of effective and sustainable antiviral compounds to reduce viral transmission remains a critical challenge. Here, we investigated the antiviral properties of tree bark, a rich source of secondary metabolites with diverse chemical structures. Extracts from the bark of eight boreal tree species were obtained by maceration in ethanol/water (1:1) at room temperature. The total phenolic content (TPC) showed interspecific variation, with larch and alder bark showing the highest levels and birch bark the lowest. Ultrahigh-resolution mass spectrometry revealed the distinct chemical fingerprints of each bark extract, which contained hundreds of compounds including phenolics, terpenoids, organic acids, fatty acids and carbohydrates. We evaluated the antiviral activity of the extracts against non-enveloped enteroviruses, coxsackievirus A9 (CVA9) and enterovirus 71 (EV71), and the enveloped seasonal human coronavirus OC43 (HCoV-OC43). All bark extracts, except for aspen, reduced viral infectivity in a dose dependent manner. The rowan and pine bark extracts completely inhibited viral infections at concentrations of 500–1000 µg/mL, spruce and birch demonstrated significant activity. The extracts from alder, larch, and juniper bark showed a more moderate and mixed performance against the tested viral strains. Surprisingly, our findings demonstrate that extract’s antiviral efficiency does not correlate with its TPC but is instead linked to specific metabolites and their synergistic interactions. This study represents the first comprehensive comparison of the chemical fingerprints and antiviral efficiency of bark extracts, obtained under mild extraction conditions that preserve native metabolites, highlighting the potential and versatility of tree bark-derived chemicals as sustainable source of antiviral agents. • Secondary metabolites present in bark possess antiviral properties. • Bark extracts deactivate viruses, including enveloped and non-enveloped viruses. • Antiviral activity is not correlated with a high total phenolic content. • The extracts contain phenolics, terpenoids, organic acids, and carbohydrates.