A mixture of hop and elder extracts to counteract respiratory viral infections: an in vitro study

Background. Respiratory infections are the third leading cause of mortality. Due to the increasing antiviral resistance and the variable efficacy of seasonal vaccines, there is an emerging need for novel antiviral and immune boosting strategies [1]. To this end, redox-sensitive pathways and medicinal plants, source of redox-modulating agents, represent a potential strategy [2]. Based on previous evidence [3,4], in the present study, a mixture of extracts from hop (Humulus lupulus L., Cannabaceae) and elder (Sambucus nigra L., Adoxaceae), endowed with cytoprotective and antiviral properties, was developed to be harnessed in the battle against viral respiratory infections. Methodologies. Two hydroalcoholic extracts from hop cones and elder flowers, provided by EPO s.r.l., were studied both alone and in combination for the cytoprotective properties towards the pro-oxidant agent tert-butyl hydroperoxide (tBOOH) and for the antiviral power against PR8/H1N1 influenza strain in human airways cell models. The polyphenolic profile of the extracts was characterized by spectrophotometric and chromatographic analysis. Cell viability and intracellular levels of reactive oxygen species (ROS) were assessed by standardized methods [7]. The antiviral activity was assessed in terms of viral titer and viral protein expression; moreover, the modulation of Nrf2 (Nuclear factor erythroid 2-related factor 2), involved in antioxidant defence, was investigated [7]. Results. Under our experimental conditions, the developed mixture of extracts was able to counteract the oxidative damage of tBOOH, by restoring cell viability and lowering the intracellular ROS levels, with an increased potency with respect to the extract alone. Moreover, a marked lowering in the viral titer and in the expression of viral protein, involved in various stages of the viral life cycle, was found, and was associated to an increased expression of Nrf2, impaired by influenza infection. The polyphenolic composition in the tested mixture could be responsible for these bioactivities, although the contribution of other unidentified compounds cannot be excluded. Conclusion. Altogether the obtained results highlight the ability of the developed mixture to boost the antioxidant host defence and to counteract different stages of the viral infection, as also confirmed by the increased expression of Nrf2, and to potentiate the bioactivities of the extracts alone. The mixture may be exploited as an adjuvant strategy to prevent and treat respiratory viral infections. However, further studies are needed to clarify the involved cytoprotective effects and the contribution of the bioactive compounds for possible future nutraceutical applications. References [1] Han et al. Curr Med Chem 2018,25,5115–5127. [2] Checconi et al. Int J Mol Sci 2020,21,4084. [3] Di Sotto et al. Oxid Med Cell Longev 2018,5919237. [4] Santin et al. J Ethnopharmacol 2022,283,114736. [5] Percaccio et al. Nutrients 2023,15(20),4380.