The identification of antiviral natural products as new lead structures has become a major task in medical science. Especially saponins have gained high interest for their antiviral activity. Antiviral effects of the saponin-containing plant Anagallis arvensis, widely used in traditional medicine, have been described, while mode of action or detailed phytochemical and functional investigations are still missing. A saponin enriched extract (AAS) from the aerial material of A. arvensis was characterized in detail by LC-HRMS, indicating the presence of a complex mixture of triterpene saponins and flavonoid glycosides. Plaque assays with Herpes simplex virus 1 (HSV-1) on Vero cells indicated strong inhibition of viral spread after infection of the host cells, resulting in reduced plaque size. The strongest effect was achieved by treating host cells post infection, which points towards an interference with the viral post-entry step. Using a specific HSV-1 fusion assay, AAS was shown to inhibit HSV-1 glycoprotein-mediated cell fusion at >2 μg/mL. Bioassay-guided fractionation of AAS yielded one active subfraction, which significantly reduced HSV-1 plaque size on Vero cells. The membrane-fusion inhibiting effect was correlated to the presence of desglucoanagalloside B 9. Interestingly, this compound was also detected in relevant amounts in herbal preparations from traditional medicine, which again could rationalize the use of A. arvensis as antiviral remedy in folk medicine. Relevant antiviral activity against SARS-CoV-2 was not detected.
