Viral infections pose a major challenge to modern medicine due to the increasing resistance of viruses and the limited number of effective antiviral drugs. The medicinal plant immortelle (Helichrysum italicum) is an important source of bioactive molecules with potential for the development of novel therapeutics. In this master’s thesis we used an in vitro model – mouse hepatitis virus (MHV) and L929 cells and established a new model – adenovirus type 5 (AdV5) and HeLa cells. We optimized procedures for culturing, passaging, freezing, and thawing HeLa cells, as well as the propagation of AdV5, and quantified its concentration using the TCID50 method. The CPE and plaque assay methods with AdV5 were not fully optimised, therefore we evaluated the antiviral activity of selected compounds and extracts on the MHV–L929 model with the plaque assay method and different time of compound addition strategies (pre-, co-, and post-incubation). Among the tested compounds and extracts, quercetin (SI = 53.87) and the immortelle macerate (SI = 11,376) demonstrated strong antiviral activity and low cytotoxicity in co-incubation assays. The effectiveness of quercetin most likely results from inhibition of viral entry into the cell and direct viral inactivation, while the macerate acts as a complex mixture of bioactive compounds with synergistic effects. These findings contribute to a better understanding of the possible mechanisms of action of the compounds and extracts and support the development of new nature-derived therapeutic approaches against viral infections.
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