Abstract

Membrane fusion is a fundamental process in cell biology, crucial for endocytosis, exocytosis, and viral entry, and its dysregulation is implicated in various pathologies. This study investigates the inhibitory potential of extracts from **Chaga** (*Inonotus obliquus*) and **Buckthorn** leaves (*Hippophae rhamnoides*) on **lipid vesicle fusion**, a model system for biological membranes. The primary objective was to elucidate the underlying mechanisms by which these natural extracts interfere with the fusion process. Using a fluorescence-based assay with large unilamellar vesicles (LUVs) composed of physiologically relevant lipids, the extracts were tested against both calcium- and polyethylene glycol (PEG)-induced fusion. The results demonstrate that both Chaga and Buckthorn leaf extracts exhibit a significant, dose-dependent inhibition of lipid vesicle fusion. Mechanistic analysis suggests that the extracts' rich content of **polyphenols** and other bioactive compounds interact directly with the lipid bilayer, altering membrane fluidity and curvature stress, thereby stabilizing the membrane against the formation of the fusion stalk intermediate. These findings highlight the potential of these plant extracts as sources of novel **membrane-active agents** that could be developed into therapeutic inhibitors for membrane-enveloped viruses or as tools for studying membrane dynamics.