Mechanisms of Inhibition of Lipid Vesicles Fusion by Extracts of Chaga and Buckthorn Leaves

The ability of extracts of grapefruit seeds (ESG), sea buckthorn leaves (ESBL), and chaga (EC) to inhibit membrane fusion was evaluated. It was established that ESBL and EC inhibited the fusion of phosphatidylglycerol-enriched lipid vesicles under the action of calcium: the inhibition index was about 90 and 100%, respectively. ESG did not inhibit the fusion of negatively charged liposomes induced by the introduction of calcium. EC also inhibited the fusion of vesicles made from a mixture of phosphatidylcholine and cholesterol under the action of polyethylene glycol with a molecular weight of 8000 Da (inhibition index was 80%). ESG and ESBL had no effect on the polymer-induced fusion of uncharged liposomes. The effects of some major components of the tested extracts on the fusion of vesicles were also evaluated. It was shown that the major flavonols of ESBL, quercetin and myricetin, inhibited the fusion of negatively charged membranes under the action of calcium (the inhibition index was about 85 and 60%, respectively), while rutin had no effect. The ability of quercetin and myricetin to decrease the melting temperature of phosphatidylglycerol and to increase the half-width of the main peak was demonstrated. The observed correlation between the parameters characterizing the lipid thermotropic behavior in the presence of quercetin and myricetin and their antifusogenic activity may indicate the relationship between the ability of flavonols to influence the lipid packing and to inhibit vesicle fusion. Pentacyclic triterpenoids of EC, betulin and lupeol, did not suppress the fusion of vesicles under the action of either calcium or polyethylene glycol, and their presence in EC could not be responsible for the antifusogenic activity of the extract. The ability of EC to suppress membrane fusion may indicate a possible antiviral activity of these extracts against enveloped viruses.