No abstract

This paper discusses the possibility of using plant polyphenols as viral fusion inhibitors with a lipid-mediated mechanism of action. The studied agents are promising candidates for the role of antiviral compounds due to their high lipophilicity, low toxicity, bioavailability, and relative cheapness. Fluorimetry of calcein release at the calcium-mediated fusion of liposomes, composed of a ternary mixture of dioleoyl phosphatidylcholine, dioleoyl phosphatidylglycerol, and cholesterol, in the presence of 4′-hydroxychalcone, cardamonin, isoliquiritigenin, phloretin, resveratrol, piceatannol, daidzein, biochanin A, genistein, genistin, liquiritigenin, naringenin, catechin, taxifolin, and honokiol, was performed. It was found that piceatannol significantly inhibited the calcium-induced fusion of negatively charged vesicles, while taxifolin and catechin showed medium and low antifusogenic activity, respectively. As a rule, polyphenols containing at least two OH-groups in both phenolic rings were able to inhibit the calcium-mediated fusion of liposomes. In addition, there was a correlation between the ability of the tested compounds to inhibit vesicle fusions and to perturb lipid packing. We suggest that the antifusogenic action of polyphenols was determined by the depth of immersion and the orientation of the molecules in the membrane.

The ability of extracts of grapefruit seeds (ESG), sea buckthorn leaves (ESBL), and chaga (EC) to inhibit membrane fusion was evaluated. It was found that ESBL and EC inhibited Ca 2+ -mediated fusion of phosphatidylglycerol-enriched lipid vesicles; the inhibition indexes were about 90 and 100%, respectively. ESG did not inhibit the fusion of negatively charged liposomes induced by calcium. In addition to calcium-mediated liposome fusion, EC inhibited the fusion of vesicles from a mixture of phosphatidylcholine and cholesterol under the action of polyethylene glycol with a molecular weight of 8000 Da (the inhibition index was 80%). The other two extracts had no effect on polymer-induced fusion of uncharged membranes. The effect of some major components of the tested extracts on the fusion of vesicles was evaluated. It has been shown that flavonols, quercetin and myricetin, which are major components of ESBL, inhibited the fusion of negatively charged membranes under the action of calcium (the inhibition indexes were about 85 and 60%, respectively). Another flavonol of ESBL, the glycoside of quercetin rutin, did not have such an effect. The data obtained made it possible to relate the ESBL suppression of calcium-induced fusion of lipid vesicles with the presence of quercetin and myricetin in its composition. These flavonols had virtually no effect on polyethylene glycol-induced vesicle fusion, which is consistent with the absence of ESBL action on liposome fusion under the action of polymer. The ability of quercetin and myricetin to reduce the melting temperature of phosphatidylglycerol with saturated hydrocarbon chains and to increase the half-width of the peak corresponding to melting has been demonstrated. The observed correlation between the parameters characterizing the thermotropic behavior of the lipid in the presence of quercetin and myricetin and the index of inhibition of calcium-mediated liposome fusion by these compounds may indicate a relationship between the ability of flavonols to influence the packaging of membrane lipids and inhibit vesicle fusion. Pentacyclic triterpenoids, betulin and lupeol, which are part of EC, did not inhibit the fusion of vesicles under the action of both calcium and polyethylene glycol, and their presence in EC cannot be responsible for the antifusogenic activity of EC.

With the resurgence of the coronavirus pandemic, the repositioning of FDA-approved drugs against coronovirus and finding alternative strategies for antiviral therapy are both important. We previously identified the viral lipid envelope as a potential target for the prevention and treatment of SARS-CoV-2 infection with plant alkaloids. Here, we investigated the effects of eleven cyclic lipopeptides (CLPs), including well-known antifungal and antibacterial compounds, on the liposome fusion triggered by calcium, polyethylene glycol 8000, and a fragment of SARS-CoV-2 fusion peptide (816-827) by calcein release assays. Differential scanning microcalorimetry of the gel-to-liquid-crystalline and lamellar-to-inverted hexagonal phase transitions and confocal fluorescence microscopy demonstrated the relation of the fusion inhibitory effects of CLPs to alterations in lipid packing, membrane curvature stress and domain organization. The effects of the compounds were evaluated in an in vitro Vero-based cell model, and aculeacin A, anidulafugin, iturin A, and mycosubtilin attenuated the cytopathogenicity of SARS-CoV-2 without specific toxicity.