How Does the Antibiotic Amphotericin B Enter Membranes and What Does It Do There?

Amphotericin B is a popular antifungal antibiotic, but the exact way it works is still a matter of debate. Here, we used monolayers composed of phosphatidylcholine with ergosterol as a model of fungal lipid membranes to study drug incorporation from the aqueous phase and analyze the molecular reorganization of membranes underlying the biological activity of the antibiotic. The results show that the internalization of antibiotic molecules into membranes occurs only in the presence of ergosterol in the lipid phase. Comparison of images of solid-supported monolayers obtained by atomic force microscopy and lifetime imaging fluorescence microscopy shows the formation of intramembrane clusters of various sizes in the lipid phase, consisting mainly of antibiotic dimers and relatively large membrane pores (∼15 nm in diameter). The results reveal multiple modes of action of amphotericin B, acting simultaneously, each of which adversely affects the structural properties of the lipid membranes and their physiological functionality.

Amphotericin B-Silver Hybrid Nanoparticles Help to Unveil the Mechanism of Biological Activity of the Antibiotic: Disintegration of Cell Membranes.

Amphotericin B is a popular antifungal antibiotic, and despite decades of pharmacological application, the exact mode of its biological activity is still a matter of debate. Amphotericin B-silver hybrid nanoparticles (AmB-Ag) have been reported to be an extremely effective form of this antibiotic to combat fungi. Here, we analyze the interaction of AmB-Ag with C. albicans cells with the application of molecular spectroscopy and imaging techniques, including Raman scattering and Fluorescence Lifetime Imaging Microscopy. The results lead to the conclusion that among the main molecular mechanisms responsible for the antifungal activity of AmB is the disintegration of the cell membrane, which occurs on a timescale of minutes.

Enhanced Antifungal Activity of Amphotericin B Bound to Albumin: A "Trojan Horse" Effect of the Protein.

Amphotericin B (AmB) is a life-saving and widely used antifungal antibiotic, but its therapeutic applicability is limited due to severe side effects. Here, we report that the formulation of the drug based on a complex with albumin (BSA) is highly effective against Candida albicans at relatively low concentrations, which implies lower toxicity to patients. This was also concluded based on the comparison with antifungal activities of other popular commercial formulations of the drug, such as Fungizone and AmBisome. Several molecular spectroscopy and imaging techniques, e.g., fluorescence lifetime imaging microscopy (FLIM), were applied to understand the phenomenon of enhanced antifungal activity of the AmB-BSA complex. The results show that the drug molecules bound to the protein remain mostly monomeric and are most likely bound in the pocket responsible for the capture of small molecules by this transport protein. The results of molecular imaging of single complex particles indicate that in most cases, the antibiotic-protein stoichiometry is 1:1. All of the analyses of the AmB-BSA system exclude the presence of the antibiotic aggregates potentially toxic to patients. Cell imaging shows that BSA-bound AmB molecules can readily bind to fungal cell membranes, unlike drug molecules present in the aqueous phase, which are effectively retained by the cell wall barrier. The advantages and prospects of pharmacological use of AmB complexed with proteins are discussed.