How Do Sterols Determine the Antifungal Activity of Amphotericin B? Free Energy of Binding between the Drug and Its Membrane Targets

Abstract

Amphotericin B (AmB) is a well-known polyene antibiotic used to treat systemic fungal infections. It is commonly accepted that the presence of sterols in the membrane is essential for the AmB biological activity, that is, for the formation of transmembrane ion channels. The selective toxicity of AmB for fungal cells is attributed to the fact that it is more potent against fungal cell membranes containing ergosterol than against the mammalian membranes with cholesterol. According to the "primary complex" hypothesis, AmB associates with sterols in a membrane to form binary complexes, which may subsequently assemble into a barrel-stave channel. To elucidate the molecular nature of the AmB selectivity for ergosterol-containing membranes, in the present work, we used computational methods to study the formation of the putative AmB/sterol complexes in a lipid bilayer. The free energy profiles for the AmB-sterol association in phospholipid bilayers containing 30 mol % of sterols were calculated and thoroughly analyzed. The results obtained confirm the formation of specific AmB/ergosterol complexes and are used to determine the energetic and structural origin of the enhanced affinity of AmB for ergosterol than for cholesterol. The significance of this affinity difference for the mechanism of action of AmB is discussed. The data obtained allowed us also to suggest a possible origin of the increased selectivity of a novel class of less toxic AmB derivatives.

Evaluation of Antifungal Activity and Mechanism of Action of Citral against Candida albicans

“…The selective toxicity of the drug for the fungal cell is ascribed to the fact that it is more potent against fungal cell membranes containing ergosterol than against mammalian membranes with cholesterol [67]. …”

Lipid polyunsaturation determines the extent of membrane structural changes induced by Amphotericin B in Pichia pastoris yeast

“…53 Amphotericin B [3] (AmB) has the broadest spectrum of antifungal 54 activity and has been used as an antibiotic against systemic fungal and 55 parasitic infections for more than 50 years [4,5] without the develop- 56 ment of significant microbial resistance. The polyene structure contain- 57 ing one hydrophilic and one hydrophobic face [6], gives it an ability to 58 interact preferentially with ergosterol, but also to a lower extent with 59 cholesterol, giving rise to toxic side effects that are often dose-limiting 60 and still represent a major problem [7,8]. 61 The classical model used to describe the AmB mode of action against 62 fungal cells is based on aqueous pores formed by AmB-sterol complexes, 63 which make the membrane permeable and lead to cell death [9-12].…”

Synthesis-enabled functional group deletions reveal key underpinnings of amphotericin B ion channel and antifungal activities

“…Third, both the C41 carboxylate and mycosamine appendages are hypothesized to promote the direct binding of membrane-embedded sterols ( Fig. 1E) (11)(12)(13)(30)(31)(32)(33)(34)(35)(36)(37)). An often invoked alternative model states that indirect effects on global membrane properties, rather than any direct binding interactions, are responsible for the impacts of membrane sterols on the biological activity of AmB (21)(22)(23)(24)(25)(26)(27)(28)(29).…”

“…Specifically, the C41 carboxylate and/or mycosamine appendages of AmB are proposed to form key polar interactions with the 3-β-hydroxyl group of a sterol. Combined with favorable hydrophobic interactions between the polyene and sterol cores, these polar interactions are predicted to stabilize a direct AmB/sterol complex (30)(31)(32)(33)(34)(35)(36)(37). Studies designed to probe this putative interaction in solution or in liposomes have traditionally relied primarily on UV/Vis and/or CD spectroscopy (10).…”