Differences in the interaction of the polyene antibiotic amphotericin B with cholesterol- or ergosterol-containing phospholipid vesicles. A circular dichroism and permeability study

Abstract

The selective toxicity of the polyene antibiotic amphotericin B between pathogenic eukaryotic organisms and animal cells has often been said to originate in the presence of ergosterol in fungal membranes instead of cholesterol, found in membranes of animal cells. We have tested this hypothesis by measuring the proton efflux induced by amphotericin B in egg yolk phosphatidylcholine small unilamellar vesicles. By measuring circular dichroism under the same conditions, we monitored the interaction of the antibiotic and its conformational changes. Sterol-free vesicles are sensitive to amphotericin B, but the sensitivity of sterol-containing vesicles is always greater and increasingly so with increasing sterol concentration. Ergosterol-containing vesicles are more sensitive than cholesterol-containing vesicles. On the other hand, numerous amphotericin B conformers can be detected in sterol-containing vesicles, depending upon both the concentration of sterol and the amphotericin B sterol ratio. It appears that one conformer, or maybe two at high amphotericin B concentration, is responsible for the induced permeability. From their circular dichroism spectra, these two conformers are the same in the presence of ergosterol or cholesterol. The concentration of amphotericin B necessary to obtain the two conformers is higher with cholesterol than with ergosterol, which agrees with the permeability results.

Molecular modeling of amphotericin B–ergosterol primary complex in water II

“…Still, there are quite strong experimental indicators supporting hypotheses on sequential formation of the AmB-sterol channel in model membranes [6,7]. The first stage of such a process appears to be an aggregation of several molecules into so called primary complexes.…”

“…Antibiotic and sterol molecules consist of hydrophilic and hydrophobic domains, AmB is amphoteric in addition, thus there is no doubt that the molecules should highly tend to complex. UV, CD and NMR studies on antibiotic self-association and complexing with sterols in membranes and water or hydroalcoholic media show existence of various species besides AmB-AmB or antibiotic-sterol complexes of 1:1 stoichiometry [7,8,14]. Theoretical works on the AmB dimer behavior [15][16][17], energy calculations of AmB higher aggregates [17,18] and the above mentioned raw energy calculations of 2:1 complexes [12] also indicate possible stability of such more or less organized species.…”

Amphotericin B: current understanding of mechanisms of action

“…More avid binding of AmB to ergosterol than to cholesterol (22) and to ergosterolcontaining membranes than to cholesterol-containing membranes (54) has been demonstrated by spectrophotometry.…”

Separation and evaluation of natural antileishmanial potential against Leishmania major and infuntum isolated from the Tunisia strains

“…based on a combination with the parasite ergosterol membrane which increases permeability and leads to the parasite death (Vertut-Croquin et al, 1983;Fournier et al, 1998;Gagos et al, 2001;Herec et al, 2005;Umegawa et al, 2008;Grudzinski et al, 2016).…”