Amphotericin B−Dipalmitoyl Phosphatidyl Glycerol Interactions Responsible for the Reduced Toxicity of Liposomal Formulations:  A Monolayer Study

Abstract

Mixtures of amphotericin B (AmB) and dipalmitoyl phosphatidyl glycerol (DPPG) were studied as floating Langmuir monolayers at the air/water interface. The films were analyzed using surface pressure-area (π-A) isotherms and compressional modulus-surface pressure (Cs -1 -π) plots in addition to Brewster angle microscopy. The film components were found to interact with each other with the strongest interactions occurring at the ca. 2:1 AmB:DPPG mixed film composition (XAmB ) 0.66), suggesting the formation of stable complexes composed of two horizontally oriented AmB molecules and one vertically oriented DPPG molecule. It has been suggested that the interactions between AmB and the phospholipid may compete in vivo with those between the antibiotic molecules and cellular membrane sterols. The toxic effects of AmB formulations containing free AmB (Fungizone) are thought to be due to the presence of free drug molecules that can interact with cellular membrane sterols, forming channels responsible for the observed toxicity. In liposomal AmB formulations on the other hand, AmB molecules are "immobilized" by their interactions with liposomal phospholipids, and therefore, are not as toxic to host cells.

N-(1-Piperidinepropionyl)amphotericin B methyl ester (PAME)— a new derivative of the antifungal antibiotic amphotericin B: Searching for the mechanism of its reduced toxicity

“…Although the monolayer experiments for mixtures of AmB and sterols/lipids have already been published [3,13,[30][31][32][33][34]36] in none of these studies was dimethylformamide (DMF) used to dissolve all the molecules investigated. The spreading solvent affects the shape of AmB isotherms as well as the stoichiometry of the antibiotic/sterol complexes.…”

Thermodynamic characteristics of mixed monolayers of amphotericin B and cholesterol

“…It has been shown from toxicity studies that the most toxic form of the antibiotic is the aggregated state [23,24]. It has been reported that small aggregates, as small as dimers, of AmB are required to induce a cooperative association between it and cholesterol.…”

Interactions of amphotericin B derivative of low toxicity with biological membrane components—the Langmuir monolayer approach

“…This important clinical drug induces differential membrane permeability changes in ergosterol-and cholesterol-containing fungal and mammalian cells, respectively (reviewed in [34,35]). The Langmuir monolayer studies were of help in understanding the mechanism of a higher affinity of AmB towards ergosterol as compared to cholesterol (which has been confirmed both in mixed monolayers [24][25][26] and in penetration experiments [22,32], and to get insight into the reduced toxicity of liposomal formulations of AmB [5,36].…”