How does the N-acylation and esterification of amphotericin B molecule affect its interactions with cellular membrane components-the Langmuir monolayer study.

This work presents the results of Langmuir monolayers study of two amphotericin B derivatives obtained by N-acylation (N-acetylamphotericin B, Ac-AmB) and esterification (amphotericin B methyl ester, AME) of the parent AmB molecule. The main objective of present investigations was to examine the strength and nature of interactions of Ac-AmB and AME with natural membrane components as compared to AmB, and verify the monolayer results with biological studies in vitro. Our experiments were based on surface pressure-area measurements of mixed monolayers formed by the investigated antibiotics and sterols/DPPC. The interactions were analyzed with the following dependencies: compression modulus-surface pressure, mean molecular area-composition, excess molecular area-composition and excess free energy-composition plots. It has been found that both Ac-AmB and AME form monolayers of a liquid expanded state and their stability is highest as compared to AmB films. The investigated compounds mix in monolayers with natural membrane components within the whole range of the antibiotic mole fraction. The quantitative analysis of the interactions of the investigated antibiotics with sterols and DPPC as well as sterols/DPPC interactions allow us to verify the monolayer results with biological results. A good correlation between both kinds of studies has been found.

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.

N-(1-piperidinepropionyl)amphotericin B methyl ester (in short, PAME), a low-toxicity amphotericin B derivative, has been investigated in Langmuir monolayers at the air/water interface alone and in mixtures with cellular membrane sterols (a mammalian sterol, cholesterol, and a fungal sterol, ergosterol) and a model phospholipid (DPPC). The analysis of the strength of interaction between PAME and both sterols as well as DPPC was based, on surface pressure measurements and analysis of the isothermal compressibility (C(s)(-1)), the mean area per molecule (A(12)), the excess free energy of mixing (DeltaG(Exc)) and the total free energy of mixing (DeltaG(M)). It has been found that the interactions between PAME and sterols are attractive; however, their strength is significantly weaker for mixtures of PAME with cholesterol than with ergosterol. This casts light on the improved selectivity of PAME toward fungal cells. The strongest interactions, found for PAME/DPPC mixtures, proved an important role of DPPC in the mechanism of reduced toxicity of PAME as compared to amphotericin B. Due to stable complex formation between PAME and DPPC the antibiotic is immobilized with DPPC molecules, which reduces the concentration of free antibiotic, which is capable of interacting with membrane sterols.

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

Amphotericin B (AmB)--a polyene macrolide antibiotic--exhibits strong antifungal activity, however, is known to be very toxic to mammalian cells. In order to decrease AmB toxicity, a number of its derivatives have been synthesized. Basing on in vitro and in vivo research, it was evidenced that one of AmB derivatives, namely N-methyl-N-D-fructopyranosylamphotericin B methyl ester (in short MF-AME) retained most of the antifungal activity of the parent antibiotic, however, exhibited dramatically lower animal toxicity. Therefore, MF-AME seems to be a very promising modification product of AmB. However, further development of this derivative as potential new antifungal drug requires the elucidation of its molecular mechanism of reduced toxicity, which was the aim of the present investigations. Our studies were based on examining the binding energies by determining the strength of interaction between MF-AME and membrane sterols (ergosterol-fungi sterol, and cholesterol-mammalian sterol) and DPPC (model membrane phospholipid) using the Langmuir monolayer technique, which serves as a model of cellular membrane. Our results revealed that at low concentration the affinity of MF-AME to ergosterol is considerably stronger as compared to cholesterol, which correlates with the improved selective toxicity of this drug. It is of importance that the presence of phospholipids is essential since--due to very strong interactions between MF-AME and DPPC--the antibiotic used in higher concentration is "immobilized" by DPPC molecules, which reduces the concentration of free antibiotic, thus enabling it to selectively interact with both sterols.

Thermodynamic study of adsorption of homologous anionic and cationic surfactants.

The simplified form of an integral adsorption isotherm based on Butler's equation was applied to describe surface behavior of a series of anionic (sodium alkylsulfonates) and cationic (alkylpyridinium halides) surfactants. This theory allows for the calculation of the free energy of adsorption (Delta G jk) value corresponding to the ability of a particular surfactant to undergo adsorption. The obtained results indicate that the value of Delta G jk depends linearly on the length of the hydrocarbon chain as well as on the kind and concentration of the added inorganic electrolyte. Moreover, it has been found that in the case of surfactants, which have the same length of the alkyl chain and adsorb from solutions containing the same inorganic electrolyte, the charge of hydrophilic group has insignificant influence on the value of Delta G jk.