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

Emerging Role of Sphingolipids in Amphotericin B Drug Resistance

Invasive fungal infections in humans are common in people with compromised immune systems and are difficult to treat, resulting in high mortality. Amphotericin B (AmB) is one of the main antifungal drugs available to treat these infections. AmB binds with plasma membrane ergosterol, causing leakage of cellular ions and promoting cell death. The increasing use of available antifungal drugs to combat pathogenic fungal infections has led to the development of drug resistance. AmB resistance is not very common and is usually caused by changes in the amount or type of ergosterol or changes in the cell wall. Intrinsic AmB resistance occurs in the absence of AmB exposure, whereas acquired AmB resistance can develop during treatment. However, clinical resistance arises due to treatment failure with AmB and depends on multiple factors such as the pharmacokinetics of AmB, infectious fungal species, and host immune status. Candida albicans is a common opportunistic pathogen that can cause superficial infections of the skin and mucosal surfaces, thrush, to life-threatening systemic or invasive infections. In addition, immunocompromised individuals are more susceptible to systemic infections caused by Candida, Aspergillus, and Cryptococcus. Several antifungal drugs with different modes of action are used to treat systemic to invasive fungal infections and are approved for clinical use in the treatment of fungal diseases. However, C. albicans can develop a variety of defenses against antifungal medications. In fungi, plasma membrane sphingolipid molecules could interact with ergosterol, which can lead to the alteration of drug susceptibilities such as AmB. In this review, we mainly summarize the role of sphingolipid molecules and their regulators in AmB resistance.

Ca2+-mediated enhancement of anesthetic diffusion across phospholipid multilamellar systems

Although sharing common properties with other divalent cations, calcium ions induce fine-tuned electrostatic effects essential in many biological processes. Not only related with protein structure or ion channels, calcium is also determinant for other biomolecules such as lipids or even drugs. Cellular membranes are the first interaction barriers for drugs. Depending on their hydrophilic, hydrophobic or amphipathic properties, they have to overcome such barriers to permeate and diffuse through inner lipid bilayers, cells or even tissues. In this context, the role of calcium in the permeation of cationic amphiphilic drugs (CADs) through lipid membranes is not well understood. We combine differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR) to investigate the effect of Ca²⁺ on the interlamellar diffusion kinetics of the local anesthetic tetracaine (TTC) in multilamellar artificial membrane systems. Our DSC results show the interesting phenomenon that TTC diffusion can be modified in two different ways in the presence of Ca²⁺. Furthermore, TTC diffusion exhibits a thermal-dependent membrane interaction in the presence of Ca²⁺. The FTIR results suggest the presence of ion-dipole interactions between Ca²⁺ and the carbonyl group of TTC, leading us to hypothesize that Ca²⁺ destabilizes the hydration shell of TTC, which in turn diffuses deeper into the multilamellar lipid structures. Our results demonstrate the relevance of the Ca²⁺ ion in the drug permeation and diffusion through lipid bilayers.

Terpene-Based Ionic Liquids from Natural Renewable Sources As Selective Agents in Antifungal Therapy

In this study, we present a new approach toward the design of ionic liquids with biological activity. Structural analysis of bioactive compounds was performed to design-in a technological and economic manner-salts with potential antifungal properties. The length of the alkyl chain as well as the task-specific component in the cation, the type of amine core, and the type of anion were considered as having an essential impact on achieving desired biological activity. Herein, we present the synthesis and characterization of ionic liquids based on monoterpene derivatives-namely, (1R,2S,5R)-(-)-menthol or bicyclic (1R)-endo-(+)-fenchol-from renewable sources. These new salts were synthesized with high yields (>96%) in mild conditions via a two-step procedure. Physicochemical properties (i.e., melting point, thermal stability, crystal shape, specific rotation, surfactant content, solubility, and surface activity) were analyzed in detail. The obtained results suggested the influence of the steric hindrance of the discussed salts on the reactivity, solubility, thermal stability, and surface properties of the studied compounds. Their potential selectivity in antifungal therapy was studied using Langmuir monolayer mimicking fungal (ergosterol) and mammalian (cholesterol) membranes. The model study confirmed the selective destabilizing activity of terpene-based ionic liquids on the fungus membrane.

Pore-forming activity of new conjugate antibiotics based on amphotericin B

A series of amides of the antifungal antibiotic amphotericin B (AmB) and its conjugates with benzoxaboroles was tested to determine whether they form pores in lipid bilayers and to compare their channel characteristics. The tested derivatives produced pores of larger amplitude and shorter lifetime than those of the parent antibiotic. The pore conductance was related to changes in the partial charge of the hydrogens of the hydroxyl groups in the lactone ring that determined the anion coordination in the channel. Neutralization of one of the polar group charges in the AmB head during chemical modification produced a pronounced effect by diminishing the dwell time of the polyene channel compared to modification of both groups. In this study, compounds that had a modification of one carboxyl or amino group were less effective in initializing phase separation in POPC-membranes compared to derivatives that had modifications of both polar groups as well as the parent antibiotic. The effects were attributed to the restriction of the aggregation process by electrical repulsion between charged derivatives in contrast to neutral compounds. The significant correlation between the ability of derivatives to increase the permeability of model membranes—causing the appearance of single channels in lipid bilayers or inducing calcein leakage from unilamellar vesicles—and the minimal inhibitory concentration indicated that the antifungal effect of the conjugates was due to pore formation in the membranes of target cells.

Sucrose esters as biocompatible surfactants for penetration enhancement: An insight into the mechanism of penetration enhancement studied using stratumcorneum model lipids and Langmuir monolayers

Up to now, the molecular mechanism of the penetration enhancing effect of sucrose esters (SEs) on stratumcorneum (SC) has not been explained in details. In this study, variety of surface sensitive techniques, including surface pressure-area (π-A) isotherms, infrared reflection-absorption spectroscopy (IRRAS), and Brewster angle microscopy (BAM), have been used to investigate interactions between SEs and SC intercellular lipids. A monolayer of the mixture of ceramide AS C18:18, stearic acid and cholesterol in the molar ratio of 1:1:0.7 on an aqueous subphase is a good model to mimic a single layer of intercellular SC lipids. The π-A isotherms of mixed monolayers and parameters derived from the curves demonstrated the interaction between nonionic surfactants such as SEs and SC lipids. With increasing SE concentration, the resultant monolayer films became more fluid and better compressible. IRRAS measurements showed that SEs disordered the acyl chains of SC lipids, and the BAM images demonstrated the modification of the domain structures in SC monolayers. Longer chain-SE has a stronger disordering effect and is better miscible with ceramides in comparison to SE with a shorter hydrophobic part. In conclusion, this study demonstrates the disordering effect of SEs on the biomimetic SC model, pointing out that small changes in the structure of surfactant may have a strong influence on a penetration enhancement of lipophilic drugs through intercellular lipids of skin.

The effect of hydroxyl moieties and their oxosubstitution on bile acid association studied in floating monolayers

Bile salt aggregates are promising candidates for drug delivery vehicles due to their unique fat-solubilizing ability. However, the toxicity of bile salts increases with improving fat-solubilizing capability and so an optimal combination of efficient solubilization and low toxicity is necessary. To improve hydrophilicity (and decrease toxicity), we substituted hydroxyl groups of several natural bile acid (BA) molecules for oxogroups and studied their intrinsic molecular association behavior. Here we present the comparative Langmuir trough study of the two-dimensional (2D) association behavior of eight natural BAs and four oxoderivatives (traditionally called keto-derivatives) floated on an aqueous subphase. The series of BAs and derivatives showed systematic changes in the shape of the compression isotherms. Two types of association could be distinguished: the first transition was assigned to the formation of dimers through H-bonding and the second to the hydrophobic aggregation of BA dimers. Hydrophobic association of BA molecules in the films is linked to the ability of forming H-bonded dimers. Both H-bond formation and hydrophobic association weakened with increasing number of hydroxyl groups, decreasing distance between hydroxyl groups, and increasing oxosubstitution. The results also show that the Langmuir trough method is extremely useful in selecting appropriate BA molecules to design drug delivery systems.

Recent progress in the study of the interactions of amphotericin B with cholesterol and ergosterol in lipid environments

In the past decade substantial progress has been made in understanding the organization and biological activity of amphotericin B (AmB) in the presence of sterols in lipid environments. This review concentrates mainly on interactions of AmB with lipids and sterols, AmB channel formation in membranes, AmB aggregation, AmB modifications important for understanding its biological activity, and AmB models explaining its mechanism of action. Most of the reviewed studies concern monolayers at the water–gas interface, monolayers deposited on a solid substrate by use of the Langmuir–Blodgett technique, micelles, vesicles, and multi-bilayers. Liposomal AmB formulations and drug delivery are intentionally omitted, because several reviews dedicated to this subject are already available.

Effect of cholesterol and ergosterol on the antibiotic amphotericin B interactions with dipalmitoylphosphatidylcholine monolayers: X-ray reflectivity study

Amphotericin B is a Streptomyces nodosus metabolite and one of the oldest polyene antibiotics used in the treatment of invasive systemic fungal infections. Despite its over 50-year existence in clinical practice and the recognition of amphotericin B as the gold standard in the treatment of serious systemic mycosis, it still remains one of the most toxic pharmaceuticals. Understanding of the processes at the molecular levels and the interactions between amphotericin B with lipid membranes containing sterols should elucidate the mechanisms of the action and toxicity of this widely used antibiotic. In this work, we use X-ray reflectivity to study the structural changes on a molecular scale after amphotericin B incorporation. These changes are accompanied by an increase in monolayer surface pressure which is more pronounced for ergosterol - rather than cholesterol-rich membranes. The data indicate that this difference is not due to the higher affinity of amphotericin B towards ergosterol-containing membranes but is rather due to a ~3Angstrom corrugation of the monolayer. Furthermore, the total quantity of amphotericin B incorporated into lipid monolayers containing cholesterol and ergosterol is the same.

Gel formulation containing mixed surfactant and lipids associating with carboplatin

The interaction of amphiphilic molecules such as lipids and surfactants with the hydrophilic drug carboplatin was investigated to identify suitable self-assembling components for a potential gel-based delivery formulation. (1) H-NMR Studies in sodium bis(2-ethylhexyl) sulfosuccinate (aerosol-OT, AOT)-based reverse micelles show that carboplatin associates and at least partially penetrates the surfactant interface. Langmuir monolayers formed by dipalmitoyl(phosphatidyl)choline are penetrated by carboplatin. Carboplatin was found to also penetrate the more rigid monolayers containing cholesterol. A combined mixed surfactant gel formulation containing carboplatin and cholesterol for lymphatic tissue targeting was investigated for the intracavitary treatment of cancer. This formulation consists of a blend of the surfactants lecithin and AOT (1 : 3 ratio), an oil phase of isopropyl myristate, and an aqueous component. The phases of the system were defined within a pseudo-ternary phase diagram. At low oil content, this formulation produces a gel-like system over a wide range of H(2) O content. The carboplatin release from the formulation displays a prolonged discharge with a rate three to five times slower than that of the control. Rheological properties of the formulation exhibit pseudoplastic behavior. Microemulsion and Langmuir monolayer studies support the interactions between carboplatin and amphiphilic components used in this formulation. To target delivery of carboplatin, two formulations containing cholesterol were characterized. These two formulations with cholesterol showed that, although cholesterol does little to alter the phases in the pseudo-ternary system or to increase the initial release of the drug, it contributes significantly to the structure of the formulation under physiological temperature, as well as increases the rate of steady-state discharge of carboplatin.

Influence of the nature of the sterol on the behavior of palmitic acid/sterol mixtures and their derived liposomes

The phase behavior of mixtures formed with palmitic acid (PA) and one of the following sterols (dihydrocholesterol, ergosterol, 7-dehydrocholesterol, stigmasterol and stigmastanol), in a PA/sterol molar ratio of 3/7, has been characterized by IR and (2)H NMR spectroscopy at different pH. Our study shows that it is possible to form liquid-ordered (lo) lamellar phases with these binary non-phospholipid mixtures. The characterization of alkyl chain dynamics of PA in these systems revealed the large ordering effect of the sterols. It was possible to extrude these systems, using standard extrusion techniques, to form large unilamellar vesicles (LUVs), except in the case of ergosterol-containing mixture. The resulting LUVs displayed a very limited passive permeability consistent with the high sterol concentration. In addition, the stability of these PA/sterol self-assembled bilayers was also found to be pH-sensitive, therefore, potentially useful as nanovectors. By examining different sterols, we could establish some correlations between the structure of these bilayers and their permeability properties. The structure of the side chain at C17 of the sterol appears to play a prime role in the mixing properties with fatty acid.

Biophysical interactions with model lipid membranes: applications in drug discovery and drug delivery

The transport of drugs or drug delivery systems across the cell membrane is a complex biological process, often difficult to understand because of its dynamic nature. In this regard, model lipid membranes, which mimic many aspects of cell-membrane lipids, have been very useful in helping investigators to discern the roles of lipids in cellular interactions. One can use drug-lipid interactions to predict pharmacokinetic properties of drugs, such as their transport, biodistribution, accumulation, and hence efficacy. These interactions can also be used to study the mechanisms of transport, based on the structure and hydrophilicity/hydrophobicity of drug molecules. In recent years, model lipid membranes have also been explored to understand their mechanisms of interactions with peptides, polymers, and nanocarriers. These interaction studies can be used to design and develop efficient drug delivery systems. Changes in the lipid composition of cells and tissue in certain disease conditions may alter biophysical interactions, which could be explored to develop target-specific drugs and drug delivery systems. In this review, we discuss different model membranes, drug-lipid interactions and their significance, studies of model membrane interactions with nanocarriers, and how biophysical interaction studies with lipid model membranes could play an important role in drug discovery and drug delivery.

Amphotericin B interactions with soluble oligomers of amyloid Abeta1-42 peptide

Amphotericin B has recently been suggested as an efficient inhibitor of amyloid peptide fibril formation; however its interactions with more neurotoxic, soluble forms of amyloid peptides have not been reported to date. Circular dichroism spectroscopy allowed for distinguishing between the binding and inhibition of aggregation events: amphotericin B distinctly interacts with both unordered and ordered, beta-structure-rich soluble oligomeric forms of Abeta1-42 peptide, yet amphotericin B has no measurable impact neither on the secondary structure nor on time-dependent aggregation profile of the amyloid peptide.

The influence of fatty acids on model cholesterol/phospholipid membranes

The aim of this work was to verify the influence of the saturated (SFA) (stearic acid) and the unsaturated (UFA) (oleic and alpha-linolenic) fatty acids on model cholesterol/phospholipid membranes. The experiments were based on the Langmuir monolayer technique. Cholesterol and phospholipid were mixed in the molar ratio that corresponds to the proportion of these lipids in the majority of natural human membranes. Into the binary cholesterol/phospholipid monolayers, various amounts of fatty acids were incorporated. Our investigations were based on the analysis of the interactions between molecules in ternary (cholesterol/phospholipids/fatty acid) mixtures, however, also binary (cholesterol/fatty acid and phospholipids/fatty acid) mixed system were examined. It was concluded that the influence of the fatty acids on model cholesterol/phospholipid membrane is closely connected with the shape of the fatty acid molecule, resulting from the saturation degree of the hydrocarbon chain. It was found that the saturated fatty acid makes the model membrane more rigid, while the presence of unsaturated fatty acid increases its fluidity. The increasing amount of stearic acid gradually destabilizes model membrane, however, this effect is the weakest at low content of SFA in the mixed monolayer. Unsaturated fatty acids in a small proportion make the membrane thermodynamically more stable, while higher content of UFA decreases membrane stability. This explains low proportion of the free fatty acids to other lipids in natural membrane.

Thermodynamic and Infrared Analyses of the Interaction of Chlorpromazine with Phospholipid Monolayers

An investigation has been made of the interaction between chlorpromazine (CPZ) and monolayers of 1,2-dipalmitoyl-sn-3-glycerophosphatidylcholine (DPPC) and 1,2-dipalmitoyl-sn-3-glycero[phospho-rac-(1-glycerol)] (DPPG), both at the air/water interface and in transferred Langmuir-Blodgett films. The Gibbs free energy, DeltaG, and the compressibility modulus (C(S)(-1)), obtained from the surface pressure isotherms, indicated changes in the in-plane interactions of CPZ/DPPG mixed monolayers, with positive values of DeltaG. The arrangement of CPZ in the zwitterionic DPPC monolayers causes a weaker interaction in CPZ/DPPC mixed monolayers, with the DeltaG fluctuating around zero. IR measurements in transferred monolayers showed that CPZ did not affect the conformational order of the acyl chains, its effects being limited to the bands corresponding to the headgroups. Furthermore, since no shift was observed for the acyl chain bands, the phase transition induced by CPZ is not a liquid expanded (LE) to liquid condensed (LC) transition, as the latter is associated with chain ordering. Taken together, the IR and compressibility results demonstrate that the effect from CPZ cannot be correlated with temperature changes in the subphase for pure monolayers, in contrast to models proposed by other authors.