Brewster Angle Microscopy Images Research Articles

Interaction of nitrofurantoin with lipid langmuir monolayers as cellular membrane models distinguished with tensiometry and infrared spectroscopy

Knowing how a drug interacts with cell membranes is important to understand and predict its effects at the molecular level. Therefore, we aimed to study the interaction of nitrofurantoin (NFT), a compound with potential antibiotic and antitumor properties, with lipidic biological interfaces using Langmuir monolayers. We employed the phospholipids 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phospho-l-serine (DPPS), which were spread on the surface of water to form Langmuir films, to investigate the membrane-drug interactions. The interaction of the drug with the lipid monolayers was evaluated by using surface pressure-area isotherms, surface pressure-time kinetic curves, Brewster angle microscopy (BAM), and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS). Nitrofurantoin shifted the isotherms to lower DPPC molecular areas, indicating monolayer condensation, and to higher DPPS molecular areas, indicating monolayer expansion. Meanwhile, BAM images showed the appearance of interfacial aggregates for DPPS, but not for DPPC, in the presence of NFT. PM-IRRAS spectra showed that bands related to methylene stretches changed their relative intensities and maximum position related to their asymmetric and symmetric modes for both lipids. This suggested an alteration of the monolayer packing degree and the conformational order of the lipid alkyl chains, which were related to an increase in configurational order for DPPS, but disorder for DPPC. In conclusion, NFT caused distinctive changes in the thermodynamic, morphological, and structural properties of DPPC and DPPS monolayers, which may be associated with its bioactivity in cellular membranes and other lipidic interfaces of pharmaceutical interest.

Heterostructured Langmuir-Blodgett Films of Ruthenium Bipyridine with 1,3,4-Naphthooxadiazole-Derived Amphiphile Complex as a Charge Storage Electrode

The molecular control in Langmuir-Blodgett (LB) films may be exploited in charge storage electrodes provided a suitable choice of molecular architecture and components is made. In this paper, we employed a naphtyl-1,3,4-oxadiazole amphiphile (NFT1) and its complex [Ru(bpy)2NFT1]PF6 (RuNFT1) (bpy = 2,2’-bipyridine) in heterostructured LB films in a proof-of-principle production of charge storage. The optimized architecture contained a one-layer RuNFT1 deposited on a 9-layer NFT1 LB film, where the efficient packing of NFT1 inferred from spectroscopic measurements and Brewster angle microscopy (BAM) images was considered as relevant for ion diffusion. This packing was achieved owing to the π-stacking warranted by the planarity of the NFT1 naphtyl 1,3,4-oxadiazole ring, as confirmed with density functional theory (DFT) calculations. The top layer of the redox-active RuNFT1 provided an additional contribution with its Faradaic charge storage to the double layer capacitance of NFT1. Taken together, these results demonstrate that synergy may be achieved in combining distinct compounds in LB films toward efficient charge storage.

A detailed investigation on interactions between magnetite nanoparticles functionalized with aminated chitosan and a cell model membrane.

Magnetite nanoparticles are promising materials for application in magnetic resonance imaging, targeted drug delivery, enzyme immobilization and cancer therapies based on hyperthermia thanks to their biocompatibility, wide chemical affinity and superparamagnetic properties. However, there is still the lack of the knowledge of interactions between magnetite nanoparticles covered with the bioactive polymers and biological cells. In order to fulfil this gap, we have investigated interactions of newly synthetized magnetite nanoparticles functionalized with aminated chitosan (Fe3O4-aminated chitosan) and a model biological membrane made of dipalmitoylphosphatidylcholine (DPPC) using a Langmuir technique. Surface pressure-mean area per DPPC molecule isotherms and Brewster angle microscope images (BAM) recorded during compression of the two-component Fe3O4-aminated chitosan:DPPC films revealed the strong influence of the Fe3O4-aminated chitosan nanoparticles on the stability, phase state and structure of the phospholipid membrane. The studies on the adsorption/incorporation process of the Fe3O4-aminated chitosan nanoparticles showed that they can adsorb/incorporate into the DPPC model membrane at the surface pressure corresponding to this present in the cellular membrane under the biological conditions (35mN·m-1). The number of the adsorbed/incorporated Fe3O4-aminated chitosan nanoparticles can be regulated by the nanoparticles concentration in the neighbourhood of the DPPC model membrane even at high surface pressure of 35mN·m-1.

Rapid biophysical analyses of gastric aspirates from risk newborns for lung maturity assessment after corticosteroid therapy

BackgroundOne of the main causes for the higher mortality among risk newborn children (including preterm infants) is neonatal respiratory distress syndrome (NRDS), which develops as a result of primary deficiency or secondary inactivation of alveolar surfactant (AS). Therefore, fast and early diagnostics of risk newborns lung maturity is crucial for their prompt therapy. Materials and methodsGastric aspirates (GA) were collected from 77 infants divided into three groups: a control of 38 healthy full-term infants; 16 prematurely newborns with NRDS, and 23 prematurely born infants after in vitro fertilization and corticosteroid therapy (CST). Surface parameters: equilibrium (γeq), maximal (γmax) and minimal (γmin) surface tension, and the shape of hysteresis curves of GA monolayers were measured by axisymmetric drop shape analysis (ADSA) of a pending drop. In addition, the morphology of GA monolayers was studied by Brewster angle microscopy (BAM). ResultsOur results showed that only γmin values were reliable and were significantly lower in full-term infants, as compared to the risk neonates. The results obtained were proved by the shape of hysteresis curves of GA surface active films. BAM images of GA monolayers from NRDS group showed impaired surface morphology due to the surfactant insufficiency, as compared to the control group. Corticosteroid therapy improved both GA surface characteristics and monolayer morphology. ConclusionsGAs analyses by ADSA and BAM are fast and informative approaches for lung maturity assessment. In addition, the corticosteroid therapy applied improved all GAs surface parameters due to AS maturation.

Synergy in the interaction of amoxicillin and methylene blue with dipalmitoyl phosphatidyl choline (DPPC) monolayers

Understanding molecular-level mechanisms in the action of emergent pollutants is essential to correlate with their possible impact on living organisms in the environment and on human health. In this study, we investigate the interactions between two widely used compounds classified as emerging pollutants and Langmuir monolayers of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) that represent a simplified model of the lipidic structure of cell membranes. The pollutants studied were the antibiotic amoxicillin (AMX) and methylene blue (MB), a pharmaceutical drug also used as a dye in industry. AMX and MB were found to expand the surface pressure isotherms of DPPC, also affecting its morphology according to Brewster angle microscopy images. Significantly, when these compounds were mixed (MIX), monolayer expansion increased. The synergy in MIX activity was confirmed with in-situ polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) measurements, which indicated that electrostatic interaction with DPPC head groups was considerably stronger than for either AMX or MB. An adduct formed between AMX and MB in MIX also caused the DPPC monolayer thickness to increase, as inferred from measurements with grazing-incidence X-ray scattering out of the specular plane (GIXOS), in contrast to the decreased thickness induced by AMX or MB. That a mixture potentiates the interaction between contaminants and cell membrane models may be relevant for cocktail effects on living organisms.

Effects of Phenylalanine on the Liquid-Expanded and Liquid-Condensed States of Phosphatidylcholine Monolayers.

Background:Phenylalanine (Phe) is involved in physiological and pathological processes in cell membranes in which expanded and condensed states coexist. In this direction, it was reported that surface hydration is important for the binding affinity of the amino acid which significantly perturbs 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayer structure and morphology. A deeper insight showed that Phe inserts in DPPC monolayer defects as a monomer at pH 5 and forms aggregates that adsorb to the membrane surface generating a reconfiguration of the lipid arrangement in areas of higher packing. This new arrangement in the monolayer causes the reorientation of dipoles of lipid and water molecules which is congruent with the dehydration and surface tension changes reported above. With this background, this article studies the affinity of Phe in liquid-expanded 1,2-dimyristoyl-sn-glycero-3 phosphocholine (LE DMPC) and liquid-condensed 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (LC DPPC) monolayers and their effects on membrane properties.Results:The adsorption of Phe can be described by a cooperative process in non-independent sites suggesting that Phe/lipid systems reorganize to form new structures at a high degree of coverage. Compressibility modulus and Brewster angle microscopy (BAM) images allow to propose that Phe causes a new phase in 1,2-dimyristoyl-sn-glycero-3 phosphocholine (DMPC) and DPPC.Conclusions:Phe imposes new arrangements in the lipid phase to form new structures with different compressibility behavior than lipid binary mixtures of DMPC and DPPC. Phe interaction with the LC and LE phases gives place to a process in which a synergistic effect between non-independent sites can be produced. These features of Phe/lipid interaction would be of great importance to understand the multiple effects of Phe on cell membranes.

Structural Change in Dimyristoyl Phosphatidyl Choline (DMPC) Molecule Alkyl Chains on the Addition of Cholesterol to DMPC Monolayer: Specific Addition Effect of Cholesterol

We have investigated the morphology of dimyristoyl phosphatidyl choline (DMPC)—cholesterol mixed monolayer formed on the water surface by dropping method using surface tension measurement (STm), Brewster angle microscopy (BAM), and infrared external reflection spectroscopy (IERS). STm results showed negative deviation of the limiting molecular area (A0) of cholesterol occurred when cholesterol was added to the DMPC monolayer. BAM images showed the expandable DMPC monolayer changed to the condensed rigid monolayer at more than cholesterol mole fraction (xChol) 0.4. IERS recordings showed that the addition of cholesterol at xChol = 0.4 occurred structural change from gauche- to trans- conformation of two DMPC molecule alkyl chains. From these results, it is found that cholesterol molecule has specific properties that cause structural transition of DMPC molecule alkyl chains.

Interaction of Artepillin C with model membranes: Effects of pH and ionic strength

Artepillin C is the major constituent of green propolis, one of the most consumed products in popular medicine owing to its therapeutic effects, including antitumor activity. Artepillin C differs from other cinnamic acid derivatives due to the presence of two prenylated groups in its structure, believed to enhance access to the cell membrane and resulting in pharmacological activity. The membrane outer leaflet of tumor cells is exposed to an acidic extracellular environment, which could modulate the protonation state of antitumor drugs and hence their interaction with the cell membrane. Herein, we investigated the interaction of Artepillin C with Langmuir monolayers and giant unilamellar vesicles (GUVs) of 1,2‑dipalmitoyl‑sn‑glycerol‑3‑phosphocholine (DPPC) used as model membranes, in physiological and acidic environments. We observed that protonation of the carboxyl group of Artepillin C is essential for the interaction, with larger shifts induced in the surface pressure isotherms of DPPC monolayers in comparison with deprotonated Artepillin C. Also observed was a decrease in lipid packing inferred from the compressibility modulus and Brewster angle microscopy (BAM) images for monolayers on acidic subphases. Results with microscopy techniques on GUVs confirmed that.Artepillin C causes a curvature stress of the lipid bilayer only in its neutral state, causing the GUVs to burst. The stronger effects of neutral Artepillin C on both monolayers and GUVs were maintained when the ionic strength was increased. Taken together, the results indicate that Artepillin C may have preferential attachment to a more acidic environment which might be an important feature for its antitumor activity.

The influence of the essential oil extracted from hops on monolayers and bilayers imitating plant pathogen bacteria membranes.

Many plant-derived compounds possess antimicrobial, antioxidant and even anticancer activities. Therefore, they are considered as substances that can be used instead of synthetic compounds in various applications. In this work, the essential oil from hop cones was extracted and analyzed, and then its effects on model bacteria membranes were studied to verify whether the hop essential oils could be used as ecological pesticides. The experiments involved surface pressure-area measurements, penetration studies and Brewster angle microscopy (BAM) imaging of lipid monolayers as well as hydrodynamic diameter, zeta potential, steady-state fluorescence anisotropy and Cryo-Transmission Electron Microscopy (cryo-TEM) measurements of liposomes. Finally the bactericidal tests on plant pathogen bacteria Pseudomonas syringae pv. lachrymans PCM 1410 were performed. The obtained results showed that the components of the essential oils from hop cones incorporate into lipid monolayers and bilayers and alter their fluidity. However, the observed effect is determined by the system composition, its condensation and the oil concentration. Interestingly, at a given dose, the effect of the essential oil on membranes was found to stabilize. Moreover, BAM images proved that hop oil prevents the formation of a large fraction of a condensed phase at the interface. Both the studies on model membranes as well as the in vitro tests allow one to conclude that the hop essential oil could likely be considered as the candidate to be used in agriculture as a natural pesticide.

Effects of saturated and polyunsaturated fatty acids on interactions with cholesterol versus 7-ketocholesterol in Langmuir monolayers and their potential biological implications.

In this work the Langmuir monolayer technique was used to study interactions between cholesterol (chol) and 7-ketocholesterol (7-KC) with saturated (arachidic acid, AA) and polyunsaturated fatty acids (PUFAs) (ω-3 α-linolenic acid, α-LA,and ω-6 γ- linolenic, γ-LA) in order to get insight into their potential role in atherosclerosis. For this study, surface pressure (π)-area (A) isotherms, compressibility modulus (Cs-1) versus π plots, Brewster angle microscopy (BAM) images and excess functions (Aexc and ΔGexc) were analysed. Different behaviour has been observed. For cholesterol/AA mixed monolayers, components immiscibility occurs, whatever the surface pressure or the mixtures composition is, whereas for the 7-KC/AA mixed system, ideal behaviour was observed at low and high surface pressures for all the investigated compositions. However, the remaining mixed studied systems (sterol/PUFA) exhibit negative deviations from the ideality, although some differences do occurr. The magnitude of these deviations depend on the kind of a PUFA (for ω-3 PUFA greater than for ω-6) - attributed to the different geometry of their acyl chains- and the type of a sterol (for 7-KC greater than for cholesterol).The strength of attractive interactions followed the order: chol/ γ-LA <7-KC/γ-LA < chol/α-LA < 7-KC/ α-LA, postulating the formation of stable complexes of 1:2 stoichiometry for 7-KC/α-LA mixed monolayers and 1:1 stoichiometry for chol/α-LA mixed films. For 7-KC/γ-LA system, the formation of a low stability complex of 2:1 stoichiometry was suggested. The existence of these complexes can play an important role in diminishing the circulating sterols in the blood stream, thus decreasing the probability of atherosclerotic plaques formation.

Lipids mediating the interaction of metronidazole with cell membrane models at the air-water interface.

In this paper, metronidazole, a known compound with microbicide effect, was incorporated in Langmuir monolayers of selected phospholipids in order to investigate the interactions of this compound with cell membrane models by using tensiometric, spectroscopic and morphological techniques. Surface pressure-area isotherms showed that selected amounts of metronidazole condense DPPC monolayers, but expand DPPE monolayers. Vibrational spectroscopy pointed that metronidazole adsorbs on the polar heads of the phospholipids, affecting the gauche conformations of the aliphatic chains, and different patterns were observed for DPPC and DPPE monolayers containing metronidazole in terms of Brewster angle microscopy images. As a result, distinctive interactions with DPPC and DPPE could be pointed regarding the incorporation of metronidazole with each lipid, leading to particular molecular arrangements at the air-water interface.

Phase behavior of DSPC/PEG40St mixtures at higher emulsifier contents.

Phase behaviors of 1,2-Distearoyl-sn-glycero-3-phosphocholine (DSPC) and polyoxyethylene(40)stearate (PEG40St) were investigated with Langmuir monolayer isotherms and Brewster angle microscopy (BAM) imaging at DSPC/PEG40St molar ratios ranging from 9:1 to 5:5. Two plateaus were found in the Langmuir isotherms which were relatively shorter for the 9:1 mixture and extended significantly by increasing the PEG40St content, indicating that the PEG40St squeezed out whereas more emulsifier retained in the monolayer at higher PEG40St contents. A strong hysteresis was observed when the mixed monolayers were subjected to compression-expansion cycles. The degree of hysteresis for the first cycles also increased with increasing PEG40St content in the monolayer. Gray scale intensities in the Brewster angle microscopy images were determined for pure DSPC and pure PEG40St and a scale was established to better interpret the morphologies for the mixtures. Bud and vessels formed during the PEG40St squeezed out upon compression. Upon expansion, PEG40St and DSPC is reappeared on the monolayer. When considered BAM images together with the Langmuir isotherm, PEG40St molecules were found to be well distributed within the DSPC molecules at lower DSPC/PEG40St mole ratios and mostly phase separated at higher mole ratios. It was concluded that higher PEG40St content would be advantageous for the design of an efficient and cheaper ultrasound contrast agents.

Daunorubicin and doxorubicin molecular interplay with 2D membrane models

The anthracyclines daunorubicin and doxorubicin are widely used antineoplastic agents due to their therapeutic activity against a broad variety of human cancers. Although, the classical model to explain anthracyclines’ cytotoxicity has been based in the direct interference with nucleic acid function, evidence suggests that the plasma membrane is also involved in the drug’s mechanism of action.In this work, the interaction of these drugs with two-dimensional membrane models were studied in order to gain further insights at the molecular level regarding anthracyclines membrane interactions. For that purpose, Langmuir monolayers composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), sphingomyelin (SM) and cholesterol (Chol) were used, since these are the most common lipids found in biological membranes. Several biophysical techniques were employed: surface pressure (π) – area (A) isotherms measurements were used to investigate the adsorption and penetration of drugs, polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) to acquire structural information and Brewster angle microscopy (BAM) to record images of the monolayers on the micrometer scale.The interactions of anthracyclines were assessed by alterations in the monolayers’ shape, characteristic parameters (Cs−1 values and area per lipid molecule at 30mN·m−1 and under maximum packing conditions) and morphology of each 2D model studied. The presence of the drugs in the interface led to the production of less ordered monolayers, as evidenced by the decrease in the compressibility modulus. In addition, the drugs’ effect on the membrane organization is related with their chemical structure and depends on the membraneś phase. For lower surface pressures, both electrostatic and hydrophobic interactions led to significant modifications in the monolayer order. With further compression, the impact of such interactions is reduced, resulting in the squeezing-out of some drug molecules from the interface. Furthermore, BAM images showed a clear anticancer drug interplay with the lipid monolayer by changes in the domains shape and appearance of bright dots, which are located in the frontier between the condensed and expanded lipid phases.

Interaction of levofloxacin with lung surfactant at the air-water interface

The molecular-level interaction of levofloxacin with lung surfactant was investigated using Langmuir monolayers and atomistic molecular dynamics (MD) simulations. In the simulation, the DPPC/POPC mixed monolayer was used as a lung surfactant model and the molecules of levofloxacin were placed at the air-lipid interface to mimic the adsorption process on the lung surfactant model. The simulation results indicate that amphoteric levofloxacin expands the lung surfactant, also stabilizing the film for levofloxacin fractions until 10% w/w at least. The Langmuir monolayers made with the lung surfactant Curosurf had expanded isotherms upon incorporation of levofloxacin, without changes in monolayer elasticity. In fact, levofloxacin induced film stability with increased collapse pressures in the Curosurf isotherms and delayed the phase transition, according to Brewster angle microscopy (BAM) imaging. Using polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS), we found that levofloxacin is preferentially located in the head group region, inducing an increased organization of the Curosurf film. This location of levofloxacin was confirmed with MD simulations. The stability inferred demonstrates that the lung surfactant can be used as a drug delivery system for the administration via inhalation or intratracheal instillation of levofloxacin to treat lung diseases such as pneumonia and respiratory distress syndrome.

The film tells the story: Physical-chemical characteristics of IgG at the liquid-air interface.

The presence of liquid-air interfaces in protein pharmaceuticals is known to negatively impact product stability. Nevertheless, the mechanisms behind interface-related protein aggregation are not yet fully understood. Little is known about the physical-chemical behavior of proteins adsorbed to the interface. Therefore, the combinatorial use of appropriate surface-sensitive analytical methods such as Langmuir trough experiments, Infrared Reflection-Absorption Spectroscopy (IRRAS), Brewster Angle Microscopy (BAM), and Atomic Force Microscopy (AFM) is highly expedient to uncover structures and events at the liquid-air interface directly. Concentration-dependent adsorption of a human immunoglobulin G (IgG) and characteristic surface-pressure/area isotherms substantiated the amphiphilic nature of the protein molecules as well as the formation of a compressible protein film at the liquid-air interface. Upon compression, the IgG molecules do not readily desorb but form a highly compressible interfacial film. IRRA spectra proved not only the presence of the protein at the interface, but also showed that the secondary structure does not change considerably during adsorption or compression. IRRAS experiments at different angles of incidence indicated that the film thickness and/or packing density increases upon compression. Furthermore, BAM images exposed the presence of a coherent but heterogeneous distribution of the protein at the interface. Topographical differences within the protein film after adsorption, compression and decompression were revealed using underwater AFM. The combinatorial use of physical-chemical, spectroscopic and microscopic methods provided useful insights into the liquid-air interfacial protein behavior and revealed the formation of a continuous but inhomogeneous film of native-like protein molecules whose topographical appearance is affected by compressive forces.

The influence of the polarity of fractionated asphaltenes on their Langmuir-film properties

The amphiphilic and aggregation properties of fractionated asphaltenes have been studied using Langmuir trough experiments and Brewster angle microscopy (BAM). In particular, two fractions from three different crude oils have been extracted by using two n-pentane:crude oil volume ratios (3:1 and 18:1) in a two-step precipitation procedure. The concentration dependence of the surface properties and the variations in their ability to form true monolayers at the air–water and liquid–liquid interfaces are investigated. The shape of the resulting isotherms are decidedly different. The greater amphiphilic character of the second fraction provides more expanded isotherms and well-behaved hysteresis cycles with more homogeneous domains in comparison with the first one. These results inferred from interface experiments corroborated previous experiments carried out with the pendant drop method. Finally, high contrast BAM images revealed a different aggregation state of the two fractions. The first fraction presents lower surface activity as derived from the air–liquid and liquid–liquid interface experiments and forms aggregates separated by empty spaces at low surfaces pressures according to BAM images. The second fraction show a more homogeneous film structure even at higher surface pressures.

Characterization of planar biomimetic lipid films composed of phosphatidylethanolamines and phosphatidylglycerols from Escherichia coli

We have characterized planar lipid films composed of phosphatidylethanolamines (PE) and phosphatidylglycerols (PG) from E. coli bacteria. The nature of the interactions and miscibility of PE and PG components within mixed lipid films was evaluated based on surface pressure measurements and Brewster angle microscopy imaging at the air-water interface. We have found that PE and PG components show tendency to form separated domains at surface pressures relevant for biological membranes. Further, we have directly compared mechanisms of formation of supported lipid bilayers either on mica or Au(111) by spreading of small unilamellar vesicles. The bilayer formation was monitored by in situ atomic force microscopy imaging. The pathways of the vesicles spreading on each substrate are substantially different and the buildup of the bilayer on Au(111) occurs through complex multistep mechanism. The morphology and nanomechanical properties of the resulting PE/PG bilayers were thoroughly compared. We have found that the interactions between lipids and supporting substrate significantly affect molecular organization within the films since the bilayer on Au(111) is uniform in terms of the topography, while the same lipid composition on mica results in formation of distinct gel and liquid disordered domains. Different molecular organization affects also nanomechanical properties of lipid films. The latter were expressed in terms of Young's moduli and bending stiffness.

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.

Implications of lipid monolayer charge characteristics on their selective interactions with a short antimicrobial peptide

Many antimicrobial peptides (AMPs) target bacterial membranes and they kill bacteria by causing structural disruptions. One of the fundamental issues however lies in the selective responses of AMPs to different cell membranes as a lack of selectivity can elicit toxic side effects to mammalian host cells. A key difference between the outer surfaces of bacterial and mammalian cells is the charge characteristics. We report a careful study of the binding of one of the representative AMPs, with the general sequence G(IIKK)4I-NH2 (G4), to the spread lipid monolayers of DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and DPPG (1,2-dipalmitoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (sodium salt)) mimicking the charge difference between them, using the combined measurements from Langmuir trough, Brewster angle microscopy (BAM) and neutron reflection (NR). The difference in pressure rise upon peptide addition into the subphase clearly demonstrated the different interactions arising from different lipid charge features. Morphological changes from the BAM imaging confirmed the association of the peptide into the lipid monolayers, but there was little difference between them. However, NR studies revealed that the peptide bound 4 times more onto the DPPG monolayer than onto the DPPC monolayer. Importantly, whilst the peptide could only be associated with the head groups of DPPC it was well penetrated into the entire DPPG monolayer, showing that the electrostatic interaction strengthened the hydrophobic interaction and that the combined molecular interactive processes increased the power of G4 in disrupting the charged membranes. The results are discussed in the context of general antibacterial actions as observed from other AMPs and membrane lytic actions.

Effect of the Amphotericin B and Its Copper Complex on a Model of the Outer Leaflet of Human Erythrocyte Membrane.

A comparative study on the effect of an antibiotic amphotericin B (AmB) and its copper complex on the multicomponent monolayers imitating the outer leaflet of human erythrocyte membrane has been performed by means of the Langmuir monolayer technique. The properties of mixed films were analyzed by thermodynamic description of the interactions between the molecules complemented with the morphology of monolayers established by Brewster angle microscopy (BAM). The results revealed differences in the molecular organization of the two antibiotic forms at the air/water interface, which were explained by the different spatial structure of the complex. The lipophilicity of the complex contributed to considerably more effective interactions with the components of the model membrane, compared to pure antibiotic, expressed by negative values of the excess of free energy of mixing ΔGexc in the whole range of mole fractions. The mixed films with AmB were more stable as the proportion of lipids in the mixture increased. BAM images demonstrated that the addition of antibiotic at high content into the lipid mixture led to the formation of crystallite structures within the film, probably caused by the expelling of AmB molecules from mixed monolayers. These findings could help to explain the mechanism of the hemolytic activity of polyene antibiotics.