Interaction of a β-lactam calixarene derivative with a model eukaryotic membrane affects the activity of PLA2

Nanoarchitectonics and Simulation on the Molecular-Level Interactions between p-Sulfonic Acid Calix[4]arene and Langmuir Monolayers Representing Healthy and Cancerous Cell Membranes

The design of chemotherapeutic drug carriers requires precise information on their interaction with the plasma membrane since the carriers should be internalized by cells without disrupting or compromising the overall integrity of the membrane. In this study, we employ Langmuir monolayers mimicking the outer leaflet of plasma membranes of healthy and cancerous cells to determine the molecular-level interactions with a water-soluble calixarene derivative, p-sulfonic acid calix[4]arene (SCX4), which is promising as drug carrier. The cancer membrane models comprised either 40% 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 30% cholesterol (Chol), 20% 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), and 10% 1,2-dipalmitoyl-sn-glycero-3-phospho-l-serine (DPPS). The healthy membrane models were composed of 60% DPPC or DOPC, 30% Chol, and 10% DPPE. SCX4 expanded the surface pressure isotherms and decreased compressional moduli in all membrane models, altering their morphologies as seen in Brewster angle microscopy images. A combination of polarization-modulated infrared reflection absorption spectroscopy and molecular dynamics simulations revealed that SCX4 interacts preferentially with lipid headgroups in cancer membrane models through electrostatic interactions with the amine groups of DPPS and DPPE. In healthy membrane models, SCX4 interacts mostly with cholesterol through van der Waals forces. Using a multidimensional projection technique to compare data from the distinct membrane models, we observed that SCX4 effects depend on membrane composition with no preference for cancer or healthy membrane models, which is consistent with its biocompatibility. Furthermore, the interactions and close location of SCX4 to the headgroups indicate that it does not compromise membrane integrity, confirming that SCX4 may be a suitable drug carrier.

The lung surfactant activity probed with molecular dynamics simulations

The surface of pulmonary alveolar subphase is covered with a mixture of lipids and proteins. This lung surfactant plays a crucial role in lung functioning. It shows a complex phase behavior which can be altered by the interaction with third molecules such as drugs or pollutants. For studying multicomponent biological systems, it is of interest to couple experimental approach with computational modelling yielding atomic-scale information. Simple two, three, or four-component model systems showed to be useful for getting more insight in the interaction between lipids, lipids and proteins or lipids and proteins with drugs and impurities. These systems were studied theoretically using molecular dynamic simulations and experimentally by means of the Langmuir technique. A better understanding of the structure and behavior of lung surfactants obtained from this research is relevant for developing new synthetic surfactants for efficient therapies, and may contribute to public health protection.

The antibacterial activity of p-tert-butylcalix[6]arene and its effect on a membrane model: molecular dynamics and Langmuir film studies

The antibacterial activity of a calixarene derivative, p-tert-butylcalix[6]arene (Calix6), was assessed and was shown not to inhibit the growth of E. coli, S. aureus and B. subtilis bacteria. With the aim of gaining more insights into the absence of antibacterial activity of Calix6, the interaction of this derivative with DPPG, a bacterial cell membrane lipid, was studied. Langmuir monolayers were used as the model membrane. Pure DPPG and pure Calix6 monolayers, as well as binary DPPG:Calix6 mixtures were studied using surface pressure measurements, compressional modulus, Brewster angle and fluorescence microscopies, ellipsometry, polarization-modulation infrared reflection absorption spectroscopy and molecular dynamics simulations. Thermodynamic properties of the mixed monolayers were additionally calculated using thermodynamic parameters. The analysis of isotherms showed that Calix6 significantly affects the DPPG monolayers, modifying the isotherm profile and increasing the molecular area, in agreement with the molecular dynamics simulations. The presence of Calix6 in the mixed monolayers decreased the interfacial elasticity, indicating that calixarene disrupts the strong intermolecular interactions of DPPG hindering its organization into a compact arrangement. At low molar ratios of Calix6, the DPPG:Calix6 interactions are preferentially attractive, due to the interactions between the hydrophobic tails of DPPG and the tert-butyl groups of Calix6. Increasing the proportion of calixarene generates repulsive interactions. Calix6 significantly affects the hydrophobic tail organization, which was confirmed by PM-IRRAS measurements. Calix6 appears to be expelled from the mixed films at a biologically relevant surface pressure, π = 30 mN m-1, indicating a low interaction with the cell membrane model related to the absence of antibacterial activity.

The role of DPPG in lung surfactant exposed to benzo[a]pyrene

Lung surfactant (LS) occurs at the air-water interface in the alveoli. Its main function is to reduce the work needed to expand the alveoli during inhalation and prevent the alveolar collapse during exhalation. Disturbance of this complex interfacial system by the uptake of pollutant molecules can lead to changes in fluidity, permeability, phase separation and domain formation, which in turn can lead to serious impairment in lung function. Knowledge of the LS-pollutant interaction is essential for understanding the mechanism of this process. In this study, we investigate the interaction of LS models with benzo[a]pyrene (BaP). Dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG) sodium salt, and their 4 : 1 mixture are used as LS models. Surface pressure-area isotherms and molecular dynamics simulations are employed to study the properties of LS monolayers. It was found that the addition of BaP has a destabilizing effect on the mixed DPPC/DPPG monolayer, manifested by the decrease in surface pressure. Compression of a monolayer during a respiratory cycle may expel BaP to the bulk solution. It was demonstrated that DPPG is an active component that prevents the BaP molecule from entering the water subphase; as a minor component of LS it can effectively reduce this process. In addition, the presence of BaP in LS models induces the reduction of monolayer hydration in the hydrophilic region and the increase in chain ordering in the hydrophobic region. The observed changes in monolayer fluidity and phase behavior can be a source of various lung function disorders.

Two antibacterial nalidixate calixarene derivatives in cholesterol monolayers: Molecular dynamics and physicochemical effects

The interaction of two antibacterial calixarene derivatives with cholesterol, a eukaryotic cell membrane lipid, was investigated with the aim to get more insight in the potential advers effects on our cells. The derivatives used had one or two nalidixic acid arms grafted on the lower rim of the calixarene aromatic crown. Monomolecular films spread at the air-water interface were used as model lipid membranes. Pure cholesterol and pure calixarene derivatives, as well as binary cholesterol - calixarene derivative mixtures were studied using surface pressure measurements, polarization-modulation infrared reflection absorption spectroscopy and molecular dynamics simulations. The properties of the mixed monolayers were described quantitatively using thermodynamic models. The analysis of surface pressure-area isotherms of mixed monolayers shows that cholesterol may form homogenous but metastable domains with both nalidixate derivatives. This phenomenon is more clearly observed with mono-substituted calixarene. A detailed modeling analysis indicates that cholesterol favors dehydration of the calixarene polar headgroups and transfer of the derivatives from the aqueous to the gas phase. This effect, more pronounced in the case of the monosubstituted calixarene, can be linked to the hydrophobic interaction with cholesterol. This observation may be useful for developing new calixarene derivatives allowing us to control disease-causing bacteria without harming our own cells.

The selective interactions of cationic tetra-p-guanidinoethylcalix[4]arene with lipid membranes: theoretical and experimental model studies

Behavior of cationic tetra-p-guanidinoethylcalix[4]arene (CX1) and its building block, p-guanidinoethylphenol (mCX1) in model monolayer lipid membranes was investigated using all atom molecular dynamics simulations and surface pressure measurements. Members of two classes of lipids were taken into account: zwitterionic 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and anionic 1,2-dimyristoyl-sn-glycero-3-phospho-l-serine sodium salt (DMPS) as models of eukaryotic and bacterial cell membranes, respectively. It was demonstrated that CX1 and mCX1 accumulate near the negatively charged DMPS monolayers. The adsorption to neutral monolayers was negligible. In contrast to mCX1, CX1 penetrated into the hydrophobic part of the monolayer. The latter effect, which is possible due to a flip-flop inversion of the CX1 orientation in the lipid layer compared to the aqueous phase, may be responsible for its antibacterial activity.

Impact of two different saponins on the organization of model lipid membranes

Saponins, naturally occurring plant compounds are known for their biological and pharmacological activity. This activity is strongly related to the amphiphilic character of saponins that allows them to aggregate in aqueous solution and interact with membrane components. In this work, Langmuir monolayer techniques combined with polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) and Brewster angle microscopy were used to study the interaction of selected saponins with lipid model membranes. Two structurally different saponins were used: digitonin and a commercial Merck Saponin. Membranes of different composition, namely, cholesterol, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine or 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol) were formed at the air/water and air/saponin solution interfaces. The saponin-lipid interaction was characterized by changes in surface pressure, surface potential, surface morphology and PM-IRRAS signal. Both saponins interact with model membranes and change the physical state of membranes by perturbing the lipid acyl chain orientation. The changes in membrane fluidity were more significant upon the interaction with Merck Saponin. A higher affinity of saponins for cholesterol than phosphatidylglycerols was observed. Moreover, our results indicate that digitonin interacts strongly with cholesterol and solubilize the cholesterol monolayer at higher surface pressures. It was shown, that digitonin easily penetrate to the cholesterol monolayer and forms a hydrogen bond with the hydroxyl groups. These findings might be useful in further understanding of the saponin action at the membrane interface and of the mechanism of membrane lysis.

A Study of the Interaction between a Family of Gemini Amphiphilic Pseudopeptides and Model Monomolecular Film Membranes Formed with a Cardiolipin

The interaction between five gemini amphiphilic pseudopeptides (GAPs) differing by the length of the central spacer and a model membrane lipid, 1,3-bis[1,2-dimyristoyl-sn-glycero-3-phospho]-sn-glycerol (cardiolipin) were studied with the aim to evaluate their possible antimicrobial properties. To this end, monomolecular films were formed at the air/water interface with pure cardiolipin or cardiolipin/GAPs mixtures; film properties were determined using surface pressure and surface potential measurements, as well as polarization-modulation infrared reflection-absorption spectroscopy. Moreover, to better understand the GAPs-phospholipid interaction at the molecular level, molecular dynamics simulations were performed. The results obtained indicate that the length of the central spacer has an effect on the interaction of GAPs with cardiolipin and on the properties of the lipid film. The GAPs with the longer linkers can be expected to be useful for biological membrane modification and for possible antimicrobial applications.

Supramolecular p-sulfonated calix[4,6,8]arene for tryptophan detection

Numerous techniques have focused on the ability of p-sulfonated calix[n]arene to form complexes with tryptophan. Scanning electron microscopy and Fourier transform infrared spectroscopy were utilized to study the organization and molecular structure of different layers of the electrode surface. Scanning electron microscopy results showed that SC4A displayed a cubic structure whereas SC6A and SC8A displayed dendrite structures. The electrochemical properties and potential complex formation between SCnA and tryptophan were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Cyclic voltammetry experiments showed that the gold electrode was successfully functionalized by self-assembled cysteamine and SC4A. Electrochemical impedance spectroscopy results showed the observation of the tryptophan–SCnA interaction and indicated that SC4A had the highest sensitivity to tryptophan and allowed 2.04 μg L−1 tryptophan to be detected. Electrochemical impedance spectroscopy analysis and molecular modeling calculation confirmed that SC4A has higher tryptophan sensitivity than SC6A and SC8A.

Interaction between ganglioside G(M1) and diosgenin in langmuir monolayers at the air/water interface

The interaction between ganglioside GM1 (GM1) and diosgenin (Dios) in mixed monolayers was investigated using surface pressure measurements and atomic force microscopy (AFM). The miscibility and stability of the mixed monolayer was evaluated both in a qualitative and quantitative way in terms of the excess mean molecular area (ΔAex), excess Gibbs energy (ΔGex). The ΔAex of mixed GM1/Dios monolayer was found to have positive deviations from ideality at low Dios mole fractions (XDios = 0.2). Above XDios = 0.2, there was a marked negative deviation from ideal mixing, indicating attractive interaction between G(M1) and Dios. According to the values of excess Gibbs energy of mixing monolayers, the more stable monolayers assayed was: XDios = 0.6. The compressibility coefficient was assessed at various surface pressures. The monolayer of Dios was more elasticity or rigid than G(M1). The AFM images for the mixed monolayers at 30 mN/m indicated there was obvious phase separation in the mixed monolayers. These findings will provide useful information for understanding the interaction between drug and lipids.

Interaction of para-tert-butylcalix[6]arene molecules in Langmuir films with cadmium ions and their effects on molecular conformation and surface potential

The SFG data show the orientation of Calix6 molecules at the air/water interface, and their interaction with Cd ions.