Model Lipid Research Articles

Cellular excitability and ns-pulsed electric fields: Potential involvement of lipid oxidation in the action potential activation

Recent studies showed that nanosecond pulsed electric fields (nsPEFs) can activate voltage-gated ion channels (VGICs) and trigger action potentials (APs) in excitable cells. Under physiological conditions, VGICs’ activation takes place on time scales of the order 10–100 µs. These time scales are considerably longer than the applied pulse duration, thus activation of VGICs by nsPEFs remains puzzling and there is no clear consensus on the mechanisms involved. Here we propose that changes in local electrical properties of the cell membrane due to lipid oxidation might be implicated in AP activation. We first use MD simulations of model lipid bilayers with increasing concentration of primary and secondary lipid oxidation products and demonstrate that oxidation not only increases the bilayer conductance, but also the bilayer capacitance. Equipped with MD-based characterization of electrical properties of oxidized bilayers, we then resort to AP modelling at the cell level with Hodgkin-Huxley-type models. We confirm that a local change in membrane properties, particularly the increase in membrane conductance, due to formation of oxidized membrane lesions can be high enough to trigger an AP, even when no external stimulus is applied. However, excessive accumulation of oxidized lesions (or other conductive defects) can lead to altered cell excitability.

Measuring the Interactions and Influence of Amphipathic Copolymers with Lipid Monolayers and Bilayers as Models of Biological Membranes

AbstractAmphipathic copolymers are useful materials for nanomedicine, owing to their ability to self‐assemble into nanoparticles, act as surfactants for inorganic materials, or for their favorable interactions with lipid membranes. Despite their widespread use, there is still a range of questions about the physicochemical properties that are necessary to drive their interactions at biological interfaces. To fully understand these interactions requires a diverse range of complementary analytical techniques. In this work, a library of neutral amphipathic methacrylate copolymers is synthesized by reversible addition‐fragmentation chain‐transfer polymerization (RAFT) polymerization, to investigate the effect of polymer composition and nature of the hydrophobic comonomer on interactions with model lipid membranes. These materials are shown to interact with Langmuir lipid monolayers, and neutron reflectometry demonstrates that hydrophobic interactions lead to the polymers intercalating with the monolayers. More complex models of lipid bilayers are studied using an in situ quartz crystal microbalance (QCM) model and shows while the composition and hydrophobic comonomer affect the stability of these interactions, there is no effect on the viscoelasticity of the lipid membranes. The in‐depth understanding of these interfacial interactions afforded by this suite of analytical tools will allow for more complex copolymers to be studied, providing a greater understanding of key processes in nanomedicine, such as cellular entry and endosomal escape.

Generation and validation of a classification model to diagnose familial hypercholesterolaemia in adults

Background and aimsThe early diagnosis of familial hypercholesterolaemia is associated with a significant reduction in cardiovascular disease (CVD) risk. While the recent use of statistical and machine learning algorithms has shown promising results in comparison with traditional clinical criteria, when applied to screening of potential FH cases in large cohorts, most studies in this field are developed using a single cohort of patients, which may hamper the application of such algorithms to other populations. In the current study, a logistic regression (LR) based algorithm was developed combining observations from three different national FH cohorts, from Portugal, Brazil and Sweden. Independent samples from these cohorts were then used to test the model, as well as an external dataset from Italy. MethodsThe area under the receiver operating characteristics (AUROC) and precision-recall (AUPRC) curves was used to assess the discriminatory ability among the different samples. Comparisons between the LR model and Dutch Lipid Clinic Network (DLCN) clinical criteria were performed by means of McNemar tests, and by the calculation of several operating characteristics. ResultsAUROC and AUPRC values were generally higher for all testing sets when compared to the training set. Compared with DLCN criteria, a significantly higher number of correctly classified observations were identified for the Brazilian (p < 0.01), Swedish (p < 0.01), and Italian testing sets (p < 0.01). Higher accuracy (Acc), G mean and F1 score values were also observed for all testing sets. ConclusionsCompared to DLCN criteria, the LR model revealed improved ability to correctly classify observations, and was able to retain a similar number of FH cases, with less false positive retention. Generalization of the LR model was very good across all testing samples, suggesting it can be an effective screening tool if applied to different populations.

Genetic dissection of serum vaspin highlights its causal role in lipid metabolism.

Vaspin (visceral adipose tissue derived serine protease inhibitor, SERPINA12) is associated with obesity-related metabolic traits, but its causative role is still elusive. The role of genetics in serum vaspin variability to establish its causal relationship with metabolically relevant traits was investigated. A meta-analysis of genome-wide association studies for serum vaspin from six independent cohorts (N = 7446) was conducted. Potential functional variants of vaspin were included in Mendelian randomization (MR) analyses to assess possible causal pathways between vaspin and homeostasis model assessment and lipid traits. To further validate the MR analyses, data from Genotype-Tissue Expression (GTEx) were analyzed, db/db mice were treated with vaspin, and serum lipids were measured. A total of 468 genetic variants represented by five independent variants (rs7141073, rs1956709, rs4905216, rs61978267, rs73338689) within the vaspin locus were associated with serum vaspin (all p < 5×10-8 , explained variance 16.8%). MR analyses revealed causal relationships between serum vaspin and triglycerides, low-density lipoprotein, and total cholesterol. Gene expression correlation analyses suggested that genes, highly correlated with vaspin expression in adipose tissue, are enriched in lipid metabolic processes. Finally, in vivo vaspin treatment reduced serum triglycerides in obese db/db mice. The data show that serum vaspin is strongly determined by genetic variants within vaspin, which further highlight vaspin's causal role in lipid metabolism.

Mutual impact of alternative mechanisms of a dopant embedding into an ordered medium: a case of gramicidin S in model lipid membranes

Mutual impact of alternative mechanisms of a dopant embedding into an ordered medium: a case of gramicidin S in model lipid membranes

The influence of Leucidal – eco-preservative from radish – on model lipid membranes and selected pathogenic bacteria

In this work the effect of Leucidal - a natural preservative from radish dedicated to be used in cosmetics - on bacteria cells and model bacteria membranes was investigated. To get insight into the mechanism of action of this formulation the lipid Langmuir monolayers imitating Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) membranes were prepared. Then, the influence of Leucidal on model systems was investigated by means of the surface pressure/area measurements, penetration studies and Brewster Angle Microscopy (BAM) visualization. Similar experiments were done also for one component monolayers formed from the model membrane lipids. The in vitro tests were done on five different bacteria species (E. coli, Enterococcus faecalis, S. aureus, Salmonella enterica, Pseudomonas aeruginosa). Leucidal was found to decrease packing of the monolayers, however, it was excluded from the films at higher concentrations. Model membrane experiments evidenced also a stronger affinity of the components of this eco-preservative to E. coli vs S. aureus membrane. Among one component films, those formed from phosphatidylglycerols and cardiolipins were more sensitive to the presence of Leucidal. However, in vitro tests evidenced that Leucidal exerts stronger inhibitory effect against S. aureus bacteria as compared to E. coli strain. These findings were discussed from the point of view of the role of Leucidal components and the lipid membrane properties in the membrane - based mechanism of action of this preservative. The results allow one to suggest that the membrane may not be the main site of action of Leucidal on bacteria. Moreover, since high concentration of the tested preparation exerted antibacterial activity in relation to all tested bacteria, a low selectivity of Leucidal can be postulated, which may be problematic from the point of view of its effect on the skin microbiome.

Dual mechanical impact of β-escin on model lipid membranes

Understanding the mechanical behavior of biological membranes is of paramount importance in cell biophysics and in developing new biomaterials for medicine. In this study, we delve into the mechanical impact of β-escin, commonly referred to as escin, a naturally occurring biosurfactant derived from the seeds of the horse chestnut tree. To examine the modulable interaction between escin and dimyristoylphosphatidylcholine (DMPC), which is an archetypical fluid phospholipid and an essential constituent of the cellular fluid membrane, we have used artificial models based on the liquid crystal structure, such as bilayer vesicles and Langmuir monolayers. We have focused on the energetic and kinetic aspects of escin insertion when transversally adsorbed or longitudinally integrated within these model membranes. By employing surface microscopies of epifluorescence and Brewster angle reflectivity, we have elucidated the structural phase behavior of hybrid escin–phospholipid membranes, which exhibit dual mechanical properties characterized by high rigidity and reduced fluidity. Notably, at low temperatures, we observe a soft, glassy rheological behavior reminiscent of liquid crystalline ordered phases, which turns into a fluid-like viscoelasticity resembling more disordered phases at physiological temperatures. The hybrid membranes behave in one way or another as both are driven by an adsorption potential well imposed by escin cohesivity. These intriguing findings are discussed from a physicochemical perspective, highlighting their potential for future pharmacological designs and biomedical applications that exploit the dual mechanical impact of escin on biological membranes.

Effects of Indonesian Shortfin Eel (Anguilla bicolor) By-Product Oil Supplementation on HOMA-IR and Lipid Profile in Obese Male Wistar Rats.

The prevalence of people being overweight and obese has increased globally over the past decades. The use of omega-3 fatty acids-a compound usually primarily found in fish oil-has been known to improve the metabolic profile of obese patients. As the demand for eels increases, the number of waste products from the eels increases and creates environmental problems. This study was conducted to investigate the effect of a newly discovered Indonesian Shortfin eel by-product oil supplementation on the Homeostasis Model Assessment-Estimated Insulin Resistance (HOMA-IR) and lipid profiles of obese male (Lee index ≥ 0.3) Wistar rats (Rattus norvegicus). The oil was extracted from waste products (heads). Fifteen obese rats were divided into three groups and were administered NaCl (C), commercial fish oil (CO), and Indonesian shortfin eel by-product oil (EO). All groups had statistically significant differences in total cholesterol, LDL, and triglyceride levels (p < 0.05). The CO and EO group showed a significant decrease in total cholesterol, LDL, and triglyceride after treatment. However, no significant difference was found in HDL levels and HOMA-IR. The supplementation of Indonesian shortfin eel by-product oil significantly improved lipid profile while effectively mitigating environmental challenges.

Localization of the ibuprofen molecule in model lipid membranes revealed by spin-label-enhanced NMR relaxation

Non-steroidal anti-inflammatory drugs (NSAIDs) have antipyretic, anti-inflammatory and analgesic effects, and can be used in the treatment of various diseases. These drugs have also a number of side effects, which may be related to their interaction with lipid membranes. In this study, we use the spin-labeled NSAID ibuprofen (ibuprofen-SL) as a relaxation enhancer to study its interaction with model lipid membranes employing liquid-state 1H NMR at 500 MHz. The high magnetic moment of unpaired electron in the spin label made it possible to reduce the concentration of the studied drug in the membrane to tenths of a mole percent. As model membranes, unilamellar POPC liposomes and bicelles consisting of a 2:1 mixture of DHPC:DMPC or DHPC:POPC lipids were used. An increase in the rate of proton spin-lattice relaxation, T1−1, selectively detected for protons at different positions in the lipid molecule, showed that ibuprofen-SL is localized in the hydrophobic part of the lipid bilayer. As the concentration of ibuprofen-SL increases to 0.5 mol%, the distribution of positions of ibuprofen-SL across the bilayer becomes wider. In the presence of 20 mol% of cholesterol, ibuprofen-SL is displaced from the core of the membrane to a region closer to the head group of the bilayer. This displacement was also confirmed by the NMR NOESY experiment conducted with unlabeled ibuprofen. For bilayers containing unsaturated POPC lipids, the distribution of ibuprofen positions across the bilayer becomes narrower compared to the presence of saturated DMPC lipids.

Phase behaviour and structural properties of SOPC model lipid system in a sucrose solution

Lipid membranes are an important component of the biological cell. The profound understanding of their structure and functionality, as well as, the influence of various biologically relevant admixtures on their main characteristics is of great importance for research and development in medicine and pharmacology. The effect of sugars on the behaviour of the membrane cell enjoys an ever-increasing interest as they are biologically significant substances. We have studied the influence of the disaccharide sucrose on the physicochemical properties of SOPC (1-stearoyl-2-oleoyl-sn- glycero-3-phosphocholine) lipid system aiming to gain better understanding of the mechanisms of the interaction between both substances. For that purpose, we have used differential scanning calorimetry and Fourier-transform infrared spectroscopy. Our results show that adding sugar up to 300 mM concentration substantially alters the thermodynamic and structural properties of SOPC. The DSC thermograms at heating reveal a general lowering of the SOPC transition temperature Tm from gel to liquid crystalline phase (main phase transition, ordered-disordered phase transition) in the presence of sugar. The corresponding peaks are smeared and harder to trace. In agreement with this, a gradual decrease of the enthalpy values up to 300 mM was measured. The IR spectroscopy study provided spectral evidence for two states of hydration of the phosphate groups in the sugar-SOPC model systems suggesting a mechanism of interaction where only part of the phospholipid headgroups are hydrogen bonded to the sugar molecules. The obtained results are in good agreement with various earlier data including results about the bending elasticity moduli, as well as, some theoretical simulations on the sugar-lipid interactions. The current results also reinforce the potential of sucrose to be used as a cell protector against drought at, both, high and low temperatures.

Small-angle scattering from flat bilayers containing correlated scattering length density inhomogeneities.

Model lipid bilayers have been widely employed as a minimal system to investigate the structural properties of biological membranes by small-angle X-ray (SAXS) and neutron scattering (SANS) techniques. These have nanometre resolution and can give information regarding membrane thickness and scattering length densities (SLDs) of polar and apolar regions. However, biological membranes are complex systems containing different lipids and protein species, in which lipid domains can be dynamically assembled and disassembled. Therefore, SLD variations can occur within the biomembrane. In this work, a novel method has been developed to simulate SAXS and SANS profiles obtained from large unilamellar vesicles containing SLD inhomogeneities that are spatially correlated over the membrane surface. Such inhomogeneities are represented by cylindrical entities with equivalent SLDs. Stacking of bilayers is also included in the model, with no correlation between horizontal and vertical order. The model is applied to a lipid bilayer containing SLD inhomogeneities representing pores, lipid domains, and transmembrane, partially immersed and anchored proteins. It is demonstrated that all the structural information from the host lipid bilayer and from the SLD inhomogeneity can be consistently retrieved by a combined analysis of experimental SAXS and SANS data through the methodology proposed here.

Statin Action Targets Lipid Rafts of Cell Membranes: GIXD/PM-IRRAS Investigation of Langmuir Monolayers.

Lipid rafts are condensed regions of cell membranes rich in cholesterol and sphingomyelin, which constitute the target for anticholesterolemic drugs - statins. In this work, we use for the first time a combined grazing-incidence X-ray diffraction (GIXD)/polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS)/Brewster angle microscopy (BAM) approach to show the statin effect on model lipid rafts and its components assembled in Langmuir monolayers at the air-water interface. Two representatives of these drugs, fluvastatin (FLU) and cerivastatin (CER), of different hydrophobicity were chosen, while cholesterol (Chol) and sphingomyelin (SM), and their 1:1 mixture were selected to form condensed monolayers of lipid rafts. The effect of statins on the single components of lipid rafts indicated that both the hydrophobicity of the drugs and the organization of the layer determined the drug-lipid interaction. For cholesterol monolayers, only the most hydrophobic CER was effectively changing the film structure, while for the less organized sphingomyelin, the biggest effect was observed for FLU. This drug affected both the polar headgroup region as shown by PM-IRRAS results and the 2D crystalline structure of the SM monolayer as evidenced by GIXD. Measurements performed for Chol/SM 1:1 models proved also that the statin effect depends on the presence of Chol-SM complexes. In this case, the less hydrophobic FLU was not able to penetrate the binary layer at all, while exposure to the hydrophobic CER resulted in the phase separation and formation of ordered assemblies. The changes in the membrane properties were visualized by BAM images and GIXD patterns and confirmed by thermodynamic parameters of hysteresis in the Langmuir monolayer compression-decompression experiments.

Influence of docosahexaenoic acid on the interfacial behavior of cholesterol-containing lipid membranes: Interactions with small amphiphiles and hydration properties

Cholesterol is known to significantly modify both the structural and the dynamical properties of lipid membranes. On one side, the presence of free cholesterol molecules has been determined to stiffen the membrane bilayer by stretching the hydrophobic tails. Additionally, recent experimental and computational findings have made evident the fact that cholesterol also alters the dynamics and the hydration properties of the polar head groups of DPPC model lipid membranes. In turn, we have recently shown that the Omega-3 fatty acid docosahexaenoic acid, DHA, counteracts the effect of cholesterol on DPPC membrane's mechanical properties by fluidizing the bilayer. However, such behavior represents in fact a global outcome dominated by the larger lipid hydrophobic tails that neither discriminates between the different parts of the membrane nor elucidates the effect on membrane hydration and binding properties. Thus, we now perform molecular dynamics simulations to scrutinize the influence of DHA on the interfacial behavior of cholesterol-containing lipid membranes by characterizing their hydration properties and their binding to amphiphiles. We find that while cholesterol destabilizes interactions with amphiphiles and slightly weakens the lipid's hydration layer, the incorporation of DHA practically restores the interfacial behavior of pure DPPC.

Accelerating Lipid Flip-Flop at Low Concentrations: A General Mechanism for Membrane Binding Peptides.

We report a physicochemical investigation of the lipid transport properties of model lipid membranes in the presence of the antimicrobial peptide indolicidin through comparisons of experimental SANS/SAXS scattering techniques to fully atomistic molecular dynamics simulations. In agreement with the experiment, we show that upon peripheral binding of the peptides, even at low concentrations, lipid flip-flop dynamics is greatly accelerated. Computer modeling elucidates the interplay between structural changes and lipid dynamics induced by peptides and proposes a mechanism for the mode of action of antimicrobial peptides, assessing the major role of entropy for the catalysis of the flipping events. The mechanism introduced here is universal for all peptides with preferential peripheral binding to the membrane as it does not depend on the specific amino acid sequence.

Ostwald Ripening of Triacylglycerol Droplets Embedded in Glass-Supported Phospholipid Bilayers.

Lipid droplets are fat storage organelles that consist of a neutral lipid core surrounded by a phospholipid monolayer. Because of their important biological functions, reconstituting model lipid droplets in synthetic phospholipid membranes is of great interest. In the present study, we investigated the incorporation of triacylglycerol droplets into glass-supported phospholipid bilayers by using fluorescence microscopy. We adsorbed triolein emulsions onto a glass surface that was partially covered with planar bilayers. After adsorption, triolein droplets were found to be immobilized in the bilayer membrane. The volume of each bound droplet varied over time. Large droplets grew, whereas small droplets shrank. Additionally, data on fluorescence recovery after photobleaching obtained for a phospholipid probe indicate that phospholipids on and near triolein droplets were fully mobile. Furthermore, photobleaching data obtained for a triacylglycerol probe indicate that triolein molecules diffused between different droplets along the planar bilayer. These results demonstrate Ostwald ripening, where triolein molecules in a small droplet dissolved in the bilayer, diffused laterally, and eventually bound to the interfaces of larger droplets. We investigated the ripening rate by using the average of the cube root of the fluorescence emission obtained for individual droplets. The ripening slowed after the addition of trilinolein to the triolein phase. Finally, we investigated the time dependence of the size distributions of the triolein droplets. The distribution was initially nearly unimodal and subsequently became bimodal.

Electrostatic interactions control the adsorption of extracellular vesicles onto supported lipid bilayers

Communication between cells located in different parts of an organism is often mediated by membrane-enveloped nanoparticles, such as extracellular vesicles (EVs). EV binding and cell uptake mechanisms depend on the heterogeneous composition of the EV membrane. From a colloidal perspective, the EV membrane interacts with other biological interfaces via both specific and non-specific interactions, where the latter include long-ranged electrostatic and van der Waals forces, and short-ranged repulsive “steric-hydration” forces. While electrostatic forces are generally exploited in most EV immobilization protocols, the roles played by various colloidal forces in controlling EV adsorption on surfaces have not yet been thoroughly addressed. In the present work, we study the adsorption of EVs onto supported lipid bilayers (SLBs) carrying different surface charge densities using a combination of quartz crystal microbalance with dissipation monitoring (QCM-D) and confocal laser scanning microscopy (CLSM). We demonstrate that EV adsorption onto lipid membranes can be controlled by varying the strength of electrostatic forces and we theoretically describe the observed phenomena within the framework of nonlinear Poisson-Boltzmann theory. Our modelling results confirm the experimental observations and highlight the crucial role played by attractive electrostatics in EV adsorption onto lipid membranes. They furthermore show that simplified theories developed for model lipid systems can be successfully applied to the study of their biological analogues and provide new fundamental insights into EV-membrane interactions with potential use in developing novel EV separation and immobilization strategies.

The influence of amphiphilic carbosilane dendrons on lipid model membranes

Amphiphilic dendrons represent a relatively novel class of molecules which may show many unique properties suitable for applications in a field of molecular biology and nanomedicine. They were frequently studied as platforms suitable for drug delivery systems as were, e.g. polymersomes or hybrid lipid-polymer nanoparticles. Recently, natural extracellular lipid vesicles (EVs), called exosomes (EXs), were shown to be a promising candidate in drug delivery applications. Formation of hybrid exosome-dendron nanovesicles could bring benefits in their simple conjugation with selective targeting moieties. Unfortunately, the complex architecture of biological membranes, EXs included, makes obstacles in elucidating the important parameters and mechanisms of interaction with the artificial amphiphilic structures.The aim of the presented work was to study the interaction of two types of amphiphilic carbosilane dendritic structures (denoted as DDN-1 and DDN-2) suitable for further modification with streptavidin (DDN-1) or using click-chemistry approach (DDN-2), with selected neutral and negatively charged lipid model membranes, partially mimicking the basic properties of natural EXs biomembranes. To meet the goal, a number of biophysical methods were used for determination of the degree and mechanisms of the interaction. The results showed that the strength of interactions of amphiphilic dendrons with liposomes was related with surface charge of liposomes. Several steps of interactions were disclosed. The initialization step was mainly coupled with amphiphilic dendrons - liposomes surface interaction resulting in destabilization of large self-assembled amphiphilic dendrons structures. Such destabilization was more significant with liposomes of higher negative charge. With increasing concentration of amphiphilic dendrons in a solution the interactions were taking place also in the hydrophobic part of bilayer. Further increase of nanoparticle concentration resulted in a gradual dendritic cluster formation in a lipid bilayer structure.Due to high affinity of amphiphilic dendrons to model lipid bilayers the conclusion can be drawn that they represent promising platforms also for decoration of exosomes or other kinds of natural lipid vehicles. Such organized hybrid dendron-lipid biomembranes may be advantageous for their subsequent post-functionalization with small molecules, large biomacromolecules or polymers suitable for targeted drug-delivery or theranostic applications.

Conformational State of Fenamates at the Membrane Interface: A MAS NOESY Study.

The present work analyzes the 1H NOESY MAS NMR spectra of three fenamates (mefenamic, tolfenamic, and flufenamic acids) localized in the lipid-water interface of phosphatidyloleoylphosphatidylcholine (POPC) membranes. The observed cross-peaks in the two-dimensional NMR spectra characterized intramolecular proximities between the hydrogen atoms of the fenamates as well as intermolecular interactions between the fenamates and POPC molecules. The peak amplitude normalization for an improved cross-relaxation (PANIC) approach, the isolated spin-pair approximation (ISPA) model, and the two-position exchange model were used to calculate the interproton distances indicative of specific conformations of the fenamates. The results showed that the proportions of the A+C and B+D conformer groups of mefenamic and tolfenamic acids in the presence of POPC were comparable within the experimental error and amounted to 47.8%/52.2% and 47.7%/52.3%, respectively. In contrast, these proportions for the flufenamic acid conformers differed and amounted to 56.6%/43.4%. This allowed us to conclude that when they bind to the POPC model lipid membrane, fenamate molecules change their conformational equilibria.

Is lipophilicity the main factor determining the effective drug penetration through lipid membranes? Combined GIXD and PM-IRRAS studies on the example of anthracyclines

Cell membranes constitute the first barrier for the drugs on their way to the cell. Therefore, their penetration determines the effectivity of the treatment and is defined by the drug-lipid interactions. A systematic, comprehensive study to assess the impact of different aspects influencing the effective penetration of model lipid membranes by the drugs including lipophilicity, charge, ability to form dimers as well as stearic hindrance was performed. Four anthracyclines differing in the structure and with lipophilicity increasing in the following order: doxorubicin (DOx) < pirarubicin (THP) < daunorubicin (DNR) < idarubicin (IDA) were chosen to assess their impact on 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine (DMPS) monolayers mimicking cancer cell membranes. The investigation performed at the air–water interface involved the application of multiple surface-sensitive techniques to assess the drug interactions with both polar heads of the phospholipid and the penetration of the acyl chain region. The obtained results allowed us to state that although electrostatic interactions and lipophilicity of the drug are one of the key factors, the ability to form dimers as well as stearic hinderance may strongly prevent from the effective penetration of the phospholipid monolayers even for drugs with higher lipophilicity and therefore have to be also taken into account in the development of new therapeutic agents.

Photoswitchable Calixarene Activators for Controlled Peptide Transport across Lipid Membranes.

Supramolecular synthetic transporters are crucial to understand and activate the passage across lipid membranes of hydrophilic effector molecules. Herein, we introduce photoswitchable calixarenes for the light-controlled transport activation of cationic peptide cargos across model lipid bilayers and inside living cells. Our approach was based on rationally designed p-sulfonatocalix[4]arene receptors equipped with a hydrophobic azobenzene arm, which recognize cationic peptide sequences at the nM range. Activation of membrane peptide transport is confirmed, in synthetic vesicles and living cells, for calixarene activators featuring the azobenzene arm in the E configuration. Therefore, this method allows the modulation of the transmembrane transport of peptide cargos upon Z-E photoisomerization of functionalized calixarenes using 500 nm visible light. These results showcase the potential of photoswitchable counterion activators for the light-triggered delivery of hydrophilic biomolecules and pave the way for potential applications in remotely controlled membrane transport and photopharmacology applications of hydrophilic functional biomolecules.