Interactions of anticancer drugs with biomembranes: what can we learn from model membranes?

Biophysical and molecular interactions of enantiomeric piperonal-derived trans β-aryl-δ-iodo-γ-lactones with cancer cell membranes, protein and DNA: Implications for anticancer activity

Developing novel anticancer agents requires understanding their interactions with biological systems at both the cellular and molecular levels. Enantiomeric lactones have demonstrated notable cytotoxic activities against various cancer cell lines. Building on this foundation, we investigated enantiomeric piperonal-derived trans-β-aryl-δ-iodo-γ-lactones ((-)-(4S,5R,6S) and (+)-(4R,5S,6R)), focusing on their impact on cancer cells membrane (Jurkat and GL-1), model membranes, and biomacromolecules such as human serum albumin (HSA) and DNA. Also, the cytotoxicity toward red blood cells and the antitumor activity of the compounds were evaluated against a set of canine lymphoma and/or leukemia cell lines. Membrane interaction studies revealed that both enantiomers interact with the hydrophobic core of lipid bilayers, enhancing lipid acyl chain packing, with the (-)-(4S,5R,6S) isomer showing a stronger impact on membrane fluidity. Comprehensive spectroscopic and theoretical studies revealed distinct stereochemical differences in binding affinities to HSA, where the (-)-(4S,5R,6S) isomer showed higher binding affinity and significant hydrophobic interactions. Detailed biological studies demonstrated that both enantiomers exhibit antiproliferative and proapoptotic activities, with the (-)-(4S,5R,6S) enantiomer showing higher activity. This study underscores the biological activity and interactions of enantiomeric iodolactones derived from piperonal with biomacromolecules, providing comprehensive insights into their biophysical behavior and potential anticancer properties.

Impact of a Palladium(II)-tris(2-carboxyethyl)phosphine Complex on Normal Cells: Toxicity and Membrane Interaction

Palladium(II) complexes with tris(2-carboxyethyl)phosphine (PdTCEP) show promise for biomedical applications due to their distinct chemical characteristics. This study explored the toxicity of PdTCEP towards normal human cells and examined its interactions with model cell membranes. Two cell types were used to evaluate cytotoxicity: human microvascular endothelial cells (HMEC-1) and red blood cells (RBCs). In HMEC-1 cells, PdTCEP reduced survival to about 80% at 15 µM, with the most significant drop-down to 40%-occurring at 40 µM. The production of reactive oxygen species (ROS) increased in a manner dependent on both dose and time, especially after 72 h of incubation. Despite these effects, PdTCEP caused only minor hemolysis in RBCs, with hemolysis levels staying below 10% even at higher concentrations. Fluorescence anisotropy measurements showed that PdTCEP minimally affects the hydrophobic core of the lipid bilayer, with slight changes observed at concentrations above 40 µM. Generalized polarization (GP) analysis indicated a slight decrease in lipid polar head packing with increasing PdTCEP concentration. Complementary FTIR analysis supported these findings by providing detailed insights into PdTCEP-membrane interactions. This research underscores PdTCEP's selective cytotoxicity and structural effects on membranes, suggesting its promise for more in-depth biological and pharmacological studies.

DSC and FTIR study on the interaction between pentacyclic triterpenoid lupeol and DPPC membrane

Natural products are a great resource for physiologically active substances. It is widely recognized that a major percentage of current medications are derived from natural compounds or their synthetic analogues. Triterpenoids are widespread in nature and can prevent cancer formation and progression. Despite considerable interest in these triterpenoids, their interactions with lipid bilayers still need to be thoroughly investigated. The aim of this study is to examine the interactions of lupeol, a pentacyclic triterpenoid, with model membranes composed of 1,2‑dipalmitoyl‑sn‑glycerol‑3‑phosphocholine (DPPC) by using non-invasive techniques such as differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The DSC study demonstrated that the incorporation of lupeol into DPPC membranes shifts the Lβ'-to-Pβ' and Pβ'-to-Lα phase transitions toward lower values, and a loss of main phase transition cooperativity is observed. The FTIR spectra indicated that the increasing concentration (10 mol%) of lupeol causes an increase in the molecular packing and membrane fluidity. In addition, it is found that lupeol's OH group preferentially interacts with the head group region of the DPPC lipid bilayer. These findings provide detailed information on the effect of lupeol on the DPPC head group and the conformation and dynamics of the hydrophobic chains. In conclusion, the effect of lupeol on the structural features of the DPPC membrane, specifically phase transition and lipid packing, has implications for understanding its biological function and its applications in biotechnology and medicine.

Improving the Accuracy of Permeability Data to Gain Predictive Power: Assessing Sources of Variability in Assays Using Cell Monolayers

The ability to predict the rate of permeation of new compounds across biological membranes is of high importance for their success as drugs, as it determines their efficacy, pharmacokinetics, and safety profile. In vitro permeability assays using Caco-2 monolayers are commonly employed to assess permeability across the intestinal epithelium, with an extensive number of apparent permeability coefficient (Papp) values available in the literature and a significant fraction collected in databases. The compilation of these Papp values for large datasets allows for the application of artificial intelligence tools for establishing quantitative structure-permeability relationships (QSPRs) to predict the permeability of new compounds from their structural properties. One of the main challenges that hinders the development of accurate predictions is the existence of multiple Papp values for the same compound, mostly caused by differences in the experimental protocols employed. This review addresses the magnitude of the variability within and between laboratories to interpret its impact on QSPR modelling, systematically and quantitatively assessing the most common sources of variability. This review emphasizes the importance of compiling consistent Papp data and suggests strategies that may be used to obtain such data, contributing to the establishment of robust QSPRs with enhanced predictive power.

New insights into the interaction of emodin with lipid membranes

Emodin is a natural anthraquinone derivative found in nature, widely known as an herbal medicine. Here, the partition, location, and interaction of emodin with lipid membranes of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) are experimentally investigated with different techniques. Our studies have considered the neutral form of emodin (EMH) and its anionic/deprotonated form (EM-), and their interaction with a more and less packed lipid membrane, DMPC at the gel and fluid phases, respectively. Though DSC results indicate that the two species, EMH and EM-, similarly disrupt the packing of DMPC bilayers, spin labels clearly show that EMH causes a stronger bilayer disruption, both in gel and fluid DMPC. Fluorescence spectroscopy shows that both EMH and EM- have a high affinity for DMPC: the binding of EM- to both gel and fluid DMPC bilayers was found to be quite similar, and similar to that of EMH to gel DMPC, Kp = (1.4 ± 0.3)x103. However, EMH was found to bind twice more strongly to fluid DMPC bilayers, Kp = (3.2 ± 0.3)x103. Spin labels and optical absorption spectroscopy indicate that emodin is located close to the lipid bilayer surface, and suggest that EM- is closer to the lipid/water interface than EMH, as expected. The present studies present a relevant contribution to the current understanding of the effect the two species of emodin, EMH and EM-, present on different microregions of an organism, as local pH values can vary significantly, can cause in a neutral lipid membrane, either more or less packed, liked gel and fluid DMPC, respectively, and could be extended to lipid domains of biological membranes.

Differential scanning calorimetry in drug-membrane interactions

Differential Scanning Calorimetry (DSC) is a central technique in investigating drug - membrane interactions, a critical component of pharmaceutical research. DSC measures the heat difference between a sample of interest and a reference as a function of temperature or time, contributing essential knowledge on the thermally induced phase changes in lipid membranes and how these changes are affected by incorporating pharmacological substances. The manuscript discusses the use of phospholipid bilayers, which can form structures like unilamellar and multilamellar vesicles, providing a simplified yet representative membrane model to investigate the complex dynamics of how drugs interact with and penetrate cellular barriers. The manuscript consolidates data from various studies, providing a comprehensive understanding of the mechanisms underlying drug - membrane interactions, the determinants that influence these interactions, and the crucial role of DSC in elucidating these components. It further explores the interactions of specific classes of drugs with phospholipid membranes, including non-steroidal anti-inflammatory drugs, anticancer agents, natural products with antioxidant properties, and Alzheimer's disease therapeutics. The manuscript underscores the critical importance of DSC in this field and the need for continued research to improve our understanding of these interactions, acting as a valuable resource for researchers.

Liposome bilayer stability: emphasis on cholesterol and its alternatives

Liposomes are spherical lipidic nanocarriers composed of natural or synthetic phospholipids with a hydrophobic bilayer and aqueous core, which are arranged into a polar head and a long hydrophobic tail, forming an amphipathic nano/micro-particle. Despite numerous liposomal applications, their use encounters many challenges related to the physicochemical properties strongly affected by their constituents, colloidal stability, and interactions with the biological environment. This review aims to provide a perspective and a clear idea about the main factors that regulate the liposomes' colloidal and bilayer stability, emphasising the roles of cholesterol and its possible alternatives. Moreover, this review will analyse strategies that offer possible approaches to provide more stable in vitro and in vivo liposomes with enhanced drug release and encapsulation efficiencies.

Effect of Trastuzumab on the thermodynamic behavior and roughness of fluid membrane using unsaturated phospholipid/cholesterol mixed monolayer model

The microenvironment near the receptor on biological membrane plays an important role in regulating drug-receptor interaction, and the interaction between drugs and lipids on membrane can also affect the microenvironment of membrane, which may affect drugs' efficacy or cause the drug resistance. Trastuzumab (Tmab) is a monoclonal antibody, used to treat early breast cancer associated with the overexpression of Human Epidermal growth factor Receptor 2 (HER2). But its effectiveness is limited due to its tendency to make tumor cells resistant to the drug. In this work, the monolayer mixed by unsaturated phospholipids (DOPC, DOPE and DOPS) and cholesterol were used as a model to simulate the fluid membrane region on biological membrane. The phospholipid/cholesterol mixed monolayers in molar ratio 7:3 and 1:1, were respectively used to simulate the one layer of simplified normal cell membrane and tumor cell membrane. The influence of this drug on the phase behavior, elastic modulus, intermolecular force, relaxation and the surface roughness of the unsaturated phospholipid/cholesterol monolayer was investigated. The results show that at 30 mN/m the increase or decrease of the elastic modulus and surface roughness of the mixed monolayer caused by Tamb depends on the type of phospholipid, but the intensity of the effect depends on the content of cholesterol, and the intensity of influence is more significant at the presence of 50% cholesterol. However, the effect of Tmab on the ordering of the DOPC/cholesterol or DOPS/cholesterol mixed monolayer is stronger when the content of cholesterol is 30%, but it was stronger for the DOPE/cholesterol mixed monolayer when the content of cholesterol is 50%. This study is helpful to understand the effects of anticancer drugs on microenvironment of cell membrane, and it has a certain reference value for the design of drug delivery system and drug target identification.

NMR and EPR study of the interaction of tris(3-hydroxy-4-pyridinonato) Ga(III) complexes with liposomes that mimic plant membranes

We performed an NMR and EPR study of the interaction of four [Ga(3,4-HPO)₃] chelates with liposomes derived from a soybean extract (SEL) and simpler formulations using POPC (100%) and POPE:POPC (50%). Parent [Fe(3,4-HPO)₃] chelates are eligible to prevent Iron Deficiency Chlorosis and we took advantage of the likenesses of the ions Fe (III) and Ga (III), and the fact their metal ion complexes are isostructural, to perform a combined NMR and EPR study to get information about the permeation properties of the complexes. The results demonstrate the presence of liposomes loaded with Ga-chelates and that the distribution of complexes alongside the bilayer is dependent on their structure. Two compounds, [Ga(mpp)₃] and [Ga(etpp)₃], have a higher affinity for the polar region of the liposome bilayer thus suggesting that their structure facilitates their permanence at the root-rhizosphere interface. Chelates [Ga(dmpp)₃] and [Ga(mrb13)₃] interact with all types of protons of the lipid bilayer thus implying that they travel all along the bilayer structure indicating their higher permeation properties through soybean membranes. The results obtained for compound, [Ga(mrb13)₃], which has been included in this work but was not yet tested in plant supplementation experiments, encourage its testing in in vivo plant studies once this study revealed that it interacts strongly with the model membranes. If the results of the future experiments in plants are positive and consistent with the present membrane-interaction studies the latter could constitute a good screening test for future compounds thus saving reagents and time.

New Meloxicam Derivatives-Synthesis and Interaction with Phospholipid Bilayers Measured by Differential Scanning Calorimetry and Fluorescence Spectroscopy

The purpose of the present paper was to assess the ability of five newly designed and synthesized meloxicam analogues to interact with phospholipid bilayers. Calorimetric and fluorescence spectroscopic measurements revealed that, depending on the details of the chemical structure, the studied compounds penetrated bilayers and affected mainly their polar/apolar regions, closer to the surface of the model membrane. The influence of meloxicam analogues on the thermotropic properties of DPPC bilayers was clearly visible because these compounds reduced the temperature and cooperativity of the main phospholipid phase transition. Additionally, the studied compounds quenched the fluorescence of prodan to a higher extent than laurdan, what pointed to a more pronounced interaction with membrane segments close to its surface. We presume that a more pronounced intercalation of the studied compounds into the phospholipid bilayer may be related to the presence of the molecule of a two-carbon aliphatic linker with a carbonyl group and fluorine substituent/trifluoromethyl group (compounds PR25 and PR49) or the three-carbon linker together with the trifluoromethyl group (PR50). Moreover, computational investigations of the ADMET properties have shown that the new meloxicam analogues are characterized by beneficial expected physicochemical parameters, so we may presume that they will have a good bioavailability after an oral administration.

A Thermodynamic Study on the Interaction between RH-23 Peptide and DMPC-Based Biomembrane Models

Investigation of the interaction between drugs and biomembrane models, as a strategy to study and eventually improve drug/substrate interactions, is a crucial factor in preliminary screening. Synthesized peptides represent a source of potential anticancer and theragnostic drugs. In this study, we investigated the interaction of a novel synthesized peptide, called RH-23, with a simplified dimyristoylphosphatidylcholine (DMPC) model of the cellular membrane. The interaction of RH-23 with DMPC, organized either in multilamellar vesicles (MLVs) and in Langmuir-Blodgett (LB) monolayers, was assessed using thermodynamic techniques, namely differential scanning calorimetry (DSC) and LB. The calorimetric evaluations showed that RH-23 inserted into MLVs, causing a stabilization of the phospholipid gel phase that increased with the molar fraction of RH-23. Interplay with LB monolayers revealed that RH-23 interacted with DMPC molecules. This work represents the first experimental thermodynamic study on the interaction between RH-23 and a simplified model of the lipid membrane, thus providing a basis for further evaluations of the effect of RH-23 on biological membranes and its therapeutic/diagnostic potential.

Monitoring membranes: The exploration of biological bilayers with second harmonic generation

Nature's seemingly controlled chaos in heterogeneous two-dimensional cell membranes stands in stark contrast to the precise, often homogeneous, environment in an experimentalist's flask or carefully designed material system. Yet cell membranes can play a direct role, or serve as inspiration, in all fields of biology, chemistry, physics, and engineering. Our understanding of these ubiquitous structures continues to evolve despite over a century of study largely driven by the application of new technologies. Here, we review the insight afforded by second harmonic generation (SHG), a nonlinear optical technique. From potential measurements to adsorption and diffusion on both model and living systems, SHG complements existing techniques while presenting a large exploratory space for new discoveries.

Interaction of Lipophilic Cytarabine Derivatives with Biomembrane Model at the Air/Water Interface

Cell membrane models are useful for obtaining molecular-level information on the interaction of biologically active molecules whose activity is believed to depend also on their effects on the membrane. Cytarabine was conjugated with fatty acids to improve the drug lipophilicity and the interaction with the biomembrane model. Cytarabine was conjugated with fatty acids of different lengths to form the trimyristoyl cytarabine and the tristearoyl cytarabine derivatives. Their interaction with biomembrane models constituted by dimyristoylphosphatidylcholine (DMPC) monolayers was studied by employing the Langmuir-Blodgett technique. DMPC/cytarabine, DMPC/trimyristoyl cytarabine and DMPC/tristearoyl cytarabine mixed monolayers at increasing molar fractions of the compound were prepared and placed on the subphase. The mean molecular area/surface pressure isotherms were recorded at 37 °C. Between the molecules of DMPC and those of cytarabine or prodrugs, repulsive forces act. However, these forces are very weak between DMPC and cytarabine and stronger between DMPC and the cytarabine derivatives, thus avoiding the expulsion of the compounds at higher surface pressure and modifying the stability of the mixed monolayer. The fatty acid moieties could then modulate the affinity of cytarabine for biomembranes.

Interaction of Bortezomib with Cell Membranes Regulates Its Toxicity and Resistance to Therapy

Bortezomib (BTZ) is a potent proteasome inhibitor currently being used to treat multiple myeloma. However, its high toxicity and resistance to therapy severely limit the treatment outcomes. Drug-membrane interactions have a crucial role in drugs' behavior in vivo, affecting their bioavailability and pharmacological activity. Additionally, drugs' toxicity often occurs due to their effects on the cell membranes. Therefore, studying BTZ's interactions with cell membranes may explain the limitations of its therapy. Due to the cell membranes' complexity, lipid vesicles were proposed here as biomembrane models, focusing on the membrane's main constituents. Two models with distinct composition and complexity were used, one composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and the other containing DMPC, cholesterol (Chol), and sphingomyelin (SM). BTZ's interactions with the models were evaluated regarding the drugs' lipophilicity, preferential location, and effects on the membrane's physical state. The studies were conducted at different pH values (7.4 and 6.5) to mimic the normal blood circulation and the intestinal environment, respectively. BTZ revealed a high affinity for the membranes, which proved to be dependent on the drug-ionization state and the membrane complexity. Furthermore, BTZ's interactions with the cell membranes was proven to induce changes in the membrane fluidity. This may be associated with its resistance to therapy, since the activity of efflux transmembrane proteins is dependent on the membrane's fluidity.

Interaction of Docetaxel with Phosphatidylcholine Membranes: A Combined Experimental and Computational Study

The antineoplastic drug Docetaxel is a second generation taxane which is used against a great variety of cancers. The drug is highly lipophilic and produces a great array of severe toxic effects that limit its therapeutic effectiveness. The study of the interaction between Docetaxel and membranes is very scarce, however, it is required in order to get clues in relation with its function, mechanism of toxicity and possibilities of new formulations. Using phosphatidylcholine biomimetic membranes, we examine the interaction of Docetaxel with the phospholipid bilayer combining an experimental study, employing a series of biophysical techniques like Differential Scanning Calorimetry, X-Ray Diffraction and Infrared Spectroscopy, and a Molecular Dynamics simulation. Our experimental results indicated that Docetaxel incorporated into DPPC bilayer perturbing the gel to liquid crystalline phase transition and giving rise to immiscibility when the amount of the drug is increased. The drug promotes the gel ripple phase, increasing the bilayer thickness in the fluid phase, and is also able to alter the hydrogen-bonding interactions in the interfacial region of the bilayer producing a dehydration effect. The results from computational simulation agree with the experimental ones and located the Docetaxel molecule forming small clusters in the region of the carbon 8 of the acyl chain palisade overlapping with the carbonyl region of the phospholipid. Our results support the idea that the anticancer drug is embedded into the phospholipid bilayer to a limited amount and produces structural perturbations which might affect the function of the membrane.

Multimodal Investigation into the Interaction of Quinacrine with Microcavity-Supported Lipid Bilayers

Quinacrine is a versatile drug that is widely recognized for its antimalarial action through its inhibition of the phospholipase enzyme. It also has antianthelmintic and antiprotozoan activities and is a strong DNA binder that may be used to combat multidrug resistance in cancer. Despite extensive cell-based studies, a detailed understanding of quinacrine's influence on the cell membrane, including permeability, binding, and rearrangement at the molecular level, is lacking. Herein, we apply microcavity-suspended lipid bilayers (MSLBs) as in vitro models of the cell membrane comprising DOPC, DOPC:Chol(3:1), and DOPC:SM:Chol(2:2:1) to investigate the influence of cholesterol and intrinsic phase heterogeneity induced by mixed-lipid composition on the membrane interactions of quinacrine. Using electrochemical impedance spectroscopy (EIS) and surface-enhanced Raman spectroscopy (SERS) as label-free surface-sensitive techniques, we have studied quinacrine interaction and permeability across the different MSLBs. Our EIS data reveal that the drug is permeable through ternary DOPC:SM:Chol and DOPC-only bilayer compositions. In contrast, the binary cholesterol/DOPC membrane arrested permeation, yet the drug binds or intercalates at this membrane as reflected by an increase in membrane impedance. SERS supported the EIS data, which was utilized to gain structural insights into the drug-membrane interaction. Our SERS data also provides a simple but powerful label-free assessment of drug permeation because a significant SERS enhancement of the drug's Raman signature was observed only if the drug accessed the plasmonic interior of the pore cavity passing through the membrane. Fluorescent lifetime correlation spectroscopy (FLCS) provides further biophysical insight, revealing that quinacrine binding increases the lipid diffusivity of DOPC and the ternary membrane while remarkably decreasing the lipid diffusivity of the DOPC:Chol membrane. Overall, because of its adaptability to multimodal approaches, the MSLB platform provides rich and detailed insights into drug-membrane interactions, making it a powerful tool for in vitro drug screening.

Graphene Quantum Dot Assisted Translocation of Daunomycin through an Ordered Lipid Membrane: A Study by Fluorescence Lifetime Imaging Microscopy and Resonance Energy Transfer

Daunomycin (DN) is a well-known chemotherapy drug frequently used in treating acute myeloid and lymphoblastic leukemia. It needs to be delivered to the therapeutic target by a delivering agent that beats the blood-brain barrier. DN is known to be specifically located at the membrane surface and scantly to the bilayer. Penetration of DN into the membrane bilayer depends on the molecular packing of the lipid. It does not travel promptly to the interior of the cells and needs a carrier to serve the purpose. Here, we have demonstrated, by fluorescence lifetime imaging spectroscopy (FLIM) and resonance energy transfer (RET) phenomenon, that ultrasmall graphene quantum dots (GQDs) can be internalized into the aqueous pool of giant unilamellar vesicles (GUVs) made from dipalmitoylphosphatidylcholine (DPPC) lipids, which, in turn, help in fast translocation of DN through the membrane without any delivery vehicle.

The Past and the Future of Langmuir and Langmuir-Blodgett Films

The Langmuir-Blodgett (LB) technique, through which monolayers are transferred from the air/water interface onto a solid substrate, was the first method to allow for the controlled assembly of organic molecules. With its almost 100 year history, it has been the inspiration for most methods to functionalize surfaces and produce nanocoatings, in addition to serving to explore concepts in molecular electronics and nanoarchitectonics. This paper provides an overview of the history of Langmuir monolayers and LB films, including the potential use in devices and a discussion on why LB films are seldom considered for practical applications today. Emphasis is then given to two areas where these films offer unique opportunities, namely, in mimicking cell membrane models and exploiting nanoarchitectonics concepts to produce sensors, investigate molecular recognitions, and assemble molecular machines. The most promising topics for the short- and long-term prospects of the LB technique are also highlighted.

Unveiling the Molecular Dynamics in a Living Cell to the Subcellular Organelle Level Using Second-Harmonic Generation Spectroscopy and Microscopy

Second-harmonic generation (SHG) microscopy has been proved to be a powerful method for investigating the structures of biomaterials. SHG spectra were also generally used to probe the adsorption and cross-membrane transport of molecules on lipid bilayers in situ and in real time. In this work, we applied SHG and two-photon fluorescence (TPF) spectra to investigate the dynamics of an amphiphilic ion with an SHG and TPF chromophore, D289 (4-(4-diethylaminostyry)-1-methyl-pyridinium iodide), on the surface of human chronic myelogenous leukemia (K562) cells and the subcellular structures inside the cells. The adsorption and cross-membrane transport of D289 into the cells and then into the organelles such as mitochondria were revealed. SHG images were also recorded and used to demonstrate their capability of probing molecular dynamics in organelles in K562 cells. This work demonstrated the first SHG investigation of the cross-membrane transport dynamics on the surface of subcellular organelles. It may also shed light on the differentiation of different types of subcellular structures in cells.

Mechanistic Understanding from Molecular Dynamics in Pharmaceutical Research 2: Lipid Membrane in Drug Design

We review the use of molecular dynamics (MD) simulation as a drug design tool in the context of the role that the lipid membrane can play in drug action, i.e., the interaction between candidate drug molecules and lipid membranes. In the standard "lock and key" paradigm, only the interaction between the drug and a specific active site of a specific protein is considered; the environment in which the drug acts is, from a biophysical perspective, far more complex than this. The possible mechanisms though which a drug can be designed to tinker with physiological processes are significantly broader than merely fitting to a single active site of a single protein. In this paper, we focus on the role of the lipid membrane, arguably the most important element outside the proteins themselves, as a case study. We discuss work that has been carried out, using MD simulation, concerning the transfection of drugs through membranes that act as biological barriers in the path of the drugs, the behavior of drug molecules within membranes, how their collective behavior can affect the structure and properties of the membrane and, finally, the role lipid membranes, to which the vast majority of drug target proteins are associated, can play in mediating the interaction between drug and target protein. This review paper is the second in a two-part series covering MD simulation as a tool in pharmaceutical research; both are designed as pedagogical review papers aimed at both pharmaceutical scientists interested in exploring how the tool of MD simulation can be applied to their research and computational scientists interested in exploring the possibility of a pharmaceutical context for their research.

Restoring structural parameters of lipid mixtures from small-angle X-ray scattering data

Small-angle X-ray scattering (SAXS) is widely utilized to study soluble macromolecules, including those embedded into lipid carriers and delivery systems such as surfactant micelles, phospho-lipid vesicles and bilayered nanodiscs. To adequately describe the scattering from such systems, one needs to account for both the form factor (overall structure) and long-range-order Bragg reflections emerging from the organization of bilayers, which is a non-trivial task. Presently existing methods separate the analysis of lipid mixtures into distinct procedures using form-factor fitting and the fitting of the Bragg peak regions. This article describes a general approach for the computation and analysis of SAXS data from lipid mixtures over the entire angular range of an experiment. The approach allows one to restore the electron density of a lipid bilayer and simultaneously recover the corresponding size distribution and multilamellar organization of the vesicles. The method is implemented in a computer program, LIPMIX, and its performance is demonstrated on an aqueous solution of layered lipid vesicles undergoing an extrusion process. The approach is expected to be useful for the analysis of various types of lipid-based systems, e.g. for the characterization of interactions between target drug molecules and potential carrier/delivery systems.

Mimicking the Mammalian Plasma Membrane: An Overview of Lipid Membrane Models for Biophysical Studies

Cell membranes are very complex biological systems including a large variety of lipids and proteins. Therefore, they are difficult to extract and directly investigate with biophysical methods. For many decades, the characterization of simpler biomimetic lipid membranes, which contain only a few lipid species, provided important physico-chemical information on the most abundant lipid species in cell membranes. These studies described physical and chemical properties that are most likely similar to those of real cell membranes. Indeed, biomimetic lipid membranes can be easily prepared in the lab and are compatible with multiple biophysical techniques. Lipid phase transitions, the bilayer structure, the impact of cholesterol on the structure and dynamics of lipid bilayers, and the selective recognition of target lipids by proteins, peptides, and drugs are all examples of the detailed information about cell membranes obtained by the investigation of biomimetic lipid membranes. This review focuses specifically on the advances that were achieved during the last decade in the field of biomimetic lipid membranes mimicking the mammalian plasma membrane. In particular, we provide a description of the most common types of lipid membrane models used for biophysical characterization, i.e., lipid membranes in solution and on surfaces, as well as recent examples of their applications for the investigation of protein-lipid and drug-lipid interactions. Altogether, promising directions for future developments of biomimetic lipid membranes are the further implementation of natural lipid mixtures for the development of more biologically relevant lipid membranes, as well as the development of sample preparation protocols that enable the incorporation of membrane proteins in the biomimetic lipid membranes.

Interactions of Cationic Diruthenium Trithiolato Complexes with Phospholipid Membranes Studied by NMR Spectroscopy

To apprehend the possible mechanisms involved in the cellular uptake and the membrane interactions of cytotoxic dinuclear p-cymene trithiolato ruthenium(II) complexes, the interactions of the complexes [(η⁶-p-MeC₆H₄Prⁱ)₂Ru₂(R¹)₂(R²)]⁺ (R¹ = R² = SC₆H₄-m-Prⁱ:1; R¹ = SC₆H₄-p-OMe, R² = SC₆H₄-p-OH:2; R¹ = SCH₂C₆H₄-p-OMe, R² = SC₆H₄-p-OH:3) with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) vesicles and 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) micelles were studied using nuclear magnetic resonance (NMR) spectroscopy. ¹H NMR, nuclear Overhauser effect (NOE), diffusion ordered spectroscopy (DOSY), and T₁ and T₂ relaxation data provided information on interactions between the complexes and the model membranes and on the submolecular localization of the complexes at the membrane interface. The results suggest that (a) the interaction takes place without new covalent adduct formation, (b) the cationic diruthenium complexes interact with DOPC head groups most likely involving electrostatic interactions while remaining structurally unchanged, (c) the changes indicating interactions are more pronounced for the most lipophilic complex 1, and (d) the diruthenium complexes remain at the exterior vesicle surface and are unlikely inserted between the phospholipid chains. The complexes also interact with micellar/free DHPC and seem to induce micellization or aggregation in solutions below critical micelle concentration (CMC). Our study suggests high affinity of the Ru complexes for the membrane surface that likely plays a key role in cellular uptake and possibly also in redistribution in mitochondria.

TPGS2k-PLGA composite nanoparticles by depleting lipid rafts in colon cancer cells for overcoming drug resistance

Recently, studies showed that the drug-resistant cell membranes have formed high-density lipid rafts regions; traditional targeted drug delivery systems can hardly break through the hard shell and deliver drugs to drug-resistant cells. Here, α-tocopherol polyethylene glycol 2000 succinate (TPGS_2k) was successfully synthesized and used to modify poly (lactic-glycolic acid) nanoparticles co-loaded with doxorubicin (DOX) and simvastatin (SV) (SV/DOX@TPGS_2k-PLGA NPs). The purpose of this study is to explore the synergistic effect between SV consuming cholesterol in lipid rafts and directly down-regulating P-gp expression on the intracellular drugs retention. The research highlights these nanoparticles interrupted lipid rafts (cholesterol-rich domains, where P-gp is often located), which inhibited drug efflux by down-regulating P-gp, promoted the mitochondria apoptosis and made SW620/AD300 cells (DOX-resistant colon cancer cell line) re-sensitized to DOX. Therefore, the carrier can become a promising SV-based nano-delivery system with depleting cholesterol in lipid rafts to reverse drug resistance.

Toxic effects of the anticancer drug epirubicin in vitro assayed in human erythrocytes

Epirubicin is a cytotoxic drug used in the treatment of different types of cancer and increasing evidence suggests that its target is cell membranes. In order to gain insight on its toxic effects, intact red blood cells (RBC), human erythrocyte membranes and molecular models were used. The latter consisted in bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), phospholipid classes found mainly in the outer and inner monolayers of the human erythrocyte membrane, respectively. The results obtained by X-ray diffraction displayed that epirubicin induced structural perturbations in multilayers of DMPC. Differential scanning calorimetry (DSC) showed that epirubicin disturbed the thermotropic behavior of both DMPC and DMPE vesicles, whereas fluorescence spectroscopy demonstrated alterations in the fluidity of DMPC vesicles and the erythrocyte membrane. Scanning electron microscopy (SEM) revealed that epirubicin changed the normal discoid form of RBC to echinocytes and stomatocytes. Electron paramagnetic resonance (EPR) disclosed that this drug induced conformational changes in the erythrocyte membrane proteins. These findings demonstrate that epirubicin interacts with lipids and proteins of the human erythrocyte membrane, effects that might compromise the integrity and function of cell membranes. This is the first time that its toxic effects on the human erythrocyte membrane have been described.

Molecular dynamics study of lipid bilayers modeling outer and inner leaflets of plasma membranes of mouse hepatocytes. I. Differences in physicochemical properties between the two leaflets

Outer and inner leaflets of plasma cell membranes have different lipid compositions, and the membrane properties of each leaflet can differ from each other significantly due to these composition differences. However, because of the experimental difficulty in measuring the membrane properties for each leaflet separately, the differences are not well understood at a molecular level. In this study, we constructed two lipid bilayer systems, modeling outer and inner leaflets of plasma membranes of mouse hepatocytes based on experimental composition data. The ion concentration in the interlamellar water phase was also set to match the concentration in extra- and intracellular fluids. The differences in physical properties between the outer and inner leaflets of mouse hepatocyte cell membrane models were investigated by performing 1.2 μs-long all-atomistic molecular dynamics calculations under physiological temperature and pressure conditions (310.15 K and 1 atm). The calculated electron density profiles along the bilayer normal for each model bilayer system captured well the asymmetric feature of the experimental electron density profile across actual cell plasma membranes, indicating that our procedure of modeling the outer and inner leaflets of the cell plasma membranes was satisfactory. We found that compared to the outer leaflet model, the inner leaflet model had a very bulky and soft structure in the lateral direction. To confirm the differences, membrane fluidity was measured from the lateral diffusivity and relaxation times. The fluidity was significantly higher in the inner leaflet model than in the outer leaflet model. We also discuss two topics that are of wide interest in biology, i.e., the interdigitation of acyl tails of lipid molecules between two monolayers and the lateral concentration fluctuation of lipid molecules in the bilayers.

Self-assembly of Organic Nanomaterials and Biomaterials: The Bottom-Up Approach for Functional Nanostructures Formation and Advanced Applications

In this paper, we survey recent advances in the self-assembly processes of novel functional platforms for nanomaterials and biomaterials applications. We provide an organized overview, by analyzing the main factors that influence the formation of organic nanostructured systems, while putting into evidence the main challenges, limitations and emerging approaches in the various fields of nanotechology and biotechnology. We outline how the building blocks properties, the mutual and cooperative interactions, as well as the initial spatial configuration (and environment conditions) play a fundamental role in the construction of efficient nanostructured materials with desired functional properties. The insertion of functional endgroups (such as polymers, peptides or DNA) within the nanostructured units has enormously increased the complexity of morphologies and functions that can be designed in the fabrication of bio-inspired materials capable of mimicking biological activity. However, unwanted or uncontrollable effects originating from unexpected thermodynamic perturbations or complex cooperative interactions interfere at the molecular level with the designed assembly process. Correction and harmonization of unwanted processes is one of the major challenges of the next decades and requires a deeper knowledge and understanding of the key factors that drive the formation of nanomaterials. Self-assembly of nanomaterials still remains a central topic of current research located at the interface between material science and engineering, biotechnology and nanomedicine, and it will continue to stimulate the renewed interest of biologist, physicists and materials engineers by combining the principles of molecular self-assembly with the concept of supramolecular chemistry.

Microcavity-Supported Lipid Bilayers; Evaluation of Drug-Lipid Membrane Interactions by Electrochemical Impedance and Fluorescence Correlation Spectroscopy

Many drugs have intracellular or membrane-associated targets, thus understanding their interaction with the cell membrane is of value in drug development. Cell-free tools used to predict membrane interactions should replicate the molecular organization of the membrane. Microcavity array-supported lipid bilayer (MSLB) platforms are versatile biophysical models of the cell membrane that combine liposome-like membrane fluidity with stability and addressability. We used an MSLB herein to interrogate drug-membrane interactions across seven drugs from different classes, including nonsteroidal anti-inflammatories: ibuprofen (Ibu) and diclofenac (Dic); antibiotics: rifampicin (Rif), levofloxacin (Levo), and pefloxacin (Pef); and bisphosphonates: alendronate (Ale) and clodronate (Clo). Fluorescence lifetime correlation spectroscopy (FLCS) and electrochemical impedance spectroscopy (EIS) were used to evaluate the impact of drug on 1,2-dioleyl- sn-glycerophosphocholine and binary bilayers over physiologically relevant drug concentrations. Although FLCS data revealed Ibu, Levo, Pef, Ale, and Clo had no impact on lipid lateral mobility, EIS, which is more sensitive to membrane structural change, indicated modest but significant decreases to membrane resistivity consistent with adsorption but weak penetration of drugs at the membrane. Ale and Clo, evaluated at pH 5.25, did not impact the impedance of the membrane except at concentrations exceeding 4 mM. Conversely, Dic and Rif dramatically altered bilayer fluidity, suggesting their translocation through the bilayer, and EIS data showed that resistivity of the membrane decreased substantially with increasing drug concentration. Capacitance changes to the bilayer in most cases were insignificant. Using a Langmuir-Freundlich model to fit the EIS data, we propose R_sat as an empirical value that reflects permeation. Overall, the data indicate that Ibu, Levo, and Pef adsorb at the interface of the lipid membrane but Dic and Rif interact strongly, permeating the membrane core modifying the water/ion permeability of the bilayer structure. These observations are discussed in the context of previously reported data on drug permeability and log P.

Understanding the Dynamic Behavior of an Anticancer Drug, Doxorubicin, on a Lipid Membrane Using Multiple Spectroscopic Techniques

The interaction, including the adsorption and embedding, of a widely applied anticancer drug, doxorubicin, with a lipid membrane was investigated. Second harmonic generation and two photon fluorescence were used as a powerful combination capable in revealing this dynamic process at the interface. The adsorption, association, deassociation and embedding of doxorubicin on the lipid membrane were clearly identified based on the consistency in the dynamic parameters revealed by the time dependent second harmonic generation and two-photon fluorescence measurements. This work also presents a new approach for in situ measurement of the adsorption density of doxorubicin on lipid membrane, benefiting from the two-photon fluorescence signal of doxorubicin being significantly altered by its chemical environment. The analysis of the location and molecular density based on the fluorescent efficiency of the chromophores makes the fluorescence measurement a "surface sensitive" technique as well. The analytical procedures used in this work are expected to aid in understanding the interaction between fluorescent molecules and lipid membranes in general.

Effects of artepillin C on model membranes displaying liquid immiscibility

It has been hypothesized that the therapeutic effects of artepillin C, a natural compound derived from Brazilian green propolis, are likely related to its partition in the lipid bilayer component of biological membranes. To test this hypothesis, we investigated the effects of the major compound of green propolis, artepillin C, on model membranes (small and giant unilamelar vesicles) composed of ternary lipid mixtures containing cholesterol, which display liquid-ordered (l_o) and liquid-disordered (l_d) phase coexistence. Specifically, we explored potential changes in relevant membrane parameters upon addition of artepillin C presenting both neutral and deprotonated states by means of small angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and confocal and multiphoton excitation fluorescence microscopy. Thermotropic analysis obtained from DSC experiments indicated a loss in the lipid cooperativity of l_o phase at equilibrium conditions, while at similar conditions spontaneous formation of unilamellar vesicles from SAXS experiments showed that deprotonated artepillin C preferentially located at the surface of the membrane. Time-resolved experiments using fluorescence microscopy showed that at doses above 100 µM, artepillin C in its neutral state interacted with both liquid-ordered and liquid-disordered phases, inducing curvature stress and promoting dehydration at the membrane interface.

Engineering Anticancer Amphipathic Peptide-Dendronized Compounds for Highly-Efficient Plasma/Organelle Membrane Perturbation and Multidrug Resistance Reversal

Discovering new strategies for combating drug-resistant tumors becomes a worldwide challenge. Thereinto, stubborn drug-resistant tumor membrane is a leading obstacle on chemotherapy. Herein, we report a novel tumor-activatable amphipathic peptide-dendronized compound, which could form nanoaggregates in aqueous solutions, for perturbing tumor plasma/organelle membrane and reversing multidrug resistance. Distinguished from classical linear amphipathic peptide drugs for membrane disturbance, dendritic lysine-based architecture is designed as a multivalent scaffold to amplify the supramolecular interactions of cationic compound with drug-resistant tumor membrane. Moreover, arginine-rich residues as terminal groups are hopeful to generate multiple hydrogen bonding and electrostatic interactions with tumor membrane. On the other hand, antitumor molecule (doxorubicin) is devised as a hydrophobic moiety to intensify the membrane-inserting ability owing to the prominent interactions with hydrophobic domains of drug-resistant tumor membrane. As expected, these amphipathic peptide-dendronized compounds within the nanoaggregates could severely disturb both the structures and functions of tumor plasma/organelle membrane system, thereby resulting in the rapid leakage of many critical biomolecules, highly efficient apoptotic activation and antiapoptotic inhibition. This strategy on tumor membrane perturbation demonstrates a bran-new antitumor activity with high contributions to cell cycle arrest (at the S phase), strong apoptosis-inducing ability and satisfying cytotoxicity to a variety of drug-resistant tumor cell lines.

Soft nanoparticles charge expression within lipid membranes: The case of amino terminated dendrimers in bilayers vesicles

Interactions of charged nanoparticles with model bio-membranes provide important insights about the soft interaction involved and the physico-chemical parameters that influence lipid bilayers stability, thus providing key features of their cytotoxicity effects onto cellular membranes. With this aim, the self-assembly processes between polyamidoamine dendrimers (generation G = 2.0 and G = 4.0) and dipalmitoylphosphatidylcholine (DPPC) lipids were investigated by means of Zeta potential analysis, x-rays, Raman and quasielastic light scattering experiments. Raman scattering data evidenced that dendrimers penetration produce a perturbation of the DPPC vesicles alkyl chains. A linear increase of liposome zeta-potential with increasing PAMAM concentration evidenced that only a fraction of the dendrimers effective charge contributes to the expression of the charge at the surface of the DPPC liposome. The linear region of the zeta-potential extends toward higher PAMAM concentrations as the dendrimer generation decreases from G = 4.0 to G = 2.0. Further increase in PAMAM concentration, outside of the linear region, causes a perturbation of the bilayer characterized by the loss in multilamellar correlation and the increase of DPPC liposome hydrodynamic radius. The findings of our investigation help to rationalize the effect of nanoparticles electrostatic interaction within lipid vesicles as well as to provide important insights about the perturbation of lipid bilayers membrane induced by nanoparticles inclusion.

Synthesis and interaction of sterol-uridine conjugate with DMPC liposomes studied by differential scanning calorimetry

Differential scanning calorimetry (DSC) is a thermoanalytical technique which provides information on the interaction between drugs and models of cell membranes. Studies on the calorimetric behavior of hydrated phospholipids within liposomes are employed to shed light on the changes in the physico-chemical properties when interacting with drugs. In this report, new potential anti-cancer drugs such as uridine and uridine derivatives (acetonide and its succinate), 3β-5α,8α-endoperoxide-cholestan-6-en-3-ol (5,8-epidioxicholesterol) and conjugate (uridine acetonide-epidioxicholesterol succinate) have been synthesized. Steglich esterification method using coupling agents allowed to obtain the uridine acetonide-sterol conjugate. The study on the interaction between the drugs and dimiristoyl-phophatidilcholine (DMPC) liposomes has been conducted by the use of DSC. The analysis of the DSC curves indicated that the uridine and derivatives (acetonide and its succinate) present a very soft interaction with the DMPC liposomes, whereas the 5,8-epidioxicholesterol and the conjugate showed a strong effect on the thermotropic behavior. Our results suggested that the lipophilic character of uridine acetonide-sterol conjugate improves the affinity with the DMPC liposomes.

Molecular Evidence of Adenosine Deaminase Linking Adenosine A2A Receptor and CD26 Proteins

Adenosine is an endogenous purine nucleoside that acts in all living systems as a homeostatic network regulator through many pathways, which are adenosine receptor (AR)-dependent and -independent. From a metabolic point of view, adenosine deaminase (ADA) is an essential protein in the regulation of the total intracellular and extracellular adenosine in a tissue. In addition to its cytosolic localization, ADA is also expressed as an ecto-enzyme on the surface of different cells. Dipeptidyl peptidase IV (CD26) and some ARs act as binding proteins for extracellular ADA in humans. Since CD26 and ARs interact with ADA at opposite sites, we have investigated if ADA can function as a cell-to-cell communication molecule by bridging the anchoring molecules CD26 and A2AR present on the surfaces of the interacting cells. By combining site-directed mutagenesis of ADA amino acids involved in binding to A2AR and a modification of the bioluminescence resonance energy transfer (BRET) technique that allows detection of interactions between two proteins expressed in different cell populations with low steric hindrance (NanoBRET), we show direct evidence of the specific formation of trimeric complexes CD26-ADA-A2AR involving two cells. By dynamic mass redistribution assays and ligand binding experiments, we also demonstrate that A2AR-NanoLuc fusion proteins are functional. The existence of this ternary complex is in good agreement with the hypothesis that ADA could bridge T-cells (expressing CD26) and dendritic cells (expressing A2AR). This is a new metabolic function for ecto-ADA that, being a single chain protein, it has been considered as an example of moonlighting protein, because it performs more than one functional role (as a catalyst, a costimulator, an allosteric modulator and a cell-to-cell connector) without partitioning these functions in different subunits.

In vitro effects of benzimidazole/thioether-copper complexes with antitumor activity on human erythrocytes

Two cytotoxic copper(II) complexes with N-H and N-methylated benzimidazole-derived ligands (Cu-L¹ and Cu-L^1Me; L¹=bis(2-methylbenzimidazolyl)(2-methylthioethyl)amine, L^1Me=bis(1-methyl-2-methylbenzimidazolyl)(2-methylthioethyl)amine) were synthesized and exposed to human erythrocytes and molecular models of its membrane. The latter were bilayers built-up of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), classes of lipids present in the external and internal moieties of the human red cell membrane, respectively. Scanning electron microscopy (SEM) of erythrocytes incubated with solutions of both Cu(II) complexes showed that they induced morphological changes to the normal cells to echinocytes, and hemolysis at higher concentrations. Real-time observation of the dose-dependent effects of the complexes on live erythrocytes by defocusing microscopy (DM) confirmed SEM results. The formation of echinocytes implied that complex molecules inserted into the outer moiety of the red cell membrane. X-ray diffraction studies on DMPC and DMPE showed that none of these complexes interacted with DMPE and only Cu-L¹ interacted with DMPC. This difference was explained by the fact that Cu-L^1Me complex is more voluminous than Cu-L¹ because it has two additional methyl groups; on the other hand, DMPC molecule has three methyl groups in its bulky terminal amino end. Thus, by steric hindrance Cu-L^1Me molecules cannot intercalate into DMPC bilayer, which besides is present in the gel phase. These results, together with the increased antiproliferative capacity of the N-methylated complex Cu-L^1Me over that of Cu-L¹ are rationalized mainly based on its higher lipophilicity.

Interaction of Newly Platinum(II) with Tris(2-carboxyethyl)phosphine Complex with DNA and Model Lipid Membrane

Structural properties of plasmid DNA and model lipid membrane treated with newly synthesized platinum(II) complex cis-[PtCl₂{P(CH₂CH₂COOH)₃}₂] (cis-DTCEP for short) were studied and compared with effects of anticancer drug cisplatin, cis-[Pt(NH₃)₂Cl₂] (cis-DDP for short). Time Correlated Single Photon Counting Fluorescence Correlation Spectroscopy (TCSPC-FCS) was employed to study interactions between those platinum complexes and DNA. The TCSPC-FCS results suggest that bonding of cis-DTCEP derivative to DNA leads to plasmid strain realignment towards much more compact structure than in the case of cis-DDP. Application of both differential scanning calorimetry and infrared spectroscopy to platinum complexes/DPPC showed that cis-DTCEP slightly increases the phospholipid’s main phase transition temperature resulting in decreased fluidity of the model membrane. The newly investigated compound—similarly to cis-DDP—interacts mainly with the DPPC head group however not only by the means of electrostatic forces: this compound probably enters into hydrophilic region of the lipid bilayer and forms hydrogen bonds with COO groups of glycerol and PO₂⁻ group of DPPC.

Lipid Bilayers Are Long-Lived on Solvent Cleaned Plasma-Oxidized poly(dimethyl)siloxane (ox-PDMS)

Although it is well known that phospholipids self-assemble on hydrophilic plasma-oxidized PMDS surfaces (ox-PDMS) to form cell membrane mimetic bilayers, the temporal stability of phospholipid membranes on these surfaces is unknown. Here we report that phospholipid bilayers remain stable on solvent-cleaned ox-PDMS for at least 132 hours after preparation. Absent solvent cleaning, the bilayers were stable for only 36 hours. We characterized the phospholipid bilayers, i) through quantitative comparative analysis of the fluorescence intensity of phospholipid bilayers on ox-PDMS and phospholipid monolayers on native PDMS and, ii) through measurements of the diffusive mobility of the lipids through fluorescence recovery after photobleaching (FRAP). The fluorescence intensity of the phospholipid layer remained consistent with that of a bilayer for 132 hours. The evolution of the diffusive mobility of the phospholipids in the bilayer on ox-PDMS over time was similar to lipids in control bilayers prepared on glass surfaces. Solvent cleaning was essential for the long-term stability of the bilayers on ox-PDMS. Without cleaning in acetone and isopropanol, phospholipid bilayers prepared on ox-PDMS surfaces peeled off in large patches within 36 hours. Importantly, we find that phospholipid bilayers supported on solvent-cleaned ox-PDMS were indistinguishable from phospholipid bilayers supported on glass for at least 36 hours after preparation. Our results provide a link between the two common surfaces used to prepare in vitro biomimetic phospholipid membranes-i) glass surfaces used predominantly in fundamental biophysical experiments, for which there is abundant physicochemical information, with ii) ox-PDMS, the dominant material used in practical, applications-oriented systems to build micro-devices, topographically-patterned surfaces, and biosensors where there is a dearth of information.

Resveratrol Interaction with Lipid Bilayers: A Synchrotron X-ray Scattering Study

Resveratrol belongs to the large group of biologically active polyphenol compounds, with several beneficial health effects including antioxidant activity, anti-inflammatory action, cardiovascular protection, neuroprotection, and cancer chemoprevention. In the present study, the possibility that the effects of resveratrol described above are caused by resveratrol membrane interactions and structural modifications of lipid bilayers is evaluated. In this context, it is possible that resveratrol interacts selectively with lipid domains present in biological membranes, thereby modulating the localization of the anchored proteins and controlling their intracellular cascades. This study was conducted in a synchrotron particle accelerator, where the influence of resveratrol in the structural organization of lipid domains in bilayers was investigated using small- and wide-angle X-ray scattering (SAXS and WAXS) techniques. Membrane mimetic systems composed of egg l-α-phosphatidylcholine (EPC), cholesterol (CHOL), and sphingomyelin (SM), with different molar ratios, were used to access the effects of resveratrol on the order and structure of the membrane. The results revealed that resveratrol induces phase separation, promoting the formation of lipid domains in EPC, EPC:CHOL [4:1], and EPC:CHOL:SM [1:1:1] bilayers, which brings some structural organization to membranes. Therefore, resveratrol controls lipid packing of bilayers by inducing the organization of lipid rafts. Moreover, the formation of lipid domains is important for modulating the activity of many receptors, transmembrane proteins, and enzymes whose activity depends on the structural organization of the membrane and on the presence or absence of these organized domains. This evidence can thereby explain the therapeutic effects of resveratrol.

Novel Application of Cellulose Paper As a Platform for the Macromolecular Self-Assembly of Biomimetic Giant Liposomes

We report a facile and scalable method to fabricate biomimetic giant liposomes by using a cellulose paper-based materials platform. Termed PAPYRUS for Paper-Abetted liPid hYdRation in aqUeous Solutions, the method is general and can produce liposomes in various aqueous media and at elevated temperatures. Encapsulation of macromolecules and production of liposomes with membranes of complex compositions is straightforward. The ease of manipulation of paper makes practical massive parallelization and scale-up of the fabrication of giant liposomes, demonstrating for the first time the surprising usefulness of paper as a platform for macromolecular self-assembly.

Effect of anionic and cationic polyamidoamine (PAMAM) dendrimers on a model lipid membrane

In spite of the growing variety of biological applications of dendrimer-based nanocarriers, a major problem of their potential applications in bio-medicine is related to the disruption of lipid bilayers and the cytotoxicity caused by the aggregation processes involved onto cellular membranes. With the aim to study model dendrimer-biomembrane interaction, the self-assembly processes of a mixture of charged polyamidoamine (PAMAM) dendrimers and dipalmitoylphosphatidylcholine (DPPC) lipids were investigated by means of Zeta potential analysis, Raman and x-ray scattering. Zwitterionic DPPC liposomes showed substantially different behaviors during their interaction with negatively charged (generation G=2.5) sodium carboxylate terminated (COO^- Na⁺) dendrimers or positively charged (generation G=3.0) amino terminated (-NH₂) dendrimers. More specifically the obtained results evidence the sensitive interactions between dendrimer terminals and lipid molecules at the surface of the liposome, with an enhancement of the liposome surface zeta potential, as well as in the hydrophobic region of the bilayers, where dendrimer penetration produce a perturbation of the hydrophobic alkyl chains of the bilayers. Analysis of the SAXS structure factor with a suitable model for the inter-dendrimers electrostatic potential allows an estimation of an effective charge of 15 ǀeǀ for G=2.5 and 7.6 ǀeǀ for G=3.0 PAMAM dendrimers. Only a fraction (about 1/7) of this charge contributes to the linear increase of liposome zeta-potential with increasing PAMAM/DPPC molar fraction. The findings of our investigation may be applied to rationalize the effect of the nanoparticles electrostatic interaction in solution environments for the design of new drug carriers combining dendrimeric and liposomal technology.

Soft Interaction in Liposome Nanocarriers for Therapeutic Drug Delivery

The development of smart nanocarriers for the delivery of therapeutic drugs has experienced considerable expansion in recent decades, with the development of new medicines devoted to cancer treatment. In this respect a wide range of strategies can be developed by employing liposome nanocarriers with desired physico-chemical properties that, by exploiting a combination of a number of suitable soft interactions, can facilitate the transit through the biological barriers from the point of administration up to the site of drug action. As a result, the materials engineer has generated through the bottom up approach a variety of supramolecular nanocarriers for the encapsulation and controlled delivery of therapeutics which have revealed beneficial developments for stabilizing drug compounds, overcoming impediments to cellular and tissue uptake, and improving biodistribution of therapeutic compounds to target sites. Herein we present recent advances in liposome drug delivery by analyzing the main structural features of liposome nanocarriers which strongly influence their interaction in solution. More specifically, we will focus on the analysis of the relevant soft interactions involved in drug delivery processes which are responsible of main behaviour of soft nanocarriers in complex physiological fluids. Investigation of the interaction between liposomes at the molecular level can be considered an important platform for the modeling of the molecular recognition processes occurring between cells. Some relevant strategies to overcome the biological barriers during the drug delivery of the nanocarriers are presented which outline the main structure-properties relationships as well as their advantages (and drawbacks) in therapeutic and biomedical applications.