The anti-inflammatory drug indomethacin alters nanoclustering in synthetic and cell plasma membranes

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.

A Biomimetic Multiparametric Assay to Characterise Anti-Amyloid Drugs

Alzheimer's disease (AD) is the most widespread form of senile dementia worldwide and represents a leading socioeconomic problem in healthcare. Although it is widely debated, the aggregation of the amyloid β peptide (Aβ) is linked to the onset and progression of this neurodegenerative disease. Molecules capable of interfering with specific steps in the fibrillation process remain of pharmacological interest. To identify such compounds, we have set up a small molecule screening process combining multiple experimental methods (UV and florescence spectrometry, ITC, and ATR-FTIR) to identify and characterise potential modulators of Aβ1-42 fibrillation through the description of the biochemical interactions (molecule-membrane Aβ peptide). Three known modulators, namely bexarotene, Chicago sky blue and indomethacin, have been evaluated through this process, and their modulation mechanism in the presence of a biomembrane has been described. Such a well-adapted physico-chemical approach to drug discovery proves to be an undeniable asset for the rapid characterisation of compounds of therapeutic interest for Alzheimer's disease. This strategy could be adapted and transposed to search for modulators of other amyloids such as tau protein.

Aspirin Interacts with Cholesterol-Containing Membranes in a pH-Dependent Manner

Aspirin has been used for broad therapeutic treatment, including secondary prevention of cardiovascular disease associated with increased cholesterol levels. Aspirin and other nonsteroidal anti-inflammatory drugs have been shown to interact with lipid membranes and change their biophysical properties. In this study, mixed lipid model bilayers made from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) or 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) comprising varying concentrations of cholesterol (10:1, 4:1, and 1:1 mole ratio of lipid:chol), prepared by the droplet interface bilayer method, were used to examine the effects of aspirin at various pH on transbilayer water permeability. The presence of aspirin increases the water permeability of POPC bilayers in a concentration-dependent manner, with a greater magnitude of increase at pH 3 compared to pH 7. In the presence of cholesterol, aspirin is similarly shown to increase water permeability; however, the extent of the increase depends on both the concentration of cholesterol and the pH, with the least pronounced enhancement in water permeability at high cholesterol levels at pH 7. A fusion of data from differential scanning calorimetry, confocal Raman microspectrophotometry, and interfacial tensiometric measurements demonstrates that aspirin can promote significant thermal, structural, and interfacial property perturbations in the mixed-lipid POPC or DOPC membranes containing cholesterol, indicating a disordering effect on the lipid membranes. Our findings suggest that aspirin fluidizes phosphocholine membranes in both cholesterol-free and cholesterol-enriched states and that the overall effect is greater when aspirin is in a neutral state. These results confer a deeper comprehension of the divergent effects of aspirin on biological membranes having heterogeneous compositions, under varying physiological pH and different cholesterol compositions, with implications for a better understanding of the gastrointestinal toxicity induced by the long term use of this important nonsteroidal anti-inflammatory molecule.

Insight into the effect of ibuprofen on the permeability of the membrane: a molecular dynamic simulation study

Studying interactions between drugs and cell membranes is of great interest to designing novel drugs, optimizing drug delivery, and discerning drug mechanism action. In this study, we investigated the physical properties of the bilayer membrane model of POPC upon interaction with ibuprofen (IBU) using molecular dynamics simulations. The area per lipid (APL) was calculated to describe the effect of ibuprofen on the packing properties of the lipid bilayer. The APL was 0.58 nm2 and 0.63 nm2 for the membrane in low and high IBU respectively, and 0.57 nm2 for the membrane without IBU. Our finding showed that the mean square deviation (MSD) increased with increased ibuprofen content. In addition, the order parameter for the hydrocarbon chain of lipids increased with increased ibuprofen content. There was an increment in the transfer free energy after the head group region while it was maximum in the hydrophobic core for hydrogen peroxide (H2O2) (∼6.2 kcal.mol-1) and H2O (∼3.4 kcal.mol-1) which then decreased to respective values of (∼4.6 kcal.mol-1), and (∼2.3 kcal.mol-1) at the center of the bilayer in the presence of IBU. It seems that in the presence of ibuprofen, the free energy profile of the permeability of water and H2O2 significantly decreased. These findings show that ibuprofen significantly influences the physical properties of the bilayer by decreasing the packing and intermolecular interaction in the hydrocarbon chain region and increasing the water permeability of the bilayer. These results may provide insights into the local cytotoxic side effects of ibuprofen and its underlying molecular mechanisms.Communicated by Ramaswamy H. Sarma.

Spin-Labeled Diclofenac: Synthesis and Interaction with Lipid Membranes

Diclofenac is a non-steroidal anti-inflammatory drug (NSAID) from the group of phenylacetic acid derivatives, which has analgesic, anti-inflammatory and antipyretic properties. The interaction of non-steroidal anti-inflammatory drugs with cell membranes can affect their physicochemical properties, which, in turn, can cause a number of side effects in the use of these drugs. Electron paramagnetic resonance (EPR) spectroscopy could be used to study the interaction of diclofenac with a membrane, if its spin-labeled analogs existed. This paper describes the synthesis of spin-labeled diclofenac (diclofenac-SL), which consists of a simple sequence of transformations such as iodination, esterification, Sonogashira cross-coupling, oxidation and saponification. EPR spectra showed that diclofenac-SL binds to a lipid membrane composed of palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). 2H electron spin echo spectroscopy (ESEEM) was used to determine the position of the diclofenac-SL relative to the membrane surface. It was established that its average depth of immersion corresponds to the 5th position of the carbon atom in the lipid chain.

RAS nanoclusters are cell surface transducers that convert extracellular stimuli to intracellular signalling

Mutations of rat sarcoma virus (RAS) oncogenes (HRAS, KRAS and NRAS) can contribute to the development of cancers and genetic disorders (RASopathies). The spatiotemporal organization of RAS is an important property that warrants further investigation. In order to function, wild-type or oncogenic mutants of RAS must be localized to the inner leaflet of the plasma membrane (PM), which is driven by interactions between their C-terminal membrane-anchoring domains and PM lipids. The isoform-specific RAS-lipid interactions promote the formation of nanoclusters on the PM. As main sites for effector recruitment, these nanoclusters are biologically important. Since the spatial distribution of lipids is sensitive to changing environments, such as mechanical and electrical perturbations, RAS nanoclusters act as transducers to convert external stimuli to intracellular mitogenic signalling. As such, effective inhibition of RAS oncogenesis requires consideration of the complex interplay between RAS nanoclusters and various cell surface and extracellular stimuli. In this review, we discuss in detail how, by sorting specific lipids in the PM, RAS nanoclusters act as transducers to convert external stimuli into intracellular signalling.

Assessment of Pharmacological Potential of Novel Exopolysaccharide Isolated from Marine Kocuria sp. Strain AG5: Broad-Spectrum Biological Investigations

With more than 17 clinically approved Drugs and over 20 prodrugs under clinical investigations, marine bacteria are believed to have a potential supply of innovative therapeutic bioactive compounds. In the current study, Kocuria sp. strain AG5 isolated from the Red Sea was identified and characterized by biochemical and physiological analysis, and examination of a phylogenetic 16S rRNA sequences. Innovative exopolysaccharide (EPS) was separated from the AG5 isolate as a major fraction of EPS (EPSR5, 6.84 g/L⁻¹). The analysis of EPSR5 revealed that EPSR5 has a molecular weight (Mw) of 4.9 × 10⁴ g/mol and number average molecular weight (Mn) of 5.4 × 10⁴ g/mol and contains sulfate (25.6%) and uronic acid (21.77%). Analysis of the monosaccharide composition indicated that the EPSR5 fraction composes of glucose, galacturonic acid, arabinose, and xylose in a molar ratio of 2.0:0.5:0.25:1.0, respectively. Assessment of the pharmacological potency of EPSR5 was explored by examining its cytotoxicity, anti-inflammatory, antioxidant, and anti-acetylcholine esterase influences. The antioxidant effect of EPSR5 was dose- and time-dependently increased and the maximum antioxidant activity (98%) was observed at 2000 µg/mL after 120 min. Further, EPSR5 displayed a significant repressive effect regarding the proliferation of HepG-2, A-549, HCT-116, MCF7, HEP2, and PC3 cells with IC₅₀ 453.46 ± 21.8 µg/mL, 873.74 ± 15.4 µg/mL, 788.2 ± 32.6 µg/mL, 1691 ± 44.2 µg/mL, 913.1 ± 38.8 µg/mL, and 876.4 ± 39.8 µg/mL, respectively. Evaluation of the inhibitory activity of the anti-inflammatory activity of EPSR5 indicated that EPSR5 has a significant inhibitory activity toward lipoxygenase (5-LOX) and cyclooxygenase (COX-2) activities (IC₅₀ 15.39 ± 0.82 µg/mL and 28.06 ± 1.1 µg/mL, respectively). Finally, ESPR5 presented a substantial hemolysis suppressive action with an IC₅₀ of 65.13 ± 0.89 µg /mL, and a considerable inhibitory activity toward acetylcholine esterase activity (IC₅₀ 797.02 μg/mL). Together, this study reveals that secondary metabolites produced by Kocuria sp. strain AG5 marine bacteria serve as an important source of pharmacologically active compounds, and their impact on human health is expected to grow with additional global work and research.

Ibuprofen and the Phosphatidylcholine Bilayer: Membrane Water Permeability in the Presence and Absence of Cholesterol

The interactions between drugs and cell membranes can modulate the structural and physical properties of membranes. The resultant perturbations of the membrane integrity may affect the conformation of the proteins inserted within the membrane, disturbing the membrane-hosted biological functions. In this study, the droplet interface bilayer (DIB), a model cell membrane, is used to examine the effects of ibuprofen, a nonsteroidal anti-inflammatory drug (NSAID), on transbilayer water permeability, which is a fundamental membrane biophysical property. Our results indicate that the presence of neutral ibuprofen (pH 3) increases the water permeability of the lipid membranes composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). When cholesterol is present with the DOPC, however, the water permeability is not influenced by addition of ibuprofen, regardless of the cholesterol content in DOPC. Given the fact that cholesterol is generally considered to impact packing in the hydrocarbon chain regions, our findings suggest that a potential competition between opposing effects of ibuprofen molecules and cholesterol on the hydrocarbon core environment of the phospholipid assembly may influence the overall water transport phenomena. Results from confocal Raman microspectroscopy and interfacial tensiometry show that ibuprofen molecules induce substantial structural and dynamic changes in the DOPC lipid bilayer. These results, demonstrating that the presence of ibuprofen increases the water permeability of pure DOPC but not that of DOPC-cholesterol mixtures, provide insight into the differential effect of a representative NSAID on heterogeneous biological membranes, depending upon the local composition and structure, results which will signal increased understanding of the gastrointestinal damage and toxicity induced by these molecules.

Interactions of Non-steroidal Anti-inflammatory Drugs and Their Bismuth Analogues (BiNSAIDs) with Biological Membrane Mimics at Physiological pH

Previous studies have demonstrated the potential for non-steroidal anti-inflammatory drugs (NSAIDs), in particular aspirin, to be used as chemopreventives for colorectal cancer; however, a range of unwanted gastrointestinal side effects limit their effectiveness. Due to the role of bismuth in the treatment of gastrointestinal disorders, it is hypothesized that bismuth-coordinated NSAIDs (BiNSAIDs) could be used to combat the gastrointestinal side effects of NSAIDs while still maintaining their chemopreventive potential. To further understand the biological activity of these compounds, the present study examined four NSAIDs, namely, tolfenamic acid (tolfH), aspirin (aspH), indomethacin (indoH), and mefenamic acid (mefH) and their analogous homoleptic BiNSAIDs ([Bi(L)₃]_n), to determine how these compounds interact with biological membrane mimics composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) or a mixture of POPC and cholesterol. Electrical impedance spectroscopy studies revealed that each of the NSAIDs and BiNSAIDs influenced membrane conductance, suggesting that temporary pore formation may play a key role in the previously observed cytotoxicity of tolfH and Bi(tolf)₃. Quartz crystal microbalance with dissipation monitoring showed that all the compounds were able to interact with membrane mimics composed of solely POPC or POPC/cholesterol. Finally, neutron reflectometry studies showed changes in membrane thickness and composition. The location of the compounds within the bilayer could not be determined with certainty; however, a complex interplay of interactions governs the location of small molecules, such as NSAIDs, within lipid membranes. The charged nature of the parent NSAIDs means that interactions with the polar headgroup region are most likely with larger hydrophobic sections, potentially leading to deeper penetration.

Dioctadecyldimethylammonium bromide, a surfactant model for the cell membrane: Importance of microscopic dynamics

Cationic lipid membranes have recently attracted huge attention both from a fundamental point of view and due to their practical applications in drug delivery and gene therapy. The dynamical behavior of the lipids in the membrane is a key parameter controlling various physiological processes and drug release kinetics. Here, we review the dynamical and thermotropic phase behavior of an archetypal cationic lipid membrane, dioctadecyldimethylammonium bromide (DODAB), as studied using neutron scattering and molecular dynamics simulation techniques. DODAB membranes exhibit interesting phase behavior, specifically showing coagel, gel, and fluid phases in addition to a large hysteresis when comparing heating and cooling cycles. The dynamics of the lipid membrane is strongly dependent on the physical state of the bilayer. Lateral diffusion of the lipids is faster, by an order of magnitude, in the fluid phase than in the ordered phase. It is not only the characteristic times but also the nature of the segmental motions that differ between the ordered and fluid phases. The effect of different membrane active molecules including drugs, stimulants, gemini surfactants, and unsaturated lipids, on the dynamical and thermotropic phase behavior of the DODAB membrane, is also discussed here. Various interesting features such as induced synchronous ordering between polar head groups and tails, sub diffusive behavior, etc., are observed. The results shed light on the interaction between these additives and the membrane, which is found to be a complex interplay between the physical state of the membrane, charge, concentration, molecular architecture of the additives, and their location within the membrane.

Growth inhibitory effects of PC-NSAIDs on human breast cancer subtypes in cell culture

The potential role of non-steroidal anti-inflammatory drug (NSAID) therapy in the prevention and treatment of cancer has generated considerable research interest. Phosphatidylcholine (PC)-associated NSAIDs decrease the gastrointestinal side effects of NSAID therapy, and may be more effective than traditional NSAIDs in limiting tumor growth. In the present study, human cells representing three major breast cancer subtypes were cultured with aspirin, indomethacin and PC-associated forms of each drug, with PC alone as a control. All tested drugs decreased the tumor cell number after 8 days of culture, with PC-NSAIDs having the greatest inhibitory effect, and NSAIDs alone, particularly aspirin, having the least effect. PC alone was effective in limiting the proliferation of all cell lines, suggesting that the two components of PC-NSAIDs have an additive effect. The ELISA results did not support a strong role for inhibition of cyclooxygenase enzymes in the decrease in cancer cell proliferation, which may account for the limited effectiveness of aspirin alone. PC-NSAIDs, particularly indomethacin-PC, are attractive candidate drugs in the prevention and treatment of different types of breast cancer, including triple negative breast cancer.

Dynamic Landscape in Self-Assembled Surfactant Aggregates

A process in which a disordered system of pre-existing molecules generates an organized structure through specific, local interactions among the molecules themselves is termed molecular self-assembly. Micelles, microemulsions, and vesicles are examples of such self-assembled systems where amphiphilic molecules are involved. As the functional properties of these systems (such as wetting and emulsification, release of solubilized drugs, etc.) are dictated by the dynamic behavior of the surfactants at the molecular level, it is of immense interest to investigate these systems for the same. The dynamics in soft matter systems is quite complex, involving different time and length scales. We used a combination of neutron scattering and molecular dynamics simulation studies in probing the dynamic landscape in various self-assembled surfactant aggregates. Neutron scattering experiments were carried out using several spectrometers covering a wide dynamic range to probe motions on different time scales. The interaction between the surfactants can be varied by changing the molecular architecture, counterion concentration, temperature, and so forth. It is important to study the effect of these parameters on the dynamics of surfactants in these aggregates. We have carried out experiments on various ionic (anionic as well as cationic) micelles with varied counterion concentrations, vesicles, and lipid bilayers to unravel the complex dynamic features present in these systems. In this feature article, we will discuss some important results of our recent work on dynamics in these self-assembled surfactant aggregates.

Effects of NSAIDs on the Dynamics and Phase Behavior of DODAB Bilayers

Despite well-known side effects, nonsteroidal anti-inflammatory drugs (NSAIDs) are one of the most prescribed drugs worldwide for their anti-inflammatory and antipyretic properties. Here, we report the effects of two NSAIDs, aspirin and indomethacin, on the thermotropic phase behavior and the dynamics of a dioctadecyldimethylammonium bromide (DODAB) lipid bilayer as studied using neutron scattering techniques. Elastic fixed window scans showed that the addition of aspirin and indomethacin affects the phase behavior of a DODAB bilayer in both heating and cooling cycles. Upon heating, there is a change in the coagel- to fluid-phase transition temperature from 327 K for pure DODAB bilayer to 321 and 323 K in the presence of aspirin and indomethacin, respectively. More strikingly, upon cooling, the addition of NSAIDs suppresses the formation of the intermediate gel phase observed in pure DODAB. The suppression of the gel phase on addition of the NSAIDs evidences the synchronous ordering of a lipid headgroup and chain. Analysis of quasi-elastic neutron scattering data showed that only localized internal motion exists in the coagel phase, whereas both internal and lateral motions exist in the fluid phase. The internal motion is described by a fractional uniaxial rotational diffusion model in the coagel phase and by a localized translation diffusion model in the fluid phase. In the coagel phase, the rotational diffusion coefficient of DODAB is found to be almost twice for the addition of the drugs, whereas the mobility fraction did not change for indomethacin but becomes twice for aspirin. In the fluid phase, the lateral motion, described well by a continuous diffusion model, is found to be slower by about ∼30% for indomethacin but almost no change for aspirin. For the internal motion, addition of aspirin leads to enhancement of the internal motion, whereas indomethacin did not show significant effect. This study shows that the effect of different NSAIDs on the dynamics of the lipid membrane is not the same; hence, one must consider these NSAIDs individually while studying their action mechanism on the cell membrane.

Differential targeting of membrane lipid domains by caffeic acid and its ester derivatives

Phenolic acids have been associated to a wide range of important health benefits underlain by a common molecular mechanism of action. Considering that significant membrane permeation is prevented by their hydrophilic character, we hypothesize that their main effects result from the interplay with cell membrane surface. This hypothesis was tested using the paradigmatic caffeic acid (CA) and two of its ester derivatives, rosmarinic (RA) and chlorogenic (CGA) acids, for which we predict, based on molecular dynamics simulations, a shallow location in phospholipid bilayers dependent on the protonation-state. Using complementary experimental approaches, an interaction with the membrane was definitely revealed for the three compounds, with RA exhibiting the highest lipid bilayer partition, and the redox signals of membrane-bound RA and CA being clearly detected. Cholesterol decreased the compounds bilayer partition, but not their ability to lower membrane dipole potential. In more complex membrane models containing also sphingomyelin, with liquid disordered (ld)/ liquid ordered (lo) phases coexistence, mimicking domains in the external leaflet of human plasma membrane, all compounds were able to affect nanodomains lateral organization. RA, and to a lesser extent CGA, decreased the size of lo domains. The most significant effect of CA was the possible formation of a rigid gel-like phase, enriched in sphingomyelin. In addition, all phenolic acids decreased the order of lo domains. In sum, phenolic acid effects on the membrane are enhanced in cholesterol-rich lo phases, which predominate in the outer leaflet of human cell membranes and are involved in many key cellular processes.

Thermodynamics of Indomethacin Adsorption to Phospholipid Membranes

Using second-harmonic generation, we directly monitored adsorption of indomethacin, a nonsteroidal anti-inflammatory drug, to supported lipid bilayers composed of phospholipids of varying phase, cholesterol content, and head group charge without the use of extrinsic labels at therapeutically relevant aqueous concentrations. Indomethacin adsorbed to gel-phase lipids with a high binding affinity, suggesting that like other arylacetic acid-containing drugs, it preferentially interacts with ordered lipid domains. We discovered that adsorption of indomethacin to gel-phase phospholipids was endothermic and entropically driven, whereas adsorption to fluid-phase phospholipids was exothermic and enthalpically driven. As temperature increased from 19 to 34 °C, binding affinities to gel-phase lipids increased by 7-fold but relative surface concentration decreased to one-fifth of the original value. We also compared our results to the entropies reported for indomethacin adsorbed to surfactant micelles, which are used in drug delivery systems, and assert that adsorbed water molecules in the phospholipid bilayer may be buried deeper into the acyl chains and less accessible for disruption. The thermodynamic studies reported here provide mechanistic insight into indomethacin interactions with mammalian plasma membranes in the gastrointestinal tract and inform studies of drug delivery, where indomethacin is commonly used as a prototypical, hydrophobic small-molecule drug.

The Lipid Bilayer Provides a Site for Cortisone Crystallization at High Cortisone Concentrations

Cortisone is an injected anti-inflammatory drug that can cause painful side effects known as "steroid flares" which are caused by cortisone crystallizing at the injection site. We used molecular dynamics simulations and X-ray diffraction to study the interaction of cortisone with model lipid membranes made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) at drug concentrations from 0 mol% to 50 mol%. Cortisone was found to partition in the lipid bilayer and locate in the hydrophilic to hydrophobic interface of the membranes. Cortisone strongly affects the integrity of the membrane, as quantified by a decreased membrane thickness, increased area per lipid, and decreased lipid tail order parameters. At cortisone concentrations of more than 20 mol%, signals from crystallized cortisone were observed. These crystallites are embedded in the bilayers and orient with the membranes. While the cortisone molecules align parallel to the bilayers at low concentrations, they start to penetrate the hydrophobic core at higher concentrations. Trans-membrane crystallites start to nucleate when the membrane thickness has decreased such that cortisone molecules in the different leaflets can find partners from the opposite leaflet resulting in a non-zero density of cortisone molecules in the bilayer center. We suggest that the lipid bilayer provides a site for cortisone crystallization.

Usefulness of targeting lymphocyte Kv1.3-channels in the treatment of respiratory diseases

T lymphocytes predominantly express delayed rectifier K(+)-channels (Kv1.3) in their plasma membranes. Patch-clamp studies revealed that the channels play crucial roles in facilitating the calcium influx necessary to trigger lymphocyte activation and proliferation. Using selective channel inhibitors in experimental animal models, in vivo studies further revealed the clinically relevant relationship between the channel expression and the development of chronic respiratory diseases, in which chronic inflammation or the overstimulation of cellular immunity in the airways is responsible for the pathogenesis. In chronic respiratory diseases, such as chronic obstructive pulmonary disease, asthma, diffuse panbronchiolitis and cystic fibrosis, in addition to the supportive management for the symptoms, the anti-inflammatory effects of macrolide antibiotics were shown to be effective against the over-activation or proliferation of T lymphocytes. Recently, we provided physiological and pharmacological evidence that macrolide antibiotics, together with calcium channel blockers, HMG-CoA reductase inhibitors, and nonsteroidal anti-inflammatory drugs, effectively suppress the Kv1.3-channel currents in lymphocytes, and thus exert anti-inflammatory or immunomodulatory effects. In this review article, based on the findings obtained from recent in vivo and in vitro studies, we address the novel therapeutic implications of targeting the lymphocyte Kv1.3-channels for the treatment of chronic or acute respiratory diseases.

Cholesterol expels ibuprofen from the hydrophobic membrane core and stabilizes lamellar phases in lipid membranes containing ibuprofen

There is increasing evidence that common drugs, such as aspirin and ibuprofen, interact with lipid membranes. Ibuprofen is one of the most common over the counter drugs in the world, and is used for relief of pain and fever. It interacts with the cyclooxygenase pathway leading to inhibition of prostaglandin synthesis. From X-ray diffraction of highly oriented model membranes containing between 0 and 20 mol% ibuprofen, 20 mol% cholesterol, and dimyristoylphosphatidylcholine (DMPC), we present evidence for a non-specific interaction between ibuprofen and cholesterol in lipid bilayers. At a low ibuprofen concentrations of 2 mol%, three different populations of ibuprofen molecules were found: two in the lipid head group region and one in the hydrophobic membrane core. At higher ibuprofen concentrations of 10 and 20 mol%, the lamellar bilayer structure is disrupted and a lamellar to cubic phase transition was observed. In the presence of 20 mol% cholesterol, ibuprofen (at 5 mol%) was found to be expelled from the membrane core and reside solely in the head group region of the bilayers. 20 mol% cholesterol was found to stabilize lamellar membrane structure and the formation of a cubic phase at 10 and 20 mol% ibuprofen was suppressed. The results demonstrate that ibuprofen interacts with lipid membranes and that the interaction is strongly dependent on the presence of cholesterol.

Trace membrane additives affect lipid phases with distinct mechanisms: a modified Ising model

The addition of trace molecules into membranes can significantly alter the morphology of the co-existing liquid phases and lipid phase transition temperature. Membrane additives may affect lipid phase dynamics through preferentially partitioning to the boundary between lipid phases or preferentially mixing into one lipid phase. The characteristic differences between these mechanisms are demonstrated here in a minimalistic nearest neighbor model to provide a framework for how slight changes to membrane composition may affect lipid-phase-dependent processes, such as lipid-raft formation, immunological signaling, and molecular sorting preceding endocytosis with coexisting liquid phases. Within the low mole fractions explored here (≤3 mol%), increasing the additive concentration linearly changed the phase miscibility temperature. Rotationally asymmetric Janus particles reduced the miscibility transition temperature for all fractions and degree of phase polarization. Rotationally symmetric additives, however, either increased or decreased the phase miscibility temperature depending on the phase preference of the additive. While most experimental molecules may contain aspects of both of these idealized additives, this model provides a broad framework to quantify the effects of membrane additives in regard to lipid phase preference, lipid-raft association, and contribution to lipid phase-dependent molecular sorting.

Rab-NANOPS: FRET biosensors for Rab membrane nanoclustering and prenylation detection in mammalian cells

Rab proteins constitute the largest subfamily of Ras-like small GTPases. They are central to vesicular transport and organelle definition in eukaryotic cells. Unlike their Ras counterparts, they are not a hallmark of cancer. However, a number of diseases, including cancer, show a misregulation of Rab protein activity. As for all membrane-anchored signaling proteins, correct membrane organization is critical for Rabs to operate. In this chapter, we provide a detailed protocol for the use of a flow cytometry-based Fluorescence Resonance Energy Transfer (FRET)-biosensors assay, which allows to detect changes in membrane anchorage, subcellular distribution, and of the nanoscale organization of Rab-GTPases in mammalian cell lines. This assay is high-throughput amenable and can therefore be utilized in chemical-genomic and drug discovery efforts.

Ras nanoclusters: Versatile lipid-based signaling platforms

Ras proteins assemble into transient nanoclusters on the plasma membrane. Nanoclusters are the sites of Ras effector recruitment and activation and are therefore essential for signal transmission. The dynamics of nanocluster formation and disassembly result in interesting emergent properties including high-fidelity signal transmission. More recently the lipid structure of Ras nanoclusters has been reported and shown to contribute to isoform-specific Ras signaling. In addition specific lipids play critical roles in mediating the formation, stability and dynamics of Ras nanoclusters. In consequence the spatiotemporal organization of these lipids has emerged as important and novel regulators of Ras function. This article is part of a Special Issue entitled: Nanoscale membrane organisation and signalling.

Liquid general anesthetics lower critical temperatures in plasma membrane vesicles

A large and diverse array of small hydrophobic molecules induce general anesthesia. Their efficacy as anesthetics has been shown to correlate both with their affinity for a hydrophobic environment and with their potency in inhibiting certain ligand-gated ion channels. In this study we explore the effects that n-alcohols and other liquid anesthetics have on the two-dimensional miscibility critical point observed in cell-derived giant plasma membrane vesicles (GPMVs). We show that anesthetics depress the critical temperature (Tc) of these GPMVs without strongly altering the ratio of the two liquid phases found below Tc. The magnitude of this affect is consistent across n-alcohols when their concentration is rescaled by the median anesthetic concentration (AC50) for tadpole anesthesia, but not when plotted against the overall concentration in solution. At AC50 we see a 4°C downward shift in Tc, much larger than is typically seen in the main chain transition at these anesthetic concentrations. GPMV miscibility critical temperatures are also lowered to a similar extent by propofol, phenylethanol, and isopropanol when added at anesthetic concentrations, but not by tetradecanol or 2,6 diterbutylphenol, two structural analogs of general anesthetics that are hydrophobic but have no anesthetic potency. We propose that liquid general anesthetics provide an experimental tool for lowering critical temperatures in plasma membranes of intact cells, which we predict will reduce lipid-mediated heterogeneity in a way that is complimentary to increasing or decreasing cholesterol. Also, several possible implications of our results are discussed in the context of current models of anesthetic action on ligand-gated ion channels.

Caveolae regulate the nanoscale organization of the plasma membrane to remotely control Ras signaling

Caveolae transduce mechanical stress into plasma membrane lipid alterations that disrupt Ras organization in an isoform-specific manner and modulate downstream signal transduction.

The molecular mechanisms whereby caveolae exert control over cellular signaling have to date remained elusive. We have therefore explored the role caveolae play in modulating Ras signaling. Lipidomic and gene array analyses revealed that caveolin-1 (CAV1) deficiency results in altered cellular lipid composition, and plasma membrane (PM) phosphatidylserine distribution. These changes correlated with increased K-Ras expression and extensive isoform-specific perturbation of Ras spatial organization: in CAV1-deficient cells K-RasG12V nanoclustering and MAPK activation were enhanced, whereas GTP-dependent lateral segregation of H-Ras was abolished resulting in compromised signal output from H-RasG12V nanoclusters. These changes in Ras nanoclustering were phenocopied by the down-regulation of Cavin1, another crucial caveolar structural component, and by acute loss of caveolae in response to increased osmotic pressure. Thus, we postulate that caveolae remotely regulate Ras nanoclustering and signal transduction by controlling PM organization. Similarly, caveolae transduce mechanical stress into PM lipid alterations that, in turn, modulate Ras PM organization.

Bile acids modulate signaling by functional perturbation of plasma membrane domains

Eukaryotic cell membranes are organized into functional lipid and protein domains, the most widely studied being membrane rafts. Although rafts have been associated with numerous plasma membrane functions, the mechanisms by which these domains themselves are regulated remain undefined. Bile acids (BAs), whose primary function is the solubilization of dietary lipids for digestion and absorption, can affect cells by interacting directly with membranes. To investigate whether these interactions affected domain organization in biological membranes, we assayed the effects of BAs on biomimetic synthetic liposomes, isolated plasma membranes, and live cells. At cytotoxic concentrations, BAs dissolved synthetic and cell-derived membranes and disrupted live cell plasma membranes, implicating plasma membrane damage as the mechanism for BA cellular toxicity. At subtoxic concentrations, BAs dramatically stabilized domain separation in Giant Plasma Membrane Vesicles without affecting protein partitioning between coexisting domains. Domain stabilization was the result of BA binding to and disordering the nonraft domain, thus promoting separation by enhancing domain immiscibility. Consistent with the physical changes observed in synthetic and isolated biological membranes, BAs reorganized intact cell membranes, as evaluated by the spatial distribution of membrane-anchored Ras isoforms. Nanoclustering of K-Ras, related to nonraft membrane domains, was enhanced in intact plasma membranes, whereas the organization of H-Ras was unaffected. BA-induced changes in Ras lateral segregation potentiated EGF-induced signaling through MAPK, confirming the ability of BAs to influence cell signal transduction by altering the physical properties of the plasma membrane. These observations suggest general, membrane-mediated mechanisms by which biological amphiphiles can produce their cellular effects.

Interaction of nonsteroidal anti-inflammatory drugs with membranes: in vitro assessment and relevance for their biological actions

Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most commonly used drugs in the world due to their anti-inflammatory, analgesic and antipyretic properties. Nevertheless, the consumption of these drugs is still associated with the occurrence of a wide spectrum of adverse effects. Regarding the major role of membranes in cellular events, the hypothesis that the biological actions of NSAIDs may be related to their effect at the membrane level has triggered the in vitro assessment of NSAIDs-membrane interactions. The use of membrane mimetic models, cell cultures, a wide range of experimental techniques and molecular dynamics simulations has been providing significant information about drugs partition and location within membranes and also about their effect on diverse membrane properties. These studies have indeed been providing evidences that the effect of NSAIDs at membrane level may be an additional mechanism of action and toxicity of NSAIDs. In fact, the pharmacokinetic properties of NSAIDs are closely related to the ability of these drugs to interact and overcome biological membranes. Moreover, the therapeutic actions of NSAIDs may also result from the indirect inhibition of cyclooxygenase due to the disturbing effect of NSAIDs on membrane properties. Furthermore, increasing evidences suggest that the disordering effects of these drugs on membranes may be in the basis of the NSAIDs-induced toxicity in diverse organ systems. Overall, the study of NSAIDs-membrane interactions has proved to be not only important for the better understanding of their pharmacological actions, but also for the rational development of new approaches to overcome NSAIDs adverse effects.

Advent of novel phosphatidylcholine-associated nonsteroidal anti-inflammatory drugs with improved gastrointestinal safety

The mucosa of the gastrointestinal (GI) tract exhibits hydrophobic, nonwettable properties that protect the underlying epithelium from gastric acid and other luminal toxins. These biophysical characteristics appear to be attributable to the presence of an extracellular lining of surfactant-like phospholipids on the luminal aspects of the mucus gel layer. Phosphatidylcholine (PC) represents the most abundant and surface-active form of gastric phospholipids. PC protected experimental rats from a number of ulcerogenic agents and/or conditions including nonsteroidal anti-inflammatory drugs (NSAIDs), which are chemically associated with PC. Moreover, preassociating a number of the NSAIDs with exogenous PC prevented a decrease in the hydrophobic characteristics of the mucus gel layer and protected rats against the injurious GI side effects of NSAIDs while enhancing and/or maintaining their therapeutic activity. Bile plays an important role in the ability of NSAIDs to induce small intestinal injury. NSAIDs are rapidly absorbed from the GI tract and, in many cases, undergo enterohepatic circulation. Thus, NSAIDs with extensive enterohepatic cycling are more toxic to the GI tract and are capable of attenuating the surface hydrophobic properties of the mucosa of the lower GI tract. Biliary PC plays an essential role in the detoxification of bile salt micelles. NSAIDs that are secreted into the bile injure the intestinal mucosa via their ability to chemically associate with PC, which forms toxic mixed micelles and limits the concentration of biliary PC available to interact with and detoxify bile salts. We have worked to develop a family of PC-associated NSAIDs that appear to have improved GI safety profiles with equivalent or better therapeutic efficacy in both rodent model systems and pilot clinical trials.

Fendiline inhibits K-Ras plasma membrane localization and blocks K-Ras signal transmission

Ras proteins regulate signaling pathways important for cell growth, differentiation, and survival. Oncogenic mutant Ras proteins are commonly expressed in human tumors, with mutations of the K-Ras isoform being most prevalent. To be active, K-Ras must undergo posttranslational processing and associate with the plasma membrane. We therefore devised a high-content screening assay to search for inhibitors of K-Ras plasma membrane association. Using this assay, we identified fendiline, an L-type calcium channel blocker, as a specific inhibitor of K-Ras plasma membrane targeting with no detectable effect on the localization of H- and N-Ras. Other classes of L-type calcium channel blockers did not mislocalize K-Ras, suggesting a mechanism that is unrelated to calcium channel blockade. Fendiline did not inhibit K-Ras posttranslational processing but significantly reduced nanoclustering of K-Ras and redistributed K-Ras from the plasma membrane to the endoplasmic reticulum (ER), Golgi apparatus, endosomes, and cytosol. Fendiline significantly inhibited signaling downstream of constitutively active K-Ras and endogenous K-Ras signaling in cells transformed by oncogenic H-Ras. Consistent with these effects, fendiline blocked the proliferation of pancreatic, colon, lung, and endometrial cancer cell lines expressing oncogenic mutant K-Ras. Taken together, these results suggest that inhibitors of K-Ras plasma membrane localization may have utility as novel K-Ras-specific anticancer therapeutics.

Aspirin-induced microscopic surface changes stimulate thrombopoiesis in rat megakaryocytes

During the process of thrombopoiesis, invaginations of the plasma membrane occur in megakaryocytes. Since acetylsalicylic acid (aspirin), the most commonly used anti-inflammatory and antiplatelet drug, interacts with the lipid bilayers of the plasma membranes, this drug would affect the process of thrombopoiesis. In the present study, employing a standard patch-clamp whole-cell recording technique, we examined the effects of aspirin on delayed rectifier K(+)-channel (Kv1.3) currents and the membrane capacitance in megakaryocytes. Using confocal imaging of di-8-butyl-amino-naphthyl-ethylene-pyridinium-propyl-sulfonate (di-8-ANEPPS) staining, we also monitored the membrane invaginations in megakaryocytes. Aspirin suppressed both the peak and the pulse-end currents with a significant increase in the membrane capacitance. Massive di-8-ANEPPS staining after treatment with aspirin demonstrated the impaired membrane micro-architecture of megakaryocytes. This study demonstrated for the first time that aspirin induces microscopic surface changes in megakaryocytes. Such surface changes were thought to stimulate thrombopoiesis in megakaryocytes as detected by the increase in the membrane invaginations.

Insight into NSAID-induced membrane alterations, pathogenesis and therapeutics: characterization of interaction of NSAIDs with phosphatidylcholine

Nonsteroidal anti-inflammatory drugs (NSAIDs) are one of the most widely consumed pharmaceuticals, yet both the mechanisms involved in their therapeutic actions and side-effects, notably gastrointestinal (GI) ulceration/bleeding, have not been clearly defined. In this study, we have used a number of biochemical, structural, computational and biological systems including; Fourier Transform InfraRed (FTIR). Nuclear Magnetic Resonance (NMR) and Surface Plasmon Resonance (SPR) spectroscopy, and cell culture using a specific fluorescent membrane probe, to demonstrate that NSAIDs have a strong affinity to form ionic and hydrophobic associations with zwitterionic phospholipids, and specifically phosphatidylcholine (PC), that are reversible and non-covalent in nature. We propose that the pH-dependent partition of these potent anti-inflammatory drugs into the phospholipid bilayer, and possibly extracellular mono/multilayers present on the luminal interface of the mucus gel layer, may result in profound changes in the hydrophobicity, fluidity, permeability, biomechanical properties and stability of these membranes and barriers. These changes may not only provide an explanation of how NSAIDs induce surface injury to the GI mucosa as a component in the pathogenic mechanism leading to peptic ulceration and bleeding, but potentially an explanation for a number of (COX-independent) biological actions of this family of pharmaceuticals. This insight also has proven useful in the design and development of a novel class of PC-associated NSAIDs that have reduced GI toxicity while maintaining their essential therapeutic efficacy to inhibit pain and inflammation.

Nonsteroidal anti-inflammatory drugs alter the spatiotemporal organization of Ras proteins on the plasma membrane

Ras proteins on the inner leaflet of the plasma membrane signal from transient nanoscale proteolipid assemblies called nanoclusters. Interactions between the Ras lipid anchors and plasma membrane phospholipids, cholesterol, and actin cytoskeleton contribute to the formation, stability, and dynamics of Ras nanoclusters. Many small biological molecules are amphiphilic and capable of intercalating into membranes and altering lipid immiscibility. In this study we systematically examined whether amphiphiles such as indomethacin influence Ras protein nanoclustering in intact plasma membrane. We found that indomethacin, a nonsteroidal anti-inflammatory drug, induced profound and complex effects on Ras spatial organization, all likely related to liquid-ordered domain stabilization. Indomethacin enhanced the clustering of H-Ras.GDP and N-Ras.GTP in cholesterol-dependent nanoclusters. Indomethacin also abrogated efficient GTP-dependent lateral segregation of H- and N-Ras between cholesterol-dependent and cholesterol-independent clusters, resulting in mixed heterotypic clusters of Ras proteins that normally are separated spatially. These heterotypic Ras nanoclusters showed impaired Raf recruitment and kinase activation resulting in significantly compromised MAPK signaling. All of the amphiphilic anti-inflammatory agents we tested had similar effects on Ras nanoclustering and signaling. The potency of these effects correlated with the membrane partition coefficients of the individual agents and was independent of COX inhibition. This study shows that biological amphiphiles have wide-ranging effects on plasma membrane heterogeneity and protein nanoclustering, revealing a novel mechanism of drug action that has important consequences for cell signaling.

Suppressive effects of nonsteroidal anti-inflammatory drugs diclofenac sodium, salicylate and indomethacin on delayed rectifier K+-channel currents in murine thymocytes

Lymphocytes predominantly express delayed rectifier K(+)-channels (Kv1.3) in their plasma membranes, and the channels play crucial roles in the lymphocyte activation and proliferation. Since nonsteroidal anti-inflammatory drugs (NSAIDs), the most commonly used analgesic and antipyretic drugs, exert immunomodulatory effects, they would affect the channel currents in lymphocytes. In the present study, employing the standard patch-clamp whole-cell recording technique, we examined the effects of diclofenac sodium, salicylate and indomethacin on the channel currents in murine thymocytes and the membrane capacitance. Diclofenac sodium and salicylate significantly suppressed the pulse-end currents of the channel. However, indomethacin suppressed both the peak and the pulse-end currents with a significant increase in the membrane capacitance. This study demonstrated for the first time that NSAIDs, such as diclofenac sodium, salicylate and indomethacin, exert inhibitory effects on thymocyte Kv1.3-channel currents. The slow inactivation pattern induced by indomethacin was thought to be associated with microscopic changes in the plasma membrane surface detected by the increase in the membrane capacitance.

Ras trafficking, localization and compartmentalized signalling

Ras proteins are proto-oncogenes that are frequently mutated in human cancers. Three closely related isoforms, HRAS, KRAS and NRAS, are expressed in all cells and have overlapping but distinctive functions. Recent work has revealed how differences between the Ras isoforms in their trafficking, localization and protein-membrane orientation enable signalling specificity to be determined. We review the various strategies used to characterize compartmentalized Ras localization and signalling. Localization is an important contextual modifier of signalling networks and insights from the Ras system are of widespread relevance for researchers interested in signalling initiated from membranes.