Grazing Incidence Diffraction and X-ray Reflectivity Studies of the Interactions of Inorganic Mercury Salts with Membrane Lipids in Langmuir Monolayers at the Air/Water Interface

Interactions of Brominated Flame Retardants with Membrane Models of Dehalogenating Bacteria: Langmuir Monolayer and Grazing Incidence X-ray Diffraction Studies

Brominated flame retardants (BFRs) are small organic molecules containing several bromine substituents added to plastics to limit their flammability. BFRs can constitute up to 30% of the weight of some plastics, which is why they are produced in large quantities. Along with plastic waste and microplastic particles, BFRs end up in the soil and can easily leach causing contamination. As polyhalogenated molecules, multiple BFRs were classified as persistent organic pollutants (POPs), meaning that their biodegradation in the soils is especially challenging. However, some anaerobic bacteria as Dehaloccocoides can dehalogenate BFRs, which is important in the bioremediation of contaminated soils. BFRs are hydrophobic, can accumulate in plasma membranes, and disturb their function. On the other hand, limited membrane accumulation is necessary for BFR dehalogenation. To study the BFR-membrane interaction, we created membrane models of soil dehalogenating bacteria and tested their interactions with seven legacy and novel BFRs most common in soils. Phospholipid Langmuir monolayers with appropriate composition were used as membrane models. These membranes were doped in the selected BFRs, and the incorporation of BFR molecules into the phospholipid matrix and also the effects of BFR presence on membrane physical properties and morphology were studied. It turned out that the seven BFRs differed significantly in their membrane affinity. For some, the incorporation was very limited, and others incorporated effectively and could affect membrane properties, while one of the tested molecules induced the formation of bilayer domains in the membranes. Thus, Langmuir monolayers can be effectively used for pretesting BFR membrane activity.

Morphology Observation of Two-Dimensional Monolayers of Model Proteins on Water Surface as Revealed by Dropping Method

We have investigated the morphology of two-dimensional monolayers of gramicidin-D (GD) and alamethicin (Al) formed on the water surface by the dropping method (DM) using surface tension measurement (STm), Brewster angle microscopy (BAM), and atomic force microscopy (AFM). Dynamic light scattering (DLS) revealed that GD in alcoholic solutions formed a dimeric helical structure. According to the CD and NMR spectroscopies, GD molecules existed in dimer form in methanol and lipid membrane environments. The STm results and BAM images revealed that the GD dimer monolayer was in a liquid expanded (LE) state, whereas the Al monolayer was in a liquid condensed (LC) state. The limiting molecular area (A0) was 6.2 ± 0.5 nm2 for the GD-dimer and 3.6 ± 0.5 nm2 for the Al molecule. The AFM images also showed that the molecular long axes of both the GD-dimer and Al were horizontal to the water surface. The stability of each monolayer was confirmed by the time dependence of the surface pressure (π) observed using the STm method. The DM monolayer preparation method for GD-dimer and Al peptide molecules is a useful technique for revealing how the model biological membrane's components assemble in two dimensions on the water surface.

Photoinduced bidirectional switching in lipid membranes containing azobenzene glycolipids

Following the reaction of biological membranes to external stimuli reveals fundamental insights into cellular function. Here, self-assembled lipid monolayers act as model membranes containing photoswitchable azobenzene glycolipids for investigating structural response during isomerization by combining Langmuir isotherms with X-ray scattering. Controlled in-situ trans/cis photoswitching of the azobenzene N = N double bond alters the DPPC monolayer structure, causing reproducible changes in surface pressure and layer thickness, indicating monolayer reorientation. Interestingly, for monolayers containing azobenzene glycolipids, along with the expected DPPC phase transitions an additional discontinuity is observed. The associated reorintation represents a crossover point, with the surface pressure and layer thickness changing in opposite directions above and below. This is evidence that the azobenzene glycolipids themselves change orientation within the monolayer. Such behaviour suggests that azobenzene glycolipids can act as a bidirectional switch in DPPC monolayers providing a tool to investigate membrane structure-function relationships in depth.

“Interplay of lipid-head group and packing defects in driving Amyloid-beta mediated myelin-like model membrane deformation”

Accumulating evidence suggests that amyloid plaque associated myelin lipid loss as a result of elevated amyloid burden might also contribute to Alzheimer's disease. The amyloid fibrils though closely associated with lipids under physiological conditions, however, the progression of membrane remodeling events leading to lipid-fibril assembly remains unknown. Here we first reconstitute the interaction of Aβ-40 with myelin-like model membrane and show that the binding of Aβ-40 induces extensive tubulation. To look into the mechanism of membrane tubulation we chose a set of membrane conditions varying in lipid packing density and net charge that allows us to dissect the contribution of lipid specificity of Aβ-40 binding, aggregation kinetics, and subsequent changes in membrane parameters such as fluidity, diffusion, and compressibility modulus. We show that the binding of Aβ-40 depends predominantly on the lipid packing defect densities and electrostatic interactions and results in rigidification of the myelin-like model membrane during the early phase of amyloid aggregation. Furthermore, elongation of Aβ-40 into higher oligomeric and fibrillar species leads to eventual fluidization of the model membrane followed by extensive lipid membrane tubulation observed in the late phase. Taken together, our results capture mechanistic insights into snapshots of temporal dynamics of Aβ-40 - myelin-like model membrane interaction and demonstrate how short timescale, local phenomena of binding, and fibril-mediated load generation results in the consequent association of lipids with growing amyloid fibrils.

Cholesterol enhances the negative impact of vaping additives on lung surfactant model systems

Aims: Vaping has given rise to e-cigarette or vaping product use-associated lung injury. Model lung surfactant films were used to assess the impact of vape additives (vitamin E, vitamin E acetate, tetrahydrocannabinol, cannabidiol). This work builds upon our previous findings, by incorporating cholesterol, to understand the interplay between the additives and the sterol in surfactant function. Materials & methods: Compression-expansion cycles of lipid monofilm at the air-water interface and Brewster angle microscopy allowed elucidating the effects of vape additives. Results & conclusion: Vape additives at 5 mol% inhibited proper lipid packing and reduced film stability. Cholesterol enhanced the additive effects, resulting in significantly destabilized films and altered domains. The observed impact could signify dysfunctional lung surfactant and impaired lung function.

Vaping additives negatively impact the stability and lateral film organization of lung surfactant model systems

Aims: Inhalation of vaping additives has recently been shown to impair respiratory function, leading to e-cigarette or vaping product use associated with lung injuries. This work was designed to understand the impact of additives (vitamin E, vitamin E acetate, tetrahydrocannabinol and cannabidiol) on model lung surfactants. Materials & methods: Lipid monofilms at the air-water interface and Brewster angle microscopy were used to assess the impact of vaping additives on model lung surfactant films. Results & conclusion: The addition of 5 mol % of vaping additives, and even more so mixtures of vitamins and cannabinoids, negatively impacts lipid packing and film stability, induces material loss upon cycling and significantly reduces functionally relevant lipid domains. This range of detrimental effects could affect proper lung function.

Biophysical analysis of gelatin and PLGA nanoparticle interactions with complex biomimetic lung surfactant models

Biocompatible materials are increasingly used for pulmonary drug delivery, and it is essential to understand their potential impact on the respiratory system, notably their effect on lung surfactant, a monolayer of lipids and proteins, responsible for preventing alveolar collapse during breathing cycles. We have developed a complex mimic of lung surfactant composed of eight lipids mixed in ratios reported for native lung surfactant. A synthetic peptide based on surfactant protein B was added to better mimic the biological system. This model was used to evaluate the impact of biocompatible gelatin and poly(lactic-co-glycolic acid) nanoparticles. Surface pressure–area isotherms were used to assess lipid packing, film compressibility and stability, whereas the lateral organization was visualized by Brewster angle microscopy. Nanoparticles increased film fluidity and altered the monolayer collapse pressure. Bright protruding clusters formed in their presence indicate a significant impact on the lateral organization of the surfactant film. Altogether, this work indicates that biocompatible materials considered to be safe for drug delivery still need to be assessed for their potential detrimental impact before use in therapeutic applications

Biodegradable nanoparticles drastically alters lateral organization of lung surfactant lipid- peptide model system.

Self-Assembly of Graphene Oxide Nanoflakes in a Lipid Monolayer at the Air-Water Interface

The graphene family, especially graphene oxide (GO), has captured increasing prospects in the biomedical field due to its excellent physicochemical properties. Understanding the health and environmental impact of GO is of great importance for guiding future applications. Although their interactions with living organisms are omnipresent, the exact molecular mechanism is yet to be established. The cellular membrane is the first barrier for a foreign molecule to interact before entering into the cell. In the present study, a model system consisting of a lipid monolayer at the air-water interface represents one of the leaflets of this membrane. Surface pressure-area isotherms and advanced synchrotron X-ray scattering techniques have been employed to comprehend the interaction by varying the electrostatics of the membrane. The results depict a strong GO interaction with positively charged phospholipids, weak interaction with zwitterionic lipids, and interestingly negligible interaction with negatively charged lipids. GO flakes induce significant changes in the out-of-plane organization of a positively charged lipid monolayer with a minor influence on in-plane assembly of lipid chains. This interaction is packing-specific, and the influence of GO is much stronger at lower surface pressure. Even though for zwitterionic phospholipids, the GO flakes may partly insert into the lipid chains, the X-ray scattering results indicate that the flakes preferentially lie horizontally underneath the positively charged lipid monolayer. This in-depth structural description may pave new perspectives for the scientific community for the development of GO-based biosensors and biomedical materials.

The degree and position of phosphorylation determine the impact of toxic and trace metals on phosphoinositide containing model membranes

This work assessed effects of metal binding on membrane fluidity, liposome size, and lateral organization in biomimetic membranes composed of 1 mol% of selected phosphorylated phosphoinositides in each system. Representative examples of phosphoinositide phosphate, bisphosphate and triphosphate were investigated. These include phosphatidylinositol-(4,5)-bisphosphate, an important signaling lipid constituting a minor component in plasma membranes whereas phosphatidylinositol-(4,5)-bisphosphate clusters support the propagation of secondary messengers in numerous signaling pathways. The high negative charge of phosphoinositides facilitates electrostatic interactions with metals. Lipids are increasingly identified as toxicological targets for divalent metals, which potentially alter lipid packing and domain formation. Exposure to heavy metals, such as lead and cadmium or elevated levels of essential metals, like cobalt, nickel, and manganese, implicated with various toxic effects were investigated.  Phosphatidylinositol-(4)-phosphate and phosphatidylinositol-(3,4,5)-triphosphate containing membranes are rigidified by lead, cobalt, and manganese whilst cadmium and nickel enhanced fluidity of membranes containing phosphatidylinositol-(4,5)-bisphosphate. Only cobalt induced liposome aggregation. All metals enhanced lipid clustering in phosphatidylinositol-(3,4,5)-triphosphate systems, cobalt in phosphatidylinositol-(4,5)-bisphosphate systems, while all metals showed limited changes in lateral film organization in phosphatidylinositol-(4)-phosphate matrices. These observed changes are relevant from the biophysical perspective as interference with the spatiotemporal formation of intricate domains composed of important signaling lipids may contribute to metal toxicity.

Differential impact of synthetic antitumor lipid drugs on the membrane organization of phosphatidic acid and diacylglycerol monolayers

Anti-tumour lipids are synthetic analogues of lysophosphatidylcholine. These drugs are both cytotoxic and cytostatic, and more interestingly, exert these effects preferentially in tumour cells. While the exact mechanism of action isn't fully elucidated, these drugs appear to preferentially partition into rigid lipid domains in cell membranes. Upon insertion, the compounds alter membrane domain organization, disrupt normal signal transduction, and cause cell death. Recently, it has been reported that these drugs induce accumulation of diacylglycerol in yeast cells which in turn sensitizes cells to the drugs. Conversely, phosphatidic acid accumulation appears to protect cells against the drugs. In the current work, the aim was to compare the biophysical effects of the drugs edelfosine, miltefosine and perifosine on monolayers of dimyristoyl phosphatidic acid, dimyristoyl glycerol and an equimolar mixture, to understand how these lipids modulate the mode of action. Surface pressure - area isotherms, compression moduli and Brewster angle microscopy were used to compare drug effects on lipid packing, monolayer compressibility and lateral domain organization of these films. Results suggest that edelfosine and miltefosine have stabilizing effects on all of the monolayers, while perifosine destabilizes dimyristoyl glycerol and the equimolar mixture. Additionally, all three drugs change the morphology of the domains observed. Based on these results the stabilization of diacylgylcerol by edelfosine and miltefosine may contribute to the mode of action as diacylglycerol is a known disruptor of bilayers. Perifosine however does not stabilize diacylglycerol, and therefore cell death may occur through a more direct inhibition of specific signal transduction. These results suggest that perifosine may illicit cytotoxicity through a different mechanism compared to the other antitumor lipid drugs.

Newly Synthesized Lipid-Porphyrin Conjugates: Evaluation of Their Self-Assembling Properties, Their Miscibility with Phospholipids and Their Photodynamic Activity In Vitro

Lipid-porphyrin conjugates are considered nowadays as promising building blocks for the conception of supramolecular structures with multifunctional properties, required for efficient cancer therapy by photodynamic therapy (PDT). The synthesis of two new lipid-porphyrin conjugates coupling pheophorbide-a (Pheo-a), a photosensitizer derived from chlorophyll-a, to either chemically modified lyso-phosphatidylcholine (PhLPC) or egg lyso-sphingomyelin (PhLSM) is reported. The impact of the lipid backbone of these conjugates on their self-assembling properties, as well as on their physicochemical properties, including interfacial behavior at the air/buffer interface, fluorescence and absorption properties, thermotropic behavior, and incorporation rate in the membrane of liposomes were studied. Finally, their photodynamic activity was evaluated on esophageal squamous cell carcinoma (ESCC) and normal esophageal squamous epithelium cell lines. The liposome-like vesicles resulting from self-assembly of the pure conjugates were unstable and turned into aggregates with undefined structure within few days. However, both lipid-porphyrin conjugates could be efficiently incorporated in lipid vesicles, with higher loading rates than unconjugated Pheo-a. Interestingly, phototoxicity tests of free and liposome-incorporated lipid-porphyrin conjugates demonstrated a better selectivity in vitro to esophageal squamous cell carcinoma relative to normal cells.

Evaluating polymeric biomaterial-environment interfaces by Langmuir monolayer techniques

Polymeric biomaterials are of specific relevance in medical and pharmaceutical applications due to their wide range of tailorable properties and functionalities. The knowledge about interactions of biomaterials with their biological environment is of crucial importance for developing highly sophisticated medical devices. To achieve optimal in vivo performance, a description at the molecular level is required to gain better understanding about the surface of synthetic materials for tailoring their properties. This is still challenging and requires the comprehensive characterization of morphological structures, polymer chain arrangements and degradation behaviour. The review discusses selected aspects for evaluating polymeric biomaterial-environment interfaces by Langmuir monolayer methods as powerful techniques for studying interfacial properties, such as morphological and degradation processes. The combination of spectroscopic, microscopic and scattering methods with the Langmuir techniques adapted to polymers can substantially improve the understanding of their in vivo behaviour.

Iron Ion and Iron Hydroxide Adsorption to Charge-Neutral Phosphatidylcholine Templates

Surface-sensitive X-ray scattering and spectroscopy techniques reveal significant adsorption of iron ions and iron-hydroxide (Fe(III)) complexes to a charge-neutral zwitterionic template of phosphatidylcholine (PC). The PC template is formed by a Langmuir monolayer of dipalmitoyl-PC (DPPC) that is spread on the surface of 2 to 40 μM FeCl3 solutions at physiological levels of KCl (100 mM). At 40 μM of Fe(III) as many as ∼3 iron atoms are associated with each PC group. Grazing incidence X-ray diffraction measurements indicate a significant disruption in the in-plane ordering of DPPC molecules upon iron adsorption. The binding of iron-hydroxide complexes to a neutral PC surface is yet another example of nonelectrostatic, presumably covalent bonding to a charge-neutral organic template. The strong binding and the disruption of in-plane lipid structure has biological implications on the integrity of PC-derived lipid membranes, including those based on sphingomyelin.

Biophysical characterization of monofilm model systems composed of selected tear film phospholipids

The tear film protects the eye from foreign particles and pathogens, prevents excess evaporation, provides lubrication, and maintains a high quality optical surface necessary for vision. The anterior layer of tear film consists of polar and non-polar lipid layers. The polar lipids form a monolayer on the aqueous subphase, acting as surfactants for the non-polar lipid multilayer. A tear film polar lipid biomimetic consisting of dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylethanolamine (DPPE), palmitoyl glucosylceramide (PGC), and palmitoyl sphingomyelin (PSM) was characterized using Langmuir monolayers and Brewster angle microscopy (BAM). Lipid combinations formed very stable monolayers, especially those containing DPPC or PSM. Surface experiments and elasticity analyses revealed that PGC resulted in more condensed and rigid mixed monolayers. DPPE provided resistance to large changes in lipid ordering over a wide surface pressure range. Ternary mixtures containing DPPE and PGC with either DPPC or PSM experienced the greatest lipid ordering within the natural tear film surface pressure range suggesting that these lipids are important to maintain tear film integrity during the inter-blink period. Finally, BAM images revealed unique structures within monolayers of DPPC, DPPE, and PGC at the natural tear film surface pressure. 3D analysis of these domains suggested either the formation of multilayers or outward protrusions at surface pressures far below the point of irreversible collapse as seen on the isotherm. This entails that the polar lipids of tear film may be capable of multilayer formation or outward folding as a mechanism to prevent rupture of the tear film during a blink.

The structural and functional effects of Hg(II) and Cd(II) on lipid model systems and human erythrocytes: A review

The anthropogenic mobilization of mercury and cadmium into the biosphere has led to an increased and ineludible entry of these metals into biological systems. Here we discuss the impact of Hg(II) and Cd(II) on lipid model systems and human erythrocytes from a biophysical perspective. After a brief introduction to their implications on human health, studies that have investigated the effects of Hg(II) and Cd(II) on lipid model systems and human erythrocytes are discussed. In terms of lipids as toxicological target sites, predominantly variations in lipid head groups have been the source of investigation. However, as research in this field progresses, the effects of Hg(II) and Cd(II) on other structural features, such as acyl chain length and unsaturation, and other important lipid components and complex biomimetic lipid mixtures, will require further examinations. This review provides an analysis of what has been learned collectively from the diverse methodologies and experimental conditions used thus far. Consequently, there is a need for more comprehensive and thorough investigations into the effects of Hg(II) and Cd(II) on lipid membranes under consistent experimental conditions such as pH, ionic strength, temperature, and choice of lipid model system.

Langmuir monolayers as models to study processes at membrane surfaces

The use of new sophisticated and highly surface sensitive techniques as synchrotron based X-ray scattering techniques and in-house infrared reflection absorption spectroscopy (IRRAS) has revolutionized the monolayer research. Not only the determination of monolayer structures but also interactions between amphiphilic monolayers at the soft air/liquid interface and molecules dissolved in the subphase are important for many areas in material and life sciences. Monolayers are convenient quasi-two-dimensional model systems. This review focuses on interactions between amphiphilic molecules in binary and ternary mixtures as well as on interfacial interactions with interesting biomolecules dissolved in the subphase. The phase state of monolayers can be easily triggered at constant temperature by increasing the packing density of the lipids by compression. Simultaneously the monolayer structure changes are followed in situ by grazing incidence X-ray diffraction or IRRAS. The interactions can be indirectly determined by the observed structure changes. Additionally, the yield of enzymatic reaction can be quantitatively determined, secondary structures of peptides and proteins can be measured and compared with those observed in bulk. In this way, the influence of a confinement on the structural properties of biomolecules can be determined. The adsorption of DNA can be quantified as well as the competing adsorption of ions at charged interfaces. The influence of modified nanoparticles on model membranes can be clearly determined. In this review, the relevance and utility of Langmuir monolayers as suitable models to study physical and chemical interactions at membrane surfaces are clearly demonstrated.

Affinity of alkylphosphocholines to biological membrane of prostate cancer: studies in natural and model systems

The effectiveness of two alkylphosphocholines (APCs), hexadecylphosphocholine (miltefosine) and erucylphosphocholine to combat prostate cancer has been studied in vitro with artificial cancerous membrane, modelled with the Langmuir monolayer technique, and on cell line (Du-145). Studies performed with the Langmuir method indicate that both the investigated drugs have the affinity to the monolayer mimicking prostate cancer membrane (composed of cholesterol:POPC = 0.428) and the drug-membrane interactions are stronger for erucylphosphocholine as compared to hexadecylphosphocholine. Moreover, both studied drugs were found to fluidize the model membrane, which may lead to apoptosis. Indeed, biological studies confirmed that in Du-145 cell line both investigated alkylphosphocholines cause cell death primarily by apoptosis while necrotic cells constitute only a small percentage of APC-treated cells.

Grazing incidence X-ray diffraction studies of condensed double-chain phospholipid monolayers formed at the soft air/water interface

The use of highly brilliant synchrotron light sources in the middle of the 1980s for X-ray diffraction has revolutionized the research of condensed monolayers. Since then, monolayers gained popularity as convenient quasi two-dimensional model systems widely used in biophysics and material science. This review focuses on structures observed in one-component phospholipid monolayers used as simplified two-dimensional models of biological membranes. In a monolayer system the phase transitions can be easily triggered at constant temperature by increasing the packing density of the lipids by compression. Simultaneously the monolayer structure changes are followed in situ by grazing incidence X-ray diffraction. Competing interactions between the different parts of the molecule are responsible for the different monolayer structures. These forces can be modified by chemical variations of the hydrophobic chain region, of the hydrophilic head group region or of the interfacial region between chains and head groups. Modifications of monolayer structures triggered by changes of the chemical structure of double-chain phospholipids are highlighted in this paper.

Hg- and Cd-induced modulation of lipid packing and monolayer fluidity in biomimetic erythrocyte model systems

The public health consequences that are associated with the low level exposure of various human populations to Cd(2+) and Hg(2+) are incompletely understood. In order to assess if interactions between these inorganic pollutants and erythrocyte biomembranes may contribute to their chronic toxicity, we have used a Langmuir trough to probe the effect of HgCl2 and CdCl2 on the packing and elasticity properties of biomimetic lipid monolayers using different lipid mixtures. These lipid films were deposited at room temperature on a biologically relevant subphase (1mM phosphate, 100mM NaCl at pH 7.4) in the absence and presence of 100μM HgCl2, CdCl2 and 1:1 mixtures thereof. The interactions of heavy metals with the lipids were monitored as changes in the surface pressure (π)-area (A) isotherms. In addition, metal induced changes to the elastic properties of the model systems were analyzed by area and compressibility data of phosphatidylcholine (PC) systems containing 0, 15, 30, 45 and 100% phosphatidylethanolamine (PE) and phosphatidylserine (PS). These mixtures revealed changes in lateral lipid packing as indicated by area expansion as well as enhanced film rigidity. The results demonstrate that both heavy metals affected the various lipid matrices, but metal mixtures showed the strongest impact. Based on these data, the adverse interaction of Hg(2+) and Cd(2+) with lipid bilayer membranes is identified as a feasible mechanism by which these toxic metals exert toxicity in mammalian cells. Interestingly, these metal interactions were found to depend on the lipid composition.

Two-dimensional order in mercury-supported langmuir films of fatty diacids

The structure of mercury-supported Langmuir films of dicarboxylic acid molecules with 13 ≤ n ≤ 22 carbons is studied by X-ray methods and surface tensiometry. The molecules lie surface-parallel, forming mono-, bi-, or trilayers, depending on coverage. All films exhibit a full 2D order of the same single-molecule oblique unit cell. In particular, the distinct odd-even structure difference of 3D crystals of the same molecules is not observed. The unit cell's width and angle show a small systematic decrease with n, while the length increases commensurately with the molecular length. These results show the films to consist of closely packed, extended, polymer-like chains of diacid molecules, bound by their carboxyl end groups. Evidence is presented for the inclusion of a single mercury atom in the carboxyl-carboxyl bond. The possible conformation of this bond and implications of the parity-independent structure are discussed.

Novel lipid-soluble thiol-redox antioxidant and heavy metal chelator, N,N'-bis(2-mercaptoethyl)isophthalamide (NBMI) and phospholipase D-specific inhibitor, 5-fluoro-2-indolyl des-chlorohalopemide (FIPI) attenuate mercury-induced lipid signaling leading to protection against cytotoxicity in aortic endothelial cells

Here, we investigated thiol-redox-mediated phospholipase D (PLD) signaling as a mechanism of mercury cytotoxicity in mouse aortic endothelial cell (MAEC) in vitro model utilizing the novel lipid-soluble thiol-redox antioxidant and heavy metal chelator, N,N'-bis(2-mercaptoethyl)isophthalamide (NBMI) and the novel PLD-specific inhibitor, 5-fluoro-2-indolyl des-chlorohalopemide (FIPI). Our results demonstrated (i) mercury in the form of mercury(II) chloride, methylmercury, and thimerosal induced PLD activation in a dose- and time-dependent manner; (ii) NBMI and FIPI completely attenuated mercury- and oxidant-induced PLD activation; (iii) mercury induced upstream phosphorylation of extracellular-regulated kinase 1/2 (ERK1/2) leading to downstream threonine phosphorylation of PLD(1) which was attenuated by NBMI; (iv) mercury caused loss of intracellular glutathione which was restored by NBMI; and (v) NBMI and FIPI attenuated mercury- and oxidant-induced cytotoxicity in MAECs. For the first time, this study demonstrated that redox-dependent and PLD-mediated bioactive lipid signaling was involved in mercury-induced vascular EC cytotoxicity which was protected by NBMI and FIPI.

Ion-specific induced charges at aqueous soft interfaces

Ionic specificity effects, i.e., ions of the same valence leading to different macroscopic effects, are studied by considering a Langmuir monolayer of arachidic acid over a solution containing either Fe(3+) or La(3+). We systematically vary pH levels as a way to control the interfacial surface charge and characterize the system by surface-sensitive x-ray scattering and spectroscopic techniques. We show that the critical surface pressure at the tilted (L2) to untilted (LS) transition is ionic specific and varies with pH. While the maximum density of surface bound La(3+) per head group of arachidic acid is ∼0.3, the amount necessary to neutralize the surface charge, for Fe(3+) it is nearly 0.6 and it is accompanied with a significant accumulation of the coions Cl(-) as revealed by surface x-ray spectroscopy. We account for the experimental observations by a statistical mechanical model including ion specificity.