Changes In Membrane Structure Research Articles

Real-time measurement of membrane conformational states induced by antimicrobial peptides: balance between recovery and lysis.

The disruption of membranes by antimicrobial peptides is a multi-state process involving significant structural changes in the phospholipid bilayer. However, direct measurement of these membrane structural changes is lacking. We used a combination of dual polarisation interferometry (DPI), surface plasmon resonance spectroscopy (SPR) and atomic force microscopy (AFM) to measure the real-time changes in membrane structure through the measurement of birefringence during the binding of magainin 2 (Mag2) and a highly potent analogue in which Ser8, Gly13 and Gly18 has been replaced with alanine (Mag-A). We show that the membrane bilayer undergoes a series of structural changes upon peptide binding before a critical threshold concentration is reached which triggers a significant membrane disturbance. We also propose a detailed model for antimicrobial peptide action as a function of the degree of bilayer disruption to provide an unprecedented in-depth understanding of the membrane lysis in terms of the interconversion of different membrane conformational states in which there is a balance between recovery and lysis.

Three-dimensional imaging of HIV-1 virological synapses reveals membrane architectures involved in virus transmission.

HIV transmission efficiency is greatly increased when viruses are transmitted at virological synapses formed between infected and uninfected cells. We have previously shown that virological synapses formed between HIV-pulsed mature dendritic cells (DCs) and uninfected T cells contain interdigitated membrane surfaces, with T cell filopodia extending toward virions sequestered deep inside invaginations formed on the DC membrane. To explore membrane structural changes relevant to HIV transmission across other types of intercellular conjugates, we used a combination of light and focused ion beam scanning electron microscopy (FIB-SEM) to determine the three-dimensional (3D) architectures of contact regions between HIV-1-infected CD4(+) T cells and either uninfected human CD4(+) T cells or human fetal astrocytes. We present evidence that in each case, membrane extensions that originate from the uninfected cells, either as membrane sheets or filopodial bridges, are present and may be involved in HIV transmission from infected to uninfected cells. We show that individual virions are distributed along the length of astrocyte filopodia, suggesting that virus transfer to the astrocytes is mediated, at least in part, by processes originating from the astrocyte itself. Mechanisms that selectively disrupt the polarization and formation of such membrane extensions could thus represent a possible target for reducing viral spread. Our findings lead to new insights into unique aspects of HIV transmission in the brain and at T cell-T cell synapses, which are thought to be a predominant mode of rapid HIV transmission early in the infection process.

New covalent modifications of phosphatidylethanolamine by alkanals: mass spectrometry based structural characterization and biological effects.

The pathophysiology of numerous human disorders, such as atherosclerosis, diabetes, obesity and Alzheimer's disease, is accompanied by increased production of reactive oxygen species (ROS). ROS can oxidatively damage nearly all biomolecules, including lipids, proteins and nucleic acids. In particular, (poly)unsaturated fatty acids within the phospholipid (PL) structure are easily oxidized by ROS to lipid peroxidation products (LPP) carrying reactive carbonyl groups. Carbonylated LPP are characterized by high in vivo toxicity due to their reactivity with nucleophilic substrates (Lys-, Cys-and His-residues in proteins or amino groups of phosphatidylethanolamines [PE]). Adducts of unsaturated LPP with PE amino groups have been reported before, whereas less is known about the reactivity of saturated alkanals – which are significantly increased in vivo under oxidative stress conditions – towards nucleophilic groups of PLs.Here, we present a study of new alkanal-dipalmitoyl-phosphatidylethanolamine (DPPE) adducts by MS-based approaches, using consecutive fragmentation (MSn) and multiple reaction monitoring techniques. At least eight different DPPE–hexanal adducts were identified, including Schiff base and amide adducts, six of which have not been reported before. The structures of these new compounds were determined by their fragmentation patterns using MSn experiments. The new PE-hexanal adducts contained dimeric and trimeric hexanal conjugates, including cyclic adducts. A new pyridine ring containing adduct of DPPE and hexanal was purified by HPLC, and its biological effects were investigated. Incubation of peripheral blood mononuclear cells and monocytes with modified DPPE did not result in increased production of TNF-α as one selected inflammation marker. However, incorporation of modified DPPE into 1,2-dipalmitoleoyl-sn-phosphatidylethanolamine multilamellar vesicles resulted in a negative shift of the transition temperature, indicating a possible role of alkanal-derived modifications in changes of membrane structure. © 2014 The Authors. Journal of Mass Spectrometry published by John Wiley & Sons, Ltd.

Effects of Ozone Treatment on Wool Morphology and Mechanical Properties

The aim of this study was to investigate the ozone treating effects on wool scales and wool mechanical property through experiments and observation. For this purpose, a detailed investigation on the role of mechanical properties surfacing topography, changes in component and membrane structure were investigated. After this, a micro explanation was given to discuss the mechanism of wool shrinkage. For the scales is the element factor for shrinking, so this study is of great significance to the work of shrinkproofing.

Dietary PUFA and cancer.

The aim of the present paper is to give a brief overview on the role of dietary fat in carcinogenesis and as possible anticancer agents. Dietary fat is an essential nutrient and important source for the essential fatty acids (FA), linoleic and α-linolenic acids, which contribute to proper growth and development. However, dietary fat has been associated with the development of colorectal, breast, prostate, endometrial and ovarian cancers, with the type and quality of fat playing an underlying role. Tumour growth is the disruption of the homoeostatic balance regulating cell differentiation, proliferation and apoptosis and is associated with altered lipid metabolism. Animal cancer models and human cancer biopsy tissue demonstrate that a characteristic lipid profile is associated with the growth and development of neoplastic lesions. This entails alterations in membrane cholesterol, phospholipid and PUFA metabolism. Particularly, alterations in cell membrane FA metabolism involving the n-6 and n-3 PUFA, are associated with changes in membrane structure, function, cellular oxidative status, activity of enzymes and signalling pathways. These events are a driving force in sustaining the altered growth of cancerous lesions and provide unique targets for intervention/cancer modulation. Challenges in utilising FA in cancer modulation exist regarding intake and effect on cell structure and biochemical interactions within the cell in the prevention of cancer development. Therefore, utilising dietary PUFA in a specific n-6:n-3 ratio may be an important chemopreventive tool in altering the growth characteristics of cancer cells.

Preparation and characterizations of poly(vinylidene fluoride)/oxidized multi-wall carbon nanotube membranes with bi-continuous structure by thermally induced phase separation method

Poly(vinylidene fluoride)/oxidized multi-wall carbon nanotube (PVDF/O-MWCNT) flat membranes with bi-continuous structures were successfully prepared via the thermally induced phase separation (TIPS) method. The effects of O-MWCNT content, PVDF concentration and quenching temperature on the membrane properties were systematically discussed. The results indicate that the membrane structure changes to a denser one and the pure water fluxes (PWFs) of the resultant membranes decline with the increase of O-MWCNT content. With the addition of O-MWCNTs from 0.0 to 0.6wt%, the BSA rejections of the resultant PVDF/O-MWCNT membranes are improved dramatically. The highest BSA rejection attained is above 90.0%, implying that a novel PVDF/O-MWCNT ultrafiltration membrane is fabricated. The surface hydrophilicity and anti-fouling ability of the membranes are improved with the addition of O-MWCNTs. Furthermore, the mechanical properties of the resultant membranes are enhanced compared with the pristine PVDF membranes. This work demonstrates that O-MWCNTs play a critical role in determining the morphologies and performances of PVDF/O-MWCNT membranes prepared via the TIPS method.

Preparation and characterization of polysulfone mixed matrix membrane incorporated with palladium nanoparticles in the inversed microemulsion for hydrogen separation

Polysulfone (PSf) membrane shows acceptable gas separation performance, but its application is limited by the “trade-off” between selectivity and permeability. In this study, PSf mixed matrix membranes (MMMs) incorporated with palladium (Pd) nanoparticles in the inversed microemulsion were proposed for hydrogen (H2) separation. Pd nanoparticles can be kinetically stabilized and dispersed using electrostatic and/or steric forces of a stabilizer which is typically introduced during the formation of Pd nanoparticles in the inversed microemulsion. Pd nanoparticles were synthesized by loading (PdCl2) into the polymeric matrix, polyethylene glycol (PEG) which acts as reducing agent and stabilizer. The dry–wet phase inversion method was applied for the preparation of asymmetric PSf MMMs. The effects of Pd (0–4wt%) on the membrane characteristics and separation performance were studied. Experimental findings verified that the MMMs are able to achieved a high H2/N2 selectivity of 21.69 and a satisfactory H2 permeance of 46.24GPU due to the changes in membrane structure from fully developed finger-like structure to closed cell structure besides the growth of dense layer. However, the selectivity of H2/CO2 decreased due to the addition of PEG.

A New theraphosid Spider Toxin Causes Early Insect Cell Death by Necrosis When Expressed In Vitro during Recombinant Baculovirus Infection

Baculoviruses are the most studied insect viruses in the world and are used for biological control of agricultural and forest insect pests. They are also used as versatile vectors for expression of heterologous proteins. One of the major problems of their use as biopesticides is their slow speed to kill insects. Thus, to address this shortcoming, insect-specific neurotoxins from arachnids have been introduced into the baculovirus genome solely aiming to improve its virulence. In this work, an insecticide-like toxin gene was obtained from a cDNA derived from the venom glands of the theraphosid spider Brachypelma albiceps. The mature form of the peptide toxin (called Ba3) has a high content of basic amino acid residues, potential for three possible disulfide bonds, and a predicted three-stranded β-sheetDifferent constructions of the gene were engineered for recombinant baculovirus Autographa californica multiple nuclepolyhedrovirus (AcMNPV) expression. Five different forms of Ba3 were assessed; (1) the full-length sequence, (2) the pro-peptide and mature region, (3) only the mature region, and the mature region fused to an (4) insect or a (5) virus-derived signal peptide were inserted separately into the genome of the baculovirus. All the recombinant viruses induced cell death by necrosis earlier in infection relative to a control virus lacking the toxin gene. However, the recombinant virus containing the mature portion of the toxin gene induced a faster cell death than the other recombinants. We found that the toxin construct with the signal peptide and/or pro-peptide regions delayed the necrosis phenotype. When infected cells were subjected to ultrastructural analysis, the cells showed loss of plasma membrane integrity and structural changes in mitochondria before death. Our results suggest this use of baculovirus is a potential tool to help understand or to identify the effect of insect-specific toxic peptides when produced during infection of insect cells.

Desalination of seawater ion complexes by MFI-type zeolite membranes: Temperature and long term stability

Ceramic membranes made from zeolites possess the nanoporous structure required for desalination of saline water including seawater. In this research, an α-Al2O3 supported MFI-type silicalite membrane was synthesised by the direct in-situ crystallisation method via a single hydrothermal treatment in an autoclave under autogenous pressure. Desalination performance of the prepared silicalite membrane was carried out with a seawater solution (0.3wt% TDS (total dissolved solids)) over a long period of around 180 days at a constant pressure of 700kPa at various temperatures. The prepared silicalite membrane achieved a high rejection (>93%) for all major seawater ions including Na+ (except for K+, 83%) at an applied pressure of 700kPa and room temperature (22°C), but showed a continuous decrease in ion rejection when increasing the temperature from 22°C and 90°C. Permeation flux of the zeolite membrane significantly increased with increasing in temperature. Upon closer observation of the major cations, size selective diffusion in the zeolite membrane was observed over the temperatures tested. Larger ions Ca2+ and Mg2+ were less responsive to temperature than smaller ions Na+ and K+. No changes in membrane structure were observed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) after 180 days seawater exposure. However, energy-dispersive X-ray spectroscopy (EDS) mapping on the surface of the membrane revealed a small quantity of tightly bound divalent cations present in the structure, which appear to have penetrated the zeolite, accelerated by temperature. They were suspected to have altered the permstructure, explaining why original high rejections at room temperature were not reversed after heat exposure. The work has shown that zeolite membranes can desalinate seawater, but other unusual effects such as ion selective diffusion as a function of temperature indicate a unique property for desalination membrane materials.

1,2-Naphthoquinone Stimulates Lipid Peroxidation and Cholesterol Domain Formation in Model Membranes

Naphthalene induces cataract formation through the accumulation of its reactive metabolite, 1,2-naphthoquinone (1,2-NQ), in the ocular lens. 1,2-NQ increases lens protein oxidation and disrupts fiber cell membrane function; however, the association of these effects with changes in membrane structure is not understood. The goal of this study was to determine the direct effects of 1,2-NQ on membrane lipid oxidation and structural organization. Iodometric approaches were used to measure the effects of naphthalene and 1,2-NQ on lipid hydroperoxide (LOOH) formation in model membranes composed of cholesterol and dilinoleoylphosphatidylcholine. Membrane samples were prepared at various cholesterol-to-phospholipid mole ratios and subjected to autoxidation at 37°C for 48 hours in the absence or presence of either agent alone (0.1-5.0 μM) or in combination with vitamin E. Small-angle x-ray diffraction was used to measure the effects of naphthalene and 1,2-NQ on membrane structure before and after exposure to oxidative stress. 1,2-NQ increased LOOH formation by 250% (P < 0.001) and 350% (P < 0.001) at 1.0 and 5.0 μM, respectively, whereas naphthalene decreased LOOH levels by 25% (P < 0.01) and 10% (NS). The pro-oxidant effect of 1,2-NQ was inversely affected by membrane cholesterol enrichment and completely blocked by vitamin E. 1,2-NQ also increased cholesterol domain formation by 360% in membranes exposed to oxidative stress; however, no significant changes in membrane lipid organization were observed with naphthalene under the same conditions. These data suggest a novel mechanism for naphthalene-induced cataract, facilitated by the direct effects of 1,2-NQ on lipid peroxidation and cholesterol domain formation.

Modified alumina nanofiber membranes for protein separation

Large-scale purification/separation of bio-substances is a key technology required for rapid production of biological substances in bioengineering. Membrane filtration is a new separation process and has potential to be used for concentration (removal of solvent), desalting (removal of low molecular weight compounds), clarification (removal of particles), and fractionation (protein-protein separation). In this study, we developed an efficient membrane for protein separation based on ceramic nanofibers. Alumina nanofibers were prepared on a porous support and formed large flow passages. The radical changes in membrane structure provided new ceramic membranes with a large porosity (more than 70%) due to the replacement of bulk particles with fine fibers as building components. The pore size had an average of 11nm and pure water flux was approximately 360Lh−1m−2bar−1. Further surface modification with a self-assembled monolayer of (3-aminopropyl) triethoxysilane enhanced the membrane filtration properties. Characterization with SEM, FTIR, contact angle, and proteins separation tests indicated that the fibril layers uniformly spread on the surface of the porous support. Moreover, the membrane surface was changed from hydrophilic to hydrophobic after silane groups were grafted. It demonstrated that the silane-grafted alumina fiber membrane can reject 100% BSA protein and 92% cellulase protein. It was also able to retain 75% trypsin protein while maintaining a permeation flux of 48Lh−1m−2bar−1.

Effect of Diet and Nutrient on Cell Signaling: Is the Tissue the Main Issue, Proposes Dr. Wilson?

Western diet is characterized with energy dense, refined, ready prepared foods with a high glycemic index (e.g. refined starches; bread, biscuits, candies, cornflakes, pizza, potato chips, cola drinks and sugar) and unhealthy lipids (e.g. trans fats, saturated fat , w-6 rich oils) poor in w-3 fatty acids, phytochemicals and fiber that are abundant in the Mediter- ranean type of diet. Western type of diets are known to predispose inflammation and increase in free fatty acids causing endothelial cell and beta cell dysfunction leading to the epidemic of cardiovascular diseases (CVDs). The cell signaling and the changes in cell membrane properties of the tissues induced by dietary lipids may have important consequences on the development of obesity, atherosclerosis and hypertension. The structural properties and function of cell membrane proteins appear to be modified in hypertensive humans and animal models of hypertension and atherosclerosis. Diet in- duced alterations in membrane lipid composition of hypertensive subjects have been associated with alterations in the transmembrane fluxes of Na + and K + , including Na + -Li + countertransport, which is a marker of essential hypertension, and in cell signaling proteins that participate in the control of blood pressure. It has been demonstrated that dietary lipids have an effect on membrane lipid composition and cell signaling proteins. Since changes in the dietary lipid composition yield to variations in the biophysical properties of the plasma membrane, it is likely that cellular functional changes could result from alterations in the structure of the lipid membrane properties under influence of the diet. Thus, the changes in mem- brane properties induced by dietary lipids may have important consequences on blood pressure regulation. The Mediterra- nean diet has been associated with changes in membrane structure and function. Consumption of olive oil-rich diets in- creases the concentration of oleic acid in plasma membrane lipids of different rat and human cells, with beneficial conse- quences on membrane functionality. In contrast, very little is currently known regarding the effects of nuts, another key ingredient of such diets, on membrane lipid composition and structure. CVD, diabetes mellitus and obesity, that are asso- ciated with increased production of thromboxane A2(TXA2), leukotrienes, prostacyclin, interleukins-1 and 6, tumor ne- crosis factor-alpha and C-reactive proteins in the tissues, is the major issue. Increased dietary intake of w-6 fatty acids is known to enhance all these biomarkers as well as atherogenicity of cholesterol in the tissues which have adverse pro- inflammatory effects resulting in CAD. Mediterranean diet rich in fruits, vegetables, nuts, mustard oil, and olive oil char- acterized with low w-6/w-3 ratio in the diet, can modulate inflammation and endothelial dysfunction of the tissues and may be protective against risk of coronary artery disease (CAD) and all-cause mortality. Inflammation appears to be an important unifying hypothesis, because in the absence of inflammation in the tissues, total cholesterol and other lipids may have neutral effects in the arterial tissues and myocardium. Therefore, it seems that endothelial dysfunction and in- flammation in the tissue is the main issue for treatment.

Combined Mass and Structural Kinetic Analysis of Multistate Antimicrobial Peptide–Membrane Interactions

Kinetic analysis of peptide-membrane interactions generally involves a curve fitting process with no information about what the different curves may physically correspond to. Given the multistep process of peptide-membrane interactions, a computational method that utilizes physical parameters that relate to both peptide binding and membrane structure would provide new insight into this complex process. In this study, kinetic models accounting for two-state and three-state mechanisms were fitted to our previously reported simultaneous real-time measurements of mass and birefringence during the binding and dissociation of the peptide HPA3 (Hirst, D.; Lee, T.-H.; Swann, M.; Unabia, S.; Park, Y.; Hahm, K.-S.; Aguilar, M. Eur. Biophys. J. 2011, 40, 503-514); significantly, the mass and birefringence are constrained by the same set of kinetic constants, allowing the unification of peptide binding patterns with membrane structure changes. For the saturated phospholipid dimyristoyl-phosphatidylcholine (DMPC) the two-state model was sufficient to account for the observed changes in mass and birefringence, whereas for the unsaturated phospholipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) the two-state model was found to be inadequate and a three-state model gave a significantly better fit. The third state of interaction for POPC was found to disrupt the bilayer much more than the previous two states. We propose a hypothesis for the mechanism of membrane permeabilization based on the results featuring a loosely bound first state, a tightly bound second state, and a highly membrane-disrupting third state. The results demonstrate the importance of the difference in membrane fluidity between the gel phase DMPC and the liquid crystal phase POPC for peptide-membrane interactions and establish the combination of DPI and kinetic modeling as a powerful tool for revealing features of peptide-membrane interaction mechanisms, including intermediate states between initial binding and full membrane disruption.

Membrane Structure Correlates to Function of LLP2 on the Cytoplasmic Tail of HIV-1 gp41 Protein

Mutation studies previously showed that the lentivirus lytic peptide (LLP2) sequence of the cytoplasmic C-terminal tail of the HIV-1 gp41 envelope protein inhibited viral-initiated T-cell death and T-cell syncytium formation, at which time in the HIV life cycle the gp41 protein is embedded in the T-cell membrane. In striking contrast, the mutants did not affect virion infectivity, during which time the gp41 protein is embedded in the HIV envelope membrane. To examine the role of LLP2/membrane interactions, we applied synchrotron x-radiation to determine structure of hydrated membranes. We focused on WT LLP2 peptide (+3 charge) and MX2 mutant (−1 charge) with membrane mimics for the T-cell and the HIV-1 membranes. To investigate the influence of electrostatics, cholesterol content, and peptide palmitoylation, we also studied three other LLP2 variants and HIV-1 mimics without negatively charged lipids or cholesterol as well as extracted HIV-1 lipids. All LLP2 peptides bound strongly to T-cell membrane mimics, as indicated by changes in membrane structure and bending. In contrast, none of the weakly bound LLP2 variants changed the HIV-1 membrane mimic structure or properties. This correlates well with, and provides a biophysical basis for, previously published results that reported lack of a mutant effect in HIV virion infectivity in contrast to an inhibitory effect in T-cell syncytium formation. It shows that interaction of LLP2 with the T-cell membrane modulates biological function.

Role of Ionic Strength on n-Butanol Partitioning into Anionic Dipalmitoyl Phosphatidylcholine/Phosphatidylglycerol Vesicles

Bacteria adjust their membrane lipid composition to counteract the fluidizing effects of alcohol and to adapt to elevated alcohol concentrations during fermentation. Bacterial membranes are rich in anionic phosphatidylglycerols (PGs), but little is known regarding alcohol partitioning into anionic membranes, particularly for n-butanol. This work examines the effects of lipid charge on n-butanol partitioning into anionic membrane vesicles composed of dipalmitoyl phosphatidylcholine (DPPC) and dipalmitoyl phosphatidylglycerol (DPPG) in the absence and presence of salt (phosphate-buffered saline, PBS; 0.152 and 1.52 M). Above 0.135 M n-butanol, the membranes were interdigitated irrespective of DPPG or salt concentration, consistent with previous results for neutral membranes, such as DPPC. Increasing salt concentration led to greater n-butanol partitioning in DPPC membranes and caused aggregation/fusion. However, aggregation/fusion was prevented with increasing DPPG concentration (i.e., increasing membrane charge) and small vesicles were observed. The results suggest that n-butanol partitioning, and subsequent changes in membrane and vesicle structure, was driven by a balance between the "salting-out" of n-butanol, interlipid electrostatic interactions, and interfacial cation binding and hydration. This is the first study to the best of our knowledge to examine the effects of n-butanol partitioning on model cell membranes composed of negatively charged lipids in the presence of salts.

Dialysate cancer antigen 125 in long-term peritoneal dialysis patients

Structural and functional peritoneal membrane changes are associated with long-term peritoneal dialysis. These changes can lead to ultrafiltration failure and peritoneal fibrosis, reducing the efficacy of the peritoneal membrane to remove waste and balance fluid and electrolytes. The loss of mesothelial cells from the basement membrane is one of the major characteristics in peritoneal membrane structural change. Thus, if the reduction of peritoneal mesothelial cell mass in peritoneal dialysis patients is monitored, signs of ultrafiltration failure and peritoneal fibrosis can be detected early. One of biomarkers that can be used to indicate the change in peritoneal mesothelial cell mass is CA125, which is produced by mesothelial cells. In this article, we review the measurement and clinical use of CA125 in peritoneal dialysate effluent. Additionally, we address the data and studies on the association between dialysate CA125 levels and factors related to ultrafiltration failure and peritoneal fibrosis, including the parameters used to monitor the functional status of the peritoneal membrane. Our review shows that dialysate CA125 can be used to evaluate the peritoneal membrane in noninfected patients to predict peritoneal fibrosis, and it can also be used as a biomarker of biocompatible dialysis solutions.

Fabrication of porous polymeric nanocomposite membranes with enhanced anti-fouling properties: Effect of casting composition

A mixed matrix porous polymeric membranes with anti-fouling properties were prepared by phase-inversion method from a quaternary system of polysulfone/N,N-dimethylformamide/polyvinilpyrrolidone (PVP)/nanosilver (nAg). The effect of casting mixture composition on the membrane morphology, performance, and anti-fouling (including anti-biofouling) properties was evaluated by microscopic, spectroscopic and surface characterization techniques. The results showed a substantial effect of casting mixture composition on the morphology and selectivity of membranes. The incorporation of nAg to a casting mixture containing 5wt% PVP induced morphological changes in membrane structure including increase in pore sizes, suppression of macrovoids and thinning of the skin layer. These changes were further resembled in the separation and anti-fouling properties of membranes. The permeate flux of membranes increased regardless of PVP concentration, while the separation properties of membranes formed from a casting mixture containing 5wt% PVP were significantly compromised as compared to those formed with 1wt% PVP. Under the same nAg loading, the membrane casted from a mixture contained 1wt% PVP had better anti-fouling properties with respect to bovine serum albumin. The bioassays with Pseudomonas aeruginosa revealed that anti-biofouling properties of membranes (including antibacterial and anti-adhesive properties) were significantly induced upon addition of nAg. The findings of this study highlight the importance of casting mixture composition and interactions between its components for the optimization of membrane anti-fouling behavior while maintaining high separation properties.

Rapid cortisol signaling in response to acute stress involves changes in plasma membrane order in rainbow trout liver

The activation of genomic signaling in response to stressor-mediated cortisol elevation has been studied extensively in teleosts. However, very little is known about the rapid signaling events elicited by this steroid. We tested the hypothesis that cortisol modulates key stress-related signaling pathways in response to an acute stressor in fish liver. To this end, we investigated the effect of an acute stressor on biophysical properties of plasma membrane and on stressor-related protein phosphorylation in rainbow trout (Oncorhynchus mykiss) liver. A role for cortisol in modulating the acute cellular stress response was ascertained by blocking the stressor-induced elevation of this steroid by metyrapone. The acute stressor exposure increased plasma cortisol levels and liver membrane fluidity (measured by anisotropy of 1,6-diphenyl-1,3,5-hexatriene), but these responses were abolished by metyrapone. Atomic force microscopy further confirmed biophysical alterations in liver plasma membrane in response to stress, including changes in membrane domain topography. The changes in membrane order did not correspond to any changes in membrane fatty acid components after stress, suggesting that changes in membrane structure may be associated with cortisol incorporation into the lipid bilayer. Plasma cortisol elevation poststress correlated positively with activation of intracellular stress signaling pathways, including increased phosphorylation of extracellular signal-related kinases as well as several putative PKA and PKC but not Akt substrate proteins. Together, our results indicate that stressor-induced elevation of plasma cortisol level is associated with alterations in plasma membrane fluidity and rapid activation of stress-related signaling pathways in trout liver.

Correlative ultrastructural investigations of airway epithelium following experimental exposure to defined air pollutants and lifestyle exposure to tobacco smoke

Context: Investigations of cell/molecular level effects of in vivo exposure of airway mucosa of experimental animals to common irritant gases have demonstrated structural and physiological changes reflective of breaches in epithelial barrier function, presence of inflammatory cell infiltrate and compromised ciliary function. These experimental animal studies provided useful perspectives of plausible, but more subtle pathologic outcomes having relevance to lifestyle exposure to gaseous environmental irritants including tobacco smoke.Methods: Freeze-fracture technology was applied to ultrastructural examination of large airway epithelium, with appropriate controls, from guinea pigs exposed to ozone and of nasal mucosa of human subjects exposed to ozone or sulfur dioxide, and nasal mucosa of active smokers.Results: We documented substantive membrane structural changes to tight junctional complexes and cilia as well as an infiltrate of neutrophils into the surface mucosal layer in exposed animals. These patterns also were evident but not as pervasive among human subjects acutely exposed experimentally to irritant gases and those chronically exposed by their lifestyle to tobacco smoke.Discussion: Our intent was to characterize respiratory tract mucosal membrane disorganization associated with high level acute irritant exposures in an experimental animal model and to evaluate evidence of similar but perhaps more subtle pathologic change associated with lower level experimental or lifestyle exposures. Our studies demonstrate continuity, albeit subtle, of pathologic change from high dosage experimental animal exposure to low dosage human exposures.Conclusions: This study represents the first report of ultrastructural airway epithelial membrane anomalies associated with lifestyle exposure to tobacco smoke irritants.

Improved Coarse-Grained Modeling of Cholesterol Activation in Lipid Bilayers

Cholesterol (Chol) concentration is highly regulated in mammalian cells, which in turn is coupled to LDL levels in blood plasma and cardiovascular health. In one regulatory mechanism, Chol exchange between the plasma and endoplasmic reticulum membranes is regulated by sterol- and sterol derivative-induced changes in membrane structure. Experiments and united atom (UA) simulations show that binary Chol-phospholipid bilayers thin significantly, and Chol accessibility increases, at Chol concentrations of 40 % and higher, which is about the level at which Chol becomes accessible to external acceptors. Here, to reduce computational cost so that larger and more complex systems involved in Chol regulation (i.e. with proteins, ER membranes) can be simulated, we modify the published MARTINI coarse-grained force field to improve its predictions of sterol-induced membrane restructuring, by comparison to united atom simulations. We adjust key bonded parameters and forcefield terms for phospholipid and cholesterol to more accurately reflect the conformational distributions observed in UA simulations, and we further adjust the interaction energies among lipid and sterol beads to reproduce membraneradial distribution functions and the Chol tilt distribution. With these corrections, we are able to reproduce both the area condensation/membrane thickening seen at less than 30% Chol and the thinning seen at above 40%. Furthermore, a “coarse-grained oxysterol” variant of our refined model captures the broad tilt distribution previously seen in UA simulations of bilayers containing 10-18% 25-hydroxycholesterol (oxysterol). Finally, addition of coarse-grained oxysterol to Chol/phospholipid bilayer simulations distinctly shifts the membrane thickness curve to lower concentrations, as seen in experiments. Thus, we have substantially improved the accuracy of MARTINI so that insights can be learned about lipid/sterol systems themselves, and so that large and complex systems also containing proteins can be investigated in the future.