Properties of Langmuir and solid supported lipid films with sphingomyelin

In situ interaction between the hormone 17α-ethynylestradiol and the liquid-ordered phase composed of the lipid rafts sphingomyelin and cholesterol

Hormone treatments are frequently associated with cardiovascular diseases and cancers in women. Additionally, the detrimental effects of their presence as contaminants in water remain a concern. The transport of hormones through cell membranes is essential for their biological action, but investigating cell permeability is challenging owing to the experimental difficulty in dealing with whole cells. In this paper, we study the interaction of the synthetic hormone 17α-ethynylestradiol (EE2) with membrane models containing the key raft components sphingomyelin (SM) and cholesterol (Chol). The models consisted of Langmuir monolayers and giant unilamellar vesicles (GUVs) that represent bilayers. EE2 induced expansion of SM monolayers upon interacting with the non-hydrated amide group of SM head, but it had practically no effect on SM GUVs because these group are not available for interaction in bilayers. In contrast, EE2 interacted with hydrated phosphate group (PO2-) and amide group of SM/Chol mixture monolayer, which could explain the loss in phase contrast of liquid-ordered GUVs suggesting pore formation. A comparison with reported EE2 effects on GUVs in the fluid phase, for which no loss in phase contrast was observed, indicates that the liquid-ordered phase consisting of lipid rafts is relevant to be associated with the changes on cell permeability caused by the hormones.

Surface Properties of Graffiti Coatings on Sensitive Surfaces Concerning Their Removal with Formulations Based on the Amino-Acid-Type Surfactants

Water-in-oil (w/o) nanoemulsions stabilized with amino acid surfactants (AAS) are one example of nanotechnology detergents of the "brush on, wipe off"-type for removing graffiti coatings from different sensitive surfaces. The high-pressure homogenization (HPH) process was used to obtain the nanostructured fluids (NSFs), including the non-toxic and eco-friendly components such as AAS, esterified vegetable oils, and ethyl lactate. The most effective NSF detergent was determined by response surface methodology (RSM) optimization. Afterwards, several surface properties, i.e., topography, wettability, surface free energy, and the work of water adhesion to surfaces before and after their coverage with the black graffiti paint, as well as after the removal of the paint layers by the eco-remover, were determined. It was found that the removal of graffiti with the use of the NSF detergent is more dependent on the energetic properties and microporous structure of the paint coatings than on the properties of the substrates on which the layers were deposited. The use of NSFs and knowledge of the surface properties could enable the development of versatile detergents that would remove unwanted contamination from various surfaces easily and in a controlled way.

Reorganization of the outer layer of a model of the plasma membrane induced by a neuroprotective aminosterol

Trodusquemine is an amphipathic aminosterol that has recently shown therapeutic benefit in neurodegenerative diseases altering the binding of misfolded proteins to the cell membrane. To unravel the underlying mechanism, we studied the interactions between Trodusquemine (TRO) and lipid monolayers simulating the outer layer of the plasma membrane. We selected two different compositions of dioleoylphosphatidylcholine (DOPC), sphingomyelin (SM), cholesterol (Chol) and monosialotetrahexosylganglioside (GM1) lipid mixture mimicking either a lipid-raft containing membrane (L_d+S_o phases) or a single-phase disordered membrane (L_d phase). Surface pressure-area isotherms and surface compressional modulus-area combined with Brewster Angle Microscopy (BAM) provided the thermodynamic and morphological information on the lipid monolayer in the presence of increasing amounts of TRO in the monolayer. Experiments revealed that TRO forms stable spreading monolayers at the buffer-air interface where it undergoes multiple reversible phase transitions to bi- and tri-layers at the interface. When TRO was spread at the interface with the lipid mixtures, we found that it distributes in the lipid monolayer for both the selected lipid compositions, but a maximum TRO uptake in the rafts-containing monolayer was observed for a Lipid/TRO molar ratio equal to 3:2. Statistical analysis of BAM images revealed that TRO induces a decrease in the size of the condensed domains, an increase in their number and in the thickness mismatch between the L_d and S_o phase. Experiments and MD simulations converge to indicate that TRO adsorbs preferentially at the border of the S_o domains. Removal of GM1 from the lipid L_d+S_o mixture resulted in an even greater TRO-mediated reduction of the size of the S_o domains suggesting that the presence of GM1 hinders the localization of TRO at the S_o domains boundaries. Taken together these observations suggest that Trodusquemine influences the organization of lipid rafts within the neuronal membrane in a dose-dependent manner whereas it evenly distributes in disordered expanded phases of the membrane model.

Influence of the Lipid Backbone on Electrochemical Phase Behavior

Sphingolipids are an important class of lipids found in mammalian cell membranes with important structural and signaling roles. They differ from another major group of lipids, the glycerophospholipids, in the connection of their hydrocarbon chains to their headgroups. In this study, a combination of electrochemical and structural methods has been used to elucidate the effect of this difference on sphingolipid behavior in an applied electric field. N-Palmitoyl sphingomyelin forms bilayers of similar coverage and thickness to its close analogue di-palmitoyl phosphatidylcholine. Grazing incidence diffraction data show slightly closer packing and a smaller chain tilt angle from the surface normal. Electrochemical IR results at low charge density show that the difference in tilt angle is retained on deposition to form bilayers. The bilayers respond differently to increasing electric field strength: chain tilt angles increase for both molecules, but sphingomyelin chains remain tilted as field strength is further increased. This behavior is correlated with disruption of the hydrogen-bonding network of small groups of sphingomyelin molecules, which may have significance for the behavior of molecules in lipid rafts in the presence of strong fields induced by ion gradients or asymmetric distribution of charged lipids.

Landscape of Cellular Bioeffects Triggered by Ultrasound-Induced Sonoporation

Sonoporation is the process of transient pore formation in the cell membrane triggered by ultrasound (US). Numerous studies have provided us with firm evidence that sonoporation may assist cancer treatment through effective drug and gene delivery. However, there is a massive gap in the body of literature on the issue of understanding the complexity of biophysical and biochemical sonoporation-induced cellular effects. This study provides a detailed explanation of the US-triggered bioeffects, in particular, cell compartments and the internal environment of the cell, as well as the further consequences on cell reproduction and growth. Moreover, a detailed biophysical insight into US-provoked pore formation is presented. This study is expected to review the knowledge of cellular effects initiated by US-induced sonoporation and summarize the attempts at clinical implementation.

Study on the mechanism of reducing biofilm toxicity and increasing antioxidant activity in vinegar processing phytomedicines containing pentacyclic triterpenoid saponins

ETHNOPHARMACOLOGICAL RELEVANCE

Pentacyclic triterpenoid saponin (PTS) is a kind of particular chemicals with various pharmacological activities, as well as surface activity, mucosal irritation and hemolysis. PTS is closely related to the exertion of efficacy or adverse reactions in plant medicines rich in this component. For the better clinical application of natural resources, how to reduce toxicity and enhance curative efficacy is an important problem which needs to be solved at present. Till now, there has been few studies directly investigating the problem.

AIM OF STUDY

Through comparison study of Radix Bupleuri (Chai hu) and Pulsatilla chinensis (Bai tou weng), which are typical traditional Chinese medicines containing PTS, explore the potential change rule of material basis and the mechanism of detoxification and synergistic effect of vinegar processing.

MATERIALS AND METHODS

Composition change rule after vinegar processing was applied by UPLC-QTOF-MS/MS coupled with principal component analysis (PCA). Based on our previous research, this paper expounded the action mechanism from the perspective of reducing biofilm toxicity and increasing antioxidant activity. Direct toxicity reducing information was obtained at the cellular level including cellular morphology, MTT assays, western blots and RT-PCR in L02 cells with overload sphingomyelin (SM). The synergistic effect was investigated through histological examinations, mesenteric hemorheology, ELISA, flow cytometry and confocal microscopy.

RESULTS

It was found that the structure of PTS take place a series of chemical reactions in the process of vinegar processing which enabled the more toxic components transformed into less toxic components and components with clear efficacy, so as to achieve the purpose of detoxification and synergistic effect. The results indicated that the mechanism of detoxification in vinegar processing was that vinegar processing could act on SM, cause less balance disturbance to sphingomyelin/ceramide (SM/Cer), inhibit apoptosis and then alleviate toxicity. In addition, the pharmacodynamic results showed that the vinegar processing could have an obvious synergistic effect through anti-oxidant stress.

CONCLUSIONS

By changing the structures of the PTS, the SM/Cer disrupt was reduced and the antioxidant activity was enhanced, so as to decrease toxicity and increase efficiency in vinegar processing phytomedicines containing PTS.

Different effects of oxysterols on a model lipid raft - Langmuir monolayer study complemented with theoretical calculations

Three oxysterols (7β-hydroxycholesterol; 7β-OH, 7-ketocholesterol; 7-K and 25-hydroxycholesterol, 25-OH) differing in the site of oxidation (ring system versus chain) and kind of polar group (hydroxyl versus carbonyl) were studied in lipid raft environment using the Langmuir monolayer technique complemented with theoretical calculations. Experiments were performed for the unmodified raft system, composed of sphingomyelin (SM) and cholesterol (Chol), and in the next step the raft was modified by the incorporation of oxysterol in different proportions. In the examined three-component system (Chol:SM:oxysterol), apart from interactions between the lipid raft components, the affinity of Chol to its oxidized derivatives also plays an important role. 25-OH was found to enhance interactions between SM and Chol and thus stabilize the raft, contrary to 7β-OH and 7-K, which exterted the fluidizing effect as well as the destabilization of the raft. Different action of oxysterols on model raft was observed. 7β-OH and 7-K, which are highly potent inducers of cell dath caused raft destabilization, while 25-OH, which is the least toxic of the investigated oxysterols, was found to stabilize the raft.

Designing a Useful Lipid Raft Model Membrane for Electrochemical and Surface Analytical Studies

A model biomimetic system for the study of protein reconstitution or drug interactions should include lipid rafts in the mixed lipid monolayer, since they are usually the domains embedding membrane proteins and peptides. Four model lipid films composed of three components: 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), cholesterol (Chol) and sphingomyelin (SM) mixed in different molar ratios were proposed and investigated using surface pressure measurements and thermodynamic analysis of the monolayers at the air-water interface and imaged by Brewster angle microscopy. The ternary monolayers were transferred from the air-water onto the gold electrodes to form bilayer films and were studied for the first time by electrochemical methods: alternative current voltammetry and electrochemical impedance spectroscopy and imaged by atomic force microscopy. In excess of DOPC, the ternary systems remained too liquid for the raft region to be stable, while in the excess of cholesterol the layers were too solid. The layers with SM in excess lead to the formation of Chol:SM complexes but the amount of the fluid matrix was very low. The equimolar content of the three components lead to the formation of a stable and well-organized assembly with well-developed raft microdomains of larger thickness, surrounded by the more fluid part of the bilayer. The latter is proposed as a convenient raft model membrane for further physicochemical studies of interactions with drugs or pollutants or incorporation of membrane proteins.

Cholesterol modulates the interaction between paclitaxel and Langmuir monolayers simulating cell membranes

The composition of Langmuir monolayers used as cell membrane models is an essential factor for the interaction with biologically-relevant molecules, including pharmaceutical drugs. In this paper, we report the modulation of effects from the antineoplastic drug paclitaxel by the relative concentration of cholesterol in the Langmuir monolayers of ternary mixtures of dipalmitoylphosphatidylcholine, sphingomyelin, and cholesterol. Since the dependence on cholesterol concentration for these monolayers simulating lipid rafts is non-monotonic, we analyzed the surface pressure and compressibility modulus data with the multidimensional projection technique referred to as interactive document mapping (IDMAP). The maximum expansion induced by paclitaxel in surface pressure isotherms was observed for 27% cholesterol, while the compressibility modulus decreased most strongly for the monolayer with 48% cholesterol. Therefore, the physiological action of paclitaxel may vary depending on whether it is associated with penetration in the membrane or with changes in the membrane elasticity.

How the replacement of cholesterol by 25-hydroxycholesterol affects the interactions with sphingolipids: The Langmuir Monolayer Study complemented with theoretical calculations

In this paper, a representative of chain-oxidized sterols, 25-hydroxycholesterol (25-OH), has been studied in Langmuir monolayers mixed with the sphingolipids sphingomyelin (SM) and ganglioside (GM₁) to build lipid rafts. A classical Langmuir monolayer approach based on thermodynamic analysis of interactions was complemented with microscopic visualization of films (Brewster angle microscopy), surface-sensitive spectroscopy (polarization modulation-infrared reflection-absorption spectroscopy) and theoretical calculations (density functional theory modelling and molecular dynamics simulations). Strong interactions between 25-OH and both investigated sphingolipids enabled the formation of surface complexes. As known from previous studies, 25-OH in pure monolayers can be anchored to the water surface with a hydroxyl group at either C(3) or C(25). In this study, we investigated how the presence of additional strong interactions with sphingolipids modifies the surface arrangement of 25-OH. Results have shown that, in the 25-OH/GM₁ system, there are no preferences regarding the orientation of the 25-OH molecule in surface complexes and two types of complexes are formed. On the other hand, SM enforces one specific orientation of 25-OH: being anchored with the C(3)-OH group to the water. The strength of interactions between the studied sphingolipids and 25-OH versus cholesterol is similar, which indicates that cholesterol may well be replaced by oxysterol in the lipid raft system. In this way, the composition of lipid rafts can be modified, changing their rheological properties and, as a consequence, influencing their proper functioning.

Pulsatilla chinensis saponins cause liver injury through interfering ceramide/sphingomyelin balance that promotes lipid metabolism dysregulation and apoptosis

BACKGROUND

P. chinensis saponins (PRS) are pentacyclic triterpenoid bioactive constituents from Pulsatilla chinensis (Bunge) Regel. In our previous study, PRS caused chronic liver injury (CLI) with the significant changes of lipid metabolites including sphingomyelin (SM) in serum after long-term administration. The SM in the hepatocytes membrane plays an indispensable role in maintaining cell membrane stability and regulating the extracellular and intracellular signal transduction. However, it is still unknown the pathway related to SM and the mechanism of CLI on hepatocyte.

PURPOSE

The purpose of this study was to explore the hepatotoxicity mechanism of PRS in vivo and in vitro, to reveal the action of mechanism of SM and the pathway related to liver injury.

METHODS

SD rats were orally administered with PRS for 240 days and liver injury was evaluated by histological examinations. Metabolomics analysis was used to explore the liver metabolic pathway affected by PRS, and the expressions of related proteins were evaluated by western blots. To discover and elucidate the underlying mechanisms of metabolites changes induced by PRS at the cellular level, cellular morphology, MTT assays, western blots and cell membrane potential measurements were carried out using LO2 cells. Furthermore, the roles of SM and cholesterol (Chol) in hepatocyte injury were investigated individually in overload Chol and SM groups. Sphingolipid metabolic pathway related with ceramide/sphingomyelin (Cer/SM) balance was explored using cellular lipidomics and RT-PCR.

RESULTS

PRS gradually damaged the rat's liver in a time-dependent manner. The analysis of liver metabolism profiles showed that lipids metabolites were changed, including sphingolipid, bile acid, linoleic acid and fatty acid. We found that PRS induced apoptosis by interfering with bile acid-mediated sphingolipid metabolic pathway and Cer/SM balance in CLI. In in vitro experiments, PRS led to the increase of LDH leakage, depolarized cell membrane potential and caused cell membrane toxicity. Furthermore, PRS inducedG0/G1 phase cell cycle arrest in LO2 cells, simultaneously activated cellular extrinsic and intrinsic apoptosis pathways. PRS acted on SM and interfered with Cer/SM balance, which promote lipid metabolism dysregulation and apoptosis.

CONCLUSION

PRS acted on SM to interfere Cer/SM balance on LO2 cell. Both in vivo and in vitro, PRS induced Cer/SM imbalance which promoted lipid metabolism disorder and apoptosis. Apoptosis and lipids changes gradually damaged the rats liver, and ultimately developed into CLI.

Cholesterol Regulates the Incorporation and Catalytic Activity of Tissue-Nonspecific Alkaline Phosphatase in DPPC Monolayers

Matrix vesicles (MVs) are a special class of extracellular vesicles that drive bone and dentin mineralization by providing the essential enzymes and ions for the nucleation and propagation of mineral crystals. Tissue-nonspecific alkaline phosphatase (TNAP) is an integral protein of MV membrane and participates in biomineralization by hydrolyzing extracellular pyrophosphate (PP_i), a strong mineralization inhibitor, and forming inorganic phosphate (P_i), necessary for the growth of mineral crystals inside MVs and their propagation once released in the extracellular matrix. MV membrane is enriched in cholesterol (CHOL), which influences the incorporation and activity of integral proteins in biologic membranes; however, how CHOL controls the incorporation and activity of TNAP in MV membrane has not yet been elucidated. In the present study, Langmuir monolayers were used as a MV membrane biomimetic model to assess how CHOL affects TNAP incorporation and activity. Surface pressure-area (π-A) isotherms of binary dipalmitoilphosphatidylcholine (DPPC)/CHOL monolayers showed that TNAP incorporation increases with CHOL concentration. Infrared spectroscopy showed that CHOL influences the conformation and orientation of the enzyme. Optical-fluorescence micrographs of the monolayers revealed the tendency of TNAP to incorporate into CHOL-rich microdomains. These data suggest that TNAP penetrates more efficiently and occupies a higher surface area into monolayers with a lower CHOL concentration due to the higher membrane fluidity. However, the quantity of enzyme transferred to solid supports as well as the enzymatic activity were higher using monolayers with a higher CHOL concentration due to increased rigidity that changes the enzyme orientation at the air-solid interface. These data provide new insights regarding the interfacial behavior of TNAP and CHOL in MVs and shed light on the biochemical and biophysical processes occurring in the MV membrane during biomineralization at the molecular level.

Langmuir-Blodgett films of membrane lipid in the presence of hybrid silsesquioxane, a promising component of biomaterials

Functionalized polyhedral oligomeric silsesquioxanes (POSS) derivatives have great potential in biomedical applications such as tissue engineering, drug delivery, biosensors, dental composites and biomedical devices. Having the above in mind, in this paper, the study of the surface characteristics of binary Langmuir-Blodgett films consisting of an open cage silsesquioxane POSS-poly (ethylene glycol) (POSS-PEG) and 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE), as a representative of phospholipid was conducted based on contact angle measurements of three liquids. The measured values of the contact angle (with water, formamide and diiodomethane as the wetting liquids) allowed to calculate surface free energy of the films from van Oss et al. approach. The film structure of the deposited layers was evaluated using an atomic force microscope. Analysis of the obtained results led to the conclusion, that the pure DMPE molecules create agglomerates onto a solid substrate, whereas the POSS-PEG molecules form a homogenous monolayer. After an addition of POSS-PEG to lipid film, changes in the surface properties are visible. The wettability as well as surface free energy depend on the molar ratio of both components. The AFM images shed more light on the changes of the DMPE monolayer topography caused by the POSS-PEG addition.

The influence of an antitumor lipid - erucylphosphocholine - on artificial lipid raft system modeled as Langmuir monolayer

Outer layer of cellular membrane contains ordered domains enriched in cholesterol and sphingolipids, called 'lipid rafts', which play various biological roles, i.e., are involved in the induction of cell death by apoptosis. Recent studies have shown that these domains may constitute binding sites for selected drugs. For example alkylphosphocholines (APCs), which are new-generation antitumor agents characterized by high selectivity and broad spectrum of activity, are known to have their molecular targets located at cellular membrane and their selective accumulation in tumor cells has been hypothesized to be linked with the alternation of biophysical properties of lipid rafts. To get a deeper insight into this issue, interactions between representative APC: erucylphosphocholine, and artificial lipid raft system, modeled as Langmuir monolayer (composed of cholesterol and sphingomyelin mixed in 1:2 proportion) were investigated. The Langmuir monolayer experiments, based on recording surface pressure-area isotherms, were complemented with Brewster angle microscopy results, which enabled direct visualization of the monolayers structure. In addition, the investigated monolayers were transferred onto solid supports and studied with AFM. The interactions between model raft system and erucylphosphocholine were analyzed qualitatively (with mean molecular area values) as well as quantitatively (with ΔG(exc) function). The obtained results indicate that erucylphosphocholine introduced to raft-mimicking model membrane causes fluidizing effect and weakens the interactions between cholesterol and sphingomyelin, which results in phase separation at high surface pressures. This leads to the redistribution of cholesterol molecules in model raft, which confirms the results observed in biological studies.