Function Of Lipid Concentration Research Articles

Mechanistic Pathway of Lipid Phase-Dependent Lipid Corona Formation on Phenylalanine-Functionalized Gold Nanoparticles: A Combined Experimental and Molecular Dynamics Simulation Study.

In recent years, the underlying mechanism of formation of the lipid corona and its stability have begun to garner interest in the nanoscience community. However, until now, very little is known about the role of different properties of nanoparticles (NPs) (surface charge density, hydrophobicity, and size) in lipid corona formation. Apart from the physicochemical properties of NPs, the different properties of lipids remain elusive in lipid corona formation. In the present contribution, we have investigated the interaction of phenylalanine-functionalized gold NPs (Au-Phe NPs) with different zwitterionic lipid vesicles of different phase states (sol-gel and liquid crystalline at room temperature) as a function of lipid concentration. The main objective of the present work is to understand how the lipid phase affects lipid corona formation and lipid-induced aggregation in various media. Our results establish that the lipid phase state, area per lipid head group, and the buffer medium play important roles in lipid-induced aggregation. The lipid corona occurs for NPs at high lipid concentration, irrespective of the phase states and area per lipid head group of the lipid bilayer. Notably, the lipid corona also forms at a low concentration of lipid vesicles in the liquid crystalline phase (1,2-dioleoyl-sn-glycero-3-phosphocholine). The corona formation brings in remarkable stability to NPs against freeze-thaw cycles. Based on the stability, for the first time, we classify lipid corona as "hard lipid corona" and "soft lipid corona". This distinct classification will help to develop suitable nanomaterials for various biomedical applications.

Mitochondrial respiration and ROS emission during β-oxidation in the heart: An experimental-computational study.

Lipids are main fuels for cellular energy and mitochondria their major oxidation site. Yet unknown is to what extent the fuel role of lipids is influenced by their uncoupling effects, and how this affects mitochondrial energetics, redox balance and the emission of reactive oxygen species (ROS). Employing a combined experimental-computational approach, we comparatively analyze β-oxidation of palmitoyl CoA (PCoA) in isolated heart mitochondria from Sham and streptozotocin (STZ)-induced type 1 diabetic (T1DM) guinea pigs (GPs). Parallel high throughput measurements of the rates of oxygen consumption (VO2) and hydrogen peroxide (H2O2) emission as a function of PCoA concentration, in the presence of L-carnitine and malate, were performed. We found that PCoA concentration < 200 nmol/mg mito protein resulted in low H2O2 emission flux, increasing thereafter in Sham and T1DM GPs under both states 4 and 3 respiration with diabetic mitochondria releasing higher amounts of ROS. Respiratory uncoupling and ROS excess occurred at PCoA > 600 nmol/mg mito prot, in both control and diabetic animals. Also, for the first time, we show that an integrated two compartment mitochondrial model of β-oxidation of long-chain fatty acids and main energy-redox processes is able to simulate the relationship between VO2 and H2O2 emission as a function of lipid concentration. Model and experimental results indicate that PCoA oxidation and its concentration-dependent uncoupling effect, together with a partial lipid-dependent decrease in the rate of superoxide generation, modulate H2O2 emission as a function of VO2. Results indicate that keeping low levels of intracellular lipid is crucial for mitochondria and cells to maintain ROS within physiological levels compatible with signaling and reliable energy supply.

Negatively Charged Lipid Membranes Catalyze Supramolecular Hydrogel Formation.

In this contribution we show that biological membranes can catalyze the formation of supramolecular hydrogel networks. Negatively charged lipid membranes can generate a local proton gradient, accelerating the acid-catalyzed formation of hydrazone-based supramolecular gelators near the membrane. Synthetic lipid membranes can be used to tune the physical properties of the resulting multicomponent gels as a function of lipid concentration. Moreover, the catalytic activity of lipid membranes and the formation of gel networks around these supramolecular structures are controlled by the charge and phase behavior of the lipid molecules. Finally, we show that the insights obtained from synthetic membranes can be translated to biological membranes, enabling the formation of gel fibers on living HeLa cells.

Drug–liposome distribution phenomena studied by capillary electrophoresis‐frontal analysis

The potential of using CE frontal analysis (CE-FA) for the study of low-molecular-weight drug-liposome interactions was assessed. The interaction of bupivacaine, brompheniramine, chlorpromazine, imipramine, and ropivacaine with net negatively charged 80/20 mol% 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine/egg yolk phosphatidic acid liposome suspensions in HEPES buffer at pH 7.4 was investigated. The fraction of free drug as a function of lipid concentration was measured and apparent liposome-buffer distribution coefficients were determined for the basic drug substances. The distribution coefficients increased in the order ropivacaine, bupivacaine, brompheniramine, imipramine, and chlorpromazine. The developed CE method was relatively fast allowing estimates of drug-liposome affinity to be obtained within 15 min. CE-FA may have the potential to become a valuable tool for the characterization of drug-liposome interactions in relation to estimation of drug lipophilicity and for the evaluation of drug distribution in liposomal drug delivery systems.

Preparation and cytotoxicity of cisplatin-containing liposomes

We encapsulated cisplatin into stealth pH-sensitive liposomes and studied their stability, cytotoxicity and accumulation in a human small-cell lung carcinoma cell line (GLC4) and its resistant subline (GLC4/CDDP). Since reduced cellular drug accumulation has been shown to be the main mechanism responsible for resistance in the GLC4/CDDP subline, we evaluated the ability of this new delivery system to improve cellular uptake. The liposomes were composed of dioleoylphosphatidylethanolamine (DOPE), cholesteryl hemisuccinate (CHEMS), and distearoylphosphatidylethanolamine-polyethyleneglycol 2000 (DSPE-PEG2000) and were characterized by determining the encapsulation percentage as a function of lipid concentration. Among the different formulations, DOPE/CHEMS/DSPE-PEG liposomes (lipid concentration equal to 40 mM) encapsulated cisplatin more efficiently than other concentrations of liposomes (about 20.0%, mean diameter of 174 nm). These liposomes presented good stability in mouse plasma which was obtained using a 0.24-M EDTA solution (70% cisplatin was retained inside the liposomes after 30 min of incubation). Concerning cytotoxic effects, they are more effective (1.34-fold) than free cisplatin for growth inhibition of the human lung cancer cell line A549. The study of cytotoxicity to GLC4 and GLC4/CDDP cell lines showed similar IC50 values (approximately 1.4 microM), i.e., cisplatin-resistant cells were sensitive to this cisplatin formulation. Platinum accumulation in both sensitive and resistant cell lines followed the same pattern, i.e., approximately the same intracellular platinum concentration (4.0 x 10-17 mol/cell) yielded the same cytotoxic effect. These results indicate that long-circulating pH-sensitive liposomes, also termed as stealth pH-sensitive liposomes, may present a promising delivery system for cisplatin-based cancer treatment. This liposome system proved to be able to circumvent the cisplatin resistance, whereas it was not observed when using non-long-circulating liposomes composed of phosphatidylcholine, phosphatidylserine, and cholesterol.

Giant Polymerlike Micelles Formed by Nucleoside-Functionalized Lipids

We report an investigation on the aggregation of 1,2-dilauroyl-sn-glycero-3-phosphatidyluridine (DLPU), a surfactant molecule that merges the self-assembling properties of lecithins with the molecular recognition characteristics of nucleic bases in a phosphate-buffered aqueous solution at physiological pH and as a function of lipid concentration. Because spontaneous self-assembly and interfacial properties are the result of a delicate balance between hydrophobic interactions and polar-head interactions, a structural characterization is essential for a complete and full understanding of base−base properties in the aggregates, as observed by spectroscopic techniques. Small-angle neutron scattering, static light scattering, and quasi-elastic light scattering have been employed to assess the structural evolution of the binary system as the lipid concentration is increased. The data indicate the presence of rather flexible elongated aggregates, whose local structure is cylindrical and remains essentially uncha...

A Silicate Gel for Promoting Deposition of Lipid Bilayers

A simple method for modifying a polymer surface to induce lipid bilayer formation by vesicle fusion is described. A silicate gel was prepared by condensation of tetraethyl orthosilicate (TEOS) in the presence of acid. When applied to a poly(methylmethacrylate) substrate, either a rough or a smooth layer could be produced, depending on the method used for the application. The smooth surface induced formation of a supported lipid bilayer by fusion of lipid vesicles; the rough silicate surface induced adsorption of a vesicle layer. A high-frequency acoustic waveguide device was used to follow the initial adsorption of vesicles, the transition from a vesicle layer to a bilayer, and the formation of a complete bilayer; the time required to form a bilayer was determined as a function of lipid concentration in suspension. The presence of a bilayer on the smooth silicate surface was confirmed by fluorescence recovery after photobleaching. An additional procedure is described to modify a gold surface to induce bilayer formation.

Europium III Binding and the Reorientation of Magnetically Aligned Bicelles: Insights from Deuterium NMR Spectroscopy

Solid-state deuterium ( 2H) NMR spectroscopy was used to study the reorientation of magnetically ordered bicelles in the presence of the paramagnetic lanthanide Eu 3+. Bicelles were composed of 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) plus 1,2-dihexanoyl- sn-glycero-3-phosphocholine plus either the anionic lipid 1,2-dimyristoyl- sn-3-phosphoglycerol, or the cationic lipid 1,2-dimyristoyl-3-trimethyl ammonium propane. Alignment of the bicelles in the magnetic field produced 2H NMR spectra consisting of a pair of quadrupole doublets, one from the α-deuterons and one from the β-deuterons of DMPC- α, β- d 4. Eu 3+ addition induced the appearance of a second set of quadrupole doublets, having approximately twice the quadrupolar splittings of the originals, and growing progressively in intensity with increasing Eu 3+, at the expense of the intensity of the originals. The new resonances were attributed to bicelles having a parallel alignment with respect to the magnetic field, as opposed to the perpendicular alignment preferred in the absence of Eu 3+. Therefore, the equilibrium degree and kinetics of reorientation could be evaluated from the 2H NMR spectra. For more cationic initial surface charges, higher amounts of added Eu 3+ were required to induce a given degree of reorientation. However, the equilibrium degree of bicellar reorientation was found to depend solely on the amount of bound Eu 3+, regardless of the bicelle composition. The kinetics of reorientation were a function of lipid concentration. At high lipid concentration, a single fast rate of reorientation (minutes) described the approach to the equilibrium degree of orientation. At lower lipid concentrations, two rates processes were discernible: one fast (minutes) and one slow (hours). The data indicate, therefore, that bicelle reorientation is a phase transition made critical by bicelle-bicelle interactions.

Role of Hydrophobic Residues in the C1b Domain of Protein Kinase C δ on Ligand and Phospholipid Interactions

The C1 domains of conventional and novel protein kinase C (PKC) isoforms bind diacylglycerol and phorbol esters with high affinity. Highly conserved hydrophobic residues at or near the rim of the binding cleft in the second cysteine-rich domain of PKC-delta (PKC-deltaC1b) were mutated to probe their roles in ligand recognition and lipid interaction. [(3)H]Phorbol 12,13-dibutyrate (PDBu) binding was carried out both in the presence and absence of phospholipids to determine the contribution of lipid association to the ligand affinity. Lipid dependence was determined as a function of lipid concentration and composition. The binding properties of a high affinity branched diacylglycerol with lipophilicity similar to PDBu were compared with those of PDBu to identify residues important for ligand selectivity. As expected, Leu-20 and Leu-24 strongly influenced binding. Substitution of either by aspartic acid abolished binding in either the presence or absence of phosphatidylserine. Mutation of Leu-20 to Arg or of Leu-24 to Lys caused a dramatic (340- and 250-fold, respectively) reduction in PDBu binding in the presence of lipid but only a modest reduction in the weaker binding of PDBu observed in the absence of lipid, suggesting that the main effect was on C1 domain -phospholipid interactions. Mutation of Leu-20 to Lys or of Trp-22 to Lys had modest (3-fold) effects and mutation of Phe-13 to Tyr or Lys was without effect. Binding of the branched diacylglycerol was less dependent on phospholipid and was more sensitive to mutation of Trp-22 to Tyr or Lys, especially in the presence of phospholipid, than was PDBu. In terms of specific PKC isoforms, our results suggest that the presence of Arg-20 in PKC-zeta may contribute to its lack of phorbol ester binding activity. More generally, the results emphasize the interplay between the C1 domain, ligand, and phospholipid in the ternary binding complex.

The effect of temperature on food emulsifiers at fluid–fluid interfaces

Heat-induced interfacial aggregation of a whey protein isolate (WPI) with a high content of β-lactoglobulin (>92%), previously adsorbed at the oil–water interface, was studied by means of interfacial dynamic characteristics performed in an automatic drop tensiometer. Protein concentration in aqueous bulk phase ranging between 1×10 −1 and 1×10 −5 % wt/wt was studied as a variable. The experiments were carried out at temperatures ranging from 20–80°C with different thermal regimes. During the heating period, competition exists between the effect of temperature on the film fluidity and the increase in mechanical properties associated with the interfacial gelation process. Interfacial crystallisation of food polar lipids (monopalmitin, monoolein, and monolaurin) previously adsorbed at the oil–water interface, was studied by interfacial dynamic characteristics (interfacial tension and surface dilational properties). The temperature, ranging between 40 and 2°C, and the lipid concentration in aqueous oil phase, ranging between 1×10 −2 and 1×10 −4 % wt/wt, were studied as variables. Significant changes in interfacial dynamic characteristics associated with interfacial lipid crystallisation were observed as a function of lipid concentration in the bulk phase. Interfacial crystallisation of food polar lipids (monopalmitin, monoolein, and monolaurin) at the air–water interface, was studied by π-A isotherms performed in a Langmuir trough coupled with Brewster angle microscopy (BAM). A condensation in monoglyceride monolayers towards lower molecular area was observed as the temperature decreased. This effect was attributed to lipid crystallisation at lower temperatures. BAM images corroborated the effect of temperature on the monolayer structure, as a function of the monoglyceride type.

α-Amylase kinetic parameters modulation by lecithin vesicles: binding versus entrapment

The effect of α-amylase–lipid interaction and entrapment inside lipidic soybean lecithin (PC) vesicles on the kinetic parameters of the enzyme was investigated. Human saliva was used as enzyme source and starch as substrate. Reaction kinetics were followed by measuring the consumption of starch as revealed by the decrease in the absorbance at 600 nm of the I 2–starch complex. The presence of PC induced a decrease in A 600 at low concentrations; above 0.1 g PC/l light scattering became important and an increase in absorbance was observed as a function of lipid concentration. These effects were taking into account in the interpretation of results. Multilamellar vesicles (MLVs) and giant unilamellar vesicles (GUVs) were prepared by established procedures; enzyme was ‘entrapped’ by the inclusion of saliva, conveniently diluted, in the buffer used for lipid dispersion during the preparation of vesicles. The kinetic parameters K M and V max were determined by adjusting saturation curves to the Michaelis–Menten equation by a computer assisted nonlinear regression analysis by the least squares method. The presence of PC in MLVs induced an increment of the value of K M of α-amylase for starch as the substrate both in the condition we designated as ‘entrapped’ and when the enzyme was applied to the already formed liposomes (‘untrapped’). The effects exerted by PCs MLVs on K M and V max were statistically significant only at the highest PC/protein mass ratio used (28 g/g). GUVs affected amylase K M only in some of the ‘entrapped’ samples at random suggesting certain aggresiveness of the GUVs preparation method. V max decreased significantly only in the ‘entrapped’ samples. The higher effect of MLVs in reducing the affinity of the enzyme for starch compared with that of GUVs is probably due to a higher protein adsorbing capacity of the lower molecular packing, higher surface tension and more curved MLV surface compared with the GUV surface. The binding of the enzyme to the lipidic surface is reversible and can be modulated by the presence of high salt concentrations or with the pH of the media which affect the surface electrostatics of both, the lipidic and the protein surfaces. The conclusions drown from the present experiments represent the average behavior of all the isozymes that represent α-amylase from human saliva and may be useful for understanding α-amylase activity in heterogenous media of physiological and technological importance.

Comparative investigation of Langmuir–Blodgett films and Self-Assembled Monolayers on metal surfaces

We studied a single chain thiol and a double chain dithiocarbammate with alkyl chains of comparable length and sulphur containing head-groups. We preliminary characterised the spreading monolayers of both compounds at the water–air interface. The formation of self-assembled films on metal substrates as a function of lipid concentration and immersion time was investigated by contact angle, ellipsometric and FT-IR measurements. The same techniques were used to characterise Langmuir–Blodgett (LB) films of the same substances. The results showed that the behaviour at water–air interface strongly conditioned the properties of the resulting LB films, whereas the structural features of Self-Assembled Monolayers (SAM) samples depended mainly on the adsorption sites distribution of the metal surface.

Small-Angle Neutron Scattering of Bilayer Vesicles Made with Synthetic Phospholipids

AbstractWe have used Small-Angle Neutron Scattering to investigate the structure of bilayer lipid membranes in aqueous solution. The lipids consist of equimolar concentrations of two molecules DMPG and DMPC (see text). The structures consist of solvent filled cores surrounded by shells composed of the lipid bilayers. In particular the radii of the core and shell thickness are measured as a function of lipid concentration and temperature. Other features which reveal themselves are vesicle forming ability of the lipids, additional larger structures and inter-vesicle interactions at large vesicle concentrations. The study is motivated by the possible use of these systems as delivery vehicles for various beneficial therapeutic compounds.

The size dependence of cholate-dialyzed vesicles on phosphatidylcholine concentration

The size dependence of vesicles prepared by dialysis of cholate from phosphatidylcholine (PC) dispersions has been investigated as a function of lipid concentration (at a constant applied lipid:detergent molar ratio of 0.7). Gel filtration of dialyzed samples produced a symmetrical profile shape, although quasielastic laser light scattering analysis of the fractions revealed an asymmetrical range of sizes about the peak for solutions containing elevated lipid concentrations. Vesicle diameters increased by approximately 20 nm for PC concentrations ranging from 10 to a maximum of 45 mg/ml. This was attributed to mixed micelle sizes being proportional to lipid concentration, since the diameters of vesicles produced from dialysis are determined by mixed micelle sizes. Before commencement of dialysis, mixed micelle sizes are proportional to lipid concentration and, although dialysis causes an increase in mixed micelle sizes, the phase ratios attained are larger for solutions containing elevated lipid concentrations.

Effect of tryptophan derivatives on the phase properties of bilayers

Binding of several tryptophan derivatives and tryptophan-containing peptides to bilayers is examined by monitoring fluorescence enhancement as a function of lipid concentration. The thermodynamic and spectral parameters of the solutes in the bilayers of vesicles and liposomes do not exhibit any anomalous dependence upon the gel or the liquid-crystalline phase state of the bilayer. Effects of these solutes on the phase-transition profiles of the bilayers of liposomes and vesicles are examined, and the lowering of the phase-transition temperature is correlated with the mole fraction of the solute in the bilayer. The partition coefficients do not change at the main phase-transition temperature. These observations contradict the thermodynamic explanation of the solute-induced lowering of the phase-transition temperature which is based on the Van't Hoff relationship for distribution of the solute in the two coexisting phases at the phase-transition temperature. It is postulated that solute molecules bound to defect sites in bilayers modulate the phase properties of bilayers. These defect sites are induced in the gel phase of bilayers of liposomes above the subtransition temperature.

Interactions of pyrene derivatives with lipid bilayers and with (Ca2+-Mg2+)-ATPase.

The intensities of fluorescence emission for pyrene and a number of its derivatives increase on binding to lipid bilayers and to the (Ca2+-Mg2+)-ATPase purified from rabbit muscle sarcoplasmic reticulum. The effect is particularly marked for the less water-soluble derivatives. Changes in intensity for monomer and excimer emission as a function of lipid concentration can be fitted to a simple model to obtain binding parameters. The number of binding sites per lipid is 0.2-0.4. For the ATPase system, at least two classes of sites are necessary to fit the data, one corresponding to the lipid component and one to sites on the ATPase. Excimer emission from the postulated sites on the ATPase is less marked than that from lipid. Pyrene-dodecanoic acid and pyreneundecyltrimethylammonium bromide, which bind to a large number of sites on the ATPase, cause marked inhibition of ATPase activity at high concentration. Pyrene and a number of water-soluble derivatives cause stimulation of the ATPase reconstituted with dimyristoleoylphosphatidylcholine and little inhibition and bind to a small number of sites on the ATPase. It is concluded that excimer emission from pyrene derivatives in systems containing proteins cannot be used to obtain reliable information about rates of diffusion in the lipid component of the membrane.

Osmotic behavior of liposomes of phosphatidylcholine and phosphatidylsulfocholine as a function of lipid concentration

A relationship between the initial rate of liposome swelling, d(1/ A)/ dt and the reciprocal of the lipid concentration of the liposomes has been derived and then utilized to describe the osmotic swelling behavior of serially diluted liposomes and chloroplasts exposed to hypertonic urea solutions. The slopes of plots of d(1/ A)/ dt vs. the reciprocal of the lipid concentration of liposomes were not affected by differences in the initial absorbance of phosphatidylcholine-sterol bilayers, and were used to assess the ability of sterols to reduce the initial rates of urea permeation through dimyristoylphosphatidylcholine (DMPC) bilayers in the liquid-crystalline state. Multilamellar liposomes and sonicated vesicles were prepared from dimyristoylphosphatidylsulfocholine (DMPSC), in which the quaternary ammonium group of choline is replaced by -S +(CH 3) 2. Cholesterol reduced the initial rate of osmotic urea penetration into liposomes and the rate of 6-carboxyfluorescein efflux from vesicles at 35°C. The effect of cholesterol on bilayers of phosphatidylsulfocholine and phosphatidylcholine was very similar, suggesting that no strict structural requirements need be met in the choline moiety for lecithin-cholesterol interaction. The sulfonium analog could thus functionally replace phosphatidylcholine in natural membranes.

Preparation and properties of liposome-associated gentamicin

Gentamicin was successfully incorporated into neutral, anionic, and cationic liposomes, and the percentage of gentamicin incorporated was found to be a function of lipid concentration. Gentamicin did not leak out of the liposomes over a 3-week period at 4 degrees C. When liposome-associated gentamicin was administered intravenously to rabbits, its serum half-life was greatly prolonged. Intragastric administration of dipalmitoylphosphatidylcholine liposomes containing gentamicin resulted in the appearance of gentamicin in serum. Liposome-associated gentamicin, when administered intravenously, led to the appearance of gentamicin in the liver and spleen, which was not observed when rabbits were injected with free gentamicin.

THE USE OF MONOSOMICS TO DETECT GENES CONDITIONING LIPID CONTENT IN ZEA MAYS L. EMBRYOS

The effects of monosomy of specific chromosomes on the lipid content of Zea mays embryos were studied. The lipid content of single kernels was measured by wide-line nuclear magnetic resonance spectroscopy. Significantly less lipid was found in embryos monosomic for chromosomes 2, 6, or 10 of a uniform genetic background than in their diploid controls. Thus, genes or gene complexes determining lipid content that exhibit dosage effects are located on these chromosomes. The distribution of lipid content of monosomic 8 embryos is the same as in the control; thus, monosomy per se does not decrease lipid content. Genetic control of lipid content within the embryo of monosomic 2 plants is a function of lipid concentration and not of embryo size. This study demonstrates that monosomic analysis can be used to determine whether genes expressing dosage effects reside on a given chromosome.

Polymorphism of phosphatidylethanolamines from two natural sources

Two pure phosphatidylethanolamines, isolated from porcine erythrocytes (PPE) and from larvae of Phormia regina (FPE), were analysed and found to differ only in their fatty-acyl composition. An X-ray diffraction study was made of the equilibrium structures formed by these two lipids, in water, as a function of lipid concentration and of temperature. They behave identically and the structural parameters of a widely occurring lamellar phase were determined and found to be similar to phosphatidylcholine. The lamellar phase, composed of alternating layers of lipid, of thickness d 1, and water, of thickness d w , swells only to a limited extent ( d w maximum is 13 Å) and d 1 varies from 38 Å to 43 Å as the lipid concentration varies from 70% to 90% dry weight. The equilibrium structures formed by FPE and PPE in low pH buffers are quite different, PPE being identical to that in water but FPE forming a cubic phase. The reason for the difference is unclear, but the results suggest the importance of fatty-acyl composition and of the effect of pH on the polymorphism of these systems.