Osmotic dependence of the lysophosphatidylcholine lytic action on liposomes in the gel state

Manipulation of encapsulated artificial phospholipid membranes using sub-micellar lysolipid concentrations

Droplet Interface Bilayers (DIBs) constitute a commonly used model of artificial membranes for synthetic biology research applications. However, their practical use is often limited by their requirement to be surrounded by oil. Here we demonstrate in-situ bilayer manipulation of submillimeter, hydrogel-encapsulated droplet interface bilayers (eDIBs). Monolithic, Cyclic Olefin Copolymer/Nylon 3D-printed microfluidic devices facilitated the eDIB formation through high-order emulsification. By exposing the eDIB capsules to varying lysophosphatidylcholine (LPC) concentrations, we investigated the interaction of lysolipids with three-dimensional DIB networks. Micellar LPC concentrations triggered the bursting of encapsulated droplet networks, while at lower concentrations the droplet network endured structural changes, precisely affecting the membrane dimensions. This chemically-mediated manipulation of enclosed, 3D-orchestrated membrane mimics, facilitates the exploration of readily accessible compartmentalized artificial cellular machinery. Collectively, the droplet-based construct can pose as a chemically responsive soft material for studying membrane mechanics, and drug delivery, by controlling the cargo release from artificial cell chassis.

Breakdown of classical paradigms in relation to membrane structure and functions

Updates of the mosaic fluid membrane model implicitly sustain the paradigms that bilayers are closed systems conserving a state of fluidity and behaving as a dielectric slab. All of them are a consequence of disregarding water as part of the membrane structure and its essential role in the thermodynamics and kinetics of membrane response to bioeffectors. A correlation of the thermodynamic properties with the structural features of water makes possible to introduce the lipid membrane as a responsive structure due to the relaxation of water rearrangements in the kinetics of bioeffectors' interactions. This analysis concludes that the lipid membranes are open systems and, according to thermodynamic of irreversible formalism, bilayers and monolayers can be reasonable compared under controlled conditions. The inclusion of water in the complex structure makes feasible to reconsider the concept of dielectric slab and fluidity.

Interaction of N-acetylcysteine with DPPC liposomes at different pH: a physicochemical study

The N-acetylcysteine (NAC) is a commonly used mucolytic and antioxidant agent.

Functional Hydration Behavior: Interrelation between Hydration and Molecular Properties at Lipid Membrane Interfaces

Water is an abundant commodity and has various important functions. It stabilizes the structure of biological macromolecules, controls biochemical activities, and regulates interfacial/intermolecular interactions. Common aspects of interfacial water can be obtained by overviewing fundamental functions and properties at different temporal and spatial scales. It is important to understand the hydrogen bonding and structural properties of water and to evaluate the individual molecular species having different hydration properties. Water molecules form hydrogen bonds with biomolecules and contribute to the adjustment of their properties, such as surface charge, hydrophilicity, and structural flexibility. In this review, the fundamental properties of water molecules and the methods used for the analyses of water dynamics are summarized. In particular, the interrelation between the hydration properties, determined by molecules, and the properties of molecules, determined by their hydration properties, are discussed using the lipid membrane as an example. Accordingly, interesting water functions are introduced that provide beneficial information in the fields of biochemistry, medicine, and food chemistry.

Structural and functional properties of hydration and confined water in membrane interfaces

The scope of the present review focuses on the interfacial properties of cell membranes that may establish a link between the membrane and the cytosolic components. We present evidences that the current view of the membrane as a barrier of permeability that contains an aqueous solution of macromolecules may be replaced by one in which the membrane plays a structural and functional role. Although this idea has been previously suggested, the present is the first systematic work that puts into relevance the relation water-membrane in terms of thermodynamic and structural properties of the interphases that cannot be ignored in the understanding of cell function. To pursue this aim, we introduce a new definition of interphase, in which the water is organized in different levels on the surface with different binding energies. Altogether determines the surface free energy necessary for the structural response to changes in the surrounding media. The physical chemical properties of this region are interpreted in terms of hydration water and confined water, which explain the interaction with proteins and could affect the modulation of enzyme activity. Information provided by several methodologies indicates that the organization of the hydration states is not restricted to the membrane plane albeit to a region extending into the cytoplasm, in which polar head groups play a relevant role. In addition, dynamic properties studied by cyclic voltammetry allow one to deduce the energetics of the conformational changes of the lipid head group in relation to the head-head interactions due to the presence of carbonyls and phosphates at the interphase. These groups are, apparently, surrounded by more than one layer of water molecules: a tightly bound shell, that mostly contributes to the dipole potential, and a second one that may be displaced by proteins and osmotic stress. Hydration water around carbonyl and phosphate groups may change by the presence of polyhydroxylated compounds or by changing the chemical groups esterified to the phosphates, mainly choline, ethanolamine or glycerol. Thus, surface membrane properties, such as the dipole potential and the surface pressure, are modulated by the water at the interphase region by changing the structure of the membrane components. An understanding of the properties of the structural water located at the hydration sites and the functional water confined around the polar head groups modulated by the hydrocarbon chains is helpful to interpret and analyze the consequences of water loss at the membranes of dehydrated cells. In this regard, a correlation between the effects of water activity on cell growth and the lipid composition is discussed in terms of the recovery of the cell volume and their viability. Critical analyses of the properties of water at the interface of lipid membranes merging from these results and others from the literature suggest that the interface links the membrane with the aqueous soluble proteins in a functional unit in which the cell may be considered as a complex structure stabilized by water rather than a water solution of macromolecules surrounded by a semi permeable barrier.

Lysophosphatidylcholine-arbutin complexes form bilayer-like structures

Arbutin is known to suppress melanin production in murine B16 melanoma cells and inhibit phospholipase action. This encourages the possibility to stabilize it in lipid aggregates for its administration in medical applications. Thus, it was of interest to demonstrate that monomyristoylphosphatidylcholine (14:0 lysoPC) and arbutin may form association complexes. This was studied by Electron Microscopy (EM), 31P Nuclear Magnetic Resonance (31P NMR), Electronic Paramagnetic Resonance (EPR) and Fourier Transform Infrared Spectroscopy (FTIR). EM images show the formation of particles of c.a. 6 nm in diameter. For a 1:1 lysoPC-arbutin molar ratio 31P NMR shows a spectrum with a shoulder that resembles the axially symmetric spectrum characteristic of vesicles. The addition of La3+ ions to the arbutin-lysoPC complex allows one to distinguish two phosphorous populations. These results suggest that arbutin-lysoPC forms vesicles with bilayers stabilized in an interdigitated array. FTIR spectroscopy shows that arbutin interacts with the hydrated population of the carbonyl groups and with the phosphates through the formation of hydrogen bonds. It is interpreted that hydrophobic interactions among the phenol group of arbutin and the acyl chain of lysoPC are responsible for the decrease in acyl chain mobility observed at the 5th C level by EPR. A model proposing the formation of interdigitated bilayers of arbutin-lysoPC could explain the experimental results.

Arbutin blocks defects in the ripple phase of DMPC bilayers by changing carbonyl organization

The effect of arbutin, a 4-hydroxyphenyl-beta-glucopyranoside, on dimyristoylphosphatidylcholine (DMPC) bilayers was studied by turbidimetry, EPR and FTIR spectroscopies. The disruption of DMPC multilamellar vesicles (MLV's) with monomyristoylphosphatidylcholine (lysoPC), a product of hydrolysis of phospholipase A(2) (PLA(2)), is more efficient at 18 degrees C, where DMPC MLV's are known to be in the ripple P(beta') phase, than at 10 degrees C (L(beta') flat gel phase). Disruption at 18 degrees C was inhibited by increasing concentrations of arbutin in the solution. This inhibition was correlated with the disappearance of the ripple phase in MLV's when arbutin is present. Shifts in FTIR carbonyl bands caused by arbutin or by temperature changes allow us to propose a model. It is interpreted that the changes in the water-hydrocarbon interface caused by arbutin, forcing a reaccommodation of the carbonyl groups, eliminate the topological defects in the lattice due to mismatches among regions with different area per lipid where lysoPC can insert.

FTIR analysis of the interaction of arbutin with dimyristoyl phosphatidylcholine in anhydrous and hydrated states

In this paper, the interaction of arbutin with dimyristoylphosphatidylcholine bilayers was studied by FTIR spectrometry. The results show that arbutin interacts in different extents with the phosphate and carbonyl groups of membranes in the gel state, the liquid crystalline state or subjected to osmotic stress. The effect, in the presence of water, on the antisymmetric stretching of the phosphate groups is qualitatively similar to that found with other molecules composed by a glucose moiety such as trehalose and sucrose. However, significant differences were found between these compounds and arbutin in the carbonyl region. Arbutin displaces the PO2- antisymmetric stretching to lower frequencies in lipids dispersed in water. This indicates strong hydrogen bonding. In contrast, in the solid state, this frequency increases. The effect on the carbonyl groups varies depending on the hydration state of the bilayer, which is achieved by changing the phase state of the bilayer or by osmotic stress. The hydrocarbon region is not affected by arbutin in the excess of water. However, symmetric and antisymmetric stretching of CH2 and CH3 are strongly affected in the dry state.

Evolution of a rippled membrane during phospholipase A2 hydrolysis studied by time-resolved AFM

The sensitivity of phospholipase A(2) (PLA(2)) for lipid membrane curvature is explored by monitoring, through time-resolved atomic force microscopy, the hydrolysis of supported double bilayers in the ripple phase. The ripple phase presents a corrugated morphology. PLA(2) is shown to have higher activity toward the ripple phase compared to the gel phase in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) membranes, indicating its preference for this highly curved membrane morphology. Hydrolysis of the stable and metastable ripple structures is monitored for equimolar DMPC/1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)-supported double bilayers. As shown by high-performance liquid chromatography results, DSPC is resistant to hydrolysis at this temperature, resulting in a more gradual hydrolysis of the surface that leads to a change in membrane morphology without loss of membrane integrity. This is reflected in an increase in ripple spacing, followed by a sudden flattening of the lipid membrane during hydrolysis. Hydrolysis of the ripple phase results in anisotropic holes running parallel to the ripples, suggesting that the ripple phase has strip regions of higher sensitivity to enzymatic attack. Bulk high-performance liquid chromatography measurements indicate that PLA(2) preferentially hydrolyzes DMPC in the DMPC/DSPC ripples. We suggest that this leads to the formation of a flat gel-phase lipid membrane due to enrichment in DSPC. The results point to the ability of PLA(2) for inducing a compositional phase transition in multicomponent membranes through preferential hydrolysis while preserving membrane integrity.

Dehydration of carbonyls and phosphates of phosphatidylcholines determines the lytic action of lysoderivatives

The purpose of this study was to correlate the effectiveness of the lysoPC to disrupt bilayers with the effects of trehalose and sucrose on the hydration sites of a lipid bilayer. The vibration frequencies of carbonyls and phosphates was measured at 18 degrees C for different ratios of monomyristoylphosphatidylcholine and dimyristoylphosphatidylcholine vesicles prepared in water, sucrose and trehalose. The disruption point of the bilayer, evaluated by following the changes in the turbidity of the suspension of unilamellar vesicles, was decreased when the vesicles were prepared in 100 mM sucrose. The increase of the lytic action is directly related to the extent of hydration of the carbonyl populations. It is interpreted that the insertion of the sucrose molecule in the interface causes local changes in interfacial structure, such as the dehydration of the second population of the carbonyls that may be identified as defects of packing. In contrast, the insertion of trehalose by replacing water simultaneously at the carbonyls and the phosphates does not cause defects of packing. For this reason, the lytic action is produced at a concentration very similar to that found in water.

Synergistic permeability enhancing effect of lysophospholipids and fatty acids on lipid membranes

The permeability-enhancing effects of the two surfactants, 1-palmitoyl-2-lyso-sn-gycero-3-phosphocholine (lysoPPC) and palmitic acid (PA), on lipid membranes that at physiological temperatures are in the gel, fluid, and liquid-ordered phases were determined using the concentration-dependent self-quenching properties of the hydrophilic marker, calcein. Adding lysoPPC to lipid membranes in the gel-phase induced a time-dependent calcein release curve that can be described by the sum of two exponentials, whereas PA induces a considerably more complex release curve. However, when lysoPPC and PA were added simultaneously in equimolar concentrations, a dramatic synergistic permeability-enhancing effect was observed. In contrast, when both lysoPPC and PA are added to liposomal membranes that are in the fluid or liquid-ordered phases, no effect on the transmembrane permeation of calcein was observed.

Surface changes induced by osmotic shrinkage on large unilamellar vesicles

Osmotic shrinkage changes the surface properties of dipalmitoylphosphatidylcholine large unilamellar vesicles depending on the phase state of the bilayer. In the gel state, shrinkage produces an increase in the adsorption of hydrophobic dyes, such as Merocyanine 540 (MC540) monomers, toluidine and anilinonaphthalene sulfonic acid (TNS, ANS). In the fluid state, shrinkage does not affect the bilayer surface when gradients between the inner and the outer compartments below 0.2-0.25 M NaCl (higher concentration outside) are applied. Larger differences in concentrations produce an increase in packing as inferred from the desorption of the MC monomers. Kinetic experiments show that the surface changes correlate with the volume decrease produced by the water extrusion from the vesicle interior. It is interpreted that the decrease of water content compels the vesicles to a state in which defects at the membrane surface are likely to occur when the bilayer is in the gel state.

Properties of gel phase lipid-trehalose bilayers upon rehydration

When dipalmitoylphosphatidylcholine bilayers dried under vacuum in different concentrations of trehalose are rehydrated in buffer without the sugar they show different physicochemical properties in the gel state in comparison to the normal gel state. Dry DPPC/trehalose mixtures are readily dispersed in buffer below the phase transition showing by electron microscopy a morphology similar to liposomes prepared by dispersing the lipids in buffer above the phase transition temperature. In these conditions, an increase in the peak at 570 nm of merocyanine after the dehydration-rehydration process in the presence of the sugar is observed and the water permeation increases to values comparable to those found in the fluid state as indicated by the activation energy values and the osmotic volume. The trehalose-dried liposomes rehydrated in buffer show a similar osmotic response to hypertonic gradient as DPPC liposomes without sugar near the phase transition temperature. In accordance with this behavior the trehalose-dried liposomes are lysed below the phase transition temperature by lysoderivatives. These modifications of the gel state of hydrated phospholipids by trehalose can only be achieved if a drastic dehydration is performed in the presence of the sugar. After rehydration the changes in the gel state can be detected after dyalizing the rehydrated membranes in media without trehalose during at least 24 h. These results suggest that trehalose is still intercalated between the phospholipids after restoring water to the dried liposomes either at temperatures below or above the phase transition.

The local anesthetic tetracaine destabilizes membrane structure by interaction with polar headgroups of phospholipids

The effect of the local anesthetic tetracaine at less than 10 mM on the water permeability of the phospholipid membrane was examined using liposomes composed of various molar ratios of negatively charged cardiolipin to electrically neutral phosphatidylcholine by monitoring their osmotic shrinkage in hypertonic glucose solution at 30 degrees C. The concentration of tetracaine causing the maximum velocity of shrinkage of liposomes increased with increase in the molar ratio of cardiolipin. Tetracaine increased the zeta-potential of the negatively charged liposomal membrane toward the positive side due to the binding of its cationic form to the negatively charged polar headgroups in the membrane. The maximum velocity of water permeation induced by osmotic shock was observed at essentially the same tetracaine concentration giving a zeta-potential of the liposomal membrane of 0 mV. These concentrations were not affected by change in the sort of acyl-chain of phospholipids in the liposomes when their negative charges were the same. These results suggests that the membrane integrity is governed mainly by the electrical charge of phospholipid polar headgroups when phospholipid bilayers are in the highly fluid state, and that positively charged tetracaine molecules neutralize the negative surface charge, lowering the barrier for water permeation through phospholipid bilayers.

Effect of Ca2+ on the cryoprotective action of trehalose

The competitive effect of Ca2+ on the cryoprotective action of carbohydrates has been investigated during freeze-thaw processes of unilamellar egg phosphatidylcholine vesicles. Ca2+ inhibits the cryoprotection achieved by trehalose to a greater extent than other sugars such as galactose, sucrose, and fructose. The cryoprotection by trehalose is also dependent on the Ca2+ concentration in the inside solution of the vesicle, even in the absence of external Ca2+. The competitive effect of Ca2+/trehalose is interpreted as a consequence of the different amount of interfacial water displaced by each compound in their adsorption on the water/lipid interface.

Ca2+ action on the stability of egg phosphatidylcholine sonicated vesicles during freeze-thaw cycles

The stability of unilamellar vesicles during freeze-thaw cycles strongly depends on the Ca2+ concentration in the aqueous solution. Experiments performed at equal ionic strengths with Na+ and Ca2+ solutions indicate that the effect observed is specific for Ca2+. This is interpreted to be a consequence of the adsorption of Ca2+ on the vesicle bilayers. The variation of lipid and Ca2+ concentrations indicates that stability is achieved at a particular Ca2+/lipid ratio of 8 mol/mol above which vesicles are stable. The stability appears to be mainly conferred by the external Ca2+ in both slow and rapid cycles, independent of the ionic vesicle content. However, internal Ca2+ seems to increase the stability according to the F/T cycle rate to some extent in the absence of Ca2+ in the external solution.

Effect of insulin on the lytic action of lysophosphatidylcholine in lipid bilayers

The effect of insulin on the bilayer properties of dimyristoylphosphatidylcholine liposomes at the gel and the liquid crystalline state was measured by differential scanning calorimetry and absorbance at 450 nm. It is found that insulin promotes a decrease in the enthalpy of the gel-liquid crystalline transition without displacing the transition temperature. Under these conditions the lytic action of monomyristoylphospatidylcholine is enhanced, decreasing the critical lytic concentrations to values comparable to the bilayer at the gel state. The effect of the lysoderivate on liposomes in contact with increasing concentrations of insulin promotes a reorganization of the lipids into smaller particles as inferred from fluorescence dequenching, turbidity and exclusion chromatography assay. It is concluded that the action of lysoderivates can be enhanced, at temperatures above the transition temperature, by proteins that without spanning the lipid bilayers can perturb the bilayer interface.

Amphiphile-induced antihaemolysis is not causally related to shape changes and vesiculation

A wide variety of structurally different antihaemolytic amphiphiles were tested for their ability to induce exovesiculation (acetylcholinesterase (AChE) release, transmission electron microscopic (TEM) studies), endovesiculation (fluorescein isothiocyanate conjugated dextran (FITC-dextran) internalization, TEM studies) and shape changes in human erythrocytes at concentrations where they exert maximum protection against hypotonic haemolysis. The results show that vesiculation is a common phenomenon induced by amphiphiles in erythrocytes. Sphero-echinocytogenic amphiphiles induced exovesiculation, whereas stomatocytogenic amphiphiles induced endovesiculation. The antihaemolytic potency of the amphiphiles was not related to their ability to induce exo- or endovesiculation, or to the type or extent of shape changes induced, and it could not be ascribed to any molecular feature of the amphiphiles or to their charge. It is proposed that amphiphiles, when intercalated into the lipid bilayer of the membrane, rapidly induce rearrangements within the bilayer and that these rearrangements are associated with an increase in the permeability of the membrane; it is suggested that a rapid efflux of ions decreases the difference in osmotic pressure between cell interior and hypotonic buffer, thereby protecting cells from being lysed.