Effect of Gd^{3+} on the colloidal stability of liposomes (original) (raw)
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Interaction of gadolinium with phospholipids bilayer membranes
Journal of Thermal Analysis and Calorimetry, 2007
The effects of concentration of gadolinium ions Gd 3+ on dipalmitoyl L-α-phosphatidylcholine (DPPC) unilamellar vesicles in aqueous media were studied by photon correlation spectroscopy (PCS) and differential scanning calorimeter. The theoretical predictions of the colloidal stability of liposomes were followed using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Changes in the size of liposomes were observed as Gd 3+ concentration increases, suggesting that this cation induces the aggregation of vesicles. To determine the effect of Gd 3+ on the transition temperature (T c ) and on the enthalpy (ΔH c ) associated with the process differential scanning calorimetry (DSC) has been used. The addition of the metal ion provided DSC curves with different behavior to DPPC bilayer.
La3+ and Gd3+ induce shape change of giant unilamellar vesicles of phosphatidylcholine
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2002
Lanthanides such as La 3 + and Gd 3 + are well known to have large effects on the function of membrane proteins such as mechanosensitive ionic channels and voltage-gated sodium channels, and also on the structure of phospholipid membranes. In this report, we have investigated effects of La 3 + and Gd 3 + on the shape of giant unilamellar vesicle (GUV) of dioleoylphosphatidylcholine (DOPC-GUV) and GUV of DOPC/cholesterol by the phase-contrast microscopy. The addition of 10-100 AM La 3 + (or Gd 3 +) through a 10-Am diameter micropipette near the DOPC-GUV (or DOPC/cholesterol-GUV) triggered several kinds of shape changes. We have found that a very low concentration (10 AM) of La 3 + (or Gd 3 +) induced a shape change of GUV such as the discocyte via stomatocyte to inside budded shape transformation, the two-spheres connected by a neck to prolate transformation, and the pearl on a string to cylinder (or tube) transformation. To understand the effect of these lanthanides on the shape of the GUV, we have also investigated phase transitions of 30 AM dipalmitoylphosphatidylcholinemultilamellar vesicle (DPPC-MLV) by the ultra-sensitive differential scanning calorimetry (DSC). The chain-melting phase transition temperature and the L hV to P hV phase transition temperature of DPPC-MLV increased with an increase in La 3 + concentration. This result indicates that the lateral compression pressure of the membrane increases with an increase in La 3 + concentration. Thereby, the interaction of La 3 + (or Gd 3 +) on the external monolayer membrane of the GUV induces a decrease in its area (A ex), whereas the area of the internal monolayer membrane (A in) keeps constant. Therefore, the shape changes of the GUV induced by these lanthanides can be explained reasonably by the decrease in the area difference between two monolayers (DA = A ex À A in).
Biophysical Journal, 2002
The structural phase behavior of phospholipid mixtures consisting of short-chain (dihexanoyl phosphatidylcholine) and long-chain lipids (dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylglycerol), with and without lanthanide ions was investigated by small-angle neutron scattering (SANS). SANS profiles were obtained from 10°C to 55°C using lipid concentrations ranging from 0.0025 g/ml to 0.25 g/ml. The results reveal a wealth of distinct morphologies, including lamellae, multi-lamellar vesicles, unilamellar vesicles, and bicellar disks.
On the Effect of Ca 2+ and La 3+ on the Colloidal Stability of Liposomes
Langmuir, 2005
This work deals with the effect of Ca 2+ and La 3+ on the colloidal stability of phosphatidylcholine (PC) liposomes in aqueous media. As physical techniques, nephelometry, photon correlation spectroscopy, electrophoretic mobility, and surface tension were used. The theoretical predictions of the colloidal stability of liposomes were followed using the Derjaguin-Landau-Verwey-Overbeek theory. Changes in the size of liposomes and high polydispersity values were observed as La 3+ concentration increases, suggesting that this cation induces the aggregation of liposomes. However, changes in polydispersity were not observed with Ca 2+ , suggesting a coalescence mechanism or fusion of liposomes. The stability factor (W), calculated from the nephelometry measurements indicated that aggregation/fusion occurs at a critical concentration (c.c.) of 0.3 and 0.7 M for La 3+ and Ca 2+ , respectively. To gain a better insight into the interaction mechanism between the liposomes and the studied ions, the interaction between PC monolayers and Ca 2+ and La 3+ was studied. Changes in the surface area per lipid molecule (A0) in the monolayer at the c.c. values were found for both ions, with a more pronounced effect in the case of Ca 2+ . This corresponds with a larger reduction of the steric repulsive interaction between the headgroups at the phospholipid membrane (πhead). The experimental result validates the hypothesis made on the liposome fusion in the presence of Ca 2+ and liposome aggregation in the presence of La 3+ . These aggregation mechanisms have also been confirmed by transmission electron microscopy.
Biophysical Journal, 2003
Poly(ethylene glycol) (PEG) decorated lipid bilayers are widely used in biomembrane and pharmaceutical research. The success of PEG-lipid stabilized liposomes in drug delivery is one of the key factors for the interest in these polymer/lipid systems. From a more fundamental point of view, it is essential to understand the effect of the surface grafted polymers on the physical-chemical properties of the lipid bilayer. Herein we have used cryo-transmission electron microscopy and dynamic light scattering to characterize the aggregate structure and phase behavior of mixtures of PEG-lipids and distearoylphosphatidylcholine or dipalmitoylphosphatidylcholine. The PEG-lipids contain PEG of molecular weight 2000 or 5000. We show that the transition from a dispersed lamellar phase (liposomes) to a micellar phase consisting of small spherical micelles occurs via the formation of small discoidal micelles. The onset of disk formation already takes place at low PEG-lipid concentrations (\5 mol %) and the size of the disks decreases as more PEG-lipid is added to the lipid mixture. We show that the results from cryo-transmission electron microscopy correlate well with those obtained from dynamic light scattering and that the disks are well described by an ideal disk model. Increasing the temperature, from 258C to above the gel-to-liquid crystalline phase transition temperature for the respective lipid mixtures, has a relatively small effect on the aggregate structure.
Archives of Biochemistry and Biophysics, 2007
The effect of the excitation or emission wavelengths on Laurdan generalized polarization (GP) can be evaluated by GPS, a quantitative, simplified determination of the GP spectrum slope, the thermotropic dependence of which allows the assessment of phospholipid lamellar membrane phase, as shown in a recent publication of our laboratory [J.B. Velázquez, M.S. Fernández, Arch. Biochem. Biophys. 455 (2006) 163-174]. In the present work, we applied Laurdan GPS to phase transition studies of mixed, two-phosphatidylcholine liposomes prepared from variable proportions of dimyristoyl-and dipalmitoylphosphatidylcholine (DMPC and DPPC, respectively). We have found that the GPS function reports a clear limit between the gel/liquid-crystalline phase coexistence region and the liquid-crystalline state, not only at a certain temperature T c for liposomes of constant composition submitted to temperature scans, but also at a defined mole fraction X c , for two-component liposomes of variable composition at constant temperature. The T c or the X c values obtained from GPS vs. temperature or GPS vs. composition plots, respectively, allow the construction of a partial phase diagram for the DMPC-DPPC mixtures, showing the boundary between the two-phase coexisting region and the liquid-crystalline state. Likewise, at the onset of the transition region, i.e., the two-phase coexisting region as detected by GPS, it is possible to determine, although with less precision, a temperature T o or a mole fraction X o defining a boundary located below but near the limit between the gel and ripple phase, reported in the literature. These GPS results are consistent with the proposal by several authors that a fraction of L a phospholipids coexists with gel phospholipids in the rippled phase.
Phospholipid-cationic lipid interactions: influences on membrane and vesicle properties
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2001
Liposomes composed of synthetic dialkyl cationic lipids and zwitterionic phospholipids such as dioleoylphosphatidylethanolamine have been studied extensively as vehicles for gene delivery, but the broader potentials of these cationic liposomes for drug delivery have not. An understanding of phospholipid-cationic lipid interactions is essential for rational development of this potential. We evaluated the effect of the cationic lipid DOTAP (N-[1-(2,3-dioleoyloxy)propyl]-N,N,Ntrimethylammonium) on liposome physical properties such as size and membrane domain structure. DSC (differential scanning calorimetry) showed progressive decrease and broadening of the phase transition temperature of dipalmitoylphosphatidylcholine (DPPC) with increasing fraction of DOTAP, in the range of 0.4^20 mol%. Laurdan (6-dodecanolyldimethylamino-naphthalene), a fluorescent probe of membrane domain structure, showed that DOTAP and DPPC remained miscible at all ratios tested. DOTAP reduced the size of spontaneously-forming PC-containing liposomes, regardless of the acyl chain length and degree of saturation. The anionic lipid DOPG (dioleoylphosphatidylglycerol) had similar effects on DPPC membrane fluidity and size. However, DOTAP/DOPC (50/50) vesicles were taken up avidly by OVCAR-3 human ovarian tumor cells, in contrast to DOPG/DOPC (50/50) liposomes. Overall, DOTAP exerts potent effects on bilayer physical properties, and may provide advantages for drug delivery.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2006
Upon storage of phospholipid liposome samples, lysolipids, fatty acids, and glycerol-3-phosphatidylcholine are generated as a result of acid-or base-catalyzed hydrolysis. Accumulation of hydrolysis products in the liposome membrane can induce fusion, leakage, and structural transformations of the liposomes, which may be detrimental or beneficial to their performance depending on their applications as, e.g., drug delivery devices. We investigated in the present study the influence of phospholipid hydrolysis on the aggregate morphology of DPPC/DSPE-PEG 2000 liposomes after transition of the phospholipid membrane from the gel phase to liquid crystalline phase using high performance liquid chromatography (HPLC) in combination with static light scattering, dynamic light scattering, and cryo-transmission electron microscopy (cryo-TEM). The rates of DPPC hydrolysis in DPPC/DSPE-PEG 2000 liposomes were investigated at a pH of 2, 4, or 6.5 and temperatures of 22°C or 4°C
Chemistry and Physics of Lipids, 1985
The effect of the presence of ganglioside GM1, up to 20% by mol, on the size, stability upon aging, and changes with dilution, of small unilamellar vesicles of egg phosphatidylcholine (EPC) was studied by static and dynamic laser-light scattering technique. Standardised conditions were preliminarily set up for the preparation of small unilamellar vesicles by the sonication-ultracentrifugation method. Under these conditions the presence of ganglioside caused a progressive decrease of lipid concentration in the upper 2.2 ml of high speed supernatant, from the original 9 pmol/ml to 1.3 pmol/ml reached with vesicles containing 20% of GM1. The hydrodynamic radius (RH), apparent molecular weight (M) and polydispersity index (v) decreased in the presence of ganglioside from the values of 16 nm, 3.3 × 106 and 0.15, respectively, to 11 nm, 1.9 × 106 and 0.10, in vesicle preparations with 20% of GM1. R H and v of EPC vesicles increased by only 3% and 12%, respectively, upon aging at 37°C for 6 h. The variations of the same parameters in vesicles containing up to 15% of GM1 were still lower, indicating that the presence of ganglioside tends to increase the stability upon aging of small unilamellar vesicles. Dilution of vesicle dispersions down to 0.1 pmol/ml caused a modest, but significant increase of RH, M and ~,. The extent of increase was similar for EPC and EPC/GM1 vesicles with a GM1 proportion lower than 20%.