Dipalmitoylphosphatidylcholine Multilamellar Vesicles Research Articles

Hypelcin A, an alpha-aminoisobutyric acid containing antibiotic peptide, induced permeability change of phosphatidylcholine bilayers.

Interactions of hypelcin A, an alpha-aminoisobutyric acid containing antibiotic peptide, with phosphatidylcholine vesicles were investigated to obtain information on its bioactive mechanism. The peptide induced the leakage of a fluorescent dye, calcein, entrapped in sonicated vesicles. The leakage rate depended on both the peptide and the lipid concentrations. Analysis of this dependency indicated that the leakage was due to the monomeric peptide and that the membrane-perturbing activity of the monomer was higher for solid distearoylphosphatidylcholine vesicles than for fluid egg yolk phosphatidylcholine vesicles. Hypelcin A also affected the gel to liquid-crystalline phase transition of dipalmitoylphosphatidylcholine multilamellar vesicles. The transition was broadened with a reduced transition enthalpy, suggesting the peptide strongly binds the surrounding lipids to perturb the bilayer lipid packing. A circular dichroism study revealed that the helical content of hypelcin A increases upon membrane binding. We concluded that the monomeric peptide with an increased helical content, complexed with the lipids, perturbs the lipid organization and induces the increased permeability.

Persistence at low temperature of the P β′ ripple in dipalmitoylphosphatidylcholine multilamellar vesicles containing either glycosphingolipids or cholesterol

The disappearance and reappearance of the P β′ ripple in multilamellar liposomes of dipalmitoylphosphatidylcholine (DPPC) has been examined by freeze-etch electron microscopy. The presence of less than 10 mol% of various glycosphingolipids or cholesterol in the liposomes markedly increases the time required for ripple disappearance when the vesicles are cooled from 38°C to 30°C, as compared to the pure phospholipid. Once the ripples have begun to disappear in the two-component vesicles, they do not uniformly reappear until the system is heated above the main transition of DPPC and allowed to cool into the pertransition region. These results suggest that the long time for ripple disappearance in the two-component systems reflects a slow molecular reorganization process which occurs when the systems are forced to change from the P β′ gel to the L β′ gel by a temperature downshift.

Interaction of trans-parinaric acid with phosphatidylcholine bilayers: comparison with the effect of other fluorophores

The effect of the fluorophore trans-parinaric acid on the structure of lipid bilayer was studied and compared with the effect of other ‘perturbants’. These include commonly used fluorophores (diphenylhexatriene, heptadecylhydroxycoumarin, cis-parinaric acid and two fatty acids, palmitic and oleic acids). Differential scanning calorimetry (DSC) and proton nuclear magnetic resonance techniques were used to evaluate structural changes in the lipid bilayers. The thermodynamic parameters of dipalmitoylphosphatidylcholine multilamellar vesicles obtained from the DSC thermograms suggest that trans-parinaric acid differs from the other ‘perturbants’- trans-Parinaric acid has the most pronounced impact on the T m, the width ( ΔT 1 2 ) and the index of asymmetry of the main gel to liquid crystalline phase transition without any effect on its transition, ΔH. The presence of trans-parinaric acid in the lipid bilayer of dimyristoylphosphatidylcholine small unilamellar vesicles influences the chemical shift difference between the choline protons of phosphatidylcholine molecules present in the two leaflets of the vesicle bilayer ( ΔδH). This suggests that trans-parinaric acid affects the head group packing in the bilayer. Its main effect is abolishing the major alterations in head group packing that occur through the phase transition. The above data indicate that trans-parinaric acid is concentrated in the gel phase domains, whereby it stabilizes the phase separation between the gel and liquid crystalline phases, probably by affecting lipid molecules present in the boundary regions between these two domain types.

Deuterium nuclear magnetic resonance investigation of the exchangeable sites on gramicidin A and gramicidin S in multilamellar vesicles of dipalmitoylphosphatidylcholine

Solid gramicidin A and S and their interaction with DPPC bilayers were examined by 2H NMR as well as 31P NMR and differential scanning calorimetry (DSC). The deuterium spectra arose from deuterons associated with the peptide through chemical exchange in 2H2O. The spectra from both peptides were characterized by a quadrupolar splitting parameter, omega Q/2 pi approximately 150 kHz, and an asymmetry parameter, eta approximately 0.17. An additional 33 kHz, eta = 0 component arising from deuterons on mobile ornithine side chains was present in gramicidin S. In the gel phase of dipalmitoylphosphatidylcholine liposomes the gramicidins gave spectra that had components identical with those obtained from the solids. In the liquid-crystalline phase gramicidin A containing samples gave multicomponent spectra with a maximum quadrupolar splitting value of 133 kHz, eta = 0. A minimum in the T2e was observed, coinciding with the onset of the broadened phase transition measured by DSC and 31P NMR, due to the onset of axial rotation of the peptide in the bilayer. The different powder patterns in the liquid-crystalline spectra from gramicidin A probably arise from different amide sites along the transmembrane channel. The broad component of the 2H NMR spectra from gramicidin S in liposome preparations was not affected by the lipid-phase transition. The T2e was also constant over this temperature range. The results are consistent with a location of gramicidin S at the membrane surface.

Perturbation of egg phosphatidylcholine and dipalmitoylphosphatidylcholine multilamellar vesicles by n-alkanols. A fluorescent probe study

The perturbing effects of n-alkanols (pentanol, decanol and tetradecanol) in egg phosphatidylcholine and dipalmitoylphosphatidylcholine multilamellar vesicles were studied with five fluorescent probes, 1-(4′-trimethylaminophenyl)- 6-phenylhexa-1,3,5-triene (TMA-DPH), 1,6-diphenyl-1,3,5-hexatriene, and 2-, 7-, and 12-(9- anthroxyloxy)stearic acid (2-, 7-, and 12-AS). These probes localize at various depths in the membrane, enabling study of the membrane-order gradient. Phase-modulation fluorescence spectroscopy was used to measure steady-state anisotropies, excited-state lifetimes and differential polarized lifetimes from which the limiting hindered anisotropies ( r ∞) and the logarithm of the rotational rate (log R) were calculated. The probes that localize at about the same depth in the membrane (TMA-DPH and 2-AS, diphenylhexatriene and 12-AS) generally, but not always, showed similar changes in r ∞ and log R with added alkanols. However, the absolute values of r ∞ and log R were usually different. The inconsistencies are attributed to differences in the probes' sizes, structures, photophysical properties and perturbing abilities. The perturbation of membranes by alkanols is chain-length-dependent. Pentanol disorders the membrane at all depths but is more effective in the membrane center than nearer to the polar headgroups of the phospholipids, tetradecanol can be accomodated into the membrane without effect or with increased order and the effects of decanol are intermediate between pentanol and tetradecanol. Our results with alkanols indicate that: (1) a single perturber can have different effects on membrane order at different depths in the bilayer; (2) the perturbation is observed at and distant from the perturbers' location in the membrane, and (3) the bilayer center is more susceptible to perturbation by alkanols than the region of the bilayer near the phospholipid headgroups.

Cholesteryl sulfate‐phosphatidylcholine interactions

AbstractThe effect of cholesteryl sulfate, a natural membrane component, on the physical state of dipalmitoyl phosphatidylcholine multilamellar vesicles was investigated using fluorescence polarization and differential scanning calorimetry techniques. Cholesteryl sulfate increased the order of acyl chains for those temperatures higher than the gel‐to‐liquid crystalline transition temperature while it decreased the order for those temperatures below the phase transition temperature. At equimolar concentrations, cholesteryl sulfate suppressed the crystal liquid‐to‐gel phase transition of dipalmitoyl phosphatidylcholine. These data suggest that sterol sulfates may provide new tools for the elucidation of molecular mechanisms involved in sterollipid interactions.

PH‐Dependent structural modification of dipalmitoylphosphatidylcholine vesicle membranes by a degradable poly(carboxylic acid) of pharmacological importance

The real and potential applications of phospholipid and surfactant vesicles in areas such as drug delivery, solar energy conversion, and chemical reactivity control have been discussed by Fendler. Additional applications may be foreseen for vesicles which can be made to respond to environmental stimuli such as heat, light, or specific chemical substances. One might imagine, for example, the use of such sensitized vesicles for selective release of drugs in targets of local hyperthermia) or low ambient pH). We have recently demonstrated that multilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC) are rendered sensitive to pH in the presence of synthetic poly(carboxylic acid)s related to poly(acrylic acid). In biomedical applications, however, the non-degradability of these poly(acrylic acid) derivatives may be a serious limitation. In this paper, we show that a similar pH-dependent modification of DPPC vesicle structure may be effected by poly(P-malic acid) (PMLA 100), a degradable poly(carboxylic acid). PMLA 100 has been recently introduced to tailor-made macromolecular prodrugs and microemulsion-like systems for solubilization of hydrophobic drugs in aqueous media).

The interaction of cortisone esters with liposomes as studied by differential scanning calorimetry

The interaction of a series of cortisone esters with dipalmitoylphosphatidylcholine (DPPC) multilamellar vesicles (MLV) has been investigated using differential scanning calorimetry (DSC). The extent of the interaction is dependent on the ester chain-length with increased interaction observed as the chain lengthens. For cortisone hexadecanoate the maximum incorporation is 11.25 mole· %. The presence of cholesterol excludes cortisone hexadecanoate from DPPC liposomes. This effect increases with increasing cholesterol concentrations. Cortisone hexadecanoate is incorporated into DPPC liposomes in such a manner that it is probable that the steroid moiety interacts strongly with the bilayer. A correlation exists between the in vitro cortisone ester release rate at 37°C from DPPC liposomes and broadening of DPPC MLV thermograms only over the range of 6–14 carbon chain-length. This indicates that the interaction of the ester chain of the steroid with the acyl chain of the lecithin are not necessarily the sole factors controlling efflux rate.

Effect of dipalmitoylphosphatidylcholine vesicle curvature on the reaction with human apolipoprotein A-I.

Large unilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC) were prepared by sonication and were fractionated by gel filtration on Sepharose Cl-2B in the size range from 180- to 380-A Stokes radii. Negatively stained electron micrographs of these preparations indicated the presence of unilamellar, spheroidal structures of the expected size. Fluorescence polarization of diphenylhexatriene, dissolved in the vesicles, revealed progressively broader phase transitions, shifted to lower temperatures for vesicles of decreasing sizes. The fractionated unilamellar vesicles and multilamellar vesicles of DPPC were reacted with human apolipoprotein A-I at 41 degrees C for periods from 1 to 120 h. The reaction mixtures were then passed through a Bio-Gel A-5m column to separate unreacted lipid vesicles and protein from micellar complexes of DPPC with apolipoprotein A-I. Smaller vesicles were much more reactive than larger vesicles or multilamellar vesicles with the apolipoprotein. This difference in reactivity was explained by the increasing bilayer curvature of smaller vesicles which changes the packing of DPPC molecules in the bilayer and facilitates its penetration by the apolipoprotein.