Search PubMed⌕ Search

Biomedical subjects

D Papahadjopoulos

Publications and source records attributed to D Papahadjopoulos.

At least 145 records · Page 8Linked to original sources
PubMed1978

Identification of a potential artifact in the use of electron microscope autoradiography to localize saturated phospholipids in cells.

The suitability of electron microscope autoradiography for sutdying the uptake and intracellular localization of lipid vesicles (liposomes) containing radiolabeled saturated phospholipids has been examined. Data are presented showing that preparation of specimens for electron microscope autoradiography by conventional methods is accompanied by significant translocation and intercellular redistribution of radiolabeled saturated lipids, causing spurious labeling patterns. Intercellular redistribution of radiolabeled lipid was demonstrated by mixing glutaraldehyde-fixed mous L1210 cells that had been incubated with sonicated lipid vesicles containing [H] dipalmitoyl phosphatidylcholine with an indicator cell population (fixed avian erythrocytes) which had not been exposed to vesicles and showing that after electron microscope processing radiolabeled grains were present in both cell types. The same redistribution artifact also probably affects the intracellular localization of radiolabeled lipids. This artifact is discussed in relation to previous work in which autoradiographic methods have been used for ultrastructural localization saturated phospholipids in cells and tissues.

Animals↗
PubMed1978

Specificity of Ca2+ and Mg2+ binding to phosphatidylserine vesicles and resultant phase changes of bilayer membrane structure.

Differences in the interaction of Ca2+ and Mg2+ with phosphatidylserine vesicles were revealed by binding studies, differential scanning calorimetry and X-ray diffraction. The two cations produced structurally different complexes with phosphatidylserine as evidenced by phase transition characteristics, lamellar spacings, and hydrocarbon packing. Ca2+ effectively completes with Mg2+ for phosphatidylserine binding sites. Analysis of the binding data showed that Ca2+ had a ten-fold greater intrinsic binding constant for phosphatidylserine.

Binding Sites↗
PubMed1978

The effect of free fatty acids on the thermotropic phase transition of dimyristoyl glycerophosphocholine.

The effect of free fatty acids on the phase transition characteristics and fluidity of bilayers of dimyristoyl glycerophosphocholine were studied by pyrene eximer fluorescence and differential scanning calorimetry. High melting saturated fatty acids with chain lenghts of 12--18 carbon atoms raise the phase transition temperature and enhance the ability of pyrene to form clusters in the gel state while not affecting the fluidity of the membrane in the liquid crystal state. Low melting unsaturated fatty acids lower the phase transition temperature and decrease the ability of pyrene to form clusters in the gel state while not affecting the fluidity of the membrane in the liquid crystal state. The effects of the very long chain fatty acids, arachidic (C 20) and behenic (C 22) appears to be similar to those of cholesterol in that they cause a broadening of the phase transition with a lowering of the transition enthalpy but have little effect on the temperature at which the phase transition occurs.

Calorimetry↗
PubMed1978

Procedure for preparation of liposomes with large internal aqueous space and high capture by reverse-phase evaporation.

Large unilamellar and oligolamellar vesicles are formed when an aqueous buffer is introduced into a mixture of phospholipid and organic solvent and the organic solvent is subsequently removed by evaporation under reduced pressure. These vesicles can be made from various lipids or mixtures of lipids and have aqueous volume to lipid ratios that are 30 times higher than sonicated preparations and 4 times higher than multilamellar vesicles. Most importantly, a substantial fraction of the aqueous phase (up to 62% at low salt concentrations) is entrapped within the vesicles, encapsulating even large macromolecular assemblies with high efficiency. Thus, this relatively simple technique has unique advantages for encapsulating valuable water-soluble materials such as drugs, proteins, nucleic acids, and other biochemical reagents. The preparation and properties of the vesicles are described in detail.

Chemical Phenomena↗
PubMed1977

Fluorescent probes in model membranes I: anthroyl fatty acid derivatives in monolayers and liposomes of dipalmitoylphosphatidylcholine.

A study of three fluorescent anthroyl probes has been carried out using pure and mixed monomolecular films with dipalmitoylphosphatidylcholine. In addition, fluorescence depolarization and differential scanning calorimetry data were obtained from dipalmitoylphosphatidylcholine vesicles with incorporated anthroyl probes. The three probes used were 2-(9-anthroyl)palmitic acid. 12-(9-anthroyl)stearic acid, and 16-(9-anthroyl)palmitic acid. The latter probe was synthesized for these studies. In monolayers the probes shifted the onset of the liquid-condensed/liquid-expanded monolayer phase transition with the extent of the shift decreasing in the order: 2-(9-anthroyl)palmitic acid greater than 12-(9-anthroyl)stearic acid greater than 16-(9-anthroyl)stearic acid. A corresponding decrease in the gel-liquid crystalline bilayer transition temperature (Tc) showed the same order of perturbation in both the fluorescence depolarization and differential scanning calorimetry data. Locating the anthroyl entity in the center of the bilayer would appear to provide a minimum perturbation.

Anthracenes↗
PubMed1977

Lateral diffusion in phospholipid multibilayers measured by fluorescence recovery after photobleaching.

The method of fluorescence recovery after photobleaching has been used to measure the temperature dependence of the lateral diffusion coefficients (D) of two fluorescent lipid analogues in phospholipid multibilayers of various compositions. The probes employed were 3,3-dioctadecyloxocarbocyanine (diO-C18(3) and N-4-nitrobenz-2-oxa-1,3-diazole phosphatidylethanolamine (NBD-PE). In fluid egg phosphatidylcholine multibilayers at 25 degrees C, D was about 4 X 10(-8) cm2/s for NBD-PE and 1.5 X 10(-7) cm2/s for diO-C18(3) and was moderately temperature dependent (2-fold change over 10 degrees C). Equimolar cholesterol reduced D for NBD-PE in these multibilayers by a factor of 2. A greater than 100-fold decrease in D was detected in dimyristoylphosphatidylcholine multibilayers at approximately 23 degree C, which coincides with the gel-to-liquid-crystalline transition temperature, Tm (D 5 X 10(-8) cm2/s at T greater than Tm to D less than 5 X 10(-10) cm2/s at T less than Tm). Equimolar cholesterol abolished this transition behavior, raising D below Tm and decreasing D above Tm. These results confirm and extend previous studies of lateral diffusion employing magnetic resonance and other optical techniques and give additional confidence in the fluorescence methods.

Cholesterol↗
PubMed1977

Lipid phase separation induced by a hydrophobic protein in phosphatidylserine--phosphatidylcholine vesicles.

Differential scanning calorimetry (DSC) was used to detect phase separation induced by hydrophobic myelin protein, lipophilin, in a mixture of phosphatidylserine (PS) and dipalmitoylphosphatidylcholine (DPPC). Preferential binding of PS to the boundary layer of lipophilin causes a decrease in the PS content of the remaining lamellar phase with a resultant shift in the phase-transition temperature to a higher temperature. The phase diagram for this mixture in the presence and absence of lipophilin is presented. From the phase diagram, it can be estimated that for an equimolar mixture of PS and DPPC, the boundary layer contains only PS, although for higher DPPC contents, some DPPC can also be found in the boundary layer. In the case where partial phase separation in induced in this mixture by Ca2+ alone, lipophilin increases the phase separation indicating that it also binds PS preferentially in the presence of Ca2+. Preferential binding of two other acidic lipids, phosphatidic acid and phosphatidyl-glycerol, to the boundary layer was also found, including a mixture where the acidic lipid was the higher melting component in the mixture.

Calcium↗
PubMed1977

Studies on membrane fusion. III. The role of calcium-induced phase changes.

The interaction of phosphatidylserine vesicles with Ca2+ and Mg2+ has been examined by several techniques to study the mechanism of membrane fusion. Data are presented on the effects of Ca2+ and Mg2+ on vesicle permeability, thermotropic phase transitions and morphology determined by differential scanning calorimetry, X-ray diffraction, and freeze-fracture electron microscopy. These data are discussed in relation to information concerning Ca2+ binding, charge neutralization, molecular packing, vesicle aggregation, phase transitions, phase separations and vesicle fusion. The results indicate that at Ca2+ concentrations of 1.0-2.0 mM, a highly cooperative phenomenon occurs which results in increased vesicle permeability, aggregation and fusion of the vesicles. Under these conditions the hydrocarbon chains of the lipid bilayers undergo a phase change from a fluid to a crystalline state. The aggregation of vesicles that is observed during fusion is not sufficient range of 2.0-5.0 mM induces aggregation of phosphatidylserine vesicles but no significant fusion nor a phase change. From the effect of variations in pH, temperature, Ca2+ and Mg2+ concentration on the fusion of vesicles, it is concluded that the key event leading to vesicle membrane fusion is the isothermic phase change induced by the bivalent metals. It is proposed that this phase change induces a transient destabilization of the bilayer membranes that become susceptible to fusion at domain boundaries.

Calcium↗
PubMed1977

Biological properties of poliovirus encapsulated in lipid vesicles: antibody resistance and infectivity in virus-resistant cells.

We present evidence that poliovirus can be encapsulated in synthetic large phospholipid vesicles. The virus associated with the vesicles is found to be (i) resistant to antiserum against poliovirus and (ii) infectious for cells that are normally resistant to virus infection because of a membrane restriction. Our interpretation of these results is that the virus is entrapped in the interior aqueous space of the vesicles and that this vesicle-associated virus is introduced directly into the cytoplasm of the cells via fusion of the vesicles with the cellular plasma membrane, bypassing the surface receptor-mediated restriction.

Antibodies, Viral↗