Influence Of Vesicle Size Research Articles

The Influence of Vesicle Size and Composition on α-Synuclein Structure and Stability

Monomeric α-synuclein ( αSN), which has no persistent structure in aqueous solution, is known to bind to anionic lipids with a resulting increase in α-helix structure. Here we show that at physiological pH and ionic strength, αSN incubated with different anionic lipid vesicles undergoes a marked increase in α-helical content at a temperature dictated either by the temperature of the lipid phase transition, or (in 1,2-DilauroylSN-Glycero-3-[Phospho-rac-(1-glycerol)] (DLPG), which is fluid down to 0°C) by an intrinsic cold denaturation that occurs around 10–20°C. This structure is subsequently lost in a thermal transition around 60°C. Remarkably, this phenomenon is only observed for vesicles >100 nm in diameter and is sensitive to lipid chain length, longer chain lengths, and larger vesicles giving more cooperative unfolding transitions and a greater degree of structure. For both vesicle size and chain length, a higher degree of compressibility or permeability in the lipid thermal transition region is associated with a higher degree of αSN folding. Furthermore, the degree of structural change is strongly reduced by an increase in ionic strength or a decrease in the amount of anionic lipid. A simple binding-and-folding model that includes the lipid phase transition, exclusive binding of αSN to the liquid disordered phase, the thermodynamics of unfolding, and the electrostatics of binding of αSN to lipids is able to reproduce the two thermal transitions as well as the effect of ionic strength and anionic lipid. Thus the nature of αSN's binding to phospholipid membranes is intimately tied to the lipids' physico-chemical properties.

Particle size of liposomes influences dermal delivery of substances into skin

In the present study, the influence of vesicle size on the penetration of two fluorescently labeled substances into the human skin was investigated. For the measurements either a hydrophilic fluorescent compound [carboxyfluorescein (CF)] or a lipophilic one [1,1′-dioctadecyl-3,3,3′,3′-tertramethylindocarbo-cyanine perchlorate (DiI)] were encapsulated into vesicles. Liposomal formulations were prepared by extruding the vesicles through polycarbonate membrane filters with pores of different sizes. In vitro penetration studies into human abdominal skin were performed by using the Franz diffusion cell and a standardized skin stripping technique in attempt to find an optimum size for topical drug delivery by liposomes. Confocal laser scanning microscopy (CLSM) was used to visualize the effect of penetration ability of liposomal DiI. The maximum DiI fluorescence in the skin was observed with smaller liposomes of 71 nm diameter. The liposomes with a size of 120 nm diameter showed statistically enhanced penetration of CF into the skin as compared to larger ones. The results indicated that the CF penetration was inversely related to the size of the liposomes, which was confirmed by the data of the confocal laser scanning microscopy studies.

Liposomes and influenza viruses as an in vitro model for membrane interactions II. Influence of vesicle size and preparation methods

As previously demonstrated, membrane fusion and transfer of prodrug-type molecules between membranes can be studied with the octadecylrhodamine B chloride (R18) marker. We use this assay with PR8 influenza viruses and small (SUV) or large (LUV) unilamellar liposomes containing the virus receptor G D1a as interacting partners in order to analyse the effect of membrane curvature on fusion and transfer. Computer analysis revelaed no difference in the kinetics of fusion between PR8 with large or small liposomes respectively. Lipid transfer, however, is about 5 to 6 times faster from SUV than from LUV. We also tested the influence of the production method for liposomes, namely detergent dialysis, sonication and extrusion on membrane interactions. Fusion is not affected by either, whereas transfer is slower with liposomes produced by sonication.

Osmotic swelling of unilamellar vesicles by the stopped-flow light scattering method. Influence of vesicle size, solute, temperature, cholesterol and three α,ω-dihydroxycarotenoids

α,ω-Dihydroxycarotenoids are postulated to play the rôle of membrane reinforcers in certain procaryotes, like cholesterol in eucaryotes. In order to evaluate the rigidifying effect of these polyterpenoids on lipid bilayers, osmotic swelling of unilamellar vesicles has been followed by measuring the light scattering intensity changes in a stopped-flow apparatus. A model based upon the Rayleigh-Gans theory was developped. It shows that the variation of light scattering intensity ( ΔI I 0 ) is proportional to that of vesicle radius ( ΔR R 0 ) for a given R 0 (initial vesicle radius). An emperical relationship between −ΔI I 0 and Z (dissymmetry measured by light scattering) was established: −ΔI I 0 is proportional to ( Z − 1). Therefore, the value −ΔI (I 0 · (Z − 1)) is independent of vesicle radius and can be used for the evaluation of bilayer rigidity. The water permeability was measured and it was shown that it is the limiting factor of the kinetics of swelling. When incorporated into dimyristoylphophatidylcholine vesicles, cholesterol and α,ω-dihydroxycarotenoids lower the water permeability and the value of −ΔI (I 0 · (Z − 1)) . So, at least on model systems, α,ω-dihydroxycarotenoids exert on a phospholipid bilayer a reinforcement effect similar to cholesterol.

Influence of vesicle size on complement-dependent immune damage to liposomes

Complement-dependent antibody-mediated damage to multilamellar lipid vesicles (MLVs) normally results in a maximum release of 50–60% of trapped aqueous marker. The most widely accepted explanation for this is that only the outermost lamellae of MLVs are attacked by complement. To test this hypothesis, complement damage to two different types of large unilamellar vesicles (LUVs), large unilamellar vesicles prepared by the reverse-phase evaporation procedure (REVs) and large unilamellar vesicles prepared by extrusion techniques (LUVETs), were determined. In the presence of excess antibody and complement the LUVs released a maximum of only approx. 25 to 40% of trapped aqueous marker, instead of close to 100% that would be expected. Since small unilamellar vesicles apparently differ from LUVs in that they can release 100% of trapped aqueous marker it appeared that the size of the vesicles was an important factor. Because of these observations the influence of MLV size on marker release was examined. Three populations of MLVs of different sizes were separated by a fluorescence activated cell sorter. Assays of the separated MLV populations showed that the degree of complement-dependent marker release was inversely related to MLV size. No detectable glucose was taken up by MLVs when glucose was present only outside the liposomes during complement lysis. Our results can all be explained by the closing, or loss, of complement channels. We conclude that complement channels are only transiently open in liposomes, and that loss of channel patency may be due to either channel closing or to loss of channels.

Influence of vesicle size and oxidase content on respiratory control in reconstituted cytochrome oxidase vesicles.

Previous work has shown that the respiratory control or coupling exhibited by reconstituted cytochrome oxidase systems can be markedly sensitive to the lipid composition, the lipid to protein ratio, and the vesicle size. In this work we have attempted to ascertain which, if any, of these factors plays a definitive role in determining the observed coupling. Vesicles prepared from dioleoylphosphatidylcholine-dioleoylphosphatidylethanolamine (1:4) were fractionated by DEAE chromatography to obtain a population homogeneous with respect to their lipid to protein ratio. This subpopulation was then applied to a Sepharose 4B-CL column to separate the vesicles by size. Fractions eluted from the column were assayed for enzyme activity in the presence and absence of carbonyl cyanide ( trifluoromethoxy )phenylhydrazone plus valinomycin. The coupling ratio was found to be dependent upon vesicle size; the smaller the vesicles, the higher the ratio. This suggests that lipid composition per se does not determine coupling characteristics. Reducing vesicle size for a given lipid to protein ratio has two effects. First, the radius of curvature is increased and, second, the average number of oxidase molecules per vesicle is reduced. In order to identify which of these factors was responsible for the observed tighter coupling, the oxidase was reconstituted with dioleoylphosphatidylcholine into vesicles of a defined size and the number of oxidase molecules per vesicle varied. The highest coupling ratios were observed for vesicles containing on average only one oxidase dimer. As the fraction of vesicles containing more than one protein was increased, the coupling ratio rapidly declined.(ABSTRACT TRUNCATED AT 250 WORDS)