Giant liposomes

While most vesicles are formed from double-tail amphiphiles such as lipids, they can also be made from some single chain fatty acids [73], surfactant-cosurfactant mixtures [71], and bola (two-headed) amphiphiles [74]. In addition to the more common spherical shells, tubular vesicles have been observed in DMPC-alcohol mixtures [70]. Polymerizable lipids allow photo- or chemical polymerization that can sometimes stabilize the vesicle [65] however, the structural change in the bilayer on polymerization can cause giant vesicles to bud into smaller shells [76]. Multivesicular liposomes are collections of hundreds of bilayer enclosed water-filled compartments that are suitable for localized drug delivery [77]. The structures of these water-in-water vesicles resemble those of foams (see Section XIV-7) with the polyhedral structure persisting down to molecular dimensions as shown in Fig. XV-11. 

Freeze-thawing If SUV are freeze-thawed in the presence of a high concentration of electrolytes and subsequently dialyzed against a low electrolyte concentration, unilamellar liposomes with a diameter of more than 10 pm are formed. The formation of these giant... 

Oku, N., and MacDonald, R. C. (1983a). Differential effects of alkali metal chlorides on formation of giant liposomes by freezing and thawing and dialysis. Biochemistry. 22. 855-863. 

Antimisiaris, S.C., Jayasekera, P., and Gregoriadis, C. (1993) Liposomes are vaccine carriers Incorporation of soluble and particulate antigens in giant vesicles./. Immunol. Meth. 166, 271-280. 

Fig. 5 Membrane models for NMR structure analysis, (a) An isotropic detergent micelle (left) is compared to the dimensions of lipid bilayers (right), (b) Macroscopically oriented membrane samples can be prepared on solid support, as nanodiscs, or as magnetically oriented bicelles. (c) Nomenclature and variability of liposomes small (SUV, 20-40 nm), intermediate (IUV, 40-60 nm), large (LUV, 100-400 nm), and giant unilamellar vesicles (GUV, 1 pm) multi-lamellar (MLV), oligo-lamellar (OLV) and highly heterogeneous multi-oligo-lamellar vesicles (MOLV)...

Roux A, Cappello G, Cartaud J, Prost J, Goud B, Bassereau P (2002) A minimal system allowing tabulation with molecular motors pulling on giant liposomes. Proc. Natl. Acad. Sci. USA 99 5394-5399. 

The obtained suspension is generally a mixture of liposomes of all sizes (typically from 20 to 2000 nm), and different species are generally observed, as shown in Figure 9.21. We will see later on that giant vesicles, spanning over a 100 p,m diameter, can also be formed. 

Tsumoto, K., Nomura, S. M., Nakatani, Y., and Yoshikawa, K. (2002). Giant liposome as a biochemical reactor transcription of DNA and transportation by laser tweezers. Langmuir, 17,7225-8. 

Cell-sized giant liposomes [311-313] have been prepared and their mechanical properties have been extensively investigated [312-315]. Utilization of these systems as containers for advanced materials awaits the interested researcher. 

Angelova MI, et al. Interactions of DNA with giant liposomes. Chem Phys Lipids 1999 101(1) 123 137. 

Preliminary experiments with 6-CF loaded mixed vesicles of dipalmitoylphosphat-idylcholine (DPPC) and diacetylenic lipid (22) exhibit only a very slow release of 6-CF after the addition of phopholipase A2. Reasons for this may be headgroup interactions which decrease the enzymatic activity or the fact that multilamellar vesicles were used for this study. Further experiments will be carried out with giant liposomes (visible under the light microscope) which are unilamellar and provide a higher enclosure percentage and low surface curvature (see 4.3.2). 

In a general preparation technique for giant liposomes the lipid (3 mg) is dissolved in 1 ml chloroform/methanol 10 1 and the solvent is evaporated in a horizontally rotating cylindrical reaction vessel. During this process the lipid adheres to the... 

During the fusion process the relative surface area decreases with increasing volume indicating a loss of membrane material (about 22% in Fig. 51). In analogy to the fusion process of protoplasts it can be assumed that the excess lipid is removed in form of small, submicroscopic vesicles (Fig. 52). The electric breakdown in the membrane contact zone leads to the formation of several pores in which lipid molecules are randomly oriented (Fig. 52 b). The molecules reorient forming submicroscopic vesicles and the new membrane of the fused vesicle (Fig. 52c). Thus, fused giant liposomes should contain small, submicroscopic vesicles. This could possibly be proven by using fluorescence-labelled lipids for liposome fusion. 

In preliminaty experiments, problems occured during the fusion of giant liposomes with cells. The induced dipole of cells is much larger than that of vesicles leading primarily to cell-cell contacts and thus to cell-cell fusion. By using vesicles filled with electrolyte or multilamellar vesicle dispersions this problem could be overcome. 

Fig. 52a-c. Scheme of the fusion process of giant liposomes and the formation of small unilamellar vesicles (SUV) at the interface, a) lipid bilayers in contact b) pores generated by electric breakdown and lipid reorientation forming SUVs c) reconstitution of lipid membranes formation of a fused giant liposome and SUVs . 

INTERACTIONS BETWEEN LAMELLAR AND INVERTED HEXAGONAL Hn PHASE OF CL/DNA COMPLEXES AND ANIONIC GIANT LIPOSOMES MIMICKING THE CELL PLASMA MEMBRANE... 

Kinnunen, Paavo, K., Giant Liposomes as Model Biomembranes for Roles of Lipids in Cellular Signalling, 6, 273. 

More recent penetration experiments were carried out in biological systems, that is, large intact nuclei [35], giant liposomes [36], and mammalian cells [37]. Such experiments can provide information about the distribution of electroactive species inside the cell, potentials, and ion transfers across biological membranes (see Section V.F). 

The transport of molecules across biological cell membranes and biomimetic membranes, including planar bilayer lipid membranes (BLMs) and giant liposomes, has been studied by SECM. The approaches used in those studies are conceptually similar to generation-collection and feedback SECM experiments. In the former mode, an amperometric tip is used to measure concentration profiles and monitor fluxes of molecules crossing the membrane. In a feedback-type experiment, the tip process depletes the concentration of the transferred species on one side of the membrane and in this way induces its transfer across the membrane. 

Most recently, Zhan and Bard used submicrometer-sized conical carbon fiber tips to approach, image, and puncture individual giant liposomes containing [Ru(bpy)3]2+ [36]. The leakage of [Ru(bpy)3]2+ through the lipid membrane was observed. A higher stability of liposomes as compared to lipid bilayers... 

Akashi, K., Miyata, H., Itoh. H., and Kinoshita, K., Jr. (1996), Preparation of giant liposomes in physiological conditions and their characterization under an optical microscope, Biophys. /., 71, 3242-3250. 

Shohda, K., Toyota, T.,Yomo,T., and Saguwara,T. (2003), Direct visualization of DNA duplex formation on the surface of a giant liposome, Chembiochem., 4,778-781. 

Liposomes occur in nature, but can also be easily synthesized in the laboratory. Depending on the preparation method used, whioh influenoes their size — in relation to the number of bilayer shells — and physical properties, liposomes are olassified as small unilamellar vesicles (SUVs, 25-50 nm), large unilamellar vesioles (LUVs, 100 nm to 1 pm), giant unilamellar vesicles (GUVs, 1.0-200 pm) multilamellar vesioles (MLVs, 0.1-15 pm), and multi-vesicular vesicles (MWs, 1.6-10.5 pm) the last consists of several small vesicles. Bicelles, which contain surfactant molecules in the lipid bilayer, constitute a special type of liposome. 

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