Liposome fusion

Connor J, Yatvin MB, Huang L. pH-sensitive liposomes acid-induced liposome fusion. Proc Natl Acad Sci USA 1984 81(6) 1715-1718. 

Spermine has been found to enhance the transfection efficiency of DNA-cationic liposome complexes in cell culture and in animal studies this biogenic polyamine at high concentrations caused liposome fusion most likely promoted by the simultaneous interaction of one molecule of spermine (four positively charged amino groups) with the polar head groups of two or more molecules of lipids. At low concentrations (0.03-0.1 mM) it promoted anchorage of the liposome-DNA complex to the surface of cells and enhanced significantly transfection efficiency. 

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. 

Between the methods of Agrobacterium and microprojectile transfer, nearly every plant species can be transformed effectively [35]. However, these methods are covered by patent claims and may result in limited transformation efficiency for some cell types. For this reason, the use of alternative gene-transfer methods is an active area of research for all cell types. Alternative gene-transfer techniques include electroporation, microinjection, liposome fusion, direct transfer into protoplasts, and laser treatment [38]. In electroporation, DNA is transferred into the cell using a high-voltage electrical pulse [39]. Standard... 

Swanson, W.J. and Vacquier, V.D. (1995a). Liposome fusion by a Mr 18,000 protein localized to the acrosomal region of acrosome-reacted abalone spermatozoa. Biochemistry 54 14202-14209. 

The best results occurred when the lyophilization of SLN was obtained with the cryoprotectors glucose, mannose, maltose, and trehalose in concentrations of 10 to 15% [50], The observations come into line with the results of studies on liposome lyophilization, which indicated that trehalose was the most sufficient substance to prevent liposome fusion and leakage of the incorporated drug [51]. 

Morgan, C.G., Yianni, Y.P., Sandhu, S.S., and Mitchell, A.C. (1995a) Liposome fusion and lipid exchange on ultraviolet irradiation of liposomes containing a photochromic phospholipid, Photochem. Photobiol., 62, 24—29. 

Using the in vitro liposome fusion assay, researchers have tested the ability of various combinations of individual v-SNARE and t-SNARE proteins to mediate fusion of donor and target membranes. Of the very large number of different combinations tested, only a small number mediated membrane fusion. To a remarkable degree the functional combinations of v-SNAREs and t-SNAREs revealed in these in vitro experiments correspond to the actual SNARE protein interactions that mediate known membrane-fusion events in the yeast cell. Thus the specificity of the interaction between SNARE proteins can account for the specificity of fusion between a particular vesicle and its target membranes. 

Connor J M, Yatvin B, Huang L (1984). pH-sensitive liposomes Acid-induced liposome fusion, Proc. of the National Academy of Sciences of the United States of America. 81 1715-1718. 

Pak C C, Ali S, Janoff A S, et al. (1998). Triggerable liposomal fusion by enzyme cleavage of a novel peptide-lipid conjugate. Biochim. Biophys. Acta. 1372 13-27. 

Fluorescence Microscopy of Liposome Fusion onto a DOPC-coated Hg Interface... 

In this study, the efficiency of chromatophore-liposome fusion was improved by several cycles of freeze-thaw-sonication 5 cycles gave optimal results as judged from the disappearance of the chromatophore band in sucrose gradients. With this procedure, a set of fused preparations was obtained in which the buoyant densities varied between that of liposomes and chromatophores (1.030 and 1.156 g/cm, respectively) (Table 1). The relative phospholipid contents of the lipid-enriched membranes increased up to 15 fold and indicated that 50 to 80% of added lipid was incorporated into the pigmented membranes. The specific BChl values showed that relative pigment and protein contents remained essentially unchanged during fusion. 

Pillot X Lins L, Goethals M, et al. The 118-135 peptide of the human prion protein forms amyloid fibrils and induces liposome fusion. / Mol Biol. 1997 274(3) 381-393. 

It has been thought that membrane fusion plays an important role in cationic liposome-mediated transfection DNA is transferred into Qdoplasm via direct fusion between cationic hposomes and plasma membrane and/or fusion between cationic liposomes and endosomal membrane after being taken up by the cell through endocytosis. Thus, the effect of temperature on fusion between the polymer-modified cationic liposomes with the anionic liposomes was examined. Liposome fusion was detected by the change in resonance energy transfer efficiency from N-(7-nitrobenz-2-oxa-l,3-diazol-4-yl)phosphatidylethanolamine (NBD-PE) to lissamine rhodamine B-sulfonyl phosphatidylethanolamine (Rh-PE) due to dilution of these fluorescent lipids in the liposomal membrane. We have already shown that the fluorescence intensity ratio of NBD to Rh (R) is useful to follow membrane fusion. ... 

In contrast, fusion between the poly(APr)-2C 2-modified cationic liposome and EYPC/PA liposome was enhanced with temperature, while a very intensive enhancement of the fusion was seen around 45°C which is close to the LCST of poly(APr). Polymer chains in the poly(APr)-2Ci2-modified liposome might have higher conformational freedom than those in the copoly(APr-NDDAM)-modified liposome, because of the difference of attachment to the liposome. Also, density of the polymer chain in the vicinity of surface of the former liposome might be lower than that of the latter liposome due to the same reason. The differences in mobility and in density of polymer chains might result in the different temperature-dependence of liposome fusion. 

Cationic liposomes are also able to interact with negatively charged cell membranes more readily than classical liposomes. Fusion between cationic vesicles and cell surfaces might result in delivery of the DNA directly across the plasma membrane. This process bypasses the endosomal-lysosomal route which leads to degradation of anionic liposome formulations. Cationic liposomes can be formed from a variety of cationic lipids, and they usually incorporate a neutral lipid such as DOPE (dioleoylphosphatidyl-ethanolamine) into the formulation in order to faciUtate membrane fiision " . A variety of cationic lipids have been developed to interact with... 

A number of lipid transfer proteins similar to liposomes have been detected in plasma, and lipid exchange can also occur in the absence of enzymatic activity and in liposome fusion with cells [3,15,24]. Lipid transfer occurs by two separate processes associated with transfer proteins either by direct contact of solubilized molecules in the aqueous phase or upon liposome collisions with cells. During lipid exchange there is practically no mixing of liposomes and cell contents. 

The fusion of liposomes with cells is envisioned to deliver their contents directly to the cytoplasm [15,26]. However, whereas the fusion is an essential cellular process in endocytosis, it appears that the liposome fusion with the cells occurs very rarely and is enhanced by reconstitution of viral surface proteins. Therefore, it is apparent that this process is largely controlled by membrane protein of a cell or virus. This can be done not by a simple fusion of bilayers with cells but by incorporating fusogenic proteins or, in vitro, addition of fusogens. 

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