Lipoplexes structure

Cellular anionic lipids have a twofold effect on DNA release from the lipo-plexes. They compensate the cationic lipid surface charge and eliminate the electrostatically driven DNA binding to the membrane interface, and they also disrupt the lipoplex structure and facilitate DNA departure into the solution by inducing formation of nonlamellar phases upon mixing with the lipoplex lipids. 

Koynova R, Wang L, MacDonald RC (2008) Cationic phospholipids forming cubic phases lipoplex structure and transfection efficiency. Mol Pharm 5 739-744... 

Ewert K, Evans H, Ahmad A, Slack L, Lin A, Martin-Herranz A, Safinya CR (2005) Lipoplex structures and their distinct cellular pathways. In Huang L, Hung M-C, Wagner E (eds) Nonviral vectors for gene therapy, 2nd edn. Part I (Advances in genetics 53). Elsevier, San Diego... 

Shape. Lin et al. demonstrated a correlation between lipoplex structure and transfection efficiency [102]. Liposomes that formed hexagonal structures were more efficient in gene delivery than those that formed a lamellar, owing to improved fusion with mouse cell membranes (both endosomal and plasma membranes), whereas lamellar structures remained stable inside the cell. This correlation of structure and transfection efficiency was used to explain the increased efficiency of DOTAP DOPE liposomes (hexagonal structures) compared to DOTAP DOPC liposomes (lamellar structures) [102],... 

Whereas lipoplexes/polyplexes generally protect the plasmid from serum nucleases, the overall positive charge characteristic of these structures leads to their non-specific interactions with cells... 

Despite the fact that many different cationic lipids have been synthesized and tested for transfection (25 34), relatively few systematic structure activity TE-relationship studies have been performed (35 39). As a result, no general relationship between chemical structure and TE could be drawn from these studies. One reason for this is that the chemical structure of a cationic lipid is not directly responsible for TE. TE rather depends on the biophysical characteristics of the cationic lipid aggregate (e.g., liposomes and lipoplexes), which, for its part, is dependent on the chemical structure of the lipids. In a previous study with analogs of the transfection lipid A-[l-(2,3-dioleoyloxy) propyl]-A,A,A-trimethylammoniumchloride (DOTAP) (40) which differ in their nonpolar hydrocarbon chains, it could be shown that the TE strongly depended on the biophysical properties of the resulting liposomes and lipoplexes (35). Minimal alterations of biophysical properties by using lipids with different hydrocarbon chains or by mixing the lipid with different neutral helper lipids could completely allow or prevent transfection. 

Ferrari M, et al. Trends in lipoplex physical properties dependent on cationic lipid structure, vehicle and complexation procedure do not correlate with biological activity. Nucl Acids Res 2001 29 1539. 

Gene therapy results to date using this approach have been mixed. The process of lipoplex formation is not easily controlled and hence different batches made under seemingly identical conditions may not be structurally identical. Furthermore, in vitro test results using such lipoplexes can correlate very poorly with subsequent in vivo performance. Clearly, more research is required to underpin the rational use of lipoplexes for gene therapy purposes. The same is true... 

Cationic lipids interact electrostatically and form stable complexes (lipoplexes) with the polyanionic nucleic acids. The structure of most lipoplexes is a multi-lamellar sandwich in which lipid bilayers alternate with layers of DNA strands [16, 62-64] (Fig. 20). Although infrequent, nonlamellar structures have also been found. The free energy gain upon lipoplex formation was shown to be essentially of entropic nature resulting from the counterion release and macromolecule dehydration [65, 66]. 

Fig. 25 (a) DNA release from EDOPC-DNA lipoplexes after addition of negatively charged lipid dispersion, as monitored by FRET (CM, oleic acid DOPA, dioleoyl phosphatidic acid DOPG, dioleoyl phosphatidylglycerol CL, cardiolipin DOPS, dioleoyl phosphatidylserine PI, phospha-tidylinositol). (b) Fraction of released DNA from EDOPC lipoplexes 10 min after addition of the respective anionic liposomes (c) X-ray diffraction patterns of mixtures of EDOPC and anionic liposome dispersions the respective structures are shown schematically on the left side (reproduced with permission from [98] copyright (2004) Biophysical Society)... 

Given the need for intermixing of membrane lipids with lipoplex lipids as an important step in the sequence of transfection events, a set of recent findings, discussed below, takes on particular significance. These findings demonstrate that transfection efficiency closely correlates both with the cationic PC chain structure (Fig. 13a) [26] and with its effect on the lamellar-to-nonlamellar phase progressions observed in membrane lipids upon mixing with cationic PCs (Fig. 13, 26, and 27). 

Numerous scientific groups have been working on the development of different cationic phospholipids for gene delivery (Table 10.2), but the structure of the DNA—phospholipids complex (or lipoplex) is still poorly... 

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