Effect of "helper lipid" on lipoplex electrostatics.

Lipoplexes, which are complexes between cationic liposomes (L+) and nucleic acids, are commonly used as a nucleic acid delivery system in vitro and in vivo. This study aimed to better characterize cationic liposome and lipoplex electrostatics, which seems to play a major role in the formation and the performance of lipoplexes in vitro and in vivo. We characterized lipoplexes based on two commonly used monocationic lipids, DOTAP and DMRIE, and one polycationic lipid, DOSPA--each with and without helper lipid (cholesterol or DOPE). Electrical surface potential (Psi0) and surface pH were determined using several surface pH-sensitive fluorophores attached either to a one-chain lipid (4-heptadecyl hydroxycoumarin (C17HC)) or to the primary amino group of the two-chain lipids (1,2-dioleyl-sn-glycero-3-phosphoethanolamine-N-carboxyfluorescein (CFPE) and 1,2-dioleyl-sn-glycero-3-phosphoethanolamine-N-7-hydroxycoumarin) (HC-DOPE). Zeta potentials of the DOTAP-based cationic liposomes and lipoplexes were compared with Psi0 determined using C17HC. The location and relatively low sensitivity of fluorescein to pH changes explains why CFPE is the least efficient in quantifying the differences between the various cationic liposomes and lipoplexes used in this study. The fact that, for all cationic liposomes studied, those containing DOPE as helper lipid have the least positive Psi0 indicates neutralization of the cationic charge by the negatively-charged phosphodiester of the DOPE. Zeta potential is much less positively charged than Psi0 determined by C17HC. The electrostatics affects size changes that occurred to the cationic liposomes upon lipoplex formation. The largest size increase (based on static light scattering measurements) for all formulations occurred at DNA-/L+ charge ratios 0.5-1. Comparing the use of the one-chain C17HC and the two-chain HC-DOPE for monitoring lipoplex electrostatics reveals that both are suitable, as long as there is no serum (or other lipidic assemblies) present in the medium; in the latter case, only the two-chain HC-DOPE gives reliable results. Increasing NaCl concentrations decrease surface potential. Neutralization by DNA is reduced in a NaCl-concentration-dependent manner.

Enhancing effect of vaxfectin on the ability of a Japanese encephalitis DNA vaccine to induce neutralizing antibody in mice.

Vaxfectin, a recently developed adjuvant, was evaluated for its enhancing effect on immunogenicity of a Japanese encephalitis (JE) DNA vaccine plasmid encoding the JE virus premembrane (prM) and envelope (E) genes (designated pcJEME), using BALB/c and ICR mice. Formulation of pcJEME with Vaxfectin provided > or =8-fold higher neutralizing antibody titers than those induced by pcJEME alone and reduced the amount of pcJEME to one-tenth to induce comparable levels of neutralizing antibody. Use of Vaxfectin did not alter a Th1 type IgG isotype immune response (IgG1 < IgG2a) induced by pcJEME in mice. These results indicate that Vaxfectin has an ability to enhance immunogenicity of pcJEME and is considered as a useful adjuvant for DNA vaccines in murine experimental models.

Synergy between cationic lipid and co-lipid determines the macroscopic structure and transfection activity of lipoplexes.

The large number of cytofectin and co-lipid combinations currently used for lipoplex-mediated gene delivery reflects the fact that the optimal cytofectin/co-lipid combination varies with the application. The effects of structural changes in both cytofectin and co-lipid were systematically examined to identify structure-activity relationships. Specifically, alkyl chain length, degree of unsaturation and the head group to which the alkyl side chain was attached were examined to determine their effect on lipoplex structure and biological activity. The macroscopic lipoplex structure was assessed using a dye-binding assay and the biological activity was examined using in vitro transfection in three diverse cell lines. Lipoplexes were formulated in three different vehicles currently in use for in vivo delivery of naked plasmid DNA (pDNA) and lipoplex formulations. The changes in dye accessibility were consistent with structural changes in the lipoplex, which correlated with alterations in the formulation. In contrast, transfection activity of different lipoplexes was cell type and vehicle dependent and did not correlate with dye accessibility. Overall, the results show a correlation between transfection and enhanced membrane fluidity in both the lipoplex and cellular membranes.

Photochemical transfection: a technology for efficient light-directed gene delivery.

Most synthetic gene delivery vectors are taken up in the cell by endocytosis, and inefficient escape of the transgene from endocytic vesicles often is a major barrier for gene transfer by such vectors. To improve endosomal release we have developed a new technology, named photochemical internalization (PCI). PCI is based on photochemical reactions initiated by photosensitizing compounds localized in endocytic vesicles, inducing rupture of these vesicles upon light exposure. PCI constitutes an efficient light-inducible gene transfer method in vitro, which potentially can be developed into a site-specific method for gene delivery in in vivo gene therapy. In this paper the principle behind the PCI technology and the effect of PCI on transfection with different synthetic gene delivery vectors are reviewed. PCI treatment by the photosensitizer aluminum phthalocyanine (AlPcS2a) strongly improves transfection mediated by cationic polymers (e.g., poly-L-lysine and polyethylenimine), while the effect on transfection with cationic lipids is more variable. The timing of the light treatment relative to the transfection period was also important, indicating that release of the DNA from early endosomes is important for the outcome of PCI-induced transfection. The possibilities of using PCI as a technology for efficient, site-specific gene delivery in in vivo gene therapy is discussed.