Elucidation of the molecular and formulation requirements for efficient lipofection is a prerequisite to enhance the biological activity of cationic lipid-mediated gene delivery systems. To this end, the in vitro lipofection activity of the ionizable asymmetric 1,2-dialkoylamidopropane-based derivatives bearing a single primary amine group as the cationic head group was evaluated. The electrostatic interactions of these cationic lipids with plasmid DNA in serum-free medium were investigated by means of gel electrophoresis retardation and Eth-Br quenching assays. The effect of the inclusion of the helper lipid DOPE in the formulation on these interactions was also considered. The physicochemical properties of these lipids in terms of bilayer fluidity and extent of ionization were investigated using fluorescence anisotropy and surface potential techniques, respectively. The results showed that only the active lipid, 1,2lmp[5], existed in a liquid crystalline state at physiological temperature. Moreover, the extent of ionization of this lipid in assemblies was significantly higher that it's saturated analogues. Inclusion of the helper lipid DOPE improved the encapsulation and association between 1,2lmp[5] and plasmid DNA, which was reflected by the significant boost of lipofection activity of the 1,2lmp[5]/DOPE formulation as compared to the lipid alone. In conclusion, membrane fluidity and sufficient protonation of ionizable cationic lipid are required for efficient association and encapsulation of plasmid DNA and elicit of improved in vitro lipofection activity.
Keywords: Cationic lipids; Fluorescence anisotropy; Gene delivery; Lipofection; Membrane fluidity; Surface potential.
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