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Dramatic Influence of the Orientation of Linker between Hydrophilic and Hydrophobic Lipid Moiety in Liposomal Gene Delivery
journal contribution
posted on 2007-09-19, 00:00 authored by Mukthavaram Rajesh, Joyeeta Sen, Marepally Srujan, Koushik Mukherjee, Bojja Sreedhar, Arabinda ChaudhuriA number of prior studies have demonstrated that the DNA-binding and gene transfection
efficacies of cationic amphiphiles crucially depend on their various structural parameters including
hydrophobic chain lengths, headgroup functionalities, and the nature of the linker-functionality used in
tethering the polar headgroup and hydrophobic tails. However, to date addressing the issue of linker
orientation remains unexplored in liposomal gene delivery. Toward probing the influence of linker orientation
in cationic lipid mediated gene delivery, we have designed and synthesized two structurally isomeric
remarkably similar cationic amphiphiles 1 and 2 bearing the same hydrophobic tails and the same polar
headgroups connected by the same ester linker group. The only structural difference between the cationic
amphiphiles 1 and 2 is the orientation of their linker ester functionality. While lipid 1 showed high gene
transfer efficacies in multiple cultured animal cells, lipid 2 was essentially transfection incompetent. Findings
in both transmission electron microscopic and dynamic laser light scattering studies revealed no significant
size difference between the lipoplexes of lipids 1 and 2. Findings in confocal microscopic and fluorescence
resonance energy transfer (FRET) experiments, taken together, support the notion that the remarkably
higher gene transfer efficacies of lipid 1 compared to those of lipid 2 presumably originate from higher
biomembrane fusogenicity of lipid 1 liposomes. Differential scanning calorimetry (DSC) and fluorescence
anisotropy studies revealed a significantly higher gel-to-liquid crystalline temperature for the lipid 2 liposomes
than that for lipid 1 liposomes. Findings in the dye entrapment experiment were also consistent with the
higher rigidity of lipid 2/cholesterol (1:1 mole ratio) liposomes. Thus, the higher biomembrane fusibility of
lipid 1 liposomes than that of lipid 2 liposomes presumably originates from the more rigid nature of lipid 2
cationic liposomes. Taken together, the present findings demonstrate for the first time that even as minor
a structural variation as linker orientation reversal in cationic amphiphiles can profoundly influence DNA-binding characteristics, membrane rigidity, membrane fusibility, cellular uptake, and consequently gene
delivery efficacies of cationic liposomes.
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gene transfer efficaciesester linker groupgene transfection efficacieslinker ester functionalityHydrophobic Lipid Moietylipid 2 cationic liposomesDifferential scanning calorimetrycationic amphiphiles 1cationic amphiphilesDSCdye entrapment experimentlipid 2lipid 1lipid 2 liposomeslipid 1 liposomeslinker orientation reversallinker orientationFRETLiposomal Gene DeliveryA numberfluorescence resonance energy transferfluorescence anisotropy studiesgene delivery efficaciesliposomal gene delivery