Effect of headgroup structure on catonic
lipid-mediated transfection was investigated with either a (i) tertiary
amine, (ii) quaternary
amine with a
hydroxyl, or (iii) quaternary
amine with
mesylate as headgroups.
Liposomes were formulated using
cholesterol or dioleoyl phosphatidyl
ethanolamine (DOPE) as colipids, and transfection efficiencies were determined in rapidly dividing colon
carcinoma (CT 26) and rat aortic smooth muscle (RASM) cells as well as in nondividing human pancreatic islets using
luciferase and
green fluorescent protein expression plasmids, pcDNA3-Luc and pCMS-EGFP, respectively.
Liposome/pDNA complexes were evaluated for
DNA conformational state by circular dichroism (CD),
DNA condensation by electrophoretic mobility shift assay (EMSA), particle size and zeta potential by
laser diffraction technique, and surface morphology by transmission electron microscopy (TEM). Encouraging transfection results were obtained with the
mesylate headgroup based
lipid in
liposome formulations with DOPE as a colipid, which were higher than the commercially available
Lipofectamine formulation. We hypothesize that the additional hydrogen bonding or covalent interactions of the headgroup with the plasmid
DNA, leading to higher binding affinity of the cationic
lipids to pDNA, results in higher transfection. This hypothesis is supported by TEM observations where elongated complexes were observed and more
lipid was seen associated with the
DNA.