DOTAP/DOPE and DC-Chol/DOPE lipoplexes for gene delivery: zeta potential measurements and electron spin resonance spectra

Abstract

Non-viral vectors represent an important alternative in gene delivery. Among these vectors, cationic liposomes are widely studied, because of their ability to form stable complexes with DNA fragments (lipoplexes). In the present work, we report on the characterization by electron spin resonance (ESR) spectroscopy and zeta potential measurements of cationic liposomes and of their complexes with oligonucleotides. Liposomes were made with a zwitterionic lipid, DOPE, and a cationic lipid, either DOTAP or DC-Chol. Oligonucleotides were the 20-base single strand polyA, the 20-base single strand polyT, and the corresponding double strand dsAT. The zeta potential as a function of the oligonucleotide/lipid+ ratio gave an S-shaped titration curve. Well-defined surface potential changes took place upon charge compensation between the cationic lipid heads and the phosphate groups on the oligonucleotides. The inversion point depended on the specific system under study. The bilayer properties and the changes that occurred with the incorporation of DNA fragments were also monitored by ESR spectroscopy of appropriately tailored spin probes. For all the systems investigated, the ESR spectra showed that no major alteration took place after lipoplex formation and molecular packing remained substantially unchanged. Both zeta potential and ESR measurements were in favor of an external mode of packing of the lipoplexes.

Varying the Unsaturation in N4,N9-Dioctadecanoyl Spermines: Nonviral Lipopolyamine Vectors for More Efficient Plasmid DNA Formulation

“…Ciani et al (43) found neutralization N/P charge ratios of 6 and 2 with intact liposomes. Similarly, also wor-king with liposomes, Lobo et al (44) and Wiethoff et al (45) reported that neutralization charge ratios of cationic lipidYDNA complexes occurred at N/P charge ratios of 3.5, 2.5, and 1.5.…”

Cell Biological and Biophysical Aspects of Lipid-mediated Gene Delivery

“…Maximization of efficiency is the primary objective in the attempts to identify transfection parameters that influence the transfection efficiency. Lipoplexes have been investigated by dynamic light scattering, electron microscopy [91], enzyme probes [92], electrophoresis [93], centrifugation [94], nuclear magnetic resonance [67] and X-ray diffraction [69] providing insights pertaining to cationic lipid-DNA interactions.…”

“…Further, the media in which the lipoplex potential was monitored influence these measurements. Several papers have reported the measurement of zeta potential of lipoplexes to relate the transfection efficiency to a property of the lipoplex [93,109]. Though positive complexes are invariably found to be essential for efficient transfection, lipoplex with positive potential does not guarantee transfection.…”

Domain Formation in DODAB–Cholesterol Mixed Systems Monitored via Nile Red Anisotropy

“…In cationic vesicles this has been found to be enhanced by inclusion of a "helper" lipid [1][2][3][4][5][6][7][8] although the mechanism responsible for this effect is not fully understood. Zhang and Anchordoquy [9] have studied the relationship between the effect of cholesterol in cationiclipid complexes and the charge density of the lipoplex.…”