title: A theoretical and experimental approach to the compaction process of DNA by dioctadecyldimethylammonium bromide/zwitterionic mixed liposomes.
abstract: The compaction of DNA by cationic liposomes constituted by a mixture of a cationic lipid, dioctadecyldimethylammonium bromide (DODAB), and a zwitterionic lipid, 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) or 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), has been evaluated by means of experimental studies (electrophoretic mobility, conductometry, cryogenic electron transmission microscopy or cryo-TEM, and fluorescence spectroscopy) as well as theoretical calculations. This information reveals that DODAB/DOPE and DODAB/DLPC liposomes are mostly spherical and unilamellar, with a mean diameter of around 70 and 61 nm, respectively, a bilayer thickness of 4.5 nm, and gel-to-fluid transition temperatures, T(m), of around 19 and 28 degrees C, respectively. Their positively charged surfaces efficiently compact the negatively charged DNA by means of a strong entropically driven surface interaction that yields DODAB/DOPE-DNA and DODAB/DLPC-DNA lipoplexes as confirmed by zeta potential and ethidium bromide fluorescence intercalation assays. These experiments have permitted as well the evaluation of the different microenvironments of varying polarity of the DNA helix, liposomes, and/or lipoplexes. DODAB/DOPE-DNA and DODAB/DLPC-DNA lipoplexes have been characterized by isoneutrality ratios (L/D)(phi) of around 4.7 and 4.8, respectively, a more fluid membrane than that of the parent liposomes, and T(m) around 24 and 28 degrees C, respectively, as revealed by fluorescence anisotropy. Cryo-TEM micrographs reveal a rich scenario of nanostructures and morphologies, from unilamellar DNA-coated liposomes to multilamellar lipoplexes passing through cluster-like structures. Phase diagrams (aggregation and re-entrant condensation phenomena), calculated by means of a phenomenological theory, have confirmed the experimental concentration domains and the isoneutrality conditions. The influence of helper lipid in the compaction process, as well as the optimum choice among those herein chosen, has been analyzed.
authors.affiliation: Departamento de Química Física I, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040-Madrid, Spain.
authors.forename: Alberto
authors.initials: A
authors.lastname: Rodríguez-Pulido
authors.forename: Alberto
authors.initials: A
authors.lastname: Martín-Molina
authors.forename: César
authors.initials: C
authors.lastname: Rodríguez-Beas
authors.forename: Oscar
authors.initials: O
authors.lastname: Llorca
authors.forename: Emilio
authors.initials: E
authors.lastname: Aicart
authors.forename: Elena
authors.initials: E
authors.lastname: Junquera
mesh_terms: D002412:Cations / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D004996:Ethidium; D008081:Liposomes / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry; D010714:Phosphatidylethanolamines / Q000737:chemistry; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: C410262:1,2-dioleoyl-glycero-3-phosphatidyl ethanolamine; D002412:Cations; D008081:Liposomes; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D000644:Quaternary Ammonium Compounds; C015831:dimethyldioctadecylammonium; C002448:1,2-linoleoylphosphatidylcholine; D004247:DNA; D004996:Ethidium