Interactions between DNA and cationic vesicles

Author(s)

Irene Satiko Kikuchi

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ)
• Defense date: 2000-11-24

Examining board members

Ana Maria Carmona Ribeiro; Hugo Aguirre Armelin; Mauricio da Silva Baptista; Maria Teresa Lamy Freund; Anselmo Gomes de Oliveira

• Advisor: Ana Maria Carmona Ribeiro

Abstract

In this work, interactions between DNA and cationic liposomes made up of dioctadecyldimethylammonium bromide (DODAB) are evaluated from a physicochemical point of view. The following models were used: 1) 2\'-deoxyadenosine 5\'-monophosphate (DMP), a model of monomeric unity of polymer, the DNA; 2) DNAs of T2, T4, T5, T7 and λ bacteriophages; 3) small vesicles of DODAB prepared by sonication; 4) large vesicles of DODAB prepared by heating (56 ºC/30 minutes) or by chloroform vaporization. The interaction between 2\'deoxyadenosine 5\'-monophosphate (DMP) and cationic liposomes made up of dioctadecyldimethylammonium bromide (DODAB) in water is described. At maximal adsorption, the molar ratio DODAB/DMP is 2:1 and electrophoretic mobility for the liposomes attains a minimum at a positive value. At 5 mM ionic strength, maximal DMP adsorption on the liposome becomes close to zero, demonstrating that the electrostatic attraction essentially drives the DODAB/DMP complexation. Over the millimolar range of DMP concentrations (0.4-1.5 mM), upon nucleotide addition, turbidity of the liposome dispersion (0.08 mM DODAB) steeply increases as a function of time in contrast with the much smaller flocculation rates upon NaCl addition over a much higher range of NaCl concentrations (40-120 mM). The nucleotide behaves as a hydrophobic anion with an affinity for the membrane that is much higher than that exhibited by a simple anion as chloride. DMP-induced rupture of liposomes containing [14C]sacarose was evaluated from dialysis of DMP/liposomes mixtures. In water, DMP-induced leakage of radioactive liposomal contents suggests that the DMP/bilayer interaction is not superficial. Although the interaction preserves the positive liposome charge, it doesn\'t preserve its integrity. At maximal adsorption, DMP insertion in the cationic bilayer is the most reasonable explanation for the remaining positive charge on the vesicle, the 2:1 DODAB : DMP molar ratio, and leakage of internal contents from the liposome. The DODAB/DNA interaction is also driven by the electrostatic attraction between DNA and bilayer. Probes located on DNA or in the bilayer are displaced from their DNA or bilayer sites. Under conditions of DODAB excess, at maximal DODAB adsorption on DNA, there are ca. 70 DODAB molecules adsorbed per nucleotide on DNA, a molar proportion (MP) that does not depend on DNA type. The DODAB/DNA interaction led to formation of globules as visualized from dark-field optical microscopy and to occurrence of a linear dependence between turbidity for the mixture and 1/λ2, where λ is the wavelength of incident light. At maximal DODAB adsorption, the formation of DODAB/DNA globular complexes causes loss of doublestranded DNA hypochromism as detected from temperature effects on DNA absorbance at 260 nm in the presence or absence of DODAB. In summary, liposome loses its integrity and DNA loses its double helix becoming single-stranded. The hydrophobic attraction between nitrogenous bases on DNA and hydrocarbon chains on liposome bilayers plays an important role in determining structure of the complex. (AU)