A supramolecular polymerisation model for the structurisation of DNA–lipid complexes

Complexes formed by DNA and lipid mixtures have great interest for the assessment of self-assembling mechanisms in open biological systems. X-ray diffraction has revealed that minor alterations of the cationic/neutral lipid composition produced major alterations to the liquid crystalline structure and the hydration of the complexes. We have extended to these systems by an approach based on the identification of a fundamental repeating unit that grows according to the general principles of supramolecular polymerisation and liquid crystallinity. Structural reorganisations that optimise the electrostatic and hydrophobic compensation are enhanced by competition between the rigidity of the polyelectrolyte and the cohesion of the lipid assembly. The non-hydrated hexagonal structure revealed by X-ray examination is represented by a dendritic-type supramolecular polymerisation of DNA units decorated by the aliphatic tails of dissociated liposomes. An increase in the cationic/neutral lipid component ratio enhances the stability of planar bilayers, favouring the formation of the partly hydrated lamellar structure revealed by X-ray diffraction.     

Characterization of Monoolein-Based Lipoplexes Using Fluorescence Spectroscopy

Lipoplexes are commonly used as delivery systems in vitro and in vivo, the role of a neutral lipid as helper being of extreme importance in these systems. Cationic liposomes composed of dioctadecyldimethylammonium bromide (DODAB) with monoolein (MO) as a helper, at different molar ratios (1:2; 1:1 and 1:0.5) were prepared, and subsequently titrated to DNA. The structural and physicochemical properties of the lipid/DNA complexes were assessed by ethidium bromide (EtBr) exclusion, 90° static light scattering (90° SLS) assays and fluorescence resonance energy transfer (FRET). In EtBr exclusion assays, the steady-state fluorescence spectra of EtBr were decomposed into the sum of two lognormal emissions, emanating from two different environments – H₂O and DNA, and the effect of charge ratio (+/-) was observed. 90° SLS assays gave an important contribution, detecting size variations in systems with different MO fractions on the lipoplexes. In FRET assays, 2-(3-(diphenylhexatrienyl)propanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine (DPH-HPC) was used as donor and EtBr as acceptor. The DNA component previously calculated by EtBr exclusion, was used to determine the energy transfer efficiency, as an indirect measurement of the lipoplexes structural and physicochemical properties. Our results demonstrate that the inclusion of monoolein in the cationic liposomes formulation significantly modifies the rate of DNA complexation, being DODAB:MO (1:1) the system with higher DNA condensation efficiency.     

Comparison of different commercially available cationic liposome-DNA lipoplexes: Parameters influencing toxicity and transfection efficiency

Lipid–DNA complexes (lipoplexes) are widely used, since several years, as gene carriers. However, their transfection efficiency, both in vitro and in vivo, depends, in a rather complex way, on different interconnected parameters, ranging from the chemical composition of the lipid components to the size and size distribution of the complexes and, moreover, to the composition of the suspending medium. In this paper, we have investigated the behavior of nine different commercially available transfection agents (liposomal and non-liposomal) and their lipoplexes, at different molar charge ratios and in different experimental conditions. The size and the time stability of the resulting lipoplexes were investigated by means of dynamic light scattering methods and their toxicity and transfection efficiency were assayed in vitro in a model tumor cell line (C6 rat glioma cell line). An attempt to correlate the different parameters governing the complex phenomenology observed has been made. Whereas all the formulations investigated display a low toxicity, that increases with the increase of the lipid–DNA molar charge ratio, the transfection efficiency markedly depends, besides the molar charge ratio, on the lipid composition and on the lipoplex size, in a rather correlated way. The aim of this work is to present, in a wide scenario, an example of the inter-correlation among the different parameters that influence the transfection efficiency of lipoplexes and to suggest the role exerted by the average size of the resulting aggregates in their overall effectiveness as carriers in gene therapy.