Thermotropic phase behavior and headgroup interactions of the nonbilayer lipids phosphatidylethanolamine and monogalactosyldiacylglycerol in the dry state

<p>Abstract</p> <p>Background</p> <p>Although biological membranes are organized as lipid bilayers, they contain a substantial fraction of lipids that have a strong tendency to adopt a nonlamellar, most often inverted hexagonal (H_II) phase. The polymorphic phase behavior of such nonbilayer lipids has been studied previously with a variety of methods in the fully hydrated state or at different degrees of dehydration. Here, we present a study of the thermotropic phase behavior of the nonbilayer lipids egg phosphatidylethanolamine (EPE) and monogalactosyldiacylglycerol (MGDG) with a focus on interactions between the lipid molecules in the interfacial and headgroup regions.</p> <p>Results</p> <p>Liposomes were investigated in the dry state by Fourier-transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry (DSC). Dry EPE showed a gel to liquid-crystalline phase transition below 0°C and a liquid-crystalline to H_IItransition at 100°C. MGDG, on the other hand, was in the liquid-crystalline phase down to -30°C and showed a nonbilayer transition at about 85°C. Mixtures (1:1 by mass) with two different phosphatidylcholines (PC) formed bilayers with no evidence for nonbilayer transitions up to 120°C. FTIR spectroscopy revealed complex interactions between the nonbilayer lipids and PC. Strong H-bonding interactions occurred between the sugar headgroup of MGDG and the phosphate, carbonyl and choline groups of PC. Similarly, the ethanolamine moiety of EPE was H-bonded to the carbonyl and choline groups of PC and probably interacted through charge pairing with the phosphate group.</p> <p>Conclusions</p> <p>This study provides a comprehensive characterization of dry membranes containing the two most important nonbilayer lipids (PE and MGDG) in living cells. These data will be of particular relevance for the analysis of interactions between membranes and low molecular weight solutes or soluble proteins that are presumably involved in cellular protection during anhydrobiosis.</p

Anionic liposomal delivery system for DNA transfection

The present study investigates the use of novel anionic lipoplexes composed of physiological components for plasmid DNA delivery into mammalian cells in vitro. Liposomes were prepared from mixtures of endogenously occurring anionic and zwitterionic lipids, 1,2-dioleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (sodium salt) (DOPG) and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), respectively, at a molar ratio of 17∶83 (DOPG:DOPE). Anionic lipoplexes were formed by complexation between anionic liposomes and plasmid DNA molecules encoding green fluorescence protein (GFP) using Ca2+ ions. Transfection and toxicity were evaluated in CHO-K1 cells using flow cytometry and propidium iodide staining, respectively. Controls included Ca2+-DNA complexes (without lipids), anionic liposomes (no Ca2+), and a cationic liposomal formulation. Efficient delivery of plasmid DNA and subsequent GFP expression was achieved using anionic lipoplexes. Transfection efficiency increased with Ca2+ concentration up to 14 mM Ca2+, where transfection efficiency was 7-fold higher than in untreated cells, with minimum toxicity. Further increase in Ca2+ decreased transfection. Transfection efficiency of anionic lipoplexes was similar to that of cationic liposomes (lipofect Amine), whereas their toxicity was significantly lower. Ca2+-DNA complexes exhibited minimal and irregular transfection with relatively high cytotoxicity. A model was developed to explain the basis of anionic lipoplex uptake and transfection efficacy. Effective transfection is explained on the formation of nonbilayer hexagonal lipid phases. Efficient and relatively safe DNA transfection using anionic lipoplexes makes them an appealing alternative to be explored for gene delivery