Structure of polymerizable lipid bilayers VII: lateral organization of diacetylenic phosphatidylcholines with short proximal acyl chains

Diacetylenic lipids in the design of stable lipopolymers able to complex and protect plasmid DNA

Different viral and non-viral vectors have been designed to allow the delivery of nucleic acids in gene therapy. In general, non-viral vectors have been associated with increased safety for in vivo use; however, issues regarding their efficacy, toxicity and stability continue to drive further research. Thus, the aim of this study was to evaluate the potential use of the polymerizable diacetylenic lipid 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC8,9PC) as a strategy to formulate stable cationic lipopolymers in the delivery and protection of plasmid DNA. Cationic lipopolymers were prepared following two different methodologies by using DC8,9PC, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and the cationic lipids (CL) 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), stearylamine (SA), and myristoylcholine chloride (MCL), in a molar ratio of 1:1:0.2 (DMPC:DC8,9PC:CL). The copolymerization methodology allowed obtaining cationic lipopolymers which were smaller in size than those obtained by the cationic addition methodology although both techniques presented high size stability over a 166-day incubation period at 4°C. Cationic lipopolymers containing DOTAP or MCL were more efficient in complexing DNA than those containing SA. Moreover, lipopolymers containing DOTAP were found to form highly stable complexes with DNA, able to resist serum DNAses degradation. Furthermore, neither of the cationic lipopolymers (with or without DNA) induced red blood cell hemolysis, although metabolic activity determined on the L-929 and Vero cell lines was found to be dependent on the cell line, the formulation and the presence of DNA. The high stability and DNA protection capacity as well as the reduced toxicity determined for the cationic lipopolymer containing DOTAP highlight the potential advantage of using lipopolymers when designing novel non-viral carrier systems for use in in vivo gene therapy. Thus, this work represents the first steps toward developing a cationic lipopolymer-based gene delivery system using polymerizable and cationic lipids.

Ultraviolet irradiation of diacetylenic liposomes as a strategy to improve size stability and to alter protein binding without cytotoxicity enhancement

Membrane-modification effects, induced by ultraviolet (UV) irradiation in diacetylenic liposomes, were analyzed upon contact with cells, biological membranes, and proteins. Liposomes formulated with mixtures of unsaturated 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine and saturated 1,2-dimyristoyl-sn-glycero-3-phosphocholine, in a 1:1 molar ratio, were compared with those that were UV-irradiated and analyzed in several aspects. Membrane polymerization inherence on size stability was studied as well as its impact on mitochondrial and microsomal membrane peroxidation induction, hemolytic activity, and cell viability. Moreover, in order to gain insight about the possible irradiation effect on interfacial membrane properties, interaction with bovine serum albumin (BSA), lysozyme (Lyso), and apolipoprotein (apoA-I) was studied. Improved size stability was found for polymerized liposomes after a period of 30 days at 4°C. In addition, membrane irradiation had no marked effect on cell viability, hemolysis, or induction of microsomal and mitochondrial membrane peroxidation. Interfacial membrane characteristics were found to be altered after polymerization, since a differential protein binding for polymerized or nonpolymerized membranes was observed for BSA and Lyso, but not for apoA-I. The substantial contribution of this work is the finding that even when maintaining the same lipid composition, changes induced by UV irradiation are sufficient to increase size stability and establish differences in protein binding, in particular, reducing the amount of bound Lyso and BSA, without increasing formulation cytotoxicity. This work aimed at showing that the usage of diacetylenic lipids and UV modification of membrane interfacial properties should be strategies to be taken into consideration when designing new delivery systems.

DESIGN OF LIPOSOMES CONTAINING PHOTOPOLYMERIZABLE PHOSPHOLIPIDS FOR TRIGGERED RELEASE OF CONTENTS

We describe a novel class of light-triggerable liposomes prepared from a photo-polymerizable phospholipid DC(8,9)PC (1,2- bis (tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine) and DPPC (1,2-Dipalmitoyl-sn-Glycero-3-Phosphocholine). Exposure to UV (254 nm) radiation for 0-45 minutes at 25 degrees C resulted in photo-polymerization of DC(8,9)PC in these liposomes and the release of an encapsulated fluorescent dye (calcein). Kinetics and extents of calcein release correlated with mol% of DC(8,9)PC in the liposomes. Photopolymerization and calcein release occurred only from DPPC/DC(8,9)PC but not from Egg PC/DC(8,9)PC liposomes. Our data indicate that phase separation and packing of polymerizable lipids in the liposome bilayer are major determinants of photo-activation and triggered contents release.

Biostability and biocompatibility of a surface-grafted phospholipid monolayer on a solid substrate

We have previously demonstrated phosphorylcholine monolayer chemically grafted onto a methacryloyl-terminated solid substrate by in situ polymerization. The in situ polymerization was carried out at the interface between a pre-assembled acrylated phospholipid monolayer produced by vesicle fusion and a methacryloyl-terminated substrate using a water-soluble initiator, 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPD). Herein, we examined the biostability and biocompatibility of a surface-grafted phospholipid monolayer (poly-PC) on a methacryloyl-terminated substrate using a "wash off' test, in vitro protein adsorption and in vivo cage implantation for time intervals of 4, 7, 14 and 21 days, respectively. In order to compare the biostability and biocompatibility of phospholipid surfaces on solid substrates, we used two types of phospholipid surfaces: a physically adsorbed phospholipid monolayer (PC) and a poly-PC. Atomic force microscopy and water contact angle measurements indicated that the poly-PC surface was more stable in PBS, Triton X-100 and to EO gas sterilization than the PC surface. The adsorption of proteins such as albumin, fibrinogen, IgG and human plasma proteins on the poly-PC surfaces were significantly reduced, in vitro. Moreover, the poly-PC surface greatly reduced macrophage adhesion and the formation of foreign body giant cells, in vivo.

Preparation of a stable phospholipid monolayer grafted onto a methacryloyl-terminated substrate as blood compatible materials

We have prepared a surface-grafted phospholipid monolayer by in situ polymerization carried out at the interface between a pre-assembled phospholipid monolayer and a methacryloyl-terminated substrate. The phospholipid containing an acryloyl moiety, 1-stearoyl-2-[12-(acryloyloxy)-dodecanoyll-sn-glycero-3-phosphocholine (acryloyl-PC), was pre-assembled by vesicle fusion onto methacryloyl-terminated substrates which were silanized with 3-(trimethoxysilyl)propyl methacrylate (TSM). The acryloyl-PC monolayer and methacryloyl-terminated substrates were then polymerized in situ by adding a water-soluble initiator, 2,2-azobis(2-methylpropionamidine) dihydrochloride (AAPD), at 60 degrees C for 15 min. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) measurements indicated that the polymerized phospholipid surface on the TSM-silanized substrates formed a lipid monolayer structure with some defects. The polymerized phospholipid surfaces also showed good stability in methanol due to chemical bonding to solid surfaces. The grafting efficiency of acryloyl-PC monolayer on the TSM substrate, which was calculated by the relative carbon ratio of the polymerized acryloyl-PC monolayer on TSM substrate before and after methanol washing, was 94.5%. For comparative analysis, the acryloyl-PC monolayer was also polymerized onto dimethyl-terminated substrates silanized with dichlorodimethylsilane (DCM). In the absence of surface grafting moieties on solid substrates, the laterally polymerized acryloyl-PC monolayer physically adsorbed on substrates was easily removed in an organic solvent. The surface-grafted phospholipid monolayer was also greatly effective in the prevention of platelet adhesion.

Characterization of diacetylenic liposomes as carriers for oral vaccines

In order to evaluate liposomes as vehicle for oral vaccines the characterization and stability of polymerized and non-polymerized liposomes were examined. Mixtures of 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3 phosphocholine) (DC8,9PC) with saturated 1,2-dimiristoyl-sn-glycero-3-phosphocholine in molar ratio 1:1 were used. Saturated and non-saturated lipids were combined to give a chemically modified membrane by UV polymerization derived from DC8,9PC. Characterization was carried out by electronic microscopy, differential scanning calorimetry (DSC) and by hydrophobicity factor (HF). The stability towards the digestive tract (including saliva): acidic solutions, bile and pancreatin are compared to buffer pH 7.4, measuring the release of Glucose-6-phosphate or bovine plasma albumin entrapment. The polymerized liposomes showed further augmentation of the HF and the size. DSC showed phase separation and lower Tt if compared to data obtained for DC8,9PC. The HF, as main factor is discussed in relation to in vitro stability, suggesting that polymerized and non-polymerized liposomes would serve effectively as an oral delivery vehicle.