Cationic Phospholipid Research Articles

Saturated Anionic Phospholipids Enhance Transdermal Transport by Electroporation

Anionic phospholipids, but not cationic or neutral phospholipids, were found to enhance the transdermal transport of molecules by electroporation. When added as liposomes to the milieus of water-soluble molecules to be delivered through the epidermis of porcine skin by electroporation, these phospholipids enhance, by one to two orders of magnitude, the transdermal flux. Encapsulation of molecules in liposomes is not necessary. Dimyristoylphosphatidylserine (DMPS), phosphatidylserine from bovine brain (brain-PS), dioleoylphosphatidylserine (DOPS), and dioleoylphosphatidylglycerol (DOPG) were used to test factors affecting the potency of anionic lipid transport enhancers. DMPS with saturated acyl chains was found to be a much more potent transport enhancer than those with unsaturated acyl chains (DOPS and DOPG). There was no headgroup preference. Saturated DMPS was also more effective in delaying resistance recovery after pulsing, and with a greater affinity in the epidermis after pulsing. Using fluorescent carboxyl fluorescein and fluorescein isothiocyanate (FITC)-labeled Dextrans as test water-soluble molecules for transport, and rhodamine-labeled phospholipids to track anionic phospholipids, we found, by conventional and confocal fluorescence microscopy, that transport of water-soluble molecules was localized in local transport spots or regions (LTRs) created by the electroporation pulses. Anionic phospholipids, especially DMPS, were located at the center of the LTRs and spanned the entire thickness of the stratum corneum (SC). The degree of saturation of anionic phospholipids made no difference in the densities of LTRs created. We deduce that, after being driven into the epidermis by negative electric pulses, saturated anionic phospholipids mix and are retained better by the SC lipids. Anionic lipids prefer loose layers or vesicular rather than multilamellar forms, thereby prolonging the structural recovery of SC lipids to the native multilamellar form. In the presence of 1 mg/ml DMPS in the transport milieu, the flux of FITC-Dextran-4k was enhanced by 80-fold and reached 175 μg/cm 2/min. Thus, the use of proper lipid enhancers greatly extends the upper size limit of transportable chemicals. Understanding the mechanism of lipid enhancers enables one to rationally design better enhancers for transdermal drug and vaccine delivery by electroporation.

Lipid Phase Dependence of DNA−Cationic Phospholipid Bilayer Interactions Examined Using Atomic Force Microscopy

Magnetic AC mode atomic force microscopy was used to study DNA adsorption onto supported cationic phospholipid (CL) bilayers in the fluid (L α ) and gel (L β ) phases. A L α phase CL bilayer was used as a model system to study DNA-CL complex formation at the single molecule level. Pure and mixed bilayers of dioleoyltrimethylammonium propane (DOTAP), dioleoylphosphatidylethanolamine (DOPE), dioleoylphosphatidylcholine (DOPC), and dipalmitoyltrimethylammonium propane (DPTAP) were investigated. The adsorption of small oligodeoxynucleotide DNA (14 base pairs) and large (1000-3000 base pairs) was examined and revealed that the behavior of the DNA-CL complex depends on the length and density of DNA. Once adsorbed to the bilayer, large DNA induced changes in the bilayer coverage of the mica support, while short DNA did not destabilize the bilayer. There was a strong dependence of the bilayer destabilization on the type of neutral helper lipid mixed with the cationic lipid, with DOTAP/DOPE being much less stable to DNA adsorption than DOTAP/DOPC. The characteristics of pure and mixed DOTAP, DOPE, and DOPC supported phospholipid bilayers were investigated to understand the stability changes induced by DNA. Images of the DNA-free phospholipid bilayer revealed the dependence of supported planar bilayer structure and stability on the chemical nature of the headgroup and on the phase of the bilayer. Finally, it was illuminating to image DNA on DPTAP bilayers as a function of temperature. When the system was examined above the L α -L β phase transition, images similar to those recorded for DNA-DOTAP (L α ) and DNA-DOTAP/DOPC (L α ) were observed.

Interaction of a hepatitis A synthetic antigen [105,109ABU]VP3(101-121) with lipid monolayers

We describe the synthesis and characterization of an antigenic peptide: [ 105,109 ABU]VP3(101-121), corresponding to the (101-121) sequence of VP3 protein from Hepatitis A virus. The physicochemical properties of the peptide were studied using lipid monolayers as a model membrane by means the Langmuir-Blodgett film technique. The main goal of the research was to get insight into the possible mechanism of action of the peptide at the membrane level and therefore, to better understand the proliferation and infection processes of the virus in the host. For that reason, interaction of the peptide with neutral, anionic and cationic phospholipids was studied by the determination of the penetration kinetics and compression isotherms. The peptide had surface activity, concentration dependent and was able to incorporate into lipid monolayers.

On the mechanism whereby cationic lipids promote intracellular delivery of polynucleic acids.

The mechanism whereby cationic lipids destabilize cell membranes to facilitate the intracellular delivery of macromolecules such as plasmid DNA or antisense oligonucleotides is not well understood. Here, we show that cationic lipids can destabilize lipid bilayers by promoting the formation of nonbilayer lipid structures. In particular, we show that mixtures of cationic lipids and anionic phospholipids preferentially adopt the inverted hexagonal (H(II)) phase. Further, the presence of 'helper' lipids such as dioleoylphosphatidylethanolamine or cholesterol, lipids that enhance cationic lipid-mediated transfection of cells also facilitate the formation of the H(II)phase. It is suggested that the ability of cationic lipids to promote nonbilayer structures in combination with anionic phospholipids leads to disruption of the endosomal membrane following uptake of nucleic acid-cationic lipid complexes into cells, thus facilitating cytoplasmic release of the plasmid or oligonucleotide.

Measurement of Wall Zeta Potentials and Their Time-Dependent Changes Due to Adsorption Processes: Liposome Adsorption on Glass

A novel method of measuring the zeta potential associated with the planar glass surface of an electrophoresis cell by laser Doppler velocimetry has been developed. The method exploits the observation that the terminal velocity of particles subjected to an electric field is reached at least an order of magnitude more quickly than the establishment of electroosomotic flow at the planar glass surface of the cell. By using a fast field reversal technique so that the particle velocity is unaffected by electroosomic flow in conjunction with a mixed mode measurement, it is possible to obtain the electrophoretic mobility of a particle without the need to make measurements at the stationary layer. In addition, the methods give data for the zeta potential at the cell wall. The cell wall zeta potential is sensitive to adsorption of solutes from solution and may be used to follow both the kinetics of adsorption and to construct an adsorption isotherm. The method has been applied to the study of the adsorption of cationic and anionic phospholipid liposomes. The wall zeta potentials reflect the adsorption process in that the cationic liposomes cause a reversal of the wall zeta potentials from the negative value of the clean glass surface to positive values after 1−3 h. In contrast, the anionic liposomes increase the negative wall zeta potentials. At equilibrium, limiting potentials may be fitted to a Langmuir isotherm. The results from the fitting are compared with the adsorption of liposomes to silica particles in suspension.

Partitioning of uncharged local anesthetic benzocaine into model biomembranes

The partitioning of uncharged local anesthetic benzocaine (BzC) into molecular aggregates formed by cationic surfactant decylammonium chloride (DeAC) and phospholipid dipalmitoylphosphatidylcholine (DPPC) was studied from the surface tension and light transmittance measurements. The quantities concerning the partitioning of BzC, the compositions of BzC in the surface-adsorbed film and micelle and three kinds of differential partition coefficients corresponding to phase transitions of the DPPC bilayer membrane were evaluated from thermodynamic analysis of the experimental data. The surface-adsorbed film and micelle were more abundant in BzC than the aqueous solution and significantly large differential partition coefficients for the DPPC membranes were observed. The results clearly showed that the BzC molecules greatly partitioned into hydrophobic environments produced by surfactant-monolayer and phospholipid-bilayer membranes. The partitioning behavior of BzC was also compared with that of charged local anesthetic procaine hydrochloride (PC·HCl). It was shown that the PC·HCl molecule did not or hardly partition into such hydrophobic environments. The contrasting results of the partitioning between BzC and PC·HCl are attributable to the drastic decrease of hydrophilicity of BzC due to the lacking of ionic polar head group in comparison with PC·HCl.

Contribution of plasmid DNA to hepatotoxicity after systemic administration of lipoplexes.

Several studies have demonstrated that intravenous administration of DNA complexed with cationic lipid vectors induces the production of large quantities of proinflammatory cytokines. In this study we confirm these observations, using cationic lipid DOTAP and cationic phospholipid compounds. Moreover, we demonstrate that although intravenous administration of lipid-DNA complexes does not induce toxic effects in the lung, high transgene expression in lung correlates with histopathological lesions in liver, this fact being documented by high transaminase levels in serum of treated mice. We examine the contribution of various components of the lipoplexes in this observed liver toxicity, as well as in the increasing level of transaminases, and more particularly the role of nonmethylated CpG sequences of plasmid DNA. We show that blood samples from animals treated either with cationic lipid alone, or with cationic lipid complexed with methylated plasmid DNA, contain low levels of transaminases. The significant decrease in transaminase levels after injection of cationic lipid-methylated pDNA complexes leads us to believe that nonmethylated CpG sequences could play a major role in this hepatoxicity. Similar results were observed when using a vector that did not encode a transgene, demonstrating that the expression of luciferase in lung was not responsible for this liver toxicity. All these observations suggest that significant work should be devoted to understand more clearly the mechanism of cationic lipid-DNA complex toxicity, and to overcome the problems subsequent to administration of non-methylated CpG sequences of plasmid DNA.

Cholesterol stabilizes hemifused phospholipid bilayer vesicles

Cholesterol was found to inhibit full fusion of oppositely charged phospholipid bilayer vesicles by stabilizing the contacting membranes at the stage of the hemifused intermediate. Vesicles of opposite charge containing different amounts of cholesterol were prepared using cationic (1,2-dioleoyl- sn-glycero-3-ethylphosphocholine) and anionic (dioleoylphosphatidylglycerol) phospholipids. Pairwise interactions between such vesicles were observed by fluorescence video microscopy in real time after electrophoretically maneuvering the vesicles into contact. Hemifusion accounted for more than 80% of the observed events when the vesicles contained 33–50 mole% cholesterol. In contrast, vesicles containing only a small proportion of cholesterol (≤10 mole%), underwent full fusion in approx. 70% of the interactions monitored. The role of cholesterol is explained both as favoring the formation of the hemifused intermediate according to the adhesion-condensation mechanism of bilayer fusion and as disfavoring the transition from hemifusion to full fusion on the basis of reduced tension in the vesicle bilayers.

Electrostatic Control of Phospholipid Polymorphism

A regular progression of polymorphic phase behavior was observed for mixtures of the anionic phospholipid, cardiolipin, and the cationic phospholipid derivative, 1,2-dioleoyl- sn-glycero-3-ethylphosphocholine. As revealed by freeze-fracture electron microscopy and small-angle x-ray diffraction, whereas the two lipids separately assume only lamellar phases, their mixtures exhibit a symmetrical (depending on charge ratio and not polarity) sequence of nonlamellar phases. The inverted hexagonal phase, H II, formed from equimolar mixtures of the two lipids, i.e., at net charge neutrality (charge ratio (CR (+/−)) = 1:1). When one type of lipid was in significant excess (CR (+/−) = 2:1 or CR (+/−) = 1:2), a bicontinuous cubic structure was observed. These cubic phases were very similar to those sometimes present in cellular organelles that contain cardiolipin. Increasing the excess of cationic or anionic charge to CR (+/−) = 4:1 or CR (+/−) = 1:4 led to the appearance of membrane bilayers with numerous interlamellar contacts, i.e., sponge structures. It is evident that interactions between cationic and anionic moieties can influence the packing of polar heads and hence control polymorphic phase transitions. The facile isothermal, polymorphic interconversion of these lipids may have important biological and technical implications.

Characteristics and biodistribution of cationic liposomes and their DNA complexes

We have developed some novel liposome formulations for gene transfection. The formulations consisting of O, O′-ditetradecanoyl- N-(α-trimethyl ammonio acetyl) diethanolamine chloride (DC-6-14) as a cationic lipid, phospholipid and cholesterol showed effective gene transfection activity in cultured cells with serum and in vivo, i.e., intraperitoneal injection in mice. In this report, the physicochemical characteristics and biodistribution of the liposomes containing DC-6-14 (DC-6-14 liposomes) as a drug (gene) carrier for gene therapy were investigated in vitro and in vivo. DC-6-14 liposome–DNA complexes were usually thought to have positive surface charge. However, depending on the ratio of DNA to liposomes, zeta-potential of the complexes became negative. The diameter of the complexes also depended on the DNA–liposome ratio, and showed a maximum when their surface potential was neutral. When biodistribution of the complexes was determined after intravenous injection, positively charged complexes showed an immediate lung accumulation. On the other hand, negatively charged complexes did not show lung accumulation. These results have suggested that biodistribution of the DNA–liposome complexes, prepared with DC-6-14 liposomes, depends on their surface charge. Therefore, some surface modification of DC-6-14 liposomes may improve the biodistribution and hence the targetability of their DNA complexes.

Factors Governing the Assembly of Cationic Phospholipid-DNA Complexes

The interaction of DNA with a novel cationic phospholipid transfection reagent, 1,2-dioleoyl- sn-glycero-3-ethylphosphocholine (EDOPC), was investigated by monitoring thermal effects, particle size, vesicle rupture, and lipid mixing. By isothermal titration calorimetry, the heat of interaction between large unilamellar EDOPC vesicles and plasmid DNA was endothermic at both physiological and low ionic strength, although the heat absorbed was slightly larger at the higher ionic strength. The energetic driving force for DNA-EDOPC association is thus an increase in entropy, presumably due to release of counterions and water. The estimated minimum entropy gain per released counterion was 1.4 cal/mole-°K (about 0.7 kT), consistent with previous theoretical predictions. All experimental approaches revealed significant differences in the DNA-lipid particle, depending upon whether complexes were formed by the addition of DNA to lipid or vice versa. When EDOPC vesicles were titrated with DNA at physiological ionic strength, particle size increased, vesicles ruptured, and membrane lipids became mixed as the amount of DNA was added up to a 1.6:1 (+:−) charge ratio. This charge ratio also corresponded to the calorimetric end point. In contrast, when lipid was added to DNA, vesicles remained separate and intact until a charge ratio of 1:1 (+:−) was exceeded. Under such conditions, the calorimetric end point was 3:1 (+:−). Thus it is clear that fundamental differences in DNA-cationic lipid complexes exist, depending upon their mode of formation. A model is proposed to explain the major differences between these two situations. Significant effects of ionic strength were observed; these are rationalized in terms of the model. The implications of the analysis are that considerable control can be exerted over the structure of the complex by exploiting vectorial preparation methods and manipulating ionic strength.

Physical and Biological Properties of Cationic Triesters of Phosphatidylcholine

The properties of a new class of phospholipids, alkyl phosphocholine triesters, are described. These compounds were prepared from phosphatidylcholines through substitution of the phosphate oxygen by reaction with alkyl trifluoromethylsulfonates. Their unusual behavior is ascribed to their net positive charge and absence of intermolecular hydrogen bonding. The O-ethyl, unsaturated derivatives hydrated to generate large, unilamellar liposomes. The phase transition temperature of the saturated derivatives is very similar to that of the precursor phosphatidylcholine and quite insensitive to ionic strength. The dissociation of single molecules from bilayers is unusually facile, as revealed by the surface activity of aqueous liposome dispersions. Vesicles of cationic phospholipids fused with vesicles of anionic lipids. Liquid crystalline cationic phospholipids such as 1,2-dioleoyl- sn-glycero-3-ethylphosphocholine triflate formed normal lipid bilayers in aqueous phases that interacted with short, linear DNA and supercoiled plasmid DNA to form a sandwich-structured complex in which bilayers were separated by strands of DNA. DNA in a 1:1 (mol) complex with cationic lipid was shielded from the aqueous phase, but was released by neutralizing the cationic charge with anionic lipid. DNA-lipid complexes transfected DNA into cells very effectively. Transfection efficiency depended upon the form of the lipid dispersion used to generate DNA-lipid complexes; in the case of the O-ethyl derivative described here, large vesicle preparations in the liquid crystalline phase were most effective.

O‐ethylphosphatidylcholine: A metabolizable cationic phospholipid which is a serum‐compatible DNA transfection agent

1,2‐Dioleoyl‐sn‐glycero‐3‐ethylphosphocholine was prepared in a one‐step reaction from phosphatidylcholine by reaction with ethyl trifluoromethanesulfonate. This and related O‐alkyl phosphati‐dylcholines constitute the first chemically stable triesters of biological lipid structures and the first cationic derivatives of phospholipids consisting entirely of biological metabolites linked with ester bonds. The complex of cationic phospholipid and plasmid DNA transfected cells with high efficiency. Maximum efficiency of transfection was obtained with complexes in which the positive charge was a few percent in excess over the negative charge. Modest stimulation of transfection of common cell lines was obtained by continuous culture in the presence of 10% serum. Incubation of the phospholipid complex for at least 2 h at 37 °C in nearly pure serum had no deleterious effects on transfection efficiency. The lipid has low toxicity; BHK cells tolerated amounts of 2 mg/2 × 106 cells at concentrations of 1 mg/mL. The lipid is biodegradable; it was hydrolyzed by phospholipase A2 in vitro and was metabolized with a half‐life of a few days in cells in culture. The synthetic route to cationic phospholipids is well suited to the preparation of derivatives that are tailor‐made to have a wide variety of different properties.

Directly observed membrane fusion between oppositely charged phospholipid bilayers.

A novel method was developed for the direct examination of pairwise encounters between positively and negatively charged phospholipid bilayer vesicles. Giant bilayer vesicles (unilamellar, 4-20 micron in diameter) prepared from 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine, a new cationic phospholipid derivative, were electrophoretically maneuvered into contact with individual anionic phospholipid vesicles. Fluorescence video microscopy revealed that such vesicles commonly underwent fusion within milliseconds (1 video field) after contact, without leakage. Fusion occurred at constant volume and, since flaccid vesicles were rare, the excess membrane was not available after fusion. Hemifusion (the outer monolayers of each vesicle fused while the inner monolayers remained intact) was inferred from membrane-bound dye transfer and a change in the contact area. Hemifusion was observed as a final stable state and as an intermediate to fusion of vesicles composed of charged phospholipids plus zwitterionic phospholipids. Hemifusion occurred in one of three ways following adhesion: either delayed with an abrupt increase in area of contact, immediately with a gradual increase in area of contact, or with retraction during which adherent vesicles dissociated from a flat contact to a point contact. Phosphatidylethanolamine strongly promoted immediate hemifusion; the resultant hemifused state was stable and seldom underwent complete fusion. Although sometimes single contacts between vesicles led to rupture of both, in other cases, a single vesicle underwent multiple fusion events. Direct observation has unequivocally demonstrated the fusion of two, isolated bilayer-bounded bodies to yield a stable, non-leaky product, as occurs in cells, in the absence of proteins.

Contribution of Hydrogen Bonding to the Association of Liposomes and an Anionic Hydrophobically Modified Poly(N-isopropylacrylamide)

The interactions between a random copolymer of N-isopropylacrylamide (NIPAM), N-[4-(1-pyrenyl)-butyl]-N-n-octadecylacrylamide, and N-glycylacrylamide (Gly) (PNIPAM-Py-Gly) with a series of vesicles have been examined by fluorescence spectroscopy, centrifugation assays, and capillary electrophoresis. The copolymer exhibits pH-sensitivity due to the carboxylic acid group of the glycine residues (15 mol %), thermosensitivity due to the NIPAM residues (84 mol %), and amphiphilic characteristics due to the pyrenyl octadecyl moieties (1 mol %). In the presence of salts, complex formation was detected between the copolymer and cationic or anionic nonphospholipid liposomes based on the nonionic surfactant n-octadecyldiethylene oxide ((EO) 2 C 18 H 37 ) and cationic phospholipid liposomes. Weak interaction was detected between the copolymer and neutral phospholipid liposomes under the same conditions. The effects of the charge density of the liposomes and the lipid concentration on the copolymer/liposome interactions were examined as a function of pH and temperature. The binding of the copolymer to the liposomes is shown to be controlled primarily through hydrogen bond formation between the hydroxyl groups of the (EO) 2 C 18 H 37 and the amide groups of the NIPAM residues, through electrostatic interactions between the charged surfactants of the bilayer and the glycine residues, and, a lesser extent, by hydrophobic forces.

The visualisation of the targeting of phospholipid liposomes to bacteria

Anionic and cationic phospholipid liposomes have been prepared from dipalmitoylphosphatidylcholine (DPPC) — phosphatidylinositol (PI) and DPPC-cholesterol-stearylamine (SA) mixtures over a range of composition and targeted to biofilms of the skin-associated bacterium Staphylococcus epidermidis to establish the optimum PI and SA content for targeting. The interaction of liposomes of optimum composition with the bacteria were visualized by electron microscopy using negative staining with uranyl acetate and phosphotungstic acid. It has been demonstrated that the liposomes absorb extensively to the bacterial surface. Immunoliposomes have been prepared with a covalently linked monoclonal antibody raised to antigenic determinants on the surface of the oral bacterium Streptococcus oralis. The targeting of the immunoliposomes to this bacterium has been visualized using a second gold labelled anti-antibody. As for the anionic and cationic liposomes the immunoliposomes adsorb to the surface of the bacteria. The results add support to the concept of using liposomes for the delivery of bactericides or therapeutic agents to bacteria.

Involvement of phospholipid molecular species in controlling structural order of vertebrate brain synaptic membranes during thermal evolution.

Fluorescence anisotropy parameter of [p-(6-phenyl)-1,3,5-hexatrienyl]phenyl-propionic acid (DPH-PA) and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) embedded in synaptic plasma membranes prepared from brains of cold (5 degrees C) and warm (22 degrees C) adapted fish (Cyprinus carpio L.), rat (Rattus norvegicus) and bird (Branta canadensis), was studied. Fatty acid composition of total lipids as well as molecular species composition of diacyl phosphatidylcholines and phosphatidylethanolamines was also determined. The amount of long-chain polyunsaturated fatty acids decreased with increasing body temperature. There was a near-complete compensation of membrane structural order for environmental/body temperature over the evolutionary scale as seen by DPH-PA. Using TMA-DPH, the compensation was partial with rat and bird. Since DPH-PA and TMA-DPH differ in their charges, it is proposed, that the former reported membrane regions rich in cationic or zwitterionic (neutral) phospholipids and the latter, membrane regions rich in negatively charged phospholipids in the synaptic plasma membranes. Many different molecular species (20-25) of diacyl phosphatidylcholines and diacyl phosphatidylethanolamines were identified. The level of 16:0/22:6 phosphatidylcholine decreased while disaturated phosphatidylcholines increased with increase of environmental/body temperature from the fish through the bird. Level of 1-monoenoic, 2-polyenoic phosphatidylethanolamines also decreased with an increase in environmental/body temperature. Experiments using vesicles made of mixed synthetic phosphatidylcholine vesicles (16:0/16:0, 16:0/18:1, 16:0/22:6 in various proportions) showed that increase in disaturated phosphatidylcholine species does not explain the observed complete adjustment of membrane structural order in synaptic plasma membranes. Change in level of 1-monoenoic, 2-polyenoic phosphatidylethanolamines might be one of the factors involved in controlling the biophysical properties of the membrane according to the temperature.

Synthesis of Phosphotriester Cationic Phospholipids. Cationic Lipids 21

Synthesis of Phosphotriester Cationic Phospholipids. Cationic Lipids 21

The effect of bilayer composition on calcium ion transport facilitated by fluid shear stress

Passive calcium ion permeability across liposome bilayers is increased during exposure to fluid shear forces attainable in the mammalian vasculature. In this study, liposomes prepared from three different lipid mixtures (phosphatidylcholine alone; phosphatidylcholine and cholesterol; a mixture of anionic and cationic phospholipids plus cholesterol) are exposed to uniform shear stress in a rotational viscometer. Liposome permeability to calcium ion is estimated from continuous measurement of free intraliposome calcium ion concentration using a fluorescence technique. Calcium ion permeability in the absence of fluid force and susceptibility to shear-induced permeability modulation are positively correlated with estimated bilayer compressibility. Fluid shear forces are presumed to influence bilayer packing and modulate defect formation in proportion to bilayer compressibility. Bilayer defects produced by fluid forces may increase liposome permeability.

A new cationic liposome encapsulating genetic material. A potential delivery system for polynucleotides.

The endeavour to enhance gene therapy has led to increased research on the development of simple, efficient and safe delivery systems. This study deals with the use of an artificial cationic lipid on the encapsulation of genetic material in liposomes. The addition of a biologically degradable cationic phospholipid, dipalmitoyl-L-alpha-phosphatidylethanolamine covalently coupled to L-lysine, in a standard liposome formulation allowed us to obtain vesicles with high entrapment of various polynucleotides. Polynucleotide degradation by nucleases is markedly prevented by these liposomes. The preparations were stable in both culture medium and human plasma. This latter finding is consistent with the weak binding of plasma proteins on the liposome surface. The efficiency of this new delivery system was demonstrated in antiviral assays. Finally, these liposomes displayed a relatively low cellular toxicity. All these findings indicate that these cationic vesicles are very suitable for genetic material vehiculation.