dioleoyl-phosphatidylethanolamine and fluorexon

Novel polymers containing quaternary functional groups, with and without (control copolymer) PEG side chains, were synthesized and characterized for their ability to lyse the phospholipid membranes of liposome vesicles. Calcein loaded unilamellar vesicles composed of 1,2-dioleoyl- sn-glycero-3-phosphatidylcholine (DOPC) were used to mimic red-blood cell membranes, and a 80:20 (mol/mol) mixture of 1,2-dioleoyl- sn-glycero-3-phosphatidyl ethanolamine (DOPE) and 1,2-dioleoyl- sn- glycero-3-[phospho- rac-(1-glycerol)] (DOPG) was used to mimic the outer cell-membrane of the gram-negative bacteria, E. coli. For DOPE/DOPG = 80:20 (mol/mol) liposome vesicles, the PEG bottle brush copolymer caused leakage of the encapsulated Calcein dye, whereas the control copolymer did not cause any leakage. Both the bottle brush copolymer and the copolymer without PEG side chains had no effect on the zwitterionic DOPC liposome vesicles indicating that the RBC membrane composition is not disrupted by either copolymer architecture. The PEG bottle brush copolymer did not affect the colloidal size of the DOPE/DOPG = 80:20 (mol/mol) liposome vesicles, but on the addition of Triton-X 100, the vesicles disappeared. This provided evidence that the dye leakage was caused by compromising the integrity of the vesicle membrane by the bottle brush polymer architecture. Such partial disruption was preceded by the entropic templating of lipid membranes by the PEG side chains of the bottle brush copolymer. By careful comparison with non-PEGylated cationic polymers, Quart, the importance of PEG side chains in the membrane disrupting activity of the PEGylated cationic polymer, QPEG, was demonstrated. This finding itself is interesting and can contribute to the expansion of the design of membrane disrupting materials.

Topics: Coloring Agents; Fluoresceins; Phosphatidylcholines; Phosphatidylethanolamines; Phosphatidylglycerols; Polyamines; Polyethylene Glycols; Unilamellar Liposomes

The effect of membrane composition on calcein release from dioleoylphosphatidylethanolamine (DOPE)-based liposomes on exposure to low doses of 1.13 MHz focused ultrasound (US) was investigated by multivariate analysis, with the goal of designing liposomes for US-mediated drug delivery. Regression analysis revealed a strong correlation between sonosensitivity and the non-bilayer forming lipids DOPE and pegylated distearoylphosphatidylethanolamine (DSPE-PEG 2000), with DOPE having the strongest impact. Unlike most of the previously studied distearoylphosphatidylethanolamine (DSPE)-based liposomes, all the current DOPE-based liposome formulations were found stable in 20% serum in terms of drug retention.

Topics: Antineoplastic Agents; Drug Stability; Fluoresceins; Liposomes; Models, Chemical; Multivariate Analysis; Phosphatidylethanolamines; Polyethylene Glycols; Regression Analysis; Ultrasonics

An exciting new direction in responsive liposome research is endogenous triggering of liposomal payload release by overexpressed enzyme activity in affected tissues and offers the unique possibility of active and site-specific release. Bringing to fruition the fully expected capabilities of this new class of triggered liposomal delivery system requires a collection of liposome systems that respond to different upregulated enzymes; however, a relatively small number currently exist. Here we show that stable, approximately 100 nm diameter liposomes can be made from previously unreported quinone-dioleoyl phosphatidylethanolamine (Q-DOPE) lipids, and complete payload release (quenched fluorescent dye) from Q-DOPE liposomes occurs upon their redox activation when the quinone headgroup possesses specific substituents. The key component of the triggerable, contents-releasing Q-DOPE liposomes is a "trimethyl-locked" quinone redox switch attached to the N-terminus of DOPE lipids that undergoes a cleavage event upon two-electron reduction. Payload release by aggregation and leakage of "uncapped" Q-DOPE liposomes is supported by results from liposomes wherein deliberate alteration of the "trimethyl-locked" switch completely deactivates the redox-destructible phenomena (liposome opening). We expect that Q-DOPE liposomes and their variants will be important in treatment of diseases with associated tissues that overexpress quinone reductases, such as cancers and inflammatory diseases, because the quinone redox switch is a known substrate for this group of reductases.

Topics: Drug Carriers; Fluoresceins; Fluorescent Dyes; Liposomes; Oxidation-Reduction; Phosphatidylethanolamines; Quinones

The enzymatically degradable poly(amino acid)-lipid conjugate poly(hydroxyethyl l-glutamine)-N-succinyl-dioctadecylamine (PHEG-DODASuc) has been shown to effectively prolong liposome circulation times. In this paper, we investigated whether PHEG-DODASuc can stabilize liposomes composed of the fusogenic, non-bilayer-forming lipid dioleoyl phosphatidylethanolamine (DOPE). Moreover, we evaluated the release of an entrapped compound after enzyme-induced shedding of the PHEG-coating, interbilayer contact and membrane destabilizing phase changes. Contents release was monitored using the fluorescent model compound calcein. Liposome destabilization and lipid mixing was studied by dynamic light scattering (DLS), fluorescence resonance energy transfer (FRET) and cryogenic-temperature transmission electron microscopy (cryo-TEM). It was shown that PHEG-DODASuc is able to stabilize DOPE-based liposomes and that contents release can be triggered by shedding of the PHEG-coating.

Topics: Amino Acids; Cryoelectron Microscopy; Drug Carriers; Drug Compounding; Enzymes; Fluoresceins; Fluorescence Resonance Energy Transfer; Indicators and Reagents; Light; Liposomes; Microscopy, Electron, Transmission; Ninhydrin; Phosphatidylethanolamines; Scattering, Radiation; Solubility

Four structurally related, acid-labile polyethylene glycol (PEG) conjugated vinyl ether lipids have been synthesized and used at low molar ratios to stabilize the nonlamellar, highly fusogenic lipid, dioleoylphosphatidyl ethanolamine, as unilamellar liposomes. Acid-catalyzed hydrolysis of the vinyl ether bond destabilized these liposomes by removal of the sterically-stabilizing PEG layer, thereby promoting contents release on the hours timescale at pH<5. Structure-property correlations of these compounds suggested that single vinyl ether linkages between the PEG headgroup and the lipid backbone produce faster leakage rates. These studies also suggested that the presence of a slight negative charge at the membrane surface can accelerate the acid-catalyzed leakage process.

Topics: Acids; Fluoresceins; Hydrogen-Ion Concentration; Indicators and Reagents; Lipids; Liposomes; Magnetic Resonance Spectroscopy; Phosphatidylethanolamines; Polyethylene Glycols; Vinyl Compounds

To obtain temperature-sensitive liposomes which release their contents around the physiological temperature, we designed dioleoylphosphatidylethanolamine liposomes modified with copolymers of N-isopropylacrylamide and acryloylpyrrolidine. Copolymers of acryloylpyrrolidine and N-isopropylacrylamide, which exhibit a lower critical solution temperature around the physiological temperature, were prepared by free radical copolymerization using azobis(isobutyronitrile) as the initiator. The copolymers with anchors to the liposome membrane were obtained by using N, N-didodecylacrylamide as an additional comonomer. The copolymer having the anchor group at the terminal of the polymer chain was also synthesized by copolymerization of these monomers in the presence of 2-aminoethanethiol and subsequent conjugation of N, N-didodecyl succinamic acid to the terminal amino group of the copolymer. Calcein-loaded dioleoylphosphatidylethanolamine liposomes modified with these copolymers were prepared and release of the contents from these liposomes was investigated. It was found that the release from these copolymer-modified liposomes was promoted around and above the lower critical temperature of the copolymer. Also, the liposomes modified with the terminal anchor-type copolymer released the contents more drastically responding to a small temperature change than the liposomes modified with random copolymers containing N,N-didodecylacrylamide units as the anchor.

Topics: Acrylamides; Body Temperature; Fluoresceins; Fluorescent Dyes; Liposomes; Permeability; Phosphatidylethanolamines; Polymers; Pyrrolidines; Solutions; Surface Properties; Temperature

To obtain cationic liposomes of which affinity to negatively charged membranes can be controlled by temperature, cationic liposomes consisting of 3beta-[N-(N', N'-dimethylaminoethane)carbamoyl]cholesterol and dioleoylphosphatidylethanolamine were modified with poly(N-acryloylpyrrolidine), which is a thermosensitive polymer exhibiting a lower critical solution temperature (LCST) at ca. 52 degrees C. The unmodified cationic liposomes did not change its zeta potential between 20-60 degrees C. The polymer-modified cationic liposomes revealed much lower zeta potential values below the LCST of the polymer than the unmodified cationic liposomes. However, their zeta potential increased significantly above this temperature. The unmodified cationic liposomes formed aggregates and fused intensively with anionic liposomes consisting of egg yolk phosphatidylcholine and phosphatidic acid in the region of 20-60 degrees C, due to the electrostatic interaction. In contrast, aggregation and fusion of the polymer-modified cationic liposomes with the anionic liposomes were strongly suppressed below the LCST. However, these interactions were enhanced remarkably above the LCST. In addition, the polymer-modified cationic liposomes did not cause leakage of calcein from the anionic liposomes below the LCST, but promoted the leakage above this temperature as the unmodified cationic liposomes did. Temperature-induced conformational change of the polymer chains from a hydrated coil to a dehydrated globule might affect the affinity of the polymer-modified cationic liposomes to the anionic liposomes.

Topics: Anions; Cations; Cholesterol; Drug Carriers; Fluoresceins; Liposomes; Microscopy, Electron; Molecular Structure; Phosphatidic Acids; Phosphatidylcholines; Phosphatidylethanolamines; Phospholipids; Polymers; Static Electricity; Temperature

As a novel temperature-sensitive liposome, dioleoylphosphatidylethanolamine vesicles bearing poly(N-isopropylacrylamide), which shows a lower critical solution temperature (LCST) near 32 degrees C, were designed. Poly(N-isopropylacrylamide) having long alkyl chains which are anchors to the lipid membranes was prepared by radical copolymerization of N-isopropylacrylamide and octadecyl acrylate using azobisisobutyronitrile as the initiator. The copolymer obtained revealed the LCST at about 30 degrees C in an aqueous solution. Dioleoylphosphatidylethanolamine vesicles coated with the copolymer was prepared and release property of the copolymer-coated vesicles was investigated. While release of calcein encapsulated in the copolymer-coated vesicles was limited below 30 degrees C, the release was drastically enhanced between 30 and 35 degrees C. Complete release from the vesicles was achieved within several seconds at 40 degrees C. This temperature-controlled release property of the vesicles can be attributable to stabilization and destabilization of the vesicle membranes induced by the copolymer fixed on the vesicles below and above the LCST, respectively. Moreover, the fluorometric measurement using dioleoyl-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)phosphatidylethan ola mine suggested that the extensive release of calcein observed above the LCST is resulted from the bilayer to HII phase transition of the vesicle membranes. Since LCST of the copolymer is controllable, these vesicles might have potential usefulness as a drug delivery system with high temperature-sensitivity.

Topics: Acrylic Resins; Calorimetry; Drug Carriers; Fluoresceins; Fluorescent Dyes; Liposomes; Nitriles; Phosphatidylcholines; Phosphatidylethanolamines; Spectrometry, Fluorescence; Temperature; Thermodynamics