Typical methods used for encapsulating antisense oligodeoxynucleotides (ODN) and plasmid DNA in lipid vesicles result in very low encapsulation efficiencies or employ cationic lipids that exhibit unfavorable pharmacokinetic and toxicity characteristics when administered intravenously. In this study, we describe and characterize a novel formulation process that utilizes an ionizable aminolipid (1,2-dioleoyl-3-dimethylammonium propane, DODAP) and an ethanol-containing buffer system for encapsulating large quantities (0.15--0.25 g ODN/g lipid) of polyanionic ODN in lipid vesicles. This process requires the presence of up to 40% ethanol (v/v) and initial formulation at acidic pH values where the DODAP is positively charged. In addition, the presence of a poly(ethylene glycol)-lipid was required during the formulation process to prevent aggregation. The 'stabilized antisense-lipid particles' (SALP) formed are stable on adjustment of the external pH to neutral pH values and the formulation process allows encapsulation efficiencies of up to 70%. ODN encapsulation was confirmed by nuclease protection assays and (31)P NMR measurements. Cryo-electron microscopy indicated that the final particles consisted of a mixed population of unilamellar and small multilamellar vesicles (80--140 nm diameter), the relative proportion of which was dependent on the initial ODN to lipid ratio. Finally, SALP exhibited significantly enhanced circulation lifetimes in mice relative to free antisense ODN, cationic lipid/ODN complexes and SALP prepared with quaternary aminolipids. Given the small particle sizes and improved encapsulation efficiency, ODN to lipid ratios, and circulation times of this formulation compared to others, we believe SALP represent a viable candidate for systemic applications involving nucleic acid therapeutics.

A detergent dialysis procedure is described which allows of up to 70% and permits inclusion of 'fusigenic' lipids such encapsulation of plasmid DNA within a lipid envelope, as dioleoylphosphatidylethanolamine (DOPE). The in vitro where the resulting particle is stabilized in aqueous media transfection capabilities of SPLP are demonstrated to be by the presence of a poly(ethyleneglycol) (PEG) coating. strongly dependent on the length of the acyl chain conThese 'stabilized plasmid-lipid particles' (SPLP) exhibit an tained in the ceramide group used to anchor the PEG polyaverage size of 70 nm in diameter, contain one plasmid mer to the surface of the SPLP. Shorter acyl chain lengths per particle and fully protect the encapsulated plasmid from result in a PEG coating which can dissociate from the digestion by serum nucleases and E. coli DNase I. Encap-SPLP surface, transforming the SPLP from a stable parsulation is a sensitive function of cationic lipid content, with ticle to a transfection-competent entity. It is suggested that maximum entrapment observed at dioleoyldimethylam-SPLP may have utility as systemic gene delivery systems monium chloride (DODAC) contents of 5 to 10 mol%. The for gene therapy protocols. formulation process results in plasmid-trapping efficiencies

The pH-indicator dye fluorescein was covalently bound to the surface of the purple membrane at position 72 on the extracellular side of bacteriorhopsin and at positions 101, 105, 160, or 231 on the cytoplasmic side by reacting bromomethylfluorescein with the sulfhydryl groups of cysteines introduced by site-directed mutagenesis. At position 72, on the extracellular surface, the light-induced proton release was detected 71 ± 4 p.s after the flash (conditions: pH 7.3, 22°C, and 150 mM KCI). On the cytoplasmic side with the dye at positions 101, 105, and 160, the corresponding values were 77, 76, and 74 ± 5 ,us, respectively. Under the same conditions, the proton release time in the bulk medium as detected by pyranine was around 880 p,s-i.e., slower by a factor of more than 10. The fact that the proton that is released on the extracellular side is detected much faster on the cytoplasmic surface than in the aqueous bulk phase demonstrates that it is retained on the surface and migrates along the purple membrane to the other side. These findings have interesting implications for bioenergetics and support models of local proton coupling. From the small difference between the proton detection times by labels on opposite sides of the membrane, we estimate that at 22°C the proton surface diffusion constant is greater than 3 x 10-5 cm2/s. At 5°C, the proton release detection time at position 72 equals the faster of the two main rise times of the M intermediate (deprotonation of the Schiff base). At higher temperatures this correlation is gradually lost, but the curved Arrhenius plot for the proton release time is tangential to the linear Arrhenius plot for the rise of M at low temperatures. These observations are compatible with kinetic coupling between Schiff base deprotonation and proton release.Models of localized energy coupling by proton gradients require a transient confinement of protons near the membrane, allowing lateral proton transport along the surface between proton sources and sinks (1). Thus, protons must be retained at the surface long enough for significant lateral diffusion to occur. This requires that the rate of proton transfer into the bulk is slow compared with the rate of transport along the surface (2, 3). To determine these rates, dynamic methods of sufficient time resolution are required (4). The purple membrane of Halobacterium salinarium offers an ideal model system to study these questions. The purple membrane patches of about 0.5-,gm diameter contain approximately 104 lightdriven proton pumps. Using a nanosecond light flash these proton pumps are simultaneously activated, and protons are released on the extracellular side of the membrane about 50-100 ,ts after excitation. Thus, a transient jump in proton concentration is generated along the extracellular side of the membrane, which dissipates by diffusion along the membrane and by transfer into the bulk phase. Proton arrival times at different sites on either side of the membrane can be measured spectroscopically with surface-bound pH...

On the basis of data obtained by spectroscopic analysis and chromatography of retinal extracts, a consensus has been adopted that dark-adapted purple membrane (pm) contains 13-cis- and all-trans-retinal in equal amounts, whereas the light-adapted membrane contains all-trans-retinal only. We have developed an improved extraction technique which extracts up to 70% of the retinal in pm within 4 min. In the extracts from dark-adapted pm at room temperature, we consistently find 66-67% 13-cis-retinal and 33-34% all-trans-retinal, and more than 98.5% all-trans isomer in light-adapted samples. The spectrum obtained by reconstitution of bacterioopsin with 13-cis-retinal at 2 degrees C (to minimize isomerization) shows an absorbance maximum at 554 nm and agrees well with the spectrum for the 13-cis component calculated from the dark-adapted and light-adapted bR spectra with our extraction data. The ratio of 13-cis:all-trans isomer in dark-adapted pm is 2:1 and nearly constant between 0 and 38 degrees C but begins to decrease distinctly above 40 degrees C, and more rapidly near 70 degrees C, reaching 0.75 at 90 degrees C. The van't Hoff plot of the isomer ratio shows a nonlinear temperature dependence above 40 degrees C, indicating a more complex system than a simple thermal 13-cis/all-trans isomer equilibrium. We attribute the broadening, absorbance decrease, and blut shift of the visible absorption band with increasing temperature to the appearance of at least one and possibly two or three new chromophores which contain, mainly or exclusively, the all-trans isomer.(ABSTRACT TRUNCATED AT 250 WORDS)

This study describes the effect of ethanol and the presence of poly(ethylene) glycol (PEG) lipids on the interaction of nucleotide-based polyelectrolytes with cationic liposomes. It is shown that preformed large unilamellar vesicles (LUVs) containing a cationic lipid and a PEG coating can be induced to entrap polynucleotides such as antisense oligonucleotides and plasmid DNA in the presence of ethanol. The interaction of the cationic liposomes with the polynucleotides leads to the formation of multilamellar liposomes ranging in size from 70 to 120 nm, only slightly bigger than the parent LUVs from which they originated. The degree of lamellarity as well as the size and polydispersity of the liposomes formed increases with increasing polynucleotide-to-lipid ratio. A direct correlation between the entrapment efficiency and the membrane-destabilizing effect of ethanol was observed. Although the morphology of the liposomes is still preserved at the ethanol concentrations used for entrapment (25-40%, v/v), entrapped low-molecular-weight solutes leak rapidly. In addition, lipids can flip-flop across the membrane and exchange rapidly between liposomes. Furthermore, there are indications that the interaction of the polynucleotides with the cationic liposomes in ethanol leads to formation of polynucleotide-cationic lipid domains, which act as adhesion points between liposomes. It is suggested that the spreading of this contact area leads to expulsion of PEG-ceramide and triggers processes that result in the formation of multilamellar systems with internalized polynucleotides. The high entrapment efficiencies achieved at high polyelectrolyte-to-lipid ratios and the small size and neutral character of these novel liposomal systems are of utility for liposomal delivery of macromolecular drugs.