Synthesis and characterization of PEGylated bolaamphiphiles with enhanced retention in liposomes.

Long-circulating liposomes are typically prepared with poly(ethylene glycol)- (PEG-) modified lipids, where the lipid portion is inserted in the lipid bilayers as an anchor and the hydrophilic PEG coats the surface to prevent liposome aggregation and rapid clearance in vivo. However, these steric protection effects are compromised upon systemic administration due to low retention of PEGylated lipids within liposome membranes upon dilution. Hence, a series of PEGylated bolaamphiphiles (PEG-bolas) were for the first time developed to increase retention in the lipid bilayer, presumably leading to enhanced integrity of the PEG protective layer upon dilution.

Two successive calcium-dependent transitions mediate membrane binding and oligomerization of daptomycin and the related antibiotic A54145.

Daptomycin and A54145 are homologous lipopeptide antibiotics that permeabilize the cell membranes of Gram-positive bacteria. Membrane permeabilization depends on the presence of both phosphatidylglycerol (PG) and calcium, and it involves the formation of oligomeric transmembrane pores that consist of approximately 6-8 subunits. We here show that each lipopeptide molecule binds two calcium ions in separable, successive steps.

Biscationic Tartaric Acid-Based Amphiphiles: Charge Location Impacts Antimicrobial Activity.

Cationic amphiphiles have received increasing attention as antimicrobials given their unique ability to disrupt bacteria cell membranes. While extensive research has demonstrated that amphiphiles' hydrophobic-to-charge ratio significantly modulates antibacterial activity, less work has focused on elucidating the specific impact of charge location on amphiphile bioactivity. In this study, two series of cationic amphiphiles, termed bola-like and gemini-like, were synthesized with analogous hydrophobic-to-charge ratios yet differing charge location, and their resulting antibacterial activity was assessed.

Cationic amphiphilic macromolecule (CAM)-lipid complexes for efficient siRNA gene silencing.

The accumulated evidence has shown that lipids and polymers each have distinct advantages as carriers for siRNA delivery. Composite materials comprising both lipids and polymers may present improved properties that combine the advantage of each. Cationic amphiphilic macromolecules (CAMs) containing a hydrophobic alkylated mucic acid segment and a hydrophilic poly(ethylene glycol) (PEG) tail were non-covalently complexed with two lipids, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), to serve as a siRNA delivery vehicle.

Cardiolipin prevents membrane translocation and permeabilization by daptomycin.

Daptomycin is an acidic lipopeptide antibiotic that, in the presence of calcium, forms oligomeric pores on membranes containing phosphatidylglycerol. It is clinically used against various Gram-positive bacteria such as Staphylococcus aureus and Enterococcus species. Genetic studies have indicated that an increased content of cardiolipin in the bacterial membrane may contribute to bacterial resistance against the drug.

Mutual inhibition through hybrid oligomer formation of daptomycin and the semisynthetic lipopeptide antibiotic CB-182,462.

Daptomycin is a clinically important lipopeptide antibiotic that kills Gram-positive bacteria through membrane depolarization. Its activity requires calcium and the presence of phosphatidylglycerol in the target membrane. Calcium and phosphatidylglycerol also promote the formation of daptomycin oligomers, which have been assumed but not proven to be required for the bactericidal effect.

Molecular dynamic simulation study of cholesterol and conjugated double bonds in lipid bilayers.

Conjugated linoleic acids (CLA) are found naturally in dairy products. Two isomers of CLA, that differ only in the location of cis and trans double bonds, are found to have distinct and different biological effects. The cis 9 trans 11 (C9T11) isomer is believed to have anti-carcinogenic effects, while the trans 10 cis 12 (T10C12) isomer is believed to be associated with anti-obesity effects.

Thermodynamic and physical interactions between novel polymeric surfactants and lipids: toward designing stable polymer-lipid complexes.

Surfactant amphiphilic macromolecules (AMs) were complexed with a 1:1 ratio of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), either by a coevaporation (CE) or postaddition (PA) method, to form AM-lipid complexes with enhanced drug delivery applications. By characterizing the surfactant-lipid interactions, these heterogeneous drug delivery systems can be better controlled and engineered for optimal therapeutic outcomes. In this study, the physical interactions between DOPE:DOTAP liposomes and AM surfactants were investigated.

Interaction of two oxysterols, 7-ketocholesterol and 25-hydroxycholesterol, with phosphatidylcholine and sphingomyelin in model membranes.

Oxidized analogs of cholesterol (oxysterols) are produced through both enzymatic and non-enzymatic pathways and have been shown to perturb membrane properties in vitro and in vivo. In the present study, the membrane behavior of two naturally occurring oxysterols, 25-hydroxycholesterol and 7-ketocholesterol, was examined in two model systems. The presence of an additional oxygen moiety was found to alter membrane properties compared to native cholesterol and to each other in lipid monolayers, composed of either pure sterol or sterol-glycerophospholipid and sterol-sphingomyelin binary films, as well as in mixed multilamellar vesicles.

Differential effects of conjugated linoleic acid isomers on the biophysical and biochemical properties of model membranes.

Conjugated linoleic acids (CLA) are known to exert several isomer-specific biological effects, but their mechanisms of action are unclear. In order to determine whether the physicochemical effects of CLA on membranes play a role in their isomer-specific effects, we synthesized phosphatidylcholines (PCs) with 16:0 at sn-1 position and one of four CLA isomers (trans 10 cis 12 (A), trans 9 trans 11 (B), cis 9 trans 11 (C), and cis 9 cis 11 (D)) at sn-2, and determined their biophysical properties in monolayers and bilayers. The surface areas of the PCs with the two natural CLA (A and C) were similar at all pressures, but they differed significantly in the presence of cholesterol, with PC-A condensing more than PC-C.

First synthesis of free cholesterol-BODIPY conjugates.

Analogues of cholesterol (compounds 1 and 2) and coprostanol (compound 3) containing the BODIPY fluorophore in the aliphatic tail of the free sterol have been synthesized starting with bisnorcholenic acid, cholenic acid 3beta-acetate, and lithocholic acid, respectively. An ester linkage joining the fluorophore to the sterol nucleus interfered with the ability of the fluorescent sterol to pack with phospholipids in monolayers. However, an analogue in which the linker was devoid of polar atoms exhibited a substantially similar physical behavior to cholesterol in model membranes with respect to localization in raft domains.

Lysophosphatidic acid and lipopolysaccharide bind to the PIP2-binding domain of gelsolin.

The binding of the gelsolin P2 peptide (residues 150-169) with lysophosphatidic acid (LPA) and lipopolysaccharide (LPS) was investigated by isothermal titration calorimetry. P2 binds to LPS with higher affinity than to LPA. For the interaction of 1-oleoyl-LPA with P2 in the absence of salt, K(d) and deltaH degrees were 920 nM and -2.

The critical micelle concentrations of lysophosphatidic acid and sphingosylphosphorylcholine.

The critical micelle concentrations (CMC) of lysophosphatidic acid (LPA) and sphingosylphosphorylcholine (SPC) were measured by isothermal titration calorimetry. The CMC of LPA decreases with salt concentration and acyl chain length. In water at 25 degrees C, the CMC values of 1-acyl-2-lyso-sn-glycero-3-phosphatidic acid are 1.

Behavior of a photoactivatable analog of cholesterol, 6-photocholesterol, in model membranes.

6-Photocholesterol, a new photoactivatable analog of cholesterol in which a diazirine functionality replaces the 5,6-double bond in the steroid nucleus, was used recently to identify cholesterol-binding proteins in neuroendocrine cells [Thiele, C., Hannah, M.J.