Label-Free Characterization of Peptide–Lipid Interactions Using Immobilized Lipodisks

Lipodisks, planar lipid bilayer structures stabilized by PEG-ylated lipids, were in the present study covalently bound and immobilized onto sensors for quartz crystal microbalance with dissipation monitoring (QCM-D) studies. It is shown that the modified sensors can be used to characterize the interaction of lipodisks with α-helical amphiphilic peptides with an accuracy similar to that obtained with well established fluorimetric approximations. The method presented has the great advantage that it can be used with peptides in their native form even if no fluorescent residues are present. The potential of the method is illustrated by determining the parameters describing the association of melittin, mastoparan X, and mastoparan with immobilized lipodisks. Both thermodynamic and kinetic analyses are possible. The presented method constitutes a useful tool for fundamental studies of peptide–membrane interactions and can also be applied to optimize the design of lipodisks, for example, for sustained release of antimicrobial peptides in therapeutic applications

Self-Assembly in Mixtures of an Anionic and a Cationic Surfactant: A Comparison between Small-Angle Neutron Scattering and Cryo-Transmission Electron Microscopy

The self-assembly in SOS-rich mixtures of the anionic surfactant sodium octyl sulfate (SOS) and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) has been investigated with the complementary techniques small-angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM). Both techniques confirm the simultaneous presence of open and closed bilayer structures in highly diluted samples as well as the existence of small globular and large elongated micelles at higher concentrations. However, the two techniques sometimes differ with respect to which type of aggregates is present in a particular sample. In particular, globular or wormlike micelles are sometimes observed with cryo-TEM in the vicinity of the micelle-to-bilayer transition, although only bilayers are present according to SANS and the samples appear bluish to the eye. A similar discrepancy has previously been reported but could not be satisfactorily rationalized. On the basis of our comparison between in situ (SANS) and ex situ (cryo-TEM) experimental techniques, we suggest that this discrepancy appears mainly as a result of the non-negligible amount of surfactant adsorbed at interfaces of the thin sample film created during the cryo-TEM specimen preparation. Moreover, from our detailed SANS data analysis, we are able to observe the unusually high amount of free surfactant monomers present in SOS-rich mixtures of SOS and CTAB, and the experimental results give excellent agreement with model calculations based on the Poisson–Boltzmann mean field theory. Our careful comparison between model calculations and experiments has enabled us to rationalize the dramatic microstructural transformations frequently observed upon simply diluting mixtures of an anionic and a cationic surfactant

Spontaneous Transformations between Surfactant Bilayers of Different Topologies Observed in Mixtures of Sodium Octyl Sulfate and Hexadecyltrimethylammonium Bromide

The influence of adding salt on the self-assembly in sodium octyl sulfate (SOS)-rich mixtures of the anionic surfactant SOS and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) have been investigated with the two complementary techniques, small-angle neutron scattering (SANS) and cryo-transmission electron microscopy. We are able to conclude that addition of a substantial amount of inert salt, NaBr, mainly has three effects on the structural behaviors: (i) the micelles become much larger at the transition from micelles to bilayers, (ii) the fraction of bilayer disks increases at the expense of vesicles, and (iii) bilayer aggregates perforated with holes are formed in the most diluted samples. A novel form factor valid for perforated bilayer vesicles and disks is introduced for the first time and, as a result, we are able to directly observe the presence of perforated bilayers by means of fitting SANS data with an appropriate model. Moreover, we are able to conclude that the morphology of bilayer aggregates changes according to the following sequence of different bilayer topologies, vesicles → disks → perforated bilayers, as the electrolyte concentration is increased and surfactant mole fraction in the bilayer aggregates approaches equimolarity. We are able to rationalize this sequence of transitions as a result of a monotonous increase of the bilayer saddle-splay constant (<i>k̅</i>_<i>c</i>^bi) with decreasing influence from electrostatics, in agreement with theoretical predictions as deduced from the Poisson–Boltzmann theory

The anticancer activity of diethyldithiocarbmamate (DDC) is dependent on copper.

<p><b>(A)</b> Disulfiram is metabolized to diethyldithiocarbamate (DDC) and DDC complexes with Copper (Cu) (II). <b>(B)</b> Cytotoxicity curves for DSF (●) and DSF + CuSO₄ (■) were obtained with the IN CELL Analyzer using U87 glioblastoma cells where cell viability was assessed based on loss of plasma membrane integrity 72 hours following treatment; i.e. total cell count and dead cell count were determined using Hoechst 33342 and ethidium homodimer staining, respectively. <b>(C)</b> Cytotoxicity curves for DDC (●) and DDC + CuSO₄ (■); where cytotoxicity was measured as described above. <b>(D)</b> DDC and Cu(DDC)₂ IC₅₀ for U251, MDA-231-BR, and A549 cancer cell lines as well as HBEcP a normal cell line; averages (±SEM) are reported from three separate experiments each done in triplicate. <b>(E)</b> Photograph of DDC, CuSO₄ and Cu(DDC)₂ solutions in water.</p

Preliminary tolerability and plasma elimination profiles for liposomal formulations of Cu(DDC)₂, Cu(CQ)₂, CuQu and CuCX-5461 after intravenous injection into CD-1 mice.

<p>Mice were injected with a single dose of 15 mg/kg Cu(DDC)₂ (-●-), 30mg/kg Cu(CQ)₂ (-■-), 70mg/kg CuQu (-▲-) and 50 mg/kg Cu-CX-5461 (-▼-). <b>(A)</b> Changes in body weight following administration of the indicated liposomal formulation where body weights were measured over 14 days after injection (n = 3). <b>(B)</b> Preliminary plasma elimination profiles of the indicated liposomal formulations where the copper-complexed compound was measured at 1, 4, 8 and 24 hrs after administration (n = 4); concentrations were measured using HPLC or AAS as described in the Methods.</p

Diethyldithiocarbamate (DDC) loading into DSPC/Chol (55:45) liposomes prepared with encapsulated 300 mM CuSO₄.

<p><b>(A)</b> Photograph of solutions consisting of DDC (5mg/mL) and added to CuSO₄-containing DSPC/Chol (55:45) liposomes (20 mM liposomal lipid) over a 1 hour at 25°C. <b>(B)</b> Formation of Cu(DDC)₂ inside DSPC/Chol liposomes (20 mM) as a function of time over 1 hour at 4(●), 25(■) and 40(▲)°C following addition of DDC at a final DDC concentration of (5 mM); Cu(DDC)₂ was measured using a UV-Vis spectrophotometer and lipid was measured using scintillation counting. <b>(C)</b> Cu(DDC)₂ formation inside DSPC/Chol (55:45) liposomes over time where the external pH was 7.4 (▲) and 3.5 (▼). <b>(D)</b> Measured Cu(DDC)₂ as a function of increasing DDC added, represented as the theoretical Cu(DDC)₂ to total liposomal lipid ratio; where the lipid concentration was fixed at 20 mM and final DDC concentration was varied. <b>(E)</b> Cryo-electron microscopy photomicrograph of CuSO₄- containing DSPC/Chol (55:45) liposomes and the same liposomes after formation of encapsulated Cu(DDC)₂. <b>(F)</b> Size of the CuSO₄- containing liposomes and liposomes with encapsulated Cu(DDC)₂ as determined by quasi-electric light scattering and cryo-electron microscopy; data points are given as mean ± SD.</p

Characterization of copper-complex loading method.

<p><b>(A)</b> Measured (AAS) copper to liposomal lipid ratio (black bars) compared to measured Cu(DDC)₂ (UV-Vis spectrophotometer) to liposomal lipid ratio (grey bars) after DDC was added to CuSO₄-containing DSPC/Chol liposomes prepared with different amounts of DSPE-PEG₂₀₀₀ (ranging from 0 to 5 mole%). <b>(B)</b> Formation of Cu(DDC)₂ inside CuSO₄-containing DSPC/Chol liposomes as a function of the CuSO₄ concentration used to prepare the liposomes (ranging from 0 to 300 mM); where the measured copper (AAS) to liposomal lipid ratio (black bar) is compared to the measured Cu(DDC)₂ (UV-Vis spectrophotometer) to liposomal lipid ratio (grey bar). <b>(C)</b> Linear regression analysis comparing measured (AAS) copper concentration (assuming encapsulated copper was free in solution) to measured Cu(DDC)₂ (UV-Vis spectrophotometer) concentration (assuming encapsulated Cu(DDC)₂ was free in solution); R² = 0.9754; each data point represents a mean ± SEM determined from at least three separate experiments done in duplicate.</p

Characterization of Oil-Free and Oil-Loaded Liquid-Crystalline Particles Stabilized by Negatively Charged Stabilizer Citrem

The present study was designed to evaluate the effect of the negatively charged food-grade emulsifier citrem on the internal nanostructures of oil-free and oil-loaded aqueous dispersions of phytantriol (PHYT) and glyceryl monooleate (GMO). To our knowledge, this is the first report in the literature on the utilization of this charged stabilizing agent in the formation of aqueous dispersions consisting of well-ordered interiors (either inverted-type hexagonal (H₂) phases or inverted-type microemulsion systems). Synchrotron small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM) were used to characterize the dispersed and the corresponding nondispersed phases of inverted-type nonlamellar liquid-crystalline phases and microemulsions. The results suggest a transition between different internal nanostructures of the aqueous dispersions after the addition of the stabilizer. In addition to the main function of citrem as a stabilizer that adheres to the surface of the dispersed particles, it has a significant impact on the internal nanostructures, which is governed by the following factors: (1) its penetration between the hydrophobic tails of the lipid molecules and (2) its degree of incorporation into the lipid–water interfacial area. In the presence of citrem, the formation of aqueous dispersions with functionalized hydrophilic domains by the enlargement of the hydrophilic nanochannels of the internal H₂ phase in hexosomes and the hydrophilic core of the L₂ phase in emulsified microemulsions (EMEs) could be particularly attractive for solubilizing and controlling the release of positively charged drugs

A T-Shaped Amphiphilic Molecule Forms Closed Vesicles in Water and Bicelles in Mixtures with a Membrane Lipid

The T-shaped amphiphilic molecule A6/6 forms a columnar hexagonal liquid-crystalline phase between the crystalline and the isotropic liquid when studied in bulk (Chen et al., 2005). Because of the hydrophilic and flexible oligo­(oxyethylene) side chain terminated by a 1-acylamino-1-deoxy-d-sorbitol moiety attached to a rigid terphenyl core with terminal hexyloxy alkyl chains, it was expected that also formation of lyotropic phases could be possible. We therefore studied the behavior of A6/6 in water and also in mixtures with bilayer-forming phospholipids, such as dipalmitoyl-phosphatidylcholine (DPPC), using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), cryo-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and solid-state nuclear magnetic resonance (ssNMR). DSC showed for the pure A6/6 suspended in water a phase transition at ca. 23 °C. TEM and cryo-TEM showed vesicular as well as layered structures for pure A6/6 in water below and above this phase transition. By atomic force microscopy (AFM), the thickness of the layer was found to be 5–6 nm. This leads to a model for a bilayer formed by A6/6 with the laterally attached polar side chains shielding the hydrophobic layer built up by the terphenyl core with the terminal alkyl chains of the molecules. For DPPC:A6/6 mixtures (10:1), the DSC curves indicated a stabilization of the lamellar gel phase of DPPC. Negative staining TEM and cryo-TEM images showed planar bilayers with hexagonal morphology and diameters between 50 and 200 nm. The hydrodynamic radius of these aggregates in water, investigated by dynamic light scattering (DLS) as a function of time and temperature, did not change indicating a very stable aggregate structure. The findings lead to the proposition of a new bicellar structure formed by A6/6 with DPPC. In this model, the bilayer edges are covered by the T-shaped amphiphilic molecules preventing very effectively the aggregation to larger structures