The validity of the Smoluchowski equation in electrophoretic studies of lipid membranes

Probing nanoliposomes using single particle analytical techniques: effect of excipients, solvents, phase transition and zeta potential

There has been a steady increase in the interest towards employing nanoliposomes as colloidal drug delivery systems, particularly in the last few years. Their biocompatibility nature along with the possibility of encapsulation of lipid-soluble, water-soluble and amphipathic molecules and compounds are among the advantages of employing these lipidic nanocarriers. A challenge in the successful formulation of nanoliposomal systems is to control the critical physicochemical properties, which impact their in vivo performance, and validating analytical techniques that can adequately characterize these nanostructures. Of particular interest are the chemical composition of nanoliposomes, their phase transition temperature, state of the encapsulated material, encapsulation efficiency, particle size distribution, morphology, internal structure, lamellarity, surface charge, and drug release pattern. These attributes are highly important in revealing the supramolecular arrangement of nanoliposomes and incorporated drugs and ensuring the stability of the formulation as well as consistent drug delivery to target tissues. In this article, we present characterization of nanoliposomal formulations as an example to illustrate identification of key in vitro characteristics of a typical nanotherapeutic agent. Corresponding analytical techniques are discussed within the context of nanoliposome assessment, single particle analysis and ensuring uniform manufacture of therapeutic formulations with batch-to-batch consistency.

A novel combinational approach of microstimulation and bioluminescence imaging to study the mechanisms of action of cerebral electrical stimulation in mice

Deep brain stimulation (DBS) is used to treat a number of neurological conditions and is currently being tested to intervene in neuropsychiatric conditions. However, a better understanding of how it works would ensure that side effects could be minimized and benefits optimized. We have thus developed a unique device to perform brain stimulation (BS) in mice and to address fundamental issues related to this methodology in the pre-clinical setting. This new microstimulator prototype was specifically designed to allow simultaneous live bioluminescence imaging of the mouse brain, allowing real time assessment of the impact of stimulation on cerebral tissue. We validated the authenticity of this tool in vivo by analysing the expression of toll-like receptor 2 (TLR2), corresponding to the microglial response, in the stimulated brain regions of TLR2-fluc-GFP transgenic mice, which we further corroborated with post-mortem analyses in these animals as well as in human brains of patients who underwent DBS to treat their Parkinson's disease. In the present study, we report on the development of the first BS device that allows for simultaneous live in vivo imaging in mice. This tool opens up a whole new range of possibilities that allow a better understanding of BS and how to optimize its effects through its use in murine models of disease.

Nanostructure of complexes between cationic lipids and an oppositely charged polyelectrolyte

The morphology of aqueous solutions of polyelectrolytes and oppositely charged lipids is the subject of extensive colloid science research, because of their application in industry and medicine, the latter especially for gene therapy. In this work, we show that complexes of two different cationic lipids with the polyelectrolyte sodium poly(acrylic acid), PAA, share similar morphology with the complexes of those lipids with nucleic acids, implying a broader and universal packing phenomenon. We characterized by direct-imaging cryogenic-temperature transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and zeta (ζ)-potential two cationic lipids, 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and bis(11-ferrocenylundecyl) dimethylammonium bromide (BFDMA), which are used in gene transfection, at equivalent lipid/polyelectrolyte charge ratio. Our results revealed that, for both types of complexes, onion-like multilamellar nanostructures formed, which exhibited similar morphology as in complexes of DNA or oligonucleotides (lipoplexes), based on the same lipids. Our findings suggest that the onion-like packing may be energetically favorable for a wide range of polyelectrolyte-liposome systems, from oligonucleotides and DNA to PAA.

Development and in vitro evaluation of Letrozole loaded biodegradable nanoparticles for breast cancer therapy

The objectives of our study were to prepare and evaluate a biodegradable nanoparticulate system of Letrozole (LTZ) intended for breast cancer therapy. LTZ loaded poly(lactide-co-glycolide) nanoparticles (LTZ-PLGA-NPs) were prepared by emulsion-solvent evaporation method using methylene chloride and polyvinyl alcohol. Percentage of drug (with respect to polymer) was selected as formulation variable. LTZ-PLGA-NPs were characterized by particle size, zeta potential, infrared spectra, drug entrapment efficiency and in vitro release. Sonication was done with an ultrasound pulse sonicator at 70 W, 30 kHz for 90 sec to produce stable NPs of mean size range from 64 nm to 255 nm with high entrapment efficiency (68% to 82%). Percentage of drug significantly influenced particle size, entrapment efficiency and release (p <0.05). The system sustained release of LTZ significantly and further investigation could exhibit its potential usefulness in breast cancer therapy.

Partitioning of propranolol in the phospholipid bilayer coat of anionic magnetoliposomes

This work deals with the partitioning of the cationic amphiphilic drug, propranolol, in the coating of so-called magnetoliposomes (MLs), which consist of nanometre-sized, magnetizable iron oxide cores covered with a phospholipid bilayer. MLs of two types were used: either the ML coat consisted entirely of anionic dimyristoylphosphatidylglycerol, or it was mixed with zwitterionic dimyristoylphosphatidylcholine in a 5/95 molar ratio. To separate sorbed from non-sorbed propranolol, high-gradient magnetophoresis was used. The sorption profiles clearly show that electrostatic interactions play a key role in the sorption process as drug incorporation in the ML coat was favoured by increasing the anionic character of the ML envelope and by reducing the salt concentration of the medium. Also, upon drug binding some phospholipid molecules were expelled from the ML coat. The observations may be of relevance in the biomedical field, i.e. in the development of ML-based, intracellular theranostics.

Evaluation of the interaction of propranolol with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes: the partitioning model

The sorption behavior of the amine containing beta-receptor blocking agent propranolol (Ppn) in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) vesicles was investigated. Both protonated and unprotonated Ppn were measured in the continuous phase after removal of the vesicles containing sorbed Ppn by centrifugation. In contrast, by analyzing the surface charge density, deduced from electrophoretic mobility measurements, only the sorbed protonated Ppn was determined. A partitioning model was used to describe the sorption behavior. Sensitivity analysis revealed that sufficiently reliable and independent parameters were obtained. The partition coefficient of the unprotonated Ppn was about 22 times higher than that of the protonated analogue. Statistical analysis revealed a significant increase in the intrinsic partition coefficients of both Ppn analogues with an increase in the salt concentration.

Strategy for selection of methods for separation of bioparticles from particle mixtures

The desired product of bioprocesses is often produced in particulate form, either as an inclusion body (IB) or as a crystal. Particle harvesting is then a crucial and attractive form of product recovery. Because the liquid phase often contains other bioparticles, such as cell debris, whole cells, particulate biocatalysts or particulate by-products, the recovery of product particles is a complex process. In most cases, the particulate product is purified using selective solubilization or extraction. However, if selective particle recovery is possible, the already high purity of the particles makes this downstream process more favorable. This work gives an overview of typical bioparticle mixtures that are encountered in industrial biotechnology and the various driving forces that may be used for particle-particle separation, such as the centrifugal force, the magnetic force, the electric force, and forces related to interfaces. By coupling these driving forces to the resisting forces, the limitations of using these driving forces with respect to particle size are calculated. It shows that centrifugation is not a general solution for particle-particle separation in biotechnology because the particle sizes of product and contaminating particles are often very small, thus, causing their settling velocities to be too low for efficient separation by centrifugation. Examples of such separation problems are the recovery of IBs or virus-like particles (VLPs) from (microbial) cell debris. In these cases, separation processes that use electrical forces or fluid-fluid interfaces show to have a large potential for particle-particle separation. These methods are not yet commonly applied for large-scale particle-particle separation in biotechnology and more research is required on the separation techniques and on particle characterization to facilitate successful application of these methods in industry.

Effect of “helper lipid” on lipoplex electrostatics

Lipoplexes, which are complexes between cationic liposomes (L+) and nucleic acids, are commonly used as a nucleic acid delivery system in vitro and in vivo. This study aimed to better characterize cationic liposome and lipoplex electrostatics, which seems to play a major role in the formation and the performance of lipoplexes in vitro and in vivo. We characterized lipoplexes based on two commonly used monocationic lipids, DOTAP and DMRIE, and one polycationic lipid, DOSPA--each with and without helper lipid (cholesterol or DOPE). Electrical surface potential (Psi0) and surface pH were determined using several surface pH-sensitive fluorophores attached either to a one-chain lipid (4-heptadecyl hydroxycoumarin (C17HC)) or to the primary amino group of the two-chain lipids (1,2-dioleyl-sn-glycero-3-phosphoethanolamine-N-carboxyfluorescein (CFPE) and 1,2-dioleyl-sn-glycero-3-phosphoethanolamine-N-7-hydroxycoumarin) (HC-DOPE). Zeta potentials of the DOTAP-based cationic liposomes and lipoplexes were compared with Psi0 determined using C17HC. The location and relatively low sensitivity of fluorescein to pH changes explains why CFPE is the least efficient in quantifying the differences between the various cationic liposomes and lipoplexes used in this study. The fact that, for all cationic liposomes studied, those containing DOPE as helper lipid have the least positive Psi0 indicates neutralization of the cationic charge by the negatively-charged phosphodiester of the DOPE. Zeta potential is much less positively charged than Psi0 determined by C17HC. The electrostatics affects size changes that occurred to the cationic liposomes upon lipoplex formation. The largest size increase (based on static light scattering measurements) for all formulations occurred at DNA-/L+ charge ratios 0.5-1. Comparing the use of the one-chain C17HC and the two-chain HC-DOPE for monitoring lipoplex electrostatics reveals that both are suitable, as long as there is no serum (or other lipidic assemblies) present in the medium; in the latter case, only the two-chain HC-DOPE gives reliable results. Increasing NaCl concentrations decrease surface potential. Neutralization by DNA is reduced in a NaCl-concentration-dependent manner.

Electrostatics of PEGylated micelles and liposomes containing charged and neutral lipopolymers

The electrostatics of large unilamellar vesicles (LUVs) of various lipid compositions were determined and correlated with steric stabilization. The compositional variables studied include (a) degree of saturation, comparing the unsaturated egg phosphatidylcholine (EPC) and the fully hydrogenated soy phosphatidylcholine (HSPC) as liposome-forming lipids; (b) the effect of 40 mol % cholesterol; (c) the effect of mole % of three methyl poly(ethylene glycol) (mPEG)-lipids (the negatively charged mPEG-distearoyl phosphoethanolamine (DSPE) and two uncharged lipopolymers, mPEG-distearoyl glycerol (DSG) and mPEG-oxycarbonyl-3-amino-1,2-propanediol distearoyl ester (DS)); and (d) the negatively charged phosphatidyl glycerol (PG). The lipid phases were as follows: liquid disordered (LD) for the EPC-containing LUV, solid ordered (SO) for the HSPC-containing LUV, and liquid ordered (LO) for either of those LUV with the addition of 40 mol % cholesterol. The LUV zeta potential and electrical surface potential (psi(0)) were determined. It was found that progressive addition of mPEG(2k)-DSPE to liposomes increases negative surface potential and reduces surface pH to a similar extent as the addition of PG. However, due to the "hidden charge effect", zeta potential was more negative for liposomes containing PG than for those containing mPEG(2k)-DSPE. Replacing mPEG-DSPE with mPEG(2k)-DS or mPEG-DSG had no effect on surface pH and surface potential, and zeta potential was approximately zero. Addition of low concentrations of cationic peptides (protamine sulfate and melittin) to PG- or mPEG-DSPE-containing liposomes neutralized the liposome negative surface potential to a similar extent. However, only in liposomes containing PG, did liposome aggregation occur. Replacing the negatively charged lipopolymer mPEG-DSPE with the neutral lipopolymers mPEG-DS or mPEG-DSG eliminates or reduces such interactions. The relevance of this effect to the liposome performance in vivo is discussed.

A highly effective method for removing suspended poliovirus from water using a positively-charged carbon felt electrode

We developed an effective system to eliminate poliovirus from modified tap water using a positively-charged carbon felt electrode. The zeta potential of polioviruses was measured using laser microscopic electrophoresis. Poliovirus adsorption to the electrode was examined by indirect immunofluorescence. The tissue culture infective dose (TCID) of poliovirus type 2 (Sabin strain) was determined using human rhabdomyosarcoma cells (RD cells). Poliovirus VP2 gene copy numbers were assessed by reverse transcription followed by a quantitative real-time polymerase chain reaction. The mean zeta potential of the viruses was -20 mV. Relatively large numbers of polioviruses (10(3) or 4 x 10(3) TCID(50)/0.1 ml) could be removed by adsorption to the electrode, drastically decreasing TCID and copy numbers of poliovirus genome in the water. Virus elimination was dependent on electric current and time. Thus, the positively-charged carbon felt electrode effectively adsorbed polioviruses. The system may prove applicable to the elimination of certain viruses from water.

The Dukhin-Deryaguin equation for the electrophoretic mobility in monovalent electrolytes with arbitrary ion mobilities

The Dukhin-Deryaguin equation, used in the modern theory of electrophoresis for the calculation of electrophoretic mobility (EPM) in the region of double layer polarization, is known from literature [4-6] in its form (DD1) valid for the equal mobilities of the cation and anion in solutions of symmetrical electrolytes. Here we describe the other version of this equation (DD2), for arbitrary ion mobilities in 1:1 electrolytes. The EPMs calculated from this latter version are in good agreement with an exact computer solution [12]. The use of DD2 is illustrated in a series of EMP vs. IgC curves, calculated for selected examples of negatively charged lipid membranes. In addition, we describe two simplified versions of DD2, which are valid, respectively, for the high zeta potentials and when the electroosmotic component of ions' fluxes at the charged surface is neglected. Comparing DD2 with DD1 shows that the latter equation results in an error which may exceed the experimental dispersion of EPM values in the absence of specific ion binding. This error is reduced if the counter-ion binding is not small; hence, DD1 may also be used in some cases for solutions with arbitrary ion mobilities.