Effect of PEG lipid on fusion and fission of phospholipid vesicles in the process of freeze-thawing

A quality by design approach for the development of lyophilized liposomes with simvastatin

Lyophilization is used to ensure an increased shelf-life of liposomes, by preserving them in dry state, more stable than the aqueous dispersions. When stored as aqueous systems, the encapsulated drugs are released and the liposomes might aggregate or fuse. The aim of this study was to develop and optimize a lyophilized formulation of simvastatin (SIM) loaded into long circulating liposomes using the Quality by Design (QbD) approach. Pharmaceutical development by QbD aims to identify characteristics that are critical for the final product quality, and to establish how the critical process parameters can be varied to consistently produce a product with the desired characteristics. In the case of lyophilized liposomes, the choice of the optimum formulation and technological parameters has to be done, in order to protect the integrity of the liposomal membrane during lyophilization. Thus, the influence of several risk factors (3 formulation factors: PEG proportion, cholesterol concentration, the cryoprotectant to phospholipids molar ratio, and 2 process parameters: the number of extrusions through 100 nm polycarbonate membranes and the freezing conditions prior lyophilization) over the critical quality attributes (CQAs) of lyophilized long circulating liposomes with simvastatin (lyo-LCL-SIM), i.e. the size, the encapsulated SIM concentration, the encapsulated SIM retention, the Tm change and the residual moisture content, was investigated within the current study using the design of experiments tool of QbD. Moreover, the design space for lyo-LCL-SIM was determined, in which the established quality requirements of the product are met, provided that the risk factors vary within the established limits.

Effects of Membrane PEGylation on Entry and Location of Antifungal Drug Itraconazole and Their Pharmacological Implications

Itraconazole (ITZ) is an antifungal agent used clinically to treat mycotic infections. However, its therapeutic effects are limited by low solubility in aqueous media. Liposome-based delivery systems (LDS) have been proposed as a delivery mechanism for ITZ to alleviate this problem. Furthermore, PEGylation, the inclusion in the formulation of a protective "stealth sheath" of poly(ethylene glycol) around carrier particles, is widely used to increase circulation time in the bloodstream and hence efficacy. Together, these themes highlight the importance of mechanistic and structural understanding of ITZ incorporation into liposomes both with and without PEGylation because it can provide a potential foundation for the rational design of LDS-based systems for delivery of ITZ, using alternate protective polymers or formulations. Here we have combined atomistic simulations, cryo-TEM, Langmuir film balance, and fluorescence quenching experiments to explore how ITZ interacts with both pristine and PEGylated liposomes. We found that the drug can be incorporated into conventional and PEGylated liposomes for drug concentrations up to 15 mol % without phase separation. We observed that, in addition to its protective properties, PEGylation significantly increases the stability of liposomes that host ITZ. In a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer without PEGylation, ITZ was found to reside inside the lipid bilayer between the glycerol and the double-bond regions of POPC, adopting a largely parallel orientation along the membrane surface. In a PEGylated liposome, ITZ partitions mainly to the PEG layer. The results provide a solid basis for further development of liposome-based delivery systems.

Small molecule therapeutic-loaded liposomes as therapeutic carriers: from development to clinical applications

In this review, various methods and mechanisms for encapsulation of small therapeutic molecules in liposomes for targeted delivery and triggered release, as well as their potential in the clinical uses, are discussed.

[World constructed by self-organization of some amphiphils--with a focus on vesicle formation--]

The world constructed by self-organization of some amphiphils was discussed on the basis of micelle formation, vesicle formation, and oriented-nano-wire formation. First, the micelle formation of a both water- and oil- soluble surfactant, Aerosol OT, was discussed. Solution states of micelles and monomer were discussed on the basis of thermodinamic and NMR spectroscopic analyses of micelle formation. Next, micelle-vesicle transition was discussed. It was proposed that the phospholipid LUV formation by removing detergents and destruction by adding detergents occurred via 4 stages. The 4 stage model instead of the 3 stage model could not only elucidate the complicated phenomena observed during micelle-vesicle transition, but predicted the size and properties of the vesicles formed by detergent removal from mixed micelles. Next, the vesicle formation of a fatty acid with a single hydrophobic chain different from phospholipid, which has two hydorophobic chains, was discussed. The vesicle formation was strongly affected by the presence of preformed vesicles and the size was biased on the preformed vesicles. It was shown there exist two pass ways in the process of micelle-vesicle transition by pH jump. One is fission of the preformed vesicles after transfer of monomers from newly added oleate micelles and the other is transition from the mixed micelles after partial solubilization by the oreate micelles. Then, the vesicle formation of HCO-10, which has 3 hydrophobic chains, the mixed vesicle formation of phosphatidylethanolamine and lysophosphtidylcholine, which can not form vesicles, and the phospholipid vesicle formation and destruction by removing and adding PEG-lipid, were discussed. Lastly, oriented nano wire formation of mulamyldipeptid-conjugated lipids with ca 5 nm of diameter was discussed.

Effect of freeze-thawing on lipid bilayer-protected gold nanoparticles

In this study, varieties of lipid bilayer-protected gold nanoparticles (AuNPs) were synthesized through a simple wet chemical method, and then the effect of freeze-thawing on the as-prepared AuNPs was investigated. The freeze-thawing process induced fusion or fission of lipid bilayers tethered on the AuNPs. The UV-vis spectra and transmission electron microscopy experiments revealed that the disruption of lipid bilayer structures on the nanoparticles led to the fusion or aggregation of AuNPs. The role of freeze-thawing in the evolution of lipid bilayer-protected AuNPs was studied. The addition of adequate sucrose, a well-known cryoprotectant, effectively prevented the fusion or aggregation of lipid bilayer-protected AuNPs undergoing the freeze-thawing process. The possible mechanism of sucrose preserving the integrity of the lipid bilayer-protected AuNPs was also discussed.

Polymer-supported lipid shells, onions, and flowers

Phospholipid-enveloped biodegradable polymer microparticles and nanoparticles synthesized by an emulsion/solvent evaporation process were characterized by confocal and cryoelectron microscopies to show that the lipid envelope exhibits two-dimensional fluidity and can be configured into 'shell', 'onion', or 'flower' nanostructures, depending on the quantity and composition of lipids employed in the synthesis.

Influence of preparation path on the formation of discs and threadlike micelles in DSPE-PEG(2000)/lipid systems

In a recent study we showed that the surfactant 1,2-distearoyl-sn-glycero-3-phosphatidylethanolamine-N-[methoxy(polyethylene glycol)-2000 (DSPE-PEG(2000)) induce mixed micelles of either threadlike or discoidal shape when mixed with different types of lipids. In certain lipid systems the discoidal micelles adapt sizes large enough to be characterized as bilayer discs. The discs hold great potential for use in various biotechnical applications and may e.g. be used as model membranes in drug/membrane partition studies. Depending on the application, discs with certain characteristics, such as a particular size or size homogeneity, may be required. These factors can in our experience be influenced by the preparation method. In this study we systematically investigated three different PEG-lipid/lipid mixtures prepared by four commonly used preparation techniques. The techniques used were simple hydration, freeze-thawing, sonication and detergent depletion, and the aggregate size and structure was analyzed by cryo transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS). Our results show that the type and size of the micellar structure found, as well as the structure homogeneity of the preparation, can be modified by the choice of preparation path.