Formation of drug nanocrystals under nanoconfinement afforded by liposomes

Nanocrystals of drug substances have important therapeutic applications, but their preparation is often difficult due to size control in bottom up approaches, or energetic milling and surface activation in top down processing. In this study, confinement within liposome nanocompartments is demonstrated to enable drug crystallization with a high aspect ratio but limited growth resulting in nanocrystals, using a simple freeze–thaw process which is anticipated to be amenable to large scale preparation. After the freeze–thaw, cryo-transmission electron microscopy (cryoTEM) imaging and cryo-electron tomography revealed that the majority of the liposomes contained a single drug nanocrystal, observed to physically stretch but not burst the liposomes, and the composition of the freeze–thaw medium altered the aspect ratio of the drug nanocrystals. Small angle X-ray scattering and dynamic depolarized light scattering were used to confirm the asymmetric nature of particles in suspension to exclude the cryoTEM preparation process as a contributor to the particle morphology. In assessing potential use in controlled release drug delivery, the in vitro release rate of ciprofloxacin from liposomes containing the nanocrystals revealed that the rate of dissolution of the nanocrystals became the rate controlling step, in contrast to the lipid bilayer rate controlling function prior to the formation of the crystals. The ability to modulate the release rate of the active ingredient in a complex formulation using simple physical means (e.g., freeze/thaw) is an attractive possibility, especially in highly regulated industries such as pharmaceuticals where qualitative and quantitative changes of composition would require extensive safety evaluations

pH-responsive micelles based on caprylic acid

Free fatty acids play a vital role as fuel for cells and in lipid metabolism. During lipid digestion in the gastrointestinal tract, triglycerides are hydrolyzed, resulting in free fatty acid and monoglyceride amphiphilic products. These components, together with bile salts, are responsible for the transport of lipids and poorly water-soluble nutrients and xenobiotics from the intestine into the circulatory system of the body. In this study, we show that the self-assembly of digestion products from medium-chain triglycerides (tricaprylin) in combination with bile salt and phospholipid is highly pH-responsive. Individual building blocks of caprylic acid within the mixed colloidal structures are mapped using a combination of small-angle X-ray and neutron scattering combined with both solvent contrast variation and selective deuteration. Modeling of the scattering data shows transitions in the size and shape of the micelles in combination with a transfer of the caprylic acid from the core of the micelles to the shell or into the bulk water upon increasing pH. The results help to understand the process of lipid digestion with a focus on colloidal structure formation and transformation for the delivery of triglyceride lipids and other hydrophobic functional molecules. © 2014, American Chemical Society

Formation of highly structured cubic micellar lipid nanoparticles of soy phosphatidylcholine and glycerol dioleate and their degradation by triacylglycerol lipase

Lipid nanoparticles of reversed internal phase structures, such as cubic micellar (I2) structure show good drug loading ability of peptides and proteins as well as some small molecules. Due to their controllable small size and inner morphology, such nanoparticles are suitable for drug delivery using several different administration routes, including intravenous, intramuscular and subcutaneous injection. A very interesting system in this regard, is the two component soy phosphatidylcholine (SPC)/glycerol dioleate (GDO) system, which depending on the ratio of the lipid components form a range of reversed liquid crystalline phases. For a 50/50 (wt/wt) ratio in excess water, these lipids have been shown to form a reversed cubic micellar (I2) phase of the Fd3m structure. Here we demonstrate that this SPC/GDO phase, in the presence of small quantities (5-10 wt%) of Polysorbate 80 (P80), can be dispersed into nanoparticles, still with well-defined Fd3m structure. The resulting nanoparticle dispersion has a narrow size distribution and exhibit good long-term stability. In pharmaceutical applications, biodegradation pathways of the drug delivery vehicles and their components are important considerations. In the second part of the study we show how the structure of the particles evolves during exposure to a triacylglycerol lipase (TGL) under physiological-like temperature and pH. TGL catalyses the lipolytic degradation of acylglycerides, such as GDO, to monoglycerides, glycerol and free fatty acids. During the degradation, the interior phase of the particles is shown to undergo continuous phase transitions from the reversed I2 structure to structures of less negative curvature (2D hexagonal, bicontinuous cubic and sponge), ultimately resulting in the formation of multi-lamellar vesicles