Poly(D,L-lactide) nanocapsules prepared by a solvent displacement process: influence of the composition on physicochemical and structural properties.

Nanocapsules (NC) were prepared by interfacial deposition of preformed biodegradable polymer (PLA(50)) after a solvent displacement process. The influence of the composition used for the preparation of NC was evaluated in terms of particle size, polydispersity, zeta potential, homogeneity, and structural characteristics of the systems. The nature of the oil phase, polymer molecular weight, type and concentration of different surfactants were investigated to optimize the formulation to obtain NC suitable for intravenous administration. The influence of the physicochemical properties of the different oils used in NC preparation on the NC size was evaluated. The interfacial tension between the oil and water phases seems to have a greater effect on NC size than the oil viscosity. Miglyol 810 and ethyl oleate lead to the formation of smaller NC, probably because of the reduced interfacial tension. The polymer molecular weight plays only a small role in NC surface charge in the presence of lecithin, whereas NC surface charge, size, polydispersity, and short-term stability were highly influenced by lecithin purity. It appears that the absence of poloxamer 188 leads to smaller polydispersity, less contamination with nanospheres, and reduced formation of structures other than NC. Furthermore, electron microscopy and density gradient density techniques were used to examine the structure of the particles formed and their homogeneity. NC formation was evidenced by the bands with intermediate density between nanoemulsion and nanospheres; however, other bands of low intensity were observed. The presence of liposomes and multilayers in NC preparation was confirmed by electron microscopy. The percentage of carboxyfluorescein entrapped in different NC formulations allowed us to estimate the contamination by liposomes. It has been show that, under our experimental conditions, an excess of lecithin is an essential prerequisite for a stable preparation of PLA NC.

Insulin in w/o/w multiple emulsions: preparation characterization and determination of stability towards proteases in vitro.

In this work two w/o/w multiple emulsions composed of soybean oil or medium-chain triglycerides and containing insulin were studied. These emulsions were prepared by means of two-step emulsification procedure. The w/o/w emulsions obtained were stable for at least 6 months of storage at 4-6 degrees C. The yield of encapsulation of insulin was > 95%. The main release mechanism is a swelling-breakdown phenomenon. In vitro, the two w/o/w multiple emulsions were able to protect insulin against enzymatic degradation. These results indicate that multiple emulsions have potential as a carrier of insulin for oral administration.

Insulin in w/o/w multiple emulsions: biological activity after oral administration in normal and diabetic rats.

In this work the biological effects of two w/o/w multiple emulsions composed of the soybean oil (EHS) or medium-chain triglycerides (ETCM), containing insulin, were studied. The release mechanism of insulin from multiple emulsions proposed in our previous in-vitro investigations was confirmed by subcutaneous administration. This mechanism is the swelling-breakdown phenomenon which occurs when the emulsions are diluted under hypo-osmotic condition. The biological effect after oral administration, evaluated in two experimental protocols, single administration in normal and diabetic rats and short-term treatment in diabetic rats, shows that in diabetic rats small amounts of biologically active insulin were absorbed from these emulsions. In these experiments no significant difference between EHS and ETCM was found.

Preparation and characterization of dipalmitoylphosphatidylcholine liposomes containing interleukin-2.

Human recombinant interleukin-2 (IL-2) has been associated or mixed with small unilamellar vesicles prepared from dipalmitoylphosphatidylcholine (DPPC). Whatever the mode of IL-2 introduction, a considerable proportion of the added protein was associated with the liposomes, as determined by gel filtration and ultrafiltration/centrifugation, suggesting that IL-2 can interact with the lipid bilayer as well as being entrapped within the aqueous phase. Moreover, IL-2 prevented the aggregation/fusion of the vesicles at 4 degrees C. Liposome-associated protein was partially protected from digestion by pepsin, especially at the C-terminal, since no fluorescence emission from the tryptophan in this region was detected in the resulting peptides after separation by HPLC. Such systems could constitute a sustained release form of IL-2 for immunotherapy.

An in vitro release kinetic examination and comparative evaluation between submicron emulsion and polylactic acid nanocapsules of clofibride.

Polylactic acid nanocapsules of clofibride containing soybean oil (SO) or medium-chain triglycerides (MCT) as the oil core were prepared. The in-vitro drug release kinetic profiles were determined and compared to those of a clofibride submicron emulsion using two different kinetic techniques: the bulk equilibrium reverse dialysis sac technique, and the centrifugal ultrafiltration technique. The former technique was shown to be inadequate for in-vitro kinetic comparison purposes as a result of drug diffusion limitations through the dialysis membrane. The latter technique yielded rapid in-vitro release profiles of clofibride from both emulsion and nanocapsule delivery systems under perfect sink conditions although a consistent lower maximum drug amount was released from the MCT nanocapsules as compared to the corresponding emulsion. This was attributed to the relatively higher aqueous solubility of MCT as compared to SO. This comparative study, carried out, to the best of our knowledge, for the first time, clearly showed that both colloidal carriers behave similarly with respect to drug release despite their different morphological characteristics. The kinetic results clearly exclude either the use of submicron emulsion or of nanocapsules as colloidal controlled release delivery systems for any administration route where perfect sink conditions should prevail.