High Encapsulation Yield Research Articles

Antisense Oligonucleotide Nanocapsules Efficiently Inhibit EWS-Fli1 Expression in a Ewing's Sarcoma Model

The cytogenetic abnormality of Ewing's sarcoma is related to the presence of a balanced t(11;22) translocation expressing the EWS-Fli1 chimeric fusion protein. Oligonucleotides (ODNs) are specific compounds that inhibit gene expression at the transcriptional level. They possess a poor bioavailability and are degraded by nucleases very rapidly. Therefore, there is a strong need for the development of ODN drug delivery systems. In the present study, polyisobutylcyanoacrylate nanocapsules entrapping ODNs in their aqueous core were prepared, with high encapsulation yield (99%). Previous studies have demonstrated that such complexes were able to inhibit tumor growth in mice. Nevertheless, no information was available about their mode of action at the cellular level. The aim of this study was to investigate the efficacy of these ODN nanocapsules on cultured tumor cells. We found that nanocapsules were capable of protecting ODN against degradation. Using confocal microscopy, we observed that cell uptake and nuclear accumulation of ODNs were importantly enhanced when ODNs were associated with these nanocapsules. Consequently, a specific cellular growth inhibition and suppression of EWSFli1 fusion gene expression was noticed. In conclusion, it was demonstrated that nanocapsules as nonviral vectors show great potential for the delivery of ODNs to cells.

Hyaluronan-based microspheres as tools for drug delivery: a comparative study

The present paper describes the production of biodegradable microparticles using different hyaluronan polymers, such as native hyaluronan, the esterified derivative of hyaluronan Hyaff 11p50 (where 50% of the carboxy groups of hyaluronic acid are esterified with benzyl alcohol) and the autocross-linked polymer (ACP) internally esterified derivative of hyaluronan, by solvent evaporation and spray-drying methods. As model drugs cromolyn sodium salt, metronidazole and prednisolone hemisuccinate sodium salt were employed. The influence of polymer and preparation procedure has been evaluated on microparticle characteristics (i.e. morphology and encapsulation yield) and on the drug release profiles. The use of solvent evaporation method, a polymeric matrix constituted of Hyaff 11p50 3% (w/v), a dispersing phase constituted of 80 g of mineral oil (w/o ratio: 0.1), Span 85 0.1% (w/w) as stabilizer, and a stirring speed of 700 rpm resulted in the production of microspheres characterized by spherical shape, absence of aggregates, a mean diameter of 6.4 μm and a recovery of 90% (w/w). The production of drug containing microspheres led to an increase of mean diameter of microspheres and to high encapsulation yields. Moreover in vitro models have demonstrated that in all cases drugs were released from Hyaff 11p50 microspheres in a controlled fashion. Finally mathematical analysis of the drug release modalities has evidenced that drug release from Hyaff 11p50 microspheres is more consistent with kinetics of the diffusion rather than of the dissolution type.

Preparation of oily core polyamide microcapsules via interfacial polycondensation

AbstractMicrocapsules obtained by interfacial polycondensation from an original system based on the polyaddition of specific di‐ or polyamines and more classical acyl chloride molecules were studied. The originality of the system lies in the fact that the encapsulated agent is the internal phase allowing its incorporation without an organic solvent, which is an advantage from the point of view of environmental protection. Once the optimal parameters of the emulsion were determined, the membrane formation was studied by optimizing the emulsification and reaction times in relation to simultaneous acyl chloride hydrolysis. The microcapsules were obtained by interfacial polycondensation between an excess of amine functions (diamine and diethylenetriamine) and acyl chloride (sebacoyl chloride and 1,3,5‐benzene tricarbonyl trichloride) from an oil‐in‐water emulsion in the presence of 88% hydrolyzed poly(vinyl alcohol) as a surfactant. Various formulations in terms of COCl concentration, crosslinking agent concentration, excess of amine functions, emulsification and reaction times were prepared. The hydrolysis of acyl halide functions is the main parameter which influences the growth of the membrane. The increase in acyl chloride function concentration allows compensation for that lost by hydrolysis, and increases the encapsulation yield to about 90%. The degree of crosslinking of the membrane was controlled in order to minimize the subsequent release of oil by the addition of trifunctional monomers. An optimal formulation was developed offering high encapsulation yield and optimal elastic behaviour. Almost spherical capsules, with a membrane thickness of approximately 500 nm, relatively smooth internal walls and crumpled external walls, were observed by scanning electron microscopy.© 2003 Society of Chemical Industry

Essential oil formulations useful as a new tool for insect pest control.

This study investigated the effects of some essential oils on Limantria dispar (Lepidoptera: Lymantridae, gypsy moth) larvae, one of the most serious pests of cork oak forests. The essential oils were first formulated as oil in water (o/w) emulsions and used in laboratory bioassays to assess their lethal concentration (LC50). Microcapsules containing the most promising oils (Rosmarinus officinalis and Thymus herba-barona) were then prepared by a phase separation process, followed by freeze-drying. The formulations thus obtained, characterized in terms of essential oil content and composition, morphology, storage stability, and release profile, were tested on gypsy moth larvae. The results showed that the tested oils possess interesting larvicidal effects that make them suitable for application in integrated control strategies. The microencapsulation process gave high encapsulation yields (over 98%) with both essential oils, which have different chemical compositions. The microcapsules had toxic effects at a concentration similar to that usually employed for localized treatments with microgranular synthetic pesticides. Toxicity appeared to be maximized when the microparticles adhered to the typical hair structures of several defoliator families. These formulations seem to be able to protect the core material against environmental agents and could be considered for use in controlled drug release systems. The natural active principles they contain could provide an alternative system in insect pest control.

In vitro study of alcohol dehydrogenase and acetaldehyde dehydrogenase encapsulated into human erythrocytes by an electroporation procedure

The optimal conditions for electroporated/resealed loading of alcohol dehydrogenase (ADH) and/or acetaldehyde dehydrogenase (ALDH) into human erythrocytes were established prior to the study, with the following characteristics: 300 V, 1 ms pulse time, eight pulses every 15 min and 1 h resealing at 37°C. High encapsulation yield and carrier cell recoveries were achieved. Cell volumes increase while hemoglobin contents decrease; in consequence a decrease in cell hemoglobin concentration was observed. A lower hypotonic resistance of loading erythrocytes (throughout osmotic fragility curves) and unaltered oxygen transport capability (as given by oxygen equilibrium curves) were observed. The stability against time (up to 168 h–7 days) of encapsulated individual enzymes, either ADH- or ALDH-red blood cells (RBCs), was studied at 4°C and 37°C, in comparison with that of free enzyme solutions. Both enzymes were released from carrier RBCs to the incubation medium. The stability of carrier RBCs was studied under similar conditions. Non-significant variations in hematological parameters were observed. However, the hemoglobin derivative forms showed modifications. The continuous degradation of ethanol by ADH-RBCs and coencapsulated ADH- and ALDH-RBCs, as a function of time (up to 70 h) suggests the use of these carrier RBCs as agents for complete metabolization of ethanol. The mentioned properties bare the possibility of using ADH and ALDH as carrier systems in in vivo situations.

Optimization of HSA and NGF encapsulation yields in PLGA microparticles

The aim of this study was to prepare, in a reproducible manner, poly( d, l-lactide-co-glycolide) (PLGA) biodegradable microparticles with high encapsulation yield of nerve growth factor (NGF), a neurotrophic factor of interest in the treatment of neurodegenerative diseases. Human serum albumin (HSA) was co-encapsulated with NGF by the w/o/w emulsion solvent evaporation/extraction method to stabilize the primary emulsion and to protect NGF. The encapsulation yield optimization was first carried out with HSA alone since it was the major component in the final microspheres, as compared to NGF. The effects of ten process factors on HSA entrapment in PLGA microspheres were examined using a fractional factorial design. Four major factors were identified. The presence of carboxymethylcellulose sodium or mannitol in the internal aqueous phase, the increase of the internal aqueous volume and the concentration of HSA led to a decrease of the encapsulation yield. Two main factors, namely the internal aqueous phase volume and the proportion of acetone in the organic phase, previously identified as a predominant factor, were studied through a response surface methodology. The observed range of HSA encapsulation yield was 87.4–100%. NGF was encapsulated according to the optimal conditions found for the entrapment of HSA. The encapsulation yield was then 97.3±5.0%.

Encapsulation of cytochrome C by multilayer microcapsules. A model for improved enzyme immobilization

Cytochrome C was used as a model compound to study the behavior of proteins during the encapsulation procedure in alginate microcapsules and the loss by diffusion during storage. Alginate gel beads were coated with a multilayer membrane consisting of alternating layers of poly( N-vinylamine) and poly(acrylic acid) or water soluble anionic cellulose derivatives, respectively. To obtain high encapsulation yields, it is recommended to use the lowest possible concentration of salts in the precipitation bath. Loss during storage (and use) is minimized by applying at least two polycation/polyanion double layers for the membrane. Cellulose derivatives are superior over poly(acrylic acid). Single layer membranes are not able to retain cytochrome C.