J.L. Vila-Jato

Novel hydrophilic chitosan-polyethylene oxide nanoparticles as protein carriers

Hydrophilic nanoparticulate carriers have important potential applications for the administration of therapeutic molecules. The recently developed hydrophobic-hydrophilic carriers require the use of organic solvents for their preparation and have a limited protein-loading capacity. To address these limitations a new approach for the preparation of nanoparticles made solely of hydrophilic polymers is presented. The preparation technique, based on an ionic gelation process, is extremely mild and involves the mixture of two aqueous phases at room temperature. One phase contains the polysaccharide chitosan (CS) and a diblock copolymer of ethylene oxide and propylene oxide (PEO-PPO) and, the other, contains the polyanion sodium tripolyphosphate (TPP). Size (200–1000 nm) and zeta potential (between +20 mV and +60 mV) of nanoparticles can be conveniently modulated by varying the ratio CS/PEO-PPO. Furthermore, using bovine serum albumin (BSA) as a model protein it was shown that these new nanoparticles have a great protein loading capacity (entrapment efficiency up to 80% of the protein) and provide a continuous release of the entrapped protein for up to 1 week.

Design of microencapsulated chitosan microspheres for colonic drug delivery

Among the different approaches to achieve colon-selective drug delivery, the use of polymers, specifically biodegraded by colonic bacteria, holds great promise. In this work a new system which combines specific biodegradability and pH-dependent release is presented. The system consists of chitosan (CS) microcores entrapped within acrylic microspheres. Sodium diclofenac (SD), used as a model drug, was efficiently entrapped within CS microcores using spray-drying and then microencapsulated into Eudragit L-100 and Eudragit S-100 using an oil-in-oil solvent evaporation method. The size of the CS microcores was small (1.8-2.9 microns) and they were encapsulated within Eudragit microspheres (size between 152 and 233 microns) forming a multireservoir system. Even though CS dissolves very fast in acidic media, at pH 7.4, SD release from CS microcores was delayed, the release rate being adjustable (50% dissolved within 30-120 min) by changing the CS molecular weight (MW) or the type of CS salt. Furthermore, by coating the CS microcores with Eudragit, perfect pH-dependent release profiles were attained. No release was observed at acidic pHs, however, when reaching the Eudragit pH solubility, a continuous release for a variable time (8-12 h) was achieved. A combined mechanism of release is proposed, which considers the dissolution of the Eudragit coating, the swelling of the CS microcores and the dissolution of SD and its further diffusion through the CS gel cores. In addition, infrared (IR) spectra revealed that there was an ionic interaction between the amine groups of CS and the carboxyl groups of Eudragit, which provided the system with a new element for controlling the release. In conclusion, this work presents new approaches for the modification of CS as well as a new system with a great potential for colonic drug delivery.

The role of PEG on the stability in digestive fluids and in vivo fate of PEG-PLA nanoparticles following oral administration

The aim of the present work was to evaluate if the presence of a polyethylenglycol (PEG) coating around PLA nanoparticles would affect their interaction with biological surfaces, following oral administration to rats. For this purpose, a model antigen, 125I-radiolabeled tetanus toxoid, was encapsulated in PLA and PLA-PEG nanoparticles by a modified water-in-oil-in-water solvent evaporation technique. Firstly, the stability of the nanoparticles in simulated gastrointestinal fluids was evaluated. Results showed an interaction between the nanoparticles and the enzymes of the digestive fluids, this interaction being considerably reduced by the PEG coating around the particles. On the other hand, the PLA forming the nanoparticles was found to be only slightly degraded (9% converted to lactate for PLA nanoparticles and 3% for PLA-PEG nanoparticles) and that the encapsulated tetanus toxoid remained mostly associated to the nanoparticles upon incubation in the digestive fluids for up to 4 h. Finally, the in vivo experiments showed that, after oral administration to rats, the levels of encapsulated radioactive antigen in the blood stream and lymphatics were higher for PLA-PEG nanoparticles than for PLA nanoparticles. In conclusion, the PLA-PEG nanoparticles have a promising future as protein delivery systems for oral administration.

Development of biodegradable microspheres and nanospheres for the controlled release of cyclosporin A

Abstract With the aim to develop a new controlled release dosage form of administration for cyclosporin A (CyA), several formulations of CyA-loaded microspheres and nanospheres based on poly( dl -lactide-co-glycolide) (PLGA) were designed. Microspheres and nanospheres, prepared by the solvent evaporation process, were characterized with respect to morphology, size distribution, drug content, internal structure and in vitro drug release. The micro- and nanospheres designed displayed various sizes (from 0.2 to 30 μm), spherical shape and smooth surface. The loading capacity was high for all formulations although it was influenced by the microsphere size. Results obtained by reversed-phase high-performance liquid chromatography, gel-permeation chromatography, differential scanning calorimetry, X-ray powder diffraction and Fourier transform infrared spectroscopy revealed that the peptide forms a molecular dispersion in the co-polymer matrix and no chemical interaction between co-polymer and drug occurs. Release profiles of CyA from the microspheres developed displayed a biphasic shape. The duration and intensity of each phase were affected by the microsphere size and the molecular weight of PLGA. Consequently, using PLGA it is possible to design micro- and nanospheres which allow the controlled release of CyA over a prolonged period of time. This may represent an interesting approach to provide therapeutic levels of the drug for extended periods of time.

Improvement of Ocular Penetration of Amikacin Sulphate by Association to Poly(butylcyanoacrylate) Nanoparticles

Abstract— The main objective of this paper was to investigate the ability of polycyanoacrylate nanoparticles to improve the corneal penetration of hydrophilic drugs. Three different nanoparticle formulations were prepared by changing the nature of the stabilizer agent (Dextran 70000, Synperonic F 68 and sodium lauryl sulphate). The significant influence of the stabilizer type on the particle size, electrophoretic mobility and on the drug loading efficiency was proved. Moreover, the ocular disposition of amikacin was affected by its association to nanoparticles, displaying the most interesting results when Dextran 70000 was employed for preparation of nanoparticles. The increase of the amikacin concentration in cornea and aqueous humour was statistically significant for this nanoparticle formulation with respect to the other formulations and the control solution. The in‐vitro release profiles obtained using a dialysis system were similar for all the nanoparticle formulations and for the control solution, indicating that drug molecules are desorbed from the nanoparticles quickly enough to maintain the equilibrium concentration in the dialysis system.

Study of the mechanism of interaction of poly(ϵ-caprolactone) nanocapsules with the cornea by confocal laser scanning microscopy

Abstract With the aim of exploring the potential of poly(ϵ-caprolactone) (PECL) nanocapsules as drug carriers for ocular administration, the present study examined the mechanism of interaction of these nanocapsules with the corneal and conjunctival epithelia. In the first stage of this work, corneas were mounted in a perfusion cell, incubated with a suspension of rhodamine 6G-loaded PECL nanocapsules and subsequently observed by confocal laser scanning microscopy. Fluorescence signals were only observed within the epithelial cells, but not in the intercellular junctions, thus demonstrating the intracellular localization of the fluorescent nanocapsules. To determine whether this penetration could be associated with cellular lysis or endocytotic uptake, corneas were pretreated with blank nanocapsules and then stained with propidium iodide, a fluorescent dye which distinguishes viable from non-viable cells. Confocal images of the pretreated corneas did not display any fluorescence signal, thus indicating that PECL nanocapsules penetrate the corneal epithelial cells by an endocytotic mechanism. In the second stage of the work, rabbit corneas and conjunctivas were removed after in vivo instillation of the nanocapsule suspension and then analyzed by confocal laser scanning microscopy. The in vivo results corroborated the endocytosis uptake mechanism of nanocapsules by the cornea. On the other hand, no nanocapsules were observed in the conjunctival epithelium, which indicates a selective interaction of the PECL nanocapsules for the cornea vs the conjunctiva. These results suggest the ability of these colloidal carriers to specifically target drugs to the cornea while avoiding systemic drug loss through the conjunctiva. To summarize, PECL nanocapsules are shown to be the first demonstrated targeted corneal drug delivery system. Consequently, they may represent a useful approach to promote corneal penetration while simultaneously reducing conjunctival systemic absorption of drugs. This implies a potential increase in therapeutic effect and a reduction of systemic side effects.

Effect of chitosan and chitosan glutamate enhancing the dissolution properties of the poorly water soluble drug nifedipine

Abstract In this study, a significant effect of chitosan increasing nifedipine dissolution has been demonstrated. This effect was dependent on the polymer:drug mixing weight ratio, the chitosan type and the method used to disperse the drug within the polymer. The greater the chitosan content the higher the drug dissolution was, up to a maximum corresponding to a polymer:drug ratio of 3:1. Significant differences within the various tested chitosans were observed. The lower the M w the more important the polymer effect was which, in turn, was more noticeable for the glutamate salt than for the chitosan base. The various chitosan:nifedipine solid mixtures were ordered, according to the efficiency of improving the drug dissolution, as follows: solid dispersion>kneaded mixture>co-ground mixture>physical mixture. The drug dissolution enhancement was attributed to the decreased drug crystallinity and size and polymer wetting effect. Co-grinding of chitosan along with nifedipine in a 3:1 ratio, which leads to solid mixtures exhibiting a significantly improved dissolution profile without requiring the addition of organic solvents or high temperatures for its preparation, appears to be the more simple and convenient method.

Development of new chitosan–cellulose multicore microparticles for controlled drug delivery

Chitosan (CS) is a very interesting biomaterial for drug delivery; however its use in oral administration is restricted by its fast dissolution in the stomach and limited capacity for controlling the release of drugs. To address this limitation, a new microparticulate CS controlled release system, consisting of hydrophilic CS microcores entrapped in a hydrophobic cellulosic polymer, such as cellulose acetate butyrate (CAB) or ethyl cellulose (EC) was proposed. These microparticles were obtained with different types of CS and various core/coat ratios, with the particle size in all cases being smaller that 70 microns. Using sodium diclofenac (SD) and fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA) as model compounds, the properties of these new microparticles for the entrapment and controlled release of drugs and proteins were investigated. Results showed that the entrapment efficiency of SD was very high irrespective of the processing conditions. Furthermore, for both model compounds (SD and FITC-BSA) it was possible to modulate the in vitro release of the encapsulated molecules by changing the core properties (CS salt, Mw, core/coat ratio) or the coating polymer. The microparticles were stable at low pH and thus, suitable for oral delivery without requiring any harmful cross-linkage treatment.

A proton nuclear magnetic resonance study of the inclusion complex of naproxen with β-cyclodextrin

We report a 1H-NMR study of the complex formed between naproxen (NAP) and β-cyclodextrin (β-CD) in aqueous medium. Our results confirm that inclusion occurs. Analysis of our data by the continuous variation method shows that the complex has 1 : 1 stoicheiometry. Using Scotts modification of the Benesi-Hildebrand method, we estimate the apparent stability constant of the complex at 298 K in alkaline medium to be 420 M−1. Finally, with the aid of a molecular modelling program, we have determined the most probable structure of the complex. In general our results confirm those of previous studies, although our estimate of the apparent stability constant differs slightly from that reported on the basis of phase solubility results.

Preparation and evaluation of ketoconazole-β-cyclodextrin multicomponent complexes

Abstract Increase in poor buffer pH 5 and 6 solubility of ketoconazole was studied. Two systems were used: binary complexes prepared with β -cyclodextrin and multicomponent systems (β-cyclodextrin and an acid compound), obtained by spray-drying. X-ray diffractometry and differential scanning calorimetry showed differences between ketoconazole/cyclodextrin complexes and their corresponding physical mixtures and individual components. The solubility of ketoconazole increased significantly with the cyclodextrin complexes. However, enhancement was better from the multicomponent systems.