Dolores Torres

Design of a new multiparticulate system for potential site-specific and controlled drug delivery to the colonic region

A multiparticulate dosage form consisting of a hydrophobic core coated with a pH-dependent polymer is proposed for colonic specific delivery of drugs. Different approaches for colon-specific drug delivery have been studied over the last decade, including prodrugs, polymeric coating using pH-sensitive or bacterial degradable polymers and matrices. In this work, we present a new multiparticulate system to deliver active molecules to the colonic region, which combines pH-dependent and controlled drug release properties. This system was constituted by drug loaded cellulose acetate butyrate (CAB) microspheres coated by an enteric polymer (Eudragit(R) S). Both, CAB cores and pH-sensitive microcapsules, were prepared by the emulsion-solvent evaporation technique in an oily phase. Ondansetron (OS) and budesonide (BDS), two interesting drugs with a potentially new application for the local treatment of intestinal disorders, were efficiently microencapsulated in CAB microspheres at different polymer concentrations (6 and 8%). These hydrophobic cores (about 60 and 110 micrometer in size, respectively) were then microencapsulated with Eudragit(R) S, resulting in multinucleated structures, except in the case of BDS-CAB microspheres prepared at 8% CAB concentration, in which more mononucleated microcapsules were obtained. The in vitro drug release studies of pH-sensitive microcapsules containing the hydrophobic cores showed that no drug was released below pH 7. After that, CAB microspheres efficiently controlled the release of BDS, the release behavior being affected by the different polymer concentration used in their preparation. However, OS-CAB microspheres did not maintain their controlled-release properties once the enteric polymer dissolved. The extraction of the drug by the Eudragit(R) solvent during the second microencapsulation process was in this case the cause for the failure of the controlling release mechanism.

Chitosan–hyaluronic acid nanoparticles loaded with heparin for the treatment of asthma

The purpose of this study was to produce mucoadhesive nanocarriers made from chitosan (CS) and hyaluronic acid (HA), and containing the macromolecular drug heparin, suitable for pulmonary delivery. For the first time, this drug was tested in ex vivo experiments performed in mast cells, in order to investigate the potential of the heparin-loaded nanocarriers in antiasthmatic therapy. CS and mixtures of HA with unfractionated or low-molecular-weight heparin (UFH and LMWH, respectively) were combined to form nanoparticles by the ionotropic gelation technique. The resulting nanoparticles loaded with UFH were between 162 and 217 nm in size, and those prepared with LMWH were 152 nm. The zeta potential of the nanoparticle formulations ranged from +28.1 to +34.6 mV, and in selected nanosystems both types of heparin were associated with a high degree of efficiency, which was approximately 70%. The nanosystems were stable in phosphate buffered saline (PBS), pH 7.4, for at least 24h, and released 10.8% of UFH and 79.7% of LMWH within 12h of incubation. Confocal microscopy experiments showed that fluorescent heparin-loaded CS-HA nanoparticles were effectively internalized by rat mast cells. Ex vivo experiments aimed at evaluating the capacity of heparin to prevent histamine release in rat mast cells indicated that the free or encapsulated drug exhibited the same dose-response behaviour.

The potential of chitosan for the oral administration of peptides

Over recent years, a major challenge in drug delivery has been the design of appropriate vehicles for the oral administration of macromolecular drugs (peptides and proteins). Indeed, despite the increasing market value of these complex molecules, their clinical use has been highly limited by their reduced oral bioavailability. Among the different delivery approaches explored so far, those based on the use of the polysaccharide chitosan have opened promising alternatives towards this ambitious goal. This is due to the interesting physicochemical and biopharmaceutical properties of this polymer. This article describes the advances that have been made in the design of chitosan-based systems specially adapted for the oral administration of peptides. These systems include solutions, microspheres, nanoparticles, nanocapsules and liposomes. More specifically, this article discusses the efficacy of the different delivery approaches for improving the absorption of peptides, and analyses the various mechanisms that have been proposed for the understanding of their efficacy.

Controlled-release liquid suspensions based on ion-exchange particles entrapped within acrylic microcapsules

Eudragit RS/RL polymers were used to prepare microcapsules containing terbutaline-loaded ion-exchange resins, with the final aim of formulating this anti-asthmatic drug in a controlled-release liquid form. Oil-in-oil (o/o) and oil-in-water (o/w) solvent evaporation procedures were conveniently modified in order to encapsulate the resin cores. The microcapsules were then suspended in a hydroxypropylmethylcellulose solution of adequate viscosity and palatability, and stored at 20 degrees C and ambient humidity conditions for a 6-month period. Stability studies of the dispersed microparticles were performed in order to evaluate the changes occurred in the diffusion of the drug to the suspending medium and in the dissolution behaviour during storage. The morphological alterations of the stored microcapsules were followed throughout the duration of the study by scanning electron microscopy. The polymer coatings of microcapsules prepared by the o/o method broke up on the first day of storage, while those made by the aqueous procedure remained intact during all the storage period. This agreed with the modification observed in the controlled-release profiles of terbutaline in the case of microcapsules prepared by the o/o method, which completely changed after the first week of storage. On the contrary, the microcapsules prepared by the aqueous method showed identical controlled-release profiles for all the stability study. The different behaviour of both types of microcapsules was attributed to the swelling suffered by the resin particles in contact with the aqueous suspending medium, which was higher in the microcapsules prepared by the o/o technique. In fact, in the anhydrous procedure, the microencapsulation was carried out on the shrunken resin particles, whereas in the o/w method, the presence of water during the microencapsulation process allowed the coating of the swollen particles, thus avoiding the further problem of rupture of the polymer coating.

Highly Efficient System To Deliver Taxanes into Tumor Cells : Docetaxel-Loaded Chitosan Oligomer Colloidal Carriers

Chitosan (CS) colloidal carriers, which consist of an oily core and a CS coating, were developed to facilitate a controlled intracellular delivery of docetaxel. The systems presented a particle size of <200 nm and a positive surface charge. As shown by the flow cytometry analysis, fluorescent CS carriers were rapidly internalized by human tumor cells. Fluorescence was observed in more than 80% of MCF7 (human breast adenocarcinoma) and almost 100% of A549 (human lung carcinoma) cells when a 2 h treatment with fluorescent CS carriers was given. A total of 24 h after treatment, docetaxel-loaded CS carriers had an effect on cell proliferation that was significantly greater than that of free docetaxel. These results indicate that docetaxel remains fully active upon its encapsulation into the colloidal carriers and that these systems actively transport docetaxel into cancer cells and, thus, result in a significant increase in its antiproliferative effect.

Preparation and in vivo evaluation of mucoadhesive microparticles containing amoxycillin-resin complexes for drug delivery to the gastric mucosa.

In this work, microparticles consisting of amoxycillin-loaded ion-exchange resin encapsulated in mucoadhesive polymers (polycarbophil and Carbopol 934) were prepared with the aim of increasing the efficacy of amoxycillin in the treatment of peptic ulcers by achieving targeted delivery to the gastric mucosa and prolonged drug release. An oil-in-oil solvent evaporation technique was conveniently modified in order to obtain polymer microparticles containing multiple amoxycillin-resin cores. Polycarbophil microparticles were spherical, Carbopol 934 microparticles irregular. In vitro release of amoxycillin was rapid with or without a polymer coating. Gastrointestinal transit in rats was investigated by fluorescence microscopy using particles loaded with fluorescein instead of amoxycillin: gastric residence time was longer, and the distribution of the particles on the mucosa apparently better, without any polymer coating.

Colon-specific delivery of budesonide from microencapsulated cellulosic cores: evaluation of the efficacy against colonic inflammation in rats

Budesonide (BDS) is a potent corticosteroid that has important implications in the pharmaco‐therapy of inflammatory bowel disease, especially in the treatment of ulcerative colitis and Crohns disease. BDS is available on the market in the form of enteric‐coated preparations. However these products, similar to other available site‐specific dosage forms, are not sufficiently selective to treat colonic inflammatory bowel disease. The objective of this study was to evaluate the efficacy of a new microparticulate system containing BDS, to treat experimentally induced colitis in rats. This microparticulate system consisted of BDS‐containing hydrophobic cores, microencapsulated within an enteric polymer, which solubilizes at above pH 7, thus combining pH‐sensitive and controlled‐release properties. Colonic injury and inflammation were assessed by measuring colon/bodyweight ratio, myeloperoxidase (MPO) activity, and by scoring macroscopic and histological damage in colitic rats. Rats were treated orally with BDS, included in the developed system, once a day for 4 days after the induction of inflammation. A BDS suspension and BDS‐containing enteric microparticles were included as control formulations in the experimental design. The administration of the new BDS delivery system significantly reduced the colon/bodyweight ratio compared with the administration of control formulations. Similarly, MPO activity and macroscopic and histological damage of the inflamed colonic segments decreased significantly when the BDS formulation was administered, compared with the results obtained after oral administration of the drug suspension. There were no significant differences, however, when the new treatment was compared with the control formulation consisting of simple enteric microparticles.

A new drug nanocarrier consisting of polyarginine and hyaluronic acid.

The purpose of this study was to produce and characterize a variety of nanostructures comprised of the polyaminoacid polyarginine (PArg) and the polysaccharide hyaluronic acid (HA) as a preliminary stage before evaluating their potential application in drug delivery. PArg was combined with high- or low-molecular-weight HA (HMWHA or LMWHA, respectively) to form nanoparticles by simply mixing polymeric aqueous solutions at room temperature. The average size of the resulting nanocarriers was between 116 and 155 nm, and their zeta potential value ranged from +31.3 to -35.9 mV, indicating that the surface composition of the particle could be conveniently modified according to the mass ratio of the polymers. Importantly, the systems prepared with HMWHA remained stable after isolation by centrifugation and in conditions that mimic the physiological medium, whereas particles that incorporated LMWHA were unstable. Transmission electron microscopy showed that the nanostructures made with HMWHA were spherical. Finally, the systems were stable for at least three months at storage conditions (4°C).

Chitosan nanocapsules: a new carrier for nasal peptide delivery

This work describes the preparation and characterization of chitosan (CS)-coated oil nanodroplets (named CS nanocapsules) as well as the evaluation of their potential for enhancing the nasal absorption of peptide drugs, using salmon calcitonin (sCT) as a model peptide. CS nanocapsules were obtained by the solvent displacement technique. The presence of the CS coating in the nanocapsules was noted by transmission electron microscopy and confirmed by the increase in their size and the inversion in the zeta potential (from negative to positive). The association efficiency of sCT to the nanocapsules was high and affected by the presence of the CS coating. After nasal administration to rats, CS nanocapsules led to a hypocalcemic effect significantly enhanced and prolonged in comparison to that corresponding to the uncoated sCT-loaded oil nanodroplets (named also uncoated nanoemulsion) or to the sCT aqueous solutions containing CS. Consequently, the results highlight the critical role of the CS coating in enhancing the transport of the associated peptide and, hence, the potential utility of CS nanocapsules for nasal peptide delivery.

Development of a microencapsulated form of cefuroxime axetil using pH-sensitive acrylic polymers

Cefuroxime axetil (CA) was encapsulated in pH-sensitive acrylic microspheres in order to formulate a suspension dosage form. Using this microencapsulated form it was expected to prevent leaching of the drug from the microspheres into the suspension medium and to assure the release of the drug in the first part of the intestine, thus avoiding changes to its bioavailability. For this purpose, CA was microencapsulated within several types of acrylic polymers by the solvent evaporation and the solvent extraction techniques. The acrylic polymers selected were: Eudragit E (positively charged and soluble at pH 5), Eudragit L-55 (negatively charged and soluble at pH > 5.5) and Eudragit RL (neutral, insoluble, but readily permeable). The influence of the polymer electrical charge on the stability and in vitro release of CA was investigated. Though Eudragit E microspheres presented good morphological characteristics and dissolution behaviour, the analysis of the stability of CA in the presence of Eudragit E by HPLC, indicated a negative interaction between both compounds. However, formulations made of Eudragit L-55 and RL in the ratios 100:0 and 90:10 were adequate in terms of the stability of the encapsulated CA. The dissolution studies showed a critical pH between 5.2 and 6.0, which allowed the complete release of CA in a short period. Furthermore, these polymer microspheres were shown to be efficient in masking the taste of CA.