Polysaccharide colloidal particles as delivery systems for macromolecules

Mucosal delivery of complex molecules such as peptides, proteins, oligonucleotides, and plasmids is one of the most intensively studied subjects. The use of colloidal carriers made of hydrophilic polysaccharides, i.e. chitosan, has arisen as a promising alternative for improving the transport of such macromolecules across biological surfaces. This article reviews the approaches which have aimed to associate macromolecules to chitosan in the form of colloidal structures and analyzes the evidence of their efficacy in improving the transport of the associated molecule through mucosae and epithelia. Chitosan has been shown to form colloidal particles and entrap macromolecules through a number of mechanisms, including ionic crosslinking, desolvation, or ionic complexation, though some of these systems have been realized only in conjunction with DNA molecules. An alternative involving the chemical modification of chitosan has also been useful for the association of macromolecules to self-assemblies and vesicles. To date, the in vivo efficacy of these chitosan-based colloidal carriers has been reported for two different applications: while DNA-chitosan hybrid nanospheres were found to be acceptable transfection carriers, ionically crosslinked chitosan nanoparticles appeared to be efficient vehicles for the transport of peptides across the nasal mucosa. The potential applications and future prospects of these new systems for mucosal delivery of macromolecules are highlighted at the end of the chapter.

Chitosan and chitosan/ethylene oxide-propylene oxide block copolymer nanoparticles as novel carriers for proteins and vaccines

PURPOSE

The aim of this study was to investigate the interaction between the components of novel chitosan (CS) and CS/ethylene oxide-propylene oxide block copolymer (PEO-PPO) nanoparticles and to evaluate their potential for the association and controlled release of proteins and vaccines.

METHODS

The presence of PEO-PPO on the surface of the nanoparticles and its interaction with the CS was identified by X-ray photoelectron spectroscopy (XPS). The mechanism of protein association was elucidated using several proteins, bovine serum albumin (BSA), and tetanus and diphtheria toxoids, and varying the formulation conditions (different pH values and concentrations of PEO-PPO), and the stage of protein incorporation into the nanoparticles formation medium.

RESULTS

BSA and tetanus and diphtheria toxoids were highly associated with CS nanoparticles partly due to electrostatic interactions between the carboxyl groups of the protein and the amine groups of CS. PEO-PPO also interacted electrostatically with CS, thus competing with the proteins for association with CS nanoparticles. A visible amount of PEO-PPO was projected towards the outer phase of the nanoparticles. Proteins were released from the nanoparticles at an almost constant rate, the intensity of which was closely related to the protein loading. Furthermore, the tetanus vaccine was released in the active form for at least 15 days.

CONCLUSIONS

CS and CS/PEO-PPO nanoparticles prepared by a very mild ionic crosslinking technique are novel and suitable systems for the entrapment and controlled release of proteins and vaccines.

Chitosan nanoparticles as delivery systems for doxorubicin

The aim of this paper was to evaluate the potential of chitosan nanoparticles as carriers for the anthracycline drug, doxorubicin (DOX). The challenge was to entrap a cationic, hydrophilic molecule into nanoparticles formed by ionic gelation of the positively charged polysaccharide chitosan. To achieve this objective, we attempted to mask the positive charge of DOX by complexing it with the polyanion, dextran sulfate. This modification doubled DOX encapsulation efficiency relative to controls and enabled real loadings up to 4.0 wt.% DOX. Separately, we investigated the possibility of forming a complex between chitosan and DOX prior to the formation of the particles. Despite the low complexation efficiency, no dissociation of the complex was observed upon formation of the nanoparticles. Fluorimetric analysis of the drug released in vitro showed an initial release phase, the intensity of which was dependent on the association mode, followed by a very slow release. The evaluation of the activity of DOX-loaded nanoparticles in cell cultures indicated that those containing dextran sulfate were able to maintain cytostatic activity relative to free DOX, while DOX complexed to chitosan before nanoparticle formation showed slightly decreased activity. Additionally, confocal studies showed that DOX was not released in the cell culture medium but entered the cells while remaining associated to the nanoparticles. In conclusion, these preliminary studies showed the feasibility of chitosan nanoparticles to entrap the basic drug DOX and to deliver it into the cells in its active form.

Chitosan nanoparticles: a new vehicle for the improvement of the delivery of drugs to the ocular surface. Application to cyclosporin A

Present limitations in the management of extraocular diseases include the inability to provide long-term extraocular drug delivery without compromising intraocular structures and/or systemic drug exposure. In the present study, the potential of chitosan (CS) nanoparticles as a new vehicle for the improvement of the delivery of drugs to the ocular mucosa was investigated. Cyclosporin A (CyA) was chosen as a model compound because of its potential usefulness for the treatment of these local diseases. An ionic gelation technique was conveniently modified in order to produce CyA-loaded CS nanoparticles. These nanoparticles had a mean size of 293 nm, a zeta potential of +37 mV and high CyA association efficiency and loading (73 and 9%, respectively). In vitro release studies, performed under sink conditions, revealed a fast release during the first hour followed by a more gradual drug release during a 24-h period. In vivo experiments showed that, following topical instillation of CyA-loaded CS nanoparticles to rabbits, it was possible to achieve therapeutic concentrations in external ocular tissues (i.e., cornea and conjunctiva) during at least 48 h while maintaining negligible or undetectable CyA levels in inner ocular structures (i.e., iris/ciliary body and aqueous humour), blood and plasma. These levels were significantly higher than those obtained following instillation of a CS solution containing CyA and an aqueous CyA suspension. From these results, we can conclude that CS nanoparticles may represent an interesting vehicle in order to enhance the therapeutic index of clinically challenging drugs with potential application at extraocular level.

Design of biodegradable particles for protein delivery

Major research issues in protein delivery include the stabilization of proteins in delivery devices and the design of appropriate protein carriers in order to overcome mucosal barriers. We have attempted to combine both issues through the conception of new biodegradable polymer nanoparticles: (i) poly(ethylene glycol) (PEG)-coated poly(lactic acid) (PLA) nanoparticles, chitosan (CS)-coated poly(lactic acid-glycolic acid (PLGA) nanoparticles and chitosan (CS) nanoparticles. These nanoparticles have been tested for their ability to load proteins, to deliver them in an active form, and to transport them across the nasal and intestinal mucosae. Additionally, the stability of some of these nanoparticles in simulated physiological fluids has been studied. Results showed that the PEG coating improves the stability of PLA nanoparticles in the gastrointestinal fluids and helps the transport of the encapsulated protein, tetanus toxoid, across the intestinal and nasal mucosae. Furthermore, intranasal administration of these nanoparticles provided high and long-lasting immune responses. On the other hand, the coating of PLGA nanoparticles with the mucoadhesive polymer CS improved the stability of the particles in the presence of lysozyme and enhanced the nasal transport of the encapsulated tetanus toxoid. Finally, nanoparticles made solely of CS were also stable upon incubation with lysozyme. Moreover, these particles were very efficient in improving the nasal absorption of insulin as well as the local and systemic immune responses to tetanus toxoid, following intranasal administration. In summary, these results show that a rational modification in the composition and structure of the nanoparticles, using safe materials, increases the prospects of their usefulness for mucosal protein delivery and transport.

Enhancement of nasal absorption of insulin using chitosan nanoparticles

PURPOSE

To investigate the potential of chitosan nanoparticles as a system for improving the systemic absorption of insulin following nasal instillation.

METHODS

Insulin-loaded chitosan nanoparticles were prepared by ionotropic gelation of chitosan with tripolyphosphate anions. They were characterized for their size and zeta potential by photon correlation spectroscopy and laser Doppler anemometry, respectively. Insulin loading and release was determined by the microBCA protein assay. The ability of chitosan nanoparticles to enhance the nasal absorption of insulin was investigated in a conscious rabbit model by monitoring the plasma glucose levels.

RESULTS

Chitosan nanoparticles had a size in the range of 300-400 nm, a positive surface charge and their insulin loading can be modulated reaching values up to 55% [insulin/nanoparticles (w/w): 55/100]. Insulin association was found to be highly mediated by an ionic interaction mechanism and its release in vitro occurred rapidly in sink conditions. Chitosan nanoparticles enhanced the nasal absorption of insulin to a greater extent than an aqueous solution of chitosan. The amount and molecular weight of chitosan did not have a significant effect on insulin response.

CONCLUSIONS

Chitosan nanoparticles are efficient vehicles for the transport of insulin through the nasal mucosa.

Influence of experimental parameters on the characteristics of poly(lactic acid) nanoparticles prepared by a double emulsion method

Nanoparticles were prepared by the double emulsion method (w/o/w), using methylene chloride as an organic solvent and polyvinyl alcohol (PVA) or human serum albumin (HSA) as a surfactant. Experimental parameters such as the preparation temperature, the solvent evaporation methods, the internal aqueous phase volume, the surfactant concentration and the polymer molecular weight were investigated for particle size, the zeta potential, the residual surfactant percentage and the polydispersity index. Preparation parameters leading to particles with well-defined characteristics such as an average size around 200 nm and a polydispersity index lower than 0.1 were identified. The conditions were optimized to ensure protein encapsulation: a cool temperature, a short processing time, a sufficient internal aqueous phase and careful washing. It appeared that the higher the surfactant concentration in the external aqueous phase was, the smaller the particles, the lower the polydispersity index and the higher the residual amount of surfactant were. For PVA or HSA, the agreement between the convenient surfactant concentration and its critical aggregation concentration could be emphasized. Otherwise, an increased polymer molecular weight led both to a slightly decreased particle size and to a lower polydispersity index. Moreover, multilayer absorption of PVA which does not depend on Poly(lactic-acid) molecular weight was exhibited. Finally, the zeta potential resulted from the polymer molecular weight and the residual PVA.

Stealth PLA-PEG nanoparticles as protein carriers for nasal administration

PURPOSE

The aim of the study was to encapsulate a model protein antigen, tetanus toxoid (TT), within hydrophobic (PLA) and surface hydrophilic (PLA-PEG) nanoparticles and to evaluate the potential of these colloidal carriers for the transport of proteins through the nasal mucosa.

METHODS

TT-loaded nanoparticles, prepared by a modified water-in-oil-in-water solvent evaporation technique, were characterized in their size, zeta potential and hydrophobicity. Nanoparticles were also assayed in vitro for their ability to deliver active antigen for extended periods of time. Finally, 125I-TT-loaded nanoparticles were administered intranasally to rats and the amount of radioactivity recovered in the blood compartment, lymph nodes and other relevant tissues was monitored for up to 48 h.

RESULTS

PLA and PLA-PEG nanoparticles had a similar particle size (137-156 nm) and negative surface charge, but differed in their surface hydrophobicity: PLA were more hydrophobic than PLA-PEG nanoparticles. PLA-PEG nanoparticles, especially those containing gelatine as an stabilizer, provided extended delivery of the active protein. The transport of the radiolabeled protein through the rat nasal mucosa was highly affected by the surface properties of the nanoparticles: PLA-PEG nanoparticles led to a much greater penetration of TT into the blood circulation and the lymph nodes than PLA nanoparticles. Furthermore, after administration of 125I-TT-loaded PLA-PEG nanoparticles, it was found that a high amount of radioactivity persisted in the blood compartment for at least 48 h.

CONCLUSIONS

A novel nanoparticulate system has been developed with excellent characteristics for the transport of proteins through the nasal mucosa.

Comparative uptake studies of bioadhesive and non-bioadhesive nanoparticles in human intestinal cell lines and rats: the effect of mucus on particle adsorption and transport

PURPOSE

The interaction of nanoparticles (NP), consisting of hydrophobic polystyrene, bioadhesive chitosan, and stealth PLA-PEG with two human intestinal cell lines, the enterocyte-like Caco-2 and mucus-secreting MTX-E12, was investigated and compared to the in vivo NP uptake in rats.

METHODS

The extent and mechanism of cellular association of different NP with Caco-2 and MTX-E12 was investigated using confocal laser scanning microscopy (CLSM) and a cellular association assay. In vitro results were compared to gastrointestinal distribution of chitosan NP in rats after intra-duodenal injection.

RESULTS

Cellular association of NP with Caco-2 cell monolayers showed the following rank order: polystyrene > chitosan >> PLA-PEG. Mucus (MTX-E12) significantly decreased the association of hydrophobic polystyrene NP. While no mucus binding was observed for PLA-PEG, association of chitosan NP with mucus strongly increased. Intra-duodenal administration of chitosan NP in rats confirmed these in vitro results, demonstrating that NP could be detected in both epithelial cells and Peyer's patches. Chitosan NP internalization was saturable, as well as energy- and temperature-dependent. It could be inhibited by an excess of protamine and by removal of anionic sites of the apical membrane. By contrast, polystyrene NP uptake was found to be largely independent of these factors, except for a temperature-dependency.

CONCLUSIONS

In contrast to Caco-2 cells, the presence of mucus presented a major barrier for the uptake of hydrophobic polystyrene NP and showed an even more profound effect upon the uptake of chitosan NP. A correlation between the uptake in cell culture models and in vivo rat epithelial cells was confirmed for chitosan NP. Moreover, chitosan NP seemed to be taken up and transported by adsorptive transcytosis, while polystyrene NP uptake was probably mediated by non-adsorptive transcytosis.

Transmucosal macromolecular drug delivery

Mucosal surfaces are the most common and convenient routes for delivering drugs to the body. However, macromolecular drugs such as peptides and proteins are unable to overcome the mucosal barriers and/or are degraded before reaching the blood stream. Among the approaches explored so far in order to optimize the transport of these macromolecules across mucosal barriers, the use of nanoparticulate carriers represents a challenging but promising strategy. The present paper aims to compare the characteristics and potential of nanostructures based on the mucoadhesive polysaccharide chitosan (CS). These are CS nanoparticles, CS-coated oil nanodroplets (nanocapsules) and CS-coated lipid nanoparticles. The characteristics and behavior of CS nanoparticles and CS-coated lipid nanoparticles already reported [A. Vila, A. Sanchez, M. Tobio, P. Calvo, M.J. Alonso, Design of biodegradable particles for protein delivery, J. Control. Rel. 78 (2002) 15-24; R. Fernandez-Urrusuno, P. Calvo, C. Remunan-Lopez, J.L. Vila-Jato, M.J. Alonso, Enhancement of nasal absorption of insulin using chitosan nanoparticles, Pharm. Res. 16 (1999) 1576-1581; M. Garcia-Fuentes, D. Torres, M.J. Alonso, New surface-modified lipid nanoparticles as delivery vehicles for salmon calcitonin (submitted for publication).] are compared with those of CS nanocapsules originally reported here. The three types of systems have a size in the nanometer range and a positive zeta potential that was attributed to the presence of CS on their surface. They showed an important capacity for the association of peptides such as insulin, salmon calcitonin and proteins, such as tetanus toxoid. Their mechanism of interaction with epithelia was investigated using the Caco-2 model cell line. The results showed that CS-coated systems caused a concentration-dependent reduction in the transepithelial resistance of the cell monolayer. Moreover, within the range of concentrations investigated, these systems were internalized in the monolayer in a concentration-dependent manner. This uptake was slightly enhanced by the presence of the CS coating but, as compared with previously published results [M. Garcia-Fuentes, C. Prego, D. Torres, M.J. Alonso, Triglyceride-chitosan nanostructures for oral calcitonin delivery: evaluation in the Caco-2 cell model and in vivo (submitted for publication)], highly dependent on the nature of the lipid core. Nevertheless, these differences in the uptake of the CS-coated systems (solid lipid core or oily core) by the Caco-2 cells did not have a consequence in the in vivo behaviour. Indeed, both CS-coated systems (nanocapsules and CS-coated nanoparticles) showed an important capacity to enhance the intestinal absorption of the model peptide, salmon calcitonin, as shown by the important and long-lasting decrease in the calcemia levels observed in rats.

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.

Chitosan Nanoparticles as New Ocular Drug Delivery Systems: in Vitro Stability, in Vivo Fate, and Cellular Toxicity

PURPOSE

To assess the potential of chitosan (CS) nanoparticles for ocular drug delivery by investigating their interaction with the ocular mucosa in vivo and also their toxicity in conjunctival cell cultures.

METHODS

Fluorescent (CS-fl) nanoparticles were prepared by ionotropic gelation. The stability of the particles in the presence of lysozyme was investigated by determining the size and their interaction with mucin, by measuring the viscosity of the mucin dispersion. The in vivo interaction of CS-fl nanoparticles with the rabbit cornea and conjunctiva was analyzed by spectrofluorimetry and confocal microscopy. Their potential toxicity was assessed in a human conjunctival cell line by determining cell survival and viability.

RESULTS

CS-fl nanoparticles were stable upon incubation with lysozyme and did not affect the viscosity of a mucin dispersion. In vivo studies showed that the amounts of CS-fl in cornea and conjunctiva were significantly higher for CS-fl nanoparticles than for a control CS-fl solution, these amounts being fairly constant for up to 24 h. Confocal studies suggest that nanoparticles penetrate into the corneal and conjunctival epithelia. Cell survival at 24 h after incubation with CS nanoparticles was high and the viability of the recovered cells was near 100%.

CONCLUSIONS

CS nanoparticles are promising vehicles for ocular drug delivery.

Poly(lactic acid)-poly(ethylene glycol) nanoparticles as new carriers for the delivery of plasmid DNA

The purpose of the present work was to produce and characterize poly(lactic acid)-poly(ethylene glycol) (PLA-PEG) nanoparticles (size lower than 300 nm) containing a high loading of plasmid DNA in a free form or co-encapsulated with either poly(vinyl alcohol) (PVA) or poly(vinylpyrrolidone) (PVP). The plasmid alone or with PVA or PVP was encapsulated by two different techniques: an optimized w/o/w emulsion-solvent evaporation technique as well as by a new w/o emulsion-solvent diffusion technique. Particle size, zeta potential, plasmid DNA loading and in vitro release were determined for the three plasmid-loaded formulations. The influence of the initial plasmid loadings (5, 10, 20 microg plasmid DNA/mg PLA-PEG) on those parameters was also investigated. The plasmid loaded into the nanoparticles and released in vitro was quantified by fluorimetry and the different molecular forms were identified by gel electrophoresis. PLA-PEG nanoparticles containing plasmid DNA in a free form or co-encapsulated with PVA or PVP were obtained in the range size of 150-300 nm and with a negative zeta potential, both parameters being affected by the preparation technique. Encapsulation efficiencies were high irrespective of the presence of PVA or PVP (60-90%) and were slightly affected by the preparation technique and by the initial loading. The final plasmid DNA loading in the nanoparticles was up to 10-12 microg plasmid DNA/mg polymer. Plasmid DNA release kinetics varied depending on the plasmid incorporation technique: nanoparticles prepared by the w/o diffusion technique released their content rapidly whereas those obtained by the w/o/w showed an initial burst followed by a slow release for at least 28 days. No significant influence of the plasmid DNA loading and of the co-encapsulation of PVP or PVA on the in vitro release rate was observed. In all cases the conversion of the supercoiled form to the open circular and linear forms was detected. In conclusion, plasmid DNA can be very efficiently encapsulated, either in a free form or in combination with PVP and PVA, into PLA-PEG nanoparticles. Additionally, depending on the processing conditions, these nanoparticles release plasmid DNA either very rapidly or in a controlled manner.

Biodegradable microspheres as controlled-release tetanus toxoid delivery systems

Purified tetanus toxoid, a high-molecular-weight protein, was entrapped within poly(L-lactic acid) (PLA) and poly(D,L-lactic/glycolic acid) (PLGA) microspheres prepared by either a solvent extraction or a solvent evaporation method carried out in a multiple emulsion system (water-in-oil-in-water). The physical integrity and antigenicity of the protein treated under different processing conditions were investigated. A reduction of antigenicity that was related to the percentage of aggregated protein was noticed under some experimental conditions. This partial loss of antigenicity was associated with the lyophilization process and affected by the nature of the organic solvent. All types of microspheres prepared with different molecular weight PLA and PLGA displayed a high protein-loading efficiency (> 80%) but their size was strongly influenced by polymer molecular weight (3000 versus 100,000). Protein release pattern was influenced by both polymer molecular weight and composition (PLA versus PLGA). A constant release pattern after an induction period of 10 days was observed for microspheres composed of high-molecular-weight polymers (PLA and PLGA). The release rate was lower from PLA microspheres than from PLGA microspheres. In contrast, a continuously increasing release rate preceded by a burst was observed for low-molecular-weight (3000) PLGA microspheres. Microencapsulated tetanus toxoid was significantly more immunogenic in mice than fluid toxoid as determined by IgG anti-tetanus antibody levels and neutralizing antibodies. However, the magnitude and duration of the antibody response did not differ significantly from a similar dose of aluminium phosphate-adsorbed toxoid. We conclude that microencapsulated tetanus toxoid shows significant adjuvant activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Chitosan–PEG nanocapsules as new carriers for oral peptide delivery

We have previously reported the ability of chitosan nanocapsules to enhance and prolong the oral absorption of peptides. In the present work, our goal was to design a new type of nanocapsules, using chitosan chemically modified with poly(ethylene glycol) (PEG) (0.5% and 1% pegylation degree) and to investigate the consequences of this modification on the in vitro and in vivo behaviour of the nanocapsules. Chitosan-PEG nanocapsules and the control PEG-coated nanoemulsions were obtained by the solvent displacement technique. Their size was in the range of 160-250 nm. Their zeta potential was greatly affected by the nature of the coating, being positive for chitosan-PEG nanocapsules and negative in the case of PEG-coated nanoemulsions. The presence of PEG, whether alone or grafted to chitosan, improved the stability of the nanocapsules in the gastrointestinal fluids. Using the Caco-2 model cell line it was observed that the pegylation of chitosan reduced the cytotoxicity of the nanocapsules. In addition, these nanocapsules did not cause a significant change in the transepithelial resistance of the monolayer. Finally, the results of the in vivo studies showed the capacity of chitosan-PEG nanocapsules to enhance and prolong the intestinal absorption of salmon calcitonin. Additionally, they indicated that the pegylation degree affected the in vivo performance of the nanocapsules. Therefore, by modulating the pegylation degree of chitosan, it was possible to obtain nanocapsules with a good stability, a low cytotoxicity and with absorption enhancing properties.

Current status of selected oral peptide technologies in advanced preclinical development and in clinical trials

The development of oral dosage forms that allows absorption of therapeutic peptides to the systemic circulation is one of the greatest challenges for the pharmaceutical industry. Currently, a number of technologies including either mixtures of penetration enhancers or protease inhibitors and/or nanotechnology-based products are under clinical development. Typically, these formulations are presented in the form of enteric-coated tablets or capsules. Systems undergoing preclinical investigation include further advances in nanotechnology, including intestinal microneedle patches, as well as their combination with regional delivery to the colon. This review critically examines four selected promising oral peptide technologies at preclinical stage and the twelve that have progressed to clinical trials, as indicated in www.clinicaltrials.gov. We examined these technologies under the criteria of peptide selection, formulation design, system components and excipients, intestinal mechanism of action, efficacy in man, and safety issues. The conclusion is that most of the technologies in clinical trials are incremental rather than paradigm-shifting and that even the more clinically advanced oral peptide drugs examples of oral bioavailability appear to yield oral bioavailability values of only 1-2% and are, therefore, only currently suitable for a limited range of peptides.

Role of hippocampal signaling pathways in long-term memory formation of a nonassociative learning task in the rat

Long-term habituation to a novel environment is one of the most elementary forms of nonassociative learning. Here we studied the effect of pre- or posttraining intrahippocampal administration of drugs acting on specific molecular targets on the retention of habituation to a 5-min exposure to an open field measured 24 h later. We also determined whether the exposure to a novel environment resulted in the activation of the same intracellular signaling cascades previously shown to be activated during hippocampal-dependent associative learning. The immediate posttraining bilateral infusion of CNQX (1 microg/side), an AMPA/kainate glutamate receptor antagonist, or of muscimol (0.03 microg/side), a GABA(A) receptor agonist, into the CA1 region of the dorsal hippocampus impaired long-term memory of habituation. The NMDA receptor antagonist AP5 (5 microg/side) impaired habituation when infused 15 min before, but not when infused immediately after, the 5-min training session. In addition, KN-62 (3.6 ng/side), an inhibitor of calcium calmodulin-dependent protein kinase II (CaMKII), was amnesic when infused 15 min before or immediately and 3 h after training. In contrast, the cAMP-dependent protein kinase (PKA) inhibitor Rp-cAMPS, the mitogen-activated protein kinase kinase (MAPKK) inhibitor PD098059, and the protein synthesis inhibitor anisomycin, at doses that fully block memory formation of inhibitory avoidance learning, did not affect habituation to a novel environment. The detection of spatial novelty is associated with a sequential activation of PKA, ERKs (p44 and p42 MAPKs) and CaMKII and the phosphorylation of c-AMP responsive element-binding protein (CREB) in the hippocampus. These findings suggest that memory formation of spatial habituation depends on the functional integrity of NMDA and AMPA/kainate receptors and CaMKII activity in the CA1 region of the hippocampus and that the detection of spatial novelty is accompanied by the activation of at least three different hippocampal protein kinase signaling cascades.

Nanomedicines for overcoming biological barriers

Drug delivery is an interdisciplinary area of research that aims at making the administration of complex new drugs feasible, as well as adding critical value to the drugs that are currently in the market. At present, one of the most attractive areas of research in drug delivery is the design of nanomedicines consisting of nanosystems that are able to deliver drugs to the right place, at appropriate times. The goal of the present article is to review the advances we have made in the development and characterization of nanosystems intended to be used as drug carriers for mucosal administration. These nanocarriers are able to protect the associated drug against degradation and facilitate its transport across critical and specific barriers. Some of them, are further able to release the associated drug to the target tissue in a controlled manner. These nanocarriers have been made of safe materials, including synthetic biodegradable polymers, lipids and polysaccharides. A number of nanotechnologies have been developed that enable the association of a variety of drugs to these nanocarriers, ranging from classical small drug to large DNA fragments. The in vitro cell culture studies and the in vivo experiments have evidenced the potential of these nanocarriers for overcoming important mucosal barriers, such as the intestinal, nasal and ocular barriers. Hopefully, this will soon represent a strategy for making cheaper and faster, more efficacious medicines.

Protein encapsulation and release from poly(lactide-co-glycolide) microspheres: effect of the protein and polymer properties and of the co-encapsulation of surfactants

Despite the recognised role of the poly(lactide-co-glycolide) (PLGA) in the encapsulation and release of proteins from PLGA microspheres, the importance that the characteristics of the protein have in these processes has not yet been sufficiently investigated. The aim of this work was to study the simultaneous effect of the protein and PLGA properties and of the microencapsulation process on the physicochemical and in vitro release characteristics of protein-loaded PLGA microspheres. Two model proteins of different isoelectric points (pI), bovine serum albumin (BSA) (pI = 4.6) and lysozyme (LZM) (pI = 11.2), and two different molecular weights (Mw) of PLGA were selected. Microspheres were prepared using the water-in-oil-in-water (w/o/w) solvent extraction and the oil-in-oil (o/o) solvent evaporation techniques. Results showed that BSA was efficiently encapsulated independent of the PLGA Mw, whereas the encapsulation of LZM was favoured with the low Mw PLGA. The co-encapsulation of a surfactant (poloxamer 188 or 331) reduced the protein encapsulation efficiency, especially of BSA. These results suggested that the tensoactive properties of the protein and its affinity for the PLGA are major determinants of the protein encapsulation. Both proteins released faster from the microspheres prepared by the o/o solvent evaporation procedure, with respect to those prepared by the w/o/w solvent extraction technique. In addition, both polymer Mw and protein type had an effect on the protein release rate. The release rate of both proteins, in the absence of a surfactant, was faster from the low Mw PLGA microspheres. However, the release rate constant was higher for BSA than for LZM irrespective of the PLGA Mw. In addition, the co-encapsulation of a surfactant led, in most cases, to a faster release of the encapsulated protein. To conclude, these results suggest that protein release from PLGA microspheres is not only governed by the PLGA erosion rate and protein diffusion through the water-filled channels, but is highly affected by the protein properties and its possible interaction with PLGA and its degradation products.

The ubiquitin-proteasome cascade is required for mammalian long-term memory formation

It has been recently demonstrated that ubiquitin-proteasome-mediated proteolysis is required for long-term synaptic facilitation in Aplysia. Here we show that the hippocampal blockade of this proteolytic pathway is also required for the formation of long-term memory in the rat. Bilateral infusion of lactacystin, a specific proteasome inhibitor, to the CA1 region caused full retrograde amnesia for a one-trial inhibitory avoidance learning when given 1, 4 or 7h, but not 10 h, after training. Proteasome inhibitor I produced similar effects. In addition, inhibitory avoidance training resulted in an increased ubiquitination and 26S proteasome proteolytic activity and a decrease in the levels of IkappaB, a substrate of the ubiquitin-proteasome cascade, in hippocampus 4 h after training. Together, these findings indicate that the ubiquitin-proteasome cascade is crucial for the establishment of LTM in the behaving animal.

Self-assembled particles of an elastin-like polymer as vehicles for controlled drug release

Elastin-like polymers (ELPs) are a new kind of protein-based polymers showing interesting properties in the biomaterial field. This work explored the use of self-assembled poly(VPAVG) micro- and nanoparticles as vehicles for the controlled release of the model drug dexamethasone phosphate (DMP). Poly(VPAVG) has shown to form stable particles with a size below 3 mum as a water or PBS polymer solution was warmed above its transition temperature ( approximately 30 degrees C). Due to the peculiar composition of the monomer, the formation and redissolution of the self-assembled microparticles shows an interesting hysteresis behaviour by which the particles are formed at this temperature but do not redissolve until a strong undercooling of approximately 12-15 degrees C is achieved. Therefore, the particles, once formed, are stable either at room or body temperature. These self-assembled particles are able to encapsulate significant amounts of the model drug when self-assembling was carried out in a co-solution polymer-DMP. The release profiles showed a sustained DMP release for about 30 days. Being the potential of this new polymeric carrier high, further research is being conducted to functionalise the poly(VPAVG) base as a way to induce a stronger polymer-drug binding and, accordingly, a more sustained release.

Determinants of release rate of tetanus vaccine from polyester microspheres

Controlled-release formulations based on poly(lactic) (PLA) and poly(lactic/glycolic) acid (PLGA) microspheres containing tetanus vaccine were designed. The polymers forming the microspheres were L-PLA of different molecular weights and DL-PLGA, 50:50. These microspheres were prepared by two solvent elimination procedures, both using a double emulsion, and were characterized for size, morphology, and toxoid release kinetics. The influence of formulation variables such as polymer type, vaccine composition, and vaccine/polymer ratio was also investigated. Both techniques yielded microspheres with similar size, morphology, and release properties. Microsphere size was dependent on the type of polymer and the presence of the surfactant L-alpha-phosphatidylcholine, which led to a reduction in microsphere size. On the other hand, the release kinetics of encapsulated protein were affected by the polymer properties (ratio lactic/glycolic acid and molecular weight) as well as by the vaccine composition, vaccine loading, and microsphere size. Moreover, for some formulations, a decrease in microsphere size occurred simultaneously, with an increase in porosity leading to an augmentation of release rate. The changes in the PLA molecular weight during in vitro release studies indicated that release profiles of tetanus toxoid from these microspheres were only marginally influenced by polymer degradation. A significant fraction of protein (between 15 and 35%) was initially released by diffusion through water-filled channels. In contrast, the decrease in the PLGA molecular weight over the first 10 days of incubation suggested that erosion of the polymer matrix substantially affects protein release from these microspheres. Among all formulations developed, two differing in microsphere size, polymer hydrophobicity, and release profile were selected for in vivo administration to mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative in vitro evaluation of several colloidal systems, nanoparticles, nanocapsules, and nanoemulsions, as ocular drug carriers

Three different colloidal carriers, namely, nanoparticles and nanocapsules made of poly-epsilon-caprolactone and submicron emulsions, were designed, and their capacity for increasing the comeal penetration of drugs was investigated. The three systems differed in their inner structure and composition, but they had a similar size (200-250 nm) and a negative superficial charge (-16 to -42 mV). Indomethacin, which was used as a model drug, was dispersed at a molecular level within the colloidal systems, no chemical interaction between the polymer and the drug being detected. Release of the encapsulated indomethacin occurred very rapidly upon high dilution in a buffered medium and was independent of the composition of the system. The in vitro comeal penetration of the encapsulated indomethacin was more than 3-fold that of the commercial eye drops. This increased penetration was similar for the three formulations investigated, which therefore excludes the influence of the inner structure or chemical composition of the colloidal systems on the comeal penetration of indomethacin. Thus, it could be stated that the main factor responsible for the favorable comeal transport of indomethacin is the colloidal nature of these carriers rather than their inner structure or composition.

Chitosan nanoparticles as a potential drug delivery system for the ocular surface: toxicity, uptake mechanism and in vivo tolerance

PURPOSE

To study the in vitro and in vivo interaction of chitosan nanoparticles (CSNPs), a new particulate drug carrier, with epithelial cells on the ocular surface.

METHODS

CSNPs labeled with fluorescein isothiocyanate-bovine serum albumin were produced by ionotropic gelation. Human conjunctival epithelial cells (IOBA-NHC) were exposed for 15, 30, 60, and 120 minutes to three different CSNP concentrations. Immediately after treatment and after a 24-hour recovery period in culture medium, cell survival, and viability were measured. The association of CSNPs with IOBA-NHC cells was investigated by confocal microscopy. The influence of temperature and the effect of metabolic inhibition were studied by fluorometry. The in vivo uptake and acute tolerance of the ocular surface to CSNPs were evaluated in rabbits.

RESULTS

Cell survival and viability of CSNP-exposed cells were equivalent to that of the control. Uptake of CSNPs was continuous for the 2-hour duration of these experiments and was temperature dependent. Metabolic inhibition by sodium azide had no effect on CSNP uptake. The rabbit ocular surface showed no signs of inflammation or alteration after CSNP exposure compared with the control. Fluorescence microscopy of rabbit eyeball and lid sections confirmed in vivo uptake by conjunctival and corneal epithelia.

CONCLUSIONS

CSNPs were internalized by IOBA-NHC cells by an active transport mechanism that did not compromise cell viability. Moreover, these nanoparticles were well tolerated by the ocular surface tissues. These facts add further support for the potential use of these colloidal systems to delivery drugs to the ocular surface.

Genetic induction of proinflammatory immunity in children with biliary atresia

BACKGROUND

Biliary atresia is the commonest cause of pathological jaundice in infants and the leading indication for liver transplantation in children worldwide. The cause and pathogenesis remain largely unknown. Because of clinical heterogeneity and experimental difficulties in addressing molecular mechanisms underlying multifactorial disorders in human beings, we searched for genomic signatures of biliary atresia in affected infants.

METHODS

We generated pools of biotinylated cRNA from livers of 14 infants with biliary atresia and six with neonatal intrahepatic cholestasis (diseased controls) and hybridised the cRNA against oligonucleotide-based gene chips. Immunohistochemistry and reverse transcriptase (RT)-PCR were used to assess the specificity of the findings and functional commitment of lymphocytes in affected livers.

FINDINGS

Data filtering, to identify genes that are differentially expressed, and cluster analysis revealed a predominant and coordinated activation of immunity/inflammation genes within the livers of infants with biliary atresia. Most of the genes showed differential lymphocyte function, with activation of osteopontin, a regulator of cell-mediated (T-helper 1 [Th-1]) immunity in T-helper lymphocytes, and suppression of immunoglobulin genes in early stages of disease. These findings were associated with production of interferon gamma in 65% of infants with biliary atresia and no diseased control. However, histologically similar inflammatory infiltrates were present in livers of both groups, implying differential activation states of similar cell types.

INTERPRETATION

Livers of infants with biliary atresia have a coordinated activation of genes involved in lymphocyte differentiation. Among these genes, the overexpression of osteopontin and interferon gamma points to a potential role of Th-1-like cytokines in disease pathogenesis.