C. Prego

Chitosan-based nanoparticles for improving immunization against hepatitis B infection

The design of effective vaccine delivery vehicles is opening up new possibilities for making immunization more equitable, safe and efficient. In this work, we purpose polysaccharidic-based nanoparticles as delivery structures for virus-like particle antigens, using recombinant hepatitis B surface antigen (rHBsAg) as a model. Polysaccharidic-based nanoparticles were prepared using a very mild ionic gelation technique, by cross-linking the polysaccharide chitosan (CS) with a counter ion. The resulting nanoparticles could be easily isolated with a size in the nanometric range (160-200 nm) and positive surface charge (+6 to +10 mV). More importantly, CS-based nanoparticles allowed the efficient association of the antigen (>60%) while maintaining the antigenic epitope intact, as determined by ELISA and Western blot. The entrapped antigen was further released in vitro from the nanoparticles in a sustained manner without compromising its antigenicity. In addition, loaded CS-based nanoparticles were stable, and protected the associated antigen during storage, either as an aqueous suspension under different temperature conditions (+4 degrees C and -20 degrees C), or as a dried form after freeze-drying the nanoparticles. Finally, immunization studies showed the induction of important seroprotection rates after intramuscular administration of the nanoparticles, indicating their adjuvant capacity. In fact, CS-based nanoparticles were able to induce anti-HBsAg IgG levels up to 5500 mIU/ml, values 9-fold the conventional alum-adsorbed vaccine. In conclusion, we report here a polysaccharidic nanocarrier which exhibits a number of in vitro and in vivo features that make it a promising adjuvant for vaccine delivery of subunit antigens.

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.

Surface-modified PLGA-based nanoparticles that can efficiently associate and deliver virus-like particles

AIM To design and develop a new nanocarrier appropriately engineered for the adequate accommodation of a virus-like particle, the recombinant hepatitis B surface antigen (22 nm), and intended to be used for the transmucosal delivery of the associated antigen. The nanoparticles consisted of a core blend of poly(D,L-lactide-co-glycolide) and poloxamer 188, and a hydrophilic shell of chitosan. RESULTS By by conveniently adapting the nanoprecipitation technique, it was possible to associate a significant amount of active antigen (44%) to the nanocarrier. The resulting nanosystems had a size of around 200 nm and positive zeta potential attributed to the association of chitosan. The nanoparticles were able to deliver the associated antigen in a controlled manner for up to 14 days without compromising its activity, as determined by ELISA. Moreover, the antigenicity of the recombinant hepatitis B surface antigen was preserved for at least 14 days, when stored as an aqueous suspension, and for at least 3 months when converted in a freeze-dried powder. CONCLUSION Poly(D,L,lactic-co-glycolic acid)-based nanoparticles represent a promising approach for the delivery of virus-like-particles.

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.

From single-dose vaccine delivery systems to nanovaccines

The application of micro- and nanotechnologies to the development of vaccine delivery systems started in the 70s. From that time onwards, significant advances in this field have opened up opportunities in the research of new adjuvants and the design of safer and more effective vaccines. The versatility of vaccine delivery vehicles represents an important feature in vaccine development. Indeed, the modulation of the composition, particle size and/or surface properties, offers a wide range of possibilities for overcoming natural barriers and controlling antigen release. Thus, it is currently accepted that besides their ability to enhance the low immunogenicity of new subunit and DNA vaccines, these delivery carriers represent a promising strategy for needle-free and single-dose vaccination. In this review article we aim to present the historical advances made in the field of vaccine delivery, particularly the progress made in the last two decades, describing our specific contribution, ranging from the idea of single-dose vaccination to the current concept of nanovaccines. Overall, this review illustrates the potential of nanosciences and nanotechnologies to solve the current problems of vaccination and, thus, to expand the immunization coverage worldwide.