Catarina Gonçalves

Self-Assembled Hydrogel Nanoparticles for Drug Delivery Applications

Hydrogel nanoparticles—also referred to as polymeric nanogels or macromolecular micelles—are emerging as promising drug carriers for therapeutic applications. These nanostructures hold versatility and properties suitable for the delivery of bioactive molecules, namely of biopharmaceuticals. This article reviews the latest developments in the use of self-assembled polymeric nanogels for drug delivery applications, including small molecular weight drugs, proteins, peptides, oligosaccharides, vaccines and nucleic acids. The materials and techniques used in the development of self-assembling nanogels are also described.

Dextrin nanoparticles: Studies on the interaction with murine macrophages and blood clearance

The uptake of nanoparticles by cells of the mononuclear phagocytic system limits its use as colloidal drug carriers, reducing the blood circulation time and the ability to reach biological targets. In this work, the interaction between dextrin nanoparticles--recently developed in our laboratory--and murine bone marrow-derived macrophages was evaluated. Cytotoxicity and nitric oxide production were studied, using the MTT assay and the Griess method, respectively. FITC labelled nanoparticles were used to assess the phagocytic uptake and blood clearance after intravenous injection. The phagocytic uptake was analysed in vitro by confocal laser scanning microscopy and fluorescence activated cell sorting. The results show that the nanoparticles are not cytotoxic and do not stimulate the production of nitric oxide by macrophages, in the range of concentrations studied. Nanoparticles are phagocytosed by macrophages and are detected inside the cells, concentrated in cellular organelles. The blood clearance study showed that the blood removal of the nanoparticles occurs with a more pronounced rate in the first 3 h after intravenous administration, with about 30% of the material remaining in systemic circulation at this stage. Given the fairly high blood circulation time and biocompatibility, the dextrin nanoparticles are promising carriers for biomedical applications. Both applications targeting phagocytic, antigen-presenting cells (for vaccination purposes) and different tissues (as drug carriers) may be envisaged, by modulation of the surface properties.

Biological activity of heterologous murine interleukin-10 and preliminary studies on the use of a dextrin nanogel as a delivery system

Interleukin-10 (IL-10) is an anti-inflammatory cytokine, which active form is a non-covalent homodimer with two intramolecular disulphide bonds essential for its biological activity. A mutated form of murine IL-10 was successfully expressed in E. coli, recovered and purified from inclusion bodies. Its ability to reduce tumor necrosis factor α synthesis and down-regulate class II major histocompatibility complex molecules expression on endotoxin-stimulated bone marrow-derived macrophages was confirmed, and shown to be similar to that of a commercially available IL-10. Given the potential of IL-10 for application in various medical conditions, it is essential to develop systems that can effectively deliver the protein. In this work it is shown that a dextrin nanogel effectively incorporate IL-10, stabilize, and enable the slow release of biologically active IL-10 over time. Altogether, these results demonstrate the suitability of dextrin nanogel to be used as a system for the controlled release of IL-10.

Characterization of dextrin hydrogels by FTIR spectroscopy and solid state NMR spectroscopy

Abstract Fourier transform infrared (FTIR) and 13C solid state nuclear magnetic resonance (NMR) spectroscopy were used to study dextrin structural changes occurring upon hydrogel formation by vinyl acrylate (VA) grafting and subsequent free radical polymerization. The degrees of VA substitution (DS) and polymerization (DP) were quantified up to 40%VA by FTIR intensity measurements and partial least squares (PLS)/FTIR, the latter being a faster and less error-prone method. Above 40%VA, both parameters are underestimated by FTIR. A spin counting NMR experiment showed high carbon observabilities for hydrogels and improved PLS/NMR models were achieved for DS and DP determination. Alternative NMR integration methods are hindered by the broad VA peaks and need for area correction, due to their CP dynamics. NMR changes in C1 profile showed that a single helical conformation predominates at lower %VA, being replaced by disordered conformations as %VA increases. Furthermore, a correlation FTIR/NMR study indicated that ring conformations are significantly affected in hydrogels, compared to unpolymerized dextrin.

A novel crosslinked hyaluronic acid nanogel for drug delivery.

An amphiphilic hyaluronic acid conjugate is successfully developed based on grafting a thiolated hydrophobic molecule to the polysaccharide backbone. The engineered conjugate is capable of assembling into nanostructures once dispersed in water, with average diameter of 80.2 ± 0.4 nm (n = 5), stable up to 6 months. The thiolated HyA conjugate is reticulated by dissulfide bond with a homofunctional crosslinker-1,4-Bis(3-[2-pyridyldithio]propionamido)butane (DPDPB). The drug loading efficiency of the reticulated and non-reticulated nanogel is accessed with two hydrophobic drugs, curcumin and simvastatin. Results suggest that crosslinked nanogel exhibit higher stability upon dilution and drug loading efficiency and proves to be a redox sensitive material. The nanogels hold great potential as stealth carriers of lipophilic drugs.

Studies on the biodistribution of dextrin nanoparticles

The characterization of biodistribution is a central requirement in the development of biomedical applications based on the use of nanoparticles, in particular for controlled drug delivery. The blood circulation time, organ biodistribution and rate of excretion must be well characterized in the process of product development. In this work, the biodistribution of recently developed self-assembled dextrin nanoparticles is addressed. Functionalization of the dextrin nanoparticles with a DOTA-monoamide-type metal chelator, via click chemistry, is described. The metal chelator functionalized nanoparticles were labelled with a gamma-emitting (153)Sm(3+) radioisotope and the blood clearance rate and organ biodistribution of the nanoparticles were obtained. The effect of PEG surface coating on the blood clearance rate and organ biodistribution of the nanoparticles was also studied.

Dextrin-based nanomagnetogel: in vivo biodistribution and stability

The biodistribution profile of a new dextrin nanomagnetogel, which consists of γ-Fe2O3 superparamagnetic nanoparticles loaded within a polymeric matrix of modified dextrin, was studied in mice. The nanomagnetogel bear a monomodal size distribution profile (average diameter 110 nm) close to neutral surface charge and higher relaxivity (r2 = 215-248 mM(-1) s(-1) and r2/r1 = 13-11) than those of commercial formulations (r2 = 160-177 mM(-1) s(-1) and r2/r1 = 4-7). Also, the observed blood half-life-approximately 4 h-is superior to that of similar commercially available formulations, which remain for a few minutes in circulation. PEGylation resulted in 1.7- and 1.2-fold lower accumulation in the liver and spleen, respectively, within the first 24 h. Noteworthy, a good correlation was obtained between the amount of polymer (quantified by scintigraphy) in the spleen, 48 h after administration, and the amount of iron physically loaded through hydrophobic interactions (quantified by ICP) indicating the absence of iron leakage from the polymeric matrix. This study provides evidence of the in vivo stability of a self-assembled nanomagnetogel, a relevant feature which is seldom reported in the literature.

Potential of mannan or dextrin nanogels as vaccine carrier/adjuvant systems

Polymeric nanogels have been sophisticatedly designed promising a new generation of vaccine delivery/adjuvant systems capable of boosting immune response, a strategic priority in vaccine design. Here, nanogels made of mannan or dextrin were evaluated for their potential as carriers/adjuvants in vaccine formulations. Since lymph nodes are preferential target organs for vaccine delivery systems, nanogels were biotin-labeled, injected in the footpad of rats, and their presence in draining lymph nodes was assessed by immunofluorescence. Nanogels were detected in the popliteal and inguinal lymph nodes by 24 h upon subcutaneous administration, indicating entrapment in lymphatic organs. Moreover, the model antigen ovalbumin was physically encapsulated within nanogels and physicochemically characterized concerning size, zeta potential, ovalbumin loading, and entrapment efficiency. The immunogenicity of these formulations was assessed in mice intradermally immunized with ovalbumin–mannan or ovalbumin–dextrin by determining ovalbumin-specific antibody serum titers. Intradermal vaccination using ovalbumin–mannan elicited a humoral immune response in which ovalbumin-specific IgG1 levels were significantly higher than those obtained with ovalbumin alone, indicating a TH2-type response. In contrast, dextrin nanogel did not show adjuvant potential. Altogether, these results indicate that mannan nanogel is a material that should be explored as a future antigen delivery system.