Encapsulation of proteins in micro- and nano-hydrogel carrier systems for controlled drug delivery

摘要

Introduction: Therapeutic proteins like antibodies or signaling proteins have a high potential for pharmaceutical applications. Drug delivery systems are needed to protect these proteins from in-vivo degradation. Furthermore, the proteins are able to induce unwanted side effects. A local administration close to the diseased area and a slow drug release can minimize these effects. Hydrogels provide a protein friendly environment and can have good biocompatibility. Therefore they are well suited as drug delivery systems. Diffusion and/or degradation are the main release mechanism. The relation between network structure and release was studied for bulk hydrogels and micro gels. Furthermore the in vitro and in-vivo release was studied and compared. Materials and Methods: Hydroxyethyl starch was modified with polyethylene glycolmethacrylate HES-PEGMA, which can be photochemically cross-linked in aqueous solution in order to obtain hydrogels or injectable hydrogel microspheres. The release was investigated and correlated with the mesh size. Green fluorescent protein (GFP) loaded hydrogels have been analyzed by fluorescence methods with two-photon excitation. Via fluorescence anisotropy the inner rotational motions can be studied. Fluorescence recovery after photo-bleaching (FRAP) gives information about the translational diffusion. In vitro release rates were compared with in vivo release rates employing fluorescently labelled proteins and an IVIS®-system. Furthermore, a nanogel system prepared from chitosan and tripolyphosphate (TPP) was investigated regarding entrapment efficiency and release of signaling proteins. Fig.1: Chemical structure of the HES derivatives Fig. 2: Bulk hydrogels and injectabie micro particles were prepared from the HES derivatives Results and Discussion: The mesh size of the hydrogel network can be adjusted via the degree of substitution and the polymer concentration. The bulk hydrogels and the micro particles have similar structures and release profiles when prepared from the same polymer and concentration. The results of the fluorescence anisotropy suggest an unrestricted GFP rotation within the hydrogel, while the FRAP measurements indicate that translational mobility of GFP is restricted in the hydrogel. The comparison of in vitro and in vivo release rates indicates a good comparability depending on the acceptor medium used in the in vitro experiments. The chitosan/TPP nanoparticles are well suited to deliver biologically active BMP2. Conclusions: Hydrogels as micro- or nanoparticles are well suited for delivery of therapeutic proteins. By adjusting the preparation methods the drug release can be tailored.