Klaus-Peter Prof. Dr.-Ing. Schmitz

Nuclear entry of hyperbranched polylysine nanoparticles into cochlear cells.

Background: Gene therapy is a potentially effective therapeutic modality for treating sensorineural hearing loss. Nonviral gene delivery vectors are expected to become extremely safe and convenient, and nanoparticles are the most promising types of vectors. However, infrequent nuclear localization in the cochlear cells limits their application for gene therapy. This study aimed to investigate the potential nuclear entry of hyperbranched polylysine nanoparticles (HPNPs) for gene delivery to cochlear targets. Methods: Rat primary cochlear cells and cochlear explants generated from newborn rats were treated with different concentrations of HPNPs. For the in vivo study, HPNPs were administered to the rats’ round window membranes. Subcellular distribution of HPNPs in different cell populations was observed with confocal microscope 24 hours after administration. Results: Nuclear entry was observed in various cochlear cell types in vitro and in vivo. In the primary cochlear cell culture, concentration-dependent internalization was observed. In the cochlear organotypic culture, abundant HPNPs were found in the modiolus, including the spiral ganglion, organ of Corti, and lateral wall tissues. In the in vivo study, a gradient distribution of HPNPs through different layers of the round window membrane was observed. HPNPs were also distributed in the cells of the middle ear tissue. Additionally, efficient internalization of HPNPs was observed in the organ of Corti and spiral ganglion cells. In primary cochlear cells, HPNPs induced higher transfection efficiency than did Lipofectamine™. Conclusion: These results suggest that HPNPs are potentially an ideal carrier for gene delivery into the cochlea.

Drug delivery by nanoparticles — facing the obstacles

There are numerous concepts of nanoparticle mediated drug delivery. The major advantage will be the option of targeted drug delivery to specific target cells thus avoiding high systemic loads of potentially toxic chemicals. Any kind of drug delivery by nanoparticles relies on delivery of the drug into the cell. In most cases that means drug delivery into the cytoplasm, and in some instances delivery of the drug to extracellular domains of transmembrane signalling molecules. Whenever viable cells are confronted with nanoparticles these are ingested by endocytosis rather then passage through the cell plasma membrane. Once inside endosomal vesicles the nanoparticles or at least their drug payload requires release into the cytoplasm in order to exert it’s biological effect. In order to monitor whether a drug delivered by nanoparticles is biologically active a toxic model drug, disulfiram, was chosen as a payload with micelle and liposome nanoparticles. L929 mouse fibroblasts were incubated with these disulfiram loaded naoparticles and cell viability was determined by quantification of celluar reductase activity. Applied nanoparticles are toxic to the cells. However, with respect to the disulfiram payload a 100-fold higher disulfiram concentration is required in comparison to free disulfiram for a biological effect. Hence, the toxic effect is most likely not due to the disulfiram delivered by the nanoparticles but rather to the amount of free disulfiram that is present in the nanoparticle preparation. Therefore it is advised to carefully characterize the nanoparticle suspension for the amount of free payload molecules.