Synthesis and Characterization of Iron Oxide Nanoparticles and Investigation of their Biocompatibility on Astrocyte Cultures

Abstract

Magnetic iron oxide nanoparticles (IONPs) are used as tools for a wide range of biomedical and (neuro)biological applications, for example as contrast agent in magnetic resonance imaging, as transporter for drug delivery across biological barriers or for cancer treatment by magnetic field-induced hyperthermia. However, the knowledge on the effects of such particles on brain cells have only recently been addressed. This thesis describes the synthesis and characterization of citrate- and dimercaptosuccinate (DMSA)-coated IONPs. In addition, the uptake, reactivity and biocompatibility of such particles were investigated for astrocyte-rich primary cultures as a model system for brain astrocytes. Citrate- and DMSA-coated IONPs were accumulated by viable cultured astrocytes in a time- and concentration-dependent process leading to more than 100fold elevated specific cellular iron contents. Electron microscopy revealed that IONPs were present in intracellular vesicles as well as attached extracellularly to the cell membrane. Lowering the incubation temperature to 4°C reduced the iron accumulation to about 50% which represented almost exclusively membrane associated extracellular IONPs. Presence of an external magnetic field increased the amount of cellular iron by 2-4fold, while presence of serum strongly reduced IONP-accumulation by up to 90% compared with the respective controls. Application of endocytosis inhibitors revealed that clathrin-mediated endocytosis and macropinocytosis contributed to IONP-uptake in serum-containing conditions. However, additional mechanisms are responsible for IONP-uptake under serum-free conditions. Prolonged presence of IONPs in cultured astrocytes for up to 7 d after a transient loading period of 4 h neither compromised cell viability nor affected basic metabolic pathways. However, a transient formation of reactive oxygen species and a delayed upregulation of cellular ferritin indicate that iron ions were liberated from the accumulated particles. In summary, this thesis revealed that viable astrocytes efficiently take up and safely store IONPs and IONP-derived iron, supporting the view that such particles can be used as save tools for diagnostic or therapeutic approaches in the brain.