AbstractsBiology & Animal Science

Iron oxide nanoparticles (IONPs) are used in various biomedical applications and are already applied in human therapy. Since IONPs can reach the brain, detailed knowledge on uptake and effects of IONPs on neural cells is required. In the present thesis, IONPs were synthesized and fluorescently labeled by attaching the green fluorescent dye BODIPY to the coating material dimercaptosuccinate. When 1.5% of the thiol groups of dimercaptosuccinate were functionalized, IONPs had identical physicochemical properties to the non-fluorescent version of the IONPs and were therefore considered as suitable fluorescent tool to study uptake and intracellular localization of dimercaptosuccinate-coated IONPs. Cellular uptake, localization and potential toxic effects of IONPs were investigated in cell culture models of the four major neural cell types (neurons, astrocytes, microglia, oligodendrocytes). In general, neural cell cultures efficiently accumulated IONPs which led to an increase of the specific cellular iron contents to maximal levels of up to 3000 nmol iron per mg protein. The uptake of IONPs in cultured brain cells strongly depended on experimental conditions such as time of incubation, IONP concentration, temperature and on the absence or presence of serum. In the presence of serum, the accumulation of IONPs was decreased by 80-90% in all cell types investigated compared to serum-free conditions. Dependent on the cell type investigated, IONP uptake in presence of serum was strongly lowered by known inhibitors of endocytotic processes suggesting involvement of clathrin-mediated endocytosis and/or macropinocytosis. In contrast, for IONP uptake in absence of serum the pathways involved remain to be elucidated. A direct comparison of cultured astrocytes, neurons and microglia revealed that microglia were most efficient in IONP accumulation but also highly vulnerable to IONP exposure. Microglial cell death was prevented by neutralizing lysosomes or by chelating iron ions, suggesting that toxicity is mediated by rapid transfer of IONPs to lysosomes and fast IONP degradation in the acidic environment which resulted in microglial death by iron-mediated oxidative stress. In contrast to microglia, primary astrocytes, neurons and oligodendroglial OLN-93 cells were not acutely damaged within hours upon IONP exposure. However, at least neurons which had accumulated substantial amounts of IONPs during a short time exposure suffered from delayed toxicity after removal of exogenous IONPs. The data presented in this thesis reveal that brain cells deal well with low amounts of IONPs. However, higher iron contents after IONP exposure cause acute or delayed toxicity in some neural cell types. Among the different cell types, especially microglia were vulnerable to IONPs. Hence, concerning biomedical application of IONPs to the brain one should consider protecting microglia from IONP-derived stress to reduce or prevent potential adverse effects to the brain.