Repulsive Apoptosis During Exposure of Mesencephalic Neural Stem Cells to Silver Nanoparticles in a Neurosphere Assay In Vitro.

Neurodevelopmental toxicity of silver nanoparticles (AgNPs) remains largely unknown. In this study, we applied a neurosphere assay for neurodevelopmental effects of AgNPs. The neural stem cells were isolated from rat mesencephalon. They were cultured as a sphere. In an assay with coated plates, cells appeared by anchoraging on the dish and then started to migrate along the radial axis from the neurosphere. AgNPs inhibited cell migration in a dose-dependent manner. There was a linear correlation between the inhibition of migration and the logarithm of the particle concentration (1.25-10 μg/ml); the half-maximal inhibitory concentration was 0.41 μg/ml for 16-h exposure. Preceding migrated cells were retarded and/or collapsed by exposure to AgNPs: lower doses of AgNPs (0.31-1.2 μg/ml) caused a 42% retardation for 48 h, while higher doses of AgNPs (2.5-10 μg/ml) collasped migrating cells. Furthermore, collapsed cells were TUNEL-positive and showed a defect in the mitochondrial membrane potential. Thus, we showed the neurodevelopmental toxicity of AgNPs using an in vitro neurosphere assay system.