Long-Term Effects of Nanoscale Magnetite on Human Forebrain-like Tissue Development in Stem-Cell-Derived Cortical Spheroids.

The environmental nanoscale iron magnetite may contribute to the risk of developing neurodegenerative diseases. In addition, iron oxides can be used as the contrast agents in magnetic resonance imaging of neural tissues. The potential long-term impact of nanoscale iron oxides on cellular stress and neuro-inflammation remains unknown. The objective of this study is to evaluate the long-term effects of nanoscale iron oxide exposure on human pluripotent stem cell-derived cortical spheroids that mimic human forebrain-like tissue development. In particular, the cortical spheroids were treated with 8 nm and 15-20 nm magnetite at 0.023, 2.3, and 23 μg/mL for 4-30 days. The cell viability did not show significant differences among different test groups. The neuronal marker β-tubulin III, cell proliferation marker Ki67, and antioxidant enzyme SOD2 did not show significant changes either. The molecular levels of cellular stress, inflammation, cell apoptosis, DNA damage and repair, and the reactive oxygen species (ROS) response were measured. A negative effect (i.e., increased inflammation and ROS response genes) of 8 nm iron oxide exposure and a positive effect (i.e., decreased inflammation, apoptosis, and ROS response and clean up genes) for 15-20 nm iron oxide exposure were observed. It is postulated that the intracellular iron content and the aggregation of iron oxides contribute to the observed differential response. Although our results demonstrate similar intracellular iron content for 8 nm and 15-20 nm groups, the aggregation is more severe for the 8 nm group (∼500 nm) than the 15 nm group (∼220-250 nm). Therefore, our data indicate an iron oxide aggregate size-dependent effects on cellular stress, inflammation, cell apoptosis, DNA damage, and the ROS response in the developing human forebrain-like tissue.