Cell motility of neural stem cells is reduced after SPIO‐labeling,which is mitigated after exocytosis

MRI is used for tracking of superparamagnetic iron oxide (SPIO)‐labeled neural stem cells. Studies have shown that long‐term MR tracking of rapidly dividing cells underestimates their migration distance. Time‐lapse microscopy of random cellular motility and cell division was performed to evaluate the effects of SPIO‐labeling on neural stem cell migration. Labeled cells divided symmetrically and exhibited no changes in cell viability, proliferation, or apoptosis. However, SPIO‐labeling resulted in decreased motility of neural stem cells as compared with unlabeled controls. When SPIO‐labeled neural stem cells and human induced pluripotent stem cells were transplanted into mouse brain, rapid exocytosis of SPIO by live cells was observed as early as 48 h postengraftment, with SPIO‐depleted cells showing the farthest migration distance. As label dilution is negligible at this early time point, we conclude that MRI underestimation of cell migration can also occur as a result of reduced cell motility, which appears to be mitigated following SPIO exocytosis. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.