Objective: Quantitative magnetic resonance imaging (MRI) can serially and noninvasively assess the degree of injury in rat pup models of hypoxic ischemic injury (HII). It can also noninvasively monitor stem cell migration following iron oxide prelabeling. Reports have shown that neural stem cells (NSCs) may help mediate neuroprotection or stimulate neuroreparative responses in adult and neonatal models of ischemic injury. We investigated the ability of high-field MRI to monitor and noninvasively quantify the migration, proliferation, and location of iron oxide-labeled NSCs over very long time periods (58 weeks) in real time while contemporaneously correlating this activity with the evolving severity and extent of neural damage.
Methods: Labeled clonal murine NSCs (mNSCs) were implanted 3 days after unilateral HII in 10-day-old rat pups into the contralateral striatum or ventricle. We developed methods for objectively quantifying key aspects of dynamic NSC behavior (eg, viability; extent, and speed of migration; degree of proliferation; extent of integration into host parenchyma). MRI images were validated with histological and immunohistochemical assessments.
Results: mNSCs rapidly migrated (100 μm/day) to the lesion site. Chains of migrating NSCs were observed in the corpus callosum. In pups subjected to HII, though not in intact control animals, we observed a 273% increase in the MR-derived volume of mNSCs 4 weeks after implantation (correlating with the known proliferative behavior of endogenous and exogenous NSCs) that slowly declined over the 58-week time course, with no adverse consequences. Large numbers of now quiescent mNSCs remained at the site of injury, many retaining their iron oxide label.
Interpretation: Our studies demonstrate that MRI can simultaneously monitor evolving neonatal cerebral injury as well as NSC migration and location. Most importantly, it can noninvasively monitor proliferation dynamically for prolonged time periods. To be able to pursue clinical trials in newborns using stem cell therapies it is axiomatic that safety be insured through the long-term real time monitoring of cell fate and activity, particularly with regard to observing unanticipated risks to the developing brain. This study supports the feasibility of reliably using MRI for this purpose.
Copyright © 2010 American Neurological Association.