Objective      To investigate the effects of target delivery of superparamagnetic iron oxide (SPIO)-labeled bone marrow me

senchymal stem cells (BMSCs) driven by magnetic field in vitro on a rat model of spinal cord injury (SCI) and on growth-associated protein 43 (GAP-43) expression in spinal cord.       Methods      BMSCs from Sprague-Dawley (SD) rats were cultured in vitro. The expression of CD29

CD45

and CD54 was checked by flow cytometry. The BMSCs were labeled with SPIO with label rate tested by Prussian blue staining. The viability of the labeled cells was evaluated by trypan blue staining. CCK-8 assay was used to detect the proliferation of the labeled cells in the presence of magnetic field. Effects of magnetic field on the differentiation of labeled cells were investigated by Western blotting for detection of nestin and GFAP expression. Rats were induced by the clip compression method to establish the SCI model. The BMSCs labeled with SPIO were injected in tail vein. Neurological functions were evaluated using Basso-Beattie-Bresnahan (BBB) score in 3 and 7 d after cells transplantation. The transplanted labeled cells in recipient rat spinal cord were analyzed by Prussian blue staining. The spinal cord ischemia area was checked by TTC staining. The GAP-43 protein expression in the spinal cord of SCI rats after cell transplantation was investigated by Western blotting.       Results      Flow cytometry results showed that BMSCs expressed the mesenchymal stem cells markers CD29 and CD54 but not the hematopoietic stem cells marker CD45. The Prussian blue staining results showed that the percentage of BMSCs labeled with SPIO was close to 100%. Trypan blue staining showed that there was no significant difference on the viability between the labeled cells and the control group (

P

0.05). CCK-8 assay did not show any significant difference on proliferation between the magnetic field-treated group and the control group (

P

0.05). The Western blot results showed that the presence of magnetic field had no effect on the differentiation of BMSCs (

P

0.05). The BBB score of the magnetic field-treated group was better tha

n that of the control group (

P

0.05). Prussian blue staining of spinal cord slices showed a higher number of Prussian blue-positive BMSCs in the group with SCI and the presence of magnetic field than that in the SCI group without magnetic field. TTC staining showed the average ischemia size in the spinal cord with magnetic field treatment was significantly smaller than that without magnetic field treatment (

P

0.05). The Western blot results showed significantly higher expression of GAP-43 in the group with magnetic field treatment as compared to the other two groups on day 3 and day 7 after cell transplantation (

P

0.05).       Conclusion      External magnetic field drives the target delivery of more SPIO-labeled BMSCs to the injury area of spinal cord in vivo

relieving SCI and upregulating GAP-43 expression which helps the recovery of SCI.