In vivo MRI tracking of iron oxide nanoparticle-labeled human mesenchymal stem cells in limb ischemia

Xiang-Xiang Li,^1,2,* Kang-An Li,^3,* Jin-Bao Qin,^1,2 Kai-Chuang Ye,^1,2 Xin-Rui Yang,^1,2 Wei-Min Li,^1,2 Qing-Song Xie,⁴ Mi-Er Jiang,^1,2 Gui-Xiang Zhang,³ Xin-Wu Lu<sup>1,2

1</sup>Department of Vascular Surgery, Shanghai Ninth People's Hospital Affiliated to Shanghai Jiao Tong University, School of Medicine, ²Vascular Center, Shanghai JiaoTong University, ³Department of Radiology, Shanghai First People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, People's Republic of China; ⁴Department of Neurosurgery, Cixi Municipal People's Hospital, Zhejiang Province, People's Republic of China

*These authors contributed equally to this work

Background: Stem cell transplantation has been investigated for repairing damaged tissues in various injury models. Monitoring the safety and fate of transplanted cells using noninvasive methods is important to advance this technique into clinical applications.
Methods: In this study, lower-limb ischemia models were generated in nude mice by femoral artery ligation. As negative-contrast agents, positively charged magnetic iron oxide nanoparticles (aminopropyltriethoxysilane-coated Fe₂O₃) were investigated in terms of in vitro labeling efficiency, effects on human mesenchymal stromal cell (hMSC) proliferation, and in vivo magnetic resonance imaging (MRI) visualization. Ultimately, the mice were sacrificed for histological analysis three weeks after transplantation.
Results: With efficient labeling, aminopropyltriethoxysilane-modified magnetic iron oxide nanoparticles (APTS-MNPs) did not significantly affect hMSC proliferation. In vivo, APTS-MNP-labeled hMSCs could be monitored by clinical 3 Tesla MRI for at least three weeks. Histological examination detected numerous migrated Prussian blue-positive cells, which was consistent with the magnetic resonance images. Some migrated Prussian blue-positive cells were positive for mature endothelial cell markers of von Willebrand factor and anti-human proliferating cell nuclear antigen. In the test groups, Prussian blue-positive nanoparticles, which could not be found in other organs, were detected in the spleen.
Conclusion: APTS-MNPs could efficiently label hMSCs, and clinical 3 Tesla MRI could monitor the labeled stem cells in vivo, which may provide a new approach for the in vivo monitoring of implanted cells.

Keywords: hind-limb ischemia, magnetic resonance imaging, iron oxide particles, stem cell implant