Ultrastructural characterization of mesenchymal stromal cells labeled with ultrasmall superparamagnetic iron-oxide nanoparticles for clinical tracking studies

Abstract

Introduction. To evaluate survival and engraftment of mesenchymal stromal cells (MSCs) in vivo, it is necessary to track implanted cells non-invasively with a method, which does not influence cellular ultrastructure and functional characteristics. Iron-oxide particles have been applied for cell tracking for years, but knowledge regarding possible cytotoxic ultrastructural changes subsequent to iron-oxide particle labeling is limited. Hence, the purpose of this study was to label MSCs with dextran-coated ultrasmall super-paramagnetic iron-oxide (USPIO) particles conjugated with the transduction sequence of trans-activator of transcription (TAT) (IODEX-TAT) and evaluate the effect of labeling on ultrastructure, viability, phenotype and proliferative capacity of the cells. Materials and methods. MSCs were labeled with 5 and 10 μg IODEX-TAT/10⁵ cells for 2, 6 and 21 hours. IODEX-TAT uptake and cellular ultrastructure were determined by electron microscopy. Cell viability was determined by propidium iodide staining and cell proliferation capacity by 5-bromo-2-deoxyuridine (BrdU) incorporation. Maintenance of stem cell surface markers was determined by flow cytometry. Results. IODEX-TAT labeling for 2, 6 and 21 h did not influence cellular ultrastructure or viability. Moreover, neither stem cell surface markers nor cell proliferation capacity was affected by labeling with IODEX-TAT. Conclusion. Our results demonstrate that labeling of MSCs for 21 h with a clinically relevant dose of 10 μg IODEX-TAT/10⁵ cells is feasible and does not affect MSC ultrastructure, viability, phenotype or proliferation capacity.

Key Words::

• Electron microscopy
• labeling
• MSC
• SPIO
• stem cells
• toxicity
• ultrastructure
• USPIO

Acknowledgements

Bente Stærgaard, Hanne Kruse, Robert Burdorf and Zanne Henriksen are thanked for excellent technical assistance.

Declaration of interest: The authors have no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

The present study was supported by the Aase and Ejner Danielsens Foundation and the Arvid Nilssons Foundation.