Background. Superparamagnetic iron oxides (SPIO) are being used to label cells for in vivo monitoring by magnetic resonance imaging (MRI). The purpose of this study is to present protocols using SPIO and a polycationic transfection agent for magnetic labeling of cells as a basis for cellular MRI. Methods. Various concentrations of ferumoxides (FE)-poly-L-lysine (PLL) complexes were used to magnetically label cells. Iron incorporation into cells along with cell viability and short- and long-term toxicity were evaluated. Results. Rapidly growing cell suspension and adherent cells were effectively labeled by means of endocytosis into endosomes at low concentrations of FE (25 μg/mL media) and PLL (0.75 μ/mL media). Hematopoietic stem cells and lymphocytes required higher concentrations of PLL (1.5 μg/mL) in serum-free media during initial FE-PLL complex formation before labeling the cells in culture. Total iron concentration in cells depended on the cell type, concentration of FEPLL complexes in media, cellular density, and incubation time. Iron concentrations after overnight incubation with given FE at 25 μg/mL media resulted in, for example, T cells being labeled with 1 to 3 pg/cell of intracytoplasmic endosomal iron and 15 to 20 pg/cell of intracytoplasmic iron in mesenchymal stem cells compared with 0.01 to 0.1 pg/cell for unlabeled cells. Protocols developed for this study demonstrated no adverse effect on the cell viability, functional capacity, or toxicity. Conclusion. This technique can be used to label cells for in vivo MRI tracking of stem cells and lymphocytes. FE at a concentration of 25 to 50 μg/mL with a ratio of SPIO to PLL of 1:0.03 to 1:0.06 would be sufficient to label cells for cellular MRI.
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