Characterization of biophysical and metabolic properties of cells labeled with superparamagnetic iron oxide nanoparticles and transfection agent for cellular MR imaging

PURPOSE

To evaluate the effect of using the ferumoxides-poly-l-lysine (PLL) complex for magnetic cell labeling on the long-term viability, function, metabolism, and iron utilization of mammalian cells.

MATERIALS AND METHODS

PLL was incubated with ferumoxides for 60 minutes, incompletely coating the superparamagnetic iron oxide (SPIO) through electrostatic interactions. Cells were coincubated overnight with the ferumoxides-PLL complex, and iron uptake, cell viability, apoptosis indexes, and reactive oxygen species formation were evaluated. The disappearance or the life span of the detectable iron nanoparticles in cells was also evaluated. The iron concentrations in the media also were assessed at different time points. Data were expressed as the mean +/- 1 SD, and one-way analysis of variance and the unpaired Student t test were used to test for significant differences.

RESULTS

Intracytoplasmic nanoparticles were stained with Prussian blue when the ferumoxides-PLL complex had magnetically labeled the human mesenchymal stem and HeLa cells. The long-term viability, growth rate, and apoptotic indexes of the labeled cells were unaffected by the endosomal incorporation of SPIO, as compared with these characteristics of the nonlabeled cells. In nondividing human mesenchymal stem cells, endosomal iron nanoparticles could be detected after 7 weeks; however, in rapidly dividing cells, intracellular iron had disappeared by five to eight divisions. A nonsignificant transient increase in reactive oxygen species production was seen in the human mesenchymal stem and HeLa cell lines. Labeled human mesenchymal stem cells did not differentiate to other lineage. A significant increase in iron concentration was observed in both the human mesenchymal stem and HeLa cell media at day 7.

CONCLUSION

Magnetic cellular labeling with the ferumoxides-PLL complex had no short- or long-term toxic effects on tumor or stem cells.

Intracytoplasmic tagging of cells with ferumoxides and transfection agent for cellular magnetic resonance imaging after cell transplantation: methods and techniques

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 microg/mL media) and PLL (0.75 microg/mL media). Hematopoietic stem cells and lymphocytes required higher concentrations of PLL (1.5 microg/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 FE-PLL complexes in media, cellular density, and incubation time. Iron concentrations after overnight incubation with given FE at 25 microg/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 microg/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.