Comparison of Superparamagnetic Iron Oxide Labeling Efficiency between Poly-L-Lysine and Protamine Sulfate for Human Mesenchymal Stem Cells: Quantitative Analysis Using Multi-Echo T2 Magnetic Resonance Imaging

To quantify in vitro labeling efficiency of protamine sulfate (PS) and poly-L-lysine (PLL) for labeling of human mesenchymal stem cells (hMSCs) with superparamagnetic iron oxide (SPIO) using multi-echo T2 magnetic resonance (MR) imaging at 4.7 T. The hMSCs were incubated with SPIO-PS or SPIO-PLL complexes. Their effects on the cell metabolism and differentiation capability were evaluated, respectively. The decrease of iron concentrations in the labeled cells were assessed immediately, and at 4 d after labeling using multi-echo T2 MR imaging at 4.7 T. The results were compared with those of Prussian blue colorimetry. The hMSCs were labeled more efficiently by SPIO-PLL than SPIO-PS without any significant effect on cell metabolism and differentiation capabilities. It was feasible to quantify the iron concentrations in SPIO-agarose-phantoms and in agarose mixture with the labeled cells from T2 maps obtained from multi-echo T2 MRI. However, the iron concentration of the labeled cells was significantly higher by T2-maps than the results of Prussian blue colorimetry. The hMSCs can be effectively labeled with SPIO-PLL complexes more than with SPIO-PS without significant change in cell metabolism and differentiation. In vitro quantification of the iron concentrations of the labeled is feasible from multi-echo T2 MRI, but needs further investigation.