Labeling of mesenchymal stem cells with different superparamagnetic particles of iron oxide and detectability with MRI at 3T

Purpose: In vitro evaluation of labeling efficiency of human mesenchymal stem cells (hMSCs) with different types of superparamagnetic iron oxide nanoparticles as well as detection and quantification by MRI at 3T. Material and methods: hMSCs were incubated for 24 hours with 5 ultrasmall superparamagnetic particles of iron oxide (USPIO) contrast agents (1:30-1:30,000) of different size, coating and core compound: Endorem registered, Resovist registered, citric acid coated magnetite cores of 3 nm (CMF3), 7 nm (CMF7) and 12 nm (CoF; core: cobalt ferrite). Iron uptake, intracellular retention, detection and quantification were evaluated with MRI up to 5 weeks after incubation by cytological analysis (Prussian blue) atomic absorption spectrometry and MR relaxometry measurements. Results: An effective labeling of hMSCs was achieved using Resovist registered, CMF3 and CMF7 with mean iron concentrations of 5.1/1.8, 1.9/1.4 and 1.5/1.0 pg/cell (dilutions 1:30 [933, 2100, 2800 μg Fe/ml]/1:300 [93, 210, 280 μg Fe/ml)] compared with 0.58/0.34 and 0.43/0.30 pg/cell (Endorem registered, CoF, dilution 1:30 [400, 4200 μg Fe/ml]/1:300 [40, 420 μg Fe/ml] unlabelled control cells: 0.01 pg/cell). Particle uptake correlated with the concentration of USPIO in the incubation medium. Detection of 5 x 104 labelled cells/ml with MRI was possible up to 5 weeks after incubation (Resovist registered, CMF7 and CMF3). MR relaxometry measurements showed a strong correlation between cellular iron load and R2* (1/T2*), r > 0.78. No changes in cell viability or toxic effects were found. Conclusion: Efficiency of labeling hMSCs with USPIOs depends on coating, size and core compound of used particles. Carboxydextran-coated, clinically approved SPIO (Resovist registered, 50 nm) or ultrasmall citrate-coated particles (< 10 mm) result in an improved cellular uptake. In principle, the long intracellular retention of particles offers the possibility of cell tracking and migration monitoring in MRI. (orig.)