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Keywords:

  • MR imaging;
  • molecular imaging;
  • stem cells;
  • cartilage;
  • tissue engineering;
  • iron oxides;
  • cell tracking

Abstract

For in vivo applications of magnetically labeled stem cells, biological effects of the labeling procedure have to be precluded. This study evaluates the effect of different ferucarbotran cell labeling protocols on chondrogenic differentiation of human mesenchymal stem cells (hMSC) as well as their implications for MR imaging. hMSC were labeled with ferucarbotran using various protocols: cells were labeled with 100 µg Fe/ml for 4 and 18 h and additional samples were cultured for 6 or 12 days after the 18 h labeling. Supplementary samples were labeled by transfection with protamine sulfate. Iron uptake was quantified by ICP-spectrometry and labeled cells were investigated by transmission electron microscopy and by immunostaining for ferucarbotran. The differentiation potential of labeled cells was compared with unlabeled controls by staining with Alcian blue and Hematoxylin and Eosin, then quantified by measurements of glucosaminoglycans (GAG). Contrast agent effect at 3 T was investigated on days 1 and 14 of chondrogenic differentiation by measuring signal-to-noise ratios on T2-SE and T2*-GE sequences. Iron uptake was significant for all labeling protocols (p< 0.05). The uptake was highest after transfection with protamine sulfate (25.65 ± 3.96 pg/cell) and lowest at an incubation time of 4 h without transfection (3.21 ± 0.21 pg/cell). While chondrogenic differentiation was decreased using all labeling protocols, the decrease in GAG synthesis was not significant after labeling for 4 h without transfection. After labeling by simple incubation, chondrogenesis was found to be dose-dependent. MR imaging showed markedly lower SNR values of all labeled cells compared with the unlabeled controls. This contrast agent effect persisted for 14 days and the duration of differentiation. Magnetic labeling of hMSC with ferucarbotran inhibits chondrogenesis in a dose-dependent manner when using simple incubation techniques. When decreasing the incubation time to 4 h, inhibition of chondrogenesis was not significant. Copyright © 2009 John Wiley & Sons, Ltd.