MR tracking of SPIO-labeled mesenchymal stem cells in rats with liver fibrosis could not monitor the cells accurately

Our previous study showed that in vivo magnetic resonance (MR) imaging is effective in tracking superparamagnetic iron oxide (SPIO)-labeled bone marrow mesenchymal stem cells (BMSCs) in rats with liver fibrosis. SPIO-labeling-induced signal reduction on MR images was completely reversed within 15 days after transplantation. It is still unclear whether the signal changes in MR imaging could reflect the number of transplanted cells in the liver. In the present study, BMSCs of male rats were doubly labeled with enhanced green fluorescent protein (EGFP) and SPIO and injected intravascularly into female rats with liver fibrosis. At different time points after injection, MR imaging was performed. The distribution of SPIO particles and EGFP-positive cells was determined by Prussian blue staining and EGFP immunohistochemistry, respectively. The distribution of transplanted BMSCs in various organs was assessed by detection of the SRY gene using real-time quantitative PCR. At 15 days post transplantation, the numbers of transplanted cells were significantly decreased in the lung, kidney, spleen and muscle, but not liver and heart, in comparison with those at 7 days after transplantation. EGFP staining-positive cells were observed in the liver intralobular parenchyma, while Prussian blue staining was negative at 42 days after transplantation. Taken together, SPIO particles and EGFP-labeled BMSCs show a different tissue distribution pattern in rats with liver fibrosis after a long-term period of monitoring. SPIO-based MR imaging may not be suitable for long-term tracking of transplanted BMSCs in vivo. Copyright (C) 2015 John Wiley & Sons, Ltd.