Heparin-coated superparamagnetic iron oxide for in vivo MR imaging of human MSCs

Human mesenchymal stem cells (hMSCs) offer significant therapeutic potential in the field of regenerative medicine and high-resolution magnetic resonance imaging (MRI) is useful modality to visualize in vivo kinetics of transplanted stem cells. For successful MR imaging, there is a great need for effective contrast agents for stem cell labeling with high uptake yield and low toxicity. Here, we present superparamagnetic iron oxide (SPIO) nanoparticles coated with unfractionated heparin (UFH-SPIO) as a new negative contrast agent for in vivo MR imaging of hMSCs. The uptake of UFH-SPIO by hMSCs was effective without the aid of transfection agents, which was dependent on the concentration and exposure time. The uptake efficiency of UFH-SPIO was greater than that of DEX-SPIO (SPIO coated with dextran) by approximately 3 folds when treated for 1 h. TEM and Prussian blue staining confirmed that UFH-SPIO nanoparticles were internalized into the cytosol of hMSCs which existed during in vitro subculture for 28 days. Low temperature endocytosis inhibition assay demonstrated that the incorporation of UFH-SPIO into hMSCs was likely to be mediated by endocytosis. When the phantom of UFH-SPIO-labeled hMSCs was visualized with 3-T T-2-weighted MRI, the hypointensity signals of UFH-SPIO-labeled hMSCs were linearly correlated with the concentration of the nanoparticles. The cellular labeling using UFH-SPIO did not reduce the viability, proliferation or differentiation potential to osteogenic and adipogenic lineages of hMSCs. When the UFH-SPIO-labeled hMSCs were transplanted into the left renal subcapsular membranes of nude mice, they were successfully visualized and detected by T-2 and T-2*-weighted MRI for a month. Collectively, these results suggest that UFH-SPIO nanoparticles are promising as a new MRI contrast agent for in vivo long-term tracking of hMSCs. (c) 2012 Elsevier Ltd. All rights reserved.This work is supported by the National Research Foundation of Korea (NRF) funded by Ministry of Education, Science and Technology (MEST) (Grant numbers 2011-0015222, 2011-0016101)