OBJECTIVETo investigate the feasibility of in vitro and in vivo magnetic resonance imaging (MRI) and fluorescence imaging tracking of transplanted bone mesenchymal stem cells (BMSCs) dual-labeled with ultrasmall superparamagnetic iron oxide (USPIO) and red fluorescence protein (RFP).

METHODSBMSCs were incubated with culture medium containing USPIO for 24 hours. The Prussian-blue staining, transmission electron microscopy and trypan-blue staining were used to study the efficacy and safety of labeling. F344 rat model of acute myocardial infarction was established by ligating the left anterior descending coronary artery. The dual-labeled BMSCs were injected into the margin of the infraction myocardium. Then MRI and fluorescence imaging were performed to trace the cells both in vitro and in vivo. Postmortal study was carried out to observe the distribution of transplanted cells in myocardium.

RESULTSThe percentage of dual-labeled BMSCs reached 99% after co-incubating with USPIO for 24 hours. USPIO particles were mainly located in lysosomes. As demonstrated by trypan-blue staining, there was no significant deference in viability between labeled and unlabeled groups (P>0.05). All dual-labeled transplanted BMSCs showed a significant decreasing signal on MRI, and the signal intensity changes had no significant difference over 4 weeks (P=0.66). In vitro cell tracing with fluorescence imaging of isolated heart from F344 rats was successful,while in vivo cell tracing with fluorescence imaging failed. Prussian blue staining showed that USPIO distributed near the infarcted myocardium, corresponding with the fluorescence imaging.

CONCLUSIONMRI can be used to trace the dual-labeled BMSCs transplanted into F344 rat hearts in vivo, while fluorescence imaging and pathological fluorescence imaging can trace the transplanted cells in vitro.