OBJECTIVETo explore the feasibility of magnetic resonance imaging (MR) on detecting transplanted nanometer small superparamagnetic iron oxides (SPIO) labeled mesenchymal stem cells (MSCs) in swine model with acute myocardial infarction (MI).

METHODSMSCs isolated from swine were incubated with nanometer SPIO for 24 hours and the third-passage MSCs were labeled with DNA dye 4'-6-diamidino-2-phenylindole (DAPI) and aliphatic red fluorescent dye PKH(26)-GL. Presence of small particles of SPIO in MSCs was assessed by Prussian Blue staining and electron microscopy. Three animals in each group received SPIO-labeled MSCs (5 x 10(5); 1 x 10(6); 2 x 10(6)) and MSCs without SPIO (1 x 10(6)) injections into the infarcted myocardium approximately 1 hour following left anterior descending coronary artery. MRI (1.5-T) was performed 20 to 24 hours post infarction in all animals and the animals were subsequently sacrificed for histology 1 hour post MRI.

RESULTSIn vitro Prussian Blue staining and electron microscopy examination revealed numerous iron particles in the cytoplasm of MSCs. Low signal intensity spots with the scanning T(2)(*)WI-Flash 2d sequence were detected in all SPIO-MSCs but not in SPIO-negative-MSCs injected myocardial sites in vivo with the clinical 1.5 T scanner. Prussian blue, DAPI and PKH(26) positive cells were detected histologically in sections corresponding to low signal intensity spots area shown on MRI.

CONCLUSIONMagnetically labeled MSCs transplanted in myocardial ischemia area of swine can be visualized in vivo with a clinical 1.5-T MRI and could be used for tracking SPIO-MSCs clinically.