Long-Term In Vivo Magnetic Resonance Imaging Tracking of Endothelial Progenitor Cells Transplanted in Rat Ischemic Limbs and Their Angiogenic Potential

Stem cell therapy has been used to repair ischemic tissues in the limbs, in myocardial infarctions, and in the brain. To understand the mechanisms of healing, a contrast agent capable of inducing sufficient magnetic resonance (MR) contrast would be useful in providing fundamental information about the cell migration and incorporation into the ischemic tissue. A magnetic resonance imaging contrast agent composed of dextran and gadolinium chelate was synthesized. Hydroxyl groups of dextran were activated with 1,1'-carbonylbis-1H-imidazole and reacted with propanediamine to obtain aminated dextran. This modified polymer was then reacted with mono-N-succinimidyl 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate, then with fluorescein isothiocyanate, and finally reacted with gadolinium chloride solution (Dex-DOTA-Gd3(+)). Endothelial progenitor cells (EPCs) were selected as a stem cell model for magnetic resonance imaging tracking. Cells were isolated from the bone marrow harvested from the femurs and tibias of rats. Dex-DOTA-Gd3(+) was then introduced into the EPCs by electroporation. The intracellular stability and cytotoxicity of Dex-DOTA-Gd3(+) were evaluated in vitro. Dex-DOTA-Gd3(+)-labeled EPCs were transplanted into a rat model of ischemic limb, and MR images were acquired. Dex-DOTA-Gd3(+) was found to efficiently label EPCs over a long duration without significant cytotoxicity. This provides an MR signal sufficient for tracking the EPCs intramuscularly injected into the limb.