Non-invasive cell tracking of SPIO labeled cells in an intrinsic regenerative environment: The axolotl limb

Non-invasive methods to track the progress of stem cell therapies are important in the development of future regenerative therapies. Super-paramagnetic iron oxide particles (SPIOs) have previously been applied to track cells using magnetic resonance imaging (MRI) in vivo in non-regenerative animal models. To the best of the author's knowledge, the present study investigated for the first time, the feasibility of tracking SPIO labeled cells in an intrinsic regenerative environment, the regenerating limb of the axolotl, and investigated the homing of stem cell-like blastema cells to the regenerative zone. Viability and labeling success of labeled axolotl blastema cells was tested in vitro using cell culture and histology. SPIO labeling was performed in situ by intramuscular injections and mapped using MRI. Enhanced permeability and retention (EPR) effects were evaluated in the blastema, liver, heart, kidney and a back muscle. Finally, SPIO/Fluorophore-labeled blastema cells were injected intravascularly and tracked using MRI and fluorescence imaging. It was demonstrated that SPIO labeling had no effect on axolotl cell viability in vitro. In situ labeling resulted in an MRI signal alteration during 48 days of regeneration. EPR effect of unbound SPIO was observed only in the liver. MRI tracking revealed increased concentrations of SPIO labeled blastema cells in the liver, kidney and heart, however not the blastema of intravascularly injected axolotls. In conclusion, the results demonstrated that SPIO labeling facilitated non-invasive tracking of injected cells in the regenerating axolotl limb. An early homing mechanism of injected blastema cells to an injury site was not observed.