Labeling and tracing of bone marrow mesenchymal stem cells for tendon-to-bone tunnel healing

Purpose To investigate the effects of bone marrow mesenchymal stem cells (BMSCs) on tendon-to-bone tunnel healing and provide experimental evidence for labeling and tracing of stem cells. Methods Rat BMSCs were harvested using the adherence separation technique and labeled by super paramagnetic iron oxide (SPIO) and 1,1-Dioctadecyl-3,3,3,3-tetramethylindocarbocyanine perchlorate (Dil) particles. Thirtynine male Sprague–Dawley (SD) rats aged 8 weeks were randomly divided into two groups: experimental (n = 21) and control (n = 18). Rats from the experimental group were injected with SPIO- and Dil-labeled BMSCs and Pluronic F-127, and rats from the control group were only injected with Pluronic F-127. At 2, 4, and 8 weeks after surgery, biomechanical analysis was performed to evaluate tendon-to-bone tunnel healing. The transplanted BMSCs were observed by fluorescence microscope at 2, 4, and 8 weeks after surgery and traced by magnetic resonance (MR) imaging at 0, 3, and 7 days after surgery. Results BMSCs were labeled effectively by SPIO and Dil particles. At 2, 4, and 8 weeks after surgery, Dil-labeled cells were observed at tendon-bone interface by fluorescence microscope. In the experimental group, no obvious signal changes of tendon-bone interface were observed by MR imaging. The maximum biomechanical pull-out strength was not statistically different between experimental and control groups at 2 weeks, but significantly higher in the experimental group at 4 and 8 weeks after surgery (P\0.05). Conclusion The present study indicated that the transplanted BMSCs could promote tendon-to-bone tunnel healing at 4–8 weeks postoperatively. Dil- and SPIOlabeled transplanted BMSCs distributed at the tendon-bone interface and might play a role in promoting tendon-tobone tunnel healing, which may be translated into practical cytotherapy for patients those who need earlier rehabilitation for ligament reconstruction surgery in clinic.