Scintigraphic tracking of 99m Technetium-labelled equine peripheral blood-derived mesenchymal stem cells after intravenous, intramuscular, and subcutaneous injection in healthy dogs

Background Mesenchymal stem cell treatments in dogs have been investigated as a potential innovative alternative to current conventional therapies for a variety of conditions. So far, the precise mode of action of the MSCs has yet to be determined. The aim of this study was to gain more insights into the pharmacokinetics of MSCs by evaluating their biodistribution in healthy dogs after different injection routes. Methods Three different studies were performed in healthy dogs to evaluate the biodistribution pattern of radiolabelled equine peripheral blood-derived mesenchymal stem cells following intravenous, intramuscular and subcutaneous administration in comparison with free 99m Technetium. The labelling of the equine peripheral blood-derived mesenchymal stem cells was performed using stannous chloride as a reducing agent. Whole-body scans were obtained using a gamma camera during a 24-h follow-up. Results The labelling efficiency ranged between 59.58 and 83.82%. Free 99m Technetium accumulation was predominantly observed in the stomach, thyroid, bladder and salivary glands, while following intravenous injection, the 99m Technetium-labelled equine peripheral blood-derived mesenchymal stem cells majorly accumulated in the liver throughout the follow-up period. After intramuscular and subcutaneous injection, the injected dose percentage remained very high at the injection site. Conclusions A distinct difference was noted in the biodistribution pattern of the radiolabelled equine peripheral blood-derived mesenchymal stem cells compared to free 99m Technetium indicating equine peripheral blood-derived mesenchymal stem cells have a specific pharmacokinetic pattern after systemic administration in healthy dogs. Furthermore, the biodistribution pattern of the used xenogeneic equine peripheral blood-derived mesenchymal stem cells appeared to be different from previously reported experiments using different sources of mesenchymal stem cells.