Distribution of injected technetium(99m)-labeled mesenchymal stem cells in horses with naturally occurring tendinopathy.

The research investigates how effectively mesenchymal stem cells (MSCs), used for treating tendon and ligament injuries in horses, survive and distribute via different administration routes. The best method was found to be local injection at the injury site even though a considerable number of cells were lost; intravenous injection did not lead to significant cell accumulation at the injury site.

Objective of the research

• The study sought to investigate how immediate cell survival and distribution varies with different routes of stem cell administration in naturally occurring tendon injuries. It aimed to determine the proportion of MSCs that remain at the lesion site and elsewhere in the body after intra-lesional, intravenous, and regional perfusion administration methods.

Methodology

• The researchers injected 10 million MSCs, labeled with technetium-99m (Tc99m) hexamethylpropyleneamine oxime, into 13 horses suffering from tendon or ligament injuries through three different routes.
• The distribution and survival of the cells were monitored up to 48 hours after the injection using gamma scintigraphy, a form of imaging used to examine the inside of the body’s functionality.

Results

• The labeling efficiencies of Tc99m varied between 1.8% and 18.5% with an average of 9.3%.
• When the stem cells were injected directly into the damaged area (intra-lesional administration), cells were retained in that area. However, 24 hours post-injection, only about 24% of the cells remained within the tendon.
• Following intravenous administration, the cells were majorly distributed to the lung fields with no detectable cells found in the tendon lesions.
• Regional perfusion resulted in significant labeling of the tendon lesions in 11 out of 12 horses but at a lower level than with the intra-lesional injection.
• The intra-lesional injection retained the highest number of cells despite the considerable cell loss, making it the preferred MSC delivery method according to this study. Conversely, the efficiency of cell retention after regional perfusion suggests it as an available alternative for MSC delivery.

Implications and conclusion

• The cells did not “home,” i.e. move towards the injured tendon in large numbers when administered intravenously.
• The lungs appeared to be the most common site for cell accumulation following intravenous administration, but without causing adverse effects.
• The study’s findings on low cell retention, especially with the intravenous and regional perfusion administration methods, create implications for designing more effective clinical therapies. Such therapies could potentially benefit not only veterinary medicine but also human clinical application, especially for tendon or ligament injury treatment.