Disclosures: Beatrice Deschenes St-Pierre, MD, MSc: No disclosure data submitted.

Objective: To determine whether the injection of Mesenchymal Stem Cells (MSC) and/or celastrol-conditioned MSC promote histopathological healing in rodent Achilles tendinopathy model compared to saline injection.

Design: Prospective Randomized Controlled Trial.

Setting: Research Centre (cages with controlled lighting, water, food, temperature)

Participants: 18 Sprague-Dawley rats (36 Achilles tendons)

Interventions: All 18 rats (36 tendons) were injected with collagenase type 1A (25 international units) under echographic guidance. After 1 week, rats were assigned to receive a repeat injection, also under echographic guidance, with either: 1) 60 μL of Phosphate-Buffered Saline (PB-saline; 2) 2.4M MSC derived from rat bone marrow aspirate or; 3) 2.4M MSC conditioned with celastrol (HSP90 inhibitor and antioxidant).

Main Outcome Measures: The histopathological changes were assessed using Modified Bonar Score (tenocytes morphology, cellularity, vascularity, mucin in fundamental substance and collagen organization) graded by a blinded experienced pathologist at 4 weeks (8 tendons/group) and at 12 weeks (4 tendons/group).

Results: There were no statistically significant differences between groups, both at 4 weeks and 12 weeks (α > 0.05). However, at 12 weeks, there was a trend towards better Modified Bonar Scores in the tendons treated with MSC (0.48 ± 0.46) and conditioned-MSC (1.51 ± 0.81) compared to tendons injected with PB-saline (2.26 ± 1.90).

Conclusions: No difference was found between groups at 4 weeks. The number of rats that were observed until 12 weeks for pathologic analysis was insufficient to draw conclusion. Nevertheless, these results underline that we need to host rats for a longer period for pathologic analysis. We are currently expanding this experiment with a larger number of rats to be assessed at 12 weeks.

Level of Evidence: Level I

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/mesenchymal-stem-cells-injection-as-a-therapy-in-a-rat-model-of-collagenase-induced-tendinopathy/