Combined ascorbic acid and T3 produce better healing compared to bone marrow mesenchymal stem cells in an Achilles tendon injury rat model: a proof of concept study

Background: This pilot study aimed to ascertain whether the local application of ascorbic acid (AA), of T-3, and of rat (r) bone marrow mesenchymal stem cells (BMSCs), alone or in all possible combinations, promoted healing after an Achilles tendon injury in a rat model. Methods: An Achilles tendon defect was produced in 24 6-8-week-old male inbred Lewis rats. The animals were then randomly divided into eight groups of three rats each. The tendon defect was filled with 50 mu L of phosphate-buffered saline (PBS) containing (1) 50 mu g/mL AA (AA group), (2) 10(-7) M T-3 (T-3 group), (3) 4 x 10(6) rBMSCs (rBMSC group), (4) 50 mu g/mL AA + 10(-7) M T-3 (AA + T-3 group), (5) 4 x 10(6) rBMSCs + 50 mu g/mL AA (rBMSC + AA group), (6) 4 x1 0(6) rBMSCs + 10(-7) M T-3 (rBMSC + T-3 group), (7) 4 x 10(6) rBMSCS + 50 mu g/mL AA + 10(-7) M T-3 (rBMSC + AA + T-3 group), and (8) PBS only (control group: CTRL). All treatments were administered by local injection immediately after the tendons had been damaged; additionally, AA was injected also on the second and fourth day from the first injection (for groups 1, 4, 5, and 7), and T-3 was injected again every day for 4 days (for groups 2, 4, 6, and 7). At 30 days from initial treatment, tendon samples were harvested, and the quality of tendon repair was evaluated using histological and histomorphological analysis. The structure and morphology of the injured Achilles tendons were evaluated using the modified Svensson, Soslowsky, and Cook score, and the collagen type I and III ratio was calculated. Results: The group treated with AA combined with T-3 displayed the lowest Svensson, Soslowsky, and Cook total score value of all tissue sections at histopathological examination, with fiber structure close to regular orientation, normal-like tendon vasculature, and no cartilage formation. AA + T-3 also showed the highest collagen I and the lowest collagen III values compared to all other treatments including the CTRL. Conclusion: There are potential benefits using a combination of AA and T-3 to accelerate tendon healing.