Therapeutic Efficacy of Intratendinous Delivery of Dexamethasone Using Porous Microspheres for Amelioration of Inflammation and Tendon Degeneration on Achilles Tendinitis in Rats

A Novel Tendon Injury Model, Induced by Collagenase Administration Combined with a Thermo-Responsive Hydrogel in Rats, Reproduces the Pathogenesis of Human Degenerative Tendinopathy

Patellar tendinopathy is a common clinical problem, but its underlying pathophysiology remains poorly understood, primarily due to the absence of a representative experimental model. The most widely used method to generate such a model is collagenase injection, although this method possesses limitations. We developed an optimized rat model of patellar tendinopathy via the ultrasound-guided injection of collagenase mixed with a thermo-responsive Pluronic hydrogel into the patellar tendon of sixty male Wistar rats. All analyses were carried out at 3, 7, 14, 30, and 60 days post-injury. We confirmed that our rat model reproduced the pathophysiology observed in human patients through analyses of ultrasonography, histology, immunofluorescence, and biomechanical parameters. Tendons that were injured by the injection of the collagenase-Pluronic mixture exhibited a significant increase in the cross-sectional area (p < 0.01), a high degree of tissue disorganization and hypercellularity, significantly strong neovascularization (p < 0.01), important changes in the levels of types I and III collagen expression, and the organization and presence of intra-tendinous calcifications. Decreases in the maximum rupture force and stiffness were also observed. These results demonstrate that our model replicates the key features observed in human patellar tendinopathy. Collagenase is evenly distributed, as the Pluronic hydrogel prevents its leakage and thus, damage to surrounding tissues. Therefore, this model is valuable for testing new treatments for patellar tendinopathy.

Advances toward transformative therapies for tendon diseases

Approved therapies for tendon diseases have not yet changed the clinical practice of symptomatic pain treatment and physiotherapy. This review article summarizes advances in the development of novel drugs, biologic products, and biomaterial therapies for tendon diseases with perspectives for translation of integrated therapies. Shifting from targeting symptom relief toward disease modification and prevention of disease progression may open new avenues for therapies. Deep evidence-based clinical, cellular, and molecular characterization of the underlying pathology of tendon diseases, as well as therapeutic delivery optimization and establishment of multidiscipline interorganizational collaboration platforms, may accelerate the discovery and translation of transformative therapies for tendon diseases.

17β-Estradiol attenuates inflammation and tendon degeneration in a rat model of Achilles tendinitis

INTRODUCTION

17β-Estradiol (E2) is an immune-regulatory agent with anti-inflammatory effects. However, it is still unknown whether E2 exerts pharmacological properties against Achilles tendinitis (AT). This study aims to investigate the effects of E2 on AT and its underlying mechanisms.

MATERIALS AND METHODS

The established model of Achilles tendinitis was intraperitoneally injected with E2 (10, 20, or 30 μg/kg/d). After 8 weeks, biomechanical properties of the Achilles tendon were determined. Hydroxyproline content and tendon degeneration-related biomarkers were determined. The levels of inflammatory cytokines and apoptotic-related biomarkers in tendon tissues were determined. Furthermore, western blotting was determined to detect the expressions of ER-α and the PI3K/Akt pathway in tendon tissues.

RESULTS

E2 relieved AT-related symptoms in a dose-dependent manner. E2 ameliorated tendon degeneration by regulating tendon degeneration-related biomarkers (e.g., collagen type I and III, Decorin (DCN), and tenascin-C). Besides, treatment with E2 suppressed inflammatory cytokines and increased anti-inflammatory cytokines. Treatment with E2 also regulated cell apoptosis in tendon tissues. The underlying mechanism study revealed that treatment with E2 activated ER-α and upregulated the PI3K/Akt pathway.

CONCLUSION

The regulatory effects of E2 on inflammation and tendon degeneration in a rat model of AT were associated with the ER-α and the PI3K/Akt signaling pathways.