Dose-Related and Time-Dependent Development of Collagenase-Induced Tendinopathy in Rats

Novel In Vitro Platform for Studying the Cell Response to Healthy and Diseased Tendon Matrices

Current in vitro models poorly represent the healthy or diseased tendon microenvironment, limiting the translation of the findings to clinics. The present work aims to establish a physiologically relevant in vitro tendon platform that mimics biophysical aspects of a healthy and tendinopathic tendon matrix using a decellularized bovine tendon and to characterize tendon cells cultured using this platform. Bovine tendons were subjected to various decellularization techniques, with the efficacy of decellularization determined histologically. The biomechanical and architectural properties of the decellularized tendons were characterized using an atomic force microscope. Tendinopathy-mimicking matrices were prepared by treating the decellularized tendons with collagenase for 3 h or collagenase-chondroitinase (CC) for 1 h. The tendon tissue collected from healthy and tendinopathic patients was characterized using an atomic force microscope and compared to that of decellularized matrices. Healthy human tendon-derived cells (hTDCs) from the hamstring tendon were cultured on the decellularized matrices for 24 or 48 h, with cell morphology characterized using f-actin staining and gene expression characterized using real-time PCR. Tendon matrices prepared by freeze-thawing and 48 h nuclease treatment were fully decellularized, and the aligned structure and tendon stiffness (1.46 MPa) were maintained. Collagenase treatment prepared matrices with a disorganized architecture and reduced stiffness (0.75 MPa), mimicking chronic tendinopathy. Treatment with CC prepared matrices with a disorganized architecture without altering stiffness, mimicking early tendinopathy (1.52 MPa). hTDCs on a healthy tendon matrix were elongated, and the scleraxis (SCX) expression was maintained. On tendinopathic matrices, hTDCs had altered morphological characteristics and lower SCX expression. The expression of genes related to actin polymerization, matrix degradation and remodeling, and immune cell invasion were higher in hTDCs on tendinopathic matrices. Overall, the present study developed a physiological in vitro system to mimic healthy tendons and early and late tendinopathy, and it can be used to better understand tendon cell characteristics in healthy and diseased states.

Cellular and Structural Changes in Achilles and Patellar Tendinopathies: A Pilot In Vivo Study

Tendinopathies continue to be a challenge for both patients and the medical teams providing care as no universal clinical practice guidelines have been established. In general, tendinopathies are typically characterized by prolonged, localized, activity-related pain with abnormalities in tissue composition, cellularity, and microstructure that may be observed on imaging or histology. In the lower limb, tendinopathies affecting the Achilles and the patellar tendons are the most common, showing a high incidence in athletic populations. Consistent diagnosis and management have been challenged by a lack of universal consensus on the pathophysiology and clinical presentation. Current management is primarily based on symptom relief and often consists of medications such as non-steroidal anti-inflammatories, injectable therapies, and exercise regimens that typically emphasize progressive eccentric loading of the affected structures. Implementing the knowledge of tendon stem/progenitor cells (TSPCs) and assessing their potential in enhancing tendon repair could fill an important gap in this regard. In the present pilot in vivo study, we have characterized the structural and cellular alterations that occur soon after tendon insult in models of both Achilles and patellar tendinopathy. Upon injury, CD146+ TSPCs are recruited from the interfascicular tendon matrix to the vicinity of the paratenon, whereas the observed reduction in M1 macrophage polarization is related to a greater abundance of reparative CD146+ TSPCs in situ. The robust TSPCs' immunomodulatory effects on macrophages were also demonstrated in in vitro settings where TSPCs can effectively polarize M1 macrophages towards an anti-inflammatory therapeutic M2 phenotype. Although preliminary, our findings suggest CD146+ TSPCs as a key phenotype that could be explored in the development of targeted regenerative therapies for tendinopathies.

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.

Antioxidant and anti-inflammatory injectable hydrogel microspheres for in situ treatment of tendinopathy

Tendinopathy is a common disorder that causes local dysfunction and reduces quality of life. Recent research has indicated that alterations in the inflammatory microenvironment play a vital role in the pathogenesis of tendinopathy. Herein, injectable methacrylate gelatin (GelMA) microspheres (GM) were fabricated and loaded with heparin-dopamine conjugate (HDC) and hepatocyte growth factor (HGF). GM@HDC@HGF were designed to balance the inflammatory microenvironment by inhibiting oxidative stress and inflammation, thereby regulating extracellular matrix (ECM) metabolism and halting tendon degeneration. Combining growth factors with heparin was expected to improve the encapsulation rate and maintain the long-term efficacy of HGF. In addition, the catechol groups on dopamine have adhesion and antioxidant properties, allowing potential attachment at the injured site, and better function synergized with HGF. GM@HDC@HGF injected in situ in rat Achilles tendinopathy (AT) models significantly down-regulated oxidative stress and inflammation, and ameliorated ECM degradation. In conclusion, the multifunctional platform developed presents a promising alternative for the treatment of tendinopathy.

Regeneration process of myotendinous junction injury induced by collagenase injection between Achilles tendon and soleus muscle in mice

Recently, it has become clear that peri-muscular tissues play a significant role in the deterioration of muscle function. Understanding the function and regeneration of muscle, as well as its surrounding tissues, is crucial to determining the causes of muscular illnesses. However, the regeneration process of the myotendinous junction (MTJ), the most closely related peri-muscular tissue, is still unknown. Therefore, we generated a mouse model of MTJ injury by collagenase injection and searched for the process of regeneration of the MTJ and its adjacent regions. The MTJ region was damaged by collagenase injection, which greatly increased the tendon cross sectional area. Collagenase injections increased the proportion of myofibers with a central nucleus, which is a characteristic of regenerating muscle. The collagenase injection group had myofibers with central nuclei and expressing MTJ markers. Additionally, we measured the length of MTJs using serial cross sections of the soleus muscle and discovered that MTJs at 2 weeks after collagenase injection were shorter compared to the control group, with a propensity to progressively recover their length over time. The results showed that MTJs undergo morphological regeneration even when severely damaged, and that this regeneration occurs in conjunction with muscle regeneration. We anticipate that these findings will be valuable in upcoming research on motor unit regeneration.

Animal model for tendinopathy

Background

Tendinopathy is a common motor system disease that leads to pain and reduced function. Despite its prevalence, our mechanistic understanding is incomplete, leading to limited efficacy of treatment options. Animal models contribute significantly to our understanding of tendinopathy and some therapeutic options. However, the inadequacies of animal models are also evident, largely due to differences in anatomical structure and the complexity of human tendinopathy. Different animal models reproduce different aspects of human tendinopathy and are therefore suitable for different scenarios. This review aims to summarize the existing animal models of tendinopathy and to determine the situations in which each model is appropriate for use, including exploring disease mechanisms and evaluating therapeutic effects.

Methods

We reviewed relevant literature in the PubMed database from January 2000 to December 2022 using the specific terms ((tendinopathy) OR (tendinitis)) AND (model) AND ((mice) OR (rat) OR (rabbit) OR (lapin) OR (dog) OR (canine) OR (sheep) OR (goat) OR (horse) OR (equine) OR (pig) OR (swine) OR (primate)). This review summarized different methods for establishing animal models of tendinopathy and classified them according to the pathogenesis they simulate. We then discussed the advantages and disadvantages of each model, and based on this, identified the situations in which each model was suitable for application.

Results

For studies that aim to study the pathophysiology of tendinopathy, naturally occurring models, treadmill models, subacromial impingement models and metabolic models are ideal. They are closest to the natural process of tendinopathy in humans. For studies that aim to evaluate the efficacy of possible treatments, the selection should be made according to the pathogenesis simulated by the modeling method. Existing tendinopathy models can be classified into six types according to the pathogenesis they simulate: extracellular matrix synthesis-decomposition imbalance, inflammation, oxidative stress, metabolic disorder, traumatism and mechanical load.

Conclusions

The critical factor affecting the translational value of research results is whether the selected model is matched with the research purpose. There is no single optimal model for inducing tendinopathy, and researchers must select the model that is most appropriate for the study they are conducting.

The translational potential of this article

The critical factor affecting the translational value of research results is whether the animal model used is compatible with the research purpose. This paper provides a rationale and practical guide for the establishment and selection of animal models of tendinopathy, which is helpful to improve the clinical transformation ability of existing models and develop new models.

A pilot study testing an Achilles tendinopathy human cadaver model using intratendinous injection of collagenase

BACKGROUND

Achilles tendinopathy is one of the most frequently occurring soft-tissue injuries. Despite decades of research, there is still much that is unknown about the progression of tendinopathy. Animal models, such as collagenase injection, allow researchers to gain insight into disease progression and investigate clinical interventions, yet are limited in their direct application to humans. Establishment of a cadaver model of tendinopathy would provide another method of investigating clinical interventions in human tissues. The purpose of this study is to develop such a model and evaluate biomechanical changes in cadaveric Achilles tendons using ultrasound elastography.

METHODS

Achilles tendons of five female foot/ankle cadavers were injected with two different concentrations (three with 10 mg/mL, two 20 mg/mL) of collagenase and incubated for 24 h. Ultrasound elastography images were collected at baseline, 16 and 24 h post-injection. Elasticity of tendons was calculated using a custom image analysis program.

FINDINGS

Elasticity decreased over time in both dosage groups. In the 10 mg/mL group, mean elasticity decreased from 642 ± 246 kPa at baseline to 392 ± 38.3 kPa at 16 h and 263 ± 87.3 kPa at 24 h. In the 20 mg/mL group, mean elasticity decreased from 628 ± 206 kPa at baseline to 176 ± 152 kPa at 16 h and 188 ± 120 kPa at 24 h.

INTERPRETATION

Injection of collagenase into cadaveric Achilles tendons resulted in decreases in elasticity. Decreases were observed in tendons that received injections with both 10 and 20 mg/mL collagenase dosages. Further biomechanical and histological testing is needed to evaluate this cadaveric tendinopathy.

Irreversible Electroporation Improves Tendon Healing in a Rat Model of Collagenase-Induced Achilles Tendinopathy

BACKGROUND

Treatment of painful chronic tendinopathy is challenging, and there is an urgent need to develop new regenerative methods. Irreversible electroporation (IRE) can lead to localized cell ablation by electrical pulses and induce new cell and tissue growth. Previously, the authors' group reported that electroporation-ablated tendons fully regenerated.

PURPOSE

To assess the efficiency of IRE in improving tendon healing using a collagenase-induced Achilles tendinopathy rat model.

STUDY DESIGN

Controlled laboratory study.

METHODS

After screening for the IRE ablation parameters, a collagenase-induced Achilles tendinopathy rat model was used to assess the efficacy of IRE in improving tendon healing via biomechanical, behavioral, histological, and immunofluorescence assessments.

RESULTS

The experiments showed that the parameter of 875 V/cm 180 pulses could ablate most tenocytes, and apoptosis was the main type of death in vitro. In vivo, IRE promoted the healing process of chronic tendinopathy in the Achilles tendon of rats, based on biomechanical, behavioral, and histological assessments. Finally, immunofluorescence results revealed that IRE improved blood supply in the early stages of tendon repair and could potentially reduce neuropathic pain.

CONCLUSION

IRE enhanced tendon tissue healing in a rat model of collagenase-induced Achilles tendinopathy.

CLINICAL RELEVANCE

IRE may as a potential alternative treatment for tendinopathy in clinical usage.

Quantitative analysis of tendon histopathology using digital pathology in rat models with Achilles tendon injury

Although digital image analysis methods that quantify histopathologic features have emerged, no validated quantitative methods are available to evaluate tendon injury. This study aimed to propose and validate a quantitative analysis method to identify the histopathologic features of tendon injuries. The histopathologic features of two Achilles tendon injury models (a partial full-thickness defect model and a collagenase injection model) using Sprague-Dawley rats were evaluated by semiquantitative grading and a quantitative analysis method using a digital pathology software at weeks 1 and 4 after tendon injury (six tendons per group at each time point). The outcome variables between tendon injury models and between time points were compared, and the correlation between semiquantitative scores and the results of the quantitative analysis was investigated. The proposed analysis method quantified the severity of the histopathological features after tendon injury. Quantitative analysis differentiated the cell morphology between tendon injury models and time points better than semiquantitative scoring. The results from quantitative measurements correlated significantly with the semiquantitative scores. The proposed quantitative method can be effective in evaluating the histopathology of tendon injuries.

Long-term anti-inflammatory effects of injectable celecoxib nanoparticle hydrogels for Achilles tendon regeneration

The treatment of chronic Achilles tendonitis (AT) often requires prolonged therapy and invasive therapeutic methods such as surgery or therapeutic endoscopy. To prevent the progression of chronic AT, excessive inflammation must be alleviated at an early stage. Corticosteroids or nonsteroidal anti-inflammatory drugs are generally prescribed to control inflammation; however, the high doses and long therapeutic periods required may lead to serious side effects. Herein, a local injectable poly(organophosphazene) (PPZ) - celecoxib (CXB) nanoparticle (PCNP) hydrogel system with long-term anti-inflammatory effects was developed for the treatment of tendonitis. The amphiphilic structure and thermosensitive mechanical properties of PPZ means that the hydrophobic CXB can be easily incorporated into the hydrophobic core to form PCNP at 4 °C. Following the injection of PCNP into the AT, PCNP hydrogel formed at body temperature and induced long-term local anti-inflammatory effects via sustained release of the PCNP. The therapeutic effects of the injectable PCNP system can alleviate excessive inflammation during the early stages of tissue damage and boost tissue regeneration. This study suggests that PCNP has significant potential as a long-term anti-inflammatory agent through sustained nonsteroidal anti-inflammatory drugs (NSAIDs) delivery and tissue regeneration boosting. STATEMENT OF SIGNIFICANCE: In the treatment of Achilles tendinitis, a long-term anti-inflammatory effect is needed to alleviate excessive inflammation and induce regeneration of the damaged Achilles tendon. Injectable poly(organophosphazene)(PPZ)-celecoxib(CXB) nanoparticles (PCNP) generated a long-term, localized-anti-inflammatory effect in the injected region, which successfully induced the expression of anti-inflammatory cytokines and suppressed pro-inflammatory cytokines, while the PCNPs degraded completely. Accordingly, regeneration of the damaged Achilles tendon was achieved through the long-term anti-inflammatory effect induced by a single PCNP injection. The PCNP system therefore has great potential in long-term NSAIDs delivery for various tissue engineering applications.

Antioxidant effect of nicotinamide mononucleotide in tendinopathy

Background

A link between tendinopathy and oxidative stress has been recently reported. Nicotinamide mononucleotide (NMN) is a precursor of nicotinamide adenine dinucleotide, which plays an important role in cell redox homeostasis. The aim of this study was to evaluate the antioxidant effect of NMN on tendinopathy in vitro and in vivo.

Methods

Tenocytes from healthy Sprague-Dawley rats were cultured in regular glucose (RG) and high-glucose (HG) conditions with or without NMN, and were divided into four groups: RG NMN(−), RG NMN(+), HG NMN(−), and HG NMN(+). Cell viability, reactive oxygen species (ROS) accumulation, apoptotic rate, and mRNA expression of nicotinamide adenine dinucleotide phosphate oxidase (NOX)1, NOX4, interleukin (IL)6, sirtuin (SIRT)1, and SIRT6 were investigated. In addition, rats with collagenase-induced tendinopathy were treated with or without NMN. Immunostaining of NOX1 and NOX4; mRNA expression of SIRT1, SIRT6, and IL6; and superoxide dismutase (SOD) activity measurements in the Achilles tendon were performed.

Results

NMN increased the expression of SIRT1 and SIRT6 in rat tenocytes, but decreased the levels of NOX1, NOX4, IL6, ROS, and apoptosis. In Achilles tendons with collagenase-induced tendinopathy, NMN increased the mRNA expression of SIRT1 and SIRT6, as well as SOD activity; while suppressing protein expression of NOX1 and NOX4, and mRNA expression of IL6.

Conclusion

The in vitro and in vivo results of this study show that NMN exerts an antioxidant effect on tendinopathy by promoting the expression of SIRT while inhibiting that of NOX.

Evaluation of Therapeutic Effects of Quercetin Against Achilles Tendinopathy in Rats via Oxidative Stress, Inflammation, Apoptosis, Autophagy, and Metalloproteinases

BACKGROUND

Achilles tendinopathy, seen in athletes and manual labor workers, is an inflammatory condition characterized by chronic tendon pain. Owing to the toxicity that develops in various organs attributed to the use of anti-inflammatory drugs, there is a need for new therapeutic agents.

PURPOSE

In the present study, the effects of quercetin (Que), the one that attracted the most attention of researchers studying this group of flavonoids, were investigated against collagenase-induced tendinopathy.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 35 Sprague-Dawley rats were used in the study. Tendinopathy was created by injecting a single dose of collagenase (10 μL; 10 mg/mL) into the tendons of rats. Thirty minutes after the injection, Que was administered at doses of 25 or 50 mg/kg. Que administration was carried out for 7 days. Animals underwent a motility test at the end of the study. In addition, markers of oxidative stress, inflammation, apoptosis, and autophagy, as well as the expression levels of matrix metalloproteinases (MMPs 2, 3, 9, and 13), ICAM-1, and STAT3, were measured in tendon tissues with biochemical, molecular, and Western blot techniques.

RESULTS

The results showed that oxidative stress, inflammation, apoptosis, and autophagy were triggered by the injection of collagenase. In addition, MMPs, ICAM-1, and STAT3 were activated to participate in the development of tendinopathy. Que was found to reduce ICAM-1 levels in tendon tissue. Moreover, Que showed antioxidant, anti-inflammatory, antiapoptotic, and antiautophagic effects on tendons against tendinopathy. More important, Que suppressed the expression of MMPs in the tendon tissues.

CONCLUSION

Que has protective properties against collagenase-induced tendon damage in rats.

CLINICAL RELEVANCE

We believe that with further study, Que may be shown to be an alternative treatment option for athletes or others who experience tendon injuries.

Collagenase-Induced Patellar Tendinopathy with Neovascularization: First Results towards a Piglet Model of Musculoskeletal Embolization

Background: Therapeutic strategies targeting neovessels responsible for musculoskeletal chronic pain have emerged, including neovessels embolization. Our study aimed to develop a large animal model of patellar tendinopathy with neovascularization. Methods: Nine 3-month-old male piglets (18 patellar tendons) received percutaneous injections of increasing doses of collagenase (0 to 50 mg) at day 0 (D0). Tendinopathy was evaluated by ultrasound (D7 and D14). Neovascularization was evaluated visually and on angiographies. Bonar score was used for histological analysis (D14). Correlations were evaluated using Spearman’s rank (Rs) test. Results: Research protocol was well tolerated. All tendons were enlarged with a median increase of 31.58% [25–40.28] at D7 (p = 0.244) at D7 and 57.52% [48.41–91.45] at D14 (p = 0.065). Tendons with collagenase injection had more hypoechoic changes, with one tendon rupture (p = 0.012). Neovascularization was reported above 5 mg collagenase (p < 0.01) at D7 and D14 with dose-related neovessels induction (Rs = 0.8, p < 0.001). The Bonar score increased above 5 mg collagenase, correlated with the dose (Rs = 0.666, p = 0.003). Conclusions: The study shows the feasibility, safety and reproducibility of this new large animal model of patellar tendinopathy with neovascularization after collagenase injection. It will allow studying new treatments on direct embolization of neovessels by endovascular approach.

Changes in Gene Expression Associated with Collagen Regeneration and Remodeling of Extracellular Matrix after Percutaneous Electrolysis on Collagenase-Induced Achilles Tendinopathy in an Experimental Animal Model: A Pilot Study

Percutaneous electrolysis is an emerging intervention proposed for the management of tendinopathies. Tendon pathology is characterized by a significant cell response to injury and gene expression. No study investigating changes in expression of those genes associated with collagen regeneration and remodeling of extracellular matrix has been conducted. The aim of this pilot study was to investigate gene expression changes after the application of percutaneous electrolysis on experimentally induced Achilles tendinopathy with collagenase injection in an animal model. Fifteen Sprague Dawley male rats were randomly divided into three different groups (no treatment vs. percutaneous electrolysis vs. needling). Achilles tendinopathy was experimentally induced with a single bolus of collagenase injection. Interventions consisted of 3 sessions (one per week) of percutaneous electrolysis or just needling. The rats were euthanized, and molecular expression of genes involved in tendon repair and remodeling, e.g., Cox2, Mmp2, Mmp9, Col1a1, Col3a1, Vegf and Scx, was examined at 28 days after injury. Histological tissue changes were determined with hematoxylin–eosin and safranin O analyses. The images of hematoxylin–eosin and Safranin O tissue images revealed that collagenase injection induced histological changes compatible with a tendinopathy. No further histological changes were observed after the application of percutaneous electrolysis or needling. A significant increase in molecular expression of Cox2, Mmp9 and Vegf genes was observed in Achilles tendons treated with percutaneous electrolysis to a greater extent than after just needling. The expression of Mmp2, Col1a1, Col3a1, or Scx genes also increased, but did not reach statistical significance. This animal study demonstrated that percutaneous electrolysis applied on an experimentally induced Achilles tendinopathy model could increase the expression of some genes associated with collagen regeneration and remodeling of extracellular matrix. The observed gene overexpression was higher with percutaneous electrolysis than with just needling.

Pulsed electromagnetic fields improve the healing process of Achilles tendinopathy: a pilot study in a rat model

Aims

In the context of tendon degenerative disorders, the need for innovative conservative treatments that can improve the intrinsic healing potential of tendon tissue is progressively increasing. In this study, the role of pulsed electromagnetic fields (PEMFs) in improving the tendon healing process was evaluated in a rat model of collagenase-induced Achilles tendinopathy.

Methods

A total of 68 Sprague Dawley rats received a single injection of type I collagenase in Achilles tendons to induce the tendinopathy and then were daily exposed to PEMFs (1.5 mT and 75 Hz) for up to 14 days - starting 1, 7, or 15 days after the injection - to identify the best treatment option with respect to the phase of the disease. Then, 7 and 14 days of PEMF exposure were compared to identify the most effective protocol.

Results

The daily exposure to PEMFs generally provided an improvement in the fibre organization, a decrease in cell density, vascularity, and fat deposition, and a restoration of the physiological cell morphology compared to untreated tendons. These improvements were more evident when the tendons were exposed to PEMFs during the mid-acute phase of the pathology (7 days after induction) rather than during the early (1 day after induction) or the late acute phase (15 days after induction). Moreover, the exposure to PEMFs for 14 days during the mid-acute phase was more effective than for 7 days.

Conclusion

PEMFs exerted a positive role in the tendon healing process, thus representing a promising conservative treatment for tendinopathy, although further investigations regarding the clinical evaluation are needed.

Cite this article: Bone Joint Res 2020;9(9):613–622.

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

Achilles tendinitis caused by overuse, aging, or gradual wear induces pain, swelling, and stiffness of Achilles tendon and leads to tendon rupture. This study was performed to investigate the suppression of inflammation responses in interleukin-1β- (IL-1β-) stimulated tenocytes in vitro and the suppression of the progression of Achilles tendinitis-induced rat models in vivo using dexamethasone-containing porous microspheres (DEX/PMSs) for a sustained intratendinous DEX delivery. DEX from DEX/PMSs showed the sustained release of DEX. Treatment of IL-1β-stimulated tenocytes with DEX/PMSs suppressed the mRNA levels for COX-2, IL-1β, IL-6, and TNF-α. The intratendinous injection of DEX/PMSs into Achilles tendinitis rats both decreased the mRNA levels for these cytokines and increased mRNA levels for anti-inflammatory cytokines IL-4 and IL-10 in tendon tissues. Furthermore, DEX/PMSs effectively prevented tendon degeneration by enhancing the collagen content and biomechanical properties. Our findings suggest that DEX/PMSs show great potential as a sustained intratendinous delivery system for ameliorating inflammation responses as well as tendon degeneration in Achilles tendinitis.

T1- and T2*-Mapping for Assessment of Tendon Tissue Biophysical Properties: A Phantom MRI Study

OBJECTIVES

The aim of this study was to quantitatively assess changes in collagen structure using MR T1- and T2*-mapping in a novel controlled ex vivo tendon model setup.

MATERIALS AND METHODS

Twenty-four cadaveric bovine flexor tendons underwent MRI at 3 T before and after chemical modifications, representing mechanical degeneration and augmentation. Collagen degradation (COL), augmenting collagen fiber cross-linking (CXL), and a control (phosphate-buffered saline [PBS]) were examined in experimental groups, using histopathology as standard of reference. Variable echo-time and variable-flip angle gradient-echo sequences were used for T2*- and T1-mapping, respectively. Standard T1- and T2-weighted spin-echo sequences were acquired for visual assessment of tendon texture. Tendons were assessed subsequently for their biomechanical properties and compared with quantitative MRI analysis.

RESULTS

T1- and T2*-mapping was feasible and repeatable for untreated (mean, 545 milliseconds, 2.0 milliseconds) and treated tendons. Mean T1 and T2* values of COL, CXL, and PBS tendons were 1459, 934, and 1017 milliseconds, and 5.5, 3.6, and 2.5 milliseconds, respectively. T2* values were significantly different between enzymatically degraded tendons, cross-linked tendons, and controls, and were significantly correlated with mechanical tendon properties (r = -0.74, P < 0.01). T1 values and visual assessment could not differentiate CXL from PBS tendons. Photo-spectroscopy showed increased autofluorescence of cross-linked tendons, whereas histopathology verified degenerative lesions of enzymatically degraded tendons.

CONCLUSIONS

T2*-mapping has the potential to detect and quantify subtle changes in tendon collagen structure not visible on conventional clinical MRI. Tendon T2* values might serve as a biomarker for biochemical alterations associated with tendon pathology.

The effect of surgery on patellar tendinopathy: Novel use of MRI questions the exploitability of the rat collagenase model to humans

BACKGROUND

patellar tendinopathy is an overuse condition most commonly affecting jumping athletes. Surgery is reserved for refractory cases; however, it lacks high level clinical evidence and basic science to support its use. The purpose of this study was to determine the biomechanical and histological response of surgical excision on patellar tendinopathy in the rat collagenase tendinopathy model and correlate MRI findings.

METHODS

Forty-eight Long Evans rats were divided into three groups: i) no patellar tendinopathy with surgical excision, ii) patella tendinopathy with surgical excision, and iii) patellar tendinopathy with no surgical excision. Endpoints included histology, mechanical testing, and MRI pre- and post-surgical intervention at one and four weeks.

RESULTS

No difference in failure load or histological grading was seen between the groups at all time points. MRIs showed initial loss of tendon continuity followed by complete healing with elongated and thickened tendons in all groups.

CONCLUSIONS

While other research has reported immunohistochemistry and histology of collagenase-induced tendinopathy may be correlated with human pathogenesis, the novel MRI findings from our study suggest that the rat collagenase tendinopathy surgical model may be limited when extrapolating to humans. Further work is needed to determine if any correlation exists between the dosing, location, and animal effect of the collagenase injection model with MRI findings. This is needed before any collagenase model can be used to determine the effect of surgery in the pathogenic response to patella tendinopathy.

Treatment with Human Amniotic Suspension Allograft Improves Tendon Healing in a Rat Model of Collagenase-Induced Tendinopathy

Treatment of tendon injuries is challenging, with neither conservative nor surgical approaches providing full recovery. Placental-derived tissues represent a promising tool for the treatment of tendon injuries. In this study, human amniotic suspension allograft (ASA) was investigated in a pre-clinical model of Achilles tendinopathy. Collagenase type I was injected in the right hind limb of Sprague Dawley rats to induce disease. Contralateral tendons were either left untreated or injected with saline as controls. Seven days following induction, tendons were injected with saline, ASA, or left untreated. Rats were sacrificed 14 and 28 days post-treatment. Histological and biomechanical analysis of tendons was completed. Fourteen days after ASA injection, improved fiber alignment and reduced cell density demonstrated improvement in degenerated tendons. Twenty-eight days post-treatment, tendons in all treatment groups showed fewer signs of degeneration, which is consistent with normal tendon healing. No statistically significant differences in histological or biomechanical analyses were observed between treatment groups at 28 days independent of the treatment they received. In this study, ASA treatment was safe, well-tolerated, and resulted in a widespread improvement of the tissue. The results of this study provide preliminary insights regarding the potential use of ASA for the treatment of Achilles tendinopathy.

Use of Human Placenta-Derived Cells in a Preclinical Model of Tendon Injury

BACKGROUND

Emerging data suggest that human cells derived from extraembryonic tissues may have favorable musculoskeletal repair properties. The purpose of this study was to determine whether the injection of human placenta-derived mesenchymal-like stromal cells, termed placental expanded cells (PLX-PAD), would improve tendon healing in a preclinical model of tendinopathy.

METHODS

Sixty male Sprague-Dawley rats underwent bilateral patellar tendon injection with either saline solution (control) or PLX-PAD cells (2 × 10 cells/100 µL) 6 days after collagenase injection to induce tendon degeneration. Animals were killed at specific time points for biomechanical, histological, and gene expression analyses of the healing patellar tendons.

RESULTS

Biomechanical testing 2 weeks after the collagenase injury demonstrated better biomechanical properties in the tendons treated with PLX-PAD cells. The load to failure of the PLX-PAD-treated tendons was higher than that of the saline-solution-treated controls at 2 weeks (77.01 ± 10.51 versus 58.87 ± 11.97 N, p = 0.01). There was no significant difference between the 2 groups at 4 weeks. There were no differences in stiffness at either time point. Semiquantitative histological analysis demonstrated no significant differences in collagen organization or cellularity between the PLX-PAD and saline-solution-treated tendons. Gene expression analysis demonstrated higher levels of interleukin-1β (IL-1β) and IL-6 early in the healing process in the PLX-PAD-treated tendons.

CONCLUSIONS

Human placenta-derived cell therapy induced an early inflammatory response and a transient beneficial effect on tendon failure load in a model of collagenase-induced tendon degeneration.

CLINICAL RELEVANCE

Human extraembryonic tissues, such as the placenta, are an emerging source of cells for musculoskeletal repair and may hold promise as a point-of-care cell therapy for tendon injuries.

Photobiomodulation of Matrix Metalloproteinases in Rat Calcaneal Tendons

Objective: The main objective was to verify the modulatory effects of MMP-1, MMP-3, and MMP-13 levels on the partially injured calcaneal tendons of rat exposure to photobiomodulation. Background: Photobiomodulation has been shown to have anti-inflammatory and regenerative effects on tendon injuries. However, there is still uncertainty regarding the beneficial effects in matrix metalloproteinase (MMP) levels, especially MMP-1, -3, and -13. Materials and methods: Sixty-five male Wistar rats were used. Sixty were submitted to a direct trauma on the calcaneal tendons and were randomly distributed into the following six groups: LASER 1, 3, and 7 (10 partially injured calcaneal tendons in each group treated with photobiomodulation for 1, 3, and 7 days, respectively) and Sham 1, 3, and 7 (same injury, with simulated photobiomodulation). The remaining five animals were allocated to the normal group (no injury or treatment procedure). The 780 nm low-level laser was applied with 70 mW of mean power and 17.5 J/cm² of fluency for 10 sec, once a day. The tendons were surgically removed and analyzed for MMP-1, MMP-3, and MMP-13 through immunohistochemistry. Results: MMP-3 levels remained close to normal in all experimental groups (p > 0.05); however, reductions (p < 0.05) in MMP-1 and MMP-13 levels were detected in the groups submitted to one, three, and seven low level laser therapy applications. Conclusions: The photobiomodulation protocol was able to reduce MMP-1 and MMP-13 levels in injured calcaneal tendons.

Activation of JNK signaling in osteoblasts is inversely correlated with collagen synthesis in age-related osteoporosis

The age-related reduction in the function of osteoblasts plays a central role in the pathogenesis of bone loss and osteoporosis. Collagen synthesis is a primary function of differentiated osteoblasts, however, the mechanisms for age-related changes in collagen synthesis in human osteoblasts remain elusive. We use Gene Ontology (GO) analysis and Gene Set Enrichment Analysis (GSEA) analysis to exploit the transcriptional profiles of osteoblasts from young and old donors. A panel of collagen members was downregulated in aged osteoblasts, including COL12A1, COL5A1, COL5A3, COL8A1 and COL8A2. Co-expression analysis followed by GO analysis revealed that oxidoreductase activity and kinase activity were inversely correlated with collagen synthesis in osteoblasts. GESA analysis further showed that JNK signaling was upregulated in aged osteoblasts. Consistently, MAP3K4 and MAP4K2, upstream of JNK, were also increased in aged osteoblasts. Moreover, expression levels of MAP3K4 were significantly inversely correlated with levels of the collagen genes. Those transcriptomic results were further verified by examining clinical specimens of osteoporosis by immunohistochemistry. These results provide transcriptomic evidence that deregulated JNK signaling may impair collagen synthesis in osteoblasts and imply a therapeutic value of JNK inhibitors for treating osteoporosis and preventing skeletal aging by counteracting the age-related reduction in the function of osteoblasts.

Novel animal model for Achilles tendinopathy: Controlled experimental study of serial injections of collagenase in rabbits

Our goal was to develop a novel technique for inducing Achilles tendinopathy in animal models which more accurately represents the progressive histological and biomechanical characteristic of chronic Achilles tendinopathy in humans. In this animal research study, forty-five rabbits were randomly assigned to three groups and given bilateral Achilles injections. Low dose (LD group) (n = 18) underwent a novel technique with three low-dose (0.1mg) injections of collagenase that were separated by two weeks, the high dose group (HD) (n = 18) underwent traditional single high-dose (0.3mg) injections, and the third group were controls (n = 9). Six rabbits were sacrificed from each experimental group (LD and HD) at 10, 12 and 16 weeks. Control animals were sacrificed after 16 weeks. Histological and biomechanical properties were then compared in all three groups. At 10 weeks, Bonar score and tendon cross sectional area was highest in HD group, with impaired biomechanical properties compared to LD group. At 12 weeks, Bonar score was higher in LD group, with similar biomechanical findings when compared to HD group. After 16 weeks, Bonar score was significantly increased for both LD group (11,8±2,28) and HD group (5,6±2,51), when compared to controls (2±0,76). LD group showed more pronounced histological and biomechanical findings, including cross sectional area of the tendon, Young’s modulus, yield stress and ultimate tensile strength. In conclusion, Achilles tendinopathy in animal models that were induced by serial injections of low-dose collagenase showed more pronounced histological and biomechanical findings after 16 weeks than traditional techniques, mimicking better the progressive and chronic characteristic of the tendinopathy in humans.

A review on animal models and treatments for the reconstruction of Achilles and flexor tendons

Tendon is a connective tissue mainly composed of collagen fibers with peculiar mechanical properties essential to functional movements. The increasing incidence of tendon traumatic injuries and ruptures-associated or not with the loss of tissue-falls on the growing interest in the field of tissue engineering and regenerative medicine. The use of animal models is mandatory to deepen the knowledge of the tendon healing response to severe damages or acute transections. Thus, the selection of preclinical models is crucial to ensure a successful translation of effective and safe innovative treatments to the clinical practice. The current review is focused on animal models of tendon ruptures and lacerations or defective injuries with large tissue loss that require surgical approaches or grafting procedures. Data published between 2000 and 2016 were examined. The analyzed articles were compiled from Pub Med-NCBI using search terms, including animal model(s) AND tendon augmentation OR tendon substitute(s) OR tendon substitution OR tendon replacement OR tendon graft(s) OR tendon defect(s) OR tendon rupture(s). This article presents the existing preclinical models - considering their advantages and disadvantages-in which translational progresses have been made by using bioactive sutures or tissue engineering that combines biomaterials with cells and growth factors to efficiently treat transections or large defects of Achilles and flexor tendons.