Large animal models for the study of tendinopathy

Understanding the structure and mechanics of the sheep calcaneal enthesis: a relevant animal model to design scaffolds for tissue engineering applications

Tendon or enthesis injuries are a worldwide clinical problem. Along the enthesis, collagen fibrils show a progressive loss of anisotropy and an increase in mineralization reaching the bone. This causes gradients of mechanical properties. The design of scaffolds to regenerate these load-bearing tissues requires validation in vivo in relevant large animal models. The sheep tendon of triceps surae muscle is an optimal animal model for this scope with limited knowledge about its structure and mechanics. We decided to investigate in-depth its structure and full-field mechanics. Collagen fibrils morphology was investigated via scanning electron microscopy revealing a marked change in orientation/dimensions passing from the tendon to the enthesis. Backscatter electron images and nanoindentation at the enthesis/bone marked small gradients of mineralization at the mineralized fibrocartilage reaching 27%wt and indentation modulus around 17-30 GPa. The trabecular bone instead had indentation modulus around 15-22 GPa. Mechanical tensile tests with digital image correlation confirmed the typical non-linear behavior of tendons (failure strain = 8.2 ± 1.0 %; failure force = 1369 ± 187 N) with maximum principal strains reaching mean values of εp1 ∼ 7 %. The typical auxetic behavior of tendon was highlighted by the minimum principal strains (εp2 ∼ 5 %), progressively dampened at the enthesis. Histology revealed that this behavior was caused by a local thickening of the epitenon. Cyclic tests showed a force loss of 21 ± 7 % at the last cycle. These findings will be fundamental for biofabrication and clinicians interested in designing the new generation of scaffolds for enthesis regeneration.

Neural Markers Predict Tendon Healing Outcomes in an Ovine Achilles Tendon Injury Model: Spontaneous Repair Versus Amniotic Epithelial Cell-Induced Regeneration

Tendon injuries pose a clinical challenge due to tendons' limited recovery. Emerging evidence points to the nervous system's critical role in tendon healing, with neural markers NGF, NF-200, NPY, CGRP, and GAL modulating inflammation, cell proliferation, and extracellular matrix (ECM) remodeling. This study investigates the predictive role of selected neural markers in a validated ovine Achilles tendon injury model, comparing spatio-temporal expression patterns in regenerating tendons transplanted with amniotic epithelial stem cells (AECs) versus spontaneous healing (CTR) 14 and 28 days post-injury (p.i.). AEC-treated tissues showed a spatio-temporal modulation of NF-200, NGF, NPY, CGRP, GAL, and enhanced ECM remodeling, with greater cell alignment, lower angle deviation, and accelerated collagen maturation, with a favorable Collagen type 1 (COL1) to Collagen type 3 (COL3) ratio. Pearson's matrix analysis revealed significant positive correlations between NGF, CGRP, and GAL expression, along a positive correlation between the three neural markers and cell alignment and angle deviation. As opposed to CTR, in AEC-treated tendons, lower levels of NGF, CGRP, and GAL correlated positively with improved tissue organization, suggesting these markers may predict successful tendon regeneration. The findings highlight the neuro-mediated activity of AECs in tendon regeneration, with NGF, CGRP, and GAL emerging as key predictive biomarkers for tendon healing.

Equine adult, fetal and ESC-tenocytes have differential migratory, proliferative and gene expression responses to factors upregulated in the injured tendon

Tendon injuries are a common problem in humans and horses. There is a high re-injury rate in both species due to the poor regeneration of adult tendon and the resulting formation of scar tissue. In contrast, fetal tendon injuries undergo scarless regeneration, but the mechanisms which underpin this are poorly defined. It is also unclear if tendon cells derived from embryonic stem cells (ESCs) would aid tendon regeneration. In this study we determined the responses of adult, fetal and ESC-derived equine tenocytes to a range of cytokines, chemokines and growth factors that are upregulated following a tendon injury using both 2-dimensional (2D) and 3-dimensional (3D) in vitro wound models. We demonstrated that in 2D proliferation assays, the responses of fetal and adult tenocytes to the factors tested are more similar to each other than to ESC-tenocytes. However, in 2D migration assays, fetal tenocytes have similarities to both adult and ESC-tenocytes. In 3D wound closure assays the response of fetal tenocytes also appears to be intermediary between adult and ESC-tenocytes. We further demonstrated that while TGFβ3 increases 3D gel contraction and wound healing by adult and fetal tenocytes, FGF2 results in a significant inhibition by adult cells. In conclusion, our findings suggest that differential cellular responses to the factors upregulated following a tendon injury may be involved in determining if tendon repair or regeneration subsequently occurs. Understanding the mechanisms behind these responses is required to inform the development of cell-based therapies to improve tendon regeneration.

Treatment options for Achilles tendinopathy: a scoping review of preclinical studies

Background

Achilles tendinopathy (AT) management can be difficult, given the paucity of effective treatment options and the degenerative nature of the condition. Innovative therapies for Achilles tendinopathy are therefore direly needed. New therapeutic developments predominantly begin with preclinical animal and in vitro studies to understand the effects at the molecular level and to evaluate toxicity. Despite the publication of many preclinical studies, a comprehensive, quality-assessed review of the basic molecular mechanisms in Achilles tendinopathy is lacking.

Objectives

This scoping review aims to summarize the literature regarding in vitro and in vivo animal studies examining AT treatments and evaluate their effect on tendon properties. Also, a quality assessment of the included animal studies is done. We provide a comprehensive insight into the current state of preclinical AT treatment research which may guide preclinical researchers in future research.

Eligibility criteria

Treatment options of Achilles tendinopathy in chemically or mechanically induced in vivo or in vitro Achilles tendinopathy models, reporting biomechanical, histological, and/or biochemical outcomes were included.

Sources of evidence

A systematically conducted scoping review was performed in PubMed, Embase.com, Clarivate Analytics/Web of Science, and the Wiley/Cochrane Library. Studies up to May 4, 2023 were included.

Charting Methods

Data from the included articles were extracted and categorized inductively in tables by one reviewer. The risk-of-bias quality assessment of the included animal studies is done with Systematic Review Centre for Laboratory Animal Experimentation risk-of-bias tool.

Results

A total of 98 studies is included, which investigated 65 different treatment options. 80% of studies reported significant improvement in the Achilles tendon characteristics after treatment. The main results were; maximum load and stiffness improvement; fibre structure recovered and less inflammation was observed; collagen I fibrils increased, collagen III fibrils decreased, and fewer inflammatory cells were observed after treatment. However, 65.4% to 92.5% of the studies had an uncertain to high risk of bias according to the risk-of-bias tool of the Systematic Review Centre for Laboratory Animal Experimentation.

Conclusions

Despite promising preclinical treatment outcomes, translation to clinical practice lags behind. This may be due to the poor face validity of animal models, heterogeneity in Achilles tendinopathy induction, and low quality of the included studies. Preclinical treatments that improved the biomechanical, histological, and biochemical tendon properties may be interesting for clinical trial investigation. Future efforts should focus on developing standardized preclinical Achilles tendinopathy models, improving reporting standards to minimize risk of bias, and facilitating translation to clinical practice.

Diverse and multifunctional roles for perlecan (HSPG2) in repair of the intervertebral disc

Perlecan is a widely distributed, modular, and multifunctional heparan sulfate proteoglycan, which facilitates cellular communication with the extracellular environment to promote tissue development, tissue homeostasis, and optimization of biomechanical tissue functions. Perlecan-mediated osmotic mechanotransduction serves to regulate the metabolic activity of cells in tissues subjected to tension, compression, or shear. Perlecan interacts with a vast array of extracellular matrix (ECM) proteins through which it stabilizes tissues and regulates the proliferation or differentiation of resident cell populations. Here we examine the roles of the HS-proteoglycan perlecan in the normal and destabilized intervertebral disc. The intervertebral disc cell has evolved to survive in a hostile weight bearing, acidic, low oxygen tension, and low nutrition environment, and perlecan provides cytoprotection, shields disc cells from excessive compressive forces, and sequesters a range of growth factors in the disc cell environment where they aid in cellular survival, proliferation, and differentiation. The cells in mechanically destabilized connective tissues attempt to re-establish optimal tissue composition and tissue functional properties by changing the properties of their ECM, in the process of chondroid metaplasia. We explore the possibility that perlecan assists in these cell-mediated tissue remodeling responses by regulating disc cell anabolism. Perlecan's mechano-osmotic transductive property may be of potential therapeutic application.

Effect of a single versus serial platelet-rich plasma injection on the healing of acute patellar tendon defect: an experimental study

BACKGROUND

There is no consensus on the frequency and timing of platelet-rich plasma (PRP) injection in tendon healing. We aimed to evaluate the effectiveness of single versus multiple PRP injections in the healing of patellar tendon defects in the experimental model, through histological and biomechanical investigation.

METHODS

Forty-four male skeletally mature Dutch rabbits were randomly divided into the five study groups ( A, B,C, D,E). After creating a longitudinal acute patellar tendon defect on both knees (One-third the width of the patella tendon), the right legs of the rabbits were used as the intervention group and the left legs as the control groups. Animals in groups A, B, and C were euthanized on days 7, 14, and 28, respectively, after the first PRP injection. Animals in group D received the second PRP injection on day 10 and was euthanized on day 14. Animals in group D received the second and third PRP injections on days 10 and 20, respectively, and were euthanized on day 28. The outcomes were evaluated histologically (modification of Movin's Grading) and biomechanically.

RESULTS

The inflammatory condition was exaggerated in groups D and E. Load at failure was higher in the non-injected side of groups D and E, while there was no significant difference between the right and left legs of the three groups A, B and C. In other word, groups with a single PRP injection were more resistant to the increasing load compared to the groups with multiple PRP injections.

CONCLUSIONS

PRP improves tendon healing if injected early after injury, while its injection after the initial phase of injury hampers tendon healing. In addition, a single PRP injection seems to be more effective than multiple PRP injection. Therefore, in cases where PRP injection is indicated for tendon repair, such as acute tendon injury, we recommend using a single PRP injection during tendon repair surgery.

Noninvasive release of tendons using MRI guided focused ultrasound: a hybrid therapy using long-pulse focused ultrasound followed by thermal ablation

INTRODUCTION

Magnetic Resonance-guided Focused Ultrasound (MRgFUS) thermal ablation is an effective noninvasive ultrasonic therapy to disrupt in vivo porcine tendon but is prone to inducing skin burns. We evaluated the safety profile of a novel hybrid protocol that minimizes thermal spread by combining long-pulse focused ultrasound followed by thermal ablation.

METHODS

In-vivo Achilles tendons (hybrid N = 15, thermal ablation alone N = 21) from 15 to 20 kg Yorkshire pigs were randomly assigned to 6 treatment groups in two studies. The first (N = 21) was ablation (600, 900, or 1200 J). The second (N = 15) was hybrid: pulsed FUS (13.5 MPa peak negative pressure) followed by ablation (600, 900, or 1200 J). Measurements of ankle range of motion, tendon temperature, thermal dose (240 CEM43), and assessment of skin burn were performed in both groups.

RESULTS

Rupture was comparable between the two protocols: 1/5 (20%), 5/5 (100%) and 5/5 (100%) for hybrid protocol, compared to 2/7 (29%), 6/7 (86%) and 7/7 (100%) for the ablation-only protocol with energies of 600, 900, and 1200 J, respectively. The hybrid protocol produced lower maximum temperatures, smaller areas of thermal dose, fewer thermal injuries to the skin, and fewer full-thickness skin burns. The standard deviation for the area of thermal injury was also smaller for the hybrid protocol, suggesting greater predictability.

CONCLUSION

This study demonstrated a hybrid MRgFUS protocol combining long-pulse FUS followed by thermal ablation to be noninferior and safer than an ablation-only protocol for extracorporeal in-vivo tendon rupture for future clinical application for noninvasive release of contracted tendon.

The rat as a novel model for chronic rotator cuff injuries

Chronic rotator cuff injuries (CRCIs) still present a great challenge for orthopaedics surgeons. Many new therapeutic strategies are developed to facilitate repair and improve the healing process. However, there is no reliable animal model for chronic rotator cuff injury research. To present a new valuable rat model for future chronic rotator cuff injuries (CRCIs) repair studies, and describe the changes of CRCIs on the perspectives of histology, behavior and MRI. Sixty male Wistar rats were enrolled and underwent surgery of the left shoulder joint for persistent subacromial impingement. They were randomly divided into experimental group (n = 30, a 3D printed PEEK implant shuttled into the lower surface of the acromion) and sham operation group (n = 30, insert the same implant, but remove it immediately). Analyses of histology, behavior, MRI and inflammatory pain-related genes expression profiles were performed to evaluate the changes of CRCIs. After 2-weeks running, the rats in the experimental group exhibited compensatory gait patterns to protect the injured forelimb from loading after 2-weeks running. After 8-weeks running, the rats in the experimental group showed obvious CRCIs pathological changes: (1) acromion bone hyperplasia and thickening of the cortical bone; (2) supraspinatus muscle tendon of the humeral head: the bursal-side tendon was torn and layered with disordered structure, forming obvious gaps; the humeral-side tendon is partially broken, and has a neatly arranged collagen. Partial fat infiltration is found. The coronal T2-weighted images showed that abnormal tendon-to-bone junctions of the supraspinatus tendon. The signal intensity and continuity were destroyed with contracted tendon. At the nighttime, compared with the sham operation group, the expression level of IL-1β and COX-2 increased significantly (P = 0063, 0.0005) in the experimental group. The expression of COX-2 in experimental group is up-regulated about 1.5 times than that of daytime (P = 0.0011), but the expression of IL-1β, TNF-a, and NGF are all down-regulated (P = 0.0146, 0.0232, 0.0161). This novel rat model of chronic rotator cuff injuries has the similar characteristics with that of human shoulders. And it supplies a cost-effective, reliable animal model for advanced tissue engineered strategies and future therapeutic strategies.

Biocompatibility of hydrogel derived from equine tendon extracellular matrix in horses subcutaneous tissue

Tendinopathies account for a substantial proportion of musculoskeletal injuries. To improve treatment outcomes for partial and total tendon ruptures, new therapies are under investigation. These include the application of mesenchymal stem cells (MSCs) and biocompatible scaffolds derived from the Extracellular Matrix (ECM). Synthetic polymer hydrogels have not demonstrated results as promising as those achieved with ECM hydrogels sourced from the original tissue. This study aimed to evaluate the biocompatibility of a hydrogel formulated from equine tendon ECM. Six horses were administered three subcutaneous doses of the hydrogel, with a saline solution serving as a control. Biopsies were conducted on days 7, 14, and 56 post-application to gauge the hydrogel's impact. Throughout the experiment, the horse's physical condition remained stable. Thermographic analyses revealed a temperature increase in the treated groups compared to the control group within the initial 12 h. The von Frey test, used to measure the mechanical nociceptive threshold, also showed significant differences between the treated group and the control group at 6 h, 21 days, and 28 days. Histopathological analyses identified an inflammatory response on day 7, which was absent on days 14 and 56. Transmission electron microscopy indicated a decrease in inflammatory cellularity, while immunohistochemistry staining suggested an increased presence of inflammatory factors on day 14. In summary, the hydrogel is easily injectable, triggers a temporary local inflammatory response, and integrates into the adjacent tissue from day 14 onwards.

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.

Equine tendon mechanical behaviour: Prospects for repair and regeneration applications

Tendons are dense connective tissues that play an important role in the biomechanical function of the musculoskeletal system. The mechanical forces have been implicated in every aspect of tendon biology. Tendon injuries are frequently occurring and their response to treatments is often unsatisfactory. A better understanding of tendon biomechanics and mechanobiology can help develop treatment options to improve clinical outcomes. Recently, tendon tissue engineering has gained more attention as an alternative treatment due to its potential to overcome the limitations of current treatments. This review first provides a summary of tendon mechanical properties, focusing on recent findings of tendon mechanobiological responses. In the next step, we highlight the biomechanical parameters of equine energy-storing and positional tendons. The final section is devoted to how mechanical loading contributes to tenogenic differentiation using bioreactor systems. This study may help develop novel strategies for tendon injury prevention or accelerate and improve tendon healing.