Animal models of tendinopathy

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.

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.

Mechanoepigenetic regulation of extracellular matrix homeostasis via Yap and Taz

Cells integrate mechanical cues to direct fate specification to maintain tissue function and homeostasis. While disruption of these cues is known to lead to aberrant cell behavior and chronic diseases, such as tendinopathies, the underlying mechanisms by which mechanical signals maintain cell function are not well understood. Here, we show using a model of tendon de-tensioning that loss of tensile cues in vivo acutely changes nuclear morphology, positioning, and expression of catabolic gene programs, resulting in subsequent weakening of the tendon. In vitro studies using paired ATAC/RNAseq demonstrate that the loss of cellular tension rapidly reduces chromatin accessibility in the vicinity of Yap/Taz genomic targets while also increasing expression of genes involved in matrix catabolism. Concordantly, the depletion of Yap/Taz elevates matrix catabolic expression. Conversely, overexpression of Yap results in a reduction of chromatin accessibility at matrix catabolic gene loci, while also reducing transcriptional levels. The overexpression of Yap not only prevents the induction of this broad catabolic program following a loss of cellular tension, but also preserves the underlying chromatin state from force-induced alterations. Taken together, these results provide novel mechanistic details by which mechanoepigenetic signals regulate tendon cell function through a Yap/Taz axis.

Antinociceptive Action of Thymoquinone-Loaded Liposomes in an In Vivo Model of Tendinopathy

Tendinopathies represent about 45% of musculoskeletal lesions and they are a big burden in clinics characterized by activity-related pain, focal tendon tenderness and intra-tendinous imaging changes. Many approaches have been proposed for tendinopathies' management (e.g., nonsteroidal anti-inflammatory drugs, corticosteroids, eccentric exercises, laser therapy), unfortunately with very little support of efficacy or serious side effects, thus making the identification of new treatments fundamental. The aim of the study was to test the protective and pain reliever effect of thymoquinone (TQ)-loaded formulations in a rat model of tendinopathy induced by carrageenan intra-tendon injection (20 µL of carrageenan 0.8% on day 1). Conventional (LP-TQ) and hyaluronic acid (HA)-coated TQ liposomes (HA-LP-TQ) were characterized and subjected to in vitro release and stability studies at 4 °C. Then, TQ and liposomes were peri-tendon injected (20 µL) on days 1, 3, 5, 7 and 10 to evaluate their antinociceptive profile using mechanical noxious and non-noxious stimuli (paw pressure and von Frey tests), spontaneous pain (incapacitance test) and motor alterations (Rota rod test). Liposomes containing 2 mg/mL of TQ and covered with HA (HA-LP-TQ2) reduced the development of spontaneous nociception and hypersensitivity for a long-lasting effect more than the other formulations. The anti-hypersensitivity effect matched with the histopathological evaluation. In conclusion, the use of TQ encapsulated in HA-LP liposomes is suggested as a new treatment for tendinopathies.

Development and application of a novel in vivo overload model of the Achilles tendon in rat

Repetitive overload is a primary factor in tendon injury, causing progressive accumulation of matrix damage concurrent with a cellular response. However, it remains unclear how these events occur at the initial stages of the disease, making it difficult to identify appropriate treatment approaches. Here, we describe the development of a new model to cyclically load the Achilles tendon (AT) of rats in vivo and investigate the initial structural and cellular responses. The model utilizes controlled dorsiflexion of the ankle joint applied near maximal dorsiflexion, for 10,000 cycles at 3 Hz. Animals were subjected to a single bout of in vivo loading under anaesthesia, and either culled immediately (without recovery from anaesthesia), or 48 h or 4-weeks post-loading. Macro strains were assessed in cadavers, whilst tendon specific microdamage was assessed through collagen-hybridizing peptide (CHP) immunohistochemistry which highlighted a significant rise in CHP staining in loaded ATs compared to contralateral controls, indicating an accumulation of overload-induced damage. Staining for pro-inflammatory mediators (IL-6 and COX-2) and matrix degradation markers (MMP-3 and -13) also suggests an initial cellular response to overload. Model validation confirmed our approach was able to explore early overload-induced damage within the AT, with microdamage present and no evidence of broader musculoskeletal damage. The new model may be implemented to map the progression of tendinopathy in the AT, and thus study potential therapeutic interventions.

Large extracellular vesicles secreted by human iPSC-derived MSCs ameliorate tendinopathy via regulating macrophage heterogeneity

Tendinopathy is a common musculoskeletal disorder which results in chronic pain and reduced performance. The therapeutic effect of stem cell derived-small extracellular vesicles (sEVs) for tendinopathy has been validated in recent years. However, whether large extracellular vesicles (lEVs), another subset of extracellular vesicles, possesses the ability for the improvement of tendinopathy remains unknown. Here, we showed that lEVs secreted from iPSC-derived MSCs (iMSC-lEVs) significantly mitigated pain derived from tendinopathy in rats. Immunohistochemical analysis showed that iMSC-lEVs regulated the heterogeneity of infiltrated macrophages and several inflammatory cytokines in rat tendon tissue. Meanwhile, in vitro experiments revealed that the M1 pro-inflammatory macrophages were repolarized towards M2 anti-inflammatory macrophages by iMSC-lEVs, and this effect was mediated by regulating p38 MAPK pathway. Moreover, liquid chromatography-tandem mass spectrometry analysis identified 2208 proteins encapsulated in iMSC-lEVs, including 134 new-found proteins beyond current Vesiclepedia database. By bioinformatics and Western blot analyses, we showed that DUSP2 and DUSP3, the negative regulator of p38 phosphorylation, were enriched in iMSC-lEVs and could be transported to macrophages. Further, the immunomodulatory effect of iMSC-lEVs on macrophages was validated in explant tendon tissue from tendinopathy patients. Taken together, our results demonstrate that iMSC-lEVs could reduce inflammation in tendinopathy by regulating macrophage heterogeneity, which is mediated via the p38 MAPK pathway by delivery of DUSP2 and DUSP3, and might be a promising candidate for tendinopathy therapy.

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iMSC-lEVs significantly ameliorate tendinopathy both in a rat model and explant tendon tissue from human patient.

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iMSC-lEVs modulate macrophages polarization via p38 MAPK signaling pathway.

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Proteomics analysis of iMSC-lEVs discovers a new set of 134 proteins beyond current Vesiclepedia Database.

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The p38 MAPK signaling pathway-mediated macrophage repolarization was partly regulated by the delivery of DUSP2 and DUSP3.

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The immunoregulatory function of iMSC-lEVs are similar with iMSC-sEVs.

Histological and Biomechanical Effects of Local Anesthetics and Steroids on Achilles Tendon: A Study in Rats

BACKGROUND

Peritendinous injection of local anesthetics, alone or in combination with corticosteroids, is widely used in the treatment of tendinopathies. Toxicity of local anesthetics has been demonstrated in many cells, including myocytes, chondrocytes, and neurons. Bupivacaine and lidocaine are known to have time- and dose-dependent cytotoxicity in these cells. The effects of these agents on the tendon remain unknown.

PURPOSE

To show histological and biomechanical effects after the injection of different local anesthetics and steroids, both single and combined, at different concentrations into the peritendinous sheath of rat Achilles tendon.

STUDY DESIGN

Controlled laboratory study.

METHODS

In the study, 100 rats were divided into 10 groups with equal body weights. Inflammation was induced in both Achilles tendons of each rat by means of the ball drop technique; 7 hours later, injections were made into the peritendinous sheaths of both Achilles tendons using lidocaine, bupivacaine, and dexamethasone as appropriate for the rat's group. At the end of the first week, the right Achilles tendons of the rats were removed for histological study. Left Achilles tendons were evaluated in terms of biomechanics.

RESULTS

Histological findings demonstrated that the group with the most toxicity to the tendon was the group that received injection of dexamethasone alone. The groups with the least toxicity were those receiving dexamethasone combined with low- or high-dose bupivacaine. Biomechanical findings showed that the experimental groups had similar results to each other with the exception of the groups receiving 0.25% bupivacaine alone and dexamethasone alone, in which tendons revealed higher tensile strength.

CONCLUSION

Local anesthetic and steroid applications have different histological and biomechanical effects on the tendon. Although the dexamethasone-injected group was the most affected in terms of histology, these changes could not be demonstrated biomechanically.

CLINICAL RELEVANCE

In future clinical studies, the effect of steroids on the tendon should be investigated more comprehensively. Whether biomechanical results overlap with histological results should be investigated further.

Leucine rich repeat containing 32 accelerates tenogenic differentiation of tendon-derived stem cells and promotes Achilles tendon repair in rats

Although many surgical or non-operative therapies have been developed to treat Achilles tendon injuries, the prognosis of which is often unsatisfactory. Recently, biologic approaches using multipotent stem cells like tendon-derived stem cells (TDSCs) pose a possible treatment option. To evaluate whether the Leucine rich repeat containing 32 (Lrrc32) affects the tenogenic differentiation of TDSCs and thus promotes Achilles tendon healing. TDSCs were infected with the recombinant Lrrc32-overexpressing lentivirus (LV-Lrrc32) and then locally injected into the injured site of rat. Four weeks after surgery, the Achilles tendon tissue (~0.5 cm) around the injured area was harvested for analysis. Pathological results showed that Lrrc32-overexpressing TDSCs significantly improved the morphological changes of the injured tendons. Specifically, the increased collagen-I expression and hydroxyproline content in extracellular matrix, and more orderly arrangement of the regenerated collagen fibers were observed in the Lrrc32 overexpression group. Moreover, 4 weeks after injection of Lrrc32-overexpressing TDSCs, the expression of tenocyte-related genes such as tenomodulin (Tnmd), scleraxis (Scx) and decorin (Dcn) were upregulated in the area of the healing tendon. These findings indicated that Lrrc32 promoted the tenogenic differentiation of TDSCs in vivo. Additionally, Lrrc32 overexpression also increased the expression of TGF-β1 and p-SMAD2/3, suggesting that the beneficial effects of Lrrc32 on tendon repair might be associated with the expression of TGF-β1 and p-SMAD2/3. Our findings collectively revealed that Lrrc32-overexpressed TDSCs promoted tendon healing more effectively than TDSCs alone.

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.

Restorative and pain-relieving effects of fibroin in preclinical models of tendinopathy

The term tendinopathy indicates a wide spectrum of conditions characterized by alterations in tendon tissue homeostatic response and damage to the extracellular matrix. The current pharmacological approach involves the use of nonsteroidal anti-inflammatory drugs and corticosteroids often with unsatisfactory results, making essential the identification of new treatments. In this study, the pro-regenerative and protective effects of an aqueous fibroin solution (0.5-500 μg/mL) against glucose oxidase (GOx)-induced damage in rat tenocytes were investigated. Then, fibroin anti-hyperalgesic and protective actions were evaluated in two models of tendinopathy induced in rats by collagenase or carrageenan injection, respectively. In vitro, 5-10 μg/mL fibroin per se increased cell viability and reverted the morphological alterations caused by GOx (0.1 U/mL). Fibroin 10 μg/mL evoked proliferative signaling upregulating the expression of decorin, scleraxin, tenomodulin (p < 0.001), FGF-2, and tenascin-C (p < 0.01) genes. Fibroin enhanced the basal FGF-2 and MMP-9 protein concentrations and prevented their GOx-mediated decrease. Furthermore, fibroin positively modulated the production of collagen type I. In vivo, the peri-tendinous injection of fibroin (5 mg) reduced the development of spontaneous pain and hypersensitivity (p < 0.01) induced by the intra-tendinous injection of collagenase; the efficacy was comparable to that of triamcinolone. The pain-relieving action of fibroin (peri-tendinous) was confirmed in the model of tendinopathy induced by carrageenan (intra-tendinous) where this fibrous protein was also able to improve tendon matrix organization, normalizing the orientation of collagen fibers. In conclusion, the use of fibroin in tendinopathies is suggested taking advantage of its excellent mechanical properties, pain-relieving effects, and ability to promote tissue regeneration processes.

Controlled vitamin D delivery with injectable hyaluronic acid-based hydrogel for restoration of tendinopathy

Tendinopathy is a term used to describe tendon disorders that are marked by pain and a loss of function. Recent studies demonstrated that inflammation plays an important role throughout the broad spectrum of tendinopathy. Conventional treatments such as steroid injections, analgesics, and physical modalities simply give pain relief and do not alter the disease progression without the tendon regeneration effect. Tenocytes are responsible for maintaining the tendon matrix and understanding how they function is essential to studying new treatments for tendinopathy. Our previous study showed the protective effects of vitamin D (Vit D) on damaged tenocytes. Besides its well-known effects on bone metabolism, the non-classical action of Vit D is the pleiotropic effects on modulating immune function. In the present study, we developed a Vit D delivery system with hyaluronic acid (HA), which is one of the major components of the extracellular matrix that has anti-inflammation and wound-healing properties. A novel Vit D delivery system with cross-linked HA hydrogel (Gel) and Tween 80 (T80), Vit D@Gel/T80, could be a new regeneration technique for the treatment of tendinopathy. Vit D@Gel/T80 reduced TNF-α induced damage to human tenocytes in vitro. In an animal study, the Vit D@Gel/T80 injected group demonstrated tendon restoration features. As a result, this Vit D@Gel/T80 system might be a local injection material in the treatment for tendinopathy.

Tissue predictability of elastography is low in collagenase induced deep digital flexor tendinopathy

Elastography is an emerging imaging modality for characterizing tendon injury in horses, but its ability to differentiate tissue deformability relative to treatment group and biochemical properties using a prospective, experimental study design remain unknown. Objectives of the current study were to (a) to investigate differences in glycosaminoglycan, DNA, and soluble collagen levels in mesenchymal stem cell (MSC) treated limbs compared to untreated control limbs utilizing a collagenase model of tendinopathy; (b) compare elastographic features between treatment groups; and (c) determine tissue-level predictive capabilities of elastography in relation to biochemical outcomes. Bone marrow was collected for MSC culture and expansion. Tendinopathy of both forelimb deep digital flexor tendons (DDFTs) was induced with collagenase under ultrasonographic guidance. One randomly assigned limb was treated with intra-lesional MSC injection with the opposite limb serving as an untreated control. Horses were placed into a controlled exercise program with elastographic evaluations performed baseline (0) and 14, 60, 90, and 214 days post-treatment. Postmortem biochemical analysis was performed. MSC-treated limbs demonstrated significantly less (42%) glycosaminoglycan (P = .006). Significant differences in elastographic region of interest (ROI) percent hardness, ROI color histogram, and subjective lesion stiffness were appreciated between treatment groups at various study time points. Elastographic outcome parameters were weak predictors of biochemical tissue analysis, with all R² values ≤ 0.50. Within this range of differences in glycosaminoglycan content between treatment groups, elastography outcomes did not predict biochemical differences. Tissue-specific differences between DDFTs treated with MSCs compared to controls were apparent biochemically, but not predicted by elastography.

CD146 Delineates an Interfascicular Cell Sub-Population in Tendon That Is Recruited during Injury through Its Ligand Laminin-α4

The interfascicular matrix (IFM) binds tendon fascicles and contains a population of morphologically distinct cells. However, the role of IFM-localised cell populations in tendon repair remains to be determined. The basement membrane protein laminin-α4 also localises to the IFM. Laminin-α4 is a ligand for several cell surface receptors, including CD146, a marker of pericyte and progenitor cells. We used a needle injury model in the rat Achilles tendon to test the hypothesis that the IFM is a niche for CD146+ cells that are mobilised in response to tendon damage. We also aimed to establish how expression patterns of circulating non-coding RNAs alter with tendon injury and identify potential RNA-based markers of tendon disease. The results demonstrate the formation of a focal lesion at the injury site, which increased in size and cellularity for up to 21 days post injury. In healthy tendon, CD146+ cells localised to the IFM, compared with injury, where CD146+ cells migrated towards the lesion at days 4 and 7, and populated the lesion 21 days post injury. This was accompanied by increased laminin-α4, suggesting that laminin-α4 facilitates CD146+ cell recruitment at injury sites. We also identified a panel of circulating microRNAs that are dysregulated with tendon injury. We propose that the IFM cell niche mediates the intrinsic response to injury, whereby an injury stimulus induces CD146+ cell migration. Further work is required to fully characterise CD146+ subpopulations within the IFM and establish their precise roles during tendon healing.

Species variations in tenocytes' response to inflammation require careful selection of animal models for tendon research

For research on tendon injury, many different animal models are utilized; however, the extent to which these species simulate the clinical condition and disease pathophysiology has not yet been critically evaluated. Considering the importance of inflammation in tendon disease, this study compared the cellular and molecular features of inflammation in tenocytes of humans and four common model species (mouse, rat, sheep, and horse). While mouse and rat tenocytes most closely equalled human tenocytes’ low proliferation capacity and the negligible effect of inflammation on proliferation, the wound closure speed of humans was best approximated by rats and horses. The overall gene expression of human tenocytes was most similar to mice under healthy, to horses under transient and to sheep under constant inflammatory conditions. Humans were best matched by mice and horses in their tendon marker and collagen expression, by horses in extracellular matrix remodelling genes, and by rats in inflammatory mediators. As no single animal model perfectly replicates the clinical condition and sufficiently emulates human tenocytes, fit-for-purpose selection of the model species for each specific research question and combination of data from multiple species will be essential to optimize translational predictive validity.

Enhanced tendon restoration effects of anti-inflammatory, lactoferrin-immobilized, heparin-polymeric nanoparticles in an Achilles tendinitis rat model

Gradual wear and tear can cause a local inflammatory response in tendons. The trauma and inflammatory reaction eventually impair the biomechanical properties of the tendon. In this study, we prepared lactoferrin-immobilized, heparin-anchored, poly(lactic-co-glycolic acid) nanoparticles (LF/Hep-PLGA NPs) and evaluated their in vitro anti-inflammatory effects on interleukin-1β (IL-1β)-treated tenocytes and in vivo tendon healing effects in a rat model of Achilles tendinitis. Long-term LF-deliverable NPs (LF/Hep-PLGA NPs) remarkably decreased mRNA levels of pro-inflammatory factors [cyclooxygenase-2 (COX-2), IL-1β, matrix metalloproteinase-3 (MMP-3), MMP-13, IL-6, and tumor necrosis factor-α (TNF-α)] and increased mRNA levels of anti-inflammatory cytokines (IL-4 and IL-10) in both IL-1β-treated tenocytes and the Achilles tendons of a collagenase-induced Achilles tendinitis rat model. Interestingly, anti-inflammatory LF/Hep-PLGA NPs greatly enhanced collagen content, mRNA levels of tenogenic markers [collagen type I (COL1A1), decorin (DCN), tenascin-C (TNC)], and biomechanical properties such as tendon stiffness and tensile strength. These results suggest that anti-inflammatory LF/Hep-PLGA NPs are effective at restoring tendons in Achilles tendinitis.

Targeting the NF-κB signaling pathway in chronic tendon disease

Tendon disorders represent the most common musculoskeletal complaint for which patients seek medical attention; inflammation drives tendon degeneration before tearing and impairs healing after repair. Clinical evidence has implicated the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway as a correlate of pain-free return to function after surgical repair. However, it is currently unknown whether this response is a reaction to or a driver of pathology. Therefore, we aimed to understand the clinically relevant involvement of the NF-κB pathway in tendinopathy, to determine its potential causative roles in tendon degeneration, and to test its potential as a therapeutic candidate. Transcriptional profiling of early rotator cuff tendinopathy identified increases in NF-κB signaling, including increased expression of the regulatory serine kinase subunit IKKβ, which plays an essential role in inflammation. Using cre-mediated overexpression of IKKβ in tendon fibroblasts, we observed degeneration of mouse rotator cuff tendons and the adjacent humeral head. These changes were associated with increases in proinflammatory cytokines and innate immune cells within the joint. Conversely, genetic deletion of IKKβ in tendon fibroblasts partially protected mice from chronic overuse-induced tendinopathy. Furthermore, conditional knockout of IKKβ improved outcomes after surgical repair, whereas overexpression impaired tendon healing. Accordingly, targeting of the IKKβ/NF-κB pathway in tendon stromal cells may offer previously unidentified therapeutic approaches in the management of human tendon disorders.

Intratendon delivery of leukocyte-rich platelet-rich plasma at early stage promotes tendon repair in a rabbit Achilles tendinopathy model

Tendinopathy is a great obstacle in clinical practice due to its poor regenerative capacity. The influence of different stages of tendinopathy on effects of leukocyte-rich platelet-rich plasma (Lr-PRP) has not been elucidated. The aim of this study is to investigate the optimal time point for delivery of Lr-PRP on tendinopathy. A tendinopathy model was established by local collagenase injection on the rabbit Achilles tendon. Then after collagenase induction, following treatments were applied randomly on the lesion: (a) 200 μl of Lr-PRP at 1 week (PRP-1 group), (b) 200 μl of saline at 1 week (Saline-1 group), (c) 200 μl of Lr-PRP at 4 weeks (PRP-2 group), and (d) 200 μl of saline at 4 weeks (Saline-2 group). Six weeks after collagenase induction, outcomes were assessed by magnetic resonance imaging, cytokine quantification, gene expression, histology, and transmission electron microscopy. Our results demonstrated that PRP-1 group had the least cross-sectional area and lesion percent of the involved tendon, as well as the lowest signal intensity in magnetic resonance imaging among all groups. However, the PRP-2 group showed larger cross-sectional area than saline groups. Enzyme-linked immunosorbent assay indicated that PRP-1 group had a higher level of interleukin-10 but lower level of interleukin-6 when compared with PRP-2 and saline groups. Meanwhile, the highest expression of collagen (Col) 1 in PRP-1 and Col 3, matrix metalloproteinase (MMP)-1, and MMP-3 in PRP-2 was found. Histologically, the PRP-1 showed better general scores than PRP-2, and no significant difference was found between the PRP-2 and saline groups. For transmission electron microscopy, PRP-1 had the largest mean collagen fibril diameter, and the PRP-2 group showed even smaller mean collagen fibril diameter than saline groups. In conclusion, intratendon delivery of Lr-PRP at early stage showed beneficial effect for repair of tendinopathy but not at late stage. For translation of our results to clinical circumstances, further studies are still needed.

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.

Characterization of moderate tendinopathy in ex vivo stress-deprived rat tail tendons

Background

Stress deprivation (SD) has frequently been used as a model to study tendinopathy. Most of these studies have investigated either short-term (early tendinopathy) or long-term SD (advanced tendinopathy), while the transient mid-term SD has been given less attention. Therefore, the main objective of this study was to characterize mid-term SD.

Methods

To this end, live, healthy rat tail tendons (RTTs) were harvested and cultured without mechanical stress and then were divided into five groups based on their culture time (fresh, 2-day SD, 4-day SD, 6-day SD, and 10-day SD). For each group, the tendons were subjected to traction testing and pathohistology, immunohistochemistry, and viability assays.

Results

Our results showed that 4 days of SD resulted in moderate pathological changes in RTTs. These changes included increases in the space area between fibers, cell density, and fiber tortuosity as well as a decrease in collagen density and elongation of cell nuclei. No changes in the stress at failure of tendons were observed at this time point.

Conclusions

This simple ex vivo model is expected to be useful for studying the progression of tendinopathy as well as for testing potential mechanobiological or pharmacological therapy strategies to stop or reverse the progression of the pathology.

Effects of Therapy with Light Emitting Diode (LED) in the Calcaneal Tendon Lesions of Rats: A Literature Review

The objective of this review was to analyze original articles about the effects of therapy with LED in experimental models of calcaneal tendon lesions of rats. The search was performed in the period from February to May 2018, in the following electronic databases: MEDLINE, SciELO, and LILACS, besides the Google Scholar, using the descriptors “Achilles tendon”, “Rats”, “LED”, “Tendinopathy”, and “Low-level Light Therapy”, as well as their matching parts in the Portuguese and Spanish languages, related to and in association with the relevant terms to the content sought. From the descriptors used 215 works were found. After application of eligibility criteria 8 works were selected, in which positive results were found after the application of the LED. Regarding the main results found with phototherapy, we observed a significant reduction in inflammation. Only one article mentioned little reduction of inflammation. In relation to the number of sessions, there was wide variation, with an average of approximately 5 sessions every 24 hours. Studies in this review pointed out, therefore, positive results in the repair of the calcaneal tendon after therapy with irradiation LED; however, carrying out more experimental studies that help the standardization of parameters to be used in this therapy for further clinical studies becomes necessary.

Long-term local PDGF delivery using porous microspheres modified with heparin for tendon healing of rotator cuff tendinitis in a rabbit model

In this study, we prepared the platelet-derived growth factor-containing porous microspheres modified with heparin (PDGF/Hep-PMSs) and investigated their anti-inflammatory and tendon healing effects on rotator cuff (RC) tendinitis rabbit model. PDGF/Hep-PMSs suppressed the mRNA levels of six pro-inflammatory cytokines (i.e., MMP-3, MMP-13, COX-2, ADAMTS-5, IL-6, and TNF-α) in inflamed tenocytes. Long-term local delivery of PDGF/Hep-PMSs into tendon tissues of RC tendinitis decreased the mRNA levels of six pro-inflammatory cytokines and increased the mRNA levels of anti-inflammatory cytokines including IL-4, IL-10, and IL-13. Anti-inflammatory effects of PDGF/Hep-PMSs might have contributed to enhance the collagen content, tenogenic markers, stiffness, and tensile strength of tendons, eventually leading to tendon restoration. Our findings suggest that the long-term local PDGF delivery of PDGF/Hep-PMSs have a great potential to enhance tendon healing of RC tendinitis by suppressing inflammation responses.

Patella tendinopathy Zoobiquity - What can we learn from dogs?

BACKGROUND

Patella tendinopathy is an overuse condition. Pathogenesis and identification of intrinsic risk factors have largely eluded the orthopaedic world. The cranial cruciate ligament (CrCL) in dogs is the equivalent to the human anterior cruciate ligament (ACL). We report the effect of two canine proximal tibial osteotomy procedures in the veterinary literature on patella tendon moment arm and describe the biomechanical rationale for a tibial tubercle osteotomy for treatment of patella tendinopathy in the human.

METHODS

A literature review of studies reporting clinical complications of TTA and TPLO to form an observational animal cohort study in dogs.

RESULTS

The veterinary literature reports an overall clinical complication rate of up to 61% for TTA and up to 50% for TPLO respectively. Complications associated with the extensor mechanism of the knee are <1% for TTA compared to 1.9-19% for TPLO. Radiographic thickening of the patella tendon and tendinopathy is seen in one to 80% of TPLO cases. The TPLO decreases the moment arm of the extensor mechanism meaning increased force is required in the patella tendon to achieve the same torque when compared to the TTA which increases the efficiency of the extensor mechanism. This difference may account, in part, for the post-operative complications reported to the patella and patella tendon following TPLO.

CONCLUSION

This observational animal cohort study demonstrates a biomechanical rationale for investigating diagnostic and potential treatment options, including a tibial tubercle osteotomy, for patella tendinopathy in humans based on this principle.

Tendon Remodeling in Response to Resistance Training, Anabolic Androgenic Steroids and Aging

Exercise training (ET), anabolic androgenic steroids (AAS), and aging are potential factors that affect tendon homeostasis, particularly extracellular matrix (ECM) remodeling. The goal of this review is to aggregate findings regarding the effects of resistance training (RT), AAS, and aging on tendon homeostasis. Data were gathered from our studies regarding the impact of RT, AAS, and aging on the calcaneal tendon (CT) of rats. We demonstrated a series of detrimental effects of AAS and aging on functional and biomechanical parameters, including the volume density of blood vessel cells, adipose tissue cells, tendon calcification, collagen content, the regulation of the major proteins related to the metabolic/development processes of tendons, and ECM remodeling. Conversely, RT seems to mitigate age-related tendon dysfunction. Our results suggest that AAS combined with high-intensity RT exert harmful effects on ECM remodeling, and also instigate molecular and biomechanical adaptations in the CT. Moreover, we provide further information regarding the harmful effects of AAS on tendons at a transcriptional level, and demonstrate the beneficial effects of RT against the age-induced tendon adaptations of rats. Our studies might contribute in terms of clinical approaches in favor of the benefits of ET against tendinopathy conditions, and provide a warning on the harmful effects of the misuse of AAS on tendon development.

The use of an IL1-receptor antagonist to reverse the changes associated with established tendinopathy in a rat model

Interleukin-1 (IL1) is a cytokine that plays a role in inflammation and is a potential contributor to the inflammation present in tendinopathy. Its inhibition may be of use in the treatment of tendinopathy and has been a target for treatment. To evaluate how an IL1-receptor antagonist (IL1-RA) reverses pathologic changes associated with established patellar tendinopathy, we randomized 48 Sprague-Dawley retired breeder rats into three groups having weekly bilateral patellar tendon injections for 6 weeks. The control group received 0.1 mL saline for 6 weeks. The intervention groups were treated with 0.1 mL 2% carrageenan for 4 weeks. Beginning at week three, the IL1-RA group received 0.94 mg of the IL1-RA (2.5 mg/kg) added to the 0.1 mL 2% carrageenan and 0.94 mg of the IL1-RA alone for the final 2 weeks, while the CAR received 0.1 mL saline for the final 2 weeks. Animals were euthanized 6 weeks after initial injection. The CAR group demonstrated significantly (P < 0.05) shorter tendon lengths (7.81 ± 0.44 mm) than the control (8.25 ± 0.58 mm) and IL1-RA (8.34 ± 0.52 mm) group (P < 0.05). Macroscopically, plaque-like formations were reduced and margins of the tendon were more evident in the IL1-RA group compared to the CAR group. CAR group demonstrated significantly greater histopathologic changes (inflammatory cell density, disorganization of collagen, nuclear rounding, and angiogenesis) than the control and IL1-RA group. No significant difference in mechanical properties of the tendon was noted. These findings demonstrate IL1-RA can reduce pathologic changes in the patellar tendon in an established tendonitis model although did not demonstrate a difference in mechanical properties.

Can Genipin-coated Sutures Deliver a Collagen Crosslinking Agent to Improve Suture Pullout in Degenerated Tendon? An Ex Vivo Animal Study

BACKGROUND

The suture-tendon interface is often the weakest link in tendon-to-tendon or tendon-to-bone repair. Genipin is an exogenous collagen crosslink agent derived from the gardenia fruit that can enhance suture force to failure of the tendon-suture interface. Viable methods for intraoperative clinical delivery of genipin could be of clinical utility, but to our knowledge have not yet been extensively studied.

QUESTIONS/PURPOSES

The purposes of this study were (1) to evaluate whether sutures precoated with genipin can augment the suture-tendon interface to improve force to failure, stiffness, and work to failure in healthy and degenerated tendons; and (2) to determine the effect of genipin on the extent and distribution of crosslinking.

METHODS

Single-stitch suture pullout tests were performed ex vivo on 25 bovine superficial digital flexor tendons. To assess effects on native tissue, one group of 12 tendons was cut in proximal and distal halves and randomized to treatment (n = 12) and control groups (n = 12) in a matched-pair design. One simple stitch with a loop with either a normal suture or genipin-coated suture was applied to tendons in both groups. To simulate a degenerative tendon condition, a second group of 13 tendons was cut in proximal and distal halves, injected with 0.2 mL of collagenase D (8 mg/mL) and incubated for 24 hours before suturing with either a genipin-coated suture (n = 13) or their matched controls (n = 13). Sutures from all groups then were loaded to failure on a universal materials testing machine 24 hours after suturing. Suture pullout force, stiffness, and work to failure were calculated from force-displacement data and compared between the groups. Additionally, fluorescence was measured to determine the degree of crosslinking quantitatively and a qualitative analysis of the distribution pattern was performed by microscopy.

RESULTS

In healthy tendon pairs, the median maximum pullout force was greater with genipin-coated sutures than with control sutures (median, 42 N [range, 24-73 N] versus 29 N [range, 13-48 N]; difference of medians, 13 N; p = 0.003) with corresponding increases in the required work to failure (median, 275 mJ [range, 48-369 mJ] versus 148 mJ [range, 83-369 mJ]; difference of medians, 127 mJ; p = 0.025) but not stiffness (median, 4.1 N/mm [range, 2.3-8.1 N/mm] versus 3.3 N/mm [range, 1.1-9.6 N/mm]; difference of medians, 0.8 N/mm; p = 0.052). In degenerated tendons, median maximum pullout force was greater with genipin-coated sutures than with control sutures (median, 16 N [range, 9-36 N] versus 13 N [range, 5-28 N]; difference of medians, 3 N; p = 0.034) with no differences in work to failure (median, 75 mJ [range, 11-249 mJ] versus 53 mJ [range, 14-143 mJ]; difference of medians, 22 mJ; p = 0.636) or stiffness (median, 1.9 N/mm [range, 0.7-13.4 N/mm] versus 1.6 N/mm [range, 0.5-5.6 N/mm]; difference of medians, 0.3 N/mm; p = 0.285). Fluorescence was higher in tendons treated with genipin-coated sutures compared with the control group, whereas higher fluorescence was observed in the treated healthy compared with the degenerated tendons (difference of means -3.16; standard error 1.08; 95% confidence interval [CI], 0.97-5.34; p = 0.006/healthy genipin: mean 13.04; standard error 0.78; 95% CI, 11.47-14.62; p < 0.001/degenerated genipin: mean 9.88; SD 0.75; 95% CI, 8.34-11.40; p < 0.001).

CONCLUSIONS

Genipin-coated sutures improved force to failure of a simple stitch at the tendon-suture interface in healthy and degenerated tendons in an ex vivo animal model. Fluorescence was higher in tendons treated with genipin-coated sutures compared with the control group.

CLINICAL RELEVANCE

A genipin-coated suture represents a potential delivery vehicle for exogenous crosslink agents to augment suture retention properties. In vivo animal studies are the next logical step to assess safety and efficacy of the approach.

Tendinopathy diagnosis and treatment monitoring using attenuated total reflectance-Fourier transform infrared spectroscopy

Tendinopathy, an important sports injury afflicting athletes and general public, is associated with huge economic losses. The currently used diagnostic tests are subjective, show moderate sensitivity and specificity; while treatment failures persist despite advances in therapy. This highlights the need for tendinopathy diagnostic and treatment monitoring tools. This study investigates tendon injury, natural healing and effect of treatment using ATR-FTIR complemented with histopathology. Control (C), injured (I) and treated (T) rat tendons were extracted 3, 7, 14 and 28 days post-injury/treatment, representing phases of healing; and subjected to hematoxylin & eosin staining as well as spectroscopy. While C showed no change, I- and T-related histological changes could be clearly observed in stained sections. ATR-FTIR spectra highlighted the biochemical changes within groups. Multivariate analysis could classify C, I and T with 75%; different days between groups with 84%; and different days within group with 65% efficiency. Results suggest that such analysis can not only identify C, I or T but also different phases of healing. Difference between I and T at different time points also suggest change in rate of healing. Further studies may help develop this technique for clinical diagnosis and treatment monitoring in future.

Evaluation of Stem Cell Therapies in a Bilateral Patellar Tendon Injury Model in Rats

Regenerative medicine provides novel alternatives to conditions that challenge traditional treatments. The prevalence and morbidity of tendinopathy across species, combined with the limited healing properties of this tissue, have prompted the search for cellular therapies and propelled the development of experimental models to study their efficacy. Umbilical cord matrix-derived mesenchymal stem cells (UCM-MSC) are appealing candidates because they are abundant, easy to collect, circumvent the ethical concerns and risk of teratoma formation, yet resemble primitive embryonic stem cells more closely than adult tissue-derived MSCs. Significant interest has focused on chitosan as a strategy to enhance the properties of MSCs through spheroid formation. This paper details techniques to isolate UCM-MSCs, prepare spheroids on chitosan film, and analyze the effect of spheroid formation on surface marker expression. Consequently, creation of a bilateral patellar tendon injury model in rats is described for in vivo implantation of UCM-MSC spheroids formed on chitosan film. No complication was observed in the study with respect to morbidity, stress rising effects, or tissue infection. The total functional score of the operated rats at 7 days was lower than that of normal rats, but returned to normal within 28 days after surgery. Histological scores of tissue-healing confirmed the presence of a clot in treated defects evaluated at 7 days, absence of foreign body reaction, and progressing healing at 28 days. This bilateral patella tendon defect model controls inter-individual variation via creation of an internal control in each rat, was associated with acceptable morbidity, and allowed detection of differences between untreated tendons and treatments.

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.

Glycine improves the remodeling process of tenocytes in vitro

Tendinitis changes the biochemical and morphological properties of the tendon, promoting an increase of activity of metalloproteinases and disorganization of collagen bundles. Tenocytes, the primary cells in tendon, are scattered throughout the collagenic fibers, and are responsible of tendon remodeling and tissue repair in pathological condition. In vivo, glycine, component of the typical Gly-X-Y collagen tripeptide, showed beneficial effects in biochemical and biomechanical properties of Achilles tendon with tendinitis. In this study, we analyzed the effect of glycine in tenocytes subjected to inflammation. Tenocytes from Achilles tendon of rats were treated with TNF-α (10 ng/mL) with and without previous treatment with glycine (20 mM). Cell proliferation and migration were evaluated, as well as the expression of matrix molecules such as glycosaminoglycans, metalloproteinases (MMPs), TIMPs, and collagen I. Glycine can revert the inflammation due to the action of TNF-α by controlling the MMPs quantity and activity. These data indicated that the molecules involved to remodeling process of extracellular matrix are modulated both by TNF-α and the availability of collagen precursors; in fact, this study indicates the glycine can be useful for treatment of inflammation and for modulating tenocytes metabolism in tendons.

Piperine ameliorates collagenase-induced Achilles tendon injury in the rat

Tendinopathy is a common clinical pathology found in athletes and workers with mixed treatment results. Piperine, a major alkaloid found in the black and long pepper, has been demonstrated to have variety of pharmacological properties such as analgesic and anti-inflammatory effects. The present study was designed to investigate the effects of piperine on collagenase-induced Achilles tendon injury. Rats were intratendineously injected with collagenase in the right Achilles tendon, followed by intragastrical administration of piperine (100 mg/kg). Morphological structure and biochemical analysis of glycosaminoglycans, hydroxyproline, collagen III, and the activity of matrix metallopeptidases in the tendon tissues were performed. Our results showed that collagenase injection resulted in clear degenerative changes in the tendon. Administration of piperine improved the morphological structure of tendon, increased glycosaminoglycans and hydroxyproline levels, and inhibited the expression and activities of MMP-2 and MMP-9. Furthermore, piperine inhibited the activation of ERK and p38 signaling pathways in injured tendon. These results indicate a beneficial role of piperine against collagenase-induced tendon injury.

Dynamic weight bearing analysis is effective for evaluation of tendinopathy using a customized corridor with multi-directional force sensors in a rat model

Few studies discuss kinetic changes in tendinopathy models. We propose a customized corridor to evaluate dynamic weight bearing (DWB) and shearing forces. Sixty rats were randomly given ultrasound-assisted collagenase injections (Collagenase rats) or needle punctures (Control rats) in their left Achilles tendons, and then evaluated 1, 4, and 8 weeks later. The Collagenase rats always had significantly (p < 0.001) higher histopathological and ultrasound feature scores than did the Controls, significantly lower DWB values in the injured than in the right hindlimbs, and compensatorily higher (p < 0.05) DWB values in the contralateral than in the left forelimbs. The injured hindlimbs had lower outward shearing force 1 and 4 weeks later, and higher (p < 0.05) push-off shearing force 8 weeks later, than did the contralateral hindlimbs. Injured Control rat hindlimbs had lower DWB values than did the contralateral only at week 1. The Collagenase rats had only lower static weight bearing ratios (SWBRs) values than did the Controls at week 1 (p < 0.05). Our customized corridor showed changes in DWB compatible with histopathological and ultrasound feature changes in the rat tendinopathy model. The hindlimb SWBRs did not correspond with any tendinopathic changes.

MicroRNA29a Treatment Improves Early Tendon Injury

Tendon injuries (tendinopathies) are common in human and equine athletes and characterized by dysregulated collagen matrix, resulting in tendon damage. We have previously demonstrated a functional role for microRNA29a (miR29a) as a post-transcriptional regulator of collagen 3 expression in murine and human tendon injury. Given the translational potential, we designed a randomized, blinded trial to evaluate the potential of a miR29a replacement therapy as a therapeutic option to treat tendinopathy in an equine model that closely mimics human disease. Tendon injury was induced in the superficial digital flexor tendon (SDFT) of 17 horses. Tendon lesions were treated 1 week later with an intralesional injection of miR29a or placebo. miR29a treatment reduced collagen 3 transcript levels at week 2, with no significant changes in collagen 1. The relative lesion cross-sectional area was significantly lower in miR29a tendons compared to control tendons. Histology scores were significantly better for miR29a-treated tendons compared to control tendons. These data support the mechanism of microRNA-mediated modulation of early pathophysiologic events that facilitate tissue remodeling in the tendon after injury and provides a strong proof of principle that a locally delivered miR29a therapy improves early tendon healing.

Intratendon Delivery of Leukocyte-Poor Platelet-Rich Plasma Improves Healing Compared With Leukocyte-Rich Platelet-Rich Plasma in a Rabbit Achilles Tendinopathy Model

BACKGROUND

Chronic tendinopathy is a commonly occurring clinical problem that affects both athletes and inactive middle-aged patients. Although some studies have shown that different platelet-rich plasma (PRP) preparations could exert various therapeutic effects in vitro, the role of leukocytes in PRP has not yet been defined under tendinopathy conditions in vivo.

PURPOSE

This study compared the effects of the intratendon delivery of leukocyte-poor PRP (Lp-PRP) versus leukocyte-rich PRP (Lr-PRP) in a rabbit chronic tendinopathy model in vivo.

STUDY DESIGN

Controlled laboratory study.

METHODS

Four weeks after a local injection of collagenase in the Achilles tendon, the following treatments were randomly administered on the lesions: injections of (1) 200 μL of Lp-PRP (n = 8), (2) 200 μL of Lr-PRP (n = 8), or (3) 200 μL of saline (n = 8). Healing outcomes were assessed at 4 weeks after therapy with magnetic resonance imaging (MRI), cytokine quantification, real-time polymerase chain reaction analysis of gene expression, histology, and transmission electron microscopy (TEM).

RESULTS

MRI revealed that the Lr-PRP and saline groups displayed higher signal intensities compared with the Lp-PRP group with T2 mapping. Histologically, the Lp-PRP group displayed significantly better general scores compared with the Lr-PRP ( P = .001) and saline ( P < .001) groups. Additionally, TEM showed that the Lp-PRP group had larger collagen fibril diameters than the Lr-PRP group ( P < .001). Enzyme-linked immunosorbent assay showed a significantly lower level of catabolic cytokine IL-6 in the Lp-PRP group compared with the Lr-PRP ( P = .001) and saline ( P = .021) groups. The Lp-PRP group displayed significantly increased expression of collagen I compared with the saline group ( P = .004) but not the Lr-PRP group. Both the Lp-PRP and Lr-PRP groups exhibited significantly lower matrix metalloproteinase (MMP)-1 and MMP-3 expression levels compared with the saline group. However, only the Lp-PRP group displayed significantly higher expression of TIMP-1 than the saline group ( P = .024).

CONCLUSION

Compared with Lr-PRP, Lp-PRP improves tendon healing and is a preferable option for the clinical treatment of tendinopathy.

CLINICAL RELEVANCE

PRP is widely used in the clinical management of chronic tendinopathy. However, the clinical results are ambiguous. It is imperative to understand the influence of leukocytes on PRP-mediated tissue healing in vivo, which could facilitate the better clinical management of chronic tendinopathy. Further studies are needed to translate our findings to the clinical setting.

Tendon stem/progenitor cells regulate inflammation in tendon healing via JNK and STAT3 signaling

Tendon stem/progenitor cells (TSCs) have been found in different anatomic locations and showed a promising regenerative potential. We identified a role of TSCs in the regulation of inflammation during healing of acute tendon injuries. Delivery of connective tissue growth factor (CTGF) into full-transected rat patellar tendons significantly increased the number of CD146⁺ TSCs, leading to enhanced healing. In parallel, CTGF delivery significantly reduced the number of iNOS⁺ M1 macrophages and increased the expression of anti-inflammatory IL-10 at 2 d after surgery, with over 85% CD146⁺ TSCs expressing IL-10. By 1 wk, the elevated IL-10 expression remained, and IL-6 expression was significantly attenuated in CTGF-delivered tendon healing. Matrix metalloproteinase (MMP)-3 expression in CTGF-delivered tendon was organized along with the reorienting collagen fibers by 1 wk after surgery, in comparison with the control group showing the abundant MMP-3 expression localized at healing junction. Tissue inhibitor of metalloprotease (TIMP)-3 was expressed in CD146⁺ TSCs at 1 wk with CTGF, in contrast to control with no TIMP-3 expression. In vitro, IL-10 expression was detected only when tendon cells were stimulated with IL-1β, and CTGF and significantly higher in CD146⁺ TSCs than CD146^- tendon cells. Similarly, TIMP-3 expression was detected only when treated with CTGF or CTGF and IL-1β that is significantly higher in CD146⁺ TSCs compared to CD146^- tendon cells. Signaling study with specific inhibitors and Western blot analysis demonstrated that CTGF-induced expression of IL-10 and TIMP-3 in CD146⁺ TSCs are regulated by JNK/signal transducer and activator of transcription 3 signaling. Taken together, these findings suggest anti-inflammatory roles of CTGF-stimulated TSCs that are likely associated with improved tendon healing.-Tarafder, S., Chen, E., Jun, Y., Kao, K., Sim, K. H., Back, J., Lee, F. Y., Lee, C. H. Tendon stem/progenitor cells regulate inflammation in tendon healing via JNK and STAT3 signaling.

Achilles Tendon Vascularization of Proximal, Medial, and Distal Portion Before and After Partial Lesion in Rats Treated with Phototherapy

BACKGROUND

The Achilles tendon is one of the tendons most commonly injured by microtraumas and overuse during sports practice. This tendon is especially fragile because of the low blood supply in its central part. Nevertheless, the literature does not offer enough scientific support to explain the composition and vascular dynamic of animal tendons, despite the relevance of being able to observe if the animal tendon undergoes the same processes of vascularization in different regions, as occurs in humans.

METHODS

We used 28 rats weighing 280 ± 20 g, which were divided into four groups with seven animals each (control, sham, 830 nm, 660 nm). The laser parameters were: power output 60 mW for both lasers, 40 J/cm(2) of energy density, total energy 1.1 J, power density 2.14 W/cm(2), and application time 18.6 sec. This study evaluated the vascular constitution of healthy and injured calcaneous tendons. The tendons of each animal were processed to be embedded in Paraplast and, after that, they were divided into three parts: proximal, medial, and distal. Afterwards, they were cut in slices of 6 μm were made, then they were stained with hematoxylin and eosin. Using an ocular lens reticulated with magnification × 400, we analyzed the number and the area density of the blood vessels using morphometric methods. Data were analyzed with the Shapiro-Wilk test, followed by Tukey, considering p as <0.05.

RESULTS

The area density and the number of blood vessels in the proximal part were 36% and 42%, respectively, of the values found in the medial part. The distal part had 64% more vessels and 52.8% more area density (p < 0.05) than the medial part.

CONCLUSIONS

Low-level laser therapy (LLLT) had no effect on the studied parameters. The vascularization of rat tendon is similar to that of humans, which contributes to the studies of therapies that have been applied in humans.

Efficacy of autologous leukocyte-reduced platelet-rich plasma therapy for patellar tendinopathy in a rat treadmill model

BACKGROUND

An autologous platelet-rich plasma (PRP) therapy has currently been applied for the tendinopathy; however, its efficacy and an optimal platelets concentration in PRP were uncertain. We analyzed them in an animal model prepared using a repetitive running exercise.

METHODS

We made the tendinopathy rat model of patellar tendon using a rodent treadmill machine. Rats with tendinopathy were injected with leukocyte-reduced PRP at the platelets concentration of 1.0×10⁶/μL (P10 group), PRP at the platelets concentration of 5.0×10⁵/μL (P5 group) or normal saline (control group) into the space between the patellar tendon and the fat pad bilaterally or were multiply dry-needled at the tibial insertion site (MN group) at once. To assess the pain-reliving effect, the spontaneous locomotor activities at night (12 h) were measured every day. Histological sections of the patellar tendon stained with hematoxylineosin or prepared by TdT-mediated dUTP nick end labeling were microscopically analyzed.

RESULTS

The numbers of spontaneous locomotor activities in the P10 group were significantly larger than those in the P5, MN or control groups and they recovered up to a healthy level. On histologic examinations, the numbers of microtears, laminations, or apoptotic cells in the patellar tendons in the P10 or P5 groups were significantly lower than those in the MN or control groups, although no significant differences were observed between the P10 and P5 groups.

CONCLUSIONS

The injections of an autologous leukocyte-reduced PRP were effective for pain relief and for partial restoration of the patellar tendon in the tendinopathy rat model. The injections of a PRP at the platelets concentration of 1.0×10⁶/μL completely relieved the pain and were more effective than those at the platelets concentration of 5.0×10⁵/μL whereas there was no difference for the effect of histological restoration or apoptosis inhibition between them.

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

Tendinopathy is a big burden in clinics and it represents 45% of musculoskeletal lesions. Despite the relevant social impact, both pathogenesis and development of the tendinopathy are still under-investigated, thus limiting the therapeutic advancement in this field. The purpose of this study was to evaluate the dose-dependent and time-related tissue-level changes occurring in a collagenase-induced tendinopathy in rat Achilles tendons, in order to establish a standardized model for future pre-clinical studies. With this purpose, 40 Sprague Dawley rats were randomly divided into two groups, treated by injecting collagenase type I within the Achilles tendon at 1 mg/mL (low dose) or 3 mg/mL (high dose). Tendon explants were histologically evaluated at 3, 7, 15, 30 and 45 days. Our results revealed that both the collagenase doses induced a disorganization of collagen fibers and increased the number of rounded resident cells. In particular, the high dose treatment determined a greater neovascularization and fatty degeneration with respect to the lower dose. These changes were found to be time-dependent and to resemble the features of human tendinopathy. Indeed, in our series, the acute phase occurred from day 3 to day 15, and then progressed towards the proliferative phase from day 30 to day 45 displaying a degenerative appearance associated with a very precocious and mild remodeling process. The model represents a good balance between similarity with histological features of human tendinopathy and feasibility, in terms of tendon size to create lesions and costs when compared to other animal models. Moreover, this model could contribute to improve the knowledge in this field, and it could be useful to properly design further pre-clinical studies to test innovative treatments for tendinopathy.

Developmental Biology and Regenerative Medicine: Addressing the Vexing Problem of Persistent Muscle Atrophy in the Chronically Torn Human Rotator Cuff

Persistent muscle atrophy in the chronically torn rotator cuff is a significant obstacle for treatment and recovery. Large atrophic changes are predictive of poor surgical and nonsurgical outcomes and frequently fail to resolve even following functional restoration of loading and rehabilitation. New insights into the processes of muscle atrophy and recovery gained through studies in developmental biology combined with the novel tools and strategies emerging in regenerative medicine provide new avenues to combat the vexing problem of muscle atrophy in the rotator cuff. Moving these treatment strategies forward likely will involve the combination of surgery, biologic/cellular agents, and physical interventions, as increasing experimental evidence points to the beneficial interaction between biologic therapies and physiologic stresses. Thus, the physical therapy profession is poised to play a significant role in defining the success of these combinatorial therapies. This perspective article will provide an overview of the developmental biology and regenerative medicine strategies currently under investigation to combat muscle atrophy and how they may integrate into the current and future practice of physical therapy.

Use of an IL1-receptor antagonist to prevent the progression of tendinopathy in a rat model

This study evaluated if inhibiting IL1-β activity with an IL1-receptor antagonist (IL1-RA) will prevent pathologic changes commonly seen in tendinopathy. Thirty-six Sprague-Dawley retired-breeder rats were divided into three groups having weekly bilateral patellar tendon injections: CON (0.1 ml Saline), CAR (0.1 ml 2% carrageenan), IL1-RA (0.1 ml 2% CAR plus 0.94 mg of the IL1-RA, 2.5 mg/kg). Carrageenan was used to establish tendinopathy in two groups due to its ability to develop tendinopathy in prior studies. Animals were euthanized 3 weeks after initial injection. The CAR group demonstrated significantly (p < 0.05) shorter tendon lengths (8.61 ± 0.38 mm) relative to CON (8.94 ± 0.38 mm) that was prevented in the IL1-RA (9.02 ± 0.30 mm) as well as significantly increased collagenase activity in the CAR (0.061 ± 0.043) compared to CON (0.027 ± 0.015) (p<  0.05). By histological evaluation, the CAR group demonstrated significantly greater inflammation than IL1-RA, and CON (p < 0.05). CAR showed a trend for increased cross-sectional area relative to CON that was absent in the IL1-RA. IL1-RA can effectively inhibit the development of mechanical, chemical, and histologic changes seen with carrageenan-induced tendonitis.

LASERTERAPIA EM AFECÇÕES LOCOMOTORAS: REVISÃO SISTEMÁTICA DE ESTUDOS EXPERIMENTAIS

RESUMO Introdução: Ao longo dos anos a fisioterapia tem contribuído para o tratamento das lesões musculotendíneas e osteoarticulares pela utilização de diversos recursos eletrotermofototerapêuticos como, por exemplo, o laser de baixa potência. Objetivo: A finalidade desse estudo foi identificar mediante revisão sistemática, o efeito da laserterapia de baixa potência em afecções do sistema locomotor de ratos, com destaque para a dose de energia e o comprimento de onda utilizado, assim como para a resposta ao tratamento. Métodos: Foram consultadas as bases de dados Medline, Lilacs, PEDro e SciELO, entre janeiro de 2005 a maio de 2013, utilizando os termos "tendinopathy", "laser therapy", "rats", "tendon", "muscle", "bone", "low-level laser therapy", assim como "tendinopatia", "laserterapia", "ratos", "tendão", "músculo", "osso" e "laser de baixa potência". Apenas foram incluídos estudos experimentais publicados nos idiomas português e inglês, que induziram lesão em tendões, músculos, ossos e/ou articulação, tratada com laserterapia, associada ou não a outros tratamentos. Resultados: Foi encontrado um total de 30 estudos experimentais nas bases de dados consultadas, dos quais 15 (50%) foram realizados em tendão, 10 (33,33%) em músculo e cinco (16,66%) em osso e/ou articulação. As doses de energia mais comumente utilizadas foram de 3 J (26,66%) e 1 J (16,66%). Já os comprimentos de onda foram de 904 nm (21,21%) e 830 nm (21,21%). Conclusão: A informação mais expressiva obtida com a terapia foi a diminuição da resposta inflamatória (36,66%) em lesões ortopédicas agudas.

Harnessing endogenous stem/progenitor cells for tendon regeneration

Current stem cell-based strategies for tissue regeneration involve ex vivo manipulation of these cells to confer features of the desired progenitor population. Recently, the concept that endogenous stem/progenitor cells could be used for regenerating tissues has emerged as a promising approach that potentially overcomes the obstacles related to cell transplantation. Here we applied this strategy for the regeneration of injured tendons in a rat model. First, we identified a rare fraction of tendon cells that was positive for the known tendon stem cell marker CD146 and exhibited clonogenic capacity, as well as multilineage differentiation ability. These tendon-resident CD146+ stem/progenitor cells were selectively enriched by connective tissue growth factor delivery (CTGF delivery) in the early phase of tendon healing, followed by tenogenic differentiation in the later phase. The time-controlled proliferation and differentiation of CD146+ stem/progenitor cells by CTGF delivery successfully led to tendon regeneration with densely aligned collagen fibers, normal level of cellularity, and functional restoration. Using siRNA knockdown to evaluate factors involved in tendon generation, we demonstrated that the FAK/ERK1/2 signaling pathway regulates CTGF-induced proliferation and differentiation of CD146+ stem/progenitor cells. Together, our findings support the use of endogenous stem/progenitor cells as a strategy for tendon regeneration without cell transplantation and suggest this approach warrants exploration in other tissues.

Focal experimental injury leads to widespread gene expression and histologic changes in equine flexor tendons

It is not known how extensively a localised flexor tendon injury affects the entire tendon. This study examined the extent of and relationship between histopathologic and gene expression changes in equine superficial digital flexor tendon after a surgical injury. One forelimb tendon was hemi-transected in six horses, and in three other horses, one tendon underwent a sham operation. After euthanasia at six weeks, transected and control (sham and non-operated contralateral) tendons were regionally sampled (medial and lateral halves each divided into six 3 cm regions) for histologic (scoring and immunohistochemistry) and gene expression (real time PCR) analysis of extracellular matrix changes. The histopathology score was significantly higher in transected tendons compared to control tendons in all regions except for the most distal (P ≤ 0.03) with no differences between overstressed (medial) and stress-deprived (lateral) tendon halves. Proteoglycan scores were increased by transection in all but the most proximal region (P < 0.02), with increased immunostaining for aggrecan, biglycan and versican. After correcting for location within the tendon, gene expression for aggrecan, versican, biglycan, lumican, collagen types I, II and III, MMP14 and TIMP1 was increased in transected tendons compared with control tendons (P < 0.02) and decreased for ADAMTS4, MMP3 and TIMP3 (P < 0.001). Aggrecan, biglycan, fibromodulin, and collagen types I and III expression positively correlated with all histopathology scores (P < 0.001), whereas lumican, ADAMTS4 and MMP14 expression positively correlated only with collagen fiber malalignment (P < 0.001). In summary, histologic and associated gene expression changes were significant and widespread six weeks after injury to the equine SDFT, suggesting rapid and active development of tendinopathy throughout the entire length of the tendon. These extensive changes distant to the focal injury may contribute to poor functional outcomes and re-injury in clinical cases. Our data suggest that successful treatments of focal injuries will need to address pathology in the entire tendon, and that better methods to monitor the development and resolution of tendinopathy are required.

Green tea and glycine aid in the recovery of tendinitis of the Achilles tendon of rats

PURPOSE

Green tea (GT) is widely used due to its anti-inflammatory properties. Previous studies have shown beneficial effects of a glycine diet on the remodeling process in inflamed tendons. Tendinitis is commonly observed in athletes and is of concern to surgeons due to the slowness of the recovery process. Our hypothesis is that GT + a glycine diet may improve tendinitis.

AIM OF THE STUDY

To analyze the effect of GT and/or glycine in the diet on tendinitis.

MATERIALS AND METHODS

Wistar rats were divided into seven groups (G): control group (C); G1 and G4, tendinitis; G2 and G5, tendinitis supplied with GT; and G3 and G6, tendinitis supplied with GT and a glycine diet for 7 or 21 days, respectively. We performed zymography for metalloproteinase, biochemical, morphological and biomechanics tests.

RESULTS

G2, G3 and G5 showed high levels of hydroxyproline in relation to G1, while G4 showed high levels of glycosaminoglycans. High activity of metalloproteinase-2 was detected in G3. The organization of collagen bundles was better in G2 and G3. G5 showed similar birefringence measurements compared with C. G5 withstood a larger load compared with G4.

CONCLUSIONS

The presence of metalloproteinase-2 indicates that a tissue is undergoing a remodeling process. High birefringence suggests a better organization of collagen bundles. After 21 days, G5 sustained a high load before rupture, unlike G4. The results suggest that GT + a glycine diet has beneficial effects that aid in the recovery process of the tendon after tendinitis.

Fatigue loading of tendon

Tendon injuries, often called tendinopathies, are debilitating and painful conditions, generally considered to develop as a result of tendon overuse. The aetiology of tendinopathy remains poorly understood, and whilst tendon biopsies have provided some information concerning tendon appearance in late-stage disease, there is still little information concerning the mechanical and cellular events associated with disease initiation and progression. Investigating this in situ is challenging, and numerous models have been developed to investigate how overuse may generate tendon fatigue damage and how this may relate to tendinopathy conditions. This article aims to review these models and our current understanding of tendon fatigue damage. We review the strengths and limitations of different methodologies for characterizing tendon fatigue, considering in vitro methods that adopt both viable and non-viable samples, as well as the range of different in vivo approaches. By comparing data across model systems, we review the current understanding of fatigue damage development. Additionally, we compare these findings with data from tendinopathic tissue biopsies to provide some insights into how these models may relate to the aetiology of tendinopathy. Fatigue-induced damage consistently highlights the same microstructural, biological and mechanical changes to the tendon across all model systems and also correlates well with the findings from tendinopathic biopsy tissue. The multiple testing routes support matrix damage as an important contributor to tendinopathic conditions, but cellular responses to fatigue appear complex and often contradictory.

Equine tendonitis therapy using mesenchymal stem cells and platelet concentrates: a randomized controlled trial

INTRODUCTION

Tendon injury is a major cause of lameness and decreased performance in athletic equines. Various therapies for tendonitis have been described; however, none of these therapies results in complete tissue regeneration, and the injury recurrence rate is high even after long recovery periods involving rest and physiotherapy.

METHODS

A lesion was induced with collagenase gel in the superficial digital flexor tendon in the center portion of the metacarpal region of eight equines of mixed breed. After two weeks, the lesions of the animals in the treated and control groups were treated through the intralesional administration of mesenchymal stem cells derived from adipose tissue (adMSCs) suspended in platelet concentrate (PC) and with phosphate buffered saline (PBS), respectively. Serial ultrasound analyses were performed every two weeks. After 16 weeks of therapy, a biopsy was performed for histopathological, immunohistochemical and gene expression (type I collagen (COL1A1), type III collagen (COL3A1), tenascin-C (TNC), tenomodulin (TNMD), and scleraxis (SCX)) analyses.

RESULTS

Differences in the ultrasound and histopathological analyses were observed between the groups. Improved results were reported in the group treated with adMSCs suspended in PC. There was no difference in the gene expression levels observed after the different treatments. The main results observed from the histopathological evaluation of the treated group were as follows: a prevention of the progression of the lesion, a greater organization of collagen fibers, and a decreased inflammatory infiltrate. A lack of progression of the lesion area and its percentage was observed in the ultrasound image, and increased blood flow was measured by Power Doppler.

CONCLUSIONS

The use of adMSCs combined with PC for the therapy of experimentally induced tendonitis prevented the progression of the tendon lesion, as observed in the ultrasound examination, and resulted in a greater organization and decreased inflammation, as observed in the histopathological evaluation. These data demonstrate the therapeutic potential of this therapy for the treatment of equine tendonitis.