A Novel Minimally Invasive Surgically Induced Skeletal Muscle Injury Model in Sheep.

Sports-related muscle injuries account for 10-55% of all injuries, which is a growing concern, especially given the aging world population. To evaluate the process of skeletal muscle injury and compare it with muscle lesions observed in humans, we developed a novel in vivo model in sheep. In this model, muscle injury was induced by an ultrasound-guided transverse biopsy at the myotendinous junction of the medial gastrocnemius muscle. Twelve male sheep were examined at 3, 7, 14, and 28 days post-injury. Histological, immunofluorescence, and MRI analyses indicate that our sheep model could resemble key human clinicopathological features. Statistically significant differences (p < 0.05) were observed in collagen I, dMHC, α-SMA, and CD68 immunohistochemical detection when comparing injured and healthy muscles. The injured gastrocnemius muscle exhibited elevated levels of type I collagen, infiltration of CD68(+) macrophages, angiogenesis, and the emergence of newly regenerated dMHC(+) myofibers, which persisted for up to 4 weeks post-injury. Similarly, the progression of muscle injury in the sheep model was assessed using advanced clinical 3 T MRI and compared with MRI scans from human patients. The data indicate that the sheep muscle injury model presents features similar to those observed in human skeletal muscle injuries. This makes it a valuable large animal model for studying muscle injuries and developing novel therapeutic strategies.

Muscle Precursor Cells Enhance Functional Muscle Recovery and Show Synergistic Effects With Postinjury Treadmill Exercise in a Muscle Injury Model in Rats.

BACKGROUND: Skeletal muscle injuries represent a major concern in sports medicine. Cell therapy has emerged as a promising therapeutic strategy for muscle injuries, although the preclinical data are still inconclusive and the potential clinical use of cell therapy has not yet been established. PURPOSE: To evaluate the effects of muscle precursor cells (MPCs) on muscle healing in a small animal model. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 27 rats were used in the study. MPCs were isolated from rat (n = 3) medial gastrocnemius muscles and expanded in primary culture. Skeletal muscle injury was induced in 24 rats, and the animals were assigned to 3 groups. At 36 hours after injury, animals received treatment based on a single ultrasound-guided MPC (105 cells) injection (Cells group) or MPC injection in combination with 2 weeks of daily exercise training (Cells+Exercise group). Animals receiving intramuscular vehicle injection were used as controls (Vehicle group). Muscle force was determined 2 weeks after muscle injury, and muscles were collected for histological and immunofluorescence evaluation. RESULTS: Red fluorescence-labeled MPCs were successfully transplanted in the site of the injury by ultrasound-guided injection and were localized in the injured area after 2 weeks. Transplanted MPCs participated in the formation of regenerating muscle fibers as corroborated by the co-localization of red fluorescence with developmental myosin heavy chain (dMHC)-positive myofibers by immunofluorescence analysis. A strong beneficial effect on muscle force recovery was detected in the Cells and Cells+Exercise groups (102.6% ± 4.0% and 101.5% ± 8.5% of maximum tetanus force of the injured vs healthy contralateral muscle, respectively) compared with the Vehicle group (78.2% ± 5.1%). Both Cells and Cells+Exercise treatments stimulated the growth of newly formed regenerating muscles fibers, as determined by the increase in myofiber cross-sectional area (612.3 ± 21.4 µm2 and 686.0 ± 11.6 µm2, respectively) compared with the Vehicle group (247.5 ± 10.7 µm2), which was accompanied by a significant reduction of intramuscular fibrosis in Cells and Cells+Exercise treated animals (24.2% ± 1.3% and 26.0% ± 1.9% of collagen type I deposition, respectively) with respect to control animals (40.9% ± 4.1% in the Vehicle group). MPC treatment induced a robust acceleration of the muscle healing process as demonstrated by the decreased number of dMHC-positive regenerating myofibers (enhanced replacement of developmental myosin isoform by mature myosin isoforms) (4.3% ± 2.6% and 4.1% ± 1.5% in the Cells and Cells+Exercise groups, respectively) compared with the Vehicle group (14.8% ± 13.9%). CONCLUSION: Single intramuscular administration of MPCs improved histological outcome and force recovery of the injured skeletal muscle in a rat injury model that imitates sports-related muscle injuries. Cell therapy showed a synergistic effect when combined with an early active rehabilitation protocol in rats, which suggests that a combination of treatments can generate novel therapeutic strategies for the treatment of human skeletal muscle injuries. CLINICAL RELEVANCE: Our study demonstrates the strong beneficial effect of MPC transplant and the synergistic effect when the cell therapy is combined with an early active rehabilitation protocol for muscle recovery in rats; this finding opens new avenues for the development of effective therapeutic strategies for muscle healing and clinical trials in athletes undergoing MPC transplant and rehabilitation protocols.

Generación de un nuevo modelo de tendinopatía rotuliana en ratas que imita la patología deportiva humana: estudio piloto / Generation of a new model of patellar tendinopathy in rats which mimics the human sports pathology: A pilot study

Introducción: La fisiopatología de la tendinopatía rotuliana no es del todo conocida. Es difícil obtener muestras clínicas de deportistas que permitan conocer el desarrollo de la tendinopatía, sobre todo en las primeras etapas. Por este motivo, el propósito de este estudio es desarrollar, en una primera fase, un modelo experimental de tendinopatía rotuliana en ratas que simule la tendinopatía humana mediante la aplicación in vivo de colagenasa en la porción proximal del tendón rotuliano. Material y métodos: El modelo experimental utilizado fueron ratas Wistar macho de 8 semanas de edad (n = 4). La administración de colagenasa se realizó, tras anestesia e inmovilización de los animales, mediante punción guiada por ecografía a nivel de la porción proximal y profunda del tendón rotuliano. La lesión tendinosa se evaluó 48 h después de la lesión mediante resonancia magnética, tras lo cual se procedió a la eutanasia de los animales y a la extracción de los tendones rotulianos para su evaluación histológica. Resultados: El modelo de lesión inducida con colagenasa demostró similitud a nivel de la histología con la tendinopatía rotuliana humana en la región de su inserción proximal. Conclusiones: El modelo experimental de tendinopatía rotuliana en ratas induce la degeneración y distorsión de la arquitectura del tendón rotuliano en su porción proximal, situación similar a la observada en la tendinopatía rotuliana humana, y representa un excelente modelo preclínico para el estudio de nuevas terapias enfocadas al tratamiento de la tendinopatía (AU)

Introduction: Patellar tendon pathophysiology is not still fully understood. The collection of clinical samples from athletes that could permit the analysis of the tendinopathy progression, especially in the early stages, is difficult. For that reason, the purpose of this study is to develop a new experimental animal model of patellar tendinopathy in rats which mimics the human tendinopathy by in vivo intratendinous collagenase injection in the proximal portion of the patellar tendon. Material and methods: The experimental model used was 8-week-old male Wistar rats (n = 4). The administration of collagenase was performed by ultrasound-guided puncture at the level of the proximal and deep portion of the patellar tendon in anesthetized animals. The tendon lesion was evaluated 48 h after injury by magnetic resonance and then, the animals were euthanized and the patellar tendons were collected for histological evaluation. Results: The collagenase-induced lesion model demonstrated important similarities with the human patellar tendinopathy in the region of the proximal insertion. Conclusions: The experimental model of patellar tendinopathy in rat model induces a degeneration and distortion of the patellar tendon architecture in its proximal portion, which closely mimics to that seen in human patellar tendinopathy, and could represent an excellent preclinical model for the study of new therapies focused on treatment of tendinopathy (AU)

Postinjury Exercise and Platelet-Rich Plasma Therapies Improve Skeletal Muscle Healing in Rats But Are Not Synergistic When Combined.

BACKGROUND: Skeletal muscle injuries are the most common sports-related injury and a major concern in sports medicine. The effect of platelet-rich plasma (PRP) injections on muscle healing is still poorly understood, and current data are inconclusive. PURPOSE: To evaluate the effects of an ultrasound-guided intramuscular PRP injection, administered 24 hours after injury, and/or posttraumatic daily exercise training for 2 weeks on skeletal muscle healing in a recently established rat model of skeletal muscle injury that highly mimics the muscle trauma seen in human athletes. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 40 rats were assigned to 5 groups. Injured rats (medial gastrocnemius injury) received a single PRP injection (PRP group), daily exercise training (Exer group), or a combination of a single PRP injection and daily exercise training (PRP-Exer group). Untreated and intramuscular saline-injected animals were used as controls. Muscle force was determined 2 weeks after muscle injury, and muscles were harvested and evaluated by means of histological assessment and immunofluorescence microscopy. RESULTS: Both PRP (exhibiting 4.8-fold higher platelet concentration than whole blood) and exercise training improved muscle strength (maximum tetanus force, TetF) in approximately 18%, 20%, and 30% of rats in the PRP, PRP-Exer, and Exer groups, respectively. Specific markers of muscle regeneration (developmental myosin heavy chain, dMHC) and scar formation (collagen I) demonstrated the beneficial effect of the tested therapies in accelerating the muscle healing process in rats. PRP and exercise treatments stimulated the growth of newly formed regenerating muscle fibers (1.5-, 2-, and 2.5-fold increase in myofiber cross-sectional area in PRP, PRP-Exer, and Exer groups, respectively) and reduced scar formation in injured skeletal muscle (20%, 34%, and 41% of reduction in PRP, PRP-Exer, and Exer groups, respectively). Exercise-treated muscles (PRP-Exer and Exer groups) had significantly reduced percentage of dMHC-positive regenerating fibers (35% and 47% decrease in dMHC expression, respectively), indicating that exercise therapies accelerated the muscle healing process witnessed by the more rapid replacement of the embryonic-developmental myosin isoform by mature muscle myosin isoforms. CONCLUSION: Intramuscular PRP injection and, especially, treadmill exercise improve histological outcome and force recovery of the injured skeletal muscle in a rat injury model that imitates sports-related muscle injuries in athletes. However, there was not a synergistic effect when both treatments were combined, suggesting that PRP does not add any beneficial effect to exercise-based therapy in the treatment of injured skeletal muscle. CLINICAL RELEVANCE: This study demonstrates the efficacy of an early active rehabilitation protocol or single intramuscular PRP injection on muscle recovery. The data also reveal that the outcome of the early active rehabilitation is adversely affected by the PRP injection when the two therapies are combined, and this could explain why PRP therapies have failed in randomized clinical trials where the athletes have adhered to postinjection rehabilitation protocols based on the principle of early, active mobilization.