Erythropoietin stimulates patellar tendon healing in rats
Introduction
Rupture of the patellar tendon is a rare injury that occurs most frequently in patients younger than 40 years of age [1], usually after indirect trauma due to a sudden quadriceps contraction with the knee in slight flexion. It is generally agreed that a healthy patellar tendon will not tear, and that tearing usually involves a tendon weakened by iterative micro trauma [2] or local corticoid injections. Surgery is mandatory, regardless of age and physical activity, and should be undertaken as early as possible after injury [3]. Erythropoietin (EPO) is a glycoprotein hormone produced primarily by the kidneys that regulates the production of red blood cells. The most common indications for EPO treatment are chronic renal failure, anaemia, and anaemia of prematurity [4]. EPO has been shown to exert protective and regenerative activity in a variety of non-haematopoietic tissues [5]. The prevention of programed cell death, reduction of proinflammatory cytokine-induced injury, and provision of tissue protection are some of the functions of EPO [6]. The treatment of patellar tendon rupture by conventional surgical methods alone may not be sufficient to regain initial knee function. Recurrent ruptures of the patellar tendon tend to occur in patients with systemic disease such as diabetes mellitus or chronic renal failure.
Three phases of tendon healing have been identified in animal models [7], [8] and cell cultures [9]: inflammation, fibroplasia, and remodeling. The role of intrinsic and extrinsic healing models has been investigated [10]. Both of these mechanisms are likely critical for proper tendon healing. Both the period of time after tendon injury and local extracellular environmental differences affect the intrinsic and extrinsic tendon healing processes [11], [12].
Tendon rupture is characterized by a disruption of blood vessels and the extracellular matrix (ECM). Platelets interact directly or indirectly with newly exposed collagen, leading to their activation, aggregation, and degranulation [13]. During the early inflammatory phase, biochemical mediators released into the local environment stimulate endothelial cells to express ligands or adhesion molecules. Leukocytes are then recruited into tissues through interactions with the vessel wall, as mediated by selectins and integrins [14]. Proteins such as basic fibroblast growth factor, vascular endothelial growth factor (VEGF), thrombospondin-1, platelet factor-4, intercellular adhesion molecule-2, epidermal growth factor, platelet-derived growth factor, insulin-like growth factor-1, and transforming growth factor (TGF)-β are important molecules in the tendon healing process [15].
In this study, we tested our hypothesis that EPO treatment in combination with patellar tendon surgery would stimulate inflammation and re-vascularization in tendons post-injury and influence cell proliferation, angiogenesis, collagen deposition, and mechanical recovery in a rat model. This study is the first to assess the role of EPO in the tendon healing process with a focus on biomechanical, histopathologic features and tendon tissue protein mRNA expression levels.
Section snippets
Animals
The study included 126 four-month-old male Sprague–Dawley rats weighing between 250–400 g each. All animal procedures were conducted with approval from the Institutional Committee on the Care and Use of Animals of Bolu Izzet Baysal University School of Medicine (Bolu, Turkey) (issue 2012/24). Prior to experimentation, the animals were fed standard rat chow and water and housed in cages with a controlled temperature and 12-h light/dark cycle.
Surgical procedures
Under intramuscular ketamine (200 mg/kg) plus xylazine
Results
Group 1, control group (no treatment) with mean initial body weight of 245 ± 10 g (SE) and mean final body weight of 240 ± 8 (SE); group 2, isotonic saline with mean initial body weight of 238 ± 8 g (SE) and mean final body weight 235 ± 6 g (SE); and group 3, EPO with mean initial body weight of 242 ± 8 g (SE) and mean final body weight of 238 ± 8 g (SE).
Discussion
This study is the first to show that low-dose EPO treatment not only improved healing of the injured patellar tendon after surgical application, it also made the intact tendon stronger against breaking forces biomechanically. EPO stimulated fibroblast proliferation, collagen fiber organization, capillary vessel formation, and local inflammation according to the control groups. Col I, Col III, TGF-β1, and VEGF protein mRNA expressions also were positively affected.
We modified the standard tendon
Conclusions
This is the first experimental study to analyze the relationship between EPO treatment and the patellar tendon repair process by biomechanical, histopathological, and tendon tissue mRNA expression methodologies. Intraperitoneal supplementation with low-dose EPO once a day for 10 days accelerated patellar tendon healing in a healthy rat model. The histopathologic, genetic, and biomechanical improvement in the repair process as a result of EPO use appears to depend on the enhancement of
Conflict of interests
As a main author I received benefits for this research article by Düzce University Research Fund (project number 2012.04.02.91).
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