Abstract
Autologous protein solution (APS) has been used anecdotally for intralesional treatment of tendon and ligament injuries, however, its use in these injuries has never been studied in vivo. Our objective was to evaluate the effect of APS on tendon healing in an equine superficial digital flexor (SDF) tendonitis model. We hypothesized intralesional injection of APS would result in superior structural and biomechanical healing. SDF tendonitis was induced in both forelimbs of eight horses using collagenase injection. One forelimb was randomly assigned to receive an intralesional injection of APS, while the other was injected with saline. Ultrasonographic examinations were performed at weeks −1, 0, 2, 4, 8, and 12 following treatment. At 12 weeks, horses were euthanized and SDF samples harvested. Histologic evaluation, biomechanical testing, gene expression analysis, total glycosaminoglycan (GAG) and total DNA quantification were performed. Collagen type III (COL3A1) expression was significantly higher (p = 0.028) in saline treated tendon than in normal tendon. Otherwise, there were no significant differences in gene expression. There were no significant differences in histologic or ultrasonographic scores between groups. Mean total DNA content was significantly higher (p = 0.024) in saline treated tendons than normal tendons, whereas total DNA content was not significantly different between APS treated tendon and normal tendon. Elastic modulus was higher in APS treated than saline treated tendon, but the difference was not significant. Reduced expression of COL3A1 in APS treated tendon may indicate superior healing. Increased total DNA content in saline treated tendon may indicate ongoing healing processes, vs. APS treated tendons which may be in the later stages of healing. Limitations include a relatively short study period and inconsistency in size and severity of induced lesions. Intralesional injection of APS resulted in some improvements in healing characteristics.
Highlights
Tendon and ligament injuries are common in athletic horses, leading to decreased performance and often career-ending injuries
Treatment of surgically induced superficial digital flexor tendonitis with intralesional leukocyte-rich platelet rich plasma (PRP) resulted in an increased concentration of collagen and significantly higher load at failure with increased elasticity in comparison to lesions treated with saline [6]
Autologous protein solution (APS) may improve tendon healing by combining the beneficial effects of autologous conditioned serum (ACS), which contains concentrated interleukin-1 receptor antagonist (IL-1ra) and interleukin-10 (IL-10), with the beneficial effects of PRP, which contains a multitude of growth factors and anti-inflammatory cytokines [16, 17, 20]
Summary
Tendon and ligament injuries are common in athletic horses, leading to decreased performance and often career-ending injuries. Several studies have shown that these therapies enhance endogenous tendon repair, resulting in superior biochemical, biomechanical, and histological healing [6,7,8,9,10,11,12,13]. Treatment of naturally occurring tendonitis with MSCs has resulted in improved biomechanical and morphological characteristics [14], and decreased reinjury rate [8]. In a collagenase induced tendonitis model, treatment with fetal derived embryonic like stem cells resulted in improved histological and ultrasonographic scores [15]. Treatment of surgically induced superficial digital flexor tendonitis with intralesional leukocyte-rich PRP resulted in an increased concentration of collagen and significantly higher load at failure with increased elasticity in comparison to lesions treated with saline [6]. Another study showed that intralesional PRP treatment in a tendonitis model resulted in early increased neovascularization compared to controls, likely due to high concentrations of vascular endothelial growth factor (VEGF) within PRP [9]
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