Abstract
BackgroundAchilles tendinopathy is a painful musculoskeletal condition that is common among athletes, and which limits training capacity and competitive performance. The lack of biomarkers for tendinopathy limits research into risk factors and also the evaluation of new treatments. Cytokines and growth factors involved in regulating the response of tendon cells to mechanical load have potential as biomarkers for tendinopathy.MethodsThis case–control study compared serum concentration of cytokines and growth factors (TNF-α, IL-1β, bFGF, PDFG-BB, IFN-γ, VEGF) between individuals with chronic Achilles tendinopathy and controls. These were measured in fasting serum from 22 individuals with chronic Achilles tendinopathy and 10 healthy controls. Results were analysed in relation to gender and physical activity pattern.ResultsTNF-α concentration was lower in the entire tendinopathy group compared with the entire control group; none of the other cytokines were significantly different. TNF-α levels were nevertheless highly correlated with the other cytokines measured, in most of the subgroups. Analysed by gender, TNF-α and PDGF-BB concentrations were lower in the female tendinopathy group but not the male tendinopathy group. A trend was seen for lower IL-1β in the female tendinopathy group. Physical activity was correlated with TNF-α, PDGF-BB and IL-1β to varying extents for control subgroups, but not for the female tendinopathy group. No correlations were seen with BMI or duration of symptoms.ConclusionsThis pilot study indicates a lower level of TNF-α and PDGF-BB, and to some extent IL-1β among females, but not males, in the chronic phase of Achilles tendinopathy. It is suggested that future studies on tendinopathy biomarkers analyse male and female data separately. The lack of correlation between cytokine level and physical activity in the female tendinopathy group warrants further study.
Highlights
Achilles tendinopathy is a painful musculoskeletal condition that is common among athletes, and which limits training capacity and competitive performance
Much work has focussed on cytokine and growth factor expression at the tissue level, this approach is
What this study adds to existing knowledge In this study, we found lower levels of tumour necrosis factor alpha (TNF-α) and platelet derived growth factor BB (PDGF-BB) among females with chronic Achilles tendinopathy
Summary
Achilles tendinopathy is a painful musculoskeletal condition that is common among athletes, and which limits training capacity and competitive performance. Among non-athletic individuals, systemic factors such as diabetes [7] and blood lipids [8] may decrease the capacity of the tendon to tolerate everyday loads and contribute to tendinopathy in the absence of high tendon loading. Serum biomarkers such as tumour necrosis factor alpha (TNF-α) are useful for monitoring disease severity and can even help to confirm a suspected diagnosis. The TNF-α system is strongly involved in inflammatory disorders such as inflammatory bowel disease and rheumatoid arthritis Blood levels of both TNF-α and the soluble form of tumour necrosis factor receptor 1 (sTNFR1) [11] are increased among inflammatory bowel disease patients. The presence of TNF-α and its two receptors has been confirmed in human Achilles tendon [17]
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