title: A pilot study on biomarkers for tendinopathy: lower levels of serum TNF-α and other cytokines in females but not males with Achilles tendinopathy.
abstract: BACKGROUND
  Achilles 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.
  
  
  METHODS
  This 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.
  
  
  RESULTS
  TNF-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.
  
  
  CONCLUSIONS
  This 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.
authors.affiliation: University of Canberra Research Institute for Sport and Exercise (UCRISE), Canberra, Australia ; Discipline of Physiotherapy, University of Canberra, ACT 2601 Canberra, Australia ; Department of Surgical and Perioperative Sciences, Sports Medicine, Umeå University, Umeå, Sweden ; Department of Integrative Medical Biology, Anatomy Section, Umeå University, Umeå, Sweden.
authors.forename: James E
authors.identifier: 0000-0002-4504-9188
authors.initials: JE
authors.lastname: Gaida
authors.affiliation: Department of Community Medicine and Rehabilitation, Umeå University, S-901 87 Umeå, Sweden ; Institute of Sport Exercise and Health, University College Hospital London, London, UK.
authors.forename: Håkan
authors.initials: H
authors.lastname: Alfredson
authors.affiliation: Department of Integrative Medical Biology, Anatomy Section, Umeå University, Umeå, Sweden.
authors.forename: Sture
authors.initials: S
authors.lastname: Forsgren
authors.affiliation: La Trobe University Sport and Exercise Medicine Research Centre, Melbourne, Australia.
authors.forename: Jill L
authors.initials: JL
authors.lastname: Cook
keywords: Biomarkers; Cytokines; Musculoskeletal pain; Tumor necrosis factor alpha