title: Achilles tendinosis: changes in biochemical composition and collagen turnover rate.
abstract: BACKGROUND
  Understanding biochemical and structural changes of the extracellular matrix in Achilles tendinosis might be important for developing mechanism-based therapies.
  
  
  OBJECTIVE
  In Achilles tendinosis, changes occur in biochemical composition and collagen turnover rate.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  METHODS
  From 10 patients undergoing surgery for Achilles tendinopathy, 1 tendinosis biopsy specimen and 1 biopsy specimen of macroscopically healthy tendon tissue adjacent to the lesion were collected. Furthermore, biopsy samples were collected from 3 donors with asymptomatic Achilles tendons. Water content, collagen content, percentage of denatured collagen, amount of lysine hydroxylation, number of enzymatic and nonenzymatic crosslinks, matrix metalloproteinase activity, and matrix metalloproteinase and collagen gene-expression levels were analyzed.
  
  
  RESULTS
  In tendinotic lesions, the water content was highest, and collagen content was subnormal with higher amounts of denatured/damaged collagen. Low pentosidine levels in tendinotic tissue indicated the presence of relatively young collagenous matrix. More hydroxylated lysine residues were present in tendinotic samples, but enzymatic crosslinks revealed no differences between tendinotic, adjacent, and healthy samples. In tendinotic specimens, matrix metalloproteinase activity was higher, matrix metalloproteinase gene-expression profile was altered, and collagen type I and III gene expression were upregulated.
  
  
  CONCLUSIONS
  In Achilles tendinosis, the collagen turnover rate is increased, and the natural biochemical composition of the collagenous matrix is compromised.
  
  
  CONCLUSIONS
  Although tendon tissue directly adjacent to an Achilles tendinosis lesion looks macroscopically healthy, histological and biochemical degenerative changes in adjacent tissue are evident, which may have implications for surgical interventions.
authors.affiliation: Department of Orthopaedics, Erasmus MC University Medical Center, Rotterdam, The Netherlands. m.demos@erasmusmc.nl
authors.forename: Marieke
authors.initials: M
authors.lastname: de Mos
authors.forename: Benno
authors.initials: B
authors.lastname: van El
authors.forename: Jeroen
authors.initials: J
authors.lastname: DeGroot
authors.forename: Holger
authors.initials: H
authors.lastname: Jahr
authors.forename: Hans T M
authors.initials: HT
authors.lastname: van Schie
authors.forename: Ewoud R
authors.initials: ER
authors.lastname: van Arkel
authors.forename: Hans
authors.initials: H
authors.lastname: Tol
authors.forename: Rien
authors.initials: R
authors.lastname: Heijboer
authors.forename: Gerjo J V M
authors.initials: GJ
authors.lastname: van Osch
authors.forename: Jan A N
authors.initials: JA
authors.lastname: Verhaar
mesh_terms: D000125:Achilles Tendon / Q000378:metabolism* / Q000473:pathology / Q000502:physiology / Q000503:physiopathology; D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D003094:Collagen / Q000235:genetics / Q000378:metabolism*; D005260:Female; D015870:Gene Expression; D006801:Humans; D008297:Male; D019278:Matrix Metalloproteinase 3 / Q000235:genetics / Q000378:metabolism; D008875:Middle Aged; D052256:Tendinopathy / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D014867:Water / Q000032:analysis
chemical_list: D014867:Water; D003094:Collagen; D019278:Matrix Metalloproteinase 3