title: Assessment of the effects of age and joint disease on hydroxyproline and glycosaminoglycan concentrations in synovial fluid from the metacarpophalangeal joint of horses.
abstract: OBJECTIVE
  To assess the effects of age and joint disease on hydroxyproline and glycosaminoglycan (GAG) concentrations in synovial fluid from the metacarpophalangeal joint of horses and evaluate the association of those concentrations with severity of osteoarthritis and general matrix metalloproteinase (MMP) activity.
  
  
  METHODS
  Synovial fluid was collected from the metacarpophalangeal joints of foals at birth (n = 10), 5-month-old foals (10), 11-month-old foals (5), and adult horses (73).
  
  
  METHODS
  Hydroxyproline and GAG concentrations were determined in synovial fluid samples. The severity of osteoarthritis in adult joints was quantified by use of a cartilage degeneration index (CDI) and assessment of general MMP-activity via a fluorogenic assay.
  
  
  RESULTS
  Hydroxyproline and GAG concentrations in synovial fluid were highest in neonates and decreased with age. Concentrations reached a plateau in adults by 4 years and remained constant in healthy joints. In synovial fluid from osteoarthritic joints, hydroxyproline and GAG concentrations were not increased, compared with unaffected joints, but hydroxyproline were significantly correlated with the CDI and general MMP activity. There was no significant correlation between GAG concentration and CDI value or MMP activity.
  
  
  CONCLUSIONS
  Changes in hydroxyproline concentration in synovial fluid appeared to indicate damage to collagen of the articular cartilage. In joints with osteoarthritis, the lack of high GAG concentration in synovial fluid and the absence of a significant correlation between GAG concentration and CDI values or MMP activity may severely limit the usefulness of this marker for monitoring equine joint disease.
authors.affiliation: Department of Equine Sciences, Faculty of Veterinary Medicine, University of Utrecht, Utrecht, The Netherlands.
authors.forename: Robin
authors.initials: R
authors.lastname: van den Boom
authors.forename: Pieter A J
authors.initials: PA
authors.lastname: Brama
authors.forename: Geesje H
authors.initials: GH
authors.lastname: Kiers
authors.forename: Jeroen
authors.initials: J
authors.lastname: de Groot
authors.forename: P René
authors.initials: PR
authors.lastname: van Weeren
mesh_terms: D000367:Age Factors; D000818:Animals; D005552:Forelimb / Q000378:metabolism; D006025:Glycosaminoglycans / Q000378:metabolism*; D006734:Horse Diseases / Q000378:metabolism*; D006736:Horses; D006909:Hydroxyproline / Q000378:metabolism*; D020782:Matrix Metalloproteinases / Q000378:metabolism; D010003:Osteoarthritis / Q000378:metabolism / Q000662:veterinary*; D013582:Synovial Fluid / Q000378:metabolism
chemical_list: D006025:Glycosaminoglycans; D020782:Matrix Metalloproteinases; D006909:Hydroxyproline