title: Crosslinking of fibrinogen and fibronectin by free radicals: a possible initial step in adhesion formation in osteoarthritis of the temporomandibular joint.
abstract: OBJECTIVE
  Adhesion formation in osteoarthritis (OA) of the temporomandibular joint (TMJ) typically results in a sustained limitation of joint movement. We propose the hypothesis that free-radical-mediated crosslinking of proteins underlies this adhesion formation in affected joints. Free radicals may cause oxidative modification of proteins, creating an opportunity for the formation of intramolecular and intermolecular crosslinks via covalent bonds. This may stabilize protein aggregates, rendering them more resistant to degradation. In this study, the free-radical-mediated crosslinking of model proteins (fibrinogen and fibronectin) was investigated to test our hypothesis that free radicals contribute to adhesion formation via this mechanism in OA of the TMJ.
  
  
  METHODS
  Physiological clot formation of fibrinogen by thrombin and free-radical-induced crosslinking of fibrinogen and of fibronectin were analyzed using spectrophotometric turbidity measurements, light-scattering techniques, polyacrylamide gel electrophoresis (PAGE), and rotary shadowing.
  
  
  RESULTS
  Fibrinogen was shown to aggregate after free radical treatment, as detected using turbidity measurements and light-scattering techniques. Using PAGE, fibrinogen as well as fibronectin was shown to degrade under low oxidative stress. Under high oxidative stress, however, fragments from both proteins were found to be covalently crosslinked, resulting in high-molecular-weight protein aggregates. The aggregation was shown to be at random with rotary shadowing.
  
  
  CONCLUSIONS
  The study shows that high oxidative stress contributes to the formation of crosslinked proteins that may serve as an initial scaffolding for the development of adhesions frequently seen in OA of the TMJ.
authors.affiliation: Department of Oral and Maxillofacial Surgery, Groningen University Hospital, The Netherlands. l.c.digkgraaf@kchir. azg.nl
authors.forename: Leonore C
authors.initials: LC
authors.lastname: Dijkgraaf
authors.forename: Gustavo
authors.initials: G
authors.lastname: Zardeneta
authors.forename: Fabian W
authors.initials: FW
authors.lastname: Cordewener
authors.forename: Robert S b
authors.initials: RS
authors.lastname: Liem
authors.forename: John P
authors.initials: JP
authors.lastname: Schmitz
authors.forename: Lambert G m
authors.initials: LG
authors.lastname: de Bont
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Milam
mesh_terms: D003432:Cross-Linking Reagents / Q000737:chemistry; D003720:Densitometry; D004591:Electrophoresis, Polyacrylamide Gel; D005296:Ferrous Compounds / Q000737:chemistry; D005340:Fibrinogen / Q000737:chemistry*; D005353:Fibronectins / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D006801:Humans; D008027:Light; D008854:Microscopy, Electron; D009391:Nephelometry and Turbidimetry; D010003:Osteoarthritis / Q000209:etiology*; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D011485:Protein Binding; D017382:Reactive Oxygen Species / Q000737:chemistry; D012542:Scattering, Radiation; D016626:Shadowing Technique, Histology; D013053:Spectrophotometry; D013705:Temporomandibular Joint Disorders / Q000209:etiology*; D000267:Tissue Adhesions / Q000209:etiology
chemical_list: D003432:Cross-Linking Reagents; D005296:Ferrous Compounds; D005353:Fibronectins; D005609:Free Radicals; D017382:Reactive Oxygen Species; C020748:ferrous sulfate; D005340:Fibrinogen