title: Molecular mechanisms of the effect of ultrasound on the fibrinolysis of clots.
abstract: BACKGROUND
  Ultrasound accelerates tissue-type plasminogen activator (t-PA)-induced fibrinolysis of clots in vitro and in vivo.
  
  
  OBJECTIVE
  To identify mechanisms for the enhancement of t-PA-induced fibrinolysis of clots.
  
  
  METHODS
  Turbidity is an accurate and convenient method, not previously used, to follow the effects of ultrasound. Deconvolution microscopy was used to determine changes in structure, while fluorescence recovery after photobleaching was used to characterize the kinetics of binding/unbinding and transport.
  
  
  RESULTS
  The ultrasound pulse repetition frequency affected clot lysis times, but there were no thermal effects. Ultrasound in the absence of t-PA produced a slight but consistent decrease in turbidity, suggesting a decrease in fibrin diameter due solely to the action of the ultrasound, likely caused by an increase in protofibril tension because of vibration from ultrasound. Changes in fibrin network structure during lysis with ultrasound were visualized in real time by deconvolution microscopy, revealing that the network becomes unstable when 30-40% of the protein in the network was digested, whereas without ultrasound, the fibrin network was digested gradually and retained structural integrity. Fluorescence recovery after photobleaching during lysis revealed that the off-rate of oligomers from digesting fibers was little affected, but the number of binding/unbinding sites was increased.
  
  
  CONCLUSIONS
  Ultrasound causes a decrease in the diameter of the fibers due to tension as a result of vibration, leading to increased binding sites for plasmin(ogen)/t-PA. The positive feedback of this structural change together with increased mixing/transport of t-PA/plasmin(ogen) is likely to account for the observed enhancement of fibrinolysis by ultrasound.
authors.affiliation: Department Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA, USA.
authors.forename: I N
authors.initials: IN
authors.lastname: Chernysh
authors.forename: C E
authors.initials: CE
authors.lastname: Everbach
authors.forename: P K
authors.initials: PK
authors.lastname: Purohit
authors.forename: J W
authors.initials: JW
authors.lastname: Weisel
mesh_terms: D001665:Binding Sites; D005337:Fibrin / Q000378:metabolism* / Q000648:ultrastructure; D005342:Fibrinolysis / Q000187:drug effects*; D005343:Fibrinolytic Agents / Q000378:metabolism / Q000494:pharmacology*; D036681:Fluorescence Recovery After Photobleaching; D006801:Humans; D007700:Kinetics; D008853:Microscopy; D009391:Nephelometry and Turbidimetry; D011485:Protein Binding; D011487:Protein Conformation; D055550:Protein Stability; D059748:Proteolysis; D013696:Temperature; D010959:Tissue Plasminogen Activator / Q000378:metabolism / Q000494:pharmacology*; D014465:Ultrasonics; D014732:Vibration
chemical_list: D005343:Fibrinolytic Agents; D005337:Fibrin; D010959:Tissue Plasminogen Activator
keywords: fibrin; fibrinolysis; microscopy; plasma; ultrasound