title: An ultrasound contrast agent targeted to P-selectin detects activated platelets at supra-arterial shear flow conditions.
abstract: OBJECTIVE
  To evaluate targeting of a microbubble contrast agent to platelets under high shear flow using the natural selectin ligand sialyl Lewis.
  
  
  METHODS
  Biotinylated polyacrylamide Sialyl Lewis or biotinylated carbohydrate-free polymer (used as a control) were attached to biotinylated microbubbles via a streptavidin linker. Activated human platelets were isolated and attached to fibrinogen-coated culture dishes. Fibrinogen-coated dishes without platelets or platelet dishes blocked by an anti-P-selectin antibody served as negative control substrates. Dishes coated by recombinant P-selectin served as a positive control substrate. Microbubble adhesion was assessed by microscopy in an inverted parallel plate flow chamber, with wall shear stress values of 40, 30, 20, 10, and 5 dynes/cm2. The ratio of binding and passing microbubbles was defined as capture efficiency.
  
  
  RESULTS
  There was no significant difference between the groups regarding the number of microbubbles in the fluid flow at each shear rate. Sialyl Lewis-targeted microbubbles were binding and slowly rolling on the surface of activated platelets and P-selectin-coated dishes at all the flow conditions including 40 dynes/cm2. Capture efficiency of targeted microbubbles to activated platelets and recombinant P-selectin decreased with increasing shear flow: at 5 dynes/cm2, capture efficiency was 16.11% on activated platelets versus 21.83% on P-selectin, and, at 40 dynes/cm2, adhesion efficiency was still 3.4% in both groups. There was neither significant adhesion of Sialyl Lewis-targeted microbubbles to control substrates, nor adhesion of control microbubbles to activated platelets or to recombinant P-selectin.
  
  
  CONCLUSIONS
  Microbubble targeting using sialyl Lewis, a fast-binding ligand to P-selectin, is a promising strategy for the design of ultrasound contrast binding to activated platelets under high shear stress conditions.
authors.affiliation: Department of Cardiology and Angiology, University Hospital of Freiburg, Freiburg, Germany. felix.guenther@uniklinik-freiburg.de
authors.forename: Felix
authors.initials: F
authors.lastname: Guenther
authors.forename: Constantin
authors.initials: C
authors.lastname: von zur Muhlen
authors.forename: Elisa A
authors.initials: EA
authors.lastname: Ferrante
authors.forename: Sebastian
authors.initials: S
authors.lastname: Grundmann
authors.forename: Christoph
authors.initials: C
authors.lastname: Bode
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Klibanov
mesh_terms: D001158:Arteries / Q000000981:diagnostic imaging*; D001783:Blood Flow Velocity; D001792:Blood Platelets / Q000000981:diagnostic imaging* / Q000201:enzymology; D002448:Cell Adhesion; D003287:Contrast Media; D005340:Fibrinogen; D006801:Humans; D008024:Ligands; D045423:Microbubbles; D019007:P-Selectin; D015539:Platelet Activation / Q000276:immunology*; D011994:Recombinant Proteins; D033081:Shear Strength; D014463:Ultrasonography
chemical_list: D003287:Contrast Media; D008024:Ligands; D019007:P-Selectin; D011994:Recombinant Proteins; D005340:Fibrinogen
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