title: Molecular MRI of early thrombus formation using a bimodal alpha2-antiplasmin-based contrast agent.
abstract: OBJECTIVE
  We aimed to investigate whether early thrombus formation can be visualized with in vivo magnetic resonance imaging (MRI) by the use of a novel bimodal alpha(2)-antiplasmin-based contrast agent (CA).
  
  
  BACKGROUND
  Thrombus formation plays a central role in several vascular diseases. During the early phases of thrombus formation, activated factor XIII (FXIIIa) covalently cross-links alpha(2)-antiplasmin to fibrin, indicating the potential of alpha(2)-antiplasmin-based CAs in the detection of early thrombus formation.
  
  
  METHODS
  A bimodal CA was synthesized by coupling gadolinium-diethylene triamine pentaacetic acid and rhodamine to an alpha(2)-antiplasmin-based peptide. For the control CA, a glutamine residue essential for cross-linking was replaced by alanine. In vitro-generated thrombi were exposed to both CAs and imaged by MRI and 2-photon laser-scanning microscopy. Immunohistochemistry was performed on human pulmonary thromboemboli sections to determine the presence of alpha(2)-antiplasmin and FXIII in different thrombus remodeling phases. In vivo feasibility of the CA in detecting early thrombus formation specifically was investigated with MRI.
  
  
  RESULTS
  In vitro-generated thrombi exposed to the alpha(2)-antiplasmin-based CA showed hyperintense magnetic resonance signal intensities at the thrombus edge. No hyperintense signal was observed when we used the alpha(2)-antiplasmin-based CA in the presence of FXIII inhibitor dansylcadaverine nor when we used the control CA. Two-photon laser-scanning microscopy demonstrated that the alpha(2)-antiplasmin-based CA bound to fibrin. Immunohistochemistry demonstrated substantial alpha(2)-antiplasmin staining in fresh compared with lytic and organized thrombi. The administration of CA in vivo within seconds after inducing thrombus formation increased contrast-to-noise ratios (CNRs 2.28 +/- 0.39, n=6) at the site of thrombus formation compared with the control CA (CNRs -0.14 +/- 0.55, p = 0.003, n = 6) and alpha(2)-antiplasmin-based CA administration 24 to 48 h after thrombus formation (CNRs 0.11 +/- 0.23, p = 0.006, n = 6).
  
  
  CONCLUSIONS
  A bimodal CA was developed, characterized, and validated. Our results showed that this bimodal CA enabled noninvasive in vivo magnetic resonance visualization of early thrombus formation.
authors.affiliation: Department of Radiology, Maastricht University Medical Centre, Maastricht, the Netherlands.
authors.forename: Robbert-Jan J H M
authors.initials: RJ
authors.lastname: Miserus
authors.forename: M Veronica
authors.initials: MV
authors.lastname: Herías
authors.forename: Lenneke
authors.initials: L
authors.lastname: Prinzen
authors.forename: Marc B I
authors.initials: MB
authors.lastname: Lobbes
authors.forename: Robert-Jan
authors.initials: RJ
authors.lastname: Van Suylen
authors.forename: Anouk
authors.initials: A
authors.lastname: Dirksen
authors.forename: Tilman M
authors.initials: TM
authors.lastname: Hackeng
authors.forename: Johan W M
authors.initials: JW
authors.lastname: Heemskerk
authors.forename: Jos M A
authors.initials: JM
authors.lastname: van Engelshoven
authors.forename: Mat J A P
authors.initials: MJ
authors.lastname: Daemen
authors.forename: Marc A M J
authors.initials: MA
authors.lastname: van Zandvoort
authors.forename: Sylvia
authors.initials: S
authors.lastname: Heeneman
authors.forename: Marianne Eline
authors.initials: ME
authors.lastname: Kooi
mesh_terms: D000818:Animals; D002103:Cadaverine / Q000031:analogs & derivatives / Q000494:pharmacology; D003287:Contrast Media; D004195:Disease Models, Animal; D005176:Factor XIII / Q000378:metabolism; D026122:Factor XIIIa / Q000378:metabolism; D005240:Feasibility Studies; D005337:Fibrin / Q000378:metabolism; D019786:Gadolinium DTPA / Q000031:analogs & derivatives / Q000493:pharmacokinetics; D006801:Humans; D007150:Immunohistochemistry; D008279:Magnetic Resonance Imaging; D051379:Mice; D036641:Microscopy, Fluorescence, Multiphoton; D011237:Predictive Value of Tests; D011655:Pulmonary Embolism / Q000097:blood / Q000175:diagnosis* / Q000473:pathology; D015203:Reproducibility of Results; D012235:Rhodamines / Q000493:pharmacokinetics; D013927:Thrombosis / Q000097:blood / Q000175:diagnosis* / Q000473:pathology; D000979:alpha-2-Antiplasmin / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D003287:Contrast Media; D012235:Rhodamines; D000979:alpha-2-Antiplasmin; D005337:Fibrin; D005176:Factor XIII; D026122:Factor XIIIa; C008542:monodansylcadaverine; D019786:Gadolinium DTPA; D002103:Cadaverine