Molecular MRI of early thrombus formation using a bimodal alpha2-antiplasmin-based contrast agent.
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.
Miserus
Robbert-Jan J H M
RJ
Department of Radiology, Maastricht University Medical Centre, Maastricht, the Netherlands.
Herías
M Veronica
MV
Prinzen
Lenneke
L
Lobbes
Marc B I
MB
Van Suylen
Robert-Jan
RJ
Dirksen
Anouk
A
Hackeng
Tilman M
TM
Heemskerk
Johan W M
JW
van Engelshoven
Jos M A
JM
Daemen
Mat J A P
MJ
van Zandvoort
Marc A M J
MA
Heeneman
Sylvia
S
Kooi
Marianne Eline
ME
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
D003287:Contrast Media; D012235:Rhodamines; D000979:alpha-2-Antiplasmin; D005337:Fibrin; D005176:Factor XIII; D026122:Factor XIIIa; C008542:monodansylcadaverine; D019786:Gadolinium DTPA; D002103:Cadaverine