Molecular imaging of activated von Willebrand factor to detect high-risk atherosclerotic phenotype.
OBJECTIVE
We hypothesized that noninvasive molecular imaging of activated von Willebrand factor (vWF) on the vascular endothelium could be used to detect a high-risk atherosclerotic phenotype.


BACKGROUND
Platelet-endothelial interactions have been linked to increased inflammatory activation and prothrombotic state in atherosclerosis. These interactions are mediated, in part, by platelet glycoprotein (GP) Ibα, suggesting that dysregulated endothelial vWF is a marker for high-risk atherosclerotic disease.


METHODS
Microbubbles targeted to activated vWF were prepared by surface conjugation of recombinant GPIbα. Flow-chamber studies were used to evaluate attachment of targeted microbubbles to immobile platelet aggregates bearing activated vWF. Contrast-enhanced ultrasound (CEU) molecular imaging of the aorta from mice was performed: 1) ex vivo after focal crush injury and blood perfusion; and 2) in vivo in mice with advanced atherosclerosis produced by deletion of the low-density lipoprotein receptor and ApoBec-1 editing peptide (LDLR(-/-)/ApoBec-1(-/-)).


RESULTS
In flow-chamber studies, tracer attachment to vWF was >10-fold greater for microbubbles bearing GPIbα compared with control microbubbles (p < 0.01). In the ex vivo aortic injury model, CEU signal enhancement for vWF-targeted microbubbles occurred primarily at the injury site and was 4-fold greater than at noninjured sites (p < 0.05). In LDLR(-/-)/ApoBec-1(-/-) mice, inflammatory cell infiltrates and dense vWF expression on the intact endothelium were seen in regions of severe plaque formation. Scanning electron microscopy demonstrated widespread platelet-endothelial interaction and only few sites of endothelial erosion. On CEU, signal enhancement for vWF-targeted microbubbles was approximately 4-fold greater (p < 0.05) in LDLR(-/-)/ApoBec-1(-/-) compared with wild-type mice. En face aortic microscopy demonstrated regions where platelet adhesion and microbubble attachment colocalized.


CONCLUSIONS
Molecular imaging using GPIbα as a targeting moiety can detect the presence of activated vWF on the vascular endothelium. This strategy may provide a means to noninvasively detect an advanced prothrombotic and inflammatory phenotype in atherosclerotic disease.
McCarty
Owen J T
OJ
Division of Biomedical Engineering, Oregon Health & Science University, Portland, Oregon, USA.
Conley
Robert B
RB
Shentu
Weihui
W
Tormoen
Garth W
GW
Zha
Daogang
D
Xie
Aris
A
Qi
Yue
Y
Zhao
Yan
Y
Carr
Chad
C
Belcik
Todd
T
Keene
Douglas R
DR
de Groot
Philip G
PG
Lindner
Jonathan R
JR
D000818:Animals; D001011:Aorta / Q000000981:diagnostic imaging / Q000648:ultrastructure; D050197:Atherosclerosis / Q000097:blood* / Q000000981:diagnostic imaging / Q000503:physiopathology; D015415:Biomarkers; D003287:Contrast Media; D004195:Disease Models, Animal; D004730:Endothelium, Vascular / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D008562:Membrane Glycoproteins / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D045423:Microbubbles; D008855:Microscopy, Electron, Scanning; D018716:Molecular Mimicry; D010641:Phenotype; D015539:Platelet Activation / Q000502:physiology; D019038:Platelet Glycoprotein GPIb-IX Complex; D033081:Shear Strength / Q000502:physiology; D014463:Ultrasonography; D014841:von Willebrand Factor / Q000502:physiology*
D015415:Biomarkers; D003287:Contrast Media; D008562:Membrane Glycoproteins; D019038:Platelet Glycoprotein GPIb-IX Complex; C094990:adhesion receptor; C023592:glycocalicin; D014841:von Willebrand Factor