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Combined Near-infrared Fluorescent Imaging and Micro-computed Tomography for Directly Visualizing Cerebral Thromboemboli
Published on: September 25, 2016
Molecular MRI of early thrombus formation using a bimodal alpha2-antiplasmin-based contrast agent
Robbert-Jan J H M Miserus1, M Veronica Herías, Lenneke Prinzen
1Department of Radiology, Maastricht University Medical Centre, Maastricht, the Netherlands.
Objectives:
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.
Insights
A novel bimodal contrast agent (CA) allows for early thrombus visualization using magnetic resonance imaging (MRI). This alpha(2)-antiplasmin-based CA specifically targets early clot formation, enabling noninvasive detection of vascular diseases.
Area of Science:
- Biomedical Imaging
- Vascular Biology
- Contrast Agent Development
Background:
- Thrombus formation is critical in vascular diseases.
- Activated factor XIII (FXIIIa) cross-links alpha(2)-antiplasmin to fibrin in early thrombus.
- This interaction suggests alpha(2)-antiplasmin-based agents for early thrombus detection.
Purpose of the Study:
- To develop and evaluate a novel bimodal alpha(2)-antiplasmin-based contrast agent (CA).
- To assess the CA's ability to visualize early thrombus formation using in vivo magnetic resonance imaging (MRI).
Main Methods:
- Synthesized a bimodal CA by conjugating gadolinium and rhodamine to an alpha(2)-antiplasmin peptide.
- Used a control CA with a modified glutamine residue for comparison.
- Evaluated CA efficacy in vitro using MRI and 2-photon microscopy, and in vivo using MRI on induced thrombi.
Main Results:
- The alpha(2)-antiplasmin-based CA showed hyperintense signals at the thrombus edge in vitro, binding to fibrin.
- In vivo MRI demonstrated significantly increased contrast-to-noise ratios for early thrombus detection with the novel CA.
- Control CA and delayed administration of the novel CA did not yield significant signal enhancement.
Conclusions:
- A novel bimodal alpha(2)-antiplasmin-based contrast agent was successfully developed and validated.
- This CA enables noninvasive in vivo magnetic resonance imaging visualization of early thrombus formation.
- The findings highlight the potential of this agent for early diagnosis of thrombotic events.
