In Vivo Detection of Activated Platelets Allows Characterizing Rupture of Atherosclerotic Plaques with Molecular Magnetic Resonance Imaging in Mice

Abstract

BackgroundEarly and non-invasive detection of platelets on micro atherothrombosis provides a means to identify unstable plaque and thereby allowing prophylactic treatment towards prevention of stroke or myocardial infarction. Molecular magnetic resonance imaging (mMRI) of activated platelets as early markers of plaque rupture using targeted contrast agents is a promising strategy. In this study, we aim to specifically image activated platelets in murine atherothrombosis by in vivo mMRI, using a dedicated animal model of plaque rupture.MethodsAn antibody targeting ligand-induced binding sites (LIBS) on the glycoprotein IIb/IIIa-receptor of activated platelets was conjugated to microparticles of iron oxide (MPIO) to form the LIBS-MPIO contrast agent causing a signal-extinction in T2*-weighted MRI. ApoE−/− mice (60 weeks-old) were fed a high fat diet for 5 weeks. Using a small needle, the surface of their carotid plaques was scratched under blood flow to induce atherothrombosis. In vivo 9.4 Tesla MRI was performed before and repetitively after intravenous injection of either LIBS-MPIO versus non-targeted-MPIO.ResultsLIBS-MPIO injected animals showed a significant signal extinction (p<0.05) in MRI, corresponding to the site of plaque rupture and atherothrombosis in histology. The signal attenuation was effective for atherothrombosis occupying ≥2% of the vascular lumen. Histology further confirmed significant binding of LIBS-MPIO compared to control-MPIO on the thrombus developing on the surface of ruptured plaques (p<0.01).Conclusion in vivo mMRI detected activated platelets on mechanically ruptured atherosclerotic plaques in ApoE−/− mice with a high sensititvity. This imaging technology represents a unique opportunity for noninvasive detection of atherothrombosis and the identification of unstable atherosclerotic plaques with the ultimate promise to prevent strokes and myocardial infarctions.

Dual-Contrast Molecular Imaging Allows Noninvasive Characterization of Myocardial Ischemia/Reperfusion Injury After Coronary Vessel Occlusion in Mice by Magnetic Resonance Imaging

“…16,22 The LIBS antibody also binds to human platelets, also in an activation-specific manner, which is an important step toward the translation of this promising technology to application in humans. 17 The presence of LIBS-MPIOs in ischemic/reperfused heart correlates well with the histological presence of platelets in the heart. This is an important prerequisite for noninvasive characterization of pathologies by MRI.…”

“…Using this approach, we were able to detect even small amounts of activated platelets in coronary and carotid artery thrombosis, plaque rupture, and cerebral inflammation in mice. [16][17][18] In this study, we induced ischemia/reperfusion injury in C57BL/6N mice by temporary ligation of the left anterior descending coronary artery and then performed molecular MRI of activated platelets by LIBS-MPIOs to characterize platelet accumulation contributing to microvascular obstruction and ischemia/reperfusion-associated inflammation. Furthermore, in a dual MRI approach, myocardial necrosis was directly assessed by LGE in the same animals.…”

Advances in MRI for the evaluation of carotid atherosclerosis

“…In a study by von Elverfeldt et al, 75 the activated platelets in murine atherothrombosis were imaged by in vivo mMRI, using a dedicated animal model of plaque rupture. An antibody-targeting ligandinduced binding site (LIBS) on the glycoprotein IIb/IIIa receptor of activated platelets was conjugated to microparticles of iron oxide (MPIO) to form the LIBS-MPIO contrast agent causing a signalextinction in T 2 * weighted MRILIBS-MPIO.…”

Fe₃O₄-based PLGA nanoparticles as MR contrast agents for the detection of thrombosis

“…A variety of particles have been reported in the literature for thrombosis detection. [4][5][6][7][8][9][10][11][12][13][14][15][16][17] Compared with ultrasound, [4][5][6][7][8] nuclear medicine, 9,10,18 and computed tomography (CT), 11 the advantages of magnetic resonance imaging (MRI) that are particularly relevant in the context of cardiovascular diseases are its high temporal and spatial imaging resolution, high soft tissue contrast,…”

“…In recent years, MR contrast agents, such as gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA), superparamagnetic iron oxide (SPIO), and ultra-small superparamagnetic particles of iron oxide (USPIOs), have been successfully encapsulated into macromolecular polymer particles to create novel contrast agents. [12][13][14][15][16][17] The fibrin-targeted MR molecular probe EP-2104R has entered clinical trials with encouraging results. 19 Comparatively Gd-DTPA, SPIO and USPIO have the advantages of long half-lives, high relaxation rates, and minimal side effects.…”