Molecular MRI of Atherosclerotic lesions

This thesis describes the use of MRI contrast agents and vessel wall parameters to image different stages of atherosclerosis. Chapter 2 summerizes different MRI contrast agents targeted towards vulnerable plaques that have been presented in literature. Chapter 3 illustrates accumulation of paramagnetic micelles and liposomes in atherosclerosis, yet have complex kinetics when followed over time. In chapter 4 the use of self-gated MRI was validated to detect contrast agent accumulation in atherosclerotic plaques and assess the vessel wall compliance. The potential of both techniques to monitor plaque progression and anti-atherosclerotic therapy was assessed. In chapter 5 we developed a scavenger receptor-A1 targeted USPIO to detect vulnerable lesions. Chapter 6 describes the application of VCAM-1 targeted USPIO. Imaging at different time points, allows to discriminate early plaques from advanced lesions and can be used to monitor treatment response in ApoE-/- mice. In Chapter 7 an E-selectin targeted USPIO was validated. This USPIO allowed discrimination of lesions rich in macrophages from early lesions. In Chapter 8 we developed a micelle encapsulating rosiglitazone. Targeted delivery to the plaque lead to an anti-atheroscle rotic response without cardiac side-effects. Finally in Chapter 9 the potentials and pitfalls of histological validation of MRI contrast agents are illustrated.NHS (Nederlandse Hartstichting), Guerbet Nederlan

Z-disc protein CHAPb induces cardiomyopathy and contractile dysfunction in the postnatal heart

The Z-disc is a crucial structure of the sarcomere and is implicated in mechanosensation/transduction. Dysregulation of Z-disc proteins often result in cardiomyopathy. We have previously shown that the Z-disc protein Cytoskeletal Heart-enriched Actin-associated Protein (CHAP) is essential for cardiac and skeletal muscle development. Furthermore, the CHAP gene has been associated with atrial fibrillation in humans. Here, we studied the misregulated expression of CHAP isoforms in heart disease. Mice that underwent transverse aortic constriction and calcineurin transgenic (Tg) mice, both models of experimental heart failure, displayed a significant increase in cardiac expression of fetal isoform CHAPb. To investigate whether increased expression of CHAPb postnatally is sufficient to induce cardiomyopathy, we generated CHAPb Tg mice under the control of the cardiac-specific αMHC promoter. CHAPb Tg mice displayed cardiac hypertrophy, interstitial fibrosis and enlargement of the left atrium at three months, which was more pronounced at the age of six months. Hypertrophy and fibrosis were confirmed by evidence of activation of the hypertrophic gene program (Nppa, Nppb, Myh7) and increased collagen expression, respectively. Connexin40 and 43 were downregulated in the left atrium, which was associated with delayed atrioventricular conduction. Tg hearts displayed both systolic and diastolic dysfunction partly caused by impaired sarcomere function evident from a reduced force generating capacity of single cardiomyocytes. This co-incided with activation of the actin signalling pathway leading to the formation of stress fibers. This study demonstrated that the fetal isoform CHAPb initiates progression towards cardiac hypertrophy, which is accompanied by delayed atrioventricular conduction and diastolic dysfunction. Moreover, CHAP may be a novel therapeutic target or candidate gene for screening in cardiomyopathies and atrial fibrillatio

Molecular MRI of Atherosclerotic lesions

This thesis describes the use of MRI contrast agents and vessel wall parameters to image different stages of atherosclerosis. Chapter 2 summerizes different MRI contrast agents targeted towards vulnerable plaques that have been presented in literature. Chapter 3 illustrates accumulation of paramagnetic micelles and liposomes in atherosclerosis, yet have complex kinetics when followed over time. In chapter 4 the use of self-gated MRI was validated to detect contrast agent accumulation in atherosclerotic plaques and assess the vessel wall compliance. The potential of both techniques to monitor plaque progression and anti-atherosclerotic therapy was assessed. In chapter 5 we developed a scavenger receptor-A1 targeted USPIO to detect vulnerable lesions. Chapter 6 describes the application of VCAM-1 targeted USPIO. Imaging at different time points, allows to discriminate early plaques from advanced lesions and can be used to monitor treatment response in ApoE-/- mice. In Chapter 7 an E-selectin targeted USPIO was validated. This USPIO allowed discrimination of lesions rich in macrophages from early lesions. In Chapter 8 we developed a micelle encapsulating rosiglitazone. Targeted delivery to the plaque lead to an anti-atheroscle rotic response without cardiac side-effects. Finally in Chapter 9 the potentials and pitfalls of histological validation of MRI contrast agents are illustrated

Molecular magnetic resonance imaging for the detection of vulnerable plaques : Is it possible? RETRACTED!

Recent advances in molecular resonance imaging of atherosclerosis enable to visualize atherosclerotic plaques in vivo using molecular targeted contrast agents. This offers opportunities to study atherosclerosis development and plaque vulnerability noninvasively. In this review, we discuss MRI contrast agents targeted toward atherosclerotic plaques and illustrate how these new imaging platforms could assist in our understanding of atherogenesis and atheroprogression. In particular, we highlight the challenges and limitations of the different contrast agents and hurdles for clinical application. We describe the most promising existing compounds to detect atherosclerosis and plaque vulnerability. Of particular interest are the fibrin-targeted compounds that detect thrombi and, furthermore, the contrast agents targeted to integrins that allow to visualize plaque neovascularization. Moreover, vascular cell adhesion molecule 1-targeted iron oxides seem promising for early detection of atherosclerosis. These targeted MRI contrast agents, however promising and well characterized in (pre)clinical models, lack specificity for plaque vulnerability

Contrast-to-Noise determination in the aortic arch.

<p>Region of interest (ROI) placement in the MR images were used to determine the contrast to noise ratios (CNR) in the atherosclerotic plaques in black blood images of a cross section of the aortic arch. ROI1 is placed in the atherosclerotic plaque in the vessel wall (Iwall). ROI2 is positioned in a muscle and used for normalization purposes (Imuscle). Noise levels were determined in ROI 3, placed in a region without signal. The standard deviation of the noise (stdevnoise) was used for normalization purposes.</p

Vessel wall chracteristics measured by MRI.

<p>A. Diameter of the aortic arch in mm measured at end-diastole and end-systole measured in CINE MRI images from 3 months and 12 months old ApoE^−/− mice B. Distensibility of the aortic arch measured by the average maximal circumferential strain calculated for both age groups.</p

Atherosclerotic plaque detection in a cross-section of the aortic arch, including the effect of Gd-loaded micelles.

<p>A. Ten movie frames of a cross section of the aortic arch are generated. The black blood images used for positive contrast agent detection in the aortic arch are typically as those in image 6–8 (underlined). Circles indicate the region of the aortic arch cross section. White blood images 1–3 (dashed line), were used for the analysis of negative contrast agents B. A cross section of the aortic arch is shown before injection of micelles. Presumptive plaque regions are difficult to discriminate (arrow). C. Cross section of the aortic arch 12 hours after injection of micelles shows contrast enhancement on the basis of the aortic arch (arrow) D. Contrast to Noise Ratio (D1) and delta CNR (D2) of atherosclerotic plaques on the inner curvature of the aortic arch in 3 months old and 12–14 months old ApoE^−/− mice on a western diet.</p

Histological validation of atherosclerosis and MRI.

<p>A. Lipid depositions on the basis of the aortic arch and in the branches to the carotid and brachiocephalic arteries were shown by Oil Red O staining. B. Regions with atherosclerotic plaques corresponding to the regions in A are depicted in this MR image of the aortic arch. C. Plaque sizes of the 3 treatment groups in µm2 determined on histological slices. D. Anti-Gd-DTPA immunohistochemical DAB staining localized the micelles in atherosclerotic plaques. E. Iron deposits are visualized with Prussian blue enhanced with DAB in the wall of the aortic arch. F. Correlation CNR of atherosclerotic plaques on the inner curvature of the aortic arch (F1 micelles, F2 USPIO) with plaque sizes of the 3 groups determined on histological slices. G. Correlation of the aortic arch lesion area with the circumferential strain of the 3 treatment groups. H. Correlation of the CNR of both micelles (H1) as well as USPIO (H2) with the circumferential strain for all data-points together.</p