The efficient delivery of nanomaterials to specific targets for in vivo biomedical imaging is hindered by rapid sequestration by the reticuloendothelial system (RES) and consequent short circulation times. To overcome these two problems, we have prepared a new stealth PEG polymer conjugate containing a terminal 1,1-bisphosphonate (BP) group for strong and stable binding to the surface of ultrasmall-superparamagnetic oxide nanomaterials (USPIOs). This polymer, PEG(5)-BP, can be used to exchange the hydrophobic surfactants commonly used in the synthesis of USPIOs very efficiently and at room temperature using a simple method in 1 h. The resulting nanoparticles, PEG(5)-BP-USPIOs are stable in water or saline for at least 7 months and display a near-zero ζ-potential at neutral pH. The longitudinal (r1) and transverse (r2) relaxivities were measured at a clinically relevant magnetic field (3 T), revealing a high r1 of 9.5 mM–1 s–1 and low r2/r1 ratio of 2.97, making these USPIOs attractive as T1-weighted MRI contrast agents at high magnetic fields. The strong T1-effect was demonstrated in vivo, revealing that PEG(5)-BP-USPIOs remain in the bloodstream and enhance its signal 6-fold, allowing the visualization of blood vessels and vascular organs with high spatial definition. Furthermore, the optimal relaxivity properties allow us to inject a dose 4 times lower than with other USPIOs. PEG(5)-BP-USPIOs can also be labeled using a radiolabeled-BP for visualization with single photon emission computed tomography (SPECT), and thus affording dual-modality contrast. The SPECT studies confirmed low RES uptake and long blood circulation times (t1/2 = 2.97 h). These results demonstrate the potential of PEG(5)-BP-USPIOs for the development of targeted multimodal imaging agents for molecular imaging.

Background-Endothelial dysfunction promotes atherosclerosis and precedes acute cardiovascular events. We investigated whether in vivo magnetic resonance imaging with the use of an albumin-binding contrast agent, gadofosveset, could detect endothelial damage associated with atherosclerosis in apolipoprotein E-deficient (ApoE Ϫ/Ϫ ) mice. Furthermore, we tested whether magnetic resonance imaging could noninvasively assess endothelial function by measuring the endothelial-dependent vasodilation in response to acetylcholine. Methods and Results-ApoEϪ/Ϫ mice were imaged at 4, 8, and 12 weeks after commencement of a high-fat diet. Statin-treated ApoE Ϫ/Ϫ mice were scanned after 12 weeks of a high-fat diet. Wild-type mice were imaged before and 48 hours after injection of Russell's viper venom, an endothelial toxin. Delayed enhancement magnetic resonance imaging and T1 mapping of the brachiocephalic artery, 30 minutes after injection of gadofosveset, showed increased vessel wall enhancement and relaxation rate (R 1 ) with progression of atherosclerosis in ApoE (R 1 ϭ3.0Ϯ0.65) mice showed less enhancement. Uptake of gadofosveset correlated with Evans blue staining, morphological changes of endothelial cells, and widening of the cell-cell junctions, suggesting that uptake occurs in regions of increased vascular permeability. Endothelial-dependent vasomotor responses showed vasoconstriction of the arteries of the ApoE Ϫ/Ϫ (Ϫ22.22Ϯ7.95%) and Russell's viper venom-injected (Ϫ10.37Ϯ17.60%) mice compared with wild-type mice (32.45Ϯ12.35%). Statin treatment improved endothelium morphology and function (Ϫ8.12Ϯ8.22%). Conclusions-We demonstrate the noninvasive assessment of endothelial permeability and function with the use of an albumin-binding magnetic resonance contrast agent. Blood albumin leakage could be a surrogate marker for the in vivo evaluation of interventions that aim to restore the endothelium. (Circulation. 2012;126:707-719.)Key Words: atherosclerosis Ⅲ endothelial dysfunction Ⅲ gadofosveset Ⅲ magnetic resonance imaging Ⅲ permeability A therosclerosis is a chronic disease of the vessels and a major cause of death in Western societies. Dysfunction of the vascular endothelium triggers leukocyte transmigration, platelet activation, smooth muscle cell proliferation, and vasoconstriction, which collectively promote the development of atherosclerosis. 1 Additionally, damaged endothelium can precipitate the complications of atherosclerosis through vasospasm and thrombosis, causing life-threatening cardiovascular events. Clinical Perspective on p 719Transport across the normal endothelium occurs between endothelial cells (ECs) (intercellular pathway) and/or through the ECs (transcytosis). Intercellular junctions with a diameter of Ϸ2 nm allow transport of small water-soluble molecules up to that diameter, 2 whereas breaks in the tight junctions with a diameter of Ϸ20 nm 3,4 accommodate the influx of albumin (diameter of Ϸ6 nm) and Evans blue dye (EBD). At the molecular level, oxidized low-density lipoprotein (1) decreases...

Disruption and thrombosis of atherosclerotic plaques cause most acute cardiovascular events, but their systematic study has been hampered by the lack of suitable animal models. To assess the value of a modified rabbit model of atherothrombosis, we performed detailed histology of rabbit aortic plaques. Atherosclerosis was induced with a high cholesterol diet fed 2 weeks prior to and 6 weeks after balloon injury of the aorta, followed by 4 weeks of normal diet. We found six out of eight types of plaques cataloged by the American Heart Association in the rabbit aorta. Vulnerable plaques were defined as those with attached platelet and fibrin-rich thrombi after pharmacological triggering with Russellʼs viper venom and histamine. Ruptured plaques had, as also described for human plaques: i) marked medial and adventitial changes, including neovascularization and inflammation; ii) cholesterol monohydrate crystals and liquid crystalline cholesterol esters in the intima and the fibrous cap; and iii) inflamed, thin fibrous caps. Increased cholesterol monohydrate area, internal elastic lamina area, positive remodeling, fibrous cap inflammation, adventitia breakdown, and inflammation were independent predictors of plaque disruption. Our findings reveal novel insights into plaque vulnerability and could guide the design of noninvasive imaging approaches for detecting and treating high-risk plaques.-Phinikaridou, A., K. J. Hallock, Y. Qiao, and J. A. Hamilton. A robust rabbit model of human atherosclerosis and atherothrombosis. J. Lipid Res. 2009. 50: 787-797.

The ECM is the key structural component determining dilatation and aneurysm formation in the aortic wall. 8 Abdominal aortic aneurysms (AAAs) are characterized by loss of elastin and increased collagen turnover. Apart from miR-29, the miR-15 family has been implicated in collagen remodeling and the characteristic postnatal silencing of elastin.9 The miR-15 family consists of 6 highly conserved microRNAs (miR-15a, miR15b, miR-16-1, miR-16-2, miR-195, and miR-497), which are clustered on 3 separate chromosomes. They have a common seed region (AGCAGCA) and varying degrees of sequence homology in the 3′ region of the mature microRNA.

The source of the T1 signal in the thrombus results from the oxidation of iron (released from the lysis of trapped erythrocytes in the thrombus) to its paramagnetic Fe3+ form. Quantification of T1 relaxation time appears to be a good predictor of the success of thrombolysis.

Background-The ability to identify atherosclerotic plaques with a high risk for sudden disruption before stroke or myocardial infarction would be of great utility. We used a rabbit model of controlled atherothrombosis to test whether in vivo MRI can noninvasively distinguish between plaques that disrupt after pharmacological triggering (vulnerable) and those that do not (stable). Methods and Results-Atherosclerosis was induced in male New Zealand White (nϭ17) rabbits by cholesterol diet and endothelial denudation of the abdominal aorta. After baseline (pretrigger) MRI with and without gadolinium contrast, the rabbits underwent 2 pharmacological triggerings to induce atherothrombosis, followed by another MRI 48 hours later (post-triggering). Atherosclerosis was identified by the pretriggered images in all rabbits, and thrombosis was identified in 9 of 17 animals (53%) by post-trigger MRI. After the animals were euthanized, 95 plaques were analyzed; 28 (29.5%) had thrombi (vulnerable) and 67 did not (stable) (70.5%). Pretriggered MRI revealed comparable stenosis in stable and vulnerable plaques, but vulnerable plaques had a larger plaque area (4.8Ϯ1.6 versus 3.0Ϯ1.0 mm 2 ; Pϭ0.01), vessel area (9.2Ϯ3.0 versus. 15.8Ϯ4.9 mm 2 ; Pϭ0.01), and higher remodeling ratio (1.16Ϯ0.2 versus 0.93Ϯ0.2; Pϭ0.01) compared with stable plaques. Furthermore, vulnerable plaques more frequently exhibited (1) positive remodeling (67.8% versus 22.3%; Pϭ0.01), in which the plaque is hidden within the vessel wall instead of occluding the lumen; and (2) enhanced gadolinium uptake (78.6% versus 20.9%; Pϭ0.01) associated with histological findings of neovascularization, inflammation, and tissue necrosis. Conclusions-We demonstrate that in vivo MRI at 3.0 T detects features of vulnerable plaques in an animal model of controlled atherothrombosis. These findings suggest that MRI may be used as a noninvasive modality for localization of plaques that are prone to disruption. (Circ Cardiovasc Imaging. 2010;3:323-332.)Key Words: MRI Ⅲ atherosclerosis Ⅲ thrombosis Ⅲ gadolinium Ⅲ remodeling A cute coronary syndromes (ACS) such as unstable angina pectoris and myocardial infarction are the leading causes of death in the United States. 1 Histological studies demonstrate that ACS are usually triggered by rupture/erosion of vulnerable atherosclerotic plaques, which results in luminal thrombosis. 2,3 X-ray angiographic studies, which do not provide information about plaque composition, suggest that the majority of high-risk plaques cause Ͻ50% luminal narrowing. 4,5 In vivo MRI can estimate the degree of luminal narrowing and identify plaque components. 6 -9 Contrast-enhanced MRI (CE-MRI) using gadolinium-diethylenetriamine penta-acetic acid (Gd-DTPA) has improved the discrimination between the fibrous cap and the lipid core 10,11 and necrotic core 12 and the visualization of coronary atherosclerosis. 13,14 Furthermore, dynamic CE-MRI has shown that uptake of Gd-DTPA is correlated with neovascularization 15,16 and inflammation, 17 both of which are increa...

Objective-Studies in humans support a role for the oral pathogen Porphyromonas gingivalis in the development of inflammatory atherosclerosis. The goal of this study was to determine if P. gingivalis infection accelerates inflammation and atherosclerosis in the innominate artery of mice, an artery which has been reported to exhibit many features of human atherosclerotic disease, including plaque rupture.Methods and Results-Apolipoprotein E-deficient (ApoE −/− ) mice were orally infected with P. gingivalis, and Magnetic Resonance Imaging (MRI) was used to monitor the progression of atherosclerosis in live mice. P. gingivalis infected mice exhibited a statistically significant increase in atherosclerotic plaque in the innominate artery as compared to uninfected mice. Polarized light microscopy and immunohistochemistry revealed that the innominate arteries of infected mice had increased lipids, macrophages and T cells as compared to uninfected mice. Increases in plaque, total cholesterol esters and cholesterol monohydrate crystals, macrophages, and T cells were prevented by immunization with heat-killed P. gingivalis prior to pathogen exposure.Conclusions-These are the first studies to demonstrate progression of inflammatory plaque accumulation in the innominate arteries by in-vivo MRI analysis following pathogen exposure, and to document protection from plaque progression in the innominate artery via immunization. * Corresponding Author. Caroline A. Genco, 650 Albany St. Boston, MA 02118, USA,, cgenco@bu.edu. 1 These authors contributed equally to this work. Disclosure None.Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptAtherosclerosis. Author manuscript; available in PMC 2012 March 1. We previously demonstrated that oral infection with Porphyromonas gingivalis, the etiological agent of human periodontal disease, accelerates plaque accumulation in the aortic sinus in an apolipoprotein E (ApoE −/− ) mouse model [5,8]. While these studies in the ApoE −/− mouse model have described atherosclerotic lesions of the aortic sinus by histological analysis, intra-plaque rupture or signs of plaque disruption at the aortic sinus have not been reported [9]. In contrast, recent studies have documented the presence of ruptured plaques in the innominate artery of ApoE −/− mice [10][11][12][13][14]. The innominate artery has been reported to undergo a high degree of lesion progression, and lesions in this artery reported to express features characteristic of clinical disease in humans [10,11,[15][16][17]. However, the ability of infectious agents t...

Background-Persistent intracoronary thrombus after plaque rupture is associated with an increased risk of subsequent myocardial infarction and mortality. Coronary thrombus is usually visualized invasively by x-ray coronary angiography. Non-contrast-enhanced T1-weighted magnetic resonance (MR) imaging has been useful for direct imaging of carotid thrombus and intraplaque hemorrhage by taking advantage of the short T1 of methemoglobin present in acute thrombus and intraplaque hemorrhage. The aim of this study was to investigate the use of non-contrast-enhanced MR for direct thrombus imaging (MRDTI) in patients with acute myocardial infarction. Methods and Results-Eighteen patients (14 men; age, 61Ϯ9 years) underwent MRDTI within 24 to 72 hours of presenting with an acute coronary syndrome before invasive x-ray coronary angiography; MRDTI was performed with a T1-weighted, 3-dimensional, inversion-recovery black-blood gradient-echo sequence without contrast administration. Ten patients were found to have intracoronary thrombus on x-ray coronary angiography (left anterior descending, 4; left circumflex, 2; right coronary artery, 4; and right coronary artery-posterior descending artery, 1), and 8 had no visible thrombus. We found that MRDTI correctly identified thrombus in 9 of 10 patients (sensitivity, 91%; posterior descending artery thrombus not detected) and correctly classified the control group in 7 of 8 patients without thrombus formation (specificity, 88%). The contrast-to-noise ratio was significantly greater in coronary segments containing thrombus (nϭ10) compared with those without visible thrombus (nϭ131; mean contrast-to-noise ratio, 15.9 versus 2.6; PϽ0.001). Conclusion-Use of MRDTI allows selective visualization of coronary thrombus in a patient population with a high probability of intracoronary thrombosis. (Circulation. 2011;124:416-424.)