Imaging of atherosclerotic cardiovascular disease

Radial modulation contrast imaging using a 20-MHz single-element intravascular ultrasound catheter

Contrast-enhanced intravascular ultrasound imaging is a promising tool for the characterization of coronary vasa vasorum proliferation, which has been identified as a marker of, and possible etiologic factor in, the development of high-risk atherosclerotic plaques. Resonance-based nonlinear detection methods have required the development of prototype catheters which are not commercially available, thus limiting clinical translation. In this study, we investigated the performances of a radial modulation imaging approach (25/3 MHz combination) using simulations, implemented it on a clinical 20-MHz rotating catheter, and tested it in a wall-less tissue-mimicking flow phantom perfused with lipid-encapsulated microbubbles (MBs). The effects of the phase lag, low-frequency pressure, and MB concentration on the envelope subtracted radial modulation signals were investigated as a function of depth. Our dual-pulse dual-frequency approach produced contrast- specific images with contrast-to-tissue improvements over B-mode of 15.1 ± 2.1 dB at 2 mm and 6.8 ± 0.1 dB at 4 mm depths. Using this imaging strategy, 200-μm-diameter cellulose tubing perfused with MBs could be resolved while surrounding tissue scattering was suppressed. These results raise promise for the detection of coronary vasa vasorum and may ultimately facilitate the detection of plaque at risk for rupture.

Hybrid FMT-MRI applied to in vivo atherosclerosis imaging

Combining Fluorescent Molecular Tomography (FMT) with anatomical imaging, e.g. MRI facilitates interpreting functional information. Furthermore, using a heterogeneous model for light propagation has been shown in simulations to be superior to homogeneous modeling to quantify fluorescence. Here, we present a combined FMT-MRI system and apply it to heart and aorta molecular imaging, a challenging area due to strong tissue heterogeneity and the presence of air-voids due to lungs. First investigating performance in a phantom and mouse corpse, the MRI-enabled heterogeneous models resulted in an improved quantification of fluorescence reconstructions. The system was then used in mice for in vivo atherosclerosis molecular imaging. Results show that, when using the heterogeneous model, reconstructions were in agreement with the ex vivo measurements. Therefore, the proposed system might serve as a powerful imaging tool for atherosclerosis in mice.

Atherosclerotic plaque component segmentation in combined carotid MRI and CTA data incorporating class label uncertainty

Atherosclerotic plaque composition can indicate plaque vulnerability. We segment atherosclerotic plaque components from the carotid artery on a combination of in vivo MRI and CT-angiography (CTA) data using supervised voxelwise classification. In contrast to previous studies the ground truth for training is directly obtained from 3D registration with histology for fibrous and lipid-rich necrotic tissue, and with μCT for calcification. This registration does, however, not provide accurate voxelwise correspondence. We therefore evaluate three approaches that incorporate uncertainty in the ground truth used for training: I) soft labels are created by Gaussian blurring of the original binary histology segmentations to reduce weights at the boundaries between components, and are weighted by the estimated registration accuracy of the histology and in vivo imaging data (measured by overlap), II) samples are weighted by the local contour distance of the lumen and outer wall between histology and in vivo data, and III) 10% of each class is rejected by Gaussian outlier rejection. Classification was evaluated on the relative volumes (% of tissue type in the vessel wall) for calcified, fibrous and lipid-rich necrotic tissue, using linear discriminant (LDC) and support vector machine (SVM) classification. In addition, the combination of MRI and CTA data was compared to using only one imaging modality. Best results were obtained by LDC and outlier rejection: the volume error per vessel was 0.9±1.0% for calcification, 12.7±7.6% for fibrous and 12.1±8.1% for necrotic tissue, with Spearman rank correlation coefficients of 0.91 (calcification), 0.80 (fibrous) and 0.81 (necrotic). While segmentation using only MRI features yielded low accuracy for calcification, and segmentation using only CTA features yielded low accuracy for necrotic tissue, the combination of features from MRI and CTA gave good results for all studied components.

Visualizing the atherosclerotic plaque: a chemical perspective

Atherosclerosis is the major underlying pathologic cause of coronary artery disease. An early detection of the disease can prevent clinical sequellae such as angina, myocardial infarction, and stroke. The different imaging techniques employed to visualize the atherosclerotic plaque provide information of diagnostic and prognostic value. Furthermore, the use of contrast agents helps to improve signal-to-noise ratio providing better images. For nuclear imaging techniques and optical imaging these agents are absolutely necessary. We report on the different contrast agents that have been used, are used or may be used in future in animals, humans, or excised tissues for the distinct imaging modalities for atherosclerotic plaque imaging.

Macrophage-targeted delivery systems for nucleic acid therapy of inflammatory diseases

Inflammation is an immune response that marks several pathophysiological conditions in our body. Though adaptive immune cells play a major role in the progression of the disease, components of innate immune system, mainly monocytes and macrophages play the central role in onset of inflammation. Tissue-associated macrophages are widely distributed in the body showing tremendous anatomical and functional diversity and are actively involved in maintaining the homeostasis. They exhibit different phenotypes depending on their residing tissue microenvironment and the two major functional phenotypes are classically activated M1 phenotype showing pro-inflammatory characteristics and alternatively activated M2 phenotype demonstrating anti-inflammatory nature. Several cytokines, chemokines and other regulatory mediators delicately govern the balance of the two phenotypes in a tissue. This balance, however, is subverted during infection, injury or autoimmune response leading to increased population of M1 phenotype and subsequent chronic inflammatory disease states. This review underlines the role of macrophages in inflammatory diseases with an insight into potential molecular targets for nucleic acid therapy. Finally, some recent nanotechnology-based approaches to devise macrophage-specific targeted therapy have been highlighted.

Nature-inspired nanoformulations for contrast-enhanced in vivo MR imaging of macrophages

Magnetic resonance imaging (MRI) of macrophages in atherosclerosis requires the use of contrast-enhancing agents. Reconstituted lipoprotein particles that mimic native high-density lipoproteins (HDL) are a versatile delivery platform for Gd-based contrast agents (GBCA) but require targeting moieties to direct the particles to macrophages. In this study, a naturally occurring methionine oxidation in the major HDL protein, apolipoprotein (apo) A-I, was exploited as a novel way to target HDL to macrophages. We also tested if fully functional GBCA-HDL can be generated using synthetic apo A-I peptides. The fluorescence and MRI studies reveal that specific oxidation of apo A-I or its peptides increases the in vitro macrophage uptake of GBCA-HDL by 2-3 times. The in vivo imaging studies using an apo E-deficient mouse model of atherosclerosis and a 3.0 T MRI system demonstrate that this modification significantly improves atherosclerotic plaque detection using GBCA-HDL. At 24 h post-injection of 0.05 mmol Gd kg(-1) GBCA-HDL containing oxidized apo A-I or its peptides, the atherosclerotic wall/muscle normalized enhancement ratios were 90 and 120%, respectively, while those of GBCA-HDL containing their unmodified counterparts were 35 and 45%, respectively. Confocal fluorescence microscopy confirms the accumulation of GBCA-HDL containing oxidized apo A-I or its peptides in intraplaque macrophages. Together, the results of this study confirm the hypothesis that specific oxidation of apo A-I targets GBCA-HDL to macrophages in vitro and in vivo. Furthermore, our observation that synthetic peptides can functionally replace the native apo A-I protein in HDL further encourages the development of these contrast agents for macrophage imaging.

Spatio-temporal texture (SpTeT) for distinguishing vulnerable from stable atherosclerotic plaque on dynamic contrast enhancement (DCE) MRI in a rabbit model

PURPOSE

To develop a new spatio-temporal texture (SpTeT) based method for distinguishing vulnerable versus stable atherosclerotic plaques on DCE-MRI using a rabbit model of atherothrombosis.

METHODS

Aortic atherosclerosis was induced in 20 New Zealand White rabbits by cholesterol diet and endothelial denudation. MRI was performed before (pretrigger) and after (posttrigger) inducing plaque disruption with Russell's-viper-venom and histamine. Of the 30 vascular targets (segments) under histology analysis, 16 contained thrombus (vulnerable) and 14 did not (stable). A total of 352 voxel-wise computerized SpTeT features, including 192 Gabor, 36 Kirsch, 12 Sobel, 52 Haralick, and 60 first-order textural features, were extracted on DCE-MRI to capture subtle texture changes in the plaques over the course of contrast uptake. Different combinations of SpTeT feature sets, in which the features were ranked by a minimum-redundancy-maximum-relevance feature selection technique, were evaluated via a random forest classifier. A 500 iterative 2-fold cross validation was performed for discriminating the vulnerable atherosclerotic plaque and stable atherosclerotic plaque on per voxel basis. Four quantitative metrics were utilized to measure the classification results in separating between vulnerable and stable plaques.

RESULTS

The quantitative results show that the combination of five classes of SpTeT features can distinguish between vulnerable (disrupted plaques with an overlying thrombus) and stable plaques with the best AUC values of 0.9631 ± 0.0088, accuracy of 89.98% ± 0.57%, sensitivity of 83.71% ± 1.71%, and specificity of 94.55% ± 0.48%.

CONCLUSIONS

Vulnerable and stable plaque can be distinguished by SpTeT based features. The SpTeT features, following validation on larger datasets, could be established as effective and reliable imaging biomarkers for noninvasively assessing atherosclerotic risk.

Noninvasive assessment of hypoxia in rabbit advanced atherosclerosis using ¹⁸F-fluoromisonidazole positron emission tomographic imaging

BACKGROUND

Hypoxia is an important microenvironmental factor influencing atherosclerosis progression by inducing foam-cell formation, metabolic adaptation of infiltrated macrophages, and plaque neovascularization. Therefore, imaging plaque hypoxia could serve as a marker of lesions at risk.

METHODS AND RESULTS

Advanced aortic atherosclerosis was induced in 18 rabbits by atherogenic diet and double balloon endothelial denudation. Animals underwent (18)F-fluoromisonidazole positron emission tomographic and (18)F-fluorodeoxyglucose positron emission tomographic imaging after 6 to 8 months (atherosclerosis induction) and 12 to 16 months (progression) of diet initiation. Four rabbits fed standard chow served as controls. Radiotracer uptake of the abdominal aorta was measured using standardized uptake values. After imaging, plaque hypoxia (pimonidazole), macrophages (RAM-11), neovessels (CD31), and hypoxia-inducible factor-1α were assessed by immunohistochemistry.(18)F-fluoromisonidazole uptake increased with time on diet (standardized uptake value mean, 0.10±0.01 in nonatherosclerotic animals versus 0.20±0.03 [P=0.002] at induction and 0.25±0.03 [P<0.001] at progression). Ex vivo positron emission tomographic imaging corroborated the (18)F-fluoromisonidazole uptake by the aorta of atherosclerotic rabbits. (18)F-fluorodeoxyglucose uptake also augmented in atherosclerotic animals, with an standardized uptake value mean of 0.43±0.02 at induction versus 0.35±0.02 in nonatherosclerotic animals (P=0.031) and no further increase at progression. By immunohistochemistry, hypoxia was mainly located in the macrophage-rich areas within the atheromatous core, whereas the macrophages close to the lumen were hypoxia-negative. Intraplaque neovessels were found predominantly in macrophage-rich hypoxic regions (pimonidazole(+)/hypoxia-inducible factor-1α(+)/RAM-11(+)).

CONCLUSIONS

Plaque hypoxia increases with disease progression and is present in macrophage-rich areas associated with neovascularization. (18)F-fluoromisonidazole positron emission tomographic imaging emerges as a new tool for the detection of atherosclerotic lesions.

Cardiac macrophages and their role in ischaemic heart disease

Cardiac macrophages are abundant in the healthy heart and after myocardial infarction (MI). Different macrophage phenotypes likely promote myocardial health vs. disease. Infarct macrophages are inflammatory and derive from circulating monocytes produced by the haematopoietic system. These cells are centrally involved in inflammatory tissue remodelling, resolution of inflammation during post-MI healing, and left ventricular remodelling. Presumably, macrophages interact with myocytes, endothelial cells, and fibroblasts. Although macrophages are primarily recruited to the ischaemic myocardium, the remote non-ischaemic myocardium macrophage population changes dynamically after MI. Macrophages' known roles in defending the steady state and their pathological actions in other disease contexts provide a road map for exploring cardiac macrophages and their phenotypes, functions, and therapeutic potential. In our review, we summarize recent insights into the role of cardiac macrophages, focus on their actions after ischaemia, and highlight emerging research topics.

Probing nanoparticle translocation across the permeable endothelium in experimental atherosclerosis

Therapeutic and diagnostic nanomaterials are being intensely studied for several diseases, including cancer and atherosclerosis. However, the exact mechanism by which nanomedicines accumulate at targeted sites remains a topic of investigation, especially in the context of atherosclerotic disease. Models to accurately predict transvascular permeation of nanomedicines are needed to aid in design optimization. Here we show that an endothelialized microchip with controllable permeability can be used to probe nanoparticle translocation across an endothelial cell layer. To validate our in vitro model, we studied nanoparticle translocation in an in vivo rabbit model of atherosclerosis using a variety of preclinical and clinical imaging methods. Our results reveal that the translocation of lipid-polymer hybrid nanoparticles across the atherosclerotic endothelium is dependent on microvascular permeability. These results were mimicked with our microfluidic chip, demonstrating the potential utility of the model system.

Pharmacogenomics in the development and characterization of atheroprotective drugs

Atherosclerosis is the main cause of cardiovascular disease (CVD) and can lead to stroke, myocardial infarction, and death. The clinically available atheroprotective drugs aim mainly at reducing the levels of circulating low-density lipoprotein (LDL), increasing high-density lipoprotein (HDL), and attenuating inflammation. However, the cardiovascular risk remains high, along with morbidity, mortality, and incidence of adverse drug events. Pharmacogenomics is increasingly contributing towards the characterization of existing atheroprotective drugs, the evaluation of novel ones, and the identification of promising, unexplored therapeutic targets, at the global molecular pathway level. This chapter presents highlights of pharmacogenomics investigations and discoveries that have contributed towards the elucidation of pharmacological atheroprotection, while opening the way to new therapeutic approaches.

Flexible integration of high-imaging-resolution and high-power arrays for ultrasound-induced thermal strain imaging (US-TSI)

Ultrasound-induced thermal strain imaging (USTSI) for carotid artery plaque detection requires both high imaging resolution (<100 μm) and sufficient US-induced heating to elevate the tissue temperature (~1°C to 3°C within 1 to 3 cardiac cycles) to produce a noticeable change in sound speed in the targeted tissues. Because the optimization of both imaging and heating in a monolithic array design is particularly expensive and inflexible, a new integrated approach is presented which utilizes independent ultrasound arrays to meet the requirements for this particular application. This work demonstrates a new approach in dual-array construction. A 3-D printed manifold was built to support both a high-resolution 20 MHz commercial imaging array and 6 custom heating elements operating in the 3.5 to 4 MHz range. For the application of US-TSI in carotid plaque characterization, the tissue target site is 20 to 30 mm deep, with a typical target volume of 2 mm (elevation) × 8 mm (azimuthal) × 5 mm (depth). The custom heating array performance was fully characterized for two design variants (flat and spherical apertures), and can easily deliver 30 W of total acoustic power to produce intensities greater than 15 W/cm(2) in the tissue target region.

MR imaging of the arterial vessel wall: molecular imaging from bench to bedside

Cardiovascular diseases remain the leading cause of morbidity and mortality in the Western world and developing countries. In clinical practice, in vivo characterization of atherosclerotic lesions causing myocardial infarction, ischemic stroke, and other complications remains challenging. Imaging methods, limited to the assessment luminal stenosis, are the current reference standard for the assessment of clinically significant coronary and carotid artery disease and the guidance of treatment. These techniques do not allow distinction between stable and potentially vulnerable atherosclerotic plaque. Magnetic resonance (MR) imaging is a modality well suited for visualization and characterization of the relatively thin arterial vessel wall, because it allows imaging with high spatial resolution and excellent soft-tissue contrast. In clinical practice, atherosclerotic plaque components of the carotid artery and aorta may be differentiated and characterized by using unenhanced vessel wall MR imaging. Additional information can be gained by using clinically approved nonspecific contrast agents. With the advent of targeted MR contrast agents, which enhance specific molecules or cells, pathologic processes can be visualized at a molecular level with high spatial resolution. In this article, the pathophysiologic changes of the arterial vessel wall underlying the development of atherosclerosis will be first reviewed. Then basic principles and properties of molecular MR imaging contrast agents will be introduced. Additionally, recent advances in preclinical molecular vessel wall imaging will be reviewed. Finally, the clinical feasibility of arterial vessel wall imaging at unenhanced and contrast material-enhanced MR imaging of the aortic, carotid, and coronary vessel wall will be discussed.

Contrast-enhanced imaging of SPIO-labeled platelets using magnetomotive ultrasound

The ability to image platelets in vivo can provide insight into blood clotting processes and coagulopathies, and aid in identifying sites of vascular endothelial damage related to trauma or cardiovascular disease. Toward this end, we have developed a magnetomotive ultrasound (MMUS) system that provides contrast-enhanced imaging of superparamagnetic iron oxide (SPIO) labeled platelets via magnetically-induced vibration. Platelets are a promising platform for functional imaging contrast because they readily take up SPIOs and are easily harvested from blood. Here we report a novel MMUS system that accommodates an arbitrarily thick sample while maintaining portability. We employed a frequency- and phase-locked motion detection algorithm based on bandpass filtering of the differential RF phase, which allows for the detection of sub-resolution vibration amplitudes on the order of several nanometers. We then demonstrated MMUS in homogenous tissue phantoms at SPIO concentrations as low as 0.09 mg ml(-1) Fe (p < 0.0001, n = 6, t-test). Finally, we showed that our system is capable of three-dimensional imaging of a 185 µL simulated clot containing SPIO-platelets. This highlights the potential utility for non-invasive imaging of platelet-rich clots, which would constitute a fundamental advance in technology for the study of hemostasis and detection of clinically relevant thrombi.

Progression of coronary artery atherosclerosis in rheumatoid arthritis: comparison with participants from the Multi-Ethnic Study of Atherosclerosis

INTRODUCTION

In cross-sectional studies, patients with rheumatoid arthritis (RA) have higher coronary artery calcium (CAC) than controls. However, their rate of progression of CAC and the predictors of CAC progression have heretofore remained unknown.

METHODS

Incidence and progression of CAC were compared in 155 patients with RA and 835 control participants. The association of demographic characteristics, traditional cardiovascular risk factors, RA disease characteristics and selected inflammatory markers with incidence and progression of CAC were evaluated.

RESULTS

The incidence rate of newly detected CAC was 8.2/100 person-years in RA and 7.3/100 person-years in non-RA control subjects [IRR 1.1 (0.7-1.8)]. RA patients who developed newly detectable CAC were older (59 ± 7 vs. 55 ± 6 years old, p=0.03), had higher triglyceride levels (137 ± 86 vs. 97 ± 60 mg/dL, p=0.03), and higher systolic blood pressure (129 ± 17 vs. 117 ± 15 mm Hg, p=0.01) compared to those who did not develop incident CAC. Differences in blood pressure and triglyceride levels remained significant after adjustment for age (p<=0.05). RA patients with any CAC at baseline had a median rate of yearly progression of 21 (7-62) compared to 21 (5-70) Agatston units in controls. No statistical differences between RA progressors and RA non-progressors were observed for inflammatory markers or for RA disease characteristics.

CONCLUSIONS

The incidence and progression of CAC did not differ between RA and non-RA participants. In patients with RA, incident CAC was associated with older age, higher triglyceride levels, and higher blood pressure, but not with inflammatory markers or RA disease characteristics.

Noninvasive detection of lipids in atherosclerotic plaque using ultrasound thermal strain imaging: in vivo animal study

OBJECTIVES

This study sought to examine the feasibility of in vivo detection of lipids in atherosclerotic plaque (AP) by ultrasound (US) thermal (or temporal) strain imaging (TSI).

BACKGROUND

Intraplaque lipid content is thought to contribute to plaque stability. Lipid exhibits a distinctive physical characteristic of temperature-dependent US speed compared with water-bearing tissues. As tissue temperature changes, US radiofrequency (RF) echoes shift in time of flight, which produces an apparent strain (thermal or temporal strain [TS]).

METHODS

US heating-imaging pulse sequences and transducers were designed and integrated into commercial US scanners for US-TSI of arterial segments. US-RF data were collected while gradually increasing tissue temperature. Phase-sensitive speckle tracking was applied to reconstruct TS maps coregistered to B-scans. Segments from injured atherosclerotic and uninjured nonatherosclerotic common femoral arteries (CFA) in cholesterol-fed New Zealand rabbits, and segments from control normal diet-fed rabbits (N =14) were scanned in vivo at different time points up to 12 weeks.

RESULTS

Lipid-rich atherosclerotic lesions exhibited distinct positive TS (+0.19 ± 0.08%) compared with that in nonatherosclerotic (-0.10 ± 0.13%) and control (-0.09 ± 0.09%) segments (p < 0.001). US-TSI enabled serial monitoring of lipids during atherosclerosis development. The coregistered set of morphological and compositional information of US-TSI showed good agreement with histology.

CONCLUSIONS

US-TSI successfully detected and longitudinally monitored lipid progression in atherosclerotic CFA. US-TSI of relatively superficial arteries may be a modality that could be integrated into a commercial US system for noninvasive lipid detection in AP.

Spectroscopic Imaging of Deep Tissue through Photoacoustic Detection of Molecular Vibration

The quantized vibration of chemical bonds provides a way of imaging target molecules in a complex tissue environment. Photoacoustic detection of harmonic vibrational transitions provides an approach to visualize tissue content beyond the ballistic photon regime. This method involves pulsed laser excitation of overtone transitions in target molecules inside a tissue. Fast relaxation of the vibrational energy into heat results in a local temperature rise on the order of mK and a subsequent generation of acoustic waves detectable with an ultrasonic transducer. In this perspective, we review recent advances that demonstrate the advantages of vibration-based photoacoustic imaging and illustrate its potential in diagnosing cardiovascular plaques. An outlook into future development of vibrational photoacoustic endoscopy and tomography is provided.

Multimodal iron oxide nanoparticles for hybrid biomedical imaging

Iron oxide core nanoparticles are attractive imaging agents because their material properties allow the tuning of pharmacokinetics as well as the attachment of multiple moieties to their surface. In addition to affinity ligands, these include fluorochromes and radioisotopes for detection with optical and nuclear imaging. As the iron oxide core can be detected by MRI, options for combining imaging modalities are manifold. Already, preclinical imaging strategies have combined noninvasive imaging with higher resolution techniques, such as intravital microscopy, to gain unprecedented insight into steady-state biology and disease. Going forward, hybrid iron oxide nanoparticles will help to merge modalities, creating a synergy that will enable imaging in basic research and, potentially, also in the clinic.

Biological imaging of atherosclerosis: moving beyond anatomy

Biological or molecular imaging is now providing exciting new strategies to study atherosclerosis in both animals and humans. These technologies hold the promise to provide disease-specific, molecular information within the context of a systemic or organ-specific disease beyond traditional anatomical-based imaging. By integration of biological, chemical, and anatomical imaging knowledge into diagnostic strategies, a more comprehensive and predictive picture of atherosclerosis is likely to emerge. As such, biological imaging is well positioned to study different stages of atherosclerosis and its treatment, including the sequence of atheroma initiation, progression, and plaque rupture. In this review, we describe the evolving concepts in atherosclerosis imaging with a focus on coronary artery disease, and we provide an overview of recent exciting translational developments in biological imaging. The illuminated examples and discussions will highlight how biological imaging is providing new clinical approaches to identify high-risk plaques, and to streamline the development process of new atherosclerosis therapies.

Nano-sized CT contrast agents

Computed tomography (CT) is one of the most widely used clinical imaging modalities. In order to increase the sensitivity of CT, small iodinated compounds are used as injectable contrast agents. However, the iodinated contrast agents are excreted through the kidney and have short circulation times. This rapid renal clearance not only restricts in vivo applications that require long circulation times but also sometimes induces serious adverse effects related to the excretion pathway. In addition, the X-ray attenuation of iodine is not efficient for clinical CT that uses high-energy X-ray. Due to these limitations, nano-sized iodinated CT contrast agents have been developed that can increase the circulation time and decrease the adverse effects. In addition to iodine, nanoparticles based on heavy atoms such as gold, lanthanides, and tantalum are used as more efficient CT contrast agents. In this review, we summarize the recent progresses made in nano-sized CT contrast agents.

Aliskiren effect on plaque progression in established atherosclerosis using high resolution 3D MRI (ALPINE): a double-blind placebo-controlled trial

Background

The renin–angiotensin system is well recognized as a mediator of pathophysiological events in atherosclerosis. The benefits of renin inhibition in atherosclerosis, especially when used in combination with angiotensin-converting enzyme inhibitors/angiotensin receptor blockers (ACEIs/ARBs) are currently not known. We hypothesized that treatment with the renin inhibitor aliskiren in patients with established cardiovascular disease will prevent the progression of atherosclerosis as determined by high-resolution magnetic resonance imaging (MRI) measurements of arterial wall volume in the thoracic and abdominal aortas of high-risk patients with preexisting cardiovascular disease.

Methods and Results

This was a single-center, randomized, double-blind, placebo-controlled trial in patients with established cardiovascular disease. After a 2-week single-blind placebo phase, patients were randomized to receive either placebo (n=37, mean±SD age 64.5±8.9 years, 3 women) or 150 mg of aliskiren (n=34, mean±SD age 63.9±11.5 years, 9 women). Treatment dose was escalated to 300 mg at 2 weeks and maintained during the remainder of the study. Patients underwent dark-blood, 3-dimensional MRI assessment of atherosclerotic plaque in the thoracic and abdominal segments at baseline and on study completion or termination (up to 36 weeks of drug or matching placebo). Aliskiren use resulted in significant progression of aortic wall volume (normalized total wall volume 5.31±6.57 vs 0.15±4.39 mm³, P=0.03, and percentage wall volume 3.37±2.96% vs 0.97±2.02%, P=0.04) compared with placebo. In a subgroup analysis of subjects receiving ACEI/ARB therapy, atherosclerosis progression was observed only in the aliskiren group, not in the placebo group.

Conclusions

MRI quantification of atheroma plaque burden demonstrated that aliskiren use in patients with preexisting cardiovascular disease resulted in an unexpected increase in aortic atherosclerosis compared with placebo. Although preliminary, these results may have implications for the use of renin inhibition as a therapeutic strategy in patients with cardiovascular disease, especially in those receiving ACEI/ARB therapy.

Clinical Trial Registration

URL: http://ClinicalTrials.gov Unique identifier: NCT01417104.

Biodegradable synthetic high-density lipoprotein nanoparticles for atherosclerosis

Atherosclerosis remains one of the most common causes of death in the United States and throughout the world because of the lack of early detection. Macrophage apoptosis is a major contributor to the instability of atherosclerotic lesions. Development of an apoptosis targeted high-density lipoprotein (HDL)-mimicking nanoparticle (NP) to carry contrast agents for early detection of vulnerable plaques and the initiation of preventative therapies that exploit the vascular protective effects of HDL can be attractive for atherosclerosis. Here, we report the construction of a synthetic, biodegradable HDL-NP platform for detection of vulnerable plaques by targeting the collapse of mitochondrial membrane potential that occurs during apoptosis. This HDL mimic contains a core of biodegradable poly(lactic-co-glycolic acid), cholesteryl oleate, and a phospholipid bilayer coat that is decorated with triphenylphosphonium (TPP) cations for detection of mitochondrial membrane potential collapse. The lipid layer provides the surface for adsorption of apolipoprotein (apo) A-I mimetic 4F peptide, and the core contains diagnostically active quantum dots (QDs) for optical imaging. In vitro uptake, detection of apoptosis, and cholesterol binding studies indicated promising detection ability and therapeutic potential of TPP-HDL-apoA-I-QD NPs. In vitro studies indicated the potential of these NPs in reverse cholesterol transport. In vivo biodistribution and pharmacokinetics indicated favorable tissue distribution, controlled pharmacokinetic parameters, and significant triglyceride reduction for i.v.-injected TPP-HDL-apoA-I-QD NPs in rats. These HDL NPs demonstrate excellent biocompatibility, stability, nontoxic, and nonimmunogenic properties, which prove to be promising for future translation in early plaque diagnosis and might find applications to prevent vulnerable plaque progression.

Hypercortisolism is associated with increased coronary arterial atherosclerosis: analysis of noninvasive coronary angiography using multidetector computerized tomography

BACKGROUND

Observational studies show that glucocorticoid therapy and the endogenous hypercortisolism of Cushing's syndrome (CS) are associated with increased rates of cardiovascular morbidity and mortality. However, the causes of these findings remain largely unknown.

OBJECTIVE

To determine whether CS patients have increased coronary atherosclerosis.

DESIGN

A prospective case-control study was performed.

SETTING

Subjects were evaulated in a clinical research center.

SUBJECTS

Fifteen consecutive patients with ACTH-dependent CS, 14 due to an ectopic source and 1 due to pituitary Cushing's disease were recruited. Eleven patients were studied when hypercortisolemic; 4 patients were eucortisolemic due to medication (3) or cyclic hypercortisolism (1). Fifteen control subjects with at least one risk factor for cardiac disease were matched 1:1 for age, sex, and body mass index.

PRIMARY OUTCOME VARIABLES

Agatston score a measure of calcified plaque and non-calcified coronary plaque volume were quantified using a multidetector CT (MDCT) coronary angiogram scan. Additional variables included fasting lipids, blood pressure, history of hypertension or diabetes, and 24-hour urine free cortisol excretion.

RESULTS

CS patients had significantly greater noncalcified plaque volume and Agatston score (noncalcified plaque volume [mm(3)] median [interquartile ranges]: CS 49.5 [31.4, 102.5], controls 17.9 [2.6, 25.3], P < .001; Agatston score: CS 70.6 [0, 253.1], controls 0 [0, 7.6]; P < .05). CS patients had higher systolic and diastolic blood pressures than controls (systolic: CS 143 mm Hg [135, 173]; controls, 134 [123, 136], P < .02; diastolic CS: 86 [80, 99], controls, 76 [72, 84], P < .05).

CONCLUSIONS

Increased coronary calcifications and noncalcified coronary plaque volumes are present in patients with active or previous hypercortisolism. Increased atherosclerosis may contribute to the increased rates of cardiovascular morbidity and mortality in patients with glucocorticoid excess.

Monocyte-directed RNAi targeting CCR2 improves infarct healing in atherosclerosis-prone mice

BACKGROUND

Exaggerated and prolonged inflammation after myocardial infarction (MI) accelerates left ventricular remodeling. Inflammatory pathways may present a therapeutic target to prevent post-MI heart failure. However, the appropriate magnitude and timing of interventions are largely unknown, in part because noninvasive monitoring tools are lacking. Here, we used nanoparticle-facilitated silencing of CCR2, the chemokine receptor that governs inflammatory Ly-6C(high) monocyte subset traffic, to reduce infarct inflammation in apolipoprotein E-deficient (apoE(-/-)) mice after MI. We used dual-target positron emission tomography/magnetic resonance imaging of transglutaminase factor XIII (FXIII) and myeloperoxidase (MPO) activity to monitor how monocyte subset-targeted RNAi altered infarct inflammation and healing.

METHODS AND RESULTS

Flow cytometry, gene expression analysis, and histology revealed reduced monocyte numbers and enhanced resolution of inflammation in infarcted hearts of apoE(-/-) mice that were treated with nanoparticle-encapsulated siRNA. To follow extracellular matrix cross-linking noninvasively, we developed a fluorine-18-labeled positron emission tomography agent ((18)F-FXIII). Recruitment of MPO-rich inflammatory leukocytes was imaged with a molecular magnetic resonance imaging sensor of MPO activity (MPO-Gd). Positron emission tomography/magnetic resonance imaging detected anti-inflammatory effects of intravenous nanoparticle-facilitated siRNA therapy (75% decrease of MPO-Gd signal; P<0.05), whereas (18)F-FXIII positron emission tomography reflected unimpeded matrix cross-linking in the infarct. Silencing of CCR2 during the first week after MI improved ejection fraction on day 21 after MI from 29% to 35% (P<0.05).

CONCLUSION

CCR2-targeted RNAi reduced recruitment of Ly-6C(high) monocytes, attenuated infarct inflammation, and curbed post-MI left ventricular remodeling.

CD44 targeting magnetic glyconanoparticles for atherosclerotic plaque imaging

PURPOSE

The cell surface adhesion molecule CD44 plays important roles in the initiation and development of atherosclerotic plaques. We aim to develop nanoparticles that can selectively target CD44 for the non-invasive detection of atherosclerotic plaques by magnetic resonance imaging.

METHODS

Magnetic glyconanoparticles with hyaluronan immobilized on the surface have been prepared. The binding of these nanoparticles with CD44 was evaluated in vitro by enzyme linked immunosorbent assay, flow cytometry and confocal microscopy. In vivo magnetic resonance imaging of plaques was performed on an atherosclerotic rabbit model.

RESULTS

The magnetic glyconanoparticles can selectively bind CD44. In T2* weighted magnetic resonance images acquired in vivo, significant contrast changes in aorta walls were observed with a very low dose of the magnetic nanoparticles, allowing the detection of atherosclerotic plaques. Furthermore, imaging could be performed without significant delay after probe administration. The selectivity of hyaluronan nanoparticles in plaque imaging was established by several control experiments.

CONCLUSIONS

Magnetic nanoparticles bearing surface hyaluronan enabled the imaging of atherosclerotic plaques in vivo by magnetic resonance imaging. The low dose of nanoparticles required, the possibility to image without much delay and the high biocompatibility are the advantages of these nanoparticles as contrast agents for plaque imaging.

Contrast enhancement by lipid-based MRI contrast agents in mouse atherosclerotic plaques; a longitudinal study

The use of contrast-enhanced MRI to enable in vivo specific characterization of atherosclerotic plaques is increasing. In this study the intrinsic ability of two differently sized gadolinium-based contrast agents to enhance atherosclerotic plaques in ApoE(-/-) mice was evaluated with MRI. We obtained a kinetic profile for contrast enhancement, as the literature data on optimal imaging time points is scarce, and assessed the longer-term kinetics. Signal enhancement in the wall of the aortic arch, following intravenous injection of paramagnetic micelles and liposomes, was followed for 1 week. In vivo T(1)-weighted MRI plaque enhancement characteristics were complemented by fluorescence microscopy of NIR(664) incorporated in the contrast agents and quantification of tissue and blood Gd-DTPA. Both micelles and liposomes enhanced contrast in T(1)-weighted MR images of plaques in the aortic arch. The average contrast-to-noise ratio increased after liposome or micelle injection to 260 or 280% respectively, at 24 h after injection, compared with a pre-scan. A second wave of maximum contrast enhancement was observed around 60-72 h after injection, which only slowly decreased towards the 1 week end-point. Confocal fluorescence microscopy and whole body fluorescence imaging confirmed MRI-findings of accumulation of micelles and liposomes. Plaque permeation of contrast agents was not strongly dependent on the contrast agent size in this mouse model. Our results show that intraplaque accumulation over time of both contrast agents leads to good plaque visualization for a long period. This inherent intraplaque accumulation might make it difficult to discriminate passive from targeted accumulation. This implies that, in the development of targeted contrast agents on a lipid-based backbone, extensive timing studies are required.

Collagen-specific peptide conjugated HDL nanoparticles as MRI contrast agent to evaluate compositional changes in atherosclerotic plaque regression

OBJECTIVES

This study sought to develop magnetic resonance contrast agents based on high-density lipoprotein (HDL) nanoparticles to noninvasively visualize intraplaque macrophages and collagen content in mouse atherosclerotic plaques.

BACKGROUND

Macrophages and collagen are important intraplaque components that play central roles in plaque progression and/or regression. In a Reversa mouse model, plaque regression with compositional changes (from high macrophage, low collagen to low macrophage, high collagen) can be induced.

METHODS

This study labeled HDL nanoparticles with amphiphilic gadolinium chelates to enable target-specific imaging of intraplaque macrophages. To render HDL nanoparticles specific for the extracellular matrix, labeled HDL nanoparticles were functionalized with collagen-specific EP3533 peptides (EP3533-HDL) via poly(ethylene glycol) spacers embedded in the HDL lipid layers. The association of nanoparticles with collagen was examined in vitro by optical methods. The in vivo magnetic resonance efficacy of these nanoparticles was evaluated in a Reversa mouse model of atherosclerosis regression. Ex vivo confocal microscopy was applied to corroborate the in vivo findings and to evaluate the fate of the different HDL nanoparticles.

RESULTS

All nanoparticles had similar sizes (10 ± 2 nm) and longitudinal relaxivity r1 (9 ± 1 s(-1) mmol/l(-1)). EP3533-HDL showed strong association with collagen in vitro. After 28 days of plaque regression in Reversa mice, EP3533-HDL showed significantly increased (p < 0.05) in vivo magnetic resonance signal in aortic vessel walls (normalized enhancement ratio [NERw] = 85 ± 25%; change of contrast-to-noise ratio [ΔCNRw] = 17 ± 5) compared with HDL (NERw = -7 ± 23%; ΔCNRw = -2 ± 4) and nonspecific control EP3612-HDL (NERw = 4 ± 24%; ΔCNRw = 1 ± 6) at 24 h after injection. Ex vivo confocal images revealed the colocalization of EP3533-HDL with collagen. Immunohistostaining analysis confirmed the changes of collagen and macrophage contents in the aortic vessel walls after regression.

CONCLUSIONS

This study shows that the HDL nanoparticle platform can be modified to monitor in vivo plaque compositional changes in a regression environment, which will facilitate understanding plaque regression and the search for therapeutic interventions.

Molecular imaging to identify the vulnerable plaque--from basic research to clinical practice

Cardiovascular disease (CVD) is still the leading cause of death in the Western World. Adverse outcomes of CVD include stroke, myocardial infarction, and heart failure. Atherosclerosis is considered to be the major cause of CVD and is estimated to cause half of all deaths in developed countries. Atherosclerotic lesions of the vessel wall may obstruct blood flow mechanically through stenosis, but rupture of atherosclerotic plaques causing formation of occlusive thrombi is far more prevalent. Unfortunately, conventional diagnostic tools fail to assess whether a plaque is vulnerable to rupture. Research over the past decade identified the biological processes that are implicated in the course towards plaque rupture, like cell death and inflammation. Knowledge about plaque biology propelled the development of imaging techniques that target biologic processes in order to predict the vulnerable plaque. This paper discusses novel and existing molecular imaging targets and addresses advantages and disadvantages of these targets and respective imaging techniques in respect of clinical application and socio-economic impact.

Challenges and opportunities in cardiovascular health informatics

Cardiovascular health informatics is a rapidly evolving interdisciplinary field concerning the processing, integration/interpretation, storage, transmission, acquisition, and retrieval of information from cardiovascular systems for the early detection, early prediction, early prevention, early diagnosis, and early treatment of cardiovascular diseases (CVDs). Based on the first author's presentation at the first IEEE Life Sciences Grand Challenges Conference, held on October 4-5, 2012, at the National Academy of Sciences, Washington, DC, USA, this paper, focusing on coronary arteriosclerotic disease, will discuss three significant challenges of cardiovascular health informatics, including: 1) to invent unobtrusive and wearable multiparameter sensors with higher sensitivity for the real-time monitoring of physiological states; 2) to develop fast multimodal imaging technologies with higher resolution for the quantification and better understanding of structure, function, metabolism of cardiovascular systems at the different levels; and 3) to develop novel multiscale information fusion models and strategies with higher accuracy for the personalized predication of the CVDs. At the end of this paper, a summary is given to suggest open discussions on these three and more challenges that face the scientific community in this field in the future.

Integrated intravascular optical coherence tomography (OCT) - ultrasound (US) catheter for characterization of atherosclerotic plaques in vivo

A miniature integrated intravascular optical coherence tomography (OCT) - ultrasound (US) catheter for real-time imaging of atherosclerotic plaques has been developed, providing high resolution and deep tissue penetration at the same time. This catheter, with an outer diameter of 1.18mm, is suitable for imaging in human coronary arteries. The first in vivo 3D imaging of atherosclerotic microstructure in a rabbit abdominal aorta obtained by an integrated OCT-US catheter is presented. In addition, in vitro imaging of cadaver coronary arteries were conducted to demonstrate the imaging capabilities of this integrated catheter to classify different atherosclerotic plaque types.

Carotid plaque characteristics and disease activity in rheumatoid arthritis

OBJECTIVE

Carotid plaques (CP) are predictive of acute coronary syndrome in patients with rheumatoid arthritis (RA), suggesting that atherosclerotic plaques in these patients are vulnerable. The objective of our study was to characterize vulnerability of CP in patients with RA compared to a control population, and between RA patients with different levels of disease activity.

METHODS

Ultrasound examination of carotid arteries was performed in 152 patients with RA and 89 controls. CP echolucency was evaluated by the Gray-Scale Median (GSM) technique. Lower GSM values indicate higher vulnerability of plaques. CP characteristics were compared between RA patients with active disease and in remission, and between patients and controls. All analyses were performed with adjustment for confounding factors (sex, age, smoking, and blood pressure). Poisson regression analysis was used for count data, mixed modeling for GSM and area per plaque, and analysis of covariance for minimum GSM value per patient.

RESULTS

Patients with RA more frequently had CP (median 2, range 0, 4) compared with controls (median 1, range 0, 3; p < 0.001), after adjustment for age and sex. Patients with active RA disease according to the Clinical Disease Activity Index (CDAI) had lower median GSM (p = 0.03), minimum GSM (p = 0.03), and a larger CP area (although the latter finding was not significant; p = 0.27), compared with patients with RA in remission. These findings were not confirmed for other disease measures (Simplified Disease Activity Index, Disease Activity Score-28, C-reactive protein, erythrocyte sedimentation rate).

CONCLUSION

Patients with RA had more CP compared with controls and patients in CDAI remission, and controls had more stable CP than patients with active disease; these findings point to the importance of achieving remission in RA.

Association of the CCR5Δ32 polymorphism and its ligand RANTES-403G/A polymorphism with coronary artery disease: a meta-analysis

INTRODUCTION

To explore the relationship between polymorphisms in the RANTES and CCR5 genes and the risk of coronary artery disease (CAD).

MATERIALS AND METHODS

We conducted a meta-analysis on two genetic variants (RANTES-403G/A and CCR5Δ32). Publication bias was tested by the Egger's regression test and Begg's test. Sensitivity analysis and subgroup analyses were performed to explore the heterogeneity among studies.

RESULTS

No significant association of RANTES-403G/A polymorphism and CAD risk was observed (dominant model: RR=1.02, 95%CI=0.90-1.06; recessive model: RR=1.27, 95%CI=0.90-1.80). However, after excluding the study conducted by Yangsoo et al., the pooled relative ratio (RR) in the dominant model suggested that the RANTES-403G/A polymorphism was positively associated with CAD risk. The subgroup analyses found that a positive relationship between the polymorphism and CAD risk was restricted to the Caucasian population. A meta-analysis of studies on the CCR5Δ32 polymorphism showed no significant association with CAD risk both in dominant (RR=1.05, 95%CI=0.92-1.21) and recessive (RR=1.27, 95%CI=0.90-1.80) models. Moreover, no association was identified in the subgroup analyses.

CONCLUSIONS

The RANTES-403G/A polymorphism is not associated with CAD risk, but does most likely increase CAD risk in Caucasians. Moreover, no relationship between the CCR5∆32 polymorphism and risk of CAD was found.

Polymeric nanoparticle PET/MR imaging allows macrophage detection in atherosclerotic plaques

RATIONALE

Myeloid cell content in atherosclerotic plaques associates with rupture and thrombosis. Thus, imaging of lesional monocytes and macrophages could serve as a biomarker of disease progression and therapeutic intervention.

OBJECTIVE

To noninvasively assess plaque inflammation with dextran nanoparticle (DNP)-facilitated hybrid positron emission tomography/magnetic resonance imaging (PET/MRI).

METHODS AND RESULTS

Using clinically approved building blocks, we systematically developed 13-nm polymeric nanoparticles consisting of cross-linked short chain dextrans, which were modified with desferoxamine for zirconium-89 radiolabeling ((89)Zr-DNP) and a near-infrared fluorochrome (VT680) for microscopic and cellular validation. Flow cytometry of cells isolated from excised aortas showed DNP uptake predominantly in monocytes and macrophages (76.7%) and lower signal originating from other leukocytes, such as neutrophils and lymphocytes (11.8% and 0.7%, P<0.05 versus monocytes and macrophages). DNP colocalized with the myeloid cell marker CD11b on immunohistochemistry. PET/MRI revealed high uptake of (89)Zr-DNP in the aortic root of apolipoprotein E knock out (ApoE(-/-)) mice (standard uptake value, ApoE(-/-) mice versus wild-type controls, 1.9±0.28 versus 1.3±0.03; P<0.05), corroborated by ex vivo scintillation counting and autoradiography. Therapeutic silencing of the monocyte-recruiting receptor C-C chemokine receptor type 2 with short-interfering RNA decreased (89)Zr-DNP plaque signal (P<0.05) and inflammatory gene expression (P<0.05).

CONCLUSIONS

Hybrid PET/MRI with a 13-nm DNP enables noninvasive assessment of inflammation in experimental atherosclerotic plaques and reports on therapeutic efficacy of anti-inflammatory therapy.

Nanocrystal Core Lipoprotein Biomimetics for Imaging of Lipoproteins and Associated Diseases

Lipoproteins are natural nanoparticles composed of phospholipids and apolipoproteins that transport lipids throughout the body. As key effectors of lipid homeostasis, the functions of lipoproteins have been demonstrated to be crucial during the development of cardiovascular diseases. Therefore various strategies have been used to study their biology and detect them in vivo. A recent approach has been the production of lipoprotein biomimetic particles loaded with diagnostically active nanocrystals in their core. These include, but are not limited to: quantum dots, iron oxide or gold nanocrystals. Inclusion of these nanocrystals enables the utilization of lipoproteins as probes for a variety of imaging modalities (computed tomography, magnetic resonance imaging, fluorescence) while preserving their biological activity. Furthermore as some lipoproteins naturally accumulate in atherosclerotic plaque or specific tumor tissues, nanocrystal core lipoprotein biomimetics have been developed as contrast agents for early diagnosis of these diseases.

Painting blood vessels and atherosclerotic plaques with an adhesive drug depot

The treatment of diseased vasculature remains challenging, in part because of the difficulty in implanting drug-eluting devices without subjecting vessels to damaging mechanical forces. Implanting materials using adhesive forces could overcome this challenge, but materials have previously not been shown to durably adhere to intact endothelium under blood flow. Marine mussels secrete strong underwater adhesives that have been mimicked in synthetic systems. Here we develop a drug-eluting bioadhesive gel that can be locally and durably glued onto the inside surface of blood vessels. In a mouse model of atherosclerosis, inflamed plaques treated with steroid-eluting adhesive gels had reduced macrophage content and developed protective fibrous caps covering the plaque core. Treatment also lowered plasma cytokine levels and biomarkers of inflammation in the plaque. The drug-eluting devices developed here provide a general strategy for implanting therapeutics in the vasculature using adhesive forces and could potentially be used to stabilize rupture-prone plaques.

HMGB1 is associated with atherosclerotic plaque composition and burden in patients with stable coronary artery disease

OBJECTIVES

The role of inflammation in atherosclerosis is widely appreciated. High mobility group box 1 (HMGB1), an injury-associated molecular pattern molecule acting as a mediator of inflammation, has recently been implicated in the development of atherosclerosis. In this study, we sought to investigate the association of plasma HMGB1 with coronary plaque composition in patients with suspected or known coronary artery disease (CAD).

DESIGN

HMGB1, high sensitive troponin T (hsTnT) and high sensitive C-reactive protein (hsCRP) were determined in 152 consecutive patients with suspected or known stable CAD who underwent clinically indicated 256-slice coronary computed tomography angiography (CCTA). Using CCTA, we assessed 1) coronary calcification, 2) non-calcified plaque burden and 3) the presence of vascular remodeling in areas of non-calcified plaques.

RESULTS

Using univariate analysis, hsCRP, hsTnT and HMGB1 as well as age, and atherogenic risk factors were associated with non-calcified plaque burden (r = 0.21, p = 0.009; r = 0.48, p<0.001 and r = 0.34, p<0.001, respectively). By multivariate analysis, hsTnT and HMGB1 remained independent predictors of the non-calcified plaque burden (r = 0.48, p<0.01 and r = 0.34, p<0.001, respectively), whereas a non-significant trend was noticed for hs-CRP (r = 0.21, p = 0.07). By combining hsTnT and HMGB1, a high positive predictive value for the presence of non-calcified and remodeled plaque (96% and 77%, respectively) was noted in patients within the upper tertiles for both biomarkers, which surpassed the positive predictive value of each marker separately.

CONCLUSIONS

In addition to hs-TnT, a well-established cardiovascular risk marker, HMGB1 is independently associated with non-calcified plaque burden in patients with stable CAD, while the predictive value of hs-CRP is lower. Complementary value was observed for hs-TnT and HMGB1 for the prediction of complex coronary plaque.

Interleukin-10: an anti-inflammatory marker to target atherosclerotic lesions via PEGylated liposomes

Atherosclerosis (AS) causes cardiovascular disease, which leads to fatal clinical end points like myocardial infarction or stroke, the most prevalent causes of death in developed countries. An early, noninvasive method of detection and diagnosis of atherosclerotic lesions is necessary to prevent and treat these clinical end points. Working toward this goal, we examined recombinant interleukin-10 (IL-10), stealth liposomes with nanocargo potency for NMRI relevant contrast agents, and IL-10 coupled to stealth liposomes in an ApoE-deficient mouse model using confocal laser-scanning microscopy (CLSM). Through ex vivo incubation and imaging with CLSM, we showed that fluorescently labeled IL-10 is internalized by AS plaques, and a low signal is detected in both the less injured aortic surfaces and the arteries of wild-type mice. In vivo experiments included intravenous injections of (i) fluorescent IL-10, (ii) IL-10 targeted carboxyfluorescin (CF-) labeled stealth liposomes, and (iii) untargeted CF-labeled stealth liposomes. Twenty-four hours after injection the arteries were dissected and imaged ex vivo. Compared to free IL-10, we observed a markedly stronger fluorescence intensity with IL-10 targeted liposomes at AS plaque regions. Moreover, untargeted CF-labeled liposomes showed only weak, unspecific binding. Neither free IL-10 nor IL-10 targeted liposomes showed significant immune reaction when injected into wild-type mice. Thus, the combined use of specific anti-inflammatory proteins, high payloads of contrast agents, and liposome particles should enable current imaging techniques to better recognize and visualize AS plaques for research and prospective therapeutic strategies.

Radioiodinated peptide probe for selective detection of oxidized low density lipoprotein in atherosclerotic plaques

INTRODUCTION

Despite the significant effort in developing radioprobes for atherosclerosis, few have low molecular weight. Oxidized LDL (OxLDL), a highly proinflammatory and proatherogenic factor that is abundant in atherosclerotic plaques, plays a pivotal role in plaque destabilization, which makes OxLDL a relevant probe target. We developed a radioiodinated short peptide, AHP7, as a low molecular weight probe for specific OxLDL imaging and evaluated its utility using myocardial infarction-prone Watanabe heritable hyperlipidemic rabbits (WHHLMI).

METHODS

[¹²⁵I]AHP7 was designed and synthesized based on the sequence of Asp-hemolysin, an OxLDL binding protein extracted from Aspergillus fumigatus. In vitro binding studies with OxLDL having varying degrees of oxidation were performed. Radioactivity accumulation in the aorta was measured 30 min post-administration in rabbits. Autoradiography and histological studies were performed using serial aorta sections. A radioiodinated scrambled peptide ([¹²⁵I]AHP scramble) was used as a negative control.

RESULTS

[¹²⁵I]AHP7 bound to OxLDL in proportion to the degree of oxidation (R=0.91, P<0.0001) and was inhibited by unlabeled AHP7 in a concentration-dependent manner. The aorta accumulation level and aorta/blood and aorta/muscle ratios of [¹²⁵I]AHP7 in WHHLMI were 2.8-, 1.3- and 1.8-fold higher, respectively, than those in control rabbits (P<0.001). Co-administration of AHP7 significantly reduced [¹²⁵I]AHP7 radioactivity in aorta sections (P<0.0001). Regional radioactivity levels in the aorta sections showed nonuniformity but similarity to the immunohistochemical OxLDL density.

CONCLUSIONS

The potential of radioiodinated AHP7 for selectively imaging OxLDL was demonstrated both in vitro and in vivo.

Inflammation modulates murine venous thrombosis resolution in vivo: assessment by multimodal fluorescence molecular imaging

OBJECTIVE

Assessment of thrombus inflammation in vivo could provide new insights into deep vein thrombosis (DVT) resolution. Here, we develop and evaluate 2 integrated fluorescence molecular-structural imaging strategies to quantify DVT-related inflammation and architecture and to assess the effect of thrombus inflammation on subsequent DVT resolution in vivo.

METHODS AND RESULTS

Murine DVT were created with topical 5% FeCl(3) application to thigh or jugular veins (n=35). On day 3, mice received macrophage and matrix metalloproteinase activity fluorescence imaging agents. On day 4, integrated assessment of DVT inflammation and architecture was performed using confocal fluorescence intravital microscopy. Day 4 analyses showed robust relationships among in vivo thrombus macrophages, matrix metalloproteinase activity, and fluorescein isothiocyanate-dextran deposition (r>0.70; P<0.01). In a serial 2-time point study, mice with DVT underwent intravital microscopy at day 4 and day 6. Analyses revealed that the intensity of thrombus inflammation at day 4 predicted the magnitude of DVT resolution at day 6 (P<0.05). In a second approach, noninvasive fluorescence molecular tomography-computed tomography was used and detected macrophages within jugular DVT (P<0.05 versus sham controls).

CONCLUSIONS

Integrated fluorescence molecular-structural imaging demonstrates that the DVT-induced inflammatory response can be readily assessed in vivo and can inform the magnitude of thrombus resolution.