Molecular Imaging Of Atherosclerotic Plaques Research Articles

Inflammation imaging to define vulnerable plaque or vulnerable patient.

The role of nuclear imaging in the characterization of high-risk atherosclerotic plaque is increasing thanks to its high sensitivity to detect radiopharmaceuticals signal in tissues. Currently, 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) is the most studied and widely used radiopharmaceutical for the molecular imaging of atherosclerotic plaques with positron emission tomography (PET). [18F]FDG PET is a valuable tool to non-invasively detect, monitor and quantify inflammatory processes occurring in atherosclerotic plaques. The aim of this review is to gather insights provided by [18F]FDG PET to better understand the role of inflammation in the definitions of the vulnerable plaque and the vulnerable patient. Alternatives radiopharmaceuticals targeting inflammation and other potential high-risk plaque related processed are also discussed.

Molecular imaging of atherosclerotic plaque with lipid nanobubbles as targeted ultrasound contrast agents

Molecularly-targeted nanobubbles (NBs) offer opportunities to improve the ability of ultrasound imaging to identify specific pathological tissue from healthy tissue. In this work, we aimed to design ligands-conjugated, nanosized, lipid ultrasound contrast agents (UCAs) and apply the agents in the ultrasound imaging of atherosclerotic plaque. Anti-VEGFR-2 ligands were conjugated to UCAs using the noncovalent biotin-avidin linker method. Several investigations were used to determine the morphology and performance of the targeted UCAs, including surface morphology, size distribution and ligands conjunction efficiency. The prepared targeted UCAs were utilized in vivo ultrasound imaging to detect rabbit abdominal aorta atherosclerotic plaque and to investigate the acoustic behavior in a rabbit kidney model. The results implied that the nanosized UCAs carrying anti-VEGFR-2 ligands would facilitate site-specific recognition of atherosclerosis and can provide unique advantages in targeted ultrasound molecular imaging.

Recent advances in molecular imaging of atherosclerotic plaques and thrombosis.

As the complications of atherosclerosis such as myocardial infarction and stroke are still one of the leading causes of mortality worldwide, the development of new diagnostic tools for the early detection of plaque instability and thrombosis is urgently needed. Advanced molecular imaging probes based on functional nanomaterials in combination with cutting edge imaging techniques are now paving the way for novel and unique approaches to monitor the inflammatory progress in atherosclerosis. This review focuses on the development of various molecular probes for the diagnosis of plaques and thrombosis in atherosclerosis, along with perspectives of their diagnostic applications in cardiovascular diseases. Specifically, we summarize the biological targets that can be used for atherosclerosis and thrombosis imaging. Then we describe the emerging molecular imaging techniques based on the utilization of engineered nanoprobes together with their challenges in clinical translation.

Nuclear Imaging: Focus on Vascular Probes

Noninvasive imaging technologies offer to identify several anatomic and molecular features of high-risk plaques. For the noninvasive molecular imaging of atherosclerotic plaques, nuclear medicine constitutes one of the best imaging modalities, thanks to its high sensitivity for the detection of probes in tissues. 18F-fluorodeoxyglucose (FDG) is currently the most widely used radiopharmaceutical for molecular imaging of atherosclerotic plaques with positron emission tomography. The intensity of FDG uptake in the vascular wall correlates closely with the degree of macrophage infiltration in atherosclerotic plaques. FDG positron emission tomographic imaging has become a powerful tool to identify and monitor noninvasively inflammatory activities in atherosclerotic plaques over time. This review examines how FDG positron emission tomographic imaging has given us deeper insight into the role of inflammation in atherosclerotic plaque progression and discusses perspectives for alternative radiopharmaceuticals to FDG that could provide a more specific and simple identification of high-risk lesions and help improve risk stratification of atherosclerotic patients. Visual Overview- An online visual overview is available for this article.

Statistical Permutation-based Artery Mapping (SPAM): a novel approach to evaluate imaging signals in the vessel wall

BackgroundCardiovascular diseases are the leading cause of death worldwide. A prominent cause of cardiovascular events is atherosclerosis, a chronic inflammation of the arterial wall that leads to the formation of so called atherosclerotic plaques. There is a strong clinical need to develop new, non-invasive vascular imaging techniques in order to identify high-risk plaques, which might escape detection using conventional methods based on the assessment of the luminal narrowing. In this context, molecular imaging strategies based on fluorescent tracers and fluorescence reflectance imaging (FRI) seem well suited to assess molecular and cellular activity. However, such an analysis demands a precise and standardized analysis method, which is orientated on reproducible anatomical landmarks, ensuring to compare equivalent regions across different subjects.MethodsWe propose a novel method, Statistical Permutation-based Artery Mapping (SPAM). Our approach is especially useful for the understanding of complex and heterogeneous regional processes during the course of atherosclerosis. Our method involves three steps, which are (I) standardisation with an additional intensity normalization, (II) permutation testing, and (III) cluster-enhancement. Although permutation testing and cluster enhancement are already well-established in functional magnetic resonance imaging, to the best of our knowledge these strategies have so far not been applied in cardiovascular molecular imaging.ResultsWe tested our method using FRI images of murine aortic vessels in order to find recurring patterns in atherosclerotic plaques across multiple subjects. We demonstrate that our pixel-wise and cluster-enhanced testing approach is feasible and useful to analyse tracer distributions in FRI data sets of aortic vessels.ConclusionsWe expect our method to be a useful tool within the field of molecular imaging of atherosclerotic plaques since cluster-enhanced permutation testing is a powerful approach for finding significant differences of tracer distributions in inflamed atherosclerotic vessels.

The relationship between the alterations of myocardial nuclear imaging parameter and myocardial dysfunction in dilated cardiomyopathy, the molecular imaging of atherosclerotic plaque, and the myocardial microciculatory dysfunction in dialysis patient evaluated using ammonia PET myocardial perfusion imaging

The relationship between the alterations of myocardial nuclear imaging parameter and myocardial dysfunction in dilated cardiomyopathy, the molecular imaging of atherosclerotic plaque, and the myocardial microciculatory dysfunction in dialysis patient evaluated using ammonia PET myocardial perfusion imaging

Near-infrared fluorescence imaging of murine atherosclerosis using an oxidized low density lipoprotein-targeted fluorochrome

The aim of this study was to explore the feasibility of detecting plaques using an NIR797 fluorochrome-labeled, anti-oxLDL antibody (anti-oxLDL-NIR797) and near-infrared fluorescence (NIRF) imaging in a murine model of atherosclerosis. Anti-mouse oxLDL polyclonal antibodies were conjugated to NIR797 dyes to synthesis oxLDL-targeted NIRF probe. In situ and ex vivo NIRF imaging of the high-cholesterol diet-induced atherosclerotic lesions of apoE-/- mice (baseline) as well as ex vivo NIRF imaging in the progression and regression group (without or with atorvastatin treatment for another 8 weeks) were performed 24 h after an intravenous injection of 1 mg/kg of anti-oxLDL-NIR797, while phosphate-buffered saline (PBS) was used for the controls. The plaque areas were investigated using Oil Red O (ORO) staining. Aortas isolated from the apoE-/- mice 24 h post-injection exhibited a selective, strong, heterogeneous NIRF signal enhancement in the aortic root, arch, and bifurcation, whereas the PBS and competitive inhibition groups had limited NIRF signal changes (p < 0.05). There was a significant correlation between ORO staining and NIRF in the atherosclerotic aortas that received anti-oxLDL-NIR797. Immunofluorescence studies confirmed the colocalization of the oxLDL/macrophages and NIR797 fluorochromes. Furthermore, the atherosclerotic lesions of atorvastatin-treated mice showed reduced anti-oxLDL-NIR797 uptake and oxLDL expression. These results indicate that NIRF plaque imaging is feasible with an oxLDL-targeted NIRF probe. Thus, oxLDL-based molecular imaging of atherosclerotic plaques is feasible and may provide important methods for characterizing vulnerable plaques and monitoring the response to therapeutic interventions for atherosclerosis.

The Complementary Roles of Imaging and ‘Omics’ for Future Anti-Atherosclerotic Drug Development

With the rising global incidence and burden of atherosclerotic disease, there is a need to identify new molecular targets that may not only serve as biomarkers of clinical risk, but also therapeutic targets. The efficiency of drug-development processes needs to improve in order to allocate finite resources towards the evaluation of the most promising compounds. Atherosclerosis imaging provides key information regarding mechanistic efficacy of novel compounds, as an intermediary endpoint, prior to the consideration of embarking upon a large-scale, multi-center randomized placebo-controlled trial. Coronary intravascular ultrasonography and B-mode sonography of carotid intima-media thickness will continue to play an important role in evaluating the efficacy of novel anti-atherosclerotic compounds. Functional, molecular imaging of atherosclerotic plaque is emerging as an exciting experimental tool, allowing for an even greater understanding of processes that drive the progression and instability of atherosclerotic disease. However, given the complexity and heterogeneity of biological systems, a global, non-targeted, systems biological approach to biomarker discovery is likely to yield the discovery of novel molecular footprints of disease. As such, metabolomic and lipidomic approaches will elucidate metabolite signatures of interest for biomarker evaluation, for clinical risk prediction, as well as safety and toxicity of experimental treatment compounds. Imaging studies will remain important for evaluating novel therapeutic strategies gleaned from omics-based discoveries, as well acting as a triage to further undertake large-scale clinical evaluation of these promising therapeutic strategies. These approaches will provide an opportunity to better understand atherosclerosis, its complications and effective treatments across multiple ethnic populations worldwide.

VCAM‐1‐targeting gold nanoshell probe for photoacoustic imaging of atherosclerotic plaque in mice

The development of molecular probes and novel imaging modalities, allowing better resolution and specificity, is associated with an increased potential for molecular imaging of atherosclerotic plaques especially in basic and pre-clinical research applications. In that context, a photoacoustic molecular probe based on gold nanoshells targeting VCAM-1 in mice (immunonanoshells) was designed. The molecular probe was validated in vitro and in vivo, showing no noticeable acute toxic effects. We performed the conjugation of gold nanoshells displaying near-infrared absorption properties with VCAM-1 antibody molecules and PEG to increase their biocompatibility. The resulting immunonanoshells obtained under different conditions of conjugation were then assessed for specificity and sensitivity. Photoacoustic tomography was performed to determine the ability to distinguish gold nanoshells from blood both in phantoms and in vivo. Ex vivo optical projection tomography of hearts and aortas from atherosclerotic and control mice confirmed the selective accumulation of the immunonanoshells in atherosclerotic-prone regions in mice, thus validating the utility of the probe in vivo in small animals for pre-clinical research. These immunonanoshells represent an adequate mean to target atherosclerotic plaques in small animals, leading to new tools to follow the effect of therapies on the progression or regression of the disease.

Molecular MRI of Atherosclerosis with USPIO

Inflammation in atherosclerosis is a risk factor for plaque rupture and atherothrombosis. USPIO-enhanced MRI is capable of evaluating the inflammatory activity in vivo on a cellular as well as a sub-cellular level. This paper reviews the recent advances in USPIO-enhanced MRI of atherosclerotic plaque inflammation. Imaging strategies for evidentiating the presence of the USPIO label in plaques take advantage of the susceptibility effect induced by the nanoparticles in their surroundings to obtain a negative contrast (T2* weighted imaging) or a positive contrast (the White Maker and Susceptibility Gradient Mapping). Quantitative methods have more recently been adapted to in vivo imaging of USPIO in atherosclerotic plaques, and showed great promise in detecting treatment responses. When they are not taken up rapidly from blood by the reticulo-endothelial system (RES), USPIOs nanoparticles passively target inflammation in atherosclerosis by engulfment in intra-plaque phagocytic cells. This has been demonstrated in both animal models and human patients. However, by modifying the surface of coating materials, nanoparticles can actively target atherosclerosis molecular and cellular actors in animal models. The goal of molecular imaging of atherosclerotic plaques is to identify events in the early onset of the disease, as well as critical evolution to vulnerable plaques. USPIO agents are preferred as basis to develop targeted agents because of the ability to overcome the toxicity issue of long-term body residence of Gd-based agents, and their lower sensitivity based on their relaxivity properties. MRI agents capable of efficiently targeting oxidized LDL, cell adhesion molecules (VCAM-1, P-selectin, E-selection), apoptosis and activated platelets have been demonstrated in animal models. The use of these methodologies at the clinical level will depend on the availability and toxicity profiles of the agents, and will require standardized state of the art imaging techniques.

Molecular Imaging of Atherosclerotic Plaques Targeted to Oxidized LDL Receptor LOX-1 by SPECT/CT and Magnetic Resonance

The oxidized low-density lipoprotein receptor (LDLR) LOX-1 plays a crucial role in atherosclerosis. We sought to detect and assess atherosclerotic plaque in vivo by using single-photon emission computed tomography/computed tomography and magnetic resonance imaging and a molecular probe targeted at LOX-1. Apolipoprotein E(-/-) mice fed a Western diet and LDLR(-/-) and LDLR(-/-)/LOX-1(-/-) mice fed an atherogenic diet were used. Imaging probes consisted of liposomes decorated with anti-LOX-1 antibodies or nonspecific immunoglobulin G, (111)indium or gadolinium, and 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine fluorescence markers. In vivo imaging was performed 24 hours after intravenous injection (150 microL) of LOX-1 or nonspecific immunoglobulin G probes labeled with either (111)indium (600 muCi) or gadolinium (0.075 mmol/kg), followed by aortic excision for phosphor imaging and Sudan IV staining, or fluorescence imaging and hematoxylin/eosin staining. The LOX-1 probe also colocalized with specific cell types, apoptosis, and matrix metalloproteinase-9 expression in frozen aortic sections. Single-photon emission computed tomography/computed tomography imaging of the LOX-1 probe showed aortic arch "hot spots" in apolipoprotein E(-/-) mice (n=8), confirmed by phosphor imaging. Magnetic resonance imaging showed significant Gd enhancement in atherosclerotic plaques in LDLR(-/-) mice with the LOX-1 (n=7) but not with the nonspecific immunoglobulin G (n=5) probe. No signal enhancement was observed in LDLR(-/-)/LOX-1(-/-) mice injected with the LOX-1 probe (n=5). These results were confirmed by ex vivo fluorescence imaging. The LOX-1 probe bound preferentially to the plaque shoulder, a region with vulnerable plaque features, including extensive LOX-1 expression, macrophage accumulation, apoptosis, and matrix metalloproteinase-9 expression. LOX-1 can be used as a target for molecular imaging of atherosclerotic plaque in vivo. Furthermore, the LOX-1 imaging signal is associated with markers of rupture-prone atherosclerotic plaque.

Recent advances and future trends in multimodality cardiac imaging

The cardiovascular imaging field has experienced marked growth and technical advancement in the past several decades. In the future, multimodality imaging will provide enhanced characterisation of disease states. Myocardial perfusion imaging will become more quantitative, permitting measurement of absolute blood flow and coronary flow reserves during stress states. A greater use of positron emission tomography (PET) can be expected for both assessing blood flow quantitatively and molecular imaging of atherosclerotic plaques and myocardial disease states. SPECT and PET imaging of myocardial metabolism and cardiac neuronal imaging have already shown great promise for identifying high-risk patients with coronary heart disease and nonischaemic cardiomyopathy. Further progress will occur in computed tomography imaging of the heart and coronary arteries and cardiac magnetic resonance imaging including quantitative estimates of coronary blood flow, coronary and peripheral vessel plaque characterisation, and detection of myocardial cellular dysfunction. Fusion imaging, in which two disparate image data sets are merged into one functional image, will become commonplace. Major breakthroughs in CV imaging will depend on discoveries in basic research, further refinement of instrumentation and software for image processing and analysis, and outcomes research demonstrating the worth of imaging technologies in reducing cardiovascular death and morbidity.

Dual targeting improves microbubble contrast agent adhesion to VCAM-1 and P-selectin under flow

To improve ultrasound contrast agents targeted to the adhesion molecules P-selectin and VCAM-1 for the purpose of molecular imaging of atherosclerotic plaques, perfluorocarbon-filled phospholipid microbubble contrast agents were coupled by a polyethylene glycol–biotin–streptavidin bridge with mAb MVCAM.A(429), a sialyl Lewis x polymer (PAA-sLe x), or both (dual). Approximately three hundred thousand antibody molecules were coupled to the surface of each microbubble. Recombinant mouse P-selectin and/or VCAM-1 coated on flow chambers showed saturation of binding at approximately 15 ng/μl, resulting in 800 and 1200 molecules/µm 2 for P-selectin and VCAM-1, respectively. Dual substrates coated with equal concentrations of P-selectin and VCAM-1 had site densities between 50 and 60% of single substrates. When microbubbles were perfused through flow chambers at 5 × 10 6 microbubbles/ml (wall shear stress from 1.5 to 6 dyn/cm 2) dual-targeted microbubbles adhered almost twice as efficiently as single-targeted microbubbles at 6 dyn/cm 2. The present study suggests that dual-targeted contrast agents may be useful for atherosclerotic plaque detection at physiologically relevant shear stresses.

Molecular imaging of atherosclerotic plaque targeted to oxidized LDL receptor LOX-1 using magnetic resonance

Molecular imaging of atherosclerotic plaque targeted to oxidized LDL receptor LOX-1 using magnetic resonance

Magnetic nanoparticles for MR imaging: agents, techniques and cardiovascular applications

Magnetic nanoparticles (MNP) are playing an increasingly important role in cardiovascular molecular imaging. These agents are superparamagnetic and consist of a central core of iron-oxide surrounded by a carbohydrate or polymer coat. The size, physical properties and pharmacokinetics of MNP make them highly suited to cellular and molecular imaging of atherosclerotic plaque and myocardial injury. MNP have a sensitivity in the nanomolar range and can be detected with T1, T2, T2*, off resonance and steady state free precession sequences. Targeted imaging with MNP is being actively explored and can be achieved through either surface modification or through the attachment of an affinity ligand to the nanoparticle. First generation MNP are already in clinical use and second generation agents, with longer blood half lives, are likely to be approved for routine clinical use in the near future.

Molecular Beacons Illuminate Subcellular Events

Building on decades of technological advances and imaging experience, during which noninvasive imaging of cardiac structure and function, myocardial perfusion and viability, and noncoronary vascular pathology have become intimately entwined in routine clinical practice, advanced imaging techniques are now poised to deliver noninvasive coronary arteriograms and to delineate the coronary artery wall in exquisite detail. At the same time that these highly promising methods for anatomic imaging at the macroscopic level are creating great excitement among physicians, their patients, and the public, a quieter imaging revolution is underway with steady progress in detecting and tracking fundamental biological processes at the cellular and subcellular levels. In the era of genomic research, molecular biology, and stem cell therapies, these methods have great potential to accelerate understanding of basic pathophysiological processes in animals and humans and to develop new tools for early diagnosis and drug development. Cardiovascular molecular imaging is taking hold. See p 1800 Molecular imaging is the science of visually representing, characterizing, and quantifying cellular/subcellular biological processes in intact organisms. These processes include gene expression, protein–protein interaction, signal transduction, cellular metabolism, and both intracellular and intercellular trafficking. Molecular imaging has the potential to quantify these events, to monitor multiple events simultaneously, to localize these events in 3 dimensions, and to monitor these events serially. Thus, biological processes can be identified and studied in time and space, providing “4-dimensional” information. The emergence of molecular imaging has coincided with and has been made possible by the enormous progress in molecular biology, cell biology, and transgenic animal models, as well as the development of imaging probes that are specific, reproducible, and quantifiable.1 Molecular imaging was once the sole domain of nuclear medicine, with tracers developed for both positron emission tomography (PET) and single photon emission computed tomography (SPECT). Examples include antimyosin antibodies for …

Molecular imaging of atherosclerotic plaques with technetium-99m-labelled antisense oligonucleotides

The purpose of this study was to visualise experimental atherosclerotic lesions using radiolabelled antisense oligonucleotides (ASONs). Atherosclerosis was induced in New Zealand White rabbits fed 1% cholesterol for approximately 60 days. In vivo and ex vivo imaging was performed in atherosclerotic rabbits and normal control rabbits after i.v. injection of 92.5+/-18.5 MBq (99m)Tc-labelled ASON or (99m)Tc-labelled sense oligonucleotides. Immediately after the in vivo imaging, the animals were sacrificed and ex vivo imaging of the aortic specimens was performed. Biodistribution of radiolabelled c-myc ASON was evaluated in vivo in atherosclerotic rabbits. Planar imaging revealed accumulation of (99m)Tc-labelled c-myc ASON in atherosclerotic lesions along the artery wall. Ex vivo imaging further demonstrated that the area of activity accumulation matched the area of atherosclerotic lesions. In contrast, no atherosclerotic lesions were found in the vessel wall and no positive imaging results were obtained in animals of the control group. This molecular imaging approach has potential for non-invasive imaging of atherosclerotic plaques at an early stage.

Molecular Imaging of Atherosclerotic Plaques Using a Human Antibody Against the Extra-Domain B of Fibronectin

Current imaging modalities of human atherosclerosis, such as angiography, ultrasound, and computed tomography, visualize plaque morphology. However, methods that provide insight into plaque biology using molecular tools are still insufficient. The extra-domain B (ED-B) is inserted into the fibronectin molecule by alternative splicing during angiogenesis and tissue remodeling but is virtually undetectable in normal adult tissues. Angiogenesis and tissue repair are also hallmarks of advanced plaques. For imaging atherosclerotic plaques, the human antibody L19 (specific against ED-B) and a negative control antibody were labeled with radioiodine or infrared fluorophores and injected intravenously into atherosclerotic apolipoprotein E-null (ApoE-/-) or normal wild-type mice. Aortas isolated 4 hours, 24 hours, and 3 days after injection exhibited a selective and stable uptake of L19 when using radiographic or fluorescent imaging. L19 binding was confined to the plaques as assessed by fat staining. Comparisons between fat staining and autoradiographies 24 hours after 125I-labeled L19 revealed a significant correlation (r=0.89; P<0.0001). Minimal antibody uptake was observed in normal vessels from wild-type mice receiving the L19 antibody and in atherosclerotic vessels from ApoE-/- mice receiving the negative control antibody. Immunohistochemical studies revealed increased expression of ED-B not only in murine but also in human plaques, in which it was found predominantly around vasa vasorum and plaque matrix. In summary, we demonstrate selective targeting of atheromas in mice using the human antibody to the ED-B domain of fibronectin. Thus, our findings may set the stage for antibody-based molecular imaging of atherosclerotic plaques in the intact organism.