Detection and Characterization of Thrombosis in Humans Using Fibrin-Targeted Positron Emission Tomography and Magnetic Resonance

X-ray Attenuating Vesicles with Neutrophil Extracellular Trap (NET) Specificity: Synthesis and Testing in a Model System

X-ray attenuating contrast agents for imaging thrombi directly during endovascular thrombectomy (EVT) are urgently needed for shortening the wait time for treatment and for reducing the chances of blood clot fragmentation. Neutrophil extracellular traps (NETs) are a product of an innate immune system response by which neutrophils release decondensed chromatin strands decorated with granule and cytosolic proteins, including neutrophil elastase and citrullinated histone H3 (CitH3). NETs are frequently found within fibrous thrombi in pathology and represent a promising target for thrombi-specific imaging agents due to their common occurrence in human cerebrovascular thrombi. We designed and tested 200 nm lipid vesicles (LV) formulated in the presence of a combination of hydrophilic and hydrophobic computed tomography (CT) contrast agents with resultant efficacy of X-ray attenuation corresponding to 312 ± 54 mg/mL iodine. The LV incorporated trans-cyclooctene-terminated pegylated distearoylphosphatidylethanolamine (TCO-PEG-DSPE) for rapid conjugation of methyltetrazine(mTz)-modified monoclonal immunoglobulin G (IgG) with anti-citH3 binding specificity. By using differential fluorescent labeling of the antibody and lipid components, we determined that 80 ± 3% of mTz-linked IgG coprecipitated with the LV after conjugation in contrast to 0.1-0.2% of control IgG. The engineered NET-specific LV were tested in vitro using differentiated human HL60 promyeloblasts (dHL60) as a standard model of NETing neutrophils. Using fibrin meshwork-incorporated dHL60 as well as monolayer cell cultures, we determined that anti-citH3 LV showed specific and high-affinity binding to dHL60 cells, which were stimulated to undergo NETosis. This work suggests the high promise of NET-specific agents in providing thrombus-specific imaging contrast during EVT.

Multi-modality imaging for assessment of the microcirculation in peripheral artery disease: Bench to clinical practice

Peripheral artery disease (PAD) is a highly prevalent disorder with a high risk of mortality and amputation despite the introduction of novel medical and procedural treatments. Microvascular disease (MVD) is common among patients with PAD, and despite the established role as a predictor of amputations and mortality, MVD is not routinely assessed as part of current standard practice. Recent pre-clinical and clinical perfusion and molecular imaging studies have confirmed the important role of MVD in the pathogenesis and outcomes of PAD. The recent advancements in the imaging of the peripheral microcirculation could lead to a better understanding of the pathophysiology of PAD, and result in improved risk stratification, and our evaluation of response to therapies. In this review, we will discuss the current understanding of the anatomy and physiology of peripheral microcirculation, and the role of imaging for assessment of perfusion in PAD, and the latest advancements in molecular imaging. By highlighting the latest advancements in multi-modality imaging of the peripheral microcirculation, we aim to underscore the most promising imaging approaches and highlight potential research opportunities, with the goal of translating these approaches for improved and personalized management of PAD in the future.

Translational molecular imaging: Thrombosis imaging with positron emission tomography

A key focus of cardiovascular medicine is the detection, treatment, and prevention of disease, with a move towards more personalized and patient-centred treatments. To achieve this goal, novel imaging approaches that allow for early and accurate detection of disease and risk stratification are needed. At present, the diagnosis, monitoring, and prognostication of thrombotic cardiovascular diseases are based on imaging techniques that measure changes in structural anatomy and biological function. Molecular imaging is emerging as a new tool for the non-invasive detection of biological processes, such as thrombosis, that can improve identification of these events above and beyond current imaging modalities. At the forefront of these evolving techniques is the use of high-sensitivity radiotracers in conjunction with positron emission tomography imaging that could revolutionise current diagnostic paradigms by improving our understanding of the role and origin of thrombosis in a range of cardiovascular diseases.

Plasma NEDD9 is increased following SARS-CoV-2 infection and associates with indices of pulmonary vascular dysfunction

Compared to healthy volunteers, participants with post-acute sequelae of SARS-CoV-2 infection (PASC) demonstrated increased plasma levels of the prothrombotic protein NEDD9, which associated inversely with indices of pulmonary vascular function. This suggests persistent pulmonary vascular dysfunction may play a role in the pathobiology of PASC.

Noninvasive In Vivo Coronary Artery Thrombus Imaging

BACKGROUND

The diagnosis and management of myocardial infarction are increasingly complex, and establishing the presence of intracoronary thrombosis has major implications for both the classification and treatment of myocardial infarction.

OBJECTIVES

The aim of this study was to investigate whether positron emission tomographic (PET) and computed tomographic (CT) imaging could noninvasively detect in vivo thrombus formation in human coronary arteries using a novel glycoprotein IIb/IIIa receptor antagonist-based radiotracer, 18F-GP1.

METHODS

In a single-center observational case-control study, patients with or without acute myocardial infarction underwent coronary 18F-GP1 PET/CT angiography. Coronary artery 18F-GP1 uptake was assessed visually and quantified using maximum target-to-background ratios.

RESULTS

18F-GP1 PET/CT angiography was performed in 49 patients with and 50 patients without acute myocardial infarction (mean age: 61 ± 9 years, 75% men). Coronary 18F-GP1 uptake was apparent in 39 of the 49 culprit lesions (80%) in patients with acute myocardial infarction. False negative results appeared to relate to time delays to scan performance and low thrombus burden in small-caliber distal arteries. On multivariable regression analysis, culprit vessel status was the only independent variable associated with higher 18F-GP1 uptake. Extracoronary cardiac 18F-GP1 findings included a high frequency of infarct-related intramyocardial uptake (35%) as well as left ventricular (8%) or left atrial (2%) thrombus.

CONCLUSIONS

Coronary 18F-GP1 PET/CT angiography is the first noninvasive selective technique to identify in vivo coronary thrombosis in patients with acute myocardial infarction. This novel approach can further define the role and location of thrombosis within the heart and has the potential to inform the diagnosis, management, and treatment of patients with acute myocardial infarction. (In-Vivo Thrombus Imaging With 18F-GP1, a Novel Platelet PET Radiotracer [iThrombus]; NCT03943966).

Imaging of intracoronary thrombus

The identification of intracoronary thrombus and atherothrombosis is central to the diagnosis of acute myocardial infarction, with the differentiation between type 1 and type 2 myocardial infarction being crucial for immediate patient management. Invasive coronary angiography has remained the principal imaging modality used in the investigation of patients with myocardial infarction. More recently developed invasive intravascular imaging approaches, such as angioscopy, intravascular ultrasound and optical coherence tomography, can be used as adjunctive imaging modalities to provide more direct visualisation of coronary atheroma and the causes of myocardial infarction as well as to improve the sensitivity of thrombus detection. However, these invasive approaches have practical and logistic constraints that limit their widespread and routine application. Non-invasive angiographic techniques, such as CT and MRI, have become more widely available and have improved the non-invasive visualisation of coronary artery disease. Although they also have a limited ability to reliably identify intracoronary thrombus, this can be overcome by combining their anatomical and structural characterisation of coronary anatomy with positron emission tomography. Specific radiotracers which bind with high specificity and sensitivity to components of thrombus, such as activated platelets, fibrin and factor XIIIa, hold promise for the non-invasive detection of intracoronary thrombus. The development of these novel non-invasive approaches has the potential to inform clinical decision making and patient management as well as to provide a non-invasive technique to assess the efficacy of novel antithrombotic therapies or interventional strategies. However, these have yet to be realised in routine clinical practice.

In vivo real-time red blood cell migration and microcirculation flow synergy imaging-surveyed thrombolytic therapy with iron-oxide complexes

Nanotherapeutics as a nascent method has attracted widely interest on the treatment of thrombosis. However, due to the limited temporal and spatial resolution of conventional imaging modalities, the dynamic visualization the thrombogenesis and evaluation of the effect of thrombolytic drugs are facing severely difficulties in vivo. In addition, the development of high targeting, short circulation time, and small size thrombolysis nanotherapeutics agents requires further research. Herein, we report a synergy imaging modality that combining a label-free capillary microscopy and laser speckle microcirculation imaging, which realized dynamic visualization of single red blood cell migration and large-field dynamic blood flow. In this work, we investigated the red blood cells migration and blood flow velocity response before and after treated through introducing a functional nano-thrombolytics, iron-oxide complexes coated urokinase (IPN@UK) on an orthotopic animal model in vivo. The functionalized IPN@UK nanocomposites exhibited outstanding thrombolysis effect. Significantly, whole-course changes, including red blood cell activity, complex thrombolytic therapeutics, were well surveilled and evaluated using dual-modality combining imaging strategy. These results show this synergy imaging strategy not only can achieve multiscale non-invasive visualization of dynamic thrombus events in real-time, but also can quantify hemodynamics information of thrombus. Our study demonstrates the potential of this synergy imaging method, which for early detection of thrombus, evaluation of the effect of drug thrombolysis, developing the thrombolytic drugs, and imaging-guide thrombolytic therapy in living systems.

Imaging High-Risk Atherothrombosis Using a Novel Fibrin-Binding Positron Emission Tomography Probe

BACKGROUND AND PURPOSE

High-risk atherosclerosis is an underlying cause of cardiovascular events, yet identifying the specific patient population at immediate risk is still challenging. Here, we used a rabbit model of atherosclerotic plaque rupture and human carotid endarterectomy specimens to describe the potential of molecular fibrin imaging as a tool to identify thrombotic plaques.

METHODS

Atherosclerotic plaques in rabbits were induced using a high-cholesterol diet and aortic balloon injury (N=13). Pharmacological triggering was used in a group of rabbits (n=9) to induce plaque disruption. Animals were grouped into thrombotic and nonthrombotic plaque groups based on gross pathology (gold standard). All animals were injected with a novel fibrin-specific probe ⁶⁸Ga-CM246 followed by positron emission tomography (PET)/magnetic resonance imaging 90 minutes later. ⁶⁸Ga-CM246 was quantified on the PET images using tissue-to-background (back muscle) ratios and standardized uptake value.

RESULTS

Both tissue-to-background (back muscle) ratios and standardized uptake value were significantly higher in the thrombotic versus nonthrombotic group (P<0.05). Ex vivo PET and autoradiography of the abdominal aorta correlated positively with in vivo PET measurements. Plaque disruption identified by ⁶⁸Ga-CM246 PET agreed with gross pathology assessment (85%). In ex vivo surgical specimens obtained from patients undergoing elective carotid endarterectomy (N=12), ⁶⁸Ga-CM246 showed significantly higher binding to carotid plaques compared to a D-cysteine nonbinding control probe.

CONCLUSIONS

We demonstrated that molecular fibrin PET imaging using ⁶⁸Ga-CM246 could be a useful tool to diagnose experimental and clinical atherothrombosis. Based on our initial results using human carotid plaque specimens, in vivo molecular imaging studies are warranted to test ⁶⁸Ga-CM246 PET as a tool to stratify risk in atherosclerotic patients.