Nuclear Imaging

Discovery of σ2R/TMEM97 as a Novel Biomarker for Atherosclerotic Plaques: A PET Imaging and Validation Study

BACKGROUND

The aims of this study were to evaluate σ2R (sigma-2 receptor)/TMEM97 (transmembrane protein 97) expression in atherosclerotic plaques, and assess the feasibility of in vivo atherosclerotic plaques imaging using the σ2R/TMEM97 targeting probe 1-(4-(5,6-dimethoxyisoindolin-2-yl)butyl)-3-(2-[18F]fluoroethyl)-1,3-dihydro-2H-benzo[d]imidazol-2-one ([18F]SYB-NF) developed in our laboratory.

METHODS

Hematoxylin and eosin and immunohistochemical staining were performed on both human coronary endarterectomy specimens and mouse samples. The expression of σ2R/TMEM97 in RAW264.7 cells incubated with ox-LDL (oxidized low-density lipoprotein) was analyzed using western blot analysis. Positron emission tomography imaging with [18F]SYB-NF, [18F]NaF, and [18F]fluoro-2-deoxy-d-glucose was conducted in wide-type C57BL/6 and ApoE-/- mice. Specific binding was evaluated by coinjecting [18F]SYB-NF with the σ2R/TMEM97 antagonist CM398. Autoradiography and Oil Red O staining were performed on harvested aortas and corresponding sections.

RESULTS

Staining results demonstrated significant upregulation of σ2R/TMEM97 expression during both early plaque formation and atherosclerosis progression. Western blot analysis indicated that incubation of macrophages with ox-LDL led to increased σ2R/TMEM97 expression. [18F]SYB-NF specifically accumulated in the aortic arch of ApoE-/- mice. Treatment with CM398 significantly reduced the standardized uptake value in the aortic arch of ApoE-/- mice. [18F]SYB-NF exhibited a higher standardized uptake value in the aortic arch (0.67±0.09 versus 0.51±0.07) and higher aortic arch-to-heart ratio (2.58 versus 0.56) in ApoE-/- mice compared with [18F]fluoro-2-deoxy-d-glucose, and a higher aortic arch-to-bone ratio (2.24 versus 0.44) compared with [18F]NaF. Autoradiography analysis revealed a strong correlation between the positive area in Oil Red O staining and autoradiography (Pearson correlation coefficient=0.993; P=0.001), further supporting the association between elevated σ2R/TMEM97 expression and plaque formation.

CONCLUSIONS

σ2R/TMEM97 may serve as a potential biomarker for atherosclerotic plaques, and σ2R/TMEM97 positron emission tomography imaging may be used to monitor plaque formation and progression, as well as the efficacy of emerging therapeutic strategies for atherosclerotic plaques.

Multimodality Imaging in HIV-Associated Cardiovascular Complications: A Comprehensive Review

Human immunodeficiency virus (HIV) infection is a leading cause of mortality and morbidity worldwide. The introduction of antiretroviral therapy (ART) has significantly reduced the risk of developing acquired immune deficiency syndrome and increased life expectancy, approaching that of the general population. However, people living with HIV have a substantially increased risk of cardiovascular diseases despite long-term viral suppression using ART. HIV-associated cardiovascular complications encompass a broad spectrum of diseases that involve the myocardium, pericardium, coronary arteries, valves, and systemic and pulmonary vasculature. Traditional risk stratification tools do not accurately predict cardiovascular risk in this population. Multimodality imaging plays an essential role in the evaluation of various HIV-related cardiovascular complications. Here, we emphasize the role of multimodality imaging in establishing the diagnosis and aetiopathogenesis of various cardiovascular manifestations related to chronic HIV disease. This review also provides a critical appraisal of contemporary data and illustrative cases.

Emerging Nuclear Medicine Imaging of Atherosclerotic Plaque Formation

Atherosclerosis is a chronic widespread cardiovascular disease and a major predisposing factor for cardiovascular events, among which there are myocardial infarction and ischemic stroke. Atherosclerotic plaque formation is a process that involves different mechanisms, of which inflammation is the most common. Plenty of radiopharmaceuticals were developed to elucidate the process of plaque formation at different stages, some of which were highly specific for atherosclerotic plaque. This review summarizes the current nuclear medicine imaging landscape of preclinical and small-scale clinical studies of these specific RPs, which are not as widespread as labeled FDG, sodium fluoride, and choline. These include oxidation-specific epitope imaging, macrophage, and other cell receptors visualization, neoangiogenesis, and macrophage death imaging. It is shown that specific radiopharmaceuticals have strength in pathophysiologically sound imaging of the atherosclerotic plaques at different stages, but this also may induce problems with the signal registration for low-volume plaques in the vascular wall.

Positron Emission Tomography in Atherosclerosis Research

Positron emission tomography (PET) is a quantitative imaging technique that uses molecules labeled with positron-emitting radionuclides to visualize and measure biochemical processes in the tissues of living subjects. In recent years, different PET tracers have been evaluated for their ability to characterize the atherosclerotic process in order to study the activity of the disease. Here, we describe detailed PET methods for preclinical studies of atherosclerosis and summarize the key methodological aspects of PET imaging in clinical studies of atherosclerosis.

The Role of Multimodality Imaging in HIV-Associated Cardiomyopathy

Despite marked advances in therapeutics, HIV infection remains a leading cause of morbidity and mortality worldwide. HIV infection is associated with cardiovascular complications including myocardial dysfunction. The description of HIV-associated cardiomyopathy (HIVAC) has evolved over time from a predominantly dilated cardiomyopathy with systolic dysfunction to one of subclinical diastolic dysfunction. Multimodality cardiovascular imaging plays an integral role in our understanding of the etiology and pathogenesis of HIVAC. Such imaging is also essential in the evaluation of individuals with chronic HIV disease who present with cardiac symptoms, especially of heart failure. In the present review, we will highlight current evidence for the role of multimodality imaging in establishing the diagnosis, etiology and pathophysiology of HIVAC as well as guiding treatment and assessing prognosis.

Evaluation of glucagon-like peptide-1 receptor expression in nondiabetic and diabetic atherosclerotic mice using PET tracer 68Ga-NODAGA-exendin-4

Cardiovascular effects of glucagon-like peptide-1 receptor (GLP-1R) agonist therapies are potentially mediated by anti-inflammatory effects on atherosclerosis. Our study demonstrates that ⁶⁸Ga-NODAGA-exendin-4, a radioligand specifically targeting GLP-1R, detects GLP-1R expression in inflamed atherosclerotic lesions in nondiabetic and diabetic hypercholesterolemic mice. Immunofluorescence staining suggests that GLP-1R is primarily localized in M2 macrophages in lesions. This study describes a new potential tool that may have translational relevance for studies of pharmacological modification of GLP-1R signaling in atherosclerosis.

Recent Advances in Vascular Imaging

Recent advances in vascular imaging have enabled us to uncover the underlying mechanisms of vascular diseases both ex vivo and in vivo. In the past decade, efforts have been made to establish various methodologies for evaluation of atherosclerotic plaque progression and vascular inflammatory changes in addition to biomarkers and clinical manifestations. Several recent publications in Arteriosclerosis, Thrombosis, and Vascular Biology highlighted the essential roles of in vivo and ex vivo vascular imaging, including magnetic resonance image, computed tomography, positron emission tomography/scintigraphy, ultrasonography, intravascular ultrasound, and most recently, optical coherence tomography, all of which can be used in bench and clinical studies at relative ease. With new methods proposed in several landmark studies, these clinically available imaging modalities will be used in the near future. Moreover, future development of intravascular imaging modalities, such as optical coherence tomography-intravascular ultrasound, optical coherence tomography-near-infrared autofluorescence, polarized-sensitive optical coherence tomography, and micro-optical coherence tomography, are anticipated for better management of patients with cardiovascular disease. In this review article, we will overview recent advances in vascular imaging and ongoing works for future developments.

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.