Alphavbeta3-targeted detection of arteriopathy in transplanted human coronary arteries: an autoradiographic study

Evaluation of cardiac allograft vasculopathy by positron emission tomography

Cardiac allograft vasculopathy (CAV) remains one of the most important late occurring complications in heart transplant (HT) recipients significantly effecting graft survival. Recently, there has been tremendous focus on the development of effective and safe non-invasive diagnostic strategies for the diagnosis of CAV employing a wide range of imaging technologies. During the past decade multiple studies have been published using positron emission tomography (PET) myocardial perfusion imaging, establishing the value of PET myocardial blood flow quantification for the evaluation of CAV. These independent investigations demonstrate that PET can be successfully used to establish the diagnosis of CAV, can be utilized for prognostication and may be used for serial monitoring of HT recipients. In addition, molecular imaging techniques have started to emerge as new tools to enhance our knowledge to better understand the pathophysiology of CAV.

Emerging imaging techniques after cardiac transplantation

Improvements in survival after cardiac transplantation have in part been driven by improved graft surveillance. Graft surveillance relies mainly on 3 techniques: coronary angiography, endomyocardial biopsy and echocardiography. Developments in invasive and non-invasive imaging technology have revolutionized assessment of the heart in both health and disease, offering new insights into tissue composition and myocardial metabolism. Herein we aim to review the strengths and weaknesses of these techniques, and summarize the evidence in the following 5 fields of cardiac imaging after transplantation: cardiovascular magnetic resonance; computed tomography; positron emission tomography; single-photon emission computed tomography; and optical coherence tomography and molecular imaging techniques.

Molecular imaging of vascular endothelial growth factor receptors in graft arteriosclerosis

OBJECTIVE

Vascular endothelial growth factor (VEGF) signaling plays a key role in the pathogenesis of vascular remodeling, including graft arteriosclerosis. Graft arteriosclerosis is the major cause of late organ failure in cardiac transplantation. We used molecular near-infrared fluorescent imaging with an engineered Cy5.5-labeled single-chain VEGF tracer (scVEGF/Cy) to detect VEGF receptors and vascular remodeling in human coronary artery grafts by molecular imaging.

METHODS AND RESULTS

VEGF receptor specificity of probe uptake was shown by flow cytometry in endothelial cells. In severe combined immunodeficiency mice, transplantation of human coronary artery segments into the aorta followed by adoptive transfer of allogeneic human peripheral blood mononuclear cells led to significant neointima formation in the grafts over a period of 4 weeks. Near-infrared fluorescent imaging of transplant recipients at 4 weeks demonstrated focal uptake of scVEGF/Cy in remodeling artery grafts. Uptake specificity was demonstrated using an inactive homolog of scVEGF/Cy. scVEGF/Cy uptake predominantly localized in the neointima of remodeling coronary arteries and correlated with VEGF receptor-1 but not VEGF receptor-2 expression. There was a significant correlation between scVEGF/Cy uptake and transplanted artery neointima area.

CONCLUSIONS

Molecular imaging of VEGF receptors may provide a noninvasive tool for detection of graft arteriosclerosis in solid organ transplantation.

Integrin-targeted imaging of inflammation in vascular remodeling

OBJECTIVE

Inflammation plays a key role in the development of vascular diseases. Monocytes and macrophages express α(v)β(3) integrin. We used an α(v) integrin-specific tracer, (99m)Tc-NC100692, to investigate integrin-targeted imaging for detection vessel wall inflammation.

METHODS AND RESULTS

The binding of a fluorescent homologue of NC100692 to α(v)β(3) on human monocytes and macrophages was shown by flow cytometry. Vessel wall inflammation and remodeling was induced in murine carotid arteries through adventitial exposure to CaCl(2). NC100692 micro single photon computed tomography/CT imaging was performed after 2 and 4 weeks and showed significantly higher uptake of the tracer in CaCl(2)-exposed left carotids compared with sham-operated contralateral arteries. Histological analysis at 4 weeks demonstrated significant remodeling of left carotid arteries and considerable macrophage infiltration, which was confirmed by real-time polymerase chain reaction. There was no significant difference in normalized α(v), β(3), or β(5) mRNA expression between right and left carotid arteries. Finally, NC100692 uptake strongly correlated with macrophage marker expression in carotid arteries.

CONCLUSIONS

NC100692 imaging can detect vessel wall inflammation in vivo. If further validated, α(v)-targeted imaging may provide a noninvasive approach for identifying patients who are at high risk for vascular events and tracking the effect of antiinflammatory treatments.

Molecular imaging of coronary atherosclerosis and myocardial infarction: considerations for the bench and perspectives for the clinic

Motivated by the promise to transform preclinical research and clinical care, cardiovascular molecular imaging has made advances toward targeting coronary atherosclerosis and heart failure. Here, we discuss recent progress in the field, highlight how molecular imaging may facilitate preventive patient care, and review specific challenges associated with coronary and heart failure imaging. Practical considerations stress the potential of fluorescence imaging for basic research and discuss hybrid protocols such as FMT-CT and PET-MRI.

Imaging atherosclerosis and vulnerable plaque

Identifying patients at high risk for an acute cardiovascular event such as myocardial infarction or stroke and assessing the total atherosclerotic burden are clinically important. Currently available imaging modalities can delineate vascular wall anatomy and, with novel probes, target biologic processes important in plaque evolution and plaque stability. Expansion of the vessel wall involving remodeling of the extracellular matrix can be imaged, as can angiogenesis of the vasa vasorum, plaque inflammation, and fibrin deposits on early nonocclusive vascular thrombosis. Several imaging platforms are available for targeted vascular imaging to acquire information on both anatomy and pathobiology in the same imaging session using either hybrid technology (nuclear combined with CT) or MRI combined with novel probes targeting processes identified by molecular biology to be of importance. This article will discuss the current state of the art of these modalities and challenges to clinical translation.

ESDN is a marker of vascular remodeling and regulator of cell proliferation in graft arteriosclerosis

Vascular remodeling is a common feature of many vasculopathies, including graft arteriosclerosis (GA). We investigated whether endothelial and smooth muscle cell-derived neuropilin-like protein (ESDN) is a marker of vascular remodeling in GA. Immunostaining of human coronary arteries demonstrated high levels of ESDN in GA, but not in normal arteries. In a model of GA, where a segment of human coronary is transplanted into a severe combined immunodeficient mouse, followed by allogeneic human peripheral blood mononuclear cell (PBMC) reconstitution, ESDN was minimally expressed in transplanted human arteries in the absence of reconstitution. By 2 weeks following PBMC reconstitution, at a time corresponding to maximal vascular cell proliferation, high levels of ESDN were detected in the transplanted arteries. Similarly, injury-induced vascular remodeling in apoE(-/-) mice was associated with early and transient ESDN upregulation, in parallel with cell proliferation. In vascular smooth muscle cell (VSMC) cultures, ESDN expression was significantly higher in proliferating, as compared to growth-arrested cells. ESDN overexpression in VSMC led to a decline in growth curves, while ESDN knock down had the opposite effect. We conclude that ESDN is a marker of vascular remodeling and regulator of VSMC proliferation. ESDN may serve as a therapeutic or diagnostic target for GA.

Activated alphavbeta3 integrin targeting in injury-induced vascular remodeling

There is currently no imaging modality to track the remodeling process, a common feature of a broad spectrum of vasculopathies, in vivo. alphavbeta3 Integrin is up-regulated in proliferating vascular cells. RP748, a novel peptidomimetic tracer, binds specifically to the activated alphavbeta3 conformer and exhibits favorable binding characteristics for in vivo imaging. In a model of injury-induced vascular remodeling in apoE null mice, RP748 localization to the injured carotid arteries parallels vascular cell proliferation, providing an opportunity to image the remodeling process in vivo.

Molecular cardiovascular imaging using scintigraphic methods

Molecular cardiovascular imaging plays an increasingly important role both in basic research and in clinical diagnosis. Scintigraphic methods have long been used to study pathophysiological changes on a cellular and molecular level, and they are likely to remain important molecular imaging modalities in the foreseeable future. This article provides an overview over current developments in cardiovascular molecular imaging using scintigraphic methods. The focus lies on imaging of cardiac innervation, plaque instability, hypoxia and angiogenesis, gene expression and stem and progenitor cell migration and proliferation.