Molecular Imaging of Angiogenesis and Vascular Remodeling in Cardiovascular Pathology

Metformin in cardiovascular diabetology: a focused review of its impact on endothelial function

As a first-line treatment for diabetes, the insulin-sensitizing biguanide, metformin, regulates glucose levels and positively affects cardiovascular function in patients with diabetes and cardiovascular complications. Endothelial dysfunction (ED) represents the primary pathological change of multiple vascular diseases, because it causes decreased arterial plasticity, increased vascular resistance, reduced tissue perfusion and atherosclerosis. Caused by “biochemical injury”, ED is also an independent predictor of cardiovascular events. Accumulating evidence shows that metformin improves ED through liver kinase B1 (LKB1)/5'-adenosine monophosphat-activated protein kinase (AMPK) and AMPK-independent targets, including nuclear factor-kappa B (NF-κB), phosphatidylinositol 3 kinase-protein kinase B (PI3K-Akt), endothelial nitric oxide synthase (eNOS), sirtuin 1 (SIRT1), forkhead box O1 (FOXO1), krüppel-like factor 4 (KLF4) and krüppel-like factor 2 (KLF2). Evaluating the effects of metformin on endothelial cell functions would facilitate our understanding of the therapeutic potential of metformin in cardiovascular diabetology (including diabetes and its cardiovascular complications). This article reviews the physiological and pathological functions of endothelial cells and the intact endothelium, reviews the latest research of metformin in the treatment of diabetes and related cardiovascular complications, and focuses on the mechanism of action of metformin in regulating endothelial cell functions.

Non-oncological applications of RGD-based single-photon emission tomography and positron emission tomography agents

INTRODUCTION

Non-invasive imaging techniques (especially single-photon emission tomography and positron emission tomography) apply several RGD-based imaging ligands developed during a vast number of preclinical and clinical investigations. The RGD (Arg-Gly-Asp) sequence is a binding moiety for a large selection of adhesive extracellular matrix and cell surface proteins. Since the first identification of this sequence as the shortest sequence required for recognition in fibronectin during the 1980s, fundamental research regarding the molecular mechanisms of integrin action have paved the way for development of several pharmaceuticals and radiopharmaceuticals with clinical applications. Ligands recognizing RGD may be developed for use in the monitoring of these interactions (benign or pathological). Although RGD-based molecular imaging has been actively investigated for oncological purposes, their utilization towards non-oncology applications remains relatively under-exploited.

METHODS AND SCOPE

This review highlights the new non-oncologic applications of RGD-based tracers (with the focus on single-photon emission tomography and positron emission tomography). The focus is on the last 10 years of scientific literature (2009-2020). It is proposed that these imaging agents will be used for off-label indications that may provide options for disease monitoring where there are no approved tracers available, for instance Crohn's disease or osteoporosis. Fundamental science investigations have made progress in elucidating the involvement of integrin in various diseases not pertaining to oncology. Furthermore, RGD-based radiopharmaceuticals have been evaluated extensively for safety during clinical evaluations of various natures.

CONCLUSION

Clinical translation of non-oncological applications for RGD-based radiopharmaceuticals and other imaging tracers without going through time-consuming extensive development is therefore highly plausible. Graphical abstract.

Targeting Fluorescent Nanodiamonds to Vascular Endothelial Growth Factor Receptors in Tumor

The increased expression of vascular endothelial growth factor (VEGF) and its receptors is associated with angiogenesis in a growing tumor, presenting potential targets for tumor-selective imaging by way of targeted tracers. Though fluorescent tracers are used for targeted in vivo imaging, the lack of photostability and biocompatibility of many current fluorophores hinder their use in several applications involving long-term, continuous imaging. To address these problems, fluorescent nanodiamonds (FNDs), which exhibit infinite photostability and excellent biocompatibility, were explored as fluorophores in tracers for targeting VEGF receptors in growing tumors. To explore FND utility for imaging tumor VEGF receptors, we used click-chemistry to conjugate multiple copies of an engineered single-chain version of VEGF site-specifically derivatized with trans-cyclooctene (scVEGF-TCO) to 140 nm FND. The resulting targeting conjugates, FND-scVEGF, were then tested for functional activity of the scVEGF moieties through biochemical and tissue culture experiments and for selective tumor uptake in Balb/c mice with induced 4T1 carcinoma. We found that FND-scVEGF conjugates retain high affinity to VEGF receptors in cell culture experiments and observed preferential accumulation of FND-scVEGF in tumors relative to untargeted FND. Microspectroscopy provided unambiguous determination of FND within tissue by way of the unique spectral shape of nitrogen-vacancy induced fluorescence. These results validate and invite the use of targeted FND for diagnostic imaging and encourage further optimization of FND for fluorescence brightness.

Effect of Breviscapine on Recovery of Viable Myocardium and Left Ventricular Remodeling in Chronic Total Occlusion Patients After Revascularization: Rationale and Design for a Randomized Controlled Trial

BACKGROUND How to speed the recovery of viable myocardium in chronic total occlusion (CTO) patients after revascularization is still an unsolved problem. Breviscapine is widely used in cardiovascular diseases. However, there has been no study focused on the effect of breviscapine on viable myocardium recovery and left ventricular remodeling after CTO revascularization. MATERIAL AND METHODS We propose to recruit 78 consecutive coronary artery disease (CAD) patients with CTO during a period of 12 months. They will be randomly assigned to receive either breviscapine (40 mg) or placebo in the following 12 months. Blood tests, electrocardiogram, and Major Adverse Cardiac Events (MACE) will be collected at baseline and the follow-up visits at 1, 3, 6, 9, and 12 months. Low-dose dobutamine MRI will be applied for the assessment of viable myocardium, microcirculation perfusion, and left ventricular remodeling, and the concentrations of angiogenic cytokine, vascular endothelial growth factor (VEGF), and basic fibroblast growth factor (bFGF) will be investigated at baseline and at 1- and 12-month follow-up. The recovery of viable myocardium after revascularization in CTO patients was the primary endpoint. Improvement of microcirculation perfusion, left ventricular remodeling, peripheral concentrations of VEGF and bFGF as well as MACE will be the secondary endpoints. RESULTS Breviscapine treatment obviously improve the recovery of viable myocardium, myocardial microcirculation perfusion, and left ventricular remodeling after revascularization in CTO patients, and reduce the occurrence of MACE. We also will determine if breviscapine increases the peripheral blood angiogenic cytokine concentrations of VEGF and bFGF. CONCLUSIONS This study will aim to demonstrate the effect of breviscapine on the recovery of viable myocardium and left ventricular remodeling in CTO patients after revascularization.

Exposure to PM2.5 via vascular endothelial growth factor relationship: Meta-analysis

This study investigated the association of PM2.5 exposure with VEGF by conducting a systematic review of existing literature and performing a meta-analysis. We searched all the studies published in the Cochrane Library, PUBMED, Embase, China National Knowledge Infrastructure China National Knowledge Infrastructure, and WanFang Electronic Database before June 2017. Finally six studies were identified. It confirmed that the increase in VEGF (β = 1.23 pg/ml, 95% CI: 0.45, 2.01) was significantly associated with the PM2.5 mass concentration of 10 μg/m³. Studies from Canada showed that PM2.5 exposure statistically elevated the level of VEGF level that an increase of 1.20 pg/ml (95% CI: 0.88, 1.52) in VEGF was associated with per 10 μg/m³ increase in PM2.5 concentration. Other subgroup analyses indicated that the effects of PM2.5 exposure on VEGF differed per the in different exposure assessment methods, study designs, and study settings. It was concluded that elevated VEGF levels was significantly positive associated with PM2.5 exposure. Exposure assessment methods and study countries were the major sources of heterogeneity among studies.

Novel molecular imaging ligands targeting matrix metalloproteinases 2 and 9 for imaging of unstable atherosclerotic plaques

Molecular imaging of matrix metalloproteinases (MMPs) may allow detection of atherosclerotic lesions vulnerable to rupture. In this study, we develop a novel radiolabelled compound that can target gelatinase MMP subtypes (MMP2/9) with high selectivity and inhibitory potency. Inhibitory potencies of several halogenated analogues of MMP subtype-selective inhibitors (N-benzenesulfonyliminodiacetyl monohydroxamates and N-halophenoxy-benzenesulfonyl iminodiacetyl monohydroxamates) were in the nanomolar range for MMP2/9. The analogue with highest inhibitory potency and selectivity was radiolabelled with [123I], resulting in moderate radiochemical yield, and high radiochemical purity. Biodistribution studies in mice, revealed stabilization in blood 1 hour after intravenous bolus injection. Intravenous infusion of the radioligand and subsequent autoradiography of excised aortas showed tracer uptake in atheroprone mice. Distribution of the radioligand showed co-localization with MMP2/9 immunohistochemical staining. In conclusion, we have developed a novel selective radiolabeled MMP2/9 inhibitor, suitable for single photon emission computed tomography (SPECT) imaging that effectively targets atherosclerotic lesions in mice.

Nano-sized and other improved reporters for magnetic resonance imaging of angiogenesis

Magnetic Resonance Imaging (MRI) enables to provide anatomical, functional and molecular information of pathological angiogenesis when used with properly tailored imaging probes. Functional studies have been the domain of Dynamic Contrast Enhancement (DCE) -MRI protocols from which it is possible to extract quantitative estimations on key parameters such as the volumes of vascular and extracellular compartments and the rates of the bidirectional exchange of the imaging reporters across the endothelial barrier. Whereas paramagnetic Gd-complexes able to reversibly bind to serum albumin act better than the clinically used small-sized, hydrophilic species, new findings suggest that an accurate assessment of the vascular volume is possible by analyzing images acquired upon the i.v. administration of Gd-labelled Red Blood Cells (RBCs). As far as it concerns molecular MRI, among the many available biomarkers, α_vβ₃ integrins are the most investigated ones. The low expression of these targets makes mandatory the use of nano-sized systems endowed with the proper signal enhancing capabilities. A number of targeted nano-particles have been investigated including micelles, liposomes, iron oxides and perfluorocarbon containing systems. Finally, a growing attention is devoted to the design and testing of "theranostic" agents based on the exploitation of MRI to monitor drug delivery processes and therapeutic outcome.

99mTc-labeled bevacizumab for detecting atherosclerotic plaque linked to plaque neovascularization and monitoring antiangiogenic effects of atorvastatin treatment in ApoE-/- mice

Atherosclerotic neovascularization plays a significant role in plaque instability as it provides additional lipids and inflammatory mediators to lesions, and resulting in intraplaque hemorrhage. Vascular endothelial growth factor-A (VEGF-A) is considered the predominant proangiogenic factor in angiogenesis. Bevacizumab, a humanized monoclonal antibody, specifically binds to all VEGF-A isoforms with high affinity. Therefore, in this study, we designed ^99mTc-MAG₃-bevacizumab as a probe, and then investigated its usefulness as a new imaging agent for the detection of plaque neovessels, while also assessing the therapeutic effect of atorvastatin treatment. The ApoE^−/− mice treated with atorvastatin were used as the treatment group, and C57BL/6 J mice were selected as the control group. ^99mTc-MAG₃-bevacizumab uptake was visualized on atherosclerotic lesions by non-invasive in-vivo micro-SPECT/CT and ex-vivo BSGI planar imaging. The value of P/B in each part of the aorta of ApoE^−/− mice was higher than in the treatment group and the C57BL/6 J mice, which was confirmed by Oil Red O staining, CD31 staining and VEGF immunohistochemistry staining. ^99mTc-MAG₃-bevacizumab imaging allowed for the non-invasive diagnosis and assessment of plaque neovascularization. Furthermore, this probe may be used as a new molecular imaging agent to assess the antiangiogenic effect of atorvastatin.

Potential of α7 nicotinic acetylcholine receptor PET imaging in atherosclerosis

Atherosclerotic events are usually acute and often strike otherwise asymptomatic patients. Although multiple clinical risk factors have been associated with atherosclerosis, as of yet no further individual prediction can be made as to who will suffer from its consequences based on biomarker analysis or traditional imaging methods like CT, MRI or angiography. Previously, non-invasive imaging with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET was shown to potentially fill this niche as it offers high sensitive detection of metabolic processes associated with inflammatory changes in atherosclerotic plaques. However, ¹⁸F-FDG PET imaging of arterial vessels suffers from non-specificity and has still to be proven to reliably identify vulnerable plaques, carrying a high risk of rupture. Therefore, it may be regarded only as a secondary marker for monitoring treatment effects and it does not offer alternative treatment options or direct insight in treatment mechanisms. In this review, an overview is given of the current status and the potential of PET imaging of inflammation and angiogenesis in atherosclerosis in general and special emphasis is given to imaging of α7 nicotinic acetylcholine receptors (α7 nAChRs). Due to the gaps that still exist in our understanding of atherogenesis and the limitations of the available PET tracers, the search continues for a more specific radioligand, able to differentiate between stable atherosclerosis and plaques prone to rupture. The potential role of the α7 nAChR as imaging marker for plaque vulnerability is explored. Today, strong evidence exists that nAChRs are involved in the atherosclerotic disease process. They are suggested to mediate the deleterious effects of the major tobacco component, nicotine, a nAChR agonist. Mainly based on in vitro data, α7 nAChR stimulation might increase plaque burden via increased neovascularization. However, in animal studies, α7 nAChR manipulation appears to reduce plaque size due to its inhibitory effects on inflammatory cells. Thus, reliable identification of α7 nAChRs by in vivo imaging is crucial to investigate the exact role of α7 nAChR in atherosclerosis before any therapeutic approach in the human setting can be justified. In this review, we discuss the first experience with α7 nAChR PET tracers and developmental considerations regarding the "optimal" PET tracer to image vascular nAChRs.

Contrast agents for cardiovascular magnetic resonance imaging: an overview

Contrast agents for Cardiovascular Magnetic Resonance (CMR) play a major role in research and clinical cardiology.

CD200Fc attenuates inflammatory responses and maintains barrier function by suppressing NF-κB pathway in cigarette smoke extract induced endothelial cells

BACKGROUND

Recent evidence suggests that CD200 fusion protein (CD200Fc), a CD200R1 agonist may attenuate inflammatory responses in autoimmune diseases and neuro-degeneration. While, little is known about the function of CD200Fc in cigarette smoke extract (CSE)-induced mouse Cardiac Microvascular Endothelial Cells (mCMECs). The present study was designed to elucidate the effects of CD200Fc on CSE-induced vascular endothelial barrier (VEB) dysfunction and inflammatory responses, which is a highly clinically relevant model of smoking related cardiovascular diseases.

METHODS

mCMECs were pre-treated with 1, 10 and 100μg/ml CD200Fc for 24h respectively, and then treated with 250μg/ml CSE for different times (24h or 120min). The transepithelial electrical resistance (TEER) and transport of fluorescent markers were used to measure VEB function in CSE-induced mCMECs. Western blot and immunofluorescent staining analysis were used to detect the expression of tight junction proteins, such as Zona Occludens-1 (ZO-1) and Claudin-1 in CSE-induced mCMECs. We measured the expression of pro-inflammatory cytokines in CSE-induced mCMECs by using ELISA and RT-PCR. In addition, the NF-κB activity in CSE-induced mCMECs were investigated by using nuclear/cytosol fractionation and western blot analysis.

RESULTS

In vitro treatment with CSE increased the transport of fluorescent markers and decreased TEER levels in mCMECs, respectively, which were attenuated by CD200Fc (10 and 100μg/ml) pretreatment. The CSE-induced up-regulation of pro-inflammatory cytokines such as Cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), platelet endothelial cell adhesion molecule-1 (PECAM-1), vascular cell adhesion molecule-1 (ICAM-1), Prostaglandin E2 (PGE2), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and IL-8 in mCMECs was also abrogated by CD200Fc (10 and 100μg/ml) pretreatment. CD200Fc also inhibited CSE-induced nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation in mCMECs, such as inhibition of its DNA binding activity, phosphorylated expression, and translocation to nucleus.

CONCLUSION

Thus, CD200Fc exert anti-inflammatory effect and protect VEB function in CSE-induced mCMECs. The vasoprotective effects of CD200Fc may be specifically beneficial in pathophysiological conditions associated with smoking related cardiovascular diseases.