Leukocyte trafficking-associated vascular adhesion protein 1 is expressed and functionally active in atherosclerotic plaques

Association Between Vascular Adhesion Protein-1 (VAP-1) and MACE in Patients with Coronary Heart Disease: A Cohort Study

Background

Vascular adhesion protein-1 (VAP-1), an inflammation-inducible endothelial cell molecule, was reported to be implicated in a variety of cardiovascular diseases. However, the clinical significance of circulating VAP-1 levels in patients with coronary heart disease (CHD) remains less studied.

Patients and Methods

We retrospectively analyzed clinical data of 336 hospitalized patients in the Second Affiliated Hospital of Soochow University from May 2020 to September 2022, 174 of which were diagnosed with CHD. Serum VAP-1 was measured by enzyme-linked immunosorbent assay at enrollment. The primary end point of this study was the occurrence of major adverse cardiovascular events (MACE). The coronary stenosis and clinical manifestations of CHD were assessed and recorded from medical records or follow-up calls. The relevant results were obtained, and the reliability of the conclusions was verified through regression analysis, curve fitting, and survival curve.

Results

After adjusting for potential confounders, higher serum VAP-1 level was associated with increased risk of MACE in patients with CHD [(HR = 5.11, 95% CI = 1.02-25.59), (HR = 5.81, 95% CI = 1.16-29.11)]. The results of curve fitting and survival analysis were consistent with those of regression analysis. However, no significant association was observed between VAP-1 and MACE in the entire study population [(HR = 5.11, 95% CI = 0.41-1.93), (HR = 1.17, 95% CI = 0.52-2.62)]. Furthermore, the level of VAP-1 did not show a significant correlation with coronary stenosis and the clinical manifestations of CHD.

Conclusion

These findings suggested that CHD patients with higher serum levels of VAP-1 are at a higher risk of adverse cardiovascular outcomes.

Vascular adhesion protein-1-targeted PET imaging in autoimmune myocarditis

BACKGROUND

Vascular adhesion protein-1 (VAP-1) is an adhesion molecule and primary amine oxidase, and Gallium-68-labeled 1,4,7,10-tetraazacyclododecane-N,N',N″,N‴-tetra-acetic acid conjugated sialic acid-binding immunoglobulin-like lectin 9 motif containing peptide ([68Ga]Ga-DOTA-Siglec-9) is a positron emission tomography (PET) tracer targeting VAP-1. We evaluated the feasibility of PET imaging with [68Ga]Ga-DOTA-Siglec-9 for the detection of myocardial lesions in rats with autoimmune myocarditis.

METHODS

Rats (n = 9) were immunized twice with porcine cardiac myosin in complete Freund's adjuvant. Control rats (n = 6) were injected with Freund's adjuvant alone. On day 21, in vivo PET/computed tomography (CT) imaging with [68Ga]Ga-DOTA-Siglec-9 was performed, followed by ex vivo autoradiography, histology, and immunohistochemistry of tissue sections. In addition, myocardial samples from three patients with cardiac sarcoidosis were studied.

RESULTS

[68Ga]Ga-DOTA-Siglec-9 PET/CT images of immunized rats showed higher uptake in myocardial lesions than in myocardium outside lesions (SUVmean, 0.5 ± 0.1 vs 0.3 ± 0.1; P = .003) or control rats (SUVmean, 0.2 ± 0.03; P < .0001), which was confirmed by ex vivo autoradiography of tissue sections. Immunohistochemistry showed VAP-1-positive staining in lesions of rats with myocarditis and in patients with cardiac sarcoidosis.

CONCLUSION

VAP-1-targeted [68Ga]Ga-DOTA-Siglec-9 PET is a potential novel technique for the detection of myocardial lesions.

Update of Potential Biomarkers in Risk Prediction and Monitoring of Atherosclerosis in Systemic Lupus Erythematosus to Prevent Cardiovascular Disease

Systemic lupus erythematosus is a chronic connective tissue disease associated with an increased risk of premature atherosclerosis. It is estimated that approximately 10% of SLE patients develop significant atherosclerosis each year, which is responsible for premature cardiovascular disease that is largely asymptomatic. This review summarizes the most recent reports from the past few years on biomarkers of atherosclerosis in SLE, mainly focusing on immune markers. Persistent chronic inflammation of the vascular wall is an important cause of cardiovascular disease (CVD) events related to endothelial dysfunction, cell proliferation, impaired production and function of nitric oxide and microangiopathic changes. Studies on pathogenic immune mediators involved in atherosclerosis will be crucial research avenues for preventing CVD.

PET/MR imaging of inflammation in atherosclerosis

Myocardial infarction, stroke, mental disorders, neurodegenerative processes, autoimmune diseases, cancer and the human immunodeficiency virus impact the haematopoietic system, which through immunity and inflammation may aggravate pre-existing atherosclerosis. The interplay between the haematopoietic system and its modulation of atherosclerosis has been studied by imaging the cardiovascular system and the activation of haematopoietic organs via scanners integrating positron emission tomography and resonance imaging (PET/MRI). In this Perspective, we review the applicability of integrated whole-body PET/MRI for the study of immune-mediated phenomena associated with haematopoietic activity and cardiovascular disease, and discuss the translational opportunities and challenges of the technology.

Vascular adhesion protein-1 (VAP-1) in vascular inflammatory diseases

Summary: Vascular adhesion protein-1 (VAP-1) also known as amino oxidase copper containing 3 (AOC3) is a pro-inflammatory and versatile molecule with adhesive and enzymatic properties. VAP-1 is a primary amine oxidase belonging to the semicarbazide-sensitive amine oxidase (SSAO) family, which catalyzes the oxidation of primary amines leading to the production of ammonium, formaldehyde, methylglyoxal, and hydrogen peroxide. VAP-1 is mainly expressed by endothelial cells, smooth muscle cells, adipocytes and pericytes. It is involved in a repertoire of biological functions, e.g., immune cell extravasation, angiogenesis, and vascularization. Research into VAP-1 has intensified within the last decade on its role as a novel clinical biomarker and as a potential therapeutic target of vascular inflammatory disorders such as atherosclerosis, stroke, diabetes, neurovascular disorders (e.g., Alzheimer’s Disease), hepatic disease (e.g., non-alcoholic steatohepatitis), and skin conditions (e.g., psoriasis). This is the most up-to-date and comprehensive review on VAP-1 focusing on the translational aspects of VAP-1. Compared to recent reviews, our review provides novel insights on VAP-1 and heart failure, stroke and frailty, diabetes, endometriosis, osteoarthritis, COVID-19, conjunctivitis associated systemic lupus erythematosus, hematopoietic stem cells, gliomas, treatment of colorectal cancer with a novel VAP-1 inhibitor (U-V269), promoting recovery of motor functions and habit learning with a novel VAP-1 inhibitor (PXS-4681A), and 68Ga-DOTA-Siglec-9, a labelled peptide of Siglec-9 (a VAP-1 ligand), which appears to be a safe PET tracer for inflammation in rheumatoid arthritis. Finally, we present the emerging role of VAP-1 in pregnancy as a gatekeeper of immune cells, which are critical for spiral arterial remodeling, the deficiency of which could lead to vascular disorders of pregnancy such as preeclampsia. Future research should prioritize clinical trials on VAP-1 small-molecule inhibitors and monoclonal antibodies, thus, maximizing the potential of VAP-1 targeted therapy as well as research into sVAP-1 as a clinical biomarker of diseases and its prognosis.

Increased atherosclerotic plaque in AOC3 knock-out in ApoE−/− mice and characterization of AOC3 in atherosclerotic human coronary arteries

Introduction

Amine oxidase copper containing 3 (AOC3) displays adhesion between leukocytes and endothelial cells and enzymatic functions. Given its controversial role in atherogenesis, we proposed to investigate the involvement of AOC3 in the formation of atherosclerotic plaques in ApoE^−/−AOC3^−/− mice and human coronary arteries.

Methods

Lesions, contractile markers, and AOC3 were studied in aortic tissues from 15- and 25-week-old mice and different stages of human coronary atherosclerotic arteries by immunohistochemistry (IHC) and/or western blot. Human VSMCs, treated or not with LJP1586, an AOC3 inhibitor, were used to measure differentiation markers by qPCR. AOC3 co-localization with specific cell markers was studied by using confocal microscopy in mice and human samples.

Results

At 15 weeks old, the absence of AOC3 was associated with increased lesion size, α-SMA, and CD3 staining in the plaque independently of a cholesterol modification. At 25 weeks old, advanced plaques were larger with equivalent staining for α-SMA while CD3 increased in the media from ApoE^−/−AOC3^−/− mice. At both ages, the macrophage content of the lesion was not modified. Contractile markers decreased whereas MCP-1 appeared augmented only in the 15-week-old ApoE^−/−AOC3. AOC3 is mainly expressed by mice and human VSMC is slightly expressed by endothelium but not by macrophages.

Conclusion

AOC3 knock-out increased atherosclerotic plaques at an early stage related to a VSMC dedifferentiation associated with a higher T cells recruitment in plaques explained by the MCP-1 augmentation. This suggests that AOC3 may have an important role in atherosclerosis independent of its canonical inflammatory effect. The dual role of AOC3 impacts therapeutic strategies using pharmacological regulators of SSAO activity.

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.

Vascular adhesion protein-1 and microvascular diabetic complications

Vascular adhesion protein-1 (VAP-1) is a bifunctional protein that has the ability to catalyze the deamination of primary amines and is involved in the production of hydrogen peroxide, aldehydes, and advanced glycation end products (AGEs). VAP-1 is usually stored in intracellular vesicles of endothelial cells, smooth muscles, and adipocytes. It is responsible for leukocyte transmigration and adhesion. Overexpression of VAP-1 exacerbates oxidative stress and modulates a variety of inflammatory mediators linked with diabetic complications. Numerous studies have suggested the association of increased insulin levels with serum VAP-1 (sVAP-1). Preclinical research evidence suggests the increased activity of sVAP-1 in type 1 and 2 diabetes. Scientific reports on VAP-1 inhibitors have shown a reduction in severity in diabetic animal models. VAP-1 is a potential target of a therapeutically effective line of treatment for diabetes and diabetic complications such as nephropathy and retinopathy. The primary focus of this review is the role of VAP-1 in diabetes and its associated microvascular complications.

Advances in Radiopharmaceutical Sciences for Vascular Inflammation Imaging: Focus on Clinical Applications

Biomedical imaging technologies offer identification of several anatomic and molecular features of disease pathogenesis. Molecular imaging techniques to assess cellular processes in vivo have been useful in advancing our understanding of several vascular inflammatory diseases. For the non-invasive molecular imaging of vascular inflammation, nuclear medicine constitutes one of the best imaging modalities, thanks to its high sensitivity for the detection of probes in tissues. 2-[¹⁸F]fluoro-2-deoxy-d-glucose ([¹⁸F]FDG) is currently the most widely used radiopharmaceutical for molecular imaging of vascular inflammatory diseases such as atherosclerosis and large-vessel vasculitis. The combination of [¹⁸F]FDG and positron emission tomography (PET) imaging has become a powerful tool to identify and monitor non-invasively inflammatory activities over time but suffers from several limitations including a lack of specificity and avid background in different localizations. The use of novel radiotracers may help to better understand the underlying pathophysiological processes and overcome some limitations of [¹⁸F]FDG PET for the imaging of vascular inflammation. This review examines how [¹⁸F]FDG PET has given us deeper insight into the role of inflammation in different vascular pathologies progression and discusses perspectives for alternative radiopharmaceuticals that could provide a more specific and simple identification of pathologies where vascular inflammation is implicated. Use of these novel PET tracers could lead to a better understanding of underlying disease mechanisms and help inform the identification and stratification of patients for newly emerging immune-modulatory therapies. Future research is needed to realize the true clinical translational value of PET imaging in vascular inflammatory diseases.

Vascular Adhesion Protein-1 (VAP-1)/Semicarbazide-Sensitive Amine Oxidase (SSAO): A Potential Therapeutic Target for Atherosclerotic Cardiovascular Diseases

Vascular adhesion protein-1 (VAP-1) is a semicarbazide-sensitive amine oxidase (SSAO), whose enzymatic activity regulates the adhesion/exudation of leukocytes in/from blood vessels. Due to its abundant expressions in vascular systems and prominent roles in inflammations, increasing attentions have been paid to the roles of VAP-1/SSAO in atherosclerosis, a chronic vascular inflammation that eventually drives clinical cardiovascular events. Clinical studies have demonstrated a potential value of soluble VAP-1 (sVAP-1) for the diagnosis and prognosis of cardiovascular diseases. Recent findings revealed that VAP-1 is expressed in atherosclerotic plaques and treatment with VAP-1 inhibitors alleviates the progression of atherosclerosis. This review will focus on the roles of VAP-1/SSAO in the progression of atherosclerotic lesions and therapeutic potentials of VAP-1 inhibitors for cardiovascular diseases.

First-in-Humans Study of 68Ga-DOTA-Siglec-9, a PET Ligand Targeting Vascular Adhesion Protein 1

Sialic acid–binding immunoglubulinlike lectin 9 (Siglec-9) is a ligand of vascular adhesion protein 1. A ⁶⁸Ga-labeled peptide of Siglec-9, ⁶⁸Ga-DOTA-Siglec-9, holds promise as a novel PET tracer for imaging of inflammation. This first-in-humans study investigated the safety, tolerability, biodistribution, and radiation dosimetry of this radiopharmaceutical. Methods: Six healthy men underwent dynamic whole-body PET/CT. Serial venous blood samples were drawn from 1 to 240 min after intravenous injection of 162 ± 4 MBq of ⁶⁸Ga-DOTA-Siglec-9. In addition to γ-counting, the plasma samples were analyzed by high-performance liquid chromatography to detect intact tracer and radioactive metabolites. Radiation doses were calculated using the OLINDA/EXM software, version 2.2. In addition, a patient with early rheumatoid arthritis was studied with both ⁶⁸Ga-DOTA-Siglec-9 and ¹⁸F-FDG PET/CT to determine the ability of the new tracer to detect arthritis. Results:⁶⁸Ga-DOTA-Siglec-9 was well tolerated by all subjects. ⁶⁸Ga-DOTA-Siglec-9 was rapidly cleared from the blood circulation, and several radioactive metabolites were detected. The organs with the highest absorbed doses were the urinary bladder wall (0.38 mSv/MBq) and kidneys (0.054 mSv/MBq). The mean effective dose was 0.022 mSv/MBq (range, 0.020–0.024 mSv/MBq). Most importantly, however, ⁶⁸Ga-DOTA-Siglec-9 was comparable to ¹⁸F-FDG in detecting arthritis. Conclusion: Intravenous injection of ⁶⁸Ga-DOTA-Siglec-9 was safe and biodistribution was favorable for testing of the tracer in larger group of patients with rheumatoid arthritis, as is planned for the next phase of clinical trials. The effective radiation dose of ⁶⁸Ga-DOTA-Siglec-9 was within the same range as the effective radiation doses of other ⁶⁸Ga-labeled tracers. Injection of 150 MBq of ⁶⁸Ga-DOTA-Siglec-9 would expose a subject to 3.3 mSv. These findings support the possible repeated clinical use of ⁶⁸Ga-DOTA-Siglec-9, such as in trials to elucidate the treatment efficacy of novel drug candidates.

Molecular imaging of inflammation - Current and emerging technologies for diagnosis and treatment

Inflammation is a key factor in multiple diseases including primary immune-mediated inflammatory diseases e.g. rheumatoid arthritis but also, less obviously, in many other common conditions, e.g. cardiovascular disease and diabetes. Together, chronic inflammatory diseases contribute to the majority of global morbidity and mortality. However, our understanding of the underlying processes by which the immune response is activated and sustained is limited by a lack of cellular and molecular information obtained in situ. Molecular imaging is the visualization, detection and quantification of molecules in the body. The ability to reveal information on inflammatory biomarkers, pathways and cells can improve disease diagnosis, guide and monitor therapeutic intervention and identify new targets for research. The optimum molecular imaging modality will possess high sensitivity and high resolution and be capable of non-invasive quantitative imaging of multiple disease biomarkers while maintaining an acceptable safety profile. The mainstays of current clinical imaging are computed tomography (CT), magnetic resonance imaging (MRI), ultrasound (US) and nuclear imaging such as positron emission tomography (PET). However, none of these have yet progressed to routine clinical use in the molecular imaging of inflammation, therefore new approaches are required to meet this goal. This review sets out the respective merits and limitations of both established and emerging imaging modalities as clinically useful molecular imaging tools in addition to potential theranostic applications.

Human Copper-Containing Amine Oxidases in Drug Design and Development

Two members of the copper-containing amine oxidase family are physiologically important proteins: (1) Diamine oxidase (hDAO; AOC1) with a preference for diamines is involved in degradation of histamine and (2) Vascular adhesion protein-1 (hVAP-1; AOC3) with a preference for monoamines is a multifunctional cell-surface receptor and an enzyme. hVAP-1-targeted inhibitors are designed to treat inflammatory diseases and cancer, whereas the off-target binding of the designed inhibitors to hDAO might result in adverse drug reactions. The X-ray structures for both human enzymes are solved and provide the basis for computer-aided inhibitor design, which has been reported by several research groups. Although the putative off-target effect of hDAO is less studied, computational methods could be easily utilized to avoid the binding of VAP-1-targeted inhibitors to hDAO. The choice of the model organism for preclinical testing of hVAP-1 inhibitors is not either trivial due to species-specific binding properties of designed inhibitors and different repertoire of copper-containing amine oxidase family members in mammalian species. Thus, the facts that should be considered in hVAP-1-targeted inhibitor design are discussed in light of the applied structural bioinformatics and structural biology approaches.

Current and Emerging Preclinical Approaches for Imaging-Based Characterization of Atherosclerosis

Atherosclerotic plaques can remain quiescent for years, but become life threatening upon rupture or disruption, initiating clot formation in the vessel lumen and causing acute myocardial infarction and ischemic stroke. Whether and how a plaque ruptures is determined by its macroscopic structure and microscopic composition. Rupture-prone plaques usually consist of a thin fibrous cap with few smooth muscle cells, a large lipid core, a dense infiltrate of inflammatory cells, and neovessels. Such lesions, termed high-risk plaques, can remain asymptomatic until the thrombotic event. Various imaging technologies currently allow visualization of morphological and biological characteristics of high-risk atherosclerotic plaques. Conventional protocols are often complex and lack specificity for high-risk plaque. Conversely, new imaging approaches are emerging which may overcome these limitations. Validation of these novel imaging techniques in preclinical models of atherosclerosis is essential for effective translational to clinical practice. Imaging the vessel wall, as well as its biological milieu in small animal models, is challenging because the vessel wall is a small structure that undergoes continuous movements imposed by the cardiac cycle as it is adjacent to circulating blood. The focus of this paper is to provide a state-of-the-art review on techniques currently available for preclinical imaging of atherosclerosis in small animal models and to discuss the advantages and limitations of each approach.

Safety Study of Single-Dose Intravenously Administered DOTA-Siglec-9 Peptide in Sprague Dawley Rats

The peptide-based radioactive compound [68Ga]Ga-DOTA-Siglec-9 is a novel agent for imaging of inflammation with positron emission tomography. The drug target of [68Ga]Ga-DOTA-Siglec-9 is vascular adhesion protein 1. Previous studies have obtained promising results with [68Ga]Ga-DOTA-Siglec-9 in experimental animals. However, before taking this novel imaging agent into clinical trials, safety and toxicological studies need to be performed with the nonradioactive precursor compound DOTA-Siglec-9. This extended single-dose toxicity study was designed to provide information on the major toxic effects of DOTA-Siglec-9 and to indicate possible target organs after a single intravenous (iv) injection in rats. The study was performed using 60 adult Hsd: Sprague Dawley rats and included a control group and a treatment group to investigate the toxicity of DOTA-Siglec-9 solution at a final concentration of 0.2 mg/mL after a single iv injection of 582 µg/kg. The maximum dose tested was 1,000-fold the clinical dose on a mg/kg basis as indicated in European Medicines Agency International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use guideline M3(R2). The planned human clinical dose is approximately 0.582 µg of DOTA-Siglec-9 per kg of body mass. This study demonstrates that iv administration of DOTA-Siglec-9 at a dose of 582 µg/kg was well tolerated in rats and did not produce toxicologically significant adverse effects.

Vascular Adhesion Protein-1: A Cell Surface Amine Oxidase in Translation

Significance: Vascular adhesion protein-1 (VAP-1) is an ectoenzyme that oxidates primary amines in a reaction producing also hydrogen peroxide. VAP-1 on the blood vessel endothelium regulates leukocyte extravasation from the blood into tissues under physiological and pathological conditions. Recent Advances: Inhibition of VAP-1 by neutralizing antibodies and by several novel small-molecule enzyme inhibitors interferes with leukocyte trafficking and alleviates inflammation in many experimental models. Targeting of VAP-1 also shows beneficial effects in several other diseases, such as ischemia/reperfusion, fibrosis, and cancer. Moreover, soluble VAP-1 levels may serve as a new prognostic biomarker in selected diseases. Critical Issues: Understanding the contribution of the enzyme activity-independent and enzyme activity-dependent functions, which often appear to be mediated by the hydrogen peroxide production, in the VAP-1 biology will be crucial. Similarly, there is a pressing need to understand which of the VAP-1 functions are regulated through the modulation of leukocyte trafficking, and what is the role of VAP-1 synthesized in adipose and smooth muscle cells. Future Directions: The specificity and selectivity of new VAP-1 inhibitors, and their value in animal models under therapeutic settings need to be addressed. Results from several programs studying the therapeutic potential of VAP-1 inhibition, which now are in clinical trials, will reveal the relevance of this amine oxidase in humans.

Inhibition of semicarbazide-sensitive amine oxidase reduces atherosclerosis in apolipoprotein E-deficient mice

Inflammation, oxidative stress, and formation of advanced glycated end products (AGEs) and advanced lipoxidation end products (ALEs) are important for atherosclerosis. Vascular adhesion protein-1 (VAP-1) participates in inflammation and has semicarbazide-sensitive amine oxidase (SSAO) activity, which catalyzes oxidative deamination to produce hydrogen peroxide and aldehydes, leading to generation of AGEs and ALEs. However, the effect of VAP-1/SSAO inhibition on atherosclerosis remains controversial, and no studies used coronary angiography to evaluate if plasma VAP-1/SSAO is a biomarker for coronary artery disease (CAD). Here, we examined if plasma VAP-1/SSAO is a biomarker for CAD diagnosed by coronary angiography in humans and investigated the effect of VAP-1/SSAO inhibition by a specific inhibitor PXS-4728A on atherosclerosis in cell and animal models. In the study, VAP-1/SSAO expression was increased in plaques in humans and in apolipoprotein E (ApoE)-deficient mice, and colocalized with vascular endothelial cells and smooth muscle cells (SMCs). Patients with CAD had higher plasma VAP-1/SSAO than those without CAD. Plasma VAP-1/SSAO was positively associated with the extent of CAD. In ApoE-deficient mice, VAP-1/SSAO inhibition reduced atheroma and decreased oxidative stress. VAP-1/SSAO inhibition attenuated the expression of adhesion molecules, chemoattractant proteins, and proinflammatory cytokines in the aorta, and suppressed monocyte adhesion and transmigration across human umbilical vein endothelial cells. Consequently, the expression of markers for macrophage recruitment and activation in plaques was decreased by VAP-1/SSAO inhibition. Besides, VAP-1/SSAO inhibition suppressed proliferation and migration of A7r5 SMC. Our data suggest that plasma VAP-1/SSAO is a novel biomarker for the presence and the extent of CAD in humans. VAP-1/SSAO inhibition by PXS-4728A is a potential treatment for atherosclerosis.

Inhibition of Semicarbazide-sensitive Amine Oxidase Reduces Atherosclerosis in Cholesterol-fed New Zealand White Rabbits

Inflammation, oxidative stress, and the formation of advanced glycated end-products (AGEs) are important components of atherosclerosis. Vascular adhesion protein-1 (VAP-1) participates in inflammation. Its enzymatic activity, semicarbazide-sensitive amine oxidase (SSAO), can catalyze oxidative deamination reactions to produce hydrogen peroxide and aldehydes, leading to the subsequent generation of AGEs. This study aimed to investigate the effect of VAP-1/SSAO inhibition on atherosclerosis. In our study, immunohistochemical staining showed that atherosclerotic plaques displayed higher VAP-1 expression than normal arterial walls in apolipoprotein E-deficient mice, cholesterol-fed New Zealand White rabbits and humans. In cholesterol-fed rabbits, VAP-1 was expressed on endothelial cells and smooth muscle cells in the thickened intima of the aorta. Treatment with PXS-4728A, a selective VAP-1/SSAO inhibitor, in cholesterol-fed rabbits significantly decreased SSAO-specific hydrogen peroxide generation in the aorta and reduced atherosclerotic plaques. VAP-1/SSAO inhibition also lowered blood low-density lipoprotein cholesterol, reduced the expression of adhesion molecules and inflammatory cytokines, suppressed recruitment and activation of macrophages, and decreased migration and proliferation of SMC. In conclusion, VAP-1/SSAO inhibition reduces atherosclerosis and may act through suppression of several important mechanisms for atherosclerosis.

Proteolytic cleavage of vascular adhesion protein-1 induced by vascular endothelial growth factor in retinal capillary endothelial cells

PURPOSE

To investigate the mechanism of soluble vascular adhesion protein-1 (sVAP-1) accumulation induced by vascular endothelial growth factor (VEGF) in the vitreous of patients with diabetic retinopathy (DR).

STUDY DESIGN

Experimental.

METHODS

Protein levels of sVAP-1 and N epsilon-(hexanoyl)lysine (HEL), an oxidative stress marker, in the vitreous samples from patients with proliferative diabetic retinopathy (PDR) with or without intravitreal bevacizumab (IVB) injection were determined by ELISA. The effect of VEGF on both mRNA expression of Vap-1 and secretion of sVAP-1 in rat retinal capillary endothelial cells (TR-iBRB2) was analyzed by real-time PCR and western blotting, respectively. In addition, the impact of VEGF on production and activation ratios of matrix metalloproteinase (MMP)-2 and MMP-9 was examined by gelatin zymography. Hydrogen peroxide production and reactive oxygen species (ROS) levels were assessed in the supernatants of TR-iBRB2 cells treated with VEGF.

RESULTS

IVB injection decreased vitreous levels of sVAP-1 and HEL in patients with PDR. VEGF stimulation released sVAP-1 protein from TR-iBRB2 cells as a consequence of membrane-anchored VAP-1 shedding by MMP-2 and MMP-9. In addition, VEGF increased hydrogen peroxide generation and ROS augmentation through spermine oxidation by sVAP-1 as semicarbazide-sensitive amine oxidase (SSAO) in the supernatant of cultured endothelial cells.

CONCLUSIONS

The current data demonstrate that proangiogenic factor VEGF induces sVAP-1 release from retinal capillary endothelial cells and facilitates hydrogen peroxide generation via enzymatic property of sVAP-1, followed by the increase of oxidative stress, one of the crucial factors in the pathogenesis of DR.

Exploring Alternative Radiolabeling Strategies for Sialic Acid-Binding Immunoglobulin-Like Lectin 9 Peptide: [68Ga]Ga- and [18F]AlF-NOTA-Siglec-9

Amino acid residues 283–297 from sialic acid-binding immunoglobulin-like lectin 9 (Siglec-9) form a cyclic peptide ligand targeting vascular adhesion protein-1 (VAP-1). VAP-1 is associated with the transfer of leukocytes from blood to tissues upon inflammation. Therefore, analogs of Siglec-9 peptide are good candidates for visualizing inflammation non-invasively using positron emission tomography (PET). Gallium-68-labeled 1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid (DOTA)-conjugated Siglec-9 has been evaluated extensively for this purpose. Here, we explored two alternative strategies for radiolabeling Siglec-9 peptide using a 1,4,7-triazacyclononane-triacetic acid (NOTA)-chelator to bind [⁶⁸Ga]Ga or [¹⁸F]AlF. The radioligands were evaluated by in vivo PET imaging and ex vivo γ-counting of turpentine-induced sterile skin/muscle inflammation in Sprague-Dawley rats. Both tracers showed clear accumulation in the inflamed tissues. The whole-body biodistribution patterns of the tracers were similar.

Prospective of 68Ga Radionuclide Contribution to the Development of Imaging Agents for Infection and Inflammation

During the last decade, the utilization of ⁶⁸Ga for the development of imaging agents has increased considerably with the leading position in the oncology. The imaging of infection and inflammation is lagging despite strong unmet medical needs. This review presents the potential routes for the development of ⁶⁸Ga-based agents for the imaging and quantification of infection and inflammation in various diseases and connection of the diagnosis to the treatment for the individualized patient management.

Adventures in radiosynthesis of clinical grade [68Ga]Ga-DOTA-Siglec-9

[⁶⁸Ga]Ga-DOTA-Siglec-9 is the first vascular adhesion protein-1 targeting radiopharmaceutical for positron emission tomography imaging of inflammation, and here we present its long-awaited clinical grade radiosynthesis.

Comparison of 68Ga-DOTA-Siglec-9 and 18F-Fluorodeoxyribose-Siglec-9: Inflammation Imaging and Radiation Dosimetry

Sialic acid-binding immunoglobulin-like lectin 9 (Siglec-9) is a ligand of inflammation-inducible vascular adhesion protein-1 (VAP-1). We compared ⁶⁸Ga-DOTA- and ¹⁸F-fluorodeoxyribose- (FDR-) labeled Siglec-9 motif peptides for PET imaging of inflammation. Methods. Firstly, we examined ⁶⁸Ga-DOTA-Siglec-9 and ¹⁸F-FDR-Siglec-9 in rats with skin/muscle inflammation. We then studied ¹⁸F-FDR-Siglec-9 for the detection of inflamed atherosclerotic plaques in mice and compared it with previous ⁶⁸Ga-DOTA-Siglec-9 results. Lastly, we estimated human radiation dosimetry from the rat data. Results. In rats, ⁶⁸Ga-DOTA-Siglec-9 (SUV, 0.88 ± 0.087) and ¹⁸F-FDR-Siglec-9 (SUV, 0.77 ± 0.22) showed comparable (P = 0.29) imaging of inflammation. In atherosclerotic mice, ¹⁸F-FDR-Siglec-9 detected inflamed plaques with a target-to-background ratio (1.6 ± 0.078) similar to previously tested ⁶⁸Ga-DOTA-Siglec-9 (P = 0.35). Human effective dose estimates for ⁶⁸Ga-DOTA-Siglec-9 and ¹⁸F-FDR-Siglec-9 were 0.024 and 0.022 mSv/MBq, respectively. Conclusion. Both tracers are suitable for PET imaging of inflammation. The easier production and lower cost of ⁶⁸Ga-DOTA-Siglec-9 present advantages over ¹⁸F-FDR-Siglec-9, indicating it as a primary choice for clinical studies.

Identification of Key Pathways and Genes in Advanced Coronary Atherosclerosis Using Bioinformatics Analysis

Background

Coronary artery atherosclerosis is a chronic inflammatory disease. This study aimed to identify the key changes of gene expression between early and advanced carotid atherosclerotic plaque in human.

Methods

Gene expression dataset GSE28829 was downloaded from Gene Expression Omnibus (GEO), including 16 advanced and 13 early stage atherosclerotic plaque samples from human carotid. Differentially expressed genes (DEGs) were analyzed.

Results

42,450 genes were obtained from the dataset. Top 100 up- and downregulated DEGs were listed. Functional enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) identification were performed. The result of functional and pathway enrichment analysis indicted that the immune system process played a critical role in the progression of carotid atherosclerotic plaque. Protein-protein interaction (PPI) networks were performed either. Top 10 hub genes were identified from PPI network and top 6 modules were inferred. These genes were mainly involved in chemokine signaling pathway, cell cycle, B cell receptor signaling pathway, focal adhesion, and regulation of actin cytoskeleton.

Conclusion

The present study indicated that analysis of DEGs would make a deeper understanding of the molecular mechanisms of atherosclerosis development and they might be used as molecular targets and diagnostic biomarkers for the treatment of atherosclerosis.

Monitoring inflammation injuries in the progression of atherosclerosis with contrast enhanced ultrasound molecular imaging

Purpose

The upregulation of vascular cell adhesion molecule-1(VCAM-1) on vascular endothelium plays a great role in the progression of atherosclerosis (AS). In this study, ultrasound molecular imaging was performed to monitor the inflammation injuries in the onset and progression of atherosclerosis with microbubbles targeted to VCAM-1.

Methods

Mice deficient for the apolipoprotein E (ApoE^-/-mice) with high-cholesterol diet were studied as an age-dependent model of atherosclerosis. At 8, 16, 24, and 32 weeks of age, contrast enhanced ultrasound (CEU) molecular imaging of proximal ascending aorta was performed with microbubbles targeted to VCAM-1. Plaque size, monocytes infiltration and the expression of VCAM-1 in the proximal ascending aorta were assessed by histology and western blot analysis, separately.

Results

In ApoE^-/- mice, molecular imaging for VCAM-1 detected selective signal enhancement (P<0.01 versus non-targeted microbubbles) at all ages of ApoE^-/- mice. Moreover, signals from targeted microbubbles increased from 8wks to 32wks age (P<0.05 for trend) in ApoE^-/- mice, indicating the upregulation of VCAM-1 with the progression of atherosclerosis. Consistent with CEU imaging results, both western blot analysis and immunohistochemistry revealed the expression of VCAM-1 and monocytes infiltration were age-dependent in ApoE^-/- mice.

Conclusions

CEU molecular imaging can be used to noninvasively detect the VCAM-1 expression on the endothelium in the progression of atherosclerosis. By investigating specific molecular biomarkers, it could help to monitor the inflammation and the progression of AS, which may in some extent contribute to the prediction of vulnerable plaque.

Exploring the radiosynthesis and in vitro characteristics of [68 Ga]Ga-DOTA-Siglec-9

Vascular adhesion protein 1 is a leukocyte homing-associated glycoprotein, which upon inflammation rapidly translocates from intracellular sources to the endothelial cell surface. It has been discovered that the cyclic peptide residues 283-297 of sialic acid-binding IgG-like lectin 9 (Siglec-9) "CARLSLSWRGLTLCPSK" bind to vascular adhesion protein 1 and hence makes the radioactive analogues of this compound ([⁶⁸ Ga]Ga-DOTA-Siglec-9) interesting as a noninvasive visualizing marker of inflammation. Three different approaches to the radiosynthesis of [⁶⁸ Ga]Ga-DOTA-Siglec-9 are presented and compared with previously published methods. A simple, robust radiosynthesis of [⁶⁸ Ga]Ga-DOTA-Siglec-9 with a yield of 62% (non decay-corrected) was identified, and it had a radiochemical purity >98% and a specific radioactivity of 35 MBq/nmol. Furthermore, the protein binding and stability of [⁶⁸ Ga]Ga-DOTA-Siglec-9 were analyzed in vitro in mouse, rat, rabbit, pig, and human plasma and compared with in vivo pig results. The plasma in vitro protein binding of [⁶⁸ Ga]Ga-DOTA-Siglec-9 was the lowest in the pig followed by rabbit, human, rat, and mouse. It was considerably higher in the in vivo pig experiments. The in vivo stability in pigs was lower than the in vitro stability. Despite considerable species differences, the observed characteristics of [⁶⁸ Ga]Ga-DOTA-Siglec-9 are suitable as a positron emission tomography tracer.

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.