Vascular adhesion protein-1 is involved in both acute and chronic inflammation in the mouse

Vascular-adhesion protein 1 in giant cell arteritis and polymyalgia rheumatica

Vascular adhesion protein-1 (VAP-1) is a type 2 transmembrane sialoglycoprotein with oxidative deamination functionality, encoded by the amine oxidase copper-containing 3 (AOC3) gene. VAP-1 is widely expressed across various tissues, particularly in highly vascularized tissues and organs essential for lymphocyte circulation. In the vascular system, VAP-1 is predominantly found in vascular smooth muscle cells and endothelial cells, with higher expression levels in vascular smooth muscle cells. Under inflammatory conditions, VAP-1 rapidly translocates to the endothelial cell surface, facilitating leukocyte adhesion and migration through interactions with specific ligands, such as sialic acid-binding immunoglobulin-type lectins (Siglec)-9 on neutrophils and monocytes, and Siglec-10 on B cells, monocytes, and eosinophils. This interaction is crucial for leukocyte transmigration into inflamed tissues. Furthermore, VAP-1's enzymatic activity generates hydrogen peroxide and advanced glycation end-products, contributing to cytotoxic damage and vascular inflammation. In this context, the soluble form of VAP-1 (sVAP-1), produced by matrix metalloproteinase cleavage from its membrane-bound counterpart, also significantly influences leukocyte migration. This review aims to elucidate the multifaceted pathophysiological roles of VAP-1 in vascular inflammation, particularly in giant cell arteritis (GCA) and associated polymyalgia rheumatica (PMR). By exploring its involvement in immune cell adhesion, migration, and its enzymatic contributions to oxidative stress and tissue damage, we investigate the importance of VAP-1 in GCA. Additionally, we discuss recent advancements in imaging techniques targeting VAP-1, such as [68Ga]Ga-DOTA-Siglec-9 PET/CT, which have provided new insights into VAP-1's role in GCA and PMR. Overall, understanding VAP-1's comprehensive roles could pave the way for improved strategies in managing these conditions.

The role of vascular adhesion protein-1 in diabetes and diabetic complications

Vascular adhesion protein-1 (VAP-1) plays a dual role with its adhesive and enzymatic properties, facilitating leukocyte migration to sites of inflammation and catalyzing the breakdown of primary amines into harmful by-products, which are linked to diabetic complications. Present in various tissues, VAP-1 also circulates in a soluble form in the bloodstream. Diabetes is associated with several complications such as cardiovascular disease, retinopathy, nephropathy, and neuropathy, significantly contributing to disability and mortality. These complications arise from hyperglycemia-induced oxidative stress, inflammation, and the formation of advanced glycation end-products (AGEs). Earlier research, including our own from the 1990s and early 2000s, has underscored the critical role of VAP-1 in these pathological processes, prompting extensive investigation into its contribution to diabetic complications. In this review, we examine the involvement of VAP-1 in diabetes and its complications, alongside its link to other conditions related to diabetes, such as cancer and metabolic dysfunction-associated fatty liver disease. We also explore the utility of soluble VAP-1 as a biomarker for diabetes, its complications, and other related conditions. Since the inhibition of VAP-1 to treat diabetic complications is a novel and promising treatment option, further studies are needed to translate the beneficial effect of VAP-1 inhibitors observed in animal studies to clinical trials recruiting human subjects. Besides, future studies should focus on using serum sVAP-1 levels for risk assessment in diabetic patients, identifying those who need intensive glycemic control, and determining the patient population that would benefit most from VAP-1 inhibitor therapies.

Detection of Intestinal Inflammation by Vascular Adhesion Protein-1-Targeted [68Ga]Ga-DOTA-Siglec-9 Positron Emission Tomography in Murine Models of Inflammatory Bowel Disease

PURPOSE

Inflammatory bowel disease (IBD) can be imaged with positron emission tomography (PET), but existing PET radiopharmaceuticals have limited diagnostic accuracy. Vascular adhesion protein-1 (VAP-1) is an endothelial cell surface molecule that controls leukocyte extravasation into sites of inflammation. However, the role of inflammation-induced VAP-1 expression in IBD is still unclear. Therefore, this study investigated the utility of VAP-1-targeted [68Ga]Ga-DOTA-Siglec-9 positron emission tomography/computed tomography (PET/CT) for assessing inflammation in two mouse models of IBD.

PROCEDURES

Studies were performed using K8-/- mice that develop a chronic colitis-phenotype and C57Bl/6NCrl mice with acute intestinal inflammation chemically-induced using 2.5% dextran sodium sulfate (DSS) in drinking water. In both diseased and control mice, uptake of the VAP-1-targeting peptide [68Ga]Ga-DOTA-Siglec-9 was assessed in intestinal regions of interest using in vivo PET/CT, after which ex vivo gamma counting, digital autoradiography, and histopathological analyses were performed. Immunofluorescence staining was performed to determine VAP-1-expression in the intestine, including in samples from patients with ulcerative colitis.

RESULTS

Intestinal inflammation could be visualized by [68Ga]Ga-DOTA-Siglec-9 PET/CT in two murine models of IBD. In both models, the in vivo PET/CT and ex vivo studies of [68Ga]Ga-DOTA-Siglec-9 uptake were significantly higher than in control mice. The in vivo uptake was increased on average 1.4-fold in the DSS model and 2.0-fold in the K8-/- model. Immunofluorescence staining revealed strong expression of VAP-1 in the inflamed intestines of both mice and patients.

CONCLUSIONS

This study suggests that the VAP-1-targeting [68Ga]Ga-DOTA-Siglec-9 PET tracer is a promising tool for non-invasive imaging of intestinal inflammation. Future studies in patients with IBD and evaluation of the potential value of [68Ga]Ga-DOTA-Siglec-9 in diagnosis and monitoring of the disease are warranted.

Serum vascular adhesion protein-1 is associated with twelve-year risk of incident cancer, cancer mortality, and all-cause mortality: a community-based cohort study

Background

Vascular adhesion protein-1 (VAP-1), a dual-function glycoprotein, has been reported to play a crucial role in inflammation and tumor progression. We conducted a community-based cohort study to investigate whether serum VAP-1 could be a potential biomarker for predicting incident cancers and mortality.

Method

From 2006 to 2018, we enrolled 889 cancer-free subjects at baseline. Serum VAP-1 levels were measured using a time-resolved immunofluorometric assay. Cancer and vital status of the participants were obtained by linking records with the computerized cancer registry and death certificates in Taiwan.

Results

During a median follow-up of 11.94 years, 69 subjects developed incident cancers and 66 subjects died, including 29 subjects who died from malignancy. Subjects in the highest tertile of serum VAP-1 had a significantly higher risk of cancer incidence (p=0.0006), cancer mortality (p=0.0001), and all-cause mortality (p=0.0002) than subjects in the other tertiles. The adjusted hazard ratios per one standard deviation increase in serum VAP-1 concentrations were 1.28 for cancer incidence (95% CI=1.01-1.62), 1.60 for cancer mortality (95% CI=1.14-2.23), and 1.38 for all-cause mortality (95% CI=1.09-1.75). The predictive performance of serum VAP-1 was better than that of gender, smoking, body mass index, hypertension, diabetes, and estimated glomerular filtration rate but lower than that of age for cancer incidence, cancer mortality, and all-cause mortality, as evidenced by higher increments in concordance statistics and area under the receiver operating characteristic curve.

Conclusion

Serum VAP-1 levels are associated with a 12-year risk of incident cancer, cancer mortality, and all-cause mortality in a general population.

Prognosis-related metabolic genes in the development of colorectal cancer progress and perspective

Colorectal cancer (CRC) is one of the most commonplace malignant tumors in the world. The occurrence and development of CRC are involved in numerous events. Metabolic reprogramming is one of the hallmarks of cancer and is convoluted and associated with carcinogenesis. Lots of metabolic genes are involved in the occurrence and progression of CRC. Study methods combining tumor genomics and metabolomics are more likely to explore this field in depth. In this mini-review, we make the latest progress and future prospects into the different molecular mechanisms of seven prognosis-related metabolic genes, we screened out in previous research, involved in the occurrence and development of CRC.

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.

[68Ga]Ga-DOTA-Siglec-9 Detects Pharmacodynamic Changes of FAP-Targeted IL2 Variant Immunotherapy in B16-FAP Melanoma Mice

Vascular adhesion protein-1 (VAP-1) is an inflammation-inducible adhesion molecule, which supports contact between leukocytes and inflamed endothelium. There is evidence that VAP-1 is involved in the recruitment of leukocytes to melanoma tumors. Interleukin-2 (IL-2)-based immunotherapy is an efficient therapy that promotes immune system activity against cancers but is associated with toxicity. In the present study, we evaluated the feasibility of PET/CT imaging using the radiotracer [⁶⁸Ga]Ga-DOTA-Siglec-9, which is targeted to VAP-1, to monitor pharmacodynamic effects of a novel FAP-IL2v immunocytokine (a genetically engineered variant of IL-2 fused with fibroblast activation protein) in the B16-FAP melanoma model. At 9 days after the inoculation of B16-FAP melanoma cells, mice were studied with [⁶⁸Ga]Ga-DOTA-Siglec-9 PET/CT as a baseline measurement. Immediately after baseline imaging, mice were treated with FAP-IL2v or vehicle, and treatment was repeated 3 days later. Subsequent PET/CT imaging was performed 3, 5, and 7 days after baseline imaging. In addition to in vivo PET imaging, ex vivo autoradiography, histology, and immunofluorescence staining were performed on excised tumors. B16-FAP tumors were clearly detected with [⁶⁸Ga]Ga-DOTA-Siglec-9 PET/CT during the follow-up period, without differences in tumor volume between FAP-IL2v-treated and vehicle-treated groups. Tumor-to-muscle uptake of [⁶⁸Ga]Ga-DOTA-Siglec-9 was significantly higher in the FAP-IL2v-treated group than in the vehicle-treated group 7 days after baseline imaging, and this was confirmed by tumor autoradiography analysis. FAP-IL2v treatment did not affect VAP-1 expression on the tumor vasculature. However, FAP-IL2v treatment increased the number of CD8⁺ T cells and natural killer cells in tumors. The present study showed that [⁶⁸Ga]Ga-DOTA-Siglec-9 can detect B16-FAP tumors and allows monitoring of FAP-IL2v treatment.

Downregulation of VAP-1 in OSCC suppresses tumor growth and metastasis via NF-κB/IL-8 signaling and reduces neutrophil infiltration

BACKGROUND

Vascular adhesion protein-1 (VAP-1) is believed to play a role in inflammation. Studies have suggested that VAP-1-mediated activation of inflammation is dependent on NF-κB, leading to secretion of the interleukin(IL)-8; however, no reports have addressed the association between VAP-1 and NF-κB/IL-8 signaling in oral squamous cell carcinoma (OSCC). This study aimed to investigate the role of VAP-1 in OSCC and further explore whether VAP-1 is involved in the regulation of neutrophil infiltration in the tumor microenvironment (TME).

METHODS

Immunochemistry staining was used to observe VAP-1 expression. CCK-8 and Transwell assays were used to measure cell proliferation, migration, and invasion. OSCC xenograft mouse models were used for in vivo verification of the VAP-1 function. The expression of NF-κB and IL-8 were determined by qRT-PCR and western blot. ELISA for IL-8 was also conducted. The relationship between VAP-1 expression and neutrophil infiltration was analyzed by immunofluorescence.

RESULTS

VAP-1 was overexpressed in human OSCC tissues. Downregulation of VAP-1 suppressed OSCC cells proliferation, migration, and invasion in vitro and inhibited tumor proliferation and metastasis in vivo. Additionally, downregulation of VAP-1 inhibited NF-κB/IL-8 signaling in vitro and in vivo. VAP-1 expression was positively correlated with neutrophil infiltration in human OSCC tissues. Moreover, blocking VAP-1 decreased neutrophil infiltration by reducing IL-8 production.

CONCLUSIONS

VAP-1 downregulation in OSCC suppresses tumor growth and metastasis by inhibiting NF-κB/IL-8 signaling and reducing neutrophil infiltration in the TME, suggesting that VAP-1 may be a potential therapeutic target for OSCC.

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.

Role of Hydrogen Sulfide, Substance P and Adhesion Molecules in Acute Pancreatitis

Inflammation is a natural response to tissue injury. Uncontrolled inflammatory response leads to inflammatory disease. Acute pancreatitis is one of the main reasons for hospitalization amongst gastrointestinal disorders worldwide. It has been demonstrated that endogenous hydrogen sulfide (H₂S), a gasotransmitter and substance P, a neuropeptide, are involved in the inflammatory process in acute pancreatitis. Cell adhesion molecules (CAM) are key players in inflammatory disease. Immunoglobulin (Ig) gene superfamily, selectins, and integrins are involved at different steps of leukocyte migration from blood to the site of injury. When the endothelial cells get activated, the CAMs are upregulated which leads to them interacting with leukocytes. This review summarizes our current understanding of the roles H₂S, substance P and adhesion molecules play in acute pancreatitis.

Amine oxidase copper-containing 3 (AOC3) inhibition: a potential novel target for the management of diabetic retinopathy

Background

Diabetic retinopathy (DR), a microvascular complication of diabetes, is the leading cause of visual impairment in people aged 20–65 years and can go undetected until vision is irreversibly lost. There is a need for treatments for non-proliferative diabetic retinopathy (NPDR) which, in comparison with current intravitreal (IVT) injections, offer an improved risk–benefit ratio and are suitable for the treatment of early stages of disease, during which there is no major visual impairment. Efficacious systemic therapy for NPDR, including oral treatment, would be an important and convenient therapeutic approach for patients and physicians and would reduce treatment burden. In this article, we review the rationale for the investigation of amine oxidase copper-containing 3 (AOC3), also known as semicarbazide-sensitive amine oxidase and vascular adhesion protein 1 (VAP1), as a novel target for the early treatment of moderate to severe NPDR. AOC3 is a membrane-bound adhesion protein that facilitates the binding of leukocytes to the retinal endothelium. Adherent leukocytes reduce blood flow and in turn rupture blood vessels, leading to ischemia and edema. AOC3 inhibition reduces leukocyte recruitment and is predicted to decrease the production of reactive oxygen species, thereby correcting the underlying hypoxia, ischemia, and edema seen in DR, as well as improving vascular function.

Conclusion

There is substantial unmet need for convenient, non-invasive treatments targeting moderately severe and severe NPDR to reduce progression and preserve vision. The existing pharmacotherapies (IVT corticosteroids and IVT anti-vascular endothelial growth factor-A) target inflammation and angiogenesis, respectively. Unlike these treatments, AOC3 inhibition is predicted to address the underlying hypoxia and ischemia seen in DR. AOC3 inhibitors represent a promising therapeutic strategy for treating patients with DR and could offer greater choice and reduce treatment burden, with the potential to improve patient compliance.

SSAO/VAP-1 in Cerebrovascular Disorders: A Potential Therapeutic Target for Stroke and Alzheimer's Disease

The semicarbazide-sensitive amine oxidase (SSAO), also known as vascular adhesion protein-1 (VAP-1) or primary amine oxidase (PrAO), is a deaminating enzyme highly expressed in vessels that generates harmful products as a result of its enzymatic activity. As a multifunctional enzyme, it is also involved in inflammation through its ability to bind and promote the transmigration of circulating leukocytes into inflamed tissues. Inflammation is present in different systemic and cerebral diseases, including stroke and Alzheimer’s disease (AD). These pathologies show important affectations on cerebral vessels, together with increased SSAO levels. This review summarizes the main roles of SSAO/VAP-1 in human physiology and pathophysiology and discusses the mechanisms by which it can affect the onset and progression of both stroke and AD. As there is an evident interrelationship between stroke and AD, basically through the vascular system dysfunction, the possibility that SSAO/VAP-1 could be involved in the transition between these two pathologies is suggested. Hence, its inhibition is proposed to be an interesting therapeutical approach to the brain damage induced in these both cerebral pathologies.

Protective effects of the novel amine-oxidase inhibitor multi-target drug SZV 1287 on streptozotocin-induced beta cell damage and diabetic complications in rats

Diabetes mellitus is a common metabolic disease leading to hyperglycemia due to insufficient pancreatic insulin production or effect. Amine oxidase copper containing 3 (AOC3) is an enzyme that belongs to the semicarbazide-sensitive amine oxidase family, which may be a novel therapeutic target to treat diabetic complications. We aimed to explore the effects of AOC3 inhibition and to test the actions of our novel AOC3 inhibitor multi-target drug candidate, SZV 1287, compared to a selective reference compound, LJP 1207, in an 8-week long insulin-controlled streptozotocin (STZ)-induced (60 mg/kg i.p.) rat diabetes model. Both AOC3 inhibitors (20 mg/kg, daily s.c. injections) were protective against STZ-induced pancreatic beta cell damage determined by insulin immunohistochemistry and radioimmunoassay, neuropathic cold hypersensitivity measured by paw withdrawal latency decrease from 0 °C water, and retinal dysfunction detected by electroretinography. SZV 1287 showed greater inhibitory effects on beta cell damage, and reduced retinal apoptosis shown by histochemistry. Mechanical hypersensitivity measured by aesthesiometry, cardiac dysfunction and nitrosative stress determined by echocardiography and immunohistochemistry/Western blot, respectively, serum Na⁺, K⁺, fructosamine, and urine microalbumin, creatinine, total protein/creatinine ratio alterations did not develop in response to diabetes. None of these parameters were influenced by the treatments except for SZV 1287 reducing serum fructosamine and LJP 1207 increasing urine creatinine. We provide the first evidence for protective effects of AOC3 inhibition on STZ-induced pancreatic beta cell damage, neuropathic cold hypersensitivity and diabetic retinal dysfunction. Long-term treatment with our novel multi-target analgesic candidate, SZV 1287, is safe and effective also under diabetic conditions.

Carotid imaging changes and serum IL-1β, sICAM-1, and sVAP-1 levels in benign paroxysmal positional vertigo

Benign paroxysmal positional vertigo (BPPV) is the most common cause of vertigo. This study was performed to evaluate serum levels of inflammatory factors and changes in B-mode carotid ultrasound findings in patients with BPPV. The study population consisted of 90 BPPV patients and 90 age- and sex-matched controls. ELISA was used to compare the levels of inflammatory factors, such as interleukin-1β (IL-1β), tumor necrosis factor-alpha (TNF-α), soluble intercellular adhesion molecule-1 (sICAM-1), prostaglandin-E2 (PG-E2), and soluble vascular adhesion protein-1 (sVAP-1), between BPPV patients and controls. In addition, the results of ultrasonographic imaging to determine carotid intima-media thickness (C-IMT), carotid atheromatous plaque, and vertebral artery stenosis were also compared between the BPPV and control groups. Serum levels of IL-1β, sICAM-1, and sVAP-1 were significantly higher in BPPV patients than controls (P < 0.001, P < 0.05, and P < 0.001, respectively). C-IMT and vertebral artery stenosis were significantly different in BPPV patients compared to controls (both P < 0.05). There were no significant relations between other parameters and BPPV. IL-1β, sICAM-1, and sVAP-1 are potentially associated with the pathogenesis of BPPV, and C-ITM and carotid vertebral stenosis may be useful reference imaging findings for the diagnosis of BPPV.

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.

Evolution and functional classification of mammalian copper amine oxidases

Mammalian copper-containing amine oxidases (CAOs), encoded by four genes (AOC1-4) and catalyzing the oxidation of primary amines to aldehydes, regulate many biological processes and are linked to various diseases including inflammatory conditions and histamine intolerance. Despite the known differences in their substrate preferences, CAOs are currently classified based on their preference for either primary monoamines (EC 1.4.3.21) or diamines (EC 1.4.3.22). Here, we present the first extensive phylogenetic study of CAOs that, combined with structural analyses of the CAO active sites, provides in-depth knowledge of their relationships and guidelines for classification of mammalian CAOs into AOC1-4 sub-families. The phylogenetic results show that CAOs can be classified based on two residues, X1 and X2, from the active site motif: T/S-X1-X2-N-Y-D. Residue X2 discriminates among the AOC1 (Tyr), AOC2 (Gly), and AOC3/AOC4 (Leu) proteins, while residue X1 further classifies the AOC3 (Leu) and AOC4 (Met) proteins that so far have been poorly identified and annotated. Residues X1 and X2 conserved within each sub-family and located in the catalytic site seem to be the key determinants for the unique substrate preference of each CAO sub-family. Furthermore, one residue located at 10 Å distance from the catalytic site is different between the sub-families but highly conserved within each sub-family (Asp in AOC1, His in AOC2, Thr in AOC3 and Asn in AOC4) and likely contributes to substrate selectivity. Altogether, our results will benefit the design of new sub-family specific inhibitors and the design of in vitro tests to detect individual CAO levels for diagnostic purposes.

68Ga-DOTA-E[c(RGDfK)]2 PET Imaging of SHARPIN-Regulated Integrin Activity in Mice

Shank-associated RH domain-interacting protein (SHARPIN) is a cytosolic protein that plays a key role in activation of nuclear factor κ-light-chain enhancer of activated B cells and regulation of inflammation. Furthermore, SHARPIN controls integrin-dependent cell adhesion and migration in several normal and malignant cell types, and loss of SHARPIN correlates with increased integrin activity in mice. Arginyl-glycyl-aspartic acid (RGD), a cell adhesion tripeptide motif, is an integrin recognition sequence that facilitates PET imaging of integrin upregulation during tumor angiogenesis. We hypothesized that increased integrin activity due to loss of SHARPIN protein would affect the uptake of α_vβ₃-selective cyclic, dimeric peptide ⁶⁸Ga-DOTA-E[c(RGDfK)]₂, where E[c(RGDfk)]₂ = glutamic acid-[cyclo(arginyl-glycyl-aspartic acid-D-phenylalanine-lysine)], both in several tissue types and in the tumor microenvironment. To test this hypothesis, we used RGD-based in vivo PET imaging to evaluate wild-type (wt) and SHARPIN-deficient mice (Sharpin ^cpdm , where cpdm = chronic proliferative dermatitis in mice) with and without melanoma tumor allografts. Methods: Sharpin ^cpdm mice with spontaneous null mutation in the Sharpin gene and their wt littermates with or without B16-F10-luc melanoma tumors were studied by in vivo imaging and ex vivo measurements with cyclic-RGD peptide ⁶⁸Ga-DOTA-E[c(RGDfK)]₂ After the last ⁶⁸Ga-DOTA-E[c(RGDfK)]₂ peptide PET/CT, tumors were cut into cryosections for autoradiography, histology, and immunohistochemistry. Results: The ex vivo uptake of ⁶⁸Ga-DOTA-E[c(RGDfK)]₂ in the mouse skin and tumor was significantly higher in Sharpin ^cpdm mice than in wt mice. B16-F10-luc tumors were detected 4 d after inoculation, without differences in volume or blood flow between the mouse strains. PET imaging with ⁶⁸Ga-DOTA-E[c(RGDfK)]₂ peptide at day 10 after inoculation revealed significantly higher uptake in the tumors transplanted into Sharpin ^cpdm mice than in wt mice. Furthermore, tumor vascularization was increased in the Sharpin ^cpdm mice. Conclusion: Sharpin ^cpdm mice demonstrated increased integrin activity and vascularization in B16-F10-luc melanoma tumors, as demonstrated by RGD-based in vivo PET imaging. These data indicate that SHARPIN, a protein previously associated with increased cancer growth and metastasis, may also have important regulatory roles in controlling the tumor microenvironment.

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.

Vascular adhesion protein-1 is actively involved in the development of inflammatory lesions in rat models of multiple sclerosis

Background

Vascular adhesion protein-1 (VAP-1) is an inflammation-inducible endothelial cell molecule and primary amine oxidase that mediates leukocyte entry to sites of inflammation. However, there is limited knowledge of the inflammation-related expression of VAP-1 in the central nervous system (CNS). Therefore, we investigated the expression of VAP-1 within the CNS vasculature in two focal rat models of experimental autoimmune encephalomyelitis (EAE) mimicking multiple sclerosis (MS).

Methods

EAE was induced either with Bacillus Calmette-Guérin, resulting in a delayed-type hypersensitivity-like pathogenesis (fDTH-EAE), or with myelin oligodendrocyte glycoprotein (fMOG-EAE). A subgroup of fMOG-EAE rats were treated daily with a selective VAP-1 inhibitor (LJP1586; 5 mg/kg). On 3 and 14 days after lesion activation, rat brains were assessed using magnetic resonance imaging (MRI), and ex vivo autoradiography was conducted to evaluate the binding of Gallium-68-labelled VAP-1 ligand. Histology and immunohistochemistry (OX-42, VAP-1, intercellular adhesion protein-1 [ICAM-1], P-selectin) supported the ex vivo autoradiography.

Results

EAE lesions showed MRI-detectable signal changes and binding of the VAP-1-targeting radiotracer in both rat models. Some of the VAP-1 positive vessels showed morphological features typical for high endothelial-like venules at sites of inflammation. Inhibition of VAP-1 activity with small molecule inhibitor, LJP1586, decreased lymphocyte density in the acute inflammatory phase of fMOG-EAE lesions (day 3, P = 0.026 vs. untreated), but not in the remission phase (day 14, P = 0.70 vs. untreated), and had no effect on the amount of OX-42-positive cells in either phase. LJP1586 treatment reduced VAP-1 and ICAM-1 expression in the acute inflammatory phase, whereas P-selectin remained not detectable at all studied stages of the disease.

Conclusions

Our results revealed that VAP-1 is expressed and functionally active in vasculature within the induced focal EAE lesions during the acute phase of inflammation and remains expressed after the acute inflammation has subsided. The study indicates that VAP-1 is actively involved in the development of inflammatory CNS lesions. During this process, the endothelial cell lesion-related vasculature seem to undergo a structural transformation from regular flat-walled endothelium to HEV-like endothelium.

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.

Inflammatory Markers for Arterial Stiffness in Cardiovascular Diseases

Arterial stiffness predicts an increased risk of cardiovascular events. Inflammation plays a major role in large arteries stiffening, related to atherosclerosis, arteriosclerosis, endothelial dysfunction, smooth muscle cell migration, vascular calcification, increased activity of metalloproteinases, extracellular matrix degradation, oxidative stress, elastolysis, and degradation of collagen. The present paper reviews main mechanisms explaining the crosstalk between inflammation and arterial stiffness and the most common inflammatory markers associated with increased arterial stiffness, considering the most recent clinical and experimental studies. Diverse studies revealed significant correlations between the severity of arterial stiffness and inflammatory markers, such as white blood cell count, neutrophil/lymphocyte ratio, adhesion molecules, fibrinogen, C-reactive protein, cytokines, microRNAs, and cyclooxygenase-2, in patients with a broad variety of diseases, such as metabolic syndrome, diabetes, coronary heart disease, peripheral arterial disease, malignant and rheumatic disorders, polycystic kidney disease, renal transplant, familial Mediterranean fever, and oral infections, and in women with preeclampsia or after menopause. There is strong evidence that inflammation plays an important and, at least, partly reversible role in the development of arterial stiffness, and inflammatory markers may be useful additional tools in the assessment of the cardiovascular risk in clinical practice. Combined assessment of arterial stiffness and inflammatory markers may improve non-invasive assessment of cardiovascular risk, enabling selection of high-risk patients for prophylactic treatment or more regular medical examination. Development of future destiffening therapies may target pro-inflammatory mechanisms.

Inhibition of semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 reduces lipopolysaccharide-induced neuroinflammation

BACKGROUND AND PURPOSE

Neuroinflammation is initiated by a variety of stimuli including infections, sepsis, neurodegenerative diseases or traumatic brain injury and, if not adequately controlled, can lead to various degrees of neuronal damage and behavioural impairment. A critical event in the initial steps of inflammation is neutrophil extravasation. Semicarbazide-sensitive amine oxidase (SSAO, also known as vascular adhesion protein 1 or VAP-1) regulates neutrophil adhesion and extravasation. Here, we elucidate the role of SSAO/VAP-1 in the early stage inflammatory response after LPS insult in the brain.

EXPERIMENTAL APPROACH

PXS-4681A, a selective and irreversible SSAO/VAP-1 inhibitor, was tested in two rat models of neuroinflammation, following systemic or i.c.v. LPS. Immunohistochemical and immunofluorescence techniques were used to measure neutrophils and microglia. VAP-1 was quantitated by Western blotting.

KEY RESULTS

Both systemic and i.c.v. administration of LPS induced an increase in neutrophil recruitment and microglial response in various brain areas including the substantia nigra and striatum. PXS-4681A produced a significant inhibition of neutrophil recruitment and extravasation after i.c.v. LPS injection and also reversed microglial cell recruitment and morphological changes to the level of the sham controls in both LPS models.

CONCLUSIONS AND IMPLICATIONS

PXS-4681A acted as an effective anti-inflammatory agent after both systemic and i.c.v. LPS injections suggesting that SSAO/VAP-1 inhibition could be beneficial in the treatment of brain inflammation.

Hypoxia serves a key function in the upregulated expression of vascular adhesion protein‑1 in vitro and in a rat model of hemorrhagic shock

Hemorrhagic shock following major trauma results in mortality, but the function of vascular adhesion protein-1 (VAP-1), implicated in intracranial hemorrhage, remains unknown. This study aimed to determine whether expression of the AOC3 gene and its encoded protein, VAP-1, is altered by hypoxia. Rat hepatic sinusoidal endothelial cells (RHSECs) and rat intestinal microvascular endothelial cells (RIMECs) were transduced with a viral vector carrying AOC3, and AOC3 mRNA expression levels were measured by reverse transcription-quantitative polymerase chain reaction. VAP-1 protein expression levels were measured by western blot analysis and compared between normoxic and hypoxic conditions. Following this, AOC3 mRNA and VAP-1 protein expression levels in hepatic and intestinal tissues were assessed in a rat model of hemorrhagic shock with or without fluid resuscitation; and serum semicarbazide-sensitive amine oxidase (SSAO) activity was measured by fluorometric assays. The effects of 2-bromoethylamine (2-BEA) on AOC3/VAP-1 levels and 24 h survival were investigated. AOC3 mRNA and VAP-1 protein levels were increased in RHSECs and RIMECs by hypoxia, and in hepatic and intestinal tissues from rats following hemorrhagic shock. Hypoxia increased serum SSAO activity in these animals. 2-BEA reduced AOC3 mRNA and VAP-1 protein levels in hepatic and intestinal tissues from rats following hemorrhagic shock, and appeared to improve survival in animals not receiving resuscitation following hemorrhagic shock. In conclusion, hemorrhagic shock upregulates AOC3/VAP-1 expressions, and this potentially occurs via hypoxia. Therefore, inhibition of VAP-1 may be beneficial in the setting of hemorrhagic shock. Further studies are required to confirm these findings and to establish whether VAP-1 may be a valid target for the development of novel therapies for hemorrhagic shock.

Synthesis and pharmacological evaluation of glycine amide derivatives as novel vascular adhesion protein-1 inhibitors without CYP3A4 and CYP2C19 inhibition

Vascular adhesion protein-1 (VAP-1) is a promising therapeutic target for the treatment of diabetic nephropathy. Here, we conducted optimization studies of our lead compound 1, which we previously reported as a novel VAP-1 inhibitor, to enhance the inhibition of human VAP-1 and to reduce CYP3A4 and CYP2C19 inhibition. As a result, we identified 3-chloro-4-{4-[5-(3-{[glycyl(methyl)amino]methyl}phenyl)pyrimidin-2-yl]piperazin-1-yl}benzoic acid (17h) as a novel orally active VAP-1 inhibitor, with 14-fold increased human VAP-1 inhibitory activity compared to 1, without CYP3A4 and CYP2C19 inhibition. Oral administration of 17h significantly inhibited the progression of proteinuria in streptozotocin (STZ) induced diabetic rats at 0.3 and 1mg/kg, suggesting that this compound has potential to be a therapeutic agent for the treatment of diabetic nephropathy.

Amine oxidase activity regulates the development of pulmonary fibrosis

In pulmonary fibrosis, an inflammatory reaction and differentiation of myofibroblasts culminate in pathologic deposition of collagen. Amine oxidase copper containing-3 (AOC3) is a cell-surface-expressed oxidase that regulates leukocyte extravasation. Here we analyzed the potential role of AOC3 using gene-modified and inhibitor-treated mice in a bleomycin-induced pulmonary fibrosis model. Inflammation and fibrosis of lungs were assessed by histologic, flow cytometric, and quantitative PCR analysis. AOC3-deficient mice showed a 30-50% reduction in fibrosis, collagen synthesis, numbers of myofibroblasts, and accumulation of CD4⁺ lymphocytes, NK T cells, macrophages, and type 2 innate lymphoid cells compared with wild-type control mice. AOC3-knock-in mice, which express a catalytically inactive form of AOC3, were also protected from lung fibrosis. In wild-type mice, a small-molecule AOC3 inhibitor treatment reduced leukocyte infiltration, myofibroblast differentiation, and fibrotic injury both in prophylactic and early therapeutic settings by about 50% but was unable to reverse the established fibrosis. AOC3 was also induced in myofibroblasts in human idiopathic pulmonary fibrosis. Thus, the oxidase activity of AOC3 contributes to the development of lung fibrosis mainly by regulating the accumulation of pathogenic leukocyte subtypes, which drive the fibrotic response.-Marttila-Ichihara, F., Elima, K., Auvinen, K., Veres, T. Z., Rantakari, P., Weston, C., Miyasaka, M., Adams, D., Jalkanen, S., Salmi, M. Amine oxidase activity regulates the development of pulmonary fibrosis.

Vascular adhesion protein-1 in hemodialysis and hemodiafiltration patients: effect of single hemodialysis session on its level in regard to type of anticoagulant

PURPOSE

Traditional anticoagulants used in intermittent hemodialysis (HD) are unfractionated heparin (UFH) and increasingly low molecular weight heparins (LMWHs). Repeated and prolonged exposure to UFH and/or LMWHs may further disturb hemostasis in uremic patients. Vascular adhesion protein-1 (VAP-1) is secreted by vascular smooth muscle cells, adipocytes and endothelial cells with functional monoamine oxidase activity and is elevated in atherosclerosis, diabetes mellitus and obesity. The aim of this study was to assess the effects of UFH and LMWHs on VAP-1 concentration in HD patients. The effects on single HD session on VAP-1 were also evaluated as well as VAP-1 levels in regard to type of renal replacement therapy.

METHODS

We studied 82 hemodialyzed patients (mean age 63 years, dialysis vintage 59 months) and 17 patients treated by means of hemodiafiltration (HDF) (mean age 59 years, HD vintage 84 months, HDF 7 months). Patients were anticoagulated with enoxaparin (n = 46), dalteparin (n = 10), nadroparin (n = 6) or UFH (n = 20) during their HD sessions. VAP-1 was assessed using kits from BioVendor, Modrice, Czech Republic.

RESULTS

Patients on HDF had significantly lower VAP-1 when compared with HD patients. We found that VAP-1 concentration in patients dialyzed by using LMWH or UFH was similar. There was no effect on HD session on VAP-1 concentration. Diabetic patients had higher serum VAP-1 than non-diabetic.

CONCLUSIONS

HDF is associated with lower VAP-1 levels indicating less pronounced endothelial cell injury than hemodialysis. Type of heparin seems to have no effect on VAP-1 levels in hemodialyzed patients. However, the cross-sectional but not prospective design is a limitation of this study.

Multivalent Interactions of Human Primary Amine Oxidase with the V and C22 Domains of Sialic Acid-Binding Immunoglobulin-Like Lectin-9 Regulate Its Binding and Amine Oxidase Activity

Sialic acid-binding immunoglobulin-like lectin-9 (Siglec-9) on leukocyte surface is a counter-receptor for endothelial cell surface adhesin, human primary amine oxidase (hAOC3), a target protein for anti-inflammatory agents. This interaction can be used to detect inflammation and cancer in vivo, since the labeled peptides derived from the second C2 domain (C2₂) of Siglec-9 specifically bind to the inflammation-inducible hAOC3. As limited knowledge on the interaction between Siglec-9 and hAOC3 has hampered both hAOC3-targeted drug design and in vivo imaging applications, we have now produced and purified the extracellular region of Siglec-9 (Siglec-9-EC) consisting of the V, C2₁ and C2₂ domains, modeled its 3D structure and characterized the hAOC3–Siglec-9 interactions using biophysical methods and activity/inhibition assays. Our results assign individual, previously unknown roles for the V and C2₂ domains. The V domain is responsible for the unusually tight Siglec-9–hAOC3 interactions whereas the intact C2₂ domain of Siglec-9 is required for modulating the enzymatic activity of hAOC3, crucial for the hAOC3-mediated leukocyte trafficking. By characterizing the Siglec-9-EC mutants, we could conclude that R120 in the V domain likely interacts with the terminal sialic acids of hAOC3 attached glycans whereas residues R284 and R290 in C2₂ are involved in the interactions with the active site channel of hAOC3. Furthermore, the C2₂ domain binding enhances the enzymatic activity of hAOC3 although the sialic acid-binding capacity of the V domain of Siglec-9 is abolished by the R120S mutation. To conclude, our results prove that the V and C2₂ domains of Siglec-9-EC interact with hAOC3 in a multifaceted and unique way, forming both glycan-mediated and direct protein-protein interactions, respectively. The reported results on the mechanism of the Siglec-9–hAOC3 interaction are valuable for the development of hAOC3-targeted therapeutics and diagnostic tools.

The inhibitor of semicarbazide-sensitive amine oxidase, PXS-4728A, ameliorates key features of chronic obstructive pulmonary disease in a mouse model

BACKGROUND AND PURPOSE

Chronic obstructive pulmonary disease (COPD) is a major cause of illness and death, often induced by cigarette smoking (CS). It is characterized by pulmonary inflammation and fibrosis that impairs lung function. Existing treatments aim to control symptoms but have low efficacy, and there are no broadly effective treatments. A new potential target is the ectoenzyme, semicarbazide-sensitive mono-amine oxidase (SSAO; also known as vascular adhesion protein-1). SSAO is elevated in smokers' serum and is a pro-inflammatory enzyme facilitating adhesion and transmigration of leukocytes from the vasculature to sites of inflammation.

EXPERIMENTAL APPROACH

PXS-4728A was developed as a low MW inhibitor of SSAO. A model of COPD induced by CS in mice reproduces key aspects of human COPD, including chronic airway inflammation, fibrosis and impaired lung function. This model was used to assess suppression of SSAO activity and amelioration of inflammation and other characteristic features of COPD.

KEY RESULTS

Treatment with PXS-4728A completely inhibited lung and systemic SSAO activity induced by acute and chronic CS-exposure. Daily oral treatment inhibited airway inflammation (immune cell influx and inflammatory factors) induced by acute CS-exposure. Therapeutic treatment during chronic CS-exposure, when the key features of experimental COPD develop and progress, substantially suppressed inflammatory cell influx and fibrosis in the airways and improved lung function.

CONCLUSIONS AND IMPLICATIONS

Treatment with a low MW inhibitor of SSAO, PXS-4728A, suppressed airway inflammation and fibrosis and improved lung function in experimental COPD, demonstrating the therapeutic potential of PXS-4728A for this debilitating disease.

Synthesis and structure activity relationships of glycine amide derivatives as novel Vascular Adhesion Protein-1 inhibitors

Vascular Adhesion Protein-1 (VAP-1) is a promising therapeutic target for the treatment of several inflammatory-related diseases including diabetic microvascular complication. We identified glycine amide derivative 3 as a novel structure with moderate VAP-1 inhibitory activity. Structure-activity relationship studies of glycine amide derivatives revealed that the tertiary amide moiety is important for stability in rat blood and that the position of substituents on the left phenyl ring plays an important role in VAP-1 inhibitory activity. We also found that low TPSA values and weak basicity are both important for high PAMPA values for glycine amide derivatives. These findings led to the identification of a series of orally active compounds with enhanced VAP-1 inhibitory activity. Of these compounds, 4g exhibited the most potent ex vivo efficacy, with plasma VAP-1 inhibitory activity of 60% after oral administration at 1mg/kg.

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

Given the important role of inflammation and the potential association of the leukocyte trafficking-associated adhesion molecule vascular adhesion protein 1 (VAP-1) with atherosclerosis, this study examined whether functional VAP-1 is expressed in atherosclerotic lesions and, if so, whether it could be targeted by positron emission tomography (PET). First, immunohistochemistry revealed that VAP-1 localized to endothelial cells of intra-plaque neovessels in human carotid endarterectomy samples from patients with recent ischemic symptoms. In low-density lipoprotein receptor-deficient mice expressing only apolipoprotein B100 (LDLR^-/-ApoB^100/100), VAP-1 was expressed on endothelial cells lining inflamed atherosclerotic lesions; normal vessel walls in aortas of C57BL/6N control mice were VAP-1-negative. Second, we discovered that the focal uptake of VAP-1 targeting sialic acid-binding immunoglobulin-like lectin 9 based PET tracer [⁶⁸Ga]DOTA-Siglec-9 in atherosclerotic plaques was associated with the density of activated macrophages (r = 0.58, P = 0.022). As a final point, we found that the inhibition of VAP-1 activity with small molecule LJP1586 decreased the density of macrophages in inflamed atherosclerotic plaques in mice. Our results suggest for the first time VAP-1 as a potential imaging target for inflamed atherosclerotic plaques, and corroborate VAP-1 inhibition as a therapeutic approach in the treatment of atherosclerosis.

Inactivation of Semicarbazide-Sensitive Amine Oxidase Stabilizes the Established Atherosclerotic Lesions via Inducing the Phenotypic Switch of Smooth Muscle Cells

Given that the elevated serum semicarbazide-sensitive amine oxidase (SSAO) activity is associated with the severity of carotid atherosclerosis in clinic, the current study aims to investigate whether SSAO inactivation by semicarbazide is beneficial for established atherosclerotic lesions in LDLr knockout mice on a high-fat/high- cholesterol Western-type diet or after dietary lipid lowering. Despite no impact on plasma total cholesterol levels, the infiltration of circulating monocytes into peripheral tissues, and the size of atherosclerotic lesions, abrogation of SSAO activity resulted in the stabilization of established lesions as evidenced by the increased collagen contents under both conditions. Moreover, SSAO inactivation decreased Ly6Chigh monocytosis and lesion macrophage contents in hypercholesterolemic mice, while no effect was observed in mice after normalization of hypercholesterolemia by dietary lipid lowering. Strikingly, abrogation of SSAO activity significantly increased not only the absolute numbers of smooth muscle cells (SMCs), but also the percent of SMCs with a synthetic phenotype in established lesions of mice regardless of plasma cholesterol levels. Overall, our data indicate that SSAO inactivation in vivo stabilizes the established plaques mainly via inducing the switch of SMCs from a contractile to a synthetic phenotype. Targeting SSAO activity thus may represent a potential treatment for patients with atherosclerosis.

Inactivation of semicarbazide-sensitive amine oxidase induces the phenotypic switch of smooth muscle cells and aggravates the development of atherosclerotic lesions

BACKGROUND AND AIMS

Clinical studies have demonstrated that serum semicarbazide-sensitive amine oxidase (SSAO) activities positively correlate with the progression of atherosclerosis. The aim of the present study is to investigate the effect of SSAO inactivation on the development of atherosclerosis.

METHODS

Female LDLr knockout (KO) mice were given the Western-type diet for 6 and 9 weeks to induce the formation of early and advanced lesions, and semicarbazide (SCZ, 0.125%) was added into the drinking water to inactivate SSAO in vivo.

RESULTS

Despite no impact on plasma total cholesterol levels, abrogation of SSAO by SCZ not only resulted in the enlargement of both early (1.5-fold, p = 0.0043) and advanced (1.8-fold, p = 0.0013) atherosclerotic lesions, but also led to reduced/increased lesion contents of macrophages/smooth muscle cells (SMCs) (macrophage: ∼0.74-fold, p = 0.0002(early)/0.0016(advanced); SMC: ∼1.55-fold, p = 0.0003(early)/0.0001(advanced)), respectively. Moreover, SSAO inactivation inhibited the migration of circulating monocytes into peripheral tissues and reduced the amount of circulating Ly6C(high) monocytes (0.7-fold, p = 0.0001), which may account for the reduced macrophage content in lesions. In contrast, the increased number of SMCs in lesions of SCZ-treated mice is attributed to an augmented synthetic vascular SMC phenotype switch as evidenced by the increased proliferation of SMCs and accumulation of collagens in vivo.

CONCLUSION

SSAO inactivation by SCZ promotes the phenotypic switch of SMCs and the development of atherosclerosis. The enzymatic activity of SSAO may thus represent a potential target in the prevention and/or treatment of atherosclerosis.

Overexpression of vascular adhesion protein-1 is associated with poor prognosis of astrocytomas

Vascular adhesion protein-1 (VAP-1) is one of the endothelial adhesion molecules that is believed to play a role in tumor progression and metastasis, supporting cancer cell extravasation. Very few studies have been performed on analyzing the contribution of VAP-1 in brain tumor. Astrocytomas are the most common type of brain tumors, which are classified by World Health Organization (WHO) into four grades according to the degree of malignancy. This study was designed to investigate VAP-1 expression level in different astrocytoma grades and its correlation with clinicopathological features as well as prognosis of astrocytoma patients. Eighty-seven patients with different grades of astrocytoma (WHO Grade I-Grade IV) were enrolled in this study. The expression of VAP-1 was assayed by immunohistochemistry. The correlation between VAP-1 expression and clinicopathological features was evaluated by Chi-square test, and overall survival was analyzed by Kaplan-Meier method. Cox regression analysis was applied to analyze the independent influence of each parameter on overall survival. The expression level of VAP-1 was significantly higher in diffuse astrocytoma than those of pilocytic astrocytoma (p < 0.0001). In the subgroup analysis, upregulated VAP-1 expression was frequently found in older age patients (≥50 years). The VAP-1 expression was found to be significantly correlated with the overall survival (p = 0.0002). There was a statistical correlation between VAP-1(high) tumors in diffuse astrocytoma and VAP-1(low) tumors in pilocytic astrocytoma (p < 0.0001). Multivariate Cox analysis indicated VAP-1 was an independent predictive marker for poorer prognosis (p = 0.0036). Therefore, VAP-1 could be a promising prognostic biomarker in astrocytoma.

Leukocyte Trafficking to the Small Intestine and Colon

Leukocyte trafficking to the small and large intestines is tightly controlled to maintain intestinal immune homeostasis, mediate immune responses, and regulate inflammation. A wide array of chemoattractants, chemoattractant receptors, and adhesion molecules expressed by leukocytes, mucosal endothelium, epithelium, and stromal cells controls leukocyte recruitment and microenvironmental localization in intestine and in the gut-associated lymphoid tissues (GALTs). Naive lymphocytes traffic to the gut-draining mesenteric lymph nodes where they undergo antigen-induced activation and priming; these processes determine their memory/effector phenotypes and imprint them with the capacity to migrate via the lymph and blood to the intestines. Mechanisms of T-cell recruitment to GALT and of T cells and plasmablasts to the small intestine are well described. Recent advances include the discovery of an unexpected role for lectin CD22 as a B-cell homing receptor GALT, and identification of the orphan G-protein-coupled receptor 15 (GPR15) as a T-cell chemoattractant/trafficking receptor for the colon. GPR15 decorates distinct subsets of T cells in mice and humans, a difference in species that could affect translation of the results of mouse colitis models to humans. Clinical studies with antibodies to integrin α4β7 and its vascular ligand mucosal vascular addressin cell adhesion molecule 1 are proving the value of lymphocyte trafficking mechanisms as therapeutic targets for inflammatory bowel diseases. In contrast to lymphocytes, cells of the innate immune system express adhesion and chemoattractant receptors that allow them to migrate directly to effector tissue sites during inflammation. We review the mechanisms for innate and adaptive leukocyte localization to the intestinal tract and GALT, and discuss their relevance to human intestinal homeostasis and inflammation.

Evaluation of Serum Vascular Adhesion Protein-1 as a Potential Biomarker in Thyroid Cancer

Vascular adhesion protein-1 (VAP-1) is a glycoprotein that mediates tissue-selective lymphocyte adhesion. The prognostic value of VAP-1 has been determined in gastric cancer. The aim of this study was to evaluate the changes and the predictive value of serum VAP-1 in patients with thyroid cancer. A total of 126 patients with thyroid nodules and 53 healthy controls participated in this study. The patients were further divided into subgroup 1 (69 cases with benign thyroid nodules) and subgroup 2 (57 cases with thyroid cancer). Serum VAP-1 was measured by time-resolved immunofluorometric assay. Diagnostic value of presurgical VAP-1 for thyroid cancer was conducted by receiver operating characteristic (ROC) curves. Serum levels of VAP-1 were significantly lower in thyroid cancer group than in healthy control and benign thyroid nodule groups. VAP-1 concentrations negatively correlated with serum thyroglobulin (Tg) levels in thyroid cancer patients (r = -0.81; p < 0.001). The optimum cut-off value of VAP-1 was 456.6 ng/mL with a 77.4% specificity and 66.7% sensitivity for thyroid cancer diagnosis. Serum VAP-1 decreased in thyroid cancer patients and VAP-1 could be a potential useful adjunct biomarker in the diagnosis of thyroid cancer.

Vascular adhesion protein-1: Role in human pathology and application as a biomarker

Vascular adhesion protein-1 (VAP-1) is a member of the copper-containing amine oxidase/semicarbazide-sensitive amine oxidase (AOC/SSAO) enzyme family. SSAO enzymes catalyze oxidative deamination of primary amines, which results in the production of the corresponding aldehyde, hydrogen peroxide and ammonium. VAP-1 is continuously expressed as a transmembrane glycoprotein in the vascular wall during development and facilitates the accumulation of inflammatory cells into the inflamed environment in concert with other leukocyte adhesion molecules. The soluble form of VAP-1 is released into the circulation mainly from vascular endothelial cells. Over- and under-expression of sVAP-1 result in alterations of the reported reaction product levels, which are involved in the pathogenesis of multiple human diseases. The combination of enzymatic and adhesion capacities as well as its strong association with inflammatory pathologies makes VAP-1 an interesting therapeutic target for drug discovery. In this article, we will review the general characteristics and biological functions of VAP-1, focusing on its important role as a prognostic biomarker in human pathologies. In addition, the potential therapeutic application of VAP-1 inhibitors will be discussed.

Circulating renalase, catecholamines, and vascular adhesion protein 1 in hypertensive patients

The aim of the study was to estimate and correlate circulating levels of renalase, vascular adhesion protein-1 (VAP-1), catecholamines in patients with primary hypertension. The renalase, VAP-1, and catecholamines concentration was estimated in 121 hypertensive patients. The correlation between renalase, VAP-1 levels and catecholamine concentration in blood, blood pressure control, pharmacological therapy, and medical history were taken in to consideration. The median office blood pressure was 145.5/86 mm Hg and was significantly higher than the median home blood pressure measurement value, which was 135/80 mm Hg, P < .05. Circulating renalase and VAP-1 (Me 9.57 μg/mL and Me = 326.7 ng/mL) levels were significantly higher in patients with hypertension comparing to healthy individuals (3.83 μg/mL and 248.37 ng/mL, P < .05). The correlation between renalase and noradrenalin concentration in blood was observed (r = 0.549; P < .05), also the correlation between VAP-1 and noradrenaline was noticed (r = 0.21, P = .029). Renalase level was higher in patients with coronary artery disease and correlated with decreased ejection fraction. VAP-1 concentration correlated also with left ventricular ejection fraction (r = -0.23, P = .013). Hypertensive patients with diabetes mellitus had almost statistically significant higher VAP-1 concentration compared with hypertensive patients without diabetes mellitus (Me = 403.22 ng/mL vs. Me = 326,68 ng/mL, P = .064). In multiple regression analysis, renalase was predicted by plasma dopamine and norepinephrine as also diastolic office blood pressure and left ventricle ejection fraction. Circulating renalase and VAP-1 levels are elevated in patients with poor blood pressure control. Its correlation with noradrenalin concentration need further studies to find out the role of renalase as also VAP-1 in pathogenesis and treatment of hypertension.

Plasma soluble vascular adhesion protein-1 concentration correlates with arterial stiffness: A cross-sectional study

BACKGROUND

Arterial stiffness is related to inflammation, oxidative stress, advanced glycation end products (AGEs), and endothelial dysfunction. Vascular adhesion protein-1 (VAP-1) is both as an adhesion molecule involving in inflammation and as an amine oxidase producing aldehyde and hydrogen peroxide involved in protein cross-linking, oxidative stress and endothelial injury.

OBJECTIVE

We explored the associations of plasma soluble VAP-1 (sVAP-1) with arterial stiffness.

DESIGN

Cross-sectional study.

SETTING

Health Examination Center at the General Hospital of the Air Force in Beijing, China.

SUBJECTS

568 Han Chinese healthy persons living in Beijing (aged 50.7 ± 8.0 years).

METHODS

sVAP-1 concentration was assessed by enzyme-linked immunosorbent assay. Arterial stiffness was measured as brachial-ankle pulse wave velocity (baPWV) on both left and right sides of the examinees, and the larger and the mean values were recorded. Cardiovascular risk factors were investigated.

RESULTS

sVAP-1 was significantly associated with maximal or mean baPWV in subjects of age ≥ 60 years after adjusting for baPWV-related confounders (β=36.922, p<0.05 or β=32.512, p<0.05) or after adjusting for all the variables (β=37.924, p<0.05 or β=33.193, p<0.05), but not in subjects of age <60 years. sVAP-1 had an independent and positive correlation with age (r=0.222, p<0.001).

CONCLUSIONS

Plasma sVAP-1, increased with age, is associated with arterial stiffness in older individuals. VAP-1 may be important mechanism for vascular aging.

Vascular adhesion protein-1 promotes liver inflammation and drives hepatic fibrosis

Nonalcoholic fatty liver disease (NAFLD) encompasses a range of manifestations, including steatosis and cirrhosis. Progressive disease is characterized by hepatic leukocyte accumulation in the form of steatohepatitis. The adhesion molecule vascular adhesion protein-1 (VAP-1) is a membrane-bound amine oxidase that promotes leukocyte recruitment to the liver, and the soluble form (sVAP-1) accounts for most circulating monoamine oxidase activity, has insulin-like effects, and can initiate oxidative stress. Here, we determined that hepatic VAP-1 expression is increased in patients with chronic liver disease and that serum sVAP-1 levels are elevated in patients with NAFLD compared with those in control individuals. In 4 murine hepatic injury models, an absence or blockade of functional VAP-1 reduced inflammatory cell recruitment to the liver and attenuated fibrosis. Moreover, disease was reduced in animals expressing a catalytically inactive form of VAP-1, implicating enzyme activity in the disease pathogenesis. Within the liver, hepatic stromal cells expressed functional VAP-1, and evaluation of cultured cells revealed that sVAP-1 promotes leukocyte migration through catalytic generation of ROS, which depended on VAP-1 enzyme activity. VAP-1 enhanced stromal cell spreading and wound closure and modulated expression of profibrotic genes. Together, these results link the amine oxidase activity of VAP-1 with hepatic inflammation and fibrosis and suggest that targeting VAP-1 has therapeutic potential for NAFLD and other chronic fibrotic liver diseases.

Absence of Nkx2-3 homeodomain transcription factor reprograms the endothelial addressin preference for lymphocyte homing in Peyer's patches

Although the homing of lymphocytes to GALT has been extensively studied, little is known about how high endothelial venules (HEVs) within Peyer's patches (PPs) are patterned to display dominantly mucosal addressin cell adhesion molecule 1 (MAdCAM-1). In this study, we report that Nkx2-3-deficient mice show gradual loss of MAdCAM-1 in PPs postnatally and increased levels of mRNA for peripheral lymph node addressin (PNAd) backbone proteins as well as enhanced expression of MECA79 sulfated glycoepitope at the luminal aspect of HEVs, thus replacing MAdCAM-1 with PNAd. Induction of PNAd in mutant PPs requires lymphotoxin β receptor activity, and its upregulation needs the presence of mature T and B cells. Furthermore, treatment with MECA-79 anti-PNAd mAb in vivo effectively blocks lymphocyte homing to mutant PPs. Despite the replacement of MAdCAM-1 by PNAd in HEV endothelia, lymphocytes could efficiently home to PPs in mutant mice. We conclude that although Nkx2-3 activity controls the addressin balance of HEVs in GALT, the general HEV functionality is preserved independently from Nkx2-3, indicating a substantial plasticity in the specification of GALT HEV endothelium.

Endothelial amine oxidase AOC3 transiently contributes to adaptive immune responses in the airways

Amine oxidase, copper containing 3 (AOC3, also known as vascular adhesion protein-1 (VAP-1)) is an endothelial adhesion molecule that contributes to the extravasation of neutrophils, macrophages, and lymphocytes to sites of inflammation. However, the role of AOC3/VAP-1 in allergic responses remains unknown. Here, we studied eosinophil and CD4+ T-cell recruitment to the airways using AOC3/VAP-1-deficient mice. In an OVA-triggered asthma model, AOC3/VAP-1 slightly contributed to the accumulation of leukocytes in lungs in an age-dependent manner. We then established a new model to kinetically measure recruitment of OVA-specific CD4+ T cells to different airway immune compartments during the priming and effector phases of an adaptive immune response. The results showed that in the absence of AOC3/VAP-1, recruitment of antigen-specific CD4+ T cells to draining bronchial lymph nodes is reduced by 89% on day 3 after tracheal allergen exposure, but this difference was not observed on day 6. The dispersal of effector cells to lung and tracheal mucosa is AOC3/VAP-1 independent. Thus, in allergic airway reactions, AOC3/VAP-1 transiently contributes to the antigen-specific, CD4+ T-cell traffic to secondary lymphatic tissues, but not to airway mucosa or lung parenchyma. Our results suggest a largely redundant function for AOC3/VAP-1 in allergic inflammatory responses of the airways.

Soluble vascular adhesion protein-1 predicts incident major adverse cardiovascular events and improves reclassification in a finnish prospective cohort study

BACKGROUND

Vascular adhesion protein-1 (VAP-1) associates to subclinical atherosclerotic manifestations in young people, but its association to incident major adverse cardiovascular events (MACEs) and cardiovascular mortality in a general population is not known.

METHODS AND RESULTS

We used a newly developed ELISA to measure soluble VAP-1 (sVAP-1) levels in 2775 participants (mean age, 60 years) from a prospective cohort study (the FINRISK 2002). During a mean follow-up of 9 years, 265 participants underwent a MACE, and these participants had higher levels of sVAP-1 than those without MACE (868 ng/mL and 824 ng/mL, respectively, P<0.001). In multivariate-adjusted Cox proportional hazard model including traditional Framingham risk factors (age, sex, systolic blood pressure, cholesterol, high-density lipoprotein cholesterol, smoking, prevalent diabetes mellitus, and antihypertensive treatment), sVAP-1 independently predicted incident MACE (P=0.0046) and MACE mortality (P=0.026). The impact of sVAP-1 in predicting the 9-year absolute risk of MACE was analyzed using integrated discrimination improvement and net reclassification improvement with 10-fold cross-validation. Inclusion of sVAP-1 in the Framingham model improved integrated discrimination improvement (P=0.042), and the clinical net reclassification improvement by correctly reclassifying 9% (P=0.0019) of people in the intermediate risk (5%-20%) group.

CONCLUSIONS

sVAP-1 associated with increased risk of MACE and MACE mortality in people aged >50 years without prior MACE, and inclusion of sVAP-1 in the risk prediction model improved the clinical net reclassification improvement of incident MACE. Thus, sVAP-1 may be a potential new biomarker for cardiovascular diseases.

Serum vascular adhesion protein-1 level predicts risk of incident cancers in subjects with type II diabetes

BACKGROUND

Serum vascular adhesion protein-1 (VAP-1) predicts cancer-related mortality in diabetic subjects. However, whether serum VAP-1 predicts cancer incidence or cancer progression remains unclear. We conducted a cohort study to investigate whether serum VAP-1 and related clinical variables predict incident cancers in type II diabetic subjects.

METHODS

From 1996 to 2003, we enrolled 568 type II diabetic subjects who were free of cancer at baseline. Serum VAP-1 at enrollment was measured by time-resolved immunofluorometric assay. Chronic kidney disease (CKD) was defined as estimated glomerular filtration rate <60 mL/min per 1.73 m(2). The subjects were followed until first occurrence of cancer or until December 31, 2011.

RESULTS

During a mean follow-up of 11.3 years, 71 subjects developed incident cancers. The HRs for incident cancers in subjects with highest tertile of serum VAP-1 and in subjects with CKD were 2.95 [95% confidence interval (CI), 1.31-6.63; P = 0.009] and 2.29 (95% CI, 1.18-4.44; P = 0.015), respectively, after multivariate adjustment. There was an interaction between serum VAP-1 and CKD on the risk of incident cancers (P = 0.01 for log-transformed VAP-1 × CKD). The relationship among serum VAP-1, CKD, and incident cancers was similar if death was considered in the competing risk models or if subjects with shorter follow-up period were excluded.

CONCLUSIONS

Higher serum VAP-1 and CKD can independently predict future development of cancers in type II diabetic subjects.

IMPACT

Physicians should be aware of the early signs of cancer in diabetic individuals with elevated VAP-1 or renal dysfunction. More aggressive treatment strategies might be considered.

Ectoenzymes in leukocyte migration and their therapeutic potential

Inflammation causes or accompanies a huge variety of diseases. Migration of leukocytes from the blood into the tissues, in the tissues, and from the tissues to lymphatic vasculature is crucial in the formation and resolution of inflammatory infiltrates. In addition to classical adhesion and activation molecules, several other molecules are known to contribute to the leukocyte traffic. Several of them belong to ectoenzymes, which are cell surface molecules having catalytically active sites outside the cell. We will review here how several ectoenzymes present on leukocytes or endothelial cell surface function as adhesins and/or modulate the extravasation cascade through their enzymatic activities. Moreover, their therapeutic potential as immune modulators in different experimental inflammation models and in clinical trials will be discussed.