Vascular adhesion protein-1 plays an important role in postischemic inflammation and neuropathology in diabetic, estrogen-treated ovariectomized female rats subjected to transient forebrain ischemia

Inhibition of vascular adhesion protein 1 protects dopamine neurons from the effects of acute inflammation and restores habit learning in the striatum

Background

Changes in dopaminergic neural function can be induced by an acute inflammatory state that, by altering the integrity of the neurovasculature, induces neuronal stress, cell death and causes functional deficits. Effectively blocking these effects of inflammation could, therefore, reduce both neuronal and functional decline. To test this hypothesis, we inhibited vascular adhesion protein 1 (VAP-1), a membrane-bound protein expressed on the endothelial cell surface, that mediates leukocyte extravasation and induces oxidative stress.

Method

We induced dopaminergic neuronal loss by infusing lipopolysaccharide (LPS) directly into the substantia nigra (SN) in rats and administered the VAP-1 inhibitor, PXS-4681A, daily.

Results

LPS produced: an acute inflammatory response, the loss of dopaminergic neurons in the SN, reduced the dopaminergic projection to SN target regions, particularly the dorsolateral striatum (DLS), and a deficit in habit learning, a key function of the DLS. In an attempt to protect SN neurons from this inflammatory response we found that VAP-1 inhibition not only reduced neutrophil infiltration in the SN and striatum, but also reduced the associated striatal microglia and astrocyte response. We found VAP-1 inhibition protected dopamine neurons in the SN, their projections to the striatum and promoted the functional recovery of habit learning. Thus, we reversed the loss of habitual actions, a function usually dependent on dopamine release in DLS and sensitive to striatal dysfunction.

Conclusions

We establish, therefore, that VAP-1 inhibition has an anti-inflammatory profile that may be beneficial in the treatment of dopamine neuron dysfunction caused by an acute inflammatory state in the brain.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02288-8.

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.

Dysregulation of Leukocyte Trafficking in Type 2 Diabetes: Mechanisms and Potential Therapeutic Avenues

Type 2 Diabetes Mellitus (T2DM) is a chronic inflammatory disorder that is characterized by chronic hyperglycemia and impaired insulin signaling which in addition to be caused by common metabolic dysregulations, have also been associated to changes in various immune cell number, function and activation phenotype. Obesity plays a central role in the development of T2DM. The inflammation originating from obese adipose tissue develops systemically and contributes to insulin resistance, beta cell dysfunction and hyperglycemia. Hyperglycemia can also contribute to chronic, low-grade inflammation resulting in compromised immune function. In this review, we explore how the trafficking of innate and adaptive immune cells under inflammatory condition is dysregulated in T2DM. We particularly highlight the obesity-related accumulation of leukocytes in the adipose tissue leading to insulin resistance and beta-cell dysfunction and resulting in hyperglycemia and consequent changes of adhesion and migratory behavior of leukocytes in different vascular beds. Thus, here we discuss how potential therapeutic targeting of leukocyte trafficking could be an efficient way to control inflammation as well as diabetes and its vascular complications.

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.

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.

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.

Heparanase promotes neuroinflammatory response during subarachnoid hemorrhage in rats

BACKGROUND

Heparanase, a mammalian endo-β-D-glucoronidase that specifically degrades heparan sulfate, has been implicated in inflammation and ischemic stroke. However, the role of heparanase in neuroinflammatory response in subarachnoid hemorrhage (SAH) has not yet been investigated. This study was designed to examine the association between heparanase expression and neuroinflammation during subarachnoid hemorrhage.

METHODS

Rats were subjected to SAH by endovascular perforation, and the expression of heparanase was determined by Western blot analysis and immunofluorescence in the ipsilateral brain cortex at 24 h post-SAH. Pial venule leukocyte trafficking was monitored by using intravital microscopy through cranial window.

RESULTS

Our results indicated that, compared to their sham-surgical controls, the rats subjected to SAH showed marked elevation of heparanase expression in the ipsilateral brain cortex. The SAH-induced elevation of heparanase was accompanied by increased leukocyte trafficking in pial venules and significant neurological deficiency. Intracerebroventricular application of a selective heparanase inhibitor, OGT2115, which was initiated at 3 h after SAH, significantly suppressed the leukocyte trafficking and improved the neurological function.

CONCLUSIONS

Our findings indicate that heparanase plays an important role in mediating the neuroinflammatory response after SAH and contributes to SAH-related neurological deficits and early brain injury following SAH.

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.

Diabetic aggravation of stroke and animal models

Cerebral ischemia in diabetics results in severe brain damage. Different animal models of cerebral ischemia have been used to study the aggravation of ischemic brain damage in the diabetic condition. Since different disease conditions such as diabetes differently affect outcome following cerebral ischemia, the Stroke Therapy Academic Industry Roundtable (STAIR) guidelines recommends use of diseased animals for evaluating neuroprotective therapies targeted to reduce cerebral ischemic damage. The goal of this review is to discuss the technicalities and pros/cons of various animal models of cerebral ischemia currently being employed to study diabetes-related ischemic brain damage. The rational use of such animal systems in studying the disease condition may better help evaluate novel therapeutic approaches for diabetes related exacerbation of ischemic brain damage.

Vascular adhesion protein-1 enhances neutrophil infiltration by generation of hydrogen peroxide in renal ischemia/reperfusion injury

Vascular adhesion protein-1 (VAP-1) is a unique molecule since it acts as an adhesion molecule as well as an ectoenzyme catalyzing oxidative deamination of primary amines and generates hydrogen peroxide in the extracellular space. While VAP-1 is implicated in various inflammatory diseases, its role in acute kidney injury is less characterized. Here we studied VAP-1 expression in the kidney and the effect of its inhibition in a rat model of renal ischemia/reperfusion injury. VAP-1 was predominantly expressed in pericytes, which released enzymatically active enzyme. In vivo, a specific VAP-1 inhibitor, RTU-1096, significantly ameliorated rat renal ischemia/reperfusion injury and decreased neutrophil infiltration measured 12 hours after injury without altering macrophage or T lymphocyte populations. The protective effect of VAP-1 inhibition was lost in neutrophil-depleted rats, suggesting its inhibition ameliorated renal ischemia/reperfusion injury by suppressing neutrophil infiltration. To investigate whether hydrogen peroxide generated by VAP-1 enzyme reaction enhances neutrophil infiltration, we conducted an under-agarose migration assay with purified human neutrophils. Recombinant human VAP-1 significantly induced neutrophil migration, which was almost completely inhibited by RTU-1096 or catalase. Thus, VAP-1 plays a critical role in the pathophysiology of renal ischemia/reperfusion injury by enhancement of neutrophil infiltration generating a local hydrogen peroxide gradient. Hence, VAP-1 inhibition may be a novel therapy in ischemic acute kidney injury.

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.

Analgesic and Anti-Inflammatory Effects of the Novel Semicarbazide-Sensitive Amine-Oxidase Inhibitor SzV-1287 in Chronic Arthritis Models of the Mouse

Semicarbazide-sensitive amine oxidase (SSAO) catalyses oxidative deamination of primary amines. Since there is no data about its function in pain and arthritis mechanisms, we investigated the effects of our novel SSAO inhibitor SzV-1287 in chronic mouse models of joint inflammation. Effects of SzV-1287 (20 mg/kg i.p./day) were investigated in the K/BxN serum-transfer and complete Freund's adjuvant (CFA)-evoked active immunization models compared to the reference SSAO inhibitor LJP-1207. Mechanonociception was assessed by aesthesiometry, oedema by plethysmometry, clinical severity by scoring, joint function by grid test, myeloperoxidase activity by luminescence, vascular leakage by fluorescence in vivo imaging, histopathological changes by semiquantitative evaluation, and cytokines by Luminex assay. SzV-1287 significantly inhibited hyperalgesia and oedema in both models. Plasma leakage and keratinocyte chemoattractant production in the tibiotarsal joint, but not myeloperoxidase activity was significantly reduced by SzV-1287 in K/BxN-arthritis. SzV-1287 did not influence vascular and cellular mechanisms in CFA-arthritis, but significantly decreased histopathological alterations. There was no difference in the anti-hyperalgesic and anti-inflammatory actions of SzV-1287 and LJP-1207, but only SzV-1287 decreased CFA-induced tissue damage. Unlike SzV-1287, LJP-1207 induced cartilage destruction, which was confirmed in vitro. SzV-1287 exerts potent analgesic and anti-inflammatory actions in chronic arthritis models of distinct mechanisms, without inducing cartilage damage.

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.

VAP-1 blockade prevents subarachnoid hemorrhage-associated cerebrovascular dilating dysfunction via repression of a neutrophil recruitment-related mechanism

Our previous findings indicated that in rats subjected to subarachnoid hemorrhage (SAH), suppression of post-SAH neuroinflammation via vascular adhesion protein-1 (VAP-1) blockade provides significant neuroprotection. We and others have reported that neuroinflammation contributes to cerebral microvascular impairment. Thus, in the present study, we tested the hypotheses that: (1) treatment with LJP-1586, a selective VAP-1 blocker, prevents SAH-associated pial arteriolar dilating dysfunction; and (2) the vasculoprotective effect of LJP-1586 arises from inhibiting SAH-elicited neutrophil recruitment. We utilized an endovascular perforation model of SAH. Rats subjected to SAH were either treated with LJP-1586 or rendered neutropenic via anti-neutrophil-antibody treatment. Findings from these groups were compared to their respective control groups. At 48 h post-SAH, rats were evaluated for neurobehavioral function, pial venular leukocyte trafficking, and pial arteriolar reactivity to topically-applied acetylcholine (ACh) and S-nitroso-N-acetyl penicillamine (SNAP). Pial arteriolar responses decreased at 48 h post-SAH. However, in the presence of LJP-1586, those responses were significantly preserved. Neutrophil-depletion yielded a substantial suppression of SAH-associated leukocyte adhesion and infiltration. This was accompanied by a significant preservation of pial arteriolar dilating function, suggesting a direct link between neutrophil recruitment and the loss of cerebral microvascular reactivity. Moreover, neutrophil depletion also was associated with significant protection of neurobehavioral function. The present findings suggest that attenuating SAH-linked elevation in neutrophil trafficking will protect against the development of microvascular dysfunction and subsequent neurological impairment.

Neurogenesis and inflammation after ischemic stroke: what is known and where we go from here

This review covers the pathogenesis of ischemic stroke and future directions regarding therapeutic options after injury. Ischemic stroke is a devastating disease process affecting millions of people worldwide every year. The mechanisms underlying the pathophysiology of stroke are not fully understood but there is increasing evidence demonstrating the contribution of inflammation to the drastic changes after cerebral ischemia. This inflammation not only immediately affects the infarcted tissue but also causes long-term damage in the ischemic penumbra. Furthermore, the interaction between inflammation and subsequent neurogenesis is not well understood but the close relationship between these two processes has garnered significant interest in the last decade or so. Current approved therapy for stroke involving pharmacological thrombolysis is limited in its efficacy and new treatment strategies need to be investigated. Research aimed at new therapies is largely about transplantation of neural stem cells and using endogenous progenitor cells to promote brain repair. By understanding the interaction between inflammation and neurogenesis, new potential therapies could be developed to further establish brain repair mechanisms.

Pharmacologic blockade of vascular adhesion protein-1 lessens neurologic dysfunction in rats subjected to subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is a potentially devastating clinical problem. Despite advances in the diagnosis and treatment of SAH, outcome remains unfavorable. An increased inflammatory state, one that is characterized by enhanced leukocyte trafficking has been reported to contribute to neuronal injury in association with multiple brain insults, including hemorrhagic and ischemic stroke. This study was designed to investigate, in rats, the neuropathologic consequences of heightened leukocyte trafficking following SAH, induced via endovascular perforation of the anterior cerebral artery. Experiments focused on the initial 48 h post-SAH and sought to establish whether blockade of vascular adhesion protein-1 (VAP-1), with LJP-1586, was able to provide dose-dependent neuroprotection. Treatment with LJP-1586 was initiated at 6h post-SAH. An intravital microscopy and closed cranial window system, that permitted examination of temporal patterns of rhodamine-6G-labeled leukocyte adhesion/extravasation, was used. Effects of LJP-1586 on neurologic outcomes and leukocyte trafficking at 24 h and 48 h post-SAH were examined. In VAP-1-inhibited vs control rats, results revealed a significant attenuation in leukocyte trafficking at both 24 h and 48 h after SAH, along with an improvement in neurologic outcome. In conclusion, our findings support the involvement of an amplified inflammatory state, characterized by enhanced leukocyte trafficking, during the first 48 h after SAH. VAP-1 blockade yielded neuroprotection that was associated with an attenuation of leukocyte trafficking and improved neurologic outcome.

Human copper-dependent amine oxidases

Copper amine oxidases (CAOs) are a class of enzymes that contain Cu(2+) and a tyrosine-derived quinone cofactor, catalyze the conversion of a primary amine functional group to an aldehyde, and generate hydrogen peroxide and ammonia as byproducts. These enzymes can be classified into two non-homologous families: 2,4,5-trihydroxyphenylalanine quinone (TPQ)-dependent CAOs and the lysine tyrosylquinone (LTQ)-dependent lysyl oxidase (LOX) family of proteins. In this review, we will focus on recent developments in the field of research concerning human CAOs and the LOX family of proteins. The aberrant expression of these enzymes is linked to inflammation, fibrosis, tumor metastasis/invasion and other diseases. Consequently, there is a critical need to understand the functions of these proteins at the molecular level, so that strategies targeting these enzymes can be developed to combat human diseases.

Lack of association between VAP-1/SSAO activity and corneal neovascularization in a rabbit model

The aim of this study is to determine the efficacy of a potent and specific vascular adhesive protein-1/semicarbazide-sensitive amine oxidase (VAP-1/SSAO) inhibitor, LJP 1207, as a potential antiangiogenic and anti-inflammatory agent in the therapy of corneal neovascularization. Corneal neovascularization was induced with intrastromal suturing in rabbits (n = 20). Topical treatment with VAP-1/SSAO inhibitor LJP 1207 (n = 5, 4 times a day), bevacizumab (n = 5, daily), their combination (n = 5) and vehicle only (n = 5, 4 times a day) were applied postoperatively for 2 weeks. The development and extent of corneal neovascularization were evaluated by digital image analysis. At the end of the observation period, the level of corneal and serum VAP-1/SSAO activity was measured fluorometrically and radiochemically. The corneal VAP-1/SSAO activity was significantly elevated in the suture-challenged vehicle-treated group (3,075 ± 1,009 pmol/mg/h) as compared to unoperated controls (464.2 ± 135 pmol/mg/h, p < 0.001). Treatment with LJP 1207 resulted in slower early phase neovascularization compared to vehicle-treated animals (not significant). At days 7-14, there was no significant difference in the extent of corneal neovascularization between inhibitor- and vehicle-treated corneas, even though inhibitor treatment caused a normalization of corneal VAP-1/SSAO activity (885 ± 452 pmol/mg/h). Our results demonstrate that the significant elevation of VAP-1/SSAO activity due to corneal injury can be prevented with VAP-1/SSAO inhibitor LJP 1207 treatment. However, normalization of VAP-1/SSAO activity in this model does not prevent the development of corneal neovascularization.

Nuclear imaging of inflammation: homing-associated molecules as targets

The golden standard in nuclear medicine imaging of inflammation is the use of autologous radiolabeled leukocytes. Although their diagnostic accuracy is precise, the preparation of the leukocytes is both laborious and potentially hazardous for laboratory personnel. Molecules involved in leukocyte migration (homing-associated molecules) could serve as targets for the development of imaging agents for inflammation. An excellent target would be a molecule that is absent or expressed at low levels in healthy tissues, but is present or upregulated at the sites of inflammation. In this paper, we will review the literature concerning the use of homing-associated molecules as imaging targets. We will especially concentrate on vascular adhesion protein-1 due to the promising results regarding its use as a target for the imaging of inflammation.

Post-ischemic vascular adhesion protein-1 inhibition provides neuroprotection in a rat temporary middle cerebral artery occlusion model

We examined the neuroprotective efficacy associated with post-ischemic vascular adhesion protein-1 (VAP-1) blockade in rats subjected to transient (1 h) middle cerebral artery occlusion (MCAo). We compared saline-treated control rats to rats treated with a highly selective VAP-1 inhibitor, LJP-1586 [Z-3-fluoro-2-(4-methoxybenzyl) allylamine hydrochloride]. Initial intraperitoneal LJP-1586 (or saline control) treatments were delayed until 6 h or 12 h reperfusion. At 72-h reperfusion, LJP-1586-treated rats displayed 51% and 33% smaller infarct volumes, relative to their controls, in the 6- and 12-h treatment groups, respectively. However, only in the 6-h treatment group was the infarct volume reduction significant (p < 0.05). On the other hand, we observed significantly improved neurologic functions in both 6- and 12-h treatment groups, versus their matched controls (p < 0.05). Also, the effect of 6-h LJP-1586 treatment on post-ischemic leukocyte trafficking in pial venules overlying the ischemic cortex was evaluated using intravital microscopy. These experiments revealed that: 1) LJP-1586 did not affect intravascular leukocyte (largely neutrophil) adhesion, at least out to 12-h reperfusion; and 2) the onset of neutrophil extravasation, which occurred between 6-8-h reperfusion in control rats, was prevented by LJP-1586-treatment. In conclusion, in rats subjected to transient MCAo, selective VAP-1 pharmacologic blockade provided neuroprotection, with a prolonged therapeutic window of 6-12-h reperfusion.

The discovery and development of selective 3-fluoro-4-aryloxyallylamine inhibitors of the amine oxidase activity of semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 (SSAO/VAP-1)

A new class of 3-fluoroallyl amine-based SSAO/VAP-1 inhibitors is reported. These compounds have excellent selectivity over diamine oxidase, MAO-A and MAO-B. Synthesis and SAR studies leading to compound 28 (PXS-4159A) are reported. The pharmacokinetic profile of 28 in the rat, together with activity in a murine model of lung inflammation are also disclosed.

Bioluminescent Method for Assaying Multiple Semicarbazide-Sensitive Amine Oxidase (SSAO) Family Members in Both 96- and 384-Well Formats

Vascular adhesion protein–1 (VAP-1), also known as semicarbazide-sensitive amine oxidase (SSAO) or copper-containing amine oxidase (AOC3, EC 1.4.3.6), catalyzes oxidative deamination of primary amines. One endogenous substrate has recently been described (Siglec 10), and although its mechanism of action in vivo is not completely understood, it is suggested to play a role in immune cell trafficking, making it a target of interest for autoimmune and inflammatory diseases. Much of the enzymology performed around this target has been conducted with absorbance, fluorescent, or radiometric formats that can have some limitations for high-throughput screening and subsequent compound profiling. The authors present the use of a bioluminescent assay, originally developed for monoamine oxidase enzymes, in a high-throughput format. It can be used for related SSAOs such as AOC1 given their substrate similarity with VAP-1. The authors also demonstrate that it is compatible with different sources of VAP-1, both purified recombinant and VAP-1 overexpressed on live cells.

Future forms of immunotherapy and immunomodulators in allergic disease

Future forms of immunotherapy, particularly toll-like receptor agonists, have shown promising results in animal models of allergic disease although most have failed to translate into successful human clinical trials. These results have helped to elucidate the pleotropic roles of cytokines as well as the diverse phenotypes of allergic diseases, particularly asthma. The goals of these therapies are to improve patient symptoms and quality of life, to prevent and favorably alter disease course, and to maintain a good risk/benefit ratio along with a cost-effective profile.

Semicarbazide-sensitive amine oxidase/vascular adhesion protein-1: a patent survey

INTRODUCTION

Vascular adhesion protein-1 (VAP-1)/semicarbazide-sensitive amine oxidase (SSAO) is an adhesion protein involved in leukocyte trafficking and inflammatory processes, with a special amine oxidase activity. Inhibitors have been mainly developed for treating chronic inflammatory disorders. The utility of inhibitors as antiangiogenic agents in ophthalmological and oncological diseases is currently under evaluation. SSAO substrates may mimic several insulin effects, although their utility for the treatment of diabetes is still far from being fully understood.

AREAS COVERED

This paper reviews the patent literature of SSAO/VAP-1 inhibitors and substrates, for the period of 1990 - 2010. The current stage of SSAO/VAP-1-interacting agents published in patents is described, along with their chemical structures and pharmacological uses.

EXPERT OPINION

SSAO/VAP-1 is a promising anti-inflammatory target. Another important field for therapeutic application of these inhibitors may be ophthalmology, due to their antiangiogenic effects. SSAO substrates might also be of therapeutic value in the treatment of diabetes; however, more extensive research has to be undertaken to validate this approach.

Vascular adhesion protein-1 inhibition provides antiinflammatory protection after an intracerebral hemorrhagic stroke in mice

The systemic immune response has a vital role in propagating the damage of an intracerebral hemorrhage (ICH). Vascular adhesion protein-1 (VAP-1), a semicarbazide (SCZ)-sensitive-amine-oxidase, was found in previous studies to have a role in migration of immune cells. In this study, we hypothesize that VAP-1 inhibition may decrease brain injury by attenuating the transmigration of immune cells to the injury site, and by doing so, reduce cerebral edema and improve neurobehavioral function in mice. Two VAP-1 inhibitors, LJP1586 and SCZ were given 1 hour after ICH induction by either collagenase or autologous blood injection. The VAP-1 siRNA, a VAP-1 gene silencer, and human recombinant AOC3 protein, a VAP-1 analogue, were delivered by intracerebroventricular injection. Postassessment included neurobehavioral testing, brain edema measurement, quantification of neutrophil infiltration and microglia/macrophage activation, and measurement of intercellular adhesion molecule-1 (ICAM-1), P-selectin, monocyte chemoattractant protein-1 (MCP-1), and tumor necrosis factor-α (TNF-α) expression 24 hours after ICH. We found that LJP1586 and SCZ reduced brain edema and neurobehavioral deficits 24 hours after ICH induction. These two drugs were also found to decrease levels of ICAM-1, MCP-1, TNF-α, and inhibit neutrophilic infiltration and microglia/macrophage activation. We conclude that VAP-1 inhibition provided antiinflammation effect by reducing adhesion molecule expression and immune cell infiltration after ICH.

Inhibition of semicarbazide-sensitive amine oxidase attenuates myocardial ischemia-reperfusion injury in an in vivo rat model

AIMS

This study tested the hypothesis that the inhibition of semicarbazide-sensitive amine oxidase (SSAO) after ischemia could attenuate myocardial ischemia-reperfusion (I/R) injury.

MAIN METHODS

Anesthetized male Sprague-Dawley rats underwent myocardial I/R injury. Saline, semicarbazide (SCZ, 30 mg/kg), hydralazine (HYD, 10mg/kg), or LJP 1207 (30 mg/kg) was administered intraperitoneally 3 min before reperfusion. After 30 min of ischemia and 180 min of reperfusion, the myocardial infarct size was determined using nitroblue tetrazolium staining. Myocardial myeloperoxidase activity was determined through biochemical assay. HE staining was used for histopathological evaluation. Myocardial SSAO activity was assayed with high performance liquid chromatography analysis. Additionally, the endothelial expression of P-selectin was evaluated using immunohistochemistry after 30 min of ischemia and 20 min of reperfusion.

KEY FINDINGS

Myocardial SSAO activity was increased in myocardial I/R injury. Administration of SCZ, HYD, or LJP 1207 reduced the myocardial infarct size and decreased leukocyte infiltration and endothelial P-selectin expression in myocardial I/R injury in vivo.

SIGNIFICANCE

These data suggest that myocardial I/R injury up-regulates myocardial SSAO activity, and the inhibition of SSAO prior to reperfusion is able to attenuate acute myocardial I/R injury.

Plasma VAP-1/SSAO activity predicts intracranial hemorrhages and adverse neurological outcome after tissue plasminogen activator treatment in stroke

BACKGROUND AND PURPOSE

Vascular adhesion protein-1 (VAP-1) is a cell surface and circulating enzyme involved in recruitment of lymphocytes and neutrophils through its semicarbazide-sensitive amine oxidase (SSAO) activity. We aimed to study plasma VAP-1/SSAO activity in relation to the risk for intracranial bleeding complications in patients with stroke treated with tissue plasminogen activator (tPA), the greatest safety concern with this treatment.

METHODS

In 141 patients with ischemic stroke, we measured VAP-1/SSAO activity in plasma taken before tPA administration. Hemorrhagic events were classified according to brain CT criteria and functional outcomes evaluated using the National Institutes of Health Stroke Scale. We also assessed the potential therapeutic effect of blocking VAP-1/SSAO activity in a rat embolic stroke model treated with tPA.

RESULTS

We saw significantly higher levels of plasma VAP-1/SSAO activity in patients who subsequently experienced hemorrhagic transformation. Elevated plasma VAP-1/SSAO activity also predicted worse neurological outcome in these patients. In the rat model, we confirmed that use of the inhibitor semicarbazide prevented adverse effects caused by delayed tPA administration, leading to a smaller infarct volume.

CONCLUSIONS

Our data demonstrate that baseline VAP-1/SSAO activity predicts parenchymal hemorrhage after tPA, suggesting the safety of thrombolytic agents could be improved by considering VAP-1/SSAO activity. Furthermore, anti-VAP-1/SSAO drugs given with tPA may prevent neurological worsening in patients with ischemic stroke.

Aldose reductase inhibition ameliorates the detrimental effect of estrogen replacement therapy on neuropathology in diabetic rats subjected to transient forebrain ischemia

Estrogen replacement therapy (ERT) elicits a deleterious, instead of protective, effect on neuropathology in diabetic ovariectomized (OVX) rats subjected to cerebral ischemia. This transformation may be linked to an estrogen-associated increase in function of the receptor for advanced glycation end-products (RAGE). Moreover, under diabetic conditions, advanced glycation end-products (AGEs) are excessively generated through the aldose reductase (AR)-polyol pathway. As such, in diabetic rats given ERT, a RAGE-related exacerbation of post-ischemic brain injury can occur. Thus, in the present study, we evaluated the contribution of AR in estrogen's detrimental effect on diabetic animals subjected to transient forebrain ischemia (TFI). Streptozotocin- and 17-beta estradiol-treated OVX female rats were divided into two groups, where AR activity was blocked using epalrestat; or AGEs production was restricted, via administrating the protein glycation crosslink breaker, ALT-711. In all animals, ERT was initiated approximately 10days before TFI. Pial venular leukocyte adhesion was evaluated over 10h post-TFI using a cranial window/intravital microscopy technique. In vehicle-treated control groups, a significant increase in leukocyte adhesion was observed post-TFI. Leukocyte extravasation, starting at approximately 6h post-TFI, was detected in most of the control animals. Chronic administration of either epalrestat or ALT-711 was associated with a marked decrease in post-TFI leukocyte adhesion, and the complete prevention of leukocyte extravasation. Animals receiving either epalrestat or ALT-711 exhibited a significant improvement in neurologic function, at 72h post-ischemia, compared to vehicle-treated controls. Post-ischemic (72h) histopathology was significantly reduced by epalrestat. Compared to the non-diabetic (ND) controls, diabetic OVX rats in the absence or presence of ERT showed a significant 2-fold or 3-fold increase in cortical AR mRNA levels, respectively. In contrast, only a modest increase in AR protein expression, relative to ND control, was detected in the two diabetic groups. The present findings suggest that AR participates in estrogen's deleterious action on post-ischemic neuropathology in diabetics by promoting inflammation. Targeting the AR-controlled polyol pathway may be a clinically promising strategy to restore the neuroprotection of ERT in diabetic females.

Small-molecule inhibitors of vascular adhesion protein-1 reduce the accumulation of myeloid cells into tumors and attenuate tumor growth in mice

Vascular adhesion protein-1 (VAP-1) is an endothelial, cell surface-expressed oxidase involved in leukocyte traffic. The adhesive function of VAP-1 can be blocked by anti-VAP-1 Abs and small-molecule inhibitors. However, the effects of VAP-1 blockade on antitumor immunity and tumor progression are unknown. In this paper, we used anti-VAP-1 mAbs and small-molecule inhibitors of VAP-1 in B16 melanoma and EL-4 lymphoma tumor models in C57BL/6 mice. Leukocyte accumulation into tumors and neoangiogenesis were evaluated by immunohistochemistry, flow cytometry, and intravital videomicroscopy. We found that both anti-VAP-1 Abs and VAP-1 inhibitors reduced the number of leukocytes in the tumors, but they targeted partially different leukocyte subpopulations. Anti-VAP-1 Abs selectively inhibited infiltration of CD8-positive lymphocytes into tumors and had no effect on accumulation of myeloid cells into tumors. In contrast, the VAP-1 inhibitors significantly reduced only the number of proangiogenic Gr-1(+)CD11b(+) myeloid cells in melanomas and lymphomas. Blocking of VAP-1 by either means left tumor homing of regulatory T cells and type 2 immune-suppressing monocytes/macrophages intact. Notably, VAP-1 inhibitors, but not anti-VAP-1 Abs, retarded the growth of melanomas and lymphomas and reduced tumor neoangiogenesis. The VAP-1 inhibitors also reduced the binding of Gr-1(+) myeloid cells to the tumor vasculature. We conclude that tumors use the catalytic activity of VAP-1 to recruit myeloid cells into tumors and to support tumor progression. Small-molecule VAP-1 inhibitors therefore might be a potential new tool for immunotherapy of tumors.

Estrogen replacement therapy in diabetic ovariectomized female rats potentiates postischemic leukocyte adhesion in cerebral venules via a RAGE-related process

In this study, we tested the hypothesis that the documented transformation of 17beta-estradiol (E2) from a counterinflammatory hormone in nondiabetic (ND) rats to a proinflammatory agent in rats with diabetes mellitus (DM) is due to an enhanced contribution from the receptor for advanced glycation end products (RAGE). Rhodamine 6G-labeled leukocytes were observed through a closed cranial window in rats. In vivo pial venular leukocyte adherence and infiltration were measured over 10 h reperfusion after transient forebrain ischemia in DM (streptozotocin) versus ND intact, ovariectomized (OVX), and E2-replaced (for 7-10 days) OVX (OVE) females. The role of RAGE was examined in two ways: 1) RAGE knockdown via topical application of RAGE antisense versus missense oligodeoxynucleotide or 2) intracerebroventricular injection of the RAGE decoy inhibitor, soluble RAGE. Among diabetic rats, the lowest levels of cortical RAGE mRNA and immunoreactivity of the RAGE ligand, AGE, were seen in OVX females, with significantly higher levels exhibited in intact and OVE females. However, results from the analysis of cortical RAGE protein only partially tracked those findings. When comparing ND to DM rats, cortical AGE immunoreactivity was significantly lower in OVE and intact females but similar in OVX rats. In DM rats, the level of postischemic leukocyte adhesion and infiltration (highest to lowest) was OVE>intact>>untreated OVX. In NDs, adhesion was highest in the untreated OVX group. Leukocyte extravasation was observed at >6 h postischemia but only in diabetic OVE and intact females and in ND OVX (untreated) rats. Pretreatment with RAGE antisense-oligodeoxynucleotide or soluble RAGE attenuated postischemic leukocyte adhesion and prevented infiltration but only in the diabetic OVE and intact groups. These results indicate that the exacerbation of postischemic leukocyte adhesion by chronic E2 replacement therapy in diabetic OVX females involves a RAGE-related mechanism. Targeting RAGE may restore the neuroprotective effect of E2 replacement therapy in diabetic females.

Ischemia-reperfusion injury is attenuated in VAP-1-deficient mice and by VAP-1 inhibitors

Neutrophils mediate the damage caused by ischemia-reperfusion both at the site of primary injury and in remote organs. Vascular adhesion protein-1 (VAP-1) is an ectoenzyme expressed on endothelial cells and it has been shown to regulate leukocyte extravasation. Here we show for the first time using VAP-1-deficient mice that VAP-1 plays a significant role in the intestinal damage and acute lung injury after ischemia-reperfusion. Separate inhibition of VAP-1 by small molecule enzyme inhibitors and a function-blocking monoclonal antibody in WT mice revealed that the catalytic activity of VAP-1 is responsible for its pro-inflammatory action. The use of transgenic humanized VAP-1 mice also showed that the enzyme inhibitors alleviate both the ischemia-reperfusion injury in the gut and neutrophil accumulation in the lungs. These data thus indicate that VAP-1 regulates the inflammatory response in ischemia-reperfusion injury and suggest that blockade of VAP-1 may have therapeutic value.

VAP-1 and CD73, Endothelial Cell Surface Enzymes in Leukocyte Extravasation

Leukocyte extravasation from the blood into tissues is crucial for normal immune surveillance and in inflammation. Traditionally molecules belonging to selectin, chemokine, integrin, and immunoglobulin super families are thought to mediate the multiple adhesive and activation events needed for a successful emigration cascade. Recently, emerging evidence suggests that enzymes expressed on the surface of endothelial cells and leukocytes also contribute to the leukocyte extravasation cascade. Here we briefly review the role of vascular adhesion protein-1 (VAP-1) and CD73, 2 cell surface enzymes, in leukocyte migration form the blood into the tissues. Importantly, specific enzyme inhibitors, gene-deficient mice, and recombinant enzymes have recently unambiguously shown that the catalytic activity of these enzymes regulates the leukocyte traffic. The concept of enzymatic regulation of leukocyte extravasation provides new insight into the multi-step adhesion cascade and opens new possibilities for inhibiting inappropriate inflammatory reaction through the use of small molecule enzyme inhibitors.

Anti-inflammatory effects of LJP 1586 [Z-3-fluoro-2-(4-methoxybenzyl)allylamine hydrochloride], an amine-based inhibitor of semicarbazide-sensitive amine oxidase activity

Semicarbazide-sensitive amine oxidase (SSAO, amine oxidase, copper-containing 3, and vascular adhesion protein-1) is a copper-containing enzyme that catalyzes the oxidative deamination of primary amines to an aldehyde, ammonia, and hydrogen peroxide. SSAO is also involved in leukocyte migration to sites of inflammation, and the enzymatic activity of SSAO is essential to this role. Thus, inhibition of SSAO enzyme activity represents a target for the development of small molecule anti-inflammatory compounds. Here, we have characterized the novel SSAO inhibitor, Z-3-fluoro-2-(4-methoxybenzyl)allylamine hydrochloride (LJP 1586), and assessed its anti-inflammatory activity. LJP 1586 is a potent inhibitor of rodent and human SSAO activity, with IC(50) values between 4 and 43 nM. The selectivity of LJP 1586 was confirmed with a broad panel of receptors and enzymes that included the monoamine oxidases A and B. Oral administration of LJP 1586 resulted in complete inhibition of rat lung SSAO, with an ED(50) between 0.1 and 1 mg/kg, and a pharmacodynamic half-life of greater than 24 h. In a mouse model of inflammatory leukocyte trafficking oral dosing with LJP 1586 resulted in significant dose-dependent inhibition of neutrophil accumulation, with an effect comparable to that of anti-leukocyte function-associated antigen-1 antibody. In a rat model of LPS-induced lung inflammation, administration of 10 mg/kg LJP 1586 resulted in a 55% significant reduction in transmigrated cells recovered by bronchoalveolar lavage. The results demonstrate that a selective, orally active small molecule inhibitor of SSAO is an effective anti-inflammatory compound in vivo and provide further support for SSAO as a therapeutic anti-inflammatory target.

Benefit of inhibiting SSAO in relapsing experimental autoimmune encephalomyelitis

We have developed several series of potent and selective small molecule inhibitors of SSAO (AOC3/VAP-1) that also block trafficking of leukocytes to sites of inflammation. Blocking of SSAO-mediated leukocyte adhesion has recently been shown efficacious in several models of inflammatory diseases. We have examined the potential of SSAO inhibitors in neurological diseases, having previously demonstrated the efficacy of SSAO inhibition in a rat model of stroke. Here we show the effect of the small molecule SSAO inhibitor LJP 1207 (IC(50) human SSAO 17 nM; ratio IC(50) SSAO:MAO >5000), on relapsing-remitting experimental autoimmune encephalomyelitis (EAE), a mouse model that shares many characteristics with human multiple sclerosis. Clinical efficacy was observed when dosing with LJP 1207 was initiated either at the peak of initial flare or during remission. These data demonstrate the potential clinical benefit of small molecule anti-SSAO therapy in this model.

Vascular amine oxidases are needed for leukocyte extravasation into inflamed joints in vivo

OBJECTIVE

Leukocyte traffic from the blood to the joints is crucial in the pathogenesis of arthritis. A bifunctional endothelial cell-surface glycoprotein, AOC3 (amine oxidase, copper-containing 3; also known as vascular adhesion protein 1), has both adhesive and enzymatic properties. We undertook this study to determine the contribution of AOC3 and its oxidase activity to leukocyte trafficking into inflamed joints in vivo.

METHODS

We used gene-modified animals, molecular modeling, an AOC3 enzyme inhibitor, oxidase assays, and arthritis models (adjuvant-induced arthritis [AIA] in rats and anti-type II collagen antibody-induced arthritis in mice) to dissect the importance of AOC3 in vivo.

RESULTS

The AOC3 inhibitor fitted well with a covalent binding mode into the active site of the AOC3 crystal structure. It selectively blocked the oxidase activity of AOC3 in enzyme assays. Intraperitoneal and oral administration of the AOC3 inhibitor significantly ameliorated rat AIA. In anti-type II collagen antibody-induced arthritis in mice, the AOC3 inhibitor also improved the outcome of the joint inflammation. The acute semicarbazide-sensitive amine oxidase blockade by the inhibitor had even more pronounced effects than genetic deletion of AOC3. Enzymatic analyses showed that the inhibitor also blocked 2 other structurally very closely related AOCs, but not any of more than 100 other enzymes tested.

CONCLUSION

These are the first data to demonstrate that the enzymatic activity of the atypical endothelial adhesion molecule AOC3, and possibly that of other closely related ecto-oxidases, is crucial for leukocyte exit from the vessels in inflamed joints in vivo.

Influence of sex steroid hormones on cerebrovascular function

The cerebral vasculature is a target tissue for sex steroid hormones. Estrogens, androgens, and progestins all influence the function and pathophysiology of the cerebral circulation. Estrogen decreases cerebral vascular tone and increases cerebral blood flow by enhancing endothelial-derived nitric oxide and prostacyclin pathways. Testosterone has opposite effects, increasing cerebral artery tone. Cerebrovascular inflammation is suppressed by estrogen but increased by testosterone and progesterone. Evidence suggests that sex steroids also modulate blood-brain barrier permeability. Estrogen has important protective effects on cerebral endothelial cells by increasing mitochondrial efficiency, decreasing free radical production, promoting cell survival, and stimulating angiogenesis. Although much has been learned regarding hormonal effects on brain blood vessels, most studies involve young, healthy animals. It is becoming apparent that hormonal effects may be modified by aging or disease states such as diabetes. Furthermore, effects of testosterone are complicated because this steroid is also converted to estrogen, systemically and possibly within the vessels themselves. Elucidating the impact of sex steroids on the cerebral vasculature is important for understanding male-female differences in stroke and conditions such as menstrual migraine and preeclampsia-related cerebral edema in pregnancy. Cerebrovascular effects of sex steroids also need to be considered in untangling current controversies regarding consequences of hormone replacement therapies and steroid abuse.