Vascular adhesion protein-1 blockade suppresses choroidal neovascularization

ADP-Ribosylation Factor 6 Pathway Acts as a Key Executor of Mesenchymal Tumor Plasticity

Despite the "big data" on cancer from recent breakthroughs in high-throughput technology and the development of new therapeutic modalities, it remains unclear as to how intra-tumor heterogeneity and phenotypic plasticity created by various somatic abnormalities and epigenetic and metabolic adaptations orchestrate therapy resistance, immune evasiveness, and metastatic ability. Tumors are formed by various cells, including immune cells, cancer-associated fibroblasts, and endothelial cells, and their tumor microenvironment (TME) plays a crucial role in malignant tumor progression and responses to therapy. ADP-ribosylation factor 6 (ARF6) and AMAP1 are often overexpressed in cancers, which statistically correlates with poor outcomes. The ARF6-AMAP1 pathway promotes the intracellular dynamics and cell-surface expression of various proteins. This pathway is also a major target for KRAS/TP53 mutations to cooperatively promote malignancy in pancreatic ductal adenocarcinoma (PDAC), and is closely associated with immune evasion. Additionally, this pathway is important in angiogenesis, acidosis, and fibrosis associated with tumor malignancy in the TME, and its inhibition in PDAC cells results in therapeutic synergy with an anti-PD-1 antibody in vivo. Thus, the ARF6-based pathway affects the TME and the intrinsic function of tumors, leading to malignancy. Here, we discuss the potential mechanisms of this ARF6-based pathway in tumorigenesis, and novel therapeutic strategies.

Animal model of subretinal fibrosis without active choroidal neovascularization

Subretinal fibrosis can occur during neovascular age-related macular degeneration (nAMD) and consequently provokes progressing deterioration of AMD patient's vision. Intravitreal anti-vascular endothelial growth factor (VEGF) injections decrease choroidal neovascularization (CNV), however, subretinal fibrosis remains principally unaffected. So far, no successful treatment nor established animal model for subretinal fibrosis exists. In order to investigate the impact of anti-fibrotic compounds on solely fibrosis, we refined a time-dependent animal model of subretinal fibrosis without active choroidal neovascularization (CNV). To induce CNV-related fibrosis, wild-type (WT) mice underwent laser photocoagulation of the retina with rupture of Bruch's membrane. The lesions volume was assessed with optical coherence tomography (OCT). CNV (Isolectin B4) and fibrosis (type 1 collagen) were separately quantified with confocal microscopy of choroidal whole-mounts at every time point post laser induction (day 7-49). In addition, OCT, autofluorescence and fluorescence angiography were carried out at designated timepoints (day 7, 14, 21, 28, 35, 42, 49) to monitor CNV and fibrosis transformation over time. From 21 to 49 days post laser lesion leakage in the fluorescence angiography decreased. Correspondingly, Isolectin B4 decreased in lesions of choroidal flat mounts and type 1 collagen increased. Fibrosis markers, namely vimentin, fibronectin, alpha-smooth muscle actin (α-SMA) and type 1 collagen were detected at different timepoints of tissue repair in choroids and retinas post laser. These results prove that the late phase of the CNV-related fibrosis model enables screening of anti-fibrotic compounds to accelerate the therapeutic advancement for the prevention, reduction, or inhibition of subretinal fibrosis.

Recombinant sulfated CCR2 peptide trap reduces retinal degeneration in mice

Chemokine receptors are generally sulfated at tyrosine residues of the N-terminal region. Tyrosine sulfation of the C-C chemokine receptor type 2 (CCR2) enhances its interaction with the chemokine ligand CCL2. Here, we generated a recombinant sulfated CCR2 peptide trap (mCCR2-S2) and investigated its effects on retinal degeneration in mice. Treatment with mCCR2-S2 reduced choroidal neovascularization (CNV) in a laser-induced CNV mouse model. In NaIO₃-injected mice, treatment with mCCR2-S2 increased the outer nuclear layer thickness and rhodopsin expression in the retinas compared to that in mice treated with mCCR2-wild-type or glutathione S-transferase controls. Furthermore, glial fibrillary acidic protein (GFAP) expression and macrophage infiltration were decreased in mCCR2-S2-treated retinas. Recombinant mCCR2-S2 suppressed CNV development and retinal degeneration, possibly by regulating macrophage infiltration. Thus, the sulfated form of the CCR2 peptide trap may be a useful tool for treating patients with retinal degeneration, such as those with age-related macular degeneration and intraocular inflammatory disorders.

Choriocapillaris: Fundamentals and advancements

The choriocapillaris is the innermost structure of the choroid that directly nourishes the retinal pigment epithelium and photoreceptors. This article provides an overview of its hemovasculogenesis development to achieve its final architecture as a lobular vasculature, and also summarizes the current histological and molecular knowledge about choriocapillaris and its dysfunction. After describing the existing state-of-the-art tools to image the choriocapillaris, we report the findings in the choriocapillaris encountered in the most frequent retinochoroidal diseases including vascular diseases, inflammatory diseases, myopia, pachychoroid disease spectrum disorders, and glaucoma. The final section focuses on the development of imaging technology to optimize visualization of the choriocapillaris as well as current treatments of retinochoroidal disorders that specifically target the choriocapillaris. We conclude the article with pertinent unanswered questions and future directions in research for the choriocapillaris.

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.

Regulation of Pain Genes-Capsaicin vs Resiniferatoxin: Reassessment of Transcriptomic Data

Emerging evidence has shown a strong association between neuropathic pain and chronic diseases. In recent years, the treatment of neuropathic pain has attracted more attention. Natural products, such as capsaicin and resiniferatoxin, have been well utilized to treat this disease. In this study, we aim to compare the regulatory effects of capsaicin and resiniferatoxin on pain-related genes as well as on genes with no direct association with pain. Public transcriptomic and microarray data on gene expression in the dorsal root ganglia and genes associated with TRPV1 (+) neurons were obtained from the GEO database and then analyzed. Differentially expressed genes were selected for further functional analysis, including pathway enrichment, protein-protein interaction, and regulatory network analysis. Pain-associated genes were extracted with the reference of two pain gene databases and the effects of these two natural drugs on the pain-associated genes were measured. The results of our research indicate that as compared to capsaicin, resiniferatoxin (RTX) regulates more non pain-associated genes and has a negative impact on beneficial genes (off-targets) which are supposed to alleviate nociception and hypersensitivity by themselves. So, based on this study, we may conclude that capsaicin may be less potent when compared to RTX, but it will elicit considerably less adverse effects too. Thereby confirming that capsaicin could be used for the efficient alleviation of neuropathic pain with possibly fewer side effects.

Pathological Role of Unsaturated Aldehyde Acrolein in Diabetic Retinopathy

With increasing prevalence of diabetes and a progressively aging society, diabetic retinopathy is emerging as one of the global leading causes of blindness. Recent studies have shown that vascular endothelial growth factor (VEGF) plays a central role in the pathogenesis of diabetic retinopathy and anti-VEGF agents have become the first-line therapy for the vision-threatening disease. However, recent studies have also demonstrated that diabetic retinopathy is a multifactorial disease and that VEGF-independent mechanism(s) also underlie much of the pathological changes in diabetic retinopathy. Acrolein is a highly reactive unsaturated aldehyde and is implicated in protein dysfunction. As acrolein is common in air pollutants, previous studies have focused on it as an exogenous causative factor, for instance, in the development of respiratory diseases. However, it has been discovered that acrolein is also endogenously produced and induces cell toxicity and oxidative stress in the body. In addition, accumulating evidence suggests that acrolein and/or acrolein-conjugated proteins are associated with the molecular mechanisms in diabetic retinopathy. This review summarizes the pathological roles and mechanisms of endogenous acrolein production in the pathogenesis of diabetic retinopathy.

PPARα Agonist Oral Therapy in Diabetic Retinopathy

Diabetic retinopathy (DR) is an eye condition that develops after chronically poorly-managed diabetes, and is presently the main cause for blindness on a global scale. Current treatments for DR such as laser photocoagulation, topical injection of corticosteroids, intravitreal injection of anti-vascular endothelial growth factor (VEGF) agents and vitreoretinal surgery are only applicable at the late stages of DR and there are possibilities of significant adverse effects. Moreover, the forms of treatment available for DR are highly invasive to the eyes. Safer and more effective pharmacological treatments are required for DR treatment, in particular at an early stage. In this review, we cover recently investigated promising oral pharmacotherapies, the methods of which are safer, easier to use, patient-friendly and pain-free, in clinical studies. We especially focus on peroxisome proliferator-activator receptor alpha (PPARα) agonists in which experimental evidence suggests PPARα activation may be closely related to the attenuation of vascular damages, including lipid-induced toxicity, inflammation, an excess of free radical generation, endothelial dysfunction and angiogenesis. Furthermore, oral administration of selective peroxisome proliferator-activated receptor alpha modulator (SPPARMα) agonists may induce hepatic fibroblast growth factor 21 expression, indirectly resulting in retinal protection in animal studies. Our review will enable more comprehensive approaches for understanding protective roles of PPARα for the prevention of DR development.

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.

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

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

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

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

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

PURPOSE

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

STUDY DESIGN

Experimental.

METHODS

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

RESULTS

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

CONCLUSIONS

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

Differential proteomic analysis of white adipose tissues from T2D KKAy mice by LC-ESI-QTOF

Type 2 diabetes (T2D) has become a worldwide increasingly social health burden for its high morbidity and heightened prevalence. As one of the main tissues involved in uptake of glucose under the stimulation of insulin, WAT plays very important role in metabolic and homeostasis regulation. We performed a differential proteomics study to investigate alterations in epididymis fat pad of high fat diet fed T2D KKAy mice compared to normal fed C57BL/6J mice, by ¹⁸ O-labeling relative quantitative technique. Among 329 confidently identified proteins, 121 proteins showed significant changes with CV ≤ 20% (fold changes of >2 or <0.5 as threshold). According to GO classification, we found that altered proteins contained members of biological processes of metabolic process, oxidative stress, ion homeostasis, apoptosis and cell division. In metabolic, proteins assigned to fatty acid biosynthesis (FAS etc.) were decreased, the key enzyme (ACOX3) in β-oxidation process was increased. Increased glycolysis enzymes (ENOB etc.) and decreased TCA cycle related enzymes (SCOT1 etc.) suggested that glucose metabolism in mitochondria of T2D mice might be impaired. Elevated oxidative stress was observed with alterations of a series of oxidordeuctase (QSOX1 etc.). Besides, alterations of ion homeostasis (AT2C1 etc.) proteins were also observed. The enhancement of cell proliferation associated proteins (ELYS etc.) and inhibition of apoptosis associated proteins (RASF6 etc.) in WAT might contributed to the fat pad and body weight gain. Overall, these changes in WAT may serve as a reference for understanding the functional mechanism of T2D.

Cytochrome P450 monooxygenase lipid metabolites are significant second messengers in the resolution of choroidal neovascularization

Age-related macular degeneration (AMD) is the most common cause of blindness for individuals age 50 and above in the developed world. Abnormal growth of choroidal blood vessels, or choroidal neovascularization (CNV), is a hallmark of the neovascular (wet) form of advanced AMD and leads to significant vision loss. A growing body of evidence supports a strong link between neovascular disease and inflammation. Metabolites of long-chain polyunsaturated fatty acids derived from the cytochrome P450 (CYP) monooxygenase pathway serve as vital second messengers that regulate a number of hormones and growth factors involved in inflammation and vascular function. Using transgenic mice with altered CYP lipid biosynthetic pathways in a mouse model of laser-induced CNV, we characterized the role of these lipid metabolites in regulating neovascular disease. We discovered that the CYP-derived lipid metabolites epoxydocosapentaenoic acids (EDPs) and epoxyeicosatetraenoic acids (EEQs) are vital in dampening CNV severity. Specifically, overexpression of the monooxygenase CYP2C8 or genetic ablation or inhibition of the soluble epoxide hydrolase (sEH) enzyme led to increased levels of EDP and EEQ with attenuated CNV development. In contrast, when we promoted the degradation of these CYP-derived metabolites by transgenic overexpression of sEH, the protective effect against CNV was lost. We found that these molecules work in part through their ability to regulate the expression of key leukocyte adhesion molecules, on both leukocytes and endothelial cells, thereby mediating leukocyte recruitment. These results suggest that CYP lipid signaling molecules and their regulators are potential therapeutic targets in neovascular diseases.

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.

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.

Cytochrome P450-generated metabolites derived from ω-3 fatty acids attenuate neovascularization

Ocular neovascularization, including age-related macular degeneration (AMD), is a primary cause of blindness in individuals of industrialized countries. With a projected increase in the prevalence of these blinding neovascular diseases, there is an urgent need for new pharmacological interventions for their treatment or prevention. Increasing evidence has implicated eicosanoid-like metabolites of long-chain polyunsaturated fatty acids (LCPUFAs) in the regulation of neovascular disease. In particular, metabolites generated by the cytochrome P450 (CYP)-epoxygenase pathway have been shown to be potent modulators of angiogenesis, making this pathway a reasonable previously unidentified target for intervention in neovascular ocular disease. Here we show that dietary supplementation with ω-3 LCPUFAs promotes regression of choroidal neovessels in a well-characterized mouse model of neovascular AMD. Leukocyte recruitment and adhesion molecule expression in choroidal neovascular lesions were down-regulated in mice fed ω-3 LCPUFAs. The serum of these mice showed increased levels of anti-inflammatory eicosanoids derived from eicosapentaenoic acid and docosahexaenoic acid. 17,18-epoxyeicosatetraenoic acid and 19,20-epoxydocosapentaenoic acid, the major CYP-generated metabolites of these primary ω-3 LCPUFAs, were identified as key lipid mediators of disease resolution. We conclude that CYP-derived bioactive lipid metabolites from ω-3 LCPUFAs are potent inhibitors of intraocular neovascular disease and show promising therapeutic potential for resolution of neovascular AMD.

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.

Semicarbazide-sensitive amine oxidase and kidney disease

With better understanding of the molecular mechanisms underpinning chronic kidney disease, the roles of inflammation and fibrosis are becoming increasingly inseparable. The progression of renal disease is characterized by pathomorphological changes that consist of early inflammatory responses followed by tubulointerstitial fibrosis, tubular atrophy, and glomerular and vascular sclerosis. Currently available therapies that reduce hypertension, proteinuria, hyperglycemia, and interruption of the renin-angiotensin-aldosterone system are at best only partially effective. Hence, there remains a need to explore agents targeting nonrenin-angiotensin-aldosterone system pathways. In this review, we discuss mechanistic aspects in the physiological and pathological role of semicarbazide-sensitive amine oxidase, a protein enzyme involved in cellular trafficking and inflammation, with respect to the kidney. We explore the evidence for the use of semicarbazide-sensitive amine oxidase inhibitors as potential agents in renal fibrosis to delay the onset and progression of chronic kidney disease.

Vascular adhesion protein 1 in the eye

Semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 (SSAO/VAP-1), a dual-function molecule with adhesive and enzymatic properties, is expressed on the surface of vascular endothelial cells of mammals. It also exists as a soluble form (sVAP-1), which is implicated in oxidative stress via its enzymatic activity and can be a prognostic biomarker. Recent evidence suggests that VAP-1 is an important therapeutic target for several inflammation-related ocular diseases, such as uveitis, age-related macular degeneration (AMD), and diabetic retinopathy (DR), by involving in the recruitment of leukocytes at sites of inflammation. Furthermore, VAP-1 plays an important role in the pathogenesis of conjunctival inflammatory diseases such as pyogenic granulomas and the progression of conjunctival lymphoma. VAP-1 may be an alternative therapeutic target in ocular diseases. The in vivo imaging of inflammation using VAP-1 as a target molecule is a novel approach with a potential for early detection and characterization of inflammatory diseases. This paper reviews the critical roles of VAP-1 in ophthalmological diseases which may provide a novel research direction or a potent therapeutic strategy.

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.

Ocular neovascularization

Retinal and choroidal vascular diseases constitute the most common causes of moderate and severe vision loss in developed countries. They can be divided into retinal vascular diseases, in which there is leakage and/or neovascularization (NV) from retinal vessels, and subretinal NV, in which new vessels grow into the normally avascular outer retina and subretinal space. The first category of diseases includes diabetic retinopathy, retinal vein occlusions, and retinopathy of prematurity, and the second category includes neovascular age-related macular degeneration (AMD), ocular histoplasmosis, pathologic myopia, and other related diseases. Retinal hypoxia is a key feature of the first category of diseases resulting in elevated levels of hypoxia-inducible factor-1 (HIF-1) which stimulates expression of vascular endothelial growth factor (VEGF), platelet-derived growth factor-B (PDGF-B), placental growth factor, stromal-derived growth factor-1 and their receptors, as well as other hypoxia-regulated gene products such as angiopoietin-2. Although hypoxia has not been demonstrated as part of the second category of diseases, HIF-1 is elevated and thus the same group of hypoxia-regulated gene products plays a role. Clinical trials have shown that VEGF antagonists provide major benefits for patients with subretinal NV due to AMD and even greater benefits are seen by combining antagonists of VEGF and PDGF-B. It is likely that addition of antagonists of other agents listed above will be tested in the future. Other appealing strategies are to directly target HIF-1 or to use gene transfer to express endogenous or engineered anti-angiogenic proteins. While substantial progress has been made, the future looks even brighter for patients with retinal and choroidal vascular diseases.

The regulatory roles of apoptosis-inducing factor in the formation and regression processes of ocular neovascularization

The role of apoptosis in the formation and regression of neovascularization is largely hypothesized, although the detailed mechanism remains unclear. Inflammatory cells and endothelial cells both participate and interact during neovascularization. During the early stage, these cells may migrate into an angiogenic site and form a pro-angiogenic microenvironment. Some angiogenic vessels appear to regress, whereas some vessels mature and remain. The control mechanisms of these processes, however, remain unknown. Previously, we reported that the prevention of mitochondrial apoptosis contributed to cellular survival via the prevention of the release of proapoptotic factors, such as apoptosis-inducing factor (AIF) and cytochrome c. In this study, we investigated the regulatory role of cellular apoptosis in angiogenesis using two models of ocular neovascularization: laser injury choroidal neovascularization and VEGF-induced corneal neovascularization in AIF-deficient mice. Averting apoptosis in AIF-deficient mice decreased apoptosis of leukocytes and endothelial cells compared to wild-type mice and resulted in the persistence of these cells at angiogenic sites in vitro and in vivo. Consequently, AIF deficiency expanded neovascularization and diminished vessel regression in these two models. We also observed that peritoneal macrophages from AIF-deficient mice showed anti-apoptotic survival compared to wild-type mice under conditions of starvation. Our data suggest that AIF-related apoptosis plays an important role in neovascularization and that mitochondria-regulated apoptosis could offer a new target for the treatment of pathological angiogenesis.

Understanding age-related macular degeneration (AMD): relationships between the photoreceptor/retinal pigment epithelium/Bruch's membrane/choriocapillaris complex

There is a mutualistic symbiotic relationship between the components of the photoreceptor/retinal pigment epithelium (RPE)/Bruch's membrane (BrMb)/choriocapillaris (CC) complex that is lost in AMD. Which component in the photoreceptor/RPE/BrMb/CC complex is affected first appears to depend on the type of AMD. In atrophic AMD (~85-90% of cases), it appears that large confluent drusen formation and hyperpigmentation (presumably dysfunction in RPE) are the initial insult and the resorption of these drusen and loss of RPE (hypopigmentation) can be predictive for progression of geographic atrophy (GA). The death and dysfunction of photoreceptors and CC appear to be secondary events to loss in RPE. In neovascular AMD (~10-15% of cases), the loss of choroidal vasculature may be the initial insult to the complex. Loss of CC with an intact RPE monolayer in wet AMD has been observed. This may be due to reduction in blood supply because of large vessel stenosis. Furthermore, the environment of the CC, basement membrane and intercapillary septa, is a proinflammatory milieu with accumulation of complement components as well as proinflammatory molecules like CRP during AMD. In this toxic milieu, CC die or become dysfunction making adjacent RPE hypoxic. These hypoxic cells then produce angiogenic substances like VEGF that stimulate growth of new vessels from CC, resulting in choroidal neovascularization (CNV). The loss of CC might also be a stimulus for drusen formation since the disposal system for retinal debris and exocytosed material from RPE would be limited. Ultimately, the photoreceptors die of lack of nutrients, leakage of serum components from the neovascularization, and scar formation. Therefore, the mutualistic symbiotic relationship within the photoreceptor/RPE/BrMb/CC complex is lost in both forms of AMD. Loss of this functionally integrated relationship results in death and dysfunction of all of the components in the complex.

Targeting of junctional adhesion molecule-C inhibits experimental choroidal neovascularization

PURPOSE

To identify the expression of junctional adhesion molecule-C (JAM-C) in choroidal neovascularization (CNV) and evaluate the effect of JAM-C targeting on CNV formation and on cellular functions relevant to CNV in vitro, such as macrophage transmigration, human retinal pigment epithelial (hRPE) cell migration, and monolayer RPE permeability.

METHODS

JAM-C expression in CNV was analyzed by real-time PCR, immunoblot analysis, and immunofluorescence staining. CNV area and blood vessel leakage were quantified using isolectin B4 staining and fluorescein angiography, respectively, 1 week after laser treatment. Macrophage infiltration within the CNV area was measured by immunofluorescence, and transmigration through monolayer RPE was analyzed using a transepithelial migration assay. After JAM-C shRNA transfection, human RPE cell migration was quantified using a transwell assay, and monolayer RPE permeability was determined by measuring the apical-to-basolateral movements of sodium fluorescein.

RESULTS

JAM-C expression was upregulated during CNV formation after laser treatment in a time-dependent manner. However, no change in JAM-C expression was found in the retina up to 14 days after laser treatment. JAM-C targeting by intravitreal injection of JAM-C Fc chimera inhibited CNV, blood vessel leakage, and macrophage infiltration. JAM-C Fc chimera inhibited basolateral-to-apical transmigration in vitro through a monolayer of hRPE of macrophages from patients with wet AMD. In addition, shRNA-mediated JAM-C knockdown inhibited hRPE cell migration and hRPE permeability.

CONCLUSIONS

JAM-C blockade may prove useful for CNV suppression by inhibiting macrophage transmigration, RPE cell migration, and monolayer RPE barrier malfunction.

Blockade of vascular adhesion protein-1 attenuates choroidal neovascularization

PURPOSE

Vascular adhesion protein (VAP)-1 is an adhesion molecule elucidated as a mediator of the leukocyte recruitment cascade. The purpose of this study was to investigate the role of VAP-1 in ocular inflammatory neovascularization using a mouse laser-induced choroidal neovascularization (CNV) model.

METHODS

CNV was induced with 532 nm laser irradiation in C57BL/6 mice, and production of VAP-1 protein in the retinal pigment epithelium (RPE) choroid during CNV formation was examined. CNV animals were treated with the specific VAP-1 inhibitor U-V002 or vehicle solution, and the volume of CNV tissue was evaluated with volumetric measurements. Macrophage infiltration into the CNV lesions was evaluated using two different techniques, flatmount staining and real-time polymerase chain reaction (PCR) for F4/80. The protein levels of intercellular adhesion molecule (ICAM)-1, monocyte chemoattractant protein (MCP)-1, P-selectin, and vascular endothelial growth factor (VEGF) in the RPE-choroid were measured with enzyme-linked immunosorbent assay (ELISA).

RESULTS

VAP-1 inhibition significantly suppressed CNV formation in a dose-dependent manner and reduced macrophage infiltration into CNV lesions. Furthermore, VAP-1 blockade decreased the expression of ICAM-1 and MCP-1, both of which play a pivotal role in macrophage recruitment.

CONCLUSIONS

Our data suggest VAP-1 has an important role during ocular inflammatory neovascularization through leukocyte recruitment. VAP-1 inhibition may be a novel and potent therapeutic strategy in treating CNV formation.

Monocyte chemoattractant protein-1 in the aqueous humour of patients with age-related macular degeneration

BACKGROUND

  To investigate the role of inflammation in age-related macular degeneration by measuring the levels of cytokines in the aqueous humour.

METHODS

  Samples of aqueous humour were collected from 34 patients with age-related macular degeneration and 16 age-matched control subjects undergoing cataract surgery. Age-related macular degeneration stage was determined clinically, before surgery. Levels of cytokines were measured using Luminex X-MAP technology, and positive results were verified by Western blot.

RESULTS

  Age-related macular degeneration was moderate in 18 patients and advanced in 16. The advanced age-related macular degeneration group was further divided into patients with active choroidal neovascularization (n = 7), disciform scar (n = 7) or central geographic atrophy (n = 2). Higher-than-normal levels of monocyte chemoattractant protein-1 in the aqueous humour were associated with advanced age-related macular degeneration (200 ± 140 pg/mL vs. 100 ± 61 pg/mL; P = 0.03), especially active choroidal neovascularization (255 ± 155 pg/mL; P = 0.02), Western blot analysis verified the monocyte chemoattractant protein-1 findings. Patients with disciform scar showed a trend of abnormally high levels of interleukin-12 (p70) (1.7 ± 2.4 pg/mL vs. 0.2 ± 1 pg/mL; P = 0.07), tumour necrosis factor-α (1.8 ± 2.4 pg/mL vs. 0.3 ± 1 pg/mL; P = 0.06) and interleukin-12 (4.7 ± 6.4 pg/mL vs. 1.2 ± 2.1 pg/mL; P = 0.08).

CONCLUSION

  Elevated levels of inflammation-related cytokines in the aqueous humour in various stages of age-related macular degeneration may suggest a pathogenic role of inflammation. Monocyte chemoattractant protein-1 may be indicative of the angiogenic phase. Further corroborative studies are required.

Suppression and regression of choroidal neovascularization in mice by a novel CCR2 antagonist, INCB3344

PURPOSE

To investigate the effect of an intravitreally administered CCR2 antagonist, INCB3344, on a mouse model of choroidal neovascularization (CNV).

METHODS

CNV was induced by laser photocoagulation on Day 0 in wild type mice. INCB3344 or vehicle was administered intravitreally immediately after laser application. On Day 14, CNV areas were measured on retinal pigment epithelium (RPE)-choroid flat mounts and histopathologic examination was performed on 7 µm-thick sections. Macrophage infiltration was evaluated by immunohistochemistry on RPE-choroid flat mounts and quantified by flow cytometry on Day 3. Expression of vascular endothelial growth factor (VEGF) protein in RPE-choroid tissue was examined by immunohistochemistry and ELISA, VEGF mRNA in sorted macrophages in RPE-choroid tissue was examine by real-time PCR and expression of phosphorylated extracellular signal-regulated kinase (p-ERK 1/2) in RPE-choroid tissue was measured by Western blot analysis on Day 3. We also evaluated the efficacy of intravitreal INCB3344 to spontaneous CNV detected in Cu, Zn-superoxide dismutase (SOD1) deficient mice. Changes in CNV size were assessed between pre- and 1week post-INCB3344 or vehicle administration in fundus photography and fluorescence angiography (FA).

RESULTS

The mean CNV area in INCB3344-treated mice decreased by 42.4% compared with the vehicle-treated control mice (p<0.001). INCB3344 treatment significantly inhibited macrophage infiltration into the laser-irradiated area (p<0.001), and suppressed the expression of VEGF protein (p = 0.012), VEGF mRNA in infiltrating macrophages (p<0.001) and the phosphorylation of ERK1/2 (p<0.001). The area of spontaneous CNV in Sod1⁻/⁻ mice regressed by 70.35% in INCB3344-treated animals while no change was detected in vehicle-treated control mice (p<0.001).

CONCLUSIONS

INCB3344 both inhibits newly forming CNV and regresses established CNV. Controlling inflammation by suppressing macrophage infiltration and angiogenic ability via the CCR-2/MCP-1 signal may be a useful therapeutic strategy for treating CNV associated with age-related macular degeneration.

Leukocyte adhesion molecules in diabetic retinopathy

Diabetes is a systemic disease that causes a number of metabolic and physiologic abnormalities. One of the major microvascular complications of diabetes is diabetic retinopathy (DR), a leading cause of blindness in people over age 50. The mechanisms underlying the development of DR are not fully understood; however, extensive studies have recently implicated chronic, low-grade inflammation in the pathophysiology of DR. During inflammation leukocytes undergo sequential adhesive interactions with endothelial cells to migrate into the inflamed tissues, a process known as the “leukocyte recruitment cascade” which is orchestrated by precise adhesion molecule expression on the cell surface of leukocytes and the endothelium. This paper summarizes the recent clinical and preclinical works on the roles of leukocyte adhesion molecules in DR.

GEP100-Arf6-AMAP1-cortactin pathway frequently used in cancer invasion is activated by VEGFR2 to promote angiogenesis

Angiogenesis and cancer invasiveness greatly contribute to cancer malignancy.

Arf6 and its effector, AMAP1, are frequently overexpressed in breast cancer, and constitute a central pathway to induce the invasion and metastasis. In this pathway, Arf6 is activated by EGFR via GEP100. Arf6 is highly expressed also in human umbilical vein endothelial cells (HUVECs) and is implicated in angiogenesis. Here, we found that HUVECs also highly express AMAP1, and that vascular endothelial growth factor receptor-2 (VEGFR2) recruits GEP100 to activate Arf6. AMAP1 functions by binding to cortactin in cancer invasion and metastasis. We demonstrate that the same GEP100-Arf6-AMAP1-cortactin pathway is essential for angiogenesis activities, including cell migration and tubular formation, as well as for the enhancement of cell permeability and VE-cadherin endocytosis of VEGF-stimulated HUVECs. Components of this pathway are highly expressed in pathologic angiogenesis, and blocking of this pathway effectively inhibits VEGF- or tumor-induced angiogenesis and choroidal neovascularization. The GEP100-Arf6-AMAP1-cortactin pathway, activated by receptor tyrosine kinases, appears to be common in angiogenesis and cancer invasion and metastasis, and provides their new therapeutic targets.

VAP-1-mediated M2 macrophage infiltration underlies IL-1β- but not VEGF-A-induced lymph- and angiogenesis

Vascular adhesion protein-1 (VAP-1) contributes to inflammatory and angiogenic diseases, including cancer and age-related macular degeneration. It is expressed in blood vessels and contributes to inflammatory leukocyte recruitment. The cytokines IL-1β and vascular endothelial growth factor A (VEGF-A) modulate angiogenesis, lymphangiogenesis, and leukocyte infiltration. The lymphatic endothelium expresses intercellular adhesion molecule-1 and vascular adhesion molecule-1, which facilitate leukocyte transmigration into the lymphatic vessels. However, whether lymphatics express VAP-1 and whether they contribute to cytokine-dependent lymph- and angiogenesis are unknown. We investigated the role of VAP-1 in IL-1β- and VEGF-A-induced lymph- and angiogenesis using the established corneal micropocket assay. IL-1β increased VAP-1 expression in the inflamed cornea. Our in vivo molecular imaging revealed significantly higher VAP-1 expression in neovasculature than in the preexisting vessels. VAP-1 was expressed in blood but not lymphatic vessels in vivo. IL-1β-induced M2 macrophage infiltration and lymph- and angiogenesis were blocked by VAP-1 inhibition. In contrast, VEGF-A-induced lymph- and angiogenesis were unaffected by VAP-1 inhibition. Our results indicate a key role for VAP-1 in lymph- and angiogenesis-related macrophage recruitment. VAP-1 might become a new target for treatment of inflammatory lymph- and angiogenic diseases, including cancer.

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.

Parstatin suppresses ocular neovascularization and inflammation

PURPOSE

Parstatin is a 41-mer peptide formed by proteolytic cleavage on activation of the PAR1 receptor. The authors recently showed that parstatin is a potent inhibitor of angiogenesis. The purpose of the present study was to evaluate the therapeutic effect of parstatin on ocular neovascularization.

METHODS

Choroidal neovascularization was generated in mice using laser-induced rupture of Bruch's membrane and was assessed after 14 days after perfusion of FITC-dextran. Oxygen-induced retinal neovascularization was established in neonatal mice by exposing them to 75% O(2) at postnatal day (P)7 for 5 days and then placing them in room air for 5 days. Evaluation was performed on P17 after staining with anti-mouse PECAM-1. The effect of parstatin was tested after intravitreal administration. The effects of subconjunctival-injected parstatin on corneal neovascularization and inflammation in rats were assessed 7 days after chemical burn-induced corneal neovascularization. Retinal leukostasis in mice was assessed after perfusion with FITC-conjugated concanavalin A.

RESULTS

Parstatin potently inhibited choroidal neovascularization with an IC(50) of approximately 3 μg and a maximum inhibition of 59% at 10 μg. Parstatin suppressed retinal neovascularization with maximum inhibition of 60% at 3 μg. Ten-microgram and 30-μg doses appeared to be toxic to the neonatal retina. Subconjunctival parstatin inhibited corneal neovascularization, with 200 μg the most effective dose (59% inhibition). In addition, parstatin significantly inhibited corneal inflammation and VEGF-induced retinal leukostasis. In all models tested, scrambled parstatin was without any significant effect.

CONCLUSIONS

Parstatin is a potent antiangiogenic agent of ocular neovascularization and may have clinical potential in the treatment of angiogenesis-related ocular disorders.

Inflammatory mediators and angiogenic factors in choroidal neovascularization: pathogenetic interactions and therapeutic implications

Choroidal neovascularization (CNV) is a common and severe complication in heterogeneous diseases affecting the posterior segment of the eye, the most frequent being represented by age-related macular degeneration. Although the term may suggest just a vascular pathological condition, CNV is more properly definable as an aberrant tissue invasion of endothelial and inflammatory cells, in which both angiogenesis and inflammation are involved. Experimental and clinical evidences show that vascular endothelial growth factor is a key signal in promoting angiogenesis. However, many other molecules, distinctive of the inflammatory response, act as neovascular activators in CNV. These include fibroblast growth factor, transforming growth factor, tumor necrosis factor, interleukins, and complement. This paper reviews the role of inflammatory mediators and angiogenic factors in the development of CNV, proposing pathogenetic assumptions of mutual interaction. As an extension of this concept, new therapeutic approaches geared to have an effect on both the vascular and the extravascular components of CNV are discussed.

Expression of stem cell factor/c-kit signaling pathway components in diabetic fibrovascular epiretinal membranes

PURPOSE

Stem cell factor (SCF)/c-kit signaling promotes recruitment of endothelial progenitor cells and contributes to ischemia-induced new vessel formation. We investigated the expression of the components of this pathway, including c-kit, SCF, granulocyte colony-stimulating factor (G-CSF), endothelial nitric oxide synthase (eNOS), and the chemokine receptor CXCR4, in proliferative diabetic retinopathy (PDR) epiretinal membranes.

METHODS

Membranes from eight patients with active PDR and 12 patients with inactive PDR were studied by immunohistochemistry.

RESULTS

Blood vessels expressed c-kit, SCF, G-CSF, eNOS, and CXCR4 in 18, 15, 19, 20, and 20 out of 20 membranes, respectively. Significant correlations were detected between the number of blood vessels expressing CD34 and the number of blood vessels expressing SCF (r=0.463; p=0.04), G-CSF (r=0.87; p<0.001), eNOS (r=0.864; p<0.001), and CXCR4 (r=0.864; p<0.001). Stromal cells expressed c-kit, SCF, eNOS, and CXCR4 in 19, 15, 20, and 20 membranes, respectively. The numbers of blood vessels expressing CD34 (p=0.005), c-kit (p=0.03), G-CSF (p=0.007), eNOS (p=0.001), and CXCR4 (p=0.018) and stromal cells expressing c-kit (p=0.013), SCF (p<0.001), eNOS (p=0.048), and CXCR4 (p=0.003) were significantly higher in active membranes than in inactive membranes.

CONCLUSIONS

SCF/c-kit signaling might contribute to neovascularization in PDR.

Platelet-derived growth factor-DD targeting arrests pathological angiogenesis by modulating glycogen synthase kinase-3beta phosphorylation

Platelet-derived growth factor-DD (PDGF-DD) is a recently discovered member of the PDGF family. The role of PDGF-DD in pathological angiogenesis and the underlying cellular and molecular mechanisms remain largely unexplored. In this study, using different animal models, we showed that PDGF-DD expression was up-regulated during pathological angiogenesis, and inhibition of PDGF-DD suppressed both choroidal and retinal neovascularization. We also demonstrated a novel mechanism mediating the function of PDGF-DD. PDGF-DD induced glycogen synthase kinase-3beta (GSK3beta) Ser(9) phosphorylation and Tyr(216) dephosphorylation in vitro and in vivo, leading to increased cell survival. Consistently, GSK3beta activity was required for the antiangiogenic effect of PDGF-DD targeting. Moreover, PDGF-DD regulated the expression of GSK3beta and many other genes important for angiogenesis and apoptosis. Thus, we identified PDGF-DD as an important target gene for antiangiogenic therapy due to its pleiotropic effects on vascular and non-vascular cells. PDGF-DD inhibition may offer new therapeutic options to treat neovascular diseases.

Atrial natriuretic peptide reduces vascular leakage and choroidal neovascularization

Atrial natriuretic peptide (ANP) is a hormone with diuretic, natriuretic, and vasodilatory properties. ANP blocks vascular endothelial growth factor (VEGF) production and signaling in vitro; however, its role in vascular leakage and angiogenesis is unknown. In vitro, retinal barrier permeability (transepithelial electrical resistance (TEER)) was measured in cultured retinal endothelial (HuREC) and retinal epithelial (ARPE-19) cells with VEGF (10 ng/ml), ANP (1 pM to 1 micromol/L), and/or isatin, an ANP receptor antagonist. In vivo, blood-retinal barrier (BRB) leakage was studied using the Evans Blue dye technique in rats treated with intravitreal injections of ANP, VEGF, or vehicle. Choroidal neovascularization was generated by laser injury, and 7 days later, lesion size and leakage was quantitated. ANP significantly reversed VEGF-induced BRB TEER reduction in both HuREC and ARPE-19 cells, modeling the inner and the outer BRB, respectively. Isatin, a specific ANP receptor antagonist, reversed ANP's effect. ANP reduced the response of ARPE-19 cells to VEGF apically but not basolaterally, suggesting polarized expression of the ANP receptors in these cells. ANP's TEER response was concentration but not time dependent. In vivo, ANP significantly reduced VEGF-induced BRB leakage and the size of laser-induced choroidal neovascularization lesions. In sum, ANP is an effective inhibitor of VEGF-induced vascular leakage and angiogenesis in vivo. These results may lead to new treatments for ocular diseases where VEGF plays a central role, such as age-related macular degeneration or diabetic retinopathy.

Localization of vascular adhesion protein-1 (VAP-1) in the human eye

Recently we showed a critical role for Vascular Adhesion Protein-1 (VAP-1) in rodents during acute ocular inflammation, angiogenesis, and diabetic retinal leukostasis. However, the expression of VAP-1 in the human eye is unknown. VAP-1 localization was therefore investigated by immunohistochemistry. Five micrometer thick sections were generated from human ocular tissues embedded in paraffin. Sections were incubated overnight with primary mAbs against VAP-1 (5 microg/ml), smooth muscle actin (1 microg/ml), CD31 or isotype-matched IgG at 4 degrees C. Subsequently, a secondary mAb was used for 30 min at room temperature, followed by Dako Envision + HRP (AEC) System for signal detection. The stained sections were examined using light microscopy and the signal intensity was quantified by two evaluators and graded into 4 discrete categories. In all examined ocular tissues, VAP-1 staining was confined to the vasculature. VAP-1 labeling showed the highest intensity in both arteries and veins of neuronal tissues: retina and optic nerve, and the lowest intensity in the iris vasculature (p < 0.05). Scleral and choroidal vessels showed moderate staining for VAP-1. VAP-1 intensity was significantly higher in the arteries compared to veins (p < 0.05). Furthermore, VAP-1 staining in arteries colocalized with both CD31 and smooth muscle actin (sm-actin) staining, suggesting expression of VAP-1 in endothelial cells, smooth muscle cells or potentially pericytes. In conclusion, immunohistochemistry reveals constitutive expression of VAP-1 in human ocular tissues. VAP-1 expression is nearly exclusive to the vasculature with arteries showing significantly higher expression than veins. Furthermore, VAP-1 expression in the ocular vasculature is heterogeneous, with the vessels of the optic nerve and the retina showing highest expressions. These results characterize VAP-1 expression in human ocular tissues.

The unique substrate specificity of human AOC2, a semicarbazide-sensitive amine oxidase

Semicarbazide-sensitive amine oxidases (SSAOs) catalyze oxidative deamination of primary amines, but the true physiological function of these enzymes is still poorly understood. Here, we have studied the functional and structural characteristics of a human cell-surface SSAO, AOC2, which is homologous to the better characterized family member, AOC3. The preferred in vitro substrates of AOC2 were found to be 2-phenylethylamine, tryptamine and p-tyramine instead of methylamine and benzylamine, the favored substrates of AOC3. Molecular modeling suggested structural differences between AOC2 and AOC3, which provide AOC2 with the capability to use the larger monoamines as substrates. Even though AOC2 mRNA was expressed in many tissues, the only tissues with detectable AOC2-like enzyme activity were found in the eye. Characterization of AOC2 will help in evaluating the contribution of this enzyme to the pathological processes attributed to the SSAO activity and in designing specific inhibitors for the individual members of the SSAO family.

Vascular adhesion protein-1 regulates leukocyte transmigration rate in the retina during diabetes

Vascular adhesion protein-1 (VAP-1) is an endothelial adhesion molecule that possesses semicarbazide-sensitive amine oxidase (SSAO) activity and is involved in leukocyte recruitment. Leukocyte adhesion to retinal vessels is a predominant feature of experimentally induced diabetic retinopathy (DR). However, the role of VAP-1 in this process is unknown. Diabetes was induced by i.p. injection of Streptozotocin in Long-Evans rats. The specific inhibitor of VAP-1, UV-002, was administered by daily i.p. injections. The expression of VAP-1 mRNA in the retinal extracts of normal and diabetic animals was measured by real-time quantitative polymerase chain reaction (PCR). Firm leukocyte adhesion was quantified in retinal flatmounts after intravascular staining with concanavalin A (ConA). Leukocyte transmigration rate was quantified by in vivo acridine orange leukocyte staining (AOLS). In diabetic rats, the rate of leukocyte transmigration into the retinal tissues of live animals was significantly increased, as determined by AOLS. When diabetic animals were treated with daily injections of the VAP-1 inhibitor (0.3 mg/kg), leukocyte transmigration rate was significantly reduced (P < 0.05). However, firm adhesion of leukocytes in diabetic animals treated with the inhibitor did not differ significantly from vehicle-treated diabetic controls. This work provides evidence for an important role of VAP-1 in the recruitment of leukocyte to the retina in experimental DR. Our results reveal the critical contribution of VAP-1 to leukocyte transmigration, with little impact on firm leukocyte adhesion in the retinas of diabetic animals. VAP-1 inhibition might be beneficial in the treatment of DR.