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

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

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

ROBIN: a randomised, double-masked, placebo-controlled Phase IIa study of the AOC3 inhibitor BI 1467335 in diabetic retinopathy

OBJECTIVE

To evaluate the safety and efficacy of BI 1467335 in patients with non-proliferative diabetic retinopathy (NPDR).

METHODS

ROBIN is a Phase IIa, double-masked, randomised, placebo-controlled study (NCT03238963). Patients with NPDR and without centre-involved diabetic macular oedema were included; all had a best corrected visual acuity letter score of ≥70 Early Treatment Diabetic Retinopathy Study letters in the study eye at screening. Patients received oral BI 1467335 10 mg or placebo once daily for 12 weeks. Post-treatment follow-up was 12 weeks. The primary endpoint was the proportion of patients over the 24 weeks with ocular adverse events (AEs). Secondary endpoints were the proportion of patients with ≥2-step improvement from baseline in DRSS severity level at Week 12 and the proportion of patients with non-ocular AEs at 24 weeks.

RESULTS

Seventy-nine patients entered the study (BI 1467335, n = 40; placebo, n = 39). The proportion of patients with ocular AEs over 24 weeks was greater in the BI 1467335 versus the placebo group (35.0% vs 23.1%, respectively). Treatment-related AEs were reported for similar numbers of patients in the placebo and BI 1467335 group (7.7% vs 7.5%, respectively). At Week 12, 5.7% (n = 2) of patients in the BI 1467335 group had a 2-step improvement in DRSS severity level from baseline, compared with 0% in the placebo group.

CONCLUSIONS

BI 1467335 was well tolerated by patients with NPDR. There was a high variability in DRSS levels for individual patients over time, with no clear efficacy signal.

Diabetic Retinopathy: New Treatment Approaches Targeting Redox and Immune Mechanisms

Diabetic retinopathy (DR) represents a severe complication of diabetes mellitus, characterized by irreversible visual impairment resulting from microvascular abnormalities. Since the global prevalence of diabetes continues to escalate, DR has emerged as a prominent area of research interest. The development and progression of DR encompass a complex interplay of pathological and physiological mechanisms, such as high glucose-induced oxidative stress, immune responses, vascular endothelial dysfunction, as well as damage to retinal neurons. Recent years have unveiled the involvement of genomic and epigenetic factors in the formation of DR mechanisms. At present, extensive research explores the potential of biomarkers such as cytokines, molecular and cell therapies, antioxidant interventions, and gene therapy for DR treatment. Notably, certain drugs, such as anti-VEGF agents, antioxidants, inhibitors of inflammatory responses, and protein kinase C (PKC)-β inhibitors, have demonstrated promising outcomes in clinical trials. Within this context, this review article aims to introduce the recent molecular research on DR and highlight the current progress in the field, with a particular focus on the emerging and experimental treatment strategies targeting the immune and redox signaling pathways.

A randomised Phase IIa trial of amine oxidase copper-containing 3 (AOC3) inhibitor BI 1467335 in adults with non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is a progressive, inflammatory liver disease with no approved pharmacological treatment. This Phase IIa, double-blind, placebo-controlled, multicentre trial (ClinicalTrials.gov: NCT03166735) investigated pharmacodynamics and safety of BI 1467335, an amine oxidase copper-containing 3 (AOC3) inhibitor, in adults with NASH from Europe and North America. Participants from 44 centres across the US, Germany, Spain, Belgium, the UK, Netherlands, Canada, France and Ireland were randomised (2:1:1:1:2; 27 July 2017 to 14 June 2019) to daily oral BI 1467335 1 mg (n = 16), 3 mg (n = 16), 6 mg (n = 17), 10 mg (n = 32) or placebo (n = 32) for 12 weeks, with follow-up to Week 16. Primary endpoint was AOC3 activity relative to baseline (%), 24 hours post-dose after 12 weeks' treatment. Secondary biomarker endpoints included changes from baseline at Week 12 in alanine aminotransferase (ALT) and caspase-cleaved cytokeratin 18 (CK-18 caspase). Mean AOC3 activities relative to baseline at Week 12: 90.4% (placebo; n = 32), 26.5% (1 mg; n = 16), 10.4% (3 mg; n = 16), 5.0% (6 mg; n = 16), 3.3% (10 mg; n = 32). These changes indicated that BI 1467335 dose-dependently inhibited AOC3 activity; ≥3 mg doses achieved >80% inhibition ( < 20% activity) at Week 4. At Week 12 following doses of BI 1467335 ≥ 3 mg, ALT and CK-18 caspase decreased dose-dependently. All tested BI 1467335 doses were well tolerated, with no clinically relevant treatment-emergent safety signals. BI 1467335 strongly inhibited AOC3 in participants with NASH, with doses ≥3 mg dose-dependently reducing the levels of liver injury biomarkers, ALT and CK-18. This trial was registered with ClinicalTrials.gov (NCT03166735) and the European Union Drug Regulating Authorities Clinical Trials Database (EudraCT 2016-000499-83).

Diabetic Macular Edema: Current Understanding, Molecular Mechanisms and Therapeutic Implications

Diabetic retinopathy (DR), with increasing incidence, is the major cause of vision loss and blindness worldwide in working-age adults. Diabetic macular edema (DME) remains the main cause of vision impairment in diabetic patients, with its pathogenesis still not completely elucidated. Vascular endothelial growth factor (VEGF) plays a pivotal role in the pathogenesis of DR and DME. Currently, intravitreal injection of anti-VEGF agents remains as the first-line therapy in DME treatment due to the superior anatomic and functional outcomes. However, some patients do not respond satisfactorily to anti-VEGF injections. More than 30% patients still exist with persistent DME even after regular intravitreal injection for at least 4 injections within 24 weeks, suggesting other pathogenic factors, beyond VEGF, might contribute to the pathogenesis of DME. Recent advances showed nearly all the retinal cells are involved in DR and DME, including breakdown of blood-retinal barrier (BRB), drainage dysfunction of Müller glia and retinal pigment epithelium (RPE), involvement of inflammation, oxidative stress, and neurodegeneration, all complicating the pathogenesis of DME. The profound understanding of the changes in proteomics and metabolomics helps improve the elucidation of the pathogenesis of DR and DME and leads to the identification of novel targets, biomarkers and potential therapeutic strategies for DME treatment. The present review aimed to summarize the current understanding of DME, the involved molecular mechanisms, and the changes in proteomics and metabolomics, thus to propose the potential therapeutic recommendations for personalized treatment of DME.

Neuroinflammation and neurodegeneration in diabetic retinopathy

Diabetic retinopathy (DR) is the most common complication of diabetes and has been historically regarded as a microangiopathic disease. Now, the paradigm is shifting toward a more comprehensive view of diabetic retinal disease (DRD) as a tissue-specific neurovascular complication, in which persistently high glycemia causes not only microvascular damage and ischemia but also intraretinal inflammation and neuronal degeneration. Despite the increasing knowledge on the pathogenic pathways involved in DR, currently approved treatments are focused only on its late-stage vasculopathic complications, and a single molecular target, vascular endothelial growth factor (VEGF), has been extensively studied, leading to drug development and approval. In this review, we discuss the state of the art of research on neuroinflammation and neurodegeneration in diabetes, with a focus on pathophysiological studies on human subjects, in vivo imaging biomarkers, and clinical trials on novel therapeutic options.

Vascular adhesion protein-1 and microvascular diabetic complications

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

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

Background

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

Conclusion

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

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

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

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

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

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.

Innate immune response in retinal homeostasis and inflammatory disorders

Innate immune cells such as neutrophils, monocyte-macrophages and microglial cells are pivotal for the health and disease of the retina. For the maintenance of retinal homeostasis, these cells and immunosuppressive molecules in the eye actively regulate the induction and the expression of inflammation in order to prevent excessive activation and subsequent tissue damage. In the disease context, these regulatory mechanisms are modulated genetically and/or by environmental stimuli such as damage-associated molecular patterns (DAMPs), and a chronic innate immune response regulates or contributes to the formation of diverse retinal disorders such as uveitis, retinitis pigmentosa, retinal vascular diseases and retinal fibrosis. Here we summarize the recent knowledge regarding the innate immune response in both ocular immune regulation and inflammatory retinal diseases, and we describe the potential of the innate immune response as a biomarker and therapeutic target.

Primary outcomes of the VIDI study: phase 2, double-masked, randomized, active-controlled study of ASP8232 for diabetic macular edema

Background

ASP8232 is a potent and specific small molecule vascular adhesion protein-1 (VAP-1) inhibitor. This study evaluated the effect of ASP8232 on excess retinal thickness when given alone or in combination with ranibizumab in patients with center-involved diabetic macular edema (CI-DME).

Methods

This was a phase 2a, placebo and sham-injection controlled, double-masked, randomized, parallel-group clinical trial. Participants were patients with CI-DME and central subfield thickness (CST) ≥ 375 µm in the study eye as assessed by spectral domain optical coherence tomography. Eligible patients were randomized to (1) daily oral ASP8232 40 mg monotherapy; (2) combination therapy of daily oral ASP8232 40 mg and monthly intravitreal ranibizumab 0.3 mg; or (3) monthly intravitreal ranibizumab 0.3 mg monotherapy. The treatment period was 12 weeks. CST and best corrected visual acuity (BCVA) were assessed at baseline and at Weeks 2, 4, 8, 12, 16 and 24. The primary outcome was the mean percent change from baseline in excess CST at Week 12. Secondary outcomes were BCVA, safety and tolerability, and pharmacokinetic and pharmacodynamic characteristics of ASP8232.

Results

After 12 weeks, the mean (95% confidence interval) percent change in excess CST was 11.4% (− 15.0%, 37.8%) in the ASP8232 group, − 61.7% (− 86.1%, − 37.2%) in the ASP8232/ranibizumab group, and − 75.3% (− 94.8%, − 55.8%) in the ranibizumab group. The change from baseline in the two ranibizumab arms was statistically significant (P < 0.001) as was the difference between the ranibizumab groups and the ASP8232 group (P < 0.001). Mean (SD) increase in BCVA score from baseline was 3.1 (7.3) in the ASP8232 group, 5.2 (7.1) in the ASP8232/ranibizumab group, and 8.2 (9.5) in the ranibizumab group. The increase from baseline in BCVA score was statistically and clinically significant in the ranibizumab group compared with the ASP8232 group (P = 0.015). ASP8232 resulted in near complete inhibition of plasma VAP-1 activity whilst ranibizumab had no effect.

Conclusions

Near complete inhibition of plasma VAP-1 activity with ASP8232 had no effect on CST in patients with CI-DME. Furthermore, combination therapy did not provide additional benefit to treatment with ranibizumab alone, which significantly reduced CST and improved BCVA.

Trial registration clinicaltrials.gov; NCT02302079. Registered on November 26, 2014

Electronic supplementary material

The online version of this article (10.1186/s40942-019-0178-7) contains supplementary material, which is available to authorized users.

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.

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.

Association of HMGB1 with oxidative stress markers and regulators in PDR

PURPOSE

We investigated the link among the proinflammatory cytokine high-mobility group box 1 (HMGB1) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) as a marker of oxidative DNA damage, the endothelial adhesion molecule and oxidase enzyme vascular adhesion protein-1 (VAP-1), and the inducible cytoprotective molecule heme oxygenase-1 (HO-1) in proliferative diabetic retinopathy (PDR). We correlated the levels of these molecules with clinical disease activity and studied the proinflammatory activities of HMGB1 on rat retinas and human retinal microvascular endothelial cells (HRMECs).

METHODS

Vitreous samples from 47 PDR and 19 non-diabetic patients, epiretinal membranes from 11 patients with PDR, human retinas (16 from diabetic patients and 16 from non-diabetic subjects), rat retinas, and HRMECs were studied by enzyme-linked immunosorbent assay, immunohistochemistry, western blot immunofluorescence, and RT-PCR analyses. In addition, we assessed the adherence of leukocytes to HMGB1-stimulated HRMECs.

RESULTS

HMGB1, 8-OHdG, and soluble VAP-1 (sVAP-1) levels were significantly higher in vitreous samples from PDR patients than in those from non-diabetics (p = 0.001, <0.0001, <0.0001, respectively). The HMGB1, 8-OHdG, sVAP-1, and HO-1 levels in PDR with active neovascularization were significantly higher than those in inactive PDR (p = 0.025, <0.0001, <0.0001, 0.012, respectively). Significant positive correlations were observed between the levels of HMGB1 and the levels of 8-OHdG (r = 0.422; p = 0.001) and sVAP-1 (r = 0.354; p = 0.004) and between the levels of 8-OHdG and the levels of sVAP-1 (r = 0.598; p<0.0001). In epiretinal membranes, VAP-1 and 8-OHdG were expressed in vascular endothelial cells and stromal cells. Significant increases in the VAP-1 mRNA and protein levels were detected in the RPE, but not in the neuroretina of diabetic patients. Treatment of HRMEC with HMGB1, diabetes induction, and an intravitreal injection of HMGB1 in normal rats induced a significant upregulation of the adhesion molecule intercellular adhesion molecule-1 (ICAM-1) in HRMECs and retinas. On the other hand, the expressions of vascular cell adhesion molecule-1 and VAP-1 were not affected. Oral administration of the HMGB1 inhibitor glycyrrhizin in rats attenuated the diabetes-induced upregulation of the retinal ICAM-1 expression. Treatment of HRMECs with HMGB1 increased leukocyte adhesion and induced the upregulation of 8-OHdG and HO-1 and the membranous translocation of VAP-1.

CONCLUSIONS

Our results suggest a potential link among the proinflammatory cytokine HMGB1, VAP-1, oxidative stress, and HO-1 in the pathogenesis of PDR.

Soluble Vascular Adhesion Protein-1 Mediates Spermine Oxidation as Semicarbazide-Sensitive Amine Oxidase: Possible Role in Proliferative Diabetic Retinopathy

Purpose/Aim of the study: To explore the possible role of vascular adhesion protein-1 (VAP-1) via its enzymatic function as a semicarbazide-sensitive amine oxidase (SSAO) in the pathogenesis of proliferative diabetic retinopathy (PDR).

MATERIALS AND METHODS

The levels of soluble VAP-1/SSAO and the unsaturated aldehyde acrolein (ACR)-conjugated protein, N^ε-(3-formyl-3, 4-dehydropiperidino) lysine adduct (FDP-Lys), were measured in vitreous fluid samples of PDR and non-diabetic patients using ELISA. Recombinant human VAP-1/SSAO (rhVAP-1/SSAO) was incubated with spermine, with or without semicarbazide or RTU-1096 (a specific inhibitor for VAP-1/SSAO). Immunofluorescence assays were performed to assess the localization of VAP-1/SSAO and FDP-Lys in fibrovascular tissues from patients with PDR. The impact of ACR on cultured retinal capillary endothelial cells was assessed using a cell viability assay and total glutathione (GSH) measurements.

RESULTS

The levels of sVAP-1/SSAO and FDP-Lys were elevated in the vitreous fluid of patients with PDR. Incubation of rhVAP-1 with spermine resulted in the generation of hydrogen peroxide and FDP-Lys and the production was inhibited by semicarbazide and RTU-1096. In fibrovascular tissues, FDP-Lys and VAP-1/SSAO were present in endothelial cells. ACR stimulation reduced GSH levels in the cultured endothelial cells in a dose-dependent manner and caused cellular toxicity.

CONCLUSIONS

Our results indicate the pathological role of sVAP-1/SSAO to generate hydrogen peroxide and toxic aldehyde ACR, both of which are associated with oxidative stress, as a consequence of spermine oxidation in eyes with PDR.

A novel 3-(4,5-diphenyl-1,3-oxazol-2-yl)propanal oxime compound is a potent Transient Receptor Potential Ankyrin 1 and Vanilloid 1 (TRPA1 and V1) receptor antagonist

Transient Receptor Potential Ankyrin 1 and Vanilloid 1 (TRPA1, TRPV1) ion channels expressed on nociceptive primary sensory neurons are important regulators of pain and inflammation. TRPA1 is activated by several inflammatory mediators including formaldehyde and methylglyoxal that are products of the semicarbazide-sensitive amine-oxidase enzyme (SSAO). SZV-1287 is a new 3-(4,5-diphenyl-1,3-oxazol-2-yl)propanal oxime SSAO inhibitor, its chemical structure is similar to other oxime derivatives described as TRPA1 antagonists. Therefore, we investigated its effects on TRPA1 and TRPV1 receptor activation on the cell bodies and peripheral terminals of primary sensory neurons and TRPA1 or TRPV1 receptor-expressing cell lines. Calcium influx in response to the TRPA1 agonist allyl-isothiocyanate (AITC) (200 μM) and the TRPV1 stimulator capsaicin (330 nM) in rat trigeminal neurons or TRPA1 and TRPV1 receptor-expressing cell lines was measured by microfluorimetry or radioactive (45)Ca(2+) uptake experiments. Calcitonin gene-related peptide (CGRP) release as the indicator of 100 μM AITC - or 100 nM capsaicin-induced peripheral sensory nerve terminal activation was measured by radioimmunoassay. SZV-1287 (100, 500 and 1000 nM) exerted a concentration-dependent significant inhibition on both AITC- and capsaicin-evoked calcium influx in trigeminal neurons and TRPA1 or TRPV1 receptor-expressing cell lines. It also significantly inhibited the TRPA1, but not the TRPV1 activation-induced CGRP release from the peripheral sensory nerve endings in a concentration-dependent manner. In contrast, the reference SSAO inhibitor LJP 1207 with a different structure had no effect on TRPA1 or TRPV1 activation in either model system. This is the first evidence that our novel oxime compound SZV-1287 originally developed as a SSAO inhibitor has a potent dual antagonistic action on TRPA1 and TRPV1 ion channels on primary sensory neurons.

Nonbiological pharmacotherapies for the treatment of diabetic macular edema

INTRODUCTION

During the past decade, there have been significant advances in the pharmacotherapies for the treatment of diabetic macular edema (DME). Among the presently available treatment options, anti-vascular endothelial growth factors (anti-VEGF) agents are the most favored agents due to their efficacy and safety. The index review focuses on nonbiological therapies that have entered in phase 3 clinical trials for DME.

AREAS COVERED

An extensive review of the literature was performed to identify various nonbiological immunotherapies i.e., drugs other than '-mAbs' (monoclonal antibodies including anti-VEGF agents), '-mibs' (proteasome inhibitors), '-NAbs' (nanoparticle albumin-bound), and '-nibs' (small molecule inhibitor/tyrosine kinase inhibitors), among others. Extended-release low-dose corticosteroid devices have been recently approved for the treatment of DME. Other compounds such as non-steroidal anti-inflammatory drugs, antibody mimetic proteins, nonbiological growth factor inhibitors, and inhibitors of protein kinase C have been described.

EXPERT OPINION

A number of therapies are under development for the pharmacological management of DME. Due to the rising healthcare costs associated with anti-VEGF agents, a number of alternate treatment options have been explored recently. Some of these agents have reached phase 3 in clinical trials and appear to have a promising role in the management of DME. As further research is conducted, the role of each individual agent will become more defined, alone or in combination therapy.

Novel Therapies in Development for Diabetic Macular Edema

Diabetic macular edema (DME) secondary to diabetic retinopathy (DR) is a major cause for functional visual loss in the developed world. Laser photocoagulation has been used for decades in the treatment of DME. However, the advent of anti-vascular endothelial growth factor (anti-VEGF) has revolutionized the treatment of DME. Three important anti-VEGF agents whose efficacy has been well established via phase III clinical trials include ranibizumab, bevacizumab, and aflibercept. However, even in the era of anti-VEGF therapies, there are some challenges that retina specialists have to confront in managing patients with DME. These include the need for frequent treatment and an unpredictable response to therapy. There is evidence to suggest that pathways other than the VEGF pathway may be playing a role in the development of DME. Thus, extensive research is focused on development of novel agents that target these pathways. This review focuses on novel therapeutic agents in development, which may be used as a monotherapy or in combination with anti-VEGF agents, for the management of DME in the future.

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.

CD18 expression in granulocytes infiltrating the vitreous fluid in patients with diabetic retinopathy

AIM

To assess the levels of CD18 on the surface of granulocytes infiltrating the vitreous fluid in patients with diabetic retinopathy (DR).

METHODS

Vitreous samples from twelve patients with non-proliferative DR with significant macula edema (group A), 33 patients with proliferative DR (grade 3 as group B, n=14, and, grade 4 as group C, n=19) were obtained during pars plana vitrectomy. Vitreous samples from 12 patients with macular hole as controls (group D) were analyzed together. The infiltrating of granulocytes and its surface level of CD18 were measured by flow cytometry. The level of CD18 was presented as the mean channel fluorescence (MCF) on a logarithmic scale.

RESULTS

Granulocytes were detected in 6 of 12 vitreous samples from group A, 9 of 14 from group B, 15 of 19 from group C, and none of 12 from group D. MCF of CD18 on granulocytes from groups A, B, and C were 2.978±1.446, 3.201±0.692, and 4.072±0.837, respectively. The difference was significant (F=4.354, P=0.021). Subjects with more severe DR were more likely to have a higher level of CD18 MCF (trend test, χ (2)=7.351, P=0.007). CD18 MCF was significantly associated with the development of DR (r=0.46, P=0.005 and β=0.147, P=0.035).

CONCLUSION

Our results confirm the presence of granulocytes and the elevated levels of CD18 on the surface of them in the vitreous fluid from DR patients. These results may provide indirect evidence shown that granulocytes activation also has occurred in the retinal local compared to non-DR control.

Plasma semicarbazide-sensitive amine oxidase activity in type 1 diabetes is related to vascular and renal function but not to glycaemia

PURPOSE

Associations of semicarbazide-sensitive amine oxidase (SSAO) activity with renal and vascular function, oxidative stress, glycaemia and diabetes complications were determined.

METHODS

Plasma SSAO activity in 94 type 1 diabetes (T1DM) patients, including 34 with microvascular complications T1DM CX[+], and in 96 healthy subjects (CON) was measured by production of benzaldehyde using high-performance liquid chromatography (HPLC).

RESULTS

SSAO activity (mean ± SD) was greater in T1DM than in CON (1049 ± 294 vs 749 ± 204 mU/L; p < 0.00001) and was higher in T1DM CX[+] vs complication-free DM subjects (1148 ± 313 mU/L vs 982 ± 269 mU/L; p = 0.01). In T1DM, SSAO activity correlated with renal dysfunction [estimated glomerular filtration rate (eGFR): r = -0.44; p = 0.0001; cystatin C: r = 0.47; p = 0.0001] and markers of inflammation [soluble vascular cell adhesion molecule-1 (sVCAM-1): r = 0.41, p = 0.0001; soluble intercellular adhesion molecule-1 (sICAM-1): r = 0.33, p = 0.002] and was inversely related to small artery elasticity (SAE) (r = -0.23, p = 0.03). In CON, SSAO activity correlated with HbA1c (r = 0.26; p = 0.02).

CONCLUSION

In T1DM, SSAO activity correlates with renal dysfunction, but not with glycaemia, and may promote vascular inflammation and be a therapeutic target.

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.

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.

Serum vascular adhesion protein-1 correlates with vascular endothelial growth factor in patients with type II diabetes

AIMS

To study serum levels of soluble vascular adhesion protein (sVAP)-1 in type II diabetic patients with retinopathy.

METHODS

Serum samples were obtained from 53 consecutive patients, including 14 cases with non-angiogenic ocular diseases, i.e., epiretinal membrane (ERM) and idiopathic macular hole (MH), 19 cases with age-related macular degeneration (AMD), and 20 cases with diabetic retinopathy (DR). Protein levels of sVAP-1, intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, and vascular endothelial growth factor (VEGF) were determined by enzyme-linked immunosorbent assay. Enzymatic activity of semicarbazide-sensitive amine oxidase (SSAO) was also measured.

RESULTS

Serum level of sVAP-1 showed a moderate correlation with SSAO activity in all cases. Patients with DR had higher levels of serum sVAP-1 than subjects with ERM and MH, or those with AMD; however, severity of DR is not related to the serum levels of sVAP-1. Serum sVAP-1 correlated positively with VEGF in patients with DR, but not in those with ERM and MH, or those with AMD. Neither soluble ICAM-1 nor VCAM-1 correlated with VEGF, even in subjects with DR.

CONCLUSION

The current data demonstrate the elevated serum levels of sVAP-1 and correlation between sVAP-1 and VEGF in patients with type II diabetes.

Intraocular hemorrhage causes retinal vascular dysfunction via plasma kallikrein

PURPOSE

Retinal hemorrhages occur in a variety of sight-threatening conditions including ocular trauma, high altitude retinopathy, and chronic diseases such as diabetic and hypertensive retinopathies. The goal of this study is to investigate the effects of blood in the vitreous on retinal vascular function in rats.

METHODS

Intravitreal injections of autologous blood, plasma kallikrein (PK), bradykinin, and collagenase were performed in Sprague-Dawley and Long-Evans rats. Retinal vascular permeability was measured using vitreous fluorophotometry and Evans blue dye permeation. Leukostasis was measured by fluorescein isothiocyanate-coupled concanavalin A lectin and acridine orange labeling. Retinal hemorrhage was examined on retinal flatmounts. Primary cultures of bovine retinal pericytes were cultured in the presence of 25 nM PK for 24 hours. The pericyte-conditioned medium was collected and the collagen proteome was analyzed by tandem mass spectrometry.

RESULTS

Intravitreal injection of autologous blood induced retinal vascular permeability and retinal leukostasis, and these responses were ameliorated by PK inhibition. Intravitreal injections of exogenous PK induced retinal vascular permeability, leukostasis, and retinal hemorrhage. Proteomic analyses showed that PK increased collagen degradation in pericyte-conditioned medium and purified type IV collagen. Intravitreal injection of collagenase mimicked PK's effect on retinal hemorrhage.

CONCLUSIONS

Intraocular hemorrhage increases retinal vascular permeability and leukostasis, and these responses are mediated, in part, via PK. Intravitreal injections of either PK or collagenase, but not bradykinin, induce retinal hemorrhage in rats. PK exerts collagenase-like activity that may contribute to blood-retinal barrier dysfunction.

Vascular adhesion protein-1 and renalase in regard to diabetes in hemodialysis patients

INTRODUCTION

Vascular adhesion protein-1 (VAP-1) is a copper-containing semicarbazide-sensitive amine oxidase (SSAO) secreted by vascular smooth muscle cells, adipocytes, and endothelial cells with functional monoamine oxidase activity. Renalase, with possible monoamine oxidase activity, which breaks down catecholamines like SSAO, is also expressed in the endothelium as well as in the kidney. The aim of the study was to assess VAP-1 level and its correlation with renalase level in 60 hemodialyzed (HD) patients.

MATERIAL AND METHODS

Complete blood count, urea, serum lipids, fasting glucose and creatinine were studied by the standard laboratory method in the hospital central laboratory. We assessed VAP-1 and renalase with commercially available assays.

RESULTS

The mean level of VAP-1 as well as renalase was significantly higher in HD patients when compared to the control group (291.01 ±94.91 ng/ml vs. 158.34 ±56.89 ng/ml, p < 0.01; 27.53 ±9.394.91 µg/ml vs. 4.00 ±1.37 µg/ml, p < 0.001, respectively). In hemodialysis patients VAP-1 correlated with presence of diabetes (r = 0.27, p < 0.05), presence of hypertension (r = 0.32, p < 0.05), use of calcium channel blockers (r = 0.30, p < 0.05), use of β-blockers (r = 0.25, p < 0.05), ejection fraction (r = -0.38, p < 0.01), systolic blood pressure before (r = 0.52, p < 0.001) and after hemodialysis (r = 0.30, p < 0.01), and weight gain (r = 0.41, p < 0.01). Renalase was not significantly different in diabetic and non-diabetic patients or between hypertensive and normotensive patients. In multiple regression analysis VAP-1 was predicted 77% by serum ejection fraction and fibrinogen.

CONCLUSIONS

Vascular adhesion protein-1, elevated in patients on hemodialysis, was predominantly dependent on blood pressure and diabetes, both factors associated with endothelial damage and promoting cardiovascular complications. Renalase appeared to be unrelated to VAP, at least in the HD population.

VAP-1, a novel molecule linked to endothelial damage and kidney function in kidney allograft recipients

BACKGROUND/AIMS

VAP-1 (vascular adhesion protein-1) is a copper-containing SSAO (semicarbazide sensitive amine oxidase) secreted by vascular smooth muscle cells, adipocytes, endothelial cells with functional monoamine oxidase activity. The oxidation process generates harmful products that may be involved in atherosclerosis and vascular damage. Elevation of SSAO activity is observed in atherosclerosis, diabetes mellitus and obesity. On the other hand, renalase, with possible monoamine oxidase activity, which breaks down catecholamines like SSAO, is also expressed in the endothelium as well as in the kidney. The aim of the study was to assess VAP-1 levels and its correlations with endothelial injury markers and renalase in 50 kidney allograft recipients.

METHODS

Hemoglobin, urea, creatinine, rate were studied by standard laboratory method in the hospital central laboratory. We assessed markers of endothelial function/injury: vWF, thrombomodulin, ICAM, VCAM, CD40L, CD44, CD146, inflammation: hsCRP, and IL-6 and adipocytokines: leptin, adiponectin, visfatin, apelin with commercially available assays.

RESULTS

The mean serum VAP-1 in Tx was significantly higher comparing to the control group. In kidney transplant recipients VAP-1 correlated with BMI (r=0.39, p<0.01), CD44 (r=0.27, p<0.05), hsCRP (r=0.28, p<0.05), serum creatinine (r=0.29, p<0.05), eGFR (CKD-EPI formula r=-0.27, p<0.05, MDRD r=-0.27,p<0.05, Cockcroft-Gault r=-0.35,p<0.01), serum urea (r=0.27, p<0.05), CD146 (r=0.49, p<0.001), CD40L (r=0.26, p<0.06), and renalase (r=0.34, p<0.05). In multiple regression analysis VAP-1 was predicted 80% by serum creatinine (beta value 0.33, p=0.01), and CD146 (beta value 43, p=0.0005).

CONCLUSION

VAP-1, elevated in kidney transplant recipients, is predominantly dependent on endothelial damage and kidney function, which deteriorated with time after kidney transplantation.

Ocular application of the kinin B1 receptor antagonist LF22-0542 inhibits retinal inflammation and oxidative stress in streptozotocin-diabetic rats

PURPOSE

Kinin B(1) receptor (B(1)R) is upregulated in retina of Streptozotocin (STZ)-diabetic rats and contributes to vasodilation of retinal microvessels and breakdown of the blood-retinal barrier. Systemic treatment with B(1)R antagonists reversed the increased retinal plasma extravasation in STZ rats. The present study aims at determining whether ocular application of a water soluble B(1)R antagonist could reverse diabetes-induced retinal inflammation and oxidative stress.

METHODS

Wistar rats were made diabetic with STZ (65 mg/kg, i.p.) and 7 days later, they received one eye drop application of LF22-0542 (1% in saline) twice a day for a 7 day-period. The impact was determined on retinal vascular permeability (Evans blue exudation), leukostasis (leukocyte infiltration using Fluorescein-isothiocyanate (FITC)-coupled Concanavalin A lectin), retinal mRNA levels (by qRT-PCR) of inflammatory (B(1)R, iNOS, COX-2, ICAM-1, VEGF-A, VEGF receptor type 2, IL-1β and HIF-1α) and anti-inflammatory (B(2)R, eNOS) markers and retinal level of superoxide anion (dihydroethidium staining).

RESULTS

Retinal plasma extravasation, leukostasis and mRNA levels of B(1)R, iNOS, COX-2, VEGF receptor type 2, IL-1β and HIF-1α were significantly increased in diabetic retinae compared to control rats. All these abnormalities were reversed to control values in diabetic rats treated with LF22-0542. B(1)R antagonist also significantly inhibited the increased production of superoxide anion in diabetic retinae.

CONCLUSION

B(1)R displays a pathological role in the early stage of diabetes by increasing oxidative stress and pro-inflammatory mediators involved in retinal vascular alterations. Hence, topical application of kinin B(1)R antagonist appears a highly promising novel approach for the treatment of diabetic retinopathy.

Lymphatics and lymphangiogenesis in the eye

Lymphatic is a prerequisite for the maintenance of tissue fluid balance and immunity in the body. A body of evidence also shows that lymphangiogenesis plays important roles in the pathogenesis of diseases such as tumor metastasis and inflammation. The eye was thought to lack lymphatic vessels except for the conjunctiva; however, advances in the field, including the identification of lymphatic endothelial markers (e.g., LYVE-1 or podoplanin) and lymphangiogenic factors (e.g., VEGF-C), have revealed the exsitence and possible roles of lymphatics and lymphangiogenesis in the eye. Recent studies have shown that corneal limbus, ciliary body, lacrimal gland, orbital meninges, and extraocular muscles contain lymphatic vessels and that the choroid might have a lymphatic-like system. There is no known lymphatic outflow from the eye. However, several lymphatic channels including uveolymphatic pathway might serve the ocular fluid homeostasis. Furthermore, lymphangiogenesis plays important roles in pathological conditions in the eye including corneal transplant rejection and ocular tumor progression. Yet, the role of lymphangiogenesis in most eye diseases, especially inflammatory disease or edema, remains unknown. A better understanding of lymphatic and lymphangiogenesis in the eye will open new therapeutic opportunities to prevent vision loss in ocular diseases.

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.

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.

Cannabidiol as an emergent therapeutic strategy for lessening the impact of inflammation on oxidative stress

Oxidative stress with reactive oxygen species generation is a key weapon in the arsenal of the immune system for fighting invading pathogens and initiating tissue repair. If excessive or unresolved, however, immune-related oxidative stress can initiate further increasing levels of oxidative stress that cause organ damage and dysfunction. Targeting oxidative stress in various diseases therapeutically has proven more problematic than first anticipated given the complexities and perversity of both the underlying disease and the immune response. However, growing evidence suggests that the endocannabinoid system, which includes the CB₁ and CB₂ G-protein-coupled receptors and their endogenous lipid ligands, may be an area that is ripe for therapeutic exploitation. In this context, the related nonpsychotropic cannabinoid cannabidiol, which may interact with the endocannabinoid system but has actions that are distinct, offers promise as a prototype for anti-inflammatory drug development. This review discusses recent studies suggesting that cannabidiol may have utility in treating a number of human diseases and disorders now known to involve activation of the immune system and associated oxidative stress, as a contributor to their etiology and progression. These include rheumatoid arthritis, types 1 and 2 diabetes, atherosclerosis, Alzheimer disease, hypertension, the metabolic syndrome, ischemia-reperfusion injury, depression, and neuropathic pain.

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.

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.

Oral Administration of Semicarbazide Limits Weight Gain together with Inhibition of Fat Deposition and of Primary Amine Oxidase Activity in Adipose Tissue

An enzyme hitherto named semicarbazide-sensitive amine oxidase (SSAO), involved in the oxidation of primary amines, is abundantly expressed in adipocytes. Although SSAO physiological functions remain unclear, several molecules inhibiting its activity have been described to limit fat accumulation in preadipocyte cultures or to reduce body weight gain in obese rodents. Here, we studied whether oral administration of semicarbazide, a prototypical SSAO inhibitor, limits fat deposition in mice. Prolonged treatment with semicarbazide at 0.125% in drinking water limited food and water consumption, hampered weight gain, and deeply impaired fat deposition. The adiposomatic index was reduced by 31%, while body mass was reduced by 15%. Such treatment completely inhibited SSAO, but did not alter MAO activity in white adipose tissue. Consequently, the insulin-like action of the SSAO substrate benzylamine on glucose transport was abolished in adipocytes from semicarbazide-drinking mice, while their insulin sensitivity was not altered. Although semicarbazide is currently considered as a food contaminant with deleterious effects, the SSAO inhibition it induces appears as a novel concept to modulate adipose tissue development, which is promising for antiobesity drug discovery.

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.