Resistance to anti-VEGF therapy in neovascular age-related macular degeneration: a comprehensive review

Biomarkers as Predictive Factors of Anti-VEGF Response

Age-related macular degeneration is the main cause of irreversible vision in developed countries, and intravitreal anti-vascular endothelial growth factor (anti-VEGF) injections are the current gold standard treatment today. Although anti-VEGF treatment results in important improvements in the course of this disease, there is a considerable number of patients not responding to the standardized protocols. The knowledge of how a patient will respond or how frequently retreatment might be required would be vital in planning treatment schedules, saving both resource utilization and financial costs, but today, there is not an ideal biomarker to use as a predictive response to ranibizumab therapy. Whole blood and blood mononuclear cells are the samples most studied; however, few reports are available on other important biofluid samples for studying this disease, such as aqueous humor. Moreover, the great majority of studies carried out to date were focused on the search for SNPs in genes related to AMD risk factors, but miRNAs, proteomic and metabolomics studies have rarely been conducted in anti-VEGF-treated samples. Here, we propose that genomic, proteomic and/or metabolomic markers could be used not alone but in combination with other methods, such as specific clinic characteristics, to identify patients with a poor response to anti-VEGF treatment to establish patient-specific treatment plans.

Long Non-Coding RNA PNKY Modulates the Development of Choroidal Neovascularization

Long non-coding RNAs (lncRNAs) have been widely implicated in human diseases. Our aim was to explore the regulatory role of changes in the expression levels of PNKY and its linked signaling networks in mediating stress-induced choroidal neovascularization. PNKY expression levels were reduced in mice by laser and exposure of endothelial cell to hypoxic stress. PNKY silencing exacerbated the formation of CNV in a laser-induced CNV model and an ex vivo model, while overexpression inhibited CNV development. Silencing or overexpression of PNKY altered the viability, proliferation, migration, and tube-forming capacity of endothelial cells in vitro. Mechanistically, through the lncRNA–RNA binding protein–miRNA interaction analysis involving loss of function and gain-of-function experiments, we found that lncRNA PNKY inhibited the binding of miR124 to PTBP1 and maintained the homeostasis of choroidal vascular function by promoting Bcl-2 like protein 11 (BIM), and its dysfunction led to exacerbation of CNV lesion. Therefore, this study suggests that the lncPNKY/PTBP1–miR-124 axis is involved in regulating the development of CNV, providing a potential therapeutic target for the treatment of CNV.

Novel Possible Protein Targets in Neovascular Age-Related Macular Degeneration: A Pilot Study Experiment

Age-related macular degeneration (AMD) is among the world's leading causes of blindness. In its neovascular form (nAMD), around 25% of patients present further anatomical and visual deterioration due to persistence of neovascular activity, despite gold-standard treatment protocols using intravitreal anti-VEGF medications. Thus, to comprehend, the molecular pathways that drive choroidal neoangiogenesis, associated with the vascular endothelial growth factor (VEGF), are important steps to elucidate the mechanistic events underneath the disease development. This is a pilot study, a prospective, translational experiment, in a real-life context aiming to evaluate the protein profiles of the aqueous humor of 15 patients divided into three groups: group 1, composed of patients with nAMD, who demonstrated a good response to anti-VEGF intravitreal injections during follow-up (good responsive); group 2, composed of patients with anti-VEGF-resistant nAMD, who demonstrated choroidal neovascularization activity during follow-up (poor/non-responsive); and group 3, composed of control patients without systemic diseases or signs of retinopathy. For proteomic characterization of the groups, mass spectrometry (label-free LC-MS/MS) was used. A total of 2,336 proteins were identified, of which 185 were distinctly regulated and allowed the differentiation of the clinical conditions analyzed. Among those, 39 proteins, including some novel ones, were analyzed as potential disease effectors through their pathophysiological implications in lipid metabolism, oxidative stress, complement system, inflammatory pathways, and angiogenesis. So, this study suggests the participation of other promising biomarkers in neovascular AMD, in addition to the known VEGF.

Proteomic Profiling of Aqueous Humor Exosomes from Age-related Macular Degeneration Patients

Purpose: The alteration of the exosomal proteins in the aqueous humor (AH) is linked to the development of eye diseases. The goal of this study was to examine the exosomal protein profile of patients with age-related macular degeneration (AMD) to better understand their role in the pathogenesis of AMD. Methods: Exosomes were isolated from the AH of 28 AMD and 25 control eyes. The quality, concentration, and size distribution of exosomes were measured using a nanoparticle tracking analysis system (NTA). Total exosomal proteins from each sample were purified and digested with trypsin for liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Results: Based on LC-MS/MS analysis, we got 105 exosomal peptides from AMD and control patients. Gene ontology (GO) analysis in the biology process revealed that exosomal proteins of AMD were enriched in the lipoprotein metabolic process. T-test analysis revealed six exosomal proteins in patients with AMD were significantly different from controls. Comparing the exosomal protein profile of AMD patients who were receiving anti-VEGF therapy, we observed the amount of two proteins decreased with the duration of the anti-VEGF treatment time. Conclusions: In this study, we successfully isolated and purified AH exosomes. Our results provide pioneering findings for the exosomal protein profile in AMD development and under therapy. These unique proteins could be the new targets for drug discovery or biological markers for evaluating therapeutic efficacy.

Synthetic anti-angiogenic genomic therapeutics for treatment of neovascular age-related macular degeneration

In light of the intriguing potential of anti-angiogenic approach in suppressing choroidal neovascularization, we attempted to elaborate synthetic gene delivery systems encapsulating anti-angiogenic plasmid DNA as alternatives of clinical antibody-based therapeutics. Herein, block copolymer of cyclic Arg-Gly-Asp-poly(ethylene glycol)-poly(lysine-thiol) [RGD-PEG-PLys(thiol)] with multifunctional components was tailored in manufacture of core-shell DNA delivery nanoparticulates. Note that the polycationic PLys segments were electrostatically complexed with anionic plasmid DNA into nanoscaled core, and the tethered biocompatible PEG segments presented as the spatial shell (minimizing non-specific reactions in biological milieu). Furthermore, the aforementioned self-assembly was introduced with redox-responsive disulfide crosslinking due to the thiol coupling. Hence, reversible stabilities, namely stable in extracellular milieu but susceptible to disassemble for liberation of the DNA payloads in intracellular reducing microenvironment, were verified to facilitate transcellular gene transportation. In addition, RGD was installed onto the surface of the proposed self-assemblies with aim of targeted accumulation and internalization into angiogenic endothelial cells given that RGD receptors were specifically overexpressed on their cytomembrane surface. The proposed anti-angiogenic DNA therapeutics were validated to exert efficient expression of anti-angiogenic proteins in endothelial cells and elicit potent inhibition of ocular neovasculature post intravitreous administration. Hence, the present study approved the potential of gene therapy in treatment of choroidal neovascularization. In light of sustainable gene expression properties of DNA therapeutics, our proposed synthetic gene delivery system inspired prosperous potentials in long-term treatment of choroidal neovascularization, which should be emphasized to develop further towards clinical translations.

[Anti-VEGF therapy for neovascular age-related macular degeneration: causes of incomplete response]

Neovascular age-related macular degeneration (nAMD) is one of the leading causes of decreased vision in the elderly population in many countries, including Russia. Anti-VEGF therapy is undoubtedly the «gold standard» of treatment for the disease, but its use in different patients is known to produce results with significant interindividual differences. This article reviews modern ideas about the clinical assessment of the degree of response to anti-VEGF therapy, possible reasons for its insufficient effectiveness (clinical, pharmacological, or related to nAMD pathogenesis), discusses the potential applications of the existing therapeutic strategies, and considers the prospects for the emergence of new strategies that could be used for solving that problem.

Effect of Probenecid on Endothelial Cell Growth Rate and Retinal Angiogenesis in an Oxygen-Induced Retinopathy Model

Objectives: Probenecid is an anion transport inhibitor, which, according to the connectivity map (CMap; a biological application database), interferes with hypoxia-induced gene expression changes in retinal vascular endothelial cells (ECs). Here, we investigated the influence of probenecid on retinal EC cytotoxicity and retinal neovascularization in a murine oxygen-induced retinopathy (OIR) model.

Methods: The retinal EC growth rate in the presence of hypoxia-mimicking concentrations of cobalt chloride (CoCl₂) was determined using the thiazolyl blue tetrazolium bromide (MTT) assay and proliferating cell nuclear antigen (PCNA) expression. In OIR rats, probenecid was administered by intraperitoneal injection (i.p.) from postnatal day (P) 1 to P7. The concentrations of vitreous humor vascular endothelial growth factor (VEGF), hypoxia-inducible factor (HIF)-1α, and placental growth factor (PlGF) were determined by using the ELISA kit at P21. The amount of newly formed vascular lumen was evaluated by histopathological examination. Retinopathy and neovascularization were assessed by scoring isolectin B4 fluorescein–stained retinal flat mounts. Western blots for liver tissue HIF-1α and hepcidin (HAMP) were performed.

Results:In vitro, probenecid led to the recession of the hypoxia-induced EC growth rate. In vivo, compared to the OIR retina, the upregulation of VEGF, HIF-1α, and PlGF in phase II retinopathy of prematurity (ROP) was inhibited by probenecid administration. Moreover, probenecid ameliorated neovascularization and resulted in significantly reduced relative leakage fluorescence signal intensity in fluorescein-stained retinal flat mounts (p < 0.05). Probenecid alleviated the liver overactivation of HAMP and downregulation of HIF-1α in OIR rats.

Conclusions: This is the first demonstration that implies that probenecid might be a protective compound against retinal angiogenesis in OIR. These changes are accompanied with decreased hyperoxia-mediated hepcidin overproduction. Although the relevance of the results to ROP needs further research, these findings may help establish potential pharmacological targets based on the CMap database.

Inhibition of Vascular Growth by Modulation of the Anandamide/Fatty Acid Amide Hydrolase Axis

Supplemental Digital Content is available in the text.

Objective:

Pathological angiogenesis is a hallmark of various diseases characterized by local hypoxia and inflammation. These disorders can be treated with inhibitors of angiogenesis, but current compounds display a variety of side effects and lose efficacy over time. This makes the identification of novel signaling pathways and pharmacological targets involved in angiogenesis a top priority.

Approach and Results:

Here, we show that inactivation of FAAH (fatty acid amide hydrolase), the enzyme responsible for degradation of the endocannabinoid anandamide, strongly impairs angiogenesis in vitro and in vivo. Both, the pharmacological FAAH inhibitor URB597 and anandamide induce downregulation of gene sets for cell cycle progression and DNA replication in endothelial cells. This is underscored by cell biological experiments, in which both compounds inhibit proliferation and migration and evoke cell cycle exit of endothelial cells. This prominent antiangiogenic effect is also of pathophysiological relevance in vivo, as laser-induced choroidal neovascularization in the eye of FAAH^−/− mice is strongly reduced.

Conclusions:

Thus, elevation of endogenous anandamide levels by FAAH inhibition represents a novel antiangiogenic mechanism.

Efficacy of Anti-Vascular Endothelial Growth Factor Treatment in Neovascular Age-Related Macular Degeneration and Systemic Cardiovascular Risk Factors

This study evaluates whether the presence of cardiovascular risk factors (CRFs) affects functional and morphological responses to anti–vascular endothelial growth factor (VEGF) therapy in patients with neovascular age-related macular degeneration (nAMD). Retrospective analysis included 98 treatment-naïve eyes followed for at least 12 months. Patients received intravitreal injections of ranibizumab or aflibercept with the dosage and regimen set according to each manufacturer’s recommendations for their product. Parameters evaluated at each follow-up visit included best-corrected visual acuity and central retinal thickness. Additionally, the presence of the following CRFs was evaluated: male sex, age of older than 70 years, history of current or past smoking, systemic arterial hypertension, diabetes mellitus, total hypercholesterolemia, low-density lipoprotein hypercholesterolemia, high-density lipoprotein concentration of 45 mg/dL or less, atherogenic dyslipidemia, family history of cardiovascular disease, and chronic kidney disease. A statistically significant better letter gain in visual acuity (p = 0.012) and greater percentage of responders (p = 0.035)—that is patients in whom best corrected visual acuity was stabilized or improved at 12 months—were noted among patients without a diagnosis of arterial hypertension. A statistically significant better mean visual improvement was also achieved in patients with higher total cholesterol plasma levels (p = 0.004), but this finding was not reflected in the significantly higher percentage of responders. The presence of remaining analyzed risk factors did not substantially affect the results of treatment. Systemic arterial hypertension is an independent factor leading to a poor functional outcome following anti-VEGF therapy in patients with nAMD. Effects of anti-VEGF treatment in patients with high total cholesterol levels should be analyzed in further research.

Inhibition of APE1/Ref-1 for Neovascular Eye Diseases: From Biology to Therapy

Proliferative diabetic retinopathy (PDR), neovascular age-related macular degeneration (nvAMD), retinopathy of prematurity (ROP) and other eye diseases are characterized by retinal and/or choroidal neovascularization, ultimately causing vision loss in millions of people worldwide. nvAMD and PDR are associated with aging and the number of those affected is expected to increase as the global median age and life expectancy continue to rise. With this increase in prevalence, the development of novel, orally bioavailable therapies for neovascular eye diseases that target multiple pathways is critical, since current anti-vascular endothelial growth factor (VEGF) treatments, delivered by intravitreal injection, are accompanied with tachyphylaxis, a high treatment burden and risk of complications. One potential target is apurinic/apyrimidinic endonuclease 1/reduction-oxidation factor 1 (APE1/Ref-1). The multifunctional protein APE1/Ref-1 may be targeted via inhibitors of its redox-regulating transcription factor activation activity to modulate angiogenesis, inflammation, oxidative stress response and cell cycle in neovascular eye disease; these inhibitors also have neuroprotective effects in other tissues. An APE1/Ref-1 small molecule inhibitor is already in clinical trials for cancer, PDR and diabetic macular edema. Efforts to develop further inhibitors are underway. APE1/Ref-1 is a novel candidate for therapeutically targeting neovascular eye diseases and alleviating the burden associated with anti-VEGF intravitreal injections.

Role of Activating Transcription Factor 4 in Murine Choroidal Neovascularization Model

Neovascular age-related macular degeneration (nAMD) featuring choroidal neovascularization (CNV) is the principal cause of irreversible blindness in elderly people in the world. Integrated stress response (ISR) is one of the intracellular signals to be adapted to various stress conditions including endoplasmic reticulum (ER) stress. ISR signaling results in the upregulation of activating transcription factor 4 (ATF4), which is a mediator of ISR. Although recent studies have suggested ISR contributes to the progression of some age-related disorders, the effects of ATF4 on the development of CNV remain unclear. Here, we performed a murine model of laser-induced CNV and found that ATF4 was highly expressed in endothelial cells of the blood vessels of the CNV lesion site. Exposure to integrated stress inhibitor (ISRIB) reduced CNV formation, vascular leakage, and the upregulation of vascular endothelial growth factor (VEGF) in retinal pigment epithelium (RPE)-choroid-sclera complex. In human retinal microvascular endothelial cells (HRMECs), ISRIB reduced the level of ATF4 and VEGF induced by an ER stress inducer, thapsigargin, and recombinant human VEGF. Moreover, ISRIB decreased the VEGF-induced cell proliferation and migration of HRMECs. Collectively, our findings showed that pro-angiogenic effects of ATF4 in endothelial cells may be a potentially therapeutic target for patients with nAMD.

Multicentre, randomised clinical trial comparing intravitreal aflibercept monotherapy versus aflibercept combined with reduced-fluence photodynamic therapy (RF-PDT) for the treatment of polypoidal choroidal vasculopathy

PURPOSE

To compare the efficacy and safety of intravitreal aflibercept (IVA) monotherapy versus aflibercept combined with reduced-fluence photodynamic therapy (RF-PDT) (IVA+RF-PDT) for the treatment of polypoidal choroidal vasculopathy (PCV).

METHODS AND ANALYSIS

Multicentred, double-masked, randomised controlled trial to compare the two treatment modalities. The primary outcome of the study is to compare the 52-week visual outcome of IVA versus IVA+RF PDT. One hundred and sixty treatment-naïve patients with macular PCV confirmed on indocyanine green angiography will be recruited from three centres in Singapore. Eligible patients will be randomised (1:1 ratio) into one of the following groups: IVA monotherapy group-aflibercept monotherapy with sham photodynamic therapy (n=80); combination group-aflibercept with RF-PDT (n=80). Following baseline visit, all patients will be monitored at 4 weekly intervals during which disease activity will be assessed based on best-corrected visual acuity (BCVA), ophthalmic examination findings, optical coherence tomography (OCT) and angiography where indicated. Eyes that meet protocol-specified retreatment criteria will receive IVA and sham/RF-PDT according to their randomisation group. Primary endpoint will be assessed as change in BCVA at week 52 from baseline. Secondary endpoints will include anatomical changes based on OCT and dye angiography as well as safety assessment. Additionally, we will be collecting optical coherence tomography angiography data prospectively for exploratory analysis.

ETHICS AND DISSEMINATION

This study will be conducted in accordance with the ethical principles that have their origin in the Declaration of Helsinki and that are consistent with the ICH E6 guidelines of Good Clinical Practice and the applicable regulatory requirements. Approval from the SingHealth Centralised Institutional Review Board has been sought prior to commencement of the study.

TRIAL REGISTRATION NUMBER

NCT03941587.

Economic burden of age-related macular degeneration in routine clinical practice: the RAMDEBURS study

PURPOSE

To describe and evaluate the main direct health costs, in routine clinical practice, of age-related macular degeneration (AMD) patients, from hospital perspective, in Spain.

METHODS

Retrospective, multicenter, and observational study conducted on five third-level Spanish hospitals, between December 2018 and December 2019. The study included patients who were diagnosed of AMD before December 2018. Direct healthcare costs were obtained from a Spanish database. Study variables included demographic and clinical variables, and resources, such as treatment, diagnostic tests, medical examination, and surgery. Among the 1414 screened AMD patients, 1164 patients were included. In the overall study patients, the total cost was €5,386,511.0, with a mean cost per patient of €4627.6 ± 2383.9. The largest cost items were diagnostic examinations (€2.832.902,0) and vascular endothelial growth factor inhibitors (anti-VEGF) treatment (€2.038.257,2). Bevacizumab was administered to 325 (27.9%) patients, ranibizumab to 328 (28.2%), and aflibercept to 626 (53.8%); 115 (10.7%) patients received two anti-VEGF treatments, while 90 (7.7%) did not receive any. Over the course of the study, a total of 6,057 anti-VEGF injections were administered, with a mean (95% confidence interval) of 4.8 (4.4-5.2) injections per patient. Regarding safety, 29 patients experience injection-related adverse events, among them 12 patients had cataract and 11 ones elevated intraocular pressure (IOP). The incidence of endophthalmitis was 0.5% (6/1164).

CONCLUSIONS

AMD was associated with considerable healthcare costs for regional healthcare systems. Diagnostic examinations, particularly OCT examinations, and anti-VEGF treatment represented the largest cost items.

Future Perspectives of Therapeutic, Diagnostic and Prognostic Aptamers in Eye Pathological Angiogenesis

Aptamers are single-stranded DNA or RNA oligonucleotides that are currently used in clinical trials due to their selectivity and specificity to bind small molecules such as proteins, peptides, viral particles, vitamins, metal ions and even whole cells. Aptamers are highly specific to their targets, they are smaller than antibodies and fragment antibodies, they can be easily conjugated to multiple surfaces and ions and controllable post-production modifications can be performed. Aptamers have been therapeutically used for age-related macular degeneration, cancer, thrombosis and inflammatory diseases. The aim of this review is to highlight the therapeutic, diagnostic and prognostic possibilities associated with aptamers, focusing on eye pathological angiogenesis.

Eph Receptors and Ephrins in Retinal Diseases

Retinal diseases are the leading cause of irreversible blindness. They affect people of all ages, from newborns in retinopathy of prematurity, through age-independent diabetic retinopathy and complications of retinal detachment, to age-related macular degeneration (AMD), which occurs mainly in the elderly. Generally speaking, the causes of all problems are disturbances in blood supply, hypoxia, the formation of abnormal blood vessels, and fibrosis. Although the detailed mechanisms underlying them are varied, the common point is the involvement of Eph receptors and ephrins in their pathogenesis. In our study, we briefly discussed the pathophysiology of the most common retinal diseases (diabetic retinopathy, retinopathy of prematurity, proliferative vitreoretinopathy, and choroidal neovascularization) and collected available research results on the role of Eph and ephrins. We also discussed the safety aspect of the use of drugs acting on Eph and ephrin for ophthalmic indications.

Improvements of Retinal Sensitivity after Intravitreal Injection of Aflibercept in Eyes with Neovascular Age-Related Macular Degeneration with or without Polypoidal Choroidal Vasculopathy

PURPOSE

We aim to determine the effects of intravitreal aflibercept (IVA) on the mean sensitivity (MS) of the central retina, best-corrected visual acuity (BCVA), and central foveal thickness (CFT) in eyes with neovascular age-related macular degeneration (nAMD) with or without polypoidal choroidal vasculopathy (PCV).

METHODS

This was a prospective, interventional study. All eyes were treatment-naive with nAMD with or without PCV. Each eye received 3 monthly IVA injections followed by an IVA injection every 2 months for 12 months. The primary outcome was the change in the MS within the central 2°. The secondary outcomes were the changes in BCVA, CFT, greatest linear dimension (GLD), and percentage of eyes with a dry macula.

RESULTS

Thirty-seven eyes of 37 patients were studied. A significant improvement of the MS (dB) was observed +4.9 ± 4.6 dB (mean ± standard deviation) at 3 M (p < 0.001), +5.5 ± 4.9 dB at 6 (p < 0.001), and +7.0 ± 3.4 dB at 12 M (p < 0.001) compared to the baseline in all eyes. The MS of the eyes with non-PCV was not significantly different from that of eyes with PCV (p = 1.00, 1.00, 1.00, and 0.76 at baseline, 3, 6, and 12 M, respectively). The MS of 11 patients whose BCVA remained unchanged was significantly improved by +6.5 ± 2.8 dB at 3 M (p < 0.001), +6.1 ± 4.3 dB at 6 M (p < 0.001), and +6.4 ± 4.8 dB at 12 M (p = 0.003) compared to the baseline. The mean BCVA was significantly improved from the baseline to 3 M (p < 0.001), 6 M (p = 0.027), and 12 M (p = 0.003) in all eyes. The BCVA was improved or maintained in 97% of the patients at 12 M. The mean CFT and GLD were significantly reduced at 12 M (p < 0.001). Twenty-two eyes (71%) had a dry macula at 12 M.

CONCLUSIONS

IVA administered by a fixed dosing regimen led to significant improvements of the central MS, BCVA, and macular morphology at 1 year in eyes with nAMD with or without PCV. These results were not significantly different between eyes with non-PCV and with PCV. The improvements of the MS of the retina of the central 2° in a subgroup whose BCVA remained unchanged through the 12-month experimental period was also significant. We conclude that the MS of the central 2° might be a better marker than the BCVA in determining the effectiveness of IVA treatments and might be helpful in determining early effects on the retina before BCVA changes can be detected.

Galectins in the Pathogenesis of Common Retinal Disease

Diseases of the retina are major causes of visual impairment and blindness in developed countries and, due to an ageing population, their prevalence is continually rising. The lack of effective therapies and the limitations of those currently in use highlight the importance of continued research into the pathogenesis of these diseases. Vascular endothelial growth factor (VEGF) plays a major role in driving vascular dysfunction in retinal disease and has therefore become a key therapeutic target. Recent evidence also points to a potentially similarly important role of galectins, a family of β-galactoside-binding proteins. Indeed, they have been implicated in regulating fundamental processes, including vascular hyperpermeability, angiogenesis, neuroinflammation, and oxidative stress, all of which also play a prominent role in retinopathies. Here, we review direct evidence for pathological roles of galectins in retinal disease. In addition, we extrapolate potential roles of galectins in the retina from evidence in cancer, immune and neuro-biology. We conclude that there is value in increasing understanding of galectin function in retinal biology, in particular in the context of the retinal vasculature and microglia. With greater insight, recent clinical developments of galectin-targeting drugs could potentially also be of benefit to the clinical management of many blinding diseases.

Angiopoietin/Tie2 signalling and its role in retinal and choroidal vascular diseases: a review of preclinical data

The angopoietin/tyrosine kinase with immunoglobulin and epidermal growth factor homology domains (Ang/Tie) pathway is an emerging key regulator in vascular development and maintenance. Its relevance to clinicians and basic scientists as a potential therapeutic target in retinal and choroidal vascular diseases is highlighted by recent preclinical and clinical evidence. The Ang/Tie pathway plays an important role in the regulation of vascular stability, in angiogenesis under physiological and pathological conditions, as well as in inflammation. Under physiological conditions, angiopoietin-1 (Ang-1) binds to and phosphorylates the Tie2 receptor, leading to downstream signalling that promotes cell survival and vascular stability. Angiopoietin-2 (Ang-2) is upregulated under pathological conditions and acts as a context-dependent agonist/antagonist of the Ang-1/Tie2 axis, causing vascular destabilisation and sensitising blood vessels to the effects of vascular endothelial growth factor-A (VEGF-A). Ang-2 and VEGF-A synergistically drive vascular leakage, neovascularisation and inflammation, key components of retinal vascular diseases. Preclinical evidence suggests that modulating the Ang/Tie pathway restores vascular stabilisation and reduces inflammation. This review discusses how targeting the Ang/Tie pathway or applying Ang-2/VEGF-A combination therapy may be a valuable therapeutic strategy for restoring vascular stability and reducing inflammation in the treatment of retinal and choroidal vascular diseases.

Transient receptor potential vanilloid 4 channel deletion regulates pathological but not developmental retinal angiogenesis

Transient receptor potential vanilloid 4 (TRPV4) channels are mechanosensitive ion channels that regulate systemic endothelial cell (EC) functions such as vasodilation, permeability, and angiogenesis. TRPV4 is expressed in retinal ganglion cells, Müller glia, pigment epithelium, microvascular ECs, and modulates cell volume regulation, calcium homeostasis, and survival. TRPV4-mediated physiological or pathological retinal angiogenesis remains poorly understood. Here, we demonstrate that TRPV4 is expressed, functional, and mechanosensitive in retinal ECs. The genetic deletion of TRPV4 did not affect postnatal developmental angiogenesis but increased pathological neovascularization in response to oxygen-induced retinopathy (OIR). Retinal vessels from TRPV4 knockout mice subjected to OIR exhibited neovascular tufts that projected into the vitreous humor and displayed reduced pericyte coverage compared with wild-type mice. These results suggest that TRPV4 is a regulator of retinal angiogenesis, its deletion augments pathological retinal angiogenesis, and that TRPV4 could be a novel target for the development of therapies against neovascular ocular diseases.

Pachychoroid Neovasculopathy Disguising as Age-Related Macular Degeneration Treated by Spironolactone and Anti-VEGF Combination Therapy

Nonresponse of neovascular age-related macular degeneration (nAMD) to anti-vascular endothelial growth factor (anti-VEGF) therapy can often be attributed to misdiagnosis, and pathologies mimicking AMD might require different therapeutic concepts. In the following, we want to outline a case of presumed nAMD which revealed to be pachychoroid neovasculopathy (PNV) and was successfully treated by the addition of spironolactone. A 67-year-old female patient was referred for nonresponse of nAMD on her left eye after 29 intravitreal injections of aflibercept with no complete resolution of subretinal fluid. On fundoscopy, both maculae presented with pigment epithelium alterations, while the left eye showed subretinal fluid on optical coherence tomography (OCT) with an associated pigment epithelium detachment, which revealed to contain a neovascular network on OCT angiography. There was faint leakage on fluorescence (FAG) and indocyanine green angiography (ICGA) and some focal vascular dilation of the neovascular network on ICGA. Due to the absence of Drusen on any eye, a thick choroid, and the presence of a gravitational tract on blue autofluorescence (BAF), chronic central serous chorioretinopathy with a choroidal neovascularization, defined as PNV in the pachychoroid disease was diagnosed. Upon the addition of spironolactone to anti-VEGF treatment, choroidal thickness significantly decreased, and subretinal fluid resolution was observed and maintained for the first time. In conclusion, PNV should be ruled out in cases of presumed nAMD nonresponding to anti-VEGF. In these cases, a combination therapy of anti-VEGF and mineralocorticoid antagonists can facilitate fluid resorption.

Therapeutic Efficacy of a Novel Acetylated Tetrapeptide in Animal Models of Age-Related Macular Degeneration

It has been shown previously that a novel tetrapeptide, Arg-Leu-Tyr-Glu (RLYE), derived from human plasminogen inhibits vascular endothelial growth factor (VEGF)-induced angiogenesis, suppresses choroidal neovascularization in mice by an inhibition of VEGF receptor-2 (VEGFR-2) specific signaling pathway. In this study, we report that a modified tetrapeptide (Ac-RLYE) showed improved anti-choroidal neovascularization (CNV) efficacy in a number of animal models of neovascular age-related macular degeneration (AMD) which include rat, rabbit, and minipig. The preventive and therapeutic in vivo efficacy of Ac-RLYE via following intravitreal administration was determined to be either similar or superior to that of ranibizumab and aflibercept. Assessment of the intraocular pharmacokinetic and toxicokinetic properties of Ac-RLYE in rabbits demonstrated that it rapidly reached the retina with minimal systemic exposure after a single intravitreal dose, and it did not accumulate in plasma during repetitive dosing (bi-weekly for 14 weeks). Our results suggested that Ac-RLYE has a great potential for an alternative therapeutics for neovascular (wet) AMD. Since the amino acids in human VEGFR-2 targeted by Ac-RLYE are conserved among the animals employed in this study, the therapeutic efficacies of Ac-RLYE evaluated in those animals are predicted to be observed in human patients suffering from retinal degenerative diseases.

Aflibercept therapy for exudative age-related macular degeneration resistant to bevacizumab and ranibizumab

Background

Despite the good outcomes achieved with intravitreal angiogenic therapy, a subset of neovascular age-related macular degeneration (AMD) patients experience resistance to therapy after repeated injections. Switching drugs could offer benefit to this group of patients.

Purpose

To determine visual and anatomical outcomes in a cohort of neovascular AMD patients resistant to repeated injections of bevacizumab/ranibizumab after switching to aflibercept therapy.

Methods

This was a retrospective chart review of patients who had a diagnosis of neovascular AMD and persistent intraretinal (IRF) and/or subretinal fluid (SRF) on optical coherence tomography (OCT) for at least 3 months despite monthly bevacizumab and/or ranibizumab injections prior to transition to aflibercept. We reviewed patients’ records and OCT images obtained at baseline, 1, 3, 6 and 12 months after transition to aflibercept. Data collected included demographics, best-corrected visual acuity (BCVA), number of injections received and the occurrence of any adverse events. Studied OCT parameters included central macular thickness (CMT) values and the presence or absence of SRF, IRF and/or pigment epithelial detachment (PED) at each visit.

Results

We included 53 eyes of 48 patients. Mean change in BCVA from baseline was 0.05 ± 0.13 (P = 0.01) at M1, 0.04 ± 0.16 (P = 0.08) at M3, 0.01 ± 0.22 (P = 0.9) at M6, and 0.02 ± 0.28 (P = 1) at M12, while the mean change in CMT from baseline was 64 ± 75 μm (P < 0.0001) at M1, 42 ± 85 μm (P = 0.002) at M3, 47 ± 69 μm (P < 0.0001) at M6, and 46 ± 99 μm (P = 0.001) at M12. The percentage of eyes with SRF decreased from 77.4% at baseline to 39.6% at M1, then increased to 47.2% at M3, then decreased to 43.4% at M6, and to 41.5% at M12 (All p < 0.001, compared to baseline). Compared to baseline, there was a statistically significant decrease in the percentage of eyes having IRF from 47.2 to 20.8% at M1 (p < 0.001), 30.2% at M3, 24.5% at M6 and 26.4% at M12 (p < 0.01, each). The number of bevacizumab and/or ranibizumab injections (7.36 ± 1.85) was significantly higher than that of aflibercept (6.47 ± 2.45, p = 0.001). A significant direct relationship between CMT reduction and BCVA improvement was demonstrated at M1 (p = 0.01, r = 0.36), M3 (p = 0.03, r = 0.30) and M12 (p = 0.03, r = 0.30). Eyes with IRF had significantly poorer BCVA than eyes without IRF at baseline (p = 0.02) and M3 (p = 0.04).

Conclusion

Switching to intravitreal aflibercept therapy in a cohort of neovascular AMD patients resistant to chronic bevacizumab and/or ranibizumab injections can lead to significant visual improvement in the short term and sustained reduction of central macular thickness over 1 year of followup.

Intracameral anti-VEGF injection for advanced neovascular glaucoma after vitrectomy with silicone oil tamponade

AIM

To evaluate the effect of intracameral injection of conbercept for the treatment of advanced neovascular glaucoma (NVG) after vitrectomy with silicone oil tamponade.

METHODS

Conbercept 0.5 mg/0.05 mL was injected into the anterior chamber of 5 eyes, which had developed advanced NVG after vitrectomy with silicone oil tamponade. Then, trabeculectomy with mitomycin C and pan-retinal photocoagulation (PRP) or extra-PRP were conducted within 2d. The follow-up time was 6mo. Best-corrected visual acuity (BCVA), intraocular pressure (IOP), neovascularization of iris (NVI) were recorded before and after treatment.

RESULTS

Within 2d after injection, IOP control, and NVI regression were optimal for trabeculectomy. Hyphema occurred in one eye in the process of injection. But none of them present hyphema after trabeculectomy. At the end of follow-up time, all eyes had improved BCVA, well-controlled IOP, and completely regressed NVI.

CONCLUSION

Intracameral injection of conbercept is safe and effective in the treatment of patients with advanced NVG after vitrectomy with silicone oil tamponade. Within 2d after injection is the optimal time window for trabeculectomy, which can maximally reduce the risk of perioperative hyphema.

A specific RIP3+ subpopulation of microglia promotes retinopathy through a hypoxia-triggered necroptotic mechanism

Retinopathy is the leading cause of blindness, and development of effective therapy is urgently needed. Here, we defined an unprecedented subgroup of microglia that is responsible for causing retinopathy under hypoxia. Mechanistic studies demonstrated the signaling pathway of hypoxia-induced necroptosis of retinal microglia, i.e., the hypoxia–RIP1–RIP3–MLKL signaling axis, triggered an explosive release of FGF2, which in its turn to induce retinal neovascularization. Simultaneous targeting of necroptosis–FGF2 pathway and VEGF produces synergistic effects for treating retinopathy. On the basis of our findings, we propose a concept of necroptotic microglia-induced retinal angiogenesis and highlight a combination therapy for effective treatment of retinopathy.

Retinal neovascularization is a leading cause of severe visual loss in humans, and molecular mechanisms of microglial activation-driven angiogenesis remain unknown. Using single-cell RNA sequencing, we identified a subpopulation of microglia named sMG2, which highly expressed necroptosis-related genes Rip3 and Mlkl. Genetic and pharmacological loss of function demonstrated that hypoxia-induced microglial activation committed to necroptosis through the RIP1/RIP3-mediated pathway. Specific deletion of Rip3 gene in microglia markedly decreased retinal neovascularization. Furthermore, hypoxia induced explosive release of abundant FGF2 in microglia through RIP3-mediated necroptosis. Importantly, blocking signaling components of the microglia necropotosis–FGF2 axis largely ablated retinal angiogenesis and combination therapy with simultaneously blocking VEGF produced synergistic antiangiogenic effects. Together, our data demonstrate that targeting the microglia necroptosis axis is an antiangiogenesis therapy for retinal neovascular diseases.

COCO/DAND5 inhibits developmental and pathological ocular angiogenesis

Neovascularization contributes to multiple visual disorders including age-related macular degeneration (AMD) and retinopathy of prematurity. Current therapies for treating ocular angiogenesis are centered on the inhibition of vascular endothelial growth factor (VEGF). While clinically effective, some AMD patients are refractory or develop resistance to anti-VEGF therapies and concerns of increased risks of developing geographic atrophy following long-term treatment have been raised. Identification of alternative pathways to inhibit pathological angiogenesis is thus important. We have identified a novel inhibitor of angiogenesis, COCO, a member of the Cerberus-related DAN protein family. We demonstrate that COCO inhibits sprouting, migration and cellular proliferation of cultured endothelial cells. Intravitreal injections of COCO inhibited retinal vascularization during development and in models of retinopathy of prematurity. COCO equally abrogated angiogenesis in models of choroidal neovascularization. Mechanistically, COCO inhibited TGFβ and BMP pathways and altered energy metabolism and redox balance of endothelial cells. Together, these data show that COCO is an inhibitor of retinal and choroidal angiogenesis, possibly representing a therapeutic option for the treatment of neovascular ocular diseases.

Taurine and oxidative stress in retinal health and disease

Retinal disorders are leading causes of blindness and are due to an imbalance between reactive oxygen species and antioxidant scavenger (in favor of pro‐oxidant species) or a disruption of redox signaling and control. Indeed, it is well known that oxidative stress is one of the leading causes of retinal degenerative diseases. Different approaches using nutraceuticals resulted in protective effects in these disorders. This review will discuss the impact of oxidative stress in retinal neurodegenerative diseases and the potential strategies for avoiding or counteracting oxidative damage in retinal tissues, with a specific focus on taurine. Increasing data indicate that taurine may be effective in slowing down the progression of degenerative retinal diseases, thus suggesting that taurine can be a promising candidate for the prevention or as adjuvant treatment of these diseases. The mechanism by which taurine supplementation acts is mainly related to the reduction of oxidative stress. In particular, it has been demonstrated to improve retinal reduced glutathione, malondialdehyde, superoxide dismutase, and catalase activities. Antiapoptotic effects are also involved; however, the protective mechanisms exerted by taurine against retinal damage remain to be further investigated.

SLC7A11 Reduces Laser-Induced Choroidal Neovascularization by Inhibiting RPE Ferroptosis and VEGF Production

In age-related macular degeneration (AMD), one of the principal sources of vascular endothelial growth factor (VEGF) is retinal pigment epithelium (RPE) cells under hypoxia or oxidative stress. Solute carrier family 7 member 11 (SLC7A11), a key component of cystine/glutamate transporter, regulates the level of cellular lipid peroxidation, and restrains ferroptosis. In our study, we assessed the role of SLC7A11 in laser-induced choroidal neovascularization (CNV) and explored the underlying mechanism. We established a mouse model of CNV to detect the expression level of SLC7A11 and VEGF during disease progression. We found the expression of the SLC7A11 protein in RPE cells peaked at 3 days after laser treatment, which was correlated with the expression of VEGF. Intraperitoneal injection of SLC7A11 inhibitor expanded the area of CNV. We examined functional proteins related to oxidative stress and Fe²⁺ and found laser-induced ferroptosis accompanied by increased Fe²⁺ content and GPX4 expression in the RPE-choroidal complex after laser treatment. We verified the expression of SLC7A11 in the ARPE19 cell line and the effects of its inhibitors on cell viability and lipid peroxidation in vitro. Application of SLC7A11 inhibitor and SLC7A11 knockdown increased the level of lipid peroxidation and reduced the cell viability of ARPE19 which can be rescued by ferroptosis inhibitors ferrostatin-1 (Fer-1) and liproxstatin-1 (Lip-1). Conversely, SLC7A11 overexpression induced resistance to erastin or RSL3-induced ferroptosis. Moreover, we tested the possible regulatory transcription factor NF-E2-related factor 2 (NRF2) of SLC7A11 by Western blot. Knock-down of NRF2 decreased the expression of SLC7A11. Our study suggests that SLC7A11 plays a key role in the laser-induced CNV model by protecting RPE cells from ferroptosis. SLC7A11 provides a new therapeutic target for neovascular AMD patients.

Relapse of pathological angiogenesis: functional role of the basement membrane and potential treatment strategies

Blinding eye diseases such as corneal neovascularization, proliferative diabetic retinopathy, and age-related macular degeneration are driven by pathological angiogenesis. In cancer, angiogenesis is key for tumor growth and metastasis. Current antiangiogenic treatments applied clinically interfere with the VEGF signaling pathway-the main angiogenic pathway-to inhibit angiogenesis. These treatments are, however, only partially effective in regressing new pathologic vessels, and the disease relapses following cessation of treatment. Moreover, the relapse of pathological angiogenesis can be rapid, aggressive and more difficult to treat than angiogenesis in the initial phase. The manner in which relapse occurs is poorly understood; however, recent studies have begun to shed light on the mechanisms underlying the revascularization process. Hypotheses have been generated to explain the rapid angiogenic relapse and increased resistance of relapsed disease to treatment. In this context, the present review summarizes knowledge of the various mechanisms of disease relapse gained from different experimental models of pathological angiogenesis. In addition, the basement membrane-a remnant of regressed vessels-is examined in detail to discuss its potential role in disease relapse. Finally, approaches for gaining a better understanding of the relapse process are discussed, including prospects for the management of relapse in the context of disease.

Viral-Vector-Delivered Anti-Angiogenic Therapies to the Eye

Pathological vessel growth harms vision and may finally lead to vision loss. Anti-angiogenic gene therapy with viral vectors for ocular neovascularization has shown great promise in preclinical studies. Most of the studies have been conducted with different adeno-associated serotype vectors. In addition, adeno- and lentivirus vectors have been used. Therapy has been targeted towards blocking vascular endothelial growth factors or other pro-angiogenic factors. Clinical trials of intraocular gene therapy for neovascularization have shown the treatment to be safe without severe adverse events or systemic effects. Nevertheless, clinical studies have not proceeded further than Phase 2 trials.

Molecular Biomarkers of Neovascular Age-Related Macular Degeneration With Incomplete Response to Anti-Vascular Endothelial Growth Factor Treatment

The standard treatment for neovascular age-related macular degeneration (nAMD) consists of intravitreal anti-vascular endothelial growth factors (VEGF). However, for some patients, even maximal anti-VEGF treatment does not entirely suppress exudative activity. The goal of this study was to identify molecular biomarkers in nAMD with incomplete response to anti-VEGF treatment. Aqueous humor (AH) samples were collected from three groups of patients: 17 patients with nAMD responding incompletely to anti-VEGF (18 eyes), 17 patients affected by nAMD with normal treatment response (21 eyes), and 16 control patients without any retinopathy (16 eyes). Proteomic and multiplex analyses were performed on these samples. Proteomic analyses showed that nAMD patients with incomplete anti-VEGF response displayed an increased inflammatory response, complement activation, cytolysis, protein-lipid complex, and vasculature development pathways. Multiplex analyses revealed a significant increase of soluble vascular cell adhesion molecule-1 (sVCAM-1) [ p = 0.001], interleukin-6 (IL-6) [ p = 0.009], bioactive interleukin-12 (IL-12p40) [ p = 0.03], plasminogen activator inhibitor type 1 (PAI-1) [ p = 0.004], and hepatocyte growth factor (HGF) [ p = 0.004] levels in incomplete responders in comparison to normal responders. Interestingly, the same biomarkers showed a high intercorrelation with r2 values between 0.58 and 0.94. In addition, we confirmed by AlphaLISA the increase of sVCAM-1 [ p < 0.0001] and IL-6 [ p = 0.043] in the incomplete responder group. Incomplete responders in nAMD are associated with activated angiogenic and inflammatory pathways. The residual exudative activity of nAMD despite maximal anti-VEGF treatment may be related to both angiogenic and inflammatory responses requiring specific adjuvant therapy. Data are available via ProteomeXchange with identifier PXD02247

β-elemene down-regulates HIF-lα, VEGF and iNOS in human retinal pigment epithelial cells under high glucose conditions

AIM

To investigate the effects and mechanism of β-elemene on the expressions of hypoxia-inducible factor-1α (HIF-lα), vascular endothelial growth factor (VEGF) and inducible nitric oxide synthase (iNOS) in human retinal pigment epithelial (RPE) cells under high glucose conditions.

METHODS

ARPE-19 cell line was cultured under eight conditions: 1) low glucose (LG; 5.5 mmol/L); 2) high glucose (HG; 33 mmol/L); 3) high glucose with 20 µg/mL β-elemene (HG+20E); 4) high glucose with 40 µg/mL β-elemene (HG+40E); 5) high glucose with SB203590 [HG+SB203590, p38-mitogen-activated protein kinase (p38-MAPK) pathway inhibitor]; 6) high glucose with LY294002 [HG+LY294002, phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) pathway inhibitor]; 7) high glucose with 40 µg/mL β-elemene and SB203590 (HG+40E+SB203590); and 8) high glucose with 40 µg/mL β-elemene and LY294002 (HG+40E+LY294002). Cells were treated in conditions 1-4 for 24 and 48h, while for 48h in conditions 5-8. Then mRNA and protein levels of HIF-1α, VEGF and iNOS in cells were measured by real-time polymerase chain reaction (qPCR), immunofluorescence and Western blotting, respectively. Furthermore, protein levels of total p38-MAPK, phosphorylated p38-MAPK (p38-MAPK-P), total Akt and phosphorylated Akt (Akt-P) in cells of conditions 2 and 4 which treated for 48h were measured by Western blotting.

RESULTS

The mRNA levels and protein levels of HIF-1α, VEGF and iNOS in cells were significantly reduced in conditions 3-8 when compared with those in condition 2 (P<0.05). These reductions were more obvious in conditions treated for 48h than in conditions treated for 24h. The protein levels of p38-MAPK-P and Akt-P in cells of condition 4 were significantly lower than in condition 2 (P<0.01).

CONCLUSION

β-elemene down-regulates HIF-1α, VEGF and iNOS in ARPE-19 cells under a high glucose condition. The inhibitory effect of β-elemene is more significant when its concentration and treatment time are increased, as well as it is combined with SB203590 or LY294002 treatment. P38-MAPK and PI3K/Akt signaling pathways may play a role in this inhibitory effect.

SHP-2-Induced Activation of c-Myc Is Involved in PDGF-B-Regulated Cell Proliferation and Angiogenesis in RMECs

Background: Aberrant neovascularization resulting from inappropriate angiogenic signaling is closely related to many diseases, such as cancer, cardiovascular disease, and proliferative retinopathy. Although some factors involved in regulating pathogenic angiogenesis have been identified, the molecular mechanisms of proliferative retinopathy remain largely unknown. In the present study, we determined the role of platelet-derived growth factor-B (PDGF-B), one of the HIF-1-responsive gene products, in cell proliferation and angiogenesis in retinal microvascular endothelial cells (RMECs) and explored its regulatory mechanism.

Methods: Cell counting kit-8 (CCK-8), bromodeoxyuridine (BrdU) incorporation, tube formation, cell migration, and Western blot assays were used in our study.

Results: Our results showed that PDGF-B promoted cell proliferation and angiogenesis by increasing the activity of Src homology 2 domain-containing tyrosine phosphatase 2 (SHP-2) in RMECs, which was attenuated by the inhibition of PDGF receptor (PDGFR) or SHP-2 knockdown. Moreover, activation of c-Myc was involved in the processes of PDGF-B/SHP-2-driven cell proliferation in RMECs. The promoting effects of PDGF-B/SHP-2 on c-Myc expression were mediated by the Erk pathway.

Conclusion: These results indicate that PDGF-B facilitates cell proliferation and angiogenesis, at least in part, via the SHP-2/Erk/c-Myc pathway in RMECs, implying new potential treatment candidates for retinal microangiopathy.

Red Wine Extract Inhibits VEGF Secretion and Its Signaling Pathway in Retinal ARPE-19 Cells to Potentially Disrupt AMD

Age-related macular degeneration (AMD) is a degenerative disease of the retina where the molecular mechanism involves the production of vascular endothelial growth factor (VEGF), a factor of poor prognosis of the progression of the disease. Previous studies have shown that resveratrol, a polyphenol of grapevines, can prevent VEGF secretion induced by stress from retinal cells. Considering the fundamental role played by VEGF in development and progression of AMD, we investigate the potential effect of red wine extract (RWE) on VEGF secretion and its signaling pathway in human retinal cells ARPE-19. To examine the effect of RWE in ARPE-19, a quantitative and qualitative analysis of the RWE was performed by HPLC MS/MS. We show for the first time that RWE decreased VEGF-A secretion from ARPE-19 cells and its protein expression in concentration-dependent manner. RWE-induced alteration in VEGF-A production is associated with a down of VEGF-receptor 2 (VEGF-R2) protein expression and its phosphorylated intracytoplasmic domain. Subsequently, the activation of kinase pathway is disturbing and RWE prevents the phosphorylation of MEK and ERK 1/2 in human retinal cells ARPE-19. Finally, this study sheds light on the interest that the use of polyphenolic cocktails could represent in a prevention strategy.

Rice Bran and Vitamin B6 Suppress Pathological Neovascularization in a Murine Model of Age-Related Macular Degeneration as Novel HIF Inhibitors

Pathological neovascularization in the eye is a leading cause of blindness in all age groups from retinopathy of prematurity (ROP) in children to age-related macular degeneration (AMD) in the elderly. Inhibiting neovascularization via antivascular endothelial growth factor (VEGF) drugs has been used for the effective treatment. However, anti-VEGF therapies may cause development of chorioretinal atrophy as they affect a physiological amount of VEGF essential for retinal homeostasis. Furthermore, anti-VEGF therapies are still ineffective in some cases, especially in patients with AMD. Hypoxia-inducible factor (HIF) is a strong regulator of VEGF induction under hypoxic and other stress conditions. Our previous reports have indicated that HIF is associated with pathological retinal neovascularization in murine models of ROP and AMD, and HIF inhibition suppresses neovascularization by reducing an abnormal increase in VEGF expression. Along with this, we attempted to find novel effective HIF inhibitors from natural foods of our daily lives. Food ingredients were screened for prospective HIF inhibitors in ocular cell lines of 661W and ARPE-19, and a murine AMD model was utilized for examining suppressive effects of the ingredients on retinal neovascularization. As a result, rice bran and its component, vitamin B6 showed inhibitory effects on HIF activation and suppressed VEGF mRNA induction under a CoCl₂-induced pseudo-hypoxic condition. Dietary supplement of these significantly suppressed retinal neovascularization in the AMD model. These data suggest that rice bran could have promising therapeutic values in the management of pathological ocular neovascularization.

Sodium Butyrate Inhibits Neovascularization Partially via TNXIP/VEGFR2 Pathway

Control of neovascularization with small molecules is a promising tactics. Here, we tested the roles of sodium butyrate (NaBu) on the neovascularization and primary explained its underlining molecular links. We used models including cell and ex vivo culture of choroid and mouse, as well as the biochemical and cellular techniques, to confirm our hypothesis. We found that treating HUVEC cells with NaBu (both 2.5 mM and 5 mM) significantly inhibited its ability in tube formation and proliferation. This inhibitory effect was also observed in choroid sprouting experiments, compared to the control. Interestingly, the choroid sprouting suppressed by NaBu can proliferate again after removing it, indicating that the cell cycle progression might be arrested. The laser-induced choroid neovascularization (CNV) was significantly alleviated by assessing the CNV size (decreased to 0.73 fold) in contrast with the vehicle control group after 2.5 mM NaBu injection for 7 days. Mechanistically, we found an enhanced TXNIP expression in response to NaBu treatment in all the three models. Overexpressing TXNIP in HUVEC cells blocked its tube formation and inhibited its proliferation; on the other hand, knocking down its expression with shRNA reversed those phenotypes in context of NaBu treatment. Further investigation showed the expression of VEGF receptor 2 (VEGFR2) in HUVEC cells was regulated by TXNIP undergoing NaBu treatment. We therefore argued that NaBu inhibited neovascularization partially through TXNIP-regulated VEGFR2 signal pathway.

Neovascular Age-Related Macular Degeneration: Therapeutic Management and New-Upcoming Approaches

Age-related macular degeneration (AMD) constitutes a prevalent, chronic, and progressive retinal degenerative disease of the macula that affects elderly people and cause central vision impairment. Despite therapeutic advances in the management of neovascular AMD, none of the currently used treatments cures the disease or reverses its course. Medical treatment of neovascular AMD experienced a significant advance due to the introduction of vascular endothelial growth factor inhibitors (anti-VEGF), which dramatically changed the prognosis of the disease. However, although anti-VEGF therapy has become the standard treatment for neovascular AMD, many patients do not respond adequately to this therapy or experience a slow loss of efficacy of anti-VEGF agents after repeated administration. Additionally, current treatment with intravitreal anti-VEGF agents is associated with a significant treatment burden for patients, caregivers, and physicians. New approaches have been proposed for treating neovascular AMD. Among them, designed ankyrin repeat proteins (DARPins) seem to be as effective as monthly ranibizumab, but with greater durability, which may enhance patient compliance with needed injections.

Slug regulates the Dll4-Notch-VEGFR2 axis to control endothelial cell activation and angiogenesis

Slug (SNAI2), a member of the well-conserved Snail family of transcription factors, has multiple developmental roles, including in epithelial-to-mesenchymal transition (EMT). Here, we show that Slug is critical for the pathological angiogenesis needed to sustain tumor growth, and transiently necessary for normal developmental angiogenesis. We find that Slug upregulation in angiogenic endothelial cells (EC) regulates an EMT-like suite of target genes, and suppresses Dll4-Notch signaling thereby promoting VEGFR2 expression. Both EC-specific Slug re-expression and reduced Notch signaling, either by γ-secretase inhibition or loss of Dll4, rescue retinal angiogenesis in SlugKO mice. Conversely, inhibition of VEGF signaling prevents excessive angiogenic sprouting of Slug overexpressing EC. Finally, endothelial Slug (but not Snail) is activated by the pro-angiogenic factor SDF1α via its canonical receptor CXCR4 and the MAP kinase ERK5. Altogether, our data support a critical role for Slug in determining the angiogenic response during development and disease.

Slug supports heart development and tumor metastasis, but its role in blood vessel formation is less clear. Here the authors show that endothelial cell-expressed Slug regulates both physiologic and pathological angiogenesis, at least in part through the modulation of Notch signalling.

Pyruvate dehydrogenase kinase/lactate axis: a therapeutic target for neovascular age-related macular degeneration identified by metabolomics

Neovascular age-related macular degeneration (nAMD) is the leading cause of blindness in aging populations. Here, we applied metabolomics to human sera of patients with nAMD during an active (exudative) phase of the pathology and found higher lactate levels and a shift in the lipoprotein profile (increased VLDL-LDL/HDL ratio). Similar metabolomics changes were detected in the sera of mice subjected to laser-induced choroidal neovascularization (CNV). In this experimental model, we provide evidence for two sites of lactate production: first, a local one in the injured eye, and second a systemic site associated with the recruitment of bone marrow-derived inflammatory cells. Mechanistically, lactate promotes the angiogenic response and M2-like macrophage accumulation in the eyes. The therapeutic potential of our findings is demonstrated by the pharmacological control of lactate levels through pyruvate dehydrogenase kinase (PDK) inhibition by dichloroacetic acid (DCA). Mice treated with DCA exhibited normalized lactate levels and lipoprotein profiles, and inhibited CNV formation. Collectively, our findings implicate the key role of the PDK/lactate axis in AMD pathogenesis and reveal that the regulation of PDK activity has potential therapeutic value in this ocular disease. The results indicate that the lipoprotein profile is a traceable pattern that is worth considering for patient follow-up. KEY MESSAGES: Lactate and lipoprotein profile are associated with the active phase of AMD and CNV development. Lactate is a relevant and functional metabolite correlated with AMD progression. Modulating lactate through pyruvate dehydrogenase kinase led to a decrease of CNV progression. Pyruvate dehydrogenase kinase is a new therapeutic target for neovascular AMD.

Gene Therapy Intervention in Neovascular Eye Disease: A Recent Update

Aberrant growth of blood vessels (neovascularization) is a key feature of severe eye diseases that can cause legal blindness, including neovascular age-related macular degeneration (nAMD) and diabetic retinopathy (DR). The development of anti-vascular endothelial growth factor (VEGF) agents has revolutionized the treatment of ocular neovascularization. Novel proangiogenic targets, such as angiopoietin and platelet-derived growth factor (PDGF), are under development for patients who respond poorly to anti-VEGF therapy and to reduce adverse effects from long-term VEGF inhibition. A rapidly advancing area is gene therapy, which may provide significant therapeutic benefits. Viral vector-mediated transgene delivery provides the potential for continuous production of antiangiogenic proteins, which would avoid the need for repeated anti-VEGF injections. Gene silencing with RNA interference to target ocular angiogenesis has been investigated in clinical trials. Proof-of-concept gene therapy studies using gene-editing tools such as CRISPR-Cas have already been shown to be effective in suppressing neovascularization in animal models, highlighting the therapeutic potential of the system for treatment of aberrant ocular angiogenesis. This review provides updates on the development of anti-VEGF agents and novel antiangiogenic targets. We also summarize current gene therapy strategies already in clinical trials and those with the latest approaches utilizing CRISPR-Cas gene editing against aberrant ocular neovascularization.

The Role of Inflammation in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a blinding eye disease which incidence gradually increases with age. Inflammation participates in AMD pathogenesis, including choroidal neovascularization and geographic atrophy. It is also a kind of self-protective regulation from injury for the eyes. In this review, we described inflammation in AMD pathogenesis, summarized the roles played by inflammation-related cytokines, including pro-inflammatory and anti-inflammatory cytokines, as well as leukocytes (macrophages, dendritic cells, neutrophils, T lymphocytes and B lymphocytes) in the innate or adaptive immunity in AMD. Possible clinical applications such as potential diagnostic biomarkers and anti-inflammatory therapies were also discussed. This review overviews the inflammation as a target of novel effective therapies in treating AMD.

The effects of early diabetes on inner retinal neurons

Diabetic retinopathy is now well understood as a neurovascular disease. Significant deficits early in diabetes are found in the inner retina that consists of bipolar cells that receive inputs from rod and cone photoreceptors, ganglion cells that receive inputs from bipolar cells, and amacrine cells that modulate these connections. These functional deficits can be measured in vivo in diabetic humans and animal models using the electroretinogram (ERG) and behavioral visual testing. Early effects of diabetes on both the human and animal model ERGs are changes to the oscillatory potentials that suggest dysfunctional communication between amacrine cells and bipolar cells as well as ERG measures that suggest ganglion cell dysfunction. These are coupled with changes in contrast sensitivity that suggest inner retinal changes. Mechanistic in vitro neuronal studies have suggested that these inner retinal changes are due to decreased inhibition in the retina, potentially due to decreased gamma aminobutyric acid (GABA) release, increased glutamate release, and increased excitation of retinal ganglion cells. Inner retinal deficits in dopamine levels have also been observed that can be reversed to limit inner retinal damage. Inner retinal targets present a promising new avenue for therapies for early-stage diabetic eye disease.

Fibrotic Changes and Endothelial-to-Mesenchymal Transition Promoted by VEGFR2 Antagonism Alter the Therapeutic Effects of VEGFA Pathway Blockage in a Mouse Model of Choroidal Neovascularization

Many patients with wet age-related macular degeneration do not respond well to anti- vascular endothelial growth factor A (VEGFA) therapy for choroidal neovascularization (CNV), and the efficacy of anti-VEGFA decreases over time. We investigated the hypothesis that fibrotic changes, in particular via endothelial-to-mesenchymal transition (EndoMT), play a role in CNV and alter the therapeutic effects of VEGFA pathway blockage. Induction of EndoMT of primary human retinal endothelial cells led to a significantly reduced response to VEGFA at the level of gene expression, cellular proliferation, migration, and tube formation. Suppression of EndoMT restored cell responsiveness to VEGFA. In a mouse model of spontaneous CNV, fibrotic changes and EndoMT persisted as the CNV lesions became more established over time. VEGFA receptor-2 (VEGFR2) antagonism further induced fibrosis and EndoMT in the CNV. The combination of VEGFR2 antagonism and fibrosis/EndoMT inhibition was more effective than either individual treatment in reducing CNV. Our data indicate that fibrosis and EndoMT are involved in the progression of CNV, are exacerbated by VEGFR2 inhibition, and could provide an explanation for the reduced efficacy of anti-VEGFA treatment over time.

Soluble ligands as drug targets

Historically, the main classes of drug targets have been receptors, enzymes, ion channels and transporters. However, owing largely to the rise of antibody-based therapies in the past two decades, soluble protein ligands such as inflammatory cytokines have become an increasingly important class of drug targets. In this Review, we analyse drugs targeting ligands that have reached clinical development at some point since 1992. We identify 291 drugs that target 99 unique ligands, and we discuss trends in the characteristics of the ligands, drugs and indications for which they have been tested. In the last 5 years, the number of ligand-targeting drugs approved by the FDA has doubled to 34, while the number of clinically validated ligand targets has doubled to 22. Cytokines and growth factors are the predominant types of targeted ligands (70%), and inflammation and autoimmune disorders, cancer and ophthalmological diseases are the top therapeutic areas for both approved agents and agents in clinical studies, reflecting the central role of cytokine and/or growth factor pathways in such diseases.

Comparative Analysis of Multiplex Platforms for Detecting Vitreous Biomarkers in Diabetic Retinopathy

Purpose

To evaluate the feasibility of using the Proximity Extension Assay (PEA) platform to detect biomarkers in vitreous and to compare the findings with results obtained with an electrochemiluminescent (ECL) sandwich immunoassay.

Methods

Vitreous samples from patients with proliferative diabetic retinopathy (PDR) and non-diabetic controls were tested using two different proteomics platforms. Forty-one assays were completed with the ECL platform and 459 with the PEA platform. Spearman's rank correlation coefficient (r_s) was used to determine the direction and strength of the relationship between protein levels detected by both platforms.

Results

Three hundred sixty-six PEA assays detected the tested protein in at least 25% of samples, and the difference in protein abundance between PDR and controls was statistically significant for 262 assays. Seventeen ECL assays yielded a detection rate ≥ 25%, and the difference in protein concentration between PDR and controls was statistically significant for 13 proteins. There was a subset of proteins that were detected by both platforms, and for those the Spearman's correlation coefficient was higher than 0.8.

Conclusions

PEA is suitable for the analysis of vitreous samples, showing a strong correlation with the ECL platform. The detection rate of PEA panels was higher than the panels tested with ECL. The levels of several proinflammatory and angiogenic cytokines were significantly higher in PDR vitreous compared to controls.

Translational Relevance

This study provides new information on the yields of small-volume assays that can detect proteins of interest in ocular specimens, and it identifies patterns of cytokine dysregulation in PDR.

Imaging of Therapeutic Effects of Anti-Vascular Endothelial Growth Factor Inhibitors by Optical Coherence Tomography Angiography in a Rat Model

Purpose

The aim of the study was to investigate optical coherence tomography angiography (OCTA) as a high-resolution in vivo imaging modality for monitoring therapeutic response to different vascular endothelial growth factor inhibitors in the rat model of laser-induced choroidal neovascularization (CNV). Further, OCTA findings were compared with fluorescein angiography (FA) and fluorescence microscopy.

Methods

Laser treatment at day (D)0 was followed by intravitreal injection of aflibercept, AF564, and NaCl in dark agouti rats. Imaging with OCTA and FA was performed at D2, D7, D14, and D21. OCTA was compared to FA as well as confocal imaged flat mounts and analysis included quantification of CNV area, pixel intensity, vessel density, and number of vessel junctions.

Results

Within laser lesions, neovascularization were visible especially in deeper retinal layers on OCTA, but not on FA images. Using OCTA, mean CNV area (D21) at the level of the outer nuclear layer (ONL) was 0.017 mm² following aflibercept administration, 0.016 mm² following AF564 and 0.026 mm² following NaCl injection (P = 0.04 and P = 0.03). Similar differences between treatment groups were determined by FA and histology, although the overall CNV area was always larger on FA due to dye leakage (P ≤ 0.0001, all layers).

Conclusions

Compared to FA, OCTA imaging allows for a more precise and quantitative analysis of new blood vessel formation and therapeutic response to vascular endothelial growth factor (VEGF)-inhibitors, whereas it does not permit assessment of leakage.

Translational Relevance

These findings suggest that OCTA may be particularly useful for the investigation of new treatment targets in the animal model.

Asthma Promotes Choroidal Neovascularization via the Transforming Growth Factor beta1/Smad Signaling Pathway in a Mouse Model

INTRODUCTION

The association between age-related macular degeneration (AMD) and asthma is controversial. Transforming growth factor beta (TGF-β), which plays a critical role in asthma, has been extensively studied with regard to its function in choroidal neovascularization (CNV). In the present study, we aimed to investigate the role of TGF-β and the possible mechanism of CNV formation complicated with asthma and to explore the effect of a TGF-β inhibitor on CNV development in asthma mouse models.

METHODS

Laser-induced CNV and ovalbumin-induced asthma mouse models were divided into five groups: control group, acute asthma group, chronic asthma group, inhibitor-treated acute asthma group, and inhibitor-treated chronic asthma group. The gene expression patterns of angiogenic cytokines, vascular endothelial growth factor (VEGF) receptors and inflammasomes in the control group, acute asthma group and chronic asthma group were detected using a QuantiGene Plex 6.0 Reagent System. Fundus fluorescein angiography (FFA) and histology of CNV lesions stained with haematoxylin-eosin (HE) were performed to evaluate CNV formation. Quantitative real-time PCR and western blotting were used to assess TGF-β1, TGF-β2, and VEGF expression and Smad2/3, AKT, p38 MAPK, and ERK1/2 signal transduction and phosphorylation in retinal and choroidal tissue from each group.

RESULTS

In this study, we verified that laser treatment led to more CNV and vascular leakage in asthmatic mice than that in control mice. The changes were particularly notable in the chronic asthma group. The respective TGF-β1, VEGF, and phosphorylated Smad2/3 (p-Smad2/3) mRNA and protein levels in retinal and choroidal tissue were significantly upregulated in both the acute and chronic asthma groups. After injection of a TGF-β inhibitor, a distinct decline in VEGF, TGF-β1, and p-Smad2/3 protein and mRNA levels was observed, and the mean CNV area also decreased.

CONCLUSION

We provide new evidence that asthma could be a risk factor for CNV development via the TGF-β1/Smad signalling pathway. A TGF-β inhibitor can be applied as a useful, adjunctive therapeutic strategy for preventing CNV formation in asthmatic patients.

Differential Expression of Kinin Receptors in Human Wet and Dry Age-Related Macular Degeneration Retinae

Kinins are vasoactive peptides and mediators of inflammation, which signal through two G protein-coupled receptors, B1 and B2 receptors (B1R, B2R). Recent pre-clinical findings suggest a primary role for B1R in a rat model of wet age-related macular degeneration (AMD). The aim of the present study was to investigate whether kinin receptors are differentially expressed in human wet and dry AMD retinae. The cellular distribution of B1R and B2R was examined by immunofluorescence and in situ hybridization in post-mortem human AMD retinae. The association of B1R with inflammatory proteins (inducible nitric oxide synthase (iNOS) and vascular endothelial growth factor A (VEGFA)), fibrosis markers and glial cells was also studied. While B2R mRNA and protein expression was not affected by AMD, a significant increase of B1R mRNA and immunoreactivity was measured in wet AMD retinae when compared to control and dry AMD retinae. B1R was expressed by Müller cells, astrocytes, microglia and endothelial/vascular smooth muscle cells, and colocalized with iNOS and fibrosis markers, but not with VEGFA. In conclusion, the induction and upregulation of the pro-inflammatory and pro-fibrotic kinin B1R in human wet AMD retinae support previous pre-clinical studies and provide a clinical proof-of-concept that B1R represents an attractive therapeutic target worth exploring in this retinal disease.

Investigating the Role of PPARβ/δ in Retinal Vascular Remodeling Using Pparβ/δ-Deficient Mice

Peroxisome proliferator-activated receptor (PPAR)β/δ is a member of the nuclear receptor superfamily of transcription factors, which plays fundamental roles in cell proliferation and differentiation, inflammation, adipogenesis, and energy homeostasis. Previous studies demonstrated a reduced choroidal neovascularization (CNV) in Pparβ/δ-deficient mice. However, PPARβ/δ's role in physiological blood vessel formation and vessel remodeling in the retina has yet to be established. Our study showed that PPARβ/δ is specifically required for disordered blood vessel formation in the retina. We further demonstrated an increased arteriovenous crossover and wider venous caliber in Pparβ/δ-haplodeficient mice. In summary, these results indicated a critical role of PPARβ/δ in pathological angiogenesis and blood vessel remodeling in the retina.

Intravitreal injection of resveratrol inhibits laser-induced murine choroidal neovascularization

AIM

To determine the effects of intravitreal resveratrol (RSV) on murine laser-induced choroidal neovascularization (CNV).

METHODS

The toxicity of RSV to choroidal endothelial cell (CEC) was measured using thiazolyl blue tetrazolium bromide (MTT) assay. Effects of RSV on choroidal endothelial cell (CEC) migration were evaluated with a modified Boyden chamber assay, while tube formation was evaluated in a 2-D gel assay. CNV was induced by laser photocoagulation in mice. The effects of intravitreal injection of RSV on CNV development were evaluated by fluorescein angiography (FA), confocal analysis of isolectin B4 labeled choroidal flat mounts, and histologic examination of CNV membranes. Immunostaining was used to analyze the expression and phosphorylation of vascular endothelial growth factor receptor 2 (VEGFR2).

RESULTS

No significant cell toxicity was observed in CEC if the concentration of RSV was less than 200 µmol/L (P>0.05). RSV inhibited vascular endothelial growth factor (VEGF)-induced CEC migration (P<0.05) and tube formation (P<0.05) in vitro. Furthermore, intravitreal injection of RSV significantly inhibited laser induced CNV formation in mice. The FA leakage, CNV volume and CNV area analysis revealed that there were 41%, 45%, and 58% reduction in RSV-treated eyes (1.691±0.1032, 178 163±78 623 µm³ and 6508±619.0 µm², respectively) compared with those in control (2.724±0.08447, 379 676±98 382 µm³ and 16 576±2646 µm², respectively; P<0.05). Phospho-VEGFR2 expression was much weaker in the sections of CNV lesions in RSV injected mice compared with that in control (P<0.05).

CONCLUSION

Intravitreal injection of RSV exerts an inhibitory effect on CNV, which may through suppressing endothelial cell migration, tube formation and VEGFR2 phosphorylation.

Exploration of Oxygen-Induced Retinopathy Model to Discover New Therapeutic Drug Targets in Retinopathies

Oxygen-induced retinopathy (OIR) is a pure hypoxia-driven angiogenesis model and the most widely used model for ischemic retinopathies, such as retinopathy of prematurity (ROP), proliferative diabetic retinopathy (PDR), and retinal vein occlusion (RVO). OIR model has been used to test new potential anti-angiogenic factors for human diseases. We have recently performed the most comprehensive characterization of OIR by a relatively novel mass spectrometry (MS) technique, sequential window acquisition of all theoretical fragment ion mass spectra (SWATH-MS) proteomics and used genetically modified mice strains to identify novel molecular drug targets in angiogenic retinal diseases. We have confirmed the relevance of the identified molecular targets to human diseases by determining their expression pattern in neovascular membranes obtained from PDR and RVO patients. Based on our results, crystallins were the most prominent proteins induced by early hypoxic environment during the OIR, while actomyosin complex and Filamin A-R-Ras axis, that regulates vascular permeability of the angiogenic blood vessels, stood out at the peak of angiogenesis. Our results have revealed potential new therapeutic targets to address hypoxia-induced pathological angiogenesis and the associated vascular permeability in number of retinal diseases.