Inhibition of choroidal neovascularization by intravenous injection of adenoviral vectors expressing secretable endostatin

The Role of Reactive Oxygen Species in Age-Related Macular Degeneration: A Comprehensive Review of Antioxidant Therapies

This review article delves into the intricate roles of reactive oxygen species (ROS) in the pathogenesis of age-related macular degeneration (AMD). It presents a detailed analysis of the oxidative stress mechanisms that contribute to the development and progression of these diseases. The review systematically explores the dual nature of ROS in ocular physiology and pathology, underscoring their essential roles in cellular signaling and detrimental effects when in excess. In the context of AMD, the focus is on the oxidative impairment in the retinal pigment epithelium and Bruch's membrane, culminating in the deterioration of macular health. Central to this review is the evaluation of various antioxidant strategies in the prevention and management of AMD. It encompasses a wide spectrum of antioxidants, ranging from dietary nutrients like vitamins C and E, lutein, and zeaxanthin to pharmacological agents with antioxidative properties. The review also addresses novel therapeutic approaches, including gene therapy and nanotechnology-based delivery systems, aiming to enhance antioxidant defense mechanisms in ocular tissues. The article concludes by synthesizing current research findings, clinical trial data, and meta-analyses to provide evidence-based recommendations. It underscores the need for further research to optimize antioxidant therapies, considering individual patient factors and disease stages. This comprehensive review thus serves as a valuable resource for clinicians, researchers, and healthcare professionals in ophthalmology, offering insights into the potential of antioxidants in mitigating the burden of AMD.

Age-related macular degeneration: Epidemiology, genetics, pathophysiology, diagnosis, and targeted therapy

Age-related macular degeneration (AMD) is a complex eye disorder and is the leading cause of incurable blindness worldwide in the elderly. Clinically, AMD initially affects the central area of retina known as the macula and it is classified as early stage to late stage (advanced AMD). The advanced AMD is classified into the nonexudative or atrophic form (dry AMD) and the exudative or neovascular form (wet AMD). More severe vision loss is typically associated with the wet form. Multiple genetic factors, lipid metabolism, oxidative stress and aging, play a role in the etiology of AMD. Dysregulation in genetic to AMD is established to 46%-71% of disease contribution, with CFH and ARMS2/HTRA1 to be the two most notable risk loci among the 103 identified AMD associated loci so far. Chronic cigarette smoking is the most proven consistently risk living habits for AMD. Deep learning algorithm has been developed based on image recognition to distinguish wet AMD and normal macula with high accuracy. Currently, anti-vascular endothelial growth factor (VEGF) therapy is highly effective at treating wet AMD. Several new generation AMD drugs and iPSC-derived RPE cell therapy are in the clinical trial stage and are promising to improve AMD treatment in the near future.

Endostatin as a Mediator Between Endothelial Function and Cognitive Performance in Those at Risk for Vascular Cognitive Impairment

Background:

Patients with coronary artery disease have an increased risk for developing vascular cognitive impairment. Endothelial function is often diminished and has been associated with lower cognitive performance in these patients. The link between endothelial function and cognition in coronary artery disease is not fully understood. Angiogenesis may play a role in mediating the association between endothelial function and cognition since angiogenic processes rely heavily on the endothelium.

Objective:

The aim of this study was to determine if markers of angiogenesis mediate the relationship between endothelial function and cognition in coronary artery disease patients.

Methods:

In 50 participants with coronary artery disease, endothelial function was assessed using peripheral arterial tonometry. Vascular endothelial growth factor (pro-angiogenic) and endostatin (anti-angiogenic) were measured in peripheral serum samples. Cognition was assessed using the Montreal Cognitive Assessment. A mediation analysis, using a bias corrected inferential bootstrapping method with 10,000 permutations, was used to determine if vascular endothelial growth factor or endostatin mediated an association between peripheral arterial tonometry measures and cognitive performance on the Montreal Cognitive Assessment.

Results:

Endostatin, but not vascular endothelial growth factor, mediated a relationship between endothelial function and cognitive performance when controlling for total years of education, body mass index, coronary artery bypass graft, stent, diabetes, and diuretic use. This analysis was also significant when delayed recall was substituted for the overall score on the Montreal Cognitive Assessment.

Conclusion:

These results suggest that endostatin mediates an association between endothelial function and cognitive performance in coronary artery 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.

Bruch's Membrane and the Choroid in Age-Related Macular Degeneration

A healthy choroidal vasculature is necessary to support the retinal pigment epithelium (RPE) and photoreceptors, because there is a mutualistic symbiotic relationship between the components of the photoreceptor/retinal pigment epithelium (RPE)/Bruch's membrane (BrMb)/choriocapillaris (CC) complex. This relationship is compromised in age-related macular degeneration (AMD) by the dysfunction or death of the choroidal vasculature. This chapter will provide a basic description of the human Bruch's membrane and choroidal anatomy and physiology and how they change in AMD.The choriocapillaris is the lobular, fenestrated capillary system of choroid. It lies immediately posterior to the pentalaminar Bruch's membrane (BrMb). The blood supply for this system is the intermediate blood vessels of Sattler's layer and the large blood vessels in Haller's layer.In geographic atrophy (GA), an advanced form of dry AMD, large confluent drusen form on BrMb, and hyperpigmentation (presumably dysfunction in RPE) appears to be the initial insult. The resorption of these drusen and loss of RPE (hypopigmentation) can be predictive for progression of GA. The death and dysfunction of CC and photoreceptors appear to be secondary events to loss in RPE. The loss of choroidal vasculature may be the initial insult in neovascular AMD (nAMD). We have observed a loss of CC with an intact RPE monolayer in nAMD, by making RPE hypoxic. These hypoxic cells then produce angiogenic substances like vascular endothelial growth factor (VEGF), which stimulate growth of new vessels from CC, resulting in choroidal neovascularization (CNV). Reduction in blood supply to the CC, often stenosis of intermediate and large blood vessels, is associated with CC loss.The polymorphisms in the complement system components are associated with AMD. In addition, the environment of the CC, basement membrane and intercapillary septa, is a proinflammatory milieu with accumulation of proinflammatory molecules like CRP and complement components during AMD. In this toxic milieu, CC die or become dysfunctional even early in AMD. The loss of CC might be a stimulus for drusen formation since the disposal system for retinal debris and exocytosed material from RPE would be limited. Ultimately, the photoreceptors die of lack of nutrients, leakage of serum components from the neovascularization, and scar formation.Therefore, the mutualistic symbiotic relationship of the photoreceptor/RPE/BrMb/CC complex is lost in both forms of AMD. Loss of this functionally integrated relationship results in death and dysfunction of all of the components in the complex.

Sustained suppression of VEGF for treatment of retinal/choroidal vascular diseases

Neovascular age-related macular degeneration (NVAMD) is the most prevalent choroidal vascular disease, and diabetic retinopathy (DR) and retinal vein occlusion (RVO) are the most prevalent retinal vascular diseases. In each of these, hypoxia plays a central role by stabilizing hypoxia-inducible factor-1 which increases production of vascular endothelial growth factor (VEGF) and other hypoxia-regulated gene products. High VEGF causes excessive vascular permeability, neovascularization, and in DR and RVO, promotes closure of retinal vessels exacerbating hypoxia and creating a positive feedback loop. Hence once VEGF expression is elevated it tends to remain elevated and drives disease progression. While other hypoxia-regulated gene products also contribute to pathology in these disease processes, it is remarkable how much pathology is reversed by selective inhibition of VEGF. Clinical trials have demonstrated outstanding visual outcomes in patients with NVAMD, DR, or RVO from frequent intraocular injections of VEGF-neutralizing proteins, but for a variety of reasons injection frequency has been substantially less in clinical practice and visual outcomes are disappointing. Herein we discuss the rationale, preclinical, and early clinical results of new approaches that provide sustained suppression of VEGF. These approaches will revolutionize the management of these prevalent retinal/choroidal vascular diseases.

An Endostatin-lentivirus (ES-LV)-EPC gene therapy agent for suppression of neovascularization in oxygen-induced retinopathy rat model

BACKGROUND

Transplantation of gene transfected endothelial progenitor cells (EPCs) has provided novel methods for tumor neovascularization therapy but not for ocular disease therapy. This study aimed to investigate the efficacy of endostatin transfected EPCs in retinal neovascularization therapy.

RESULTS

Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) showed the high expression of endostatin in endostatin-lentivirus-EPCs. The neovascularization leakage area and the number of preretinal neovascular cell nuclei were significantly decreased in the endostatin-lentivirus and endostatin-lentivirus-EPC groups, and the effects of these two treatments on inhibiting retinal neovascularization were almost the same. These two groups also showed the greater retinal distribution of endostatin. Intravitreal injections of endostatin-lentivirus-EPCs inhibited retinal neovascularization, vascular endothelial growth factor (VEGF) and CD31 expression, and increased endostatin expression in vivo. Endostatin-lentivirus-EPCs targeted and prevented pathologic retinal neovascularization.

CONCLUSIONS

Gene-combined EPCs represent a potential new therapeutic agent for the treatment of neovascular eye diseases.

Fibulin-7 C-terminal fragment and its active synthetic peptide suppress choroidal and retinal neovascularization

Wet age-related macular degeneration (AMD) and diabetic retinopathy are the leading causes of blindness through increased angiogenesis. Although VEGF-neutralizing proteins provide benefit, inconsistent responses indicate a need for new therapies. We previously identified the Fibulin-7 C-terminal fragment (Fbln7-C) as an angiogenesis inhibitor in vitro. Here we show that Fbln7-C inhibits neovascularization in vivo, in both a model of wet AMD involving choroidal neovascularization (CNV) and diabetic retinopathy involving oxygen-induced ischemic retinopathy. Furthermore, a short peptide sequence from Fbln7-C is responsible for the anti-angiogenic properties of Fbln7-C. Our work suggests Fbln7-C as a therapeutic candidate for wet AMD and ischemic retinopathy.

Associations of microRNAs, Angiogenesis-Regulating Factors and CFH Y402H Polymorphism-An Attempt to Search for Systemic Biomarkers in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) remains the leading cause of blindness in elderly people, but the pathophysiology of this disease is still largely unknown. We investigated the systemic expression of angiogenesis-regulating growth factors and selected miRNAs known to regulate angiogenesis in AMD patients. We also focused on possible correlations of their expression with the presence of CFH Y402H or ARMS A69S risk variants. A total of 354 AMD patients and 121 controls were enrolled in this study. The levels of angiogenesis-regulating factors were analyzed in plasma samples using Luminex technology. The expression of selected miRNAs was analyzed in peripheral blood plasma using real-time qPCR. The genetic analysis was performed with an Illumina NextSeq500 system. AMD was an independent factor associated with lower levels of angiogenin (β = −0.29, p < 0.001), endostatin (β = −0.18, p < 0.001), FGF-basic (β = −0.18, p < 0.001), PlGF (β = −0.24, p < 0.001), miRNA-21-3p (β = −0.13, p = 0.01) and miRNA-155-5p (β = −0.16, p = 0.002); and with higher levels of FGF-acidic (β = 0.11, p = 0.03), miRNA-23a-3p (β = 0.17, p < 0.001), miRNA-126-5p (β = 0.13, p = 0.009), miRNA-16-5p (β = 0.40, p < 0.001), miRNA-17-3p (β = 0.13, p = 0.01), miRNA-17-5p (β = 0.17, p < 0.001), miRNA-223-3p (β = 0.15, p = 0.004), and miRNA-93 (β = 0.11, p = 0.04). The expression of analyzed miRNA molecules significantly correlated with the levels of tested angiogenesis-regulating factors and clinical parameters in AMD patients, whereas such correlations were not observed in controls. We also found an association between the CFH Y402H polymorphism and miRNA profiles, whereby TT homozygotes showed evidently higher expression of miRNA-16-5p than CC homozygotes or TC heterozygotes (p = 0.0007). Our results suggest that the balance between systemic pro- and anti-angiogenic factors and miRNAs is vital in multifactorial AMD pathogenesis.

Novel stem cell and gene therapy in diabetic retinopathy, age related macular degeneration, and retinitis pigmentosa

Degenerative retinal disease leads to significant visual morbidity worldwide. Diabetic retinopathy and macular degeneration are leading causes of blindness in the developed world. While current therapies for these diseases slow disease progression, stem cell and gene therapy may also reverse the effects of these, and other, degenerative retinal conditions. Novel therapies being investigated include the use of various types of stem cells in the regeneration of atrophic or damaged retinal tissue, the prolonged administration of neurotrophic factors and/or drug delivery, immunomodulation, as well as the replacement of mutant genes, and immunomodulation through viral vector delivery. This review will update the reader on aspects of stem cell and gene therapy in diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa and other less common inherited retinal dystrophies. These therapies include the use of adeno-associated viral vector-based therapies for treatment of various types of retinitis pigmentosa and dry age-related macular degeneration. Other potential therapies reviewed include the use of mesenchymal stem cells in local immunomodulation, and the use of stem cells in generating structures like three-dimensional retinal sheets for transplantation into degenerative retinas. Finally, aspects of stem cell and gene therapy in diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, and other less common inherited retinal dystrophies will be reviewed.

Gene therapy and the adeno-associated virus in the treatment of genetic and acquired ophthalmic diseases in humans: Trials, future directions and safety considerations

Voretigene neparvovec-rzyl was recently approved for the treatment of Leber congenital amaurosis, and the use of gene therapy for eye disease is attracting even greater interest. The eye has immune privileged status, is easily accessible, requires a reduced dosage of therapy due to its size and is highly compartmentalized, significantly reducing systemic spread. Adeno-associated virus (AAV), with its low pathogenicity, prolonged expression profile and ability to transduce multiple cell types, has become the leading gene therapy vector. Target diseases have moved beyond currently untreatable inherited dystrophies to common, partially treatable acquired conditions such as exudative age-related macular degeneration and glaucoma, but use of the technology in these conditions imposes added obligations for caution in vector design. This review discusses the current status of AAV gene therapy trials in genetic and acquired ocular diseases, and explores new scientific developments, which could help ensure effective and safe use of the therapy in the future.

Cell-specific gene therapy driven by an optimized hypoxia-regulated vector reduces choroidal neovascularization

Aberrant growth of blood vessels in the choroid layer of the eye, termed choroidal neovascularization (CNV), is the pathological hallmark of exudative age-related macular degeneration (AMD), causing irreversible blindness among the elderly. Co-localization of proangiogenic factors and hypoxia inducible factors (HIF) in neovascular membranes from AMD eyes suggests the role of hypoxia in pathogenesis of CNV. In order to utilize hypoxic conditions in RPE for therapeutic purposes, we developed an optimized hypoxia regulated, RPE cell-specific gene therapy to inhibit choroidal neovascularization. An adeno-associated virus (AAV2) vector comprising a RPE-specific promoter and HIF-1 response elements (HRE) was designed to regulate production of human endostatin (a powerful angiostatic protein) in RPE. The vector was tested in a mouse model of laser-induced CNV using subretinal delivery. Spectral domain optical coherence tomography (SD-OCT) images from live mice and confocal images from lectin stained RPE flat mount sections demonstrated reduction in CNV areas by 80% compared to untreated eyes. Quantitative real-time polymerase chain reaction (qPCR) confirmed exogenous endostatin mRNA expression from the regulated vector that was significantly elevated 3, 7, and 14 days following laser treatment, but its expression was completely shut off after 45 days. Thus, RPE-specific, hypoxia-regulated delivery of anti-angiogenic proteins could be a valuable therapeutic approach to treat neovascular AMD at the time and in the ocular space where it arises.

KEY POINTS

An optimized gene therapy vector targeting hypoxia and tissue-specific expression has been designed. The inhibitory role of gene therapy vector was tested in a mouse model of laser-induced CNV. An 80% reduction in choroidal neovascularization was achieved by the optimized vector. The expression of endostatin was limited to retinal pigment epithelium and regulated by hypoxia.

Clinical applications of retinal gene therapies

Retinal degenerative diseases are a major cause of blindness. Retinal gene therapy is a trail-blazer in the human gene therapy field, leading to the first FDA approved gene therapy product for a human genetic disease. The application of Clustered Regularly Interspaced Short Palindromic Repeat/Cas9 (CRISPR/Cas9)-mediated gene editing technology is transforming the delivery of gene therapy. We review the history, present, and future prospects of retinal gene therapy.

Collagen XVIII in tissue homeostasis and dysregulation - Lessons learned from model organisms and human patients

Collagen XVIII is a ubiquitous basement membrane (BM) proteoglycan produced in three tissue-specific isoforms that differ in their N-terminal non-collagenous sequences, but share collagenous and C-terminal non-collagenous domains. The collagenous domain provides flexibility to the large collagen XVIII molecules on account of multiple interruptions in collagenous sequences. Each isoform has a complex multi-domain structure that endows it with an ability to perform various biological functions. The long isoform contains a frizzled-like (Fz) domain with Wnt-inhibiting activity and a unique domain of unknown function (DUF959), which is also present in the medium isoform. All three isoforms share an N-terminal laminin-G-like/thrombospondin-1 sequence whose specific functions still remain unconfirmed. The proteoglycan nature of the isoforms further increases the functional diversity of collagen XVIII. An anti-angiogenic domain termed endostatin resides in the C-terminus of collagen XVIII and is proteolytically cleaved from the parental molecule during the BM breakdown for example in the process of tumour progression. Recombinant endostatin can efficiently reduce tumour angiogenesis and growth in experimental models by inhibiting endothelial cell migration and proliferation or by inducing their death, but its efficacy against human cancers is still a subject of debate. Mutations in the COL18A1 gene result in Knobloch syndrome, a genetic disorder characterised mainly by severe eye defects and encephalocele and, occasionally, other symptoms. Studies with gene-modified mice have elucidated some aspects of this rare disease, highlighting in particular the importance of collagen XVIII in the development of the eye. Research with model organisms have also helped in determining other structural and biological functions of collagen XVIII, such as its requirement in the maintenance of BM integrity and its emerging roles in regulating cell survival, stem or progenitor cell maintenance and differentiation and inflammation. In this review, we summarise current knowledge on the properties and endogenous functions of collagen XVIII in normal situations and tissue dysregulation. When data is available, we discuss the functions of the distinct isoforms and their specific domains.

Lentiviral Vector Gene Transfer of Endostatin/Angiostatin for Macular Degeneration (GEM) Study

Neovascular age-related macular degeneration (NVAMD) is a prevalent cause of vision loss. Intraocular injections of VEGF-neutralizing proteins provide benefit, but many patients require frequent injections for a prolonged period. Benefits are often lost over time due to lapses in treatment. New treatments that sustain anti-angiogenic activity are needed. This study tested the safety and expression profile of a lentiviral Equine Infectious Anemia Virus (EIAV) vector expressing endostatin and angiostatin (RetinoStat^®). Patients with advanced NVAMD were enrolled at three centers in the United States, and the study eye received a subretinal injection of 2.4 × 10⁴ (n = 3), 2.4 × 10⁵ (n = 3), or 8.0 × 10⁵ transduction units (TU; n = 15). Each of the doses was well-tolerated with no dose-limiting toxicities. There was little or no ocular inflammation. There was one procedure-related serious adverse event (AE), a macular hole, which was managed without difficulty and resolved. There was a vector dose-related increase in aqueous humor levels of endostatin and angiostatin with high reproducibility among subjects within cohorts. Mean levels of endostatin and angiostatin peaked between 12 and 24 weeks after injection of 2.4 × 10⁵ TU or 8.0 × 10⁵ TU at 57-81 ng/mL for endostatin and 15-27 ng/mL for angiostatin, and remained stable through the last measurement at week 48. Long-term follow-up demonstrated expression was maintained at last measurement (2.5 years in eight subjects and >4 years in two subjects). Despite an apparent reduction in fluorescein angiographic leakage that broadly correlated with the expression levels in the majority of patients, only one subject showed convincing evidence of anti-permeability activity in these late-stage patients. There was no significant change in mean lesion size in subjects injected with 8.0 × 10⁵ TU. These data demonstrate that EIAV vectors provide a safe platform with robust and sustained transgene expression for ocular gene therapy.

Augmented anti-angiogenesis activity of polysulfated heparin-endostatin and polyethylene glycol-endostatin in alkali burn-induced corneal ulcers in rabbits

Endostatin (ES) is an endogenous angiogenesis inhibitor that has the ability to inhibit tumor growth and metastasis. However, its clinical application is limited by a number of disadvantages, such as poor stability, short half-life and the requirement of high doses to maintain its efficacy. The chemical modification on ES may offer a solution to these disadvantages. The aim of the present study was to evaluate the effects of ES, polysulfated heparin-endostatin (PSH-ES) and polyethylene glycol-endostatin (PEG-ES) on the endothelial cell proliferation and angiogenesis associated with corneal neovascularization (CNV) and to determine their mechanisms of action. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) was used to study the effects of ES and its derivatives on endothelial cell proliferation in vitro, and rabbits were used to evaluate the effects of ES and its derivatives on CNV in vivo. In the evaluation of CNV, the expression of vascular endothelial growth factor in the cornea was measured via immunohistochemistry and microvessels were counted. ES and its derivatives significantly inhibited endothelial cell proliferation in vitro (P<0.05) and suppressed CNV in vivo. Among the compounds examined, ES most effectively inhibited endothelial cell proliferation in vitro (P<0.05); however, PSH-ES and PEG-ES most effectively inhibited CNV in vivo (P<0.05). These results indicate that PSH-ES and PEG-ES are candidate anti-angiogenesis drugs.

Enhanced production of secretory glycoprotein VSTM1-v2 with mouse IgGκ signal peptide in optimized HEK293F transient transfection

VSTM1-v2 is a secretory glycoprotein identified by our laboratory. Our previous study revealed that VSTM1-v2 could promote differentiation and activation of Th17 cells. To explore the role of VSTM1-v2 in the immune system further, a source of abundant high-quality recombinant protein is warranted. However, high-level expression of bioactive VSTM1-v2 is difficult due to its weak secretion capacity. To obtain sufficient recombinant VSTM1-v2, we developed an improved expression and purification system by replacing the native signal peptide with a mouse IgGκ signal peptide that did not alter the protein cleavage site. We also optimized parameters for a transient gene expression system in HEK293F cells suspended in serum-free media with polyethyleneimine. Finally, 3.6 mg/L recombinant VSTM1-v2 protein with N-glycosylation and no less than 95% purity was obtained through one-step purification with Ni affinity chromatography. The final yield after purification was increased by more than 7-fold compared to the yield from our previously reported HEK293T system (from 0.5 mg/L to 3.6 mg/L). More importantly, VSTM1-v2 protein exhibited excellent bioactivity. In conclusion, the improved system is not only a dependable source of abundant bioactive VSTM1-v2 for functional studies but also demonstrates a highly efficient approach for enhancing the production of proteins in a short time period, especially for secretory proteins with poor yields.

Molecular pathogenesis of retinal and choroidal vascular diseases

There are two major types of ocular neovascularization that affect the retina, retinal neovascularization (NV) and subretinal or choroidal NV. Retinal NV occurs in a group of diseases referred to as ischemic retinopathies in which damage to retinal vessels results in retinal ischemia. Most prevalent of these are diabetic retinopathy and retinal vein occlusions. Subretinal and choroidal NV occur in diseases of the outer retina and Bruch's membrane, the most prevalent of which is age-related macular degeneration. Numerous studies in mouse models have helped to elucidate the molecular pathogenesis underlying retinal, subretinal, and choroidal NV. There is considerable overlap because the precipitating event in each is stabilization of hypoxia inducible factor-1 (HIF-1) which leads to upregulation of several hypoxia-regulated gene products, including vascular endothelial growth factor (VEGF), angiopoietin 2, vascular endothelial-protein tyrosine phosphatase (VE-PTP), and several others. Stimulation of VEGF signaling and suppression of Tie2 by angiopoietin 2 and VE-PTP are critical for sprouting of retinal, subretinal, and choroidal NV, with perturbation of Bruch's membrane also needed for the latter. Additional HIF-1-regulated gene products cause further stimulation of the NV. It is difficult to model macular edema in animals and therefore proof-of-concept clinical trials were done and demonstrated that VEGF plays a central role and that suppression of Tie2 is also important. Neutralization of VEGF is currently the first line therapy for all of the above disease processes, but new treatments directed at some of the other molecular targets, particularly stabilization of Tie2, are likely to provide additional benefit for subretinal/choroidal NV and macular edema. In addition, the chronicity of these diseases as well as the implication of VEGF as a cause of retinal nonperfusion and progression of background diabetic retinopathy make sustained delivery approaches for VEGF antagonists a priority.

Key endothelial cell angiogenic mechanisms are stimulated by the circulating milieu in sickle cell disease and attenuated by hydroxyurea

As hypoxia-induced inflammatory angiogenesis may contribute to the manifestations of sickle cell disease, we compared the angiogenic molecular profiles of plasma from sickle cell disease individuals and correlated these with in vitro endothelial cell-mediated angiogenesis-stimulating activity and in vivo neovascularization. Bioplex demonstrated that plasma from patients with steady-state sickle cell anemia contained elevated concentrations of pro-angiogenic factors (angiopoietin-1, basic fibroblast growth factor, vascular endothelial growth factor, vascular endothelial growth factor-D and placental growth factor) and displayed potent pro-angiogenic activity, significantly increasing endothelial cell proliferation, migration and capillary-like structure formation. In vivo neovascularization of Matrigel plugs was significantly greater in sickle cell disease mice than in non-sickle cell disease mice, consistent with an up-regulation of angiogenesis in the disease. In plasma from patients with hemoglobin SC disease without proliferative retinopathy, anti-angiogenic endostatin and thrombospondin-2 were significantly elevated. In contrast, plasma from hemoglobin SC individuals with proliferative retinopathy had a pro-angiogenic profile and more significant effects on endothelial cell proliferation and capillary formation than plasma from patients without retinopathy. Hydroxyurea therapy was associated with significant reductions in plasma angiogenic factors and inhibition of endothelial cell-mediated angiogenic mechanisms and neovascularization. Thus, individuals with sickle cell anemia or hemoglobin SC disease with retinopathy present a highly angiogenic circulating milieu, capable of stimulating key endothelial cell-mediated angiogenic mechanisms. Combination anti-angiogenic therapy to prevent the progression of unregulated neovascularization and associated manifestations in sickle cell disease, such as pulmonary hypertension, may be indicated; furthermore, the benefits and drawbacks of the potent anti-angiogenic effects of hydroxyurea should be clarified.

Suppression of choroidal neovascularization by Endostar in rats

Choroidal neovascularization (CNV) is common in various retinal and choroidal diseases, and may result in severe and irreversible loss of vision. Our previous studies suggested that Endostar, a novel recombinant endostatin, is able to inhibit the proliferation and migration of choroid‑retinal endothelial cells. To further evaluate the effect of Endostar on the formation of CNV in vivo, a rat model of laser‑induced CNV was constructed and Endostar or phosphate‑buffered saline treatment was administered intravitreally every other day. Using fluorescein angiography (FA), reduced CNV incidence and leakage grade was observed in the Endostar group. In addition, CNV area and maximal thickness were prominently reduced in the Endostar group measured by choroid flat mounts and sections. Furthermore, vascular endothelial growth factor (VEGF), hypoxia‑inducible factor 1α and chemokine C‑X‑C motif ligand 1 were markedly reduced in the Endostar group as determined by quantitative polymerase chain reaction and downregulation of VEGF was also verified by western blot analysis at the protein level. This study demonstrates that Endostar suppressed CNV in a rat model, which may be largely mediated by the downregulation of VEGF and other angiogenic molecules.

Endostar inhibits hypoxia-induced cell proliferation and migration via the hypoxia-inducible factor-1α/vascular endothelial growth factor pathway in vitro

Endostar, a recombinant human endostatin, is recognized as one of the most effective angiogenesis inhibitors. The angiogenesis inhibitory effects of Endostar suggest a possible beneficial role of Endostar in choroidal neovascularization (CNV), which is predominantly induced by hypoxia. In our previous study, it was reported that Endostar may inhibit the proliferation and migration of RF/6A choroid‑retinal endothelial cells. However, the inhibitory effect of Endostar on hypoxia‑induced cell proliferation and migration in RF/6A cells has not yet been elucidated. Therefore, the present study investigated the effect of Endostar on hypoxia‑induced cell proliferation and migration in RF/6A cells and the possible mechanisms underlying this effect. Under chemical hypoxia conditions, cell viability was increased to 114.9±10.1 and 123.6±9.6% in cells treated with 100 and 200 µm CoCl2, respectively, compared with the control (P<0.01). Pretreatment with 10‑100 µg/ml Endostar significantly inhibited CoCl2‑induced cell proliferation (P<0.05), and pre‑treatment with 10 µg/ml Endostar for 24, 48 and 96 h attenuated CoCl2‑promoted cell migration by 60.5, 48.3 and 39.6%, respectively, compared with the control (P<0.001). In addition, pretreatment with 10 µg/ml Endostar reversed the cell cycle arrest at S phase and the increased expression of hypoxia‑inducible factor‑1α (HIF‑1α) and vascular endothelial growth factor (VEGF) mRNA in RF/6A cells treated with 200 µM CoCl2. These data indicate that Endostar inhibited CoCl2‑induced hypoxic proliferation and migration, and limited cell cycle progression in vitro possibly through the HIF‑1α/VEGF pathway.

Gene Therapies for Neovascular Age-Related Macular Degeneration

Pathological neovascularization is a key component of the neovascular form (also known as the wet form) of age-related macular degeneration (AMD) and proliferative diabetic retinopathy. Several preclinical studies have shown that antiangiogenesis strategies are effective for treating neovascular AMD in animal models. Vascular endothelial growth factor (VEGF) is one of the main inducers of ocular neovascularization, and several clinical trials have shown the benefits of neutralizing VEGF in patients with neovascular AMD or diabetic macular edema. In this review, we summarize several preclinical and early-stage clinical trials with intraocular gene therapies, which have the potential to reduce or eliminate the repeated intravitreal injections that are currently required for the treatment of neovascular AMD.

A hypoxia-responsive glial cell-specific gene therapy vector for targeting retinal neovascularization

PURPOSE

Müller cells, the major glial cell in the retina, play a significant role in retinal neovascularization in response to tissue hypoxia. We previously designed and tested a vector using a hypoxia-responsive domain and a glial fibrillary acidic protein (GFAP) promoter to drive green fluorescent protein (GFP) expression in Müller cells in the murine model of oxygen-induced retinopathy (OIR). This study compares the efficacy of regulated and unregulated Müller cell delivery of endostatin in preventing neovascularization in the OIR model.

METHODS

Endostatin cDNA was cloned into plasmids with hypoxia-regulated GFAP or unregulated GFAP promoters, and packaged into self-complementary adeno-associated virus serotype 2 vectors (scAAV2). Before placement in hyperoxia on postnatal day (P)7, mice were given intravitreal injections of regulated or unregulated scAAV2, capsid, or PBS. Five days after return to room air, on P17, neovascular and avascular areas, as well as expression of the transgene and vascular endothelial growth factor (VEGF), were compared in OIR animals treated with a vector, capsid, or PBS.

RESULTS

The hypoxia-regulated, glial-specific, vector-expressing endostatin reduced neovascularization by 93% and reduced the central vaso-obliteration area by 90%, matching the results with the unregulated GFAP-Endo vector. Retinas treated with the regulated endostatin vector expressed substantial amounts of endostatin protein, and significantly reduced VEGF protein. Endostatin production from the regulated vector was undetectable in retinas with undamaged vasculature.

CONCLUSIONS

These findings suggest that the hypoxia-regulated, glial cell-specific vector expressing endostatin may be useful for treatment of neovascularization in proliferative diabetic retinopathy.

Interleukin-18 has antipermeablity and antiangiogenic activities in the eye: reciprocal suppression with VEGF

Interleukin-18 (IL-18) is increased along with IL-1β by activation of the inflammasome and has been implicated in inflammatory and autoimmune diseases, but its role in the eye is uncertain. In patients with macular edema due to retinal vein occlusion, intraocular IL-18 levels increased significantly (P < 0.001) after treatment with ranibizumab particularly in patients with high baseline IL-18 which correlated with good visual outcome (P < 0.05). In mice with ischemic retinopathy, suppression of VEGF caused an increase in IL18 mRNA due to an increase in IL-18-positive myeloid cells. VEGF significantly and specifically inhibited IL-18 production by myeloid cells stimulated with lipopolysaccharide (P < 0.001). Intraocular injection of IL-18 reduced VEGF-induced leakage and neovascularization, and reversed VEGF-induced suppression of Claudin5 expression and Claudin 5 labeling of vascular tight junctions. Injection of IL-18 also increased expression of Thrombospondin 1 and reduced ischemia-induced retinal neovascularization relevant to diabetic retinopathy and subretinal neovascularization relevant to neovascular age-related macular degeneration. Thus, VEGF and IL-18 suppress each other's production and effects on the vasculature suggesting that IL-18 may provide benefit in multiple retinal/choroidal vascular diseases.

Microvascular complications and diabetic retinopathy: recent advances and future implications

Retinal microvascular alterations have been observed during diabetic retinopathy (DR) due to the retinal susceptibility towards subtle pathological alterations. Therefore, retinal microvascular pathology is essential to understand the nature of retinal degenerations during DR. In this review, the role of retinal microvasculature complications during progression of DR, along with recent efforts to normalize such alterations for better therapeutic outcome, will be underlined. In addition, current therapeutics and future directions for advancement of standard treatment for DR patients will be discussed.

A comprehensive review of retinal gene therapy

Blindness, although not life threatening, is a debilitating disorder for which few, if any treatments exist. Ocular gene therapies have the potential to profoundly improve the quality of life in patients with inherited retinal disease. As such, tremendous focus has been given to develop such therapies. Several factors make the eye an ideal organ for gene-replacement therapy including its accessibility, immune privilege, small size, compartmentalization, and the existence of a contralateral control. This review will provide a comprehensive summary of (i) existing gene therapy clinical trials for several genetic forms of blindness and (ii) preclinical efficacy and safety studies in a variety of animal models of retinal disease which demonstrate strong potential for clinical application. To be as comprehensive as possible, we include additional proof of concept studies using gene replacement, neurotrophic/neuroprotective, optogenetic, antiangiogenic, or antioxidative stress strategies as well as a description of the current challenges and future directions in the ocular gene therapy field to this review as a supplement.

Ocular neovascularization

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

Age-related macular degeneration revisited--piecing the puzzle: the LXIX Edward Jackson memorial lecture

PURPOSE

To present the current understanding of age-related macular degeneration (AMD) pathogenesis, based on clinical evidence, epidemiologic data, histopathologic examination, and genetic data; to provide an update on current and emerging therapies; and to propose an integrated model of the pathogenesis of AMD.

DESIGN

Review of published clinical and experimental studies.

METHODS

Analysis and synthesis of clinical and experimental data.

RESULTS

We are closer to a complete understanding of the pathogenesis of AMD, having progressed from clinical observations to epidemiologic observations and clinical pathologic correlation. More recently, modern genetic and genomic studies have facilitated the exploration of molecular pathways. It seems that AMD is a complex disease that results from the interaction of genetic susceptibility with aging and environmental factors. Disease progression also seems to be driven by a combination of genetic and environmental factors.

CONCLUSIONS

Therapies based on pathophysiologic features have changed the paradigm for treating neovascular AMD. With improved understanding of the underlying genetic susceptibility, we can identify targets to halt early disease and to prevent progression and vision loss.

Comparison of the effects between intravitreal and periocular injections of adenoviral vectored pigment epithelium-derived factor on suppressing choroidal neovascularization in rats

PURPOSE

To compare the effects between intravitreal and periocular injections of adenoviral vectored pigment epithelium-derived factor (AdPEDF) on suppressing established choroidal neovascularization (CNV) in rats.

METHODS

Sixty-eight female BN rats (136 eyes) aged 6-8 weeks were involved in this study. The CNV animal models were created with laser photocoagulation. After CNV, 16 rats underwent intravitreal injection with AdPEDF 1 µl (group A), 16 rats received intravitreal injection with control vector (AdNull) 1 µl (group B), 16 rats had periocular injection with AdPEDF 1 µl (group C), and 16 rats had periocular injection with AdNull 1 µl (group D). The effects between intravitreal and periocular AdPEDF injections on suppressing established CNV in rats were compared and evaluated by fundus fluorescein angiography (FFA), maximal thickness of CNV, histopathology and transferase-mediated uridine nick end labeling (TUNEL) staining 3, 7, 14 and 28 days after treatment.

RESULTS

(1) There were no significant changes in leakage in groups A and C 3 days after injection compared with that before injection seen by FFA (p > 0.05). The leakages in groups A and C decreased significantly 7 days after injection compared with that before injection (p < 0.05). (2) There was no significant difference in the incidence of CNV between groups A and B, as well as groups C and D 3 days after injection (p > 0.05). The incidence of CNV decreased significantly in group A compared with that in group B 7, 14 and 28 days after injection (p < 0.01). CNV retained fibrovascular proliferation in groups B and D 7 days after injection. (3) The maximal thickness of CNV in groups A and C diminished significantly compared with that in the control group after injection, and it still diminished with time (p < 0.05). There was no significant difference in maximal thickness of CNV between 14 and 28 days after injection of AdPEDF (p > 0.05). The maximal thickness of CNV in group A was larger than that in group C 3 days after injection (p < 0.05), yet it was smaller than that in group C 14 and 28 days after injection (p < 0.05). (4) Histopathologically, a great deal of CNV was shown 3 days after injection of AdPEDF or AdNull. CNV decreased significantly with lumen diminution 14 days after injection of AdPEDF. (5) TUNEL cells appeared in groups A and C 7, 14 and 28 days after injection, and there were no TUNEL cells in groups B and D. TUNEL cells were not seen in choroidal inherent vascular endothelial cells in all groups.

CONCLUSION

Compared with the effect of periocular AdPEDF injection on suppressing established CNV in rats, the effect of intravitreal injection started slowly, but lasted longer. The effect appeared on day 7, reached the peak on day 14 and remained stable on day 28 after the treatment.

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

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

The polyamidoamine-mediated inhibition of bcl-2 by small hairpin RNA to induce apoptosis in human lens epithelial cells

PURPOSE

To investigate whether apoptosis of human lens epithelial cells (HLECs) can be induced with the polyamidoamine (PAMAM)-mediated inhibition of bcl-2 (b-cell lymphoma 2) by small hairpin RNA (shRNA).

METHODS

HLECs (SRA01/04) were transfected with the fifth generation of PAMAM (PAMAM G5) by bcl-2 shRNA. At 24, 48, and 72 h after transfection, the transfection rate was measured by flow cytometry. The transfection rates mediated by PAMAM and liposome were compared. The bcl-2 mRNA level was detected by real-time PCR. Whole cell protein was extracted and the bcl-2 protein level was detected by western blotting. The percentage of HLECs undergoing apoptosis was measured by Annexin V-FITC/PI staining. The nuclear morphology of HLECs was observed by staining with Hoechst 33258. The expression of cytochrome c and the activity of cleaved caspase-3 were analyzed by western blotting.

RESULTS

At 24, 48, and 72 h after transfection, the rate of transfection of bcl-2 shRNA mediated by PAMAM was higher than in the liposome-mediated group (p<0.05). The mRNA and protein levels of bcl-2 were greatly downregulated. The percentage of HLECs undergoing apoptosis was greatly improved. Hoechst staining showed that bcl-2 shRNA transfected cells had a lower growth status with nuclear fragmentation. The expression of cytochrome c and the activity of cleaved caspase-3 was greatly improved (p<0.05).

CONCLUSIONS

PAMAM-mediated bcl-2 shRNA can downregulate the expression of bcl-2 and induce the apoptosis of HLECs by engaging the mitochondrial pathway, including catalytic activation of the caspases.

Down-regulation of vascular endothelial growth factor and up-regulation of pigment epithelium derived factor make low molecular weight heparin-endostatin and polyethylene glycol-endostatin potential candidates for anti-angiogenesis drug

The aim was to study the effects and action mechanism of endostatin (ES), low molecular weight heparin-endostatin (LMWH-ES) and polyethylene glycol-endostatin (PEG-ES) on endothelial cell proliferation, choroidal neovascularization and zebrafish angiogenesis. Three-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazoliumbromide was used to study the effects of ES and its derivatives on endothelial cell proliferation in vitro. Choroidal neovascularization model was used to evaluate the effects of ES and its derivatives on choroidal neovascularization in vivo. Western blotting was employed to study the effects of ES and its derivatives on the expression of vascular endothelial growth factor (VEGF) and pigment epithelium derived factor (PEDF) in chorioid tissues. Zebrafish model was also used to study the anti-angiogenesis activities of ES and its derivatives. The results showed that ES and its derivatives could significantly inhibit endothelial cell proliferation in vitro (p<0.05), suppress choroidal neovascularization by down-regulating expression of VEGF and up-regulating expression of PEDF in chorioid tissues, and restrain angiogenesis in zebrafish. ES showed better activity in inhibiting endothelial cell proliferation in vitro (p<0.05), but LMWH-ES and PEG-ES showed higher activity in inhibiting choroidal neovascularization in vivo (p<0.05) and angiogenesis in zebrafish (p<0.05). These results indicate that LMWH-endostatin and PEG-endostatin are potential candidates for anti-angiogenesis drug.

Gene transfer for ocular neovascularization and macular edema

Diseases complicated by abnormal growth of vessels or excessive leakage are the most prevalent cause of moderate or severe vision loss in developed countries. Recent progress unraveling the molecular pathogenesis of several of these disease processes has led to new drug therapies that have provided major benefits to patients. However, those treatments often require frequent intraocular injections, and despite monthly injections, some patients have a suboptimal response. Gene transfer of antiangiogenic proteins is an alternative approach that has the potential to provide long-term suppression of neovascularization (NV) and/or excessive vascular leakage in the eye. Studies in animal models of ocular NV have demonstrated impressive results with a number of transgenes, and a clinical trial in patients with advanced neovascular age-related macular degeneration has provided proof-of-concept. Two ongoing clinical trials, one using an adeno-associated viral (AAV) vector to express a vascular endothelial growth factor-binding protein and another using a lentiviral vector to express endostatin and angiostatin, will provide valuable information that should help to inform future trials and provide a foundation on which to build.

A potential therapeutic strategy for inhibition of ocular neovascularization with a new endogenous protein: rhEDI-8t

BACKGROUND

Endogenous angiogenesis inhibitors act as natural negative feedback in the focal area during the neovascularization process, and have less interference on physiological angiogenesis, and thus fewer negative side-effects. These inhibitors are potential candidates to combine with or substitutes for current popular anti-angiogenesis treatments to have synergistic effect. In this study, the effects of recombinant endothelial growth inhibitor protein (rhEDI-8t), a novel endogenous protein originated from collagen VIII, was investigated on ocular neovascularization (NV). Endostatin, a well-identified endogenous angiogenesis inhibitor, was compared in parallel and served as a positive control.

METHODS

The inhibitory effect of rhEDI-8t on vascular endothelial cells was evaluated by a human umbilical vascular endothelial cells (HUVEC) proliferation test and a bovine aortic endothelial cells (BAEC) migration experiment. The effect of rhEDI-8t on ocular NV was further investigated in mice with choroidal neovascularization (choroidal NV) induced by laser, ischemic retinopathy and transgenic mice with expression of VEGF in photoreceptors (rho/VEGF) respectively.

RESULTS

RhEDI-8t inhibited the growth of HUVECs and migration of BAECs stimulated by basic fibroblast growth factor (bFGF). Mice intravitreally treated with rhEDI-8t showed a significant reduction of choroidal NV, retinal NV and subretinal NV.

CONCLUSION

Endogenous angiogenesis inhibitor rhEDI-8t showed a potent anti-angiogenesis effect in both in vitro and in vivo experiments. It contributed to the suppression of ocular NV. The study suggested that rhEDI-8t could be a subsidiary potent therapeutic medicine in addition to anti-VEGF therapy in future clinical anti-angiogenesis treatment.

Gene transfer for neovascular age-related macular degeneration

Age-related macular degeneration (AMD) is a complex disease that has two phases: a degenerative phase often referred to as nonneovascular AMD (non-NVAMD) or dry AMD and a phase dominated by growth of new blood vessels in the subretinal space, referred to as NVAMD or wet AMD. Advances in the understanding of the molecular pathogenesis of NVAMD have led to new drug therapies that have provided major benefits to patients. However, those treatments require frequent intraocular injections that in many patients must be continued indefinitely to maintain visual benefits. Gene transfer to augment expression of endogenous antiangiogenic proteins is an alternative approach that has the potential to provide long-term stability in patients with NVAMD. Studies in animal models that mimic aspects of NVAMD have identified several possible transgenes, and a clinical trial in patients with advanced NVAMD has suggested that the approach may be feasible. Many important questions remain, but the rationale and preliminary data are compelling. The results of two ongoing clinical trials may answer several of the questions and help direct future research.

Agents that bind annexin A2 suppress ocular neovascularization

TM601 is a synthetic polypeptide with sequence derived from the venom of the scorpion Leiurus quinquestriatus that has anti-neoplastic activity. It has recently been demonstrated to bind annexin A2 on cultured tumor and vascular endothelial cells and to suppress blood vessel growth on chick chorioallantoic membrane. In this study, we investigated the effects of TM601 in models of ocular neovascularization (NV). When administered by intraocular injection, intravenous injections, or periocular injections, TM601 significantly suppressed the development of choroidal NV at rupture sites in Bruch's membrane. Treatment of established choroidal NV with TM601 caused apoptosis of endothelial cells and regression of the NV. TM601 suppressed ischemia-induced and vascular endothelial growth factor-induced retinal NV and reduced excess vascular permeability induced by vascular endothelial growth factor. Immunostaining with an antibody directed against TM601 showed that after intraocular or periocular injection, TM601 selectively bound to choroidal or retinal NV and co-localized with annexin A2, which is undetectable in normal retinal and choroidal vessels, but is upregulated in endothelial cells participating in choroidal or retinal NV. Intraocular injection of plasminogen or tissue plasminogen activator, which like TM601 bind to annexin A2, also suppressed retinal NV. This study supports the hypothesis that annexin A2 is an important target for treatment of neovascular diseases and suggests that TM601, through its interaction with annexin A2, causes suppression and regression of ocular NV and reduces vascular leakage and thus may provide a new treatment for blinding diseases such as neovascular age-related macular degeneration and diabetic retinopathy.

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

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

Adeno-associated vector (type 8)-mediated expression of soluble Flt-1 efficiently inhibits neovascularization in a murine choroidal neovascularization model

To assess the feasibility of a gene therapeutic approach to treating choroidal neovascularization (CNV), we generated a recombinant adeno-associated viral (AAV) vector (type 8) encoding soluble Flt-1 (AAV-sflt-1), and determined its ability to inhibit angiogenesis. When we treated human umbilical vein endothelial cells (HUVECs) with the supernatant of cells transduced with AAV-sflt-1 or AAV-EGFP (control), we found that tube formation was significantly inhibited by the former but not the latter (area: 25,121 +/- 557 vs. 68,628 +/- 1357 pixels [p < 0.01]; length: 4811 +/- 246 vs. 10,894 +/- 297 pixels [p < 0.01]). CNV was induced in C57BL/6 mice by making four separate choroidal burns around the optic nerve in each eye, using a diode laser. Thereafter, 2 microl (5 x 10(11) vector genomes/ml) of AAV-sflt-1 (n = 11) or control AAV-LacZ (n = 12) was injected into the subretinal space, and 2 weeks later the eyes were removed for flatmount analysis of CNV surface area. Notably, subretinal delivery of AAV-sflt-1 significantly diminished CNV at the laser lesions, as compared with AAV-LacZ (555 +/- 304 vs. 1470 +/- 1000 microm(2); p = 0.007). These results suggest that there was diffusion of the secreted sFlt-1 across the retina and that long-term suppression of CNV is possible through the use of stable rAAV-mediated sflt-1 expression. In vivo gene therapy thus appears to be a feasible approach to the clinical management of CNV in conditions such as age-related macular degeneration.

Equine infectious anemia viral vector-mediated codelivery of endostatin and angiostatin driven by retinal pigmented epithelium-specific VMD2 promoter inhibits choroidal neovascularization

Equine infectious anemia virus (EIAV) is a nonprimate lentivirus that does not cause human disease. Subretinal injection into mice of a recombinant EIAV lentiviral vector in which lacZ is driven by a CMV promoter (EIAV CMV LacZ) resulted in rapid and strong expression of LacZ in retinal pigmented epithelial (RPE) cells and some other cells including ganglion cells, resulting in the presence of 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside within the optic nerve. Substitution of the RPE-specific promoter from the vitelliform macular dystrophy (VMD2) gene for the CMV promoter resulted in prolonged (at least 1 year) expression of LacZ that was restricted to RPE cells, albeit reduced 6- to 10-fold compared with the CMV promoter. Similarly, the amount of FLAG-tagged endostatin detected in eyes injected with the EIAV VMD2 Endo(FLAG) vector was similar to that seen in eyes injected with a vector that expressed both endostatin and angiostatin [EIAV VMD2 Endo(FLAG)/Angio]; expression was approximately 6-fold lower than with identical vectors in which the CMV promoter drove expression. Compared with murine eyes treated with a control EIAV vector, subretinal injection of EIAV vectors expressing murine endostatin alone or in combination with angiostatin driven by either the CMV or VMD2 promoter caused significant suppression of choroidal neovascularization (NV) at laser-induced rupture sites in Bruch's membrane. These data support proceeding toward clinical studies with EIAV-based gene therapy for choroidal NV, using the VMD2 promoter to selectively drive expression of a combination of endostatin and angiostatin in RPE cells.

Suppression and regression of choroidal neovascularization by the multitargeted kinase inhibitor pazopanib

OBJECTIVE

To investigate pazopanib hydrochloride, a multitargeted kinase inhibitor, for treatment of choroidal neovascularization (CNV).

METHODS

Choroidal neovascularization was induced in mice by rupture of Bruch membrane with laser photocoagulation. Mice were treated with pazopanib by gavage or periocular injection, and the area of CNV was measured.

RESULTS

Twice-daily gavage of pazopanib, 100 mg/kg, suppressed the development of CNV by 93%. Treatment of established CNV between days 7 and 14 with 8, 40, or 200 mg/kg per day reduced CNV by 0%, 58%, and 71%, respectively. Substantial regression (40%) of CNV was also achieved after periocular injection of pazopanib. A single oral dose of 4 or 100 mg/kg resulted in an area under the curve from time 0 to the last quantifiable concentration of 129.6 and 752.0 microg x h/mL, respectively. After 7 days of 4, 20, or 100 mg/kg twice a day by gavage, plasma levels were 1300, 4900, and 5800 ng/mL and levels in the retina/choroid were 4800, 28 800, and 38 000 ng/g of tissue.

CONCLUSIONS

Orally administered pazopanib has good bioavailability to the retina/choroid and strongly suppresses CNV in mice. Treatment with pazopanib after CNV is established causes dose-dependent regression of CNV.

CLINICAL RELEVANCE

Pazopanib may be useful for treatment of CNV in humans.

Alternate serotype adenovector provides long-term therapeutic gene expression in the eye

PURPOSE

To determine whether the duration of transgene expression from an alternate adenovector serotype, Ad35, can provide advantages over an Ad5 serotype vector following a single intravitreal (IVT) administration.

METHODS

To assess the transgene expression profile, mice received one IVT injection of Ad5- or Ad35-based vectors expressing green fluorescent protein (GFP), luciferase or pigment epithelium-derived factor (PEDF). At specified time points following vector administration, eyes were monitored for GFP expression, or eyes were harvested and assayed for adenovector genomes, luciferase activity or PEDF levels. Ad35-based vector in vivo biologic activity was investigated using a mouse model of laser-induced choroidal neovascularization (CNV). On Day 0, mice received one IVT injection of Ad5.PEDF or Ad35.PEDF (HI-RGD) followed by laser-induced CNV on Day 28. Fourteen days later, animals were perfused with fluorescein-labeled dextran and CNV lesion size quantitated in choroidal flat mounts.

RESULTS

These studies demonstrate that following a single IVT adenovector administration: 1) gene expression is prolonged following administration of an Ad35 compared to an Ad5-based vector; 2) the amount of vector genomes in the eye remain constant out to 60 days post injection of both Ad5 and Ad35-based vectors; and 3) an Ad35.PEDF (HI-RGD) vector inhibits CNV in a mouse model at 42 days post injection.

CONCLUSIONS

These studies show that transgene and genome levels are prolonged in the eye following 1 IVT injection of an Ad35-based vector. Moreover, therapeutic gene levels from 1 IVT administration of Ad35.PEDF (HI-RGD) vector block abnormal blood vessel growth in a laser-induced CNV mouse model.

Inhibition of VEGF secretion and experimental choroidal neovascularization by picropodophyllin (PPP), an inhibitor of the insulin-like growth factor-1 receptor

INTRODUCTION

Choroidal neovascularization (CNV) is a debilitating complication of age-related macular degeneration (AMD) and a leading cause of vision loss. Along with other angiogenic factors like vascular endothelial growth factor (VEGF), insulin-like growth factor (IGF-1) and its receptor, IGF-1R, have been implicated in CNV.

PURPOSE

We have previously shown that the cyclolignan picropodophyllin (PPP) efficiently blocks the insulin-like growth factor-1 receptor (IGF-1R) activity and causes cell death in uveal melanoma cell lines and in an in-vivo model. In this study we investigated the effect of PPP on VEGF expression both in vitro and in vivo and whether this effect has anti-angiogenic consequences in a murine CNV model.

MATERIALS AND METHODS

C57BL/6J mice with laser-induced CNVs were treated with PPP. Effects on CNV area were assayed by image analysis. VEGF levels in choroids and retinal pigment epithelial cells (APRE-19) were measured by Western blot or ELISA. Transcriptional activation of the VEGF promoter was determined by luciferase reporter gene assay.

RESULTS

Mice treated with PPP, administered intraperitoneally or orally, showed 22-32% (p = 0.002) decrease in CNV area. Furthermore, VEGF levels in the choroids were significantly reduced. In cultured APRE-19 cells, IGF-1 was shown to increase VEGF secretion. This increase was completely blocked by PPP. We could confirm that PPP reduced the level of transcriptional activity of VEGF promoter.

CONCLUSIONS

PPP reduces IGF-1 dependent VEGF expression and CNV in vivo. Accordingly, IGF-1R inhibitors may be useful tools in the therapy of conditions associated with CNV including neovascular AMD.

Implications of bevacizumab on vascular endothelial growth factor and endostatin in human choroidal neovascularisation

AIM

To evaluate the implications of intravitreal bevacizumab on proangiogenic vascular endothelial growth factor (VEGF) with regard to the endogenous angiogenesis inhibitor endostatin in human choroidal neovascularisation (CNV) secondary to age-related macular degeneration.

METHODS

Retrospective review of an interventional case series of 48 patients who underwent full macular translocation surgery with removal of CNV. Twenty-five patients were treated with intravitreal bevacizumab injection 1 to 154 days prior to surgery (bevacizumab CNV). Twenty-three CNV without any kind of previous treatment were used as controls (control CNV). CNV were stained for CD34, cytokeratin18, VEGF, endostatin and E-selectin. A "predominance score of VEGF over endostatin" (PS) was defined by the difference between VEGF and endostatin staining scores.

RESULTS

Bevacizumab CNV revealed a weaker VEGF expression in endothelial cells (p = 0.0245) but significantly more intense endostatin in retina pigment epithelium (RPE) (p = 0.0001) and stroma (p<0.0001). Consequently, PS was significantly lower in RPE (p = 0.02), vessels (p = 0.03) and stroma (p = 0.0004) in bevacizumab CNV. The intensity of E-selectin expression in bevacizumab CNV was comparable with that in control CNV.

CONCLUSIONS

A shift within the angiogenic balance in terms of decreased VEGF predominance over endostatin is detected in human CNV treated with bevacizumab.

Persistent expression of PEDF in the eye using high-capacity adenovectors

Ocular neovascularization, the growth of abnormal blood vessels in the eye, is a factor shared by the most common blinding diseases in developed countries. Pigment epithelium-derived factor (PEDF) is a potent antiangiogenic and neuroprotective protein that is normally produced in the eye. When delivered via an adenovector, PEDF can block the growth of new blood vessels and trigger the selective regression of abnormal vessels in animal models of ocular disease. Because of the absence of adenoviral genes, high-capacity (HC) adenovectors offer the potential for persistent transgene expression and enhanced tolerability. We have assessed the durability of PEDF expression and the induction of ocular inflammation following delivery of a PEDF-expressing HC adenovector compared to earlier generation vectors. The HC vector mediated prolonged PEDF expression in tissue-cultured pigmented epithelial cells and when delivered by intravitreal injection into the mouse eye. Delivery of first-generation adenovectors resulted in a dose-dependent increase in cytokine/chemokine gene expression, which correlated with the infiltration of inflammatory cells in the eye. In comparison, the levels of inflammatory gene expression and the intraocular infiltrate were substantially reduced following delivery of the HC vector. These results support the development of the HC adenovector gene delivery system for ocular disease.