Intravitreal VEGF and bFGF produce florid retinal neovascularization and hemorrhage in the rabbit

Eye on the horizon: The metabolic landscape of the RPE in aging and disease

To meet the prodigious bioenergetic demands of the photoreceptors, glucose and other nutrients must traverse the retinal pigment epithelium (RPE), a polarised monolayer of cells that lie at the interface between the outer retina and the choroid, the principal vascular layer of the eye. Recent investigations have revealed a metabolic ecosystem in the outer retina where the photoreceptors and RPE engage in a complex exchange of sugars, amino acids, and other metabolites. Perturbation of this delicate metabolic balance has been identified in the aging retina, as well as in age-related macular degeneration (AMD), the leading cause of blindness in the Western world. Also common in the aging and diseased retina are elevated levels of cytokines, oxidative stress, advanced glycation end-products, increased growth factor signalling, and biomechanical stress - all of which have been associated with metabolic dysregulation in non-retinal cell types and tissues. Herein, we outline the role of these factors in retinal homeostasis, aging, and disease. We discuss their effects on glucose, mitochondrial, lipid, and amino acid metabolism in tissues and cell types outside the retina, highlighting the signalling pathways through which they induce these changes. Lastly, we discuss promising avenues for future research investigating the roles of these pathological conditions on retinal metabolism, potentially offering novel therapeutic approaches to combat age-related retinal disease.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Nonproliferative and Proliferative Lesions of Nonrodent Ocular Tissues

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions) Project (www.toxpath.org/ inhand.asp) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying lesions observed in ocular tissues (eyes and glands and ocular adnexa) from laboratory nonrodent species (rabbits, dogs, minipigs, and nonhuman primates) used in nonclinical safety studies with an emphasis on ocular-targeted dosing. Some of the lesions are illustrated by color photomicrographs. The standardized nomenclature presented in this document is also available electronically on the Internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes descriptions and visual depictions of spontaneous lesions and lesions induced by exposure to various test materials. A widely accepted and utilized internationally harmonized nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

Ocular therapies with biomacromolecules: From local injection to eyedrop and emerging noninvasive delivery strategies

The last two decades have witnessed a continuously increasing number of biomacromolecules approved for the treatment of ocular diseases. The eye possesses multiple protective mechanisms to resist the invasion of exogenous substances, but meanwhile these physiological defense systems also act as strong barriers, impeding absorption of most biomacromolecules into the eye. As a result, local injections play predominant roles for posterior ocular delivery of biomacromolecules in clinical practice. To achieve safe and convenient application of biomacromolecules, alternative strategies to realize noninvasive intraocular delivery are necessary. Various nanocarriers, novel penetration enhancers and physical strategies have been explored to facilitate delivery of biomacromolecules to both anterior and posterior ocular segments but still suffered difficulties in clinical translation. This review compares the anatomical and physiological characteristics of the eyes from those frequently adopted experimental species and profiles the well-established animal models of ocular diseases. We also summarize the ophthalmic biomacromolecules launched on the market and put emphasis on emerging noninvasive intraocular delivery strategies of peptides, proteins and genes.

Nervous System-Driven Osseointegration

Implants are essential therapeutic tools for treating bone fractures and joint replacements. Despite the in-depth study of osseointegration for more than fifty years, poor osseointegration caused by aseptic loosening remains one of the leading causes of late implant failures. Osseointegration is a highly sophisticated and spatiotemporal process in vivo involving the immune response, angiogenesis, and osteogenesis. It has been unraveled that the nervous system plays a pivotal role in skeletal health via manipulating neurotrophins, neuropeptides, and nerve cells. Herein, the research related to nervous system-driven osseointegration was systematically analyzed and reviewed, aiming to demonstrate the prominent role of neuromodulation in osseointegration. Additionally, it is indicated that the implant design considering the role of neuromodulation might be a promising way to prevent aseptic loosening.

Intraocular Cytokine Changes in Patients with Polypoidal Choroidal Vasculopathy Treated with Ranibizumab

Purpose: To investigate the changes in intraocular cytokines after ranibizumab treatment in patients with polypoidal choroidal vasculopathy (PCV).Methods: This multicenter, prospective study enrolled patients with PCV treated with three monthly ranibizumab followed by a pro re nata regimen for 24 weeks. Best corrected visual acuity, slit lamp examination, fundus photography, and optical coherence tomography were performed every 4 weeks. Aqueous humor was collected to measure intraocular cytokines at baseline, week 8, and the time of recurrence or week 20. The association of changes in intraocular cytokines with visual acuity, central macular thickness, central choroidal thickness, area of abnormal vessels, and polyp closure was assessed.Results: This study included 25 eyes. The mean patient age was 70.3 ± 6.1 years. The vascular endothelial growth factor (VEGF) concentration decreased at week 8, but only interferon (IFN)-γ, tissue inhibitors of matrix metalloproteinases (TIMP)-2, and monocyte chemoattractant protein (MCP)-2 decreased at the time of recurrence. The recurrence interval was positively associated with the baseline epithelial-neutrophil activating peptide (ENA)-78, interleukin (IL)-17, leptin, and transforming growth factor-β1, and baseline central macular thickness was positively correlated with the baseline fibroblast growth factor-4 and IL-10. Thick central choroidal thickness was associated with a low basic fibroblast growth factor and high IFN-γ at baseline. The MCP-3 and Tie-2 levels decreased in two eyes with polyp closure.Conclusions: Ranibizumab significantly reduced intraocular VEGF concentrations and consequently improved PCV. However, the cytokines IFN-γ, TIMP-2, and MCP-2, rather than VEGF, were associated with PCV recurrence. Further studies of intraocular cytokines involved in neovascularization in PCV are needed.

Animal models of diabetic retinopathy

The retina is the posterior neuro-integrated layer of the eye that conducts impulses induced by light to the optic nerve for human vision. Diseases of the retina often leads to diminished vision and in some cases blindness. Diabetes mellitus (DM) is a worldwide public health issue and globally, there is an estimated 463 million people that are affected by DM and its consequences. Diabetic retinopathy (DR) is a blinding complication of chronic uncontrolled DM and is the most common cause of blindness in the United States between the ages 24-75. It is estimated that the global prevalence of DR will increase to 191.0 million by 2030, of those 56.3 million possessing vision-threatening diabetic retinopathy (VTDR). For the most part, current treatment modalities control the complications of DR without addressing the underlying pathophysiology of the disease. Therefore, there is an unmet need for new therapeutics that not only repair the damaged retinal tissue, but also reverse the course of DR. The key element in developing these treatments is expanding our basic knowledge by studying DR pathogenesis in animal models of proliferative and non-proliferative DR (PDR and NPDR). There are numerous models available for the research of both PDR and NPDR with substantial overlap. Animal models available include those with genetic backgrounds prone to hyperglycemic states, immunologic etiologies, or environmentally induced disease. In this review we aimed to comprehensively summarize the available animal models for DR while also providing insight to each model's ocular therapeutic potential for drug discovery.

Predicting wet age-related macular degeneration (AMD) using DARC (detecting apoptosing retinal cells) AI (artificial intelligence) technology

OBJECTIVES

To assess a recently described CNN (convolutional neural network) DARC (Detection of Apoptosing Retinal Cells) algorithm in predicting new Subretinal Fluid (SRF) formation in Age-related-Macular-Degeneration (AMD).

METHODS

Anonymized DARC, baseline and serial OCT images (n = 427) from 29 AMD eyes of Phase 2 clinical trial (ISRCTN10751859) were assessed with CNN algorithms, enabling the location of each DARC spot on corresponding OCT slices (n = 20,629). Assessment of DARC in a rabbit model of angiogenesis was performed in parallel.

RESULTS

A CNN DARC count >5 at baseline was significantly (p = 0.0156) related to development of new SRF throughout 36 months. Prediction rate of eyes using unique DARC spots overlying new SRF had positive predictive values, sensitivities and specificities >70%, with DARC count significantly (p < 0.005) related to the magnitude of SRF accumulation at all time points. DARC identified earliest stages of angiogenesis in-vivo.

CONCLUSIONS

DARC was able to predict new wet-AMD activity. Using only an OCT-CNN definition of new SRF, we demonstrate that DARC can identify early endothelial neovascular activity, as confirmed by rabbit studies. Although larger validation studies are required, this shows the potential of DARC as a biomarker of wet AMD, and potentially saving vision-loss.

Inflammatory and angiogenic biomarkers in diabetic retinopathy

Diabetic retinopathy (DR) is one of the most common microvascular complications of diabetes mellitus (DM) and a leading cause of blindness in working-age adults in developed countries. Numerous investigations have recognised inflammation and angiogenesis as important factors in the development of this complication of diabetes. Current methods of DR treatment are predominantly used at advanced stages of the disease and could be associated with serious side effects. Therefore, new diagnostic methods are needed in order to identify the initial stages of DR as well as monitoring the effects of applied therapy. Biochemical biomarkers are molecules found in blood or other biological fluid and tissue that indicate the existence of an abnormal condition or disease. They could be a valuable tool in detecting early stages of DR, identifying patients most susceptible to retinopathy progression and monitoring treatment outcomes. Biomarkers related to DR can be measured in the blood, retina, vitreous, aqueous humour and recently in tears. As the retina represents a small part of total body mass, a circulating biomarker for DR needs to be highly specific. Local biomarkers are more reliable as indicators of the retinal pathology; however, obtaining a sample of aqueous humour, vitreous or retina is an invasive procedure with potential serious complications. As a non-invasive novel method, tear analysis offers a promising direction in further research for DR biomarker detection. The aim of this paper is to review systemic and local inflammatory and angiogenic biomarkers relevant to this sight threatening diabetic complication.

Photo-mediated Ultrasound Therapy to Treat Retinal Neovascularization

This report describes a novel therapeutic technique called photo-mediated ultrasound therapy (PUT). PUT applies synchronized short pulse duration (nanosecond) laser and ultrasound burst on targeted tissue, offering high-precision localized treatment. PUT is based on controlled induction and promotion of micro-cavitation activity in the target tissue. PUT is able to safely and effectively treat retinal neovascularization in rabbits with persistent nonperfusion up to 4 weeks after PUT in the choroidal vasculature.Clinical Relevance- PUT can selectively remove retinal angiogenesis in clinically-relevant disease models in humansized eyes (rabbit) without damaging surrounding tissue.

In Vivo 3D Imaging of Retinal Neovascularization Using Multimodal Photoacoustic Microscopy and Optical Coherence Tomography Imaging

The pathological process of neovascularization of the retina plays a critical role in causing vision loss in several diseases, including diabetes, retinal vein occlusion, and sickle cell disease. Retinal neovascularization can lead to vitreous hemorrhage and retinal detachment, yet the pathological process of neovascularization is a complex phenomenon under active investigation. Understanding and monitoring retinal neovascularization is critically important in clinical ophthalmology. This study describes a novel multimodal ocular imaging system which combines photoacoustic microscopy (PAM) and a spectral domain optical coherence tomography (SD-OCT) to improve the visualization of retinal neovascularization (RNV), their depth, and the surrounding anatomy in living rabbits. RNV was induced in New Zealand rabbits by intravitreal injection of vascular endothelial growth factor (VEGF). The retinal vasculature before and after injection at various times was monitored and evaluated using multimodal imaging including color fundus photography, fluorescein angiography (FA), OCT, and PAM. In vivo experiments demonstrate that PAM imaging distinctly characterized the location as well as the morphology of individual RNV with high contrast at a safe laser energy of 80 nJ. SD-OCT was used to identify a cross-sectional structure of RNV. In addition, dynamic changes in the retinal morphology and retinal neovascularization were observed at day 4, 5, 6, 7, 9, 11, 14, 28, and day 35 after VEGF injection. PAM demonstrated high-resolution optical absorption of hemoglobin and vascular imaging of the retina and choroid with increased depth of penetration. With the current multimodal imaging system, RNV can be easily visualized in both 2D and 3D angiography. This multimodal ocular imaging system provides improved characterization of the microvasculature in a safe manner in larger rabbit eyes.

A novel model of persistent retinal neovascularization for the development of sustained anti-VEGF therapies

Anti-vascular endothelial growth factor (VEGF) therapies lead to a major breakthrough in treatment of neovascular retinal diseases such as age-related macular degeneration or diabetic retinopathy. Current management of these conditions require regular and frequent intravitreal injections to prevent disease recurrence once the effect of the injected drug wears off. This has led to a pressing clinical need of developing sustained release formulations or therapies with longer duration. A major drawback in developing such therapies is that the currently available animal models show spontaneous regression of vascular leakage. They therefore not only fail to recapitulate retinal vascular disease in humans, but also prevent to discern if regression is due to prolonged therapeutic effect or simply reflects spontaneous healing. Here, we described the development of a novel rabbit model of persistent retinal neovascularization (PRNV). Retinal Müller glial are essential for maintaining the integrity of the blood-retinal barrier. Intravitreal injection of DL-alpha-aminoadipic acid (DL-AAA), a selective retinal glial (Müller) cell toxin, results in persistent vascular leakage for up to 48 weeks. We demonstrated that VEGF concentrations were significantly increased in vitreous suggesting VEGF plays a significant role in mediating the leakage observed. Intravitreal administration of anti-VEGF drugs (e.g. bevacizumab, ranibizumab and aflibercept) suppresses vascular leakage for 8-10 weeks, before recurrence of leakage to pre-treatment levels. All three anti-VEGF drugs are very effective in re-ducing angiographic leakage in PRNV model, and aflibercept demonstrated a longer duration of action compared with the others, reminiscent of what is observed with these drugs in human in the clinical setting. Therefore, this model provides a unique tool to evaluate novel anti-VEGF formulations and therapies with respect to their duration of action in comparison to the currently used drugs.

High-resolution, in vivo multimodal photoacoustic microscopy, optical coherence tomography, and fluorescence microscopy imaging of rabbit retinal neovascularization

Photoacoustic microscopy (PAM) is an emerging imaging technology that can non-invasively visualize ocular structures in animal eyes. This report describes an integrated multimodality imaging system that combines PAM, optical coherence tomography (OCT), and fluorescence microscopy (FM) to evaluate angiogenesis in larger animal eyes. High-resolution in vivo imaging was performed in live rabbit eyes with vascular endothelial growth factor (VEGF)-induced retinal neovascularization (RNV). The results demonstrate that our multimodality imaging system can non-invasively visualize RNV in both albino and pigmented rabbits to determine retinal pathology using PAM and OCT and verify the leakage of neovascularization using FM and fluorescein dye. This work presents high-resolution visualization of angiogenesis in rabbits using a multimodality PAM, OCT, and FM system and may represent a major step toward the clinical translation of the technology.

Blue-light filtering alters angiogenic signaling in human retinal pigmented epithelial cells culture model

Background

Light exposure and more specifically the spectrum of blue light contribute to the oxidative stress in Age-related macular degeneration (AMD). The purpose of the study was to establish whether blue light filtering could modify proangiogenic signaling produced by retinal pigmented epithelial (RPE) cells under different conditions simulating risk factors for AMD.

Methods

Three experiments were carried out in order to expose ARPE-19 cells to white light for 48 h with and without blue light-blocking filters (BLF) in different conditions. In each experiment one group was exposed to light with no BLF protection, a second group was exposed to light with BLF protection, and a control group was not exposed to light. The ARPE-19 cells used in each experiment prior to light exposure were cultured for 24 h as follows: Experiment 1) Normoxia, Experiment 2) Hypoxia, and Experiment 3) Lutein supplemented media in normoxia. The media of all groups was harvested after light exposure for sandwich ELISA-based assays to quantify 10 pro-angiogenic cytokines.

Results

A significant decrease in angiogenin secretion levels and a significant increase in bFGF were observed following light exposure, compared to dark conditions, in both normoxia and hypoxia conditions. With the addition of a blue light-blocking filter in normoxia, a significant increase in angiogenin levels was observed. Although statistical significance was not achieved, blue light filters reduce light-induced secretion of bFGF and VEGF to near normal levels. This trend is also observed when ARPE-19 cells are grown under hypoxic conditions and when pre-treated with lutein prior to exposure to experimental conditions.

Conclusions

Following light exposure, there is a decrease in angiogenin secretion by ARPE-19 cells, which was abrogated with a blue light - blocking filter. Our findings support the position that blue light filtering affects the secretion of angiogenic factors by retinal pigmented epithelial cells under normoxic, hypoxic, and lutein-pretreated conditions in a similar manner.

Small Molecular-Sized Artesunate Attenuates Ocular Neovascularization via VEGFR2, PKCα, and PDGFR Targets

Ocular neovascularization (NV) is the primary cause of blindness in many ocular diseases. Large molecular weight anti- vascular endothelial growth factor (VEGF) protein drugs, such as Avastin and Lucentis, have saved the vision of millions. However, approximately 20-30% of patients respond poorly to anti-VEGF treatment. We found that artesunate (ART), a small molecular derivative of artemisinin, had a significant inhibitory effect on ocular NV by downregulating the expression of VEGFR2, PKCα, and PDGFR. ART significantly inhibited retinal NV in rabbits and macular edema in monkeys with greater anterior chamber penetrability and more durable efficacy than Avastin. Our pilot study showed that intravitreal injection of 80 μg ART significantly inhibited iris and corneal NV in a severe retinal detachment case. Our results suggest that ART might be a potential persistent small-molecule drug to manage ocular NV via multi-targets.

Protein Kinase D1 Signaling in Angiogenic Gene Expression and VEGF-Mediated Angiogenesis

Protein kinase D 1 (PKD-1) is a signaling kinase important in fundamental cell functions including migration, proliferation, and differentiation. PKD-1 is also a key regulator of gene expression and angiogenesis that is essential for cardiovascular development and tumor progression. Further understanding molecular aspects of PKD-1 signaling in the regulation of angiogenesis may have translational implications in obesity, cardiovascular disease, and cancer. The author will summarize and provide the insights into molecular mechanisms by which PKD-1 regulates transcriptional expression of angiogenic genes, focusing on the transcriptional regulation of CD36 by PKD-1-FoxO1 signaling axis along with the potential implications of this axis in arterial differentiation and morphogenesis. He will also discuss a new concept of dynamic balance between proangiogenic and antiangiogenic signaling in determining angiogenic switch, and stress how PKD-1 signaling regulates VEGF signaling-mediated angiogenesis.

[Vascular endothelial growth factors (VEGF): role in pathological processes]

Russian and foreign literature sources on vascular endothelial growth factors (VEGF) from different parts of the human body, their prevalence and involvement in pathological processes were analyzed. A conclusion has been drawn that further research on different types of VEGF is needed.

Diabetic Retinopathy: Vascular and Inflammatory Disease

Diabetic retinopathy (DR) is the leading cause of visual impairment in the working-age population of the Western world. The pathogenesis of DR is complex and several vascular, inflammatory, and neuronal mechanisms are involved. Inflammation mediates structural and molecular alterations associated with DR. However, the molecular mechanisms underlying the inflammatory pathways associated with DR are not completely characterized. Previous studies indicate that tissue hypoxia and dysregulation of immune responses associated with diabetes mellitus can induce increased expression of numerous vitreous mediators responsible for DR development. Thus, analysis of vitreous humor obtained from diabetic patients has made it possible to identify some of the mediators (cytokines, chemokines, and other factors) responsible for DR pathogenesis. Further studies are needed to better understand the relationship between inflammation and DR. Herein the main vitreous-related factors triggering the occurrence of retinal complication in diabetes are highlighted.

Animal models of age-related macular degeneration and their translatability into the clinic

Age-related macular degeneration (AMD) is a leading cause of blindness in people over the age of 55. Despite its common nature, the etiology of the disease involves both genetic and environmental factors, the interaction of which is not fully understood. Animal models, including the mouse, rat, rabbit, pig and non-human primate, have been developed to study various aspects of the disease and to evaluate novel therapies; however, no single model has been developed to emulate all aspects of the disease. This review will discuss the various existing models of AMD, their strengths and limitations and examples of their use in current AMD research.

Vaccination with a mutated variant of human Vascular Endothelial Growth Factor (VEGF) blocks VEGF-induced retinal neovascularization in a rabbit experimental model

Vascular Endothelial Growth Factor (VEGF) is a key driver of the neovascularization and vascular permeability that leads to the loss of visual acuity of eye diseases like wet age-related macular degeneration, diabetic macular edema, and retinopathy of premature. Among the several anti-VEGF therapies under investigation for the treatment of neovascular eye diseases, our group has developed the vaccine candidate CIGB-247-V that uses a mutated form of human VEGF as antigen. In this work we evaluated if the vaccine could prevent or attenuate VEGF-induced retinal neovascularization in the course of a rabbit eye neovascularization model, based on direct intravitreal injection of human VEGF. Our experimental findings have shown that anti-VEGF IgG antibodies induced by the vaccine were available in the retina blood circulation, and could neutralize in situ the neovascularization effect of VEGF. CIGB-247-V vaccination proved to effectively reduce retinal neovascularization caused by intravitreal VEGF injection. Altogether, these results open the way for human studies of the vaccine in neovascular eye syndromes, and inform on the potential mechanisms involved in its effect.

Quantification of vascular tortuosity as an early outcome measure in oxygen induced retinopathy (OIR)

Oxygen-induced retinopathy (OIR) in mice is a popular model system to study pathological angiogenesis in the retinal vasculature. The system is based on vessel depletion by exposure to hyperoxia, which results in acute retinal hypoxia upon return to room air. This hypoxia then triggers neovascularization in the remaining vessels after 5 days. Here we aimed to establish an additional and earlier experimental readout of the vascular response to hypoxia by quantifying the tortuosity of retinal arteries after 2 days. Mouse pups from three different mouse strains were exposed to hyperoxia from postnatal day (P) 7 to P12 and retinas were analysed at P12, P14 and P17. Hypoxia was assessed by staining with the hypoxia marker EF5 and by measuring Vegf mRNA by qPCR. The retinal vasculature was stained in whole mount retinas and tortuosity of radial arterioles was quantified. C57BL/6J mice were used because the vascular response at P17 is well characterised in this strain. We also used C3H/HeJ mice, which contain the retinal degeneration 1 (Rd1) mutation (Pde6b(Rd1)) and have abnormally thin retinas. These thinner, C3H/HeJ retinas do not become ischemic during the OIR model and do not develop neovascularization. They can therefore be used as a control. In addition, we included C3H/HeJ mice that lack the Rd1 mutation (C3H/He(Rd1-)), with normal thickness retinas, to control for strain differences between C57BL/6J and C3H/HeJ. Quantification of vessel tortuosity at P14 showed tortuous arteries in normal thickness retinas (C57BL/6J and C3H/He(Rd1-)) and straight arteries in the thin C3H/HeJ retinas. This correlated with hypoxia, which was severe in normal thickness retinas and mild in the thin C3H/HeJ retinas. Furthermore, at P17 the normal thickness retinas showed strong neovascularisation whereas in the thin C3H/HeJ retinas the retinal vasculature regenerated normally. In conclusion we have demonstrated that arterial tortuosity can act as an early readout for hypoxia in the OIR model before neovascularisation develops.

Animal models of diabetic retinopathy: summary and comparison

Diabetic retinopathy (DR) is a microvascular complication associated with chronic exposure to hyperglycemia and is a major cause of blindness worldwide. Although clinical assessment and retinal autopsy of diabetic patients provide information on the features and progression of DR, its underlying pathophysiological mechanism cannot be deduced. In order to have a better understanding of the development of DR at the molecular and cellular levels, a variety of animal models have been developed. They include pharmacological induction of hyperglycemia and spontaneous diabetic rodents as well as models of angiogenesis without diabetes (to compensate for the absence of proliferative DR symptoms). In this review, we summarize the existing protocols to induce diabetes using STZ. We also describe and compare the pathological presentations, in both morphological and functional aspects, of the currently available DR animal models. The advantages and disadvantages of using different animals, ranging from zebrafish, rodents to other higher-order mammals, are also discussed. Until now, there is no single model that displays all the clinical features of DR as seen in human. Yet, with the understanding of the pathological findings in these animal models, researchers can select the most suitable models for mechanistic studies or drug screening.

Fluorescein angiography, optical coherence tomography, and histopathologic findings in a VEGF(165) animal model of retinal angiogenesis

BACKGROUND

To establish an animal model of retinal neovascularization using vascular endothelial growth factor (VEGF165) and analyze the model using optical coherence tomography (OCT), fluorescein angiography (FA), and histopathologic evaluation.

METHODS

Twelve rabbits were divided into groups as follows: group 1 (n = 3), sham intravitreous injections of 0.1 ml of balanced saline; group 2 (n = 6), one 10-μg intravitreal injection of VEGF165 on day 0; and group 3 (n = 3), two 10-μg intravitreal injections of VEGF165, one on day 0 and one on day 7. Follow-up evaluations (days 0, 3, 7, 14, 21, 28) included obtaining fundus color photographs and FA, OCT, and histopathologic examinations. Eyes were enucleated and stained with hematoxylin and eosin (H&E).

RESULTS

One injection of VEGF (group 2) was associated with dilatation and tortuosity of the retinal blood vessels that developed within 72 h. Retinal neovascularization was present by day 7 and regressed by day 14. However, even on day 28, the capillaries were still tortuous. Two VEGF injections (group 3) caused increased leakage and neovascularization up to day 14; severe capillary nonperfusion was seen during week 4. At the end of the follow-up period, OCT and histopathologic examination of group 3 showed peripapillary tractional retinal detachments. By day 7, the differences between the retinal thickness seen on OCT in groups 2 and 3 and the group 1 control group were significant (p < 0.001). The histologic findings showed increased vessel size in groups 2 and 3 by days 14 and 28 compared with the controls.

CONCLUSIONS

FA, OCT, and histopathologic findings showed that this retinal neovascularization model is efficient, sustainable, and reliable. One injection of VEGF165 created neovascularization that peaked after 1 week; two injections created more intense neovascularization that evolved to retinal detachments after 4 weeks.

Morpholino-mediated increase in soluble Flt-1 expression results in decreased ocular and tumor neovascularization

Background

Angiogenesis is a key process in several ocular disorders and cancers. Soluble Flt-1 is an alternatively spliced form of the Flt-1 gene that retains the ligand-binding domain, but lacks the membrane-spanning and intracellular kinase domains of the full-length membrane bound Flt-1 (mbFlt-1) protein. Thus, sFlt-1 is an endogenous inhibitor of VEGF-A mediated angiogenesis. Synthetic mopholino oligomers directed against splice site targets can modulate splice variant expression. We hypothesize that morpholino-induced upregulation of sFlt-1 will suppress angiogenesis in clinically relevant models of macular degeneration and breast cancer.

Methods and Findings

In vivo morpholino constructs were designed to target murine exon/intron 13 junction of the Flt-1 transcript denoted VEGFR1_MOe13; standard nonspecific morpholino was used as control. After nucleofection of endothelial and breast adenocarcinoma cell lines, total RNA was extracted and real-time RT-PCR performed for sFlt-1 and mbFlt-1. Intravitreal injections of VEGFR1_MOe13 or control were done in a model of laser-induced choroidal neovascularization and intratumoral injections were performed in MBA-MD-231 xenografts in nude mice. VEGFR1_MOe13 elevated sFlt-1 mRNA expression and suppressed mbFlt-1 mRNA expression in vitro in multiple cellular backgrounds (p<0.001). VEGFR1_MOe13 also elevated sFlt/mbFlt-1 ratio in vivo after laser choroidal injury 5.5 fold (p<0.001) and suppressed laser-induced CNV by 50% (p = 0.0179). This latter effect was reversed by RNAi of sFlt-1, confirming specificity of morpholino activity through up-regulation of sFlt-1. In the xenograft model, VEGFR1_MOe13 regressed tumor volume by 88.9%, increased sFlt-1 mRNA expression, and reduced vascular density by 50% relative to control morpholino treatment (p<0.05).

Conclusions

Morpholino oligomers targeting the VEGFR1 mRNA exon/intron 13 junction promote production of soluble FLT-1 over membrane bound FLT-1, resulting in suppression of lesional volume in laser induced CNV and breast adenocarcinoma. Thus, morpholino manipulation of alternative splicing offers translational potential for therapy of angiogenic disorders.

Effect of multiple injections of small divided doses vs single injection of intravitreal bevacizumab on retinal neovascular model in rabbits

BACKGROUND

To compare effects of multiple injections of small divided doses of intravitreal bevacizumab vs a single injection using a retinal neovascular model in rabbits.

METHODS

We assigned 12 pigmented rabbits to four groups of three each. All groups received an intravitreal injection of vascular endothelial growth factor (VEGF, 10 microg) on the first day. Group A received an intravitreal loading dose of bevacizumab (0.5 mg) on day 3, followed by five smaller injections (0.15 mg), one every third day. Those in groups B and C received a single intravitreal injection of bevacizumab (1.25 mg) on day 3, followed by five injections of sham, one every third day in group C. Group D received only intravitreal VEGF. Follow-up examinations were performed for 26 days.

RESULTS

In groups A and B, vascular changes associated with VEGF injection decreased substantially in the first 3 days, and continued to show gradual regression during each follow-up interval. No statistically significant differences were found between the changes of mean retinal thicknesses in groups A and B in both areas. In group C, the extra sham injections did not lead to any further vascular changes. The mean retinal thickness in groups B and C did not have a statistically significant difference during the follow-up period. In group D, vascular changes resolved more gradually than in other groups. The difference in retinal thickness between group D and the other groups was statistically significant on day 6 in both groups (medullary and inferior part; p = 0.0003) and in medullary wing on day 12 (p = 0.03).

CONCLUSIONS

Frequent smaller doses of bevacizumab can control VEGF-induced vascular changes as well as the currently utilized model of single large monthly injections. Dividing of currently used single injection (1.25 mg) of bevacizumab to multiple small doses can control VEGF-induced vascular changes as effectively as one large injection.

A mechanosensitive transcriptional mechanism that controls angiogenesis

Angiogenesis is controlled by physical interactions between cells and extracellular matrix as well as soluble angiogenic factors, such as VEGF. However, the mechanism by which mechanical signals integrate with other microenvironmental cues to regulate neovascularization remains unknown. Here we show that the Rho inhibitor, p190RhoGAP (also known as GRLF1), controls capillary network formation in vitro in human microvascular endothelial cells and retinal angiogenesis in vivo by modulating the balance of activities between two antagonistic transcription factors, TFII-I (also known as GTF2I) and GATA2, that govern gene expression of the VEGF receptor VEGFR2 (also known as KDR). Moreover, this new angiogenesis signalling pathway is sensitive to extracellular matrix elasticity as well as soluble VEGF. This is, to our knowledge, the first known functional cross-antagonism between transcription factors that controls tissue morphogenesis, and that responds to both mechanical and chemical cues.

Angiogenic inhibition reduces germinal matrix hemorrhage

The germinal matrix of premature infants is selectively vulnerable to hemorrhage within the first 48 h of life. To assess the role of vascular immaturity in germinal matrix hemorrhage (GMH), we evaluated germinal matrix angiogenesis in human fetuses and premature infants, as well as in premature rabbit pups, and noted active vessel remodeling in all three. Vascular endothelial growth factor (VEGF), angiopoietin-2 and endothelial cell proliferation were present at consistently higher levels in the germinal matrix relative to the white matter anlagen and cortical mantle. On that basis, we asked whether prenatal treatment with either of two angiogenic inhibitors, the COX-2 inhibitor celecoxib, or the VEGFR2 inhibitor ZD6474, could suppress the incidence of GMH in premature rabbit pups. Celecoxib treatment decreased angiopoietin-2 and VEGF levels as well as germinal matrix endothelial proliferation. Furthermore, treatment with celecoxib or ZD6474 substantially decreased the incidence of GMH. Thus, by suppressing germinal matrix angiogenesis, prenatal celecoxib or ZD6474 treatment may be able to reduce both the incidence and severity of GMH in susceptible premature infants.

The role of cytokines and trophic factors in epiretinal membranes: Involvement of signal transduction in glial cells

Idiopathic epiretinal membranes (ERMs) in the macular region can cause a reduction in vision and sometimes recurs after surgical removal, but its pathogenic mechanisms are still unknown. On the other hand, the presence of secondary ERMs has been associated with various clinical conditions including proliferative diabetic retinopathy (PDR) and proliferative vitreoretinopathy (PVR). Recent studies have shown a significant association between clinical grades of PDR or PVR, and the expression levels of specific cytokines and/or growth factors in the vitreous fluid. Expression of these factors and their receptors are also observed in secondary ERMs. ERMs are composed of many cell types such as retinal pigment epithelial cells and vascular endothelial cells, however the role of glial cells is yet unclear. Interestingly, glial cells in ERMs express some trophic factor receptors and transcription factors, such as NF-kappaB, suggesting an involvement of glial signal transduction in the pathogenesis of ERMs. In this review, we summarize recent progress regarding the clinical and laboratory findings of ERMs.

Anti-angiogenic activities of hypericin in vivo: potential for ophthalmologic applications

Hypericin, a perihydroxylated dianthraquinone is shown here to be a highly potent inhibitor of angiogenesis in several ocular models examined in rat eyes. Extensive angiogenesis induced in the cornea and iris by intra-ocular administration of FGF-2 was effectively inhibited by a minimum of four dose regimens of hypericin (2 mg/kg) administered via the intraperitoneal route at 48 h intervals. Maximal inhibition was achieved when animal treatment with hypericin was initiated 48 h prior to inoculation of FGF-2. The molecular basis for the hypericin-mediated inhibition of angiogenesis in the anterior eye compartment appears to involve several sites in the cascade leading to angiogenesis. We show that the activating phosphorylation of extracellular signal-regulated MAP kinases (ERK1/2) is inhibited by hypericin in human retinal pigment epithelial cells and in EA.hy926 cells, an endothelial hybridoma expressing endothelial cell properties. ERK1/2 activity is required for the transactivation of hypoxia-inducible factor 1 alpha (HIF-1alpha) and in VEGF-induced blood vessel sprouting. MT1-MMP activity in human microvascular endothelial cells was also inhibited. The findings identify hypericin as a potentially useful agent in the treatment of ophthalmic neovascularization pathogeneses.

Corticosteroids inhibit VEGF-induced vascular leakage in a rabbit model of blood-retinal and blood-aqueous barrier breakdown

PURPOSE

Recent clinical studies show that a single intravitreal injection of the corticosteroid triamcinolone acetonide (TAA) may reduce edematous retinal swelling and improve visual acuity in patients with diabetic macular edema (DME). In addition, clinical and experimental studies strongly suggest that blood-retinal barrier breakdown in diabetes is induced by vascular endothelial growth factor (VEGF). These results suggest that corticosteroids may modulate VEGF-mediated responses in vivo. To test this hypothesis directly, the current study evaluated the effects of TAA and dexamethasone (DEX) in a newly developed rabbit model of VEGF-induced blood-retinal barrier and blood-aqueous (iris) barrier breakdown.

METHODS

VEGF165 or vehicle was injected intravitreally in female Dutch Belt rabbits, and scanning ocular fluorophotometry was used to non-invasively measure fluorescein leakage from retinal and iris vasculature. VEGF-induced retinal vasculopathy was further assessed with fundus imaging, fluorescein angiography, and ocular coherence tomography. For pharmacologic studies, rabbits were treated with either DEX (2 mg kg(-1) daily, s.c.), TAA (2 or 4 mg, intravitreal), indomethacin (20 mg kg(-1) daily, s.c.), or vehicle (s.c. or intravitreal). Human umbilical vein endothelial cells (HUVEC) were loaded with the fluorescent Ca2+ indicator dye fluo-4 and treated with dexamethasone (0.1-10 microM) or vehicle for either 2 or 24 hr prior to stimulation with 10 ng ml(-1) VEGF165.

RESULTS

VEGF injected intravitreally induced a time and dose-dependent breakdown of the blood-retinal and blood-aqueous barriers. Maximal vascular leakage was measured at 48 hr after intravitreal injection with a dose of 500 ng VEGF. Other effects of VEGF included prominent retinal vasodilation, vessel tortuousity, fluorescein leakage from retinal vessels, and inner retinal edema. These VEGF-mediated responses are transient and approach baseline by 1 week. VEGF-induced blood-retinal and blood-aqueous barrier breakdown was completely blocked by the corticosteroid DEX administered systemically for 3 days. In contrast, the non-steroidal anti-inflammatory drug, indomethacin, had no effect. In a separate study with VEGF injected intravitreally at six different time points over 5 months, a single intravitreal 2 mg dose of TAA completely blocked VEGF-induced retinal and iris leakage for 45 days. VEGF/VEGF receptor-2-mediated Ca2+ mobilization in endothelial cells was not affected by 2 or 24 hr pretreatment with dexamethasone.

CONCLUSION

These results indicate that one mechanism by which corticosteroids block blood-ocular barrier breakdown and edema is via their modulation of signaling or effector proteins downstream of the VEGF receptor.

Effect of COX inhibitors on VEGF-induced retinal vascular leakage and experimental corneal and choroidal neovascularization

The primary objective of this study was to evaluate the effect of cyclooxygenase (COX) inhibitors, non-steroidal anti-inflammatory drugs (NSAIDs), in two in vivo models of VEGF-dependent corneal and choroidal angiogenesis and two in vivo models of VEGF-mediated vascular leakage. Non-selective COX inhibitors (the NSAIDs indomethacin and flunixin, p.o. or i.p.), the COX-1 selective inhibitor SC-560 (s.c. or i.p.), and the COX-2 selective inhibitor NS-398 (s.c. or i.p.) were evaluated in four experimental models. Choroidal neovascularization was induced in Brown Norway rats by argon laser photocoagulation and measured after ten days. Corneal neovascularization was induced by alkaline cautery in Sprague-Dawley rats and measured after four days. VEGF protein levels in the cornea were quantified by ELISA. VEGF-induced intradermal extravasation of Evans blue dye (EBD)-albumin was assayed in Hartley guinea pigs. Intravitreal VEGF-induced blood-retinal barrier breakdown was assayed by scanning ocular fluorophotometry in Dutch Belt rabbits. Indomethacin (1 or 3 mg kg(-1) day(-1), p.o.), SC-560 (20 mg kg(-1) day(-1), s.c.), and NS-398 (20 mg kg(-1) day(-1), s.c.) failed to inhibit laser-induced CNV. CNV was inhibited, however, by the corticosteroid dexamethasone (0.5 mg kg(-1) day(-1); p.o. or s.c.; 99% or 90% inhibition; p<0.01 or p<0.001, respectively). In contrast, cautery-induced corneal angiogenesis was inhibited partially by the NSAID indomethacin and the COX-2 selective inhibitor NS-398. Indomethacin, 3.5 or 7 mg kg(-1) day(-1), inhibited corneal neovascularization by 56% (p<0.001) or 68% (p<0.001) respectively. Similar partial inhibition of angiogenesis in the cornea model was observed with NS-398 (10 or 20 mg kg(-1) day(-1), s.c. or i.p.; 54% inhibition, p<0.001), but not with the COX-1 selective SC-560 (10 or 20 mg kg(-1) day(-1), s.c.). In the cornea, VEGF protein is dramatically upregulated 24 and 48 hr after cautery, and both indomethacin and NS-398-but not SC-560-significantly inhibited this VEGF upregulation. In experimental models of VEGF-induced vascular leakage, COX inhibitors had no effect on dermal or retinal vascular responses to VEGF. The NSAIDs indomethacin (7.5 or 20 mg kg(-1), p.o. or i.p.) and flunixin (12.5 mg kg(-1), i.p.) failed to inhibit VEGF-induced dermal extravasation of EBD-albumin in guinea pigs. In contrast, L-NAME (25 or 50 mg kg(-1), p.o.)-an anti-vasodilatory inhibitor of nitric oxide synthase-dose-dependently inhibited up to 64% (p<0.001) of this dermal vascular leakage. VEGF-mediated retinal vascular leakage was not blocked by COX inhibition. Intravitreal VEGF-induced BRB breakdown--which was completely blocked by VEGF neutralizing s-Flt-1/Fc protein (intravitreal co-administration; p<0.001)--was not inhibited by indomethacin (20 mg kg(-1) day(-1), s.c.). Although COX inhibitors were ineffective at blocking experimental CNV, both non-selective and COX-2 selective inhibitors partially blocked severe inflammatory corneal angiogenesis and its concurrent upregulation of VEGF protein. These results suggest that eicosanoids produced by inducible COX-2 are among multiple mediators that modulate VEGF expression as a stimulus in inflammation-associated angiogenesis. The lack of effect with COX inhibitors on either VEGF-mediated dermal extravasation or VEGF-mediated blood-retinal barrier breakdown indicates that COX activity is not required for vascular leakage responses to VEGF.

A selective and oral small molecule inhibitor of vascular epithelial growth factor receptor (VEGFR)-2 and VEGFR-1 inhibits neovascularization and vascular permeability

Vascular endothelial growth factor (VEGF) is a key driver of the neovascularization and vascular permeability that leads to the loss of visual acuity in diabetic retinopathy and neovascular age-related macular degeneration. Our aim was to identify an orally active, selective small molecule kinase inhibitor of vascular endothelial growth factor receptor (VEGFR)-2 with activity against both VEGF-induced angiogenesis and vascular permeability. We used a biochemical assay to identify 3-[5-methyl-2- (2-oxo-1,2-dihydro-indol-3-ylidenemethyl)-1H-pyrrol-3-yl]-proprionic acid (SU10944), a pyrrole indolinone, which is a potent ATP-competitive inhibitor of VEGFR-2 (Ki of 21 +/- 5 nM). In cellular assays, SU10944 inhibited VEGF-induced receptor autophosphorylation (IC50 of 227 +/- 80 nM) as well as downstream signaling (IC50 of 102 +/- 27 nM). In biochemical assays, SU10944 exhibits potent inhibitory activity against VEGFR-1; weak activity against other related subgroup members, including stem cell factor receptor (SCFR), platelet-derived growth factor receptor beta (PDGFRbeta), and fibroblast growth factor receptor-1 (FGFR-1); and no detectable activity against other protein tyrosine kinases such as epidermal growth factor receptor (EGFR), Src, and hepatocyte growth factor receptor. In cellular assays, the selectivity for SU10944 to inhibit VEGFR is maintained compared with other tyrosine kinases (IC50 for SCFR of 1.6 +/- 0.3 microM, for PDGFRbeta of 30.6 +/- 13.3 microM, for FGFR-1 of >50 microM, and for EGFR of >50 microM). Upon oral administration, SU10944 gave a clear dose response in the corneal micropocket model with an ED50 value for inhibition of neovascularization of approximately 30 mg/kg and a maximum inhibition of 95% at 300 mg/kg. Similarly, upon oral administration in the Miles assay, SU10944 potently inhibited VEGF-induced vascular permeability. Our data indicate that small molecule inhibitors of VEGFR signaling have the potential to ameliorate VEGF-induced neovascularization as well as vascular permeability.