Oligodeoxynucleotides inhibit retinal neovascularization in a murine model of proliferative retinopathy

Angiogenic footprints in diabetic retinopathy: opportunities for drug development

Diabetic retinopathy is one of the withering disorders that has been making the lives of patients miserable. Arising as a result of chronic high blood sugar levels in diabetes patients, retinopathy has become a major reason causing permanent blindness, retinal detachment, vitreous humor, rage, or glaucoma among patients. Angiogenesis being the major culprit behind the development of this condition is the growth of new blood vessels from the earlier ones existing. The abnormal growth and poor development of blood vessels also lead to aggravation of the conditions, with vascular endothelial growth factor (VEGF) playing a major role in the process. Various anti-angiogenic therapies or anti-VEGF therapies are being explored for the treatment of this condition. 4 widely explored drugs being-Bevacizumab, pegaptanib sodium, ranibizumab, and aflibercept. The review article tries to summarize studies illustrating the efficacy of these drugs in the treatment of diabetic retinopathy along with some of the herbal therapeutic paradigms displaying anti-angiogenic action that is being used to treat this condition.

A small molecular multi-targeting tyrosine kinase inhibitor, anlotinib, inhibits pathological ocular neovascularization

Ocular neovascularization is a devastating pathology observed in numerous ocular diseases and is a major cause of blindness. However, all current treatments have their limitations. Hence, it is important to explore new therapeutic strategies. This study aimed to investigate the role of anlotinib, a small molecular multi-targeting tyrosine kinase inhibitor, in ocular neovascularization. Anlotinib administration did not induce any cytotoxicity and tissue toxicity at the tested concentrations. Cellular functional experiments demonstrated that anlotinib inhibited the viability, proliferation, migration, and tube formation ability of endothelial cells (ECs) and pericytes. Western blot analysis demonstrated that anlotinib significantly inhibited the phosphorylation of vascular endothelial growth factor receptor 2 (VEGFR2) and platelet-derived growth factor receptor β (PDGFR-β), as well as their downstream signaling pathways stimulated by VEGF or PDGF-BB, in a concentration-dependent manner in ECs and pericytes. Using an oxygen-induced retinopathy (OIR) model, our results demonstrated that injection of anlotinib reduced avascular areas and pathological neovascular tufts. Furthermore, using a laser-induced choroidal neovascularization (CNV) model, we observed that the combined treatment of anlotinib and Lucentis reduced the size and thickness of CNV lesions compared to Lucentis monotherapy alone. Taken together, our results suggest that anlotinib could be a promising drug candidate for ocular neovascularization.

Postnatal weight gain and retinopathy of prematurity

Infants meeting retinopathy of prematurity (ROP) screening guidelines based on birth weight and gestational age undergo serial examinations by ophthalmologists for detection and treatment. However, less than 10% require treatment, and less than half develop ROP. Slow postnatal weight gain is highly predictive of ROP, and investigators have incorporated weight gain measures to develop more specific criteria for ROP screening. Such clinical prediction model use involves a large development study, validation studies specific to the target populations, and ongoing impact surveillance, with adjustment as necessary. Of the many weight gain inclusive prediction models intended to improve the precision of ROP screening, the Postnatal Growth and ROP (G-ROP) modified screening criteria were developed using the largest dataset and may provide the most robust model for clinical use. A recently completed G-ROP validation study will evaluate the generalizability of these modified criteria prior to clinical use.

Analysis of Anti-Vascular Endothelial Growth Factor Injection Claims Data in US Medicare Part B Beneficiaries From 2012 to 2015

Importance

The frequency of anti-vascular endothelial growth factor (VEGF) injections has grown exponentially with the introduction of bevacizumab, ranibizumab, and most recently aflibercept. The cost associated with these medications has garnered significant national attention, warranting a granular analysis of their use.

Objective

To analyze trends in anti-VEGF injections for US Medicare Part B beneficiaries from 2012 to 2015.

Design, Setting, and Participants

This observational cohort study used 2012-2015 data from the Centers for Medicare & Medicaid Services Medicare Part B Provider Utilization Files to analyze trends in intravitreal injections of anti-VEGF medications among Medicare Part B beneficiaries and their health care professionals.

Main Outcomes and Measures

The primary outcome measure was distribution of and change over time in the number of anti-VEGF injections performed for ranibizumab, aflibercept, and bevacizumab.

Results

A total of 2 574 124 intravitreal injections were performed by 3348 ophthalmologists in the outpatient setting for Medicare Part B beneficiaries during the 2015 calendar year; 100 ophthalmologists (3.0%) performed the highest volume of intravitreal injections. The total number of intravitreal injections administered in 2015 was 870 843 for aflibercept, 697 412 for ranibizumab, and 1 147 432 for bevacizumab. Ranibizumab injections decreased by 7.1% from 2012 to 2015 and bevacizumab injections decreased by 17.1%. From 2013 to 2015, aflibercept injections increased by 69.4%. The 100 ophthalmologists performing the highest volume of ranibizumab injections, as gauged by number of injections administered, accounted for 31.0% (95% CI, 30.994%-30.997%) of all ranibizumab injections nationally. The 100 ophthalmologists performing the highest volume of aflibercept injections accounted for 17.6% (95% CI, 17.638%-17.641%) of all aflibercept injections and the 100 ophthalmologists performing the highest volume of bevacizumab injections accounted for 19.6% (95% CI, 19.649%-19.653%) of all bevacizumab injections administered nationally to Medicare Part B beneficiaries. The highest number of injections per 1000 Medicare Part B beneficiaries occurred in Nebraska (aflibercept), Tennessee (ranibizumab), and South Dakota (bevacizumab).

Conclusions and Relevance

A total of 3.0% of ophthalmologists account for 17.6% to 31.0% of the total number of anti-VEGF injections administered nationally in the Medicare Part B population. Overall, bevacizumab and ranibizumab injections have decreased, coinciding with a 69.4% increase in aflibercept injections.

Retinal Vasculature in Development and Diseases

The retina is one of the most metabolically active tissues in the body, consuming high levels of oxygen and nutrients. A well-organized ocular vascular system adapts to meet the metabolic requirements of the retina to ensure visual function. Pathological conditions affect growth of the blood vessels in the eye. Understanding the neuronal biological processes that govern retinal vascular development is of interest for translational researchers and clinicians to develop preventive and interventional therapeutics for vascular eye diseases that address early drivers of abnormal vascular growth. This review summarizes the current knowledge of the cellular and molecular processes governing both physiological and pathological retinal vascular development, which is dependent on the interaction among retinal cell populations, including neurons, glia, immune cells, and vascular endothelial cells. We also review animal models currently used for studying retinal vascular development.

POSTNATAL SERUM INSULIN-LIKE GROWTH FACTOR I AND RETINOPATHY OF PREMATURITY

PURPOSE

Low serum IGF-1 has been associated with development of severe ROP, but no U.S. studies have been reported. We sought to determine the relationship between postnatal serum IGF-1 levels and severe ROP in a racially diverse U.S. cohort.

METHODS

Prospective cohort study of 74 infants with birth weight <1,251 g and a known ROP outcome at 3 Philadelphia hospitals. Weekly postnatal filter paper blood spot IGF-1 assays were measured through 42 weeks postmenstrual age.

RESULTS

The cohort included 20 white, 45 black, 2 Asian, and 9 other infants; median gestational age was 27.6 weeks (range 23-33 weeks), and median birth weight was 975 g (range 490-1,250 g). During postmenstrual age Weeks 28 to 33, mean IGF-1 was 20.0 ng/mL (standard error 0.52) for no ROP (n = 46), 18.0 (0.49) for Stage 1 or 2 (n = 23), and 17.0 (0.70) for Stage 3 (n = 5, 2 lasered) (P = 0.003). Adjustment for birth weight and gestational age showed similar results.

CONCLUSION

The presence and timing of an association between low postnatal serum IGF and ROP in a racially diverse U.S. sample were found to be consistent with those of European cohorts. This association provides the pathophysiological basis for growth-based predictive models, which could improve efficiency of ROP screening.

Study protocol: safety and efficacy of propranolol 0.2% eye drops in newborns with a precocious stage of retinopathy of prematurity (DROP-ROP-0.2%): a multicenter, open-label, single arm, phase II trial

BACKGROUND

Retinopathy of prematurity (ROP) still represents one of the leading causes of visual impairment in childhood. Systemic propranolol has proven to be effective in reducing ROP progression in preterm newborns, although safety was not sufficiently guaranteed. On the contrary, topical treatment with propranolol eye micro-drops at a concentration of 0.1% had an optimal safety profile in preterm newborns with ROP, but was not sufficiently effective in reducing the disease progression if administered at an advanced stage (during stage 2). The aim of the present protocol is to evaluate the safety and efficacy of propranolol 0.2% eye micro-drops in preterm newborns at a more precocious stage of ROP (stage 1).

METHODS

A multicenter, open-label, phase II, clinical trial, planned according to the Simon optimal two-stage design, will be performed to analyze the safety and efficacy of propranolol 0.2% eye micro-drops in preterm newborns with stage 1 ROP. Preterm newborns with a gestational age of 23-32 weeks, with a stage 1 ROP will receive propranolol 0.2% eye micro-drops treatment until retinal vascularization has been completed, but for no longer than 90 days. Hemodynamic and respiratory parameters will be continuously monitored. Blood samplings checking metabolic, renal and liver functions, as well as electrocardiogram and echocardiogram, will be periodically performed to investigate treatment safety. Additionally, propranolol plasma levels will be measured at the steady state, on the 10th day of treatment. To assess the efficacy of topical treatment, the ROP progression from stage 1 ROP to stage 2 or 3 with plus will be evaluated by serial ophthalmologic examinations.

DISCUSSION

Propranolol eye micro-drops could represent an ideal strategy in counteracting ROP, because it is definitely safer than oral administration, inexpensive and an easily affordable treatment. Establishing the optimal dosage and treatment schedule is to date a crucial issue.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier NCT02504944, registered on July 19, 2015, updated July 12, 2016. EudraCT Number 2014-005472-29.

Vascular Endothelial Growth Factor and Diabetic Retinal Disease

Diabetic retinal disease remains a leading cause of blindness among working-aged adults around the world. Until this decade, laser photocoagulation for both proliferative diabetic retinopathy and diabetic macular edema had been the standard of care for millions of patients. The introduction of vascular endothelial growth factor inhibitors (anti-VEGF) and subsequent clinical trials demonstrating their efficacy for treatment of diabetic eye disease have established a new standard in treatment of center-involved diabetic macular edema that is highly specific to the pathologic process and highly effective in preserving and improving vision. This review focuses on clinically relevant developments that led to the shift from focal/grid laser photocoagulation to anti-VEGF injections in the treatment of center-involved diabetic macular edema (DME), with an overview of the disease pathophysiology, clinical disease course, and available anti-VEGF agents. This article also reviews the scientific evidence exploring the use of anti-VEGF agents in nonproliferative and proliferative diabetic retinopathy.

Neurovascular cross talk in diabetic retinopathy: Pathophysiological roles and therapeutic implications

Diabetic retinopathy (DR) is the leading cause of blindness in the working-age population in developed countries, and its prevalence will increase as the global incidence of diabetes grows exponentially. DR begins with an early nonproliferative stage in which retinal blood vessels and neurons degenerate as a consequence of chronic hyperglycemia, resulting in vasoregression and persistent retinal ischemia, metabolic disequilibrium, and inflammation. This is conducive to overcompensatory pathological neovascularization associated with advanced proliferative DR. Although DR is considered a microvascular complication, the retinal microvasculature is intimately associated with and governed by neurons and glia; neurodegeneration, neuroinflammation, and dysregulation of neurovascular cross talk are responsible in part for vascular abnormalities in both early nonproliferative DR and advanced proliferative DR. Neuronal activity directly regulates microvascular dilation and blood flow in the process of neurovascular coupling. Retinal neurons also secrete guidance cues in response to injury, ischemia, or metabolic stress that may either promote or suppress vascular outgrowth, either alleviating or exacerbating DR, contingent on the stage of disease and retinal microenvironment. Neurodegeneration, impaired neurovascular coupling, and dysregulation of neuronal guidance cues are key events in the pathogenesis of DR, and correcting these events may prevent or delay development of advanced DR. The review discusses the mechanisms of neurovascular cross talk and its dysregulation in DR, and their potential therapeutic implications.

VEGF inhibitors in glaucoma surgery

Vascular endothelial growth factor (VEGF) is a signaling protein, that controls vasculogenesis, angiogenesis, vascular support and stimulates permeability of small blood vessels. The following isoforms are presently known: VEGF-A, VEGF-B, VEGF-C, VEGF-В and PGF. VEGF-A, that regulates neoangiogenesis and fibroblast formation, is thought to play the most important role in human organism. Increased expression of VEGF may lead to development and aggravation of pathological conditions including oncology. The article presents a review of preclinical and clinical studies of the main VEGF-inhibitors - bevacizumab and ranibizumab, as well as a brief account on other existing medications of this group. It describes ophthalmological indications for the use of antiangiogenetic agents, as well as the ways of their possible off-label use. The review presents investigations of intravitreal and intracameral injections of VEGF-inhibitors in patients with retinal, chorioidal, iris, and anterior chamber angle neovascularization. It gives examples of successful anti-VEGF use before Ahmed glaucoma valve drainage device implantation and in cases of neovascular glaucoma, induced by radiation therapy for intraocular tumors. Tenon’s capsule’s fibroblasts take part in the process of postoperative wound healing and scarring. According to the latest research, this process could be modulated by angiogenesis inhibitors. This review also recounts the use of anti-angiogenic agents to inhibit postoperative fibroblast proliferation, when used as monotherapy, or as an adjuvant to mitomycin С or 5-fluorouracil. It reviews the research on VEGF-inibitors use in combination with postoperative needling.

Association of gene polymorphism with serum levels of inflammatory and angiogenic factors in Pakistani patients with age-related macular degeneration

PURPOSE

To study the association of serum levels of inflammatory mediators and angiogenic factors with genetic polymorphism in Pakistani age-related macular degeneration (AMD) patients.

METHODS

This was a cross-sectional and case-control study that included 90 AMD patients diagnosed through slit-lamp examination, fundoscopy, and ocular coherence tomography. For reference and comparison purposes, 100 healthy age-matched subjects (controls) were also recruited. IL-6, IL-8, VEGF, and CRP levels were estimated in the serum samples of patients and control subjects. Using restriction fragment length polymorphism, single nucleotide polymorphisms were studied in IL-6 (rs1800795, rs1800796, rs1800797), IL-8 (rs4073, rs2227306, rs2227543), VEGF (rs3025039, rs699947), and CRP genes (rs1205, rs1130864). Since the data were obtained from a sample population, the Box-Cox transformation algorithm was applied to reduce heterogeneity of error. Multivariate analyses of variance (M-ANOVA) were applied on the transformed data to investigate the association of serum levels of IL-6, IL-8, VEGF, and CRP with AMD. Genotype and allele frequencies were compared through χ(2) tests applying Hardy-Weinberg equilibrium. The serum concentrations of IL-6 and IL-8, VEGF, and CRP between homozygotes and heterozygotes were compared through one-way ANOVA. Significance level was p<0.05.

RESULTS

Compared to control subjects, serum IL-6 (p<0.0001), IL-8 (p<0.0001), VEGF (p<0.0001), and CRP (p<0.0001) levels were significantly elevated in the AMD patients. For rs1800795, patients with the GG genotype showed significantly raised levels of IL-6 compared to those with GC and CC genotypes (p<0.0001). Serum IL-8 levels were significantly higher in patients with the GG genotype compared to the GC and CC genotypes for the single nucleotide polymorphism (SNP) rs2227543 (p<0.002). Similarly, significantly higher VEGF levels were detected for genotype TT for rs3025039 SNP (p<0.038). However, no significant alteration in serum CRP levels was detected in hetero- or homozygotes for rs1205 and rs1130864 SNPs.

CONCLUSIONS

Serum IL-6, IL-8, and VEGF levels are substantially increased in AMD, and the levels coincide with polymorphism in the respective gene. No such relationship appears to exist with regard to SNPs of CRP.

Temporal and spatial changes in VEGF, αA- and αB-crystallin expression in a mouse model of oxygen-induced retinopathy

OBJECTIVE

Retinal neovascularization is an iconic change in retinopathies. Vascular Endothelial Growth Factor (VEGF) and α-crystallins have been identified to mediate the pathogenesis of retinopathy. However, the special and temporal changes in their expression associated with retinal neovascularization have not yet been determined. Therefore, we examined the expression and distribution of VEGF, αA- and αB-crystallins in the retina using a mouse model of oxygen-induced retinopathy (OIR).

METHODS

90 C57/BL mice were randomly divided into the OIR and control groups. The OIR group at postnatal day 7 (P7) were kept at high oxidation state (75 ± 5%) for 5 days before returned to normal environment. Retinal tissue was cut into sections. Oxygen induced retinal neovascularization and vascular structural changes were evaluated using retinal fluorescein angiography. The number of endothelial cell nuclei breaking through the retinal internal limiting membrane was counted after H&E staining. The mRNA expression levels of VEGF, αA- and αB-crystallins in the mouse retina were determined using real-time RT-PCR. The distribution of αA- and αB-crystallins in the retina was detected by fluorescent immunohistochemistry staining.

RESULTS

Oxygen induction triggered new blood vessel formation in the retina and impaired the structure of the retinal vascular network. The number of endothelial cell nuclei breaking through the retinal internal limiting membrane was significantly increased in the OIR group compared to the control group at P13, P17 and P21 (P < 0.01), reaching the peak on P17. The expression levels of VEGF, αA- and αB-crystalllins were also significantly different between the OIR and control groups. VEGF expression was highest on P15, αA-crystallin expression was highest on P17, whereas αB-crystallin expression kept increasing during the time frame of our study. Both αA- and αB-crystallins were expressed in the ganglion cell layer and the inner nuclear cell layer. While αA- and αB-crystallins were only located on the cell membrane in the outer ganglion cell layer, they were observed both on the cell membrane and in the cytoplasm in the inner layer of cells.

CONCLUSION

Using our mouse model of oxygen-induced retinopathy, we showed that the expression patterns of VEGF, αA- and αB-crystallins during retinal neovascularization in both spatially and temporally manners, providing significant insights into the molecular mechanisms of retinopathy and the associated neovascularization.

[Off-label use of intravitreal bevacizumab for severe retinopathy of prematurity]

OBJECTIVE

To examine the quality of evidence and the variability in the off-label use of intravitreal bevacizumab for retinopathy of prematurity (ROP).

METHODS

A wide review of the literature was performed using Pubmed, Medline, and Cochrane database, using the words vascular endothelial growth factor (VEGF), retinopathy of prematurity, treatment and bevacizumab.

RESULTS

Case reports, case series, reviews, one sistematic review and one randomized controlled trial were found on the use of intravitreal bevacizumab in severe ROP, as monotherapy or combined with láser and/or vitrectomy.

CONCLUSIONS

The results shown on the use of intravitreal bevacizumab in ROP stage 3+ in zone I or in aggressive posterior ROP are promising. However, uncertainty remains regarding its maximum tolerable dose in the neonatal group, its ocular and systemic safety profile, or its efficacy and bioactivity in a developing child. This report found no significant differences in the recurrence rates of ROP stage 3+ in zone II in patients treated with intravitreal bevacizumab monotherapy in comparison to láser, although the latter is the best option due to long-term safety and efficacy. The use of intravitreal bevacizumab is not indicated in stages 1 and 2 of ROP as the risk of severe visual loss is low and VEFG is necessary for normal retinal vessel development. On the other hand, the use of intravitreal bevacizumab would be contraindicated in stages 4 and 5 because the retinal detachment is accelerated.

RNA interference-based therapy for spinocerebellar ataxia type 7 retinal degeneration

Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant neurodegenerative disease characterized by loss of motor coordination and retinal degeneration with no current therapies in the clinic. The causative mutation is an expanded CAG repeat in the ataxin-7 gene whose mutant protein product causes cerebellar and brainstem degeneration and retinal cone-rod dystrophy. Here, we reduced the expression of both mutant and wildtype ataxin-7 in the SCA7 mouse retina by RNA interference and evaluated retinal function 23 weeks post injection. We observed a preservation of normal retinal function and no adverse toxicity with ≥50% reduction of mutant and wildtype ataxin-7 alleles. These studies address an important safety concern regarding non-allele specific silencing of ataxin-7 for SCA7 retinal therapy.

Current and investigational pharmacotherapeutic approaches for modulating retinal angiogenesis

Retinal vascular development is a carefully orchestrated developmental process during which retinal and choroidal vasculature form to provide a dual vascular supply to the neurosensory retina and retinal pigment epithelium. The most common causes of vision loss in children and adults involve at least in part perturbation of the normal vascular physiology or development. Vascular endothelial growth factor has emerged as a key molecular regulator of retinal vascular development as well as retinal and choroidal neovascularization, which underlie the pathophysiology of many retinal diseases. Over the past decade, the advent of injectable pharmacotherapeutic agents into the vitreous cavity of the eye has revolutionized our management of neovascular age-related macular degeneration and other retinal diseases and has, for the first time, offered an opportunity to improve vision rather than just slow the progression of disease processes. The transient duration of these agents, however, requires chronic treatment with repeated intraocular injections and significant treatment burden for patients and the healthcare system. Novel treatments modulating retinal angiogenesis offer the promise of improved efficacy, decreased treatment burden and improved cost-effectiveness.

The pathophysiology of retinopathy of prematurity: an update of previous and recent knowledge

Retinopathy of prematurity (ROP) is a disease that can cause blindness in very low birthweight infants. The incidence of ROP is closely correlated with the weight and the gestational age at birth. Despite current therapies, ROP continues to be a highly debilitating disease. Our advancing knowledge of the pathogenesis of ROP has encouraged investigations into new antivasculogenic therapies. The purpose of this article is to review the findings on the pathophysiological mechanisms that contribute to the transition between the first and second phases of ROP and to investigate new potential therapies. Oxygen has been well characterized for the key role that it plays in retinal neoangiogenesis. Low or high levels of pO2 regulate the normal or abnormal production of hypoxia-inducible factor 1 and vascular endothelial growth factors (VEGF), which are the predominant regulators of retinal angiogenesis. Although low oxygen saturation appears to reduce the risk of severe ROP when carefully controlled within the first few weeks of life, the optimal level of saturation still remains uncertain. IGF-1 and Epo are fundamentally required during both phases of ROP, as alterations in their protein levels can modulate disease progression. Therefore, rhIGF-1 and rhEpo were tested for their abilities to prevent the loss of vasculature during the first phase of ROP, whereas anti-VEGF drugs were tested during the second phase. At present, previous hypotheses concerning ROP should be amended with new pathogenetic theories. Studies on the role of genetic components, nitric oxide, adenosine, apelin and β-adrenergic receptor have revealed new possibilities for the treatment of ROP. The genetic hypothesis that single-nucleotide polymorphisms within the β-ARs play an active role in the pathogenesis of ROP suggests the concept of disease prevention using β-blockers. In conclusion, all factors that can mediate the progression from the avascular to the proliferative phase might have significant implications for the further understanding and treatment of ROP.

Mast cell chymase and tryptase as targets for cardiovascular and metabolic diseases

Mast cells are critical effectors in inflammatory diseases, including cardiovascular and metabolic diseases and their associated complications. These cells exert their physiological and pathological activities by releasing granules containing histamine, cytokines, chemokines, and proteases, including mast cell-specific chymases and tryptases. Several recent human and animal studies have shown direct or indirect participation of mast cell-specific proteases in atherosclerosis, abdominal aortic aneurysms, obesity, diabetes, and their complications. Animal studies have demonstrated the beneficial effects of highly selective and potent chymase and tryptase inhibitors in several experimental cardiovascular and metabolic diseases. In this review, we summarize recent discoveries from in vitro cell-based studies to experimental animal disease models, from protease knockout mice to treatments with recently developed selective and potent protease inhibitors, and from patients with preclinical disorders to those affected by complications. We hypothesize that inhibition of chymases and tryptases would benefit patients suffering from cardiovascular and metabolic diseases.

Algorithms for the prediction of retinopathy of prematurity based on postnatal weight gain

Current ROP screening guidelines represent a simple risk model with two dichotomized factors, birth weight and gestational age at birth. Pioneering work has shown that tracking postnatal weight gain, a surrogate for low insulin-like growth factor 1, may capture the influence of many other ROP risk factors and improve risk prediction. Models including weight gain, such as WINROP, ROPScore, and CHOP ROP, have demonstrated accurate ROP risk assessment and a potentially large reduction in ROP examinations, compared to current guidelines. However, there is a need for larger studies, and generalizability is limited in countries with developing neonatal care systems.

The biology of retinopathy of prematurity: how knowledge of pathogenesis guides treatment

Retinopathy of prematurity occurs because the retina of a preterm infant at birth is incompletely vascularized, and if the postnatal environment does not match the in utero environment that supported retinal development, the vessels and neural retina will not grow normally. Risk factors determined from many clinical studies and animal studies fall into 2 categories: prenatal factors and postnatal factors.

Reactive oxygen species, Nox and angiotensin II in angiogenesis: implications for retinopathy

Pathological angiogenesis is a key feature of many diseases including retinopathies such as ROP (retinopathy of prematurity) and DR (diabetic retinopathy). There is considerable evidence that increased production of ROS (reactive oxygen species) in the retina participates in retinal angiogenesis, although the mechanisms by which this occurs are not fully understood. ROS is produced by a number of pathways, including the mitochondrial electron transport chain, cytochrome P450, xanthine oxidase and uncoupled nitric oxide synthase. The family of NADPH oxidase (Nox) enzymes are likely to be important given that their primary function is to produce ROS. Seven isoforms of Nox have been identified named Nox1-5, Duox (dual oxidase) 1 and Duox2. Nox1, Nox2 and Nox4 have been most extensively studied and are implicated in the development of conditions such as hypertension, cardiovascular disease and diabetic nephropathy. In recent years, evidence has accumulated to suggest that Nox1, Nox2 and Nox4 participate in pathological angiogenesis; however, there is no clear consensus about which Nox isoform is primarily responsible. In terms of retinopathy, there is growing evidence that Nox contribute to vascular injury. The RAAS (renin-angiotensin-aldosterone system), and particularly AngII (angiotensin II), is a key stimulator of Nox. It is known that a local RAAS exists in the retina and that blockade of AngII and aldosterone attenuate pathological angiogenesis in the retina. Whether the RAAS influences the production of ROS derived from Nox in retinopathy is yet to be fully determined. These topics will be reviewed with a particular emphasis on ROP and DR.

HIF-1α siRNA reduces retinal neovascularization in a mouse model of retinopathy of prematurity

OBJECTIVE

To explore the effect of HIF-1α specific siRNA expression vector pSUPERH1-siHIF-1α on retinal neovascularization in a mouse model of retinopathy of prematurity (ROP).

METHODS

Forty-eight newborn C57BL/6J mice were randomly divided into the control and experimental groups (n=24 apiece) to create the model of ROP following the methods described by Smith et al. Twelve days after birth, the experimental group received intravitreal injection with pSUPERH1-siHIF-1α; meanwhile, mice in the control group were injected with empty vectors. The expressions of HIF-1α and vascular endothelia growth factor (VEGF) in the retina were examined by Western blotting in both groups. The differences in the neovascular endothelial cell count were compared based on the FITC-Dextran fluorescence stretched preparation/sections.

RESULTS

Compared with the control group, the expressions of HIF-1α and VEGF significantly decreased in the experimental group (P<0.01). Meanwhile, the number of retinal neovascular endothelial nuclei that had protruded the internal limiting membrane was significantly lower in the experimental group than in control group (P<0.01).

CONCLUSIONS

RNA interference targeting HIF-1α can effectively inhibit the retinal neovascularization of ROP.

Therapeutic interventions against inflammatory and angiogenic mediators in proliferative diabetic retinopathy

The global prevalence of diabetes is estimated to be 336 million people, with diabetic complications contributing to significant worldwide morbidity and mortality. Diabetic retinopathy results from cumulative microvascular damage to the retina and inflammation is recognized as a critical driver of this disease process. This paper outlines the pathophysiology leading to proliferative diabetic retinopathy and highlights many of the inflammatory, angiogenic, and cytokine mediators implicated in the development and progression of this disease. We focus a detailed discussion on the current targeted therapeutic interventions used to treat diabetic retinopathy.

Anti-VEGF therapy for the treatment of glaucoma: a focus on ranibizumab and bevacizumab

INTRODUCTION

Anti-VEGF therapy has been widely used in the treatment of ocular neovascular diseases. Because of their anti-angiogenic and anti-fibrotic properties, anti-VEGF antibodies such as bevacizumab and ranibizumab have emerged as an adjunctive treatment modality in glaucoma to improve success of conventional treatments.

AREAS COVERED

Ranibizumab is an anti-VEGF-A antigen binding fragment currently indicated in neovascular age-related macular degeneration as well as macular edema following retinal vein occlusion. Several off-label uses include the treatment of neovascular glaucoma to regress/suppress iris and iridocorneal angle neovascularization and the modulation of wound healing after glaucoma filtration surgery. Bevacizumab is a full-length anti-VEGF antibody, which is also being used in aforementioned eye conditions off-label. An overview of these anti-VEGF antibodies and the results of preclinical and clinical studies regarding their use in the treatment of glaucoma are presented.

EXPERT OPINION

Early studies on the utility of both bevacizumab and ranibizumab in neovascular glaucoma and filtration surgery reported promising results. However, a large-scale randomized clinical trial as well as comparative studies between the two anti-VEGF antibodies are currently lacking. A single dose of ranibizumab costs approximately 40 times as much as a single dose of bevacizumab. Clinicians should take this into account, in addition to their differences in the efficacy and safety, when treating patients.

A brief history of anti-VEGF for the treatment of ocular angiogenesis

In 1994, The American Journal of Pathology published a key article reporting that hypoxic retina produces vascular endothelial growth factor (VEGF), suggesting a role for VEGF in ocular neovascularization. Subsequent developments in anti-VEGF treatment for neovascular eye disease have improved visual outcomes and changed the standard of care in retinal medicine and ophthalmology.

The role of angiogenesis in the development of proliferative diabetic retinopathy: impact of intravitreal anti-VEGF treatment

Although cellular and molecular bases of proliferative diabetic retinopathy are only partially understood, it is evident that this complication of diabetes is characterized by the formation of new vessels inside the retina showing abnormal architecture and permeability. This process, if not controlled by selective laser photocoagulation, leads to irreversible retinal damages and loss of vision. Angiogenesis, that is, the condition characterized by the growth of new blood vessels originated from preexisting ones, was shown to have a major role in the pathogenesis of proliferative retinopathy and, as a consequence, intravitreal antiangiogenic injection was suggested as a feasible treatment for this disease. Here, we describe the different antiangiogenic approaches used to treat this disease along with the respective advantages and limitations when compared to laser treatment. Altogether, even though further and longer studies are still needed to clarify the best possible therapeutic protocol, the antiangiogenic treatment will reasonably have a future role in the therapy and prevention of proliferative diabetic retinopathy.

[Pharmacological treatment for retinopathy of prematurity]

Mandatory screening performed by an experience ophthalmologist remains the most important pillar in the management of retinopathy of prematurity (ROP). The current gold standard for treatment of proliferative ROP is still panretinal laser photocoagulation, depending on severity, in combination with vitreoretinal surgery if necessary. The first case series of off-label intravitreal anti-VEGF treatment are encouraging. In addition to intravitreal anti-VEGF therapy, other treatment concepts such as supplementation with IGF-1 or omega-3 fatty acids also represent interesting pharmacological approaches to the management of ROP. However, larger controlled trials are required to validate the benefits and safety of these systemic treatment approaches.

From oxygen to erythropoietin: relevance of hypoxia for retinal development, health and disease

Photoreceptors and other cells of the retina consume large quantities of energy to efficiently convert light information into a neuronal signal understandable by the brain. The necessary energy is mainly provided by the oxygen-dependent generation of ATP in the numerous mitochondria of retinal cells. To secure the availability of sufficient oxygen for this process, the retina requires constant blood flow through the vasculature of the retina and the choroid. Inefficient supply of oxygen and nutrients, as it may occur in conditions of disturbed hemodynamics or vascular defects, results in tissue ischemia or hypoxia. This has profound consequences on retinal function and cell survival, requiring an adaptational response by cells to cope with the reduced oxygen tension. Central to this response are hypoxia inducible factors, transcription factors that accumulate under hypoxic conditions and drive the expression of a large variety of target genes involved in angiogenesis, cell survival and metabolism. Prominent among these factors are vascular endothelial growth factor and erythropoietin, which may contribute to normal angiogenesis during development, but may also cause neovascularization and vascular leakage under pathologically reduced oxygen levels. Since ischemia and hypoxia may have a role in various retinal diseases such as diabetic retinopathy and retinopathy of prematurity, studying the cellular and molecular response to reduced tissue oxygenation is of high relevance. In addition, the concept of preconditioning with ischemia or hypoxia demonstrates the capacity of the retina to activate endogenous survival mechanisms, which may protect cells against a following noxious insult. Part of these mechanisms is the local production of protective factors such as erythropoietin. Due to its plethora of effects in the retina including neuro- and vaso-protective activities, erythropoietin has gained strong interest as potential therapeutic factor for retinal degenerative diseases.

Nano-vectors for the Ocular Delivery of Nucleic Acid-based Therapeutics

Nucleic acid-based therapeutics have gained a lot of interest for the treatment of diverse ophthalmic pathologies. The first to enter in clinic has been an oligonucleotide, Vitravene^® for the treatment of cytomegalovirus infection. More recently, research on aptamers for the treatment of age related macular degeneration has led to the development of Macugen^®. Despite intense potential, effective ocular delivery of nucleic acids is a major challenge since therapeutic targets for nucleic acid-based drugs are mainly located in the posterior eye segment, requiring repeated invasive administration. Of late, nanotechnology-based nano-vectors have been developed in order to overcome the drawbacks of viral and other non-viral vectors. The diversity of nano-vectors allows for ease of use, flexibility in application, low-cost of production, higher transfection efficiency and enhanced genomic safety. Using nano-vector strategies, nucleic acids can be delivered either encapsulated or complexed with cationic lipids, polymers or peptides forming sustained release systems, which can be tailored according to the ocular tissue being targeted. The present review focuses on developments and advances in various nano-vectors for the ocular delivery of nucleic acid-based therapeutics, the barriers that such delivery systems face and methods to overcome them.

Effect of brimonidine on retinal and choroidal neovascularization in a mouse model of retinopathy of prematurity and laser-treated rats

PURPOSE

To determine whether chronic treatment with brimonidine (BRI) attenuates retinal vascular leakage and neovascularization in neonatal mice after exposure to high oxygen in a mouse model of retinopathy of prematurity (ROP), and choroidal neovascularization (CNV) in rats after laser treatment.

METHODS

Experimental CNV was induced by laser treatment in Brown Norway (BN) rats. BRI or vehicle (VEH) was administered by osmotic minipumps, and CNV formation was measured 11 days after laser treatment. Oxygen-induced retinopathy was generated in neonatal mice by exposure to 75% oxygen from postnatal day (P)7 to P12. BRI or VEH was administered by gavage, and vitreoretinal vascular endothelial growth factor (VEGF) concentrations and retinal vascular leakage, neovascularization, and vaso-obliteration were measured on P17. Experimental CNV was induced in rabbits by subretinal lipopolysaccharide/fibroblast growth factor-2 injection.

RESULTS

Systemic BRI treatment significantly attenuated laser-induced CNV formation in BN rats when initiated 3 days before or within 1 hour after laser treatment. BRI treatment initiated during exposure to high oxygen significantly attenuated vitreoretinal VEGF concentrations, retinal vascular leakage, and retinal neovascularization in P17 mice subjected to oxygen-induced retinopathy. Intravitreal treatment with BRI had no effect on CNV formation in a rabbit model of nonischemic angiogenesis.

CONCLUSIONS

BRI treatment significantly attenuated vitreoretinal VEGF concentrations, retinal vascular leakage, and retinal and choroidal neovascularization in animal models of ROP and CNV. BRI may inhibit underlying event(s) of ischemia responsible for upregulation of vitreoretinal VEGF and thus reduce vascular leakage and retinal-choroidal neovascularization.

Novel protective properties of IGFBP-3 result in enhanced pericyte ensheathment, reduced microglial activation, increased microglial apoptosis, and neuronal protection after ischemic retinal injury

This study was conducted to determine the perivascular cell responses to increased endothelial cell expression of insulin-like growth factor binding protein-3 (IGFBP-3) in mouse retina. The contribution of bone marrow cells in the IGFBP-3-mediated response was examined using green fluorescent protein-positive (GFP(+)) adult chimeric mice subjected to laser-induced retinal vessel occlusion injury. Intravitreal injection of an endothelial-specific IGFBP-3-expressing plasmid resulted in increased differentiation of GFP(+) hematopoietic stem cells (HSCs) into pericytes and astrocytes as determined by immunohistochemical analysis. Administration of IGFBP-3 plasmid to mouse pups that underwent the oxygen-induced retinopathy model resulted in increased pericyte ensheathment and reduced pericyte apoptosis in the developing retina. Increased IGFBP-3 expression reduced the number of activated microglial cells and decreased apoptosis of neuronal cells in the oxygen-induced retinopathy model. In summary, IGFBP-3 increased differentiation of GFP(+) HSCs into pericytes and astrocytes while increasing vascular ensheathment of pericytes and decreasing apoptosis of pericytes and retinal neurons. All of these cytoprotective effects exhibited by IGFBP-3 overexpression can result in a more stable retinal vascular bed. Thus, endothelial expression of IGFBP-3 may represent a physiologic response to injury and may represent a therapeutic strategy for the treatment of ischemic vascular eye diseases, such as diabetic retinopathy and retinopathy of prematurity.

Diabetic retinopathy: pathogenic mechanisms and current treatments

Since diabetes is now a global epidemic, the incidence of retinopathy, a leading cause of blindness in patients aged 20-74 years, is also expected to rise to alarming levels. The risk of development and progression of diabetic retinopathy is closely associated with the type and duration of diabetes, blood glucose, blood pressure and possibly lipids. It is an unmet medical need that can lead to severe and irreversible loss of vision in people of working age worldwide. The aim of this review is to give an overview of the clinical and anatomical changes during the progression of retinopathy, the underlying pathogenic mechanisms that link hyperglycemia with retinal tissue damage, current treatments, and the emerging pharmacological therapies for this sight-threatening complication of diabetes.

Expression of vascular endothelial growth factor and pigment epithelial-derived factor in a rat model of retinopathy of prematurity

OBJECTIVE

To determine the effects of oxygen fluctuations on pigment epithelial-derived factor (PEDF) and vascular endothelial growth factor (VEGF)/PEDF ratios in a relevant rat model of retinopathy of prematurity (ROP).

METHODS

The expression of retinal PEDF mRNA and of VEGF and PEDF protein were determined using real-time polymerase chain reaction or enzyme-linked immunosorbent assays at different postnatal day ages for rat pups raised in room air (RA) or in a rat model mimicking ROP. Statistical outcomes were determined with factorial analyses of variance. Mean VEGF and PEDF protein levels were determined at different ages for rats in the ROP model and for RA-raised rats, and the ratio of VEGF/PEDF protein versus age was plotted. At postnatal day (P) 14, inner retinal plexus vascularization had extended to the ora serrata in pups raised in RA. In the ROP model, avascular retina persisted at P14 and intravitreous neovascularization developed at P18. Therefore, VEGF and PEDF expression was determined in the ROP model and in RA-raised rat pups at P14 and P18.

RESULTS

Older age was associated with increased PEDF mRNA (p<0.001), PEDF protein (p=0.005), and VEGF protein (p=0.005), and VEGF protein (p<0.0001). Exposure to fluctuations of oxygen in the 50/10 oxygen-induced retinopathy model compared to RA was associated with increased PEDF mRNA (p=0.0185), PEDF protein (p<0.0001), or VEGF protein (p<0.0001). The VEGF/PEDF ratio favored angiogenic inhibition (<1.0) before but not on P14, when avascular retina persisted in the ROP model but not in RA. The VEGF/PEDF ratio favored angiogenesis (>1.0) at P14 and P 18 when intravitreous neovascularization occurred in the ROP model.

CONCLUSIONS

Increased expression levels of VEGF and PEDF are associated with older postnatal day age or with exposure to fluctuations in oxygen in the 50/10 oxygen-induced retinopathy model compared to RA. PEDF protein more closely associates with avascular retinal features and neovascularization than does VEGF protein or the VEGF/PEDF in the ROP model. Although PEDF has been proposed as a potential treatment in ROP, interventional studies using PEDF in an ROP model to potentially reduce intravitreous neovascularization are required to determine timing, efficacy, and dose of PEDF.

5-Lipoxygenase metabolite 4-HDHA is a mediator of the antiangiogenic effect of ω-3 polyunsaturated fatty acids

Lipid signaling is dysregulated in many diseases with vascular pathology, including cancer, diabetic retinopathy, retinopathy of prematurity, and age-related macular degeneration. We have previously demonstrated that diets enriched in ω-3 polyunsaturated fatty acids (PUFAs) effectively reduce pathological retinal neovascularization in a mouse model of oxygen-induced retinopathy, in part through metabolic products that suppress microglial-derived tumor necrosis factor-α. To better understand the protective effects of ω-3 PUFAs, we examined the relative importance of major lipid metabolic pathways and their products in contributing to this effect. ω-3 PUFA diets were fed to four lines of mice deficient in each key lipid-processing enzyme (cyclooxygenase 1 or 2, or lipoxygenase 5 or 12/15), retinopathy was induced by oxygen exposure; only loss of 5-lipoxygenase (5-LOX) abrogated the protection against retinopathy of dietary ω-3 PUFAs. This protective effect was due to 5-LOX oxidation of the ω-3 PUFA lipid docosahexaenoic acid to 4-hydroxy-docosahexaenoic acid (4-HDHA). 4-HDHA directly inhibited endothelial cell proliferation and sprouting angiogenesis via peroxisome proliferator-activated receptor γ (PPARγ), independent of 4-HDHA's anti-inflammatory effects. Our study suggests that ω-3 PUFAs may be profitably used as an alternative or supplement to current anti-vascular endothelial growth factor (VEGF) treatment for proliferative retinopathy and points to the therapeutic potential of ω-3 PUFAs and metabolites in other diseases of vasoproliferation. It also suggests that cyclooxygenase inhibitors such as aspirin and ibuprofen (but not lipoxygenase inhibitors such as zileuton) might be used without losing the beneficial effect of dietary ω-3 PUFA.

PEI-g-PEG-RGD/small interference RNA polyplex-mediated silencing of vascular endothelial growth factor receptor and its potential as an anti-angiogenic tumor therapeutic strategy

Tumor angiogenesis appears to be achieved by the expression of vascular endothelial growth factor (VEGF) within solid tumors that stimulate host vascular endothelial cell mitogenesis and possibly chemotaxis. VEGF's angiogenic actions are mediated through its high-affinity binding to 2 endothelium-specific receptor tyrosine kinase, Flt-1 (VEGFR1), and Flk-1/KDR (VEGFR2). RNA interference-mediated knockdown of protein expression at the messenger RNA level provides a new therapeutic strategy to overcome various diseases. To achieve high efficacy in RNA interference-mediated therapy, it is critical to develop an efficient delivering system to deliver small interference RNA (siRNA) into tissues or cells site-specifically. We previously reported an angiogenic endothelial cell-targeted polymeric gene carrier, PEI-g-PEG-RGD. This targeted carrier was developed by the conjugation of the ανβ3/ανβ5 integrin-binding RGD peptide (ACDCRGDCFC) to the cationic polymer, branched polyethylenimine, with a hydrophilic polyethylene glycol (PEG) spacer. In this study, we used PEI-g-PEG-RGD to deliver siRNA against VEGFR1 into tumor site. The physicochemical properties of PEI-g-PEG-RGD/siRNA complexes was evaluated. Further, tumor growth profile was also investigated after systemic administration of PEI-g-PEG-RGD/siRNA complexes.

A clinical prediction model to stratify retinopathy of prematurity risk using postnatal weight gain

OBJECTIVE

To develop an efficient clinical prediction model that includes postnatal weight gain to identify infants at risk of developing severe retinopathy of prematurity (ROP). Under current birth weight (BW) and gestational age (GA) screening criteria, <5% of infants examined in countries with advanced neonatal care require treatment.

PATIENTS AND METHODS

This study was a secondary analysis of prospective data from the Premature Infants in Need of Transfusion Study, which enrolled 451 infants with a BW < 1000 g at 10 centers. There were 367 infants who remained after excluding deaths (82) and missing weights (2). Multivariate logistic regression was used to predict severe ROP (stage 3 or treatment).

RESULTS

Median BW was 800 g (445-995). There were 67 (18.3%) infants who had severe ROP. The model included GA, BW, and daily weight gain rate. Run weekly, an alarm that indicated need for eye examinations occurred when the predicted probability of severe ROP was >0.085. This identified 66 of 67 severe ROP infants (sensitivity of 99% [95% confidence interval: 94%-100%]), and all 33 infants requiring treatment. Median alarm-to-outcome time was 10.8 weeks (range: 1.9-17.6). There were 110 (30%) infants who had no alarm. Nomograms were developed to determine risk of severe ROP by BW, GA, and postnatal weight gain.

CONCLUSION

In a high-risk cohort, a BW-GA-weight-gain model could have reduced the need for examinations by 30%, while still identifying all infants requiring laser surgery. Additional studies are required to determine whether including larger-BW, lower-risk infants would reduce examinations further and to validate the prediction model and nomograms before clinical use.

Targets of chymase inhibitors

INTRODUCTION

Chymase converts angiotensin I to angiotensin II and it can also convert precursors of TGF-β and MMP-9 to their active forms. Therefore, diseases related to angiotensin II TGF-β, and MMP-9 could potentially be treated with chymase inhibitors.

AREAS COVERED

This review discusses the appropriate targets and safety of chymase inhibitors. Six diseases with notable mortality or morbidity as targets of chymase inhibitors are focused on; abdominal aortic aneurysms (AAAs), nephropathy and retinopathy, cardiomyopathy, nonalcoholic steatohepatitis (NASH), organ fibrosis and intestinal diseases.

EXPERT OPINION

If chymase inhibition proves to be a useful strategy for the attenuation of angiotensin II, TGF-β and MMP-9 in vivo, the application of chymase inhibitors is likely to become widespread in various diseases in the clinical setting. Chymase inhibitors are anticipated not to interfere with the homeostasis of resting tissues, that is, those not affected by injury or inflammation.

Review of therapeutic advances in diabetic retinopathy

Diabetic retinopathy is a common microvascular complication of prolonged diabetes. It is one of the leading causes of vision loss in working age adults and a significant source of morbidity. To reduce the incidence and severity of diabetic retinopathy, it is important to identify patients at risk and promptly implement intensive glycemic and hypertensive control. To date, there are many interventions that can limit moderate and severe vision loss in people with diabetes, including laser photocoagulation, vitrectomy surgery, and intravitreal pharmacological injections. This review aims to define the different stages of diabetic retinopathy and the important therapeutic advances developed to address the major causes of vision loss in each stage.

Studies on the pathogenesis of avascular retina and neovascularization into the vitreous in peripheral severe retinopathy of prematurity (an american ophthalmological society thesis)

PURPOSE

To study vascular endothelial growth factor (VEGF) regulation in the development of intravitreous neovascularization and peripheral avascular retina in peripheral severe retinopathy of prematurity (ROP).

METHODS

The rat 50/10 model of ROP mimics zone II, stage 3 severe ROP and recreates fluctuations in transcutaneous oxygen levels in preterm infants. On postnatal (p) day ages p0, p8, p11-p14, and p18, retinas from the model or room-air (RA) age-matched pups were analyzed for mRNA of VEGF splice variants and receptors using real-time polymerase chain reaction or VEGF protein using enzyme-linked immunosorbent assay.

RESULTS

On p14, when retinas were only 70% vascularized in the model but fully vascularized in RA, VEGF₁₆₄ expression was threefold greater in the model compared to RA. On p18, intravitreous neovascularization was associated with a 5-fold increase in VEGF₁₆₄ mRNA in the model compared to RA. By analysis of variance, VEGF₁₆₄ and VEGFR2 mRNAs were up-regulated in association with increasing developmental age (P<.0001 for both comparisons) or exposure to the model compared to RA (P<.0001 and P=.0247, respectively), whereas increasing developmental age was associated only with up-regulated VEGF₁₂₀ (P=.0006), VEGF₁₈₈ (P=.0256), and VEGFR1 (P<.0001) mRNAs. VEGF protein increased significantly in the model and on p14 and p18 compared to RA (P<.0001).

CONCLUSIONS

The model mimics contemporary severe ROP in the United States unlike other models of oxygen-induced retinopathy. Compared to RA retinas, VEGF significantly increased in association with avascular retina and intravitreous neovascularization. A hypothesis is proposed that VEGF up-regulation plays a role in the development of both important features.

Moderation of calpain activity promotes neovascular integration and lumen formation during VEGF-induced pathological angiogenesis

Background

Successful neovascularization requires that sprouting endothelial cells (ECs) integrate to form new vascular networks. However, architecturally defective, poorly integrated vessels with blind ends are typical of pathological angiogenesis induced by vascular endothelial growth factor-A (VEGF), thereby limiting the utility of VEGF for therapeutic angiogenesis and aggravating ischemia-related pathologies. Here we investigated the possibility that over-exuberant calpain activity is responsible for aberrant VEGF neovessel architecture and integration. Calpains are a family of intracellular calcium-dependent, non-lysosomal cysteine proteases that regulate cellular functions through proteolysis of numerous substrates.

Methodology/Principal Findings

In a mouse skin model of VEGF-driven angiogenesis, retroviral transduction with dominant-negative (DN) calpain-I promoted neovessel integration and lumen formation, reduced blind ends, and improved vascular perfusion. Moderate doses of calpain inhibitor-I improved VEGF-driven angiogenesis similarly to DN calpain-I. Conversely, retroviral transduction with wild-type (WT) calpain-I abolished neovessel integration and lumen formation. In vitro, moderate suppression of calpain activity with DN calpain-I or calpain inhibitor-I increased the microtubule-stabilizing protein tau in endothelial cells (ECs), increased the average length of microtubules, increased actin cable length, and increased the interconnectivity of vascular cords. Conversely, WT calpain-I diminished tau, collapsed microtubules, disrupted actin cables, and inhibited integration of cord networks. Consistent with the critical importance of microtubules for vascular network integration, the microtubule-stabilizing agent taxol supported vascular cord integration whereas microtubule dissolution with nocodazole collapsed cord networks.

Conclusions/Significance

These findings implicate VEGF-induction of calpain activity and impairment of cytoskeletal dynamics in the failure of VEGF-induced neovessels to form and integrate properly. Accordingly, calpain represents an important target for rectifying key vascular defects associated with pathological angiogenesis and for improving therapeutic angiogenesis with VEGF.

A novel antiangiogenic peptide derived from hepatocyte growth factor inhibits neovascularization in vitro and in vivo

PURPOSE

To study the antiangiogenic activity of two small peptides (H-RN and H-FT) derived from the hepatocyte growth factor kringle 1 domain (HGF K1) using in vitro and in vivo assays.

METHODS

RF/6A rhesus macaque choroid-retina endothelial cells were used for in vitro studies. The inhibiting effect of two peptides on a vascular endothelial growth factor (VEGF)-stimulated cell proliferation, cell migration, and endothelial cell tube formation were investigated. For in vivo assays, the antiangiogenic activity of H-RN and H-FT in the chick chorioallantoic membrane model (CAM) and a mice oxygen-induced retinopathy model (OIR) were studied. A recombinant mouse VEGF-neutralizing antibody, bevacizumab, and a scrambled peptide were used as two control groups in separate studies.

RESULTS

H-RN effectively inhibited VEGF-stimulated RF/6A cell proliferation, migration, and tube formation on Matrigel™, while H-FT did not. H-RN was also able to inhibit angiogenesis when applied to the CAM, and had antineovascularization activity in the retinal neovascularization of a mouse OIR model when administrated as an intravitreous injection. The antiangiogenic activity of H-RN was not as strong as that of VEGF antibodies. The H-FT and scrambled peptide had no such activity.

CONCLUSIONS

H-RN, a new peptide derived from the HGF K1 domain, was shown to have antiangiogenic activity in vitro and in vivo. It may lead to new potential drug discoveries and the development of new treatments for pathological retinal angiogenesis.

Calpain inhibitors reduce retinal hypoxia in ischemic retinopathy by improving neovascular architecture and functional perfusion

In ischemic retinopathies, underlying hypoxia drives abnormal neovascularization that damages retina and causes blindness. The abnormal neovasculature is tortuous and leaky and fails to alleviate hypoxia, resulting in more pathological neovascularization and retinal damage. With an established model of ischemic retinopathy we found that calpain inhibitors, when administered in moderation, reduced architectural abnormalities, reduced vascular leakage, and most importantly reduced retinal hypoxia. Mechanistically, these calpain inhibitors improved stability and organization of the actin cytoskeleton in retinal endothelial cells undergoing capillary morphogenesis in vitro, and they similarly improved organization of actin cables within new blood vessels in vivo. Hypoxia induced calpain activity in retinal endothelial cells and severely disrupted the actin cytoskeleton, whereas calpain inhibitors preserved actin cables under hypoxic conditions. Collectively, these findings support the hypothesis that hyper-activation of calpains by hypoxia contributes to disruption of the retinal endothelial cell cytoskeleton, resulting in formation of neovessels that are defective both architecturally and functionally. Modest suppression of calpain activity with calpain inhibitors restores cytoskeletal architecture and promotes formation of a functional neovasculature, thereby reducing underlying hypoxia. In sharp contrast to "anti-angiogenesis" strategies that cannot restore normoxia and may aggravate hypoxia, the therapeutic strategy described here does not inhibit neovascularization. Instead, by improving the function of neovascularization to reduce underlying hypoxia, moderate calpain inhibition offers a method for alleviating retinal ischemia, thereby suggesting a new treatment paradigm based on improvement rather than inhibition of new blood vessel growth.

Moderate GSK-3β inhibition improves neovascular architecture, reduces vascular leakage, and reduces retinal hypoxia in a model of ischemic retinopathy

In ischemic retinopathies, unrelieved hypoxia induces the formation of architecturally abnormal, leaky blood vessels that damage retina and ultimately can cause blindness. Because these newly formed blood vessels are functionally defective, they fail to alleviate underlying hypoxia, resulting in more pathological neovascularization and more damage to retina. With an established model of ischemic retinopathy, we investigated inhibition of glycogen synthase kinase-3β (GSK-3β) as a means for improving the architecture and functionality of pathological blood vessels in retina. In vitro, hypoxia increased GSK-3β activity in retinal endothelial cells, reduced β-catenin, and correspondingly impaired integrity of cell/cell junctions. Conversely, GSK-3β inhibitors restored β-catenin, improved cell/cell junctions, and enhanced the formation of capillary cords in three-dimensional collagen matrix. In vivo, GSK-3β inhibitors, at appropriately moderate doses, strongly reduced abnormal vascular tufts, reduced abnormal vascular leakage, and improved vascular coverage and perfusion during the proliferative phase of ischemia-driven retinal neovascularization. Most importantly, these improvements in neovasculature were accompanied by marked reduction in retinal hypoxia, relative to controls. Thus, GSK-3β inhibitors offer a promising strategy for alleviating retinal hypoxia by correcting key vascular defects typically associated with ischemia-driven neovascularization.