Variable oxygen and retinal VEGF levels: correlation with incidence and severity of pathology in a rat model of oxygen-induced retinopathy

Retinopathy of Prematurity in Very Low Birthweight Neonates of Gestation Less Than 32 weeks in Malaysia

OBJECTIVES

To determine the screening rates and incidence of retinopathy of prematurity (ROP), and risk factors associated with ROP in very low birthweight (VLBW, <1500 g) neonates of gestation <32 wk admitted to neonatal intensive care units (NICUs) in a middle-income country.

METHODS

It was a retrospective cohort study of prospectively submitted data by 44 Malaysian NICUs participating in the Malaysian National Neonatal Registry. All VLBW neonates of gestation <32 wk born in 2015-2020 and survived to discharge were included.

RESULTS

Of 11768 survivors, 90.5% (n = 10436) had ROP screening; 16.1% (1685/10436) had ROP. ROP was significantly more common in neonates <28 wk gestation (extremely preterm, EPT) than ≥28 wk gestation (37.7% vs. 9.7%; p <0.001), and more common in those with birthweight <1000 g (extremely low birthweight, ELBW) than ≥1000 g (32.9% vs. 9.1%; p <0.001). Multiple logistic regression analysis showed that the significant independent factors associated with increased risk of ROP were ELBW, EPT, Indian ethnic group, vaginal delivery, mechanical ventilation >5 d, high frequency ventilation, total parenteral nutrition, late-onset sepsis, bronchopulmonary dysplasia, and intraventricular hemorrhage. Receiving oxygen therapy at birth was associated with significantly lower risk of ROP.

CONCLUSIONS

The incidence and severity of ROP increased with decreasing gestation and birthweight. Prolonged duration of oxygen therapy, infection, invasive respiratory support, and conditions commonly causing fluctuations of oxygenation were significant factors associated with increased risk of ROP. Receiving oxygen at birth did not increase risk.

Animal Models of Retinopathy of Prematurity: Advances and Metabolic Regulators

Retinopathy of prematurity (ROP) is a primary cause of visual impairment and blindness in premature newborns, characterized by vascular abnormalities in the developing retina, with microvascular alteration, neovascularization, and in the most severe cases retinal detachment. To elucidate the pathophysiology and develop therapeutics for ROP, several pre-clinical experimental models of ROP were developed in different species. Among them, the oxygen-induced retinopathy (OIR) mouse model has gained the most popularity and critically contributed to our current understanding of pathological retinal angiogenesis and the discovery of potential anti-angiogenic therapies. A deeper comprehension of molecular regulators of OIR such as hypoxia-inducible growth factors including vascular endothelial growth factors as primary perpetrators and other new metabolic modulators such as lipids and amino acids influencing pathological retinal angiogenesis is also emerging, indicating possible targets for treatment strategies. This review delves into the historical progressions that gave rise to the modern OIR models with a focus on the mouse model. It also reviews the fundamental principles of OIR, recent advances in its automated assessment, and a selected summary of metabolic investigation enabled by OIR models including amino acid transport and metabolism.

Pathophysiology of Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a complex disease involving development of the neural retina, ocular circulations, and other organ systems of the premature infant. The external stresses of the ex utero environment also influence the pathophysiology of ROP through interactions among retinal neural, vascular, and glial cells. There is variability among individual infants and presentations of the disease throughout the world, making ROP challenging to study. The methods used include representative animal models, cell culture, and clinical studies. This article describes the impact of maternal-fetal interactions; stresses that the preterm infant experiences; and biologic pathways of interest, including growth factor effects and cell-cell interactions, on the complex pathophysiology of ROP phenotypes in developed and emerging countries.

80 Years of vision: preventing blindness from retinopathy of prematurity

Retinopathy of prematurity (ROP) is one of the leading yet preventable causes of childhood blindness worldwide. The purpose of this review is to provide a practical template for observational and treatment methods in order to reduce the overall incidence of any ROP and to improve both short-term and long-term outcomes once Type 1 ROP (treatable ROP) develops.

Protective Effects and Molecular Signaling of n-3 Fatty Acids on Oxidative Stress and Inflammation in Retinal Diseases

Oxidative stress and inflammation play crucial roles in the development and progression of retinal diseases. Retinal damage by various etiologies can result in retinopathy of prematurity (ROP), diabetic retinopathy (DR), and age-related macular degeneration (AMD). n-3 fatty acids are essential fatty acids and are necessary for homeostasis. They are important retinal membrane components and are involved in energy storage. n-3 fatty acids also have antioxidant and anti-inflammatory properties, and their suppressive effects against ROP, DR, and AMD have been previously evaluated. α-linolenic acid (ALA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and their metabolites have been shown to alleviate retinal oxidative stress and inflammation involving various biological signaling pathways. In this review, we summarize the current understanding of the n-3 fatty acids effects on the mechanisms of these retinal diseases and how they exert their therapeutic effects, focusing on ALA, EPA, DHA, and their metabolites. This knowledge may provide new remedial strategies for n-3 fatty acids in the prevention and treatment of retinal diseases associated with oxidative stress and inflammation.

Enhancing Retinal Endothelial Glycolysis by Inhibiting UCP2 Promotes Physiologic Retinal Vascular Development in a Model of Retinopathy of Prematurity

Purpose

We address the hypothesis that uncoupling protein 2 (UCP2), a cellular glucose regulator, delays physiologic retinal vascular development (PRVD) by interfering with glucose uptake through glucose transporter 1 (Glut1).

Methods

In the rat 50/10 oxygen-induced retinopathy (OIR) model, retinal Glut1 and UCP2 were measured and compared to room air (RA)-raised pups at postnatal day 14 (p14). Pups in OIR and RA received intraperitoneal genipin, an UCP2 inhibitor, or control every other day from p3 until p13. Analyses at p14 included avascular/total retinal area (AVA), Western blots of retinal UCP2 and Glut1, and immunostaining of Glut1 in retinal cryosections. Intravitreal neovascular/total retinal area (IVNV) was analyzed at p18, and electroretinograms were performed at p26. Glut1 and phosphorylated VEGFR2 (p-VEGFR2), glucose uptake, adenosine triphosphate (ATP) production, and cell proliferation were measured in human retinal microvascular endothelial cells (hRMVECs) pretreated with genipin or transfected with UCP2siRNA, Glut1siRNA, or control siRNA when incubated with VEGF or PBS.

Results

At p14, OIR pups had increased AVA with decreased Glut1 and increased UCP2 in the retina compared to RA retinas. Intraperitoneal genipin increased retinal Glut1 and reduced AVA. Compared to control, treatment with genipin or knockdown of UCP2 significantly increased Glut1, glucose uptake, ATP production, VEGF-induced p-VEGFR2 and cell proliferation in hRMVECs. Knockdown of Glut1 inhibited VEGF-induced p-VEGFR2. Genipin-treated OIR pups with decreased AVA at p14 had reduced IVNV at p18 and increased amplitudes in a- and b-waves at p26.

Conclusions

Extending PRVD by increasing retinal endothelial glucose uptake may represent a strategy to prevent severe retinopathy of prematurity and vision loss.

Intermittent hypoxemia and oxidative stress in preterm infants

Intermittent hypoxemia events (IH) are common in extremely preterm infants and are associated with many poor outcomes including retinopathy or prematurity, wheezing, bronchopulmonary dysplasia, cognitive or language delays and motor impairment. More recent data in animal and rodent models have suggested that specific patterns of IH may increase the risk for morbidity. The pathway by which these high risk patterns of IH initiate a pathological cascade is unknown but animal models suggest that oxidative stress may play a role. This review describes early postnatal patterns of IH in preterm infants, their relationship with morbidity, oxidative stress biomarkers relevant to the newborn infant and the relationship between IH and reactive oxygen species.

Therapeutic Effects of a Novel Phenylphthalimide Analog for Corneal Neovascularization and Retinal Vascular Leakage

Purpose

Neovascularization (NV) and retinal vascular leakage are major causes of impaired vision in ocular diseases. The purpose of this study was to identify novel phenylphthalimide analogs with therapeutic effects on NV and vascular leakage and to explore the mechanism of action.

Methods

Antiangiogenic activities of novel phenylphthalimide analogs were assessed in vitro by using VEGF ELISA and endothelial cell proliferation assay. Their efficacies on retinal vascular leakage were evaluated using rat models of oxygen-induced retinopathy (OIR) and streptozotocin (STZ)-induced diabetes. The in vivo antiangiogenic activity was evaluated using topical administration in the alkali burn-induced corneal NV model. The expression of VEGF and intercellular adhesion molecule-1 (ICAM-1) were measured using ELISA.

Results

Thalidomide and three novel analogs all showed inhibitory effects on endothelial cell proliferation and VEGF expression in vitro. Through intravitreal injection, all of the compounds reduced retinal vascular leakage in the OIR and STZ-induced diabetic models. Among these compounds, (2,6-diisopropylphenyl)-5-amino-1H-isoindole-1,3-dione (DAID) displayed the most potent efficacy and reduced retinal vascular leakage in a dose-dependent manner in both the OIR and STZ-diabetes models. Topical administration of DAID also inhibited alkali burn-induced corneal NV. Furthermore, DAID attenuated the overexpression of VEGF and ICAM-1 in the retina of the OIR model. Intravitreal injection of DAID did not result in any detectable side effects, as shown by electroretinogram and retinal histological analysis.

Conclusions

DAID is a novel phenylphthalimide analog with potent effects on NV and retinal vascular leakage through downregulation of VEGF and inflammatory factors and has therapeutic potential.

MnTBAP or Catalase Is More Protective against Oxidative Stress in Human Retinal Endothelial Cells Exposed to Intermittent Hypoxia than Their Co-Administration (EUK-134)

Retinopathy of prematurity is a blinding disease that affects extremely low gestational age neonates. Its etiology is due to extrauterinehyperoxia in an immature antioxidant system culminating as oxidative stress on the retina. Our aim is to elucidate the role of pharmacological antioxidants in modulating the biochemical and molecular response of human retinal microvascular endothelial cells (HRECs) exposed to oxidative stress. HRECs were treated with MnTBAP [a superoxide dismutase (SOD) mimetic], catalase, EUK-134 (SOD + catalase), or saline prior to exposure to normoxia (Nx), hyperoxia (Hx), or intermittent hypoxia (IH). Media levels of SOD, catalase, glutathione peroxidase (GPx), 8-isoPGF2α, and H2O2; cellular SOD and catalase; cellular function (migration and tube formation); and antioxidant gene expression were assessed. Pharmacological antioxidants had delayed suppressive effect on 8-isoPGF2α. MnTBAP and catalase were more effective for H2O2 scavenging in the media than co-administration in the form of EUK-134. A delayed response was noted in SOD and catalase media activity in MnTBAP- and catalase-treated cells, respectively in 50% and IH. MnTBAP had progressively increased media GPx in all oxygen conditions. Antioxidants resulted in normal, but more abundant tubulogenesis in IH and Hx. The distinct temporal response to oxidative stress reflected the respective antioxidant's potency and catalytic properties. The cell permeability of the antioxidants limited the ability to scavenge intracellular free radicals. The results support that MnTBAP or catalase may be more effective for the prevention of oxidative stress in oxygen-induced retinopathy.

Cnidium officinale extract and butylidenephthalide inhibits retinal neovascularization in vitro and in vivo

BACKGROUND

Retinal neovascularization, which is the pathological growth of new blood vessels, is associated with retinopathy of prematurity, neovascular age-related macular degeneration, diabetic retinopathy and retinal vein occlusion. In this study, we evaluated the effect of an extract of Cnidium officinale Makino (COE) and its bioactive compound, butylidenephthalide (BP), on the migration and tube formation of human umbilical vein endothelial cells (HUVECs), and on retinal pathogenic neovascularization in the oxygen-induced retinopathy (OIR) mouse model.

METHOD

The HUVECs were incubated with COE and BP (0.1-10 μg/ml). The mice were exposed to 75 % oxygen for 5 days starting on the 7(th) postnatal day (P7-P12). Then, the mice were returned to room air and intraperitoneally injected with COE (100 mg/kg) and BP (5 mg/kg) once per day for 5 days (P12-P16). On P17, we measured retinal neovascularization and analyzed the angiogenesis-related proteins expression using protein arrays.

RESULTS

COE and BP inhibit the HUVECs migration and the tube formation in a dose-dependent manner. In addition, COE significantly decreased retinal neovascularization in the OIR mice. COE reduced the expression levels of AREG, ANG, DLL4, Endostatin, IGFBP-2 and VEGF. Additionally, BP also inhibited the retinal neovascularization and down-regulated the expression of AREG, ANG, DLL4 and VEGF.

CONCLUSION

These results suggest that COE and BP exerts antiangiogenic effects on retinal neovascularization by inhibiting the expression of AREG, ANG, DLL4 and VEGF, indicating that antiangiogenic activities of COE may be in part due to its bioactive compound, BP.

Serum concentrations of vascular endothelial growth factor in relation to retinopathy of prematurity

BACKGROUND

The role of vascular endothelial growth factor (VEGF) in the pathogenesis of retinopathy of prematurity (ROP) has been clearly established. However, little is known about temporal changes in circulating VEGF concentrations in the preterm infant. The objective was to determine the longitudinal serum concentrations of VEGF in relation to ROP.

METHODS

This study included 52 infants born at <31 wk gestational age (non-ROP n = 33, nonproliferative ROP n = 10, treated for ROP n = 9). VEGF concentrations were analyzed in blood samples collected at birth, at 3 d postnatal age, and then weekly until at least a gestational age of 35 wk.

RESULTS

VEGF concentrations at birth did not differ between groups, independent of later ROP status. In contrast, VEGF serum concentrations were significantly higher at first detection of ROP in infants who were later treated for ROP compared to infants without ROP. At the time of laser therapy, serum VEGF concentrations did not differ between groups.

CONCLUSION

Circulatory concentrations of VEGF, in infants who later developed severe ROP, were elevated at the time when ROP first was detected but not at the time when current treatment most often occurred. This supports the need for further studies of circulating VEGF in relation to the timing of ROP treatment.

Inner retinal oxygen metabolism in the 50/10 oxygen-induced retinopathy model

Retinopathy of prematurity (ROP) represents a major cause of childhood vision loss worldwide. The 50/10 oxygen-induced retinopathy (OIR) model mimics the findings of ROP, including peripheral vascular attenuation and neovascularization. The oxygen metabolism of the inner retina has not been previously explored in this model. Using visible-light optical coherence tomography (vis-OCT), we measured the oxygen saturation of hemoglobin and blood flow within inner retinal vessels, enabling us to compute the inner retinal oxygen delivery (irDO₂) and metabolic rate of oxygen (irMRO₂). We compared these measurements between age-matched room-air controls and rats with 50/10 OIR on postnatal day 18. To account for a 61% decrease in the irDO₂ in the OIR group, we found an overall statistically significant decrease in retinal vascular density affecting the superficial and deep retinal vascular capillary networks in rats with OIR compared to controls. Furthermore, matching the reduced irDO₂, we found a 59% decrease in irMRO₂, which we correlated with a statistically significant reduction in retinal thickness in the OIR group, suggesting that the decreased irMRO₂ was due to decreased neuronal oxygen utilization. By exploring these biological and metabolic changes in great detail, our study provides an improved understanding of the pathophysiology of OIR model.

The role of cytochrome P450 epoxygenases in retinal angiogenesis

PURPOSE

The purpose of this study was to investigate the role(s) of cytochrome P450 epoxygenases (CYPs) and their products, the epoxyeicosatrienoic acids (EETs), in hypoxia-induced VEGF production and pathologic retinal angiogenesis.

METHODS

Human retinal astrocytes, Müller cells, and retinal microvascular endothelial cells (HRMEC) were exposed to hypoxia, and relative CYP2C expression was measured by RT-PCR. Astrocyte and Müller cell VEGF production was measured by ELISA after exposure to hypoxia and treatment with the general CYP inhibitor, SKF-525a. Human retinal microvascular endothelial cells were treated with the CYP product, 11,12-epoxyeicosatrienoic acid [EET], or SKF-525a in the presence or absence of VEGF. Proliferation of HRMEC and tube formation were assayed. Oxygen-induced retinopathy (OIR) was induced in newborn rats. Retinal CYP2C11 and CYP2C23 expression were measured by RT-PCR. The OIR rats received SKF-525a by intravitreal injection and preretinal neovascularization (NV) was quantified. Retinal VEGF protein levels were measured by ELISA.

RESULTS

Human retinal astrocytes were the only cells to exhibit significant induction of CYP2C8 and CYP2C9 mRNA expression by hypoxia. Astrocytes, but not Müller cells, exhibited reduced hypoxia-induced VEGF production when treated with SKF-525a. 11,12-EET induced HRMEC proliferation and tube formation, and SKF-525a inhibited VEGF-induced proliferation. Oxygen-induced retinopathy induced expression of CYP2C23, but had no effect on CYP2C11. SKF-525a inhibited retinal NV and reduced retinal VEGF levels in OIR rats.

CONCLUSIONS

The CYP-derived 11,12-EET may exhibit a proangiogenic biological function in the retina following stimulation by hypoxia in astrocytes. Inhibition of CYP may provide a rational therapy against retinal NV, because it can reduce VEGF production and VEGF-induced angiogenic responses in endothelial cells.

Mitigation of oxygen-induced retinopathy in α2β1 integrin-deficient mice

PURPOSE

The α2β1 integrin plays an important but complex role in angiogenesis and vasculopathies. Published GWAS studies established a correlation between genetic polymorphisms of the α2β1 integrin gene and incidence of diabetic retinopathy. Recent studies indicated that α2-null mice demonstrate superior vascularization in both the wound and diabetic microenvironments. The goal of this study was to determine whether the vasculoprotective effects of α2-integrin deficiency extended to the retina, using the oxygen-induced retinopathy (OIR) model for retinopathy of prematurity (ROP).

METHODS

In the OIR model, wild-type (WT) and α2-null mice were exposed to 75% oxygen for 5 days (postnatal day [P] 7 to P12) and subsequently returned to room air for 6 days (P12-P18). Retinas were collected at postnatal day 7, day 13, and day 18 and examined via hematoxylin and eosin and Lectin staining. Retinas were analyzed for retinal vascular area, neovascularization, VEGF expression, and Müller cell activation. Primary Müller cell cultures from WT and α2-null mice were isolated and analyzed for hypoxia-induced VEGF-A expression.

RESULTS

In the retina, the α2β1 integrin was minimally expressed in endothelial cells and strongly expressed in activated Müller cells. Isolated α2-null primary Müller cells demonstrated decreased hypoxia-induced VEGF-A expression. In the OIR model, α2-null mice displayed reduced hyperoxia-induced vaso-attenuation, reduced pathological retinal neovascularization, and decreased VEGF expression as compared to WT counterparts.

CONCLUSIONS

Our data suggest that the α2β1 integrin contributes to the pathogenesis of retinopathy. We describe a newly identified role for α2β1 integrin in mediating hypoxia-induced Müller cell VEGF-A production.

Quantitative analyses of retinal vascular area and density after different methods to reduce VEGF in a rat model of retinopathy of prematurity

PURPOSE

Targeted inhibition of Müller cell (MC)-produced VEGF or broad inhibition of VEGF with an intravitreal anti-VEGF antibody reduces intravitreal neovascularization in a rat model of retinopathy of prematurity (ROP). In this study, we compared the effects of these two approaches on retinal vascular development and capillary density in the inner and deep plexi in the rat ROP model.

METHODS

In the rat model of ROP, pups received 1 μL of (1) subretinal lentivector-driven short hairpin RNA (shRNA) to knockdown MC-VEGFA (VEGFA.shRNA) or control luciferase shRNA, or (2) intravitreal anti-VEGF antibody (anti-VEGF) or control isotype goat immunoglobulin G (IgG). Analyses of lectin-stained flat mounts at postnatal day 18 (p18) included: vascular/total retinal areas (retinal vascular coverage) and pixels of fluorescence/total retinal area (capillary density) of the inner and deep plexi determined with the Syncroscan microscope, and angles between cleavage planes of mitotic vascular figures labeled with anti-phosphohistone H3 and vessel length.

RESULTS

Retinal vascular coverage and density increased in both plexi between p8 and p18 in room air (RA) pups. Compared with RA, p18 ROP pups had reduced vascular coverage and density of both plexi. Compared with respective controls, VEGFA.shRNA treatment significantly increased vascular density in the deep plexus, whereas anti-VEGF reduced vascular density in the inner and deep plexi. Vascular endothelial growth factor-A.shRNA caused more cleavage angles predicting vessel elongation and fewer mitotic figures, whereas anti-VEGF treatment led to patterns of pathologic angiogenesis.

CONCLUSIONS

Targeted treatment with lentivector-driven VEGFA.shRNA permitted physiologic vascularization of the vascular plexi and restored normal orientation of dividing vascular cells, suggesting that regulation of VEGF signaling by targeted treatment may be beneficial.

SRPK1 inhibition modulates VEGF splicing to reduce pathological neovascularization in a rat model of retinopathy of prematurity

PURPOSE

We tested the hypothesis that recombinant human VEGF-A165b and the serine arginine protein kinase (SRPK) inhibitor, SRPIN340, which controls splicing of the VEGF-A pre-mRNA, prevent neovascularization in a rodent model of retinopathy of prematurity (ROP).

METHODS

In the 50/10 oxygen-induced retinopathy (50/10 OIR) model that exposes newborn rats to repeated cycles of 24 hours of 50% oxygen alternating with 24 hours of 10% oxygen, pups received intraocular injections of SRPIN340, vehicle, VEGF165b, anti-VEGF antibody, or saline. Whole mounts of retinas were prepared for isolectin immunohistochemistry, and preretinal or intravitreal neovascularization (PRNV) determined by clock hour analysis.

RESULTS

The anti-VEGF antibody (P < 0.04), rhVEGF165b (P < 0.001), and SRPIN340 (P < 0.05) significantly reduced PRNV compared with control eyes. SRPIN340 reduced the expression of proangiogenic VEGF165 without affecting VEGF165b expression.

CONCLUSIONS

These results suggest that splicing regulation through selective downregulation of proangiogenic VEGF isoforms (via SRPK1 inhibition) or competitive inhibition of VEGF signaling by rhVEGF165b has the potential to be an effective alternative to potential cyto- and neurotoxic anti-VEGF agents in the treatment of pathological neovascularization in the eye.

Apelin in epiretinal fibrovascular membranes of patients with retinopathy of prematurity and the changes after intravitreal bevacizumab

PURPOSE

Apelin, a novel cytokine, was reported to regulate angiogenesis. The aim of this study was to investigate the correlation between apelin and retinopathy of prematurity (ROP), between apelin and the other known angiogenic cytokines including vascular endothelial growth factor (VEGF) and hypoxia-induced factor-1a (HIF-1a).

METHODS

The study included 36 ROP patients who underwent vitrectomy. Previous intravitreal bevacizumab (IVB) was performed in 18 patients (IVB group). The other ROP eyes belonged to non-IVB group. Surgical removed membranes from 10 patients who underwent vitrectomy for idiopathic preretinal membranes or macular hole served as control. The expression of apelin and angiotensin-1-like receptor (APJ) in the excised membranes was examined by fluorescence immunostaining. Quantitative reverse transcription polymerase chain reaction was used to examine the expression of apelin, VEGF, and HIF-1a mRNA.

RESULTS

The density of neovascularization in fibrovascular membranes was significantly correlated with the age and postconception age of ROP patients (r = -0.94, P < 0.01; r = -0.83, P = 0.04). In the non-IVB group, colocalization of the endothelial marker CD31 with the marker for apelin and colocalization of CD31 and APJ were observed. In the IVB group, staining of apelin and APJ were positive, whereas the staining of CD31 was negative. Expression of apelin mRNA, HIF-1a mRNA, and VEGF mRNA were significantly higher in ROP membranes than idiopathic epiretinal membranes. Expression of apelin mRNA and VEGF mRNA significantly correlate with HIF-1a mRNA (r = 0.64, P = 0.04; and r = 0.96, P < 0.01, respectively), but the expression of apelin mRNA did not significantly correlate with VEGF mRNA (r = 0.491, P = 0.15).

CONCLUSION

The apelin/APJ system may be involved in the development of retinal neovascularization of ROP. The present results showed that the effect of apelin was related to HIF-1a but independent with VEGF.

Genetic polymorphisms of vascular endothelial growth factor and risk for retinopathy of prematurity in South of Iran

Retinopathy of prematurity (ROP) is a multifactorial disease, that cause visual impairment in premature children. The exact pathogenesis and etiology of ROP is unknown and genetic susceptibility is considered as risk factor. Vascular endothelial growth factor (VEGF) plays a major role in retinal neovascularization and subsequently retinal detachment. VEGF polymorphism is associated with proliferative ROP in some studies. We examined the possible association of the VEGF gene polymorphisms with ROP in preterm infants in south of Iran. A total of 111 preterm infants were examined by ophthalmologist and after that were genotyped. Genotyping of the VEGF +405 (rs2010963) and VEGF +936 (rs3025039) was done by the polymerase chain reaction and restriction fragment length polymorphism methods. The frequency of VEGF alleles, genotypes and haplotype distribution were compared between groups. The patients were divided in three groups: 66 to the normal group (normal fundoscopy), and 45 to the ROP group; 30 infants were not treated with Lasertherapy (Regressive group) and 15 treated with Lasertherapy. The frequency of VEGF +405 and VEGF +936 G/C genotypes as well as allele frequencies was not different between groups. No significant difference was found between ROP with treatment and ROP without lasertherapy. Our report indicate that there is no association between the carrier states of gene polymorphisms VEGF +405, VEGF +936 and progression or spontaneous regression of ROP in preterm infants in Iranian population. However, it should be considered that angiogenesis is a complex process and genetic factors in addition to environmental factors are contributed in this pathway.

The relationship between patterns of intermittent hypoxia and retinopathy of prematurity in preterm infants

BACKGROUND

We have previously shown an increased incidence of intermittent hypoxemia (IH) events in preterm infants with severe retinopathy of prematurity (ROP). Animal models suggest that patterns of IH events may play a role in ROP severity as well. We hypothesize that specific IH event patterns are associated with ROP in preterm infants.

METHODS

Variability in IH event duration, severity, and the time interval between IH events (≤80%, ≥10 s, and ≤3 min) along with the frequency spectrum of the oxygen saturation (SpO2) waveform were assessed.

RESULTS

Severe ROP was associated with (i) an increased mean and SD of the duration of IH event (P < 0.005), (ii) more variability (histogram entropy) of the time interval between IH events (P < 0.005), (iii) a higher IH nadir (P < 0.05), (iv) a time interval between IH events of 1-20 min (P < 0.05), and (v) increased spectral power in the range of 0.002-0.008 Hz (P < 0.05), corresponding to SpO2 waveform oscillations of 2-8 min in duration. Spectral differences were detected as early as 14 d of life.

CONCLUSION

Severe ROP was associated with more variable, longer, and less severe IH events. Identification of specific spectral components in the SpO2 waveform may assist in early identification of infants at risk for severe ROP.

Perfluorocarbon Emulsions Prevent Hypoxia of Pancreatic β-Cells

As oxygen carriers, perfluorocarbon emulsions might be useful to decrease hypoxia of pancreatic islets before transplantation. However, their hydrophobicity prevents their homogenisation in culture medium. To increase the surface of contact between islets and Perfluorooctyl bromide (PFOB), and consequently oxygen delivery, we tested effect of a PFOB emulsion in culture medium on β-cell lines and rat pancreatic islets. RINm5F β-cell line or pancreatic rat islets were incubated for 3 days in the presence of PFOB emulsion in media (3.5% w/v). Preoxygenation of the medium was performed before culture. Cell viability was assessed by apoptotic markers (Bax and Bcl-2) and by staining (fluoresceine diacetate and propidium iodide). β-Cell functionality was determined by insulin release during a glucose stimulation test and. Hypoxia markers, HIF-1α and VEGF, were studied at days 1 and 3 using RT-PCR, Western blotting, and ELISA. PFOB emulsions preserved viability and functionality of RINm5F cells with a decrease of HIF-1α and VEGF expression. Islets viability was preserved during 3 days of culture. Secretion of VEGF was higher in untreated control (0.09 ± 0.041 μg VEGF/mg total protein) than in PFOB emulsion incubated islets (0.02 ± 0.19 μg VEGF/mg total protein, n = 4, p < 0.05) at day 1. At day 3, VEGF secretion was increased as compared to day 1 in control (0.23 ± 0.04 μg VEGF/mg total protein) but it was imbalance by the presence of PFOB emulsion (0.09 ± 0.03 μg VEGF/mg total protein, n = 5, p < 0.05). While insulin secretion was maintained in response to a glucose stimulation test until day 3 when islets were incubated in the presence of PFOB emulsion preoxygenated (0.81 ± 0.16 at day 1 vs. 0.75 ± 0.24 at day 3), the ability to secrete insulin in the presence of high glucose concentration was lost in islets controls (0.51 ± 0.18 at day 1 vs. 0.21 ± 0.13 at day 3). Atmospheric oxygen delivery by PFOB emulsion might be sufficient to decrease islets hypoxia. However, to improve islets functionality, overoxygenation is needed. Finally, maintenance of islet viability and functionality for several days after isolation could improve the outcome of islets transplantation.

Aberrant kinetics of bone marrow-derived endothelial progenitor cells in the murine oxygen-induced retinopathy model

PURPOSE

Retinopathy of prematurity (ROP) causes serious blindness because of the vasculopathy that results from the abnormal oxygen dynamics. However, the systemic kinetics of bone marrow-derived endothelial progenitor cells (BM-derived EPCs) during the "postnatal vasculogenesis " of ROP has yet to be elucidated. Thus, the authors investigated the kinetics of BM-derived EPCs using a murine oxygen-induced retinopathy (OIR) model.

METHODS

OIR was induced in C57BL/6J mice by continual aeration with 75% oxygen from postnatal day (P) 7 to P12 that afterward returned to normal room air.

RESULTS

The frequency of circulating EPCs (Sca-1(+)/c-Kit(+) cells in blood) in an OIR model estimated by FACS decreased immediately after the hyperoxic phase (P12) and then increased at the hypoxic phase (P17) compared with control. Further, EPC colony-forming assay of BM-Lin(-)/Sca-1(+) (BM-LS) cells exhibited a conversion from the predominant primitive EPC colony production at P12 to the definitive EPC colony at P17. In the OIR retinas of BM-transplanted mice with BM-LS cells of EGFP transgenic mice, there was less incorporation of GFP(+) cells into vascular structures at P12, whereas there was a drastic recruitment into the "tufts " and for the intact vasculature at P17. Moreover, the definitive EPC colony cells intravitreally injected into OIR significantly abrogated pathologic versus primitive vascular growth.

CONCLUSIONS

Taken together, these findings propose that the deviation of functional bioactivities of BM-derived EPCs contributing to intact vascular development under the abnormal oxygen dynamics may provide important mechanistic insight into pathologic vascular development in ROP.

Identification of a novel inhibitor of the canonical Wnt pathway

Wnt signaling is known to regulate multiple processes including angiogenesis, inflammation, and fibrosis. Here, we identified a novel inhibitor of the Wnt pathway, pigment epithelium-derived factor (PEDF), a multifunctional serine proteinase inhibitor. Both overexpression of PEDF in transgenic mice and administration of PEDF protein attenuated Wnt signaling induced by retinal ischemia. Furthermore, PEDF knockdown by small interfering RNA (siRNA) and PEDF knockout in PEDF(-/-) mice induced activation of Wnt signaling. PEDF bound to LRP6, a Wnt coreceptor, with high affinity (K(d) [dissociation constant] of 3.7 nM) and blocked the Wnt signaling induced by Wnt ligand. The physical interaction of PEDF with LRP6 was confirmed by a coprecipitation assay, which showed that PEDF bound to LRP6 at the E1E2 domain. In addition, binding of PEDF to LRP6 blocked Wnt ligand-induced LRP6-Frizzled receptor dimerization, an essential step in Wnt signaling. These results suggest that PEDF is an endogenous antagonist of LRP6, and blocking Wnt signaling may represent a novel mechanism for its protective effects against diabetic retinopathy.

Biomolecular effects of JB1 (an IGF-I peptide analog) in a rat model of oxygen-induced retinopathy

Low-serum IGF-I levels at birth is a risk factor for the development of retinopathy of prematurity in extremely LBW infants. We tested the hypothesis that JB1 (an IGF-I analog) prevents oxygen-induced retinopathy in our rat model. Neonatal rats were exposed to 50% oxygen with brief, clustered, hypoxic (12%) episodes from birth to P14. The pups were treated with s.c. injections of 1) JB1 (1 μg/d) on P1, P2, and P3 (JB1x3); 2) JB1 (1 μg/d) on alternate days from P1 to P13 (JB1x7); or 3) equivalent volume saline. Control littermates were raised in room air (RA) with all conditions identical except for inspired O2. Groups were analyzed after hyperoxia/hypoxia (H/H) cycling at P14 or allowed to recover in RA until P21. Systemic and ocular VEGF, soluble VEGFR-1, and IGF-I; retinal vasculature; and gene profile of retinal angiogenesis were assessed. JB1x3 was more effective with associated increases in sVEGFR-1 and decreased retinal pathologies than JB1x7. We conclude that early short-term exposure to systemic JB1 treatment normalizes retinal abnormalities seen with H/H cycling, an effect that may involve sVEGFR-1.

Oxygen saturation in premature infants at risk for threshold retinopathy of prematurity

PURPOSE

We aimed to determine if oxygen saturation, desaturations, and saturation variability play a role in progression of retinopathy of prematurity (ROP) and need for laser treatment.

METHODS

This was a retrospective case-control study. We performed chart review of premature infants in a university hospital neonatal intensive care unit consecutively examined for ROP between May 2000 and December 2001. We compared birthweight, postmenstrual age, and oxygen saturation for 3 weeks before laser treatment for threshold ROP in group 1 (n=19) (average weight at treatment 2508 grams) and group 2 (n=18) before they reached 2500 grams. Outcome measures were retinopathy progression and need for treatment.

RESULTS

Adjusting for birthweight and postmenstrual age, known predictors of ROP progression, we found that babies requiring laser treatment (group 1) had lower average daily oxygen saturation levels in the study period, significantly on 5/20 days (25%). These babies had saturations below 95% on 18/20 days (90%). Babies not requiring laser (group 2) had saturations below 95% on 2/20 days (10%). The last day on which pretreatment saturations differed significantly was 2 days before laser. Group 1 had more desaturations below 80% (6.0±3.2) than group 2 (3.2±1.2), p=0.0002 (independent samples t tests). Saturations varied more for individual group 1 infants.

CONCLUSIONS

Decreased oxygen saturation as early as 3 weeks and as late as 2 days before laser, increased number of desaturations, and saturation variability were seen in babies eventually requiring laser treatment for ROP.

Mediators of ocular angiogenesis

Angiogenesis is the formation of new blood vessels from pre-existing vasculature. Pathologic angiogenesis in the eye can lead to severe visual impairment. In our review, we discuss the roles of both pro-angiogenic and anti-angiogenic molecular players in corneal angiogenesis, proliferative diabetic retinopathy, exudative macular degeneration and retinopathy of prematurity, highlighting novel targets that have emerged over the past decade.

Effect of hyperoxic resuscitation on propensity of germinal matrix haemorrhage and cerebral injury

AIMS

Intraventricular haemorrhage (IVH) and cerebral injury are major neurological disorders of premature infants. The effect of hyperoxic resuscitation on the occurrence of IVH and cerebral injury is elusive. Therefore, we asked whether hyperoxia during neonatal resuscitation increased the incidence and severity of IVH and cerebral injury in premature newborns.

METHODS

Premature rabbit pups, delivered by C-section, were sequentially assigned to receive 100%, 40% or 21% oxygen for 15 or 60 min at birth. The pups were treated with intraperitoneal glycerol at 24-h postnatal age to determine the incidence and severity of glycerol-induced IVH. Vascular endothelial growth factor and angiopoietin-2 genes and protein expression, endothelial proliferation as well as free radical levels and antioxidants were assessed in the germinal matrix, white matter and cortex of pups exposed to 100% oxygen and to 21% oxygen.

RESULTS

Exposure with 100% oxygen for 1 h did not adversely exacerbate the incidence of glycerol-induced IVH in premature rabbit pups. Compared with room air, 100% oxygen enhanced mRNA expression of both vascular endothelial growth factor and angiopoietin-2 as well as reactive oxygen species levels in the germinal matrix. Hyperoxia did not affect endothelial proliferation, apoptosis or neuronal degeneration in the forebrain.

CONCLUSION

Our data suggest that 100% oxygen exposure for 1 h does not increase the risk of IVH or cerebral injury in premature rabbit pups. Although extrapolating rabbit neural developmental data into humans has obvious limitations, we speculate that hyperoxia of short duration at birth in premature infants may not result in major neurological adverse effects.

The effects of nepafenac and amfenac on retinal angiogenesis

PURPOSE

Nepafenac is a potent NSAID that rapidly penetrates the eye following topical ocular administration. In the eye, nepafenac is converted to amfenac, which has unique time-dependent inhibitory properties for COX-1 and COX-2. The purpose of the present study was to investigate the capacity of amfenac to inhibit discrete aspects of the angiogenic cascade in vitro, and to test the efficacy of amfenac and nepafenac in vivo, using the rat OIR model.

METHODS

Müller cells were treated with amfenac, celecoxib (COX-2), or SC-560 (COX-1), and hypoxia-induced VEGF and PGE(2) assessed. Endothelial cells were treated with amfenac, celecoxib, or SC-560, and VEGF-induced proliferation and tube formation assessed. Rat pups were subjected to OIR, received intravitreal injections of amfenac, celecoxib, or SC-560, and neovascularization (NV), prostanoid production, and VEGF assessed. Other OIR-exposed pups were treated with topical nepafenac, ketorolac, or diclofenac, and inhibition of NV assessed.

RESULTS

Amfenac treatment failed to inhibit hypoxia-induced VEGF production. Amfenac treatment significantly inhibited VEGF-induced tube formation and proliferation by EC. Amfenac treatment significantly reduced retinal prostanoid production and NV in OIR. Nepafenac treatment significantly reduced retinal NV in OIR; ketorolac and diclofenac had no effect.

CONCLUSIONS

Nepafenac and amfenac inhibit OIR more effectively than the commercially available topical and injectable NSAIDs used in this study. Our data suggests there are COX-dependent and COX-independent mechanisms by which amfenac inhibits OIR. Because it is bioavailable to the posterior segment following topical delivery, nepafenac appears to be a promising advancement in the development of therapies for neovascular eye diseases.

The effects of oxygen stresses on the development of features of severe retinopathy of prematurity: knowledge from the 50/10 OIR model

The objective of this study is to determine growth factor expression and activation of signaling pathways associated with intravitreous neovascularization and peripheral avascular retina using a model of retinopathy of prematurity (ROP) relevant to today with oxygen monitoring in neonatal units. Studies using 50/10 oxygen-induced retinopathy (OIR) and 50/10 OIR+SO models were reviewed. Repeated fluctuations in oxygen increased retinal vascular endothelial growth factor (VEGF) even while peripheral avascular retina persisted and prior to the development of intravitreous neovascularization. Repeated fluctuations in oxygen increased VEGF(164) expression but not VEGF(120). Neutralizing VEGF bioactivity significantly reduced intravitreous neovascularization and arteriolar tortuosity without interfering with ongoing retinal vascularization. Repeated oxygen fluctuations led to retinal hypoxia and increased reactive oxygen species (ROS). Inhibiting ROS with NADPH oxidase inhibitor, apocynin, reduced avascular retina by interfering with apoptosis. Supplemental oxygen reduced retinal VEGF concentration and exacerbated NADPH oxidase activation to contribute to intravitreous neovascularization through activation of the JAK/STAT pathway. Oxygen stresses relevant to those experienced by preterm infants today trigger signaling of different pathways to cause avascular retina and intravitreous neovascularization. Increased signaling of VEGF appears important to the development of both avascular retina and intravitreous neovascularization.

Maintaining retinal astrocytes normalizes revascularization and prevents vascular pathology associated with oxygen-induced retinopathy

Astrocytes are well known modulators of normal developmental retinal vascularization. However, relatively little is known about the role of glial cells during pathological retinal neovascularization (NV), a leading contributor to vision loss in industrialized nations. We demonstrate that the loss of astrocytes and microglia directly correlates with the development of pathological NV in a mouse model of oxygen-induced retinopathy (OIR). These two distinct glial cell populations were found to have cooperative survival effects in vitro and in vivo. The intravitreal injection of myeloid progenitor cells, astrocytes, or astrocyte-conditioned media rescued endogenous astrocytes from degeneration that normally occurs within the hypoxic, vaso-obliterated retina following return to normoxia. Protection of the retinal astrocytes and microglia was directly correlated with accelerated revascularization of the normal retinal plexuses and reduction of pathological intravitreal NV normally associated with OIR. Using astrocyte-conditioned media, several factors were identified that may contribute to the observed astrocytic protection and subsequent normalization of the retinal vasculature, including vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF). Injection of VEGF or bFGF at specific doses rescued the retinas from developing OIR-associated pathology, an effect that was also preceded by protection of endogenous glia from hypoxia-induced degeneration. Together, these data suggest that vascular-associated glia are also required for normalized revascularization of the hypoxic retina. Methods developed to target and protect glial cells may provide a novel strategy by which normalized revascularization can be promoted and the consequences of abnormal NV in retinal vascular diseases can be prevented.

The development of the rat model of retinopathy of prematurity

Retinopathy of prematurity (ROP) is a potentially blinding disease affecting premature infants. ROP is characterized by pathological ocular angiogenesis or retinal neovascularization (NV). Models of ROP have yielded much of what is currently known about physiological and pathological blood vessel growth in the retina. The rat provides a particularly attractive and cost effective model of ROP. The rat model of ROP consistently produces a robust pattern of NV, similar to that seen in humans. This model has been used to study gross aspects of angiogenesis. More recently, it has been used to identify and therapeutically target specific genes and molecular mechanisms involved in the angiogenic cascade. As angiogenesis occurs as a complication of many diseases, knowledge gained from these studies has the potential to impact nonocular angiogenic conditions. This article provides historical perspective on the development and use of the rat model of ROP. Key findings generated through the use of this model are also summarized.

Combustion smoke exposure induces up-regulated expression of vascular endothelial growth factor, aquaporin 4, nitric oxide synthases and vascular permeability in the retina of adult rats

Retinal cells respond to various experimental stimuli including hypoxia, yet it remains to be investigated whether they react to smoke inhalation. We show here that retinal cells in rats, notably the ganglion cells, Müller cells, astrocytes and blood vessels responded vigorously to a smoke challenge. The major changes included up-regulated expression of vascular endothelial growth factor (VEGF), aquaporin 4 (AQP4) and nitric oxide synthase (NOS). VEGF expression was localized in the ganglion cells, Müller cells, astrocytes and associated blood vessels. AQP4 was markedly enhanced in both astrocytes and Müller cells. Increase in vascular permeability after smoke exposure was evidenced by extravasation of serum derived rhodamine isothiocyanate which was internalized by Müller cells and ganglion cells. The tracer leakage was attenuated by aminoguanidine and N(G)-nitro-L-arginine methyl ester (L-NAME) treatment which suppressed retinal tissue NOS and nitric oxide (NO) levels concomitantly. It is suggested that VEGF, AQP4 and NO are involved in increased vascular permeability following acute smoke exposure in which hypoxia was ultimately implicated as shown by blood gases analysis. NOS inhibitors effectively reduced the vascular leakage and hence may ameliorate possible retinal edema in smoke inhalation.

Effects of brief, clustered versus dispersed hypoxic episodes on systemic and ocular growth factors in a rat model of oxygen-induced retinopathy

Oxygen fluctuation patterns in preterm infants who develop retinopathy of prematurity (ROP) are varied and poorly represented in animal models. We examined the hypothesis that clustered (CL) episodes of hypoxia during hyperoxia results in a more severe form of oxygen-induced retinopathy (OIR) than dispersed episodes. Rat pups were exposed to alternating cycles of 1) 50% O2 with three CL episodes of 12% O2 every 6 h; or 2) 50% O2 with one episode of 12% O2 every 2 h, for 7 (P7) or 14 (P14) days postnatal age. Pups were killed after hyperoxia, or placed in room air (RA) until P21. RA littermates were killed at P7, P14, and P21. Systemic and ocular vascular endothelial growth factor (VEGF), soluble VEGFR-1 (sVEGFR-1), insulin-like growth factor I (IGF-I), and growth hormone were examined. All hyperoxia-exposed retinas had evidence of neovascularization. Animals in the CL group had a more severe form of OIR at P21 evidenced by vascular tufts, leaky vessels, retinal hemorrhage, and vascular overgrowth. These characteristics were associated with low body weight; high systemic and ocular VEGF; and low systemic and high ocular sVEGFR-1 and IGF-I. These data suggest that preterm infants who experience CL fluctuations in Pao2 during supplemental O2 therapy are at a higher risk for severe ROP.

The clinical role of vascular endothelial growth factor (VEGF) system in the pathogenesis of retinopathy of prematurity

BACKGROUND

Recent experimental studies suggest that vascular endothelial growth factor (VEGF) can play an important role in the development of retinopathy of prematurity (ROP). There are interesting observations of VEGF concentration in the serum, depending on its gene polymorphism which can have an impact on abnormal vessel development in the retina.

AIM

Analysis of: (1) association of VEGF gene polymorphisms and the incidence of ROP, (2) correlation between serum concentration of VEGF and soluble VEGF receptor 1 (sVEGFR-1) during the 1st month of life and the risk of ROP, and (3) correlation between VEGF gene polymorphisms and VEGF serum concentrations.

METHODS

A sample of 181 newborns with mean birthweight 1054 g (range: 500-1500 g) was prospectively evaluated. Molecular analysis of VEGF -460T>C and 405G>C polymorphisms were performed in the whole studied population, and concentrations of VEGF and sVEGFR-1 were measured by Elisa assay in the 2nd, 3rd and 4th weeks of life in the group of 128 children. The infants were divided into 3 groups: A) no ROP (n = 101), B) ROP not requiring treatment (n = 20), and C) ROP requiring laser or cryotherapy (n = 60).

RESULTS

The frequency of VEGF 405G>C polymorphism was similar in all studied groups. The carriage of polymorphic allele -460 T was significantly overrepresented in ROP newborns who required treatment as compared to the no ROP group (54.2% vs 42.6%; OR: 1.63; 95% CI: 1.03-2.55). VEGF serum concentrations in the patients ascribed to different groups depending on the 405G>C or -460 T>C polymorphisms were similar. VEGF and sVEGFR-1 concentration on the 10th day of life did not differ significantly between the studied groups. Consecutive measurements showed a gradual increase in VEGF serum concentration in children without ROP, whereas in children with ROP requiring treatment the levels remained low.

CONCLUSIONS

Based on our observations and previously published data, the association of the VEGF gene promoter polymorphisms and the risk of advanced ROP is weak. VEGF serum concentration assessment as early as on the 20th day of life appears to be a promising approach to recognize newborns at risk of the development of advanced ROP.

Vascular endothelial growth factor in eye disease

Collectively, angiogenic ocular conditions represent the leading cause of irreversible vision loss in developed countries. In the US, for example, retinopathy of prematurity, diabetic retinopathy and age-related macular degeneration are the principal causes of blindness in the infant, working age and elderly populations, respectively. Evidence suggests that vascular endothelial growth factor (VEGF), a 40kDa dimeric glycoprotein, promotes angiogenesis in each of these conditions, making it a highly significant therapeutic target. However, VEGF is pleiotropic, affecting a broad spectrum of endothelial, neuronal and glial behaviors, and confounding the validity of anti-VEGF strategies, particularly under chronic disease conditions. In fact, among other functions VEGF can influence cell proliferation, cell migration, proteolysis, cell survival and vessel permeability in a wide variety of biological contexts. This article will describe the roles played by VEGF in the pathogenesis of retinopathy of prematurity, diabetic retinopathy and age-related macular degeneration. The potential disadvantages of inhibiting VEGF will be discussed, as will the rationales for targeting other VEGF-related modulators of angiogenesis.

Physiology and pathology of somatostatin in the mammalian retina: a current view

In the retina, peptidergic signalling participates in multiple circuits of visual information processing. The neuropeptide somatostatin (SRIF) is localised to amacrine cells and, in some instances, in a subset of ganglion cells. The variegated expression patterns of SRIF receptors (sst(1)-sst(5)) and the variety of signalling mechanisms activated by retinal SRIF suggest that this peptide may exert multiple actions on retinal neurons and on retinal physiology, although our current understanding reflects a rather complicated picture. SRIF, mostly through sst(2), may act as a positive factor in the retina by regulating retinal homeostasis and protecting neurons against damage. In this respect, SRIF analogues seem to constitute a promising therapeutic arsenal to cure different retinal diseases, as for instance, ischemic and diabetic retinopathies. However, further investigations are needed not only to fully understand the functional role of the SRIF system in the retina but also to exploit new chemical space for drug-like molecules.

Robo4 stabilizes the vascular network by inhibiting pathologic angiogenesis and endothelial hyperpermeability

The angiogenic sprout has been compared to the growing axon, and indeed, many proteins direct pathfinding by both structures. The Roundabout (Robo) proteins are guidance receptors with well-established functions in the nervous system; however, their role in the mammalian vasculature remains ill defined. Here we show that an endothelial-specific Robo, Robo4, maintains vascular integrity. Activation of Robo4 by Slit2 inhibits vascular endothelial growth factor (VEGF)-165-induced migration, tube formation and permeability in vitro and VEGF-165-stimulated vascular leak in vivo by blocking Src family kinase activation. In mouse models of retinal and choroidal vascular disease, Slit2 inhibited angiogenesis and vascular leak, whereas deletion of Robo4 enhanced these pathologic processes. Our results define a previously unknown function for Robo receptors in stabilizing the vasculature and suggest that activating Robo4 may have broad therapeutic application in diseases characterized by excessive angiogenesis and/or vascular leak.

Geldanamycin, a HSP90 inhibitor, attenuates the hypoxia-induced vascular endothelial growth factor expression in retinal pigment epithelium cells in vitro

Hypoxia is the most common factor contributing to the pathogenesis of choroidal neovascularization, which is the major cause for blindness and occurs in proliferative diabetic retinopathy and age-related macular degeneration. The purpose of this study is to investigate the role of retinal pigment epithelial (RPE) cells in the regulation of subretinal neovascularization under hypoxia and the possible function of a heat shock protein 90 (HSP90) inhibitor, geldanamycin (GA), in the regulation of VEGF expression. An in vitro hypoxic experimental model was used to mimic the ischemic microenvironment of RPE cells. The cell growth was measured by proliferation assay and the morphological observation was documented by microscope. The gene expression of VEGF, hsp70, hsp90alpha and hsp90beta were measured using semi-quantitative RT-PCR. The VEGF release from RPE cells were detected by ELISA. No alteration in growth rate and cell morphology under 1% O(2) condition for 24h was noticed. The proangiogenic growth factor VEGF, but not bFGF, released from hypoxia-treated cells were significantly higher than those of normoxic controls. A similar tendency of VEGF(165) isoform gene expression, detected by RT-PCR, was noticed in hypoxia-treated cells. Heat shock pretreatment elevated hsp70 and VEGF(165) gene expression and augmented the hypoxia-induced VEGF gene expression and protein release. Pretreatment with GA can significantly suppress the hypoxia-induced VEGF gene expression in and peptide release from RPE cells. These in vitro findings suggest that HSP90 inhibitors could be considered as novel anti-angiogenesis agents for diseases with intraocular neovascularization.

AKAP12 regulates human blood-retinal barrier formation by downregulation of hypoxia-inducible factor-1alpha

Many diseases of the eye such as retinoblastoma, diabetic retinopathy, and retinopathy of prematurity are associated with blood-retinal barrier (BRB) dysfunction. Identifying the factors that contribute to BRB formation during human eye development and maintenance could provide insights into such diseases. Here we show that A-kinase anchor protein 12 (AKAP12) induces BRB formation by increasing angiopoietin-1 and decreasing vascular endothelial growth factor (VEGF) levels in astrocytes. We reveal that AKAP12 downregulates the level of hypoxia-inducible factor-1alpha (HIF-1alpha) protein by enhancing the interaction of HIF-1alpha with pVHL (von Hippel-Lindau tumor suppressor protein) and PHD2 (prolyl hydroxylase 2). Conditioned media from AKAP12-overexpressing astrocytes induced barriergenesis by upregulating the expression of tight junction proteins in human retina microvascular endothelial cells (HRMECs). Compared with the retina during BRB maturation, AKAP12 expression in retinoblastoma patient tissue was markedly reduced whereas that of VEGF was increased. These findings suggest that AKAP12 may induce BRB formation through antiangiogenesis and barriergenesis in the developing human eye and that defects in this mechanism can lead to a loss of tight junction proteins and contribute to the development of retinal pathologies such as retinoblastoma.

D-Penicillamine administration and the incidence of retinopathy of prematurity

OBJECTIVE

We compared the development of retinopathy of prematurity (ROP) among 49 preterm neonates:; 15 who were treated during the first 2 weeks of life with D-penicillamine and 34 who were not.

METHODS

During a 15-month period beginning 1 March, 2005, 15 preterm neonates <1000 g birth weight or < or =29 weeks gestation enterally received a 14-day course of D-penicillamine, and 34 did not, in an open-label non-randomized trial. We compared the outcomes of developing 'ROP any stage' and 'ROP requiring surgery' in the recipients vs the non-recipients. Potential toxicities of the D-penicillamine were examined by comparing specific laboratory tests, growth velocities, transfusion requirements, discharge hemoglobin concentrations and supplemental O(2) at discharge.

RESULTS

The 34 non-treated and the 15 D-penicillamine treated patients were of similar gestational age (26.5+/-1.8 vs 26.6+/-2.2 weeks, mean+/-s.d.) and birth weight (887+/-222 vs 849+/-187 g). Four of the 34 non-recipients died. Eighteen of the 30 survivors (60%) developed ROP and seven of the 30 (23%) had ROP surgery. One of the 15 D-penicillamine recipients died. Three of the 14 survivors (21%) developed ROP (P=0.01 vs non-recipients) and all three had ROP laser surgery. No increase in elevated creatinine, direct or indirect bilirubin, thrombocytopenia or neutropenia was apparent in those treated with D-penicillamine. The D-penicillamine recipients did not receive more transfusions and did not have lower hemoglobin concentrations at discharge. They did not have lower velocities of weight gain at 14, 28 and 56 days, and were not discharged on supplemental O(2) at a rate exceeding that of the non-recipients.

CONCLUSIONS

In this non-randomized, single-centered comparison analysis, a 14-day course of D-penicillamine resulted in no apparent short-term toxicity. The treatment was associated with elimination of Stage I and Stage II ROP, decreasing the overall odds of developing ROP from 60 to 21%. However, this approach did not reduce the odds of ROP surgery. Perhaps higher doses of D-penicillamine or longer treatment periods or other prophylactic approaches will be required to reduce ROP surgery among the most immature neonates.

Intravitreal Bevacizumab in Aggressive Posterior Retinopathy of Prematurity

The anatomic response to intravitreal bevacizumab injection in three patients with aggressive, posterior retinopathy of prematurity is described. In all cases, the worse eye was treated with a single intravitreal injection of 0.75 mg of bevacizumab as monotherapy or complementary to laser therapy. In 24 hours, all injected eyes showed regression of the tunica vasculosa lentis and iris vessel engorgement and disappearance of iris rigidity. In addition, plus disease and retinal proliferation began to regress. None of the eyes required additional treatment. Follow-up of up to 10 months

Triamcinolone reduces neovascularization, capillary density and IGF-1 receptor phosphorylation in a model of oxygen-induced retinopathy

PURPOSE

To study the effects of intravitreous triamcinolone acetonide (TA) on neovascularization (NV), capillary density, and retinal endothelial cell (REC) viability in a model of oxygen-induced retinopathy (OIR).

METHODS

Newborn rats exposed to OIR underwent intravitreous injections (right eye) at day 14 to achieve intravitreous concentrations of: dexamethasone (DEX) (0.3 mg/mL), triamcinolone (TA; 0.4-4 mg/mL), or PBS. Animals were removed to room air and at day 18, retinal flatmounts were assayed for clock hours of NV, percent peripheral avascular retina, capillary density, apoptosis, and VEGF protein. At day 15, retinas were assayed for insulin-like growth factor (IGF)-1 receptor phosphorylation (IGF-1Rphos). Human RECs exposed to TA were assayed for trypan blue exclusion or activated caspase-3.

RESULTS

TA but not DEX or PBS reduced NV (ANOVA, P < 0.001), capillary density (ANOVA, P < 0.001), and systemic weight gain (ANOVA, P = 0.002). VEGF protein was not different between TA- and PBS-injected or noninjected groups. Apoptosis was not increased in vivo or in vitro between groups, but there was a dose-dependent toxic effect of TA on cultured RECs (P < 0.001). At day 15, retinas from the 4 mg/mL TA-injected OIR group had a trend toward reduced IGF-1Rphos compared with room air-raised PBS- or non-injected OIR groups.

CONCLUSIONS

TA caused dose-dependent reductions in NV, retinal vascularization, and systemic weight gain associated with a reduction in IGF-1Rphos. Long-term studies are needed to assess TA toxicity in vivo. TA doses should be carefully considered before administering the drug in diseases with ongoing retinal vascular development, such as retinopathy of prematurity.

Oxygen-dependent diseases in the retina: Role of hypoxia-inducible factors

The function of the retina is sensitive to oxygen tension. Any change in the perfusion pressure of the eye affects the retina although the eye is able to autoregulate its hemodynamics. Systemic hypoxemia (lung or heart disease) or a vascular disease in the retina can cause retinal hypoxia. All the hypoxia-dependent events in cells appear to share a common denominator: hypoxia-inducible factor (HIF), which is a heterodimeric transcription factor, a protein. HIF comprises a labile alpha subunit (1-3), which is regulated, and a stable beta subunit, which is constitutively expressed. Both are helix-loop-helix factors and belong to the PAS-domain family of transcription factors. Oxygen plays the key role in stabilizing HIF-1alpha and its function. When the oxygen tension is normal, HIF-1alpha is rapidly oxidized by hydroxylase enzymes, but when cells become hypoxic, HIF-1alpha escapes the degradation and starts to accumulate, triggering the activation of a large number of genes, like vascular endothelial growth factor (VEGF) and erythropoietin. HIF-1alpha has been shown to have, either clinically or experimentally, a mediating or contributing role in several oxygen-dependent retinal diseases such as von Hippel-Lindau, proliferative diabetic retinopathy, retinopathy of prematurity and glaucoma. In retinitis pigmentosa and high-altitude retinopathy, however, the evidence is still indirect. There are three different strategies available for treating retinal diseases, which have all shown promising results: retinal cell transplantation or replacement, gene replacement, and pharmacological intervention. Specifically, recent results show that the HIF pathway can be used as a therapeutic target, although there is still a long way to go from bench to clinic. HIF can be stabilized by inhibiting prolyl hydroxylase or by blocking the VHL:HIF-alpha complex if angiogenesis is the goal, as in retinitis pigmentosa. On the other hand, the downregulation of HIF has a pivotal role if we are to inhibit neovascularization, as in proliferative diabetic retinopathy. To date, several small-molecule inhibitors of HIF have been developed and are entering clinical trials. HIF is a remarkable example of a single transcription factor that can be regarded as a "master switch" regulating all the oxygen-dependent retinal diseases.

Adeno-associated virus-vectored gene therapy for retinal disease

Recombinant adeno-associated viral (AAV) vectors have become powerful gene delivery tools for the treatment of retinal degeneration in a variety of animal models that mimic corresponding human diseases. AAV vectors possess a number of features that render them ideally suited for retinal gene therapy, including a lack of pathogenicity, minimal immunogenicity, and the ability to transduce postmitotic cells in a stable and efficient manner. In the sheltered environment of the retina, AAV vectors are able to maintain high levels of transgene expression in the retinal pigmented epithelium (RPE), photoreceptors, or ganglion cells for long periods of time after a single treatment. Each cell type can be specifically targeted by choosing the appropriate combination of AAV serotype, promoter, and intraocular injection site. The focus of this review is on examples of AAV-mediated gene therapy in those animal models of inherited retinal degeneration caused by mutations directly affecting the interacting unit formed by photoreceptors and the RPE. In each case discussed, expression of the therapeutic gene resulted in significant recovery of retinal structure and/or visual function. Because of the key role of the vasculature in maintaining a healthy retina, a summary of AAV gene therapy applications in animal models of retinal neovascular diseases is also included.