Signaling pathways triggered by oxidative stress that mediate features of severe retinopathy of prematurity

Retinopathy of Prematurity-Targeting Hypoxic and Redox Signaling Pathways

Retinopathy of prematurity (ROP) is a proliferative vascular ailment affecting the retina. It is the main risk factor for visual impairment and blindness in infants and young children worldwide. If left undiagnosed and untreated, it can progress to retinal detachment and severe visual impairment. Geographical variations in ROP epidemiology have emerged over recent decades, attributable to differing levels of care provided to preterm infants across countries and regions. Our understanding of the causes of ROP, screening, diagnosis, treatment, and associated risk factors continues to advance. This review article aims to present the pathophysiological mechanisms of ROP, including its treatment. Specifically, it delves into the latest cutting-edge treatment approaches targeting hypoxia and redox signaling pathways for this condition.

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.

Modifiable Risk Factors and Preventative Strategies for Severe Retinopathy of Prematurity

Severe ROP is characterized by the development of retinal fibrovascular proliferation that may progress to retinal detachment. The purpose of this report is to review five of the most common and well-studied perinatal and neonatal modifiable risk factors for the development of severe ROP. Hyperoxemia, hypoxia, and associated prolonged respiratory support are linked to the development of severe ROP. While there is a well-established association between clinical maternal chorioamnionitis and severe ROP, there is greater variability between histologic chorioamnionitis and severe ROP. Neonatal sepsis, including both bacterial and fungal subtypes, are independent predictors of severe ROP in preterm infants. Although there is limited evidence related to platelet transfusions, the risk of severe ROP increases with the number and volume of red blood cell transfusions. Poor postnatal weight gain within the first six weeks of life is also strongly tied to the development of severe ROP. We also discuss preventative strategies that may reduce the risk of severe ROP. Limited evidence-based studies exist regarding the protective effects of caffeine, human milk, and vitamins A and E.

Prenatal Carotenoid Supplementation With Lutein or Zeaxanthin Ameliorates Oxygen-Induced Retinopathy (OIR) in Bco2-/- Macular Pigment Mice

Purpose

Premature infants at risk of retinopathy of prematurity (ROP) miss placental transfer of the carotenoids lutein (L) and zeaxanthin (Z) during the third trimester. We previously demonstrated that prenatal L and Z supplementation raised carotenoid levels in infants at birth in the Lutein and Zeaxanthin in Pregnancy (L-ZIP) study (NCT03750968). Based on their antioxidant effects and bioavailability, we hypothesized that prenatal maternal supplementation with macular carotenoids would reduce the risk of ROP. To test this hypothesis, we utilized "macular pigment mice" genetically engineered to take up L and Z into the retina in a model of oxygen-induced retinopathy (OIR).

Methods

Pregnant Bco2-/- mice were divided into nine experimental subgroups based on the type of supplementation (L, Z, or placebo) and on the maternal supplementation start date corresponding to the three trimesters of human fetal development (E0, E11, and P1). Pups and nursing mothers were exposed to 75% O2 for 5 days (P7-P12) and returned to room air for 5 days (P12-P17). Pups were killed at P12 and P17, and their retinas were analyzed for vaso-obliteration and intravitreal neovascularization.

Results

Pups of pregnant mice supplemented with L or Z had significant reductions in areas of vaso-obliteration and intravitreal neovascularization compared to placebo. Prenatal carotenoid supplementation starting at E0 or E11 was significantly more protective against OIR than postnatal supplementation starting at P1.

Conclusions

Prenatal supplementation with L and Z was beneficial in a mouse OIR model. We recommend testing prenatal L and Z supplementation in future human clinical trials to prevent ROP.

Retinopathy of prematurity: A review of pathophysiology and signaling pathways

Retinopathy of prematurity (ROP) is a vasoproliferative disorder of the retina and a leading cause of visual impairment and childhood blindness worldwide. The disease is characterized by an early stage of retinal microvascular degeneration, followed by neovascularization that can lead to subsequent retinal detachment and permanent visual loss. Several factors play a key role during the different pathological stages of the disease. Oxidative and nitrosative stress and inflammatory processes are important contributors to the early stage of ROP. Nitric oxide synthase and arginase play important roles in ischemia/reperfusion-induced neurovascular degeneration. Destructive neovascularization is driven by mediators of the hypoxia-inducible factor pathway, such as vascular endothelial growth factor and metabolic factors (succinate). The extracellular matrix is involved in hypoxia-induced retinal neovascularization. Vasorepulsive molecules (semaphorin 3A) intervene preventing the revascularization of the avascular zone. This review focuses on current concepts about signaling pathways and their mediators, involved in the pathogenesis of ROP, highlighting new potentially preventive and therapeutic modalities. A better understanding of the intricate molecular mechanisms underlying the pathogenesis of ROP should allow the development of more effective and targeted therapeutic agents to reduce aberrant vasoproliferation and facilitate physiological retinal vascular development.

Protective Effect of NO2-OA on Oxidative Stress, Gliosis, and Pro-Angiogenic Response in Müller Glial Cells

Inflammation and oxidative and nitrosative stress are involved in the pathogenesis of proliferative retinopathies (PR). In PR, a loss of balance between pro-angiogenic and anti-angiogenic factors favors the secretion of vascular endothelial growth factor (VEGF). This vascular change results in alterations in the blood-retinal barrier, with extravasation of plasma proteins such as α₂-macroglobulin (α₂M) and gliosis in Müller glial cells (MGCs, such as MIO-M1). It is well known that MGCs play important roles in healthy and sick retinas, including in PR. Nitro-fatty acids are electrophilic lipid mediators with anti-inflammatory and cytoprotective properties. Our aim was to investigate whether nitro-oleic acid (NO₂-OA) is beneficial against oxidative stress, gliosis, and the pro-angiogenic response in MGCs. Pure synthetic NO₂-OA increased HO-1 expression in a time- and concentration-dependent manner, which was abrogated by the Nrf2 inhibitor trigonelline. In response to phorbol 12-myristate 13-acetate (PMA) and lipopolysaccharide (LPS), NO₂-OA prevented the ROS increase and reduced the gliosis induced by α₂M. Finally, when hypoxic MGCs were incubated with NO₂-OA, the increase in VEGF mRNA expression was not affected, but under hypoxia and inflammation (IL-1β), NO₂-OA significantly reduced VEGF mRNA levels. Furthermore, NO₂-OA inhibited endothelial cell (BAEC) tubulogenesis. Our results highlight NO₂-OA's protective effect on oxidative damage, gliosis; and the exacerbated pro-angiogenic response in MGCs.

Ferrostatin-1 attenuates pathological angiogenesis in oxygen-induced retinopathy via inhibition of ferroptosis

Retinopathy of prematurity (ROP) is a vision-threatening ocular disease that occurs in premature infants, but the underlying mechanism is still unclear. Since oxidative stress has been well documented in the ROP development, we aimed to investigate whether ferroptosis, a new type of cell death characterized by lipid peroxidation and iron overload, is also involved in ROP. We detected the lipid peroxidation, oxidative stress and the expression of ferroptosis markers in the retina of mouse model of oxygen-induced retinopathy. After ferroptosis inhibitor, ferrostatin-1, was administered by intravitreal injection, ferroptosis marker, lipid peroxidation, retinal vasculature and glial cell activation were examined. We found decreased expression of SLC7A11 and GPX4, increased expression of FTH1 and TFRC, as well as increase of lipid peroxidation in the retina of OIR mice. Ferrostatin-1 administration significantly reduced lipid peroxidation, and also reversed the change of ferroptosis marker. Neovascular area and avascular area were suppressed and the pathological vasculature changes including acellular vessels and ghost pericytes were decreased. Microglial cell and Müller cell activation was not evidently influenced by ferrostatin-1 treatment. Our findings suggest that ferroptosis is involved in the pathological angiogenesis and might be a promising target for ROP therapy.

The Effects of Nicotinamide Adenine Dinucleotide Phosphate (NADPH) Oxidase and Erythropoietin, and Their Interactions in Angiogenesis: Implications in Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a leading cause of vision impairment and blindness in premature infants. Oxidative stress is implicated in its pathophysiology. NADPH oxidase (NOX), a major enzyme responsible for reactive oxygen species (ROS) generation in endothelial cells, has been studied for its involvement in physiologic and pathologic angiogenesis. Erythropoietin (EPO) has gained interest recently due to its tissue protective and angiogenic effects, and it has been shown to act as an antioxidant. In this review, we summarize studies performed over the last five years regarding the role of various NOXs in physiologic and pathologic angiogenesis. We also discuss the effect of EPO in tissue and vasoprotection, and the intersection of EPO and NOX-mediated oxidative stress in angiogenesis and the pathophysiology of ROP.

Retinopathy of prematurity: contribution of inflammatory and genetic factors

Retinopathy of prematurity (ROP) is a retinal vasoproliferative disorder that represents an important cause of childhood visual impairment and blindness. Although oxidative stress has long been implicated in ROP etiology, other prenatal and perinatal factors are also involved. This review focuses on current research involving inflammation and genetic factors in the pathogenesis of ROP. Increasing evidence suggests that perinatal inflammation or infection contributes to ROP pathogenesis. Cytokines and chemokines with a fundamental role in inflammatory responses and that significantly contributing to angiogenesis are analyzed. Microglia cells, the retinal-resident macrophages, are crucial for retinal homeostasis, however, under sustained pathological stimuli release exaggerated amounts of inflammatory mediators and can promote pathological neovascularization. Current modulation of angiogenic cytokines, such as treatment with antibodies to vascular endothelial growth factor (anti-VEGF), has shown efficacy in the treatment of ocular neovascularization; however, some patients are refractory to anti-VEGF agents, suggesting that other angiogenic or anti-angiogenic cytokines need to be identified. Much evidence suggests that genetic factors contribute to the phenotypic variability of ROP. Several studies have implicated the involvement of candidate genes from different signaling pathways in the development of ROP. However, a genetic component with a major impact on ROP has not yet been discovered. Most studies have limitations and did not replicate results. Future research involving bioinformatics, genomics, and proteomics may contribute to finding more genes associated with ROP and may allow discovering better solutions in the management and treatment of ROP.

Stress Signal Regulation by Na/K-ATPase As a New Approach to Promote Physiological Revascularization in a Mouse Model of Ischemic Retinopathy

Purpose

The identification of target pathways to block excessive angiogenesis while simultaneously restoring physiological vasculature is an unmet goal in the therapeutic management of ischemic retinopathies. pNaKtide, a cell-permeable peptide that we have designed by mapping the site of α1 Na/K-ATPase (NKA)/Src binding, blocks the formation of α1 NKA/Src/reactive oxygen species (ROS) amplification loops and restores physiological ROS signaling in a number of oxidative disease models. The aim of this study was to evaluate the importance of the NKA/Src/ROS amplification loop and the effect of pNaKtide in experimental ischemic retinopathy.

Methods

Human retinal microvascular endothelial cells (HRMECs) and retinal pigment epithelium (ARPE-19) cells were used to evaluate the effect of pNaKtide on viability, proliferation, and angiogenesis. Retinal toxicity and distribution were assessed in those cells and in the mouse. Subsequently, the role and molecular mechanism of NKA/Src in ROS stress signaling were evaluated biochemically in the retinas of mice exposed to the well-established protocol of oxygen-induced retinopathy (OIR). Finally, pNaKtide efficacy was assessed in this model.

Results

The results suggest a key role of α1 NKA in the regulation of ROS stress and the Nrf2 pathway in mouse OIR retinas. Inhibition of α1 NKA/Src by pNaKtide reduced pathologic ROS signaling and restored normal expression of hypoxia-inducible factor 1-α/vascular endothelial growth factor (VEGF). Unlike anti-VEGF agents, pNaKtide did promote retinal revascularization while inhibiting neovascularization and inflammation.

Conclusions

Targeting α1 NKA represents a novel strategy to develop therapeutics that not only inhibit neovascularization but also promote physiological revascularization in ischemic eye diseases.

Lower oxygen saturation targets in preterm infants are not associated with increased rates of pulmonary hypertension

BACKGROUND

The optimal oxygen saturation target in preterm infants is not known. In this study, we aimed to assess the effect of lower oxygen saturation targets on the rate of bronchopulmonary dysplasia (BPD), retinopathy of prematurity (ROP), and pulmonary hypertension (PH) in preterm infants.

METHODS

Retrospective cohort study comparing BPD, ROP, and PH incidence among two cohorts of infants born at≤32 weeks gestation with different oxygen saturation targets at≥34 weeks post-menstrual age (PMA): cohort 1, 94-98% (n = 126); cohort 2, 92-97% (n = 121). Groups compared by Chi-square test, t-test, and multivariable logistic regression.

RESULTS

When comparing cohort 1 (average gestational age 29.8 weeks, average birth weight 1271g) with cohort 2 (average gestational age 29.6 weeks, average birth weight 1299g), there was no difference in rate of BPD (24% vs. 19%, p = 0.38), ROP (4% vs. 3%, p = 0.49), or PH (2% vs. 4%, p = 0.44).

CONCLUSION

An oxygen saturation target of 92-97% at≥34 weeks PMA was not associated with a higher rate of PH or lower rate of BPD or ROP when compared with a higher target of 94-98%.

Evaluation of Plasma Amino Acid Levels in Preterm Infants and Their Potential Correlation with Retinopathy of Prematurity

Aim

The aim of this study is to ascertain whether the level of circulating amino acids (aa) is associated with retinopathy of prematurity (ROP).

Methods

This is a randomized controlled study of 55 infants born at gestational age (GA) ≤32 weeks or birth weight (BW) ≤1500 grams. Serum samples were obtained from two groups: Group A comprised of 26 preterm infants with ROP and Group B comprised of 29 preterm infants without ROP. Plasma aa levels were analyzed using liquid chromatography with tandem mass spectrometry (LC-MS/MS). Correlation test and multivariate regression analysis were used to evaluate the relationship between plasma aa levels and variables.

Results

The mean serum arginine and glutamine levels were significantly higher, but the mean lysine and aspartic acid levels were significantly lower in Group A, compared to Group B (p = 0.04, p = 0.002, p = 0.029, and p = 0.002, respectively). In multivariate analysis, the mean arginine and lysine levels were significantly associated with the stage of the disease (p = 0.03 and p = 0.01, respectively). No significant differences were determined between the groups in terms of alanine, asparagine, valine, leucine, phenylalanine, tyrosine, serine, proline, citrulline, cysteine, ornithine, tryptophan, methionine, threonine, taurine, and isoleucine amino acids (p > 0.05, respectively).

Conclusions

These results indicate a significant association between high arginine and glutamine, with low lysine and aspartic acid serum concentrations with ROP. Due to higher serum concentrations in ROP, extra arginine-glutamine supplementation in hyperoxic conditions may be unfavorable through pathways involving reactive oxygen, particularly in patients with ROP.

Oxidative Stress Markers and the Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a leading cause of potentially preventable blindness in low birth weight preterm infants. Several perinatal and postnatal factors contribute to the incomplete maturation of retinal vascularization, leading to oxidative stress damage. Literature data suggest that the lack of equilibrium between pro-oxidants and anti-oxidants plays a key role. In the last decade, there has been an increasing interest in identifying the antecedents of ROP and the relevant pathogenic mechanisms involved. In this context, a panel of biomarkers was investigated in order to achieve early detection of oxidative stress occurrence and to prevent retinal damage. Several nutritional elements have been found to play a relevant role in ROP prevention. At this stage, no conclusive data have been shown to support the usefulness of one biomarker over another. Recently, the Food and Drugs Administration, the European Medicine Agency, and the National Institute of Health proposed a series of criteria in order to promote the inclusion of new biomarkers in perinatal clinical guidelines and daily practice. The aim of the present review is to offer an update on a panel of biomarkers, currently investigated as potential predictors of ROP, highlighting their strengths and weaknesses.

Epithelial Membrane Protein 2 (EMP2) Promotes VEGF-Induced Pathological Neovascularization in Murine Oxygen-Induced Retinopathy

Purpose

Retinopathy of prematurity (ROP) is a leading cause of childhood blindness. ROP occurs as a consequence of postnatal hyperoxia exposure in premature infants, resulting in vasoproliferation in the retina. The tetraspan protein epithelial membrane protein-2 (EMP2) is highly expressed in the retinal pigment epithelium (RPE) in adults, and it controls vascular endothelial growth factor (VEGF) production in the ARPE-19 cell line. We, therefore, hypothesized that Emp2 knockout (Emp2 KO) protects against neovascularization in murine oxygen-induced retinopathy (OIR).

Methods

Eyes were obtained from wildtype (WT) and Emp2 KO mouse pups at P7, P12, P17, and P21 after normoxia or hyperoxia (P7-P12) exposure. Following hyperoxia exposure, RNA sequencing was performed using the retina/choroid layers obtained from WT and Emp2 KO at P17. Retinal sections from P7, P12, P17, and P21 were evaluated for Emp2, hypoxia-inducible factor 1α (Hif1α), and VEGF expression. Whole mount images were generated to assess vaso-obliteration at P12 and neovascularization at P17.

Results

Emp2 KO OIR mice demonstrated a decrease in pathologic neovascularization at P17 compared with WT OIR mice through evaluation of retinal vascular whole mount images. This protection was accompanied by a decrease in Hif1α at P12 and VEGFA expression at P17 in Emp2 KO animals compared with the WT animals in OIR conditions. Collectively, our results suggest that EMP2 enhances the effects of neovascularization through modulation of angiogenic signaling.

Conclusions

The protection of Emp2 KO mice against pathologic neovascularization through attenuation of HIF and VEGF upregulation in OIR suggests that hypoxia-induced upregulation of EMP2 expression in the neuroretina modulates HIF-mediated neuroretinal VEGF expression.

Stanniocalcin-1 is a Modifier of Oxygen-Induced Retinopathy Severity

Purpose/Aim: Abnormal activation of signaling pathways related to angiogenesis, inflammation, and oxidative stress has been implicated in the pathophysiology of retinopathy of prematurity (ROP), a leading cause of blindness in pre-term infants. Therapies for ROP include laser and anti-vascular endothelial growth factor agents. However, these therapies have side effects, and even with adequate treatment, visual acuity can be impaired. Novel therapeutic options are needed. Stanniocalcin-1 (STC-1) is a neuroprotective protein with anti-inflammatory and anti-oxidative stress properties. Rodent models of oxygen-induced retinopathy (OIR) were selected to determine whether STC-1 plays a role in the development of OIR.Materials and methods: STC-1 gene and protein expression was first evaluated in the Sprague Dawley rat OIR model that is most similar to human ROP. OIR was then induced in wild-type and Stc-1-/- mice. Retinas were isolated and evaluated for avascular and neovascular area on retinal flat mounts. Quantification of gene expression by quantitative real-time PCR was performed. VEGF was assayed by ELISA in media obtained from induced pluripotent stem-cell-derived retinal pigment epithelial (iPS-RPE) cells following treatment with recombinant STC-1.Results: STC-1 was significantly upregulated in a rat model of OIR compared to room air controls at the gene (P < .05) and protein (P < .001) level. Stc-1-/- OIR mice showed significantly worse ROP compared to wild-type mice as assessed by avascular (20.2 ± 2.4% vs 15.2 ± 2.5%; P = .02) and neovascular area (14.3 ± 2.7% vs 8.8 ± 3.7%; P < .05). Transcript levels of vascular endothelial growth factor-A were significantly higher in Stc-1-/- OIR mice compared to wild-type controls (P = .03). STC-1 reduced VEGF production in iPS-RPE cells (P = .01).Conclusions: STC-1 plays a role in the OIR stress response and development of pathologic vascular features in rodent OIR models by regulating VEGF levels.

Metabolomic changes of blood plasma associated with two phases of rat OIR

Although acute hyperoxia/hypoxia alternation can shift sharply physiological processes of vessel development, e.g. oxygen induced retinopathy (OIR), very little is known of metabolic products resulted from the neovascularization disorder. In this study, the influence of abnormal oxygen exposures on the plasma metabolomic profiles of rats with OIR was investigated by the gas chromatography mass spectrometry (GC-MS). Rat pups were divided into four groups, each with 12 individuals: (i) reared in room air and sampled at P12 (CT1); (ii) exposed to high oxygen for 5 days and sampled at P12 (HO1, simulating the vaso-obeliteration process (phase I)); (iii) reared in room air and sampled at P17 (CT2); (iv) exposed to high oxygen for 5 days then followed by room air for 5 days and sampled at P17 (HO2, simulating the neovasculization one (phase II)). Plasma samples were analyzed with GC-MS, resulted in 122 metabolite species. Distinct differences in the plasma metabolome were found between groups of CT1 vs. HO1, and HO1 vs. HO2, by using univariate and multivariate analyses. Alternating hyperoxia/hypoxia conditions induced significant changes of richness of proline, ornithine and glutamine, that were important components of 'arginine and proline metabolism' pathway. These metabolites contributed largely to plasma sample classification, determined with receiver operating characteristic curve analysis and were involved profoundly in the proline-dependent production of reactive oxygen species (ROS) related to the cellular redox reactions. Our results from the rat OIR model suggest proline and 'arginine and proline metabolism' pathway as the potential biomarkers for human retinopathy of prematurity (ROP) diagnosis.

Clinical Efficacy of Topical CoQ10 and Vitamin-E Eye-drop in Retinopathy of Prematurity

Treatment strategy for retinopathy of prematurity (ROP) includes anti-vascular endothelial growth factor (anti-VEGF) and/or laser therapy. The aim of this study was to investigate the clinical effects of topical Coqun® eye drop (CoQ10 and Vitamin-E) on the progression and treatment of ROP. One hundred and ten infants with type 1 ROP who received Coqun® (Coqun group) and 131 infants with type 1 ROP who did not receive Coqun® (control group) were included in this retrospective analysis. All patients were follow-up until retinal vascular maturation was complete. Intravitreal bevacizumab (IVB) injection or laser photocoagulation (LPC) were apply if needed. Treatment frequency, treatment response and mean follow-up time were compare. The number of IVB was similar between the groups, but infants in the Coqun group underwent significantly fewer LPC procedure than those in the control group (P = 0.022). The mean follow-up time was significantly shorter in infants receiving Coqun® in stage 1 ROP (P = 0.017) and similar in stages 2-4 ROP and aggressive posterior retinopathy of prematurity (APROP). The number of LPC procedure was fewer in the Coqun group in APROP (P = 0.043). These results indicate that faster retinal vascular maturation in infants with low-grade ROP and lower number of treatments with APROP could be achieve with Coqun® therapy.

Non-invasive assessment of oxidative stress in preterm infants

Preterm newborns have an immature antioxidant defense system and are especially susceptible to oxidative stress. Resuscitation, mechanical ventilation, intermittent hypoxia and apneic episodes require frequently oxygen supplementation which leads to oxidative stress in preterm newborns. The consequences of oxidative damage are increased short and long-term morbidities, neurodevelopmental impairment and increased mortality. Oxidative stress biomarkers are determined in blood samples from preterm children during their stay in neonatal intensive care units especially for research purposes. However, there is a tendency towards reducing invasive and painful techniques in the NICU (Neonatal Intensive Care Unit) and avoiding excessive blood extractions procedures. In this paper, it has been described some studies that employed non-invasive samples to determine oxidative stress biomarkers form preterm infants in order to perform a close monitoring biomarker with a significant greater predictive value. Among these methods we describe a previously developed and validated high-performance liquid chromatography tandem mass spectrometry method that allow to accurately determine the most reliable biomarkers in biofluids, which are non-invasively and painlessly obtained.

Is There A Role for Abscisic Acid, A Proven Anti-Inflammatory Agent, in the Treatment of Ischemic Retinopathies?

Ischemic retinopathies (IRs) are the main cause of severe visual impairment and sight loss, and are characterized by loss of blood vessels, accompanied by hypoxia, and neovascularization. Actual therapies, based on anti-vascular endothelial growth factor (VEGF) strategies, antioxidants or anti-inflammatory therapies are only partially effective or show some adverse side effects. Abscisic acid (ABA) is a phytohormone present in vegetables and fruits that can be naturally supplied by the dietary intake and has been previously studied for its benefits to human health. It has been demonstrated that ABA plays a key role in glucose metabolism, inflammation, memory and tumor growth. This review focuses on a novel and promising role of ABA as a potential modulator of angiogenesis, oxidative status and inflammatory processes in the retina, which are the most predominant characteristics of the IRs. Thus, this nutraceutical compound might shed some light in new therapeutic strategies focused in the prevention or amelioration of IRs-derived pathologies.

Oxidative stress upregulates Wnt signaling in human retinal microvascular endothelial cells through activation of disheveled

Abnormal retinal neovascularization associated with various retinopathies can result in irreversible vision loss. Although the mechanisms involved in this occurrence is unclear, increasing evidence suggests that aberrant Wnt signaling participates in the pathogenesis of abnormal neovascularization. Because Wnt signaling upregulation can be induced by oxidative stress through the activation of disheveled (DVL), a key molecule in the Wnt signaling pathway, we investigated whether oxidative stress can activate Wnt signaling and induce angiogenic phenotypes in human retinal microvascular endothelial cells (HRMECs). We found that increased Wnt signaling activity, as well as enhanced angiogenic phenotypes, such as tube formation and cell migration, were detected in the hydrogen peroxide-treated HRMECs. Moreover, these effects were effectively suppressed by a small-molecule Wnt inhibitor targeting the PDZ domain of DVL. Therefore, we propose that targeting abnormal Wnt signaling at the DVL level with a small-molecule inhibitor may represent a novel approach in retinal neovascularization treatment and prevention.

Antifungal Treatment and Outcome in Very Low Birth Weight Infants: A Population-based Observational Study of the German Neonatal Network

BACKGROUND

The diagnostic proof of fungal infection in preterm infants is difficult. Antifungal treatment (AFT) is often initiated empirically when infants with suspected infection do not improve despite broad-spectrum antibiotic therapy. It was the aim of our study to determine the rate of exposure to empirical AFT in a large cohort of very low birth weight infants (VLBWI) of the German Neonatal Network and to address associated risks and outcomes.

METHODS

The epidemiologic database consisted of n = 13,343 VLBWI born in 54 German Neonatal Network centers between 2009 and 2015. AFT was defined as number of neonates who got any dose of at least one of the following antifungal drugs: fluconazole, amphotericin B, voriconazole and caspofungin (denominator: number of infants enrolled in German Neonatal Network) for treatment (not prophylaxis) of (suspected) fungal infection. Univariate and logistic regression analyses were used to identify risk factors for exposure to AFT and associated short-term morbidities and long-term outcomes at 5-year follow-up.

RESULTS

In our cohort, 724 out of 13,343 (5.4%) VLBWI were exposed to empiric AFT and had a mean gestational age of 25.7 (±2.1) weeks. Forty-four out of 13,343 (0.3%) had proven bloodstream infection with Candida spp. The main risk factors for exposure to AFT were gestational age, postnatal steroid treatment, need for abdominal surgery and use of carbapenems. Notably, AFT was associated with adverse outcomes such as bronchopulmonary dysplasia [adjusted odds ratio (OR): 1.9; 95% confidence interval (CI): 1.6-2.3; P < 0.001) and retinopathy of prematurity requiring intervention (adjusted OR: 1.69; 95% CI: 1.3-2.3; P <0.001) but not mortality. In the subgroup of infants available for 5-year follow-up (n = 895), exposure to AFT was associated with a risk for cerebral palsy (adjusted OR: 2.79; 95% CI: 1.11-7.04; P = 0.04) and intelligence quotient < 85 (adjusted OR: 2.07; 95% CI: 1.01-4.28; P = 0.049).

CONCLUSIONS

A significant proportion of VLBWI is exposed to AFT, specifically those born <26 weeks. Exposed infants were found to have a higher risk for adverse outcomes, which may reflect their significant vulnerability in general. Given the observational design of our study, it remains unclear whether potential side effects of empirical or target AFT itself contribute to adverse outcome. Future studies need to include risk-based strategies and stewardship programs to restrict the use of antifungal management in VLBWI.

Misoprostol regulates Bnip3 repression and alternative splicing to control cellular calcium homeostasis during hypoxic stress

The cellular response to hypoxia involves the activation of a conserved pathway for gene expression regulated by the transcription factor complex called hypoxia-inducible factor (HIF). This pathway has been implicated in both the adaptive response to hypoxia and in several hypoxic-ischemic-related pathologies. Perinatal hypoxic injury, often associated with prematurity, leads to multi-organ dysfunction resulting in significant morbidity and mortality. Using a rodent model of neonatal hypoxia and several representative cell lines, we observed HIF1α activation and down-stream induction of the cell death gene Bnip3 in brain, large intestine, and heart which was mitigated by administration of the prostaglandin E1 analog misoprostol. Mechanistically, we determined that misoprostol inhibits full-length Bnip3 (Bnip3-FL) expression through PKA-mediated NF-κB (P65) nuclear retention, and the induction of pro-survival splice variants. We observed that the dominant small pro-survival variant of Bnip3 in mouse cells lacks the third exon (Bnip3ΔExon3), whereas human cells produce a pro-survival BNIP3 variant lacking exon 2 (BNIP3ΔExon2). In addition, these small Bnip3 splice variants prevent mitochondrial dysfunction, permeability transition, and necrosis triggered by Bnip3-FL by blocking calcium transfer from the sarco/endoplasmic reticulum to the mitochondria. Furthermore, misoprostol and Bnip3ΔExon3 promote nuclear calcium accumulation, resulting in HDAC5 nuclear export, NFAT activation, and adaptive changes in cell morphology and gene expression. Collectively, our data suggests that misoprostol can mitigate the potential damaging effects of hypoxia on multiple cell types by activating adaptive cell survival pathways through Bnip3 repression and alternative splicing.

Genetic association of single nucleotide polymorphisms of FZD4 and BDNF genes with retinopathy of prematurity

BACKGROUND

Retinopathy of prematurity (ROP) is a multifactorial disease occurring in preterm neonates, caused by incorrect development of retinal blood vessels. It has been suggested that, in addition to gestational age, weight, and oxygen supplementation, genetic factors can play a role in the pathogenesis of ROP.

METHODS

In the present prospective study, 97 neonates were enrolled based on the gestational age and weight, and genomic DNA from patients diagnosed with ROP and premature newborns without ROP was collected. The DNA sequence of protein coding and 5´and 3´ untranslated regions (UTRs) of the frizzled-4 (FZD4) gene and the genotype of the locus rs7934165:G˃A (NM_170731.4: c.3 + 10976 C˃T) within the brain-derived neurotrophic factor gene (BDNF) were determined.

RESULTS

We detected a significant association between rs61749246:C˃A (NM_012193.3: c.*2G˃T) and ROP in a general genetic model as well as in a multiplicative model and by the Cochran-Armitage test for trend. Moreover, rs61749246 was strongly associated with ROP, requiring surgical intervention.

CONCLUSION

We suggest that rs61749246:C˃A of the FZD4 gene is likely associated with the development of ROP. It is necessary to confirm this suggestion in larger studies.

Oxidative stress in the retina: implications for Retinopathy of Prematurity

Oxygen supplementation has been used as a part of respiratory care for preterm and term newborns since the beginning of 19^th century. Although oxygen administration can be life-saving, reactive oxygen species (ROS) and reactive nitrogen species (RNS) due to hyperoxia can have detrimental effects in the developing organs of the preterm infants, with both short and long term consequences. Oxygen toxicity on the immature tissues of preterm infants can contribute to the development of several diseases like retinopathy of prematurity (ROP) and bronchopulmonary dysplasia (BPD). The vascular development of human retina is completed at term, whereas the neural retina develops up to 5 years of age. Disruption of the normal retinal neurovascular growth is the pathognomonic feature of ROP, and can lead to vision threatening disease or even blindness. It is estimated that at least 100,000 infants all over the world will be blind every year due to ROP, which is the leading cause of blindness in children. In this review we will discuss the role of ROS and RNS in the development of ROP, and how through historical, epidemiological, and developmental aspects of this devastating disease, we can design future research for its prevention and treatment.

Abnormal Complement Activation and Inflammation in the Pathogenesis of Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a neurovascular complication in preterm babies, leading to severe visual impairment, but the underlying mechanisms are yet unclear. The present study aimed at unraveling the molecular mechanisms underlying the pathogenesis of ROP. A comprehensive screening of candidate genes in preterms with ROP (n = 189) and no-ROP (n = 167) was undertaken to identify variants conferring disease susceptibility. Allele and genotype frequencies, linkage disequilibrium and haplotypes were analyzed to identify the ROP-associated variants. Variants in CFH (p = 2.94 × 10⁻⁷), CFB (p = 1.71 × 10⁻⁵), FBLN5 (p = 9.2 × 10⁻⁴), CETP (p = 2.99 × 10⁻⁵), and CXCR4 (p = 1.32 × 10⁻⁸) genes exhibited significant associations with ROP. Further, a quantitative assessment of 27 candidate proteins and cytokines in the vitreous and tear samples of babies with severe ROP (n = 30) and congenital cataract (n = 30) was undertaken by multiplex bead arrays and further validated by western blotting and zymography. Significant elevation and activation of MMP9 (p = 0.038), CFH (p = 2.24 × 10⁻⁵), C3 (p = 0.05), C4 (p = 0.001), IL-1ra (p = 0.0019), vascular endothelial growth factor (VEGF) (p = 0.0027), and G-CSF (p = 0.0099) proteins were observed in the vitreous of ROP babies suggesting an increased inflammation under hypoxic condition. Along with inflammatory markers, activated macrophage/microglia were also detected in the vitreous of ROP babies that secreted complement component C3, VEGF, IL-1ra, and MMP-9 under hypoxic stress in a cell culture model. Increased expression of the inflammatory markers like the IL-1ra (p = 0.014), MMP2 (p = 0.0085), and MMP-9 (p = 0.03) in the tears of babies at different stages of ROP further demonstrated their potential role in disease progression. Based on these findings, we conclude that increased complement activation in the retina/vitreous in turn activated microglia leading to increased inflammation. A quantitative assessment of inflammatory markers in tears could help in early prediction of ROP progression and facilitate effective management of the disease, thereby preventing visual impairment.

Ischemic Retinopathies: Oxidative Stress and Inflammation

Ischemic retinopathies (IRs), such as retinopathy of prematurity (ROP), diabetic retinopathy (DR), and (in many cases) age-related macular degeneration (AMD), are ocular disorders characterized by an initial phase of microvascular changes that results in ischemia, followed by a second phase of abnormal neovascularization that may culminate into retinal detachment and blindness. IRs are complex retinal conditions in which several factors play a key role during the development of the different pathological stages of the disease. Increasing evidence reveals that oxidative stress and inflammatory processes are important contributors to the pathogenesis of IRs. Despite the beneficial effects of the photocoagulation and anti-VEGF therapy during neovascularization phase, the need to identify novel targets to prevent initial phases of these ocular pathologies is still needed. In this review, we provide an update on the involvement of oxidative stress and inflammation in the progression of IRs and address some therapeutic interventions by using antioxidants and anti-inflammatory agents.

Advances in understanding and management of retinopathy of prematurity

The understanding, diagnosis, and treatment of retinopathy of prematurity have changed in the 70 years since the original description of retrolental fibroplasia associated with high oxygenation. It is now recognized that retinopathy of prematurity differs in appearance worldwide and as ever smaller and younger premature infants survive. New methods are being evaluated to image the retina, diagnose severe retinopathy of prematurity, and determine windows of time for treatment to save eyes and improve visual and neural outcomes. New treatments to promote physiologic retinal vascular development, vascular repair, and inhibit vasoproliferation by regulating proteins involved in vascular endothelial growth factor, insulin-like growth factor, or erythropoietin signaling. Reducing excessive oxidative/nitrosative stress and understanding progenitor cells and neurovascular and glial vascular interactions are being studied.

Treatment with polyamine oxidase inhibitor reduces microglial activation and limits vascular injury in ischemic retinopathy

Retinal vascular injury is a major cause of vision impairment in ischemic retinopathies. Insults such as hyperoxia, oxidative stress and inflammation contribute to this pathology. Previously, we showed that hyperoxia-induced retinal neurodegeneration is associated with increased polyamine oxidation. Here, we are studying the involvement of polyamine oxidases in hyperoxia-induced injury and death of retinal vascular endothelial cells. New-born C57BL6/J mice were exposed to hyperoxia (70% O2) from postnatal day (P) 7 to 12 and were treated with the polyamine oxidase inhibitor MDL 72527 or vehicle starting at P6. Mice were sacrificed after different durations of hyperoxia and their retinas were analyzed to determine the effects on vascular injury, microglial cell activation, and inflammatory cytokine profiling. The results of this analysis showed that MDL 72527 treatment significantly reduced hyperoxia-induced retinal vascular injury and enhanced vascular sprouting as compared with the vehicle controls. These protective effects were correlated with significant decreases in microglial activation as well as levels of inflammatory cytokines and chemokines. In order to model the effects of polyamine oxidation in causing microglial activation in vitro, studies were performed using rat brain microvascular endothelial cells treated with conditioned-medium from rat retinal microglia stimulated with hydrogen peroxide. Conditioned-medium from activated microglial cultures induced cell stress signals and cell death in microvascular endothelial cells. These studies demonstrate the involvement of polyamine oxidases in hyperoxia-induced retinal vascular injury and retinal inflammation in ischemic retinopathy, through mechanisms involving cross-talk between endothelial cells and resident retinal microglia.

Revisiting the mouse model of oxygen-induced retinopathy

Abnormal blood vessel growth in the retina is a hallmark of many retinal diseases, such as retinopathy of prematurity (ROP), proliferative diabetic retinopathy, and the wet form of age-related macular degeneration. In particular, ROP has been an important health concern for physicians since the advent of routine supplemental oxygen therapy for premature neonates more than 70 years ago. Since then, researchers have explored several animal models to better understand ROP and retinal vascular development. Of these models, the mouse model of oxygen-induced retinopathy (OIR) has become the most widely used, and has played a pivotal role in our understanding of retinal angiogenesis and ocular immunology, as well as in the development of groundbreaking therapeutics such as anti-vascular endothelial growth factor injections for wet age-related macular degeneration. Numerous refinements to the model have been made since its inception in the 1950s, and technological advancements have expanded the use of the model across multiple scientific fields. In this review, we explore the historical developments that have led to the mouse OIR model utilized today, essential concepts of OIR, limitations of the model, and a representative selection of key findings from OIR, with particular emphasis on current research progress.

Anti-VEGF therapy in the management of retinopathy of prematurity: what we learn from representative animal models of oxygen-induced retinopathy

Retinopathy of prematurity (ROP) remains a leading cause of childhood blindness, affecting infants born prematurely. ROP is characterized by the onset of delayed physiological retinal vascular development (PRVD) and followed by pathologic neovascularization into the vitreous instead of the retina, called intravitreal neovascularization (IVNV). Therefore, the therapeutic strategy for treating ROP is to promote PRVD and inhibit or prevent IVNV. Vascular endothelial growth factor (VEGF) plays an important role in the pathogenesis of ROP. There is a growing body of studies testing the use of anti-VEGF agents as a treatment for ROP. Intravitreal anti-VEGF treatment for ROP has potential advantages compared with laser photocoagulation, the gold standard for the treatment of severe ROP; however, intravitreal anti-VEGF treatment has been associated with reactivation of ROP and suppression of systemic VEGF that may affect body growth and organ development in preterm infants. Therefore, it is important to understand the role of VEGF in PRVD and IVNV. This review includes the current knowledge of anti-VEGF treatment for ROP from animal models of oxygen-induced retinopathy (OIR), highlighting the importance of VEGF inhibition by targeting retinal Müller cells, which inhibits IVNV and permits PRVD. The signaling events involved in mediating VEGF expression and promoting VEGF-mediated angiogenesis, including hypoxia-dependent signaling, erythropoietin/erythropoietin receptor-, oxidative stress-, beta-adrenergic receptor-, integrin-, Notch/Delta-like ligand 4- and exon guidance molecules-mediated signaling pathways, are also discussed.

Genomics in the neonatal nursery: Focus on ROP

Retinopathy of prematurity (ROP) is a complex disease that is influenced by both genetic and environmental factors. Several small studies have found genetic variants in EPAS1, VEGF, SOD, and members of the WNT family in association with ROP. Design in genetic studies is challenging because of changing recommendations for the management of prematurity and ROP, the fact ROP is rare, and that availability of resources for managing premature infants can vary throughout the world. In addition, there is a shortage of ophthalmologists with the ability to diagnose and characterize severe ROP. Careful determination of the degree of prematurity is important when evaluating genetic studies. Controlling for significant epidemiologic factors and multiple comparisons is also important to consider when evaluating genetic studies. One large candidate gene study controlled for degree of prematurity, significant epidemiologic factors, and multiple comparisons and found variants within the intron of BDNF associated with severe ROP. Future studies using unbiased techniques to assess genetic risk are important as are in-depth study of BDNF through deep sequencing and associated mechanistic studies using appropriate experimental models.

The effect of thiamine pyrophosphate on ethambutol-induced ocular toxicity

CONTEXT

Ethambutol-induced retinal oxidative damage in patients with tuberculosis is still not being adequately treated. The protective effect of thiamine pyrophosphate against oxidative damage in some tissues has been reported, but no information on the protective effects of thiamine pyrophosphate against ethambutol-induced oxidative retinal damage has been found in the medical literature.

OBJECTIVE

The objective is to investigate whether thiamine pyrophosphate has a protective effect against oxidative retinal damage in rats induced by ethambutol.

MATERIALS AND METHODS

Experimental animals divided into four groups (n = 10): the healthy group (HG), the ethambutol control group (EMB), thiamine + ethambutol group (Thi-EMB) and thiamine pyrophosphate + ethambutol group (TPP-EMB). The rats in the TPP-EMB and Thi-EMB groups were administered thiamine pyrophosphate and thiamine, respectively, at doses of 20 mg/kg intraperitoneally. Distilled water was administered intraperitoneally to the HG and the EMB groups as a solvent in the same volumes. One hour after drug injection, 30 mg/kg ethambutol was administered via an oral gavage to the TPP-EMB, Thi-EMB and EMB groups. This procedure was repeated once a day for 90 days. At the end of this period, all rats were euthanized under high-dose thiopental sodium anesthesia, and biochemical and histopathological investigations of the retinal tissue were performed.

RESULTS

Malondialdehyde (MDA) and DNA damage product 8-hydroxyguanine levels were significantly lower in the retinal tissue of TPP-EMB and HG groups compared to those of the Thi-EMB and EMB groups, and total glutathione (tGSH) was also found to be higher. In addition, severe retinal tissue vascularization, edema and loss of ganglion cells were observed in the Thi-EMB and EMB groups, whereas histopathological findings for the TPP-EMB group were observed to be close to normal.

DISCUSSION AND CONCLUSION

These findings suggest that thiamine pyrophosphate protects retinal tissues from ethambutol-induced oxidative damage, and thiamine does not. This positive effect of thiamine pyrophosphate may be useful in the prevention of ocular toxicity that occurs during ethambutol use.

Photocoagulation of human retinal pigment epithelium in vitro: unravelling the effects on ARPE-19 by transcriptomics and proteomics

PURPOSE

Despite the extensive use of retinal photocoagulation for ischaemia and vascular leakage in retinal vascular disease, the molecular mechanisms behind its clinical beneficial effects are still poorly understood. One important target of laser irradiation is the retinal pigment epithelium (RPE). In this study, we aimed at identifying the isolated effects of photocoagulation of RPE at both the mRNA and protein expression levels.

METHODS

Human ARPE-19 cells were exposed to photocoagulation. Gene expression and protein expression were compared to untreated cells using microarray and liquid chromatography-mass spectrometry analysis. Genes and proteins queried by microarray and mass spectrometry were subjected to the Kyoto Encyclopedia of Genes and Genomes (KEGG) database pathway analyses.

RESULTS

Laser irradiation resulted in an induction of the cytoprotective heat-shock protein subfamily Hsp70 as well as in a suppression of the vascular permeability factor carbonic anhydrase 9 (CA9). These expression patterns were evident at both the mRNA and protein levels. KEGG pathway analyses revealed genes and proteins involved in cellular turnover, repair and inflammation.

CONCLUSIONS

By characterizing the transcriptional and translational effects of laser coagulation on the RPE cells in culture, we have revealed responses, which might contribute to some of the beneficial effects obtained by photocoagulation for ischaemia and vascular leakage in retinal vascular disease.

Ebselen by modulating oxidative stress improves hypoxia-induced macroglial Müller cell and vascular injury in the retina

Oxidative stress is an important contributor to glial and vascular cell damage in ischemic retinopathies. We hypothesized that ebselen via its ability to reduce reactive oxygen species (ROS) and augment nuclear factor-like 2 (Nrf2) anti-oxidants would attenuate hypoxia-induced damage to macroglial Müller cells and also lessen retinal vasculopathy. Primary cultures of rat Müller cells were exposed to normoxia (21% O2), hypoxia (0.5% O2) and ebselen (2.5 μM) for up to 72 h. Oxygen-induced retinopathy (OIR) was induced in C57BL/6J mice while control mice were housed in room air. Mice received vehicle (saline, 5% dimethyl sulfoxide) or ebselen (10 mg/kg) each day between postnatal days 6-18. In cultured Müller cells, flow cytometry for dihydroethidium revealed that ebselen reduced the hypoxia-induced increase in ROS levels, whilst increasing the expression of Nrf2-regulated anti-oxidant genes, heme oxygenase 1, glutathione peroxidase-1, NAD(P)H dehydrogenase quinone oxidoreductase 1 and glutamate-cysteine ligase. Moreover, in Müller cells, ebselen reduced the hypoxia-induced increase in protein levels of pro-angiogenic and pro-inflammatory factors including vascular endothelial growth factor, interleukin-6, monocyte chemoattractant-protein 1 and intercellular adhesion molecule-1, and the mRNA levels of glial fibrillary acidic protein (GFAP), a marker of Müller cell injury. Ebselen improved OIR by attenuating capillary vaso-obliteration and neovascularization and a concomitant reduction in Müller cell gliosis and GFAP. We conclude that ebselen protects against hypoxia-induced injury of retinal Müller cells and the microvasculature, which is linked to its ability to reduce oxidative stress, vascular damaging factors and inflammation. Agents such as ebselen may be potential treatments for retinopathies that feature oxidative stress-mediated damage to glia and the microvasculature.

NADPH oxidase 4-derived H2O2 promotes aberrant retinal neovascularization via activation of VEGF receptor 2 pathway in oxygen-induced retinopathy

NADPH oxidase 4 (Nox4) is a major isoform of NADPH oxidase in retinal endothelial cells. Our previous study suggests that upregulation of Nox4 in retinal endothelial cells contributes to retinal vascular leakage in diabetes. In the current study, we investigated the role and mechanism of Nox4 in regulation of retinal neovascularization (NV), a hallmark of proliferative diabetic retinopathy (PDR), using a mouse model of oxygen-induced retinopathy (OIR). Our results confirmed that Nox4 was expressed predominantly in retinal vasculature of mouse retina. Retinal expression of Nox4 was markedly increased in OIR, in parallel with enhanced phosphorylation of ERK. In human retinal microvascular endothelial cells (HRECs), overexpression of Nox4 by adenovirus significantly increased extracellular H2O2 generation, resulting in intensified VEGFR2 activation and exacerbated angiogenesis upon VEGF stimulation. In contrast, silencing Nox4 expression or scavenging H2O2 by polyethylene glycol- (PEG-) conjugated catalase inhibited endothelial migration, tube formation, and VEGF-induced activation of VEGFR2 signaling. Importantly, knockdown of retinal Nox4 by adenovirus-delivered siRNA significantly reduced ERK activation and attenuated retinal NV formation in OIR. Taken together, our data indicate that Nox4 promotes retinal NV formation through H2O2/VEGFR2/ERK signaling pathway. Reducing retinal Nox4 expression may represent a promising therapeutic approach for neovascular retinal diseases such as PDR.

Pathophysiology and mechanisms of severe retinopathy of prematurity

Retinopathy of prematurity (ROP) affects only premature infants, but as premature births increase in many areas of the world, ROP has become a leading cause of childhood blindness. Blindness can occur from aberrant developmental angiogenesis that leads to fibrovascular retinal detachment. To treat severe ROP, it is important to study normal developmental angiogenesis and the stresses that activate pathologic signaling events and aberrant angiogenesis in ROP. Vascular endothelial growth factor (VEGF) signaling is important in both physiologic and pathologic developmental angiogenesis. Based on studies in animal models of oxygen-induced retinopathy (OIR), exogenous factors such as oxygen levels, oxidative stress, inflammation, and nutritional capacity have been linked to severe ROP through dysregulated signaling pathways involving hypoxia-inducible factors and angiogenic factors like VEGF, oxidative species, and neuroprotective growth factors to cause phases of ROP. This translational science review focuses on studies performed in animal models of OIR representative of human ROP and highlights several areas: mechanisms for aberrant growth of blood vessels into the vitreous rather than into the retina through over-activation of VEGF receptor 2 signaling, the importance of targeting different cells in the retina to inhibit aberrant angiogenesis and promote physiologic retinal vascular development, toxicity from broad and targeted inhibition of VEGF bioactivity, and the role of VEGF in neuroprotection in retinal development. Several future translational treatments are discussed, including considerations for targeted inhibition of VEGF signaling instead of broad intravitreal anti-VEGF treatment.

Current concepts of oxygen management in retinopathy of prematurity

Retinopathy of prematurity (ROP) is a potentially blinding disorder in premature infants. The underlying pathophysiology is incompletely understood, limiting the prevention and treatment of this devastating condition. Current therapies are directed toward management of aberrant neovascularization thought to result from retinal ischemia in the developing preterm retina. The molecular mediators important for development of retinal ischemia and subsequent neovascular pathology are not fully understood. However, oxygen has been shown to be a key mediator of disease and the oxygen environment for preterm infants has been extensively studied. Despite this, the optimal oxygen environment for preterm infants remains unclear and recent works seeking to clarify this relationship demonstrate somewhat disparate findings. These data further substantiate that ROP is a complex disease with multifactorial etiology including genetic and environmental factors. Therefore, while environmental factors such as oxygen are important to our understanding of the disease process and care of preterm infants, identification of the molecular mediators downstream of oxygen which are necessary for development of ROP pathology will be critical to improve prevention, diagnosis and treatment strategies.