Oxidants, nitric oxide and prostanoids in the developing ocular vasculature: a basis for ischemic retinopathy

Lutein supplementation for early-life health and development: current knowledge, challenges, and implications

Macular carotenoids, which consist of lutein, zeaxanthin, and meso-zeaxanthin, are dietary antioxidants and macular pigments in the eyes, protecting the macula from light-induced oxidative stress. Lutein is also the main carotenoid in the infant brain and is involved in cognitive development. While a few articles reviewed the role of lutein in early health and development, the current review is the first that focuses on the outcomes of lutein supplementation, either provided to mothers or to infants. Additionally, lutein status and metabolism during pregnancy and lactation, factors that limit the potential application of lutein as a nutritional intervention, and solutions to overcome the limitation are also discussed. In brief, the lutein intake in pregnant and lactating women in the United States may not be optimal. Furthermore, preterm and formula-fed infants are known to have compromised lutein status compared to term and breast-fed infants, respectively. While lutein supplementation via both maternal and infant consumption improves lutein status in infants, the application of lutein as a nutritional intervention may be compromised by its low bioavailability. Various encapsulation techniques have been developed to enhance the delivery of lutein in adult animals or human but should be further evaluated in neonatal models.

Does the use of higher versus lower oxygen concentration improve neurodevelopmental outcomes at 18-24 months in very low birthweight infants?

BACKGROUND

Immediately after birth, the oxygen saturation is between 30 and 50%, which then increases to 85-95% within the first 10 min. Over the last 10 years, recommendations regarding the ideal level of the initial fraction of inspired oxygen (FiO2) for resuscitation in preterm infants have changed from 1.0, to room air to low levels of oxygen (< 0.3), up to moderate concentrations (0.3-0.65). This leaves clinicians in a challenging position, and a large multi-center international trial of sufficient sample size that is powered to look at safety outcomes such as mortality and adverse neurodevelopmental outcomes is required to provide the necessary evidence to guide clinical practice with confidence.

METHODS

An international cluster, cross-over randomized trial of initial FiO2 of 0.3 or 0.6 during neonatal resuscitation in preterm infants at birth to increase survival free of major neurodevelopmental outcomes at 18 and 24 months corrected age will be conducted. Preterm infants born between 230/7 and 286/7 weeks' gestation will be eligible. Each participating hospital will be randomized to either an initial FiO2 concentration of either 0.3 or 0.6 to recruit for up to 12 months' and then crossed over to the other concentration for up to 12 months. The intervention will be initial FiO2 of 0.6, and the comparator will be initial FiO2 of 0.3 during respiratory support in the delivery room. The sample size will be 1200 preterm infants. This will yield 80% power, assuming a type 1 error of 5% to detect a 25% reduction in relative risk of the primary outcome from 35 to 26.5%. The primary outcome will be a composite of all-cause mortality or the presence of a major neurodevelopmental outcome between 18 and 24 months corrected age. Secondary outcomes will include the components of the primary outcome (death, cerebral palsy, major developmental delay involving cognition, speech, visual, or hearing impairment) in addition to neonatal morbidities (severe brain injury, bronchopulmonary dysplasia; and severe retinopathy of prematurity).

DISCUSSION

The use of supplementary oxygen may be crucial but also potentially detrimental to preterm infants at birth. The HiLo trial is powered for the primary outcome and will address gaps in the evidence due to its pragmatic and inclusive design, targeting all extremely preterm infants. Should 60% initial oxygen concertation increase survival free of major neurodevelopmental outcomes at 18-24 months corrected age, without severe adverse effects, this readily available intervention could be introduced immediately into clinical practice.

TRIAL REGISTRATION

The trial was registered on January 31, 2019, at ClinicalTrials.gov with the Identifier: NCT03825835.

NCX 470 Exerts Retinal Cell Protection and Enhances Ophthalmic Artery Blood Flow After Ischemia/Reperfusion Injury of Optic Nerve Head and Retina

Purpose

The purpose of this study was to assess the retinal protective activity and ocular hemodynamics after NCX 470 (0.1%) compared to bimatoprost administered as the US Food and Drug Administration (FDA)-approved drug (Lumigan - 0.01% ophthalmic solution, LUM) and at an equimolar dose (0.072%, BIM) to that released by NCX 470.

Methods

Endothelin-1 (ET-1) induced ischemia/reperfusion injury model in rabbits was used. ET-1 was injected nearby the optic nerve head (ONH) twice/week for 6 weeks. Starting on week 3, the animals received vehicle (VEH), NCX 470, LUM, or BIM (30 µL/eye, twice daily, 6 days/week) until the end of ET-1 treatment. Intraocular pressure (IOP), ophthalmic artery resistive index (OA-RI), and electroretinogram (ERG) data were collected prior to dosing and at different time points postdosing. Reduced glutathione, 8-Hydroxy 2-deoxyguanosine, and Caspase-3 were determined in the retina of treated eyes. DNA fragmentation was determined by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) staining.

Results

ET-1 increased IOP (VEHIOP_Baseline = 20.5 ± 0.8 and VEHIOP_Week6 = 24.8 ± 0.3 mmHg) and OA-RI (VEHOA-RI_Baseline = 0.36 ± 0.02 and VEHOA-RI_Week6 = 0.55 ± 0.01) and reduced rod/cone responses over time. Oxidative stress, inflammation, and apoptotic markers increased in ET-1-treated eyes. NCX 470 prevented IOP (NCX 470IOP_Week6 = 18.1 ± 0.6 mmHg) and OA-RI changes (NCX 470OA-RI_Week6 = 0.33 ± 0.01) and restored ERG amplitude leaving unaltered the respective latency; these effects were only partially demonstrated by LUM or BIM. Additionally, NCX 470 reduced oxidative stress, inflammation, and apoptosis in the retinas of treated eyes. BIM and LUM were numerically less effective on these parameters.

Conclusions

NCX 470 repeated ocular dosing ameliorates ocular hemodynamics and retinal cell dysfunction caused by ischemia/reperfusion via nitric oxide- and bimatoprost-mediated mechanisms.

Translational Relevance

If confirmed in clinical setting our data may open new therapeutic opportunities to reduce visual field loss in glaucoma.

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.

Neurovascular abnormalities in retinopathy of prematurity and emerging therapies

Blood vessels in the developing retina are formed in concert with neural growth, resulting in functional neurovascular network. Disruption of the neurovascular coordination contributes to the pathogenesis of retinopathy of prematurity (ROP), a potentially blinding retinal neovascular disease in preterm infants that currently lacks an approved drug therapy in the USA. Despite vasculopathy as predominant clinical manifestations, an increasing number of studies revealed complex neurovascular interplays among neurons, glial cells and blood vessels during ROP. Coordinated expression of glia-derived vascular endothelial growth factor (VEGF) in spatio-temporal gradients is pivotal to the formation of well-organized vascular plexuses in the healthy retina, whereas uncoordinated VEGF expression triggers pathological angiogenesis with disorganized vascular tufts in ROP. In contrast with VEGF driving both pathological and physiological angiogenesis, neuron-derived angiogenic factor secretogranin III (Scg3) stringently regulates ROP but not healthy retinal vessels in animal models. Anti-VEGF and anti-Scg3 therapies confer similar high efficacies to alleviate ROP in preclinical studies but are distinct in their disease selectivity and safety. This review discusses neurovascular communication among retinal blood vessels, neurons and glial cells during retinal development and ROP pathogenesis and summarizes the current and emerging therapies to address unmet clinical needs for the disease.

Ductus Arteriosus of Extremely Preterm Twins is More Resistant to Cyclooxygenase Inhibitors Than Those of Singletons

Symptomatic patent ductus arteriosus (sPDA) is common among preterm infants, and can lead to several complications. This is particularly true for extremely preterm infants, as closure of the ductus arteriosus using cyclooxygenase inhibitors is often difficult. A recent study using a preterm sheep model showed that intimal thickening-required for anatomical closure of the ductus arteriosus-is less developed in twins than in singletons. Therefore, this study primarily aimed to prove that the ductus arteriosus of extremely preterm twins is more resistant to cyclooxygenase inhibitors than those of extremely preterm singletons. Its secondary aim was to assess whether the resistance against cyclooxygenase inhibitors differed according to chorionicity. In this retrospective case-control study, medical records of 162 extremely preterm infants (gestational age < 28 weeks) were reviewed, and the treatment course of sPDA was subsequently compared between singletons (n = 131) and twins (n = 31). The median indomethacin doses for sPDA and the necessity for surgical ligation were significantly higher in twins than in singletons (5 vs 2 [p < 0.001] and 42% vs 21% [p = 0.018], respectively). No significant differences in sPDA treatment, including the number of indomethacin doses and the necessity for surgical ligation, were observed between monochorionic diamniotic and dichorionic diamniotic twins. This study confirms that the ductus arteriosus of extremely preterm twins is more resistant to cyclooxygenase inhibitors than those of singletons. However, there was no significant difference in sPDA treatment by chorionicity.

Endothelial nitric oxide synthase G894T, intron 4 VNTR, and T786C polymorphisms in retinopathy of prematurity

BACKGROUND

Our objective in this study was to assess the association between eNOS gene, that achieves synthesis of nitric oxide especially in the endothelial cells known to have an important role in angiogenesis and vasculogenesis, G894T, intron 4 VNTR (27-bp repeat) and T786C functional polymorphisms and retinopathy of prematurity (ROP), which is an important cause of morbidity in premature or low birth weight babies.

METHODS

A total of 139 babies who were followed up in our neonatal intensive care unit because of premature birth in our hospital or admitted to our unit. 69 of them had retinopathy of prematurity and comprised the patients group. The remaining 70 babies who did not have ROP comprised the control group. An additional of 1 ml of blood samples were drawn from babies who were in the study groups during routine laboratory analysis. eNOS gene polymorphisms were determined by using polymerase chain reaction method.

RESULTS

eNOS G894T, intron 4 VNTR and T786C gene polymorphisms did not differ between the patient and control groups (p >  0.05). Using logistic regression analysis; while gender did not differ between two groups; gestational age, birth weight, time on mechanical ventilation differ between two groups. After adjustment for variables other than eNOS gene polymorphisms, we found no significant difference in the genotype distribution of eNOS G894T, intron 4 VNTR and T786C polymorphisms (p >  0.05).

CONCLUSION

We observed no association between ROP and eNOS gene polymorphisms but needs more investigation.

Reduced Retinal Microvascular Perfusion in Patients With Stroke Detected by Optical Coherence Tomography Angiography

Currently there is a shortage of biomarkers for stroke, one of the leading causes of death and disability in aging populations. Retinal vessels offer a unique and accessible “window” to study the microvasculature in vivo. However, the relationship between the retinal microvasculature and stroke is not entirely clear. To investigate the retinal microvascular characteristics in stroke, we recruited patients with stroke and age-matched control subjects from a tertiary hospital in China. The macular vessel density (VD) in the superficial capillary plexus (SCP) and deep capillary plexus (DCP), foveal avascular zone (FAZ) metrics, and optical coherence tomography angiography (OCTA) measured optic disc VD were recorded for analysis. A total of 189 patients with stroke and 195 control subjects were included. After adjusting for sex, visual acuity, systolic and diastolic blood pressure, a history of smoking, levels of hemoglobulin (HbA1c), cholesterol, and high-density lipoprotein (HDL), the macular VD of SCP and DCP in all sectors was decreased in patients with stroke. In the stroke group, the VD around the FAZ and the VD of the optic disk were lower. Logistic regression found the parafovea-superior-hemi VD of DCP > 54.53% [odds ratio (OR): 0.169] as a protective factor of stroke. Using the integration of all OCTA parameters and traditional risk factors, the area under the receiver operating characteristic (AUC) curve of distinguishing patients with stroke was 0.962, with a sensitivity of 0.944 and a specificity of 0.871. Our study demonstrates that the retinal VD is decreased in patients with stroke independently of the traditional risk factors of stroke, which may shed light on the monitoring of stroke using the retinal microvascular parameters.

Modeling the Removal and Addition of Eggs in the Current US Diet is Linked to Choline and Lutein + Zeaxanthin Usual Intakes in Childhood

BACKGROUND

Limited data are available examining nutritional implications for removing/adding eggs in childhood dietary patterns. Additionally, usual intake data are lacking for choline and lutein + zeaxanthin in childhood.

OBJECTIVES

To determine usual intakes of choline and lutein + zeaxanthin in egg consumers and model the removal and addition of eggs within dietary patterns on choline and lutein + zeaxanthin intakes.

METHODS

Data from the NHANES, 2011-2014, were analyzed in egg consumers (infants, n = 130; children/adolescents, n = 980) of various age groups during childhood. Additionally, a modeling analysis was conducted to examine choline and lutein + zeaxanthin intake following the removal and addition of eggs to the current American diet of children.

RESULTS

Overall, modeling removal of eggs from the diet in all age groups examined showed decreases in choline intakes, resulting in significantly fewer subjects above the recommended Adequate Intake (AI) for choline. In contrast, the addition of 1 egg per week to the current American eating pattern resulted in nearly 10% more infants 6-23 months of age being above the AI for choline intake. The addition of 7 eggs per week to the current dietary pattern of infants would nearly achieve 100% of infants meeting the AI for choline. In children 2-8 years old, modeling an additional 7 eggs per week to the current dietary pattern resulted in approximately 94% of children being above the AI for choline, while the addition of 7 eggs per week increases the percentages above the AI to 23.0% and 52.4% in children aged 9-18 and 2-18 years, respectively. In children aged 2-8 and 2-18 years old, the addition of 7 eggs per week also showed meaningful increases in lutein + zeaxanthin usual intakes relative to the current dietary pattern (i.e., lutein + zeaxanthin increased from nearly 775 mcg/day to approximately 916 mcg/day and 780 mcg/day to approximately 931 mcg/day, respectively).

CONCLUSIONS

The current data support egg consumption as part of healthy dietary patterns to help meet established choline recommendations, while concurrently increasing lutein and zeaxanthin intakes in childhood.

Prognostic Value of Oxidative Stress Markers in Patients with Pulmonary Arterial or Chronic Thromboembolic Pulmonary Hypertension

Oxidative stress is regarded to play a crucial role in the pathophysiology of pulmonary arterial hypertension (PAH) and inoperable chronic thromboembolic pulmonary hypertension (CTEPH). This study evaluated the prognostic value of serum oxidative stress markers (malondialdehyde (MDA), total antioxidant capacity (TAC), catalase activity (CAT), and superoxide activity (SOD)) in patients with PAH and CTEPH (n = 45). During 13 months of follow-up (median 9 months), clinical deterioration occurred in 14 patients (including 2 deaths). On the Cox regression analysis, MDA, TAC, and CAT were associated with clinical deterioration (p = 0.0068, HR = 1.42, 95% CI: 1.10-1.82; p = 0.0038, HR = 0.033, 95% CI: 0.0032-0.33; and p = 0.046, HR = 0.20, 95% CI: 0.04-0.98, respectively). There was no significant difference in SOD (p = 0.53, HR = 0.97, 95% CI: 0.87-1.08). The cut-off value derived from ROC curve analysis was 3.79 μM (p = 0.0048, AUC = 0.76, 95% CI: 0.62-0.91) for MDA, 0.49 mM (p = 0.027, AUC = 0.71, 95% CI: 0.18-0.47) for TAC, and 1.34 U/L (p = 0.029, AUC = 0.71, 95% CI: 0.55-0.86) for CAT. MDA in the group with deterioration was higher (p = 0.0041), while TAC as well as CAT were lower (p = 0.027 and p = 0.028, respectively) when compared to stable patients. Survival without clinical deterioration was significantly longer in patients with lower MDA (p = 0.037, HR = 0.37, 95% CI: 0.12-1.14, log-rank), higher TAC (p = 0.0018, HR = 0.19, 95% CI: 0.06-0.60, log-rank), and higher CAT (p = 0.044, HR = 0.31 95% CI: 0.11-0.88, log-rank). Markers of oxidative stress such as MDA, TAC, and CAT were associated with adverse clinical outcomes in patients with PAH and inoperable or residual CTEPH.

Pharmacologic interventions for the prevention and treatment of retinopathy of prematurity

Retinopathy of Prematurity (ROP) is a preventable neovascular retinal disease with a lifetime impact on vision and ocular morbidities. Retinal vessel immaturity and oxygen therapy, influenced or modulated by several risk factors including oxidative stress, intermittent hypoxia and desaturations, inflammation, infection, malnutrition, retinal growth factor deficiencies or excesses, and others are determinant factors of pathologic retinal angiogenesis and ROP. These factors are pharmacologic targets for prevention and/or rescue therapy. These drugs, include intravitreal anti-vascular endothelial growth factor drugs, erythropoietin, ocular propranolol, caffeine, antioxidants, insulin-like growth factor-I, and omega 3 poly-unsaturated fatty acids, and are promising therapies to prevent ROP, but require further studies. Topical ocular non-steroidal anti-inflammatory drugs (NSAIDs) target inflammatory cascade but the best, safest, and most effective ocular NSAID and formulation remain to be developed. Timing of drug intervention appears critical. Moreover, the complex interactions of the various pathophysiologic mechanisms resulting in aberrant angiogenesis thence ROP strongly suggest that drug combinations and synergisms may be required for effective prevention of ROP and a lifetime of blindness.

Oxygen therapy in premature low birth weight infants is associated with capillary loss and increases in blood pressure: a pilot study

Low birth weight (LBW) and premature birth are known risk factors for future cardiovascular disease and in particular essential hypertension (EH). Capillary rarefaction (CR) is an established hallmark of EH and is known to occur in individuals with a history of LBW. We previously reported that LBW infants do not have CR at birth but rather increased capillary density (CD). We hypothesized that LBW infants undergo a process of accelerated CR in early life, triggered in part by oxygen therapy. We studied 26 LBW infants, of whom 10 infants received oxygen therapy, and compared them to 14 normal birth weight (NBW) infants. We measured CD at 1, 5 and 10 days after birth and again after 40 weeks adjusted gestational age equivalent to birth at full term. We confirmed that LBW infants had higher CD at birth compared to NBW infants and found that significant structural CR occurred at term age in LBW infants who had received oxygen therapy (mean difference -22 capillaries/field, p = 0.007) and in those who did not receive oxygen therapy (mean difference -29 capillaries/field, p < 0.001) compared to baseline at birth. Both LBW groups showed a significant rise in BP at 40 weeks adjusted term age and the rise in systolic (mean difference 24 mm Hg, p < 0.0001) and diastolic BP (mean difference 14 mm Hg, p < 0.001) was more pronounced in the oxygen treated group compared to the nonoxygen group (mean difference 14 mm Hg, p = 0.043 and mean difference = 9 mm Hg p = 0.056 respectively). In conclusion, oxygen therapy in premature LBW infants may induce significant increases in their BP in early life.

Lutein and zeaxanthin: The possible contribution, mechanisms of action and implications of modern dietary intake for cognitive development in children

Background:Studies suggest that lutein and zeaxanthin may be important for cognitive development in children, but a comprehensive evidence synthesis is lacking. The purpose of this evidence synthesis was to analyse the available data regarding the role of lutein and zeaxanthin for cognition in children and propose a theoretical basis for future studies.Methods:The PubMed, Scopus, the ISRCTN registry and Cochrane Library databases were searched for studies that evaluated the relationship between lutein and zeaxanthin and cognitive function in children. Reference list and ancestry searches were performed on relevant articles. A total of 543 articles were identified, of which six cross-sectional studies were included.Results:The literature search revealed that the evidence concerning the effect of lutein and zeaxanthin on cognition in children is sparse. However, there is some preliminary evidence indicating a positive association between lutein and zeaxanthin and cognition in childhood.Conclusions:The cross-sectional nature of the few studies available and the lack of RCT data indicates a need for further investigation before any firm conclusions can be drawn.

Vascular Interstitial Cells in Retinal Arteriolar Annuli Are Altered During Hypertension

Purpose

It has been suggested that arteriolar annuli localized in retinal arterioles regulate retinal blood flow acting as sphincters. Here, the morphology and protein expression profile of arteriolar annuli have been analyzed under physiologic conditions in the retina of wild-type, β-actin-Egfp, and Nestin-gfp transgenic mice. Additionally, to study the effect of hypertension, the KAP transgenic mouse has been used.

Methods

Cellular architecture has been studied using digested whole mount retinas and transmission electron microscopy. The profile of protein expression has been analyzed on paraffin sections and whole mount retinas by immunofluorescence and histochemistry.

Results

The ultrastructural analysis of arteriolar annuli showed a different cell population found between endothelial and muscle cells that matched most of the morphologic criteria established to define interstitial Cajal cells. The profile of protein expression of these vascular interstitial cells (VICs) was similar to that of interstitial Cajal cells and different from the endothelial and smooth muscle cells, because they expressed β-actin, nestin, and CD44, but they did not express CD31 and α-SMA or scarcely express F-actin. Furthermore, VICs share with pericytes the expression of NG2 and platelet-derived growth factor receptor beta (PDGFR-β). The high expression of Ano1 and high activity of nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase observed in VICs was diminished during hypertensive retinopathy suggesting that these cells might play a role on the motility of arteriolar annuli and that this function is altered during hypertension.

Conclusions

A novel type of VICs has been described in the arteriolar annuli of mouse retina. Remarkably, these cells undergo important molecular modifications during hypertensive retinopathy and might thus be a therapeutic target against this disease.

Retinopathy of prematurity: inflammation, choroidal degeneration, and novel promising therapeutic strategies

Retinopathy of prematurity (ROP) is an important cause of childhood blindness globally, and the incidence is rising. The disease is characterized by initial arrested retinal vascularization followed by neovascularization and ensuing retinal detachment causing permanent visual loss. Although neovascularization can be effectively treated via retinal laser ablation, it is unknown which children are at risk of entering this vision-threatening phase of the disease. Laser ablation may itself induce visual field deficits, and there is therefore a need to identify targets for novel and less destructive treatments of ROP. Inflammation is considered a key contributor to the pathogenesis of ROP. A large proportion of preterm infants with ROP will have residual visual loss linked to loss of photoreceptor (PR) and the integrity of the retinal pigment epithelium (RPE) in the macular region. Recent studies using animal models of ROP suggest that choroidal degeneration may be associated with a loss of integrity of the outer retina, a phenomenon so far largely undescribed in ROP pathogenesis. In this review, we highlight inflammatory and neuron-derived factors related to ROP progression, as well, potential targets for new treatment strategies. We also introduce choroidal degeneration as a significant cause of residual visual loss following ROP. We propose that ROP should no longer be considered an inner retinal vasculopathy only, but also a disease of choroidal degeneration affecting both retinal pigment epithelium and photoreceptor integrity.

Health Effects of Carotenoids during Pregnancy and Lactation

Adequate nutrition is particularly important during pregnancy since it is needed not only for maintaining the health of the mother, but also determines the course of pregnancy and its outcome, fetus development as well as the child’s health after birth and during the later period of life. Data coming from epidemiological and interventions studies support the observation that carotenoids intake provide positive health effects in adults and the elderly population. These health effects are the result of their antioxidant and anti-inflammatory properties. Recent studies have also demonstrated the significant role of carotenoids during pregnancy and infancy. Some studies indicate a correlation between carotenoid status and lower risk of pregnancy pathologies induced by intensified oxidative stress, but results of these investigations are equivocal. Carotenoids have been well studied in relation to their beneficial role in the prevention of preeclampsia. It is currently hypothesized that carotenoids can play an important role in the prevention of preterm birth and intrauterine growth restriction. Carotenoid status in the newborn depends on the nutritional status of the mother, but little is known about the transfer of carotenoids from the mother to the fetus. Carotenoids are among the few nutrients found in breast milk, in which the levels are determined by the mother’s diet. Nutritional status of the newborn directly depends on its diet. Both mix feeding and artificial feeding may cause depletion of carotenoids since infant formulas contain only trace amounts of these compounds. Carotenoids, particularly lutein and zeaxanthin play a significant role in the development of vision and nervous system (among others, they are important for the development of retina as well as energy metabolism and brain electrical activity). Furthermore, more scientific evidence is emerging on the role of carotenoids in the prevention of disorders affecting preterm infants, who are susceptible to oxidative stress, particularly retinopathy of prematurity.

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.

Pharmacologic synergism of ocular ketorolac and systemic caffeine citrate in rat oxygen-induced retinopathy

BACKGROUND

Caffeine or ketorolac decrease the risk of retinopathy of prematurity and may act synergistically to improve beneficial effect. Combination of caffeine (Caff) and ketorolac (Keto) to prevent oxygen-induced retinopathy was studied.

METHODS

Newborn rats exposed to room air (RA) or intermittent hypoxia (IH) consisting of 12% O2 during hyperoxia (50% O2) from birth (P0) had single daily IP injections of Caff from P0-P13 or saline; and/or ocular Keto (Acuvail, 0.45% ophthalmic solution) administered subcutaneously over the eyes from P5-P7. Pups were studied at P14 or placed in RA for recovery from IH (IHR) until P21. Eyes were examined for neovascularization, histopathology, growth factors, and VEGF-signaling genes.

RESULTS

Severe retinal damage noted during IHR in the untreated groups evidenced by hemorrhage, neovascularization, and oxygen-induced retinopathy (OIR) pathologies were prevented with Keto/Caff treatment. Keto and/or Caff treatment in IH also promoted retinal neural development evidenced by eye opening (92%, P < 0.001 vs. 31% in the placebo-treated IH group). No corneal pathologies were noted with Keto.

CONCLUSION

Caff or Keto given individually reduced retinal neovascularization, but the two drugs given together prevented severe OIR.

Pharmacologic interventions for the prevention and treatment of retinopathy of prematurity

Retinopathy of prematurity (ROP), a significant morbidity in prematurely born infants, is the most common cause of visual impairment and blindness in children and persists till adulthood. Strict control of oxygen therapy and prevention of intermittent hypoxia are the keys in the prevention of ROP, but pharmacologic interventions have decreased risk of ROP. Various drug classes such as methylxanthines (caffeine), VEGF inhibitors, antioxidants, and others have decreased ROP occurrence. The timing of pharmacologic intervention remains unsettled, but early prevention rather than controlling disease progression may be preferred. These drugs act through different mechanisms, and synergistic approaches should be considered to maximize efficacy and safety.

Models of Oxygen Induced Retinopathy in Rodents

Much of the knowledge we have gained into the development of pathological ocular angiogenesis has come from the development of in vivo models that enable functional assessment of key components of signaling pathways in disease progression. Indeed, rodent models have facilitated identification of several therapeutics that target pathological angiogenesis. Two of the most widely used rodent models of oxygen induced retinopathy (OIR), Smith's mouse model and Penn's rat model reproducibly induce neovascularization reminiscent of the disease retinopathy of prematurity (ROP). In this chapter we discuss development of ROP in humans and compare features with that of the rat and mouse models, focusing both on the benefits and caveats of using such models. Furthermore, we discuss in detail the methodology of both procedures and discuss the importance of various features of the model.

Role of macular xanthophylls in prevention of common neovascular retinopathies: retinopathy of prematurity and diabetic retinopathy

Retinopathy of prematurity (ROP) and diabetic retinopathy (DR) are important causes of blindness among children and working-age adults, respectively. The development of both diseases involves retinal microvascular degeneration, vessel loss and consequent hypoxic and inflammatory pathologic retinal neovascularization. Mechanistic studies have shown that oxidative stress and subsequent derangement of cell signaling are important factors in disease progression. In eye and vision research, role of the dietary xanthophyll carotenoids, lutein and zeaxanthin, has been more extensively studied in adult onset macular degeneration than these other retinopathies. These carotenoids also may decrease severity of ROP in preterm infants and of DR in working-age adults. A randomized controlled clinical trial of carotenoid supplementation in preterm infants indicated that lutein has functional effects in the neonatal eye and is anti-inflammatory. Three multicenter clinical trials all showed a trend of decreased ROP severity in the lutein supplemented group. Prospective studies on patients with non-proliferative DR indicate serum levels of lutein and zeaxanthin are significantly lower in these patients compared to normal subjects. The present review describes recent advances in lutein and zeaxanthin modulation of oxidative stress and inflammation related to ROP and DR and discusses potential roles of lutein/zeaxanthin in preventing or lessening the risks of disease initiation or progression.

Arginase 2 deficiency prevents oxidative stress and limits hyperoxia-induced retinal vascular degeneration

Background

Hyperoxia exposure of premature infants causes obliteration of the immature retinal microvessels, leading to a condition of proliferative vitreoretinal neovascularization termed retinopathy of prematurity (ROP). Previous work has demonstrated that the hyperoxia-induced vascular injury is mediated by dysfunction of endothelial nitric oxide synthase resulting in peroxynitrite formation. This study was undertaken to determine the involvement of the ureahydrolase enzyme arginase in this pathology.

Methods and Findings

Studies were performed using hyperoxia-treated bovine retinal endothelial cells (BRE) and mice with oxygen-induced retinopathy (OIR) as experimental models of ROP. Treatment with the specific arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH) prevented hyperoxia-induced apoptosis of BRE cells and reduced vaso-obliteration in the OIR model. Furthermore, deletion of the arginase 2 gene protected against hyperoxia-induced vaso-obliteration, enhanced physiological vascular repair, and reduced retinal neovascularization in the OIR model. Additional deletion of one copy of arginase 1 did not improve the vascular pathology. Analyses of peroxynitrite by quantitation of its biomarker nitrotyrosine, superoxide by dihydroethidium imaging and NO formation by diaminofluoroscein imaging showed that the protective actions of arginase 2 deletion were associated with blockade of superoxide and peroxynitrite formation and normalization of NOS activity.

Conclusions

Our data demonstrate the involvement of arginase activity and arginase 2 expression in hyperoxia-induced vascular injury. Arginase 2 deletion prevents hyperoxia-induced retinal vascular injury by preventing NOS uncoupling resulting in decreased reactive oxygen species formation and increased nitric oxide bioavailability.

Melatonin prevents retinal oxidative stress and vascular changes in diabetic rats

PURPOSE

To evaluate the role of melatonin, an antioxidant agent, in diabetic oxidative stress and vascular damage.

METHODS

Diabetes was induced in 21 male Wistar rats by intraperitoneal (IP) administration of streptozotocin and then the rats were equally and randomly allocated to diabetic, melatonin, and vehicle groups. Seven healthy normal rats with similar features comprised the control group as the fourth group. All animals were followed for 12 weeks. The melatonin group received IP melatonin daily and the vehicle group received 2.5% ethanol IP at the last month. At the end of 12 weeks, the rats were killed and retinas were harvested. The retinas were investigated for the existence of hypoxia-inducible factor 1-α (HIF-1α), vascular endothelial growth factor A (VEGF-A), and pigment epithelium-derived factor (PEDF) by ELISA. Retinal oxidative stress is quantitated by measuring nitrotyrosine and malondialdehyde levels. Retinal immunohistochemistry with antibody against CD31 antigen was carried out on retinal cross-sections. For statistics, ANOVA test was used for multiple comparisons.

RESULTS

Hyperglycemia increased retinal oxidation as measured through levels of nitrotyrosine and malondialdehyde. Diabetic retinas are also associated with abnormal vascular changes such as dilatation and deformation. HIF-1α, VEGF-A, and PEDF were all increased because of diabetic injury. Melatonin showed a potential beneficial effect on retinopathy in diabetic rats. It decreased retinal nitrotyrosine and malondialdehyde levels, showing an antioxidative support. The vasculomodulator cytokines are decreased accordingly by melatonin therapy. Melatonin normalized retinal vascular changes as well.

CONCLUSION

Melatonin may show some advantage on diabetic vascular changes through decreasing oxidative stress and vessel-related cytokines.

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

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

Hydrogen peroxide accumulation in the choroid during intermittent hypoxia increases risk of severe oxygen-induced retinopathy in neonatal rats

PURPOSE

Extremely low gestational age neonates (ELGANs) requiring oxygen therapy often experience frequent episodes of intermittent hypoxia (IH) and are at high risk for severe retinopathy of prematurity (ROP). Using an established model for oxygen-induced retinopathy (OIR), we examined the hypothesis that there is a critical number of daily brief IH episodes which will result in irreversible retinal oxidative damage.

METHODS

Newborn rats were exposed to increasing daily clustered IH episodes (12% O₂ with 50% O₂) from postnatal day (P) 0 to P7 or P0 to P14, or placed in room air (RA) until P21 following 7- or 14-day IH. RA littermates at P7, P14, and P21 served as controls. A group exposed to constant 50% O₂ (CH) served as a second control. Blood gases, eye opening at P14, retinal, and choroidal oxidative stress and lipid peroxidation (8-isoPGF(2α)), oxidants (H₂O₂) and antioxidants (catalase and SOD), retinal pathology (adenosine diphosphatase (ADPase)-stained retinal flatmounts), and mitochondria-related genes were assessed.

RESULTS

pO₂ levels were higher with increasing IH episodes and remained elevated during the reoxygenation period. High SO₂ levels were associated with most severe OIR. Levels of all measured biomarkers peaked with six IH episodes and decreased with 8 to 12 episodes. H₂O₂ accumulated in the choroid during the reoxygenation period with irreversible retinal damage.

CONCLUSIONS

Our data suggest that six is the maximum number of IH episodes that the retina can sustain. Accumulation of H₂O₂ in the choroid may result in high levels being delivered to the entire retina, ultimately resulting in irreversible retinal oxidative damage.

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.

Hypoxia-inducible factor-1 (HIF-1): a potential target for intervention in ocular neovascular diseases

Constant oxygen supply is essential for proper tissue development, homeostasis and function of all eukaryotic organisms. Cellular response to reduced oxygen levels is mediated by the transcriptional regulator hypoxia-inducible factor-1 (HIF-1). It is a heterodimeric complex protein consisting of an oxygen dependent subunit (HIF-1α) and a constitutively expressed nuclear subunit (HIF-1β). In normoxic conditions, de novo synthesized cytoplasmic HIF-1α is degraded by 26S proteasome. Under hypoxic conditions, HIF-1α is stabilized, binds with HIF-1β and activates transcription of various target genes. These genes play a key role in regulating angiogenesis, cell survival, proliferation, chemotherapy, radiation resistance, invasion, metastasis, genetic instability, immortalization, immune evasion, metabolism and stem cell maintenance. This review highlights the importance of hypoxia signaling in development and progression of various vision threatening pathologies such as diabetic retinopathy, retinopathy of prematurity, age-related macular degeneration and glaucoma. Further, various inhibitors of HIF-1 pathway that may have a viable potential in the treatment of oxygen-dependent ocular diseases are also discussed.

Phytochemicals in ocular health: Therapeutic potential and delivery challenges

Diabetic retinopathy (DR) and age-related macular degeneration (AMD) are the leading causes of blindness in adults. The impact of these conditions on the quality of life is increasing in significance with a rise in life expectancy. The role of hyperglycemia, oxidative stress and inflammatory responses in the development and/or progression of DR and AMD, and several other sight threatening ocular diseases, is well established. In proliferative retinopathy, signals sent by the retina for nourishment, triggers the growth of fragile and abnormal blood vessels. Changes in ocular pressure may lead to rupture of these blood vessels causing severe vision problems. Recent in vitro and preclinical studies demonstrate that certain phytochemicals possessing potent antioxidant and anti-inflammatory activity and ocular blood flow enhancing properties may be very useful in the treatment of, or as a prophylactic measure for, DR and AMD. Apart from these properties they have also been investigated for their anti-bacterial, hormonal, enzyme stimulation, and anti-angiogenic activities. The attractive aspect of these potential therapeutic candidates is that they can act on multiple pathways identified in the etiology of DR, AMD, cataract and other ocular diseases. However, results from clinical trials have been somewhat ambiguous, raising questions about the concentrations of these bioflavonoids achieved in the neural retina following oral administration. Unfortunately, as of date, an efficient noninvasive means to deliver therapeutic agents/candidates to the back-of-the eye is still not available. This review examines some of these promising natural agents and discusses the challenges encountered in delivering them to the posterior segment ocular tissues through the oral route.

Triamcinolone acetonide prevents enhancement of hypoxia-induced neuronal and inducible nitric oxide synthases in the retinas of rats with oxygen-induced retinopathy

PURPOSE

We investigated whether oxygen-induced retinopathy (OIR) results in changes in the protein expression of neuronal and inducible nitric oxide synthases (nNOS and iNOS, respectively) in rat model of OIR. In addition, we evaluated whether treatment of rats with triamcinolone acetonide (TA) prevents this response.

METHODS

To promote OIR, Sprague-Dawley rats were exposed to hyperoxia from postnatal day 2 (P2) to P14. They were then returned to normoxia after P15. TA was injected into the right vitreous of P15 rats, while saline was injected into the left vitreous. At P18 the expression of nNOS and iNOS was determined using Western blotting and immunostaining techniques in retinas obtained from control rats.

RESULTS

In P18 OIR rats, the abundance of nNOS and iNOS protein was significantly increased compared with controls. These increases were not observed in the retinas of rats treated with TA. The change in expression of nNOS and iNOS were specific to parvalbumin and glial fibrillary acidic protein-positive cells. Treatment with TA prevented the increased expression of nNOS and iNOS in all samples.

CONCLUSIONS

Hypoxia upregulates expression of nNOS and iNOS in OIR rat retinas, which is can be prevented by treatment with TA.

Molecular mechanisms regulating the vascular prostacyclin pathways and their adaptation during pregnancy and in the newborn

Prostacyclin (PGI(2)) is a member of the prostanoid group of eicosanoids that regulate homeostasis, hemostasis, smooth muscle function and inflammation. Prostanoids are derived from arachidonic acid by the sequential actions of phospholipase A(2), cyclooxygenase (COX), and specific prostaglandin (PG) synthases. There are two major COX enzymes, COX1 and COX2, that differ in structure, tissue distribution, subcellular localization, and function. COX1 is largely constitutively expressed, whereas COX2 is induced at sites of inflammation and vascular injury. PGI(2) is produced by endothelial cells and influences many cardiovascular processes. PGI(2) acts mainly on the prostacyclin (IP) receptor, but because of receptor homology, PGI(2) analogs such as iloprost may act on other prostanoid receptors with variable affinities. PGI(2)/IP interaction stimulates G protein-coupled increase in cAMP and protein kinase A, resulting in decreased [Ca(2+)](i), and could also cause inhibition of Rho kinase, leading to vascular smooth muscle relaxation. In addition, PGI(2) intracrine signaling may target nuclear peroxisome proliferator-activated receptors and regulate gene transcription. PGI(2) counteracts the vasoconstrictor and platelet aggregation effects of thromboxane A(2) (TXA(2)), and both prostanoids create an important balance in cardiovascular homeostasis. The PGI(2)/TXA(2) balance is particularly critical in the regulation of maternal and fetal vascular function during pregnancy and in the newborn. A decrease in PGI(2)/TXA(2) ratio in the maternal, fetal, and neonatal circulation may contribute to preeclampsia, intrauterine growth restriction, and persistent pulmonary hypertension of the newborn (PPHN), respectively. On the other hand, increased PGI(2) activity may contribute to patent ductus arteriosus (PDA) and intraventricular hemorrhage in premature newborns. These observations have raised interest in the use of COX inhibitors and PGI(2) analogs in the management of pregnancy-associated and neonatal vascular disorders. The use of aspirin to decrease TXA(2) synthesis has shown little benefit in preeclampsia, whereas indomethacin and ibuprofen are used effectively to close PDA in the premature newborn. PGI(2) analogs have been used effectively in primary pulmonary hypertension in adults and have shown promise in PPHN. Careful examination of PGI(2) metabolism and the complex interplay with other prostanoids will help design specific modulators of the PGI(2)-dependent pathways for the management of pregnancy-related and neonatal vascular disorders.

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

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

Prolyl hydroxylase domain protein 2 (PHD2) mediates oxygen-induced retinopathy in neonatal mice

Retinopathy of prematurity is a major side effect of oxygen therapy for preterm infants, and is a leading cause of blindness in children. To date, it remains unclear whether the initial microvascular obliteration is triggered by degradation of hypoxia inducible factor (HIF) α proteins or by other mechanisms such as oxidative stress. Here we show that prolyl hydroxylase domain protein 2 (PHD2), an enzyme mostly responsible for oxygen-induced degradation of HIF-α proteins, plays a major role in oxygen-induced retinopathy in mice. In neonatal mice expressing normal amounts of PHD2, exposure to 75% oxygen caused significant degradation of retinal HIF-α proteins, accompanied by massive losses of retinal microvessels. PHD2 deficiency significantly stabilized HIF-1α, and to some extent HIF-2α, in neonatal retinal tissues, and protected retinal microvessels from oxygen-induced obliteration. After hyperoxia-treated neonatal mice were returned to ambient room air, retinal vasculature in PHD2-deficient mice remained mostly intact and showed very little neoangiogenesis. These findings demonstrate a close association between PHD2-dependent HIF-α degradation and oxygen-induced retinal microvascular obliteration, and imply that PHD2 may be a promising therapeutic target to prevent oxygen-induced retinopathy.

Nutritional influences on visual development and function

Experiments conducted on many different species reveal a fundamental paradox about the vertebrate eye; it is damaged by its own operation. This vulnerability stems from the need to respond to visible light, often actinic, but also from the intrinsic metabolic and structural state of the eye's internal structures. Photoreceptor outer segments, for instance, have high concentrations of diet-derived long-chain polyunsaturated fatty acids and these membrane lipids are highly prone to peroxidation due to the high oxygen tension of the outer retina. Such a high diathesis for damage would be catastrophic if it were not balanced by an equally impressive system for responding to such stressors. The retina (and to a lesser extent the crystalline lens), for instance, is especially rich in dietary antioxidants such as vitamin E, vitamin C and the macular carotenoids (lutein and zeaxanthin) putatively to retard light-induced oxidative damage. The nutrients that support both essential function (e.g., retinal, the vitamin form of vitamin A, in photopigment) and protection operate in a highly integrated manner. For instance, Vitamin E is a lipophillic chain-breaking anti-oxidant (protecting DHA-rich outer segment membranes) that regenerates itself through reaction with vitamin C (a primary anti-oxidant against aqueous radicals) and is spatially distributed in complement with the carotenoids lutein and zeaxanthin. Nor are these interactions relegated to simply providing protection and the basic elements needed for transduction. Macular lutein and zeaxanthin, for example, improve visual performance (e.g., reduce glare disability and discomfort, speed photostress recovery, and enhance chromatic contrast) through purely optical means (by absorbing short-wave light anterior to the foveal cones). The vulnerability of the eye to exogenous insult, and the sensitivity of the eye to dietary components, is not static: infants have more vulnerable retinas due to clearer lenses and higher metabolic activity; the elderly are more vulnerable due to such factors as increased inflammatory stress and a higher content of photosensitizers (such as lipofuscin) creating cascading oxidative effects. Hence, optimal dietary prophylaxis changes as the eye ages. The eye, perhaps more than most other biological structures, has evolved an exquisite and shifting sensitivity to dietary intake throughout the lifespan, not just for its basic operation (e.g., Vitamin A for transduction), but also for its very preservation.

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.

Role of Nrf2 in retinal vascular development and the vaso-obliterative phase of oxygen-induced retinopathy

In the initial stage of retinopathy of prematurity (ROP), hyperoxia causes retinal blood vessel obliteration. This is thought to occur in part through oxidative stress-induced apoptosis of endothelial cells. This study was designed to determine what role NF-E2-related factor 2 (Nrf2) plays in this process. Nrf2 is a transcription factor of the anti-oxidant response element that, if induced, may protect the retina from hyperoxia-induced oxidative stress. Nrf2 knockout mice (Nrf2-/-), Nrf2 wild type control mice (Nrf2+/+), and C57BL/6 mice were exposed to hyperoxia (75% O(2)) or normoxia from P7 through P12. Mice were sacrificed on P9 and P12 and the retinas were stained with GSA lectin-Cy3 to visualize retinal blood vessels. Hyperoxia exposed retinas were flat mounted and photographed, then the size of the avascular areas was determined. Additionally, retinas were cryopreserved after lectin staining and area analysis and then sectioned. Secondary or deep capillaries were then hand-counted in sections. In hyperoxia-treated mice, the avascular areas in Nrf2-/- P9 mice were significantly larger than those in Nrf2+/+ P9 mice (P = 0.01). However, there was no significant difference between Nrf2-/- and Nrf2+/+ mice at P12. Avascular areas at P12 were significantly smaller than that at P9 in Nrf2-/-, Nrf2+/+, and C57BL/6 mice (P = 0.0011, P = 0.009, and P = 0.001 respectively). The numbers of deep or secondary capillaries in air-reared Nrf2-/- mice were significantly decreased, when compared to Nrf2+/+ mice at P9 (P = 0.0082). On the other hand, there was no significant difference in deep capillary formation between air-reared Nrf2-/- and Nrf2+/+ mice at P12. Akt signaling activates Nrf2 and Akt was localized to retinal blood vessels in all animals and was increased in Nrf2+/+ and Nrf2-/- mice exposed to hyperoxia as compared to normoxia mice. Interestingly, during normal development this protection by Nrf2 occurs in a specific window of time that is also shared by angiogenesis. Hyperoxia treatment revealed a similar window of time where Nrf2 regulated anti-oxidant production was beneficial and contributed to the endothelial survival.

Oxygen toxicity and reactive oxygen species: the devil is in the details

Reactive oxygen species (ROS) serve as cell signaling molecules for normal biologic processes. However, the generation of ROS can also provoke damage to multiple cellular organelles and processes, which can ultimately disrupt normal physiology. An imbalance between the production of ROS and the antioxidant defenses that protect cells has been implicated in the pathogenesis of a variety of diseases, such as cancer, asthma, pulmonary hypertension, and retinopathy. The nature of the injury will ultimately depend on specific molecular interactions, cellular locations, and timing of the insult. This review will outline the origins of endogenous and exogenously generated ROS. The molecular, cellular, pathologic, and physiologic targets will then be discussed with a particular emphasis on aspects relevant to child development. Finally, antioxidant defenses that scavenge ROS and mitigate associated toxicities will be presented, with a discussion of potential therapeutic approaches for the prevention and/or treatment of human diseases using enzymatic and nonenzymatic antioxidants.

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.

Intrinsic vasomotricity and adrenergic effects in a model of isolated rabbit eye

PURPOSE

We aimed to investigate the responsiveness of the ocular arteries to adrenergic drugs in a model of perfused isolated rabbit eye.

METHODS

Rabbit external ophthalmic arteries (n = 15) in a head-mounted preparation were cannulated and the retinal and uveal vasculature perfused at a constant flow with warmed tyrode. The three-way polypropylene catheter was further connected to a pressure transducer and intraluminal pressure was taken as a measure of vascular resistance. Effects of intra-arterial injections of phenylephrine (group A, n = 5), prazosin (group B, n = 5) and phentolamine (group C, n = 5) on the recorded pressure were obtained. Student's paired-t test and one-way analysis of variance were used for statistical analysis (p < 0.05).

RESULTS

Intrinsic vasomotricity was observed in all preparations prior to any drug administration. Phenylephrine produced an increase in total vascular resistance. Intrinsic vasomotricity became more evident, showing a lower frequency but higher amplitude of oscillations. Evoked vasomotor responses with phenylephrine (250 microg/ml) were inhibited by intra-arterial administration of the selective alpha(1)-adrenergic antagonist, prazosin (0.5 mg/ml), as well as the non-selective alpha-adrenergic antagonist phentolamine (6 mg/ml).

CONCLUSIONS

Rabbit external ophthalmic arteries showed spontaneous contractions under constant perfusion. Phenylephrine elicited a vasoconstrictor response that was inhibited by adrenergic antagonists. In addition, the intrinsic vasomotricity was enhanced by phenylephrine and blocked by adrenergic antagonists. These results show that under in vitro perfusion the territory presents similar responses to adrenergic drugs to those observed in in vivo models and also provides evidence of myogenic autoregulatory properties in the rabbit ophthalmic artery and/or choroid.

ADAM9 is involved in pathological retinal neovascularization

Pathological ocular neovascularization, caused by diabetic retinopathy, age-related macular degeneration, or retinopathy of prematurity, is a leading cause of blindness, yet much remains to be learned about its underlying causes. Here we used oxygen-induced retinopathy (OIR) and laser-induced choroidal neovascularization (CNV) to assess the contribution of the metalloprotease-disintegrin ADAM9 to ocular neovascularization in mice. Pathological neovascularization in both the OIR and CNV models was significantly reduced in Adam9(-/-) mice compared to wild-type controls. In addition, the level of ADAM9 expression was strongly increased in endothelial cells in pathological vascular tufts in the OIR model. Moreover, tumor growth from heterotopically injected B16F0 melanoma cells was reduced in Adam9(-/-) mice compared to controls. In cell-based assays, the overexpression of ADAM9 enhanced the ectodomain shedding of EphB4, Tie-2, Flk-1, CD40, VCAM, and VE-cadherin, so the enhanced expression of ADAM9 could potentially affect pathological neovascularization by increasing the shedding of these and other membrane proteins from endothelial cells. Finally, we provide the first evidence for the upregulation of ADAM9-dependent shedding by reactive oxygen species, which in turn are known to play a critical role in OIR. Collectively, these results suggest that ADAM9 could be an attractive target for the prevention of proliferative retinopathies, CNV, and cancer.

Possible role for dietary lutein and zeaxanthin in visual development

The possibility that the macular carotenoids, lutein (L), and zeaxanthin (Z), could retard age-related changes in the eye and prevent the eye diseases that result from such changes (namely, cataract and macular degeneration) has been carefully studied. A role for the carotenoids very early in life, however, has received far less attention. Nevertheless, an influence on visual development is likely. Retinal L and Z, for instance, would influence the development of the visual system if they 1) altered input during a critical/sensitive period of visual development and/or 2) influenced maturation and/or 3) protected the retina during a period when it was particularly vulnerable. The available evidence indicates that the pigments may play a role in all three of these areas.