Protective effect of maternal uteroplacental insufficiency on oxygen-induced retinopathy in offspring: removing bias of premature birth

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.

Retinopathy of prematurity protection conferred by uteroplacental insufficiency through erythropoietin signaling in an experimental Murine Model

BACKGROUND

Recent clinical studies suggest that preeclampsia, characterized by uteroplacental insufficiency (UPI) and infant intrauterine growth restriction (IUGR), may be protective against retinopathy of prematurity (ROP) in preterm infants. Experimental models of UPI/IUGR have found an association of erythropoietin (EPO) with less severe oxygen-induced retinopathy (OIR); however, it is unclear if EPO/EPO receptor (EPOR) signaling was involved. We hypothesized that maternal UPI and resultant infant IUGR would protect against features of ROP through EPO/EPOR signaling.

METHODS

We compared transgenic mice with hypoactive EPOR signaling (hWtEPOR) to littermate wild-type mice (mWtEpoR) in a novel combined model of IUGR and ROP. Thromboxane A2 (TXA2) was infused into pregnant C57Bl/6J dams to produce UPI/IUGR; postnatal pups and their foster dams were subjected to a murine OIR model.

RESULTS

Following hyperoxia, hematocrits were similar between littermate wild-type (mWtEpoR) TXA2/OIR and vehicle/OIR pups. mWtEpoR TXA2/OIR had increased serum EPO, retinal EPO and VEGF, and decreased avascular retinal area (AVA) compared to vehicle/OIR pups. In comparison to the mWtEpoR TXA2/OIR pups, AVA was not reduced in hWtEPOR TXA2/OIR pups.

CONCLUSION

Our findings provide biologic evidence that UPI/OIR-induced endogenous EPOR signaling confers protection against hyperoxia-induced vascular damage that may be related to pathophysiology in ROP.

IMPACT

Maternal preeclampsia and infant growth restriction confer retinovascular protection against high oxygen-induced damage through endogenous erythropoietin signaling.

Perspectives on frailty as a total life-course disease with consideration of the fetal environment

Frailty attracts research as it represents a significant target for intervention to extend the healthy life span. An unanswered question in this field is the time point during the life-course at which an individual becomes predisposed to frailty. Here, we propose that frailty has a fetal origin and should be regarded as part of the spectrum of the developmental origins of health and disease. The developmental origins of health and disease theory originated from findings linking the fetal environment to lifestyle-related disorders such as hypertension and diabetes. Coincidentally, a recent trend in frailty research also centers on vascular dysfunction and metabolic alterations as the causality of lifestyle-related disorders such as sarcopenia and dementia. Here, we explore the relationship between fetal programming, frailty-related disorders (sarcopenia and dementia), and other age-related diseases mainly based on reports on intrauterine growth restriction. We propose a "total" life-course approach to combat frailty. With this viewpoint, not only physicians and gerontologists but also obstetricians and pediatricians should team up to overcome age-related diseases in the elderly. Geriatr Gerontol Int 2023; ••: ••-••.

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.

The Serine Protease HTRA-1 Is a Biomarker for ROP and Mediates Retinal Neovascularization

Retinopathy of prematurity (ROP) is a blinding aberrancy of retinal vascular maturation in preterm infants. Despite delayed onset after preterm birth, representing a window for therapeutic intervention, we cannot prevent or cure ROP blindness. A natural form of ROP protection exists in the setting of early-onset maternal preeclampsia, though is not well characterized. As ischemia is a central feature in both ROP and preeclampsia, we hypothesized that angiogenesis mediators may underlie this protection. To test our hypothesis we analyzed peripheral blood expression of candidate proteins with suggested roles in preeclamptic and ROP pathophysiology and with a proposed angiogenesis function (HTRA-1, IGF-1, TGFβ-1, and VEGF-A). Analysis in a discovery cohort of 40 maternal-infant pairs found that elevated HTRA-1 (high-temperature requirement-A serine peptidase-1) was significantly associated with increased risk of ROP and the absence of preeclampsia, thus fitting a model of preeclampsia-mediated ROP protection. We validated these findings and further demonstrated a dose-response between systemic infant HTRA-1 expression and risk for ROP development in a larger and more diverse validation cohort consisting of preterm infants recruited from two institutions. Functional analysis in the oxygen-induced retinopathy (OIR) murine model of ROP supported our systemic human findings at the local tissue level, demonstrating that HtrA-1 expression is elevated in both the neurosensory retina and retinal pigment epithelium by RT-PCR in the ROP disease state. Finally, transgenic mice over-expressing HtrA-1 demonstrate greater ROP disease severity in this model. Thus, HTRA-1 may underlie ROP protection in preeclampsia and represent an avenue for disease prevention, which does not currently exist.

Current evidence and outcomes for retinopathy of prematurity prevention: insight into novel maternal and placental contributions

Retinopathy of prematurity (ROP) is a blinding morbidity of preterm infants, which represents a significant clinical problem, accounting for up to 40% of all childhood blindness. ROP displays a range of severity, though even mild disease may result in life-long visual impairment. This is complicated by the fact that our current treatments have significant ocular and potentially systemic effects. Therefore, disease prevention is desperately needed to mitigate the life-long deleterious effects of ROP for preterm infants. Although ROP demonstrates a delayed onset of retinal disease following preterm birth, representing a potential window for prevention, we have been unable to sufficiently alter the natural disease course and meaningfully prevent ROP. Prevention therapeutics requires knowledge of early ROP molecular changes and risk, occurring prior to clinical retinal disease. While we still have an incomplete understanding of these disease mechanisms, emerging data integrating contributions of maternal/placental pathobiology with ROP are poised to inform novel approaches to prevention. Herein, we review the molecular basis for current prevention strategies and the clinical outcomes of these interventions. We also discuss how insights into early ROP pathophysiology may be gained by a better understanding of maternal and placental factors playing a role in preterm birth.

Automatic analysis of the retinal avascular area in the rat oxygen-induced retinopathy model

Purpose

The aim of this study was to create an algorithm to automate, accelerate, and standardize the process of avascular area segmentation in images from a rat oxygen-induced retinopathy (OIR) model.

Methods

Within 6 h of birth, full-term pups born to Sprague Dawley rat dams that had undergone partial bilateral uterine artery ligation at embryonic day 19.5 were placed into a controlled oxygen environment (Oxycycler, BioSpherix, Parish, NY) at 50% oxygen for 48 h, followed by cycling between 10% and 50% oxygen every 24 h until day 15. The pups were then moved into room air until day 18.5. Ten lectin-stained retinal flat mounts were imaged in montage fashion at 10x magnification. Three masked human reviewers measured two parameters, total retinal area and peripheral avascular area, for each image using the ImageJ freehand selection tool. The outputs of each read were measured as number of pixels. The gold standard value for each image was the mean of the three human reads. Interrater agreement for the measurement of total retinal area, avascular area, and percent avascular area was calculated using type A intraclass correlation coefficients (ICCs) with a two-way random effects model. Automated avascular area identification (A3ID) is a method written in ImageJ Macro that is intended for use in the Fiji (Fiji is Just ImageJ) image processing platform. The input for A3ID is a rat retinal image, and the output is the avascular area (in pixels). A3ID utilizes a random forest classifier with a connected-components algorithm and post-processing filters for size and shape. A separate algorithm calculates the total retinal area. We compared the output of both algorithms to gold standard measurements by calculating ICCs, performing linear regression, and determining the Dice coefficients for both algorithms. We also constructed a Bland-Altman plot for A3ID output.

Results

The ICC for percent peripheral avascular/total area between human readers was 0.995 (CI: 0.974-0.999), with p<0.001. The ICC between A3ID and the gold standard was calculated for three image parameters-avascular area: 0.974 (CI: 0.899-0.993), with p<0.001; total retinal area: 0.465 (CI: 0.0-0.851), with p=0.001; and the percent peripheral avascular/total area: 0.94 (CI: 0.326-0.989), with p<0.001. In the linear regression analysis, the slope for prediction of the gold standard percent peripheral avascular/total area from A3ID was 0.98, with R2=0.975. A3ID and the total retinal area algorithm achieve an average Dice coefficient of 0.891 and 0.952, respectively. The Bland-Altman analysis revealed a trend for computer underestimation of the peripheral avascular area in images with low peripheral avascular area and overestimation of peripheral avascular area in images with large peripheral avascular areas.

Conclusions

A3ID reliably predicts peripheral avascular area based on rat OIR retinal images. When the peripheral avascular area is particularly high or low, hand segmentation of images may be superior.

Effect of subretinal injection on retinal structure and function in a rat oxygen-induced retinopathy model

PURPOSE

Subretinal injections are used to deliver agents in experimental studies of retinal diseases, often through viral vectors. However, few studies have investigated the effects of subretinal injections alone on the structure and function of the healthy or diseased retina, particularly in models of oxygen-induced retinopathy (OIR). We report on the effects of subretinal injections in a rat OIR model, which is used to study mechanisms of retinopathy of prematurity.

METHODS

Within 6 h of birth, neonatal rat pups were exposed to repeated cycles of oxygen between 50% and 10% O₂ every 24 h for 14 days and subsequently moved to room air. On postnatal day 8 (P8), animals were treated in both eyes with advancement of the injection needle into the vitreous (pilot-treated) or with a subretinal PBS injection (sPBS-treated) or were left untreated (untreated). Additional control animals were exposed to microscope light after eyelid opening only (light-treated). Retinal fundus images were recorded on P26. Areas of the avascular retina and intravitreal neovascularization were determined in flat mounted retinas stained with isolectin B4 on P32. Retinal function of the respective eyes was assessed with the Ganzfeld electroretinogram (ERG) on P31 or P32 and with focal ERG in the central retina on P28 or P29. The thickness of the retinal layers was measured with spectral domain optical coherence tomography (OCT) on P30 and in opsin- and TO-PRO 3-stained retinal cryosections from pups euthanized on P32. Two sections were analyzed in each pup. For each section, three images of three different locations were analyzed accounting for 18 thickness measurements per pup.

RESULTS

Compared to untreated animals, the avascular area of the retina was greater in the pilot-treated (p<0.05) and sPBS-treated eyes (p<0.01), and the sPBS-treated eyes had a greater avascular retinal area compared to the pilot-treated eyes (p<0.01). The intravitreal neovascular area was larger in the sPBS-treated eyes compared to the untreated eyes (p<0.01). The outer nuclear and outer segment layers were thinner in the pilot- (p<0.01) and sPBS-treated eyes (p<0.05) compared to the untreated eyes as measured with OCT and immunohistochemical staining of the retinal cryosections. Compared to the untreated eyes, the amplitudes of the scotopic a- and b-waves in the Ganzfeld ERG were reduced in the pilot-treated eyes (p<0.001 and p<0.01, respectively), but only the a-wave was reduced in the sPBS-treated eyes (p<0.001). The a-wave amplitude in the focal ERG was reduced in the pilot- and sPBS-treated eyes, and no difference was seen in the b-wave amplitude between any of the groups. There was no difference between the light-treated and untreated eyes in the areas of the avascular retina or intravitreal neovascularization or Ganzfeld or focal ERG.

CONCLUSIONS

Pilot injections alone without injection into the subretinal space resulted in an increased avascular retinal area, reduced thickness of the photoreceptors, and reduced ERG function compared to the untreated animals. Although subretinal PBS injections further increased the areas of avascular retina and intravitreal neovascularization and resulted in similar retinal thinning compared to the pilot treatment, inner retinal function was improved, as evidenced by higher Ganzfeld b-wave amplitudes. Differences in the Ganzfeld and focal ERGs may indicate that the peripheral retina is more susceptible to remote beneficial effects from potential protective mechanisms induced by subretinal injection. This study stresses the importance of appropriate controls in experiments with subretinal delivery of agents.

Association of Maternal Preeclampsia With Infant Risk of Premature Birth and Retinopathy of Prematurity

Importance

Studies report conflicting associations between preeclampsia and retinopathy of prematurity (ROP). This study provides explanations for the discrepancies to clarify the relationship between preeclampsia and ROP.

Objective

To evaluate the association of maternal preeclampsia and risk of ROP among infants in an unrestricted birth cohort and a restricted subcohort of preterm, very low birth weight (P-VLBW) infants.

Design, Setting, and Participants

A retrospective review of 290 992 live births within the Intermountain Healthcare System in Utah from January 1, 2001, through December 31, 2010, was performed. Generalized estimating equations for logistic regressions with covariate adjustment were applied to relate ROP to preeclampsia among the full cohort and in a subcohort of P-VLBW infants born at younger than 31 weeks' gestation and weighing less than 1500 g.

Main Outcomes and Measures

The occurrence of ROP was related to maternal preeclampsia in the full cohort and in a subcohort of P-VLBW infants.

Results

In the full cohort, 51% of the infants were male and the mean (SD) gestational age was 38.38 (1.87) weeks. In the P-VLBW cohort, 55% were male and the mean (SD) gestational age was 26.87 (2.40) weeks. In the full cohort, preeclampsia was associated with an increased risk of all ROP (adjusted odds ratio [aOR], 2.46; 95% CI, 2.17-2.79; P < .001), severe ROP (aOR, 5.21; 95% CI, 3.44-7.91; P < .001), infant death (aOR, 1.66; 95% CI, 1.16-2.38; P = .006), and giving birth to a P-VLBW infant (aOR, 7.74; 95% CI, 6.92-8.67; P < .001). In the P-VLBW subcohort, preeclampsia was inversely associated with the development of all ROP (aOR, 0.79; 95% CI, 0.68-0.92; P = .003), severe ROP (aOR, 0.62; 95% CI, 0.36-1.06; P = .08), and infant death (aOR, 0.19; 95% CI, 0.11-0.32; P < .001).

Conclusions and Relevance

Preeclampsia was associated with an increased risk of developing ROP among an unrestricted cohort but with a reduced risk of ROP among a restricted subcohort of P-VLBW infants. Although the conflicting associations in the full and P-VLBW cohorts may reflect true differences, the association of a reduced risk of ROP among the P-VLBW subcohort also may reflect biases from restricting the cohort to prematurity, because prematurity is an outcome of preeclampsia.