Intermittent hypoxemia and oxidative stress in preterm infants

β3-Adrenoceptor Agonism to Mimic the Biological Effects of Intrauterine Hypoxia: Taking Great Strides Toward a Pharmacological Artificial Placenta

At different stages of life, from embryonic to postnatal, varying oxygen concentrations modulate cellular gene expression by enhancing or repressing hypoxia-inducible transcription factors. During embryonic/fetal life, these genes encode proteins involved in adapting to a low-oxygen environment, including the induction of specific enzymes related to glycolytic metabolism, erythropoiesis, angiogenesis, and vasculogenesis. However, oxygen concentrations fluctuate during intrauterine life, enabling the induction of tissue-specific differentiation processes. Fetal well-being is thus closely linked to the physiological benefits of a dynamically hypoxic environment. Premature birth entails the precocious exposure of the immature fetus to a more oxygen-rich environment compared to the womb. As a result, preterm newborns face a condition of relative hyperoxia, which alters the postnatal development of organs and contributes to prematurity-related diseases. However, until recently, the molecular mechanism by which high oxygen tension alters normal fetal differentiation remained unclear. In this review, we discuss the research trajectory followed by our research group, which suggests that early exposure to a relatively hyperoxic environment may impair preterm neonates due to reduced expression of the β3-adrenoceptor. Additionally, we explore how these impairments could be prevented through the pharmacological stimulation of the remaining β3-adrenoceptors. Recent preclinical studies demonstrate that pharmacological stimulation of the β3-adrenoceptor can decouple exposure to hyperoxia from its harmful effects, offering a glimpse of the possibility to recreating the conditions typical of intrauterine life, even after premature birth.

Brain tissue microstructure in a prospective, longitudinal, population-based cohort of preterm and term-born young adults

BACKGROUND

Fifteen million infants annually are born prematurely, placing them at high risk for life-long adverse neurodevelopmental outcomes. Whether brain tissue abnormalities that accompany preterm birth persist into young adulthood and are associated with long-term cognitive or psychiatric outcomes is not known.

METHODS

From infancy into young adulthood, we followed a population-based sample of consecutively identified preterm infants and their matched term controls. The preterm group was born at an average gestational age of 31.5 ± 2.6 weeks. We obtained Diffusion Tensor Imaging scans and assessed cognitive and psychiatric outcomes in young adulthood, at a mean age of 19 (range 17.6-20.8) years. Usable data were acquired from 180 participants (89 preterm, 91 term).

RESULTS

Preterm birth was associated with lower fractional anisotropy (FA) and higher average diffusion coefficient (ADC) values in deep white matter tracts of the internal capsule, cerebral peduncles, inferior frontal-occipital fasciculus, sagittal stratum and splenium of the corpus callosum, as well as in grey matter of the caudate, putamen and thalamus. A younger gestational age at birth accentuated these tissue abnormalities. Perinatal characteristics, including lower 5-min APGAR score, history of bronchopulmonary dysplasia, more days of oxygen supplementation and multiple births all increased ADC values in deep white matter tracts and grey matter throughout the brain. Preterm individuals had significantly lower full-scale IQ and more frequent lifetime psychiatric disorders. Those with psychiatric illnesses had significantly higher ADC and lower FA values throughout the deep posterior white matter.

CONCLUSIONS

Abnormalities in brain tissue microstructure associated with preterm birth persist into young adulthood and likely represent disordered myelination and accompanying axonal pathology. These disturbances are associated with a higher likelihood of developing a psychiatric disorder by young adulthood. Brain tissue disturbances were accentuated in those born at younger gestational ages and in those with a history of perinatal complications associated with infection and inflammation.

The Impact of the Delivery Method on Oxidative Stress in Neonates: A Cross-Sectional Study

Background/Objectives: Oxidative stress is a factor that may adversely affect the development of the foetus, the course of labour, and newborn health. This study aimed to determine the association between the labour method, oxidative stress parameters, and neonatal condition. Methods: The study material was umbilical cord blood from newborns delivered vaginally (n = 60) or by caesarean section (n = 108). The total antioxidant status (TAS), superoxide dismutase activity (SOD), glutathione peroxidase activity (GPx), and glutathione reductase activity (GR) were determined using colorimetric methods. The concentration of the chemical elements (Zn, Cu, Mn) was estimated, using atomic absorption spectrometry (ASA). Results: The SOD activity was significantly lower in newborns with an Apgar score below 10 at the 5th minute of life compared to newborns with the highest Apgar points (p = 0.041). In neonates delivered by caesarean section (CS), but not vaginally born (VB) neonates, the SOD activity was significantly lower in newborns with Apgar scores less than 10 at the 5th minute of life compared to newborns with the maximum number of Apgar points (p = 0.02). Conclusions: The reduced SOD activity in the umbilical cord blood of newborns with Apgar scores less than 10 could be related to increased oxidative stress during labour. Bupivacaine-induced oxidative stress seems to be the cause of SOD downregulation in caesarean-delivered newborns. The observed SOD downregulation in neonates delivered by CS and with a decreased Apgar score requires confirmation based on a larger cohort of neonates.

Apnea of Prematurity and Oxidative Stress: Potential Implications

Apnea of prematurity (AOP) occurs in 85% of neonates ≤34 weeks of gestational age. AOP is frequently associated with intermittent hypoxia (IH). This narrative review reports on the putative relationship of AOP with IH and the resulting oxidative stress (OS). Preterm infants are susceptible to OS due to an imbalance between oxidant and antioxidant systems with the excessive free radical load leading to serious morbidities that may include retinopathy of prematurity, bronchopulmonary dysplasia, and neurodevelopmental delay. Current therapeutic approaches to minimize the adverse effects of AOP and optimize oxygen delivery include noninvasive ventilation and xanthine inhibitor therapy, but these approaches have only been partially successful in decreasing the incidence of AOP and associated morbidities.

Gut microbiome and inflammation in response to increasing intermittent hypoxia in the neonatal rat

BACKGROUND

Intermittent hypoxia (IH) and oxidative stress play key roles in gut dysbiosis and inflammation. We tested the hypothesis that increasing numbers of daily IH episodes cause microbiome dysbiosis and severe gut injury.

METHODS

Neonatal rats were exposed to hyperoxia (Hx), growth restriction, and IH. For IH, pups were exposed to 2-12 daily episodes from birth (P0) to postnatal day 7 (7D) or P0-P14 (14D), with or without recovery in room air (RA) until P21. Animals raised in RA from P0 to P21 served as normoxia controls. Stool was expressed from the large intestines for microbiome analysis, and tissue samples were assessed for histopathology and biomarkers of inflammation.

RESULTS

Hx and IH caused a significant reduction in the number and diversity of organisms. The severity of gut injury and levels of inflammatory cytokines and TLR4 increased, while total glutathione (tGSH) declined, with increasing daily IH episodes. The number of organisms correlated with the villi number (p < 0.05) and tGSH depletion (p < 0.001).

CONCLUSIONS

The critical number of daily IH episodes that the newborn gut may sustain is 6, beyond which irreversible damage occurs. The immature gut is highly susceptible to IH-induced injury, and IH may contribute to pathological outcomes in the immature gut.

IMPACT STATEMENT

1. The neonatal gut at birth is highly susceptible to intermittent hypoxia (IH) injury. 2. IH causes gut dysbiosis, inflammation, and glutathione depletion. 3. The severity of gut injury worsens as a function of increasing daily IH episodes. 4. The critical number of daily IH episodes that the newborn gut may sustain is 6, beyond which irreversible damage occurs.

Caffeine: The Story beyond Oxygen-Induced Lung and Brain Injury in Neonatal Animal Models-A Narrative Review

Caffeine is one of the most commonly used drugs in intensive care to stimulate the respiratory control mechanisms of very preterm infants. Respiratory instability, due to the degree of immaturity at birth, results in apnea of prematurity (AOP), hyperoxic, hypoxic, and intermittent hypoxic episodes. Oxidative stress cannot be avoided as a direct reaction and leads to neurological developmental deficits and even a higher prevalence of respiratory diseases in the further development of premature infants. Due to the proven antioxidant effect of caffeine in early use, largely protective effects on clinical outcomes can be observed. This is also impressively observed in experimental studies of caffeine application in oxidative stress-adapted rodent models of damage to the developing brain and lungs. However, caffeine shows undesirable effects outside these oxygen toxicity injury models. This review shows the effects of caffeine in hyperoxic, hypoxic/hypoxic-ischemic, and intermittent hypoxic rodent injury models, but also the negative effects on the rodent organism when caffeine is administered without exogenous oxidative stress. The narrative analysis of caffeine benefits in cerebral and pulmonary preterm infant models supports protective caffeine use but should be given critical consideration when considering caffeine treatment beyond the recommended corrected gestational age.

Lower plasma melatonin levels in non-hypoxic premature newborns associated with neonatal pain

We analyzed plasma melatonin levels in different groups of preterm newborns without hypoxia and their relationship with several perinatal variables like gestational age or neonatal pain. Prospective cohort study of preterm newborns (PTNB) without perinatal hypoxia, Apgar > 6 at 5 min, and oxygen needs on the third day of life. We compared melatonin levels at day 3 of life in different groups of non-hypoxic preterm infants (Student's t-tests, Mann-Whitney U, and chi2) and analyzed the relationship of melatonin with GA, birth weight, neonatal pain (Premature Infant Pain Profile (PIPP) scale), caffeine treatment, parenteral nutrition, or the development of free radical diseases (correlation study, linear regression) and factors associated with moderate/intense pain and free radical diseases (logistic regression analysis). Sixty-one preterm infants with gestational age (GA) of 30.7 ± 2.0 weeks with no oxygen requirements at day 3 of life were studied with plasma melatonin levels of 33.8 ± 12.01 pg/ml. Preterm infants weighing < 1250 g at birth had lower plasma melatonin levels (p = 0.05). Preterm infants with moderate or severe pain (PPIPP > 5) have lower melatonin levels (p = 0.01), and being preterm with PIPP > 5 is associated with lower plasma melatonin levels (p = 0.03). Being very preterm (GA < 32 GS), having low weight for gestational age (LWGA), receiving caffeine treatment, or requiring parenteral nutrition did not modify melatonin levels in non-hypoxic preterm infants (p = NS). Melatonin on day 3 of life in non-hypoxic preterm infants is not associated with later development of free radical diseases (BPD, sepsis, ROP, HIV, NEC).

CONCLUSION

We observed that preterm infants with moderate to severe pain have lower melatonin levels. These findings are relevant because they reinforce the findings of other authors that melatonin supplementation decreases pain and oxidative stress in painful procedures in premature infants. Further studies are needed to evaluate whether melatonin could be used as an analgesic in painful procedures in preterm infants.

TRIAL REGISTRATION

Trial registration was not required since this was an observational study.

WHAT IS KNOWN

• Melatonin is a potent antioxidant and free radical scavenger in newborns under stress conditions: hypoxia, acidosis, hypotension, painful procedures, or parenteral nutrition. • Pain stimulates the production of melatonin. • Various studies conclude that melatonin administration decreases pain during the neonatal period.

WHAT IS NEW

• Non-hypoxic preterm infants with moderate to severe pain (PIPP>5) have lower levels of melatonin. • Administration of caffeine and treatment with parenteral nutrition do not modify melatonin levels in non-hypoxic preterm infants.

Development of a bronchopulmonary dysplasia nutrition focused physical examination tool: A modified Delphi study

OBJECTIVE

The objectives of this study were to identify factors impacting nutrition needs in infants and children with bronchopulmonary dysplasia (BPD). A modified Delphi approach to obtain consensus among pediatric registered dietitian nutritionists (RDNs) was used to create a BPD-specific nutrition focused physical examination (NFPE) tool.

STUDY DESIGN

RDNs, recruited through pediatric nutrition professional associations, completed a survey rating proposed NFPE components on a Likert scale of 1-5 allowing open-ended responses in a two-round Delphi. Responses were analyzed, deidentified, and results were returned to panelists for in-round feedback. Consensus was defined a priori as 75% agreement for usefulness or relevance ± 1 standard deviation.

RESULTS

Six domains (anthropometrics, body composition, development, gastrointestinal, respiratory, and physical signs) and 38 components achieved consensus.

CONCLUSION

Components for an evidence-based tool to enhance nutrition assessment in infants and children with BPD were identified with consensus agreement by an expert panel of 19 pediatric RDNs.

Randomised control trial of oxygen assist module in preterm infants on high-flow nasal cannula support

OBJECTIVE

To evaluate the efficacy of automatic oxygen control (A-FiO2) in reducing the extremes of oxygen saturations (SpO2<80% and SpO2>98%) in preterm infants on high-flow nasal cannula (HFNC) respiratory support using Vapotherm Precision Flow.

DESIGN

A parallel-arm randomised controlled trial.

SETTING

A level-III neonatal intensive care unit.

PATIENTS

Preterm infants born <33 (23+0 to 32+6) weeks receiving HFNC as respiratory support.

INTERVENTIONS

A-FiO2 versus manual (M-FiO2) oxygen control during the full course of HFNC support.

OUTCOMES

The primary outcome of this study is percentage of time spent in extreme oxygen saturations (<80% and >98%) in preterm infants when receiving HFNC as respiratory support. Secondary outcomes were time with SpO2 between 90% and 95% plus time >95% without supplemental oxygen.

RESULTS

60 infants were randomised equally to either A-FiO2 or M-FiO2 arm. Their baseline characteristics were comparable. They spent a median of 5.3 (IQR: 2.0-8.4) and 6.5 (IQR: 2.9-13.7) days in the study, A-FiO2 and M-FiO2, respectively. The percentage of time spent in SpO2<80% (median of 0.4% (0.1%-0.8%) vs 1.6% (0.6%-2.6%), p=0.002) and >98% (median 0.2% (0.1%-0.9%) vs 1.9% (0.7%-4%), p<0.001) were significantly lower in A-FiO2 compared with M-FiO2. The difference in median percentage of time in target range between the two arms was 26% (81% (74%-93%) in A-FiO2 vs 55% (48%-72%) in M-FiO2).

CONCLUSION

A-FiO2 was associated with statistically significant reduction in the percentage of time spent in extremes of saturation when compared with M-FiO2 in preterm infants receiving HFNC.

TRIAL REGISTRATION NUMBER

NCT04687618.

Evaluation of Oxidative Stress Levels and Dynamic Thiol-disulfide Balance in Patients with Retinopathy of Prematurity

PURPOSE

The aim of this study is to evaluate both dynamic thiol-disulfide homeostasis and oxidative stress (OS) levels in patients with retinopathy of prematurity (ROP).

METHODS

A total of 129 infants of <34 weeks gestational age were enrolled in the present study. The thiol-disulfide homeostasis was determined by using the new, cost-effective and fully automated colorimetric method. Total antioxidant status (TAS), Total oxidant status (TOS) and Oxidative stress index (OSI) levels were evaluated.

RESULTS

We found serum TAS levels were lower while serum TOS and OSI levels were significantly higher in patients with ROP compare to the without ROP group (p < .05). However, native, total and disulfide values were not statistically significant between the groups (p > .05). In addition, we also evaluated the native, total and disulfide levels in patients with ROP according to grades and no statistically significant results were found (p > .05). Low birth weight (p = .001), gestational age (p = .001) and 5-min Apgar score were significantly lower in the ROP group.

CONCLUSION

This study revealed that dynamic thiol-disulfide homeostasis was changed in patients with ROP. Increased TOS and decreased TAS levels may be associated with functional reduction of the antioxidant system due to increased OS. This indicate that ROP patients are highly sensitive to OS. The dynamic thiol-disulfide homeostasis may conduce to the pathophysiological mechanism and disease follow-up in patients with ROP. The results of this study show that ROP patients are highly sensitive to oxidative stress.

Hypoxemia events in preterm neonates are associated with urine oxidative biomarkers

BACKGROUND

Intermittent hypoxemia (IH) events are common in preterm neonates and are associated with adverse outcomes. Animal IH models can induce oxidative stress. We hypothesized that an association exists between IH and elevated peroxidation products in preterm neonates.

METHODS

Time in hypoxemia, frequency of IH, and duration of IH events were assessed from a prospective cohort of 170 neonates (<31 weeks gestation). Urine was collected at 1 week and 1 month. Samples were analyzed for lipid, protein, and DNA oxidation biomarkers.

RESULTS

At 1 week, adjusted multiple quantile regression showed positive associations between several hypoxemia parameters with various individual quantiles of isofurans, neurofurans, dihomo-isoprostanes, dihomo-isofurans, and ortho-tyrosine and a negative correlation with dihomo-isoprostanes and meta-tyrosine. At 1 month, positive associations were found between several hypoxemia parameters with quantiles of isoprostanes, dihomo-isoprostanes and dihomo-isofurans and a negative correlation with isoprostanes, isofurans, neuroprostanes, and meta-tyrosine.

CONCLUSIONS

Preterm neonates experience oxidative damage to lipids, proteins, and DNA that can be analyzed from urine samples. Our single-center data suggest that specific markers of oxidative stress may be related to IH exposure. Future studies are needed to better understand mechanisms and relationships to morbidities of prematurity.

IMPACT

Hypoxemia events are frequent in preterm infants and are associated with poor outcomes. The mechanisms by which hypoxemia events result in adverse neural and respiratory outcomes may include oxidative stress to lipids, proteins, and DNA. This study begins to explore associations between hypoxemia parameters and products of oxidative stress in preterm infants. Oxidative stress biomarkers may assist in identifying high-risk neonates.

Comparison of hyperoxia or normoxia resolution of intermittent hypoxia and intermittent hyperoxia episodes on liver histopathology, IGF-1, IGFBP-3, and GHBP in neonatal rats

OBJECTIVE

Extremely low gestational age neonates requiring oxygen therapy for chronic lung disease experience repeated fluctuations in arterial oxygen saturation, or intermittent hypoxia (IH), during the first few weeks of life. These events are associated with a high risk for reduced growth, hypertension, and insulin resistance in later life. This study tested the hypothesis that IH, or intermittent hyperoxia have similar negative effects on the liver; somatic growth; and liver insulin-like growth factor (IGF)-I, IGF binding protein (BP)-3, and growth hormone binding protein (GHBP), regardless of resolution in normoxia or hyperoxia between episodes.

DESIGN

Newborn rats on the first day of life (P0) were exposed to two IH paradigms: 1) hyperoxia (50% O2) with brief hypoxia (12% O2); or 2) normoxia (21% O2) with hypoxia (12% O2); intermittent hypoxia (50% O2/21% O2); hyperoxia only (50% O2); or room air (RA, 21% O2). Pups were euthanized on P14 or placed in RA until P21. Controls remained in RA from P0-P21. Growth, liver histopathology, apoptosis, IGFI, IGFBP-3, and GHBP were assessed.

RESULTS

Pathological findings of the liver hepatocytes, including cellular swelling, steatosis, apoptosis, necrosis and focal sinusoid congestion were seen in the IH and intermittent hyperoxia groups, and were particularly severe in the 21-12% O2 group during exposure (P14) with no significant improvements during recovery/reoxygenation (P21). These effects were associated with induction of HIF1α, and reductions in liver IGFI, IGFBP-3, and GHBP.

CONCLUSIONS

Exposure to IH or intermittent hyperoxia during the first few weeks of life regardless of resolution in RA or hyperoxia is detrimental to the immature liver. These findings may suggest that interventions to prevent frequent fluctuations in oxygen saturation during early neonatal life remain a high priority.

The role of oxygen in the development and treatment of bronchopulmonary dysplasia

Oxygen (O2) is crucial for both the development and treatment of one of the most important consequences of prematurity: bronchopulmonary dysplasia (BPD). In fetal life, the hypoxic environment is important for alveolar development and maturation. After birth, O2 becomes a double-edged sword. While O2 is needed to prevent hypoxia, it also causes oxidative stress leading to a plethora of morbidities, including retinopathy and BPD. The advent of continuous O2 monitoring with pulse oximeters has allowed clinicians to recognize the narrow therapeutic margins of oxygenation for the preterm infant, but more knowledge is needed to understand what these ranges are at different stages of the preterm infant's life, including at birth, in the neonatal intensive care unit and after hospital discharge. Future research, especially in innovative technologies such as automated O2 control and remote oximetry, will improve the understanding and treatment of the O2 needs of infants with BPD.

Biomarkers of lung alveolarization and microvascular maturation in response to intermittent hypoxia and/or early antioxidant/fish oil supplementation in neonatal rats

OBJECTIVE

Extremely preterm infants experience frequent intermittent hypoxia (IH) episodes during oxygen therapy which causes significant damage to the lungs and curtails important signaling pathways that regulate normal lung alveolarization and microvascular maturation. We tested the hypothesis that early supplementation with fish oil and/or antioxidants in rats exposed to neonatal IH improves expression of lung biomarkers of alveolarization and microvascular maturation, and reduces IH-induced lung injury.

STUDY DESIGN/METHODS

From birth (P0) to P14, rat pups were exposed to room air (RA) or neonatal IH during which they received daily oral supplementation with either: (1) olive oil (OO) (control); (2) Coenzyme Q10 (CoQ10) in OO; (3) fish oil; (4) glutathione nanoparticles (nGSH); or (5) fish oil +CoQ10. At P14 pups were placed in RA until P21 with no further treatment. RA controls were similarly treated. Lung growth and alveolarization, histopathology, apoptosis, oxidative stress and biomarkers of alveolarization and microvascular maturation were determined.

RESULTS

Neonatal IH was associated with reduced lung weights and severe histopathological outcomes. These effects were curtailed with fish oil and nGSH. nGSH was also protective against apoptosis, while CoQ10 prevented IH-induced ROS production. Of all treatments, nGSH and CoQ10 + fish oil-induced vascular endothelial growth factor165 and CD31 (Platelet endothelial cell adhesion molecule-1), which are associated with angiogenesis. CoQ10 + fish oil improved alveolarization in RA and IH despite evidence of hemorrhage.

CONCLUSIONS

The benefits of nGSH and CoQ10 + fish oil suggest an antioxidant effect which may be required to curtail IH-induced lung injury. Further clinical assessment of the effectiveness of nGSH is warranted.

Fluctuations in Oxygen Saturation during Synchronized Nasal Intermittent Positive Pressure Ventilation and Nasal High-Frequency Oscillatory Ventilation in Very Low Birth Weight Infants: A Randomized Crossover Trial

BACKGROUND

Very low birth weight (VLBW) infants on noninvasive ventilation (NIV) experience frequent fluctuations in oxygen saturation (SpO2) that are associated with an increased risk for mortality and severe morbidities.

METHODS

In this randomized crossover trial, VLBW infants (n = 22) born 22+3 to 28+0 weeks on NIV with supplemental oxygen were allocated on two consecutive days in random order to synchronized nasal intermittent positive pressure ventilation (sNIPPV) and nasal high-frequency oscillatory ventilation (nHFOV) for 8 h. nHFOV and sNIPPV were set to equivalent mean airway pressure and transcutaneous pCO2. Primary outcome was the time spent within the SpO2 target (88-95%).

RESULTS

During sNIPPV, VLBW infants spent significantly more time within the SpO2 target (59.9%) than during nHFOV (54.6%). The proportion of time spent in hypoxemia (22.3% vs. 27.1%) and the mean fraction of supplemental oxygen (FiO2) (29.4% vs. 32.8%) were significantly reduced during sNIPPV, while the respiratory rate (50.1 vs. 42.6) was significantly higher. Mean SpO2, SpO2 above the target, number of prolonged (>1 min) and severe (SpO2 <80%) hypoxemic episodes, parameters of cerebral tissue oxygenation using NIRS, number of FiO2 adjustments, heart rate, number of bradycardias, abdominal distension and transcutaneous pCO2 did not differ between both interventions.

CONCLUSIONS

In VLBW infants with frequent fluctuations in SpO2, sNIPPV is more efficient than nHFOV to retain the SpO2 target and to reduce FiO2 exposure. These results demand more detailed investigations into cumulative oxygen toxicities during different modes of NIV over the weaning period, particularly with regard to consequences for long-term outcomes.

A consequence of immature breathing induces persistent changes in hippocampal synaptic plasticity and behavior: a role of prooxidant state and NMDA receptor imbalance

Underdeveloped breathing results from premature birth and causes intermittent hypoxia during the early neonatal period. Neonatal intermittent hypoxia (nIH) is a condition linked to the increased risk of neurocognitive deficit later in life. However, the mechanistic basis of nIH-induced changes to neurophysiology remains poorly resolved. We investigated the impact of nIH on hippocampal synaptic plasticity and NMDA receptor (NMDAr) expression in neonatal mice. Our findings indicate that nIH induces a prooxidant state that leads to an imbalance in NMDAr subunit composition favoring GluN2B over GluN2A expression and impairs synaptic plasticity. These consequences persist in adulthood and coincide with deficits in spatial memory. Treatment with an antioxidant, manganese (III) tetrakis (1-methyl-4-pyridyl)porphyrin (MnTMPyP), during nIH effectively mitigated both immediate and long-term effects of nIH. However, MnTMPyP treatment post-nIH did not prevent long-lasting changes in either synaptic plasticity or behavior. In addition to demonstrating that the prooxidant state has a central role in nIH-mediated neurophysiological and behavioral deficits, our results also indicate that targeting the prooxidant state during a discrete therapeutic window may provide a potential avenue for mitigating long-term neurophysiological and behavioral outcomes that result from unstable breathing during early postnatal life.

Comparison of Bevacizumab and Aflibercept for Suppression of Angiogenesis in Human Retinal Microvascular Endothelial Cells

Bevacizumab (Avastin) is a vascular endothelial growth factor (VEGF) inhibitor that is widely used for aggressive posterior retinopathy of prematurity (APROP). Its use is associated with multiple adverse effects. Aflibercept (Eylea) is a VEGFR-1 analogue that is approved for ocular use, but its efficacy for APROP is less studied. We tested the hypothesis that Eylea is as effective as Avastin for suppression of intermittent hypoxia (IH)-induced angiogenesis. Human retinal microvascular endothelial cells (HRECs) were treated with Avastin and low- or high-dose Eylea and exposed to normoxia, hyperoxia (50% O₂), or neonatal IH for 24, 48, or 72 h. Cells were assessed for migration and tube formation capacities, as well as biomarkers of angiogenesis and oxidative stress. Both doses of Eylea suppressed migration and tube formation in all oxygen environments, although the effect was not as robust as Avastin. Furthermore, the lower dose of Eylea appeared to be more effective than the higher dose. Eylea induced soluble VEGFR-1 (sVEGFR-1) coincident with high IGF-I levels and decreased Notch/Jagged-1, demonstrating a functional association. Given the role of VEGFR-1 and Notch as guidance cues for vascular sprouting, these data suggest that Eylea may promote normal vascular patterning in a dose-dependent manner.

Does Perinatal Intermittent Hypoxia Affect Cerebrovascular Network Development?

Perinatal hypoxia is an inadequate delivery of oxygen to the fetus in the period immediately before, during, or after the birth process. The most frequent form of hypoxia occurring in human development is chronic intermittent hypoxia (CIH) due to sleep-disordered breathing (apnea) or bradycardia events. CIH incidence is particularly high with premature infants. During CIH, repetitive cycles of hypoxia and reoxygenation initiate oxidative stress and inflammatory cascades in the brain. A dense microvascular network of arterioles, capillaries, and venules is required to support the constant metabolic demands of the adult brain. The development and refinement of this microvasculature is orchestrated throughout gestation and in the initial weeks after birth, at a critical juncture when CIH can occur. There is little knowledge on how CIH affects the development of the cerebrovasculature. However, since CIH (and its treatments) can cause profound abnormalities in tissue oxygen content and neural activity, there is reason to believe that it can induce lasting abnormalities in vascular structure and function at the microvascular level contributing to neurodevelopmental disorders. This mini-review discusses the hypothesis that CIH induces a positive feedback loop to perpetuate metabolic insufficiency through derailment of normal cerebrovascular development, leading to long-term deficiencies in cerebrovascular function.

Race, hypoxaemia and oxidative stress in prematurely-born infants

BACKGROUND

Disparities in neonatal respiratory outcomes in prematurely-born infants might be partially explained by racial differences and the relationship of hypoxia and oxidative stress.

AIMS

To determine if Black, preterm infants were exposed more frequently to hypoxaemia compared to White infants and had a higher level of oxidative damage.

STUDY DESIGN

Single-centre retrospective cohort study at King's College Hospital, London, UK between 2018 and 2021.

SUBJECTS

Infants born before 32 completed weeks of gestational age.

OUTCOME MEASURES

The median arterial oxygen saturation (SaO₂) over the first seven days was measured. The maximum carboxyhaemoglobin (COHb) level for the first three days was also recorded as an index of oxidative stress.

RESULTS

Two thousand and sixty blood gases from 87 infants (38 Black) with a median (IQR) gestational age of 26.4 (24.6-28.3) weeks were analysed. The median (IQR) SaO₂ was not significantly different in Black [96.1 (95.2-96.8) %] compared to White infants [96.7 (95.6-97.7) %, p = 0.24]. The median (IQR) COHb was not significantly different in Black infants [1.9 (1.7-2.4) %] compared to White infants [1.9 (1.7-2.3) %, p = 0.77]. The highest COHb was significantly related to the median SaO₂ in all infants (r = -0.51, p < 0.001) and separately in Black (r = -0.50, p = 0.002) and White (r = -0.56, p < 0.001) infants.

CONCLUSIONS

Preterm, Black infants were not exposed more frequently to hypoxaemia compared to White infants. Lower saturation levels were associated with higher maximum carboxyhaemoglobin levels indicating a higher risk of oxidative stress, irrespective of racial background.

A Consequence of Immature Breathing induces Persistent Changes in Hippocampal Synaptic Plasticity and Behavior: A Role of Pro-Oxidant State and NMDA Receptor Imbalance

Underdeveloped breathing results from premature birth and causes intermittent hypoxia during the early neonatal period. Neonatal intermittent hypoxia (nIH) is a condition linked to the increased risk of neurocognitive deficit later in life. However, the underlying mechanistic consequences nIH-induced neurophysiological changes remains poorly resolved. Here, we investigated the impact of nIH on hippocampal synaptic plasticity and NMDA receptor (NMDAr) expression in neonatal mice. Our findings indicate that nIH induces a pro-oxidant state, leading to an imbalance in NMDAr subunit composition that favors GluN2A over GluN2B expression, and subsequently impairs synaptic plasticity. These consequences persist in adulthood and coincide with deficits in spatial memory. Treatment with the antioxidant, manganese(III) tetrakis(1-methyl-4-pyridyl)porphyrin (MnTMPyP), during nIH effectively mitigated both immediate and long-term effects of nIH. However, MnTMPyP treatment post-nIH did not prevent the long-lasting changes in either synaptic plasticity or behavior. Our results underscore the central role of the pro-oxidant state in nIH-mediated neurophysiological and behavioral deficits and importance of stable oxygen homeostasis during early life. These findings suggest that targeting the pro-oxidant state during a discrete window may provide a potential avenue for mitigating long-term neurophysiological and behavioral outcomes when breathing is unstable during early postnatal life.

Highlights

Untreated immature breathing leads neonatal intermittent hypoxia (nIH).nIH promotes a pro-oxidant state associated with increased HIF1a activity and NOX upregulation.nIH-dependent pro-oxidant state leads to NMDAr remodeling of the GluN2 subunit to impair synaptic plasticity.Impaired synaptic plasticity and NMDAr remodeling caused by nIH persists beyond the critical period of development.A discrete window for antioxidant administration exists to effectively mitigate neurophysiological and behavioral consequences of nIH.

Noninvasive Ventilation and Rapid Enteral Feeding Advances in Preterm Infants-2-Year Follow-Up of the STENA-Cohort

The importance of nutritional supply for somatic growth and neurodevelopmental outcome in very-low-birthweight infants is an established medical strategy for reducing long-term morbidities. Our cohort study on rapid enteral feeding advances using a standardized protocol (STENA) previously demonstrated a 4-day reduction of parenteral nutrition. STENA did not impede the success of noninvasive ventilations strategies but significantly less infants required mechanical ventilation. Most importantly, STENA resulted in improved somatic growth at 36 weeks of gestation. Here, we evaluated our cohort for psychomotor outcomes and somatic growth at 2 years of age. n = 218 infants of the original cohort were followed-up (74.4%). Z-scores for weight and length did not differ but the benefits of STENA for head circumference persisted until the age of 2 years (p = 0.034). Concerning the psychomotor outcome, we neither found any statistically significant differences in the mental developmental index (MDI) (p = 0.738), norin the psychomotor developmental index (PDI) (p = 0.122). In conclusion, our data adds important insights on the topic of rapid enteral feeding advances and confirms the safety of STENA with respect to somatic growth and psychomotor outcome measures.

Automatic oxygen control for reducing extremes of oxygen saturation: a randomised controlled trial

OBJECTIVE

The objective of this study was to evaluate the efficacy of the automatic oxygen control (A-Fio₂) in reducing the percentage of time spent in severe hypoxaemia (Spo₂ <80%) in preterm infants for the time period on invasive ventilation and/or nasal continuous positive airway pressure (NCPAP) delivered by AVEA ventilator.

DESIGN

A parallel arm randomised controlled trial.

SETTING

A level-III neonatal intensive care unit.

PATIENTS

Preterm infants (<33 weeks birth gestation) who received invasive ventilation or NCPAP in the first 72 hours of age.

INTERVENTIONS

A-Fio₂ vs manual (M-Fio₂) oxygen control.

OUTCOMES

The primary outcome of the study was percentage of time spent in severe hypoxaemia (Spo₂ <80%).

RESULTS

44 infants were randomised to either A-Fio₂ or M-Fio₂ arm and continued in the study for the period of respiratory support (invasive ventilation and/or NCPAP). The total number of study days in A-Fio2 and M-Fio₂ arm were 194 and 204 days, respectively. The percentage of time spent in Spo₂ <80% was significantly lower with A-Fio₂ compared with M-Fio₂ (median of 0.1% (IQR: 0.07-0.7) vs 0.6% (0.2-2); p=0.03). The number of prolonged episodes (>60 s) of Spo₂ <80% per day was also significantly lower in A-Fio₂ (0.3 (0.0-2) vs 2 (0.6-6); p=0.02).

CONCLUSION

A-Fio₂ was associated with statistically significant reduction in the percentage of time spent in severe hypoxaemia when compared with M-Fio₂ in preterm infants receiving respiratory support.

TRIAL REGISTRATION NUMBER

NCT04223258.

Antenatal and Postnatal Sequelae of Oxidative Stress in Preterm Infants: A Narrative Review Targeting Pathophysiological Mechanisms

The detrimental effects of oxidative stress (OS) can start as early as after conception. A growing body of evidence has shown the pivotal role of OS in the development of several pathological conditions during the neonatal period, which have been therefore defined as OS-related neonatal diseases. Due to the physiological immaturity of their antioxidant defenses and to the enhanced antenatal and postnatal exposure to free radicals, preterm infants are particularly susceptible to oxidative damage, and several pathophysiological cascades involved in the development of prematurity-related complications are tightly related to OS. This narrative review aims to provide a detailed overview of the OS-related pathophysiological mechanisms that contribute to the main OS-related diseases during pregnancy and in the early postnatal period in the preterm population. Particularly, focus has been placed on pregnancy disorders typically associated with iatrogenic or spontaneous preterm birth, such as intrauterine growth restriction, pre-eclampsia, gestational diabetes, chorioamnionitis, and on specific postnatal complications for which the role of OS has been largely ascertained (e.g., respiratory distress, bronchopulmonary dysplasia, retinopathy of prematurity, periventricular leukomalacia, necrotizing enterocolitis, neonatal sepsis). Knowledge of the underlying pathophysiological mechanisms may increase awareness on potential strategies aimed at preventing the development of these conditions or at reducing the ensuing clinical burden.

Perinatal Oxidative Stress and Kidney Health: Bridging the Gap between Animal Models and Clinical Reality

Oxidative stress arises when the generation of reactive oxygen species or reactive nitrogen species overwhelms antioxidant systems. Developing kidneys are vulnerable to oxidative stress, resulting in adult kidney disease. Oxidative stress in fetuses and neonates can be evaluated by assessing various biomarkers. Using animal models, our knowledge of oxidative-stress-related renal programming, the molecular mechanisms underlying renal programming, and preventive interventions to avert kidney disease has grown enormously. This comprehensive review provides an overview of the impact of perinatal oxidative stress on renal programming, the implications of antioxidant strategies on the prevention of kidney disease, and the gap between animal models and clinical reality.

Cumulative hypoxia, socioeconomic deprivation and neurodevelopmental outcomes in preterm infants

BACKGROUND

Hypoxia can adversely affect cognition, while socioeconomic deprivation has also been associated with impaired neurodevelopment in the newborn. We aimed to assess the impact of hypoxia and socioeconomic deprivation on the neurodevelopmental outcomes of preterm infants.

METHODS

Retrospective cohort study at a tertiary neonatal unit between 2015 and 2018. The motor, cognitive and language domain scores of the Bayley-III assessment were recorded at 24 months of corrected gestational age. The percentage of time with pulse oximetry (SpO₂) < 75% was measured from the nursing records, from admission to 36 weeks postmenstrual age in infants born < 30 weeks gestational age. The multiple deprivation index (MDI) and the main care giver's education domain of the MDI were also recorded.

RESULTS

A total of 93,767 data points from 80 infants (34 male) with a median (IQR) gestational age of 27.9(25.9-29.0) weeks and a birth weight of 0.94(0.74-1.23) kg were analysed. The median (IQR) motor score [103(91-110)] was significantly related to the median (IQR) time with SpO₂ < 75% [1.5(0.9-3.4)%, adjusted p = 0.020]. The median (IQR) cognitive score [100(90-105)] was negatively significantly related to the time with SpO₂ < 75% (adjusted p = 0.012) and the median (IQR) education decile of the MDI [7(6-9), adjusted p = 0.011]. The median (IQR) language score [91(77-100)] was significantly positively related to the education domain of the MDI (adjusted p = 0.025).

CONCLUSIONS

Hypoxia in preterm infants exerted a negative impact on motor function and cognition and conversely, higher educational attainment had a positive impact on cognition and language.

Vital signs as physiomarkers of neonatal sepsis

Neonatal sepsis accounts for significant morbidity and mortality, particularly among premature infants in the Neonatal Intensive Care Unit. Abnormal vital sign patterns serve as physiomarkers of sepsis and provide early warning of illness before overt clinical decompensation. The systemic inflammatory response to pathogens signals the autonomic nervous system, leading to changes in temperature, respiratory rate, heart rate, and blood pressure. In infants with comorbidities of prematurity, vital sign abnormalities often occur in the absence of infection, which confounds sepsis diagnosis. This review will cover the mechanisms of vital sign changes in neonatal sepsis, including the cholinergic anti-inflammatory pathway mediated by the vagus nerve, which is critical to the host response to infectious and inflammatory insults. We will also review the clinical implications of vital sign changes in neonatal sepsis, including their use in early warning scores and systems to direct clinicians to the bedside of infants with physiologic changes that might be due to sepsis. IMPACT: This manuscript summarizes and reviews the relevant literature on the physiological manifestations of neonatal sepsis and how we monitor and analyze these through vital signs and advanced analytics.

Free Radicals and Neonatal Brain Injury: From Underlying Pathophysiology to Antioxidant Treatment Perspectives

Free radicals play a role of paramount importance in the development of neonatal brain injury. Depending on the pathophysiological mechanisms underlying free radical overproduction and upon specific neonatal characteristics, such as the GA-dependent maturation of antioxidant defenses and of cerebrovascular autoregulation, different profiles of injury have been identified. The growing evidence on the detrimental effects of free radicals on the brain tissue has led to discover not only potential biomarkers for oxidative damage, but also possible neuroprotective therapeutic approaches targeting oxidative stress. While a more extensive validation of free radical biomarkers is required before considering their use in routine neonatal practice, two important treatments endowed with antioxidant properties, such as therapeutic hypothermia and magnesium sulfate, have become part of the standard of care to reduce the risk of neonatal brain injury, and other promising therapeutic strategies are being tested in clinical trials. The implementation of currently available evidence is crucial to optimize neonatal neuroprotection and to develop individualized diagnostic and therapeutic approaches addressing oxidative brain injury, with the final aim of improving the neurological outcome of this population.

Diabetic mellitus, vascular calcification and hypoxia: A complex and neglected tripartite relationship

DM (diabetic mellitus) and its common vascular complications VC (vascular calcification), are increasingly harmful to human health. In recent years, the research on the relationship between DM and VC is also deepening. Hypoxia, as one of the pathogenic factors of many disease models, is also closely related to the occurrence of DM and VC. There are some studies on the role of hypoxia in the pathogenesis of DM and VC respectively, but no one has made an in-depth summary of the systematic connection between hypoxia, DM and VC. Therefore, what we want to review in this article are the relationship between DM, VC and hypoxia, respectively, as well as the role of hypoxia in the development of DM and VC, which has little concern but is a novel and potentially target that may provide some new ideas for the prevention and treatment of DM, VC, especially diabetic VC.

Antioxidant Effect of Melatonin in Preterm Newborns

Introduction

Preterm infants are at risk of free radical-mediated diseases from oxidative stress (OS) injury. Increased free radical generation has been demonstrated in preterm infants during the first seven days of life. Melatonin (MEL) is a powerful antioxidant and scavenger of free radicals. In preterm neonates, melatonin deficiency has been reported. Exogenous melatonin administration appears a promising strategy in the treatment of neonatal morbidities in which OS has a leading role.

Objective

The aim was to evaluate plasma MEL concentrations and OS biomarkers in preterm newborns after early administration of melatonin.

Methods

A prospective, randomized double-blind placebo-controlled pilot study was conducted from January 2019 to September 2020. Thirty-six preterm newborns were enrolled. Starting from the first day of life, 21 received a single dose of oral melatonin 0.5 mg/kg once a day, in the morning (MEL group); 15 newborns received an equivalent dose of placebo (placebo group). Samples of 0.2 mL of plasma were collected at 24 and 48 hours after MEL administration. Plasma concentrations of melatonin, non-protein-bound iron (NPBI), advanced oxidation protein products (AOPP), and F2-isoprostanes (F2-Isopr) were measured. Babies were clinically followed until discharge.

Results

At 24 and 48 hours after MEL administration, the MEL concentrations were significantly higher in the MEL group than in the placebo group (52759.30 ± 63529.09 vs. 28.57 ± 46.24 pg/mL and 279397.6 ± 516344.2 vs. 38.50 ± 44.01 pg/mL, respectively). NPBI and AOPP did not show any statistically significant differences between the groups both at 24 and 48 hours. At 48 hours, the mean blood concentrations of F2-Isopr were significantly lower in the MEL group than in the placebo group (36.48 ± 33.85 pg/mL vs.89.97 ± 52.01 pg/mL).

Conclusions

Early melatonin administration in preterm newborns reduces lipid peroxidation in the first days of life showing a potential role to protect high-risk newborns. Trial Registration. This trial is registered with NCT04785183, Early Supplementation of Melatonin in Preterm Newborns: the Effects on Oxidative Stress.

Association between Intermittent Hypoxemia and Severe Bronchopulmonary Dysplasia in Preterm Infants

Rationale: Bronchopulmonary dysplasia increases the risk of disability in extremely preterm infants. Although the pathophysiology remains uncertain, prior exposure to intermittent hypoxemia may play a role in this relationship. Objectives: To determine the association between prolonged episodes of intermittent hypoxemia and severe bronchopulmonary dysplasia. Methods: A post hoc analysis of extremely preterm infants in the Canadian Oxygen Trial who survived to 36 weeks' postmenstrual age was performed. Oxygen saturations <80% for ⩾1 minute and the proportion of time per day with hypoxemia were quantified using continuous pulse oximetry data that had been sampled every 10 seconds from within 24 hours of birth until 36 weeks' postmenstrual age. The study outcome was severe bronchopulmonary dysplasia as defined in the 2001 NIH Workshop Summary. Measurements and Main Results: Of 1,018 infants, 332 (32.6%) developed severe bronchopulmonary dysplasia. The median number of hypoxemic episodes ranged from 0.8/day (interquartile range, 0.2-1.1) to 60.2/day (interquartile range, 51.4-70.3) among the least and most affected 10% of infants. Compared with the lowest decile of exposure to hypoxemic episodes, the adjusted relative risk of severe bronchopulmonary dysplasia increased progressively from 1.72 (95% confidence interval, 1.55-1.90) at the 2nd decile to 20.40 (95% confidence interval, 12.88-32.32) at the 10th decile. Similar risk gradients were observed for time in hypoxemia. Significant differences in the rates of hypoxemia between infants with and without severe bronchopulmonary dysplasia emerged within the first week after birth. Conclusions: Prolonged intermittent hypoxemia beginning in the first week after birth was associated with an increased risk of developing severe bronchopulmonary dysplasia among extremely preterm infants. Clinical trial registered with www.isrctn.com (ISRCTN62491227) and www.clinicaltrials.gov (NCT00637169).

Oxidative Stress in Preterm Newborns

Preterm babies are highly susceptible to oxidative stress (OS) due to an imbalance between the oxidant and antioxidant systems. The generation of free radicals (FR) induces oxidative damage to multiple body organs and systems. OS is the main factor responsible for the development of typical premature infant diseases, such as bronchopulmonary dysplasia, retinopathy of prematurity, necrotizing enterocolitis, intraventricular hemorrhage, periventricular leukomalacia, kidney damage, eryptosis, and also respiratory distress syndrome and patent ductus arteriosus. Many biomarkers have been detected to early identify newborns at risk of developing a free radical-mediated disease and to investigate new antioxidant strategies. This review reports the current knowledge on OS in the preterm newborns and the newest findings concerning the use of OS biomarkers as diagnostic tools, as well as in implementing antioxidant therapeutic strategies for the prevention and treatment of these diseases and their sequelae.

Oxygen Toxicity to the Immature Lung-Part I: Pathomechanistic Understanding and Preclinical Perspectives

In utero, the fetus and its lungs develop in a hypoxic environment, where HIF-1α and VEGFA signaling constitute major determinants of further development. Disruption of this homeostasis after preterm delivery and extrauterine exposure to high fractions of oxygen are among the key events leading to bronchopulmonary dysplasia (BPD). Reactive oxygen species (ROS) production constitutes the initial driver of pulmonary inflammation and cell death, altered gene expression, and vasoconstriction, leading to the distortion of further lung development. From preclinical studies mainly performed on rodents over the past two decades, the deleterious effects of oxygen toxicity and the injurious insults and downstream cascades arising from ROS production are well recognized. This article provides a concise overview of disease drivers and different therapeutic approaches that have been successfully tested within experimental models. Despite current studies, clinical researchers are still faced with an unmet clinical need, and many of these strategies have not proven to be equally effective in clinical trials. In light of this challenge, adapting experimental models to the complexity of the clinical situation and pursuing new directions constitute appropriate actions to overcome this dilemma. Our review intends to stimulate research activities towards the understanding of an important issue of immature lung injury.

Oxygen Toxicity to the Immature Lung-Part II: The Unmet Clinical Need for Causal Therapy

Oxygen toxicity continues to be one of the inevitable injuries to the immature lung. Reactive oxygen species (ROS) production is the initial step leading to lung injury and, subsequently, the development of bronchopulmonary dysplasia (BPD). Today, BPD remains the most important disease burden following preterm delivery and results in life-long restrictions in lung function and further important health sequelae. Despite the tremendous progress in the pathomechanistic understanding derived from preclinical models, the clinical needs for preventive or curative therapies remain unmet. This review summarizes the clinical progress on guiding oxygen delivery to the preterm infant and elaborates future directions of research that need to take into account both hyperoxia and hypoxia as ROS sources and BPD drivers. Many strategies have been tested within clinical trials based on the mechanistic understanding of ROS actions, but most have failed to prove efficacy. The majority of these studies were tested in an era before the latest modes of non-invasive respiratory support and surfactant application were introduced or were not appropriately powered. A comprehensive re-evaluation of enzymatic, antioxidant, and anti-inflammatory therapies to prevent ROS injury is therefore indispensable. Strategies will only succeed if they are applied in a timely and vigorous manner and with the appropriate outcome measures.

Inflammatory biomarkers in very preterm infants during early intravenous paracetamol administration

BACKGROUND

Paracetamol promotes early closure of patent ductus arteriosus (PDA), and it may affect inflammation after preterm birth.

OBJECTIVE

The aim of this study was to evaluate the association between paracetamol treatment and serum inflammatory biomarkers in very preterm infants with respiratory distress.

STUDY DESIGN

The infants were randomly assigned to intravenous paracetamol or placebo during the first 4 days of life, and others received a lower dose of paracetamol unblinded. Serum samples were used for the analysis of 10 cytokines, C-reactive protein (CRP) and malondialdehyde (MDA). The impact of paracetamol on the biomarkers was evaluated, based on the levels during the early (<60 h) and the later (60-120 h) postnatal age.

RESULTS

Altogether, 296 serum samples from 31 paracetamol and 25 placebo group infants were analysed. Paracetamol had no effect on cytokine levels during the first 60 h when most induced PDA contractions took place. Later paracetamol treatment was associated with lower serum levels of several cytokines, including interleukin (IL-) 10, interferon gamma-induced protein (IP-) 10, and monocyte chemoattractant protein-1. CRP levels were lower in the paracetamol group during the early treatment. Amongst the infants who had severe morbidities, MDA was higher (p = .045), regardless of paracetamol treatment.

CONCLUSION

No significant differences in the cytokine levels were evident between the treatment and placebo groups. However, during early treatment, CRP levels were lower in the paracetamol group. To clarify whether this was due to a decrease in cardiopulmonary distress, or a distinct anti-inflammatory effect, requires further studies.

Dose Response of Bumetanide on Aquaporins and Angiogenesis Biomarkers in Human Retinal Endothelial Cells Exposed to Intermittent Hypoxia

Aquaporins (AQPs) are important for regulating cellular water, solute transport, and balance. Recently, AQPs have also been recognized as playing a key role in cell migration and angiogenesis. In the retina, hypoxia induces vascular endothelial growth factor (VEGF), a potent angiogenic and vascular permeability factor, resulting in retinal edema, which is facilitated by AQPs. Bumetanide is a diuretic agent and AQP 1–4 blocker. We tested the hypothesis that bumetanide suppression of AQPs ameliorates intermittent hypoxia (IH)-induced angiogenesis and oxidative stress in human microvascular retinal endothelial cells (HMRECs). HMRECs were treated with a low-dose (0.05 µg/mL) or high-dose (0.2 µg/mL) of bumetanide and were exposed to normoxia (Nx), hyperoxia (50% O₂), or IH (50% O₂ with brief hypoxia 5% O₂) for 24, 48, and 72 h. Angiogenesis and oxidative stress biomarkers were determined in the culture media, and the cells were assessed for tube formation capacity and AQP-1 and -4 expression. Both doses of bumetanide significantly decreased oxidative stress and angiogenesis biomarkers. This response was reflected by reductions in tube formation capacity and AQP expression. These findings confirm the role of AQPs in retinal angiogenesis. Therapeutic targeting of AQPs with bumetanide may be advantageous for IH-induced aberrant retinal development.

Effects of omega 3 polyunsaturated fatty acids, antioxidants, and/or non-steroidal inflammatory drugs in the brain of neonatal rats exposed to intermittent hypoxia

Preterm infants experience frequent arterial oxygen desaturations during oxygen therapy, or intermittent hypoxia (IH). Neonatal IH increases oxidative distress which contributes to neuroinflammation and brain injury. We tested the hypotheses that exposure to neonatal IH is detrimental to the immature brain and that early supplementation with antioxidants and/or omega 3 polyunsaturated fatty acids (n-3 PUFAs) combined with non-steroidal anti-inflammatory drugs (NSAIDs) is protective. Newborn rats were exposed to brief hypoxia (12% O₂ ) during hyperoxia (50% O₂ ) from the first day of life (P0) until P14 during which they received daily oral supplementation with antioxidants, namely coenzyme Q10 (CoQ10) or glutathione nanoparticles (nGSH), n-3 PUFAs and/or topical ocular ketorolac. Placebo controls received daily oral olive oil and topical ocular saline. Room air (RA) littermates remained in 21% O₂ from birth to P21 with all treatments identical. At P14 animals were allowed to recover in RA until P21 with no further treatment. Whole brains were harvested for histopathology and morphometric analyses, and assessed for biomarkers of oxidative stress and inflammation, as well as myelin injury. Neonatal IH resulted in higher brain/body weight ratios, an effect that was reversed with n-3 PUFAs and n-3 PUFAs+CoQ10 with or without ketorolac. Neonatal IH was also associated with hemorrhage, oxidative stress, and elevations in inflammatory prostanoids. Supplementation with n-3 PUFAs and nGSH with and without ketorolac were most beneficial for myelin growth and integrity when administered in RA. However, the benefit of n-3 PUFAs was significantly curtailed in neonatal IH. Neonatal IH during a critical time of brain development causes inflammation and oxidative injury. Loss of therapeutic benefits of n-3 PUFAs suggest its susceptibility to oxidation in neonatal IH and therefore indicate that co-administration with antioxidants may be necessary to sustain its efficacy.

The relationship between intermittent hypoxemia events and neural outcomes in neonates

This brief review examines 1) patterns of intermittent hypoxemia in extremely preterm infants during early postnatal life, 2) the relationship between neonatal intermittent hypoxemia exposure and outcomes in both human and animal models, 3) potential mechanistic pathways, and 4) future alterations in clinical care that may reduce morbidity. Intermittent hypoxemia events are pervasive in extremely preterm infants (<28 weeks gestation at birth) during early postnatal life. An increased frequency of intermittent hypoxemia events has been associated with a range of poor neural outcomes including language and cognitive delays, motor impairment, retinopathy of prematurity, impaired control of breathing, and intraventricular hemorrhage. Neonatal rodent models have shown that exposure to short repetitive cycles of hypoxia induce a pathophysiological cascade. However, not all patterns of intermittent hypoxia are deleterious and some may even improve neurodevelopmental outcomes. Therapeutic interventions include supplemental oxygen, pressure support and pharmacologic drugs but prolonged hyperoxia and pressure exposure have been associated with cardiopulmonary morbidity. Therefore, it becomes imperative to distinguish high risk from neutral and/or even beneficial patterns of intermittent hypoxemia during early postnatal life. Identification of such patterns could improve clinical care with targeted interventions for high-risk patterns and minimal or no exposure to treatment modalities for low-risk patterns.

Perinatal Hypoxemia and Oxygen Sensing

The development of the control of breathing begins in utero and continues postnatally. Fetal breathing movements are needed for establishing connectivity between the lungs and central mechanisms controlling breathing. Maturation of the control of breathing, including the increase of hypoxia chemosensitivity, continues postnatally. Insufficient oxygenation, or hypoxia, is a major stressor that can manifest for different reasons in the fetus and neonate. Though the fetus and neonate have different hypoxia sensing mechanisms and respond differently to acute hypoxia, both responses prevent deviations to respiratory and other developmental processes. Intermittent and chronic hypoxia pose much greater threats to the normal developmental respiratory processes. Gestational intermittent hypoxia, due to maternal sleep-disordered breathing and sleep apnea, increases eupneic breathing and decreases the hypoxic ventilatory response associated with impaired gasping and autoresuscitation postnatally. Chronic fetal hypoxia, due to biologic or environmental (i.e. high-altitude) factors, is implicated in fetal growth restriction and preterm birth causing a decrease in the postnatal hypoxic ventilatory responses with increases in irregular eupneic breathing. Mechanisms driving these changes include delayed chemoreceptor development, catecholaminergic activity, abnormal myelination, increased astrocyte proliferation in the dorsal respiratory group, among others. Long-term high-altitude residents demonstrate favorable adaptations to chronic hypoxia as do their offspring. Neonatal intermittent hypoxia is common among preterm infants due to immature respiratory systems and thus, display a reduced drive to breathe and apneas due to insufficient hypoxic sensitivity. However, ongoing intermittent hypoxia can enhance hypoxic sensitivity causing ventilatory overshoots followed by apnea; the number of apneas is positively correlated with degree of hypoxic sensitivity in preterm infants. Chronic neonatal hypoxia may arise from fetal complications like maternal smoking or from postnatal cardiovascular problems, causing blunting of the hypoxic ventilatory responses throughout at least adolescence due to attenuation of carotid body fibers responses to hypoxia with potential roles of brainstem serotonin, microglia, and inflammation, though these effects depend on the age in which chronic hypoxia initiates. Fetal and neonatal intermittent and chronic hypoxia are implicated in preterm birth and complicate the respiratory system through their direct effects on hypoxia sensing mechanisms and interruptions to the normal developmental processes. Thus, precise regulation of oxygen homeostasis is crucial for normal development of the respiratory control network. © 2021 American Physiological Society. Compr Physiol 11:1653-1677, 2021.

Pharmacodynamic Effects of Standard versus High Caffeine Doses in the Developing Brain of Neonatal Rats Exposed to Intermittent Hypoxia

(1) Background: Caffeine citrate, at standard doses, is effective for reducing the incidence of apnea of prematurity (AOP) and may confer neuroprotection and decrease neonatal morbidities in extremely low gestational age neonates (ELGANs) requiring oxygen therapy. We tested the hypothesis that high-dose caffeine (HiC) has no adverse effects on the neonatal brain. (2) Methods: Newborn rat pups were randomized to room air (RA), hyperoxia (Hx) or neonatal intermittent hypoxia (IH), from birth (P0) to P14 during which they received intraperitoneal injections of LoC (20 mg/kg on P0; 5 mg/kg/day on P1-P14), HiC (80 mg/kg; 20 mg/kg), or equivalent volume saline. Blood gases, histopathology, myelin and neuronal integrity, and adenosine receptor reactivity were assessed. (3) Results: Caffeine treatment in Hx influenced blood gases more than treatment in neonatal IH. Exposure to neonatal IH resulted in hemorrhage and higher brain width, particularly in layer 2 of the cerebral cortex. Both caffeine doses increased brain width in RA, but layer 2 was increased only with HiC. HiC decreased oxidative stress more effectively than LoC, and both doses reduced apoptosis biomarkers. In RA, both caffeine doses improved myelination, but the effect was abolished in Hx and neonatal IH. Similarly, both doses inhibited adenosine 1A receptor in all oxygen environments, but adenosine 2A receptor was inhibited only in RA and Hx. (4) Conclusions: Caffeine, even at high doses, when administered in normoxia, can confer neuroprotection, evidenced by reductions in oxidative stress, hypermyelination, and increased Golgi bodies. However, varying oxygen environments, such as Hx or neonatal IH, may alter and modify pharmacodynamic actions of caffeine and may even override the benefits caffeine.

Neurotoxicity of Unconjugated Bilirubin in Neonatal Hypoxic-Ischemic Brain Injury in vitro

Background: The pathophysiology of bilirubin neurotoxicity in course of hypoxic-ischemic encephalopathy (HIE) in term and preterm infants is still poorly understood. We hypothesized that oxidative stress may be a common mechanism that link hyperbilirubinemia and HIE. Objectives: The objective of the present study was to evaluate whether unconjugated bilirubin (UCB) may enhance the HI brain injury by increasing oxidative stress and to test pioglitazone and allopurinol as new antioxidant therapeutic drugs in vitro. Methods: The effects of UCB were tested on organotypic hippocampal slices subjected to 30 min oxygen-glucose deprivation (OGD), used as in vitro model of HIE. The experiments were performed on mature (14 days in culture) and immature (7 days in culture) slices, to mimic the brains of term and preterm infants, respectively. Mature and immature slices were exposed to UCB, human serum albumin (HSA), pioglitazone, and/or allopurinol for 24 h, immediately after 30 min OGD. Neuronal injury was assessed using propidium iodide (PI) fluorescence. ROS formation was quantified by using the 2',7'-dichlorodihydrofluorescein diacetate (DCF-DA) method. Results: In mature slices, we found that the neurotoxicity, as well as oxidative stress, induced by OGD were enhanced by UCB. HSA significantly prevented UCB-increased neurotoxicity, but had a slight reduction on ROS production. Allopurinol, but not pioglitazone, significantly reduced UCB-increased neurotoxicity induced by OGD. In immature slices exposed to OGD, no increase of neuronal death was observed, whereas oxidative stress was detected after UCB exposure. HSA, pioglitazone and allopurinol have no protective effects on both OGD-induced neuronal death and on UCB-induced oxidative stress. For this reason, UCB, pioglitazone and allopurinol was also tested on ischemic preconditioning protocol. We found that UCB abolished the neuroprotection induced by preconditioning and increased oxidative stress. These effects were restored by allopurinol but not pioglitazone. Conclusions: UCB characterized a different path of neuronal damage and oxidative stress in mature and immature hippocampal slice model of HIE. Management of hyperbilirubinemia in a complex pathological condition, such as HIE and hyperbilirubinemia, should be very careful. Allopurinol could deserve attention as a novel pharmacological intervention for hyperbilirubinemia and HIE.

Oxidative stress biomarkers in the preterm infant

Oxidative stress (OS) plays a key role in the pathophysiology of preterm infants. Accurate assessment of OS remains an analytical challenge that has been partially addressed during the last few decades. A plethora of approaches have been developed to assess preterm biofluids to demonstrate a link postnatally with preterm OS, giving rise to a set of widely employed biomarkers. However, the vast number of different analytic methods and lack of standardization hampers reliable comparison of OS-related biomarkers. In this chapter, we discuss approaches for the study of OS in prematurity with respect to methodologic considerations, the metabolic source of different biomarkers and their role in clinical studies.

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.

Oxidative Stress in Preterm Infants: Overview of Current Evidence and Future Prospects

Preterm birth (PTB), defined as parturition prior to 37 weeks of gestation, is the leading cause of morbidity and mortality in the neonatal population. The incidence and severity of complications of prematurity increase with decreasing gestational age and birthweight. The aim of this review study is to select the most current evidence on the role of oxidative stress in the onset of preterm complication prevention strategies and treatment options with pre-clinical and clinical trials. We also provide a literature review of primary and secondary studies on the role of oxidative stress in preterm infants and its eventual treatment in prematurity diseases. We conducted a systematic literature search of the Medline (Pubmed), Scholar, and ClinicalTrials.gov databases, retroactively, over a 7-year period. From an initial 777 articles identified, 25 articles were identified that met the inclusion and exclusion criteria. Of these, there were 11 literature reviews: one prospective cohort study, one experimental study, three case-control studies, three pre-clinical trials, and six clinical trials. Several biomarkers were identified as particularly promising, such as the products of the peroxidation of polyunsaturated fatty acids, those of the oxidation of phenylalanine, and the hydroxyl radicals that can attack the DNA chain. Among the most promising drugs, there are those for the prevention of neurological damage, such as melatonin, retinoid lactoferrin, and vitamin E. The microbiome also has an important role in oxidative stress. In conclusion, the most recent studies show that a strong relationship between oxidative stress and prematurity exists and that, unfortunately, there is still little therapeutic evidence reported in the literature.

Cardiorespiratory Events in Infants Born Preterm during the Transitional Period

OBJECTIVE

To investigate the features of cardiorespiratory events in infants born preterm during the transitional period, and to evaluate whether different neonatal characteristics may correlate with event type, duration, and severity.

STUDY DESIGN

Infants with gestational age (GA) <32 weeks and/or birth weight <1500 g were enrolled in this observational prospective study. Heart rate (HR) and peripheral oxygen saturation (SpO₂) were recorded continuously over the first 72 hours. Cardiorespiratory events of ≥10 seconds were clustered into isolated desaturation (SpO₂ <85%), isolated bradycardia (HR <100 bpm or <70% of baseline), or combined desaturation/bradycardia and classified as mild, moderate, or severe. The daily incidences of isolated desaturation, isolated bradycardia, and combined desaturation and bradycardia were analyzed. The effects of relevant clinical variables on cardiorespiratory event type and severity were assessed using generalized estimating equations.

RESULTS

Among the 1050 events analyzed, isolated desaturations were the most frequent (n = 625) and isolated bradycardias the least common (n = 171). The number of cardiorespiratory events increased significantly from day 1 to day 2 (P = .028). One in 5 events had severe characteristics; event severity was highest for combined desaturation and bradycardia (P < .001). Compared with other event types, the incidence of combined desaturation and bradycardia was inversely correlated with GA (P = .029) and was higher with the use of continuous positive airway pressure (P = .002). The presence of a hemodynamically significant patent ductus arteriosus was associated with the occurrence of isolated desaturations (P = .001) and with a longer duration of cardiorespiratory events (P = .003).

CONCLUSIONS

Cardiorespiratory events during transition exhibit distinct types, duration, and severity. Neonatal characteristics are associated with the clinical features of these events, indicating that a tailored clinical approach may reduce the hypoxic burden in preterm infants aged 0-72 hours.

Oxygen in the neonatal period: Oxidative stress, oxygen load and epigenetic changes

Preterm infants frequently require positive pressure ventilation and oxygen supplementation in the first minutes after birth. It has been shown that the amount of oxygen provided during stabilization, the oxygen load, if excessive may cause hyperoxia, and oxidative damage to DNA. Epidemiologic studies have associated supplementation with pure oxygen in the first minutes after birth with childhood cancer. Recent studies have shown that the amount of oxygen supplemented to preterm infants after birth modifies the epigenome. Of note, the degree of DNA hyper-or hypomethylation correlates with the oxygen load provided upon stabilization. If these epigenetic modifications would persist, oxygen supplied in the first minutes after birth could have long term consequences. Further studies with a robust power calculation and long-term follow up are needed to bear out the long-term consequences of oxygen supplementation during postnatal stabilization of preterm infants.

Intermittent hypoxia and bronchial hyperreactivity

The premature neonate is at high risk for childhood airway hyperreactivity and episodes of wheezing. Intermittent hypoxic events are frequently observed during the first weeks and months of life in these infants. Intermittent hypoxemia has been associated with adverse outcomes in extremely premature infants; including the diagnosis of bronchopulmonary dysplasia, reported wheezing, and use of prescription asthma medications. We review the incidence of intermittent hypoxia, their potential role in short and longer term respiratory morbidity, and the translational newborn models now being used to investigate common pathways by which intermittent hypoxia contributes to respiratory disease.

Recent advances in our understanding of the mechanisms of lung alveolarization and bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the most common cause of morbidity and mortality in preterm infants. A key histopathological feature of BPD is stunted late lung development, where the process of alveolarization-the generation of alveolar gas exchange units-is impeded, through mechanisms that remain largely unclear. As such, there is interest in the clarification both of the pathomechanisms at play in affected lungs, and the mechanisms of de novo alveoli generation in healthy, developing lungs. A better understanding of normal and pathological alveolarization might reveal opportunities for improved medical management of affected infants. Furthermore, disturbances to the alveolar architecture are a key histopathological feature of several adult chronic lung diseases, including emphysema and fibrosis, and it is envisaged that knowledge about the mechanisms of alveologenesis might facilitate regeneration of healthy lung parenchyma in affected patients. To this end, recent efforts have interrogated clinical data, developed new-and refined existing-in vivo and in vitro models of BPD, have applied new microscopic and radiographic approaches, and have developed advanced cell-culture approaches, including organoid generation. Advances have also been made in the development of other methodologies, including single-cell analysis, metabolomics, lipidomics, and proteomics, as well as the generation and use of complex mouse genetics tools. The objective of this review is to present advances made in our understanding of the mechanisms of lung alveolarization and BPD over the period 1 January 2017-30 June 2019, a period that spans the 50th anniversary of the original clinical description of BPD in preterm infants.

Brain oxidative damage in murine models of neonatal hypoxia/ischemia and reoxygenation

The brain is one of the main organs affected by hypoxia and reoxygenation in the neonatal period and one of the most vulnerable to oxidative stress. Hypoxia/ischemia and reoxygenation leads to impairment of neurogenesis, disruption of cortical migration, mitochondrial damage and neuroinflammation. The extent of the injury depends on the clinical manifestation in the affected regions. Preterm newborns are highly vulnerable, and they exhibit severe clinical manifestations such as intraventricular hemorrhage (IVH), retinopathy of prematurity (ROP) and diffuse white matter injury (DWMI) among others. In the neonatal period, the accumulation of high levels of reactive oxygen species exacerbated by the immature antioxidant defense systems in represents cellular threats that, if they exceed or bypass physiological counteracting mechanisms, are responsible of significant neuronal damage. Several experimental models in mice mimic the consequences of perinatal asphyxia and the use of oxygen in the reanimation process that produce brain injury. The aim of this review is to highlight brain damage associated with oxidative stress in different murine models of hypoxia/ischemia and reoxygenation.