Neonatal Intermittent Hypoxia Research Articles

Comparison of Glutathione Nanoparticles, CoEnzyme Q10, and Fish Oil for Prevention of Oxygen-Induced Retinopathy in Neonatal Rats.

Notch ligands and receptors are important for cell specification and angiogenesis, but their role in oxygen-induced retinopathy (OIR) is not well studied. Delta-like ligand (DLL)-4/Notch inhibits angiogenesis, while Jagged-1/Notch promotes angiogenesis. We tested the hypothesis that early supplementation with antioxidants and/or fish oil curtails severe OIR by inducing DLL-4/Notch and reducing Jagged-1/Notch. Newborn rats were exposed to brief intermittent hypoxia (IH) during hyperoxia, during which they received daily oral supplements of (1) fish oil, (2) coenzyme Q10 (CoQ10) in olive oil (OO), (3) glutathione nanoparticles (nGSH), (4) fish oil + CoQ10, or (5) OO (controls) from birth (P0) to P14. At P14, the pups were placed in room air (RA) until P21, with no further treatment. Oxidative stress, apoptosis, ocular histopathology, and Notch signaling were assessed. Neonatal IH resulted in severe retinal damage consistent with retinopathy of prematurity (ROP). Retinal damage was associated with induced oxidative stress and Jagged-1/Notch signaling, as well as reduced DLL-4/Notch signaling. All treatments reversed these outcomes, but nGSH produced the most beneficial outcomes. Severe OIR promoted the induction of Jagged-1/Notch and curtailed DLL-4/Notch, which was an effect that could be reversed with nGSH supplementation. These findings may indicate a potential alternate pathway for ROP treatment and/or prevention.

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.

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

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. 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 RAuntil 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. 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. 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.

Neonatal intermittent hypoxia-dependent oxidative stress prevents NMDAr subunit remodeling during the critical period producing deficits in synaptic plasticity and spatial memory during adulthood

Early postnatal life represents a critical window of brain development that sets the foundation for neurophysiology later in adulthood. Apneas of Prematurity (AoP) is clinical condition that can emerge in neonates born less than 34 weeks and is hypothesized to have long-lasting impact on neurocognition. Untreated AoP produces periodic cessations in breathing leading to neonatal intermittent hypoxia (nIH). The objective of this study is to investigate how nIH impacts NMDAr-dependent synaptic plasticity during and following the critical period of development. To test this, neonatal mice (P4-5) were exposed to ten days of nIH. Biochemical analyses immediately following nIH, revealed that nIH caused oxidative stress corresponding with a greater GluN2B:GluN2A subunit ratio in the hippocampus. These effects were accompanied by a reduced contribution of GluN2A to LTP. Administration of the antioxidant MnTMPyP during nIH prevented these changes. In adult mice, six weeks after exposure to nIH, deficits in behavioral performance in spatial memory tasks were evident. These neurocognitive changes, correlated with a persistent increase in the GluN2B:GluN2A ratio and dysregulated LTP in the adult hippocampus. Administration of MnTMPyP, following nIH was not effective in mitigating the effects observed during adulthood. Our findings suggest that a narrow interventional window exists for mitigating oxidative stress that drive nIH‑dependent changes in hippocampal physiology and spatial memory during adulthood. This work was supported by NIH: R01NS107421 This work was supported by NIH: R01NS107421 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Coenzyme Q10 and Fish Oil Supplementation for Reducing Retinal Oxidative Stress in a Rat Model

Extremely low gestational-age neonates requiring supplemental oxygen experience intermittent hypoxia (IH) episodes, which predispose them to oxidative stress and retinopathy of prematurity. We tested the hypothesis that early supplementation with fish oil or CoQ10 confers benefits reducing the severity of IH-induced retinopathy. At birth, rat pups were exposed to two clinically relevant neonatal IH paradigms with recovery in either hyperoxia (50% O2) or room air (RA) between episodes for 14 days, during which they received daily oral fish oil, coenzyme Q10 (CoQ10) in olive oil (OO), or OO only (vehicle). At postnatal day 14 (P14), pups were allowed to recover in RA with no further treatment until P21. Retinas were examined at P14 and at P21. Both IH paradigms resulted in severe ocular oxidative stress and retinopathy regardless of recovery in hyperoxia or RA in the vehicle groups. Although early supplementation with fish oil was beneficial, CoQ10 provided superior benefits for reducing IH-induced oxidative stress and retinopathy. These effects were associated with lower retinal antioxidants and biomarkers of angiogenesis. The therapeutic benefits of CoQ10 suggest a potential treatment for IH-induced retinopathies. Further studies are needed to establish appropriate, safe, and effective doses for use in preterm infants.

Biomarkers of growth and carbohydrate metabolism in neonatal rats supplemented with fish oil and/or antioxidants during intermittent hypoxia

ObjectiveExtremely low gestational age neonates (ELGANs) experience frequent intermittent hypoxia (IH) episodes during therapeutic oxygen. ELGANs exhibit poor postnatal growth requiring lipid supplementation. Lipids are targets of reactive oxygen species resulting in lipid peroxidation and cell death, particularly in preterm infants with compromised antioxidant systems. We tested the hypothesis that early supplementation with lipids and/or antioxidants promotes growth and influences biomarkers of carbohydrate metabolism in neonatal rats exposed to IH. DesignNewborn rats (n = 18/group) were exposed to brief hypoxia (12% O2) during hyperoxia (50% O2), or room air (RA), from birth (P0) to P14 during which they received daily oral supplementation with: 1) fish oil; 2) Coenzyme Q10 (CoQ10) in olive oil; 3) glutathione nanoparticles (nGSH); 4) fish oil+CoQ10; or 5) olive oil. At P21, plasma samples were assessed for glucose, insulin, glucokinase (GCK), glucagon, glucagon-like peptide (GLP)-1, growth hormone (GH), corticosterone, and ghrelin. Liver was assessed for histopathology, apoptosis (terminal deoxynucleotidyl transferase dUTP nick end labeling, TUNEL stain), and GH, insulin-like growth factor (IGF)-I, GH binding protein (GHBP), and IGF binding protein (IGFBP)-3. ResultsNeonatal IH resulted in decreased liver weight and liver/body weight ratios, as well as hepatocyte swelling, steatosis, and apoptosis, which were attenuated with fish oil, nGSH, and combined fish oil+CoQ10. IH also decreased plasma glucose, insulin, GCK, and ghrelin, but increased GLP-1. All treatments improved plasma glucose in IH, but insulin was higher with CoQ10 and nGSH only. Glucagon was increased with CoQ10, fish oil, and CoQ10 + fish oil, while corticosterone was higher with nGSH and CoQ10 + fish oil. IGF-I and IGFBP-3 were significantly higher in the liver with CoQ10 in IH, while deficits in GH were noted with CoQ10 and fish oil in RA and IH. Treatment with nGSH and combined CoQ10 + fish oil reduced IGF-I in RA and IH but increased IGFBP-3. ConclusionsNeonatal IH impairs liver growth with significant hepatocyte damage. Of all supplements in IH, nGSH and combined fish oil+CoQ10 were most effective for preserving liver growth and carbohydrate metabolism. Data suggest that these supplements may improve poor postnatal organ and body growth; and metabolic dysfunction associated with neonatal IH.

Neonatal intermittent hypoxia persistently impairs lung vascular development and induces long-term lung mitochondrial DNA damage.

Adults born preterm have an increased risk of pulmonary vascular disease. Extreme preterm infants often require supplemental oxygen but they also exhibit frequent intermittent hypoxemic episodes (IH). Here, we test the hypothesis that neonatal IH induces lung endothelial cell mitochondrial DNA (mitDNA) damage and contributes to long-term pulmonary vascular disease and pulmonary hypertension (PH). Newborn C57BL/6J mice were assigned to the following groups: 1) normoxia, 2) hyperoxia (O2 65%), 3) normoxia cycling with IH (O2 21% + O2 10%), and 4) hyperoxia cycling with IH (O2 65% + O2 10%) for 3 wk. IH episodes were initiated on postnatal day 7. Lung angiogenesis, PH, and mitDNA lesions were assessed at 3 wk and 3 mo. In vitro, the effect of IH on tubule formation and mitDNA lesions was evaluated in human pulmonary microvascular endothelial cells (HPMECs). Data were analyzed by ANOVA. In vitro, IH exposure reduced tubule formation and increased mitDNA lesions in HPMECs. This was most marked in HPMECs exposed to hyperoxia cycling with IH. In vivo, neonatal IH increased lung mitDNA lesions, impaired angiogenesis, and induced PH in 3-wk-old mice. These findings were pronounced in mice exposed to hyperoxia cycling with IH. At 3 mo follow-up, mice exposed to neonatal IH had persistently increased lung mitDNA lesions and impaired lung angiogenesis, even without concomitant hyperoxia exposure. Neonatal IH induces lung endothelial cell mitDNA damage and causes persistent impairment in lung angiogenesis. These findings provide important mechanistic insight into the pathogenesis of pulmonary vascular disease in preterm survivors.NEW & NOTEWORTHY Our current study demonstrates that neonatal intermittent hypoxia (IH) alters lung endothelial cell function, induces mitochondrial DNA lesions, and impairs lung vascular growth into adulthood. Moreover, when superimposed on hyperoxia, neonatal IH induces a severe lung vascular phenotype that is seen in preterm infants with PH. These findings suggest that neonatal IH contributes to PH in adults born preterm and importantly, that mitochondrial protection strategies may mitigate these deleterious effects.

Postnatal age influences how Intermittent Hypoxia impacts hippocampal synaptic plasticity and NMDA receptor subunit expression

The ability to scale synaptic strength supports the robustness and flexibility of learning and memory throughout a lifetime. Intermittent Hypoxia (IH) is a hallmark of several clinical conditions such as sleep apnea and apneas of prematurity. These conditions are associated with neurocognitive deficits. We recently demonstrated that IH phenocopies aging by causing oxidative stress and suppressing NMDAr‐dependent synaptic plasticity. However, the basis of these IH‐dependent phenomena appears to be driven through a mechanism independent of aging where IH causes downregulation of GluN1, the obligatory subunit of NMDAr. Based on these findings, we sought do determine how IH exposure during early postnatal life impacts hippocampal neurophysiology. Electrophysiological studies and protein analyses were performed using hippocampal brain slices taken from mice (P14‐P15) exposed to ten days of neonatal IH (nIH, starting at P4‐P5). In contrast to the IH‐mediated effects in the adult hippocampus, nIH neither suppressed GluN1 expression nor eliminated NMDAr‐dependent synaptic plasticity, but rather caused NMDAr subunit remodeling by causing GluN2A downregulation and GluN2B upregulation. Moreover, the preserved synaptic plasticity after nIH was maintained was dependent on a larger contribution of GluN2B. These findings indicate that postnatal age is a significant factor influencing the mechanistic consequences of IH on hippocampal neurophysiology.

Renal biomarkers of acute kidney injury in response to increasing intermittent hypoxia episodes in the neonatal rat

BackgroundWe tested the hypotheses that: 1) early exposure to increasing episodes of clinically relevant intermittent hypoxia (IH) is detrimental to the developing kidneys; and 2) there is a critical number of daily IH episodes which will result in irreparable renal damage that may involve angiotensin (Ang) II and endothelin (ET)-1.MethodsAt birth (P0), neonatal rat pups were exposed to brief IH episodes from the first day of life (P0) to P7 or from P0-P14. Pups were either euthanized immediately or placed in room air (RA) until P21. RA littermates served as controls. Kidneys were harvested at P7, P14, and P21 for histopathology; angiotensin converting enzyme (ACE), ACE-2, ET-1, big ET-1, and malondialdehyde (MDA) levels; immunoreactivity of ACE, ACE-2, ET-1, ET-2, ET receptors (ETAR, ETBR), and hypoxia inducible factor (HIF)1α; and apoptosis (TUNEL stain).ResultsHistopathology showed increased renal damage with 8–12 IH episodes/day, and was associated with Ang II, ACE, HIF1α, and apoptosis. ACE-2 was not expressed at P7, and minimally increased at P14. However, a robust ACE-2 response was seen during recovery with maximum levels noted in the groups recovering from 8 IH episodes/day. ET-1, big ET-1, ETAR, ETBR, and MDA increased with increasing levels of neonatal IH.ConclusionsChronic neonatal IH causes severe damage to the developing kidney with associated elevations in vasoconstrictors, suggesting hypertension, particularly with 8 neonatal IH episodes. ACE-2 is not activated in early postnatal life, and this may contribute to IH-induced vasoconstriction. Therapeutic targeting of ACE and ET-1 may help decrease the risk for kidney injury in the developing neonate to prevent and/or treat neonatal acute kidney injury and/or chronic kidney disease.

Neonatal intermittent hypoxia, fish oil, and/or antioxidant supplementation on gut microbiota in neonatal rats.

Background.Preterm infants frequently experience intermittent hypoxia (IH) episodes, rendering them susceptible to oxidative stress and gut dysbiosis. We tested the hypothesis that early supplementation with antioxidants and/or fish oil promotes gut biodiversity and mitigates IH-induced gut injury.Methods.Newborn rats were exposed to neonatal IH from birth (P0) to P14 during which they received daily oral supplementation with: 1) coenzyme Q10 (CoQ10) in olive oil; 2) fish oil; 3) glutathione nanoparticles (nGSH); 4) CoQ10+fish oil; or 5) olive oil (placebo control). Pups were placed in room air (RA) from P14 to P21 with no further treatment. RA controls were similarly treated. Stool samples were assessed for microbiota and terminal ileum for histopathology and morphometry; total antioxidant capacity; lipid peroxidation; and biomarkers of gut injury.Results.Neonatal IH induced histopathologic changes consistent with necrotizing enterocolitis which were associated with increased lipid peroxidation, toll-like receptor, transforming growth factor, and nuclear factor kappa B. Combination CoQ10+fish oil, and nGSH were most effective for preserving gut integrity, reducing biomarkers of gut injury, and increasing commensal organisms.Conclusions.Combination antioxidants and fish oil may confer synergistic benefits to mitigate IH-induced injury in the terminal ileum.

Comparison of coenzyme Q10 or fish oil for prevention of intermittent hypoxia-induced oxidative injury in neonatal rat lungs

BackgroundNeonatal intermittent hypoxia (IH) results in oxidative distress in preterm infants with immature antioxidant systems, contributing to lung injury. Coenzyme Q10 (CoQ10) and fish oil protect against oxidative injury. We tested the hypothesis that CoQ10 is more effective than fish oil for prevention of IH-induced lung injury in neonatal rats.MethodsNewborn rats were exposed to two clinically relevant IH paradigms at birth (P0): (1) 50% O2 with brief hypoxia (12% O2); or (2) room air (RA) with brief hypoxia (12% O2), until P14 during which they were supplemented with daily oral CoQ10, fish oil, or olive oil from P0 to P14. Pups were studied at P14 or placed in RA until P21 with no further treatment. Lungs were assessed for histopathology and morphometry; biomarkers of oxidative stress and lipid peroxidation; and antioxidants.ResultsOf the two neonatal IH paradigms 21%/12% O2 IH resulted in the most severe outcomes, evidenced by histopathology and morphometry. CoQ10 was effective for preserving lung architecture and reduction of IH-induced oxidative stress biomarkers. In contrast, fish oil resulted in significant adverse outcomes including oversimplified alveoli, hemorrhage, reduced secondary crest formation and thickened septae. This was associated with elevated oxidants and antioxidants activities.ConclusionsData suggest that higher FiO2 may be needed between IH episodes to curtail the damaging effects of IH, and to provide the lungs with necessary respite. The negative outcomes with fish oil supplementation suggest oxidative stress-induced lipid peroxidation.

Antioxidants and/or fish oil reduce intermittent hypoxia-induced inflammation in the neonatal rat terminal ileum

Intermittent hypoxia (IH) is associated with the pathogenesis of necrotizing enterocolitis (NEC). We tested the hypothesis that early supplementation with antioxidants and/or fish oil protects the terminal ileum from oxidative injury induced by neonatal IH. Newborn rats were exposed to neonatal IH from birth (P0) until P14 during which they received daily fish oil, coenzyme Q10 (CoQ10), glutathione nanoparticles (nGSH), fish oil + CoQ10, or olive oil. Pups were then placed in room air from P14 to P21 with no further supplementation. Terminal ileum was assessed for IH-induced injury and inflammatory biomarkers. Neonatal IH induced severe damage consistent with NEC, and was associated with oxidative stress and elevations in PGE2, PGF2α, TxB2, NOS-2 and TLR-4, effects that were ameliorated with nGSH and combination CoQ10+fish oil. Early postnatal supplementation with antioxidants and/or fish oil during neonatal IH may be favorable for preserving gut integrity and reducing oxidative injury.

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.

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.

Long-term Cardiopulmonary Effects of Neonatal Intermittent Hypoxia Exposure

Long-term Cardiopulmonary Effects of Neonatal Intermittent Hypoxia Exposure

Ocular Versus Oral Propranolol for Prevention and/or Treatment of Oxygen-Induced Retinopathy in a Rat Model.

Purpose: Propranolol, a nonselective B1/B2 adrenoceptor antagonist, promotes the regression of infantile hemangiomas likely through suppression of vascular endothelial growth factor (VEGF), which prompted its use for the prevention of retinopathy of prematurity. We tested the hypothesis that topical ocular propranolol is safe and effective for reducing the severity of oxygen-induced retinopathy (OIR) in the neonatal rat intermittent hypoxia (IH) model. Methods: At birth (P0), rat pups were randomly assigned to room air or neonatal intermittent hypoxia (IH) consisting of 50% O2 with brief episodes of hypoxia (12% O2) from P0 to P14, during which they received a single daily dose of oral propranolol (1 mg/kg/day in 50 μL in sterile normal saline) or topical ocular propranolol (0.2% in 10 μL in normal saline) from P5 to P14. Placebo-controlled littermates received 50 μL oral or 10 μL topical ocular sterile normal saline. Retinal vascular and astrocyte integrity; retinal histopathology and morphometry; and angiogenesis biomarkers were determined. Results: Topical ocular propranolol improved retinal vascular damage and preserved the astrocytic template, but did not completely prevent OIR. The beneficial effects of propranolol were associated with reduced ocular VEGF and increased endogenous soluble inhibitor, sVEGFR-1, when administered topically. Conclusions: Propranolol failed to completely prevent severe OIR, however, it prevented astrocyte degeneration resulting from neonatal IH-induced damage. We conclude that the mechanisms of propranolol's beneficial effects in neonatal IH may involve in part, astrocyte preservation.

Acute and chronic effects of intravitreal bevacizumab on lung biomarkers of angiogenesis in the rat exposed to neonatal intermittent hypoxia

Purpose/Aim Intravitreal bevacizumab (Avastin) is an irreversible vascular endothelial growth factor (VEGF) inhibitor used to treat severe retinopathy of prematurity (ROP) in extremely low gestational age neonates (ELGANs). ELGANs who are at the highest risk for developing severe ROP often experience brief intermittent hypoxia (IH) episodes which may cause oxidative damage. We tested the hypothesis that intravitreal Avastin leaks into the systemic circulation during exposure to IH and has adverse effects on biomarkers of pulmonary microvascular maturation, thus leading to pulmonary hemorrhage and long-term pulmonary sequelae. Methods Neonatal rats at postnatal day (PN) 0 (birth) were exposed to either: 1) hyperoxia (50% O2) or 2) neonatal IH (50% O2 with brief episodes of 12% O2) from PN0 to PN14. Room air (RA) littermates served as controls. At PN14, the time of eye opening in rats, a single dose of Avastin (0.125 mg in 5 µL) was injected into the vitreous cavity of the left eyes. A control group received equivalent volume saline. At PN23 and PN45, blood gases, lung-to-body weight ratios, histology, immunofluorescence, and lung biomarkers of angiogenesis were examined. Results At PN23, Avastin increased lung VEGF, nitric oxide derivatives (NOx), and hypoxia-inducible factor (HIF)1a in the hyperoxia-exposed groups, but decreased soluble VEGFR-1 (sVEGFR-1). At PN45, lungs from animals exposed to neonatal IH and treated with Avastin were severely hemorrhagic with morphologic changes in lung architecture consistent with chronic lung disease. This was associated with higher VEGF and NOx levels, and lower insulin-like growth factor (IGF)-I and sVEGFR-1. Conclusions These findings prove our hypothesis that intravitreal Avastin penetrates the blood–ocular barrier in IH and alters lung biomarkers of angiogenesis. Avastin targeting of VEGF could affect normal lung development which may be exaggerated under pathologic conditions such as IH, ultimately leading to vascular permeability, vessel rupture, and pulmonary hemorrhage.

Occlusion of activity dependent synaptic plasticity by late hypoxic long term potentiation after neonatal intermittent hypoxia

To elucidate the mechanisms of memory impairment after chronic neonatal intermittent hypoxia (IH), we employed a mice model of severe IH administered at postnatal days 3 to 7. Since prior studies in this model did not demonstrate increased cell death, our primary hypothesis was that IH causes a functional disruption of synaptic plasticity in hippocampal neurons.In vivo recordings of Schaffer collateral stimulation-induced synaptic responses during and after IH in the CA1 region of the hippocampus revealed pathological late phase hypoxic long term potentiation (hLTP) (154%) that lasted more than four hours and could be reversed by depotentiation with low frequency stimulation (LFS), or abolished by NMDA and PKA inhibitors (MK-801 and CMIQ). Furthermore, late phase hLTP partially occluded normal physiological LTP (pLTP) four hours after IH. Early and late hLTP phases were induced by neuronal depolarization and Ca2+ influx, determined with manganese enhanced fMRI, and had increased both AMPA and NMDA – mediated currents. This was consistent with mechanisms of pLTP in neonates and also consistent with mechanisms of ischemic LTP described in vitro with OGD in adults. A decrease of pLTP was also recorded on hippocampal slices obtained 2 days after IH. This decrease was ameliorated by MK-801 injections prior to each IH session and restored by LFS depotentiation. Occlusion of pLTP and the observed decreased proportion of NMDA-only silent synapses after neonatal hLTP may explain long term memory, behavioral deficits and abnormal synaptogenesis and pruning following neonatal IH.