Antioxidants as therapy in the newborn: some words of caution

Reactive oxygen species augment contractile responses of saphenous artery in 10-15-day-old but not adult rats: Substantial role of NADPH oxidases

Reactive oxygen species (ROS) produced by NADPH oxidases (NOX, a key source of ROS in vascular cells) are involved in the regulation of vascular tone, but this has been explored mainly for adult organisms. Importantly, the mechanisms of vascular tone regulation differ significantly in early postnatal ontogenesis and adulthood, while the vasomotor role of ROS in immature systemic arteries is poorly understood. We tested the hypothesis that the functional contribution of NADPH oxidase-derived ROS to the regulation of peripheral arterial tone is higher in the early postnatal period than in adulthood. We studied saphenous arteries from 10- to 15-day-old ("young") and 3- to 4-month-old ("adult") male rats using lucigenin-enhanced chemiluminescence, quantitative PCR, Western blotting, and isometric myography. We demonstrated that both basal and NADPH-stimulated superoxide anion radical (O2•-) production was significantly higher in the arteries from young in comparison to adult rats. Importantly, pan-inhibitor of NADPH oxidase VAS2870 (10 μM) reduced NADPH-induced O2•- production in arteries of young rats. Saphenous arteries of both young and adult rats demonstrated high levels of Nox2 and Nox4 mRNAs, while Nox1 and Nox3 mRNAs were not detected. The protein contents of NOX2 and NOX4 were significantly higher in arterial tissue of young compared to adult animals. Moreover, VAS2870 (10 μM) had no effect on methoxamine-induced contractile responses of adult arteries but decreased them significantly in young arteries; such effect of VAS2870 persisted after removal of the endothelium. Finally, NOX2 inhibitor GSK2795039 (10 μM), but not NOX1/4 inhibitor GKT137831 (10 μM) weakened methoxamine-induced contractile responses of arteries from young rats. Thus, ROS produced by NOX2 have a pronounced contractile influence in saphenous artery smooth muscle cells of young, but not adult rats, which is associated with the increased vascular content of NOX2 protein at this age.

Parenteral Nutrition and Oxidant Load in Neonates

Neonates with preterm, gastrointestinal dysfunction and very low birth weights are often intolerant to oral feeding. In such infants, the provision of nutrients via parenteral nutrition (PN) becomes necessary for short-term survival, as well as long-term health. However, the elemental nutrients in PN can be a major source of oxidants due to interactions between nutrients, imbalances of anti- and pro-oxidants, and environmental conditions. Moreover, neonates fed PN are at greater risk of oxidative stress, not only from dietary sources, but also because of immature antioxidant defences. Various interventions can lower the oxidant load in PN, including the supplementation of PN with antioxidant vitamins, glutathione, additional arginine and additional cysteine; reduced levels of pro-oxidant nutrients such as iron; protection from light and oxygen; and proper storage temperature. This narrative review of published data provides insight to oxidant molecules generated in PN, nutrient sources of oxidants, and measures to minimize oxidant levels.

Oxygen radical disease in the newborn, revisited: Oxidative stress and disease in the newborn period

Thirty years ago, there was an emerging appreciation for the significance of oxidative stress in newborn disease. This prompted a renewed interest in the impact of oxygen therapy for the newborn in the delivery room and beyond, especially in premature infants. Today, the complexity of oxidative stress both in normal regulation and pathology is better understood, especially as it relates to neonatal mitochondrial oxidative stress responses to hyperoxia. Mitochondria are recipients of oxidative damage and have a propensity for oxidative self-injury that has been implicated in the pathogenesis of neonatal lung diseases. Similarly, both intrauterine growth restriction (IUGR) and macrosomia are associated with mitochondrial dysfunction and oxidative stress. Additionally, reoxygenation with 100% O₂ in a hypoxic-ischemic newborn lamb model increased the production of pro-inflammatory cytokines in the brain. Moreover, the interplay between inflammation and oxidative stress in the newborn is better understood because of animal studies. Transcriptomic analyses have found a number of genes to be differentially expressed in murine models of bronchopulmonary dysplasia (BPD). Epigenetic changes have also been detected both in animal models of BPD and premature infants exposed to oxygen. Antioxidant therapy to prevent newborn disease has not been very successful; however, new therapeutic principles, like melatonin, are under investigation.

Parenteral nutrition and oxidant stress in the newborn: A narrative review

There is strong evidence that oxidant molecules from various sources contaminate solutions of parenteral nutrition following interactions between the mixture of nutrients and some of the environmental conditions encountered in clinical practice. The continuous infusion of these organic and nonorganic peroxides provided us with a unique opportunity to study in cells, in vascular and animal models, the mechanisms involved in the deleterious reactions of oxidation in premature infants. Potential clinical impacts of peroxides infused with TPN include: a redox imbalance, vasoactive responses, thrombosis of intravenous catheters, TPN-related hepatobiliary complications, bronchopulmonary dysplasia and mortality. This is a narrative review of published data.

Oxygen Toxicity in the Neonate: Thinking Beyond the Balance

Fetal development occurs in a relatively hypoxemic environment, and birth represents significant oxidative stress. Premature infants are disadvantaged by a lack of maternal antioxidant transfer and impaired endogenous antioxidant responses. O₂ metabolism is essential for life and its biochemical reactions are dynamic, compartmentalized, and difficult to characterize in vivo. There is a growing appreciation for the role of reactive oxygen species in nonpathologic processes, including regulation of cell signaling and mitochondrial function. There are several gaps in the knowledge about the role of reactive oxygen species in normal development and how oxidative stress alters normal signaling and subsequent development.

Adult Consequences of Extremely Preterm Birth: Cardiovascular and Metabolic Diseases Risk Factors, Mechanisms, and Prevention Avenues

Extremely preterm babies are exposed to various sources of injury during critical stages of development. The extremely preterm infant faces premature transition to ex utero physiology and undergoes adaptive mechanisms that may be deleterious in the long term because of permanent alterations in organ structure and function. Perinatal events can also directly cause structural injury. These disturbances induce morphologic and functional changes in their organ systems that might heighten their risks for later adult chronic diseases. This review examines the pathophysiology of programming of long-term health and diseases after preterm birth and associated perinatal risk factors.

Oxygen Saturation Targeting and Bronchopulmonary Dysplasia

Oxygen saturation targeting is widely used in neonatal intensive care, but the optimal target range in very preterm infants has been uncertain and is the subject of recent debate and research. This review briefly discusses the technology of oxygen monitoring and the role of oxygen toxicity in preterm infants. The background to the recent trials of oxygen saturation targeting in acute and continuing care of very preterm infants is reviewed, and the findings and implications of the recent trials, particularly with respect to bronchopulmonary dysplasia, are discussed.

Bronchopulmonary Dysplasia and Chronic Lung Disease: Stem Cell Therapy

Bronchopulmonary dysplasia (BPD), a major complication of premature birth, still lacks safe and effective treatment. Mesenchymal stem cells (MSCs) have been proven to ameliorate critical aspects of the BPD pathogenesis. MSCs seem to exert therapeutic effects through the paracrine secretion of anti-inflammatory, antioxidant, antiapoptotic, trophic, and proangiogenic factors. Although these findings are promising, understanding the mechanism of action of MSCs and MSC manufacturing is still evolving. Several aspects can affect the efficacy of MSC therapy. Further research is required to optimize this potentially game-changing treatment but the translation of regenerative cell therapies for patients has begun.

Accelerated senescence of cord blood endothelial progenitor cells in premature neonates is driven by SIRT1 decreased expression

We demonstrate that PT promotes ECFCs dysfunction by inducing stress-induced premature senescence. Our data reveal that SIRT1 deficiency drives PT-ECFC senescence, and acts as a critical determinant of the PT-ECFC angiogenic defect.

Effect of repeated oral administration of bifenthrin on lipid peroxidation and anti-oxidant parameters in Wistar rats

The oxidative stress-inducing potential of the pyrethroid insecticide, bifenthrin, was evaluated in rats at 5.8 mg/kg body weight once daily for 20 or 30 days. Bifenthrin treated animals showed significantly increased lipid peroxidation, evidenced by increased blood malondialdehyde levels. Blood glutathione levels and activities of catalase and glutathione peroxidase decreased significantly in the bifenthrin treated animals after both 20 and 30 days of treatment, whereas, the activities of superoxide dismutase and glutathione S-transferase decreased significantly only on the 30th day. In conclusion, bifenthrin has a potential to induce severe oxidative stress in rats exposed to sublethal concentrations.

The role of oxidative stress in renal injury induced in rats by losartan exposure during lactation

INTRODUCTION

Rats exposed to angiotensin II (AII) receptor antagonists during lactation present progressive disturbances in renal development that lead to progressive alterations in renal function and structure. This study evaluates the role of oxidative stress in the renal changes induced by exposure to losartan, a type 1 AII receptor antagonist, in rats during lactation.

MATERIALS AND METHODS

Male Wistar pups were divided into: Control, pups of dams that received 2% sucrose solution; Control-tempol, pups of dams that received tempol (0.34 g/l), a superoxide dismutase mimetic compound; Losartan, pups of dams that received losartan (100 mg/kg/day), and Losartan-tempol, pups of dams that received losartan and tempol. Losartan and/or tempol were administered during lactation. Blood and urine samples were collected at 21 or 60 days, and the kidneys were removed.

RESULTS

Losartan-treated pups exhibited disturbances in renal function and structure that persisted into adulthood. Tempol treatment reduced oxidative stress and attenuated the changes induced by losartan in the glomerular filtration rate, desmin expression at the glomerular edge, vimentin in tubular cells, as well as apoptosis and inflammatory infiltration in the renal cortex.

CONCLUSION

Oxidative stress contributes at least in part to the renal injury observed in pups exposed to losartan during lactation.

Lipid hydroperoxide formation regulates postnatal rat lung cell apoptosis and alveologenesis

An acute increase in oxygen tension after birth imposes an oxidative stress upon the lung. We hypothesized that the resultant increase in reactive oxygen species, specifically lipid hydroperoxides, would trigger postnatal alveologenesis and physiological lung cell apoptosis in the neonatal rat. Neonatal rats were either untreated or treated daily with subcutaneous vehicle or diphenyl phenyl diamine, a scavenger of lipid hydroperoxides and inhibitor of lipid peroxidation, from day 1 to 6 of life. Alveolar formation and physiological lung cell apoptosis were assessed by morphometry, immunohistochemistry, and Western blot analyses on day 7 samples. Substitution experiments were conducted using the prototypic lipid hydroperoxide t-butylhydroperoxide. At a minimum effective dose of 15μg/g body wt, treatment with diphenyl phenyl diamine resulted in a significant increase in tissue fraction and mean linear intercept and significant reductions in small peripheral blood vessels, secondary crest formation, lung and secondary crest cell DNA synthesis, and estimated alveolar number. Decreased numbers of apoptotic type II pneumocytes and mesenchymal cells, and decreased contents of proapoptotic cleaved caspase-3 and -7 and cytoplasmic cytochrome c, and an increase in antiapoptotic Bcl-xL were found in lungs treated with diphenyl phenyl diamine. A prevention of selected changes induced by diphenyl phenyl diamine was observed with concurrent treatment with intraperitoneal t-butylhydroperoxide, at a minimally effective dose of 187μg/g body wt. We conclude that oxidative stress after birth induces lipid hydroperoxide formation, which, in turn, triggers postnatal alveologenesis and physiological lung cell apoptosis in the neonatal rat.

Lung injury in preterm neonates: the role and therapeutic potential of stem cells

Continuous improvements in perinatal care have allowed the survival of ever more premature infants, making the task of protecting the extremely immature lung from injury increasingly challenging. Premature infants at risk of developing chronic lung disease or bronchopulmonary dysplasia (BPD) are now born at the late canalicular stage of lung development, just when the airways become juxtaposed to the lung vasculature and when gas-exchange becomes possible. Readily available strategies, including improved antenatal management (education, regionalization, steroids, and antibiotics), together with exogenous surfactant and exclusive/early noninvasive ventilatory support, will likely decrease the incidence/severity of BPD over the next few years. Nonetheless, because of the extreme immaturity of the developing lung, the extent to which disruption of lung growth after prematurity and neonatal management lead to an earlier or more aggravated decline in respiratory function in later life is a matter of concern. Consequently, much more needs to be learned about the mechanisms of lung development, injury, and repair. Recent insight into stem cell biology has sparked interest for stem cells to repair damaged organs. This review summarizes the exciting potential of stem cell-based therapies for lung diseases in general and BPD in particular.

Renal Development and Blood Pressure in Offspring from Dams Submitted to High-Sodium Intake during Pregnancy and Lactation

Exposure to an adverse environment in utero appears to programme physiology and metabolism permanently, with long-term consequences for health of the fetus or offspring. It was observed that the offspring from dams submitted to high-sodium intake during pregnancy present disturbances in renal development and in blood pressure. These alterations were associated with lower plasma levels of angiotensin II (AII) and changes in renal AII receptor I (AT₁) and mitogen-activated protein kinase (MAPK) expressions during post natal kidney development. Clinical and experimental evidence show that the renin-angiotensin system (RAS) participates in renal development. Many effects of AII are mediated through MAPK pathways. Extracellular signal-regulated protein kinases (ERKs) play a pivotal role in cellular proliferation and differentiation. In conclusion, high-sodium intake during pregnancy and lactation can provoke disturbances in renal development in offspring leading to functional and structural alterations that persist in adult life. These changes can be related at least in part with the decrease in RAS activity considering that this system has an important role in renal development.

Impact of fetal programming, birth weight, and infant feeding on later hypertension

The concept of developmental origins of adult disease derives from both epidemiologic and basic sciences. This brief review considers the impact of the intrauterine milieu, intrauterine growth retardation, premature birth, and infant feeding on later hypertension and kidney disease.

Therapeutic strategies to protect the immature newborn myocardium during resuscitation following asphyxia

Perinatal asphyxia contributes to over one million newborn deaths worldwide annually, and may progress to multiorgan failure. Cardiac dysfunction, of varying severity, is seen in 50%-70% of asphyxiated newborns. Resuscitation is necessary to restore oxygenation to deprived tissues, including the heart. However, reoxygenation of asphyxiated newborns may lead to generation of reactive oxygen species (ROS) and further myocardial damage, termed reperfusion injury. The newborn heart is especially vulnerable to oxidative stress and reperfusion injury due to immature antioxidant defense mechanisms and increased vulnerability to apoptosis. Currently, newborn myocardial protective strategies are aimed at reducing the generation of ROS through controlled reoxygenation, boosting antioxidant defenses, and attenuating cellular injury via mitochondrial stabilization.

Disruption of paraoxonase 3 impairs proliferation and antioxidant defenses in human A549 cells and causes embryonic lethality in mice

We had shown previously that paraoxonase 3 (PON3), a putative circulating antioxidant, was systemically upregulated in late-gestation rat, sheep, and human fetuses. Our overarching hypothesis is that preterm human infants are delivered with low levels of PON3 and that this contributes to a state of oxidative stress. We sought to determine whether absence of Pon3 was associated with reduced neonatal viability in mice and studied the offspring from crosses between Pon3(+/-) mice. The number of Pon3(-/-) animals at E10.5 and E17.5 was significantly lower than the expected 25% (9.3 and 7.9% respectively, P < 0.001). On the first day of postnatal life, this was reduced further (2.4%, significantly less than the proportion in fetal life, P = 0.04). Pon3(+/-) animals had lower body and placental weights than wild-type littermates at E17.5, an effect that was independent of the parent of origin of the mutant allele. We then studied the effect of PON3 knockdown in a human cell line, A549. Stable knockdown of PON3 using short-hairpin RNA reduced cell proliferation in 21% oxygen. We then studied the effect of transient knockdown of PON3 using short interfering RNA (siRNA) in the same cell line in low (2%) or ambient (21%) oxygen. Knockdown of PON3 using siRNA reduced total antioxidant capacity in 21% (P = 0.008) but not 2% oxygen. We conclude that the absence of Pon3 in mice resulted in increased rates of early fetal and neonatal death. Knockdown of PON3 in human cells reduced cell proliferation and total antioxidant capacity.

Targeting inflammation to prevent bronchopulmonary dysplasia: can new insights be translated into therapies?

Bronchopulmonary dysplasia (BPD) frequently complicates preterm birth and leads to significant long-term morbidity. Unfortunately, few therapies are known to effectively prevent or treat BPD. Ongoing research has been focusing on potential therapies to limit inflammation in the preterm lung. In this review we highlight recent bench and clinical research aimed at understanding the role of inflammation in the pathogenesis of BPD. We also critically assess currently used therapies and promising developments in the field.

Potential utility of melatonin as an antioxidant during pregnancy and in the perinatal period

Reactive oxygen species (ROS) play a critical role in the pathogenesis of various diseases during pregnancy and the perinatal period. Newborns are more prone to oxidative stress than individuals later in life. During pregnancy, increased oxygen demand augments the rate of production of ROS and women, even during normal pregnancies, experience elevated oxidative stress compared with non-pregnant women. ROS generation is also increased in the placenta during preeclampsia. Melatonin is a highly effective direct free-radical scavenger, indirect antioxidant, and cytoprotective agent in human pregnancy and it appears to be essential for successful pregnancy. This suggests a role for melatonin in human reproduction and in neonatal pathologies (asphyxia, respiratory distress syndrome, sepsis, etc.). This review summarizes current knowledge concerning the role for melatonin in human pregnancy and in the newborn. Numerous studies agree that short-term melatonin therapy is highly effective in reducing complications during pregnancy and in the neonatal period. No significant toxicity or treatment-related side effects with long-term melatonin therapy in children and adults have been reported. Treatment with melatonin might result in a wide range of health benefits, including improved quality of life and reduced healthcare costs.

Oxygen supplementation in the delivery room: updated information

Resuscitation is the most common procedure performed in neonatology. However, new contributions based on scientific evidence challenge the traditional procedures. Of these new contributions, the use of room-air instead of 100% oxygen and titration of the oxygen inspiratory fraction according to oximetry and heart rate represent a new approach in the resuscitation of both term and preterm newborns.

Sustained lung activity of a novel chimeric protein, SOD2/3, after intratracheal administration

Delivery of recombinant superoxide dismutase to the lung is limited by its short half-life and poor tissue penetration. We hypothesized that a chimeric protein, SOD2/3, containing the enzymatic domain of manganese superoxide dismutase (SOD2) and the heparan-binding domain of extracellular superoxide dismutase (SOD3), would allow for the delivery of more sustained lung and pulmonary vascular antioxidant activity compared to SOD2. We administered SOD2/3 to rats by intratracheal (i.t.), intraperitoneal (i.p.), or intravenous (i.v.) routes and evaluated the presence, localization, and activity of lung SOD2/3 1 day later using Western blot, immunohistochemistry, and SOD activity gels. The effect of i.t. SOD2/3 on the pulmonary and systemic circulation was studied in vivo in chronically catheterized rats exposed to acute hypoxia. Active SOD2/3 was detected in lung 1 day after i.t. administration but not detected after i.p. or i.v. SOD2/3 administration or i.t. SOD2. The physiologic response to acute hypoxia, vasoconstriction in the pulmonary circulation and vasodilation in the systemic circulation, was enhanced in rats treated 1 day earlier with i.t. SOD2/3. These findings indicate that i.t. administration of SOD2/3 effectively delivers sustained enzyme activity to the lung as well as pulmonary circulation and has a longer tissue half-life compared to native SOD2. Further testing in models of chronic lung or pulmonary vascular diseases mediated by excess superoxide should consider the longer tissue half-life of SOD2/3 as well as its potential systemic vascular effects.

The protective effect of overexpression of extracellular superoxide dismutase on nitric oxide bioavailability in the lung after exposure to hyperoxia stress

The objective of this study was to determine whether overexpression of human extracellular superoxide dismutase (hEC-SOD) can preserve nitric oxide (NO) bioavailability. In vitro studies examined the transient expression of hEC-SOD in mouse epithelial (C10) cells and its effect on extracellular accumulation of NO, intracellular cyclic guanosine monophosphate (cGMP), and nuclear factor kappa B (NF-κB) activation under normal and oxidative stress conditions. In vivo, newborn rabbits were treated with a plasmid containing hEC-SOD cDNA or vehicle plasmid alone, followed by exposure to hyperoxia (Fio₂ = 95% for 7 days). A third group was raised under normoxic conditions. cGMP and NF-κB activation were studied. There was significantly higher NO accumulation in cells expressing hEC-SOD exposed to oxidative stress compared with nontransfected cells. Accumulation of cGMP was significantly higher in cells expressing hEC-SOD. Oxidative stress induced NF-κB activation, which was abrogated by hEC-SOD expression. In vivo, there was significantly higher cGMP accumulation in transfected neonatal rabbit lung tissue at 3 and 7 days of hyperoxic exposure. Immunostaining for NF-κB, showed a marked increase in NF-κB concentration in nontreated neonatal rabbit lung tissue compared to transfected neonatal lung with hEC-SOD and the control air group. These results show that transient EC-SOD overexpression maintains NO bioavailability, which directly leads to maintenance of cGMP activity and reduction of NF-κB activation under oxidative stress.

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

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

Is 100% oxygen necessary for the resuscitation of newborn infants?

This paper reproduces in detail the debate 'pro-and-con' regarding the use of 100% oxygen or room air in the resuscitation of the asphyxiated newly born infants, celebrated in Oslo at the 2002 European Association of Perinatal Medicine (EAPM) meeting, in which both co-authors participated as featured speakers. The authors describe their arguments which are based on medical tradition, clinical experience, basic science, and prospective randomized and pseudo-randomized clinical studies that have been reported in the past years. Both authors stress the importance of the long-term consequences of the use of high oxygen concentrations in the perinatal period and conclude that there is a need for further research in the way of ample prospective randomized clinical trials.

Oxidative stress of the newborn in the pre- and postnatal period and the clinical utility of melatonin

Newborns, and especially those delivered preterm, are probably more prone to oxidative stress than individuals later in life. Also during pregnancy, increased oxygen demand augments the rate of production of reactive oxygen species (ROS) and women, even with normal pregnancies, experience elevated oxidative stress and lipid peroxidation compared with nonpregnant women. Also, there appears to be an increase in ROS generation in the placenta of pre-eclamptic women. In comparison with healthy adults, newborn infants have lower levels of plasma antioxidants such as vitamin E, beta-carotene, and sulphydryl groups, lower levels of plasma metal binding proteins including ceruloplasmin and transferrin, and reduced activity of erythrocyte superoxide dismutase. This review summarizes conditions of newborns where there is elevated oxidative stress. Included in this group of conditions is asphyxia, respiratory distress syndrome and sepsis and the review also summarizes the literature related to clinical trials of antioxidant therapies and of melatonin, a highly effective antioxidant and free radical scavenger. The authors document there is general agreement that short-term melatonin therapy may be highly effective and that it has a remarkably benign safety profile, even when neonates are treated with pharmacological doses. Significant complications with long-term melatonin therapy in children and adults also have not been reported. None of the animal studies of maternal melatonin treatment or in postnatal life have shown any treatment-related side effects. The authors conclude that treatment with melatonin might result in a wide range of health benefits, improved quality of life and reduced healthcare costs and may help reduce complications in the neonatal period.

Oxygen free radicals: effects in the newborn period

Free radical production occurs continuously in all cells as a by-product of cell metabolism. In tandem, the human body has developed endogenous antioxidant systems as well as taken advantage of dietary exogenous antioxidants to process and detoxify free radicals appropriately. However, certain conditions may increase free radical production beyond the body's endogenous and exogenous antioxidant systems. The neonatal period is a vulnerable time for free radical damage and injury, particularly for preterm infants whose antioxidant defense systems have not fully matured. Endogenous and passively acquired exogenous antioxidant defense systems do not accelerate in maturation until late in the third trimester. To explore the complexities of these concepts, this article includes a description, an evolutionary perspective of oxygen, and a basic background on free radical chemistry in biology. In addition, this chemistry is applied to the etiology of many of the most common diseases seen in the neonatal period. Finally, the current research addressing clinical strategies in this area is critically appraised. Implications for practice and directions for further research are presented with an emphasis on strategies that support the prudent use of oxygen therapies.

Oxygen in neonatal and infant anesthesia--current practice in the UK

BACKGROUND

There is an increasing awareness of the role of oxygen free radicals in the pathogenesis of many conditions associated with prematurity, which has led to caution in the use of oxygen in neonatal resuscitation. We surveyed the practice of UK pediatric anesthetists with regard to oxygen use in neonatal and infant anesthesia.

METHODS

A postal questionnaire survey of 460 UK-based members of the Association of Pediatric Anesthetists of Great Britain and Ireland.

RESULTS

Responses were received from 247 pediatric anesthetists (54%). Seventy-five percent of anesthetists aim to avoid the use of 100% oxygen during routine infant anesthesia and 52% aim for an FiO(2) of < 0.4 in neonates. The factors most influencing choice of carrier gas are optimal oxygenation and the avoidance of pulmonary atelectasis. Sixteen percent stated that unavailability of medical air is a factor. Opinion was divided on concern about the effects of anesthetic agents on the developing brain. Moderate levels of concern were expressed about the potential toxic effects of oxygen on the eyes and lungs of premature newborns but this concern does not extend to term newborns. Only 20% of anesthetists had any recent knowledge of these issues.

CONCLUSIONS

This survey indicates that there is no consistency in attitudes and practices and demonstrates considerable variation in the use of oxygen during anesthesia in premature and newborn babies and infants. This may reflect the paucity of evidence in the anesthetic literature on the potential harmful effects of high concentrations of oxygen in vulnerable groups of infants.

Activated NAD(P)H oxidase from supplemental oxygen induces neovascularization independent of VEGF in retinopathy of prematurity model

PURPOSE

To study NAD(P)H oxidase-dependent outcomes after oxygen stresses that are similar to those experienced by preterm infants today using a rat model of retinopathy of prematurity.

METHODS

Within 4 hours of birth, pups and their mothers were cycled between 50% and 10% oxygen daily for 14 days and were returned to room air (21% O2, 50/10 oxygen-induced retinopathy [OIR]) or supplemental oxygen (28% O2, 50/10 OIR+SO) for 4 days. Pups received intraperitoneal injections of the specific NAD(P)H oxidase inhibitor apocynin (10 mg/kg/d) or of PBS from postnatal day (P)12 to P17, and some received intraperitoneal injections of hypoxyprobe before kill. Intravitreous neovascularization (IVNV), avascular/total retinal areas, vascular endothelial growth factor (VEGF), NAD(P)H oxidase activity, or hypoxic retina (conjugated hypoxyprobe) were determined in neurosensory retinas. Human retinal microvascular endothelial cells (RMVECs) treated with apocynin or control were exposed to 1% or 21% O2 and assayed for phosphorylated (p-)Janus kinase (JNK) and NAD(P)H oxidase activity.

RESULTS

Retinas from 50/10 OIR+SO had increased NAD(P)H oxidase activity and lower VEGF than did retinas from 50/10 OIR. Apocynin treatment reduced the IVNV area and hypoxic retina in 50/10 OIR+SO. RMVECs treated with 1% O2 had increased p-JNK compared with RMVECs exposed to room air.

CONCLUSIONS

Different oxygen stresses activate NAD(P)H oxidase to varying degrees to trigger disparate pathways (angiogenesis or apoptosis). The oxygen stresses and outcomes used in this study are relevant to human ROP and may explain some of the complexity in the pathophysiology of ROP resulting from oxygen exposure.

Contribution of xanthine oxidase-derived superoxide to chronic hypoxic pulmonary hypertension in neonatal rats

Xanthine oxidase (XO)-derived reactive oxygen species (ROS) formation contributes to experimental chronic hypoxic pulmonary hypertension in adults, but its role in neonatal pulmonary hypertension has received little attention. In rats chronically exposed to hypoxia (13% O2) for 14 days from birth, we examined the effects of ROS scavengers (U74389G 10 mg·kg−1·day−1 or Tempol 100 mg·kg−1·day−1 ip) or a XO inhibitor, Allopurinol (50 mg·kg−1·day−1 ip). Both ROS scavengers limited oxidative stress in the lung and attenuated hypoxia-induced vascular remodeling, confirming a critical role for ROS in this model. However, both interventions also significantly inhibited somatic growth and normal cellular proliferation in distal air spaces. Hypoxia-exposed pups had evidence of increased serum and lung XO activity, increased vascular XO-derived superoxide production, and vascular nitrotyrosine formation. These changes were all prevented by treatment with Allopurinol, which also attenuated hypoxia-induced vascular remodeling and partially reversed inhibited endothelium-dependent arterial relaxation, without affecting normal growth and proliferation. Collectively, our findings suggest that XO-derived superoxide induces endothelial dysfunction, thus impairing pulmonary arterial relaxation, and contributes to vascular remodeling in hypoxia-exposed neonatal rats. Due to the potential for adverse effects on normal growth, targeting XO may represent a superior “antioxidant” strategy to ROS scavengers for neonates with pulmonary hypertension.

Mechanisms underlying developmental programming of elevated blood pressure and vascular dysfunction: evidence from human studies and experimental animal models

Cardiovascular-related diseases are the leading cause of death in the world in both men and women. In addition to the environmental and genetic factors, early life conditions are now also considered important contributing elements to these pathologies. The concept of 'fetal' or 'developmental' origins of adult diseases has received increased recognition over the last decade, yet the mechanism by which altered perinatal environment can lead to dysfunction mostly apparent in the adult are incompletely understood. This review will focus on the mechanisms and pathways that epidemiological studies and experimental models have revealed underlying the adult cardiovascular phenotype dictated by the perinatal experience, as well as the probable key causal or triggering elements. Programmed elevated blood pressure in the adult human or animal is characterized by vascular dysfunction and microvascular rarefaction. Developmental mechanisms that have been more extensively studied include glucocorticoid exposure, the role of the kidneys and the renin-angiotensin system. Other pathophysiological pathways have been explored, such as the role of the brain and the sympathetic nervous system, oxidative stress and epigenetic changes. As with many complex diseases, a unifying hypothesis linking the perinatal environment to elevated blood pressure and vascular dysfunction in later life cannot be presumed, and a better understanding of those mechanisms is critical before clinical trials of preventive or 'deprogramming' measures can be designed.

Effects of vitamin E on the response of the fetal middle cerebral artery to the pressure test

OBJECTIVE

To examine the effects of the maternal administration of vitamin E on the vasoreactivity of the middle cerebral artery (MCA) in preterm fetuses.

STUDY DESIGN

The vasoconstrictive response of the proximal segment of the MCA to brief and partial external occlusions of the umbilical vein (pressure test) was studied in 22 fetuses between 21 and 35 weeks of gestation, before, and 3 to 7 days after, the maternal administration of oral vitamin E (50 mg daily).

RESULTS

The vasoconstrictive activity of the MCA was eliminated in 15 fetuses (68.2%), unchanged in six (27.3%), and decreased in one (4.5%). In the latter seven cases, vasoconstriction of the proximal MCA in response to the pressure test was eliminated by increasing the vitamin E dosage to 100 mg/day.

CONCLUSION

Vitamin E administered to the mothers had a pronounced effect on the proximal MCA reactivity in preterm fetuses.

Effect of hyperoxia on cortical neuronal nuclear function and programmed cell death mechanisms

There is growing concern over detrimental neurologic effects to human newborns caused by increased inspired oxygen concentrations. We hypothesize that hyperoxia (FiO(2)>0.95) results in increased high-affinity Ca(2+)-ATPase activity, Ca(2+)-influx, and proapoptotic protein expression in cortical neuronal nuclei of newborn piglets. Neuronal cerebral energy metabolism was documented by determining ATP and phosphocreatine levels. Neuronal nuclear conjugated dienes and fluorescent compounds were measured as indices of lipid peroxidation. High-affinity Ca(2+)-ATPase activity and ATP-dependent Ca(2+)-influx were determined to document neuronal nuclear membrane function. Hyperoxia resulted in increases in lipid peroxidation, high-affinity Ca(2+)-ATPase activity, ATP-dependent Ca(2+)-influx, and Bax/Bcl-2 ratio in the cortical neuronal nuclei of newborn piglets. We conclude that hyperoxia results in modification of neuronal nuclear membrane function leading to increased nuclear Ca(2+)-influx, and propose that hyperoxia-induced increases in intranuclear Ca(2+) activates the Ca(2+)/calmodulin-dependent protein kinase pathway, triggering increased CREB protein-mediated apoptotic protein expression in hyperoxic neurons.

Antenatal antioxidant prevents adult hypertension, vascular dysfunction, and microvascular rarefaction associated with in utero exposure to a low-protein diet

Developmental programming of hypertension is associated with vascular dysfunction characterized by impaired vasodilatation to nitric oxide, exaggerated vasoconstriction to ANG II, and microvascular rarefaction appearing in the neonatal period. Hypertensive adults have indices of increased oxidative stress, and newborns that were nutrient depleted during fetal life have decreased antioxidant defenses and increased susceptibility to oxidant injury. To test the hypothesis that oxidative stress participates in early life programming of hypertension, vascular dysfunction, and microvascular rarefaction associated with maternal protein deprivation, pregnant rats were fed a normal, low protein (LP), or LP plus lazaroid (lipid peroxidation inhibitor) isocaloric diet from the day of conception until delivery. Lazaroid administered along with the LP diet prevented blood pressure elevation, enhanced vasomotor response to ANG II, impaired vasodilatation to sodium nitroprusside, and microvascular rarefaction in adult offspring. Liver total glutathione was significantly decreased in LP fetuses, and kidney eight-isoprostaglandin F2α (8-isoPGF2α) levels were significantly increased in adult LP offspring; these modifications were prevented by lazaroid. Renal nitrotyrosine abundance and blood levels of 1,4-dihydroxynonene and 4-hydroxynonenal-protein adducts were not modified by antenatal diet exposure. This study shows in adult offspring of LP-fed dams prevention of hypertension, vascular dysfunction, microvascular rarefaction, and of an increase in indices of oxidative stress by the administration of lazaroid during gestation. Lazaroid also prevented the decrease in antioxidant glutathione levels in fetuses, suggesting an antenatal mild oxidative stress in offspring of LP-fed dams. These studies support the concept that perinatal oxidative insult can lead to permanent alterations in the cardiovascular system development.

CXCR2 blockade reduces radical formation in hyperoxia-exposed newborn rat lung

Inflammation contributes greatly to the pathogenesis of bronchopulmonary dysplasia. In previous studies, we showed that blocking neutrophil influx by treatment with SB265610, a selective CXCR2 antagonist, could partly reduce superoxide accumulation and preserve alveolar development in 60% O(2)-exposed newborn rats. The purpose of this study was to further investigate the role of neutrophils in the formation of reactive oxygen and nitrogen species mediating hyperoxia-impaired lung development. We found that hydroxyl radical formation and lipid peroxidation in rat lungs were significantly increased during 60% O(2) exposure. These increases were attenuated by the administration of SB265610. In addition, SB265610 largely inhibited protein nitration induced by hyperoxia. SB265610 partly prevented the hyperoxia-enhanced bronchoalveolar lavage (BAL) protein content in 60% O(2)-exposed animals. Our results demonstrate that neutrophils have a pivotal role in hydroxyl radical formation, lipid peroxidation and protein nitration. Taken together with our previous studies, the present findings show that blocking neutrophil influx protects alveolar development and improves lung function in part by preventing reactive oxygen/nitrogen species accumulation.

Perfluorochemical liquids enhance delivery of superoxide dismutase to the lungs of juvenile rabbits

Previous studies suggest acute lung injury (ALI) in premature newborns is associated with relative deficiency of antioxidant enzymes that may be ameliorated by recombinant human superoxide dismutase (rhSOD). Perfluorochemicals (PFCs) are distributed homogeneously and support gas exchange in diseased lungs. We investigated whether PFCs could provide an effective delivery system for rhSOD. Juvenile rabbits were lung-lavaged, treated with surfactant, and randomized: group I: fluorescently labeled rhSOD (5 mg/kg in 2 mL/kg saline); group II: fluorescently labeled rhSOD (5 mg/kg in 18 mL/kg PFC). Animals were ventilated with oxygen for 4 h; the lungs were harvested for analysis of SOD distribution and oxidative injury. Cardiopulmonary indices remained stable and similar between groups. Qualitative assessment (QA) showed a more homogeneous lung SOD distribution in group II and a better histologic profile. QA of lung SOD distribution showed significant increase in SOD concentrations in group II (7.37 +/- 1.54 microg/mg protein) compared with group I (1.65 +/- 0.23 microg/mg protein). Oxidative injury as assessed by normalized protein carbonyl was 149.1 +/- 26.8% SEM in group II compared with 200.5 +/- 7.3% SEM in group I. Plasma SOD was significantly higher in group II. Administration of rhSOD with or without PFCs does not compromise cardiovascular function or impede lung recovery after ALI. PFCs enhance rhSOD delivery to the lungs by 400% while decreasing lung oxidative damage by 25% compared with rhSOD alone. These data suggest that PFCs optimize lung rhSOD delivery and might enhance the beneficial effects of rhSOD in preventing acute and chronic lung injury.

Reactive Oxygen Species—(ROS) Pathogens or Sources of Vital Energy? Part 1. ROS in Normal and Pathologic Physiology of Living Systems

Free radicals and reactive oxygen species (ROS) are considered to be dangerous pathogens as they may damage key molecular constituents of cells. However this concept approach does not take into account vital functions of ROS in normal physiology. Information has emerged that a substantial share of oxygen consumed by aerobic organisms is used for ROS production and that ROS are indispensable for regulation of multiple functions of living cells. Yet, each cell is equipped with powerful means to eliminate ROS immediately. Explanations of the mechanisms of regulatory action of ROS upon a wide spectrum of biochemical and physiologic reactions and of ROS therapeutic efficacy raise serious problems in the framework of the conventional biochemical paradigm. Here data concerning ROS production and utilization are considered with an emphasis on an apparent paradox: Why does the body produce a lot of ROS and then eliminate them as soon as they appear?

Effects of human milk and spermine on hydrogen peroxide-induced oxidative damage in IEC-6 cells

OBJECTIVE

Oxidative stress is intimately involved in the pathologic processes of serious diseases in the perinatal period. Human milk (HM) contains various bioactive substances, some of which are known as antioxidants, including polyamines such as spermine (SPM). We examined the antioxidative properties of HM and SPM in an intestinal epithelial cell line.

METHOD

Confluent Intestinal Epithelial Cells-6 (IEC-6) cells were preincubated with 100-fold dilutions of defatted HM, bovine milk, or three artificial milks for 24 hours, followed by hydrogen peroxide (H2O2) challenge (0.5 mM, 30 min) for oxidative stress. Cells were preincubated with either HM or increasing concentrations (within the range of HM) of SPM for 24 hours followed by an H2O2 challenge (0.25 mM, 30 min).

RESULTS

HM-treated cells showed the highest survival rate (50%) compared with no pretreatment (27%), bovine milk-treated (6%), or artificial formula-treated (13-16%) cells. Significantly higher survival rates were observed in the cells treated with HM (44.0%) and in those treated with 0.5, 1, or 5 microM of SPM (12.6, 13.1, or 22.2%, respectively) in comparison with the nontreated cells (7.0%).

CONCLUSION

Our results demonstrated that HM and SPM alleviated H2O2-induced oxidative damage in IEC-6 cells, whereas bovine milk and artificial formula did not show any antioxidative capacity. These results suggest that HM acts as an antioxidant in the gastrointestinal tract of infants and that SPM plays an important role in the antioxidative properties of HM.

Oxidative Stress in the Newborn – A 30-Year Perspective

In this review the development of the concept 'hypoxia-reoxygenation injury' is outlined. An update of some important factors and mechanisms related to oxidative stress injury in newborn infants is presented, including the metabolism of glutathione, the role of antioxidants, iron and nitric oxide, and how these may influence health and disease in the newborn and contribute to 'oxygen radical disease of the newborn'. New insight into how hyperoxia and hypoxia may induce changes leading to retinopathy of prematurity by vascular endothelial growth factor acting in concert with insulin-like growth factor is briefly summarized. Inflammation and oxidative stress seem to be two sides of the same coin in newborn babies both contributing to injury partly through similar mechanisms.

Antioxidant defenses in the preterm lung: role for hypoxia-inducible factors in BPD?

Pulmonary antioxidants and their therapeutic implications have been extensively studied during past decades. The purpose of this review is to briefly summarize the key findings of these studies as well as to elaborate on some novel approaches with respect to potential preventive treatments for neonatal chronic lung disease bronchopulmonary dysplasia (BPD). Such new ideas include, for example, modification of transcription factors governing the hypoxic response pathways, important in angiogenesis, cell survival, and glycolytic responses. The fundamental strategy behind that approach is that fetal lung normally develops under hypoxic conditions and that this hypoxic, growth-favoring environment is interrupted by a premature birth. Importantly, during fetal lung development, alveolar development appears to be dependent on vascular development. Therefore, enhancement of signaling factors that occur during hypoxic fetal life ('continued fetal life ex utero'), including angiogenic responses, could potentially lead to improved lung growth and thereby alleviate the alveolar and vascular hypoplasia characteristic of BPD.

Modeling and Remodeling of the Lung in Neonatal Chronic Lung Disease

Neonatal chronic lung disease (CLD) is the major long-term pulmonary complication of preterm birth affecting about 20% of infants who need mechanical ventilation. CLD is the result of abnormal repair processes following inflammatory lung injury that lead to remodeling of the lung. Inflammation may be initiated by a variety of stimuli including mechanical ventilation, oxygen toxicity and infection. The resultant neutrophil chemotaxis and degranulation leads to the release of enzymes such as matrix metalloproteinases that can cause proteolysis of the lung extracellular matrix. Abnormal healing with remodeling leads to poorly compliant lungs with reduced capacity for gas exchange. Drugs can influence the normal process of lung modeling or remodeling. Fetal lung development can be influenced by glucocorticosteroids and inflammation. Both can cause abnormal lung modeling with fewer, larger alveoli and accelerated lung maturation, which confers benefits in terms of reduced morbidity and mortality from respiratory distress syndrome but potentially increases the risk of subsequent lung injury. Antioxidants, such as retinol (vitamin A), administered post-natally may reduce the effects of oxidative stress leading to a modest reduction in CLD but they require repeated intramuscular injections. Postnatal glucocorticosteroid therapy can modify the lung inflammatory response and reduce CLD but it can also have detrimental effects on the developing brain and lung, thereby creating a clinical dilemma for neonatologists. Proteinase inhibitors may be a rational therapy but more research is needed before they can be accepted as a treatment for preterm neonates.'Modeling' is defined as planning or forming that follows a set pattern. The term is used to describe the normal process of lung growth and development that culminates in mature branching alveolar air spaces surrounded by a network of capillaries. Normal lung modeling occurs under a variety of genetic and hormonal influences that can be altered, leading to abnormal patterns of growth. 'Remodeling' is defined as altering the structure of or re-making and, in the case of the lung, is used to describe the abnormal patterns of lung growth that occur after lung injury. Modeling and remodeling of the lungs occur to an extent throughout life but never more rapidly than during the fetal and early neonatal periods, and factors that influence this process may lead to development of neonatal CLD. Some of the factors involved in normal and abnormal lung modeling and inflammation and glucocorticosteroid-induced remodeling in the perinatal period, in the context of neonatal CLD, are reviewed with considerations of how various drugs may influence these processes.

Resuscitation with 100% O2 increases cerebral injury in hypoxemic piglets

Perinatal asphyxia is a major cause of immediate and postponed brain injury in the newborn. We hypothesized that resuscitation with 100% O2 compared with ambient air is detrimental to the cerebral tissue. We assessed cerebral injury in newborn piglets that underwent global hypoxia and subsequent resuscitation with 21 or 100% O2 by extracellular glycerol, matrix metalloproteinase (MMP) expression levels, and oxidative stress. Extracellular glycerol was sampled by cerebral microdialysis. MMP levels were analyzed in cerebral tissue by gelatin zymography, broad matrix degrading capacity, and real-time PCR. Total endogenous antioxidant capacity was measured by the oxygen radical absorbance capacity assay. Extracellular glycerol increased 50% after resuscitation with 100% O2 compared with 21% O2. Total MMP activity was doubled in resuscitated animals at endpoint compared with baseline (p=0.018), and the MMP-2 activity was significantly increased in piglets that were resuscitated with 21% O(2) (p=0.003) and 100% O2 (p=0.001) compared with baseline. MMP-2 mRNA level was 100% increased in piglets that were resuscitated with 100% O2 as compared with 21% O2 (p < 0.05). Oxygen radical absorbance capacity values in piglets that were resuscitated with 100% O2 were considerably reduced compared with both baseline (p=0.001) and piglets that were resuscitated with 21% O2 (p=0.001). In conclusion, our data show increased MMP-2 activity at both gene and protein levels, accompanied with cerebral leakage of glycerol, presumably triggered by augmented oxidative stress. Our findings suggest that resuscitation of asphyxiated piglets with 100% O2 is detrimental to the piglet brain compared with resuscitation with 21% O2.

Neonatal anesthesia

The physiology of the preterm and term neonate is characterized by a high metabolic rate, limited pulmonary, cardiac and thermoregulatory reserve, and decreased renal function. Multisystem immaturity creates important developmental differences in drug handling and response when compared to the older child or adult. Neonatal anesthetic management requires an understanding of the pharmacophysiologic limitations of the neonate as well as the pathophysiology of coexisting surgical disease. This review addresses the pertinent aspects of neonatal physiology and pharmacology, general considerations in the anesthetic care of surgical neonates, and concludes with a brief review of the anesthetic management of neonates with necrotizing enterocolitis, diaphragmatic hernia, and tracheoesophageal fistula.