Oxidative Stress in the Newborn – A 30-Year Perspective

Newborn vitamin A supplementation reduced infant mortality in rural Bangladesh

OBJECTIVES

We assessed the effect of supplementing newborns with 50000 IU of vitamin A on all-cause infant mortality through 24 weeks of age.

PATIENTS AND METHODS

This was a community-based, double-masked, cluster-randomized, placebo-controlled trial conducted in 19 unions in rural northwest Bangladesh. The study was nested into and balanced across treatment arms of an ongoing placebo-controlled, weekly maternal vitamin A or beta-carotene supplementation trial. Study-defined sectors (N = 596) were evenly randomized for newborns of participating mothers to receive a single, oral supplement of vitamin A (50000 IU) or placebo as droplets of oil squeezed from a gelatinous capsule. Mothers provided informed consent for newborn participation at approximately 28 weeks' gestation. After birth, typically at home (where >90% of births occurred), infants were supplemented and their vital status was followed through 24 weeks of age. The main outcome measure was mortality through 24 weeks of age.

RESULTS

We obtained maternal consent to dose 17116 live-born infants (99.8% of all eligible) among whom 15937 (93.1%) were visited to be supplemented <30 days after birth and for whom vital status at 24 weeks of age was known. Dosed infants (n = 15902 [99.8%]) received their study supplement at a median age of 7 hours. Relative to control subjects, the risk of death in vitamin A-supplemented infants was 0.85, reflecting a 15% reduction in all-cause mortality. Protective relative risks were indistinguishable by infant gender, gestational age, birth weight, age at dosing, maternal age, parity, or across the 3 treatment arms of the maternal supplementation trial.

CONCLUSIONS

Newborn vitamin A dosing improved infant survival through the first 6 months of life in Bangladesh. These results corroborate previous findings from studies in Indonesia and India and provide additional evidence that vitamin A supplementation shortly after birth can reduce infant mortality in South Asia.

Achievement of targeted saturation values in extremely low gestational age neonates resuscitated with low or high oxygen concentrations: a prospective, randomized trial

OBJECTIVE

Extremely low gestational age neonates have very low oxygen saturation in utero and an immature antioxidant defense system. Abrupt increases in oxygen saturation after birth may cause oxidative stress. We compared achievement of a targeted oxygen saturation of 85% at 10 minutes of life when resuscitation was initiated with low or high fractions of inspired oxygen and levels were adjusted according to preductal pulse oxygen saturation values.

METHODS

A prospective, randomized, clinical trial was performed in 2 level III neonatal referral units. Patients of < or = 28 weeks of gestation who required active resuscitation were randomly assigned to the low-oxygen group (fraction of inspired oxygen: 30%) or the high-oxygen group (fraction of inspired oxygen: 90%). Every 60 to 90 seconds, the fraction of inspired oxygen was increased in 10% steps if bradycardia occurred (< 100 beats per minute) or was decreased in similar steps if pulse oxygen saturation reached values of > 85%. Preductal pulse oxygen saturation was continuously monitored.

RESULTS

The fraction of inspired oxygen in the low-oxygen group was increased stepwise to 45% and that in the high-oxygen group was reduced to 45% to reach a stable pulse oxygen saturation of approximately 85% at 5 to 7 minutes in both groups. No differences in oxygen saturation in minute-to-minute registers were found independent of the initial fraction of inspired oxygen used 4 minutes after cord clamping. No differences in mortality rates in the early neonatal period were detected.

CONCLUSIONS

Resuscitation can be safely initiated for extremely low gestational age neonates with a low fraction of inspired oxygen (approximately 30%), which then should be adjusted to the infant's needs, reducing the oxygen load to the neonate.

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.

Antioxidant activity in the newborn brain: a luciferase mouse model

INTRODUCTION

Oxidative stress in the newborn period may cause cell injury and inflammation if the antioxidant capacity is insufficient. To monitor antioxidant and inflammatory activity we examined by in vivo imaging various strains of luciferase reporter mice whose light-emitting properties were regulated by response elements or complete promoters related to oxidative stress and/or inflammation. The aim of this study is to present a model that can monitor genetic activity in vivo during pregnancy and the first 10 days of life.

METHODS

One mouse strain reports the activity of nuclear factor-kappaB (NF-kappaB) activity, a transcription factor essential for modulating inflammation, apoptosis, differentiation and cell growth. A second mouse strain reports on superoxide dismutase 1-promoter activity. A third strain reports the promoter activity of gamma-glutamylcysteine synthetase, the rate limiting enzyme in glutathione production, and the last strain reports on antioxidant responsive element (ARE)/electrophil responsive element. Wild-type female mice mated with NF-kappaB mice were imaged through pregnancy to monitor intrauterine NF-kappaB activation.

RESULTS

Intrauterine NF-kappaB activity increased dramatically from day 17 towards labor. During the first 4 days of life luminescence measured was intense in all mice with distinct strain differences. All strains had high luminescence levels at day 1 and a considerably lower level at day 10.

CONCLUSION

This model allows investigation of the transcriptional regulation of key proteins related to oxidative stress and inflammation in pregnancy and the first days of life. With very little stress to the newborn animals genetic activity can be monitored day by day.

Intima-media thickness of the abdominal aorta of neonate with different gestational ages

PURPOSE

To determine aortic intima-media thickness (aIMT) values in newborns with different gestational ages and to asses the effect of antenatal steroids on aIMT.

METHODS

Two hundred forty newborns from healthy mothers had their distal abdominal aIMT measured during abdominal sonographic examination. The neonates were divided into 4 groups (60 in each group) according to gestational age: group I (25-28 weeks), group II (29-32 weeks), group III (33-37 weeks), and group IV (38-42 weeks).

RESULTS

The interobserver and intersubject intraclass correlation coefficient was 0.93 and 0.94, respectively. Mean aIMT was 0.316 mm, 0.335 mm, 0.348 mm, and 0.385 mm, respectively, in group I, II, III, and IV, increasing significantly with gestational age at birth (p < 0.0001). There was no apparent effect of antenatal steroid use on aIMT. Multivariate regression models for mean aIMT demonstrated a significant association with aortic lumen diameter (p < 0.0001).

CONCLUSION

Abdominal aIMT can be reproducibly measured in neonates and may be a useful tool for epidemiologic studies.

Anti-oxidant strategies

Oxidative stress plays an important role in causing organ injury in the compromised fetus and neonate. Recent experimental research and clinical studies have clarified important pathways in the production of reactive oxygen and nitrogen species. Free radicals are involved in causing cerebral damage after perinatal hypoxia-ischemia affecting membrane lipids, proteins, and DNA. Anti-oxidant strategies can be used as add-on neuroprotective therapy after perinatal oxidative stress. Selective inhibitors of neuronal and inducible nitric oxide synthase, allopurinol, melatonin, and erythropoietin are among the first compounds that are ready for clinical trials.

Oxidative kidney damage in preterm newborns during perinatal period

BACKGROUND

Oxidative stress has recently been found to play a key role in post-ischemic kidney damage. We tested the hypothesis that oxidative kidney damage due to perinatal hypoxia in preterm newborns is associated with an increased production of oxidative free radicals in plasma.

METHODS

Blood and urine samples were obtained at birth and on days 7 and 14, from 55 preterm newborns, without any known congenital abnormalities. Total hydroperoxides (TH) and advanced oxidation protein products (AOPP) as indices of oxidative stress, xanthine (Xa) and hypoxanthine (Hx) as indices of hypoxia, alpha1-microglobulin and N-acetyl-beta-D-glucosaminidase (NAG) as indices of kidney damage were assayed.

RESULTS

Statistically significant correlations (p<0.05) were found between biochemical markers of hypoxia, oxidative stress and proximal tubules damage at days 7 and 14.

CONCLUSIONS

Perinatal oxidative stress is associated with a variable degree of kidney damage detectable at birth and continuing up to 14 days.

Perinatal adaptation in mammals: the impact of metabolic rate

Mammalian birth is accompanied by profound changes in metabolic rate that can be described in terms of body size relationship (Kleiber's rule). Whereas the fetus, probably as an adaptation to the low intrauterine pO2, exhibits an "inappropriately" low, adult-like specific metabolic rate, the term neonate undergoes a rapid metabolic increase up to the level to be expected from body size. A similar, albeit slowed, "switching-on" of metabolic size allometry is found in human preterm neonates whereas animals that are normally born in a very immature state are able to retard or even suppress the postnatal metabolic increase in favor of weight gain and O2 supply. Moreover, small immature mammalian neonates exhibit a temporary oxyconforming behavior which enhances their hypoxia tolerance, yet is lost to the extent by which the size-adjusted metabolic rate is "locked" by increasing mitochondrial density. Beyond the perinatal period, there are no other deviations from metabolic size allometry among mammals except in hibernation where the temporary "switching-off" of Kleiber's rule is accompanied by a deep reduction in tissue pO2. This gives support to the hypothesis that the postnatal metabolic increase represents an "escape from oxygen" similar to the evolutionary roots of mitochondrial respiration, and that the overall increase in specific metabolic rate with decreasing size might contribute to prevent tissues from O2 toxicity.

Pre-ductal and post-ductal O2 saturation in healthy term neonates after birth

OBJECTIVE

To determine the pre- and post-ductal oxygen saturation (SpO2) levels during the first minutes after birth in healthy term infants.

STUDY DESIGN

In a prospective cohort study, sensors were placed on the right hand and on 1 foot of the neonate. Pre- and post-ductal SpO2 levels were recorded during the first 15 minutes after birth. Exclusion criteria were gestational age <37 weeks, presence of risk factors for asphyxia, emergency cesarean delivery (C/D), congenital anomalies, and multiple pregnancies. Infants who were treated with O2 or positive pressure ventilation were also excluded from the study.

RESULTS

The mean (SD) gestational age of the 110 infants was 39 weeks (1.1), and the mean birth weight was 3340 grams (359). At 5 minutes, the mean pre-ductal SpO2 level was 89% (7), and the mean post-ductal SpO2 level was 81% (10). Pre- and post-ductal SpO2 levels were significantly different during the first 15 minutes after birth. The SpO2 level was lower in babies delivered by C/D in comparison to babies born by vaginal delivery.

CONCLUSIONS

In healthy newly born infants, oxygen saturation rises slowly and does not usually reach 90% in the first 5 minutes of life. A gradient between pre- and post-ductal SpO2 levels remains significant for the first 15 minutes of life.

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.

Different degrees of fetal oxidative stress in elective and emergent cesarean section

BACKGROUND

Several studies have addressed the influence of labor and mode of delivery on oxidative stress. Still it is unclear whether oxidative stress is related to delivery itself or whether it reflects a pre-existing fetal oxidative status.

OBJECTIVE

To investigate whether the degree of fetal oxidative stress is different between distressed fetuses that were delivered by emergent cesarean section and non-distressed fetuses that were delivered by elective cesarean section.

METHODS

The protocol of this prospective study was approved by the Institutional Review Board Committee. Amniotic fluid and umbilical artery blood were prospectively collected from 21 parturients who were delivered by an emergent cesarean section for non-reassuring fetal heart rate pattern and from 21 parturients who were delivered by an elective cesarean section in a tertiary care center. Oxidative stress was evaluated in amniotic fluid, umbilical cord plasma and erythrocytes by determining malondialdehyde concentration and glutathione peroxidase (GPX) activity.

RESULTS

Malondialdehyde concentration was higher in amniotic fluid (mean +/- SEM) (2.2 +/- 0.7 nmol/l vs. 0.6 +/- 0.02 nmol/l, p < 0.05), in umbilical cord plasma (1.2 +/- 0.2 nmol/l vs. 0.7 +/- 0.3 nmol/l, p < 0.05) and in umbilical cord erythrocytes (159.6 +/- 48.6 nmol/g Hb vs. 85.8 +/- 5.2 nmol/g Hb, p < 0.05) in women delivering by emergent cesarean compared to those delivering by elective cesarean. GPX activity was enhanced in amniotic fluid (12.4 +/- 2.2 U/l vs. 5.1 +/- 0.6 U/l, p < 0.05) and GPX activity/hemoglobin ratio was higher in cord blood (22.0 +/- 0.8 U/g Hb vs. 18.7 +/- 0.9 U/g Hb, p < 0.05) in women delivering by emergent cesarean compared to those delivering by elective cesarean.

CONCLUSION

Distressed fetuses delivered by emergency cesarean exhibited increased malondialdehyde concentrations, an indicative parameter for oxidative damage, and enhanced GPX activity an antioxidant enzyme, in amniotic fluid and umbilical cord blood compared to non-distressed fetuses delivered by elective cesarean section. This is probably an indication of higher fetal oxidative stress.

Immunomodulatory effect of vitamin C on intracytoplasmic cytokine production in neonatal cord blood cells

BACKGROUND

Vitamin C (ascorbic acid) is an essential water-soluble antioxidant in cells and plasma. Besides metabolic functions, vitamin C is also known to contribute to immune homeostasis. Recently, it has been demonstrated that vitamin C has an inhibitory effect on the expression of pro-inflammatory cytokines such as interleukin (IL)-6 and tumor necrosis factor alpha (TNF-alpha) in adult whole blood cells in vitro. It has been postulated that vitamin C might be an interesting compound for modulation of an over-exuberant immune response, e.g., in patient cohorts susceptible for the development of systemic inflammatory response syndrome such as neonates. It was the aim of this study to investigate the modulatory effects of vitamin C on the production of inflammatory mediators in neonatal cord blood cells.

METHODS

The intracytoplasmic production of pro-inflammatory cytokines in neonatal cord blood cells stimulated with lipopolysaccharide or phorbol 12-myristate 13-acetate/ionomycin was assessed by flow-cytometry.

RESULTS

In contrast to our previous observations from adult whole blood cells, 20 mM vitamin C mildly stimulated the percentage of neonatal monocytes producing IL-6 after lipopolysaccharide stimulation (e.g., 11.3% increase compared to control, p = 0.005). In the presence of 20 mM vitamin C, even a stronger stimulatory effect was noted for the percentage of IL-8 (e.g., 46.7% increase, p < 0.001) and TNF-alpha producing neonatal monocytes (e.g., 69.2% increase, p = 0.004; n = 20). In accordance with adult data, the percentage of neonatal lymphocytes producing IL-2 after phorbol 12-myristate 13-acetate/ionomycin stimulation was dose-dependently reduced (e.g., 41.3% inhibition, p = 0.001, 20 mM vitamin C), while the percentage of TNF-alpha producing lymphocytes was mildly stimulated (e.g., 20.8% increase, p = 0.003, 20 mM vitamin C).

CONCLUSIONS

Interestingly, vitamin C was demonstrated to enhance pro-inflammatory responses in CD14(+) cord blood cells while only intracellular IL-2 production in CD3(+) cells was diminished. These data suggest that vitamin C differentially influences intracytoplasmic cytokine production in adults and neonates, and further studies are needed to elucidate the underlying mechanisms of this selective immunomodulation.

Melatonin levels during the first week of life and their relation with the antioxidant response in the perinatal period

AIM

Melatonin is a potent free radical scavenger and an indirect antioxidant. Knowledge about the behavior of melatonin secretion in the early neonatal period, which may relate to its properties at a vital stage during very high antioxidant demands, is limited.

PATIENTS AND METHODS

We studied 35 newborns admitted to the Neonatal Unit with respiratory distress syndrome (RDS) and with no signs of sepsis, severe anemia, hemodynamic compromise or malformation. The gestational age of the newborns was 26-40 weeks (mean value 32.5 weeks) and the weight at birth was 870-4,400 g (mean value 1,800 g). They were classified into two groups: <or=1,500 g or >1,500 g birthweight. In all cases, at 09:00 h on their 1st, 3rd and 7th days of life, serum melatonin was measured by RIA. The clinical history was recorded and treatment and follow-up were performed according to established neonatology practice, and the resultant data recorded. Informed consent from the parents or guardians was obtained in accordance with the Declaration of Helsinki. Statistical analysis was carried out using ANOVA-II (factor I: day of sample; factor II: birthweight).

RESULTS

There were significant increases in melatonin levels with increasing birthweight (p = 0.017), but no changes by day of sample. Although in both study groups melatonin levels increased during the first few days this was not statistically significant.

CONCLUSIONS

In newborns of low birthweight, we report high melatonin concentrations in the morning and during the first week of life. These increase with maturation, and at full-term were similar to nocturnal levels during the acrophase of pineal gland secretion in toddlers and schoolage children, when pineal gland secretion is maximal and takes place reflecting environmental variations. In the early neonatal period these high levels of melatonin seem to derive from extrapineal sources, which mature to provide antioxidant protection in accordance with other elements of the antioxidant network to compensate for the high levels of oxidative stress that are present in the perinatal period.

Optimal oxygenation at birth and in the neonatal period

BACKGROUND

In recent years it has become clear that even a brief exposure to high oxygen concentration at birth and an oxygen saturation (SaO(2)) >93-95% in extremely low birth weight (ELBW) infants is more toxic than previously believed.

OBJECTIVE

To summarize and review clinical studies published to date either dealing with resuscitation of newborn infants with different oxygen concentrations or the use of high or low SaO(2) in the neonatal period of ELBW infants.

RESULTS

Three systematic reviews of five trials and seven individual studies including up to 2,011 newborn infants have shown that neonatal mortality is reduced by 30-40% if resuscitation is carried out with 21% instead of 100% O(2). Room air resuscitation also leads to faster early recovery and need for shorter duration of resuscitation. Six studies of ELBW infants have shown that retinopathy of prematurity and chronic lung disease are significantly reduced if SaO(2) is kept <93-95% compared with higher saturations. Avoidance of fluctuations in SaO(2) also seems to be important. Two observational studies suggest a significant 2.5- to 3.5-fold increased risk of childhood cancer in infants resuscitated with 100% O(2) for a few minutes.

CONCLUSIONS

To date there are sufficient data available to recommend that newborn resuscitation should not be carried out with 100% O(2). In ELBW infants, SaO(2) levels should be kept between 85 and 93% or possibly between 88 and 95%, but should definitely not exceed 95%. Fluctuations should be avoided.

Inflammation and bronchopulmonary dysplasia: a continuing story

Increasing evidence indicates that bronchopulmonary dysplasia (BPD) results, at least in part, from an imbalance between pro-inflammatory and anti-inflammatory mechanisms, with a persistent imbalance that favours pro-inflammatory mechanisms. The inflammatory response is characterised by an accumulation of neutrophils and macrophages in the airways and pulmonary tissue of preterm infants and, moreover, by an arsenal of pro-inflammatory mediators which affect the alveolar capillary unit and tissue integrity. As well as pro-inflammatory cytokines and toxic oxygen radicals, various lipid mediators as well as potent proteases may be responsible for acute lung injury. During the last decade it has become evident that multiple pre- and postnatal events contribute to the development of BPD in preterm infants. Chorioamnionitis and cytokine exposure in utero, plus sequential lung injury caused by postnatal resuscitation, oxygen toxicity, volu-, barotrauma and infection all lead to a pulmonary inflammatory response which is most probably associated with aberrant wound healing and an inhibition of alveolarisation as well as vascular development in the immature lungs of very preterm infants, causing the 'new BPD'.

Pulmonary inflammation and bronchopulmonary dysplasia

Various pre- and postnatal risk factors, which act additively or synergistically induce an injurious inflammatory response in the airways and the pulmonary interstitium of preterm infants with bronchopulmonary dysplasia. This inflammatory response is characterized by an accumulation of neutrophils and macrophages as well as an arsenal of proinflammatory mediators that affect the endothelium and alveolar-capillary integrity. Besides proinflammatory cytokines and toxic oxygen radicals, lipid mediators as well as potent proteases may be responsible for acute lung injury. There is increasing evidence that an imbalance between pro- and anti-inflammatory factors, which should protect the alveoli and lung tissue, are key features in the pathogenesis of bronchopulmonary dysplasia. In addition, a subnormal generation of growth factors may affect alveolarization and vascular development in preterm infants with bronchopulmonary dysplasia. In this condensed review article, the current concepts on the possible role of inflammation in the evolution of bronchopulmonary dysplasia will be summarized.

Oxygen and retinopathy of prematurity

Retinopathy of prematurity is on the rise and a third epidemic has been identified. In spite of extensive research and progress in the understanding of this disease in recent years, 50 000 children worldwide are blinded by this condition each year. The relation between hyperoxia, low-gestational age, growth retardation, oxygen dependent growth factors, and oxidative stress are now being understood more clearly. We know that in the first phase of retinopathy of prematurity, hyperoxia inhibits vascular endothelial growth factor. In the second phase, vascular endothelial growth factor rises, and when insulin-like growth factor-1 reaches a threshold around 32 to 34 weeks postconceptional age, uncontrolled neovascularization may occur. It is not known whether this new knowledge will have implications for future therapy. However, by strictly avoiding hyperoxia, that is, SaO2>92-93% and avoiding fluctuations in SaO2, it is possible to control and prevent severe retinopathy of prematurity in most cases.

Brain injury in the infant: the old, the new, and the uncertain

Although neonatal brain injury occurs most frequently after a perinatal hypoxic-ischemic insult, recently studies have noted that variable causes such as metabolic and reperfusion events can result in, or aggravate, a brain insult. Current data suggest that about 2 to 5 of 1,000 live births in the United States and more so in developing countries experience a brain injury Approximately 20% to 40% of infants who survive the brain injury develop significant neurological and developmental impairments. The resulting impact on the child, family, and society presents a formidable challenge to health care professionals. Although several important insights have been gained in the last several years about the epidemiology, diagnosis, and mechanism of brain injury, management remains mostly a cocktail of controversial trials. This article provides a comprehensive review of the pathology, clinical manifestations, and timely management of infants with brain injury.