Chronic lung disease: the role of oxidative stress

MitoQ as an antenatal antioxidant treatment improves markers of lung maturation in healthy and hypoxic pregnancy

Chronic fetal hypoxaemia is a common pregnancy complication that increases the risk of infants experiencing respiratory complications at birth. In turn, chronic fetal hypoxaemia promotes oxidative stress, and maternal antioxidant therapy in animal models of hypoxic pregnancy has proven to be protective with regards to fetal growth and cardiovascular development. However, whether antenatal antioxidant therapy confers any benefit on lung development in complicated pregnancies has not yet been investigated. Here, we tested the hypothesis that maternal antenatal treatment with MitoQ will protect the developing lung in hypoxic pregnancy in sheep, a species with similar fetal lung developmental milestones as humans. Maternal treatment with MitoQ during late gestation promoted fetal pulmonary surfactant maturation and an increase in the expression of lung mitochondrial complexes III and V independent of oxygenation. Maternal treatment with MitoQ in hypoxic pregnancy also increased the expression of genes regulating liquid reabsorption in the fetal lung. These data support the hypothesis tested and suggest that MitoQ as an antenatal targeted antioxidant treatment may improve lung maturation in the late gestation fetus. KEY POINTS: Chronic fetal hypoxaemia promotes oxidative stress, and maternal antioxidant therapy in hypoxic pregnancy has proven to be protective with regards to fetal growth and cardiovascular development. MitoQ is a targeted antioxidant that uses the cell and the mitochondrial membrane potential to accumulate within the mitochondria. Treatment of healthy or hypoxic pregnancy with MitoQ, increases the expression of key molecules involved in surfactant maturation, lung liquid reabsorption and in mitochondrial proteins driving ATP synthesis in the fetal sheep lung. There were no detrimental effects of MitoQ treatment alone on the molecular components measured in the present study, suggesting that maternal antioxidant treatment has no effect on other components of normal maturation of the surfactant system.

Oxidative stress and peripartum outcomes (Review)

Pregnancy, labor and childbirth are accompanied by excessive oxidative aggression. The excessive formation of free radicals [reactive oxygen species (ROS), reactive nitrogen species (RNS), chlorine reactive species (CRS)] causes cellular oxidative damage, which can be scavenged by enzymatic or non-enzymatic antioxidants in normal healthy pregnancy, physiological labor and delivery without any complications. An imbalance between the pro-oxidant and antioxidant factors may lead to oxidative stress, which contributes to the development of many diseases. This oxidative aggression can be a precursor for pathologies in the pregnant woman including eclampsia, miscarriage, preterm labor, and intrauterine growth retardation; in the offspring it may lead to bronchopulmonary dysplasia/chronic lung disease, necrotizing enterocolitis, retinopathy of prematurity, and periventricular leukomalacia. This review summarizes the studies conducted to identify the mechanisms of oxidative stress and the effect of cell membrane oxidation, the mechanisms that are behind oxidative stress-related diseases, and also those studies which have demonstrated the effect of antioxidants in preventing diseases or diminishing the effects of oxidative stress in the body, in obstetrics and neonatology.

Biomarkers of Oxidative Stress for Neonatal Lung Disease

The transition from prenatal to postnatal life causes a significant increase in arterial oxygen tension and the activation of metabolic pathways enabling the newborn's adaptation to the extra-uterine environment. The balance between pro-oxidant and anti-oxidant systems is critical to preserve cellular functions. Indeed, oxidative stress (OS) occurs when the production of free radicals is not balanced by the activity of intracellular antioxidant systems, contributing to cellular and tissue damage. Perinatal OS may have serious health consequences during the postnatal period and later in life. Namely, OS has been recognized as the major cause of lung injury in newborns, especially those preterm born, due to their immature lung and antioxidant systems. The development of OS biomarkers has gained increasing research interest since they may provide useful insights about pathophysiological pathways underlying OS-mediated pulmonary diseases in newborns. Moreover, their implementation in clinical settings may help to early identify high risk-newborns and to provide targeted treatment. Ideally, a biomarker should demonstrate ease of use, biological validity and reproducibility, high sensitivity and specificity. However, none of the clinically validated biomarkers so far have been qualified for neonatal lung disease. Additionally, the complex technical procedures and the high cost of such determinations have hampered the use of OS biomarkers in clinical practice. This review aims to evaluate the current evidence on the application of biomarkers of oxidative stress for neonatal lung disease and exploring the most relevant issues affecting their implementation in practice, as well as the associated evidence gaps and research limitations.

What is bronchopulmonary dysplasia and does caffeine prevent it?

Bronchopulmonary dysplasia (BPD) is among the most severe complications of very premature birth. Clinical and laboratory studies indicate that lung immaturity, inflammatory lung injury, and disordered lung repair are the primary mechanisms responsible for the development of BPD. Caffeine, initiated within the first 10 days after birth, is one of few drug therapies shown to significantly decrease the risk of BPD in very low birth weight infants. This benefit is likely derived, at least in part, from reduced exposure to positive airway pressure and supplemental oxygen with caffeine therapy. Additional cardiorespiratory benefits of caffeine that may contribute to the lower risk of BPD include less frequent treatment for a PDA, improved pulmonary mechanics, and direct effects on pulmonary inflammation, alveolarization, and angiogenesis. Routine administration of caffeine is indicated in the vast majority of very low birth weight infants. However, current preventative strategies including widespread use of caffeine do not avert BPD in all cases. As such, there is continued need for novel methods to further reduce the risk of BPD in very low birth weight infants.

Use of Melatonin in Oxidative Stress Related Neonatal Diseases

Reactive oxygen species have a crucial role in the pathogenesis of perinatal diseases. Exposure to inflammation, infections, or high oxygen concentrations is frequent in preterm infants, who have high free iron levels that enhance toxic radical generation and diminish antioxidant defense. The peculiar susceptibility of newborns to oxidative stress supports the prophylactic use of melatonin in preventing or decreasing oxidative stress-mediated diseases. Melatonin, an effective direct free-radical scavenger, easily diffuses through biological membranes and exerts pleiotropic activity everywhere. Multiple investigations have assessed the effectiveness of melatonin to reduce the “oxygen radical diseases of newborn” including perinatal brain injury, sepsis, chronic lung disease (CLD), and necrotizing enterocolitis (NEC). Further studies are still awaited to test melatonin activity during perinatal period.

Ventilation strategies for preventing oxidative stress-induced injury in preterm infants with respiratory disease: an update

Reactive oxygen and nitrogen species are produced by several inflammatory and structural cells of the airways. The lungs of preterm newborns are susceptible to oxidative injury induced by both reactive oxygen and nitrogen species. Increased oxidative stress and imbalance in antioxidant enzymes may play a role in the pathogenesis of inflammatory pulmonary diseases. Preterm infants are frequently exposed to high oxygen concentrations, infections or inflammation; they have reduced antioxidant defense and high free iron levels which enhance toxic radical generation. Multiple ventilation strategies have been studied to reduce injury and improve outcomes in preterm infants. Using lung protective strategies, there is the need to reach a compromise between satisfaction of gas exchange and potential toxicities related to over-distension, derecruitment of lung units and high oxygen concentrations. In this review, the authors summarize scientific evidence concerning oxidative stress as it relates to resuscitation in the delivery room and to the strategies of ventilation.

Oxidative stress early in infancy and neurodevelopmental outcome in very low-birthweight infants

BACKGROUND

Reactive oxygen species may be involved in serious diseases in premature infants. The objective of this study was to assess the relationship between neurodevelopmental outcome and oxidative stress marker level in the urine of very low-birthweight (VLBW) infants.

METHODS

Spot urine samples were collected from 35 VLBW infants. Urinary excretion of 8-hydroxy-2″-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, and 8-iso-prostaglandin F2α (8-isoPGF), a marker of lipid peroxidation, was measured at 1, 2, 4, and 6 weeks of age. Neurodevelopmental outcome at 18 months' corrected age was assessed using the Bayley Scales of Infant Development (BSID)-II.

RESULTS

Significant correlations were found between urinary 8-OHdG at 2 and 4 weeks and the Mental Development Index of the BSID-II. No significant correlation was found between urinary 8-isoPGF and indices of the BSID-II.

CONCLUSIONS

In VLBW infants, urinary 8-OHdG level correlated with mental development rather than psychomotor development at 18 months' corrected age; urinary 8-OHdG might be a predictive marker of neurodevelopmental outcome in VLBW infants.

Oxidative stress and bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the major cause of pulmonary disease in infants. The pathophysiology and management of BPD changed with the improvement of neonatal intensive care unit (NICU) management and with the increase of survival rates. Despite the improvements made, BPD is still a public health concern, resulting in frequent hospitalizations with high rates of mortality, impaired weight and height growth, and neurodevelopmental disorders. Lung injury in the neonatal period has multiple etiologic factors - genetic, hemodynamic, metabolic, nutritional, mechanical, and infectious mechanisms - act in a cumulative and synergic way. Free radical (FR) generation is largely recognized as the major cause of lung damage. Oxidative stress (OS) is the final common endpoint for a complex convergence of events, some genetically determined and some triggered by in utero stressors. Inflammatory placental disorders and chorioamnionitis also play an important role due to the coexistence of inflammatory and oxidative lesions. In addition, the contribution of airway inflammation has been extensively studied. The link between inflammation and OS injury involves the direct activation of inflammatory cells, especially granulocytes, which potentiates the inflammatory reaction. Individualized interventions to support ventilation, minimize oxygen exposure, minimize apnea, and encourage growth should decrease both the frequency and severity of BPD. Future perspectives suggest supplementation with enzymatic and/or non-enzymatic antioxidants. The use of antioxidants in preterm newborns particularly exposed to OS and at risk for BPD represents a logical strategy to ameliorate FRs injury, but further studies are needed to support this hypothesis.

Epidemiology of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is among the most common and serious sequelae of preterm birth. BPD affects at least one-quarter of infants born with birth weights less than 1500 g. The incidence of BPD increases with decreasing gestational age and birth weight. Additional important risk factors include intrauterine growth restriction, sepsis, and prolonged exposure to mechanical ventilation and supplemental oxygen. The diagnosis of BPD predicts multiple adverse outcomes including chronic respiratory impairment and neurodevelopmental delay. This review summarizes the diagnostic criteria, incidence, risk factors, and long-term outcomes of BPD.

Protective role of melatonin in neonatal diseases

Oxidative stress contributes to the severity of several newborn conditions to the extent that Saugstad coined the phrase “oxygen radical diseases of neonatology.” In order to counteract free radicals damage many strategies to augment antioxidant status in ill-term and preterm infants have been proposed and several medications have been experimented with mixed results. Several studies have tested the efficacy of melatonin to counteract oxidative damage in diseases of newborns such as chronic lung disease, perinatal brain injury, necrotizing enterocolitis, and retinopathy of prematurity, giving promising results. The peculiar perinatal susceptibility to oxidative stress indicates that prophylactic use of antioxidants as melatonin could help to prevent or at least reduce oxidative stress related diseases in newborns. However, more studies are needed to confirm these beneficial effects.

Predictors of bronchopulmonary dysplasia

Although significant advances in respiratory care have been made in neonatal medicine, bronchopulmonary dysplasia (BPD) remains the most common serious pulmonary morbidity in premature infants. The development of BPD is the result of the complex interactions between multiple perinatal and postnatal factors. Early identification of infants at the most risk of developing BPD through the use of estimators and models may allow a targeted approach at reducing BPD in the future.

Synergistic protection against hyperoxia-induced lung injury by neutrophils blockade and EC-SOD overexpression

Background

Oxygen may damage the lung directly via generation of reactive oxygen species (ROS) or indirectly via the recruitment of inflammatory cells, especially neutrophils. Overexpression of extracellular superoxide dismutase (EC-SOD) has been shown to protect the lung against hyperoxia in the newborn mouse model. The CXC-chemokine receptor antagonist (Antileukinate) successfully inhibits neutrophil influx into the lung following a variety of pulmonary insults. In this study, we tested the hypothesis that the combined strategy of overexpression of EC-SOD and inhibiting neutrophil influx would reduce the inflammatory response and oxidative stress in the lung after acute hyperoxic exposure more efficiently than either single intervention.

Methods

Neonate transgenic (Tg) (with an extra copy of hEC-SOD) and wild type (WT) were exposed to acute hyperoxia (95% FiO₂ for 7 days) and compared to matched room air groups. Inflammatory markers (myeloperoxidase, albumin, number of inflammatory cells), oxidative markers (8-isoprostane, ratio of reduced/oxidized glutathione), and histopathology were examined in groups exposed to room air or hyperoxia. During the exposure, some mice received a daily intraperitoneal injection of Antileukinate.

Results

Antileukinate-treated Tg mice had significantly decreased pulmonary inflammation and oxidative stress compared to Antileukinate-treated WT mice (p < 0.05) or Antileukinate-non-treated Tg mice (p < 0.05).

Conclusion

Combined strategy of EC-SOD and neutrophil influx blockade may have a therapeutic benefit in protecting the lung against acute hyperoxic injury.

May oxidative stress biomarkers in cord blood predict the occurrence of necrotizing enterocolitis in preterm infants?

INTRODUCTION

Oxidative stress (OS) is strongly involved in the pathogenesis of many preterm newborn diseases; this is due to the low efficiency of neonatal antioxidant systems unable to counteract the harmful effects of free radicals (FRs). Hypoxic-ischemic events and inflammation, involved in necrotizing enterocolitis (NEC) pathogenesis, are responsible of the overproduction of FRs, generating OS.

AIM

To test the hypotesis that OS markers levels in cord blood may early identify the newborns at high risk to develop NEC.

MATERIALS AND METHODS

332 preterm newborns of gestational age (GA) between 24 and 33 week and birth weight (BW) between 460 and 2540 g were consecutively recruited in three european neonatal intensive care units. Markers of potential OS risk: non-protein bound iron (NPBI), and markers of FRs damage: advanced oxidation protein products (AOPP) and total hydroperoxides (TH), were measured in the cord blood. Associations between NEC and OS markers were checked through inferential analysis.

RESULTS

Out of 332 preterm babies, 29 developed NEC. Babies with NEC had a BW and a GA significantly lower than healthy babies. AOPP, TH and NPBI cord blood levels were significantly higher in babies with NEC than in babies without (respectively mean AOPP = 28.05 ± 21 vs 15.80 ± 7.14; p < 0.05; TH = 154.48 ± 84.67 vs 107.40 ± 61.01; p < 0.05; NPBI = 2.21 ± 3.98 vs 0.95 ± 1.59; p < 0.05).

CONCLUSIONS

The determination of OS biomarkers in cord blood can be useful in identifying babies at high risk for NEC and in devising new strategies to ameliorate perinatal outcome.

Oxidative stress in neurodegeneration

It has been demonstrated that oxidative stress has a ubiquitous role in neurodegenerative diseases. Major source of oxidative stress due to reactive oxygen species (ROS) is related to mitochondria as an endogenous source. Although there is ample evidence from tissues of patients with neurodegenerative disorders of morphological, biochemical, and molecular abnormalities in mitochondria, it is still not very clear whether the oxidative stress itself contributes to the onset of neurodegeneration or it is part of the neurodegenerative process as secondary manifestation. This paper begins with an overview of how oxidative stress occurs, discussing various oxidants and antioxidants, and role of oxidative stress in diseases in general. It highlights the role of oxidative stress in neurodegenerative diseases like Alzheimer's, Parkinson's, and Huntington's diseases and amyotrophic lateral sclerosis. The last part of the paper describes the role of oxidative stress causing deregulation of cyclin-dependent kinase 5 (Cdk5) hyperactivity associated with neurodegeneration.

Oxidative stress induced carbonylation in human plasma

The focus of this study was on the assessment of technology that might be of clinical utility in identification, quantification, characterization of carbonylation in human plasma proteins. Carbonylation is widely associated with oxidative stress diseases. Breast cancer patient samples were chosen as a stress positive case based on the fact that oxidative stress has been reported to be elevated in this disease. Measurements of 8-isoprostane in plasma confirmed that breast cancer patients in this study were indeed experiencing significant oxidative stress. Carbonyl groups in proteins from freshly drawn blood were derivatized with biotin hydrazide after which the samples were dialyzed and the biotinylated proteins subsequently selected, digested and labeled with iTRAQ™ heavy isotope coding reagent(s). Four hundred sixty proteins were identified and quantified, 95 of which changed 1.5 fold or more in concentration. Beyond confirming the utility of the analytical method, association of protein carbonylation was examined as well. Nearly one fourth of the selected proteins were of cytoplasmic, nuclear, or membrane origin. Analysis of the data by unbiased knowledge assembly methods indicated the most likely disease associated with the proteins was breast neoplasm. Pathway analysis showed the proteins which changed in carbonylation were strongly associated with Brca1, the breast cancer type-1 susceptibility protein. Pathway analysis indicated the major molecular functions of these proteins are defense, immunity and nucleic acid binding.

Correlation of urinary inflammatory and oxidative stress markers in very low birth weight infants with subsequent development of bronchopulmonary dysplasia

Currently, bronchopulmonary dysplasia (BPD) occurs almost exclusively in pre-term infants. In addition to prematurity, other factors like oxygen toxicity and inflammation can contribute to the pathogenesis. This study aimed to compare urinary inflammatory and oxidative stress markers between the no/mild BPD group and moderate/severe BPD group and between BPD cases with significant early lung disease like respiratory distress syndrome (RDS) ('classic' BPD) and with minimal early lung disease ('atypical' BPD). A total of 60 patients who were a gestational age < 30 weeks or a birth weight < 1250 g were included. Urine samples were obtained on the 1(st), 3(rd) and 7(th) day of life and measured the levels of leukotriene E(4) (LTE(4)) and 8-hydroxydeoxyguanosine (8-OHdG). The 8-OHdG values on the 3(rd) day showed significant correlation to duration of mechanical ventilation. The 8-OHdG levels on the 7(th) day were the independent risk factor for developing moderate/severe BPD. In 'classic' BPD, the 8-OHdG values on the 3(rd) day were higher than those of 'atypical' BPD. In 'atypical' BPD, the LTE(4) values on the 7(th) day were higher than the values in 'classic' BPD. These results suggest that oxidative DNA damage could be the crucial mechanism in the pathogenesis of current BPD and the ongoing inflammatory process could be an important mechanism in 'atypical' BPD.

Early identification of the risk for free radical-related diseases in preterm newborns

BACKGROUND

Despite recent advances in preterm newborns healthcare, perinatal pathologies and disabilities are increasing. Oxidative stress (OS) is determinant for the onset of an unbalance between free radicals (FRs) production and antioxidant systems which plays a key role in pathogenesis of pathologies such as retinopathy of prematurity (ROP), bronchopulmonary dysplasia (BPD), necrotizing enterocolitis (NEC), intraventricular hemorrhage (IVH), grouped as 'free radical-related diseases' (FRD).

AIM

This study tests the hypothesis that OS markers levels in cord blood may predict the onset of FRD pathologies.

PATIENTS AND METHODS

168 preterm newborns of GA: 24-32weeks (28.09+/-1.99); and BW: 470-2480 gr (1358.11+/-454.09) were consecutively recruited. Markers of potential OS risk (non-protein bound iron, NPBI; basal superoxide anion, BSA; under stimulation superoxide anion, USSA) and markers of OS-related damage (total hydroperoxides, TH; advanced oxidation protein products, AOPP) were assessed in cord blood. Associations between FRD onset and OS markers were checked through inferential analysis (univariate logistic regression).

RESULTS

The development of FRD was significantly associated to high cord blood levels of TH, AOPP and NPBI (respectively p=0.000, OR=1.025, 95%CI=1.013-1.038; p=0.014, OR=1.092, 95%CI=1.018-1.172; p=0.007, OR=1.26995%CI=1.066-1.511).

CONCLUSIONS

Elevated levels of TH, AOPP and, above all, NPBI, in cord blood are associated with increased risk for FRD. OS markers allow the early identification of infants at risk for FRD because of perinatal oxidant exposure. This can be useful in devising strategies to prevent or ameliorate perinatal outcome.

Preterm resuscitation with low oxygen causes less oxidative stress, inflammation, and chronic lung disease

OBJECTIVE

The goal was to reduce adverse pulmonary adverse outcomes, oxidative stress, and inflammation in neonates of 24 to 28 weeks of gestation initially resuscitated with fractions of inspired oxygen of 30% or 90%.

METHODS

Randomized assignment to receive 30% (N = 37) or 90% (N = 41) oxygen was performed. Targeted oxygen saturation values were 75% at 5 minutes and 85% at 10 minutes. Blood oxidized glutathione (GSSG)/reduced glutathione ratio and urinary o-tyrosine, 8-oxo-dihydroxyguanosine, and isoprostane levels, isofuran elimination, and plasma interleukin 8 and tumor necrosis factor alpha levels were determined.

RESULTS

The low-oxygen group needed fewer days of oxygen supplementation (6 vs 22 days; P < .01) and fewer days of mechanical ventilation (13 vs 27 days; P < .01) and had a lower incidence of bronchopulmonary dysplasia at discharge (15.4% vs 31.7%; P < .05). GSSG/reduced glutathione x 100 ratios at day 1 and 3 were significantly higher in the high-oxygen group (day 1: high-oxygen group: 13.36 +/- 5.25; low-oxygen group: 8.46 +/- 3.87; P < .01; day 3: high-oxygen group: 8.87 +/- 4.40; low-oxygen group: 6.97 +/- 3.11; P < .05). Urinary markers of oxidative stress were increased significantly in the high-oxygen group, compared with the low-oxygen group, in the first week after birth. GSSG levels on day 3 and urinary isofuran, o-tyrosine, and 8-hydroxy-2'-deoxyguanosine levels on day 7 were correlated significantly with development of chronic lung disease.

CONCLUSIONS

Resuscitation of preterm neonates with 30% oxygen causes less oxidative stress, inflammation, need for oxygen, and risk of bronchopulmonary dysplasia.

Effects of exclusive formula or breast milk feeding on oxidative stress in healthy preterm infants

BACKGROUND

Compared to formula, breast milk is considered to have superior antioxidant properties and consequently may reduce the occurrence of a number of diseases of prematurity associated with oxidative stress.

AIMS

To test whether the antioxidant properties of breast milk in healthy premature infants are different to those of formula milk by comparing vitamin E levels in milk and determining the excretion of malondialdehyde (MDA) in urine.

METHODS

Vitamin E was measured in the breast milk of 20 mothers who had given birth prematurely. Urinary MDA was measured in 10 exclusively breast milk fed and 10 exclusively formula fed healthy preterm infants receiving no vitamin supplements. MDA was measured after derivatisation with 2,4-dinitrophenylhydrazine and consecutive HPLC with UV detection.

RESULTS

Urinary MDA concentrations were consistently very low (0.074+/-0.033 microM/mM Cr and 0.078+/-0.026 microM/mM Cr in breast and formula fed infants respectively) and not significantly different between healthy breast milk and formula fed infants. Both breast and formula milk contained satisfactory levels (0.3-3.0 mg/100 ml) of vitamin E.

CONCLUSION

Antioxidant properties of both breast milk and formulae are sufficient to prevent significant lipid peroxidation in healthy premature infants.

Effects of volume-targeted synchronized intermittent mandatory ventilation on spontaneous episodes of hypoxemia in preterm infants

BACKGROUND

Hypoxemic episodes in ventilated preterm infants are frequently caused by reduced ventilation due to a decrease in lung volume and acute worsening of respiratory mechanics.

OBJECTIVE

To compare the efficacy of conventional time-cycled, pressure-limited flow synchronized intermittent mandatory ventilation (SIMV) and volume-targeted SIMV (VT-SIMV) in reducing the frequency and severity of these episodes.

METHODS

SIMV and VT-SIMV were compared in preterm infants with frequent spontaneous episodes of hypoxemia. VT-SIMV was provided with the Draeger Babylog 8000plus ventilator in volume-guarantee mode.

RESULTS

In all, 32 infants (birth weight 668 +/- 126 g, gestational age 24.8 +/- 1.1 weeks, age 37.5 +/- 17.3 days) were studied during 2-hour periods of SIMV and VT-SIMV in random sequence. In an initial phase, a group of 12 infants was supported during VT-SIMV with a target tidal volume of 4.5 ml/kg (VT-SIMV 4.5). A planned interim analysis did not show differences in frequency and duration of hypoxemia between VT-SIMV 4.5 and SIMV, and the initial phase was stopped. In a second phase of the study, 20 infants were studied while supported with a target tidal volume of 6.0 ml/kg during VT-SIMV (VT-SIMV 6.0). In the second phase of the study, the frequency of the hypoxemic episodes did not change but the mean episode duration was shorter during VT-SIMV compared to SIMV. The proportion of mechanical breaths with small tidal volumes (< or =3 ml/kg) was reduced during VT-SIMV 6.0 versus SIMV, while the peak inspiratory pressure and mean airway pressure were increased.

CONCLUSION

VT-SIMV did not reduce the frequency of hypoxemic episodes, but VT-SIMV 6.0 was effective in reducing the duration of the hypoxemic episodes.

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.

Opposing Effects of 60% Oxygen and Neutrophil Influx on Alveologenesis in the Neonatal Rat

The lungs of newborn rats exposed to 60% oxygen for 14 days develop an injury that shares morphologic similarities to human bronchopulmonary dysplasia (BPD). Neutrophil influx into the lung, as part of an inflammatory response, may play a pivotal role in the development of BPD. A neutrophil chemokine, cytokine-induced neutrophil chemoattractant-1, which signals through the neutrophil CXC chemokine receptor-2, is increased in the lung tissue of newborn rats exposed to 60% oxygen. The purpose of this study was to explore the role of neutrophils in the rat model of BPD by inhibiting neutrophil influx using SB265610, a selective CXC chemokine receptor-2 antagonist. SB265610, administered to 60% oxygen-exposed newborn rats from birth to 14 days, completely inhibited neutrophil influx. It also attenuated increased production of reactive oxygen species in newborn rat lung tissue after exposure to 60% oxygen for 4 days. Lung morphometric analysis revealed that 60% oxygen for 14 days, when accompanied by treatment with SB265610 to prevent neutrophil accumulation, increased alveolar formation over that seen in newborn rats exposed to air. These data suggest that exposure of the neonatal lung to moderate hyperoxia may enhance postnatal lung growth, provided postnatal pulmonary inflammation is suppressed.

Pulmonary antioxidant defenses in the preterm newborn with respiratory distress and bronchopulmonary dysplasia in evolution: implications for antioxidant therapy

Preterm neonates with respiratory distress are exposed not only to the relative hyperoxia ex utero, but also to life-saving mechanical ventilation with high inspired oxygen (O2) concentrations, which is considered a major risk factor for the development of bronchopulmonary dysplasia, also referred to as chronic lung disease of infancy. O2 toxicity is mediated through reactive oxygen species (ROS). ROS are constantly generated as byproducts of normal cellular metabolism, but their production is increased in various pathological states, and also upon exposure to exogenous oxidants, such as hyperoxia. Antioxidants, either enzymatic or nonenzymatic, protect the lung against the deleterious effects of ROS. Expression of various pulmonary antioxidants is developmentally regulated in many species so that the expression is increased toward term gestation, as if in anticipation of birth into an O2-rich extrauterine environment. Therefore, the lungs of prematurely born infants may be ill-adapted for protection against ROS. While premature birth interrupts normal lung development, the clinical condition necessitating the administration of high inhaled O2 concentrations may lead to permanent impairment of alveolar development. An understanding of the processes involved in lung growth, especially in alveolarization and vascularization, as well as in repair of injured lung tissue, may facilitate development of strategies to enhance these processes.

Current perspectives on the prevention and management of chronic lung disease in preterm infants

Chronic lung disease (CLD) or bronchopulmonary dysplasia is a recognized sequel of preterm birth. With improving survival of infants at lower gestational ages, the incidence is on the rise. Pathological features of CLD include alveolar maldevelopment, with or without areas of pulmonary fibrosis. Assisted ventilation, infection/inflammation, oxygen administration, and fluid overload are the major risk factors in the evolution of CLD.Interventions, including the treatment of maternal infection, administration of prenatal glucocorticoids, and postnatal surfactant replacement therapy, improve the survival of preterm infants; however, their effect on CLD is difficult to determine. Strategies that have been effective in reducing CLD are the administration of retinol (vitamin A), high frequency oscillatory ventilation, and administration of glucocorticoids. Previous concerns regarding neurological problems associated with high frequency ventilation have not been substantiated in recent studies. Current recommendations do not advise the routine use of glucocorticoids due to concerns regarding long-term neurodevelopment. Therapies that were found to be ineffective in reducing the incidence of CLD include prenatal thyrotropin, cromolyn sodium (sodium cromoglycate), alpha-1 antitrypsin, superoxide dismutase, tocopherol (vitamin E), ascorbic acid (vitamin C), allopurinol, ambroxol, inositol, inhaled bronchodilators, and fluid restriction. Strategies that may be effective in reducing lung injury and subsequent CLD include avoiding assisted ventilation, lung protective ventilatory maneuvers, permissive hypercapnia, prevention of infection, early aggressive nutrition, and the treatment of a patent ductus arteriosus. The use of inhaled glucocorticoids improves pulmonary dynamics but long-term effects are unknown. The management of infants with established CLD has not been studied adequately, and the role of various ventilatory strategies for infants with established CLD is not clear. Adequate oxygenation should be maintained to prevent hypoxic episodes. Diuretics are helpful during acute decompensation; however, their long-term impact has not been well studied. Provision of adequate nutrition, immunization (routine and against respiratory syncytial virus), follow-up, and monitoring are the key elements in the long-term management of infants with CLD. Future research priorities should be to identify strategies to prevent/treat inflammation and promote the healing processes in the injured lung. The long-term effects of lung-protective ventilation strategies need to be studied.

Review article: oxidative stress as a pathogenic factor in inflammatory bowel disease--radicals or ridiculous?

Virtually all inflammatory mediators investigated to date seem to be dysregulated in the inflamed intestinal mucosa of patients with inflammatory bowel disease. However, which of these are actually involved in the initiation and perpetuation of intestinal tissue damage is still not fully understood. Amongst these mediators are the reactive oxygen metabolites, produced in large amounts by the massively infiltrating leucocytes. These reactive oxygen metabolites are believed to constitute a major tissue-destructive force and may contribute significantly to the pathogenesis of inflammatory bowel disease. This paper provides a concise overview of reactive oxygen metabolite biochemistry, the types of cell and tissue damage potentially inflicted by them, and the endogenous antioxidants which should prevent these harmful effects. An up-to-date summary of the available human experimental data suggests that reactive oxygen metabolite-mediated injury is important in both the primary and downstream secondary pathophysiological mechanisms underlying intestinal inflammation. Nonetheless, how the individual components of the mucosal antioxidant enzymatic cascade respond to inflammatory conditions is a neglected area of research. This particular aspect of intestinal mucosal oxidative stress therefore merits further study, in order to provide a sound, scientific basis for the design of antioxidant-directed treatment strategies for inflammatory bowel disease patients.

Regulation of 1-cys peroxiredoxin expression in lung epithelial cells

1-cys peroxiredoxin (1-cys Prx), the only member of a Prx subfamily that contains a single conserved cysteine residue, is abundant in lung. This bifunctional protein has both glutathione peroxidase and phospholipase A2 activities compatible with a role both in protection against lung oxidant injury and also in lung phospholipid metabolism. Here we studied the developmental expression of 1-cys Prx in rat lungs and hormonal effects on protein expression in human and rat lung cells. There was little change in 1-cys Prx expression during the prenatal period, but a marked increase in expression immediately after birth. Enzymatic (peroxidase and phospholipase) activities increased gradually after birth and reached adult level at 7-14 postnatal days. Expression of the protein was induced in the presence of dexamethasone (Dex) in cultured human and rat lung epithelial cells and also was upregulated in neonatal rat lung in vivo. cAMP treatment had no effect on expression, although there was a modest synergistic effect when combined with Dex in human fetal lung epithelial cells. The increased expression of 1-cys Prx at birth may be important for surfactant phospholipid turnover related to the phopholipase A2 activity of the protein and for antioxidant defense based on its peroxidase function.

Thromboxane A(2) receptors mediate pulmonary hypertension in 60% oxygen-exposed newborn rats by a cyclooxygenase-independent mechanism

Endothelin-1 (ET-1) mediates the development of pulmonary hypertension (PHT) in newborn rats exposed to 60% O(2) for 14 days, a model for human chronic neonatal lung injury. ET-1 production by d-14 rat pulmonary artery smooth muscle cells in vitro was markedly increased by thromboxane (TX) A(2) receptor agonists and inhibited by a competitive antagonist. We hypothesized that stimulation of the TX A(2) receptor contributed to O(2)-mediated PHT in vivo. Newborn rat pups received daily intraperitoneal injections of L670596, a competitive TX A(2) receptor antagonist, or 5,5-dimethyl-3-(3-fluorophenyl)4-(4-methylsulfonyl)phenyl-2(5H)-furanone (DFU), a cyclooxygenase-2 inhibitor, during 14 days of 60% O(2) or air exposure. L670596, but not DFU, prevented 60% O(2)-mediated right ventricular and small pulmonary vessel smooth muscle hypertrophy. Lung ET-1 content was significantly reduced by L670596 in 60% O(2)-exposed animals. We conclude that TX A(2) receptor activation, though not by TX A(2), caused upregulation of ET-1 and PHT in this model. A likely mediator is the stable lipid peroxidation product, 8-iso-prostane, which acts as an incidental ligand of the TX A(2) receptor and is a potent inducer of ET-1 production by cultured d-14 rat pulmonary artery smooth muscle cells in vitro.

Increased sensitivity of homozygous Sod2 mutant mice to oxygen toxicity

Induction or overexpression of pulmonary manganese superoxide dismutase (MnSOD) has been shown to protect against oxygen (O2) toxicity. Genetic inactivation of MnSOD (Sod2) results in multiple organ failure and early neonatal death. However, lungs or O2-tolerance of Sod2 knockout mice have not been investigated. We evaluated survival, lung histopathology, and other pulmonary antioxidants (glutathione cycle) of homozygous (-/-) and heterozygous (+/-) Sod2 mutant mice compared with wild-type controls (Sod2+/+) following 48 h exposure to either room air or to O2. The ability of antioxidant N-acetylcysteine to compensate for the loss of MnSOD was explored. Mortality of Sod2-/- mice increased from 0% in room air to 18 and 83% in 50 and 80% O2, respectively. N-acetylcysteine did not alter mortality of Sod2-/- mice. Histopathological analysis revealed abnormalities in saccules of Sod2-/- mice exposed either to room air or to 50% O2 suggestive of delayed postnatal lung development. In 50% O2, activities of glutamate-cysteine ligase (GCL) (previously known as gamma-glutamylcysteine synthetase, gamma-GCS) and glutathione peroxidase increased in Sod2-/- (35 and 70%, respectively) and Sod2+/- (12 and 70%, respectively) mice, but glutathione levels remained unaltered. We conclude that MnSOD is required for normal O2 tolerance and that in the absence of MnSOD there is a compensatory increase in pulmonary glutathione-dependent antioxidant defense in hyperoxia.

Antioxidants as therapy in the newborn: some words of caution

Reactive oxygen and nitrogen species are considered to play a major role in the pathogenesis of a wide range of human disorders. This may be a particularly important pathogenetic mechanism in the newborn nursery. The phrase "oxygen radical disease of prematurity" has been coined to collectively describe a wide range of neonatal disorders based on the belief that premature newborns are deficient in antioxidant defenses at a time when they are subjected to acute and chronic oxidant stresses. This belief has led to a number of clinical trials of antioxidant therapies being undertaken in neonatal patients. The realization that reactive oxygen species play a critical role in neonatal illnesses has only recently been paralleled by an increased understanding of their physiologic roles. A major concern is that effective scavenging of reactive oxygen species, to attenuate their toxic effects, will also inhibit essential cellular functions such as growth in potential target organs such as lung, brain, intestine, and retina.

Type I collagenases in bronchoalveolar lavage fluid from preterm babies at risk of developing chronic lung disease

OBJECTIVE

To assess whether increased collagenolysis precedes severe chronic lung disease (CLD).

METHODS

Matrix metalloproteinase-1 (MMP-1) and MMP-8 (enzymes that degrade type I collagen, the main structural protein of lung extracellular matrix) were measured by enzyme linked immunosorbent assay in 100 bronchoalveolar lavage samples taken during the first 6 postnatal days from 45 ventilated preterm babies < 33 weeks gestation. The median value for each baby was calculated. CLD was defined as an oxygen requirement after the 36th week after conception.

RESULTS

MMP-8 levels in bronchoalveolar lavage fluid were higher (median 13 ng/ml) in 20 babies who developed CLD than in 25 without CLD (median 2 ng/ml). No MMP-1 was detected in any sample.

CONCLUSIONS

MMP-8 can be detected in bronchoalveolar lavage fluid from preterm babies, and higher levels are found in those who later develop CLD. MMP-8 may contribute to lung injury that occurs as a prelude to CLD.

Superoxide dismutase for preventing chronic lung disease in mechanically ventilated preterm infants

BACKGROUND

Free oxygen radicals have been implicated in the pathogenesis of chronic lung disease in preterm infants. Superoxide dismutase is a naturally occurring enzyme which provides a defence against such oxidant injury. Exogenously administered superoxide dismutase has been tested in clinical trials to prevent chronic lung disease in preterm infants.

OBJECTIVES

To determine if exogenously administered superoxide dismutase is efficacious in the prevention of chronic lung disease in preterm infants who are mechanically ventilated, and efficacious in decreasing the following outcomes: bronchopulmonary dysplasia, intraventricular hemorrhage, periventricular leukomalacia, retinopathy of prematurity, necrotizing enterocolitis, patent ductus arteriosus and mortality. To determine the frequency and nature of adverse effects of superoxide dismutase.

SEARCH STRATEGY

We searched Medline (1966 - 2000) and the Cochrane Controlled Trials Register (CCTR) using the following keywords: [bronchopulmonary dysplasia OR chronic lung disease] AND superoxide dismutase, limited to human studies in newborn infants (infant, newborn). We hand searched the reference lists of articles located and the abstracts of the Society for Pediatric Research (USA) (published in Pediatric Research) from 1980 - 2000.

SELECTION CRITERIA

Randomized controlled trials where subjects were preterm infants who had developed or were at risk of developing respiratory distress syndrome requiring assisted ventilation and who were randomly allocated to receive either superoxide dismutase (in any form, by any route) or placebo or no treatment. We included studies which reported any of the following outcomes: chronic lung disease, bronchopulmonary dysplasia, any intraventricular hemorrhage, intraventricular hemorrhage grades III/IV, patent ductus arteriosus, periventricular leukomalacia, retinopathy of prematurity, necrotizing enterocolitis, neonatal mortality, death prior to discharge and neurodevelopmental outcome.

DATA COLLECTION AND ANALYSIS

We extracted and assessed separately all data for each study and entered final data into RevMan. We did not perform subgroup analyses (which were originally planned) because only two studies were eligible for inclusion. We assessed the methodological quality of the studies by assessing the risk for bias. We pooled the outcomes of infants who had developed bronchopulmonary dysplasia at 28 days with those who had died at 28 days to derive the combined outcome of bronchopulmonary dysplasia or death at 28 days. Similarly we pooled the outcomes of infants who had respiratory problems after discharge with those who had died prior to discharge to derive the combined outcome of respiratory problems after discharge or death. We used the standard method of the Cochrane Neonatal Review Group for statistical analysis, using a fixed effect model.

MAIN RESULTS

Two randomized controlled trials were included for analysis. No differences were found in either study or in the pooled data in death prior to discharge, oxygen dependency at 36 weeks corrected age, oxygen dependency at 28 days of life or in other outcomes. In one study (Rosenfeld 1984), survivors who had been treated with superoxide dismutase had a shorter duration of continuous positive airway pressure (4.9 vs 9.7 days), a lower frequency of respiratory problems after discharge (relative risk 0.33, 95% confidence limits 0.11, 0.96) and a lower frequency of chest radiograph abnormalities (relative risk 0.30, 95% confidence limits 0.11, 0.87) compared to survivors who received placebo. A third study was available only in abstract form and will be evaluated for inclusion after publication.

REVIEWER'S CONCLUSIONS

Based on currently available published trials, there is insufficient evidence to draw firm conclusions about the efficacy of superoxide dismutase in preventing chronic lung disease of prematurity. Data from a small number of treated infants suggest that it is well tolerated and has no serious adverse effects.

Effect of early ambroxol treatment on lung functions in mechanically ventilated preterm newborns who subsequently developed a bronchopulmonary dysplasia (BPD)

In a randomized trial in 102 preterm newborns with respiratory distress syndrome (RDS) it has been shown that early Ambroxol treatment (30 mg kg(-1) over the first 5 days) significantly reduces the incidence of RDS-associated complications [bronchopulmonary dysplasia (BPD), intraventricular haemorrhage, post-natal acquired pneumonia]. The aim of the present analysis was to investigate the effect of Ambroxol treatment on lung function in newborns who developed BPD. Respiratory function testing (RFT) was performed immediately after extubation and at day 28. Tidal volume (VT) and respiratory frequency (f) were measured during tidal breathing using the deadspace free flow-through technique. The lung mechanic parameter VT/maxPes was determined by measuring the maximal oesophageal pressure changes, maxPes, with a catheter tip pressure transducer. In the placebo group 36/50 infants were extubated within the first 28 days of life and 13/36 (36%) developed BPD. In the Ambroxol group 44/52 were extubated and 9/44 (20%) developed BPD. After extubation, RFT showed (i) no statistically significant difference in the ventilatory parameters of either treatment group, (ii) improved (P<0.05) lung mechanics (VT/maxPes) in Ambroxol group compared to controls (94+/-27 ml kPa(-1) vs. 8.1+/-2.6 ml kPa(-1)) and (iii) no statistically significant difference in lung function between infants with and without BPD. At day 28 we found (i) no effect of early Ambroxol treatment on lung functions, (ii) significantly (P < 0.05) higher f (58.5+/-11.7 min(-1) vs. 49.7+/-10.1 min(-1)) and significantly (P<0.01) lower V(T) (9.6+/-1.9 ml vs. 12.3+/-2.7 ml) and V(T)/maxPes (8.9+/-2.6 ml kPa(-1)] vs. 12.0+/-2.9 ml kPa(-1)) in infants with BPD compared to infants without and (iii) these differences are not influenced by early Ambroxol treatment. If the process of BPD development is induced, early Ambroxol treatment has no influence on impaired lung function at day 28.

Age and organ dependent spontaneous generation of nuclear 8-hydroxydeoxyguanosine in male Fischer 344 rats

8-Hydroxydeoxyguanosine (8-OHdG) is a major oxidative DNA adduct playing roles in senescence, carcinogenesis and various disease processes. High-performance liquid chromatography with an electrochemical detection (HPLC-ECD) method has been widely used to assess organ levels of 8-OHdG, and a recently introduced immunohistochemical approach has made it possible to clarify intra-organ localization. In the present study, these methods were employed to reveal age-dependent changes in nuclear 8-OHdG within various tissues of male Fischer 344 rats between 18 fetal days and 104 weeks of age. 8-OHdG was detected in the nuclei of cerebellar small granule and small cortical cells, cerebral nerve cells, and choroid plexus epithelia of the brain and ependymal cells of the spinal cord; parenchymal cells in the anterior lobe of the pituitary and adrenal glands (mainly cortex); bronchial epithelium of the lung; intra-hepatic bile duct, pancreatic duct, glandular gastric and intestinal epithelial cells; renal tubular epithelial cells (mainly medulla); and spermatogonia and spermatocytes of the testis and seminal vesicle epithelia. The nuclear 8-OHdG levels were high (more than two lesions per 10(6) deoxyguanosines) from 7 days to 104 weeks of age in the brain, 3 to 6 weeks in the adrenal gland, 6 to 104 weeks in the lung, and 3 to 52 weeks in the testis. In the other organs, the nuclear 8-OHdG levels remained low throughout. These findings provide a basis for research dealing with oxidative stress by indicating organ-specific and age- but not aging-dependent changes in the localization of spontaneously generated nuclear 8-OHdG in intact rats. The immunohistochemical approach has advantages for assessing variation of 8-OHdG formation at the cellular level not accessible to the HPLC-ECD method.