Timing of hyperoxic exposure during alveolarization influences damage mediated by leukotrienes

Cathelicidin Attenuates Hyperoxia-Induced Lung Injury by Inhibiting Ferroptosis in Newborn Rats

High oxygen concentrations are often required to treat newborn infants with respiratory distress but have adverse effects, such as increased oxidative stress and ferroptosis and impaired alveolarization. Cathelicidins are a family of antimicrobial peptides that exhibit antioxidant activity, and they can reduce hyperoxia-induced oxidative stress. This study evaluated the effects of cathelicidin treatment on lung ferroptosis and alveolarization in hyperoxia-exposed newborn rats. Sprague Dawley rat pups were either reared in room air (RA) or hyperoxia (85% O₂) and then randomly given cathelicidin (8 mg/kg) in 0.05 mL of normal saline (NS), or NS was administered intraperitoneally on postnatal days from 1-6. The four groups obtained were as follows: RA + NS, RA + cathelicidin, O₂ + NS, and O₂ + cathelicidin. On postnatal day 7, lungs were harvested for histological, biochemical, and Western blot analyses. The rats nurtured in hyperoxia and treated with NS exhibited significantly lower body weight and cathelicidin expression, higher Fe²⁺, malondialdehyde, iron deposition, mitochondrial damage (TOMM20), and interleukin-1β (IL-1β), and significantly lower glutathione, glutathione peroxidase 4, and radial alveolar count (RAC) compared to the rats kept in RA and treated with NS or cathelicidin. Cathelicidin treatment mitigated hyperoxia-induced lung injury, as demonstrated by higher RAC and lower TOMM20 and IL-1β levels. The attenuation of lung injury was accompanied by decreased ferroptosis. These findings indicated that cathelicidin mitigated hyperoxia-induced lung injury in the rats, most likely by inhibiting ferroptosis.

Effects of Hyperoxia on Aging Biomarkers: A Systematic Review

The effects of short-term hyperoxia on age-related diseases and aging biomarkers have been reported in animal and human experiments using different protocols; however, the findings of the studies remain conflicting. In this systematic review, we summarized the existing reports in the effects of short-term hyperoxia on age-related diseases, hypoxia-inducible factor 1α (HIF-1α), and other oxygen-sensitive transcription factors relevant to aging, telomere length, cellular senescence, and its side effects. This review was done as described in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. A systematic search was done in PubMed, Google Scholar, and Cochrane Library and from the references of selected articles to identify relevant studies until May 2021. Of the total 1,699 identified studies, 17 were included in this review. Most of the studies have shown significant effects of short-term hyperoxia on age-related diseases and aging biomarkers. The findings of the studies suggest the potential benefits of short-term hyperoxia in several clinical applications such as for patients undergoing stressful operations, restoration of cognitive function, and the treatment of severe traumatic brain injury. Short-term hyperoxia has significant effects in upregulation or downregulation of transcription factors relevant to aging such as HIF-1α, nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-kB), and nuclear factor (erythroid-derived 2)-like 2 (NRF2) among others. Short-term hyperoxia also has significant effects to increase antioxidant enzymes, and increase telomere length and clearance of senescent cells. Some of the studies have also reported adverse consequences including mitochondrial DNA damage and nuclear cataract formation depending on the dose and duration of oxygen exposure. In conclusion, short-term hyperoxia could be a feasible treatment option to treat age-related disease and to slow aging because of its ability to increase antioxidant enzymes, significantly increase telomere length and clearance of senescent cells, and improve cognitive function, among others. The reported side effects of hyperoxia vary depending on the dose and duration of exposure. Therefore, it seems that additional studies for better understanding the beneficial effects of short-term hyperoxia and for minimizing side effects are necessary for optimal clinical application.

Consecutive daily administration of intratracheal surfactant and human umbilical cord-derived mesenchymal stem cells attenuates hyperoxia-induced lung injury in neonatal rats

Background

Surfactant therapy is a standard of care for preterm infants with respiratory distress and reduces the incidence of death and bronchopulmonary dysplasia in these patients. Our previous study found that mesenchymal stem cells (MSCs) attenuated hyperoxia-induced lung injury and the combination therapy of surfactant and human umbilical cord-derived MSCs (hUC-MSCs) did not have additive effects on hyperoxia-induced lung injury in neonatal rats. The aim is to evaluate the effects of 2 consecutive days of intratracheal administration of surfactant and hUC-MSCs on hyperoxia-induced lung injury.

Methods

Neonatal Sprague Dawley rats were reared in either room air (RA) or hyperoxia (85% O₂) from postnatal days 1 to 14. On postnatal day 4, the rats received intratracheal injections of either 20 μL of normal saline (NS) or 20 μL of surfactant. On postnatal day 5, the rats reared in RA received intratracheal NS, and the rats reared in O₂ received intratracheal NS or hUC-MSCs (3 × 10⁴ or 3 × 10⁵ cells). Six study groups were examined: RA + NS + NS, RA + surfactant + NS, O₂ + NS + NS, O₂ + surfactant + NS, O₂ + surfactant + hUC-MSCs (3 × 10⁴ cells), and O₂ + surfactant + hUC-MSCs (3 × 10⁵ cells). The lungs were excised for histological, western blot, and cytokine analyses.

Results

The rats reared in hyperoxia and treated with NS yielded significantly higher mean linear intercepts (MLIs) and interleukin (IL)-1β and IL-6 levels and significantly lower vascular endothelial growth factors (VEGFs), platelet-derived growth factor protein expression, and vascular density than did those reared in RA and treated with NS or surfactant. The lowered MLIs and cytokines and the increased VEGF expression and vascular density indicated that the surfactant and surfactant + hUC-MSCs (3 × 10⁴ cells) treatment attenuated hyperoxia-induced lung injury. The surfactant + hUC-MSCs (3 × 10⁵ cells) group exhibited a significantly lower MLI and significantly higher VEGF expression and vascular density than the surfactant + hUC-MSCs (3 × 10⁴ cells) group did.

Conclusions

Consecutive daily administration of intratracheal surfactant and hUC-MSCs can be an effective regimen for treating hyperoxia-induced lung injury in neonates.

Predicting Hyperoxia-Induced Lung Injury from Associated Intestinal and Lung Dysbiosis in Neonatal Mice

BACKGROUND

Preclinical studies have demonstrated that hyperoxia disrupts the intestinal barrier, changes the intestinal bacterial composition, and injures the lungs of newborn animals.

OBJECTIVES

The aim of the study was to investigate the effects of hyperoxia on the lung and intestinal microbiota and the communication between intestinal and lung microbiota and to develop a predictive model for the identification of hyperoxia-induced lung injury from intestinal and lung microbiota based on machine learning algorithms in neonatal mice.

METHODS

Neonatal C57BL/6N mice were reared in either room air or hyperoxia (85% O2) from postnatal days 1-7. On postnatal day 7, lung and intestinal microbiota were sampled from the left lung and lower gastrointestinal tract for 16S ribosomal RNA gene sequencing. Tissue from the right lung and terminal ileum were harvested for Western blot and histology analysis.

RESULTS

Hyperoxia induced intestinal injury, decreased intestinal tight junction expression, and impaired lung alveolarization and angiogenesis in neonatal mice. Hyperoxia also altered intestinal and lung microbiota and promoted bacterial translocation from the intestine to the lung as evidenced by the presence of intestinal bacteria in the lungs of hyperoxia-exposed neonatal mice. The relative abundance of these bacterial taxa was significantly positively correlated with the increased lung cytokines.

CONCLUSIONS

Neonatal hyperoxia induced intestinal and lung dysbiosis and promoted bacterial translocation from the intestine to the lung. Further studies are needed to clarify the pathophysiology of bacterial translocation to the lung.

TRIM72 mediates lung epithelial cell death upon hyperoxia exposure

BACKGROUND

Premature infants often require oxygen (O2) therapy for respiratory distress syndrome; however, excessive use of O2 can cause clinical conditions such as bronchopulmonary dysplasia. Although many treatment methods are currently available, they are not effective in preventing bronchopulmonary dysplasia. Herein, we explored the role of tripartite motif protein 72 (TRIM72), a factor involved in repairing alveolar epithelial wounds, in regulating alveolar cells upon hyperoxia exposure.

METHODS

In this in vivo study, we used Sprague-Dawley rat pups that were reared in room air or 85% O2 for 2 weeks after birth. The lungs were excised for histological analyses, and TRIM72 expression was assessed on postnatal days 7 and 14. For in vitro experiments, RLE-6TN cells (i.e., rat alveolar type II epithelial cells) and A549 cells (i.e., human lung carcinoma epithelial cells) were exposed to 85% O2 for 5 days. The cells were then analyzed for cell viability, and TRIM72 expression was determined.

RESULTS

Exposure to hyperoxia reduced body and lung weight, increased mean linear intercept values, and upregulated TRIM72 expression. In vitro study results revealed increased or decreased lung cell viability upon hyperoxia exposure depending on the suppression or overexpression of TRIM72, respectively.

CONCLUSION

Hyperoxia upregulates TRIM72 expression in neonatal rat lung tissue; moreover, it initiates TRIM72-dependent alveolar epithelial cell death, leading to hyperoxia-induced lung injury.

Human placenta-derived mesenchymal stem cells attenuate established hyperoxia-induced lung injury in newborn rats

BACKGROUND

Hyperoxia increases Sonic hedgehog (Shh) expression in neonatal rat lungs. The effect of mesenchymal stem cells (MSCs) on the hedgehog signaling pathway in hyperoxia-induced lung injury is unknown. This study evaluated whether MSCs could inhibit hedgehog signaling and improve established hyperoxia-induced lung injury in newborn rats.

METHODS

Newborn rats were assigned to room air (RA) or hyperoxia (85% O₂) groups from postnatal day 4-15, and some received intravenous injection of human MSCs (9 × 10⁵ cells) in 90 μL of normal saline (NS) through the tail vein on postnatal day 15. We obtained four study groups as follows: RA + NS, RA + MSCs, O₂ + NS, and O₂ + MSCs. Pups from each group were sacrificed on postnatal days 15 and 29, and lungs were removed for histological and Western blot analyses.

RESULTS

Neonatal hyperoxia on postnatal days 4-15 reduced the body weight, increased the mean linear intercept, and decreased the vascular density of the rats, and these effects were associated with increased Shh and Smoothened (Smo) expression and decreased Patched expression. By contrast, the MSC-treated hyperoxic pups exhibited improved alveolarization, increased vascularization, and decreased Shh and Smo expression on postnatal day 29.

CONCLUSION

Human MSC treatment reversed established hyperoxia-induced lung injury in newborn rats, probably through suppression of the hedgehog pathway.

Hyperoxia reduces STX17 expression and inhibits the autophagic flux in alveolar type II epithelial cells in newborn rats

Supplemental oxygen therapy can be life-saving for premature infants. Our previous study revealed a defect in the autophagic flux in the lung tissues of neonatal rats with hyperoxia-induced bronchopulmonary dysplasia (BPD), but the underlying mechanism remains unknown. Moreover, there are few innovative treatments that can completely alter the course of BPD. The present study examined the expression of Syntaxin 17 (STX17), a protein necessary for autophago-some-lysosome binding, in alveolar type II (AT-II) epithelial cells of neonatal rats with BPD. Neonatal Sprague-Dawley rats were randomly exposed to elevated O₂ levels [fraction of inspired oxygen (FiO₂), 0.8; model group] or normal room air (FiO₂, 0.21; control group), and the expression levels of STX17, autophagy-related [Microtubule-associated protein 1A/1B-light chain 3B (LC3B)-II, p62, lysosomal-associated membrane protein 1)] and apoptosis-related (cleaved caspase3) mRNA and proteins were examined in lung tissues. Moreover, the expression levels of the aforementioned proteins were measured in isolated primary AT-II cells cultured in vitro under hyperoxic conditions in the presence or absence of pharmacological modulators of autophagy. Transmission electron microscopy identified that AT-II cell apoptosis and autophagosome aggregation were elevated in the lungs of BPD rats compared with control rats on postnatal day 7. STX17 mRNA and protein expression levels were decreased in lung tissue and isolated AT-II cells as early as postnatal day 3 in BPD rats, while the expression levels of LC3B-II, p62 and cleaved caspase3 were increased, reaching a peak on postnatal day 7. This early reduction in STX17 expression, followed by increased expression in autophagy- and apoptosis-related proteins, was also observed in isolated AT-II cells exposed to hyperoxia in vitro. However, treatment with the autophagy inducers rapamycin or LiCl eliminated the hyperoxia-induced reduction in STX17, partially restored the autophagy flux and increased the survival of AT-II cells exposed to hyperoxia. Collectively, these results indicated that STX17 expression in AT-II cells was reduced in the early stages of BPD in neonatal rats and may be related to the subsequent hyperoxia-induced block in autophagic flux.

Cathelicidin attenuates hyperoxia-induced lung injury by inhibiting oxidative stress in newborn rats

PURPOSE

High concentrations of oxygen administered to newborn infants with respiratory failure increases oxidant stress and leads to lung injury, characterized by decreased alveolar and capillary development. Cathelicidin belongs to an important group of human antimicrobial peptides that exhibit antioxidant activity; its overexpression reduces hyperoxia-induced oxidative stress. This study evaluated the therapeutic effects of cathelicidin in hyperoxia-induced lung injury in newborn rats.

METHODS AND MATERIALS

Sprague Dawley rat pups were reared in either room air (RA) or hyperoxia (85% O₂) and then randomly treated with low-dose (4 mg/kg) and high-dose (8 mg/kg) cathelicidin in 0.05 mL of normal saline (NS) administered intraperitoneally on postnatal days 1-6. The following six groups were obtained: RA + NS, RA + low-dose cathelicidin, RA + high-dose cathelicidin, O₂ + NS, O₂ + low-dose cathelicidin, and O₂ + high-dose cathelicidin. Lungs were harvested for Western blot and histological analyses on postnatal day 7.

RESULTS

Compared with the RA-reared rats, the hyperoxia-reared rats exhibited significantly lower body weights, higher mean linear intercept (MLI), lung injury score, interleukin-6, and oxidative stress marker 8-hydroxy-2'-deoxyguanosine (8-OHdG) expression but lower superoxide dismutase 1 (SOD1) and vascular endothelial growth factor (VEGF) protein expression and vascular density. Cathelicidin treatment attenuated hyperoxia-induced lung injury as demonstrated by lower MLI and injury score and higher VEGF expression and vascular density.

CONCLUSIONS

Cathelicidin attenuated hyperoxia-induced lung injury and caused a decrease in 8-OHdG and SOD1 protein expression, most likely by inhibiting oxidative stress in the lung.

Anti-placental growth factor antibody ameliorates hyperoxia-mediated impairment of lung development in neonatal rats

This study investigates the effect of the overexpression of the placental growth factor (PGF) and hyperoxia on lung development and determines whether anti-PGF antibody ameliorates hyperoxia-mediated impairment of lung development in newborn rats. After exposure to normoxic conditions for seven days, newborn rats subjected to normoxia were intraperitoneally or intratracheally injected with physiological saline, adenovirus-negative control (Ad-NC), or adenovirus-PGF (Ad-PGF) to create the Normoxia, Normoxia+Ad-NC, and Normoxia+Ad-PGF groups, respectively. Newborn rats subjected to hyperoxia were intraperitoneally injected with physiological saline or anti-PGF antibodies to create the Hyperoxia and Hyperoxia+anti-PGF groups, respectively. Our results revealed significant augmentation in the levels of PGF and its receptor Flt-1 in the lung tissues of newborn rats belonging to the Normoxia+Ad-PGF or Hyperoxia groups. PGF overexpression in these groups caused lung injury in newborn rats, while anti-PGF antibody treatment significantly cured the hyperoxia-induced lung injury. Moreover, PGF overexpression significantly increased TNF-α and Il-6 levels in the bronchoalveolar lavage (BAL) fluid of the Normoxia+Ad-PGF and Hyperoxia groups. However, their levels were significantly reduced in the BAL fluid of the Hyperoxia+anti-PGF group. Immunohistochemical analysis revealed that PGF overexpression and hyperoxia treatment significantly increased the expression of the angiogenesis marker, CD34. However, its expression was significantly decreased upon administration of anti-PGF antibodies (compared to the control group under hyperoxia). In conclusion, PGF overexpression impairs lung development in newborn rats while its inhibition using an anti-PGF antibody ameliorates the same. These results provided new insights for the clinical management of bronchopulmonary dysplasia in premature infants.

Maternal Tn Immunization Attenuates Hyperoxia-Induced Lung Injury in Neonatal Rats Through Suppression of Oxidative Stress and Inflammation

Hyperoxia therapy is often required to treat newborns with respiratory disorders. Prolonged hyperoxia exposure increases oxidative stress and arrests alveolar development in newborn rats. Tn antigen is N-acetylgalactosamine residue that is one of the most remarkable tumor-associated carbohydrate antigens. Tn immunization increases the serum anti-Tn antibody titers and attenuates hyperoxia-induced lung injury in adult mice. We hypothesized that maternal Tn immunizations would attenuate hyperoxia-induced lung injury through the suppression of oxidative stress in neonatal rats. Female Sprague-Dawley rats (6 weeks old) were intraperitoneally immunized five times with Tn (50 μg/dose) or carrier protein at biweekly intervals on 8, 6, 4, 2, and 0 weeks before the day of delivery. The pups were reared in room air (RA) or 2 weeks of 85% O₂, creating the four study groups: carrier protein + RA, Tn vaccine + RA, carrier protein + O₂, and Tn vaccine + O₂. The lungs were excised for oxidative stress, cytokine, vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) expression, and histological analysis on postnatal day 14. Blood was withdrawn from dams and rat pups to check anti-Tn antibody using western blot. We observed that neonatal hyperoxia exposure reduced the body weight, increased 8-hydroxy-2-deoxyguanosine (8-OHdG) expression and lung cytokine (interleukin-4), increased mean linear intercept (MLI) values, and decreased vascular density and VEGF and PDGF-B expressions. By contrast, Tn immunization increased maternal and neonatal serum anti-Tn antibody titers on postnatal day 14, reduced MLI, and increased vascular density and VEGF and PDGF-B expressions to normoxic levels. Furthermore, the alleviation of lung injury was accompanied by a reduction in lung cytokine and 8-OHdG expression. Therefore, we propose that maternal Tn immunization attenuates hyperoxia-induced lung injury in neonatal rats through the suppression of oxidative stress and inflammation.

Primary culture of lung fibroblasts from hyperoxia-exposed rats and a proliferative characteristics study

Lung fibrosis is an ultimate consequence of bronchopulmonary dysplasia (BPD) which shows the excessive proliferation of lung fibroblasts (LFs). To find a better model for studying the role of LFs in hyperoxia-induced lung fibrosis at the cellular level, we isolated LFs from the lung tissue of hyperoxia- and normoxia-exposed rat lungs on postnatal days 7, 14 and 21 for primary culture to study their proliferative behavior. In the present study, the LF predominance was > 95% in our culture method. The LFs isolated from rats exposed to hyperoxia in vivo showed significantly greater proliferation than that from normoxia-exposed rats. Flow cytometry revealed that percentage of LFs in S and G2/M stage increased, and proportion in the G0/G1 stage declined at the same time. A greater presence of myofibroblasts in LFs isolated from rats exposed to hyperoxia compared with those exposed to normoxia. In addition, elevated collagen level, transforming growth factor-β and connective tissue growth factor protein expression in conditioned medium were also found in hyperoxia LFs. These data demonstrate that hyperoxia promotes LFs proliferation, myofibroblast transdifferentiation and collagen synthesis in a time-dependent manner. The primary culture of LFs from hyperoxia-exposed rats is a feasible method for studying the pathogenesis and treatment of lung fibrosis caused by BPD at the cellular level.

Reactive Oxygen Species, Biomarkers of Microvascular Maturation and Alveolarization, and Antioxidants in Oxidative Lung Injury

The lungs of extremely low gestational age neonates (ELGANs) are deficient in pulmonary surfactant and are incapable of efficient gas exchange necessary for successful transition from a hypoxic intrauterine environment to ambient air. To improve gas exchange and survival, ELGANs often receive supplemental oxygen with mechanical ventilation which disrupts normal lung developmental processes, including microvascular maturation and alveolarization. Factors that regulate these developmental processes include vascular endothelial growth factor and matrix metalloproteinases, both of which are influenced by generation of oxygen byproducts, or reactive oxygen species (ROS). ELGANs are also deficient in antioxidants necessary to scavenge excessive ROS. Thus, the accumulation of ROS in the preterm lungs exposed to prolonged hyperoxia, results in inflammation and development of bronchopulmonary dysplasia (BPD), a form of chronic lung disease (CLD). Despite advances in neonatal care, BPD/CLD remains a major cause of neonatal morbidity and mortality. The underlying mechanisms are not completely understood, and the benefits of current therapeutic interventions are limited. The association between ROS and biomarkers of microvascular maturation and alveolarization, as well as antioxidant therapies in the setting of hyperoxia-induced neonatal lung injury are reviewed in this article.

Neonatal hyperoxia increases airway reactivity and inflammation in adult mice

BACKGROUND

Supplemental O₂ to treat bronchopulmonary dysplasia (BPD) in premature infants, is a major risk factor producing alteration in lung function, airway reactivity, and predisposition to respiratory infections. This study explores inflammatory and airway responses following neonatal hyperoxia in adult mice.

METHODS

Newborn mouse litters were randomized to 85% O₂ or room air (RA) on P3 for 12 days; mice were sacrificed either on P15 or at 15 weeks following recovery in RA. Airway hyper reactivity (AHR) was assessed in vivo (8 and 12 weeks) and in vitro (15 weeks) with methacholine; Lung and BAL were assayed for inflammatory mediators, cell counts, CD3 immunohistochemistry, and histopathology.

RESULTS

Hyperoxic mice had increased airway reactivity at baseline and following methacholine challenge in vivo (8 and 12 weeks); isolated tracheal rings had a significantly higher constriction response to methacholine in vitro compared to RA group. Inflammatory markers were higher at 2 weeks (MCP-1, IL-12, INF-γ) and at 15 weeks (LTB₄ , VEGF); Lipoxin-A₄ was lower in the hyperoxia group at both time points. Increased airway smooth muscle thickness and angiogenesis in the lung was seen at 15 weeks. Hyperoxic lungs exhibited alveolar simplification at 2 and 15 weeks. Absolute lymphocyte count was higher in lavage fluid with an increased CD3 cell count at 15 weeks suggesting persistent inflammation in adult mice following neonatal hyperoxia.

CONCLUSIONS

Exposure to hyperoxia in newborn mice increases long-term airway reactivity with persistent lung inflammation associated with a marked increase in lymphocytes, suggesting long-term consequences in adults. Pediatr Pulmonol. 2016;51:1131-1141. © 2016 Wiley Periodicals, Inc.

The efficacy and safety of Montelukast sodium in the prevention of bronchopulmonary dysplasia

Purpose

The purpose of this study was to evaluate the efficacy and safety of Montelukast sodium in the prevention of bronchopulmonarydysplasia (BPD).

Methods

The Interventional study was designed as a multicenter, prospective, and randomized trial, with open labeled and parallel-experimental groups, 66 infants were enrolled and allocated to either the case group (n=30) or the control group (n=36) based on gestational age (GA). Infants in the case group were given Montelukast sodium (Singulair) based on their body weight (BW). Zero week was defined as the start time of the study.

Results

The incidence of moderate to severe BPD was not different between the groups (case group: 13 of 30 [43.3%] vs. control group: 19 of 36 [52.8%], P=0.912). Additionally, secondary outcomes such as ventilation index, mean airway pressure and resort to systemic steroids were not significantly different. There were no serious adverse drug reactions in either group, and furthermore the rate of occurrence of mild drug related-events were not significantly different (case group: 10 of 42 [23.8%] vs. control group: 6 of 48 (15.8%), P=0.414).

Conclusion

Montelukast was not effective in reducing moderate or severe BPD. There were no significant adverse drug events associated with Montelukast treatment.

Combined effects of maternal inflammation and neonatal hyperoxia on lung fibrosis and RAGE expression in newborn rats

BACKGROUND

Receptors for advanced glycation end products (RAGE) have been implicated in fibrotic processes. We hypothesized that lung fibrosis induced by maternal lipopolysaccharide (LPS)-mediated inflammation and neonatal hyperoxia involves RAGE in newborn rats.

METHODS

Pregnant Sprague-Dawley rats received intraperitoneal injections of LPS or normal saline (NS) on 20 and 21 d of gestation. The pups were reared in room air (RA) or an O2-enrich atmosphere (O2), creating the four study groups, NS + RA, NS + O2, LPS + RA, and LPS + O2. The O2 treatment was >95% O2 for 7 d, followed by 60% O2 for 14 d.

RESULTS

Rat pups born to LPS-injected dams exhibited significantly higher lung interferon-γ and interleukin-1β (IL-1β) on postnatal day 7 than the pups born to NS-injected dams. Rat pups reared in hyperoxia expressed higher lung IL-10 on postnatal day 7, compared with the RA-reared pups. The LPS + O2 group had significantly higher total collagen and transforming growth factor-β1 on postnatal days 7 and 21 than the NS+RA group. RAGE mRNA and sRAGE protein expression were significantly lower in the LPS + O2 group on postnatal day 7 than the NS+RA group.

CONCLUSION

RAGE may be involved in the pathogenesis of lung fibrosis induced by maternal systemic inflammation and postnatal hyperoxia in rat neonates.

Cyclooxygenase-2 in newborn hyperoxic lung injury

Supraphysiological O2 concentrations, mechanical ventilation, and inflammation significantly contribute to the development of bronchopulmonary dysplasia (BPD).Exposure of newborn mice to hyperoxia causes inflammation and impaired alveolarization similar to that seen in infants with BPD.Previously, we demonstrated that pulmonary cyclooxygenase-2 (COX-2) protein expression is increased in hyperoxia-exposed newborn mice.The present studies were designed to define the role of COX-2 in newborn hyperoxic lung injury.We tested the hypothesis that attenuation of COX-2 activity would reduce hyperoxia-induced inflammation and improve alveolarization.Newborn C3H/HeN micewere injected daily with vehicle, aspirin (nonselective COX-2 inhibitor), or celecoxib (selective COX-2 inhibitor) for the first 7 days of life.Additional studies utilized wild-type (C57Bl/6, COX-2(+/+)), heterozygous (COX-2(+/-)), and homozygous (COX-2(-/-)) transgenic mice.Micewere exposed to room air (21% O2) or hyperoxia (85% O2) for 14 days.Aspirin-injected and COX-2(-/-) pups had reduced levels of monocyte chemoattractant protein (MCP-1) in bronchoalveolar lavage fluid (BAL).Both aspirin and celecoxib treatment reduced macrophage numbers in the alveolar walls and air spaces.Aspirin and celecoxib treatment attenuated hyperoxia-induced COX activity, including altered levels of prostaglandin (PG)D2 metabolites.Decreased COX activity, however, did not prevent hyperoxia-induced lung developmental deficits.Our data suggest thatincreased COX-2 activity may contribute to proinflammatory responses, including macrophage chemotaxis, during exposure to hyperoxia.Modulation of COX-2 activity may be a useful therapeutic target to limit hyperoxia-induced inflammation in preterm infants at risk of developing BPD.

Plasma lipid metabolites are associated with gestational age but not bronchopulmonary dysplasia

AIM

To test the hypothesis that plasma lipid metabolite levels in premature infants are associated with the development of bronchopulmonary dysplasia (BPD). The studies also tested a secondary hypothesis that plasma lipid metabolite levels were correlated with gestational age.

METHODS

Infants born <32 weeks' gestation were enrolled during the first 72 h of life. Plasma samples were obtained and lipid levels were measured by LC-MS/MS. Clinical data were collected to determine infant outcomes and BPD diagnosis.

RESULTS

Following adjustment for confounders, lipid levels were not associated with BPD; however, levels of specific lipid metabolites were correlated with gestational age.

CONCLUSION

Immature lipid metabolism pathways in premature infants may contribute to the pathogenesis of BPD and other diseases.

Angiotensin II type 1 receptor antagonist attenuates lung fibrosis in hyperoxia-exposed newborn rats

Bronchopulmonary dysplasia (BPD) remains a major cause of morbidity and mortality during the first year of life, and many infants have significant respiratory problems throughout childhood. Currently no effective therapy is clinically available to prevent the long-term pulmonary sequelae of BPD. Previous research has demonstrated that the renin-angiotensin system is up-regulated in human lung fibroblasts. Angiotensin II type 1 receptor (AT₁R) antagonists and AT₁R short interfering RNA diminished hyperoxia-increased collagen expression, whereas AT₂R antagonists did not have any effects on these hyperoxia-induced changes. The in vivo therapeutic effects of AT₁R antagonists on hyperoxia-induced lung fibrosis remain unknown. The present study assessed the effects of an AT₁R antagonist (losartan) on preventing hyperoxia-induced lung fibrosis in newborn rats. Rat pups were exposed to 7 days of > 95% O₂ and an additional 2 weeks of 60% O₂. AT₁R antagonist-treated pups were injected intraperitoneally with losartan at a dose of 10 mg/kg/day from postnatal days 1 to 7 and a dose of 5 mg/kg/day from postnatal days 8 to 21. Control group pups were injected with an equal volume of normal saline. AT₁R antagonist treatment attenuated the hyperoxia-induced lung fibrosis on postnatal days 7 and 21 and also decreased the hyperoxia-induced expression of extracellular signal-regulated protein kinase and α-smooth muscle actin. AT₁R antagonist treatment did not affect body weight or lung weight of the rats. These data suggest that AT₁R antagonist may offer a novel therapeutic strategy for preventing hyperoxia-induced lung fibrosis.

5-Lipoxygenase-activating protein (FLAP) inhibitor MK-0591 prevents aberrant alveolarization in newborn mice exposed to 85% oxygen in a dose- and time-dependent manner

Bronchopulmonary dysplasia is characterized by prolonged oxygen dependency due to compromised gas-exchange capability. This is attributable mainly to inadequate and aberrant alveolarization resulting from insults like hyperoxia. Leukotrienes are associated with hyperoxia-induced inhibition of alveolarization. We hypothesized that a 5-lipoxygenase-activating protein (FLAP) inhibitor given while newborn mice were exposed to 85% oxygen would prevent aberrant alveolarization in a dose- and time-dependent manner. Newborn mice were exposed to either room air or hyperoxia for 14 days. Pups were treated with either vehicle or MK-0591 10, 20, or 40 mg/kg subcutaneously daily for days 1-4, 5-9, or 10-14. On day 14, the lungs were inflated, fixed, and stained for histopathological and morphometric analyses. Hyperoxia groups treated with MK-0591 20 or 40 mg/kg during days P1-P4 or P10-P14 showed alveolarization that resembled that of room air controls while untreated hyperoxia groups showed definite evidence of aberrant alveolarization but no inflammation. In a hyperoxia-exposed newborn mice model, a FLAP inhibitor given during critical window periods may prevent aberration of alveolarization in a dose- and time-dependent manner.

Differential responses in the lungs of newborn mouse pups exposed to 85% or >95% oxygen

Premature infants often develop serious clinical complications associated with respiratory failure and hyperoxic lung injury that includes lung inflammation and alterations in lung development. The goal of these studies is to test the hypothesis that there are differences in the course of lung injury in newborn mice exposed to 85% or >95% oxygen that provide models to address the differential effects of oxidation and inflammation. Our results indicate differences between the 85% and >95% O2 exposure groups by day 14 in weight gain and lung alveolarization. Inflammation, assessed by neutrophil counts, was observed in both hyperoxia groups by day 3 but was dramatically greater in the >95% O2-exposed groups by day 14 and associated with greater developmental deficits. Cytoplasmic phospholipase A2, cyclooxygenase-2, and 5-lipoxygenase levels were elevated but no patterns of differences were observed between exposure groups. Prostaglandins D2, E2, and F2alpha were increased in the tissues from mouse pups exposed to >95% O2 at 7 d indicating a differential expression of cyclooxygenase-2 products. Our data indicate that there are differences in the models of 85% or >95% O2 exposure and these differences may provide mechanistic insights into hyperoxic lung injury in an immature system.

Apoptosis and the activity of ceramide, Bax and Bcl-2 in the lungs of neonatal rats exposed to limited and prolonged hyperoxia

Background

The aim of the study is to examine the effect of limited and prolonged hyperoxia on neonatal rat lung. This is done by examining the morphologic changes of apoptosis, the expression of ceramide, an important mediator of apoptosis, the expression of inflammatory mediators represented by IL-1β and the expression of 2 proto-oncogenes that appear to modulate apoptosis (Bax and Bcl-2).

Methods

Newborn rats were placed in chambers containing room air or oxygen above 90% for 7 days. The rats were sacrificed at 3, 7 or 14 days and their lungs removed. Sections were fixed, subjected to TUNEL, Hoechst, and E-Cadherin Staining. Sections were also incubated with anti-Bcl-2 and anti-Bax antisera. Bcl-2 and Bax were quantitated by immunohistochemistry. Lipids were extracted, and ceramide measured through a modified diacylglycerol kinase assay. RT-PCR was utilized to assess IL-1β expression.

Results

TUNEL staining showed significant apoptosis in the hyperoxia-exposed lungs at 3 days only. Co-staining of the apoptotic cells with Hoechst, and E-Cadherin indicated that apoptotic cells were mainly epithelial cells. The expression of Bax and ceramide was significantly higher in the hyperoxia-exposed lungs at 3 and 14 days of age, but not at 7 days. Bcl-2 was significantly elevated in the hyperoxia-exposed lungs at 3 and 14 days. IL-1β expression was significantly increased at 14 days.

Conclusion

Exposure of neonatal rat lung to hyperoxia results in early apoptosis documented by TUNEL assay. The early rise in Bax and ceramide appears to overcome the anti-apoptotic activity of Bcl-2. Further exposure did not result in late apoptotic changes. This suggests that apoptotic response to hyperoxia is time sensitive. Prolonged hyperoxia results in acute lung injury and the shifting balance of ceramide, Bax and Bcl-2 may be related to the evolution of the inflammatory process.

Hyperoxia decreases matrix metalloproteinase-9 and increases tissue inhibitor of matrix metalloproteinase-1 protein in the newborn rat lung: association with arrested alveolarization

Matrix metalloproteinases (MMP) are likely effectors of normal lung development, especially branching morphogenesis, angiogenesis, and extracellular matrix degradation. Because hyperoxia exposure (>95% O(2)) from d 4 to 14 in newborn rat pups leads to arrest of alveolarization and mimics newborn chronic lung disease, we tested whether hyperoxia altered MMP-2 and -9 mRNA, protein, and enzymatic activity, and the mRNA and protein expression of the endogenous tissue inhibitor of MMP, TIMP-1. No changes due to hyperoxia exposure were observed in MMP-2 mRNA or pro-enzyme (72 kD) protein levels between d 6 and 14, although the overall protein mass and zymographic activity of the active (68 kD) enzyme were diminished (p < 0.05, ANOVA). However, hyperoxia significantly decreased levels of MMP-9 mRNA and pro-MMP-9 protein and diminished overall MMP-9 pro-enzyme activity. TIMP-1 mRNA was not elevated by hyperoxia until d 14, but protein levels were significantly (p < 0.001) elevated by hyperoxia from d 9 to 14. To estimate the potential of MMP inhibition to arrest alveolarization, administration of doxycycline (20 mg/kg, twice daily by gavage), a pan-MMP proteolysis inhibitor, arrested lung alveolarization. We conclude that hyperoxia decreases MMP-9 mRNA, protein, and activity and elevates TIMP-1 protein, and these changes have the potential to contribute to the arrest of normal lung development.

DNA microarray analysis of neonatal mouse lung connects regulation of KDR with dexamethasone-induced inhibition of alveolar formation

Treatment of newborn mice with dexamethasone (Dex) inhibits the subdivision of lung saccules to form alveoli; treatment with all- trans retinoic acid (RA) prevents this inhibition of septation. To better understand the early molecular signals responsible for the effects of Dex and RA, Affymetrix gene profiling was done on RNA isolated from 4-day-old mice after treatment with 1) diluent, 2) RA (1 mg/kg), 3) Dex (0.7 μg/pup), or 4) RA + Dex. Each sample was assayed in duplicate on U74Av2 GeneChips. Data were analyzed with Affymetrix suite 5.0, corrected for saturation, and evaluated with GeneSpring 5.1 software. Stringent filtering of data by the global error model and condition-to-condition comparisons was used to identify 46 genes demonstrating significantly different expression between the lungs of Dex- and RA + Dex-treated mice. A query of the gene ontology database revealed that the major biological processes affected by treatment with Dex and RA were cell growth/maintenance and cellular communication. On the basis of microarray data analysis, we hypothesize that Dex-induced inhibition of septation is associated with a block in angiogenesis due to downregulation of the kinase domain receptor (KDR), also known as VEGF receptor-2 and fetal liver kinase, and that the downregulation of KDR is prevented by treatment with RA.

Hyperoxia causes inducible nitric oxide synthase-mediated cellular damage to the immature rat brain

Relative hyperoxia is a condition frequently encountered in premature infants, either spontaneously or during treatment in the Neonatal Intensive Care Unit. The effects of high inspiratory oxygen concentrations on immature brain cells and their signaling cascades are largely unknown. The aim of the study was to investigate the effect of hyperoxia on the amount and topographic distribution of iNOS-expression (inducible nitric oxide synthase) in the immature rat brain, and to localize hyperoxia-induced formation of peroxynitrite as a potential marker of cellular damage to immature cerebral structures. Seven-day-old Wistar rat pups were exposed to >80% oxygen for 24 h and were then transcardially perfused. Following paraformaldehyde fixation, brains were paraffin-embedded and immunohistochemically stained for iNOS and nitrotyrosine. iNOS protein was quantified by Western blot; iNOS mRNA expression was studied by RT-PCR. Total brain iNOS mRNA was up-regulated, demonstrating a peak at 6 h following the onset of hyperoxia. Immunohistochemical staining was predominantly observed in microglial cells of hippocampus and frontal cortex with some iNOS reactivity in endothelial and perivascular cells. Nitrotyrosine staining was positive in apical dendrites of neurons in the frontal cortex. There was no positive staining for iNOS or nitrotyrosine in control animals. Hyperoxia causes iNOS mRNA and protein up-regulation in microglial cells of the immature rat brain. Positive neuronal nitrotyrosine staining indicates formation of peroxynitrite with potential deleterious effects for immature cellular structures in the neonatal brain.

Effects of hyperoxia on VEGF, its receptors, and HIF-2alpha in the newborn rat lung

Signaling through the hypoxia inducible factor (HIF)-VEGF-VEGF receptor system (VEGF signaling system) leads to angiogenesis and epithelial cell proliferation and is a key mechanism regulating alveolarization in lungs of newborn rats. Hyperoxia exposure (>95% O2 days 4-14) arrests lung alveolarization and may do so through suppression of the VEGF signaling system. Lung tissue mRNA levels of HIF-2alpha and VEGF increased from days 4-14 in normoxic animals, but hyperoxia suppressed these increases. Levels of HIF-2alpha and VEGF mRNA were correlated in the air but not the O2-treated group, suggesting that the low levels of HIF-2alpha observed at high O2 concentrations are not stimulating VEGF expression. VEGF164 protein levels increased with developmental age, and with hyperoxia to day 9, but continuing hyperoxia decreased levels by day 12. VEGFR1 and VEGFR2 mRNA expression also increased in air-exposed animals, and these, too, were significantly decreased by hyperoxia by day 9 and day 12, respectively. Receptor protein levels did not increase with development; however, O2 did decrease protein to less than air values. Hyperoxic suppression of VEGF signaling from days 9-14 may be one mechanism by which alveolarization is arrested.

Montelukast does not protect against hyperoxia-induced inhibition of alveolarization in newborn rats

Impaired lung development has been demonstrated in neonatal animals exposed to hyperoxia. High lung cys-leukotriene levels may be a contributing factor towards the increase in oxygen toxicity. We investigated the effect of cysteinyl-leukotriene inhibition using the receptor antagonist, montelukast (MK, Singulair), on hyperoxia-induced changes in lung parenchymal structure in neonatal rat pups. Rat pups were exposed to 21% O(2) (air) or 50% O(2) (moderate hyperoxia) from days 1-14 after birth, and were administered the cys-leukotriene receptor antagonist MK (1 mg/kg/day) or normal saline from days 4-14. Somatic growth and morphometric measurements were done on day 15. There was a significant increase in bronchoalveolar lavage fluid cysteinyl-leukotriene levels (+61.9%) when animals were exposed to hyperoxia. O(2) exposure significantly decreased the specific internal surface area by 13%. There was a nonsignificant 5.8% and 19.6% increase in mean chord length and mean alveolar diameter, respectively, as well as an 8.6% decrease in lung volume to body weight ratio. Inhibition of only one arm of the arachidonic-acid cascade by MK was not sufficient to prevent these oxygen-induced changes.