Microbial-induced Redox Imbalance in the Neonatal Lung Is Ameliorated by Live Biotherapeutics.

Bronchopulmonary dysplasia (BPD) is a common lung disease of premature infants. Hyperoxia exposure and microbial dysbiosis are contributors to BPD development. However, the mechanisms linking pulmonary microbial dysbiosis to worsening lung injury are unknown. Nrf2 (nuclear factor erythroid 2-related factor 2) is a transcription factor that regulates oxidative stress responses and modulates hyperoxia-induced lung injury. We hypothesized that airway dysbiosis would attenuate Nrf2-dependent antioxidant function, resulting in a more severe phenotype of BPD. Here, we show that preterm infants with a Gammaproteobacteria-predominant dysbiosis have increased endotoxin in tracheal aspirates, and mice monocolonized with the representative Gammaproteobacteria Escherichia coli show increased tissue damage compared with germ-free (GF) control mice. Furthermore, we show Nrf2-deficient mice have worse lung structure and function after exposure to hyperoxia when the airway microbiome is augmented with E. coli. To confirm the disease-initiating potential of airway dysbiosis, we developed a novel humanized mouse model by colonizing GF mice with tracheal aspirates from human infants with or without severe BPD, producing gnotobiotic mice with BPD-associated and non-BPD-associated lung microbiomes. After hyperoxia exposure, BPD-associated mice demonstrated a more severe BPD phenotype and increased expression of Nrf2-regulated genes, compared with GF and non-BPD-associated mice. Furthermore, augmenting Nrf2-mediated antioxidant activity by supporting colonization with Lactobacillus species improved dysbiotic-augmented lung injury. Our results demonstrate that a lack of protective pulmonary microbiome signature attenuates an Nrf2-mediated antioxidant response, which is augmented by a respiratory probiotic blend. We anticipate antioxidant pathways will be major targets of future microbiome-based therapeutics for respiratory disease.

Degradation of Lung Protective Angiotensin Converting Enzyme-2 by Meconium in Human Alveolar Epithelial Cells: A Potential Pathogenic Mechanism in Meconium Aspiration Syndrome.

BACKGROUND: Pancreatic digestive enzymes present in meconium might be responsible for meconium-induced lung injury. The local Renin Angiotensin System plays an important role in lung injury and inflammation. Particularly, angiotensin converting enzyme-2 (ACE-2) has been identified as a protective lung enzyme against the insult. ACE-2 converts pro-apoptotic Angiotensin II to anti-apoptotic Angiotensin 1-7. However, the effect of meconium on ACE-2 has never been studied before. OBJECTIVE: To study the effect of meconium on ACE-2, and whether inhibition of proteolytic enzymes present in the meconium reverses its effects on ACE-2. METHODS: Alveolar epithelial A549 cells were exposed to F-12 medium, 2.5% meconium, meconium + a protease inhibitor cocktail (PIc) and PIc alone for 16 h. At the end of incubation, apoptosis was measured with a nuclear fragmentation assay and cell lysates were collected for ACE-2 immunoblotting and enzyme activity. RESULTS: Meconium caused a fourfold increase in apoptotic nuclei (p < 0.001). The pro-apoptotic effect of meconium can be reversed by PIc. Meconium reduced ACE-2 enzyme activity by cleaving ACE-2 into a fragment detected at ~ 37 kDa by immunoblot. PIc prevented the degradation of ACE-2 and restored 50% of ACE-2 activity (p < 0.05). CONCLUSION: These data suggest that meconium causes degradation of lung protective ACE-2 by proteolytic enzymes present in meconium, since the effects of meconium can be reversed by PIc.

Expression profiling of genes regulated by sphingosine kinase1 signaling in a murine model of hyperoxia induced neonatal bronchopulmonary dysplasia.

BACKGROUND: Sphingosine- 1-Phosphate (S1P) is a bioactive lipid and an intracellular as well as an extracellular signaling molecule. S1P ligand specifically binds to five related cell surface G-protein-coupled receptors (S1P1-5). S1P levels are tightly regulated by its synthesis catalyzed by sphingosine kinases (SphKs) 1 & 2 and catabolism by S1P phosphatases, lipid phosphate phosphatases and S1P lyase. We previously reported that knock down of SphK1 (Sphk1 -/- ) in a neonatal mouse BPD model conferred significant protection against hyperoxia induced lung injury. To better understand the underlying molecular mechanisms, genome-wide gene expression profiling was performed on mouse lung tissue using Affymetrix MoGene 2.0 array. RESULTS: Two-way ANOVA analysis was performed and differentially expressed genes under hyperoxia were identified using Sphk1 -/- mice and their wild type (WT) equivalents. Pathway (PW) enrichment analyses identified several signaling pathways that are likely to play a key role in hyperoxia induced lung injury in the neonates. These included signaling pathways that were anticipated such as those involved in lipid signaling, cell cycle regulation, DNA damage/apoptosis, inflammation/immune response, and cell adhesion/extracellular matrix (ECM) remodeling. We noted hyperoxia induced downregulation of the expression of genes related to mitotic spindle formation in the WT which was not observed in Sphk1 -/- neonates. Our data clearly suggests a role for SphK1 in neonatal hyperoxic lung injury through elevated inflammation and apoptosis in lung tissue. Further, validation by RT-PCR on 24 differentially expressed genes showed 83% concordance both in terms of fold change and vectorial changes. Our findings are in agreement with previously reported human BPD microarray data and completely support our published in vivo findings. In addition, the data also revealed a significant role for additional unanticipitated signaling pathways involving Wnt and GADD45. CONCLUSION: Using SphK1 knockout mice and differential gene expression analysis, we have shown here that S1P/SphK1 signaling plays a key role in promoting hyperoxia induced DNA damage, inflammation, apoptosis and ECM remodeling in neonatal lungs. It also appears to suppress pro-survival cellular responses involved in normal lung development. We therefore propose SphK1 as a therapeutic target for the development drugs to combat BPD.

Intermittent hypoxia during recovery from neonatal hyperoxic lung injury causes long-term impairment of alveolar development: A new rat model of BPD.

Bronchopulmonary dysplasia (BPD) is a chronic lung injury characterized by impaired alveologenesis that may persist into adulthood. Rat models of BPD using varying degrees of hyperoxia to produce injury either cause early mortality or spontaneously recover following removal of the inciting stimulus, thus limiting clinical relevance. We sought to refine an established rat model induced by exposure to 60% O2 from birth by following hyperoxia with intermittent hypoxia (IH). Rats exposed from birth to air or 60% O2 until day 14 were recovered in air with or without IH (FIO2 = 0.10 for 10 min every 6 h) until day 28 Animals exposed to 60% O2 and recovered in air had no evidence of abnormal lung morphology on day 28 or at 10-12 wk. In contrast, 60% O2-exposed animals recovered in IH had persistently increased mean chord length, more dysmorphic septal crests, and fewer peripheral arteries. Recovery in IH also increased pulmonary vascular resistance, Fulton index, and arterial wall thickness. IH-mediated abnormalities in lung structure (but not pulmonary hypertension) persisted when reexamined at 10-12 wk, accompanied by increased pulmonary vascular reactivity and decreased exercise tolerance. Increased mean chord length secondary to IH was prevented by treatment with a peroxynitrite decomposition catalyst [5,10,15,20-Tetrakis(4-sulfonatophenyl)-21H,23H-porphyrin iron (III) chloride, 30 mg/kg/day, days 14-28], an effect accompanied by fewer inflammatory cells. We conclude that IH during recovery from hyperoxia-induced injury prevents recovery of alveologenesis and leads to changes in lung and pulmonary vascular function lasting into adulthood, thus more closely mimicking contemporary BPD.

Nicotinamide Adenine Dinucleotide Phosphate Oxidase 2 Regulates LPS-Induced Inflammation and Alveolar Remodeling in the Developing Lung.

In premature infants, sepsis is associated with alveolar simplification manifesting as bronchopulmonary dysplasia. The redox-dependent mechanisms underlying sepsis-induced inflammation and alveolar remodeling in the immature lung remain unclear. We developed a neonatal mouse model of sepsis-induced lung injury to investigate whether nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2) regulates Toll-like receptor (TLR)-mediated inflammation and alveolar remodeling. Six-day-old NOX2+/+ and NOX2-/- mice were injected with intraperitoneal LPS to induce sepsis. Lung inflammation and canonical TLR signaling were assessed 24 hours after LPS. Alveolar development was examined in 15-day-old mice after LPS on Day 6. The in vivo efficacy of a NOX2 inhibitor (NOX2-I) on NOX2 complex assembly and sepsis-induced lung inflammation were examined. Lung cytokine expression and neutrophil influx induced with sepsis in NOX2+/+ mice was decreased by >50% in NOX2-/- mice. LPS-induced TLR4 signaling evident by inhibitor of NF-κB kinase-ß and mitogen-activated protein kinase phosphorylation, and nuclear factor-κB/AP-1 translocation were attenuated in NOX2-/- mice. LPS increased matrix metalloproteinase 9 while decreasing elastin and keratinocyte growth factor levels in NOX2+/+ mice. An LPS-induced increase in matrix metalloproteinase 9 and decrease in fibroblast growth factor 7 and elastin were not evident in NOX2-/- mice. An LPS-induced reduction in radial alveolar counts and increased mean linear intercepts were attenuated in NOX2-/- mice. LPS-induced NOX2 assembly evident by p67phox/gp91phox coimmunoprecipitation was disrupted with NOX2-I. NOX2-I also mitigated LPS-induced cytokine expression, TLR pathway signaling, and alveolar simplification. In a mouse model of neonatal sepsis, NOX2 regulates proinflammatory TLR signaling and alveolar remodeling induced by a single dose of LPS. Our results provide mechanistic insight into the regulation of sepsis-induced alveolar remodeling in the developing lung.

Neutrophil elastase-induced elastin degradation mediates macrophage influx and lung injury in 60% O2-exposed neonatal rats.

Neutrophil (PMNL) influx precedes lung macrophage (LM) influx into the lung following exposure of newborn pups to 60% O2. We hypothesized that PMNL were responsible for the signals leading to LM influx. This was confirmed when inhibition of PMNL influx with a CXC chemokine receptor-2 antagonist, SB-265610, also prevented the 60% O2-dependent LM influx, LM-derived nitrotyrosine formation, and pruning of small arterioles. Exposure to 60% O2 was associated with increased lung contents of neutrophil elastase and α-elastin, a marker of denatured elastin, and a decrease in elastin fiber density. This led us to speculate that neutrophil elastase-induced elastin fragments were the chemokines that led to a LM influx into the 60% O2-exposed lung. Inhibition of neutrophil elastase with sivelestat or elafin attenuated the LM influx. Sivelestat also attenuated the 60% O2-induced decrease in elastin fiber density. Daily injections of pups with an antibody to α-elastin prevented the 60% O2-dependent LM influx, impaired alveologenesis, and impaired small vessel formation. This suggests that neutrophil elastase inhibitors may protect against neonatal lung injury not only by preventing structural elastin degradation, but also by blocking elastin fragment-induced LM influx, thus preventing tissue injury from LM-derived peroxynitrite formation.

Inhibition of ß-catenin signaling improves alveolarization and reduces pulmonary hypertension in experimental bronchopulmonary dysplasia.

Bronchopulmonary dysplasia (BPD) is the most common and serious chronic lung disease of preterm infants. The development of pulmonary hypertension (PH) significantly increases the mortality and morbidity of this disease. ß-Catenin signaling plays an important role in tissue development and remodeling. Aberrant ß-catenin signaling is associated with clinical and experiment models of BPD. To test the hypothesis that inhibition of ß-catenin signaling is beneficial in promoting alveolar and vascular development and preventing PH in experimental BPD, we examined the effects of ICG001, a newly developed pharmacological inhibitor of ß-catenin, in preventing hyperoxia-induced BPD in neonatal rats. Newborn rat pups were randomized at postnatal day (P)2 to room air (RA) + DMSO (placebo), RA + ICG001, 90% FiO2 (O2) + DMSO, or O2 + ICG001. ICG001 (10 mg/kg) or DMSO was given by daily intraperitoneal injection for 14 days during continuous exposure to RA or hyperoxia. Primary human pulmonary arterial smooth muscle cells (PASMCs) were cultured in RA or hyperoxia (95% O2) in the presence of DMSO or ICG001 for 24 to 72 hours. Treatment with ICG001 significantly increased alveolarization and reduced pulmonary vascular remodeling and PH during hyperoxia. Furthermore, administering ICG001 decreased PASMC proliferation and expression of extracellular matrix remodeling molecules in vitro under hyperoxia. Finally, these structural, cellular, and molecular effects of ICG001 were associated with down-regulation of multiple ß-catenin target genes. These data indicate that ß-catenin signaling mediates hyperoxia-induced alveolar impairment and PH in neonatal animals. Targeting ß-catenin may provide a novel strategy to alleviate BPD in preterm infants.

Suppression of inflammatory cell trafficking and alveolar simplification by the heme oxygenase-1 product carbon monoxide.

Bronchopulmonary dysplasia (BPD), a lung disease of prematurely born infants, is characterized in part by arrested development of pulmonary alveolae. We hypothesized that heme oxygenase (HO-1) and its byproduct carbon monoxide (CO), which are thought to be cytoprotective against redox stress, mitigate lung injury and alveolar simplification in hyperoxia-exposed neonatal mice, a model of BPD. Three-day-old C57BL/6J mice were exposed to air or hyperoxia (FiO2, 75%) in the presence or absence of inhaled CO (250 ppm for 1 h twice daily) for 21 days. Hyperoxic exposure increased mean linear intercept, a measure of alveolar simplification, whereas CO treatment attenuated hypoalveolarization, yielding a normal-appearing lung. Conversely, HO-1-null mice showed exaggerated hyperoxia-induced hypoalveolarization. CO also inhibited hyperoxia-induced pulmonary accumulation of F4/80+, CD11c+, and CD11b+ monocytes and Gr-1+ neutrophils. Furthermore, CO attenuated lung mRNA and protein expression of proinflammatory cytokines, including the monocyte chemoattractant CCL2 in vivo, and decreased hyperoxia-induced type I alveolar epithelial cell CCL2 production in vitro. Hyperoxia-exposed CCL2-null mice, like CO-treated mice, showed attenuated alveolar simplification and lung infiltration of CD11b+ monocytes, consistent with the notion that CO blocks lung epithelial cell cytokine production. We conclude that, in hyperoxia-exposed neonatal mice, inhalation of CO suppresses inflammation and alveolar simplification.

Myeloid Nrf2 Protects against Neonatal Oxidant-Stress-Induced Lung Inflammation and Alveolar Simplification in Mice.

Bronchopulmonary dysplasia (BPD) is a chronic condition affecting preterm infants, characterized by lung alveolar simplification/hypoalveolarization and vascular remodeling. The nuclear factor erythroid 2 like 2 (Nfe2l2, or Nrf2) plays a critical role in the cytoprotective response to neonatal hyperoxia, and its global deficiency exacerbates hypoalveolarization in mice. The abnormal recruitment and activation of myeloid cells are associated with the pathogenesis of BPD. Therefore, we employed a genetic approach to investigate the role of myeloid Nrf2 in regulating hyperoxia-induced hypoalveolarization. Pups, both wild-type (Nrf2f/f) and those with a myeloid Nrf2 deletion (abbreviated as Nrf2∆/∆mye), were exposed to hyperoxia for 72 h at postnatal day 1 (Pnd1), and then sacrificed at either Pnd4 or Pnd18 following a two-week recovery period. We analyzed the hypoalveolarization, inflammation, and gene expression related to cytoprotective and inflammatory responses in the lungs of these pups. The hypoalveolarization induced by hyperoxia was significantly greater in Nrf2∆/∆mye pups compared to their Nrf2f/f counterparts (35.88% vs. 21.01%, respectively) and was accompanied by increased levels of inflammatory cells and IL-1ß activation in the lungs. Antioxidant gene expression in response to neonatal hyperoxia was lower in Nrf2∆/∆mye pups compared to their Nrf2f/f counterparts. Furthermore, Nrf2-deficient macrophages exposed to hyperoxia exhibited markedly decreased cytoprotective gene expression and increased IL-1ß levels compared to Nrf2-sufficient cells. Our findings demonstrate the crucial role of myeloid Nrf2 in mitigating hyperoxia-induced lung hypoalveolarization and inflammatory responses in neonatal mice.

Types of home respiratory support in children with bronchopulmonary dysplasia and factors determining its duration: A scoping review.

Bronchopulmonary dysplasia also known as chronic lung disease of prematurity has changed as a disease entity over the last five decades and children with "new bronchopulmonary dysplasia (BPD)" have better survival rates. This necessitates strategies to prevent severe BPD and provide organized home support. Home respiratory support in these children varies from home oxygen to noninvasive ventilation and tracheostomy ventilation. This review was conducted utilizing Joanna Briggs Institute publications on evidence synthesis and presentation of results for a scoping review. The Preferred Reporting Items for Systematic Review and Meta-Analyses were used to report the results. The risk of bias assessment was done using "The Cochrane Handbook for Systematic Reviews tool for interventional studies." After screening for the duplication of results and applying inclusion and exclusion criteria, twenty-seven studies were assessed by reading the full texts. Out of these, eleven were finally included in this systematic review. The total sample size from all studies was 4794, including 2705 males. The 4/11 studies home oxygen, one study reported continuous positive airway pressure/bilevel positive airway pressure and seven studies used tracheostomy or tracheostomy ventilation. The median duration of post-natal invasive ventilation was higher in those discharged on home oxygen compared to those who did not need oxygen at discharge. There is a significant proportion of children who are tracheostomy ventilated (8.65%) at home. In the absence of established guidelines, these children are vulnerable when it comes to care at home and the timing of decannulation. For home oxygen alone, guidelines by ERS, ATS and BTS have streamlined weaning protocols and the need for having a multi-disciplinary team to care for these children.

Antimicrobial peptides modulate lung injury by altering the intestinal microbiota.

BACKGROUND: Mammalian mucosal barriers secrete antimicrobial peptides (AMPs) as critical, host-derived regulators of the microbiota. However, mechanisms that support microbiota homeostasis in response to inflammatory stimuli, such as supraphysiologic oxygen, remain unclear. RESULTS: We show that supraphysiologic oxygen exposure to neonatal mice, or direct exposure of intestinal organoids to supraphysiologic oxygen, suppresses the intestinal expression of AMPs and alters intestinal microbiota composition. Oral supplementation of the prototypical AMP lysozyme to hyperoxia-exposed neonatal mice reduced hyperoxia-induced alterations in their microbiota and was associated with decreased lung injury. CONCLUSIONS: Our results identify a gut-lung axis driven by intestinal AMP expression and mediated by the intestinal microbiota that is linked to lung injury in newborns. Together, these data support that intestinal AMPs modulate lung injury and repair. Video Abstract.

Acute Lung Functional and Airway Remodeling Effects of an Inhaled Highly Selective Phosphodiesterase 4 Inhibitor in Ventilated Preterm Lambs Exposed to Chorioamnionitis.

Phosphodiesterase (PDE) inhibition has been identified in animal studies as a new treatment option for neonatal lung injury, and as potentially beneficial for early lung development and function. However, our group could show that the inhaled PDE4 inhibitor GSK256066 could have dose-dependent detrimental effects and promote lung inflammation in the premature lung. In this study, the effects of a high and a low dose of GSK256066 on lung function, structure and alveolar development were investigated. In a triple hit lamb model of Ureaplasma-induced chorioamnionitis, prematurity, and mechanical ventilation, 21 animals were treated as unventilated (NOVENT) or 24 h ventilated controls (Control), or with combined 24 h ventilation and low dose (iPDE1) or high dose (iPDE10) treatment with inhaled GSK 256066. We found that high doses of an inhaled PDE4 inhibitor impaired oxygenation during mechanical ventilation. In this group, the budding of secondary septae appeared to be decreased in the preterm lung, suggesting altered alveologenesis. Ventilation-induced structural and functional changes were only modestly ameliorated by a low dose of PDE4 inhibitor. In conclusion, our findings indicate the narrow therapeutic window of PDE4 inhibitors in the developing lung.

Volume-Targeted Ventilation.

Volume-targeted ventilation (VTV) has been increasingly used in neonatology. In systematic reviews, VTV has been shown to reduce the risk of neonatal morbidities and improve long-term outcomes. It is adaptive ventilation using complex computer algorithms to deliver ventilator inflations with expired tidal volumes close to a target set by clinicians. Significant endotracheal tube leak and patient-ventilator interactions may complicate VTV and make ventilator parameters and waveforms difficult to interpret. In this article, we review the rationale for using VTV and the evidence supporting its use and provide practical advice for clinicians ventilating newborn infants.

Close Association Between Platelet Biogenesis and Alveolarization of the Developing Lung.

Bronchopulmonary dysplasia (BPD) is a neonatal chronic lung disease characterized by an arrest in alveolar and vascular development. BPD is secondary to lung immaturity, ventilator-induced lung injury, and exposure to hyperoxia in extremely premature infants, leading to a lifelong impairment of lung function. Recent studies indicate that the lung plays an important role in platelet biogenesis. However, the dynamic change of platelet production during lung development and BPD pathogenesis remains to be elucidated. We investigated the dynamic change of platelet parameters in extremely premature infants during BPD development, and in newborn rats during their normal development from birth to adulthood. We further studied the effect of hyperoxia exposure on platelet production and concomitant pulmonary maldevelopment in an experimental BPD rat model induced by prolonged exposure to hyperoxia. We detected a physiological increase in platelet count from birth to 36 weeks postmenstrual age in extremely premature infants, but platelet counts in extremely premature infants who developed BPD were persistently lower than gestational age-matched controls. In line with clinical findings, exposure to hyperoxia significantly decreased the platelet count in neonatal rats. Lung morphometry analysis demonstrated that platelet counts stabilized with the completion of lung alveolarization in rats. Our findings indicate a close association between platelet biogenesis and alveolarization in the developing lung. This phenomenon might explain the reduced platelet count in extremely premature infants with BPD.

Protection of Meconium-Induced Lung Epithelial Injury by Protease Inhibitors.

Earlier work form this laboratory showed that exposure of alveolar epithelial cells (AECs) to meconium caused significant cell detachment and that meconium-induced detachment of cells was prevented by a protease inhibitor cocktail. Therefore, it was hypothesized that protease inhibitors might protect AEC monolayers against meconium-induced collapse of epithelial barrier function both in vitro and in vivo. To investigate this theory in vitro, albumin flux was measured across cultured, confluent monolayers of human type II derived cell line A549 on microporous filter inserts. Human meconium was collected from seven healthy full-term neonates and the samples were pooled and diluted prior to analysis. Exposure of AECs to 5% human meconium increased albumin flux across the cultured AEC monolayers, but the increase was significantly blocked by protease inhibitors (P<0.001). In C57/BL6 mice, intratracheal instillation of 5% human meconium increased the passage of Evans Blue Dye (EBD) from the vascular compartment into the alveolar spaces, measured in bronchoalveolar lavage (BAL) fluid after intravenous injection of EBD. Moreover, intratrachial coinstillation of protease inhibitors prevented the meconium-induced increase in EBD passage into BAL fluid (P<0.01). The data presented herein clearly demonstrate that protease inhibitors protect AEC barrier function against meconium-induced injury, and suggest the future possibility of using protease inhibitors in the treatment of meconium aspiration syndrome.

Bronchopulmonary Dysplasia: Chronic Lung Disease of Infancy and Long-Term Pulmonary Outcomes.

Bronchopulmonary dysplasia (BPD) is a chronic lung disease most commonly seen in premature infants who required mechanical ventilation and oxygen therapy for acute respiratory distress. While advances in neonatal care have resulted in improved survival rates of premature infants, limited progress has been made in reducing rates of BPD. Lack of progress may in part be attributed to the limited therapeutic options available for prevention and treatment of BPD. Several lung-protective strategies have been shown to reduce risks, including use of non-invasive support, as well as early extubation and volume ventilation when intubation is required. These approaches, along with optimal nutrition and medical therapy, decrease risk of BPD; however, impacts on long-term outcomes are poorly defined. Characterization of late outcomes remain a challenge as rapid advances in medical management result in current adult BPD survivors representing outdated neonatal care. While pulmonary disease improves with growth, long-term follow-up studies raise concerns for persistent pulmonary dysfunction; asthma-like symptoms and exercise intolerance in young adults after BPD. Abnormal ventilatory responses and pulmonary hypertension can further complicate disease. These pulmonary morbidities, combined with environmental and infectious exposures, may result in significant long-term pulmonary sequalae and represent a growing burden on health systems. Additional longitudinal studies are needed to determine outcomes beyond the second decade, and define risk factors and optimal treatment for late sequalae of disease.

Roles of the Angiotensin System in Neonatal Lung Injury and Disease.

The renin-angiotensin system (RAS) has long been known as a regulator of blood pressure and fluid homeostasis. In past several decades, local renin-angiotensin systems have been discovered in various tissues and novel actions of angiotensin II (ANGII) have emerged as an immunomodulator and profibrotic molecule. The enzyme responsible for its synthesis, angiotensin-converting-enzyme (ACE), is present in high concentrations in lung tissue. ACE cleaves angiotensin I (ANG I) to generate angiotensin II (ANGII), whereas ACE2 inactivates ANGII and is a negative regulator of the system. The RAS has been implicated in the pathogenesis of pulmonary hypertension, acute lung injury and experimental lung fibrosis. Recent studies in animal and humans indicate that the RAS also plays a critical role in fetal and neonatal lung diseases. Further investigations are needed to better understand the role of RAS, ACE and ACE-2 in neonatal lung injury. With more clarity and understanding, the RAS and/or ACE-2 may ultimately prove to constitute potential therapeutic targets for the treatment of neonatal lung diseases. This manuscript reviews the evidence supporting a role for RAS in neonatal lung injury and discusses new possibilities for therapeutic approaches.

Cyclooxygenase-2 inhibition partially protects against 60% O2 -mediated lung injury in neonatal rats.

RATIONALE: Use of the anti-inflammatory agent dexamethasone in premature infants with bronchopulmonary dysplasia has been curtailed, and no alternative anti-inflammatory agents are approved for this use. Our objective was to use a neonatal rat model of bronchopulmonary dysplasia to determine if an highly selective cyclooxygenase-2 inhibitor, 5,5-dimethyl-3-(3-fluorophenyl)4-(4-methylsulfonyl)phenyl-2(5H)-furanone (DFU; 10 µg/g body weight), could prevent inflammatory cell influx and protect against lung injury. METHODS: Neonatal rats exposed to air or 60% O2 for 14 days from birth either received daily i.p. injections of (i) vehicle or DFU or (ii) vehicle or an EP(1) receptor antagonist, SC-19220. RESULTS: DFU attenuated the lung macrophage and neutrophil influx, prevented interstitial thickening and prevented the loss of peripheral blood vessels induced by 60% O2 , but did not protect against the variance in alveolar diameter induced by 60% O2 . Exposure to 60% O2 caused both an increase in lung prostaglandin E2 content and a reduction in lung mesenchymal cell mass which was reversed by DFU. Prostaglandin E2 binding to the EP(1) receptor inhibited DNA synthesis in cultures of lung fibroblasts in a dose dependent fashion. Treatment with SC-19220 attenuated the reduction in lung mesenchymal mass observed following exposure of rat pups to 60% O2 . CONCLUSIONS: An highly selective cyclooxygenase-2 inhibitor is an effective anti-inflammatory substitute for dexamethasone for preventing phagocyte influx into the neonatal lung during 60% O2 -mediated lung injury, and can modify the severity of that injury.

The preterm lung and airway: past, present, and future.

The tremendous advancement that has occurred in neonatal intensive care over the last 40-50 years can be largely attributed to greater understanding of developmental pathobiology in the newborn lung. Nonetheless, this improved survival from respiratory distress syndrome has been associated with continuing longer-term morbidity in the form of bronchopulmonary dysplasia (BPD). As a result, neonatal lung injury is a renewed focus of scientific interest. The onset of such an injury may begin in the delivery room, and this has generated interest in minimizing oxygen therapy and aggressive ventilatory support during the transition from fetal to neonatal lung. Fortunately, antenatal steroid therapy and selective use of surfactant therapy are now widely practiced, although fine tuning of this therapy for selected populations is ongoing. Newer therapeutic approaches address many aspects of BPD, including the pro-inflammatory component that characterizes this disorder. Finally, there is a greater need to understand the epidemiology and pathogenesis of the longer-term respiratory morbidity, most notably asthma, that persists in the preterm survivors of neonatal intensive care.