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1.  IL-6 Protects against Hyperoxia-Induced Mitochondrial Damage via Bcl-2–Induced Bak Interactions with Mitofusions 
Overexpression of IL-6 markedly diminishes hyperoxic lung injury, hyperoxia-induced cell death, and DNA fragmentation, and enhances Bcl-2 expression. We hypothesized that changes in the interactions between Bcl-2 family members play an important role in the IL-6–mediated protective response to oxidative stress. Consistent with this hypothesis, we found that IL-6 induced Bcl-2 expression, both in vivo and in vitro, disrupted interactions between proapoptotic and antiapoptotic factors, and suppressed H2O2-induced loss of mitochondrial membrane potential in vitro. In addition, IL-6 overexpression in mice protects against hyperoxia-induced lung mitochondrial damage. The overexpression of Bcl-2 in vivo prolonged the survival of mice exposed to hyperoxia and inhibited alveolar capillary protein leakage. In addition, apoptosis-associated DNA fragmentation was substantially reduced in these animals. This IL-6–mediated protection was lost when Bcl-2 was silenced, demonstrating that Bcl-2 is an essential mediator of IL-6 cytoprotection. Finally, Bcl-2 blocked the dissociation of Bak from mitofusion protein (Mfn) 2, and inhibited the interaction between Bak and Mfn1. Taken together, our results suggest that IL-6 induces Bcl-2 expression to perform cytoprotective functions in response to oxygen toxicity, and that this effect is mediated by alterations in the interactions between Bak and Mfns.
doi:10.1165/rcmb.2008-0302OC
PMCID: PMC2746985  PMID: 19168699
lung injury; mitochondria; apoptosis; cytochrome c; Bax
2.  The Chitinase-like Proteins Breast Regression Protein-39 and YKL-40 Regulate Hyperoxia-induced Acute Lung Injury 
Rationale: Prolonged exposure to 100% O2 causes hyperoxic acute lung injury (HALI), characterized by alveolar epithelial cell injury and death. We previously demonstrated that the murine chitinase-like protein, breast regression protein (BRP)–39 and its human homolog, YKL-40, inhibit cellular apoptosis. However, the regulation and roles of these molecules in hyperoxia have not been addressed.
Objectives: We hypothesized that BRP-39 and YKL-40 (also called chitinase-3–like 1) play important roles in the pathogenesis of HALI.
Methods: We characterized the regulation of BRP-39 during HALI and the responses induced by hyperoxia in wild-type mice, BRP-39–null (−/−) mice, and BRP-39−/− mice in which YKL-40 was overexpressed in respiratory epithelium. We also compared the levels of tracheal aspirate YKL-40 in premature newborns with respiratory failure.
Measurements and Main Results: These studies demonstrate that hyperoxia inhibits BRP-39 in vivo in the murine lung and in vitro in epithelial cells. They also demonstrate that BRP-39−/− mice have exaggerated permeability, protein leak, oxidation, inflammatory, chemokine, and epithelial apoptosis responses, and experience premature death in 100% O2. Lastly, they demonstrate that YKL-40 ameliorates HALI, prolongs survival in 100% O2, and rescues the exaggerated injury response in BRP-39−/− animals. In accord with these findings, the levels of tracheal aspirate YKL-40 were lower in premature infants treated with hyperoxia for respiratory failure who subsequently experienced bronchopulmonary dysplasia or death compared with those that did not experience these complications.
Conclusions: These studies demonstrate that hyperoxia inhibits BRP-39/YKL-40, and that BRP-39 and YKL-40 are critical regulators of oxidant injury, inflammation, and epithelial apoptosis in the murine and human lung.
doi:10.1164/rccm.200912-1793OC
PMCID: PMC2970863  PMID: 20558631
BRP-39; YKL-40; hyperoxygen; BPD; HALI
3.  Increased Hyperoxia-Induced Lung Injury in Nitric Oxide Synthase 2 Null Mice Is Mediated via Angiopoietin 2 
Supplemental oxygen is frequently prescribed. However, prolonged exposure to high concentrations of oxygen causes hyperoxic acute lung injury (HALI), which manifests as acute respiratory distress syndrome in adults and leads to bronchopulmonary dysplasia in newborns (NBs). Nitric oxide (NO), NO synthases (NOSs), and angiopoietin (Ang) 2 have been implicated in the pathogenesis of HALI. However, the mechanisms of the contributions of NOS/NO and the relationship(s) between NOS/NO and Ang2 have not been addressed. In addition, the relevance of these moieties in adults and NBs has not been evaluated. To address these issues, we compared the responses in hyperoxia of wild-type (NOS [+/+]) and NOS null (−/−) young adult and NB mice. When compared with NOS2+/+ adult controls, NOS2−/− animals manifest exaggerated alveolar–capillary protein leak and premature death. These responses were associated with enhanced levels of structural cell death, enhanced expression of proapoptotic regulatory proteins, and Ang2. Importantly, silencing RNA knockdown of Ang2 decreased the levels of cell death and the expression of proapoptotic mediators. These effects were at least partially NOS2 specific, and were development dependent, because survival was similar in adult NOS3+/+ and NOS3−/− mice and NB NOS2+/+ and NOS2−/− mice, respectively. These studies demonstrate that NOS2 plays an important protective role in HALI in adult animals. They also demonstrate that this response is mediated, at least in part, by the ability of NOS2 to inhibit hyperoxia-induced Ang2 production and thereby decrease Ang2-induced tissue injury.
doi:10.1165/rcmb.2011-0074OC
PMCID: PMC3359903  PMID: 22227562
cytokines; hyperoxia; lung
4.  IL-6 Cytoprotection in Hyperoxic Acute Lung Injury Occurs via Suppressor of Cytokine Signaling-1–Induced Apoptosis Signal–Regulating Kinase-1 Degradation 
Hyperoxic acute lung injury (HALI) is characterized by a cell death response that is inhibited by IL-6. Suppressor of cytokine signaling-1 (SOCS-1) is an antiapoptotic negative regulator of the IL-6–mediated Janus kinase–signal transducer and activator of transcription signaling pathway. We hypothesized that SOCS-1 is a critical regulator and key mediator of IL-6–induced cytoprotection in HALI. To test this hypothesis, we characterized the expression of SOCS-1 and downstream apoptosis signal–regulating kinase (ASK)-1–Jun N-terminal kinase signaling molecules in small airway epithelial cells in the presence of H2O2, which induces oxidative stress. We also examined these molecules in wild-type and lung-specific IL-6 transgenic (Tg+) mice exposed to 100% oxygen for 72 hours. In control small airway epithelial cells exposed to H2O2 or in wild-type mice exposed to 100% oxygen, a marked induction of ASK-1 and pJun N-terminal kinase was observed. Both IL-6–stimulated endogenous SOCS-1 and SOCS-1 overexpression abolished H2O2-induced ASK-1 activation. In addition, IL-6 Tg+ mice exposed to 100% oxygen exhibited reduced ASK-1 levels and enhanced SOCS-1 expression compared with wild-type mice. Interestingly, no significant changes in activation of the key ASK-1 activator, tumor necrosis factor receptor-1/tumor necrosis factor receptor–associated factor-2 were observed between wild-type and IL-6 Tg+ mice. Furthermore, the interaction between SOCS-1 and ASK-1 promotes ubiquitin-mediated degradation both in vivo and in vitro. These studies demonstrate that SOCS-1 is an important regulator in IL-6–induced cytoprotection against HALI.
doi:10.1165/rcmb.2007-0287OC
PMCID: PMC2645529  PMID: 18776134
IL-6; apoptosis signal–regulating kinase-1; suppressor of cytokine signaling-1; lung injury; tumor necrosis factor receptor-1
5.  Expression Level and Subcellular Localization of Heme Oxygenase-1 Modulates Its Cytoprotective Properties in Response to Lung Injury: A Mouse Model 
PLoS ONE  2014;9(3):e90936.
Premature infants exposed to hyperoxia suffer acute and long-term pulmonary consequences. Nevertheless, neonates survive hyperoxia better than adults. The factors contributing to neonatal hyperoxic tolerance are not fully elucidated. In contrast to adults, heme oxygenase (HO)-1, an endoplasmic reticulum (ER)-anchored protein, is abundant in the neonatal lung but is not inducible in response to hyperoxia. The latter may be important, because very high levels of HO-1 overexpression are associated with significant oxygen cytotoxicity in vitro. Also, in contrast to adults, HO-1 localizes to the nucleus in neonatal mice exposed to hyperoxia. To understand the mechanisms by which HO-1 expression levels and subcellular localization contribute to hyperoxic tolerance in neonates, lung-specific transgenic mice expressing high or low levels of full-length HO-1 (cytoplasmic, HO-1-FL(H) or HO-1-FL(L)) or C-terminally truncated HO-1 (nuclear, Nuc-HO-1-TR) were generated. In HO-1-FL(L), the lungs had a normal alveolar appearance and lesser oxidative damage after hyperoxic exposure. In contrast, in HO-1-FL(H), alveolar wall thickness with type II cell hyperproliferation was observed as well worsened pulmonary function and evidence of abnormal lung cell hyperproliferation in recovery from hyperoxia. In Nuc-HO-1-TR, the lungs had increased DNA oxidative damage, increased poly (ADP-ribose) polymerase (PARP) protein expression, and reduced poly (ADP-ribose) (PAR) hydrolysis as well as reduced pulmonary function in recovery from hyperoxia. These data indicate that low cytoplasmic HO-1 levels protect against hyperoxia-induced lung injury by attenuating oxidative stress, whereas high cytoplasmic HO-1 levels worsen lung injury by increasing proliferation and decreasing apoptosis of alveolar type II cells. Enhanced lung nuclear HO-1 levels impaired recovery from hyperoxic lung injury by disabling PAR-dependent regulation of DNA repair. Lastly both high cytoplasmic and nuclear expression of HO-1 predisposed to long-term abnormal lung cellular proliferation. To maximize HO-1 cytoprotective effects, therapeutic strategies must account for the specific effects of its subcellular localization and expression levels.
doi:10.1371/journal.pone.0090936
PMCID: PMC3944979  PMID: 24599172
6.  Inhibition of extracellular HMGB1 attenuates hyperoxia-induced inflammatory acute lung injury☆☆☆ 
Redox Biology  2014;2:314-322.
Prolonged exposure to hyperoxia results in acute lung injury (ALI), accompanied by a significant elevation in the levels of proinflammatory cytokines and leukocyte infiltration in the lungs. However, the mechanisms underlying hyperoxia-induced proinflammatory ALI remain to be elucidated. In this study, we investigated the role of the proinflammatory cytokine high mobility group box protein 1 (HMGB1) in hyperoxic inflammatory lung injury, using an adult mouse model. The exposure of C57BL/6 mice to ≥99% O2 (hyperoxia) significantly increased the accumulation of HMGB1 in the bronchoalveolar lavage fluids (BALF) prior to the onset of severe inflammatory lung injury. In the airways of hyperoxic mice, HMGB1 was hyperacetylated and existed in various redox forms. Intratracheal administration of recombinant HMGB1 (rHMGB1) caused a significant increase in leukocyte infiltration into the lungs compared to animal treated with a non-specific peptide. Neutralizing anti-HMGB1 antibodies, administrated before hyperoxia significantly attenuated pulmonary edema and inflammatory responses, as indicated by decreased total protein content, wet/dry weight ratio, and numbers of leukocytes in the airways. This protection was also observed when HMGB1 inhibitors were administered after the onset of the hyperoxic exposure. The aliphatic antioxidant, ethyl pyruvate (EP), inhibited HMGB1 secretion from hyperoxic macrophages and attenuated hyperoxic lung injury. Overall, our data suggest that HMGB1 plays a critical role in mediating hyperoxic ALI through the recruitment of leukocytes into the lungs. If these results can be translated to humans, they suggest that HMGB1 inhibitors provide treatment regimens for oxidative inflammatory lung injury in patients receiving hyperoxia through mechanical ventilation.
Graphical abstract
Highlights
•Exposure to hyperoxia results in accumulation of high levels of airway HMGB1 that precede inflammatory acute lung injury (ALI).•Airway HMGB1 is critical in mediating hyperoxia-induced inflammatory ALI via recruiting leukocytes including neutrophils.•Extracellular HMGB1-accumulated upon prolonged exposure to hyperoxia is hyperacetylated, existing in different redox states.•Small molecule EP, administrated even after the onset of hyperoxic exposure, can mitigate hyperoxia-induced inflammatory ALI by inhibiting HMGB1 release into the extracellular milieu.
doi:10.1016/j.redox.2014.01.013
PMCID: PMC3926109  PMID: 24563849
ALI, acute lung injury; BALF, bronchoalveolar lavage fluids; EP, ethyl pyruvate; GST, gluthatione-s-transferase; HMGB1, high mobility group box protein 1; MV, mechanical ventilation; NLS, nuclear localization signal; PMNs, polymorphonuclear neutrophils; RA, room air; rHMGB1, recombinant HMGB1; ROS, reactive oxygen species; Hyperoxia; Macrophage; HMGB1; Hyperacetylation; Redox state
7.  Epithelial Cell Death Is an Important Contributor to Oxidant-mediated Acute Lung Injury 
Rationale: Acute lung injury and the acute respiratory distress syndrome are characterized by increased lung oxidant stress and apoptotic cell death. The contribution of epithelial cell apoptosis to the development of lung injury is unknown.
Objectives: To determine whether oxidant-mediated activation of the intrinsic or extrinsic apoptotic pathway contributes to the development of acute lung injury.
Methods: Exposure of tissue-specific or global knockout mice or cells lacking critical components of the apoptotic pathway to hyperoxia, a well-established mouse model of oxidant-induced lung injury, for measurement of cell death, lung injury, and survival.
Measurements and Main Results: We found that the overexpression of SOD2 prevents hyperoxia-induced BAX activation and cell death in primary alveolar epithelial cells and prolongs the survival of mice exposed to hyperoxia. The conditional loss of BAX and BAK in the lung epithelium prevented hyperoxia-induced cell death in alveolar epithelial cells, ameliorated hyperoxia-induced lung injury, and prolonged survival in mice. By contrast, Cyclophilin D–deficient mice were not protected from hyperoxia, indicating that opening of the mitochondrial permeability transition pore is dispensable for hyperoxia-induced lung injury. Mice globally deficient in the BH3-only proteins BIM, BID, PUMA, or NOXA, which are proximal upstream regulators of BAX and BAK, were not protected against hyperoxia-induced lung injury suggesting redundancy of these proteins in the activation of BAX or BAK.
Conclusions: Mitochondrial oxidant generation initiates BAX- or BAK-dependent alveolar epithelial cell death, which contributes to hyperoxia-induced lung injury.
doi:10.1164/rccm.201002-0181OC
PMCID: PMC3086743  PMID: 20959557
cell death; epithelium; Bcl-2 proteins; acute respiratory distress syndrome
8.  Deletion of Caveolin-1 Protects against Oxidative Lung Injury via Up-Regulation of Heme Oxygenase-1 
Acute lung injury (ALI) is a major cause of morbidity and mortality in critically ill patients. Hyperoxia causes lung injury in animals and humans, and is an established model of ALI. Caveolin-1, a major constituent of caveolae, regulates numerous biological processes, including cell death and proliferation. Here we demonstrate that caveolin-1–null mice (cav-1−/−) were resistant to hyperoxia-induced death and lung injury. Cav-1−/− mice sustained reduced lung injury after hyperoxia as determined by protein levels in bronchoalveolar lavage fluid and histologic analysis. Furthermore, cav-1−/− fibroblasts and endothelial cells and cav-1 knockdown epithelial cells resisted hyperoxia-induced cell death in vitro. Basal and inducible expression of the stress protein heme oxygenase-1 (HO-1) were markedly elevated in lung tissue or fibroblasts from cav-1−/− mice. Hyperoxia induced the physical interaction between cav-1 and HO-1 in fibroblasts assessed by co-immunoprecipitation studies, which resulted in attenuation of HO activity. Inhibition of HO activity with tin protoporphyrin-IX abolished the survival benefits of cav-1−/− cells and cav-1−/− mice exposed to hyperoxia. The cav-1−/− mice displayed elevated phospho-p38 mitogen-activated protein kinase (MAPK) and p38β expression in lung tissue/cells under basal conditions and during hyperoxia. Treatment with SB202190, an inhibitor of p38 MAPK, decreased hyperoxia-inducible HO-1 expression in wild-type and cav-1−/− fibroblasts. Taken together, our data demonstrated that cav-1 deletion protects against hyperoxia-induced lung injury, involving in part the modulation of the HO-1–cav-1 interaction, and the enhanced induction of HO-1 through a p38 MAPK–mediated pathway. These studies identify caveolin-1 as a novel component involved in hyperoxia-induced lung injury.
doi:10.1165/rcmb.2007-0323OC
PMCID: PMC2542454  PMID: 18323531
acute lung injury; acute respiratory distress syndrome; caveolin-1; heme oxygenase-1
9.  The Triterpenoid CDDO-Imidazolide Confers Potent Protection against Hyperoxic Acute Lung Injury in Mice 
Rationale: Oxygen supplementation (e.g., hyperoxia) is used to support critically ill patients with noninfectious and infectious acute lung injury (ALI); however, hyperoxia exposure can potentially further contribute to and/or perpetuate preexisting ALI. Thus, developing novel therapeutic agents to minimize the side effects of hyperoxia is essential to improve the health of patients with severe ALI and respiratory dysfunction. We have previously shown that mice with a genetic disruption of the Nrf2 transcription factor, which squelches cellular stress by up-regulating the induction of several antioxidant enzymes and proteins, have greater susceptibility to hyperoxic lung injury. Moreover, we have recently demonstrated that Nrf2-deficiency impairs the resolution of lung injury and inflammation after nonlethal hyperoxia exposure.
Objectives: To test the hypothesis that amplification of endogenous Nrf2 activity would prevent or dampen ALI induced by hyperoxia.
Methods: Here, we tested our hypothesis using a synthetic triterpenoid compound CDDO-imidazole (CDDO-Im) (1-[2-cyano-3-,12-dioxooleana-1,9(11)-dien-28-oyl] imidazole) in Nrf2-sufficient and Nrf2-deficient mice subjected to hyperoxia-induced ALI.
Measurements and Main Results: We demonstrate that oral administration of CDDO-Im at a dose of 30 μmol/kg body weight during the hyperoxic exposure is sufficient to markedly attenuate hyperoxia-induced ALI in Nrf2-sufficient but not Nrf2-deficient mice. This protection by the CDDO-Im against hyperoxic insult was accompanied by increased levels of Nrf2-regulated cytoprotective gene expression and reduced levels of DNA damage in the lung.
Conclusions: These results suggest that up-regulation of Nrf2 signaling by CDDO-Im or its analogs may provide a novel therapeutic strategy to minimize the adverse effects of hyperoxia.
doi:10.1164/rccm.200905-0670OC
PMCID: PMC2773914  PMID: 19679692
Nrf2; Keap1; antioxidants; stress response
10.  DISRUPTION OF NRF2 IMPAIRS THE RESOLUTION OF HYPEROXIA-INDUCED ACUTE LUNG INJURY AND INFLAMMATION IN MICE 
Summary
Aberrant tissue repair and persistent inflammation following oxidant-mediated acute lung injury (ALI) can lead to the development and progression of various pulmonary diseases, but the mechanisms underlying these processes remain unclear. Hyperoxia is widely used in the treatment of pulmonary diseases, but the effects of this oxidant exposure in patients undergoing recovery from ALI are not clearly understood. Nrf2 has emerged as a crucial transcription factor that regulates oxidant stress through the induction of several detoxifying enzymes and other proteins. Using an experimental model of hyperoxia-induced ALI (HALI), we have examined the role of oxidant stress in resolving lung injury and inflammation. We found that when exposed to sub-lethal (72 h) hyperoxia, Nrf2-deficient, but not wild-type mice, succumbed to death during recovery. When both genotypes were exposed to a shorter period of HALI (48 h), the lungs of Nrf2-deficient mice during recovery exhibited persistent cellular injury, impaired alveolar and endothelial cell regeneration, and persistent cellular infiltration by macrophages and lymphocytes. GSH supplementation in Nrf2-deficient mice immediately after hyperoxia remarkably restored their ability to recover from hyperoxia-induced damage in a manner similar to that of wild-type mice. Thus, the results of the present study indicate that the Nrf2-regulated transcriptional response, and particularly GSH synthesis, is critical for lung tissue repair and the resolution of inflammation in vivo and suggests that a dysfunctional Nrf2-GSH pathway may compromise these processes in vivo.
doi:10.4049/jimmunol.0804248
PMCID: PMC2820248  PMID: 19454723
Oxidative stress; Nrf2; acute lung injury; DNA injury
11.  Hyperoxia causes angiopoietin 2–mediated acute lung injury and necrotic cell death 
Nature medicine  2006;12(11):1286-1293.
The angiogenic growth factor angiopoietin 2 (Ang2) destabilizes blood vessels, enhances vascular leak and induces vascular regression and endothelial cell apoptosis. We considered that Ang2 might be important in hyperoxic acute lung injury (ALI). Here we have characterized the responses in lungs induced by hyperoxia in wild-type and Ang2–/– mice or those given either recombinant Ang2 or short interfering RNA (siRNA) targeted to Ang2. During hyperoxia Ang2 expression is induced in lung epithelial cells, while hyperoxia-induced oxidant injury, cell death, inflammation, permeability alterations and mortality are ameliorated in Ang2–/– and siRNA-treated mice. Hyperoxia induces and activates the extrinsic and mitochondrial cell death pathways and activates initiator and effector caspases through Ang2-dependent pathways in vivo. Ang2 increases inflammation and cell death during hyperoxia in vivo and stimulates epithelial necrosis in hyperoxia in vitro. Ang2 in plasma and alveolar edema fluid is increased in adults with ALI and pulmonary edema. Tracheal Ang2 is also increased in neonates that develop bronchopulmonary dysplasia. Ang2 is thus a mediator of epithelial necrosis with an important role in hyperoxic ALI and pulmonary edema.
doi:10.1038/nm1494
PMCID: PMC2768268  PMID: 17086189
12.  Effect of recombinant IL-10 on cultured fetal rat alveolar type II cells exposed to 65%-hyperoxia 
Respiratory Research  2011;12(1):68.
Background
Hyperoxia plays an important role in the genesis of lung injury in preterm infants. Although alveolar type II cells are the main target of hyperoxic lung injury, the exact mechanisms whereby hyperoxia on fetal alveolar type II cells contributes to the genesis of lung injury are not fully defined, and there have been no specific measures for protection of fetal alveolar type II cells.
Objective
The aim of this study was to investigate (a) cell death response and inflammatory response in fetal alveolar type II cells in the transitional period from canalicular to saccular stages during 65%-hyperoxia and (b) whether the injurious stimulus is promoted by creating an imbalance between pro- and anti-inflammatory cytokines and (c) whether treatment with an anti-inflammatory cytokine may be effective for protection of fetal alveolar type II cells from injury secondary to 65%-hyperoxia.
Methods
Fetal alveolar type II cells were isolated on embryonic day 19 and exposed to 65%-oxygen for 24 h and 36 h. Cells in room air were used as controls. Cellular necrosis was assessed by lactate dehydrogenase-release and flow cytometry, and apoptosis was analyzed by TUNEL assay and flow cytometry, and cell proliferation was studied by BrdU incorporation. Release of cytokines including VEGF was analyzed by ELISA, and their gene expressions were investigated by qRT-PCR.
Results
65%-hyperoxia increased cellular necrosis, whereas it decreased cell proliferation in a time-dependent manner compared to controls. 65%-hyperoxia stimulated IL-8-release in a time-dependent fashion, whereas the anti-inflammatory cytokine, IL-10, showed an opposite response. 65%-hyperoxia induced a significant decrease of VEGF-release compared to controls, and similar findings were observed on IL-8/IL-10/VEGF genes expression. Preincubation of recombinant IL-10 prior to 65%-hyperoxia decreased cellular necrosis and IL-8-release, and increased VEGF-release and cell proliferation significantly compared to hyperoxic cells without IL-10.
Conclusions
The present study provides an experimental evidence that IL-10 may play a potential role in protection of fetal alveolar type II cells from injury induced by 65%-hyperoxia.
doi:10.1186/1465-9921-12-68
PMCID: PMC3114733  PMID: 21609457
13.  Maturational differences in lung NF-κB activation and their role in tolerance to hyperoxia 
Journal of Clinical Investigation  2004;114(5):669-678.
Neonatal rodents are more tolerant to hyperoxia than adults. We determined whether maturational differences in lung NF-κB activation could account for the differences. After hyperoxic exposure (O2 > 95%), neonatal (<12 hours old) lung NF-κB binding was increased and reached a maximum between 8 and 16 hours, whereas in adults no changes were observed. Additionally, neonatal NF-κB/luciferase transgenic mice (incorporating 2 NF-κB consensus sequences driving luciferase gene expression) demonstrated enhanced in vivo NF-κB activation after hyperoxia in real time. In the lungs of neonates, there was a propensity toward NF-κB activation as evidenced by increased lung I-κB kinase protein levels, I-κBα phosphorylation, β-transducin repeat–containing protein levels, and total I-κBα degradation. Increased lung p-JNK immunoreactive protein was observed only in the adult lung. Inhibition of pI-κBα by BAY 11-7085 resulted in decreased Bcl-2 protein levels in neonatal lung homogenates and decreased cell viability in lung primary cultures after hyperoxic exposure. Furthermore, neonatal p50-null mutant (p50–/–) mice showed increased lung DNA degradation and decreased survival in hyperoxia compared with WT mice. These data demonstrate that there are maturational differences in lung NF-κB activation and that enhanced NF-κB may serve to protect the neonatal lung from acute hyperoxic injury via inhibition of apoptosis.
doi:10.1172/JCI200419300
PMCID: PMC514581  PMID: 15343385
14.  Conditional overexpression of TGFβ1 promotes pulmonary inflammation, apoptosis and mortality via TGFβR2 in the developing mouse lung 
Respiratory Research  2015;16(1):4.
Background
Earlier studies have reported that transforming growth factor beta 1(TGFβ1) is a critical mediator of hyperoxia-induced acute lung injury (HALI) in developing lungs, leading to impaired alveolarization and a pulmonary phenotype of bronchopulmonary dysplasia (BPD). However, the mechanisms responsible for the TGFβ1-induced inflammatory signals that lead to cell death and abnormal alveolarization are poorly understood. We hypothesized that TGFβ1 signaling via TGFβR2 is necessary for the pathogenesis of the BPD pulmonary phenotype resulting from HALI.
Methods
We utilized lung epithelial cell-specific TGFβ1 overexpressing transgenic and TGFβR2 null mutant mice to evaluate the effects on neonatal mortality as well as pulmonary inflammation and apoptosis in developing lungs. Lung morphometry was performed to determine the impaired alveolarization and multicolor flow cytometry studies were performed to detect inflammatory macrophages and monocytes in lungs. Apoptotic cell death was measured with TUNEL assay, immunohistochemistry and western blotting and protein expression of angiogenic mediators were also analyzed.
Results
Our data reveals that increased TGFβ1 expression in newborn mice lungs leads to increased mortality, macrophage and immature monocyte infiltration, apoptotic cell death specifically in Type II alveolar epithelial cells (AECs), impaired alveolarization, and dysregulated angiogenic molecular markers.
Conclusions
Our study has demonstrated the potential role of inhibition of TGFβ1 signaling via TGFβR2 for improved survival, reduced inflammation and apoptosis that may provide insights for the development of potential therapeutic strategies targeted against HALI and BPD.
doi:10.1186/s12931-014-0162-6
PMCID: PMC4307226  PMID: 25591994
Transforming growth factor; Oxygen; Inflammation; Cell death; Angiopoietin; Newborn; Pulmonary; Bronchopulmonary dysplasia
15.  Extracellular BCL2 Proteins Are Danger-Associated Molecular Patterns That Reduce Tissue Damage in Murine Models of Ischemia-Reperfusion Injury 
PLoS ONE  2010;5(2):e9103.
Background
Ischemia-reperfusion (I/R) injury contributes to organ dysfunction in a variety of clinical disorders, including myocardial infarction, stroke, organ transplantation, and hemorrhagic shock. Recent investigations have demonstrated that apoptosis as an important mechanism of cell death leading to organ dysfunction following I/R. Intracellular danger-associated molecular patterns (DAMPs) released during cell death can activate cytoprotective responses by engaging receptors of the innate immune system.
Methodology/Principal Findings
Ischemia was induced in the mouse hind limb by tourniquet or in the heart by coronary artery ligation. Reperfusion injury of skeletal or cardiac muscle was markedly reduced by intraperitoneal or subcutaneous injection of recombinant human (rh)BCL2 protein or rhBCL2-related protein A1 (BCL2A1) (50 ng/g) given prior to ischemia or at the time of reperfusion. The cytoprotective activity of extracellular rhBCL2 or rhBCL2A1 protein was mapped to the BH4 domain, as treatment with a mutant BCL2 protein lacking the BH4 domain was not protective, whereas peptides derived from the BH4 domain of BCL2 or the BH4-like domain of BCL2A1 were. Protection by extracellular rhBCL2 or rhBCL2A1 was associated with a reduction in apoptosis in skeletal and cardiac muscle following I/R, concomitant with increased expression of endogenous mouse BCL2 (mBCL2) protein. Notably, treatment with rhBCL2A1 protein did not protect mice deficient in toll-like receptor-2 (TLR2) or the adaptor protein, myeloid differentiation factor-88 (MyD88).
Conclusions/Significance
Treatment with cytokine-like doses of rhBCL2 or rhBCL2A1 protein or BH4-domain peptides reduces apoptosis and tissue injury following I/R by a TLR2-MyD88-dependent mechanism. These findings establish a novel extracellular cytoprotective activity of BCL2 BH4-domain proteins as potent cytoprotective DAMPs.
doi:10.1371/journal.pone.0009103
PMCID: PMC2816997  PMID: 20161703
16.  Epithelial Ablation of Bcl-XL Increases Sensitivity to Oxygen without Disrupting Lung Development 
Recent studies indicate that the antiapoptotic Bcl-XL, one of five isoforms expressed by the Bcl-X gene, protects a variety of cell lines exposed to hyperoxia. However, its role in lung development and protection against oxidative stress in vivo is not known. Here, we show Bcl-XL is the predominant isoform expressed in the lung, and the only isoform detected in respiratory epithelium. Because loss of Bcl-XL is embryonically lethal, Bcl-XL was ablated throughout the respiratory epithelium by mating mice with a floxed exon II of the Bcl-X gene with mice expressing Cre under control of the surfactant protein-C promoter. Interestingly, the loss of Bcl-XL in respiratory epithelium was perinatally lethal in approximately 50% of the expected offspring. However, some adult mice lacking the gene were obtained. The epithelial-specific ablation of Bcl-XL did not disrupt pulmonary function, the expression of epithelial cell–specific markers, or lung development. However, it shifted the lung toward a proapoptotic state, defined by a reduction in antiapoptotic Mcl-1, an increase in proapoptotic Bak, and increased sensitivity of the respiratory epithelium to hyperoxia. Intriguingly, increased 8-oxoguanine lesions seen during hyperoxia were also evident as lungs transitioned to room air at birth, a time when perinatal lethality in some mice lacking Bcl-XL was observed. These findings reveal that the epithelial-specific expression of Bcl-XL is not required for proper lung development, but functions to protect respiratory epithelial cells against oxygen-induced toxicity, such as during hyperoxia and the lung's first exposure to ambient air.
doi:10.1165/rcmb.2009-0165OC
PMCID: PMC2933553  PMID: 19880821
apoptosis; development; oxidative stress
17.  Hyperoxia-Induced LC3B Interacts with the Fas Apoptotic Pathway in Epithelial Cell Death 
Epithelial cell death plays a critical role in hyperoxia-induced lung injury. We investigated the involvement of the autophagic marker microtubule-associated protein-1 light chain-3B (LC3B) in epithelial cell apoptosis after hyperoxia. Prolonged hyperoxia (>95% O2), which causes characteristic lung injury in mice, activated morphological and biochemical markers of autophagy. Hyperoxia induced the time-dependent expression and conversion of LC3B-I to LC3B-II in mouse lung in vivo and in cultured epithelial cells (Beas-2B, human bronchial epithelial cells) in vitro. Hyperoxia increased autophagosome formation in Beas-2B cells, as evidenced by electron microscopy and increased GFP-LC3 puncta. The augmented LC3B level after hyperoxia was transcriptionally regulated and dependent in part on the c-Jun N-terminal kinase pathway. We hypothesized that LC3B plays a regulatory role in hyperoxia-induced epithelial apoptosis. LC3B siRNA promoted hyperoxia-induced cell death in epithelial cells, whereas overexpression of LC3B conferred cytoprotection after hyperoxia. The autophagic protein LC3B cross-regulated the Fas apoptotic pathway by physically interacting with the components of death-inducing signaling complex. This interaction was mediated by caveolin-1 tyrosine 14, which is a known target of phosphorylation induced by hyperoxia. Taken together, hyperoxia-induced LC3B activation regulates the Fas apoptotic pathway and thus confers cytoprotection in lung epithelial cells. The interaction of LC3B and Fas pathways requires cav-1.
doi:10.1165/rcmb.2009-0415OC
PMCID: PMC3359946  PMID: 22095627
apoptosis; autophagy; hyperoxia; lung injury; caveolin-1
18.  The Fas System Confers Protection against Alveolar Disruption in Hyperoxia-Exposed Newborn Mice 
The functional significance of the Fas/Fas-ligand (FasL) system in hyperoxia-induced lung injury and alveolar disruption in newborn lungs in vivo remains undetermined. To assess the role of the Fas/FasL system, we compared the effects of hyperoxia (95% O2 from birth to Postnatal Day [P]7) in Fas-deficient lpr mice and wild-type mice. Alveolar disruption was more severe in hyperoxic lpr mice than in wild-type mice. In addition, a transient alveolarization defect was noted in normoxic lpr mice. Hyperoxia induced marked up-regulation of pulmonary Fas expression in wild-type mice, as well as elevated mRNA levels of pro-apoptotic Bax, Bad, and Bak. Pulmonary apoptotic activity was similar in hyperoxic wild-type and lpr mice. In contrast, lung growth and proliferation, assessed by stereologic volumetry and Ki67 proliferation studies, were significantly higher in hyperoxic wild-type mice compared with lpr mice, suggesting the Fas/FasL system has a pro-proliferative role in hyperoxic conditions. Levels of the prosurvival MAPkinase, pERK1/2, were significantly higher in hyperoxic wild-type mice compared with lpr mice, while pAkt levels were similar. These data suggest that the primary role of the Fas/FasL system in hyperoxic newborn lungs is pro-proliferative, rather than pro-apoptotic, and likely mediated through a Fas-ERK1/2 pathway. Fas-induced proliferation and lung growth in hyperoxic newborn lungs may counteract, in part, the detrimental effects of apoptosis mediated by non-Fas pathways, such as pro-apoptotic Bax/Bcl-2 family members. The capacity of the Fas/FasL signaling pathway to mediate protective rather than destructive functions in hyperoxic newborn lungs highlights the versatility of this complex pathway.
doi:10.1165/rcmb.2008-0052OC
PMCID: PMC2586047  PMID: 18587053
CD95; oxygen toxicity; apoptosis; programmed cell death; bronchopulmonary dysplasia
19.  Nitric Oxide Inhibits Hyperoxia-induced NF-κB Activation in Neonatal Pulmonary Microvascular Endothelial Cells 
Pediatric research  2010;68(6):484-489.
Inhaled nitric oxide may be protective against hyperoxic injury in the premature lung, but the mechanism is unknown. We hypothesized that nitric oxide (NO) would prevent hyperoxia-induced NF-κB activation in neonatal pulmonary microvascular endothelial cells (HPMEC) and prevent the upregulation of target genes. Following hyperoxic exposure (O2> 95%), nuclear NF-κB consensus sequence binding increased and was associated with IκBα degradation. Both of these findings were prevented by exposure to NO. Furthermore, ICAM-1 mRNA and protein levels increased in cells exposed to hyperoxia, an effect abrogated by NO. To evaluate the potentially toxic effect of NO plus hyperoxia, cell viability and proliferation were assessed. Cells exposed to NO plus hyperoxia demonstrated improved survival as measured by trypan blue exclusion when compared to cells exposed to hyperoxia alone. These differences in cell death could not be attributed to apoptosis measured by caspase-3 activity. Finally, cellular proliferation inhibited by hyperoxia was rescued by concurrent exposure to NO. These data demonstrate that NO prevents hyperoxia-induced NF-κB activation in HPMEC and results in decreased expression of adhesion molecules and decreased cellular toxicity. This may help explain the protective effects of NO on hyperoxic injury in the developing lung vasculature.
doi:10.1203/PDR.0b013e3181f917b0
PMCID: PMC3129417  PMID: 20805787
20.  Bcl-XL is the primary mediator of p21 protection against hyperoxia-induced cell death 
Experimental lung research  2010;37(2):82-91.
A tight balance between anti- and pro-apoptotic members of the Bcl-2 family controls cell survival and death. Exposure to hyperoxia shifts this balance towards a pro-death state that ultimately activates Bak and Bax-dependent cell death. Mechanisms underlying this shift are undefined; however, the cell cycle inhibitor p21 delays the loss of anti-apoptotic Mcl-1 and Bcl-XL, and protects against hyperoxia. Here, H1299 human lung adenocarcinoma cells are used to investigate how these and other members of the Bcl-2 family cooperate with p21 to protect against hyperoxia. Expression of anti-apoptotic Mcl-1 and Bcl-XL, but not Bcl-2 or A1 declined during hyperoxia while pro-apoptotic Bak, but not Bax increased. Conditional over-expression of p21 selectively delayed the loss of Mcl-1 and Bcl-XL, without affecting expression of the other members. SiRNA knockdown of Mcl-1 and Bcl-XL sensitized cells to hyperoxia, but only the loss of Bcl-XL ablated the protective effects of p21. Conversely, over-expression of Mcl-1 and Bcl-XL protected against hyperoxia, but only Bcl-XL bound Bak and Bax. Altogether, our data suggest Bcl-XL is the primary mediator by which p21 protects against hyperoxia-induced Bak/Bax-dependent cell death.
doi:10.3109/01902148.2010.521617
PMCID: PMC3749887  PMID: 21128858
apoptosis; Bcl-2 proteins; cell cycle inhibitor p21; hyperoxia; necrosis
21.  Aerosolized Human Extracellular Superoxide Dismutase Prevents Hyperoxia-Induced Lung Injury 
PLoS ONE  2011;6(10):e26870.
An important issue in critical care medicine is the identification of ways to protect the lungs from oxygen toxicity and reduce systemic oxidative stress in conditions requiring mechanical ventilation and high levels of oxygen. One way to prevent oxygen toxicity is to augment antioxidant enzyme activity in the respiratory system. The current study investigated the ability of aerosolized extracellular superoxide dismutase (EC-SOD) to protect the lungs from hyperoxic injury. Recombinant human EC-SOD (rhEC-SOD) was produced from a synthetic cassette constructed in the methylotrophic yeast Pichia pastoris. Female CD-1 mice were exposed in hyperoxia (FiO2>95%) to induce lung injury. The therapeutic effects of EC-SOD and copper-zinc SOD (CuZn-SOD) via an aerosol delivery system for lung injury and systemic oxidative stress at 24, 48, 72 and 96 h of hyperoxia were measured by bronchoalveolar lavage, wet/dry ratio, lung histology, and 8-oxo-2′-deoxyguanosine (8-oxo-dG) in lung and liver tissues. After exposure to hyperoxia, the wet/dry weight ratio remained stable before day 2 but increased significantly after day 3. The levels of oxidative biomarker 8-oxo-dG in the lung and liver were significantly decreased on day 2 (P<0.01) but the marker in the liver increased abruptly after day 3 of hyperoxia when the mortality increased. Treatment with aerosolized rhEC-SOD increased the survival rate at day 3 under hyperoxia to 95.8%, which was significantly higher than that of the control group (57.1%), albumin treated group (33.3%), and CuZn-SOD treated group (75%). The protective effects of EC-SOD against hyperoxia were further confirmed by reduced lung edema and systemic oxidative stress. Aerosolized EC-SOD protected mice against oxygen toxicity and reduced mortality in a hyperoxic model. The results encourage the use of an aerosol therapy with EC-SOD in intensive care units to reduce oxidative injury in patients with severe hypoxemic respiratory failure, including acute respiratory distress syndrome (ARDS).
doi:10.1371/journal.pone.0026870
PMCID: PMC3202580  PMID: 22046389
22.  Extracellular Administration of BCL2 Protein Reduces Apoptosis and Improves Survival in a Murine Model of Sepsis 
PLoS ONE  2011;6(2):e14729.
Background
Severe sepsis and septic shock are major causes of morbidity and mortality worldwide. In experimental sepsis there is prominent apoptosis of various cell types, and genetic manipulation of death and survival pathways has been shown to modulate organ injury and survival.
Methodology/Principal Findings
We investigated the effect of extracellular administration of two anti-apoptotic members of the BCL2 (B-cell lymphoma 2) family of intracellular regulators of cell death in a murine model of sepsis induced by cecal ligation and puncture (CLP). We show that intraperitoneal injection of picomole range doses of recombinant human (rh) BCL2 or rhBCL2A1 protein markedly improved survival as assessed by surrogate markers of death. Treatment with rhBCL2 or rhBCL2A1 protein significantly reduced the number of apoptotic cells in the intestine and heart following CLP, and this was accompanied by increased expression of endogenous mouse BCL2 protein. Further, mice treated with rhBCL2A1 protein showed an increase in the total number of neutrophils in the peritoneum following CLP with reduced neutrophil apoptosis. Finally, although neither BCL2 nor BCL2A1 are a direct TLR2 ligand, TLR2-null mice were not protected by rhBCL2A1 protein, indicating that TLR2 signaling was required for the protective activity of extracellularly adminsitered BCL2A1 protein in vivo.
Conclusions/Significance
Treatment with rhBCL2A1 or rhBCL2 protein protects mice from sepsis by reducing apoptosis in multiple target tissues, demonstrating an unexpected, potent activity of extracellularly administered BCL2 BH4-domain proteins.
doi:10.1371/journal.pone.0014729
PMCID: PMC3044724  PMID: 21390214
23.  The Inflammasome Mediates Hyperoxia-Induced Alveolar Cell Permeability 
A hallmark of hyperoxic acute lung injury is the influx of inflammatory cells to lung tissue and the production of proinflammatory cytokines, such as IL-1β; however, the mechanisms connecting hyperoxia and the inflammatory response to lung damage is not clear. The inflammasome protein complex activates caspase-1 to promote the processing and secretion of proinflammatory cytokines. We hypothesized that hyperoxia-induced K+ efflux activates the inflammasome via the purinergic P2X7 receptor to cause inflammation and hyperoxic acute lung injury. To test this hypothesis, we characterized the expression and activation of inflammasome components in primary murine alveolar macrophages exposed to hyperoxia (95% oxygen and 5% CO2) in vitro, and in alveolar macrophages isolated from mice exposed to hyperoxia (100% oxygen). Our results showed that hyperoxia increased K+ efflux, inflammasome formation, release of proinflammatory cytokines, and induction of caspase-1 and IL-1β cleavage both in vitro and in vivo. The P2X7 agonist ATP enhanced hyperoxia-induced inflammasome activation, whereas the P2X7 antagonist, oxidized ATP, inhibited hyperoxia induced inflammasome activation. In addition, when ATP was scavenged with apyrase, hyperoxia-induced inflammasome activation was significantly decreased. Furthermore, short hairpin RNA silencing of inflammasome components abrogated hyperoxia-induced secretion of proinflammatory cytokines in vitro. These results suggest that hyperoxia induces K+ efflux through the P2X7 receptor, leading to inflammasome activation and secretion of proinflammatory cytokines. These events would affect the permeability of the alveolar epithelium and ultimately lead to epithelial barrier dysfunction and cell death.
doi:10.4049/jimmunol.0902766
PMCID: PMC3780794  PMID: 20375306
24.  Targeted lung expression of interleukin-11 enhances murine tolerance of 100% oxygen and diminishes hyperoxia-induced DNA fragmentation. 
Journal of Clinical Investigation  1998;101(9):1970-1982.
Acute lung injury is a frequent and treatment-limiting consequence of therapy with hyperoxic gas mixtures. To determine if IL-11 is protective in oxygen toxicity, we compared the effects of 100% O2 on transgenic mice that overexpress IL-11 in the lung and transgene (-) controls. IL-11 markedly enhanced survival in 100% O2 with 100% of transgene (-) animals dying within 72-96 h and > 90% of transgene (+) animals surviving for more than 10 d. This protection was associated with markedly diminished alveolar-capillary protein leak, endothelial and epithelial membrane injury, lipid peroxidation, and pulmonary neutrophil recruitment. Significant differences in copper zinc superoxide dismutase and catalase activities were not noted and the levels of total, reduced and oxidized glutathione were similar in transgene (+) and (-) animals. Glutathione reductase, glutathione peroxidase, and manganese superoxide dismutase activities were slightly higher in transgene (+) as versus (-) mice after 100% O2 exposure, and IL-11 diminished hyperoxia-induced expression of IL-1 and TNF. Hyperoxia also caused cell death with DNA fragmentation in the lungs of transgene (-) animals and IL-11 markedly diminished this cell death response. These studies demonstrate that IL-11 markedly diminishes hyperoxic lung injury. They also demonstrate this protection is associated with small changes in lung antioxidants, diminished hyperoxia-induced IL-1 and TNF production, and markedly suppressed hyperoxia-induced DNA fragmentation.
PMCID: PMC508784  PMID: 9576762
25.  Hyperoxic Brain Effects Are Normalized by Addition of CO2 
PLoS Medicine  2007;4(5):e173.
Background
Hyperoxic ventilation (>21% O2) is widely used in medical practice for resuscitation, stroke intervention, and chronic supplementation. However, despite the objective of improving tissue oxygen delivery, hyperoxic ventilation can accentuate ischemia and impair that outcome. Hyperoxia results in, paradoxically, increased ventilation, which leads to hypocapnia, diminishing cerebral blood flow and hindering oxygen delivery. Hyperoxic delivery induces other systemic changes, including increased plasma insulin and glucagon levels and reduced myocardial contractility and relaxation, which may derive partially from neurally mediated hormonal and sympathetic outflow. Several cortical, limbic, and cerebellar brain areas regulate these autonomic processes. The aim of this study was to assess recruitment of these regions in response to hyperoxia and to determine whether any response would be countered by addition of CO2 to the hyperoxic gas mixture.
Methods and Findings
We studied 14 children (mean age 11 y, range 8–15 y). We found, using functional magnetic resonance imaging, that 2 min of hyperoxic ventilation (100% O2) following a room air baseline elicited pronounced responses in autonomic and hormonal control areas, including the hypothalamus, insula, and hippocampus, throughout the challenge. The addition of 5% CO2 to 95% O2 abolished responses in the hypothalamus and lingual gyrus, substantially reduced insular, hippocampal, thalamic, and cerebellar patterns in the first 48 s, and abolished signals in those sites thereafter. Only the dorsal midbrain responded to hypercapnia, but not hyperoxia.
Conclusions
In this group of children, hyperoxic ventilation led to responses in brain areas that modify hypothalamus-mediated sympathetic and hormonal outflow; these responses were diminished by addition of CO2 to the gas mixture. This study in healthy children suggests that supplementing hyperoxic administration with CO2 may mitigate central and peripheral consequences of hyperoxia.
Hyperoxic ventilation leads to responses in brain areas that modify hypothalamus-mediated sympathetic and hormonal outflow; these responses can be diminished by addition of CO2 to the gas mixture.
Editors' Summary
Background.
All cells in the human body need oxygen (O2) to keep them alive. O2 is absorbed into the blood from the air by the lungs (which also release carbon dioxide [CO2], a waste product of cells, from the blood into the air). The blood then delivers O2 to the rest of the body. For healthy people, breathing air (which contains 21% O2) is sufficient to keep their tissues healthy. But there are medical situations in which O2 delivery to tissues needs improving. For example, during resuscitation or after a stroke when the O2 supply to a part of the brain is disrupted. Premature babies often need help with O2 delivery because their immature lungs don't absorb O2 efficiently. In situations like these, the O2 supply can be increased by providing an O2-rich gas mixture to the lungs—so-called “hyperoxic (i.e., high O2) ventilation.” But, paradoxically, hyperoxic ventilation can make matters worse. Hyperoxia increases the exchange of air between the lungs and the atmosphere (hyperventilation), which reduces the CO2 level in the blood. This “hypocapnia,” i.e. low CO2, reduces the blood flow to the brain by narrowing the blood vessels. Hyperoxia also alters the heart rate and blood pressure and the blood levels of some hormones. It probably causes these changes by affecting the brain regions that control autonomic functions (body functions such as heart rate, insulin and other hormone release, sweating and gland action that are not controlled by conscious thought). All told, although hyperoxic ventilation saves lives, it can also have serious adverse effects. In premature babies, for example, although it is often essential for their survival, hyperoxic ventilation can cause serious heart muscle and brain injury or lung problems (bronchopulmonary dysplasia) if it is not carefully monitored.
Why Was This Study Done?
The addition of a little CO2 to the hyperoxic gas mix can reduce the adverse effects of hyperoxic ventilation on blood flow to the brain. However, it is unclear whether this alteration can also modify responses of brain areas that control autonomic functions and hormone release to hyperoxia. If it does, then CO2 supplementation could prevent those adverse effects of hyperoxic ventilation that affect the whole body. In this study, the researchers investigated whether hyperoxic ventilation increases neural responses in brain regions that regulate the activity of the hypothalamus (the part of the brain that controls autonomic bodily functions) and whether the addition of CO2 reduces these responses.
What Did the Researchers Do and Find?
The researchers used a technique called functional magnetic resonance imaging (fMRI) to measure the activity of different brain regions in 14 healthy young people (aged 8–15 years). Active regions of the brain draw more O2 out of the blood than inactive regions, and fMRI measures changes in blood O2 levels. fMRI images were obtained for all the study participants when they were breathing normal air and during two-minute challenges with 100% O2 or a 95% O2, 5% CO2 mix. Hyperoxic ventilation produced rapid and marked changes in the activity of brain areas involved in autonomic and hormonal control, including the hypothalamus and regions that control the hypothalamus. After the challenge with 95% O2, 5% CO2, these responses were either absent or greatly reduced in the brain regions that had responded to 100% O2.
What Do These Findings Mean?
These findings show that hyperoxic ventilation induces brain activity changes that are likely to affect autonomic functions and hormone release throughout the body. In addition, they show that the addition of CO2 to the gas mixture greatly diminishes these responses. Because the autonomic and hormonal changes induced by 100% O2 can potentially injure organs throughout the body, the addition of CO2 to hyperoxic gas mixtures could reduce many of the adverse effects of hyperoxic ventilation. These results, therefore, could influence how hyperoxic ventilation is used in medical practice. However, CO2 supplementation still needs to be tested in adults and newborn babies. Although the results presented here will probably hold true for adults, and both neonatal and developmental animal studies suggest that hyperoxia results in serious side effects in newborns over room air or hyperoxia with added CO2, the brain findings need to studied in babies, the portion of the population most likely to be treated with hyperoxic ventilation.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0040173
The American Lung Association has patient information on the lungs and lung diseases, including bronchopulmonary dysplasia (in English and Spanish)
The Medlineplus encyclopedia contains pages on hyperventilation and on premature babies, and links to other information on premature babies (in English and Spanish)
Wikipedia has pages on the lungs, oxygen toxicity, mechanical ventilation, and hypocapnia (note that Wikipedia is a free online encyclopedia that anyone can edit; available in several languages)
doi:10.1371/journal.pmed.0040173
PMCID: PMC1872042  PMID: 17518514

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