pPKCα mediated-HIF-1α activation related to the morphological modifications occurring in neonatal myocardial tissue in response to severe and mild hyperoxia

In premature babies birth an high oxygen level exposure can occur and newborn hyperoxia exposure can be associated with free radical oxygen release with impairment of myocardial function, while in adult animal models short exposure to hyperoxia seems to protect heart against ischemic injury. Thus, the mechanisms and consequences which take place after hyperoxia exposure are different and related to animals age. The aim of our work has been to analyze the role played by HIF-1α in the occurrence of the morphological modifications upon hyperoxia exposure in neonatal rat heart. Hyperoxia exposure induces connective compartment increase which seems to allow enhanced blood vessels growth. An increased hypoxia inducible factor-1α (HIF-1α) translocation and vascular endothelial growth factor (VEGF) expression has been found upon 95% oxygen exposure to induce morphological modifications. Upstream pPKC-α expression increase in newborn rats exposed to 95% oxygen can suggest PKC involvement in HIF-1α activation. Since nitric oxide synthase (NOS) are involved in heart vascular regulation, endothelial NOS (e-NOS) and inducible NOS (i-NOS) expression has been investigated: a lower eNOS and an higher iNOS expression has been found in newborn rats exposed to 95% oxygen related to the evidence that hyperoxia provokes a systemic vasoconstriction and to the iNOS pro-apoptotic action, respectively. The occurrence of apoptotic events, evaluated by TUNEL and Bax expression analyses, seems more evident in sample exposed to severe hyperoxia. All in all such results suggest that in newborn rats hyperoxia can trigger oxygen free radical mediated membrane injury through a pPKCα mediated HIF-1α signalling system, even though specificity of such response could be obtained by in vivo administration to the rats of specific inhibitors of PKCα. This intracellular signalling can switch molecular events leading to blood vessels development in parallel to pro-apoptotic events due to an immature anti-oxidant defensive system in newborn rat hearts.     

Sex differences in murine cardiac pathophysiology with hyperoxia exposure

Hyperoxia (>90% oxygen) is commonly implemented in mechanically ventilated patients. Reports suggest that hyperoxia is directly associated with in-hospital mortality in ventilated patients. Certain studies also show that mortality in women undergoing mechanical ventilation is significantly higher than that in men. Additionally, females are predisposed to certain cardiac electrophysiological risks, including QTc prolongation. In this study, we assessed the impact of hyperoxia in male and female mice (C57BL/6J) at age 8–10 weeks. On completion of either hyperoxia or normoxia exposures, physical, hemodynamic, biochemical, functional, electrophysiological, and molecular assessments were conducted. Hyperoxia-exposed mice lost a significant amount of body mass, compared with normoxia controls, in both sexes. However, while both genders developed brady-arrhythmia after hyperoxia exposure, female mice exhibited significantly reduced heart rates compared with males, with significantly elevated RR intervals. Additionally, 50% mortality was observed in females, whereas no mortality was reported in males. Furthermore, unlike in male mice, we observed no hypertrophy upon hyperoxia exposure in female mice. We reported that both hyperoxia-treated male and female mice exhibit significant hyperdynamic left ventricular ejection fraction, which is marked by % ejection fraction > 70 compared with the normoxia controls. We also noted significant reductions in stroke volume and cardiac output in both mice with hyperoxia. Surface ECG also demonstrated that hyperoxia exposure significantly augments RR, PR, QRS, QTc, and JT intervals in both sexes. Molecular analysis of left ventricular tissue demonstrated dysregulation of potassium ion channels in hyperoxia-treated males and females. In summary, we determined that sex differences are present with 72 hr hyperoxia exposure.     

Hyperoxia mediates acute lung injury and increased lethality in murine Legionella pneumonia: the role of apoptosis

Legionella pneumophila is a major cause of life-threatening pneumonia, which is characterized by a high incidence of acute lung injury and resultant severe hypoxemia. Mechanical ventilation using high oxygen concentrations is often required in the treatment of patients with L. pneumophila pneumonia. Unfortunately, oxygen itself may propagate various forms of tissue damage, including acute lung injury. The effect of hyperoxia as a cofactor in the course of L. pneumophila pneumonia is poorly understood. In this study, we show that exposure to hyperoxic conditions during the evolution of pneumonia results in a marked increase in lethality in mice with Legionella pneumonia. The enhanced lethality was associated with an increase in lung permeability, but not changes in either lung bacterial burden or leukocyte accumulation. Interestingly, accelerated apoptosis as evidenced by assessment of histone-DNA fragments and caspase-3 activity were noted in the infected lungs of mice exposed to hyperoxia. TUNEL staining of infected lung sections demonstrated increased apoptosis in hyperoxic mice, predominantly in macrophages and alveolar epithelial cells. In vitro exposure of primary murine alveolar epithelial cells to Legionella in conjunction with hyperoxia accelerated apoptosis and loss of barrier function. Fas-deficient mice demonstrated partial resistance to the lethal effects of Legionella infection induced by hyperoxia, which was associated with attenuated apoptosis in the lung. These results demonstrate that hyperoxia serves as an important cofactor for the development of acute lung injury and lethality in L. pneumophila pneumonia. Exaggerated apoptosis, in part through Fas-mediated signaling, may accelerate hyperoxia-induced acute lung injury in Legionella pneumonia.     

Oxygen radicals in cardiac surgery

Most cardiac surgical procedures require the use of prolonged induced myocardial ischemia. Experimental models of global myocardial ischemia which mimic cardiac surgical techniques have been developed to investigate the possibility of oxygen free radical development during prolonged myocardial ischemia or upon reperfusion. In such experiments, various free radical scavenging agents, including superoxide dismutase, catalase, and mannitol, have been shown to improve the tolerance of the heart to protracted global ischemia. Use of these agents has improved cardiac functional recovery and has attenuated the biochemical and structural changes which occur due to prolonged ischemia and reflow. In a recently developed porcine experimental model, the effects of preexisting regional myocardial ischemia with superimposed global ischemia and reperfusion have been studied, with free radical scavenging agents administered in an attempt to reduce myocardial infarction and improve regional functional recovery. In most such studies completed to date, free radical scavenging agents have resulted in better myocardial preservation, suggesting, at least indirectly, that there may be an oxygen free radical-mediated component of the ischemia-reperfusion injury seen in such models. Techniques for directly measuring myocardial oxygen free radical levels may allow for early clarification of the development of such toxic species in the clinical cardiac surgical setting.     

Hyperoxia disrupts pulmonary epithelial barrier in newborn rats via the deterioration of occludin and ZO-1

Background

Prolonged exposure to hyperoxia in neonates can cause hyperoxic acute lung injury (HALI), which is characterized by increased pulmonary permeability and diffuse infiltration of various inflammatory cells. Disruption of the epithelial barrier may lead to altered pulmonary permeability and maintenance of barrier properties requires intact epithelial tight junctions (TJs). However, in neonatal animals, relatively little is known about how the TJ proteins are expressed in the pulmonary epithelium, including whether expression of TJ proteins is regulated in response to hyperoxia exposure. This study determines whether changes in tight junctions play an important role in disruption of the pulmonary epithelial barrier during hyperoxic acute lung injury.

Methods

Newborn rats, randomly divided into two groups, were exposed to hyperoxia (95% oxygen) or normoxia for 1–7 days, and the severity of lung injury was assessed; location and expression of key tight junction protein occludin and ZO-1 were examined by immunofluorescence staining and immunobloting; messenger RNA in lung tissue was studied by RT-PCR; transmission electron microscopy study was performed for the detection of tight junction morphology.

Results

We found that different durations of hyperoxia exposure caused different degrees of lung injury in newborn rats. Treatment with hyperoxia for prolonged duration contributed to more serious lung injury, which was characterized by increased wet-to-dry ratio, extravascular lung water content, and bronchoalveolar lavage fluid (BALF):serum FD4 ratio. Transmission electron microscopy study demonstrated that hyperoxia destroyed the structure of tight junctions and prolonged hyperoxia exposure, enhancing the structure destruction. The results were compatible with pathohistologic findings. We found that hyperoxia markedly disrupted the membrane localization and downregulated the cytoplasm expression of the key tight junction proteins occludin and ZO-1 in the alveolar epithelium by immunofluorescence. The changes of messenger RNA and protein expression of occludin and ZO-1 in lung tissue detected by RT-PCR and immunoblotting were consistent with the degree of lung injury.

Conclusions

These data suggest that the disruption of the pulmonary epithelial barrier induced by hyperoxia is, at least in part, due to massive deterioration in the expression and localization of key TJ proteins.     

Molecular mechanisms of cardiomyocyte regeneration and therapeutic outlook

Differently from some lower vertebrates, which can completely regenerate their heart, in higher vertebrates cardiac injury generally leads to progressive failure. Induction of cycle re-entry in terminally differentiated cardiomyocytes and stem-cell transplantation are strategies to increase the regenerative potential of the heart. As experimental and clinical studies progress, demonstrating that adult stem-cell administration has a favorable impact on myocardial function, the identification of cardiac stem cells suggests that some endogenous repair mechanisms actually exist in the mammalian heart. However, a deeper understanding of the mechanism that drives cardiomyocyte proliferation and stem-cell-mediated cardiac repair is required to translate such strategies into effective therapies.     

Phosphodiesterase 4 inhibition attenuates persistent heart and lung injury by neonatal hyperoxia in rats

Phosphodiesterase (PDE) 4 inhibitors are potent anti-inflammatory drugs with antihypertensive properties, and their therapeutic role in bronchopulmonary dysplasia (BPD) is still controversial. We studied the role of PDE4 inhibition with piclamilast on normal lung development and its therapeutic value on pulmonary hypertension (PH) and right ventricular hypertrophy (RVH) in neonatal rats with hyperoxia-induced lung injury, a valuable model for premature infants with severe BPD. The cardiopulmonary effects of piclamilast treatment (5 mg·kg(-1)·day(-1)) were investigated in two models of experimental BPD: 1) daily treatment during continuous exposure to hyperoxia for 10 days; and 2) late treatment and injury-recovery in which pups were exposed to hyperoxia or room air for 9 days, followed by 9 or 42 days of recovery in room air combined with treatment started on day 6 of oxygen exposure until day 18. Prophylactic piclamilast treatment reduced pulmonary fibrin deposition, septum thickness, arteriolar wall thickness, arteriolar vascular smooth muscle cell proliferation and RVH, and prolonged survival. In the late treatment and injury-recovery model, hyperoxia caused persistent aberrant alveolar and vascular development, PH, and RVH. Treatment with piclamilast in both models reduced arteriolar wall thickness, attenuated RVH, and improved right ventricular function in the injury recovery model, but did not restore alveolarization or angiogenesis. Treatment with piclamilast did not show adverse cardiopulmonary effects in room air controls in both models. In conclusion, PDE4 inhibition attenuated and partially reversed PH and RVH, but did not advance alveolar development in neonatal rats with hyperoxic lung injury or affect normal lung and heart development.     

Sublethal hyperoxia impairs pulmonary innate immunity

Supplemental oxygen is often required in the treatment of critically ill patients. The impact of hyperoxia on pulmonary host defense is not well-established. We hypothesized that hyperoxia directly impairs pulmonary host defense, beyond effects on alveolar wall barrier function. C57BL/6 mice were kept in an atmosphere of >95% O(2) for 4 days followed by return to room air. This exposure does not lead to mortality in mice subsequently returned to room air. Mice kept in room air served as controls. Mice were intratracheally inoculated with Klebsiella pneumoniae and followed for survival. Alveolar macrophages (AM) were harvested by bronchoalveolar lavage after 4 days of in vivo hyperoxia for ex vivo experiments. Mortality from pneumonia increased significantly in mice exposed to hyperoxia compared with infected mice in room air. Burden of organisms in the lung and dissemination of infection were increased in the hyperoxia group whereas accumulation of inflammatory cells in the lung was impaired. Hyperoxia alone had no impact on AM numbers, viability, or ability to phagocytize latex microbeads. However, following in vivo hyperoxia, AM phagocytosis and killing of Gram-negative bacteria and production of TNF-alpha and IL-6 in response to LPS were significantly reduced. AM surface expression of Toll-like receptor-4 was significantly decreased following in vivo hyperoxia. Thus sublethal hyperoxia increases Gram-negative bacterial pneumonia mortality and has a significant adverse effect on AM host defense function. Impaired AM function due to high concentrations of supplemental oxygen may contribute to the high rate of ventilator-associated pneumonia seen in critically ill patients.     

Developmental differences in the responses of IL-6 and IL-13 transgenic mice exposed to hyperoxia

Our previous work has shown that adult mice with overexpression of IL-6 and IL-13 in the lung have enhanced survival in hyperoxia associated with reduced hyperoxia-induced lung injury and cell death. We hypothesized that there are developmental differences in these responses in the adult vs. the newborn (NB) animal, and these responses have clinical relevance in the human NB. We compared the responses to 100% O(2) of NB IL-6 and IL-13 transgenic mice with wild-type littermate controls by evaluating mortality, lung tissue TUNEL staining, and mRNA expression using RT-PCR. We used ELISA to measure IL-6 levels in tracheal aspirates from human neonates. Our results show that, in contrast to the cytoprotective effects in mature mice, IL-6 caused significantly increased mortality, DNA injury, caspases, cell death regulator and angiogenic factor expression in hyperoxia in the NB. Furthermore, tracheal aspirate levels of IL-6 were significantly increased in premature neonates with respiratory distress syndrome who had an adverse outcome (bronchopulmonary dysplasia/death). In contrast to the protective effects in adults, there was no survival advantage to the NB IL-13 mice in hyperoxia. These findings imply that caution should be exercised in extrapolating results from the adult to the NB.     

Cyclic stretch attenuates effects of hyperoxia on cell proliferation and viability in human alveolar epithelial cells

The treatment of severe lung disease often requires the use of high concentrations of oxygen coupled with the need for assisted ventilation, potentially exposing the pulmonary epithelium to both reactive oxygen species and nonphysiological cyclic stretch. Whereas prolonged hyperoxia is known to cause increased cell injury, cyclic stretch may result in either cell proliferation or injury depending on the pattern and degree of exposure to mechanical deformation. How hyperoxia and cyclic stretch interact to affect the pulmonary epithelium in vitro has not been previously investigated. This study was performed using human alveolar epithelial A549 cells to explore the combined effects of cyclic stretch and hyperoxia on cell proliferation and viability. Under room air conditions, cyclic stretch did not alter cell viability at any time point and increased cell number after 48 h compared with unstretched controls. After exposure to prolonged hyperoxia, cell number and [(3)H]thymidine incorporation markedly decreased, whereas evidence of oxidative stress and nonapoptotic cell death increased. The combination of cyclic stretch with hyperoxia significantly mitigated the negative effects of prolonged hyperoxia alone on measures of cell proliferation and viability. In addition, cyclic stretch resulted in decreased levels of oxidative stress over time in hyperoxia-exposed cells. Our results suggest that cyclic stretch, as applied in this study, can minimize the detrimental effects of hyperoxia on alveolar epithelial A549 cells.     

Proposed mechanism for neonatal rat tolerance to normobaric hyperoxia

Induction of two forms of superoxide dismutase, catalase and glutathione peroxidase, occurs very rapidly in neonatal rat lung tissue upon exposure of these animals to 94 + % normobaric oxygen. No such oxygen-mediated enzyme induction occurs in the lungs of adult rats. The aged-dependent pattern of enzyme induction correlates with the well-established age-dependent tolerance of neonatal rats to hyperoxia. Enzyme induction occurs in the lungs of neonates in only those species known to be resistant to oxygen-provoked lung damage. Compromise of oxygen-mediated enzyme induction predisposed the neonatal rats to pulmonary oxygen toxicity. These data have formed the basis of the proposal that oxygen induction of the superoxide dismutases catalase and glutathione peroxidase provides a vital part of the defense mechanism against oxygen toxicity. A biochemical mechanism of oxygen-provoked pulmonary damage has been elaborated to explain the role of each enzyme in the protection against oxygen and free radical toxicity.     

Depletion of pulmonary EC-SOD after exposure to hyperoxia

Extracellular superoxide dismutase (EC-SOD) is highly expressed in lung tissue. EC-SOD contains a heparin-binding domain that is sensitive to proteolysis. This heparin-binding domain is important in allowing EC-SOD to exist in relatively high concentrations in specific regions of the extracellular matrix and on cell surfaces. EC-SOD has been shown to protect the lung against hyperoxia in transgenic and knockout studies. This study tests the hypothesis that proteolytic clearance of EC-SOD from the lung during hyperoxia contributes to the oxidant-antioxidant imbalance that is associated with this injury. Exposure to 100% oxygen for 72 h resulted in a significant decrease in EC-SOD levels in the lungs and bronchoalveolar lavage fluid of mice. This correlated with a significant depletion of EC-SOD from the alveolar parenchyma as determined by immunofluorescence and immunohistochemistry. EC-SOD mRNA was unaffected by hyperoxia; however, there was an increase in the ratio of proteolyzed to uncut EC-SOD after hyperoxia, which suggests that hyperoxia depletes EC-SOD from the alveolar parenchyma by cutting the heparin-binding domain. This may enhance hyperoxic pulmonary injury by altering the oxidant-antioxidant balance in alveolar spaces.     

Streptozotocin directly impairs cardiac contractile function in isolated ventricular myocytes via a p38 map kinase-dependent oxidative stress mechanism

Streptozotocin (STZ) has long been used to induce experimental diabetes mellitus to study diabetic complications such as diabetic cardiomyopathy. However, direct impact of STZ on cardiac function is unknown. This study was designed to evaluate the cardiac contractile effect of STZ in isolated adult rat ventricular myocytes. Contractile properties were assessed with an IonOptix MyoCam system including peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR90), and maximal velocities of shortening/relengthening (+/-dL/dt). Intracellular Ca2+ handling was evaluated with the fluorescent dye fura-2. Acute exposure of STZ (10(-9)-10(-5) M) depressed PS, prolonged TR90, and decreased electrically stimulated intracellular Ca2+ rise in a concentration-dependent manner. TPS,+/-dL/dt, resting intracellular Ca2+ level, and intracellular Ca2+ clearing rate were unaffected. The STZ-induced mechanical alterations were alleviated by the antioxidant vitamin C (100 microM) and the p38 MAP kinase inhibitor SB203580 (1 microM). 2', 7'-Dichlorofluorescein diacetate staining revealed enhanced production of reactive oxygen species following STZ treatment, which was prevented by either vitamin C or SB203580. Collectively, our data provided convincing evidence that the tool drug for experimental diabetes STZ may itself cause deleterious cardiac contractile dysfunction via an oxidative stress and p38 MAP kinase-dependent mechanism. Thus, caution should be taken when assessing diabetic heart complications using STZ-induced diabetic models.     

Effect of intermittent hypoxia or hyperoxia on lung development in preterm rat neonates during constant oxygen therapy

Impaired lung development is a major negative factor in the survival of preterm neonates. The present study was aimed to investigate the impact of constant oxygen, intermittent hyperoxia, and hypoxia on the lung development in preterm rat neonates. Neonatal rats were exposed to 40% O₂ with or without brief hyperoxia episodes (95% O₂) or brief hypoxia episodes (10% O₂) from day 0 to day 14, or to room air. The body weight, radical alveolar count (RAC), and total antioxidant capacity (TAOC) were significantly lower whereas the lung coefficient and malondialdehyde (MDA) were significantly higher in the hyperoxia and hypoxia groups than the air control and constant oxygen group at day 7, day 14, and day 21 after birth. The lung function indexes were reduced by intermittent hyperoxia and hypoxia. In contrast, the constant oxygen therapy increased the lung function. HIF-1α and VEGF expression were significantly increased by hypoxia and decreased by hyperoxia. The constant oxygen therapy only decreased the HIF-1α expression at day 14 and 21. In summary, the constant oxygen treatment promoted lung function without affecting the antioxidative capacity in preterm rat neonates. While intermittent hyperoxia and hypoxia inhibited lung development, decreased antioxidative capacity, and dysregulated HIF-1α/VEGF signaling in preterm rat neonates.     

MicroRNA-192 suppresses cell proliferation and induces apoptosis in human rheumatoid arthritis fibroblast-like synoviocytes by downregulating caveolin 1

Heart disease causing cardiac cell death due to ischemia–reperfusion injury is a major cause of morbidity and mortality in the United States. Coronary heart disease and cardiomyopathies are the major cause for congestive heart failure, and thrombosis of the coronary arteries is the most common cause of myocardial infarction. Cardiac injury is followed by post-injury cardiac remodeling or fibrosis. Cardiac fibrosis is characterized by net accumulation of extracellular matrix proteins in the cardiac interstitium and results in both systolic and diastolic dysfunctions. It has been suggested by both experimental and clinical evidence that fibrotic changes in the heart are reversible. Hence, it is vital to understand the mechanism involved in the initiation, progression, and resolution of cardiac fibrosis to design anti-fibrotic treatment modalities. Animal models are of great importance for cardiovascular research studies. With the developing research field, the choice of selecting an animal model for the proposed research study is crucial for its outcome and translational purpose. Compared to large animal models for cardiac research, the mouse model is preferred by many investigators because of genetic manipulations and easier handling. This critical review is focused to provide insight to young researchers about the various mouse models, advantages and disadvantages, and their use in research pertaining to cardiac fibrosis and hypertrophy.     

Morphological alterations and NO-synthase expression in the heart after continuous light exposure of rats

Although exposure to continuous light is associated with hypertension and modulates the outcome of ischemia-reperfusion injury, less attention has been paid to its effects on cardiac morphology. We investigated whether 4-week exposure of experimental rats to continuous 24 h/day light can modify cardiac morphology, with focus on heart weight, fibrosis and collagen I/III ratio in correlation with NO-synthase expression. Two groups of male adult Wistar rats were studied: controls exposed to normal light/dark cycle (12 h/day light, 12 h/day dark) and rats exposed to continuous light. After 4 weeks of treatment the absolute and the relative heart weights were determined and myocardial fibrosis and collagen type I/III ratio were evaluated using picrosirius red staining. Endothelial and inducible NO-synthase expression was detected immunohistochemically. The exposure of rats to continuous light resulted in an increase of body weight with proportionally increased heart weight. Myocardial fibrosis remained unaffected but collagen I/III ratio increased. Neither endothelial nor inducible NO-synthase expression was altered in light-exposed rats. We conclude that the loss of structural homogeneity of the myocardium in favor of collagen type I might increase myocardial stiffness and contribute to functional alterations after continuous light exposure.     

Aerosolized human extracellular superoxide dismutase prevents hyperoxia-induced lung injury

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).     

Hyperoxia-induced signal transduction pathways in pulmonary epithelial cells

Mechanical ventilation with hyperoxia is necessary to treat critically ill patients. However, prolonged exposure to hyperoxia leads to the generation of excessive reactive oxygen species (ROS), which can cause acute inflammatory lung injury. One of the major effects of hyperoxia is the injury and death of pulmonary epithelium, which is accompanied by increased levels of pulmonary proinflammatory cytokines and excessive leukocyte infiltration. A thorough understanding of the signaling pathways leading to pulmonary epithelial cell injury/death may provide some insights into the pathogenesis of hyperoxia-induced acute inflammatory lung injury. This review focuses on epithelial responses to hyperoxia and some of the major factors regulating pathways to epithelial cell injury/death, and proinflammatory responses on exposure to hyperoxia. We discuss in detail some of the most interesting players, such as NF-kappaB, that can modulate both proinflammatory responses and cell injury/death of lung epithelial cells. A better appreciation for the functions of these factors will no doubt help us to delineate the pathways to hyperoxic cell death and proinflammatory responses.     

Lung injury caused by high tidal volume mechanical ventilation and hyperoxia is dependent on oxidant-mediated c-Jun NH2-terminal kinase activation

Both prolonged exposure to hyperoxia and large tidal volume mechanical ventilation can each independently cause lung injury. However, the combined impact of these insults is poorly understood. We recently reported that preexposure to hyperoxia for 12 h, followed by ventilation with large tidal volumes, induced significant lung injury and epithelial cell apoptosis compared with either stimulus alone (Makena et al. Am J Physiol Lung Cell Mol Physiol 299: L711-L719, 2010). The upstream mechanisms of this lung injury and apoptosis have not been clearly elucidated. We hypothesized that lung injury in this model was dependent on oxidative signaling via the c-Jun NH(2)-terminal kinases (JNK). We, therefore, evaluated lung injury and apoptosis in the presence of N-acetyl-cysteine (NAC) in both mouse and cell culture models, and we provide evidence that NAC significantly inhibited lung injury and apoptosis by reducing the production of ROS, activation of JNK, and apoptosis. To confirm JNK involvement in apoptosis, cells treated with a specific JNK inhibitor, SP600125, and subjected to preexposure to hyperoxia, followed by mechanical stretch, exhibited significantly reduced evidence of apoptosis. In conclusion, lung injury and apoptosis caused by preexposure to hyperoxia, followed by high tidal volume mechanical ventilation, induces ROS-mediated activation of JNK and mitochondrial-mediated apoptosis. NAC protects lung injury and apoptosis by inhibiting ROS-mediated activation of JNK and downstream proapoptotic signaling.