Hyperoxia-induced signal transduction pathways in pulmonary epithelial cells

Efficiency of exogenous surfactant combined with intravenous N-acetylcysteine in two-hit rodent model of ARDS

Accumulation of reactive oxygen species during hyperoxia together with secondary bacteria-induced inflammation leads to lung damage in ventilated critically ill patients. Antioxidant N-acetylcysteine (NAC) in combination with surfactant may improve lung function. We compared the efficacy of NAC combined with surfactant in the double-hit model of lung injury. Bacterial lipopolysaccharide (LPS) instilled intratracheally and hyperoxia were used to induce lung injury in Wistar rats. Animals were mechanically ventilated and treated intravenously with NAC alone or in combination with intratracheal surfactant (poractant alfa; PSUR+NAC). Control received saline. Lung functions, inflammatory markers, oxidative damage, total white blood cell (WBC) count and lung oedema were evaluated during 4 hrs. Administration of NAC increased total antioxidant capacity (TAC) and decreased IL-6. This effect was potentiated by the combined administration of surfactant and NAC. In addition, PSUR+NAC reduced the levels of TNFα, IL-1ß, and TAC compared to NAC only and improved lung injury score. The combination of exogenous surfactant with NAC suppresses lung inflammation and oxidative stress in the experimental double-hit model of lung injury.

Higher versus lower fractions of inspired oxygen or targets of arterial oxygenation for adults admitted to the intensive care unit

BACKGROUND

This is an updated review concerning 'Higher versus lower fractions of inspired oxygen or targets of arterial oxygenation for adults admitted to the intensive care unit'. Supplementary oxygen is provided to most patients in intensive care units (ICUs) to prevent global and organ hypoxia (inadequate oxygen levels). Oxygen has been administered liberally, resulting in high proportions of patients with hyperoxemia (exposure of tissues to abnormally high concentrations of oxygen). This has been associated with increased mortality and morbidity in some settings, but not in others. Thus far, only limited data have been available to inform clinical practice guidelines, and the optimum oxygenation target for ICU patients is uncertain. Because of the publication of new trial evidence, we have updated this review.

OBJECTIVES

To update the assessment of benefits and harms of higher versus lower fractions of inspired oxygen (FiO2) or targets of arterial oxygenation for adults admitted to the ICU.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, Science Citation Index Expanded, BIOSIS Previews, and LILACS. We searched for ongoing or unpublished trials in clinical trial registers and scanned the reference lists and citations of included trials. Literature searches for this updated review were conducted in November 2022.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that compared higher versus lower FiO2 or targets of arterial oxygenation (partial pressure of oxygen (PaO2), peripheral or arterial oxygen saturation (SpO2 or SaO2)) for adults admitted to the ICU. We included trials irrespective of publication type, publication status, and language. We excluded trials randomising participants to hypoxaemia (FiO2 below 0.21, SaO2/SpO2 below 80%, or PaO2 below 6 kPa) or to hyperbaric oxygen, and cross-over trials and quasi-randomised trials.

DATA COLLECTION AND ANALYSIS

Four review authors independently, and in pairs, screened the references identified in the literature searches and extracted the data. Our primary outcomes were all-cause mortality, the proportion of participants with one or more serious adverse events (SAEs), and quality of life. We analysed all outcomes at maximum follow-up. Only three trials reported the proportion of participants with one or more SAEs as a composite outcome. However, most trials reported on events categorised as SAEs according to the International Conference on Harmonisation Good Clinical Practice (ICH-GCP) criteria. We, therefore, conducted two analyses of the effect of higher versus lower oxygenation strategies using 1) the single SAE with the highest reported proportion in each trial, and 2) the cumulated proportion of participants with an SAE in each trial. Two trials reported on quality of life. Secondary outcomes were lung injury, myocardial infarction, stroke, and sepsis. No trial reported on lung injury as a composite outcome, but four trials reported on the occurrence of acute respiratory distress syndrome (ARDS) and five on pneumonia. We, therefore, conducted two analyses of the effect of higher versus lower oxygenation strategies using 1) the single lung injury event with the highest reported proportion in each trial, and 2) the cumulated proportion of participants with ARDS or pneumonia in each trial. We assessed the risk of systematic errors by evaluating the risk of bias in the included trials using the Risk of Bias 2 tool. We used the GRADEpro tool to assess the overall certainty of the evidence. We also evaluated the risk of publication bias for outcomes reported by 10b or more trials.

MAIN RESULTS

We included 19 RCTs (10,385 participants), of which 17 reported relevant outcomes for this review (10,248 participants). For all-cause mortality, 10 trials were judged to be at overall low risk of bias, and six at overall high risk of bias. For the reported SAEs, 10 trials were judged to be at overall low risk of bias, and seven at overall high risk of bias. Two trials reported on quality of life, of which one was judged to be at overall low risk of bias and one at high risk of bias for this outcome. Meta-analysis of all trials, regardless of risk of bias, indicated no significant difference from higher or lower oxygenation strategies at maximum follow-up with regard to mortality (risk ratio (RR) 1.01, 95% confidence interval (C)I 0.96 to 1.06; I2 = 14%; 16 trials; 9408 participants; very low-certainty evidence); occurrence of SAEs: the highest proportion of any specific SAE in each trial RR 1.01 (95% CI 0.96 to 1.06; I2 = 36%; 9466 participants; 17 trials; very low-certainty evidence), or quality of life (mean difference (MD) 0.5 points in participants assigned to higher oxygenation strategies (95% CI -2.75 to 1.75; I2 = 34%, 1649 participants; 2 trials; very low-certainty evidence)). Meta-analysis of the cumulated number of SAEs suggested benefit of a lower oxygenation strategy (RR 1.04 (95% CI 1.02 to 1.07; I2 = 74%; 9489 participants; 17 trials; very low certainty evidence)). However, trial sequential analyses, with correction for sparse data and repetitive testing, could reject a relative risk increase or reduction of 10% for mortality and the highest proportion of SAEs, and 20% for both the cumulated number of SAEs and quality of life. Given the very low-certainty of evidence, it is necessary to interpret these findings with caution. Meta-analysis of all trials indicated no statistically significant evidence of a difference between higher or lower oxygenation strategies on the occurrence of lung injuries at maximum follow-up (the highest reported proportion of lung injury RR 1.08, 95% CI 0.85 to 1.38; I2 = 0%; 2048 participants; 8 trials; very low-certainty evidence). Meta-analysis of all trials indicated harm from higher oxygenation strategies as compared with lower on the occurrence of sepsis at maximum follow-up (RR 1.85, 95% CI 1.17 to 2.93; I2 = 0%; 752 participants; 3 trials; very low-certainty evidence). Meta-analysis indicated no differences regarding the occurrences of myocardial infarction or stroke.

AUTHORS' CONCLUSIONS

In adult ICU patients, it is still not possible to draw clear conclusions about the effects of higher versus lower oxygenation strategies on all-cause mortality, SAEs, quality of life, lung injuries, myocardial infarction, stroke, and sepsis at maximum follow-up. This is due to low or very low-certainty evidence.

Randomization to a Liberal Versus Conservative Oxygenation Target: Redox Responses in Critically Ill Children

RATIONALE

Optimal systemic oxygenation targets in pediatric critical illness are unknown. A U-shaped relationship exists between blood oxygen levels and PICU mortality. Redox stress or iatrogenic injury from intensive treatments are potential mechanisms of harm from hyperoxia.

OBJECTIVES

To measure biomarkers of oxidative status in children admitted to PICU and randomized to conservative (oxygen-hemoglobin saturation [Sp o2 ] 88-92%) versus liberal (Sp o2 > 94%) peripheral oxygenation targets.

DESIGN

Mechanistic substudy nested within the Oxygen in PICU (Oxy-PICU) pilot randomized feasibility clinical trial ( ClinicalTrials.gov : NCT03040570).

SETTING

Three U.K. mixed medical and surgical PICUs in university hospitals.

PATIENTS

Seventy-five eligible patients randomized to the Oxy-PICU randomized feasibility clinical trial.

INTERVENTIONS

Randomization to a conservative (Sp o2 88-92%) versus liberal (Sp o2 > 94%) peripheral oxygenation target.

MEASUREMENTS AND MAIN RESULTS

Blood and urine samples were collected at two timepoints: less than 24 hours and up to 72 hours from randomization in trial participants (March 2017 to July 2017). Plasma was analyzed for markers of ischemic/oxidative response, namely thiobarbituric acid-reactive substances (TBARS; lipid peroxidation marker) and ischemia-modified albumin (protein oxidation marker). Total urinary nitrate/nitrite was measured as a marker of reactive oxygen and nitrogen species (RONS). Blood hypoxia-inducible factor (HIF)-1a messenger RNA (mRNA) expression (hypoxia response gene) was measured by reverse transcription- polymerase chain reaction. Total urinary nitrate/nitrite levels were greater in the liberal compared with conservative oxygenation group at 72 hours (median difference 32.6 μmol/mmol of creatinine [95% CI 13.7-93.6]; p < 0.002, Mann-Whitney test). HIF-1a mRNA expression was increased in the conservative group compared with liberal in less than 24-hour samples (6.0-fold [95% CI 1.3-24.0]; p = 0.032). There were no significant differences in TBARS or ischemia-modified albumin.

CONCLUSIONS

On comparing liberal with conservative oxygenation targets, we show, first, significant redox response (increase in urinary markers of RONS), but no changes in markers of lipid or protein oxidation. We also show what appears to be an early hypoxic response (increase in HIF-1a gene expression) in subjects exposed to conservative rather than liberal oxygenation targets.

Calcitonin Gene-Related Peptide Attenuates Hyperoxia-Induced Oxidative Damage in Alveolar Epithelial Type II Cells Through Regulating Viability and Transdifferentiation

As a stem cell of alveolar epithelium, the physiological status of alveolar epithelium type II cells (AECII) after hyperoxia exposure is closely related to the occurrence of hyperoxia-induced lung injury and the restoration of normal morphological function of damaged alveolar epithelium. However, the relevant mechanisms involved are not very clear. Therefore, this study aimed to explore the effect of calcitonin gene-related peptide (CGRP) on AECII exposed to hyperoxia and its potential mechanisms. The AECII viability was detected using MTT assay. The malondialdehyde (MDA) level and superoxide dismutase (SOD) activity were detected by spectrophotometry. The transdifferentiation capacity of AECII was evaluated by flow cytometry. The expression levels of Notch1, Hes, HERP, and AECII markers were detected using immunohistochemistry and/or RT-qPCR or immunofluorescence. ELISA was used for the determination of inflammatory markers. The results showed that CGRP significantly promoted cell viability, and markedly suppressed hyperoxia-induced transdifferentiation of AECII; these biological alterations were coincided with decreased MDA level, increased SOD activity, and activated Notch signaling pathway (upregulated expression levels of Notch1, Hes, and HERP). Notably, the in vitro effects of CGRP on Notch signaling pathway were further investigated in animal model, and the HE staining results showed that CGRP reduced in vivo oxidative injury and inflammation in hyperoxia-treated AECII through the promotion of structural and functional regeneration, accompanied by elevated Notch1 expression and activated Notch signaling cascade as shown by immunohistochemistry and QPCR, respectively. Immunohistochemistry of APQ-5 and SPC indicated that CGRP reversed the transdifferentiation of AECIIs in vivo. Our current results were consistent across both in vitro and in vivo settings, and provide a new direction for the prevention and treatment of bronchopulmonary dysplasia (BPD).

Light-Emitting Diode Laser Therapy for Hyperoxia-Induced Retinal Abnormalities

Introduction: Hyperoxygenation is linked to numerous effects in a variety of organ systems. It can cause tissue damage by generating reactive oxygen species (ROS), increasing oxidative stress, and inducing cell death by apoptosis. The present study aimed to evaluate the effects of low-level laser therapy on the retina in response to acute hyperoxia in animals. Methods: A total of 70 Wistar albino rats were evaluated in the present study: 10 rats were designated as a control group, and the rest were exposed to hyperoxia (O2 , 90%) for 3 days, 1 week, and 2 weeks (20 rats each). Each group was divided into two subgroups (n=10), one of which was designated as hyperoxia only. The other was treated with a 670 nm light-emitting diode laser (2 sessions/one week, ~ 9.0 J/cm2 ) in each eye. The animals were euthanized, and their retinas were dissected for analysis of protein content, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), total antioxidant capacity (TAC), hydrogen peroxide (H2 O2 ), malondialdehyde (MDA), and histological examination. Results: We found that two weeks of hyperoxia induced an increase in retinal protein content (P<0.001), an alteration in the intensities and molecular weights of protein fractions, a significant decrease in the TAC level (P<0.01), and a noticeable increase in H2 O2 and MDA levels (P<0.001). Histological examination revealed fragmentation of the photoreceptors and neovascularization in the outer and inner plexiform layers. Furthermore, the data showed remarkable improvement in the retinal protein contents, oxidative state, and retinal structure after light-emitting diode laser therapy. Conclusion: Light-emitting diode laser therapy was found to be a useful treatment paradigm for reducing hyperoxia-induced retinal damage.

Protective Effect of an Anti-HMGB-1 Neutralizing Antibody on Hemozoin-Induced Alveolar Epithelial Cell in a Model of Malaria Associated ALI/ARDS

Background:

We aimed to determine whether neutralizing high mobility group box-1 (HMGB-1) prevents the release of HMGB-1 and proinflammatory cytokines on hemozoin (Hz)-induced alveolar epithelial cell in a model of malaria associated ALI/ARDS.

Methods:

This study was conducted in the Department of Tropical Pathology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand in 2020. Human pulmonary alveolar epithelial cells (HPAEpiCs) were exposed to medium alone or 20 μM Hz for 24 h and incubated with different concentrations (1, 5, and 10 μg/ml) of anti-HMGB-1 monoclonal antibody (mAb) for various times (0, 4, 12, 24, and 48 h). The levels of HMGB-1, TNF-α and IFN-γ in the supernatants were measured by ELISA. The mRNA expression of RAGE, TLR-2 and TLR-4 were analyzed by real-time PCR.

Results:

The HPAEpiCs treated with 10 μg/ml anti-HMGB-1 mAb showed a significant reduction in HMGB-1 release into the supernatant compared with those treated with 1 and 5 μg/ml anti-HMGB-1 mAb. The levels of TNF-α and IFN-γ were significantly decreased in the supernatant of HPAEpiCs treated with 1, 5, and 10 μg/ml anti-HMGB-1 mAb for 4, 12, 24, and 48 h compared with those stimulated with Hz alone. The mRNA expression levels of RAGE, TLR-2, and TLR-4 were significantly decreased after 24 h of anti-HMGB-1 antibody treatment at all concentrations.

Conclusion:

An anti-HMGB-1 antibody could be an effective agent for inhibiting the release of HMGB-1, TNF-α and IFN-γ. Furthermore, a neutralizing anti-HMGB-1 antibody could be applicable for the treatment of malaria-associated ALI/ARDS.

HMGB1/TLR4 Signaling Affects Regulatory T Cells in Acute Lung Injury

Background

High-mobility group box-1 protein (HMGB1) serves as the prototypic damage-associated molecular pattern molecule, and TLR4 is considered a receptor for HMGB1. Regulatory T cells (Tregs) play a crucial role in infectious diseases. The role of HMGB1 in the modulation of Tregs is of great interest.

Methods

Serum HMGB1 and Treg proportions were detected in 58 patients with acute lung injury (ALI) and 36 healthy volunteers. The correlations of these parameters with disease severity were analyzed. The WT and TLR4^-/- mice were administered HMGB1 by intratracheal injection. After 48 h, the mice were sacrificed. The morphological changes and wet/dry ratio of the lung were measured. Spleen CD4⁺CD25⁺ Tregs were sorted from spleen cells, the expression of FOXP3 and CTLA-4, and releasing of cytokines was detected. CD4⁺CD25⁺ Tregs were cocultured with effector T cells, the inhibitory effect, and release of cytokines was detected.

Results

Significantly increased plasma levels of HMGB1 and reduced CD4⁺CD25⁺CD127^low Tregs were detected in ALI patients. In the mouse model, lung injury was significantly increased after HMGB1 instillation in the WT and TLR4^-/- groups compared with control group. The lung wet/dry ratio and the TNF-α and IL-1β contents in BALF were significantly increased, and the severity of WT mice was higher than that of TLR4^-/- mice. The expression of FOXP3 and CTLA-4 in TLR4^-/- mice was significantly increased compared with that in WT mice and was associated with a similar trend of IL-10 and TGF-β levels (p<0.05). In coculture with effector T cells, Tregs isolated from TLR4^-/- mice exhibited decreased IL-2 and IFN-γ and increased IL-4 levels compared with Tregs from WT mice. Increased polarization of TLR4^-/- CD4⁺CD25⁺ Treg cells to Th2 cells was observed.

Conclusion

In HMGB1-induced lung injury, HMGB1 affects the expression of FOXP3 and CTLA-4 through TLR4, thus reducing the immunosuppressive function of Treg cells.

Hyperoxia-induced miR-342-5p down-regulation exacerbates neonatal bronchopulmonary dysplasia via the Raf1 regulator Spred3

BACKGROUND AND PURPOSE

Bronchopulmonary dysplasia (BPD) is the most prevalent chronic paediatric lung disease and is linked to the development of chronic obstructive pulmonary disease. MicroRNA-based regulation of type II alveolar epithelial cell (T2AEC) proliferation and apoptosis is an important factor in the pathogenesis of BPD and warrants further investigation.

EXPERIMENTAL APPROACH

Two murine models of hyperoxic lung injury (with or without miR-342-5p or Sprouty-related, EVH1 domain-containing protein 3 [Spred3] modulation) were employed: a hyperoxia-induced acute lung injury model (100% O₂ on postnatal days 1-7) and the BPD model (100% O₂ on postnatal days 1-4, followed by room air for 10 days). Tracheal aspirate pellets from healthy control and moderate/severe BPD neonates were randomly selected for clinical miR-342-5p analysis.

KEY RESULTS

Hyperoxia decreased miR-342-5p levels in primary T2AECs, MLE12 cells and neonatal mouse lungs. Transgenic miR-342 overexpression in neonatal mice ameliorated survival rates and improved the BPD phenotype and BPD-associated pulmonary arterial hypertension (PAH). T2AEC-specific miR-342 transgenic overexpression, as well as miR-342-5p mimic therapy, also ameliorated the BPD phenotype and associated PAH. miR-342-5p targets the 3'UTR of the Raf1 regulator Spred3, inhibiting Spred3 expression. Treatment with recombinant Spred3 exacerbated the BPD phenotype and associated PAH. Notably, miR-342-5p inhibition under room air conditions did not mimic the BPD phenotype. Moderate/severe BPD tracheal aspirate pellets exhibited decreased miR-342-5p levels relative to healthy control pellets.

CONCLUSION AND IMPLICATIONS

These findings suggest that miR-342-5p mimic therapy may show promise in the treatment or prevention of BPD.

Protection of apigenin against acrylonitrile-induced sperm and testis injury in rats: involvement of activation of ASK1-JNK/p38 signaling pathway

This study aims to clarify if apigenin (AP) could play a pivotal role in attenuating acrylonitrile (ACN)-induced sperm and testis injury by inhibiting ASK1-JNK/p38 signaling pathway. Male Sprague-Dawley rats were randomly divided into five groups: a control group (corn oil), an ACN group (ACN 46 mg kg^-1), an ACN + AP1 group (ACN + AP 117 mg kg^-1), an ACN + AP2 group (ACN + AP 234 mg kg^-1) and an ACN + AP3 group (ACN + AP 351 mg kg^-1). The ACN + AP groups were given ACN by gavage after a pretreatment with different dosages of AP for 30 min, whereas the rats in the control group received an equivalent volume of corn oil. The gavage was conducted for 6 days per week in 4 weeks. The results showed that AP reduced sperm deformity rate and DNA fragment index and attenuated the testicular injury induced by ACN. AP could also alleviate oxidative stress, downregulate ASK1-JNK/p38 signaling pathway and eventually inhibit mitochondria-mediated testicular apoptosis. In brief, AP could dampen oxidative stress thereby inhibiting testicular apoptosis mediated by ASK1-JNK/p38 signaling pathway, alleviating ACN-induced sperm and testis injury and exerting a protective effect on male reproductive system.

Prevention of Oxygen-Induced Inflammatory Lung Injury by Caffeine in Neonatal Rats

Background

Preterm birth implies an array of respiratory diseases including apnea of prematurity and bronchopulmonary dysplasia (BPD). Caffeine has been introduced to treat apneas but also appears to reduce rates of BPD. Oxygen is essential when treating preterm infants with respiratory problems but high oxygen exposure aggravates BPD. This experimental study is aimed at investigating the action of caffeine on inflammatory response and cell death in pulmonary tissue in a hyperoxia-based model of BPD in the newborn rat. Material/Methods. Lung injury was induced by hyperoxic exposure with 80% oxygen for three (P3) or five (P5) postnatal days with or without recovery in ambient air until postnatal day 15 (P15). Newborn Wistar rats were treated with PBS or caffeine (10 mg/kg) every two days beginning at the day of birth. The effects of caffeine on hyperoxic-induced pulmonary inflammatory response were examined at P3 and P5 immediately after oxygen exposure or after recovery in ambient air (P15) by immunohistological staining and analysis of lung homogenates by ELISA and qPCR.

Results

Treatment with caffeine significantly attenuated changes in hyperoxia-induced cell death and apoptosis-associated factors. There was a significant decrease in proinflammatory mediators and redox-sensitive transcription factor NFκB in the hyperoxia-exposed lung tissue of the caffeine-treated group compared to the nontreated group. Moreover, treatment with caffeine under hyperoxia modulated the transcription of the adenosine receptor (Adora)1. Caffeine induced pulmonary chemokine and cytokine transcription followed by immune cell infiltration of alveolar macrophages as well as increased adenosine receptor (Adora1, 2a, and 2b) expression.

Conclusions

The present study investigating the impact of caffeine on the inflammatory response, pulmonary cell degeneration and modulation of adenosine receptor expression, provides further evidence that caffeine acts as an antioxidative and anti-inflammatory drug for experimental oxygen-mediated lung injury. Experimental studies may broaden the understanding of therapeutic use of caffeine in modulating detrimental mechanisms involved in BPD development.

Knockdown of Long Noncoding RNAs of Maternally Expressed 3 Alleviates Hyperoxia-Induced Lung Injury via Inhibiting Thioredoxin-Interacting Protein-Mediated Pyroptosis by Binding to miR-18a

Long-term hyperoxia exposure may cause lung damage with characteristic inflammation. Long noncoding RNA of maternally expressed 3 (MEG3) is up-regulated in lung tissues exposed to hyperoxia; however, the underlying mechanism is unclear. Hyperoxia-induced cells and mouse models were used to study these mechanisms. Molecular assays were used to detect cell viability, cytotoxicity, and expression of miR-18a, MEG3, and inflammatory cytokines. The interaction among MEG3, miR-18a, and thioredoxin-interacting protein (TXNIP) was verified; and pyroptosis-related proteins were analyzed. The in vivo model was established by exposing MEG3 knockdown mice to hyperoxia. Hematoxylin and eosin staining was used to assess pathologic alterations of lung tissues. Hyperoxia suppressed cell viability, induced cell damage, and exacerbated the secretion of IL-1β and IL-18. Hyperoxia inhibited miR-18a, with increased expression of MEG3, TXNIP, and nonobese diabetic-like receptor family pyrin domain containing 3 (NLRP3). MEG3 aggravated TXNIP expression by binding to miR-18a. Knockdown of MEG3 rescued hyperoxia-induced pyroptosis by up-regulating miR-18a. Furthermore, knockdown of MEG3 inhibited NLRP3 inflammasome activity and caspase-1 signaling by miR-18a. In vivo knockdown of MEG3 and overexpression of miR-18a relieved hyperoxia-induced lung injury via restraining NLRP3 inflammasome-mediated pyroptosis, whereas miR-18a inhibition reversed these effects. In conclusion, knockdown of MEG3 inhibits pyroptosis to alleviate hyperoxia lung injury by suppressing NLRP3 inflammasome and caspase-1 signaling via regulating miR-18a-TXNIP axis.

Higher versus lower fraction of inspired oxygen or targets of arterial oxygenation for adults admitted to the intensive care unit

BACKGROUND

The mainstay treatment for hypoxaemia is oxygen therapy, which is given to the vast majority of adults admitted to the intensive care unit (ICU). The practice of oxygen administration has been liberal, which may result in hyperoxaemia. Some studies have indicated an association between hyperoxaemia and mortality, whilst other studies have not. The ideal target for supplemental oxygen for adults admitted to the ICU is uncertain. Despite a lack of robust evidence of effectiveness, oxygen administration is widely recommended in international clinical practice guidelines. The potential benefit of supplemental oxygen must be weighed against the potentially harmful effects of hyperoxaemia.

OBJECTIVES

To assess the benefits and harms of higher versus lower fraction of inspired oxygen or targets of arterial oxygenation for adults admitted to the ICU.

SEARCH METHODS

We identified trials through electronic searches of CENTRAL, MEDLINE, Embase, Science Citation Index Expanded, BIOSIS Previews, CINAHL, and LILACS. We searched for ongoing or unpublished trials in clinical trials registers. We also scanned the reference lists of included studies. We ran the searches in December 2018.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) that compared higher versus lower fraction of inspired oxygen or targets of arterial oxygenation for adults admitted to the ICU. We included trials irrespective of publication type, publication status, and language. We included trials with a difference between the intervention and control groups of a minimum 1 kPa in partial pressure of arterial oxygen (PaO2), minimum 10% in fraction of inspired oxygen (FiO2), or minimum 2% in arterial oxygen saturation of haemoglobin/non-invasive peripheral oxygen saturation (SaO2/SpO2). We excluded trials randomizing participants to hypoxaemia (FiO2 below 0.21, SaO2/SpO2 below 80%, and PaO2 below 6 kPa) and to hyperbaric oxygen.

DATA COLLECTION AND ANALYSIS

Three review authors independently, and in pairs, screened the references retrieved in the literature searches and extracted data. Our primary outcomes were all-cause mortality, the proportion of participants with one or more serious adverse events, and quality of life. None of the trials reported the proportion of participants with one or more serious adverse events according to the International Conference on Harmonisation Good Clinical Practice (ICH-GCP) criteria. Nonetheless, most trials reported several serious adverse events. We therefore included an analysis of the effect of higher versus lower fraction of inspired oxygen, or targets using the highest reported proportion of participants with a serious adverse event in each trial. Our secondary outcomes were lung injury, acute myocardial infarction, stroke, and sepsis. None of the trials reported on lung injury as a composite outcome, however some trials reported on acute respiratory distress syndrome (ARDS) and pneumonia. We included an analysis of the effect of higher versus lower fraction of inspired oxygen or targets using the highest reported proportion of participants with ARDS or pneumonia in each trial. To assess the risk of systematic errors, we evaluated the risk of bias of the included trials. We used GRADE to assess the overall certainty of the evidence.

MAIN RESULTS

We included 10 RCTs (1458 participants), seven of which reported relevant outcomes for this review (1285 participants). All included trials had an overall high risk of bias, whilst two trials had a low risk of bias for all domains except blinding of participants and personnel. Meta-analysis indicated harm from higher fraction of inspired oxygen or targets as compared with lower fraction or targets of arterial oxygenation regarding mortality at the time point closest to three months (risk ratio (RR) 1.18, 95% confidence interval (CI) 1.01 to 1.37; I2 = 0%; 4 trials; 1135 participants; very low-certainty evidence). Meta-analysis indicated harm from higher fraction of inspired oxygen or targets as compared with lower fraction or targets of arterial oxygenation regarding serious adverse events at the time point closest to three months (estimated highest proportion of specific serious adverse events in each trial RR 1.13, 95% CI 1.04 to 1.23; I2 = 0%; 1234 participants; 6 trials; very low-certainty evidence). These findings should be interpreted with caution given that they are based on very low-certainty evidence. None of the included trials reported any data on quality of life at any time point. Meta-analysis indicated no evidence of a difference between higher fraction of inspired oxygen or targets as compared with lower fraction or targets of arterial oxygenation on lung injury at the time point closest to three months (estimated highest reported proportion of lung injury RR 1.03, 95% CI 0.78 to 1.36; I2 = 0%; 1167 participants; 5 trials; very low-certainty evidence). None of the included trials reported any data on acute myocardial infarction or stroke, and only one trial reported data on the effects on sepsis.

AUTHORS' CONCLUSIONS

We are very uncertain about the effects of higher versus lower fraction of inspired oxygen or targets of arterial oxygenation for adults admitted to the ICU on all-cause mortality, serious adverse events, and lung injuries at the time point closest to three months due to very low-certainty evidence. Our results indicate that oxygen supplementation with higher versus lower fractions or oxygenation targets may increase mortality. None of the trials reported the proportion of participants with one or more serious adverse events according to the ICH-GCP criteria, however we found that the trials reported an increase in the number of serious adverse events with higher fractions or oxygenation targets. The effects on quality of life, acute myocardial infarction, stroke, and sepsis are unknown due to insufficient data.

Oxidative Stress Markers to Investigate the Effects of Hyperoxia in Anesthesia

Oxygen (O₂) is commonly used in clinical practice to prevent or treat hypoxia, but if used in excess (hyperoxia), it may act as toxic. O₂ toxicity arises from the enhanced formation of Reactive Oxygen Species (ROS) that exceed the antioxidant defenses and generate oxidative stress. In this study, we aimed at assessing whether an elevated fraction of inspired oxygen (FiO₂) during and after general anesthesia may contribute to the unbalancing of the pro-oxidant/antioxidant equilibrium. We measured five oxidative stress biomarkers in blood samples from patients undergoing elective abdominal surgery, randomly assigned to FiO₂ = 0.40 vs. 0.80: hydroperoxides, antioxidants, nitrates and nitrites (NO_x), malondialdehyde (MDA), and glutathionyl hemoglobin (HbSSG). The MDA concentration was significantly higher 24 h after surgery, and the body antioxidant defense lower, in the FiO₂ = 0.80 group with respect to both the FiO₂ = 0.40 group and the baseline values (p ≤ 0.05, Student’s t-test). HbSSG in red blood cells was also higher in the FiO₂ = 0.80 group at the end of the surgery. NO_x was higher in the FiO₂ = 0.80 group than the FiO₂ = 0.40 group at t = 2 h after surgery. MDA, the main end product of the peroxidation of polyunsaturated fatty acids directly influenced by FiO₂, may represent the best marker to assess the pro-oxidant/antioxidant equilibrium after surgery.

Thiol-Redox Regulation in Lung Development and Vascular Remodeling

Significance: Redox homeostasis is finely tuned and governed by distinct intracellular mechanisms. The dysregulation of this either by external or internal events is a fundamental pathophysiologic base for many pulmonary diseases. Recent Advances: Based on recent discoveries, it is increasingly clear that cellular redox state and oxidation of signaling molecules are critical modulators of lung disease and represent a final common pathway that leads to poor respiratory outcomes. Critical Issues: Based on the wide variety of stimuli that alter specific redox signaling pathways, improved understanding of the disease and patient-specific alterations are needed for the development of therapeutic targets. Further Directions: For the full comprehension of redox signaling in pulmonary disease, it is essential to recognize the role of reactive oxygen intermediates in modulating biological responses. This review summarizes current knowledge of redox signaling in pulmonary development and pulmonary vascular disease.

Handling Oxygenation Targets in the Intensive Care Unit (HOT-ICU)-Protocol for a randomised clinical trial comparing a lower vs a higher oxygenation target in adults with acute hypoxaemic respiratory failure

BACKGROUND

Acutely ill adults with hypoxaemic respiratory failure are at risk of life-threatening hypoxia, and thus oxygen is often administered liberally. Excessive oxygen use may, however, increase the number of serious adverse events, including death. Establishing the optimal oxygenation level is important as existing evidence is of low quality. We hypothesise that targeting an arterial partial pressure of oxygen (PaO₂ ) of 8 kPa is superior to targeting a PaO₂ of 12 kPa in adult intensive care unit (ICU) patients with acute hypoxaemic respiratory failure.

METHODS

The Handling Oxygenation Targets in the ICU (HOT-ICU) trial is an outcome assessment blinded, multicentre, randomised, parallel-group trial targeting PaO₂ in acutely ill adults with hypoxaemic respiratory failure within 12 hours after ICU admission. Patients are randomised 1:1 to one of the two PaO₂ targets throughout ICU stay until a maximum of 90 days. The primary outcome is 90-day mortality. Secondary outcomes are serious adverse events in the ICU, days alive without organ support and days alive out of hospital in the 90-day period; mortality, health-related quality-of-life at 1-year follow-up as well as 1-year cognitive and pulmonary function in a subgroup; and an overall health economic analysis. To detect or reject a 20% relative risk reduction, we aim to include 2928 patients. An interim analysis is planned after 90-day follow-up of 1464 patients.

CONCLUSION

The HOT-ICU trial will test the hypothesis that a lower oxygenation target reduces 90-day mortality compared with a higher oxygenation target in adult ICU patients with acute hypoxaemic respiratory failure.

lncRNA FOXD3-AS1 is associated with clinical progression and regulates cell migration and invasion in breast cancer

For women, breast cancer is the most commonly diagnosed cancer and the leading cause of women deaths due to cancer. In recent years, increasing long noncoding RNA (lncRNA) has been discovered to be related to tumorigenesis, progression, and prognosis. FOXD3-AS1 is a lncRNA and has been identified as a cancer-promoting gene in glioma. By analysing the FOXD3-AS1 expression in The Cancer Genome Atlas (TCGA) database, we found that FOXD3-AS1 has significantly high expression in breast cancer tumour comparing with the normal tissue. And patients with low FOXD3-AS1 expression had greater survival probability, smaller tumour size, and less distant metastasis. This leads us to peep inquisitively biological function of FOXD3-AS1 in breast cancer. Biological assays demonstrated that silenced FOXD3-AS1 impaired cell proliferation and inhibited cell migration and invasion in breast cancer cell lines (BT549, MDA-MB-231). These results suggest that FOXD3-AS1 could play a potential diagnostics or prognostic biomarker for patients with breast cancer. SIGNIFICANCE OF THE STUDY: We demonstrated that lncRNA FOXD3-AS1 has significantly high expression in breast cancer cell lines comparing with the normal tissue. Besides, our findings suggested that lncRNA FOXD3-AS1 could play a potential diagnostics or prognostic biomarker for patients with breast cancer.

Alveolar-Capillary Membrane-Related Pulmonary Cells as a Target in Endotoxin-Induced Acute Lung Injury

The main function of the lungs is oxygen transport from the atmosphere into the blood circulation, while it is necessary to keep the pulmonary tissue relatively free of pathogens. This is a difficult task because the respiratory system is constantly exposed to harmful substances entering the lungs by inhalation or via the blood stream. Individual types of lung cells are equipped with the mechanisms that maintain pulmonary homeostasis. Because of the clinical significance of acute respiratory distress syndrome (ARDS) the article refers to the physiological role of alveolar epithelial cells type I and II, endothelial cells, alveolar macrophages, and fibroblasts. However, all these cells can be damaged by lipopolysaccharide (LPS) which can reach the airspaces as the major component of the outer membrane of Gram-negative bacteria, and lead to local and systemic inflammation and toxicity. We also highlight a negative effect of LPS on lung cells related to alveolar-capillary barrier and their response to LPS exposure. Additionally, we describe the molecular mechanism of LPS signal transduction pathway in lung cells.

Protective Features of Autophagy in Pulmonary Infection and Inflammatory Diseases

Autophagy is a highly conserved catabolic process involving autolysosomal degradation of cellular components, including protein aggregates, damaged organelles (such as mitochondria, endoplasmic reticulum, and others), as well as various pathogens. Thus, the autophagy pathway represents a major adaptive response for the maintenance of cellular and tissue homeostasis in response to numerous cellular stressors. A growing body of evidence suggests that autophagy is closely associated with diverse human diseases. Specifically, acute lung injury (ALI) and inflammatory responses caused by bacterial infection or xenobiotic inhalation (e.g., chlorine and cigarette smoke) have been reported to involve a spectrum of alterations in autophagy phenotypes. The role of autophagy in pulmonary infection and inflammatory diseases could be protective or harmful dependent on the conditions. In this review, we describe recent advances regarding the protective features of autophagy in pulmonary diseases, with a focus on ALI, idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD), tuberculosis, pulmonary arterial hypertension (PAH) and cystic fibrosis.

Celecoxib Protects Hyperoxia-Induced Lung Injury via NF-κB and AQP1

Objective: There is an increasing incidence of bronchopulmonary dysplasia (BDP) in preterm infants in China, which is the key issue affecting their survival rate and life quality. This study was performed to better understand the mechanism of protective effect of celecoxib on hyperoxia induced injury. Methods: Hyperoxia BPD model was established using newborn Sprague-Dawley (SD) rats exposed to high O₂ level (85%). Celecoxib treatment was also conducted. Histology of lung tissue samples were analyzed. Functional studies were systematically performed using the lung tissues and A549 cells. Results: Hyperoxia disrupted lung development in SD rats. Celecoxib alleviated the damaged lung development. NF-κB and Aquaporin (AQP) 1 were identified as the pathways in the hyperoxia-induced lung injury. We have shown that hyperoxia activated NF-κB pathway through increased nucleus translocation and repressed AQP1 expression. On the contrary, celecoxib inhibited NF-κB phosphorylation and nucleus translocation and increased AQP1 expression through inhibiting COX2 activity. Additionally, celecoxib also rescued apoptosis induced by hyperoxia. Conclusion: Our study identified NF-κB and AQP1 as the pathways in the hyperoxia-induced lung injury in the hyperoxia BPD model SD rats and it provided a better understanding of the protective effect of celecoxib. It suggests NF-κB and AQP1 may be as potential targets for treating newborns with BPD.

Oxygen supplementation for critically ill patients-A protocol for a systematic review

BACKGROUND

In critically ill patients, hypoxaemia is a common clinical manifestation of inadequate gas exchange in the lungs. Supplemental oxygen is therefore given to all critically ill patients. This can result in hyperoxaemia, and some observational studies have identified harms with hyperoxia. The objective of this systematic review is to critically assess the evidence of randomised clinical trials on the effects of higher versus lower inspiratory oxygen fractions or targets of arterial oxygenation in critically ill adult patients.

METHODS

We will search for randomised clinical trials in major international databases. Two authors will independently screen and select references for inclusion using Covidence, extract data and assess the methodological quality of the included randomised clinical trials using the Cochrane risk of bias tool. Any disagreement will be resolved by consensus. We will analyse the extracted data using Review Manager and Trial Sequential Analysis. To assess the quality of the evidence, we will create a 'Summary of Findings' table containing our primary and secondary outcomes using the GRADE assessment.

DISCUSSION

Supplemental oxygen administration is widely recommended in international guidelines despite lack of robust evidence of its effectiveness. To our knowledge, no systematic review of randomised clinical trials has investigated the effects of oxygen supplementation in critically ill patients. This systematic review will provide reliable evidence to better inform future trialists and decision-makers on clinical practice on supplemental oxygen administration in critically ill patients.

The Impact of Hyperoxia on Human Performance and Recovery

Hyperoxia results from the inhalation of mixtures of gas containing higher partial pressures of oxygen (O₂) than normal air at sea level. Exercise in hyperoxia affects the cardiorespiratory, neural and hormonal systems, as well as energy metabolism in humans. In contrast to short-term exposure to hypoxia (i.e. a reduced partial pressure of oxygen), acute hyperoxia may enhance endurance and sprint interval performance by accelerating recovery processes. This narrative literature review, covering 89 studies published between 1975 and 2016, identifies the acute ergogenic effects and health concerns associated with hyperoxia during exercise; however, long-term adaptation to hyperoxia and exercise remain inconclusive. The complexity of the biological responses to hyperoxia, as well as the variations in (1) experimental designs (e.g. exercise intensity and modality, level of oxygen, number of participants), (2) muscles involved (arms and legs) and (3) training status of the participants may account for the discrepancies.

Evaluation of oxidative stress and antioxidant status: Correlation with the severity of sepsis

Sepsis is a condition caused by infection followed by unregulated inflammatory response which may lead to the organ dysfunction. During such condition, over-production of oxidants is one of the factors which contribute cellular toxicity and ultimately organ failure and mortality. Antioxidants having free radicals scavenging activity exert protective role in various diseases. This study has been designed to evaluate the levels of oxidative and antioxidative activity in sepsis patients and their correlation with the severity of the sepsis. A total of 100 sepsis patients and 50 healthy controls subjects were enrolled in this study from the period October 2016 to June 2017. The investigation included measurements of oxidative enzyme, myeloperoxidase (MPO), antioxidant enzymes including superoxide dismutase activity (SOD) and catalase activity (CAT) and cytokines (TNF-α, IL-8 and IFN-γ). Furthermore, the level of these activities was correlated with severity of sepsis. Augmented levels of oxidants were found in sepsis as demonstrated by DMPO nitrone adduct formation and plasma MPO level activity (1.37 ± 0.51 in sepsis vs 0.405 ± 0.16 in control subjects). Cytokines were also found to be increased in sepsis patients. However, plasma SOD and CAT activities were significantly attenuated (P < .001) in the sepsis patients compared with controls subjects. Moreover, inverse relation between antioxidant enzymes (SOD and CAT) and organ failure assessment (SOFA), physiological score (APACHE II), organ toxicity specific markers have been observed as demonstrated by Pearson's correlation coefficient. This study suggests that imbalance between oxidant and antioxidant plays key role in the severity of sepsis.

Lung epithelial-specific TRIP-1 overexpression maintains epithelial integrity during hyperoxia exposure

The onset and degree of injury occurring in animals that develop hyperoxic acute lung injury (HALI) is dependent on age at exposure, suggesting that developmentally regulated pathways/factors must underlie initiation of the epithelial injury and subsequent repair. Type II TGFβ receptor interacting protein-1 (TRIP-1) is a negative regulator of TGFβ signaling, which we have previously shown is a developmentally regulated protein with modulatory effects on epithelial-fibroblastic signaling. The aim of this study was to assess if type II alveolar epithelial cells overexpressing TRIP-1 are protected against hyperoxia-induced epithelial injury, and in turn HALI. Rat lung epithelial cells (RLE) overexpressing TRIP-1 or LacZ were exposed to 85% oxygen for 4 days. A surfactant protein C (SPC)-driven TRIP-1 overexpression mouse (TRIP-1AECTg+ ) was generated and exposed to hyperoxia (>95% for 4 days) at 4 weeks of age to assess the effects TRIP-1 overexpression has on HALI. RLE overexpressing TRIP-1 resisted hyperoxia-induced apoptosis. Mice overexpressing TRIP-1 in their lung type II alveolar epithelial cells (TRIP-1AECTg+ ) showed normal lung development, increased phospho-AKT level and E-cadherin, along with resistance to HALI, as evidence by less TGFβ activation, apoptosis, alveolar macrophage influx, KC expression. Taken together, these findings point to existence of a TRIP-1 mediated molecular pathway affording protection against epithelial/acute lung injury.

Hyperoxia-induced regulation of cough reflex and its effect after antioxidant supplementation

Hyperoxia-induced lung injury is well known in animal and human studies. The respiratory epithelium including sensory nerve endings is a major target for oxidative injury that manifested in lung function changes including cough. On the basis of available information we supposed that hyperoxia alone or in combination with primary lung tissue injury should have a damaging effect on lungs, including the airway nerve endings with the changes in the sensitivity of the central and peripheral neuronal pathways regulating cough. We have previously demonstrated that long-term exposure to 100% oxygen inhibits the cough reflex in cat. This review article summarizes the effect of hyperoxia on the cough reflex in guinea pig model using different concentrations of oxygen and different time of exposure. We also present information on the potential role of antioxidants in reversal of the detrimental effects of hyperoxia on coughing and additional analysis of experiments from previously published studies were obtained and analysed for the cough reflex sensitivity.

Akap1 genetic deletion increases the severity of hyperoxia-induced acute lung injury in mice

Critically ill patients are commonly treated with high levels of oxygen, hyperoxia, for prolonged periods of time. Unfortunately, extended exposure to hyperoxia can exacerbate respiratory failure and lead to a high mortality rate. Mitochondrial A-kinase anchoring protein (Akap) has been shown to regulate mitochondrial function. It has been reported that, under hypoxic conditions, Akap121 undergoes proteolytic degradation and promotes cardiac injury. However, the role of Akap1 in hyperoxia-induced acute lung injury (ALI) is largely unknown. To address this gap in our understanding of Akap1, we exposed wild-type ( wt) and Akap1^-/- mice to 100% oxygen for 48 h, a time point associated with lung damage in the murine model of ALI. We found that under hyperoxia, Akap1^-/- mice display increased levels of proinflammatory cytokines, immune cell infiltration, and protein leakage in lungs, as well as increased alveolar capillary permeability compared with wt controls. Further analysis revealed that Akap1 deletion enhances lung NF-κB p65 activity as assessed by immunoblotting and DNA-binding assay and mitochondrial autophagy-related markers, PINK1 and Parkin. Ultrastructural analysis using electron microscopy revealed that Akap1 deletion was associated with remarkably aberrant mitochondria and lamellar bodies in type II alveolar epithelial cells. Taken together, these results demonstrate that Akap1 genetic deletion increases the severity of hyperoxia-induced acute lung injury in mice.

The Wnt7b/β-catenin signaling pathway is involved in the protective action of calcitonin gene-related peptide on hyperoxia-induced lung injury in premature rats

Background

Calcitonin gene-related peptide (CGRP) can protect against hyperoxia-induced lung injury, making the upregulation of CGRP a potential therapeutic approach for this type of injury. However, the effects of CGRP on the Wnt7b/β-catenin signaling pathway are unclear. In this study, we investigated the roles of CGRP and the Wnt7b/β-catenin signaling pathway in hyperoxia-induced lung injury.

Methods

Premature Sprague Dawley (SD) rats were exposed to 21, 40, 60 and 95% oxygen for 3, 7 and 14 days. The animals’ body weights, survival rates and endogenous CGRP levels were measured. Lung samples were harvested for histological analyses and measurements of malondialdehyde (MDA) concentration and total antioxidant capacity (TAOC). We also assessed the MDA concentration and TAOC in the lung tissues after administration of 200 nmol/kg CGRP_8–37 (a CGRP antagonist). Finally, alveolar epithelial type II (AEC II) cells were isolated from premature rats, exposed to 21 or 95% oxygen for 3, 7 and 14 days, and treated with 10^− 8 mol/l exogenous CGRP. The protein expressions of Wnt7b and β-catenin were assessed using western blotting, and TCF and c-myc mRNA expressions were assessed using qPCR.

Results

Rats exposed to 60 and 95% oxygen had significantly lower body weights and survival rates than the 21 and 40% groups, and the decrease was time dependent. Endogenous CGRP was elevated in the lung tissues of premature rats exposed to 95% oxygen. CGRP_8–37 induced apparent inflammation in the lung tissue and alveolar structural remodeling. In addition, the expression levels of Wnt7b and β-catenin were markedly increased after exposure for 3 days. They peaked at 7 days, then declined at 14 days. The levels of TCF/c-myc in AEC II cells increased significantly after CGRP treatment when compared with cells that had only undergone hyperoxia.

Conclusions

CGRP protected against hyperoxia-induced lung injury in premature rats. This process involves the Wnt7b/β-catenin signaling pathway.

Oxidative stress diseases unique to the perinatal period: A window into the developing innate immune response

The innate immune system has evolved to play an integral role in the normally developing lung and brain. However, in response to oxidative stress, innate immunity, mediated by specific cellular and molecular programs and signaling, contributes to pathology in these same organ systems. Despite opposing drivers of oxidative stress, namely hyperoxia in neonatal lung injury and hypoxia/ischemia in neonatal brain injury, similar pathways-including toll-like receptors, NFκB and MAPK cascades-have been implicated in tissue damage. In this review, we consider recent insights into the innate immune response to oxidative stress in both neonatal and adult models to better understand hyperoxic lung injury and hypoxic-ischemic brain injury across development and aging. These insights support the development of targeted immunotherapeutic strategies to address the challenge of harnessing the innate immune system in oxidative stress diseases of the neonate.

Reactive oxygen species induce injury of the intestinal epithelium during hyperoxia

Long-term therapeutic hyperoxia may exert serious toxic effects on intestinal epithelial cells in vitro and in vivo. The aim of the present study was to investigate the cause of this intestinal injury under conditions of hyperoxia. Caco-2 cells were treated with different concentrations of hydrogen peroxide (H2O2) and 85% hyperoxia for 24 h. higher rates of injury of Caco-2 cells were observed in the hyperoxia and H2O2 groups compared with the control group. The reactive oxygen species (ROS) level of the hyperoxia group was significantly higher compared with that of the 400 µM H2O2 group. The protein and gene levels of RelA, RelB, hypoxia‑inducible factor-1α, tumor necrosis factor-α and apoptosis signal‑regulating kinase 1 were significantly higher in the hyperoxia and H2O2 groups compared with those in the control group. In conclusion, during hyperoxia, intestinal epithelial cells were destroyed and the levels of ROS were increased. Therefore, ROS may play an important role in intestinal injury in a hyperoxic environment.

Hyperoxia causes miR-34a-mediated injury via angiopoietin-1 in neonatal lungs

Hyperoxia-induced acute lung injury (HALI) is a key contributor to the pathogenesis of bronchopulmonary dysplasia (BPD) in neonates, for which no specific preventive or therapeutic agent is available. Here we show that lung micro-RNA (miR)-34a levels are significantly increased in lungs of neonatal mice exposed to hyperoxia. Deletion or inhibition of miR-34a improves the pulmonary phenotype and BPD-associated pulmonary arterial hypertension (PAH) in BPD mouse models, which, conversely, is worsened by miR-34a overexpression. Administration of angiopoietin-1, which is one of the downstream targets of miR34a, is able to ameliorate the BPD pulmonary and PAH phenotypes. Using three independent cohorts of human samples, we show that miR-34a expression is increased in type 2 alveolar epithelial cells in neonates with respiratory distress syndrome and BPD. Our data suggest that pharmacologic miR-34a inhibition may be a therapeutic option to prevent or ameliorate HALI/BPD in neonates.

Long noncoding RNA FOXD3-AS1 regulates oxidative stress-induced apoptosis via sponging microRNA-150

The function of most human long noncoding RNAs (lncRNAs) remains unclear. Our studies identified a highly up-regulated mammalian lncRNA, FOXD3-AS1, known as linc1623 in mice, in the setting of hyperoxia/reactive oxygen species (ROS)-induced lung injury. We found that ROS induced a robust expression of FOXD3-AS1 in mouse lung tissue. Functionally, FOXD3-AS1 promoted oxidative stress-induced lung epithelial cell death. In human lung epithelial cells, the microRNA-150 (miR-150) was identified to interact with FOXD3-AS1; this finding was confirmed using the luciferase reporter assays. Consistently, mutation on the miR-150 pairing sequence in FOXD3-AS1 abolished the interactions between FOXD3-AS1 and miR-150. Additionally, miR-150 mimics suppressed the level of FOXD3-AS1. The antisense oligos of FOXD3-AS1 significantly augmented the intracellular level of miR-150, supporting the theory of sponging effects of FOXD3-AS1 on miR-150. We further investigated the cellular function of miR-150 in our lung injury models. MiR-150 conferred a cytoprotective role in lung epithelial cells after oxidative stress, whereas FOXD3-AS1 promoted cell death. Taken together, our studies indicated that FOXD3-AS1 serves as a sponge or as a competing endogenous noncoding RNA for miR-150, restricting its capability to promote cell growth and thereby exaggerating hyperoxia-induced lung epithelial cell death.-Zhang, D., Lee, H., Haspel, J. A., Jin, Y. Long noncoding RNA FOXD3-AS1 regulates oxidative stress-induced apoptosis via sponging microRNA-150.

Pulmonary Surfactant and Bacterial Lipopolysaccharide: The Interaction and its Functional Consequences

The respiratory system is constantly exposed to pathogens which enter the lungs by inhalation or via blood stream. Lipopolysaccharide (LPS), also named endotoxin, can reach the airspaces as the major component of the outer membrane of Gram-negative bacteria, and lead to local inflammation and systemic toxicity. LPS affects alveolar type II (ATII) cells and pulmonary surfactant and although surfactant molecule has the effective protective mechanisms, excessive amount of LPS interacts with surfactant film and leads to its inactivation. From immunological point of view, surfactant specific proteins (SPs) SP-A and SP-D are best characterized, however, there is increasing evidence on the involvement of SP-B and SP-C and certain phospholipids in immune reactions. In animal models, the instillation of LPS to the respiratory system induces acute lung injury (ALI). It is of clinical importance that endotoxin-induced lung injury can be favorably influenced by intratracheal instillation of exogenous surfactant. The beneficial effect of this treatment was confirmed for both natural porcine and synthetic surfactants. It is believed that the surfactant preparations have anti-inflammatory properties through regulating cytokine production by inflammatory cells. The mechanism by which LPS interferes with ATII cells and surfactant layer, and its consequences are discussed below.

Suplatast tosilate protects the lung against hyperoxic lung injury by scavenging hydroxyl radicals

Prolonged exposure to hyperoxia produces extraordinary amounts of reactive oxygen species (ROS) in the lung and causes hyperoxic lung injury. Although supraphysiological oxygen is routinely administered for the management of respiratory failure, there is no effective strategy to prevent hyperoxic lung injury. In our previous study, we showed that suplatast tosilate, an asthma drug that inhibits T helper 2 (Th2) cytokines, ameliorated bleomycin-induced lung injury and fibrosis through Th2-independent mechanisms. Because bleomycin also generates ROS, we hypothesized that suplatast tosilate might have antioxidant activity and protect the lung against hyperoxic lung injury. To test this hypothesis, mice exposed to hyperoxia were given suplatast tosilate through drinking water. Treatment with suplatast tosilate significantly prolonged mouse survival, reduced the increases in the numbers of inflammatory cells, levels of the pro-inflammatory cytokines/chemokines IL-6 and MCP-1, and protein in bronchoalveolar lavage fluid, and ameliorated lung injury in histological assessment. Suplatast tosilate treatment also significantly inhibited hyperoxia-induced elevations in the levels of 8-hydroxydeoxyguanosine, a marker of oxidative DNA damage, in bronchoalveolar lavage fluid and 8-isoprostane, a marker of lipid peroxidation, in lung tissue. This finding suggests that suplatast tosilate exerts an antioxidant activity in vivo. In addition, we investigated whether suplatast tosilate has a scavenging effect on hydroxyl radical, the most reactive and harmful ROS, using electron paramagnetic resonance spin-trapping. Suplatast tosilate was shown to scavenge hydroxyl radicals in a dose-dependent manner, and its reaction rate constant with hydroxyl radical was calculated as 2.6×10¹¹M^-1S^-1, which is faster than that of several well-established antioxidants, such as ascorbate, glutathione, and cysteine. These results suggest that suplatast tosilate protects the lung against hyperoxic lung injury by decreasing the degree of oxidative stress induced by ROS, particularly by scavenging hydroxyl radicals. Suplatast tosilate might become a potential therapeutic for hyperoxic lung injury.

Lung protection by inhalation of exogenous solubilized extracellular matrix

Decellularized extracellular matrix (ECM) contains complex tissue-specific components that work in concert to promote tissue repair and constructive remodeling and has been used experimentally and clinically to accelerate epithelial wound repair, leading us to hypothesize that lung-derived ECM could mitigate acute lung injury. To explore the therapeutic potential of ECM for noninvasive delivery to the lung, we decellularized and solubilized porcine lung ECM, then characterized the composition, concentration, particle size and stability of the preparation. The ECM preparation at 3.2 mg/mL with average particle size <3 μm was tested in vitro on human A549 lung epithelial cells exposed to 95% O2 for 24 hours, and in vivo by tracheal instillation or nebulization into the lungs of rats exposed intermittently or continuously to 90% O2 for a cumulative 72 hours. Our results showed that the preparation was enriched in collagen, reduced in glycosaminoglycans, and contained various bioactive molecules. Particle size was concentration-dependent. Compared to the respective controls treated with cell culture medium in vitro or saline in vivo, ECM inhalation normalized cell survival and alveolar morphology, and reduced hyperoxia-induced apoptosis and oxidative damage. This proof-of-concept study established the methodology, feasibility and therapeutic potential of exogenous solubilized ECM for pulmonary cytoprotection, possibly as an adjunct or potentiator of conventional therapy.

Harmful Effects of Hyperoxia in Postcardiac Arrest, Sepsis, Traumatic Brain Injury, or Stroke: The Importance of Individualized Oxygen Therapy in Critically Ill Patients

The beneficial effects of oxygen are widely known, but the potentially harmful effects of high oxygenation concentrations in blood and tissues have been less widely discussed. Providing supplementary oxygen can increase oxygen delivery in hypoxaemic patients, thus supporting cell function and metabolism and limiting organ dysfunction, but, in patients who are not hypoxaemic, supplemental oxygen will increase oxygen concentrations into nonphysiological hyperoxaemic ranges and may be associated with harmful effects. Here, we discuss the potentially harmful effects of hyperoxaemia in various groups of critically ill patients, including postcardiac arrest, traumatic brain injury or stroke, and sepsis. In all these groups, there is evidence that hyperoxia can be harmful and that oxygen prescription should be individualized according to repeated assessment of ongoing oxygen requirements.

Hyperbaric Environment: Oxygen and Cellular Damage versus Protection

The elevation of tissue pO2 induced by hyperbaric oxygen (HBO) is a physiological stimulus that elicits a variety of cellular responses. These effects are largely mediated by, or in response to, an increase in the production of reactive oxygen and nitrogen species (RONS). The major consequences of elevated RONS include increased oxidative stress and enhanced antioxidant capacity, and modulation of redox-sensitive cell signaling pathways. Interestingly, these phenomena underlie both the therapeutic and potentially toxic effects of HBO. Emerging evidence indicates that supporting mitochondrial health is a potential method of enhancing the therapeutic efficacy of, and preventing oxygen toxicity during, HBO. This review will focus on the cellular consequences of HBO, and explore how these processes mediate a delicate balance of cellular protection versus damage. © 2017 American Physiological Society. Compr Physiol 7:213-234, 2017.

N-methyl-D-aspartate receptor activation mediates lung fibroblast proliferation and differentiation in hyperoxia-induced chronic lung disease in newborn rats

Background

Previous studies have suggested that endogenous glutamate and its N-methyl-D-aspartate receptors (NMDARs) play important roles in hyperoxia-induced acute lung injury in newborn rats. We hypothesized that NMDAR activation also participates in the development of chronic lung injury after withdrawal of hyperoxic conditions.

Methods

In order to rule out the anti-inflammatory effects of NMDAR inhibitor on acute lung injury, the efficacy of MK-801 was evaluated in vivo using newborn Sprague-Dawley rats treated starting 4 days after cessation of hyperoxia exposure (on postnatal day 8). The role of NMDAR activation in hyperoxia-induced lung fibroblast proliferation and differentiation was examined in vitro using primary cells derived from the lungs of 8-day-old Sprague-Dawley rats exposed to hyperoxic conditions.

Results

Hyperoxia for 3 days induced acute lung injury in newborn rats. The acute injury almost completely disappeared 4 days after cessation of hyperoxia exposure. However, pulmonary fibrosis, impaired alveolarization, and decreased pulmonary compliance were observed on postnatal days 15 and 22. MK-801 treatment during the recovery period was found to alleviate the chronic damage induced by hyperoxia. Four NMDAR 2 s were found to be upregulated in the lung fibroblasts of newborn rats exposed to hyperoxia. In addition, the proliferation and upregulation of alpha-smooth muscle actin and (pro) collagen I in lung fibroblasts were detected in hyperoxia-exposed rats. MK-801 inhibited these changes.

Conclusions

NMDAR activation mediated lung fibroblast proliferation and differentiation and played a role in the development of hyperoxia-induced chronic lung damage in newborn rats.

Lung Perfusion and Ventilation During Cardiopulmonary Bypass Reduces Early Structural Damage to Pulmonary Parenchyma

BACKGROUND

It is unclear whether maintaining pulmonary perfusion and ventilation during cardiopulmonary bypass (CPB) reduces pulmonary inflammatory tissue injury compared with standard CPB where the lungs are not ventilated and are minimally perfused. In this study, we tested the hypothesis that maintenance of lung perfusion and ventilation during CPB decreases regional lung inflammation, which may result in less pulmonary structural damage.

METHODS

Twenty-seven pigs were randomly allocated into a control group only submitted to sternotomy (n = 8), a standard CPB group (n = 9), or a lung perfusion group (n = 10), in which lung perfusion and ventilation were maintained during CPB. Hemodynamics, gas exchanges, respiratory mechanics, and systemic interleukins (ILs) were determined at baseline (T0), at the end of 90 minutes of CPB (T90), and 180 minutes after CPB (T180). Bronchoalveolar lavage (BAL) ILs were obtained at T0 and T180. Dorsal and ventral left lung tissue samples were examined for optical and electron microscopy.

RESULTS

At T90, there was a transient reduction in PaO2/FIO2 in CPB (126 ± 64 mm Hg) compared with the control and lung perfusion groups (296 ± 46 and 244 ± 57 mm Hg; P < 0.001), returning to baseline at T180. Serum ILs were not different among the groups throughout the study, whereas there were significant increases in BAL IL-6 (P < 0.001), IL-8 (P < 0.001), and IL-10 (P < 0.001) in both CPB and lung perfusion groups compared with the control group. Polymorphonuclear counts within the lung tissue were smaller in the lung perfusion group than in the CPB group (P = 0.006). Electron microscopy demonstrated extrusion of surfactant vesicles into the alveolar spaces and thickening of the alveolar septa in the CPB group, whereas alveolar and capillary histoarchitecture was better preserved in the lung perfusion group.

CONCLUSIONS

Maintenance of lung perfusion and ventilation during CPB attenuated early histologic signs of pulmonary inflammation and injury compared with standard CPB. Although increased compared with control animals, there were no differences in serum or BAL IL in animals receiving lung ventilation and perfusion during CPB compared with standard CPB.

Hyperoxia-induced p47phox activation and ROS generation is mediated through S1P transporter Spns2, and S1P/S1P1&2 signaling axis in lung endothelium

Hyperoxia-induced lung injury adversely affects ICU patients and neonates on ventilator assisted breathing. The underlying culprit appears to be reactive oxygen species (ROS)-induced lung damage. The major contributor of hyperoxia-induced ROS is activation of the multiprotein enzyme complex NADPH oxidase. Sphingosine-1-phosphate (S1P) signaling is known to be involved in hyperoxia-mediated ROS generation; however, the mechanism(s) of S1P-induced NADPH oxidase activation is unclear. Here, we investigated various steps in the S1P signaling pathway mediating ROS production in response to hyperoxia in lung endothelium. Of the two closely related sphingosine kinases (SphKs)1 and 2, which synthesize S1P from sphingosine, only Sphk1(-/-) mice conferred protection against hyperoxia-induced lung injury. S1P is metabolized predominantly by S1P lyase and partial deletion of Sgpl1 (Sgpl1(+/-)) in mice accentuated lung injury. Hyperoxia stimulated S1P accumulation in human lung microvascular endothelial cells (HLMVECs), and downregulation of S1P transporter spinster homolog 2 (Spns2) or S1P receptors S1P1&2, but not S1P3, using specific siRNA attenuated hyperoxia-induced p47(phox) translocation to cell periphery and ROS generation in HLMVECs. These results suggest a role for Spns2 and S1P1&2 in hyperoxia-mediated ROS generation. In addition, p47(phox) (phox:phagocyte oxidase) activation and ROS generation was also reduced by PF543, a specific SphK1 inhibitor in HLMVECs. Our data indicate a novel role for Spns2 and S1P1&2 in the activation of p47(phox) and production of ROS involved in hyperoxia-mediated lung injury in neonatal and adult mice.

HMGB1 regulates IL-33 expression in acute respiratory distress syndrome

The development and progression of acute respiratory distress syndrome (ARDS) has been shown to be regulated by cytokines. IL-33 and HMGB1 are conventionally considered as nuclear proteins and have a proinflammatory role. Studies have confirmed that HMGB1 has a significant role in ARDS, but few studies have provided direct evidence to confirm that IL33 is involved in ARDS. The purpose of our study was to determine whether IL-33 is elevated in ARDS and the relationship between IL-33 and HMGB1 in ARDS. We established a mouse model of LPS-induced lung inflammation/injury. Serum, bronchoalveolar lavage fluid (BALF) and lung tissues were obtained to determine the related indicators. IL-33 levels in both the serum, BALF and lungs were significantly increased at 24h after LPS administration compared to the control group. We also found that HMGB1 and other Th1 cytokine/chemokine levels in serum and BALF were also significantly elevated, but the Th2 cytokine levels in serum and BALF didn't increase. To further study the relationship between IL-33 and HMGB1, mice were pretreated with glycyrrhizin (an inhibitor of HMGB1) prior to LPS administration. We found that the expression of IL-33 and HMGB1 were markedly lower than those in the LPS group and the lung injury was ameliorated. The levels of other Th1 cytokines and chemokines in serum and BALF were also significantly decreased. The results showed that IL-33 is likely a major factor in ARDS, and the release of HMGB1 may be correlated with up-regulation of IL-33 expression.

Urm1: an essential regulator of JNK signaling and oxidative stress in Drosophila melanogaster

Ubiquitin-related modifier 1 (Urm1) is a ubiquitin-like molecule (UBL) with the dual capacity to act both as a sulphur carrier and posttranslational protein modifier. Here we characterize the Drosophila melanogaster homologues of Urm1 (CG33276) and its E1 activating enzyme Uba4 (CG13090), and show that they function together to induce protein urmylation in vivo. Urm1 conjugation to target proteins in general, and to the evolutionary conserved substrate Peroxiredoxin 5 (Prx5) specifically, is dependent on Uba4. A complete loss of Urm1 is lethal in flies, although a small number of adult zygotic Urm1 (n123) mutant escapers can be recovered. These escapers display a decreased general fitness and shortened lifespan, but in contrast to their S. cerevisiae counterparts, they are resistant to oxidative stress. Providing a molecular explanation, we demonstrate that cytoprotective JNK signaling is increased in Urm1 deficient animals. In agreement, molecular and genetic evidence suggest that elevated activity of the JNK downstream target genes Jafrac1 and gstD1 strongly contributes to the tolerance against oxidative stress displayed by Urm1 (n123) null mutants. In conclusion, Urm1 is a UBL that is involved in the regulation of JNK signaling and the response against oxidative stress in the fruit fly.

MiR-15a/16 Regulates Apoptosis of Lung Epithelial Cells after Oxidative Stress

Lung epithelial cell apoptosis is an important feature of hyperoxia-induced lung injury. Death receptor-associated extrinsic pathway and mitochondria-associated intrinsic pathway both mediate the development of lung epithelial cell apoptosis. Despite decades of research, molecular mechanisms of hyperoxia-induced epithelial cell apoptosis remain incompletely understood. Here we report a novel regulatory paradigm in response to hyperoxia-associated oxidative stress. Hyperoxia markedly up-regulated miR-15a/16 levels in lung epithelial cells, broncho-alveolar lavage fluid (BALF) and lung tissue. This effect was mediated by hyperoxia-induced reactive oxygen species (ROS). Functionally, miR-15a/16 inhibitors induced caspase 3-mediated lung epithelial cell apoptosis, in the presence of hyperoxia. MiR-15a/16 inhibitors robustly enhanced FADD level and down-regulated Bcl-2 expression. Consistently, cleaved caspase 8 and 9 were highly induced in the miR-15a/16 deficient cells, after hyperoxia. Using airway epithelial cell specific, miR-15a/16^-/- mice, we found that Bcl-2 significantly reduced in lung epithelial cells in vivo after hyperoxia. In contrast, caspase 3, 8 and Bcl-2 associated death promoter (BAD) were highly elevated in the miR-15a/16^-/- epithelial cells in vivo. Interestingly, in lung epithelial malignant cells, rather than benign cells, deletion of miR-15a/16 prevented apoptosis. Furthermore, deletion of miR-15a/16 in macrophages also prohibited apoptosis, opposite to what we have found in normal lung epithelial cells. Taken together, our data suggested that miR-15a/16 may exert differential roles in different cell types. MiR-15a/16 deficiency result in lung epithelial cell apoptosis in response to hyperoxia, via modulating both intrinsic and extrinsic apoptosis pathways.

Deletion of ASK1 Protects against Hyperoxia-Induced Acute Lung Injury

Apoptosis signal-regulating kinase 1 (ASK1), a member of the MAPK kinase kinase kinase (MAP3K) family, is activated by various stimuli, which include oxidative stress, endoplasmic reticulum (ER) stress, calcium influx, DNA damage-inducing agents and receptor-mediated signaling through tumor necrosis factor receptor (TNFR). Inspiration of a high concentration of oxygen is a palliative therapy which counteracts hypoxemia caused by acute lung injury (ALI)-induced pulmonary edema. However, animal experiments so far have shown that hyperoxia itself could exacerbate ALI through reactive oxygen species (ROS). Our previous data indicates that ASK1 plays a pivotal role in hyperoxia-induced acute lung injury (HALI). However, it is unclear whether or not deletion of ASK1 in vivo protects against HALI. In this study, we investigated whether ASK1 deletion would lead to attenuation of HALI. Our results show that ASK1 deletion in vivo significantly suppresses hyperoxia-induced elevation of inflammatory cytokines (i.e. IL-1β and TNF-α), cell apoptosis in the lung, and recruitment of immune cells. In summary, the results from the study suggest that deletion of ASK1 in mice significantly inhibits hyperoxic lung injury.

Hyperoxia causes diffuse alveolar damage through mechanisms involving upregulation of c-Myc/Bax and enhanced production of reactive oxygen species

BACKGROUND

Hyperoxia is a known cause of diffuse alveolar damage (DAD). We previously reported the transcript profiling of DAD induced by hyperoxia exposure in mouse lungs and showed that the gene expression of myelocytomatosis oncogene (c-Myc) was significantly upregulated whereas that of surfactant-associated protein (SP)-C was downregulated. However, the mechanism underlying hyperoxia-induced DAD is not well understood.

METHODS

The hyperoxia-induced changes in SP-A/B/C/D, c-Myc, B-cell chronic lymphocytic leukemia/lymphoma (Bcl)-2, and Bcl-2-associated X protein (Bax) expression in mouse lungs were examined by cDNA microarray analysis. The expression levels of the above mentioned genes, cell viability, caspase activity, and reactive oxygen species (ROS) production were also examined in the human lung adenocarcinoma cell line A549 and mouse fibroblast-like cell line NIH/3T3.

RESULTS

Hyperoxia induced a decrease in SP-C/A expression in mouse lungs, and SP-C downregulation was also confirmed in A549 cells. In addition to enhanced c-Myc expression, Bax expression also increased following exposure of the mice to hyperoxia. In vitro analysis showed that expression of these genes is regulated in a cell-type-dependent manner, i.e., upregulation of c-Myc in NIH/3T3 cells and Bax in A549 cells occurred regardless of whether there was a similar decrease in cell viability and increase in caspase-3/7 activation in response to hyperoxia. ROS production and caspase-8 activation were also observed in both cells.

CONCLUSIONS

We concluded that hyperoxia induces ROS production and cell death in lung tissues through a cell-type specific mechanism involving the upregulation of c-Myc/Bax, and caspase-8 and -3/7 activation-dependent pathways, thereby leading to the development of DAD.

With-No-Lysine Kinase 4 Mediates Alveolar Fluid Regulation in Hyperoxia-Induced Lung Injury

OBJECTIVES

To investigate mechanisms involved in the regulation of epithelial ion channels and alveolar fluid clearance in hyperoxia-induced lung injury.

DESIGN

Laboratory animal experiments.

SETTING

Animal care facility procedure room in a medical center.

SUBJECTS

Wild-type, STE20/SPS1-related proline/alanine-rich kinase knockout (SPAK(-/-)), and with-no-lysine kinase 4 knockin (WNK4(D561A/+)) mice.

INTERVENTIONS

Mice were exposed to room air or 95% hyperoxia for 60 hours.

MEASUREMENTS AND MAIN RESULTS

Exposure to hyperoxia for 60 hours increased the lung expression of with-no-lysine kinase 4 and led to STE20/SPS1-related proline/alanine-rich kinase and sodium-potassium-chloride cotransporter phosphorylation, which resulted in the suppression of alveolar fluid clearance and increase of lung edema. WNK4(D561A/+) mice at the baseline presented an abundance of epithelium sodium channel and high levels of STE20/SPS1-related proline/alanine-rich kinase and sodium-potassium-chloride cotransporter phosphorylation. Compared with the wild-type group, hyperoxia caused greater epithelium sodium channel expression in WNK4(D561A/+) mice, but no significant difference in STE20/SPS1-related proline/alanine-rich kinase and sodium-potassium-chloride cotransporter phosphorylation. The functional inactivation of sodium-potassium-chloride cotransporter by gene knockout in SPAK(-/-) mice yielded a lower severity of lung injury and longer animal survival, whereas constitutive expression of with-no-lysine kinase 4 exacerbated the hyperoxia-induced lung injury. Pharmacologic inhibition of sodium-potassium-chloride cotransporter by inhaled furosemide improved animal survival in WNK4(D561A/+) mice. By contrast, inhibition of epithelium sodium channel exacerbated the hyperoxia-induced lung injury and animal death.

CONCLUSIONS

With-no-lysine kinase 4 plays a crucial role in the regulation of epithelial ion channels and alveolar fluid clearance, mainly via phosphorylation and activation of STE20/SPS1-related proline/alanine-rich kinase and sodium-potassium-chloride cotransporter.