Oxygen toxicity in mouse lung: pathways to cell death

Hyperoxic exposure alters intracellular bioenergetics distribution in human pulmonary cells

AIMS

Pulmonary oxygen toxicity is caused by exposure to a high fraction of inspired oxygen, which damages multiple cell types within the lung. The cellular basis for pulmonary oxygen toxicity includes mitochondrial dysfunction. The aim of this study was to identify the effects of hyperoxic exposure on mitochondrial bioenergetic and dynamic functions in pulmonary cells.

MAIN METHODS

Mitochondrial respiration, inner membrane potential, dynamics (including motility), and distribution of mitochondrial bioenergetic capacity in two intracellular regions were quantified using cultured human lung microvascular endothelial cells, human pulmonary artery endothelial cells and A549 cells. Hyperoxic (95 % O₂) exposures lasted 24, 48 and 72 h, durations relevant to mechanical ventilation in intensive care settings.

KEY FINDINGS

Mitochondrial motility was altered following all hyperoxic exposures utilized in experiments. Inhomogeneities in inner membrane potential and respiration parameters were present in each cell type following hyperoxia. The partitioning of ATP-linked respiration was also hyperoxia-duration and cell type dependent. Hyperoxic exposure lasting 48 h or longer provoked the largest alterations in mitochondrial motility and the greatest decreases in ATP-linked respiration, with a suggestion of decreases in respiration complex protein levels.

SIGNIFICANCE

Hyperoxic exposures of different durations produce intracellular inhomogeneities in mitochondrial dynamics and bioenergetics in pulmonary cells. Oxygen therapy is utilized commonly in clinical care and can induce undesirable decrements in bioenergy function needed to maintain pulmonary cell function and viability. There may be adjunctive or prophylactic measures that can be employed during hyperoxic exposures to prevent the mitochondrial dysfunction that signals the presence of oxygen toxcity.

Practice of oxygen use in anesthesiology – a survey of the European Society of Anaesthesiology and Intensive Care

Background

Oxygen is one of the most commonly used drugs by anesthesiologists. The World Health Organization (WHO) gave recommendations regarding perioperative oxygen administration, but the practice of oxygen use in anesthesia, critical emergency, and intensive care medicine remains unclear.

Methods

We conducted an online survey among members of the European Society of Anaesthesiology and Intensive Care (ESAIC). The questionnaire consisted of 46 queries appraising the perioperative period, emergency medicine and in the intensive care, knowledge about current recommendations by the WHO, oxygen toxicity, and devices for supplemental oxygen therapy.

Results

Seven hundred ninety-eight ESAIC members (2.1% of all ESAIC members) completed the survey. Most respondents were board-certified and worked in hospitals with > 500 beds. The majority affirmed that they do not use specific protocols for oxygen administration. WHO recommendations are unknown to 42% of respondents, known but not followed by 14%, and known and followed by 24% of them. Respondents prefer inspiratory oxygen fraction (FiO₂) ≥80% during induction and emergence from anesthesia, but intraoperatively < 60% for maintenance, and higher FiO₂ in patients with diseased than non-diseased lungs. Postoperative oxygen therapy is prescribed more commonly according to peripheral oxygen saturation (SpO₂), but shortage of devices still limits monitoring. When monitoring is used, SpO₂ ≤ 95% is often targeted. In critical emergency medicine, oxygen is used frequently in patients aged ≥80 years, or presenting with respiratory distress, chronic obstructive pulmonary disease, myocardial infarction, and stroke. In the intensive care unit, oxygen is mostly targeted at 96%, especially in patients with pulmonary diseases.

Conclusions

The current practice of perioperative oxygen therapy among respondents does not follow WHO recommendations or current evidence, and access to postoperative monitoring devices impairs the individualization of oxygen therapy. Further research and additional teaching about use of oxygen are necessary.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12871-022-01884-2.

Oxygen toxicity: cellular mechanisms in normobaric hyperoxia

In clinical settings, oxygen therapy is administered to preterm neonates and to adults with acute and chronic conditions such as COVID-19, pulmonary fibrosis, sepsis, cardiac arrest, carbon monoxide poisoning, and acute heart failure. In non-clinical settings, divers and astronauts may also receive supplemental oxygen. In addition, under current standard cell culture practices, cells are maintained in atmospheric oxygen, which is several times higher than what most cells experience in vivo. In all the above scenarios, the elevated oxygen levels (hyperoxia) can lead to increased production of reactive oxygen species from mitochondria, NADPH oxidases, and other sources. This can cause cell dysfunction or death. Acute hyperoxia injury impairs various cellular functions, manifesting ultimately as physiological deficits. Chronic hyperoxia, particularly in the neonate, can disrupt development, leading to permanent deficiencies. In this review, we discuss the cellular activities and pathways affected by hyperoxia, as well as strategies that have been developed to ameliorate injury.

Oxygen Therapy in Cluster Headache, Migraine, and Other Headache Disorders

Oxygen therapy (OT) can relieve head pain in certain primary headache disorders, including cluster headache (CH). The exact underlying mechanism is currently uncertain, but suggested mechanisms include inhibition of the trigeminoautonomic reflex, modulation of neurotransmitters, and cerebral vasoconstriction. OT is the standard for acute treatment of CH, but patients with CH often experience considerable difficulties accessing home OT due to problems with insurance coverage. Inhalation of 100% oxygen at 6–12 L/min for 15–30 min using a non-rebreather face mask is one of the most effective acute therapies for CH, but several trials have indicated the superiority of higher oxygen flow rates of up to 15 L/min and/or using a demand-valve oxygen mask that can produce very high flow rates. Two randomized controlled trials have demonstrated the efficacy of OT in migraine, but obtaining reliable evidence is considered difficult because of different inhalation protocols, varying outcome measures, and small samples. There are some reports on the efficacy of OT as an adjuvant therapy in hypnic headache, primary headache in the emergency department, and even postdural puncture headache. The goal of this review article is to expand the knowledge regarding the use of oxygen in the treatment of headache disorders.

Outcomes and Predictors of Severe Hyperoxemia in Patients Receiving Mechanical Ventilation: A Single-Center Cohort Study

RATIONALE

Supplemental oxygen is among the most commonly administered therapies in intensive care units. High supplemental oxygen exposure has been associated with harm in observational human studies and animal models. Yet no consensus exists regarding which dose and duration of high oxygen constitutes harmful hyperoxemia, and little is known regarding the clinical factors that predict potentially injurious exposure.

OBJECTIVES

To determine the level and duration of arterial oxygen (PaO2) associated with mortality among mechanically ventilated patients, and to identify the clinical factors that predict this exposure.

METHODS

We performed a retrospective cohort study of patients who received invasive mechanical ventilation at a single academic institution in 2017 and 2018. We used a generalized additive model to visualize the relationship between the measured PaO2 via arterial blood gases (ABGs) and 30-day mortality. We used multivariable logistic regression to identify patient- and hospital-level factors that predict exposure to harmful hyperoxemia.

RESULTS

We analyzed 2,133 patients with 33,310 ABGs obtained during mechanical ventilation. We identified a U-shaped relationship between PaO2 and mortality, where PaO2 was positively correlated with mortality above a threshold of 200 mmHg. 1,184 patients (55.5%) had at least one PaO2 level above this threshold. If patients spent an entire day exposed to PaO2 > 200 mmHg, they had 2.19 (95% CI 1.33 - 3.60, p = 0.002) greater odds of 30-day mortality in an adjusted analysis. Any exposure to severe hyperoxemia (PaO2 > 200 mmHg), was associated with mortality (OR 1.29, 95% CI 1.04 - 1.59, p = 0.021). The strongest clinical predictor of severe hyperoxemia exposure was the identity of the ICU in which mechanical ventilation was delivered.

CONCLUSIONS

Exposure to high arterial oxygen concentrations is common among mechanically ventilated patients, and the dose and duration of PaO2 ≥ 200 mmHg is associated with mortality. Severe hyperoxemia is highly variable across ICUs, and is far more common in clinical practice than in recent randomized trials of oxygen targeting strategies. Efforts to minimize this common and injurious exposure level are needed.

Excessive Oxygen Supplementation in the First Day of Mechanical Ventilation Is Associated With Multiple Organ Dysfunction and Death in Critically Ill Children

OBJECTIVES

To determine if greater cumulative exposure to oxygen despite adequate oxygenation over the first 24 hours of mechanical ventilation is associated with multiple organ dysfunction syndrome at 7 days and inhospital mortality in critically ill children.

DESIGN

Retrospective, observational cohort study.

SETTING

Two urban, academic PICUs.

PATIENTS

Patients less than 18 years old who required mechanical ventilation within 3 days of admission between 2010 and 2018 (Lurie Children's Hospital) or 2010 and 2016 (Comer Children's Hospital).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

There were 5,406 mechanically ventilated patients, of which 960 (17.8%) had multiple organ dysfunction syndrome on day 7 of admission and 319 died (5.9%) during their hospitalization. Cumulative exposure to greater amounts of supplemental oxygen, while peripheral oxygen saturation was 95% or more during the first 24 hours of mechanical ventilation was independently associated with an increased risk of both multiple organ dysfunction syndrome on day 7 and inhospital mortality after adjusting for confounders. Patients in the highest quartile of cumulative oxygen exposure had an increased odds of multiple organ dysfunction syndrome on day 7 (adjusted odds ratio, 3.9; 95% CI, 2.7-5.9) and inhospital mortality (adjusted odds ratio, 1.7; 95% CI, 1.1-2.9), when compared with those in the lowest quartile of cumulative oxygen exposure after adjusting for age, presence of multiple organ dysfunction syndrome on day 1 of mechanical ventilation, immunocompromised state, and study site.

CONCLUSIONS

Greater cumulative exposure to excess supplemental oxygen in the first 24 hours of mechanical ventilation is independently associated with an increased risk of multiple organ dysfunction syndrome on day 7 of admission and inhospital mortality in critically ill children.

Gelsolin Attenuates Neonatal Hyperoxia-Induced Inflammatory Responses to Rhinovirus Infection and Preserves Alveolarization

Prematurity and bronchopulmonary dysplasia (BPD) increase the risk of asthma later in life. Supplemental oxygen therapy is a risk factor for chronic respiratory symptoms in infants with BPD. Hyperoxia induces cell injury and release of damage-associated molecular patterns (DAMPs). Cytoskeletal filamentous actin (F-actin) is a DAMP which binds Clec9a, a C-type lectin selectively expressed on CD103+ dendritic cells (DCs). Co-stimulation of Clec9a and TLR3 induces maximal proinflammatory responses. We have shown that neonatal hyperoxia (a model of BPD) increases lung IL-12+Clec9a+CD103+ DCs, pro-inflammatory responses and airway hyperreactivity following rhinovirus (RV) infection. CD103+ DCs and Clec9a are required for these responses. Hyperoxia increases F-actin levels in bronchoalveolar lavage fluid (BALF). We hypothesized that the F-actin severing protein gelsolin attenuates neonatal hyperoxia-induced Clec9a+CD103+ DC-dependent pro-inflammatory responses to RV and preserves alveolarization. We exposed neonatal mice to hyperoxia and treated them with gelsolin intranasally. Subsequently we inoculated the mice with RV intranasally. Alternatively, we inoculated normoxic neonatal mice with BALF from hyperoxia-exposed mice (hyperoxic BALF), RV and gelsolin. We analyzed lung gene expression two days after RV infection. For in vitro studies, lung CD11c+ cells were isolated from C57BL/6J or Clec9a^gfp-/- mice and incubated with hyperoxic BALF and RV. Cells were analyzed by flow cytometry. In neonatal mice, gelsolin blocked hyperoxia-induced Il12p40, TNF-α and IFN-γ mRNA and protein expression in response to RV infection. Similar effects were observed when gelsolin was co-administered with hyperoxic BALF and RV. Gelsolin decreased F-actin levels in hyperoxic BALF in vitro and inhibited hyperoxia-induced D103lo DC expansion and inflammation in vivo. Gelsolin also attenuated hyperoxia-induced hypoalveolarization. Further, incubation of lung CD11c+ cells from WT and Clec9a^gfp-/- mice with hyperoxic BALF and RV, showed Clec9a is required for maximal hyperoxic BALF and RV induced IL-12 expression in CD103+ DCs. Finally, in tracheal aspirates from mechanically ventilated human preterm infants the F-actin to gelsolin ratio positively correlates with FiO2, and gelsolin levels decrease during the first two weeks of mechanical ventilation. Collectively, our findings demonstrate a promising role for gelsolin, administered by inhalation into the airway to treat RV-induced exacerbations of BPD and prevent chronic lung disease.

The Aryl Hydrocarbon Receptor (AHR): A Novel Therapeutic Target for Pulmonary Diseases?

The aryl hydrocarbon receptor (AHR) is a cytoplasmic transcription factor that is well-known for regulating xenobiotic metabolism. Studies in knockout and transgenic mice indicate that the AHR plays a vital role in the development of liver and regulation of reproductive, cardiovascular, hematopoietic, and immune homeostasis. In this focused review on lung diseases associated with acute injury and alveolar development, we reviewed and summarized the current literature on the mechanistic role(s) and therapeutic potential of the AHR in acute lung injury, chronic obstructive pulmonary disease, and bronchopulmonary dysplasia (BPD). Pre-clinical studies indicate that endogenous AHR activation is necessary to protect neonatal and adult lungs against hyperoxia- and cigarette smoke-induced injury. Our goal is to provide insight into the high translational potential of the AHR in the meaningful management of infants and adults with these lung disorders that lack curative therapies.

Electrical remodeling and cardiotoxicity precedes structural and functional remodeling of mouse hearts under hyperoxia treatment

Clinical reports suggest a high incidence of ICU mortality with the use of hyperoxia during mechanical ventilation in patients. Our laboratory is pioneer in studying effect of hyperoxia on cardiac pathophysiology. In this study for the first time, we are reporting the sequence of cardiac pathophysiological events in mice under hyperoxic conditions in time-dependent manner. C57BL/6J male mice, aged 8-10 weeks, were treated with either normal air or >90% oxygen for 24, 48, and 72 h. Following normal air or hyperoxia treatment, physical, biochemical, functional, electrical, and molecular parameters were analyzed. Our data showed that significant reduction of body weight observed as early as 24 h hyperoxia treatment, whereas, no significant changes in heart weight until 72 h. Although we do not see any fibrosis in these hearts, but observed significant increase in cardiomyocyte size with hyperoxia treatment in time-dependent manner. Our data also demonstrated that arrhythmias were present in mice at 24 h hyperoxia, and worsened comparatively after 48 and 72 h. Echocardiogram data confirmed cardiac dysfunction in time-dependent manner. Dysregulation of ion channels such as Kv4.2 and KChIP2; and serum cardiac markers confirmed that hyperoxia-induced effects worsen with each time point. From these observations, it is evident that electrical remodeling precedes structural remodeling, both of which gets worse with length of hyperoxia exposure, therefore shorter periods of hyperoxia exposure is always beneficial for better outcome in ICU/critical care units.

Application of adverse outcome pathway networks to integrate mechanistic data informing the choice of a point of departure for hydrogen sulfide exposure limits

Acute exposure to hydrogen sulfide initiates a series of hallmark biological effects that occur progressively at increasing exposure levels: odor perception, conjunctivitis, olfactory paralysis, "knockdown," pulmonary edema, and apnea. Although effects of exposure to high concentrations of hydrogen sulfide are clear, effects associated with chronic, low-level exposure in humans is under debate, leading to uncertainty in the critical effect used in regulatory risk assessments addressing low dose exposures. This study integrates experimental animal, observational epidemiology, and occupational exposure evidence by applying a pathway-based approach. A hypothesized adverse outcome pathway (AOP) network was developed from 34 studies, composed of 4 AOPs sharing 1 molecular initiating events (MIE) and culminating in 4 adverse outcomes. A comparative assessment of effect levels and weight of evidence identified an AOP leading to a biologically-plausible, low-dose outcome relative to the other outcomes (nasal lesions, 30 ppm versus olfactory paralysis, >100 ppm; neurological effects, >80 ppm; pulmonary edema, >80 ppm). This AOP (i.e. AOP1) consists of the following key events: cytochrome oxidase inhibition (>10 ppm), neuronal cell loss (>30 ppm), and olfactory nasal lesions (defined as both neuronal cell loss and basal cell hyperplasia; >30 ppm) in rodents. The key event relationships in this pathway were supported by moderate empirical evidence and have high biological plausibility due to known mechanistic understanding and consistency in observations for diverse chemicals.

Lung CD103+dendritic cells and Clec9a signaling are required for neonatal hyperoxia-induced inflammatory responses to rhinovirus infection

Premature infants, especially those with bronchopulmonary dysplasia (BPD), develop recurrent severe respiratory viral illnesses. We have shown that hyperoxic exposure of immature mice, a model of BPD, increases lung IL-12-producing Clec9a+ CD103+ dendritic cells (DCs), pro-inflammatory responses, and airway hyperreactivity following rhinovirus (RV) infection. However, the requirement for CD103+ DCs and Clec9a, a DAMP receptor that binds necrotic cell cytoskeletal filamentous actin (F-actin), for RV-induced inflammatory responses has not been demonstrated. To test this, 2-day-old C57BL/6J, CD103+ DC-deficient Batf3-/- or Clec9agfp-/- mice were exposed to normoxia or hyperoxia for 14 days. Also, selected mice were treated with neutralizing antibody against CD103. Immediately after hyperoxia, the mice were inoculated with RV intranasally. We found that compared with wild-type mice, hyperoxia-exposed Batf3-/- mice showed reduced levels of IL-12p40, IFN-γ, and TNF-α, fewer IFN-γ-producing CD4+ T cells, and decreased airway responsiveness following RV infection. Similar effects were observed in anti-CD103-treated and Clec9agfp-/- mice. Furthermore, hyperoxia increased airway dead cell number and extracellular F-actin levels. Finally, studies in preterm infants with respiratory distress syndrome showed that tracheal aspirate CLEC9A expression positively correlated with IL12B expression, consistent with the notion that CLEC9A+ cells are responsible for IL-12 production in humans as well as mice. We conclude that CD103+ DCs and Clec9a are required for hyperoxia-induced pro-inflammatory responses to RV infection. In premature infants, Clec9a-mediated activation of CD103+ DCs may promote pro-inflammatory responses to viral infection, thereby driving respiratory morbidity.

Experimental Models of Acute Lung Injury: their Advantages and Limitations

Acute damage to the lung may originate from various direct and indirect reasons. Direct lung injury may be caused by pneumonia, near-drowning, aspiration, inhalation of toxic gases etc., while indirect lung injury is secondary, following any severe extra-pulmonary disease, e.g. sepsis, acute pancreatitis, or severe trauma. Due to a complex pathophysiology of the acute lung injury, the treatment is also extremely complicated and except for lung-protective ventilation there have been no specific treatment approaches recommended. An urgent need for a reliable and sufficiently effective treatment forces the researchers into testing novel therapeutic strategies. However, most of these determinations should be done in the laboratory conditions using animals. Complex methods of preparation of various experimental models of the acute lung injury has gradually developed within decades. Nowadays, there have been the models of direct, indirect, or mixed lung injury well established, as well as the models evoked by a combination of two triggering factors. Although the applicability of the results from animal experiments to patients might be limited by many factors, animal models are essential for understanding the patho-physiology of acute lung injury and provide an exceptional opportunity to search for novel therapeutical strategies.

Oxygen-Detecting Synaptic Device for Realization of Artificial Autonomic Nervous System for Maintaining Oxygen Homeostasis

Incorporation of various functions of a biological nervous system into electronic devices is an intriguing challenge in the realization of a human-like recognition and response system. Emerging artificial synaptic devices capable of processing electronic signals through neuromorphic functions operate such biomimetic systems similarly to biological nervous systems. Here, an oxygen-sensitive artificial synaptic device that simultaneously detects oxygen concentration and generates a synaptic signal is demonstrated. The device successfully achieves an interconversion between the excitatory and inhibitory modes of the synaptic current at various oxygen concentrations by virtue of an oxygen-sensitive trilayered organic double heterojunction. The oxygen-induced traps in the organic layer modulate the majority charge carrier from holes to electrons, and this modulation induces an interconversion between the excitatory and inhibitory modes according to the environmental oxygen condition. Finally, the proposed synaptic device is applied to the realization of a negative feedback system for regulation of oxygen homeostasis, which mimics the human autonomic nervous system. The oxygen-sensitive synaptic device proposed in this study is expected to open up new possibilities for the development of a biomimetic neural system that can respond appropriately to various environmental changes.

Implementing target range oxygen in critical care: A quality improvement pilot study

Background

Iatrogenic hyperoxaemia is common on critical care units and has been associated with increased mortality. We commenced a quality improvement pilot study to analyse the views and practice of critical care staff regarding oxygen therapy and to change practice to ensure that all patients have a prescribed target oxygen saturation range.

Methods

A baseline measurement of oxygen target range prescribing was undertaken alongside a survey of staff attitudes. We then commenced a programme of change, widely promoting an agreed oxygen target range prescribing policy. The analyses of target range prescribing and staff survey were repeated four to five months later.

Results

Thirty-three staff members completed the baseline survey, compared to 29 in the follow-up survey. There was no discernible change in staff attitudes towards oxygen target range prescribing. Fifty-four patients were included in the baseline survey and 124 patients were assessed post implementation of changes. The proportion of patients with an oxygen prescription with a target range improved from 85% to 95% (χ² = 5.17, p = 0.02) and the proportion of patients with an appropriate prescribed target saturation range increased from 85% to 91% (χ² = 1.4, p = 0.24). The improvement in target range prescribing was maintained at 96% 12 months later.

Conclusions

The introduction and promotion of a structured protocol for oxygen prescribing were associated with a sustained increase in the proportion of patients with a prescribed oxygen target range on this unit.

miR‑21‑5p ameliorates hyperoxic acute lung injury and decreases apoptosis of AEC II cells via PTEN/AKT signaling in rats

Inhibiting apoptosis of type II alveolar epithelial cells (AEC II) is an effective way to decrease hyperoxic acute lung injury (HALI); however, the specific underlying molecular mechanisms have not yet been fully elucidated. Although miRNA‑21‑5p has previously been reported to decrease H2O2‑induced AEC II apoptosis by targeting PTEN in vitro, whether miR‑21‑5p can decrease HALI in vivo and the downstream molecular mechanisms remain unclear. In the present study, rats were endotracheally administered with an miR‑21‑5p‑encoding (AAV‑6‑miR‑21‑5p) or a negative control adenovirus vector, and then a HALI model was established by exposure to hyperoxia. At 3 weeks following the administration of AAV‑6‑miR‑21‑5p, the severity of HALI was decreased, as evidenced by the improved outcome of the oxygenation index, respiratory index, wet/dry weight ratio and pathological scores of the HALI lungs. To further investigate the underlying mechanisms, AEC II cells were isolated from the lungs of the experimental rats and cultured. The expression levels of miR‑21‑5p and its target gene, PTEN, were detected, as well as the levels of phosphorylated and total AKT. In addition, the apoptosis rate of AEC II was detected by flow cytometry. The results demonstrated that AAV‑6‑miR‑21‑5p administration increased the miR‑21‑5p levels in primary AEC II cells, while it decreased the expression levels of PTEN. miR‑21‑5p overexpression also increased AKT phosphorylation in AEC II cells from the HALI lungs compared with that of the HALI alone group and the control virus group. The present study indicated that miR‑21‑5p ameliorated HALI in vivo, which may have resulted from the inhibition of PTEN/AKT‑induced apoptosis of AEC II cells. These findings suggest that miR‑21‑5p and PTEN/AKT signaling might serve as potential targets for HALI treatment.

Association of Severe Hyperoxemia Events and Mortality Among Patients Admitted to a Pediatric Intensive Care Unit

Importance

A high Pao2, termed hyperoxemia, is postulated to have deleterious health outcomes. To date, the association between hyperoxemia during the ongoing management of critical illness and mortality has been incompletely evaluated in children.

Objective

To examine whether severe hyperoxemia events are associated with mortality among patients admitted to a pediatric intensive care unit (PICU).

Design, Setting, and Participants

A retrospective cohort study was conducted over a 10-year period (January 1, 2009, to December 31, 2018); all 23 719 PICU encounters at a quaternary children's hospital with a documented arterial blood gas measurement were evaluated.

Exposures

Severe hyperoxemia, defined as Pao2 level greater than or equal to 300 mm Hg (40 kPa).

Main Outcomes and Measures

The highest Pao2 values during hospitalization were dichotomized according to the definition of severe hyperoxemia and assessed for association with in-hospital mortality using logistic regression models incorporating a calibrated measure of multiple organ dysfunction, extracorporeal life support, and the total number of arterial blood gas measurements obtained during an encounter.

Results

Of 23 719 PICU encounters during the inclusion period, 6250 patients (13 422 [56.6%] boys; mean [SD] age, 7.5 [6.6] years) had at least 1 measured Pao2 value. Severe hyperoxemia was independently associated with in-hospital mortality (adjusted odds ratio [aOR], 1.78; 95% CI, 1.36-2.33; P < .001). Increasing odds of in-hospital mortality were observed with 1 (aOR, 1.47; 95% CI, 1.05-2.08; P = .03), 2 (aOR, 2.01; 95% CI, 1.27-3.18; P = .002), and 3 or more (aOR, 2.53; 95% CI, 1.62-3.94; P < .001) severely hyperoxemic Pao2 values obtained greater than or equal to 3 hours apart from one another compared with encounters without hyperoxemia. A sensitivity analysis examining the hypothetical outcomes of residual confounding indicated that an unmeasured binary confounder with an aOR of 2 would have to be present in 37% of the encounters with severe hyperoxemia and 0% of the remaining cohort to fail to reject the null hypothesis (aOR of severe hyperoxemia, 1.31; 95% CI, 0.99-1.72).

Conclusions and Relevance

Greater numbers of severe hyperoxemia events appeared to be associated with increased mortality in this large, diverse cohort of critically ill children, supporting a possible exposure-response association between severe hyperoxemia and outcome in this population. Although further prospective evaluation appears to be warranted, this study's findings suggest that guidelines for ongoing management of critically ill children should take into consideration the possible detrimental effects of severe hyperoxemia.

Exosomes secreted by endothelial progenitor cells improve the bioactivity of pulmonary microvascular endothelial cells exposed to hyperoxia in vitro

Background

Paracrine factors secreted by endothelial progenitor cells (EPCs) are suggested to be responsible, in part, for the improved microvascular development in bronchopulmonary dysplasia (BPD) models. This study aims to investigate the potential role of exosomes derived from EPCs (EPC-EXOs), a component of paracrine secretion, in angiogenesis by mediating the activity of PMVECs exposed to hyperoxia.

Methods

EPCs were isolated from bone marrow of rats. EPC-EXOs were isolated by ExoQuick-TC kits from the conditioned media of EPCs. The PMVECs were divided into three groups, including the normal group, the hyperoxia group (exposed to 85% O₂) and the EPC-EXOs treatment group (exposed to 85% O₂ and EPC-EXOs with the concentration of 100 µg/mL). The activities of proliferation, migration and tube formation of PMVECs were detected at the endpoint. The mRNA and protein expression levels of VEGF, VEGFR2 and eNOS in different groups were detected by real-time quantitative PCR and western blot.

Results

We found EPC-EXOs exhibited a cup or biconcave morphology, with the size ranging from 30 to 150 nm, and positive for the characteristic exosomal surface marker proteins, CD63 and TSG101. Comparing to the control group, Hyperoxic stress impaired the proliferation, migration, and tubule formation of PMVECs, and decreased the expression of endothelial nitric oxide synthase (eNOS), vascular endothelial growth factor (VEGF), and vascular endothelial growth factor receptor 2 (VEGFR-2) of PMVECs. Comparing to the hyperoxia group, EPC-EXOs treatment enhanced the bioactivity of PMVECs in vitro, and increased the expression of eNOS, VEGF and VEGFR2.

Conclusions

Our data demonstrate EPCs secrete exosomes that have independent angiogenic activity in vitro. This may help explain in part the protective effects of EPCs on hyperoxic injury in the developing lung vasculature and may represent a promising therapeutic strategy for BPD.

Cardiovascular Risks Associated with Gender and Aging

The aging and elderly population are particularly susceptible to cardiovascular disease. Age is an independent risk factor for cardiovascular disease (CVD) in adults, but these risks are compounded by additional factors, including frailty, obesity, and diabetes. These factors are known to complicate and enhance cardiac risk factors that are associated with the onset of advanced age. Sex is another potential risk factor in aging adults, given that older females are reported to be at a greater risk for CVD than age-matched men. However, in both men and women, the risks associated with CVD increase with age, and these correspond to an overall decline in sex hormones, primarily of estrogen and testosterone. Despite this, hormone replacement therapies are largely shown to not improve outcomes in older patients and may also increase the risks of cardiac events in older adults. This review discusses current findings regarding the impacts of age and gender on heart disease.

The effect of hyperoxia on mortality in critically ill patients: a systematic review and meta analysis

Background

Studies investigating the role of hyperoxia in critically ill patients have reported conflicting results. We did this analysis to reveal the effect of hyperoxia in the patients admitted to the intensive care unit (ICU).

Methods

Electronic databases were searched for all the studies exploring the role of hyperoxia in adult patients admitted to ICU. The primary outcome was mortality. Random-effect model was used for quantitative synthesis of the adjusted odds ratio (aOR).

Results

We identified 24 trials in our final analysis. Statistical heterogeneity was found between hyperoxia and normoxia groups in patients with mechanical ventilation (I² = 92%, P < 0.01), cardiac arrest(I² = 63%, P = 0.01), traumatic brain injury (I² = 85%, P < 0.01) and post cardiac surgery (I² = 80%, P = 0.03). Compared with normoxia, hyperoxia was associated with higher mortality in overall patients (OR 1.22, 95% CI 1.12~1.33), as well as in the subgroups of cardiac arrest (OR 1.30, 95% CI 1.08~1.57) and extracorporeal life support (ELS) (OR 1.44, 95% CI 1.03~2.02).

Conclusions

Hyperoxia would lead to higher mortality in critically ill patients especially in the patients with cardiac arrest and ELS.

Electronic supplementary material

The online version of this article (10.1186/s12890-019-0810-1) contains supplementary material, which is available to authorized users.

Impact of hyperoxia on cardiac pathophysiology

Mechanical ventilation with high oxygen therapy (hyperoxia) is widely implemented in critical care and ICU settings. Although supplemental oxygen is beneficial to treat hypoxia, its use is also associated with poor outcomes and high mortality in patients. Lung injury due to hyperoxia exposure has been well-documented in patients, including in adults and neonates. Thus, lung injury due to hyperoxia has been extensively researched in both preclinical and clinical studies. However, hyperoxia has also been shown to be associated with hemodynamic changes in patients in ICU, including reductions in heart rate, stroke volume, and cardiac output. In addition, certain experimental studies report that hyperoxia exposure in neonates results in cardiac dysfunction in later adult life. Despite this, until recently, the impact of hyperoxia within the heart has not been well studied, or reported, specifically in adult experimental models. To close this significant gap, our lab has sought to clarify hyperoxia-induced cardiac pathophysiology in adult murine models. This review discusses the current findings regarding the cardiovascular impact of hyperoxia exposure.

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.

Elevated potassium outward currents in hyperoxia treated atrial cardiomyocytes

Supplementation of 100% oxygen is a very common intervention in intensive care units (ICU) and critical care centers for patients with dysfunctional lung and lung disorders. Although there is advantage in delivering sufficient levels of oxygen, hyperoxia is reported to be directly associated with increasing in-hospital deaths. Our previous studies reported ventricular and electrical remodeling in hyperoxia treated mouse hearts, and in this article, for the first time, we are investigating the effects of hyperoxia on atrial electrophysiology using whole-cell patch-clamp electrophysiology experiments along with assessment of Kv1.5, Kv4.2, and KChIP2 transcripts and protein profiles using real-time quantitative RT-PCR and Western blotting. Our data showed that induction of hyperoxia for 3 days in mice showed larger outward potassium currents with shorter action potential durations (APD). This increase in current densities is due to significant increase in ultrarapid delayed rectifier outward K⁺ currents (I_Kur ) and rapidly activating, rapidly inactivating transient outward K+ current (I_to ) densities. We also observed a significant increase in both transcripts and protein levels of Kv1.5 and KChIP2 in hyperoxia treated atrial cardiomyocytes, whereas no significant change was observed in Kv4.2 transcripts or protein. The data presented here further support our previous findings that hyperoxia induces not only ventricular remodeling, but also atrial electrical remodeling.

Neurodevelopmental outcomes of preterm infants resuscitated with different oxygen concentration at birth

OBJECTIVE

To compare the neurodevelopmental outcomes at 18 to 21 months corrected age (CA) of infants born at <29 weeks that received room air, an intermediate oxygen concentration or 100% oxygen at the initiation of resuscitation.

STUDY DESIGN

In this retrospective cohort study, we compared neonatal and neurodevelopmental outcomes at 18 to 21 months CA among inborn infants born before 29 weeks' gestation that received room air, intermediate oxygen concentration or 100% oxygen at the initiation of resuscitation.

RESULTS

Of 1509 infants, 445 received room air, 483 received intermediate oxygen concentrations and 581 received 100% oxygen. Compared to infants that received room air, the primary outcome of death or neurodevelopmental impairment (NDI) was not different in intermediate oxygen (adjusted odds ratio (aOR) 1.01; 95% confidence interval (CI) 0.77, 1.34) or 100% oxygen (aOR 1.03; 95% CI 0.78, 1.35). Compared to room air, there was no difference in odds of death or severe NDI in intermediate oxygen (aOR 1.14; 95% CI 0.82, 1.58) or 100% oxygen group (aOR 1.22; 95% CI 0.90, 1.67). The odds of severe NDI among survivors were significantly higher in infants that received 100% oxygen as compared to room air (aOR 1.57, 95% CI 1.05, 2.35).

CONCLUSIONS

We observed no significant difference in the primary composite outcomes of death or NDI and death or severe NDI at 18 to 21 months CA between infants that received room air, intermediate oxygen concentration or 100% oxygen at the initiation of resuscitation. However, use of 100% oxygen was associated with increased odds of severe NDI among survivors as compared to room air.

Edaravone protects rats and human pulmonary alveolar epithelial cells against hyperoxia injury: heme oxygenase-1 and PI3K/Akt pathway may be involved

PURPOSE/AIM

Hyperoxic acute lung injury (HALI) is a clinical syndrome as a result of prolonged supplement of high concentrations of oxygen. As yet, no specific treatment is available for HALI. The present study aims to investigate the effects of edaravone on hyperoxia-induced oxidative injury and the underlying mechanism.

MATERIALS AND METHODS

We treated rats and human pulmonary alveolar epithelial cells with hyperoxia and different concentration of edaravone, then examined the effects of edaravone on cell viability, cell injury and two oxidative products. The roles of heme oxygenase-1 (HO-1) and PI3K/Akt pathway were explored using Western blot and corresponding inhibitors.

RESULTS

The results showed that edaravone reduced lung biochemical alterations induced by hyperoxia and mortality of rats, dose-dependently alleviated cell mortality, cell injury, and peroxidation of cellular lipid and DNA oxidative damage. It upregulated cellular HO-1 expression and activity, which was reversed by PI3K/Akt pathway inhibition. The administration of zinc protoporphyrin-IX, a HO-1 inhibitor, and LY249002, a PI3K/Akt pathway inhibitor, abolished the protective effects of edaravone in cells.

CONCLUSIONS

This study indicates that edaravone protects rats and human pulmonary alveolar epithelial cells against hyperoxia-induced injury and the antioxidant effect may be related to upregulation of HO-1, which is regulated by PI3K/Akt pathway.

Novel Double-Hit Model of Radiation and Hyperoxia-Induced Oxidative Cell Damage Relevant to Space Travel

Spaceflight occasionally requires multiple extravehicular activities (EVA) that potentially subject astronauts to repeated changes in ambient oxygen superimposed on those of space radiation exposure. We thus developed a novel in vitro model system to test lung cell damage following repeated exposure to radiation and hyperoxia. Non-tumorigenic murine alveolar type II epithelial cells (C10) were exposed to >95% O₂ for 8 h only (O₂), 0.25 Gy ionizing γ-radiation (IR) only, or a double-hit combination of both challenges (O₂ + IR) followed by 16 h of normoxia (ambient air containing 21% O₂ and 5% CO₂) (1 cycle = 24 h, 2 cycles = 48 h). Cell survival, DNA damage, apoptosis, and indicators of oxidative stress were evaluated after 1 and 2 cycles of exposure. We observed a significant (p < 0.05) decrease in cell survival across all challenge conditions along with an increase in DNA damage, determined by Comet analysis and H2AX phosphorylation, and apoptosis, determined by Annexin-V staining, relative to cells unexposed to hyperoxia or radiation. DNA damage (GADD45α and cleaved-PARP), apoptotic (cleaved caspase-3 and BAX), and antioxidant (HO-1 and Nqo1) proteins were increased following radiation and hyperoxia exposure after 1 and 2 cycles of exposure. Importantly, exposure to combination challenge O₂ + IR exacerbated cell death and DNA damage compared to individual exposures O₂ or IR alone. Additionally levels of cell cycle proteins phospho-p53 and p21 were significantly increased, while levels of CDK1 and Cyclin B1 were decreased at both time points for all exposure groups. Similarly, proteins involved in cell cycle arrest was more profoundly changed with the combination challenges as compared to each stressor alone. These results correlate with a significant 4- to 6-fold increase in the ratio of cells in G2/G1 after 2 cycles of exposure to hyperoxic conditions. We have characterized a novel in vitro model of double-hit, low-level radiation and hyperoxia exposure that leads to oxidative lung cell injury, DNA damage, apoptosis, and cell cycle arrest.

Hyperoxic Exposure of Immature Mice Increases the Inflammatory Response to Subsequent Rhinovirus Infection: Association with Danger Signals

Infants with a history of prematurity and bronchopulmonary dysplasia have a high risk of asthma and viral-induced exacerbations later in life. We hypothesized that hyperoxic exposure, a predisposing factor to bronchopulmonary dysplasia, modulates the innate immune response, producing an exaggerated proinflammatory reaction to viral infection. Two- to 3-d-old C57BL/6J mice were exposed to air or 75% oxygen for 14 d. Mice were infected intranasally with rhinovirus (RV) immediately after O2 exposure. Lung mRNA and protein expression, histology, dendritic cells (DCs), and airway responsiveness were assessed 1-12 d postinfection. Tracheal aspirates from premature human infants were collected for mRNA detection. Hyperoxia increased lung IL-12 expression, which persisted up to 12 d postexposure. Hyperoxia-exposed RV-infected mice showed further increases in IL-12 and increased expression of IFN-γ, TNF-α, CCL2, CCL3, and CCL4, as well as increased airway inflammation and responsiveness. In RV-infected, air-exposed mice, the response was not significant. Induced IL-12 expression in hyperoxia-exposed, RV-infected mice was associated with increased IL-12-producing CD103(+) lung DCs. Hyperoxia also increased expression of Clec9a, a CD103(+) DC-specific damaged cell-recognition molecule. Hyperoxia increased levels of ATP metabolites and expression of adenosine receptor A1, further evidence of cell damage and related signaling. In human preterm infants, tracheal aspirate Clec9a expression positively correlated with the level of prematurity. Hyperoxic exposure increases the activation of CD103(+), Clec9a(+) DCs, leading to increased inflammation and airway hyperresponsiveness upon RV infection. In premature infants, danger signal-induced DC activation may promote proinflammatory airway responses, thereby increasing respiratory morbidity.

VEGF-D promotes pulmonary oedema in hyperoxic acute lung injury

Leakage of fluid from blood vessels, leading to oedema, is a key feature of many diseases including hyperoxic acute lung injury (HALI), which can occur when patients are ventilated with high concentrations of oxygen (hyperoxia). The molecular mechanisms driving vascular leak and oedema in HALI are poorly understood. VEGF‐D is a protein that promotes blood vessel leak and oedema when overexpressed in tissues, but the role of endogenous VEGF‐D in pathological oedema was unknown. To address these issues, we exposed Vegfd‐deficient mice to hyperoxia. The resulting pulmonary oedema in Vegfd‐deficient mice was substantially reduced compared to wild‐type, as was the protein content of bronchoalveolar lavage fluid, consistent with reduced vascular leak. Vegf‐d and its receptor Vegfr‐3 were more highly expressed in lungs of hyperoxic, versus normoxic, wild‐type mice, indicating that components of the Vegf‐d signalling pathway are up‐regulated in hyperoxia. Importantly, VEGF‐D and its receptors were co‐localized on blood vessels in clinical samples of human lungs exposed to hyperoxia; hence, VEGF‐D may act directly on blood vessels to promote fluid leak. Our studies show that Vegf‐d promotes oedema in response to hyperoxia in mice and support the hypothesis that VEGF‐D signalling promotes vascular leak in human HALI. © 2016 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

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.

Enhanced Resolution of Hyperoxic Acute Lung Injury as a result of Aspirin Triggered Resolvin D1 Treatment

Acute lung injury (ALI), which presents as acute respiratory failure, is a major clinical problem that requires aggressive care, and patients who require prolonged oxygen exposure are at risk of developing this disease. Although molecular determinants of ALI have been reported, the molecules involved in disease catabasis associated with oxygen toxicity have not been well studied. It has been reported that lung mucosa is rich in omega-3 fatty acid dicosahexanoic acid (DHA), which has antiinflammatory properties. Aspirin-triggered resolvin D1 (AT-RvD1) is a potent proresolution metabolite of DHA that can curb the inflammatory effects in various acute injuries, yet the effect of AT-RvD1 on hyperoxic acute lung injury (HALI) or in the oxygen toxicity setting in general has not been investigated. The effects of AT-RvD1 on HALI were determined for the first time in 8- to 10-week-old C57BL/6 mice that were exposed to hyperoxia (≥95% O2) for 48 hours. Mice were given AT-RvD1 (100 ng) in saline or a saline vehicle for 24 hours in normoxic (≈21% O2) conditions after hyperoxia. Lung tissue and bronchoalveolar lavage (BAL) fluid were collected for analysis associated with proinflammatory signaling and lung inflammation. AT-RvD1 treatment resulted in reduced oxidative stress, increased glutathione production, and significantly decreased tissue inflammation. AT-RvD1 treatment also significantly reduced the lung wet/dry ratio, protein in BAL fluid, and decreased apoptotic and NF-κB signaling. These results show that AT-RvD1 curbs oxygen-induced lung edema, permeability, inflammation, and apoptosis and is thus an effective therapy for prolonged hyperoxia exposure in this murine model.

Bench-to-bedside review: the effects of hyperoxia during critical illness

Oxygen administration is uniformly used in emergency and intensive care medicine and has life-saving potential in critical conditions. However, excessive oxygenation also has deleterious properties in various pathophysiological processes and consequently both clinical and translational studies investigating hyperoxia during critical illness have gained increasing interest. Reactive oxygen species are notorious by-products of hyperoxia and play a pivotal role in cell signaling pathways. The effects are diverse, but when the homeostatic balance is disturbed, reactive oxygen species typically conserve a vicious cycle of tissue injury, characterized by cell damage, cell death, and inflammation. The most prominent symptoms in the abundantly exposed lungs include tracheobronchitis, pulmonary edema, and respiratory failure. In addition, absorptive atelectasis results as a physiological phenomenon with increasing levels of inspiratory oxygen. Hyperoxia-induced vasoconstriction can be beneficial during vasodilatory shock, but hemodynamic changes may also impose risk when organ perfusion is impaired. In this context, oxygen may be recognized as a multifaceted agent, a modifiable risk factor, and a feasible target for intervention. Although most clinical outcomes are still under extensive investigation, careful titration of oxygen supply is warranted in order to secure adequate tissue oxygenation while preventing hyperoxic harm.

Thioredoxin-deficient mice, a novel phenotype sensitive to ambient air and hypersensitive to hyperoxia-induced lung injury

Pulmonary oxygen toxicity is a major clinical problem for patients undergoing supplemental oxygen therapy. Thioredoxin (Trx) is an endogenous antioxidant protein that regenerates oxidatively inactivated proteins. We examined how Trx contributes to oxygen tolerance by creating transgenic mice with decreased levels of functional thioredoxin (dnTrx-Tg) using a dominant-negative approach. These mice showed decreased Trx activity in the lung although the expression of mutant protein is three times higher than the wild-type mice. Additionally, we found that these mice showed increased oxidation of endogenous Trx in room air. When exposed to hyperoxia (>90% O2) for 4 days, they failed to recover and showed significant mortality. Even in normal oxygen levels, these mice displayed a significant decrease in aconitase and NADH dehydrogenase activities, decreased mitochondrial energy metabolism, increased p53 and Gadd45α expression, and increased synthesis of proinflammatory cytokines. These effects were further increased by hyperoxia. We also generated mice overexpressing Trx (Trx-Tg) and found they maintained lung redox balance during exposure to high oxygen and thus were resistant to hyperoxia-induced lung injury. These mice had increased levels of reduced Trx in the lung in normoxia as well as hyperoxia. Furthermore, the levels of aconitase and NADH dehydrogenase activities were maintained in these mice concomitant with maintenance of mitochondrial energy metabolism. The genotoxic stress markers such as p53 or Gadd45α remained in significantly lower levels in hyperoxia compared with dnTrx-Tg or wild-type mice. These studies establish that mice deficient in functional Trx exhibit a phenotype of sensitivity to ambient air and hypersensitivity to hyperoxia.

Protective effect of Xuebijing injection on paraquat-induced pulmonary injury via down-regulating the expression of p38 MAPK in rats

Background

Exposure to paraquat results in acute lung injury. A systemic inflammatory response has been widely established as a contributor to paraquat-induced acute lung injury. Recent studies have reported that consumption of Xuebijing prevents inflammatory response-induced diseases. This study investigated whether consumption of Xuebijing protected rats against paraquat-induced acute lung injury.

Methods

Adult male Sprague Dawley rats were randomly divided into four groups: control group; paraquat group; paraquat + Xuebijing group; and paraquat + dexamethasone group. Rats in the paraquat, paraquat + Xuebijing and paraquat + dexamethasone groups were intraperitoneally injected with paraquat (30 mg/kg) or administered paraquat and Xuebijing at 8 mL/kg or dexamethasone at 5 mg/kg, respectively, via an injection into the tail vein. Lung p38 MAPK, NF-κB65, IkB, p-IκB-α, HIF-1α, Nrf2 and TGF-β1 expression were essayed using western blotting. IL-6, TNF-α, IL-1β, IL-10, TGF-β1 and PIIIP were measured using ELISA. ROS, oxidised glutathione and glutathione activity were measured.

Results

After inducing acute lung injury with paraquat for 24 h, Xuebijing was observed to block lung p-p38 MAPK, NF-κB65, HIF-1α, p-IκB-α and TGF-β1 expression, and increased Nrf2 and IkB expression. The numbers of neutrophils and lymphocytes and total number of cells were significantly lower in the Xuebijing group compared with the control group. IL-6, TNF-α, IL-1β, TGF-β1 and PIIIP levels were significantly decreased in the Xuebijing group. ROS and oxidised glutathione activity were markedly inhibited by Xuebijing. Histological evaluation showed attenuation of the effects of Xuebijing on paraquat-induced lung injury. Compared with the paraquat + dexamethasone group, the Xuebijing + paraquat group showed no significant differences.

Conclusions

Inhibiting the expression of p38 MAPK and NF-κB65 was crucial for the protective effects of Xuebijing on paraquat-induced acute lung injury. The findings suggest that Xuebijing could effectively ameliorate paraquat-induced acute lung injury in rats. Xuebijing was as effective as dexamethasone at improving paraquat-induced lung injury by regulating lung inflammation, lung function and oxidative stress responses.

Deficiency of the two-pore-domain potassium channel TREK-1 promotes hyperoxia-induced lung injury

OBJECTIVES

We previously reported the expression of the two-pore-domain K channel TREK-1 in lung epithelial cells and proposed a role for this channel in the regulation of alveolar epithelial cytokine secretion. In this study, we focused on investigating the role of TREK-1 in vivo in the development of hyperoxia-induced lung injury.

DESIGN

Laboratory animal experiments.

SETTING

University research laboratory.

SUBJECTS

Wild-type and TREK-1-deficient mice.

INTERVENTIONS

Mice were anesthetized and exposed to 1) room air, no mechanical ventilation, 2) 95% hyperoxia for 24 hours, and 3) 95% hyperoxia for 24 hours followed by mechanical ventilation for 4 hours.

MEASUREMENTS AND MAIN RESULTS

Hyperoxia exposure accentuated lung injury in TREK-1-deficient mice but not controls, resulting in increase in lung injury scores, bronchoalveolar lavage fluid cell numbers, and cellular apoptosis and a decrease in quasi-static lung compliance. Exposure to a combination of hyperoxia and injurious mechanical ventilation resulted in further morphological lung damage and increased lung injury scores and bronchoalveolar lavage fluid cell numbers in control but not TREK-1-deficient mice. At baseline and after hyperoxia exposure, bronchoalveolar lavage cytokine levels were unchanged in TREK-1-deficient mice compared with controls. Exposure to hyperoxia and mechanical ventilation resulted in an increase in bronchoalveolar lavage interleukin-6, monocyte chemotactic protein-1, and tumor necrosis factor-α levels in both mouse types, but the increase in interleukin-6 and monocyte chemotactic protein-1 levels was less prominent in TREK-1-deficient mice than in controls. Lung tissue macrophage inflammatory protein-2, keratinocyte-derived cytokine, and interleukin-1β gene expression was not altered by hyperoxia in TREK-1-deficient mice compared with controls. Furthermore, we show for the first time TREK-1 expression on alveolar macrophages and unimpaired tumor necrosis factor-α secretion from TREK-1-deficient macrophages.

CONCLUSIONS

TREK-1 deficiency resulted in increased sensitivity of lungs to hyperoxia, but this effect is less prominent if overwhelming injury is induced by the combination of hyperoxia and injurious mechanical ventilation. TREK-1 may constitute a new potential target for the development of novel treatment strategies against hyperoxia-induced lung injury.

Short-term inhalation of cadmium oxide nanoparticles alters pulmonary dynamics associated with lung injury, inflammation, and repair in a mouse model

CONTEXT

Cadmium oxide nanoparticles (CdO NPs) are employed in optoelectronic devices and as a starting material for generating quantum dots as well as for medical imaging and targeting of pharmaceutical agents to disease sites. However, there are lack of data concerning short- and long-term effects of CdO NPs on the lungs.

OBJECTIVE

To determine the effects of inhaled CdO NPs at an occupationally relevant concentration on pulmonary injury and repair, and on systemic immunity in adult male mice.

METHODS

Mice were exposed to 240 μg CdO NPs/m(3) for seven days (3 h/d) and lavage levels of pulmonary injury/inflammatory markers, bacterial uptake by circulating phagocytes, and lung histology examined either one or seven days following the final exposure.

RESULTS

Levels of total protein, lactate dehydrogenase activity, cytokine markers of inflammation (i.e. interleukin-1β, tumor necrosis factor-α, and interferon-γ), tissue remodeling matrix metalloproteinases (MMP)-2 and -9 activity, and phagocytic activity of circulating phagocytes were significantly increased one day after the final exposure. By seven days post-exposure, MMP-2 activity decreased to control levels, while MMP-9 activity remained significantly above control values, although dropping by about half from day one.

CONCLUSIONS

This study demonstrates that short-term inhalation exposure to CdO NPs can stimulate pathways in the lungs associated with inflammation, cell injury, and tissue remodeling as well as alter immune function. Findings here demonstrate that even short-term inhalation exposure to CdO NPs in the workplace could lead to deleterious pulmonary effects in exposed workers.

Prevention of hyperoxia-induced bronchial hyperreactivity by sildenafil and vasoactive intestinal peptide: impact of preserved lung function and structure

Objective

Hyperoxia exposure leads to the development of lung injury and bronchial hyperreactivity (BHR) via involvement of nitric oxide (NO) pathway. We aimed at characterizing whether the stimulation of the NO pathway by sildenafil or vasoactive intestinal peptide (VIP) is able to prevent the hyperoxia-induced development of BHR. The respective roles of the preserved lung volume and alveolar architecture, the anti-inflammatory and anti-apoptotic potentials of these treatments in the diminished lung responsiveness were also characterized.

Materials and methods

Immature (28-day-old) rats were exposed for 72 hours to room air (Group C), hyperoxia (>95%, Group HC), or hyperoxia with the concomitant administration of vasoactive intestinal peptide (VIP, Group HV) or sildenafil (Group HS). Following exposure, the end-expiratory lung volume (EELV) was assessed plethysmographically. Airway and respiratory tissue mechanics were measured under baseline conditions and following incremental doses of methacholine to assess BHR. Inflammation was assessed by analyzing the bronchoalveolar lavage fluid (BALF), while biochemical and histological analyses were used to characterize the apoptotic and structural changes in the lungs.

Results

The BHR, the increased EELV, the aberrant alveolarization, and the infiltration of inflammatory cells into the BALF that developed in Group HC were all suppressed significantly by VIP or sildenafil treatment. The number of apoptotic cells increased significantly in Group HC, with no evidence of statistically significant effects on this adverse change in Groups HS and HV.

Conclusions

These findings suggest that stimulating the NO pathway by sildenafil and VIP exert their beneficial effect against hyperoxia-induced BHR via preserving normal EELV, inhibiting airway inflammation and preserving the physiological lung structure, whereas the antiapoptotic potential of these treatments were not apparent in this process.

Self-reported attitudes versus actual practice of oxygen therapy by ICU physicians and nurses

BACKGROUND

High inspiratory oxygen concentrations are frequently administered in ventilated patients in the intensive care unit (ICU) but may induce lung injury and systemic toxicity. We compared beliefs and actual clinical practice regarding oxygen therapy in critically ill patients.

METHODS

In three large teaching hospitals in the Netherlands, ICU physicians and nurses were invited to complete a questionnaire about oxygen therapy. Furthermore, arterial blood gas (ABG) analysis data and ventilator settings were retrieved to assess actual oxygen practice in the same hospitals 1 year prior to the survey.

RESULTS

In total, 59% of the 215 respondents believed that oxygen-induced lung injury is a concern. The majority of physicians and nurses stated that minimal acceptable oxygen saturation and partial arterial oxygen pressure (PaO2) ranges were 85% to 95% and 7 to 10 kPa (52.5 to 75 mmHg), respectively. Analysis of 107,888 ABG results with concurrent ventilator settings, derived from 5,565 patient admissions, showed a median (interquartile range (IQR)) PaO2 of 11.7 kPa (9.9 to 14.3) [87.8 mmHg], median fractions of inspired oxygen (FiO2) of 0.4 (0.4 to 0.5), and median positive end-expiratory pressure (PEEP) of 5 (5 to 8) cm H2O. Of all PaO2 values, 73% were higher than the upper limit of the commonly self-reported acceptable range, and in 58% of these cases, neither FiO2 nor PEEP levels were lowered until the next ABG sample was taken.

CONCLUSIONS

Most ICU clinicians acknowledge the potential adverse effects of prolonged exposure to hyperoxia and report a low tolerance for high oxygen levels. However, in actual clinical practice, a large proportion of their ICU patients was exposed to higher arterial oxygen levels than self-reported target ranges.

Analysis of the transcriptome in hyperoxic lung injury and sex-specific alterations in gene expression

Exposure to high concentration of oxygen (hyperoxia) leads to lung injury in experimental animal models and plays a role in the pathogenesis of diseases such as Acute Respiratory Distress Syndrome (ARDS) and Bronchopulmonary dysplasia (BPD) in humans. The mechanisms responsible for sex differences in the susceptibility towards hyperoxic lung injury remain largely unknown. The major goal of this study was to characterize the changes in the pulmonary transcriptome following hyperoxia exposure and further elucidate the sex-specific changes. Male and female (8-10 wk) wild type (WT) (C57BL/6J) mice were exposed to hyperoxia (FiO2>0.95) and gene expression in lung tissues was studied at 48 h. A combination of fold change ≥1.4 and false discovery rate (FDR)<5% was used to define differentially expressed genes (DEGs). Overrepresentation of gene ontology terms representing biological processes and signaling pathway impact analysis (SPIA) was performed. Comparison of DEG profiles identified 327 genes unique to females, 585 unique to males and 1882 common genes. The major new findings of this study are the identification of new candidate genes of interest and the sex-specific transcriptomic changes in hyperoxic lung injury. We also identified DEGs involved in signaling pathways like MAP kinase and NF-kappa B which may explain the differences in sex-specific susceptibility to hyperoxic lung injury. These findings highlight changes in the pulmonary transcriptome and sex-specific differences in hyperoxic lung injury, and suggest new pathways, whose components could serve as sex-specific biomarkers and possible therapeutic targets for acute lung injury (ALI)/acute respiratory distress (ARDS) in humans.

IκBβ-mediated NF-κB activation confers protection against hyperoxic lung injury

Supplemental oxygen is frequently used in an attempt to improve oxygen delivery; however, prolonged exposure results in damage to the pulmonary endothelium and epithelium. Although NF-κB has been identified as a redox-responsive transcription factor, whether NF-κB activation exacerbates or attenuates hyperoxic lung injury is unclear. We determined that sustained NF-κB activity mediated by IκBβ attenuates lung injury and prevents mortality in adult mice exposed to greater than 95% O2. Adult wild-type mice demonstrated evidence of alveolar protein leak and 100% mortality by 6 days of hyperoxic exposure, and showed NF-κB nuclear translocation that terminated after 48 hours. Furthermore, these mice showed increased expression of NF-κB-regulated proinflammatory and proapoptotic cytokines. In contrast, mice overexpressing the NF-κB inhibitory protein, IκBβ (AKBI), demonstrated significant resistance to hyperoxic lung injury, with 50% surviving through 8 days of exposure. This was associated with NF-κB nuclear translocation that persisted through 96 hours of exposure. Although induction of NF-κB-regulated proinflammatory cytokines was not different between wild-type and AKBI mice, significant up-regulation of antiapoptotic proteins (BCL-2, BCL-XL) was found exclusively in AKBI mice. We conclude that sustained NF-κB activity mediated by IκBβ protects against hyperoxic lung injury through increased expression of antiapoptotic genes.

Multiple wall in-folds sub-divide single segments during capillary regression in hyperoxic acute lung injury

The present study provides further insight into the structural processes that remodel pulmonary capillaries in the injured adult lung. Early in hyperoxia acute lung injury (HALI), many sub-dividing segments are present throughout the capillary network before segment occlusion and loss predominate and capillary density decreases later in the period. A second segment sub-division triggered in regenerating capillaries after air breathing (post-HALI) demonstrates a similar mechanism of organization at a time of contrasting change in the capillary density. As we have previously reported, the process of segment sub-division includes in-folding of the endothelial-epithelial surface (alveolar-capillary membrane) to form inter-luminal structures (ILSs) and loops, with loop separation increasing segment number. Unexpectedly, the findings support remodeling of the capillary density by wall in-folding in acute lung injury, demonstrating a similar mechanism in capillary regression as well as in regeneration in the adult lung.

Protein expression profile of rat type two alveolar epithelial cells during hyperoxic stress and recovery

In rodent model systems, the sequential changes in lung morphology resulting from hyperoxic injury are well characterized and are similar to changes in human acute respiratory distress syndrome. In the injured lung, alveolar type two (AT2) epithelial cells play a critical role in restoring the normal alveolar structure. Thus characterizing the changes in AT2 cells will provide insights into the mechanisms underpinning the recovery from lung injury. We applied an unbiased systems-level proteomics approach to elucidate molecular mechanisms contributing to lung repair in a rat hyperoxic lung injury model. AT2 cells were isolated from rat lungs at predetermined intervals during hyperoxic injury and recovery. Protein expression profiles were determined by using iTRAQ with tandem mass spectrometry. Of the 959 distinct proteins identified, 183 significantly changed in abundance during the injury-recovery cycle. Gene ontology enrichment analysis identified cell cycle, cell differentiation, cell metabolism, ion homeostasis, programmed cell death, ubiquitination, and cell migration to be significantly enriched by these proteins. Gene set enrichment analysis of data acquired during lung repair revealed differential expression of gene sets that control multicellular organismal development, systems development, organ development, and chemical homeostasis. More detailed analysis identified activity in two regulatory pathways, JNK and miR 374. A novel short time-series expression miner algorithm identified protein clusters with coherent changes during injury and repair. We concluded that coherent changes occur in the AT2 cell proteome in response to hyperoxic stress. These findings offer guidance regarding the specific molecular mechanisms governing repair of the injured lung.

Alveolar oxygen tension and angio-architecture of the distal adult lung

The present study demonstrates the fine structure of pulmonary capillaries first injured and then undergoing growth in response to a change in the ambient alveolar oxygen tension. Breathing a high fraction of inspired oxygen (FiO2 0.75) triggers restriction by endothelial cell injury and effacement leading to segment narrowing and shortening and segment loss as demonstrated by a fall in density. Subsequently, breathing a relatively low fraction (FiO2 0.21) triggers capillary assembly (angiogenesis), which reverses the changes. The data underscore the structural reprogramming (reduction and restoration) of pulmonary capillaries in response to significant shifts in oxygen tension.

670 nm light mitigates oxygen-induced degeneration in C57BL/6J mouse retina

Background

Irradiation with light wavelengths from the far red (FR) to the near infrared (NIR) spectrum (600 nm -1000 nm) has been shown to have beneficial effects in several disease models. In this study, we aim to examine whether 670 nm red light pretreatment can provide protection against hyperoxia-induced damage in the C57BL/6J mouse retina. Adult mice (90–110 days) were pretreated with 9 J/cm² of 670 nm light once daily for 5 consecutive days prior to being placed in hyperoxic environment (75% oxygen). Control groups were exposed to hyperoxia, but received no 670 nm light pretreatment. Retinas were collected after 0, 3, 7, 10 or 14 days of hyperoxia exposure (n = 12/group) and prepared either for histological analysis, or RNA extraction and quantitative polymerase chain reaction (qPCR). Photoreceptor damage and loss were quantified by counting photoreceptors undergoing cell death and measuring photoreceptor layer thickness. Localization of acrolein, and cytochrome c oxidase subunit Va (Cox Va) were identified through immunohistochemistry. Expression of heme oxygenase-1 (Hmox-1), complement component 3 (C3) and fibroblast growth factor 2 (Fgf-2) genes were quantified using qPCR.

Results

The hyperoxia-induced photoreceptor loss was accompanied by reduction of metabolic marker, Cox Va, and increased expression of oxidative stress indicator, acrolein and Hmox-1. Pretreatment with 670 nm red light reduced expression of markers of oxidative stress and C3, and slowed, but did not prevent, photoreceptor loss over the time course of hyperoxia exposure.

Conclusion

The damaging effects of hyperoxia on photoreceptors were ameliorated following pretreatment with 670 nm light in hyperoxic mouse retinas. These results suggest that pretreatment with 670 nm light may provide stability to photoreceptors in conditions of oxidative stress.

The NRF2 activation and antioxidative response are not impaired overall during hyperoxia-induced lung epithelial cell death

Lung epithelial and endothelial cell death caused by pro-oxidant insults is a cardinal feature of acute lung injury/acute respiratory distress syndrome (ALI/ARDS) patients. The NF-E2-related factor 2 (NRF2) activation in response to oxidant exposure is crucial to the induction of several antioxidative and cytoprotective enzymes that mitigate cellular stress. Since prolonged exposure to hyperoxia causes cell death, we hypothesized that chronic hyperoxia impairs NRF2 activation, resulting in cell death. To test this hypothesis, we exposed nonmalignant small airway epithelial cells (AECs) to acute (1–12 h) and chronic (36–48 h) hyperoxia and evaluated cell death, NRF2 nuclear accumulation and target gene expression, and NRF2 recruitment to the endogenous HMOX1 and NQO1 promoters. As expected, hyperoxia gradually induced death in AECs, noticeably and significantly by 36 h; ~60% of cells were dead by 48 h. However, we unexpectedly found increased expression levels of NRF2-regulated antioxidative genes and nuclear NRF2 in AECs exposed to chronic hyperoxia as compared to acute hyperoxia. Chromatin Immunoprecipitation (ChIP) assays revealed an increased recruitment of NRF2 to the endogenous HMOX1 and NQO1 promoters in AECs exposed to acute or chronic hyperoxia. Thus, our findings demonstrate that NRF2 activation and antioxidant gene expression are functional during hyperoxia-induced lung epithelial cell death and that chronic hyperoxia does not impair NRF2 signaling overall.

Mesenchymal stem cells protect against neonatal rat hyperoxic lung injury

OBJECTIVES

Bronchopulmonary dysplasia (BPD) is a significant global health problem and currently lacks effective therapy. We established a neonatal rat model of BPD to investigate therapeutic potential of bone marrow-derived mesenchymal stem cells (BMSCs) in neonatal hyperoxic lung injury.

METHODS

BMSCs were isolated, identified, and transfected by lentiviral vector carrying green fluorescent protein gene in vitro. Neonatal Sprague-Dawley rats were injected intravenously with either BMSCs or phosphate-buffered saline following 95% oxygen exposure, and assessed for the survival rate and alveolar injury during recovery.

RESULTS

Treatment with BMSCs after oxygen exposure for 7 days improved survival of neonatal rat during recovery. BMSCs protected against neonatal rat hyperoxic lung injury during recovery as demonstrated by enhanced expression of AQP5 and SP-C, likely due to the suppression of alveolar cell apoptosis and lung inflammation responses to oxygen with up-regulation of the expression of BCL-2 gene and down-regulation of the expression of BAX gene and stimulation of vascular endothelial growth factor and so on.

CONCLUSIONS

BMSCs protect against O2-mediated injury partially through stimulation of potent mediators that participate in tissue repair.