Hyperoxia impairs antibacterial function of macrophages through effects on actin

Therapeutic characteristics of alveolar-like macrophages in mouse models of hyperoxia and LPS-induced lung inflammation

Acute respiratory distress syndrome (ARDS) is a severe lung disease of high mortality (30-50%). Patients require lifesaving supplemental oxygen therapy; however, hyperoxia can induce pulmonary inflammation and cellular damage. Although alveolar macrophages (AMs) are essential for lung immune homeostasis, they become compromised during inflammatory lung injury. To combat this, stem cell-derived alveolar-like macrophages (ALMs) are a prospective therapeutic for lung diseases like ARDS. Using in vitro and in vivo approaches, we investigated the impact of hyperoxia on murine ALMs during acute inflammation. In vitro, ALMs retained their viability, growth, and antimicrobial abilities when cultured at 60% O2, whereas they die at 90% O2. In contrast, ALMs instilled in mouse lungs remained viable during exposure of mice to 90% O2. The ability of the delivered ALMs to phagocytose Pseudomonas aeruginosa was not impaired by exposure to 60 or 90% O2. Furthermore, ALMs remained immunologically stable in a murine model of LPS-induced lung inflammation when exposed to 60 and 90% O2 and effectively attenuated the accumulation of CD11b+ inflammatory cells in the airways. These results support the potential use of ALMs in patients with ARDS receiving supplemental oxygen therapy.NEW & NOTEWORTHY The current findings support the prospective use of stem cell-derived alveolar-like macrophages (ALMs) as a therapeutic for inflammatory lung disease such as acute respiratory distress syndrome (ARDS) during supplemental oxygen therapy where lungs are exposed to high levels of oxygen. Alveolar-like macrophages directly delivered to mouse lungs were found to remain viable, immunologically stable, phagocytic toward live Pseudomonas aeruginosa, and effective in reducing CD11b+ inflammatory cell numbers in LPS-challenged lungs during moderate and extreme hyperoxic exposure.

Oxy-Inflammation in Humans during Underwater Activities

Underwater activities are characterized by an imbalance between reactive oxygen/nitrogen species (RONS) and antioxidant mechanisms, which can be associated with an inflammatory response, depending on O2 availability. This review explores the oxidative stress mechanisms and related inflammation status (Oxy-Inflammation) in underwater activities such as breath-hold (BH) diving, Self-Contained Underwater Breathing Apparatus (SCUBA) and Closed-Circuit Rebreather (CCR) diving, and saturation diving. Divers are exposed to hypoxic and hyperoxic conditions, amplified by environmental conditions, hyperbaric pressure, cold water, different types of breathing gases, and air/non-air mixtures. The "diving response", including physiological adaptation, cardiovascular stress, increased arterial blood pressure, peripheral vasoconstriction, altered blood gas values, and risk of bubble formation during decompression, are reported.

13C-Metabolic flux analysis detected a hyperoxemia-induced reduction of tricarboxylic acid cycle metabolism in granulocytes during two models of porcine acute subdural hematoma and hemorrhagic shock

Introduction

Supplementation with increased inspired oxygen fractions has been suggested to alleviate the harmful effects of tissue hypoxia during hemorrhagic shock (HS) and traumatic brain injury. However, the utility of therapeutic hyperoxia in critical care is disputed to this day as controversial evidence is available regarding its efficacy. Furthermore, in contrast to its hypoxic counterpart, the effect of hyperoxia on the metabolism of circulating immune cells remains ambiguous. Both stimulating and detrimental effects are possible; the former by providing necessary oxygen supply, the latter by generation of excessive amounts of reactive oxygen species (ROS). To uncover the potential impact of increased oxygen fractions on circulating immune cells during intensive care, we have performed a 13C-metabolic flux analysis (MFA) on PBMCs and granulocytes isolated from two long-term, resuscitated models of combined acute subdural hematoma (ASDH) and HS in pigs with and without cardiovascular comorbidity.

Methods

Swine underwent resuscitation after 2 h of ASDH and HS up to a maximum of 48 h after HS. Animals received normoxemia (PaO2 = 80 - 120 mmHg) or targeted hyperoxemia (PaO2 = 200 - 250 mmHg for 24 h after treatment initiation, thereafter PaO2 as in the control group). Blood was drawn at time points T1 = after instrumentation, T2 = 24 h post ASDH and HS, and T3 = 48 h post ASDH and HS. PBMCs and granulocytes were isolated from whole blood to perform electron spin resonance spectroscopy, high resolution respirometry and 13C-MFA. For the latter, we utilized a parallel tracer approach with 1,2-13C2 glucose, U-13C glucose, and U-13C glutamine, which covered essential pathways of glucose and glutamine metabolism and supplied redundant data for robust Bayesian estimation. Gas chromatography-mass spectrometry further provided multiple fragments of metabolites which yielded additional labeling information. We obtained precise estimations of the fluxes, their joint credibility intervals, and their relations, and characterized common metabolic patterns with principal component analysis (PCA).

Results

13C-MFA indicated a hyperoxia-mediated reduction in tricarboxylic acid (TCA) cycle activity in circulating granulocytes which encompassed fluxes of glutamine uptake, TCA cycle, and oxaloacetate/aspartate supply for biosynthetic processes. We further detected elevated superoxide levels in the swine strain characterized by a hypercholesterolemic phenotype. PCA revealed cell type-specific behavioral patterns of metabolic adaptation in response to ASDH and HS that acted irrespective of swine strains or treatment group.

Conclusion

In a model of resuscitated porcine ASDH and HS, we saw that ventilation with increased inspiratory O2 concentrations (PaO2 = 200 - 250 mmHg for 24 h after treatment initiation) did not impact mitochondrial respiration of PBMCs or granulocytes. However, Bayesian 13C-MFA results indicated a reduction in TCA cycle activity in granulocytes compared to cells exposed to normoxemia in the same time period. This change in metabolism did not seem to affect granulocytes' ability to perform phagocytosis or produce superoxide radicals.

Alveolar Hyperoxia and Exacerbation of Lung Injury in Critically Ill SARS-CoV-2 Pneumonia

Acute hypoxic respiratory failure (AHRF) is a prominent feature of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) critical illness. The severity of gas exchange impairment correlates with worse prognosis, and AHRF requiring mechanical ventilation is associated with substantial mortality. Persistent impaired gas exchange leading to hypoxemia often warrants the prolonged administration of a high fraction of inspired oxygen (FiO2). In SARS-CoV-2 AHRF, systemic vasculopathy with lung microthrombosis and microangiopathy further exacerbates poor gas exchange due to alveolar inflammation and oedema. Capillary congestion with microthrombosis is a common autopsy finding in the lungs of patients who die with coronavirus disease 2019 (COVID-19)-associated acute respiratory distress syndrome. The need for a high FiO2 to normalise arterial hypoxemia and tissue hypoxia can result in alveolar hyperoxia. This in turn can lead to local alveolar oxidative stress with associated inflammation, alveolar epithelial cell apoptosis, surfactant dysfunction, pulmonary vascular abnormalities, resorption atelectasis, and impairment of innate immunity predisposing to secondary bacterial infections. While oxygen is a life-saving treatment, alveolar hyperoxia may exacerbate pre-existing lung injury. In this review, we provide a summary of oxygen toxicity mechanisms, evaluating the consequences of alveolar hyperoxia in COVID-19 and propose established and potential exploratory treatment pathways to minimise alveolar hyperoxia.

Supplemental Oxygen Alters the Airway Microbiome in Cystic Fibrosis

Features of the airway microbiome in persons with cystic fibrosis (pwCF) are correlated with disease progression. Microbes have traditionally been classified for their ability to tolerate oxygen. It is unknown whether supplemental oxygen, a common medical intervention, affects the airway microbiome of pwCF. We hypothesized that hyperoxia significantly impacts the pulmonary microbiome in cystic fibrosis. In this study, we cultured spontaneously expectorated sputum from pwCF in artificial sputum medium under 21%, 50%, and 100% oxygen conditions using a previously validated model system that recapitulates microbial community composition in uncultured sputum. Culture aliquots taken at 24, 48, and 72 h, along with uncultured sputum, underwent shotgun metagenomic sequencing with absolute abundance values obtained with the use of spike-in bacteria. Raw sequencing files were processed using the bioBakery pipeline to determine changes in taxonomy, predicted function, antimicrobial resistance genes, and mobile genetic elements. Hyperoxia reduced absolute microbial load, species richness, and diversity. Hyperoxia reduced absolute abundance of specific microbes, including facultative anaerobes such as Rothia and some Streptococcus species, with minimal impact on canonical CF pathogens such as Pseudomonas aeruginosa and Staphylococcus aureus. The effect size of hyperoxia on predicted functional pathways was stronger than that on taxonomy. Large changes in microbial cooccurrence networks were noted. Hyperoxia exposure perturbs airway microbial communities in a manner well tolerated by key pathogens. Supplemental oxygen use may enable the growth of lung pathogens and should be further studied in the clinical setting. IMPORTANCE The airway microbiome in persons with cystic fibrosis (pwCF) is correlated with lung function and disease severity. Supplemental oxygen use is common in more advanced CF, yet its role in perturbing airway microbial communities is unknown. By culturing sputum samples from pwCF under normal and elevated oxygen conditions, we found that increased oxygen led to reduced total numbers and diversity of microbes, with relative sparing of common CF pathogens such as Pseudomonas aeruginosa and Staphylococcus aureus. Supplemental oxygen use may enable the growth of lung pathogens and should be further studied in the clinical setting.

Dual effects of supplemental oxygen on pulmonary infection, inflammatory lung injury, and neuromodulation in aging and COVID-19

Clinical studies have shown a significant positive correlation between age and the likelihood of being infected with SARS-CoV-2. This increased susceptibility is positively correlated with chronic inflammation and compromised neurocognitive functions. Postmortem analyses suggest that acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), with systemic and lung hyperinflammation, can cause significant morbidity and mortality in COVID-19 patients. Supraphysiological supplemental oxygen, also known as hyperoxia, is commonly used to treat decreased blood oxygen saturation in COVID-19 patients. However, prolonged exposure to hyperoxia alone can cause oxygen toxicity, due to an excessive increase in the levels of reactive oxygen species (ROS), which can overwhelm the cellular antioxidant capacity. Subsequently, this causes oxidative cellular damage and increased levels of aging biomarkers, such as telomere shortening and inflammaging. The oxidative stress in the lungs and brain can compromise innate immunity, resulting in an increased susceptibility to secondary lung infections, impaired neurocognitive functions, and dysregulated hyperinflammation, which can lead to ALI/ARDS, and even death. Studies indicate that lung inflammation is regulated by the central nervous system, notably, the cholinergic anti-inflammatory pathway (CAIP), which is innervated by the vagus nerve and α7 nicotinic acetylcholine receptors (α7nAChRs) on lung cells, particularly lung macrophages. The activation of α7nAChRs attenuates oxygen toxicity in the lungs and improves clinical outcomes by restoring hyperoxia-compromised innate immunity. Mechanistically, α7nAChR agonist (e.g., GAT 107 and GTS-21) can regulate redox signaling by 1) activating Nrf2, a master regulator of the antioxidant response and a cytoprotective defense system, which can decrease cellular damage caused by ROS and 2) inhibiting the activation of the NF-κB-mediated inflammatory response. Notably, GTS-21 has been shown to be safe and it improves neurocognitive functions in humans. Therefore, targeting the α7nAChR may represent a viable therapeutic approach for attenuating dysregulated hyperinflammation-mediated ARDS and sepsis in COVID-19 patients receiving prolonged oxygen therapy.

Molecular mechanisms underlying hyperoxia-induced lung fibrosis

Supplemental oxygen is often used to treat newborns with respiratory disorders. Exposure to high concentration of oxygen and long-term oxygen causes inflammation and acute lung injury. The acute inflammatory phase is followed by a fibroproliferative repair phase, leading to lung fibrosis. Many infants with lung fibrosis develop significant respiratory morbidities including reactive airways dysfunction and obstructive lung disease during childhood. Despite the absence of effective treatments and the incomplete understanding regarding mechanisms underlying fibrosis, extensive literature regarding lung fibrosis from in vitro and in vivo hyperoxia-exposed models is available. In this review, we discuss molecular mediators and signaling pathways responsible for increased fibroblast proliferation and collagen production, excessive extracellular matrix accumulation, and eventually, lung fibrosis. We discuss each of these mediators separately to facilitate clear understanding as well as significant interactions occurring among these molecular mediators and signaling pathways.

β-glucan mitigation on toxicological effects in monocytes/macrophages of Nile tilapia (Oreochromis niloticus) following copper exposure

The protective effect of β-glucan against toxicological effects caused by copper oxide nanoparticles (Cu NPs) and copper ions (Cu ions) were studied in monocytes/macrophages (MO/MФ) of Nile tilapia (Oreochromis niloticus). Our results demonstrated that CuO NPs and Cu ions exposure aroused strong oxidative lesion in MO/MФ by detection of cellular reactive oxygen species (ROS) and reduced glutathione (GSH), as well as identification of several antioxidant-related cytokines. Meanwhile, the serious pro-inflammatory responses were accompanied during the processes of oxidative lesion by TNFα, IL-1β, and IL-6 genes validation. Copper induced MO/MФ underwent apoptosis through mitochondrial signaling pathway by mitochondrial membrane potential (ΔΨm) detection and Bax, Bcl-2, Cyt-c, Apaf-1, Caspase 9, Caspase 3 genes validation. Furthermore, the phagocytic abilities were inhibition in MO/MФ by evaluation of microspheres (0.5 and 1.0 μm beads) and bioparticles (S. agalactiae and A. hydrophila) uptake and LPS-induced NO production. However, β-glucan might participate in immunomodulation through C-type lectin receptor (CLR) and complement receptor 3 (CR3) to suppress pro-inflammatory responses, thereby revered all the copper induced aforementioned adverse effects in MO/MΦ. Taken together, our results provide insights on the mechanisms through β-glucan administration to mitigate toxicological effects of CuO NPs and Cu ions exposure to the MO/MΦ, which will benefit aspects related to fish farming and aquaculture production.

Nrf2 Is Required for Optimal Alveolar-Macrophage-Mediated Apoptotic Neutrophil Clearance after Oxidant Injury

Recognition and clearance of apoptotic cells by phagocytes (also known as efferocytosis), primarily mediated by macrophages, are essential to terminate lung inflammatory responses and promote tissue repair after injury. The Nrf2 transcription factor is crucial for cytoprotection and host defense. Previously, we showed sustained neutrophilic lung inflammation in Nrf2-deficient (Nrf2^−/−) mice after hyperoxia-induced lung injury in vivo, but the mechanisms underlying this abnormal phenotype remain unclear. To examine whether Nrf2 regulates apoptotic neutrophil clearance, we used the alveolar macrophages (AMФs) and bone-marrow-derived macrophages (BMDMФs) of wild-type (WT) and Nrf2^−/− mice. We found that the efferocytic ability of AMФ was impaired in hyperoxia-exposed mice’s lungs, but the effect was more pronounced in Nrf2^−/− mice. Importantly, AMФ-mediated efferocytosis remained impaired in Nrf2^−/− mice recovering from injury but was restored to the basal state in the wild-type counterparts. Hyperoxia affected apoptotic neutrophil binding, not internalization, in both WT and Nrf2^−/− BMDMФs, but the effect was more significant in the latter cells. Augmenting Nrf2 activity restored hyperoxia attenuated efferocytosis in WT, but not in Nrf2^−/− macrophages. However, the loss of Nrf2 in neutrophils affected their uptake by WT macrophages. Collectively, these results demonstrate that Nrf2 is required for optimal macrophage-mediated efferocytosis and that activating Nrf2 may provide a physiological way to accelerate apoptotic cell clearance after oxidant injury.

The Effect of Conservative Oxygen Therapy in Reducing Mortality in Critical Care Patients: A Meta-Analysis and Trial Sequential Analysis

Background: Conservative oxygen therapy can prevent both hypoxemia and hyperoxemia, but the effect on the prognosis of patients admitted to the intensive care unit (ICU) remains controversial.

Methods: All controlled studies comparing conservative oxygen therapy and conventional oxygen therapy in adult patients admitted to the ICU were searched. The primary outcome was mortality, and the secondary outcomes were length of ICU stay (ICU LOS), length of hospital stay (hospital LOS), length of mechanical ventilation (MV) hours, new organ failure during ICU stay, and new infections during ICU stay.

Results: Nine trials with a total of 5,759 patients were pooled in our final studies. Compared with conventional oxygen therapy, conservative oxygen therapy did not reduce overall mortality (Z = 0.31, p = 0.75) or ICU LOS (Z = 0.17, p = 0.86), with firm evidence from trial sequential analysis, or hospital LOS (Z = 1.98, p = 0.05) or new infections during the ICU stay (Z = 1.45, p = 0.15). However, conservative oxygen therapy was associated with a shorter MV time (Z = 5.05, p < 0.00001), reduction of new organ failure during the ICU stay (Z = 2.15, p = 0.03) and lower risk of renal replacement therapy (RRT) (Z = 2.18, p = 0.03).

Conclusion: Conservative oxygen therapy did not reduce mortality but did decrease MV time, new organ failure and risk of RRT in critically ill patients.

Systematic Review Registration: identifier [CRD42020171055].

Revisited Hyperoxia Pathophysiology in the Perioperative Setting: A Narrative Review

The widespread use of high-dose oxygen, to avoid perioperative hypoxemia along with WHO-recommended intraoperative hyperoxia to reduce surgical site infections, is an established clinical practice. However, growing pathophysiological evidence has demonstrated that hyperoxia exerts deleterious effects on many organs, mainly mediated by reactive oxygen species. The purpose of this narrative review was to present the pathophysiology of perioperative hyperoxia on surgical wound healing, on systemic macro and microcirculation, on the lungs, heart, brain, kidneys, gut, coagulation, and infections. We reported here that a high systemic oxygen supply could induce oxidative stress with inflammation, vasoconstriction, impaired microcirculation, activation of hemostasis, acute and chronic lung injury, coronary blood flow disturbances, cerebral ischemia, surgical anastomosis impairment, gut dysbiosis, and altered antibiotics susceptibility. Clinical studies have provided rather conflicting results on the definitions and outcomes of hyperoxic patients, often not speculating on the biological basis of their results, while this review highlighted what happens when supranormal PaO₂ values are reached in the surgical setting. Based on the assumptions analyzed in this study, we may suggest that the maintenance of PaO₂ within physiological ranges, avoiding unnecessary oxygen administration, may be the basis for good clinical practice.

The Positive Allosteric Modulation of alpha7-Nicotinic Cholinergic Receptors by GAT107 Increases Bacterial Lung Clearance in Hyperoxic Mice by Decreasing Oxidative Stress in Macrophages

Supplemental oxygen therapy with supraphysiological concentrations of oxygen (hyperoxia; >21% O2) is a life-saving intervention for patients experiencing respiratory distress. However, prolonged exposure to hyperoxia can compromise bacterial clearance processes, due to oxidative stress-mediated impairment of macrophages, contributing to the increased susceptibility to pulmonary infections. This study reports that the activation of the α7 nicotinic acetylcholine receptor (α7nAChR) with the delete allosteric agonistic-positive allosteric modulator, GAT107, decreases the bacterial burden in mouse lungs by improving hyperoxia-induced lung redox imbalance. The incubation of RAW 264.7 cells with GAT107 (3.3 µM) rescues hyperoxia-compromised phagocytic functions in cultured macrophages, RAW 264.7 cells, and primary bone marrow-derived macrophages. Similarly, GAT107 (3.3 µM) also attenuated oxidative stress in hyperoxia-exposed macrophages, which prevents oxidation and hyper-polymerization of phagosome filamentous actin (F-actin) from oxidation. Furthermore, GAT107 (3.3 µM) increases the (1) activity of superoxide dismutase 1; (2) activation of Nrf2 and (3) the expression of heme oxygenase-1 (HO-1) in macrophages exposed to hyperoxia. Overall, these data suggest that the novel α7nAChR compound, GAT107, could be used to improve host defense functions in patients, such as those with COVID-19, who are exposed to prolonged periods of hyperoxia.

The α7 nicotinic acetylcholine receptor agonist GTS-21 improves bacterial clearance in mice by restoring hyperoxia-compromised macrophage function

BACKGROUND

Mechanical ventilation, in combination with supraphysiological concentrations of oxygen (i.e., hyperoxia), is routinely used to treat patients with respiratory distress, such as COVID-19. However, prolonged exposure to hyperoxia compromises the clearance of invading pathogens by impairing macrophage phagocytosis. Previously, we have shown that the exposure of mice to hyperoxia induces the release of the nuclear protein high mobility group box-1 (HMGB1) into the pulmonary airways. Furthermore, extracellular HMGB1 impairs macrophage phagocytosis and increases the mortality of mice infected with Pseudomonas aeruginosa (PA). The aim of this study was to determine whether GTS-21 (3-(2,4-dimethoxybenzylidene) anabaseine), an α7 nicotinic acetylcholine receptor (α7nAChR) agonist, could (1) inhibit hyperoxia-induced HMGB1 release into the airways; (2) enhance macrophage phagocytosis and (3) increase bacterial clearance from the lungs in a mouse model of ventilator-associated pneumonia.

METHOD

GTS-21 (0.04, 0.4, and 4 mg/kg) or saline were administered by intraperitoneal injection to mice that were exposed to hyperoxia (≥ 99% O₂) and subsequently challenged with PA.

RESULTS

The systemic administration of 4 mg/kg i.p. of GTS-21 significantly increased bacterial clearance, decreased acute lung injury and decreased accumulation of airway HMGB1 compared to the saline control. To determine the mechanism of action of GTS-21, RAW 264.7 cells, a macrophage-like cell line, were incubated with different concentrations of GTS-21 in the presence of 95% O₂. The phagocytic activity of macrophages was significantly increased by GTS-21 in a dose-dependent manner. In addition, GTS-21 significantly inhibited the cytoplasmic translocation and release of HMGB1 from RAW 264.7 cells and attenuated hyperoxia-induced NF-κB activation in macrophages and mouse lungs exposed to hyperoxia and infected with PA.

CONCLUSIONS

Our results indicate that GTS-21 is efficacious in improving bacterial clearance and reducing acute lung injury via enhancing macrophage function by inhibiting the release of nuclear HMGB1. Therefore, the α7nAChR represents a possible pharmacological target to improve the clinical outcome of patients on ventilators by augmenting host defense against bacterial infections.

Effect of early hyperoxemia on the outcome in servere blunt chest trauma: A propensity score-based analysis of a single-center retrospective cohort

PURPOSE

Our study aimed to explore the association between early hyperoxemia of the first 24 h on outcomes in patients with severe blunt chest trauma.

MATERIALS AND METHODS

In a level I trauma center, we conducted a retrospective study of 426 consecutive patients. Hyperoxemic groups were classified in severe (average PaO₂ ≥ 200 mmHg), moderate (≥150 and < 200 mmHg) or mild (≥ 100 and < 200 mmHg) and compared to control group (≥60 and < 100 mmHg) using a propensity score based analysis. The first endpoint was the incidence of a composite outcome including death and hospital-acquired pneumonia occurring from admission to day 28. The secondary endpoints were the incidence of death, the number of hospital-acquired pneumonia, mechanical ventilation-free days and intensive care unit-free day at day 28.

RESULTS

The incidence of the composite endpoint was lower in the severe hyperoxemia group(OR, 0.25; 95%CI, 0.09-0.73; P < 0.001) compared with control. The 28-day mortality incidence was lower in severe (OR, 0.23; 95%CI, 0.08-0.68; P < 0.001) hyperoxemia group (OR, 0.41; 95%CI, 0.17-0.97; P = 0.04). Significant association was found between hyperoxemia and secondary outcomes.

CONCLUSION

In our cohort early hyperoxemia during the first 24 h of admission after severe blunt chest trauma was not associated with worse outcome.

Control of myeloid cell density in barrier tissues

The interface between the mammalian host and its environment is formed by barrier tissues, for example, of the skin, and the respiratory and the intestinal tracts. On the one hand, barrier tissues are colonized by site-adapted microbial communities, and on the other hand, they contain specific myeloid cell networks comprising macrophages, dendritic cells, and granulocytes. These immune cells are tightly regulated in function and cell number, indicating important roles in maintaining tissue homeostasis and immune balance in the presence of commensal microorganisms. The regulation of myeloid cell density and activation involves cell-autonomous 'single-loop circuits' including autocrine mechanisms. However, an array of microenvironmental factors originating from nonimmune cells and the microbiota, as well as the microanatomical structure, impose additional layers of regulation onto resident myeloid cells. This review discusses models integrating these factors into cell-specific programs to instruct differentiation and proliferation best suited for the maintenance and renewal of immune homeostasis in the tissue-specific environment.

Dietary Antioxidants Significantly Attenuate Hyperoxia-Induced Acute Inflammatory Lung Injury by Enhancing Macrophage Function via Reducing the Accumulation of Airway HMGB1

Mechanical ventilation with hyperoxia is the major supportive measure to treat patients with acute lung injury and acute respiratory distress syndrome (ARDS). However, prolonged exposure to hyperoxia can induce oxidative inflammatory lung injury. Previously, we have shown that high levels of airway high-mobility group box 1 protein (HMGB1) mediate hyperoxia-induced acute lung injury (HALI). Using both ascorbic acid (AA, also known as vitamin C) and sulforaphane (SFN), an inducer of nuclear factor (erythroid-derived 2)-like 2 (Nrf2), we tested the hypothesis that dietary antioxidants can mitigate HALI by ameliorating HMGB1-compromised macrophage function in phagocytosis by attenuating hyperoxia-induced extracellular HMGB1 accumulation. Our results indicated that SFN, which has been shown to attenute HALI in mice exposed to hyperoxia, dose-dependently restored hyperoxia-compromised macrophage function in phagocytosis (75.9 ± 3.5% in 0.33 µM SFN versus 50.7 ± 1.8% in dimethyl sulfoxide (DMSO) control, p < 0.05) by reducing oxidative stress and HMGB1 release from cultured macrophages (47.7 ± 14.7% in 0.33 µM SFN versus 93.1 ± 14.6% in DMSO control, p < 0.05). Previously, we have shown that AA enhances hyperoxic macrophage functions by reducing hyperoxia-induced HMGB1 release. Using a mouse model of HALI, we determined the effects of AA on hyperoxia-induced inflammatory lung injury. The i.p. administration of 50 mg/kg of AA to mice exposed to 72 h of ≥98% O₂ significantly decreased hyperoxia-induced oxidative and nitrosative stress in mouse lungs. There was a significant decrease in the levels of airway HMGB1 (43.3 ± 12.2% in 50 mg/kg AA versus 96.7 ± 9.39% in hyperoxic control, p < 0.05), leukocyte infiltration (60.39 ± 4.137% leukocytes numbers in 50 mg/kg AA versus 100 ± 5.82% in hyperoxic control, p < 0.05) and improved lung integrity in mice treated with AA. Our study is the first to report that the dietary antioxidants, ascorbic acid and sulforaphane, ameliorate HALI and attenuate hyperoxia-induced macrophage dysfunction through an HMGB1-mediated pathway. Thus, dietary antioxidants could be used as potential treatments for oxidative-stress-induced acute inflammatory lung injury in patients receiving mechanical ventilation.

The nitric oxide donor, (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NONOate/D-NO), increases survival by attenuating hyperoxia-compromised innate immunity in bacterial clearance in a mouse model of ventilator-associated pneumonia

Mechanical ventilation (MV) with supraphysiological levels of oxygen (hyperoxia) is a life-saving therapy for the management of patients with respiratory distress. However, a significant number of patients on MV develop ventilator-associated pneumonia (VAP). Previously, we have reported that prolonged exposure to hyperoxia impairs the capacity of macrophages to phagocytize Pseudomonas aeruginosa (PA), which can contribute to the compromised innate immunity in VAP. In this study, we show that the high mortality rate in mice subjected to hyperoxia and PA infection was accompanied by a significant decrease in the airway levels of nitric oxide (NO). Decreased NO levels were found to be, in part, due to a significant reduction in NO release by macrophages upon exposure to PA lipopolysaccharide (LPS). Based on these findings, we postulated that NO supplementation should restore hyperoxia-compromised innate immunity and decrease mortality by increasing the clearance of PA under hyperoxic conditions. To test this hypothesis, cultured macrophages were exposed to hyperoxia (95% O₂) in the presence or absence of the NO donor, (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NONOate/D-NO). Interestingly, D-NO (up to 37.5 µM) significantly attenuated hyperoxia-compromised macrophage migratory, phagocytic, and bactericidal function. To determine whether the administration of exogenous NO enhances the host defense in bacteria clearance, C57BL/6 mice were exposed to hyperoxia (99% O₂) and intranasally inoculated with PA in the presence or absence of D-NO. D-NO (300 µM-800 µM) significantly increased the survival of mice inoculated with PA under hyperoxic conditions, and significantly decreased bacterial loads in the lung and attenuated lung injury. These results suggest the NO donor, D-NO, can improve the clinical outcomes in VAP by augmenting the innate immunity in bacterial clearance. Thus, provided these results can be extrapolated to humans, NO supplementation may represent a potential therapeutic strategy for preventing and treating patients with VAP.

Effect of Hyperoxygenation During Surgery on Surgical Site Infection in Colorectal Surgery

Purpose

Despite the use of different surgical methods, surgical site infection is still an important cause of mortality and morbidity in patients and imposes a considerable cost on the healthcare system. Administration of supplemental oxygen during surgery has been reported to reduce surgical site infection (SSI); however, that result is still controversial. This study was performed to evaluate the effect of hyperoxygenation during colorectal surgery on the incidence of wound infection.

Methods

This study was a prospective double-blind case-control study. The main aim of the study was to evaluate the effect of hyperoxygenation during colorectal surgery on the incidence of SSI. Also, secondary outcomes, such as atelectasis, pneumonia, respiratory failure, length of hospital stay, and required hospitalization in the intensive care unit were evaluated.

Results

SSI was recorded in 2 patients (2 of 40, 5%) in the hyperoxygenation group (FiO₂ 80%) and 6 patients (6 of 40, 15%) in the control group (FiO₂ 30%) (P < 0.05). Time of hospitalization was 6 ± 6.4 days in the hyperoxygenation group and 9.2 ± 2.4 days in the control group (P < 0.05).

Conclusion

This study showed a positive effect of hyperoxygenation in reducing SSI in colorectal surgery, especially surgery in an emergency setting. When the low risk, low cost, and effectiveness of this method in patients undergoing a laparotomy are considered, it is recommended for all patients undergoing colorectal surgery.

Intra-Operative Inspired Fraction of Oxygen and the Risk of Surgical Site Infections in Patients with Type 1 Surgical Incisions

BACKGROUND

Whether the fraction of inspired oxygen (F_IO₂) influences the risk of surgical site infection (SSI) is controversial. The World Health Organization and the World Federation of Societies of Anesthesiologists offer conflicting recommendations. In this study, we evaluate simultaneously three different definitions of F_IO₂ exposure and the risk of SSI in a large surgical population.

PATIENTS AND METHODS

Patients with clean (type 1) surgical incisions who developed superficial and deep organ/space SSI within 30 days after surgery from January 2003 through December 2012 in five surgical specialties were matched to specialty-specific controls. Fraction of inspired oxygen exposure was defined as (1) nadir F_IO₂, (2) percentage of operative time with F_IO₂ greater than 50%, and (3) cumulative hyperoxia exposure, calculated as the area under the curve (AUC) of F_IO₂ by time for the duration in which F_IO₂ greater than 50%. Stratified univariable and multivariable logistic regression models tested associations between F_IO₂ and SSI.

RESULTS

One thousand two hundred fifty cases of SSI were matched to 3,248 controls. Increased oxygen exposure, by any of the three measures, was not associated with the outcome of any SSI in a multivariable logistic regression model. Elevated body mass index (BMI; 35+ vs. <25, odds ratio [OR] 1.78, 95% confidence interval [CI] 1.43-2.24), surgical duration (250+ min vs. <100 min, OR 1.93, 95% CI 1.48-2.52), diabetes mellitus (OR 1.37, 95% CI 1.13-1.65), peripheral vascular disease (OR 1.52, 95% CI 1.10-2.10), and liver cirrhosis (OR 2.48, 95% CI 1.53-4.02) were statistically significantly associated with greater odds of any SSI. Surgical sub-group analyses found higher intra-operative oxygen exposure was associated with higher odds of SSI in the neurosurgical and spine populations.

CONCLUSION

Increased intra-operative inspired fraction of oxygen was not associated with a reduction in SSI. These findings do not support the practice of increasing F_IO₂ for the purpose of SSI reduction in patients with clean surgical incisions.

Relationship between hyperoxemia and ventilator associated pneumonia

Previous studies suggest a relationship between hyperoxemia and ventilator-associated pneumonia (VAP). Hyperoxemia is responsible for denitrogenation phenomena, and inhibition of surfactant production, promoting atelectasis in mechanically ventilated patients. Further, hyperoxemia impairs the efficacy of alveolar macrophages to migrate, phagocyte and kill bacteria. Oxygen can also cause pulmonary-specific toxic effect called hyperoxic acute lung injury leading to longer duration of mechanical ventilation. All these hyperoxic effects are well-known risk factors for VAP. A recent retrospective large single center study identified hyperoxemia as an independent risk factor for VAP. However, two recent randomized controlled trials evaluated the impact of conservative oxygen strategy versus a liberal strategy, but did not confirm the role of hyperoxemia in lower respiratory tract infection occurrence. In this review, we discuss animal and human studies suggesting a relationship between these two common conditions in mechanically ventilated patients and potential interventions that should be evaluated. Further large prospective studies in carefully selected groups of patients are required to confirm the potential role of hyperoxemia in VAP pathogenesis and to evaluate the impact of a conservative oxygen strategy vs. a conventional strategy on the incidence of VAP.

WHO Needs High FIO2?

World Health Organization and the United States Center for Disease Control have recently recommended the use of 0.8 FIO₂ in all adult surgical patients undergoing general anaesthesia, to prevent surgical site infections. This recommendation has arisen several discussions: As a matter of fact, there are numerous studies with different results about the effect of FIO₂ on surgical site infection. Moreover, the clinical effects of FIO₂ are not limited to infection control. We asked some prominent authors about their comments regarding the recent recommendations.

Perioperative hyperoxia: perhaps a malady in disguise

Oxygen is an element, which is used liberally during several medical procedures. The use of oxygen during perioperative care is a controversial issue. Anesthesiologists use oxygen to prevent hypoxemia during surgical procedures, but the effects of its liberal use can be harmful. Another argument for using high oxygen concentrations is to prevent surgical site infections by increasing oxygen levels at the incision site. Although inconclusive, literature concerning the use of high oxygen concentrations during anesthesia show that this approach may cause hemodynamic changes, altered microcirculation and increased oxidative stress. In intensive care it has been shown that high oxygen concentrations may be associated with increased mortality in certain patient populations such as post cardiac arrest patients. In this paper, a review of literature had been undertaken to warn anesthesiologists about the potential harmful effects of high oxygen concentrations.

Ascorbic Acid Attenuates Hyperoxia-Compromised Host Defense against Pulmonary Bacterial Infection

Supraphysiological concentrations of oxygen (hyperoxia) can compromise host defense and increase susceptibility to bacterial infections, causing ventilator-associated pneumonia. The phagocytic activity of macrophages is impaired by hyperoxia-induced increases in the levels of reactive oxygen species (ROS) and extracellular high-mobility group box protein B1 (HMGB1). Ascorbic acid (AA), an essential nutrient and antioxidant, has been shown to be beneficial in various animal models of ROS-mediated diseases. The aim of this study was to determine whether AA could attenuate hyperoxia-compromised host defense and improve macrophage functions against bacterial infections. C57BL/6 male mice were exposed to hyperoxia (≥98% O₂, 48 h), followed by intratracheal inoculation with Pseudomonas aeruginosa, and simultaneous intraperitoneal administration of AA. AA (50 mg/kg) significantly improved bacterial clearance in the lungs and airways, and significantly reduced HMGB1 accumulation in the airways. The incubation of RAW 264.7 cells (a macrophage-like cell line) with AA (0-1,000 μM) before hyperoxic exposure (95% O₂) stabilized the phagocytic activity of macrophages in a concentration-dependent manner. The AA-enhanced macrophage function was associated with significantly decreased production of intracellular ROS and accumulation of extracellular HMGB1. These data suggest that AA supplementation can prevent or attenuate the development of ventilator-associated pneumonia in patients receiving oxygen support.

N-Acetylcysteine Synergizes with Oseltamivir in Protecting Mice from Lethal Influenza Infection

Many studies have shown that oxidative stress is important in the pathogenesis of pulmonary damage during influenza virus infections. Antioxidant molecules are therefore potentially useful against viral infection. Our previous studies show that N-acetylcysteine (NAC) has a protective effect in a model of lethal influenza infection in mice. NAC administration significantly decreased the mortality in infected mice. Further studies have demonstrated that NAC enhanced survival in combination with the antiviral agent ribavirin. In the present study, we report the effect of combined treatment with NAC and Oseltamivir, clinically used in the treatment and prevention of influenza virus infection, in a murine model of lethal influenza infection. NAC was given as a single daily dose of 1000 mg/Kg starting from 4 h before infection and until day 4 after infection; Oseltamivir was given twice daily at dose of 1 mg/Kg/die for 5 days, starting from 4 h before infection. End-point evaluation was 21-days' survival. NAC alone was slightly effective (20%), since a suboptimal treatment was used. Survival increased to 60% with Oseltamivir and to 100% with Oseltamivir and NAC used in combination. Since NAC alone does not show any antiviral action, the present findings suggest that antioxidant therapy increase survival by an improvement in host defense mechanisms, and/or by a direct antioxidant effect against oxidative stress associated with viral infection. Our studies demonstrate the effectiveness of combining agents acting through different mechanisms, such as antiviral drugs oseltamivir and the antioxidant NAC, indicating a possible advantage of combining the two treatments.

Quantitative Profiling of Protein S-Glutathionylation Reveals Redox-Dependent Regulation of Macrophage Function during Nanoparticle-Induced Oxidative Stress

Engineered nanoparticles (ENPs) are increasingly utilized for commercial and medical applications; thus, understanding their potential adverse effects is an important societal issue. Herein, we investigated protein S-glutathionylation (SSG) as an underlying regulatory mechanism by which ENPs may alter macrophage innate immune functions, using a quantitative redox proteomics approach for site-specific measurement of SSG modifications. Three high-volume production ENPs (SiO2, Fe3O4, and CoO) were selected as representatives which induce low, moderate, and high propensity, respectively, to stimulate cellular reactive oxygen species (ROS) and disrupt macrophage function. The SSG modifications identified highlighted a broad set of redox sensitive proteins and specific Cys residues which correlated well with the overall level of cellular redox stress and impairment of macrophage phagocytic function (CoO > Fe3O4 ≫ SiO2). Moreover, our data revealed pathway-specific differences in susceptibility to SSG between ENPs which induce moderate versus high levels of ROS. Pathways regulating protein translation and protein stability indicative of ER stress responses and proteins involved in phagocytosis were among the most sensitive to SSG in response to ENPs that induce subcytoxic levels of redox stress. At higher levels of redox stress, the pattern of SSG modifications displayed reduced specificity and a broader set pathways involving classical stress responses and mitochondrial energetics (e.g., glycolysis) associated with apoptotic mechanisms. An important role for SSG in regulation of macrophage innate immune function was also confirmed by RNA silencing of glutaredoxin, a major enzyme which reverses SSG modifications. Our results provide unique insights into the protein signatures and pathways that serve as ROS sensors and may facilitate cellular adaption to ENPs, versus intracellular targets of ENP-induced oxidative stress that are linked to irreversible cell outcomes.

Short-term hyperoxia does not exert immunologic effects during experimental murine and human endotoxemia

Oxygen therapy to maintain tissue oxygenation is one of the cornerstones of critical care. Therefore, hyperoxia is often encountered in critically ill patients. Epidemiologic studies have demonstrated that hyperoxia may affect outcome, although mechanisms are unclear. Immunologic effects might be involved, as hyperoxia was shown to attenuate inflammation and organ damage in preclinical models. However, it remains unclear whether these observations can be ascribed to direct immunosuppressive effects of hyperoxia or to preserved tissue oxygenation. In contrast to these putative anti-inflammatory effects, hyperoxia may elicit an inflammatory response and organ damage in itself, known as oxygen toxicity. Here, we demonstrate that, in the absence of systemic inflammation, short-term hyperoxia (100% O2 for 2.5 hours in mice and 3.5 hours in humans) does not result in increased levels of inflammatory cytokines in both mice and healthy volunteers. Furthermore, we show that, compared with room air, hyperoxia does not affect the systemic inflammatory response elicited by administration of bacterial endotoxin in mice and man. Finally, neutrophil phagocytosis and ROS generation are unaffected by short-term hyperoxia. Our results indicate that hyperoxia does not exert direct anti-inflammatory effects and temper expectations of using it as an immunomodulatory treatment strategy.

The compromise of macrophage functions by hyperoxia is attenuated by ethacrynic acid via inhibition of NF-κB-mediated release of high-mobility group box-1

The prolonged exposure to hyperoxia can compromise macrophage functions and contribute to the development of ventilator-associated pneumonia. High levels of extracellular high-mobility group box-1 (HMGB1) in the airways of mice exposed to hyperoxia can directly cause macrophage dysfunction. Hence, inhibition of the release of nuclear HMGB1 into the extracellular milieu may help to maintain macrophage functions under hyperoxic conditions. The present study investigates whether ethacrynic acid (EA) affects hyperoxia-induced HMGB1 release from macrophages and improves their functions. Macrophage-like RAW 264.7 cells and bone marrow-derived macrophages were exposed to different concentrations of EA for 24 hours in the presence of 95% O2. EA significantly decreased the accumulation of extracellular HMGB1 in cultured media. Importantly, the phagocytic activity and migration capability of macrophages were significantly enhanced in EA-treated cells. Interestingly, hyperoxia-induced NF-κB activation was also inhibited in these cells. To determine whether NF-κB plays a role in hyperoxia-induced HMGB1 release, BAY 11-7082, an inhibitor of NF-κB activation, was used. Similar to EA, BAY 11-7082 significantly inhibited the accumulation of extracellular HMGB1 and improved hyperoxia-compromised macrophage migration and phagocytic activity. Furthermore, 24-hour hyperoxic exposure of macrophages caused hyperacetylation of HMGB1 and its subsequent cytoplasmic translocation and release, which were inhibited by EA and BAY 11-7082. Together, these results suggest that EA enhances hyperoxia-compromised macrophage functions by inhibiting HMGB1 hyperacetylation and its release from macrophages, possibly through attenuation of the NF-κB activation. Therefore, the activation of NF-κB could be one of the underlying mechanisms that mediate hyperoxia-compromised macrophage functions.

The α7 nicotinic acetylcholine receptor agonist GTS-21 improves bacterial clearance in mice by restoring hyperoxia-compromised macrophage function

Mechanical ventilation with supraphysiological concentrations of oxygen (hyperoxia) is routinely used to treat patients with respiratory distress. However, prolonged exposure to hyperoxia compromises the ability of the macrophage to phagocytose and clear bacteria. Previously, we showed that the exposure of mice to hyperoxia elicits the release of the nuclear protein high mobility group box-1 (HMGB1) into the airways. Extracellular HMGB1 impairs macrophage phagocytosis and increases the mortality of mice infected with Pseudomonas aeruginosa (PA). The aim of this study was to determine whether GTS-21 [3-(2,4 dimethoxybenzylidene)-anabaseine dihydrochloride], an α7 nicotinic acetylcholine receptor (α7nAChR) agonist, could inhibit hyperoxia-induced HMGB1 release into the airways, enhance macrophage function and improve bacterial clearance from the lungs in a mouse model of ventilator-associated pneumonia. GTS-21 (0.04, 0.4 and 4 mg/kg) or saline was systemically administered via intraperitoneal injection to mice that were exposed to hyperoxia (≥99% O2) and subsequently challenged with PA. We found that systemic administration of 4 mg/kg GTS-21 significantly increased bacterial clearance, decreased acute lung injury and decreased accumulation of airway HMGB1. To investigate the cellular mechanism of these observations, RAW 264.7 cells, a macrophagelike cell line, were incubated with different concentrations of GTS-21 in the presence of 95% O2. The phagocytic activity of macrophages was significantly increased by GTS-21 in a dose-dependent manner. In addition, hyperoxia-induced hyperacetylation of HMGB1 was significantly reduced in macrophages incubated with GTS-21. Furthermore, GTS-21 significantly inhibited the cytoplasmic translocation and release of HMGB1 from these macrophages. Our results indicate that GTS-21 is effective in improving bacterial clearance and reducing acute lung injury by enhancing macrophage function via inhibiting the release of nuclear HMGB1. Therefore, the α7nAChR represents a possible pharmacological target to improve the clinical outcome of patients on ventilators by augmenting host defense against bacterial infections.

Assessment of phagocytic activity of cultured macrophages using fluorescence microscopy and flow cytometry

Phagocytosis is the process by which phagocytes, including macrophages, neutrophils and monocytes, engulf and kill invading pathogens, remove foreign particles, and clear cell debris. Phagocytes and their ability to phagocytose are an important part of the innate immune system and are critical for homeostasis of the host. Impairment in phagocytosis has been associated with numerous diseases and disorders. Different cytokines have been shown to affect the phagocytic process. Cytokines including TNFα, IL-1β, GM-CSF, and TGF-β1 were found to promote phagocytosis, whereas high mobility group box-1 (HMGB1) inhibited the phagocytic function of macrophages. Here, we describe two commonly used methods to assess the phagocytic function of cultured macrophages, which can easily be applied to other phagocytes. Each method is based on the extent of engulfment of FITC-labeled latex minibeads by macrophages under different conditions. Phagocytic activity can be assessed either by counting individual cells using a fluorescence microscope or measuring fluorescence intensity using a flow cytometer.

Dysregulation of macrophage activation profiles by engineered nanoparticles

Although the potential human health impacts from exposure to engineered nanoparticles (ENPs) are uncertain, past epidemiological studies have established correlations between exposure to ambient air pollution particulates and the incidence of pneumonia and lung infections. Using amorphous silica and superparamagnetic iron oxide (SPIO) as model high production volume ENPs, we examined how macrophage activation by bacterial lipopolysaccharide (LPS) or the lung pathogen Streptococcus pneumoniae is altered by ENP pretreatment. Neither silica nor SPIO treatment elicited direct cytotoxic or pro-inflammatory effects in bone marrow-derived macrophages. However, pretreatment of macrophages with SPIO caused extensive reprogramming of nearly 500 genes regulated in response to LPS challenge, hallmarked by exaggerated activation of oxidative stress response pathways and suppressed activation of both pro- and anti-inflammatory pathways. Silica pretreatment altered regulation of only 67 genes, but there was strong correlation with gene sets affected by SPIO. Macrophages exposed to SPIO displayed a phenotype suggesting an impaired ability to transition from an M1 to M2-like activation state, characterized by suppressed IL-10 induction, enhanced TNFα production, and diminished phagocytic activity toward S. pneumoniae. Studies in macrophages deficient in scavenger receptor A (SR-A) showed SR-A participates in cell uptake of both the ENPs and S. pneumonia and co-regulates the anti-inflammatory IL-10 pathway. Thus, mechanisms for dysregulation of innate immunity exist by virtue that common receptor recognition pathways are used by some ENPs and pathogenic bacteria, although the extent of transcriptional reprogramming of macrophage function depends on the physicochemical properties of the ENP after internalization. Our results also illustrate that biological effects of ENPs may be indirectly manifested only after challenging normal cell function. Nanotoxicology screening strategies should therefore consider how exposure to these materials alters susceptibility to other environmental exposures.

The role of RhoA and cytoskeleton in myofibroblast transformation in hyperoxic lung fibrosis

Myofibroblast transformation is a key process in the pathogenesis of lung fibrosis. We have previously reported that hyperoxia induces RhoA activation in HFL-1 lung fibroblasts and RhoA mediates collagen synthesis in hyperoxic lung fibrosis. In this study, we investigated the role of RhoA and actin cytoskeleton in hyperoxia-induced myofibroblast transformation. Exposure of HFL-1 lung fibroblasts to hyperoxia stimulated actin filament formation, shift of G-actin to F-actin, nuclear colocalization of myocardin-related transcription factor-A (MRTF-A), recruitment of MRTF-A to the α-smooth muscle actin (α-SMA) gene promoter, myofibroblast transformation, and collagen-I synthesis. Inhibition of RhoA by C3 transferase CT-04 or dominant-negative RhoA mutant T19N, and inhibition of ROCK by Y27632, prevented myofibroblast transformation and collagen-I synthesis. Moreover, inhibition of RhoA by CT-04 prevented hyperoxia-induced actin filament formation, shift of G-actin to F-actin, and nuclear colocalization of MRTF-A. In addition, disrupting actin filaments with cytochalasin D or scavenging reactive oxygen species (ROS) with tiron attenuated actin filament formation, nuclear colocalization of MRTF-A, myofibroblast transformation, and collagen-I synthesis. Furthermore, overexpression of constitutively active RhoA mutant Q63L or stabilization of actin filaments recapitulated the effects of hyperoxia on the actin cytoskeleton and nuclear colocalization of MRTF-A, myofibroblast transformation, and collagen-I synthesis. Interestingly, knocking down MRTF-A prevented hyperoxia-induced increase in the recruitment of MRTF-A to the serum response factor transcriptional complex on the α-SMA gene promoter, myofibroblast transformation, and collagen-I synthesis. Finally, Y27632 and tiron attenuated hyperoxia-induced increases in α-SMA and collagen-I in mouse lungs. Together, these results indicate that the actin cytoskeletal reorganization due to the ROS/RhoA-ROCK pathway mediates myofibroblast transformation and collagen synthesis in lung fibrosis of oxygen toxicity. MRTF-A contributes to the regulatory effect of the actin cytoskeleton on myofibroblast transformation during hyperoxia.

Molecular responses of mouse macrophages to copper and copper oxide nanoparticles inferred from proteomic analyses

The molecular responses of macrophages to copper-based nanoparticles have been investigated via a combination of proteomic and biochemical approaches, using the RAW264.7 cell line as a model. Both metallic copper and copper oxide nanoparticles have been tested, with copper ion and zirconium oxide nanoparticles used as controls. Proteomic analysis highlighted changes in proteins implicated in oxidative stress responses (superoxide dismutases and peroxiredoxins), glutathione biosynthesis, the actomyosin cytoskeleton, and mitochondrial proteins (especially oxidative phosphorylation complex subunits). Validation studies employing functional analyses showed that the increases in glutathione biosynthesis and in mitochondrial complexes observed in the proteomic screen were critical to cell survival upon stress with copper-based nanoparticles; pharmacological inhibition of these two pathways enhanced cell vulnerability to copper-based nanoparticles, but not to copper ions. Furthermore, functional analyses using primary macrophages derived from bone marrow showed a decrease in reduced glutathione levels, a decrease in the mitochondrial transmembrane potential, and inhibition of phagocytosis and of lipopolysaccharide-induced nitric oxide production. However, only a fraction of these effects could be obtained with copper ions. In conclusion, this study showed that macrophage functions are significantly altered by copper-based nanoparticles. Also highlighted are the cellular pathways modulated by cells for survival and the exemplified cross-toxicities that can occur between copper-based nanoparticles and pharmacological agents.

Actin carbonylation: from cell dysfunction to organism disorder

Protein carbonylation is an important event in the context of proteostasis because of its frequency, non-enzymatic nature and irreversible effects. The carbonylation of proteins disturbs their function and leads to protein aggregates, which may precede cellular senescence and cell death. Actin, an evolutionarily conserved cytoskeletal protein that is involved in important cellular processes, is one of the proteins most susceptible to carbonylation. Conditions resulting in oxidative stress are likely to lead to its carbonylation, loss of function and aggregate formation. In this review, we summarise actin susceptibility to carbonylation, as verified in cell free extracts, cell lines and animal models, and review its fate through the activation of cell mechanisms aimed at removing damaged proteins. Their insufficient activity may underlie age-related diseases and the ageing process. This article is part of a Special Issue entitled: Posttranslational Protein modifications in biology and Medicine.

Alterations in the pulmonary histoarchitecture of neonatal mice exposed to hyperoxia

OBJECTIVES

To analyze the effects of exposure to hyperoxia (100% oxygen) on the lung histoarchitecture of neonatal mice.

METHODS

Neonatal Balb/c mice were exposed to hyperoxia (HG) (100% oxygen) (n= 10) in a chamber (15 x 20 x 30 cm) for 24 hours with a flow of 2 L/min. The control group (CG) (n = 10) was exposed to normoxia in the same type of chamber and for the same time. After exposure, the animals were euthanized by decapitation; the lungs were removed and processed for histological examination according to the laboratory routine. Three-mm thick sections were stained with hematoxylin and eosin (H&E). The morphometric analysis was performed with in order to analyze the macrophages present in the alveolar lumen, surface density (Sv) of gas exchange, volume density (Vv) of lung parenchyma, and areas of atelectasis.

RESULTS

A decrease in the number of alveolar macrophages (MØ) was observed in the HG (HG = 0.08 ±0.01 MØ/mm(2), CG = 0.18 ± 0.03 MØ/mm(2), p=0.0475), Sv of gas exchange in HG (HG = 8.08 ± 0.12 mm(2)/mm(3), CG=8.65 ± 0.20mm(2)/mm(3), p = 0.0233), Vv of lung parenchyma in HG (HG = 54.7/33.5/83.5%/mm(2); CG = 75/56.7/107.9%/mm(2), p<0.0001) when compared with the CG. However, there was an increase in areas of atelectasis in HG (HG = 17.5/11.3/38.4 atelectasis/mm(2), CG = 14/6.1/24.4 atelectasis/mm(2), p=0.0166) when compared with the CG.

CONCLUSION

The present results indicate that hyperoxia caused alterations in lung histoarchitecture, increasing areas of atelectasis and diffuse alveolar hemorrhage.

Innate Immune Responses in Ventilator-Associated Pneumonia

Ventilator-associated pneumonia (VAP) is a common complication of mechanical ventilation, resulting in substantial morbidity, mortality, and health care cost. Early upper airway colonization by pathogenic bacteria and microaspiration are the primary pathogenic events leading to VAP. Patients at risk for VAP have defects in structural/mechanical defenses of the respiratory tract. In addition, critical illness, including sepsis, trauma, and postoperative states, is associated with profound defects in both innate and acquired antibacterial immunity, influencing antimicrobial effector functions of both leukocytes and structural/parenchymal cells. Factors present within the lung microenvironment, including alveolar stretch, cyclical atelectasis, changes in oxygen tension, and respiratory tract microbiota, substantially impact antibacterial host responses. Mechanisms accounting for dysregulated immune homeostasis are incompletely understood, but likely involve: (1) alterations in the balance of pro- and anti-inflammatory cytokines; (2) changes in pathogen recognition receptor and G-protein coupled receptor expression and downstream signaling cascades; and (3) dysregulated cell death responses. Antibiotics and preventive strategies are the mainstay of therapy in patients with VAP. However, novel approaches are needed to reverse immunological reprogramming that occurs during critical illness and/or mechanical ventilation, and to identify patients who are most likely to benefit from immunomodulatory therapy.

High Mobility Group Box-1 mediates hyperoxia-induced impairment of Pseudomonas aeruginosa clearance and inflammatory lung injury in mice

Mechanical ventilation with supraphysiological concentrations of oxygen (hyperoxia) is routinely used to treat patients with respiratory distress. However, a significant number of patients on ventilators exhibit enhanced susceptibility to infections and develop ventilator-associated pneumonia (VAP). Pseudomonas aeruginosa (PA) is one of the most common species of bacteria found in these patients. Previously, we demonstrated that prolonged exposure to hyperoxia can compromise the ability of alveolar macrophages (AMs), an essential part of the innate immunity, to phagocytose PA. This study sought to investigate the potential molecular mechanisms underlying hyperoxia-compromised innate immunity against bacterial infection in a murine model of PA pneumonia. Here, we show that exposure to hyperoxia (≥ 99% O2) led to a significant elevation in concentrations of airway high mobility group box-1 (HMGB1) and increased mortality in C57BL/6 mice infected with PA. Treatment of these mice with a neutralizing anti-HMGB1 monoclonal antibody (mAb) resulted in a reduction in bacterial counts, injury, and numbers of neutrophils in the lungs, and an increase in leukocyte phagocytic activity compared with mice receiving control mAb. This improved phagocytic function was associated with reduced concentrations of airway HMGB1. The correlation between phagocytic activity and concentrations of extracellular HMGB1 was also observed in cultured macrophages. These results indicate a pathogenic role for HMGB1 in hyperoxia-induced impairment with regard to a host's ability to clear bacteria and inflammatory lung injury. Thus, HMGB1 may provide a novel molecular target for improving hyperoxia-compromised innate immunity in patients with VAP.

Redox proteomics identification of oxidatively modified myocardial proteins in human heart failure: implications for protein function

Increased oxidative stress in a failing heart may contribute to the pathogenesis of heart failure (HF). The aim of this study was to identify the oxidised proteins in the myocardium of HF patients and analyse the consequences of oxidation on protein function. The carbonylated proteins in left ventricular tissue from failing (n = 14) and non-failing human hearts (n = 13) were measured by immunoassay and identified by proteomics. HL-1 cardiomyocytes were incubated in the presence of stimuli relevant for HF in order to assess the generation of reactive oxygen species (ROS), the induction of protein carbonylation, and its consequences on protein function. The levels of carbonylated proteins were significantly higher in the HF patients than in the controls (p<0.01). We identified two proteins that mainly underwent carbonylation: M-type creatine kinase (M-CK), whose activity is impaired, and, to a lesser extent, α-cardiac actin. Exposure of cardiomyocytes to angiotensin II and norepinephrine led to ROS generation and M-CK carbonylation with loss of its enzymatic activity. Our findings indicate that protein carbonylation is increased in the myocardium during HF and that these oxidative changes may help to explain the decreased CK activity and consequent defects in energy metabolism observed in HF.

Hyperoxia alters the mechanical properties of alveolar epithelial cells

Patients with severe acute lung injury are frequently administered high concentrations of oxygen (>50%) during mechanical ventilation. Long-term exposure to high levels of oxygen can cause lung injury in the absence of mechanical ventilation, but the combination of the two accelerates and increases injury. Hyperoxia causes injury to cells through the generation of excessive reactive oxygen species. However, the precise mechanisms that lead to epithelial injury and the reasons for increased injury caused by mechanical ventilation are not well understood. We hypothesized that alveolar epithelial cells (AECs) may be more susceptible to injury caused by mechanical ventilation if hyperoxia alters the mechanical properties of the cells causing them to resist deformation. To test this hypothesis, we used atomic force microscopy in the indentation mode to measure the mechanical properties of cultured AECs. Exposure of AECs to hyperoxia for 24 to 48 h caused a significant increase in the elastic modulus (a measure of resistance to deformation) of both primary rat type II AECs and a cell line of mouse AECs (MLE-12). Hyperoxia also caused remodeling of both actin and microtubules. The increase in elastic modulus was blocked by treatment with cytochalasin D. Using finite element analysis, we showed that the increase in elastic modulus can lead to increased stress near the cell perimeter in the presence of stretch. We then demonstrated that cyclic stretch of hyperoxia-treated cells caused significant cell detachment. Our results suggest that exposure to hyperoxia causes structural remodeling of AECs that leads to decreased cell deformability.

Hydrogen peroxide enhances phagocytosis of Pseudomonas aeruginosa in hyperoxia

Mechanical ventilation with hyperoxia is a necessary treatment for patients with respiratory distress. However, patients on mechanical ventilation have increased susceptibility to infection. Studies including ours have shown that reactive oxygen species (ROS), generated by exposure to prolonged hyperoxia, can cause a decrease in the phagocytic activity of alveolar macrophages. Hydrogen peroxide (H₂O₂) is a form of ROS generated under hyperoxic conditions. In this study, we examined whether treatment with H₂O₂ directly affects macrophage phagocytic ability in RAW 264.7 cells that were exposed to either 21% O₂ (room air) or 95% O₂ (hyperoxia). Moderate concentrations (ranging from 10 to 250 μM) of H₂O₂ significantly enhanced macrophage phagocytic activity and restored hyperoxia-suppressed phagocytosis through attenuation of hyperoxia-induced disorganization of actin cytoskeleton and actin oxidation. These results indicate that H₂O₂ at low-moderate concentrations can be beneficial to host immune responses by improving macrophage phagocytic activity.

Elevated CO2 selectively inhibits interleukin-6 and tumor necrosis factor expression and decreases phagocytosis in the macrophage

Elevated blood and tissue CO(2), or hypercapnia, is common in severe lung disease. Patients with hypercapnia often develop lung infections and have an increased risk of death following pneumonia. To explore whether hypercapnia interferes with host defense, we studied the effects of elevated P(CO2) on macrophage innate immune responses. In differentiated human THP-1 macrophages and human and mouse alveolar macrophages stimulated with lipopolysaccharide (LPS) and other Toll-like receptor ligands, hypercapnia inhibited expression of tumor necrosis factor and interleukin (IL)-6, nuclear factor (NF)-kappaB-dependent cytokines critical for antimicrobial host defense. Inhibition of IL-6 expression by hypercapnia was concentration dependent, rapid, reversible, and independent of extracellular and intracellular acidosis. In contrast, hypercapnia did not down-regulate IL-10 or interferon-beta, which do not require NF-kappaB. Notably, hypercapnia did not affect LPS-induced degradation of IkappaB alpha, nuclear translocation of RelA/p65, or activation of mitogen-activated protein kinases, but it did block IL-6 promoter-driven luciferase activity in mouse RAW 264.7 macrophages. Elevated P(CO2) also decreased phagocytosis of opsonized polystyrene beads and heat-killed bacteria in THP-1 and human alveolar macrophages. By interfering with essential innate immune functions in the macrophage, hypercapnia may cause a previously unrecognized defect in resistance to pulmonary infection in patients with advanced lung disease.

An electrostatic switch displaces phosphatidylinositol phosphate kinases from the membrane during phagocytosis

PIP5K is held at the membrane of forming phagosomes by a conserved, positively charged patch. During particle engulfment, the surface charge of the phagosome decreases, releasing PIP5K and enabling phagocytosis to proceed.

Plasmalemmal phosphatidylinositol (PI) 4,5-bisphosphate (PI4,5P₂) synthesized by PI 4-phosphate (PI4P) 5-kinase (PIP5K) is key to the polymerization of actin that drives chemotaxis and phagocytosis. We investigated the means whereby PIP5K is targeted to the membrane and its fate during phagosome formation. Homology modeling revealed that all PIP5K isoforms feature a positively charged face. Together with the substrate-binding loop, this polycationic surface is proposed to constitute a coincidence detector that targets PIP5Ks to the plasmalemma. Accordingly, manipulation of the surface charge displaced PIP5Ks from the plasma membrane. During particle engulfment, PIP5Ks detached from forming phagosomes as the surface charge at these sites decreased. Precluding the change in surface charge caused the PIP5Ks to remain associated with the phagosomal cup. Chemically induced retention of PIP5K-γ prevented the disappearance of PI4,5P₂ and aborted phagosome formation. We conclude that a bistable electrostatic switch mechanism regulates the association/dissociation of PIP5Ks from the membrane during phagocytosis and likely other processes.

Innate immunity against bacterial infection following hyperoxia exposure is impaired in NRF2-deficient mice

Oxygen supplementation is used as therapy to support critically ill patients with severe respiratory impairment. Although hyperoxia has been shown to enhance the lung susceptibility to subsequent bacterial infection, the mechanisms underlying enhanced susceptibility remain enigmatic. We have reported that disruption of NF-E2-related factor 2 (Nrf2), a master transcription regulator of various stress response pathways, enhances susceptibility to hyperoxia-induced acute lung injury in mice, and have also demonstrated an association between a polymorphism in the NRF2 promoter and increased susceptibility to acute lung injury. In this study, we show that Nrf2-deficient (Nrf2(-/-)) but not wild-type (Nrf2(+/+)) mice exposed to sublethal hyperoxia succumbed to death during recovery after Pseudomonas aeruginosa infection. Nrf2-deficiency caused persistent bacterial pulmonary burden and enhanced levels of inflammatory cell infiltration as well as edema. Alveolar macrophages isolated from Nrf2(-/-) mice exposed to hyperoxia displayed persistent oxidative stress and inflammatory cytokine expression concomitant with diminished levels of antioxidant enzymes, such as Gclc, required for glutathione biosynthesis. In vitro exposure of Nrf2(-/-) macrophages to hyperoxia strongly diminished their antibacterial activity and enhanced inflammatory cytokine expression compared with Nrf2(+/+) cells. However, glutathione supplementation during hyperoxic insult restored the ability of Nrf2(-/-) cells to mount antibacterial response and suppressed cytokine expression. Thus, loss of Nrf2 impairs lung innate immunity and promotes susceptibility to bacterial infection after hyperoxia exposure, ultimately leading to death of the host.

Application of saturation dye 2D-DIGE proteomics to characterize proteins modulated by oxidized low density lipoprotein treatment of human macrophages

Macrophages are believed to play a crucial role in atherogenesis and atherosclerotic plaque progression, mainly through their role in the accumulation of large amounts of cholesteryl ester and foam cell formation after the uptake into the arterial intima of oxidized LDL (oxLDL) particles known to be proatherogenic. The aim of this study was to use a differential proteomic approach to identify the response of human monocyte-derived macrophages after treatment with oxLDL for 24 h. Mass spectrometry analysis (MALDI-TOF) of 2D-DIGE gels made it possible to identify 9 intracellular and 3 secreted proteins that were up-regulated, 11 intracellular and 1 secreted proteins that were down-regulated, and 2 secreted proteins that were induced. This methodological approach not only confirmed the differential expression levels of proteins known to be regulated by oxLDL in macrophages, such as catalase and pyruvate kinase, but also identified oxLDL modulation of other proteins for the first time, including heat shock proteins (HSP) and Actin cytoskeletal proteins. Semiquantitative Western blot confirmed their role. The HSPs identified included heat shock cognate 71 kDa protein (Hsc70), 75 kDa glucose-regulated protein (GRP75), heat shock 70 kDa protein (Hsp70), and 60 kDa (Hsp60) proteins. These highly conserved intracellular protein chaperones, commonly seen in atherosclerotic plaques, appear to participate in protection against cellular stress. Interestingly, oxLDL also modulated several F-Actin capping proteins involved in Actin polymerization and motility: gelsolin, CapG, and CapZ. In conclusion, we have demonstrated the effects of oxLDL in the modulation of several proteins in human macrophages and established a functional profile of the human macrophage during the atherosclerotic process.

The impact of hyperoxia on the neonatal and adult developing dendritic cell

Oxygen is essential therapy for neonates with acute respiratory failure, including those with infections. However, high oxygen levels may be counterproductive for overcoming infections because hyperoxia may kill cells, including dendritic cells that are essential to the emergence of the pulmonary immune system and pivotal in mounting immune responses to infections. We studied the impact of hyperoxia on developing dendritic cells from neonatal cord blood and adult blood monocytes, comparing viability, development of maturation, and endocytic function. Our data suggest that cord blood-derived dendritic cells may be more resistant to hyperoxic-induced cell death than adult blood-derived cells. Moreover, the surviving cells in either group are those that maintain an immature phenotype. This may impair their ability to perform optimal immune function.

Antioxidants improve antibacterial function in hyperoxia-exposed macrophages

Hyperoxia and pulmonary infections are well known to increase the risk of acute and chronic lung injury in newborn infants, but it is not clear whether hyperoxia directly increases the risk of pneumonia. The purpose of this study was to examine: (1) the effects of hyperoxia and antioxidant enzymes on inflammation and bacterial clearance in mononuclear cells and (2) developmental differences between adult and neonatal mononuclear cells in response to hyperoxia. Mouse macrophages were exposed to either room air or 95% O2 for 24 h and then incubated with Pseudomonas aeruginosa. After 1 h, bacterial adherence, phagocytosis, and macrophage inflammatory protein (MIP)-1alpha production were analyzed. Bacterial adherence increased 5.8-fold (p < 0.0001), phagocytosis decreased 60% (p < 0.05), and MIP-1alpha production increased 49% (p < 0.05) in response to hyperoxia. Overexpression of MnSOD or catalase significantly decreased bacterial adherence by 30.5%, but only MnSOD significantly improved bacterial phagocytosis and attenuated MIP-1alpha production. When monocytes from newborns and adults were exposed to hyperoxia, phagocytosis was impaired in both groups. However, adult monocytes were significantly more impaired than neonatal monocytes. Data indicate that hyperoxia significantly increases bacterial adherence while impairing function of mononuclear cells, with adult cells being more impaired than neonatal cells. MnSOD reduces bacterial adherence and inflammation and improves bacterial phagocytosis in mononuclear cells in response to hyperoxia, which should minimize the development of oxidant-induced lung injury as well as reducing nosocomial infections.