Nrf2 increases survival and attenuates alveolar growth inhibition in neonatal mice exposed to hyperoxia

Myeloid Nrf2 Protects against Neonatal Oxidant-Stress-Induced Lung Inflammation and Alveolar Simplification in Mice

Bronchopulmonary dysplasia (BPD) is a chronic condition affecting preterm infants, characterized by lung alveolar simplification/hypoalveolarization and vascular remodeling. The nuclear factor erythroid 2 like 2 (Nfe2l2, or Nrf2) plays a critical role in the cytoprotective response to neonatal hyperoxia, and its global deficiency exacerbates hypoalveolarization in mice. The abnormal recruitment and activation of myeloid cells are associated with the pathogenesis of BPD. Therefore, we employed a genetic approach to investigate the role of myeloid Nrf2 in regulating hyperoxia-induced hypoalveolarization. Pups, both wild-type (Nrf2f/f) and those with a myeloid Nrf2 deletion (abbreviated as Nrf2∆/∆mye), were exposed to hyperoxia for 72 h at postnatal day 1 (Pnd1), and then sacrificed at either Pnd4 or Pnd18 following a two-week recovery period. We analyzed the hypoalveolarization, inflammation, and gene expression related to cytoprotective and inflammatory responses in the lungs of these pups. The hypoalveolarization induced by hyperoxia was significantly greater in Nrf2∆/∆mye pups compared to their Nrf2f/f counterparts (35.88% vs. 21.01%, respectively) and was accompanied by increased levels of inflammatory cells and IL-1β activation in the lungs. Antioxidant gene expression in response to neonatal hyperoxia was lower in Nrf2∆/∆mye pups compared to their Nrf2f/f counterparts. Furthermore, Nrf2-deficient macrophages exposed to hyperoxia exhibited markedly decreased cytoprotective gene expression and increased IL-1β levels compared to Nrf2-sufficient cells. Our findings demonstrate the crucial role of myeloid Nrf2 in mitigating hyperoxia-induced lung hypoalveolarization and inflammatory responses in neonatal mice.

The pleiotropic functions of reactive oxygen species in cancer

Cellular redox homeostasis is an essential, dynamic process that ensures the balance between reducing and oxidizing reactions within cells and thus has implications across all areas of biology. Changes in levels of reactive oxygen species can disrupt redox homeostasis, leading to oxidative or reductive stress that contributes to the pathogenesis of many malignancies, including cancer. From transformation and tumor initiation to metastatic dissemination, increasing reactive oxygen species in cancer cells can paradoxically promote or suppress the tumorigenic process, depending on the extent of redox stress, its spatiotemporal characteristics and the tumor microenvironment. Here we review how redox regulation influences tumorigenesis, highlighting therapeutic opportunities enabled by redox-related alterations in cancer cells.

Unlocking the protective potential of the angiotensin type 2 receptor (AT2R) in acute lung injury and age-related pulmonary dysfunction

Despite its known importance in the cardiovascular system, the specific role and impact of the angiotensin type 2 receptor (AT2R) in lung physiology and pathophysiology remain largely elusive. In this study, we highlight the distinct and specialized lung-specific roles of AT2R, primarily localized to an alveolar fibroblast subpopulation, in contrast to the angiotensin type 1 receptor (AT1R), which is almost exclusively expressed in lung pericytes. Evidence from our research demonstrates that the disruption of AT2R (AT2R-/y), is associated with a surge in oxidative stress and impaired lung permeability, which were further intensified by Hyperoxic Acute Lung Injury (HALI). With aging, AT2R-/y mice show an increase in oxidative stress, premature enlargement of airspaces, as well as increased mortality when exposed to hyperoxia as compared to age-matched WT mice. Our investigation into Losartan, an AT1R blocker, suggests that its primary HALI lung-protective effects are channeled through AT2R, as its protective benefits are absent in AT2R-/y mice. Importantly, a non-peptide AT2R agonist, Compound 21 (C21), successfully reverses lung oxidative stress and TGFβ activation in wild-type (WT) mice exposed to HALI. These findings suggest a possible paradigm shift in the therapeutic approach for lung injury and age-associated pulmonary dysfunction, from targeting AT1R with angiotensin receptor blockers (ARBs) towards boosting the protective function of AT2R.

Oxygen and mechanical stretch in the developing lung: risk factors for neonatal and pediatric lung disease

Chronic airway diseases, such as wheezing and asthma, remain significant sources of morbidity and mortality in the pediatric population. This is especially true for preterm infants who are impacted both by immature pulmonary development as well as disproportionate exposure to perinatal insults that may increase the risk of developing airway disease. Chronic pediatric airway disease is characterized by alterations in airway structure (remodeling) and function (increased airway hyperresponsiveness), similar to adult asthma. One of the most common perinatal risk factors for development of airway disease is respiratory support in the form of supplemental oxygen, mechanical ventilation, and/or CPAP. While clinical practice currently seeks to minimize oxygen exposure to decrease the risk of bronchopulmonary dysplasia (BPD), there is mounting evidence that lower levels of oxygen may carry risk for development of chronic airway, rather than alveolar disease. In addition, stretch exposure due to mechanical ventilation or CPAP may also play a role in development of chronic airway disease. Here, we summarize the current knowledge of the impact of perinatal oxygen and mechanical respiratory support on the development of chronic pediatric lung disease, with particular focus on pediatric airway disease. We further highlight mechanisms that could be explored as potential targets for novel therapies in the pediatric population.

Sex-Specific Alterations of the Lung Transcriptome at Birth in Mouse Offspring Prenatally Exposed to Vanilla-Flavored E-Cigarette Aerosols and Enhanced Susceptibility to Asthma

Currently, approximately 8 million adult Americans use electronic cigarettes (e-cigs) daily, including women of childbearing age. It is known that more than 10% of women smoke during their pregnancy, and recent surveys show that rates of maternal vaping are similar to rates of maternal cigarette smoking. However, the effects of inhaling e-cig aerosol on the health of fetuses remain unknown. The objective of the present study was to increase our understanding of the molecular effects caused by in utero exposures to e-cig aerosols on developing mouse lungs and, later in life, on the offspring's susceptibility to developing asthma.

METHODS

Pregnant mice were exposed throughout gestation to either filtered air or vanilla-flavored e-cig aerosols containing 18 mg/mL of nicotine. Male and female exposed mouse offspring were sacrificed at birth, and then the lung transcriptome was evaluated. Additionally, once sub-groups of male offspring mice reached 4 weeks of age, they were challenged with house dust mites (HDMs) for 3 weeks to assess asthmatic responses.

RESULTS

The lung transcriptomic responses of the mouse offspring at birth showed that in utero vanilla-flavored e-cig aerosol exposure significantly regulated 88 genes in males (62 genes were up-regulated and 26 genes were down-regulated), and 65 genes were significantly regulated in females (17 genes were up-regulated and 48 genes were down-regulated). Gene network analyses revealed that in utero e-cig aerosol exposure affected canonical pathways associated with CD28 signaling in T helper cells, the role of NFAT in the regulation of immune responses, and phospholipase C signaling in males, whereas the dysregulated genes in the female offspring were associated with NRF2-mediated oxidative stress responses. Moreover, we found that in utero exposures to vanilla-flavored e-cig aerosol exacerbated HDM-induced asthma in 7-week-old male mouse offspring compared to respective in utero air + HDM controls.

CONCLUSIONS

Overall, these data demonstrate that in utero e-cig aerosol exposure alters the developing mouse lung transcriptome at birth in a sex-specific manner and provide evidence that the inhalation of e-cig aerosols is detrimental to the respiratory health of offspring by increasing the offspring' susceptibility to developing lung diseases later in life.

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.

Murine Neonatal Oxidant Lung Injury: NRF2-Dependent Predisposition to Adulthood Respiratory Viral Infection and Protection by Maternal Antioxidant

NRF2 protects against oxidant-associated airway disorders via cytoprotective gene induction. To examine if NRF2 is an important determinant of respiratory syncytial virus (RSV) susceptibility after neonate lung injury, Nrf2-deficient (Nrf2^−/−) and wild-type (Nrf2^+/+) mice neonatally exposed to hyperoxia were infected with RSV. To investigate the prenatal antioxidant effect on neonatal oxidative lung injury, time-pregnant Nrf2^−/− and Nrf2^+/+ mice were given an oral NRF2 agonist (sulforaphane) on embryonic days 11.5–17.5, and offspring were exposed to hyperoxia. Bronchoalveolar lavage and histopathologic analyses determined lung injury. cDNA microarray analyses were performed on placenta and neonatal lungs. RSV-induced pulmonary inflammation, injury, oxidation, and virus load were heightened in hyperoxia-exposed mice, and injury was more severe in hyperoxia-susceptible Nrf2^−/− mice than in Nrf2^+/+ mice. Maternal sulforaphane significantly alleviated hyperoxic lung injury in both neonate genotypes with more marked attenuation of severe neutrophilia, edema, oxidation, and alveolarization arrest in Nrf2^−/− mice. Prenatal sulforaphane altered different genes with similar defensive functions (e.g., inhibition of cell/perinatal death and inflammation, potentiation of angiogenesis/organ development) in both strains, indicating compensatory transcriptome changes in Nrf2^−/− mice. Conclusively, oxidative injury in underdeveloped lungs NRF2-dependently predisposed RSV susceptibility. In utero sulforaphane intervention suggested NRF2-dependent and -independent pulmonary protection mechanisms against early-life oxidant injury.

Oxygen-mediated lung injury in mice lacking the gene for NRF2: Rescue with the cytochrome P4501A-inducer, beta-naphthoflavone (BNF), and differential sex-specific effects

BACKGROUND

Acute respiratory distress syndrome (ARDS) leads to progressive lung injury, which significantly impacts patient morbidity and mortality but may differ clinically between the sexes. Cytochrome P450 (CYP) 1A enzymes are protective against hyperoxic lung injury and may contribute to sex-dependent pathology. NRF2 is a critical transcriptional regulator of antioxidants and loss of NRF2 leads to severe hyperoxic lung injury and mortality in mice. NRF2 deficiencies and polymorphisms have been observed in patients with pulmonary diseases such as chronic obstructive pulmonary disease and severe asthma. No prior studies have evaluated whether there are sex-specific differences in oxygen-mediated lung injury in Nrf2^-/- mice and there are few rescue studies.

OBJECTIVE

To test the hypothesis that hyperoxia induces greater lung injury and inflammation in Nrf2^-/- mice compared to wild type (WT) that differs between sexes, and that this phenotype will be rescued by the administration of the cytochrome P450 (CYP) 1A inducer beta-naphthoflavone (BNF).

DESIGN/METHODS

Male and female 8-10-week-old WT or Nrf2^-/- C57BL/6 mice were pre-treated with BNF (40 mg/kg) or corn oil control and exposed to hyperoxia (95% O₂) for 68 h. Survival, pulmonary edema, neutrophil recruitment, and lung injury scores were evaluated. Gene expression of phase II detoxification enzymes, pulmonary cytokines, and Cyp1a1/2 was quantified. CYP1A1/2 protein expression and catalytic activities were also measured.

RESULTS

Hyperoxia exposure greatly reduced survival in Nrf2^-/- mice, particularly in females. BNF treatment improved survival by 182.8% in Nrf2^-/- females and by 41.4% in Nrf2^-/- males as well as in WT females by 85.7%. Females had greater pulmonary edema as measured by lung weight to body weight ratios but was attenuated in all groups except Nrf2^-/- females by BNF. Neutrophils doubled in Nrf2^-/- lungs compared to WT in hyperoxia but were decreased in BNF-treated females of both genotypes. Pulmonary cytokine gene expression including Il-6 and Tnf-α increased in hyperoxia especially in Nrf2^-/- mice and was unaffected by BNF. Pulmonary and hepatic Nqo1 gene expression w-as decreased in Nrf2^-/- mice and was largely unaffected by BNF; however pulmonary Ho-1 did not vary significantly between the genotypes and was decreased in WT animals treated with BNF. Activities and protein expression of pulmonary and hepatic CYP1A1/2 were induced via BNF across all groups. Although hepatic Cyp1a2 gene expression was higher in Nrf2^-/- males, the catalytic activity was higher in Nrf2^-/- females.

CONCLUSIONS

Hyperoxia augmented lung injury in Nrf2^-/- mice, and pre-treatment with BNF was protective against mortality and injury, eliminating the sex-dependent survival difference in both genotypes. Our results support the hypothesis that NRF2 protects mice against lung injury, and the fact that BNF rescues the lung injury phenotype in Nrf2^-/- mice suggests that augmented CYP1A expression by BNF may contribute to the beneficial effects. Further studies could lead to the development of BNF and other flavonoids for the prevention/treatment of hyperoxic lung injury, particularly in vulnerable patients with relative NRF2 deficiency, regardless of sex.

Preconditioning the immature lung with enhanced Nrf2 activity protects against oxidant-induced hypoalveolarization in mice

Bronchopulmonary dysplasia (BPD) is a chronic disease of preterm babies with poor clinical outcomes. Nrf2 transcription factor is crucial for cytoprotective response, whereas Keap1—an endogenous inhibitor of Nrf2 signaling—dampens these protective responses. Nrf2-sufficient (wild type) newborn mice exposed to hyperoxia develop hypoalveolarization, which phenocopies human BPD, and Nrf2 deficiency worsens it. In this study, we used PND1 pups bearing bearing hypomorphic Keap1 floxed alleles (Keap1^f/f) with increased levels of Nrf2 to test the hypothesis that constitutive levels of Nrf2 in the premature lung are insufficient to mitigate hyperoxia-induced hypoalveolarization. Both wildtype and Keap1^f/f pups at PND1 were exposed to hyperoxia for 72 h and then allowed to recover at room air for two weeks (at PND18), sacrificed, and lung hypoalveolarization and inflammation assessed. Hyperoxia-induced lung hypoalveolarization was remarkably lower in Keap1^f/f pups than in wildtype counterparts (28.9% vs 2.4%, wildtype vs Keap1^f/f). Likewise, Keap1^f/f pups were protected against prolonged (96 h) hyperoxia-induced hypoalveolarization. However, there were no differences in hyperoxia-induced lung inflammatory response immediately after exposure or at PND18. Lack of hypoalveolarization in Keap1^f/f pups was accompanied by increased levels of expression of antioxidant genes and GSH as assessed immediately following hyperoxia. Keap1 knockdown resulted in upregulation of lung cell proliferation postnatally but had opposing effects following hyperoxia. Collectively, our study demonstrates that augmenting endogenous Nrf2 activation by targeting Keap1 may provide a physiological way to prevent hypoalveolarization associated with prematurity.

Targeting the phosphoinositide-3-kinase/protein kinase B pathway in airway innate immunity

The airway innate immune system maintains the first line of defense against respiratory infections. The airway epithelium and associated immune cells protect the respiratory system from inhaled foreign organisms. These cells sense pathogens via activation of receptors like toll-like receptors and taste family 2 receptors (T2Rs) and respond by producing antimicrobials, inflammatory cytokines, and chemokines. Coordinated regulation of fluid secretion and ciliary beating facilitates clearance of pathogens via mucociliary transport. Airway cells also secrete antimicrobial peptides and radicals to directly kill microorganisms and inactivate viruses. The phosphoinositide-3-kinase/protein kinase B (Akt) kinase pathway regulates multiple cellular targets that modulate cell survival and proliferation. Akt also regulates proteins involved in innate immune pathways. Akt phosphorylates endothelial nitric oxide synthase (eNOS) enzymes expressed in airway epithelial cells. Activation of eNOS can have anti-inflammatory, anti-bacterial, and anti-viral roles. Moreover, Akt can increase the activity of the transcription factor nuclear factor erythroid 2 related factor-2 that protects cells from oxidative stress and may limit inflammation. In this review, we summarize the recent findings of non-cancerous functions of Akt signaling in airway innate host defense mechanisms, including an overview of several known downstream targets of Akt involved in innate immunity.

From germ cells to neonates: the beginning of life and the KEAP1-NRF2 system

The Kelch-like ECH-associated protein 1(KEAP1)-NF-E2-related factor 2 (NRF2) system is one of the most studied environmental stress response systems. In the presence of oxidative and electrophilic insults, the thiols of cysteine residues in KEAP1 are modified, and subsequently stabilized NRF2 activates its target genes that are involved in detoxification and cytoprotection. A myriad of recent studies has revealed the broad range of contributions of the KEAP1-NRF2 system to physiological and pathological processes. However, its functions during gametic and embryonic development are still open for investigation. Although oxidative stress is harmful for embryos, Nrf2-/- mice do not show any apparent morphological abnormalities during development, probably because of the compensatory antioxidant functions of NF-E2-related factor 1 (NRF1). It can also be considered that the antioxidant system is essential for protecting germ cells during reproduction. The maturation processes of germ cells in both sexes are affected by Nrf2 mutation. Hence, in this review, we focus on the stress response system related to reproduction and embryonic development through the functions of the KEAP1-NRF2 system.

The effects of gasotransmitters on bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD), which remains a major clinical problem for preterm infants, is caused mainly by hyperoxia, mechanical ventilation and inflammation. Many approaches have been developed with the aim of decreasing the incidence of or alleviating BPD, but effective methods are still lacking. Gasotransmitters, a type of small gas molecule that can be generated endogenously, exert a protective effect against BPD-associated lung injury; nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S) are three such gasotransmitters. The protective effects of NO have been extensively studied in animal models of BPD, but the results of these studies are inconsistent with those of clinical trials. NO inhalation seems to have no effect on BPD, although side effects have been reported. NO inhalation is not recommended for BPD treatment in preterm infants, except those with severe pulmonary hypertension. Both CO and H₂S decreased lung injury in BPD rodent models in preclinical studies. Another small gas molecule, hydrogen, exerts a protective effect against BPD. The nuclear factor erythroid-derived 2 (Nrf2)/heme oxygenase-1 (HO-1) axis seems to play a central role in the protective effect of these gasotransmitters on BPD. Gasotransmitters play important roles in mammals, but further clinical trials are needed to explore their effects on BPD.

PI3K/Akt-Nrf2 and Anti-Inflammation Effect of Macrolides in Chronic Obstructive Pulmonary Disease

BACKGROUND

Chronic Obstructive Pulmonary Disease (COPD) is a systematic inflammatory disease, and smoking is an important risk factor for COPD. Macrolide can reduce COPD inflammation. However, the inflammatory mechanism of COPD remains unclear and the anti-inflammatory mechanism of Macrolide is complex and not exactly known.

METHODS

We read and analysed thirty-eight articles, including original articles and reviews.

RESULTS

The expression of Nrf2 was lower in COPD patients and might have a protective role against apoptosis caused by CSE-induced oxidative stress. Nrf2 may play an important role in COPD inflammation. Nrf2 is a key factor in downstream of PI3K/Akt and is involved in the regulation of oxidative stress and inflammatory response. Therefore, PI3K/Akt pathway may play an important role in the activation of Nrf2 and COPD inflammation. Macrolide reduces lung and systemic inflammation of COPD by regulating PI3K/Akt pathway.

CONCLUSION

This review indicates that PI3K/Ak-Nrf2 may play an important role in COPD inflammation and macrolides may reduce lung and systemic inflammation of COPD by regulating PI3K/Akt-Nrf2 pathway. However, many crucial and essential questions remain to be answered. Further understanding of the mechanisms of macrolide efficacy and PI3K/Akt-Nrf2-mediated inflammatory responses may provide a new clue for exploring COPD treatment in the future.

The expression of miR-125b in Nrf2-silenced A549 cells exposed to hyperoxia and its relationship with apoptosis

Bronchopulmonary dysplasia (BPD) is a chronic lung disease that affects the quality of life of infants. At present, premature exposure to hyperoxia for extended periods of time is believed to affect the development of lung tissue and vascularity, resulting in BPD. The oxidative stress caused by hyperoxia exposure is an important risk factor for BPD in premature infants. Nuclear factor E2‐related factor 2 (Nrf2) is an important regulator of antioxidant mechanisms. As a microRNA, microRNA‐125b (miR‐125b) plays an important role in cell proliferation, differentiation and apoptosis. Although the Nrf2/ARE pathway has been extensively studied, little is known about the regulatory role of microRNAs in Nrf2 expression. In this study, the expression levels of Nrf2 and miR‐125b in the lung tissues of premature Sprague Dawley (SD) rats and A549 cells exposed to hyperoxia were detected by quantitative real‐time polymerase chain reaction (qRT‐PCR), and the apoptosis of A549 cells was detected by flow cytometry. The results showed that Nrf2 and miRNA‐125b in the lung tissues of premature rats increased significantly upon exposure to hyperoxia and played a protective role. Nrf2 was suppressed by small interfering RNA (siRNA) in A549 cells, miR‐125b was similarly inhibited, and apoptosis was significantly increased. These results suggest that miR‐125b helps protect against BPD as a downstream target of Nrf2.

Thiol-Redox Regulation in Lung Development and Vascular Remodeling

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

Antioxidants & bronchopulmonary dysplasia: Beating the system or beating a dead horse?

Preterm birth is a primary cause of worldwide childhood mortality. Bronchopulmonary dysplasia, characterized by impaired alveolar and lung vascular development, affects 25-50% of extremely low birth weight (BW; <1 kg) infants. Abnormalities in lung function persist into childhood in affected infants and are second only to asthma in terms of childhood respiratory disease healthcare costs. While advances in the medical care of preterm infants have reduced mortality, the incidence of BPD has not decreased in the past 10 years. Reactive oxygen intermediates play a key role in the development of lung disease but, despite promising preclinical therapies, antioxidants have failed to translate into meaningful clinical interventions to decrease the incidence of lung disease in premature infants. In this review we will summarize the state of the art research developments in regards to antioxidants and premature lung disease and discuss the limitations of antioxidant therapies in order to more fully comprehend the reasons why therapeutic antioxidant administration failed to prevent BPD. Finally we will review promising therapeutic strategies and targets.

Inflammaging and Oxidative Stress in Human Diseases: From Molecular Mechanisms to Novel Treatments

It has been proposed that a chronic state of inflammation correlated with aging known as inflammaging, is implicated in multiple disease states commonly observed in the elderly population. Inflammaging is associated with over-abundance of reactive oxygen species in the cell, which can lead to oxidation and damage of cellular components, increased inflammation, and activation of cell death pathways. This review focuses on inflammaging and its contribution to various age-related diseases such as cardiovascular disease, cancer, neurodegenerative diseases, chronic obstructive pulmonary disease, diabetes, and rheumatoid arthritis. Recently published mechanistic details of the roles of reactive oxygen species in inflammaging and various diseases will also be discussed. Advancements in potential treatments to ameliorate inflammaging, oxidative stress, and consequently, reduce the morbidity of multiple disease states will be explored.

Role of Nrf2 and Its Activators in Respiratory Diseases

Transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) is a major regulator of antioxidant response element- (ARE-) driven cytoprotective protein expression. The activation of Nrf2 signaling plays an essential role in preventing cells and tissues from injury induced by oxidative stress. Under the unstressed conditions, natural inhibitor of Nrf2, Kelch-like ECH-associated protein 1 (Keap1), traps Nrf2 in the cytoplasm and promotes the degradation of Nrf2 by the 26S proteasome. Nevertheless, stresses including highly oxidative microenvironments, impair the ability of Keap1 to target Nrf2 for ubiquitination and degradation, and induce newly synthesized Nrf2 to translocate to the nucleus to bind with ARE. Due to constant exposure to external environments, including diverse pollutants and other oxidants, the redox balance maintained by Nrf2 is fairly important to the airways. To date, researchers have discovered that Nrf2 deletion results in high susceptibility and severity of insults in various models of respiratory diseases, including bronchopulmonary dysplasia (BPD), respiratory infections, acute respiratory distress syndrome (ARDS), chronic obstructive pulmonary disease (COPD), asthma, idiopathic pulmonary fibrosis (IPF), and lung cancer. Conversely, Nrf2 activation confers protective effects on these lung disorders. In the present review, we summarize Nrf2 involvement in the pathogenesis of the above respiratory diseases that have been identified by experimental models and human studies and describe the protective effects of Nrf2 inducers on these diseases.

CD44v9 is associated with epithelial-mesenchymal transition and poor outcomes in esophageal squamous cell carcinoma

CD44 serves as a marker of cancer stem cells. Alternative splicing generates the CD44v9 isoform. Cancer stem cells are associated with the epithelial-mesenchymal transition in cancers, although little is known about their role in esophageal squamous cell carcinoma. Here, we aimed to clarify the relationship between CD44v9 expression, the epithelial-mesenchymal transition, and clinicopathological features of patients with esophageal squamous cell carcinoma. CD44v9 levels were higher at the tumor invasive front compared with the center of the tumor and higher in metastatic lymph nodes compared with primary tumors. High levels of CD44v9 at the tumor invasive front were significantly associated with deeper tumor invasion and shorter overall survival and recurrence-free survival. The expression of CD44v9 was increased by treatment with transforming growth factor-β, which induced esophageal squamous cell carcinoma cells to undergo the epithelial-mesenchymal transition. Moreover, inhibition of CD44v9 expression decreased the migration and invasiveness of esophageal squamous cell carcinoma cells. These results indicate that the expression of CD44v9 at the tumor invasive front induced by stemness was strongly associated with the epithelial-mesenchymal transition and poor prognosis of patients with esophageal squamous cell carcinoma. CD44v9 may therefore serve as a novel prognostic biomarker and a potential therapeutic target for esophageal squamous cell carcinoma.

Selenium supplementation of lung epithelial cells enhances nuclear factor E2-related factor 2 (Nrf2) activation following thioredoxin reductase inhibition

The trace element selenium (Se) contributes to redox signaling, antioxidant defense, and immune responses in critically ill neonatal and adult patients. Se is required for the synthesis and function of selenoenzymes including thioredoxin (Trx) reductase-1 (TXNRD1) and glutathione peroxidases (GPx). We have previously identified TXNRD1, primarily expressed by airway epithelia, as a promising therapeutic target to prevent lung injury, likely via nuclear factor E2-related factor 2 (Nrf2)-dependent mechanisms. The present studies utilized the TXNRD1 inhibitor auranofin (AFN) to test the hypothesis that Se positively influences Nrf2 activation and selenoenzyme responses in lung epithelial cells. Murine transformed Club cells (mtCCs) were supplemented with 0, 10, 25, or 100 nM Na2SeO3 to create a range of Se conditions and were cultured in the presence or absence of 0.5 μM AFN. TXNRD1 and GPX2 protein expression and enzymatic activity were significantly greater upon Se supplementation (p < 0.05). AFN treatment (0.5 μM AFN for 1 h) significantly inhibited TXNRD1 but not GPx activity (p < 0.001). Recovery of TXNRD1 activity following AFN treatment was significantly enhanced by Se supplementation (p < 0.041). Finally, AFN-induced Nrf2 transcriptional activation was significantly greater in mtCCs supplemented in 25 or 100 nM Na2SeO3 when compared to non-supplemented controls (p < 0.05). Our novel studies indicate that Se levels positively influence Nrf2 activation and selenoenzyme responses following TXNRD1 inhibition. These data suggest that Se status significantly influences physiologic responses to TXNRD1 inhibitors. In conclusion, correction of clinical Se deficiency, if present, will be necessary for optimal therapeutic effectiveness of TXNRD1 inhibitors in the prevention of lung disease.

Effects of Hyperoxia on the Developing Airway and Pulmonary Vasculature

Although it is necessary and part of standard practice, supplemental oxygen (40-90% O₂) or hyperoxia is a significant contributing factor to development of bronchopulmonary dysplasia, persistent pulmonary hypertension, recurrent wheezing, and asthma in preterm infants. This chapter discusses hyperoxia and the role of redox signaling in the context of neonatal lung growth and disease. Here, we discuss how hyperoxia promotes dysfunction in the airway and the known redox-mediated mechanisms that are important for postnatal vascular and alveolar development. Whether in the airway or alveoli, redox pathways are important and greatly influence the neonatal lung.

Aurothioglucose does not improve alveolarization or elicit sustained Nrf2 activation in C57BL/6 models of bronchopulmonary dysplasia

We previously showed that the thioredoxin reductase-1 (TrxR1) inhibitor aurothioglucose (ATG) improves alveolarization in hyperoxia-exposed newborn C3H/HeN mice. Our data supported a mechanism by which the protective effects of ATG are mediated via sustained nuclear factor E2-related factor 2 (Nrf2) activation in hyperoxia-exposed C3H/HeN mice 72 h after ATG administration. Given that inbred mouse strains have differential sensitivity and endogenous Nrf2 activation by hyperoxia, the present studies utilized two C57BL/6 exposure models to evaluate the effects of ATG on lung development and Nrf2 activation. The first model (0-14 days) was used in our C3H/HeN studies and the 2nd model (4-14 days) is well characterized in C57BL/6 mice. ATG significantly inhibited lung TrxR1 activity in both models; however, there was no effect on parameters of alveolarization in C57BL/6 mice. In sharp contrast to C3H/HeN mice, there was no effect of ATG on pulmonary NADPH quinone oxidoreductase-1 ( Nqo1) and heme oxygenase-1 ( Hmox1) at 72 h in either C57BL/6 model. In conclusion, although ATG inhibited TrxR1 activity in the lungs of newborn C57BL/6 mice, effects on lung development and sustained Nrf2-dependent pulmonary responses were blunted. These findings also highlight the importance of strain-dependent hyperoxic sensitivity in evaluation of potential novel therapies.

Regulation of redox balance in cancer and T cells

Reactive oxygen species (ROS) mediate redox signaling necessary for numerous cellular functions. Yet, high levels of ROS in cells and tissues can cause damage and cell death. Therefore, regulation of redox homeostasis is essential for ROS-dependent signaling that does not incur cellular damage. Cells achieve this optimal balance by coordinating ROS production and elimination. In this Minireview, we discuss the mechanisms by which proliferating cancer and T cells maintain a carefully controlled redox balance. Greater insight into such redox biology may enable precisely targeted manipulation of ROS for effective medical therapies against cancer or immunological disorders.

Multifaceted Roles of Glutathione and Glutathione-Based Systems in Carcinogenesis and Anticancer Drug Resistance

SIGNIFICANCE

Glutathione is the most abundant antioxidant molecule in living organisms and has multiple functions. Intracellular glutathione homeostasis, through its synthesis, consumption, and degradation, is an intricately balanced process. Glutathione levels are often high in tumor cells before treatment, and there is a strong correlation between elevated levels of intracellular glutathione/sustained glutathione-mediated redox activity and resistance to pro-oxidant anticancer therapy. Recent Advances: Ample evidence demonstrates that glutathione and glutathione-based systems are particularly relevant in cancer initiation, progression, and the development of anticancer drug resistance.

CRITICAL ISSUES

This review highlights the multifaceted roles of glutathione and glutathione-based systems in carcinogenesis, anticancer drug resistance, and clinical applications.

FUTURE DIRECTIONS

The evidence summarized here underscores the important role played by glutathione and the glutathione-based systems in carcinogenesis and anticancer drug resistance. Future studies should address mechanistic questions regarding the distinct roles of glutathione in different stages of cancer development and cancer cell death. It will be important to study how metabolic alterations in cancer cells can influence glutathione homeostasis. Sensitive approaches to monitor glutathione dynamics in subcellular compartments will be an indispensible step. Therapeutic perspectives should focus on mechanism-based rational drug combinations that are directed against multiple redox targets using effective, specific, and clinically safe inhibitors. This new strategy is expected to produce a synergistic effect, prevent drug resistance, and diminish doses of single drugs. Antioxid. Redox Signal. 27, 1217-1234.

Balancing anti-inflammatory and anti-oxidant responses in murine bone marrow derived macrophages

Rationale

The underlying pathophysiology of bronchopulmonary dysplasia includes a macrophage-mediated host response orchestrated by anti-inflammatory peroxisome proliferator-activated receptor gamma (PPARγ) and anti-oxidant nuclear factor (erythroid-derived 2)-like 2 (Nrf2). These have not yet been studied in combination. This study tested the hypothesis that combined inflammatory and oxidative stressors would interact and change PPARγ- and Nrf2-regulated gene expression and antioxidant capacity. Therefore, we investigated the effect of dual stimulation with lipopolysaccharide and hyperoxia in murine bone marrow-derived macrophages (BMDM).

Methods

Sub-confluent BMDM from wild-type C57BL/6J mice were treated with lipopolysaccharide (LPS) 1ug/mL for 2 hours followed by room air (21% oxygen) or hyperoxia (95% oxygen) for 24 hours. Taqman real time-polymerase chain reaction gene expression assays, total antioxidant capacity assays, and Luminex assays were performed.

Results

Supernatants of cultured BMDM contained significant antioxidant capacity. In room air, LPS treatment decreased expression of PPARγ and Nrf2, and increased expression of tumor necrosis factor-alpha and heme oxygenase-1; similar findings were observed under hyperoxic conditions. LPS treatment decreased cellular total antioxidant capacity in room air but not in hyperoxia. Increased expression of sulfiredoxin-1 in response to hyperoxia was not observed in LPS-treated cells. Dual stimulation with LPS treatment and exposure to hyperoxia did not have synergistic effects on gene expression. Cellular total antioxidant capacity was not changed by hyperoxia exposure.

Conclusions

Our hypothesis was supported and we demonstrate an interaction between inflammatory and oxidative stressors in a model system of bronchopulmonary dysplasia pathogenesis. The protective anti-oxidant effect of cell culture media may have protected the cells from the most deleterious effects of hyperoxia.

A c-Jun N-terminal kinase inhibitor, JNK-IN-8, sensitizes triple negative breast cancer cells to lapatinib

Triple negative breast cancers (TNBC) have poor prognosis compared to other breast cancer subtypes and represent 15-20% of breast cancers diagnosed. Unique targets and new molecularly-targeted therapies are urgently needed for this subtype. Despite high expression of Epidermal Growth Factor Receptor, inhibitors such as lapatinib have not shown therapeutic efficacy in TNBC patients. Herein, we report that treatment with the covalent JNK inhibitor, JNK-IN-8, synergizes with lapatinib to cause cell death, while these compounds as single agents have little effect. The combination significantly increases survival of mice bearing xenografts of MDA-MB-231 human TNBC cells. Our studies demonstrate that lapatinib treatment increases c-Jun and JNK phosphorylation indicating a mechanism of resistance. Combined, these compounds significantly reduce transcriptional activity of Nuclear Factor kappa B, Activating Protein 1, and Nuclear factor erythroid 2-Related Factor 2. As master regulators of antioxidant response, their decreased activity induces a 10-fold increase in reactive oxygen species that is cytotoxic, and is rescued by addition of exogenous antioxidants. Over expression of p65 or Nrf2 also significantly rescues viability during JNK-IN-8 and lapatinib treatment. Further studies combining JNK-IN-8 and lapatinib may reveal a benefit for patients with TNBC, fulfilling a critical medical need.

Thioredoxin Reductase Inhibition Attenuates Neonatal Hyperoxic Lung Injury and Enhances Nuclear Factor E2-Related Factor 2 Activation

Oxygen toxicity and antioxidant deficiencies contribute to the development of bronchopulmonary dysplasia. Aurothioglucose (ATG) and auranofin potently inhibit thioredoxin reductase-1 (TrxR1), and TrxR1 disruption activates nuclear factor E2-related factor 2 (Nrf2), a regulator of endogenous antioxidant responses. We have shown previously that ATG safely and effectively prevents lung injury in adult murine models, likely via Nrf2-dependent mechanisms. The current studies tested the hypothesis that ATG would attenuate hyperoxia-induced lung developmental deficits in newborn mice. Newborn C3H/HeN mice were treated with a single dose of ATG or saline within 12 hours of birth and were exposed to either room air or hyperoxia (85% O2). In hyperoxia, ATG potently inhibited TrxR1 activity in newborn murine lungs, attenuated decreases in body weight, increased the transcription of Nrf2-regulated genes nicotinamide adenine dinucleotide phosphate reduced quinone oxidoreductase-1 (NQO1) and heme oxygenase 1, and attenuated alterations in alveolar development. To determine the impact of TrxR1 inhibition on Nrf2 activation in vitro, murine alveolar epithelial-12 cells were treated with auranofin, which inhibited TrxR1 activity, enhanced Nrf2 nuclear levels, and increased NQO1 and heme oxygenase 1 transcription. Our novel data indicate that a single injection of the TrxR1 inhibitor ATG attenuates hyperoxia-induced alterations in alveolar development in newborn mice. Furthermore, our data support a model in which the effects of ATG treatment likely involve Nrf2 activation, which is consistent with our findings in other lung injury models. We conclude that TrxR1 represents a novel therapeutic target to prevent oxygen-mediated neonatal lung injury.

Postnatal Hyperoxia Exposure Durably Impairs Right Ventricular Function and Mitochondrial Biogenesis

Prematurity complicates 12% of births, and young adults with a history of prematurity are at risk to develop right ventricular (RV) hypertrophy and impairment. The long-term risk for pulmonary vascular disease, as well as mechanisms of RV dysfunction and ventricular-vascular uncoupling after prematurity, remain poorly defined. Using an established model of prematurity-related lung disease, pups from timed-pregnant Sprague Dawley rats were randomized to normoxia or hyperoxia (fraction of inspired oxygen, 0.85) exposure for the first 14 days of life. After aging to 1 year in standard conditions, rats underwent hemodynamic assessment followed by tissue harvest for biochemical and histological evaluation. Aged hyperoxia-exposed rats developed significantly greater RV hypertrophy, associated with a 40% increase in RV systolic pressures. Although cardiac index was similar, hyperoxia-exposed rats demonstrated a reduced RV ejection fraction and significant RV-pulmonary vascular uncoupling. Hyperoxia-exposed RV cardiomyocytes demonstrated evidence of mitochondrial dysregulation and mitochondrial DNA damage, suggesting potential mitochondrial dysfunction as a cause of RV dysfunction. Aged rats exposed to postnatal hyperoxia recapitulate many features of young adults born prematurely, including increased RV hypertrophy and decreased RV ejection fraction. Our data suggest that postnatal hyperoxia exposure results in mitochondrial dysregulation that persists into adulthood with eventual RV dysfunction. Further evaluation of long-term mitochondrial function is warranted in both animal models of premature lung disease and in human adults who were born preterm.

Potential therapeutic targets in Nrf2-dependent protection against neonatal respiratory distress disease predicted by cDNA microarray analysis and bioinformatics tools

Hyperoxia exposure of newborn rodents has served as a model for bronchopulmonary dysplasia (BPD) phenotypes found in a sub-population of human premature infants. We previously demonstrated that Nrf2 modulates molecular events during saccular-to-alveolar lung maturation and also has a protective role in the pathogenesis of hyperoxia-induced acute lung injury, mortality, arrest of saccular-to-alveolar transition, and lung injury, using Nrf2-deficient and wild-type neonate mice. In this review, we describe how whole-genome transcriptome analyses can identify the means through which Nrf2 transcriptionally modulates organ injury and morphology, cellular growth/proliferation, vasculature development, and immune response during BPD-like pathogenesis. We illustrate how recently developed bioinformatics tools can be used to identify sets of Nrf2-dependently modulated genes in the BPD model, and elucidate direct Nrf2 downstream targets and chemicals/drugs that may act on them. These approaches will provide significant insights into promising therapeutic agents for Nrf2-dependent treatments of complications of preterm birth like BPD.

Influence of SkQ1 on Expression of Nrf2 Gene, ARE-Controlled Genes of Antioxidant Enzymes and Their Activity in Rat Blood Leukocytes under Oxidative Stress

The study demonstrated that oxidative stress induced by hyperoxia (0.5 MPa for 90 min) resulted in reduction of mRNA levels of transcription factor Nrf2 and Nrf2-induced genes encoding antioxidant enzymes (SOD1, CAT, GPx4) in peripheral blood leukocytes of rats. The changes in gene expression profiles under hyperoxia were accompanied by disbalance of activity of antioxidant enzymes in the leukocytes, namely activation of superoxide dismutase and inhibition of catalase, glutathione peroxidase, and glutathione-S-transferase. Pretreatment of rats with SkQ1 (50 nmol/kg for five days) significantly increased mRNA levels of transcription factor Nrf2 and Nrf2-induced genes encoding antioxidant enzymes SOD2 and GPx4 and normalized the transcriptional activity of the SOD1 and CAT genes in the leukocytes in hyperoxia-induced oxidative stress. At the same time, the activity of catalase and glutathione peroxidase was increased, and the activity of superoxide dismutase and glutathione-S-transferase returned to the control level. It is hypothesized that protective effect of SkQ1 in hyperoxia-induced oxidative stress can be realized via a direct antioxidant property and the stimulation of the Keap1/Nrf2 redox-sensitive signaling system.

Restoration of Nrf2 Signaling Normalizes the Regenerative Niche

Chronic hyperglycemia impairs intracellular redox homeostasis and contributes to impaired diabetic tissue regeneration. The Keap1/Nrf2 pathway is a critical regulator of the endogenous antioxidant response system, and its dysfunction has been implicated in numerous pathologies. Here we characterize the effect of chronic hyperglycemia on Nrf2 signaling within a diabetic cutaneous regeneration model. We characterized the effects of chronic hyperglycemia on the Keap1/Nrf2 pathway within models of diabetic cutaneous wound regeneration. We assessed reactive oxygen species (ROS) production and antioxidant gene expression following alterations in the Nrf2 suppressor Keap1 and the subsequent changes in Nrf2 signaling. We also developed a topical small interfering RNA (siRNA)-based therapy to restore redox homeostasis within diabetic wounds. Western blotting demonstrated that chronic hyperglycemia-associated oxidative stress inhibits nuclear translocation of Nrf2 and impairs activation of antioxidant genes, thus contributing to ROS accumulation. Keap1 inhibition increased Nrf2 nuclear translocation, increased antioxidant gene expression, and reduced ROS production to normoglycemic levels, both in vitro and in vivo. Topical siKeap1 therapy resulted in improved regenerative capacity of diabetic wounds and accelerated closure. We report that chronic hyperglycemia weakens the endogenous antioxidant response, and the consequences of this defect are manifested by intracellular redox dysregulation, which can be restored by Keap1 inhibition. Targeted siRNA-based therapy represents a novel, efficacious strategy to reestablish redox homeostasis and accelerate diabetic cutaneous tissue regeneration.

Omeprazole does not Potentiate Acute Oxygen Toxicity in Fetal Human Pulmonary Microvascular Endothelial Cells Exposed to Hyperoxia

Hyperoxia contributes to the pathogenesis of broncho-pulmonary dysplasia (BPD), which is a developmental lung disease of premature infants that is characterized by an interruption of lung alveolar and pulmonary vascular development. Omeprazole (OM) is a proton pump inhibitor that is used to treat humans with gastric acid related disorders. Earlier we observed that OM-mediated aryl hydrocarbon receptor (AhR) activation attenuates acute hyperoxic lung injury in adult mice and oxygen toxicity in adult human lung cells. However, our later studies in newborn mice demonstrated that OM potentiates hyperoxia-induced developmental lung injury. Whether OM exerts a similar toxicity in primary human fetal lung cells is unknown. Hence, we tested the hypothesis that OM potentiates hyperoxia-induced cytotoxicity and ROS generation in the human fetal lung derived primary human pulmonary microvascular endothelial cells (HPMEC). OM activated AhR as evident by a dose-dependent increase in cytochrome P450 (CYP) 1A1 mRNA levels in OM-treated cells. Furthermore, OM at a concentration of 100 μM (OM 100) increased NADP(H) quinone oxidoreductase 1 (NQO1) expression. Surprisingly, hyperoxia decreased rather than increase the NQO1 protein levels in OM 100-treated cells. Exposure to hyperoxia increased cytotoxicity and hydrogen peroxide (H₂O₂) levels. Interestingly, OM 100-treated cells exposed to air had increased H₂O₂ levels. However, hyperoxia did not further augment H₂O₂ levels in OM 100-treated cells. Additionally, hyperoxia-mediated oxygen toxicity was similar in both vehicle- and OM-treated cells. These findings contradict our hypothesis and support the hypothesis that OM does not potentiate acute hyperoxic injury in HPMEC in vitro.

Alteration of serum lipid profile, SRB1 loss, and impaired Nrf2 activation in CDKL5 disorder

CDKL5 mutation is associated with an atypical Rett syndrome (RTT) variant. Recently, cholesterol homeostasis perturbation and oxidative-mediated loss of the high-density lipoprotein receptor SRB1 in typical RTT have been suggested. Here, we demonstrate an altered lipid serum profile also in CDKL5 patients with decreased levels of SRB1 and impaired activation of the defensive system Nrf2. In addition, CDKL5 fibroblasts showed an increase in 4-hydroxy-2-nonenal- and nitrotyrosine-SRB1 adducts that lead to its ubiquitination and probable degradation. This study highlights a possible common denominator between two different RTT variants (MECP2 and CDKL5) and a possible common future therapeutic target.

Gefitinib and Erlotinib Lead to Phosphorylation of Eukaryotic Initiation Factor 2 Alpha Independent of Epidermal Growth Factor Receptor in A549 Cells

Gefitinib and erlotinib are anticancer agents, which inhibit epidermal growth factor receptor (EGFR) tyrosine kinase. Interstitial lung disease (ILD) occurs in patients with non-small cell lung cancer receiving EGFR inhibitors. In the present study, we examined whether gefitinib- and erlotinib-induced lung injury related to ILD through endoplasmic reticulum (ER) stress, which is a causative intracellular mechanism in cytotoxicity caused by various chemicals in adenocarcinomic human alveolar basal epithelial cells. These two EGFR inhibitors increased Parkinson juvenile disease protein 2 and C/EBP homologous protein mRNA expressions, and activated the eukaryotic initiation factor (eIF) 2α/activating transcription factor 4 pathway without protein kinase R-like ER kinase activation in A549 cells. Gefitinib and erlotinib caused neither ER stress nor cell death; however, these agents inhibited cell growth via the reduction of cyclin-D1 expression. Tauroursodeoxycholic acid, which is known to suppress eIF2α phosphorylation, cancelled the effects of EGFR inhibitors on cyclin-D1 expression and cell proliferation in a concentration-dependent manner. The results of an EGFR-silencing study using siRNA showed that gefitinib and erlotinib affected eIF2α phosphorylation and cyclin-D1 expression independent of EGFR inhibition. Therefore, the inhibition of cell growth by these EGFR inhibitors might equate to impairment of the alveolar epithelial cell repair system via eIF2α phosphorylation and reduced cyclin-D1 expression.

Association of Nrf2 with airway pathogenesis: lessons learned from genetic mouse models

Nrf2 is a key transcription factor for antioxidant response element (ARE)-bearing genes involved in diverse host defense functions including redox balance, cell cycle, immunity, mitochondrial biogenesis, energy metabolism, and carcinogenesis. Nrf2 in the airways is particularly essential as the respiratory system continuously interfaces with environmental stress. Since Nrf2 was determined to be a susceptibility gene for a model of acute lung injury, its protective capacity in the airways has been demonstrated in experimental models of human disorders using Nrf2 mutant mice which were susceptible to supplemental respiratory therapy (e.g., hyperoxia, mechanical ventilation), cigarette smoke, allergens, virus, environmental pollutants, and fibrotic agents compared to wild-type littermates. Recent studies also determined that Nrf2 is indispensable in developmental lung injury. While association studies with genetic NRF2 polymorphisms supported a protective role for murine Nrf2 in oxidative airway diseases, somatic NRF2 mutations enhanced NRF2-ARE responses, and were favorable for lung carcinogenesis and chemoresistance. Bioinformatic tools have elucidated direct Nrf2 targets as well as Nrf2-interacting networks. Moreover, potent Nrf2-ARE agonists protected oxidant-induced lung phenotypes in model systems, suggesting a therapeutic or preventive intervention. Further investigations on Nrf2 should yield greater understanding of its contribution to normal and pathophysiological function in the airways.

Nrf2 reduces allergic asthma in mice through enhanced airway epithelial cytoprotective function

Asthma development and pathogenesis are influenced by the interactions of airway epithelial cells and innate and adaptive immune cells in response to allergens. Oxidative stress is an important mediator of asthmatic phenotypes in these cell types. Nuclear erythroid 2-related factor 2 (Nrf2) is a redox-sensitive transcription factor that is the key regulator of the response to oxidative and environmental stress. We previously demonstrated that Nrf2-deficient mice have heightened susceptibility to asthma, including elevated oxidative stress, inflammation, mucus, and airway hyperresponsiveness (AHR) (Rangasamy T, Guo J, Mitzner WA, Roman J, Singh A, Fryer AD, Yamamoto M, Kensler TW, Tuder RM, Georas SN, Biswal S. J Exp Med 202: 47-59, 2005). Here we dissected the role of Nrf2 in lung epithelial cells and tested whether genetic or pharmacological activation of Nrf2 reduces allergic asthma in mice. Cell-specific activation of Nrf2 in club cells of the airway epithelium significantly reduced allergen-induced AHR, inflammation, mucus, Th2 cytokine secretion, oxidative stress, and airway leakiness and increased airway levels of tight junction proteins zonula occludens-1 and E-cadherin. In isolated airway epithelial cells, Nrf2 enhanced epithelial barrier function and increased localization of zonula occludens-1 to the cell surface. Pharmacological activation of Nrf2 by 2-trifluoromethyl-2'-methoxychalone during the allergen challenge was sufficient to reduce allergic inflammation and AHR. New therapeutic options are needed for asthma, and this study demonstrates that activation of Nrf2 in lung epithelial cells is a novel potential therapeutic target to reduce asthma susceptibility.

Aryl hydrocarbon receptor is necessary to protect fetal human pulmonary microvascular endothelial cells against hyperoxic injury: Mechanistic roles of antioxidant enzymes and RelB

Hyperoxia contributes to the development of bronchopulmonary dysplasia (BPD) in premature infants. Activation of the aryl hydrocarbon receptor (AhR) protects adult and newborn mice against hyperoxic lung injury by mediating increases in the expression of phase I (cytochrome P450 (CYP) 1A) and phase II (NADP(H) quinone oxidoreductase (NQO1)) antioxidant enzymes (AOE). AhR positively regulates the expression of RelB, a component of the nuclear factor-kappaB (NF-κB) protein that contributes to anti-inflammatory processes in adult animals. Whether AhR regulates the expression of AOE and RelB, and protects fetal primary human lung cells against hyperoxic injury is unknown. Therefore, we tested the hypothesis that AhR-deficient fetal human pulmonary microvascular endothelial cells (HPMEC) will have decreased RelB activation and AOE, which will in turn predispose them to increased oxidative stress, inflammation, and cell death compared to AhR-sufficient HPMEC upon exposure to hyperoxia. AhR-deficient HPMEC showed increased hyperoxia-induced reactive oxygen species (ROS) generation, cleavage of poly(ADP-ribose) polymerase (PARP), and cell death compared to AhR-sufficient HPMEC. Additionally, AhR-deficient cell culture supernatants displayed increased macrophage inflammatory protein 1α and 1β, indicating a heightened inflammatory state. Interestingly, loss of AhR was associated with a significantly attenuated CYP1A1, NQO1, superoxide dismutase 1(SOD1), and nuclear RelB protein expression. These findings support the hypothesis that decreased RelB activation and AOE in AhR-deficient cells is associated with increased hyperoxic injury compared to AhR-sufficient cells.

The effects of electronic cigarette emissions on systemic cotinine levels, weight and postnatal lung growth in neonatal mice

Background/Objective

Electronic cigarette (E-cigarettes) emissions present a potentially new hazard to neonates through inhalation, dermal and oral contact. Exposure to nicotine containing E-cigarettes may cause significant systemic absorption in neonates due to the potential for multi-route exposure. Systemic absorption of nicotine and constituents of E-cigarette emissions may adversely impact weight and lung development in the neonate. To address these questions we exposed neonatal mice to E-cigarette emissions and measured systemic cotinine levels and alveolar lung growth.

Methods/Main Results

Neonatal mice were exposed to E-cigarettes for the first 10 days of life. E-cigarette cartridges contained either 1.8% nicotine in propylene glycol (PG) or PG vehicle alone. Daily weights, plasma and urine cotinine levels and lung growth using the alveolar mean linear intercept (MLI) method were measured at 10 days of life and compared to room air controls. Mice exposed to 1.8% nicotine/PG had a 13.3% decrease in total body weight compared to room air controls. Plasma cotinine levels were found to be elevated in neonatal mice exposed to 1.8% nicotine/PG E-cigarettes (mean 62.34± 3.3 ng/ml). After adjusting for sex and weight, the nicotine exposed mice were found to have modestly impaired lung growth by MLI compared to room air control mice (p<.054 trial 1; p<.006 trial 2). These studies indicate that exposure to E-cigarette emissions during the neonatal period can adversely impact weight gain. In addition exposure to nicotine containing E-cigarettes can cause detectable levels of systemic cotinine, diminished alveolar cell proliferation and a modest impairment in postnatal lung growth.

Perinatal oxygen in the developing lung

Lung diseases, such as bronchopulmonary dysplasia (BPD), wheezing, and asthma, remain significant causes of morbidity and mortality in the pediatric population, particularly in the setting of premature birth. Pulmonary outcomes in these infants are highly influenced by perinatal exposures including prenatal inflammation, postnatal intensive care unit interventions, and environmental agents. Here, there is strong evidence that perinatal supplemental oxygen administration has significant effects on pulmonary development and health. This is of particular importance in the preterm lung, where premature exposure to room air represents a hyperoxic insult that may cause harm to a lung primed to develop in a hypoxic environment. Preterm infants are also subject to increased episodes of hypoxia, which may also result in pulmonary damage and disease. Here, we summarize the current understanding of the effects of oxygen on the developing lung and how low vs. high oxygen may predispose to pulmonary disease that may extend even into adulthood. Better understanding of the underlying mechanisms will help lead to improved care and outcomes in this vulnerable population.

Heme oxygenase in neonatal lung injury and repair

SIGNIFICANCE

Premature and sick neonates are often exposed to high concentrations of oxygen, which results in lung injury and long-term adverse consequences. Nevertheless, neonates are more tolerant to hyperoxia than are adults. This may be, in part, explained by the high lung content of heme oxygenase-1 (HO-1), the rate-limiting enzyme in the degradation of heme and an important stress protein. The abundance of HO-1 dictates its cytoprotective and deleterious effects. Interestingly, in response to hyperoxia, lung HO-1 mRNA is not further up-regulated in neonates, suggesting that lung HO-1 gene expression is tightly regulated so as to optimize cytoprotection when faced with an oxidative stress such as hyperoxia.

RECENT ADVANCES

In addition to the lack of induction of HO-1 mRNA, neonatal lung HO-1 protein is observed in the nucleus in neonatal mice exposed to hyperoxia but not in adults, which is further evidence for the developmental regulation of HO-1. Nuclear HO-1 had unique properties independent of its enzymatic activity. In addition, there has been increasing evidence that nuclear HO-1 contributes to cellular proliferation and malignant transformation in several human cancers.

CRITICAL ISSUES

Since HO-1 has dual effects in cytoprotection and cellular proliferation, the titration of HO-1 effects is critical to ensure beneficial actions against oxidative stress.

FUTURE DIRECTIONS

Much more has to be understood about the specific roles of HO-1 so as to manipulate its abundance and/or nuclear migration to maximize the therapeutic benefit of this pleiotropic protein in the neonatal lung.

Superoxide dismutase 3 dysregulation in a murine model of neonatal lung injury

Bronchopulmonary dysplasia (BPD), a common chronic respiratory disease that occurs after premature birth, is believed to be secondary to oxidative damage from hyperoxia and inflammation, which leads to impaired alveolar formation and chronic lung dysfunction. We hypothesized that extracellular superoxide dismutase (SOD)3, an antioxidant uniquely targeted to the extracellular matrix (ECM) and alveolar fluid, might have a different response (down-regulation) to hyperoxic injury and recovery in room air (RA), thereby contributing to the persistent airspace injury and inflammation. We used a murine BPD model using postnatal hyperoxia (O2) (4 or 5 d) followed by short-term recovery (14 d) in RA, which mimics the durable effects after injury during alveolar development. This was associated with significantly increased mRNA expression for antioxidant genes mediated by nuclear factor erythroid 2-related factor (Nrf2) in the O2 (n = 4) versus RA group (n = 5). SOD3, an Nrf2-independent antioxidant, was significantly reduced in the O2-exposed mice compared with RA. Immunohistochemistry revealed decreased and disrupted SOD3 deposition in the alveolar ECM of O2-exposed mice. Furthermore, this distinct hyperoxic antioxidant and injury profile was reproducible in murine lung epithelial 12 cells exposed to O2. Overexpression of SOD3 rescued the injury measures in the O2-exposed cells. We establish that reduced SOD3 expression correlates with alveolar injury measures in the recovered neonatal hyperoxic lung, and SOD3 overexpression attenuates hyperoxic injury in an alveolar epithelial cell line. Such findings suggest a candidate mechanism for the pathogenesis of BPD that may lead to targeted interventions.

Noblesse oblige: NRF2 functions in the airways

The transcription factor, nuclear factor (NF), erythroid-derived 2-related factor 2 (NRF2), was discovered nearly 2 decades ago. Since then, over 4,000 papers have been published on NRF2 function in diverse biological systems, and it has been found to be a critical regulator of antioxidant and defense genes with antioxidant response elements in their promoters. NRF2 is particularly important in protecting cells and tissues under highly oxidative microenvironments, including the airways that interface with the external environment and are exposed to pollutants and other oxidant stressors. Using mice with targeted deletion of Nrf2, a protective role for this transcription factor has been determined in many model diseases, including acute lung injury, emphysema, allergy and asthma, pulmonary fibrosis, and respiratory syncytial virus disease. Recent studies have also found that murine Nrf2 is important in lung development and protection against neonatal lung injury. Moreover, functional polymorphisms in human NRF2 have been known to associate with disease severity, indicating a potentially important protective function. However, there is also a "dark side" to NRF2 function, as it has been found to enhance advanced stages of carcinogenesis in the lung and some other tissues. NRF2 inducers such as phytochemical isothyocyanates and synthetic triterpenoids, have been discovered and used in model systems of oxidant-induced lung diseases, and data suggest a potential for clinical interventions. Future investigations of NRF2 should yield further insight into its contribution to normal and pathophysiological conditions in the airways, and alternative treatment strategies to protect against oxidative respiratory disease.

Exogenous hydrogen sulfide (H2S) protects alveolar growth in experimental O2-induced neonatal lung injury

Background

Bronchopulmonary dysplasia (BPD), the chronic lung disease of prematurity, remains a major health problem. BPD is characterized by impaired alveolar development and complicated by pulmonary hypertension (PHT). Currently there is no specific treatment for BPD. Hydrogen sulfide (H₂S), carbon monoxide and nitric oxide (NO), belong to a class of endogenously synthesized gaseous molecules referred to as gasotransmitters. While inhaled NO is already used for the treatment of neonatal PHT and currently tested for the prevention of BPD, H₂S has until recently been regarded exclusively as a toxic gas. Recent evidence suggests that endogenous H₂S exerts beneficial biological effects, including cytoprotection and vasodilatation. We hypothesized that H₂S preserves normal alveolar development and prevents PHT in experimental BPD.

Methods

We took advantage of a recently described slow-releasing H₂S donor, GYY4137 (morpholin-4-ium-4-methoxyphenyl(morpholino) phosphinodithioate) to study its lung protective potential in vitro and in vivo.

Results

In vitro, GYY4137 promoted capillary-like network formation, viability and reduced reactive oxygen species in hyperoxia-exposed human pulmonary artery endothelial cells. GYY4137 also protected mitochondrial function in alveolar epithelial cells. In vivo, GYY4137 preserved and restored normal alveolar growth in rat pups exposed from birth for 2 weeks to hyperoxia. GYY4137 also attenuated PHT as determined by improved pulmonary arterial acceleration time on echo-Doppler, pulmonary artery remodeling and right ventricular hypertrophy. GYY4137 also prevented pulmonary artery smooth muscle cell proliferation.

Conclusions

H₂S protects from impaired alveolar growth and PHT in experimental O₂-induced lung injury. H₂S warrants further investigation as a new therapeutic target for alveolar damage and PHT.

Postnatal inflammation in the pathogenesis of bronchopulmonary dysplasia

Exposure to hyperoxia, invasive mechanical ventilation, and systemic/local sepsis are important antecedents of postnatal inflammation in the pathogenesis of bronchopulmonary dysplasia (BPD). This review will summarize information obtained from animal (baboon, lamb/sheep, rat and mouse) models that pertain to the specific inflammatory agents and signaling molecules that predispose a premature infant to BPD.

Modulation of oxidative stress as an anticancer strategy

The regulation of oxidative stress is an important factor in both tumour development and responses to anticancer therapies. Many signalling pathways that are linked to tumorigenesis can also regulate the metabolism of reactive oxygen species (ROS) through direct or indirect mechanisms. High ROS levels are generally detrimental to cells, and the redox status of cancer cells usually differs from that of normal cells. Because of metabolic and signalling aberrations, cancer cells exhibit elevated ROS levels. The observation that this is balanced by an increased antioxidant capacity suggests that high ROS levels may constitute a barrier to tumorigenesis. However, ROS can also promote tumour formation by inducing DNA mutations and pro-oncogenic signalling pathways. These contradictory effects have important implications for potential anticancer strategies that aim to modulate levels of ROS. In this Review, we address the controversial role of ROS in tumour development and in responses to anticancer therapies, and elaborate on the idea that targeting the antioxidant capacity of tumour cells can have a positive therapeutic impact.

Transcriptional responses of neonatal mouse lung to hyperoxia by Nrf2 status

Hyperoxia exposure can inhibit alveolar growth in the neonatal lung through induction of p21/p53 pathways and is a risk factor for the development of bronchopulmonary dysplasia (BPD) in preterm infants. We previously found that activation of nuclear factor erythroid 2 p45-related factor (Nrf2) improved survival in neonatal mice exposed to hyperoxia likely due to increased expression of anti-oxidant response genes. It is not known however, whether hyperoxic induced Nrf2 activation attenuates the growth impairment caused by hyperoxia in neonatal lung. To determine if Nrf2 activation modulates cell cycle regulatory pathway genes associated with growth arrest we examined the gene expression in the lungs of Nrf2(-/-) and Nrf2(+/+) neonatal mice at one and 3days of hyperoxia exposure.

METHODS

Microarray analysis was performed in neonatal Nrf2(+/+) and Nrf2(-/-) lungs exposed to one and 3days of hyperoxia. Sulforaphane, an inducer of Nrf2 was given to timed pregnant mice to determine if in utero exposure attenuated p21 and IL-6 gene expression in wildtype neonatal mice exposed to hyperoxia.

RESULTS

Cell cycle regulatory genes were induced in Nrf2(-/-) lung at 1day of hyperoxia. At 3days of hyperoxia, induction of cell cycle regulatory genes was similar in Nrf2(+/+) and Nrf2(-/-) lungs, despite higher inflammatory gene expression in Nrf2(-/-) lung.

CONCLUSION

p21/p53 pathways gene expression was not attenuated by Nrf2 activation in neonatal lung. In utero SUL did not attenuate p21 expression in wildtype neonatal lung exposed to hyperoxia. These findings suggest that although Nrf2 activation induces expression of anti-oxidant genes, it does not attenuate alveolar growth arrest caused by exposure to hyperoxia.

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.

Functional deficiency of aryl hydrocarbon receptor augments oxygen toxicity-induced alveolar simplification in newborn mice

Hyperoxia contributes to the development of bronchopulmonary dysplasia (BPD) in premature infants. New BPD is characterized as having alveolar simplification. We reported previously that aryl hydrocarbon receptor (AhR) deficiency increased susceptibility to hyperoxic lung injury in adult mice, and this was associated with decreased expression of cytochrome P450 1A enzymes and increased lung inflammation. Whether AhR protects newborn mice against hyperoxia-induced alveolar simplification is unknown. Thus, we tested the hypothesis that decreased activation of the pulmonary AhR augments hyperoxia-induced alveolar simplification and lung inflammation in newborn mice. Experimental groups included one-day old wild type (WT) and AhR dysfunctional (AhRd) mice exposed to 21% O₂ (air) or 85% O₂ (hyperoxia) for 14 days. Exposure of newborn WT mice to hyperoxia resulted in increased protein, enzyme and mRNA expression of the AhR-regulated lung cytochrome P450 1A1, NAD(P)H quinone oxidoreductase-1, and microsomal glutathione S-transferase 1 enzymes, suggesting that hyperoxia increases activation of the pulmonary AhR. On the other hand, in the AhRd mice, hyperoxia induced the AhR-regulated enzymes to a lesser extent probably due to the dysfunctional AhR in these mice. Alveolar simplification and lung inflammation was increased in mice exposed to hyperoxia compared with those exposed to air, and AhRd mice were more susceptible to hyperoxia-induced alveolar simplification and lung inflammation compared with WT mice. These findings suggest that decreased activation of the pulmonary AhR in newborn AhRd mice augments hyperoxia-induced alveolar simplification and lung inflammation in these mice.

Frontiers in pulmonary hypertension in infants and children with bronchopulmonary dysplasia

Pulmonary hypertension (PH) is an increasingly recognized complication of premature birth and bronchopulmonary dysplasia (BPD), and is associated with increased morbidity and mortality. Extreme phenotypic variability exists among preterm infants of similar gestational ages, making it difficult to predict which infants are at increased risk for developing PH. Intrauterine growth retardation or drug exposures, postnatal therapy with prolonged positive pressure ventilation, cardiovascular shunts, poor postnatal lung and somatic growth, and genetic or epigenetic factors may all contribute to the development of PH in preterm infants with BPD. In addition to the variability of severity of PH, there is also qualitative variability seen in PH, such as the variable responses to vasoactive medications. To reduce the morbidity and mortality associated with PH, a multi-pronged approach is needed. First, improved screening for and increased recognition of PH may allow for earlier treatment and better clinical outcomes. Second, identification of both prenatal and postnatal risk factors for the development of PH may allow targeting of therapy and resources for those at highest risk. Third, understanding the pathophysiology of the preterm pulmonary vascular bed may help improve outcomes through recognizing pathways that are dysregulated in PH, identifying novel biomarkers, and testing novel treatments. Finally, the recognition of conditions and exposures that may exacerbate or lead to recurrent PH is needed to help with developing treatment guidelines and preventative strategies that can be used to reduce the burden of disease.