Dual oxidase 1 and 2 expression in airway epithelium of smokers and patients with mild/moderate chronic obstructive pulmonary disease

NADPH Oxidases in Neurodegenerative Disorders: Mechanisms and Therapeutic Opportunities

Significance: The nicotinamide adenine dinucleotide phosphate oxidase (NOX) enzyme family, located in the central nervous system, is recognized as a source of reactive oxygen species (ROS) in the brain. Despite its importance in cellular processes, excessive ROS generation leads to cell death and is involved in the pathogenesis of neurodegenerative disorders. Recent advances: NOX enzymes contribute to the development of neurodegenerative diseases, such as Parkinson's disease (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and stroke, highlighting their potential as targets for future therapeutic development. This review will discuss NOX's contribution and therapeutic targeting potential in neurodegenerative diseases, focusing on PD, AD, ALS, and stroke. Critical issues: Homeostatic and physiological levels of ROS are crucial for regulating several processes, such as development, memory, neuronal signaling, and vascular homeostasis. However, NOX-mediated excessive ROS generation is deeply involved in the damage of DNA, proteins, and lipids, leading to cell death in the pathogenesis of a wide range of diseases, namely neurodegenerative diseases. Future directions: It is essential to understand the role of NOX homologs in neurodegenerative disorders and the pathological mechanisms undergoing neurodegeneration mediated by increased levels of ROS. This further knowledge will allow the development of new specific NOX inhibitors and their application for neurodegenerative disease therapeutics.

Cigarette Smoke-Induced Respiratory Response: Insights into Cellular Processes and Biomarkers

Cigarette smoke (CS) poses a significant risk factor for respiratory, vascular, and organ diseases owing to its high content of harmful chemicals and reactive oxygen species (ROS). These substances are known to induce oxidative stress, inflammation, apoptosis, and senescence due to their exposure to environmental pollutants and the presence of oxidative enzymes. The lung is particularly susceptible to oxidative stress. Persistent oxidative stress caused by chronic exposure to CS can lead to respiratory diseases such as chronic obstructive pulmonary disease (COPD), pulmonary fibrosis (PF), and lung cancer. Avoiding exposure to environmental pollutants, like cigarette smoke and air pollution, can help mitigate oxidative stress. A comprehensive understanding of oxidative stress and its impact on the lungs requires future research. This includes identifying strategies for preventing and treating lung diseases as well as investigating the underlying mechanisms behind oxidative stress. Thus, this review aims to investigate the cellular processes induced by CS, specifically inflammation, apoptosis, senescence, and their associated biomarkers. Furthermore, this review will delve into the alveolar response provoked by CS, emphasizing the roles of potential therapeutic target markers and strategies in inflammation and oxidative stress.

NADPH Oxidase Isoforms in COPD Patients and Acute Cigarette Smoke-Exposed Mice: Induction of Oxidative Stress and Lung Inflammation

Cigarette smoke (CS) is a major risk factor for chronic obstructive pulmonary disease (COPD), which represents the third leading cause of death worldwide. CS induces reactive oxygen species (ROS) production, leading to pulmonary inflammation and remodeling. NADPH oxidases (NOXs) represent essential sources of ROS production in the cardiovascular system. Whether and how NOX isoforms are activated in COPD patients and in response to acute cigarette smoke (ACS) remains incompletely understood. In the present study, the expression of NOX isoforms was examined in the lungs of end-stage COPD patients. In addition, mice silenced of NOX1 or NOX4 expression using in vivo RNA interference (RNAi), and NOX2-deficient (NOX2^−/y) mice, were exposed to ACS for 1 h using a standard TE-10B smoking machine. In lung sections isolated from COPD patients undergoing lung transplantation, protein expression of NOX1, NOX2, NOX4, or NOX5 was markedly upregulated compared to non-smoking donor controls. Likewise, ACS upregulated protein expression of NOX1, NOX2, and NOX4, production of ROS, inflammatory cell infiltration, and mRNA expression of proinflammatory cytokines TNF-α and KC in the mouse lung. In vivo RNAi knockdown of NOX1 or NOX4 decreased ACS induced ROS production, inflammatory cell influx, and the expression of TNF-α and KC, which were accompanied by inhibition of the NF-κB-COX-2 axis. Although ACS induced ROS production was reduced in the lungs of NOX2^−/y mice, inflammatory cell influx and expression of NF-κB/COX-2 were increased. Taken together, our results demonstrate for the first time that NOX isoforms 1, 2, 4 and 5 all remain activated in end-stage COPD patients, while NOX1 and NOX4 mediate oxidative stress and inflammatory responses in response to acute cigarette smoke. Therefore, targeting different isoforms of NOX might be necessary to treat COPD at different stages of the disease, which represents novel mechanistic insights enabling improved management of the devastating disease.

Redox Dysregulation in Aging and COPD: Role of NOX Enzymes and Implications for Antioxidant Strategies

With a rapidly growing elderly human population, the incidence of age-related lung diseases such as chronic obstructive pulmonary disease (COPD) continues to rise. It is widely believed that reactive oxygen species (ROS) play an important role in ageing and in age-related disease, and approaches of antioxidant supplementation have been touted as useful strategies to mitigate age-related disease progression, although success of such strategies has been very limited to date. Involvement of ROS in ageing is largely attributed to mitochondrial dysfunction and impaired adaptive antioxidant responses. NADPH oxidase (NOX) enzymes represent an important enzyme family that generates ROS in a regulated fashion for purposes of oxidative host defense and redox-based signalling, however, the associations of NOX enzymes with lung ageing or age-related lung disease have to date only been minimally addressed. The present review will focus on our current understanding of the impact of ageing on NOX biology and its consequences for age-related lung disease, particularly COPD, and will also discuss the implications of altered NOX biology for current and future antioxidant-based strategies aimed at treating these diseases.

Downregulation of DUOX1 function contributes to aging-related impairment of innate airway injury responses and accelerated senile emphysema

Aging is associated with a gradual loss of lung function due to increased cellular senescence, decreased regenerative capacity, and impaired innate host defense. One important aspect of innate airway epithelial host defense to nonmicrobial triggers is the secretion of alarmins such as IL-33 and activation of type 2 inflammation, which were previously found to depend on activation of the NADPH oxidase (NOX) homolog DUOX1, and redox-dependent signaling pathways that promote alarmin secretion. Here, we demonstrate that normal aging of C57BL/6J mice resulted in markedly decreased lung innate epithelial type 2 responses to exogenous triggers such as the airborne allergen Dermatophagoides pteronyssinus, which was associated with marked downregulation of DUOX1, as well as DUOX1-mediated redox-dependent signaling. DUOX1 deficiency was also found to accelerate age-related airspace enlargement and decline in lung function but did not consistently affect other features of lung aging such as senescence-associated inflammation. Intriguingly, observations of age-related DUOX1 downregulation and enhanced airspace enlargement due to DUOX1 deficiency in C57BL/6J mice, which lack a functional mitochondrial nicotinamide nucleotide transhydrogenase (NNT), were much less dramatic in C57BL/6NJ mice with normal NNT function, although the latter mice also displayed impaired innate epithelial injury responses with advancing age. Overall, our findings indicate a marked aging-dependent decline in (DUOX1-dependent) innate airway injury responses to external nonmicrobial triggers, but the impact of aging on DUOX1 downregulation and its significance for age-related senile emphysema development was variable between different C57BL6 substrains, possibly related to metabolic alterations due to differences in NNT function.

DUOX1 in mammalian disease pathophysiology

Dual oxidase 1 (DUOX1) is a member of the protein family of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases. DUOX1 has several normal physiological, immunological, and biochemical functions in different parts of the body. Dysregulated oxidative metabolism interferes with various disease pathologies and numerous therapeutic options are based on targeting cellular redox pathways. DUOX1 forms an important enzymatic source of biological oxidants, and DUOX1 expression is frequently dysregulated in various diseases. While this review shortly addresses the biochemical and cellular properties and proposed physiological roles of DUOX1, its main purpose is to summarize the current knowledge with respect to the potential role of DUOX1 enzyme in disease pathology, especially in mammalian organisms. Although DUOX1 is normally prominently expressed in epithelial lineages, it is frequently silenced in epithelial-derived cancers by epigenetic mechanisms. While an abundance of information is available on DUOX1 transcription in different diseases, an increasing number of mechanistic studies indicate a causative relationship between DUOX1 function and disease pathophysiology. Additionally, specific functions of the DUOX1 maturation factor, DUOXA1, will also be addressed. Lastly, urgent and outstanding questions on the field of DUOX1 will be discussed that could provide valuable new diagnostic tools and novel therapeutic options.

Cigarette smoke extract amplifies NADPH oxidase-dependent ROS production to inactivate PTEN by oxidation in BEAS-2B cells

Chronic obstructive pulmonary disease (COPD) is widely recognized as a global public health problem and the third leading cause of mortality worldwide by 2020. Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a dual-specificity protein and lipid phosphatase that plays an important role in COPD. However, the redox regulation of PTEN in the development of COPD was poorly studied. Our results showed that cigarette smoke extract (CSE) could oxidize PTEN in a time-dependent manner in BEAS-2B cells, whereas PTEN oxidation exposed to CSE was delayed compared to that of H₂O_2. Additionally, we found that ROS derived from DUOX1 and 2 of NADPH oxidases were mainly responsible for oxidative inactivation PTEN, also simultaneously led to Trx-1 inactivation by dimerization. Oxidative mechanism of PTEN exposed to CSE was mediated by forming a disulfide bond between Cys⁷¹and Cys¹²⁴, similar to H₂O₂. Inactivation of PTEN resulted in the increased phosphorylation of Akt. In conclusion, CSE exposure could elevate the intracellular ROS mainly from DUOX1 and 2 to oxidize PTEN and Trx-1 resulting in Akt activation, eventually cause the occurrence of COPD, suggesting that PTEN is a potential target for new therapies in COPD.

Downregulation of epithelial DUOX1 in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a chronic respiratory disease characterized by small airway remodeling and alveolar emphysema due to environmental stresses such as cigarette smoking (CS). Oxidative stress is commonly implicated in COPD pathology, but recent findings suggest that one oxidant-producing NADPH oxidase homolog, dual oxidase 1 (DUOX1), is downregulated in the airways of patients with COPD. We evaluated lung tissue sections from patients with COPD for small airway epithelial DUOX1 protein expression, in association with measures of lung function and small airway and alveolar remodeling. We also addressed the impact of DUOX1 for lung tissue remodeling in mouse models of COPD. Small airway DUOX1 levels were decreased in advanced COPD and correlated with loss of lung function and markers of emphysema and remodeling. Similarly, DUOX1 downregulation in correlation with extracellular matrix remodeling was observed in a genetic model of COPD, transgenic SPC-TNF-α mice. Finally, development of subepithelial airway fibrosis in mice due to exposure to the CS-component acrolein, or alveolar emphysema induced by administration of elastase, were in both cases exacerbated in Duox1-deficient mice. Collectively, our studies highlight that downregulation of DUOX1 may be a contributing feature of COPD pathogenesis, likely related to impaired DUOX1-mediated innate injury responses involved in epithelial homeostasis.

Oxidative stress in chronic lung disease: From mitochondrial dysfunction to dysregulated redox signaling

The lung is a delicate organ with a large surface area that is continuously exposed to the external environment, and is therefore highly vulnerable to exogenous sources of oxidative stress. In addition, each of its approximately 40 cell types can also generate reactive oxygen species (ROS), as byproducts of cellular metabolism and in a more regulated manner by NOX enzymes with functions in host defense, immune regulation, and cell proliferation or differentiation. To effectively regulate the biological actions of exogenous and endogenous ROS, various enzymatic and non-enzymatic antioxidant defense systems are present in all lung cell types to provide adequate protection against their injurious effects and to allow for appropriate ROS-mediated biological signaling. Acute and chronic lung diseases are commonly thought to be associated with increased oxidative stress, evidenced by altered cellular or extracellular redox status, increased irreversible oxidative modifications in proteins or DNA, mitochondrial dysfunction, and altered expression or activity of NOX enzymes and antioxidant enzyme systems. However, supplementation strategies with generic antioxidants have been minimally successful in prevention or treatment of lung disease, most likely due to their inability to distinguish between harmful and beneficial actions of ROS. Recent studies have attempted to identify specific redox-based mechanisms that may mediate chronic lung disease, such as allergic asthma or pulmonary fibrosis, which provide opportunities for selective redox-based therapeutic strategies that may be useful in treatment of these diseases.

Free Radical Production and Oxidative Stress in Lung Tissue of Patients Exposed to Sulfur Mustard: An Overview of Cellular and Molecular Mechanisms

Sulfur mustard (SM) is a chemical alkylating compound that primary targets lung tissue. It causes a wide variety of pathological effects in respiratory system such as chronic bronchitis, bronchiolitis obliterans, necrosis of the mucosa and inflammation, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis. However, molecular and cellular mechanisms for these pathologies are still unclear. Oxidative stress (OS) induced by reactive oxygen species (ROS) is likely a significant mechanism by which SM leads to cell death and tissues injury. SM can trigger various molecular and cellular pathways that are linked to ROS generation, OS, and inflammation. Hypoxia-induced oxidative stress, reduced activity of enzymatic antioxidants, depletion of intercellular glutathione (GSH), decreased productivity of GSH-dependent antioxidants, mitochondrial dysfunction, accumulation of leukocytes and proinflammatory cytokines, and increased expression of ROS producing-related enzymes and inflammatory mediators are the major events in which SM leads to massive production of ROS and OS in pulmonary system. Therefore, understanding of these molecules and signaling pathways gives us valuable information about toxicological effects of SM on injured tissues and the way for developing a suitable clinical treatment. In this review, we aim to discuss the possible mechanisms by which SM induces excessive production of ROS, OS, and antioxidants depletion in lung tissue of exposed patients.

The Role of Nicotinamide Adenine Dinucleotide Phosphate Oxidases in Lung Architecture Remodeling

Chronic lung disorders, such as pulmonary artery hypertension (PAH), chronic obstructive pulmonary disease (COPD), asthma and neonatal bronchopulmonary dysplasia (BPD), are characterized by airway and/or vascular remodeling. Despite differences in the pathology, reactive oxygen species (ROS) have been highlighted as a critical contributor to the initiation and development of airway and vascular remodeling. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (Nox) appear to play a pivotal role in lung signaling, leading to marked changes in pulmonary airway and vascular cell phenotypes, including proliferation, hypertrophy and apoptosis. In this review, we summarized the current literature regarding the role of Nox in the airway and vascular remodeling.

Aeroallergens Induce Reactive Oxygen Species Production and DNA Damage and Dampen Antioxidant Responses in Bronchial Epithelial Cells

Exposure to environmental allergens is a major risk factor for asthma development. Allergens possess proteolytic activity that is capable of disrupting the airway epithelium. Although there is increasing evidence pointing to asthma as an epithelial disease, the underlying mechanism that drives asthma has not been fully elucidated. In this study, we investigated the direct DNA damage potential of aeroallergens on human bronchial epithelial cells and elucidated the mechanisms mediating the damage. Human bronchial epithelial cells, BEAS-2B, directly exposed to house dust mites (HDM) resulted in enhanced DNA damage, as measured by the CometChip and the staining of DNA double-strand break marker, γH2AX. HDM stimulated cellular reactive oxygen species production, increased mitochondrial oxidative stress, and promoted nitrosative stress. Notably, expression of nuclear factor erythroid 2-related factor 2-dependent antioxidant genes was reduced immediately after HDM exposure, suggesting that HDM altered antioxidant responses. HDM exposure also reduced cell proliferation and induced cell death. Importantly, HDM-induced DNA damage can be prevented by the antioxidants glutathione and catalase, suggesting that HDM-induced reactive oxygen and nitrogen species can be neutralized by antioxidants. Mechanistic studies revealed that HDM-induced cellular injury is NADPH oxidase (NOX)-dependent, and apocynin, a NOX inhibitor, protected cells from double-strand breaks induced by HDM. Our results show that direct exposure of bronchial epithelial cells to HDM leads to the production of reactive oxygen and nitrogen species that damage DNA and induce cytotoxicity. Antioxidants and NOX inhibitors can prevent HDM-induced DNA damage, revealing a novel role for antioxidants and NOX inhibitors in mitigating allergic airway disease.

Mitochondrial alterations during oxidative stress in chronic obstructive pulmonary disease

The high incidence of chronic obstructive pulmonary disease (COPD), one of the most prevalent diseases worldwide, has attracted growing attention. Cigarette smoking is considered a major contributory factor in the pathogenesis and progression of COPD due to the tremendous oxidative burden that it causes, which induces an oxidant/antioxidant imbalance. Excessive oxidation induced by the excessive generation of mitochondrial reactive oxygen species disturbs the antioxidant systems and plays an important role in triggering and promoting chronic inflammation of airways. Given that mitochondria is one of the main sites of reactive oxygen species production by the oxidative phosphorylation process, oxidative stress may affect mitochondrial function by changing its structure and morphology and by affecting a series of mitochondrial proteins. In particular, PTEN-induced putative kinase 1/Parkin and p62 play critical roles in mitophagy. During the process, the Akt ubiquitin E3 ligase is an important mediator associated with cigarette smoke exposure-induced pulmonary endothelial cell death and dysfunction. Thus, understanding the underlying mechanisms of the signaling pathway may provide important information regarding the therapeutic treatment of COPD by application of alternative PTEN-induced putative kinase 1 targets or ubiquitin E3 ligase.

Cigarette Smoke Impairs A2A Adenosine Receptor Mediated Wound Repair through Up-regulation of Duox-1 Expression

Cigarette smoke (CS) exposure and intrinsic factors such as the NADPH oxidases produce high levels of reactive oxygen species (ROS), ensuing inflammatory tissue injury. We previously demonstrated that CS-generated ROS, particularly hydrogen peroxide (H2O2), impaired adenosine stimulated wound repair. We hypothesized that CS exposure modulates expression of Dual oxidase 1 (Duox-1), a NADPH oxidases known to generate H2O2. To test this hypothesis, we used human bronchial epithelial cell line Nuli-1 and C57BL/6 mice. Cells were treated with 5% CS extract (CSE) for various periods of time, and mice were exposed to whole body CS for six weeks. Both CSE and CS treatment induced increased expression of Duox-1, and silencing of Doux-1 improved the rate of cell wound repair induced by CSE treatment. Nuli-1 cells pretreated with thapsigargin but not calcium ionophore exhibited increased Duox-1 mRNA expression. CSE treatment stimulated PKCα activation, which was effectively blocked by pretreatment with diphenylene iodonium, a NADPH oxidase inhibitor. Compared to control, lungs from CS-exposed mice showed a significant increase in PKCα activity and Duox-1 expression. Collectively, the data demonstrated that CS exposure upregulates expression of Duox-1 protein. This further leads to H2O2 production and PKCα activation, inhibiting A2AAR-stimulated wound repair.

Sulfur mustard causes oxidants/antioxidants imbalance through the overexpression of free radical producing-related genes in human mustard lungs

The aim of this study is to analyze oxidative stress (OS) and changes in expression of reactive oxygen species (ROS) producing-related genes in mustard lungs. Human lung biopsies provided from controls (n=5) and sulfur mustard (SM)-exposed patients (n=6). Changes in expression of dual oxidases (DUOXs), aldehyde oxidase 1 (AOX1), thyroid peroxidase (TPO), myeloperoxidase (MPO) and eosinophil Peroxidase (EPO) were measured using RT(2) Profiler(™) PCR Array. OS was evaluated by determining bronchoalveolar lavage fluids (BALF) levels of total antioxidant capacity (TAC) and malondialdehyde (MDA). Higher TAC value was observed in BALF of controls compared with patients (0.138±0.02683μmol/l vs 0.0942±0.01793μmol/l), whereas a significant increase in MDA concentration was found in patients (0.486±0.04615 nmol/l vs 0.6467±0.05922 nmol/l). All ROS producing-related genes were overexpressed in the order AOX1>MPO>DUOX2>DUOX1>TPO>EPO. Upregulation of these genes may be a reason for overproduction of ROS, oxidants/antioxidants imbalance, OS and respiratory failures in mustard lungs.

Gene expression profile of oxidative stress and antioxidant defense in lung tissue of patients exposed to sulfur mustard

Sulfur mustard (SM) is a potent alkylating agent that targets several organs, especially lung tissue. Although pathological effects of SM on mustard lung have been widely considered, molecular and cellular mechanisms for these pathologies are poorly understood. We investigated changes in expression of genes related to oxidative stress (OS) and antioxidant defense caused by SM in lung tissue of patients. We performed gene expression profiling of OS and antioxidant defense in lung tissue samples from healthy controls (n=5) and SM-exposed patients (n=6). Changes in gene expression were measured using a 96-well RT(2) Profiler ™PCR Array: Human Oxidative Stress and Antioxidant Defense, which arrayed 84 genes functionally involved in cellular OS response. 47 (55.95%) genes were found to be significantly upregulated in patients with mustard lung compared with controls (p<0.05), whereas 7 (8.33%) genes were significantly downregulated (p<0.05). Among the most upregulated genes were OS responsive-1 (OXSR1), forkhead box M1 (FOXM1), and glutathione peroxidase-2 (GPX2), while metallothionein-3 (MT3) and glutathione reductase (GSR) were the most downregulated genes. Expression of hypoxia-induced genes (CYGB and MB), antioxidants and reactive oxygen species (ROS)-producing genes were significantly altered, suggesting an increased oxidative damage in mustard lungs. Mustard lungs were characterized by hypoxia, massive production of ROS, OS, disruption of epithelial cells, surfactant dysfunction, as well as increased risk of lung cancer and pulmonary fibrosis. Oxidative stress induced by ROS is the major mechanism for direct effect of SM exposure on respiratory system. Antioxidant treatment may improve the main features of mustard lungs.

NADPH Oxidase-4 Overexpression Is Associated With Epithelial Ciliary Dysfunction in Neutrophilic Asthma

BACKGROUND

Bronchial epithelial ciliary dysfunction is an important feature of asthma. We sought to determine the role in asthma of neutrophilic inflammation and nicotinamide adenine dinucleotide phosphate (NADPH) oxidases in ciliary dysfunction.

METHODS

Bronchial epithelial ciliary function was assessed by using video microscopy in fresh ex vivo epithelial strips from patients with asthma stratified according to their sputum cell differentials and in culture specimens from healthy control subjects and patients with asthma. Bronchial epithelial oxidative damage was determined by 8-oxo-dG expression. Nicotinamide adenine dinucleotide phosphate oxidase (NOX)/dual oxidase (DUOX) expression was assessed in bronchial epithelial cells by using microarrays, with NOX4 and DUOX1/2 expression assessed in bronchial biopsy specimens. Ciliary dysfunction following NADPH oxidase inhibition, using GKT137831, was evaluated in fresh epithelial strips from patients with asthma and a murine model of ovalbumin sensitization and challenge.

RESULTS

Ciliary beat frequency was impaired in patients with asthma with sputum neutrophilia (n = 11) vs those without (n = 10) (5.8 [0.6] Hz vs 8.8 [0.5] Hz; P = .003) and was correlated with sputum neutrophil count (r = -0.70; P < .001). Primary bronchial epithelial cells expressed DUOX1/2 and NOX4. Levels of 8-oxo-dG and NOX4 were elevated in patients with neutrophilic vs nonneutrophilic asthma, DUOX1 was elevated in both, and DUOX2 was elevated in nonneutrophilic asthma in vivo. In primary epithelial cultures, ciliary dysfunction did not persist, although NOX4 expression and reactive oxygen species generation was increased from patients with neutrophilic asthma. GKT137831 both improved ciliary function in ex vivo epithelial strips (n = 13), relative to the intensity of neutrophilic inflammation, and abolished ciliary dysfunction in the murine asthma model with no reduction in inflammation.

CONCLUSIONS

Ciliary dysfunction is increased in neutrophilic asthma associated with increased NOX4 expression and is attenuated by NADPH oxidase inhibition.

Dual Oxidase 2 (Duox2) Regulates Pannexin 1-mediated ATP Release in Primary Human Airway Epithelial Cells via Changes in Intracellular pH and Not H2O2 Production

Human airway epithelial cells express pannexin 1 (Panx1) channels to release ATP, which regulates mucociliary clearance. Airway inflammation causes mucociliary dysfunction. Exposure of primary human airway epithelial cell cultures to IFN-γ for 48 h did not alter Panx1 protein expression but significantly decreased ATP release in response to hypotonic stress. The IFN-γ-induced functional down-regulation of Panx1 was due to the up-regulation of dual oxidase 2 (Duox2). Duox2 suppression by siRNA led to an increase in ATP release in control cells and restoration of ATP release in cells treated with IFN-γ. Both effects were reduced by the pannexin inhibitor probenecid. Duox2 up-regulation stoichiometrically increases H2O2 and proton production. H2O2 inhibited Panx1 function temporarily by formation of disulfide bonds at the thiol group of its terminal cysteine. Long-term exposure to H2O2, however, had no inhibitory effect. To assess the role of cellular acidification upon IFN-γ treatment, fully differentiated airway epithelial cells were exposed to ammonium chloride to alkalinize the cytosol. This led to a 2-fold increase in ATP release in cells treated with IFN-γ that was also inhibited by probenecid. Duox2 knockdown also partially corrected IFN-γ-mediated acidification. The direct correlation between intracellular pH and Panx1 open probability was shown in oocytes. Therefore, airway epithelial cells release less ATP in response to hypotonic stress in an inflammatory environment (IFN-γ exposure). Decreased Panx1 function is a response to cell acidification mediated by IFN-γ-induced up-regulation of Duox2, representing a novel mechanism for mucociliary dysfunction in inflammatory airway diseases.

DUOX2 Expression Is Increased in Barrett Esophagus and Cancerous Tissues of Stomach and Colon

Aim. To detect the expression of dual oxidase (DUOX) 2 in Barrett esophagus, gastric cancer, and colorectal cancer (CRC). Materials and Methods. The endoscopic biopsies were collected from patients with Barrett esophagus, while the curative resection tissues were obtained from patients with gastric cancer, CRC, or hepatic carcinoma. The DUOX2 protein and mRNA levels were detected with immunohistochemistry (IHC) and real-time quantitative PCR (qPCR). The correlation of DUOX2 expression with clinicopathological parameters of tumors was identified. Results. Low levels of DUOX2 mRNA were detected in Barrett esophagus and the adjacent normal tissues, and there was no difference between these two groups. DUOX2 protein was found in Barrett esophagus and undetectable in the normal epithelium. The DUOX2 mRNA and protein levels in the gastric cancer and CRC were increased compared to the adjacent nonmalignant tissues. The elevated DUOX2 in the gastric cancer was significantly associated with smoking history. In CRC tissues, the DUOX2 protein expression level in stages II–IV was significantly higher than that in stage I. In both hepatic carcinoma and the adjacent nonmalignant tissue, the DUOX2 was virtually undetectable. Conclusion. DUOX2 in Barrett esophagus, gastric cancer, and CRC may be involved in the tumorigenesis of these tissues.

Proteinase activated receptor-2-mediated dual oxidase-2 up-regulation is involved in enhanced airway reactivity and inflammation in a mouse model of allergic asthma

Airway epithelial cells (AECs) express a variety of receptors, which sense danger signals from various aeroallergens/pathogens being inhaled constantly. Proteinase-activated receptor 2 (PAR-2) is one such receptor and is activated by cockroach allergens, which have intrinsic serine proteinase activity. Recently, dual oxidases (DUOX), especially DUOX-2, have been shown to be involved in airway inflammation in response to Toll-like receptor activation. However, the association between PAR-2 and DUOX-2 has not been explored in airways of allergic mice. Therefore, this study investigated the contribution of DUOX-2/reactive oxygen species (ROS) signalling in airway reactivity and inflammation after PAR-2 activation. Mice were sensitized intraperitoneally with intact cockroach allergen extract (CE) in the presence of aluminium hydroxide followed by intranasal challenge with CE. Mice were then assessed for airway reactivity, inflammation, oxidative stress (DUOX-2, ROS, inducible nitric oxide synthase, nitrite, nitrotyrosine and protein carbonyls) and apoptosis (Bax, Bcl-2, caspase-3). Challenge with CE led to up-regulation of DUOX-2 and ROS in AECs with concomitant increases in airway reactivity/inflammation and parameters of oxidative stress, and apoptosis. All of these changes were significantly inhibited by intranasal administration of ENMD-1068, a small molecule antagonist of PAR-2 in allergic mice. Administration of diphenyliodonium to allergic mice also led to improvement of allergic airway responses via inhibition of the DUOX-2/ROS pathway; however, these effects were less pronounced than PAR-2 antagonism. The current study suggests that PAR-2 activation leads to up-regulation of the DUOX-2/ROS pathway in AECs, which is involved in regulation of airway reactivity and inflammation via oxidative stress and apoptosis.

Localization of the Dual Oxidase BLI-3 and Characterization of Its NADPH Oxidase Domain during Infection of Caenorhabditis elegans

Dual oxidases (DUOX) are enzymes that contain an NADPH oxidase domain that produces hydrogen peroxide (H₂O₂) and a peroxidase domain that can utilize H₂O₂ to carry out a variety of reactions. The model organism Caenorhabditis elegans produces the DUOX, BLI-3, which has roles in both cuticle development and in protection against infection. In previous work, we demonstrated that while certain peroxidases were protective against the human bacterial pathogen Enterococcus faecalis, the peroxidase domain of BLI-3 was not, leading to the postulate that the NADPH oxidase domain is the basis for BLI-3’s protective effects. In this work, we show that a strain carrying a mutation in the NADPH oxidase domain of BLI-3, bli-3(im10), is more susceptible to E. faecalis and the human fungal pathogen Candida albicans. Additionally, less H₂O₂ is produced in response to pathogen using both an established Amplex Red assay and a strain of C. albicans, WT-OXYellow, which acts as a biosensor of reactive oxygen species (ROS). Finally, a C. elegans line containing a BLI-3::mCherry transgene was generated. Previous work suggested that BLI-3 is produced in the hypodermis and the intestine. Expression of the transgene was observed in both these tissues, and additionally in the pharynx. The amount and pattern of localization of BLI-3 did not change in response to pathogen exposure.

NADPH oxidases in lung health and disease

SIGNIFICANCE

The evolution of the lungs and circulatory systems in vertebrates ensured the availability of molecular oxygen (O2; dioxygen) for aerobic cellular metabolism of internal organs in large animals. O2 serves as the physiologic terminal acceptor of mitochondrial electron transfer and of the NADPH oxidase (Nox) family of oxidoreductases to generate primarily water and reactive oxygen species (ROS), respectively.

RECENT ADVANCES

The purposeful generation of ROS by Nox family enzymes suggests important roles in normal physiology and adaptation, most notably in host defense against invading pathogens and in cellular signaling.

CRITICAL ISSUES

However, there is emerging evidence that, in the context of chronic stress and/or aging, Nox enzymes contribute to the pathogenesis of a number of lung diseases.

FUTURE DIRECTIONS

Here, we review evolving functions of Nox enzymes in normal lung physiology and emerging pathophysiologic roles in lung disease.

Oxidants in Acute and Chronic Lung Disease

Oxidants play an important role in homeostatic function, but excessive oxidant generation has an adverse effect on health. The manipulation of Reactive Oxygen Species (ROS) can have a beneficial effect on various lung pathologies. However indiscriminate uses of anti-oxidant strategies have not demonstrated any consistent benefit and may be harmful. Here we propose that nuanced strategies are needed to modulate the oxidant system to obtain a beneficial result in the lung diseases such as Acute Lung Injury (ALI) and Chronic Obstructive Pulmonary Disease (COPD). We identify novel areas of lung oxidant responses that may yield fruitful therapies in the future.

Balancing reactive oxygen species in the epigenome: NADPH oxidases as target and perpetrator

SIGNIFICANCE

NADPH oxidases are important sources for regulated generation of reactive oxygen species (ROS). The main ROS produced are superoxide and hydrogen peroxide, both of which are redox signaling molecules in the context of various cellular functions. Redox imbalance due to excessive or insufficient ROS is a hallmark of pathophysiological aspects, including cancer development and progression.

RECENT ADVANCES

Epigenetic silencing of NADPH oxidases by hypermethylation of their promoter region or of the genes required for their assembly and activity occurs in diseases, such as lung cancer, and may represent an early stage of neoplastic transformation.

CRITICAL ISSUES

Loss of ROS-mediated signaling by epigenetic silencing may promote tumorigenesis. Conversely, increased oxidative stress caused by oncogene-induced overexpression of NADPH oxidases may also drive epigenetic instability. Thus, the cellular redox balance is likely vital in carcinogenesis.

FUTURE DIRECTIONS

NADPH oxidases may serve as prognostic tumor biomarker, especially when their individual expression is confined to accessible tissues, such as mucosal epithelia or blood. Further validation of NADPH oxidase/dual oxidase enzymes as candidate markers will require well controlled, large-scale clinical data sets. This review is focused on NADPH oxidases as targets of epigenetic changes in cancer and on the emerging role of ROS as inducers of epigenetic changes.

Activation of TLR4 is required for the synergistic induction of dual oxidase 2 and dual oxidase A2 by IFN-γ and lipopolysaccharide in human pancreatic cancer cell lines

Pancreatitis is associated with release of proinflammatory cytokines and reactive oxygen species and plays an important role in the development of pancreatic cancer. We recently demonstrated that dual oxidase (Duox)2, an NADPH oxidase essential for reactive oxygen species-related, gastrointestinal host defense, is regulated by IFN-γ-mediated Stat1 binding to the Duox2 promoter in pancreatic tumor lines. Because LPS enhances the development and invasiveness of pancreatic cancer in vivo following TLR4-related activation of NF-κB, we examined whether LPS, alone or combined with IFN-γ, regulated Duox2. We found that upregulation of TLR4 by IFN-γ in BxPC-3 and CFPAC-1 pancreatic cancer cells was augmented by LPS, resulting in activation of NF-κB, accumulation of NF-κB (p65) in the nucleus, and increased binding of p65 to the Duox2 promoter. TLR4 silencing with small interfering RNAs, as well as two independent NF-κB inhibitors, attenuated LPS- and IFN-γ-mediated Duox2 upregulation in BxPC-3 cells. Induction of Duox2 expression by IFN-γ and LPS may result from IFN-γ-related activation of Stat1 acting in concert with NF-κB-related upregulation of Duox2. Sustained extracellular accumulation of H(2)O(2) generated by exposure to both LPS and IFN-γ was responsible for an ∼50% decrease in BxPC-3 cell proliferation associated with a G(1) cell cycle block, apoptosis, and DNA damage. We also demonstrated upregulation of Duox expression in vivo in pancreatic cancer xenografts and in patients with chronic pancreatitis. These results suggest that inflammatory cytokines can interact to produce a Duox-dependent pro-oxidant milieu that could increase the pathologic potential of pancreatic inflammation and pancreatic cancer cells.

Dual oxidase-1 is required for airway epithelial cell migration and bronchiolar reepithelialization after injury

The respiratory epithelium plays a critical role in innate defenses against airborne pathogens and pollutants, and alterations in epithelial homeostasis and repair mechanisms are thought to contribute to chronic lung diseases associated with airway remodeling. Previous studies implicated the nicotinamide adenine dinucleotide phosphate-reduced oxidase dual oxidase-1 (DUOX1) in redox signaling pathways involved in in vitro epithelial wound responses to infection and injury. However, the importance of epithelial DUOX1 in in vivo epithelial repair pathways has not been established. Using small interfering (si)RNA silencing of DUOX1 expression, we show the critical importance of DUOX1 in wound responses in murine tracheal epithelial (MTE) cells in vitro, as well as its contribution to epithelial regeneration in vivo in a murine model of epithelial injury induced by naphthalene, a selective toxicant of nonciliated respiratory epithelial cells (club cells [Clara]). Whereas naphthalene-induced club-cell injury is normally followed by epithelial regeneration after 7 and 14 days, such airway reepithelialization was significantly delayed after the silencing of airway DUOX1 by oropharyngeal administration of DUOX1-targeted siRNA. Wound closure in MTE cells was related to DUOX1-dependent activation of the epidermal growth factor receptor (EGFR) and the transcription factor signal transducer and activator of transcription-3 (STAT3), known mediators of epithelial cell migration and wound responses. Moreover, in vivo DUOX1 silencing significantly suppressed naphthalene-induced activation of STAT3 and EGFR during early stages of epithelial repair. In conclusion, these experiments demonstrate for the first time an important function for epithelial DUOX1 in lung epithelial regeneration in vivo, by promoting EGFR-STAT3 signaling and cell migration as critical events in initial repair.

Roflumilast N-oxide, a PDE4 inhibitor, improves cilia motility and ciliated human bronchial epithelial cells compromised by cigarette smoke in vitro

BACKGROUND AND PURPOSE

Mucociliary malfunction occurs in chronic obstructive pulmonary disease (COPD) and compromised functions of ciliated bronchial epithelial cells may contribute to this. Cigarette smoke, a major risk factor for COPD, impairs ciliary beat frequency (CBF). cAMP augments CBF. This in vitro study addressed, in differentiated, primary human bronchial epithelial cells, whether roflumilast N-oxide, a PDE4 inhibitor, (i) augments CBF; (ii) prevents the reduction in CBF induced by cigarette smoke extract (CSE); and (iii) protects against the loss of the ciliated phenotype following long-term CSE exposure.

EXPERIMENTAL APPROACH

Air-liquid interface cultured human bronchial epithelial cells were incubated with roflumilast N-oxide and exposed to CSE. CBF was assessed by digital high speed video microscopy (DHSV). Ciliated cells were characterized by β-tubulin IV staining and analyses of Foxj1 and Dnai2 mRNA and protein (real-time quantitative PCR, Western blotting).

KEY RESULTS

Roflumilast N-oxide concentration-dependently triggered a rapid and persistent increase in CBF and reversed the decrease in CBF following CSE. Long-term incubation of bronchial epithelial cells with CSE resulted in a loss in ciliated cells associated with reduced expression of the ciliated cell markers Foxj1 and Dnai2. The PDE4 inhibitor prevented this loss in the ciliated cell phenotype and the compromised Foxj1 and Dnai2 expression. The enhanced release of IL-13 following CSE, a cytokine that diminishes the proportion of ciliated cells and in parallel, reduces Foxj1 and Dnai2, was reversed by roflumilast N-oxide.

CONCLUSION AND IMPLICATIONS

Roflumilast N-oxide protected differentiated human bronchial epithelial cells from reduced CBF and loss of ciliated cells following CSE.

NOX enzymes: potential target for the treatment of acute lung injury

Acute lung injury (ALI) and its more severe form, acute respiratory distress syndrome (ARDS), is characterized by acute inflammation, disruption of the alveolar-capillary barrier, and in the organizing stage by alveolar pneumocytes hyperplasia and extensive lung fibrosis. The cellular and molecular mechanisms leading to the development of ALI/ARDS are not completely understood, but there is evidence that reactive oxygen species (ROS) generated by inflammatory cells as well as epithelial and endothelial cells are responsible for inflammatory response, lung damage, and abnormal repair. Among all ROS-producing enzymes, the members of NADPH oxidases (NOXs), which are widely expressed in different lung cell types, have been shown to participate in cellular processes involved in the maintenance of lung integrity. It is not surprising that change in NOXs’ expression and function is involved in the development of ALI/ARDS. In this context, the use of NOX inhibitors could be a possible therapeutic perspective in the management of this syndrome. In this article, we summarize the current knowledge concerning some cellular aspects of NOXs localization and function in the lungs, consider their contribution in the development of ALI/ARDS and discuss the place of NOX inhibitors as potential therapeutical target.

A novel method for isolating individual cellular components from the adult human distal lung

A variety of lung diseases, such as pulmonary emphysema and idiopathic pulmonary fibrosis, develop in the lung alveoli. Multiple cell types are localized in the alveoli, including epithelial, mesenchymal, and endothelial cells. These resident cells participate in the pathogenesis of lung disease in various ways. To elaborate clearly on the mechanisms of these pathologic processes, cell type-specific analyses of lung disease are required. However, no method exists for individually isolating the different types of cells found in the alveoli. We report on the development of a FACS-based method for the direct isolation of individual cell types from the adult human distal lung. We obtained human lung tissue from lung resections, and prepared single-cell suspension. After depleting CD45-positive cells, a combination of antibodies against epithelial cell adhesion molecule (EpCAM), T1α, and vascular endothelial (VE)-cadherin as used to delineate alveolar cell types. Alveolar Type II cells were highly purified in the EpCAM(hi)/T1α(-) subset, whereas the EpCAM(+)/T1α(-/low) subset contained a mixed epithelial population consisting of alveolar Type I and bronchiolar epithelial cells. The EpCAM(-)/T1α(-) subset included both microvascular endothelial and mesenchymal cells, and these were separated by immunoreactivity to VE-cadherin. Lymphatic endothelial cells existed in the EpCAM(-)/T1α(hi) subset. Isolated cells were viable, and further cell culture studies could be performed. These results suggest that this novel method enables the isolation of different cellular components from normal and diseased lungs, and is capable of elucidating phenotypes specific to certain alveolar cell types indicative of lung disease.

Fine particulate matter from urban ambient and wildfire sources from California's San Joaquin Valley initiate differential inflammatory, oxidative stress, and xenobiotic responses in human bronchial epithelial cells

Environmental particulate matter (PM) exposure has been correlated with pathogenesis of acute airway inflammatory disease such as asthma and COPD. PM size and concentration have been studied extensively, but the additional effects of particulate components such as biological material, transition metals, and polycyclic aromatic hydrocarbons could also impact initial disease pathogenesis. In this study, we compared urban ambient particulate matter (APM) collected from Fresno, California with wildfire (WF) particulate matter collected from Escalon, California on early transcriptional responses in human bronchial epithelial cells (HBE). Global gene expression profiling of APM treated HBE activated genes related to xenobiotic metabolism (CYP 1B1), endogenous ROS generation and response genes (DUOX1, SOD2, PTGS2) and pro-inflammatory responses associated with asthma or COPD such as IL-1α, IL-1β, IL-8, and CCL20. WF PM treatments also induced a pro-inflammatory gene response, but elicited a more robust xenobiotic metabolism and oxidative stress response. Inhibitor studies targeting endotoxin, ROS, and trace metals, found endotoxin inhibition had modest selective inhibition of inflammation while inhibition of hydrogen peroxide and transition metals had broad effects suggesting additional interactions with xenobiotic metabolism pathways. APM induced a greater inflammatory response while WF PM had more marked metabolism and ROS related responses.

Gene expression profiling reveals upregulated UCA1 and BMF in gallbladder epithelia of children with pancreaticobiliary maljunction

BACKGROUND

Pancreaticobiliary maljunction is usually associated with choledochal cysts and often causes biliary carcinoma; however, the mechanism of carcinogenesis remains unknown. No study has analyzed overall changes in genetic expression beginning during childhood in gallbladder epithelia with pancreaticobiliary maljunction.

PATIENTS AND METHODS

The genomewide expression of gallbladder epithelia was analyzed in 6 children with pancreaticobiliary maljunction and in 4 pediatric controls. Selected genes that were expressed differentially were further analyzed by the real-time reverse transcription-polymerase chain reaction (RT-PCR). The products of upregulated genes confirmed by real-time RT-PCR were immunohistochemically analyzed using gallbladders from 19 children with pancreaticobiliary maljunction, 5 pediatric controls, and 5 children with gallstones.

RESULTS

Microarray analysis identified 188 upregulated and 160 downregulated genes. RT-PCR confirmed upregulation in 5 of 6 genes and downregulation in 1 of 5 genes, including UCA1, DUOX2, DUOXA2, ID1, BMF, and GP2. Immunohistochemistry showed a significantly higher expression of BMF in the pancreaticobiliary maljunction patients than in the controls and gallstone patients.

CONCLUSIONS

This study identified several deregulated genes in the gallbladder of children with pancreaticobiliary maljunction, which may contribute to the pathophysiology. UCA1, a noncoding RNA, is an oncofetal gene, and its upregulation may be important for biliary carcinogenesis. The elevated expression of BMF may function as an apoptotic activator in proliferative gallbladder epithelia.

Increased cytokine response of rhinovirus-infected airway epithelial cells in chronic obstructive pulmonary disease

RATIONALE

Airway inflammation is a central feature of chronic obstructive pulmonary disease (COPD). COPD exacerbations are often triggered by rhinovirus (RV) infection.

OBJECTIVES

We hypothesized that airway epithelial cells from patients with COPD maintain a proinflammatory phenotype compared with control subjects, leading to greater RV responses.

METHODS

Cells were isolated from tracheobronchial tissues of 12 patients with COPD and 10 transplant donors. Eight patients with COPD had severe emphysema, three had mild to moderate emphysema, and one had no emphysema. All had moderate to severe airflow obstruction, and six met criteria for chronic bronchitis or had at least one exacerbation the previous year. Cells were grown at air-liquid interface and infected with RV serotype 39. Cytokine and IFN expression was measured by ELISA. Selected genes involved in inflammation, oxidative stress, and proteolysis were assessed by focused gene array and real-time polymerase chain reaction.

MEASUREMENTS AND MAIN RESULTS

Compared with control subjects, cells from patients with COPD demonstrated increased mRNA expression of genes involved in oxidative stress and the response to viral infection, including NOX1, DUOXA2, MMP12, ICAM1, DDX58/RIG-I, STAT1, and STAT2. COPD cells showed elevated baseline and RV-stimulated protein levels of IL-6, IL-8/CXCL8, and growth-related oncogene-alpha/CXCL1. COPD cells demonstrated increased viral titer and copy number after RV infection, despite increased IL-29/IFN-lambda1, IL-28A/IFN-lambda2, and IFN-inducible protein-10/CXCL10 protein levels. Finally, RV-infected COPD cultures showed increased mRNA expression of IL28A/IFNlambda2, IL29/IFNlambda1, IFIH1/MDA5, DDX58/RIG-I, DUOX1, DUOX2, IRF7, STAT1, and STAT2.

CONCLUSIONS

Airway epithelial cells from patients with COPD show higher baseline levels of cytokine expression and increased susceptibility to RV infection, despite an increased IFN response.

Dual oxidases and hydrogen peroxide in a complex dialogue between host mucosae and bacteria

Among the host defense mechanisms against bacteria, leukocyte phagocytosis leads to their hydrogen peroxide (H(2)O(2))-mediated destruction. The recent discovery of dual oxidase (DUOX)-dependent H(2)O(2) generation associated with peroxidase and thiocyanate secretion at the apex of mucosal cells has been similarly interpreted as a killing mechanism. However, the rapid degradation of H(2)O(2) would be expected to reduce the efficiency of this system. It has been demonstrated that H(2)O(2) acts as a chemorepellent for bacteria, and such an effect might be sufficient to block cellular infection. Therefore, H(2)O(2) generation might represent one of the mechanisms that allows the coexistence of mucosae with potentially harmful bacteria. Here, we discuss the possible role of DUOXes and H(2)O(2) in interactions between host mucosae and bacteria to maintain mucosal homeostasis.

NOX enzymes and pulmonary disease

The primary function of the lung is to facilitate the transfer of molecular oxygen (O(2); dioxygen) from the atmosphere to the systemic circulation. In addition to its essential role in aerobic metabolism, O(2) serves as the physiologic terminal acceptor of electron transfer catalyzed by the NADPH oxidase (NOX) family of oxidoreductases. The evolution of the lungs and circulatory systems in vertebrates was accompanied by increasing diversification of NOX family enzymes, suggesting adaptive roles for NOX-derived reactive oxygen species in normal physiology. However, this adaptation may paradoxically carry detrimental consequences in the setting of overwhelming/persistent environmental stressors, both infectious and noninfectious, and during the process of aging. Here, we review current understanding of NOX enzymes in normal lung physiology and their pathophysiologic roles in a number of pulmonary diseases, including lung infections, acute lung injury, pulmonary arterial hypertension, obstructive lung disorders, fibrotic lung disease, and lung cancer.

Bibliography. Current world literature

This bibliography is compiled by clinicians from the journals listed at the end of this publication. It is based on literature entered into our database between 1 November 2007 and 31 October 2008 (articles are generally added to the database about two and a half months after publication). In addition, the bibliography contains every paper annotated by reviewers; these references were obtained from a variety of bibliographic databases and published between the beginning of the review period and the time of going to press. The bibliography has been grouped into topics that relate to the reviews in this issue.

Trachea epithelium as a "canary" for cigarette smoking-induced biologic phenotype of the small airway epithelium

The initial site of smoking-induced lung disease is the small airway epithelium, which is difficult and time consuming to sample by fiberoptic bronchoscopy. We developed a rapid, office-based procedure to obtain trachea epithelium without conscious sedation from healthy nonsmokers (n= 26) and healthy smokers (n= 19, 27 +/- 15 pack-year). Gene expression differences (fold change >1.5, p < 0.01, Benjamini-Hochberg correction) were assessed with Affymetrix microarrays. A total of 1,057 probe sets were differentially expressed in healthy smokers versus nonsmokers, representing >500 genes. Trachea gene expression was compared to an independent group of small airway epithelial samples (n= 23 healthy nonsmokers, n= 19 healthy smokers, 25 +/- 12 pack-year). The trachea epithelium is more sensitive to smoking, responding with threefold more differentially expressed genes than small airway epithelium. The trachea transcriptome paralleled the small airway epithelium, with 156 of 167 (93%) genes that are significantly up- and downregulated by smoking in the small airway epithelium showing similar direction and magnitude of response to smoking in the trachea. Trachea epithelium can be obtained without conscious sedation, representing a less invasive surrogate "canary" for smoking-induced changes in the small airway epithelium. This should prove useful in epidemiologic studies correlating gene expression with clinical outcome in assessing smoking-induced lung disease.

Heterodimerization controls localization of Duox-DuoxA NADPH oxidases in airway cells

Duox NADPH oxidases generate hydrogen peroxide at the air-liquid interface of the respiratory tract and at apical membranes of thyroid follicular cells. Inactivating mutations of Duox2 have been linked to congenital hypothyroidism, and epigenetic silencing of Duox is frequently observed in lung cancer. To study Duox regulation by maturation factors in detail, its association with these factors, differential use of subunits and localization was analyzed in a lung cancer cell line and undifferentiated or polarized lung epithelial cells. We show here that Duox proteins form functional heterodimers with their respective DuoxA subunits, in close analogy to the phagocyte NADPH oxidase. Characterization of novel DuoxA1 isoforms and mispaired Duox-DuoxA complexes revealed that heterodimerization is a prerequisite for reactive oxygen species production. Functional Duox1 and Duox2 localize to the leading edge of migrating cells, augmenting motility and wound healing. DuoxA subunits are responsible for targeting functional oxidases to distinct cellular compartments in lung epithelial cells, including Duox2 expression in ciliated cells in an ex vivo differentiated lung epithelium. As these locations probably define signaling specificity of Duox1 versus Duox2, these findings will facilitate monitoring Duox isoform expression in lung disease, a first step for early screening procedures and rational drug development.

ATP-mediated activation of the NADPH oxidase DUOX1 mediates airway epithelial responses to bacterial stimuli

Activation of the NADPH oxidase homolog dual oxidase 1 (DUOX1) within the airway epithelium represents a key mechanism of innate airway host defense, through enhanced production of H2O2, which mediates cellular signaling pathways that regulate the production of various inflammatory mediators. Production of the CXC chemokine interleukin (IL)-8/CXCL8 forms a common epithelial response to many diverse stimuli, including bacterial and viral triggers, environmental oxidants, and other biological mediators, suggesting the potential involvement of a common signaling pathway that may involve DUOX1-dependent H2O2 production. Following previous reports showing that DUOX1 is activated by extracellular ATP and purinergic receptor stimulation, this study demonstrates that airway epithelial IL-8 production in response to several bacterial stimuli involves ATP release and DUOX1 activation. ATP-mediated DUOX1 activation resulted in the activation of ERK1/2 and NF-kappaB pathways, which was associated with epidermal growth factor receptor (EGFR) ligand shedding by ADAM17 (a disintegrin and metalloproteinase-17). Although ATP-mediated ADAM17 activation and IL-8 release were not prevented by extracellular H2O2 scavenging by catalase, these responses were attenuated by intracellular scavengers of H2O2 or related oxidants, suggesting an intracellular redox signaling mechanism. Both ADAM17 activation and IL-8 release were suppressed by inhibitors of EGFR/ERK1/2 signaling, which can regulate ADAM17 activity by serine/threonine phosphorylation. Collectively, our results indicate that ATP-mediated DUOX1 activation represents a common response mechanism to several environmental stimuli, involving H2O2-dependent EGFR/ERK activation, ADAM17 activation, and EGFR ligand shedding, leading to amplified epithelial EGFR activation and IL-8 production.

Influence of ozone on traffic-related particulate matter on the generation of hydroxyl radicals through a heterogeneous synergistic effect

Epidemiologic studies suggest that ozone (O(3)) and airborne particulate matter (PM) can interact causing acute respiratory inflammation and other respiratory diseases. Recent studies investigated the hypothesis that the effects of air pollution caused by O(3) and PM are larger than the effect of these two pollutants individually. We investigated the hypothesis that ozone and traffic-related PM (PM(10) and PM(2.5), diesel and gasoline exhaust particles) interact synergistically to produce increasing amounts of highly reactive hydroxyl radicals (HO) in a heterogeneous aqueous mixture at physiological pH. Electron paramagnetic resonance (EPR) and spin trapping were used for the measurements. Results showed that HO radicals are generated by the catalytic action of PM surface area with ozone and that EPR peak intensities are two to three times higher compared to PM samples without ozone. Incubation of the nucleoside 2'-deoxyguanosine (dG) in aqueous mixtures of ozone and PM at pH 7.4 resulted in the hydroxylation at C(8) position of dG. The formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) showed a 2-2.5-fold increase over control (PM without O(3)). These results suggest that PM and O(3) act synergistically generating a sustained production of reactive HO radicals. Partitioning of O(3) into the particle phase depends on the concentration, hygroscopicity and particle size.

Membrane compartments and purinergic signalling: occurrence and function of P2X receptors in lung

P2X receptors are cation-selective ion channels activated by extracellular ATP. They form homo- and heterotrimeric complexes that differ in their functional properties and subcellular localization. These membrane ion channels are also expressed in pulmonary epithelial cells. Recent work indicates that alveolar epithelial type I cells selectively express P2X(4) and P2X(7) receptor subtypes in addition to a large number of other ion channels present in the alveolar epithelium. Up- or downregulation of their expression is associated with several disease states. This minireview analyses the role of P2X receptors and of extracellular ATP and adenosine in lung disease, the relationship of P2X receptors to other ion channels in the alveolar epithelium and their distribution in lipid rafts/caveolae.

Redox-based therapeutics for lung diseases

Because oxidative stress is such a common factor of lung diseases, we cannot help asking why so many diseases are caused by the same oxidative stress. It is likely to be a consequence of diversity in sources and location of oxidative stress, and concomitant factors. The aim of this forum is to characterize the disease-specific involvement of oxidative stress and to make use of it for therapeutics. It is also of note that oxidative-stress biomarkers are useful tools for disease management. Exhaled nitric oxide has been established as a marker of bronchial asthma in clinical practice. By using recent noninvasive techniques, such as exhaled breath condensate, other markers of lipid peroxidation or antioxidants are now under evaluation. Antioxidant therapy, as represented by N-acetylcysteine, has widely been tested as a treatment for lung disorders, but it has had limited success in clinical practice. The clinical outcome might be improved by combination therapy or better patient selection. Novel antioxidant drugs are also under investigation. Molecular targeted therapy against redox-sensitive signaling pathways could be an alternative therapeutic approach. Moreover, disease-specific pathways have been identified whose regulation could be more efficient and less toxic than regulating universal pathways.