Up-regulation of heme oxygenase-I in alveolar macrophages of newly diagnosed asthmatics

Regional variations in allergen-induced airway inflammation correspond to changes in soluble guanylyl cyclase heme and expression of heme oxygenase-1

Asthma is characterized by airway remodeling and hyperreactivity. Our earlier studies determined that the nitric oxide (NO)-soluble guanylyl cyclase (sGC)-cGMP pathway plays a significant role in human lung bronchodilation. However, this bronchodilation is dysfunctional in asthma due to high NO levels, which cause sGC to become heme-free and desensitized to its natural activator, NO. In order to determine how asthma impacts the various lung segments/lobes, we mapped the inflammatory regions of lungs to determine whether such regions coincided with molecular signatures of sGC dysfunction. We demonstrate using murine models of asthma (OVA and CFA/HDM) that the inflamed segments of these murine lungs can be tracked by upregulated expression of HO1 and these regions in turn overlap with regions of heme-free sGC as evidenced by a decreased sGC-α1β1 heterodimer and an increased response to heme-independent sGC activator, BAY 60-2770, relative to naïve uninflamed regions. We also find that NO generated from iNOS upregulation in the inflamed segments has a higher impact on developing heme-free sGC as increasing iNOS activity correlates linearly with elevated heme-independent sGC activation. This excess NO works by affecting the epithelial lung hemoglobin (Hb) to become heme-free in asthma, thereby causing the Hb to lose its NO scavenging function and exposing the underlying smooth muscle sGC to excess NO, which in turn becomes heme-free. Recognition of these specific lung segments enhances our understanding of the inflamed lungs in asthma with the ultimate aim to evaluate potential therapies and suggest that regional and not global inflammation impacts lung function in asthma.

Unveiling the potent effect of vitamin D: harnessing Nrf2/HO-1 signaling pathways as molecular targets to alleviate urban particulate matter-induced asthma inflammation

BACKGROUND

Asthma is the most common allergic disease characterized by an inflammatory response in the airways. Mechanismly, urban particulate matter (PM) is the most widely air pollutant associated with increased asthma morbidity and airway inflammation. Current research found that vitamin D is an essential vitamin with anti-inflammatory, antioxidant and other medical efficacy. Inadequate or deficient vitamin D often leads to the pathogenesis and stability of asthma. NGF exacerbates airway inflammation in asthma by promoting smooth muscle cell proliferation and inducing the Th2 immune response. Activation of the Nrf2/HO-1 signaling pathway can exert a protective effect on the inflammatory response in bronchial asthma. However, the specific mechanism of this pathway in PM-involved asthmatic airway smooth muscle cells remains unclear.

METHODS

Mice were sensitized and challenged with Ovalbumin (OVA) to establish an asthma model. They were then exposed to either PM, vitamin D or a combination of both, and inflammatory responses were observed. Including, acetylcholine stimulation at different concentrations measured airway hyperresponsiveness in mice. Bronchoalveolar lavage fluid (BALF) and serum were collected for TNF-α, IL-1β, IL-6, and Nerve growth factor (NGF) analysis. Additionally, lung tissues underwent histopathological examination to observe alveolar structure and inflammatory cell infiltration. Specific ELISA kits were utilized to determine the levels of the inflammatory factors TNF-α, IL-1β, IL-6, and Nerve growth factor (NGF). Nrf2/HO-1 signaling pathways were examined by western blot analysis. Meanwhile, we constructed a cell system with low HO-1 expression by lentiviral transfection of airway smooth muscle cells. The changes of Nrf2, HO-1, and NGF were observed after the treatment of OVA, PM, and Vit D were given.

RESULTS

The in vivo results showed that vitamin D significantly alleviated pathological changes in lung tissue of PM-exposed mice models. Mechanismly, vitamin D decreased substantial inflammatory cell infiltration in lung tissue, as well as the number of inflammatory cells in BALF. Furthermore, vitamin D reduced the heightened inflammatory factors including of TNF-α, IL-1β, IL-6, and NGF caused by PM exposure, and triggered the activity of nucleus Nrf2 and HO-1 in PM-exposed asthmatic mice. Notably, knockdown HO-1 weakens the Vitamin D- mediated inhibition to pollution toxicity in asthma. Importantly, in vitro experiments on OVA-stimulated mice airway smooth muscle cells, the results showed that OVA and PM, respectively, reduced Nrf2/HO-1 and increased NGF's expression, while vitamin D reversed the process. And in the HO-1 knockdown cell line of Lenti-si-HO-1 ASMCs, OVA and PM reduced Nrf2's expression, while HO-1 and NGF's expression were unchanged.

CONCLUSIONS

The above results demastrate that vitamin D downregulated the inflammatory response and the expression of NGF by regulating the Nrf2/HO-1 signaling pathways in airway smooth muscle cells, thereby showing potent anti-inflammatory activity in asthma.

Heterogeneous Oxidation Products of Fine Particulate Isoprene Epoxydiol-Derived Methyltetrol Sulfates Increase Oxidative Stress and Inflammatory Gene Responses in Human Lung Cells

Hydroxyl radical (·OH)-initiated oxidation of isoprene, the most abundant nonmethane hydrocarbon in the atmosphere, is responsible for substantial amounts of secondary organic aerosol (SOA) within ambient fine particles. Fine particulate 2-methyltetrol sulfate diastereoisomers (2-MTSs) are abundant SOA products formed via acid-catalyzed multiphase chemistry of isoprene-derived epoxydiols with inorganic sulfate aerosols under low-nitric oxide conditions. We recently demonstrated that heterogeneous ·OH oxidation of particulate 2-MTSs leads to the particle-phase formation of multifunctional organosulfates (OSs). However, it remains uncertain if atmospheric chemical aging of particulate 2-MTSs induces toxic effects within human lung cells. We show that inhibitory concentration-50 (IC50) values decreased from exposure to fine particulate 2-MTSs that were heterogeneously aged for 0 to 22 days by ·OH, indicating increased particulate toxicity in BEAS-2B lung cells. Lung cells further exhibited concentration-dependent modulation of oxidative stress- and inflammatory-related gene expression. Principal component analysis was carried out on the chemical mixtures and revealed positive correlations between exposure to aged multifunctional OSs and altered expression of targeted genes. Exposure to particulate 2-MTSs alone was associated with an altered expression of antireactive oxygen species (ROS)-related genes (NQO-1, SOD-2, and CAT) indicative of a response to ROS in the cells. Increased aging of particulate 2-MTSs by ·OH exposure was associated with an increased expression of glutathione pathway-related genes (GCLM and GCLC) and an anti-inflammatory gene (IL-10).

Network-based integrated analysis for toxic effects of high-concentration formaldehyde inhalation exposure through the toxicogenomic approach

Formaldehyde is a colorless, pungent, highly reactive, and toxic environmental pollutant used in various industries and products. Inhaled formaldehyde is a human and animal carcinogen that causes genotoxicity, such as reactive oxygen species formation and DNA damage. This study aimed to identify the toxic effects of inhaled formaldehyde through an integrated toxicogenomic approach utilizing database information. Microarray datasets (GSE7002 and GSE23179) were collected from the Gene Expression Omnibus database, and differentially expressed genes were identified. The network analyses led to the construction of the respiratory system-related biological network associated with formaldehyde exposure, and six upregulated hub genes (AREG, CXCL2, HMOX1, PLAUR, PTGS2, and TIMP1) were identified. The expression levels of these genes were verified via qRT-PCR in 3D reconstructed human airway tissues exposed to aerosolized formaldehyde. Furthermore, NRARP was newly found as a potential gene associated with the respiratory and carcinogenic effects of formaldehyde by comparison with human in vivo and in vitro formaldehyde-exposure data. This study improves the understanding of the toxic mechanism of formaldehyde and suggests a more applicable analytic pipeline for predicting the toxic effects of inhaled toxicants.

Immune Regulation of Heme Oxygenase-1 in Allergic Airway Inflammation

Heme oxygenase-1 (HO-1) is not only a rate-limiting enzyme in heme metabolism but is also regarded as a protective protein with an immunoregulation role in asthmatic airway inflammation. HO-1 exerts an anti-inflammation role in different stages of airway inflammation via regulating various immune cells, such as dendritic cells, mast cells, basophils, T cells, and macrophages. In addition, the immunoregulation role of HO-1 may differ according to subcellular locations.

Chinese Herbs and Repurposing Old Drugs as Therapeutic Agents in the Regulation of Oxidative Stress and Inflammation in Pulmonary Diseases

Several pro-inflammatory factors and proteins have been characterized that are involved in the pathogenesis of inflammatory diseases, including acute respiratory distress syndrome, chronic obstructive pulmonary disease, and asthma, induced by oxidative stress, cytokines, bacterial toxins, and viruses. Reactive oxygen species (ROS) act as secondary messengers and are products of normal cellular metabolism. Under physiological conditions, ROS protect cells against oxidative stress through the maintenance of cellular redox homeostasis, which is important for proliferation, viability, cell activation, and organ function. However, overproduction of ROS is most frequently due to excessive stimulation of either the mitochondrial electron transport chain and xanthine oxidase or reduced nicotinamide adenine dinucleotide phosphate (NADPH) by pro-inflammatory cytokines, such as interleukin-1β and tumor necrosis factor α. NADPH oxidase activation and ROS overproduction could further induce numerous inflammatory target proteins that are potentially mediated via Nox/ROS-related transcription factors triggered by various intracellular signaling pathways. Thus, oxidative stress is considered important in pulmonary inflammatory processes. Previous studies have demonstrated that redox signals can induce pulmonary inflammatory diseases. Thus, therapeutic strategies directly targeting oxidative stress may be effective for pulmonary inflammatory diseases. Therefore, drugs with anti-inflammatory and anti-oxidative properties may be beneficial to these diseases. Recent studies have suggested that traditional Chinese medicines, statins, and peroxisome proliferation-activated receptor agonists could modulate inflammation-related signaling processes and may be beneficial for pulmonary inflammatory diseases. In particular, several herbal medicines have attracted attention for the management of pulmonary inflammatory diseases. Therefore, we reviewed the pharmacological effects of these drugs to dissect how they induce host defense mechanisms against oxidative injury to combat pulmonary inflammation. Moreover, the cytotoxicity of oxidative stress and apoptotic cell death can be protected via the induction of HO-1 by these drugs. The main objective of this review is to focus on Chinese herbs and old drugs to develop anti-inflammatory drugs able to induce HO-1 expression for the management of pulmonary inflammatory diseases.

Macrophage metabolic reprogramming during chronic lung disease

Airway macrophages (AMs) play key roles in the maintenance of lung immune tolerance. Tissue tailored, highly specialised and strategically positioned, AMs are critical sentinels of lung homoeostasis. In the last decade, there has been a revolution in our understanding of how metabolism underlies key macrophage functions. While these initial observations were made during steady state or using in vitro polarised macrophages, recent studies have indicated that during many chronic lung diseases (CLDs), AMs adapt their metabolic profile to fit their local niche. By generating reactive oxygen species (ROS) for pathogen defence, utilising aerobic glycolysis to rapidly generate cytokines, and employing mitochondrial respiration to fuel inflammatory responses, AMs utilise metabolic reprogramming for host defence, although these changes may also support chronic pathology. This review focuses on how metabolic alterations underlie AM phenotype and function during CLDs. Particular emphasis is given to how our new understanding of AM metabolic plasticity may be exploited to develop AM-focused therapies.

Dose-dependent relationship between prenatal exposure to fine particulates and exhaled carbon monoxide in non-asthmatic children. A population-based birth cohort study

OBJECTIVES

The main goal of the study was to assess possible association between fetal exposure to fine particulate matter (PM2.5) and exhaled carbon monoxide (eCO) measured in non-asthmatic children.

MATERIAL AND METHODS

The subjects include 118 children taking part in an ongoing population-based birth cohort study in Kraków. Personal samplers of PM2.5 were used to measure fine particle mass in the fetal period and carbon monoxide (CO) in exhaled breath from a single exhalation effort at the age of 7. In the statistical analysis of the effect of prenatal PM2.5 exposure on eCO, a set of potential confounders, such as environmental tobacco smoke (ETS), city residence area, sensitization to house dust allergens and the occurrence of respiratory symptoms monitored over the seven-year follow-up was considered.

RESULTS

The level of eCO did not correlate with the self-reported ETS exposure recorded over the follow-up, however, there was a positive significant relationship with the prenatal PM2.5 exposure (non-parametric trend p = 0.042). The eCO mean level was higher in atopic children (geometric mean = 2.06 ppm, 95% CI: 1.58-2.66 ppm) than in non-atopic ones (geometric mean = 1.57 ppm, 95% CI: 1.47-1.73 ppm) and the difference was statistically significant (p = 0.036). As for the respiratory symptoms, eCO values were associated positively only with the cough severity score recorded in the follow-up (nonparametric trend p = 0.057). In the nested multivariable linear regression model, only the effects of prenatal PM2.5 and cough severity recorded in the follow-up were related to eCO level. The prenatal PM2.5 exposure represented 5.1%, while children's cough represented only 2.6% of the eCO variability.

CONCLUSION

Our study suggests that elevated eCO in non-asthmatic children may result from oxidative stress experienced in the fetal period and that heme oxygenase (HO) activity in body tissues may be programmed in the fetal period by the exposure to fine particulate matter.

Vasculoprotective effects of heme oxygenase-1 in a murine model of hyperoxia-induced bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is characterized by simplified alveolarization and arrested vascular development of the lung with associated evidence of endothelial dysfunction, inflammation, increased oxidative damage, and iron deposition. Heme oxygenase-1 (HO-1) has been reported to be protective in the pathogenesis of diseases of inflammatory and oxidative etiology. Because HO-1 is involved in the response to oxidative stress produced by hyperoxia and is critical for cellular heme and iron homeostasis, it could play a protective role in BPD. Therefore, we investigated the effect of HO-1 in hyperoxia-induced lung injury using a neonatal transgenic mouse model with constitutive lung-specific HO-1 overexpression. Hyperoxia triggered an increase in pulmonary inflammation, arterial remodeling, and right ventricular hypertrophy that was attenuated by HO-1 overexpression. In addition, hyperoxia led to pulmonary edema, hemosiderosis, and a decrease in blood vessel number, all of which were markedly improved in HO-1 overexpressing mice. The protective vascular response may be mediated at least in part by carbon monoxide, due to its anti-inflammatory, antiproliferative, and antiapoptotic properties. HO-1 overexpression, however, did not prevent alveolar simplification nor altered the levels of ferritin and lactoferrin, proteins involved in iron binding and transport. Thus the protective mechanisms elicited by HO-1 overexpression primarily preserve vascular growth and barrier function through iron-independent, antioxidant, and anti-inflammatory pathways.

Exhaled carbon monoxide in airway diseases: from research findings to clinical relevance

Breath tests have gained increasing interest in recent years mainly driven by the unmet clinical need to monitor airway diseases and to obtain information of unravelled aspects of respiratory disorders. Carbon monoxide is present in the exhaled breath and has been suggested to reflect ongoing oxidative stress, even if there are some confounding factors limiting its clinical usefulness. Increased concentration of exhaled carbon monoxide has been demonstrated in different acute and chronic airway diseases including allergic rhinitis, asthma, bronchiectasis, and post transplant bronchiolitis obliterans syndrome. Although exhaled carbon monoxide might not prove as a clinically useful biomarker of airway diseases, its measurement has helped to understand the place of heme oxygenase activity in allergic and non-allergic airway diseases. The scope of this review is the exciting field of exhaled carbon monoxide in airway diseases.

Exhaled carbon monoxide in asthmatics: a meta-analysis

Background

The non-invasive assessment of airway inflammation is potentially advantageous in asthma management. Exhaled carbon monoxide (eCO) measurement is cheap and has been proposed to reflect airway inflammation and oxidative stress but current data are conflicting. The purpose of this meta-analysis is to determine whether eCO is elevated in asthmatics, is regulated by steroid treatment and reflects disease severity and control.

Methods

A systematic search for English language articles published between 1997 and 2009 was performed using Medline, Embase and Cochrane databases. Observational studies comparing eCO in non-smoking asthmatics and healthy subjects or asthmatics before and after steroid treatment were included. Data were independently extracted by two investigators and analyzed to generate weighted mean differences using either a fixed or random effects meta-analysis depending upon the degree of heterogeneity.

Results

18 studies were included in the meta-analysis. The eCO level was significantly higher in asthmatics as compared to healthy subjects and in intermittent asthma as compared to persistent asthma. However, eCO could not distinguish between steroid-treated asthmatics and steroid-free patients nor separate controlled and partly-controlled asthma from uncontrolled asthma in cross-sectional studies. In contrast, eCO was significantly reduced following a course of corticosteroid treatment.

Conclusions

eCO is elevated in asthmatics but levels only partially reflect disease severity and control. eCO might be a potentially useful non-invasive biomarker of airway inflammation and oxidative stress in nonsmoking asthmatics.

Exhaled carbon monoxide in asthmatic adults with bronchial reactivity: a prospective study

HYPOTHESIS

We hypothesized that eCO may permit non-invasive assessment of disease activity in adults with asthma and bronchial reactivity.

METHODS

A total of 209 participants 18 to 65 years of age with a diagnosis of asthma and bronchial reactivity provided data for analysis. The association between eCO and bronchial reactivity, forced expiratory volume in one second (FEV(1)), forced vital capacity (FVC), peak expiratory flow rate measurements (PEFR), asthma symptoms score, and bronchodilator use cross-sectionally and within-subject change in eCO were analyzed in relation to change in these variables over 6 weeks.

RESULTS

There was no difference in eCO in those who were taking inhaled corticosteroids and those who were not (p = 0.33). There was also no cross-sectional or within-in subject association between eCO and bronchial reactivity, FEV(1), FVC, PEFR, symptoms score, or bronchodilator use.

CONCLUSIONS

In a population of adults with bronchial reactivity, eCO has no or very limited potential as a biomarker of asthma activity.

Carbon Monoxide: Vascular Therapeutic for the Future

In the past decade, carbon monoxide has lost its reputation as a toxic gas and has gained a following of scientists who now appreciate its potential therapeutic utility as an anti-inflammatory and cytoprotective agent. Its vasoprotective properties have also gained a tremendous amount of attention, especially its ability to inhibit intimal hyperplasia. This review will provide a historical perspective of carbon monoxide biology and summarize its function in disease modulation with a special focus on its potential role as a vascular therapeutic.

Possible contribution of endogenous carbon monoxide to the development of allergic rhinitis in guinea pigs

BACKGROUND

The mechanisms responsible for the development of allergic rhinitis(AR) are not fully understood. The present study was designed to explore the possible roles of carbon monoxide(CO) on the pathogenesis of AR.

METHODS

AR guinea pig model was established by nasal ovalbumin sensitization. Twenty-four AR guinea pigs were divided into four groups, 6 in each: Saline control group, AR sensitized group, Hemin treated group, and Zinc protoporphyrin (ZnPP) treated group. The frequency of sneezing and nose rubbing was recorded. Leukocyte infiltration in nasal lavage fluid, serum IgE level and plasma CO were measured. Expression of heme oxygenase-1 (HO-1) mRNA in nasal mucosa was determined by real time RT-PCR, and expression of HO-1 protein was detected by immunohistochemistry.

RESULTS

The frequency of sneezing and nose rubbing, leukocyte infiltration, serum IgE, plasma CO, and HO-1 mRNA levels in sensitized guinea pigs were higher than those of control (P < 0.05). Except for serum IgE level, all above parameters were even higher (P < 0.05) when treated with Hemin, a heme oxygenase-1 inducer; but significantly decreased (P < 0.05) when treated with ZnPP, a heme oxygenase inhibitor. Immunohistochemical results showed that positive staining of HO-1 was present in the lamina of mucosa of sensitized guinea pigs, and there was an increase of HO-1 immunoreactivity with Hemin administration (P < 0.05) and a decrease with ZnPP treatment.

CONCLUSION

The endogenous CO may take part in the inflammation process of AR and is positively correlated with expression of HO-1 in nasal mucosa. Endogenous CO plays a significant role in the pathogenesis of AR.

Exhaled carbon monoxide levels: as a marker of clinical severity and control of asthma

A study was conducted to evaluate the role of exhaled carbon monoxide (CO) levels in the management of patients with mild and moderate persistent bronchial asthma. Spirometry, exhaled CO measurements and symptom scoring was done before and after four weeks of treatment with inhaled corticosteroids. Exhaled CO levels were significantly elevated in patients of mild as well as moderate persistent asthma as compared to controls but the levels did not correlate with the disease severity. After four weeks of treatment, there was a decrease in exhaled CO levels in both the groups but the decrease was not found to be statistically significant. Therefore, clinically exhaled CO level is not a useful marker in bronchial asthma.

Oxidant-antioxidant imbalance as a potential contributor to the progression of human pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is the most common idiopathic interstitial pneumonia. IPF is a disease with poor prognosis and an aggressive nature, and poses major challenges to clinicians. Thus, a large part of research in the area has focused on the pathogenesis on IPF. Characteristic features in IPF include fibrotic lesions devoid of inflammatory cell infiltrates. There are experimental models of lung fibrosis (e.g., bleomycin-induced fibrosis), but they typically contain a prominent inflammatory pattern in the lung, which leads to relatively diffuse lung fibrosis. Nonetheless, experimental models have provided important information about the progression and pathways contributing to the lung fibrosis, including activation of transforming growth factor beta (TGF-beta). Both patient material and experimental models of lung fibrosis have displayed marked elevation of several markers of oxidant burden and signs for disturbed antioxidant/oxidant balance. Several studies also suggest that reactive oxygen species can cause activation of growth-regulatory cytokines, including TGF-beta. In addition, there are indications that endogenous and exogenous antioxidants/redox modulators can influence fibrogenesis, protect the lung against fibrosis, and prevent its progression. Factors that restore the antioxidant capacity and prevent sustained activation of growth-regulatory cytokines may have a therapeutic role in IPF.

Gene expression profiling of in vitro cultured macrophages after exposure to the respiratory sensitizer hexamethylene diisocyanate

Occupational exposure to chemicals is one of the main causes of respiratory allergy and asthma. Identification of chemicals that trigger allergic asthma is difficult as underlying processes and specific markers have not yet been clearly defined. Moreover, adequate classification of the respiratory toxicity of chemicals is hampered due to the lack of validated in vivo and in vitro test methods. The study of differential gene expression profiles in appropriate human in vitro cell systems is a promising approach to identify selective markers for respiratory allergy. As alveolar macrophages display important immunological and inflammatory properties in response to foreign substances in the lung, we aimed at gaining more insight in changes of human macrophages transcriptome and to identify selective genetic markers for respiratory sensitization in response to hexamethylene diisocyanate (HDI). In vitro cultures of human THP-1 cells were differentiated into macrophages and exposed to 55 microg/ml HDI for 6 and 10h. Using human oligonucleotide microarrays, changes were observed in the expression of genes that are involved in diverse biological and molecular processes, including detoxification, oxidative stress, cytokine signaling, and apoptosis, which can lead to the development of asthma. These genes are possible markers for respiratory sensitization caused by isocyanates.

Immunolocalisation of heme oxygenase isoforms in human nasal polyps

BACKGROUND

Carbon monoxide is an endogenous vasodilator gas produced by the enzyme heme oxygenase (HO). HO is expressed in human nasal mucosa, but its pathophysiological role in nasal inflammatory diseases is not fully understood. The aim of this study was to detect and compare the expression of HO-1 and -2 isoforms in nasal polyps with normal nasal mucosa.

METHODS

Immunohistochemical analysis using antibodies specific for HO-1 and -2 was conducted on nasal polyps from nine patients with allergic nasal polyposis, and on normal nasal mucosa from six controls.

RESULTS

Intense HO-1 immunoreactivity was observed in nasal polyp epithelium but was absent in normal nasal mucosa. HO-2 staining was observed in respiratory epithelium, vascular endothelium and seromucous glands, with no difference observed between nasal polyps and normal nasal mucosa.

CONCLUSIONS

HO-1 expression is up-regulated in nasal polyp epithelium, supporting the theory that respiratory epithelium plays a role in the pathogenesis of nasal polyposis.

Airway biomarkers of the oxidant burden in asthma and chronic obstructive pulmonary disease: current and future perspectives

The pathogenesis of asthma and chronic obstructive pulmonary disease (COPD) has been claimed to be attributable to increased systemic and local oxidative stress. Detection of the oxidant burden and evaluation of their progression and phenotypes by oxidant biomarkers have proved challenging and difficult. A large number of asthmatics are cigarette smokers and smoke itself contains oxidants complicating further the use of oxidant biomarkers. One of the most widely used oxidant markers in asthma is exhaled nitric oxide (NO), which plays an important role in the pathogenesis of asthma and disease monitoring. Another oxidant marker that has been widely investigated in COPD is 8-isoprostane, but it is probably not capable of differentiating asthma from COPD, or even sensitive in the early assessment of these diseases. None of the current biomarkers have been shown to be better than exhaled NO in asthma. There is a need to identify new biomarkers for obstructive airway diseases, especially their differential diagnosis. A comprehensive evaluation of oxidant markers and their combinations will be presented in this review. In brief, it seems that additional analyses utilizing powerful tools such as genomics, metabolomics, lipidomics, and proteomics will be required to improve the specificity and sensitivity of the next generation of biomarkers.

Exhaled nitric oxide and carbon monoxide in respiratory diseases

Breath tests have gained increasing interest in recent years mainly driven by the unmet clinical need to monitor airway diseases and to obtain information on unravelled aspects of respiratory disorders. A prototype of such measurement reaching clinical significance besides its use as a research tool is the measurement of exhaled nitric oxide (NO). It took hardly more than a decade after the discovery that exhaled breath contains NO for this measurement to be approved for clinical practice to monitor anti-inflammatory treatment in asthma. Recent studies demonstrate that using exhaled NO measurement to guide anti-inflammatory treatment in asthma may help clinical decision making. A similarly small molecule present in exhaled breath is carbon monoxide, which is not only a biomarker of cigarette smoking but has also been suggested to reflect ongoing oxidative stress/antioxidant defense. The scope of this review is the exciting field of exhaled monoxides. Since several other biomarkers have also been studied in the exhaled breath this review will provide a brief introduction to them.

Exhaled carbon monoxide as a biomarker of inflammatory lung disease

Carbon monoxide (CO) can be detected on the exhaled breath of humans. Exhaled CO (E-CO) originates from the inspiration of ambient CO and from endogenous metabolic sources that include heme metabolism catalyzed by heme oxygenase (HO) enzymes. HO occurs in both constitutive (HO-2) and inducible (HO-1) forms; the latter responds to pro-inflammatory or pro-oxidative stimuli. E-CO may arise in the airways from inducible HO-1 activity in the bronchial epithelium, alveolar macrophages and other lung cell types, as a consequence of local inflammation, and from the alveolae in equilibrium with carboxyhemoglobin (Hb-CO) in the pulmonary circulation. Elevations in Hb-CO in turn may reflect increases in ambient CO, as well as increased HO activity in systemic tissues. E-CO increases dramatically in active smokers and can be used to monitor the smoking habit. Elevations in E-CO have been observed in critically ill or post-surgical patients and those with various pulmonary diseases associated with inflammation, including chronic obstructive pulmonary disease (COPD), asthma, cystic fibrosis and infections. Despite improvements in the standardization and sensitivity of methods to detect E-CO, the predictive value of this measurement as a diagnostic tool remains unclear.

Protective functions of heme oxygenase-1 and carbon monoxide in the respiratory system

The respiratory system, including the lung and upper airways, succumbs to injury and disease through acute or chronic exposures to adverse environmental agents, in particular, those that promote increased oxidative or inflammatory processes. Cigarette smoke and other forms of particulate or gaseous air pollution, allergens, microorganisms infections, and changes in inspired oxygen may contribute to lung injury. Among the intrinsic defenses of the lung, the stress protein heme oxygenase-1 constitutes an inducible defense mechanism that can protect the lung and its constituent cells against such insults. Heme oxygenases degrade heme to biliverdin-IXalpha, carbon monoxide, and iron, each with candidate roles in cytoprotection. At low concentrations, carbon monoxide can confer similar cyto and tissue-protective effects as endogenous heme oxygenase-1 expression, involving antioxidative, antiinflammatory, antiproliferative, and antiapoptotic effects. Lung protection by heme oxygenase-1 or its enzymatic reaction products has been demonstrated in vitro and in vivo in a number of pulmonary disease models, including acute lung injury, cigarette smoke-induced lung injury/chronic obstructive pulmonary disease, interstitial lung diseases, ischemia/reperfusion injury, and asthma/airway inflammation. This review summarizes recent findings on the functions of heme oxygenase-1 in the respiratory system, with an emphasis on possible roles in disease progression and therapies.

Heme oxygenase-1 inhibits cytokine production by activated mast cells

Heme oxygenase-1 (HO-1) is thought to contribute to host defense reactions against various stresses. In addition, recent reports have suggested that HO-1 modulates immunocyte activation and functions. HO-1 suppresses mast cell degranulation, but whether HO-1 suppresses cytokine synthesis as well is not yet known. We examined whether rat HO-1 cDNA transfected rat basophilic leukemia (RBL)-2H3 cells have altered cytokine production in response to stimulation with anti-ovalbumin (OA) serum/OA compared to Mock transfected RBL-2H3 cells. HO-1 inhibited anti-OA serum/OA-induced IL-3 and TNF-alpha production. Inhibition of HO-1 activity by Zn (II) protoporphyrin IX, a specific HO-1 inhibitor, prevented the suppression of TNF-alpha production. The cytokine inhibition by HO-1 was associated with selective suppression of the DNA-binding activity of AP-1 transcription factors. The suppression of mast cell cytokine production by HO-1 may be an important aspect of the processes that lead to resolution of allergic inflammation.

The role of heme oxygenase-1 in pulmonary disease

Heme oxygenase (HO)-1, the inducible isoform of heme oxygenase, is a cytoprotective enzyme that plays a central role in the defense against oxidative and inflammatory insults in the lung. HO-1 catalyzes the degradation of heme, a potent oxidant, into biliverdin, iron, and carbon monoxide (CO). These downstream products of heme catabolism have recently been found to mediate the antioxidant, antiapoptotic, antiproliferative, vasodilatory, and anti-inflammatory properties of HO-1. Although absence of HO-1 is rare in humans, a number of HO-1 promoter polymorphisms have been identified that may influence HO-1 expression in vivo and lead to disease states. This review will summarize studies that implicate HO-1 and heme metabolites in the pathophysiology of pulmonary disease and discuss recent advances in the therapeutic applications of HO-1.

Exhaled carbon monoxide levels in atopic asthma: a longitudinal study

Exhaled carbon monoxide (eCO) is a potential non-invasive marker of airway inflammation. We have investigated the cross-sectional and longitudinal relationship between eCO and lung function and bronchial reactivity in 69 adults with atopic asthma, in the course of participation in a 6-week randomised placebo-controlled trial of vitamin E supplementation. At baseline, there was no cross-sectional association between absolute eCO levels and either forced expiratory volume (FEV(1)), forced vital capacity (FVC) or bronchial reactivity. However, in the longitudinal analysis within the placebo group, a rise in mean eCO was significantly associated with improvement in bronchial reactivity (change in eCO (parts per million) per natural log unit change in bronchial hyperreactivity 0.498, 95% confidence interval 0.071 to 0.924, P=0.024). These findings suggest that, contrary to previous data, there is no cross-sectional relationship between eCO and lung function or bronchial reactivity, but that there may be a longitudinal trend with bronchial reactivity that is worth further investigation.

Focus on antioxidant enzymes and antioxidant strategies in smoking related airway diseases

Cigarette smoke causes significant oxidant stress which is further enhanced by recruitment and activation of inflammatory cells to the lung. Polymorphisms in some detoxification enzymes are thought to increase the risk of developing chronic obstructive pulmonary disease (COPD), but the ultimate role of genetic variability in antioxidant and/or detoxification enzymes in COPD remains obscure. Some antioxidant enzymes are inducted, but the extent of induction is insufficient to protect the lung/alveolar epithelium against cigarette smoke. Exogenous antioxidants such as vitamins do not seem to protect against cigarette smoke related lung injury. Glutathione related synthetic drugs such as N-acetylcysteine have shown some benefits, but they may have pro-oxidant side effects. Synthetic compounds with superoxide dismutase and catalase activities have shown promising results in animal models against a variety of oxidant exposures including cigarette smoke in the lung. These results are in agreement with studies highlighting the importance of alveolar antioxidant protection mechanisms in oxidant stress and their inducibility. These new drugs need to be tested in cigarette smoking related lung injury/inflammation since inflammation/oxidant stress can continue after discontinuation of smoking.

Heme oxygenase-1: from bench to bedside

As aspects of basic science come to play an increasingly prominent role in clinical medicine, heme oxygenase-1 is one of several molecules emerging as a central player in diseases of the lung and intensive care unit. Although the apparent raison d'être of this enzyme is to dispose of heme, its activity results in cytoprotection against oxidative injury and cellular stresses. As the lung interfaces directly with an oxidizing environment, it is expected that heme oxygenase-1 would be involved in many aspects of lung health and disease. The protective effects of heme oxygenase-1 and products of its enzymatic activity, including carbon monoxide, biliverdin and bilirubin, and ferritin, have opened the door to potential therapeutic and disease-monitoring possibilities that one day may be applicable to pulmonary medicine. This article introduces readers to the history of heme oxygenase research, the role of this enzyme in the lung, and related new developments to look forward to in the fields of pulmonary and critical care medicine.

Distribution of antioxidant enzymes in developing human lung, respiratory distress syndrome, and bronchopulmonary dysplasia

We studied cell-specific protein expression of all the major antioxidant enzymes (AOEs) and related proteins, such as copper-zinc superoxide dismutase (CuZnSOD), manganese SOD (MnSOD), extracellular SOD (ECSOD), catalase, the heavy and light chains of gamma-glutamylcysteine synthetase (gamma-GCS-l and gamma-GCS-h, also called glutamate cysteine ligase), the rate-limiting enzyme in glutathione synthesis, hemeoxygenase-1 (HO-1), and thioredoxin (Trx), in developing human lung, respiratory distress syndrome, and bronchopulmonary dysplasia by immunohistochemistry. Generally, after 17 weeks of gestational age, MnSOD was predominantly expressed in bronchial epithelium, alveolar epithelium, and macrophages, CuZnSOD was expressed in bronchial epithelium, ECSOD was expressed in bronchial epithelium, vascular endothelium, and the extracellular matrix, catalase was expressed in bronchial epithelium and alveolar macrophages, gamma-GCS-h was expressed in bronchial epithelium and endothelium, and gamma-GCS-l was expressed in bronchial epithelium. Trx was restricted to bronchial epithelium and to a lesser extent to alveolar macrophages, and HO-1 found in alveolar macrophages. Basically, the expression of these enzymes was similar in normal and diseased lung. It can be concluded that various AOEs and related proteins differ in their distribution and expression in lung before term, but generally it seems that infants are better adapted to high oxygen tension than might be expected.

Heme oxygenase-1 and carbon monoxide in pulmonary medicine

Heme oxygenase-1 (HO-1), an inducible stress protein, confers cytoprotection against oxidative stress in vitro and in vivo. In addition to its physiological role in heme degradation, HO-1 may influence a number of cellular processes, including growth, inflammation, and apoptosis. By virtue of anti-inflammatory effects, HO-1 limits tissue damage in response to proinflammatory stimuli and prevents allograft rejection after transplantation. The transcriptional upregulation of HO-1 responds to many agents, such as hypoxia, bacterial lipopolysaccharide, and reactive oxygen/nitrogen species. HO-1 and its constitutively expressed isozyme, heme oxygenase-2, catalyze the rate-limiting step in the conversion of heme to its metabolites, bilirubin IXalpha, ferrous iron, and carbon monoxide (CO). The mechanisms by which HO-1 provides protection most likely involve its enzymatic reaction products. Remarkably, administration of CO at low concentrations can substitute for HO-1 with respect to anti-inflammatory and anti-apoptotic effects, suggesting a role for CO as a key mediator of HO-1 function. Chronic, low-level, exogenous exposure to CO from cigarette smoking contributes to the importance of CO in pulmonary medicine. The implications of the HO-1/CO system in pulmonary diseases will be discussed in this review, with an emphasis on inflammatory states.