Increase in exhaled carbon monoxide during exacerbations of cystic fibrosis

Redox regulation of lung inflammation by thioredoxin

The lungs are the richest in oxygen among the various organs of the body and are always subject to harmful reactive oxygen species. Regulation of the reduction/oxidation (redox) state is critical for cell viability, activation, proliferation, and organ functions. Although the protective importance of various antioxidants has been reported, few antioxidants have established their clinical usefulness. Thioredoxin (TRX), a key redox molecule, plays crucial roles as an antioxidant and a catalyst in protein disulfide/dithiol exchange. TRX also modulates intracellular signal transduction and exerts antiinflammatory effects in tissues. In addition to its beneficial effects in other organs, the protective effect of TRX in the lungs has been shown against ischemia/ reperfusion injury, influenza infection, bleomycin-induced injury, or lethal inflammation caused by interleukin- 2 and interleukin-18. Monitoring of TRX in the plasma, airway, or lung tissue may be useful for the diagnosis and follow-up of pulmonary inflammation. Promotion/modulation of the TRX system by the administration of recombinant TRX protein, induction of endogenous TRX, or gene therapies can be a therapeutic modality for oxidative stress-associated lung disorders.

Exhaled breath measures of inflammation: are they useful in neonatal chronic lung disease?

Neonatal chronic lung disease is a common problem for surviving infants of extreme prematurity. Although the precise pathophysiology is still not known, it is clear that inflammation provides a common link that amplifies the injury to the premature lung. Current invasive measures of pulmonary inflammation include markers in blood and airway effluent, with the cellular composition of tracheal fluid being the "gold standard". In this article available exhaled breath measures, particularly nitric oxide, carbon monoxide, volatile hydrocarbons, and exhaled breath condensate, are reviewed with particular reference to sample collection, analysis, and common pitfalls as they apply to the ventilated premature newborn at risk of chronic lung disease. Although they have great potential, all measures require thorough validation before being used clinically.

Heme oxygenase does not contribute to control of basal vascular tone in isolated blood-perfused rat lung

BACKGROUND

Vasoconstriction in pulmonary ischemia-reperfusion injury may involve dysfunction of the physiologic vasodilation of pulmonary arteries. Little is known of the relative importance of heme oxygenase (HO)/carbon monoxide (CO)-dependent vs nitric oxide synthase (NOS)/nitric oxide (NO)-dependent vasodilation of the pulmonary vasculature. We evaluated the significance of HO function on basal pulmonary vascular resistance (PVR) and compared it with the function of NOS.

METHODS

Using an isolated blood-perfusion model, lungs of Lewis rats were assigned to 3 groups (n = 6/group). After stabilization, either an inhibitor of HO (tin-protoporphyrin-9 [SnPP-9]) or an inhibitor of NOS (NG-nitro-L-arginine methylester [L-NAME]) was added to the perfusate (50 micromol/liter and 1 mmol/liter as the final concentration, respectively). Lungs receiving saline served as controls. Gas exchange, hemodynamic and respiratory functions and the levels of cyclic 3',5'-guanosine monophosphate (cGMP) in the perfusate were measured.

RESULTS

Inhibition of NOS by L-NAME resulted in a significant (p < 0.01) increase in PVR (DeltaPVR: 0.110 +/- 0.012 cm H(2)O/ml. min) within 5 minutes. In contrast, PVR was minimally affected by SnPP-9 (DeltaPVR: 0.005 +/- 0.005 cm H(2)O/ml. min), which was comparable to control lungs (DeltaPVR: 0.012 +/- 0.005 cm H(2)O/ml. min). The level of cGMP in the perfusate 5 minutes after drug application was markedly, but not significantly, lower in the L-NAME group (1.67 +/- 0.74 nmol/liter) when compared with controls (2.69 +/- 0.89 nmol/liter) and SnPP-9-treated lungs (2.65 +/- 0.66 nmol/liter).

CONCLUSIONS

NOS but not HO contributes to the control of basal vascular tone in the rat lung.

Heme Oxygenase-1 Expression in Human Lungs with Cystic Fibrosis and Cytoprotective Effects againstPseudomonas Aeruginosa In Vitro

Inflammation and oxidative stress play important roles in cystic fibrosis (CF) lung disease. Inflammatory/oxidant-mediated induction of heme oxygenase-1 (HO-1) is believed to be a cytoprotective response. This study examined HO-1 expression in lung samples from patients with CF using immunohistochemistry and quantitative reverse transcription-polymerase chain reaction. In addition, we evaluated myeloperoxidase staining as a marker of acute inflammation and potentially an increase in oxidant stress and Prussian blue and ferritin staining to assess iron status of the lung. Macrophage HO-1 staining was increased in diseased lungs as compared with normal control subjects and correlated with myeloperoxidase staining. Quantitative reverse transcription-polymerase chain reaction further supported an increase in HO-1 expression in CF lung disease. Although iron staining was minimal, ferritin staining was increased in diseased lungs in concert with HO-1 staining. To determine whether HO-1 induction was cytoprotective, we evaluated a CF airway epithelial cell line, IB3.1, in response to Pseudomonas aeruginosa-induced injury/apoptosis in cells overexpressing HO-1 by either transient or stable transfection of pcDNA3.1/HO-1 construct. Overexpression of HO-1 resulted in protection against P. aeruginosa-induced injury/apoptosis. This suggests that the induction of HO-1 in patients with CF is a cytoprotective event and that augmenting its expression is a potential therapy against bacterial injury.

The measurement of exhaled carbon monoxide in healthy smokers and non-smokers

The measurement of exhaled carbon monoxide (CO) level may provide an immediate, non-invasive method of assessing smoking status. The aims of this study were to use a portable CO monitor to compare the exhaled CO levels in established smokers and non-smokers. The exhaled CO levels were measured in 322 subjects (243 healthy smokers, 55 healthy non-smokers, 24 passive smokers) who applied to healthy stand during the spring student activity of Firat University in Elaziğ. Exhaled CO concentration was measured using the EC50 Smokerlyser. The mean exhaled CO level was 17.13+/-8.50 parts per million (ppm) for healthy smokers and 3.61+/-2.15 ppm for healthy non-smokers, and 5.20+/-3.38 ppm for passive smokers. There were significant positive correlation between CO levels and daily cigarette consumption, and CO levels and duration of smoking in healthy smokers (r=+0.550, P<0.001, r=+0.265, P<0.001, respectively. Spearman's test). When smokers and non-smokers were looked at as a whole, a cutoff of 6.5 ppm had a sensitivity of 90% and specificity of 83%. In conclusion, exhaled CO level provides an easy, an immediate way of assessing a subject's smoking status.

End-tidal carbon monoxide corrected for lung volume is elevated in patients with cystic fibrosis

Several factors influence levels of end-tidal carbon monoxide (ETCO). We studied determinants of ETCO corrected for inhaled CO (ETCOc) levels in healthy control subjects and compared ETCOc levels and determinants between healthy control subjects and patients with cystic fibrosis (CF). Thirty healthy control subjects (mean +/- SD age, 23 +/- 6 years) and twenty clinically stable patients with CF, aged 13.5 +/- 3.5 years were included. ETCO was measured with the CO-STAT End-Tidal Breath Analyzer (Natus Medical, Inc., San Carlos, CA), and determinants included lung volume (measured with the multiple-breath helium wash-in method), CO-diffusion capacity, and different expiratory flow rates. In healthy control subjects we found a significant correlation between ETCOc and lung volume (r = 0.64, p < 0.05) and with CO-diffusion capacity uncorrected for VA (r = 0.48, p = 0.02). There was no expiratory flow rate dependency in either group. Patients with CF showed no difference in ETCOc levels compared with control subjects (mean 1.2 +/- 0.4 ppm vs. 1.3 +/- 0.4 ppm, p = 0.32), but patients with CF had lower total lung capacity-helium than healthy control subjects. ETCOc corrected for lung volume was significantly higher in patients with CF compared with control subjects (p < 0.001). We hypothesize that a possible increase in breath CO caused by airway inflammation might be masked by differences in lung volumes between control subjects and patients with CF.

Increased leukotriene B4 and interleukin-6 in exhaled breath condensate in cystic fibrosis

Chronic neutrophilic airway inflammation is an important feature of cystic fibrosis (CF). Noninvasive inflammatory markers may be useful in monitoring CF. Leukotriene B4 (LTB4) and interleukin (IL)-6 are inflammatory mediators that are increased in chronic neutrophilic inflammation. The aim of this study was to assess whether LTB4 and IL-6 were increased in exhaled breath condensate of CF patients and whether they could be used to monitor inflammation. Twenty patients with CF (13 males, age of 28 +/- 9 years) were recruited together with 15 age-matched healthy subjects (8 males, age 35 +/- 7 years). LTB4 and IL-6 levels were markedly elevated in patients with acute exacerbations (28.8 +/- 4.3 and 8.7 +/- 0.4 pg/ml) compared with control subjects (6.8 +/- 0.7 and 2.6 +/- 0.1 pg/ml, p < 0.0001). We also observed a decrease of exhaled LTB4 and IL-6 concentrations after antibiotic treatment in six patients who were followed until clinically stable (31.1 +/- 4.4 and 9.5 +/- 0.4 pg/ml vs. 18.8 +/- 0.8 and 6.4 +/- 0.2 pg/ml, respectively) and an increase in 15 CF patients infected with Pseudomonas aeruginosa (34.3 +/- 5.0 and 9.3 +/- 0.3 pg/m) compared with those infected with other bacteria (18.3 +/- 0.7 and 6.9 +/- 0.5 pg/ml). These findings suggest that LTB4 and IL-6 levels are increased in exhaled breath condensate of patients with CF during exacerbation and could be used to monitor airway inflammation in these patients.

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.

Analysis of expired air for oxidation products

Chronic inflammation is a critical feature of chronic obstructive pulmonary disease, cystic fibrosis, and asthma. This inflammation is associated with the increased production of reactive oxygen species or oxidative stress in the lungs. Oxidative stress may have several adverse effects and may amplify the inflammatory process; however, monitoring oxidative stress is difficult and may not be reflected by changes in blood markers. We have therefore developed several noninvasive markers in the exhaled breath that may indicate oxidative stress in the lungs, and we studied these in relationship to the severity of chronic inflammatory lung diseases. We analyzed the exhaled breath for the content of nitric oxide as a marker of inflammation, carbon monoxide as a marker of oxidative stress, and ethane, which is one of the end products of lipid peroxidation. In addition, we measured the concentration of markers of oxidative stress such as isoprostanes in exhaled breath condensate. Our results confirm that there are increased inflammation, oxidative stress, and lipid peroxidation in lung disease, as shown by elevated levels of nitric oxide, carbon monoxide, and ethane, respectively. The finding of lower levels of these gases in patients on steroid treatment and of higher levels in those with more severe lung disease, as assessed by lung function tests and clinical symptoms, reinforces the hypothesis that the noninvasive measurement of exhaled gases maybe useful in monitoring the underlying pathologic pathways of lung disease. Longitudinal studies are required to assess the clinical usefulness of these measurements in the monitoring of chronic inflammatory lung disease.

Increased blood carboxyhaemoglobin concentrations in inflammatory pulmonary diseases

BACKGROUND

Exhaled carbon monoxide has been reported to increase in inflammatory pulmonary diseases and to be correlated with blood carboxyhaemoglobin (Hb-CO) concentration. A study was undertaken to determine whether arterial blood Hb-CO increases in patients with inflammatory pulmonary diseases.

METHODS

The Hb-CO concentration in arterial blood was measured with a spectrophotometer in 34 normal control subjects, 24 patients with bronchial asthma, 52 patients with pneumonia, and 21 patients with idiopathic pulmonary fibrosis (IPF).

RESULTS

The mean (SE) Hb-CO concentrations in patients with bronchial asthma during exacerbations (n=24, 1.05 (0.05)%), with pneumonia at the onset of illness (n=52, 1.08 (0.06)%), and with IPF (n=21, 1.03 (0.09)%) were significantly higher than those in control subjects (n=34, 0.60 (0.07)%) (mean difference 0.45% (95% confidence interval (CI) 0.23 to 0.67), p<0.01 in patients with bronchial asthma, mean difference 0.48% (95% CI 0.35 to 0.60), p<0.0001 in patients with pneumonia, and mean difference 0.43% (95% CI 0.26 to 0.61) p<0.001 in patients with IPF). In 20 patients with bronchial asthma the Hb-CO concentration decreased after 3 weeks of treatment with oral glucocorticoids (p<0.001). In 20 patients with pneumonia the Hb-CO concentration had decreased after 3 weeks when patients showed evidence of clinical improvement (p<0.001). The values of C-reactive protein (CRP), an acute phase protein, correlated with Hb-CO concentrations in patients with pneumonia (r=0.74, p<0.0001) and in those with IPF (r=0.46, p<0.01). In patients with bronchial asthma changes in Hb-CO concentrations were significantly correlated with those in forced expiratory volume in 1 second (FEV(1)) after 3 weeks (r=0.67, p<0.01). Exhaled carbon monoxide (CO) concentrations were correlated with Hb-CO concentrations (n=33, r=0.80, p<0.0001).

CONCLUSIONS

Hb-CO concentrations are increased in inflammatory pulmonary diseases including bronchial asthma, pneumonia, and IPF. Measurement of arterial Hb-CO may be a useful means of monitoring pulmonary inflammation.

Heme oxygenase-1: the "emerging molecule" has arrived

Organisms on our planet have evolved in an oxidizing environment that is intrinsically inimical to life, and cells have been forced to devise means of protecting themselves. One of the defenses used most widely in nature is the enzyme heme oxygenase-1 (HO-1). This enzyme performs the seemingly lackluster function of catabolizing heme to generate bilirubin, carbon monoxide, and free iron. Remarkably, however, the activity of this enzyme results in profound changes in cells' abilities to protect themselves against oxidative injury. HO-1 has been shown to have anti-inflammatory, antiapoptotic, and antiproliferative effects, and it is now known to have salutary effects in diseases as diverse as atherosclerosis and sepsis. The mechanism by which HO-1 confers its protective effect is as yet poorly understood, but this area of invetsigation is active and rapidly evolving. This review highlights current information on the function of HO-1 and its relevance to specific pulmonary and cardiovascular diseases.

Carbon monoxide: innovative anti-inflammatory properties of an age-old gas molecule

Observations of the effects of carbon monoxide (CO) on mammalian systems have been known for thousands of years. To be sure, CO is deadly under certain conditions and concentrations, but perhaps as the data presented here will make clear, it also possesses other diverse functional and immunomodulatory properties. This review, together with the other reviews in this issue, will detail that over the past three decades, fundamental functional role(s) for this gas molecule are beginning to emerge. This review outlines that at low concentrations, exogenously administered CO is a molecule involved in the regulation of the inflammatory response in a variety of disease models. CO has been shown to modulate such cellular functions as cytokine production, cell proliferation and apoptosis, protecting the lungs and hearts of rodents from such stressors as endotoxin, ischemia/reperfusion injury, cardiac xenograft rejection, and asthma. Although the mechanism by which this simple diatomic gas provides this protection remains obscure, the conclusions are the same: CO at low concentrations, concentrations that are well below those that would otherwise create toxic effects, is proving beneficial in models of acute injury. CO, akin to nitric oxide, is proving to be an extraordinary signaling molecule generated by the cell that is vital in the regulation of cellular homeostasis.

Carbon monoxide and human disease

Carbon monoxide is produced endogenously in humans through the breakdown of hemoglobin by heme oxygenase. Although originally thought to be a superfluous by-product of heme catabolism, carbon monoxide is now known to play a central role in many aspects of human health and disease. The functions of carbon monoxide that have been described to date are myriad, including blood pressure regulation, maintenance of organ-specific vascular tone, neurotransmission, stress response, platelet activation, and smooth muscle relaxation. This review outlines what is known to date about carbon monoxide as it relates to human disease.

Cross talk between carbon monoxide and nitric oxide

Carbon monoxide and nitric oxide are two endogenously produced gases that can act as second messenger molecules. Heme oxygenase and nitric oxide synthase are the enzyme systems responsible for generating carbon monoxide and nitric oxide, respectively. Both carbon monoxide and nitric oxide share similar properties, such as the ability to activate soluble guanylate cyclase to increase cyclic GMP. It is becoming increasingly clear that these two gases do not always work independently, but rather can modulate each other's activity. Although much is known about the heme oxygenase/carbon monoxide and nitric oxide synthase/nitric oxide pathways, how these two important systems interact is less well understood. This review attempts to define the current known relationship between carbon monoxide and nitric oxide as it relates to their production and physiological function.

Biomarkers of some pulmonary diseases in exhaled breath

Analysis of various biomarkers in exhaled breath allows completely non-invasive monitoring of inflammation and oxidative stress in the respiratory tract in inflammatory lung diseases, including asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), bronchiectasis and interstitial lung diseases. The technique is simple to perform, may be repeated frequently, and can be applied to children, including neonates, and patients with severe disease in whom more invasive procedures are not possible. Several volatile chemicals can be measured in the breath (nitric oxide, carbon monoxide, ammonia), and many non-volatile molecules (mediators, oxidation and nitration products, proteins) may be measured in exhaled breath condensate. Exhaled breath analysis may be used to quantify inflammation and oxidative stress in the respiratory tract, in differential diagnosis of airway disease and in the monitoring of therapy. Most progress has been made with exhaled nitric oxide (NO), which is increased in atopic asthma, is correlated with other inflammatory indices and is reduced by treatment with corticosteroids and antileukotrienes, but not (beta 2-agonists. In contrast, exhaled NO is normal in COPD, reduced in CF and diagnostically low in primary ciliary dyskinesia. Exhaled carbon monoxide (CO) is increased in asthma, COPD and CF. Increased concentrations of 8-isoprostane, hydrogen peroxide, nitrite and 3-nitrotyrosine are found in exhaled breath condensate in inflammatory lung diseases. Furthermore, increased levels of lipid mediators are found in these diseases, with a differential pattern depending on the nature of the disease process. In the future it is likely that smaller and more sensitive analyzers will extend the discriminatory value of exhaled breath analysis and that these techniques may be available to diagnose and monitor respiratory diseases in the general practice and home setting.

Exhaled monoxides as a pulmonary function test: use of exhaled nitric oxide and carbon monoxide

Although there has been tremendous improvement in the technologic ability to measure exhaled gases and monitor biologic processes in the lung, it has not yet found a clinical role outside the research laboratory. Common themes seem to be significant overlap in the amount of exhaled gases in clinically distinct populations, confounding variables such as infection, smoking, and environmental exposure, and lack of consistent change with disease management. If these tests are ever to be used by the general pulmonologist, consistent links between the measurements and the response to disease modification will need to be demonstrated at the very least and, ideally, the clinician would like to see improved outcomes when these noninvasive tests are employed regularly.

Exhaled carbon monoxide and nitric oxide in COPD

STUDY OBJECTIVES

To investigate whether exhaled carbon monoxide (CO) and nitric oxide (NO) could be used as noninvasive in vivo biomarkers of oxidative stress in the lungs of patients with COPD.

DESIGN

Single-center cross-sectional study.

PATIENTS

Ten healthy nonsmokers, 12 smokers, 15 stable ex-smokers with COPD, and 15 stable current smokers with COPD.

INTERVENTIONS

Subjects attended the outpatient clinic on one occasion for pulmonary function tests and exhaled CO and NO measurements.

MEASUREMENTS AND RESULTS

Mean (+/- SEM) CO levels in ex-smokers with COPD were higher (7.4 +/- 1.9 ppm; p < 0.05) than in nonsmoking control subjects (3.0 +/- 0.3 ppm) but were lower than in current smokers with COPD (20.0 +/- 2.6 ppm; p < 0.001). There was no correlation between exhaled CO and NO. There was no correlation between CO and lung function tests in any group of patients. Exhaled NO was higher in ex-smokers with COPD (12.0 +/- 1.0 parts per billion [ppb]; p < 0.001) than in healthy nonsmokers (6.5 +/- 0.6 ppb) and in current smokers with COPD (7.6 +/- 1.1 ppb; p < 0.01) compared to healthy smokers (3.3 +/- 0.4 ppb). Ex-smokers with COPD had higher exhaled NO levels than did current smokers with COPD (p < 0.001) There was a negative correlation between exhaled NO and FEV(1) in both ex-smokers with COPD (r = -0.60; p < 0.02) and current smokers with COPD (r = -0.59; p < 0.02).

CONCLUSION

The measurement of exhaled CO and NO may represent a new method for the noninvasive monitoring of airway inflammation and oxidant stress in COPD ex-smokers. Exhaled CO and NO are strongly affected by cigarette smoking, which limits their usefulness as biomarkers in current smokers.

"Haemoxygenase-1 induction and exhaled markers of oxidative stress in lung diseases", summary of the ERS Research Seminar in Budapest, Hungary, September, 1999

In recent years, there has been increasing interest in noninvasive monitoring of airway inflammation and oxidative stress. Several volatile and nonvolatile substances can be measured in exhaled breath and have been suggested as potential biomarkers of these events. Exhaled gases, including carbon monoxide (CO), alkanes (ethane, pentane), and substances measured in breath condensate, such as hydrogen peroxide (H2O2) and isoprostanes were all suggested as potential markers of oxidative stress in the lung. A European Respiratory Society (ERS) International Research Seminar entitled "Haemoxygenase-1 induction and exhaled markers of oxidative stress in lung diseases" was organized by the Airway Regulation and Provocation Group of the Clinical Allergy and Immunology Assembly in Budapest, Hungary in September, 1999 to integrate the latest knowledge on these issues and accelerate further improvement in this area. During this 2-day event several issues were raised about: the use and standardization of measurements in exhaled breath; problems of measuring expired H2O2 and other mediators in breath condensate; role and regulation of haemoxygenase (HO)-1 in the lung; and conditions and factors influencing exhaled CO. This report is a summary of the main presentations at the seminar, together with the current areas of research in this rapidly expanding field.