Exhaled carbon monoxide levels after a course of oral prednisone in children with asthma exacerbation

Exhaled carbon monoxide levels in infants and toddlers with episodic asthma

Objective:

There are few lung function tests available to evaluate bronchial asthma in infants and toddlers. The objective of this study was to test the hypothesis that the measurement of exhaled carbon monoxide (eCO) levels is applicable to evaluate infants and toddlers with stable asthma and during acute asthma attack.

Methods:

A one-way valve breath sampling bag was developed to collect the exhaled air of infants and toddlers. A total of 483 infants (under 2 years) and toddlers (2-5 years) were studied; 355 had an established diagnosis of asthma (182 suffering mild asthma attacks and 173 without active asthmatic symptoms), 119 had upper respiratory infection (URI) including acute bronchitis, and 9 were healthy.

Results:

In infants and toddlers, eCO levels of those with asthma attacks [median (interquartile range) = 2.0 (2.0-3.25) ppm, n=182] were significantly higher than those of subjects with asymptomatic asthma [2.0 (1.0-2.0) ppm, n=173, P < 0.0001], URI [2.0 (1.0-3.0) ppm, n=119, P < 0.0001], and healthy children [1.0 (0.0-1.0) ppm, n=9, P < 0.0001]. In 75 children with asthma petit mal, eCO levels during asthma attacks [3.0 (2.0-4.0) ppm] significantly decreased after therapy [1.0 (1.0-2.0) ppm, P < 0.0001]. In infants and toddlers with an established diagnosis of asthma (n=355), eCO cut-off >2 ppm discriminated asthma attack from an asymptomatic state with a sensitivity of 95.6%, a specificity of 43.3%, and an area under the curve (AUC) of 0.71 (95% CI: 0.65-0.76, P < 0.0001). In 401 infants and toddlers with some respiratory symptoms, of which 285 cases were finally diagnosed as asthma [eCO level = 2.0 (2.0-3.0) ppm] and 116 cases were not asthma [eCO level = 2.0 (1.0-3.0) ppm, P < 0.0001], eCO cut-off >3 ppm supported the final diagnosis of asthma with a sensitivity of 38.9%, a specificity of 74.1%, and AUC of 0.63 (95% CI: 0.56-0.69, P < 0.0001).

Conclusion:

The measurement of eCO by a novel method is applicable to evaluate asthmatic activity and treatment responsiveness, and to diagnose asthma in infants and toddlers.

A novel modelling approach to energy transport in a respiratory system

In this paper, energy transport in a respiratory tract is modelled using the finite element method for the first time. The upper and lower respiratory tracts are approximated as a 1-dimensional domain with varying cross-sectional and surface areas, and the radial heat conduction in the tissue is approximated using the 1-dimensional cylindrical coordinate system. The governing equations are solved using 1-dimensional linear finite elements with convective and evaporative boundary conditions on the wall. The results obtained for the exhalation temperature of the respiratory system have been compared with the available animal experiments. The study of a full breathing cycle indicates that evaporation is the main mode of heat transfer, and convection plays almost negligible role in the energy transport. This is in-line with the results obtained from animal experiments.

Factors influencing the levels of exhaled carbon monoxide in asthmatic children

OBJECTIVE

Bronchial asthma is characterised by chronic airway inflammation commonly associated with increased oxidative stress. Exhaled carbon monoxide (eCO) levels could act as markers of both oxidative stress and allergic inflammation. We aimed to study eCO levels in asthmatics and detect the possible factors influencing them.

METHODS

We studied 241 asthmatic children and 75 healthy children. The differences in eCO levels among various asthmatic phenotypes and the correlations between eCO and other measured parameters (spirometric indices, Asthma Control Test score, exhaled nitric oxide, total IgE, blood eosinophils and marker of oxidative damage of proteins) were analysed.

RESULTS

Levels of eCO widely differed according to the selected characteristics of asthma. Asthmatics showed higher eCO concentrations than controls (1.44 ± 0.12 ppm vs. 0.91 ± 0.11 ppm, p < 0.001). Acute exacerbation of asthma was accompanied by a significant increase in eCO compared to the clinically controlled stage (2.17 ± 0.36 ppm vs. 1.33 ± 0.13 ppm, p < 0.001). Atopic, non-atopic asthma and asthma associated with allergic rhinitis (AR) showed elevated levels of eCO. The levels of eCO negatively correlated with the marker of protein oxidation in asthmatics, especially in atopic form and during acute exacerbation.

CONCLUSIONS

In a population of asthmatic children, eCO levels could be considered as a marker of both allergic inflammation and oxidative stress in the airways. Concomitant AR and asthma control were the most important factors affecting the levels of eCO in asthmatic children. However, our results do not support the use of routine eCO in the clinical practice.

Exhaled carbon monoxide levels in preschool-age children with episodic asthma

BACKGROUND

The concentration of exhaled carbon monoxide (eCO) in young children with stable asthma and during acute asthma attack is not known.

METHODS

A sampling bag was developed to collect the exhaled air of preschool children. A total of 257 preschool-age children (≥ 3 years and ≤ 6 years old) were studied; 111 had a diagnosis of asthma (43 suffering a mild asthma attack and 68 without active asthmatic symptom), 99 had upper respiratory infection (URI) and 47 were healthy.

RESULTS

In preschool-age children, eCO levels of those with asthma attacks (mean ± SE, 2.7 ± 0.3 p.p.m., n= 43) were significantly higher than those of subjects with asymptomatic asthma (0.5 ± 0.1 p.p.m., P < 0.05), URI (0.8 ± 0.1 p.p.m., P < 0.05) and healthy children (0.4 ± 0.1 p.p.m., P < 0.05). A multivariate linear regression model showed that eCO was higher in children with asthma attacks independent of age and gender. In 33 asthmatic children followed before and after treatment, eCO levels during asthma attacks significantly decreased after inhalation therapy with a combination of salbutamol and sodium cromoglycate (before therapy, 2.9 ± 0.4 p.p.m.; after therapy, 0.6 ± 0.1 p.p.m., P < 0.0001).

CONCLUSIONS

The measurement of eCO using a novel collecting system is useful in the recognition of asthma in preschool children.

A meta-analysis of the association of exhaled carbon monoxide on asthma and allergic rhinitis

The objective of this study is to evaluate the effect of exhaled CO (eCO) on the development of asthma and allergic rhinitis (AR) by means of reviewing published literature. The literatures published between January 1997 and December 2008 from the US National Library of Medicine (NLM) Database were obtained according to inclusion criteria. Meta-analysis of randomized controlled trials (RCTs) was performed. CO levels of asthma and AR patients were compared with that of normal controls. HO-1(heme oxygenase-1) expression and effect of corticosteroids on eCO levels were also analyzed. Fifteen studies concerning asthma and four studies concerning AR were included in this analysis. Heterogeneity from different studies was evident (P < 0.0001), so a random-effects model was preferred. The meta-analysis revealed that asthmatic patients had significantly higher levels of eCO compared to normal controls. There was significant difference between asthma and control groups in terms of eCO (combined weighted mean difference (WMD) 1.33 (95% confidence interval 0.72 to 1.95), P < 0.0001), and no significant difference between AR and control (combined WMD 0.93 (95% confidence interval -0.54 to 2.40), P = 0.22). HO-1 expression were also reviewed, asthma group produced greater expression of HO-1 than control group with significant difference (combined standardized mean difference (SMD) 2.98 (95% confidence interval 1.13 to 4.84), P = 0.002). After corticosteroid therapy, significantly different levels of eCO were produced after corticosteroid therapy than did asthma group (combined WMD -1.23 (95% confidence interval -2.43 to -0.03), P = 0.04). The analysis reveals that eCO levels were significantly raised in asthma and it may attribute to high expression of HO-1, but there were no significantly high eCO levels between AR and control groups. Due to sensitivity to corticosteroid inhibition, eCO may be used as a practical marker to detect and monitor exacerbation of asthma.

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.

Carbon monoxide: endogenous mediator, potential diagnostic and therapeutic target

The primary objectives of this article are to review the potential role of carbon monoxide (CO) as an endogenous mediator, diagnostic marker for pulmonary disorders, and therapeutic target in critical illness. The review will start by focusing on the importance of the heme oxygenase (HO)-CO axis as an endogenous system as it relates to the cardiovascular and pulmonary systems. It will elucidate the influence of HO gene expression on critical events like shock, sepsis, ischemia-reperfusion and others. Our focus will then shift and look at the potential diagnostic role of exhaled CO in major inflammatory states of the lung, and finally we will highlight the activities on inhaled CO being considered as a possible therapeutic tool and the controversies surrounding it.

Redox-regulated mechanisms in asthma

Homeostasis of the reduction-oxidation (redox) state is critical to protection from oxidative stress in the lungs. Therefore, the lungs have high levels of antioxidants, including glutathione, heme oxygenase, and superoxide dismutase. The numbers of inflammatory cells -- particularly eosinophils -- are increased in the airways of asthma patients, and these pulmonary inflammatory cells release large amounts of harmful reactive oxygen species and reactive nitrogen species. Human thioredoxin 1 (TRX1) is a redox-active protein of approximately 12 kDa that contains a (32)Cys-Gly-Pro-(35)Cys sequence necessary for its activity. The strong reducing activity of the sequence results from the cysteine residues acting as proton donors and cleaving disulfide (S-S) bonds in the target protein. Endogenous or exogenous TRX1 or both protect the lungs against ischemia-reperfusion injury, influenza infection, bleomycin-induced injury, or lethal pulmonary inflammation caused by interleukin-2 and interleukin-18. We showed that exogenous TRX1 inhibits airway hyperresponsiveness and pulmonary inflammation accompanied by eosinophilia in mouse models of asthma. Recently, we reported that exogenous TRX1 improves established airway remodeling in a prolonged antigen-exposure mouse asthma model. Exogenous and endogenous TRX1 also prevents the development of airway remodeling. Here, we discuss the role and clinical benefits of TRX1 in asthma.

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.

Carbon monoxide in sepsis

Despite modern practices in critical care medicine, sepsis or systemic inflammatory response syndrome remains a leading cause of morbidity and mortality in the intensive care unit. Thus, the need to identify new therapeutic tools for the treatment of sepsis is urgent. In this context, carbon monoxide has become a promising therapeutic molecule that can potentially prevent uncontrolled inflammation in sepsis. In humans, carbon monoxide arises endogenously from the degradation of heme by heme oxygenase enzymes. Both endogenously synthesized and exogenously applied carbon monoxide can exert antiinflammatory and antiapoptotic effects in cells and tissues. Based on these properties, carbon monoxide, when applied at low concentration, conferred protection in a variety of cellular and rodent models of sepsis, and furthermore reduced morbidity and mortality in vivo. Therefore, application of carbon monoxide may have a major impact on the future of sepsis treatment. This review summarizes evidence for salutary effects of carbon monoxide in sepsis of various organs, including lung, heart, kidney, liver, and intestine, and discusses the potential translation of the data into human clinical trials.

Bias and confounding in longitudinal measures of exhaled monoxides

The measurement of exhaled nitric oxide and carbon monoxide concentrations is an emerging method of monitoring airway inflammation longitudinally in community-based studies. Inhaled concentrations of these monoxides influence exhaled concentrations. Little is known about the degree to which inhaled concentrations distort temporal trends in, or estimated effects of air pollutants on, exhaled monoxides. We sought to evaluate whether estimated effects of air pollutants on exhaled monoxides are distorted by trends in indoor and outdoor monoxides, and to characterize determinants of exhaled monoxide concentrations among residents of public housing. In a panel study, 42 residents of public housing provided over 1000 exhaled breath samples. Samples from all subjects were analyzed for nitric oxide; samples from 27 of these subjects were also analyzed for carbon monoxide. The effects of indoor and outdoor monoxide concentrations on exhaled concentrations were quantified. Confounding of associations between particulate matter concentrations and exhaled nitric oxide concentrations was explored. Determinants of exhaled monoxide concentrations among public housing residents are similar to those of other populations. Exhaled monoxide concentrations are more strongly associated with indoor than with outdoor monoxide concentrations. Approximately half of the variability in exhaled monoxide concentrations over time can be explained by changes in indoor monoxide concentrations. Indoor monoxide concentrations can markedly distort both temporal trends in exhaled concentrations as well as estimated effects of particulate matter on exhaled monoxides. Prior estimated effects of particulate matter on exhaled nitric oxide concentrations may have been confounded by nitric concentrations indoors at the time of exhaled air collection. To prevent distortions of longitudinal trends in airway inflammation and estimated health effects of air pollutants, inspiratory scrubber use is necessary but not sufficient to remove the confounding effect of indoor monoxides, and analyses should adjust exhaled monoxide concentrations for concentrations indoors.

[Carbon monoxide--poison or potential therapeutic?]

Carbon monoxide (CO) is much more than just a toxic gas. Carbon monoxide is produced endogenously by the enzyme heme oxygenase and has important functions under physiological and pathophysiological conditions. Recent studies suggested antioxidative, anti-inflammatory, antiproliferative, anti-apoptotic, and vasodilating characteristics. Regarding clinically-relevant diseases in anesthesiology and critical care medicine, such as adult respiratory distress syndrome (ARDS), sepsis, or during organ transplantation, cytoprotective properties have been demonstrated by low-dose CO in experimental models. In view of a potential CO application in future human studies, this review discusses what is known to date about CO as it relates to functional, protective and toxic aspects.

Effects of alpha tocopherol and probucol supplements on allergen-induced airway inflammation and hyperresponsiveness in a mouse model of allergic asthma

OBJECTIVE

We investigated the role of antioxidants in airway hyperresponsiveness to acetylcholine using young asthma model mice, which were sensitized and stimulated with ovalbumin.

METHODS

The mice had been fed either a normal diet, an alpha-tocopherol-supplemented diet or a probucol-supplemented diet 14 days before the first sensitization. They were immunized with antigen at intervals of 12 days and, starting from 10 days after the second immunization, they were exposed to antigen 3 times every 4th day using an ultrasonic nebulizer. Twenty-four hours after the last antigen inhalation, airway responsiveness to acetylcholine was measured and bronchoalveolar lavage fluid (BALF) was collected. A blood and lung tissue study was also carried out.

RESULTS

Twenty-four hours after the last antigen challenge, both IL-4 and IL-5 in the BALF of alpha-tocopherol-supplemented mice were significantly decreased. The IL-5 level in probucol-supplemented mice was also decreased, but there was no difference in IL-4 levels. The serum IgE level was decreased in probucol-supplemented mice. Differential cell rates of the fluid revealed a significant decrease in eosinophils due to antioxidant supplementation. Airway hyperresponsiveness to acetylcholine was also repressed in antioxidant-supplemented mice. In histological sections of lung tissue, inflammatory cells and mucus secretion were markedly reduced in antioxidant-supplemented mice. We investigated the antioxidant effect on our model mice by examining 8-isoprostane in BALF and lung tissue, and acrolein in BALF; however, our experiment gave us no evidence of the antioxidant properties of either alpha-tocopherol or probucol contributing to the reduction of airway inflammation.

CONCLUSION

These findings indicate that alpha-tocopherol and probucol suppress allergic responses in asthma model mice, although these two drugs cause suppression in different ways that are unrelated to antioxidation.

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.

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.

Childhood asthma: exhaled markers of airway inflammation, asthma control score, and lung function tests

Exhaled markers of airway inflammation become increasingly important in the management of childhood asthma. The aims of the present study are: 1) to compare exhaled markers of inflammation (nitric oxide, carbon monoxide, and acidity of breath condensate) with conventional asthma measures (lung function tests and asthma control score) in childhood asthma; and 2) to investigate the detectability of albumin, CRP, IL-6, IL-8, TNF-alpha, sICAM-1, and sTNF-R75 in the exhaled breath condensate (EBC) of asthmatic children. Thirty-two children with mild to moderate persistent asthma and healthy controls aged 6-12 years were studied. We measured exhaled NO and CO, and subsequently EBC was collected. Inflammatory mediators in EBC were measured using an enzyme-linked immunosorbent assay. Respiratory symptoms and asthma control were assessed using the asthma control questionnaire (ACQ) of Juniper et al. (Eur Respir J 1999;14:902-907). Exhaled NO showed a significant correlation with exhaled CO (r = 0.59, P < 0.05) and FEV1 (r = -0.59, P < 0.05), but not with ACQ score (r = 0.48, P = 0.06). Exhaled CO was correlated with prebronchodilator FEV1 (r = -0.45, P < 0.05), but not with asthma control (r = 0.18, P = 0.35). Acidity of EBC was significantly lower in asthmatic children than in healthy controls (P < 0.05), but did not correlate with any of the conventional asthma measures. We were not able to demonstrate the presence of CRP, IL-6, IL-8, TNF-alpha, sICAM-1, and sTNF-R75 in EBC. Albumin was found in two EBC samples of asthmatic children. We conclude that exhaled NO had a better correlation with lung function parameters and asthma control than exhaled CO and acidity of EBC, in mild to moderate persistent childhood asthma. However, exhaled NO, CO, and deaerated pH of EBC did not differ between asthmatic children and controls, possibly because of a too homogeneous and well-controlled study population. To further evaluate the clinical utility of exhaled markers in monitoring childhood asthma, more studies are required on a wider range of asthma severity, and preferably with repeated measurements of markers and of asthma control.

The oxidant-antioxidant balance in mild asthmatic patients

We investigated the oxidant-antioxidant balance and the effect of inhaled corticosteroids on this balance in mild stable asthmatics. Included in the study were 30 mild asthmatic patients (11 male, 19 female, mean age (year) +/- SD: 35.1 +/- 9.7) and 26 healthy adults (7 male, 19 female, mean age (year) +/- SD: 40.8 +/- 13.3). In all study groups, the peripheral venous blood samples were taken for plasma malonyldialdehyde (MDA), a parameter of lipid peroxidation caused by the oxidants, and erythrocyte superoxide dismutase (SOD), an antioxidant enzyme. The mean plasma MDA level was lower in the asthmatic group (5.7 +/- 1.2 nmol/ml) than in the healthy group (6.3 +/- 1.7 nmol/ml); and the mean erythrocyte SOD level was higher in asthmatic group (1086.4 +/- 247.4 U/gHb) than in the healthy group (1028.0 +/- 230.0 U/gHb). However, there were no significant differences in measurements of both plasma MDA levels and erythrocyte SOD enzyme activities between the groups (respectively, p = 0.1 and p = 0.4). When asthmatic patients were divided into subgroups as "inhaled steroid user" and "no inhaled steroid user", no significant differences were observed in the measurements of either plasma MDA level or erythrocyte SOD enzyme activity between the mentioned subgroups. According to the results of our study, we can say that oxidant-antioxidant balance is not significantly affected in mild asthmatics or measurement of plasma level of MDA and erythrocyte SOD enzyme activity is not sensitive to the oxidant-antioxidant balance in mild asthmatics.

Advances in childhood asthma: hygiene hypothesis, natural history, and management

There is significant interest in early identification and intervention in childhood asthma. Current asthma guidelines identify inhaled corticosteroids (ICS) as the preferred initial long-term control therapy even in young children. ICS clearly improve asthma control in children with mild to moderate persistent asthma, but it is not clear that they can alter the natu-ral history and progression of asthma. New insights regarding the origins of asthma and allergy and their natural history will continue to stimulate questions regarding the appropriate time for intervention and will stimulate the design of new treatment strategies and the discovery of new medications.

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.

Oxidative stress in airways: is there a role for extracellular superoxide dismutase?

Airways are exposed to high levels of environmental oxidants, yet they also have enriched extracellular antioxidants. Airways disease such as asthma, cystic fibrosis, and chronic obstructive pulmonary disease have evidence of increased oxidative stress, suggesting that reactive oxygen and nitrogen species may overwhelm antioxidant defenses in airway diseases. Extracellular superoxide dismutase is abundant in pulmonary tissues and protects the lung from increased oxidative stress; however, its role in asthma and other airway diseases has not been fully elucidated. Proteolytic processing of extracellular superoxide dismutase decreases its affinity for the extracellular matrix and may be a mechanism to regulate its distribution during conditions of inflammation or oxidative stress.