Exhaled carbon monoxide in asthmatics: a meta-analysis

Gasotransmitter Research Advances in Respiratory Diseases

Significance: Gasotransmitters are small gas molecules that are endogenously generated and have well-defined physiological functions. The most well-defined gasotransmitters currently are nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S), while other potent gasotransmitters include ammonia, methane, cyanide, hydrogen gas, and sulfur dioxide. Gasotransmitters play a role in various respiratory diseases such as asthma, chronic obstructive pulmonary disease, obstructive sleep apnea, lung infection, bronchiectasis, cystic fibrosis, primary ciliary dyskinesia, and COVID-19. Recent Advances: Gasotransmitters can act as biomarkers that facilitate disease diagnosis, indicate disease severity, predict disease exacerbation, and evaluate disease outcomes. They also have cell-protective properties, and many studies have been conducted to explore their pharmacological applications. Innovative drug donors and drug delivery methods have been invented to amplify their therapeutic effects. Critical Issues: In this article, we briefly reviewed the physiological and pathophysiological functions of some gasotransmitters in the respiratory system, the progress in detecting exhaled gasotransmitters, as well as innovative drugs derived from these molecules. Future Directions: The current challenge for gasotransmitter research includes further exploring their physiological and pathological functions, clarifying their complicated interactions, exploring suitable drug donors and delivery devices, and characterizing new members of gasotransmitters. Antioxid. Redox Signal. 40, 168-185.

Exhaled Biomarkers for Point-of-Care Diagnosis: Recent Advances and New Challenges in Breathomics

Cancers, chronic diseases and respiratory infections are major causes of mortality and present diagnostic and therapeutic challenges for health care. There is an unmet medical need for non-invasive, easy-to-use biomarkers for the early diagnosis, phenotyping, predicting and monitoring of the therapeutic responses of these disorders. Exhaled breath sampling is an attractive choice that has gained attention in recent years. Exhaled nitric oxide measurement used as a predictive biomarker of the response to anti-eosinophil therapy in severe asthma has paved the way for other exhaled breath biomarkers. Advances in laser and nanosensor technologies and spectrometry together with widespread use of algorithms and artificial intelligence have facilitated research on volatile organic compounds and artificial olfaction systems to develop new exhaled biomarkers. We aim to provide an overview of the recent advances in and challenges of exhaled biomarker measurements with an emphasis on the applicability of their measurement as a non-invasive, point-of-care diagnostic and monitoring tool.

Effect of Omega-3 Polyunsaturated Fatty Acids Intake on Eosinophil Airway Inflammation in University Athletes

Background

Though athletes have a high risk of respiratory disorders, effective prevention has not yet to be identified. Omega-3 (n-3) polyunsaturated fatty acids (PUFA) have some practical anti-inflammatory effects in allergy, and therefore may reduce airway inflammation in athletes. This study aimed to assess whether n-3 PUFA intake affects airway inflammation in university athletes.

Methods

Twenty-three males were divided into three groups: 1) the eosinophilic airway inflammation group (I_PUFA group; fractional exhaled nitric oxide (FeNO ≥ 25 ppb, n = 10); 2) the non-eosinophilic airway inflammation group (N_PUFA group; FeNO < 25 ppb, exhaled carbon dioxide (eCO) ≥ 3.6 ppm, n = 5); and 3) the control group (FeNO < 25 ppb, eCO < 3.6 ppm, n = 8). Participants took supplements containing 260 mg of docosapentaenoic acid and 600 mg of eicosapentaenoic acid (EPA) daily for 3 weeks. Baseline measurements of FeNO, respiratory impedance, respiratory function, dietary intake (food frequency questionnaires), and blood tests were performed. FeNO and respiratory impedance were measured weekly, and the rest were measured after 3 weeks.

Results

There was a significant decrease in FeNO levels from baseline at 2 and 3 weeks in the I_PUFA group (54.7 ± 8.5 ppb vs. 45.1 ± 9.1 and 45.4 ± 7.7 ppb; mean ± standard error (SE), P < 0.05). After 3 weeks, FeNO levels remained unchanged in the N_PUFA and control groups, and respiratory impedance and function remained unchanged in all groups. Blood EPA levels significantly increased in the I_PUFA and N_PUFA groups (I_PUFA, 27.7 ± 16.9 vs. 52.1 ± 12.3 µg/mL; N_PUFA, 20.8 ± 8.7 vs. 70.4 ± 36.1 µg/mL; mean ± standard deviation (SD), P < 0.05). No changes were observed in dietary intake over the 3 weeks.

Conclusions

n-3 PUFA supplementation for 3 weeks reduced airway inflammation in athletes with FeNO levels ≥ 25 ppb.

Neutrophils and Asthma

Although eosinophilic inflammation is characteristic of asthma pathogenesis, neutrophilic inflammation is also marked, and eosinophils and neutrophils can coexist in some cases. Based on the proportion of sputum cell differentiation, asthma is classified into eosinophilic asthma, neutrophilic asthma, neutrophilic and eosinophilic asthma, and paucigranulocytic asthma. Classification by bronchoalveolar lavage is also performed. Eosinophilic asthma accounts for most severe asthma cases, but neutrophilic asthma or a mixture of the two types can also present a severe phenotype. Biomarkers for the diagnosis of neutrophilic asthma include sputum neutrophils, blood neutrophils, chitinase-3-like protein, and hydrogen sulfide in sputum and serum. Thymic stromal lymphoprotein (TSLP)/T-helper 17 pathways, bacterial colonization/microbiome, neutrophil extracellular traps, and activation of nucleotide-binding oligomerization domain-like receptor family, pyrin domain-containing 3 pathways are involved in the pathophysiology of neutrophilic asthma and coexistence of obesity, gastroesophageal reflux disease, and habitual cigarette smoking have been associated with its pathogenesis. Thus, targeting neutrophilic asthma is important. Smoking cessation, neutrophil-targeting treatments, and biologics have been tested as treatments for severe asthma, but most clinical studies have not focused on neutrophilic asthma. Phosphodiesterase inhibitors, anti-TSLP antibodies, azithromycin, and anti-cholinergic agents are promising drugs for neutrophilic asthma. However, clinical research targeting neutrophilic inflammation is required to elucidate the optimal treatment.

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.

Clinical Factors Influencing Endogenous Carbon Monoxide Production and Carboxyhemoglobin Levels in Neonates

Carboxyhemoglobin (COHb) is an index of endogenous carbon monoxide formation during the hem degradation process and could be used to confirm hemolysis in neonates. The influence of other clinical factors on COHb values in neonates has not been fully investigated. We aimed to evaluate the influence of hemolysis, sepsis, respiratory distress, and postnatal age on COHb values. We retrospectively analyzed COHb measurements determined with a carbon monoxide-oximeter in 4 groups of term neonates: A-sepsis, B-respiratory distress, C-hemolysis, and D-healthy neonates. The mean COHb values were 1.41% (SD: 0.26), 1.32% (SD: 0.27), 2.5% (SD: 0.69), and 1.27% (SD: 0.19) (P<0.001) in groups A (n=8), B (n=37), C (n=16), and D (n=76), respectively. COHb in group C was significantly higher than in the other groups. There was a negative correlation between postnatal age and COHb in healthy neonates. A cut-off level of 1.7% had 93% (95% confidence interval [CI]: 89%-97%) sensitivity and 94% (95% CI: 90%-98%) specificity for diagnosis of hemolysis. COHb values were higher during the first days of life. We found that COHb levels in neonates with hemolysis were significantly higher and that the influence of sepsis and respiratory distress on COHb values was insignificant.

High inhaled oxygen concentration quadruples exhaled CO in healthy volunteers monitored by a highly sensitive laser spectrometer

Carbon monoxide (CO) monitoring in human breath is the focus of many investigations as CO could possibly be used as a marker of various diseases. Detecting CO in human breath remains a challenge because low concentrations (<ppm) must be selectively detected and short response time resolution is needed to detect the end expiratory values reflecting actual alveolar concentrations. A laser spectroscopy based instrument was developed (ProCeas) that fulfils these requirements. The aim of this study was to validate the use of a ProCeas for human breath analysis in order to measure the changes of endogenous exhaled CO (eCO) induced by different inspired fractions of oxygen (FiO₂) ranging between 21% and 100%. This study was performed on healthy volunteers. 30 healthy awaked volunteers (including asymptomatic smokers) breathed spontaneously through a facial mask connected to the respiratory circuit of an anesthesiology station. FiO₂ was fixed to 21%, 50% and 100% for periods of 5 minutes. CO concentrations were continuously monitored throughout the experiment with a ProCeas connected to the airway circuit. The respiratory cycles being resolved, eCO concentration is defined by the difference between the value at the end of the exhalation phase and the level during inhalation phase. Inhalation of 100% FiO₂ increased eCO levels by a factor of four in every subjects (smokers and non smokers). eCO returned in a few minutes to the initial value when FiO₂ was switched back to 21%. This magnification of eCO at 21% and 100% FiO₂ is greater than those described in previous publications. We hypothesize that these results can be explained by the healthy status of our subjects (with low basal levels of eCO) and also by the better measurement precision of ProCeas.

Association between exhaled carbon monoxide and asthma outcomes in Peruvian children

BACKGROUND

Asthma prevalence continues to increase in low and middle-income countries, presenting challenges in assessing asthma control in resource-poor settings. Previous studies suggest that exhaled carbon monoxide (eCO) is higher with asthma severity and lower with treatment. We hypothesized that eCO levels may be elevated in children with asthma, particularly in children with partially controlled or uncontrolled asthma in a low-resource setting in Lima, Peru.

METHODS

We compared average eCO levels between 248 children with asthma and 221 healthy controls as well as the odds of asthma by eCO quartiles (0-1, 2, 3, and ≥4 ppm) using multivariable linear and logistic regression. eCO quartiles were also used to compare the odds of partially controlled or uncontrolled asthma (score ≤19 on the Asthma Control Test) in a multivariable logistic regression model.

FINDINGS

Average adjusted eCO level was 0.56 ppm (95% CI 0.07-1.05) higher in children with asthma. The adjusted odds of asthma were 1.22 (95% CI 0.75-1.97), 1.46 (0.81-2.63), and 1.76 (0.96-3.23) in the second, third, and fourth eCO quartiles compared to the first eCO quartile, respectively. Among children with asthma, the adjusted odds of partially controlled or uncontrolled asthma in those in the second, third, and fourth eCO quartiles, compared to the first, were 1.61 (95% CI 0.74-3.48), 3.66 (95% CI 1.51-8.87), and 2.50 (95% CI 1.06-5.90), respectively.

INTERPRETATION

eCO may serve as an inexpensive biomarker for asthma control, particularly in low-resource settings.

Low Power Operation of Temperature-Modulated Metal Oxide Semiconductor Gas Sensors

Mobile applications based on gas sensing present new opportunities for low-cost air quality monitoring, safety, and healthcare. Metal oxide semiconductor (MOX) gas sensors represent the most prominent technology for integration into portable devices, such as smartphones and wearables. Traditionally, MOX sensors have been continuously powered to increase the stability of the sensing layer. However, continuous power is not feasible in many battery-operated applications due to power consumption limitations or the intended intermittent device operation. This work benchmarks two low-power, duty-cycling, and on-demand modes against the continuous power one. The duty-cycling mode periodically turns the sensors on and off and represents a trade-off between power consumption and stability. On-demand operation achieves the lowest power consumption by powering the sensors only while taking a measurement. Twelve thermally modulated SB-500-12 (FIS Inc. Jacksonville, FL, USA) sensors were exposed to low concentrations of carbon monoxide (0-9 ppm) with environmental conditions, such as ambient humidity (15-75% relative humidity) and temperature (21-27 °C), varying within the indicated ranges. Partial Least Squares (PLS) models were built using calibration data, and the prediction error in external validation samples was evaluated during the two weeks following calibration. We found that on-demand operation produced a deformation of the sensor conductance patterns, which led to an increase in the prediction error by almost a factor of 5 as compared to continuous operation (2.2 versus 0.45 ppm). Applying a 10% duty-cycling operation of 10-min periods reduced this prediction error to a factor of 2 (0.9 versus 0.45 ppm). The proposed duty-cycling powering scheme saved up to 90% energy as compared to the continuous operating mode. This low-power mode may be advantageous for applications that do not require continuous and periodic measurements, and which can tolerate slightly higher prediction errors.

Changes in breathomics from a 1-year randomized smoking cessation trial of electronic cigarettes

BACKGROUND

Electronic cigarette (EC) use is an emerging behaviour that has been shown to help smokers to reduce cigarette consumption. The aim of this study was to illustrate long-term changes in exhaled breath measurements and respiratory symptoms in smokers invited to quit or reduce their cigarette consumption by switching to ECs.

MATERIALS AND METHODS

Prospective evaluation of cigarette consumption, fractional nitric oxide concentration in exhaled breath (FeNO), exhaled carbon monoxide (eCO) and symptom scores was performed in a 1-year randomized, controlled trial of 'healthy' smokers receiving 2·4% nicotine, 1·8% nicotine or no nicotine ECs. FeNO and eCO data are presented on the basis of participants' pooled continuous smoking phenotype classification (failures, reducers and quitters).

RESULTS

A significant effect of quitting classification was found on FeNo and eCO at all time points (P < 0·0001). Among quitters, FeNO (medians and interquartile range) rose from 5·5 (4·5-6·9) ppb to 17·7 (13·3-18·9) ppb by week 52. Baseline eCO (medians and interquartile range) decreased from 17 (12-20) ppm to 3 (1-4) ppm by week 52. No significant changes in FeNO and eCO levels were observed in failures and reducers. Improvements in FeNO and eCO levels were correlated with attenuations in symptom scores.

CONCLUSIONS

Smokers invited to switch to electronic cigarettes who completely abstained from smoking showed steady progressive improvements in their exhaled breath measurements and symptom scores. FeNo and eCO normalization is highly supportive of improved respiratory health outcomes and adds to the notion that quitting from tobacco smoking can reverse harm in the lung.

Biomarkers for differentiation of causes of respiratory distress in dogs and cats: Part 2--Lower airway, thromboembolic, and inflammatory diseases

OBJECTIVES

To review the current veterinary and relevant human literature regarding biomarkers of respiratory diseases leading to dyspnea and to summarize the availability, feasibility, and practicality of using respiratory biomarkers in the veterinary setting.

DATA SOURCES

Veterinary and human medical literature: original research articles, scientific reviews, consensus statements, and recent textbooks.

HUMAN DATA SYNTHESIS

Numerous biomarkers have been evaluated in people for discriminating respiratory disease processes with varying degrees of success.

VETERINARY DATA SYNTHESIS

Although biomarkers should not dictate clinical decisions in lieu of gold standard diagnostics, their use may be useful in directing care in the stabilization process. Serum immunoglobulins have shown promise as an indicator of asthma in cats. A group of biomarkers has also been evaluated in exhaled breath. Of these, hydrogen peroxide has shown the most potential as a marker of inflammation in asthma and potentially aspiration pneumonia, but methods for measurement are not standardized. D-dimers may be useful in screening for thromboembolic disease in dogs. There are a variety of markers of inflammation and oxidative stress, which are being evaluated for their ability to assess the severity and type of underlying disease process. Of these, amino terminal pro-C-type natriuretic peptide may be the most useful in determining if antibiotic therapy is warranted. Although critically evaluated for their use in respiratory disorders, many of the biomarkers which have been evaluated have been found to be affected by more than one type of respiratory or systemic disease.

CONCLUSION

At this time, there are point-of-care biomarkers that have been shown to reliably differentiate between causes of dyspnea in dogs and cats. Future clinical research is warranted to understand of how various diseases affect the biomarkers and more bedside tests for their utilization.

Exhaled nitric oxide and carbon monoxide in mechanically ventilated brain-injured patients

The inflammatory influence and biological markers of prolonged mechanical-ventilation in uninjured human lungs remains controversial. We investigated exhaled nitric oxide (NO) and carbon monoxide (CO) in mechanically-ventilated, brain-injured patients in the absence of lung injury or sepsis at two different levels of positive end-expiratory pressure (PEEP). Exhaled NO and CO were assessed in 27 patients, without lung injury or sepsis, who were ventilated with 8 ml kg(-1) tidal volumes under zero end-expiratory pressure (ZEEP group, n  =  12) or 8 cm H2O PEEP (PEEP group, n  =  15). Exhaled NO and CO was analysed on days 1, 3 and 5 of mechanical ventilation and correlated with previously reported markers of inflammation and gas exchange. Exhaled NO was higher on day 3 and 5 in both patient groups compared to day 1: (PEEP group: 5.8 (4.4-9.7) versus 11.7 (6.9-13.9) versus 10.7 (5.6-16.6) ppb (p  <  0.05); ZEEP group: 5.3 (3.8-8.8) versus 9.8 (5.3-12.4) versus 9.6 (6.2-13.5) ppb NO peak levels for days 1, 3 and 5, respectively, p  <  0.05). Exhaled CO remained stable on day 3 but significantly decreased by day 5 in the ZEEP group only (6.3 (4.3-9.0) versus 8.1 (5.8-12.1) ppm CO peak levels for day 5 versus 1, p  <  0.05). The change scores for peak exhaled CO over day 1 and 5 showed significant correlations with arterial blood pH and plasma TNF levels (r s  =  0.49, p  =  0.02 and r s  =  -0.51 p  =  0.02, respectively). Exhaled NO correlated with blood pH in the ZEEP group and with plasma levels of IL-6 in the PEEP group. We observed differential changes in exhaled NO and CO in mechanically-ventilated patients even in the absence of manifest lung injury or sepsis. These may suggest subtle pulmonary inflammation and support application of real time breath analysis for molecular monitoring in critically ill patients.

Carbon monoxide in the treatment of sepsis

Carbon monoxide (CO), a low-molecular-weight gas, is endogenously produced in the body as a product of heme degradation catalyzed by heme oxygenase (HO) enzymes. As the beneficial roles of HO system have been elucidated in vitro and in vivo, CO itself has also been reported as a potent cytoprotective molecule. Whereas CO represents a toxic inhalation hazard at high concentration, low-dose exogenous CO treatment (~250-500 parts per million) demonstrates protective functions including but not limited to the anti-inflammatory and antiapoptotic effects in preclinical models of human diseases. Of note, CO exposure confers protection in animal models of sepsis by inhibiting inflammatory responses and also enhancing bacterial phagocytosis in leukocytes. These unique functions of CO including both dampening inflammation and promoting host defense mechanism are mediated by multiple pathways such as autophagy induction or biosynthesis of specialized proresolving lipid mediators. We suggest that CO gas may represent a novel therapy for patients with sepsis.

Noninvasive effects measurements for air pollution human studies: methods, analysis, and implications

Human exposure studies, compared with cell and animal models, are heavily relied upon to study the associations between health effects in humans and air pollutant inhalation. Human studies vary in exposure methodology, with some work conducted in controlled settings, whereas other studies are conducted in ambient environments. Human studies can also vary in the health metrics explored, as there exists a myriad of health effect end points commonly measured. In this review, we compiled mini reviews of the most commonly used noninvasive health effect end points that are suitable for panel studies of air pollution, broken into cardiovascular end points, respiratory end points, and biomarkers of effect from biological specimens. Pertinent information regarding each health end point and the suggested methods for mobile collection in the field are assessed. In addition, the clinical implications for each health end point are summarized, along with the factors identified that can modify each measurement. Finally, the important research findings regarding each health end point and air pollutant exposures were reviewed. It appeared that most of the adverse health effects end points explored were found to positively correlate with pollutant levels, although differences in study design, pollutants measured, and study population were found to influence the magnitude of these effects. Thus, this review is intended to act as a guide for researchers interested in conducting human exposure studies of air pollutants while in the field, although there can be a wider application for using these end points in many epidemiological study designs.

Point-of-care end-tidal carbon monoxide reflects severity of hemolysis in sickle cell anemia

Carbon monoxide (CO) production from heme catabolism is increased with hemolysis. A portable end-tidal CO (ETCO) monitor was used to analyze breath samples in 16 children with sickle cell anemia (SCA, 5-14 years). Median (range) ETCO for SCA was 4.35 ppm (1.8-9.7) versus 0.80 ppm (0.2-2.3) for controls (P < 0.001). ETCOc >2.1 ppm provided sensitivity and specificity of 93.8% (69.8-99.8%) for detecting SCA. ETCO correlated with reticulocytosis (P = 0.015) and bilirubin (P = 0.009), and was 32% lower in children receiving hydroxyurea (P = 0.09). Point-of-care ETCO analysis may prove useful for non-invasive monitoring of hemolysis and as a screening test for SCA.

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.

Real-time measurements of endogenous carbon monoxide production in isolated pig lungs

Ischemia-reperfusion injuries are a critical determinant of lung transplantation success. The endogenous production of carbon monoxide (CO) is triggered by ischemia-reperfusion injuries. Our aim was, therefore, to assess the feasibility of exhaled CO measurements during the ex vivo evaluation of lungs submitted to ischemia-reperfusion injuries. Five pigs were euthanized and their lungs removed after pneumoplegia. After cold storage (30 min, 4°C), the lungs were connected to an extracorporeal membrane oxygenation circuit, slowly warmed-up, and ventilated. At the end of a 45-min steady state, CO measurements were performed by optical-feedback cavity-enhanced absorption spectroscopy, a specific laser-based technique for noninvasive and real-time low gas concentration measurements. Exhaled CO concentration from isolated lungs reached 0.45±0.19  ppmv and was above CO concentration in ambient air and in medical gas. CO variations peaked during the expiratory phase. Changes in CO concentration in ambient air did not alter CO concentrations in isolated lungs. Exhaled CO level was also found to be uncorrelated to heme oxygenase (HO-1) gene expression. These results confirm the feasibility of accurate and real-time CO measurement in isolated lungs. The presented technology could help establishing the exhaled CO concentration as a biomarker of ischemia-reperfusion injury in ex vivo lung perfusion.

Asthma across the ages: knowledge gaps in childhood asthma

The Eunice Kennedy Shriver National Institute of Child Health and Human Development convened an Asthma Group in response to the Best Pharmaceuticals for Children Act. The overall goal of the Best Pharmaceuticals for Children Act Program is to improve pediatric therapeutics through preclinical and clinical drug trials that lead to drug-labeling changes. Although significant advances have been made in the understanding and management of asthma in adults with appropriately labeled medications, less information is available on the management of asthma in children. Indeed, many medications are inadequately labeled for use in children. In general, the younger the child, the less information there is available to guide clinicians. Because asthma often begins in early childhood, it is incumbent on us to continue to address the primary questions raised in this review and carefully evaluate the medications used to manage asthma in children. Meanwhile, continued efforts should be made in defining effective strategies that reduce the risk of exacerbations. If the areas of defined need are addressed in the coming years, namely prevention of exacerbations and progression of disease, as well as primary intervention, we will see continuing reduction in asthma mortality and morbidity along with improved quality of life for children with asthma.

Therapeutic applications of carbon monoxide

Heme oxygenase-1 (HO-1) is a regulated enzyme induced in multiple stress states. Carbon monoxide (CO) is a product of HO catalysis of heme. In many circumstances, CO appears to functionally replace HO-1, and CO is known to have endogenous anti-inflammatory, anti-apoptotic, and antiproliferative effects. CO is well studied in anoxia-reoxygenation and ischemia-reperfusion models and has advanced to phase II trials for treatment of several clinical entities. In alternative injury models, laboratories have used sepsis, acute lung injury, and systemic inflammatory challenges to assess the ability of CO to rescue cells, organs, and organisms. Hopefully, the research supporting the protective effects of CO in animal models will translate into therapeutic benefits for patients. Preclinical studies of CO are now moving towards more complex damage models that reflect polymicrobial sepsis or two-step injuries, such as sepsis complicated by acute respiratory distress syndrome. Furthermore, co-treatment and post-treatment with CO are being explored in which the insult occurs before there is an opportunity to intervene therapeutically. The aim of this review is to discuss the potential therapeutic implications of CO with a focus on lung injury and sepsis-related models.

Recent advances in asthma biomarker research

Asthma is characterized by recurrent and reversible airflow obstruction, which is routinely monitored by history and physical examination, spirometry and home peak flow diaries. As airway inflammation is central to asthma pathogenesis, its monitoring should be part of patient management plans. Fractional exhaled nitric oxide level (FeNO) is the most extensively studied biomarker of airway inflammation, and FeNO references were higher in Chinese (Asians) than Whites. Published evidence was inconclusive as to whether FeNO is a useful management strategy for asthma. Other biomarkers include direct (histamine, methacholine) and indirect (adenosine, hypertonic saline) challenges of bronchial hyperresponsiveness (BHR), induced sputum and exhaled breath condensate (EBC). A management strategy that normalized sputum eosinophils among adult patients resulted in reductions of BHR and asthma exacerbations. However, subsequent adult and pediatric studies failed to replicate these benefits. Asthma phenotypes as defined by inflammatory cell populations in sputum were also not stable over a 12-month period. A recent meta-analysis concluded that induced sputum is not accurate enough to be applied in routine monitoring of childhood asthma. There is poor correlation between biomarkers that reflect different asthma dimensions: spirometry (airway caliber), BHR (airway reactivity) and FeNO or induced sputum (airway inflammation). Lastly, EBC is easily obtained noninvasively by cooling expired air. Many biomarkers ranging from acidity (pH), leukotrienes, aldehydes, cytokines to growth factors have been described. However, significant overlap between groups and technical difficulty in measuring low levels of inflammatory molecules are the major obstacles for EBC research. Metabolomics is an emerging analytical method for EBC biomarkers. In conclusion, both FeNO and induced sputum are useful asthma biomarkers. However, they will only form part of the clinical picture. Longitudinal studies with focused hypotheses and well-designed protocols are needed to establish the roles of these biomarkers in asthma management. The measurement of biomarkers in EBC remains a research tool.

Elevated Carboxyhemoglobin in Active Asthma and Allergic Rhinitis as Measured by Pulse CO-Oximetry

Elevated levels of exhaled carbon monoxide have been reported in patients with active or persistent asthma or allergic rhinitis. With the recent availability of a noninvasive pulse CO-Oximeter that measures carboxyhemoglobin, measurements were made on healthy clinic staff as well as children with controlled or active asthma and asymptomatic or active allergic rhinitis to assess whether this test might have applicability in these diseases. Carboxyhemoglobin (SpCO%) was measured by a pulse CO-Oximeter during an initial clinic assessment of patients by a single physician in a Pediatric Pulmonary Clinic. Fifty-one patients with uncontrolled asthma (average age 7.8 years) had an average SpCO% of 4.8%, and 87 patients with controlled asthma (average age 8.8 years) had an average SpCO% of 0.3%, a significant difference, P<0.001. Seven patients with vocal cord dysfunction (average age 13.6 years) had an average SpCO% of 0.43%. In regard to allergic rhinitis, 122 symptomatic patients (average age 6.9 years) had an average SpCO% of 7.3%, while 40 asymptomatic patients (average age 7.4 years) had an average SpCO% of 1.5%, P<0.001%. These preliminary observations suggest that SpCO% may be a useful, noninvasive measure of asthma or allergic rhinitis activity.

Carbon monoxide in exhaled breath testing and therapeutics

Carbon monoxide (CO), a low molecular weight gas, is a ubiquitous environmental product of organic combustion, which is also produced endogenously in the body, as the byproduct of heme metabolism. CO binds to hemoglobin, resulting in decreased oxygen delivery to bodily tissues at toxicological concentrations. At physiological concentrations, CO may have endogenous roles as a potential signaling mediator in vascular function and cellular homeostasis. Exhaled CO (eCO), similar to exhaled nitric oxide (eNO), has been evaluated as a candidate breath biomarker of pathophysiological states, including smoking status, and inflammatory diseases of the lung and other organs. eCO values have been evaluated as potential indicators of inflammation in asthma, stable COPD and exacerbations, cystic fibrosis, lung cancer, or during surgery or critical care. The utility of eCO as a marker of inflammation and its potential diagnostic value remain incompletely characterized. Among other candidate 'medicinal gases' with therapeutic potential, (e.g., NO and H2S), CO has been shown to act as an effective anti-inflammatory agent in preclinical animal models of inflammatory disease, acute lung injury, sepsis, ischemia/reperfusion injury and organ graft rejection. Current and future clinical trials will evaluate the clinical applicability of this gas as a biomarker and/or therapeutic in human disease.

Clinical expert panel on monitoring potential lung toxicity of inhaled oligonucleotides: consensus points and recommendations

Oligonucleotides (ONs) are an emerging class of drugs being developed for the treatment of a wide variety of diseases including the treatment of respiratory diseases by the inhalation route. As a class, their toxicity on human lungs has not been fully characterized, and predictive toxicity biomarkers have not been identified. To that end, identification of sensitive methods and biomarkers that can detect toxicity in humans before any long term and/or irreversible side effects occur would be helpful. In light of the public's greater interests, the Inhalation Subcommittee of the Oligonucleotide Safety Working Group (OSWG) held expert panel discussions focusing on the potential toxicity of inhaled ONs and assessing the strengths and weaknesses of different monitoring techniques for use during the clinical evaluation of inhaled ON candidates. This white paper summarizes the key discussions and captures the panelists' perspectives and recommendations which, we propose, could be used as a framework to guide both industry and regulatory scientists in future clinical research to characterize and monitor the short and long term lung response to inhaled ONs.

Laparoscopic vs open herniorrhaphy in the management of pediatric inguinal hernia: a systemic review and meta-analysis

PURPOSE

Laparoscopic herniorrhaphy (LH) has been evolved as a minimally invasive technique for pediatric inguinal hernias (PIHs). Considerable debate exists regarding the benefits of LH over conventional open herniorrhaphy (OH). The aim of this review was to critique the current literature to determine the efficacy of LH.

METHODS

Published studies until July 30, 2010, were searched from Medline, Embase, Ovid, Web of Science, and Cochrane databases. Randomized controlled trials (RCTs) and observational clinical studies (OCSs) with a comparison of LH and OH were included. A systemic review and meta-analysis were performed using the odds ratios (ORs) for dichotomous variables and weighted mean differences (WMDs) for continuous variables.

RESULTS

Of 138 studies, 3 RCTs and 4 OCSs were eligible for inclusion criteria, comprising 1543 cases of LH and 657 cases of OH. Compared with OH, shorter operative time for bilateral hernias (WMD = -11.14; 95% confidence interval [CI], -20.61 to -1.68; P = .02) and lower rate of metachronic contralateral hernia (OR, 0.26; 95% CI, 0.09-0.76; P = .01) were noted in LH. However, no significant difference was observed between LH and OH in patients' age, sex, affected side, operative time for unilateral hernias, duration of hospital stay, time to resume full activity, recurrence, and complications.

CONCLUSIONS

Laparoscopic herniorrhaphy is superior to OH in the repair of bilateral PIH and lower rate of metachronic contralateral hernia, with similar operative time for unilateral hernias, length of hospital stay, recurrence, and complication rates. Because of the publishing bias, a series of RCTs with standard report format and uniform unit are necessary to explore the efficiencies of LH in the management of PIH.

Laparoscopic versus open orchiopexy for non-palpable undescended testes in children: a systemic review and meta-analysis

BACKGROUND

Laparoscopic orchidopexy (LO) has been widespread used in the management of non-palpable testis (NPT) in children. However, the real advantages of LO over traditional open orchidopexy (OO) still remain exclusive.

METHODS

Published studies until August 31, 2010 were searched from Medline, Embase, Ovid, Web of Science, and Cochrane databases. Randomized controlled trials (RCTs) and observational clinical studies (OCSs) with a comparison of LO and OO were included for a systemic review and meta-analysis.

RESULTS

Out of 226 studies, 2 RCTs and 5 OCSs were eligible for inclusion criteria, comprising 176 cases of LO and 263 cases of OO. The hospital stay of LO was significantly shorter than that of OO (WMD = -0.66; 95% confidence interval [CI] = -0.95 to -0.37; P < 0.00001). However, no significant difference was observed between LO and OO in operative time (WMD = 4.02; 95% CI = -9.89 to 17.93; P = 0.57), time to resume feeding (WMD = -2.29; 95% CI = -6.78 to 2.20; P = 0.32) or full activity (WMD = -9.71; 95% CI = -27.84 to 8.42; P = 0.29), recurrence (OR = 0.60; 95% CI = 0.13 to 2.72; P = 0.51), viable testis rate (OR = 1.61; 95% CI = 0.30 to 8.52; P = 0.58), success rate (OR = 1.41; 95% CI = 0.44 to 4.46; P = 0.56), and testicular atrophy (OR = 1.70; 95% CI = 0.49 to 5.98; P = 0.40).

CONCLUSION

Although shorter hospital stay is noted in LO, it does not provide significant advantage over open surgery for treating NPT. However, due to the publishing bias, a series of RCTs are necessary to explore the efficiencies of LO in the management of NPT in children.

Gaseotransmitters: new frontiers for translational science

Translational research on endogenous gaseous mediators--nitric oxide, carbon monoxide, and hydrogen sulfide--has exploded over the past decade. Drugs that modulate either the gaseous mediators themselves or their related intracellular signaling pathways are already in use in the clinics, and still more are being tested in preclinical models and clinical trials. Discussed here are the chemical and pharmacological properties that present challenges for the translation of these potentially toxic molecules.

Human exhaled breath analysis

OBJECTIVE

To review the fast-developing topic of assessment of exhaled breath components to improve the diagnosis and monitoring of respiratory and systemic diseases.

DATA SOURCES

Review of the literature available in monographs and journals.

STUDY SELECTION

Articles and overviews on the broad spectrum of existing experimental and routinely applied methods to assess different aspects of human exhaled breath analysis were selected for presentation in this review.

RESULTS

Exhaled breath constitutes more than 3,500 components, the bulk of which are volatile organic compounds in miniature quantities. Many of these characterize the functioning of the organism as a whole (systemic biomarkers), but some are related to processes taking place in the respiratory system and the airways in particular (lung biomarkers). Assessment of lung biomarkers has proven useful in airway inflammatory diseases. It involves direct measurement of gases such as nitric oxide and inflammatory indicators in exhaled breath condensate such as oxidative stress markers (eg, hydrogen peroxide and isoprostanes), nitric oxide derivatives (eg, nitrate and nitrates), arachidonic acid metabolites (eg, prostanoids, leukotrienes, and epoxides), adenosine, and cytokines. Integral approaches have also been suggested, such as exhaled breath temperature measurement and devices of the "electronic nose" type, which enable the capture of approaches have also been suggested, such as exhaled breath temperature measurementexhaled molecular fingerprints (breath prints). Technical factors related to standardization of the different techniques need to be resolved to reach the stage of routine applicability.

CONCLUSIONS

Examination of exhaled breath has the potential to change the existing routine approaches in human medicine. The rapidly developing new analytical and computer technologies along with novel, unorthodox ideas are prerequisites for future advances in this field.

Hydrogen peroxide in exhaled breath condensate in patients with asthma: a promising biomarker?

BACKGROUND

The measurement of hydrogen peroxide (H(2)O(2)) in exhaled breath condensate (EBC) has been proposed as a noninvasive way of monitoring airway inflammation. However, results from individual studies on EBC H(2)O(2) evaluation of asthma are conflicting. The purpose of this study was to explore whether EBC H(2)O(2) is elevated in people with asthma and whether it reflects disease severity and disease control or responds to corticosteroid treatment.

METHODS

Studies were identified by searching PubMed, Embase, Cochrane Database, Cumulative Index to Nursing and Allied Health Literature (CINAHL), and www.controlled-trials.com for relevant reports published before September 2010. Observational studies comparing levels of EBC H(2)O(2) between patients with asthma who were nonsmokers and healthy subjects were included. Data were independently extracted by two investigators and analyzed using Stata 10.0 software.

RESULTS

Eight studies (involving 728 participants) were included. EBC H(2)O(2) concentrations were significantly higher in patients with asthma who were nonsmokers compared with healthy subjects, and higher values of EBC H(2)O(2) were observed at each level of asthma, classified either by severity or control level, and the values were negatively correlated with FEV(1). In addition, EBC H(2)O(2) concentrations were lower in patients with asthma treated with corticosteroids than in patients with asthma not treated with corticosteroids.

CONCLUSIONS

H(2)O(2) might be a promising biomarker for guiding asthma treatment. However, further investigation is needed to establish its role.

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.

Endogenous carbon monoxide production in disease

Carbon monoxide (CO) in tissues and cells can originate from inhalation of CO or endogenously. Endogenous production, carboxyhemoglobin (COHb) formation, and exhaled CO levels are influenced by physiological factors, including disease. It is suggested that endogenous CO production can be used as a biomarker for oxidative and inflammatory processes. Also, endogenous CO can contribute to increased body burden of CO, which may both disrupt normal CO signaling cascades and increase the risk of CO toxicity.