Sampling Airway Surface Liquid: Non-Volatilesin the Exhaled Breath Condensate

Current Evidence Supporting the Role of miRNA as a Biomarker for Lung Cancer Diagnosis Through Exhaled Breath Condensate Collection: A Narrative Review

Lung cancer, the leading cause of cancer-related mortality, has brought exhaled breath condensate (EBC) into focus as a promising non-invasive sample for detecting molecular biomarkers, particularly microRNAs, which regulate gene expression and contribute to tumorigenesis. Ten key studies encompassing approximately 866 subjects consistently demonstrated distinct patterns of miRNA dysregulation in lung cancer. Notably, several reported panels achieved diagnostic sensitivity and specificity exceeding 75% through the identification of distinct miRNA signatures in EBC, with oncogenic miRNAs (e.g., miR-21) upregulated and tumor-suppressor miRNAs (e.g., miR-486) downregulated in lung cancer patients. Analytical advancements, including next-generation sequencing (NGS), have improved miRNA detection sensitivity and specificity, addressing prior limitations of low yield and variability. NGS enabled the identification of novel miRNAs and proved especially effective in overcoming the low RNA yield associated with EBC samples. However, challenges persist regarding standardization of collection, sample dilution, and potential contamination. Moreover, the reproducibility of miRNA signatures across diverse patient populations remains a critical issue. Large-scale, multicenter validation studies are needed to establish robust diagnostic algorithms integrating EBC-derived miRNAs with existing clinical tools. The potential of EBC miRNA profiling to support current screening strategies could significantly improve early lung cancer detection and patient outcomes. Nevertheless, its clinical transition requires further methodological optimization and biomarker validation. This review critically evaluates current evidence on miRNA detection in EBC for lung cancer diagnosis.

Breath and Sputum Analyses in Asthmatic Patients: An Overview

Recent advancements in asthma management include non-invasive methodologies such as sputum analysis, exhaled breath condensate (EBC), and fractional exhaled nitric oxide (FeNO). These techniques offer a means to assess airway inflammation, a critical feature of asthma, without invasive procedures. Sputum analysis provides detailed insights into airway inflammation patterns and cellular composition, guiding personalized treatment strategies. EBC collection, reflecting bronchoalveolar lining fluid composition, provides a non-invasive window into airway physiology. FeNO emerges as a pivotal biomarker, offering insights into eosinophilic airway inflammation and aiding in asthma diagnosis, treatment monitoring, and the prediction of exacerbation risks. Despite inherent limitations, each method offers valuable tools for a more comprehensive assessment of asthma. Combining these techniques with traditional methods like spirometry may lead to more personalized treatment plans and improved patient outcomes. Future research is crucial to refine protocols, validate biomarkers, and establish comprehensive guidelines in order to enhance asthma management with tailored therapeutic strategies and improved patient outcomes.

Biomarkers in exhaled breath condensate as fingerprints of asthma, chronic obstructive pulmonary disease and asthma-chronic obstructive pulmonary disease overlap: a critical review

Asthma, chronic obstructive pulmonary disease (COPD) and asthma-COPD overlap are the third leading cause of mortality around the world. They share some common features, which can lead to misdiagnosis. To properly manage these conditions, reliable markers for early and accurate diagnosis are needed. Over the past 20 years, many molecules have been investigated in the exhaled breath condensate to better understand inflammation pathways and mechanisms related to these disorders. Recently, more advanced techniques, such as sensitive metabolomic and proteomic profiling, have been used to obtain a more comprehensive understanding. This article reviews the use of targeted and untargeted metabolomic methodology to study asthma, COPD and asthma-COPD overlap.

HBM4EU chromates study - the measurement of hexavalent and trivalent chromium in exhaled breath condensate samples from occupationally exposed workers across Europe

The aim of this study was to investigate the practicability of exhaled breath condensate (EBC) as a biological matrix to detect and measure hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) in workers occupationally exposed to Cr(VI). EBC samples were collected from workers in France, Finland, Italy, The Netherlands and the United Kingdom from three different target activities: chrome platers, stainless steel welders and surface treatment workers. Pre and post working week EBC samples were collected from 177 exposed workers and 98 unexposed workers (control group). Hyphenated chromatography systems with inductively coupled plasma - mass spectrometry (ICP-MS) were for the analysis. The results showed that the occupationally exposed workers had significantly higher levels of Cr(VI) and Cr(III) than the control group. Chrome platers exhibited the highest Cr(VI) levels in their EBC samples, with a significant increase from their pre to post samples for both Cr(VI) and Cr(III). A significant difference was also found between pre and post EBC samples for Cr(III) in welders. This study has shown that EBC has the potential to be a valid, non-invasive biological matrix to assess occupational exposure to Cr(VI) and Cr(III) for biological monitoring assessment, with the ability to detect low level inhalation exposures.

The Differences in the Levels of Oxidative Status Marker and Soluble CD95 in Patients with Moderate to Severe COPD during an Exacerbation and a Stable Period

Studying the features of changes in markers of oxidative stress (OS) and inflammation indicators in COPD patients depending on the degree of bronchial obstruction is one of the priority directions for improving the prognosis and monitoring of the course of this pathology. We conducted a comparative investigation of changes in markers of OS and apoptosis at the systemic and local levels in patients with moderate to severe COPD during exacerbation and stable phase. 105 patients with COPD aged 46-67 and 21 healthy nonsmoking volunteers comparable in age were examined. COPD patients were divided into four groups: moderate COPD (GOLDII) during the exacerbation (GOLDIIex, $n=25$ ) and in the stable phase (GOLDIIst, $n=27$ ), severe COPD (GOLDIII) during the exacerbation (GOLDIIIex, $n=29$ ), and in the stable phase (GOLDIIIst, $n=24$ ). We studied the levels of such lipid peroxidation (LPO) products as diene conjugates (DC) and Schiff bases (SB) and parameters of induced chemiluminescence (Imax, total light sum-S, Imax/S) in blood serum, as well as sCD95 concentration in blood and exhaled breath condensate (EBC). The relationship between the values of the OS system indicators with sCD95, as well as with the parameters of lung function, was investigated. Multidirectional changes in OS indicator levels in COPD patients depending on the severity of obstructive airway disorders have been established. The maximum values of DC ( $0.26\pm 0.046\text{RU}$ ), Imax ( $0.265\pm 0.19$ RLU), and Imax/S ( $0.13\pm 0.05$ ) were typical for patients with moderate COPD, while the highest SB level ( $5.7\pm 2.3$ RU) was observed in severe COPD during an exacerbation. The exacerbation of the disease was characterized by an increase in DC concentration in both GOLDIIex ( $0.26\pm 0.046$ RU) and GOLDIIIex ( $0.209\pm 0.02$ RU) compared to the stable moderate and severe COPD ( $0.202\pm 0.028$ RU and $0.19\pm 0.03$ RU, respectively, $p<0.05$ ). The established decrease in high values of DC, Imax, Imax/S, and sCD95 and an increase in SB concentration in GOLD III can serve as quantitative indicators of the prognosis of the severity of the disease. The serum concentration of sCD95 in GOLDIIex ( $366.4\pm 70.5$  U/ml) and GOLDIIst ( $361.4\pm 72.8$  U/ml) did not differ from the control group ( $393.7\pm 80.9$  U/ml, $p>0.05$ ). In patients with $\text{FEV}1<49\%$ during the exacerbation and stable phase, the serum levels of Imax/S ( $0.058\pm 0.01$ and $0.062\pm 0.01$ ) and sCD95 ( $318.2\pm 66.3$  U/ml and $321.4\pm 42.5$  U/ml) were lower than the values of healthy volunteers ( $0.08\pm 0.01$ and $393.7\pm 80.9$  U/ml, respectively, $p<0.05$ ). A positive correlation between sCD95 concentration and airway obstruction degree in all examined COPD patients was established. The revealed numerous associations between sCD95 and OS marker levels in GOLDIII indicate a relationship between systemic radical stress and apoptosis processes both in the respiratory tract and the whole body under conditions of severe inflammation. The established correlations between the values of DC, Imax, and sCD95 in the blood serum and the lung function parameters in all studied patients allow us to consider these indicators as additional prognostic indicators of disease intensification. Our work results help clarify the participation and detail of FRO and apoptosis processes in developing pathophysiological features in moderate to severe COPD in different periods and, accordingly, improve the efficiency of diagnosis and treatment of the disease.

Breathomics: Review of Sample Collection and Analysis, Data Modeling and Clinical Applications

Metabolomics research is rapidly gaining momentum in disease diagnosis, on top of other Omics technologies. Breathomics, as a branch of metabolomics is developing in various frontiers, for early and noninvasive monitoring of disease. This review starts with a brief introduction to metabolomics and breathomics. A number of important technical issues in exhaled breath collection and factors affecting the sampling procedures are presented. We review the recent progress in metabolomics approaches and a summary of their applications on the respiratory and non-respiratory diseases investigated by breath analysis. Recent reports on breathomics studies retrieved from Scopus and Pubmed were reviewed in this work. We conclude that analyzing breath metabolites (both volatile and nonvolatile) is valuable in disease diagnoses, and therefore believe that breathomics will turn into a promising noninvasive discipline in biomarker discovery and early disease detection in personalized medicine. The problem of wide variations in the reported metabolite concentrations from breathomics studies should be tackled by developing more accurate analytical methods and sophisticated numerical analytical alogorithms.

Macromolecular biomarkers of chronic obstructive pulmonary disease in exhaled breath condensate

Biomarkers provide important diagnostic and prognostic information on heterogeneous diseases such as chronic obstructive pulmonary disease (COPD). However, finding a suitable specimen for clinical analysis of biomarkers for COPD is challenging. Exhaled breath condensate (EBC) sampling is noninvasive, rapid, cost-effective and easily repeatable. EBC sampling has also provided recent progress in the identification of biological macromolecules, such as lipids, proteins and DNA in EBC samples, which has increased its utility for clinical scientists. In this article, we review applications involving EBC sampling for the analysis of COPD biomarkers and discuss its future potential.

Metabolomics of Exhaled Breath Condensate by Nuclear Magnetic Resonance Spectroscopy and Mass Spectrometry: A Methodological Approach

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Respiratory diseases present a very high prevalence in the general population, with an increase in morbidity, mortality and health-care expenses worldwide. They are complex and heterogeneous pathologies that may present different pathological facets in different subjects, often with personal evolution. Therefore, there is a need to identify patients with similar characteristics, prognosis or treatment, defining the so-called phenotype, but also to mark specific differences within each phenotype, defining the endotypes.

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Biomarkers are very useful to study respiratory phenotypes and endotypes. Metabolomics, one of the recently introduced “omics”, is becoming a leading technique for biomarker discovery. For the airways, metabolomics appears to be well suited as the respiratory tract offers a natural matrix, the Exhaled Breath Condensate (EBC), in which several biomarkers can be measured. In this review, we will discuss the main methodological issues related to the application of Nuclear Magnetic Resonance (NMR) spectroscopy and Mass Spectrometry (MS) to EBC metabolomics for investigating respiratory diseases.

Mass Spectrometry Analysis of the Exhaled Breath Condensate and Proposal of Dermcidin and S100A9 as Possible Markers for Lung Cancer Prognosis

INTRODUCTION

New sampling techniques to analyse lung diseases, such as exhaled breath condensate (EBC), are a breakthrough in research field since they are less invasive and less traumatic for the patients compared to lung biopsies. Nevertheless, there is an increasing need to optimize not only the sampling protocols but the storage and processing of specimens to get accurate results.

METHODS

Exhaled breath condensate was sampled employing the ECoScreen device. Concentrated protein was obtained after ultracentrifugation, lyophilization and reversed-phase chromatography. MALDI-time of flight (TOF)/TOF mass spectrometry (MS) was applied to determine the protein profile in EBC. Commercially available ELISA kits were used to detect the selected biomarker in the EBC after MALDI-MS proteins identification.

RESULTS

The obtained EBC volume after two periods of 10 min doubled the amount obtained after 20 min. One hundred peptides were detected by MALDI-MS, and 18 proteins were identified after reversed-phase chromatography concentration. Dermcidin (P81605), S100A9 (P06702) and Cathepsin G (P08311) were selected to be analysed by ELISA. Dermcidin and S100A9 expression were statistically higher in lung cancer versus healthy volunteers. VEGF concentrations decreased, respectively, by 5.94 and 11.42-fold after 1 and 2 years of frozen EBC preservation in parallel with the declined number of proteins identified by MALDI-MS.

CONCLUSION

Exhaled breath condensate analysis combined with MS technique may become a valuable method for lung cancer screening and Dermcidin and S100A9 may serve as biomarkers for lung cancer diagnosis or prognosis.

Exhaled breath condensate nitrite in premature infants with bronchopulmonary dysplasia

BACKGROUND

Tracheal aspirate is the conventional method to measure biomarkers of inflammation and oxidation from premature infants on mechanical ventilation at risk for bronchopulmonary dysplasia (BPD), but this method is invasive. Exhaled breath condensate (EBC) is a novel, non-invasive method that has been used in older populations. Nitrite, a stable metabolite of nitric oxide (NO), is elevated in inflammatory conditions. We aim to investigate the feasibility of EBC nitrite collection from ventilated premature infants and to quantify EBC nitrite in infants with and without BPD. We hypothesize that EBC nitrite correlates with TA nitrite, and that EBC nitrite in the first week of life is higher in infants who will develop BPD than those without BPD.

METHODS

In a pilot prospective cohort study, TA and EBC were collected in the first week of life from mechanically ventilated premature infants. Nitrite levels were measured using chemiluminescence.

RESULTS

EBC nitrite significantly correlated with TA nitrite (r = 0.45, p = 0.025). Of 40 infants, 33 (82.5%) developed BPD. EBC and TA nitrite levels collected in the first week of life had a higher trend in infants with BPD than those without BPD (p = 0.23 and 0.38 respectively).

CONCLUSIONS

Higher trend of EBC nitrite in the first week of life was associated with the development of BPD. Correlation of nitrite level in EBC with that in TA (conventional method) highlights the utility of EBC as an alternative, non-invasive method to measure inflammation. Further refinement of conditions and timing may optimize the predictive value of EBC nitrite.

Evolution of clinical and environmental health applications of exhaled breath research: Review of methods and instrumentation for gas-phase, condensate, and aerosols

Human breath, along with urine and blood, has long been one of the three major biological media for assessing human health and environmental exposure. In fact, the detection of odor on human breath, as described by Hippocrates in 400 BC, is considered the first analytical health assessment tool. Although less common in comparison to contemporary bio-fluids analyses, breath has become an attractive diagnostic medium as sampling is non-invasive, unlimited in timing and volume, and does not require clinical personnel. Exhaled breath, exhaled breath condensate (EBC), and exhaled breath aerosol (EBA) are different types of breath matrices used to assess human health and disease state. Over the past 20 years, breath research has made many advances in assessing health state, overcoming many of its initial challenges related to sampling and analysis. The wide variety of sampling techniques and collection devices that have been developed for these media are discussed herein. The different types of sensors and mass spectrometry instruments currently available for breath analysis are evaluated as well as emerging breath research topics, such as cytokines, security and airport surveillance, cellular respiration, and canine olfaction.

Quantifying hormones in exhaled breath for physiological assessment of large whales at sea

Exhaled breath analysis is a non-invasive assessment tool that has shown promise in human diagnostics, and could greatly benefit research, management, and conservation of large whales. However, hormone assessment of whale respiratory vapor (blow) has been challenged by variable water content and unknown total volume of collected samples. To advance this technique, we investigated urea (a compound present in narrow range in circulation) as a normalizing factor to correct for blow sample concentration. Normalized progesterone, testosterone, and cortisol concentrations of 100 blow samples from 46 photo-identified North Atlantic right whales (Eubalaena glacialis) were more biologically relevant compared to absolute estimates, varying by sex, age class, or individual. Progesterone was elevated in adult females compared with other cohorts and highest in one independently confirmed pregnant female. For both sexes, testosterone was two-fold higher in reproductively mature whales but studied adult females showed the widest variation. Cortisol was present in relatively low concentrations in blow and demonstrated variation between individual whales, suggesting potential for studies of individual differences in adrenal activity. Incorporation of methodologies that normalize sample concentration are essential for blow hormone analysis of free-swimming whales, and measurement of urea could be used to optimize non-invasive physiological assessment of whales.

A feasibility study into adenosine triphosphate measurement in exhaled breath condensate: a potential bedside method to monitor alveolar deformation

Recent research suggested an important role for pulmonary extracellular adenosine triphosphate (ATP) in the development of ventilation-induced lung injury. This injury is induced by mechanical deformation of alveolar epithelial cells, which in turn release ATP to the extracellular space. Measuring extracellular ATP in exhaled breath condensate (EBC) may be a non-invasive biomarker for alveolar deformation. Here, we study the feasibility of bedside ATP measurement in EBC. We measured ATP levels in EBC in ten subjects before and after an exercise test, which increases respiratory parameters and alveolar deformation. EBC lactate concentrations were measured as a dilution marker. We found a significant increase in ATP levels in EBC (before 73 RLU [IQR 50–209] versus after 112 RLU [IQR 86–203]; p value 0.047), and the EBC ATP-to-EBC lactate ratio increased as well (p value 0.037). We present evidence that bedside measurement of ATP in EBC is feasible and that ATP levels in EBC increase after exercise. Future research should measure ATP levels in EBC during mechanical ventilation as a potential biomarker for alveolar deformation.

Determining the presence of asthma-related molecules and salivary contamination in exhaled breath condensate

Background

Researchers investigating lung diseases, such as asthma, have questioned whether certain compounds previously reported in exhaled breath condensate (EBC) originate from saliva contamination. Moreover, despite its increasing use in ‘omics profiling studies, the constituents of EBC remain largely uncharacterized. The present study aims to define the usefulness of EBC in investigating lung disease by comparing EBC, saliva, and saliva-contaminated EBC using targeted and untargeted mass spectrometry and the potential of metabolite loss from adsorption to EBC sample collection tubes.

Methods

Liquid chromatography mass spectrometry (LC-MS) was used to analyze samples from 133 individuals from three different cohorts. Levels of amino acids and eicosanoids, two classes of molecules previously reported in EBC and saliva, were measured using targeted LC-MS. Cohort 1 was used to examine contamination of EBC by saliva. Samples from Cohort 1 consisted of clean EBC, saliva-contaminated EBC, and clean saliva from 13 healthy volunteers; samples were analyzed using untargeted LC-MS. Cohort 2 was used to compare eicosanoid levels from matched EBC and saliva collected from 107 asthmatic subjects. Samples were analyzed using both targeted and untargeted LC-MS. Cohort 3 samples consisted of clean-EBC collected from 13 subjects, including smokers and non-smokers, and were used to independently confirm findings; samples were analyzed using targeted LC-MS, untargeted LC-MS, and proteomics. In addition to human samples, an in-house developed nebulizing system was used to determine the potential for EBC samples to be contaminated by saliva.

Results

Out of the 400 metabolites detected in both EBC and saliva, 77 were specific to EBC; however, EBC samples were concentrated 20-fold to achieve this level of sensitivity. Amino acid concentrations ranged from 196 pg/mL – 4 μg/mL (clean EBC), 1.98 ng/mL – 6 μg/mL (saliva-contaminated EBC), and 13.84 ng/mL – 1256 mg/mL (saliva). Eicosanoid concentration ranges were an order of magnitude lower; 10 pg/mL – 76.5 ng/mL (clean EBC), 10 pg/mL – 898 ng/mL (saliva-contaminated EBC), and 2.54 ng/mL – 272.9 mg/mL (saliva). Although the sample size of the replication cohort (Cohort 3) did not allow for statistical comparisons, two proteins and 19 eicosanoids were detected in smoker vs. non-smoker clean-EBC.

Conclusions

We conclude that metabolites are present and detectable in EBC using LC-MS; however, a large starting volume of sample is required.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-017-0538-5) contains supplementary material, which is available to authorized users.

Exhaled breath condensate for lung cancer protein analysis: a review of methods and biomarkers

Lung cancer is a leading cause of cancer-related deaths worldwide, and is considered one of the most aggressive human cancers, with a 5 year overall survival of 10-15%. Early diagnosis of lung cancer is ideal; however, it is still uncertain as to what technique will prove successful in the systematic screening of high-risk populations, with the strongest evidence currently supporting low dose computed tomography (LDCT). Analysis of exhaled breath condensate (EBC) has recently been proposed as an alternative low risk and non-invasive screening method to investigate early-stage neoplastic processes in the airways. However, there still remains a relative paucity of lung cancer research involving EBC, particularly in the measurement of lung proteins that are centrally linked to pathogenesis. Considering the ease and safety associated with EBC collection, and advances in the area of mass spectrometry based profiling, this technology has potential for use in screening for the early diagnosis of lung cancer. This review will examine proteomics as a method of detecting markers of neoplasia in patient EBC with a particular emphasis on LC, as well as discussing methodological challenges involving in proteomic analysis of EBC specimens.

The analysis of volatile organic compounds in exhaled breath and biomarkers in exhaled breath condensate in children - clinical tools or scientific toys?

Current monitoring strategies for respiratory diseases are mainly based on clinical features, lung function and imaging. As airway inflammation is the hallmark of many respiratory diseases in childhood, noninvasive methods to assess the presence and severity of airway inflammation might be helpful in both diagnosing and monitoring paediatric respiratory diseases. At present, the measurement of fractional exhaled nitric oxide is the only noninvasive method available to assess eosinophilic airway inflammation in clinical practice. We aimed to evaluate whether the analysis of volatile organic compounds (VOCs) in exhaled breath (EB) and biomarkers in exhaled breath condensate (EBC) is helpful in diagnosing and monitoring respiratory diseases in children. An extensive literature search was conducted in Medline, Embase and PubMed on the analysis and applications of VOCs in EB and EBC in children. We retrieved 1165 papers, of which nine contained original data on VOCs in EB and 84 on biomarkers in EBC. These were included in this review. We give an overview of the clinical applications in childhood and summarize the methodological issues. Several VOCs in EB and biomarkers in EBC have the potential to distinguish patients from healthy controls and to monitor treatment responses. Lack of standardization of collection methods and analysis techniques hampers the introduction in clinical practice. The measurement of metabolomic profiles may have important advantages over detecting single markers. There is a lack of longitudinal studies and external validation to reveal whether EB and EBC analysis have added value in the diagnostic process and follow-up of children with respiratory diseases. In conclusion, the use of VOCs in EB and biomarkers in EBC as markers of inflammatory airway diseases in children is still a research tool and not validated for clinical use.

Sample normalization methods in quantitative metabolomics

To reveal metabolomic changes caused by a biological event in quantitative metabolomics, it is critical to use an analytical tool that can perform accurate and precise quantification to examine the true concentration differences of individual metabolites found in different samples. A number of steps are involved in metabolomic analysis including pre-analytical work (e.g., sample collection and storage), analytical work (e.g., sample analysis) and data analysis (e.g., feature extraction and quantification). Each one of them can influence the quantitative results significantly and thus should be performed with great care. Among them, the total sample amount or concentration of metabolites can be significantly different from one sample to another. Thus, it is critical to reduce or eliminate the effect of total sample amount variation on quantification of individual metabolites. In this review, we describe the importance of sample normalization in the analytical workflow with a focus on mass spectrometry (MS)-based platforms, discuss a number of methods recently reported in the literature and comment on their applicability in real world metabolomics applications. Sample normalization has been sometimes ignored in metabolomics, partially due to the lack of a convenient means of performing sample normalization. We show that several methods are now available and sample normalization should be performed in quantitative metabolomics where the analyzed samples have significant variations in total sample amounts.

Exhaled Breath Condensate: Technical and Diagnostic Aspects

Purpose. The aim of this study was to evaluate the 30-year progress of research on exhaled breath condensate in a disease-based approach. Methods. We searched PubMed/Medline, ScienceDirect, and Google Scholar using the following keywords: exhaled breath condensate (EBC), biomarkers, pH, asthma, gastroesophageal reflux (GERD), smoking, COPD, lung cancer, NSCLC, mechanical ventilation, cystic fibrosis, pulmonary arterial hypertension (PAH), idiopathic pulmonary fibrosis, interstitial lung diseases, obstructive sleep apnea (OSA), and drugs. Results. We found 12600 related articles in total in Google Scholar, 1807 in ScienceDirect, and 1081 in PubMed/Medline, published from 1980 to October 2014. 228 original investigation and review articles were eligible. Conclusions. There is rapidly increasing number of innovative articles, covering all the areas of modern respiratory medicine and expanding EBC potential clinical applications to other fields of internal medicine. However, the majority of published papers represent the results of small-scale studies and thus current knowledge must be further evaluated in large cohorts. In regard to the potential clinical use of EBC-analysis, several limitations must be pointed out, including poor reproducibility of biomarkers and absence of large surveys towards determination of reference-normal values. In conclusion, contemporary EBC-analysis is an intriguing achievement, but still in early stage when it comes to its application in clinical practice.

Real-time monitoring of exhaled drugs by mass spectrometry

Future individualized patient treatment will need tools to monitor the dose and effects of administrated drugs. Mass spectrometry may become the method of choice to monitor drugs in real time by analyzing exhaled breath. This review describes the monitoring of exhaled drugs in real time by mass spectrometry. The biological background as well as the relevant physical properties of exhaled drugs are delineated. The feasibility of detecting and monitoring exhaled drugs is discussed in several examples. The mass spectrometric tools that are currently available to analyze breath in real time are reviewed. The technical needs and state of the art for on-site measurements by mass spectrometry are also discussed in detail. Off-line methods, which give support and are an important source of information for real-time measurements, are also discussed. Finally, some examples of drugs that have already been successfully detected in exhaled breath, including propofol, fentanyl, methadone, nicotine, and valproic acid are presented. Real-time monitoring of exhaled drugs by mass spectrometry is a relatively new field, which is still in the early stages of development. New technologies promise substantial benefit for future patient monitoring and treatment.

Determining urea levels in exhaled breath condensate with minimal preparation steps and classic LC-MS

Exhaled breath condensate (EBC) provides a relatively easy, non-invasive method for measuring biomarkers of inflammation and oxidative stress in the airways. However, the levels of these biomarkers in EBC are influenced, not only by their levels in lung lining fluid but also by the volume of water vapor that also condenses during EBC collection. For this reason, the use of a biomarker of dilution has been recommended. Urea has been proposed and utilized as a promising dilution biomarker due to its even distribution throughout the body and relatively low volatility. Current EBC urea analytical methods either are not sensitive enough, necessitating large volumes of EBC, or are labor intensive, requiring a derivatization step or other pretreatment. We report here a straightforward and reliable LC-MS approach that we developed that does not require derivatization or large sample volume (∼36 µL). An Acclaim mixed-mode hydrophilic interaction chromatography column was selected because it can produce good peak symmetry and efficiently separate urea from other polar and nonpolar compounds. To achieve a high recovery rate, a slow and incomplete evaporation method was used followed by a solvent-phase exchange. Among EBC samples collected from 28 children, urea levels were found to be highly variable, with a relative standard deviation of 234%, suggesting high variability in dilution of the lung lining fluid component of EBC. The limit of detection was found to be 0.036 µg/mL.

Concentration of exhaled breath condensate biomarkers after fractionated collection based on exhaled CO2 signal

A standard procedure for exhaled breath condensate (EBC) collection is still lacking. The aim of this study was to compare the concentration of several biomarkers in whole (W-EBC) and fractionated EBC (A-EBC), the latter collected starting from CO2 ≥ 50% increase during exhalation. Forty-five healthy non-smokers or asymptomatic light smokers were enrolled. Total protein concentrations in W-EBC and A-EBC were overlapping (median: 0.7 mg l(-1) in both cases), whereas mitochondrial DNA was higher in A-EBC (0.021 versus 0.011 ng ml(-1)), indicating a concentration rather than a dilution of lining fluid droplets in the last portion of exhaled air. H2O2 (0.13 versus 0.08 µM), 8-isoprostane (4.9 versus 4.4 pg ml(-1)), malondialdehyde (MDA) (4.2 versus 3.2 nM) and 4-hydroxy-2-nonhenal (HNE) (0.78 versus 0.66 nM) were all higher in W-EBC, suggesting a contribution from the upper airways to oxidative stress biomarkers in apparently healthy subjects. NH4(+) was also higher in W-EBC (median: 590 versus 370 µM), with an estimated increase over alveolar and bronchial air by a factor 1.5. pH was marginally, but significantly higher in W-EBC (8.05 versus 8.01). In conclusion, the fractionation of exhaled air may be promising in clinical and occupational medicine.

Biomarkers of exposure to metal dust in exhaled breath condensate: methodology optimization

In occupational assessments where workers are exposed to metal dust, the liquid condensate of exhaled breath (EBC) may provide unique indication of pulmonary exposure. The main goal of this study was to demonstrate the quality of EBC to biological monitoring of human exposure. A pilot study was performed in a group of metal dust-exposed workers and a group of nonexposed individuals working in offices. Only metal dust-exposed workers were followed along the working week to determine the best time of collection. Metal analyses were performed with inductively coupled plasma mass spectrometry (ICP-MS). Analytical methodology was tested using an EBC sample pool for several occupationally exposed metals: potassium, chromium, manganese, copper, zinc, strontium, cadmium, antimony, and lead. Metal contents in EBC of exposed workers were higher than controls at the beginning of the shift and remained augmented throughout the working week. The results obtained support the establishment of EBC as an indicator of pulmonary exposure to metals.

Exhaled breath condensate pH is influenced by respiratory droplet dilution

Several studies support that airway acid stress plays a role in the pathophysiology of asthma. Exhaled breath condensate pH (EBC pH) was suggested as a surrogate marker of airway acidification. The dilution of airway lining fluid (ALF) acids and bases by alveolar water may influence condensate pH, but it has not been studied yet. The aim of our study was to investigate the relationship between EBC pH and ALF dilution in EBC samples obtained from asthmatic and healthy subjects. EBC was collected from 55 asthmatic and 57 healthy subjects for pH and conductivity measurements. Fractional exhaled nitric oxide (FE(NO)) and lung function tests were also performed in asthmatic patients. EBC pH was determined after 10 min of argon deareation and the dilution was estimated by the measurement of conductivity in vacuum-treated samples. There was no difference either in EBC pH or dilution between the two groups. However, a significant relationship was found between EBC pH and dilution in both groups (p < 0.05, r = -0.35 and r = -0.29, asthmatic and healthy groups, respectively). Our results suggest important methodological aspect indicating that EBC pH is affected by respiratory droplet dilution, and this effect should be taken into consideration when interpreting EBC pH data.

Exhaled breath condensate collection in the mechanically ventilated patient

Collection of exhaled breath condensate (EBC) is a non-invasive means of sampling the airway-lining fluid of the lungs. EBC contains numerous measurable mediators, whose analysis could change the management of patients with certain pulmonary diseases. While initially popularized in investigations involving spontaneously breathing patients, an increasing number of studies have been performed using EBC in association with mechanical ventilation. Collection of EBC in mechanically ventilated patients follows basic principles of condensation, but is influenced by multiple factors. Effective collection requires selection of a collection device, adequate minute ventilation, low cooling temperatures, and sampling times of greater than 10 min. Condensate can be contaminated by saliva, which needs to be filtered. Dilution of samples occurs secondary to distilled water in vapors and humidification in the ventilator circuit. Dilution factors may need to be employed when investigating non-volatile biomarkers. Storage and analysis should occur promptly at -70 °C to -80 °C to prevent rapid degradation of samples. The purpose of this review is to examine and describe methodologies and problems of EBC collection in mechanically ventilated patients. A straightforward and safe framework has been established to investigate disease processes in this population, yet technical aspects of EBC collection still exist that prevent clinical practicality of this technology. These include a lack of standardization of procedure and analysis of biomarkers, and of normal reference ranges for mediators in healthy individuals. Once these procedural aspects have been addressed, EBC could serve as a non-invasive alternative to invasive evaluation of lungs in mechanically ventilated patients.

Discrimination between COPD patients with and without alpha 1-antitrypsin deficiency using an electronic nose

BACKGROUND AND OBJECTIVE

To compare the volatile organic compound patterns of patients with COPD with and without alpha 1-antitrypsin (AAT) deficiency using electronic nose technology.

METHODS

Exhaled breath condensate and pure exhaled breath of patients with COPD with (n=10) and without (n=23) AAT deficiency and healthy controls (n=10) were analysed. The effect of human recombinant AAT on the volatile organic compound profile of 11 AAT-deficient patients was also examined. Exhaled breath condensate and pure exhaled breath were measured using the Cyranose 320. Smell prints were analysed by linear discriminant analysis (LDA) using Mahalanobis distance (MD) and cross-validation values (CVVs).

RESULTS

Smell prints of patients with AAT-deficiency were different from those with COPD in exhaled breath condensate (LDA: P<0.0001, sensitivity of 1.00, specificity of 1.00, CVV 82.0%, MD 2.37) and in pure exhaled breath (LDA: P<0.0001, sensitivity of 1.00, specificity of 1.00, CVV 58.3%, MD 2.27). Smell prints of AAT-deficient patients before and after human recombinant AAT augmentation were different (LDA: P=0.001, sensitivity of 1.00, specificity of 1.00, CVV 53.3%, MD 1.79).

CONCLUSIONS

An electronic nose can detect differences in smell prints of COPD patients with and without AAT deficiency. Augmentation therapy changes the volatile organic compound pattern. The electronic nose may be helpful in the diagnosis of AAT deficiency.

Impact of different welding techniques on biological effect markers in exhaled breath condensate of 58 mild steel welders

Total mass and composition of welding fumes are predominantly dependent on the welding technique and welding wire applied. The objective of this study was to investigate the impact of welding techniques on biological effect markers in exhaled breath condensate (EBC) of 58 healthy welders. The welding techniques applied were gas metal arc welding with solid wire (GMAW) (n=29) or flux cored wire (FCAW) (n=29). Welding fume particles were collected with personal samplers in the breathing zone inside the helmets. Levels of leukotriene B(4) (LTB(4)), prostaglandin E(2) (PGE(2)), and 8-isoprostane (8-iso-PGF(2α)) were measured with immunoassay kits and the EBC pH was measured after deaeration. Significantly higher 8-iso-PGF(2α) concentrations and a less acid pH were detected in EBC of welders using the FCAW than in EBC of welders using the GMAW technique. The lowest LTB(4) concentrations were measured in nonsmoking welders applying a solid wire. No significant influences were found in EBC concentrations of PGE(2) based upon smoking status or type of welding technique. This study suggests an enhanced irritative effect in the lower airways of mild steel welders due to the application of FCAW compared to GMAW, most likely associated with a higher emission of welding fumes.

Assessment of reproducibility of exhaled hydrogen peroxide concentration and the effect of breathing pattern in healthy subjects

BACKGROUND

Hydrogen peroxide (H2O2) is detectable in exhaled breath condensate (EBC) and has been proposed to be a surrogate marker of oxidative stress in the airways. In this study we tested whether the breathing pattern during EBC collection influences the concentration of exhaled H2O2.

METHODS

EBC was collected during (1) tidal breathing and (2) breathing with increased tidal volume for 10 min from 16 healthy volunteers. On-line H2O2 measurement was performed by the EcoCheck™ biosensor system. Repeated measurements were also conducted to assess intrasubject reproducibility.

RESULTS

Minute ventilation, tidal volume, expiratory flow rate were all increased significantly when subjects were asked to perform breathing with increased tidal volume. In parallel, EBC volume increased (1413±59 vs. 1959±71 μL, p<0.001), whereas exhaled H2O2 levels decreased significantly (1400±170 vs. 840±130 nmol/L, p<0.001). H2O2 levels did not correlate with any individual breathing parameters (p>0.05). Assessment of intersubject variability of H2O2 measurements during the two types of breathing revealed a coefficient of variation of 49 and 54%, respectively. The EBC H2O2 measurement was highly reproducible (888±176 vs. 874±156 nmol/L) as tested during normal breathing.

CONCLUSIONS

These data demonstrate that the concentration of H2O2 in EBC depends on the ventilatory pattern during sample collection that has to be taken into consideration in all EBC H2O2 assays.

Breath analysis of hydrogen peroxide as a diagnostic tool

The potential diagnostic significance of exhaled hydrogen peroxide (H(2)O(2)) in pulmonary and systemic disorders has received considerable interest over the last few decades. Despite large physiologic variability and low specificity, airway H(2)O(2) generation has been found to be consistently increased by inflammatory conditions. Furthermore, the level of exhaled H(2)O(2) has been associated with efficacy of treatment in various pulmonary diseases. To evaluate this potential biomarker, detection methods including standardization protocols have been developed. Despite these advances, more comprehensive and controlled studies are required. In this manuscript we review progress to date in the analytical measurement of exhaled H(2)O(2) and speculate on its potential clinical significance as a diagnostic tool.

Breath formate is a marker of airway S-nitrosothiol depletion in severe asthma

BACKGROUND

Children with severe asthma have poor symptom control and elevated markers of airway oxidative and nitrosative stress. Paradoxically, they have decreased airway levels of S-nitrosothiols (SNOs), a class of endogenous airway smooth muscle relaxants. This deficiency results from increased activity of an enzyme that both reduces SNOs to ammonia and oxidizes formaldehyde to formic acid, a volatile carboxylic acid that is more easily detected in exhaled breath condensate (EBC) than SNOs. We therefore hypothesize that depletion of airway SNOs is related to asthma pathology, and breath formate concentration may be a proxy measure of SNO catabolism.

METHODS AND FINDINGS

We collected EBC samples from children and adolescents, including 38 with severe asthma, 46 with mild-to-moderate asthma and 16 healthy adolescent controls, and the concentration of ionic constituents was quantified using ion chromatography. The concentrations of EBC components with volatile conjugates were log-normally distributed. Formate was the principal ion that displayed a significant difference between asthma status classifications. The mean EBC formate concentration was 40% higher in samples collected from all asthmatics than from healthy controls (mean = 5.7 microM, mean+/-standard deviation = 3.1-10.3 microM vs. 4.0, 2.8-5.8 microM, p = 0.05). EBC formate was higher in severe asthmatics than in mild-to-moderate asthmatics (6.8, 3.7-12.3 microM vs. 4.9, 2.8-8.7 microM, p = 0.012). In addition, formate concentration was negatively correlated with methacholine PC(20) (r = -0.39, p = 0.002, asthmatics only), and positively correlated with the NO-derived ion nitrite (r = 0.46, p<0.0001) as well as with total serum IgE (r = 0.28, p = 0.016, asthmatics only). Furthermore, formate was not significantly correlated with other volatile organic acids nor with inhaled corticosteroid dose.

CONCLUSIONS

We conclude that EBC formate concentration is significantly higher in the breath of children with asthma than in those without asthma. In addition, amongst asthmatics, formate is elevated in the breath of those with severe asthma compared to those with mild-to-moderate asthma. We suggest that this difference is related to asthma pathology and may be a product of increased catabolism of endogenous S-nitrosothiols.

Effects of bronchoconstriction, minute ventilation, and deep inspiration on the composition of exhaled breath condensate

BACKGROUND

Exhaled breath condensate (EBC) is composed of droplets of airway surface liquid (ASL) diluted by water vapor. The goal of this study was to determine if the composition of EBC is affected by changes in airway caliber, minute ventilation, or forceful exhalation, factors that may differ among subjects with asthma in cross-sectional studies.

METHODS

In a group of subjects with asthma, we measured the effects of the following: (1) a series of three deep-inspiration and forceful-exhalation maneuvers; (2) a doubling of minute ventilation; and (3) acute bronchoconstriction induced by methacholine on EBC volume, dilution of ASL, and concentration of cysteinyl leukotrienes (CysLTs).

RESULTS

With the exception of an increase in EBC volume with increased minute ventilation, there were no significant changes in the volume, dilution, or levels of CysLTs in EBC introduced by each of these factors. The CIs surrounding the differences introduced by each factor showed that the maximum systematic errors due to these factors were modest.

CONCLUSIONS

These results indicate that changes in airway caliber, minute ventilation, or breathing pattern among subjects with asthma do not significantly alter the measurements of mediator concentrations in EBC.

Ionic determinants of exhaled breath condensate pH before and after exercise in adolescent athletes

BACKGROUND

The pH of exhaled breath condensate (EBC) of adolescent athletes engaged in vigorous physical activity is low compared to healthy controls; however, the ionic determinants of EBC pH and the acute effects of exercise on those determinants have not been definitively established.

OBJECTIVES

This study had two purposes: (1) to identify the ionic composition of EBC before and after exercise, and (2) to examine the effects of sample deaeration on EBC pH and composition.

METHODS

EBC ionic composition was determined by ion chromatography and correlated with pH measured before and after deaeration. Bicarbonate concentration was calculated from the ion balance of other measured species and pH.

RESULTS

EBC pH displayed a bimodal distribution, included values lower than expected for healthy individuals, and was correlated exclusively with volatile species, namely ammonia (mean concentration = 215 microM) and acetic (31.7 microM) and propionic acids (10.0 microM). Following exercise, raw EBC pH and ammonia concentration increased while propionic acid concentration fell. Following deaeration, EBC pH increased by one unit on average; however, the pH of samples with unusually low pH did not change significantly, and the concentrations of several ionic species were altered in a manner that cannot be explained in terms of volatility.

CONCLUSIONS

We conclude that in healthy adolescents, exercise results in an acute increase in raw EBC pH in association with an increase in ammonium and a decrease in propionate concentration. Since exercise increases systemic ammonia and urea (which is hydrolyzed by oral bacteria to form ammonia), we propose that the likely source of these changes is gas-phase diffusion from epithelial and oral surface liquids and to a lesser extent, from pulmonary circulation.

Role of exhaled breath biomarkers in environmental health science

As a discipline of public health, environmental health science is the study of the linkage from environmental pollution sources to eventual adverse health outcome. This progression may be divided into two components, (1) "exposure assessment," which deals with the source terms, environmental transport, human exposure routes, and internal dose, and (2) "health effects," which deals with metabolism, cell damage, DNA changes, pathology, and onset of disease. The primary goal of understanding the linkage from source to health outcome is to provide the most effective and efficient environmental intervention methods to reduce health risk to the population. Biomarker measurements address an individual response to a common external environmental stressor. Biomarkers are substances within an individual and are subdivided into chemical markers, exogenous metabolites, endogenous response chemicals, and complex adducts (e.g., proteins, DNA). Standard biomarker measurements are performed in blood, urine, or other biological media such as adipose tissue and lavage fluid. In general, sample collection is invasive, requires medical personnel and a controlled environment, and generates infectious waste. Exploiting exhaled breath as an alternative or supplement to established biomarker measurements is attractive primarily because it allows a simpler collection procedure in the field for numerous individuals. Furthermore, because breath is a gas-phase matrix, volatile biomarkers become more readily accessible to analysis. This article describes successful environmental health applications of exhaled breath and proposes future research directions from the perspective of U.S. Environmental Protection Agency (EPA) human exposure research.

Effects of aminoguanidine, an inhibitor of inducible nitric oxide synthase, on nitric oxide production and its metabolites in healthy control subjects, healthy smokers, and COPD patients

BACKGROUND

Nitric oxide (NO) is produced by resident and inflammatory cells in the respiratory tract by the enzyme NO synthase (NOS), which exists in three isoforms: neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS. NO production is increased in patients with COPD, and the production of NO under oxidative stress conditions generates reactive nitrogen species that may amplify the inflammatory response in COPD.

METHODS

To examine the role of increased NO in COPD, we administered a relatively selective iNOS inhibitor, aminoguanidine, by nebulization in a double-blind, placebo-controlled study in COPD patients, healthy smokers, and healthy nonsmoking subjects. We investigated whether aminoguanidine had any effect on exhaled NO produced in the central lung (flux of NO from the airways [Jno] and peripheral lungs (concentration of NO in peripheral lung [Calv], on NO metabolites (nitrite [NO(2)(-)]/nitrate [NO(3)(-)], peroxinitrite [ONOO(-)], nitrotyrosine), and on a marker of oxidative stress (8-isoprostane) in exhaled breath condensate (EBC) and in sputum.

RESULTS

Aminoguanidine administration resulted in a significant reduction in Jno compared with administration of the saline solution control in healthy subjects, smokers, and COPD patients. Calv in smokers and in COPD patients was not completely inhibited 1 h after aminoguanidine inhalation, in marked contrast to previous results in asthma. Moreover, ONOO(-) and NO(2)(-)/NO(3)(-) levels were also increased in EBC and in sputum of smokers and COPD and were not completely inhibited following aminoguanidine inhalation. 8-Isoprostane levels were also increased in smokers and in COPD patients but were not reduced after aminoguanidine inhalation.

CONCLUSIONS

These results suggest that the constitutive NOS isoform as well as iNOS might be involved in NO release and contribute to the high Calv and ONOO(-) production in patients with COPD.

TRIAL REGISTRATION

Clinicaltrials.gov Identifier: NCT00180635.

Influence of condensing equipment and temperature on exhaled breath condensate pH, total protein and leukotriene concentrations

BACKGROUND

Exhaled breath condensate analysis is an attractive but still not fully standardised method for investigating airway pathology. Adherence of biomarkers to various condensing surfaces and changes in condensing temperature has been considered to be responsible for the variability of the results. Our aims were to compare the efficacy of different types of condensers and to test the influence of condensing temperature on condensate composition.

METHODS

Breath condensates from 12 healthy persons were collected in two settings: (1) by using three condensers of different type (EcoScreen, R-Tube, Anacon) and (2) by using R-Tube condenser either cooled to -20 or -70 degrees C. Condensate pH at standardised CO(2) level was determined; protein content was measured by the Bradford method and leukotrienes by EIA.

RESULTS

Breath condensates collected using EcoScreen were more alkaline (6.45+/-0.20 vs. 6.19+/-0.23, p<0.05 and 6.10+/-0.26, p<0.001) and contained more protein (3.89+/-2.03 vs. 2.65+/-1.98, n.s. and 1.88+/-1.99 microg/ml, p<0.004) as compared to the other devices. Only parameters obtained with R-Tube and Anacon correlated. Condensing temperature affected condensate pH (5.99+/-0.20 at -20 degrees C and 5.82+/-0.07 at -70 degrees C, p<0.05) but not protein content. Leukotriene B(4) was not found in any sample and cysteinyl-leukotriene was not found in condensates collected with R-Tube or Anacon.

CONCLUSION

Condenser type influences sample pH, total protein content and cysteinyl-leukotriene concentration. Condensing temperature influences condensate pH but not total protein content. These results suggest that adherence of the biomarkers to condenser surface and condensing temperature may play a role but does not fully explain the variability of EBC biomarker levels.

Proteomics as a method for early detection of cancer: a review of proteomics, exhaled breath condensate, and lung cancer screening

The study of expressed proteins in neoplasia is undergoing a revolution with the advent of proteomic analysis. Unlike genomic studies where individual changes may have no functional significance, protein expression is closely aligned with cellular activity. This perspective will review proteomics as a method of detecting markers of neoplasia with a particular emphasis on lung cancer and the potential to sample the lung by exhaled breath condensate (EBC). EBC collection is a simple, new, and noninvasive technique, which allows sampling of lower respiratory tract fluid. EBC enables the study of a wide variety of biological markers from low molecular weight mediators to macromolecules, such as proteins, in a range of pulmonary diseases. EBC may be applied to the detection of lung cancer where it could be a tool in early diagnosis. This perspective will explore the potential of applying proteomics to the EBC from lung cancer patients as an example of detecting potential biomarkers of disease and progression.

[The pH of the exhaled breath condensate: new method for investigation of inflammatory airway diseases]

Collecting exhaled breath condensate (EBC) has become a frequently used method in respiratory researches to date. Through this method we can sample airway surface liquid non-invasively by streaming the exhaled breath through a cooled chamber and after we examine the fluid deposited on the wall of the condenser. The sample contains several mediators, biomarkers. The pH of the condensate is one of the most important markers measured in the EBC. Measuring the pH is easy, cheap and it is in the optimal range, there is no problem with the detection limit. The uncertainty of the pH assays is derived from the instability of the EBC pH which results from the altering carbon-dioxide concentration. Many articles have been published on EBC pH in different airway diseases. Acidification of the condensates has been described in bronchial asthma (especially in acute exacerbations), chronic obstructive lung disease (COPD). Due to the steroid treatment the pH has increased in both cases. In patients with bronchiectasis, cystic fibrosis and in chronic cough (bronchial asthma, gastro-esophageal reflux, postnasal drip, and unknown origin) the pH of EBC was also lower. Acidification of the airways in different diseases can play a role in the pathomechanism, and its indicator, the EBC pH might help managing patients with airway diseases.