Biomarkers in exhaled breath condensate: a review of collection, processing and analysis

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.

Exhaled breath analysis for lung cancer

Early diagnosis of lung cancer results in improved survival compared to diagnosis with more advanced disease. Early disease is not reliably indicated by symptoms. Because investigations such as bronchoscopy and needle biopsy have associated risks and substantial costs, they are not suitable for population screening. Hence new easily applicable tests, which can be used to screen individuals at risk, are required. Biomarker testing in exhaled breath samples is a simple, relatively inexpensive, non-invasive approach. Exhaled breath contains volatile and non-volatile organic compounds produced as end-products of metabolic processes and the composition of such compounds varies between healthy subjects and subjects with lung cancer. Many studies have analysed the patterns of these compounds in exhaled breath. In addition studies have also reported that the exhaled breath condensate (EBC) can reveal gene mutations or DNA abnormalities in patients with lung cancer. This review has summarised the scientific evidence demonstrating that lung cancer has distinct chemical profiles in exhaled breath and characteristic genetic changes in EBC. It is not yet possible to accurately identify individuals with lung cancer in at risk populations by any of these techniques. However, analysis of both volatile organic compounds in exhaled breath and of EBC have great potential to become clinically useful diagnostic and screening tools for early stage lung cancer detection.

Malondialdehyde and 3-nitrotyrosine in exhaled breath condensate in retired elderly coal miners with chronic obstructive pulmonary disease

Background

Chronic obstructive pulmonary disease (COPD) is an important cause of occupational mortality in miners exposed to coal mine dust. Although the inflammatory mediators involved in COPD have not been defined, many studies have shown that inflammatory mediators such as reactive oxygen and nitrogen species are involved in orchestrating the complex inflammatory process in COPD.

Methods

To investigate the relevance of exhaled biomarkers of oxidative and nitrosative stress in participants with COPD, we determined the levels of hydrogen peroxide, malondialdehyde (MDA), and 3-nitrotyrosine (3-NT) in exhaled breath condensate (EBC) in 90 retired elderly coal miners (53 non-COPD and 37 COPD participants).

Results

Mean levels of MDA (4.64 nM vs. 6.46 nM, p = 0.005) and 3-NT (3.51 nM vs. 5.50 nM, p = 0.039) in EBC were significantly higher in participants with COPD. The median level of MDA did show statistical difference among the COPD severities (p = 0.017), and the area under the receiver operating characteristic curve for MDA (0.67) for the diagnostic discrimination of COPD indicated the biomarker. The optimal cutoff values were 5.34 nM (64.9% sensitivity and 64.2% specificity) and 5.58 nM (62.2% sensitivity and 62.3% specificity) for MDA and 3-NT, respectively. The results suggest that high levels of MDA and 3-NT in EBC are associated with COPD in retired elderly miners.

Conclusion

These results showed that the elevated levels of EBC MDA and EBC 3-NT in individuals with COPD are biomarkers of oxidative or nitrosative stress.

The suitability of EBC-Pb as a new biomarker to assess occupational exposure to lead

Occupational exposure to lead (Pb) requires continuous surveillance to assure, as much as possible, safe and healthful working conditions. This study addresses the suitability of assessing Pb exposure in relevant workers using their exhaled breath condensate (EBC). This study enrolled workers of two different Pb processing industries characterized by moderate and high Pb exposure levels in the work environment, and a group of non-exposed individuals working in offices who served as baseline for Pb exposure. The EBC-Pb of workers reflected the Pb levels in the work environment of all three settings, although the relationship with B-Pb was not clear. The lack of correlation between EBC-Pb and B-Pb most probably indicates the time lag for Pb to enter in the two body pools. The EBC-Pb seems to reflect immediate exposure, providing a prompt signature of Pb in the environmental that may interact directly with the organ. By delivering short-term evaluation of exposure, EBC-Pb represents a clear advantage in biomonitoring and may become an interesting tool for estimating organ burden.

Using high-performance liquid chromatography with UV detector to quantify exhaled leukotriene B4 level in nonatopic adults

This study aimed to evaluate the feasibility of the chemical method to analyze exhaled breath condensate (EBC) leukotriene B4 (LTB4) level in humans. High-performance liquid chromatography with a UV detector was applied to quantify the inflammatory biomarker. The LTB4 concentration in the concentrated pooled EBC samples was 1.19 ng/μL, and the average LTB4 concentration of each EBC sample was 15.38 ng/μL. This analytical technique was feasible to evaluate the levels of inflammatory mediators such as LTB4 in human EBCs without any complicated sample pretreatment processes.

Analysis of Airborne Biomarkers for Point-of-Care Diagnostics

Treatable diseases continue to exact a heavy burden worldwide despite powerful advances in treatment. Diagnostics play crucial roles in the detection, management, and ultimate prevention of these diseases by guiding the allocation of precious medical resources. Motivated by globalization and evolving disease, and enabled by advances in molecular pathology, the scientific community has produced an explosion of research on miniaturized integrated biosensor platforms for disease detection. Low-cost, automated tests promise accessibility in low-resource settings by loosening constraints around infrastructure and usability. To address the challenges raised by invasive and intrusive sample collection, researchers are exploring alternative biomarkers in various specimens. Specifically, patient-generated airborne biomarkers suit minimally invasive collection and automated analysis. Disease biomarkers are known to exist in aerosols and volatile compounds in breath, odor, and headspace, media that can be exploited for field-ready diagnostics. This article reviews global disease priorities and the characteristics of low-resource settings. It surveys existing technologies for the analysis of bioaerosols and volatile organic compounds, and emerging technologies that could enable their translation to the point of care. Engineering advances promise to enable appropriate diagnostics by detecting chemical and microbial markers. Nonetheless, further innovation and cost reduction are needed for these technologies to broadly affect global health.

A curated review of recent literature of biomarkers used for assessing air pollution exposures and effects in humans

This is a cross-sectional review of biomarkers used in air pollution research from January 2009 through December 2012. After an initial keyword search in PubMed retrieving 426 articles, a comprehensive abstract review identified 54 articles of experimental design that used biomarkers of exposure or effect in human studies in the area of air pollution research during this specified time period. A thorough bibliographic search of the included articles retrieved an additional 65 articles meeting the inclusion criteria. This review presents these 119 studies and the 234 biomarkers employed in these air pollution research investigations. Data presented are 70 biomarkers of exposure with 54% relating to polycyclic aromatic hydrocarbons, 36% volatile organic carbons, and 10% classified as other. Of the 164 biomarkers of effect, 91 and 130 were used in investigating effects of short-term and chronic exposure, respectively. Results of biomarkers used in short-term exposure describe different lag times and pollutant components such as primary and secondary pollutants, and particle number associated with corresponding physiological mechanisms including airway inflammation, neuroinflammation, ocular, metabolic, early endothelial dysfunction, coagulation, atherosclerosis, autonomic nervous system, oxidative stress, and DNA damage. The review presents three different exposure scenarios of chronic, occupational, and extreme exposure scenarios (indoor cooking) with associated biomarker findings presented in three broad categories of (1) immune profile, (2) oxidative stress, and (3) DNA damage. This review offers a representation of the scope of data being explored by air pollution researchers through the use of biomarkers and has deliberately been restricted to this particular subject rather than an extensive or in-depth review. This article provides a contextualization of air pollution studies conducted with biomarkers in human subjects in given areas while also integrating this complex body of information to offer a useful review for investigators in this field of study.

Cysteinyl leukotriene levels correlate with 8-isoprostane levels in exhaled breath condensates of atopic and healthy children

BACKGROUND

Cysteinyl leukotrienes are important mediators of airway inflammation, whereas 8-isoprostane is a biomarker of oxidative stress. This study evaluated the distributions of cysteinyl leukotriene and 8-isoprostane concentrations in exhaled breath condensates (EBCs) of children. The relationship between cysteinyl leukotriene and 8-isoprostane concentrations in the EBCs was also evaluated.

METHODS

The EBCs were collected from 34 children with allergic respiratory diseases and 24 healthy children. All recruited children underwent pulmonary function testing every season. The severity of allergic respiratory diseases and medication status were assessed every month in children with allergic respiratory diseases.

RESULTS

The EBC cysteinyl leukotriene and 8-isoprostane levels were higher in children with asthma and allergic rhinitis than in those with asthma only and healthy children. In asthmatic children, cysteinyl leukotriene and 8-isoprostane levels peaked in the summer. All children showed a clear association between EBC cysteinyl leukotriene and EBC 8-isoprostane levels.

CONCLUSION

The cysteinyl leukotriene and 8-isoprostane concentrations in the EBCs of children significantly varied by season. Oxidative stress correlated with airway inflammation in children.

Fingerprinting-based metabolomic approach with LC-MS to sleep apnea and hypopnea syndrome: a pilot study

Sleep apnea and hypopnea syndrome (SAHS) is a multicomponent disorder, with associated cardiovascular and metabolic alterations, second in order of frequency among respiratory disorders. Sleep apnea is diagnosed with an overnight sleep test called a polysomnogram, which requires having the patient in hospital. In addition, a more clear classification of patients according to mild and severe presentations would be desirable. The aim of the present study was to assess the relative metabolic changes in SAHS to identify new potential biomarkers for diagnosis, able to evaluate disease severity to establish response to therapeutic interventions and outcomes. For this purpose, metabolic fingerprinting represents a valuable strategy to monitor, in a nontargeted manner, the changes that are at the base of the pathophysiological mechanism of SAHS. Plasma samples of 33 SAHS patients were collected after polysomnography and analyzed with LC coupled to MS (LC-QTOF-MS). After data treatment and statistical analysis, signals differentiating nonsevere and severe patients were detected. Putative identification of 14 statistically significant features was obtained and changes that can be related to the episodes of hypoxia/reoxygenation (inflammation) have been highlighted. Among them, the patterns of variation of platelet activating factor and lysophospholipids, together with some compounds related to differential activity of the gut microflora (bile pigments and pipecolic acid) open new lines of research that will benefit our understanding of the alterations, offering new possibilities for adequate monitoring of the stage of the disease.

Assessment of pulmonary oxygen toxicity: relevance to professional diving; a review

When breathing oxygen with partial oxygen pressures PO₂ of between 50 and 300 kPa pathological pulmonary changes develop after 3-24h depending on the PO₂. This kind of injury (known as pulmonary oxygen toxicity) is not only observed in ventilated patients but is also considered an occupational hazard in oxygen divers or mixed gas divers. To prevent these latter groups from sustaining irreversible lesions adequate prevention is required. This review summarizes the pathophysiological effects on the respiratory tract when breathing oxygen with PO₂ of 50-300 kPa (hyperoxia). We discuss to what extent the most commonly used lung function parameters change after exposure to hyperoxia and its role in monitoring the onset and development of pulmonary oxygen toxicity in daily practice. Finally, new techniques in respiratory medicine are discussed with regard to their usefulness in monitoring pulmonary oxygen toxicity in divers.

Noninvasive analysis of volatile biomarkers in human emanations for health and early disease diagnosis

Early disease diagnosis is crucial for human healthcare and successful therapy. Since any changes in homeostatic balance can alter human emanations, the components of breath exhalations and skin emissions may be diagnostic biomarkers for various diseases and metabolic disorders. Since hundreds of endogenous and exogenous volatile organic compounds (VOCs) are released from the human body, analysis of these VOCs may be a noninvasive, painless, and easy diagnostic tool. Sampling and preconcentration by sorbent tubes/traps and solid-phase microextraction, in combination with GC or GC–MS, are usually used to analyze VOCs. In addition, GC–MS-olfactometry is useful for simultaneous analysis of odorants and odor quality. Direct MS techniques are also useful for the online real-time detection of VOCs. This review focuses on recent developments in sampling and analysis of volatile biomarkers in human odors and/or emanations, and discusses future use of VOC analysis.

Sensitive and selective chemiluminescence assay for hydrogen peroxide in exhaled breath condensate using nanoparticle-based catalysis

The catalytic properties of cubiform Co3O4 nanoparticles, α-Fe2O3 nanorods, and NiO nanoparticles were studied using both microarray method and FI-CL method. These nanoarticles exhibit high specific catalytic effects on the chemiluminescence (CL) reaction of the luminol-H2O2 system in alkaline solution compared with other common catalysts. A reaction mechanism is described. It provides new insights into the application of nanoparticle materials. The CL method based on the use of the Co3O4 nanoparticles is ultrasensitive and particularly selective. Therefore, it was applied to the analysis of H2O2 which can be determined in the concentration range from 1.0 nM to 1000 nM, with a detection limit of 0.3 nM. The relative standard deviation is 2.1% at 0.1 μM of H2O2 (for n=11). The method was successfully applied to the determination of trace quantities of H2O2 in exhaled breath condensate (EBC) where it is a mediator of oxidative stress and a promising biomarker for diagnosing. The assay requires a small sample and no incubation time, and has an analytical runtime of <1 min. It is timesaving and suitable for larger studies. The levels of H2O2 in EBC are found to be elevated in healthy subjects (average=0.54 nM), rheum subjects (average=0.24 nM), and feverish subjects (average=0.16 nM). Our data suggested that the average H2O2 concentration of EBC from feverish subjects was significantly higher than healthy subjects and rheumatic subjects.

Overcoming the challenges of studying conservation physiology in large whales: a review of available methods

Large whales are subjected to a variety of conservation pressures that could be better monitored and managed if physiological information could be gathered readily from free-swimming whales. However, traditional approaches to studying physiology have been impractical for large whales, because there is no routine method for capture of the largest species and there is presently no practical method of obtaining blood samples from free-swimming whales. We review the currently available techniques for gathering physiological information on large whales using a variety of non-lethal and minimally invasive (or non-invasive) sample matrices. We focus on methods that should produce information relevant to conservation physiology, e.g. measures relevant to stress physiology, reproductive status, nutritional status, immune response, health, and disease. The following four types of samples are discussed: faecal samples, respiratory samples ('blow'), skin/blubber samples, and photographs. Faecal samples have historically been used for diet analysis but increasingly are also used for hormonal analyses, as well as for assessment of exposure to toxins, pollutants, and parasites. Blow samples contain many hormones as well as respiratory microbes, a diverse array of metabolites, and a variety of immune-related substances. Biopsy dart samples are widely used for genetic, contaminant, and fatty-acid analyses and are now being used for endocrine studies along with proteomic and transcriptomic approaches. Photographic analyses have benefited from recently developed quantitative techniques allowing assessment of skin condition, ectoparasite load, and nutritional status, along with wounds and scars from ship strikes and fishing gear entanglement. Field application of these techniques has the potential to improve our understanding of the physiology of large whales greatly, better enabling assessment of the relative impacts of many anthropogenic and ecological pressures.

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: a promising source for biomarkers of lung disease

Exhaled breath condensate (EBC) has been increasingly studied as a noninvasive research method for sampling the alveolar and airway space and is recognized as a promising source of biomarkers of lung diseases. Substances measured in EBC include oxidative stress and inflammatory mediators, such as arachidonic acid derivatives, reactive oxygen/nitrogen species, reduced and oxidized glutathione, and inflammatory cytokines. Although EBC has great potential as a source of biomarkers in many lung diseases, the low concentrations of compounds within the EBC present challenges in sample collection and analysis. Although EBC is viewed as a noninvasive method for sampling airway lining fluid (ALF), validation is necessary to confirm that EBC truly represents the ALF. Likewise, a dilution factor for the EBC is needed in order to compare across subjects and determine changes in the ALF. The aims of this paper are to address the characteristics of EBC; strategies to standardize EBC sample collection and review available analytical techniques for EBC analysis.

Cardiovascular biomarkers in exhaled breath

With each breath that we exhale, thousands of molecules are expelled in our breath, giving individuals a "breath-print" that can tell a lot about them and their state of health. Breath analysis is rapidly evolving as the new frontier in medical testing. The end of the 20th century and the beginning of the 21st century have arguably witnessed a revolution in our understanding of the constituents of exhaled breath and the development of the field of breath analysis and testing. Thanks to major breakthroughs in new technologies (infrared, electrochemical, chemiluminescence, and others) and the availability of mass spectrometers, the field of breath analysis has made considerable advances in the 21st century. Several methods are now in clinical use or nearly ready to enter that arena. Breath analysis has the potential to offer relatively inexpensive, rapid, noninvasive methods for detecting and/or monitoring a variety of diseases. Breath analysis also has applications in fields beyond medicine, including environmental monitoring, security, and others. This review will focus on exhaled breath as a potential source of biomarkers for medical applications with specific attention to applications (and potential applications) in cardiovascular disease.

Changes in NADPH oxidase mRNA level can be detected in blood at inhaled corticosteroid treated asthmatic children

AIM

Oxidative stress, observed in the asthmatic airways, is not localized only to the bronchial system. It would be a great advantage to monitor the oxidative stress markers from blood especially in childhood asthma following the inflammation. Our aim was to measure the levels of antioxidants and the oxidatively damaged biomolecules. We were also interested in the gene expression alterations of the free radical source gp91(phox) subunit (CYBB) of the NADPH oxidase system, and the antioxidant heme oxygenase-1 (HMOX-1) isoenzyme in the blood. Our findings were also examined in the context of medical treatment.

MAIN METHODS

Oxidative stress parameters via photometric methods, CYBB and HMOX-1 expressions via real-time PCR were measured in 58 asthmatic and 30 healthy children.

KEY FINDINGS

Higher blood thiobarbituric acid reactive substances (TBARS) (p<0.03) and carbonylated protein (p<0.05) levels were found in the asthmatic children than in the controls. The relative expression of CYBB was significantly lower (p<0.05) in patients treated with a low daily dose of inhaled corticosteroid (ICS), than in asthmatics not receiving ICS therapy. Higher ICS doses alone or combined with long acting β2-receptor agonists did not influence the expression significantly. No similar tendency was found as regards to HMOX-1 expression.

SIGNIFICANCE

Elevated levels of damaged lipid (TBARS) and protein (carbonylated) products corroborate the presence of oxidative stress in the blood during bronchial asthma and suggest the presence of chronic oxidative overload. Our findings also suggest that ICS treatment can influence the relative CYBB mRNA expression in circulating leukocytes in a dose dependent manner.

Cardiovascular biomarkers in exhaled breath

With each breath that we exhale, thousands of molecules are expelled in our breath, giving individuals a "breath-print" that can tell a lot about them and their state of health. Breath analysis is rapidly evolving as the new frontier in medical testing. The end of the 20th century and the beginning of the 21st century have arguably witnessed a revolution in our understanding of the constituents of exhaled breath and the development of the field of breath analysis and testing. Thanks to major breakthroughs in new technologies (infrared, electrochemical, chemiluminescence, and others) and the availability of mass spectrometers, the field of breath analysis has made considerable advances in the 21st century. Several methods are now in clinical use or nearly ready to enter that arena. Breath analysis has the potential to offer relatively inexpensive, rapid, noninvasive methods for detecting and/or monitoring a variety of diseases. Breath analysis also has applications in fields beyond medicine, including environmental monitoring, security, and others. This review will focus on exhaled breath as a potential source of biomarkers for medical applications with specific attention to applications (and potential applications) in cardiovascular disease.

Characterization of volatile organic compounds in human leukocyte antigen heterologous expression systems: a cell's "chemical odor fingerprint"

The major histocompatibility complex (MHC), or human leukocyte antigen (HLA) gene-coding region in humans, plays a significant role in infectious disease response, autoimmunity, and cellular recognition. This super locus is essential in mate selection and kin recognition because of the organism-specific odor which can be perceived by other individuals. However, how the unique MHC genetic combination of an organism correlates with generation of the organism-specific odor is not well understood. In the present work, we have shown that human B-cells produce a set of volatile organic compounds (VOCs) that can be measured by GC-MS. More importantly, our results show that specific HLA alleles are related to production of selected VOCs, and that this leads to a cell-specific odor "fingerprint". We used a C1R HLA class I A and B locus negative cell line, along with C1R cell lines that were stably transfected with specific A and B alleles. Our work demonstrates for the first time that HLA alleles can directly influence production of specific odor compounds at the cellular level. Given that the resulting odor fingerprint depends on expression of specific HLA sequences, it may yield information on unique human scent profiles, composition of exhaled breath, as well as immune response states in future studies.

Levels of Exhaled Breath Condensate pH and Fractional Exhaled Nitric Oxide in Retired Coal Miners

Inhaled inorganic dusts, such as coal, can cause inflammation and fibrosis in the lungs, known as pneumoconiosis. Diagnosis of pneumoconiosis depends on morphological changes by radiological findings and functional change by pulmonary function test (PFT) . Unfortunately, current diagnostic findings are limited only to lung fibrosis, which is usually irreversibly progressive. Therefore, it is important that research on potential and prospective biomarkers for pneumoconiosis should be conducted prior to initiation of irreversible radiological or functional changes in the lungs. Analytical techniques using exhaled breath condensate (EBC) or exhaled gas are non-invasive methods for detection of various respiratory diseases. The objective of this study is to investigate the relationship between inflammatory biomarkers, such as EBC pH or fractional exhaled nitric oxide (FENO) , and pneumoconiosis among 120 retired coal miners (41 controls and 79 pneumoconiosis patients) . Levels of EBC pH and FENO did not show a statistically significant difference between the pneumoconiosis patient group and pneumoconiosis patients with small opacity classified by International Labor Organization (ILO) classification. The mean concentration of FENO in the low percentage FEV1 (< 80%) was lower than that in the high percentage (80% ≤) (p = 0.023) . The mean concentration of FENO in current smokers was lower than that in non smokers (never or past smokers) (p = 0.027) . Although there was no statistical significance, the levels of FENO in smokers tended to decrease, compared with non smokers, regardless of pneumoconiosis. In conclusion, there was no significant relationship between the level of EBC pH or FENO and radiological findings or PFT. The effects between exhaled biomarkers and pneumoconiosis progression, such as decreasing PFT and exacerbation of radiological findings, should be monitored.

Isoprostanes-biomarkers of lipid peroxidation: their utility in evaluating oxidative stress and analysis

Isoprostanes (IsoPs) are key biomarkers for investigating the role of free radical generation in the pathogenesis of human disorders. To solve IsoPs-related problems with regard to isoprostanes, analytical tools are required. This paper reviews the problems and trends in this field focusing on the methodology for assaying biomarkers in exhaled breath condensate (EBC) samples. A large amount of work has been done in the qualitative and quantitative analysis of IsoPs, but a standardized method has yet to emerge. The methodologies described differ, either in the sample preparation steps or in the detection techniques, or both. Requiring a number of chromatographic steps, the relevant extraction and purification procedures are often critical and time-consuming, and they lead to a substantial loss of target compounds. Recent data show that EBC is a promising non-invasive tool for the evaluation of different diseases. Two main analytical approaches have been adopted for IsoPs measurement: immunological methods and mass spectrometry. The methodologies for the extraction, purification and analysis of IsoPs in EBC samples are presented.

Effects of sample processing, time and storage condition on cysteinyl leukotrienes in exhaled breath condensate

Cysteinyl leukotrienes (CysLTs) can be measured in exhaled breath condensate (EBC); however, there is considerable variation in reported EBC CysLT concentrations from asthmatic and healthy subjects between published studies, which may be partially explained by CysLT degradation during processing and storage. We assessed CysLT stability over 6 months in EBC from healthy subjects stored at -80 °C, layered with argon and then stored at -80 °C or stored in 0.2% formic acid in methanol at -80 °C following solid-phase extraction (SPE). We found significant CysLT degradation over time in both spiked and unspiked EBC samples stored at -80 °C or layered with argon. CysLT recovery was significantly greater after storage for 6 months in 0.2% formic acid in methanol following SPE; however, there was substantial variability in endogenous CysLT recovery over time, possibly attributable to inter- and intra-assay variability at the low end of the CysLT assay range. Despite the greater recovery of CysLTs in EBC stored in methanol following SPE, the degree of variability introduced by this method appears unacceptably high. We believe that the development of more sensitive and less variable methods for quantifying CysLTs in EBC are required before CysLTs can reliably be utilized as biomarkers in exhaled breath. Sample processing and storage, as well as inter- and intra-assay variability, should be carefully considered in the design of clinical studies that include assessments of EBC constituents as biomarkers.

Clinical applications of breath testing

Breath testing has the potential to benefit the medical field as a cost-effective, non-invasive diagnostic tool for diseases of the lung and beyond. With growing evidence of clinical worth, standardization of methods, and new sensor and detection technologies the stage is set for breath testing to gain considerable attention and wider application in upcoming years.

Exhaled breath condensate: lessons learned from veterinary medicine

Exhaled breath condensate (EBC) describes any sample collected by cooling exhaled breath. Because the method of condensate collection is simple, non-invasive, repeatable and does not necessarily require patient cooperation, EBC is not only an interesting, but also challenging, biological sample. Despite a period of EBC research lasting for more than 15 years, there are still many open questions with respect to EBC collection and analysis, and many biomarkers are still awaiting careful validation. In veterinary research, EBC collection has been described in conscious animals including calves, pigs, horses, cats and dogs. Numerous studies performed in these domestic animals not only contributed substantially to the current knowledge about the potentials of EBC-based diagnoses but also demonstrated pitfalls in EBC collection, analysis and interpretation. This review summarizes information about the collection of EBC and the interpretation of EBC results, particularly with respect to proteins, leukotrienes, hydrogen peroxide, urea, ammonia and pH. Published data emphasize the need to standardize approaches to produce reproducible EBC data. Quantifying the concentration of the EBC component of interest exhaled in a defined volume of exhaled breath (instead of comparing concentrations of this component analysed in liquid EBC) is an important step of standardization that might help to overcome methodological limitations deriving from the EBC collection process. Although information is based on domestic animal studies, it contributes to the general understanding in EBC research-independent of any particular mammalian species-and opens new perspectives for further studies.

Exhaled breath analysis: The new interface between medicine and engineering

Exhaled breath testing is becoming an increasingly important non-invasive diagnostic method that can be used in the evaluation of health and disease states in the lung and beyond. Potential advantages of breath tests over other conventional medical tests include their non-invasive nature, low cost, and safety. To advance in this area further, however, there has to be a close collaboration between technical experts and engineers who have devices looking for clinical application(s), the medical experts who have the clinical problems looking for a test/biomarker that can be helpful in diagnosis or monitoring, and industry/commercial experts who can build and commercialize the final product.