Exhaled Isoprene Research Articles

Photoacoustic trace-analysis of breath isoprene and acetone via interband- and Quantum Cascade Lasers

This research presents two laser-based photoacoustic approaches for analyzing exhaled breath isoprene and acetone. The integration of a PTR-ToF-MS as a reference device ensured the reliability and accuracy of the photoacoustic systems that is based on an ICL for isoprene and a QCL for acetone detection. The calibration yielded limits of detection of 26.9 ppbV and 1.7 ppbV, respectively, and corresponding normalized noise equivalent absorption coefficients (NNEAs) of 5.0E-9 Wcm−1Hz−0.5 and 4.9E-9 Wcm−1Hz−0.5. Laboratory as well as real breath sample measurements from alveolar breath revealed a robust system performance, with only one outlier within the static isoprene measurements. However, discrepancies emerged under dynamic breath sampling conditions, emphasizing the need for further optimization. Especially by knowing the dynamic nature and endogenous origin of exhaled isoprene our findings highlight the potential of breath analysis for non-invasive physio-metabolic and pathophysiological monitoring towards point-of-care devices.

Quantifying exhaled acetone and isoprene through solid phase microextraction and gas chromatography-mass spectrometry

BackgroundAcetone, isoprene, and other volatile organic compounds (VOCs) in exhaled breath have been shown to be biomarkers for many medical conditions. Researchers use different techniques for VOC detection, including solid phase microextraction (SPME), to preconcentrate volatile analytes prior to instrumental analysis by gas chromatography-mass spectrometry (GC-MS). These techniques include a previously developed method to detect VOCs in breath directly using SPME, but it is uncommon for studies to quantify exhaled volatiles because it can be time consuming due to the need of many external/internal standards, and there is no standardized or widely accepted method. The objective of this study was to develop an accessible method to quantify acetone and isoprene in breath by SPME GC-MS. ResultsA system was developed to mimic human exhalation and expose VOCs to a SPME fiber in the gas phase at known concentrations. VOCs were bubbled/diluted with dry air at a fixed flow rate, duration, and volume that was comparable to a previously developed breath sampling method. Identification of acetone and isoprene through GC-MS was verified using standards and observing overlaps in chromatographic retention/mass spectral fragmentation. Calibration curves were developed for these two analytes, which showed a high degree of linear correlation. Acetone and isoprene displayed limits of detection/quantification equal to 12 ppb/37 ppb and 73 ppb/222 ppb respectively. Quantification results in healthy breath samples (n = 15) showed acetone concentrations spanned between 71 ppb and 294 ppb, and isoprene varied between 170 ppb and 990 ppb. Both concentration ranges for acetone and isoprene in this study overlap with those reported in existing literature. SignificanceResults indicate the development of a system to quantify acetone and isoprene in breath that can be adapted to diverse sampling methods and instrumental analyses beyond SPME GC-MS.

Origin of breath isoprene in humans is revealed via multi-omic investigations

Plants, animals and humans metabolically produce volatile isoprene (C5H8). Humans continuously exhale isoprene and exhaled concentrations differ under various physio-metabolic and pathophysiological conditions. Yet unknown metabolic origin hinders isoprene to reach clinical practice as a biomarker. Screening 2000 individuals from consecutive mass-spectrometric studies, we herein identify five healthy German adults without exhaled isoprene. Whole exome sequencing in these adults reveals only one shared homozygous (European prevalence: <1%) IDI2 stop-gain mutation, which causes losses of enzyme active site and Mg2+–cofactor binding sites. Consequently, the conversion of isopentenyl diphosphate to dimethylallyl diphosphate (DMAPP) as part of the cholesterol metabolism is prevented in these adults. Targeted sequencing depicts that the IDI2 rs1044261 variant (p.Trp144Stop) is heterozygous in isoprene deficient blood-relatives and absent in unrelated isoprene normal adults. Wild-type IDI1 and cholesterol metabolism related serological parameters are normal in all adults. IDI2 determines isoprene production as only DMAPP sources isoprene and unlike plants, humans lack isoprene synthase and its enzyme homologue. Human IDI2 is expressed only in skeletal-myocellular peroxisomes and instant spikes in isoprene exhalation during muscle activity underpins its origin from muscular lipolytic cholesterol metabolism. Our findings translate isoprene as a clinically interpretable breath biomarker towards potential applications in human medicine.

Investigation of an individual with background levels of exhaled isoprene: a case study

Isoprene is one of the most abundant and most frequently evaluated volatile organic compounds in exhaled breath. Recently, several individuals with background levels of exhaled isoprene have been identified. Here, case study data are provided for an individual, identified from a previous study, with this low prevalence phenotype. It is hypothesized that the individual will illustrate low levels of exhaled isoprene at rest and during exercise. At rest, the subject (7.1 ppb) shows background (μ = 14.2 ± 7.0 ppb) levels of exhaled isoprene while the control group illustrates significantly higher quantities (μ = 266.2 ± 72.3 ppb) via proton transfer reaction mass spectrometry (PTR-MS). The result, background levels of isoprene at rest, is verified by thermal desorption gas chromatography mass spectrometry (TD-GC-MS) collections with the individual showing −3.6 ppb exhaled isoprene while the room background contained μ= −4.1 ± 0.1 ppb isoprene. As isoprene has been shown previously to increase at the initiation of exercise, exercise bike experiments were performed with the individual identified with low isoprene, yielding low and invariant levels of exhaled isoprene (μ = 6.6 ± 0.1 ppb) during the exercise while control subjects illustrated an approximate 2.5-fold increase (pre μ = 286.3 ± 43.8 ppb, exercise μ = 573.0 ± 147.8 ppb) in exhaled isoprene upon exercise start. Additionally, exhaled breath bag data showed a significant decrease in isoprene (delta post/pre, p = 0.0078) of the control group following the exercise regimen. Finally, TD-GC-MS results for exhaled isoprene from the individual’s family (mother, father, sister and maternal grandmother) illustrated that the mother and father exhibited isoprene values (28.5 ppb, 77.2 ppb) below control samples 95% confidence interval (μ = 166.8 ± 43.3 ppb) while the individual’s sister (182.0 ppb) was within the control range. These data provide evidence for a large dynamic range in exhaled isoprene in this family. Collectively, these results provide additional data surrounding the existence of a small population of individuals with background levels of exhaled isoprene.

A combined screening study for evaluating the potential of exhaled acetone, isoprene, and nitric oxide as biomarkers of lung cancer.

Background: the early lung cancer (LC) screening strategy significantly reduces LC mortality. According to previous studies, lung cancer can be effectively diagnosed by analyzing the concentration of volatile organic compounds (VOCs) in human exhaled breath and establishing a diagnosis model based on the different VOCs. This method, called breath analysis, has the advantage of being rapid and non-invasive. To develop a non-invasive, portable breath detection instrument based on cavity ring-down spectroscopy (CRDS), we explored the feasibility of establishing a model with acetone, isoprene, and nitric oxide (NO) exhaled through human breath, which can be detected on the CRDS instrument. Methods: a total of 511 participants were recruited from the Cancer Institute and Hospital, Tianjin Medical University as the discovery set and randomly split (2 : 1) into training set and internal validation set with stratification. For external validation, 51 participants were recruited from the General Hospital, Tianjin Medical University. Acetone and isoprene from exhaled breath were detected by proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS), and NO was measured using CRDS. The model was constructed using the ensemble learning method that set eXtreme gradient boosting and logistic regression as the basis model and logistic regression as the senior model. The model was evaluated based on accuracy, sensitivity, and specificity. Results: the model achieved an accuracy of 78.8%, sensitivity of 81.0%, specificity of 70.0%, and area under the receiver operating curve (ROC, AUC) of 0.8341 (95% CI from 0.8055 to 0.8852) in the internal validation set. Furthermore, it attained an accuracy of 66.7%, sensitivity of 68.2%, specificity of 65.5%, and AUC of 0.6834 (95% CI from 0.5259 to 0.7956) in the external validation set. Conclusion: the model, established with acetone, isoprene, and NO as predictors, possesses the ability to identify LC patients from healthy control (HC) participants. The CRDS instrument, which simultaneously detects acetone, isoprene, and NO, is expected to be a non-invasive, rapid, portable, and accurate device for early screening of LC.

Influence of ventilatory parameters on the concentration of exhaled volatile organic compounds in mechanically ventilated patients.

Analysis of volatile organic compounds (VOC) within exhaled breath is subject to numerous sources of methodological and physiological variability. Whilst breathing pattern is expected to influence the concentrations of selected exhaled VOCs, it remains challenging to investigate respiratory rate and depth accurately in awake subjects. Online breath sampling was performed in 20 mechanically ventilated patients using proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS). The effect of variation in respiratory rate (RR) and tidal volume (TV) on the VOC release profiles was examined. A panel of nineteen VOCs were selected, including isoprene, acetone, propofol, volatile aldehydes, acids and phenols. Variation in RR had the greatest influence on exhaled isoprene levels, with maximum and average concentrations being inversely correlated with RR. Variations in RR had a statistically significant impact on acetone, C3-C7 linear aldehydes and acetic acid. In comparison, phenols (including propofol), C8-C10 aldehydes and C3-C6 carboxylic acids were not influenced by RR. Isoprene was the only compound to be influenced by variation in TV. These findings, obtained under controlled conditions, provide useful guidelines for the optimisation of breath sampling protocols to be applied on awake patients.

ZIF-8 micro-polyhedron MOF-transformed ZnO/ZnFe2O4 nanosheets for highly selective detection of ppb-level isoprene

Isoprene as a toxic volatile organic compound usually harms human health. Instead, exhaled isoprene may serve as a versatile biomarker in diagnosing blood cholesterol and chronic liver disease. However, such isoprene sensing that is simultaneously required with ppb-level detection limit and excellent selectivity, it is still less than satisfactory. Here, a highly selective and ppb-level isoprene sensing has been developed with ZnO/ZnFe2O4 nanosheets (NSTs), which is transformed from ZIF-8 micro-polyhedron metal-organic framework (MOF). Typically, the ZnO/ZnFe2O4 NSTs are observed of ∼ 60 nm thick and heterojunction between ZnO and ZnFe2O4. Beneficially, the ZnO/ZnFe2O4 NSTs show a higher response to 1 ppm isoprene (Ra/Rg = 19.7) than that of ZnO micro-polyhedrons (Ra/Rg = 3.6) at 120 °C. Remarkably, the ZnO/ZnFe2O4 NSTs display a detection limit as low as 2 ppb and a high selectivity to isoprene even being exposed to multiple interfering gases. Theoretically, a large specific surface of ZnO/ZnFe2O4 NSTs and as-formed heterojunction between ZnO and ZnFe2O4 may widen the electron depletion layer, adsorbing more chemisorbed oxygen species to oxidize isoprene. The approach to ZnO/ZnFe2O4 NSTs might be extended to NSTs of other sensing materials and target gases, which is potential in upcoming intelligent medical diagnosis.

Metabolic and behavioral features of acute hyperpurinergia and the maternal immune activation mouse model of autism spectrum disorder.

Since 2012, studies in mice, rats, and humans have suggested that abnormalities in purinergic signaling may be a final common pathway for many genetic and environmental causes of autism spectrum disorder (ASD). The current study in mice was conducted to characterize the bioenergetic, metabolomic, breathomic, and behavioral features of acute hyperpurinergia triggered by systemic injection of the purinergic agonist and danger signal, extracellular ATP (eATP). Responses were studied in C57BL/6J mice in the maternal immune activation (MIA) model and controls. Basal metabolic rates and locomotor activity were measured in CLAMS cages. Plasma metabolomics measured 401 metabolites. Breathomics measured 98 volatile organic compounds. Intraperitoneal eATP dropped basal metabolic rate measured by whole body oxygen consumption by 74% ± 6% (mean ± SEM) and rectal temperature by 6.2˚ ± 0.3˚C in 30 minutes. Over 200 metabolites from 37 different biochemical pathways where changed. Breathomics showed an increase in exhaled carbon monoxide, dimethylsulfide, and isoprene. Metabolomics revealed an acute increase in lactate, citrate, purines, urea, dopamine, eicosanoids, microbiome metabolites, oxidized glutathione, thiamine, niacinamide, and pyridoxic acid, and decreased folate-methylation-1-carbon intermediates, amino acids, short and medium chain acyl-carnitines, phospholipids, ceramides, sphingomyelins, cholesterol, bile acids, and vitamin D similar to some children with ASD. MIA animals were hypersensitive to postnatal exposure to eATP or poly(IC), which produced a rebound increase in body temperature that lasted several weeks before returning to baseline. Acute hyperpurinergia produced metabolic and behavioral changes in mice. The behaviors and metabolic changes produced by ATP injection were associated with mitochondrial functional changes that were profound but reversible.

Breath isoprene excretion during rest and low-intensity cycling exercise is associated with skeletal muscle mass in healthy human subjects

The physiological roles of isoprene, which is one of the many endogenous volatile organic compounds contained in exhaled breath, are not well understood. In recent years, exhaled isoprene has been associated with the skeletal muscle. Some studies have suggested that the skeletal muscle produces and/or stores some of the isoprene. However, the evidence supporting this association remains sparse and inconclusive. Furthermore, aging may affect breath isoprene response because of changes in the skeletal muscle quantity and quality. Therefore, we investigated the association between the breath isoprene excretion () and skeletal muscle mass in young (n = 7) and old (n = 7) adults. The participants performed an 18 min cycling exercise after a 3 min rest. The workload corresponded to an intensity of 30% of the heart rate reserve, as calculated by the Karvonen formula. The exhaled breath of each participant was collected during the exercise test. We calculated from the product minute ventilation and isoprene concentration and, then, investigated the relationships between and muscle mass, which was measured by multi-frequency bioelectrical impedance analysis. Importantly, muscle mass persisted as a significant determinant that explained the variance in at rest even after adjusting for age. Furthermore, the muscle mass was a significant determinative factor for response during exercise, regardless of age. These data indicated that skeletal muscle mass could be one of the determinative factors for during rest and response to exercise. Thus, we suggest that the skeletal muscle may play an important role in generating and/or storing some of the endogenous isoprene. This new knowledge will help to better understand the physiological functions of isoprene in humans (Approval No. 20190079).

382-P: Exhaled Isoprene Products Change during Hypoglycemia in Type 1 Diabetes and Home Breath Capture Is Feasible as a Diagnostic Tool

Detection of hypoglycemia is important to reduce risk and optimize glucose in T1D. Noninvasive glucose detection methods have not been fully explored. Exhaled breath isoprene, a component of sterol metabolism, has been associated with hypoglycemia in controlled studies in a limited population in the laboratory setting. Home-monitoring of breath isoprene levels may permit noninvasive hypoglycemia detection. We conducted an exploratory study measuring exhaled volatile organic compounds (VOCs) in breath samples collected during hypoglycemia (CBG &amp;lt;70 mg/dL) compared to euglycemia (CBG 70-180 mg/dL) under free-living conditions in 10 subjects age 7-74 with T1D. Breath samples were collected using designated breath capture bags and processed 1-4 weeks later by proton-transfer-reaction time-of-flight (PTR TOF) mass spectrometry. Over 100 VOCs were identified in 52 breath samples (25 hypoglycemia, 27 euglycemia). During hypoglycemia, isoprene increased 37% (p&amp;lt;0.05) and its oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) decreased 59% (p&amp;lt;0.05). However, predictive modelling using metabolite concentration as the input could not reliably predict whether the breath sample was collected during hypoglycemia or euglycemia. All other measured VOCs were not statistically different. This is the first free-living study to evaluate exhaled VOCs in patients with T1D. We successfully replicated findings of a prior study done in a controlled laboratory setting suggesting isoprene concentration in human breath increases during hypoglycemia. We further describe decreased MVK and MACR during hypoglycemia and home breath capture may be feasible for diagnostics in medical conditions. In addition, the physiology of glucose changes on sterol metabolism is worthy of further study. Finally, identification of an exhaled marker of glucose levels hints at a possible mechanism of detection by so-called diabetes alert dogs. Disclosure E.A. Los: Advisory Panel; Self; Medtronic. W.L. Stone: None. G. Ford: None. Funding East Tennessee State University (18-025M)

Evaluation of a standardized collection device for exhaled breath sampling onto thermal desorption tubes

The Respiration Collector for In Vitro Analysis (ReCIVA) sampler, marketed by Owlstone Medical, provides a step forward in exhaled breath sampling through active sampling directly onto thermal desorption (TD) tubes. Although an improvement to the issues surrounding breath bag sampling, the ReCIVA device, first released in 2015, is a relatively new research and clinical tool that requires further exploration. Here, data are presented comparing two distinct ReCIVA devices. The results, comparing ReCIVA serial numbers #33 and #65, demonstrate that overall statistically insignificant results are obtained via targeted isoprene quantitation (p > 0.05). However, when the data are parsed by the TD tube type used to capture breath volatiles, either Tenax TA or the dual bed Tenax/Carbograph 5TD (5TD), a statistical difference (p < 0.05) among the two different TD tubes was present. These data, comparing the two ReCIVA devices with both Tenax TA and 5TD tubes, are further supported by a global metabolomics analysis yielding 85% of z-scores, comparing ReCIVA devices, below the limit for significance. Experiments to determine the effect of breathing rate on ReCIVA function, using guided breathing for low (7.5 breaths min−1) and high (15 breaths min−1) breathing rates, demonstrate the ReCIVA device shows no statistical difference among breathing rates for quantitated isoprene (p > 0.05). Global metabolomics analysis of the guided breathing rate data shows more than 87% of the z-scores, comparing high and low breathing rates using both the Tenax and the 5TD tubes, are below the level for significance. Finally, data are provided from a single participant who displayed background levels of isoprene while illustrating levels of acetone consistent with the remaining participants. Collectively, these data support the use of multiple ReCIVA devices for exhaled breath collection and provide evidence for an instance where exhaled isoprene is consistent with background levels.

Characterization of standardized breath sampling for off-line field use

Due to several sources of potential variability associated with exhaled breath bag sampling procedures for off-line analysis, the Respiration Collector for in vitro Analysis (ReCIVA) sampler was developed. Although designed to improve upon several pitfalls of sampling with exhaled breath bags, the ReCIVA remains a minimally studied research tool. In this manuscript, several attributes of the ReCIVA sampler are investigated among three individual tests, such as background contamination, control software version, performance of different adsorbent tubes, duplicate sample production, and comparison to exhaled breath bags. The data shows greater than a 58% reduction in background siloxanes can be achieved with submersion of ReCIVA masks in ethyl alcohol or baking the masks at a high temperature (200 °C). The results illustrate the ReCIVA control software version plays a key role in the flow rates applied to thermal desorption (TD) tubes. Using exhaled isoprene as a representative analyte, the data suggest duplicate samples among ReCIVA pump banks can be achieved using two different thermal desorption tubes, Tenax TA and Tenax/Carbograph 5TD, when using an updated control software and manually calibrating the ReCIVA pumps to uniform flow rates (Tenax p = 0.3869, 5TD p = 0.3131). Additionally, using the updated control software and manual ReCIVA flow calibration, the data suggest the ReCIVA can produce statistically similar results among TD tube types (p = 0.3824) and compared to standard exhaled breath bags (p = 0.1534). Collectively, these results establish a method for manually calibrating the flow of the ReCIVA device to allow for the most consistent results. These data support further experimentation into the use of the ReCIVA sampler for exhaled breath research.

Exhaled isoprene for monitoring recovery from acute hypoxic stress

Hypoxia-like incidents in-flight have increased over the past decade causing severe safety concerns across the aviation community. As a result, the need to monitor flight crews in real-time for the onset of hypoxic conditions is paramount for continued aeronautical safety. Here, hypoxic events were simulated in the laboratory via a reduced oxygen-breathing device to determine the effect of recovery gas oxygen concentration (21% and 100%) on exhaled breath volatile organic compound composition. Data from samples collected both serially (throughout the exposure), prior to, and following exposures yielded 326 statistically significant features, 203 of which were unique. Of those, 72 features were tentatively identified while 51 were verified with authentic standards. A comparison of samples collected serially between recovery and hypoxia time points shows a statistically significant reduction in exhaled breath isoprene (2-methyl-1,3-butadiene, log2 FC −0.399, p = 0.005, FDR = 0.034, q = 0.033), however no significant difference in isoprene abundance was observed when comparing recovery gases (21% or 100% O2, p = 0.152). Furthermore, examination of pre-/post-exposure 1 l bag breath samples illustrate an overall increase in exhaled isoprene abundance post-exposure (log2 FC 0.393, p = 0.005, FDR = 0.094, q = 0.033) but again no significant difference between recovery gas (21% and 100%, p = 0.798) was observed. A statistically significant difference in trend was observed between isoprene abundance and recovery gases O2 concentration when plotted against minimum oxygen saturation (p = 0.0419 100% O2, p = 0.7034 21% O2). Collectively, these results suggest exhaled isoprene is dynamic in the laboratory ROBD setup and additional experimentation will be required to fully understand the dynamics of isoprene in response to acute hypoxic stress.

Air sampling unit for breath analyzers.

The paper presents a portable breath sampling unit (BSU) for human breath analyzers. The developed unit can be used to probe air from the upper airway and alveolar for clinical and science studies. The BSU is able to operate as a patient interface device for most types of breath analyzers. Its main task is to separate and to collect the selected phases of the exhaled air. To monitor the so-called I, II, or III phase and to identify the airflow from the upper and lower parts of the human respiratory system, the unit performs measurements of the exhaled CO2 (ECO2) in the concentration range of 0%-20% (0-150 mm Hg). It can work in both on-line and off-line modes according to American Thoracic Society/European Respiratory Society standards. A Tedlar bag with a volume of 5 dm3 is mounted as a BSU sample container. This volume allows us to collect ca. 1-25 selected breath phases. At the user panel, each step of the unit operation is visualized by LED indicators. This helps us to regulate the natural breathing cycle of the patient. There is also an operator's panel to ensure monitoring and configuration setup of the unit parameters. The operation of the breath sampling unit was preliminarily verified using the gas chromatography/mass spectrometry (GC/MS) laboratory setup. At this setup, volatile organic compounds were extracted by solid phase microextraction. The tests were performed by the comparison of GC/MS signals from both exhaled nitric oxide and isoprene analyses for three breath phases. The functionality of the unit was proven because there was an observed increase in the signal level in the case of the III phase (approximately 40%). The described work made it possible to construct a prototype of a very efficient breath sampling unit dedicated to breath sample analyzers.

Selective sensing of isoprene by Ti-doped ZnO for breath diagnostics.

Exhaled isoprene could enable non-invasive monitoring of cholesterol-lowering therapies. Here, we report an isoprene-selective sensor at high relative humidity (RH) for the first time (to our knowledge). It is made of nanostructured, chemo-resistive Ti-doped ZnO particles (10-20 nm crystal size) produced by flame spray pyrolysis (FSP) and directly deposited in one step onto compact sensor substrates forming highly porous films. The constituent particles consist of stable Ti-doped ZnO solid solutions for Ti levels up to 10 mol% apparently by substitutional incorporation of Ti4+ into the ZnO wurtzite lattice and dominant presence at the particle surface. These Ti4+ point defects strongly enhance the isoprene sensitivity (>15 times higher than pure ZnO) and turn ZnO isoprene-selective, while also improving its thermal stability. In situ infrared spectroscopy confirms that Ti4+ intensifies the surface interaction of Ti-doped ZnO with isoprene by providing additional sites for chemisorbed hydroxyl species. In fact, at an optimal Ti content of 2.5 mol%, this sensor shows superior isoprene responses compared to acetone, NH3 and ethanol at 90% RH. Most notably, breath-relevant isoprene concentrations can be detected accurately down to 5 ppb with high (>10) signal-to-noise ratio. As a result, an inexpensive isoprene detector has been developed that could be easily incorporated into a portable breath analyzer for non-invasive monitoring of metabolic disorders (e.g. cholesterol).

Relations between isoprene and nitric oxide in exhaled breath and the potential influence of outdoor ozone: a pilot study

The role of endogenous isoprene in the human body, if any, is unclear because previous research is inconsistent and mechanistic evidence for the biologic function of isoprene is lacking. Given previous evidence that exhaled isoprene is elevated in systemic inflammatory states, we hypothesized that exhaled isoprene would be positively associated with a breath biomarker of airway inflammation, the fractional concentration of exhaled nitric oxide (FENO). We examined relationships of exhaled breath isoprene with FENO and with outdoor ozone given that ozone chemically reacts with isoprene and has been positively associated with FENO in past studies. Sixteen elderly subjects were followed with ≤12 weekly exhaled hydrocarbon and FENO collections at the subjects’ retirement community. Outdoor ozone concentrations were measured continuously on site. Mixed-effects regression analyses tested relations of FENO with isoprene, and FENO and isoprene with ozone, adjusted for temperature. We found FENO was inversely associated with isoprene, and this was not confounded by ozone. Isoprene was inversely related to ozone. FENO was positively related to ozone and this relation was not confounded by isoprene. In contrast to hypothesized relations, we conclude that exhaled isoprene is inversely associated with FENO as well as outdoor ozone, which suggests possible protective ozone-scavenging functions of endogenous isoprene. Findings may indicate chemical reactions of isoprene oxidation by ozone and by hydroxyl radicals in the presence of O2 that is dependent on NO concentration. These preliminary results need to be confirmed in additional studies of human subjects, particularly as they apply to FENO monitoring in asthma.

Mo1980 Metabolomic Analysis of Exhaled Breath to Identify Volatile Organic Compounds (VOCs) in Children With Inflammatory Bowel Disease

Background: Pediatric-onset inflammatory bowel disease (IBD) is significantly increasing in prevalence worldwide. In light of the increasing incidence of IBD and its poorly understood pathogenesis, it is important to develop a simple non-invasive tool to detect patients with IBD. Breath testing is becoming an important diagnostic method to evaluate many disease states. The aim of this study was to analyze exhaled volatile organic compounds to potentially elucidate new pathways involved in IBD pathogenesis and differentiate the breathprints of IBD from healthy controls. Methods: An IRB approved prospective study was conducted at a tertiary center. Patients (age range, 5-21 years) with documented IBD were recruited from the Pediatric Gastroenterology Clinic and healthy controls (age range, 5-21 years) were recruited from the General Pediatrics Clinic. The diagnosis of IBD was confirmed by endoscopic, histologic, and radiographic data. Exhaled breath was collected and analyzed using a selective ion flow tube (SIFT-MS) to identify new markers or patterns of IBD. Results: 117 patients were included in the study (62 with IBD and 55 healthy controls). Routinely analyzed VOCs for SIFT-MS quantification showed significant increases in exhaled isoprene, 1-decene, 1-heptene, 1-octene, and 3-methylhexane in patients with IBD (p value , 0.001) (Table 1). Discriminant analysis via stepwise variable selection of mass scanning ion peak data demonstrated five ion peaks (1-octene, H3O+121+, NO+118+, NO+120+, O2+57+) that classified subjects in a 55 patient training set with no misclassifications (-2 log likelihood 0.172; Wilks' Lambda 0.145 (p , 0.0001)) (Figure 1). The discriminant analysis model was then successfully tested in an independent 62 patient validation cohort with only four misclassifications. Conclusion: Exhaled breath analysis is a promising non-invasive method to distinguish children with IBD from healthy children. Exhaled isoprene, 1-decene, 1heptene, 1-octene, and 3-methylhexane are novel biomarkers that are significantly elevated in the breath of children with IBD as compared to healthy controls. Further analysis of these compounds may help to gain insight into pathophysiological processes and pathways leading to the development of IBD. We provide pilot data to support the hypothesis that a unique breathprint can be demonstrated for IBD in the exhaled metabolome. Table 1. Exhaled VOC concentrations

Mo1981 Reciprocal Regulation of Colonic Epithelial Cell Secretion of Osteoprotegerin by Inflammasome Cytokines

Background: Pediatric-onset inflammatory bowel disease (IBD) is significantly increasing in prevalence worldwide. In light of the increasing incidence of IBD and its poorly understood pathogenesis, it is important to develop a simple non-invasive tool to detect patients with IBD. Breath testing is becoming an important diagnostic method to evaluate many disease states. The aim of this study was to analyze exhaled volatile organic compounds to potentially elucidate new pathways involved in IBD pathogenesis and differentiate the breathprints of IBD from healthy controls. Methods: An IRB approved prospective study was conducted at a tertiary center. Patients (age range, 5-21 years) with documented IBD were recruited from the Pediatric Gastroenterology Clinic and healthy controls (age range, 5-21 years) were recruited from the General Pediatrics Clinic. The diagnosis of IBD was confirmed by endoscopic, histologic, and radiographic data. Exhaled breath was collected and analyzed using a selective ion flow tube (SIFT-MS) to identify new markers or patterns of IBD. Results: 117 patients were included in the study (62 with IBD and 55 healthy controls). Routinely analyzed VOCs for SIFT-MS quantification showed significant increases in exhaled isoprene, 1-decene, 1-heptene, 1-octene, and 3-methylhexane in patients with IBD (p value , 0.001) (Table 1). Discriminant analysis via stepwise variable selection of mass scanning ion peak data demonstrated five ion peaks (1-octene, H3O+121+, NO+118+, NO+120+, O2+57+) that classified subjects in a 55 patient training set with no misclassifications (-2 log likelihood 0.172; Wilks' Lambda 0.145 (p , 0.0001)) (Figure 1). The discriminant analysis model was then successfully tested in an independent 62 patient validation cohort with only four misclassifications. Conclusion: Exhaled breath analysis is a promising non-invasive method to distinguish children with IBD from healthy children. Exhaled isoprene, 1-decene, 1heptene, 1-octene, and 3-methylhexane are novel biomarkers that are significantly elevated in the breath of children with IBD as compared to healthy controls. Further analysis of these compounds may help to gain insight into pathophysiological processes and pathways leading to the development of IBD. We provide pilot data to support the hypothesis that a unique breathprint can be demonstrated for IBD in the exhaled metabolome. Table 1. Exhaled VOC concentrations

Decline of exhaled isoprene in lung cancer patients correlates with immune activation

Isoprene (2-methylbuta-1,3-diene) represents a precursor molecule of isoprenoids (steroids, terpens), and available data suggest that isoprene is related to cholesterol biosynthesis. Breath concentrations of isoprene have been reported to be altered in a number of clinical conditions. However, the physiological meaning of isoprene changes has not yet been established. Utilizing proton-transfer-mass spectroscopy, we analyzed isoprene concentrations (m/z 69, tentatively identified as isoprene) in breath samples in Tedlar bags collected from 79 lung cancer patients (23 females, 56 males). Results were compared to the concentrations of immune activation marker neopterin (ELISA, BRAHMS, Hennigsdorf, Germany), lipid parameters (routine enzymology) and C-reactive protein (CRP). Isoprene concentrations were median 92.5 ppb (25th–75th percentile: 79–131 ppb). There was no relationship with staging, grading or age, but isoprene concentrations correlated significantly with total cholesterol (rs = 0.281, p < 0.01) and LDL cholesterol (rs = 0.236, p < 0.05). There was no significant relationship between exhaled isoprene concentrations and HDL cholesterol (rs = 0.048), triglycerides (rs = 0.164) and CRP (rs = –0.115; all not significant). A significant inverse correlation existed between isoprene and neopterin concentrations (rs = −0.215, p < 0.05); the latter also correlated with total cholesterol (rs = −0.343, p = 0.001), HDL cholesterol (rs = −0.273, p = 0.01), LDL cholesterol (rs = −0.236, p < 0.05) and CRP (rs = 0.230, p < 0.05) but not with triglycerides (rs = 0.035, not significant). Results suggest that immune activation might play a role in the decline of isoprene which is probably related to lipid metabolic changes. Interestingly, similar relationships between elevated neopterin and decreased lipid concentrations have been reported earlier in other clinical conditions, e.g. in patients with HIV-1 infection.

Determination of ethane, pentane and isoprene in exhaled air – effects of breath‐holding, flow rate and purified air

Exhaled ethane, pentane and isoprene have been proposed as biomarkers of oxidative stress. The objectives were to explore whether ethane, pentane and isoprene are produced within the airways and to explore the effect of different sampling parameters on analyte concentrations. The flow dependency of the analyte concentrations, the concentrations in dead-space and alveolar air after breath-holding and the influence of inhaling purified air on analyte concentrations were investigated. The analytical method involved thermal desorption from sorbent tubes and gas chromatography. The studied group comprised 13 subjects with clinically stable asthma and 14 healthy controls. Ethane concentrations decreased slightly, but significantly, at higher flow rates in subjects with asthma (P = 0.0063) but not in healthy controls. Pentane levels were increased at higher flow rates both in healthy and asthmatic subjects (P = 0.022 and 0.0063 respectively). Isoprene levels were increased at higher flow rates, but only significantly in healthy subjects (P = 0.0034). After breath-holding, no significant changes in ethane levels were observed. Pentane and isoprene levels increased significantly after 20 s of breath-holding. Inhalation of purified air before exhalation resulted in a substantial decrease in ethane levels, a moderate decrease in pentane levels and an increase in isoprene levels. The major fractions of exhaled ethane, pentane and isoprene seem to be of systemic origin. There was, however, a tendency for ethane to be flow rate dependent in asthmatic subjects, although to a very limited extent, suggesting that small amounts of ethane may be formed in the airways.