Publications by authors named "Simona M Cristescu"

82 Publications

Real-Time Non-Invasive Monitoring of Short-Chain Fatty Acids in Exhaled Breath.

Front Chem 2022 26;10:853541. Epub 2022 Apr 26.

Exhaled Biomarkers and Exposure Group, Department of Analytical Chemistry & Chemometrics, Institute for Molecules and Materials, Radboud University, Nijmegen, Netherlands.

Short-chain fatty acids (SCFAs) are important metabolites produced by the gut microbiome as a result of the fermentation of non-digestible polysaccharides. The most abundant SCFAs are acetic acid, propionic acid, and butyric acid which make up 95% of this group of metabolites in the gut. Whilst conventional analysis SCFAs is done using either blood or fecal samples, SCFAs can also be detected in exhaled breath using proton transfer reaction-time-of-flight- mass spectrometry (PTR-ToF-MS) using HO for ionization. However, no investigation has been performed to characterize the reactions of SCFAs with HO and with other reagent ions, such as O and NO. Gas-phase samples of acetic acid, propionic acid, and butyric acid were analyzed with SRI/PTR-ToF-MS under dry and humid conditions. The ions generated and their distribution was determined for each reagent ion. It was found the humidity did not influence the product ion distribution for each SCFA. Using HO as a reagent ion, SRI/PTR-ToF-MS analysis of an exhaled breath sample was performed in real-time to demonstrate the methodology. The presence of SCFAs in exhaled breath was confirmed by thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS). Breath sampling repeatability was within acceptable limits (<15%) for an analytical methodology for each investigated SCFA. Nutritional intervention studies could potentially benefit from real-time monitoring of exhaled SCFAs as an alternative to measuring SCFAs invasively in blood or fecal samples since it is non-invasive, and requires minimal time investment from participants.
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http://dx.doi.org/10.3389/fchem.2022.853541DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC9285658PMC
April 2022

Peppermint protocol: first results for gas chromatography-ion mobility spectrometry.

J Breath Res 2022 05 26;16(3). Epub 2022 May 26.

Centre for Analytical Science, Department of Chemistry, Loughborough University, Loughborough, United Kingdom.

Theseeks to inform the standardisation of breath analysis methods. Fivewith gas chromatography-ion mobility spectrometry (GC-IMS), operating in the positive mode with a tritiumH 5.68 keV, 370 MBq ionisation source, were undertaken to provide benchmarkdata for this technique, to support its use in breath-testing, analysis, and research. Headspace analysis of a peppermint-oil capsule by GC-IMS with on-column injection (0.5 cm) identified 12 IMS responsive compounds, of which the four most abundant were: eucalyptol;-pinene;-pinene; and limonene. Elevated concentrations of these four compounds were identified in exhaled-breath following ingestion of a peppermint-oil capsule. An unidentified compound attributed as a volatile catabolite of peppermint-oil was also observed. The most intense exhaled peppermint-oil component was eucalyptol, which was selected as a peppermint marker for benchmarking GC-IMS. Twenty-five washout experiments monitored levels of exhaled eucalyptol, by GC-IMS with on-column injection (0.5 cm), at= 0 min, and then at+ 60,+ 90,+ 165,+ 285 and+ 360 min from ingestion of a peppermint capsule resulting in 148 peppermint breath analyses. Additionally, thedata was used to evaluate clinical deployments with a further five washout tests run in clinical settings generating an additional 35 breath samples. Regression analysis yielded an average extrapolated time taken for exhaled eucalyptol levels to return to baseline values to be 429 ± 62 min (±95% confidence-interval). The benchmark value was assigned to the lower 95% confidence-interval, 367 min. Further evaluation of the data indicated that the maximum number of volatile organic compounds discernible from a 0.5 cmbreath sample was 69, while the use of an in-line biofilter appeared to reduce this to 34.
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http://dx.doi.org/10.1088/1752-7163/ac6ca0DOI Listing
May 2022

Non-Invasive Monitoring of Inflammation in Inflammatory Bowel Disease Patients during Prolonged Exercise via Exhaled Breath Volatile Organic Compounds.

Metabolites 2022 Mar 3;12(3). Epub 2022 Mar 3.

Department of Analytical Chemistry and Chemometrics, Institute for Molecules and Materials, Radboud University, 6525 AJ Nijmegen, The Netherlands.

The aim of this study was to investigate volatile organic compounds (VOCs) in exhaled breath as possible non-invasive markers to monitor the inflammatory response in inflammatory bowel disease (IBD) patients as a result of repeated and prolonged moderate-intensity exercise. We included 18 IBD patients and 19 non-IBD individuals who each completed a 30, 40, or 50 km walking exercise over three consecutive days. Breath and blood samples were taken before the start of the exercise event and every day post-exercise to assess changes in the VOC profiles and cytokine concentrations. Proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) was used to measure exhaled breath VOCs. Multivariate analysis, particularly ANOVA-simultaneous component analysis (ASCA), was employed to extract relevant ions related to exercise and IBD. Prolonged exercise induces a similar response in breath butanoic acid and plasma cytokines for participants with or without IBD. Butanoic acid showed a significant correlation with the cytokine IL-6, indicating that butanoic acid could be a potential non-invasive marker for exercise-induced inflammation. The findings are relevant in monitoring personalized IBD management.
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http://dx.doi.org/10.3390/metabo12030224DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8948819PMC
March 2022

Volatile Organic Compounds in the / Ant-Plant Symbiosis and the Role of Black Fungi.

J Fungi (Basel) 2021 Oct 6;7(10). Epub 2021 Oct 6.

Program of Sustainability in Biosystems, Institute of Agrifood Research and Technology (IRTA), Torre Marimon, E-08140 Caldes de Montbui, Spain.

Black fungi of the order Chaetothyriales are grown by many tropical plant-mutualistic ants as small so-called "patches" in their nests, which are located inside hollow structures provided by the host plant ("domatia"). These fungi are introduced and fostered by the ants, indicating that they are important for the colony. As several species of Chaetothyriales tolerate, adsorb, and metabolize toxic volatiles, we investigated the composition of volatile organic compounds (VOCs) of selected domatia in the ant-plant mutualism. Concentrations of VOCs in ant-inhabited domatia, empty domatia, and background air were compared. In total, 211 compounds belonging to 19 chemical families were identified. Ant-inhabited domatia were dominated by ketones with 2-heptanone, a well-known ant alarm semiochemical, as the most abundant volatile. Empty domatia were characterized by relatively high concentrations of the monoterpenes d-limonene, -cymene and β-phellandrene, as well as the heterocyclic sulphur-containing compound, benzothiazole. These compounds have biocidal properties and are primarily biosynthesized by plants as a defense mechanism. Interestingly, most of the latter compounds were present at lower concentrations in ant inhabited domatia than in non-colonized ones. We suggest that Chaetothyriales may play a role in reducing the VOCs, underlining that the mutualistic nature of these fungi as VOCs accumulation might be detrimental for the ants, especially the larvae.
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http://dx.doi.org/10.3390/jof7100836DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8539435PMC
October 2021

The peppermint breath test benchmark for PTR-MS and SIFT-MS.

J Breath Res 2021 09 6;15(4). Epub 2021 Sep 6.

Department of Molecular and Laser Physics, Radboud University, Nijmegen, The Netherlands.

A major challenge for breath research is the lack of standardization in sampling and analysis. To address this, a test that utilizes a standardized intervention and a defined study protocol has been proposed to explore disparities in breath research across different analytical platforms and to provide benchmark values for comparison. Specifically, theinvolves the targeted analysis in exhaled breath of volatile constituents of peppermint oil after ingestion of the encapsulated oil. Data from theperformed by proton transfer reaction mass spectrometry (PTR-MS) and selected ion flow tube mass spectrometry (SIFT-MS) are presented and discussed herein, including the product ions associated with the key peppermint volatiles, namely limonene,- and-pinene, 1,8-cineole, menthol, menthone and menthofuran. The breath washout profiles of these compounds from 65 individuals were collected, comprising datasets from five PTR-MS and two SIFT-MS instruments. The washout profiles of these volatiles were evaluated by comparing the log-fold change over time of the product ion intensities associated with each volatile. Benchmark values were calculated from the lower 95% confidence interval of the linear time-to-washout regression analysis for all datasets combined. Benchmark washout values from PTR-MS analysis were 353 min for the sum of monoterpenes and 1,8-cineole (identical product ions), 173 min for menthol, 330 min for menthofuran, and 218 min for menthone; from SIFT-MS analysis values were 228 min for the sum of monoterpenes, 281 min for the sum of monoterpenes and 1,8-cineole, and 370 min for menthone plus 1,8-cineole. Large inter- and intra-dataset variations were observed, whereby the latter suggests that biological variability plays a key role in how the compounds are absorbed, metabolized and excreted from the body via breath. This variability seems large compared to the influence of sampling and analytical procedures, but further investigations are recommended to clarify the effects of these factors.
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http://dx.doi.org/10.1088/1752-7163/ac1fcfDOI Listing
September 2021

A Breach in Plant Defences: pv. Targets Ethylene Signalling to Overcome Pathogen Responses.

Int J Mol Sci 2021 Apr 22;22(9). Epub 2021 Apr 22.

Department of Agricultural and Food Sciences, Alma Mater Studiorum-University of Bologna, 40127 Bologna, Italy.

Ethylene interacts with other plant hormones to modulate many aspects of plant metabolism, including defence and stomata regulation. Therefore, its manipulation may allow plant pathogens to overcome the host's immune responses. This work investigates the role of ethylene as a virulence factor for pv. (Psa), the aetiological agent of the bacterial canker of kiwifruit. The pandemic, highly virulent biovar of this pathogen produces ethylene, whereas the biovars isolated in Japan and Korea do not. Ethylene production is modulated in planta by light/dark cycle. Exogenous ethylene application stimulates bacterial virulence, and restricts or increases host colonisation if performed before or after inoculation, respectively. The deletion of a gene, unrelated to known bacterial biosynthetic pathways and putatively encoding for an oxidoreductase, abolishes ethylene production and reduces the pathogen growth rate in planta. Ethylene production by Psa may be a recently and independently evolved virulence trait in the arms race against the host. Plant- and pathogen-derived ethylene may concur in the activation/suppression of immune responses, in the chemotaxis toward a suitable entry point, or in the endophytic colonisation.
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http://dx.doi.org/10.3390/ijms22094375DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8122719PMC
April 2021

Exhaled Breath Reflects Prolonged Exercise and Statin Use during a Field Campaign.

Metabolites 2021 Mar 24;11(4). Epub 2021 Mar 24.

Department of Molecular and Laser Physics, Institute for Molecules and Materials, Radboud University, 6525 XZ Nijmegen, The Netherlands.

Volatile organic compounds (VOCs) in exhaled breath provide insights into various metabolic processes and can be used to monitor physiological response to exercise and medication. We integrated and validated in situ a sampling and analysis protocol using proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) for exhaled breath research. The approach was demonstrated on a participant cohort comprising users of the cholesterol-lowering drug statins and non-statin users during a field campaign of three days of prolonged and repeated exercise, with no restrictions on food or drink consumption. The effect of prolonged exercise was reflected in the exhaled breath of participants, and relevant VOCs were identified. Most of the VOCs, such as acetone, showed an increase in concentration after the first day of walking and subsequent decrease towards baseline levels prior to walking on the second day. A cluster of short-chain fatty acids including acetic acid, butanoic acid, and propionic acid were identified in exhaled breath as potential indicators of gut microbiota activity relating to exercise and drug use. We have provided novel information regarding the use of breathomics for non-invasive monitoring of changes in human metabolism and especially for the gut microbiome activity in relation to exercise and the use of medication, such as statins.
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http://dx.doi.org/10.3390/metabo11040192DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8064097PMC
March 2021

Sensitive multi-species trace gas sensor based on a high repetition rate mid-infrared supercontinuum source.

Opt Express 2020 Aug;28(18):26091-26101

We present a multi-species trace gas sensor based on a high-repetition-rate mid-infrared supercontinuum source, in combination with a 30 m multipass absorption cell, and a scanning grating spectrometer. The output of the spectrometer is demodulated by a digital lock-in amplifier, referenced to the repetition rate of the supercontinuum source. This improved the detection sensitivity of the system by a factor 5, as compared to direct baseband operation. The spectrometer provides a spectral coverage of 950 cm (between 2.85-3.90 µm) with a resolution of 2.5 cm in 100 ms. It can achieve noise equivalent detection limits in the order of 100 ppbv Hz for various hydrocarbons, alcohols, and aldehydes.
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http://dx.doi.org/10.1364/OE.396884DOI Listing
August 2020

Cell death associated release of volatile organic sulphur compounds with antioxidant properties in chemical-challenged tobacco BY-2 suspension cultured cells.

J Plant Physiol 2020 Aug 2;251:153223. Epub 2020 Jul 2.

Wageningen University & Research, Horticulture and Product Physiology Group, Droevendaalsesteeg 1, P.O. Box 630, 6700AP, Wageningen, the Netherlands; Wageningen Food and Biobased Research, Bornse Weilanden 9, P.O. Box 17, 6700 AA Wageningen, the Netherlands. Electronic address:

The production of volatile organic compounds (VOCs) during programmed cell death (PCD) is still insufficiently studied and their implication in the process is not well understood. The present study demonstrates that the release of VOSCs with presumed antioxidant capacity (methanethiol, dimethylsulfide and dimethyldisulfide) accompanies the cell death in chemical-stressed tobacco BY-2 suspension cultured cells. The cells were exposed to cell death inducers of biotic nature mastoparan (MP, wasp venom) and camptothecin (CPT, alkaloid), and to the abiotic stress agent CdSO. The VOCs emission was monitored by proton-transfer reaction mass spectrometry (PTR-MS). The three chemicals induced PCD expressing apoptotic-like phenotype. The identified VOSCs were emitted in response to MP and CPT but not in presence of Cd. The VOSCs production occurred within few hours after the administration of the elicitors, peaked up when 20-50 % of the cells were dead and further levelled off with cell death advancement. This suggests that VOSCs with antioxidant activity may contribute to alleviation of cell death-associated oxidative stress at medium severity of cell death in response to the stress factors of biotic origin. The findings provide novel information about cell death defence mechanisms in chemical-challenged BY-2 cells and show that PCD related VOSCs synthesis depends on the type of inducer.
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http://dx.doi.org/10.1016/j.jplph.2020.153223DOI Listing
August 2020

A benchmarking protocol for breath analysis: the peppermint experiment.

J Breath Res 2020 08 10;14(4):046008. Epub 2020 Aug 10.

Exhaled Biomarkers and Exposure, Department of Molecular and Laser Physics, IMM, Radboud University, Nijmegen, The Netherlands.

Sampling of volatile organic compounds (VOCs) has shown promise for detection of a range of diseases but results have proved hard to replicate due to a lack of standardization. In this work we introduce the 'Peppermint Initiative'. The initiative seeks to disseminate a standardized experiment that allows comparison of breath sampling and data analysis methods. Further, it seeks to share a set of benchmark values for the measurement of VOCs in breath. Pilot data are presented to illustrate the standardized approach to the interpretation of results obtained from the Peppermint experiment. This pilot study was conducted to determine the washout profile of peppermint compounds in breath, identify appropriate sampling time points, and formalise the data analysis. Five and ten participants were recruited to undertake a standardized intervention by ingesting a peppermint oil capsule that engenders a predictable and controlled change in the VOC profile in exhaled breath. After collecting a pre-ingestion breath sample, five further samples are taken at 2, 4, 6, 8, and 10 h after ingestion. Samples were analysed using ion mobility spectrometry coupled to multi-capillary column and thermal desorption gas chromatography mass spectrometry. A regression analysis of the washout data was used to determine sampling times for the final peppermint protocol, and the time for the compound measurement to return to baseline levels was selected as a benchmark value. A measure of the quality of the data generated from a given technique is proposed by comparing data fidelity. This study protocol has been used for all subsequent measurements by the Peppermint Consortium (16 partners from seven countries). So far 1200 breath samples from 200 participants using a range of sampling and analytical techniques have been collected. The data from the consortium will be disseminated in subsequent technical notes focussing on results from individual platforms.
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http://dx.doi.org/10.1088/1752-7163/aba130DOI Listing
August 2020

Characterization of particulate and gaseous pollutants from a French dairy and sheep farm.

Sci Total Environ 2020 Apr 20;712:135598. Epub 2019 Nov 20.

INRA, UMR ECOSYS, INRA, AgroParisTech, Université Paris-Saclay, 78850 Thiverval-Grignon, France.

Agricultural activities highly contribute to atmospheric pollution, but the diversity and the magnitude of their emissions are still subject to large uncertainties. A field measurement campaign was conducted to characterize gaseous and particulate emissions from an experimental farm in France containing a sheep pen and a dairy stable. During the campaign, more than four hundred volatile organic compounds (VOCs) were characterized using an original combination of online and off-line measurements. Carbon dioxide (CO) and ammonia (NH) were the most concentrated compounds inside the buildings, followed by methanol, acetic acid and acetaldehyde. A CO mass balance model was used to estimate NH and VOC emission rates. To our knowledge, this study constitutes the first evaluation of emission rates for most of the identified VOCs. The measurements show that the dairy stable emitted more VOCs than the sheep pen. Despite strong VOC and NH emissions, the chemical composition of particles indicates that gaseous farm emissions do not affect the loading of fine particles inside the farm and is mainly explained by the low residence time inside the buildings. The experimental dataset obtained in this work will help to improve emissions inventories for agricultural activities.
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http://dx.doi.org/10.1016/j.scitotenv.2019.135598DOI Listing
April 2020

Time-resolved mid-infrared dual-comb spectroscopy.

Sci Rep 2019 Nov 21;9(1):17247. Epub 2019 Nov 21.

Trace Gas Research Group, Department of Molecular and Laser Physics, Institute for Molecules and Materials, Radboud University, 6525 AJ, Nijmegen, The Netherlands.

Dual-comb spectroscopy can provide broad spectral bandwidth and high spectral resolution in a short acquisition time, enabling time-resolved measurements. Specifically, spectroscopy in the mid-infrared wavelength range is of particular interest, since most of the molecules have their strongest rotational-vibrational transitions in this "fingerprint" region. Here we report time-resolved mid-infrared dual-comb spectroscopy, covering ~300 nm bandwidth around 3.3 μm with 6 GHz spectral resolution and 20 μs temporal resolution. As a demonstration, we study a CH/He gas mixture in an electric discharge, while the discharge is modulated between dark and glow regimes. We simultaneously monitor the production of CH and the vibrational excitation of CH molecules, observing the dynamics of both processes. This approach to broadband, high-resolution, and time-resolved mid-infrared spectroscopy provides a new tool for monitoring the kinetics of fast chemical reactions, with potential applications in various fields such as physical chemistry and plasma/combustion analysis.
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http://dx.doi.org/10.1038/s41598-019-53825-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6872568PMC
November 2019

Human Monocyte-Derived Dendritic Cells Produce Millimolar Concentrations of ROS in Phagosomes Per Second.

Front Immunol 2019 29;10:1216. Epub 2019 May 29.

Tumor Immunology Lab, Radboud University Medical Center, Radboud Institute for Molecular Life Sciences, Nijmegen, Netherlands.

Neutrophils kill ingested pathogens by the so-called oxidative burst, where reactive oxygen species (ROS) are produced in the lumen of phagosomes at very high rates (mM/s), although these rates can only be maintained for a short period (minutes). In contrast, dendritic cells produce ROS at much lower rates, but they can sustain production for much longer after pathogen uptake (hours). It is becoming increasingly clear that this slow but prolonged ROS production is essential for antigen cross-presentation to activate cytolytic T cells, and for shaping the repertoire of antigen fragments for presentation to helper T cells. However, despite this importance of ROS production by dendritic cells for activation of the adaptive immune system, their actual ROS production rates have never been quantified. Here, we quantified ROS production in human monocyte-derived dendritic cells by measuring the oxygen consumption rate during phagocytosis. Although a large variation in oxygen consumption and phagocytic capacity was present among individuals and cells, we estimate a ROS production rate of on average ~0.5 mM/s per phagosome. Quantitative microscopy approaches showed that ROS is produced within minutes after pathogen encounter at the nascent phagocytic cup. HDCFDA measurements revealed that ROS production is sustained for at least ~10 h after uptake. While ROS are produced by dendritic cells at an about 10-fold lower rate than by neutrophils, the net total ROS production is approximately similar. These are the first quantitative estimates of ROS production by a cell capable of antigen cross-presentation. Our findings provide a quantitative insight in how ROS affect dendritic cell function.
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http://dx.doi.org/10.3389/fimmu.2019.01216DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6548834PMC
July 2020

Nitrite and nitric oxide are important in the adjustment of primary metabolism during the hypersensitive response in tobacco.

J Exp Bot 2019 08;70(17):4571-4582

National Institute of Plant Genome Research, Aruna Asaf Ali Marg, New Delhi, India.

Nitrate and ammonia deferentially modulate primary metabolism during the hypersensitive response in tobacco. In this study, tobacco RNAi lines with low nitrite reductase (NiRr) levels were used to investigate the roles of nitrite and nitric oxide (NO) in this process. The lines accumulate NO2-, with increased NO generation, but allow sufficient reduction to NH4+ to maintain plant viability. For wild-type (WT) and NiRr plants grown with NO3-, inoculation with the non-host biotrophic pathogen Pseudomonas syringae pv. phaseolicola induced an accumulation of nitrite and NO, together with a hypersensitive response (HR) that resulted in decreased bacterial growth, increased electrolyte leakage, and enhanced pathogen resistance gene expression. These responses were greater with increases in NO or NO2- levels in NiRr plants than in the WT under NO3- nutrition. In contrast, WT and NiRr plants grown with NH4+ exhibited compromised resistance. A metabolomic analysis detected 141 metabolites whose abundance was differentially changed as a result of exposure to the pathogen and in response to accumulation of NO or NO2-. Of these, 13 were involved in primary metabolism and most were linked to amino acid and energy metabolism. HR-associated changes in metabolism that are often linked with primary nitrate assimilation may therefore be influenced by nitrite and NO production.
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http://dx.doi.org/10.1093/jxb/erz161DOI Listing
August 2019

Proton transfer reaction time-of-flight mass spectrometric measurements of volatile compounds contained in peppermint oil capsules of relevance to real-time pharmacokinetic breath studies.

J Breath Res 2019 07 18;13(4):046009. Epub 2019 Jul 18.

Institute for Breath Research, Leopold-Franzens-Universität Innsbruck, Rathausplatz 4, A-6850, Dornbirn, Austria.

With the growing interest in the use of breath volatiles in the health sciences, the lack of standardization for the sampling and analysis of exhaled breath is becoming a major issue leading to an absence of conformity, reproducibility and reliability in spectrometric measurements. Through the creation of a worldwide 'peppermint consortium', the International Association of Breath Research has set up a task force to deal with this problem. Pharmacokinetic studies are proposed, and a real-time analytical technique that is being used is proton transfer reaction-time-of-flight-mass spectrometry (PTR-ToF-MS). This paper presents details on how the volatile compounds contained in a peppermint oil capsule, and hence on breath, appear in a PTR-ToF-MS. To aid that study, the key volatiles in the headspace of peppermint oil were first identified using gas chromatography-mass spectrometry, notably: menthol, menthone, 1,8-cineole, menthofuran, limonene, α-pinene and β-pinene. A PTR-ToF-MS analysis of these compounds has been undertaken, divorced from the complexity of the peppermint oil matrix using 'normal' and 'saturated' humidity drift-tube conditions, with the latter used to mimic breath samples, and over a range of reduced electric fields. There are no characteristic product ions that can distinguish monoterpenes and 1,8-cineole, and hence, without pre-separation, a combined washout for these volatiles can only be provided. By operating the drift tube above about 130 Td, there are characteristic product ions for menthone, menthofuran and menthol, namely m/z 155.14 (protonated menthone), m/z 151.11 (protonated menthofuran), m/z 139.15 (loss of HO from protonated menthol) and m/z 83.09 (a fragment ion, CH , from menthol). These have been used to monitor, with a high specificity, the temporal profile of these three compounds in breath following the ingestion of a peppermint oil capsule. To aid in the analyses, the proton affinities and gas-phase basicities for the key volatiles investigated have been determined using density functional theory.
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http://dx.doi.org/10.1088/1752-7163/ab26e2DOI Listing
July 2019

A Broadband Mid-Infrared Trace Gas Sensor Using Supercontinuum Light Source: Applications for Real-Time Quality Control for Fruit Storage.

Sensors (Basel) 2019 May 21;19(10). Epub 2019 May 21.

Trace Gas Research Group, Institute of Molecules and Materials, Radboud University, 6525 AJ Nijmegen, The Netherlands.

We present a fully integrated and transportable multi-species trace gas sensor based on a mid-infrared (MIR) supercontinuum light source. The high brightness (surpassing synchrotron) and ultra-broad spectral bandwidth (2-4 μm) of this light source allows simultaneous detection of multiple broadband absorbing gas species. High sensitivity in the sub-ppmv level has been achieved by utilizing an astigmatic multipass cell. A grating-based spectrometer at a scanning rate of 20 Hz is developed employing a balanced detection scheme. A multi-component global fitting algorithm is implemented into a central LabVIEW program to perform real-time data analysis. The obtained concentration values are validated by the standard gas chromatography mass spectrometry (GC-MS) method. Field application of the sensor for quality control of stored fruits at a small scale is demonstrated, involving the detection of ethylene, ethanol, ethyl acetate, acetaldehyde, methanol, acetone, and water simultaneously. The sensor also shows promising potentials for other applications, such as environmental monitoring and biomedical research.
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http://dx.doi.org/10.3390/s19102334DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6566869PMC
May 2019

Interactive Responses of to Drought and Insect Feeding are Herbivore Species-Specific.

Int J Mol Sci 2018 Dec 3;19(12). Epub 2018 Dec 3.

Molecular Interaction Ecology, Institute of Water and Wetland Research, Radboud University, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands.

In nature, plants are frequently subjected to multiple biotic and abiotic stresses, resulting in a convergence of adaptive responses. We hypothesised that hormonal signalling regulating defences to different herbivores may interact with drought responses, causing distinct resistance phenotypes. To test this, we studied the hormonal and transcriptomic responses of subjected to drought and herbivory by the generalist (beet armyworm; BAW) or the specialist (Colorado potato beetle; CPB). Bioassays showed that the performance of BAW, but not CPB, decreased on plants under drought compared to controls. While drought did not alter BAW-induced hormonal responses, it enhanced the CPB-induced accumulation of jasmonic acid and salicylic acid (SA), and suppressed ethylene (ET) emission. Microarray analyses showed that under drought, BAW herbivory enhanced several herbivore-induced responses, including cell-wall remodelling and the metabolism of carbohydrates, lipids, and secondary metabolites. In contrast, CPB herbivory enhanced several photosynthesis-related and pathogen responses in drought-stressed plants. This may divert resources away from defence production and increase leaf nutritive value. In conclusion, while BAW suffers from the drought-enhanced defences, CPB may benefit from the effects of enhanced SA and reduced ET signalling. This suggests that the fine-tuned interaction between the plant and its specialist herbivore is sustained under drought.
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http://dx.doi.org/10.3390/ijms19123845DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6321310PMC
December 2018

Intensity enhancement in off-axis integrated cavity output spectroscopy.

Appl Opt 2018 Oct;57(29):8536-8542

In the field of laser-based absorption spectroscopy, off-axis integrated cavity output spectroscopy is considered to be a sensitive and robust method, employing a simple optical design. However, one of the major drawbacks of non-mode-matched cavities combined with highly reflective mirrors (>99.98%) is its low output intensity. Here, we systematically investigate the increase in cavity output intensity, using a third re-injection mirror before the absorption cavity. The presented design not only enables high transmission power but also retains a long effective path length. To investigate the intensity enhancement, we used a CO absorption line in the near-IR wavelength region at 6240.10  cm. In agreement with our simulation model, we achieved an intensity enhancement factor of 38. We achieved a noise equivalent absorption sensitivity to 1.6×10  cm Hz, which is no longer limited by the detectivity of the detector.
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http://dx.doi.org/10.1364/AO.57.008536DOI Listing
October 2018

Sensitive Spectroscopy of Acetone Using a Widely Tunable External-Cavity Quantum Cascade Laser.

Sensors (Basel) 2018 Jun 27;18(7). Epub 2018 Jun 27.

Trace Gas Research Facility, Molecular, and Laser Physics, Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.

We employed a single-mode, widely tunable (~300 cm) external-cavity quantum cascade laser operating around 8 µm for broadband direct absorption spectroscopy and wavelength modulation spectroscopy where a modulation frequency of 50 kHz was employed with high modulation amplitudes of up to 10 GHz. Using a compact multipass cell, we measured the entire molecular absorption band of acetone at ~7.4 µm with a spectral resolution of ~1 cm. In addition, to demonstrate the high modulation dynamic range of the laser, we performed direct absorption (DAS) and second harmonic wavelength modulation spectroscopy (WMS-2f) of the Q-branch peak of acetone molecular absorption band (HWHM ~10 GHz) near 1365 cm. With WMS-2f, a minimum detection limit of 15 ppbv in less than 10 s is achieved, which yields a noise equivalent absorption sensitivity of 1.9 × 10 cm Hz.
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http://dx.doi.org/10.3390/s18072050DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6068499PMC
June 2018

Quantum Cascade Lasers-Based Detection of Nitric Oxide.

Methods Mol Biol 2018 ;1747:49-57

Institute for Sustainable Agriculture, Spanish Council for Scientific Research (CSIC), Córdoba, Spain.

Despite the established importance of nitric oxide (NO) in many physiological and molecular processes in plants, most methods for quantifying NO are open to criticism This reflects the differing methods either lacking specificity or sensitivity, or even from an undue dependence of results on experimental conditions (i.e., chemical concentrations, pH, etc.). In this chapter we describe a protocol to measure gaseous NO produced by a biological sample using quantum cascade laser (QCL)-based spectroscopy. This technique is based on absorption of the laser light by the NO molecules which have been passed from a biological sample into an optical s cell that is equipped with two mirrors placed at both ends. This design greatly increases the interaction path length with the NO molecules due to multiple reflections of the light coupled inside the cell. Thus, the method is able to provide online, in planta measurements of the dynamics of NO production, being highly selective and sensitive (down to ppbv levels;1 ppbv = part per billion by volume mixing ratio = 1:10).
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http://dx.doi.org/10.1007/978-1-4939-7695-9_5DOI Listing
January 2019

Comprehensive three-dimensional ray tracing model for three-mirror cavity-enhanced spectroscopy.

Appl Opt 2018 Jan;57(2):154-163

A 3D ray tracing model is used to simulate optical reinjection in a nonresonant optical cavity, for off-axis integrated cavity output spectroscopy. The optical cavities are optimized for maximum intensity enhancement factors via a grid search and a genetic algorithm. Intensity enhancement factors up to 1400 are found for short cavities (3 cm) and up to 101 for long cavities (50 cm). The model predicts that short absorption cells can be used, having a long effective path length and a high throughput power. This opens new opportunities in the field of ultrasensitive absorption spectroscopy and allows the design of compact optical gas sensors.
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http://dx.doi.org/10.1364/AO.57.000154DOI Listing
January 2018

Laser spectroscopy for breath analysis: towards clinical implementation.

Appl Phys B 2018 28;124(8):161. Epub 2018 Jul 28.

1Trace Gas Research Group, Molecular and Laser Physics, IMM, Radboud University, 6525 AJ Nijmegen, The Netherlands.

Detection and analysis of volatile compounds in exhaled breath represents an attractive tool for monitoring the metabolic status of a patient and disease diagnosis, since it is non-invasive and fast. Numerous studies have already demonstrated the benefit of breath analysis in clinical settings/applications and encouraged multidisciplinary research to reveal new insights regarding the origins, pathways, and pathophysiological roles of breath components. Many breath analysis methods are currently available to help explore these directions, ranging from mass spectrometry to laser-based spectroscopy and sensor arrays. This review presents an update of the current status of optical methods, using near and mid-infrared sources, for clinical breath gas analysis over the last decade and describes recent technological developments and their applications. The review includes: tunable diode laser absorption spectroscopy, cavity ring-down spectroscopy, integrated cavity output spectroscopy, cavity-enhanced absorption spectroscopy, photoacoustic spectroscopy, quartz-enhanced photoacoustic spectroscopy, and optical frequency comb spectroscopy. A SWOT analysis (strengths, weaknesses, opportunities, and threats) is presented that describes the laser-based techniques within the clinical framework of breath research and their appealing features for clinical use.
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http://dx.doi.org/10.1007/s00340-018-7030-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6428385PMC
July 2018

Lipid peroxidation in cardiac surgery: towards consensus on biomonitoring, diagnostic tools and therapeutic implementation.

J Breath Res 2018 02 6;12(2):027109. Epub 2018 Feb 6.

Section of Anaesthetics, Pain Medicine and Intensive Care, Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, London, United Kingdom.

This review focuses on oxidative stress and more specifically lipid peroxidation in cardiac surgery, one of the fundamental theories of perioperative complications. We present the molecular pathways leading to lipid peroxidation and integrate analytical methods that allow detection of lipid peroxidation markers in the fluid phase with those focusing on volatile compounds in exhaled breath. In order to explore the accumulated data in the literature, we present a systematic review of quantitative analysis of malondialdehyde, a widely used lipid peroxidation product at various stages of cardiac surgery. This exploration reveals major limitations of existing studies in terms of variability of reported values and significant gaps due to discrete and variable sampling times during surgery. We also appraise methodologies that allow real-time and continuous monitoring of oxidative stress. Complimentary techniques highlight that beyond the widely acclaimed contribution of the cardiopulmonary bypass technology and myocardial reperfusion injury, the use of diathermy contributes significantly to intraoperative lipid peroxidation. We conclude that there is an urgent need to implement the theory of oxidative stress towards a paradigm change in the clinical practice. Firstly, we need to acquire definite and irrefutable information on the link between lipid peroxidation and post-operative complications by building international consensus on best analytical approaches towards generating qualitatively and quantitatively comparable datasets in coordinated multicentre studies. Secondly, we should move away from routine low-risk surgeries towards higher risk interventions where there is major unmet clinical need for improving patient journey and outcomes. There is also need for consensus on best therapeutic interventions which could be tested in convincing large scale clinical trials. As future directions, we propose combination of fluid phase platforms and 'metabography', an extended form of capnography-including real-time analysis of lipid peroxidation and volatile footprints of metabolism-for better patient phenotyping prior to and during high risk surgery towards molecular prediction, stratification and monitoring of the patient's journey.
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http://dx.doi.org/10.1088/1752-7163/aa9856DOI Listing
February 2018

Reduced nitric oxide levels during drought stress promote drought tolerance in barley and is associated with elevated polyamine biosynthesis.

Sci Rep 2017 10 17;7(1):13311. Epub 2017 Oct 17.

CSIC, Institute for Sustainable Agriculture, Córdoba, Spain.

Nitric oxide (NO) is a key messenger in plant stress responses but its exact role in drought response remains unclear. To investigate the role of NO in drought response we employed transgenic barley plants (UHb) overexpressing the barley non-symbiotic hemoglobin gene HvHb1 that oxidizes NO to NO. Reduced NO production under drought conditions in UHb plants was associated with increased drought tolerance. Since NO biosynthesis has been related to polyamine metabolism, we investigated whether the observed drought-related NO changes could involve polyamine pathway. UHb plants showed increases in total polyamines and in particular polyamines such as spermidine. These increases correlated with the accumulation of the amino acid precursors of polyamines and with the expression of specific polyamine biosynthesis genes. This suggests a potential interplay between NO and polyamine biosynthesis during drought response. Since ethylene has been linked to NO signaling and it is also related to polyamine metabolism, we explored this connection. In vivo ethylene measurement showed that UHb plants significantly decrease ethylene production and expression of aminocyclopropane-1-carboxylic acid synthase gene, the first committed step in ethylene biosynthesis compared with wild type. These data suggest a NO-ethylene influenced regulatory node in polyamine biosynthesis linked to drought tolerance/susceptibility in barley.
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http://dx.doi.org/10.1038/s41598-017-13458-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5645388PMC
October 2017

Ethylene, an early marker of systemic inflammation in humans.

Sci Rep 2017 07 31;7(1):6889. Epub 2017 Jul 31.

Department of Molecular and Laser Physics, Institute of Molecules and Materials, Radboud University, Nijmegen, The Netherlands.

Ethylene is a major plant hormone mediating developmental processes and stress responses to stimuli such as infection. We show here that ethylene is also produced during systemic inflammation in humans and is released in exhaled breath. Traces of ethylene were detected by laser spectroscopy both in vitro in isolated blood leukocytes exposed to bacterial lipopolysaccharide (LPS) as well as in vivo following LPS administration in healthy volunteers. Exposure to LPS triggers formation of ethylene as a product of lipid peroxidation induced by the respiratory burst. In humans, ethylene was detected prior to the increase of blood levels of inflammatory cytokines and stress-related hormones. Our results highlight that ethylene release is an early and integral component of in vivo lipid peroxidation with important clinical implications as a breath biomarker of bacterial infection.
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http://dx.doi.org/10.1038/s41598-017-05930-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5537290PMC
July 2017

Combining ANOVA-PCA with POCHEMON to analyse micro-organism development in a polymicrobial environment.

Anal Chim Acta 2017 04 13;963:1-16. Epub 2017 Feb 13.

Department of Analytical Chemistry, Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands. Electronic address:

Revealing the biochemistry associated to micro-organismal interspecies interactions is highly relevant for many purposes. Each pathogen has a characteristic metabolic fingerprint that allows identification based on their unique multivariate biochemistry. When pathogen species come into mutual contact, their co-culture will display a chemistry that may be attributed both to mixing of the characteristic chemistries of the mono-cultures and to competition between the pathogens. Therefore, investigating pathogen development in a polymicrobial environment requires dedicated chemometric methods to untangle and focus upon these sources of variation. The multivariate data analysis method Projected Orthogonalised Chemical Encounter Monitoring (POCHEMON) is dedicated to highlight metabolites characteristic for the interaction of two micro-organisms in co-culture. However, this approach is currently limited to a single time-point, while development of polymicrobial interactions may be highly dynamic. A well-known multivariate implementation of Analysis of Variance (ANOVA) uses Principal Component Analysis (ANOVA-PCA). This allows the overall dynamics to be separated from the pathogen-specific chemistry to analyse the contributions of both aspects separately. For this reason, we propose to integrate ANOVA-PCA with the POCHEMON approach to disentangle the pathogen dynamics and the specific biochemistry in interspecies interactions. Two complementary case studies show great potential for both liquid and gas chromatography - mass spectrometry to reveal novel information on chemistry specific to interspecies interaction during pathogen development.
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http://dx.doi.org/10.1016/j.aca.2017.01.064DOI Listing
April 2017

Herbivore-induced plant volatiles accurately predict history of coexistence, diet breadth, and feeding mode of herbivores.

New Phytol 2018 11 30;220(3):726-738. Epub 2017 Jan 30.

Molecular Interaction Ecology, Institute for Water and Wetland Research (IWWR), Radboud University, PO Box 9010, 6500, GL Nijmegen, the Netherlands.

Herbivore-induced plant volatiles (HIPVs) serve as specific cues to higher trophic levels. Novel, exotic herbivores entering native foodwebs may disrupt the infochemical network as a result of changes in HIPV profiles. Here, we analysed HIPV blends of native Brassica rapa plants infested with one of 10 herbivore species with different coexistence histories, diet breadths and feeding modes. Partial least squares (PLS) models were fitted to assess whether HIPV blends emitted by Dutch B. rapa differ between native and exotic herbivores, between specialists and generalists, and between piercing-sucking and chewing herbivores. These models were used to predict the status of two additional herbivores. We found that HIPV blends predicted the evolutionary history, diet breadth and feeding mode of the herbivore with an accuracy of 80% or higher. Based on the HIPVs, the PLS models reliably predicted that Trichoplusia ni and Spodoptera exigua are perceived as exotic, leaf-chewing generalists by Dutch B. rapa plants. These results indicate that there are consistent and predictable differences in HIPV blends depending on global herbivore characteristics, including coexistence history. Consequently, native organisms may be able to rapidly adapt to potentially disruptive effects of exotic herbivores on the infochemical network.
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http://dx.doi.org/10.1111/nph.14428DOI Listing
November 2018

Biological relevance of volatile organic compounds emitted during the pathogenic interactions between apple plants and Erwinia amylovora.

Mol Plant Pathol 2018 01 13;19(1):158-168. Epub 2017 Jan 13.

Department of Agricultural Sciences, Alma Mater Studiorum, University of Bologna, Bologna, 40127, Italy.

Volatile organic compounds emitted during the infection of apple (Malus pumila var. domestica) plants by Erwinia amylovora or Pseudomonas syringae pv. syringae were studied by gas chromatography-mass spectrometry and proton transfer reaction-mass spectrometry, and used to treat uninfected plants. Infected plants showed a disease-specific emission of volatile organic compounds, including several bio-active compounds, such as hexenal isomers and 2,3-butanediol. Leaf growth promotion and a higher resistance to the pathogen, expressed as a lower bacterial growth and migration in plant tissues, were detected in plants exposed to volatile compounds from E. amylovora-infected plants. Transcriptional analysis revealed the activation of salicylic acid synthesis and signal transduction in healthy plants exposed to volatiles produced by E. amylovora-infected neighbour plants. In contrast, in the same plants, salicylic acid-dependent responses were repressed after infection, whereas oxylipin metabolism was activated. These results clarify some metabolic and ecological aspects of the pathogenic adaptation of E. amylovora to its host.
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http://dx.doi.org/10.1111/mpp.12509DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6637988PMC
January 2018

Peptides interfering with protein-protein interactions in the ethylene signaling pathway delay tomato fruit ripening.

Sci Rep 2016 08 1;6:30634. Epub 2016 Aug 1.

Biochemical Plant Physiology, Heinrich-Heine-University Düsseldorf, D-40204 Düsseldorf, Germany.

The plant hormone ethylene is involved in the regulation of several processes with high importance for agricultural applications, e.g. ripening, aging and senescence. Previous work in our group has identified a small peptide (NOP-1) derived from the nuclear localization signal of the Arabidopsis ethylene regulator ETHYLENE INSENSITIVE-2 (EIN2) C-terminal part as efficient inhibitor of ethylene responses. Here, we show that NOP-1 is also able to efficiently disrupt EIN2-ETR1 complex formation in tomato, indicating that the NOP-1 inhibition mode is conserved across plant species. Surface application of NOP-1 on green tomato fruits delays ripening similar to known inhibitors of ethylene perception (MCP) and ethylene biosynthesis (AVG). Fruits treated with NOP-1 showed similar ethylene production as untreated controls underlining that NOP-1 blocks ethylene signaling by targeting an essential interaction in this pathway, while having no effect on ethylene biosynthesis.
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http://dx.doi.org/10.1038/srep30634DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4967898PMC
August 2016

ABA Suppresses Botrytis cinerea Elicited NO Production in Tomato to Influence H2O2 Generation and Increase Host Susceptibility.

Front Plant Sci 2016 25;7:709. Epub 2016 May 25.

Molecular Plant Pathology Group, Institute of Biological, Environmental and Rural Sciences, Aberystwyth University Aberystwyth, UK.

Abscisic acid (ABA) production has emerged a susceptibility factor in plant-pathogen interactions. This work examined the interaction of ABA with nitric oxide (NO) in tomato following challenge with the ABA-synthesizing pathogen, Botrytis cinerea. Trace gas detection using a quantum cascade laser detected NO production within minutes of challenge with B. cinerea whilst photoacoustic laser detection detected ethylene production - an established mediator of defense against this pathogen - occurring after 6 h. Application of the NO generation inhibitor N-Nitro-L-arginine methyl ester (L-NAME) suppressed both NO and ethylene production and resistance against B. cinerea. The tomato mutant sitiens fails to accumulate ABA, shows increased resistance to B. cinerea and we noted exhibited elevated NO and ethylene production. Exogenous application of L-NAME or ABA reduced NO production in sitiens and reduced resistance to B. cinerea. Increased resistance to B. cinerea in sitiens have previously been linked to increased reactive oxygen species (ROS) generation but this was reduced in both L-NAME and ABA-treated sitiens. Taken together, our data suggests that ABA can decreases resistance to B. cinerea via reduction of NO production which also suppresses both ROS and ethylene production.
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http://dx.doi.org/10.3389/fpls.2016.00709DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4879331PMC
June 2016
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