Headspace generation coupled to gas chromatography–mass spectrometry for the automated determination and quantification of endogenous compounds in urine. Aldehydes as possible markers of oxidative stress

Simple, fast and inexpensive quantification of glycolate in the urine of patients with primary hyperoxaluria type 1

In primary hyperoxaluria type 1 excessive endogenous production of oxalate and glycolate leads to increased urinary excretion of these metabolites. Although genetic testing is the most definitive and preferred diagnostic method, quantification of these metabolites is important for the diagnosis and evaluation of potential therapeutic interventions. Current metabolite quantification methods use laborious, technically highly complex and expensive liquid, gas or ion chromatography tandem mass spectrometry, which are available only in selected laboratories worldwide. Incubation of ortho-aminobenzaldehyde (oABA) with glyoxylate generated from glycolate using recombinant mouse glycolate oxidase (GO) and glycine leads to the formation of a stable dihydroquinazoline double aromatic ring chromophore with specific peak absorption at 440 nm. The urinary limit of detection and estimated limit of quantification derived from eight standard curves were 14.3 and 28.7 µmol glycolate per mmol creatinine, respectively. High concentrations of oxalate, lactate and L-glycerate do not interfere in this assay format. The correlation coefficient between the absorption and an ion chromatography tandem mass spectrometry method is 93% with a p value < 0.00001. The Bland-Altmann plot indicates acceptable agreement between the two methods. The glycolate quantification method using conversion of glycolate via recombinant mouse GO and fusion of oABA and glycine with glyoxylate is fast, simple, robust and inexpensive. Furthermore this method might be readily implemented into routine clinical diagnostic laboratories for glycolate measurements in primary hyperoxaluria type 1.

Advancement in Analytical Strategies for Quantification of Biomarkers with a Special Emphasis on Surrogate Approaches

Accurate quantification of biomarkers has always been a challenge for many bioanalytical scientists due to their endogenous nature and low concentration in biological matrices. Different analytical approaches have been developed for quantifying biomarkers including enzyme-linked immunosorbent assay, immunohistochemistry, western blotting, and chromatographic techniques assisted with mass spectrometry. Liquid chromatography-tandem mass spectrometry-based quantification of biomarkers has gained more attention over other traditional techniques due to its higher sensitivity and selectivity. However, the primary challenge lies with this technique includes the unavailability of a blank matrix for method development. To overcome this challenge, different analytical approaches are being developed including surrogate analyte and surrogate matrix approach. Such approaches include quantification of biomarkers in a surrogate matrix or quantification of an isotopically labeled surrogate analyte in an authentic matrix. To demonstrate the authenticity of the surrogate approach, it is mandatory to establish quantitative parallelism through validation employing respective surrogate analytes and surrogate matrices. In this review, different bioanalytical approaches for biomarker quantification and recent advancements in the field aiming for improvement in the specificity of the techniques have been discussed. Liquid chromatography-tandem mass spectrometry-based surrogate approaches for biomarker quantification and significance of parallelism establishment in both surrogate matrix and surrogate analyte-based approaches have been critically discussed. In addition, different methods for demonstrating parallelism in the surrogate method have been explained.

Lipid Peroxidation in Atherosclerotic Cardiovascular Diseases

Significance: Atherosclerotic cardiovascular diseases (ACVDs) continue to be a primary cause of mortality worldwide in adults aged 35-70 years, occurring more often in countries with lower economic development, and they constitute an ever-growing global burden that has a considerable socioeconomic impact on society. The ACVDs encompass diverse pathologies such as coronary artery disease and heart failure (HF), among others. Recent Advances: It is known that oxidative stress plays a relevant role in ACVDs and some of its effects are mediated by lipid oxidation. In particular, lipid peroxidation (LPO) is a process under which oxidants such as reactive oxygen species attack unsaturated lipids, generating a wide array of oxidation products. These molecules can interact with circulating lipoproteins, to diffuse inside the cell and even to cross biological membranes, modifying target nucleophilic sites within biomolecules such as DNA, lipids, and proteins, and resulting in a plethora of biological effects. Critical Issues: This review summarizes the evidence of the effect of LPO in the development and progression of atherosclerosis-based diseases, HF, and other cardiovascular diseases, highlighting the role of protein adduct formation. Moreover, potential therapeutic strategies targeted at lipoxidation in ACVDs are also discussed. Future Directions: The identification of valid biomarkers for the detection of lipoxidation products and adducts may provide insights into the improvement of the cardiovascular risk stratification of patients and the development of therapeutic strategies against the oxidative effects that can then be applied within a clinical setting.

An Optimization of Liquid-Liquid Extraction of Urinary Volatile and Semi-Volatile Compounds and Its Application for Gas Chromatography-Mass Spectrometry and Proton Nuclear Magnetic Resonance Spectroscopy

Urinary volatile compounds (VCs) have been recently assessed for disease diagnoses. They belong to very diverse chemical classes, and they are characterized by different volatilities, polarities and concentrations, complicating their analysis via a single analytical procedure. There remains a need for better, lower-cost methods for VC biomarker discovery. Thus, there is a strong need for alternative methods, enabling the detection of a broader range of VCs. Therefore, the main aim of this study was to optimize a simple and reliable liquid-liquid extraction (LLE) procedure for the analysis of VCs in urine using gas chromatography-mass spectrometry (GC-MS), in order to obtain the maximum number of responses. Extraction parameters such as pH, type of solvent and ionic strength were optimized. Moreover, the same extracts were analyzed using Proton Nuclear Magnetic Resonance Spectroscopy (1H-NMR), to evaluate the applicability of a single urine extraction for multiplatform purposes. After the evaluation of experimental conditions, an LLE protocol using 2 mL of urine in the presence of 2 mL of 1 M sulfuric acid and sodium sulphate extracted with dichloromethane was found to be optimal. The optimized method was validated with the external standards and was found to be precise and linear, and allowed for detection of >400 peaks in a single run present in at least 50% of six samples-considerably more than the number of peaks detected by solid-phase microextracton fiber pre-concentration-GC-MS (328 ± 6 vs. 234 ± 4). 1H-NMR spectroscopy of the polar and non-polar extracts extended the range to >40 more (mainly low volatility compounds) metabolites (non-destructively), the majority of which were different from GC-MS. The more peaks detectable, the greater the opportunity of assessing a fingerprint of several compounds to aid biomarker discovery. In summary, we have successfully demonstrated the potential of LLE as a cheap and simple alternative for the analysis of VCs in urine, and for the first time the applicability of a single urine solvent extraction procedure for detecting a wide range of analytes using both GC-MS and 1H-NMR analysis to enhance putative biomarker detection. The proposed method will simplify the transport between laboratories and storage of samples, as compared to intact urine samples.

Multiple headspace sampling coupled to a programmed temperature vaporizer to improve sensitivity in headspace-gas chromatography. Determination of aldehydes

The improvement of sensitivity in headspace (HS) sampling of not very volatile analytes constitutes a challenge that has usually been approached through coupling with additional techniques. Here we propose a new methodology for increasing sensitivity through a multistep approach. This proof of concept is based on direct coupling of a headspace sampler with a programmed temperature vaporizer (PTV) and a gas chromatograph (GC), with mass spectrometry (MS) detection. Analytes are extracted from the same vial in a stepwise procedure, splitting the headspace generation time of conventional HS into four periods and using the PTV to cryogenically trap the analytes during the successive HS samplings. Solvent vent mode is mandatory in order to retain the analytes, purging the gas solvent at an adequate initial low temperature and flash-heating the PTV liner in a quick ramp (720 °C/min), once the HS samplings are finished. Linear aldehydes, from pentanal to decanal, possible biomarkers of several diseases have been selected as model compounds. This multiple HS method has been compared with conventional HS, and it has been validated in terms of linearity, limits of detection, repeatability, reproducibility and accuracy. The limits of detection (LOD) ranged from 0.004 to 0.159 µg/L. Enrichment factors (EF) in relation to the conventional HS method ranged from 3.0 to 6.7, except for pentanal (EF: 0.8), which is too volatile and polar to be trapped in the PTV with the multiple HS methodology. Similar enrichment factors were obtained in a urine sample.

Multi-capillary column high-pressure photoionization time-of-flight mass spectrometry and its application for online rapid analysis of flavor compounds

High-pressure photoionization time-of-flight mass spectrometry (HPPI-TOFMS) is a versatile and highly sensitive analytical technique for online and real-time analysis of trace volatile organic compounds in complex mixtures. However, discrimination of isomers is usually a great challenge for the soft ionization method, and matrix effect is also inevitable under high pressure in the HPPI source. In this work, we describe a first attempt to develop a two-dimensional (2D) hyphenated instrument by coupling of a multi-capillary column (MCC) with a HPPI-TOFMS to overcome these problems. The capability of the MCC-HPPI-TOFMS for discrimination of isomeric compounds and elimination of the matrix effect was demonstrated by analyzing flavor mixtures. With the merits of fast separation, soft ionization and high detection sensitivity, satisfactory effects in the 2D analysis were achieved, despite the relatively low chromatographic resolution of MCC. As a result, three isomers, eucalyptol, l-menthone and linalool, in a flavor mixture were successfully categorized within 90 s, and the matrix effect caused by solvent ethanol was significantly eliminated as well. The limits of detection (LODs) down to sub-ppbv level were achieved for the investigated five flavor compounds without any enrichment process, and an excellent repeatability was obtained with the relative standard deviations (RSDs) of signal intensities ≤5%. The MCC-HPPI-TOFMS system was preliminarily applied for rapid and online analysis of flavor compounds in the exhaled gas of a volunteer after mouth rinsing with a gargle product. The rapid changes of the three flavor compounds, as well as the steady endogenous metabolite acetone, in the exhaled gas were successfully determined with a time-resolution of only 1.5 min.

Bioanalytical and Mass Spectrometric Methods for Aldehyde Profiling in Biological Fluids

Human exposure to aldehydes is implicated in multiple diseases including diabetes, cardiovascular diseases, neurodegenerative disorders (i.e., Alzheimer’s and Parkinson’s Diseases), and cancer. Because these compounds are strong electrophiles, they can react with nucleophilic sites in DNA and proteins to form reversible and irreversible modifications. These modifications, if not eliminated or repaired, can lead to alteration in cellular homeostasis, cell death and ultimately contribute to disease pathogenesis. This review provides an overview of the current knowledge of the methods and applications of aldehyde exposure measurements, with a particular focus on bioanalytical and mass spectrometric techniques, including recent advances in mass spectrometry (MS)-based profiling methods for identifying potential biomarkers of aldehyde exposure. We discuss the various derivatization reagents used to capture small polar aldehydes and methods to quantify these compounds in biological matrices. In addition, we present emerging mass spectrometry-based methods, which use high-resolution accurate mass (HR/AM) analysis for characterizing carbonyl compounds and their potential applications in molecular epidemiology studies. With the availability of diverse bioanalytical methods presented here including simple and rapid techniques allowing remote monitoring of aldehydes, real-time imaging of aldehydic load in cells, advances in MS instrumentation, high performance chromatographic separation, and improved bioinformatics tools, the data acquired enable increased sensitivity for identifying specific aldehydes and new biomarkers of aldehyde exposure. Finally, the combination of these techniques with exciting new methods for single cell analysis provides the potential for detection and profiling of aldehydes at a cellular level, opening up the opportunity to minutely dissect their roles and biological consequences in cellular metabolism and diseases pathogenesis.

A targeted metabolomic protocol for quantitative analysis of volatile organic compounds in urine of children with celiac disease

Volatile organic compounds (VOCs) in biological samples have gained popularity for disease monitoring and diagnosis. Celiac disease (CD) is one of the many prevalent health conditions which are challenging to diagnose. The aim of this study was to optimize a solid phase microextraction followed by gas chromatography-mass spectrometry, for quantitative analysis of a wide range of VOCs in the urine of patients with CD. Multivariate design of experiment was used to optimize the extraction conditions for the analysis of 15 urinary VOCs. Based on the performed experiments, extraction using 2.98 g of sodium chloride and 21 μL of 6 M hydrochloric acid for 15 min at 30 °C, using a CAR/PDMS fiber in headspace mode was found to be the most effective procedure for the analysis of the selected biomarkers. It was also demonstrated that the proposed method could distinguish between children with CD and healthy children based on the profile of VOCs. It is believed that quantitative analysis of these biomarkers will extend our understanding of CD and could be used for monitoring in patients under treatment.

High-pressure photon ionization time-of-flight mass spectrometry combined with dynamic purge-injection for rapid analysis of volatile metabolites in urine

Small molecule metabolites are widely used as biomarkers in the research field of metabolomics for disease diagnosis and exposure assessment. As a readily available biofluid containing plenty of volatile organic metabolites (VOMs), urine is ideal for non-invasive metabolomic analysis; however, there is still lack of rapid analysis method for VOMs in urine. Here we report a kind of rapid method for urine analysis by employing high-pressure photon ionization time-of-flight mass spectrometry (HPPI-TOFMS) combined with dynamic purge-injection. Various types of metabolites, such as ketones, alcohols, acids, sulfides, pyrroles and amines were detected directly by simple acidification or alkalization of urines. It is noteworthy that nitrogen-containing compounds, especially polar amines, could be ultrasensitively measured without any derivatization. The analytical capability of the direct HPPI-MS technique was demonstrated by analyzing five valuable metabolites, i.e., toluene, 2,5-dimethylpyrrole, trimethlyamine, styrene, and p-xylene, which exhibited relatively low limits of detection, wide linear range and satisfactory repeatability. Being highly sensitive and humidity-friendly, the whole analytical procedure is easily operated in less than 6 min. Interestingly, a new biomarker 2,5-dimethylpyrrole was exclusively found in the smoker's urine sample besides toluene. The work presents a novel tool for rapid nontarget disease biomarkers screening or target monitoring of specific compounds through the investigation of volatile metabolites in urine.

Determination of ketones and ethyl acetate-a preliminary study for the discrimination of patients with lung cancer

In this work, ten possible volatile biomarkers of lung cancer (acetone, 2-butanone, ethyl acetate, 2-pentanone, 4-methyl-2-pentanone, 2-hexanone, 3-heptanone, 2-heptanone, 3-octanone, and 2-nonanone) have been analyzed to evaluate their different concentration levels in urine samples from lung cancer patients (n = 12) and healthy controls (n = 12). The volatile compounds were generated with a headspace autosampler and analyzed with a gas chromatograph equipped with a programmed temperature vaporizer and mass spectrometry detector (HS-PTV-GC-MS). With the aim of evaluating the aforementioned differences, a Mann-Whitney U test and box-plots were obtained. Very good discrimination between cancer and control groups was achieved for three (ethyl acetate, 3-heptanone, and 3-octanone) of the ten analytes studied. With a view to assigning samples to the group of healthy or ill individuals, the Wilcoxon signed-rank test has been used. In spite of the small number of urine samples assayed, the results may suggest that the studied compounds could be considered useful tools in order to discern samples and they could be employed as a complementary test in a diagnosis. Graphical abstract Classification of samples (lung cancer patients and controls) with the Wilcoxon signed rank test.

Spatial characteristics of urinary BTEX concentrations in the general population

Benzene, toluene, ethylbenzene, o-, m-, and p-xylenes (BTEX) are ubiquitous outdoor and indoor air pollutants associated with both environmental and health effects. The objective of this exploratory study was to determine the magnitude and variability of urinary BTEX levels among residents of two areas located in the same city (Nicosia, Cyprus). The two areas differed with respect to their proximity to an industrial cluster and an intercity-highway. First morning urine voids were collected during a random campaign from selected households in the two urban areas (n = 48). Urinary BTEX measurements were obtained using headspace solid phase micro extraction coupled with gas chromatography-mass spectrometry. The majority of participants were females (65%) and non-smokers (85%) with a mean age of 49 years. Median urinary BTEX levels were: 118 ng L^-1, 124 ng L^-1, 9 ng L^-1, 29 ng L^-1 and 28 ng L^-1 for benzene, toluene, ethylbenzene, (p + m)-xylene and o-xylene, respectively. With the exception of benzene, participants from area 2 (closer to the industrial cluster and an intercity road than area 1) had significantly (p < 0.05) higher urinary BTEX levels than those from area 1 (regression analysis). The residence location (in area 2) was the sole significant (p < 0.05) predictor of urinary BTEX levels after adjusting for sex, smoking, age, body mass index, and educational level. This observational study showed differences in BTEX exposures between two urban areas of the same city. This baseline BTEX dataset may prove useful for future activities of natural gas extraction and handling nearby urban settings.

Solid-phase microextraction set-up for the analysis of liver volatolome to detect livestock exposure to micropollutants

Starting from a critical analysis of a first "proof of concept" study on the utility of the liver volatolome for detecting livestock exposure to environmental micropollutants (Berge et al., 2011), the primary aim of this paper is to improve extraction conditions so as to obtain more representative extracts by using an extraction temperature closer to livestock physiological conditions while minimizing analytical variability and maximizing Volatile Organic Compound (VOC) abundancies. Levers related to extraction conditions and sample preparation were assessed in the light of both abundance and coefficient of variation of 22 candidate VOC markers identified in earlier volatolomic studies. Starting with a CAR/PDMS fiber and a 30min extraction, the reduction of SPME temperature to 40°C resulted in a significant decrease in the area of 14 candidate VOC markers (p<0.05), mainly carbonyls and alcohols but also a reduction in the coefficient of variation for 17 of them. In order to restore VOC abundances and to minimize variability, two approaches dealing with sample preparation were investigated. By increasing sample defrosting time at 4°C from 0 to 24h yielded higher abundances and lower variabilities for 15 and 13 compounds, respectively. Lastly, by using additives favouring the release of VOCs (1.2g of NaCl) the sensitivity of the analysis was improved with a significant increase in VOC abundances of more than 50% for 13 out of the 22 candidate markers. The modified SPME parameters significantly enhanced the abundances while decreasing the analytical variability for most candidate VOC markers. The second step was to validate the ability of the revised SPME protocol to discriminate intentionally contaminated broiler chickens from controls, under case/control animal testing conditions. After verification of the contamination levels of the animals by national reference laboratories, data analysis by a multivariate chemometric method (Common Components and Specific Weights Analysis - ComDim) showed that the liver volatolome could reveal dietary exposure of broilers to a group of environmental pollutants (PCBs), a veterinary treatment (monensin), and a pesticide (deltamethrin), thus confirming the usefulness of this analytical set-up.

Headspace-programmed temperature vaporizer-mass spectrometry and pattern recognition techniques for the analysis of volatiles in saliva samples

A rapid method for the analysis of volatiles in saliva samples is proposed. The method is based on direct coupling of three components: a headspace sampler (HS), a programmable temperature vaporizer (PTV) and a quadrupole mass spectrometer (qMS). Several applications in the biomedical field have been proposed with electronic noses based on different sensors. However, few contributions have been developed using a mass spectrometry-based electronic nose in this field up to date. Samples of 23 patients with some type of cancer and 32 healthy volunteers were analyzed with HS-PTV-MS and the profile signals obtained were subjected to pattern recognition techniques with the aim of studying the possibilities of the methodology to differentiate patients with cancer from healthy controls. An initial inspection of the contained information in the data by means of principal components analysis (PCA) revealed a complex situation were an overlapped distribution of samples in the score plot was visualized instead of two groups of separated samples. Models using K-nearest neighbors (KNN) and Soft Independent Modeling of Class Analogy (SIMCA) showed poor discrimination, specially using SIMCA where a small distance between classes was obtained and no satisfactory results in the classification of the external validation samples were achieved. Good results were obtained when Mahalanobis discriminant analysis (DA) and support vector machines (SVM) were used obtaining 2 (false positives) and 0 samples misclassified in the external validation set, respectively. No false negatives were found using these techniques.

Headspace-programmed temperature vaporization-mass spectrometry for the rapid determination of possible volatile biomarkers of lung cancer in urine

We propose a new method for the rapid determination of five volatile compounds described in the literature as possible biomarkers of lung cancer in urine samples. The method is based on the coupling of a headspace sampler, a programmed temperature vaporizer in solvent-vent injection mode, and a mass spectrometer (HS-PTV-MS). This configuration is known as an electronic nose based on mass spectrometry. Once the method was developed, it was used for the analysis of urine samples from lung cancer patients and healthy individuals. Multivariate calibration models were employed to quantify the biomarker concentrations in the samples. The detection limits ranged between 0.16 and 21 μg/L. For the assignment of the samples to the patient group or the healthy individuals, the Wilcoxon signed-rank test was used, comparing the concentrations obtained with the median of a reference set of healthy individuals. To date, this is the first time that multivariate calibration and non-parametric methods have been combined to classify biological samples from profile signals obtained with an electronic nose. When significant differences in the concentration of one or more biomarkers were found with respect to the reference set, the sample is considered as a positive one and a new analysis was performed using a chromatographic method (HS-PTV-GC/MS) to confirm the result. The main advantage of the proposed HS-PTV-MS methodology is that no prior chromatographic separation and no sample manipulation are required, which allows an increase of the number of samples analyzed per hour and restricts the use of time-consuming techniques to only when necessary. Graphical abstract Schematic diagram of the developed methodology.

Quantification of selected volatile organic compounds in human urine by gas chromatography selective reagent ionization time of flight mass spectrometry (GC-SRI-TOF-MS) coupled with head-space solid-phase microextraction (HS-SPME)

Selective reagent ionization time of flight mass spectrometry with NO⁺as the reagent ion in conjunction with gas chromatography and head-space solid-phase microextraction was used to determine 16 volatiles in human urine.