Profiling of aldehyde-containing compounds by stable isotope labelling-assisted mass spectrometry analysis

ω-(5-Phenyl-2H-tetrazol-2-yl)alkyl-substituted glycine amides and related compounds as inhibitors of the amine oxidase vascular adhesion protein-1 (VAP-1)

Vascular adhesion protein-1 (VAP-1), also known as plasma amine oxidase or semicarbazide-sensitive amine oxidase, is an enzyme that degrades primary amines to aldehydes with the formation of hydrogen peroxide and ammonia. Among others, it plays a role in inflammatory processes as it can mediate the migration of leukocytes from the blood to the inflamed tissue. We prepared a series of ω-(5-phenyl-2H-tetrazol-2-yl)alkyl-substituted glycine amides and related compounds and tested them for inhibition of purified bovine plasma VAP-1. Compounds with submicromolar activity were obtained. Studies on the mechanism of action revealed that the glycine amides are substrate inhibitors, i.e., they are also converted to an aldehyde derivative. However, the reaction proceeds much more slowly than that of the substrate used in the assay, whose conversion is thus blocked. Examination of the selectivity of the synthesized glycine amides with respect to other amine oxidases showed that they inhibited diamine oxidase, which is structurally related to VAP-1, but only to a much lesser extent. In contrast, the activity of monoamine oxidase A and B was not affected. Selected compounds also inhibited VAP-1 in human plasma. The IC50 values measured were higher than those determined with the bovine enzyme. However, the structure-activity relationships obtained with the glycine amides were similar for both enzymes.

Determination of hydrogen gas by 1,4-bis(phenylethynyl)benzene hydrogenation coupled with gas chromatography-mass spectrometry

Knowing the H2 concentration released from polymer materials is essential to understand the degradation degree of polymer materials. In this study, a novel strategy of 1,4-bis(phenylethynyl)benzene (DEB) hydrogenation in combination with gas chromatography - mass spectrometry (GC-MS) determination of hydrogen gas (H2) was developed. In this strategy, DEB was utilized to react with H2 for establishing the quantitative analysis method of H2. A H2 analysis platform that could accurately control H2 concentration was designed and fabricated to be used to establish the quantitative method of H2. The linear regression curve was established between the H2 standard and the MS signal of the reaction products on GC-MS. Finally, the H2 released from polyethylene under gamma radiation was detected by this method. This method could be a powerful auxiliary tool for studying the content changes of H2.

Isotope-coded derivatization with designed Girard-type reagent as charged isobaric mass tags for non-targeted profiling and discovery of natural aldehydes by liquid chromatography-tandem mass spectrometry

Aldehyde-containing metabolites are reactive electrophiles that have attracted extensive attention due to their widespread occurrence in organisms and natural foods. Herein we described a newly-designed Girard's reagent, 1-(4-hydrazinyl-4-oxobutyl)pyridin-1-ium bromide (HBP), as charged tandem mass (MS/MS) tags to facilitate selective capture, sensitive detection and semi-targeted discovery of aldehyde metabolites via hydrazone formation. After HBP labeling, the detection signals of the test aldehydes were increased by 21-2856 times, with the limits of detection were 2.5-7 nM. Upon isotope-coded derivatization with a pair of labeling reagents, HBP-d₀ and its deuterium-labeled counterpart HBP-d₅, the aldehyde analytes were converted to hydrazone derivatives, which generated characteristic neutral fragments of 79 Da and 84 Da, respectively. The isobaric HBP-d₀/HBP-d₅ labeling based LC-MS/MS method was validated by relative quantification of human urinary aldehydes (slope=0.999, R² > 0.99, RSDs ≤ 8.5%) and discrimination analysis between diabetic and control samples. The unique isotopic doubles (Δm/z = 5 Da) by dual neutral loss scanning (dNLS) provided a generic reactivity-based screening strategy that allowed non-targeted profiling and identification of endogenous aldehydes even amidst noisy data. The LC-dNLS-MS/MS screening of cinnamon extracts led to finding 61 possible natural aldehydes and guided discovery of 10 previously undetected congeners in this medicinal plant.

Metabolism of sumatriptan revisited

Scientific literature describes that sumatriptan is metabolized by oxidative deamination of its dimethylaminoethyl residue by monoamine oxidase A (MAO A) and not by cytochrome P450 (CYP)-mediated demethylation, as is usual for such structural elements. Using recombinant human enzymes and HPLC-MS analysis, we found that CYP enzymes may also be involved in the metabolism of sumatriptan. The CYP1A2, CYP2C19, and CYP2D6 isoforms converted this drug into N-desmethyl sumatriptan, which was further demethylated to N,N-didesmethyl sumatriptan by CYP1A2 and CYP2D6. Otherwise, sumatriptan and its two desmethyl metabolites were metabolized by recombinant MAO A but not by MAO B to the corresponding acetaldehyde, with sumatriptan being only a poor substrate for MAO A compared to the N-demethylated and the N,N-didemethylated derivatives.

Profiling of Urine Carbonyl Metabolic Fingerprints in Bladder Cancer Based on Ambient Ionization Mass Spectrometry

The diagnosis of bladder cancer (BC) is currently based on cystoscopy, which is invasive and expensive. Here, we describe a noninvasive profiling method for carbonyl metabolic fingerprints in BC, which is based on a desorption, separation, and ionization mass spectrometry (DSI-MS) platform with N,N-dimethylethylenediamine (DMED) as a differential labeling reagent. The DSI-MS platform avoids the interferences from intra- and/or intersamples. Additionally, the DMED derivatization increases detection sensitivity and distinguishes carboxyl, aldehyde, and ketone groups in untreated urine samples. Carbonyl metabolic fingerprints of urine from 41 BC patients and 41 controls were portrayed and 9 potential biomarkers were identified. The mechanisms of the regulations of these biomarkers have been tentatively discussed. A logistic regression (LR) machine learning algorithm was applied to discriminate BC from controls, and an accuracy of 85% was achieved. We believe that the method proposed here may pave the way toward the point-of-care diagnosis of BC in a patient-friendly manner.

MS-IDF: A Software Tool for Nontargeted Identification of Endogenous Metabolites after Chemical Isotope Labeling Based on a Narrow Mass Defect Filter

Chemical isotope labeling liquid chromatography mass spectrometry (LC-MS) is an emerging metabolomic strategy for the quantification and characterization of small molecular compounds in biological samples. However, its subsequent data analysis is not straightforward due to a large amount of data produced and interference of biological matrices. In order to improve the efficiency of searching and identification of target endogenous metabolites, a new software tool for nontargeted metabolomics data processing called MS-IDF was developed based on the principle of a narrow mass defect filter. The developed tool provided two function modules, including IsoFinder and MDFinder. The IsoFinder function module applied a conventional peak extraction method by using a fixed mass differences between the heavy and light labels and by the alignment of chromatographic retention time (RT). On the other hand, MDFinder was designed to incorporate the accurate mass defect differences between or among stable isotopes in the peak extraction process. By setting an appropriate filter interval, the target metabolites can be efficiently screened out while eliminating interference. Notably, the present results showed that the efficiency in compound identification using the new MDFinder module was nearly doubled as compared to the conventional IsoFinder method (an increase from 259 to 423 compounds). The Matlab codes of the developed MS-IDF software are available from github at https://github.com/jydong2018/MS_IDF. Based on the MS-IDF software tool, a novel and effective approach from nontargeted to targeted metabolomics research was developed and applied to the exploration of potential primary amine biomarkers in patients with schizophrenia. With this approach, potential biomarkers, including N,N-dimethylglycine, S-adenosine-l-methionine, dl-homocysteine, and spermidine, were discovered.

Detection of aliphatic aldehydes by a pillar[5]arene-based fluorescent supramolecular polymer with vaporchromic behavior

The detection of volatile aliphatic aldehydes is of significance because of their chemical toxicity, physical volatility and widespread applications in chemical industrial processes. In this work, the direct detection of aliphatic aldehydes is tackled using a fluorescent supramolecular polymer with vaporchromic behavior which is contructed by pillar[5]arene-based host-guest intereactions. Thin films with strong orange-yellow fluorescence are prepared by coating the linear supramolecular polymer on glass sheets. When the thin films are exposed to aliphatic aldehydes with different carbon chain lengths, they can selectivly sensing  n -butyraldehyde ( C 4 ) and caprylicaldehyde ( C 8 ), accompanied by fluorescence quenching, indicating that the supramolecular polymer is a highly selective vapochromic response material for aliphatic aldehydes with long alkyl chains.

Neutron encoded derivatization of endothelial cell lysates for quantitation of aldehyde metabolites using nESI-LC-HRMS

Biological aldehydes are difficult to analyze by electrospray ionization mass spectrometry due to their poor proton affinity and low biological concentrations. Chemical derivatization with stable isotope tags is used here for sample multiplexing, increased throughput, improved signal intensity, and quantitation. Nine quaternary amine tags with mass differences as low as 0.0058 Da had no observable chromatographic shifts, small amounts of ion suppression, and minimal matrix effects. Low concentration perfluoropentanoic acid was used as an ion pairing reagent to improve the retention of derivatized aldehydes. Perfluoropentanoic acid addition showed an average of three-fold improvement in limits of detection, 50% reduction in peak width, and 2.5 fold increase in analyte retention. Analysis of fifteen tagged aldehydes yielded an average of 13 nM limit of detection, 9 %RSD, R² of 0.995, and linear dynamic range of 40-1000 nM. In a single 20 min separation, absolute quantitative data was obtained for 11 reactive aldehydes across 8 aortic endothelial cell samples. High glucose treatment produced significant changes to malondialdehyde, decanal, and (2E)-hexadecenal. These changes are consistent with glucose-induced oxidative stress. This method demonstrates that neutron encoded tagging of aldehydes is suitable for the analysis of complex samples.

Progress and Challenges in Quantifying Carbonyl-Metabolomic Phenomes with LC-MS/MS

Carbonyl-containing metabolites widely exist in biological samples and have important physiological functions. Thus, accurate and sensitive quantitative analysis of carbonyl-containing metabolites is crucial to provide insight into metabolic pathways as well as disease mechanisms. Although reversed phase liquid chromatography electrospray ionization mass spectrometry (RPLC-ESI-MS) is widely used due to the powerful separation capability of RPLC and high specificity and sensitivity of MS, but it is often challenging to directly analyze carbonyl-containing metabolites using RPLC-ESI-MS due to the poor ionization efficiency of neutral carbonyl groups in ESI. Modification of carbonyl-containing metabolites by a chemical derivatization strategy can overcome the obstacle of sensitivity; however, it is insufficient to achieve accurate quantification due to instrument drift and matrix effects. The emergence of stable isotope-coded derivatization (ICD) provides a good solution to the problems encountered above. Thus, LC-MS methods that utilize ICD have been applied in metabolomics including quantitative targeted analysis and untargeted profiling analysis. In addition, ICD makes multiplex or multichannel submetabolome analysis possible, which not only reduces instrument running time but also avoids the variation of MS response. In this review, representative derivatization reagents and typical applications in absolute quantification and submetabolome profiling are discussed to highlight the superiority of the ICD strategy for detection of carbonyl-containing metabolites.

Towards Aldehydomics: Untargeted Trapping and Analysis of Reactive Diet-Related Carbonyl Compounds Formed in the Intestinal Lumen

Lipid peroxidation and subsequent formation of toxic aldehydes, such as 4-hydroxynonenal, is known to be involved in numerous pathophysiological processes, possibly including the development of colorectal cancer. This work aimed at the development of an untargeted approach using high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-HRMS) for tracking aldehydes in both suspect screening and untargeted methods in fecal water, representing the aqueous environment of colon epithelial cells. This original approach is based on the introduction of a characteristic isotopic labeling by selective derivatization of the carbonyl function using a brominated reagent. Following a metabolomics workflow, the developed methodology was applied to the characterization of aldehyde compounds formed by lipid peroxidation in rats fed two different diets differentially prone to lipoperoxidation. Derivatized aldehydes were first selectively detected on the basis of their isotopic pattern, then annotated and finally identified by tandem mass spectrometry. This original approach allowed us to evidence the occurrence of expected aldehydes according to their fatty acid precursors in the diet, and to characterize other aldehydes differentiating the different diets.

[Recent advances in chemical derivatization-based chromatography-mass spectrometry methods for analysis of aldehyde biomarkers]

Human exposure to chemical pollutants in the environment can cause a variety of diseases, including cancer, diabetes, cardiovascular disease, and neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, etc.). Exogenous and environmental pollutant exposure-induced endogenous aldehydes are highly reactive electrophilic compounds that can form covalently modified products with a variety of important biological molecules in the human body, thus inducing toxic effects. Exposome research has become a hotspot since it was first proposed in 2005. Exposure studies can map the complex relationships between biomarkers and disease risk. Therefore, the measurable and characteristic changes of all biomarkers together constitute a key basis for exposome research. Aldehydes are among the main components of chemical exposure. Because of the physical and chemical properties of aldehydes and the existence of multiple matrix interferences in the samples, it is particularly difficult to analyze and characterize them. The analysis and detection methods for aldehydes mainly include sensing analysis, electrochemical methods, fluorescence imaging, chromatography, mass spectrometry (MS), and chromatography-MS. Analytical techniques based on gas chromatography-MS (GC-MS) and liquid chromatography-MS (LC-MS) have emerged as the main methods for chemical exposome research. Chemical derivatization, especially stable isotope labeling derivatization (also known as chemical isotope labeling) combined with LC-MS analytical techniques, can help circumvent the problems encountered in targeted and non-targeted metabolome and exposome analysis. The combination of chemical derivatization with chromatography-MS is one of the most important solutions for the accurate analysis of aldehydes in complex samples. Over the past five years, the development and application of chromatography-MS analytical methods based on chemical derivatization have become key topics in aldehyde analysis. This paper summarizes and reviews the latest progress in GC-MS and LC-MS methods based on chemical derivatization (2015-2020). The review focuses on analytical method development for aldehyde exposure biomarkers in bio-matrices (blood, urine, saliva, biological tissue, etc.). Various derivatization reagents for labeling small-molecule aldehydes, qualitative/quantitative analytical methods and their application value, advantages/disadvantages of different analytical methods for aldehyde exposure biomarkers, and future development trends are also included. The manuscript contents may aid the integrated development of exposome, metabolomics, and lipidomics, as well as research on the environment, ecology, and health. To clarify the complex actions of exogenous and endogenous aldehydes in physiological and pathological events, it is necessary to improve the analysis and characterization techniques and tools for studying the "aldehydome." With the development and application of sophisticated mass spectrometers, advances in high-performance chromatographic separation and bioinformatics, and advent of single-cell analysis and MS imaging, future aldehyde exposome analytical methods will have higher sensitivity and throughput. This in turn would be more useful for screening and identifying unknown aldehyde compounds and discovering new exposome biomarkers.

Options of the Main Derivatization Approaches for Analytical ESI and MALDI Mass Spectrometry

The inclusion of preliminary chemical labeling (derivatization) in the analysis process by such powerful and widespread methods as electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is a popular and widely used methodological approach. This is due to the need to remove some fundamental limitations inherent in these powerful analytic methods. Although a number of special reviews has been published discussing the utilization of derivatization approaches, the purpose of the present critical review is to comprehensively summarize, characterize and evaluate most of the previously developed and practically applied, as well as recently proposed representative derivatization reagents for ESI-MS and MALDI-MS platforms in their mostly sensitive positive ion mode and frequently hyphenated with separation techniques. The review is focused on the use of preliminary chemical labeling to facilitate the detection, identification, structure elucidation, quantification, profiling or MS imaging of compounds within complex matrices. Two main derivatization approaches, namely the introduction of permanent charge-fixed or highly proton affinitive residues into analytes are critically evaluated. In situ charge-generation, charge-switch and charge-transfer derivatizations are considered separately. The potential of using reactive matrices in MALDI-MS and chemical labeling in MS-based omics sciences is given.

Chemical Isotope Labeling LC-MS for Metabolomics

Due to the great diversity of chemical and physical properties of metabolites as well as a wide range of concentrations of metabolites present in metabolomic samples, performing comprehensive and quantitative metabolome analysis is a major analytical challenge. Conventional approach of combining various techniques and methods with each detecting a fraction of the metabolome can lead to the increase in overall metabolomic coverage. However, this approach requires extensive investment in equipment and analytical expertise with still relatively low coverage and low sample throughput. Chemical isotope labeling (CIL) liquid chromatography mass spectrometry (LC-MS) offers an alternative means of increasing metabolomic coverage while maintaining high quantification precision and accuracy. This chapter describes the CIL LC-MS method and its key features for metabolomic analysis.

Sensitive mass spectrometric analysis of carbonyl metabolites in human urine and fecal samples using chemoselective modification

Metabolites with ketone or aldehyde functionalities comprise a large proportion of the human metabolome, most notably in the form of sugars. However, these reactive molecules are also generated through oxidative stress or gut microbiota metabolism and have been linked to disease development. The discovery and structural validation of this class of metabolites over the large concentration range found in human samples is crucial to identify their links to pathogenesis. Herein, we have utilized an advanced chemoselective probe methodology alongside bioinformatic analysis to identify carbonyl-metabolites in urine and fecal samples. In total, 99 metabolites were identified in urine samples and the chemical structure for 40 metabolites were unambiguously validated using a co-injection procedure. We also describe the preparation of a metabolite-conjugate library of 94 compounds utilized to efficiently validate these ketones and aldehydes. This method was used to validate 33 metabolites in a pooled fecal sample extract to demonstrate the potential for rapid and efficient metabolite detection over a wide metabolite concentration range. This analysis revealed the presence of six metabolites that have not previously been detected in either sample type. The constructed library can be utilized for straightforward, large-scale, and expeditious analysis of carbonyls in any sample type.

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.

Lipoxidation in cardiovascular diseases

Lipids can go through lipid peroxidation, an endogenous chain reaction that consists in the oxidative degradation of lipids leading to the generation of a wide variety of highly reactive carbonyl species (RCS), such as short-chain carbonyl derivatives and oxidized truncated phospholipids. RCS exert a wide range of biological effects due to their ability to interact and covalently bind to nucleophilic groups on other macromolecules, such as nucleic acids, phospholipids, and proteins, forming reversible and/or irreversible modifications and generating the so-called advanced lipoxidation end-products (ALEs). Lipoxidation plays a relevant role in the onset of cardiovascular diseases (CVD), mainly in the atherosclerosis-based diseases in which oxidized lipids and their adducts have been extensively characterized and associated with several processes responsible for the onset and development of atherosclerosis, such as endothelial dysfunction and inflammation. Herein we will review the current knowledge on the sources of lipids that undergo oxidation in the context of cardiovascular diseases, both from the bloodstream and tissues, and the methods for detection, characterization, and quantitation of their oxidative products and protein adducts. Moreover, lipoxidation and ALEs have been associated with many oxidative-based diseases, including CVD, not only as potential biomarkers but also as therapeutic targets. Indeed, several therapeutic strategies, acting at different levels of the ALEs cascade, have been proposed, essentially blocking ALEs formation, but also their catabolism or the resulting biological responses they induce. However, a deeper understanding of the mechanisms of formation and targets of ALEs could expand the available therapeutic strategies.

Profiling of potential brassinosteroids in different tissues of rape flower by stable isotope labeling - liquid chromatography/mass spectrometry analysis

Brassinosteroids (BRs) play crucial roles in a variety of physiological processes in plants. The full elucidation of the functions of RBs relies on sensitive detection and accurate measurement of BRs in plants. However, the identification and quantification of BRs are challenging due to their low abundance as well as poor ionization efficiencies during mass spectrometry-based analysis. Herein, we developed a highly sensitive and selective strategy for profiling potential BRs in plants by stable isotope labeling liquid chromatography multiple reaction monitoring scan mass spectrometry (SIL-LC-MRM-MS) analysis. In the strategy, we used a pair of stable isotope labeling reagents 4-phenylaminomethyl-benzeneboronic acid (4-PAMBA) and d₅-4-phenylaminomethyl-benzeneboronic acid (4-PAMBA-d₅) that can react with C22-C23 cis-diol on BRs for profiling potential BRs in plant tissues. The 4-PAMBA and 4-PAMBA-d₅ labeled BRs could generate two characteristic neutral loss under collision induced dissociation (CID), respectively, which is used to establish the MRM-based detection and screening. The precursor ions of BRs labeled with 4-PAMBA and 4-PAMBA-d₅ were set according to the reported structures of BRs, and the corresponding product ions were predicted by subtracting the lost neutral loss. In this respect, corresponding precursor ions and product ions in MRM transitions are formed. The peak pairs with a fixed mass difference, similar retention times and intensities were assigned as potential BRs. Using the developed SIL-LC-MRM-MS strategy, we successfully found 13 potential BR in different tissues of rape flower. Taken together, the SIL-LC-MRM-MS analytical strategy is promising for profiling potential BRs as well as other compounds that have the same functional moiety from complex biological samples.

Determination of formylated DNA and RNA by chemical labeling combined with mass spectrometry analysis

Nucleic acids carry diverse chemical modifications that exert critical influences in a variety of cellular processes in living organisms. In addition to methylation, the emerging DNA and RNA formylation has been reported to play functional roles in various physiological processes. However, the amounts of formylated DNA and RNA are extremely low and detection of DNA and RNA formylation is therefore a challenging task. To address this issue, we developed a strategy by chemical labeling combined with in-tube solid-phase microextraction - ultra high performance liquid chromatography - electrospray ionization - tandem mass spectrometry (in-tube SPME-UPLC-ESI-MS/MS) analysis for the sensitive determination of DNA and RNA formylation. Using the developed method, we were able to simultaneously measure six formylated nucleosides, including 5-formyl-2'-deoxycytidine (5-fodC), 5-formylcytidine (5-forC), 5-formyl-2'-deoxyuridine (5-fodU), 5-formyluridine (5-forU), 2'-O-methyl-5-formylcytidine (5-forCm) and 2'-O-methyl-5- formyluridine (5-forUm), from DNA and RNA of cultured human cells and multiple mammalian tissues. The detection limits of these formylated nucleosides improved by 307-884 folds using Girard's P (GirP) labeling coupled with in-tube SPME-UPLC-ESI-MS/MS analysis. It was worth noting that 5-forU, 5-forCm and 5-forUm which have not been detected in human sample before, were discovered in cultured human cells and tissues in the current study. In addition, we observed significant increase of 5-forC and 5-forU in RNA (p = 0.027 for 5-forC; p = 0.028 for 5-forU) and 5-fodU in DNA (p = 0.002) in human thyroid carcinoma tissues compared to normal tissues adjacent to the tumor using synthesized stable isotope GirP (d₅-GirP)-assisted quantification. Our results indicated that aberrant DNA and RNA formylation may contribute to the tumor formation and development. In addition, monitoring of DNA and RNA formylation may also serve as indicator for cancer diagnostics. Taken together, the developed chemical labeling combined with in-tube SPME-UPLC-ESI-MS/MS analysis can facilitate the in-depth functional study of DNA and RNA formylation.

A High Resolution/Accurate Mass (HRAM) Data-Dependent MS3 Neutral Loss Screening, Classification, and Relative Quantitation Methodology for Carbonyl Compounds in Saliva

Reactive carbonyl compounds (RCCs) are ubiquitous in the environment and are generated endogenously as a result of various physiological and pathological processes. These compounds can react with biological molecules inducing deleterious processes believed to be at the basis of their toxic effects. Several of these compounds are implicated in neurotoxic processes, aging disorders, and cancer. Therefore, a method characterizing exposures to these chemicals will provide insights into how they may influence overall health and contribute to disease pathogenesis. Here, we have developed a high resolution accurate mass (HRAM) screening strategy allowing simultaneous identification and relative quantitation of DNPH-derivatized carbonyls in human biological fluids. The screening strategy involves the diagnostic neutral loss of hydroxyl radical triggering MS3 fragmentation, which is only observed in positive ionization mode of DNPH-derivatized carbonyls. Unique fragmentation pathways were used to develop a classification scheme for characterizing known and unanticipated/unknown carbonyl compounds present in saliva. Furthermore, a relative quantitation strategy was implemented to assess variations in the levels of carbonyl compounds before and after exposure using deuterated d 3 -DNPH. This relative quantitation method was tested on human samples before and after exposure to specific amounts of alcohol. The nano-electrospray ionization (nano-ESI) in positive mode afforded excellent sensitivity with detection limits on-column in the high-attomole levels. To the best of our knowledge, this is the first report of a method using HRAM neutral loss screening of carbonyl compounds. In addition, the method allows simultaneous characterization and relative quantitation of DNPH-derivatized compounds using nano-ESI in positive mode. Graphical Abstract ᅟ.

Analysis of liposoluble carboxylic acids metabolome in human serum by stable isotope labeling coupled with liquid chromatography-mass spectrometry

Fatty acids (FAs) are groups of liposoluble carboxylic acids (LCAs) and play important roles in various physiological processes. Abnormal contents or changes of FAs are associated with a series of diseases. Here we developed a strategy with stable isotope labeling combined with liquid chromatography-tandem mass spectrometry (IL-LC-MS) analysis for comprehensive profiling and relative quantitation of LCAs in human serum. In this strategy, a pair of isotope labeling reagents (2-dimethylaminoethylamine (DMED)) and d4-2-dimethylaminoethylamine (d4-DMED) were employed to selectively label carboxyl groups of LCAs. The DMED and d4-DMED labeled products can lose four characteristic neutral fragments of 45 and 49Da or 63 and 67Da in collision-induced dissociation. Therefore, quadruple neutral loss scan (QNLS) mode was established and used for non-targeted profiling of LCAs. The peak pairs of DMED and d4-DMED labeling with the same retention time, intensity and characteristic mass differences were extracted from the two NLS spectra respectively, and assigned as potential LCA candidates. Using this strategy, 241 LCA candidates were discovered in the human serum; 156 carboxylic acid compounds could be determined by searching HMDB and METLIN databases (FAs are over 90%) and 21 of these LCAs were successfully identified by standards. Subsequently, a modified pseudo-targeted method with multiple reaction monitoring (MRM) detection mode was developed and used for relative quantification of LCAs in human serum from type 2 diabetes mellitus (T2DM) patients and healthy controls. As a result, 81 LCAs were found to have significant difference between T2DM patients and healthy controls. Taken together, the isotope labeling combined with tandem mass spectrometry analysis demonstrated to be a powerful strategy for identification and quantification of LCA compounds in serum samples.

Urinary profiling of cis-diol-containing metabolites in rats with bisphenol A exposure by liquid chromatography-mass spectrometry and isotope labeling

A rapid UPLC-MS method combined with isotope labeling technology was developed for the detection ofcis-diolmetabolites in rat urine after bisphenol A exposure.