Measurement of S-methylcysteine and S-methyl-mercapturic acid in human urine by alkyl-chloroformate extractive derivatization and isotope-dilution gas chromatography-mass spectrometry

A biomarkers study of human skin fibroblasts exposition to glyphosate-based herbicide using an untargeted and targeted metabolomics approach

Metabolomics is a valuable tool to assess glyphosate exposure and its potential impact on human health. However, few studies have used metabolomics to evaluate human exposure to glyphosate or glyphosate-based herbicides (GBHs). In this study, an untargeted and targeted metabolomics approach was applied to human skin fibroblasts exposed to the GBH Roundup (GLYP-R). Cytotoxicity, cell death, and oxidative stress assays were performed to evaluate potential damage caused by GLYP-R in fibroblasts. The herbicide showed a cytotoxic effect at concentrations above 100.0 mg L-1, with IC50 = 164.2 ± 8.7 mg L-1, inducing significant reactive oxygen species (ROS) production and necrosis. A GC×GC/Q-TOFMS method using derivatization with propyl chloroformate/propanol was developed for untargeted analysis, allowing the identification of 400 metabolites of different classes in the samples. The most significant compounds in the discrimination and classification of the samples were fatty acids and amino acids (AA). Based on the relevance of AA in untargeted analysis, a targeted analysis of 21 AA was performed using the same validated GC×GC method. Metabolomic analyses allowed the construction of two biomarker models with performance evaluated by receiver operating characteristic (ROC) curves: an untargeted model formed by four metabolites (methylcysteine, N-acetyl-l-methionine, methyl stearate, and linoleic acid) and a targeted model formed by three AA (l-glutamic acid, l-cysteine, and γ-aminobutyric acid). This study is the first to report the use of metabolomics to evaluate human skin cells exposed to GLYP-R, contributing to the toxicological research on glyphosate.

Center-of-Mass iso-Energetic Collision-Induced Decomposition in Tandem Triple Quadrupole Mass Spectrometry

Two scan modes of the triple quadrupole tandem mass spectrometer, namely Collision Induced Dissociation Precursor Ion scan and Neutral Loss scan, allow selectively pinpointing, in a complex mixture, compounds that feature specific chemical groups, which yield characteristic fragment ions or are lost as distinctive neutral fragments. This feature of the triple quadrupole tandem mass spectrometer allows the non-target screening of mixtures for classes of components. The effective (center-of-mass) energy to achieve specific fragmentation depends on the inter-quadrupole voltage (laboratory-frame collision energy) and on the masses of the precursor molecular ion and of the collision gas, through a non-linear relationship. Thus, in a class of homologous compounds, precursor ions activated at the same laboratory-frame collision energy face different center-of-mass collision energy, and therefore the same fragmentation channel operates with different degrees of efficiency. This article reports a linear equation to calculate the laboratory-frame collision energy necessary to operate Collision-Induced Dissociation at the same center-of-mass energy on closely related compounds with different molecular mass. A routine triple quadrupole tandem mass spectrometer can operate this novel feature (iso-energetic collision-induced dissociation scan; i-CID) to analyze mixtures of endogenous metabolites by Precursor Ion and Neutral Loss scans. The latter experiment also entails the hitherto unprecedented synchronized scanning of all three quadrupoles of the triple quadrupole tandem mass spectrometer. To exemplify the application of this technique, this article shows two proof-of-principle approaches to the determination of biological mixtures, one by Precursor Ion analysis on alpha amino acid derivatized with a popular chromophore, and the other on modified nucleosides with a Neutral Fragment Loss scan.

An LC-MS/MS Method to Measure S-Methyl-l-Cysteine and S-Methyl-l-Cysteine Sulfoxide in Human Specimens Using Isotope Labelled Internal Standards

This is the first report describing an analytical method for quantitative analysis of two naturally occurring sulphur compounds, S-methyl-l-cysteine (SMC) and S-methyl-l-cysteine sulfoxide (SMCSO), in human body fluids using isotope-labelled internal standards and liquid chromatography-mass spectrometry (LC-MS)/MS techniques. This method was validated according to the guideline of the Royal Society of Chemistry Analytical Methods Committee. It offers significant advantages including simple and fast preparation of human biological samples. The limits of detection of SMC were 0.08 µM for urine and 0.04 µM for plasma. The limits of detection of SMCSO were 0.03 µM for urine and 0.02 µM for plasma. The calibration curves of all matrices showed linearity with correlation coefficients r² > 0.9987. The intra and inter day precisions in three levels of known concentrations were >10% and >20%, respectively. The quantification accuracy was 98.28 ± 5.66%. The proposed method would be beneficial for the rapid and accurate determination of the SMC and SMCSO in human plasma and urine samples using by isotope labelled internal standards.

Identification and monitoring of metabolite markers of dry bean consumption in parallel human and mouse studies

SCOPE

Aim of the study was to identify and monitor metabolite markers of dry bean consumption in parallel human and mouse studies that each had shown chemopreventive effects of dry bean consumption on colorectal neoplasia risk.

METHODS AND RESULTS

Using LC/mass spectroscopy ± ESI and GC/mass spectroscopy, serum metabolites of dry beans were measured in 46 men before and after a 4-week dry bean enriched diet (250 g/day) and 12 mice that received a standardized diet containing either 0 or 10% navy bean ethanol extract for 6 weeks; we also investigated fecal metabolites in the mice. The serum metabolites identified in these controlled feeding studies were then investigated in 212 polyp-free participants from the Polyp Prevention Trial who self-reported either increased (≥+31 g/day from baseline), high dry bean intake of ≥42 g/day in year 3 or low, unchanged dry bean consumption of <8 g/day; serum was analyzed from baseline and year 3. Serum pipecolic acid and S-methyl cysteine were elevated after dry bean consumption in human and mouse studies and reflected dry bean consumption in the Polyp Prevention Trial.

CONCLUSION

Serum levels of pipecolic acid and S-methyl cysteine are useful biomarkers of dry bean consumption.

Rapid determination of four short-chain alkyl mercapturic acids in human urine by column-switching liquid chromatography-tandem mass spectrometry

We developed and validated an analytical method for the simultaneous determination of methyl mercapturic acid (MeMA), ethyl mercapturic acid (EtMA), n-propyl mercapturic acid (PrMA) and iso-propyl mercapturic acid (iPrMA) in human urine. These alkyl mercapturic acids are known or presumed biomarkers of exposure to several alkylating agents including methyl bromide, dimethyl sulfate, ethyl bromide, 1-bromopropane and 2-bromopropane. The method involves a column switching arrangement for online solid phase extraction of the analytes with subsequent analytical separation and detection using liquid chromatography and tandem mass spectrometry. Within day and day-to-day imprecision was determined to range from 4.5 to 12.2%. The analytical method is distinguished by its wide linear working range of up to 2,500 μg/L with detection limits ranging from 2.0 μg/L (for PrMA) to 5.1 μg/L (for MeMA) that render possible the application in various biomonitoring studies regarding exposure to alkylating agents. The results of a pilot study on urine samples of 30 individuals occupationally non-exposed to alkylating agents using the new procedure confirmed the background excretion of MeMA (<5.1-35.6 μg/L) and PrMA (<2.0-95.7 μg/L).