A false positive finding in liquid chromatography/triple quadrupole mass spectrometry analysis by a non-isobaric matrix component: the case of benzotriazole in urine for human biomonitoring

A High-Resolution Mass Spectrometry-Based Quantitative Metabolomic Workflow Highlights Defects in 5-Fluorouracil Metabolism in Cancer Cells with Acquired Chemoresistance

Currently, 5-fluorouracil (5-FU)-based combination chemotherapy is the mainstay in the treatment of metastatic colorectal cancer (CRC), which benefits approximately 50% of the patients. However, these tumors inevitably acquire chemoresistance resulting in treatment failure. The molecular mechanisms driving acquired chemotherapeutic drug resistance in CRC is fundamental for the development of novel strategies for circumventing resistance. However, the specific phenomenon that drives the cancer cells to acquire resistance is poorly understood. Understanding the molecular mechanisms that regulate chemoresistance will uncover new avenues for the treatment of CRC. Among the various mechanisms of acquired chemoresistance, defects in the drug metabolism pathways could play a major role. In the case of 5-FU, it gets converted into various active metabolites, which, directly or indirectly, interferes with the replication and transcription of dividing cells causing DNA and RNA damage. In this project, we developed a high-resolution mass spectrometry-based method to effectively extract and quantify levels of the 5-FU metabolites in cell lysates and media of parental and 5-FU resistant LIM1215 CRC cells. The analysis highlighted that the levels of 5-FU metabolites are significantly reduced in 5-FU resistant cells. Specifically, the level of the nucleotide fluorodeoxyuridine monophosphate (FdUMP) is reduced with treatment of 5-FU clarifying the compromised 5-FU metabolism in resistant cells. Corroborating the metabolomic analysis, treatment of the resistant cells with FdUMP, an active metabolite of 5-FU, resulted in effective killing of the resistant cells. Overall, in this study, an effective protocol was developed for comparative quantitation of polar metabolites and nucleotide analogues from the adherent cells efficiently. Furthermore, the utility of FdUMP as an alternative for CRC therapy is highlighted.

Towards Mass Spectrometry-Based Chemical Exposome: Current Approaches, Challenges, and Future Directions

The proposal of the “exposome” concept represents a shift of the research paradigm in studying exposure-disease relationships from an isolated and partial way to a systematic and agnostic approach. Nevertheless, exposome implementation is facing a variety of challenges including measurement techniques and data analysis. Here we focus on the chemical exposome, which refers to the mixtures of chemical pollutants people are exposed to from embryo onwards. We review the current chemical exposome measurement approaches with a focus on those based on the mass spectrometry. We further explore the strategies in implementing the concept of chemical exposome and discuss the available chemical exposome studies. Early progresses in the chemical exposome research are outlined, and major challenges are highlighted. In conclusion, efforts towards chemical exposome have only uncovered the tip of the iceberg, and further advancement in measurement techniques, computational tools, high-throughput data analysis, and standardization may allow more exciting discoveries concerning the role of exposome in human health and disease.

Reaching a Vapor Sensitivity of 0.01 Parts Per Quadrillion in the Screening of Large Volume Freight

The feasibility of detecting explosives in the atmosphere at concentrations as low as 0.01 ppq hinges on the poorly known question of what interfering species exist at these or higher concentrations. To clarify the issue, hundreds of samples of ambient air, either clean or loaded with explosives (from lightly contaminated environments) have been collected in fiberglass/stainless steel filters coated with Tenax-GR, thermally desorbed at variable temperature, and ionized with Cl^- via secondary electrospray (SESI). They are analyzed with a narrow-band mobility filter (SEADM's P5 DMA) and a triple quadrupole mass spectrometer (Sciex's 5500), configured in series to transmit precursor and fragment ions of the explosives Nitroglycerin, PETN, RDX, and TNT. Blanks were sampled outdoors at a rural site (Boecillo, Valladolid, Spain), and loads were sampled at diverse locations. For RDX and TNT, atmospheric background inhibits detection below 1 part/trillion (ppt) without mobility filtering. This interference was drastically reduced by the DMA, allowing detection up to 1 part/quadrillion (ppq). Further sensitivity increase was achieved by scanning over a mobility region several percent around that of the target explosive, to separate various isobaric compounds by Gaussian deconvolution. (i) All four MS/MS channels analyzed exhibit several background peaks within the narrow mobility intervals investigated. At least one of these interferents is much stronger than the instrument background at the explosive's mobility, making DMA separation most helpful. (ii) For Nitroglycerin and PETN the combined filtering techniques have not lowered ambient chemical noise down to 0.01 ppq. (iii) Interferents are greatly reduced for TNT and RDX, resulting in minimal chemical noise: 322 blank tests for RDX yielded mean signal of 0.0012 ppq and standard deviation σ = 0.0035 ppq (mean + 3σ detection limit of 0.01 ppq).