Global Profiling of Urinary Mercapturic Acids Using Integrated Library-Guided Analysis

Abstract

Urinary mercapturic acids (MAs) are often used as biomarkers for monitoring human exposures to occupational and environmental xenobiotics. In this study, we developed an integrated library-guided analysis workflow using ultraperformance liquid chromatography–quadrupole time-of-flight mass spectrometry. This method includes expanded assignment criteria and a curated library of 220 MAs and addresses the shortcomings of previous untargeted approaches. We employed this workflow to profile MAs in the urine of 70 participants40 nonsmokers and 30 smokers. We found approximately 500 MA candidates in each urine sample, and 116 MAs from 63 precursors were putatively annotated. These include 25 previously unreported MAs derived mostly from alkenals and hydroxyalkenals. Levels of 68 MAs were comparable in nonsmokers and smokers, 2 MAs were higher in nonsmokers, and 46 MAs were elevated in smokers. These included MAs of polycyclic aromatic hydrocarbons and hydroxyalkenals and those derived from toxicants present in cigarette smoke (e.g., acrolein, 1,3-butadiene, isoprene, acrylamide, benzene, and toluene). Our workflow allowed profiling of known and unreported MAs from endogenous and environmental sources, and the levels of several MAs were increased in smokers. Our method can also be expanded and applied to other exposure-wide association studies.

Exposure of Polycyclic Aromatic Hydrocarbons (PAHs) and Crude Oil to Atlantic Haddock (Melanogrammus aeglefinus): A Unique Snapshot of the Mercapturic Acid Pathway

“…Ayala et al quantitatively measured the urinary excretion of naphthalene metabolites and found that GSH and MA accounted for >60% of the total measured metabolites in mice. MA s have also been identified as urinary metabolites in humans . Contrary to the findings of Ayala et al, MA s have been characterized as minor metabolites in cigarette smokers .…”

Discovery of Modified Metabolites, Secondary Metabolites, and Xenobiotics by Structure-Oriented LC–MS/MS

“…Structure-oriented monitoring methods are employed for the detection of multiple classes of toxicologically or pharmacologically relevant compounds. In contrast to unbiased-shotgun methodologies, structure-oriented monitoring utilizes prior knowledge of the elemental composition, structural moiety, or functional group characteristics to develop an analytical pipeline honed for the detection of a subset of compounds. , Fragmentation-based LC–MS/MS methods are routinely used to characterize phase I and phase II metabolites such as cysteinyl, ,− sulfate, ,, or glucuronide conjugated products. ,, Additionally, discovery methods have been developed to monitor for specific classes of clinically relevant molecules by diagnostic fragmentation patterns, including steroid hormones, − covalently modified DNA and RNA nucleosides, ,− and small molecules or peptides exhibiting glycosylated, phosphorylated, or other distinct functional groups modifications. − Early stage drug discovery requires extensive characterization of drug metabolism, including description of drug-related metabolites, potential reactive intermediaries, and degradation products. ,, To characterize this array of metabolically diverse drug intermediates, structure-oriented monitoring approaches were developed to screen predictable transformations frequently occurring in vivo , such as hydroxylation, dehydrogenation, and demethylation, among other common phase I or II conjugation reactions. , These approaches have been used to discover numerous drug biproducts − and nerve agents and their degradation products. , …”