Center for Advanced Technology, Adam Mickiewicz University in Poznań, Uniwersytetu Poznańskiego 10, 61-614 Poznań, Poland.
Adam Mickiewicz University in Poznań, Faculty of Chemistry, Uniwersytetu Poznańskiego 8, 61-614 Poznań, Poland.
Bioorg Chem. 2022 Aug;125:105852. doi: 10.1016/j.bioorg.2022.105852. Epub 2022 May 5.
Furan is an environmental pollutant also present in heat-treated food. The compound is toxic and carcinogenic to rats, and classified as a possible human carcinogen. Mechanisms laying behind the furan carcinogenicity remain unclear, however scientific data indicate the involvement of bioactivation catalysed by cytochrome P450 2E1. The resulted initial metabolite of furan, cis-2-butene-1,4-dial (BDA) is an extremely reactive conjugated dialdehyde able to damage important cellular components such as glutathione, proteins and nucleic acids. Earlier works showed that BDA induces protein cross-linking leading to the formation of modifications containing substituted pyrrole ring, and that the cysteine and lysine residues are prone to undergo such processes. The resulted cross-linked protein adducts are important for research aimed at exploring biomarkers of furan exposure. Due to furan's high volatility, biomarker-based methods appear to be a reliable approach to measure a level of exposure to this chemical. To date, numerous urinary and hepatocyte metabolites were identified. However, all the metabolites contain 3-substituted pyrrole ring resulted from the 1,4-addition of the cysteine thiol function to BDA followed by the condensation with the lysine free amino group. In this work we provide evidence that also 2-substituted pyrrole cross-links are formed at the physiological pH, when BDA is subjected to the reaction with N-acetylcysteine and N-acetyllysine, N-acetyllysine or lysine, respectively. The 2-substituted cross-links arise from the initial 1,2-addition of N-acetylcysteine to BDA accomplished by the condensation with lysine or its N-acetylated derivatives. Formation of the 2-substituted pyrroles sheds new light on the reactivity of cis-2-butene-1,4-dial towards amino acids, and contributes to complete characterisation of the compound chemistry. Our studies show that the 2- and 3-substituted cross-links are indistinguishable based on their MS and MS/MS spectra, and that for reliable qualitative and quantitative measurements the use of isotope-substituted synthetic internal standards is necessary. In the light of these facts, our results are important for research into furan exposure biomarkers.
呋喃是一种环境污染物，也存在于热处理食品中。该化合物对大鼠具有毒性和致癌性，被归类为可能的人类致癌物。然而，其致癌机制尚不清楚，科学数据表明与细胞色素 P450 2E1 催化的生物活化有关。呋喃的初始代谢物顺式-2-丁烯-1,4-二醛（BDA）是一种极其反应性的共轭二醛，能够破坏谷胱甘肽、蛋白质和核酸等重要细胞成分。早期的研究表明，BDA 诱导蛋白质交联，导致形成含有取代吡咯环的修饰物，并且半胱氨酸和赖氨酸残基容易发生这种过程。形成的交联蛋白加合物对于研究呋喃暴露的生物标志物很重要。由于呋喃的高挥发性，基于生物标志物的方法似乎是测量这种化学物质暴露水平的可靠方法。迄今为止，已经鉴定出许多尿和肝细胞代谢物。然而，所有的代谢物都含有 3-取代的吡咯环，这是由半胱氨酸巯基功能与 BDA 的 1,4-加成反应，然后与赖氨酸游离氨基缩合产生的。在这项工作中，我们提供了证据，证明在生理 pH 值下，当 BDA 与 N-乙酰半胱氨酸和 N-乙酰赖氨酸、N-乙酰赖氨酸或赖氨酸分别反应时，也会形成 2-取代的吡咯交联。2-取代的交联是由 N-乙酰半胱氨酸与 BDA 的初始 1,2-加成反应形成的，该反应是通过与赖氨酸或其 N-乙酰化衍生物缩合完成的。顺式-2-丁烯-1,4-二醛与氨基酸的反应性的新认识，为该化合物的化学性质的完整描述做出了贡献。我们的研究表明，基于其 MS 和 MS/MS 谱，2-和 3-取代的交联是无法区分的，为了进行可靠的定性和定量测量，需要使用同位素取代的合成内标。鉴于这些事实，我们的研究结果对呋喃暴露生物标志物的研究很重要。
