氯甲酸酯衍生化法用于通过多重稳定同位素分辨代谢组学(mSIRM)追踪细胞和组织中氨基酸的命运。

Chloroformate derivatization for tracing the fate of Amino acids in cells and tissues by multiple stable isotope resolved metabolomics (mSIRM).

机构信息

Center for Environmental and Systems Biochemistry, University of Kentucky, Lexington, KY, 40539, USA; Department of Toxicology and Cancer Biology, University of Kentucky, Lexington, KY, 40539, USA.

Center for Environmental and Systems Biochemistry, University of Kentucky, Lexington, KY, 40539, USA; Department of Toxicology and Cancer Biology, University of Kentucky, Lexington, KY, 40539, USA.

出版信息

Anal Chim Acta. 2017 Jul 11;976:63-73. doi: 10.1016/j.aca.2017.04.014. Epub 2017 Apr 10.

Abstract

Amino acids have crucial roles in central metabolism, both anabolic and catabolic. To elucidate these roles, steady-state concentrations of amino acids alone are insufficient, as each amino acid participates in multiple pathways and functions in a complex network, which can also be compartmentalized. Stable Isotope-Resolved Metabolomics (SIRM) is an approach that uses atom-resolved tracking of metabolites through biochemical transformations in cells, tissues, or whole organisms. Using different elemental stable isotopes to label multiple metabolite precursors makes it possible to resolve simultaneously the utilization of these precursors in a single experiment. Conversely, a single precursor labeled with two (or more) different elemental isotopes can trace the allocation of e.g. C and N atoms through the network. Such dual-label experiments however challenge the resolution of conventional mass spectrometers, which must distinguish the neutron mass differences among different elemental isotopes. This requires ultrahigh resolution Fourier transform mass spectrometry (UHR-FTMS). When combined with direct infusion nano-electrospray ion source (nano-ESI), UHR-FTMS can provide rapid, global, and quantitative analysis of all possible mass isotopologues of metabolites. Unfortunately, very low mass polar metabolites such as amino acids can be difficult to analyze by current models of UHR-FTMS, plus the high salt content present in typical cell or tissue polar extracts may cause unacceptable ion suppression for sources such as nano-ESI. Here we describe a modified method of ethyl chloroformate (ECF) derivatization of amino acids to enable rapid quantitative analysis of stable isotope labeled amino acids using nano-ESI UHR-FTMS. This method showed excellent linearity with quantifiable limits in the low nanomolar range represented in microgram quantities of biological specimens, which results in extracts with total analyte abundances in the low to sub-femtomole range. We have applied this method to profile amino acids and their labeling patterns in C and H doubly labeled PC9 cell extracts, cancerous and non-cancerous tissue extracts from a lung cancer patient and their protein hydrolysates as well as plasma extracts from mice fed with a liquid diet containing C-glucose (Glc). The multi-element isotopologue distributions provided key insights into amino acid metabolism and intracellular pools in human lung cancer tissues in high detail. The C labeling of Asp and Glu revealed de novo synthesis of these amino acids from C-Glc via the Krebs cycle, specifically the elevated level of C-labeled Asp and Glu in cancerous versus non-cancerous lung tissues was consistent with enhanced pyruvate carboxylation. In addition, tracking the fate of double tracers, (C-Glc + H-Gly or C-Glc + H-Ser) in PC9 cells clearly resolved pools of Ser and Gly synthesized de novo from C-Glc (C-Ser and C-Gly) versus Ser and Gly derived from external sources (H-Ser, H-Gly). Moreover the complex H labeling patterns of the latter were results of Ser and Gly exchange through active Ser-Gly one-carbon metabolic pathway in PC9 cells.

摘要

氨基酸在中心代谢中具有重要作用,包括合成代谢和分解代谢。为了阐明这些作用,仅稳定状态下的氨基酸浓度是不够的,因为每个氨基酸都参与多个途径,并在一个复杂的网络中发挥作用,这个网络也可以进行区室化。稳定同位素解析代谢组学(SIRM)是一种通过细胞、组织或整个生物体中的生化转化来追踪代谢物原子分辨率的方法。使用不同的元素稳定同位素标记多个代谢物前体,可以在单个实验中同时解析这些前体的利用情况。相反,用两个(或更多)不同元素的同位素标记一个前体,可以追踪例如 C 和 N 原子在网络中的分配。然而,这种双标记实验挑战了常规质谱仪的分辨率,因为常规质谱仪必须区分不同元素同位素之间的中子质量差异。这需要超高分辨率傅里叶变换质谱(UHR-FTMS)。当与直接注入纳升电喷雾离子源(nano-ESI)结合使用时,UHR-FTMS 可以快速、全面、定量地分析代谢物的所有可能的质量同量异位素。不幸的是,目前的 UHR-FTMS 模型很难分析非常低分子量的极性代谢物,如氨基酸,而且典型的细胞或组织极性提取物中的高盐含量可能会对 nano-ESI 等源造成不可接受的离子抑制。在这里,我们描述了一种改良的乙基氯甲酸酯(ECF)衍生化方法,用于对稳定同位素标记的氨基酸进行快速定量分析,方法是使用 nano-ESI UHR-FTMS。该方法显示出极好的线性关系,在微克量的生物样本中,可检测到低纳摩尔范围内的限量,结果提取物中的总分析物丰度在低至亚飞摩尔范围内。我们已经将该方法应用于分析 C 和 H 双重标记 PC9 细胞提取物以及肺癌患者的癌组织和非癌组织提取物及其蛋白水解物以及喂食含有 C-葡萄糖(Glc)的液体饮食的小鼠的血浆提取物中的氨基酸及其标记模式。多元素同位素同量异位素分布提供了有关人类肺癌组织中氨基酸代谢和细胞内池的详细信息。Asp 和 Glu 的 C 标记揭示了这些氨基酸从头合成于 C-Glc 通过克雷布斯循环,特别是癌症组织中 C 标记的 Asp 和 Glu 与非癌组织中的水平升高与增强的丙酮酸羧化作用一致。此外,跟踪双示踪剂(C-Glc+H-Gly 或 C-Glc+H-Ser)在 PC9 细胞中的命运,清楚地分辨出从头合成于 C-Glc 的 Ser 和 Gly 池(C-Ser 和 C-Gly)与来自外部来源的 Ser 和 Gly (H-Ser,H-Gly)。此外,后者复杂的 H 标记模式是 PC9 细胞中 Ser-Gly 一碳代谢途径中 Ser 和 Gly 交换的结果。

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