Unit of Clinical Chemistry, Central Diagnostic Laboratory, Maastricht University Medical Center, Maastricht, The Netherlands.
NUTRIM, School of Nutrition and Translational Research in Metabolism, Medicine and Life Sciences (FHML) of Maastricht University (UM), Maastricht University Medical Center, Maastricht, The Netherlands.
Adv Exp Med Biol. 2021;1306:41-59. doi: 10.1007/978-3-030-63908-2_4.
Cardiac troponin T (cTnT) is a sensitive and specific biomarker for detecting cardiac muscle injury. Its concentration in blood can be significantly elevated outside the normal reference range under several pathophysiological conditions. The classical analytical method in routine clinical analysis to detect cTnT in serum or plasma is a single commercial immunoassay, which is designed to quantify the intact cTnT molecule. The targeted epitopes are located in the central region of the cTnT molecule. However, in blood cTnT exists in different biomolecular complexes and proteoforms: bound (to cardiac troponin subunits or to immunoglobulins) or unbound (as intact protein or as proteolytic proteoforms). While proteolysis is a principal posttranslational modification (PTM), other confirmed PTMs of the proteoforms include N-terminal initiator methionine removal, N-acetylation, O-phosphorylation, O-(N-acetyl)-glucosaminylation, N(ɛ)-(carboxymethyl)lysine modification and citrullination. The immunoassay probably detects several of those cTnT biomolecular complexes and proteoforms, as long as they have the centrally targeted epitopes in common. While analytical cTnT immunoreactivity has been studied predominantly in blood, it can also be detected in urine, although it is unclear in which proteoform cTnT immunoreactivity is present in urine. This review presents an overview of the current knowledge on the pathophysiological lifecycle of cTnT. It provides insight into the impact of PTMs, not only on the analytical immunoreactivity, but also on the excretion of cTnT in urine as one of the waste routes in that lifecycle. Accordingly, and after isolating the proteoforms from urine of patients suffering from proteinuria and acute myocardial infarction, the structures of some possible cTnT proteoforms are reconstructed using mass spectrometry and presented.
心肌肌钙蛋白 T（cTnT）是检测心肌损伤的敏感和特异性生物标志物。在几种病理生理条件下，其在血液中的浓度超出正常参考范围时会显著升高。在常规临床分析中检测血清或血浆中 cTnT 的经典分析方法是单一的商业免疫分析法，旨在定量完整的 cTnT 分子。靶向表位位于 cTnT 分子的中心区域。然而，在血液中 cTnT 存在于不同的生物分子复合物和蛋白形式中：结合（与肌钙蛋白亚基结合或与免疫球蛋白结合）或未结合（作为完整蛋白或作为蛋白水解蛋白形式）。虽然蛋白水解是主要的翻译后修饰（PTM），但蛋白形式的其他已确认的 PTM 包括 N 端起始甲硫氨酸的去除、N 乙酰化、O 磷酸化、O-（N-乙酰）-葡糖胺化、N（ɛ）-（羧甲基）赖氨酸修饰和瓜氨酸化。只要具有共同的中心靶向表位，免疫测定法可能会检测到几种 cTnT 生物分子复合物和蛋白形式。虽然分析性 cTnT 免疫反应性主要在血液中进行研究，但也可以在尿液中检测到，尽管尚不清楚尿液中存在哪种蛋白形式的 cTnT 免疫反应性。本文综述了当前关于 cTnT 病理生理生命周期的知识概述。它深入了解 PTM 对分析免疫反应性的影响，以及作为该生命周期中废物途径之一的 cTnT 在尿液中的排泄的影响。因此，在从患有蛋白尿和急性心肌梗死的患者的尿液中分离出蛋白形式后，使用质谱法重建了一些可能的 cTnT 蛋白形式的结构，并进行了呈现。
