Borges Chad R, Rehder Douglas S, Jensen Sally, Schaab Matthew R, Sherma Nisha D, Yassine Hussein, Nikolova Boriana, Breburda Christian
From the ‡Department of Chemistry & Biochemistry, Arizona State University, Tempe, Arizona 85287; §Biodesign Institute at Arizona State University, Tempe, Arizona 85287;
§Biodesign Institute at Arizona State University, Tempe, Arizona 85287;
Mol Cell Proteomics. 2014 Jul;13(7):1890-9. doi: 10.1074/mcp.M114.038455. Epub 2014 Apr 15.
S-cysteinylated albumin and methionine-oxidized apolipoprotein A-I (apoA-I) have been posed as candidate markers of diseases associated with oxidative stress. Here, a dilute-and-shoot form of LC-electrospray ionization-MS requiring half a microliter of blood plasma was employed to simultaneously quantify the relative abundance of these oxidized proteoforms in samples stored at -80 °C, -20 °C, and room temperature and exposed to multiple freeze-thaw cycles and other adverse conditions in order to assess the possibility that protein oxidation may occur as a result of poor sample storage or handling. Samples from a healthy donor and a participant with poorly controlled type 2 diabetes started at the same low level of protein oxidation and behaved similarly; significant increases in albumin oxidation via S-cysteinylation were found to occur within hours at room temperature and days at -20 °C. Methionine oxidation of apoA-I took place on a longer time scale, setting in after albumin oxidation reached a plateau. Freeze-thaw cycles had a minimal effect on protein oxidation. In matched collections, protein oxidation in serum was the same as that in plasma. Albumin and apoA-I oxidation were not affected by sample headspace or the degree to which vials were sealed. ApoA-I, however, was unexpectedly found to oxidize faster in samples with lower surface-area-to-volume ratios. An initial survey of samples from patients with inflammatory conditions normally associated with elevated oxidative stress-including acute myocardial infarction and prostate cancer-demonstrated a lack of detectable apoA-I oxidation. Albumin S-cysteinylation in these samples was consistent with known but relatively brief exposures to temperatures above -30 °C (the freezing point of blood plasma). Given their properties and ease of analysis, these oxidized proteoforms, once fully validated, may represent the first markers of blood plasma specimen integrity based on direct measurement of oxidative molecular damage that can occur under suboptimal storage conditions.
S-半胱氨酸化白蛋白和甲硫氨酸氧化的载脂蛋白A-I（apoA-I）被认为是与氧化应激相关疾病的候选标志物。在此，采用一种仅需半微升血浆的稀释进样型液相色谱-电喷雾电离质谱法，同时定量测定储存在-80°C、-20°C和室温下并经历多次冻融循环及其他不利条件的样品中这些氧化蛋白变体的相对丰度，以评估蛋白质氧化是否可能因样品储存或处理不当而发生。来自健康供体和2型糖尿病控制不佳参与者的样品起始时蛋白质氧化水平相同，表现也相似；发现在室温下数小时内以及在-20°C下数天内，通过S-半胱氨酸化导致的白蛋白氧化显著增加。apoA-I的甲硫氨酸氧化发生在较长时间尺度上，在白蛋白氧化达到平台期后开始。冻融循环对蛋白质氧化影响极小。在配对样本中，血清中的蛋白质氧化与血浆中的相同。白蛋白和apoA-I氧化不受样品顶空或小瓶密封程度的影响。然而，意外发现apoA-I在表面积与体积比更低的样品中氧化更快。对通常与氧化应激升高相关的炎症性疾病患者（包括急性心肌梗死和前列腺癌）的样品进行的初步调查表明，未检测到apoA-I氧化。这些样品中的白蛋白S-半胱氨酸化与已知的但相对短暂暴露于高于-30°C（血浆冰点）的温度一致。鉴于其特性和分析简便性，这些氧化蛋白变体一旦得到充分验证，可能代表基于直接测量在次优储存条件下可能发生的氧化分子损伤的首批血浆标本完整性标志物。
