An early pathological hallmark of Alzheimer’s disease (AD) is amyloid-β (Aβ) deposits in the brain, which largely consist of up to 43 amino acids long Aβ peptides derived from the amyloid precursor protein (APP). We previously identified a series of sialylated Tyr-10 O-glycosylated Aβ peptides, 15–20 residues long, from human cerebrospinal fluid (CSF) and observed a relative increase of those in AD vs non-AD patients. We report here on the synthesis and use of an isotopically double-labeled Aβ1-15 glycopeptide, carrying the core 1 Galβ3GalNAcα1-O-Tyr-10 structure, to (1) identify by HCD LC-MS/MS the definite glycan core 1 structure of immunopurified and desialylated Aβ glycopeptides in human CSF and to (2) establish a LC-MS/MS quantification method for desialylated Aβ1-15 (and Aβ1-17) glycopeptides and to (3) compare the concentrations of these Aβ glycopeptides in CSF from 20 AD patients and 20 healthy controls. Although we unambiguously identified the core 1 structures and Tyr-10 attachment sites of the glycopeptides, we did not observe any quantitative differences, determined through both peptide and oxonium ion fragments, of the desialylated Aβ1-15 or Aβ1-17 glycopeptides between the AD and non-AD group. The new quantitative glycoproteomic approach described, using double-labeled glycopeptide standards, will undoubtedly facilitate future studies of glycopeptides as clinical biomarkers but should also embrace sialylated Aβ standards to reveal specific sialylation patterns of individual Aβ glycopeptides in AD patients and controls.

阿尔茨海默病 (AD) 的一个早期病理特征是大脑中的淀粉样蛋白-β (Aβ) 沉积，其主要由源自淀粉样蛋白前体蛋白 (APP) 的长达 43 个氨基酸的长 Aβ 肽组成。我们之前从人脑脊液 (CSF) 中鉴定出一系列唾液酸化的 Tyr-10 O-糖基化 Aβ 肽，长度为 15-20 个残基，并观察到 ​​AD 患者与非 AD 患者相比，唾液酸化的 Tyr-10 O-糖基化 Aβ 肽相对增加。我们在此报告同位素双标记 Aβ1-15 糖肽的合成和使用，该糖肽携带核心 1 Galβ3GalNAcα1- O -Tyr-10 结构，以 (1) 通过 HCD LC-MS/MS 鉴定明确的聚糖核心 1 结构分析人脑脊液中免疫纯化和去唾液酸化的 Aβ 糖肽，并 (2) 建立去唾液酸化 Aβ1-15（和 Aβ1-17）糖肽的 LC-MS/MS 定量方法，以及 (3) 比较脑脊液中这些 Aβ 糖肽的浓度20 名 AD 患者和 20 名健康对照。尽管我们明确鉴定了糖肽的核心 1 结构和 Tyr-10 附着位点，但通过肽和氧鎓离子片段确定，我们没有观察到 AD 和 AD 之间去唾液酸化的 Aβ1-15 或 Aβ1-17 糖肽有任何定量差异。非AD组。所描述的新的定量糖蛋白组学方法，使用双标记糖肽标准品，无疑将促进糖肽作为临床生物标志物的未来研究，但也应该采用唾液酸化 Aβ 标准品，以揭示 AD 患者和对照中个体 Aβ 糖肽的特定唾液酸化模式。