Department of Pathology and Laboratory Medicine, Institute on Aging, Center for Neurodegenerative Disease Research, University of Pennsylvania, Philadelphia, USA.
Alzheimers Dement. 2012 Jul;8(4):250-60. doi: 10.1016/j.jalz.2012.01.001.
The interassay variability and inconsistency of plasma β-amyloid (Aβ) measurements among centers are major factors precluding the interpretation of results and a substantial obstacle in the meta-analysis across studies of this biomarker. The goal of this investigation was to address these problems by improving the performance of the bioanalytical method.
We used the Luminex immunoassay platform with a multiplex microsphere-based reagent kit from Innogenetics. A robotic pipetting system was used to perform crucial steps of the procedure. The performance of this method was evaluated using two kit control samples and two quality control plasma samples from volunteer donors, and by retesting previously assayed patient samples in each run. This setup was applied to process 2454 patient plasma samples from the Alzheimer's Disease Neuroimaging Initiative study biofluid repository. We have additionally evaluated the correlations between our results and cerebrospinal fluid (CSF) biomarker data using mixed-effects modeling.
The average precision values of the kit controls were 8.3% for Aβ(1-40) and 4.0% for Aβ(1-42), whereas the values for the plasma quality controls were 6.4% for Aβ(1-40) and 4.8% for Aβ(1-42). From the test-retest evaluation, the average precision was 7.2% for Aβ(1-40) and 4.5% for Aβ(1-42). The range of final plasma results for Alzheimer's Disease Neuroimaging Initiative patients was 13 to 372 pg/mL (median: 164 pg/mL) for Aβ(1-40) and 3.5 to 103 pg/mL (median: 39.3 pg/mL) for Aβ(1-42). We found that sample collection parameters (blood volume and time to freeze) have a small, but significant, influence on the result. No significant difference was found between plasma Aβ levels for patients with Alzheimer's disease and healthy control subjects. We have determined multiple significant correlations of plasma Aβ(1-42) levels with CSF biomarkers. The relatively strongest, although modest, correlation was found between plasma Aβ(1-42) levels and CSF p-tau(181)/Aβ(1-42) ratio in patients with mild cognitive impairment. Plasma Aβ(1-40) correlations with CSF biomarkers were weaker and diminished completely when we used longitudinal data. No significant correlations were found for the plasma Aβ(1-42)/Aβ(1-40) ratio.
The precision of our robotized method represents a substantial improvement over results reported in the literature. Multiple significant correlations between plasma and CSF biomarkers were found. Although these correlations are not strong enough to support the use of plasma Aβ measurement as a diagnostic screening test, plasma Aβ(1-42) levels are well suited for use as a pharmacodynamic marker.
中心之间的血浆β-淀粉样蛋白（Aβ）测量的分析内变异和不一致性是阻碍结果解释和该生物标志物研究荟萃分析的主要因素。本研究的目的是通过改进生物分析方法来解决这些问题。
我们使用 Innogenetics 的基于多重微球的试剂盒的 Luminex 免疫分析平台。机器人移液系统用于执行该程序的关键步骤。使用两个试剂盒对照样本和两个来自志愿者供体的质量控制血浆样本，以及在每个运行中重新测试之前测定的患者样本，对该方法的性能进行了评估。该设置应用于处理来自阿尔茨海默病神经影像学倡议研究生物液库的 2454 名患者血浆样本。我们还使用混合效应模型评估了我们的结果与脑脊液（CSF）生物标志物数据之间的相关性。
试剂盒对照品的平均精密度值分别为 Aβ（1-40）8.3%和 Aβ（1-42）4.0%，而血浆质量对照品的平均精密度值分别为 Aβ（1-40）6.4%和 Aβ（1-42）4.8%。从测试-再测试评估来看，Aβ（1-40）的平均精密度为 7.2%，Aβ（1-42）为 4.5%。阿尔茨海默病神经影像学倡议患者的最终血浆结果范围为 13 至 372 pg/mL（中位数：164 pg/mL），Aβ（1-40）和 3.5 至 103 pg/mL（中位数：39.3 pg/mL）。我们发现样本采集参数（血容量和冷冻时间）对结果有很小但有意义的影响。未发现阿尔茨海默病患者与健康对照组之间的血浆 Aβ 水平存在显著差异。我们已经确定了多个与 CSF 生物标志物相关的血浆 Aβ（1-42）水平的显著相关性。在轻度认知障碍患者中，发现与血浆 Aβ（1-42）水平与 CSF p-tau（181）/Aβ（1-42）比值之间的相关性最强，尽管程度适中。与 CSF 生物标志物相比，血浆 Aβ（1-40）的相关性较弱，并且当我们使用纵向数据时完全消失。未发现血浆 Aβ（1-42）/Aβ（1-40）比值的显著相关性。
我们的机器人方法的精密度代表了文献报道的结果的重大改进。发现了血浆和 CSF 生物标志物之间的多个显著相关性。尽管这些相关性还不足以支持将血浆 Aβ 测量用作诊断筛选测试，但血浆 Aβ（1-42）水平非常适合用作药效标志物。
