Zhen Eugene Y, Higgs Richard E, Gutierrez Jesus A
Eli Lilly and Company, Indianapolis, IN 46285, USA.
Anal Biochem. 2013 Nov 1;442(1):1-9. doi: 10.1016/j.ab.2013.07.006. Epub 2013 Jul 16.
Apelin is emerging as an important hormone regulator of cardiovascular homoeostasis and an important biomarker for heart failure. Apelin concentrations have historically been measured by immunoassays; however, reported apelin concentrations measured in healthy volunteers show a large disparity from a few picograms per milliliter (pg/ml) to several nanograms per milliliter (ng/ml). Apelin exists in several isoforms ranging in size from 12 to 36 residues, and immunoassays generally cannot distinguish the specific forms present. In this study, an optimized method for enriching apelin peptides with cation-exchange beads followed with mass spectrometry analysis is presented. Apelin peptides are labile in plasma at physiological conditions; however, by lowering the plasma pH to 4.5, the recovery of apelin peptides can be increased significantly. Through optimizing the cation-exchange extraction process, we improved the lower limit of detection for most of the apelin peptides monitored to a few pg/ml. Using the improved method, we detected pyroglutamyl apelin-13 [(pyr)apelin-13] as the major apelin isoform present in plasma from several healthy volunteers at concentrations ranging from 7.7 to 23.3pg/ml.
Apelin正逐渐成为心血管稳态的重要激素调节因子以及心力衰竭的重要生物标志物。Apelin浓度以往是通过免疫测定法来测量的；然而，报告显示健康志愿者体内测量的Apelin浓度差异很大，从每毫升几皮克（pg/ml）到几纳克每毫升（ng/ml）不等。Apelin存在多种异构体，大小从12到36个残基不等，免疫测定法通常无法区分其中存在的具体形式。在本研究中，提出了一种用阳离子交换珠富集Apelin肽并随后进行质谱分析的优化方法。Apelin肽在生理条件下在血浆中不稳定；然而，通过将血浆pH值降至4.5，可以显著提高Apelin肽的回收率。通过优化阳离子交换提取过程，我们将所监测的大多数Apelin肽的检测下限提高到了几pg/ml。使用改进后的方法，我们检测到焦谷氨酸Apelin-13[（pyr）Apelin-13]是几名健康志愿者血浆中存在的主要Apelin异构体，浓度范围为7.7至23.3pg/ml。
