大鼠脑内 2 ppm 处 CEST 信号的分子起源分配。
Assignment of the molecular origins of CEST signals at 2 ppm in rat brain.
机构信息
Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA.
Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, Tennessee, USA.
出版信息
Magn Reson Med. 2017 Sep;78(3):881-887. doi: 10.1002/mrm.26802. Epub 2017 Jun 26.
PURPOSE
Chemical exchange saturation transfer effects at 2 ppm (CEST@2ppm) in brain have previously been interpreted as originating from creatine. However, protein guanidino amine protons may also contribute to CEST@2ppm. This study aims to investigate the molecular origins and specificity of CEST@2ppm in brain.
METHODS
Two experiments were performed: (i) samples containing egg white albumin and creatine were dialyzed using a semipermeable membrane to demonstrate that proteins and creatine can be separated by this method; and (ii) tissue homogenates of rat brain with and without dialysis to remove creatine were studied to measure the relative contributions of proteins and creatine to CEST@2ppm.
RESULTS
The experiments indicate that dialysis can successfully remove creatine from proteins. Measurements on tissue homogenates show that, with the removal of creatine via dialysis, CEST@2ppm decreases to approximately 34% of its value before dialysis, which indicates that proteins and creatine have comparable contribution to the CEST@2ppm in brain. However, considering the contribution from peptides and amino acids to CEST@2ppm, creatine may have much less contribution to CEST@2ppm.
CONCLUSIONS
The contribution of proteins, peptides, and amino acids to CEST@2ppm cannot be neglected. The CEST@2ppm measurements of creatine in rat brain should be interpreted with caution. Magn Reson Med 78:881-887, 2017. © 2017 International Society for Magnetic Resonance in Medicine.
目的
此前，在 2 ppm（CEST@2ppm）处脑内的化学交换饱和转移效应被解释为来源于肌酸。然而，蛋白质胍基胺质子也可能对 CEST@2ppm 有贡献。本研究旨在探讨脑内 CEST@2ppm 的分子起源和特异性。
方法
进行了两项实验：（i）使用半透膜对含有蛋清白蛋白和肌酸的样品进行透析，以证明该方法可以将蛋白质和肌酸分离；（ii）研究了未经透析和经透析去除肌酸的大鼠脑匀浆，以测量蛋白质和肌酸对 CEST@2ppm 的相对贡献。
结果
实验表明，透析可以成功地将肌酸从蛋白质中去除。对组织匀浆的测量表明，通过透析去除肌酸后，CEST@2ppm 降低至透析前的约 34%，这表明蛋白质和肌酸对脑内 CEST@2ppm 的贡献相当。然而，考虑到肽和氨基酸对 CEST@2ppm 的贡献，肌酸对 CEST@2ppm 的贡献可能要小得多。
结论
蛋白质、肽和氨基酸对 CEST@2ppm 的贡献不容忽视。在解释大鼠脑内 CEST@2ppm 测量值时应谨慎。磁共振医学 78：881-887，2017。© 2017 国际磁共振学会。
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