Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA.
Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, Tennessee, USA.
Magn Reson Med. 2017 Sep;78(3):881-887. doi: 10.1002/mrm.26802. Epub 2017 Jun 26.
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.
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.
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.
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.
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。
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。
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。
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。
