Assignment of the molecular origins of CEST signals at 2ppm in rat brain

作者：Zhang Xiao Yong; Xie Jingping; Wang Feng; Lin Eugene C; Xu Junzhong; Gochberg Daniel F; Gore John C; Zu Zhongliang^*

来源：Magnetic Resonance in Medicine, 2017, 78(3): 881-887.

DOI：10.1002/mrm.26802

• MRI
• chemical exchange saturation transfer (CEST)
• creatine
• proteins

PurposeChemical exchange saturation transfer effects at 2ppm (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.
MethodsTwo 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.
ResultsThe 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.
ConclusionsThe 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.

• 出版日期2017-9