Reactive oxygen species (ROS) enhance proton exchange rate (k_ex) in a small-metabolite CEST system

Reactive oxygen species (ROS) serve as key biomarkers of oxidative stress implicated in diverse diseases, including neurodegeneration and cancer. Noninvasive imaging of ROS remains a technical challenge due to their low concentration and transient nature. In previous studies, we demonstrated that ROS, particularly the hydroxyl radicals, enhance proton exchange rate (k_ex) in chemical exchange saturation transfer (CEST) MRI experiments using egg white tissues, a complex system containing varied proteins and other metabolites. This study is to further validate and confirm this using a simple small-metabolite system, creatine solutions with ROS-producing Fenton reactions. By combining the 9.4 T CEST Z-spectral MRI experiments with Bloch-McConnell modeling, we show that ROS-induced creatine CEST linewidth broadening is primarily linked to increased proton exchange rates rather than relaxation changes. These findings further support endogenous k_ex mapping as a promising MRI biomarker for in vivo ROS detection, facilitating research and clinical management of oxidative stress-related pathologies.