Synthesis and evaluation of C-13-labeled 5-5-dimethyl-1-pyrroline-N-oxide aimed at in vivo detection of reactive oxygen species using hyperpolarized C-13-MRI

摘要

Effective means to identify the role of reactive oxygen species (ROS) mediating several diseases including cancer, ischemic heart disease, stroke, Alzheimer's and other inflammatory conditions in in vivo models would be useful. The cyclic nitrone 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) is a spin trap frequently used to detect free radicals in vitro using Electron Paramagnetic Resonance (EPR) spectroscopy. In this study, we synthesized C-13-labeled DMPO for hyperpolarization by dynamic nuclear polarization, in which C-13 NMR signal increases more than 10,000-fold. This allows in vivo C-13 MRI to investigate the feasibility of in vivo ROS detection by the C-13-MRI. DMPO was C-13-labeled at C5 position, and deuterated to prolong the T-1 relaxation time. The overall yield achieved for 5-C-13-DMPO-d(9) was 15%. Hyperpolarized 5-C-13-DMPO-d(9) provided a single peak at 76 ppm in the C-13-spectrum, and the T-1 was 60 s in phosphate buffer making it optimal for in vivo C-13 MRI. The buffered solution of hyperpolarized 5-C-13-DMPO-d(9) was injected into a mouse placed in a 3 T scanner, and C-13-spectra were acquired every 1 s. In vivo studies showed the signal of 5-C-13-DMPO-d(9) was detected in the mouse, and the T-1 decay of C-13 signal of hyperpolarized 5-C-13-DMPO-d(9) was 29 s. C-13-chemical shift imaging revealed that 5-C-13-DMPO-d(9) was distributed throughout the body in a minute after the intravenous injection. A strong signal of 5-C-13-DMPO-d(9) was detected in heart/lung and kidney, whereas the signal in liver was small compared to other organs. The results indicate hyperpolarized 5-C-13-DMPO-d(9) provided sufficient C-13 signal to be detected in the mouse in several organs, and can be used to detect ROS in vivo.