title: Pulsed EPR imaging of nitroxides in mice.
abstract: Nitroxides, unlike trityl radicals, have shorter T(2)s which until now were not detectable in vivo by a time-domain pulsed Electron Paramagnetic Resonance (EPR) spectrometer at 300 MHz since their phase memory times were shorter than the spectrometer recovery times. In the current version of the time-domain EPR spectrometer with improved spectrometer recovery times, the feasibility of detecting signals from nitroxide radicals was tested. Among the nitroxides evaluated, deuterated (15)N-Tempone ((15)N-PDT) was found to have the longest T(2). The signal intensity profile as a function of concentration of these agents was evaluated and a biphasic behavior was observed; beyond a nitroxide concentration of 1.5mM, signal intensity was found to decrease as a result of self-broadening. Imaging experiments were carried out with (15)N-PDT in solutions equilibrated with 0%, 5%, 10%, and 21% oxygen using the single point imaging (SPI) modality in EPR. The image intensity in these tubes was found to depend on the oxygen concentration which in turn influences the T(2) of (15)N-PDT. In vivo experiments were demonstrated with (15)N-PDT in anesthetized mice where the distribution and metabolism of (15)N-PDT could be monitored. This study, for the first time shows the capability to image a cell-permeable nitroxide in mice using pulsed EPR in the SPI modality.
authors.affiliation: Radiation Biology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-1002, USA.
authors.forename: Fuminori
authors.initials: F
authors.lastname: Hyodo
authors.forename: Shingo
authors.initials: S
authors.lastname: Matsumoto
authors.forename: Nallathamby
authors.initials: N
authors.lastname: Devasahayam
authors.forename: Christopher
authors.initials: C
authors.lastname: Dharmaraj
authors.forename: Sankaran
authors.initials: S
authors.lastname: Subramanian
authors.forename: James B
authors.initials: JB
authors.lastname: Mitchell
authors.forename: Murali C
authors.initials: MC
authors.lastname: Krishna
mesh_terms: D000818:Animals; D002294:Carcinoma, Squamous Cell; D045744:Cell Line, Tumor; D004578:Electron Spin Resonance Spectroscopy; D005260:Female; D007202:Indicators and Reagents; D008279:Magnetic Resonance Imaging / Q000379:methods*; D051379:Mice; D008809:Mice, Inbred C3H; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental / Q000378:metabolism / Q000473:pathology; D009589:Nitrogen Oxides / Q000737:chemistry*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D013113:Spin Labels; D014216:Triacetoneamine-N-Oxyl
chemical_list: D007202:Indicators and Reagents; D009589:Nitrogen Oxides; D013113:Spin Labels; D014216:Triacetoneamine-N-Oxyl