In vivo three-dimensional EPR imaging of nitric oxide production from isosorbide dinitrate in mice

Recently, in vivo electron paramagnetic resonance (EPR) spectroscopy and imaging have been widely used to investigate free radical distribution and metabolism in tissues, organs, and whole body of small animals. Endogenous nitric oxide (NO) is an attractive target of this method. In the present study, NO production from a nitrovasodilator, isosorbide dinitrate (ISDN), in live mice was investigated by in vivo EPR spectroscopy and imaging combined with the spin-trapping technique. A highly water-soluble Fe complex with N-(dithiocarboxy)sarcosine (DTCS) was used as an NO-trapping agent. Mice received [14N]-ISDN, and the Fe-DTCS complex subcutaneously exhibited the characteristic triplet EPR signal of the NO adduct [14NO-Fe(DTCS)2]2-. Using [15N]ISDN instead of [14N]ISDN, we were able to observe that the doublet EPR signal stemmed from the 15NO adduct, which directly demonstrated that NO was produced from ISDN. The three-dimensional EPR images of the upper abdomen of living mice showed that the NO adducts were distributed in the liver and the kidneys. This EPR image combined with the ex vivo EPR measurements of the blood suggested that NO production from ISDN occurred in the liver in this experimental condition.