Development of non-invasive system for the evaluation of free radicals in brain with encephalopathy.

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Recently, some studies indicated that free radicals including reactive oxygen species (ROS) and reactive nitrogen species (RNS) associates with a collapse of redox balance in vivo, resulted in induction of several types of diseases. On the contrary, there were few studies on the association of free radicals with encephalopathy in an individual subject, because of a lack of technique, by which redox balance in brain was estimated noninvasively. In the present study, we established a novel technique to noninvasively estimate free radical reactions in brain by using the combination of in vivo ESR and a spin-probe method.In order to estimate free radical reactions and image them in the brain of living animals, a nitroxyl spin-probe, carboxy-PROXYL acetoxymethyl ester (CxP-AM) was newly synthesized. CxP-AM was designed to be hydrolyzed by esterase, but not by lipase, so that it would pass through the blood-brain barrier and be retained in the cytosolic phase of parenchymal cells in the brain after intravenous injection. The retentivity of the probe in brain was proved through an electron spin resonance computed tomographic imaging technique. Furthermore, we applied this probe to the evaluation of free radical reactions in brain with ischemia-reperfusion. Through these studies, it is elucidated that free radical reactions in the brain with ischemia-reperfusion are significantly enhanced.The goal of our study is to establish a novel technique for the non-invasive evaluation of redox balance in brain, and apply a new biological parameter on redox metabolism to brain.