Ryoma Kobayashi

Simultaneous and Spectroscopic Redox Molecular Imaging of Multiple Free Radical Intermediates Using Dynamic Nuclear Polarization-Magnetic Resonance Imaging

Redox reactions that generate free radical intermediates are essential to metabolic processes. However, their intermediates can produce reactive oxygen species, which may promote diseases related to oxidative stress. We report here the use of dynamic nuclear polarization-magnetic resonance imaging (DNP-MRI) to conduct redox molecular imaging. Using DNP-MRI, we obtained simultaneous images of free radical intermediates generated from the coenzyme Q10 (CoQ10), flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD) involved in the mitochondrial electron transport chain as well as the radicals derived from vitamins E and K1. Each of these free radicals was imaged in real time in a phantom comprising a mixture of free radicals localized in either lipophilic or aqueous environments. Changing the frequency of electron spin resonance (ESR) irradiation also allowed each of the radical species to be distinguished in the spectroscopic images. This study is the first to report the spectroscopic DNP-MRI imaging of free radical intermediates that are derived from endogenous species involved in metabolic processes.

Redox imaging of skeletal muscle using in vivo DNP-MRI and its application to an animal model of local inflammation

Disorders of skeletal muscle are often associated with inflammation and alterations in redox status. A non-invasive technique that could localize and evaluate the severity of skeletal muscle inflammation based on its redox environment would be useful for disease identification and monitoring, and for the development of treatments; however, no such technique currently exists. We describe a method for redox imaging of skeletal muscle using dynamic nuclear polarization magnetic resonance imaging (DNP-MRI), and apply this method to an animal model of local inflammation. Female C57/BL6 mice received injections of 0.5% bupivacaine into their gastrocnemius muscles. Plasma biomarkers, myeloperoxidase activity, and histological sections were assessed at 4 and 24h after bupivacaine injection to measure the inflammatory response. In vivo DNP-MRI was performed with the nitroxyl radicals carbamoyl-PROXYL (cell permeable) and carboxy-PROXYL (cell impermeable) as molecular imaging probes at 4 and 24h after bupivacaine administration. The images obtained after carbamoyl-PROXYL administration were confirmed with the results of L-band EPR spectroscopy. The plasma biomarkers, myeloperoxidase activity, and histological findings indicated that bupivacaine injection caused acute muscle damage and inflammation. DNP-MRI images of mice treated with carbamoyl-PROXYL or carboxy-PROXYL at 4 and 24h after bupivacaine injection showed similar increases in image intensity and decay rate was significantly increased at 24h. In addition, reduction rates in individual mice at 4h and 24h showed faster trends with bupivacaine injection than in their contralateral sides by image-based analysis. These findings indicate that in vivo DNP-MRI with nitroxyl radicals can non-invasively detect changes in the focal redox status of muscle resulting from locally-induced inflammation.

Development of redox metabolic imaging using endogenous molecules

Redox metabolism plays a central role in maintaining homeostasis in living organisms. The electron transfer system in mitochondria produces ATP via endogenous redox molecules such as flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), and coenzyme Q10 (CoQ10), which have flavin or quinone moieties. One-electron transfer reactions convert FMN, FAD, and CoQ10 to the free radical intermediates FMNH and FADH, and CoQ10H, respectively. Dynamic nuclear polarization-magnetic resonance imaging (DNP-MRI) allows us to visualize free radicals in vitro and in vivo. We present a spectroscopic imaging technology with DNP-MRI, which enables the imaging of multiple free radical intermediates such as FADH and CoQH. DNP-MRI can also identify various endogenous free radical intermediates derived from redox transformations.

Mobility of electrons on helium film capillary condensed on two dimensionally corrugated surface of dielectric substrate

Electrical conductivity of electrons on helium film covering a two dimensionally corrugated dielectric substrate was measured in a temperature interval between 0.4 and 1.64 K. As the temperature decreased from 1.5 K, the electrical conductivity decreases and approaches gradually to zero around 0.4 K. This temperature dependence is different from that measured in 2D electron system on bulk liquid helium. In order to understand the effect of the dielectric substrate, the dependences of electrical conductivity on magnetic field were measured by using a Corbino electrode and the mobility was evaluated in different temperatures. The results revealed that the mobility of electrons increases as the temperature decreases. Combining the data of electrical conductivity and the mobility, it is deduced that the decrease in conductivity as the temperature decreases is due to the decrease in number of mobile electrons.

Charge Transport in Quasi-One-Dimensional Electron System on Liquid Helium

We measured the electrical conductivities of quasi-one-dimensional (Q1D) electron systems on liquid helium surface as a function of temperature between 0.04 and 1.7 K. We prepared two kinds of the Q1D system with different materials. In the first system, the electrons were confined in a one-dimensional geometry on a suspended surface of liquid helium within multi channel made over plastic optical fibers. In the second system, the electrons were similarly confined in a single narrow channel made over metallic electrodes. In both systems, the electrical conductivity increased first with decreasing temperature, and passing through a maximum started to decrease. The magnitude of the maximum for the second system was much smaller than that of the first one. The peak temperature was 0.8 K for the first system and 1.2 K for the second system. From these results, we could deduce that the electrons localize near the edge of the channel at low temperature. This localization was possibly connected to the surface rou...