Toshihide Yamasaki
Kyushu University
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Toshihide Yamasaki.
Free Radical Biology and Medicine | 2012
Yuta Matsuoka; Mayumi Yamato; Toshihide Yamasaki; Fumiya Mito; Ken-ichi Yamada
Ascorbic acid is a small-molecule reductant with multiple functions in vivo. Reducing ascorbic acid intake leads to a lack of hydroxylation of prolines and lysines, causing a looser triple helix and resulting in scurvy. Ascorbic acid also acts as an antioxidant to prevent oxidative stress. Because ascorbic acid is related to disease states, rapid and convenient detection of ascorbic acid should be useful in diagnosis. Nitroxide is reduced to the corresponding hydroxylamine by ascorbic acid and a sensitive and novel approach to its detection employs covalent coupling of nitroxide with a fluorophore, leading to intramolecular quenching of fluorescence emission by electron-exchange interactions. Here, we developed a new fluorophore-nitroxide probe, Naph-DiPy nitroxide, for ascorbic acid. Naph-DiPy nitroxide rapidly reacted with ascorbic acid and showed fluorescence enhancement, but not in response to other reductants or reactive oxygen species. To confirm the practical usefulness of the fluorophore-nitroxide probe, we demonstrated the use of Naph-DiPy nitroxide for the measurement of ascorbic acid in the plasma of osteogenic disorder Shionogi rats when fed an ascorbic acid-deficient diet. The results suggest that this novel fluorophore-nitroxide probe could sensitively and easily detect ascorbic acid and be useful as a tool for the diagnosis of disease states.
Free Radical Biology and Medicine | 2010
Yuichi Kinoshita; Ken-ichi Yamada; Toshihide Yamasaki; Fumiya Mito; Mayumi Yamato; Nuttavut Kosem; Hisato Deguchi; Chisato Shirahama; Yuko Ito; Kana Kitagawa; Nobuhisa Okukado; Kiyoshi Sakai; Hideo Utsumi
Nitroxyl radicals (nitroxide) have great potential advantages as spin probes, antioxidants, contrast agents, and radiation-protecting agents. However, they are readily reduced by reductants in cells and lose their paramagnetic nature. Recently, tetraethyl-substituted nitroxyl radicals have been reported to have high stability toward reduction by ascorbic acid (AsA). We report the general considerations of tetraethyl nitroxyl radicals for in vivo application. The reason for the low reactivity to AsA reduction was the positive value of Gibbs energy between the tetraethyl nitroxyl radical and AsA. Further, these compounds had an inhibitory effect on lipid peroxidation despite having AsA resistance. They had low antiproliferative effects in HepG2 cells and HUVECs and did not have a lowering effect on blood pressure in animals. Further, after intravenous injection, the ESR signal intensities of tetraethyl-substituted piperidine nitroxyl radicals were very stable in mice over 20 min. These results suggest that tetraethyl-substituted nitroxyl radicals have stability against bioreduction with reductants such as AsA and confer onto them features as antioxidants and paramagnetic tracers/contrast agents. Hence, they will be useful in identifying the foci of oxidative stress in vivo using redox-based imaging approaches.
PLOS ONE | 2015
Masataka Ikeda; Tomomi Ide; Takeo Fujino; Shinobu Arai; Keita Saku; Takamori Kakino; Henna Tyynismaa; Toshihide Yamasaki; Ken-ichi Yamada; Dongchon Kang; Anu Suomalainen; Kenji Sunagawa
Background Mitochondrial DNA (mtDNA) copy number decreases in animal and human heart failure (HF), yet its role in cardiomyocytes remains to be elucidated. Thus, we investigated the cardioprotective function of increased mtDNA copy number resulting from the overexpression of human transcription factor A of mitochondria (TFAM) or Twinkle helicase in volume overload (VO)-induced HF. Methods and Results Two strains of transgenic (TG) mice, one overexpressing TFAM and the other overexpressing Twinkle helicase, exhibit an approximately 2-fold equivalent increase in mtDNA copy number in heart. These TG mice display similar attenuations in eccentric hypertrophy and improved cardiac function compared to wild-type (WT) mice without any deterioration of mitochondrial enzymatic activities in response to VO, which was accompanied by a reduction in matrix-metalloproteinase (MMP) activity and reactive oxygen species after 8 weeks of VO. Moreover, acute VO-induced MMP-2 and MMP-9 upregulation was also suppressed at 24 h in both TG mice. In isolated rat cardiomyocytes, mitochondrial reactive oxygen species (mitoROS) upregulated MMP-2 and MMP-9 expression, and human TFAM (hTFAM) overexpression suppressed mitoROS and their upregulation. Additionally, mitoROS were equally suppressed in H9c2 rat cardiomyoblasts that overexpress hTFAM or rat Twinkle, both of which exhibit increased mtDNA copy number. Furthermore, mitoROS and mitochondrial protein oxidation from both TG mice were suppressed compared to WT mice. Conclusions The overexpression of TFAM or Twinkle results in increased mtDNA copy number and facilitates cardioprotection associated with limited mitochondrial oxidative stress. Our findings suggest that increasing mtDNA copy number could be a useful therapeutic strategy to target mitoROS in HF.
Free Radical Biology and Medicine | 2014
Tracey Kajer; Kathryn E. Fairfull-Smith; Toshihide Yamasaki; Ken-ichi Yamada; Shanlin Fu; Steven E. Bottle; Clare L. Hawkins; Michael J. Davies
The powerful oxidant HOCl (hypochlorous acid and its corresponding anion, (-)OCl) generated by the myeloperoxidase (MPO)-H2O2-Cl(-) system of activated leukocytes is strongly associated with multiple human inflammatory diseases; consequently there is considerable interest in inhibition of this enzyme. Nitroxides are established antioxidants of low toxicity that can attenuate oxidation in animal models, with this ascribed to superoxide dismutase or radical-scavenging activities. We have shown (M.D. Rees et al., Biochem. J. 421, 79-86, 2009) that nitroxides, including 4-amino-TEMPO (4-amino-2,2,6,6-tetramethylpiperidin-1-yloxyl radical), are potent inhibitors of HOCl formation by isolated MPO and activated neutrophils, with IC50 values of ~1 and ~6 µM respectively. The utility of tetramethyl-substituted nitroxides is, however, limited by their rapid reduction by biological reductants. The corresponding tetraethyl-substituted nitroxides have, however, been reported to be less susceptible to reduction. In this study we show that the tetraethyl species were reduced less rapidly than the tetramethyl species by both human plasma (89-99% decreased rate of reduction) and activated human neutrophils (62-75% decreased rate). The tetraethyl-substituted nitroxides retained their ability to inhibit HOCl production by MPO and activated neutrophils with IC50 values in the low-micromolar range; in some cases inhibition was enhanced compared to tetramethyl substitution. Nitroxides with rigid structures (fused oxaspiro rings) were, however, inactive. Overall, these data indicate that tetraethyl-substituted nitroxides are potent inhibitors of oxidant formation by MPO, with longer plasma and cellular half-lives compared to the tetramethyl species, potentially allowing lower doses to be employed.
Archiv Der Pharmazie | 2008
Ken-ichi Yamada; Yuichi Kinoshita; Toshihide Yamasaki; Hiromi Sadasue; Fumiya Mito; Mika Nagai; Shingo Matsumoto; Mariko Aso; Hiroshi Suemune; Kiyoshi Sakai; Hideo Utsumi
Non‐invasive measurement and visualization of free radicals in vivo would be important to clarify their roles in the pathogenesis of free radical‐associated diseases. Nitroxyl radicals can react with free radicals and be derivatized to achieve specific cellular / subcellular localizing capabilities while retaining the simple spectral features useful in imaging. Overhauser‐enhanced magnetic resonance imaging (OMRI), which is a double resonance technique, creates images of free radical distributions in small animals by enhancing the water proton signal intensity via the Overhauser Effect. In this study, we synthesized various nitroxyl probes having 15N nuclei and deuterium, and measured the enhancement factor for Overhauser‐enhanced magnetic resonance imaging experiments. 15N‐D‐4‐Oxo‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (15N‐D‐oxo‐TEMPO) has the highest enhancement factor compared with other nitroxyl probes. The proton signal enhancement was higher for 15N‐labeled nitroxyl probes when compared to the 14N‐labeled analogues because of the reduced spectral multiplicity of the I = 1/2 nucleus. Furthermore, this enhancement is proportional to the line width and number of electron spin resonance lines of nitroxyl radicals. Finally, we compared the Overhauser‐enhanced magnetic resonance image of 15N‐labeled, deuterated 4‐Oxo‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl with that of 14N‐H‐TEMPOL. These results suggested that the selective deuteration of the nitroxyl probes enhanced the signal‐to‐noise ratio and thereby improved spatial and temporal resolutions.
Free Radical Research | 2011
Miho C. Emoto; Fumiya Mito; Toshihide Yamasaki; Ken-ichi Yamada; Hideo Sato-Akaba; Hiroshi Hirata; Hirotada Fujii
Abstract The loss of paramagnetism of nitroxide radicals due to reductant reactions in biological systems, places a fundamental time constraint on their application as an imaging probe in in vivo EPR imaging studies. However, in vitro studies of the newly synthesized tetraethyl-substituted piperidine nitroxide radical demonstrated high resistivity to paramagnetic reduction when exposed to ascorbic acid, a common reduction agent in biological systems. In this work we investigated the use of these nitroxides as an imaging probe in EPR imaging of small rodents. 2,2,6,6-Tetraethyl-piperidine nitroxide (TEEPONE) is not highly soluble in aqueous media, thus a lipid-based emulsion system of lecithin was used to solubilize TEEPONE. The obtained solution was homogenous and with low viscosity, allowing smooth intravenous injection into mice tail vein. Acquired three dimensional (3D) EPR images of mouse head clearly showed TEEPONE distributed in all tissues including brain tissues, with an average measurable signal half-life of more than 80 min, thus demonstrating high resistivity to reduction due to ascorbic acid in in vivo animal studies, and the potential for use of this compound in in vivo studies of animal model systems.
Free Radical Biology and Medicine | 2011
Hisato Deguchi; Keiji Yasukawa; Toshihide Yamasaki; Fumiya Mito; Yuichi Kinoshita; Tatsuya Naganuma; Suguru Sato; Mayumi Yamato; Kazuhiro Ichikawa; Kiyoshi Sakai; Hideo Utsumi; Ken-ichi Yamada
Nonsteroidal anti-inflammatory drugs are the drugs of choice in the treatment of rheumatoid arthritis (RA) because of their rapid analgesic effect. However, they induce severe gastric damage in RA patients and animals by a process mediated by reactive oxygen species (ROS). Nitroxides (nitroxyl radicals) are widely used as imaging agents and antioxidants to explore the role of ROS generation in the pathogenesis of disease. In this study, the effectiveness of the newly synthesized nitroxides 8-aza-7,7,9,9-tetramethyl-1,4-dioxaspiro[4.5]undecan-8-oxyl (compound 1) and 4-oxo-2,2,6,6-tetraethylpiperidine-1-oxyl (compound 2) in the prevention of gastric ulcers in adjuvant arthritis rats treated with indomethacin was evaluated by monitoring the reaction of reactive oxygen species in gastric tissue with Overhauser-enhanced magnetic resonance imaging (OMRI). Pretreatment with all tested nitroxides suppressed the ulcers induced by indomethacin treatment in arthritic rats. OMRI using compounds 1 and 2 as well as 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) demonstrated a redox imbalance in the stomach of these rats. Lipid peroxide and interleukin (IL)-1β levels in the gastric mucosa were significantly suppressed by compound 1 and TEMPOL, whereas CINC/gro, a member of the IL-8 family, was significantly suppressed by compound 1 only. These results suggest that the preventive effects of nitroxides on gastric ulcers may operate by different mechanisms.
Chemical Communications | 2011
Fumiya Mito; Toshihide Yamasaki; Yuko Ito; Mayumi Yamato; Hiroyuki Mino; Hiromi Sadasue; Chisato Shirahama; Kiyoshi Sakai; Hideo Utsumi; Ken-ichi Yamada
Amyloid nitroxyl radical (nitroxide) ligands were used to detect amyloid-β fibrils, the main constituents of senile plaques in Alzheimers disease, using anisotropic ESR spectra, and were found to affect the aggregation process due to the radical functionality. These compounds have great potential as novel and multifunctional probes, combining spin labels, spin probes, and fluorescence probes.
Journal of Organic Chemistry | 2011
Toshihide Yamasaki; Yuko Ito; Fumiya Mito; Kana Kitagawa; Yuta Matsuoka; Mayumi Yamato; Ken-ichi Yamada
Nitroxides have antioxidative activities toward lipid peroxidation, but the influence of steric factors is not known. We synthesized alkyl-substituted nitroxides at the α-position of the N-O moiety to enhance lipophilicity and the bulk effect. There was good correlation between the IC(50) and lipophilicity (log P(o/w)) of nitroxides with use of the thiobarbituric acid-reactive substances (TBARS) assay. Furthermore, an inhibitory effect on the TBARS assay was dependent upon the number and length of alkyl groups, though nitroxides had almost identical lipophilicity.
Free Radical Research | 2011
Fumiya Mito; Kana Kitagawa; Toshihide Yamasaki; Chisato Shirahama; Taketoshi Oishi; Yuko Ito; Mayumi Yamato; Ken-ichi Yamada
Abstract Lipid-derived radicals and peroxides are involved in the pathogenesis of oxidative stress diseases and, although lipid peroxide production is a required reaction between a lipid radical and molecular oxygen, a useful lipid radical detection method has remained tentative. Also, the effect of oxygen concentration on lipid peroxide production must be considered because of the hypoxic conditions in cancer and ischemic regions. In this study, the focus was on nitroxide reactivity, which allows spin trapping with carbon-centred radicals via radical–radical reactions and fluorophore quenching through interactions with nitroxides unpaired electron. Thus, the aim here was to demonstrate a useful detection method for lipid-derived radicals as well as to clarify the effects of oxygen concentration on lipid peroxide production using profluorescent nitroxide. This latter compound reacted with lipid-derived radicals in a manner inversely dependent on oxygen concentration, resulting in fluorescence due to alkoxyamine formation and, conversely, lipid peroxide concentrations decreased with lower oxygen in the reaction system. Furthermore, nitroxide inhibited lipid peroxide production and stopped oxygen consumption in the same solution. These results suggested that the novel application of profluorescent nitroxide could directly and sensitively detect lipid-derived radicals and that radical and peroxide production were dependent on oxygen concentration.