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Articles by Y. Saito
Total Records ( 8 ) for Y. Saito
  J.-A. Sauvaud , A. Fedorov , C. Aoustin , H.-C. Seran , E. Le Comte , M. Petiot , J. Rouzaud , Y. Saito , J. Dandouras , C. Jacquey , P. Louarn , C. Mazelle and J.-L. Medale
  Bepi Colombo is a joint mission between ESA and JAXA that is scheduled for launch in 2014 and arrival at Mercury in 2020. A comprehensive set of particle sensors will be flown onboard the two probes that form Bepi Colombo. These sensors will allow a detailed investigation of the structure and dynamics of the charged particle environment at Mercury. Onboard the Mercury Magnetospheric Orbiter (MMO) the Mercury Electron Analyzers (MEA) sensors constitute the experiment dedicated to fast electron measurements between 3 and 25,500 eV. They consist of two top-hat electrostatic analyzers for angle-energy analysis followed by microchannel plate multipliers and collecting anodes. A notable and new feature of MEA is that the transmission factor of each analyzer can be varied in-flight electronically by a factor reaching up to 100, thus allowing to largely increasing the dynamical range of the experiment. This capability is of importance at Mercury where large changes of electron fluxes are expected from the solar wind to the various regions of the Mercury magnetosphere. While the first models are being delivered to JAXA, an engineering model has been tested and proven to fulfill the expectations about geometrical factor reduction and energy-angular transmission characteristics. Taking advantage of the spacecraft rotation with a 4 s period, MEA will provide fast three-dimensional distribution functions of magnetospheric electrons, from energies of the solar wind and exospheric populations (a few eVs) up to the plasma sheet energy range (some tens of keV). The use of two sensors viewing perpendicular planes allows reaching a ¼ spin period time resolution, i.e., 1 s, to obtain a full 3D distribution.
  Y Takemoto , H Kawata , T Soeda , K Imagawa , S Somekawa , Y Takeda , S Uemura , M Matsumoto , Y Fujimura , J. i Jo , Y Kimura , Y Tabata and Y. Saito

Background— In-stent thrombosis is mainly triggered by adenosine diphosphate (ADP)-dependent platelet aggregation after percutanous coronary stent implantation. Ectonucleoside triphosphate diphosphohydrolase (E-NTPDase) rapidly hydrolyzes ADP to adenosine monophosphate, inhibiting platelet aggregation. We tested the hypothesis that local delivery of human placental E-NTPDase (pE-NTPDase) gene into injured arteries via gene-eluting stent could prevent subacute in-stent thrombosis.

Methods and Results— We generated gene-eluting stents by coating bare metal stents with cationic gelatin hydrogel containing pE-NTPDase cDNA (pE-NTPDase stent), and implanted the stents into rabbit femoral arteries (FA) prone to production of platelet-rich thrombi due to repeated balloon injury at 4-week intervals. After the second injury, E-NTPDase gene expression was severely decreased; however, the implantation of pE-NTPDase stent increased E-NTPDase mRNA levels and NTPDase activity to higher level than normal FA. The FAs with pE-NTPDase stents maintained patency in all rabbits (P<0.01), whereas the stent-implanted FAs without pE-NTPDase gene showed low patency rates (17% to 25%). The occlusive platelet-rich thrombi, excessive neointimal growth, and infiltration of macrophages were inhibited in stent implanted FA with pE-NTPDase gene, but not without pE-NTPDase gene.

Conclusions— Human pE-NTPDase gene transfer via cationic gelatin-coated stents inhibited subacute in-stent thrombosis and suppressed neointimal hyperplasia and inflammation without antiplatelet drugs.

  M.Z. Karim , S. Yokota , M.M. Rahman , J. Eizawa , Y. Saito , M.A.K. Azad , F. Ishiguri , K. Iizuka and N. Yoshizawa
  The optimum sucrose concentration and pH level were estimated for in vitro shoot regeneration from callus of Aralia elata Seem in a Broad-leaved tree (BT) medium with different concentrations of sucrose (0.0-25.0 g L-1) and a wide range of pH levels (4.5-6.8). The highest rate of shoot production was achieved in a shoot-regenerating medium with 15 g L-1 sucrose and a pH of 5.8. Shoot multiplication and growth were significantly affected by sucrose. Shoots were not formed in a sucrose-free medium. When the pH was adjusted below or above 5.8, the growth rate of the shoot significantly decreased.
  K Onoue , S Uemura , Y Takeda , S Somekawa , H Iwama , K Imagawa , T Nishida , Y Morikawa , Y Takemoto , O Asai , T Soeda , S Okayama , K Ishigami , K Nakatani , H Kawata , M Horii , T Nakajima , Y Akai , M Iwano and Y. Saito

Background— Renal dysfunction is commonly accompanied by a worsening of atherosclerosis; however, the underlying molecular mechanism is not fully understood. We examined the role played by soluble fms-like tyrosine kinase-1 (sFlt-1), an endogenous antagonist of the proatherogenic cytokine placental growth factor (PlGF), in the worsening of atherosclerosis in patients with renal dysfunction and in an animal model of renal failure.

Methods and Results— In this study, 329 patients who received cardiac catheterization and 76 patients who underwent renal biopsy were enrolled. Both plasma sFlt-1 levels and renal sFlt-1 mRNA expression were positively correlated with estimated glomerular filtration rate (P<0.01). The PlGF/sFlt-1 ratio was negatively correlated with estimated glomerular filtration rate (P<0.01), whereas plasma PlGF levels were not affected by it. The PlGF/sFlt-1 ratio was significantly higher in patients with multivessel coronary artery disease than in patients with single-vessel or no coronary artery disease. The reduction of circulating sFlt-1 and renal sFlt-1 mRNA levels was confirmed in five-sixths (5/6)–nephrectomized apolipoprotein E–deficient mice that developed experimental renal dysfunction. Atherosclerotic plaque area and macrophage infiltration into the plaque were significantly higher in 5/6–nephrectomized apolipoprotein E–deficient mice than in control mice, but replacement therapy with recombinant sFlt-1 significantly reduced both plaque formation and macrophage infiltration.

Conclusions— The present study demonstrates that a reduction in the circulating levels of sFlt-1 is associated with the worsening of atherosclerosis that accompanies renal dysfunction.

  M Matsuo , H Ebinuma , I Fukamachi , M Jiang , H Bujo and Y. Saito

Background: Vascular smooth muscle cells (SMCs) migrate from the arterial media to the intima in the progression of atherosclerosis, and dysfunction of SMCs leads to enhanced atherogenesis. A soluble form of the LDL receptor relative with 11 ligand-binding repeats (sLR11) is produced by the intimal SMCs, and the circulating concentrations of sLR11 likely reflect the pathophysiological condition of intimal SMCs. Furthermore, polymorphism of the LR11 gene has been found to be related to the onset of Alzheimer disease. This study describes the development of a sandwich immunoassay for quantifying sLR11 in human serum and cerebrospinal fluid.

Methods: We used synthetic peptides or DNA immunization to produce monoclonal antibodies (MAbs) A2-2–3, M3, and R14 against different epitopes of LR11.

Results: sLR11 was immunologically identified as a 250-kDa protein in human serum and cerebrospinal fluid by SDS-PAGE separation, and was purified from serum by use of a receptor-associated protein and MAb M3. An immunoassay for quantification of sLR11 with a working range of 0.25–4.0 µg/L was developed using the combination of MAbs M3 and R14. Treatment of serum with 5.25% n-nonanoyl-N-methyl-d-glucamine reduced the matrix effects of serum on the absorbance detection in the ELISA system. The linear dynamic range of the ELISA spanned the variation of circulating sLR11 concentrations in individuals with atherosclerosis.

Conclusions: A sandwich ELISA was established for quantifying sLR11 in serum and cerebrospinal fluid. This technique provides a novel means for assessing the pathophysiology of atherosclerosis, and possibly neurodegenerative diseases.

  S Somekawa , K Imagawa , N Naya , Y Takemoto , K Onoue , S Okayama , Y Takeda , H Kawata , M Horii , T Nakajima , S Uemura , N Mochizuki and Y. Saito

Aldosterone synthase (CYP11B2) and 11β-hydroxylase (CYP11B1) regulate aldosterone and cortisol production, respectively. The expression of these enzymes is promoted by calcium influx through Cav3.2, a T-type calcium channel. Neuron-restrictive silencer factor (NRSF) binds to neuron-restrictive silencer element (NRSE) to suppress the transcription of NRSE-containing genes. We found a NRSE-like sequence in human CYP11B2 and CYP11B1 genes as well as the CACNA1H gene of many mammalian species. The CACNA1H gene encodes the -subunit of Cav3.2. Here we investigated how NRSF/NRSE regulates aldosterone and cortisol synthesis. Inhibition of endogenous NRSF by an adenovirus-expressing dominant-negative NRSF (AD/dnNRSF) increased human CYP11B2 and CYP11B1 mRNA expression, leading to aldosterone and cortisol secretion in human adrenocortical (H295R) cells. In reporter gene experiments, NRSE suppressed luciferase reporters driven by CYP11B2 and CYP11B1 promoters and dnNRSF enhanced them. Moreover, cotransfection of dnNRSF increased luciferase activity of reporter genes after deletion or mutation of NRSE, suggesting that NRSF/NRSE regulates transcription of CYP11B2 and CYP11B1 genes indirectly. AD/dnNRSF augmented mRNA expression of rat CYP11B2 and CYP11B1 genes, neither of which contains a NRSE-like sequence in rat adrenal cells. AD/dnNRSE also significantly increased CACNA1H mRNA in H295R and rat adrenal cells. Efonidipine, a T/L-type calcium channel blocker, significantly suppressed dnNRSF-mediated up-regulation of CYP11B2 and CYP11B1 expression. Moreover, NRSF/NRSE is also involved in angiotensin II- and K+-stimulated augmentation of CYP11B2 and CYP11B1 gene transcription. In conclusion, NRSF/NRSE controls aldosterone and cortisol synthesis by regulating CYP11B2 and CYP11B1 gene transcription mainly through NRSF/NRSE-mediated enhancement of the CACNA1H gene.

  M.Z. Karim , S. Yokota , M.M. Rahman , J. Eizawa , Y. Saito , M.A.K. Azad , F. Ishiguri , K. Iizuka and N. Yoshizawa
  A highly reproducible in vitro shoot regeneration system in Aralia elata Seem. using root explants was developed in this investigation. Multiple shoots were induced in vitro directly from root explants through adventitious shoot bud regeneration. The ability of root explants to produce shoot buds depended on the supplementation of Plant Growth Regulators (PGRs). Maximum multiplication of shoots (18 shoots per explant) was achieved in a Broad-leaved Tree (BT) medium supplemented with 1.00 μM 6-benzyl aminopurine (BAP). The best and healthiest rooting was observed in a BT medium supplemented with 2.00 μM μ-naphthaleneacetic acid (NAA). Regenerated plants were successfully acclimatized under ex vitro condition.
  Y. Saito , X. Shen , K. Mishima and M. Matsubayashi

Dynamic behavior of a two-phase bubble, i.e. a steam bubble containing a droplet evaporating in the bubble, in the molten alloy was clearly visualized using high-frame-rate neutron radiography. In relation to some direct contact heat exchanger design with molten lead–bismuth (Pb–Bi), experiments have been done at JRR-3M of JAEA (Japan Atomic Energy Agency) with water droplets evaporating in a stable thermally stratified Newton's alloy pool. The instantaneous shape and size of the bubble has been iteratively estimated from the void fraction distributions and total void volume by assuming a symmetrical bubble shape.

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