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Furukawa H, Nitta S, Hioki M, Iwasaki T, Itoh T, Nonomura S. Refinement of Plas Samples by Using Afm Image and First Observation of Plas Signals on Amorphous Carbon Nitridea-CNx Films. ACTA ACUST UNITED AC 2011. [DOI: 10.1557/proc-507-465] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
ABSTRACTThe shape of several waveguide end of samples for photoluminescence absorption spectroscopy (PLAS) was studied by atomic force microscope (AFM), because there was an experimental problem where some samples for PLAS did not work. Using the result of AFM, the waveguide end was reshaped by plasma dry etching. The shortening of the etching time was an effective method to improve the structure of the waveguide end. Secondly, the PLAS method was extended to the other materials from a-Si:H. The PLAS signal of amorphous carbon nitride a-CNx was detected for the first time. Amorphous carbon nitride a-CNx film itself and the interface between a-CNx and a-Si02 are found as good as a-Si:H and the interface between a-Si:H and a-Si 3N4+x:H, respectively.
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Takita M, Matsumoto S, Noguchi H, Shimoda M, Chujo D, Itoh T, Sugimoto K, Tamura Y, Olsen GS, Naziruddin B, Onaca N, Levy MF. Secretory unit of islet transplant objects (SUITO) index can predict outcome of intravenous glucose tolerance test. Transplant Proc 2011; 42:2065-7. [PMID: 20692409 DOI: 10.1016/j.transproceed.2010.05.102] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
BACKGROUND Simple monitoring of engrafted islet function is important for follow-up of recipients after islet transplantation. We previously developed a simple assessment tool for islet graft function; the secretory unit of islet transplant objects (SUITO) index. The aim of this study was to clarify the relationship between the SUITO index and the outcomes of intravenous glucose tolerance tests (IVGTT). METHODS Fifteen series of blood samples from 6 islet recipients were collected before 3, 5, 10, 20, and 30 minutes after injection of 0.5 g/kg 50% dextrose. The SUITO index was calculated using plasma C-peptide and glucose level at fasting baseline. Samples were divided into the following 3 groups; low-SUITO (SUITO index <10; n = 3); middle-SUITO (SUITO index > or =10 to <26; n = 4); and high-SUITO (SUITO index > or =26; n = 8). RESULTS A threshold SUITO index of 26 showed good sensitivity (85.7%) and specificity (75.0%) to predict a blood glucose level of >10 mmol/L at 30 minutes. Blood glucose levels in the low-SUITO group were significantly higher than among the other 2 groups at baseline and 10, 20 and 30 minutes (P < .05). Glucose-level areas under the receiver-operating characteristic curve during IVGTT in the low-SUITO group were also significantly larger than among the other 2 groups (P < .05). CONCLUSION The SUITO index, using only a fasting blood sample, predicted IVGTT outcomes.
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Shimoda M, Noguchi H, Naziruddin B, Fujita Y, Chujo D, Takita M, Peng H, Tamura Y, Olsen GS, Sugimoto K, Itoh T, Onaca N, Levy MF, Grayburn PA, Matsumoto S. Assessment of human islet isolation with four different collagenases. Transplant Proc 2011; 42:2049-51. [PMID: 20692404 DOI: 10.1016/j.transproceed.2010.05.093] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
BACKGROUND The isolation of islets from the human pancreas critically depends on the efficiency of the digestive enzymes. Liberase HI had been used as a standard preparation until the issues concerning bovine spongiform encephalopathy. Thus, we must now use other collagenases for clinical islet transplantation, four of which we have evaluated herein. METHODS The digestion of each of 17 pancreata from brain-dead donors was performed using the following collagenases: Liberase HI (HI; Roche, n = 9); Liberase MTF C/T (MTF; Roche, n = 4); Collagenase NB1 Premium Grade (NB1; Serva, n = 7); or Clzyme Collagenase HA (CI, VitaCyte, n = 4). Islet isolations were based on the Edmonton protocol for HI, whereas our modified islet isolation method was used for the three new enzymes (MTF, NB1, and CI). RESULTS There were no significant differences in donor age, body mass index, pancreas size, and cold ischemic time among the four groups. The phase I time in the NB1 group was significantly shorter than in the CI group (P = .0014). The prepurification IEQ/g in the HI group was significantly lower than the others (P = .0003 vs MTF, .0007 vs NB1, and .0009 vs CI, respectively). The postpurification IEQ/g in the MTF group was significantly higher than in the HI group (P = .006). The viability in the NB1 group was significantly greater than the HI group (P = .003). CONCLUSION Three new enzymes (MTF, NB1, and CI) may enable us to obtain higher islet yields than with HI.
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Itoh T, Shimomura T, Hasegawa Y, Mizuguchi J, Hanaoka T, Hayashi A, Yamaguchi A, Teramae N, Ono M, Mizukami F. Assembly of an artificial biomembrane by encapsulation of an enzyme, formaldehyde dehydrogenase, into the nanoporous-walled silica nanotube–inorganic composite membrane. ACTA ACUST UNITED AC 2011. [DOI: 10.1039/c0jm01523g] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Takamatsu S, Kobayashi T, Imai T, Yamashita T, Itoh T. All Polymer Piezoelectric Film for the Application to Low Resonance Frequency Energy Harvester. ACTA ACUST UNITED AC 2011. [DOI: 10.1016/j.proeng.2011.12.050] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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Imano M, Imamoto H, Itoh T, Satou T, Peng Y, Yasuda A, Kato H, Nishiki K, Shiraishi O, Shinkai M, Tsubaki M, Yasuda T, Nishida S, Takeyama Y, Okuno K, Shiozaki H. Impact of Intraperitoneal Chemotherapy after Gastrectomy with Positive Cytological Findings in Peritoneal Washings. Eur Surg Res 2011; 47:254-259. [DOI: 10.1159/000333803] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/30/2023]
Abstract
<i>Background:</i> There is no standard treatment available for gastric cancer patients whose sole ‘non-curative factor’ is positivecytological findings in peritoneal washings (CFPW). The aim of this study was to examine the safety, pharmacokinetics and efficacy for free intraperitoneal cancer cells of intraperitoneal chemotherapy with paclitaxel after gastrectomy with en bloc D2 lymph node dissection in cases of gastric cancer with positive CFPW. <i>Methods:</i> Ten patients with gastric cancer who underwent gastrectomy and systemic lymphadenectomy with D2 dissection, without any other non-curative factors besides positive CFPW, were treated with early postoperative intraperitoneal paclitaxel. Intra-chemotherapeutic toxicity and operative complications were measured using NCI-CTC version 3.0. Intraperitoneal and plasma paclitaxel concentrations were measured using a high-performance liquid chromatographic assay. <i>Results:</i> Grade 3/4 toxic effects included anemia (20%) and neutropenia (10%) that required no treatment. Operative complications were, for example, superficial surgical site infections (10%) that were treated with antibiotics. No viable cancer cells were observed in the intra-abdominal fluid 24 h after intraperitoneal administration of paclitaxel. The intraperitoneal/plasma area under the drug concentration-time curve ratio was 2,003.3:1. <i>Conclusion:</i> Intraperitoneal chemotherapy with paclitaxel is a safe and effective treatment modality for free intraperitoneal cancer cells.
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Itoh T, Miyake K, Yamaguchi T, Tsuge M, Kaneoka H, Iijima S. Constitutive expression of the brg1 gene requires GC-boxes near to the transcriptional start site. J Biochem 2010; 149:301-9. [DOI: 10.1093/jb/mvq145] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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Shimoda M, Noguchi H, Naziruddin B, Fujita Y, Chujo D, Takita M, Peng H, Tamura Y, Olsen G, Sugimoto K, Itoh T, Onaca N, Levy M, Grayburn P, Matsumoto S. Improved Method of Human Islet Isolation for Young Donors. Transplant Proc 2010; 42:2024-6. [DOI: 10.1016/j.transproceed.2010.05.094] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Noguchi H, Naziruddin B, Shimoda M, Fujita Y, Chujo D, Takita M, Peng H, Sugimoto K, Itoh T, Tamura Y, Olsen GS, Kobayashi N, Onaca N, Hayashi S, Levy MF, Matsumoto S. Induction of insulin-producing cells from human pancreatic progenitor cells. Transplant Proc 2010; 42:2081-3. [PMID: 20692413 DOI: 10.1016/j.transproceed.2010.05.097] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
INTRODUCTION We previously established a mouse pancreatic stem cell line without genetic manipulation. In this study, we sought to identify and isolate human pancreatic stem/progenitor cells. We also tested whether growth factors and protein transduction of pancreatic and duodenal homeobox factor-1 (PDX-1) and BETA2/NeuroD into human pancreatic stem/progenitor cells induced insulin or pancreas-related gene expressions. MATERIALS AND METHOD Human pancreata from brain-dead donors were used for islet isolation with the standard Ricordi technique modified by the Edmonton protocol. The cells from a duct-rich population were cultured in several media, based on those designed for mouse pancreatic or for human embryonic stem cells. To induce cell differentiation, cells were cultured for 2 weeks with exendin-4, nicotinamide, keratinocyte growth factor, PDX-1 protein, or BETA2/NeuroD protein. RESULTS The cells in serum-free media showed morphologies similar to a mouse pancreatic stem cell line, while the cells in the medium for human embryonic stem cells formed fibroblast-like morphologies. The nucleus/cytoplasm ratios of the cells in each culture medium decreased during the culture. The cells stopped dividing after 30 days, suggesting that they had entered senescence. The cells treated with induction medium differentiated into insulin-producing cells, expressing pancreas-related genes. CONCLUSION Duplications of cells from a duct-rich population were limited. Induction therapy with several growth factors and transduction proteins might provide a potential new strategy for induction of transplantable insulin-producing cells.
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Ishii N, Uemura M, Itoh T, Horiki N, Setoyama T, Matsuda M, Suzuki S, Iizuka Y, Fukuda K, Fujita Y. Endoscopic band ligation for the treatment of bleeding colonic and ileal diverticula. Endoscopy 2010; 42 Suppl 2:E82-3. [PMID: 20195977 DOI: 10.1055/s-0029-1243828] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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Suzuki K, Okada H, Itoh T, Tada T, Tsukamoto K. Phenotypes influencing the transmissibility of highly pathogenic avian influenza viruses in chickens. J Gen Virol 2010; 91:2302-6. [DOI: 10.1099/vir.0.023267-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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Mizoguchi Y, Hirano T, Itoh T, Aso H, Takasuga A, Sugimoto Y, Watanabe T. Differentially expressed genes during bovine intramuscular adipocyte differentiation profiled by serial analysis of gene expression. Anim Genet 2010; 41:436-41. [PMID: 20219066 DOI: 10.1111/j.1365-2052.2010.02022.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Beef marbling or intramuscular fat deposition is an economically important carcass trait in Japanese Black cattle. To investigate genes involved in intramuscular adipogenesis, differential gene expression during adipogenesis in a clonal bovine intramuscular preadipocyte (BIP) cell line was profiled with serial analysis of gene expression (SAGE). We sequenced 75 283 tags for the proliferation phase (day 0) and 81 878 tags for the differentiation phase (4 days after adipogenic stimulation: day 4). A comparison of the unique SAGE tag frequencies between the day 0- and day 4-libraries revealed that 878 (2.8%) of the 30 989 unique putative transcripts were expressed at significantly different levels (P < 0.05); 401 tags (1.4%) were up-regulated and 477 tags (1.2%) were down-regulated in the day 4-library relative to the day 0-library. We confirmed up-regulation of 10 tags of the genes that were up-regulated in the previous subtraction cloning studies in BIP cells [Animal Science Journal, 76 (2005) 479]. Of the 878 differentially expressed tags, 377 were identified in the bovine RefSeq library and 356 were assigned a bovine draft genomic sequence. Fifteen tags were mapped in previously detected beef marbling quantitative trait loci (QTL) regions [Mammalian Genome, 18 (2007) 125]. These genes may be involved in the adipogenic processes of beef marbling.
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Numata Y, Itoh T, Omokawa T, Okuyama K. S1←S0 hole-burning spectroscopy of jet-cooled dithienylethylene and dithienylbutadiene vapors. Chem Phys Lett 2010. [DOI: 10.1016/j.cplett.2010.02.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Akao Y, Nakagawa Y, Hirata I, Iio A, Itoh T, Kojima K, Nakashima R, Kitade Y, Naoe T. Role of anti-oncomirs miR-143 and -145 in human colorectal tumors. Cancer Gene Ther 2010; 17:398-408. [PMID: 20094072 DOI: 10.1038/cgt.2009.88] [Citation(s) in RCA: 197] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
We examined the expression levels of microRNAs (miRNAs (miRs)) in colorectal tumors (63 cancer specimens and 65 adenoma specimens) and paired non-tumorous tissues. Decreased expression of miR-143 and -145 was frequently observed in the adenomas and cancers tested, compared with miR-34a downregulation and miR-21 upregulation. Expression profiles of miR-143 and -145 were not associated with any clinical features. As the downregulation of miR-143 and -145 was observed even in the early phase of adenoma formation, the decreased expression of both miRs would appear to contribute mainly to the initiation step of tumorigenesis, not to the progression stage, and not to clinical prognostic factors. For clinical application, we changed the sequences of the passenger strand in the miR-143 duplex and performed chemical modification at the 3'-overhang portion of miR-143, leading to greater activity and stability to nuclease. The cell growth inhibitory effect of the chemically modified synthetic miR-143 in vitro was greater than that of endogenous miR-143. The miR-143 showed a significant tumor-suppressive effect on xenografted tumors of DLD-1 human colorectal cancer cells. These findings suggest that miR-143 and -145 are important onco-related genes for the initiation step of colorectal tumor development and that the chemically modified synthetic miR-143 may be a hopeful candidate as an RNA medicine for the treatment of colorectal tumors.
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Nakagawa N, Shimakawa K, Itoh T, Ikeda Y. Dynamics of principal photoinduced effects in amorphous chalcogenides:In-situsimultaneous measurements of photodarkening, volume changes, and defect creation. ACTA ACUST UNITED AC 2010. [DOI: 10.1002/pssc.200982753] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Okumura T, Ariyoshi K, Hitomi T, Hirahara K, Itoh T, Iwamura T, Nakashima A, Motomura Y, Taki K, Suzuki K. Lessons learned from nerve agent attacks in Iran and Japan: Is it really necessary to stockpile oximes? TOXIN REV 2009. [DOI: 10.3109/15569540903338040] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Mizukami W, Kurashige Y, Ehara M, Yanai T, Itoh T. Ab initiostudy of the excited singlet states of all-transα,ω-diphenylpolyenes with one to seven polyene double bonds: Simulation of the spectral data within Franck–Condon approximation. J Chem Phys 2009; 131:174313. [DOI: 10.1063/1.3261729] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Itoh T. Emission spectra of 3,4- and 3,5-difluorobenzaldehyde vapors: Conformer-specific phosphorescence from the 3,4-derivative. J Mol Struct 2009. [DOI: 10.1016/j.molstruc.2009.08.030] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Itoh T, Numata Y. Spectroscopy and Photophysics of Low-Lying Excited Singlet States of α,ω-Dithienylbutadiene and α,ω-Dithienylethylene Vapors. J Phys Chem A 2009; 113:10160-6. [DOI: 10.1021/jp901180a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Itoh T. Electronic relaxation processes ofall-trans-2,4,6,8-decatetraene vapour revealed by the measurements of the S1and S2fluorescence. Mol Phys 2009. [DOI: 10.1080/00268970903029115] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Aoyagi T, Yamashita K, Suzuki T, Uno M, Goto R, Taniguchi M, Shimamura T, Takahashi N, Miura T, Okimura K, Itoh T, Shimizu A, Furukawa H, Todo S. A human anti-CD40 monoclonal antibody, 4D11, for kidney transplantation in cynomolgus monkeys: induction and maintenance therapy. Am J Transplant 2009; 9:1732-41. [PMID: 19519810 DOI: 10.1111/j.1600-6143.2009.02693.x] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Blockade of CD40-CD154 signaling pathway is an attractive strategy to induce potent immunosuppression and tolerance in organ transplantation. Due to its strong immunosuppressive effect shown in nonhuman primate experiments, anti-CD154 monoclonal antibodies (mAbs) have been tried in clinical settings, but it was interrupted by unexpected thromboembolic complications. Thus, inhibition of the counter molecule, CD40, has remained an alternative approach. In the previous preliminary study, we have shown that 4D11, a novel fully human anti-CD40 mAb, has a fairly potent immunosuppressive effect on kidney allograft in nonhuman primates. In this study, we aimed to confirm the efficacy and untoward events of the 2-week induction and 180-day maintenance 4D11 treatments. In both, 4D11 significantly suppressed T-cell-mediated alloimmune responses and prolonged allograft survival. Addition of weekly 4D11 administration after the induction treatment further enhanced graft survival. Complete inhibition of both donor-specific Ab and anti-4D11 Ab productions was obtained only with higher-dose maintenance therapy. No serious side effect including thromboembolic complications was noted except for a transient reduction of hematocrit in one animal, and decrease of peripheral B-cell counts in all. These results indicate that the 4D11 appears to be a promising candidate for immunosuppression in clinical organ transplantation.
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Kajikuri J, Watanabe Y, Ito Y, Ito R, Yamamoto T, Itoh T. Characteristic changes in coronary artery at the early hyperglycaemic stage in a rat type 2 diabetes model and the effects of pravastatin. Br J Pharmacol 2009; 158:621-32. [PMID: 19645710 DOI: 10.1111/j.1476-5381.2009.00348.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND AND PURPOSE Diabetes is a risk factor for the development of coronary artery disease but it is not known whether the functions of endothelium-derived nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) in coronary arteries are altered in the early stage of diabetes. Such alterations and the effects of pravastatin were examined in left anterior descending coronary arteries (LAD) from Otsuka Long-Evans Tokushima Fatty (OLETF) rats (type 2 diabetes model) at the early hyperglycaemic stage [vs. non-diabetic Long-Evans Tokushima Otsuka (LETO) rats]. EXPERIMENTAL APPROACH Isometric tension, membrane potential and superoxide production were measured, as were protein expression of NAD(P)H oxidase components and endothelial NO synthase (eNOS). KEY RESULTS Superoxide production and the protein expressions of both the nicotinamide adenine dinucleotide (phosphate) [NAD(P)H] oxidase components and eNOS were increased in OLETF rats. These changes were normalized by pravastatin administration. Not only acetylcholine (ACh)-induced endothelial NO production but also functions of endothelium-derived NO [from (i) the absolute tension induced by epithio-thromboxane A(2) (STA(2)) or high K(+); (ii) enhancement of the STA(2)-contraction by a nitric oxide synthase (NOS) inhibitor; and (iii) the ACh-induced endothelium-dependent relaxation of high K(+)-induced contraction] or EDHF [from (iv) ACh-induced endothelium-dependent smooth muscle cell hyperpolarization and relaxation in the presence of a NOS inhibitor] were similar between LETO and OLETF rats [whether or not the latter were pravastatin-treated or -untreated]. CONCLUSIONS AND IMPLICATIONS Under conditions of increased vascular superoxide production, endothelial function is retained in LAD in OLETF rats at the early hyperglycaemic stage, partly due to enhanced endothelial NOS protein expression. Inhibition of superoxide production may contribute to the beneficial vascular effects of pravastatin.
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Yang Y, Itoh T, Yokobori SI, Itahashi S, Shimada H, Satoh K, Ohba H, Narumi I, Yamagishi A. Deinococcus aerius sp. nov., isolated from the high atmosphere. Int J Syst Evol Microbiol 2009; 59:1862-6. [DOI: 10.1099/ijs.0.007963-0] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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Miyajima K, Kagotani Y, Saito S, Ashida M, Itoh T. Superfluorescent pulsed emission from biexcitons in an ensemble of semiconductor quantum dots. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:195802. [PMID: 21825497 DOI: 10.1088/0953-8984/21/19/195802] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Picosecond time-resolved photoluminescence from biexcitons in CuCl quantum dots (QDs) embedded in a NaCl matrix has been measured using an optical Kerr gate method. Ultrafast pulsed emission from the biexciton states was observed for the first time, only under resonant two-photon excitation of biexcitons. This implies that complete population inversion between the biexciton and exciton states is necessary in order to trigger the pulsed emission. In addition, the nature of the dependence of the time profiles of the pulsed emission on the excitation intensity reveals that the peak intensity is directly proportional to the square of the number of excited QDs. We conclude that this phenomenon is caused by superfluorescence, that is, the cooperative spontaneous radiative decay of many isolated excited states coupled by a resonant electromagnetic wave. Such a phenomenon has been observed for the first time in an ensemble of semiconductor QDs in this study. The results presented in this paper show that it is possible to control the microscopic coherent dynamics of electronic excited states in a QD ensemble.
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