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Biomedical subjects

K Sasaki

Publications and source records attributed to K Sasaki.

At least 19 recordsLinked to original sources
PubMed2007

Stabilization of platinum oxygen-reduction electrocatalysts using gold clusters.

We demonstrated that platinum (Pt) oxygen-reduction fuel-cell electrocatalysts can be stabilized against dissolution under potential cycling regimes (a continuing problem in vehicle applications) by modifying Pt nanoparticles with gold (Au) clusters. This behavior was observed under the oxidizing conditions of the O2 reduction reaction and potential cycling between 0.6 and 1.1 volts in over 30,000 cycles. There were insignificant changes in the activity and surface area of Au-modified Pt over the course of cycling, in contrast to sizable losses observed with the pure Pt catalyst under the same conditions. In situ x-ray absorption near-edge spectroscopy and voltammetry data suggest that the Au clusters confer stability by raising the Pt oxidation potential.

Journal Article↗
PubMed2007

Formation of bone-like apatite enhanced by hydrolysis of octacalcium phosphate crystals deposited in collagen matrix.

It has been shown that granules of synthetic octacalcium phosphate (OCP) or the composites with collagen are capable of enhancing bone regeneration, accompanied by a gradual conversion from OCP to apatite with time. The present study was designed to investigate whether formation of bone-like apatite can be accelerated by OCP deposited throughout collagen matrix (OCP collagen complex, OCC) immersed in simulated body fluid (SBF). The formation of bone-like apatite has been suggested to be essential to induce osteoconductivity of various substrates. The formation of OCP in collagen solution was investigated in calcium or phosphate ions in the range between 22.5 and 142.5 mM and pH 6.26 and 8.56. X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy (SEM) showed that condition to nucleate OCP was limited to that of a solution with Ca/P 0.43 around pH 7.16 in the presence of collagen. OCP was shown to be formed throughout the collagen matrix by SEM observation. The immersion of OCC in SBF up to 10 days enhanced apatite crystal deposition, probably through OCP-apatite conversion: the apatite formation in OCC took place within only 1 day. The present study indicated that the existence of OCP deposited throughout the collagen matrix promotes bone-like apatite formation under physiological condition.

Animals↗
PubMed2007

Sound spectrogram analysis in patients receiving Kawahara's surgical voice restoration for advanced carcinoma of the hypopharynx and cervical esophagus.

Loss of voice after total laryngectomy is a major concern that has prompted much effort to develop methods of surgical voice restoration. In 1992, Kawahara described a tracheocolic shunt for voice restoration using a revascularized ileocolic graft. With this method, aspiration through the phonatory shunt is prevented by the ileocolic valve (Bauhin's valve), while vocalization is allowed. The purpose of this study was to use sound spectrogram analysis to evaluate voices surgically restored in that way. Between 2002 and 2005, 10 consecutive patients underwent laryngopharyngoesophagectomy with Kawahara's surgical voice restoration for advanced carcinoma of the hypopharynx and/or cervical esophagus at Akita University Hospital, Japan. We then used sound spectrography to analyze and compare the voices of patients receiving Kawahara's voice restoration, against healthy volunteers and patients who underwent the same surgery without voice restoration and spoke using an electronic larynx. We also evaluated the intelligibility of conversation and performed a listening test. The sound spectrograms showed that when produced by the electronic larynx, consonant sounds and voice frequencies below 300 Hz were not clearly recognized. By contrast, in patients who received Kawahara's surgical voice restoration, consonant and vowel sounds at frequencies above and below 300 Hz were clearly recognized. Although conversation was intelligible with both Kawahara's surgical voice restoration and the electronic device, listeners judged the voice produced by the former to be superior. Thus, the voice produced by Kawahara's surgical voice restoration is superior to that produced by the electronic larynx.

Aged↗
PubMed2006

Palladium monolayer and palladium alloy electrocatalysts for oxygen reduction.

We investigated the oxygen-reduction reaction (ORR) on Pd monolayers on various surfaces and on Pd alloys to obtain a substitute for Pt and to elucidate the origin of their activity. The activity of Pd monolayers supported on Ru(0001), Rh(111), Ir(111), Pt(111), and Au(111) increased in the following order: Pd/Ru(0001) < Pd/Ir(111) < Pd/Rh(111) < Pd/Au(111) < Pd/Pt(111). Their activity was correlated with their d-band centers, which were calculated using density functional theory (DFT). We found a volcano-type dependence of activity on the energy of the d-band center of Pd monolayers, with Pd/Pt(111) at the top of the curve. The activity of the non-Pt Pd2Co/C alloy electrocatalyst nanoparticles that we synthesized was comparable to that of commercial Pt-containing catalysts. The kinetics of the ORR on this electrocatalyst predominantly involves a four-electron step reduction with the first electron transfer being the rate-determining step. The downshift of the d-band center of the Pd "skin", which constitutes the alloy surface due to the strong surface segregation of Pd at elevated temperatures, determined its high ORR activity. Additionally, it showed very high methanol tolerance, retaining very high catalytic activity for the ORR at high concentrations of methanol. Provided its stability is satisfactory, this catalyst might possibly replace Pt in fuel-cell cathodes, especially those of direct methanol oxidation fuel cells (DMFCs).

Alloys↗
PubMed2006

Leptin facilitates learning and memory performance and enhances hippocampal CA1 long-term potentiation and CaMK II phosphorylation in rats.

Leptin, an adipocytokine encoded by an obesity gene and expressed in adipose tissue, affects feeding behavior, thermogenesis, and neuroendocrine status via leptin receptors distributed in the brain, especially in the hypothalamus. Leptin may also modulate the synaptic plasticity and behavioral performance related to learning and memory since: leptin receptors are found in the hippocampus, and both leptin and its receptor share structural and functional similarities with the interleukin-6 family of cytokines that modulate long-term potentiation (LTP) in the hippocampus. We therefore examined the effect of leptin on (1) behavioral performance in emotional and spatial learning tasks, (2) LTP at Schaffer collateral-CA1 synapses, (3) presynaptic and postsynaptic activities in hippocampal CA1 neurons, (4) the intracellular Ca(2+) concentration ([Ca(2+)](i)) in CA1 neurons, and (5) the activity of Ca(2+)/calmodulin protein kinase II (CaMK II) in the hippocampal CA1 tissue that exhibits LTP. Intravenous injection of 5 and/or 50mug/kg, but not of 500mug/kg leptin, facilitated behavioral performance in passive avoidance and Morris water-maze tasks. Bath application of 10(-12)M leptin in slice experiments enhanced LTP and increased the presynaptic transmitter release, whereas 10(-10)M leptin suppressed LTP and reduced the postsynaptic receptor sensitivity to N-methyl-d-aspartic acid. The increase in the [Ca(2+)](i) induced by 10(-10)M leptin was two times greater than that induced by 10(-12)M leptin. In addition, the facilitation (10(-12)M) and suppression (10(-10)M) of LTP by leptin was closely associated with an increase and decrease in Ca(2+)-independent activity of CaMK II. Our results show that leptin not only affects hypothalamic functions (such as feeding, thermogenesis, and neuroendocrine status), but also modulates higher nervous functions, such as the behavioral performance related to learning and memory and hippocampal synaptic plasticity.

Animals↗
PubMed2006

Natural killer-like T-cell lymphoma in a calf.

A case of natural killer (NK)-like T-cell lymphoma in a 9-month-old female Holstein calf is described. The liver, spleen and lymph nodes were affected with lymphoma. The neoplastic cells showed not only epitheliotropism in the biliary epithelium and hepatic cords but also preferential homing to follicular centres of the lymph nodes. In the cytoplasm, there were eosinophilic granules of various sizes, which were positive with phosphotungstic acid haematoxylin and naphthol AS-D chloroacetate esterase. Erythrophagia by lymphoma cells was rarely detected. Immunohistochemically, the neoplastic cells expressed surface CD3, surface CD5 and CD57, and perforin expression was present in the cytoplasmic granules. The lymphoma described resembled feline NK-like T-cell lymphoma in epitheliotropism in the liver and phagocytic activity but differed in respect of follicular involvement and marked variation in granule size.

Animals↗
PubMed2006

Cytogenetic analysis of myxoid liposarcoma and myxofibrosarcoma by array-based comparative genomic hybridisation.

AIM: To investigate overall chromosomal alterations using array-based comparative genomic hybridisation (CGH) of myxoid liposarcomas (MLSs) and myxofibrosarcomas (MFSs). MATERIALS AND METHODS: Genomic DNA extracted from fresh-frozen tumour tissues was labelled with fluorochromes and then hybridised on to an array consisting of 1440 bacterial artificial chromosome clones representing regions throughout the entire human genome important in cytogenetics and oncology. RESULTS: DNA copy number aberrations (CNAs) were found in all the 8 MFSs, but no alterations were found in 7 (70%) of 10 MLSs. In MFSs, the most frequent CNAs were gains at 7p21.1-p22.1 and 12q15-q21.1 and a loss at 13q14.3-q34. The second most frequent CNAs were gains at 7q33-q35, 9q22.31-q22.33, 12p13.32-pter, 17q22-q23, Xp11.2 and Xq12 and losses at 10p13-p14, 10q25, 11p11-p14, 11q23.3-q25, 20p11-p12 and 21q22.13-q22.2, which were detected in 38% of the MFSs examined. In MLSs, only a few CNAs were found in two sarcomas with gains at 8p21.2-p23.3, 8q11.22-q12.2 and 8q23.1-q24.3, and in one with gains at 5p13.2-p14.3 and 5q11.2-5q35.2 and a loss at 21q22.2-qter. CONCLUSIONS: MFS has more frequent and diverse CNAs than MLS, which reinforces the hypothesis that MFS is genetically different from MLS. Out-array CGH analysis may also provide several entry points for the identification of candidate genes associated with oncogenesis and progression in MFS.

Adult↗
PubMed2006

Heating by an electron Bernstein wave in a spherical tokamak plasma via mode conversion.

The first successful high power heating of a high dielectric constant spherical tokamak plasma by an electron Bernstein wave (EBW) is reported. An EBW was excited by mode conversion (MC) of an mode cyclotron wave injected from the low magnetic field side of the TST-2 spherical tokamak. Evidence of electron heating was observed as increases in the stored energy and soft x-ray emission. The increased emission was concentrated in the plasma core region. A heating efficiency of over 50% was achieved, when the density gradient in the MC region was sufficiently steep.

Journal Article↗
PubMed2006

A new simple therapeutic method for chronic subdural hematoma without irrigation and drainage.

BACKGROUND: We developed a new simple therapeutic method for the treatment of chronic subdural hematoma (CSDH) without irrigation and drainage. This method is characterized by replacement of the hematoma with oxygen. METHODS: Seventy patients (seventy-eight sides) with CSDH were treated with this method from May 1994 to October 2002. For the complete replacement of the hematoma with oxygen, subdural tapping site was changed from the thickest area of the hematoma to the parietal tuber. Irrigation and drainage were not used in all patients. RESULTS: Neurological recovery after the treatment was satisfactory in all 70 patients. An average amount of replaced hematoma was 96.1 ml, ranging from 5 to 280 ml. An initial hematoma pressure ranged from 0 to 200 mm H2O (average: 92.1 mm H2O). During the follow up periods, clinical recurrence was noted in 7 patients (10%) and 7 sides (9.0%). CONCLUSION: The replacement of the hematoma with oxygen via percutaneous subdural tapping without irrigation and drainage is useful and less invasive method for the treatment of CSDH.

Aged↗
PubMed2006

High concentrations of D-amino acids in human gastric juice.

The concentrations of free D- and L-amino acids were determined in the gastric juice from four groups: patients suffering from early gastric carcinoma with or without Helicobacter pylori infection, and patients without carcinoma but with peptic ulcers, duodenal ulcers or chronic gastritis with or without H. pylori infection. H. pylori is a bacterium associated with gastric inflammation and peptic ulcers and is a risk factor for stomach cancer. The highest D-amino acid ratios (free D-amino acid concentration to the total corresponding free D- and L-amino acid concentration) were 29%, 26%, 18%, 4% and 1% for proline, alanine, serine, aspartate and glutamate, respectively. The gastric juice levels of L-alanine, L-serine, L-proline, L-glutamate and D-alanine in the samples obtained from subjects bearing early gastric carcinoma and H. pylori were significantly higher than in the samples from the other three groups. Except for D-alanine, there was no correlation between the D-amino acid concentrations and presence of carcinoma or H. pylori.

Adult↗
PubMed2006

In vivo 3-dimensional measurement of the force exerted on a tooth during clenching.

We have developed a three-dimensional (3D) force-measuring device for teeth and used it to measure functional forces in vivo. It comprises an inner part forming a metal core (abutment), a 3D piezoelectric force transducer, and an outer part forming a metal crown, all joined together with a steel screw. The force transducer can measure +/- 500 N along the z-axis and +/- 150 N along the x- and y-axes. We evaluated the relationship between output and load and the effects of hysteresis and temperature on the output. The transducer had high linearity (r>0.9999), low hysteresis (1.7% at maximum), and high thermal stability (0.05% per degree) along each axis. The measuring device was mounted on the maxillary left second molar of a healthy male subject; the tooth had been endodontically treated (neurovascular bundle removed) and prepared for metal abutment and a crown. The 3D load calculated from the outputs of the transducer was expressed as a vector of the coordinates based on the Frankfort horizontal (x-y) and sagittal (y-z) planes. The force measured during maximum voluntary clenching was about 170 N; the force vector was directed from the crown to the root medially at an angle of about 10 degrees from the y-z plane and posteriorly at an angle of about 3 degrees from the x-z plane. This transducer will enable measurement of forces applied to different types of prosthetic appliances and has the potential to provide important basic in vivo data for analysis using computer simulation.

Adult↗
PubMed2006

Characterization of dentin formed in transplanted rat molars by electron probe microanalysis.

The present study was designed to characterize dentin formed in transplanted rat molars by investigating calcium (Ca), phosphorus (P), and magnesium (Mg) concentrations using electron probe microanalysis (EPMA) as well as examining the rate of dentin matrix formation by vital staining. The unerupted immature lower right second molar in 2-week-old rats was transplanted into the upper right first molar socket. Rats were injected with oxytetracycline, calcein, and alizarin intraperitoneally at 1 day before and 1 and 2 weeks after transplantation, respectively, for vital staining. The maxillae and mandibles were fixed 3 weeks after transplantation, resected, and embedded in resin. Undemineralized sections were cut and examined by fluorescent microscopy and EPMA. The thickness of dentin formed in the first week after transplantation was significantly less than that of dentin formed in any other 1-week period in the transplanted tooth and was about one-fifth the thickness of dentin formed in control teeth. Formation of dentin recovered in the third week after transplantation. In the first week after transplantation, EPMA demonstrated a sharp increase in Mg concentration with a slight decrease in Ca concentration. Thereafter, no significant difference was identified among Ca, P, or Mg concentrations or the Ca/P ratio between transplanted and control teeth. These results suggest that disruption of the circulation and innervation by transplantation cause a temporary change in the matrix formation rate and elemental distribution of dentin, which is subsequently restored within 2 weeks after transplantation.

Animals↗
PubMed2006

Molecular mechanisms of hyperplasia induction by human papillomavirus E7.

Infections of human papillomavirus (HPV) induce a variety of benign tumors, such as warts and condylomas. During the process of aberrant cell proliferation, genetic mutations are accumulated in the cells, from which malignant tumor cells arise. The viral oncoproteins E6 and E7 are known to help disrupt the cell cycle checkpoint machinery and accelerate chromosomal instability, events which are critical in malignant conversion. However, the mechanisms involved in the hyperplasia caused by HPV infection have remained unknown. We analysed the effects of regulatory genes of HPV18, a typical high-risk-type HPV, on the formation of the epithelial organ by using an organotypic culture system, and found that E7 had potent activity to induce hyperplasia, to which the disruption of the pRb pathway was well correlated. However, analysis with the E7 variants indicated that other pocket proteins are also involved in the activity.

Cell Proliferation↗
PubMed2006

Clusterin expression in follicular dendritic cells associated with prion protein accumulation.

Peripheral accumulation of abnormal prion protein (PrP) in variant Creutzfeldt-Jakob disease and some animal models of transmissible spongiform encephalopathies (TSEs) may occur in the lymphoreticular system. Within the lymphoid tissues, abnormal PrP accumulation occurs on follicular dendritic cells (FDCs). Clusterin (apolipoprotein J) has been recognized as one of the molecules associated with PrP in TSEs, and clusterin expression is increased in the central nervous system where abnormal PrP deposition has occurred. We therefore examined peripheral clusterin expression in the context of PrP accumulation on FDCs in a range of human and experimental TSEs. PrP was detected immunohistochemically on tissue sections using a novel highly sensitive method involving detergent autoclaving pretreatment. A dendritic network pattern of clusterin immunoreactivity in lymphoid follicles was observed in association with the abnormal PrP on FDCs. The increased clusterin immunoreactivity appeared to correlate with the extent of PrP deposition, irrespective of the pathogen strains, host mouse strains or various immune modifications. The observed co-localization and correlative expression of these proteins suggested that clusterin might be directly associated with abnormal PrP. Indeed, clusterin immunoreactivity in association with PrP was retained after FDC depletion. Together these data suggest that clusterin may act as a chaperone-like molecule for PrP and play an important role in TSE pathogenesis.

Adolescent↗
PubMed2006

Comparative genomic hybridization reveals genetic progression of oral squamous cell carcinoma from dysplasia via two different tumourigenic pathways.

To clarify the genetic pathway(s) involved in the development and progression of oral squamous cell carcinoma (OSCC), as well as the relationship between genetic aberrations and biological characteristics of OSCC tumours, comparative genomic hybridization was used to analyse genetic alterations in both primary OSCCs and adjacent dysplastic lesions of the same biopsy specimens from 35 patients. Gain of 8q22-23 was the most frequent alteration in both OSCC and mild dysplasia, and was considered the earliest event in the process of oral tumourigenesis. The average number of DNA sequence copy number aberrations (DSCNAs) increased with progression from mild dysplasia to invasive carcinoma (r = 0.737, n = 70, p < 0.001). OSCC samples were classified as having a large or small number of DSCNAs (OSCC-L, 21.4 +/- 4.7 DSCNAs or OSCC-S, 10.0 +/- 1.7 DSCNAs, respectively; p < 0.0001). Gains of 3q26-qter, 8q, 11q13, 14q, and 20q and losses of 4q, 5q12-22, 6q, 8p, 13q, and 18q22-qter were common to OSCC-L and OSCC-S. Gains of 5p15, 7p, 17q11-22, and 18p and losses of 3p14-21, 4p, and 9p were detected exclusively in OSCC-L. The average number of DSCNAs depended on whether the samples showed OSCC- L or dysplasia plus OSCC-L, or showed OSCC-S or dysplasia plus OSCC-S (p = 0.001). Gain of 5p15 and losses of 4p and 9p were detected even in dysplastic lesions adjacent to OSCC-L samples. Loss of 4p was associated with node metastasis by multivariate analysis (p = 0.013). OSCC-L tumours were more often T3-T4 stage tumours than T1-T2 stage tumours (p = 0.03). These findings suggest that two different types of OSCC, OSCC-L associated with high-stage cancer and OSCC-S associated with low-stage cancer, arise from different types of dysplasia via different genetic pathways.

Aged↗
PubMed2006

Hypertrophy of the posterior longitudinal ligament in the thoracic spine.

STUDY DESIGN: This is a case report of a patient with hypertrophy of the posterior longitudinal ligament (HPLL) in the thoracic spine. This patient was followed for 10 years after surgery. OBJECTIVES: The purpose of this study was to report the long-term outcome of HPLL in the thoracic spine. SETTING: Department of orthopedic surgery, Hiroshima Red Cross and Atomic-bomb Survivors Hospital, Hiroshima, Japan. METHODS: A 58-year-old-woman with thoracic HPLL was reported. Magnetic resonance image (MRI) and computed tomography (CT) showed the expanded spinal cord compression from Th4 to Th12 due to HPLL. Anterior decompression and fusion (Th10-12) was performed. Histological findings of the surgical specimens showed thickening of the posterior longitudinal ligament with proliferation of chondroid tissue. The clinical outcome and the radiological findings (CT and MRI) were evaluated 10 years after surgery. RESULTS: The patient was asymptomatic postoperatively. However, the subsequent CT examination revealed ossification of the previously hypertrophied posterior longitudinal ligament. CONCLUSIONS: HPLL in the thoracic spine is a rare pathological condition causing myelopathy. The results of this study support the hypothesis that HPLL is one of the prodromal conditions of HPLL.

Decompression, Surgical↗