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Biomedical subjects

M Shibata

Publications and source records attributed to M Shibata.

At least 109 records · Page 6Linked to original sources
PubMed2000

Kinetic and theoretical studies on the mechanism of alkaline hydrolysis of DNA.

The reaction mechanism of alkaline hydrolysis of DNA has been investigated by kinetic analysis and density-functional-theory calculation. The rates of hydrolysis of thymidine 3'-monophosphate esters (including thymidylyl(3'-5')thymidine (Tp-OT)) monotonically decrease as the leaving groups get poorer. According to the theoretical calculation in which the solvent effects are incorporated, no intermediate is formed in the course of the reaction. In the alkaline hydrolysis of the activated Tp-OT analogues having good leaving groups, the 3',5'-cyclic monophosphate of thymidine is concurrently formed through the intramolecular attack by the 5'-alkoxide ion. In the hydrolysis of the native dinucleotide, however, this side reaction does not occur, since the transition state leading to the departure of its poor leaving group cannot be formed due to conformational restraint. These arguments are supported by the theoretical analysis on the hydrolysis of both dimethyl phosphate and its O(bridging)-->S substituted analogue.

DNA↗
PubMed2000

PQBP-1/Npw38, a nuclear protein binding to the polyglutamine tract, interacts with U5-15kD/dim1p via the carboxyl-terminal domain.

PQBP-1 was identified as a binding protein to the polyglutamine tract present in various transcription-related factors and causative genes for neurodegenerative disorders. This novel gene contains at least two functional domains, WW domain and carboxyl-terminal domain (CTD), strictly conserved beyond species. Although human PQBP-1 additionally contains the polar amino acid-rich domain by which it binds to the polyglutamine tract, genuine physiological function(s) have not been clarified. In this study, we showed that U5-15kD, human homologue of fission yeast dim1p, is a partner molecule of PQBP-1 binding to CTD. This finding suggests physiological functions of PQBP-1 in splicing, cell cycle, and ubiquitination, through which we can speculate the pathological roles of PQBP-1 in triplet repeat diseases.

Amino Acid Sequence↗
PubMed2000

Cell adhesion is a prerequisite for osteoclast survival.

The present study demonstrates that loss of cell adhesion potently promotes apoptosis in osteoclasts, a process termed "anoikis." When purified mature rabbit osteoclasts were cultured on plastic for 18 h, about 25% of them were spontaneously committed to apoptosis. The death rate increased more than twofold, after osteoclasts were subjected to suspension culture in inverted Terasaki plates. The osteoclast anoikis was significantly prevented by bongkrekic acid, an inhibitor of mitochondrial permeability transition (PT), and z-VAD-FMK, a caspase inhibitor, suggesting involvement of mitochondrial PT and caspase activation in the death process. Colony-stimulating factor-1 (CSF-1), receptor activator of NF-kappaB ligand (RANKL), and calcitonin protected adherent osteoclasts, but not floating osteoclasts from anoikis. These data show that adhesion is a primary requirement for osteoclast survival.

Animals↗
PubMed2000

Wittig reactions on photoprotoporphyrin IX: new synthetic models for the special pair of the photosynthetic reaction center.

A first example of spirochlorin-chlorin dimer with fixed distances and orientations as potential model for the "special pair" of the photosynthetic reaction center is discussed. For the preparation of such a novel structure, the Wittig reagent of the desired "spacer" 5 was reacted with photoprotoporphyrin IX dimethyl ester 3 to produce the intermediate dimer 6, which on intramolecular [4 + 2] Diels-Alder cycloaddition gave an unexpected spirochlorin-chlorin dimer 9. Dehydration of dimer 6 under acid-catalyzed conditions generated the corresponding spirochlorin-porphyrin dimer 16 in quantitative yield. The asymmetry in dimer 6 caused by the biphenyl-type anisotropic effect was confirmed by NMR and model studies. The formation of dihydrobenzoporphyrin 14 by reacting chlorin 3 with the phosphonium salt of p-methylbenzylbromide 10 and isolation of 8-phenanthrenevinylporphyrin 19 from chlorin 7 further confirmed our proposed mechanism for the formation of a spirochlorin-chlorin dimer 9. Following a similar approach, chlorin 3 on reacting with bis-phosphonium salt of 4, 4'-bischloromethylbiphenyl produced conjugated chlorin dimer 25. The spectroscopic data obtained from these dimers suggest that, in these compounds, the individual chromophores are not behaving as an individual molecule, but as a single macrocycle. To examine whether the pi-pi interaction exhibited by dimer 9 resembles the structural arrangement of bacteriochlorophylls in reaction center (RC), we investigated the geometrical parameters used to characterize the pi-pi interactions in tetrapyrrolic macrocycles. Starting from the crystallographic coordinates of 9, the molecular mechanics energy minimization was performed to obtain the model dimer structure. The geometrical parameters that measure the single pyrrole ring overlap were used to compare the model structure with the crystallographic coordinates of the special pair in photosynthetic reaction center. The results indicated that the ring A of spirochlorin and the ring C of chlorin in our model dimer 9 mimic the ring A-ring A interaction found in the crystallographic special pairs, which are strategically placed by the surrounding photosynthetic reaction center protein matrix.

Dimerization↗
PubMed2000

On the Maximum Mass of Differentially Rotating Neutron Stars.

We construct relativistic equilibrium models of differentially rotating neutron stars and show that they can support significantly more mass than their nonrotating or uniformly rotating counterparts. We dynamically evolve such "hypermassive" models in full general relativity and show that there do exist configurations that are dynamically stable against radial collapse and bar formation. Our results suggest that the remnant of binary neutron star coalescence may be temporarily stabilized by differential rotation, leading to delayed collapse and a delayed gravitational wave burst.

Journal Article↗
PubMed2000

High-intensity static magnetic fields modulate skin microcirculation and temperature in vivo.

We investigated the acute effect of static magnetic fields of up to 8 T on skin blood flow and body temperature in anesthetized rats. These variables were measured prior to, during, and following exposure to a magnetic field in a superconducting magnet with a horizontal bore. The dorsal skin was transversely incised for 1 cm to make a subcutaneous pocket. Probes of a laser Doppler flowmeter and a thermistor were inserted into the pocket and positioned at mid-dorsum to measure skin blood flow and temperature. Another thermistor probe was put into the rectum to monitor rectal temperature. After baseline measurement outside the magnet, the rat was inserted into the bore for 20 min so that mid-dorsum was exactly positioned at the center, where the magnetic field was nearly homogeneous. Post-exposure changes were then recorded for 20 min outside the bore. Sham-exposed animals were submitted to exactly the same conditions, except that the superconducting magnet was not energized. Skin blood flow and temperature decreased significantly during magnetic field exposure and recovered after removal of the animal from the magnet. The rectal temperature showed a tendency to decrease while the animal was in the magnet. The microcirculatory and thermal reactions in the present study were consistent and agreed with some of the predictions based on mathematical simulations and model experiments.

Animals↗
PubMed2000

Application of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to insoluble glucose oligomers in decomposed cellulose.

An analytical approach is described for the molecular weight characterization of glucose oligomers from cellulose which had been decomposed by hot-compressed water (HCW). Microcrystalline cellulose was decomposed to 18% of water insoluble fraction (WI) plus 82% of water soluble fraction (WS) by HCW (295 degrees C, 10 mL/min). The glucose oligomers in the WI were analyzed by pericullar anion exchange chromatography, and oligomers longer than pentamers were detected. These results were also confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Many peaks derived from glucose oligomers with molecular weights less than 4000 Da were detected in the spectra. Mass differences between peaks were 162 Da, as expected for polymers composed of glucose units. This appears to be the first report concerning molecular weight determination of water or organic solvent insoluble compounds like glucose oligomers from cellulose using MALDI-TOFMS.

Cellulose↗
PubMed2000

Increased concentrations of plasma IL-18 in patients with hepatic dysfunction after hepatectomy.

We investigated the dynamic aspects of circulatory IL-18 and other inflammatory cytokines in patients who underwent a hepatectomy. In patients with post-operative hepatic dysfunction, plasma concentrations of these cytokines increased, reflecting severe surgical trauma. IL-6, IL-10 and IFN-gamma increased in the early phase, while IL-18 increased in the later phase after 1 week. Interestingly, the increase in the plasma IL-18 concentration was correlated with that in serum bilirubin levels in hepatectomized patients. Hence, the decrease in the hepatic metabolism of IL-18 may cause the plasma accumulation of IL-18. This mechanism was confirmed using rat experiments. Intravenously administered human IL-18 was excreted into bile. Furthermore, the plasma clearance of human IL-18 was prolonged in bile duct-ligated rats. These results suggest that IL-18 is metabolized in the liver and excreted into bile, and an increase in plasma IL-18 in patients with hepatic dysfunction reflects the decreased metabolism in the liver.

Adult↗
PubMed2000

Effects of portal-systemic shunt following 90% partial hepatectomy in rats.

We studied the effects of portal-systemic shunt after massive hepatectomy. Male Wistar rats were divided into two groups: one group underwent laparotomy alone (C group) and in the other group a portal-systemic shunt was placed through laparotomy (S group). After 90% hepatectomy was performed, 3-day and 1-week survival rates and histopathology were examined, and hepatic hemodynamics during the early stage after hepatectomy were measured using dye-containing microspheres. The 3-day survival rate in the S group was significantly higher, and the 1-week survival rate was slightly higher, than those in C group. Sinusoidal dilation 7 days after hepatectomy in the S group was significantly milder than that in the C group. Fatty degeneration of hepatocytes in the S group was significantly milder than that in the C group. With respect to hepatic hemodynamics during the early stage after hepatectomy, the rate of shunt (26.3%) in the S group was significantly higher than that (9.5%) in the C group. Portal pressure, total hepatic blood flow, and total hepatic blood flow per gram of liver in the S group were significantly lower than those in the C group. These results suggest that approximately 26% shunt after 90% hepatectomy in rats increases the early survival rate and improves histological changes in surviving rats 7 days after resection.

Animals↗
PubMed2000

Elastase activity enhances the adhesion of neutrophil and cancer cells to vascular endothelial cells.

BACKGROUND: Elastase activity in cancer cells has been reported to promote their metastasis. Hence, we analyzed the influence of elastase activity of cancer cells on their responsive adhesion to vascular endothelial cells. MATERIALS AND METHODS: Human pancreatic (S2-007, S2-013, S2-020, S2-028) and colonic (COLO205) cancer cell lines were used. S2-007, S2-013, and S2-020 possess high elastase activity, whereas S2-028 and COLO205 have low elastase activity. Adhesive reactions of these cancer cells and neutrophils to TNFalpha-activated HUVEC were analyzed. Bound cells onto HUVEC were counted after incubation for 10 min. The effects of suppression of elastase activity by ZD8321, a potent elastase inhibitor, and supplementation of human neutrophil elastase (NE) on the adhesive reactions were also analyzed. In addition, E-selectin expression on HUVEC and concentrations of soluble E-selectin in the medium were measured. RESULTS: Adhesion of cells with high intracellular elastase activity to TNFalpha-activated HUVEC was suppressed by ZD8321. On the other hand, adhesion of cells with low elastase activity was enhanced by exogenous NE. Expression of E-selectin, a key molecule in leukocyte-endothelial cell interaction, on HUVEC was increased by NE. Soluble E-selectin concentration in the medium increased after the adhesive reaction between neutrophils and HUVEC. This increase was thought to be due to the shedding of cell surface E-selectin. Such responses were inhibited by ZD8321. CONCLUSION: Elastase activity has a biological function of stimulating both the E-selectin expression on HUVEC and the resultant adhesive reaction of cancer cells with them. Inhibition of elastase activity is a potent strategy for controlling cancer metastasis.

Cell Adhesion↗
PubMed2000

Age-dependent changes in phenotypes and candidate gene analysis in a polygenic animal model of Type II diabetes mellitus; NSY mouse.

AIMS/HYPOTHESIS: The Nagoya-Shibata-Yasuda (NSY) mouse closely mimics human Type II (non-insulin-dependent) diabetes mellitus in that the onset is age-dependent, the animals are not severely obese, and both insulin resistance and impaired insulin response to glucose contribute to disease development. The aim of this study was to clarify the influence of age on the pathogenesis of diabetes and to analyse a candidate gene for Type II diabetes in this strain. METHODS: Several phenotypic characteristics related to diabetes mellitus were monitored longitudinally in male NSY and control C3H/He mice. The nucleotide sequence of Glut4, a candidate gene for Nidd1nsy (a susceptibility gene for Type II diabetes) on Chromosome 11, encoding insulin-sensitive glucose transporter, was determined in NSY and C3H mice. RESULTS: Glucose intolerance worsened with age, and fasting blood glucose and fasting plasma insulin concentration increased with age in NSY mice. Pancreatic insulin content increased until 24 weeks of age but then decreased at 48 weeks of age in NSY mice. The hypoglycaemic response to insulin was statistically significantly smaller in NSY than in C3H/He mice. The nucleotide sequence of GLUT4 cDNA was identical in NSY and C3H/He mice, but both were different from the sequence reported previously. CONCLUSION/INTERPRETATION: Insulin secretion and insulin resistance, as well as ageing possibly play an important part in the disease development in NSY mice. A decline of pancreatic insulin content in older age might cause the relative insulin deficiency in this strain. Nucleotide sequencing suggests that Glut4 is unlikely to be a candidate gene for Nidd1nsy.

3T3 Cells↗
PubMed2000

Influenza A virus encephalopathy with symmetrical thalamic lesions.

UNLABELLED: During an epidemic of influenza A infection in Japan, a 7-year-old boy was admitted to our hospital because of high fever, convulsions, coma, and liver dysfunction on the 2nd day of a cold-like illness. His serum CPK was markedly elevated, but there was no hyperammonaemia or hypoglycaemia. His CSF showed an increased protein level, but the cell count and glucose level were normal. CT and MRI of the brain showed symmetrical thalamic lesions, and he was diagnosed with acute necrotizing encephalopathy in childhood. He had a significant increased in antibodies to influenza A H1N1 in serum and CSF, but the CSF was negative for influenza virus using virus isolation and a polymerase chain reaction assay. CONCLUSION: Antibody production without detectable levels of influenza virus in cerebrospinal fluid suggests that virus infection occurred, but the virus did not replicate in sufficient numbers in his central nervous system. The thalamic lesion, the hallmark of acute necrotizing encephalopathy in childhood, may be initiated by a local virus infection and develop with subsequent local changes such as breakdown of the blood-brain barrier and the extravasation of blood.

Acute Disease↗
PubMed2000

Nitrite/nitrate (NOx) levels and hemodynamics during septic shock.

Nitric oxide (NO) acts as a vasorelaxant. We investigated the relationship between nitrite/nitrate (NOx), which are the final metabolites of NO, and hemodynamics during septic shock. We also examined tumor necrosis factor alpha (TNF-alpha), interleukin-8 (IL-8), and endotoxin. A significant negative correlation was observed between NOx levels and pulmonary capillary wedge pressure (PCWP; r = -0.6075, P = 0.0028). A significant positive correlation was noted between NOx levels and the cardiac index (CI; r = 0.5934, P = 0.0038). A significant negative correlation was found between NOx levels and the systemic vascular resistance index (SVRI; r = -0.4354, P = 0.0485). A significant positive correlation was observed between NOx levels and the stroke volume index (SVI; r = 0.5040, P = 0.0186). A significantly close positive correlation was also observed between TNF-alpha levels and NOx levels (r = 0.7848, P < 0.0001). These findings suggest that NOx levels are closely associated with hemodynamics during septic shock, resulting in a vascular relaxing effect.

Adult↗
PubMed2000

Paternal-maternal effects on phenotypic characteristics in spontaneously diabetic Nagoya-Shibata-Yasuda mice.

The Nagoya-Shibata-Yasuda (NSY) mouse is an inbred strain with spontaneous development of type 2 (non-insulin-dependent) diabetes mellitus. The purpose of this study was to determine the mode of inheritance of various phenotypes related to diabetes in this strain. Two reciprocal outcrosses, female C3H/He x male NSY F1 (C3NF1) and female NSY x male C3H/He F1 (NC3F1) mice, were performed. The phenotypic characteristics in both F1 mice were investigated. The cumulative incidence of diabetes was 100% (25 of 25) in male C3NF1 mice and 97% (29 of 30) in male NC3F1 mice at 48 weeks of age, indicating that diabetes in NSY mice was transmitted to male F1 hybrids in an autosomal dominant manner. Fatty liver also showed an autosomal dominant mode of inheritance. In contrast, epididymal fat accumulation and impaired insulin secretion showed an autosomal recessive mode of inheritance. The body mass index (BMI) showed a codominant mode of inheritance. Paternal-maternal effects associated with the severity of diabetes were observed. Insulin resistance was much more severe in male F1 mice than in the parental NSY strain. These data indicate different modes of inheritance among phenotypes related to type 2 diabetes. The presence of more severe insulin resistance in F1 mice versus the parental strains suggests the interaction of both parental genomes in the development of insulin resistance. The F1 mouse is expected to be useful for studies of the pathogenesis and genetic synergism of the insulin resistance syndrome.

Animals↗
PubMed2000

Long term depletion of serotonin leads to selective changes in glutamate receptor subunits.

The present study was carried out to clarify possible modulation mechanism of serotonin (5-HT) on glutamatergic neurotransmission in the rat cerebral cortex. 5-HT was depleted by a 5-HT metabolite blocker (para-chlorophenylalanine; pCPA) for a week. Receptor binding experiments using (S)-[(3)H]alpha-amino-3-hydroxy-5-methylisoxazol-4-propionic acid (AMPA) showed a considerable increase in B(max) value of the membrane samples prepared from the cerebral cortex of rats compared with that of control animals received saline. In contrast, B(max) value of the [(3)H]MK-801 binding experiments for NMDA receptor was not changed by pCPA-treatment. Changes in the density of each AMPA receptor subtype were examined in the cerebral cortex by immunoblot analyses using antibodies against AMPA receptor subunits. The density of immunoreactive bands with receptor subtype specific antibodies against GluR2/3 and GluR2 receptors was increased, whereas that of GluR1 receptors was decreased. Considering GluR2 receptor subtype inhibits Ca(2+) influx into neurons, the present study suggests that 5-HT appears to modulate synaptic plasticity by regulating the density of each AMPA receptor subtype.

Animals↗
PubMed2000

Intrathecal lithium reduces neuropathic pain responses in a rat model of peripheral neuropathy.

We tested the ability of lithium (Li(+)) to block heat hyperalgesia, cold allodynia, mechanical allodynia and mechanical hyperalgesia in rats experimentally subjected to painful peripheral neuropathy. Chronic constrictive injury (CCI) to the sciatic nerve induced persistent hyperalgesia and allodynia. Intrathecal injection of Li(+) (2.5-40 micromol) into the region of lumbar enlargement dose-dependently reduced heat hyperalgesia, cold allodynia and mechanical allodynia for 2-6 h after injection, but had no effect on mechanical hyperalgesia. Li(+) had no significant effect on responses from control and sham-operated animals. Intrathecal injection of myo-inositol (2.5 mg) significantly reversed both the anti-hyperalgesic and anti-allodynic effect of Li(+). These findings suggest that intrathecal Li(+) suppresses neuropathic pain response in CCI rats through the intracellular phosphatidylinositol (PI) second messenger system in spinal cord neurons. Lithium (Li(+)) has already found widespread clinical application; these results suggest that its therapeutic utility may be extended to include treatment of neuropathic pain syndromes resulting from peripheral nerve injury.

Animals↗
PubMed2000

Maternal program of apoptosis activated shortly after midblastula transition by overexpression of S-adenosylmethionine decarboxylase in Xenopus early embryos.

When we studied polyamine metabolism in Xenopus embryos, we cloned the cDNA for Xenopus S-adenosylmethionine decarboxylase (SAMDC), which converts SAM (S-adenosylmethionine), the methyl donor, into decarboxylated SAM (dcSAM), the aminopropyl donor, and microinjected its in vitro transcribed mRNA into Xenopus fertilized eggs. We found here that the mRNA injection induces a SAM deficient state in early embryos due to over-function of the overexpressed SAMDC, which in turn induces inhibition of protein synthesis. Such embryos developed quite normally until blastula stage, but stopped development at the early gastrula stage, due to induction of massive cell dissociation and cell autolysis, irrespective of the dosage and stage of the mRNA injection. We found that the dissociated cells were TUNEL-positive, contained fragmented nuclei with ladder-forming DNA, and furthermore, rescued completely by coinjection of Bcl-2 mRNA. Thus, overexpression of SAMDC in Xenopus embryos appeared to switch on apoptotic program, probably via inhibition of protein synthesis. Here, we briefly review our results together with those reported from other laboratories. After discussing the general importance of this newly discovered apoptotic program, we propose that the maternal program of apoptosis serves as a surveillance mechanism to eliminate metabolically severely-damaged cells and functions as a 'fail-safe' mechanism for normal development in Xenopus embryos.

Adenosylmethionine Decarboxylase↗