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Biomedical subjects

N Kato

Publications and source records attributed to N Kato.

At least 235 records · Page 13Linked to original sources
PubMed1999

Organization of the genes involved in the ribulose monophosphate pathway in an obligate methylotrophic bacterium, Methylomonas aminofaciens 77a.

The 4.4-kb PstI fragment harboring the gene encoding 3-hexulose-6-phosphate synthase, rmpA, which was previously cloned from the chromosome of an obligate methylotroph, Methylomonas aminofaciens 77a, was investigated in detail. In addition to the rmpA gene, the fragment contained three open reading frames encoding transaldolase (rmpD), IS10-R (rmpI), and 6-phospho-3-hexuloisomerase (PHI) (rmpB). The rmpB gene product was overproduced in Escherichia coli cells, purified to homogeneity, and then enzymatically identified as PHI. The gene organization of the ribulose monophosphate pathway enzymes together with a transposon, IS10-R, is discussed from both evolutionary and regulatory aspects.

Aldehyde-Lyases↗
PubMed1999

Developmental regulation of action potential-induced Ca2+ entry in neocortical neurons.

Intracellular calcium plays a critical role in the regulation of membrane excitability, synaptic integration and synaptic plasticity. Using whole-cell recording and calcium imaging, we investigated intracellular calcium dynamics in apical dendrites of layer V pyramidal cells in the immature rat neocortex. Dendritic calcium increases induced by action potentials were only small on postnatal days 4-6 (P4-6), then underwent a gradual enhancement during the second post-natal week and were 2- to 3-fold larger on P16-18 than on P4-6. At P15-18 there were no significant differences in the calcium increases among the three subclasses of layer V pyramidal neurons: adapting regular spiking (RS), non-adapting RS and intrinsically bursting (IB) neurons. Developmental regulation of dendritic calcium dynamics may be crucial for functional maturation of the neocortex.

Action Potentials↗
PubMed1999

Postnatal development of action potential-induced dendritic calcium entry in neocortical layer II/III pyramidal cells.

By whole-cell patch-clamp recording and calcium imaging with fura-2, we investigated postnatal development of intracellular calcium dynamics in apical dendrites of layer II/III pyramidal cells in the rat visual cortex. Dendritic calcium increases, induced by single action potentials, occurred only slightly on postnatal days 8-10 (P8-10), and then underwent a gradual enhancement during the second postnatal week to become 2-3-fold larger on P16-18 than on P8-10. The results suggest that the developmental growth of calcium dynamics may play a critical role for functional development of neocortical neurons.

Action Potentials↗
PubMed1999

Enhancement of activity-dependent calcium increase by neurotrophin-4 in visual cortex pyramidal neurons.

In pyramidal neurons from rat visual cortex slices, bath-application of NT-4 (20 ng/ml) did not much affected the baseline calcium signal, but did enhance calcium signals elicited by injections of depolarizing currents (+0.5 nA, 1 s). This enhancing effect of NT-4 was abolished by co-applying K252a. With ryanodine injected intracellularly, the effect of NT-4 was significantly reduced, suggesting an involvement of intracellular calcium release in this NT-4-induced enhancement of calcium transient.

Animals↗
PubMed1999

1H NMR studies of the reactions of copper(I) and copper(II) with D-penicillamine and glutathione.

Reactions of copper ions with D-penicillamine (PSH) have been monitored by 1H NMR spectroscopy in the presence and absence of glutathione (GSH) under aerobic as well as anaerobic conditions. In D2O solution at pD = 7.4, PSH coordinates to Cu+ to form PS(-)-Cu+ under argon atmosphere as revealed from the broadening of each signal. In the presence of dioxygen, the complex was converted to the well-characterized purple cluster species consisting of Cu+, Cu2+, and PS2-. Addition of GSH into this solution quickly decomposed the cluster by the reduction of Cu2+ to Cu+. The cluster species was, however, reproduced after several hours because of the oxidation of Cu+ back to Cu2+. The solution containing both PSH and GSH formed three possible disulfides, PSSP, GSSG, and PSSG, under aerobic conditions. Addition of Cu+ to this solution again produced the purple cluster through several redox reactions. On the basis of these results, it was concluded that the co-existence of PSH and/or PSSP with Cu+ and/or Cu2+ leads to the formation of the stable cluster species regardless of the presence or absence of the other thiols such as GSH. This must be one of the reasons why PSH works in living cells as an effective drug for the Wilson disease.

Aerobiosis↗
PubMed1999

Deletions in the repeating sequences of the toxin A gene of toxin A-negative, toxin B-positive Clostridium difficile strains.

The repeating sequences of the toxin A gene from toxin A-negative, toxin B-positive (toxin A-, toxin B+) strains of Clostridium difficile which were isolated in geographically separated facilities in Japan and Indonesia were determined. All six strains tested had identical repeating sequences with two deletions (1548 and 273 nucleotides in size) in the toxin A gene. A PCR method was designed to detect the deletions and the deletions were confirmed in all 50 toxin A-, toxin B+ strains examined by this method. Western immunoblot analysis revealed that polyclonal antiserum against native toxin A did not react with the concentrated culture filtrates of the toxin A-, toxin B+ strains. These results may suggest that toxin A-, toxin B+ strains have deletions of the two thirds of the repeating regions of the toxin A gene, which encodes the epitopes fully responsible for the reaction with the polyclonal antiserum.

Adult↗
PubMed1999

Endovascular stent-graft placement for the treatment of acute aortic dissection.

BACKGROUND: The standard treatment for acute aortic dissection is either surgical or medical therapy, depending on the morphologic features of the lesion and any associated complications. Irrespective of the form of treatment, the associated mortality and morbidity are considerable. METHODS: We studied the placement of endovascular stent-grafts across the primary entry tear for the management of acute aortic dissection originating in the descending thoracic aorta. We evaluated the feasibility, safety, and effectiveness of transluminal stent-graft placement over the entry tear in 4 patients with acute type A aortic dissections (which involve the ascending aorta) and 15 patients with acute type B aortic dissections (which are confined to the descending aorta). Dissections involved aortic branches in 14 of the 19 patients (74 percent), and symptomatic compromise of multiple branch vessels was observed in 7 patients (37 percent). The stent-grafts were made of self-expanding stainless-steel covered with woven polyester or polytetrafluoroethylene material. RESULTS: Placement of endovascular stent-grafts across the primary entry tears was technically successful in all 19 patients. Complete thrombosis of the thoracic aortic false lumen was achieved in 15 patients (79 percent), and partial thrombosis was achieved in 4 (21 percent). Revascularization of ischemic branch vessels, with subsequent relief of corresponding symptoms, occurred in 76 percent of the obstructed branches. Three of the 19 patients died within 30 days, for an early mortality rate of 16 percent (95 percent confidence interval, 0 to 32 percent). There were no deaths and no instances of aneurysm or aortic rupture during the subsequent average follow-up period of 13 months. CONCLUSIONS: These initial results suggest that stent-graft coverage of the primary entry tear may be a promising new treatment for selected patients with acute aortic dissection. This technique requires further evaluation, however, to assess its therapeutic potential fully.

Acute Disease↗
PubMed1999

Induction of oxidative DNA damage in anaerobes.

We compared oxidative DNA damage in strictly anaerobic Prevotella melaninogenica, aerotolerant anaerobic Bacteroides fragilis, and facultative anaerobic Salmonella typhimurium after exposure to O2 or H2O2. Using HPLC with electrochemical detection, we measured 8-hydroxydeoxyguanosine (8OHdG) as a damage marker. O2 induced 8OHdG in P. melaninogenica but not in B. fragilis, which shows catalase activity, or in S. typhimurium. In P. melaninogenica, with catalase, O2 induced less 8OHdG; superoxide dismutase had no effect; with glucose and glucose oxidase, O2 induced more 8OHdG. H2O2 also markedly increased 8OHdG. O2 was suggested to induce 8OHdG through H2O2. O2 or H2O2 decreased survival only in P. melaninogenica. Highly sensitive to oxidative stress, P. melaninogenica could prove useful for investigating oxidative DNA damage.

Anaerobiosis↗
PubMed1999

Phosphorylation of nonstructural 5A protein of hepatitis C virus: HCV group-specific hyperphosphorylation.

We previously showed that two proteins with molecular weights of 56 and 58 kDa are produced from nonstructural protein 5A (NS5A) derived from hepatitis C virus (HCV)-1b genotype. The 56-kDa protein is phosphorylated at serine residues in NS5A, including those located in the C-terminal region of NS5A, while the 58-kDa protein, the hyperphosphorylated form of the 56-kDa protein, is phosphorylated at serine residues in the central region. This hyperphosphorylation is dependent on the presence of HCV NS4A protein. To clarify whether NS4A-dependent phosphorylation also occurs in other HCV genotypes, phosphorylation of NS5A was analyzed by two-dimensional gel electrophoresis. Here, we report that NS5A from the HCV-2a genotype was phosphorylated. However, hyperphosphorylation of NS5A occurs in the HCV-1b genotype but not in the -2a genotype. This result suggests that modification of NS5A phosphorylation reflects the virological features of HCV and that there are physiological differences in the roles of differently phosphorylated NS5A between HCV genotypes.

Alkaline Phosphatase↗
PubMed1999

Age-dependent alteration of metabolic response to photic stimulation in the human brain measured by 31P MR-spectroscopy.

Effects of photic stimulation (PS) on energy metabolism were examined in the occipital cortex of 25 healthy volunteers aged 23-69 years old using phosphorus-31 magnetic resonance spectroscopy (31P-MRS). A significant effect of photic stimulation was found only for intracellular pH (p<0.05 by repeated measures analysis of variance) but not for any peak area ratios. An interaction between intracellular pH and age were statistically significant (p<0.005), and the interaction between phosphocreatine and age was close to significance (p=0.06). In subjects aged more than 40 years old, phosphocreatine was significantly decreased during the photic stimulation (p<0.05, multiple comparison by Dunnett's method), and intracellular pH tended to be elevated just after the stimulation (p=0.07). There were no significant changes in these values in younger subjects. These results suggest that no significant effect of photic stimulation on brain energy metabolism was found in younger subjects, and that significant effects of photic stimulation on intracellular pH and phosphocreatine were found in middle-aged subjects. Metabolic response of the human brain to photic stimulation may be dependent on age.

Adult↗
PubMed1999

Anti-tumor activity of interleukin-2-producing tumor cells and recombinant interleukin 12 against mouse glioma cells located in the central nervous system.

Interleukin 12 (IL-12) exhibits anti-tumor activity in a variety of laboratory models. Although IL-12 itself activates strong anti-tumor activity, the combination of vaccine therapy with IL-2-transduced tumor cells and systemic rIL-12 has been shown to cure tumor-bearing mice more effectively than either rIL-12 or IL-2-transduced tumor vaccines alone. In the present study, regression of brain tumors established in naive mice was obtained by combined administration of an intratumoral injection of a single dose of IL-2-producing glioma cells (SR/IL-2 cells) and recombinant IL-12. Intraperitoneal rIL-12 administration substantially delayed the growth of s.c. inoculated gliomas, but not of gliomas located in the brain. Although vaccination with SR/IL-2 cells alone was not effective against s.c. inoculated gliomas, the combination therapy of vaccination with irradiated SR/IL-2 cells and systemic rIL-12 was more effective than rIL-12 alone. In our brain-tumor model, intratumoral administration of irradiated SR/IL-2 cells and of rIL-12 remarkably prolonged survival as compared with untreated mice. Efficacy was reduced when studies were performed in mice depleted of CD8+ cells or NK cells. Mice cured of their intracerebral tumors by combined administration of SR/IL-2 cells and rIL-12 demonstrated protective immunity upon rechallenge. In summary, the therapeutic potential for control of tumor growth by intratumoral administration of IL-2-producing glioma cells and rIL-12 may be useful in the development of treatment for patients with glioma.

Animals↗
PubMed1999

Distinct genotypes of a nonenveloped DNA virus associated with posttransfusion non-A to G hepatitis (TT virus) in plasma and peripheral blood mononuclear cells.

TT virus (TTV) is a nonenveloped, single-stranded DNA virus with little sequence homology to known viruses, and associated with elevated transaminase levels in the patients with posttransfusion hepatitis of unknown etiology. The DNA of TTV was detected, by semi-nested polymerase chain reaction, in peripheral blood mononuclear cells (PBMC) from the 30 healthy individuals with circulating virus in plasma. A sequence of 222 bases was determined on 6-10 TTV DNA clones each from plasma and 6 clones -each from PBMC from eight individuals selected at random from this group. TTV can be classified into genotypes separated by an evolutionary distance > 0.30, which can be divided further into subtypes separated by that of 0.15. Three individuals possessed two different TTV variants of distinct genotypes, with predominant genotypes different between plasma and PBMC. Another possessed TTV of the same genotype in both the plasma and PBMC, but clones with a subtype not seen in plasma were observed in PBMC. A third individual had TTV variants with or without a deletion mutation, and those with the deletion mutation abounded only in PBMC. The remaining three individuals were infected with TTV with the same sequence both in plasma and PBMC. These results indicate that TTV variants with phylogenetic differences could infect the same individual, and that some variants would have a predilection for PBMC. It remains to be seen, however, if TTV replicates in PBMC or whether it has been sequestered before its evolution in the host.

Base Sequence↗
PubMed1999

YMDD motif in hepatitis B virus DNA polymerase influences on replication and lamivudine resistance: A study by in vitro full-length viral DNA transfection.

Recently, lamivudine used to treat patients with hepatitis B virus (HBV) infection was revealed to have potent antiviral activity. However, HBV resistance to lamivudine has been reported and shown to have amino acid substitutions in the methionine residue of the conserved tyrosine (Y), methionine (M), aspartate (D), aspartate (D) motif of RNA-dependent DNA polymerase. To explore the consequences of substitutions in this motif (YMDD), we made 7 variants by substituting the methionine of the YMDD motif with isoleucine (I), valine (V), alanine (A), leucine (L), lysine (K), arginine (R), and threonine (T). Replication ability of these variants was evaluated by transfection into human hepatoma cells. Sensitivity to lamivudine was tested for replication-competent variants. Four variants with hydrophobic substitutions (I, V, A, and L) remained replication-competent, whereas 3 others with hydrophilic substitutions (K, R, and T) exhibited impaired replication. Of the 4 replication-competent variants, 2 (I and V) were resistant, and 2 (A and L) were sensitive to lamivudine. Because the polymerase and the surface gene overlap, the introduction of these mutations affected the secretion of hepatitis B surface antigen (HBsAg), namely 4 variants (I, V, L, and R) secreted HBsAg, whereas 3 variants (A, K, and T) did not. Our study elucidated that only one amino acid substitution in the YMDD motif was sufficient to cause lamivudine resistance in vitro. As a result of replication competence and lamivudine sensitivity, only viruses having YIDD or YVDD sequences may appear during treatment with lamivudine. This in vitro system could be used to study HBV mutations, replication competence, and their susceptibility to antivirals.

Amino Acid Sequence↗
PubMed1999

Intrathoracic omental herniation through the esophageal hiatus: report of a case.

We report herein an extremely rare case of intrathoracic omental herniation through the esophageal hiatus. In fact, according to our review of the literature, only eight other cases have been reported, most of which were misdiagnosed as mediastinal lipoma after being identified as an intrathoracic mass. We report herein the ninth case of intrathoracic omental herniation through the esophageal hiatus. A 54-year-old obese woman was admitted to our hospital for investigation of a chest roentgenographic abnormality. She was asymptomatic, and her physical examination and laboratory data were all within normal limits. Her chest X-ray demonstrated a large, sharply-defined mass, and a computed tomography scan of the thorax indicated a large mediastinal mass with fat density. A thoracotomy was performed under the diagnosis of a mediastinal lipoma which revealed an encapsulated fatty mass, 10x7.5x6 cm in size, that proved to be an omental herniation through the esophageal hiatus. There was no herniation of the stomach or intestines into the thorax. The esophageal hiatus was repaired after the omental mass and hernia sac had been resected. This case report serves to demonstrate that whenever a mass of fat density is recognized in the lower thorax, an omental herniation should be borne in mind as a possible differential diagnosis.

Diagnosis, Differential↗
PubMed1999

Complete genome searches for quantitative trait loci controlling blood pressure and related traits in four segregating populations derived from Dahl hypertensive rats.

The Dahl salt-sensitive rat is one of the principal animal models of hereditary hypertension. Genome-wide searches were undertaken to detect quantitative trait loci (QTLs) that influence blood pressure, cardiac mass, and body weight in four F2 populations derived from Dahl salt-sensitive rats and different inbred normotensive control strains of rat. We detected three QTLs associated with one or more of the phenotypes, using a stringent statistical criterion for linkage (p < 0.00003). These included a novel QTL linked to blood pressure on rat Chromosome (Chr) 12, and another QTL on rat Chr 3 linked to body weight. A QTL on rat Chr 10 for which linkage to blood pressure has been described in other crosses was found to be a principal determinant of blood pressure and cardiac mass in some but not all of the crosses examined here. Three other regions showed evidence of linkage to these phenotypes with a less stringent statistical criterion of linkage at QTLs previously reported in other studies. As part of our study, microsatellite markers have been developed for three candidate genes for investigation in hypertension, and the genes have been localized by linkage mapping. These are: the rat Gs alpha subunit (Gnas) gene, the alpha-1B adrenergic receptor (Adra1b), and the Na+, K+-ATPase beta2 subunit (Atp1b2) gene.

Animals↗
PubMed1999

Quantitative evaluation of telomerase activity in small liver tumors: analysis of ultrasonography-guided liver biopsy specimens.

BACKGROUND/AIMS: Telomerase activity which restores the length of telomere repeat arrays is frequently detectable in various malignancies, including hepatocellular carcinoma. The aim of this study was to determine the diagnostic usefulness of the quantitative measurement of telomerase activity in small liver tumors, which has not yet been established. METHODS: Fifty-eight liver specimens from tumorous and non-tumorous portions of 29 small liver tumors equal to or less than 3.0 cm were obtained by ultrasonography-guided liver biopsy, and of these, 25 were diagnosed as hepatocellular carcinoma and four as adenomatous hyperplasia. The telomerase activities in these specimens and control specimens were examined quantitatively by telomeric repeat amplification protocol with standard control. RESULTS: The mean telomerase activity in cirrhosis without liver tumor was 0.4+/-0.6 (+/-S.D.) arbitrary units (AU) and that in 29 non-tumorous parts of the tumors was 4.5+/-7.4 AU. The mean telomerase activity in 13 tumors equal to or less than 2 cm in diameter was 77.1+/-133.7 AU and that in 16 tumors more than 2 cm was 152.7+/-215.2 AU. The mean telomerase activity in the 4 adenomatous hyperplasias was 5.5+/-4.5 AU; those of hepatocellular carcinoma with Edmondson-Steiner classification I, II, III and IV were 49.6+/-47.4 (n = 10), 240.1+/-273.6 (n = 9), 119.2+/-174.6 (n = 4) and 144.6+/-80.2 (n = 2) AU, respectively. CONCLUSIONS: The telomerase activity was significantly higher in hepatocellular carcinoma compared to adenomatous hyperplasia and non-neoplastic tissue, indicating that the quantitation of telomerase activity would be useful for the diagnosis of small hepatocellular carcinoma.

Adenoma↗