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Biomedical subjects

Kenji Yamamoto

Publications and source records attributed to Kenji Yamamoto.

At least 55 records · Page 3Linked to original sources
PubMed2005

International symposium on infectious agent transmission model building--focusing on assessment of risk to communities.

The Susceptible Infected and Recovery (SIR) Model proposed by Robert May in the UK is the basis of the present mathematical model building of infectious disease epidemics. Need for model building incorporating more social and other relevant factors has been recognized. An important example is the introduction of idea of the scale-free distribution of links among the people. More refined models by taking into account the nature of a pathogen, geo-sociological factors, lifestyles of the people, etc., have been developed. For example, Koopman proposed a model for prediction of epidemic expansion based on actual epidemiological data. Eubank proposed a model assessing the bio-terror attack using a model city where every day activity is going on. The present workshop, participated by experts from the US, the UK and Japan, is the first meeting of the proposed series of conference on this issue.

Communicable Diseases↗
PubMed2005

The hospital with more beds has a higher probability of experiencing an outbreak of the hospital infection.

The dependence of the incidence of the hospital infection on the number of the beds was studied by using SIR model with the computer simulation. We obtained the result that the hospital with more beds has a higher probability of experiencing an outbreak. The integration of smaller hospitals into a larger hospital was once considered economically advantageous and such a policy has been implemented in Japan since the early 1980s. This analysis, however, warns against the policy.

Computer Simulation↗
PubMed2004

Processing of chicken progastrin at post-Phe bonds by an aspartyl protease.

Prohormones mature to biologically active peptide hormones through posttranslational modifications, which include endoproteolytic cleavages. Cleavages at mono- and dibasic sites are well characterized, and several of the responsible prohormone convertases have been identified. There is, however, evidence that endoproteolytic maturation occurs also at other sites. Among these, post-Phe cleavage occurs in the maturation of chicken progastrin, where the processing to gastrin-30 has been examined in detail. In this study we have characterized an endoprotease of the aspartic acid protease family in chicken and human tissue capable of cleaving at the Phe site. Enzymatic activity was monitored by radioimmunoassays using antibodies specific for the N- and C-termini exposed after cleavage. Analysis showed that only pepstatin, a specific inhibitor of aspartic proteases, inhibited the enzyme. The pH optimum of the enzyme ranged from pH 2 to pH 5. Amino acid substitution from Phe to Ala in the substrate completely abolished enzyme activity. The endoproteolytic activity was identified in chicken antrum and pectoral muscle as well as human cardiac and prostate extracts, suggesting that the enzyme has widespread biological functions. Experiments using recombinant cathepsin D and E indicated that neither is responsible for the endoproteolytic cleavage of chicken progastrin at post-Phe bonds.

Amino Acid Sequence↗
PubMed2004

Molecular cloning of Mucor hiemalis endo-beta-N-acetylglucosaminidase and some properties of the recombinant enzyme.

Endo-M, endo-beta-N-acetylglucosaminidase from Mucor hiemalis, is known as a useful enzyme for the synthesis of neoglycopeptides due to its transglycosylation activity. We cloned the Endo-M gene encoding a putative 744 amino acids, which shows high identity to glycoside hydrolase family 85 endo-beta-N-acetylglucosaminidases. The gene encoding Endo-M was expressed in protease-deficient Candida boidinii with a molecular mass of 85 kDa as a monomeric form. Recombinant Endo-M could liberate both high-mannose type and biantennary complex type oligosaccharides from glycopeptides, which was same as the native enzyme. The Km and Kcat values for DNS-Man6GlcNAc2Asn were 0.51 mM and 8.25 s(-1), respectively. Recombinant Endo-M also exhibited transglycosylation activity toward high-mannose type and biantennary complex type oligosaccharides, which were transferred to alcohols, monosaccharides, oligosaccharides, and glycosides. To investigate about the catalytically essential amino acids of Endo-M, site-directed mutagenesis was performed, and it was found that mutants E177G and E177Q completely abolished the hydrolytic activity and W228R partially abolished the transglycosylation activity.

Amino Acid Sequence↗
PubMed2004

Enhancement of bioactivity of Saccharomyces cerevisiae alpha-mating factor by attachment of sugar moiety to glutamine residue.

We prepared yeast Saccharomyces cerevisiae alpha-mating factor, a 13-amino acid pheromone produced by haploid alpha-cells, bound with glucose or N-acetylglucosamine at the fifth glutamine residue from the N-terminal by the chemical method of peptide synthesis. It was found that the bioactivity of glucosyl alpha-mating factor was higher than that of native alpha-mating factor. However, it was slightly lower than that of N-acetylglucosaminyl alpha-mating factor. This suggested that the N-acetylamino residue might play some important role in the enhancement of the bioactivity of alpha-mating factor. However, CD spectra analysis of alpha-mating factor and its derivatives demonstrated that their structures were almost identical. On the other hand, we attached a sialo complex type oligosaccharide to N-acetylglucosamine or its glucose residue by means of the transglycosylation activity of endo-beta-N-acetylglucosaminidase from Mucor hiemalis (Endo-M). The attachment of the oligosaccharide to both alpha-mating factors reduced their activities. However, enzymatical trimming of the sialo complex type oligosaccharide recovered its activity.

Acetylglucosamine↗
PubMed2004

Mucor hiemalis endo-beta-N-acetylglucosaminidase can transglycosylate a bisecting hybrid-type oligosaccharide from an ovalbumin glycopeptide.

We found that the recombinant endo-beta-N-acetylglucosaminidase of Mucor hiemalis (Endo-M) expressed in Candida boidinii had the transglycosylation activity of transferring a bisecting hybrid-type oligosaccharide from an ovalbumin glycopeptide to the acceptor (p-nitrophenyl 2-acetamido-2-deoxy-beta-D-glucopyranoside) in a good yield of 43%.

Acetylglucosamine↗
PubMed2004

Suppression of pathogenicity of Porphyromonas gingivalis by newly developed gingipain inhibitors.

Arg-gingipain (Rgp) and Lys-gingipain (Kgp) are cysteine proteinases produced by Porphyromonas gingivalis, a major etiological bacterium of periodontal diseases. Here we show a series of small peptide analogs able to inhibit either Rgp or Kgp, which are synthesized on the basis of the cleavage site specificity of human salivary histatins by each enzyme. Among this series of compounds, carbobenzoxy-Lys-Arg-CO-Lys-N-(CH2)2 (KYT-1) and carbobenzoxy-Glu(NHN(CH3)Ph)-Lys-CO-NHCH2Ph (KYT-36) were found to be the most potent inhibitors of Rgp and Kgp, respectively, with Ki values of 10(-11) to 10(-10) M order. Both inhibitors exhibited slight or no inhibition on mammalian proteinases such as trypsin and cathepsins B, L, and H. All of the virulence induced by the culture supernatant of P. gingivalis tested, including the degradation of various host proteins such as human type I collagen, immunoglobulins, fibronectin, and fibrinogen, disruption of the bactericidal activity of polymorphonuclear leukocytes, and enhancement of the vascular permeability, were strongly inhibited by a combined action of both inhibitors. The functions essential for the bacterium to grow and survive in the periodontal pocket, such as coaggregation and acquisition of amino acids, were also strongly inhibited by the combined action of both inhibitors. The disruption of the adhesion and viability of human fibroblasts and hemagglutination by the organism were strongly suppressed by a single use of KYT-1. These results thus indicate that the newly developed KYT-1 and KYT-36 both should provide a broader application in studies of this important class of enzymes and facilitate the development of new approaches to periodontal diseases.

Adhesins, Bacterial↗
PubMed2004

Newly discovered neutral glycosphingolipids in aureobasidin A-resistant zygomycetes: Identification of a novel family of Gala-series glycolipids with core Gal alpha 1-6Gal beta 1-6Gal beta sequences.

We found for the first time that Zygomycetes species showed resistance to Aureobasidin A, an antifungal agent. A novel family of neutral glycosphingolipids (GSLs) was found in these fungi and isolated from Mucor hiemalis, which is a typical Zygomycetes species. Their structures were completely determined by compositional sugar, fatty acid, and sphingoid analyses, methylation analysis, matrix-assisted laser desorption ionization time-of-flight/mass spectrometry, and (1)H NMR spectroscopy. They were as follows: Gal beta 1-6Gal beta 1-1Cer (CDS), Gal alpha 1-6Gal beta 1-6Gal beta 1-1Cer (CTS), Gal alpha 1-6Gal alpha 1-6Gal beta 1-6Gal beta 1-1Cer (CTeS), and Gal alpha 1-6Gal alpha 1-6Gal alpha 1-6Gal beta 1-6Gal beta 1-1Cer (CPS). The ceramide moieties of these GSLs consist of 24:0, 25:0, and 26:0 2-hydroxy acids as major fatty acids and 4-hydroxyoctadecasphinganine (phytosphingosine) as the sole sphingoid. However, the glycosylinositolphosphoceramide families that are the major GSLs components in fungi were not detected in Zygomycetes at all. This seems to be the reason that Aureobasidin A is not effective for Zygomycetes as an antifungal agent. Our results indicate that the biosynthetic pathway for GSLs in Zygomycetes is significantly different from those in other fungi and suggest that any inhibitor of this pathway may be effective for mucormycosis, which is a serious pathogenic disease for humans.

Absidia↗
PubMed2004

Transglycosylation reaction of Mucor hiemalis endo-beta-N-acetylglucosaminidase using sugar derivatives modified at C-1 or C-2 as oligosaccharide acceptors.

We investigated the transglycosylation reaction of the recombinant endo-beta-N-acetylglucosaminidase from Mucor hiemalis (Endo-M) expressed in Candida boidinii using such sugar derivatives as N-acylated d-glucosamines, C-glucosyl derivatives, and a 2-O-glycosylated disaccharide as acceptors. We found that a variety of sugar derivatives modified at C-1 or C-2 could be used as acceptors for transglycosylation by Endo-M to create novel oligosaccharides.

Acetylglucosamine↗
PubMed2004

Structural elucidation of novel phosphocholine-containing glycosylinositol-phosphoceramides in filamentous fungi and their induction of cell death of cultured rice cells.

Novel ZGLs (zwitterionic glycosphingolipids) have been found in and extracted from the mycelia of filamentous fungi ( Acremonium sp.) isolated from soil. Five ZGLs (ZGL1-ZGL5) were structurally elucidated by sugar compositional analysis, methylation analysis, periodate oxidation, matrix-assisted laser-desorption ionization-time-of-flight MS, (1)H-NMR spectroscopy and fast-atom bombardment MS. Their chemical structures were as follows: GlcN(alpha1-2)Ins1-P-1Cer (ZGL1), Man(alpha1-6)GlcN(alpha1-2)Ins1-P-1Cer (ZGL2), Man(alpha1-6)Man(alpha1-6)GlcN(alpha1-2)Ins1-P-1Cer (ZGL3), PC-->6Man(alpha1-6)GlcN(alpha1-2)Ins1- P -1Cer (ZGL4), and PC-->6Man(alpha1-6)Man(alpha1-6)GlcN(alpha1-2)Ins1-P-1Cer (ZGL5) (where Cer is ceramide and PC is phosphocholine). In addition, one acidic glycosphingolipid, which was the precursor of ZGLs, was also characterized as inositol-phosphoceramide. The core structure of the ZGLs, GlcN(alpha1-2)Ins1- P, is rather different from those found in other fungi, such as Man(alpha1-2)Ins1- P and Man(alpha1-6)Ins1- P. Interestingly, the terminal mannose residue of ZGL4 and ZGL5 was modified further with a PC group. The presence of PC-containing glycosylinositol-phosphoceramides has not been reported previously in any organism. The ceramide constituents of both ZGLs and acidic glycosphingolipid were essentially the same, and consisted of a 4-hydroxyoctadecasphinganine (phytosphingosine) as the sole sphingoid base and 2-hydroxytetracosanoic acid (>90%) as the major fatty acid. ZGLs were found to cause cell death in suspensions of cultured rice cells. The cell death-inducing activity of ZGLs is probably due to the characteristic glycan moiety of Man(alpha1-6)GlcN, and PC-containing ZGLs had high activity. This study is the first to demonstrate that fungal glycosylinositol-phosphoceramides induce cell death in cultured rice cells.

Acidic Glycosphingolipids↗
PubMed2004

High efficiency of transferring a native sugar chain from a glycopeptide by a microbial endoglycosidase in organic solvents.

We examined the transglycosylation reaction by the recombinant endo-beta-N-acetylglucosaminidase from Mucor hiemalis (Endo-M) expressed in Candida boidinii in media containing organic solvents. The recombinant Endo-M could transglycosylate a disialo biantennary complex-type oligosaccharide from hen egg yolk glycopeptide to p-nitrophenyl N-acetyl-beta-D-glucosaminide even in the presence of 30% acetone, dimethyl sulfoxide, or methanol. The yield of the transglycosylation product reached 21-34% of the total amount of acceptor, while the yield was only about 14% in aqueous solution.

Candida↗
PubMed2004

Applications of T-lymphoma labeled with fluorescent quantum dots to cell tracing markers in mouse body.

Photoluminescent semiconductor quantum dots (QDs) are novel nanometer-size probes that have found bioimaging. Here we imaged a cell line of mouse lymphocytes. QDs were actively taken into the target cells by endocytotic pathways. The fluorescence of QDs held in the endosomes could be studied for more than a week and remained stable luminescence against cell activation induced by concanavalin A, phytohemagglutinin, phorbol myristate acetate, and calcium ionophore A23187. These results suggested that QD-labeling was stable and did not affect either cell activation or cell function. When QD-labeled cells were intravenously injected into mouse, they remained in the peripheral blood in a concentration of approximately 10% up to 5 days after injection using both fluorescence microscopy and flow cytometry. In addition, approximately 20% of QDs were detected in the kidneys, liver, lung, and spleen and could still be observed 7 days after injection. These results suggested that fluorescent probes of QDs might be useful as bioimaging tools for tracing target cells over the period of a week in vivo.

Animals↗
PubMed2004

Characterization of spinal HSP72 induction and development of ischemic tolerance after spinal ischemia in rats.

Induction of heat shock protein (HSP72) has been implicated in the development of ischemic tolerance in several tissue organs including brain and spinal cord. In the present study, using an aortic balloon occlusion model in rats, we characterized the effect of transient noninjurious (3 or 6 min) or injurious intervals (10 min) of spinal ischemia followed by 4-72 h of reflow on spinal expression of HSP72 and GFAP protein. In a separate group of animals, the effect of ischemic preconditioning (3 or 6 min) on the recovery of function after injurious interval of spinal ischemia (10 min) was studied. After 3 min of ischemia, there was a modest increase in HSP72 protein immunoreactivity in the dorsal horn neurons at 12 h after reperfusion. After 6 min of ischemia, a more robust and wide spread HSP72 protein expression in both dorsal and ventral horn neurons was detected. The peak of the expression was seen at 24 h after ischemia. At the same time point, a significant increase in spinal tissue GFAP expression was measured with Western blots and corresponded morphologically with the presence of activated astrocytes in spinal segments that had been treated similarly. After 10 min of ischemia and 24 h of reflow, a significant increase in spinal neuronal HSP72 expression in perinecrotic regions was seen. Behaviorally, 3 min preconditioning ischemia led to the development of a biphasic ischemic tolerance (the first at 30 min and the second at 24 h after preconditioning) and was expressed as a significantly better recovery of motor function after exposure to a second 10-min interval of spinal ischemia. After 6 min ischemic preconditioning, a more robust ischemic tolerance at 24 h after preconditioning then seen after 3-min preconditioning was detected. These data indicate that 3 min of spinal ischemia represents a threshold for spinal neuronal HSP72 induction, however, a longer sublethal interval (6 min) of preconditioning ischemia is required for a potent neuronal HSP72 induction. More robust neurological protection, seen after 6 min of preconditioning ischemia, also indicates that HSP72 expression in spinal interneurons seen at 24 h after preconditioning may represent an important variable in modulating ischemic tolerance observed during this time frame.

Animals↗
PubMed2004

The effect of single weekly paclitaxel in heavily pretreated patients with recurrent or persistent advanced ovarian cancer.

OBJECTIVES: We have reported that single weekly paclitaxel has moderate activity in heavily pretreated ovarian cancer patients and is associated with a favorable toxicity profile. The purpose of this study was to reconfirm the effect of weekly paclitaxel in more number of cases. METHODS: Although 39 patients were enrolled, 37 patients with recurrent or persistent ovarian cancer previously treated with between one and three chemotherapeutic regimens containing platinum were eligible. Patients had measurable or assessable disease defined by clinical exam, radiographic studies, or serum CA 125. One cycle of treatment consisted of paclitaxel 80 mg/m2/week in 1-h infusion, 3 weeks on, 1 week off, and repeated at least twice. Two patients were withdrawn because of refusal of further treatment for neuropathy after the first cycle. Clinical responses were defined by established criteria. RESULTS: Thirty-seven patients were included in this intent-to-treat study. The overall clinical response rate was 45.9% (5 complete responses, 12 partial responses). The clinical response rate in patients with measurable tumor was 25.0% (2 complete responses, 1 partial response), while that in patients without measurable tumor and with assessable CA 125 levels was 56.0% (3 complete responses, 11 partial responses). Clinical response rate in patients with chemotherapy-free interval more than 6 months had about twice higher than that in patients with chemotherapy-free interval less than 6 months. The clinical response rate by number of prior regimens revealed that as number of prior regimens increases, the response rate decreases. CONCLUSION: Weekly paclitaxel has significant antitumor activity in heavily pretreated patients with recurrent or persistent ovarian carcinoma and warrants as second or third line chemotherapy in such setting.

Adult↗
PubMed2004

Chemo-enzymatic synthesis and structure-activity study of artificially N-glycosylated eel calcitonin derivatives with a complex type oligosaccharide.

Starting from N-glycosylated eel calcitonin derivatives that contain an N-acetyl-D-glucosamine residue specifically at the 3rd, 14th, 20th or 26th amino acid residue, corresponding glycopeptides with a complex-type oligosaccharide attached to the respective amino acid residue were synthesized by means of a transglycosylation reaction catalyzed by an endo-beta-N-acetylglucosaminidase from Mucor hiemalis . The use of a recombinant enzyme and an excess of a glycosyl donor led to a yield in excess of 60%. Calcitonin derivatives containing truncated oligosaccharides were also prepared via digestion of the complex-type N-glycan with exoglycosidases. Using these N-glycosylated calcitonin derivatives, the effect of carbohydrate structure and glycosylation site on the three-dimensional structure and the biological activity of the peptide were studied. The conformation of the peptide backbone did not change irrespective of the carbohydrate structure or the glycosylation site. However, hypocalcemic activity, calcitonin-receptor binding activity and the biodistribution of the derivatives were affected by the glycosylation and were dependent on both the carbohydrate structure and the glycosylation site. Although the larger oligosaccharides tended to hinder receptor binding, the biodistribution altered by N-glycosylation appeared to enhance the hypocalcemic activity in some cases, and the magnitude of the effect was dependent on the site of glycosylation.

Animals↗
PubMed2004

Role of brain perfusion single-photon emission tomography in traumatic head injury.

This investigation examined the role of brain perfusion single-photon emission tomography (SPET) in traumatic head injury in 35 patients. The results were compared with those of X-ray computerized tomography (CT) and magnetic resonance imaging (MRI). CT and MRI detected brain contusions in seven patients, subarachnoid haemorrhage in one patient and both in nine patients. In 16 of the 17 subjects (94%), SPET with technetium-99m-hexamethylpropyleneamine oxime (Tc-HMPAO) revealed CT/MRI-negative abnormalities, such as hypoperfusion in the contre-coup region, frontal hypoperfusion related to personality change and cerebellar hypoperfusion associated with vertigo. In two patients presenting with diffuse axonal injury in the brainstem, hypoperfusion in the frontal cortex on the affected side was observed on SPET. SPET demonstrated hypoperfusion in the adjacent cortex, with no abnormality on either CT or MRI, in six of seven patients exhibiting acute epidural haematoma. SPET failed to provide additional information in two of five patients with acute subdural haematoma and in one of two patients displaying chronic subdural haematoma. In four of nine patients with post-traumatic amnesia, SPET detected hypoperfusion in the temporal lobe, with no abnormality on either CT or MRI. In five of eight patients with vertigo, SPET detected hypoperfusion in the morphologically normal cerebellum. In seven cases involving personality change, frontal hypoperfusion was observed in four; moreover, a markedly non-homogeneous pattern was evident in the remaining three. Overall, SPET afforded additional information in 26 patients (74%). CT possesses an advantage with respect to the detection of haemorrhagic lesions. MRI provides more precise information regarding contusions and axonal injury. Frequently, SPET may be the only examination to reveal perfusion abnormalities which are related to symptoms in the absence of other objective findings, such as post-traumatic amnesia, vertigo or personality change.

Adolescent↗