Biomedical subjects

T Ohyama

Publications and source records attributed to T Ohyama.

At least 37 records · Page 2Linked to original sources

PubMed2002

Fracture resistance of pressable glass-ceramic fixed partial dentures.

The aim of the present study was to evaluate the mechanical strength of the Empress2 system, which is based on the use of a high-strength glass--ceramic core of lithium disilicate, and the fracture resistance of fixed partial dentures fabricated with this material. To evaluate mechanical strength, four types of ceramic materials were tested for four-point flexural strength and diametral tensile strength: Empress2 core material, Empress2 layering porcelain, conventional Empress material and Dicor. Then, using Empress2, conventional Empress and Dicor, actual clinical type anterior fixed partial dentures were fabricated for fracture testing. The results showed that the Empress2 core material, at 329 MPa, has more than twice the flexural strength of conventional materials and at 271 MPa, more than four times the diametral tensile strength of conventional materials. Furthermore, fixed partial dentures fabricated with Empress2 had a fracture resistance of 1424 N. That is, they were more than twice as fracture resistant as fixed partial dentures made with conventional materials.

Ceramics↗

PubMed2002

The influence of altered occlusal guidance on condylar displacement.

This study investigated mandibular displacement and masticatory muscle activity during clenching in lateral occlusal position in relation to the lateral occlusal pattern. Twenty healthy human subjects (mean = 26.5 years) volunteered for this study. Metallic occlusal overlays were fabricated for the lower working side canine to second molar and non-working side second molar in order to simulate a canine protected occlusion, group function occlusion and bilateral balanced occlusion (balancing contact). Three-dimensional displacements of the bilateral condyle and electromyography (EMG) activities in the bilateral masseter, anterior and posterior temporalis were recorded during maximal clenching. The experimental occlusal pattern was revealed to have statistically significant effects on both condylar displacement and EMG activity (P < 0.001 and P < 0.001, respectively). When compared to the simulated group function occlusion, the simulated canine protected occlusion and balancing contact caused statistically significant smaller superior displacements of the non-working side condyle, which suggests that they may result in reduced temporomandibular joint (TMJ) loading. Furthermore, the simulated canine protected occlusion was associated with the lowest EMG activity, which suggests that this occlusal pattern has the capacity to reduce the level of parafunctional activity.

Adult↗

PubMed2001

Role of C-terminal region of HA-33 component of botulinum toxin in hemagglutination.

Using SDS-PAGE, we found that one subcomponent, hemagglutinin (HA-33), from the Clostridium botulinum progenitor toxin of type D strain 1873 and type C strain Yoichi had slightly smaller molecular sizes than those of type C and D reference strains, but other components did not. Based on N- and C-terminal sequence analyses of HA-33, a deletion of 31 amino acid residues from the C-terminus at a specific site was observed in the HA-33 proteins of both strains. The progenitor toxins from both strains showed poor hemagglutination activities, titers of 2(1) or less, which were much lower than titers from the reference strains (2(6)), and did not bind to erythrocytes. These results suggest strongly that the short C-terminal region of the HA-33 plays an essential role in the hemagglutination activity of the botulinum progenitor toxin. Additionally, a sequence motif search predicted that the C-terminal region of HA-33 has a carbohydrate-recognition subdomain.

Amino Acid Sequence↗

PubMed2001

Linearization and integration of DNA into cells preferentially occurs at intrinsically curved regions from human LINE-1 repetitive element.

A bent DNA library was constructed from human genomic DNA, from which a new clone belonging to the human LINE-1 sequence family was isolated and characterized. This clone, with a length of 378 base pairs and termed HBC-1 (human bent clone-1), contained an intrinsically occurring curved DNA structure. By permutation analysis, the center of curvature of this fragment was mapped onto the nucleotide position 886 from the 5' terminus of the complete LINE-1 sequence. Reporter plasmids, which contain HBC-1, were effectively integrated into human chromosome, indicating that the bent DNA structure provides a preferential donor site for the integration of human LINE-1 sequences. The present finding may provide an explanation as to why some inactivated LINE-1 sequences on human chromosomes carry the deletion at their 5' termini.

3T3 Cells↗

PubMed2001

Cu-metallothioneins (Cu(I)8-MTs) in LEC rat livers 13 weeks after birth still act as antioxidants.

Redox properties of metallothioneins (MTs) and Cu in the cytosol from Long-Evans Cinnamon (LEC) rat livers 13 weeks after birth were investigated. MTs from LEC rat livers contain 8 g atoms of Cu and 1 g atom of Zn per mole of protein (Cu(I)8-MTs). Titration of Cu(I)8-MTs with CuCl2 indicates that Cu(I)8-MTs were able to reduce further 2-g atoms of cupric ions per mole MTs as bound form. Hg2+-induced hydroxyl radical generation from Cu(I)8-MTs was demonstrated by ESR using the spin trap, 5,5-dimethyl-1-pyrroline N-oxide (DMPO). The intensity of DMPO-OH signal from Cu-loaded MTs was increased with the increasing number of Cu in MTs. The used cytosol fraction contained 1.37 mM total Cu and 5 mM DTNB titrable-SH groups has a potential to reduce 2 mM CuCl2. No ESR signal due to Cu2+ was also detected with LEC rat liver cytosol, whereas strong Cu2+ signal appeared by the addition of HgCl2. The rate constants for the reaction of Cu(I)8-MTs with superoxide and hydroxyl radicals were estimated to be 2 x 10(6) and > or = 10(12) M(-1)s(-1), respectively, from competition kinetics. Cu2+-catalyzed oxidation of DNA was strongly inhibited both in the presence of Cu-unsaturated MTs and GSH. The results suggest that Cu(I)8-MTs from LEC rat livers just before hepatitis still act as antioxidants.

Animals↗

PubMed2001

MST, a physiological caspase substrate, highly sensitizes apoptosis both upstream and downstream of caspase activation.

The human serine/threonine kinase, mammalian STE20-like kinase (MST), is considerably homologous to the budding yeast kinases, SPS1 and STE20, throughout their kinase domains. The cellular function and physiological activation mechanism of MST is unknown except for the proteolytic cleavage-induced activation in apoptosis. In this study, we show that MST1 and MST2 are direct substrates of caspase-3 both in vivo and in vitro. cDNA cloning of MST homologues in mouse and nematode shows that caspase-cleaved sequences are evolutionarily conserved. Human MST1 has two caspase-cleavable sites, which generate biochemically distinct catalytic fragments. Staurosporine activates MST either caspase-dependently or independently, whereas Fas ligation activates it only caspase-dependently. Immunohistochemical analysis reveals that MST is localized in the cytoplasm. During Fas-mediated apoptosis, cleaved MST translocates into the nucleus before nuclear fragmentation is initiated, suggesting it functions in the nucleus. Transiently expressed MST1 induces striking morphological changes characteristic of apoptosis in both nucleus and cytoplasm, which is independent of caspase activation. Furthermore, when stably expressed in HeLa cells, MST highly sensitizes the cells to death receptor-mediated apoptosis by accelerating caspase-3 activation. These findings suggest that MST1 and MST2 play a role in apoptosis both upstream and downstream of caspase activation.

3T3 Cells↗

PubMed2001

Latent acquisition of timed responses in cerebellar cortex.

Evidence indicates that rabbit eyelid conditioning is mediated by plasticity in the interpositus cerebellar nucleus and in cerebellar cortex. Although the relative contributions of these sites are not fully characterized, evidence suggests that plasticity in the cerebellar cortex influences conditioned response amplitude and timing, whereas plasticity in the interpositus nucleus is necessary or permissive for conditioned response expression. Recent empirical and computational analyses suggest that, during training, plasticity is initially established in the cerebellar cortex, whereas conditioned response expression begins later as plasticity is induced in the interpositus nucleus. We used the dependence of response timing on the interstimulus interval (ISI) to test this latent learning hypothesis. Rabbits were initially trained using a tone conditioned stimulus (CS) with a relatively long ISI to a low-criterion threshold. The relative absence of plasticity in the interpositus nucleus was then examined via reversible disconnection of the cerebellar cortex. Later, to induce plasticity in the interpositus nucleus, subjects were trained to robust levels of conditioned response expression using a shorter ISI. Reversible disconnection of the cerebellar cortex at this time confirmed the presence of robust interpositus nucleus plasticity after the second phase. Subsequent probe trials with the long CS alone then revealed double-peaked responses whose peaks were appropriately timed to the two ISIs. The results are consistent with the hypothesis that temporally specific learning occurs first in the cerebellar cortex before the appearance of conditioned responses. This latent learning is expressed only after plasticity is induced in the interpositus nucleus.

Acoustic Stimulation↗

PubMed2001

Crystal structure of a depsipeptide, Boc-(Leu-Leu-Lac)3-Leu-Leu-OEt.

A sequential polydepsipeptide, Boc-(Leu-Leu-Lac)3-Leu-Leu-OEt (1) (Lac = L-lactic acid residue) has been synthesized by the segment condensation method. The sequential unit of 1, -Leu-Leu-Lac-, is consisted of two amino acid residues and one hydroxy acid residue. X-ray diffraction measurement with an imaging plate detector and a direct-methods procedure of Shake-and-Bake successfully revealed the crystal structure of 1. In the solid state, the 11-mer depsipeptide, 1, have clear alpha-helical conformation even with the three ester linkages.

Crystallization↗

PubMed2001

Intrinsic DNA bends: an organizer of local chromatin structure for transcription.

DNA with a curved trajectory of its helix axis is called bent DNA, or curved DNA. Interestingly, biologically important DNA regions often contain this structure, irrespective of the origin of DNA. In the last decade, considerable progress has been made in clarifying one role of bent DNA in prokaryotic transcription and its mechanism of action. However, the role of bent DNA in eukaryotic transcription remains unclear. Our recent study raises the possibility that bent DNA is implicated in the "functional packaging" of transcriptional regulatory regions into chromatin. In this article, I review recent progress in bent DNA research in eukaryotic transcription, and summarize the history of bent DNA research and several subjects relevant to this theme. Finally, I propose a hypothesis that bent DNA structures that mimic a negative supercoil, or have a right-handed superhelical writhe, organize local chromatin infrastructure to help the very first interaction between cis-acting DNA elements and activators that trigger transcription.

Chromatin↗

PubMed2001

Nucleotide sequence analysis and development of consensus primers of RT-PCR for detection of Norwalk-like viruses prevailing in Japan.

A total of 177 different nucleotide sequences of the RNA polymerase region of Norwalk-like viruses (NLVs) genomes, collected via a nation-wide survey project in Japan between 1989 and 1998, were examined by reverse transcription-polymerase chain reaction (RT-PCR) employing various primer pairs. The nucleotide sequences of different strains showed great diversity, with a range of 57 to 100% identities among strains. The strains could be classified into five clusters: Norwalk (NV), Snow Mountain agent/Bristol virus (SMA/BV), Toronto virus/Mexico virus (TV/MX), and Japan specific cluster 1 and 2 (JP-1 and JP-2). Within each cluster there is greater than 85% identity of amino acid sequence (more than 75% identity of nucleotide sequences), based on sequence homology analysis. We believe that two of the five clusters, JP-1and JP-2, define new specific clusters found in Japan according to phylogenetic and pair-wise comparison studies. An RT-PCR procedure was designed using new consensus primer pairs, P1/P2, P1/P3, and Y1/Y2 based on multiple alignment of collected nucleotide sequences, that are expected to detect nearly all NLVs prevailing in Japan. The usefulness of the primers was tested by ten different laboratories in Japan using a panel of ten fecal samples containing different virus strains. The identification of these primer pairs will facilitate routine diagnosis of NLV infection by RT-PCR and offers the potential for their direct detection in food and environmental samples.

Caliciviridae Infections↗

PubMed2001

Modulation of H reflex of pretibial and soleus muscles during mastication in humans.

A previous study in our laboratory demonstrated that the soleus H reflex was facilitated during mastication in humans. In the present study, we investigated whether there was any modulation of the magnitude of the pretibial H reflex during mastication in five healthy adult volunteers. The pretibial H reflex was significantly facilitated during mastication, and there was no significant difference in the facilitation between jaw-closing and jaw-opening phases; that is, the gain of the H reflex was modulated tonically but not in a phase-dependent manner during mastication. Furthermore, in the same subjects, we confirmed that the soleus H reflex was facilitated during mastication. Based on our findings, we conclude that the H reflexes in both the pretibial and soleus muscles undergo a nonreciprocal facilitation during mastication. It is suggested that mastication contributes to stabilization of postural stance in humans.

Adult↗

PubMed2001

Effects of sibutramine on the central dopaminergic system in rodents.

The effects of sibutramine on central dopaminergic system in rats and mice were examined by neurochemical and behavioral pharmacological methods. Dopamine reuptake inhibition by sibutramine in brain synaptosomes was only 4-5 times stronger than those of amitriptyline and dosulepin, which do not exhibit dopamine uptake inhibition in vivo. Single treatment with sibutramine did not alter the brain content of dopamine and DOPAC. However, similar to methamphetamine and pargyline, sibutramine antagonized methyl-4-pheny-1,2,3,6-tetrahydro-pyridine (MPTP) induced dopamine depletion in mouse brain. In forced swimming tests of reserpinized mice, sibutramine shortened the immobilized time, similar to dopaminergic drugs including nomifensine, bupropion (dopamine-reuptake inhibitor), methamphetamine, SKF 38393 (dopamine D1 agonist), quinpirole (dopamine D2 agonist) and apomorphine (dopamine D1/D2 agonist). In addition, sibutramine caused rotational behavior toward the lesioned side in rats with unilateral lesions of the substantia nigra induced by 6-hydroxydopamine. These results suggest that sibutramine exhibits neurochemical and behavioral dopaminomimetic activity in vivo, which is mediated by dopamine reuptake inhibition by the active metabolites of sibutramine.

Journal Article↗

PubMed2001

A common feature shared by bent DNA structures locating in the eukaryotic promoter region.

Eukaryotic promoters often contain a bent DNA structure, suggesting that this structure plays some role in transcription. To reveal the role, we need more information on the promoters that contain or flank a bent DNA structure. In this study, we collected such promoters by the following approach: we first isolated human genomic DNA fragments that contained at least one bent DNA structure, then shotgun cloned them into a promoter trap vector, screened DNA fragments that functioned as a promoter, and finally found the promoters of interest by determining the bent DNA locus and the region expressing promoter activity. From 1,187 recombinant plasmids, we isolated 51 that showed promoter activity. Structural and functional analyses of randomly selected 10 clones with inserts of 548-913 bp demonstrated 11 sequences that could drive transcription. Unexpectedly, all of these clones met our purpose: i.e., each segment that showed a promoter activity (67-179 bp) was very close to the bent DNA structure (spanning about 150 bp in all clones), and in some cases overlapped it. More interestingly, these bent DNA structures all had a superhelical writhe. We propose a hypothesis that in the bent-DNA-containing eukaryotic promoters. bent DNA organizes local chromatin infrastructure appropriately for transcription initiation.

Animals↗

PubMed2001

Characterization and reconstitution of functional hemagglutinin of the Clostridium botulinum type C progenitor toxin.

The purified progenitor toxin of Clostridium botulinum type C strain 6814 (C-6814) forms a large complex composed of 150-kDa neurotoxin (NT), 130-kDa nontoxic-nonhemagglutinin (NTNHA), and hemagglutinin (HA) components. The HA component consisted of a mixture of several subcomponents with molecular masses of 70, 55, 33, 26-21 and 17 kDa. We isolated the HA subcomponents from the progenitor toxin by chromatography in the presence of denaturants. The isolated HA subcomponents, designated as i-HA-33, i-HA-55, i-HA-70 and i-HA-33/17, were nearly homogeneous on SDS/PAGE, but the HA-17 and HA-26-21 components were not purified. Some HA subcomponents, designated as f-HA-33 and f-HA-33/17 complex, existed free of the progenitor toxin in the culture medium and they were separately purified. Every HA subcomponent so far isolated shows binding activity to erythrocytes. The hemagglutination activities of each HA subcomponent had a titer of 25 for the f-HA-33/17 complex, and below 23 for the other f- and i-HA subcomponents, while the parent progenitor L toxin was 28. The reconstitution of various combinations of f- and i-HA subcomponents was attempted via mixing and tested for hemagglutination activity. When the i-HA-33/17 complex and i-HA-55 were mixed, the hemagglutination activity was recovered to a titer of 29, which was slightly higher than that of the parent toxin. These data imply that a combination of at least HA-33, -17 and -55 subcomponents is required for full hemagglutination activity of the botulinum progenitor toxin, but each single HA subcomponent shows weak or no aggregation of erythrocytes.

Bacterial Proteins↗

PubMed2001

Hypnotic action of melatonin during daytime administration and its comparison with triazolam.

The present study was conducted to assess hypnotic action, effects on rectal temperature and dose dependency by daytime administration of exogenous melatonin (MLT) at 1 mg, 3 mg or 6 mg to subjects consisting of seven healthy juvenile adults. As a result, exogenous MLT significantly increased total sleep time and sleep efficiency, and MLT 6 mg was observed to demonstrate hypnotic effects that were nearly equal to those of triazolam at 0.125 mg. Rectal temperature was significantly decreased at MLT 1mg and 3 mg, there were no significant differences observed in the hypothermic effects at MLT 6 mg. These results indicate that exogenous MLT had dose-dependent hypnotic action on daytime sleep, and it is possible to consider that this hypnotic action was based on a direct-acting mechanism.

Adult↗

PubMed2001

Expression of HDL receptor, CLA-1 in human smooth-muscle cells and effect of interferon-gamma on its regulation.

High-density lipoprotein (HDL) exerts antiatherogenic effects by various mechanisms. The protective effect of HDL is thought to involve the reverse transport of cholesterol from cells in the arterial wall to the liver for disposal. We previously identified human scavenger receptor BI (hSR-BI/CLA-1) as a receptor for human HDL, but did not examine the expression of hSR-BI/CLA-1 in smooth-muscle cells. In this present study, a human aortic intima smooth-muscle cell line immortalized with SV 40 DNA was established, and the expression of hSR-BI/CLA-1 in this cell line analyzed by Western blot and RT-PCR. HSR-BI/CLA-1 mRNA and protein were detected in both this cell line and primary human aortic smooth-muscle cells. A cytokine, interferon-gamma (IFN-gamma) inhibited the hSR-BI/CLA-1 protein expression, but not mRNA expression. This observation confirmed that selective cholesterol ester uptake from HDL was inhibited by IFN-gamma. These results indicated that hSR-BI/CLA-1 may be expressed in human smooth-muscle cells, and the expression may be modulated by IFN-gamma. HSR-BI/CLA-1 on smooth-muscle cells could play an important role in atherogenesis.

Aorta, Thoracic↗

PubMed2001

A vibratory stimulation-based inhibition system for nocturnal bruxism: a clinical report.

For the single subject tested to date, the bruxism-contingent vibratory-feedback system for occlusal appliances effectively inhibited bruxism without inducing substantial sleep disturbance. Whether the reduction in bruxism would continue if the device no longer provided feedback and whether the force levels applied are optimal to induce suppression remain to be determined.

Adult↗

PubMed2001

Coaggregation of Porphyromonas gingivalis and Prevotella intermedia.

Porphyromonas gingivalis cells coaggregated with Prevotella intermedia cells. The coaggregation was inhibited with L-arginine, L-lysine, Nalpha-p-tosyl-L-lysine chloromethyl ketone, trypsin inhibitor, and leupeptin. Heat- and proteinase K-treated P. gingivalis cells showed no coaggregation with P. intermedia cells, whereas heat and proteinase K treatments of P. intermedia cells did not affect the coaggregation. The vesicles from P. gingivalis culture supernatant aggregated with P. intermedia cells, and this aggregation was also inhibited by addition of L-arginine or L-lysine and by heat treatment of the vesicles. The rgpA rgpB, rgpA kgp, rgpA rgpB kgp, and rgpA kgp hagA mutants of P. gingivalis did not coaggregate with P. intermedia. On the other hand, the fimA mutant lacking the FimA fimbriae showed coaggregation with P. intermedia as well as the wild type parent. These results strongly imply that a heat-labile and proteinous factor on the cell surface of P gingivalis, most likely the gingipain-adhesin complex, is involved in coaggregation of P. gingivalis and P. intermedia.

Adhesins, Bacterial↗