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Biomedical subjects

T Asakura

Publications and source records attributed to T Asakura.

At least 19 recordsLinked to original sources
PubMed2005

Use of microcoil probehead for determination of the structure of oriented silk fibers by solid-state NMR.

A microcoil probehead for solid-state NMR was developed with a two-channel radio-frequency circuit, and 13C observation with a proton-decoupling probehead was performed to obtain information on the distribution of the orientation of silk fibroin molecules in the fiber. The coil (1 mm (diameter) x 5 mm (length)) of the probehead was placed at the angles 90 degrees and 30 degrees , relative to the static magnetic field. Only 70 mug of [1-13C]Gly silk fibroin fiber was used in a magnet of 9.4 T (400 MHz for proton channel).

Alanine↗
PubMed2005

[Nifekalant hydrochloride as an effective treatment for postoperative ischemic heart disease].

We experienced 2 effective cases of nifekalant hydrochloride. One patient was 76-year-old female who underwent emergent coronary artery bypass grafting (CABG) because of unstable angina pectoris (AP) and ventricular fibrillation (Vf). Her cardiac function had been decreased preoperatively due to old myocardial infarction (OMI). One day after CABG, she revealed sustained ventricular tachycardia (VT) and Vf. Although administrations of neither lidocaine hydrochloride nor magnesium sulfate were effective, nifekalant hydrochloride finally stopped the life-threatening arrhythmia without hypotension. Another patient was 77-year-old male who underwent CABG and Dor operation. His cardiac function also had been decreased due to OMI. He revealed VT attack at midnight 3 days after operation. VT attack still appeared at next 2 midnight under lidocaine hydrochloride infusion, but finally it has disappeared after starting a drip infusion of nifekalant hydrochloride. Nifekalant hydrochloride is quite useful as a new therapeutic strategy for uncontrollable VT and Vf and for the patient who has a reduced left ventricular function because it has an inotropic effect.

Aged↗
PubMed2004

[Observation of the right atrial wall suture line after tricuspid valve supra-annular implantation].

Strength of the right atrial wall suture line after tricuspid valve supra-annular implantation (TVSI) is controversial. We observed the right atrial supra-annular position of a 63-year-old male during his third mitral operation who underwent mitral valve replacement (MVR) and TVSI 15 years ago. Eight years later, he received the second MVR and removal of the bioprosthetic valve from the tricuspid position due to primary tissue failures. The annular size of the tricuspid valve had decreased enough to be fixed by tricuspid annuloplasty (TAP) and re-TVSI was not needed at that time. In this operation, 7 years following bioprosthetic valve removal, the circularly bulging atrial wall still remained and seemed to have enough strength for holding the prosthetic valve. This finding may support the conclusion that the right atrial wall has enouth strength for holding a prosthetic valve in position.

Bioprosthesis↗
PubMed2003

Alteration in haemodynamics and pathological changes in the cardiovascular system during the development of Type 2 diabetes mellitus in OLETF rats.

AIMS/HYPOTHESIS: The process of cardiovascular complications in Type 2 diabetes mellitus (DM) is unclear. We investigated pathophysiological changes of the heart and vessels in the Otsuka Long-Evans Tokushima Fatty (OLETF) rat Type 2 DM model during a long time period. METHODS: Echocardiography was carried out at 22 and 62 weeks of age of OLETF ( n=10, each) and age-matched Long-Evans Tokushima Otsuka (LETO) rats ( n=10, each) as a reference. Haemodynamic measurements and histological examinations of the heart and the coronary and aortic vascular walls were done. RESULTS: The left ventricular (LV) maximal -dP/dt was reduced in OLETF rats at 62 weeks (-1085+/-35 mmHg/s) less than that at 22 weeks (-1892+/-396 mmHg/sec, p<0.05) and in LETO rats at 62 weeks (-1306+/-200 mmHg/sec, p<0.05). Wall thickening of intramyocardial coronary arteries, capillary tortuosity and thickening of basement membrane were evident in OLETF rats at 62 weeks. Intimal and medial wall thickening of the aorta were prominent in OLETF rats at 62 weeks (15+/-2.2 and 90+/-6.6 micro m, in LETO rats at 62 weeks, 2+/-0.4 and 65+/-5.2 micro m, p <0.05, and in OLETF rats at 22 weeks, 7+/-4.6 and 71+/-6.0 micro m, p<0.05, respectively). CONCLUSIONS/INTERPRETATION: In the Type 2 DM model, angiopathy, especially in coronary arteries including small vessels, as well as a LV relaxation abnormality, are induced in a late stage of DM. These are considered to be important complications in Type 2 DM.

Animals↗
PubMed2003

Prions prevent brain damage after experimental brain injury: a preliminary report.

The physiological function of the normal cellular form of prion protein (PrPC) is not yet fully understood. In the current study we used prion protein gene knock-out mice (Prnp-/-) to assess the role of PrPC in traumatic brain injury. Prnp+/- and Prnp-/- mice were subjected to weight-drop contusional brain injury over the left parietal cortex. Prnp-/- mice manifested a significantly larger lesion volume and worse neuromotor scores than did their Prnp+/- littermates. IgG immunostaining revealed that in Prnp-/- mice the breakdown in the blood-brain barrier (BBB) was more extensive at 1 month after brain injury. Our results are in agreement with previous in vitro findings of the neuroprotective role of PrPC and further support the hypothesis that functional loss of PrPC plays a pathogenic role in prion diseases. We also suggest that PrPC modulates BBB function.

Animals↗
PubMed2003

The glutamate AMPA receptor antagonist, YM872, attenuates regional cerebral edema and IgG immunoreactivity following experimental brain injury in rats.

We previously reported the neuroprotective effects of the glutamate AMPA receptor antagonist YM872 on neurobehavioral motor function and cortical tissue loss (lesion volume) in a brain-injured rat model. Here we examined its effect on brain edema and the breakdown of the blood-brain barrier (BBB). Rats subjected to severe right lateral (parasagittal) fluid-percussion brain injury or sham injury received a 4-hr intravenous infusion of YM872 (20 mg/kg/ hr, 20 mg/3 ml) or normal saline starting at 15 min post-injury. At 48 hr we removed their brains and evaluated the cerebral regional edema by the wet weight/dry weight method. Another group of rats was transcardially fixed with 10% formalin at 2 weeks after injury. Serial brain sections were immunostained for endogenous IgG and the extent and intensity of staining were evaluated. The administration of YM872 resulted in a significant reduction in regional cerebral edema in the injured parietal cortex and a markedly reduced area of IgG immunoreactivy in the injured cortex. Our results indicate that the post-traumatic administration of YM872 may be neuroprotective by reducing BBB breakdown and regional cerebral edema.

Animals↗
PubMed2003

Bypass balloon pumping: a newly developed device for mechanical circulatory support in heart failure.

Various types of assist devices have been developed for severe heart failures. Among them, intra-aortic balloon pumping (IABP) has achieved popularity, mainly in the treatment of patients with either severe cardiac infarction or low cardiac output syndrome (LOS) after open-heart surgery. However, IABP has a limitation in that although it acts as a pressure support, it cannot directly support flow volume. In cases of severe pump failure, stronger pump support would be required. However, there is a limit in the clinical use of temporary mechanical support using a pump because of the costs of the expensive equipment. With this in mind, we came up with a new idea in which the motion of a balloon in IABP system is converted into a power source for creating a one-way stream. In order to realize our idea, we made a J-shaped sample model of pulsating chamber incorporating two ball valves. In the hydrodynamic experiment using our new device, flows over 2500 ml/min (Max. 3475 ml/min) were obtained. The percent changes in parameters such as TTI, DPTI and bypass flows obtained by the experiment of left ventricular bypass have demonstrated that our assist system is effective for reducing cardiac work.

Animals↗
PubMed2002

[Lymphoscintigraphy for chylothorax after replacement of descending thoracic aortic aneurysm].

A 77-year-old female with Stanford B chronic aortic dissection, received elective replacement of descending aorta. The aorta distal to the aneurysm was encircled with a tape, and replaced using the double barrel technique. After the operation, chest X-ray showed effusion on the bilateral side. The amount of milky fluid from drain increased to 2,000 ml per day. The chemical profiles of the fluids were compatible with chylothorax. The Thoracic duct near the diaphragm was closed through left mini-thoracotomy. But the leakage of chyle did not cease. The lymphoscintigraphy showed a leakage to right lower intrathorax near the diaphragm and native aorta. A defect of the thoracic duct was closed, and chylothorax was cured. This case shows that though detailed anatomical structure of thoracic duct is not revealed, lymphoscintigraphy is useful for the localization of leakage in patients with chylothorax of post-cardiovascular-surgery.

Aged↗
PubMed2001

Suppression of GST-P by treatment with glutathione-doxorubicin conjugate induces potent apoptosis in rat hepatoma cells.

A conjugate of doxorubicin and glutathione via glutaraldehyde (GSH-DXR) inhibited glutathione S-transferase (GST) activity of rat hepatoma AH66 cells, and treatment of the cells with GSH-DXR induced caspase-3 activation and DNA fragmentation. After treatment of AH66 cells with 0.1 microM GSH-DXR, GST-P (placental type of rat GST isozymes) mRNA and its protein increased transiently and then decreased thereafter compared with the levels in nontreated cells. Caspase-3 activation and DNA fragmentation were induced following the suppression of GST-P expression by treatment with GSH-DXR. When the cells were treated with 100 microM ethacrynic acid (ECA), an inhibitor of GST, DNA fragmentation and caspase-3 activation were observed. In contrast, treatment of AH66 cells with a low concentration of ECA (1 microM) that showed little inhibition of GST activity induced slight, but significantly enhanced expression and activity of GST-P, and consequent prevention of DXR- and GSH-DXR-induced DNA fragmentation. Overexpression of GST-pi (placental type of human GST isozymes) by transfection of GST-pi sense cDNA into AH66 cells decreased sensitivities to DXR and GSH-DXR, and the suppression of GST-P by transfection of the antisense cDNA into the cells increased drug sensitivity. On the other hand, there was little change in drug sensitivity caused by overexpression of site-directedly mutated GST-P in which the active-site residue Tyr39 was replaced with His (W39H) or the substrate-binding site residue Cys48 was replaced with Ser (C48S) by transfection of those cDNAs into AH66 cells. These results suggested that the suppression of GST-P in AH66 cells treated with GSH-DXR must play an important role in the induction of apoptosis.

Animals↗
PubMed2001

Structure of Bombyx mori silk fibroin before spinning in solid state studied with wide angle x-ray scattering and (13)C cross-polarization/magic angle spinning NMR.

The structure of a crystalline form of Bombyx mori silk fibroin, commonly found before the spinning process (known as silk I), has been proposed as a repeated beta-turn type II-like structure by combining data obtained from solid-state two dimensional spin-diffusion nuclear magnetic resonance and rotational-echo double-resonance (T. Asakura et al., J Mol Biol, in press). In this paper, the WAXS pattern of alanine-glycine alternating copolypeptide, (Ala-Gly)(15) with silk I form which was used for a silk I model of B. mori silk fibroin was observed. The pattern calculated with the silk I model proposed by us is well reproduced the observed one, indicating the validity of the proposed silk I model. In addition, two peptides of the other repeated sequences which contain Tyr or Val residues in the silk fibroin,23 were synthesized; (Ala-Gly-Tyr-Gly-Ala-Gly)(5) and (X-Gly)(15) where X is Tyr for the 7th, 15th and 23th residues, and Val for the 11th residue and Ala for other residues. There are no sharp peaks in the WAXS patterns, and therefore both samples are in the non-crystalline state. This is in agreement with the (13)C CP/MAS NMR result, where the conformation is mainly random coil.

Amino Acid Sequence↗
PubMed2001

Treatment with NS3623, a novel Cl-conductance blocker, ameliorates erythrocyte dehydration in transgenic SAD mice: a possible new therapeutic approach for sickle cell disease.

The dehydration of sickle red blood cells (RBCs) through the Ca-activated K channel depends on the parallel movement of Cl ions. To study whether Cl-conductance block might prevent dehydration of sickle RBCs, a novel Cl-conductance inhibitor (NS3623) was characterized in vitro using RBCs from healthy donors and sickle cell patients and in vivo using normal mice and a transgenic mouse model of sickle cell disease (SAD mice). In vitro, NS3623 reversibly blocked human RBC Cl-conductance (g(Cl)) with an IC(50) value of 210 nmol/L and a maximal block of 95%. In vivo, NS3623 inhibited RBC g(Cl) after oral administration to normal mice (ED(50) = 25 mg/kg). Although g(Cl), at a single dose of 100 mg/kg, was still 70% inhibited 5 hours after dosing, the inhibition disappeared after 24 hours. Repeated administration of 100 mg/kg twice a day for 10 days caused no adverse effects; therefore, this regimen was chosen as the highest dosing for the SAD mice. SAD mice were treated for 3 weeks with 2 daily administrations of 10, 35, and 100 mg/kg NS3623, respectively. The hematocrit increased, and the mean corpuscular hemoglobin concentration decreased in all groups with a concomitant increase in the intracellular cation content. A loss of the densest red cell population was observed in conjunction with a shift from a high proportion of sickled to well-hydrated discoid erythrocytes, with some echinocytes present at the highest dosage. These data indicate feasibility for the potential use of Cl-conductance blockers to treat human sickle cell disease.

Anemia, Sickle Cell↗
PubMed2001

A repeated beta-turn structure in poly(Ala-Gly) as a model for silk I of Bombyx mori silk fibroin studied with two-dimensional spin-diffusion NMR under off magic angle spinning and rotational echo double resonance.

The structure of a crystalline form of Bombyx mori silk fibroin, commonly found before the spinning process (known as silk I), was proposed by combining data obtained from two-dimensional spin-diffusion nuclear magnetic resonance under off magic angle spinning, rotational-echo double-resonance (REDOR), previously reported X-ray diffraction analyses and 13C NMR chemical shifts. Instead of B. mori silk fibroin with silk I structure, we used the sequential model peptide (Ala-Gly)15. The structure of the sequential model peptide is characterized as silk I after dissolving the peptide in 9 M LiBr and then dialyzing against water. Moreover, 13C or 15N-labeled sites may be introduced easily at any position in (Ala-Gly)(15) by the solid phase synthesis method for these NMR experiments. The torsional angles of (Ala-Gly)15 with silk I structure were determined as (-60(+/-5) degrees, 130(+/-5) degrees ) and (70(+/-5) degrees, 30(+/-5) degrees ) for Ala and Gly residues, respectively. The formation of the intra-molecular hydrogen bonding along the chain was confirmed from REDOR NMR by determination of the inter-atomic distance between the nitrogen and carbon atoms comprising the intra-molecular hydrogen bonding. The structure is named a repeated beta-turn type II-like structure.

Alanine↗
PubMed2001

Hydroxyurea-induced oxidative damage of normal and sickle cell hemoglobins in vitro: amelioration by radical scavengers.

Hydroxyurea (HU) induces fetal hemoglobin (Hb F) production in patients with sickle cell anemia. The therapeutic dosage of HU used for Hb F induction often elicits myelosuppression, which becomes its major associated complication. We examined the effect of HU on hemoglobin modulation and the role of radical scavengers on these induced changes. In vitro exposure of human blood to various concentrations of HU at predetermined time intervals induced a progressive dose-dependent oxidation (MetHb formation) of both adult (Hb AA) and sickle (Hb SS) hemoglobins. The oxidative effect of HU on Hb SS was 3 times greater than its effect on Hb AA. Similar but less profound changes were observed in H2O2-treated samples. Hb F was, however, observed to be relatively resistant to HU-induced oxidative damage. A substantial protective effect of Hb by alpha-tocopherol, ascorbic acid, and D-mannitol was observed during pretreatment of Hb AA and Hb SS blood samples. Analyses of the hemoglobins and their globin chain components by high-performance liquid chromatography revealed a considerable protective effect by these free radical scavengers. These results indicate that the HU-induced damage of hemoglobin and their component globin chains can be reduced by radical scavengers.

Adolescent↗
PubMed2001

Pressure-dependent changes in the structure of the melittin alpha-helix determined by NMR.

A novel method is described, which uses changes in NMR chemical shifts to characterise the structural change in a protein with pressure. Melittin in methanol is a small alpha-helical protein, and its chemical shifts change linearly and reversibly with pressure between 1 and 2000 bar. An improved relationship between structure and HN shift has been calculated, and used to drive a molecular dynamics-based calculation of the change in structure. With pressure, the helix is compressed, with the H-O distance of the NH-O=C hydrogen bonds decreased by 0.021 +/- 0.039 A, leading to an overall compression along the entire helix of about 0.4 A, corresponding to a static compressibility of 6 x 10(-6) bar(-1). The backbone dihedral angles phi and psi are altered by no more than +/- 3 degrees for most residues with a negative correlation coefficient of -0.85 between phi(i) and psi(i - 1), indicating that the local conformation alters to maintain hydrogen bonds in good geometries. The method is shown to be capable of calculating structural change with high precision, and the results agree with structural changes determined using other methodologies.

Amides↗
PubMed2001

Interaction of mastoparan with membranes studied by 1H-NMR spectroscopy in detergent micelles and by solid-state 2H-NMR and 15N-NMR spectroscopy in oriented lipid bilayers.

Several complementary NMR approaches were used to study the interaction of mastoparan, a 14-residue peptide toxin from wasp venom, with lipid membranes. First, the 3D structure of mastoparan was determined using 1H-NMR spectroscopy in perdeuterated (SDS-d25) micelles. NOESY experiments and distance geometry calculations yielded a straight amphiphilic alpha-helix with high-order parameters, and the chemical shifts of the amide protons showed a characteristic periodicity of 3-4 residues. Secondly, solid-state 2H-NMR spectoscopy was used to describe the binding of mastoparan to lipid bilayers, composed of headgroup-deuterated dimyristoylglycerophosphocholine (DMPC-d4) and dimyristoylphosphatidylglycerol (DMPG). By correlating the deuterium quadrupole splittings of the alpha-segments and beta-segments, it was possible to differentiate the electrostatically induced structural response of the choline headgroup from dynamic effects induced by the peptide. A partial phase separation was observed, leading to a DMPG-rich phase and a DMPG-depleted phase, each containing some mastoparan. Finally, the insertion and orientation of a specifically 15N-labeled mastoparan (at position Ala10) in the bilayer environment was investigated by solid-state 15N-NMR spectroscopy, using macroscopically oriented samples. Two distinct orientational states were observed for the mastoparan helix, namely an in-plane and a trans-membrane alignment. The two populations of 90% in-plane and 10% trans-membrane helices are characterized by a mosaic spread of +/- 30 degrees and +/- 10 degrees, respectively. The biological activity of mastoparan is discussed in terms of a pore-forming model, as the peptide is known to be able to induce nonlamellar phases and facilitate a flip-flop between the monolayers.

Deuterium↗
PubMed2001

Relationship between cytocidal activity and glutathione-S-transferase inhibition using doxorubicin coupled to stereoisomers of glutathione with different substrate specificity.

To determine the cytotoxic mode of action of a glutathione (GSH)--doxorubicin (DXR) conjugate, which exhibited potent cytotoxicity against various multidrug-resistant as well as DXR-sensitive cell lines, the molecular interaction between covalent GSH--DXR conjugates and glutathione-S-transferase (GST), a possible molecular target of the conjugates, was investigated. The following four GSH molecules with stereoisomeric forms were prepared: L-Glu--L-Cys--Gly (LL-GSH), D-Glu--L-Cys--Gly (DL-GSH), L-Glu--D-Cys--Gly (LD-GSH) and D-Glu--D-Cys--Gly (DD-GSH). The enzymic activity of GST against each GSH stereoisomer was 88, 38, 8 and 4 nmol/mg/min, respectively, suggesting that the L-form cysteine residue in the molecule was an important substrate of GST. Addition of DXR conjugated with each isomer (10 microM) to a GSH-containing GST assay mixture inhibited the GST activity to 32% for LL-GSH--XR, 16% for DL-GSH-DXR and 61% for LD-GSH-DXR as compared with the solvent control. Moreover, IC50 values for these conjugates were 30, 20 and 250 nM, respectively. The cytocidal activity of each conjugate corresponded to the substrate specificity of GST activity for the GSH isomer. These conjugates bound to the GST molecule, and the binding ability was 0.746, 0.627 and 0.462 mol/mol of GST for LL-GSH--XR, DL-GSH-DXR and LD-GSH--XR, respectively. These findings suggested that GSH--DXR interacted with the substrate-binding site of the GST molecule and inhibition of GST activity exhibited potent cytotoxicity.

Animals↗