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Biomedical subjects

M Akamatsu

Publications and source records attributed to M Akamatsu.

At least 37 records · Page 2Linked to original sources
PubMed1998

Picrodendrin and related terpenoid antagonists reveal structural differences between ionotropic GABA receptors of mammals and insects.

Twenty-eight picrotoxane terpenoids, including picrodendrins isolated from the Euphorbiaceae plant, Picrodendron baccatum (L.) Krug and Urban, have been evaluated for their ability to inhibit the specific binding of [3H]EBOB, the noncompetitive antagonist of ionotropic GABA receptors, to rat-brain and housefly (Musca domestica L.)-head membranes. Picrodendrin Q was the most potent competitive inhibitor of [3H]EBOB binding, with IC50 values of 16 nM (rat) and 22 nM (Musca). We find that the spiro gamma-butyrolactone moiety at the 13-position, which contains a carbonyl group conjugated with an unsaturated bond, and the substituents at the 4-position play important roles in the interaction of picrodendrins with their binding site in rat receptors. In contrast, such structural features are not strictly required in the case of the interaction with Musca receptors; the spiro saturated gamma-butyrolactone moiety at the 13-position, which bears the 16-sp3 carbon atom, and the hydroxyl groups at various positions are somewhat tolerated. Quantitative structure-activity studies have clearly shown that the electronegativity of the 16-carbon atom and the presence or absence of the 4- and 8-hydroxyl groups are important determinants of the potency of nor-diterpenes in Musca receptors, while the negative charge on the 17-carbonyl oxygen atom is likely important in the case of rat receptors. These findings indicate that there are significant differences between the structures of the complementary binding sites in rat GABA receptors and Musca GABA receptors. We also infer differences between native Musca GABA receptors and the Drosophila Rdl subunit-containing homo-oligomeric GABA receptors in the structures of their binding sites.

Animals↗
PubMed1998

[Anticancer susceptibility test method using general-purpose dissolved oxygen meter].

Drug susceptibility of cell can be rapidly measured by continuously monitoring its metabolic changes. We focused on respiration volume as a signal of metabolic change, and developed a new dissolved oxygen measuring system which can detect respiration volume of cells. The main feature of the system is the use of a new type bare oxygen electrode which can easily detect the changing rate of dissolved oxygen concentration. In this study, single type electrode was used to evaluate this rapid anticancer drug susceptibility test. The result obtained was almost equivalent to that with MTT method, which is a conventional method for susceptibility test of HL-60 to various kinds of anticancer drugs. We have also developed multi-type electrode plate with oxygen electrodes embedded in the bottom of 96-well plate, with which clinical evaluation of this method can be easily made.

Antineoplastic Agents↗
PubMed1998

[Cystic lesions of the pancreas].

The number of the literature and classification of the cystic pancreatic diseases is increasing recently. We describe MR cholangiopancreatography (MRCP) findings of the cystic pancreatic diseases according to the clinical oriented classification. Intraductal papillary tumor, mucinous cystadenoma and serous cystadenoma showed characteristic MRCP findings. However small non-neoplastic true cysts are difficult to differentiate from cystic tumors even by MRCP.

Acute Disease↗
PubMed1997

Lasting effect of NO on glutamate release in rat striatum revealed by continuous brain dialysis.

The effect of nitric oxide (NO) on glutamate release in the brain of freely moving rats was investigated using a new, high time-resolution microdialysis system. Coperfusion with veratridine (VER) and NO donors increased glutamate release above than that obtained with VER alone. When steady-state levels were regained after co-perfusion, perfusion of VER alone further potentiated glutamate release. The effect depended on the initial level of VER-induced glutamate release, and was maximum for intermediate glutamate levels. These results suggest that NO influences the glutamate release system by affecting the level of neural activity and that its effect lasts and increases when steady-state levels are regained in rat striatum.

Animals↗
PubMed1997

Terminal deoxynucleotidyl transferase staining of malignant lymphomas in paraffin sections: a useful method for the diagnosis of lymphoblastic lymphoma.

Terminal deoxynucleotidyl transferase (TdT) is a DNA polymerase located in the cell nucleus which catalyses the polymerization of deoxynucleotides at the 3'hydroxyl ends of oligo- or polydeoxynucleotide initiators without a template. TdT is known as a useful marker for the diagnosis of acute lymphoblastic leukaemia/lymphoma, but its detection usually requires fresh tissue specimens or cell suspensions, using either an enzyme analysis or immuno-fluorescence or -peroxidase staining. Until the recent development of the use of microwave-treated paraffin sections for immunoperoxidase staining, detection of TdT in paraffin sections required rather complicated processes. This new simple technique was applied to paraffin sections from the tumour tissue specimens of 16 patients with lymphoblastic lymphoma and of seven patients with non-endemic Burkitt's lymphoma, which is sometimes difficult to differentiate from lymphoblastic lymphoma because of their similar clinicopathological characteristics. In addition, as a control, ten cases each were examined of adult T-cell leukaemia/lymphoma (ATLL) and angioimmunoblastic lymphoma (AILD), which are both peripheral T-cell lymphomas. The tumour cells from 15 of the 16 (94 per cent) patients with lymphoblastic lymphoma were found to be TdT-positive. The specificity of the anti-TdT antibody used was confirmed by immunoblot and the specific 60 kD band was detected only in a specimen of lymphoblastic lymphoma. These results show that the immunostaining of TdT on paraffin-embedded sections is a useful method for differentiating lymphoblastic lymphoma from other lymphomas. This method is applicable to a routine diagnostic service.

Adolescent↗
PubMed1997

Therapeutic trial of intensified conditioning regimen with high-dose cytosine arabinoside, cyclophosphamide and either total body irradiation or busulfan followed by allogeneic bone marrow transplantation for myelodysplastic syndrome in children.

Ten children with myelodysplastic syndrome underwent an allogeneic bone marrow transplantation (BMT) with an intensified conditioning regimen. The median age of the patients was 8 years (range 2-10), and included 6 males and 4 females. The subtype of the disease was refractory anemia (RA) in 4, RA with excess blasts (RAEB) in 4, RAEB in transformation (RAEB-T) in 1, and juvenile chronic myelogenous leukemia (JCML) in 1. All patients were conditioned with high-dose cytosine arabinoside (12000 mg/m2), cyclophosphamide (120 mg/kg) and either total body irradiation (10-13.2 Gy) or busulfan (16 mg/kg or 560 mg/m2). Cyclosporine A and/or methotrexate were used for the prophylaxis of graft-versus-host disease (GVHD). Engraftment was prompt in all but one patient. Severe acute GVHD (grade 3) (n = 1), interstitial pneumonitis (n = 1) and veno-occlusive disease of the liver (n = 1) occurred. The disease relapsed in one patient with RAEB-T. Seven of the 10 patients were alive and disease free 2-74 months after BMT. The disease-free survival rate at 4 years was 69 +/- 15%. All surviving patients were in the full performance status. The examined children with MDS tolerated this intensified conditioning regimen well.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1997

Preparatory inhibition of cortico-spinal excitability: a transcranial magnetic stimulation study in man.

In order to investigate the preparatory modulations of cortico-spinal excitability, reaction time (RT) methods were combined with transcranial magnetic stimulation (TMS) of the motor cortex. We analyzed the variations in the amplitude of motor potentials evoked in a prime mover (flexor digitorum sublimis) by TMS delivered during the foreperiod of a visual choice RT task. In experiment 1 (n = 10), the TMS was delivered either simultaneously with the warning signal or simultaneously with the response signal in two conditions of foreperiod duration: short (500 ms) and long (2500 ms). The peak amplitude of the motor evoked potentials diminished during the short foreperiod but not during the long foreperiod. Since RT was shorter when the foreperiod lasted 500 ms than when it lasted 2500 ms, this result suggests that the excitability of the cortico-spinal structures is minimal when the subject is optimally ready to react. In experiment 2 (n = 10), the time-course of this decrement was further explored. With this aim, only the short foreperiod was used and the TMS was delivered either 500 ms, 333 ms, 167 ms or 0 ms before the response signal. Cortico-spinal excitability decreased during the first 333 ms and then remained stable until the occurrence of the response signal. In light of previous studies, the present results suggest that the decrement of cortico-spinal excitability during the short foreperiod reflects an adaptative mechanism which increases the sensitivity of the motor structures to the forthcoming voluntary command.

Adult↗
PubMed1997

Potent inhibition of protein-tyrosine phosphatase by phosphotyrosine-mimic containing cyclic peptides.

In an effort to derive potent and bioavailable protein-tyrosine phosphatase inhibitors, we have previously reported hexameric peptides based on the epidermal growth factor receptor sequence EGFR988-993 (Asp-Ala-Asp-Glu-Xxx-Leu, where Xxx = Tyr), in which the tyrosyl residue has been replaced by the non-hydrolyzable phosphotyrosyl mimics phosphonomethylphenylalanine (Pmp), difluorophosphonomethylphenylalanine (F2Pmp) and O-malonyltyrosine (OMT). Inhibitory potencies (IC50 values) of these peptides against the tyrosine phosphatase PTP IB were 200, 0.2 and 10 microM, respectively. Since cellular penetration of peptides containing highly charged phosphonate residues is compromised, and good bioreversible protection strategies for the F2Pmp residue have not yet been reported, the OMT residue is of particular interest in that it affords potential new prodrug approaches. In the current study we have prepared cyclized versions of the OMT-containing EGFR988-993 peptide in order to increase its proteolytic stability and restrain conformational flexibility. Three different cyclic analogues were synthesized. Two of these were cyclized through the peptide backbone ('head to tail') using in one case a single glycine spacer (heptamer peptide) and in the second instance, two glycines (octamer peptide). In a PTPI-based assay the cyclic heptamer experienced a two-fold loss of potency (Ki = 25.2 +/- 3.9 microM) relative to the linear hexamer parent (Ki = 13 +/- 0.9 microM), while the cyclic octamer demonstrated a live-fold increase in potency (Ki = 2.60 +/- 0.11 microM). The third peptide was cyclized by means of a sulfide bridge between the side chain of a C-terminally added cysteine residue and the beta-carbon of a N-terminal acetyl residue. Although the overall size of this ring was identical to that exhibited by the preceding backbone-cyclized octamer, it displayed a three-fold enhancement in potency (Ki = 0.73 +/- 0.03 microM). The structural basis for the observed results are discussed. Conformation restrictions induced by cyclization could aid in defining geometries for peptidomimetic design. Finally, it can be speculated that cyclization of other liner PTP-inhibitory peptides, such as the F2Pmp-containing hexamer, may also increase their potency.

Biological Availability↗
PubMed1997

Why does the single neuron activity change from trial to trial during sensory-motor task?

Single neuron activities from cortical areas of a monkey were recorded while performing a sensory-motor task (a choice reaction time task). Quantitative trial-by-trial analysis revealed that the timing of peak activity exhibited large variation from trial to trial, compared to the variation in the behavioral reaction time of the task. Therefore, we developed a multi-unit dynamic neural network model to investigate the effects of structure of neural connections on the variation of the timing of peak activity. Computer simulation of the model showed that, even though the units are connected in a cascade fashion, a wide variation exists in the timing of peak activity of neurons because of parallel organization of neural network within each unit.

Animals↗
PubMed1996

4'-O-[2-(2-fluoromalonyl)]-L-tyrosine: a phosphotyrosyl mimic for the preparation of signal transduction inhibitory peptides.

Development of phosphotyrosyl (pTyr) mimetics which are stable to protein-tyrosine phosphatases (PTPs), yet can retain biological potency when incorporated into peptides, is an active area of drug development. Since a majority of pTyr mimetics derive their "phosphofunctionality" from phosphorus-containing moieties, such as phosphonates, evolution of new inhibitors and modes of prodrug derivatization have been restricted to chemistries appropriate for phosphorus-containing moieties. A new, nonphosphorus-containing pTyr mimetic has recently been reported, L-O-(2-malonyl)tyrosine (OMT,5), which can be incorporated into peptides that exhibit good PTP and Src homology 2 (SH2) domain inhibitory potency. For phosphonate-based pTyr mimetics such as phosphonomethyl phenylalanine (Pmp,2) introduction of fluorines alpha to the phosphorus has provided higher affinity pTyr mimetics. This strategy has now been applied to OMT, and herein is reported 4'-O-[2-(2-fluoromalonyl)]-L-tyrosine (FOMT,6) a new fluorine-containing nonphosphorus pTyr mimetic. Incorporation of FOMT into appropriate peptides results in good inhibition of both PTP and SH2 domains. In an assay measuring the inhibition of PTP 1B-mediated dephosphorylation of phosphorylated insulin receptor, the peptide Ac-D-A-D-E-X-L-amide exhibited a 10-fold enhancement in inhibitory potency for X = FOMT (19) (IC(50) = 10 microM) relative to the unfluorinated peptide, X = OMT (18) (IC(50) = 10 microM. Molecular modeling indicated that this increased affinity may be attributable to new hydrogen-bonding interactions between the fluorine and the enzyme catalytic site, and not due to lowering of pKa values. In a competition binding assay using the p85 PI 3-kinase C-terminal SH2 domain GST fusion construct, the inhibitory peptide, Ac-D-X-V-P-M-L-amide, showed no enhancement of inhibitory potency for X = FOMT (22) (IC(50) = 18 microM) relative to the unfluorinated peptide, X = OMT (21) (IC(50) = 14 microM). The use of FOMT would therefore appear to have particular potential for the development of PTP inhibitors.

Amino Acid Sequence↗
PubMed1996

Characterization of p21Cip1/Waf1 peptide domains required for cyclin E/Cdk2 and PCNA interaction.

The cyclin-dependent kinase inhibitor p21Cip1/Waf1 is responsible for the p53-dependent growth arrest of cells in G1 phase following DNA damage. In the present study we investigated regions of p21 involved in inhibition of the G1/S phase cyclin-dependent kinase, cyclin E/Cdk2, as well as regions of p21 important for binding to this kinase and recombinant PCNA. To perform these studies we synthesized a series of overlapping peptides spanning the entire p21 sequence and used them in in vitro assays with cyclin E/Cdk2-immune complexes and with recombinant p21 and PCNA proteins. One amino-terminal p21 peptide spanning amino acids 15-40, antagonized p21 binding and inhibition of cyclin E/Cdk2 kinase. Antagonism of p21 binding was, however, lost in a similar peptide lacking amino acids 15-20, or in a peptide in which cysteine-18 was substituted for a serine. These results suggest that this peptide region is important for p21 interaction with cyclin E/Cdk2. A second peptide (amino acids 58-77) also antagonized p21-activity, but this peptide did not affect the ability of p21 to interact with cyclin E/Cdk2. A region of p21 larger than 26 amino acids is presumably required for Cdk-inhibition because none of the peptides we tested inhibited cyclin E/Cdk2. We also found that a peptide spanning amino acids 21-45 bound recombinant p21 in ELISA assays, and additional studies revealed a requirement for amino acids 26 through 45 for this interaction. A p21 peptide spanning amino acids 139-164 was found to bind PCNA in a filter binding assay and this peptide suppressed recombinant p21-PCNA interaction. Conformational analysis revealed that peptides spanning amino acids 21-45 and 139-164 tended towards an alpha-helical conformation in trifluoroethanol buffer, indicating that these regions are probably in a coiled conformation in the native protein. Taken together, our results provide an insight into domains of p21 that are involved in cyclin E/Cdk2 and PCNA interaction. Our results also suggest that a potential p21 dimerization domain may lie in the amino-terminus of p21. Continued exploration of these domains could prove useful in assessing p21-mimetic strategies for cancer treatment.

Amino Acid Sequence↗
PubMed1996

Angiocentric immunoproliferative lesions of the lymph node.

Clinicopathologic features in 14 cases of lymph node-involved angiocentric immunoproliferative lesions (AILs) are reported. They were selected from 900 cases of lymphoproliferative disorders registered at the Department of Pathology, Fukuoka University. Four cases showed a histologic feature of AIL grade II (AIL-II) and 10 had angiocentric lymphoma (AIL-III). Immunohistologically, transformed B cells were mixed with a large number of small T cells in AIL-II. In AIL-III, there were five cases with B-cell lymphoma, and three had peripheral T-cell lymphoma with no expression of natural-killer (NK)-associated antigens. In the remaining two cases, lymphoma cells expressed both T-cell- and NK-associated antigens. These findings indicate that lymph node-involved AILs are rarely occurring (1.6%) and phenotypically different from sinonasal and cutaneous AILs. Furthermore, NK-associated antigen-positive AILs were found to rarely involve the lymph node. For Epstein-Barr virus (EBV) infection, seven cases of AILs showed many atypical lymphocytes that were positive for EBV-encoded RNA (EBER-1) by using the in situ hybridization analysis. Among them, six cases had latent membrane protein (LMP) positive and EBV nuclear antigen 2 (EBNA-2) negative atypical lymphocytes. The pattern of latent EBV infection was similar to that of Hodgkin's disease, but differed from those of sinonasal T-cell lymphoma and other subtypes of non-Hodgkin's lymphoma. Clinically, 12 patients, including all 4 AIL-II, died within 22 months of the onset of the disease, despite intensive therapy, suggesting that lymph node-involved AILs have a poor prognosis.

Adult↗
PubMed1995

L-O-(2-malonyl)tyrosine: a new phosphotyrosyl mimetic for the preparation of Src homology 2 domain inhibitory peptides.

Inhibition of Src homology 2 (SH2) domain-binding interactions affords one potential means of modulating protein-tyrosine kinase-dependent signaling. Small phosphotyrosyl (pTyr)-containing peptides are able to bind to SH2 domains and compete with larger pTyr peptides or native pTyr-containing protein ligands. Such pTyr-containing peptides are limited in their utility as SH2 domain inhibitors in vivo due to their hydrolytic lability to protein-tyrosine phosphatases (PTPs) and the poor cellular penetration of the ionized phosphate moiety. An important aspect of SH2 domain inhibitor design is the creation of pTyr mimetics which are stable to PTPs and have reasonable bioavailability. To date, most PTP-resistant pTyr mimetics which bind to SH2 domains are phosphonates such as (phosphonomethyl)phenylalanine (Pmp, 2), [(monofluorophosphono)methyl]phenylalanine (FPmp, 3) or [(difluorophosphono)methyl]-phenylalanine (F2Pmp, 4). Herein we report the incorporation of a new non-phosphorus-containing pTyr mimetic, L-O-(2-malonyl)tyrosine (L-OMT, 5), into SH2 domain inhibitory peptides using the protected analogue L-N alpha-Fmoc-O'-(O",O"-di-tert-butyl-2-malonyl)tyrosine (6) and solid-phase peptide synthesis techniques. Five OMT-containing peptides were prepared against the following SH2 domains: the PI-3 kinase C-terminal p85 SH2 domain (Ac-D-(L-OMT)-V-P-M-L-amide, 10, IC50 = 14.2 microM), the Src SH2 domain (Ac-Q-(L-OMT)-E-E-I-P-amide, 11, IC50 = 25 microM, and Ac-Q-(L-OMT)-(L-OMT)-E-I-P-amide, 14, IC50 = 23 microM), the Grb2 SH2 domain (Ac-N-(L-OMT)-V-N-I-E-amide, 12, IC50 = 120 microM), and the N-terminal SH-PTP2 SH2 domain (Ac-L-N-(L-OMT)-I-D-L-D-L-V-amide, 13, IC50 = 22.0 microM). These results show that peptides 10, 11, 13, and 14 have reasonable affinity for their respective SH2 domains, with the IC50 value for the SH-PTP2 SH2 domain-directed peptide 13 being equivalent to that previously observed for the corresponding F2Pmp-containing peptide. OMT may afford a new structural starting point for the development of novel and useful SH2 domain inhibitors.

Amino Acid Sequence↗
PubMed1995

Protein-tyrosine phosphatase inhibition by a peptide containing the phosphotyrosyl mimetic, L-O-malonyltyrosine.

Peptides containing phosphonate based non-hydrolyzable phosphotyrosyl (pTyr) mimetics previously have been shown to be competitive inhibitors of protein-tyrosine phosphatases (PTPs). These agents suffer from low cellular penetration which is partially attributable to ionization of the phosphonate group at physiological pH. We have developed the non-phosphorus containing pTyr mimetic, L-O-malonyltyrosine (L-OMT) and herein demonstrate using a PTP 1B enzyme assay that it is superior to phosphonomethyl phenylalanine (Pmp) as a pTyr mimetic when incorporated into the hexamer peptide Ac-D-A-D-E-X-L-amide (X = D,L-Pmp, IC50 = 200 microM; X = L-OMT, IC50 = 10 microM). Prodrug protection of L-OMT as its carboxylic acid diester could potentially increase cellular penetration, thereby making this a valuable reagent for cellular studies.

Amino Acid Sequence↗
PubMed1995

Cloning, sequence analysis, and expression of a mouse cDNA encoding cytochrome c oxidase subunit VIa liver isoform.

A cDNA encoding cytochrome c oxidase (COX) subunit VIa liver isoform (COX6aL) was isolated from a Mus musculus library and sequenced. The protein translated from the nucleotide sequence contains a presequence and is 91% identical to the human cognate sequence over the processed polypeptide region. Northern analysis shows the expression of COX6aL is developmentally regulated in heart, being about equally transcribed with the heart isoform (COX6aH) in 18-day embryos but consisting of less than 25% in adult heart.

Amino Acid Sequence↗
PubMed1995

CD30-positive anaplastic large cell lymphoma in a human T-cell lymphotropic virus-I endemic area.

Clinicopathological and cytogenetic studies were performed on specimens from 43 patients with CD30-positive anaplastic large cell lymphoma (ALCL). All patients were born and lived in a human T-cell lymphotropic virus (HTLV)-I endemic area. Twenty-one patients (48.8%) had serum anti-HTLV-I antibody suggesting the presence of adult T-cell leukemia/lymphoma (ATL). Seventeen of them showed a clonal integration of complete HTLV-I proviral DNA by the Southern blot hybridization method in materials obtained by biopsy. Their ages ranged from 37 to 81 years (median, 67.0), and they frequently presented with lymphadenopathy (82.4%) and extranodal tumors with (76.5%) as well as with rare leukemic changes (5.9%). Immunohistologically the lymphoma cells in 15 ATL patients showed a T-cell phenotype. In only one patient (5.9%) was there an expression of epithelial membrane antigen (EMA) in most of the lymphoma cells. Cytogenetically aberration of chromosome band 5q35 was not found in seven patients with HTLV-I proviral DNA. The overall median length of survival was 11.9 months for the patients with HTLV-I proviral DNA, indicating a worse prognosis compared with that of the age-matched patients with negative anti-HTLV-I antibody (P < .01). The specimens of the patients with HTLV-I proviral DNA had unique clinicopathological and cytogenetic features. These findings suggested that T-cell ALCL with HTLV-I proviral DNA should be considered to represent the lymphoma type of ATL.

Adult↗