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Biomedical subjects

N Hirashima

Publications and source records attributed to N Hirashima.

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

Lambert-Eaton syndrome antibodies inhibit acetylcholine release and P/Q-type Ca2+ channels in electric ray nerve endings.

1. The types of voltage-dependent calcium channels (VDCCs) present in the cholinergic terminals isolated from the electric organ of the ray, Narke japonica, were characterized on the basis of their pharmacological sensitivity to specific antagonists. Inhibition of these channel types by autoantibodies from patients with the Lambert-Eaton syndrome (LES) was then studied to determine the specificity of the pathogenic IgG. 2. In normal untreated synaptosomal preparations, maximal doses of N- and P and/or Q-type Ca2+ channel antagonists, omega-conotoxin GVIA and omega-agatoxin IVA, inhibited depolarization-evoked ACh release by 47 % and 43 %, respectively. Calciseptine, an L-type VDCC antagonist, caused a 20 % reduction in the release. This indicates that the exocytotic release process is predominantly mediated by N- and P/Q-type VDCCs. 3. LES IgG or sera caused an inhibition of ACh release by 39-45 % in comparison with the control antibody-treated preparations. The ionomycin-induced ACh release, however, was not altered by the antibodies. Additionally, the same LES antibodies inhibited whole-cell calcium currents (ICa) in bovine adrenal chromaffin cells. Thus, the pathogenic antibodies exert their action on VDCCs present in the synaptosomes. 4. The efficacy of three Ca2+ channel antagonists in blocking ACh release was determined in preparations pretreated with LES IgG. omega-Agatoxin IVA produced only an additional 3-5 % reduction in release beyond that obtained with LES antibodies. Despite the pretreatment with LES IgG, omega-conotoxin GVIA and calciseptine inhibited the release to nearly their control levels. 5. These results indicate that LES antibodies mainly downregulate P/Q-type Ca2+ channels which contribute to presynaptic transmitter release from the cholinergic nerve terminals of electric organ. 6. The present findings are consistent with the hypothesis that P/Q-type VDCCs at the neuromuscular junction are the target of LES antibodies and that their inhibition by the antibodies produces the characteristic neuromuscular defect in this disease.

Acetylcholine↗
PubMed1998

cDNA isolation of Alzheimer's amyloid precursor protein from cholinergic nerve terminals of the electric organ of the electric ray.

Alzheimer's amyloid precursor protein (APP) is a transmembrane protein containing three phosphorylation sites in its cytoplasmic domain. In the present study, we isolated cDNA of APP from electric ray electric lobe (elAPP). This APP (elAPP699) consists of 699 amino acids, contains the beta-amyloid domain and has 80.7% similarity with the human APP695 isoform. The cytoplasmic domain, including three phosphorylation sites, was completely conserved. In the nerve terminals of the cholinergic neuron from the electric ray electric organ, we found elAPP699 existed exclusively in the mature form. We found the phosphorylated form of mature elAPP699 in the nerve terminal as well as in cell body. Immature elAPP699 was not subject to phosphorylation. Our findings indicate that, in neurons, the phosphorylation of APP occurs after maturation.

Amino Acid Sequence↗
PubMed1998

Calcium responses in fibroblasts from asymptomatic members of Alzheimer's disease families.

We have previously identified alterations of K+ channel function, IP3-mediated calcium release, and Cp20 (a memory-associated GTP binding protein) in fibroblasts from Alzheimer's disease (AD) patients vs controls. Some of these alterations can be integrated into an index that distinguishes AD patients from controls with both high specificity and high sensitivity. We report here that alterations in IP3-mediated calcium responses are present in a large proportion of AD family members (i.e., individuals at high risk) before clinical symptoms of Alzheimer's disease are present. This was not the case if such members later "escaped" AD symptoms. This preclinical calcium signal correlate of later AD does not reflect, however, the presence of the PS1 familial AD gene.

Alzheimer Disease↗
PubMed1998

Membrane perturbation by the neurotoxic Alzheimer amyloid fragment beta 25-35 requires aggregation and beta-sheet formation.

The beta-amyloid peptide (beta AP) is a major proteinaceous component of senile plaques and cerebrovascular amyloid deposits found in the brain of patients with Alzheimer's disease. beta AP is reported to be neurotoxic only when it forms beta-sheet structure and aggregates. In the present study, we report that the neurotoxic core of beta AP, beta AP-25-35 (beta 25-35), perturbs liposome membranes, induces membrane current, and exhibits hemolytic activity only in a buffer condition where the peptide forms beta-sheet structure and spontaneously aggregates. In contrast, beta 25-35 in its monomeric random coil structure does not perturb lipid membranes significantly, and exhibits no hemolytic activity. Also, the membrane current was inhibited by Congo Red. The ability of beta 25-35 to interact with membranes highly correlates with its neurotoxicity reported previously. These results suggest that membrane perturbation by aggregated beta 25-35 constitutes the molecular basis of the peptide's neurotoxicity.

Amyloid beta-Peptides↗
PubMed1998

Analysis of conserved ambisense sequences within GB virus C.

No analysis has been done of the ambisense of GB virus C (GBV-C). When the anti-genomes of 16 reported sequences of GBV-C were analyzed, nucleotide codons 1758 and 1402 within the anti-genome were conserved initiation and stop codons, respectively. Nucleotide sequences were also determined within the same region of 22 GBV-C strains. The anti-genomes of 38 sequences were translated and a consensus sequence was determined. In accordance with the consensus sequence, overlapping peptides were synthesized and used for the detection of anti-synthetic peptide antibodies by ELISA. The positivity of antibodies among sera with GBV-C RNA was significantly higher than among sera without GBV-C RNA (66.7% vs. 15.6%), regardless of the simultaneous presence of hepatitis B surface antigen or antibodies to hepatitis C virus (P < .05). These results indicated that a novel protein associated with GBV-C might be expressed from the ambisense of this virus.

Antibodies, Viral↗
PubMed1998

Phospholipid translocation from the outer to the inner leaflet of synaptic vesicle membranes isolated from the electric organ of Japanese electric ray Narke japonica.

The phospholipid translocation from the outer to the inner leaflet of synaptic vesicles isolated from the electric organ of the Japanese electric ray, Narke japonica, was measured using fluorescent phospholipid probes. Phosphatidylcholine (PC), phosphatidylethanolamine (PE), or phosphatidylserine (PS) with a fluorescent NBD-labeled short acyl chain at the sn-2 position was mixed with purified synaptic vesicles and the probe in the outer leaflet of the membranes was reduced with dithionite to quench the fluorescence from time to time. The percentage of fluorescence remaining after the dithionite treatment served as an index for the phospholipid translocation. The results obtained indicated that about 30, 13, and 9% of NBD-PE, NBD-PS, and NBD-PC, respectively, were translocated from the outer to the inner leaflet in 3 h. Thus, the translocation activity in synaptic vesicle membranes was much higher for PE than for PS, in contrast to the previous results obtained with plasma membranes, including synaptosomal membranes. The percentages of the phospholipid in the inner leaflet at equilibrium were estimated to be 41, 31, and 14% for PE, PS, and PC, respectively. The translocation was inhibited by pretreatment with an SH reagent, iodoacetamide, indicating the involvement of a proteinaceous translocator. These data may provide a biochemical basis for elucidating the mechanisms of membrane fusion and exocytosis at nerve endings.

4-Chloro-7-nitrobenzofurazan↗
PubMed1998

[Combination of transcatheter arterial infusion of SMANCS and embolization (SMANCS-TAE) for hepatocellular carcinoma].

Patients with unresectable hepatocellular carcinoma (hepatoma) with hypervascularity were treated by SMANCS-TAE, which was performed by a superselective catheterization technique to inject gelatin sponge particles after administration of SMANCS. In 24 of 30 (80%) patients of first hepatoma treated by SMANCS-TAE, Grade 4 was obtained after about 1.5 (1-3) courses. The 2-year survival rate was 33%. SMANCS-TAE appears to have the same potential and safety as Lipiodol-TAE, treated selectively. Moreover, we can reduce the course of treatment and obtain good QOL of hepatoma patients except in advanced cases (vp 3 or T 4).

Aged↗
PubMed1998

[Combination of transcatheter arterial infusion of SMANCS and embolization (SMANCS-TAE) for hepatocellular carcinoma--second report].

Patients with unresectable hepatocellular carcinoma (hepatoma) with hypervascularity were treated by SMANCS-TAE. A superselective catheterization technique was used to inject gelatin sponge particles after administration of SMANCS. In 30 patients of first hepatoma treated by SMANCS-TAE. Grade 4 was obtained after 1.7(1-3) courses. The 2-year survival rate was 22%. Some of the 24 patients of second hepatoma treated by SMANCS-TAE have survived over 2 years. Sixteen patients with advanced hepatoma (Vp2-3 or T4) were treated only by SMANCS injection, but none survived over 1 year. SMANCS-TAE appears to have the same potential and safety as L-TAE, when used selectively. Moreover, we can reduce the course of treatment and obtain good QOL for hepatoma patients except in advanced cases.

Aged↗
PubMed1997

Activation of adenosine A1 and A2 receptors differentially affects acetylcholine release from electric organ synaptosomes by modulating calcium channels.

Adenosine inhibited the release of acetylcholine (ACh) evoked by high K+ depolarization from synaptosomes isolated from the electric organ of the Japanese electric ray Narke japonica. The adenosine A1 receptor agonist N6-cyclohexyladenosine was an effective inhibitor. Conversely, in the presence of an A1 receptor antagonist, 8-cyclopentyltheophylline, adenosine potentiated the release of ACh. The A2 receptor agonist N6-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)ethyl] adenosine also facilitated the evoked ACh release. Thus, adenosine inhibits the evoked release of ACh via the A1 receptor while it facilitates the release via the A2 receptor. The EC50 for inhibition and facilitation by adenosine was about 1 and 41 microM, respectively. There are three known types of calcium channels (N-, P/Q- and L-type) in synaptosomes. The effects of Ca2+ channel type-specific blockers on the modulation of ACh release by adenosine A1 or A2 receptor activation revealed that inhibition by A1 receptor activation was caused via inhibition of N-type calcium channels and the facilitative effects by A2 receptor activation was mediated by potentiation of P-type calcium channels.

Acetylcholine↗
PubMed1997

Pigment epithelium-derived factor protects cultured cerebellar granule cells against glutamate-induced neurotoxicity.

Pigment epithelium-derived factor (PEDF) is a survival factor for cerebellar granule cells in culture. In the present study, we have investigated the ability of a recombinant form of PEDF (rPEDF) to protect against glutamate neurotoxicity. When rPEDF was added to cerebellar granule cell cultures 30 min before addition of 100 microM glutamate, glutamate-induced neuronal death was significantly reduced. The protective effect of rPEDF was dose-dependent in the range from 0.023 to 7.0 nM (1-500 ng/ml), with a half-maximal dose of 0.47 nM. An antibody to rPEDF blocked this protective effect. Measurement of intraneuronal free calcium levels demonstrated that rPEDF raised the basal calcium content. However, after the elevation of intracellular calcium in response to administration of glutamate, rPEDF reduced the plateau level seen in the presence of glutamate. These data show that PEDF can protect neurons against glutamate-induced neurotoxicity, possibly via a calcium-related pathway. The finding that only 30 min of preincubation is required for the neuroprotective effect, significantly faster than other known neurotrophic factors, suggests that PEDF may be useful clinically as a neuroprotective agent in the CNS.

Animals↗
PubMed1997

Involvement of calciseptine-sensitive calcium channels in the evoked acetylcholine release from electric organ synaptosomes.

The high K(+)-evoked release of acetylcholine (ACh) from electric organ synaptosomes isolated from the Japanese marine ray, Narke japonica, was strongly inhibited by dihydropyridines at micromolar concentrations. However, this inhibition seems to be a non-specific effect since the agonist (-)-Bay K 8644 also had inhibitory effects. Calciseptine, a peptide toxin specific for L-type Ca channels, inhibited to a lesser extent the evoked acetylcholine release: the maximum inhibition was about 20%. This finding is in accord with our data (Tokumaru et al., J. Neurochem., 65, 831(1995)) regarding inhibition by a monoclonal antibody against the alpha 2 delta-subunit of the L-type Ca channel and provides evidence for the involvement of an L-type-like Ca channel in ACh release in addition to omega-conotoxin GVIA-sensitive N-type and omega-agatoxin IVA-sensitive P-type Ca channels.

Acetylcholine↗
PubMed1997

Zinostatin stimalamer-transcatheter arterial embolization for hepatocellular carcinoma: a comparison with lipiodol-transcatheter arterial embolization.

Twenty patients with unresectable hepatocellular carcinoma were treated by zinostatin stimalamer-transcatheter arterial embolization (SMANCS-TAE). After administration of SMANCS, a superselective catheterization technique was used to inject gelatin sponge particles into the artery or artery branch supplying the cancer-bearing segment. We compared the results of SMANCS-TAE with Lipiodol (Yamanouchi, Tokyo, Japan)-TAE performed during the same period. In 18 of 20 patients (90%), a tumor necrosis rate of 100% (grade 4) was obtained after one or two courses of SMANCS-TAE. The SMANCS group was superior to the Lipiodol-TAE group in terms of the tumor reduction rate, alpha-fetoprotein reduction rate, and cumulative 1.5-year survival rate, but not significantly. No severe side effects were noted after SMANCS-TAE. SMANCS-TAE appears to have potential as a new treatment for hepatocellularcarcinoma, and patients treated with this technique will be monitored to elucidate the long-term effects.

Aged↗
PubMed1996

Case report: development of hepatocellular carcinoma in a patient with chronic hepatitis C infection after a complete and sustained response to interferon-alpha.

A 60-year-old man with a chronic hepatitis C virus (HCV) infection and histological features of chronic active hepatitis was treated with interferon-alpha (IFN). He successfully responded to IFN with normalization of serum ALT and disappearance of serum HCV-RNA. His liver biochemistry profile remained normal and serum HCV-RNA was not detected throughout the entire follow-up period. One year later, a small hepatocellular carcinoma (HCC) was detected by routine ultrasonographic screening. Laparotomy revealed a small tumour with no metastasis and the non-tumorous liver demonstrated macronodular cirrhosis. Although no space-occupying lesions were detected by frequent radiological examinations prior to IFN therapy, the small size of the tumour suggested de novo development of HCC. Patients with chronic HCV infection, including those who have complete responses to IFN and lack clinical and histological evidence of cirrhosis, should be followed up for the potential development of HCC.

Antiviral Agents↗
PubMed1995

Transforming growth factor beta induces a beta-responsive calcium fluxes in neurons.

The beta-amyloid (a beta) peptide is a neurotoxic peptide that accumulates in the brains of Alzheimer patients, but is also present in body fluids at subnanomolar levels. The potential effects of these low levels of a beta are unclear. We have recently shown that physiologic levels of a beta increase tyrosine phosphorylation and induce increases in cytosolic calcium. The basement membrane mixture, Matrigel, is required for observation of the a beta-induced calcium response. We now show that transforming growth factor beta (TGF beta) is the active component in Matrigel eliciting the a beta/calcium response. The response to the type of TGF beta varies depending on the cell type with TGF beta 1 eliciting a beta responsiveness in olfactory neuroblasts, and TGF beta 2 eliciting a beta responsiveness in PC12 cells.

Amyloid beta-Peptides↗
PubMed1995

Physiological levels of beta-amyloid increase tyrosine phosphorylation and cytosolic calcium.

The a beta peptide is a neurotoxic peptide that accumulates in the brains of Alzheimer patients, but is also present in body fluids at subnanomolar levels. The potential effects of these low levels of a beta are unclear. We now show that one such action is to increase tyrosine phosphorylation in PC12 cells and olfactory neuroblasts. Application of a beta 25-35 or a beta 1-40 induces a dose-dependent increase in the tyrosine phosphorylation in both whole cells and in vitro. The increase in tyrosine phosphorylation is both rapid and sensitive, being stimulated by picomolar doses of a beta and occurring within 1 min of application. Calcium imaging experiments provide further support for the role of tyrosine phosphorylation in the action of a beta. While a beta does not alter calcium metabolism under basal conditions, the addition of a beta induces a rapid increase in cytoplasmic calcium in olfactory neuroblasts that have been treated with the tyrosine phosphatase inhibitor, sodium orthovanadate or in PC12 cells treated with nerve growth factor. These responses could be blocked by the tyrosine kinase inhibitor, herbimycin. These calcium responses displayed an obligate requirement for the presence of matrix proteins. The identification of a rapid, sensitive assay for the action of a beta may facilitate investigations of its mechanism of action.

Amyloid beta-Peptides↗
PubMed1995

A calcium channel from the presynaptic nerve terminal of the Narke japonica electric organ contains a non-N-type alpha 2 delta subunit.

A monoclonal antibody (MCC-1) that recognizes the alpha 2 delta subunit complex of L-type calcium channels from rabbit skeletal muscle membranes partially inhibited the evoked release of acetylcholine from synaptosomes isolated from the electric organ of the marine electric ray, Narke japonica. Digitonin extracts of synaptosomal plasma membranes were subjected to immunoaffinity column chromatography on MCC-1-Sepharose. The purified fraction contained a 170-kDa protein that reacts with MCC-1 and dissociates into smaller polypeptides under reducing conditions. In addition, immunoblotting analysis revealed the existence of syntaxin in the purified fraction, suggesting that the calcium channel forms a complex with syntaxin. However, MCC-1 did not immunoprecipitate an omega-conotoxin GVIA-binding protein. These findings indicate that the 170-kDa protein may be the alpha 2 delta subunit of a calcium channel that is distinct from the omega-conotoxin GVIA-sensitive N-type calcium channel and partially responsible for the calcium influx that triggers the evoked release of acetylcholine.

Acetylcholine↗