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N Sekine

Publications and source records attributed to N Sekine.

At least 19 recordsLinked to original sources
PubMed2005

Dispersive terahertz gain of a nonclassical oscillator: BLOCH oscillation in semiconductor superlattices.

We have directly determined the spectral shape of the complex conductivities of Bloch oscillating electrons by using the time-domain terahertz (THz) electro-optic sampling technique, and presented experimental evidence for a dispersive Bloch gain in superlattices. This unique dispersive gain without population inversion arises from a nonclassical nature of Bloch oscillations; that is, the phase of the Bloch oscillation is shifted by pi/2 from that of the semiclassical charged harmonic oscillation when driven by the same ac field. By increasing the bias electric field, the gain bandwidth reached approximately 3 THz in our particular sample.

Journal Article↗
PubMed2002

Application of synchrotron X-ray imaging to phase objects in orthopedics.

Novel imaging of the fine structures of the ribs of a pig and a specimen of human osteosarcoma utilizing the spatial coherence of X-rays was successfully performed with an incident X-ray energy of 30 keV at SPring-8, Japan. The image contrast appearing at the periphery of trabecular bone, small calcifications and small fractures is caused by the phase shift of the X-rays at the boundary of these objects that have different X-ray refractive indices. The image is recorded on mammography film without an intensifying screen. Comparison of the image contrast using different sample-to-film distances, Z, such as Z = 5 m and Z approximately 0 m, showed that the former images were always more informative, i.e. better in resolution and/or image contrast when imaging trabecular bone, bone marrow and small fractures in compact bone, and for imaging cartilage. Radiography using synchrotron X-rays for phase objects should be a powerful tool for diagnosis in orthopedics, especially for bone disease.

Animals↗
PubMed2001

GH inhibits interferon-gamma-induced signal transducer and activator of transcription-1 activation and expression of the inducible isoform of nitric oxide synthase in INS-1 cells.

Interferon-gamma and TNFalpha synergistically induce the inducible isoform of nitric oxide synthase and elicit severe cytotoxicity in pancreatic beta-cells. We demonstrate here that GH, the well known beta-cell mitogen, inhibits nitric oxide production by reducing inducible nitric oxide synthase gene induction by the two cytokines and counteracts their cytotoxic effect in insulin-secreting INS-1 cells. To elucidate the underlying mechanism, we examined activation of the transcription factors implicated in the induction of inducible nitric oxide synthase, signal transducer and activator of transcription-1, and nuclear factor-kappa B. GH inhibited tyrosine phosphorylation and DNA binding of signal transducer and activator of transcription-1 promoted by interferon-gamma, whereas nuclear factor-kappa B activation by TNFalpha was not affected by GH. GH was found to induce suppressor of cytokine signaling-1 and -3, both of which are able to inhibit interferon-gamma activation of signal transducer and activator of transcription-1, suggesting that they are likely to mediate the inhibitory action of GH. Finally, exposure of INS-1 cells to interferon-gamma resulted in the impairment of insulin secretion in response to glucose, which was restored by the addition of GH. These results indicate that GH counteracts the effect of interferon-gamma through the inhibition of signal transducer and activator of transcription-1. This action of GH may be sufficient to suppress the synergistic induction of inducible nitric oxide synthase by interferon-gamma and TNFalpha, thereby preventing the cytotoxicity to beta-cells.

Animals↗
PubMed2001

Insulin resistance with enhanced insulin signaling in high-salt diet-fed rats.

Previous clinical studies showed an apparent correlation between hypertension and insulin resistance, and patients with diabetes are known to have increased blood pressure responsiveness to salt loading. To investigate the effect of high salt intake on insulin sensitivity and the insulin signaling pathway, a high-salt diet (8% NaCl) or a normal diet was given to 7-week-old SD rats for 2 weeks. High salt-fed rats developed slightly but significantly higher systolic blood pressure than controls (133 +/- 2 vs. 117 +/- 2 mmHg, P < 0.001), with no change in food intake or body weight. High salt-fed rats were slightly hyperglycemic (108.5 +/- 2.8 vs. 97.8 +/- 2.5 mg/dl, P = 0.01) and slightly hyperinsulinemic (0.86 +/- 0.07 vs. 0.61 +/- 0.06 ng/ml, P = 0.026) in the fasting condition, as compared with controls. Hyperinsulinemic-euglycemic clamp study revealed a 52.7% decrease in the glucose infusion rate and a 196% increase in hepatic glucose production in high salt-fed rats, which also showed a 66.4% decrease in 2-deoxyglucose uptake into isolated skeletal muscle and a 44.5% decrease in insulin-induced glycogen synthase activation in liver, as compared with controls. Interestingly, despite the presence of insulin resistance, high salt-fed rats showed enhanced insulin-induced tyrosine phosphorylation of insulin receptor substrate (IRS)-1, IRS-2 (liver and muscle), and IRS-3 (liver only). Phosphatidylinositol (PI) 3-kinase activities associated with IRS and phosphotyrosine in the insulin-stimulated condition increased 2.1- to 4.1-fold, as compared with controls. Insulin-induced phosphorylation of Ser-473 of Akt and Ser-21 of glycogen synthase kinase-3 also increased 2.9- and 2-fold, respectively, in the liver of the high salt-fed rats. Therefore, in both the liver and muscle of high salt-fed rats, intracellular insulin signaling leading to PI 3-kinase activation is enhanced and insulin action is attenuated. The hyperinsulinemic-euglycemic clamp study showed that decreased insulin sensitivity induced with a high-salt diet was not reversed by administration of pioglitazone. The following can be concluded: 1) a high-salt diet may be a factor promoting insulin resistance, 2) the insulin-signaling step impaired by high salt intake is likely to be downstream from PI 3-kinase or Akt activation, and 3) this unique insulin resistance mechanism may contribute to the development of diabetes in patients with hypertension.

Animals↗
PubMed2001

[Sentinel node detection of patients with breast cancer by radionuclide method: consideration of radiation safety].

Sentinel node was detected by 99mTc labeled nanocolloid in five patients with breast cancer. Surgery of breast cancer was done at 16 hours after the administration of 74 MBq of 99mTc labeled nanocolloid. Sentinel node was searched by scintigraphy prior to surgery and by gamma-probe during surgery. Radioactivity of injected site, sentinel nodes, blood contaminated gauze, and other garbage was measured by GM detector. Radiation to medical staffs was monitored by a pocket radiation detector and film batches. Sentinel nodes were successfully detected both by scintigraphy and gamma-detector. More than 70% of radioactivity remained in the administered site at 16 hours. Small amount of radioactivity was detectable in the sentinel node. Almost no radioactivity was detectable in blood-contaminated gauze and other garbage. Radiation dose to the main surgeon was 4 to 6 microSv per surgery by a pocket radiation detector. Radiation dose to the assistant surgeon was 2 microSv per surgery. Radiation dose by labeling or injection was 0 to 1 microSv per procedure. No detectable radiation was measured by film batches. It is concluded that the detection of sentinel node by 99mTc labeled nanocolloid is a safe procedure from the point of radiation safety consideration.

Breast Neoplasms↗
PubMed2000

Synergistic activation of NF-kappab and inducible isoform of nitric oxide synthase induction by interferon-gamma and tumor necrosis factor-alpha in INS-1 cells.

Interferon-gamma (IFN-gamma) is known to exert deleterious effects on pancreatic beta-cells and is implicated in the development of type 1 (autoimmune) diabetes mellitus. In this study, we investigated signaling mechanisms mediating the effects of IFN-gamma in pancreatic beta-cells using a differentiated rat insulin-secreting cell line, INS-1, with special reference to the activation of transcription factors STAT (signal transducers and activators of transcription)1 and NF-kappaB. Exposure of INS-1 cells to 100 IU/ml IFN-gamma for 24 h resulted in significant inhibition of nutrient-induced insulin secretion associated with impaired metabolism. In combination with tumor necrosis factor-alpha (TNF-alpha) (50 ng/ml), IFN-gamma elicited severe cytotoxicity and induced the expression of the inducible isoform of nitric oxide synthase (iNOS) mRNA. IFN-gamma promoted tyrosine phosphorylation and DNA-binding of STAT1 through Janus kinase (JAK)1 activation without apparent phosphorylation of JAK2. TNF-alpha did not affect STAT1 activation, but stimulated DNA-binding and transcriptional activity of NF-kappaB, both of which were further increased by IFN-gamma. These effects of IFN-gamma and TNF-alpha seem physiologically relevant, because either inhibition of STAT1 by the tyrosine kinase inhibitor herbimycin A or that of NF-kappaB by sulfasalazine resulted in the reduction of iNOS mRNA expression. In conclusion, IFN-gamma activates STAT1 and potentiates TNF-alpha-induced NF-kappaB activation in INS-1 cells, thereby inducing iNOS and cell destruction.

Animals↗
PubMed2000

Prostaglandin A1 enhances c-fos expression and activating protein-1 activity.

Prostaglandin A1 (PGA1) increases heat shock element (HSE)-mediated transcription, thereby enhancing expression of HSE-bearing genes, including heat shock proteins. Because we recently found functional HSEs in the human and rodent c-fos promoters, we hypothesized that PGA1 might increase c-fos expression through the HSE. In this study, we revealed that PGA1 induces c-fos expression at least partly by increasing the binding between heat shock factor-1 and the HSE, and that PGA1 enhances activity of activating protein-1 (AP-1). Interestingly, so far as PGA, is present in the medium, AP-1-mediated transcription enhanced by PGA1 cannot be detected by the standard luciferase reporter gene assay. Instead, it can be detected by either checking luciferase mRNA levels in the presence of PGA1 or measuring luciferase activities just after removal of PGA1. These results showed that protein products of some stress-responsive genes can increase, not during the stressful condition, but immediately after recovery from stress.

Animals↗
PubMed1999

Free radical modulation of insulin release in INS-1 cells exposed to alloxan.

Generation of free radicals is thought to mediate the cytotoxic action of alloxan on the pancreatic beta-cell. In this investigation, the early effects of alloxan on cell function were studied. When INS-1D insulinoma cells were exposed to alloxan (1 mM) for 45 min followed by a 3-hr recovery period, the drug increased basal insulin release while abolishing the effect of glucose in static incubations. This was associated with impaired stimulation of cellular metabolism by glucose and reduced viability, both monitored colorimetrically with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). These alterations were largely counteracted by the antioxidant butylated hydroxyanisol (BHA). Similar changes occurred when glucose was added directly after 5 min of alloxan treatment, whereas KCl-induced secretion was only partially inhibited. In perifusion, alloxan caused transient insulin secretion to 50% of the rates obtained with glucose 30 min later. Under these conditions, epinephrine abolished the stimulation due to both agents. Membrane potential and cytosolic calcium concentrations ([Ca2+]i) were recorded to clarify the action of alloxan. Alloxan-induced insulin release correlated with depolarization of INS-1D cells and a rise in [Ca2+]i. Alloxan did not augment [Ca2+]i in the presence of BHA or the absence of extracellular calcium. Nickel chloride blocked the effect of alloxan on [Ca2+]i, whereas verapamil was ineffective. This suggests that alloxan promotes Ca2+ influx through channels distinct from L-type channels, perhaps through non-selective cation channels. Thus, alloxan causes changes in INS-1D cells prevented by antioxidant treatment, suggesting that free radicals may modulate the ionic permeability leading to functional activation.

Alloxan↗
PubMed1999

Influence of monoclonal antiplatelet glycoprotein antibodies on in vitro human megakaryocyte colony formation and proplatelet formation.

The influence of antiplatelet glycoprotein (GP) antibodies on megakaryocytopoiesis in patients with idiopathic or immune thrombocytopenic purpura (ITP) has been well studied. However, the influence of GP antibodies on proplatelet formation is poorly understood. Here we investigated whether in vitro human megakaryocyte colony formation and proplatelet formation are affected by various monoclonal antiplatelet GP antibodies (MoAb). The megakaryocyte colony formation inhibition assay was performed by methylcellulose culture with modifications, using peripheral blood nonadherent mononuclear cells. The proplatelet formation inhibition assay was performed by megakaryocytes derived from CD34(+) cells, stimulated with thrombopoietin + stem cell factor, which were then incubated with antiplatelet GP MoAb for 24 or 48 hours. Anti-GP-Ibalpha MoAb (CD42b; HIP1) slightly inhibited megakaryocyte colony formation (P < .05). and strongly inhibited proplatelet formation (after 24 hours incubation, P < .0002; after 48 hours incubation, P < .0007). Anti-GP-IIb MoAb (CD41; 5B12) inhibited only proplatelet formation (only after 24 hours incubation, P <. 03). Anti-integrin alphavbeta3 MoAb (CD51/CD61; 23C6) only slightly inhibited colony size (P < .05). However, anti-GP-IIIa MoAb (CD61; Y2/51) did not inhibit either colony formation or proplatelet formation. These results suggest that antiplatelet GP MoAbs have differing effects on in vitro megakaryocyte colony formation and proplatelet formation.

Adult↗
PubMed1999

Magnetic resonance imaging of experimentally-induced sialadenitis in rat submandibular glands.

OBJECTIVES: To correlate the features of magnetic resonance (MR) images of experimentally induced obstructive sialadenitis in rat submandibular glands with the histopathological changes. METHODS: Changes in MR images of ligated and non-ligated rat submandibular glands were compared with the histopathological changes and wet weight ratios. Spin echo T1 weighted images (SE T1WI), fast spin echo T2 weighted images (FSE T2WI), and gradient echo T2 weighted images (GE T2WI) were obtained at 1, 2, 3, 4, 5, 7 and 21 days after duct ligation with a 0.3 T MR imaging system. RESULTS: There was a significant difference (P<0.05) between the signal intensity ratios of both ligated and non-ligated glands on each day, except at 21 days on GE T2WI. On SE T1WI, small interval changes of signal intensity ratios were observed on both glands, whereas there were large interval changes at 1 - 2 days, 4 - 7 days and 21 days after duct ligation with FSE T2WI. These three periods correlated highly with three phases of histopathological changes, swelling of acinar cells at 1 - 2 days, atrophy of acinar cells and increase of duct-like structures at 3 - 7 days, and proliferation of connective tissue at 21 days, and the changes in wet weight ratios. A similar tendency was observed on GE T2WI to FSE T2WI. CONCLUSIONS: As FSE T2WI showed large changes in signal intensity that correlated highly with histopathological three phases, it is recommended as the MR sequence of choice for diagnosing the degree of damage in obstructive sialadenitis.

Animals↗
PubMed1999

Clinical evaluation of repeat apheresis donors in Japan.

BACKGROUND AND OBJECTIVES: To ascertain the safety of repeat apheresis donation, hematological and biochemical tests were performed on 511 donors with a donation rate of over 6 times per year for a period of 12-19 months. MATERIALS AND METHODS: Repeat donors who had apheresis more than 6 times in the previous year were chosen. Data for the repeat donors at the start of the experiments were compared with those at the end of the study. Blood samples were taken prior to donation. Serum protein, albumin, immunoglobulin G, A, and M, serum ferritin levels were determined by biochemical tests. RESULTS: When compared to prospective donors of 400 ml, WBC, lymphocytes, and serum ferritin levels were lower in a roughly frequency-dependent manner in female and male donor groups at the beginning of the study. All the data for the male group remained almost constant with increasing frequency of apheresis donation. However, in the female group, ferritin levels significantly decreased with over 21 donations. CONCLUSIONS: The present data showed that the serum ferritin level of the female donors decreased the most with increasing frequency of apheresis donation. The cumulative RBC left in the collecting chamber and for the laboratory test is discussed in relation to a possible cause of iron deficiency in frequent apheresis donors.

Adult↗
PubMed1998

Growth hormone-induced tyrosine phosphorylation of EGF receptor as an essential element leading to MAP kinase activation and gene expression.

GH binding to its receptor, which belongs to the cytokine receptor superfamily, activates Janus kinase (JAK) 2 tyrosine kinase, thereby activating a number of intracellular key proteins such as STAT (signal transducers and activators of transcription) proteins and mitogen-activated protein (MAP) kinases, which finally lead to GH's biological actions including gene expression. In contrast to receptor tyrosine kinases, the signalling pathways leading to MAP kinase activation by GH are poorly understood but appear to involve Grb2 and Shc. We now show that GH stimulated tyrosine phosphorylation of epidermal growth factor receptor (EGFR) and its association with Grb2, and concomitantly stimulated MAP kinase activity in liver, a major target tissue. Expression of EGFR and its mutants into CHO-GH receptor (GHR) cells revealed that GH-induced full activation of MAP kinase and c-fos expression required tyrosine phosphorylation sites of EGFR but not its intrinsic tyrosine kinase activity. Moreover, by also using dominant negative JAK2 and in vitro kinase assay, we demonstrated that tyrosine 1068 of EGFR was evidently one of the major phosphorylation and Grb2 binding sites stimulated by GH via JAK2. These data suggest that the role of EGFR in GH signalling is to be phosphorylated by JAK2, thereby providing docking sites for Grb2 and activating MAP kinases and gene expression. This novel cross talk pathway may provide the first example of the hormone and cytokine receptor superfamily transducing signals via associated nonreceptor tyrosine kinase by phosphorylating growth factor receptor and utilizing it as a docking protein independent of its receptor tyrosine kinase activity.

Adaptor Proteins, Signal Transducing↗
PubMed1998

GH signalling in pancreatic beta-cells.

GH and its related peptide PRL are known to stimulate proliferation and insulin biosynthesis in pancreatic beta-cells, and assumed to be involved in their functional maturation. We investigated signal transduction of GH and PRL in insulin-secreting cells using the differentiated rat insulinoma cell line, INS-1. In these cells, both hormones stimulated proliferation and DNA synthesis, increased viability, cellular metabolism and insulin content. GH induced cytosolic Ca2+ ([Ca2+]i) rises, which appear to be due to Ca2+-influx through voltage-gated Ca2+-channels. GH also promoted tyrosine phosphorylation of several proteins in INS-1 cells, one of which was identified as JAK2 tyrosine kinase. Moreover, GH caused changes in DNA binding of nuclear proteins to some interferon-gamma-activated sites. Verapamil inhibited neither DNA synthesis nor JAK2 phosphorylation stimulated by GH, whereas a tyrosine kinase inhibitor, lavendustin A, blocked the mitogenic effect. Involvement of cAMP is also suggested because Rp-cAMPS, a competitive inhibitor of protein kinase A, abolished both [Ca2+]i rises and DNA synthesis stimulated by GH. The effects of GH and PRL on [Ca2+]i, JAK2 phosphorylation and DNA binding of the STATs were virtually identical in INS-1 cells. Since both hormones failed to activate MAP kinase in these cells, it is strongly suggested that activation of the JAK-STAT pathway is the major signalling event for the mitogenic effects of GH and PRL in beta-cells. It remains to be clarified whether the [Ca2+]i rise mediates other effects of these hormones.

Calcium↗
PubMed1997

Tyrosine phosphorylation of the EGF receptor by the kinase Jak2 is induced by growth hormone.

When growth hormone binds to its receptor, which belongs to the cytokine receptor superfamily, it activates the Janus kinase Jak2 which has tyrosine-kinase activity and initiates an activation of several key intracellular proteins (for example, mitogen-activated protein (MAP) kinases) that eventually execute the biological actions induced by growth hormone, including the expression of particular genes. In contrast to receptors that themselves have tyrosine kinase activity, the signalling pathways leading to MAP kinase activation that are triggered by growth hormone are poorly understood, but appear to be mediated by the proteins Grb2 and Shc. We now show that growth hormone stimulates tyrosine phosphorylation of the receptor for epidermal growth factor (EGFR) and its association with Grb2 and at the same time stimulates MAP kinase activity in liver, an important target tissue of growth hormone. Expression of EGFR and its mutants revealed that growth-hormone-induced activation of MAP kinase and expression of the transcription factor c-fos requires phosphorylation of tyrosines on EGFR, but not its own intrinsic tyrosine-kinase activity. Moreover, tyrosine at residue 1,068 of the EGFR is proposed to be one of the principal phosphorylation sites and Grb2-binding sites stimulated by growth hormone via Jak2. Our results indicate that the role of EGFR in signalling by growth hormone is to be phosphorylated by Jak2, thereby providing docking sites for Grb2 and activating MAP kinases and gene expression, independently of the intrinsic tyrosine kinase activity of EGFR. This may represent a novel cross-talk pathway between the cytokine receptor superfamily and growth factor receptor.

Adaptor Proteins, Signal Transducing↗
PubMed1997

Glucose-induced insulin secretion in INS-1 cells depends on factors present in fetal calf serum and rat islet-conditioned medium.

To study the regulation of growth and differentiated function of insulin-secreting cells, the rat insulinoma cell line INS-1 was cultured in a defined serum-free medium containing prolactin, IGF-I, and triiodothyronine, which was originally reported to maintain insulin secretion of islet cells. Growth and viability, as well as cellular insulin content of INS-1 cells in the defined medium, were comparable to the control cells cultured in the complete medium containing 10% fetal calf serum. However, after a 3-day culture in this medium, insulin secretion in response to glucose, pyruvate, and leucine was markedly blunted compared with the control cells (-78, -68, and -56%, respectively), whereas the response to 30 mmol/l K+ was only slightly decreased. In these cells: 1) nutrient metabolism assessed by tetrazolium salt reduction was reduced in response to pyruvate and leucine, which are mainly metabolized in the mitochondria; 2) oxidation of both [3,4-(14)C]glucose and [1-(14)C]pyruvate was decreased (-22 and -32%, respectively); 3) glucose failed to depolarize the membrane potential, whereas tolbutamide was fully active; 4) video imaging analysis of cytosolic Ca2+ showed a decrease in the population of glucose-responsive cells, while the response to 30 mmol/l K+ was preserved; 5) serum replenishment for 3 days restored glucose-induced insulin secretion. Interestingly, conditioned serum-free medium from rat islets maintained the insulin secretory function of INS-1 cells, although glucagon, somatostatin, and some other factors failed to restore the function. In contrast, conditioned media from HepG2, PC12, and human umbilical vein endothelial cells did not substitute for serum. Thus, the impaired insulin secretion of the cells cultured in the defined medium is best explained by defective mitochondrial metabolism. Islet cells, but not INS-1 cells, produce factors required for normal signal generation by nutrient secretagogues.

Animals↗
PubMed1997

[Hematological evaluation of megakaryocytic vacuolar degeneration in patients with idiopathic thrombocytopenic purpura].

Variable degrees of vacuolar degeneration of the cytoplasm of megakaryocytes(MEG) have been recognized in patients with idiopathic thrombocytopenic purpura(ITP). It has been questioned whether this degeneration is specific to the disease, as it is not seen in all patients, and few reports have examined its physiological relationship to the disease process. This study examined the vacuolation and its relationship to platelet count(PLTc) by image analysis, measuring the vacuolar area and the MEG area. However, it was inappropriate to evaluate the vacuolar area alone, since variations in the MEG area among patients influenced the vacuolar area. When the proportion of the vacuolar area relative to total MEG was defined as %VAC, the value for ITP patients was higher than in control cases (p < 0.05). However, there was no correlation between %VAC and PLTc. It was thought that this reflected the previous reports doubting the disease specificity of this feature. When all the ITP patients were generalized, the age at onset was wide, and both chronic type and repetitive type cases were included. However, in 4 ITP cases in which it was possible to follow the treatment progress, the %VAC was well correlated with the change in PLTc. It was concluded that MEG cytoplasmic vacuolation in ITP is morphologically meaningful if it can be followed over the course of treatment.

Adult↗
PubMed1997

[Comparison of retinal breaks between patients with atopic dermatitis and mentally retarded patients with self-inflicted ocular injury].

We compared the distribution of retinal breaks in retinal detachment between patients with atopic dermatitis (AD) and mentally retarded patients who had self-inflicted ocular injury (MR). The cases of AD were 16 eyes in 14 patients (six males and eight females, ranging in age from 15 to 52 years, mean 24.5) and the cases of MR were 6 eyes in 5 patients (5 males, ranging in age from 14 to 25 years, mean 20.2). There was no corneoscleral laceration in either group. In the patients with AD, 14 (87.5%) of 16 eyes had retinal breaks at the vitreous base, and 21 (87.5%) of 24 retinal breaks in 16 eyes were at the vitreous base. In the patients with MR, five (83.3%) of 6 eyes had retinal breaks at the vitreous base and 6(66.7%) of 9 retinal breaks in 6 eyes were at the vitreous base. In both groups, ciliary epithelial breaks and peripheral retinal tears were frequently observed, suggesting that retinal detachment in AD has a pathophysiology similar to traumatic retinal detachment with repeated ocular contusion (self-inflicted injury).

Adolescent↗