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Biomedical subjects

Y Oka

Publications and source records attributed to Y Oka.

At least 109 records · Page 6Linked to original sources
PubMed1999

Hyperglycemia impairs the insulin signaling step between PI 3-kinase and Akt/PKB activations in ZDF rat liver.

Akt/PKB activation is reportedly essential for insulin-induced glucose metabolism in the liver. During the hypoinsulinemic and hyperglycemic phase in the Zucker diabetic fatty (ZDF) rat liver, insulin-induced phosphorylations of the insulin receptor (IR) and insulin receptor substrate (IRS)-1/2 were significantly enhanced. Similarly, phosphatidylinositol (PI) 3-kinase activities associated with IRS-1/2 were markedly increased in ZDF rat liver compared with those in the control lean rat liver. However, interestingly, insulin-induced phosphorylation and kinase activation of Akt/PKB were severely suppressed. The restoration of normoglycemia by sodium-dependent glucose transporter (SGLT) inhibitor to ZDF rats normalized elevated PI 3-kinase activation and phosphorylation of IR and IRS-1/2 to lean control rat levels. In addition, impaired insulin-induced Akt/PKB activation was also normalized. These results suggest that chronic hyperglycemia reduces the efficiency of the activation step from PI 3-kinase to Akt/PKB kinase and that this impairment is the molecular mechanism underlying hyperglycemia-induced insulin resistance in the liver.

Animals↗
PubMed1999

Membrane hyperpolarization by sperm-activating and -attracting factor increases cAMP level and activates sperm motility in the ascidian Ciona intestinalis.

In the ascidian Ciona intestinalis (and C. savignyi), sperm-activating and -attracting factor (SAAF) is released from the egg at fertilization and stimulates both Ca(2+) influx and a transient increase in cAMP level of the sperm, leading to the activation of sperm motility (M. Yoshida et al., 1994, Dev. Growth Differ. 36, 589-595). In this paper we show in C. intestinalis that valinomycin, a potassium-selective ionophore, as well as SAAF, activated sperm motility, and this activation was suppressed by extracellular high K(+). Membrane potential measurements showed that both SAAF and valinomycin increase K(+) permeability of sperm and induce membrane hyperpolarization, the amplitude of which depends on the external K(+) concentration. The membrane potential and intracellular K(+) concentration of Ciona sperm without SAAF were estimated to be about -50 mV and 560 +/- 40 mM, respectively. After treatment with SAAF or valinomycin the membrane potential became almost equal to the equilibrium potential of K(+) (-100 mV), and the cAMP level increased in artificial seawater. A potent voltage-dependent K(+) channel blocker, MCD peptide, at the concentration of 10 microM blocked SAAF-induced hyperpolarization of the cells, increase in cAMP, and sperm motility. These results suggest that membrane hyperpolarization produced by the opening of K(+) channels elevates cAMP synthesis and leads to the activation of sperm motility in Ciona.

Animals↗
PubMed1999

p85/p110-type phosphatidylinositol kinase phosphorylates not only the D-3, but also the D-4 position of the inositol ring.

Activation of p85/p110-type phosphatidylinositol (PI) kinase has been implicated in various cellular activities. This PI kinase phosphorylates the D-4 position with a similar or higher efficiency than the D-3 position when trichloroacetic acid-treated cell membrane is used as a substrate, although it phosphorylates almost exclusively the D-3 position of the inositol ring in phosphoinositides when purified PI is used as a substrate. Furthermore, the lipid kinase activities of p110 for both the D-3 and D-4 positions were completely abolished by introducing kinase-dead point mutations in their lipid kinase domains (DeltaKinalpha and DeltaKinbeta, respectively). In addition, both PI 3- and PI 4-kinase activities of p110alpha and p110beta immunoprecipitates were similarly inhibited by either wortmannin or LY294002, specific inhibitors of p110. Insulin induced phosphorylation of not only the D-3 position, but also the D-4 position. Indeed, overexpression of p110 in Sf9 or 3T3-L1 cells induced marked phosphorylation of the D-4 position to a level comparable to or much greater than that of D-3, whereas inhibition of endogenous p85/p110-type PI kinase via overexpression of dominant-negative p85alpha (Deltap85alpha) in 3T3-L1 adipocytes abolished insulin-induced synthesis of both. Thus, p85/p110-type PI kinase phosphorylates the D-4 position of phosphoinositides more efficiently than the D-3 position in vivo, and each of the D-3- or D-4-phosphorylated phosphoinositides may transmit signals downstream.

1-Phosphatidylinositol 4-Kinase↗
PubMed1999

Cochlear histopathology associated with mitochondrial transfer RNA(Leu(UUR)) gene mutation.

Using dot-blot hybridization and Southern blotting, the authors detected a point mutation at nucleotide pair (np) 3243 in mitochondrial DNA from temporal bone sections of a woman with diabetes and deafness. The mutation could not be detected with agarose gel electrophoresis, suggesting that the degree of heteroplasmy is low. Histologically, there was marked degeneration of the stria vascularis and outer hair cells throughout the cochlea, as well as a reduction of spiral ganglion cells in the base. These findings suggest that the mutation affects these inner ear structures preferentially and that deafness can occur even when the proportion of np 3243 mutation is low.

Cochlea↗
PubMed1999

Enhanced phosphoinositide hydrolysis via overexpression of phospholipase C beta1 or delta1 inhibits stimulus-induced insulin release in insulinoma MIN6 cells.

To study the effects of enhanced phosphoinositide hydrolysis on insulin secretion, phosphoinositide-specific phospholipase Cbeta1 (PLCbeta1) or PLCdelta1 was overexpressed in insulinoma MIN6 cells via adenoviral vectors. Inositol phosphate production stimulated by NaF (with AlCl3) in PLCbeta1-overexpressing cells and that stimulated by KCl or glucose in both PLCbeta1- and PLCdelta1-overexpressing cells were greater than that in control cells. In addition, reduced phosphatidylinositol-4,5-bisphosphate levels were observed in these cells stimulated by NaF or KCl. The greater phosphoinositide hydrolysis was accompanied by 25-45% inhibition of insulin secretion. These data suggest that excessive phosphoinositide hydrolysis inhibits secretagogue-induced insulin release in MIN6 cells.

Adenoviridae↗
PubMed1999

Microtubule-dependent movement of symbiotic algae and granules in Paramecium bursaria.

Paramecia demonstrate rotational cytoplasmic streaming, in which some cytoplasmic granules and organelles, including symbiotic algae, flow in a constant direction. To elucidate the mechanism of this streaming, we examined the effects of cytochalasins (cytochalasin B and D, and dihydrocytochalasin B) and nocodazole, which are reagents affecting microfilament and microtubule networks, respectively, in the cell. In previous reports, paramecia have been compressed with a coverslip to facilitate observation of cytoplasmic streaming. Here we found that the cytoplasmic streaming of paramecia was suppressed by such compression and then observed the process without compression in this work. In the presence of cytochalasins, cytoplasmic streaming was not affected. In contrast, treatment with nocodazole (10 microg/ml) resulted in discontinuation of cytoplasmic streaming in paramecia. Immunofluorescent microscopic observations by confocal microscopy revealed that the number of intracellular microtubules in nocodazole-treated cells was markedly decreased compared to that of controls. Electron microscopic observations confirmed the decrease. These results suggest that cytoplasmic microtubules play an important role in the cytoplasmic streaming of paramecia.

Animals↗
PubMed1999

Selective downregulation of neutrophils by a phosphatidic acid generation inhibitor in a porcine sepsis model.

Effects of lisofylline (1-(5-R-hydroxyhexyl)-3,7-dimethylxanthine), a functional inhibitor of phosphatidic acid (PA) generation derived from de novo synthesis, on neutrophil function were examined in a porcine sepsis model. Hanford minipigs (18-25 kg) were randomly separated into six groups of six animals each: (1) saline control group; (2) sepsis control group, infused with Pseudomonas aeruginosa (1 x 10(6) colony-forming units/kg/min) for 2 h; (3) lisofylline control group, given a 25 mg/kg bolus of lisofylline 30 min prior to time zero, followed by a continuous infusion of 10 mg/kg/h throughout the study; (4) lisofylline pretreatment sepsis group, given lisofylline 30 min prior to sepsis, (5) lisofylline 1-h post-treatment sepsis group, and (6) lisofylline 2-h post-treatment sepsis group. All animals were studied for 6 h. Neutrophils were isolated at -0.5, 2, and 6 h. In the pretreatment and 1-h post-treatment groups, sepsis-induced neutrophil attachment to fibronectin was significantly attenuated. Sepsis-enhanced phagocytic activity was significantly reduced in the lisofylline pretreatment sepsis group, but not in the post-treatment groups. No treatment affected phorbol 12-myristate 13-acetate-induced chemiluminescence and basal filamentous actin content, which increased in sepsis, and cap formation, which declined in sepsis. Sepsis caused neutropenia, pretreatment produced neutrophilia, and 1-h post-treatment caused the neutropenia to recover to control levels. Interestingly, toward the end of the 6-h period, the neutrophil count was higher in the lisofylline control group than in the saline control groups. Thus, the inhibition of PA generation from de novo synthesis during sepsis not only can selectively downregulate some neutrophil functions but can also reverse neutropenia.

Actins↗
PubMed1999

Overexpression of dominant negative mutant hepatocyte nuclear factor (HNF)-1alpha inhibits arginine-induced insulin secretion in MIN6 cells.

AIMS/HYPOTHESIS: To explain the mechanisms whereby mutations in the HNF-1alpha gene cause insulin secretory defects. METHODS: A truncated mutant HNF-1alpha (HNF-1alpha288t) was overexpressed in hepatoma cells (HepG2) and murine insulinoma cells (MIN6) using a recombinant adenovirus system and expression of the HNF-1alpha target genes and insulin secretion were examined. RESULTS: Expression of phenylalanine hydroxylase and alpha1-antitrypsin genes, the target genes of HNF-1alpha, was suppressed in HepG2 cells by overexpression of HNF-1alpha288t. In MIN6 cells, overexpression of HNF-1alpha288t did not change insulin secretion stimulated by glucose (5 mmol/l and 25 mmol/l) or leucine (20 mmol/l). Potentiation of insulin secretion by arginine (20 mmol/l, in the presence of 5 mmol/l or 25mmol/l glucose) was, however, reduced (p < 0.0001 and p = 0.027, respectively). Similarly reduced responses were observed when stimulated with homoarginine. Expression of the cationic amino acid transporter-2 was not reduced and insulin secretory response to membrane depolarization by 50 mmol/l KCl was intact. CONCLUSION/INTERPRETATION: The HNF-1alpha288 t, which is structurally similar to the mutant HNF-1alpha expressed from the common MODY3 allele, P291fsinsC, exerts a dominant negative effect. Suppression of HNF-1alpha in MIN6 cells severely impaired potentiation of insulin secretion by arginine, whereas glucose-stimulated and leucine-stimulated insulin secretion was intact. Our findings delineate the complex nature of beta-cell failure in patients with MODY3. This cell model will be useful for further investigation of the mechanism of insulin secretory defects in these patients.

Animals↗
PubMed1999

Diagnostic use of isotropic diffusion-weighted MRI in patients with ischaemic stroke: detection of the lesion responsible for the clinical deficit.

We examined the diagnostic use of isotropic diffusion-weighted (DW) MRI in 140 consecutive patients suspected of or diagnosed as having an ischaemic stroke. Isotropic DW imaging could demonstrate the lesion responsible for the clinical deficit in patients with multiple cerebral infarcts at an early stage, even small lesions without a perifocal oedema or mass effect. Accurate diagnosis by DW images may, however, be difficult about 2 weeks after the onset of stroke.

Adult↗
PubMed1999

Changes in visibility of intracranial arteries on MRA with normal ageing.

We investigated age-related changes in the visibility of intracranial arteries on magnetic resonance angiography (MRA) and the influence of risk factors for stroke. We studied 230 adult patients without specific neurological deficits. MRA was performed using the three-dimensional time-of-flight technique with a spoiled gradient-recalled acquisition sequence. We classified internal carotid artery (IC) and the horizontal (M1) and distal (beyond M2) middle cerebral segments into 4 grades. Linear regression revealed a significant negative relation between age and the quality of demonstration on MRA. For IC and M1, the score was significantly lower in subjects with risk factors than in those without. The distal MCA was poorly seen in patients without a history of hypertension or lacunar infarcts. A marked correlation was observed between visibility and age patients with no history of hypertension, diabetes mellitus and hyperlipidaemia. We suggest that atherosclerotic change and decline in flow velocity with normal ageing are factors leading to decreased visibility on MRA.

Adult↗
PubMed1999

Bone-peg grafting for osteochondritis dissecans of the elbow.

In the treatment of osteochondritis dissecans involving the elbow, we have used a bone-peg graft taken from the proximal part of the ulna and inserted into the defect. Thirty-two patients were followed from 2 to 10.5 years. The graft was utilised in 20 elbows, and 6 of these also had concomitant removal of a loose body. Another 6 elbows had removal of a loose body only. Ten elbows were treated conservatively in 5 of these the outcome was unsatisfactory, including 4 in which a bone-peg graft was later necessary. The bone-peg graft gave the best short-term results. Bony union of the dissecans site and reconstitution of subchondral bone required an average of 6.5 months. In 15 patients followed for a minimum of 5 years, the bone-peg graft was effective in limiting the development of osteoarthritis. Bone-peg grafting is a reliable method for treating osteochondritis dissecans of the elbow.

Adolescent↗
PubMed1999

Debridement for osteoarthritis of the elbow in athletes.

The results of surgical treatment for osteoarthritis of the elbow in athletes were investigated. Athletic activities consisted mainly of judo wrestling and baseball; and included 26 elbows. The mean age was 32 years. The radiological changes were mild in most cases. Debridement consisted of resecting osteophytes and removing loose bodies. Pain scores were improved, and the range of movement was improved by an average of 24 degrees with an average follow-up of 4 years and 2 months. Recurrence of mild symptoms occurred in most cases.

Adolescent↗
PubMed1999

Imidapril, an angiotensin-converting enzyme inhibitor, improves insulin sensitivity by enhancing signal transduction via insulin receptor substrate proteins and improving vascular resistance in the Zucker fatty rat.

Angiotensin-converting enzyme (ACE) inhibitors are antihypertensive agents, that inhibit the conversion of angiotensin I to angiotensin II, resulting in smooth-muscle relaxation and a reduction of vascular resistance. Recently, it has been suggested that ACE inhibitors improve insulin resistance in diabetic patients. To investigate the effect of an ACE inhibitor on insulin sensitivity, insulin signaling, and circulation, imidapril was administered orally or intraduodenally to Zucker fatty rats. Oral administration of imidapril improved insulin sensitivity based on the results of an oral glucose tolerance test (OGTT) and a decrease in urinary glucose secretion. Phosphatidylinositol 3-kinase (PI 3-kinase) activity associated with hepatic insulin receptor substrate-1 (IRS-1) in the insulin-stimulated condition was significantly enhanced 110% without a significant alteration in tyrosine phosphorylation of IRS-1 in the imidapril-treated group. In muscle, IRS-1 tyrosine phosphorylation and PI 3-kinase activity associated with IRS-1 in the insulin-stimulated condition were enhanced 70% and 20%, respectively, in the imidapril-treated group. In contrast, an alteration of the IRS-2 pathway was observed only in liver; a significant insulin-induced increase in the IRS-2-associated PI 3-kinase over the basal level was observed in the imidapril-treated group but not in the control. In addition, treatment with imidapril was shown to significantly reduce blood pressure and increase blood flow in the liver and muscle. These results suggest that the ACE inhibitor imidapril may improve insulin sensitivity not only by acting directly on the insulin signaling pathway but also by increasing blood flow in tissues via normalization of vascular resistance, a major cause of hypertension.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1999

Constitutive expression of the Wilms' tumor gene WT1 inhibits the differentiation of myeloid progenitor cells but promotes their proliferation in response to granulocyte-colony stimulating factor (G-CSF).

Bone marrow (BM) cells that were concentrated for hematopoietic progenitor cells by in vivo treatment with 5-FU were infected with a recombinant retrovirus containing a human full-sized, non-spliced type WT1 (Wilms' tumor gene 1) cDNA and then colony-assayed in the presence of granulocyte-colony stimulating factor (G-CSF). Significantly more colony-forming units granulocyte-monocyte (CFU-GM), colony-forming units granulocyte (CFU-G), and colony-forming units monocyte (CFU-M) colonies were formed in response to G-CSF from the BM cells infected with the WT1-containing retrovirus than from the control BM cells infected with an empty vector. Furthermore, FACS analysis of cell surface differentiation markers showed the inhibition of differentiation by constitutive WT1 expression resulting from the infection with the WT1-containing retrovirus. These results thus showed that the constitutive WT1 expression promoted the proliferation of myeloid progenitor cells but inhibited their differentiation in response to G-CSF, suggesting the alteration of G-CSF signaling pathway. The results also supported our hypothesis that the WT1 gene performs an oncogenic rather than a tumor suppressor gene function in hematopoietic progenitor cells, although the WT1 gene potentially performs both functions. This finding implies an important role of the WT1 gene in leukemogenesis.

Animals↗
PubMed1999

Hypophosphorylation of pRB and repression of cyclin D3 and cdc25A during the granulocytic differentiation of human myeloblastic leukemia ML-1 cells.

Recently we succeeded in inducing synergistic differentiation toward granulocytes in human myeloblastic leukemia ML-1 cells by treatment of ATRA in combination with GM-CSF. To research the mechanism of this differentiation process, we examined expression of cell cycle-related genes that are concerned with cell growth and differentiation. We detected change to the hypophosphorylated form of pRB and down-regulation of cyclin D3 and cdc25A during induced differentiation. Furthermore, these marked alterations were hardly detected in ML-1 cells treated with ATRA or GM-CSF alone. These results suggest that hypophosphorylation of pRB and repression of cyclin D3 and cdc25A are induced synergistically by treatment with ATRA plus GM-CSF in ML-1 cells.

Cell Differentiation↗
PubMed1999

Insulinotropin PACAP potentiates insulin-stimulated glucose uptake in 3T3 L1 cells.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is localized in pancreatic nerve fibers and islets and potently augments glucose-induced insulin secretion. The present study explored a possible extra-pancreatic action of PACAP. The specific PACAP receptor (PAC1 receptor) was expressed in the rat fat tissue and 3T3-LI adipocytes. PACAP-38 (10 nM) significantly enhanced insulin-induced 2-deoxyglucose uptake by 3T3-L1 adipocytes. Insulin-stimulated phosphatidylinositol 3-kinase activity was further increased by PACAP-38, whereas the tyrosine-phosphorylation of insulin receptor beta-subunit and insulin receptor substrate-1 was unaltered by PACAP-38. These results reveal that PACAP-38 enhances insulin-induced glucose uptake, an effect probably mediated by insulin-stimulated phosphatidyl-inositol 3-kinase, and that PACAP potentiates not only insulin secretion, but also insulin action in adipocytes.

3T3 Cells↗
PubMed1999

The Wilms' tumor gene WT1 is a good marker for diagnosis of disease progression of myelodysplastic syndromes.

The Wilms' tumor gene, WT1, is a tumor marker for leukemic blast cells. The WT1 expression levels were examined for 57 patients with myelodysplastic syndromes (MDS) (refractory anemia (RA), 35; RA with excess of blasts (RAEB) 14; RAEB in transformation (RAEB-t), six; and MDS with fibrosis, two) and 12 patients with acute myeloid leukemia (AML) evolved from MDS. These levels significantly increased in proportion to the disease progression of MDS from RA to overt AML via RAEB and RAEB-t in both bone marrow (BM) and peripheral blood (PB). WT1 expression levels in PB significantly correlated with the evolution of RAEB or RAEB-t to overt AML within 6 months. Therefore, WT1 expression levels in PB were superior to those in BM for early prediction of the evolution to AML by means of quantitation of the WT1 expression levels. Furthermore, WT1 expression in PB of patients with overt AML evolved from MDS was significantly decreased by effective chemotherapy or allogeneic stem cell transplantation and became undetectable in long-term survivors. These results clearly showed that WT1 expression levels are a tumor marker for preleukemic or leukemic blast cells of MDS and thus reflect the disease progression of MDS. Therefore, monitoring of WT1 expression levels has made continuous assessment of the disease progression of MDS possible, as well as the prediction of the evolution of RAEB or RAEB-t to overt AML within 6 months. The results also showed that quantitation of WT1 expression levels is useful for diagnosis of minimal residual disease of MDS with high sensitivity, thus making it possible to evaluate the efficacy of treatment for MDS.

Adult↗