Biomedical subjects

Y Iwami

Publications and source records attributed to Y Iwami.

At least 19 recordsLinked to original sources

PubMed2006

Resistance to acidic and alkaline environments in the endodontic pathogen Enterococcus faecalis.

BACKGROUND/AIMS: This study aimed to investigate the biochemical mechanisms employed by the endodontic pathogen Enterococcus faecalis to confer acid- and alkali-resistance and to compare these with the mechanisms of representative oral streptococci. METHODS: E. faecalis JCM8728, Streptococcus mutans NCTC10449 and Streptococcus sanguinis ATCC10556 were used to assess both acid- and alkali-resistance by examining: (i) growth in complex media; (ii) stability of intracellular pH (pH(in)); (iii) cell durability to leakage of preloaded BCECF (2',7'-bis-(2-carboxyethyl)-5,6-carboxy-fluorescein); and (iv) cell permeability to SYTOX-Green. RESULTS: Growth was initiated by E. faecalis at pH 4.0-11.0, by S. mutans at pH 4.0-9.0 and by S. sanguinis at pH 5.0-9.0. The pH(in) was similar to the extracellular pH in S. mutans and S. sanguinis at pH 5-10, while the pH(in) of E. faecalis was maintained at approximately 7.5-8.5 when extracellular pH was 7.5-10 and was maintained at levels equivalent to the extracellular pH when pH < 7.5. Cell membranes of E. faecalis were resistant to BCECF leakage when extracellular pH was 2.5-12 and to SYTOX-Green permeability at pH 4-10. The cell membrane durability to extracellular pH in E. faecalis was higher than that observed in the Streptococcus strains. CONCLUSION: Compared to S. mutans, E. faecalis was found to be equally resistant to acid and more resistant to alkalis. The results suggest that pH-resistance in E. faecalis is attributed to membrane durability against acid and alkali, in addition to cell membrane-bound proton-transport systems. These characteristics may account for why E. faecalis is frequently isolated from acidic caries lesions and from persistently infected root canals where calcium hydroxide medication is ineffective.

Acids↗

PubMed2003

Xylitol inhibition of anaerobic acid production by Streptococcus mutans at various pH levels.

Xylitol inhibits the glycolysis and growth of Streptococcus mutans. We studied the inhibitory effect of xylitol on the acid production of S. mutans at several pH levels under the strictly anaerobic conditions found in the deep layer of dental plaque. Xylitol inhibited the rate of acid production from glucose and changed the profile of acidic end products to formate-acetate dominance, with a decrease in the intracellular level of fructose 1,6-bisphosphate and an intracellular accumulation of xylitol 5-phosphate (X5P). These results were notable at pH 5.5-7.0, but were not evident at pH 5.0. Since the activity of phosphoenolpyruvate phosphotransferase for xylitol was greater at higher pH, it is suggested that xylitol could be incorporated more efficiently at higher pH and that the resultant accumulation of X5P could inhibit the glycolysis of S. mutans more effectively.

Acetic Acid↗

PubMed2002

Intracellular and extracellular pHs of Streptococcus mutans after addition of acids: loading and efflux of a fluorescent pH indicator in streptococcal cells.

A pH-sensitive fluorescent dye, 2', 7'-bis-(2-carboxyethyl)-5 and 6-carboxyfluorescein (BCECF), was used to determine intracellular pH (pH(in)). The efflux of BCECF loaded into oral streptococcal cells was determined after incubation of the cells at 35 degrees C for 20 min in the presence and absence of glucose. In the absence of glucose, the fluorescence of intracellular BCECF in Streptococcus mutans, Streptococcus sanguis, Streptococcus salivarius and Streptococcus sobrinus decreased only very slightly, indicating that the dye could be useful for pH(in) determination. In the presence of glucose, however, the fluorescence decreased by 57%. Thus, the pH(in) of S. mutans cells was measured by the BCECF method in the absence of glucose at various acidic pH levels by adding lactic, acetic and hydrochloric acids to the cell suspensions. The pH(in) was almost equal to the extracellular pH (pH(out)) for pH(out) values of between 8 and 5, indicating that protons permeated easily across the S. mutans cell membrane. For pH(out) between 5 and 4, pH(in) was constant at around 5, suggesting that the cell membrane was impermeable to protons, or that a cytoplasmic buffering system functioned. pH(in) decreased at pH(out) values of < 4. The constant pH(in) at acidic pH(out) levels could protect intracellular components, such as proteins, against acidification by sugar fermentation.

Acetic Acid↗

PubMed2001

The time-course of acid excretion, levels of fluorescence dependent on cellular nicotinamide adenine nucleotide and glycolytic intermediates of Streptococcus mutans cells exposed and not exposed to air in the presence of glucose and sorbitol.

The aim of this study was to examine glucose and sorbitol metabolism in Streptococcus mutans cells exposed and not exposed to air at the coexistence of these compounds by measuring acid excretion, levels of fluorescence dependent on cellular NADH and glycolytic intermediates. An aliquot of bacterial cells grown under strictly anaerobic conditions (anaerobic cells) was exposed temporarily to air (aerobic cells). When glucose was added to the anaerobic cells metabolizing sorbitol, the acid excretion was increased. The level of NADH decreased initially and then increased to the higher plateau level than that during glucose metabolism. The aerobic cells neither metabolized sorbitol nor contained glycolytic intermediates. However, 2 min after glucose was added in the presence of sorbitol, the acid excretion was started slowly and the intermediates appeared. The level of NADH was decreased at first and then increased. These results suggested that the anaerobic S. mutans cells metabolized glucose and sorbitol simultaneously, and that in the presence of sorbitol the aerobic cells could start to metabolize glucose 2 min after glucose was added, as the intermediates (phosphoenopyruvate potential) for the glucose transport were accumulated.

Acids↗

PubMed2001

Effect of the extracellular matrix on pancreatic endocrine cell function and its biocompatibility in dogs.

The effect of the synthetic extracellular matrix (ECM) in a diffusion chamber for a bioartificial endocrine pancreas (Bio-AEP) on pancreatic endocrine cells in vitro and its biocompatibility in dogs were investigated. Two different types of ECM were used: type I collagen treated with low antigen (type I LA), and reconstituted basement membrane matrix (Matrigel) derived from Englbreth-Holm-Swarm (EHS) mouse sarcoma. Matrigel contains growth and differentiation factors and cell adhesion molecules such as laminin, heparan sulfate proteoglycan, and entactin. Purified porcine pancreatic endocrine (PE) cells were suspended in type I LA or Matrigel and then placed into a 12-well culture plate (4 x 10(7) cells/ml gel/well). The insulin accumulation from PE cells in Matrigel was significantly greater than that in type I LA (9.3 +/- 3.6 mU/well vs. 2.3 +/- 1.3 mU/well). When Bio-AEP with Matrigel and PE cells was implanted into the abdominal cavity of a pancreatectomized diabetic dog, the exogenous insulin requirement for maintaining normoglycemia was reduced for the first 4 weeks. However, after 6 weeks of implantation, fasting blood glucose levels suddenly increased. Laparotomy revealed encapsulated Bio-AEP with thick fibrous tissue. Following removal of the Bio-AEP from the abdominal cavity, another Bio-AEP containing type I LA and PE cells was implanted into the same dog. The exogenous insulin requirement was gradually decreased to almost half that of preimplantation levels. Bio-AEPs containing type I LA or Matrigel, but not PE cells, were implanted into the abdominal cavities of four healthy dogs. After 4 weeks of implantation, the Bio-AEP with Matrigel was encapsulated with fibrous tissue similar to that in the diabetic dog, but the Bio-AEP with type I LA was not. These results indicate that Matrigel may be incompatible with dogs and that the type I LA is more suitable for Bio-AEP.

Animals↗

PubMed2000

A new electrical method for detecting marginal leakage of in vitro resin restorations.

OBJECTIVES: Ingress of bacteria at sites of marginal leakage has been suggested to cause pulpal inflammation. The purpose of this in vitro study was to evaluate the validity of a new electrical method to detect marginal leakage of restoratives by comparing the results obtained with those of a dye penetration test. METHODS: After cavities were prepared on the buccal coronal surfaces and root surfaces of 16 extracted non-carious human molar teeth, eight specimens were treated with a dentin bonding system (bonding group) and the other eight specimens were not treated (non-bonding group). Resin composites were filled in the cavities of all specimens, and physiological saline was applied to the margin of the restorative. Any excess saline was wiped off, leaving only the electrolyte, which had penetrated into the marginal gap. The change in conductance was measured continuously across the margin of each specimen during this process. The marginal leakage of specimens was confirmed using the dye penetration test, and the results were evaluated by the microleakage score. RESULTS: In both coronal and root surface cavities, the changes in conductance in the non-bonding group after filling were significantly larger than those of the bonding group (p<0.05). The change in conductance of each specimen correlated with the microleakage score (p<0.05). CONCLUSIONS: It was concluded that the relative electrical method could detect marginal leakage in both coronal and root surface cavities.

Composite Resins↗

PubMed2000

Rate-limiting steps of glucose and sorbitol metabolism in Streptococcus mutans cells exposed to air.

It has been supposed that rate of sorbitol metabolism in the air-exposed streptococcal cells could be limited by the low capacity to regenerate nicotinamide adenine dinucleotide (NAD) from reduced NAD (NADH) following inactivation of pyruvate formate-lyase by oxygen. The rate-limiting steps, however, have not been identified. The aim of this study was to examine the effect of temporary exposure of the streptococcal cells to air on the intracellular flux of glucose and sorbitol metabolism by measuring acid excretion, fluorescence dependent on cellular level of NADH, glycolytic intermediates and enzyme activities. The exposure of cells to air decreased the acid excretions during glucose and sorbitol metabolism. The analysis of the glycolytic intermediates and the fluorescence suggested that the reduced level of acid excretion in the air-exposed glucose metabolizing cells resulted from the decrease in pyruvate catabolism. In the presence of sorbitol, the decreased acid production resulted from the reduced rates of the reactions catalyzed by sorbitol-phosphoenolpyruvate phosphotransferase and sorbitol 6-phosphate dehydrogenase because of shortage of substrates for these enzymes in addition to the decrease in pyruvate catabolism.

Acetyltransferases↗

PubMed1999

Intracellular flux of glucose metabolism in streptococcal cells by simultaneous monitoring of fluorescence dependent on reduced nicotinamide adenine nucleotide and acid excretion under strictly anaerobic conditions.

Reduced nicotinamide adenine nucleotide (NADH)-dependent fluorescence and acid excretion during glucose pulse to washed Streptococcus mutans cells were monitored simultaneously at pH 7.0 with a fluorescence spectrophotometer and a pH-stat. Acid excretion started with addition of glucose. At the same time, the fluorescence dropped quickly to a minimum level and increased to a plateau level, suggesting that pyruvate metabolism started immediately after addition of glucose, then the rate of the pyruvate metabolism became almost equal to the rate of glycolysis. When the acid excretion stopped, the fluorescence increased rapidly from the plateau to the maximum level, suggesting that the pyruvate metabolism stopped first, and then began to decrease to the original level. The system used in this study for simultaneously monitoring the level of NADH and acid excretion gives us a crucial tool to clarify a biochemical mechanism of the control of sugar metabolism by streptococci.

Acids↗

PubMed1998

Effect of enamel and dentin surface wetness on shear bond strength of composites.

PURPOSE: This study investigated the effect of the wetness of human enamel and dentin surfaces on the shear bond strength of composites. MATERIAL AND METHODS: Seven dentin bonding systems were used. Three methods of preparing the enamel or dentin surface before applying primer or bonding agent were adopted as test conditions: wet (blot dried), semidry (3-second air blast), and dry (15-second air drying). Shear bond strength was measured with a universal testing machine. Mean bond strengths were analyzed with analysis of variance and Scheffe's F-test. Enamel and dentin surfaces were observed by a dissecting microscope after shear bond testing. RESULTS: Enamel specimens tested by all systems and dentin tested by two systems did not reveal significant differences in shear bond strengths (p > 0.05). Among dentin specimens tested by two systems with water-based primers, the shear bond strength values of the dry technique group were higher than those of the other two groups (p < 0.05). However, among dentin specimens tested by systems having acetone-based primers or bonding agents, bond strength values of the wet or semidry technique groups were higher than those of the dry technique group (p < 0.05). CONCLUSION: It was concluded that some water might be needed by dentin surfaces or for primers to obtain high bond strength on the dentin surface, but that drying methods did not affect bonding strength to enamel surfaces either before priming or after conditioning.

Analysis of Variance↗

PubMed1998

Effect of resin monomer composition on toothbrush wear resistance.

The purpose of this study was to compare the toothbrush abrasion resistance of seven different experimental resins which were made by changing the composition of resin monomers. The experimental resins were made by mixing four kinds of dental resin monomers (Bis-GMA, UDMA, TMPT and TEGDMA), camphorquinone (1 wt%), dimethylaminoethyl methacrylate (2 wt%) and 2,6-di-tert-butyl-p-cresol (0.05 wt%). The resin specimens were stored in air for 2 weeks, and then put on a toothbrush abrasion testing machine. After 100000 strokes, the wear loss of each specimen was determined by weight change during the wear test. TMPT-TEGDMA resin showed the most wear resistance, while Bis-GMA- and UDMA-based resins showed increased wear resistance with an increased content of TEGDMA. Also, a inverse relationship between the microhardness number and the amount of wear of the respective resins was confirmed.

Analysis of Variance↗

PubMed1998

Treatment of malignant neurocardiogenic vasovagal syncope with a rate drop algorithm in dual chamber cardiac pacing.

A 29-year-old man with malignant vasovagal syncope presented with episodes of abrupt loss of consciousness associated with an aura, totaling more than 10 episodes over 3 months. Holter monitoring showed cardiac arrest with a duration of 15 seconds. Oral propranolol and disopyramide therapy failed to prevent the syncope. A dual chamber pacemaker with a rate drop response algorithm successfully prevented the syncope but not the aura. There may be multifactors involved in the mechanism of this syndrome. The patient has returned to a normal active life. This rate drop algorithm is an effective therapy for the prevention of syncope in malignant vasovagal syncope.

Adult↗

PubMed1997

Postnatal development of B lymphocytes and immunoglobulin-containing plasma cells in the chicken oviduct: studies on cellular distribution and influence of sex hormones.

Postnatal development of B lymphocytes and plasma cells containing different classes of immunoglobulins (IgG, IgA, and IgM) was immunohistochemically studied in the oviduct of the Dekalb strain of the White Leghorn chicken. B lymphocytes first appeared in the lamina propria of the chicken oviduct at 5 weeks of age. Their frequency of occurrence peaked at 15 weeks from the infundibulum to the uterus (glandular part), while in the vagina (aglandular part) it did so at 21 weeks. Intraepithelial B lymphocytes were very rare and exclusively located in the vagina at 19 and 21 weeks. Plasma cells first appeared in the lamina propria of the oviduct at 11 weeks of age, and this frequency peaked at 32 weeks. IgG-containing plasma cells were most numerous in the glandular part, whereas in the aglandular part IgA and IgM cells were more numerous than IgG cells. When 7-day-old-chickens were treated with sex hormones, B lymphocytes and plasma cells appeared 12 h and 5 days after the hormone injection, respectively. Their frequency of occurrence was statistically higher in diethylstibestrol (DES)-treated chickens than in DES plus progesterone-treated chickens. This suggests that the postnatal development of B lymphocytes and plasma cells in the oviduct of the chicken is correlated to estrogen secretion.

Animals↗

PubMed1997

Mechanism of inhibition of acid production in Streptococcus mutans by sodium ions under strictly anaerobic conditions.

Acids excreted and intracellular levels of glycolytic intermediates during glucose metabolism in streptococcus mutans NCTC 10449 under strictly anaerobic conditions were quantified in an attempt to understand the effect of sodium ions on bacterial acid production. In the presence of NaCl (0.15-0.30 M), the total amount of individual carboxylic acids excreted was inhibited by up to 31%. The intracellular level of fructose 1,6-bisphosphate increased by 58% and levels of 3-phosphoglycerate and pyruvate decreased by 46% and 12%, respectively. Sodium ions directly inhibited the activities of fructose 1,6-phosphate aldolase and triose phosphate isomerase. This indicated that the glycolytic enzymes responsible for the catalysis of fructose 1,6-bisphosphate to 3-phosphoglycerate were inhibited. However, in spite of the expected reduction in acid production intracellularly, the intracellular pH actually decreased in the presence of sodium ions. It is possible that the low intracellular pH inhibits the activity of the glycolytic enzymes involved in the breakdown of fructose 1,6-bisphosphate to 3-phosphoglycerate.

Anaerobiosis↗

PubMed1997

Effect of sodium and potassium ions on intracellular pH and proton excretion in glycolyzing cells of Streptococcus mutans NCTC 10449 under strictly anaerobic conditions.

The effect of sodium and potassium ions on intracellular acid production and acid excretion by glycolyzing cells of Streptococcus mutans was examined. S. mutans NCTC 10449 grown under glucose-limited and strictly anaerobic conditions in a continuous culture system was loaded with bis(carboxyethyl)-carboxyfluorescein, a pH-sensitive fluorescent dye, washed and suspended in 0.00-0.30 M NaCl/KCl solution. The dye allowed for the continuous monitoring of intracellular pH while proton excretion was measured simultaneously with a pH-stat. Sodium ions inhibited and potassium ions, at low pH, accelerated the amount of measurable acid excreted extracellularly. In the presence of both NaCl and KCl, proton excretion following the addition of glucose was slightly higher or similar to that observed in the presence of 0.15 M KCl alone. Sodium and potassium ions did not affect the proton-ATPase enzyme or the intracellular level of ATP, suggesting that these ions did not directly effect proton pumping activity itself. The inhibition of proton excretion by sodium ions was considered to have probably occurred as a result of an indirect inhibition of proton-ATPase activity by the low intracellular pH induced by sodium ions.

Adenosine Triphosphate↗

PubMed1997

Effect of low levels of fluoride on proton excretion and intracellular pH in glycolysing streptococcal cells under strictly anaerobic conditions.

The effect of low levels of fluoride on intracellular acid production and proton excretion in Streptococcus mutans NCTC 10449 at different growth and extracellular pH (pHo) levels was monitored under strictly anaerobic conditions. The sensitivity of S. mutans to fluoride increased as pHo decreased. Cells grown under acidic (pH 6.0 and 5.5) conditions were more resistant to fluoride than cells grown at a neutral pH. Under acidic extracellular conditions (pHo = 5.0), 0.025 mM fluoride inhibited proton excretion by approximately 50% in cells grown at pH 7.0. Slightly higher levels of fluoride (0.05-0.07 mM) were required for 50% or more inhibition in cells exposed to alkaline extracellular conditions or cells grown at acidic pH. Such levels of fluoride are about 10-20 times lower than that reported previously. Therefore, it is possible that as pH falls during initial bacterial glycolysis, sufficient amounts of anionic fluoride may be released, from its bound form in plaque, to cause significant inhibition of net proton movement out of the bacterial cell during further glycolysis, especially under the anaerobic environment of the deep layers of plaque. In addition to proton excretion, fluoride was also found to inhibit intracellular acid production.

Anaerobiosis↗

PubMed1997

Production of a monoclonal antibody (59.4) against canine lymphocyte surface antigen and its immunohistochemical application.

A monoclonal antibody was produced by immunizing BALB/c mice with freshly prepared canine thymocytes and peripheral blood leukocytes. The antibody, designated 59.4, was of the IgG1 subclass type and mainly reacted with lymphocytes. In single-color flow cytometric analysis, lymphocytes from the peripheral blood, thymus and spleen were graded into three categories according to their fluorescence intensity labeling by antibody 59.4: weakly, moderately and intensely positive cells. Two-color analysis revealed that a major population of CD8-positive cells were intensely labeled by antibody 59.4, but less than 50% of CD4-positive cells were moderately reacted with antibody 59.4. Immunohistochemically, thymocytes in the medulla showed moderately intense immunoreactivity to 59.4, but most lymphocytes in the cortex were negative in reaction. Immunostaining using antibody 59.4 demonstrated characteristic aggregations of 59.4-positive lymphocytes in the reticulum cell-free region of the thymic medulla. In the spleen, scattered lymphocytes in the outer layer of the marginal zone and in the red pulp were intensely labeled by antibody 59.4, while lymphocytes gathering in the mantle zone and periarterial lymphatic sheath (PALS) were moderately stained. Antibody 59.4 appears to recognize an antigen which is expressed by a more-differentiated T cell-lineage but not by immature T cells in the thymic cortex.

Animals↗

PubMed1997

Exercise-induced neurally mediated syncope.

We describe a 16-year-old female referred for evaluation of syncope associated with competitive long distance running. She had experienced 4 episodes of syncope during competitive long distance racing. The syncope associated with marked bradycardia and asystole was demonstrated by head-up tilt testing without isoproterenol infusion. Oral propranolol therapy failed to prevent the syncope. Oral disopyramide therapy, however, prevented the syncope induced by both head-up tilt testing and competitive long distance racing. Caution should be urged in evaluating athletes with syncope, especially in the pediatric age group, because the cause of the syncope may result from life-threatening disorders such as cardiomyopathy, long QT syndrome, or exercise-induced arrhythmias. The head-up tilt test is an important diagnostic tool for the evaluation of exercise-associated syncope.

Adolescent↗

PubMed1997

A monoclonal antibody, 169.1, against canine leukocyte surface antigen identifies cytoskeletal components in epithelial cells and peripheral neurons.

Monoclonal antibodies were produced by immunizing BALB/c mice with freshly prepared canine thymocytes and peripheral blood leukocytes. Flow cytometric analysis of canine peripheral blood leukocytes showed that an antibody, designated 169.1, recognized about 60% of non-lymphoid cells, but reacted with less than 3% of lymphocytes. Immunohistochemistry using frozen sections showed that several types of epithelial cells such as epithelial reticulum cells in the thymus and ductal system in the parotid gland exhibited an intense positive reaction to antibody 169.1. Moreover, the ellipsoidal sheath in the spleen and non-myelinated nerve fibers in the peripheral nervous system had selectively positive reactions; in the latter, filamentous structures were visible under a light microscope. In contrast to the data from the flow cytometric analysis, no leukocytes on sections reacted with 169.1. Immunoblot assay revealed that 169.1 recognized antigens with molecular weights of 48 and 52 kDa under reducing conditions. These findings characterize 169.1 as an antibody against a cytoskeletal protein rich in epithelial cells and neurons.

Animals↗