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M Yamato

Publications and source records attributed to M Yamato.

At least 19 recordsLinked to original sources
PubMed2001

Mut-Test to detect substances suppressing spontaneous mutation due to oxidative damage.

Since it has been considered that suppression of spontaneous mutation in cells is related to suppression of spontaneous carcinogenesis, it is significant to detect substances which suppress spontaneous mutation in bacterial cells such as Escherichia coli and Salmonella typhimurium in the environment. However, since the frequency of spontaneous mutation in bacteria is usually very low, generally 10(-8)-10(-10),it is difficult to determine significant suppressive ability of such substances on spontaneous mutation. A new method, Mut-Test, was developed by us, applying Luria & Delbruck fluctuation test, to detect substances which suppress spontaneous mutation using E. coli mutT mutant in which spontaneous mutation frequency due to oxidative damage is enhanced to approximately 500-1000 times of the wild type strain. Suppressive abilities of two hydroxyl radical scavengers: D(-)-mannitol and thiourea, were examined and clear positive results were obtained, suggesting that the radical scavengers are suitable as the positive control for the test. Using Mut-Test, suppressive abilities of four vitamins: L-ascorbic acid, beta-carotene, folic acid and riboflavin; 10 polyphenols: caffeic acid, ellagic acid, (-)-epicatechin, (-)-epicatechin gallate, (-)-epigallocatechin, gallic acid, pyrocatechol, pyrogallol, quercetin and tannic acid which are recognized as antimutagens, were examined. Furthermore, the concentrations for 50% of suppressive abilities of five positive samples, L-ascorbic acid, folic acid, caffeic acid, pyrocatechol and pyrogallol were compared. Negative results were obtained in nine samples, riboflavin, tannic acid, etc. suggesting that their antimutagenic effect on cells may not be related to oxidative damage in cells.

Antimutagenic Agents↗
PubMed2001

Two-dimensional manipulation of differentiated Madin-Darby canine kidney (MDCK) cell sheets: the noninvasive harvest from temperature-responsive culture dishes and transfer to other surfaces.

A renal epithelial cell line, Madin-Darby canine kidney (MDCK) cells, adheres, spreads, and proliferates to confluency on our developed temperature-responsive culture dishes grafted with a poly(N-isopropylacrylamide) (PIPAAm) at 37 degrees C. In addition to other cell types, including hepatocytes and endothelial cells, MDCK cell sheets noninvasively were harvested from PIPAAm-grafted dishes merely by reducing the temperature. However, during the early stage of culture (up to 3 weeks), confluent MDCK cell detachment is greatly repressed. In the present study, we succeeded in the rapid harvest of confluent MDCK cell sheets and intact transfer to other culture dishes by utilizing hydrophilically modified poly(vinylidene difluoride) (PVDF) membranes as supporting materials. Immunocytochemistry with anti-beta-catenin antibody revealed that the functional cell-cell junctions were well organized in the transferred MDCK cell sheets. The viability assay showed that the transferred cells were not damaged during the two-dimensional cell-sheet manipulation. By transmission electron microscopy it was confirmed that the harvested MDCK cells retained differentiated phenotypes and had many microvilli and tight junctions at the apical and lateral plasma membranes, respectively. This two-dimensional cell-sheet manipulation technique promises to be useful in tissue engineering as well as in the investigation of epithelial cell sheets.

Animals↗
PubMed2000

Two different types of nonthrombogenic surfaces: PEG suppresses platelet adhesion ATP-independently but HEMA-St block copolymer requires ATP consumption of platelets to prevent adhesion.

Poly(ethylene glycol) (PEG) and a hydrophobic-hydrophilic microdomain structured block copolymer comprising poly(2-hydroxyethyl methacrylate) and polystyrene (HEMA-St) have been reported to show good blood compatibility owing to inhibition of platelet activation. By using a computer-assisted novel technique to analyze platelet behavior on the surfaces, we found two different mechanisms to prevent platelet adhesion. Platelets were prevented from adhesion and spreading on the microdomain surface and retained cell movement for a long time. The platelet movement velocity was not significantly different between PEG-grafted surfaces and HEMA-St block copolymer-cast surfaces. However, platelet motion was qualitatively different. Platelets on HEMA-St block copolymer-cast surfaces moved with rolling, spinning, and vibrating, whereas platelet movement was limited to oscillatory vibration on PEG-grafted surfaces. When platelets were treated with NaN(3), an adenosine triphosphate (ATP) synthesis inhibitor, before contacting the surfaces, platelets movement velocity was decreased only on HEMA-St block copolymer-cast surfaces. Such an inhibitory effect was hardly observed with platelets on PEG-grafted surfaces. We propose two different mechanisms to prevent platelet adhesion onto surfaces. One is ATP-independent as observed with PEG, and the other is ATP-dependent for HEMA-St block copolymer, where platelets consume ATP to prevent adhesion.

Adenosine Triphosphate↗
PubMed2000

Rapid cell sheet detachment from poly(N-isopropylacrylamide)-grafted porous cell culture membranes.

Fabrication of functional tissue constructs using sandwiched layers of cultured cells could prove to be an attractive approach to tissue engineering. Rapid detachment of cultured cell sheets is a very important recovery method that permits facile manipulation of the sheet and prevents functional damage. To accelerate the required culture substrate hydrophilic and hydrophobic structural changes in response to culture temperature alteration, poly(N-isopropylacrylamide) (PIPAAm) was grafted onto porous culture membranes by electron beam irradiation. Analyses by attenuated total reflection-Fourier transform IR and electron spectroscopy for chemical analysis revealed that PIPAAm was successfully grafted to surfaces of porous membranes. Atomic force microscopy (AFM) results showed that PIPAAm-grafted membranes had smoother surfaces than ungrafted controls while retaining their porous structure. The mean roughness of PIPAAm-grafted and -ungrafted porous membrane surfaces determined by digital AFM autocalculation was 4.40 +/- 0.4 and 5.9 +/- 0.4 nm, respectively. Tissue culture polystyrene (TCPS) dishes grafted with PIPAAm were compared with PIPAAm-grafted porous membranes in cell sheet detachment experiments. Approximately 75 min was required to completely detach cell sheets from PIPAAm-grafted TCPS surfaces compared to only 30 min to detach cell sheets from PIPAAm-grafted porous membranes. With porous membranes, the water accesses the PIPAAm-grafted surface from underneath and peripheral to the attached cell sheet, resulting in rapid hydration of grafted PIPAAm molecules and detachment of the cell sheet. With TCPS PIPAAm-grafted surfaces the water is supplied from only the periphery of a cell sheet, slowing detachment.

Acrylic Resins↗
PubMed2000

Temperature-responsive culture dishes allow nonenzymatic harvest of differentiated Madin-Darby canine kidney (MDCK) cell sheets.

We have developed a temperature-responsive culture dish grafted with a poly(N-isopropylacrylamide) (PIPAAm). Various types of cells adhere, spread, and proliferate on the grafted dishes in the presence of serum at 37 degrees C. By reducing only temperature, these cells can be harvested noninvasively from the dishes according to rapid hydration of the grafted polymer. Because the harvest does not need enzymatic digestion, differentiated cell phenotypes are retained. In the present study, a renal epithelial cell line, Madin-Darby canine kidney (MDCK) cell, was cultured on the dishes, and cell behavior was examined. MDCK cells showed differentiated phenotypes such as dome formation during long-term culture, similar to on ungrafted dishes. After 1-week culture at 37 degrees C, trypsin digestion disrupted cell-cell junctions but failed to liberate cells from both ungrafted and grafted dishes. However, short-term incubation at 20 degrees C released confluent MDCK cells as a single contiguous cell sheet only from the polymer-grafted dishes because of selective disruption of the cell-surface binding. Immunocytochemistry with anti-beta-catenin antibody revealed that functional cell-cell junctions were organized even in the recovered cell sheets. Intriguingly, incubation time at 20 degrees C required for cell sheet detachment gradually shortened during long-term culture before reducing temperature. The acceleration of cell detachment was correlated to the decrease of a single cell area by means of cell contractile force. These findings suggest that cell sheet detachment from PIPAAm-grafted dishes should be accomplished by both PIPAAm hydration and cellular metabolic activity such as cell contraction.

Acrylic Resins↗
PubMed2000

Identification of high-risk breast cancer patients from genetic changes of their tumors.

To identify the genetic prognostic markers for breast cancer, we analyzed loss of heterozygosity (LOH) at 11p, 16q, 17p, 17q, and 18q, as well as amplification of the ERBB2, INT2, and MYC genes, in 131 patients with breast carcinoma, 49 of whom had lymph node involvement, but none of whom had distant metastases. Among the several chromosome arms tested, LOH at 17q was correlated with lymph node metastasis. Amplification of the ERBB2, MYC, and INT2 genes was found more frequently in tumors from patients with lymph node metastases than in tumors from those without lymph node metastases. Univariate analysis demonstrated that LOH at 17q and INT2 amplification were factors influencing disease-free survival (DFS). A multivariate analysis was performed on 89 tumors that were able to be evaluated for both LOH at 17q and INT2 amplification, and the results showed that patients who had tumors with these genetic changes were more likely to have a poor prognosis. The findings of this study suggest that investigating genetic changes, in addition to conventional clinicopathologic factors, may contribute to defining groups of breast cancer patients with differences in prognosis.

Blotting, Southern↗
PubMed2000

Release of adsorbed fibronectin from temperature-responsive culture surfaces requires cellular activity.

We have previously developed a temperature-responsive cell culture surface by grafting poly(N-isopropylacrylamide) that changes its surface hydrophobicity in response to temperature. While this surface shows similar hydrophobicity to that of commercial polystyrene cell culture surfaces and facilitates cell adhesion and proliferation at 37 degrees C, grafted polymer becomes hydrophilic below 32 degrees C and releases spread cultured cells without trypsin. Temperature-regulated cell detachment requires cell metabolic activity requiring ATP consumption, signal transduction, and cytoskeleton reorganziation. Precoating these surfaces with fibronectin (FN) improves spreading of less adhesive cultured hepatocytes and reducing culture temperature releases cultured cells from FN-adsorbed grafted surfaces. Immunostaining with anti-FN antibody revealed that only FN located beneath cultured cells is removed from culture surfaces after reducing temperature. FN adsorbed to surface areas lacking direct cell attachment remained surface-bound after reducing temperature. A novel concept of active cell detachment is also discussed.

Acrylic Resins↗
PubMed2000

Temperature-dependent modulation of blood platelet movement and morphology on poly(N-isopropylacrylamide)-grafted surfaces.

Poly(N-isopropylacrylamide) (PIPAAm) exhibits a reversible, temperature-dependent soluble/insoluble transition at its lower critical solution temperature (LCST) of 32 degrees C in aqueous media. The temperature-responsive PIPAAm was grafted onto tissue culture polystyrene (TCPS) dish surfaces by electron beam irradiation. Blood platelet behaviors on PIPAAm-grafted surface were examined by computerized image analysis and scanning electron microscopy. Platelet behaviors on this surface were dramatically dependent upon temperature, but those on poly(ethylene glycol)(PEG)-grafted or polystyrene remained unchanged. Below the 32 degrees C (LCST), platelets on PIPAAm-grafted surfaces retained a rounded shape and an oscillating vibratory microbrownian motion for extended times, similarly to those on PEG-grafted surfaces. Above the LCST, platelets readily adhered, spread and developed characteristic pseudopodia on PIPAAm-grafted surface similarly to those on TCPS. An ATP synthesis inhibitor failed to hinder prevention of platelet adhesion onto PIPAAm-grafted surface (below the LCST) suggesting that the preventive mechanism is ATP-independent similarly to that of PEG-grafted surfaces. These results correlate platelet surface activation state with the hydration and structure of polymer surfaces, and demonstrate the ability to modulate such reactions by a small temperature change in situ.

Acrylamides↗
PubMed2000

Both insulin sensitivity and glucose sensitivity are impaired in patients with non-diabetic liver cirrhosis.

Background: Careful nutritional support is required in patients with liver cirrhosis due to their glucose intolerance. To elucidate the mechanism of glucose intolerance in cirrhotics, we measured insulin secretion, whole body insulin sensitivity (SI), and glucose sensitivity (SG) in non-diabetic cirrhotics.Methods: Eight patients with compensated cirrhosis who showed normal fasting blood glucose levels and non-diabetic curves on a 75 g oral glucose tolerance test participated in this study. Four normal volunteers were selected as controls. After an overnight fast, glucose was injected intravenously at 300 mg kg(-1) in 2 min followed 20 min later by intravenous insulin at 0.02 U kg(-1) in 5 min. Sequential blood samples were drawn from 20 min before the glucose injection to 3 h post-injection, and plasma glucose and insulin levels were determined. Plasma glucose and insulin disappearance curves were analyzed using the minimal compartment model, and kinetic parameters, including glucose clearance (KG), insulin secretion, SI and SG, were estimated.Results: KG was slower in cirrhosis than in controls, although not significant (P=0.051). Insulin secretion was not different between the two groups. However, SI was significantly lower in cirrhotics (0.814x10(-4) min(-1) pM(-1); 0.572-1.403x10(-4) min(-1) pM(-1)) as compared to controls (1.643x10(-4) min(-1) pM(-1); 0.678-2.085x10(-4) min(-1) pM(-1)) (P=0.029). SG was also lower in the cirrhosis (0.0154 min(-1); 0.0071-0.0208 min(-1)) than in the control group (0.0211 min(-1); 0.0184-0.0260 min(-1)) (P=0.026).Conclusion: Both SI and SG are already impaired in non-diabetic cirrhotic patients even when KG is minimally delayed and insulin secretion has not yet been affected.

Journal Article↗
PubMed2000

Temperature-Responsive surface for novel co-culture systems of hepatocytes with endothelial cells: 2-D patterned and double layered co-cultures.

We have developed two novel cell co-culture system, without any on cell type combination limitation, utilizing a polymer surface which is temperature-sensitive with respect to its cell adhesion characteristics. One system involves a patterned co-culture of primary hepatocytes with endothelial cells utilizing patterned masked of the electron-beam cured, temperature-responsive polymer, poly (N-isopropylacrylamide) (PIPAAm) by masked electron beam irradiation. Hepatocytes were cultured to confluency at 37 degrees C on these surfaces. When the culture temperature was reduced below 32 degrees C, cells detached from the PIPAAm-grafted areas without any need for trypsin. Endothelial cells were then seeded onto the same surfaces at 37 degrees C. These subsequently seeded endothelial cells adhered only to the now-exposed PIPAAm-grafted domains and could be co-cultured with the hepatocytes initially seeded at 37 degrees C in well-ordered patterns. The other system involves a double layered co-culture obtained by overlaying endothelial cell sheets of the designed shape onto hepatocyte monolayers. The endothelial cells adhered and proliferated on the PIPAAm-grafted surface, as on polystyrene tissue culture dishes at 37 degrees C. By reducing the temperature, confluent monolayers of cells detached from the PIPAAm surfaces without trypsin. Because the recovered cells maintained intact cell-cell junctions together with deposited extracellular matrix, the harvested endothelial cell sheets, with designed shapes, were transferable and readily adhered to hepatocyte monolayers. Stable double layered cell sheets could be co-cultivated. These two co-culture methods enabled long-term co-culture of primary hepatocytes with endothelial cells. Hepatocytes so co-cultured with endothelial cells maintained their differentiated functions, such as albumin synthesis for unexpectedly long periods. These novel two co-culture systems offer promising techniques for basic biologic researches upon intercellular communications, and for the clinical applications of tissue engineered constructs.

Acrylic Resins↗
PubMed1999

Thermo-responsive drug delivery from polymeric micelles constructed using block copolymers of poly(N-isopropylacrylamide) and poly(butylmethacrylate).

To achieve a combination of spatial specificity in a passive manner with a stimuli-responsive targeting mechanism, a temperature-responsive polymeric micelle is prepared using block copolymers of (poly(N-isopropylacrylamide-b-butylmethacrylate) (PIPAAm-PBMA)). The micelle inner core formed by self-aggregates of PBMA segments successfully loaded with a drug (adriamycin), and the outer shell of PIPAAm chains played a role of stabilization and initiation of micellar thermo-response. Optimum conditions were investigated for the micelle formation and drug loading into the inner cores in a view of micellar stability and function as drug carriers. Outer shell hydrophilicity that prevents inner core interaction with biocomponents and other micelles can be suddenly switched to hydrophobic at a specific site by local temperature increase beyond the LCST (lower critical solution temperature) (32.5 degrees C). These micelles showed reversible structural changes allowing drug release upon heating/cooling thermal fluctuations through the LCST. Polymeric micelles incorporated with adriamycin showed a dramatic thermo-responsive on/off switching behavior for both drug release and in vitro cytotoxicity according to the temperature responsive structural changes of a micellar shell structure. The reversible and sensitive thermo-response of the micelle opens up opportunities to construct a novel drug delivery system in conjunction with localized hyperthermia.

Acrylic Resins↗
PubMed1999

Decrease in culture temperature releases monolayer endothelial cell sheets together with deposited fibronectin matrix from temperature-responsive culture surfaces.

Bovine aortic endothelial cells were cultured on surfaces grafted with a temperature-responsive polymer, poly(N-isopropylacrylamide) (PIPAAm), in the presence of serum. Cells adhered, spread, proliferated, and reached confluency as observed on ungrafted tissue culture polystyrene dishes. A decrease in culture temperature released cells only from the grafted surfaces without enzymatic or ethylenediaminetetraacetic acid treatment. Upon lowering temperature, the culture surfaces changed from hydrophobic to hydrophilic owing to the hydration of grafted PIPAAm and thus weakened the cell attachment to the dishes. Released cells maintained cell-cell junctions composing monolayer cell sheets. Immunoblotting and immunofluorescence microscopy revealed that fibronectin (FN) was deposited and accumulated on the grafted surfaces during the culture. Furthermore, the deposited FN matrix adhering to cell sheets was also recovered from temperature-responsive surfaces by low-temperature treatment, while trypsin treatment destroyed the matrix. The recovery of FN by low-temperature treatment was as high as by physical scraping with a rubber blade. Temperature-responsive surfaces can provide a novel method to use cultured confluent cell sheets for tissue engineering, and also to elucidate structure and function of deposited extracellular matrix during cell culture.

Acrylamides↗
PubMed1999

Lethal level overexpression of gamma-tubulin in fission yeast causes mitotic arrest.

gamma-Tubulin is a member of the tubulin superfamily and plays essential roles in microtubule nucleation. While the level of other tubulins, alpha- and beta-tubulin, is strictly regulated in higher eukaryotes and overexpression of beta-tubulin is toxic in yeasts, gamma-tubulin can be overexpressed by fivefold in fission yeast without any obvious defect in growth. Extreme overexpression of gamma-tubulin in mammalian cells caused growth arrest; however, the exact level of gamma-tubulin and the critical level of gamma-tubulin necessary for growth defect were undetermined. We have constructed strains that over- or underexpress gamma-tubulin by placing the gamma-tubulin gene under the control of the inducible nmt1 promoter and its variants. Among these, the weakest promoter was able to produce enough gamma-tubulin to support normal growth when its expression was induced. A strain in which the gamma-tubulin gene was placed under the control of the strongest inducible promoter achieved 160-fold overexpression of gamma-tubulin and its growth was suppressed. Normal cytoplasmic microtubules were mostly lost in gamma-tubulin overexpressing cells and gamma-tubulin was accumulated around the periphery of nuclei. Many of the cells were arrested in mitosis. A small fraction of cells did proceed to undergo nuclear division; however, its process looked either significantly deterred or abnormal. Our results presented here suggest that excess gamma-tubulin disrupts the microtubule array and significantly deters the formation of the mitotic spindle, most likely because of random nucleation of microtubules from excess gamma-tubulin in the cytoplasm.

Blotting, Western↗
PubMed1999

Acknowledgment

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Journal Article↗
PubMed1999

Signal transduction and cytoskeletal reorganization are required for cell detachment from cell culture surfaces grafted with a temperature-responsive polymer.

We have developed a new cell culture substrate grafted with a temperature-responsive polymer, poly(N-isopropylacrylamide) (PIPAAm) using an electron beam irradiation method. These surfaces are hydrophobic in culture at 37 degrees C due to the hydration/dehydration changes intrinsic to PIPAAm at 32 degrees C, and they become highly hydrophilic below 32 degrees C. At 37 degrees C grafted and ungrafted surfaces showed no difference with regard to attachment, spreading, growth, confluent cell density, and morphology of bovine aortic endothelial cells. Stress fibers, peripheral bands, and focal contacts were established in similar ways. After the medium temperature was decreased to 20 degrees C, spread cells lost their flattened morphology, acquiring a rounded cell appearance similar to that of cells immediately after plating. After mild agitation cells floated free from the dish surface without trypsin treatment. Neither cell morphological changes nor cell detachment occurred on ungrafted surfaces. An ATP synthesis inhibitor, sodium azide, and a tyrosine kinase inhibitor, genistein, suppressed cell morphological changes and cell detachment while a protein synthesis inhibitor, cycloheximide, slightly enhanced cell detachment. An actin filament stabilizer, phalloidin, and its depolymerizer, cytochalasin D, also inhibited cell detachment. These findings suggest that cell detachment on grafted surfaces is mediated by intracellular signal transduction and reorganization of the cytoskeleton. While trypsinization causes damage to the cell membrane surface and extracellular matrix proteins, this alternative low temperature treatment is exceptionally noninvasive. The temperature-responsive cell culture surface also should prove useful for investigating the molecular machinery involved in cell-surface detachment.

Acrylic Resins↗