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Biomedical subjects

N Sawada

Publications and source records attributed to N Sawada.

At least 145 records · Page 8Linked to original sources
PubMed1989

[A study on adhesive strength of cyanoacrylate dental adhesive, 'F.H. Cement'--thermal-cycled effects].

This study investigated the adhesive strength of cyanoacrylate dental adhesive, 'F.H cement' after being thermal-cycled in order to certify its stability in water. The adhesive strength was compared using Zinc phosphate cement, Glass ionomer cement, Dental adhesive resin and F.H cement when an ivory die and a cast crown were adhered by these different cements. Results of the study indicated the following: 1. The adhesive strength after being thermal-cycled indicated that F.H cement had a greater strength than the other cements (Zinc phosphate cement and Glass ionomer cement) and was equal to that of the Dental adhesive resin. 2. F.H cement was also found to be the strongest in adhesive strength when different tapers were used.

Cyanoacrylates↗
PubMed1989

[Study on castable glass ceramics (Bioram-C)--surface treatment for enhanced bonding strength].

This study evaluated the tensile bonding strength of castable glass ceramics (Bioram-C) to three dental adhesive resin cements: Super-Bond C&B, Chemiace and Panavia EX. Treatments of the castable glass ceramic surfaces for enhanced bonding to the adhesive were examined. The surface treatments of the ceramics were sand blasting by 40 microns phi aluminum oxide and a silane coupling agent (KBM 503). Castable glass ceramics were cast and after surface treatment, bonded end-to-end and tested for tensile strength 24 hours later. Failures in the bonding were studied by a scanning electron microscope and wave dispersive X-ray Micro-analyzer. The findings were as follows: 1. Sand blasting by 40 microns phi aluminum oxide with Super-Bond C&B gave the highest mean bonding strength. 2. A significant difference (p less than 0.01) was observed between the surface treatment with the silane coupling agent and 40 microns phi aluminum oxide. The silane coupling agent employed in this study had a significant by higher average bonding strength. In examining the specimens, cohesive failure was observed in 70% of Super-Bond C&B and 50% of both Chemiace and Panavia EX bondings. 3. There were no significant difference between the three adhesives with the silane coupling agent.

Adhesives↗
PubMed1988

Reduction of potential for replicative but not unscheduled DNA synthesis in hepatocytes isolated from aged as compared to young rats.

Replicative DNA synthesis of hepatocytes obtained from 2- to 3-month-old and 28- to 30-month-old rats was examined in primary culture under serum-free conditions to clarify whether observed age-related changes in DNA replication depend exclusively on intracellular events, or whether humoral factors are involved. Hepatocyte replicative DNA synthesis of the aged rats was significantly lower (less than one tenth, P less than 0.001) than that of 2- to 3-month-old rats. EGF receptor assays, however, revealed no difference in either number or affinity of the cell surface receptors between hepatocytes from aged as opposed to young rats. Furthermore, sera obtained from aged rats did not demonstrate any inhibitory effect on DNA synthesis of young rat hepatocytes. After treatment with N-hydroxy acetylaminofluorene, N-nitroso-N-methylurea, or 254-nm UV irradiation degree of resultant UDS was similar in hepatocytes from both young and aged animals. Thus, while the results suggest that potential for DNA replication markedly diminishes with age, DNA repair systems are well preserved.

Age Factors↗
PubMed1988

Morphometric and cytochemical evaluation of clofibrate-induced peroxisomal proliferation in adult rat hepatocytes cultured on floating collagen gels.

The present ultrastructural morphometric and cytochemical studies demonstrate clofibrate induced changes in peroxisomes in adult rat hepatocytes maintained for 14 days in primary culture on floating collagen gels. Catalase activity and the number and diameter of peroxisomes were reduced in hepatocytes cultured for between 2/3 and 7 days. However, hepatocytes cultured for 7-14 days had well-developed peroxisomes containing crystalloid nucleoids. The number of anucleoid peroxisomes in hepatocytes treated with 2 mM Na clofibrate increased with culture age, and by day 14 the number was 2.9 times greater than in freshly isolated hepatocytes. Catalase activity, as well as the number of nucleoid-containing peroxisomes were much greater in treated hepatocytes than in untreated controls, but decreased slightly with culture age. The diameter of peroxisomes was not reduced in the treated cells. These results suggest that the treatment with Na clofibrate is effective both for proliferation and maintenance of peroxisomes and for enhancing catalase activity. In treated hepatocytes, matrical plates were formed in peroxisomes from days 5 to 14 and the number of plate-containing peroxisomes increased with culture age.

Animals↗
PubMed1988

Active proliferation of mouse hepatocytes in primary culture under defined conditions as compared to rat hepatocytes.

Mouse and rat hepatocytes were investigated for replicative potential in primary culture under defined conditions. Mouse hepatocytes replicated at least twice or three times by the 7th day of culture in response to EGF, while only a half of rat hepatocytes replicated once. Thus a far greater potential for proliferation was demonstrated by mouse than rat cells, although the mouse cells ceased dividing by the 10th day of culture. Immunocytochemical examination revealed that the cells produced both albumin and alpha-fetoprotein. Ultrastructural investigation revealed that these cells were immature hepatocytes in nature, based on the presence of microbodies with nucleoids. Thus, primary cultures of mouse hepatocytes seem to be a useful system for studying proliferation and transformation of hepatocytes in vitro.

Animals↗
PubMed1987

Effects of tumor-promoting agents 12-O-tetradecanoylphorbol-13-acetate and phenobarbital on DNA synthesis of rat hepatocytes in primary culture.

Both 12-O-tetradecanoylphorbol-13-acetate (TPA) and phenobarbital (PB) enhanced hepatocyte DNA synthesis stimulated with epidermal growth factor (EGF) by 60 to 80% in primary culture when measured by the incorporation of [3H]thymidine. This apparent increase was not due to changes in the specific activity of the deoxythymidine triphosphate (dTTP) pool. TPA enhanced DNA synthesis even at relatively high cell densities, but this was not found with the PB treatment. Although both TPA and PB enhanced DNA synthesis significantly, TPA was most effective when added during the late G1 and/or S phase of the hepatocyte cell cycle, whereas PB treatment was least effective in this period. The binding of EGF was transiently down-regulated by TPA, then restored to control values 6 h later, whereas the binding of this factor was significantly increased at both the 12th and 24th h after PB addition. These results suggest that EGF binding to hepatocytes is not correlated with the enhancement of DNA synthesis by TPA or PB and that the down-regulation of EGF binding is not causally related to the enhancement of DNA synthesis by TPA.

Animals↗
PubMed1987

Stimulation of DNA synthesis in primary cultures of adult rat hepatocytes by sodium butyrate.

Replicative DNA synthesis in primary cultures of adult rat hepatocytes is increased by the addition of the histone deacetylase inhibitors, propionate or butyrate. DNA synthesis was increased by the addition of 0.5 or 1.0 mM butyrate; in contrast 5.0 mM butyrate inhibited replicative DNA synthesis. Replicative DNA synthesis was increased only when low levels of butyrate were added as the hepatocytes entered the S phase. The observed apparent increase in replicative DNA synthesis was real, and not owing to changes in the specific activity of the dTTP precursor pool. The effects of butyrate and propionate on DNA synthesis appear to be related to their effects on histone acetylation.

Acetylation↗
PubMed1987

The control of DNA synthesis in primary cultures of hepatocytes from adult and young rats: interactions of extracellular matrix components, epidermal growth factor, and the cell cycle.

Hepatocytes from adult and 4-week-old rats cultured on one of several extracellular matrix components were stimulated to replicate by epidermal growth factor (EGF). DNA synthesis was increased at 44-48 hr in adult hepatocytes and at 24, 48, and 72 hr in hepatocytes from young rats when EGF was added 2 hr after explantation. When EGF was added at 24 hr, maximal DNA synthesis of adult hepatocytes was observed at 48 hr, whereas that of 4-week-old hepatocytes was seen at 48 and 72 hr. Ten ng EGF per ml was the optimal concentration for maximal DNA synthesis in both adult and young cells. DNA synthesis decreased with increasing cell density, but this effect was less in hepatocytes from young than in those from adults. When hepatocytes were cultured on substrata consisting of individual extracellular matrix components, neither the time that adult cells needed to respond to EGF nor the time from stimulation by EGF to the peak of maximal DNA synthesis was altered in either adult or young cells. The optimal EGF concentration for maximal DNA synthesis and the cell density control of replication were also not altered by the substrata used. Substrata made from each of the extracellular matrix components studied enhanced DNA synthesis of adult and young hepatocytes stimulated by EGF in the following decreasing order: fibronectin, type IV collagen, type I collagen, and laminin. In both adult and young hepatocytes the enhancement of DNA synthesis was greatest when cultured on fibronectin. Thus the initiation and magnitude of DNA synthesis in primary cultures of rat hepatocytes were altered both by the age of the donor and the substratum on which the cells were explanted.

Aging↗
PubMed1987

Effects of extracellular matrix components on the growth and differentiation of cultured rat hepatocytes.

Some effects of culturing adult rat hepatocytes on each of four different substrates--laminin (LN), collagen type I (C-I), collagen type IV (C-IV), and fibronectin (FN)--have been investigated under defined conditions. No differential effect on the attachment of the cells to the various substrates was noted; however, the spreading of hepatocytes shortly after initial plating was most strikingly enhanced by FN, whereas LN exhibited little or no such enhancement. The two collagen substrates enhanced the spreading of hepatocytes more than did LN, but less than FN. The different substrates had no differential effect on the induction of tyrosine aminotransferase by dexamethasone and glucagon for at least the first 10 d in culture. The longevity of the hepatocytes was not changed significantly by any of the substrates, at least through the 14th d of culture. During the culture periods the hepatocytes at high cell density were maintained as confluent monolayers, regardless of the substrate on which they had been cultured. After 14 d of culture, gamma-glutamyltranspeptidase activity was highest in cells cultured on C-IV, and lowest in those on FN. DNA synthesis in cultured hepatocytes at a low cell density was highest in cells cultured on FN, with decreasing levels of this parameter in cells cultured on C-IV, C-I, and LN, respectively. These results demonstrate that specific components of the extracellular matrix modulate both differentiated functions and the replication of hepatocytes cultured in serum-free medium.

Animals↗
PubMed1986

Use of a low-speed, iso-density percoll centrifugation method to increase the viability of isolated rat hepatocyte preparations.

A simple yet effective method (iso-density percoll centrifugation) has been developed for consistently preparing isolated rat liver parenchymal cells with over 98% initial viability. The method has been applied to cells isolated by a variety of collagenase digestion techniques. This procedure involves the low-speed centrifugation (50 X g) of the initial cell suspension through a percoll medium having a density of 1.06 g/ml and results in the separation of single and viable parenchymal cells from cell aggregates, debris, and nonparenchymal cells. The enriched parenchymal cells have been shown to be superior to untreated cells by a number of criteria including: preparation homogeneity, cell morphology, maintenance of cytochrome P-450, hormonal responsiveness (measured by the induction of tyrosine aminotransferase after treatment with glucagon or dexamethasone, or both), plasma membrane integrity (determined by both trypan blue exclusion and leakage of glutamic-oxaloacetic transaminase), and the DNA repair capability after treatment with benzo[a]pyrene or 2-acetylaminofluorene.

2-Acetylaminofluorene↗
PubMed1986

Extracellular matrix components influence DNA synthesis of rat hepatocytes in primary culture.

The effects of several extracellular matrix components (EMCs)--fibronectin (Fn), laminin (Ln), type I (C-I) and type IV (C-IV) collagen--on DNA synthesis in rat hepatocytes in primary culture were examined by both quantitative scintillation spectrometry and autoradiography of [3H]thymidine incorporation. Hepatocytes cultured on Fn showed the most active DNA synthesis initiated by epidermal growth factor (EGF) with decreasing levels of [3H]thymidine uptake exhibited in the cells cultured on C-IV, C-I, and Ln, respectively. The decreasing level of DNA synthesis in hepatocytes cultured on Fn, C-IV, C-I, and Ln respectively was not influenced by cell density. The number of EGF receptors of hepatocytes was also not influenced by EMCs. These data suggest that EMCs modify hepatocyte DNA synthesis by means of post-EGF-receptor mechanisms which are regulated by both growth factors and cell density.

Animals↗
PubMed1986

Effects of liver-tumor promoters on phalloidin sensitivity of rat hepatocytes.

Hepatocytes were isolated by a collagenase perfusion method from male F-344 rats fed a diet containing 0.05% phenobarbital (PB), 0.05% dichlorophenyltrichloroethane (DDT), 0.25% ethyl-alpha-p-chlorophenoxyisobutyrate (CPIB), 0.02% methapyrilene hydrochloride (MP), 0.05% amobarbital (AB) or 0.05% diphenylhydantoin (DPH) for 8 weeks. An increase in the incidence of gamma-glutamyltransferase (GGT)-positive hepatocytes was found in rats fed PB or DDT, while CPIB strikingly decreased the incidence. There was no change in the incidence in rats fed MP, AB or DPH. Sensitivity to phalloidin, in terms of formation of multiple cytoplasmic blebs, of the 1-h cultured hepatocytes of rats fed PB, DDT or MP was decreased in both GGT-negative and GGT-positive hepatocytes. The sensitivity of GGT-negative hepatocytes of rats fed CPIB was also decreased. Experiments on phalloidin consumption showed decreases in the hepatocyte toxin uptake of rats fed PB, DDT, CPIB or MP. AB and DPH had no effects on the sensitivity of both GGT-negative and GGT-positive hepatocytes.

Animals↗
PubMed1986

Expression of H-ras and c-myc protooncogenes in isolated gamma-glutamyl transpeptidase-positive rat hepatocytes and in hepatocellular carcinomas induced by diethylnitrosamine.

The appearance of gamma-glutamyl transpeptidase (GGT) in focal areas of hepatocytes is a widely used histochemical marker for the identification of preneoplastic cell populations. The characterization of these GGT-positive preneoplastic cells in relation to possible alterations in protooncogene expression may help define cellular changes occurring during the early stages of hepatocarcinogenesis. Female Sprague-Dawley rats were subjected to a two-thirds partial hepatectomy, followed 18 h later by a single intragastric administration of 30 mg of diethylnitrosamine per kg and subsequent feeding of a diet containing 0.05% phenobarbital for 6 or 11 mo. Primary cell suspensions were obtained after the perfusion of liver with collagenase. Cell debris and nonviable cells were removed with multiple washes and a Percoll gradient step. GGT-positive hepatocytes were enriched from the cell suspension by adherence to an affinity-purified GGT antibody affixed to Petri dishes. These dishes allowed the selective adherence and collection of up to 2.28 X 10(6) GGT-positive cells per liver. The starting cell population and the isolated GGT-positive and -negative cells were then used for subsequent analysis. RNA was prepared from the cell isolates and from hepatocellular carcinomas induced with the same diethylnitrosamine and phenobarbital regimen as that used to induce GGT-positive foci; 10 micrograms of total cellular RNA were used for Northern blot hybridizations. The blots were probed with 32P-labeled c-myc, H-ras, and albumin DNAs. The results indicate that GGT-positive hepatocytes do not differ from the other hepatocyte populations in either the size or amount of mRNA transcripts for the c-myc and H-ras protooncogenes. Increased expression of c-myc and H-ras was observed in some malignant lesions and may represent a secondary alteration occurring during the multistage process of hepatocarcinogenesis.

Albumins↗
PubMed1986

[Reorganization of human ovarian adenocarcinoma cells and endometrial adenocarcinoma cells cultured in double-layered floating collagen gels].

Collagen gels have been used as the substratum for epithelial cell culture to maintain their differentiated states. In this report, we proposed a double-layered floating collagen gel method for the culture of human carcinoma cells to show their differentiated structures which closely resembled those in the tumors in vivo. On the 3rd week of the culture, OMC-1 cells (human ovarian mucinous adenocarcinoma) showed organized ductular structures. PAS-positive substances were seen along the surface of the ductules and also in cytoplasms. Electron microscopically, numerous microvilli were observed at the apical surfaces of the cells, with formation of rootlets. Ishikawa line cells (human well-differentiated endometrial adenocarcinoma) formed tubular structures with back-to-back arrangements. Electron microscopically, numerous microvilli, well-developed junctional complexes, and well-developed mitochondria and Golgi apparatus were observed, similarly to those in the cells grown in vivo. SNG-M cells (human moderately-differentiated endometrial adenocarcinoma) were arranged in sheets with occasional formation of tubular structures. Mitochondria, Golgi apparatus and desmosomes were poorly developed in general; however, the cells forming tubular structures showed signs of cellular differentiation. The floating and non-floating methods were compared with the result that the former method was seen to be far superior to the latter for expressing cellular differentiation.

Adenocarcinoma↗