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Biomedical subjects

K Nagata

Publications and source records attributed to K Nagata.

At least 613 records · Page 34Linked to original sources
PubMed1992

Experimental simvastatin-induced myopathy in rabbits.

We induced experimental myopathy in rabbits by giving simvastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor. After oral administration of simvastatin (50 mg/kg/day) for 2 weeks, serum CK was elevated in 5 of 7 rabbits; degenerating or necrotic fibers were seen in 3 rabbits. Using electromyography, myotonic discharges were found in the 2 rabbits examined. The combination of myotonic discharges, necrosis and raised serum CK levels suggests that the myopathy was induced by lesions of the muscle surface membrane.

Administration, Oral↗
PubMed1992

Presence and some characterization of GDP dissociation inhibitors for a low Mr GTP-binding protein, ram p25, in rat spleen cytosol.

Two proteinous factors, designated here as ram p25 GDP dissociation inhibitor (I) and (II) (ram-GDI (I) and (II)), were detected in the cytosolic fraction of rat spleen, which inhibited the initial dissociation of GDP from ram p25 produced by E. coli by causing characteristic lag. They had very weak effects on the rate of dissociation of GDP after the lag, and did not affect the mode of the dissociation of 5'-(3-O-thio)triphosphate (GTP gamma S) from ram p25. By gel filtration, the molecular masses of ram-GDI (I) and (II) were calculated to be 90 KDa and 40 KDa, respectively. These ram-GDIs did not affect the GDP-dissociation of Ha-ras protein produced in E. coli.

Animals↗
PubMed1992

Effect of mild diabetes and dietary fructose on very-low-density lipoprotein triglyceride turnover in rats.

Very-low-density lipoprotein (VLDL) triglyceride turnover was examined in mildly streptozotocin (25 mg/kg)-diabetic rats, using Triton WR1339. Diabetic rats fed standard rat chow showed mild hyperglycemia and suppressed levels of plasma insulin. Their triglyceride secretion was significantly suppressed despite an elevated level of plasma free fatty acids. However, the plasma triglyceride level of these diabetic rats was significantly elevated compared with nondiabetic controls. This suggested that the removal of triglyceride from the circulation, as well as its entry into the circulation, was impaired in mildly insulin-deficient rats. Glucose or fructose supplementation (10% in drinking water for 14 days) significantly increased the triglyceride secretion rate of diabetic rats. Especially, fructose supplementation increased plasma insulin to normal levels, but resulted in markedly elevated plasma triglyceride levels (three times higher than glucose-supplemented or chow-fed diabetic rats) despite similar triglyceride secretion rates between the two types of sugar-supplemented diabetic rat groups. This suggested an impairment of triglyceride removal by dietary fructose. The result obtained from chow-fed diabetic rats indicates that mild but significant insulin deficiency resulted in mild hypertriglyceridemia, linked to impaired triglyceride removal rather than to an overproduction of VLDL-triglyceride, despite elevated levels of plasma free fatty acids. Furthermore, fructose feeding induced prominent hypertriglyceridemia not only by stimulating triglyceride secretion, but also by suppressing triglyceride removal from the circulation of mildly diabetic rats.

Animals↗
PubMed1992

Enzymatic properties of the mouse Mx1 protein-associated GTPase.

Murine Mx1 protein, an interferon-inducible nuclear protein present in inbred mouse Mx+ strains, confers resistance to influenza virus infection. The purified Mx1 protein was found to carry the activities of both GTPase and GTP-binding. Enzymatic properties of the Mx1-associated GTPase were examined using the Mx1 protein purified from Escherichia coli expressing Mx1 cDNA. The Mx1 protein exhibited a substrate preference for GTP. The Vmax of ATP hydrolysis was about 7.6% the rate of GTP hydrolysis. The hydrolysis of CTP and UTP was virtually negligible. The Km for GTP hydrolysis was 667 microM and the rate was 13.8 mol GTP hydrolysis per min per mol Mx1 protein. The enzymatic properties of Mx1 protein-associated GTPase were compared with those of the GTPase super-gene family and the Mx-related family.

Adenosine Triphosphate↗
PubMed1992

Reconstitution of influenza virus RNA polymerase from three subunits expressed using recombinant baculovirus system.

Influenza virus RNA polymerase catalyzes multiple step reactions in transcription and replication of the genome RNA. The core enzyme is composed of each one of the three P proteins, PB1, PB2 and PA (Honda et al. (1990) J. Biochem. 107, 624-628). For detailed analysis of the role of each P protein and of the functional domains on each P polypeptide, we expressed individual P proteins in cultured insect cells after infection with recombinant baculoviruses. PB1 and PB2 accumulated in cell nuclei whereas PA stayed in cytoplasm. Both the PB1 and PB2 proteins were purified from aggregates in the respective nuclear extract, and the PA was partially purified from the cytoplasm. RNA polymerase was reconstituted by mixing the three P proteins in a urea solution and then dialyzing against a reconstitution buffer. The reconstituted enzyme was able to transcribe model RNA templates. Minus-sense RNA was a better template than plus-sense RNA.

Animals↗
PubMed1992

Evidence of the presence of GTPase inhibiting proteins for a low M(r) GTP-binding protein, ram p25, in rat spleen and pheochromocytoma PC12 cells.

1. GTPase inhibiting activity for a low M(r) GTP-binding protein, ram p25, was detected in the cytosolic fractions of rat spleen and PC12 cells. 2. The inhibitors were heat-labile and trypsin-sensitive, indicating that they were of proteinous nature. 3. The molecular mass of the inhibitor in the spleen appeared to be about 65 kDa on the elution profile from the gel filtration column.

Adenosine Triphosphate↗
PubMed1992

Demonstration of type III collagen in the dentin of mice.

It has been reported that, although type III collagen is present in human dentin where there is dentinogenesis imperfecta and in reparative dentin, it is absent in normal dentin. In a preliminary study, however, we observed evidence showing that small amounts of fibers showing positive labeling for type III collagen are present in the molars of normal mice. In the present study, in order to localize type III in normal dentin, immunofluorescent and immunoelectron microscopic examinations of the molars of normal mice were carried out using affinity-purified antibodies to mouse type III and type I collagen. The fibers positive for type III collagen were much more frequently observed in the root than in the crown. These fibers ran in peritubular dentin or near that in parallel to them. The incidence of the existence of dentinal tubules associated with type III collagen-positive fibrils either in or near peritubular dentin was low. These fibrils positive for type III collagen showed a clear cross-banding. In dentinal tubules, unusual collagen aggregations, segment long-spacing-like and fibrous long-spacing-like structures which were intensively stained for type I collagen but weakly so for type III collagen were seldom observed. Type III collagen-positive fibers often extended towards the pulp beyond the odontoblast layer, suggesting that these fibers were produced, at least partly, by the pulp cells.

Animals↗
PubMed1992

Effect of probucol on recovery from streptozotocin diabetes in rats.

The present study was conducted to see the effect of probucol on streptozotocin diabetes in rats. After 2 weeks of a 1% probucol diet, 35 or 50 mg/kg of streptozotocin were intravenously injected into male Wistar rats. All the rats became diabetic 2 days after treatment. Thereafter, in order to see the effect of probucol on spontaneous recovery from streptozotocin diabetes, 25 mg/kg of streptozotocin was injected into rats after two weeks of probucol diet and the diet was continued for additional two weeks. All the rats with a standard diet (group CS, n = 13) and 12 of 13 rats with probucol diet (group PS) became diabetic 2 days after streptozotocin injection. One rate from group PS did not develop diabetes. Two weeks after injection, only 4 of 13 rats in groups CS showed recovery, while 11 of 12 rats in group PS showed recovery from streptozotocin diabetes (p less than 0.05). The average blood glucose levels in group PS were significantly lower than group CS (10.5 +/- 4.6 vs 18.5 +/- 0.6 mM, p less than 0.05). In addition, the pancreatic insulin content of group PS was 8 times greater than that of group CS (0.75 +/- 0.24 vs 0.09 +/- 0.03 mmol/pancreas, p less than 0.01). Thus, the in vivo diabetogenic action of streptozotocin could not be reduced by pretreatment with probucol. However, recovery from streptozotocin diabetes was induced by subsequent treatment with probucol. The precise mechanisms for this phenomenon were not known; but the present findings suggest the protective effect of probucol on beta-cell damage induced by small dose of streptozotocin.

Animals↗
PubMed1992

Age-related decline of cerebral oxygen metabolism in normal population detected with positron emission tomography.

Using positron emission tomography (PET), cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) were measured in 32 healthy volunteers aged from 27 to 67 years. In bilateral putamen, left supratemporal, left infrafrontal and left parietal cortices, CMRO2 showed a significant decline during aging. The age-related decline of CBF was seen only at the left superior temporal cortex. The mean CMRO2 was significantly lower in the elder group (over 51 years old) than in the younger group (under 50 years old), whereas no significant difference in mean CBF between the two groups. The poor correlation of CBF to the age could be explained partly by the fact that CBF is easily influenced by the physiological, psychological and/or environmental factors. The age-related changes of CMRO2 were more marked in the association cortices of the left hemisphere than in that of the right hemisphere.

Adult↗
PubMed1992

Occurrence and biochemical characterization of GTP-binding proteins in Candida albicans.

The activities of GTP-binding and GTPase in Candida albicans were present in the cytosol, KCl- and cholate-extractable fractions. At least two kinds of GTP-binding proteins were found in the cytosolic fraction; the major one with a molecular mass of about 30 kDa and the other about 500 kDa. The former specifically bound guanine nucleotides and was most likely to bind GDP since guanosine 5'-O-(thio) triphosphate (GTP gamma S)-binding was accelerated by addition of (NH4)2SO4. The latter showed no specificity in nucleotide binding and could also bind adenine nucleotides. The proteins were not ADP-ribosylated by either pertussis toxin or cholera toxin. These results indicate that ras-like monomeric, low molecular mass GTP-binding proteins distinct from heterotrimeric G proteins such as Gi, Go and Gs are present in C. albicans.

Adenosine Diphosphate↗
PubMed1992

Involvement of the stress protein HSP47 in procollagen processing in the endoplasmic reticulum.

The 47,000-D collagen-binding glycoprotein, heat shock protein 47 (HSP47), is a stress-inducible protein localized in the ER of collagen-secreting cells. The location and collagen-binding activity of this protein led to speculation that HSP47 might participate in collagen processing. Chemical crosslinking studies were used to test this hypothesis both before and after the perturbation of procollagen processing. The association of procollagen with HSP47 was demonstrated using cleavable bifunctional crosslinking reagents. HSP47 and procollagen were shown to be coprecipitated by the treatment of intact cells with anti-HSP47 or with anticollagen antibodies. Furthermore, several proteins residing in the ER were noted to be crosslinked to and coprecipitated with HSP47, suggesting that these ER-resident proteins may form a large complex in the ER. When cells were heat shocked, or when stable triple-helix formation was inhibited by treatment with alpha,alpha'-dipyridyl, coprecipitation of procollagen with HSP47 was increased. This increase was due to the inhibition of procollagen secretion and to the accumulation of procollagen in the ER. Pulse label and chase experiments revealed that coprecipitated procollagen was detectable as long as procollagen was present in the endoplasmic reticulum of alpha,alpha'-dipyridyl-treated cells. Under normal growth conditions, coprecipitated procollagen was observed to decrease after a chase period of 10-15 min, whereas total procollagen decreased only after 20-25 min. In addition, the intracellular association between HSP47 and procollagen was shown to be disrupted by a change in physiological pH, suggesting that the dissociation of procollagen from HSP47 is pH dependent. These findings support a specific role for HSP47 in the intracellular processing of procollagen, and provide evidence of a new category of "molecular chaperones" in terms of its substrate specificity and the dissociation mechanism.

2,2'-Dipyridyl↗
PubMed1992

Comparison of two reconstituted systems for in vitro transcription and replication of influenza virus.

The transcription and replication of influenza RNA can be studied in vitro by the reconstitution of functional ribonucleoprotein (RNP) complex from viral core proteins including the RNA polymerase (complex of three P protein subunits) and nucleoprotein (NP), and model templates. Here, two different core protein preparations, one based on CsCl centrifugation (CS enzyme) and the other on micrococcal nuclease treatment of viral cores (MN enzyme), were compared side-by-side. Short model RNA templates and their 3'-half molecules of both viral RNA (vRNA) and complementary RNA (cRNA) senses were reconstituted with the core protein preparations in parallel, and RNA polymerase activity was tested either in the presence or absence of ApG or globin mRNA as primers. Both enzyme preparations were active in the syntheses of short vRNA and cRNA transcripts using ApG as a primer, although the synthesis of cRNA was 2-10-fold higher (depending on the template used) than the synthesis of vRNA. The MN enzyme, however, was more active per weight of total protein than the CS enzyme, probably because of its higher content of RNA polymerase. Both enzymes failed to show primer-independent synthesis of vRNA. The differences observed in the synthesis of short transcripts using globin mRNA as a primer are discussed.

Base Sequence↗
PubMed1992

Transcription of a recombinant influenza virus RNA in cells that can express the influenza virus RNA polymerase and nucleoprotein genes.

A new transfection system for influenza virus was developed using the clone 76 cell line, in which the viral RNA polymerase and nucleoprotein (NP) genes can be expressed in response to dexamethasone. Ribonucleoprotein (RNP) complexes were reconstituted by expressing proteins from a chimeric NS-chloramphenicol acetyltransferase (CAT) RNA consisting of the full-length negative-strand RNA of the CAT gene positioned between the 5'- and 3'-terminal sequences of influenza virus RNA segment 8, and purifying NP from an NP gene-expressing Escherichia coli strain. When the reconstituted RNP was transfected into clone 76 cells, CAT was produced only when the synthesis of the three RNA polymerase subunits and NP was induced by treatment with dexamethasone.

Animals↗
PubMed1992

Serological and biological characteristics of "Streptococcus milleri" isolates from systemic purulent infections.

Ninety-one Streptococcus milleri strains isolated from various systemic purulent lesions of 68 patients were examined by physiological and serological tests. Most strains formed a smooth colony (66 strains), did not form spontaneous aggregation of cells in BHI broth culture (79), were non-beta-haemolytic (alpha-35 or non-41), and belonged to biotype Ia (49) or Ib (34) and to API taxa S. milleri I (41) or II (38). Almost all of the beta-haemolytic strains as well as two-fifths of the non-beta-haemolytic belonged to API taxon I; strains of API taxa II and III were non-beta-haemolytic and non-haemolytic, respectively. Two-fifths (38) of the isolates belonged to one of eight serotypes, a-g and k, and more than half (47) to Lancefield groups A, C, F or G, the most frequent being type b (19) and group F (33). Fifteen strains carried simultaneously type a/group A, b/C, c/C, e/G, f/F or k/G antigens. Nineteen were neither typable nor groupable. All the 38 serotypable isolates were non-beta-haemolytic and not members of API taxon III, and were serologically and physiologically similar to oral S. milleri. The isolates from various infected sites--sputum, thorax, abdomen, urogenitalia, skin, eye and dental--exhibited distinct combinations of biological and serological properties. These results suggest that serotyping, haemolytic properties and API taxon, and their combinations, would be useful methods to trace oral S. milleri in systemic infections.

Abdomen↗
PubMed1992

Quercetin, an inhibitor of heat shock protein synthesis, inhibits the acquisition of thermotolerance in a human colon carcinoma cell line.

Here, we describe the effects of quercetin on the induction of thermotolerance as examined by colony forming assay in a cell line derived from human colon carcinoma (COLO320 DM). Cells became resistant to heat treatment at 45 degrees C when they were preheated at 42 degrees C for 1.5 h or at 45 degrees C for 10 min. This induction of thermotolerance was almost completely inhibited by continuous treatment with 100 microM quercetin during the first and second heating sessions, and the interval between. This effect of quercetin was demonstrated to be dose-dependent over a concentration range of 50-200 microM. Quercetin did not increase the thermosensitivity of non-tolerant cells. The presence of quercetin during the first conditioning heating was more effective in inhibiting thermotolerance than its presence during the second heating. Quercetin was also found to inhibit the acquisition of thermotolerance induced by sodium arsenite. Cycloheximide, a nonspecific inhibitor of protein synthesis, did not affect the acquisition of thermotolerance by the same cell line. Quercetin specifically inhibits the synthesis of all heat shock proteins so far reported previously, and this leads to inhibition of the induction of thermotolerance. Such inhibition of thermotolerance by quercetin may improve the efficacy of clinical fractionated hyperthermia.

Arsenic↗
PubMed1992

[Studies on Clostridium absonum isolates from clinical specimens].

Two strains of Clostridium absonum isolated from clinical specimens and a type strain were tested for heat resistance of spores, biochemical properties and neutralization of their lecithinase by anti-C. perfringens alpha toxin antiserum. In addition, the usefulness of RapID ANA (AMUCO) and ANIDENT (API) kits for the identification of C. absonum was examined. The results were summarized as follows: 1. C. absonum isolates from clinical specimens were resistant against heating at 70 degrees C for 10 min and a type strain against heating at 85 degrees C for 10 min, less resistant than those of C. perfringens BP6K. 2. C. absonum differentiated from C. perfringens in fermentation of trehalose, melibiose and raffinose, and hydrosis of esculin and starch. 3. Lecithinase of C. absonum was not completely neutralized by anti-C. perfringens alpha toxin antiserum. 4. Both RapID ANA and ANIDENT kits were useful for differentiation of C. absonum from C. perfringens but not for the identification of C. absonum.

Adolescent↗
PubMed1992

Monoclonal antibodies against the native urease of Helicobacter pylori: synergistic inhibition of urease activity by monoclonal antibody combinations.

Monoclonal antibodies (MAbs) against the native urease of Helicobacter pylori NCTC 11637 were found to clearly inhibit the urease activity. Interestingly, synergistic inhibition by two MAbs recognizing different subunits was also observed. Ten MAbs were produced and classified as two isotypes of the immunoglobulin G (IgG) subclass, IgG1, and IgG2a. Western blot (immunoblot) analysis using sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that five MAbs recognized the large subunit and the other five recognized the small subunit of the urease. Among the MAbs, L2 and S2, which recognized the large and the small subunits, respectively, were also able to inhibit the urease activity of clinical isolates from H. pylori-infected patients. The combination of L2 and S2 led to augmented synergistic inhibition. L2, but not S2, could also inhibit the urease activity from Helicobacter mustelae; enzyme-linked immunosorbent assay and Western blot analysis showed that L2 cross-reacted with this urease. These results suggested that the epitope recognized by L2 had a structure common to both Helicobacter species and may be involved in the active site of the urease. In contrast to the MAbs, a polyclonal antibody in sera from mice immunized with H. pylori urease did not have the ability to inhibit H. pylori urease activity. However, the polyclonal antibody retained the ability to abolish the inhibitory action of these MAbs. Moreover, other MAbs which could not inhibit H. pylori urease activity also abolished the inhibitory action.

Antibodies, Bacterial↗