Biomedical subjects

M Yamazaki

Publications and source records attributed to M Yamazaki.

At least 343 records · Page 19Linked to original sources

PubMed1996

Discrimination of two functions of photoreceptor cGMP phosphodiesterase gamma subunit.

cGMP phosphodiesterase, a key enzyme in phototransduction, is composed of P alpha beta and two P gamma S. P gamma has two functions in P alpha beta regulation: (I) an inhibitor of cGMP hydrolysis and (II) a stimulator of cGMP binding to their noncatalytic sites. Here we show for the first time that these functions can be discriminated. P gamma release by GTP-bound transducing from P alpha beta was stimulated by NaCl in a concentration-dependent manner. However, phosphodiesterase activity in membranes washed with NaCl-free buffer already reached the maximum level. [3H]-cGMP binding of P alpha beta in membranes washed with NaCl required more P gamma than that in membranes washed without NaCl. Other salts had a similar effect. Identical P gamma was released under different [NaCl]. These results indicate that P gamma for the function (I) is released in low [salt], but P gamma for the function (II) is released in high [salt]. These P gamma functions may be expressed separately in phototransduction.

3',5'-Cyclic-GMP Phosphodiesterases↗

PubMed1996

Isolation of cDNA and genomic clones of a human Ras-related GTP-binding protein gene and its chromosomal localization to the long arm of chromosome 7, 7q36.

A Ras-related GTP-binding protein cDNA has been isolated from a human skin fibroblast cDNA library using a genomic subclone derived from a YAC clone as a probe. The polypeptide, consisting of 184 amino acids deduced from nucleotide sequences, contains five repeats of the Ras-related GTP-binding region and is highly homologous to the rat RHEB (Ras homologue enriched in brain) gene, which encodes a Ras-related growth factor- and synaptic activity-regulated protein, with 98.9% amino acid identity. Therefore, it is suggested to be a human homologue of the rat RHEB protein, and we have designated it human RHEB. Using fluorescence in situ hybridization, we concluded that this human RHEB gene was localized to band q36 on chromosome 7. Considering the chromosomal localization as well as the potential function of this protein, it will be very important to investigate whether it may play a role in the etiopathogenesis of holoprosencephaly type 3 or hereditary sacral agenesis, in which the disease susceptible locus is linked to the microsatellite marker, D7S22, in this chromosomal region, 7q36.

Amino Acid Sequence↗

PubMed1996

Polymorphism of F-actin assembly. 1. A quantitative phase diagram of F-actin.

We have made the first quantitative phase diagram of actin filament (F-actin) assembly represented by the concentration of F-actin and the chi parameter which characterizes solvent-solute interaction energy. We manipulated the chi value of F-actin by adding a high molecular weight poly- (ethylene glycol) with average molecular weight 6000 (PEG 6K). The preferential exclusion of PEG 6K from the region adjacent to F-actin increases the chi value of F-actin. We qualified the PEG 6K-induced increase of the chi value through analysis of the PEG-induced solubility change of protein. The phase diagram shows that F-actin changes its assembly structure from isotropic disordered distribution to anisotropic ordered phase of a lyotropic liquid crystalline with an increase in the concentration and to concentrated anisotropic ordered phase of a crystalline-like bundle with a small increase in chi respectively, in the physiological concentration range. The formation of the crystalline- like bundle suggests that some specific force may act between F-actin. The present results demonstrate that F-actin can take various assembly structures as observed in cytoplasm by itself, indicating that the versatility of F-actin assembly in cytoplasm may be based on the thermodynamic properties of F-actin as a rod-like molecule.

Actins↗

PubMed1996

Sequencing of a 23 kb fragment from Saccharomyces cerevisiae chromosome VI.

Plasmid clone gapB and lambda phage clone 4682, which contain fragments of Saccharomyces cerevisiae chromosome VI, were analysed. A 23 kb sequence was determined and ten open reading frames (ORFs) were revealed. Among them, five ORFs were identical to five yeast genes (SEC4, MSH4, SPB4, DEG1 and NIC96), two were identical to transposable elements (TYA and TYB), one (gapBorfF003) was highly homologous to a yeast expressed sequence tag, and another (4682orfF002) was predicted to be a nuclear protein. Sequence data have been submitted to DDBJ/EMBL/GenBank data library under Accession Number D44604 (clone gapB) and D44600 (clone 4682), respectively.

Amino Acid Sequence↗

PubMed1996

Primary active transport of pravastatin across the liver canalicular membrane in normal and mutant Eisai hyperbilirubinemic rats.

We have previously demonstrated that the HMG-CoA reductase inhibitor pravastatin is efficiently taken up by the liver via the 'multispecific anion transporter' in an active manner. To further examine the fate of pravastatin within the liver, its biliary excretion was studied in a single-pass liver perfusion system and isolated liver canalicular membrane vesicles (CMVs) using normal (Sprague-Dawley rats; SDRs) and mutant Eisai hyperbilirubinemic rats (EHBRs). In the liver perfusion experiments, the outflowing drug concentration reached a steady state at 30 min and the extraction ratio was approximately 0.7 in both rat strains. Both the steady-state biliary excretion rate and bile flow rate of the EHBR group were 40% those of SDRs. At steady state, the fraction of unchanged drug in bile was 25-34% in both groups. The concentration ratios of unbound drug in cytosol versus that in sinusoid and in bile versus cytosol were, respectively, 11 and 87 in SDRs, and 13 and 94 in EHBRs. After correction for membrane potential (-40 mV in cytosol), the ratios became 49 and 19 in SDRs and 58 and 21 in EHBRs, respectively. The finding that all of these values were much larger than unity suggested that active transport occurred from liver to bile, as well as from plasma to liver, in both rat strains. Furthermore, ATP-dependent uptake of pravastatin was clearly observed in CMVs prepared from EHBRs as well as SDRs, whereas the stimulation by ATP of DNP-SG transport in CMV was observed only in SDRs. It was concluded that pravastatin is excreted into bile in high concentrations and a primary active transport mechanism which is maintained in EHBRs contributes to the biliary excretion of this drug.

Animals↗

PubMed1996

Primary active transport of pravastatin across the liver canalicular membrane in normal and mutant Eisai hyperbilirubinaemic rats.

We have previously demonstrated that the HMG-CoA inhibitor pravastatin is efficiently taken up by the liver via the 'multispecific anion transporter' in an active manner. To further examine the fate of pravastatin within the liver, its biliary excretion was studied in a single-pass liver perfusion system and isolated liver canalicular membrane vesicles (CMVs) using normal (Sprague-Dawley rats; SDRs) and mutant Eisai hyperbilirubinaemic rats (EHBRs). In the liver perfusion experiments, the outflowing drug concentration reached a steady state at 30 min and the extraction ratio was approximately 0.7 in both rat strains. Both the steady state biliary excretion rate and bile flow rate of the EHBR group were 40% of those of SDRS. At steady state, the fraction of unchanged drug in bile was 25-34% in both groups. The concentration ratios of unbound drug in cytosol versus that in sinusoid and of that in bile versus that in cytosol were, respectively, 11 and 87 in SDRs, and 13 and 94 in EHBRs. After correction for the membrane potential (-40 mV in cytosol), the ratios became 49 and 19 in SDR and 58 and 21 in EHBRs, respectively. The finding that all of these values were much larger than unity suggested that active transport occurred from liver to bile, as well as from plasma to liver, in both rat strains. Furthermore, ATP-dependent uptake of pravastatin was clearly observed in CMVs prepared from EHBRs as well as SDRs, whereas the stimulation by ATP of DNP-SG transport in CMVs was observed only in SDRs. It was concluded that pravastatin is excreted into bile in high concentrations and a primary active transport mechanism which is maintained in EHBRs contributes to the biliary excretion of this drug.

Adenosine Triphosphate↗

PubMed1996

Tissue-selective uptake of pravastatin in rats: contribution of a specific carrier-mediated uptake system.

Previously we demonstrated that a hydrophilic HMG-CoA reductase inhibitor, pravastatin, was actively taken up by the liver via the 'multispecific anion transporter' using isolated rat hepatocytes (M. Yamazaki, H. Suzuki, M. Hanano, T. Tokui, T. Komai, and Y. Sugiyama, Am. J. Physiol., 264, G36-G44 (1993)). Such a carrier-mediated uptake of pravastatin may contribute to the liver selective inhibition of the cholesterol synthesis in vivo. To examine the early-phase tissue distribution of this drug, we carried out a pharmacokinetic and tissue distribution analysis of pravastatin in rats. After i.v. bolus administration of [14C]pravastatin, the time profiles of [14C]radioactivity in plasma and several tissues were determined to calculate the tissue uptake clearance (CLuptake). Among the tissues examined, liver accounted for the major uptake (CLuptake,liver = 22.8 mL min-1 kg-1), followed by kidney (CLuptake,kidney (GFR corrected) = 2.36 mL min-1 kg-1). Other tissues showed no significant uptake (less than 0.2 mL min-1 kg-1). After portal vein administration, the distribution to the liver became much larger than that to the kidney due to the extensive first-pass removal by the liver. The first-pass hepatic uptake ratio was estimated as 0.66. Administering a range of doses (0.4-400 mumol kg-1) intravenously, an increase in early-phase half-life and a decrease in CLuptake,liver were observed simultaneously at doses over 40 mumol kg-1. In addition, CLuptake,kidney decreased at doses over 4 mumol kg-1. The effect of DBSP or PAH co-infusion (i.e. typical substrates for the transport system for organic anions in liver and kidney, respectively) on the initial uptake of pravastatin was also examined. DBSP clearly inhibited both the hepatic and renal uptake; however, PAH did not reduce the hepatic uptake of pravastatin although it inhibited the renal uptake. The transport systems in liver and kidney are thus considered different, based on the different saturability and inhibitory effect of organic anions.

Animals↗

PubMed1996

Stimulation of interleukin-1beta-independent interleukin-6 production in human dental pulp cells by lipopolysaccharide.

Dental pulpal infection is most commonly caused by extensive dental caries. A principal driving force behind pulpal disease response appears to lie in the immune system's response to bacteria. However, the production of interleukin (IL)-1beta and IL-6 in human dental pulp (HDP) cells in response to lipopolysaccharide (LPS) has not been well characterized. We examined IL-1beta and IL-6 production in HDP cells by challenging with LPS from Porphyromonas endodontalis, which is a Gram-negative bacteria found in root canals. Our results presented here showed that when HDP cells were stimulated by LPS, the production of IL-6 always preceded that of IL-1beta. Since the IL-6 production was observed even in the presence of the IL-1beta receptor antagonist, we concluded IL-6 production was independent of the IL-1beta molecule in LPS-stimulated HDP cells. This idea was further supported by the results obtained from RT-PCR experiments, in which IL-6 mRNA, but not IL-1beta mRNA, was present in the RNA preparation isolated from the early stage of cells.

Cells, Cultured↗

PubMed1996

Collagen-encapsulated coagulation necrosis in cerebral infarcts: a pathological study.

Coagulation necrosis (CN)--a type of necrosis characterized by firm, eosinophilic parenchyma with recognizable cell outlines--is thought to be a result of rapid degeneration of tissue protein to a gel state and loss of water which prevents the necrotic tissue from undergoing autolysis and cellular digestion. In this study, we observed CN in cerebral infarcts of 11 of 150 consecutive autopsy cases of large cerebral infarction. Cerebral CN in patients who had survived for about 1 month had already started to be surrounded by newly formed vessels and type I collagen-positive tissue. In patients who had survived for more than 1 year, CN was deposited with calcium and cholesterin crystals and encapsulated by thick, dense collagenous tissue. Encapsulation, however, was not always complete, a finding that suggests that other factors, such as gel transformation at an early stage of CN and calcification at a later stage, are important for the persistence of CN in the infarct. The results of our study suggest that cerebral CN occurs more frequently than is generally believed.

Aged↗

PubMed1996

Hypercoagulability and high lipoprotein(a) levels in patients with type II diabetes mellitus.

Diabetes mellitus is associated with disturbances in hemostasis that could contribute to the development of diabetic vascular disease. We investigated the changes in parameters of blood coagulation and the fibrinolytic system and in plasma levels of lipoprotein(a)(Lp(a)) in 124 patients with type II diabetes mellitus and 44 healthy control subjects matched for age and body mass index (BMI) to determine whether hemostatic disturbances may lead to increased cardiovascular mortality. Median levels of fibrinogen (P < 0.0001), thrombin-antithrombin III complex (TAT) (P < 0.005), and plasminogen activator inhibitor-1 (PAI-1) activity (P < 0.05) in plasma were significantly elevated in diabetic patients compared with controls. The median concentration of Lp(a) was significantly higher in diabetic patients than in normal controls (18.2 vs. 12.6 mg/dl. P < 0.0005). Lp(a) levels tended to be elevated in patients with a prolonged history of diabetes. There was no evidence that Lp(a) levels were affected by metabolic control or by type of treatment. Twenty-two diabetics with coronary heart disease (CHD) had significantly higher levels of fibrinogen (P < 0.05), TAT (P < 0.05), and Lp(a) (24.7 vs. 13.7 mg/dl, P < 0.01) than the 51 patients without diabetic angiopathy. Our data indicate that impaired hemostatic balance in diabetes may cause hypercoagulability and may thus contribute to the increased cardiovascular mortality in diabetes.

Aged↗

PubMed1996

Ultrastructure of size-regulated hetero-spheroids composed of human keratinocytes and fibroblasts.

In order to develop a new in vitro skin model multicellular floating hetero-spheroids were prepared by culturing keratinocytes and fibroblasts on hydrophilic culture dishes coated with type I collagen and a thermo-responsive polymer. Upon decreasing the substratum's temperature to an ambient temperature, the spheroids detached from the substratum and were thereafter maintained in either: Medium I, a medium mixture of keratinocyte growth medium (KGM) and supplemented Dulbecco's modified Eagle's medium (DMEM) at a ratio of 1 to 2; or medium II, KGM for the initial 24 h followed by supplemented DMEM for the remainder of the culture periods. The spheroids displayed a typical pattern of an external rim of keratinocytes with an internal core of fibroblasts. A minute space separated the keratinocytes and fibroblasts. The stratification of cells cultured in medium II was more prominent than that of the cells cultured in medium I. Markers of the advanced stages of keratinization such as keratohyalin granules, membrane coating granules and the cornified envelope were not observed. Interestingly, keratinocytes underwent the same differentiation pathway as non-keratinized stratified epithelia such as esophagus. With consideration to keratinocyte-fibroblast interactions, it may be of interest to incorporate the study of such morphological impairments when investigating the effects of growth factors and their ligands.

Cell Aggregation↗

PubMed1996

Silver and other trace elements in a freshwater fish, Carasius auratus langsdorfii, from the Asakawa River in Tokyo, Japan.

The concentrations of silver (Ag) in a typical freshwater fish in Japan, Carasius auratus langsdorfii, and some other species have been determined to examine the Ag-contamination of fish and to specify the Ag accumulating species and part. They were dissected roughly into four parts, and analyzed by an instrumental neutron activation analysis. It was found that Ag was accumulated in the samples from the Asakawa River, and that the Ag concentration in the entrails of C. auratus langsdorfi reached 12 microg g(-1). The analysis of a C. auratus langsdorfii, which was dissected into 13 individual organs, showed that the Ag was accumulated highly in the liver, followed by the gallbladder and kidney. The inter-species and inter-part distributions of other trace elements have also been studied.

Journal Article↗

PubMed1996

Uptake is the rate-limiting step in the overall hepatic elimination of pravastatin at steady-state in rats.

PURPOSE: Of the HMG-CoA reductase inhibitors, the hydrophilic pravastatin has been shown to exhibit relatively specific inhibition of cholesterol synthesis in the liver. As one of the reasons for this relatively specific pharmacological activity, we demonstrated that the tissue distribution of pravastatin is limited because of its high hydrophilicity, while hepatic uptake by active transport takes place at the liver surface via a multispecific anion transporter (M. Yamazaki et al., Am. J. Physiol., 264, G36-44, 1993). In this study, we examined the hepatic elimination of pravastatin at steady-state. METHODS: After i.v. infusion, the plasma concentrations of pravastatin in both arterial and hepatic venous blood were measured. RESULTS: The hepatic availability at steady-state exhibited a clear increase on increasing the infusion rate of pravastatin. The total hepatic elimination rate at steady-state exhibited Michaelis-Menten type saturation with the drug concentration in the capillary defined by typical mathematical models (i.e., well-stirred, parallel-tube and dispersion models), K(m) and Vmax values being comparable with those obtained from analysis of the initial uptake velocity using in vitro isolated hepatocytes. CONCLUSIONS: These results indicate that overall hepatic intrinsic clearance of pravastatin at steady-state is regulated by the uptake process, followed by rapid metabolism and/or biliary excretion with minimal efflux to the circulating blood.

Animals↗

PubMed1996

Recent advances in carrier-mediated hepatic uptake and biliary excretion of xenobiotics.

PURPOSE: Besides renal excretion, hepatic metabolism and biliary excretion are the major pathways involved in the removal of xenobiotics. Recently, for many endogenous and exogenous compounds (including drugs), it has been reported that carrier-mediated transport contributes to hepatic uptake and/or biliary excretion. In particular, primary active transport mechanisms have been shown to be responsible for the biliary excretion of anticancer drugs, endogenous bile acids and organic anions including glutathione and glucuronic acid conjugates. Primary active excretion into bile means the positive removal of xenobiotics from the body, and this elimination process is now designated as "Phase III" (T. Ishikawa, Trends Biochem. Sci., 17, 1992) in the detoxification mechanisms for xenobiotics in addition to Phase I by P-450 and Phase II by conjugation. METHODS: The transporters, which have been called P-glycoprotein (MDR), multidrug resistance related protein (MRP) and GS-X pump and which are believed to be involved in the primary active pumping of xenobiotics from the cells, are now known as the ATP-binding cassette (ABC) transporters. In this review, we first describe the HMG-CoA reductase inhibitor, pravastatin, as a typical case of a carrier-mediated active transport system that contributes to the liver-specific distribution in the body. RESULTS: Regarding biliary excretion, we have summarized recent results suggesting the possible contribution of the ABC transporters to the biliary excretion of xenobiotics. We also focus on the multiplicities in both hepatic uptake and biliary excretion mechanisms. Analyzing these multiplicities in transport is necessary not only from a biochemical point of view, but also for our understanding of the physiological adaptability of the living body in terms of the removal (detoxification) of xenobiotics. CONCLUSIONS: Clarification of these transport mechanism may provide important information for studying the pharmacokinetics of new therapeutic drugs and furthermore, leads to the development of the drug delivery systems.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1996

Effects of high-dose granulocyte colony-stimulating factor on neutrophil functions.

We evaluated the effects of high-dose recombinant human granulocyte colony-stimulating factor (rhG-CSF) therapy on N-formyl-methionyl-leucyl-phenylalanine (FMLP)-induced chemotaxis and superoxide (O2-) production in neutrophils from four patients with aplastic anaemia. The FMLP-induced chemotaxis and O2- production in the neutrophils of all four patients were normal before the rhG-CSF treatment. After the administration of high-dose rhG-CSF, chemotaxis in agarose was decreased, adherence and O2- production were enhanced in all the patients. An excessive increase of neutrophils with augmented adhesiveness and oxygen radical production may be harmful. Care should be taken in regard to neutrophil toxicity when high-dose G-CSF is used clinically.

Adolescent↗

PubMed1996

Protective effects of DX-9065a, an orally active, novel synthesized and selective inhibitor of factor Xa, against thromboplastin-induced experimental disseminated intravascular coagulation in rats.

We investigated the protective effects of DX-9065a, an orally active, newly synthesized, and specific inhibitor of factor Xa, against experimental disseminated intravascular coagulation (DIC) in rats. Experimental DIC was induced by a 4 hour sustained infusion of thromboplastin at a dose of 2.5 mg/kg. The rats were orally administered DX-9065a at 10, 30, 100 mg/kg 30 minutes before thromboplastin injection. In this DIC model, DX-9065a showed a protective effect against DIC, at all doses and in all parameters, including fibrin(ogen) degradation products, fibrinogen level, thrombin-antithrombin III complex level, prothrombin time (PT), activated partial thromboplastin time (APTT), platelet count, and the number of renal glomeruli with fibrin thrombi. When DX-9065a was orally administered at 100 mg/kg without thromboplastin, no significant changes were seen in hemostatic parameters except PT and APTT, and no fibrin thrombi or abnormal bleeding were seen in renal specimens. These findings suggested that the new oral anti-Xa drug, DX-9065a, has a protective effect against thromboplastin-induced DIC model with little risk of bleeding.

Administration, Oral↗

PubMed1996

Hypercoagulability and high lipoprotein(a) levels in patients with aplastic anemia receiving cyclosporine.

There is some clinical evidence that cyclosporine A (CyA) is associated with thrombotic complications of bone marrow and renal transplantation. We investigated plasma concentrations of lipoprotein(a) [Lp(a)], a potentially atherothrombotic lipoprotein, and hemostatic and vascular status in ten patients with aplastic anemia receiving CyA, eleven patients not taking it, and 38 age-matched healthy controls. Patients receiving CyA had significantly higher concentrations of plasma fibrinogen (P < 0.05), prothrombin fragment 1 + 2 (F1 + 2; P < 0.05), plasminogen activator inhibitor-1 (PAI-1; P < 0.05), and von Willebrand factor antigen (P < 0.05) than did patients not taking CyA. Plasma concentrations of Lp(a) were higher in CyA-treated patients than those not receiving it (P < 0.05) or healthy controls (P < 0.05). The difference in the Lp(a) concentration between controls and patients who did not receive CyA-treatment was not significant. Our results suggest that hypercoagulability is likely to occur during CyA therapy. Further, the presence of high concentrations of Lp(a) may accelerate the process of atherosclerosis and increase thrombotic events in patients receiving long-term CyA.

Adult↗

PubMed1996

Giant mixed tumor of the face.

A 35-year-old Japanese man consulted our clinic with an eight year history of a 6 cm diameter subcutaneous tumor on the left cheek. Hematoxylin and eosin staining of the resected section showed histology corresponding to a benign chondroid syringoma. Keratin was positive in most of the constituent cells, and S-100 protein was positive in the cells distant from the lumens and in myxomatous cells. A benign chondroid syringoma of this size has only been very rarely reported in the literature.

Adenoma, Pleomorphic↗