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Biomedical subjects

A Nakashima

Publications and source records attributed to A Nakashima.

At least 37 records · Page 2Linked to original sources
PubMed2001

Fission yeast tor1 functions in response to various stresses including nitrogen starvation, high osmolarity, and high temperature.

A target of rapamycin (TOR) protein is a protein kinase that exerts cellular signal transduction to regulate cell growth in response to extracellular nutrient conditions. In the Schizosaccharomyces pombe genome database, there are two genes encoding TOR-related proteins, but their functions have not been analyzed. Here we report that one of the genes, referred to as tor1+, is required for sexual development induced by nitrogen starvation. Ste11 is a key transcription factor for the initiation of sexual development. The expression of ste11+ is normally regulated in tor1- cells; and overexpression of ste11+ hardly rescues the defect in fertility in tor1-. Upon nitrogen starvation, tor1+ cells promote two rounds of the cell cycle to become arrested at the G1 phase before initiation of sexual development. The tor1- cells do not promote such a cell cycle, suggesting that Tor1 is necessary for the response to nitrogen starvation. The tor1- cells show no growth or very slow growth under various stress conditions, including external high pH, high concentrations of salts or sorbitol, and high temperature. These results suggest that Tor1 is necessary for any response to a wide range of stresses. The vegetative growth of tor1- cells is inhibited by rapamycin, although tor1+ cells are resistant to the drug. The tor1- cells are hypersensitive to fluphenazine and cyclosporin A, which specifically inhibit calmodulin and calcineurin, respectively.

Amino Acid Sequence↗
PubMed2001

Error correcting memorization learning for noisy training examples.

In order to avoid overfitting, we propose error correcting memorization learning. This method is derived from minimization of error between outputs of a trained neural network and correct values for noisy training examples, although the correct values are unknown. We show that noise is adequately suppressed by error correcting memorization learning. The noise suppression mechanism is theoretically clarified. It is found that redundancy plays an essential role for noise suppression and depends on a set of training inputs. We give the condition for the training inputs to provide the redundancy. Moreover, by clarifying the relationships between the proposed method and the weighted least squares estimation with the Mahalanobis norm, we reveal effectiveness of the weighted least squares estimation on noise suppression.

Models, Theoretical↗
PubMed2001

Noise suppression in training examples for improving generalization capability.

For the supervised learning problem, error correcting memorization learning was proposed in order to suppress noise in teacher signals. In this paper, generalization capability of the learning method is discussed. Generalization capability is evaluated based on the projection learning criterion. We give a necessary and sufficient condition for error correcting memorization learning to provide the same level of generalization as projection learning, and suggest how to choose a training set so as to satisfy the obtained condition. Moreover, it is revealed that noise suppression based on the error correcting memorization learning criterion always has a good effect on improving generalization to the level of projection learning.

Artifacts↗
PubMed2001

Risk stratification analysis of operative mortality in heart and thoracic aorta surgery: comparison between Parsonnet and EuroSCORE additive model.

OBJECTIVE: Our purpose was to compare the performance of risk stratification model between Parsonnet and European System for Cardiac Operative Risk Evaluation (EuroSCORE) in our patient database. METHODS: From August 1994 to December 2000, 803 consecutive patients have undergone heart and thoracic aorta surgery using cardiopulmonary bypass and scored according to Parsonnet and EuroSCORE algorithm. The population was divided into five clinically relevant risk categories. We compared correlation of predicted mortality and observed mortality between these two models. Score validity was assessed by calculating the area under the receiver operating characteristic (ROC) curve. RESULTS: Overall hospital mortality was 4.5%. In Parsonnet model, predicted mortality was 2.4% for 0-4% risk, 6.7% for 5-9% risk, 12% for 10-14% risk, 17% for 15-19% risk, 25% for 20% plus risk, and 10.4% for overall patients. Observed mortality was 2.4, 0.4, 5.9, 8.7, 11, and 4.5%, respectively. The thoracic aorta and valve cohort indicated poor correlation between predicted and observed mortality compared to coronary cohort. In the EuroSCORE model, predicted mortality was 1.4% for 0-2% risk, 4.0% for 3-5% risk, 6.7% for 6-8% risk, 9.7% for 9-11% risk, 13% for 12% plus risk, and 5.3% for overall patients. Actual mortality was 0, 1.5, 6.8, 11, 21, and 4.5%, respectively. Each of the thoracic aorta, valve, and coronary cohort indicated good correlation between predicted and observed mortality. Areas under the ROC curves were 0.72 in Parsonnet and 0.82 in EuroSCORE. CONCLUSIONS: The EuroSCORE additive model yielded good predictive value for hospital mortality of Japanese patients undergoing not only cardiac but also thoracic aortic surgery.

Algorithms↗
PubMed2001

Determination of tetrahydrobiopterin in murine locus coeruleus by HPLC with fluorescence detection.

Tetrahydrobiopterin in the murine locus coeruleus was measured as its fully oxidized form, biopterin, using a HPLC coupled to a fluorescence detector, because tetrahydrobiopterin itself cannot be detected by such means. The differential oxidization method distinguished tetrahydrobiopterin-derived biopterin and dihydrobiopterin-derived biopterin. The protocol reported here is a rapid and sensitive method that facilitates the measurement of tissue and/or cellular tetrahydrobiopterin. Using this assay protocol, we were able to detect and quantify variations in the tetrahydrobiopterin content in the murine locus coeruleus.

Animals↗
PubMed2001

Exon 3 of tyrosine hydroxylase gene: lack of association with Japanese schizophrenic patients.

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in dopamine (DA) biosynthesis. Exon 3 of the human TH gene encodes the sequence from Ser31 to Glu104 of type 1 enzyme, which contains the critical parts for regulation of the catalytic activity. The amino acid residues Gly36-Arg37-Arg38 were identified as a key sequence for DA to exert its inhibitory effect on catalytic activity. Therefore, we screened the nucleotide sequences of exon 3 from 201 Japanese patients with schizophrenia to explain the elevation in the synaptic or presynaptic DA concentrations in the schizophrenic brain, based on the hypothesis that any mutation changing the amino acid sequence Gly36-Arg37-Arg38 would result in the elevation of DA synthesis, due to a reduced inhibitory effect of DA on the catalytic activity. However, no mutated sequences of exon 3 and both exon-intron boundaries were detected in any of the patients examined. Polymorphisms generating Val81 and Met81 were compared of the distributions of genotype and allele between the patients and 175 Japanese healthy controls, which did not suggest an association between the polymorphism and schizophrenia. These results indicate that exon 3 of the human TH gene lacks association with schizophrenia in Japanese patients.

Adult↗
PubMed2001

[Antioxidative effects of fluvastatin, and its major metabolites [II]].

We investigated the antioxidative effects of fluvastatin (FV or (+/-)-FV), each enantiomer ((+)-FV, (-)-FV) and its major metabolites on lipid peroxidation using rat and human liver microsomes. The extent of NADPH induced microsomal (Ms) lipid peroxidation was determined by thiobarbituric acid (TBA) assay. The antioxidative effect of each compound was shown as the percentage of inhibition on the formation of TBA reactive substance (TBARS) against vehicle control. The antioxidative effects of alpha-tocopherol (Toc), a potent antioxidative vitamin, probucol (PR), a potent antioxidative drug, pravastatin (PV) and simvastatin (SV), HMG-CoA reductase inhibitors, were also tested. The (+/-)-FV inhibit the formation of TBARS by 40 to 70% depending on Ms concentrations. The antioxidative effects of PR and TOC were comparable to those of FV. The inhibitory effects of PV and SV on the formation of TBARS were less potent than (+/-)-FV, PR and TOC. (+)-FV, (-)-FV, and (+/-)-FV inhibited the formation of TBARS by approximately 50% using rat hepatic microsomes. The antioxidative effects of (+)-FV was comparable to that of (-)-FV using human hepatic microsomes. These results indicated that the antioxidative effects of (+)-FV were comparable to those of (-)-FV, although the HMG-CoA reductase inhibitory activity of (+)-FV was 30-fold higher than that of (-)-FV.

Animals↗
PubMed2001

[Early and mid-term results after cardiac or thoracic aortic surgery in patients aged 70 years and older--survival and quality of life].

The early and mid-term survival after cardiac or thoracic aortic surgery and influence of age to the operative mortality were examined in 168 consecutive patients aged 70 years and older from August 1994 to December 1998, together with assessment of postoperative quality of life (QOL). The mean age was 74.1 +/- 3.7 years old (70 to 86 years). 80 patients had IHD, 59 had VHD, 28 had TAA. Preoperative risk score was classified in 5 groups (good, fair, poor, high, extremely high) based on Parsonnet method. Current QOL of the survivors was assessed using Asanoi method with questionnaire by a letter. There were 9 early deaths (5.4%). Following the Parsonnet model observed mortality was absolutely lower than predicted mortality. When age score was excluded in the Parsonnet model, the observed mortality became almost equal with the predicted mortality. There were 22 late deaths (6.9%/P-Y). The actuarial survival rate of age 70 to 74 group was significantly higher than the age 75 years and older group (p = 0.0021). The actuarial survival rate of TAA group was significantly lower than the VHD or IHD group (p < 0.02). Postoperative NYHA and activity score of TAA group were better than VHD or IHD group. We got satisfactory answers for operation in 95% current survivors. Patients aged 70 years and older will be undergone cardiac or thoracic aortic surgery at a reasonable risk and well satisfaction.

Aged↗
PubMed2000

Positive charge intrinsic to Arg(37)-Arg(38) is critical for dopamine inhibition of the catalytic activity of human tyrosine hydroxylase type 1.

Tyrosine hydroxylase (TH), which converts L-tyrosine to L-3, 4-dihydroxyphenylalanine, is a rate-limiting enzyme in the biosynthesis of catecholamines; its activity is regulated by the feedback inhibition of the catecholamine products including dopamine. To rationalize the significant role of the N-terminal sequence Arg(37)-Arg(38) of human TH type 1 (hTH1) in determining the efficiency of feedback inhibition, we produced mutants of which the positively charged Arg(37)-Arg(38) site was replaced by electrically neutral Gly and/or negatively charged Glu and analyzed the degree of inhibition of these mutant enzymes by dopamine. The replacement of Arg by Gly reduced the inhibitory effect of dopamine on the catalytic activity measured in the basic pH range and the replacement of Arg by Glu was enough to abolish the inhibitory effect, although these mutations brought no significant changes to the circular dichroism spectrum. The prediction of the secondary structure of N-terminal residues 1-60 by computer software specified the location of the Arg(37)-Arg(38) sequence in the turn intervening between the two alpha-helices (residues 16-29 and residues 41-59). These results suggest that the positive charge of the amino acid residues at positions 37 and 38 is one of the main factors that maintains the characteristic of the turn and is responsible for the enzyme inhibition by dopamine.

Amino Acid Sequence↗
PubMed2000

Risk factors for posttransfusion graft versus host disease, mediastinitis, and late cardiac tamponade in heart surgery. Survey of 119 Japanese institutions.

OBJECTIVE: Correlations and risk factors remain to be unclarified for post-heart-surgery posttransfusion graft-versus-host disease, mediastinitis, and late cardiac tamponade caused by deteriorated host-defense mechanisms due to cardiopulmonary bypass both with and without steroid usage. METHODS: We sent questionnaires to 298 Japanese cardiovascular institutions asking for institution profiles, including infection control, steroid use in cardiopulmonary bypass, and prevalence of mediastinitis, late cardiac tamponade, and posttransfusion graft-versus-host disease during 1994. The overall prevalence of posttransfusion graft-versus-host disease since the start of service (from establishment of institution to date) was also requested. RESULTS: The number of pump cases at the 119 institutions responding (40%) were 91.6 +/- 67.9 cases/institution (total = 10,904). The prevalence of mediastinitis was 1.2 +/- 1.8 and that of late cardiac tamponade 1.0 +/- 1.8%. Posttransfusion graft-versus-host disease occurred in 1 of 10,904 patients (0.01%) during 1994 at an institution where steroids and nonirradiated blood were used in surgery. The simple institutional mean prevalence of posttransfusion graft-versus-host disease since establishing institutions was 0.08 +/- 0.13%. Of the 119 institutions surveyed, 86 used steroids in all pump cases (72%); 11 institutions used steroids in a limited number of cases (9%). The institutional mean of methylprednisolone-converted steroid dose was 21.5 +/- 16.4 mg/kg (n = 119). In multivariate regression analysis, operation time (p = 0.005) for mediastinitis, steroid usage (all, limited, or no cases) (p = 0.01) and % aneurysm (p = 0.05) for late cardiac tamponade, and steroid dosage (p = 0.002) for posttransfusion graft-versus-host disease were identified as significant risk factors. CONCLUSION: Our results suggest that massive steroid administration for cardiopulmonary bypass may increase the risk of posttransfusion graft-versus-host disease and late cardiac tamponade, but not mediastinitis.

Aged↗
PubMed2000

Imaging features of myoepithelioma arising from the hard palate. A case report.

A 53-year-old Japanese woman presented with a mass of the hard palate that was histologically diagnosed as myoepithelioma. By CT, the well-demarcated ovoid isodense mass showed faint contrast enhancement. By MR imaging, the mass was homogeneous and isointense on T1-weighted images with homogeneous enhancement after administration of contrast material and markedly hyperintense on T2-weighted images. Myoepithelioma should be kept in mind as differential diagnosis of hard palatine tumors.

Actins↗
PubMed2000

Electrolyte disorders following massive insulin overdose in a patient with type 2 diabetes.

We present a case of a 47-year-old man with Type 2 diabetes mellitus who attempted suicide with 2,100 U of insulin injected subcutaneously. Administration of dextrose intravenously was required to maintain the blood glucose concentration normally for 5 days. Moreover, hypokalemia, hypophosphatemia, and hypomagnesemia were also seen for 24 hours after insulin injection. The serum phosphorus and magnesium concentrations decreased to nadirs of 1.6 mg/dl and 1.6 mg/dl respectively 7 hours after insulin injection. Electrolyte disorders other than hypokalemia may be induced in hypoglycemic patients by massive insulin overdose.

Blood Glucose↗
PubMed2000

Cell cycle-independent down-regulation of BCL-2 protein expression in differentiating HL-60 cells.

To understand the relationship between bcl-2 protein expression and the cell cycle during the processes of differentiation, we examined bcl-2 protein levels expressed during cell cycle phases in differentiating HL-60 human leukemia cells by using a two-color flow cytometric method. In exponentially proliferating HL-60 cells bcl-2 protein was constitutively expressed throughout the cell cycle phases, but a small population of G0/G1 cells expressed decreased levels of protein as compared with other cell cycle phases. HL-60 cells can be induced to differentiate to granulocytic pathway by retinoic acid or dimethylsulfoxide, and to monocytic/macrophagic pathway by 1, 25 dihydroxyvitamin D3 or 12-O-tetradecanoylphorbol -13-acetate. During treatment with any of these inducing agents, bcl-2 protein expression was time-dependently down-regulated after 24 h. A two-color flow cytometric analysis revealed that this down-regulation occurred throughout cell cycle phases, indicating that bcl-2 protein expression was down-regulated in cell cycle-independent manner during induction of differentiation in HL-60 cells. To our knowledge, this is the first demonstration suggesting that the regulation of bcl-2 protein expression is not related to the cell cycle during induction of differentiation in HL-60 cells.

Cell Cycle↗
PubMed1999

Expression of human tyrosine hydroxylase type I in Escherichia coli as a protease-cleavable fusion protein. Short communication.

Wild-type and N-terminal 35-, 38-, and 44-amino acid-deleted mutants of human tyrosine hydroxylase type 1 (hTH1) fused to maltose-binding protein via the target sequence for a restriction protease were expressed in Escherichia coli and purified. The fused protein was treated with the restriction protease factor Xa or enterokinase to isolate hTH1 from the fused form. The treatment of fused wild-type and 35-amino acid-deleted mutant with factor Xa and enterokinase caused non-specific cleavages in the vicinity of the phosphorylation sites, Ser19 and Ser40, due to the flexible conformation of the N-terminus of hTH1.

ATP-Binding Cassette Transporters↗
PubMed1999

Cellular uptake of fluvastatin, an inhibitor of HMG-CoA reductase, by rat cultured hepatocytes and human aortic endothelial cells.

AIMS: To clarify the mechanism for cellular uptake of fluvastatin (FV) into rat primary cultured hepatocytes and human aortic endothelial cells (HAEC). METHODS: Rat primary cultured hepatocytes and Endocell-AO as normal human aortic endothelial cells were used. Effects of incubation time, concentration- and temperature-dependency on cellular FV uptake were investigated after incubation with [14C]-FV and its enantiomers, (+)-FV and (-)-FV. Rat primary cultured hepatocytes were washed with either Na+-containing buffer or Na+-free buffer and incubated with metabolic inhibitors or bile acids. Intracellular radioactivity was measured by liquid scintillation counting. The determination of intracellular unchanged FV and its enantiomers was carried out by stereospecific h.p.l.c. RESULTS: In rat cultured hepatocytes, concentration- and temperature-dependent saturable uptake of [14C]-FV was observed (Km=37.6 microm, V max=869 pmol (mg protein)-1 min-1 ), suggesting a specific uptake mechanism. The uptake of each enantiomer also showed a specific uptake mechanism as observed for the racemate with no difference between enantiomers; (+)-FV, Km=38.5 microm, V max=611 pmol (mg protein)-1 min-1, (-)-FV, Km=41.5 microm, V max=646 pmol (mg protein)-1 min-1. In the presence of cholate and taurocholate, the uptake of FV was inhibited by 39-46%. Pravastatin inhibited FV uptake by 29%. In the absence of Na+, the uptake of FV was markedly inhibited 91-96% by bile acid. The uptake of FV into HAEC at 37 degrees C and 4 degrees C increased with the concentration of FV, but no saturable uptake was observed. CONCLUSIONS: FV transport system may be, at least in part, Na+- and ATP-dependent, and may have some features in common with the bile acid transport system and the organic anion transport system. Since saturable uptake was not observed in HAEC, FV appears to be taken up into these cells mainly via nonspecific simple diffusion.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1999

Dopamine inhibition of human tyrosine hydroxylase type 1 is controlled by the specific portion in the N-terminus of the enzyme.

Tyrosine hydroxylase (TH), which converts L-tyrosine to L-DOPA, is a rate-limiting enzyme in the biosynthesis of catecholamines; its activity is regulated by feedback inhibition by catecholamine products including dopamine. To investigate the specific portion of the N-terminus of TH that determines the efficiency of dopamine inhibition, wild-type and N-terminal 35-, 38-, and 44-amino acid-deleted mutants (del-35, del-38, and del-44, respectively) of human TH type 1 were expressed as a maltose binding protein fusion in Escherichia coli and purified as a tetrameric form by affinity and size-exclusion chromatography. The fused-form wild-type enzyme possessed almost the same specific enzymatic activity as the previously reported recombinant nonfused form. Although maximum velocities of all N-terminus-deleted forms were about one-fourth of the wild-type value, there was no difference in Michaelis constants for L-tyrosine or (6R)-(L-erythro-1',2'-dihydroxypropyl)-2-amino-4-hydroxy-5,6,7,8-tetrahy dropteridine (6RBPH4) among the four enzymes. The iron contents incorporated into the three N-terminus-deleted mutants were significantly lower than that of wild type. However, there was no substantial difference in incorporated iron contents among the three mutants. The deletion of up to no less than 38 amino acid residues in the N-terminus made the enzyme more resistant to dopamine inhibition than the wild-type or del-35 TH form. Dopamine bound to the del-38 more than to the del-35 TH form. However, when incubation with dopamine was followed by further inhibition with the cofactor 6RBPH4 dopamine was expelled more readily from the del-38 than from the del-35 TH form. These observations suggest that the amino acid sequence Gly36-Arg37-Arg38 plays a key role in determining the competition between dopamine and 6RBPH4 and affects the efficiency of dopamine inhibition of the catalytic activity.

Catalysis↗