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Biomedical subjects

K Chiba

Publications and source records attributed to K Chiba.

At least 73 records · Page 4Linked to original sources
PubMed2000

New alpha-selective thermal glycosylation of acetyl-protected 2-acetamido-2-deoxy-beta-D-glucopyranosyl diphenylphosphinate.

This paper describes new alpha-selective thermal glycosylation using acetyl-protected 2-acetamido-2-deoxy-beta-D-glucopyranosyl diphenylphosphinate (4) as a glycosyl donor. When the glycosylation of 4 with 1-hexanol was carried out under various conditions, the conditions using trimethylsilyl trifluoromethanesulfonate as a promoter in nitromethane at reflux temperature were most suitable for the formation of the alpha anomer. The glycosylation of 4 with the other common alcohols gave corresponding alpha-glycosides in relatively high yields under the conditions. When cholesterol, a very steric hindered alcohol, was used as a glycosyl acceptor, alpha-glycoside was also produced predominantly.

Acetylation↗
PubMed2000

Increased signal intensity of the spinal cord on magnetic resonance images in cervical compressive myelopathy. Does it predict the outcome of conservative treatment?

STUDY DESIGN: Correlation between a lesion of the spinal cord that elicits increased signal intensity (ISI) on magnetic resonance images (MRIs) and the outcome of conservative treatment for cervical compressive myelopathy was retrospectively investigated. OBJECTIVE: To investigate whether ISI could predict the outcome of conservative treatment for cervical compressive myelopathy. SUMMARY OF BACKGROUND DATA: It is unknown whether ISI is related to the outcome of conservative treatment for cervical compressive myelopathy. METHODS: Fifty-two patients with mild cervical myelopathy underwent conservative treatment with a cervical brace. The compressive lesions were spondylosis in 29 patients, disc herniation in 12, and an ossification of the longitudinal ligament in 11. They also underwent MRI (1.5 T), and ISI was evaluated on T2-weighted sagittal and axial images. The ISI areas were classified as focal or multisegmental. Thirty-nine patients underwent follow-up MRI after a mean interval of 2 years, 4 months. The transverse area of the spinal cord was also measured on T2-weighted axial images. The outcome of conservative treatment was assessed using the Japanese Orthopedic Association Score (JOA score). Patients showing either an improvement in the JOA score or with a JOA score of 15 or more were considered to have a satisfactory outcome. RESULTS: The average JOA score was 14.0 +/- 1.4 (range, 10-16) before conservative treatment and 14.4 +/- 1.9 (range, 10-17) at follow-up. The average gain in the JOA score was 0.4 points +/- 1.9 (range, -5 to +6). The outcome was satisfactory in 36 patients (69%). An area of ISI was observed in 34 patients (65%) before treatment (24 focal and 10 multisegmental). A satisfactory outcome was obtained in 78% of the patients without ISI, in 63% of those with focal ISI, and in 70% of those with multisegmental ISI. No statistically significant difference was seen among these three groups in the percentages of patients with satisfactory outcome, JOA scores before and after treatment or transverse spinal cord area. Of the 39 patients who were re-examined by MRI, 28 showed an area of ISI. The ISI regressed in five patients (18%). Satisfactory outcome was obtained in all 5 patients with regression of ISI, in 16 (70%) of the 23 patients without regression of ISI, and in 10 (91%) of the 11 patients without ISI apparent on the the first images (difference, not significant). CONCLUSIONS: Increased signal intensity was not related to a poor outcome of conservative treatment or severity of myelopathy in the patients with mild cervical myelopathy.

Adult↗
PubMed2000

A 130-kDa membrane protein of sperm flagella is the receptor for asterosaps, sperm-activating peptides of starfish Asterias amurensis.

Spermatozoa of the starfish, Asterias amurensis, have a specific receptor for asterosap, a sperm-activating peptide isolated from the jelly coat of homologous eggs. We characterized the receptor by using several asterosap derivatives. Analysis of equilibrium binding of radioactive di-iodinated Bolton-Hunter reagent-labeled asterosap ((125)I(2)-BHP15) to the spermatozoa indicated that the cell has 1.1 x 10(5) binding sites of high affinity (K(d) = 57 pM), and also the receptor showed positive cooperativity for asterosap binding. When spermatozoa were treated with fluorophore-labeled asterosap, the sperm flagella were labeled, indicating that the receptors are mostly localized in the sperm tail. When spermatozoa were reacted with radioactive asterosap prelabeled with photoaffinity cross-linkers, a single 130-kDa membrane protein of sperm flagella was specifically radiolabeled. This result was reproducible regardless of the length of spacer arm of cross-linkers so far studied. Therefore, the 130-kDa protein is likely to be the receptor for asterosaps. Modification of asterosap at the N-terminal region with bulky molecules such as carboxyfluorescein did not affect the activity of asterosap, suggesting that the N-terminus of asterosap is not involved in the ligand-receptor interaction. On the other hand, S-alkylated asterosaps did not compete with (125)I(2)-BHP15 for binding to the receptor, indicating that disulfide linkage of asterosap is essential for the ligand-receptor interaction. The properties of the receptor, high affinity and high concentration, enabled us to apply the fluorescence polarization technique to study the molecular interaction between asterosap and the receptor. Using this method, we performed binding experiments in almost real time and found that divalent cations are significantly involved in the interaction between asterosap and the receptor.

Affinity Labels↗
PubMed2000

Immunosuppressant FTY720 inhibits thymocyte emigration.

One major role of the thymus is to provide the peripheral immune system with mature T cells, but the mechanisms involving the cellular export are not fully understood. In this study, we examined the ability of a novel immunosuppressive reagent, FTY720, to inhibit T cell export from the thymus. Daily administration of FTY720 at a dose of 1 mg / kg resulted in a marked decrease in the number of peripheral blood T lymphocytes. In the thymus, long-term daily administration of FTY720 caused a three- to fourfold increase in the proportion of mature medullary thymocytes (CD4(+)CD8(-) and CD4(-)CD8(+)) as well as a slight decrease in the double-positive cell (CD4(+)CD8(+)) ratio. Phenotypic analysis (TCRalpha beta, H-2K(d), CD44, CD69 and CD24) revealed that these increased subsets represent possible peripheral recent thymic emigrants. High level expression of L-selectin by these subsets further suggests that they were prevented from leaving the thymus. By intrathymic labeling with fluorescein isothiocyanate, only one fourth of labeled cells could be detected in the lymph nodes and in the spleen of FTY720-treated mice compared to saline-treated control mice. Taken together, these results suggest that the immunosuppressive action of FTY720, at least in part, could be due to its inhibitory effect on T cell emigration from the thymus to the periphery.

Animals↗
PubMed2000

Determination of YM992, a novel selective serotonin reuptake inhibitor, in rat and dog plasma by high-performance liquid chromatography with fluorescence detection.

A high-performance liquid chromatographic method with fluorescence detection was developed for the determination of (S)-2-[[(7-fluoro-4-indanyl)oxy]methyl]morpholine monohydrochloride (YM992) in plasma. Plasma samples were extracted with n-hexane under alkali condition. After the organic solvent was evaporated to dryness, the residue was treated with 4-fluoro-7-nitrobezofurazan (NBD-F) in borate buffer (pH 7.5) at room temperature for 20 min. The reaction was terminated with hydrochloric acid and the resultant solution was injected onto HPLC without further purification. No interfering peak was observed at the retention time of YM992 or the internal standard. The calibration curve was linear with the concentration of YM992 up to 200 ng/ml. The limit of quantitation was 1 ng/ml. The intra- and inter-day relative standard deviation was less than 5.6% and 4.1%, respectively, and the intra- and inter-day relative error ranged from -3.0% to 17.2% and 2.8% to 7.5%, respectively. Using the assay, the plasma concentration of YM992 could be determined up to 8 and 10 h after the oral administration of YM992 to rats and dogs, respectively.

4-Chloro-7-nitrobenzofurazan↗
PubMed2000

Effect of FTY720, a novel immunosuppressant, on adjuvant-induced arthritis in rats.

OBJECTIVE AND DESIGN: Anti-arthritic effect of FTY720, a novel immunosuppressant, was compared with those of immunosuppressants cyclosporin A and tacrolimus in adjuvant-induced arthritis in rats. MATERIAL: Male LEW rats. TREATMENT: FTY720 (0.03-0.3 mg/kg), cyclosporin A (1-10 mg/kg) or tacrolimus (0.3-3 mg/kg) were orally administered to rats for 21 days beginning on the day (day 0) of adjuvant inoculation. In addition, the anti-arthritic effect of FTY720 (0.3 mg/kg) and cyclosporin A (10 mg/kg) were evaluated by administration to animals for 5 consecutive days (days 2-6, 6-10, and 10-14). METHODS: Adjuvant-induced arthritis was produced by intradermal injection of 0.5 mg heat-killed Mycobacterium tuberculosis. Hindpaw edema was measured plethysmographically. The day of arthritis onset was determined macroscopically. Bone degradation was determined by radiography. Peripheral blood leukocytes were classified microscopically. RESULTS: All test compounds inhibited the incidence of arthritis, hindpaw edema and bone destruction. In addition, FTY720 but not cyclosporin A or tacrolimus markedly decreased the number of peripheral blood lymphocytes. FTY720 treatment on days 6 to 10 inhibited the bone destruction and hindpaw edema. CONCLUSION: These results suggest that the anti-arthritic effect of FTY720 in this adjuvant-induced arthritic model was more potent than those of cyclosporin A and tacrolimus. FTY720 administered on days 6 to 10 showed the inhibitory effect on the bone destruction and hindpaw edema. FTY720 may be effective in the treatment of rheumatoid arthritis.

Animals↗
PubMed2000

Lack of differences in diclofenac (a substrate for CYP2C9) pharmacokinetics in healthy volunteers with respect to the single CYP2C9*3 allele.

OBJECTIVES: Evidence exists to suggest that diclofenac is metabolised by CYP2C9. The present study was undertaken in order to evaluate the effect of the single CYP2C9*3 variant on drug metabolism using diclofenac as a probe drug. METHODS: A single dose of diclofenac was administered orally to 12 healthy subjects in whom the genotype of CYP2C9 had been determined previously. The disposition kinetics of diclofenac were compared between homozygotes for the wild type (CYP2C9*1/*1, n = 6) and heterozygotes for the Leu359 variant (CYP2C9*1/*3, n = 6). RESULTS: For diclofenac, the following kinetic parameters were observed in the CYP2C9*1/*1 and CYP2C9*1/*3 subjects, respectively (mean +/- SD): apparent oral clearance (ml/kg/h) 355.8 +/- 56.9 and 484.4 +/- 155.3; area under plasma concentration time curve (microg h/ml) 2.7 +/- 0.7 and 1.9 +/- 0.6. The formation clearance of 4'-hydroxydiclofenac (ml/kg/h) was 63.6 +/- 19.1 in the CYP2C9*1/*1 subjects compared with 75.9 +/- 27.6 in the CYP2C9*1/*3 subjects. There were no significant differences in any of the kinetic parameters for either diclofenac disposition or formation clearance of 4'-hydroxydiclofenac between the two genotype groups. CONCLUSION: Since the disposition kinetics of diclofenac does not change in subjects with the single CYP2C9*3 mutant allele, it is suggested that the effects of CYP2C9 polymorphisms on the drug metabolism tend to be substrate specific.

Adult↗
PubMed2000

Identification of human cytochrome P450 isoforms involved in the 7-hydroxylation of chlorpromazine by human liver microsomes.

Studies to identify the cytochrome P450 (CYP) isoform(s) involved in chlorpromazine 7-hydroxylation were performed using human liver microsomes and cDNA-expressed human CYPs. The kinetics of chlorpromazine 7-hydroxylation in human liver microsomes showed a simple Michaelis-Menten behavior. The apparent Km and Vmax values were 3.4+/-1.0 microM and 200.5+/-83.7 pmol/min/mg, respectively. The chlorpromazine 7-hydroxylase activity in human liver microsomes showed good correlations with desipramine 2-hydroxylase activity (r = 0.763, p < 0.05), a marker activity for CYP2D6, and phenacetin O-deethylase activity (r = 0.638, p < 0.05), a marker activity for CYP1A2. Quinidine (an inhibitor of CYP2D6) completely inhibited while alpha-naphthoflavone (an inhibitor of CYP1A2) marginally inhibited the chlorpromazine 7-hydroxylase activity in a human liver microsomal sample showing high CYP2D6 activity. On the other hand, alpha-naphthoflavone inhibited the chlorpromazine 7-hydroxylase activity to 55-65% of control in a human liver microsomal sample showing low CYP2D6 activity. Among eleven cDNA-expressed CYPs studied, CYP2D6 and CYP1A2 exhibited significant activity for the chlorpromazine 7-hydroxylation. The Km values for the chlorpromazine 7-hydroxylation of both cDNA-expressed CYP2D6 and CYP1A2 were in agreement with the Km values of human liver microsomes. These results suggest that chlorpromazine 7-hydroxylation is catalyzed mainly by CYP2D6 and partially by CYP1A2.

Antipsychotic Agents↗
PubMed2000

The significance of timing of FTY720 administration on the immunosuppressive effect to prolong rat skin allograft survival.

FTY720, a potent immunosuppressant, dramatically decreases the number of peripheral blood lymphocytes within a few hours after administration. The current study assessed the significance of timing of FTY720 administration on the immunosuppressive effect to prolong rat skin allograft survival (WKAH donor to F344 recipient). The median survival time of allografts was 7 days in the control recipients. FTY720 (1 mg/kg/day) significantly prolonged allograft survival when administered from days 0 and 3, but failed to exert an immunosuppressive effect when administered from day 4. Intragraft T cells, especially CD8(+) T cells, were markedly increased in number from day 4 to 6, peaking on day 5 in control recipients. FTY720 markedly decreased the number of intragraft CD8(+) T cells on day 5 when administered from days 0 and 3. In recipients administered with FTY720 from day 4, the number of intragraft CD8(+) T cells were only partially decreased on day 5. Intragraft CD8(+) T-cell number in those recipients on day 5 was almost the same as that in control recipients on day 4. In addition, FTY720 did not affect the increase in frequency of CD25(+) cells in the CD8(+) T-cell subset in allografts. It is likely that recipients treated with FTY720 from day 4 reject allografts by intragraft immune responses involved in CD8(+) T cells which had infiltrated before day 4, similar to control recipients. These findings suggest that FTY720 should be administered before increase in T cell infiltration into grafts to inhibit acute allograft rejection.

Animals↗
PubMed2000

Frequencies of CYP2D6 mutant alleles in a normal Japanese population and metabolic activity of dextromethorphan O-demethylation in different CYP2D6 genotypes.

AIMS: To determine the frequencies of 11 CYP2D6 mutant alleles (CYP2D6*2, *3, *4, *5, *8, *10, *11, *12, *14, *17 and *18), and their relation to the metabolic capacity of CYP2D6 in Japanese subjects. METHODS: One hundred and sixty-two unrelated healthy Japanese subjects were genotyped with the polymerase chain reaction amplification method and 35 subjects were phenotyped with dextromethorphan. RESULTS: The frequencies of CYP2D6*2,*5, *10 and *14 were 12.9, 6.2, 38.6 and 2.2% in our Japanese subjects, respectively. CYP2D6*3, *4, *8, *11, *12, *17 and *18 were not detected. The mean log metabolic ratio of dextromethorphan in subjects with genotypes predicting intermediate metabolizers was significantly greater than that of heterozygotes for functional and defective alleles. CONCLUSIONS: CYP2D6*5 and CYP2D6*14 are the major defective alleles found in Japanese subjects. In addition, CYP2D6*10 may play a more important role than previously thought for the treatment of Japanese patients with drugs metabolized by CYP2D6.

Adult↗
PubMed2000

Identification of cytochrome P450 isoform involved in the metabolism of YM992, a novel selective serotonin re-uptake inhibitor, in human liver microsomes.

1. In vitro studies were conducted to identify the hepatic cytochrome P450 isoform involved in the metabolism of YM992, ((S)-2-[[(fluoro-4-indanyl)oxy]methyl]morpholine monohydrochloride), a novel serotonin re-uptake inhibitor, in human liver microsomes. 2. Microsomes prepared from yeast expressing CYP1A1, CYP1A2 and CYP2D6 effectively metabolized YM992. A significant correlation was observed between the rate of YM992 metabolism and 7-ethoxyresorufin O-deethylation, CYP1A1/2 specific activity, in liver microsomes from 16 individual donors (r2 = 0.628, p < 0.001). Alpha-naphtoflavone and isosafrole, CYP1A1/2 inhibitors, suppressed the metabolism of YM992 in human liver microsomes in a concentration-dependent manner. 3. The metabolism of YM992 in human liver microsomes was inhibited by approximately 95% by antibodies which recognize both CYP1A1 and CYP1A2 whereas antibodies specific for CYP1A1 did not show inhibitory effects. 4. The same major metabolites, M6 and M7, were generated from YM992 after incubation with human liver microsomes and recombinant human CYP1A2. 5. These results suggest that the metabolism of YM992 in human liver microsomes is mainly catalysed by CYP1A2, and that YM992 might increase plasma concentration of concomitant drugs metabolized by CYP1A2 due to competitive inhibition.

Benzoflavones↗
PubMed2000

Developmental changes in localization of the main ganglioside during sea urchin embryogenesis.

Ganglioside M5 (NeuGcalpha2-6Glcbeta1-1'Cer), the main ganglioside in sea urchin and sand dollar eggs, exists mainly in the endoplasmic reticulum and yolk granules in unfertilized eggs. To study the localization of ganglioside M5 after fertilization, early embryos were stained with an anti-ganglioside M5 monoclonal antibody. Using immunofluorescent and immunoelectron microscopy, intense label was observed in the outer surface and cytoplasm of embryos. These results indicate that ganglioside M5 was secreted during embryogenesis and localized in the extracellular matrix (ECM). When living embryos were incubated in sea water containing 7-nitrobenz-2-oxa-1,3-diazole labeled-ganglioside M5 (NBD-M5), the ECM and plasma membrane were strongly stained. Since the localization of NBD-M5 in the ECM was similar to that of extracellular M5, NBD-M5 was likely to be useful to examine the fate of extracellular ganglioside M5. Interestingly, NBD-M5 was incorporated in subcortical vesicles during embryogenesis, suggesting that the extracellular ganglioside M5 is transported into the cytoplasm. When fertilized eggs were incubated with NBD-M5 and tetramethylrhodamine dextran (a marker dye for endocytotic vesicles), colocalization of the dyes was observed in the vesicles. Thus, it was concluded that NBD-M5 in the ECM and/or plasma membrane was internalized in the cells by endocytosis, suggesting that extracellular M5 is transported from the ECM to endocytotic vesicles.

Animals↗
PubMed2000

QT-prolonging effects of sparfloxacin, a fluoroquinolone antibiotic, assessed in the in vivo canine model with monophasic action potential monitoring.

Sparfloxacin, a fluoroquinolone antibacterial agent, prolongs cardiac repolarization, which may predispose to torsades de pointes. This study was designed to assess simultaneously the hemodynamic and electrophysiologic effects of sparfloxacin using the halothane-anesthetized, closed-chest in vivo canine model (n = 6). Sparfloxacin was intravenously administered in the following two doses with a pause of 20 min, a clinically relevant dose of 3.0 mg/kg/10 min and a 10 times higher dose of 30 mg/kg/10 min. After the low dose of sparfloxacin, cardiac output increased, heart rate decreased, and ventricular repolarization and refractory periods were prolonged. After the high dose, cardiac output increased, whereas heart rate and mean blood pressure decreased, and ventricular repolarization and effective refractory periods were prolonged. The increment was greater in repolarization than in refractoriness, indicating an increase of electrical vulnerability. Because sparfloxacin prolonged repolarization in a reverse use-dependent manner, its negative chronotropic effect may have potentiated the QT prolongation. Left ventricle preload, left ventricular contraction, and AV nodal as well as intraventricular conduction were minimally affected. These results suggest that caution should be used when administering sparfloxacin to patients having risk factors for QT prolongation.

Action Potentials↗
PubMed2000

CYP2C9 Ile359 and Leu359 variants: enzyme kinetic study with seven substrates.

To assess the effects of Ile359 to Leu359 change on CYP2C9-mediated metabolism, we performed site-directed mutagenesis and cDNA expression in yeast for CYP2C9 and examined in detail the kinetics of seven metabolic reactions by wild-type CYP2C9 (Ile359) and its Leu359 variant. For the metabolism of all the substrates studied, the Leu359 variant exhibited smaller Vmax/Km values than did the wild-type. The differences in the Vmax/Km values between the wild-type and the Leu359 variant varied from 3.4-fold to 26.9-fold. The Leu359 variant had higher Km values than did the wild-type for all the reactions studied. Among the seven reactions studied, the greatest difference in the Vmax values between the wild-type and the Leu359 variant was for piroxicam 5'-hydroxylation (408 versus 19 pmol/min/nmol P450), whereas there were no differences in the Vmax values between the wild-type and the Leu359 variant for diclofenac 4'-hydroxylation and tolbutamide methylhydroxylation. These results indicate that the Ile359 to Leu359 change significantly decreases the catalytic activity of all the CYP2C9-mediated metabolisms studied, whereas the extent of the reduction in activity and changes of the kinetic parameters varies between substrates. Moreover, the amino acid substitution decreased the enantiomeric excess in the formation of 5-(4-hydroxyphenyl)-5-phenylhydantoin from phenytoin.

Aryl Hydrocarbon Hydroxylases↗
PubMed2000

Evaluation of neurotoxicity of alzheimer's amyloid beta protein (beta42) in cultured hippocampal cells and its prevention by propentofylline.

Neurotoxicity of beta42 (20 microM) in cultured rat hippocampal neurons was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction and lactate dehydrogenase (LDH) release methods as quantitative assays of cell death, and both methods indicated that propentofylline (PPF) had the ability to protect the neurons against the toxicity, although these two assay methods revealed different mechanisms for the toxic effect of beta42. Promotion of the active exocytotic system of the cells was suggested after treatment with beta42 in the MTT assay and in determination of 9-aminoacridine (AA) excretion from the preloaded cells after 24-h treatment with beta42. The promotion of AA exocytosis was blocked by the addition of PPF (20 microg/ml). The preventive effect of PPF on the neurotoxicity of beta42 has been proposed to be caused by elevation of the intracellular level of cAMP as a result of depression of the hydrolytic activity of cells.

Amyloid beta-Peptides↗