Biomedical subjects

K Takiguchi

Publications and source records attributed to K Takiguchi.

At least 19 recordsLinked to original sources

PubMed2006

Arrayed-waveguide grating with uniform loss properties over the entire range of wavelength channels.

We propose an arrayed-waveguide grating that shows uniform loss properties over the entire range of wavelength channels by combining two light waves with adjacent diffraction orders at its output. We applied this configuration to an arrayed-waveguide grating with 32 channels and a 50 GHz spacing and were able to reduce the deviations in loss to less than 1.0 and 1.8 dB over one and three free spectral ranges, respectively.

Journal Article↗

PubMed2005

Integrated-optic variable delay line and its application to a low-coherence reflectometer.

We propose a large-scale variable delay line based on planar light-wave circuit technology and its application as a reference arm in an optical low-coherence reflectometer. This variable delay line is composed of 16 asymmetrical delay arm pairs sandwiched between 2 optical switches, which select the path for a needed delay. This configuration enables us to eliminate the need for a moving part in the reflectometer. We can scan the reference arm over a length of 262.1 mm with a step of less than 1.0 microm in air and achieve reflectometer sensitivity of about -47 dB.

Journal Article↗

PubMed2003

Mechanical analyses of morphological and topological transformation of liposomes.

Liposomes are micro-compartments made of lipid bilayer membranes possessing the characteristics quite similar to those of biological membranes. To form artificial cell-like structures, we made liposomes that contained subunit proteins of cytoskeletons: tubulin or actin. Spherical liposomes were transformed into bipolar or cell-like shapes by mechanical forces generated by the polymerization of encapsulated subunits of microtubules. On the other hand, disk- or dumbbell-shaped liposomes were developed by the polymerization of encapsulated actin. Dynamic processes of morphological transformations of liposomes were visualized by high intensity dark-field light microscopy. Topological changes, such as fusion and division of membrane vesicles, play an essential role in cellular activities. To investigate the mechanism of these processes, we visualized the liposomes undergoing topological transformation in real time. A variety of novel topological transformations were found, including the opening-up of liposomes and the direct expulsion of inner vesicles.

Biomechanical Phenomena↗

PubMed2003

Significantly lower rate of smoking in female compared to male patients with lung adenocarcinoma.

To examine the relationship between smoking and lung adenocarcinoma in female patients, we performed a retrospective chart review for 470 patients with lung adenocarcinoma at our hospital. The proportions of non-smokers were higher in female patients than those of male patients. A significant difference in smoking history was found between female and male patients. Not only active smoking but also passive smoking may influence the development of female lung adenocarcinoma, which reinforces the need for effective programmes aimed refraining from smoking and cessation among men as well as women.

Adenocarcinoma↗

PubMed2002

Characterization of the portal signal in a nonsteady hyperglycemic state in conscious dogs.

To characterize the "portal signal" in a nonsteady hyperglycemic state, the kinetic relationship between net hepatic glucose balance (NHGB) and either hepatic glucose load (HGL) or plasma insulin level was determined during glucose infusion using a catheter technique in 36 conscious dogs. Glucose was infused intraportally (Po group) and peripherally (Pe group) at 39, 56, and 83 micromol x kg(-1) x min(-1) over 2 h. There was a linear relationship between mean NHGB and either mean HGL or plasma insulin levels at each rate in either delivery (HGL: Po r = 0.99, Pe r = 0.95; insulin: Po r = 99, Pe r = 0.79). The threshold levels for net hepatic glucose uptake were 3.8 and 11.7 mmol/l for plasma glucose and 65 and 392 pmol/l for plasma insulin, respectively. The slope of the regression line against the abscissa was four times larger in portal than in peripheral delivery (HGL: Po 0.20 vs. Pe 0.05, P < 0.05; insulin: Po 0.19 vs. Pe 0.04, P < 0.05). These results suggest that the portal signal overrules the threshold of glucose for hepatic uptake by increasing hepatic extraction rate in a nonsteady hyperglycemic state.

Animals↗

PubMed2002

Comparison of insulinotrophic actions of nateglinide with glibenclamide dissociated from absorption in conscious dogs.

Nateglinide is more rapidly absorbed than glibenclamide. Therefore, the different absorption kinetics of both drugs were eliminated by intraportal administration in conscious fasted dogs. The plasma insulin profiles were compared under similar kinetic changes in plasma drug concentrations. After a priming dose of nateglinide (1 mg/kg. 5 min) or glibenclamide (40 microg/kg. 5 min), plasma drug concentrations reached a peak at 4 minutes (nateglinide, 80 +/- 5 micromol/L, n = 6 and glibenclamide, 263 +/- 60 nmol/L, n = 6) followed by a sustained level at approximately 30% of the peak concentration at 30 minutes. Nateglinide led to a rapid and constant reduction in arterial glucose of approximately 30% basal, while glibenclamide promoted a gradual decrease to approximately 50% basal at 120 minutes. An increase in plasma insulin level by nateglinide of 4 times basal (218 +/- 58 pmol/L v 47 +/- 3 pmol/L, P <.05, n = 6) occurred at 6 to 10 minutes followed by sustained release of 1.4 times basal (67 +/- 15 pmol/L, n = 6). The insulin surge was more than doubled (484 +/- 209 pmol/L, n = 6) under a euglycemic clamp. Insulin release by glibenclamide increased gradually reaching 10-fold basal (449 +/- 166 pmol/L, n = 6) at 60 minutes. This was not enhanced during a euglycemic clamp. Lowering the primed doses of nateglinide resulted in a diminished peak plasma insulin concentration. In contrast, glibenclamide caused only a slower increase, but eventually reaching a similar peak. By increasing the continuous infusion of nateglinide, the sustained insulin release was not altered. Glibenclamide, but not nateglinide, evoked prompt and sustained insulin release in the continuing presence of the other. These results are consistent with the concept that nateglinide produces a quick, but very short-lived, interaction with sulfonylurea (SU)-receptors on plasma membrane by free access of the drug from the cell exterior. In contrast, glibenclamide promotes a slow and longer interaction with the receptor by distribution of the drug into the cell inferior. We conclude, therefore, that not only the different kinetics of gastrointestinal (GI) absorption, but also the inherent difference in the interaction with beta cells is attributed to the different insulin release characteristics between nateglinide and glibenclamide in vivo.

ATP-Binding Cassette Transporters↗

PubMed2001

Inhibitory effect of M50054, a novel inhibitor of apoptosis, on anti-Fas-antibody-induced hepatitis and chemotherapy-induced alopecia.

M50054, 2,2'-methylenebis (1,3-cyclohexanedione), was identified as a novel inhibitor of apoptosis (programmed cell death) using an in vitro cell death assay system induced in human Fas-expressing WC8 cells by soluble human Fas ligand. Furthermore, M50054 inhibited the apoptotic cell death of U937, a human monocytic leukemic cell line, induced by anticancer agents such as etoposide; it was also confirmed that M50054 inhibited apoptotic features such as DNA fragmentation and phosphatidylserine exposure in these cells. These anti-apoptotic effects were attributable to inhibition of caspase-3 activation. Additionally, M50054 significantly inhibited anti-Fas-antibody-induced elevation of plasma alanine aminotransferase and aspartate aminotransferase. Alopecia (hair loss) symptoms were also significantly improved with topical treatment with M50054. In conclusion, M50054 inhibits apoptosis induced by a variety of stimuli via inhibition of caspase-3 activation, and may thus be effective for hepatitis and chemotherapy-induced alopecia.

Alopecia↗

PubMed2001

Capabilities of liposomes for topological transformation.

Dynamic behaviors of liposomes caused by interactions between liposomal membranes and surfactant were studied by direct real-time observation by using high-intensity dark-field microscopy. Solubilization of liposomes by surfactants is thought to be a catastrophic event akin to the explosion of soap bubbles in the air; however, the actual process has not been clarified. We studied this process experimentally and found that liposomes exposed to various surfactants exhibited unusual behavior, namely continuous shrinkage accompanied by intermittent quakes, release of encapsulated liposomes, opening up, and inside-out topological inversion.

Lipids↗

PubMed2000

Bcl-2 antiapoptotic protein mediates verotoxin II-induced cell death: possible association between bcl-2 and tissue failure by E. coli O157:H7.

Verotoxin II (VTII: or Shiga-like toxin 2) is a key factor for Escherichia coli O157:H7-induced multiple tissue failure and contains a pentameric sequence (NWGRI) similar to the Bcl-2 homolog domain, BH1. In the current study, we demonstrate that VTII, but not VTI, interacts with Bcl-2 through each BH1 domain pentameric sequence (NWGRI) and that the VTII/Bcl-2 complex is necessary for cell-death induction in target cells. VTII translocates to mitochondria and induces cell death only when target cells are expressing Bcl-2. In addition, interruption of VTII-Bcl-2 complex formation by a pentameric BH1 synthetic peptide suppresses VTII-induced cell death. In the present article, we propose that Bcl-2 mediates VTII-induced target cell death by the interaction with each pentameric sequence of BH1 domain.

Amino Acid Sequence↗

PubMed2000

Structural and functional study of K453E mutant protective protein/cathepsin A causing the late infantile form of galactosialidosis.

To clarify the molecular basis of the late infantile form of galactosialidosis, we characterized a defective protective protein/cathepsin A (PPCA) gene product with the K453E mutation newly found in an Arabic patient with this disease. Immunocytochemical, expression, and metabolic studies revealed that the precursor PPCA was synthesized but not processed to the mature form, and it was degraded in the mutant. A structural model of the mutant PPCA was constructed by amino acid substitution of 453glutamic acid for lysine in the crystal structure of the wild type PPCA precursor reported. The results show that the K453E mutation is located at the dimer interface of the PPCA and reduces the hydrogen bond formation in the dimer. This structural change may cause instability of the PPCA dimer.

Amino Acid Substitution↗

PubMed2000

Molecular and structural studies of Japanese patients with sialidosis type 1.

To gain insight into the pathogenesis of sialidosis type 1, we performed molecular investigations of two unrelated Japanese patients. Both of them are compound heterozygotes for base substitutions of 649G-to-A and 727G-to-A, which result in amino acid alterations V217M and G243R, respectively. Using homology modeling, the structure of human lysosomal neuraminidase was constructed and the structural changes caused by these missense mutations were deduced. The predicted change due to V217M was smaller than that caused by G243R, the latter resulting in a drastic, widespread alteration. The overexpressed gene products containing these mutations had the same molecular weight as that of the wild type, although the amounts of the products were moderately decreased. A biochemical study demonstrated that the expressed neuraminidase containing a V217M mutation was partly transported to lysosomes and showed residual enzyme activity, although a G243R mutant was retained in the endoplasmic reticulum/Golgi area and had completely lost the enzyme activity. Considering the data, we surmise that the V217M substitution may be closely associated with the phenotype of sialidosis type 1 with a late onset and moderate clinical course.

Adult↗

PubMed2000

Artificial phosphorylation removes Gelsolin's dependence on calcium.

Gelsolin is one of the best known actin-binding proteins with several distinct activities regulated by calcium. Using a kinase fraction isolated from mitotic HeLa cells, we found that the plasma form of gelsolin can be phosphorylated at a site located within the NH2-terminus region which does not exist in the cytoplasmic form. After this phosphorylation, gelsolin no longer requires Ca2+ for activity; it severs and subsequently caps actin filaments, and nucleates filament formation in Ca2+-free solution. These findings may clarify the mechanism of gelsolin regulation by Ca2+, and indicate that changes in electrical interactions between the NH2- and COOH-terminal ends are important for this regulation. Moreover, since only a single site is phosphorylated, and since the phosphorylated region does not contribute to this protein's own activity, the results suggest that a single chemical charge modification at a site away from the protein's core structure, such as this phosphorylation site, is sufficient to alter the protein's function.

Actins↗

PubMed1999

A statistical mechanical theory for the adsorption of protein to liposomal membranes.

The observed topology change of spherical lipid vesicles to coffee cups [Saitoh, A. et al., Proc. Natl. Acad. Sci. USA 95 (1998) 1026] was analyzed by a statistical mechanical theory. The topology change was due to the adsorption of talin molecules to the orifices of the coffee cups. The adsorption isotherm of talin between an aqueous solution and the vesicle membrane was analyzed by taking account of the bending energy of the membrane. The equilibrium is determined by the balance of the energy gain for the adsorption of talin to the periphery of the vesicles and the change of the bending energy of the membrane due to the shape change. The observed coexistence of coffee cups and sheet-like vesicles were reproduced. Vesicles with two orifices were also analyzed and theoretically reproduced.

Journal Article↗

PubMed1999

Stable expression of protective protein/cathepsin A-green fluorescent protein fusion genes in a fibroblastic cell line from a galactosialidosis patient. Model system for revealing the intracellular transport of normal and mutated lysosomal enzymes.

Fibroblastic cell lines derived from a galactosialidosis patient, stably expressing the chimaeric green fluorescent protein variant (EGFP) gene fused to the wild-type and mutant human lysosomal protective protein/cathepsin A (PPCA) cDNA, were first established as a model system for revealing the sorting and processing of lysosomal enzymes and for investigating the molecular bases of their deficiencies. In the cell line expressing the wild-type PPCA-EGFP chimaera gene (EGFP-PPwild), an 81 kDa form (27 kDa EGFP fused to the C-terminus of the 54 kDa PPCA precursor) was produced, then processed into the mature 32/20 kDa two-chain form free of the EGFP domain. The intracellular cathepsin A, alpha-N-acetylneuraminidase and beta-galactosidase activities, which are deficient in the parent fibroblastic cells, could also be significantly restored in the cells. In contrast with the uniform and strong fluorescence throughout the cytoplasm and nucleus in the mock-cell line expressing only EGFP cDNA, weak reticular and punctate fluorescence was distributed throughout the EGFP-PPwild cell line. Bafilomycin A1, a potent inhibitor of vacuolar ATPase and intracellular acidification, induced the distribution of Golgi-like perinuclear fluorescence throughout the living and fixed cells, in which only the 81 kDa product was detected. After removal of the agent, time-dependent transport of the chimaeric protein from the Golgi apparatus to the prelysosomal structure in living cells was monitored with a confocal laser scanning microscope system. Leupeptin caused the distribution of lysosome-like granular fluorescence throughout the cytoplasm in the fixed cells, although it was hardly observed in living cells. The latter agent also dose-dependently induced an increase in the intracellular amount of the 81 kDa product containing the EGFP domain and inhibited the restoration of cathepsin A activity in the EGFP-PPwild cells after the removal of bafilomycin A1. In parallel, both the mature two-chain form and PPCA function disappeared. These results suggested that the chimaera gene product was transported to acidic compartments (endosomes/lysosomes), where proteolytic processing of the PPCA precursor/zymogen, quenching of the fluorescence, and random degradation of the EGFP portion occurred. A cell line stably expressing a chimaeric gene with a mutant PPCA cDNA containing an A1184-->G (Y395C) mutation, commonly detected in Japanese severe early-infantile type of galactosialidosis patients, showed an endoplasmic reticulum (ER)-like reticular fluorescence pattern. The PPCA-immunoreactive gene product was hardly detected in this cell line. The mutant chimaeric product was suggested to be degraded rapidly in the ER before transport to post-ER compartments. A cell line expressing the chimaeric gene with a T746-->A (Y249N) PPCA mutation exhibited both ER-like reticular and granular fluorescence on the reticular structure that was stronger than that in the EGFP-PPwild cells. Some of them contained large fluorescent inclusion-body-like structures. The ineffectiveness of transport inhibitors in the distribution changes in the two mutant chimaeric proteins suggested that they were not delivered to acidic compartments. Therefore this expression system can possibly be applied to the direct analysis of the sorting defects of mutant gene products in living cells and will be useful for the molecular investigation of lysosomal diseases, including galactosialidosis.

Amino Acid Sequence↗

PubMed1999

Morphogenesis of liposomes encapsulating actin depends on the type of actin-crosslinking.

To study the morphogenesis of cells caused by the organization of their internal cytoskeletal network, we characterized the transformation of liposomes encapsulating actin and its crosslinking proteins, fascin, alpha-actinin, or filamin, using real-time high-intensity dark-field microscopy. With increasing temperature, the encapsulated G-actin polymerized into actin filaments and formed bundles or gels, depending on the type of actin-crosslinking protein that was co-encapsulated, causing various morphological changes of liposomes. The differences in morphology among transformed liposomes indicate that actin-crosslinking proteins determine liposome shape by organizing their specific actin networks. Morphological analysis reveals that the crosslinking manner, i.e. distance and angular flexibility between adjacent crosslinked actin filaments, is essential for the morphogenesis rather than their binding affinity and stoichiometry to actin filaments.

Actinin↗

PubMed1999

Nerve-sparing surgery for advanced rectal cancer patients: special reference to Dukes C patients.

Several nerve-sparing operations for advanced rectal cancer that aim to preserve genitourinary function without compromising tumor clearance have been developed in Japan. The aim of this study was to evaluate the survival and local recurrence of these procedures in Dukes B and C patients. A total of 177 patients with advanced rectal cancer underwent curative nerve-sparing surgery (NSS) over the last 11 years; 52 were Dukes B patients and 54 were Dukes C. Altogether 36 had Dukes C1 and 18 had Dukes C2 tumors, 13 with lateral lymph node metastases, designated lateral LN(+). The 5-year survival rate was 92% for Dukes B, 67% for Dukes C1, and 39% for Dukes C2 patients: 11% for Dukes C2 patients with lateral LN(+). The local recurrence rate was 6% for Dukes B, 11% for Dukes C1, and 33% for Dukes C2 patients: 20% for the lateral LN(-) group and 39% for the lateral LN(+) group. Almost all of the patients undergoing NSS could micturate spontaneously, but preservation of sexual function was not as successful. Although there is no guarantee of preserving satisfactory sexual function, our NSS is an acceptable procedure for Dukes B, C1, and C2 patients without lateral lymph node metastases.

Adult↗

PubMed1998

Opening-up of liposomal membranes by talin.

Morphological changes of liposomes caused by interactions between liposomal membranes and talin, a cytoskeletal submembranous protein, were studied by direct, real-time observation by using high-intensity dark-field microscopy. Surprisingly, when talin was added to a liposome solution, liposomes opened stable holes and were transformed into cup-shaped liposomes. The holes became larger with increasing talin concentration, and finally the cup-shaped liposomes were transformed into lipid bilayer sheets. These morphological changes were reversed by protein dilution, i.e., the sheets could be transformed back into closed spherical liposomes. We demonstrated that talin was localized mainly along the membrane verges, presumably avoiding exposure of its hydrophobic portion at the edge of the lipid bilayer. This is the first demonstration that a lipid bilayer can stably maintain a free verge in aqueous solution. This finding refutes the established dogma that all lipid bilayer membranes inevitably form closed vesicles and suggests that talin is a useful tool for manipulating liposomes.

Animals↗

PubMed1997

Application of a deductive database system to search for topological and similar three-dimensional structures in protein.

A deductive database system PACADE (Protein Atomic Coordinate Analyzer with Deductive Engine) has been developed for protein structure analysis. With this system, super-secondary structures described in logical and declarative rules can be retrieved effectively. For protein structure analysis, comparison of local structures in different proteins is a necessary mean. A function to search for similar structures has, therefore, been added to the PACADE system. We describe herein the result of searches for the same topological structures and three-dimensionally similar ones. A user of PACADE can select these two levels of similarity by changing parameters. This function enables the inference system to retrieve similar structures, according to the restraints of variables defined by the user. Similar super-secondary structures among proteins can be searched for automatically, which is useful for protein structure analysis. The retrieved similar super-secondary structures can serve as criteria for protein spatial alignment.

Algorithms↗