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Biomedical subjects

T Okano

Publications and source records attributed to T Okano.

At least 235 records · Page 13Linked to original sources
PubMed1995

Molecular basis for tetrachromatic color vision.

Determination of the primary structures of six kinds of vertebrate visual pigments enabled us to classify them into four groups of cone-type pigments. The phylogenetic tree demonstrated that an ancestor of vertebrate visual pigments evolved into four kinds of cone-type pigments, from one of which rhodopsins diverged. Tetrachromatic color vision of chicken is discussed on the basis of both the absorption spectra of purified cone pigments and the filtering effect of colored oil-droplets.

Amino Acid Sequence↗
PubMed1995

Physical entrapment of adriamycin in AB block copolymer micelles.

The entrapment of Adriamycin (ADR) in micelles composed of AB block copolymers (poly(ethylene oxide-co-beta-benzyl L-aspartate) (PEO-PBLA)) was investigated. The loading process involved transfer of ADR and PEO-PBLA into an aqueous milieu from dimethylformamide (DMF) through a dialysis procedure. Evidence for the physical entrapment of ADR in the polymeric micelles was derived from fluorescence spectroscopy and gel permeation chromatography (GPC). The total fluorescence intensity of ADR was low, suggesting that the drug was self-associated in the micelles. In addition, quenching experiments, using a water-soluble quencher (iodide (I-)), showed that the fluorescence of ADR present in micellar solutions was largely unaffected by I-, whereas the fluorescence of free ADR was readily quenched. From Stern-Volmer plots, quenching constants (KSV) of 2.2 and 17 M-1 were determined for ADR in micellar solutions and free ADR, respectively. As a result of the entrapment of ADR in the micelles, ADR binds only slightly serum albumin as evidenced by GPC. In contrast, ADR readily binds serum albumin in aqueous solutions. The findings suggest that ADR is stably entrapped in PEO-PBLA micelles. ADR entrapment in polymeric micelles is expected to affect markedly the pharmacokinetics of ADR.

Chromatography, Gel↗
PubMed1995

Novel sensing system for glucose based on the complex formation between phenylborate and fluorescent diol compounds.

From the standpoints of long-term stability and simple handling, a glucose sensor composed of totally synthetic sensing moieties should be of great advantage. This study was performed to demonstrate the feasibility of a novel glucose sensing system in an aqueous milieu based on a change in the fluorescence on competitive binding between a fluorescent diol compound and glucose toward a phenylborate compound. 6,7-Dihydroxy-4-methyl-coumarin (DHMC) was selected as a fluorophore, and 3-propionamidophenylboronic acid (PAPBA) as a phenylborate compound. The relationship between the glucose concentration and fluorescence intensity was linear in the range of 0 to 500 mg/dl of glucose. The availability of various derivatives of DHMC and phenylborate compounds allows the incorporation of these functionalities on the tip of an optical fiber to construct an opto-sensing system for glucose.

Boronic Acids↗
PubMed1995

Nonthrombogenic polymer vascular prosthesis.

Although many synthetic vascular grafts have been developed and evaluated experimentally or clinically, none of them have met long-term patency when applied as a small diameter vascular substitute. We have recently developed a small caliber vascular graft (3 mm i.d.) using a nonthrombogenic polymer coating. The graft consists of three layered structures: Dacron for the outer layer, polyurethane in the middle layer, and a HEMA/styrene block copolymer (HEMA-st) coating for the inner layer. HEMA-st is an amphiphilic block copolymer composed of 2-hydroxyethyl methacrylate and styrene which has demonstrated improved blood compatibility over existing biomedical polymers in both in vitro and ex vivo experiments. Ten grafts were evaluated in a dog bilateral carotid replacement model. The grafts were electively retrieved at 7, 14, 30, 92, and 372 days after implantation. All grafts were patent without detectable thrombi along the graft length including anastomotic sites. Scanning electron micrographs of retrieved graft lumen showed fairly clean surfaces covered with a homogenous protein-like layer without microthrombi or endothelial cell lining. The thickness of the surface protein layer measured by a transmission electron microscopy was what can be described as monolayer protein adsorption regardless of implantation periods of as much as 372 days. A stable monolayer adsorbed protein layer formed on HEMA-st surfaces demonstrated nonthrombogenic activities in vivo and secure long-term patency of small caliber vascular grafts with the absence of an endothelial cell lining.

Animals↗
PubMed1995

Cytoplasmic calcium level and membrane fluidity of platelets contacting poly(acrylamide-co-methacrylic acid) particles with different surface properties.

Changes in cytoplasmic free calcium levels and membrane fluidity of platelets in contact with poly(acrylamide-co-methacrylic acid) (PAAmMAc) particles were examined to analyze the mechanistic aspect of regulating platelet function. Our previous studies demonstrated interesting features of PAAmMAc particles during interaction with platelets: (1) PAAmMAc particles induce no calcium increase but enhance membrane fluidity of platelets: (2) thrombin induces no calcium increase in platelets when the platelets were mixed previously with PAAmMAc particles; and (3) PAAmMAc particles induce a calcium increase in platelets when they were treated previously with sodium azide (NaN3). These results suggest the possibility that PAAmMAc surfaces may regulate the calcium level by influencing platelet metabolism. In this study, non-cross-linked PAAmMAc solution with the same chemical composition as the particles showed a suppressive effect on thrombin-induced calcium increase, but, no influence on membrane fluidity. This result indicates that aggregated macromolecular surface assemblies of PAAmMAc may dominate the increase in membrane fluidity of platelets although the calcium change is induced by discrete molecular level interaction between the PAAmMAc and platelet membranes. It was also revealed that the suppression of thrombin-induced calcium increase and the membrane fluidity increase in platelets by PAAmMAc particles were reduced by albumin-treatment of the particles. This result suggests that such phenomena may be due to a decrease in any physicochemical interaction of PAAmMAc surfaces with albumin, rather than platelet metabolic change. PAAmMAc particle surfaces with higher carboxyl groups exhibited a more suppressive effect on thrombin-induced calcium increase, whereas those with lower carboxyl groups derived a higher calcium increase when the platelets were treated previously with NaN3. These results suggest the importance of electrostatic and any other physicochemical interaction of PAAmMAc chains on regulating cytoplasmic calcium levels.

Acrylic Resins↗
PubMed1995

Endothelial cell differentiation into capillary structures by copolymer surfaces with phenylboronic acid groups.

A ternary copolymer composed of m-acrylamidophenylboronic acid, N,N-dimethylaminopropylmethacrylamide and N-isopropylacrylamide was synthesized. Long-term culture of bovine aortic endothelial cells on this copolymer substrate demonstrated adhesion and proliferation of the cells. After 26 days in culture, endothelial cells spontaneously developed into capillary networks. The interactions between phenylboronic acid groups in copolymer and glycoconjugates on endothelial cell plasma membranes are proposed to regulate the induction of tissue formation, since phenylboronic acid groups are known to specifically form reversible complexes with cis-diol compounds such as glucose. This copolymer is a novel material capable of mediating specific signals analogous to extracellular matrix to promote proliferation of endothelial cells, inducing capillary structures and prompt angiogenesis.

Acrylamides↗
PubMed1995

Bioavailability of calcium from calcium carbonate, DL-calcium lactate, L-calcium lactate and powdered oyster shell calcium in vitamin D-deficient or -replete rats.

The bioavailability of calcium from various calcium sources in humans and animals has been the subject of investigation for many years and there is considerable controversy as to the relative bioavailability of different calcium salts. Most of the studies have used a calcium balance technique which has numerous problems in terms of performance and interpretation. Using a method for evaluating the efficacy of calcium from calcium salts used for plasma calcium metabolism and bone mineralization, we examined the bioavailability of calcium from four commercially available calcium salts, namely calcium carbonate, DL-calcium lactate, L-calcium lactate and powdered oyster shell-calcium in vitamin D-deficient or -replete rats. Among the calcium salts, the differences in bioavailability were small and not statistically significant as tested by analysis of variance in both groups of rats. Thus, we conclude that calcium is utilized to the same extent from calcium carbonate, DL-calcium lactate, L-calcium lactate and powered oyster shell-calcium in both vitamin D-deficient and -replete rats.

Animals↗
PubMed1995

Effects of dietary vitamin D intake on plasma levels of parathyroid hormone and vitamin D metabolites in healthy Japanese.

To clarify the nutritional status of vitamin D in Japanese, effects of dietary intake of vitamin D on plasma levels of intact and highly sensitive parathyroid hormone (I-PTH and HS-PTH), 25-hydroxyvitamin D (25-OH-D), 1,25-dihydroxyvitamin D (1,25(OH)2D), calcium (Ca) and phosphorus (P(i)) in 79 healthy Japanese were investigated. The plasma levels of 25-OH-D in men were significantly higher than those in women, whereas those of HS-PTH in men were significantly lower than those in women. The levels of 25-OH-D in men were generally higher than those in women. Significant correlations were observed between the dietary vitamin D intake and the plasma 25-OH-D or HS-PTH levels. Correlations between the plasma 25-OH-D levels and the plasma HS-PTH levels were also significant. These results suggest that dietary intake of sufficient amounts of vitamin D is effective for improving the vitamin D nutritional status through normalizing PTH levels.

Adult↗
PubMed1995

Urachal adenocarcinoma accompanied by a large spherical calcified mass.

We report a case of urachal adenocarcinoma, accompanied by a large spherical calcified mass adherent to the bladder dome of a 63-year-old man. The patient underwent partial cystectomy including en bloc resection of the urachus, and remains free from the disease after a 32-month follow-up period.

Adenocarcinoma↗
PubMed1994

Pinopsin is a chicken pineal photoreceptive molecule.

In avian pinealocytes, an environmental light signal resets the phase of the endogenous circadian pacemaker that controls the rhythmic production of melatonin. Investigation of the pineal phototransduction pathway should therefore reveal the molecular mechanism of the biological clock. The presence of rhodopsin-like photoreceptive pigment, transducin-like immunoreaction, and cyclic GMP-dependent cation-channel activity in the avian pinealocytes suggests that there is a similarity between retinal rod cells and pinealocytes in the phototransduction pathway. We have now cloned chicken pineal cDNA encoding the photoreceptive molecule, which is 43-48% identical in amino-acid sequence to vertebrate retinal opsins. Pineal opsin, produced by transfection of complementary DNA into cultured cells, was reconstituted with 11-cis-retinal, resulting in formation of a blue-sensitive pigment (lambda max approximately 470 nm). In the light of this functional evidence and because the gene is specifically expressed only in the pineal gland, we conclude that it is a pineal photosensor and name it pinopsin.

Amino Acid Sequence↗
PubMed1994

Differential sensitivity of organic anion transporters in rat renal brush-border membrane to diethyl pyrocarbonate.

The effect of various chemical modifiers on p-aminohippurate (PAH) uptake by a potential-sensitive system and by an anion exchanger was studied in rat renal brush-border membrane vesicles. Among various chemical modifiers, diethyl pyrocarbonate (DEPC) selectively inhibited potential-sensitive PAH uptake but not the uptake by the anion exchanger. The inhibitory effect of DEPC on potential-sensitive PAH uptake was not due to the facilitated dissipation of membrane potential, which was evidenced by the studies with a potential-sensitive fluorescence dye diS-C3(5). The potential-sensitive PAH uptake was inhibited by DEPC in a concentration-dependent manner, and kinetic analysis showed that the decreased uptake of PAH in DEPC-treated vesicles was due to the decrease of Vmax. The inhibition of the PAH uptake was protected by the presence of organic anions during the DEPC treatment. These findings indicate that PAH transport by the potential-sensitive system and by the anion exchanger is mediated by structurally distinct transporters. Amino acid residue(s) modified by DEPC, most likely a histidine residue, should play an important role in the potential-sensitive transport of PAH in rat renal brush-border membrane.

Animals↗
PubMed1994

Rapid superoxide production by endothelial cells and their injury upon reperfusion.

Cultured human umbilical vein endothelial cells (EC) were exposed to hypoxia for various time periods followed by reoxygenation, and production of both O2- and H2O2 by EC was measured using the cytochrome c and scopoletin methods, respectively. Production of significant amounts of O2- was observed as early as 1 min after reoxygenation, reached maximum at 3 min and seemed to decline thereafter. Production of H2O2 was observed slightly later than that of O2-. Endothelial cell injury during hypoxia/reoxygenation was determined by both the trypan blue dye exclusion and chromium release methods. Significant increase of EC injury was detected after reoxygenation by both methods. This injury was significantly inhibited by allopurinol but not by superoxide dismutase or catalase. These results indicate that the production of reactive oxygen metabolites by EC and EC injury occur very rapidly after reoxygenation, which has not been reported, and these should be taken in consideration for the understanding and treatment of the clinical reperfusion injury.

Allopurinol↗
PubMed1994

Limitation of panoramic radiography in diagnosing adenomatoid odontogenic tumors.

Adenomatoid odontogenic tumor is frequently not diagnosed preoperatively even when radiographs are available. This study evaluates radiographic findings with special emphasis on the characteristic radiopacities of adenomatoid odontogenic tumor. In correlating radiologic findings with pathologic findings, differences in diagnostic accuracy between intraoral periapical and panoramic radiographs were found. The intraoral periapical radiograph allows perception of the radiopacities in adenomatoid odontogenic tumor as discrete foci having a flocculent pattern within radiolucency even with minimal calcified deposits. Panoramic radiography was often unable to demonstrate radiopacities in adenomatoid odontogenic tumor when the calcification was minimal. The result indicates that intraoral radiographs may be essential for correct radiographic interpretation of an adenomatoid odontogenic tumor in the presence of minimal quantities of calcified deposits.

Adolescent↗
PubMed1994

Preparation and characterization of a glucose-responsive insulin-releasing polymer device.

A new glucose-responsive insulin delivery system composed of phenylboronic acid (PBA) groups was prepared and investigated. Complexation of various diol-containing molecules with PBA gel beads was evaluated using frontal chromatography. The structural features of the diol-containing molecules strongly influenced their binding to PBA gel beads. In particular, open-chain monosaccharides demonstrated higher association constants (ca 9.5 x 10(2) to 5.1 x 10(3) l/mol) than glucose (ca 6.3 x 10(2) l/mol). Furthermore, a model system utilizing a fluorescent derivative of tris(hydroxymethyl)aminomethane was synthesized and bound to PBA gel beads. The molecules were released in a pulsatile manner in response to glucose. In addition, gluconic acids were chemically attached to insulin molecules. The modified insulin, containing two gluconic acid units per insulin molecule, was isolated using ion-exchange chromatography. This gluconic acid-modified insulin (G-Ins) was bound onto a PBA gel column, and the G-Ins release profile in response to varying glucose concentrations was investigated. The results demonstrate that the PBA gel beads release G-Ins in response to glucose concentration. Thus, this new system may be applied for self-regulated insulin delivery.

Animals↗