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Biomedical subjects

H Takayama

Publications and source records attributed to H Takayama.

At least 127 records · Page 7Linked to original sources
PubMed1998

Synthesis and biological evaluation of (23R)- and (23S)-24,24-difluoro-1 alpha,23,25-trihydroxyvitamin D3.

The syntheses and biological evaluations of (23R)- and (23S)-24,24-difluoro-1 alpha,23,25-trithydroxyvitamin D3 (3a and 3b), new C-24 fluorinated analogs of 1 alpha,25-dihydroxyvitamin D3, are described. The syntheses of these compounds were achieved in 3 steps from (5Z,7E,20R)-1 alpha,3 beta-bis-[(tert-butyldimethylsilyl)oxy]-20-formylmethyl-9,10-seco- 5,7,10(19) pregnatriene (5) which is derived from vitamin D2. The absolute configuration at the C-23 position of 3a and 3b was determined by the modified Mosher method. The relative affinities of 3a and 3b to the vitamin D receptor were both 10 and 14 times lower than that of 1 alpha,25-dihydroxyvitamin D3 (1), and to vitamin D binding protein were also both 130 and 40 times lower. The HL-60 cell differentiating activity of 3a was 6 times more potent than that of 1, while there was no remarkable difference in activity between 3b and 1.

Animals↗
PubMed1998

Inhibitory effects of corymine-related compounds on glycine receptors expressed in Xenopus oocytes.

We examined the effects of 4 corymine-related compounds on glycine-induced chloride current in Xenopus oocytes. Dihydrocorymine, N-demethyl-3-epi-dihydrocorymine and deformylcorymine dose-dependently decreased the glycine current with IC50 values of 34, 37 and 55 microM, respectively. The effect of these compounds on the glycine current was more potent than that of pleiocarpamine (IC50 > 1 mM). N-demethyl-3-epi-dihydrocorymine and dihydrocorymine, at 100 microM, also decreased the gamma-aminobutyric acid-induced current by 65% and 22%, respectively, whereas deformylcorymine and pleiocarpamine failed. The inhibitory action of deformylcorymine on the glycine current was noncompetitive. These results suggest that deformylcorymine is a novel specific noncompetitive glycine receptor antagonist. The structure-activity relationship of these compounds was discussed.

Alkaloids↗
PubMed1998

A mesenteric liposarcoma with production of granulocyte colony-stimulating factor.

A 77-year-old female was admitted to our hospital because of pyrexia and a right retroperitoneal mass. Leukocytosis and other inflammatory findings were noted. Bone-marrow aspiration revealed hypercellularity with no malignant cells. An additional mass was detected sonographically in the pelvis. The serum concentration of granulocyte colony-stimulating factor (G-CSF) was highly elevated (299 pg/ml). The tumors were removed at laparotomy, and the pelvic mass was found to arise from the ileocecal mesentery. Postoperatively, white blood cell count and serum G-CSF concentrations decreased to normal levels. The mesenteric tumor showed weakly positive immunostaining for human G-CSF, and Northern and polymerase chain reaction (PCR) analyses detected CSF and its mRNA in the mesenteric tumor.

Aged↗
PubMed1997

Alpha-pompilidotoxin (alpha-PMTX), a novel neurotoxin from the venom of a solitary wasp, facilitates transmission in the crustacean neuromuscular synapse.

A new neurotoxin, named alpha-pompilidotoxin (alpha-PMTX) has been found in the venom of the solitary wasp Anoplius safnariensis. In the neuromuscular synapse of the lobster walking leg preparation, alpha-PMTX (10-100 micro/M) caused great enhancement of both the excitatory and inhibitory postsynaptic potentials. Recordings of the excitatory post synaptic currents (EPSCs) at the synaptic sites showed that alpha-PMTX reversibly and dose-dependently potentiates EPSCs. Alpha-PMTX may act primarily on the presynaptic membrane but the mode of action of the toxin is clearly different from other known facilitatory neurotoxins, such as alpha-latrotoxin, apamin or charybdotoxin. This novel toxin will serve as a useful tool in the research field of neuroscience.

Animals↗
PubMed1997

A novel association of Fc receptor gamma-chain with glycoprotein VI and their co-expression as a collagen receptor in human platelets.

The mechanism by which occupancy of collagen receptors is coupled to platelet activation has been uncertain. Our group previously demonstrated that glycoprotein (GP) VI, an uncharacterized platelet membrane protein, is specifically required for collagen-platelet interaction leading to activation of protein-tyrosine kinase Syk. Since collagen stimulation of platelets has recently been found to induce tyrosine phosphorylation of Fc receptor (FcR) gamma-chain, a signal-generating subunit of FcR, we further investigated the relationships between FcR gamma-chain and GPVI in human platelets. Our present study revealed the following. FcR gamma-chain was physically and stably associated with GPVI in human platelets; both FcR gamma-chain and GPVI were proportionally absent in GPVI-deficient platelets; GPVI cross-linking or collagen stimulation of platelets resulted in tyrosine phosphorylation of GPVI-associated FcR gamma-chain accompanied by Syk association and activation. These findings strongly suggest that the associated complex of GPVI and FcR gamma-chain is a collagen receptor featuring the signaling through immune receptors.

Blood Platelets↗
PubMed1997

Leukocyte function-associated antigen-1-dependent lysis of Fas+ (CD95+/Apo-1+) innocent bystanders by antigen-specific CD8+ CTL.

Exquisite specificity toward Ag-bearing cells (cognate targets) is one of the most important properties of CD8+ CTL-mediated cytotoxicity. Using highly Ag-specific CD8+ CTL lines and clones, which spare noncognate, Ag-free targets, we found that in the presence of Ag-bearing targets the CTL acquire the ability to lyse noncognate target cells (bystanders). It is shown that the unexpectedly rapid and efficient lysis of bystanders by Ag-activated CTL is mediated by a Fas ligand (FasL)/Fas-based mechanism and does not depend on perforin. The CTL lysed Fas-expressing bystanders, but spared the Fas-negative or anti-Fas mAb-resistant bystander cells. Accordingly, the FasL-deficient gld/gld CTL did not kill bystanders, while perforin-deficient CTL did. Unlike anti-Fas mAb-induced cell death, the lysis of bystanders was not only FasL/Fas dependent but also required adhesion molecule LFA-1 on the surface of the activated CTL. Lysis of bystanders is viewed as acceptable "collateral" damage, but the persistent presence of activated CTL could result in immunopathologies involving functional Fas-expressing tissues.

Animals↗
PubMed1997

Inhibitory effects of corymine, an alkaloidal component from the leaves of Hunteria zeylanica, on glycine receptors expressed in Xenopus oocytes.

We previously reported that corymine, an alkaloidal compound extracted from the leaves of Hunteria zeylanica native to Thailand, potentiated convulsions induced by either picrotoxin or strychnine. Therefore, to clarify the mechanism of action of corymine, the effects of corymine on gamma-aminobutyric acid (GABA) and glycine receptors were examined. We used Xenopus oocytes expressing these receptors and the two-electrode voltage-clamp method. The receptors expressed in oocytes injected with rat brain and spinal cord RNA showed the pharmacological properties of GABAA and glycine receptors, respectively. Corymine (1-100 microM) partially (20-30%) reduced the GABA responses in oocytes injected with rat brain RNA, while marked (up to 80%) dose-dependent reductions were observed in the glycine responses in oocytes injected with rat spinal cord RNA. These observations suggest that corymine was more effective against the glycine receptors than the GABA receptors. The ED50 of corymine on the glycine response was 10.8 microM. Corymine, at 30 microM, caused a shift to the right, with a lower maximal response, of the glycine concentration-response curve. This indicated that the action of corymine on glycine receptors is neither competitive nor purely non-competitive. These observations suggest that a binding site other than the glycine recognition site of the glycine receptors is the site of action of corymine.

Alkaloids↗
PubMed1997

1alpha,25-dihydroxyvitamin D3-24-hydroxylase (CYP24) hydroxylates the carbon at the end of the side chain (C-26) of the C-24-fluorinated analog of 1alpha,25-dihydroxyvitamin D3.

The sequential oxidation and cleavage of the side chain of 1alpha, 25-dihydroxyvitamin D3 (1alpha,25(OH)2D3) initiated by the hydroxylation at C-24 is considered to be the major pathway of this hormone in the target cell metabolism. In this study, we examined renal metabolism of a synthetic analog of 1alpha,25(OH)2D3, 24, 24-difluoro-1alpha,25-dihydroxyvitamin D3 (F2-1alpha,25(OH)2D3), C-24 of which was designed to resist metabolic hydroxylation. When kidney homogenates prepared from 1alpha,25(OH)2D3-supplemented rats were incubated with F2-1alpha,25(OH)2D3, it was mainly converted to a more polar metabolite. We isolated and unequivocally identified the metabolite as 24,24-difluoro-1alpha,25,26-trihydroxyvitamin D3 (F2-1alpha,25,26(OH)3D3) by ultraviolet absorption spectrometry, frit-fast atom bombardment liquid chromatography/mass spectroscopy analysis, and direct comparison with chemically synthesized F2-1alpha,25,26(OH)3D3. Metabolism of F2-1alpha,25(OH)2D3 into F2-1alpha,25,26(OH)3D3 by kidney homogenates was induced by the prior administration of 1alpha,25(OH)2D3 into rats. The C-24 oxidation of 1alpha,25(OH)2D3 in renal homogenates was inhibited by F2-1alpha,25(OH)2D3 in a concentration-dependent manner. Moreover, F2-1alpha,25,26(OH)3D3 was formed in ROS17/2.8 cells transfected with a plasmid expressing 1alpha,25(OH)2D3-24-hydroxylase (CYP24) but not in the cells transfected with that expressing vitamin D3-25-hydroxylase (CYP27) or containing inverted CYP27 cDNA. These results show that CYP24 catalyzes not only hydroxylation at C-24 and C-23 of 1alpha,25(OH)2D3 but also at C-26 of F2-1alpha,25(OH)2D3, indicating that this enzyme has a broader substrate specificity of the hydroxylation sites than previously considered.

Animals↗
PubMed1997

Protein-tyrosine-kinase-dependent expression of cyclo-oxygenase-1 and -2 mRNAs in human endothelial cells.

Endothelial cells possess constitutive or inducible cyclo-oxygenase (COX) isoenzymes for prostacyclin production, but the mechanisms for their expression are largely unknown. We found that vanadate, an inhibitor of protein-tyrosine phosphatases, induced the expression of two COX isoenzyme mRNAs in human umbilical vein endothelial cells (HUVEC) in a time- and dose-dependent manner. Vanadate also stimulated an increase in COX-2 protein levels, but did not affect significantly the levels of constitutively expressed COX-1 protein. Synergistic enhancement of expression of the two COX isoenzyme mRNAs was observed on stimulation of HUVEC with vanadate plus interleukin-1alpha. Tyrphostin-47, which as an inhibitor of protein-tyrosine kinases abolished vanadate-induced protein-tyrosine phosphorylation, inhibited expression of the two COX isoenzyme mRNAs in HUVEC stimulated with vanadate or interleukin-1alpha. These data provide conclusive evidence that activation of protein-tyrosine kinases is causally linked to expression of the mRNAs for the two COX isoenzymes in HUVEC.

Cyclooxygenase 1↗
PubMed1997

Diverse tumorigenesis associated with aberrant development in mice overexpressing hepatocyte growth factor/scatter factor.

Hepatocyte growth factor/scatter factor (HGF/SF) is a mesenchymally derived, multifunctional paracrine regulator possessing mitogenic, motogenic, and morphogenetic activities in cultured epithelial cells containing its tyrosine kinase receptor, Met. c-met has been implicated in oncogenesis through correlation of expression with malignant phenotype in specific cell lines and tumors. Paradoxically, however, HGF/SF can also inhibit the growth of some tumor cells. To elucidate the oncogenic role of HGF/SF in vivo, transgenic mice were created such that HGF/SF was inappropriately targeted to a variety of tissues. HGF/SF transgenic mice developed a remarkably broad array of histologically distinct tumors of both mesenchymal and epithelial origin. Many neoplasms arose from tissues exhibiting abnormal development, including the mammary gland, skeletal muscle, and melanocytes, suggesting a functional link between mechanisms regulating morphogenesis and those promoting tumorigenesis. Most neoplasms, especially melanomas, demonstrated overexpression of both the HGF/SF transgene and endogenous c-met, and had enhanced Met kinase activity, strongly suggesting that autocrine signaling broadly promotes tumorigenesis. Thus, subversion of normal mesenchymal-epithelial paracrine regulation through the forced misdirection of HGF/SF expression induces aberrant morphogenesis and subsequent malignant transformation of cells of diverse origin.

Animals↗
PubMed1997

Collagen-stimulated activation of Syk but not c-Src is severely compromised in human platelets lacking membrane glycoprotein VI.

Activation of circulating platelets by subendothelial collagen is an essential event in vascular hemostasis. In human platelets, two membrane glycoprotein (GP) abnormalities, integrin alpha2 beta1 deficiency and GPVI deficiency, have been reported to result in severe hyporesponsiveness to fibrillar collagen. Although it has been well established that integrin alpha2 beta1, also known as the GPIa-IIa complex, functions as a primary platelet adhesion receptor for collagen, the mechanism by which GPVI contributes to collagen-platelet interaction has been ill defined to date. However, our recent observation that GPVI cross-linking couples to cyclic AMP-insensitive activation of c-Src and Syk tyrosine kinases suggested a potential role for GPVI in regulating protein-tyrosine phosphorylation by collagen (Ichinohe, T., Takayama, H., Ezumi, Y., Yanagi, S., Yamamura, H., and Okuma, M. (1995) J. Biol. Chem. 270, 28029-28036). To further investigate this hypothesis, here we examined the collagen-induced protein-tyrosine phosphorylation in GPVI-deficient platelets expressing normal amounts of alpha2 beta1. In response to collagen, these platelets exhibited alpha2 beta1-dependent c-Src activation accompanied by tyrosine phosphorylation of several substrates including cortactin. In contrast, severe defects were observed in collagen-stimulated Syk activation and tyrosine phosphorylation of phospholipase C-gamma2, Vav, and focal adhesion kinase, implicating a specific requirement of GPVI for recruiting these molecules to signaling cascades evoked by collagen-platelet interaction.

Adult↗
PubMed1997

Age-related changes of platelet arachidonic acid metabolism in normal subjects.

Platelet activation and thrombosis play a crucial role in cardiovascular diseases. It has been suggested that enhanced platelet function in vivo are present in the elderly and that they are associated with the development of these diseases [1-3]. In the present study, we addressed the question of whether platelet arachidonate metabolism was altered with aging.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1997

Prediction of effect of interferon on chronic hepatitis C.

Clinical, pathological, and virological analysis including hypervariable region-1 of hepatitis C virus (HCV) was performed to predict the effect of interferon (IFN) on 41 patients with chronic hepatitis type C. The low virus load, low frequency of the mutation in the hypervariable region-1 as the change of amino acid and high level of serum aminotransferase make one estimate the good effect of IFN on patients with HCV. Mutation in the hypervariable region-1 of HCV measured by fast assay fluorescence single-stranded conformational polymorphism was more frequent in nonresponders to IFN than responders. The most frequently mutated position was amino acid number 406. This indicates that the specific mutation site might affect the response of IFN.

Amino Acid Sequence↗
PubMed1997

Inactivation and proteolytic degradation of perforin within lytic granules upon neutralization of acidic pH.

In our recent studies, an inhibitor of vacuolar-type H(+)-ATPase, concanamycin A (CMA) has been shown to neutralize acidic pH in vacuolar organelles, including lytic granules, and to decrease the perforin content markedly. In the present paper, we have further investigated the role of acidification in perforin storage by using CMA. In CD8+ cytotoxic T-lymphocyte (CTL) clones, the amount of perforin decreased rapidly at 30-90 min but no more decrease occurred at 90-120 min after the addition of CMA. Since exposure to actinomycin D, cycloheximide, or brefeldin A failed to reduce the perforin content, the perforin decrease in CMA-treated cells seems to be largely due to a reduction in the perforin already stored in lytic granules, rather than to the inhibition of the de novo synthesis or the intracellular glycoprotein transport of perforin. Diisopropylfluorophosphoridate (DFP) markedly antagonized the decrease in the perforin content in CMA-treated cells, while other protease inhibitors, i.e. antipain, E-64, leupeptin, pepstatin A and phenylmethylsulphonyl fluoride, did not. Nevertheless, DFP hardly reversed the abrogation of the killing activity by CMA. Indeed, the lytic granules prepared from DFP plus CMA-treated cells showed only a marginal level of haemolytic activity. In cell-free experiments using perforin-enriched granule fractions, acidic pH completely blocked the perforin activity. Under the acidic conditions, perforin was more resistant to an inactivation by calcium when exposed to calcium prior to the haemolysis test. Thus, these data suggest that perforin is primarily inactivated, possibly in a calcium-dependent manner, and is subsequently hydrolysed by DFP-sensitive proteases in the lytic granules at neutral pH. We conclude that acidic pH plays an essential role to maintain the integrity of perforin within the lytic granules.

Animals↗
PubMed1997

Thiadiazole derivatives: highly potent and selective inhibitors of human immunodeficiency virus type 1 (HIV-1) replications in vitro.

We have recently reported that thiadiazole (TDA) derivatives are highly potent inhibitors of human immunodeficiency virus type 1 (HIV-1) replication. These compounds belong to the family of nonnucleoside reverse transcriptase inhibitors (NNRTIs). In an attempt to develop more effective and pharmacologically favorable compounds, novel TDA derivatives have been synthesized and examined for their anti-HIV-1 activity in vitro. Among them, RD4-2217 was found to be the most potent inhibitor of HIV-1 replication. It inhibited replication of the HTLV-IIIB strain in MT-4 cells at a concentration of 6 nM. RD4-2217 was also inhibitory to clinical isolates and zidovudine-resistant mutants of HIV-1. The combination of RD4-2217 with zidovudine or the protease inhibitor A-75925 synergistically inhibited HIV-1 replication. Studies on the emergence of drug-resistant mutants revealed that, although much higher concentrations (1-10 microM) were required, RD4-2217 completely suppressed the breakthrough of HIV-1 in the supernatants during long-term culturing of infected cells. Furthermore, RD4-2217 at low concentrations (10 or 100 nM), in combination with zidovudine, also completely inhibited viral breakthrough. In addition, RD4-2217 had lower lipophilicity and improved protein binding as compared to its congener RD4-2024 and loviride. These results suggest that RD4-2217, one of the TDA derivatives, is worth pursuing as a candidate drug for the treatment of HIV-1 infections.

Anti-HIV Agents↗
PubMed1997

Early administration of Bifidobacterium breve to preterm infants: randomised controlled trial.

AIM: To investigate the colonisation with Bifidobacterium breve of the bowels of very low birthweight (VLBW) infants. METHODS: The adverse effects of B breve were examined in 66 VLBW infants (preliminary study). A prospective randomised clinical study of 91 VLBW infants was also completed and these infants were followed up for three years. Precise viable bacterial counts of serial stool specimens were examined for the first eight weeks after birth in 10 infants. The colonisation rates of administered bacteria were examined using immunohistochemical staining of stool specimens with a B breve specific monoclonal antibody. RESULTS: In the preliminary study there were no side effects attributable to the bacteria. Immunohistochemical staining of stool specimens showed that the colonisation rates of the administered bacteria were 73% at 2 weeks of age, but only 12% in the control group. Early administration of B breve significantly decreased aspirated air volume from the stomach and improved weight gain. CONCLUSIONS: B breve can colonise the immature bowel very effectively and is associated with fewer abnormal abdominal signs and better weight gain in VLBW infants, probably as a result of stabilisation of their intestinal flora and accelerated feeding schedules.

Bifidobacterium↗
PubMed1997

Effects of mitragynine on cAMP formation mediated by delta-opiate receptors in NG108-15 cells.

Mitragynine, a major constituent of the young leaves of Mitragyna speciosa KORTH., has been reported to exert antinociceptive activity in mice. To determine the mechanism the influence of mitragynine on cAMP content was measured in NG108-15 cells which possess delta opioid receptors and alpha 2B-adrenoceptors. Mitragynine inhibited the forskolin-stimulated cAMP content in a concentration dependent manner as well as morphine and noradrenaline. Mitragynine- and morphine-induced inhibition of cAMP content were blocked by naloxone. Although idazoxane inhibited noradrenaline-induced inhibition of the cAMP content, idazoxane had no effect on mitragynine-induced inhibition. These results suggest that mitragynine acts directly on opioid receptors, but not on alpha 2-adrenoceptors, to show antinociceptive activity.

Analgesics↗