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Biomedical subjects

K Maeda

Publications and source records attributed to K Maeda.

At least 325 records · Page 18Linked to original sources
PubMed1998

Serum CA 125 level as a predictor of peritoneal dissemination in patients with gastric carcinoma.

BACKGROUND: Prediction of peritoneal dissemination is very difficult using current diagnostic tools such as computed tomography, ultrasonography, or various tumor markers. The predictive value of serum CA 125 levels for peritoneal metastasis from gastric carcinoma was studied. METHODS: The sera from 384 patients with gastric carcinoma were measured for CA 125 titer using an immunoradiometric assay. Carcinoembryonic antigen, carbohydrate antigen 19-9, and sialyl-Tn antigen were measured in the same samples. RESULTS: The serum CA 125 level was elevated according to the degree of peritoneal dissemination. The reference value for peritoneal dissemination was determined to be 35 U/mL, resulting in a sensitivity of 39.4%, specificity of 95.7%, and diagnostic accuracy of 90.8%. The diagnostic ability was more reliable than the other imaging modalities including computed tomography and ultrasonography and the other useful tumor markers for gastric carcinoma. The serum CA 125 level was elevated after gastrectomy for approximately 2 months, most likely due to the continuous inflammation of the peritoneum and lost predictive significance for peritoneal dissemination during this period. CONCLUSIONS: Measurement of the serum CA 125 titer may be a powerful predictor of peritoneal metastases in patients with gastric carcinoma.

Adult↗
PubMed1998

Stereoselective blood-brain barrier transport of histidine in rats.

The transport characteristics of l- and d-histidine through the blood-brain barrier (BBB) were studied using cultured rat brain microvascular endothelial cells (BMEC). l-Histidine uptake was a saturable process. A decrease in incubation temperature from 37 to 0 degreesC or the addition of metabolic inhibitors (DNP and rotenone) reduced the uptake rate of l-histidine. Ouabain, an inhibitor of (Na+, K+)-ATPase, also reduced uptake of l-histidine. Moreover, the substitution of Na+ with choline chloride and choline bicarbonate in the incubation buffer decreased the initial l- and d-histidine uptake rates. These results suggested that l-histidine is actively uptaken by a carrier-mediated mechanism into the BMEC, with energy supplied by Na+. However, l-histidine uptake at 0 degreesC was not completely inhibited, and it was reduced in the presence of an Na+-independent System-L substrate, BCH, suggesting facilitated diffusion (the Na+-independent process) by a carrier-mediated mechanism into the BMEC. l-histidine uptake in rat BMEC also appeared to be System-N mediated since uptake was inhibited by glutamine, aspargine and l-glutamic acid gamma-monohydroxamate. System-N mediated transport was not pH sensitive. d-histidine transport was also studied in rat BMEC. d-histidine transport by rat BMEC has similar characteristics to l-histidine. However, System-N transport did not play a role in d-histidine uptake. The uptake of l-histidine was also greater than that of the d-isomer, indicating the stereoselective uptake of histidine in rat BMEC.

Animals↗
PubMed1998

PKC and tyrosine kinase involvement in amyloid beta (25-35)-induced chemotaxis of microglia.

Microglia are activated by amyloid beta (Abeta) in vivo and in vitro, and Abeta-activated microglia may be involved in the pathogenesis of Alzheimer's disease (AD). We investigated the mechanism of microglial chemotaxis induced by Abeta (25-35), an active fragment of Abeta. Abeta (25-35) 0.1 and 1 nM stimulated microglial chemotaxis. The protein kinase C (PKC) inhibitors chelerythrine (0.5 and 2 microM), calphostin C (1 microM) and staurospine (10 nM) significantly inhibited the microglial chemotaxis induced by Abeta (25-35) (1 nM). The chemotactic effect of Abeta (25-35) on microglia was desensitized by pretreatment of microglia with 1 ng/ml 12-O-tetradecanoylphorbol 13-acetate (TPA). Pretreatment of cells with Abeta (25-35) (1 nM) also desensitized the chemotactic effect by Abeta (25-35) (1 nM). The desensitization by TPA or Abeta (25-35) was inhibited when staurosporine was present in the pretreatment media. The tyrosine kinase inhibitor herbimycin A (0.1 and 1 microM) significantly inhibited the microglial chemotaxis induced by Abeta (25-35) (1 nM). Based on these observations, it seems likely that PKC and tyrosine kinase are involved in the Abeta-induced chemotaxis of microglia.

Alkaloids↗
PubMed1998

Age-related changes in the brains of senescence-accelerated mice (SAM): association with glial and endothelial reactions.

Twelve substrains of inbred senescence-accelerated mice (SAM) have been developed, among which the SAMP8 and SAMP10 strains show a significant age-related deterioration in learning and memory for passive and active avoidance tasks. These strains have, respectively, a low and high incidence of systemic senile amyloidosis. Although we found no amyloid deposits in their brain parenchyma, a variety of age-related alterations were identified, involving neurons, glia, and vessels in the brain tissues. Here we review the degenerative changes in aged SAMP8 and SAMP10 brains. These changes are generally similar to the pathology of aging human brain and may be characterized by their association with some specific glial reactions.

Aging↗
PubMed1998

A protein kinase, PKN, accumulates in Alzheimer neurofibrillary tangles and associated endoplasmic reticulum-derived vesicles and phosphorylates tau protein.

A possible role for a protein kinase, PKN, a fatty acid-activated serine/threonine kinase with a catalytic domain homologous to the protein kinase C family and a direct target for Rho, was investigated in the pathology of Alzheimer's disease (AD) using a sensitive immunocytochemistry on postmortem human brain tissues and a kinase assay for human tau protein. The present study provides evidences by light, electron, and confocal laser microscopy that in control human brains, PKN is enriched in neurons, where the kinase is concentrated in a subset of endoplasmic reticulum (ER) and ER-derived vesicles localized to the apical compartment of juxtanuclear cytoplasm, as well as late endosomes, multivesicular bodies, Golgi bodies, secretary vesicles, and nuclei. In AD-affected neurons, PKN was redistributed to the cortical cytoplasm and neurites and was closely associated with neurofibrillary tangles (NFTs) and their major constituent, abnormally modified tau. PKN was also found in degenerative neurites within senile plaques. In addition, we report that human tau protein is directly phosphorylated by PKN both in vitro and in vivo. Thus, our results suggest a specific role for PKN in NFT formation and neurodegeneration in AD damaged neurons.

Aged↗
PubMed1998

Ig receptor binding protein 1 (alpha4) is associated with a rapamycin-sensitive signal transduction in lymphocytes through direct binding to the catalytic subunit of protein phosphatase 2A.

Rapamycin is an immunosuppressant that effectively controls various immune responses; however, its action in the signal transduction of lymphocytes has remained largely unknown. We show here that a phosphoprotein encoded by mouse alpha4 (malpha4) gene transmitting a signal through B-cell antigen receptor (BCR) is associated with the catalytic subunit of protein phosphatase 2A (PP2Ac). The middle region of alph4, consisting of 109 amino acids (94-202), associates directly with PP2Ac, irrespective of any other accessory molecule. Rapamycin treatment disrupts the association of PP2Ac/alpha4 in parallel with the inhibitory effect of lymphoid cell proliferation. The effect of rapamycin was inhibited with an excess amount of FK506 that potentially completes the binding to FKBP. Rapamycin treatment also suppresses the phosphatase activity of cells measured by in vitro phosphatase assay. Introduction of the malpha4 cDNA into Jurkat cells or the increased association of PP2Ac/alpha4 by the culture with low serum concentration confers cells with rapamycin resistance. Moreover, glutathione S-transferase (GST)-alpha4 augments the PP2A activity upon myelin basic protein (MBP) and histone in the in vitro assay. These results suggest that alpha4 acts as a positive regulator of PP2A and as a new target of rapamycin in the activation of lymphocytes.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Separation of lac dye components by high-speed counter-current chromatography.

High-speed counter-current chromatography has been successfully applied to the separation of the lac dye components. A 25-mg quantity of the sample was separated using a two-phase solvent system composed of tert.-butyl methyl ether-n-butanol-acetonitrile-water (2:2:1:5). The fractions were analyzed by high-performance liquid chromatography and electrospray tandem mass spectrometry. The separation yielded 2.6 mg of 97.2% pure laccaic acid C, 9.5 mg of 98.1% pure laccaic acid A, 3.6 mg of 98.2% pure laccaic acid B, and 0.5 mg of a 95.0% pure anthraquinonedicarboxylic acid with a molecular mass of 360.

Azo Compounds↗
PubMed1998

Insulin-like growth factor I stimulates proliferation and Fas-mediated apoptosis of human osteoblasts.

In vitro studies have shown that insulin-like growth factor I (IGF-I) is a potent growth factor for osteoblasts, although both bone formation and resorption are upregulated by IGF-I in vivo. To understand the difference in the action of IGF-I observed in vitro and in vivo experiments, we examined the effect of IGF-I on the proliferation and Fas-mediated apoptosis of human osteoblasts in vitro. Human osteoblastic cell line MG63 and human primary osteoblast-like cells obtained from biopsy specimens were used as human osteoblasts. Cells were cultured with or without various concentrations of IGF-I followed by determination of the proliferative response and Fas-mediated apoptosis. IGF-I dose dependently stimulated the proliferation of cultured human osteoblasts. Both Fas expression and the degree of anti-Fas IgM-induced apoptosis of human osteoblasts was also augmented by IGF-I. Furthermore, the cytotoxicity of Fas ligand (FasL) cDNA transformants against human osteoblasts was increased when IGF-I-stimulated osteoblasts were used as target cells, indicating that stimulation of IGF-I increased functional Fas expression on human osteoblasts as well as their proliferation. The addition of DEVD-CHO, a specific inhibitor of CPP32, to the culture resulted in a significant inhibition of Fas-mediated apoptosis of both unstimulated and IGF-I-stimulated osteoblasts, although it did not affect the proliferative response or Fas expression. Our data suggest that activation of CPP32 is necessary for Fas-mediated apoptosis of human osteoblasts, and treatment of IGF-I increased this signaling pathway. In contrast, regulation of proliferation and Fas expression of the cells were probably not affected by CPP32 activation. Our results suggest that IGF-I acts on cultured human osteoblasts by increasing their proliferation and induction of Fas-mediated apoptosis by neighbouring FasL+ cells such as osteoclasts, thus probably functioning as a local coupling factor in the bone in vivo, stimulating both bone formation and resorption.

Apoptosis↗
PubMed1998

Imidazolium crosslinks derived from reaction of lysine with glyoxal and methylglyoxal are increased in serum proteins of uremic patients: evidence for increased oxidative stress in uremia.

Glyoxal (GO) and methylglyoxal (MGO) are reactive dicarbonyl compounds formed during autoxidation of both carbohydrates and lipids. They may react with lysine and arginine residues of proteins in Maillard or browning reactions, yielding advanced glycation or lipoxidation end products. Among these are the imidazolium crosslinks, N,N(-di(N(epsilon)-lysino))imidazolium (glyoxal-lysine dimer, GOLD) and N,N(-di(N(epsilon)-lysino))-4-methyl-imidazolium (methylglyoxal-lysine dimer, MOLD). We have detected and measured GOLD and MOLD in human serum by electrospray ionization/mass spectrometry/mass spectrometry (ESI/MS/MS), using 15N4-GOLD and 15N4-MOLD as internal standards. In this report we show that levels of GOLD and MOLD are significantly elevated (3-4-fold, P< 0.01) in sera of non-diabetic uremic patients, compared to age-matched controls, and represent a major class of non-enzymatic, Maillard reaction crosslinks in plasma proteins. These results provide strong evidence for increased non-enzymatic crosslinking of tissue proteins by GO and MGO in uremia, implicating oxidative stress and resultant advanced glycation and lipoxidation reactions in tissue damage in uremia.

Cross-Linking Reagents↗
PubMed1998

Differences in the cerebrovascular anatomy of C57black/6 and SV129 mice.

The vascular architecture of the brain of C57Black/6 and SV129 mice was studied following microvascular injection of carbon black stained latex. The dorsal brain surface was photographed to determine the number, diameter, and position of pial anastomotic vessels between the middle and anterior cerebral arteries. The mean number and diameter of anastomoses were not significantly different, but the line of anastomoses interconnecting the half way points of anastomotic vessels was located significantly closer to the midline in C57Black/6 mice, demonstrating that the middle cerebral artery had a larger vascular supplying territory than in SV129 mice. This explains the larger infarct volume previously reported in C57Black/6 mice, and raises concerns about the use of C57Black/6 and SV129 mice as parent strains for genetically modified animals in stroke research.

Animals↗
PubMed1998

Thermal unfolding of three acclimation temperature-associated isoforms of carp light meromyosin expressed by recombinant DNAs.

Differential scanning calorimetry (DSC) was performed to investigate thermodynamic properties of three carp fast skeletal light meromyosin (LMM) isoforms expressed in Escherichia coli by recombinant DNAs. Three isoforms were the 10 degreesC-, intermediate-, and 30 degreesC-type LMM predominantly expressed in carp acclimated to 10, 20, and 30 degreesC. The isoforms expressed in E. coli by recombinant DNAs exhibited a typical pattern of alpha-helix in CD spectroscopy with two minima at 222 and 208 nm. Moreover, the three isoforms formed paracrystals typical of LMM, suggesting that expressed proteins retained intact structural properties. When the LMM isoforms were subjected to DSC analysis, the 10 degreesC and 30 degreesC types showed endotherms having transition temperatures (Tm) at 35.1 and 39.5 degreesC, respectively, which are responsible for thermal unfolding of alpha-helix. The intermediate type exhibited two comparable endotherms with Tm values at 34.9 and 40.6 degreesC, implying that it has intermediate thermodynamic properties between those of 10 degreesC and 30 degreesC types. However, a chimeric LMM having the 10 degreesC and 30 degreesC type as N- and C-terminal halves, respectively, showed the DSC pattern typical of the whole 30 degreesC-type molecule. On the other hand, another chimeric LMM composed of the N-terminal 30 degreesC type and C-terminal 10 degreesC type gave the pattern of the full 10 degreesC type. These results suggest that thermodynamic properties of the C-terminal half largely account for thermal unfolding of the whole molecule.

Acclimatization↗
PubMed1998

Crystal structure of troponin C in complex with troponin I fragment at 2.3-A resolution.

Troponin (Tn), the complex of three subunits (TnC, TnI, and TnT), plays a key role in Ca2+-dependent regulation of muscle contraction. To elucidate the interactions between the Tn subunits and the conformation of TnC in the Tn complex, we have determined the crystal structure of TnC (two Ca2+ bound state) in complex with the N-terminal fragment of TnI (TnI1-47). The structure was solved by the single isomorphous replacement method in combination with multiple wavelength anomalous dispersion data. The refinement converged to a crystallographic R factor of 22.2% (Rfree = 32.6%). The central, connecting alpha-helix observed in the structure of uncomplexed TnC (TnCfree) is unwound at the center (residues Ala-87, Lys-88, Gly-89, Lys-90, and Ser-91) and bent by 90 degrees. As a result, TnC in the complex has a compact globular shape with direct interactions between the N- and C-terminal lobes, in contrast to the elongated dumb-bell shaped molecule of uncomplexed TnC. The 31-residue long TnI1-47 alpha-helix stretches on the surface of TnC and stabilizes its compact conformation by multiple contacts with both TnC lobes. The amphiphilic C-end of the TnI1-47 alpha-helix is bound in the hydrophobic pocket of the TnC C-lobe through 38 van der Waals interactions. The results indicate the major difference between Ca2+ receptors integrated with the other proteins (TnC in Tn) and isolated in the cytosol (calmodulin). The TnC/TnI1-47 structure implies a mechanism of how Tn regulates the muscle contraction and suggests a unique alpha-helical regulatory TnI segment, which binds to the N-lobe of TnC in its Ca2+ bound conformation.

Amino Acid Sequence↗
PubMed1998

The gene structure and promoter analysis of mouse lymphocyte signal transduction molecule alpha 4 that is related to the yeast TAP42 involved in a rapamycin-sensitive pathway.

The mouse alpha 4 phosphoprotein encoding a component associated with the B cell antigen receptor (BCR)-mediated signal transduction is suggested to be involved in a unique rapamycin-sensitive pathway. We studied the structure and the molecular mechanism of the expression of alpha 4 gene by isolating two phage clones, named #10 and #23, covering entire exons of the mouse alpha 4 gene. The alpha 4 gene is located within about 25 kb and composed of six exons. To analyze the regulation of alpha 4 gene expression, we determined the nucleotide sequence toward 2 kb upstream of the translation start site of the alpha 4 gene. The 5'-flanking region does not contain a typical TATA box or the initiation consensus sequence, but it contains a CCAAT box, E-boxes, and several DNA binding motifs such as c-Myc, c-Myb, and c-Ets. Transcription of the alpha 4 gene starts at four different sites, determined by primer extension analysis, that were surrounded by Y-rich sequences. We further characterized the functional promoter of the alpha 4 gene at the region between -263 and the transcription start site of alpha 4 gene by luciferase assay system and suggested that the 5' upstream region of alpha 4 gene contains the silencer element of MT repetitive sequence.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Glial and neuronal localization of neuronal nitric oxide synthase immunoreactivity in the median eminence of female rats.

Localization of neuronal nitric oxide synthase-immunoreactivity (nNOS-IR) in the median eminence of female rats (n=4) was examined by electron microscopy to explore the possibility that nitric oxide is involved in the terminal regulation of neurosecretory peptides such as GnRH. Under light microscopy, a dense distribution of nNOS-IR was observed in this region. Electronmicroscopically, nNOS-IR was found in glial elements and nerve terminals containing dense-core vesicles. We also found a few nNOS-immunopositive synapses, in which intense immunoreactivity was found on the postsynaptic density and mitochondrial membrane. The localization of nNOS-IR in nerve terminals and glial elements in the median eminence might indicate that nNOS plays a role in regulating the release of neurosecretory peptide.

Animals↗
PubMed1998

Single-channel activity of the Ca2+-dependent K+ channel is modulated by FK506 and rapamycin.

Single-channel patch clamp recordings were performed in primary cultured neurons from rat dorsal hippocampi. Ca2+-dependent and TEA-sensitive K+ current was recorded from the neurons. Application of immunosuppressants FK506 and rapamycin to the channel inside the plasma membrane of the neurons significantly prolonged the mean open time of the channel. Calcineurin autoinhibitory fragment and W-7 induced no significant alteration in the mean open time of the channel. These results suggest that modulation of the activity of the Ca2+-dependent K+ channel by FK506 and rapamycin is directly through association of immunosuppressants with FKBP12.

Animals↗