Kiichi Miyashita

Nihon University, Tokyo, Tokyo-to, Japan

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Publications (13)50.83 Total impact

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    ABSTRACT: We previously reported that many ingenol compounds derived from Euphorbia kansui exhibit topoisomerase inhibitory activity and/or inhibitory activity of cell proliferation. The inhibitory effects of 20-O-(2'E,4'Z-decadienoyl) ingenol and 3-O-(2'E,4'Z-decadienoyl)-ingenol among these compounds on topoisomerase II activity and on the cell proliferative activity and arrest phase of the cell cycle were studied using a mouse breast cancer (MMT) cell line. Although 20-O-ingenolEZ exerted inhibitory effects on both topoisomerase II activity and cell proliferative activity, 3-O-ingenolEZ exerted inhibitory activity on neither. The 20-O-ingenolEZ-induced cell arrest of MMT-cell proliferation led to a cell cycle arrest in the G2/M phase. Topoisomerase II inhibition can be divided into the poison and catalytic inhibitor types. A checkpoint mechanism is activated when cells are treated with these topoisomerase II inhibitors. Poison-type inhibition occurs via induction of the DNA damage checkpoint and the catalytic-type inhibition occurs via induction of the DNA-decatenation checkpoint, suggestive of distinct checkpoint reactions. 20-O-ingenolEZ inhibited topoisomerase IIalpha activity through inhibition of ATPase, and induced DNA-decatenation checkpoint without signaling for phosphorylation of H2AX.
    Cancer Science 02/2010; 101(2):374-8. · 3.48 Impact Factor
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    ABSTRACT: It is unclear how hepatic adiponectin resistance and sensitivity mediated by the adiponectin receptor, AdipoR2, contributes to the progression of nonalcoholic steatohepatitis (NASH). The aim of this study was to examine the roles of hepatic AdipoR2 in NASH, using an animal model. We fed C57BL/6 mice a methionine-deficient and choline-deficient (MCD) diet for up to 8 weeks and analyzed changes in liver pathology caused by either an AdipoR2 short hairpin RNA-expressing adenovirus or an AdipoR2-overexpressing adenovirus. Inhibition of hepatic AdipoR2 expression aggravated the pathological state of NASH at all stages: fatty changes, inflammation, and fibrosis. In contrast, enhancement of AdipoR2 expression in the liver improved NASH at every stage, from the early stage to the progression of fibrosis. Inhibition of AdipoR2 signaling in the liver diminished hepatic peroxisome proliferator activated receptor (PPAR)-alpha signaling, with decreased expression of acyl-CoA oxidase (ACO) and catalase, leading to an increase in lipid peroxidation. Hepatic AdipoR2 overexpression had the opposite effect. Reactive oxygen species (ROS) accumulation in liver increases hepatic production of transforming growth factor (TGF)-beta1 at all stages of NASH; adiponectin/AdipoR2 signaling ameliorated TGF-beta-induced ROS accumulation in primary cultured hepatocytes, by enhancing PPAR-alpha activity and catalase expression. CONCLUSION: The adiponectin resistance and sensitivity mediated by AdipoR2 in hepatocytes regulated steatohepatitis progression by changing PPAR-alpha activity and ROS accumulation, a process in which TGF-beta signaling is implicated. Thus, the liver AdipoR2 signaling pathway could be a promising target in treating NASH.
    Hepatology 09/2008; 48(2):458-73. · 12.00 Impact Factor
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    ABSTRACT: Recent studies suggest that nuclear factor-kappaB (NF-kappaB) activation has an important role in leading to beta cell dysfunction in both type 1 and type 2 diabetes. In this study we tested this hypothesis by investigating the effects of dehydroxymethylepoxyquinomicin (DHMEQ), a novel NF-kappaB inhibitor, on tumor necrosis factor-alpha (TNF-alpha)-induced beta cell dysfunction. INS-1 cells were incubated with TNF- alpha and with or without DHMEQ for 24 hours. Glucose-stimulated insulin secretion, cell viability, mRNA expression and NF-kappaB activation were investigated. DHMEQ suppressed TNF-alpha-induced NF-kappaB activation and partially ameliorated glucose-stimulated insulin secretion in a dose-dependent manner. DHMEQ also partially ameliorated decreased cell viability and insulin mRNA level induced by TNF-alpha. DHMEQ suppressed NF-kappaB activation and ameliorated beta cell dysfunction induced by TNF- alpha. Inhibition of activated NF-kappaB in beta cells may be important to ameliorate beta cell dysfunction in diabetes.
    Endocrine Journal 06/2008; 55(2):433-8. · 2.23 Impact Factor
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    ABSTRACT: GPR40 is a member of the G-protein-coupled receptors. Recent studies suggest that GPR40 is highly expressed in pancreatic beta cells and insulin-secreting cell lines, and that fatty acids increase intracellular calcium concentration and amplify glucose-stimulated insulin secretion by activating GPR40. Despite identification of the Arg211His polymorphism in the GPR40 gene, there have been no clinical studies concerning this polymorphism. The present study was performed to investigate the effects of the GPR40 gene Arg211His polymorphism on clinical and metabolic parameters, including serum insulin level, in 327 healthy Japanese men, using the TaqMan polymerase chain reaction method. Serum insulin level, homeostasis model of insulin resistance (HOMA-IR), and beta-cell function (HOMA-beta were significantly different (P = .0075, .0152, and .0039, respectively) and were lowest in Arg/Arg homozygotes and highest in His/His homozygotes, although plasma glucose and serum lipids were not significantly different. Multiple regression analyses showed that serum insulin level, HOMA-IR, and HOMA- beta were significantly correlated with this polymorphism after adjusting for age and body mass index. After Bonferroni's correction for multiple comparisons was made, only HOMA- beta was significantly different among the 3 genotypes. These results suggest that the Arg211His polymorphism in the GPR40 gene may contribute to the variation of insulin secretory capacity in Japanese men.
    Metabolism 04/2005; 54(3):296-9. · 3.10 Impact Factor
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    ABSTRACT: Leptin plays an important role in the regulation of body weight and is known to circulate in both free and bound forms. One of the leptin receptor isoforms exists in a circulating soluble form that can bind leptin. Clinical studies have shown that soluble leptin receptor (sOB-R) levels are lower in obese individuals. In the present study, we measured the serum sOB-R level in 419 healthy Japanese subjects (198 men and 221 women, aged 30 to 65 years, body mass index [BMI] 21.7 +/- 2.6 [SD] kg/m2) and in 150 type 2 diabetic patients (96 men and 54 women, BMI 24.3 +/- 3.8 kg/m2). We investigated the relationships between serum sOB-R level and BMI, blood pressure, homeostasis model assessment-insulin resistance index (HOMA-IR), serum leptin and adiponectin levels, lipid profile, and leptin receptor (LEPR) gene Lys109Arg and Gln223Arg polymorphisms. Serum leptin and sOB-R levels were measured by radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA), respectively. The serum sOB-R level in men was significantly higher than that in women. The serum sOB-R level was negatively correlated with BMI, fasting insulin, HOMA-IR, and serum leptin level and positively correlated with high-density lipoprotein (HDL)-cholesterol and serum adiponectin levels. The correlations between serum sOB-R level and fasting insulin, HOMA-IR, serum leptin, adiponectin, and HDL-cholesterol levels were significant even after adjustment for age, sex, and BMI in healthy subjects. There was no association between serum sOB-R level and the LEPR polymorphisms examined. These findings suggest that the serum sOB-R level is negatively correlated with HOMA-IR and serum leptin level and positively correlated with HDL-cholesterol level and serum adiponectin level, independent of age, sex, and BMI, in the Japanese population.
    Metabolism 08/2004; 53(7):879-85. · 3.10 Impact Factor
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    ABSTRACT: We analyzed the genes that exhibit transcriptional changes during sex differentiation in Xenopus, using fluorescent differential display (FDD). Search was then undertaken for sequences that were homologous to the differentially displayed DNA. In this report, trans-acting factors of activating transcription factor 4 (ATF 4) and heat shock proteins were selected, on the basis of homology, from candidate genes thought to be involved in the expression cascade of aromatase and estrogen receptor genes. The stage and tissue specificities and the effect of estradiol treatment on the expression of these genes were then examined using real-time quantitative polymerase chain reaction (RQ-RT-PCR). The expression of ATF 4, a member of the ATF/cAMP-responsive element-binding protein (CREB) family of genes, peaked in the gonads at stage 50 of development. Interestingly, expression of the genes encoding the heat shock cognate protein70. II (Hsc70. II) and the heat shock protein 70 (Hsp70) binding protein was strongly activated at stages 50 and 48 of development, respectively. The three genes revealed a higher transcription activity in the gonads than in other tissues. Although the expression of all of the genes encoding ATF 4, aromatase, Hsc70. II, and Hsp70 binding protein was activated in vitro by estrogen treatment, that of Hsc70. II and Hsp70 binding protein was found to be transient.
    General and Comparative Endocrinology 06/2004; 136(3):382-8. · 2.82 Impact Factor
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    ABSTRACT: Although peroxisome proliferator-activated receptor (PPAR)gamma agonists ameliorate insulin resistance, they sometimes cause body weight gain, and the effect of PPAR agonists on insulin secretion is unclear. We evaluated the effects of combination therapy with a PPARgamma agonist, pioglitazone, and a PPARalpha agonist, bezafibrate, and a dual agonist, KRP-297, for 4 wk in male C57BL/6J mice and db/db mice, and we investigated glucose-stimulated insulin secretion (GSIS) by in situ pancreatic perfusion. Body weight gain in db/db mice was less with KRP-297 treatment than with pioglitazone or pioglitazone + bezafibrate treatment. Plasma glucose, insulin, triglyceride, and nonesterified fatty acid levels were elevated in untreated db/db mice compared with untreated C57BL/6J mice, and these parameters were significantly ameliorated in the PPARgamma agonist-treated groups. Also, PPARgamma agonists ameliorated the diminished GSIS and insulin content, and they preserved insulin and GLUT2 staining in db/db mice. GSIS was further increased by PPARgamma and -alpha agonists. We conclude that combination therapy with PPARgamma and PPARalpha agonists may be more useful with respect to body weight and pancreatic GSIS in type 2 diabetes with obesity.
    AJP Endocrinology and Metabolism 06/2003; 284(5):E966-71. · 4.51 Impact Factor
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    ABSTRACT: The effects of heteropolyoxotungstate (K(7)[PTi(2)W(10)O(40)]. 6H(2)O; PM-19) on the replication of herpes simplex virus type 2 (HSV-2) were examined using a semiquantitative polymerase chain reaction of intracellular viral DNA established by us and also other methods. Vero cells were infected with HSV-2 strains: either the standard strain 169, or the acyclovir-resistant strain YS-4C-1. PM-19 was added at various stages during the replication of HSV-2. PM-19 strongly inhibited the synthesis of viral genomic DNA when it was added at the time of infection. The addition of PM-19 60-90 min after viral inoculation time-dependently decreased the antiviral activity and increased the relative yield of viral DNA, and the addition of PM-19 was completely ineffective at times later than 90 min. These results suggested that PM-19 inhibited viral penetration but did not affect the synthesis of viral DNA. Furthermore, PM-19 strongly inhibited a second round of infection.
    Pharmacology 03/2003; 67(2):83-9. · 1.60 Impact Factor
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    ABSTRACT: Adiponectin is an adipocyte-derived protein, which possesses an anti-atherosclerotic action and improves insulin sensitivity. Peroxisome proliferator-activated receptor gamma (PPAR(gamma)) regulates the transcription of many adipocyte-specific genes. A Pro12Ala polymorphism has been detected in the PPAR(gamma)2 gene, and this substitution has been reported to reduce transactivation activity in vitro. We hypothesized that individuals possessing this Ala12 allele may have a lower serum adiponectin level, because of the observation that PPAR(gamma) agonists increase the plasma adiponectin level in humans. To test this hypothesis, we investigated the effects of the PPAR(gamma)2 Pro12Ala polymorphism on anthropometric and metabolic parameters, including serum adiponectin level, in 478 Japanese men and 117 women aged 30 to 65 years. There were no homozygous subjects for the Ala12 allele of the PPAR(gamma)2 gene in this study. Plasma adiponectin levels were significantly lower in subjects with the Ala12 allele in the Japanese population of both sexes, although body mass index (BMI), plasma glucose, serum lipids, and insulin resistance index were not significantly different between subjects with and without this polymorphism. It is suggested that the Pro12Ala polymorphism of the PPAR(gamma)2 gene may reduce serum adiponectin level in the Japanese population.
    Metabolism 12/2002; 51(11):1407-9. · 3.10 Impact Factor
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    ABSTRACT: The keggin-type heteropolyoxotungstate K(7)[PTi(2)W(10)O(40)].6H(2)O (PM-19) is a potent polyoxometalate (PM) inhibitor of the replication of herpes simplex virus (HSV). Pretreatment of Vero cells with PM-19 prior to HSV-2 infection enhanced the antiviral potency of PM-19 almost 10-fold compared with treatment of the cells only after infection. The pretreatment effect of PM-19 is called "the memory effect". The memory effect was reflected by inhibition of plaque formation and decrease of intracellular virus DNA quantity, and was strongest when PM-19 was present during the penetration stage of HSV-2 infection. The effect was maintained under conditions of fusion induced by polyethyleneglycol treatment. This suggests that PM-19 does not act at the fusion stage of infection. Using the infectious center assay method, it was clarified that a second round of infection was inhibited by about 30% in the presence of PM-19 at the penetration stage compared with the virus control in nontreated cells. The inhibition was enhanced to about 60% by PM-19 pretreatment prior to infection. This suggests that PM-19 pretreatment of the cells protects them against HSV-2 infection.
    Pharmacological Research 11/2002; 46(4):357-61. · 4.35 Impact Factor
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    ABSTRACT: Recent studies point to a key role for the estrogen synthesizing enzyme P450 aromatase (P450 arom) in ovary determination in fish, birds and reptiles. It is unclear whether estrogen synthesis is important in sex determination of Xenopus gonad. To determine whether the aromatase gene is transcribed in the gonads of Xenopus tadpoles during the sex determination, we cloned a P450 arom cDNA and examined the level of P450 arom and estrogen receptor (ER) gene expression in association with estrogen activity. cDNA clones for P450 arom were isolated from a Xenopus ovarian cDNA library. There was an open reading frame (ORF) of 1500 bp from the ATG start to TAA stop codons encoding 500 predicted amino acids. cDNAs for P450 arom have previously been cloned from various vertebrates. The homology between the Xenopus P450 aromatase and the human P450 arom was higher. The expression of the P450 arom gene was mainly limited to reproductive organs. To determine the beginning of estrogen activity in gonads of embryos, expression of the aromatase and ER gene was also examined by RQ-RT-PCR. Both Xenopus aromatase and ER mRNA was detected at stage 51 in gonads. These observations are consistent with estrogens having a key role in ovarian development in various other vertebrates.
    The Journal of Steroid Biochemistry and Molecular Biology 01/2001; 75(2-3):101-7. · 3.98 Impact Factor
  • K Dan, K Miyashita, Y Seto, T Yamase
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    ABSTRACT: A method for quantitation of the DNA of Herpes simplex virus type 2 (HSV-2)-infected Vero cells by the polymerase chain reaction (PCR) was developed. This method allowed recognition of several molecules of viral DNA among the total DNA extracted from cells. The method could be applied to a very large range (10(-0)-10(-7)) of initial amounts of template. Products of PCR were collected after each cycle for kinetic analysis. Products were subjected to electrophoresis and amplified bands were stained with ethidium bromide. The intensity of fluorescence of each band was measured with a charge-coupled device (CCD) image analyzer. The time course of increases in the relative yield of viral DNA was determined. Two-fold amplification of viral DNA occurred each 6-h cycle from 7 h after infection. Using this method, the yields of viral DNA after treatment with the drug acyclovir (ACV) at 0.1 and 2 microg/ml were about 1/10 and 1/80 of those from nontreated infected cells, respectively. These results indicate that this method makes clear the inhibitory effect of ACV on the synthesis of viral DNA.
    Journal of Virological Methods 01/1999; 76(1-2):73-9. · 1.90 Impact Factor
  • S Miyata, K Miyashita, Y Hosoyama
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    ABSTRACT: SRY-related genes are known as Sox (Sry-box) genes. Two Sox cDNAs from Xenopus oocytes were analyzed. The deduced product of the Xenopus Sox gene (xSox-11) consisted of the standard domains of an HMG box, glycine/alanine-rich region and glutamic acid/aspartic acid-rich region and may be involved in the control of transcription. The other Sox gene (xSox-11-D) had a deletion of 262 nucleotides at one end of the HMG box in the xSox-11 cDNA. The deletion resulted in a frame-shift and in variations in base pair composition and the length of the trinucleotide repeat in the C-terminal coding region. The amino acid sequence of the C-terminal domain encoded by xSox-II-D was highly basic and might be involved, together with the HMG box, in the binding to DNA.
    Biochimica et Biophysica Acta 08/1996; 1308(1):23-7. · 4.66 Impact Factor

Publication Stats

275 Citations
50.83 Total Impact Points


  • 2004–2010
    • Nihon University
      • Department of Chemistry
      Tokyo, Tokyo-to, Japan
  • 1996–2010
    • Keio University
      • • Institute for Advanced Medical Research
      • • Department of Internal Medicine
      • • School of Medicine
      Tokyo, Tokyo-to, Japan