Akihito Yokosuka

Tokyo University of Pharmacy and Life Science, Edo, Tōkyō, Japan

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Publications (82)208.61 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Six spirostanol glycosides (1–6) and 12 known compounds were isolated from the underground parts of Dracaena thalioides (Agavaceae). A spirostanol glycosides was the most cytotoxic to HL-60 cells and it caused apoptotic cell death via capase-3 activation.
    Phytochemistry 11/2014; · 3.35 Impact Factor
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    ABSTRACT: The N-methyl-D-aspartate (NMDA) receptor plays a key role in learning and memory. Our recent studies have shown that nobiletin from citrus peels activates the cAMP response element-binding protein (CREB) signaling pathway and ameliorates NMDA receptor antagonist-induced learning impairment by activating extracellular signal-regulated kinase. For the first time, we have shown that nobiletin significantly upregulated mRNA expression of the NMDA receptor subunits NR1, NR2A, and NR2B in PC12D cells. Furthermore, c-Fos mRNA expression also increased due to the action of nobiletin. Our results indicate that nobiletin modulates the expression of essential genes for learning and memory by activating the CREB signaling pathway, and suggest that this action mechanism of nobiletin plays a crucial role in improving NMDA receptor antagonist-induced learning impairment in model animals with dementia.
    Biological & Pharmaceutical Bulletin 06/2014; · 1.85 Impact Factor
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    ABSTRACT: Neprilysin (NEP) is one of the candidate amyloid β protein (Aβ) degrading enzymes affecting brain Aβ clearance. This enzyme declines in the brain with age, which leads to the increased Aβ deposition in Alzheimer's disease (AD). Pharmacological activation of NEP during the aging process, therefore, represents a potential strategy to prevent the development of AD. To examine the influence of nobiletin on neprilysin activity, we measured cellular NEP activity in SK-N-SH cells. Moreover, NEP expression was examined by using reverse transcription - polymerase chain reaction and Western blotting. Measurement of cellular NEP activity showed that nobiletin stimulated this in a dose- and time-dependent manner in SK-N-SH cells. Moreover, nobiletin increased the expression of NEP mRNA, and then the levels of NEP protein, also in a dose- and time-dependent manner. Our findings showed that nobiletin promoted NEP gene and protein expression, resulting in enhancement of cellular NEP activity in SK-N-SH cells. This compound could be a novel Aβ-degrading compound for use in the development of disease-modifying drugs to prevent and (or) cure AD.
    Canadian Journal of Physiology and Pharmacology 05/2014; 92(5):351-355. · 1.56 Impact Factor
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    ABSTRACT: Six steroidal glycosides and 14 known compounds were isolated from the underground parts of Yucca glauca. Two of the compounds, including 1, exhibited cytotoxic activities against HL-60 cells and induced apoptosis.
    Phytochemistry 05/2014; · 3.35 Impact Factor
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    ABSTRACT: Nobiletin, a polymethoxylated flavonoid found in citrus fruit peel, reportedly improves memory impairment in rodent models. Here we report its effect on 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-induced motor and cognitive deficits. Nobiletin administration (50 mg/kg i.p.) for 2 consecutive weeks improved motor deficits seen in MPTP-induced Parkinson model mice by 2 weeks, an effect that continued until 2 weeks after drug withdrawal. Drug treatment promoted similar rescue of MPTP-induced cognitive impairment at equivalent time points. Nonetheless, nobiletin treatment did not block loss of dopaminergic neurons seen in the MPTP-treated mouse midbrain, nor did it rescue decreased tyrosine hydroxylase (TH) protein levels seen in the striatum or hippocampal CA1 region of these mice. Interestingly, nobiletin administration (50 mg/kg i.p.) rescued reduced levels of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation and phosphorylation at Thr-34 of dopamine- and cAMP-regulated phosphoprotein-32 (DARPP-32) in striatum and hippocampal CA1 to levels seen in sham-operated mice. Likewise, CaMKII- and cAMP kinase-dependent TH phosphorylation was significantly restored by nobiletin treatment. MPTP-induced reduction of dopamine contents in the striatum and hippocampal CA1 region was improved by nobiletin administration (50 mg/kg i.p.). Acute intraperitoneal administration of nobiletin also enhanced dopamine release in striatum and hippocampal CA1, an effect partially inhibited by treatment with nifedipine (a L-type Ca(2+) channel inhibitor) or NNC 55-0396 (a T-type Ca(2+) channel inhibitor) and completely abolished by combined treatment with both. Overall, our study describes a novel nobiletin activity in brain and suggests that nobiletin rescues motor and cognitive dysfunction in MPTP-induced Parkinson model mice, in part by enhancing dopamine release.
    Neuroscience 12/2013; · 3.33 Impact Factor
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    ABSTRACT: We previously demonstrated that nobiletin, a polymethoxylated flavone isolated from citrus peels, has the potential to improve cognitive dysfunction in patients with Alzheimer's disease (AD). Recent studies suggest that the generation of intraneuronal amyloid-beta (Aβ) oligomers is an early event in the pathogenesis of AD. Aβ oligomers cause deficits in the regulation of the extracellular signal-regulated kinase (ERK) signaling which is critical for consolidation of the memory. Our previous studies revealed that nobiletin activated ERK signaling and subsequent cyclic AMP response element-dependent transcription. In this study, the effects of five nobiletin analogs, 6-demethoxynobiletin, tangeretin, 5-demethylnobiletin, sinensetin, and 6-demethoxytangeretin, isolated from citrus peels were assessed on ERK phosphorylation in PC12D cells, and the structure--activity relationships were examined. PC12D cells were treated with nobiletin or its analogs, and the cell extracts were analyzed by Western blotting using an antibody specific to phosphorylated ERK. 6-Demethoxynobiletin markedly enhanced ERK phosphorylation in a concentration-dependent manner. These results may be useful in developing drugs and functional foods using citrus peels for the treatment of dementia including AD.
    Biological & Pharmaceutical Bulletin 08/2013; · 1.85 Impact Factor
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    ABSTRACT: Increased expression of thioredoxin-interacting protein (TXNIP) has recently been proved to be a crucial event for irremediable endoplasmic reticulum (ER) stress resulting in the programmed cell death (apoptosis) of pancreatic β-cells. The present study demonstrated that treatment with 1-10μg/ml tunicamycin, a potent revulsant of ER stress, drastically induced TXNIP expression accompanied by the generation of cleaved caspase-3 as an indicator of apoptosis in SK-N-SH human neuroblastoma cells. This result substantiated that TXNIP is also involved in neurodegeneration triggered by ER stress. Moreover, we evaluated the effects of nobiletin, a citrus polymethoxyflavonoid, on tunicamycin-induced apoptosis and TXNIP expression in SK-N-SH cells, because we reported previously that this flavonoid might be able to reduce TXNIP expression. Co-treatment of SK-N-SH cells with 100μM nobiletin and 1μg/ml tunicamycin for 24h strongly suppressed apoptosis and increased TXNIP expression induced by 1μg/ml tunicamycin treatment alone. In addition, we proved that the ability of 100μM nobiletin treatment to reduce TXNIP expression is exerted from 3h after the onset of treatment. Therefore, the protective and ameliorative effects of nobiletin on neuronal degeneration and impaired memory, which several studies using animal models have demonstrated, might arise in part from nobiletin's ability to repress TXNIP expression.
    Neuroscience Letters 06/2013; · 2.06 Impact Factor
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    ABSTRACT: Senescence-accelerated mouse prone 8 (SAMP8) is a model of aging characterized by the early onset of learning and memory impairment and various pathological features of Alzheimer's disease (AD). Our recent studies have demonstrated that nobiletin, a polymethoxylated flavone from citrus peels, ameliorates learning and memory impairment in olfactory-bulbectomized mice, amyloid precursor protein transgenic mice, and NMDA receptor antagonist-treated mice. Here, we present evidence that this natural compound improves age-related cognitive impairment and reduces oxidative stress and tau phosphorylation in SAMP8 mice. Treatment with nobiletin (10 or 50mg/kg) reversed the impairment of recognition memory and context-dependent fear memory in SAMP8 mice. Treatment with nobiletin also restored the decrease in the GSH/GSSG ratio in the brain of SAMP8 mice. In addition, increases in glutathione peroxidase and manganese-superoxide dismutase activities, as well as a decrease in protein carbonyl level, were observed in the brain of nobiletin-treated SAMP8 mice. Furthermore, nobiletin reduced tau phosphorylation in the hippocampus of SAMP8 mice. Together, the markedly beneficial effects of nobiletin represent a potentially useful treatment for ameliorating the learning and memory deficits, oxidative stress, and hyperphosphorylation of tau in aging as well as age-related neurodegenerative diseases such as AD.
    Behavioural brain research 05/2013; · 3.22 Impact Factor
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    ABSTRACT: cAMP/PKA/ERK/CREB signaling linked to CRE-mediated transcription is crucial for learning and memory. We originally found nobiletin as a natural compound that stimulates this intracellular signaling and exhibits anti-dementia action in animals. Citrus reticulata or C.unshiu peels are employed as "chinpi" and include a small amount of nobiletin. We here provide the first evidence for beneficial pharmacological actions on the cAMP/PKA/ERK/CREB cascade of extracts from nobiletin-rich C.reticulata peels designated as Nchinpi, the nobiletin content of which was 0.83 ± 0.13 % of the dry weight or 16-fold higher than that of standard chinpi extracts. Nchinpi extracts potently facilitated CRE-mediated transcription in cultured hippocampal neurons, whereas the standard chinpi extracts showed no such activity. Also, the Nchinpi extract, but not the standard chinpi extract, stimulated PKA/ERK/CREB signaling. Interestingly, treatment with the Nchinpi extract at the concentration corresponding to approximately 5 μM nobiletin more potently facilitated CRE-mediated transcriptional activity than did 30 μM nobiletin alone. Consistently, sinensetin, tangeretin, 6-demethoxynobiletin, and 6-demethoxytangeretin were also identified as bioactive substances in Nchinpi that facilitated the CRE-mediated transcription. Purified sinensetin enhanced the transcription to a greater degree than nobiletin. Furthermore, samples reconstituted with the four purified compounds and nobiletin in the ratio of each constituent's content in the extract showed activity almost equal to that of the Nchinpi extract to stimulate CRE-mediated transcription. These findings suggest that above four compounds and nobiletin in the Nchinpi extract mainly cooperated to facilitate potently CRE-mediated transcription linked to the upstream cAMP/PKA/ERK/CREB pathway in hippocampal neurons.
    Journal of Neural Transmission 04/2013; 120(10). · 2.87 Impact Factor
  • Akihito Yokosuka, Atsushi Sekiguchi, Yoshihiro Mimaki
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    ABSTRACT: Two new furostanol bisdesmosides (1 and 2) and seven known compounds (3-9) were isolated from the leaves of Dracaena thalioides (Agavaceae). The structures of the new compounds were determined on the basis of spectroscopic data and the results of hydrolytic cleavage. The isolated compounds were evaluated for cytotoxic activity against HL-60 human promyelocytic leukemia cells. Compound 5, a glyceroglycolipid-related compound assigned as (2S)-1-O-linoleoyl-3-O-beta-D-galactopyranosylglycerol, was found to induce apoptotic cell death in HL-60 cells with an IC50 value of 25.8 microM.
    Natural product communications 03/2013; 8(3):315-8. · 0.92 Impact Factor
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    ABSTRACT: Glaziovianin A, an isoflavone isolated from the leaves of Ateleia glazioviana, inhibits the cell cycle progression in M-phase with an abnormal spindle structure, but its inhibitory mechanism has not been revealed. Here, we report that glaziovianin A and its derivatives are microtubule dynamics inhibitors. Glaziovianin A extended the time lag of tubulin polymerization without changing the net amount of polymerized tubulin in vitro and suppressed microtubule dynamics in cells. Furthermore, glaziovianin A inhibited the transport of endosomes containing EGF-stimulated EGFR and prolonged the EGFR activation. Consistent with the prolonged activation of EGFR, glaziovianin A enhanced the EGF-dependent apoptosis in A431 cells. These results strongly suggested that microtubule dynamics is important for endosome transport and maturation, and that glaziovianin A shows cytotoxicity by two pathways, the mitotic arrest and inadequate activation of receptor kinases via the inhibition of endosome maturation.
    ACS Chemical Biology 02/2013; · 5.44 Impact Factor
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    ABSTRACT: Nobiletin, a polymethoxylated flavonoid that is highly contained in the peels of citrus fruits, exerts a wide variety of beneficial effects, including anti-proliferative effects in cancer cells, repressive effects in hyperlipidemia and hyperglycemia, and ameliorative effects in dementia at in vitro and in vivo levels. In the present study, to further understand the mechanisms of these actions of nobiletin, the nobiletin-mediated alterations of gene expressionin three organ-derived cell lines -- 3Y1 rat fibroblasts, HuH-7 human hepatocarcinoma cells, and SK-N-SH human neuroblastoma cells -- were first examined with DNA microarrays.In all three cell lines, treatments with nobiletin (100 μM) for 24 h resulted in more than 200% increases in the expression levels of five genes, including the endoplasmic reticulum stress-responsive genesDdit3, Trib3, and Asns, and in less than 50% decreases in the expression levels of seven genes, including the cell cycle-regulating genesCcna2, Ccne2, and E2f8 and the oxidative stress-promoting geneTxnip. It was also confirmed that in each nobiletin-treated cell line, the levels of the DDIT3 (DNA-damage-inducible transcript 3, also known as CHOP and GADD153)and ASNS (asparagine synthetase) proteins were increased, while the level of the TXNIP (thioredoxin-interacting protein, also known as VDUP1 and TBP-2) protein was decreased.All these findings suggest that nobiletin exerts a wide variety of biological effects, at least partly, through induction of endoplasmic reticulum stress and suppressions of oxidative stress and cell proliferation.
    Biochemical and Biophysical Research Communications 01/2013; · 2.28 Impact Factor
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    ABSTRACT: Ras, a small G-protein, physiologically directs cell proliferation and cell cycle via regulation of mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling cascade. Dysregulation of Ras/MEK/ERK signaling has been reported to cause tumorigenesis and gliomas. Nobiletin, a citrus flavonoid, has been shown to have anti-tumor cells action. However, it remains elusive whether nobiletin could affect Ras activity. In this study, we provide the first evidence that nobiletin suppresses the proliferation by inhibiting Ras activity in C6 glioma cells, a rat glioma cell line. First, Ras pull-down assay showed that nobiletin inhibits Ras activity in a concentration-dependent manner in C6 cells. Second, farnesyltransferase inhibitor I, a Ras inhibitor, and U0126, a MEK inhibitor, induced an inhibition of the cell proliferation in C6 cells, while the cell proliferation was inhibited by nobiletin as well. Third, western blotting revealed that nobiletin showed inhibitory effects on MEK and ERK phopsphorylation levels in a concentration-dependent manner. Finally, such an inhibitory effect on the level of ERK phosphorylation by nobiletin was appreciably prevented by Gö6976, a selective inhibitor of conventional protein kinase Cs (PKCs) showing Ca(2+)-sensitivity, while GF109203X, a general inhibitor for PKCs, and BAPTA, a cell-permeable Ca(2+) chelator, to a lesser extent, suppressed a reduction of the phosphorylation. These findings suggest that the proliferation of C6 cells is Ras- and MEK/ERK signaling-dependent, and that nobiletin suppresses the cell proliferation by inhibiting Ras activity and MEK/ERK signaling cascade probably via a Ca(2+)-sensitive PKC-dependent mechanism. Thus, the natural compound has potential to be a therapeutic agent for glioma.
    Biological & Pharmaceutical Bulletin 01/2013; 36(4):540-7. · 1.85 Impact Factor
  • Akihito Yokosuka, Kenichi Takagi, Yoshihiro Mimaki
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    ABSTRACT: Six new cholestane glycosides (1, 5, 6, 10, 12, and 13) and two new sterols (9 and 11), along with five known compounds (2-4, 7, and 8), were isolated from the underground parts of Chamaelirium luteum (Liliaceae). The structures of these new compounds were determined by spectroscopic analysis and the results of hydrolytic cleavage. The isolated compounds and aglycones were evaluated for their cytotoxic activity against HL-60 human leukemia cells. Compounds 6a, 10a, 12a, 13, and 13a were cytotoxic to HL-60 cells, with IC(50) values of 12.8, 9.8, 15.3, 6.2, and 10.2 µM, respectively.
    Journal of Natural Medicines 11/2012; · 1.52 Impact Factor
  • Akihito Yokosuka, Takeyuki Suzuki, Yoshihiro Mimaki
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    ABSTRACT: Four new cholestane glycosides (1-4) were isolated from the leaves of Cordyline terminalis (Agavaceae). The structures of the new compounds were determined on the basis of spectroscopic analysis and a few chemical transformations followed by chromatographic and spectroscopic analyses.
    Chemical & pharmaceutical bulletin 08/2012; 60(2):275-9. · 1.70 Impact Factor
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    ABSTRACT: Seven new triterpene glycosides on the basis of the lupane skeleton (1–7) were isolated from the pericarps of Stryphnodendron fissuratum (Leguminosae). The structures of 1–7 were determined on the basis of extensive spectroscopic analysis, including two-dimensional NMR data, and the results of hydrolytic cleavage.
    Phytochemistry Letters 09/2011; 4(3):259-266. · 1.54 Impact Factor
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    ABSTRACT: We recently demonstrated that nobiletin, a citrus flavonoid, exhibits anti-dementia action in animals. However, no determination methods for the content of nobiletin with beneficial action in the brain of nobiletin-administered animals have been developed, nor has its pharmacokinetics been revealed completely. Here, we established the high-performance liquid chromatography/photodiode array detection method for nobiletin determination using Bond Elut C18 SPE cartridges for extraction, where the calibration curve was linear over 0.025-10 ng, with coefficient of variation of less than 6.76%. This method enabled us to determine pharmacokinetic parameters of nobiletin given intraperitoneally or per os in the brain of mice.
    Analytical and Bioanalytical Chemistry 05/2011; 400(10):3635-41. · 3.66 Impact Factor
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    ABSTRACT: An alcoholic extract of Lycoris albiflora (Amaryllidaceae) showed potent cytotoxic activity against HL-60 cells with an IC50 value of 1.7 microg/mL. Phytochemical examination of the extract resulted in the isolation of 15 alkaloids, including two phenanthridine-type alkaloids (1, 2), one benzylphenethylamine-type alkaloid (3), two crinane-type alkaloids (4, 5), one pyrrolophenanthridine-type alkaloid (6), six lycorenan-type alkaloids (7-12), and three galanthamine-type alkaloids (13-15), together with three neolignans (16-18), two flavans (19, 20), and two acetophenone derivatives (21, 22). Compound 3 (hostasinine A) has not been isolated from Amaryllidaceae plants, and 1, 2, 4, 5, 7-9, 11, 12 and 14-22 are the first isolation and identification from L. albiflora. The phenanthridine-type alkaloids (1, 2), as well as the alkaloids (3-5), exhibited potent cytotoxic activities against not only HL-60 cells but also HSC-2 cells, thus leading to the conclusion that these alkaloids are mainly responsible for the cytotoxicity of the L. albiflora extract. Compound 1 (lycoricidinol), with the most potent cytotoxic activities, induced apoptosis in both HL-60 cells and HSC-2 cells. It is notable that 1 induced transient autophagy and morphological changes in mitochondria in the early stages of the apoptotic cell death process in HSC-2 cells.
    Natural product communications 02/2011; 6(2):187-92. · 0.92 Impact Factor
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    ABSTRACT: Two new lignan glycosides, named larrealignans A (1) and B (2), and a known lignan (3) were isolated from the aerial parts of Larrea tridentata (Zygophyllaceae). The structures of 1 and 2 were determined on the basis of spectroscopic analysis and the results of hydrolytic cleavage. The isolated compounds (1-3) and aglycones (1a, 2a) of 1 and 2 were evaluated for their cytotoxic activities against HL-60 human leukemia cells.
    Chemical & pharmaceutical bulletin 01/2011; 59(12):1467-70. · 1.70 Impact Factor
  • Akihito Yokosuka, Yoshihiro Mimaki, Yutaka Sashida
    ChemInform 12/2010; 33(52).

Publication Stats

950 Citations
208.61 Total Impact Points


  • 1998–2014
    • Tokyo University of Pharmacy and Life Science
      • • School of Pharmacy
      • • Department of Medicinal Pharmacognosy
      Edo, Tōkyō, Japan
  • 2007–2013
    • Tohoku University
      • Graduate School of Pharmaceutical Sciences
      Sendai, Kagoshima-ken, Japan