Akihito Yokosuka

Tokyo University of Pharmacy and Life Science, Tokyo, Tokyo-to, Japan

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Publications (106)

  • Tomofumi Fujino · Akihito Yokosuka · Hideaki Higurashi · [...] · Makio Hayakawa
    [Show abstract] [Hide abstract] ABSTRACT: Here, we show that AU-1, spirostanol saponin isolated from Agavaceae plants, causes a transient increase in cyclin-dependent kinase inhibitor (CDKI) p21/Cip1 through the upregulation of miRNAs, miR-34 and miR-21. AU-1 stimulated p21/Cip1 expression without exerting cytotoxicity against different types of carcinoma cell lines. In renal adenocarcinoma ACHN cells, AU-1 transiently elevated the expression level of p21/Cip1 protein without marked increases in p21/Cip1 mRNA levels. Rapid and transient increases in miR-34 and miR-21, both of which are known to upregulate p21/Cip1, were observed in AU-1-treated cells. Inhibitor for miR-34 and for miR-21 significantly blocked the AU-1-caused increase in p21/Cip1, indicating that elevation of p21/Cip1 protein by AU-1 is dependent on these microRNAs. We further clarified that NAD-dependent deacetylase SIRT1, a direct target of miR-34, is decreased by the treatment with AU-1. Furthermore, we found that SIRT1-knockdown increases p21/Cip1 protein levels in an miR-21-dependent manner. On the other hand, ectopic expression of p21/Cip1 resulted in the lowered expression of miR-34 and miR-21, suggesting that reciprocal regulation exists between p21/Cip1 and these miRNAs. We propose that the following feedback network composed of miR-34/SIRT1/miR-21/p21 is triggered by the treatment with AU-1: in cells treated with AU-1, transient elevation of miR-34 leads to the downregulation of SIRT1, thereby miR-21 is freed from SIRT1-dependent suppression. Then, elevated miR-21 upregulates p21/Cip1 protein, followed by the suppression of miR-34 expression.
    Article · Jul 2016 · Journal of Natural Medicines
  • Akihito Yokosuka · Genki Okabe · Satoru Tatsuno · Yoshihiro Mimaki
    [Show abstract] [Hide abstract] ABSTRACT: Ten new triterpene glycosides, stryphnosides G–P (1–10), were isolated from the pericarps of Stryphnodendron fissuratum (Legminosae). The structures of 1–10 were determined based on spectroscopic analyses, including various two-dimensional NMR spectroscopic techniques, and the results of hydrolytic cleavage. The sugar moiety attached to C-3 of the aglycone of 4, 5, and 7–10 is composed of five or six monosaccharides, of which the terminal α-L-arabinosyl unit has a 1C4 conformation. Compounds 2 and 5 differ from the other isolates in having an α-L-rhamnosyl unit at the C-21 hydroxy group. The cytotoxic activity of 1–10, stryphnosides A–F (11–16), and their aglycones (1a, 11a, 14a, and 16a) against HL-60 cells was also examined.
    Article · Jul 2016
  • [Show abstract] [Hide abstract] ABSTRACT: Prevention and treatment of Alzheimer disease are urgent problems for elderly people in developed countries. We previously reported that nobiletin, a poly-methoxylated flavone from the citrus peel, improved the symptoms in various types of animal models of memory loss and activated the cAMP responsive element (CRE)-dependent transcription in PC12 cells. Nobiletin activated the cAMP/PKA/MEK/Erk/MAPK signaling pathway without using the TrkA signaling activated by nerve growth factor (NGF). Here, we examined the effect of combination of nobiletin and NGF on the CRE-dependent transcription in PC12 cells. Although NGF alone had little effect on the CRE-dependent transcription, NGF markedly enhanced the CRE-dependent transcription induced by nobiletin. The NGF-induced enhancement was neutralized by a TrkA antagonist, K252a. This effect of NGF was effective on the early signaling event elicited by nobiletin. These results suggested that there was crosstalk between NGF and nobiletin signaling in activating the CRE-dependent transcription in PC12 cells.
    Article · Feb 2016 · Canadian Journal of Physiology and Pharmacology
  • Akihito Yokosuka
    [Show abstract] [Hide abstract] ABSTRACT: Numerous clinically valuable medicines, including anticancer drugs, have been developed from biologically active natural compounds and their structurally related derivatives. This review discusses novel natural compounds with promising biological activities and those with novel chemical structures. Glaziovianin A, an isoflavone isolated from the leaves of Ateleia glazioviana (Legminosae), inhibited cell cycle progression at the M-phase with an abnormal spindle structure. AU-1 and YG-1, 5β-steroidal glycosides isolated from the whole plants of Agave utahensis and the underground parts of Yucca glauca (Agavaceae), induced apoptosis of HL-60 cells via caspase-3 activation. Lycolicidinol, an alkaloid isolated from the bulbs of Lycoris albiflora (Amaryllidaceae), induced transient autophagy and morphological changes in mitochondria in the early stage of the apoptotic cell death process in HSC-2 cells. Taccasterosides isolated from the rhizomes of Tacca chantrieri (Taccaceae) and stryphnosides isolated from the pericarps of Stryphnodendron fissuratum (Legminosae) are steroidal and triterpene glycosides with unique chemical structures having novel sugar sequences.
    Article · Oct 2015 · Yakugaku zasshi journal of the Pharmaceutical Society of Japan
  • Akihito Yokosuka · Yoshikazu Koyama · Yoshihiro Mimaki
    [Show abstract] [Hide abstract] ABSTRACT: Three new isoflavonoid glycosides (1, 5, and 9) and 10 known compounds (2-4, 6-8, and 10-13) were isolated from the underground parts of Iris florentina (Iridaceae). The structures of the new compounds were determined based on extensive spectroscopic data and the results of hydrolytic cleavage. The isolated compounds and the aglycones were evaluated for cytotoxic activity against HL-60 human promyelocytic leukemia cells. Compound 12 induced apoptotic cell death in the HL-60 cells.
    Article · Jun 2015 · Natural product communications
  • Satoshi Kubo · Minpei Kuroda · Akihito Yokosuka · [...] · Yoshihiro Mimaki
    [Show abstract] [Hide abstract] ABSTRACT: Five new cardenolide glycosides, amurensiosides L-P (1-5), were isolated from the roots of Adonis amurensis. Their structures were determined based on extensive spectroscopic analysis, including two-dimensional (2D) NMR data, and on the results of hydrolytic cleavage. Compounds 1-5 were evaluated for their cytotoxic activities against HL-60 human promyelocytic leukemia and HSC-2 human oral squamous cell carcinoma cell lines.
    Article · Apr 2015 · Natural product communications
  • [Show abstract] [Hide abstract] ABSTRACT: Alzheimer's disease (AD), the most common form of dementia among the elderly, is characterized by the progressive decline of cognitive function. Increasing evidence indicates that the production and accumulation of amyloid β (Aβ), particularly soluble Aβ oligomers, is central to the pathogenesis of 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, NMDA receptor antagonist-treated mice, and senescence-accelerated mouse prone 8. Here, we present evidence that this natural compound improves cognitive impairment and reduces soluble Aβ levels in a triple transgenic mouse model of AD (3XTg-AD) that progressively develops amyloid plaques, neurofibrillary tangles, and cognitive impairments. Treatment with nobiletin (30mg/kg) for 3 months reversed the impairment of short-term memory and recognition memory in 3XTg-AD mice. Our ELISA analysis also showed that nobiletin reduced the levels of soluble Aβ1-40 in the brain of 3XTg-AD mice. Furthermore, nobiletin reduced ROS levels in the hippocampus of 3XTg-AD as well as wild-type mice. These results suggest that this natural compound has potential to become a novel drug for the treatment and prevention of AD. Copyright © 2015. Published by Elsevier B.V.
    Article · Apr 2015 · Behavioural brain research
  • Article · Mar 2015
  • [Show abstract] [Hide abstract] ABSTRACT: Six spirostanol glycosides (1-6) and 12 known compounds (7-18) were isolated from the underground parts of Dracaena thalioides (Agavaceae). Their structures were determined by spectroscopic analysis, including 2D NMR spectroscopic data, and chemical transformations. The isolated compounds were evaluated for cytotoxic activity against HL-60 human leukemia cells. Compounds 1,3-6, and 8-18 showed cytotoxicity against HL-60 cells, of which 10, a bisdesmosidic spirostanol derivative, showed potent cytotoxicity against HL-60 cells with an IC50 value of 0.38 mu M and induced apoptosis in HL-60 cells.
    Article · Nov 2014 · Phytochemistry
  • [Show abstract] [Hide abstract] 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.
    Article · Jun 2014 · Biological & Pharmaceutical Bulletin
  • [Show abstract] [Hide abstract] 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.
    Article · May 2014 · Canadian Journal of Physiology and Pharmacology
  • Akihito Yokosuka · Tomoka Suzuki · Satoru Tatsuno · Yoshihiro Mimaki
    [Show abstract] [Hide abstract] ABSTRACT: Six steroidal glycosides and 14 known compounds were isolated from the underground parts of Yucca glauca (Agavaceae). Their structures were determined from extensive spectroscopic analysis, including analysis of two-dimensional NMR data, and from chemical transformations. The compounds were also evaluated for cytotoxic activities against HL-60 human leukemia cells and A549 human lung adenocarcinoma cells. Four spirostanol glycosides and three furostanol glycosides exhibited cytotoxic activities against both HL-60 and A549 cells. Two of the compounds induced apoptosis in HL-60 cells.
    Article · May 2014 · Phytochemistry
  • Ayaka Ikeda · Shingo Miyata · Akihito Yokosuka · [...] · Kiyomitsu Nemoto
    [Show abstract] [Hide abstract] ABSTRACT: Nobiletin, a citrus polymethoxyflavonoid compound, has been considered useful in the development of drugs and functional foods for various diseases, including dementia and diabetes. It is therefore important to understand its toxic effects. We previously reported that nobiletin treatment at a dose of 100 µM induced the expression of DDIT3 and TRIB3 genes and proteins, which are well known to contribute to apoptosis caused by endoplasmic reticulum (ER) stress, commonly in three cell lines, such as SK-N-SH human neuroblastoma cells. Therefore, their increased expression raises concerns that nobiletin might exert a toxic effect by inducing ER stress. In the present study, SK-N-SH cells were treated with 100 µM nobiletin or 1 µg/mL tunicamycin, a potent inducer of ER stress, for 3, 6, 12, and 24 hr. The maximum expression of those proteins appeared later and was much weaker in the nobiletin-treated cells than in the tunicamycin-treated cells. The expression level of BiP protein, one of the chaperons, which increases in response to ER stress, was not changed in the nobiletin-treated cells, whereas it was strongly induced 12 and 24 hr after the onset of tunicamycin treatment. In addition, cleavages of caspase-3 and poly (ADP-ribose) polymerase occurred 24 hr after the onset of tunicamycin treatment, whereas cleavage did not occur at any point during nobiletin treatment. Therefore, although nobiletin has the ability to induce the expression of DDIT3 and TRIB3, those increased levels, at doses up to at least 100 µM, cannot be enough to lead to ER stress resulting in apoptosis.
    Article · Jan 2014
  • Yasushi Yabuki · Yasushi Ohizumi · Akihito Yokosuka · [...] · Kohji Fukunaga
    [Show abstract] [Hide abstract] 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.
    Article · Dec 2013 · Neuroscience
  • Junko Kimura · Kiyomitsu Nemoto · Akihito Yokosuka · [...] · Yasushi Ohizumi
    [Show abstract] [Hide abstract] 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.
    Article · Aug 2013 · Biological & Pharmaceutical Bulletin
  • [Show abstract] [Hide abstract] 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.
    Article · Jun 2013 · Neuroscience Letters
  • [Show abstract] [Hide abstract] 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.
    Article · May 2013 · Behavioural brain research
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    [Show abstract] [Hide abstract] 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.
    Full-text Article · Apr 2013 · Journal of Neural Transmission
  • Koichi Aoki · Akihito Yokosuka · Yoshihiro Mimaki · [...] · Tohru Yamakuni
    [Show abstract] [Hide abstract] 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.
    Article · Apr 2013 · Biological & Pharmaceutical Bulletin
  • Akihito Yokosuka · Atsushi Sekiguchi · Yoshihiro Mimaki
    [Show abstract] [Hide abstract] 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.
    Article · Mar 2013 · Natural product communications