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Search Results: 1 - 10 of 6061 matches for " Joo-Taek Choi "
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Regulation of cerebrospinal fluid production by caffeine consumption
Myoung-Eun Han, Hak-Jin Kim, Young-Suk Lee, Dong-Hyun Kim, Joo-Taek Choi, Chul-Sik Pan, Sik Yoon, Sun-Yong Baek, Bong-Seon Kim, Jae-Bong Kim, Sae-Ock Oh
BMC Neuroscience , 2009, DOI: 10.1186/1471-2202-10-110
Abstract: In the present study we found that the long-term consumption of caffeine can induce ventriculomegaly; this was observed in 40% of the study rats. In the caffeine-treated rats with ventriculomegaly, there was increased production of CSF, associated with the increased expression of Na+, K+-ATPase and increased cerebral blood flow (CBF). In contrast to the chronic effects, acute treatment with caffeine decreased the production of CSF, suggesting 'effect inversion' associated with caffeine, which was mediated by increased expression of the A1 adenosine receptor, in the choroid plexus of rats chronically treated with caffeine. The involvement of the A1 adenosine receptor in the effect inversion of caffeine was further supported by the induction of ventriculomegaly and Na+, K+-ATPase, in A1 agonist-treated rats.The results of this study show that long-term consumption of caffeine can induce ventriculomegaly, which is mediated in part by increased production of CSF. Moreover, we also showed that adenosine receptor signaling can regulate the production of CSF by controlling the expression of Na+, K+-ATPase and CBF.Methylxanthine caffeine is present in many common beverages, and is widely consumed worldwide [1,4]. Caffeine consumption has been estimated to be 76 mg per person per day worldwide, as high as 238 mg per person per day in the United States and Canada, and more than 400 mg per person per day in Sweden and Finland [5,6]. Caffeine is absorbed rapidly after oral administration and distributed to various organs and tissues. In the liver, caffeine is metabolized to dimethyl- and monomethylxanthines, dimethyl and monomethyl uric acids, trimethyl- and dimethylallantoin, and uracil derivatives. Some metabolites of caffeine including 1,3-dimethylxanthine (theophylline) and 1,7-dimethylxanthine (paraxanthine) have pharmacological activity similar to caffeine [4]. The half-life of caffeine is ~5 hours in humans and ~1 hour in rats [4,7].The main mechanism of action of caffei
The prelimbic cortex is critical for context-dependent fear expression
Eun Joo Kim,Namsoo Kim,Hyun Taek Kim,June-Seek Choi
Frontiers in Behavioral Neuroscience , 2013, DOI: 10.3389/fnbeh.2013.00073
Abstract: The ability to regulate emotional responses in various circumstances would provide adaptive advantages for an individual. Using a context-dependent fear discrimination (CDFD) task in which the tone conditioned stimulus (CS) is paired with the footshock unconditioned stimulus (US) in one context but presented alone in another context, we investigated the role of the prelimbic (PL) cortex in contextual modulation of the conditioned fear response. After 3 days of CDFD training, rats froze more to the CS presented in the fearful than in the safe context. Following bilateral lesions of the PL, rats showed similar levels of freezing to the CS in both contexts, in contrast to the sham-lesioned control animals. The lesions did not impair the rats' ability to discriminate contexts per se, as indicated by intact differential responses in a separate experiment which employed a simple context discrimination task. Consistent with the lesion data, single-unit recordings from the PL showed that the majority of CS-responsive neurons fired at a higher rate in the fearful context than in the safe context, paralleling the behavioral discrimination. Taken together, the current results suggest that the PL is involved in selective expression of conditioned fear to an explicit (tone) cue that is fully dependent on contextual information.
Endoplasmic Reticulum Stress-Induced JNK Activation Is a Critical Event Leading to Mitochondria-Mediated Cell Death Caused by β-Lapachone Treatment
Hyemi Lee,Moon-Taek Park,Bo-Hwa Choi,Eun-Taex Oh,Min-Jeong Song,Jeonghun Lee,Chulhee Kim,Byung Uk Lim,Heon Joo Park
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0021533
Abstract: β-lapachone (β-lap) is a bioreductive agent that is activated by the two-electron reductase NAD(P)H quinone oxidoreductase 1 (NQO1). Although β-lap has been reported to induce apoptosis in various cancer types in an NQO1-dependent manner, the signaling pathways by which β-lap causes apoptosis are poorly understood.
NMR and GC-MS Based Metabolic Profiling and Free-Radical Scavenging Activities of Cordyceps pruinosa Mycelia Cultivated under Different Media and Light Conditions
Taek-Joo Oh, Sun-Hee Hyun, Seul-Gi Lee, Young-Jin Chun, Gi-Ho Sung, Hyung-Kyoon Choi
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0090823
Abstract: Variation of metabolic profiles in Cordyceps pruinosa mycelia cultivated under various media and light conditions was investigated using 1H nuclear magnetic resonance (NMR) analysis and gas chromatography mass spectrometry (GC-MS) with multivariate statistical analysis. A total of 71 metabolites were identified (5 alcohols, 21 amino acids, 15 organic acids, 4 purines, 3 pyrimidines, 7 sugars, 11 fatty acids, and 5 other metabolites) by NMR and GC-MS analysis. The mycelia grown in nitrogen media and under dark conditions showed the lowest growth and ergosterol levels, essential to a functional fungal cell membrane; these mycelia, however, had the highest levels of putrescine, which is involved in abiotic stress tolerance. In contrast, mycelia cultivated in sabouraud dextrose agar with yeast extract (SDAY) media and under light conditions contained relatively higher levels of fatty acids, including valeric acid, stearic acid, lignoceric acid, myristic acid, oleic acid, palmitoleic acid, hepadecenoic acid, and linoleic acid. These mycelia also had the highest phenolic content and antioxidant activity, and did not exhibit growth retardation due to enhanced asexual development caused by higher levels of linoleic acid. Therefore, we suggested that a light-enriched environment with SDAY media was more optimal than dark condition for cultivation of C. pruinosa mycelia as biopharmaceutical or nutraceutical resources.
β-Lapachone Significantly Increases the Effect of Ionizing Radiation to Cause Mitochondrial Apoptosis via JNK Activation in Cancer Cells
Moon-Taek Park, Min-Jeong Song, Hyemi Lee, Eun-Taex Oh, Bo-Hwa Choi, Seong-Yun Jeong, Eun-Kyung Choi, Heon Joo Park
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0025976
Abstract: Background β-lapachone (β-lap), has been known to cause NQO1-dependnet death in cancer cells and sensitize cancer cells to ionizing radiation (IR). We investigated the mechanisms underlying the radiosensitization caused by β-lap. Methodology/Principal Findings β-lap enhanced the effect of IR to cause clonogenic cells in NQO1+-MDA-MB-231 cells but not in NQO1?-MDA-MB-231 cells. β-lap caused apoptosis only in NQO1+ cells and not in NQO1? cells and it markedly increased IR-induced apoptosis only in NQO1+ cells. Combined treatment of NQO1+ cells induced ROS generation, triggered ER stress and stimulated activation of ERK and JNK. Inhibition of ROS generation by NAC effectively attenuated the activation of ERK and JNK, induction of ER stress, and subsequent apoptosis. Importantly, inhibition of ERK abolished ROS generation and ER stress, whereas inhibition of JNK did not, indicating that positive feedback regulation between ERK activation and ROS generation triggers ER stress in response to combined treatment. Furthermore, prevention of ER stress completely blocked combination treatment-induced JNK activation and subsequent apoptotic cell death. In addition, combined treatment efficiently induced the mitochondrial translocation of cleaved Bax, disrupted mitochondrial membrane potential, and the nuclear translocation of AIF, all of which were efficiently blocked by a JNK inhibitor. Caspases 3, 8 and 9 were activated by combined treatment but inhibition of these caspases did not abolish apoptosis indicating caspase activation played a minor role in the induction of apoptosis. Conclusions/Significance β-lap causes NQO1-dependent radiosensitization of cancer cells. When NQO1+ cells are treated with combination of IR and β-lap, positive feedback regulation between ERK and ROS leads to ER stress causing JNK activation and mitochondrial translocation of cleaved Bax. The resultant decrease in mitochondrial membrane leads to translocation of AIF and apoptosis.
Network architectural conditions for prominent and robust stochastic oscillations
Jaewook Joo,Jinmyung Choi
Quantitative Biology , 2011,
Abstract: Understanding relationship between noisy dynamics and biological network architecture is a fundamentally important question, particularly in order to elucidate how cells encode and process information. We analytically and numerically investigate general network architectural conditions that are necessary to generate stochastic amplified and coherent oscillations. We enumerate all possible topologies of coupled negative feedbacks in the underlying biochemical networks with three components, negative feedback loops, and mass action kinetics. Using the linear noise approximation to analytically obtain the time-dependent solution of the master equation and derive the algebraic expression of power spectra, we find that (a) all networks with coupled negative feedbacks are capable of generating stochastic amplified and coherent oscillations; (b) networks with a single negative feedback are better stochastic amplified and coherent oscillators than those with multiple coupled negative feedbacks; (c) multiple timescale difference among the kinetic rate constants is required for stochastic amplified and coherent oscillations.
One-Dimensional Hydrogen-Bonded Infinite Chain from Nickel(II) Tetraaza Macrocyclic Complex and 1,2-Cyclopentanedicarboxylate Ligand
In-Taek Lim,Ki-Young Choi
International Journal of Molecular Sciences , 2011, DOI: 10.3390/ijms12042232
Abstract: The reaction of [Ni(L)]Cl 2·2H 2O (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo [14,4,0 1.18,0 7.12]docosane) with trans-1,2-cyclopentanedicarboxylic acid (H 2-cpdc) yields a 1D hydrogen-bonded infinite chain with formula [Ni(L)(H-cpdc -) 2] ( 1). This complex has been characterized by X-ray crystallography, spectroscopy and cyclic voltammetry. The crystal structure of 1 exhibits a distorted octahedral geometry about Ni atom with four nitrogen atoms of the macrocycle and two oxygen atoms of the H-cpdc - ligand at the axial position. Compound 1 crystallizes in the monoclinic system P2 1/c with a = 8.7429(17), b = 10.488(2), c = 18.929(4) ?, β = 91.82(2), V = 1734.8(6) ? 3, Z = 2. Electronic spectrum of 1 reveals a high-spin octahedral environment. Cyclic voltammetry of 1 undergoes two waves of a one-electron transfer corresponding to Ni II/Ni III and Ni II/Ni I processes.
Self-Assembly of a 1D Hydrogen-Bonded Polymer from a Hexamethyltetraaza Macrocyclic Nickel(II) Complex and Isophthalic Acid
In-Taek Lim,Ki-Young Choi
Molecules , 2013, DOI: 10.3390/molecules18066608
Abstract: The compound [Ni(L)(isoph) 2][Ni(L)]·8H 2O (1; L = C- meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane; H 2-isoph = isophthalic acid) has been synthesized and structurally characterized. Complex 1 exhibits a geometrically symmetric core with a {4/6} coordination number set. The coordination environment around the Ni(1) ion is a distorted octahedron, while the geometry around the four-coordinate Ni(2) is depicted as square planar in 1D hydrogen-bonded infinite chain. The compound crystallizes in the triclinic system P-1 with a = 8.602(2), b = 10.684(7), c = 16.550(3) ?, a = 91.04(4), b = 94.09(2), g = 111.09(4)°, V = 1413.9(10) ? 3, Z = 1. The cyclic voltammogram of 1 undergoes one-electron wave corresponding to Ni II/Ni I process. The electronic spectra, electrochemical and TGA behavior of the complex are significantly affected by the nature of the hexamethyltetraaza macrocycle and the axial isoph 2? ligand.
Polarization in B_c -> J/ψmu nu
Myoung-Taek Choi,Jae Kwan Kim
Physics , 1998,
Abstract: We study the polarization of the J/\psi meson of the B_c -> J/\psi mu nu decay process, followed by J/\psi -> mu+ mu-, with the help of the heavy-quark spin symmetry formalism (HQSS). We adapt the ISGW wave function. Due to the clean signature of the decay mode, measurements of the polarization of the J/\psi meson can play a special role in extracting |V_{cb}|, the quark mixing-matrix element. We compare the results with the predictions of other quark models.
Determination of $|V_{cb}|$ from the polarization of vector meson in the semileptonic decay of $B$ and $B_c$ meson
Myoung-Taek Choi,Jae Kwan Kim
Physics , 1998, DOI: 10.1016/S0370-2693(97)01480-9
Abstract: Since the degree of polarization of the vector particle in semileptonic decay strongly influences the decay width of the particles, it can be used as a measure of CKM matrix elements. We show that |V_{cb}| can be determined from the measurement of polarization of vector meson in B,B_c --> V l nu decay, where $V$ is vector meson.
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