• BMB Reports
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• 제35권1호
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• pp.67-86
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• 2002

Three routes have been identified triggering neuronal death under physiological and pathological conditions. Excess activation of ionotropic glutamate receptors cause influx and accumulation of $Ca^{2+}$ and $Na^+$ that result in rapid swelling and subsequent neuronal death within a few hours. The second route is caused by oxidative stress due to accumulation of reactive oxygen and nitrogen species. Apoptosis or programmed cell death that often occurs during developmental process has been coined as additional route to pathological neuronal death in the mature nervous system. Evidence is being accumulated that excitotoxicity, oxidative stress, and apoptosis propagate through distinctive and mutually exclusive signal transduction pathway and contribute to neuronal loss following hypoxic-ischemic brain injury. Thus, the therapeutic intervention of hypoxic-ischemic neuronal injury should be aimed to prevent excitotoxicity, oxidative stress, and apoptosis in a concerted way.

• The Korean Journal of Physiology and Pharmacology
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• 제5권5호
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• pp.389-396
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• 2001

Neuroprotective properties of lithium were investigated by using in vivo NMDA excitotoxicity model. The appearance of TUNEL positive cells was prominent within 24 h of NMDA (70 mg/kg, i.p.) injection in the regions of the cortex, hippocampal formation, and thalamus of mouse cerebrum. NMDA treatment resulted in the extensive enhancement of Bax immunoreactivity in the cortical and hippocampal regions. NMDA also increased the immunoreactivity of caspase 8 in the similar regions of the mouse cerebrum. However, the increased immunoreactivity of Bax and caspase 8 were dramatically attenuated by chronic lithium pretreatment (lithium chloride, 300 mg/kg/d, i.p. for $7{\sim}10$ days). At the same time, lithium ion blocked the appearance of TUNEL positive cells, and the morphological assessment indicated an effective neuroprotection by lithium against NMDA excitotoxicity. Although the exact action mechanism of lithium is not straightforward at this time, we propose that the inhibition of Bax and caspase cascade is involved in the neuroprotective action of lithium.

• International Journal of Oral Biology
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• 제34권2호
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• pp.97-103
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• 2009

L-trans-pyrrolidine-2,4-dicarboxylate (PDC) is a potent inhibitor of glutamate transporters. In our current study, we investigated whether the neuronal death induced by PDC involves mechanisms other than excitotoxicity in mixed mouse cortical cultures. Cortical cultures at 13-14 days in vitro were used and cell death was assessed by measuring the lactate dehydrogenase efflux into bathing media. Glutamate and PDC both induced neuronal death in a concentration-dependent manner but the neurotoxic effects of glutamate were found to be more potent than those of PDC. Treatment with 10, 100 and 200 ${\mu}$M PDC equally potentiated 50 ${\mu}$M glutamate-induced neuronal death. The neuronal death induced by 75 ${\mu}$M glutamate was almost abolished by treatment with the NMDA antagonists, MK-801 and AP-5, but was unaffected by NBQX (an AMPA antagonist), trolox (antioxidant), BDNF or ZVAD-FMK (a pan-caspase inhibitor). However, the neuronal death induced by 200 ${\mu}$M PDC was partially but significantly attenuated by single treatments with MK-801, AP-5, trolox, BDNF or ZVAD-FMK but not NBQX. Combined treatments with MK-801 plus trolox, MK-801 plus ZVAD-FMK or MK-801 plus BDNF almost abolished neuronal death, whereas combined treatments with trolox plus ZVADFMK, trolox plus BDNF or ZVAD-FMK plus BDNF did not enhance the inhibitory action of any single treatment with these drugs. These results demonstrate that the neuronal death induced by PDC involves not only in the excitotoxicity induced by the accumulation of glutamate but also the oxidative stress induced by free radical generation. This suggests that apoptotic neuronal death plays a role in PDCinduced oxidative neuronal injury.

• The Korean Journal of Physiology and Pharmacology
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• 제20권1호
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• pp.101-109
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• 2016

Reducing $[Mg^{2+}]_o$ to 0.1 mM can evoke repetitive $[Ca^{2+}]_i$ spikes and seizure activity, which induces neuronal cell death in a process called excitotoxicity. We examined the issue of whether cultured rat hippocampal neurons preconditioned by a brief exposure to 0.1 mM $[Mg^{2+}]_o$ are rendered resistant to excitotoxicity induced by a subsequent prolonged exposure and whether $Ca^{2+}$ spikes are involved in this process. Preconditioning by an exposure to 0.1 mM $[Mg^{2+}]_o$ for 5 min inhibited significantly subsequent 24 h exposure-induced cell death 24 h later (tolerance). Such tolerance was prevented by both the NMDA receptor antagonist D-AP5 and the L-type $Ca^{2+}$ channel antagonist nimodipine, which blocked 0.1 mM $[Mg^{2+}]_o$-induced $[Ca^{2+}]_i$ spikes. The AMPA receptor antagonist NBQX significantly inhibited both the tolerance and the $[Ca^{2+}]_i$ spikes. The intracellular $Ca^{2+}$ chelator BAPTA-AM significantly prevented the tolerance. The nonspecific PKC inhibitor staurosporin inhibited the tolerance without affecting the $[Ca^{2+}]_i$ spikes. While $G{\ddot{o}}6976$, a specific inhibitor of $PKC{\alpha}$ had no effect on the tolerance, both the $PKC{\varepsilon}$ translocation inhibitor and the $PKC{\zeta}$ pseudosubstrate inhibitor significantly inhibited the tolerance without affecting the $[Ca^{2+}]_i$ spikes. Furthermore, JAK-2 inhibitor AG490, MAPK kinase inhibitor PD98059, and CaMKII inhibitor KN-62 inhibited the tolerance, but PI-3 kinase inhibitor LY294,002 did not. The protein synthesis inhibitor cycloheximide significantly inhibited the tolerance. Collectively, these results suggest that low $[Mg^{2+}]_o$ preconditioning induced excitotoxic tolerance was directly or indirectly mediated through the $[Ca^{2+}]_i$ spike-induced activation of $PKC{\varepsilon}$ and $PKC{\xi}$, JAK-2, MAPK kinase, CaMKII and the de novo synthesis of proteins.

• 대한약학회:학술대회논문집
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• 대한약학회 2003년도 Proceedings of the Convention of the Pharmaceutical Society of Korea Vol.1
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• pp.72-74
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• 2003

Excitatory amino acid (EAA) receptor, particularly NMDA receptor, are now known to be one of major transmitter receptors involved in synaptic excitation. Excessive release of EAA neurotransmitter, glutamate, is an important causative factor in the neurodegenerative processes and can cause neuronal damage and cell death. This excitotoxicity has been shown to be $Ca^{++}$ dependent. (omitted)

• 한국미생물생명공학회:학술대회논문집
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• 한국미생물생명공학회 2001년도 Proceedings of 2001 KSAM Annual Meeting
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• pp.6-6
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• 2001

• 대한약학회:학술대회논문집
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• 대한약학회 2000년도 춘계총회 및 학술대회
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• pp.191.1-191.1
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• 2000

• BMB Reports
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• 제49권2호
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• pp.69-70
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• 2016

Mutations of orthodentricle homeobox 2 (OTX2) in human and mice often cause retinal dystrophy and nyctalopia, suggesting a role of OTX2 in mature retina, in addition to its functions in the development of the eye and retina. In support of this, the number of bipolar cells in Otx2^+/− post-natal mouse retina was found to be significantly lower than normal. Degeneration of the cells becomes greater as the mice age, leading to the loss of vision. Especially, the type-2 OFF-cone bipolar cells, which do not express Otx2 mRNA but carry Otx2 protein, are most sensitive to Otx2 haplodeficiency. Interestingly, this bipolar cell subpopulation imports Otx2 protein from photoreceptors to protect itself from glutamate excitotoxicity in the dark. Moreover, in the bipolar cells, the exogenous Otx2 relocates to the mitochondria to support mitochondrial ATP synthesis. This novel mitochondrial activity of exogenous Otx2 highlights the therapeutic potential of Otx2 protein transduction in retinal dystrophy.

• Archives of Pharmacal Research
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• 제22권1호
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• pp.35-43
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• 1999

Overstimulation of both kainate (KA) and N-methyl-D-aspartate (NMDA) receptors has been reported to induce excitatoxicity which can be characterized by neuronal damage and formation of reactive oxygen free radicals. Neuroprotective effect of melatonin against KA-induced excitotoxicity have been documented in vitro and in vivo. It is, however, not clear whether melationin is also neuroportective against excitotoxicity mediated by NMDA receptors. In the present work, we tested the in vivo protective effects of striatally infused melatonin against the oxidative stress and neuronal damage induced by the injection of KA and NMDA receptors into the rat striatum. Melatonin implants consisting of 22-gauge stainless-steel cannule with melatonin fused inside the tip were placed bilaterally in the rat brain one week prior to intrastriatal injection of glutamate receptor subtype agonists. Melatonin showed protective effects against the elevation of lipid peroxidation induced by either KA or NMDA and recovered Cu, Zn-superoxide dismutase activities reduced by both KA and NMDA into the control level. Melatonin also clearly blocked both KA- and NMDA-receptor mediated neuronal damage assessed by the determination of choline acetyltransferase activity in striatal monogenages and by microscopic observation of rat brain section stained with cresyl violet. The protective effects of melatonin are comparable to those of DNQX and MK801 which are the KA- and NMDA-receptor antagonist, respectively. It is suggested that melatonin could protect against striatal oxidative damages mediated by glutamate receptors, both non-NMDA and NMDA receptors.

• Archives of Pharmacal Research
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• 제29권8호
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• pp.699-706
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• 2006

The present study evaluated antioxidant and neuroprotective activities of hesperidin, a flavanone mainly isolated from citrus fruits, and its aglycone hesperetin using cell-free bioassay system and primary cultured rat cortical cells. Both hesperidin and hesperetin exhibited similar patterns of 1,1-diphenyl-2-picrylhydrazyl radical scavenging activities. While hesperidin was inactive, hesperetin was found to be a potent antioxidant, inhibiting lipid peroxidation initiated in rat brain homogenates by $Fe^{2+}$ and L-ascorbic acid. In consistence with these findings, hesperetin protected primary cultured cortical cells against the oxidative neuronal damage induced by $H_2O_2$ or xanthine and xanthine oxidase. In addition, it was shown to attenuate the excitotoxic neuronal damage induced by excess glutamate in the cortical cultures. When the excitotoxicity was induced by the glutamate receptor subtype-selective ligands, only the N-methyl-D-aspartic acid-induced toxicity was selectively and markedly inhibited by hesperetin. Furthermore, hesperetin protected cultured cells against the $A_{{\beta}(25-35)}-induced$ neuronal damage. Hesperidin, however, exerted minimal or no protective effects on the neuronal damage tested in this study. Taken together, these results demonstrate potent antioxidant and neuroprotective effects of hesperetin, implying its potential role in protecting neurons against various types of insults associated with many neurodegenerative diseases.