title: Neuroprotective effects of (-)-epigallocatechin-3-gallate against quinolinic acid-induced excitotoxicity via PI3K pathway and NO inhibition.
abstract: Excessive stimulation of the NMDA receptor induces neuronal cell death and is implicated in the development of several neurodegenerative diseases. While EGCG suppresses apoptosis induced by NMDA receptor-mediated excitotoxicity, the mechanisms underlying this process have yet to be completely determined. This study was designed to investigate whether (-)-epigallocatechin-3-gallate (EGCG) plays a neuroprotective role by inhibiting nitric oxide (NO) production and activating cellular signaling mechanisms including MAP kinase, PI3K, and GSK-3beta and acting on the antiapoptotic and the proapoptotic genes in N18D3 neural cells. The cells were pretreated with EGCG for 2 h and then exposed to quinolinic acid (QUIN), a NMDA receptor agonist, 30 mM for 24 h. MTT assay and DAPI staining were used to identify cell viability and apoptosis, respectively, and demonstrated that EGCG significantly increased cell viability and protected the cells from apoptotic death. In addition, EGCG had a capacity to reduce QUIN-induced excitotoxic cell death not only by blocking increase of intracellular calcium levels but also by inhibiting NO production. Gene expression analysis revealed that EGCG prevented the QUIN-induced expression of the proapoptotic gene, caspase-9, and increased that of the antiapoptotic genes, Bcl-XL, Bcl-2, and Bcl-w. Further examination about potential cell signaling candidate involved in this neuroprotective effect showed that immunoreacitivity of PI3K was significantly increased in the cells treated with EGCG. These results suggest that the neuroprotective mechanism of EGCG against QUIN-induced excitotoxic cell death includes regulation of PI3K and modulation of cell survival and death genes through decreasing of intracellular calcium levels and controlling of NO production.
authors.affiliation: Department of Physiology, Chonnam National University Medical School, Gwangju 501-190, Republic of Korea.
authors.forename: Sujeong
authors.initials: S
authors.lastname: Jang
authors.forename: Han-Seong
authors.initials: HS
authors.lastname: Jeong
authors.forename: Jong-Seong
authors.initials: JS
authors.lastname: Park
authors.forename: Yeong-Seon
authors.initials: YS
authors.lastname: Kim
authors.forename: Chun-Yan
authors.initials: CY
authors.lastname: Jin
authors.forename: Myung Bok
authors.initials: MB
authors.lastname: Seol
authors.forename: Byeong-Chae
authors.initials: BC
authors.lastname: Kim
authors.forename: Min-Cheol
authors.initials: MC
authors.lastname: Lee
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D051379:Mice; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D018696:Neuroprotective Agents / Q000494:pharmacology*; D009498:Neurotoxins / Q000633:toxicity*; D009569:Nitric Oxide / Q000037:antagonists & inhibitors* / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017378:Quinolinic Acid / Q000633:toxicity*; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors
chemical_list: D018696:Neuroprotective Agents; D009498:Neurotoxins; D016194:Receptors, N-Methyl-D-Aspartate; D009569:Nitric Oxide; D002392:Catechin; C045651:epigallocatechin gallate; D019869:Phosphatidylinositol 3-Kinases; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3; D017378:Quinolinic Acid; D002118:Calcium