title: Tropisetron as a neuroprotective agent against glutamate-induced excitotoxicity and mechanisms of action.
abstract: The objective of this study was to determine the neuroprotective role of tropisetron on retinal ganglion cells (RGCs) as well as to explore the possible mechanisms associated with alpha7 nAChR-induced neuroprotection. Adult pig RGCs were isolated from all other retinal tissue using a two-step panning technique. Once isolated, RGCs were cultured for 3 days under control untreated conditions, in the presence of 500 μM glutamate to induce excitotoxicity, and when tropisetron was applied before glutamate to induce neuroprotection. 500 μM glutamate decreased RGC survival by an average of 62% compared to control conditions. However, RGCs pretreated with 100 nM tropisetron before glutamate increased cell survival to an average of 105% compared to controls. Inhibition studies using the alpha7 nAChR antagonist, MLA (10 nM), support the hypothesis that tropisetron is an effective neuroprotective agent against glutamate-induced excitotoxicity; mediated by α7 nAChR activation. ELISA studies were performed to determine if signaling cascades normally associated with excitotoxicity and neuroprotection were up- or down-regulated after tropisetron treatment. Tropisetron had no discernible effects on pAkt levels but significantly decreased p38 MAPK levels associated with excitotoxicity from an average of 15 ng/ml to 6 ng/ml. Another mechanism shown to be associated with neuroprotection involves internalization of NMDA receptors. Double-labeled immunocytochemistry and electrophysiology studies provided further evidence that tropisetron caused internalization of NMDA receptor subunits. The findings of this study suggest that tropisetron could be an effective therapeutic agent for the treatment of degenerative disorders of the central nervous system that involves excitotoxicity.
authors.affiliation: Western Michigan University, Department of Biological Sciences, Kalamazoo, MI 49008, USA.
authors.forename: Michael M
authors.initials: MM
authors.lastname: Swartz
authors.forename: David M
authors.initials: DM
authors.lastname: Linn
authors.forename: Cindy L
authors.initials: CL
authors.lastname: Linn
mesh_terms: D000157:Aconitine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D018698:Glutamic Acid / Q000633:toxicity*; D007211:Indoles / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D018696:Neuroprotective Agents / Q000494:pharmacology*; D018722:Nicotinic Agonists / Q000494:pharmacology*; D018733:Nicotinic Antagonists / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013552:Swine; D000077526:Tropisetron; D064569:alpha7 Nicotinic Acetylcholine Receptor / Q000819:agonists* / Q000037:antagonists & inhibitors; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D007211:Indoles; D018696:Neuroprotective Agents; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D064569:alpha7 Nicotinic Acetylcholine Receptor; C054634:methyllycaconitine; D018698:Glutamic Acid; D000077526:Tropisetron; D051057:Proto-Oncogene Proteins c-akt; D048051:p38 Mitogen-Activated Protein Kinases; D000157:Aconitine
keywords: (1R,5S)-8-methyl-8-azabicyclo[3.2.1]octan-3-yl 1methyl-indole-3-carboxylate; 4-(2-Aminoethyl) benzenesulfonyl fluoride hydrochloride; 5-HT(3); ACh; AEBSF; ANOVA; CNS; EDTA; EGTA; ELISA; Excitotoxicity; FBS; GluRs; IgG; IgM; MAPK; MLA; N-methyl-d-aspartate; NGF; NMDA; Neuroprotection; PBS; PMSF; Pig; RGC; Retina; Retinal ganglion cells; SDS; TEA; Thy; Tropisetron; acetylcholine; alpha7 nicotinic acetylcholine receptor; analysis-of-variance; central nervous system; enzyme-linked immunosorbent assay; ethylene glycol tetraacetic acid; ethylenediaminetetraacetic acid; fetal bovine serum; glutamate receptors; glycoprotein originally identified in thymus gland; immunoglobulin G; immunoglobulin M; methyllycaconitine; mitogen activated protein kinase; nAChR; nerve growth factor; nicotinic acetylcholine receptor; phenylmethylsulfonyl fluoride; phosphate buffered saline; retinal ganglion cell; serotonin; sodium dodecyl sulfate; tetraethylammonium chloride; tropisetron; α7 nAChR