title: Diltiazem-induced neuroprotection in glutamate excitotoxicity and ischemic insult of retinal neurons.
abstract: OBJECTIVE
  Cell death is often related to an abnormal increase in Ca(2+) flux. In the retina, Ca(2+) channels are mainly from the L-type that do not inactivate with time. Under excitotoxic and ischemic conditions, their continuous activation may therefore contribute significantly to the lethal Ca(2+) influx. To assess this hypothesis, the Ca(2+) channel blocker, diltiazem, was applied in excitotoxic and ischemic conditions.
  
  
  METHODS
  To induce excitotoxicity, retinal cell cultures from newborn rats were incubated with glutamate. The toxicity of glutamate was quantified by neuronal immunostaining with an antibody directed against the neuron specific enolase. Glutamate receptor function in vitro was assessed in pig retinal cell cultures by patch clamp recording. Retinal ischemia was induced by raising the intraocular pressure in adult rats. Retinal cell loss was quantified on retinal sections by measuring nuclear cell densities.
  
  
  RESULTS
  In retinal cell culture, glutamate application induced a major cell loss. This cell loss was attributed to glutamate excitotoxicity because glutamate receptor blockers like MK-801 and CNQX increased significantly neuronal survival. MK-801 and CNQX, which block NMDA and AMPA/Kainate receptors, respectively, had additive effects. Expression of AMPA/Kainate glutamate receptors in mixed adult retinal cell cultures was attested by patch clamp recording. In newborn rat retinal culture, glutamate excitotoxicity was significantly reduced by addition of the L-type Ca(2+) channel blocker, diltiazem. In in vivo experiments, the increase in ocular pressure induced a decrease in cell number in the inner nuclear and ganglion cell layers. When animals received diltiazem injections, the ischemic treatment induced a less severe reduction in retinal cells; this neuroprotection was statistically significant in the ganglion cell layer.
  
  
  CONCLUSIONS
  These results are consistent with previous studies suggesting that Ca(2+) channel activation contributes to retinal cell death following either glutamate excitotoxicity or retinal ischemia. Under both conditions, the L-type Ca(2+) channel blocker, diltiazem, can limit cell death. These results extend the potential application of diltiazem in retinal neuroprotection to retinal pathologies involving glutamate excitotoxicity and ischemia.
authors.affiliation: Laboratoire de Physiopathologie Cellulaire et Moléculaire de la Rétine, UPMC, INSERM U-592, Hôpital Saint-Antoine, Bâtiment Kourilsky, Paris, France.
authors.forename: Géraldine
authors.initials: G
authors.lastname: Vallazza-Deschamps
authors.forename: Céline
authors.initials: C
authors.lastname: Fuchs
authors.forename: David
authors.initials: D
authors.lastname: Cia
authors.forename: Luc-Henri
authors.initials: LH
authors.lastname: Tessier
authors.forename: José A A
authors.initials: JA
authors.lastname: Sahel
authors.forename: Henri
authors.initials: H
authors.lastname: Dreyfus
authors.forename: Serge
authors.initials: S
authors.lastname: Picaud
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004110:Diltiazem / Q000494:pharmacology*; D018698:Glutamic Acid / Q000633:toxicity; D066298:In Vitro Techniques; D007511:Ischemia / Q000139:chemically induced / Q000188:drug therapy* / Q000378:metabolism; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D009498:Neurotoxins / Q000633:toxicity; D051381:Rats; D017208:Rats, Wistar; D012160:Retina / Q000187:drug effects* / Q000378:metabolism / Q000503:physiopathology; D013552:Swine
chemical_list: D002121:Calcium Channel Blockers; D009498:Neurotoxins; D018698:Glutamic Acid; D004110:Diltiazem