title: The role of N-methyl-D-aspartate receptor activation in homocysteine-induced death of retinal ganglion cells.
abstract: OBJECTIVE
  Elevated plasma homocysteine has been implicated in glaucoma, a vision disorder characterized by retinal ganglion cell death. The toxic potential of homocysteine to ganglion cells is known, but the mechanisms are not clear. A mechanism of homocysteine-induced death of cerebral neurons is via N-methyl-D-aspartate (NMDA) receptor overstimulation, leading to excess calcium influx and oxidative stress. This study examined the role of the NMDA receptor in homocysteine-mediated ganglion cell death.
  
  
  METHODS
  Primary mouse ganglion cells were used for these experiments. NMDA receptor stimulation by homocysteine was determined by patch clamp analysis and fluorescent detection of intracellular calcium. NMDA receptor involvement in homocysteine-mediated cell death was determined through assessment of lactate dehydrogenase release and TUNEL analysis. These experiments used the NMDA receptor blocker MK-801. Induction of reactive species superoxide, nitric oxide, and peroxynitrite was measured by electron paramagnetic resonance spectroscopy, chemiluminescent nitric oxide detection, and immunoblotting for nitrotyrosine, respectively.
  
  
  RESULTS
  50 μM homocysteine stimulated the NMDA receptor in presence of 100 μM glycine. Homocysteine induced 59.67 ± 4.89% ganglion cell death that was reduced to 19.87 ± 3.03% with cotreatment of 250 nM MK-801. Homocysteine elevated intracellular calcium ∼7-fold, which was completely prevented by MK-801. Homocysteine treatment increased superoxide and nitric oxide levels by ∼40% and ∼90%, respectively, after 6 hours. Homocysteine treatment elevated peroxynitrite by ∼85% after 9 hours.
  
  
  CONCLUSIONS
  These experiments provide compelling evidence that homocysteine induces retinal ganglion cell toxicity through direct NMDA receptor stimulation and implicate, for the first time, the induction of oxidative stress as a potent mechanism of homocysteine-mediated ganglion cell death.
authors: Department of Cellular Biology and Anatomy, Georgia Health Sciences, University, Medical College of Georgia, Augusta, GA, USA.
authors: Preethi S
authors: PS
authors: Ganapathy
authors: Richard E
authors: RE
authors: White
authors: Yonju
authors: Y
authors: Ha
authors: B Renee
authors: BR
authors: Bozard
authors: Paul L
authors: PL
authors: McNeil
authors: R William
authors: RW
authors: Caldwell
authors: Sanjiv
authors: S
authors: Kumar
authors: Stephen M
authors: SM
authors: Black
authors: Sylvia B
authors: SB
authors: Smith
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D006711:Homocystine / Q000633:toxicity*; D020287:In Situ Nick-End Labeling; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009569:Nitric Oxide / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D018408:Patch-Clamp Techniques; D017382:Reactive Oxygen Species / Q000378:metabolism; D018091:Receptors, AMPA / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D012165:Retinal Ganglion Cells / Q000378:metabolism / Q000473:pathology*; D013481:Superoxides / Q000378:metabolism
chemical_list: D018691:Excitatory Amino Acid Antagonists; D017382:Reactive Oxygen Species; D018091:Receptors, AMPA; D016194:Receptors, N-Methyl-D-Aspartate; D013481:Superoxides; D009569:Nitric Oxide; D006711:Homocystine; D016291:Dizocilpine Maleate; D007770:L-Lactate Dehydrogenase; D002118:Calcium