title: Ketamine causes mitochondrial dysfunction in human induced pluripotent stem cell-derived neurons.
abstract: OBJECTIVE
  Ketamine toxicity has been demonstrated in nonhuman mammalian neurons. To study the toxic effect of ketamine on human neurons, an experimental model of cultured neurons from human induced pluripotent stem cells (iPSCs) was examined, and the mechanism of its toxicity was investigated.
  
  
  METHODS
  Human iPSC-derived dopaminergic neurons were treated with 0, 20, 100 or 500 μM ketamine for 6 and 24 h. Ketamine toxicity was evaluated by quantification of caspase 3/7 activity, reactive oxygen species (ROS) production, mitochondrial membrane potential, ATP concentration, neurotransmitter reuptake activity and NADH/NAD+ ratio. Mitochondrial morphological change was analyzed by transmission electron microscopy and confocal microscopy.
  
  
  RESULTS
  Twenty-four-hour exposure of iPSC-derived neurons to 500 μM ketamine resulted in a 40% increase in caspase 3/7 activity (P < 0.01), 14% increase in ROS production (P < 0.01), and 81% reduction in mitochondrial membrane potential (P < 0.01), compared with untreated cells. Lower concentration of ketamine (100 μM) decreased the ATP level (22%, P < 0.01) and increased the NADH/NAD+ ratio (46%, P < 0.05) without caspase activation. Transmission electron microscopy showed enhanced mitochondrial fission and autophagocytosis at the 100 μM ketamine concentration, which suggests that mitochondrial dysfunction preceded ROS generation and caspase activation.
  
  
  CONCLUSIONS
  We established an in vitro model for assessing the neurotoxicity of ketamine in iPSC-derived neurons. The present data indicate that the initial mitochondrial dysfunction and autophagy may be related to its inhibitory effect on the mitochondrial electron transport system, which underlies ketamine-induced neural toxicity. Higher ketamine concentration can induce ROS generation and apoptosis in human neurons.
authors.affiliation: Department of Anesthesiology, Tokyo Medical and Dental University, Graduate School of Medical and Dental Sciences, Yushima, Bunkyo-ku, Tokyo, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ito
authors.affiliation: Department of Anesthesiology, Tokyo Medical and Dental University, Graduate School of Medical and Dental Sciences, Yushima, Bunkyo-ku, Tokyo, Japan.
authors.forename: Tokujiro
authors.initials: T
authors.lastname: Uchida
authors.affiliation: Department of Anesthesiology, Tokyo Medical and Dental University, Graduate School of Medical and Dental Sciences, Yushima, Bunkyo-ku, Tokyo, Japan.
authors.forename: Koshi
authors.initials: K
authors.lastname: Makita
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D002461:Cell Line, Transformed; D059290:Dopaminergic Neurons / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007649:Ketamine / Q000494:pharmacology*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects*; D008928:Mitochondria / Q000378:metabolism* / Q000473:pathology; D009243:NAD / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000378:metabolism; D039904:Pluripotent Stem Cells / Q000378:metabolism* / Q000473:pathology; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D018377:Neurotransmitter Agents; D017382:Reactive Oxygen Species; D009243:NAD; D007649:Ketamine; D000255:Adenosine Triphosphate; C505407:CASP3 protein, human; C505520:CASP7 protein, human; D053148:Caspase 3; D053179:Caspase 7