Ketamine Induces Toxicity in Human Neurons Differentiated from Embryonic Stem Cells via Mitochondrial Apoptosis Pathway

Ketamine is widely used for anesthesia in pediatric patients. Growing evidence indicates that ketamine causes neurotoxicity in a variety of developing animal models. Our understanding of anesthesia neurotoxicity in humans is currently limited by difficulties in obtaining neurons and performing developmental toxicity studies in fetal and pediatric populations. It may be possible to overcome these challenges by obtaining neurons from human embryonic stem cells (hESCs) in vitro. hESCs are able to replicate indefinitely and differentiate into every cell type. In this study, we investigated the toxic effect of ketamine on neurons differentiated from hESCs. Two-week-old neurons were treated with different doses and durations of ketamine with or without the reactive oxygen species (ROS) scavenger, Trolox. Cell viability, ultrastructure, mitochondrial membrane potential (Delta Psi(m)), cytochrome c distribution within cells, apoptosis, and ROS production were evaluated. Here we show that ketamine induced ultrastructural abnormalities and dose- and timedependently caused cell death. In addition, ketamine decreased Delta Psi(m) and increased cytochrome c release from mitochondria. Ketamine also increased ROS production and induced differential expression of oxidative stress-related genes. Specifically, abnormal ultrastructural and Delta Psi(m) changes occurred earlier than cell death in the ketamine-induced toxicity process. Furthermore, Trolox significantly decreased ROS generation and attenuated cell death caused by ketamine in a dose- dependent manner. In conclusion, this study illustrates that ketamine time- and dose-dependently induces human neurotoxicity at supraclinical concentrations via ROS-mediated mitochondrial apoptosis pathway and that these side effects can be prevented by the antioxidant agent Trolox. Thus, hESC-derived neurons might provide a promising tool for studying anesthetic-induced developmental neurotoxicity and prevention strategies.