General anesthetics (GAs) are widely used for various essential surgical or medical procedures. Recent studies implicate the GAs has dual effects of neuroprotection and neurotoxicity on neurogenesis with unclear mechanisms. This minireview summarizes recent studies on GAs mediated effects on neurogenesis and proposed mechanisms, with focus on autophagy regulation and intracellular calcium homeostasis.
Academic Editor: Cheng Wang, National Center for Toxicological Research/FDA (USA)
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Copyright © 2017 Yan Wang, et al.
The authors have declared that no competing interests exist.
Each year, millions of fetuses, infants and preschool children are exposed to general anesthetics (GAs) worldwide for various essential surgical or medical procedures. Unfortunately, a large number of preclinical works have demonstrated that prolonged exposure to most, if not all, general anesthetics, either volatile or intravenous, to the developing brain, can cause widespread neuronal cell death, which may be associated with long-term memory and learning disabilities.1, 2, 3 Many mechanisms have been proposed to explain GAs mediated neurotoxicity, including activation of NMDA and GABA receptors4, 5, mitochondrial damage with excessive free radicals6, 7, 8, activation of P75 growth factor9, 10, excessive inflammation11, 12, and disruption of intracellular Ca2+ homeostasis13, 14, 15. Recent studies have also suggested neurogenesis impairment may play a role, since neurotoxic effects of anesthetics occur both in vitro16, 17, 18, 19 and in vivo20, 21, 22. As methods improve, a full mechanistic understanding of neurotoxicity becomes more realistic. For example, with the development of an in vitro neurogenesis system using hESCs, induced pluripotent stem cells (iPSCs), and neural stem cells (NSCs), investigators can now study the mechanisms underlying brain development and screen the toxic effects of various anesthetics under controlled conditions (dose, number of exposures, or developmental stage). New neuroprotective strategies to avoid the anesthetics mediated toxicity, then, can be generated through neurogenesis modeling.23
Creeley et al 24reported exposure of third-trimester fetal macaque monkeys to isoflurane in utero caused widespread apoptosis of neurons and oligodendroglia critical for myelination. They use high concentrations of isoflurane, which was adjusted by painful stimulation. The volatile anesthetic concentration was titrated according to a predefined clinical endpoint that represents an intermediate surgical plane of anesthesia, where there was no motor response and only a mild sympathetic response with an increase of 10% or less in heart rate or blood pressure. Researchers achieved this endpoint via deep nail-bed stimulation at the hand and foot (mosquito-clamp pinch). The turning points of anesthetic concentration and duration varied among different animal species and in human beings and depended on the combination of both anesthetic concentration and exposure duration. Our previous study by Li et al25, showed 1.3% isoflurane for 6 hours reduced apoptosis in the rat fetal brain, while our follow up study by Wang et al26 demonstrated that 3% isoflurane for only 1 hour significantly increased neuroapoptosis in the fetal developing brains. These studies supported our view of an association between the dual effects of GA-mediated neuroprotection and neurotoxicity and anesthetic concentration and exposure duration. Our previous studies in both cell cultures27 and animals28, 29 demonstrated that isoflurane for short exposure did not induced neuronal cell damage by itself, but significantly inhibited neurodegeneration induced by isoflurane for prolonged use. Unfortunately, we did not examine the possible dual effects of general anesthetics on stem or neuroprogenitor cells in these studies.
Recent stem cell studies have opened up avenues for research in GA induced developmental toxicity16, 18, 20. Accumulated data indicate that ketamine can cause neuronal damage in several major brain regions in animal models during certain periods of development30, 31. On the other hand, ketamine at concentrations ranging from 1 to 500 mM did not cause significant toxicity in NSCs.32 In addition, ketamine may have dual effects of both increasing and inhibiting human NSCs proliferation and inducing neuronal death in a time- and dose-dependent manner.33, 31, 32, 33, 34, 35, 36
We have focused on studying the role of intracellular calcium regulation in GA mediated effects on autophagy and neurogenesis. Our previous studies clearly demonstrated that GAs, especially isoflurane, at low concentrations for short exposure, provide neuroprotection by adequate activation of inositol triphosphate receptors or ryanodine receptors (InsP3R and RYR) on the membrane of the endoplasmic reticulum (ER). However, GAs at high concentrations for prolonged use cause neurotoxicity.37, 38, 39 Our previous study further demonstrated that isoflurane affects ReNcell CX (human neural progenitor cell (NPC) line, immortalized by retroviral transduction with the c-myc oncogene and derived from the cortical region of the human fetal brain) proliferation and differentiation via differential activation of InsP3R and RYR and elevation of cytosolic Ca2+ concentration ([Ca2+]c). Isoflurane at a low concentration (0.6%) increased proliferation of these neural progenitor cells, whereas no effect was seen with a higher clinically relevant isoflurane concentration (1.2%). In contrast, isoflurane at high concentration (2.4%) decreased proliferation.16 Dual effects of cytoprotection and cytotoxicity by general anesthetics have been demonstrated in various in vitro18, 40, 41, 42 and in vivo model systems.43, 44, 45 Our findings suggest that isoflurane may affect ReNcell CX NPC survival and neurogenesis in a dual manner through differential activation of InsP3 and/or RYR.
Propofol has become one of the most widely used intravenous GAs.46Twaroski et al found that a high dose of propofol induced developmental toxicity.47 On the other hand, Jeffrey et alfound that propofol at clinically relevant concentrations (<7.1μmol/L) increases neuronal differentiation but is not toxic to hippocampal neural precursor cells in vitro.48 Other studies showed that very low doses of propofol inhibit neuronal arborization in vitro49, and increase the number of neuronal spines on differentiated cells in vivo.50 It is clear that high concentrations of propofol causes cell damage, but the detailed mechanisms remain unclear. We have recently studied the role of intracellular calcium regulation on propofol mediated effects on cell death and neurogenesis and its relationship with propofol-mediated effects on autophagy in ReNcell CX NPCs. Our recent unpublished data suggested that propofol increased [Ca2+]c via activation of InsP3R/RYR. Like isoflurane, propofol demonstrated the dual effects of promoting and inhibiting ReNcell CX NPC neuronal proliferation and differentiation dose- and time-dependently via differential activation of InsP3R and/or RYR. This was associated with propofol’s effects on autophagy regulation. Propofol induced NPC cytotoxicity in a time- and dose-dependent manner through excessive autophagy via over-activation of InsP3R and/or RYR. Particularly, high pharmacological concentrations of propofol decreased human NPC cell viability in vitro by excessive autophagy through a Ca2+-mediated pathway, while clinically relevant doses of propofol enhanced proliferation of NPCs and increased neuronal fate differentiation by a Ca2+-related non-autophagy mechanism. Additionally, autophagy biomarker microtubule-associated protein 1 light chain 3 (LC3 II) was absent in autophagy-related gene ATG 5 deficient fibroblasts (ATG5-/-), which was not affected by the use of propofol. The effects of propofol on ATG5-/- cell proliferation and survival was also significantly impaired dose-dependently compared to wild type cells, suggesting physiological autophagy can inhibit propofol mediated impairment of cell survival. Both isoflurane and propofol dose-dependently impaired lysosome and autophagy flux and function in knock-in cells carrying the Familiar Alzheimer’s Disease (FAD)’s presenilin-1 mutation.
Figure 1.Role of autophagy in anesthetic mediated dual effects of neuroprotection and neurotoxicity. General anesthetics at low concentrations for short exposure induce physiological autophagy, which in turn inhibits apoptosis and promotes neurogenesis and eventually provides neuroprotection (left side). On the other hand, general anesthetics at high concentrations for prolonged use result in impairment of autophagy, which in turn promotes apoptosis and inhibits neurogenesis and eventually causes neurotoxicity (right side).
In summary, from our previous studies and our recent data, we have proposed mechanisms for GA mediated dual effects of neuroprotection and neurotoxicity via their effects on cell death by apoptosis, neurogenesis and regulation of autophagy (Figure 1). GAs, such as isoflurane and propofol, at low concentrations for short exposures, may promote physiological autophagy and then inhibit apoptosis but promote neurogenesis, providing neuroprotection. On the other hand, GAs at high concentrations for prolonged use may induce pathological autophagy, such as impairment of autophagy flux, and then promote apoptosis but inhibit neurogenesis, inducing neurotoxicity. Although it is difficult to provide clear cut on GA concentrations and durations that transform GAs from being neuroprotective to neurotoxic in clinical practice, the principle seems clear that GA exposure should be minimized to avoid its detrimental effects of apoptosis and impairment of neurogenesis.
- 1.Soriano S G, Liu Q, Li J. (2010) Ketamine activates cell cycle signaling and apoptosis in the neonatal rat brain. , Anesthesiology 112(5), 1155-1163.
- 2.Zheng H, Dong Y, Xu Z. (2013) Sevoflurane anesthesia in pregnant mice induces neurotoxicity in fetal and offspring mice. , Anesthesiology 118(3), 516-526.
- 3.Boscolo A, Starr J A, Sanchez V. (2012) The abolishment of anesthesia-induced cognitive impairment by timely protection of mitochondria in the developing rat brain: the importance of free oxygen radicals and mitochondrial integrity. Neurobiol Dis. 45(3), 1031-1041.
- 4.Olney J W, Farber N B, Wozniak D F, Jevtovic-Todorovic V, Ikonomidou C. (2000) Environmental agents that have the potential to trigger massive apoptotic neurodegeneration in the developing brain. Environ Health Perspect.108. , (Suppl3): 383-388.
- 5.Zhao Y L, Xiang Q, Shi Q Y. (2011) GABAergic excitotoxicity injury of the immature hippocampal pyramidal neurons' exposure to isoflurane. , Anesth Analg 113(5), 1152-1160.
- 6.Boscolo A, Starr J A, Sanchez V. (2012) The abolishment of anesthesia-induced cognitive impairment by timely protection of mitochondria in the developing rat brain: the importance of free oxygen radicals and mitochondrial integrity. Neurobiol Dis. 45(3), 1031-1041.
- 7.Zhang Y, Xu Z, Wang H. (2012) Anesthetics isoflurane and desflurane differently affect mitochondrial function, learning, and memory. , Ann Neurol 71(5), 687-698.
- 8.Zhang Y, Dong Y, Wu X. (2010) The mitochondrial pathway of anesthetic isoflurane-induced apoptosis. , J Biol Chem 285(6), 4025-4037.
- 9.Head B P, Patel H H, Niesman I R, Drummond J C, Roth D M et al. (2009) Inhibition of p75 neurotrophin receptor attenuates isoflurane-mediated neuronal apoptosis in the neonatal central nervous system. , Anesthesiology 110(4), 813-825.
- 10.Pearn M L, Hu Y, Niesman I R. (2012) Propofol neurotoxicity is mediated by p75 neurotrophin receptor activation. , Anesthesiology 116(2), 352-361.
- 11.Shen X, Dong Y, Xu Z. (2013) Selective anesthesia-induced neuroinflammation in developing mouse brain and cognitive impairment. , Anesthesiology 118(3), 502-515.
- 12.Yang B, Liang G, Khojasteh S. (2014) Comparison of neurodegeneration and cognitive impairment in neonatal mice exposed to propofol or isoflurane. , PLoSOne 9(6), 99171.
- 13.Wei H F, Liang G, Yang H. (2008) The common inhalational anesthetic isoflurane induces apoptosis via activation of inositol 1,4,5-trisphosphate receptors. , Anesthesiology 108(2), 251-260.
- 14.Yang H, Liang G, Hawkins B J, Madesh M, Pierwola A et al. (2008) Inhalational anesthetics induce cell damage by disruption of intracellular calcium homeostasis with different potencies. , Anesthesiology 109(2), 243-250.
- 15.Wei H. (2011) The role of calcium dysregulation in anesthetic-mediated neurotoxicity. , Anesth Analg 113(5), 972-974.
- 16.Zhao X, Yang Z, Liang G. (2013) . Dual Effects of Isoflurane on Proliferation, Differentiation, and Survival in Human Neuroprogenitor Cells. Anesthesiology 118(3), 537-549.
- 17.Sall J W, Stratmann G, Leong J. (2009) Isoflurane inhibits growth but does not cause cell death in hippocampal neural precursor cells grown in culture. , Anesthesiology 110(4), 826-833.
- 18.Culley D J, Boyd J D, Palanisamy A. (2011) Isoflurane decreases self-renewal capacity of rat cultured neural stem cells. , Anesthesiology 115(4), 754-763.
- 19.Velly L, Mantz J, Bruder N. (2013) Dual effects of isoflurane on neuronal proliferation/differentiation: a substrate to impaired cognitive function?. , Anesthesiology 118(3), 487-489.
- 20.Palanisamy A, Friese M B, Cotran E. (2016) . Prolonged Treatment with Propofol Transiently Impairs Proliferation but Not Survival of Rat Neural Progenitor Cells In Vitro. PLoS One 11(7), 0158058.
- 21.Stratmann G, Sall J W, LDV May. (2009) Isoflurane Differentially Affects Neurogenesis and Long-term Neurocognitive Function in 60-day-old and 7-day-old Rats. , Anesthesiology 110(4), 834-848.
- 22.Zhu C, Gao J, Karlsson N. (2010) Isoflurane anesthesia induced persistent, progressive memory impairment, caused a loss of neural stem cells, and reduced neurogenesis in young, but not adult, rodents. JCerebBlood Flow Metab. 30(5), 1017-1030.
- 23.Bai X, Twaroski D, Bosnjak Z J. (2013) Modeling anesthetic developmental neurotoxicity using human stem cells. Semin Cardiothorac Vasc Anesth. 17(4), 276-287.
- 24.Creeley C E, Dikranian K T, Dissen G A, Back S A, Olney J W et al. (2014) Isoflurane-induced apoptosis of neurons and oligodendrocytes in the fetal rhesus macaque brain. , Anesthesiology 120(3), 626-638.
- 25.Li Y, Liang G, Wang S, Meng Q, Wang Q et al. (2007) Effects of fetal exposure to isoflurane on postnatal memory and learning in rats. , Neuropharmacology 53(8), 942-950.
- 26.Wang S, Peretich K, Zhao Y, Liang G, Meng Q et al. (2009) Anesthesia-induced neurodegeneration in fetal rat brains. Pediatr Res. 66(4), 435-440.
- 27.Wei H, Liang G, Yang H. (2007) Isoflurane preconditioning inhibited isoflurane-induced neurotoxicity. , Neurosci Lett 425(1), 59-62.
- 28.Liang G, Ward C, Peng J, Zhao Y, Huang B et al. (2010) Isoflurane causes greater neurodegeneration than an equivalent exposure of sevoflurane in the developing brain of neonatal mice. , Anesthesiology 112(6), 1325-1334.
- 29.Peng J, Drobish J K, Liang G. (2014) Anesthetic preconditioning inhibits isoflurane-mediated apoptosis in the developing rat brain. , Anesth Analg 119(4), 939-946.
- 30.Zou X, Patterson T A, Divine R L. (2009) Prolonged exposure to ketamine increases neurodegeneration in the developing monkey brain. , Int J Dev Neurosci 27(7), 727-731.
- 31.Zou X, Patterson T A, Sadovova N. (2009) Potential neurotoxicity of ketamine in the developing rat brain. , Toxicol Sci 108(1), 149-158.
- 32.Liu F, Rainosek S W, Sadovova N. (2014) Protective effect of acetyl-L-carnitine on propofol-induced toxicity in embryonic neural stem cells. , Neurotoxicology 42, 49-57.
- 33.Bai X, Yan Y, Canfield S. (2013) Ketamine enhances human neural stem cell proliferation and induces neuronal apoptosis via reactive oxygen species-mediated mitochondrial pathway. , Anesth Analg 116(4), 869-880.
- 34.Bosnjak Z J, Yan Y, Canfield S. (2012) Ketamine induces toxicity in human neurons differentiated from embryonic stem cells via mitochondrial apoptosis pathway. Curr Drug Saf. 7(2), 106-119.
- 35.Bosnjak Z J. (2012) Developmental neurotoxicity screening using human embryonic stem cells. , Exp Neurol 237(1), 207-210.
- 36.Wang C, Liu F, Patterson T A, Paule M G, Slikker W. (2016) Relationship between ketamine-induced developmental neurotoxicity and NMDA receptor-mediated calcium influx in neural stem cell-derived neurons. , Neurotoxicology
- 37.Peng J, Drobish J K, Liang G. (2014) Anesthetic preconditioning inhibits isoflurane-mediated apoptosis in the developing rat brain. , Anesth Analg 119(4), 939-946.
- 38.Wei H, Liang G, Yang H. (2007) Isoflurane preconditioning inhibited isoflurane-induced neurotoxicity. , Neurosci Lett 425(1), 59-62.
- 39.Wei H, Inan S. (2013) Dual effects of neuroprotection and neurotoxicity by general anesthetics: Role of intracellular calcium homeostasis. Prog Neuro-Psychopharmacol Biol Psychiatry.
- 40.Zheng S, Zuo Z. (2003) Isoflurane preconditioning reduces purkinje cell death in an in vitro model of rat cerebellar ischemia. , Neuroscience 118(1), 99-106.
- 41.Xie Z, Dong Y, Maeda U. (2007) The inhalation anesthetic isoflurane induces a vicious cycle of apoptosis and amyloid beta-protein accumulation. , J Neurosci 27(6), 1247-1254.
- 42.Bickler P E, Zhan X, Fahlman C S. (2005) Isoflurane preconditions hippocampal neurons against oxygen-glucose deprivation: role of intracellular Ca2+ and mitogen-activated protein kinase signaling. , Anesthesiology 103(3), 532-539.
- 43.Kitano H, Kirsch J R, Hurn P D, Murphy S J. (2007) Inhalational anesthetics as neuroprotectants or chemical preconditioning agents in ischemic brain. , J Cereb Blood Flow Metab 27(6), 1108-1128.
- 44.Ma D, Williamson P, Januszewski A. (2007) Xenon mitigates isoflurane-induced neuronal apoptosis in the developing rodent brain. , Anesthesiology 106(4), 746-753.
- 45.Dong Y, Zhang G, Zhang B. (2009) The common inhalational anesthetic sevoflurane induces apoptosis and increases beta-amyloid protein levels. , Arch Neurol 66(5), 620-631.
- 46.Lee S. (2013) Guilty, or not guilty?: a short story of propofol abuse. , Korean J Anesthesiol 65(5), 377-378.
- 47.Twaroski D M, Yan Y, Olson J M, Bosnjak Z J, Bai X. (2014) Down-regulation of microRNA-21 is involved in the propofol-induced neurotoxicity observed in human stem cell-derived neurons. , Anesthesiology 121(4), 786-800.
- 48.Sall J W, Stratmann G, Leong J, Woodward E, Bickler P E. (2012) Propofol at clinically relevant concentrations increases neuronal differentiation but is not toxic to hippocampal neural precursor cells in vitro. , Anesthesiology 117(5), 1080-1090.
- 49.Vutskits L, Gascon E, Tassonyi E, Kiss J Z. (2005) Clinically relevant concentrations of propofol but not midazolam alter in vitro dendritic development of isolated gamma-aminobutyric acid-positive interneurons. , Anesthesiology 102(5), 970-976.