Modeling anesthetic developmental neurotoxicity using human stem cells

Research progress on the effects and mechanisms of anesthetics on neural stem cells

Exposure to anesthetic drugs has been proven to seriously affect developing animals in terms of neural stem cells' (NSCs') proliferation, differentiation, and apoptosis. This can severely hamper the development of physiological learning and memory skills. Studies on the effects of anesthetics on NSCs' proliferation and differentiation are thus reviewed here, with the aim to highlight which specific drug mechanisms are the least harmful to NSCs. PubMed has been used as the preferential searching database of relevant literature to identify studies on the effects and mechanisms of NSCs' proliferation and differentiation. It was concluded that propofol and sevoflurane may be the safest options for NSCs during pregnancy and in pediatric clinical procedures, while dexmedetomidine has been found to reduce opioid-related damage in NSCs. It was also found that the growth environment may impact neurodevelopment even more than narcotic drugs. Nonetheless, the current scientific literature available further highlights how more extensive clinical trials are absolutely required for corroborating the conclusion drawn here.

Long Noncoding RNA SPRY4-IT1 Modulates Ketamine-Induced Neurotoxicity in Human Embryonic Stem Cell-Derived Neurons through EZH2

OBJECTIVE

This study aimed to investigate whether long noncoding RNA sprouty receptor tyrosine kinase signaling antagonist 4-intronic transcript 1 (SPRY4-IT1) is involved in the regulation of ketamine-induced neurotoxicity.

METHODS

Human embryonic stem cells (hESCs) were induced into neurons in vitro and treated with ketamine. Apoptosis and neurite degeneration assays were used to determine ketamine-induced neurotoxicity and qRT-PCR to determine SPRY4-IT1 expression. SPRY4-IT1 was downregulated in hESC-induced neurons to examine its regulation on ketamine-induced neurotoxicity. The correlation between enhancer of zeste homolog 2 (EZH2) and SPRY4-IT1 was also examined. EZH2 was upregulated in SPRY4-IT1-downregualted hESC-induced neurons to further examine its participation in SPRY4-IT1-mediated ketamine neurotoxicity.

RESULTS

Ketamine-induced dose-dependent apoptosis, neurite degeneration, and SPRY4-IT1 upregulation in hESC-induced neurons. Lentivirus-mediated SPRY4-IT1 downregulation protected ketamine neurotoxicity. EZH2 expression was positively correlated with SPRY4-IT1 in hESC-induced neurons. EZH2 overexpression markedly reversed the protective effects of SPRY4-IT1 knockdown on ketamine neurotoxicity.

CONCLUSIONS

SPRY4-IT1 is involved in anesthesia-induced neurotoxicity, possibly through the regulation on EZH2 gene.

Maternal anesthesia with sevoflurane during the mid-gestation induces social interaction deficits in offspring C57BL/6 mice

Sevoflurane anesthesia in pregnant mice could induce neurotoxicity in the developing brain and disturb learning and memory in the offspring mice. Whether it could impair social behaviors in the offspring mice is uncertain. Therefore, we assessed the neurobehavioral effect of in-utero exposure to sevoflurane on social interaction behaviors in C57BL/6 mice. The pregnant mice were anesthetized with 2.5% sevoflurane in 100% oxygen for 2 h, and their offspring mice were tested in three-chambered social paradigm, which includes three 10-min sessions of habituation, sociability, and preference for social novelty. At the juvenile age, the offspring mice showed abnormal sociability, as proved by not taking more time sniffing at the stranger 1 mouse compared with the empty enclosure (108.5 ± 25.4 vs. 108.2 ± 44.0 s, P = 0.9876). Meanwhile, these mice showed impaired preference for social novelty, as evidenced by not taking more time sniffing at the stranger 2 compared with the stranger 1 mouse (92.1 ± 52.2 vs. 126.7 ± 50.8 s, P = 0.1502). At the early adulthood, the offspring mice retrieved the normal sociability (145.6 ± 33.2 vs. 76.0 ± 31.8 s, P = 0.0001), but remained the impaired preference for social novelty (100.6 ± 29.3 vs. 118.0 ± 47.9 s, P = 0.3269). Collectively, these results suggested maternal anesthesia with sevoflurane could induce social interaction deficits in their offspring mice. Although the disturbance of sociability could be recoverable, the impairment of preference for social novelty could be long-lasting.

LncRNA KCNQ1OT1 Sponges miR-206 to Ameliorate Neural Injury Induced by Anesthesia via Up-Regulating BDNF

OBJECTIVE

Widely used in anesthesia, ketamine is reported to induce neurotoxicity in patients. This study aimed to investigate the molecular regulatory mechanism of long non-coding RNA (lncRNA) KCNQ1 opposite strand/antisense transcript 1 (KCNQ1OT1) in ameliorating ketamine-induced neural injury.

MATERIALS AND METHODS

Sprague-Dawley rats were intraperitoneally injected with ketamine to induce neuronal injury. PC-12 cells treated with ketamine were used as the cell model. Ketamine-induced aberrant expression of KCNQ1OT1, miR-206 and brain-derived neurotrophic factor (BDNF) were examined by quantitative real-time polymerase chain reaction (qRT-PCR). The effects of KCNQ1OT1 and miR-206 on ketamine-induced neural injury in PC-12 cells were then examined by MTT and LDH assay. The regulatory relationships between KCNQ1OT1 and miR-206, and miR-206 and BDNF were detected by dual-luciferase reporter assay.

RESULTS

Ketamine induced the apoptosis of neurons of the hippocampus in rats, and the apoptosis of PC-12 cells, accompanied by down-regulation of KCNQ1OT1 and BDNF expressions, and up-regulation of miR-206 expression. Overexpression of KCNQ1OT1 enhanced the resistance to apoptosis of PC-12 cells and significantly ameliorated ketamine-induced nerve injury, while transfection of miR-206 had opposite effects. Mechanistically, KCNQ1OT1 could target miR-206 and reduce its expression level, in turn indirectly increase the expression level of BDNF, and play a protective role in neural injury.

CONCLUSION

KCNQ1OT1/miR-206/BDNF axis is demonstrated to be an important regulatory mechanism in regulating ketamine-induced neural injury. Our study helps to clarify the mechanism by which ketamine exerts its toxicological effects and provides clues for the neuroprotection during anesthesia.

Traditional Chinese medicine, Kami-Shoyo-San protects ketamine-induced neurotoxicity in human embryonic stem cell-differentiated neurons through activation of brain-derived neurotrophic factor

BACKGROUND

Anesthesia-induced neurotoxicity may cause permanent dysfunctions in human brains. In this work, we used a cell-based in-vitro model to demonstrate that traditional Chinese medicine, Kami-Shoyo-San may protect ketamine-induced neuronal apoptosis in human embryonic stem cell-differentiated neurons.

METHODS

Human embryonic stem cell-differentiated neurons were cultured in vitro and treated with high-concentration ketamine to induce neuronal apoptosis. Pre-incubation of Kami-Shoyo-San was conducted to evaluate its neuroprotection on ketamine-injured neurons. Quantitative real-time PCR and western blot assays were used to assess brain-derived neurotrophic factor and its receptor, tropomyosin receptor kinase B, in response to Kami-Shoyo-San and ketamine treatment. Brain-derived neurotrophic factor/tropomyosin receptor kinase B signaling pathway was then deactivated, by siRNA application, to further explore its functional role in Kami-Shoyo-San-mediated protection on ketamine-induced apoptosis among human embryonic stem cell-differentiated neurons.

RESULTS

High concentration of ketamine-induced significant apoptosis, whereas pre-incubation of Kami-Shoyo-San markedly rescued ketamine-induced apoptosis, in human embryonic stem cell-differentiated neurons. Kami-Shoyo-San activated brain-derived neurotrophic factor/tropomyosin receptor kinase B signaling pathway by upregulating brain-derived neurotrophic factor and inducing tropomyosin receptor kinase B phosphorylation. Conversely, siRNA-mediated brain-derived neurotrophic factor/tropomyosin receptor kinase B signaling pathway deactivation reversed the neuroprotection of Kami-Shoyo-San in ketamine-injured human embryonic stem cell-differentiated neurons.

CONCLUSION

Kami-Shoyo-San could protect ketamine-induced neurotoxicity, and the underlying mechanism may involve brain-derived neurotrophic factor/tropomyosin receptor kinase B signaling pathway.

Studying Human Neurological Disorders Using Induced Pluripotent Stem Cells: From 2D Monolayer to 3D Organoid and Blood Brain Barrier Models

Neurological disorders have emerged as a predominant healthcare concern in recent years due to their severe consequences on quality of life and prevalence throughout the world. Understanding the underlying mechanisms of these diseases and the interactions between different brain cell types is essential for the development of new therapeutics. Induced pluripotent stem cells (iPSCs) are invaluable tools for neurological disease modeling, as they have unlimited self-renewal and differentiation capacity. Mounting evidence shows: (i) various brain cells can be generated from iPSCs in two-dimensional (2D) monolayer cultures; and (ii) further advances in 3D culture systems have led to the differentiation of iPSCs into organoids with multiple brain cell types and specific brain regions. These 3D organoids have gained widespread attention as in vitro tools to recapitulate complex features of the brain, and (iii) complex interactions between iPSC-derived brain cell types can recapitulate physiological and pathological conditions of blood-brain barrier (BBB). As iPSCs can be generated from diverse patient populations, researchers have effectively applied 2D, 3D, and BBB models to recapitulate genetically complex neurological disorders and reveal novel insights into molecular and genetic mechanisms of neurological disorders. In this review, we describe recent progress in the generation of 2D, 3D, and BBB models from iPSCs and further discuss their limitations, advantages, and future ventures. This review also covers the current status of applications of 2D, 3D, and BBB models in drug screening, precision medicine, and modeling a wide range of neurological diseases (e.g., neurodegenerative diseases, neurodevelopmental disorders, brain injury, and neuropsychiatric disorders). © 2019 American Physiological Society. Compr Physiol 9:565-611, 2019.

MicroRNA-107 regulates anesthesia-induced neural injury in embryonic stem cell derived neurons

Ketamine, though widely used in pediatric anesthesia, may induce cortical neurotoxicity in young patients. This study focused on an in vitro model of rat brain embryonic stem cell (ESC)-derived neurons to investigate the effects of microRNA-107 (miR-107) on ketamine-induced neural injury. Rat brain ESCs were proliferated in vitro and differentiated toward neuronal fate. Ketamine induced neural injury in ESC-derived neurons was inspected by TUNEL and neurite growth assays. Ketamine-induce aberrant miR-107 expression was examined by qRT-PCR. MiR-107 was downregulated in ESCs through lentiviral transduction. Its effect on ketamine-induced neural injury in ESC-derived neurons was then examined. Potential downstream target of miR-107, brain derived neurotrophin factor (BDNF), was inspected by dual-luciferase reporter assay and qRT-PCR. BDNF was knocked down, through siRNA transfection, in NSCs to investigate its functional involvement in miR-107 mediated neural protection in ketamine-injured NSC-derived neurons. Ketamine induced apoptosis, neurite degeneration, and upregulated miR-107 in NSC-derived neurons. Lentivirus-mediated miR-107 downregulation attenuated ketamine-induced neural injury. BDNF was proven to be directly and inversely regulated by miR-107 in NSC-derived neurons. SiRNA-mediated BDNF inhibition reversed the protective effect of miR-107 downregulation on ketamine injury in NSC-derived neurons. MiR-107 / BDNF was demonstrated to be an important epigenetic signaling pathway in regulating ketamine-induced neural injury in cortical neurons. © 2018 The Authors. IUBMB Life published by Wiley Periodicals,Inc. on behalf of International Union of Biochemistry and Molecular Biology., 71(1):20-27, 2019.

Long noncoding RNA SNHG16 reduced ketamine-induced neurotoxicity in human embryonic stem cell-derived neurons

BACKGROUND

Clinical evidence demonstrates that prolonged exposure to ketamine may cause irreversible injury to immature human brains. In this study, we utilized an in vitro model to examine the function of long noncoding RNA (lncRNA) SNHG16 in ketamine-induced neurotoxicity in human embryonic stem cell (hESC)-derived neurons.

METHODS

HESCs were induced toward neuronsin vitro, and treated with ketamine, at various concentrations, for 48 h. Viability, apoptosis, caspase-3 activity and ROS activity were then examined among hESC-derived neurons. Ketamine-induced gene expression change of SNHG16 was assessed by qRT-PCR. SNHG16 was overexpressed in hESC-derived neurons, which were then treated with ketamine, followed by biochemical assays to assess the effects of SNHG16 upregulation on ketamine-induced neurotoxicity. Correlation between SNHG16 and NeuroD1 gene was assess by qRT-PCR. In SNHG16-upregulated hESC-derived neurons, they were double transfected with siRNA to knock down NeuroD1. The functions of NeuroD1 inhibition on SNHG16-associated neural protection on ketamine-induced neurotoxicity were further assessed.

RESULTS

48-h in vitro treatment of ketamine induced significant neurotoxicity, and downregulated SNHG16 among hESC-derived neurons. Conversely, SNHG16 upregulation reduced ketamine-induced neurotoxicity. NeuroD1 expression was downregulated by ketamine in hESC-derived neurons, and concomitantly upregulated by SNHG16 overexpression. SiRNA-mediated NeuroD1 inhibition reversed the protection of SNHG16 upregulation on ketamine-induced neurotoxicity.

CONCLUSIONS

SNHG16 is an important epigenetic factor which may functionally modulate ketamine-induced neurotoxicity through NeuroD1.

Inhibition of GSK-3beta Signaling Pathway Rescues Ketamine-Induced Neurotoxicity in Neural Stem Cell-Derived Neurons

Clinical application of anesthetic reagent, ketamine (Keta), may induce irreversible neurotoxicity in central nervous system. In this work, we utilized an in vitro model of neural stem cells-derived neurons (nSCNs) to evaluate the role of GSK-3 signaling pathway in Keta-induced neurotoxicity. Embryonic mouse-brain neural stem cells were differentiated into neurons in vitro. Keta (50 μM)-induced neurotoxicity in cultured nSCNs was monitored by apoptosis, immunohistochemical and western blot assays, respectively. GSK-3 signaling pathways, including GSK-3α and GSK-3β, were inhibited by siRNA in the culture. The subsequent effects of GSK-3α or GSK-3β downregulation on Keta-induced neurotoxicity, including apoptosis and neurite loss, were then evaluated in nSCNs. Finally, caspase and Akt/ERK signal pathways were further examined by western blot to evaluate the regulatory effect of GSK-3 signaling pathways on Keta-induced neural injury. Keta (50 μM) caused markedly nSCN apoptosis and neurite degeneration in vitro. Keta decreased GSK-3β phosphorylation, but had no effect on GSK-3α phosphorylation. SiRNA-induced GSK-3β downregulation rescued Keta-induced neurotoxicity in nSCNs by reducing neuronal apoptosis and preventing neurite degeneration. On the other hand, GSK-3α downregulation had no effect on Keta-induced neurotoxicity. Western blot showed that, in Keta-injured nSCNs, GSK-3β downregulation reduced Caspase-1/3 proteins, but left phosphorylated Akt/ERK unchanged. GSK-3β, not GSK-3α, was specifically involved in the process of Keta-induced neurotoxicity in nSCNs. Inhibiting GSK-3β may be an effective approach to counter toxic effect of ketamine on central neurons in clinical and experimental applications.

Adverse outcome pathways: Application to enhance mechanistic understanding of neurotoxicity

Recent developments have prompted the transition of empirically based testing of late stage toxicity in animals for a range of different endpoints including neurotoxicity to more efficient and predictive mechanistically based approaches with greater emphasis on measurable key events early in the progression of disease. The adverse outcome pathway (AOP) has been proposed as a simplified organizational construct to contribute to this transition by linking molecular initiating events and earlier (more predictive) key events at lower levels of biological organization to disease outcomes. As such, AOPs are anticipated to facilitate the compilation of information to increase mechanistic understanding of pathophysiological pathways that are responsible for human disease.

In this review, the sequence of key events resulting in adverse outcome (AO) defined as parkinsonian motor impairment and learning and memory deficit in children, triggered by exposure to environmental chemicals has been briefly described using the AOP framework. These AOPs follow convention adopted in an Organization for Economic Cooperation and Development (OECD) AOP development program, publically available, to permit tailored application of AOPs for a range of different purposes.

Due to the complexity of disease pathways, including neurodegenerative disorders, a specific symptom of the disease (e.g. parkinsonian motor deficit) is considered as the AO in a developed AOP. Though the description is necessarily limited by the extent of current knowledge, additional characterization of involved pathways through description of related AOPs interlinked into networks for the same disease has potential to contribute to more holistic and mechanistic understanding of the pathophysiological pathways involved, possibly leading to the mechanism-based reclassification of diseases, thus facilitating more personalized treatment.

Developing and applying the adverse outcome pathway concept for understanding and predicting neurotoxicity

The Adverse Outcome Pathway (AOP) concept has recently been proposed to support a paradigm shift in regulatory toxicology testing and risk assessment. This concept is similar to the Mode of Action (MOA), in that it describes a sequence of measurable key events triggered by a molecular initiating event in which a stressor interacts with a biological target. The resulting cascade of key events includes molecular, cellular, structural and functional changes in biological systems, resulting in a measurable adverse outcome. Thereby, an AOP ideally provides information relevant to chemical structure-activity relationships as a basis for predicting effects of structurally similar compounds. AOPs could potentially also form the basis for qualitative and quantitative predictive modeling of the human adverse outcome resulting from molecular initiating or other key events for which higher-throughput testing methods are available or can be developed. A variety of cellular and molecular processes are known to be critical for normal function of the central (CNS) and peripheral nervous systems (PNS). Because of the biological and functional complexity of the CNS and PNS, it has been challenging to establish causative links and quantitative relationships between key events that comprise the pathways leading from chemical exposure to an adverse outcome in the nervous system. Following introduction of the principles of MOA and AOPs, examples of potential or putative adverse outcome pathways specific for developmental or adult neurotoxicity are summarized and aspects of their assessment considered. Their possible application in developing mechanistically informed Integrated Approaches to Testing and Assessment (IATA) is also discussed.

Induced Pluripotent Stem Cell Models to Enable In Vitro Models for Screening in the Central Nervous System

There is great need to develop more predictive drug discovery tools to identify new therapies to treat diseases of the central nervous system (CNS). Current nonpluripotent stem cell-based models often utilize non-CNS immortalized cell lines and do not enable the development of personalized models of disease. In this review, we discuss why in vitro models are necessary for translational research and outline the unique advantages of induced pluripotent stem cell (iPSC)-based models over those of current systems. We suggest that iPSC-based models can be patient specific and isogenic lines can be differentiated into many neural cell types for detailed comparisons. iPSC-derived cells can be combined to form small organoids, or large panels of lines can be developed that enable new forms of analysis. iPSC and embryonic stem cell-derived cells can be readily engineered to develop reporters for lineage studies or mechanism of action experiments further extending the utility of iPSC-based systems. We conclude by describing novel technologies that include strategies for the development of diversity panels, novel genomic engineering tools, new three-dimensional organoid systems, and modified high-content screens that may bring toxicology into the 21st century. The strategic integration of these technologies with the advantages of iPSC-derived cell technology, we believe, will be a paradigm shift for toxicology and drug discovery efforts.

Importance of being Nernst: Synaptic activity and functional relevance in stem cell-derived neurons

Functional synaptogenesis and network emergence are signature endpoints of neurogenesis. These behaviors provide higher-order confirmation that biochemical and cellular processes necessary for neurotransmitter release, post-synaptic detection and network propagation of neuronal activity have been properly expressed and coordinated among cells. The development of synaptic neurotransmission can therefore be considered a defining property of neurons. Although dissociated primary neuron cultures readily form functioning synapses and network behaviors in vitro, continuously cultured neurogenic cell lines have historically failed to meet these criteria. Therefore, in vitro-derived neuron models that develop synaptic transmission are critically needed for a wide array of studies, including molecular neuroscience, developmental neurogenesis, disease research and neurotoxicology. Over the last decade, neurons derived from various stem cell lines have shown varying ability to develop into functionally mature neurons. In this review, we will discuss the neurogenic potential of various stem cells populations, addressing strengths and weaknesses of each, with particular attention to the emergence of functional behaviors. We will propose methods to functionally characterize new stem cell-derived neuron (SCN) platforms to improve their reliability as physiological relevant models. Finally, we will review how synaptically active SCNs can be applied to accelerate research in a variety of areas. Ultimately, emphasizing the critical importance of synaptic activity and network responses as a marker of neuronal maturation is anticipated to result in in vitro findings that better translate to efficacious clinical treatments.

In vivo and in vitro ketamine exposure exhibits a dose-dependent induction of activity-dependent neuroprotective protein in rat neurons

Anesthetic doses of ketamine induce apoptosis, as well as gene expression of activity-dependent neuroprotective protein (ADNP), a putative homeodomain transcription factor in rat pups (P7). This study investigated if ketamine induced ADNP protein in a dose-dependent manner in vitro and in vivo using primary cultures of cortical neurons and neonatal pups (P7). In vivo immunohistochemistry demonstrated a sub-anesthetic dose of ketamine increased ADNP in the somatosensory cortex (SCC) which was previously identified to be damaged by repeated exposure to anesthetic doses of ketamine. Administration of low-dose ketamine prior to full sedation prevented caspase-3 activation in the hippocampus and SCC. Primary cultures of cortical neurons treated with ketamine (10 μM-10mM) at 3 days-in vitro (3 DIV) displayed a concentration-dependent decrease in expanded growth cones. Furthermore, neuronal production and localization of ADNP varied as a function of both ketamine concentration and length of exposure. Taken together, these data support the model that ADNP induction may be partially responsible for the efficacy of a low-dose ketamine pre-treatment in preventing ketamine-induced neuronal cell death.