Developmental neurotoxicity testing in vitro: models for assessing chemical effects on neurite outgrowth

Optimization of a human induced pluripotent stem cell-derived sensory neuron model for the in vitro evaluation of taxane-induced neurotoxicity

Human induced pluripotent stem cell-derived sensory neuron (iPSC-dSN) models are a valuable resource for the study of neurotoxicity but are affected by poor replicability and reproducibility, often due to a lack of optimization. Here, we identify experimental factors related to culture conditions that substantially impact cellular drug response in vitro and determine optimal conditions for improved replicability and reproducibility. Treatment duration and cell seeding density were both found to be significant factors, while cell line differences also contributed to variation. A replicable dose-response in viability was demonstrated after 48-h exposure to docetaxel or paclitaxel. Additionally, a replicable dose-dependent reduction in neurite outgrowth was demonstrated, demonstrating the applicability of the model for the examination of additional phenotypes. Overall, we have established an optimized iPSC-dSN model for the study of taxane-induced neurotoxicity.

The role of m6A modification in the risk prediction and Notch1 pathway of Alzheimer's disease

N6-methyladenosine (m6A) methylation and abnormal immune responses are implicated in neurodegenerative diseases, yet their relationship in Alzheimer's disease (AD) remains unclear. We obtained AD datasets from GEO databases and used AD mouse and cell models, observing abnormal expression of m6A genes in the AD group, alongside disruptions in the immune microenvironment. Key m6A genes (YTHDF2, LRPPRC, and FTO) selected by machine learning were associated with the Notch pathway, with FTO and Notch1 displaying the strongest correlation. Specifically, FTO expression decreased and m6A methylation of Notch1 increased in AD mouse and cell models. We further silenced FTO expression in HT22 cells, resulting in upregulation of the Notch1 signaling pathway. Additionally, increased Notch1 expression in dendritic cells heightened inflammatory cytokine secretion in vitro. These results suggest that reduced FTO expression may contribute to the pathogenesis of AD by activating the Notch1 pathway to interfere with the immune response.

Assessment of poly(hexamethylenebicyanoguanide-hexamethylenediamine) hydrochloride-induced developmental neurotoxicity via oxidative stress mechanism: Integrative approaches with neuronal cells and zebrafish

Poly(hexamethylenebicyanoguanide-hexamethylenediamine) hydrochloride (PHMB) is a biocide with a broad spectrum of antibacterial activity. Its use as a disinfectant and preservative in consumer products results in human exposure to PHMB. Toxicity studies on PHMB mainly focus on systemic toxicity or skin irritation; however, its effects on developmental neurotoxicity (DNT) and the underlying mechanisms are poorly understood. In this study, the DNT effects of PHMB were evaluated using IMR-32 and SH-SY5Y cell lines and zebrafish. In both cell lines, PHMB concentrations ≥ 10 µM reduced neurite outgrowth, and cytotoxicity was observed at concentrations up to 40 µM. PHMB regulated expression of neurodevelopmental genes and induced reactive oxygen species (ROS) production and mitochondrial dysfunction. Treatment with N-acetylcysteine reversed the toxic effects of PHMB. Toxicity tests on zebrafish embryos showed that PHMB reduced viability and heart rate and caused irregular hatching. PHMB concentrations of 1-4 µM reduced the width of the brain and spinal cord of transgenic zebrafish and attenuated myelination processes. Furthermore, PHMB modulated expression of neurodevelopmental genes in zebrafish and induced ROS accumulation. These results suggested that PHMB exerted DNT effects in vitro and in vivo through a ROS-dependent mechanism, highlighting the risk of PHMB exposure.

Proteomics revealed an association between ribosome-associated proteins and amyloid beta deposition in Alzheimer's disease

Most scholars believe that amyloid-beta (Aβ) has the potential to induce apoptosis, stimulate an inflammatory cascade, promote oxidative stress and exacerbate the pathological progression of Alzheimer's disease (AD). Therefore, it is crucial to investigate the deposition of Aβ in AD. At approximately 6 months of age, APP/PS1 double transgenic mice gradually exhibit the development of plaques, as well as spatial and learning impairment. Notably, the hippocampus is specifically affected in the course of AD. Herein, 6-month-old APP/PS1 double transgenic mice were utilized, and the differentially expressed (DE) proteins in the hippocampus were identified and analyzed using 4D label-free quantitative proteomics technology and parallel reaction monitoring (PRM). Compared to wild-type mice, 29 proteins were upregulated and 25 proteins were downregulated in the AD group. Gene Ontology (GO) enrichment analysis of biological processes (BP) indicated that the DE proteins were mainly involved in 'ribosomal large subunit biogenesis'. Molecular function (MF) analysis results were primarily associated with '5.8S rRNA binding' and 'structural constituent of ribosome'. In terms of cellular components (CC), the DE proteins were mainly found in 'polysomal ribosome', 'cytosolic large ribosomal subunit', 'cytosolic ribosome', and 'large ribosomal subunit', among others. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis demonstrated that the results were mainly enriched in the 'Ribosome signaling pathway'. The key target proteins identified were ribosomal protein (Rp)l18, Rpl17, Rpl19, Rpl24, Rpl35, and Rpl6. The PRM verification results were consistent with the findings of the 4D label-free quantitative proteomics analysis. Overall, these findings suggest that Rpl18, Rpl17, Rpl19, Rpl24, Rpl35, and Rpl6 may have potential therapeutic value for the treatment of AD by targeting Aβ.

Effect of a New Substance with Pyridoindole Structure on Adult Neurogenesis, Shape of Neurons, and Behavioral Outcomes in a Chronic Mild Stress Model in Rats

Despite an accumulating number of studies, treatments for depression are currently insufficient. Therefore, the search for new substances with antidepressant potential is very important. In this study, we hypothesized that treatment with a newly synthesized pyridoindole derivative compound SMe1EC2M3 would result in protective and antidepressant-like effects on behavioral outcomes and reverse the impaired adult hippocampal neurogenesis caused by chronic mild stress (CMS). We found that chronic administration of 5 mg/kg and 25 mg/kg SMe1EC2M3 to adult Sprague Dawley rats ameliorated the consequences of CMS on immobility and swimming time in a forced swim test. A slight sedative effect of the highest dose of SMe1EC2M3 in the nonstress group was observed in the open field. SMe1EC2M3 in the highest dose ameliorated CMS-induced decreases in the sucrose preference test. Administration of SMe1EC2M3 significantly increased SOX2-positive cells in the hippocampal dentate gyrus (DG) in CMS compared to control animals. A significant reduction in glial fibrillary acid protein (GFAP)-positive cells in the DG of CMS compared to control animals was observed. Administration of both 5 and 25 mg/kg SMe1EC2M3 significantly increased signal of GFAP-positive cells in the DG of CMS animals. No such effects of SMe1EC2M3 were observed in the cornu ammonis hippocampal area. Additionally, we found that incubation of primary hippocampal neurons in the presence of 1.50 µM SMe1EC2M3 significantly stimulated the length of neurites. Overall, we found that the negative effects of CMS on depression-like behavior are partially reduced by the administration of SMe1EC2M3 and are associated with changes in hippocampal neurogenesis and neuronal differentiation. SMe1EC2M3 represents a potential drug candidate with positive neuroplastic effects and neurogenesis-associated effects in therapeutic approaches to depression.

Copper pyrithione and zinc pyrithione induce cytotoxicity and neurotoxicity in neuronal/astrocytic co-cultured cells via oxidative stress

Previous studies on copper pyrithione (CPT) and zinc pyrithione (ZPT) as antifouling agents have mainly focused on marine organisms. Even though CPT and ZPT pose a risk of human exposure, their neurotoxic effects remain to be elucidated. Therefore, in this study, the cytotoxicity and neurotoxicity of CPT and ZPT were evaluated after the exposure of human SH-SY5Y/astrocytic co-cultured cells to them. The results showed that, in a co-culture model, CPT and ZPT induced cytotoxicity in a dose-dependent manner (~ 400 nM). Exposure to CPT and ZPT suppressed all parameters in the neurite outgrowth assays, including neurite length. In particular, exposure led to neurotoxicity at concentrations with low or no cytotoxicity (~ 200 nM). It also downregulated the expression of genes involved in neurodevelopment and maturation and upregulated astrocyte markers. Moreover, CPT and ZPT induced mitochondrial dysfunction and promoted the generation of reactive oxygen species. Notably, N-acetylcysteine treatment showed neuroprotective effects against CPT- and ZPT-mediated toxicity. We concluded that oxidative stress was the major mechanism underlying CPT- and ZPT-induced toxicity in the co-cultured cells.

A perspective on In vitro developmental neurotoxicity test assay results: An expert panel review

For decades, there has been increasing concern about the potential developmental neurotoxicity (DNT) associated with chemicals. Regulatory agencies have historically utilized standardized in vivo testing to evaluate DNT. Owing to considerations including higher-throughput screening for DNT, reduction in animal use, and potential cost efficiencies, the development of alternative new approach methods (NAMs) occurred; specifically, the advent of the DNT in vitro test battery (DNT IVB). SciPinion convened an expert panel to address specific questions related to the interpretation of in vitro DNT test data. The consensus of the expert panel was that the DNT IVB might be used during initial screening, but it is not presently a complete or surrogate approach to determine whether a chemical is a DNT in humans. By itself, the DNT IVB does not have the ability to capture nuances and complexity of the developing nervous system and associated outcomes including behavioral ontogeny, motor activity, sensory function, and learning/memory. Presently, such developmental landmarks cannot be adequately assessed in the DNT IVB or by other NAMs. The expert panel (all who serve as co-authors of this review) recommended that additional data generation and validation is required before the DNT IVB can be considered for application within global regulatory frameworks for decision-making.

SP600125 Enhances Temperature-Controlled Repeated Thermal Stimulation-Induced Neurite Outgrowth in PC12-P1F1 Cells

This study evaluated the mechanism of temperature-controlled repeated thermal stimulation (TRTS)-mediated neuronal differentiation. We assessed the effect of SP600125, a c-Jun N-terminal kinase (JNK) inhibitor, on neuronal differentiation of rat PC12-P1F1 cells, which can differentiate into neuron-like cells by exposure to TRTS or neurotrophic factors, including bone morphogenetic protein (BMP) 4. We evaluated neuritogenesis by incubating the cells under conditions of TRTS and/or SP600125. Cotreatment with SP600125 significantly enhanced TRTS-mediated neuritogenesis, whereas that with other selective mitogen-activated protein kinase (MAPK) inhibitors did not-e.g., extracellular signal-regulated kinase (ERK)1/2 inhibitor U0126, and p38 MAPK inhibitor SB203580. We tried to clarify the mechanism of SP600125 action by testing the effect of U0126 and the BMP receptor inhibitor LDN193189 on the SP600125-mediated enhancement of intracellular signaling. SP600125-enhanced TRTS-induced neuritogenesis was significantly inhibited by U0126 or LDN193189. Gene expression analysis revealed that TRTS significantly increased β3-Tubulin, MKK3, and Smad7 gene expressions. Additionally, Smad6 and Smad7 gene expressions were substantially attenuated through SP600125 co-treatment during TRTS. Therefore, SP600125 may partly enhance TRTS-induced neuritogenesis by attenuating the negative feedback loop of BMP signaling. Further investigation of the mechanisms underlying the effect of SP600125 during TRTS-mediated neuritogenesis may contribute to the future development of regenerative neuromedicine.

Native Planar Asymmetric Suspended Membrane for Single-Molecule Investigations: Plasma Membrane on a Chip

Cellular plasma membranes, in their role as gatekeepers to the external environment, host numerous protein assemblies and lipid domains that manage the movement of molecules into and out of cells, regulate electric potential, and direct cell signaling. The ability to investigate these roles on the bilayer at a single-molecule level in a controlled, in vitro environment while preserving lipid and protein architectures will provide deeper insights into how the plasma membrane works. A tunable silicon microarray platform that supports stable, planar, and asymmetric suspended lipid membranes (SLIM) using synthetic and native plasma membrane vesicles for single-molecule fluorescence investigations is developed. Essentially, a "plasma membrane-on-a-chip" system that preserves lipid asymmetry and protein orientation is created. By harnessing the combined potential of this platform with total internal reflection fluorescence (TIRF) microscopy, the authors are able to visualize protein complexes with single-molecule precision. This technology has widespread applications in biological processes that happen at the cellular membranes and will further the knowledge of lipid and protein assemblies.

Neural stem cell research in Africa: current realities and future prospects

Neural stem cells (NSCs) are immature progenitor cells that are found in developing and adult brains that have the potential of dividing actively and renewing themselves, with a complex form of gene expression. The generation of new brain cells in adult individuals was initially considered impossible, however, the landmark discovery of human neural stem cells in the hippocampus has been followed by further discoveries in other discreet regions of the brain. Investigation into the current state in Africa of the research and use of NSCs shows relatively limited activities on the continent. Information on the African application of NSCs for modelling disease mechanisms, drug discovery, and therapeutics is still limited. The International Brain Research Organization (IBRO)-African Regional Committee (ARC), with support from the Company of Biologists, and the Movement Disorder Society, sponsored the first African Basic School on NSC in Ibadan, Nigeria, with the vision of bringing together young neuroscientists and physicians across different fields in neuroscience to learn from leaders who have applied NSCs in stem cell research, the pathophysiology of neurodegenerative diseases, neuroanatomy, and neurotherapeutics. Twenty early-career researchers in academic institutions at junior and senior faculty cadres were selected from South Africa, Uganda and Nigeria. The students and organizer of the school, who wrote this review on the state of NSCs research in Africa, recommended the following: (1) other African countries can take a cue from South Africa and Nigeria in probing the phenomena of adult neurogenesis in unique animal species on the continent; (2) Africa should leverage the expertise and facilities of South African scientists and international collaborators in scaling up NSC research into these unique species and (3) Centers of Excellence should be established on the continent to serve as research hubs for training postgraduate students, and facilities for African scientists who trained overseas on NSCs.

Comparison of fractal and grid electrodes for studying the effects of spatial confinement on dissociated retinal neuronal and glial behavior

Understanding the impact of the geometry and material composition of electrodes on the survival and behavior of retinal cells is of importance for both fundamental cell studies and neuromodulation applications. We investigate how dissociated retinal cells from C57BL/6J mice interact with electrodes made of vertically-aligned carbon nanotubes grown on silicon dioxide substrates. We compare electrodes with different degrees of spatial confinement, specifically fractal and grid electrodes featuring connected and disconnected gaps between the electrodes, respectively. For both electrodes, we find that neuron processes predominantly accumulate on the electrode rather than the gap surfaces and that this behavior is strongest for the grid electrodes. However, the 'closed' character of the grid electrode gaps inhibits glia from covering the gap surfaces. This lack of glial coverage for the grids is expected to have long-term detrimental effects on neuronal survival and electrical activity. In contrast, the interconnected gaps within the fractal electrodes promote glial coverage. We describe the differing cell responses to the two electrodes and hypothesize that there is an optimal geometry that maximizes the positive response of both neurons and glia when interacting with electrodes.

High-Throughput Neurite Outgrowth Assay Using GFP-Labeled iPSC-Derived Neurons

The potential neurotoxicity from an increasing number of drugs and untested environmental chemicals creates a need to develop reliable and efficient in vitro methods for identifying chemicals that may adversely affect the nervous system. An important process in neurodevelopment is neurite outgrowth, which can be affected by developmental neurotoxicity. Currently, neurite outgrowth assays rely mainly on staining, which requires multiple sample processing steps, particularly washing steps, that may introduce variation and limit throughput. Here, we describe a neurite outgrowth assay that uses induced pluripotent stem cell (iPSC)-derived human cortical glutamatergic neurons and/or spinal motor neurons labeled with green fluorescent protein (GFP) to test compounds in a high-content and high-throughput format. This method enables live and time-lapse imaging of GFP-labeled neurons using an assay plate that is continuously imaged at multiple times after chemical treatment. In this article, we describe how to thaw frozen GFP-labeled neurons, culture them, treat them with a compound of interest, and analyze neurite outgrowth using a high-content imaging platform. In this assay, GFP-labeled iPSC-derived human neurons represent a promising tool for identifying and prioritizing compounds with potential developmental neurotoxicity for further hazard characterization. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA. Basic Protocol 1: Thawing and seeding of iPSC-derived neurons Basic Protocol 2: Compound plate preparation and treatment of neurons Basic Protocol 3: High-content imaging and analysis.

Developmental neurotoxicity induced by glutaraldehyde in neuron/astrocyte co-cultured cells and zebrafish

The genotoxicity, development toxicity, carcinogenicity, and acute or chronic toxic effects of glutaraldehyde (GA), particularly during occupational exposure through its use as a fixative, disinfectant, and preservative, are well-documented but its effects on neurotoxicity have not been investigated. We performed in vitro and in vivo studies to examine the developmental neurotoxicity (DNT) of GA. Neurite outgrowth was examined in an in vitro co-culture model consisting of SH-SY5Y human neuroblastoma cells and human astrocytes. Cell Counting Kit-8, lactate dehydrogenase assay, and high-content screening revealed that GA significantly inhibited neurite outgrowth at non-cytotoxic concentration. Further studies showed that GA upregulated the mRNA expression of the astrocyte markers GFAP and S100β and downregulated the expression of the neurodevelopmental genes Nestin, βIII-tubulin, GAP43, and MAP2. Furthermore, in vivo zebrafish embryo toxicity tests explored the effects of GA on neural morphogenesis. GA adversely affected the early development of zebrafish embryos, resulting in decreased survival, irregular hatching, and reduced heart rate in a time- and concentration-dependent manner. Furthermore, the width of the brain and spinal cord was reduced, and the myelination of Schwann cells and oligodendrocytes was decreased by GA in transgenic zebrafish lines. These data suggest that GAs have potential DNT in vitro and in vivo, highlighting the need for caution regarding the neurotoxicity of GA.

Monitoring Mixture Effects of Neurotoxicants in Surface Water and Wastewater Treatment Plant Effluents with Neurite Outgrowth Inhibition in SH-SY5Y Cells

Cell-based assays covering environmentally relevant modes of action are widely used for water quality monitoring. However, no high-throughput assays are available for testing developmental neurotoxicity of water samples. We implemented an assay that quantifies neurite outgrowth, which is one of the neurodevelopmental key events, and cell viability in human neuroblastoma SH-SY5Y cells using imaging techniques. We used this assay for testing of extracts of surface water collected in agricultural areas during rain events and effluents from wastewater treatment plants (WWTPs), where more than 200 chemicals had been quantified. Forty-one chemicals were tested individually that were suspected to contribute to the mixture effects among the detected chemicals in environmental samples. Sample sensitivity distributions indicated higher neurotoxicity for surface water samples than for effluents, and the endpoint of neurite outgrowth inhibition was six times more sensitive than cytotoxicity in the surface water samples and only three times more sensitive in the effluent samples. Eight environmental pollutants showed high specificity, and those ranged from pharmaceuticals (mebendazole and verapamil) to pesticides (methiocarb and clomazone), biocides (1,2-benzisothiazolin-3-one), and industrial chemicals (N-methyl-2-pyrrolidone, 7-diethylamino-4-methylcoumarin, and 2-(4-morpholinyl)benzothiazole). Although neurotoxic effects were newly detected for some of our test chemicals, less than 1% of the measured effects were explained by the detected and toxicologically characterized chemicals. The neurotoxicity assay was benchmarked against other bioassays: activations of the aryl hydrocarbon receptor and the peroxisome proliferator-activated receptor were similar in sensitivity, highly sensitive and did not differ much between the two water types, with surface water having slightly higher effects than the WWTP effluent. Oxidative stress response mirrored neurotoxicity quite well but was caused by different chemicals in the two water types. Overall, the new cell-based neurotoxicity assay is a valuable complement to the existing battery of effect-based monitoring tools.

In vitro neurotoxicity evaluation of biocidal disinfectants in a human neuron-astrocyte co-culture model

Biocidal disinfectants (BDs) that kill microorganisms or pathogens are widely used in hospitals and other healthcare fields. Recently, the use of BDs has rapidly increased as personal hygiene has become more apparent owing to the pandemic, namely the coronavirus outbreak. Despite frequent exposure to BDs, toxicity data of their potential neurotoxicity (NT) are lacking. In this study, a human-derived SH-SY5Y/astrocyte was used as a co-culture model to evaluate the chemical effects of BDs. Automated high-content screening was used to evaluate the potential NT of BDs through neurite growth analysis. A set of 12 BD substances classified from previous reports were tested. Our study confirms the potential NT of benzalkonium chloride (BKC) and provides the first evidence of the potential NT of poly(hexamethylenebicyanoguanide-hexamethylenediamine) hydrochloride (PHMB). BKC and PHMB showed significant NT at concentrations without cytotoxicity. This test system for analyzing the potential NT of BDs may be useful in early screening studies for NT prior to starting in vivo studies.

Study of lead-induced neurotoxicity in cholinergic cells differentiated from bone marrow-derived mesenchymal stem cells

The developing brain is susceptible to the neurotoxic effects of lead. Exposure to lead has main effects on the cholinergic system and causes reduction of cholinergic neuron function during brain development. Disruption of the cholinergic system by chemicals, which play important roles during brain development, causes of neurodevelopmental toxicity. Differentiation of stem cells to neural cells is recently considered a promising tool for neurodevelopmental toxicity studies. This study evaluated the toxicity of lead acetate exposure during the differentiation of bone marrow-derived mesenchyme stem cells (bone marrow stem cells, BMSCs) to cholinergic neurons. Following institutional animal care review board approval, BMSCs were obtained from adult rats. The differentiating protocol included two stages that were pre-induction with β-mercaptoethanol (BME) for 24 h and differentiation to cholinergic neurons with nerve growth factor (NGF) over 5 days. The cells were exposed to different lead acetate concentrations (0.1-100 μm) during three stages, including undifferentiated, pre-induction, and neuronal differentiation stages; cell viability was measured by MTT assay. Lead exposure (0.01-100 μg/ml) had no cytotoxic effect on BMSCs but could significantly reduce cell viability at 50 and 100 μm concentrations during pre-induction and neuronal differentiation stages. MAP2 and choline acetyltransferase (ChAT) protein expression were investigated by immunocytochemistry. Although cells treated with 100 μm lead concentration expressed MAP2 protein in the differentiation stages, they had no neuronal cell morphology. The ChAT expression was negative in cells treated with lead. The present study showed that differentiated neuronal BMSCs are sensitive to lead toxicity during differentiation, and it is suggested that these cells be used to study neurodevelopmental toxicity.

Current status and future directions for a neurotoxicity hazard assessment framework that integrates in silico approaches

Neurotoxicology is the study of adverse effects on the structure or function of the developing or mature adult nervous system following exposure to chemical, biological, or physical agents. The development of more informative alternative methods to assess developmental (DNT) and adult (NT) neurotoxicity induced by xenobiotics is critically needed. The use of such alternative methods including in silico approaches that predict DNT or NT from chemical structure (e.g., statistical-based and expert rule-based systems) is ideally based on a comprehensive understanding of the relevant biological mechanisms. This paper discusses known mechanisms alongside the current state of the art in DNT/NT testing. In silico approaches available today that support the assessment of neurotoxicity based on knowledge of chemical structure are reviewed, and a conceptual framework for the integration of in silico methods with experimental information is presented. Establishing this framework is essential for the development of protocols, namely standardized approaches, to ensure that assessments of NT and DNT based on chemical structures are generated in a transparent, consistent, and defendable manner.

Human Umbilical Cord Mesenchymal Stem Cell-Based in vitro Model for Neurotoxicity Testing

Neurotoxicity (NT) testing for regulatory purposes is based on in vivo animal testing. There is general consensus, however, about the need for the development of alternative methodologies to allow researchers to more rapidly and cost effectively screen large numbers of chemicals for their potential to cause NT, or to investigate their mode of action. In vitro assays are considered an important source of information for making regulatory decisions, and human cell-based systems are recommended as one of the most relevant models in toxicity testing, to reduce uncertainty in the extrapolation of results from animal-based models. Human neuronal models range from various neuroblastoma cell lines to stem cell-derived systems, including those derived from mesenchymal stem/stromal cells (hMSC). hMSCs exhibit numerous advantages, including the fact that they can be obtained in high yield from healthy human adult tissues, can be cultured with a minimal laboratory setup and without genetic manipulations, are able of continuous and repeated self-renewal, are nontumorigenic, and can form large populations of stably differentiated cells representative of different tissues, including neuronal cells. hMSCs derived from human umbilical cord (hUC) in particular possess several prominent advantages, including a painless, non-invasive, and ethically acceptable collection procedure, simple and convenient preparation, and high proliferation capacity. In addition, hMSCs can be efficiently differentiated into neuron-like cells (hNLCs), which can then be used for the assessment of neuronal toxicity of potential neurotoxic compounds in humans. Here, we describe a step-by-step procedure to use hMSCs from the umbilical cord for in vitro neurotoxicity testing. First, we describe how to isolate, amplify, and store hMSCs derived from the umbilical cord. We then outline the steps to transdifferentiate these cells into hNLCs, and then use the hNLCs for neurotoxicity testing by employing multiple common cytotoxicity assays after treatment with test compounds. The approach follows the most updated guidance on using human cell-based systems. These protocols will allow investigators to implement an alternative system for obtaining primary NLCs of human origin, and support advancement in neurotoxicity research. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Isolation and maintenance of human mesenchymal stem/stromal cells (hMSCs) obtained from the umbilical cord lining membrane Basic Protocol 2: Transdifferentiation of hMSCs into neuron-like cells (hNLCs) and basic neurotoxicity assessment.

Cryopreservation of Induced Pluripotent Stem Cell-Derived Dopaminergic Neurospheres for Clinical Application

BACKGROUND

Pluripotent stem cell (PSC)-derived dopaminergic (DA) neurons are an expected source of cell therapy for Parkinson's disease. The transplantation of cell aggregates or neurospheres, instead of a single cell suspension has several advantages, such as keeping the 3D structure of the donor cells and ease of handling. For this PSC-based therapy to become a widely available treatment, cryopreservation of the final product is critical in the manufacturing process. However, cryopreserving cell aggregates is more complicated than cryopreserving single cell suspensions. Previous studies showed poor survival of the DA neurons after the transplantation of cryopreserved fetal ventral-mesencephalic tissues.

OBJECTIVE

To achieve the cryopreservation of induced pluripotent stem cell (iPSC)-derived DA neurospheres toward clinical application.

METHODS

We cryopreserved iPSC-derived DA neurospheres in various clinically applicable cryopreservation media and freezing protocols and assessed viability and neurite extension. We evaluated the population and neuronal function of cryopreserved cells by the selected method in vitro. We also injected the cells into 6-hydroxydopamine (6-OHDA) lesioned rats, and assessed their survival, maturation and function in vivo.

RESULTS

The iPSC-derived DA neurospheres cryopreserved by Proton Freezer in the cryopreservation medium Bambanker hRM (BBK) showed favorable viability after thawing and had equivalent expression of DA-specific markers, dopamine secretion, and electrophysiological activity as fresh spheres. When transplanted into 6-OHDA-lesioned rats, the cryopreserved cells survived and differentiated into mature DA neurons, resulting in improved abnormal rotational behavior.

CONCLUSION

These results show that the combination of BBK and Proton Freezer is suitable for the cryopreservation of iPSC-derived DA neurospheres.

Integration of toxicodynamic and toxicokinetic new approach methods into a weight-of-evidence analysis for pesticide developmental neurotoxicity assessment: A case-study with DL- and L-glufosinate

DL-glufosinate ammonium (DL-GLF) is a registered herbicide for which a guideline Developmental Neurotoxicity (DNT) study has been conducted. Offspring effects included altered brain morphometrics, decreased body weight, and increased motor activity. Guideline DNT studies are not available for its enriched isomers L-GLF acid and L-GLF ammonium; conducting one would be time consuming, resource-intensive, and possibly redundant given the existing DL-GLF DNT. To support deciding whether to request a guideline DNT study for the L-GLF isomers, DL-GLF and the L-GLF isomers were screened using in vitro assays for network formation and neurite outgrowth. DL-GLF and L-GLF isomers were without effects in both assays. DL-GLF and L-GLF (1-100 μM) isomers increased mean firing rate of mature networks to 120-140% of baseline. In vitro toxicokinetic assessments were used to derive administered equivalent doses (AEDs) for the in vitro testing concentrations. The AED for L-GLF was ∼3X higher than the NOAEL from the DL-GLF DNT indicating that the available guideline study would be protective of potential DNT due to L-GLF exposure. Based in part on the results of these in vitro studies, EPA is not requiring L-GLF isomer guideline DNT studies, thereby providing a case study for a useful application of DNT screening assays.

Inhibition of neurite outgrowth and enhanced effects compared to baseline toxicity in SH-SY5Y cells

Early life exposure to environmental chemicals can cause developmental neurotoxicity (DNT). The impairment of key neurodevelopmental processes such as neurite outgrowth inhibition can be used as endpoints for screening of DNT effects. We quantified neurite-specific effects using the ratio of effect concentrations for cytotoxicity and neurite outgrowth inhibition (SR_cytotoxicity). Baseline cytotoxicity, the minimal toxicity of any chemical, was used to quantify enhanced cytotoxicity (toxic ratio, TR) and neuronal-specific toxicity (SR_baseline) by comparing baseline cytotoxicity with the effects on cell viability and neurite outgrowth, respectively. The effects on cell viability and neurite length were measured based on image analysis in human neuroblastoma SH-SY5Y cells. Baseline cytotoxicity was predicted from hydrophobicity descriptors using a previously published model for SH-SY5Y cells. Enhanced cytotoxicity and neuronal-specific toxicity were more often observed for hydrophilic chemicals, which indicates that they are more likely to act through specific modes of action (MOA) on cell viability and neurite outgrowth. Hydrophobic chemicals showed a tendency to act through baseline toxicity without showing specific or enhanced toxicity, but were highly potent considering their low effect concentrations for both cytotoxicity and neurite outgrowth inhibition. The endpoint-specific controls (narciclasine, colchicine, cycloheximide, and rotenone), two carbamates (3-hydroxycarbofuran and carbaryl), and two redox cyclers (diquat and paraquat) showed distinct neurite-specific effects (SR_cytotoxicity > 4). By comparing neurite-specific effects with enhanced cytotoxicity, one can explain whether the observed effects involve specific inhibition of neurite outgrowth, other specific MOAs, or merely baseline toxicity arising from hydrophobicity.

Neuron Compatibility and Antioxidant Activity of Barium Titanate and Lithium Niobate Nanoparticles

The biocompatibility and the antioxidant activity of barium titanate (BaTiO₃) and lithium niobate (LiNbO₃) were investigated on a neuronal cell line, the PC12, to explore the possibility of using piezoelectric nanoparticles in the treatment of inner ear diseases, avoiding damage to neurons, the most delicate and sensitive human cells. The cytocompatibility of the compounds was verified by analysing cell viability, cell morphology, apoptotic markers, oxidative stress and neurite outgrowth. The results showed that BaTiO₃ and LiNbO₃ nanoparticles do not affect the viability, morphological features, cytochrome c distribution and production of reactive oxygen species (ROS) by PC12 cells, and stimulate neurite branching. These data suggest the biocompatibility of BaTiO₃ and LiNbO₃ nanoparticles, and that they could be suitable candidates to improve the efficiency of new implantable hearing devices without damaging the neuronal cells.

The impact of SBF2 on taxane-induced peripheral neuropathy

Taxane-induced peripheral neuropathy (TIPN) is a devastating survivorship issue for many cancer patients. In addition to its impact on quality of life, this toxicity may lead to dose reductions or treatment discontinuation, adversely impacting survival outcomes and leading to health disparities in African Americans (AA). Our lab has previously identified deleterious mutations in SET-Binding Factor 2 (SBF2) that significantly associated with severe TIPN in AA patients. Here, we demonstrate the impact of SBF2 on taxane-induced neuronal damage using an ex vivo model of SBF2 knockdown of induced pluripotent stem cell-derived sensory neurons. Knockdown of SBF2 exacerbated paclitaxel changes to cell viability and neurite outgrowth while attenuating paclitaxel-induced sodium current inhibition. Our studies identified paclitaxel-induced expression changes specific to mature sensory neurons and revealed candidate genes involved in the exacerbation of paclitaxel-induced phenotypes accompanying SBF2 knockdown. Overall, these findings provide ex vivo support for the impact of SBF2 on the development of TIPN and shed light on the potential pathways involved.

Reliable identification and quantification of neural cells in microscopic images of neurospheres

Neurosphere cultures consisting of primary human neural stem/progenitor cells (hNPC) are used for studying the effects of substances on early neurodevelopmental processes in vitro. Differentiating hNPCs migrate and differentiate into radial glia, neurons, astrocytes, and oligodendrocytes upon plating on a suitable extracellular matrix and thus model processes of early neural development. In order to characterize alterations in hNPC development, it is thus an essential task to reliably identify the cell type of each migrated cell in the migration area of a neurosphere. To this end, we introduce and validate a deep learning approach for identifying and quantifying cell types in microscopic images of differentiated hNPC. As we demonstrate, our approach performs with high accuracy and is robust against typical potential confounders. We demonstrate that our deep learning approach reproduces the dose responses of well-established developmental neurotoxic compounds and controls, indicating its potential in medium or high throughput in vitro screening studies. Hence, our approach can be used for studying compound effects on neural differentiation processes in an automated and unbiased process.

Knock-Down of Heterogeneous Nuclear Ribonucleoprotein A1 Results in Neurite Damage, Altered Stress Granule Biology, and Cellular Toxicity in Differentiated Neuronal Cells

Heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) is an RNA binding protein (RBP) that is localized within neurons and plays crucial roles in RNA metabolism. Its importance in neuronal functioning is underscored from the study of its pathogenic features in many neurodegenerative diseases where neuronal hnRNP A1 is mislocalized from the nucleus to the cytoplasm resulting in loss of hnRNP A1 function. Here, we model hnRNP A1 loss-of-function by siRNA-mediated knock-down in differentiated Neuro-2a cells. Through RNA sequencing (RNA-seq) followed by gene ontology (GO) analyses, we show that hnRNP A1 is involved in important biological processes, including RNA metabolism, neuronal function, neuronal morphology, neuronal viability, and stress granule (SG) formation. We further confirmed several of these roles by showing that hnRNP A1 knock-down results in a reduction of neurite outgrowth, increase in cell cytotoxicity and changes in SG formation. In summary, these findings indicate that hnRNP A1 loss-of-function contributes to neuronal dysfunction and cell death and implicates hnRNP A1 dysfunction in the pathogenesis of neurodegenerative diseases.

Culture of Rat Primary Cortical Cells for Microelectrode Array (MEA) Recordings to Screen for Acute and Developmental Neurotoxicity

Neurotoxicity testing of chemicals, drug candidates, and environmental pollutants still relies on extensive in vivo studies that are very costly, time-consuming, and ethically debated due to the large number of animals typically used. Currently, rat primary cortical cultures are widely used for in vitro neurotoxicity studies, as they closely resemble the in vitro brain with respect to the diversity of cell types, their physiological functions, and the pathological processes that they undergo. Common in vitro assays for neurotoxicity screening often focus on very target-specific endpoints such as morphological, biochemical, or electrophysiological changes, and such narrow focus can hamper translation and interpretation. Microelectrode array (MEA) recordings provide a non-invasive platform for extracellular recording of electrical activity of cultured neuronal cells, thereby enabling the evaluation of changes in neuronal (network) function as a sensitive and integrated endpoint for neurotoxicity screening. Here, we describe an in vitro approach for assessing changes in neuronal network function as a measure for neurotoxicity, using rat primary cortical cultures grown on MEAs. We provide a detailed protocol for the culture of rat primary cortical cells, and describe several experimental procedures to address acute, subchronic, and chronic exposure scenarios. We additionally describe the steps for processing and analyzing MEA and cell viability data. © 2021 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Isolation and culture of rat primary cortical cells on 48-well MEA plates Support Protocol 1: Pretreatment and washing of 48-well MEA plates before first use or for re-use Support Protocol 2: Coating of 48-well MEA plates with 0.1% PEI solution Basic Protocol 2: MEA measurements during acute exposure Alternate Protocol 1: MEA measurements during subchronic exposure Alternate Protocol 2: MEA measurements during chronic exposure Support Protocol 3: Determination of cell viability after MEA experiments Basic Protocol 3: MEA data processing Basic Protocol 4: Analyzing MEA experiments after acute and subchronic exposure Alternate Protocol 3: Analyzing MEA experiments after chronic exposure.

A Propagated Skeleton Approach to High Throughput Screening of Neurite Outgrowth for In Vitro Parkinson's Disease Modelling

Neuronal models of neurodegenerative diseases such as Parkinson's Disease (PD) are extensively studied in pathological and therapeutical research with neurite outgrowth being a core feature. Screening of neurite outgrowth enables characterization of various stimuli and therapeutic effects after lesion. In this study, we describe an autonomous computational assay for a high throughput skeletonization approach allowing for quantification of neurite outgrowth in large data sets from fluorescence microscopic imaging. Development and validation of the assay was conducted with differentiated SH-SY5Y cells and primary mesencephalic dopaminergic neurons (MDN) treated with the neurotoxic lesioning compound Rotenone. Results of manual annotation using NeuronJ and automated data were shown to correlate strongly (R2-value 0.9077 for SH-SY5Y cells and R2-value 0.9297 for MDN). Pooled linear regressions of results from SH-SY5Y cell image data could be integrated into an equation formula (y=0.5410·x+1792; y=0.8789·x+0.09191 for normalized results) with y depicting automated and x depicting manual data. This automated neurite length algorithm constitutes a valuable tool for modelling of neurite outgrowth that can be easily applied to evaluate therapeutic compounds with high throughput approaches.

Evaluation of chemical compounds that inhibit neurite outgrowth using GFP-labeled iPSC-derived human neurons

Due to the increasing number of drugs and untested environmental compounds introduced into commercial use, there is recognition for a need to develop reliable and efficient screening methods to identify compounds that may adversely impact the nervous system. One process that has been implicated in neurodevelopment is neurite outgrowth; the disruption of which can result in adverse outcomes that persist later in life. Here, we developed a green fluorescent protein (GFP) labeled neurite outgrowth assay in a high-content, high-throughput format using induced pluripotent stem cell (iPSC) derived human spinal motor neurons and cortical glutamatergic neurons. The assay was optimized for use in a 1536-well plate format. Then, we used this assay to screen a set of 84 unique compounds that have previously been screened in other neurite outgrowth assays. This library consists of known developmental neurotoxicants, environmental compounds with unknown toxicity, and negative controls. Neurons were cultured for 40 h and then treated with compounds at 11 concentrations ranging from 1.56 nM to 92 μM for 24 and 48 h. Effects of compounds on neurite outgrowth were evaluated by quantifying total neurite length, number of segments, and maximum neurite length per cell. Among the 84 tested compounds, neurite outgrowth in cortical neurons and motor neurons were selectively inhibited by 36 and 31 compounds, respectively. Colchicine, rotenone, and methyl mercuric (II) chloride inhibited neurite outgrowth in both cortical and motor neurons. It is interesting to note that some compounds like parathion and bisphenol AF had inhibitory effects on neurite outgrowth specifically in the cortical neurons, while other compounds, such as 2,2',4,4'-tetrabromodiphenyl ether and caffeine, inhibited neurite outgrowth in motor neurons. The data gathered from these studies show that GFP-labeled iPSC-derived human neurons are a promising tool for identifying and prioritizing compounds with developmental neurotoxicity potential for further hazard characterization.

Lipopolysaccharide Pre-conditioning Attenuates Pro-inflammatory Responses and Promotes Cytoprotective Effect in Differentiated PC12 Cell Lines via Pre-activation of Toll-Like Receptor-4 Signaling Pathway Leading to the Inhibition of Caspase-3/Nuclear Factor-κappa B Pathway

Lipopolysacharide (LPS) pre-conditioning (PC), has been shown to exert protective effects against cytotoxic effects. Therefore, we hypothesized, the tolerance produced by LPS PC will be resulted by the alterations and modifications in gene and protein expression. With reference to the results of MTT assays, AO/PI staining, and Annexin V-FITC analyses of LPS concentration (0.7815-50 μg/mL) and time-dependent (12-72 h) experiments, the pre-exposure to 3 μg/mL LPS for 12 h protected the differentiated PC12 cells against 0.75 mg/mL LPS apoptotic concentration. LPS-treated cells secreted more inflammatory cytokines like IL-1α, IL-1β, IL-2, IL-3, IL-4, IL-6, IL-17, IFN-γ, and TNF-α than LPS-PC cells. The production of inflammatory mediators ROS and NO was also higher in the LPS-induced cells compared to LPS-PC cells. Conversely, anti-inflammatory cytokines (like IL-10, IL-13, CNTF, and IL-1Ra) were upregulated in the LPS-PC cells but not in the LPS-induced cells. Meanwhile, the LPS initiated caspase-8 which in turn activates effector caspase 3/7. When the activities of caspases in the LPS-induced cells were inhibited using z-VADfmk and z-DEVDfmk, the expressions of c-MYC and Hsp70 were increased, but p53 was reduced. The potential molecules associated with protective and destructive effect was measured by RT² Profiler PCR array to elucidate the signaling pathways and suggested inhibition NF-κB/caspase-3 signaling pathway regulates the cytoprotective genes and proto-oncogenes. In conclusion, this study provides a basis for future research to better understand the molecular mechanism underlying LPS pre-conditioning /TLR4 pre-activation and its functional role in offering cytoprotective response in neuronal environment.

Prostaglandin E2 Increases Neurite Length and the Formation of Axonal Loops, and Regulates Cone Turning in Differentiating NE4C Cells Via PKA

Prostaglandin E2 (PGE2) is a membrane-derived lipid signaling molecule important in neuronal development. Abnormal levels of PGE2, due to environmental insults prenatal development, have been linked to brain pathologies. We have previously shown that the addition of PGE2 to neuroectodermal (NE4C) stem cells affects early stages of neuronal differentiation (day 0-8) including increased stem cell motility, accelerated formation of neurospheres, and elevated calcium levels in growth cones. In this study, we further examine whether PGE2 can influence actin-dependent neuronal morphology in later stages (day 8-12) of NE4C cell differentiation. We show that exposure to PGE2 from the initiation of differentiation increased neurite length and the proportion of neurites that formed axonal loops. We also observed changes in the proportion of turning growth cones as the differentiation progressed, with a reduced likelihood of observing turning (or asymmetrical) growth cones on day 8 and increased odds on days 10 and 12. Moreover, we showed for the first time that the observed changes in cytoskeletal morphology were PGE2/PKA dependent. Interestingly, we also found that PGE2 decreased the total protein levels of the actin-bound form of spinophilin and increased levels of unbound PKA-phosphorylated ser94-spinophilin. Hence, we propose that exposure to PGE2 can destabilize the actin cytoskeleton at various stages of neuronal differentiation due to dissociation of ser94-spinophilin causing changes in neuronal morphology.

Human Induced Pluripotent Stem Cell Derived Sensory Neurons are Sensitive to the Neurotoxic Effects of Paclitaxel

Chemotherapy‐induced peripheral neuropathy (CIPN) is a dose‐limiting adverse event associated with treatment with paclitaxel and other chemotherapeutic agents. The prevention and treatment of CIPN are limited by a lack of understanding of the molecular mechanisms underlying this toxicity. In the current study, a human induced pluripotent stem cell–derived sensory neuron (iPSC‐SN) model was developed for the study of chemotherapy‐induced neurotoxicity. The iPSC‐SNs express proteins characteristic of nociceptor, mechanoreceptor, and proprioceptor sensory neurons and show Ca²⁺ influx in response to capsaicin, α,β‐meATP, and glutamate. The iPSC‐SNs are relatively resistant to the cytotoxic effects of paclitaxel, with half‐maximal inhibitory concentration (IC₅₀) values of 38.1 µM (95% confidence interval (CI) 22.9–70.9 µM) for 48‐hour exposure and 9.3 µM (95% CI 5.7–16.5 µM) for 72‐hour treatment. Paclitaxel causes dose‐dependent and time‐dependent changes in neurite network complexity detected by βIII‐tubulin staining and high content imaging. The IC₅₀ for paclitaxel reduction of neurite area was 1.4 µM (95% CI 0.3–16.9 µM) for 48‐hour exposure and 0.6 µM (95% CI 0.09–9.9 µM) for 72‐hour exposure. Decreased mitochondrial membrane potential, slower movement of mitochondria down the neurites, and changes in glutamate‐induced neuronal excitability were also observed with paclitaxel exposure. The iPSC‐SNs were also sensitive to docetaxel, vincristine, and bortezomib. Collectively, these data support the use of iPSC‐SNs for detailed mechanistic investigations of genes and pathways implicated in chemotherapy‐induced neurotoxicity and the identification of novel therapeutic approaches for its prevention and treatment.

A human relevant mixture of persistent organic pollutants (POPs) and perfluorooctane sulfonic acid (PFOS) enhance nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells

Disruption of neurite outgrowth is a marker for neurotoxicity. Persistent organic pollutants (POPs) are potential developmental neurotoxicants. We investigated their effect on neurite outgrowth in PC12 rat pheochromocytoma cells, in absence or presence of nerve growth factor (NGF), an inducer of neuronal differentiation. Cells were exposed for 72 h to a defined mixture of POPs with chemical composition and concentrations based on blood levels in the Scandinavian population. We also evaluated perfluorooctane sulfonic acid (PFOS) alone, the most abundant compound in the POP mixture. Only higher concentrations of POP mixture reduced tetrazolium salt (MTT) conversion. High-content analysis showed a decrease in cell number, but no changes for nuclear and mitochondrial cellular health parameters. Robust glutathione levels were observed in NGF-differentiated cells. Live imaging, using the IncuCyte ZOOM platform indicated ongoing cell proliferation over time, but slower in presence of NGF. The pollutants did not inhibit neuritogenesis, but rather increased NGF-induced neurite length. PFOS induced neurite outgrowth to about 50 % of the level seen with the POP mixture. Neither the POP mixture nor PFOS affected neurite length in the absence of NGF. Our observations indicate that realistic complex mixtures of environmental pollutants can affect neuronal connectivity via NGF-induced neurite outgrowth.

Characterization of PC12 Cell Subclones with Different Sensitivities to Programmed Thermal Stimulation

Neuritogenesis is the process underling nervous system regeneration; however, optimal extracellular signals that can promote neuronal regenerative activities require further investigation. Previously, we developed a novel method for inducing neuronal differentiation in rat PC12 cells using temperature-controlled repeated thermal stimulation (TRTS) with a heating plate. Based on neurogenic sensitivity to TRTS, PC12 cells were classified as either hyper- or hyposensitive. In this study, we aimed to investigate the mechanism of hyposensitivity by establishing two PC12-derived subclones according to TRTS sensitivity during differentiation: PC12-P1F1, a hypersensitive subclone, and PC12-P1D10, a hyposensitive subclone. To characterize these subclones, cell size and neuritogenesis were evaluated in subclones treated with nerve growth factor (NGF), bone morphogenetic protein (BMP), or various TRTS. No significant differences in cell size were observed among the parental cells and subclones. BMP4- or TRTS-induced neuritogenesis was increased in PC12-P1F1 cells compared to that in the parental cells, while no neuritogenesis was observed in PC12-P1D10 cells. In contrast, NGF-induced neuritogenesis was observed in all three cell lines. Furthermore, a BMP inhibitor, LDN-193189, considerably inhibited TRTS-induced neuritogenesis. These results suggest that the BMP pathway might be required for TRTS-induced neuritogenesis, demonstrating the useful aspects of these novel subclones for TRTS research.

A locust embryo as predictive developmental neurotoxicity testing system for pioneer axon pathway formation

Exposure to environmental chemicals during in utero and early postnatal development can cause a wide range of neurological defects. Since current guidelines for identifying developmental neurotoxic chemicals depend on the use of large numbers of rodents in animal experiments, it has been proposed to design rapid and cost-efficient in vitro screening test batteries that are mainly based on mixed neuronal/glial cultures. However, cell culture tests do not assay correct wiring of neuronal circuits. The establishment of precise anatomical connectivity is a key event in the development of a functional brain. Here, we expose intact embryos of the locust (Locusta migratoria) in serum-free culture to test chemicals and visualize correct navigation of identified pioneer axons by fluorescence microscopy. We define separate toxicological endpoints for axonal elongation and navigation along a stereotyped pathway. To distinguish developmental neurotoxicity (DNT) from general toxicity, we quantify defects in axonal elongation and navigation in concentration-response curves and compare it to the biochemically determined viability of the embryo. The investigation of a panel of recognized DNT-positive and -negative test compounds supports a rather high predictability of this invertebrate embryo assay. Similar to the semaphorin-mediated guidance of neurites in mammalian cortex, correct axonal navigation of the locust pioneer axons relies on steering cues from members of this family of cell recognition molecules. Due to the evolutionary conserved mechanisms of neurite guidance, we suggest that our pioneer axon paradigm might provide mechanistically relevant information on the DNT potential of chemical agents on the processes of axon elongation, navigation, and fasciculation.

Development of an N-Cadherin Biofunctionalized Hydrogel to Support the Formation of Synaptically Connected Neural Networks

In vitro models of the human central nervous system (CNS), particularly those derived from induced pluripotent stem cells (iPSCs), are becoming increasingly recognized as useful complements to animal models for studying neurological diseases and developing therapeutic strategies. However, many current three-dimensional (3D) CNS models suffer from deficits that limit their research utility. In this work, we focused on improving the interactions between the extracellular matrix (ECM) and iPSC-derived neurons to support model development. The most common ECMs used to fabricate 3D CNS models often lack the necessary bioinstructive cues to drive iPSC-derived neurons to a mature and synaptically connected state. These ECMs are also typically difficult to pattern into complex structures due to their mechanical properties. To address these issues, we functionalized gelatin methacrylate (GelMA) with an N-cadherin (Cad) extracellular peptide epitope to create a biomaterial termed GelMA-Cad. After photopolymerization, GelMA-Cad forms soft hydrogels (on the order of 2 kPa) that can maintain patterned architectures. The N-cadherin functionality promotes survival and maturation of single-cell suspensions of iPSC-derived glutamatergic neurons into synaptically connected networks as determined by viral tracing and electrophysiology. Immunostaining reveals a pronounced increase in presynaptic and postsynaptic marker expression in GelMA-Cad relative to Matrigel, as well as extensive colocalization of these markers, thus highlighting the biological activity of the N-cadherin peptide. Overall, given its ability to enhance iPSC-derived neuron maturity and connectivity, GelMA-Cad should be broadly useful for in vitro studies of neural circuitry in health and disease.

N-alkylisatin-based microtubule destabilizers bind to the colchicine site on tubulin and retain efficacy in drug resistant acute lymphoblastic leukemia cell lines with less in vitro neurotoxicity

BACKGROUND

Drug resistance and chemotherapy-induced peripheral neuropathy continue to be significant problems in the successful treatment of acute lymphoblastic leukemia (ALL). 5,7-Dibromo-N-alkylisatins, a class of potent microtubule destabilizers, are a promising alternative to traditionally used antimitotics with previous demonstrated efficacy against solid tumours in vivo and ability to overcome P-glycoprotein (P-gp) mediated drug resistance in lymphoma and sarcoma cell lines in vitro. In this study, three di-brominated N-alkylisatins were assessed for their ability to retain potency in vincristine (VCR) and 2-methoxyestradiol (2ME2) resistant ALL cell lines. For the first time, in vitro neurotoxicity was also investigated in order to establish their suitability as candidate drugs for future use in ALL treatment.

METHODS

Vincristine resistant (CEM-VCR R) and 2-methoxyestradiol resistant (CEM/2ME2-28.8R) ALL cell lines were used to investigate the ability of N-alkylisatins to overcome chemoresistance. Interaction of N-alkylisatins with tubulin at the the colchicine-binding site was studied by competitive assay using the fluorescent colchicine analogue MTC. Human neuroblastoma SH-SY5Y cells differentiated into a morphological and functional dopaminergic-like neurotransmitter phenotype were used for neurotoxicity and neurofunctional assays. Two-way ANOVA followed by a Tukey's post hoc test or a two-tailed paired t test was used to determine statistical significance.

RESULTS

CEM-VCR R and CEM/2ME2-28.8R cells displayed resistance indices of > 100 to VCR and 2-ME2, respectively. CEM-VCR R cells additionally displayed a multi-drug resistant phenotype with significant cross resistance to vinblastine, 2ME2, colchicine and paclitaxel consistent with P-gp overexpression. Despite differences in resistance mechanisms observed between the two cell lines, the N-alkylisatins displayed bioequivalent dose-dependent cytotoxicity to that of the parental control cell line. The N-alkylisatins proved to be significantly less neurotoxic towards differentiated SH-SY5Y cells than VCR and vinblastine, evidenced by increased neurite length and number of neurite branch points. Neuronal cells treated with 5,7-dibromo-N-(p-hydroxymethylbenzyl)isatin showed significantly higher voltage-gated sodium channel function than those treated with Vinca alkaloids, strongly supportive of continued action potential firing.

CONCLUSIONS

The N-alkylisatins are able to retain cytotoxicity towards ALL cell lines with functionally distinct drug resistance mechanisms and show potential for reduced neurotoxicity. As such they pose as promising candidates for future implementation into anticancer regimes for ALL. Further in vivo studies are therefore warranted.

Human Induced Pluripotent Stem Cell-Derived 3D-Neurospheres are Suitable for Neurotoxicity Screening

We present a hiPSC-based 3D in vitro system suitable to test neurotoxicity (NT). Human iPSCs-derived 3D neurospheres grown in 96-well plate format were characterized timewise for 6-weeks. Changes in complexity and homogeneity were followed by immunocytochemistry and transmission electron microscopy. Transcriptional activity of major developmental, structural, and cell-type-specific markers was investigated at weekly intervals to present the differentiation of neurons, astrocytes, and oligodendrocytes. Neurospheres were exposed to different well-known toxicants with or without neurotoxic effect (e.g., paraquat, acrylamide, or ibuprofen) and examined at various stages of the differentiation with an ATP-based cell viability assay optimized for 3D-tissues. Concentration responses were investigated after acute (72 h) exposure. Moreover, the compound-specific effect of rotenone was investigated by a panel of ER-stress assay, TUNEL assay, immunocytochemistry, electron microscopy, and in 3D-spheroid based neurite outgrowth assay. The acute exposure to different classes of toxicants revealed distinct susceptibility profiles in a differentiation stage-dependent manner, indicating that hiPSC-based 3D in vitro neurosphere models could be used effectively to evaluate NT, and can be developed further to detect developmental neurotoxicity (DNT) and thus replace or complement the use of animal models in various basic research and pharmaceutical applications.

Human epicardium-derived cells reinforce cardiac sympathetic innervation

RATIONALE

After cardiac damage, excessive neurite outgrowth (sympathetic hyperinnervation) can occur, which is related to ventricular arrhythmias/sudden cardiac death. Post-damage reactivation of epicardium causes epicardium-derived cells (EPDCs) to acquire a mesenchymal character, contributing to cardiac regeneration. Whether EPDCs also contribute to cardiac re/hyperinnervation, is unknown.

AIM

To investigate whether mesenchymal EPDCs influence cardiac sympathetic innervation.

METHODS AND RESULTS

Sympathetic ganglia were co-cultured with mesenchymal EPDCs and/or myocardium, and neurite outgrowth and sprouting density were assessed. Results showed a significant increase in neurite density and directional (i.e. towards myocardium) outgrowth when ganglia were co-cultured with a combination of EPDCs and myocardium, as compared to cultures with EPDCs or myocardium alone. In absence of myocardium, this outgrowth was not directional. Neurite differentiation of PC12 cells in conditioned medium confirmed these results via a paracrine effect, in accordance with expression of neurotrophic factors in myocardial explants co-cultured with EPDCs. Of interest, EPDCs increased the expression of nerve growth factor (NGF) in cultured, but not in fresh myocardium, possibly due to an "ischemic state" of cultured myocardium, supported by TUNEL and Hif1α expression. Cardiac tissues after myocardial infarction showed robust NGF expression in the infarcted, but not remote area.

CONCLUSION

Neurite outgrowth and density increases significantly in the presence of EPDCs by a paracrine effect, indicating a new role for EPDCs in the occurrence of sympathetic re/hyperinnervation after cardiac damage.

Potential Effects of Indole-3-Lactic Acid, a Metabolite of Human Bifidobacteria, on NGF-induced Neurite Outgrowth in PC12 Cells

Gut microbiota-derived tryptophan metabolites such as indole derivatives are an integral part of host metabolome that could mediate gut-brain communication and contribute to host homeostasis. We previously reported that infant-type Human-Residential Bifidobacteria (HRB) produced higher levels of indole-3-lactic acid (ILA), suggesting the former might play a specific role in microbiota-host crosstalk by producing ILA in human infants. Nonetheless, the biological meaning of bifidobacteria-derived ILA in infant health development remains obscure. Here, we sought to explore the potential role of ILA in neuronal differentiation. We examined the neurite outgrowth and acetylcholinesterase (AchE) activity of PC12 cells following exposure to ILA and NGF induction. We found that ILA substantially enhanced NGF-induced neurite outgrowth of PC12 cells in a dose-dependent manner, and had the most prominent effect at 100 nM. Significant increases in the expression of TrkA receptor, ERK1/2 and CREB were observed in ILA-treated PC12 cells, suggesting ILA potentiated NGF-induced neurite outgrowth through the Ras/ERK pathway. Additionally, ILA was found to act as the aryl hydrocarbon receptor (AhR) agonist and evoked NGF-induced neurite outgrowth in an AhR-mediated manner. These new findings provide clues into the potential involvement of ILA as the mediator in bifidobacterial host-microbiota crosstalk and neuronal developmental processes.

Protective effects of butein on corticosterone-induced cytotoxicity in Neuro2A cells

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Butein protected Neuro2A cells from CORT-induced apoptosis via mitochondrial dysfunction, caspase-3 activation, and DNA damage.

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CORT suppressed retinoic acid-induced neurite outgrowth in Neuro2A cells.

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Butein inhibited CORT-suppressed neurite outgrowth in Neuro2A cells.

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High doses of butein induced cytotoxicity in Neuro2A cells.

A functional understanding of the relationship between glucocorticoids and neuronal apoptosis induced by the production of reactive oxygen species (ROS) may lead to a novel strategy for the treatment or prevention of depression. Previous reports suggest that butein, a type of flavonoids, may be a potent candidate against depression-related neuronal cell apoptosis caused by oxidative stress; however, the protective effects of butein on damaged corticosterone (CORT)-treated neuronal cells has not been elucidated. In the present study, we examined the protective effect of butein on CORT-induced cytotoxicity and neurite growth during cell differentiation of mouse neuroblastoma Neuro2A (N2A) cells. Moreover, the effect on cultured cells by high concentrations of butein was confirmed. Our results demonstrate that CORT treatment significantly decreases cell viability and induces cell death. CORT was suggested to induce apoptosis via mitochondrial dysfunction and caspase-3 activation; this apoptosis may be attributed to DNA damage by ROS generation, found in this study to be significantly inhibited by pretreatment with butein. We found that CORT produced significant growth suppression of retinoic acid-induced neurite outgrowth in N2A cells; however, butein significantly increased neurite length and induced dose-dependent apoptotic cytotoxicity in N2A cells. This study suggests that low concentration of butein can prevent CORT-induced cytotoxicity in N2A cells, and provides preliminary results supporting some of the beneficial roles of butein in neuroprotection.

Toxicologic evidence of developmental neurotoxicity of Type II pyrethroids cyfluthrin and alpha-cypermethrin in SH-SY5Y cells

We attempted to identify cellular mechanisms as an approach to screen chemicals for the potential to cause developmental neurotoxicity. We examine, in SH-SY5Y cells, whether apoptosis and oxidative stress via reactive oxygen species (ROS) generation, caspase 3/7 activation, gene expression (Bax, Bcl-2, Casp-3, BNIP3, p53 and Nrf2) alterations and necrosis by release of cytosolic adenylate kinase (AK), underlie direct effects of the pyrethroids cyfluthrin and alpha-cypermethrin. We also determined transcriptional alterations of genes (TUBB3, NEFL, NEFH, GAP43, CAMK2A, CAMK2B, WNT3A, WNT5A, WNT7A, SYN1 and PIK3C3) linked to neuronal development and maturation. Our results indicate that cyfluthrin and alpha-cypermethrin have the ability to elicit concentration-dependent increases in AK release, cellular ROS production, caspase 3/7 activity and gene expression of apoptosis and oxidative stress mediators. Both pyrethroids caused changes in mRNA expression of key target genes linked to neuronal development. These changes might reflect in a subsequent neuronal dysfunction. Our study shows that SH-SY5Y cell line is a valuable in vitro model for predicting development neurotoxicity. Our research provides evidence that cyfluthrin and alpha-cypermethrin have the potential to act as developmental neurotoxic compounds. Additional information is needed to improve the utility of this in vitro model and/or better understand its predictive capability.

High-content imaging of 3D-cultured neural stem cells on a 384-pillar plate for the assessment of cytotoxicity

The assessment of neurotoxicity has been performed traditionally with animals. However, in vivo studies are highly expensive and time-consuming, and often do not correlate to human outcomes. Thus, there is a need for cost-effective, high-throughput, highly predictive alternative in vitro test methods based on early markers of mechanisms of toxicity. High-content imaging (HCI) assays performed on three-dimensionally (3D) cultured cells could provide better understanding of the mechanism of toxicity needed to predict neurotoxicity in humans. However, current 3D cell culture systems lack the throughput required for screening neurotoxicity against a large number of chemicals. Therefore, we have developed miniature 3D neural stem cell (NSC) culture on a unique 384-pillar plate, which is complementary to conventional 384-well plates. Mitochondrial membrane impairment, intracellular glutathione level, cell membrane integrity, DNA damage, and apoptosis have been tested against 3D-cultured ReNcell VM on the 384-pillar plate with four model compounds rotenone, 4-aminopyridine, digoxin, and topotecan. The HCI assays performed in 3D-cultured ReNcell VM on the 384-pillar plates were highly robust and reproducible as indicated by the average Z' factor of 0.6 and CV values around 12%. From concentration-response curves and IC₅₀ values, mitochondrial membrane impairment appears to be the early stage marker of cell death by the compounds.

Functional and Mechanistic Neurotoxicity Profiling Using Human iPSC-Derived Neural 3D Cultures

Neurological disorders affect millions of people worldwide and appear to be on the rise. Whereas the reason for this increase remains unknown, environmental factors are a suspected contributor. Hence, there is an urgent need to develop more complex, biologically relevant, and predictive in vitro assays to screen larger sets of compounds with the potential for neurotoxicity. Here, we employed a human induced pluripotent stem cell (iPSC)-based 3D neural platform composed of mature cortical neurons and astrocytes as a model for this purpose. The iPSC-derived human 3D cortical neuron/astrocyte co-cultures (3D neural cultures) present spontaneous synchronized, readily detectable calcium oscillations. This advanced neural platform was optimized for high-throughput screening in 384-well plates and displays highly consistent, functional performance across different wells and plates. Characterization of oscillation profiles in 3D neural cultures was performed through multi-parametric analysis that included the calcium oscillation rate and peak width, amplitude, and waveform irregularities. Cellular and mitochondrial toxicity were assessed by high-content imaging. For assay characterization, we used a set of neuromodulators with known mechanisms of action. We then explored the neurotoxic profile of a library of 87 compounds that included pharmaceutical drugs, pesticides, flame retardants, and other chemicals. Our results demonstrated that 57% of the tested compounds exhibited effects in the assay. The compounds were then ranked according to their effective concentrations based on in vitro activity. Our results show that a human iPSC-derived 3D neural culture assay platform is a promising biologically relevant tool to assess the neurotoxic potential of drugs and environmental toxicants.

Review of high-content screening applications in toxicology

High-content screening (HCS) technology combining automated microscopy and quantitative image analysis can address biological questions in academia and the pharmaceutical industry. Various HCS experimental applications have been utilized in the research field of in vitro toxicology. In this review, we describe several HCS application approaches used for studying the mechanism of compound toxicity, highlight some challenges faced in the toxicological community, and discuss the future directions of HCS in regards to new models, new reagents, data management, and informatics. Many specialized areas of toxicology including developmental toxicity, genotoxicity, developmental neurotoxicity/neurotoxicity, hepatotoxicity, cardiotoxicity, and nephrotoxicity will be examined. In addition, several newly developed cellular assay models including induced pluripotent stem cells (iPSCs), three-dimensional (3D) cell models, and tissues-on-a-chip will be discussed. New genome-editing technologies (e.g., CRISPR/Cas9), data analyzing tools for imaging, and coupling with high-content assays will be reviewed. Finally, the applications of machine learning to image processing will be explored. These new HCS approaches offer a huge step forward in dissecting biological processes, developing drugs, and making toxicology studies easier.

A rapid and accurate method to quantify neurite outgrowth from cell and tissue cultures: Two image analytic approaches using adaptive thresholds or machine learning

BACKGROUND

Assessments of axonal outgrowth and dendritic development are essential readouts in many in vitro models in the field of neuroscience. Available analysis software is based on the assessment of fixed immunolabelled tissue samples, making it impossible to follow the dynamic development of neurite outgrowth. Thus, automated algorithms that efficiently analyse brightfield images, such as those obtained during time-lapse microscopy, are needed.

NEW METHOD

We developed and validated algorithms to quantitatively assess neurite outgrowth from living and unstained spinal cord slice cultures (SCSCs) and dorsal root ganglion cultures (DRGCs) based on an adaptive thresholding approach called NeuriteSegmantation. We used a machine learning approach to evaluate dendritic development from dissociate neuron cultures.

RESULTS

NeuriteSegmentation successfully recognized axons in brightfield images of SCSCs and DRGCs. The temporal pattern of axonal growth was successfully assessed. In dissociate neuron cultures the total number of cells and their outgrowth of dendrites were successfully assessed using machine learning.

COMPARISON WITH EXISTING METHODS

The methods were positively correlated and were more time-saving than manual counts, having performing times varying from 0.5-2 min. In addition, NeuriteSegmentation was compared to NeuriteJ®, that uses global thresholding, being more reliable in recognizing axons in areas of intense background.

CONCLUSION

The developed image analysis methods were more time-saving and user-independent than established approaches. Moreover, by using adaptive thresholding, we could assess images with large variations in background intensity. These tools may prove valuable in the quantitative analysis of axonal and dendritic outgrowth from numerous in vitro models used in neuroscience.

MicroRNA-24-3p regulates neuronal differentiation by controlling hippocalcin expression

Hippocalcin (HPCA) is a neuron-specific calcium-binding protein predominantly expressed in the nervous system. In the present study, we demonstrate that HPCA regulates neuronal differentiation in SH-SY5Y cells. We observed that the expression level of HPCA was increased during neuronal differentiation. Depletion of HPCA inhibited both neurite outgrowth and synaptophysin (SYP) expression, whereas overexpression of HPCA enhanced neuronal differentiation. Interestingly, we also found that the expression of HPCA mRNA was modulated by miR-24-3p. Using a dual-luciferase assay, we showed that co-transfection of a plasmid containing the miR-24-3p binding site from the 3'-untranslated region (3'UTR) of the HPCA gene and an miR-24-3p mimic effectively reduced luminescence activity. This effect was abolished when miR-24-3p seed sequences in the 3'UTR of the HPCA gene were mutated. miR-24-3p expression was decreased during differentiation, suggesting that the decreased expression level of miR-24-3p might have upregulated mRNA expression of HPCA. As expected, upregulation of miR-24-3p by an miRNA mimic led to reduced HPCA expression, accompanied by diminished neuronal differentiation. In contrast, downregulation of miR-24-3p by an antisense inhibitor promoted neurite outgrowth as well as levels of SYP expression. Taken together, these results suggest that miR-24-3p is an important miRNA that regulates neuronal differentiation by controlling HPCA expression.

Human Embryonic Stem Cell-Derived Neural Lineages as In Vitro Models for Screening the Neuroprotective Properties of Lignosus rhinocerus (Cooke) Ryvarden

In the biomedical field, there is growing interest in using human stem cell-derived neurons as in vitro models for pharmacological and toxicological screening of bioactive compounds extracted from natural products. Lignosus rhinocerus (Tiger Milk Mushroom) is used by indigenous communities in Malaysia as a traditional medicine to treat various diseases. The sclerotium of L. rhinocerus has been reported to have medicinal properties, including various bioactivities such as neuritogenic, anti-inflammatory, and anticancer effects. This study aims to investigate the neuroprotective activities of L. rhinocerus sclerotial extracts. Human embryonic stem cell (hESC)-derived neural lineages exposed to the synthetic glucocorticoid, dexamethasone (DEX), were used as the in vitro models. Excess glucocorticoids have been shown to adversely affect fetal brain development and impair differentiation of neural progenitor cells. Screening of different L. rhinocerus sclerotial extracts and DEX on the hESC-derived neural lineages was conducted using cell viability and neurite outgrowth assays. The neuroprotective effects of L. rhinocerus sclerotial extracts against DEX were further evaluated using apoptosis assays and Western blot analysis. Hot aqueous and methanol extracts of L. rhinocerus sclerotium promoted neurite outgrowth of hESC-derived neural stem cells (NSCs) with negligible cytotoxicity. Treatment with DEX decreased viability of NSCs by inducing apoptosis. Coincubation of L. rhinocerus methanol extract with DEX attenuated the DEX-induced apoptosis and reduction in phospho-Akt (pAkt) level in NSCs. These results suggest the involvement of Akt signaling in the neuroprotection of L. rhinocerus methanol extract against DEX-induced apoptosis in NSCs. Methanol extract of L. rhinocerus sclerotium exhibited potential neuroprotective activities against DEX-induced toxicity in hESC-derived NSCs. This study thus validates the use of human stem cell-derived neural lineages as potential in vitro models for screening of natural products with neuroprotective properties.