Neurotoxicity Testing Research Articles

MicroRNA Profiling as Tool for Developmental Neurotoxicity Testing (DNT).

microRNAs (miRNAs) are small non-coding RNA molecules functioning as post-transcriptional regulators of gene expression. miRNAs play a significant role in organism development, regulating developmental timing, cell differentiation, and specification. In the developing brain, miRNAs regulate neural stem cell differentiation, lineage specification, synaptogenesis, and brain morphogenesis. Temporal and spatial specificity of miRNA expression make them an attractive marker to study cellular responses to toxicant exposure. Neural differentiation of murine embryonic stem cells (mESCs) has been established as an alternative method to study developmental neurotoxicity (DNT) in vitro. This unit will describe a method for miRNA profiling (miRNomics) as a molecular end point to study developmental neurotoxicity. A protocol for neural differentiation of mESC will be described as a cellular model for DNT testing. The miRNomics protocol is versatile and can be used with other DNT cellular systems such as primary cultures, human embryonic stem cells (hESCs), or induced pluripotent stem cells (iPSCs).

Behavioural changes observed in demyelination model shares similarities with white matter abnormalities in humans

Multiple sclerosis (MS) is a chronic, inflammatory, demyelinating disease of the central nervous system (CNS). Further to the symptoms resulting from demyelination, new studies point to the involvement of neuroinflammation and white matter abnormalities in psychiatric disorders and neurodegenerative diseases. Cuprizone, a model of MS, produces consistent demyelination and elicits behavioural, morphological and inflammatory changes in animals that share some similarities with those observed in humans. In this study, we used the cuprizone model in Lewis rats to evaluate clinical signs triggered by the demyelination process which could be comparable with the symptoms seen in white matter abnormalities in human beings. To induce the demyelination process, 0.6% cuprizone was added to the Lewis rats’ diet for 4 weeks. We proceeded with behavioural, morphological and immunological analyses. Animals fed with cuprizone exhibited behavioural changes: higher scores in the neurotoxicity test, reduced exploratory and locomotion behaviour, and also an increase of permanency in the closed arm of the elevated plus maze test, were observed. In these analyses, the animals showed motor coordination impairment and anxiety-like behaviour. Demyelination also triggered changes in discrimination of objects identified by an increase in the time spent close to a familiar object. These behavioural alterations were associated with a significant increase in the levels of TNF-alpha and corticosterone, consistent with the activation of microglia and astrocytes. Taken together, the results of this work show the cuprizone/Lewis rat model demyelination as an attractive paradigm for studying the correlation between white matter abnormalities and behaviour.

Literature review on in vitro and alternative Developmental Neurotoxicity (DNT) testing methods

Literature review on in vitro and alternative Developmental Neurotoxicity (DNT) testing methods

International STakeholder NETwork (ISTNET): creating a developmental neurotoxicity (DNT) testing road map for regulatory purposes.

A major problem in developmental neurotoxicity (DNT) risk assessment is the lack of toxicological hazard information for most compounds. Therefore, new approaches are being considered to provide adequate experimental data that allow regulatory decisions. This process requires a matching of regulatory needs on the one hand and the opportunities provided by new test systems and methods on the other hand. Alignment of academically and industrially driven assay development with regulatory needs in the field of DNT is a core mission of the International STakeholder NETwork (ISTNET) in DNT testing. The first meeting of ISTNET was held in Zurich on 23–24 January 2014 in order to explore the concept of adverse outcome pathway (AOP) to practical DNT testing. AOPs were considered promising tools to promote test systems development according to regulatory needs. Moreover, the AOP concept was identified as an important guiding principle to assemble predictive integrated testing strategies (ITSs) for DNT. The recommendations on a road map towards AOP-based DNT testing is considered a stepwise approach, operating initially with incomplete AOPs for compound grouping, and focussing on key events of neurodevelopment. Next steps to be considered in follow-up activities are the use of case studies to further apply the AOP concept in regulatory DNT testing, making use of AOP intersections (common key events) for economic development of screening assays, and addressing the transition from qualitative descriptions to quantitative network modelling.

Zebrafish as a systems toxicology model for developmental neurotoxicity testing.

The developing brain is extremely sensitive to many chemicals. Exposure to neurotoxicants during development has been implicated in various neuropsychiatric and neurological disorders, including autism spectrum disorder, attention deficit hyperactive disorder, schizophrenia, Parkinson's disease, and Alzheimer's disease. Although rodents have been widely used for developmental neurotoxicity testing, experiments using large numbers of rodents are time-consuming, expensive, and raise ethical concerns. Using alternative non-mammalian animal models may relieve some of these pressures by allowing testing of large numbers of subjects while reducing expenses and minimizing the use of mammalian subjects. In this review, we discuss some of the advantages of using zebrafish in developmental neurotoxicity testing, focusing on central nervous system development, neurobehavior, toxicokinetics, and toxicodynamics in this species. We also describe some important examples of developmental neurotoxicity testing using zebrafish combined with gene expression profiling, neuroimaging, or neurobehavioral assessment. Zebrafish may be a systems toxicology model that has the potential to reveal the pathways of developmental neurotoxicity and to provide a sound basis for human risk assessments.

Novel scalable 3D cell based model for in vitro neurotoxicity testing: Combining human differentiated neurospheres with gene expression and functional endpoints

There is an urgent need for new in vitro strategies to identify neurotoxic agents with speed, reliability and respect for animal welfare. Cell models should include distinct brain cell types and represent brain microenvironment to attain higher relevance. The main goal of this study was to develop and validate a human 3D neural model containing both neurons and glial cells, applicable for toxicity testing in high-throughput platforms. To achieve this, a scalable bioprocess for neural differentiation of human NTera2/cl.D1 cells in stirred culture systems was developed. Endpoints based on neuronal- and astrocytic-specific gene expression and functionality in 3D were implemented in multi-well format and used for toxicity assessment. The prototypical neurotoxicant acrylamide affected primarily neurons, impairing synaptic function; our results suggest that gene expression of the presynaptic marker synaptophysin can be used as sensitive endpoint. Chloramphenicol, described as neurotoxicant affected both cell types, with cytoskeleton markers’ expression significantly reduced, particularly in astrocytes. In conclusion, a scalable and reproducible process for production of differentiated neurospheres enriched in mature neurons and functional astrocytes was obtained. This 3D approach allowed efficient production of large numbers of human differentiated neurospheres, which in combination with gene expression and functional endpoints are a powerful cell model to evaluate human neuronal and astrocytic toxicity.

Metoclopramide

The Food Safety Commission of Japan (FSCJ) conducted a risk assessment of metoclopramide (CAS No. 364-62-5) as a veterinary medicinal product used to gastrointestinal motility disorder, based on the documents submitted from the Ministry of Health, Labour and Welfare (MHLW). Various in vivo and in vitro genotoxicity studies suggested no apparent genotoxicity of metoclopramide relevant to human health. No carcinogenicity study nor the detail of chronic toxicity study was available, but metoclopramide is unlikely a genotoxic carcinogen. FSCJ concluded, therefore, that the acceptable daily intake (ADI) for metoclopramide can be specified. The lowest value among no-observed-adverse-effect levels (NOAELs) and lowest-observed-adverse-effect levels (LOAELs) in various toxicological studies was 0.5 mg/kg bw/day in a 6-month subacute toxicity study in dogs (LOAEL), as a toxic indicator of clinical signs including restlessness. FSCJ considered it appropriate to apply an additional safety factor of 10 on the specification of the ADI based on the LOAEL, taking into account of the lack of carcinogenicity tests, reproductive toxicity tests and neurotoxicity tests, and insufficient data of chronic toxicity tests. Accordingly, the specified ADI is 0.0005 mg/kg bw/day for metoclopramide, applying a safety factor of 1,000 (10 for species difference, 10 for individual difference and 10 for the additional factor) to the LOAEL of 0.5 mg/kg bw/day in a 6-month subacute toxicity study in dogs.

In vitro detection of cardiotoxins or neurotoxins affecting ion channels or pumps using beating cardiomyocytes as alternative for animal testing

The present study investigated if and to what extent murine stem cell-derived beating cardiomyocytes within embryoid bodies can be used as a broad screening in vitro assay for neurotoxicity testing, replacing for example in vivo tests for marine neurotoxins. Effect of nine model compounds, acting on either the Na+, K+, or Ca2+ channels or the Na+/K+ ATP-ase pump, on the beating was assessed. Diphenhydramine, veratridine, isradipine, verapamil and ouabain induced specific beating arrests that were reversible and none of the concentrations tested induced cytotoxicity. Three K+ channel blockers, amiodarone, clofilium and sematilide, and the Na+/K+ ATPase pump inhibitor digoxin had no specific effect on the beating. In addition, two marine neurotoxins i.e. saxitoxin and tetrodotoxin elicited specific beating arrests in cardiomyocytes. Comparison of the results obtained with cardiomyocytes to those obtained with the neuroblastoma neuro-2a assay revealed that the cardiomyocytes were generally somewhat more sensitive for the model compounds affecting Na+ and Ca2+ channels, but less sensitive for the compounds affecting K+ channels. The stem cell-derived cardiomyocytes were not as sensitive as the neuroblastoma neuro-2a assay for saxitoxin and tetrodotoxin. It is concluded that the murine stem cell-derived beating cardiomyocytes provide a sensitive model for detection of specific neurotoxins and that the neuroblastoma neuro-2a assay may be a more promising cell-based assay for the screening of marine biotoxins.

Fundamentals of translational neuroscience in toxicologic pathology: optimizing the value of animal data for human risk assessment.

A half-day Society of Toxicologic Pathology continuing education course on "Fundamentals of Translational Neuroscience in Toxicologic Pathology" presented some current major issues faced when extrapolating animal data regarding potential neurological consequences to assess potential human outcomes. Two talks reviewed functional-structural correlates in rodent and nonrodent mammalian brains needed to predict behavioral consequences of morphologic changes in discrete neural cell populations. The third lecture described practical steps for ensuring that specimens from rodent developmental neurotoxicity tests will be processed correctly to produce highly homologous sections. The fourth talk detailed demographic factors (e.g., species, strain, sex, and age); physiological traits (body composition, brain circulation, pharmacokinetic/pharmacodynamic patterns, etc.); and husbandry influences (e.g., group housing) known to alter the effects of neuroactive agents. The last presentation discussed the appearance, unknown functional effects, and potential relevance to humans of polyethylene glycol (PEG)-associated vacuoles within the choroid plexus epithelium of animals. Speakers provided real-world examples of challenges with data extrapolation among species or with study design considerations that may impact the interpretability of results. Translational neuroscience will be bolstered in the future as less invasive and/or more quantitative techniques are devised for linking overt functional deficits to subtle anatomic and chemical lesions.

Synthesis, in silico preclinical evaluation, antidepressant potential of 5-substituted phenyl-3-(thiophen-2-yl)-4,5-dihydro-1h-pyrazole-1-carboxamides

In the context of the discovery of new potential antidepressant candidates and in the light of promising antidepressant action of pyrazoline nucleus, a new series of thiophene bearing pyrazoline carboxamides were synthesized and examined for their antidepressant effect by two behavioural models viz. Forced Swim Test (FST) and Tail Suspension Test (TST). Neurotoxicity of the compounds were accessed by rotarod test. The titled compounds were characterized by IR, 1H NMR, 13C NMR and mass and elemental analyses. The preclinical evaluation the compounds were predicted by in silico toxicity, blood-brain barrier and human oral absorption. In this series, 5-(3-nitrophenyl)-3-(thiophen-2-yl)-4,5-dihydro-1H-pyrazole-1-carboxamide (TSe) reduced immobility time 60.43 and 63.47% in both FST and TST, respectively at 10mg/kg dose level when compared to the standard imipramine. Moreover, it was observed that the compounds possessing electron-releasing groups such as dimethyl amino, methoxy and electron-withdrawing chlorine in the 4th position of aromatic rings of the scaffold showed good antidepressant activity when compared to the pyrazolines having no substituents on the phenyl rings. All the compounds in the series have passed neurotoxicity test.

Development of a pluripotent stem cell derived neuronal model to identify chemically induced pathway perturbations in relation to neurotoxicity: Effects of CREB pathway inhibition

According to the advocated paradigm shift in toxicology, acquisition of knowledge on the mechanisms underlying the toxicity of chemicals, such as perturbations of biological pathways, is of primary interest. Pluripotent stem cells (PSCs), such as human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), offer a unique opportunity to derive physiologically relevant human cell types to measure molecular and cellular effects of such pathway modulations. Here we compared the neuronal differentiation propensity of hESCs and hiPSCs with the aim to develop novel hiPSC-based tools for measuring pathway perturbation in relation to molecular and cellular effects in vitro. Among other fundamental pathways, also, the cAMP responsive element binding protein (CREB) pathway was activated in our neuronal models and gave us the opportunity to study time-dependent effects elicited by chemical perturbations of the CREB pathway in relation to cellular effects. We show that the inhibition of the CREB pathway, using 2-naphthol-AS-E-phosphate (KG-501), induced an inhibition of neurite outgrowth and synaptogenesis, as well as a decrease of MAP2+ neuronal cells. These data indicate that a CREB pathway inhibition can be related to molecular and cellular effects that may be relevant for neurotoxicity testing, and, thus, qualify the use of our hiPSC-derived neuronal model for studying chemical-induced neurotoxicity resulting from pathway perturbations.

In vitro relative potency of Type II pyrethroids and mixture dose-effects on oxidative stress cytotoxicity in SH-SY5Y, HepG2 and Caco-2 human cell lines

s / Toxicology Letters 229S (2014) S40–S252 S45 further advance simpler and more highly detectable assay, we aim to generate genetically engineered mES cells that express luminescence marker genes as convenient reporters for neurotoxicity and establish efficient in vitro neurotoxicity tests. We therefore worked on DNA microarray analysis of the culture samples conditioned by the high content imaging system to search for candidate neurotoxicitymarker genes related to neurite outgrowth Acknowledgement: This study is supported by a research grant from the Ministry of Economy, Trade and Industry (METI) of Japan. http://dx.doi.org/10.1016/j.toxlet.2014.06.195

Synthesis and anticonvulsant activity of novel purine derivatives

A series of new purines containing triazole and other heterocycle substituents was synthesized and evaluated for their preliminary anticonvulsant activity and neurotoxicity by using the maximal electroshock (MES), subcutaneous pentylenetetrazole (scPTZ) and rotarod neurotoxicity (TOX) tests. Among the compounds studied, 9-decyl-6-(1H-1,2,4-triazol-1-yl)-9H-purine (5e) was the most potent compound, with a median effective dose of 23.4 mg/kg and a high protective index of more than 25.6 after intraperitoneal administration in mice. Compound 5e showed significant oral activity against MES-induced seizures in mice, with an ED50 of 39.4 mg/kg and a PI above 31.6. These results demonstrate that compound 5e possesses better anticonvulsant activity and is safer than the commercially available drugs carbamazepine and valproate in MES, scPTZ and TOX models.

Single-neuron axonal pathfinding under geometric guidance: low-dose-methylmercury developmental neurotoxicity test.

Because the nervous system is most vulnerable to toxicants during development, there is a crucial need for a highly sensitive developmental-neurotoxicity-test model to detect potential toxicants at low doses. We developed a lab-on-chip wherein single-neuron axonal pathfinding under geometric guidance was created using soft lithography and laser cell-micropatterning techniques. After coating the surface with L1, an axon-specific member of the Ig family of cell adhesion molecules (CAMs), and optimizing microunit geometric parameters, we introduced low-dose methylmercury, a well-known, environmentally significant neurotoxicant, in the shared medium. Its developmental neurotoxicity was evaluated using a novel axonal pathfinding assay including axonal turning and branching rates at turning points in this model. Compared to the conventional neurite-outgrowth assay, this model's detection threshold for low-dose methylmercury was 10-fold more sensitive at comparable exposure durations. These preliminary results support study of developmental effects of known and potential neurotoxicants on axon pathfinding. This novel assay model would be useful to study neuronal disease mechanisms at the single-cell level. To our knowledge, the potential of methylmercury chloride to cause acute in vitro developmental neurotoxicity (DNT) at such a low dosage has not been reported. This is the first DNT test model with high reproducibility to use single-neuron axonal pathfinding under precise geometric guidance.

MicroRNA profiling as tool for in vitro developmental neurotoxicity testing: the case of sodium valproate.

Studying chemical disturbances during neural differentiation of murine embryonic stem cells (mESCs) has been established as an alternative in vitro testing approach for the identification of developmental neurotoxicants. miRNAs represent a class of small non-coding RNA molecules involved in the regulation of neural development and ESC differentiation and specification. Thus, neural differentiation of mESCs in vitro allows investigating the role of miRNAs in chemical-mediated developmental toxicity. We analyzed changes in miRNome and transcriptome during neural differentiation of mESCs exposed to the developmental neurotoxicant sodium valproate (VPA). A total of 110 miRNAs and 377 mRNAs were identified differently expressed in neurally differentiating mESCs upon VPA treatment. Based on miRNA profiling we observed that VPA shifts the lineage specification from neural to myogenic differentiation (upregulation of muscle-abundant miRNAs, mir-206, mir-133a and mir-10a, and downregulation of neural-specific mir-124a, mir-128 and mir-137). These findings were confirmed on the mRNA level and via immunochemistry. Particularly, the expression of myogenic regulatory factors (MRFs) as well as muscle-specific genes (Actc1, calponin, myosin light chain, asporin, decorin) were found elevated, while genes involved in neurogenesis (e.g. Otx1, 2, and Zic3, 4, 5) were repressed. These results were specific for valproate treatment and―based on the following two observations―most likely due to the inhibition of histone deacetylase (HDAC) activity: (i) we did not observe any induction of muscle-specific miRNAs in neurally differentiating mESCs exposed to the unrelated developmental neurotoxicant sodium arsenite; and (ii) the expression of muscle-abundant mir-206 and mir-10a was similarly increased in cells exposed to the structurally different HDAC inhibitor trichostatin A (TSA). Based on our results we conclude that miRNA expression profiling is a suitable molecular endpoint for developmental neurotoxicity. The observed lineage shift into myogenesis, where miRNAs may play an important role, could be one of the developmental neurotoxic mechanisms of VPA.

SIGNIFICANT DOWN-REGULATION OF EIF2 AND ASSOCIATED RIBOSOMAL PROTEINS IN ONS CELL MODEL OF SCHIZOPHRENIA

According to the advocated paradigm shift in toxicology, acquisition of knowledge on the mechanisms underlying the toxicity of chemicals, such as perturbations of biological pathways, is of primary interest. Pluripotent stem cells (PSCs), such as human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), offer a unique opportunity to derive physiologically relevant human cell types to measure molecular and cellular effects of such pathway modulations. Here we compared the neuronal differentiation propensity of hESCs and hiPSCs with the aim to develop novel hiPSC-based tools for measuring pathway perturbation in relation to molecular and cellular effects in vitro. Among other fundamental pathways, also, the cAMP responsive element binding protein (CREB) pathway was activated in our neuronal models and gave us the opportunity to study time-dependent effects elicited by chemical perturbations of the CREB pathway in relation to cellular effects. We show that the inhibition of the CREB pathway, using 2-naphthol-AS-E-phosphate (KG-501), induced an inhibition of neurite outgrowth and synaptogenesis, as well as a decrease of MAP2+ neuronal cells. These data indicate that a CREB pathway inhibition can be related to molecular and cellular effects that may be relevant for neurotoxicity testing, and, thus, qualify the use of our hiPSC-derived neuronal model for studying chemical-induced neurotoxicity resulting from pathway perturbations.

ANTICONVULSANT AND NEUROTOXICITY EVALUATION OF SOME NEWLY SYNTHESIZED THIAZOLYL COUMARIN DERIVATIVES

The present series of compounds were synthesized with the aim to develop newer anticonvulsant agents t hat are comparatively more efficacious and safer than t he currently used anticonvulsant agents. Various thiazolyl coumarins were synthesized by the reactio n of 3-(bromoacetyl)-2H-chromen-2-one with different substituted aryl thiourea. The structures of the sy nthesized compounds were confirmed by spectral data and elemental analyses. Compounds were tested for antic onvulsant activity utilizing Pen Tylenetetra Zoleinduced seizure (PTZ) and Maximal Electroshock Seizure (MES) tests at 30, 100 and 300 mg kg -1 dose level. Neurotoxicity and ethanol potentiation test of the compounds were also assessed at the same dose level. Two compounds of the series 3g and 3j exhibi ted significant anticonvulsant activity at 30 mg kg -1 dose level with lesser neurotoxicity than the stand ard drug phenytoin.

Preliminary anticonvulsant and toxicity screening of substituted benzylidenehydrazinyl-N-(6-substituted benzo[d]thiazol-2-yl)propanamides.

Keeping in view the structural requirements suggested in the pharmacophore model for anticonvulsant activity, a new series of 3-(2-(substitutedbenzylidene)hydrazinyl)-N-(substituted benzo[d]thiazol-2-yl)-propanamides were synthesized with aromatic hydrophobic aryl ring (A), NH–C=O as hydrogen bonding domain (HBD), nitrogen atom as electron donor (D), and phenyl as distal aryl ring (C). Synthesized compounds were characterized by FTIR, 1H NMR, 13C NMR, mass spectroscopy, and elemental analysis. Preliminary in vivo anticonvulsant screening (phase I) was performed by two most adopted seizure models, maximal electroshock seizure (MES) and subcutaneous pentylenetetrazole (scPTZ). Based on anticonvulsant screening results, two compounds, 5h and 5p, were found to be most active; they exhibited activity comparable to standard drugs phenytoin (PHY) and carbamazepine (CBZ). These active compounds were subjected to phase II and phase III screening, where they displayed much higher protective index (PI) in comparison to the standard drugs. In phase IV screening, the bioavailability of active compounds was assessed on oral administration. Further, preliminary safety profiles of 5h and 5p were evaluated by the neurotoxicity testing and liver enzyme estimation.

International STakeholder NETwork (ISTNET) for creating a developmental neurotoxicity testing (DNT) roadmap for regulatory purposes.

223 International STakeholder NETwork (ISTNET) for Creating a Developmental Neurotoxicity Testing (DNT) Roadmap for Regulatory Purposes Kevin Crofton , Ellen Fritsche 2, Timo Ylikomi 3, and Anna Bal-Price 4 National Centre for Computational Toxicology, Office of Research and Development, U.S. Environmental Protection Agency, RTP, NC, USA; IUF – Leibniz Research Institute for Environmental Medicine, Dusseldorf, Germany; School of Medicine, University of Tampere, Tampere, Finland; Joint Research Centre of the European Commission, Institute for Health and Consumer Protection, Ispra, Italy

High-Content Screening Assay for Identification of Chemicals Impacting Spontaneous Activity in Zebrafish Embryos

Although cell-based assays exist, rapid and cost-efficient high-content screening (HCS) assays within intact organisms are needed to support prioritization for developmental neurotoxicity testing in rodents. During zebrafish embryogenesis, spontaneous tail contractions occur from late-segmentation (∼19 h postfertilization, hpf) through early pharyngula (∼29 hpf) and represent the first sign of locomotion. Using transgenic zebrafish (fli1:egfp) that stably express eGFP beginning at ∼14 hpf, we have developed and optimized a 384-well-based HCS assay that quantifies spontaneous activity within single zebrafish embryos after exposure to test chemicals in a concentration-response format. Following static exposure of one embryo per well from 5 to 25 hpf, automated image acquisition procedures and custom analysis protocols were used to quantify total body area and spontaneous activity in live embryos. Survival and imaging success rates across control plates ranged from 87.5 to 100% and 93.3-100%, respectively. Using our optimized procedures, we screened 16 chemicals within the US EPA's ToxCast Phase-I library, and found that exposure to abamectin and emamectin benzoate-both potent avermectins-abolished spontaneous activity in the absence of gross malformations. Overall, compared to existing locomotion-based zebrafish assays conducted later in development, this method provides a simpler discovery platform for identifying potential developmental neurotoxicants.