Growth and differentiation of aggregating fetal brain cells in a serum-free defined medium

Molecular and Functional Characterization of Different BrainSphere Models for Use in Neurotoxicity Testing on Microelectrode Arrays

The currently accepted methods for neurotoxicity (NT) testing rely on animal studies. However, high costs and low testing throughput hinder their application for large numbers of chemicals. To overcome these limitations, in vitro methods are currently being developed based on human-induced pluripotent stem cells (hiPSC) that allow higher testing throughput at lower costs. We applied six different protocols to generate 3D BrainSphere models for acute NT evaluation. These include three different media for 2D neural induction and two media for subsequent 3D differentiation resulting in self-organized, organotypic neuron/astrocyte microtissues. All induction protocols yielded nearly 100% NESTIN-positive hiPSC-derived neural progenitor cells (hiNPCs), though with different gene expression profiles concerning regional patterning. Moreover, gene expression and immunocytochemistry analyses revealed that the choice of media determines neural differentiation patterns. On the functional level, BrainSpheres exhibited different levels of electrical activity on microelectrode arrays (MEA). Spike sorting allowed BrainSphere functional characterization with the mixed cultures consisting of GABAergic, glutamatergic, dopaminergic, serotonergic, and cholinergic neurons. A test method for acute NT testing, the human multi-neurotransmitter receptor (hMNR) assay, was proposed to apply such MEA-based spike sorting. These models are promising tools not only in toxicology but also for drug development and disease modeling.

Enteric Neural Network Assembly Was Promoted by Basic Fibroblast Growth Factor and Vitamin A but Inhibited by Epidermal Growth Factor

Extending well beyond the original use of propagating neural precursors from the central nervous system and dorsal root ganglia, neurosphere medium (NSM) and self-renewal medium (SRM) are two distinct formulas with widespread popularity in enteric neural stem cell (ENSC) applications. However, it remains unknown what growth factors or nutrients are crucial to ENSC development, let alone whether the discrepancy in their components may affect the outcomes of ENSC culture. Dispersed enterocytes from murine fetal gut were nurtured in NSM, SRM or their modifications by selective component elimination or addition to assess their effects on ENSC development. NSM generated neuriteless neurospheres, whereas SRM, even deprived of chicken embryo extract, might wire ganglia together to assemble neural networks. The distinct outcomes came from epidermal growth factor, which inhibited enteric neuronal wiring in NSM. In contrast, basic fibroblast growth factor promoted enteric neurogenesis, gangliogenesis, and neuronal wiring. Moreover, vitamin A derivatives might facilitate neuronal maturation evidenced by p75 downregulation during ENSC differentiation toward enteric neurons to promote gangliogenesis and network assembly. Our results might help to better manipulate ENSC propagation and differentiation in vitro, and open a new avenue for the study of enteric neuronal neuritogenesis and synaptogenesis.

Organophosphorus flame retardants are developmental neurotoxicants in a rat primary brainsphere in vitro model

Due to regulatory bans and voluntary substitutions, halogenated polybrominated diphenyl ether (PBDE) flame retardants (FR) are increasingly substituted by mainly organophosphorus FR (OPFR). Leveraging a 3D rat primary neural organotypic in vitro model (rat brainsphere), we compare developmental neurotoxic effects of BDE-47-the most abundant PBDE congener-with four OPFR (isopropylated phenyl phosphate-IPP, triphenyl phosphate-TPHP, isodecyl diphenyl phosphate-IDDP, and tricresyl phosphate (also known as trimethyl phenyl phosphate)-TMPP). Employing mass spectroscopy-based metabolomics and transcriptomics, we observe at similar human-relevant non-cytotoxic concentrations (0.1-5 µM) stronger developmental neurotoxic effects by OPFR. This includes toxicity to neurons in the low µM range; all FR decrease the neurotransmitters glutamate and GABA (except BDE-47 and TPHP). Furthermore, n-acetyl aspartate (NAA), considered a neurologic diagnostic molecule, was decreased by all OPFR. At similar concentrations, the FR currently in use decreased plasma membrane dopamine active transporter expression, while BDE-47 did not. Several findings suggest astrogliosis induced by the OPFR, but not BDE-47. At the 5 µM concentrations, the OPFR more than BDE-47 interfered with myelination. An increase of cytokine gene and receptor expressions suggests that exposure to OPFR may induce an inflammatory response. Pathway/category overrepresentation shows disruption in 1) transmission of action potentials, cell-cell signaling, synaptic transmission, receptor signaling, (2) immune response, inflammation, defense response, (3) cell cycle and (4) lipids metabolism and transportation. Taken together, this appears to be a case of regretful substitution with substances not less developmentally neurotoxic in a primary rat 3D model.

In Vitro Methods as a Tool in Neurotoxicity Studies

— There are several hundred industrial chemicals with neurotoxic potential. The neurotoxic risks of most of these chemicals are unknown. Additional methods are needed to assess the risks more effectively and to elucidate the mechanisms of neurotoxicity more accurately than is possible with the conventional methods.

This paper deals with general tasks concerning the use of in vitro models in the evaluation of neurotoxic risks. It is based on our previous studies with various in vitro models and on recent literature. The induction of glial fibrillary acidic protein in astrocyte cultures after treatment with known neurotoxicants (mercury compounds and aluminium) is discussed in more detail as an important response which can be detected in vitro.

When used appropriately with in vivo tests and with previous toxicological data, in vitro neurotoxicity testing considerably improves risk assessment. The incorporation of in vitro tests into the early stages of risk evaluation can reduce the number of animals used in routine toxicity testing, by identifying chemicals with high neurotoxic potential.

Model-based estimation of lowest observed effect concentration from replicate experiments to identify potential biomarkers of in vitro neurotoxicity

A paradigm shift is occurring in toxicology following the report of the National Research Council of the USA National Academies entitled "Toxicity testing in the 21st Century: a vision and strategy". This new vision encourages the use of in vitro and in silico models for toxicity testing. In the goal to identify new reliable markers of toxicity, the responsiveness of different genes to various drugs (amiodarone: 0.312-2.5 [Formula: see text]; cyclosporine A: 0.25-2 [Formula: see text]; chlorpromazine: 0.625-10 [Formula: see text]; diazepam: 1-8 [Formula: see text]; carbamazepine: 6.25-50 [Formula: see text]) is studied in 3D aggregate brain cell cultures. Genes' responsiveness is quantified and ranked according to the Lowest Observed Effect Concentration (LOEC), which is estimated by reverse regression under a log-logistic model assumption. In contrast to approaches where LOEC is identified by the first observed concentration level at which the response is significantly different from a control, the model-based approach allows a principled estimation of the LOEC and of its uncertainty. The Box-Cox transform both sides approach is adopted to deal with heteroscedastic and/or non-normal residuals, while estimates from repeated experiments are summarized by a meta-analytic approach. Different inferential procedures to estimate the Box-Cox coefficient, and to obtain confidence intervals for the log-logistic curve parameters and the LOEC, are explored. A simulation study is performed to compare coverage properties and estimation errors for each approach. Application to the toxicological data identifies the genes Cort, Bdnf, and Nov as good candidates for in vitro biomarkers of toxicity.

Protein pathway analysis to study development-dependent effects of acute and repeated trimethyltin (TMT) treatments in 3D rat brain cell cultures

Trimethyltin is an organometallic compound, described to be neurotoxic and to trigger neuroinflammation and oxidative stress. Previous studies associated TMT with the perturbation of mitochondrial function, or neurotransmission. However, the mechanisms of toxicity may differ depending on the duration of exposure and on the stage of maturation of brain cells. This study aim at elucidating whether the toxicity pathways triggered by a known neurotoxicant (TMT) differs depending on cell maturation stage or duration of exposure. To this end omics profiling of immature and differentiated 3D rat brain cell cultures exposed for 24 h or 10 days (10-d) to 0.5 and 1 μM of TMT was performed to better understand the underlying mechanisms of TMT associated toxicity. Proteomics identified 55 and 17 proteins affected by acute TMT treatment in immature and differentiated cultures respectively, while 10-day treatment altered 96 proteins in immature cultures versus 353 in differentiated. The results suggest different sensitivity to TMT depending on treatment duration and cell maturation. In accordance with known TMT mechanisms oxidative stress and neuroinflammation was observed after 10-d treatment at both maturation stages, whereas the neuroinflammatory process was more prominent in differentiated cultures than in the immature, no development-dependent difference could be detected for oxidative stress or synaptic neurodegeneration. Pathway analysis revealed that both vesicular trafficking and the synaptic machinery were strongly affected by 10-d TMT treatment in both maturation stages, as was GABAergic and glutamatergic neurotransmission. This study shows that omics approaches combined with pathway analysis constitutes an improved tool-set in elucidating toxicity mechanisms.

Organoid technology and applications in cancer research

During the past decade, the three-dimensional organoid technology has sprung up and become more and more popular among researchers. Organoids are the miniatures of in vivo tissues and organs, and faithfully recapitulate the architectures and distinctive functions of a specific organ.

These amazing three-dimensional constructs represent a promising, near-physiological model for human cancers, and tremendously support diverse potential applications in cancer research. Up to now, highly efficient establishment of organoids can be achieved from both normal and malignant tissues of patients. Using this bioengineered platform, the links of infection-cancer progression and mutation-carcinogenesis are feasible to be modeled. Another potential application is that organoid technology facilitates drug testing and guides personalized therapy. Although organoids still fail to model immune system accurately, co-cultures of organoids and lymphocytes have been reported in several studies, bringing hope for further application of this technology in immunotherapy. In addition, the potential value in regeneration medicine might be another paramount branch of organoid technology, which might refine current transplantation therapy through the replacement of irreversibly progressively diseased organs with isogenic healthy organoids.

In conclusion, organoids represent an excellent preclinical model for human tumors, promoting the translation from basic cancer research to clinical practice. In this review, we outline organoid technology and summarize its applications in cancer research.

Design and validation of an ontology-driven animal-free testing strategy for developmental neurotoxicity testing

Developmental neurotoxicity entails one of the most complex areas in toxicology. Animal studies provide only limited information as to human relevance. A multitude of alternative models have been developed over the years, providing insights into mechanisms of action. We give an overview of fundamental processes in neural tube formation, brain development and neural specification, aiming at illustrating complexity rather than comprehensiveness. We also give a flavor of the wealth of alternative methods in this area. Given the impressive progress in mechanistic knowledge of human biology and toxicology, the time is right for a conceptual approach for designing testing strategies that cover the integral mechanistic landscape of developmental neurotoxicity. The ontology approach provides a framework for defining this landscape, upon which an integral in silico model for predicting toxicity can be built. It subsequently directs the selection of in vitro assays for rate-limiting events in the biological network, to feed parameter tuning in the model, leading to prediction of the toxicological outcome. Validation of such models requires primary attention to coverage of the biological domain, rather than classical predictive value of individual tests. Proofs of concept for such an approach are already available. The challenge is in mining modern biology, toxicology and chemical information to feed intelligent designs, which will define testing strategies for neurodevelopmental toxicity testing.

Three-Dimensional Models of the Human Brain Development and Diseases

Deciphering the human brain pathophysiology remains one of the greatest challenges of the 21st century. Neurological disorders represent a significant proportion of diseases burden; however, the complexity of the brain physiology makes it challenging to model its diseases. Simple in vitro models have been very useful for precise measurements in controled conditions. However, existing models are limited in their ability to replicate complex interactions between various cells in the brain. Studying human brain requires sophisticated models to reconstitute the tangled architecture and functions of brain cells. Recently, advances in the development of three-dimensional (3D) brain cell culture models have begun to recapitulate various aspects of the human brain physiology in vitro and replicate basic disease processes of Alzheimer's disease, amyotrophic lateral sclerosis, and microcephaly. In this review, we discuss the progress, advantages, limitations, and future directions of 3D cell culture systems for modeling the human brain development and diseases.

Potential mechanisms of development-dependent adverse effects of the herbicide paraquat in 3D rat brain cell cultures

Exposure to environmental toxicants during vulnerable windows of brain development is suspected to raise the prevalence for neurological dysfunctions at later stages in life. Differentiation processes and changes in morphology, as well as a lack of physiological barriers, might be reasons that render a developing brain more susceptible to neurotoxicants than an adult. However, also the intrinsic capacity of cells to combat toxicant induced cellular stress might differ between the immature- and mature brain. In order to study whether this intrinsic protection capacity differs between immature and maturated brain cells we chose to study the maturation-dependent adverse effects of the known neurotoxicant Paraquat Dichloride (PQ) in 3D rat brain cell cultures. This in vitro system consists of the major brain cell types - neurons, astrocytes, oligodendrocytes and microglia - and over the time in vitro cultured cells undergo differentiation and maturation into a tissue-like organization. PQ was applied repeatedly over ten days in the sub-micromolar range, and effects were evaluated on neurons and glial cells. We observed that despite a higher PQ-uptake in mature cultures, PQ-induced adverse effects on glutamatergic-, GABAergic- and dopaminergic neurons, as assessed by gene expression and enzymatic activity, were more pronounced in immature cultures. This was associated with a stronger astrogliosis in immature- as compared to mature cultures, as well as perturbations of the glutathione-mediated defense against oxidative stress. Furthermore we observed evidence of microglial activation only in mature cultures, whereas immature cultures appeared to down-regulate markers for neuroprotective M2-microglial phenotype upon PQ-exposure. Taken together our results indicate that immature brain cell cultures have less intrinsic capacity to cope with cellular stress elicited by PQ as compared to mature cells. This may render immature brain cells more susceptible to the adverse effects of PQ.

Implications of the thyroid hormone on neuronal development with special emphasis on the calmodulin-kinase IV pathway

Thyroid hormones influence brain development through regulation of gene expression. This is especially true for Ca²⁺-dependent regulation since a major pathway is controlled by the Ca²⁺/calmodulin-dependent protein kinase IV (CaMKIV) which in turn is induced by the thyroid hormone T₃. In addition, CaMKIV is involved in regulation of alternative splicing of a number of protein isoforms, among them PMCA1a, the neuronal specific isoform of the plasma membrane calcium pump. On the other hand, hypothyroidism or CaMKIV deficiency can have a severe influence on brain development. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

Development and characterization of a human embryonic stem cell-derived 3D neural tissue model for neurotoxicity testing

Alternative models for more rapid compound safety testing are of increasing demand. With emerging techniques using human pluripotent stem cells, the possibility of generating human in vitro models has gained interest, as factors related to species differences could be potentially eliminated. When studying potential neurotoxic effects of a compound it is of crucial importance to have both neurons and glial cells. We have successfully developed a protocol for generating in vitro 3D human neural tissues, using neural progenitor cells derived from human embryonic stem cells. These 3D neural tissues can be maintained for two months and undergo progressive differentiation. We showed a gradual decreased expression of early neural lineage markers, paralleled by an increase in markers specific for mature neurons, astrocytes and oligodendrocytes. At the end of the two-month culture period the neural tissues not only displayed synapses and immature myelin sheaths around axons, but electrophysiological measurements also showed spontaneous activity. Neurotoxicity testing - comparing non-neurotoxic to known neurotoxic model compounds - showed an expected increase in the marker of astroglial reactivity after exposure to known neurotoxicants methylmercury and trimethyltin. Although further characterization and refinement of the model is required, these results indicate its potential usefulness for in vitro neurotoxicity testing.

In vitro acute and developmental neurotoxicity screening: an overview of cellular platforms and high-throughput technical possibilities

Neurotoxicity and developmental neurotoxicity are important issues of chemical hazard assessment. Since the interpretation of animal data and their extrapolation to man is challenging, and the amount of substances with information gaps exceeds present animal testing capacities, there is a big demand for in vitro tests to provide initial information and to prioritize for further evaluation. During the last decade, many in vitro tests emerged. These are based on animal cells, human tumour cell lines, primary cells, immortalized cell lines, embryonic stem cells, or induced pluripotent stem cells. They differ in their read-outs and range from simple viability assays to complex functional endpoints such as neural crest cell migration. Monitoring of toxicological effects on differentiation often requires multiomics approaches, while the acute disturbance of neuronal functions may be analysed by assessing electrophysiological features. Extrapolation from in vitro data to humans requires a deep understanding of the test system biology, of the endpoints used, and of the applicability domains of the tests. Moreover, it is important that these be combined in the right way to assess toxicity. Therefore, knowledge on the advantages and disadvantages of all cellular platforms, endpoints, and analytical methods is essential when establishing in vitro test systems for different aspects of neurotoxicity. The elements of a test, and their evaluation, are discussed here in the context of comprehensive prediction of potential hazardous effects of a compound. We summarize the main cellular characteristics underlying neurotoxicity, present an overview of cellular platforms and read-out combinations assessing distinct parts of acute and developmental neurotoxicology, and highlight especially the use of stem cell-based test systems to close gaps in the available battery of tests.

Cell type-specific expression and localization of cytochrome P450 isoforms in tridimensional aggregating rat brain cell cultures

Within the Predict-IV FP7 project a strategy for measurement of in vitro biokinetics was developed, requiring the characterization of the cellular model used, especially regarding biotransformation, which frequently depends on cytochrome P450 (CYP) activity. The extrahepatic in situ CYP-mediated metabolism is especially relevant in target organ toxicity. In this study, the constitutive mRNA levels and protein localization of different CYP isoforms were investigated in 3D aggregating brain cell cultures. CYP1A1, CYP2B1/B2, CYP2D2/4, CYP2E1 and CYP3A were expressed; CYP1A1 and 2B1 represented almost 80% of the total mRNA content. Double-immunolabeling revealed their presence in astrocytes, in neurons, and to a minor extent in oligodendrocytes, confirming the cell-specific localization of CYPs in the brain. These results together with the recently reported formation of an amiodarone metabolite following repeated exposure suggest that this cell culture system possesses some metabolic potential, most likely contributing to its high performance in neurotoxicological studies and support the use of this model in studying brain neurotoxicity involving mechanisms of toxication/detoxication.

Developmental neurotoxicity - challenges in the 21st century and in vitro opportunities

In recent years neurodevelopmental problems in children have increased at a rate that suggests lifestyle factors and chemical exposures as likely contributors. When environmental chemicals contribute to neurodevelopmental disorders developmental neurotoxicity (DNT) becomes an enormous concern. But how can it be tackled? Current animal test- based guidelines are prohibitively expensive, at $ 1.4 million per substance, while their predictivity for human health effects may be limited, and mechanistic data that would help species extrapolation are not available. A broader screening for substances of concern requires a reliable testing strategy, applicable to larger numbers of substances, and sufficiently predictive to warrant further testing. This review discusses the evidence for possible contributions of environmental chemicals to DNT, limitations of the current test paradigm, emerging concepts and technologies pertinent to in vitro DNT testing and assay evaluation, as well as the prospect of a paradigm shift based on 21st century technologies.

Build-a-brain

A major barrier in understanding nervous system development is modeling the cellular interactions that form the human brain. Recently, in the journal Nature, Lancaster et al. (2013) established a protocol for culturing pluripotent stem cell (PSC)-derived "cerebral organoids" that mimics the developing human brain's cellular organization, segregates into distinct brain regions, and models microcephaly.

State-of-the-art of 3D cultures (organs-on-a-chip) in safety testing and pathophysiology

Integrated approaches using different in vitro methods in combination with bioinformatics can (i) increase the success rate and speed of drug development; (ii) improve the accuracy of toxicological risk assessment; and (iii) increase our understanding of disease. Three-dimensional (3D) cell culture models are important building blocks of this strategy which has emerged during the last years. The majority of these models are organotypic, i.e., they aim to reproduce major functions of an organ or organ system. This implies in many cases that more than one cell type forms the 3D structure, and often matrix elements play an important role. This review summarizes the state of the art concerning commonalities of the different models. For instance, the theory of mass transport/metabolite exchange in 3D systems and the special analytical requirements for test endpoints in organotypic cultures are discussed in detail. In the next part, 3D model systems for selected organs--liver, lung, skin, brain--are presented and characterized in dedicated chapters. Also, 3D approaches to the modeling of tumors are presented and discussed. All chapters give a historical background, illustrate the large variety of approaches, and highlight up- and downsides as well as specific requirements. Moreover, they refer to the application in disease modeling, drug discovery and safety assessment. Finally, consensus recommendations indicate a roadmap for the successful implementation of 3D models in routine screening. It is expected that the use of such models will accelerate progress by reducing error rates and wrong predictions from compound testing.

Biological and medical applications of a brain-on-a-chip

The desire to develop and evaluate drugs as potential countermeasures for biological and chemical threats requires test systems that can also substitute for the clinical trials normally crucial for drug development. Current animal models have limited predictivity for drug efficacy in humans as the large majority of drugs fails in clinical trials. We have limited understanding of the function of the central nervous system and the complexity of the brain, especially during development and neuronal plasticity. Simple in vitro systems do not represent physiology and function of the brain. Moreover, the difficulty of studying interactions between human genetics and environmental factors leads to lack of knowledge about the events that induce neurological diseases. Microphysiological systems (MPS) promise to generate more complex in vitro human models that better simulate the organ's biology and function. MPS combine different cell types in a specific three-dimensional (3D) configuration to simulate organs with a concrete function. The final aim of these MPS is to combine different "organoids" to generate a human-on-a-chip, an approach that would allow studies of complex physiological organ interactions. The recent discovery of induced pluripotent stem cells (iPSCs) gives a range of possibilities allowing cellular studies of individuals with different genetic backgrounds (e.g., human disease models). Application of iPSCs from different donors in MPS gives the opportunity to better understand mechanisms of the disease and can be a novel tool in drug development, toxicology, and medicine. In order to generate a brain-on-a-chip, we have established a 3D model from human iPSCs based on our experience with a 3D rat primary aggregating brain model. After four weeks of differentiation, human 3D aggregates stain positive for different neuronal markers and show higher gene expression of various neuronal differentiation markers compared to 2D cultures. Here we present the applications and challenges of this emerging technology.

Chemically defined medium for rat astroglial cells in primary culture

We have developed a serum-free defined medium that supports the growth in primary culture of rat astroglial cells. Cells dissociated from cerebral hemispheres of newborn rats were maintained for 4 days in a basal medium (Waymouth's medium) containing 10% fetal calf serum, which was substituted by a serum-free medium. The basal medium was supplemented with insulin (5 μg/ml) and fatty acid free bovine serum albumin (0.5 mg/ml). Under these conditions the cells proliferate as estimated by cell counts and DNA content; however, growth was less than in Waymouth's medium supplemented with 10% fetal calf serum. In contrast, a very similar morphology was observed between cultures grown in the serum-free or serum-containing media. The serum-free medium allows some maturation of the astroglial cells as shown by the presence of glial fibrillary acidic (GFA) protein, S-100 protein and glutamine synthetase (GS) activity. The astroglial cells can survive and grow in this chemically defined medium for up to 5 weeks. The ability to culture astroglial cells in such a minimal defined medium should facilitate investigations concerning the effects of growth factors on their proliferation and maturation.

State-of-the-art of 3D cultures (organs-on-a-chip) in safety testing and pathophysiology

Integrated approaches using different in vitro methods in combination with bioinformatics can (i) increase the success rate and speed of drug development; (ii) improve the accuracy of toxicological risk assessment; and (iii) increase our understanding of disease. Three-dimensional (3D) cell culture models are important building blocks of this strategy which has emerged during the last years. The majority of these models are organotypic, i.e., they aim to reproduce major functions of an organ or organ system. This implies in many cases that more than one cell type forms the 3D structure, and often matrix elements play an important role. This review summarizes the state of the art concerning commonalities of the different models. For instance, the theory of mass transport/metabolite exchange in 3D systems and the special analytical requirements for test endpoints in organotypic cultures are discussed in detail. In the next part, 3D model systems for selected organs--liver, lung, skin, brain--are presented and characterized in dedicated chapters. Also, 3D approaches to the modeling of tumors are presented and discussed. All chapters give a historical background, illustrate the large variety of approaches, and highlight up- and downsides as well as specific requirements. Moreover, they refer to the application in disease modeling, drug discovery and safety assessment. Finally, consensus recommendations indicate a roadmap for the successful implementation of 3D models in routine screening. It is expected that the use of such models will accelerate progress by reducing error rates and wrong predictions from compound testing.

Validation of whole chick embryo cultures, whole rat embryo cultures and aggregating embryonic brain cell cultures using six pairs of coded compounds

A comparative study was performed to assess the effects of six pairs of coded compounds using cultures of whole chick and rat embryos as well as aggregating brain cell cultures. Developed originally for basic studies in developmental biology, these three culture systems have been adapted for the screening of chemicals in the field of prenatal toxicology. Chick and rat embryos were cultured for 2 days during the early stages of organogenesis. Aggregating cell cultures were prepared from early foetal rat telecephalon and grown for 14 days in a chemically defined medium. Concentration-response relationships were established by treating whole embryos in vitro for 2 days, and aggregating brain cell cultures for 9 days. After decoding the compounds, the results showed that, in the three test systems, specific effects were induced at comparable concentration levels. Similar compound-related malformations could be observed in both chick and rat whole embryo cultures. In aggregating brain cell cultures, neuron- and glia-specific effects could be distinguished. Based on the results obtained in the three in vitro systems, the following concentration ranges were determined for the teratogenic/toxic potencies of the test compounds (in mol/litre): <10(-6): retinoids (Ro 13-6307, Ro 1-5488), 6-aminonicotinamide, ketoconazole; 10(-6)-10(-3): 4-hydroxypyridine, sulfadiazine, sulfanilamide, caffeine, theophylline, metronidazole, methoxyacetic acid; >10(-3): methoxyethanol. In general, the three in vitro test systems were found to provide concordant and complementary data on the toxicity and teratogenicity of a given compound. These data were also comparable with those available from in vivo studies. It is therefore concluded that such a test battery could contribute significantly to risk assessment and to the reduction of in vivo experimentation in reproductive toxicology.

Evaluation of aggregating brain cell cultures for the detection of acute organ-specific toxicity

As part of the ACuteTox project aimed at the development of non-animal testing strategies for predicting human acute oral toxicity, aggregating brain cell cultures (AGGR) were examined for their capability to detect organ-specific toxicity. Previous multicenter evaluations of in vitro cytotoxicity showed that some 20% of the tested chemicals exhibited significantly lower in vitro toxicity as expected from in vivo toxicity data. This was supposed to be due to toxicity at supracellular (organ or system) levels. To examine the capability of AGGR to alert for potential organ-specific toxicants, concentration-response studies were carried out in AGGR for 86 chemicals, taking as endpoints the mRNA expression levels of four selected genes. The lowest observed effect concentration (LOEC) determined for each chemical was compared with the IC20 reported for the 3T3/NRU cytotoxicity assay. A LOEC lower than IC20 by at least a factor of 5 was taken to alert for organ-specific toxicity. The results showed that the frequency of alerts increased with the level of toxicity observed in AGGR. Among the chemicals identified as alert were many compounds known for their organ-specific toxicity. These findings suggest that AGGR are suitable for the detection of organ-specific toxicity and that they could, in conjunction with the 3T3/NRU cytotoxicity assay, improve the predictive capacity of in vitro toxicity testing.

In vitro modeling of central nervous system myelination and remyelination

This review aims to summarize the current techniques to study myelination and remyelination in culture systems. We attempt to put these into historical context, and to identify the strengths and weaknesses of each approach, which vary depending on the experimental question to be tested. We discuss the difficulty and importance of quantification of myelination and in particular remyelination. Finally, we provide our predictions of how these techniques will and should develop in the future.

Ochratoxin A at nanomolar concentration perturbs the homeostasis of neural stem cells in highly differentiated but not in immature three-dimensional brain cell cultures

Ochratoxin A (OTA), a fungal contaminant of basic food commodities, is known to be highly cytotoxic, but the pathways underlying adverse effects at subcytotoxic concentrations remain to be elucidated. Recent reports indicate that OTA affects cell cycle regulation. Therefore, 3D brain cell cultures were used to study OTA effects on mitotically active neural stem/progenitor cells, comparing highly differentiated cultures with their immature counterparts. Changes in the rate of DNA synthesis were related to early changes in the mRNA expression of neural stem/progenitor cell markers. OTA at 10nM, a concentration below the cytotoxic level, was ineffective in immature cultures, whereas in mature cultures it significantly decreased the rate of DNA synthesis together with the mRNA expression of key transcriptional regulators such as Sox2, Mash1, Hes5, and Gli1; the cell cycle activator cyclin D2; the phenotypic markers nestin, doublecortin, and PDGFRα. These effects were largely prevented by Sonic hedgehog (Shh) peptide (500ngml(-1)) administration, indicating that OTA impaired the Shh pathway and the Sox2 regulatory transcription factor critical for stem cell self-renewal. Similar adverse effects of OTA in vivo might perturb the regulation of stem cell proliferation in the adult brain and in other organs exhibiting homeostatic and/or regenerative cell proliferation.

Minocycline promotes remyelination in aggregating rat brain cell cultures after interferon-γ plus lipopolysaccharide-induced demyelination

Minocycline has been shown to inhibit microglia reactivity, and to decrease the severity and progression of experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. It remained to be examined whether minocycline was also able to promote remyelination. In the present study, myelinating aggregating brain cell cultures were used as a model to study the effects of minocycline on microglial reactivity, demyelination, and remyelination. Cultures were treated simultaneously with two inflammatory agents, interferon-γ (IFN-γ) and lipopolysaccharide (LPS), which caused an inflammatory response accompanied by demyelination. The inflammatory response was characterized by microglial reactivity, upregulation of inflammatory cytokines and iNOS, and increased phophorylation of P38 and P44/42 mitogen activated protein (MAP) kinases. Minocycline inhibited microglial reactivity, and attenuated the increased phophorylation of P38 and P44/42 MAP kinases. Demyelination, determined by a decrease in myelin basic protein (MBP) content and immunoreactivity 48 h after the treatment with the inflammatory agents, was not prevented by minocycline. However, 1 week after demyelination was assessed, the MBP content was restored in presence of minocycline, indicating that remyelination was promoted. Concomitantly, in cultures treated with minocycline, the markers of oligodendrocyte precursors cells (OPCs) and immature oligodendrocytes NG2 and O4, respectively, were decreased compared to cultures treated with the inflammatory agents only. These results suggest that minocycline attenuates microglial reactivity and favors remyelination by enhancing the differentiation of OPCs and immature oligodendrocytes.

Preparation, maintenance, and use of serum-free aggregating brain cell cultures

Serum-free aggregating brain cell cultures are free-floating three-dimensional primary cell cultures able to reconstitute spontaneously a histotypic brain architecture to reproduce critical steps of brain development and to reach a high level of structural and functional maturity. This culture system offers, therefore, a unique model for neurotoxicity testing both during the development and at advanced cellular differentiation, and the high number of aggregates available combined with the excellent reproducibility of the cultures facilitates routine test procedures. This chapter presents a detailed description of the preparation, maintenance, and use of these cultures for neurotoxicity studies and a comparison of the developmental characteristics between cultures derived from the telencephalon and cultures derived from the whole brain. For culture preparation, mechanically dissociated embryonic brain tissue is used. The initial cell suspension, composed of neural stem cells, neural progenitor cells, immature postmitotic neurons, glioblasts, and microglial cells, is kept in a serum-free, chemically defined medium under continuous gyratory agitation. Spherical aggregates form spontaneously and are maintained in suspension culture for several weeks. Within the aggregates, the cells rearrange and mature, reproducing critical morphogenic events, such as migration, proliferation, differentiation, synaptogenesis, and myelination. For experimentation, replicate cultures are prepared by the randomization of aggregates from several original flasks. The high yield and reproducibility of the cultures enable multiparametric endpoint analyses, including "omics" approaches.

Inflammatory responses in aggregating rat brain cell cultures subjected to different demyelinating conditions

To study inflammatory reactions occurring in relation to demyelination, aggregating rat brain cell cultures were subjected to three different demyelinating insults, i.e., (i) lysophosphatidylcholine (LPC), (ii) interferon-gamma combined with lipopolysaccharide (IFN-gamma+LPS), and (iii) anti-MOG antibodies plus complement (alpha-MOG+C). Demyelination was assessed by measuring the expression of myelin basic protein (MBP) and myelin oligodendrocyte glycoprotein (MOG), and the activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP). The accompanying inflammatory reactions were examined by the quantification of microglia-specific staining, by immunostaining for glial fibrillary acidic protein (GFAP), and by measuring the mRNA expression of a panel of inflammation-related genes. It was found that all three demyelinating insults decreased the expression of MBP and MOG, and induced microglial reactivity. LPC and alpha-MOG+C, but not IFN-gamma+LPS, decreased CNP activity; they also caused the appearance of macrophagic microglia, and increased GFAP staining indicating astrogliosis. LPC affected also the integrity of neurons and astrocytes. LPC and IFN-gamma+LPS upregulated the expression of the inflammation-related genes IL-6, TNF-alpha, Ccl5, Cxcl1, and iNOS, although to different degrees. Other inflammatory markers were upregulated by only one of the three insults, e.g., Cxcl2 by LPC; IL-1beta and IL-15 by IFN-gamma+LPS; and IFN-gamma by alpha-MOG+C. These findings indicate that each of the three demyelinating insults caused distinct patterns of demyelination and inflammatory reactivity, and that of the demyelinating agents tested only LPC exhibited general toxicity.

Optimization of chemically defined cell culture media--replacing fetal bovine serum in mammalian in vitro methods

Quality assurance is becoming increasingly important. Good laboratory practice (GLP) and good manufacturing practice (GMP) are now established standards. The biomedical field aims at an increasing reliance on the use of in vitro methods. Cell and tissue culture methods are generally fast, cheap, reproducible and reduce the use of experimental animals. Good cell culture practice (GCCP) is an attempt to develop a common standard for in vitro methods. The implementation of the use of chemically defined media is part of the GCCP. This will decrease the dependence on animal serum, a supplement with an undefined and variable composition. Defined media supplements are commercially available for some cell types. However, information on the formulation by the companies is often limited and such supplements can therefore not be regarded as completely defined. The development of defined media is difficult and often takes place in isolation. A workshop was organised in 2009 in Copenhagen to discuss strategies to improve the development and use of serum-free defined media. In this report, the results from the meeting are discussed and the formulation of a basic serum-free medium is suggested. Furthermore, recommendations are provided to improve information exchange on newly developed serum-free media.

Stem cell-derived dopamine neurons for brain repair in Parkinson’s disease

One of the prospects for a curative treatment for Parkinson’s disease is to replace the lost dopaminergic neurons. Preclinical and clinical trials have demonstrated that dissected fetal dopaminergic neurons have the potential to markedly improve motor function in animal models and Parkinson’s disease patients. However, this source of cells will never be sufficient to use as a widespread therapy. Over the last 20 years, scientists have been searching for other reliable sources of midbrain dopamine neurons, and stem cells appear to be strong candidates. This article reviews the potential of different types of stem cells, from embryonic to adult to induced pluripotent stem cells, to see how well the cells can be differentiated into fully functional dopamine neurons, which cells might be the best candidates and how much more research is required before stem cell technology might be translated to a clinical therapy for Parkinson’s disease.

Effects of Low-dose X-irradiation on Mouse-brain Aggregation Cultures

Biochemical and morphological differentiation in reaggregating mouse-brain cell cultures after low-dose radiation (0.5 Gy) in vitro was studied. Cells were irradiated on culture day 2, corresponding to embryonic day 15-16, and different glial and neuronal markers were followed through development to postnatal day 40. The shape and size of irradiated aggregates were more irregular and smaller compared with controls. Total amounts of DNA and protein were significantly lower in irradiated aggregates than in controls between days 8 and 20. After 30 days in culture activities of the glial markers glutamine synthetase (GS) and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) were lower in X-irradiated aggregates than in controls. However, after 40 days the CNP activity in irradiated aggregates increased to levels above those of the controls. Irradiated and control aggregates did not differ significantly in neuronal marker enzyme activities, i.e. choline acetyltransferase (ChAT), acetylcholine esterase (AChE) and glutamic acid decarboxylase (GAD) measured on a per mg protein basis. On days 20 and 30 the amount of nerve growth factor (NGF) was two-fold higher in irradiated aggregates compared with non-irradiated ones, suggesting that, after irradiation, surviving cells in culture were induced to produce more NGF. After 40 days the amount of NGF in irradiated aggregates had decreased to the level found in the control aggregates.

Effects of the PPAR-beta agonist GW501516 in an in vitro model of brain inflammation and antibody-induced demyelination

Background

Brain inflammation plays a central role in numerous brain pathologies, including multiple sclerosis (MS). Microglial cells and astrocytes are the effector cells of neuroinflammation. They can be activated also by agents such as interferon-γ (IFN-γ) and lipopolysaccharide (LPS). Peroxisome proliferator-associated receptor (PPAR) pathways are involved in the control of the inflammatory processes, and PPAR-β seems to play an important role in the regulation of central inflammation. In addition, PPAR-β agonists were shown to have trophic effects on oligodendrocytes in vitro, and to confer partial protection in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. In the present work, a three-dimensional brain cell culture system was used as in vitro model to study antibody-induced demyelination and inflammatory responses. GW 501516, a specific PPAR-β agonist, was examined for its capacity to protect from antibody-mediated demyelination and to prevent inflammatory responses induced by IFN-γ and LPS.

Methods

Aggregating brain cells cultures were prepared from embryonal rat brain, and used to study the inflammatory responses triggered by IFN-γ and LPS and by antibody-mediated demyelination induced by antibodies directed against myelin-oligodendrocyte glycoprotein (MOG). The effects of GW 501516 on cellular responses were characterized by the quantification of the mRNA expression of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), inducible NO synthase (i-NOS), PPAR-β, PPAR-γ, glial fibrillary acidic protein (GFAP), myelin basic protein (MBP), and high molecular weight neurofilament protein (NF-H). GFAP expression was also examined by immunocytochemistry, and microglial cells were visualized by isolectin B4 (IB4) and ED1 labeling.

Results

GW 501516 decreased the IFN-γ-induced up-regulation of TNF-α and iNOS in accord with the proposed anti-inflammatory effects of this PPAR-β agonist. However, it increased IL-6 m-RNA expression. In demyelinating cultures, reactivity of both microglial cells and astrocytes was observed, while the expression of the inflammatory cytokines and iNOS remained unaffected. Furthermore, GW 501516 did not protect against the demyelination-induced changes in gene expression.

Conclusion

Although GW 501516 showed anti-inflammatory activity, it did not protect against antibody-mediated demyelination. This suggests that the protective effects of PPAR-β agonists observed in vivo can be attributed to their anti-inflammatory properties rather than to a direct protective or trophic effect on oligodendrocytes.

Quetiapine facilitates oligodendrocyte development and prevents mice from myelin breakdown and behavioral changes

Recent neuroimaging and postmortem studies have reported abnormalities in white matter of schizophrenic brains, suggesting the involvement of oligodendrocytes in the etiopathology of schizophrenia. This view is being supported by gene microarray studies showing the downregulation of genes related to oligodendrocyte function and myelination in schizophrenic brain compared to control subjects. However, there is currently little information available on the response of oligodendrocytes to antipsychotic drugs (APDs), which could be invaluable for corroborating the oligodendrocyte hypothesis. In this study we found: (1) quetiapine (QUE, an atypical APD) treatment in conjunction with addition of growth factors increased the proliferation of neural progenitors isolated from the cerebral cortex of embryonic rats; (2) QUE directed the differentiation of neural progenitors to oligodendrocyte lineage through extracellular signal-related kinases; (3) addition of QUE increased the synthesis of myelin basic protein and facilitated myelination in rat embryonic cortical aggregate cultures; (4) chronic administration of QUE to C57BL/6 mice prevented cortical demyelination and concomitant spatial working memory impairment induced by cuprizone, a neurotoxin. These findings suggest a new neural mechanism of antipsychotic action of QUE, and help to establish a role for oligodendrocytes in the etiopathology and treatment of schizophrenia.

TRANSIENT MAINTENANCE IN BIOREACTOR IMPROVES HEALTH OF NEURONAL CELLS

To examine whether a neuronal cell suspension can be held in vitro for a relatively short period without compromising survival rates and functionality, we have set up an experimental protocol planning 24 h of suspension culture in a rotary wall vessel (RWV) bioreactor before plating in a conventional adherent system. Apoptosis measurement and activated caspase-8, -9, and -3 detection have demonstrated that survey of the cells was not affected. The activity of major antioxidant enzymes (AOE), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT), was significantly decreased in RWV-maintained cells. A significant decrease of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) is coupled with a level of activated nuclear factor-kappaB (NF-kappaB) protein significantly lower in RVW cells than in the control. On the contrary, the level of IL-6 expression did not change between the test and the control. A significant up-regulation of growth-associated protein-43 (GAP-43), peroxisome proliferator-activated receptor-beta/delta (PPARbeta/delta), and acyl-CoA synthetase 2 (ACS2) in RWV cells has been detected. We provide the evidence that primary neuronal cells, at an early stage of development, can be maintained in a suspension condition before adherent plating. This experimental environment does not induce detrimental effects but may have an activator role, leading cells to development and maturation in a tridimensional state.

Effects of simulated microgravity on the development and maturation of dissociated cortical neurons

Although a wealth of evidence supports the hypothesis that some functions of the nervous system may be altered during exposure to microgravity, the possible changes in basic neuronal physiology are not easy to assess. Indeed, few studies have examined whether microgravity affects the development of neurons in culture. In the present study, a suspension of dissociated cortical cells from rat embryos were exposed to 24 h of simulated microgravity before plating in a normal adherent culture system. Both preexposed and control cells were used after a period of 7-10 d in vitro. The vitality and the level of reactive oxygen species of cultures previously exposed did not differ from those of normal cultures. Cellular characterization by immunostaining with a specific antibody displayed normal neuronal phenotype in control cells, whereas pretreatment in simulated microgravity revealed an increase of glial fibrillary acidic protein fluorescence in the elongated stellate glial cells. Electrophysiological recording indicated that the electrical properties of neurons preexposed were comparable with those of controls. Overall, our results indicate that a short time of simulated microgravity preexposure does not affect dramatically the ability of dissociated neural cells to develop and differentiate in an adherent culture system.

Expression of thyroid hormone receptor isoforms in the oligodendrocyte lineage

Thyroid hormone (T3) regulates brain development and function and in particular ensures normal myelination. Animal models and in vitro systems have been employed to demonstrate the effects of T3, which acts via nuclear hormone receptors. T3 receptors (TRs) are transcription factors that activate or suppress target gene expression, such as myelin basic protein (MBP), in a hormone-dependent or -independent fashion. Two distinct genes, TR alpha and TR beta, encode several receptor isoforms with specific functions. This overview summarizes current knowledge on the cellular expression and the role of these isoforms and also examines the action of T3 on oligodendrocyte lineage cell types at defined developmental stages. Re-expression of TRs and also that of other transcription factors in oligodendrocytes may constitute some of the metabolic changes required for succesfull remyelination in the adult central nervous system after demyelinating lesions.

Characterization of long-term mouse brain aggregating cultures: Evidence for maintenance of neural precursor cells

An extensive characterization of fetal mouse brain cell aggregates has been performed using immunohistochemical and stereological methods. Single cell suspensions from mechanically dissociated cortex and hippocampus were cultured in serum-free, B27-supplemented medium under constant gyratory agitation for up to 56 days. Three-dimensional aggregates started to form immediately after seeding and reached a final average size of 500 microm in diameter. Among the cell types identified, neurons were the most abundant cells in the aggregates, followed by astrocytes, microglia, and oligodendrocytes. Western blotting for synaptophysin and immunostaining for neurotransmitter-related molecules indicated the presence of well-defined phenotypic characteristics of the neurons in this culture system, suggesting functionality. Proliferating cells, many with neural precursor cell properties, were seen throughout the culture period and could be isolated from the aggregates even after 2 months in culture. Neural precursor cells were isolated from the aggregates after more than 1 month in culture; these cells were successfully differentiated into neurons, astrocytes, and oligodendrocytes. The aggregate culture system may provide a versatile tool for molecular dissection of processes identified in mouse models, including transgenic animals and manipulation of neural precursor cells.

Regulated exocytosis of an H+/myo-inositol symporter at synapses and growth cones

Phosphoinositides, synthesized from myo-inositol, play a critical role in the development of growth cones and in synaptic activity. As neurons cannot synthesize inositol, they take it up from the extracellular milieu. Here, we demonstrate that, in brain and PC12 cells, the recently identified H(+)/myo-inositol symporter HMIT is present in intracellular vesicles that are distinct from synaptic and dense-core vesicles. We further show that HMIT can be triggered to appear on the cell surface following cell depolarization, activation of protein kinase C or increased intracellular calcium concentrations. HMIT cell surface expression takes place preferentially in regions of nerve growth and at varicosities and leads to increased myo-inositol uptake. The symporter is then endocytosed in a dynamin-dependent manner and becomes available for a subsequent cycle of stimulated exocytosis. HMIT is thus expressed in a vesicular compartment involved in activity-dependent regulation of myo-inositol uptake in neurons. This may be essential for sustained signaling and vesicular traffic activities in growth cones and at synapses.

Aggregating neural cell cultures

When freshly dissociated embryonic tissues are kept under gyratory agitation, the cells aggregate to form three-dimensional spheroids in which the cells can migrate and organize themselves, attaining maximal cellular differentiation after weeks of culture. The three-dimensional architecture of the aggregates permits direct cell-to-cell interactions and the formation of a natural cell matrix, which is fundamental to the acquisition of the histotypic properties of the aggregates. This unit describes protocols for preparing forebrain cells from embryonic rodents for aggregating cultures and maintaining these cultures to the differentiated state.

Ammonium-induced impairment of axonal growth is prevented through glial creatine

Hyperammonemia in neonates and infants affects brain development and causes mental retardation. We report that ammonium impaired cholinergic axonal growth and altered localization and phosphorylation of intermediate neurofilament protein in rat reaggregated brain cell primary cultures. This effect was restricted to the phase of early maturation but did not occur after synaptogenesis. Exposure to NH4Cl decreased intracellular creatine, phosphocreatine, and ADP. We demonstrate that creatine cotreatment protected axons from ammonium toxic effects, although this did not restore high-energy phosphates. The protection by creatine was glial cell-dependent. Our findings suggest that the means to efficiently sustain CNS creatine concentration in hyperammonemic neonates and infants should be assessed to prevent impairment of axonogenesis and irreversible brain damage.

Alteration of amino acid metabolism in neuronal aggregate cultures exposed to hypoglycaemic conditions

The neuronal effects of glucose deficiency on amino acid metabolism was studied on three-dimensional cultures of rat telencephalon neurones. Transient (6 h) exposure of differentiated cultures to low glucose (0.25 mm instead of 25 mm) caused irreversible damage, as judged by the marked decrease in the activities of two neurone-specific enzymes and lactate dehydrogenase, 1 week after the hypoglycemic insult. Quantification of amino acids and ammonia in the culture media supernatants indicated increased amino acid utilization and ammonia production during glucose-deficiency. Measurement of intracellular amino acids showed decreased levels of alanine, glutamine, glutamate and GABA, while aspartate was increased. Added lactate (11 mm) during glucose deficiency largely prevented the changes in amino acid metabolism and ammonia production, and attenuated irreversible damage. Higher media levels of glutamine (4 mm instead of 0.25 mm) during glucose deprivation prevented the decrease of intracellular glutamate and GABA, while it further increased intracellular aspartate, ammonia production and neuronal damage. Both lactate and glutamine were readily oxidized in these neuronal cultures. The present results suggest that in neurones, glucose deficiency enhances amino acid deamination at the expense of transamination reactions. This results in increased ammonia production and neuronal damage.

Ensaculin (KA-672 HCl): a multitransmitter approach to dementia treatment

Ensaculin, a novel benzopyranone substituted with a piperazine moiety, showed memory-enhancing effects in paradigms of passive and conditioned avoidance in both normal and artificially amnesic rodents. It exhibited neuroprotective activities in an NMDA toxicity model and neurotrophic effects in primary cultured rat brain cells. The compound could be characterized as a weak NMDA receptor-operated channel blocker. In receptor-binding studies, ensaculin was found to have high affinities to serotonergic 5-HT(1A) and 5-HT(7) receptors, adrenergic alpha(1), and dopaminergic D(2) and D(3) receptors. Due to its unique pharmacodynamic profile, ensaculin may have potential as an antidementia agent acting on various transmitter systems.