Human cord blood-derived neural stem cell line—Possible implementation in studying neurotoxicity

In vitro models of medulloblastoma: Choosing the right tool for the job

The recently-defined four molecular subgroups of medulloblastoma have required updating of our understanding of in vitro models to include molecular classification and risk stratification features from clinical practice. This review seeks to build a more comprehensive picture of the in vitro systems available for modelling medulloblastoma. The subtype classification and molecular characterisation for over 40 medulloblastoma cell-lines has been compiled, making it possible to identify the strengths and weaknesses in current model systems. Less than half (18/44) of established medulloblastoma cell-lines have been subgrouped. The majority of the subgrouped cell-lines (11/18) are Group 3 with MYC-amplification. SHH cell-lines are the next most common (4/18), half of which exhibit TP53 mutation. WNT and Group 4 subgroups, accounting for 50% of patients, remain underrepresented with 1 and 2 cell-lines respectively. In vitro modelling relies not only on incorporating appropriate tumour cells, but also on using systems with the relevant tissue architecture and phenotype as well as normal tissues. Novel ways of improving the clinical relevance of in vitro models are reviewed, focusing on 3D cell culture, extracellular matrix, co-cultures with normal cells and organotypic slices. This paper champions the establishment of a collaborative online-database and linked cell-bank to catalyse preclinical medulloblastoma research.

Joint analysis of extracellular spike waveforms and neuronal network bursts

BACKGROUND

Neuronal networks are routinely assessed based on extracellular electrophysiological microelectrode array (MEA) measurements by spike sorting, and spike and burst statistics. We propose to jointly analyze sorted spikes and detected bursts, and hypothesize that the obtained spike type compositions of the bursts can provide new information on the functional networks.

NEW METHOD

Spikes are detected and sorted to obtain spike types and bursts are detected. In the proposed joint analysis, each burst spike is associated with a spike type, and the spike type compositions of the bursts are assessed.

RESULTS

The proposed method was tested with simulations and MEA measurements of in vitro human stem cell derived neuronal networks under different pharmacological treatments. The results show that the treatments altered the spike type compositions of the bursts. For example, 6-cyano-7-nitroquinoxaline-2,3-dione almost completely abolished two types of spikes which had composed the bursts in the baseline, while bursts of spikes of two other types appeared more frequently. This phenomenon was not observable by spike sorting or burst analysis alone, but was revealed by the proposed joint analysis.

COMPARISON WITH EXISTING METHODS

The existing methods do not provide the information obtainable with the proposed method: for the first time, the spike type compositions of bursts are analyzed.

CONCLUSIONS

We showed that the proposed method provides useful and novel information, including the possible changes in the spike type compositions of the bursts due to external factors. Our method can be employed on any data exhibiting sortable action potential waveforms and detectable bursts.

An Overview on Human Umbilical Cord Blood Stem Cell-Based Alternative In Vitro Models for Developmental Neurotoxicity Assessment

The developing brain is found highly vulnerable towards the exposure of different environmental chemicals/drugs, even at concentrations, those are generally considered safe in mature brain. The brain development is a very complex phenomenon which involves several processes running in parallel such as cell proliferation, migration, differentiation, maturation and synaptogenesis. If any step of these cellular processes hampered due to exposure of any xenobiotic/drug, there is almost no chance of recovery which could finally result in a life-long disability. Therefore, the developmental neurotoxicity (DNT) assessment of newly discovered drugs/molecules is a very serious concern among the neurologists. Animal-based DNT models have their own limitations such as ethical concerns and lower sensitivity with less predictive values in humans. Furthermore, non-availability of human foetal brain tissues/cells makes job more difficult to understand about mechanisms involve in DNT in human beings. Although, the use of cell culture have been proven as a powerful tool for DNT assessment, but many in vitro models are currently utilizing genetically unstable cell lines. The interpretation of data generated using such terminally differentiated cells is hard to extrapolate with in vivo situations. However, human umbilical cord blood stem cells (hUCBSCs) have been proposed as an excellent tool for alternative DNT testing because neuronal development from undifferentiated state could exactly mimic the original pattern of neuronal development in foetus when hUCBSCs differentiated into neuronal cells. Additionally, less ethical concern, easy availability and high plasticity make them an attractive source for establishing in vitro model of DNT assessment. In this review, we are focusing towards recent advancements on hUCBSCs-based in vitro model to understand DNTs.

In vitro models for neurotoxicology research

The nervous system has a highly complex organization, including many cell types with multiple functions, with an intricate anatomy and unique structural and functional characteristics; the study of its (dys)functionality following exposure to xenobiotics, neurotoxicology, constitutes an important issue in neurosciences.

Which form of collagen is suitable for nerve cell culture?

In this study, we investigated the effects of hydrolyzed and non-hydrolyzed collagen and two-dimensional and three-dimensional collagen matrices on cell survival, attachment and neurite outgrowth of primary cultured nerve cells using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay and inverted microscopy. Hydrolyzed collagen facilitated nerve cell survival and neurite outgrowth, but it had no obvious influences on cell attachment. In contrast, non-hydrolyzed two-dimensional collagen matrix had no obvious effects on neurite outgrowth. These findings suggest that hydrolyzed collagen is an ideal nerve cell culture media.

Human pluripotent stem cells for modeling toxicity

The development of xenobiotics, driven by the demand for therapeutic, domestic and industrial uses continues to grow. However, along with this increasing demand is the risk of xenobiotic-induced toxicity. Currently, safety screening of xenobiotics uses a plethora of animal and in vitro model systems which have over the decades proven useful during compound development and for application in mechanistic studies of xenobiotic-induced toxicity. However, these assessments have proven to be animal-intensive and costly. More importantly, the prevalence of xenobiotic-induced toxicity is still significantly high, causing patient morbidity and mortality, and a costly impediment during drug development. This suggests that the current models for drug safety screening are not reliable in toxicity prediction, and the results not easily translatable to the clinic due to insensitive assays that do not recapitulate fully the complex phenotype of a functional cell type in vivo. Recent advances in the field of stem cell research have potentially allowed for a readily available source of metabolically competent cells for toxicity studies, derived using human pluripotent stem cells harnessed from embryos or reprogrammed from mature somatic cells. Pluripotent stem cell-derived cell types also allow for potential disease modeling in vitro for the purposes of drug toxicology and safety pharmacology, making this model possibly more predictive of drug toxicity compared with existing models. This article will review the advances and challenges of using human pluripotent stem cells for modeling metabolism and toxicity, and offer some perspectives as to where its future may lie.

Transferability of a modified embryonic stem cell test using a new endpoint for developmental neurotoxicity

We developed and analyzed a new surrogate endpoint of the mouse embryonic stem cell test (EST) for developmental neurotoxicity. To determine the sensitivity, specificity, and transferability of the new endpoint, a pre-validation team from three independent laboratories optimized and standardized the protocol for neuronal differentiation of mouse embryonic stem cells (mESCs) by measuring the neuronal differentiation rates of mESCs under different culture conditions, such as the presence or absence of basic fibroblast growth factor (bFGF) in the growth media and varying lengths of culture. In addition, a component ratio of neuronal cells was measured by using flow cytometry analysis of β-III tubulin (Tuj1)-positive cells and real-time polymerase chain reaction analysis of microtubule-associated protein 2 (MAP2) mRNA. Our results showed that the best growth was achieved by culturing mESCs for 12 d in N2B27 medium without bFGF or ascorbic acid. Lead (II) acetate and aroclor 1254 were used to test the usefulness of the new endpoint. When we used the known ID(50) values for lead (II) acetate in the EST model, it was classified as non-embryotoxic; however, when we used the new ID(50) values that we determined in this study, it was classified as weakly embryotoxic. Aroclor 1254 and penicillin G were also classified as weakly embryotoxic and non-embryotoxic compounds, respectively, when cardiac and neuronal differentiation ID(50) values were used. Therefore, our new surrogate endpoint for developmental neurotoxicity is not only sensitive and specific but also transferable among laboratories.

Neural stem cells for developmental neurotoxicity studies

The developing nervous system is particularly susceptible to toxicants, and exposure during development may result in long-lasting neurological impairments. The damage can range from subtle to severe, and it may impose substantial burdens on affected individuals, their families, and society. Given the little information available on developmental neurotoxicity (DNT) and the growing number of chemicals that need to be tested, new testing strategies and approaches are necessary to identify developmental neurotoxic agents with speed, reliability, and respect for animal welfare. So far, there are no validated alternative methods for DNT testing. Recently, neural stem/progenitor cells have been proposed as relevant models for alternative DNT testing. In this chapter, we provide detailed protocols for culturing neural stem cells (NSCs), in vitro experimental models, including primary cultures of rat and human embryonic NSCs, rat and mouse adult NSCs, as well as the mouse NSC line C17.2 that we have implemented and successfully used for neurotoxicity studies.

Artificial human tissues from cord and cord blood stem cells for multi-organ regenerative medicine: viable alternatives to animal in vitro toxicology

New medicinal products and procedures must meet very strict safety criteria before being applied for use in humans. The laboratory procedures involved require the use of large numbers of animals each year. Furthermore, such investigations do not always give an accurate translation to the human setting. Here, we propose a viable alternative to animal testing, which uses novel technology featuring human cord and cord blood stem cells. With over 130 million children born each year, cord and cord blood remains the most widely available alternative to the use of animals or cadaveric human tissues for in vitro toxicology.

A human stem cell-based model for identifying adverse effects of organic and inorganic chemicals on the developing nervous system

The aim of our study was to investigate whether a human neural stem cell line derived from umbilical cord blood (HUCB-NSC) can serve as a reliable test model for developmental neurotoxicity (DNT). We assessed the sensitivity of HUCB-NSCs at different developmental stages to a panel of neurotoxic (sodium tellurite, methylmercury chloride, cadmium chloride, chlorpyrifos, and L-glutamate) and non-neurotoxic (acetaminophen, theophylline, and D-glutamate) compounds. In addition, we investigated the effect of some compounds on key neurodevelopmental processes like cell proliferation, apoptotic cell death, and neuronal and glial differentiation. Less differentiated HUCB-NSCs were generally more sensitive to neurotoxicants, with the notable exception of L-glutamate, which showed a higher toxicity to later stages. The relative potencies of the compounds were: cadmium chloride > methylmercury chloride >> chlorpyrifos >> L-glutamate. Fifty nanomolar methylmercury chloride (MeHgCl) inhibited proliferation and induced apoptosis in early-stage cells. At the differentiated stage, 1 muM MeHgCl induced selective loss of S100 beta-expressing astrocytic cells. One millimolar L-glutamate did not influence the early stages of HUCB-NSC development, but it affected late stages of neuronal differentiation. A valuable system for in vitro DNT assessment should be able to discriminate between neurotoxic and non-neurotoxic compounds and show different susceptibilities to chemicals according to developmental stage and cell lineage. Although not exhaustive, this work shows that the HUCB-NSC model fulfils these criteria and may serve as a human in vitro model for DNT priority setting.

An Integrated Decision-tree Testing Strategy for Repeat Dose Toxicity with Respect to the Requirements of the EU REACH Legislation

This paper presents some results of a joint research project conducted by FRAME and Liverpool John Moores University, and sponsored by Defra, on the status of alternatives to animal testing with regard to the European Union REACH (Registration, Evaluation and Authorisation of Chemicals) system for the safety testing and risk assessment of chemicals. The project covered all the main toxicity end-points associated with REACH. This paper focuses on the use of alternative (non-animal) methods (both in vitro and in silico) for repeat dose (sub-acute, sub-chronic and chronic) toxicity testing. It reviews the limited number of in silico and in vitro tests available for this endpoint, and outlines new technologies which could be used in the future, e.g. the use of biomarkers and the ‘omics’ technologies. An integrated testing strategy is proposed, which makes use of as much non-animal data as possible, before any essential in vivo studies are performed. Although none of the non-animal tests are currently undergoing validation, their results could help to reduce the number of animals required for testing for repeat dose toxicity.

Micro-stamped surfaces for the patterned growth of neural stem cells

We present a method for patterning neural stem cells based on pre-patterning polypeptides on a cell-repellent surface (poly(ethylene) oxide-like, PEO-like, plasma-deposited films). The method ensures cell attachment and stability for several weeks, as well as it allows cell migration and differentiation. Various patterns of approximately 1 nm thick cell adhesive poly-L-lysine (PLL) have been created on a cell-repellent PEO-like matrix by microcontact printing using different array configurations and printing conditions. The cell-repellent property of PEO-like film determined the confinement of the cells on the printed patterns. Optimization of the printing method showed that the most homogeneous patterns over large areas were obtained using PLL diluted in carbonate buffer (100mM) at pH 8.4. Neural stem cells cultured on the PLL patterns in low serum and in differentiating medium over 20 days exhibited a good confinement to the polypeptide domains. The number of cells attached increased linearly with the micro-stamped PLL area. The cells were able to extend random axon-like projections to the outside of the patterns and presented high amount of ramifications when cultured in differentiating medium. Migration and axon-like outgrowth have been successfully guided by means of an interconnected squares configuration. The surfaces are suitable for controlling the patterning of stem cells and provide a platform for the assessment of the way how different cell arrangements and culture conditions influence cell interactions and cell developmental processes.

An Integrated Decision-tree Testing Strategy for Repeat Dose Toxicity with Respect to the Requirements of the EU REACH Legislation

This paper presents some results of a joint research project conducted by FRAME and Liverpool John Moores University, and sponsored by Defra, on the status of alternatives to animal testing with regard to the European Union REACH (Registration, Evaluation and Authorisation of Chemicals) system for the safety testing and risk assessment of chemicals. The project covered all the main toxicity end-points associated with REACH. This paper focuses on the use of alternative (non-animal) methods (both in vitro and in silico) for repeat dose (sub-acute, sub-chronic and chronic) toxicity testing. It reviews the limited number of in silico and in vitro tests available for this endpoint, and outlines new technologies which could be used in the future, e.g. the use of biomarkers and the ‘omics’ technologies. An integrated testing strategy is proposed, which makes use of as much non-animal data as possible, before any essential in vivo studies are performed. Although none of the non-animal tests are currently undergoing validation, their results could help to reduce the number of animals required for testing for repeat dose toxicity.

Workgroup report: incorporating in vitro alternative methods for developmental neurotoxicity into international hazard and risk assessment strategies

This is the report of the first workshop on Incorporating In Vitro Alternative Methods for Developmental Neurotoxicity (DNT) Testing into International Hazard and Risk Assessment Strategies, held in Ispra, Italy, on 19-21 April 2005. The workshop was hosted by the European Centre for the Validation of Alternative Methods (ECVAM) and jointly organized by ECVAM, the European Chemical Industry Council, and the Johns Hopkins University Center for Alternatives to Animal Testing. The primary aim of the workshop was to identify and catalog potential methods that could be used to assess how data from in vitro alternative methods could help to predict and identify DNT hazards. Working groups focused on two different aspects: a) details on the science available in the field of DNT, including discussions on the models available to capture the critical DNT mechanisms and processes, and b) policy and strategy aspects to assess the integration of alternative methods in a regulatory framework. This report summarizes these discussions and details the recommendations and priorities for future work.

Function of ID1 protein in human cord blood-derived neural stem-like cells

The effect of dominant-negative regulator of basic helix-loop-helix (bHLH) transcription factors, an ID1 protein, on growth and differentiation of neural stem-like cell line derived from human umbilical cord blood (HUCB-NSC) was investigated. This nontransformed, mesodermal germ layer-originated line contains high levels of ID1 protein, whose intercellular distribution reflects HUCB-NSC differentiation status. Whereas cells remained undifferentiated and self-renewing in serum-free (SF) cultures, ID1 protein, although highly expressed, did not attain cell nuclei and was localized mainly in cytoplasm. In long-term-expanded cultures of partially committed (primed) HUCB-NSC grown in a low serum concentration (LS cultures) ID1 protein became translocated toward cell nuclei. Further neuronal differentiation of the cells, either spontaneous in the presence of serum or induced by neuromorphogens (dBcAMP, RA), resulted in almost complete depletion of ID1 mRNA and protein. Accordingly, HUCB-NSC transfectants overexpressing the ID1 gene were significantly inhibited in their differentiation. Notably, only neuronal and not glial development was affected after ID1 overexpression. A similar gain-of-function effect of ID1 transfection was observed in human NSC-like line (DEV) of medullobastoma origin, which is constitutively devoid of ID1 expression. Thus, our results on HUCB-NSC confirm further its neural-specific behavior and the crucial role of ID1 protein as a potent negative regulator of neural stem cell differentiation, pointing out that this protein distribution between cytoplasmic and nuclear cell compartments can be one of the most important steps in differentiation signal transduction.

Neuronal differentiation of human umbilical cord blood neural stem-like cell line

The expanding population of neural stem/progenitor cells can be selected from human cord blood nonhematopoietic (CD34-negative) mononuclear fraction. Due to repeated expansion and selection of these cells we have established the first clonogenic, nonimmortalized human umbilical cord blood neural stem-like cell (HUCB-NSC) line. This line can be maintained at different stages of neural progenitor development by the presence of trophic factors, mitogens and neuromorphogens in culture media. Neurogenic potential of HUCB-NSC was established for serum-free and low-serum cultured cells. Commitment of HUCB-NSC by serum was shown to be important for the optimal response to the signals provided by surrounding environment in vitro. Enhanced neuronal differentiation induced by dBcAMP treatment was accompanied by expression of several functional proteins including glutamatergic, GABAergic, dopamine, serotonin and acetylcholine receptors, which was shown by microarray, immunocytochemistry and electrophysiology. Electrophysiological studies, whole-cell patch-clamp recordings, revealed in differentiated HUCB-NSC two types of voltage-sensitive and several ligand-gated currents typical for neuronal cells. The above HUCB-NSC characteristic conceivably implicates that cord blood-derived progenitors could be effectively differentiated into functional neuron-like cells in vitro.

Early appearance of stem/progenitor cells with neural-like characteristics in human cord blood mononuclear fraction cultured in vitro

OBJECTIVE

The exposure of human umbilical cord blood mononuclear cells devoid of hematopoietic stem cells (HUCB-MNCsCD34-) to defined culture condition promotes their conversion into neural lineage. We have asked the question if observed fate change of HUCB-MNCsCD34- results from direct conversion of hematopoietic precursors into neural-like phenotypes due to expression of overlapping genetic program or, alternatively, these neural phenotypes arise from sequential differentiation of more primitive progenitors (embryonic-like cells) preexisting in HUCB-MNCsCD34- fraction.

MATERIALS AND METHODS

HUCB-MNCs negatively selected for CD34 antigens were cultured in vitro up to 14 days. Changes in stem/neural cell genes and proteins were successively evaluated during this period and after evoked neuronal differentiation of cells in the presence of RA or BDNF or cocultured with neonatal rat brain astrocytes.

RESULTS

Freshly isolated HUCB-MNCsCD34- expressed pluripotent cell markers: Oct3/4, Sox2, and Rex1 genes. During 24 hours of culture the frequency of Oct3/4 immunopositive cells increased markedly with parallel enlargement of "side population" and CD133+ cell appearance. Concomitantly, cultured cells start to form aggregates and express pro-neural genes, i.e., enhanced Sox2, OTX1, Nestin, GFAP, and NF-200. During the next days of culture immunoreactions for beta-tubulin III, MAP2, GFAP, S100beta, Doublecortin, and GalC were induced with reciprocal lowering of stem cell gene and protein markers. At this stage cells successively adhered to the bottom, dispersed, and decreased proliferation rate (Ki67 expression). Additional treatments with neuromorphogenes or coculturing with rat brain primary culture induced further differentiation of these neural precursors toward more advanced neuronal phenotypes.

CONCLUSIONS

HUCB-MNCs(CD34-) fraction contains embryonic-like stem/progenitor cells which increase rapidly but transiently in culture, then differentiate spontaneously after cell aggregate adhesion toward neural lineage. Neurally promoted cells from 10-14 DIV culture acquire three main neural-like phenotypes, i.e., neurons, astrocytes, and oligodendrocytes. In this respect they are promising candidates for experimental treatment of neuronal injury; however, the final proof for conversion of HUCB cells to neural cells can be obtained through transplantation experiments.

Evaluation of neurotoxic potential by use of in vitro systems

In vitro systems have been proposed, but not yet demonstrated, as a method to assess the neurotoxicity of compounds in an efficient and rapid manner. Although such tests are desired both for pharmaceuticals and environmental agents, such a battery has yet to be developed that is based on known processes of nervous system dysfunction. In this review article, characteristics and potential limitations associated with in vitro methods are discussed. Many of these features have been identified from a larger body of work examining the neurotoxicity of environmental agents and the mechanisms underlying activity of known neurotoxicants. These issues include relevant drug concentrations, factors that limit or alter drug accessibility to the nervous system, and the need for assays to reflect biologically meaningful end points. This commentary briefly surveys in vitro systems of increasing biological complexity currently available for toxicity testing, from single cell types to systems that preserve some aspects of tissue structure and function. A small number of studies to evaluate drugs for cytotoxicity and biological responses in vitro are presented as representative of the current state of the field and to provide a reference and direction for additional development of methods to assess a compound's potential for neurotoxicity.

Voltage-Sensitive and Ligand-Gated Channels in Differentiating Neural Stem-Like Cells Derived from the Nonhematopoietic Fraction of Human Umbilical Cord Blood

Fetal cells with the characteristics of neural stem cells (NSCs) can be derived from the nonhematopoietic fraction of human umbilical cord blood (HUCB), expanded as a nonimmortalized cell line (HUCB-NSC), and further differentiated into neuron-like cells (HUCB-NSCD); however, the functional and neuronal properties of these cells are poorly understood. To address this issue, we used whole-cell patch-clamp recordings, gene microarrays, and immunocytochemistry to identify voltage-gated channels and ligand-gated receptors on HUCB-NSCs and HUCB-NSCDs. Gene microarray analysis identified genes for voltage-dependent potassium and sodium channels and the neurotransmitter receptors acetylcholine (ACh), gamma-aminobutyric acid (GABA), glutamate, glycine, 5-hydroxytryptamine (5-HT), and dopamine (DA). Several of these genes (GABA-A, glycine and glutamate receptors, voltage-gated potassium channels, and voltage-gated sodium type XII alpha channels) were not expressed in the HUCB mono-nuclear fraction (HUCB-MC), which served as a starting cell population for HUCB-NSC. HUCB-NSCD acquired neuronal phenotypes and displayed an inward rectifying potassium current (Kir) and an outward rectifying potassium current (I(K+)). Kir was present on most HUCB-NSCs and HUCB-NSCDs, whereas I(K+) was present only on HUCB-NSCDs. Many HUCB-NSCDs were immunopositive for glutamate, glycine, nicotinic ACh, DA, 5-HT, and GABA receptors. Kainic acid (KA), a non-N-methyl-D-asparate (NMDA) glutamate-receptor agonist, induced an inward current in some HUCB-NSCDs. KA, glycine, DA, ACh, GABA, and 5-HT partially blocked Kir through their respective receptors. These results suggest that HUCB-NSCs differentiate toward neuron-like cells, with functional voltage- and ligand-gated channels identified in other neuronal systems.