The establishment of a reliable cytotoxic system with SK-N-SH neuroblastoma cell culture

A Biomimetic Upconversion Nanobait-Based Near Infrared Light Guided Photodynamic Therapy Alleviates Alzheimer's Disease by Inhibiting β-Amyloid Aggregation

Aberrant β-amyloid (Aβ) fibrillation is the key event in Alzheimer's disease (AD), the inhibition and degradation of which are recognized as a promising therapeutic strategy to alleviate the nerve damage of AD. Photodynamic therapy (PDT) holds great potential for modulation of Aβ self-assembly, which is nevertheless limited by the inefficient utilization of reactive oxygen species (ROS). Herein, an erythrocyte membrane (EM)-modified core-shell upconversion nanoparticle (UCNP/Cur@EM) is designed and fabricated as a biomimetic nanobait to improve the PDT efficiency in AD. The UCNP with the outlayer of mesoporous silica is synthesized to load a high amount of the photosensitizer (curcumin), the unique optical feature of which can trigger curcumin to generate ROS upon near-infrared light (NIR) irradiation. Integration of EM enables the biomimetic nanobait to attract Aβ peptides trapped in the phospholipid bilayer, restraining the growth of Aβ monomers to form aggregates and improving the utilization rate of ROS to degrade the preformed Aβ aggregates. In vivo studies demonstrate that UCNP/Cur@EM irradiated by NIR enables to decrease Aβ deposits, ameliorates memory deficits, and rescues cognitive functions in the APP/PS1 transgenic mouse model. A biocompatible and controllable way is provided here to inhibit the amyloid protein-associated pathological process of AD.

Enhancing the neuroprotective effect of squid outer skin astaxanthin against rotenone-induced neurotoxicity in in-vitro model for Parkinson's disease

Rotenone is a widely used organic pesticide that induces neurotoxicity via inhibition of mitochondrial complex I and oxidative stress actions for the most of dopaminergic neurons as that occurring in Parkinsonism disease (PD). Astaxanthin (ASX) is a natural pigment (carotenoids) and a potent therapeutic compound due to its antioxidant and anti-inflammatory properties. The commercially important cephalopod Doryteuthis singhalensis is widely distributed in tropical and subtropical waters in World Ocean. D. singhalensis is an important source of astaxanthin that contains valuable biological active compounds with many valuable pharmacological effects. The present study evaluated the effect of astaxanthin in preventing rotenone-induced toxicity of SK-N-SH human neuroblastoma cells in an in vitro model of experimental Parkinsonism. The results revealed the strongly significant antioxidant capability of extracted squid astaxanthin in 1,1- diphenyl- 2- picrylhydrazyl (DPPH) radical scavenging activity. In addition, astaxanthin treatment based on dose dependent manner significantly attenuated rotenone induced cytotoxicity, mitochondrial dysfunction and oxidative stress in SKN- SH cells. It is concluded that the marine squid derived astaxanthin could be used as a potential neuroprotector against rotenone induced toxicity due to its antioxidant, and anti-apoptotic properties. Consequently, it could be a supportive remedy for neurodegenerative diseases like Parkinson's disease.

In vitro Model Systems for Studies Into Retinal Neuroprotection

Therapy development for neurodegenerative diseases of the retina constitutes a major unmet medical need, and this may be particularly relevant for inherited diseases of the retina, which are largely untreatable to this day. Therapy development necessitates appropriate models to improve the understanding of the underlying degenerative mechanisms, as well as for the testing and evaluation of novel treatment approaches. This review provides an overview of various in vitro model systems used to study retinal neuroprotection. The in vitro methods and technologies discussed range from primary retinal cell cultures and cell lines, to retinal organoids and organotypic retinal explants, to the cultivation of whole eyeballs. The advantages and disadvantages of these methods are compared and evaluated, also in view of the 3R principles (i.e., the refinement, reduction, and replacement of live animal testing), to identify suitable in vitro alternatives for in vivo experimentation. The article further expands on the use of in vitro models to test and evaluate neuroprotective treatments and to aid the development of retinal drug delivery systems. Among the pharmacological agents tested and characterized in vitro are such that interfere with aberrant cyclic guanosine monophosphate (cGMP) -signaling or such that inhibit the activities of poly (ADP-ribose) polymerase (PARP), histone deacetylases (HDAC), calpain-type proteases, as well as unfolded protein response-related stress. We then introduce nanoparticle-based drug delivery systems and discuss how different in vitro systems may be used to assess their efficacy in the treatment of retinal diseases. The summary provides a brief comparison of available in vitro models and relates their advantages and limitations to the various experimental requirements, for instance, for studies into disease mechanisms, novel treatments, or retinal toxicity. In many cases, combinations of different in vitro models may be required to obtain a comprehensive view of the efficacy of a given retinal neuroprotection approach.

TV 3326 for Alzheimer's dementia: a novel multimodal ChE and MAO inhibitors to mitigate Alzheimer's-like neuropathology

OBJECTIVES

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative disorders and a well-recognized cause of dementia with ageing. In this review, we have represented the ChE and MAO inhibitory potential of TV 3326 against AD based on current scientific evidence.

KEY FINDINGS

The aetiology of AD is quite complex and not completely understood. However, it has been observed that AD involves the deposition of abnormal amyloid beta (Aβ), along with hyperphosphorylation of tau, oxidative stress, low acetylcholine (ACh) level and biometal dyshomeostasis. Due to the complex nature of AD aetiology, active research is required in the areas of development of multitarget drugs with 2 or more complementary biological functions, as they might represent significant progress in the AD treatment. Interestingly, it has been found that TV 3326 (i.e. ladostigil) is regarded as a novel therapeutic agent since it has the potential to cause inhibition of monoamine oxidase (MAO) A and B, and acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in the brain. Furthermore, it has the capacity to reverse memory impairments, which further suggests the ability of this drug to elevate cholinergic activity in the brain.

SUMMARY

TV 3326 can avert oxidative-nitrative stress and gliosis. It has also been confirmed that TV 3326 contains neuroprotective and anti-apoptotic properties. Therefore, this distinctive combined inhibition of ChE and MAO along with its neuroprotective property makes TV 3326 a useful drug in the treatment of AD.

Cellular metabolomics reveals glutamate and pyrimidine metabolism pathway alterations induced by BDE-47 in human neuroblastoma SK-N-SH cells

Polybrominated diphenyl ethers (PBDEs) as potential neurotoxicants in environment may possess hazards to human health. Previous studies have reported that PBDEs exposure could induce oxidative stress and disturb mitochondrial functions in mammalian cells. However, the toxicological mechanism remains to be clarified. In this work, the neurotoxic effect and underlying mechanism of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) was investigated by using human neuroblastoma SK-N-SH cells as an effective model. A liquid chromatography-mass spectrometry (LC-MS)-based metabolomics approach combined with cell viability assay was applied to elucidate the metabolic perturbations and relevant toxicological pathways upon BDE-47 exposure. Our results shown that the SK-N-SH cell viability decreased in a dose-dependent manner after exposure to BDE-47 at 24 h within the concentration range of 5-250 μM, and an IC₅₀ value of 88.8 μM was obtained. Based on the dose-response curve and cell morphological observation, the 5 and 10 μM BDE-47 doses (equal to IC₅ and IC₁₀, respectively) were used for metabolomics study to capture the sensitive metabolic response following BDE-47 exposure. After BDE-47 treatment, nine metabolites were identified as potential biomarkers, and the most disturbed metabolic pathways were mainly involved in alanine, aspartate and glutamate metabolism, glutathione metabolism, tyrosine and phenylalanine metabolism, and pyrimidine metabolism, which imply that metabolic changes related to neurotransmitters, oxidative stress, and nucleotide-mediated signal transduction systems were the sensitive pathways mostly influenced. Our findings reported here may provide potential neurotoxic effect biomarkers and prompt deep understanding of the molecular and metabolic mechanisms triggered by BDE-47 exposure.

Inhibition of protein misfolding and aggregation by natural phenolic compounds

Protein misfolding and aggregation into fibrillar deposits is a common feature of a large group of degenerative diseases affecting the central nervous system or peripheral organs, termed protein misfolding disorders (PMDs). Despite their established toxic nature, clinical trials aiming to reduce misfolded aggregates have been unsuccessful in treating or curing PMDs. An interesting possibility for disease intervention is the regular intake of natural food or herbal extracts, which contain active molecules that inhibit aggregation or induce the disassembly of misfolded aggregates. Among natural compounds, phenolic molecules are of particular interest, since most have dual activity as amyloid aggregation inhibitors and antioxidants. In this article, we review many phenolic natural compounds which have been reported in diverse model systems to have the potential to delay or prevent the development of various PMDs, including Alzheimer's and Parkinson's diseases, prion diseases, amyotrophic lateral sclerosis, systemic amyloidosis, and type 2 diabetes. The lower toxicity of natural compounds compared to synthetic chemical molecules suggest that they could serve as a good starting point to discover protein misfolding inhibitors that might be useful for the treatment of various incurable diseases.

Expression Profiles of SIRT1 and APP Genes in Human Neuroblastoma SK-N-SH Cells Treated with Two Epigenetic Agents

In our previous studies, significant hypermethylation of the sirtuin 1 (SIRT1) gene and demethylation of the β-amyloid precursor protein (APP) gene were found in patients with Alzheimer's disease (AD) compared with the normal population. Moreover, the expression of SIRT1 was significantly decreased while that of APP was increased in AD patients. These results indicated a correlation of DNA methylation with gene expression levels in AD patients. To further investigate the epigenetic mechanism of gene modulation in AD, we used two epigenetic drugs, the DNA methylation inhibitor 5-aza-2'-deoxycytidine (DAC) and the histone deacetylase inhibitor trichostatin A (TSA), to treat human neuroblastoma SK-N-SH cells in the presence of amyloid β-peptide Aβ25-35(Aβ25-35). We found that DAC and TSA had different effects on the expression trends of SIRT1 and APP in the cell model of amyloid toxicity. Although other genes, such as microtubule-associated protein τ, presenilin 1, presenilin 2, and apolipoprotein E, were up-regulated after Aβ25-35 treatment, no significant differences were found after DAC and/or TSA treatment. These results support the evidence in AD patients and reveal a strong correlation of SIRT1/APP expression with DNA methylation and/or histone modification, which may help understand the pathogenesis of AD.

The activation of type 1 corticotropin releasing factor receptor (CRF-R1) inhibits proliferation and promotes differentiation of neuroblastoma cells in vitro via p27(Kip1) protein up-regulation and c-Myc mRNA down-regulation

Our group has previously shown that corticotropin releasing factor (CRF) inhibits proliferation of human endocrine-related cancer cell lines via the activation of CRF type-1 receptors (CRF-R1). Tumors originating from the nervous system also express CRF receptors but their role on neoplastic cell proliferation was poorly investigated. Here we investigated the effect of CRF receptor stimulation on nervous system-derived cancer cells, using the SK-N-SH (N) human neuroblastoma cell line as an experimental model. We found that SK-N-SH (N) cells express functionally active CRF-R1, whose activation by CRF and the cognate peptide urocortin (UCN) is associated to reduced cell proliferation and motility, as well as neuronal-like differentiation. UCN did not interfere with cell viability and cell-cycle arrest. Those effects seem to be mediated by a mechanism involving the activation of cAMP/PKA/CREB pathway and the subsequent downstream increase in p27(Kip1) and underphosphorylated retinoblastoma protein levels, as well as reduced c-Myc mRNA accumulation.

Benchmarking organic micropollutants in wastewater, recycled water and drinking water with in vitro bioassays

Thousands of organic micropollutants and their transformation products occur in water. Although often present at low concentrations, individual compounds contribute to mixture effects. Cell-based bioassays that target health-relevant biological endpoints may therefore complement chemical analysis for water quality assessment. The objective of this study was to evaluate cell-based bioassays for their suitability to benchmark water quality and to assess efficacy of water treatment processes. The selected bioassays cover relevant steps in the toxicity pathways including induction of xenobiotic metabolism, specific and reactive modes of toxic action, activation of adaptive stress response pathways and system responses. Twenty laboratories applied 103 unique in vitro bioassays to a common set of 10 water samples collected in Australia, including wastewater treatment plant effluent, two types of recycled water (reverse osmosis and ozonation/activated carbon filtration), stormwater, surface water, and drinking water. Sixty-five bioassays (63%) showed positive results in at least one sample, typically in wastewater treatment plant effluent, and only five (5%) were positive in the control (ultrapure water). Each water type had a characteristic bioanalytical profile with particular groups of toxicity pathways either consistently responsive or not responsive across test systems. The most responsive health-relevant endpoints were related to xenobiotic metabolism (pregnane X and aryl hydrocarbon receptors), hormone-mediated modes of action (mainly related to the estrogen, glucocorticoid, and antiandrogen activities), reactive modes of action (genotoxicity) and adaptive stress response pathway (oxidative stress response). This study has demonstrated that selected cell-based bioassays are suitable to benchmark water quality and it is recommended to use a purpose-tailored panel of bioassays for routine monitoring.

Retinoic acid inhibits the cytoproliferative response to weak 50‑Hz magnetic fields in neuroblastoma cells

We previously reported that intermittent exposure to a 50‑Hz magnetic field (MF) at 100 µT stimulates cell proliferation in the human neuroblastoma cell line NB69. The present study aimed to investigate whether the magnetic field-induced growth promotion also occurs at a lower magnetic flux density of 10 µT. To this purpose, NB69 cells were subjected for 42 h to intermittent exposure, 3 h on/3 h off, to a 50‑Hz MF at a 10 or 100 µT magnetic flux density. The field exposure took place either in the presence or in the absence of the antiproliferative agent retinoic acid. At the end of the treatment and/or incubation period, the cell growth was estimated by hemocytometric counting and spectrophotometric analysis of total protein and DNA contents. Potential changes in DNA synthesis were also assessed through proliferating cell nuclear antigen (PCNA) immunolabeling. The results confirmed previously reported data that a 42-h exposure to a 50‑Hz sine wave MF at 100 µT promotes cell growth in the NB69 cell line, and showed that 10 µT induces a similar proliferative response. This effect, which was significantly associated and linearly correlated with PCNA expression, was abolished by the presence of retinoic acid in the culture medium.

M3 muscarinic receptors promote cell survival through activation of the extracellular regulated kinase (ERK1/2) pathway

Activation of certain subtypes of the muscarinic acetylcholine receptor can enhance cell survival. In SK-N-SH human neuroblastoma cells, muscarinic acetylcholine receptor activation induces phosphorylation of CREB and induction of EGR1, transcription factors associated with cell growth and survival. We identified the M3 muscarinic acetylcholine receptor subtype as being primarily responsible for these transcription factor responses after stimulation with carbachol, using subtype-preferring receptor antagonists and muscarinic snake toxins. In a cell survival/death model in SK-N-SH cells deprived of serum growth factors, carbachol increased cell viability, an effect blocked by the non-specific muscarinic antagonist atropine and the M3-preferring antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP), suggesting that the M3 receptor is also driving the survival response in these cells. This cytoprotection is largely dependent on activation of the p44/42 extracellular regulated kinase (ERK1/2) pathway. Understanding such survival signalling pathways is important for both potential interventions in neurodegenerative disease and for targeting neuroblastoma and malignancies of the central nervous system.

Evaluation of the importance of astrocytes when screening for acute toxicity in neuronal cell systems

Reliable, high throughput, in vitro preliminary screening batteries have the potential to greatly accelerate the rate at which regulatory neurotoxicity data is generated. This study evaluated the importance of astrocytes when predicting acute toxic potential using a neuronal screening battery of pure neuronal (NT2.N) and astrocytic (NT2.A) and integrated neuronal/astrocytic (NT2.N/A) cell systems derived from the human NT2.D1 cell line, using biochemical endpoints (mitochondrial membrane potential (MMP) depolarisation and ATP and GSH depletion). Following exposure for 72 h, the known acute human neurotoxicants trimethyltin-chloride, chloroquine and 6-hydroxydopamine were frequently capable of disrupting biochemical processes in all of the cell systems at non-cytotoxic concentrations. Astrocytes provide key metabolic and protective support to neurons during toxic challenge in vivo and generally the astrocyte containing cell systems showed increased tolerance to toxicant insult compared with the NT2.N mono-culture in vitro. Whilst there was no consistent relationship between MMP, ATP and GSH log IC(50) values for the NT2.N/A and NT2.A cell systems, these data did provide preliminary evidence of modulation of the acute neuronal toxic response by astrocytes. In conclusion, the suitability of NT2 neurons and astrocytes as cell systems for acute toxicity screening deserves further investigation.

Neuroprotective mesenchymal stem cells are endowed with a potent antioxidant effect in vivo

Experimental autoimmune encephalomyelitis (EAE), an animal model for human multiple sclerosis, is characterized by demyelination, inflammation and neurodegeneration of CNS in which free radicals play a role. Recently, the efficacy of murine mesenchimal stem cells (MSCs) as treatment of EAE induced in mice by the encephalitogenic peptide MOG(35-55) was demonstrated. The present study analyzed some markers of oxidative stress, inflammation/degeneration and apoptosis such as metallothioneins (MTs), antioxidant enzymes (superoxide dismutase, catalase and glutathione-S-transferase), poly(ADP-ribose) polymerase-1 and p53 during EAE progression and following MSC treatment. Expression of the three brain MT isoforms increased significantly in EAE mice compared with healthy controls, but while expression of MT-1 and MT-3 increased along EAE course, MT-2 was up-regulated at the onset, but returned to levels similar to those of controls in chronic phase. The changes in the transcription and activity of the antioxidant enzymes and in expression of poly(ADP-ribose) polymerase-1 and p53 showed the same kinetics observed for MT-1 and MT-3 during EAE. Interestingly, i.v. administration of MSCs reduced the EAE-induced increases in levels/activities of all these proteins. These results support an antioxidant and neuroprotective activity for MSCs that was also confirmed in vitro on neuroblastoma cells exposed to an oxidative insult.

Extracts of Cynomorium songaricum protect SK-N-SH human neuroblastoma cells against staurosporine-induced apoptosis potentially through their radical scavenging activity

In traditional Chinese medicine a number of herbs are used to alleviate the symptoms of aging, among them the stems of Cynomorium songaricum, Cynomoriaceae. This study evaluated the protective effect of different extracts of C. songaricum on staurosporine-induced apoptotic cell death in SK-N-SH neuroblastoma cells. Staurosporine (100 nm) reduced cell viability to about 55%. The ethyl acetate fraction of C. songaricum significantly attenuated staurosporine-induced cell death at concentrations of 100 and 10 microg/mL. On the other hand, the dichloromethane as well as water fractions showed no protective effects. In order to further analyse the protective mode of action, the superoxide anion scavenging activity of two extracts was evaluated in a xanthine/xanthine oxidase system. In this system, the EtOAc extract showed a good scavenging activity (IC(50) value 2.9 microg/mL) without inhibition of xanthine oxidase. In conclusion, the results prove the neuroprotective activity of C. songaricum extracts in vitro, thus supporting its traditional use.

Multifunctional neuroprotective derivatives of rasagiline as anti-Alzheimer's disease drugs

The recent therapeutic approach in which drug candidates are designed to possess diverse pharmacological properties and act on multiple targets has stimulated the development of the multimodal drugs, ladostigil (TV3326) [(N-propargyl-(3R) aminoindan-5yl)-ethyl methyl carbamate] and the newly designed multifunctional antioxidant iron chelator, M-30 (5-[N-methyl-N-propargylaminomethyl]-8-hydroxyquinoline). Ladostigil combines, in a single molecule, the neuroprotective/neurorestorative effects of the novel anti-Parkinsonian drug and selective monoamine oxidase (MAO)-B inhibitor, rasagiline (Azilect, Teva Pharmaceutical Co.) with the cholinesterase (ChE) inhibitory activity of rivastigmine. A second derivative of rasagiline, M-30 was developed by amalgamating the propargyl moiety of rasagiline into the skeleton of our novel brain permeable neuroprotective iron chelator, VK-28. Preclinical experiments showed that both compounds have anti-Alzheimer's disease activities and thus, the clinical development is oriented toward treatment of this type of dementia. This review discusses the multimodal effects of two rasagiline-containing hybrid molecules, namely ladostigil and M-30, concerning their neuroprotective molecular mechanisms in vivo and in vitro, including regulation of amyloid precursor protein processing, activation of protein kinase C, and mitogen-activated protein kinase signaling pathways, inhibition of cell death markers and upregulation of neurotrophic factors. Altogether, these scientific findings make these multifunctional compounds potentially valuable drugs for the treatment of Alzheimer's disease.

The novel cholinesterase-monoamine oxidase inhibitor and antioxidant, ladostigil, confers neuroprotection in neuroblastoma cells and aged rats

The current therapeutic advance in which future drugs are designed to possess varied pharmacological properties and act on multiple targets has stimulated the development of the multimodal drug, ladostigil (TV3326; (N-propargyl-(3R) aminoindan-5yl)-ethyl methyl carbamate). Ladostigil combines neuroprotective effects with monoamine oxidase (MAO)-A and MAO-B and cholinesterase (ChE) inhibitory activities in a single molecule, as a potential treatment for Alzheimer's disease (AD) and Lewy body disease. In the present study, we demonstrate that ladostigil (10(-6)-10 muM) dose-dependently increased cell viability, associated with increased activity of catalase and glutathione reductase and decrease of intracellular reactive oxygen species production in a cytotoxic model of human SH-SY5Y neuroblastoma cells exposed to hydrogen peroxide (H(2)O(2)). In addition, ladostigil significantly upregulated mRNA levels of several antioxidant enzymes (catalase, NAD(P)H quinone oxidoreductase 1 and peroxiredoxin 1) in both H(2)O(2)-treated SH-SY5Y cells, as well as in the high-density human SK-N-SH neuroblastoma cultured apoptotic models. In vivo chronic treatment with ladostigil (1 mg/kg per os per day for 30 days) markedly upregulated mRNA expression levels of various enzymes involved in metabolism and oxidation processes in aged rat hippocampus. In addition to its unique combination of ChE and MAO enzyme inhibition, these results indicate that ladostigil displays neuroprotective activity against oxidative stress-induced cell apoptosis, which might be valuable for aging and age-associated neurodegenerative diseases.

The neuroprotective effect of ladostigil against hydrogen peroxide-mediated cytotoxicity

The multifunctional, anti-Alzheimer drug, ladostigil (TV3326) [(N-propargyl-(3R) aminoindan-5yl)-ethyl methyl carbamate] combines the neuroprotective effects of the anti-Parkinson drug, rasagiline, a selective monoamine oxidase (MAO)-B inhibitor, with the cholinesterase (ChE) inhibitory activity of rivastigmine in a single molecule. Ladostigil has been shown to possess potent antiapoptotic and neuroprotective activities in various oxidative insults in vitro and in vivo, such as prevention of the fall in mitochondrial membrane potential and regulation of Bcl-2 family proteins. In the present study, we demonstrate that ladostigil (1 microM) increased cell viability, associated with the increase of catalase activity and decrease of intracellular reactive oxygen species (ROS) production in human SH-SY5Y neuroblastoma cells exposed to (hydrogen peroxide) H(2)O(2). Furthermore, ladostigil significantly elevated mRNA levels of the antioxidants enzymes, catalase, NAD(P)H quinone oxidoreductase 1 (NQO1) and peroxiredoxin 1 (Prx 1) in H(2)O(2)-treated SH-SY5Y cells. Chronic treatment with ladostigil (1 mg/kg gavage per day for 30 days) markedly up-regulated mRNA expression levels of various antioxidant enzymes in aged rat hippocampus (e.g. glutathione peroxidase precursor (GSHPX-P), glutathione S-transferase (GST) and glucose-6-phosphate dehydrogenase (G6PD)). These findings indicate that in addition to its multiple neuroprotective characteristics, ladostigil also possesses antioxidant properties, which might be beneficial for the treatment of oxidative stress (OS) in aging and age-associated neurodegenerative diseases.

DE-71-induced apoptosis involving intracellular calcium and the Bax-mitochondria-caspase protease pathway in human neuroblastoma cells in vitro

Polybrominated diphenyl ethers (PBDEs) are used extensively as flame-retardants and are ubiquitous in the environment and in wildlife and human tissue. Recent studies have shown that PBDEs induce neurotoxic effects in vivo and apoptosis in vitro. However, the signaling mechanisms responsible for these events are still unclear. In this study, we investigated the action of a commercial mixture of PBDEs (pentabrominated diphenyl ether, DE-71) on a human neuroblastoma cell line, SK-N-SH. A cell viability test showed a dose-dependent increase in lactate dehydrogenase leakage and 3-(4,5-dimethylthia-zol-2-yl)-2,5-diphenyl-tetrazolium bromide reduction. Cell apoptosis was observed through morphological examination, and DNA degradation in the cell cycle and cell apoptosis were demonstrated using flow cytometry and DNA laddering. The formation of reactive oxygen species was not observed, but DE-71 was found to significantly induce caspase-3, -8, and -9 activity, which suggests that apoptosis is not induced by oxidative stress but via a caspase-dependent pathway. We further investigated the intracellular calcium ([Ca(2+)](i)) levels using flow cytometry and observed an increase in the intracellular Ca(2+) concentration with a time-dependent trend. We also found that the N-methyl d-aspartate (NMDA) receptor antagonist MK801 (3 microM) significantly reduced DE-71-induced cell apoptosis. The results of a Western blotting test demonstrated that DE-71 treatment increases the level of Bax translocation to the mitochondria in a dose-dependent fashion and stimulates the release of cytochrome c (Cyt c) from the mitochondria into the cytoplasm. Overall, our results indicate that DE-71 induces the apoptosis of [Ca(2+)](i) in SK-N-SH cells via Bax insertion, Cyt c release in the mitochondria, and the caspase activation pathway.

p38 MAPK as a negative regulator of VEGF/VEGFR2 signaling pathway in serum deprived human SK-N-SH neuroblastoma cells

Evidence suggests that vascular endothelial growth factor (VEGF) mediates neuroprotection to prevent an apoptotic cell death. The p38 mitogen-activated protein kinase (MAPK) pathway is implicated as an important mediator of neuronal apoptosis but its role in VEGF-mediated neuroprotection is unclear. Herein, we show that treatments with the p38 MAPK inhibitor, SB202190, enhanced VEGF-mediated survival in serum deprived SK-N-SH neuroblastoma cells by decreasing caspase-3/7 activation while increasing the phosphorylation of the extracellular signal-regulated kinase (ERK1/2) and Akt signaled through the VEGF receptor, VEGFR2. A blockade of VEGFR2 signaling with a selective inhibitor, SU1498 or gene silencing with VEGFR2 siRNA in SB202190 treated cells abrogated this prosurvival response and induced high activation levels of caspase-3/7. These findings suggested that the protection elicited by p38 MAPK inhibition in serum starved cells was dependent on a functional VEGF/VEGFR2 pathway. However, p38 MAPK inhibition attenuated caspase-3 cleavage in SU1498/SB202190 treated cells, indicating that p38 MAPK and caspase-3 only contributed in part to the total levels of caspase-3/7 induced by VEGFR2 inhibition. Pretreatments with the pan caspase inhibitor, z-VAD-fmk, prevented the apoptosis induced by VEGFR2 inhibition and promoted survival in serum starved cells irrespective of p38 MAPK inhibition. Collectively, our findings suggest that p38 MAPK exerts a negative effect on VEGF-mediated signaling through VEGFR2 in serum starved neuroblastoma cells. Furthermore, VEGF signals protection against a caspase-mediated cell death that is regulated by p38 MAPK-dependent and -independent mechanisms.

The neuroprotective effect of Activin A and B: implication for neurodegenerative diseases

Activin is a member of the transforming growth factor-beta superfamily which comprises a growing list of multifunctional proteins that function as modulators of cell proliferation, differentiation, hormone secretion and neuronal survival. This study examined the neuroprotective effect of both Activin A and B in serum withdrawal and oxidative stress apoptotic cellular models and investigated the expression of pro- and anti-apoptotic proteins, which may account for the mechanism of Activin-induced neuroprotection. Here, we report that recombinant Activin A and B are neuroprotective against serum deprivation- and toxin- [either the parkinsonism-inducing neurotoxin, 6-hydroxydopamine (6-OHDA) or the peroxynitrite donor, 3-(4-morpholinyl) sydnonimine hydrochloride (SIN-1)] induced neuronal death in human SH-SY5Y neuroblastoma cells. Furthermore, we demonstrate for the first time that transient transfection with Activin betaA or betaB significantly protect SH-SY5Y and rat pheochromocytoma PC12 cells against serum withdrawal-induced apoptosis. This survival effect is mediated by the Bcl-2 family members and involves inhibition of caspase-3 activation; reduction of cleaved poly-ADP ribose polymerase and phosphorylated H2A.X protein levels and elevation of tyrosine hydroxylase expression. These results indicate that both Activin-A and -B share the potential to induce neuroprotective activity and thus may have positive impact on aging and neurodegenerative diseases to retard the accelerated rate of neuronal degeneration.

Aminoindan and hydroxyaminoindan, metabolites of rasagiline and ladostigil, respectively, exert neuroprotective properties in vitro

The anti-Parkinson, selective irreversible monoamine oxidase B inhibitor drug, rasagiline (Azilect), recently approved by the US Food and Drug Administration, has been shown to possess neuroprotective-neurorescue activities in in vitro and in vivo models. Recent preliminary studies indicated the potential neuroprotective effect of the major metabolite of rasagiline, 1-(R)-aminoindan. In the current study, the neuroprotective properties of 1-(R)-aminoindan were assessed employing a cytotoxic model of human neuroblastoma SK-N-SH cells in high-density culture-induced neuronal death. We show that aminoindan (0.1-1 mumol/L) significantly reduced the apoptosis-associated phosphorylated protein, H2A.X (Ser139), decreased the cleavage of caspase 9 and caspase 3, while increasing the anti-apoptotic proteins, Bcl-2 and Bcl-xl. Protein kinase C (PKC) inhibitor, GF109203X, prevented the neuroprotection, indicating the involvement of PKC in aminoindan-induced cell survival. Aminoindan markedly elevated pPKC(pan) and specifically that of the pro-survival PKC isoform, PKCepsilon. Additionally, hydroxyaminoindan, a metabolite of a novel bifunctional drug, ladostigil [(N-propargyl-(3R) aminoindan-5yl)-ethyl methyl carbamate], combining cholinesterase and monoamine oxidase inhibitor activity, exerted similar neuroprotective properties. Aminoindan and hydroxyaminoindan also protected rat pheochromacytoma PC-12 cells against the neurotoxin, 6-hydroxydopamine. Our findings suggest that both metabolites may contribute to the overall neuroprotective activity of their respective parent compounds, further implicating rasagiline and ladostigil as potentially valuable drugs for treatment of a wide variety of neurodegenerative disorders of aging.

Cholesterol supports the retinoic acid-induced synaptic vesicle formation in differentiating human SH-SY5Y neuroblastoma cells

Synaptic vesicle formation, vesicle activation and exo/endocytosis in the pre-synaptic area are central steps in neuronal communication. The formation and localization of synaptic vesicles in human SH-SY5Y neuroblastoma cells, differentiated with 12-o-tetradecanoyl-phorbol-13-acetate, dibutyryl cyclic AMP, all-trans-retinoic acid (RA) and cholesterol, was studied by fluorescence microscopy and immunocytochemical methods. RA alone or together with cholesterol, produced significant neurite extension and formation of cell-to-cell contacts. Synaptic vesicle formation was followed by anti-synaptophysin (SypI) and AM1-43 staining. SypI was only weakly detected, mainly in cell somata, before 7 days in vitro, after which it was found in neurites. Depolarization of the differentiated cells with high potassium solution increased the number of fluorescent puncta, as well as SypI and AM1-43 co-localization. In addition to increase in the number of synaptic vesicles, RA and cholesterol also increased the number and distribution of lysosome-associated membrane protein 2 labeled lysosomes. RA-induced Golgi apparatus fragmentation was partly avoided by co-treatment with cholesterol. The SH-SY5Y neuroblastoma cell line, differentiated by RA and cholesterol and with good viability in culture, is a valuable tool for basic studies of neuronal metabolism, specifically as a model for dopaminergic neurons.

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.

Pyruvate protects mitochondria from oxidative stress in human neuroblastoma SK-N-SH cells

Oxidative stress is implicated in neurodegenerative diseases including stroke, Alzheimer's disease and Parkinson's disease, and has been extensively studied as a potential target for therapeutic intervention. Pyruvate, a natural metabolic intermediate and energy substrate, exerts antioxidant effects in brain and other tissues susceptible to oxidative stress. We tested the protective effects of pyruvate on hydrogen peroxide (H(2)O(2)) toxicity in human neuroblastoma SK-N-SH cells and the mechanisms underlying its protection. Hydrogen peroxide insult resulted in 85% cell death, but co-treatment with pyruvate dose-dependently attenuated cell death. At concentrations of >or=1 mM, pyruvate totally blocked the cytotoxic effects of H(2)O(2). Pyruvate exerted its protective effects even when its administration was delayed up to 2 h after H(2)O(2) insult. As a scavenger of reactive oxygen species (ROS), pyruvate dose-dependently attenuated H(2)O(2)-induced ROS formation, assessed from 2,7-dichlorofluorescein diacetate fluorescence. Furthermore, pyruvate suppressed superoxide production by submitochondrial particles, and attenuated oxidative stress-induced collapse of the mitochondrial membrane potential. Collectively, these results suggest that pyruvate protects neuronal cells through its antioxidant actions on mitochondria.

Implications of co-morbidity for etiology and treatment of neurodegenerative diseases with multifunctional neuroprotective-neurorescue drugs; ladostigil

The recent therapeutic approach in which drug candidates are designed to possess diverse pharmacological properties and act on multiple targets has stimulated the development of several multifunction drugs. These include ladostigil (TV3326) [(N-propargyl-(3R) aminoindan-5yl)-ethyl methyl carbamate], which combines the pharmacophore-neuroprotective effects of rasagiline, a selective monoamine oxidase (MAO)-B inhibitor, with the cholinesterase (ChE) inhibitory activity of rivastigmine or iron chelating moiety such as M30. In the case of M30 the pharmacophore of brain permeable iron chelator VK-28 plus the MAO inhibitor-neuroprotective propargylamine moiety of rasagiline are combined in a single molecule as a potential treatment for Alzheimer's disease, Lewy body disease, and Parkinson's disease with dementia. Here, we discuss the activities of ladostigil in terms of its cholinesterase cognitive enhancing potential, antiParkinson, antidepressant, neuroprotection and APP (amyloid precursor protein) processing potential. One major attribute of ladostigil is its neuroprotective activity in neuronal cell cultures and in vivo. Employing an apoptotic model of neuroblastoma SK-N-SH cells, the molecular mechanism of its neuroprotective activity has been determined. The current studies show that ladostigil significantly decreased apoptosis via inhibition of the cleavage and prevention of caspase-3 activation through a mechanism related to regulation of the Bcl-2 family proteins, resulting in reduced levels of Bad and Bax and induced levels of Bcl-2. In addition, ladostigil elevated the levels of pPKC(pan). We have also followed the regulation of APP processing and found that ladostigil markedly decreased apoptotic-induced levels of holo-APP, as well as stimulated the release of the non-amyloidogenic soluble APP (sAPPalpha) into the conditioned medium via a established protein kinsae C-MAPkinase dependent pathway. Similar to ladostigil, its S-isomer, TV3279, which is a ChE inhibitor lacking MAO inhibitory activity, exerted similar neuroprotective properties and APP processing, suggesting that the mode of action is independent of MAO inhibition. These effects were shown to reside in the propargylamine moiety. These findings indicate that the dual actions of the anti-apoptotic-neuroprotective activity and the ability to modulate APP processing, could make ladostigil a potentially valuable drug for the treatment of Alzheimer's disease.

A multifunctional, neuroprotective drug, ladostigil (TV3326), regulates holo‐APP translation and processing

The recent therapeutic approach in which drug candidates are designed to possess diverse pharmacological properties and act on multiple targets has stimulated the development of the bifunctional drug ladostigil (TV3326) [(N-propargyl-(3R) aminoindan-5yl)-ethyl methyl carbamate]. Ladostigil combines the neuroprotective effects of the antiparkinson drug rasagiline, a selective monoamine oxidase (MAO)-B inhibitor, with the cholinesterase (ChE) inhibitory activity of rivastigmine in a single molecule, as a potential treatment for Alzheimer's disease (AD) and Lewy Body disease. Here, we assessed the dual effects of lodostigil in terms of the molecular mechanism of neuroprotection and amyloid precursor protein (APP) regulation/processing by using an apoptotic model of neuroblastoma SK-N-SH cells. Ladostigil dose-dependently decreased cell death via inhibition of the cleavage and prevention of caspase-3 activation (IC50=1.05 microM) through a mechanism related to regulation of the Bcl-2 family proteins, which resulted in reduced levels of Bad and Bax and induced levels of Bcl-2 gene and protein expression. We have also followed APP regulation/processing and found that ladostigil markedly decreased apoptotic-induced levels of holo-APP protein without altering APP mRNA levels, suggesting a posttranscriptional mechanism. In addition, the drug-elevated phosphorylated protein kinase C (pPKC) levels and stimulated the release of the nonamyloidogenic alpha-secretase proteolytic pathway. Similar to ladostigil, its S-isomer, TV3279, which is a ChE inhibitor but lacks MAO inhibitory activity, exerted neuroprotective properties and regulated APP processing, indicating that these effects are independent of MAO inhibition.

Effect of Aβ exposure on the mRNA expression patterns of voltage-sensitive calcium channel α1 subunits (α1A–α1D) in human SK-N-SH neuroblastoma

Evidence for loss of Ca(2+) homeostasis through voltage-sensitive Ca(2+) channels (VSCCs) contribution to neuronal degeneration induced by beta-amyloid protein (Abeta) is considerable and rapidly increasing. Thus, the expression patterns of four alpha(1) subunits for P/Q (alpha(1A))-, N (alpha(1B))-, and L (alpha(1C) and alpha(1D))-type VSCCs before and after Abeta exposure were investigated in human SK-N-SH neuroblastoma. Reverse transcription-polymerase chain reaction (RT-PCR) analysis showed a constitutive and abundant co-expression of mRNA for alpha(1A) and alpha(1D) subunit in control cells. The mRNA expression of another L-type subunit alpha(1C) was undetectable in control cells while N-type subunit alpha(1B) was relative lower when compared to alpha(1A) and alpha(1D) subunits. Interestingly, mRNA levels of alpha(1A), alpha(1B), and alpha(1C) were remarkably and time-dependently increased in response to Abeta (20 microM) for 72 h culture period. In contrast, the constitutively expressed alpha(1D) mRNA was not further modified during Abeta exposure. Western blot analysis of four alpha(1) subunits expression was consistent with the findings obtained by RT-PCR. In conclusion, our results suggested that P/Q-, N-, as well as L-type Ca(2+) channel genes might be existed in SK-N-SH cells. Among them, mRNA for alpha(1A), alpha(1B), and alpha(1D) were expressed constitutively while alpha(1C) were inducible. Furthermore, Abeta exposure selectively modulates the transcription of alpha(1A), alpha(1B), and alpha(1C) subunits. These suggested that except activating of existed VSCCs, up-regulation of alpha(1) subunits expression might also contribute to Abeta-induced neuronal toxicity and the complex of these VSCCs expression may participate in Ca(2+) current disturbance in Alzheimer's disease.

Divergent role of calcium on Aβ- and MPTP-induced cell death in SK-N-SH neuroblastoma

We attempted to clarify the role of Ca2+ in cell death caused by beta-amyloid protein (Abeta) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in SK-N-SH neuroblastoma, respectively. Two insults both reduced cell viability in a concentration-dependent manner and induced equal cytotoxicity in the presence of 20 microM Abeta and 0.4 mM MPTP for 72 h, respectively (68+/-7 vs. 64+/-6% viability). Time-related study showed that Abeta evoked cell death occurred quickly at 24 h. Relatively, MPTP exhibited a delayed cell death significantly after 72 h of culture. Pretreating the cells with nimodipine and chelating of Ca2+ by EGTA plus 1,2-bis-(O-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM) successfully rescued Abeta-induced cell death but failed to prevent MPTP toxicity. ELISA determination of mono/oligonucleosomes accumulation showed the mode of cell death evoked by MPTP was presumably apoptosis while by Abeta was necrosis. SK-N-SH cells constitutively expressed the alpha(1C) subunit of L-type Ca2+ channel and exposure to Abeta or MPTP for 96 h did not further modify its expression. By contrast, alpha(1D) subunit was undetectable or low level expressed in basal condition, but was induced to express after Abeta and MPTP stimulation in a time-dependent manner. Functional assay revealed that KCl-evoked [Ca2+]i rise was significantly greater in Abeta-, but not in MPTP-treated cells when compared with control. Taken together, these results showed that Abeta and MPTP elicited different mode of cell death in SK-N-SH. Nevertheless, Ca2+ overload seems to solely display a crucial role in Abeta-induced cytotoxicity and over-expressed alpha(1D) may contribute to the disruption of cellular Ca2+ homeostasis.

Regulation of Bcl-2 family proteins, neurotrophic factors, and APP processing in the neurorescue activity of propargylamine

The anti-Parkinson drug, rasagiline (N-propargyl-(1R)-aminoindan) promotes neuronal survival, via neuroprotective activity related to its propargyl moiety (propargylamine). We have investigated the neurorescue effects of propargylamine, in a progressive neuronal death model, induced by long-term serum deprivation in human SH-SY5Y neuroblastoma cells. Propargylamine (0.1-10 microM) dose-dependently reduced the levels of the early apoptosis-associated phosphorylated protein, H2A-X (ser 139), as well as decreased the cleavage of caspase-3 and its substrate poly-ADP ribose polymerase (PARP). In addition, the compound markedly reversed the apoptotic effects induced by long-term serum withdrawal, including down-regulation of the antiapoptotic protein, Bcl-2, as well as up-regulation of the proapoptotic proteins, Bax, Bad, and Bim. Real-time RT-PCR demonstrated that propargylamine elevated gene expression levels of Bcl-2, and the neurotrophic factors glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) and reduced Bax gene expression. Serum deprivation increased mRNA and protein levels of holo-amyloid precursor protein (APP), which was markedly decreased by propargylamine. This was accompanied by inducing the release of the nonamyloidogenic alpha-secretase form of soluble APP (sAPPalpha) into the medium. Similar effects on cell survival and APP regulation/processing were demonstrated for rasagiline. These results indicate that both rasagiline and propargylamine possess neurorescue activity, associated with regulation of Bcl-2 family proteins, neurotrophic factors, and APP metabolism.

Effect of an insulin-like growth factor binding protein fusion protein on thymidine incorporation in neuroblastoma and rhabdomyosarcoma cell lines

A fusion protein, FP 6/3, composed of IGF binding protein (IGFBP)-6 and IGFBP-3 was synthesized where the complete sequences of each binding protein were fused together into a single chimeric protein. The orientation of this fusion protein's structure has the N terminus of IGFBP-3 fused to the C terminus of IGFBP-6, leaving the key binding areas of each open. FP 6/3 bound to cells via its IGFBP-3 component and retained the increased affinity for IGF-II via its IGFBP-6 component. The effect of FP 6/3 on growth was determined in cell lines from both neuroblastoma and rhabdomyosarcoma, where IGF-II is an autocrine growth factor. In studies using FP 6/3, IGFBP-3, or IGFBP-6, a growth inhibition effect was shown for all when present under coincubation conditions with IGF-II. However, with transient exposure, FP 6/3 was the only IGFBP that retained this growth-inhibition property. Under transient exposure conditions, FP 6/3 was found to be effective when exposure was limited to as few as 10 min and concentrations were as low as 1 nm. These findings with FP 6/3 suggest that it potentially could lead be used as therapy against cancers in which IGF-II is an autocrine growth factor because it brings an inhibition action directly to tumor cells.

Protective role of Bcl-2 on β-amyloid-induced cell death of differentiated PC12 cells: reduction of NF-κB and p38 MAP kinase activation

Activation of the apoptosis program by an increased production of beta-amyloid peptides (Abeta) has been implicated in the neuronal cell death of Alzheimer's disease (AD). Bcl-2 is a well-demonstrated anti-apoptotic protein, however, the mechanisms of anti-apoptotic action of Bcl-2 in Abeta-induced neuronal cell death are not fully understood. In the present study, we therefore have investigated the possibility that overexpression of Bcl-2 may prevent Abeta-induced cell death through inhibition of pro-apoptotic activation of p38 MAP kinase and the transcription factor NF-kappaB in nerve growth factor (NGF)-induced differentiated PC12 cells. Treatment of Abeta into differentiated PC12 cells transfected with plasmid alone resulted in increase of cell death determined by measurement of cytotoxicity and apoptosis in a dose dependent manner. Consistent with the increase of cell death, treatment of Abeta resulted in increase of p38 MAP kinase and NF-kappaB activation. However, overexpression of Bcl-2 reduced Abeta-induced apoptosis, and suppressed the activation of p38 MAP kinase and NF-kappaB. In addition, a p38 MAP kinase specific inhibitor SB 203580 attenuated Abeta-induced apoptosis. This inhibitory effect was correlated well with the inhibition of p38 MAP kniase and NF-kappaB activation. Moreover, inhibition of NF-kappaB activation by sodium salicylates reduced Abeta-induced apoptosis and activation of p38 MAP kinase, and up regulated Bcl-2 expression. These results suggest that Bcl-2 overexpression protects against Abeta-induced cell death of differentiated PC12, and its protective effect may be related to the reduction of Abeta-induced activation of p38 MAP kinase and NF-kappaB.

The neuroprotective effects of estrogen in SK-N-SH neuroblastoma cell cultures

Estrogen has been considered to be a neuroprotectant and a neuromodulator in many neuronal cell lines and tissue preparations. The protective effects of estrogen may be mediated through classical estrogen receptors (ERs), or may be due to its anti-oxidant properties which are independent of receptors. The current studies show that 17beta-estradiol (E2) is neuroprotective against beta-amyloid protein 25-35 (Abeta)-, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-, high density culture condition-, and serum deprivation-induced neuronal death in SK-N-SH human neuroblastoma cells. SK-N-SH cells express ERbeta, but not ERalpha, as detected by Western blot analysis. Among all the insults, MPTP, high density culture and serum deprivation induce apoptotic cell death in this cell system as detected by ELISA determination of mono/oligonucleosomes and DNA laddering, while Abeta induces necrotic cell death. The protective effects of E2 are abolished by the addition of tamoxifen and ICI 182,780 in the MPTP treated cells, but not in the other models, suggesting that the effect of E2 in the MPTP model is probably associated with activation of ERbeta. The addition of ICI 182,780 shows a mitogenic effect in SK-N-SH cells in the presence of E2 in control culture or in the Abeta treated groups. Also, ICI 182,780 induced expression of ERalpha. Collectively, the current studies suggest that E2 is neuroprotective in apoptotic and necrotic death induced by multiple insults in SK-N-SH human neuroblastoma cells. Involvement of ER is insult type dependent. ICI 182,780 is able to influence the expression of ERs, probably through upregulation of ERalpha when ERbeta is totally antagonized.

Method for measuring neurotoxicity of aggregating polypeptides with the MTT assay on differentiated neuroblastoma cells

Reliable in vitro assays are essential for study of the effects of neurotoxic compounds such as beta-amyloid peptides (Abeta). The MTT assay has been used in cultures of different cells, e.g. SH-SY5Y neuroblastoma cells, for the quantitative measurement of Abeta toxicity. In our laboratory differentiated SH-SY5Y cells were used in the MTT assay. Cell differentiation with 10 microM all-trans-retinoic acid resulted in a constant cell number. The cells possess highly developed neurites and exhibit high sensitivity against Abeta. Owing to the constant cell number in differentiated SH-SY5Y cultures the decrease of the redox activity is directly proportional to the neurotoxicity of the substances, no correction is needed. The results of the MTT assay of Abeta peptides on differentiated SH-SY5Y cells displayed a good correlation also with the in vivo results. The present experiments reveal an effective assay for the study of potentially neurotoxic compounds.