3D human stem-cell-derived neuronal spheroids for in vitro neurotoxicity testing of methylglyoxal, highly reactive glycolysis byproduct and potent glycating agent.

Human-derived three-dimensional (3D) in vitro models are advanced human cell-based model for their complexity, relevance and application in toxicity testing. Intracellular accumulation of methylglyoxal (MGO), the most potent glycating agent in humans, mainly generated as a by-product of glycolysis, is associated with age-related diseases including neurodegenerative disorders. In our study, 3D human stem-cell-derived neuronal spheroids were set up and applied to evaluate cytotoxic effects after short-term (5 to 48 h) treatments with different MGO concentrations, including low levels, taking into consideration several biochemical endpoints. In MGO-treated neurospheroids, reduced cell growth proliferation and decreased cell viability occurred early from 5-10 µM, and their compactness diminished starting from 100 µM, apparently without affecting spheroid size. MGO markedly caused loss of the neuronal markers MAP-2 and NSE from 10-50 µM, decreased the detoxifying Glo1 enzyme from 50 µM, and activated NF-kB by nuclear translocation. The cytochemical evaluation of the 3D sections showed the presence of necrotic cells with loss of nuclei. Apoptotic cells were observed from 50 µM MGO after 48 h, and from 100 µM after 24 h. MGO (50-10 µM) also induced modifications of the cell-cell and cell-ECM interactions. These effects worsened at the higher concentrations (300-500 µM). In 3D neuronal spheroids, MGO tested concentrations comparable to human samples levels measured in MGO-associated diseases, altered neuronal key signalling endpoints relevant for the pathogenesis of neurodegenerative diseases and aging. The findings also demonstrated that the use of 3D neuronal spheroids of human origin can be useful in a strategy in vitro for testing MGO and other dicarbonyls evaluation.

Methylglyoxal-induced neurotoxic effects in primary neuronal-like cells transdifferentiated from human mesenchymal stem cells: Impact of low concentrations.

In the last decades, advanced glycation end-products (AGEs) have aroused the interest of the scientific community due to the increasing evidence of their involvement in many pathophysiological processes including various neurological disorders and cognitive decline age related. Methylglyoxal (MG) is one of the reactive dicarbonyl precursors of AGEs, mainly generated as a by-product of glycolysis, whose accumulation induces neurotoxicity. In our study, MG cytotoxicity was evaluated employing a human stem cell-derived model, namely, neuron-like cells (hNLCs) transdifferentiated from mesenchymal stem/stromal cells, which served as a source of human based species-specific "healthy" cells. MG increased ROS production and induced the first characteristic apoptotic hallmarks already at low concentrations (≥10 µM), decreased the cell growth (≥5-10 µM) and viability (≥25 µM), altered Glo-1 and Glo-2 enzymes (≥25 µM), and markedly affected the neuronal markers MAP-2 and NSE causing their loss at low MG concentrations (≥10 µM). Morphological alterations started at 100 µM, followed by even more marked effects and cell death after few hours (5 h) from 200 µM MG addition. Substantially, most effects occurred as low as 10 µM, concentration much lower than that reported from previous observations using different in vitro cell-based models (e.g., human neuroblastoma cell lines, primary animal cells, and human iPSCs). Remarkably, this low effective concentration approaches the level range measured in biological samples of pathological subjects. The use of a suitable cellular model, that is, human primary neurons, can provide an additional valuable tool, mimicking better the physiological and biochemical properties of brain cells, in order to evaluate the mechanistic basis of molecular and cellular alterations in CNS.

Human Astrocyte Spheroids as Suitable In Vitro Screening Model to Evaluate Synthetic Cannabinoid MAM2201-Induced Effects on CNS.

There is growing concern about the consumption of synthetic cannabinoids (SCs), one of the largest groups of new psychoactive substances, its consequence on human health (general population and workers), and the continuous placing of new SCs on the market. Although drug-induced alterations in neuronal function remain an essential component for theories of drug addiction, accumulating evidence indicates the important role of activated astrocytes, whose essential and pleiotropic role in brain physiology and pathology is well recognized. The study aims to clarify the mechanisms of neurotoxicity induced by one of the most potent SCs, named MAM-2201 (a naphthoyl-indole derivative), by applying a novel three-dimensional (3D) cell culture model, mimicking the physiological and biochemical properties of brain tissues better than traditional two-dimensional in vitro systems. Specifically, human astrocyte spheroids, generated from the D384 astrocyte cell line, were treated with different MAM-2201 concentrations (1-30 µM) and exposure times (24-48 h). MAM-2201 affected, in a concentration- and time-dependent manner, the cell growth and viability, size and morphological structure, E-cadherin and extracellular matrix, CB1-receptors, glial fibrillary acidic protein, and caspase-3/7 activity. The findings demonstrate MAM-2201-induced cytotoxicity to astrocyte spheroids, and support the use of this human 3D cell-based model as species-specific in vitro tool suitable for the evaluation of neurotoxicity induced by other SCs.

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

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

Three-dimensional spheroid cell culture of human MSC-derived neuron-like cells: New in vitro model to assess magnetite nanoparticle-induced neurotoxicity effects.

As nanoparticles (NPs) can access the brain and impact on CNS function, novel in vitro models for the evaluation of NPs-induced neurotoxicity are advocated. Three-dimensional spheroids of primary neuron-like cells (hNLCs) of human origin have been generated, from differentiation of human umbilical cord mesenchymal stem cells (MSCs). The study evaluated Fe3 O4 NP impact on the differentiation process by applying the challenge at complete 3D hNLC spheroid formation (after 4 days, T4) or at beginning of neurogenic induction/simultaneously 3D forming (T0). Different endpoints were monitored over time (up to 10 days): spheroid growth, size, morphology, ATP, cell death, neuronal markers (ß-Tub III, MAP-2, and NSE), NP uptake. At T0 application, a marked concentration- and time-dependent cell mortality occurred: effect started early (day 2) and low concentration (1 µg/ml) and exacerbated (80% mortality) after prolonged time (day 6) and increased concentrations (50 µg/ml). ATP was strikingly affected. All neuronal markers were downregulated, and spheroid morphology altered in a concentration-dependent manner (from ≥5 µg/ml) after day 2. Fe3 O4 NPs applied at complete 3D formation (T4) still induced adverse effects although less severe: cell mortality (20-60%) and ATP content decrease (10-40%) were observed in a concentration-dependent manner (from ≥ 5 µg/ml). A neuronal-specific marker effect and spheroid size reduction from 25 µg/ml without morphology alteration were evidenced. This finding provides additional information on neurotoxic effects of Fe3 O4 NPs in a new 3D hNLC spheroid model derived from MSCs that could find a consistent application as in a testing strategy serving in first step hazard identification for correct risk assessment.

Developmental Neurotoxicity Screening for Nanoparticles Using Neuron-Like Cells of Human Umbilical Cord Mesenchymal Stem Cells: Example with Magnetite Nanoparticles.

Metallic nanoparticles (NPs), as iron oxide NPs, accumulate in organs, cross the blood-brain barrier and placenta, and have the potential to elicit developmental neurotoxicity (DNT). Human stem cell-derived in vitro models may provide more realistic platforms to study NPs effects on neural cells, and to obtain relevant information on the potential for early or late DNT effects in humans. Primary neuronal-like cells (hNLCs) were generated from mesenchymal stem cells derived from human umbilical cord lining and the effects caused by magnetite (Fe3O4NPs, 1-50 µg/mL) evaluated. Neuronal differentiation process was divided into stages: undifferentiated, early, mid- and fully-differentiated (from day-2 to 8 of induction) based on different neuronal markers and morphological changes over time. Reduction in neuronal differentiation induction after NP exposure was observed associated with NP uptake: ß-tubulin III (ß-Tub III), microtubule-associated protein 2 (MAP-2), enolase (NSE) and nestin were downregulated (10-40%), starting from 25 µg/mL at the early stage. Effects were exacerbated at higher concentrations and persisted up to 8 days without cell morphology alterations. Adenosine triphosphate (ATP) and caspase-3/7 activity data indicated Fe3O4NPs-induced cell mortality in a concentration-dependent manner and increases of apoptosis: effects appeared early (from day-3), started at low concentrations (≥5 µg/mL) and persisted. This new human cell-based model allows different stages of hNLCs to be cultured, exposed to NPs/chemicals, and analyzed for different endpoints at early or later developmental stage.

In vitro evaluation of magnetite nanoparticles in human mesenchymal stem cells: comparison of different cytotoxicity assays.

This work was aimed at defining the suitable test for evaluating Fe3O4 NPs cytotoxicity after short-term exposure in human mesenchymal stem cells (hMSCs) using different viability tests, namely NRU, MTT and TB assays, paralleled by cell morphology analyses for cross checking. MTT and NRU data (culture medium with/without hMSCs plus Fe3O4NPs) indicated artificial/false increments in cell viability after Fe3O4NPs. These observations did not fit with the morphological analyses showing reduced cell density, loss of monolayer features, and morphological alterations at Fe3O4NPs ≥50 µg/ml. Fe3O4NPs alone induced a substantial increased absorbance at the wavelength required for MTT and NRU. A significant death (25%) of hMSC at Fe3O4NPs ≥10 µg/ml, with a maximum effect (45%) at 300 µg/ml after 24 h, exacerbated after 48 h, was observed when applying TB test. These results paralleled the effects on cell morphology. The optical properties and stability of Fe3O4NP suspension (tendency to agglomerate in a specific culture medium) represent factors that limit in vitro result interpretation. These findings suggest the non applicability of the spectrophotometric assays for hMSC culture conditions, while TB is an accurate method for determining cell viability after Fe3O4NP exposure in this model. In relation to NPs safety assessment: cell-based assays must be considered on case-by-case basis; selection of relevant cell models is also important for predictive toxicological studies; application of a testing strategy is fundamental for understanding the toxicity pathways driving cellular responses.

In vitro toxicity screening of magnetite nanoparticles by applying mesenchymal stem cells derived from human umbilical cord lining.

Despite the growing interest in nanoparticles (NPs), their toxicity has not yet been defined and the development of new strategies and predictive models are required. Human stem cells (SCs) offer a promising and innovative cell-based model. Among SCs, mesenchymal SCs (MSCs) derived from cord lining membrane (CL) may represent a new species-specific tool for establishing efficient platforms for primary screening and toxicity/safety testing of NPs. Superparamagnetic iron oxide NPs, including magnetite (Fe3 O4 NPs), have aroused great public health and scientific concerns despite their extensive uses. In this study, CL-MSCs were characterized and applied for in vitro toxicity screening of Fe3 O4 NPs. Cytotoxicity, internalization/uptake, differentiation and proliferative capacity were evaluated after exposure to different Fe3 O4 NP concentrations. Data were compared with those obtained from bone marrow (BM)-MSCs. We observed, at early passages (P3), that: (1) cytotoxicity occurred at 10 µg/mL in CL-MSCs and 100 µg/mL in BM-MSCs (no differences in toxicity, between CL- and BM-MSCs, were observed at higher dosage, 100-300 µg/mL); (2) cell density decrease and monolayer features loss were affected at ≥50 µg/mL in CL-MSCs only; and (3) NP uptake was concentration-dependent in both MSCs. After 100 µg/mL Fe3 O4 NP exposures, the capacity of proliferation was decreased (P5-P9) in CL-MSCs without morphology alteration. Moreover, a progressive decrease of intracellular Fe3 O4 NPs was observed over culture time. Antigen surface expression and multilineage differentiation were not influenced. These findings suggest that CL-MSCs could be used as a reliable cell-based model for Fe3 O4 NP toxicity screening evaluation and support the use of this approach for improving the confidence degree on the safety of NPs to predict health outcomes.

Neuron-Like Cells Generated from Human Umbilical Cord Lining-Derived Mesenchymal Stem Cells as a New In Vitro Model for Neuronal Toxicity Screening: Using Magnetite Nanoparticles as an Example.

The wide employment of iron nanoparticles in environmental and occupational settings underlines their potential to enter the brain. Human cell-based systems are recommended as relevant models to reduce uncertainty and to improve prediction of human toxicity. This study aimed at demonstrating the in vitro differentiation of the human umbilical cord lining-derived-mesenchymal stem cells (hCL-MSCs) into neuron-like cells (hNLCs) and the benefit of using them as an ideal primary cell source of human origin for the neuronal toxicity of Fe3O4NPs (magnetite-nanoparticles). Neuron-like phenotype was confirmed by: live morphology; Nissl body staining; protein expression of different neuronal-specific markers (immunofluorescent staining), at different maturation stages (i.e., day-3-early and day-8-full differentiated), namely ß-tubulin III, MAP-2, enolase (NSE), glial protein, and almost no nestin and SOX-2 expression. Synaptic makers (SYN, GAP43, and PSD95) were also expressed. Fe3O4NPs determined a concentration- and time-dependent reduction of hNLCs viability (by ATP and the Trypan Blue test). Cell density decreased (20-50%) and apoptotic effects were detected at ≥10 µg/mL in both types of differentiated hNLCs. Three-day-differentiated hNLCs were more susceptible (toxicity appeared early and lasted for up to 48 h) than 8-day-differentiated cells (delayed effects). The study demonstrated that (i) hCL-MSCs easily differentiated into neuronal-like cells; (ii) the hNCLs susceptibility to Fe3O4NPs; and (iii) human primary cultures of neurons are new in vitro model for NP evaluation.

Cytotoxic Effects of 3,4-Catechol-PV (One Major MDPV Metabolite) on Human Dopaminergic SH-SY5Y Cells.

3,4-Methylenedioxypyrovalerone (MDPV), one of the most commonly abused synthetic cathinones, has caused several intoxications and deaths despite its short presence on the market. Apart from its effects on the monoamine systems in the brain, recent in vitro investigations have revealed cytotoxicity. In this study, the effects of increasing concentrations (10-1000 µM) of 3,4-Catechol-PV, one of major MDPV metabolites, on cell viability, morphology, and apoptosis have been evaluated after acute exposure (24-48 h) in human neuroblastoma SH-SY5Y cells-undifferentiated and differentiated to a more mature neuronal-like phenotype. Results indicated the following: (i) Cell viability: concentration-dependent decrease (15-55%) in differentiated SH-SY5Y after 24 h, with no exacerbation after 48 h (LC50 values 1028 and 951 µM, respectively); marked concentration-dependent decrease after 48 h (20-63%) in undifferentiated SH-SY5Y (LC50 553.9 µM) with mild effect (18-22% cell death) after 24 h at ≥ 500 µM only; the lowest toxic concentrations were 500 and 100 µM after 24 h, for undifferentiated and differentiated SH-SY5Y, respectively, and 10 µM after 48 h. (ii) Concentration- and time-dependent alterations of cell morphology in both SH-SY5Y types characterized by several intracellular cytoplasmic vesicles (undifferentiated more susceptible (effect at ≥ 50 µM) than differentiated cells (effect at ≥ 100 µM)), loss of the typical cell shape, neurite retraction, and cell density decrease. (iii) Activation of caspase-3 enzyme in differentiated and undifferentiated cells after 48 h. These findings suggest the potential involvement of 3,4-Catechol-PV in MDPV-induced neurotoxicity and support the use of this human cellular model as a species-specific in vitro tool to clarify the neurotoxicity mechanisms of synthetic cathinones and metabolites.

Human 3D Cultures as Models for Evaluating Magnetic Nanoparticle CNS Cytotoxicity after Short- and Repeated Long-Term Exposure.

Since nanoparticles (NPs) can translocate to the brain and impact the highly vulnerable central nervous system (CNS), novel in vitro tools for the assessment of NP-induced neurotoxicity are advocated. In this study, two types of CNS spheroids have been developed from human D384 astrocyte- and SH-SY5Y neuronal-like cells, and optimized in combination with standard assays (viability readout and cell morphology) to test neurotoxic effects caused by Fe3O4NPs, as NP-model, after short- (24­48 h; 1­100µg/ml) and long-term repeated exposure (30days; 0.1­25µg/ml). Short-term exposure of 3D-spheroids to Fe3O4NP induced cytotoxicity at 10 µg/mL in astrocytes and 25 µg/mL neurons. After long-term repeated dose regimen, spheroids showed concentration- and time-dependent cell mortality at 10 µg/mL for D384 and 0.5 µg/mL for SH-SY5Y, indicating a higher susceptibility of neurons than astrocytes. Both spheroid types displayed cell disaggregation after the first week of treatment at ≥0.1 µg/mL and becoming considerably evident at higher concentrations and over time. Recreating the 3D-spatial environment of the CNS allows cells to behave in vitro more closely to the in vivo situations, therefore providing a model that can be used as a stand-alone test or as a part of integrated testing strategies. These models could drive an improvement in the species-relevant predictivity of toxicity testing.

Human Co-culture Model of Neurons and Astrocytes to Test Acute Cytotoxicity of Neurotoxic Compounds.

Alternative methods and their use in planning and conducting toxicology experiments have become essential for modern toxicologists, thus reducing or replacing living animals. Although in vitro human co-culture models allow the establishment of biologically relevant cell-cell interactions that recapitulate the tissue microenvironment and better mimic its physiology, the number of publications is limited specifically addressing this scientific area and utilizing this test method which could provide an additional valuable model in toxicological studies. In the present study, an in vitro model based on central nervous system (CNS) cell co-cultures was implemented using a transwell system combining human neuronal cells (SH-SY5Y cell line) and glial cells, namely astrocytes (D384 cell line), to investigate neuroprotection of D384 on SH-SY5Y and vice versa. The model was applied to test acute (24-48 hours) cytotoxicity of 3 different neurotoxicants: (1) methyl mercury (1-2.5 µM), (2) Fe3O4 nanoparticles (1-100 µg/mL), and (3) methylglyoxal (0.5-1 mM). Data were compared to mono-cultures evaluating the mitochondrial function and cell morphology. The results clearly showed that all compounds tested affected the mitochondrial activity and cell morphology in both mono-culture and co-culture conditions. However, astrocytes, when cultured together with neurons, diminish the neurotoxicant-induced cytotoxic effects that occurred in neurons cultured alone, and astrocytes become more resistant in the presence of neurons. This human CNS co-culture system seems a suitable cell model to feed high-throughput acute screening platforms and to evaluate both human neuronal and astrocytic toxicity and neuroprotective effects of new and emerging materials (eg, nanomaterials) and new products with improved sensitivity due to the functional neuron-astrocyte metabolic interactions.

Human neuronal cell based assay: A new in vitro model for toxicity evaluation of ciguatoxin.

Ciguatoxins (CTXs) are emerging marine neurotoxins representing the main cause of ciguatera fish poisoning, an intoxication syndrome which configures a health emergency and constitutes an evolving issue constantly changing due to new vectors and derivatives of CTXs, as well as their presence in new non-endemic areas. The study applied the neuroblastoma cell model of human origin (SH-SY5Y) to evaluate species-specific mechanistic information on CTX toxicity. Metabolic functionality, cell morphology, cytosolic Ca2+i responses, neuronal cell growth and proliferation were assessed after short- (4-24h) and long-term exposure (10days) to P-CTX-3C. In SH-SY5Y, P-CTX-3C displayed a powerful cytotoxicity requiring the presence of both Veratridine and Ouabain. SH-SY5Y were very sensitive to Ouabain: 10 and 0.25nM appeared the optimal concentrations, for short- and long-term toxicity studies, respectively, to be used in co-incubation with Veratridine (25µM), simulating the physiological and pathological endogenous Ouabain levels in humans. P-CTX-3C cytotoxic effect, on human neurons co-incubated with OV (Ouabain+Veratridine) mix, was expressed starting from 100pM after short- and 25pM after long-term exposure. Notably, P-CTX-3C alone at 25nM induced cytotoxicity after 24h and prolonged exposure. This human brain-derived cell line appears a suitable cell-based-model to evaluate cytotoxicity of CTX present in marine food contaminated at low toxic levels and to characterize the toxicological profile of other/new congeners.

Cytotoxicity and proliferative capacity impairment induced on human brain cell cultures after short- and long-term exposure to magnetite nanoparticles.

Since magnetic iron oxide nanoparticles (IONP) as magnetite (Fe3 O4 NPs) have potential applications in life sciences, industrial fields and biomedical care, the risks for occupational, general population and patients rises correspondingly. Excessive IONP accumulation in central nervous system (CNS) cells can lead to a disruption of normal iron metabolism/homeostasis, which is a characteristic hallmark resembling that of several neurodegenerative disorders. Fe3 O4 NPs- versus Fe3 O4 bulk-induced toxic effects have been assessed in two human CNS cells namely astrocytes (D384) and neurons (SH-SY5Y) after short-term exposure (4-24-48 h) to 1-100 µg ml-1 , and long-term exposure to lower concentrations. Short-term Fe3 O4 NPs induced significant concentration- and time-dependent alterations of mitochondrial function in D384 (25-75% cell viability decrease): effects started at 25 µg ml-1 after 4 h, and 1 µg ml-1 after 48 h. SH-SY5Y were less susceptible: cytotoxicity occurred after 48  h only with 35-45% mortality (10-100 µg ml-1 ). Accordingly, a more marked intracellular iron accumulation was observed in astrocytes than neurons. Membrane integrity was unaltered in both CNS cell types. Lowering Fe3 O4 NP concentrations (0.05-10 µg ml-1 ) and prolonging the exposure time (up to 10 days), D384 toxicity was again observed (colony number decrease at ≥0.05 µg ml-1 , morphology alterations and colony size reduction at ≥0.5 µg ml-1 ). Effects on SH-SY5Y appeared at the highest concentration only. Fe3 O4 bulk was always remarkably toxic toward both cells. In summary, human cultured astrocytes were susceptible to both Fe3 O4 NP and bulk forms following short-term and extended exposure to low concentrations, while neurons were more resistant to NPs. Cellular iron overload may trigger adverse responses by releasing iron ions (particularly in astrocytes) thus compromising the normal functions of CNS. Copyright © 2016 John Wiley & Sons, Ltd.

Toxicity Evaluation of Iron Oxide (Fe3O4) Nanoparticles on Human Neuroblastoma-Derived SH-SY5Y Cell Line.

Several studies suggest that Iron Oxide nanoparticles may arrive to central nervous system independently of the route of administration. Actually, evidences indicate that the presence iron oxide nanoparticles into nervous system are linked to several neurodegenerative diseases. In this regard, our goal was to assess in vitro PolyVinylPirrolidone coated Iron Oxide nanoparticles, diameter of 20 nm, neuro-toxicity and their mechanism of action, which was fixed over the human neuronal cell line SH-SY5Y. Inducted biological effects were evaluated after 4­48 hours at crescents doses 1­100 µg/mL using the following endpoints: (i) Membrane integrity: Nanoparticles have produced no effect over cellular membrane for every dose and time evaluated; (ii) Mitochondrial activity: Starting at 10 µg/mL with a decrease of cellular vitality of 35%, and a maximum decrease of 45% at highest dose (100 µg/mL); (iii) Cellular morphology: Cells have evidenced no alteration after 48 hours of exposure; (iv) Cellular uptake: Dose-time dependent accumulation has observed: blue spots have been found at 10 µg/mL and over. Concluding, mitochondria are apparently the target: considering that the toxic effect produced by PolyVinylPirrolidone coated Iron Oxide nanoparticles after 48 hours of exposure in a dose-time dependent manner was evident.

Brief exposure to nanosized and bulk titanium dioxide forms induces subtle changes in human D384 astrocytes.

Although nanosized-titanium dioxide particles (TiO2NPs)-containing products are constantly placed on the market, little is known about their possible impact on human health, even regarding to CNS effects. In this study, mechanistic pathways, by which TiO2NPs induce cellular damage and death, have been investigated in human (astrocytes-like) D384 cells and comparatively weighed against the effects produced by the bulk counterpart. Cellular signals evaluated by multiple set of in vitro tests after 24h exposure to TiO2NP concentrations (0.5-125µg/ml) were: ROS production, p-p53, p53, p21, Bax, Bcl-2 and caspase 3. TiO2 cellular uptake was also estimated by both light microscopy and ICP-MS. ROS were generated starting at 1.5µg/ml and further increased at the highest concentrations (≥31µg/ml). At the same low concentration, an increased expression of p-p53, p53, p21, Bax, and activated caspase3 were also observed. Parallely, Bcl-2 decreased along with TiO2NP concentration increase. Similar alterations were observed when testing TiO2 bulk: cellular checkpoint perturbations were associated with rising intracellular Ti. The present data demonstrated that low TiO2NP concentrations were capable, after 24h, to induce subtle cellular perturbation in D384 cells after a single cell treatment, supporting the evidence that both oxidative stress and apoptotic mechanisms may occur in this type of CNS cells.

Enhanced toxicity of silver nanoparticles in transgenic Caenorhabditis elegans expressing amyloidogenic proteins.

The increasing number of applications of silver nanoparticles (AgNP) prompted us to assess their toxicity in vivo. We have investigated their effects on wild type and transgenic Caenorhabditis elegans (C. elegans) strains expressing two prototypic amyloidogenic proteins: ß2-microglobulin and Aß peptide3-42. The use of C. elegans allowed us to highlight AgNP toxicity in the early phase of the worm's life cycle (LC50 survival, 0.9 µg/ml). A comparative analysis of LC50 values revealed that our nematode strains were more sensitive to assess AgNP toxicity than the cell lines, classically used in toxicity tests. Movement and superoxide production in the adult population were significantly affected by exposure to AgNP; the transgenic strains were more affected than the wild type worms. Our screening approach could be applied to other types of nanomaterials that can enter the body and express any nanostructure-related bioactivities. We propose that C. elegans reproducing the molecular events associated with protein misfolding diseases, e.g. Alzheimer's disease and systemic amyloidosis, may help to investigate the specific toxicity of a range of potentially harmful molecules. Our study suggests that transgenic C. elegans may be used to predict the effect of chemicals in a "fragile population", where an underlying pathologic state may amplify their toxicity.

Comparative cellular toxicity of titanium dioxide nanoparticles on human astrocyte and neuronal cells after acute and prolonged exposure.

Although in the last few decades, titanium dioxide nanoparticles (TiO2NPs) have attracted extensive interest due to their use in wide range of applications, their influences on human health are still quite uncertain and less known. Evidence exists indicating TiO2NPs ability to enter the brain, thus representing a realistic risk factor for both chronic and accidental exposure with the consequent needs for more detailed investigation on CNS. A rapid and effective in vitro test strategy has been applied to determine the effects of TiO2NPs anatase isoform, on human glial (D384) and neuronal (SH-SY5Y) cell lines. Toxicity was assessed at different levels: mitochondrial function (by MTT), membrane integrity and cell morphology (by calcein AM/PI staining) after acute exposure (4-24-48 h) at doses from 1.5 to 250 µg/ml as well as growth and cell proliferation (by clonogenic test) after prolonged exposure (7-10 days) at sub-toxic concentrations (from 0.05 to 31 µg/ml). The cytotoxic effects of TiO2NPs were compared with those caused by TiO2 bulk counterpart treatment. Acute TiO2NP exposure produced (i) dose- and time-dependent alterations of the mitochondrial function on D384 and SH-SY5Y cells starting at 31 and 15 µg/ml doses, respectively, after 24h exposure. SH-SY5Y were slightly more sensitive than D384 cells; and (ii) cell membrane damage occurring at 125 µg/ml after 24h exposure in both cerebral cells. Comparatively, the effects of TiO2 bulk were less pronounced than those induced by nanoparticles in both cerebral cell lines. Prolonged exposure indicated that the proliferative capacity (colony size) was compromised at the extremely low TiO2NP doses namely 1.5 µg/ml and 0.1 µg/ml for D384 and SH-SY5Y, respectively; cell sensitivity was still higher for SH-SY5Y compared to D384. Colony number decrease (15%) was also evidenced at ≥0.2 µg/ml TiO2NP dose. Whereas, TiO2 bulk treatment affected cell morphology only. TiO2 internalization in SH-SY5Y and D384 cells was appreciated using light microscopy. These findings indicated, that (i) human cerebral SH-SY5Y and D384 cell lines exposed to TiO2NPs were affected not only after acute but even after prolonged exposure at particularly low doses (≥ 0.1 µg/ml), (ii) these in vitro critical doses were comparable to literature brain Ti levels detected in lab animal intranasally administered with TiO2NP and associated to neurotoxic effects. In summary, the applied cell-based screening platform seems to provide effective means to initial evaluation of TiO2NP toxicity on CNS.

Assessment of cellular responses after short- and long-term exposure to silver nanoparticles in human neuroblastoma (SH-SY5Y) and astrocytoma (D384) cells.

Silver nanoparticle (AgNP, 20 nm) neurotoxicity was evaluated by an integrated in vitro testing protocol employing human cerebral (SH-SY5Y and D384) cell lines. Cellular response after short-term (4-48 h, 1-100 µ g/ml) and prolonged exposure (up to 10 days, 0.5-50 µ g/ml) to AgNP was assessed by MTT, calcein-AM/PI, clonogenic tests. Pulmonary A549 cells were employed for data comparison along with silver nitrate as metal ionic form. Short-term data: (i) AgNP produced dose- and time-dependent mitochondrial metabolism changes and cell membrane damage (effects starting at 25 µ g/ml after 4 h: EC50s were 40.7 ± 2.0 and 49.5 ± 2.1 µ g/ml for SH-SY5Y and D384, respectively). A549 were less vulnerable; (ii) AgNP doses of ≤ 18 µ g/ml were noncytotoxic; (iii) AgNO3 induced more pronounced effects compared to AgNP on cerebral cells. Long-term data: (i) low AgNP doses (≤ 1 µ g/ml) compromised proliferative capacity of all cell types (cell sensibility: SHSY5Y > A549 > D384). Colony number decrease in SH-SY5Y and D384 was 50% and 25%, respectively, at 1 µ g/ml, and lower dose (0.5 µ g/ml) was significantly effective towards SH-SY5Y and pulmonary cells; (ii) cell proliferation activity was more affected by AgNO3 than AgNPs. In summary, AgNP-induced cytotoxic effects after short-term and prolonged exposure (even at low doses) were evidenced regardless of cell model types.