In vitro models for assessing neurotoxicity of mixtures

Time and space-resolved quantification of plasma membrane sialylation for measurements of cell function and neurotoxicity

While there are many methods to quantify the synthesis, localization, and pool sizes of proteins and DNA during physiological responses and toxicological stress, only few approaches allow following the fate of carbohydrates. One of them is metabolic glycoengineering (MGE), which makes use of chemically modified sugars (CMS) that enter the cellular biosynthesis pathways leading to glycoproteins and glycolipids. The CMS can subsequently be coupled (via bio-orthogonal chemical reactions) to tags that are quantifiable by microscopic imaging. We asked here, whether MGE can be used in a quantitative and time-resolved way to study neuronal glycoprotein synthesis and its impairment. We focused on the detection of sialic acid (Sia), by feeding human neurons the biosynthetic precursor N-acetyl-mannosamine, modified by an azide tag. Using this system, we identified non-toxic conditions that allowed live cell labeling with high spatial and temporal resolution, as well as the quantification of cell surface Sia. Using combinations of immunostaining, chromatography, and western blotting, we quantified the percentage of cellular label incorporation and effects on glycoproteins such as polysialylated neural cell adhesion molecule. A specific imaging algorithm was used to quantify Sia incorporation into neuronal projections, as potential measure of complex cell function in toxicological studies. When various toxicants were studied, we identified a subgroup (mitochondrial respiration inhibitors) that affected neurite glycan levels several hours before any other viability parameter was affected. The MGE-based neurotoxicity assay, thus allowed the identification of subtle impairments of neurochemical function with very high sensitivity.

An aggregation-induced emission-based fluorescence turn-on probe for Hg2+ and its application to detect Hg2+ in food samples

In this work, we presented a new tetraphenylethene-derived fluorescent probe TPE-M for Hg²⁺ detection in an aqueous solution. Probe TPE-M is molecularly dissolved in CH₃OH/PBS (20 mM, pH = 7.4) (3 : 7, v/v) mixed solution and is almost non-emissive. Reaction of TPE-M with Hg²⁺ leads to release of an AIE-active precursor 4, and results in a significant fluorescence enhancement. The Hg²⁺ recognition process has some distinct advantages including rapid response, high selectivity and sensitivity, strong anti-interference ability, and a low detection limit (4.16 × 10⁻⁶ M). Moreover, the probe is applicable to detect Hg²⁺ in real food samples such as shrimp, crab and teas, suggesting the practical applicability of TPE-M.

A new AIE-based fluorescent probe TPE-M for Hg²⁺ detection in an aqueous solution has been developed.

Aluminium and Acrylamide Disrupt Cerebellum Redox States, Cholinergic Function and Membrane-Bound ATPase in Adult Rats and Their Offspring

Accumulation of aluminium and acrylamide in food is a major source of human exposure. Their adverse effects are well documented, but there is no information about the health problems arising from their combined exposure. The aim of the present study was to examine the possible neurotoxic effects after co-exposure of pregnant and lactating rats to aluminium and acrylamide in order to evaluate redox state, cholinergic function and membrane-bound ATPases in the cerebellum of adult rats and their progeny. Pregnant female rats have received aluminium (50 mg/kg body weight) via drinking water and acrylamide (20 mg/kg body weight) by gavage, either individually or in combination from the 14th day of pregnancy until day 14 after delivery. Exposure to these toxicants provoked an increase in malondialdehyde (MDA) and advanced oxidation protein product (AOPP) levels and a decrease in SOD, CAT, GPx, Na⁺K⁺-ATPase, Mg²⁺-ATPase and AChE activities in the cerebellum of mothers and their suckling pups. A reduction in GSH, NPSH and vitamin C levels was also observed. These changes were confirmed by histological results. Interestingly, co-exposure to these toxicants exhibited synergism based on physical and biochemical variables in the cerebellum of mothers and their progeny.

Urinary delta-ALA: a potential biomarker of exposure and neurotoxic effect in rats co-treated with a mixture of lead, arsenic and manganese

Lead (Pb), arsenic (As) and manganese (Mn) are neurotoxic elements that often occur in mixtures for which practically no information is available on biomarkers (BMs) for the evaluation of exposure/effects. Exposures to these metals may increase delta-aminolevulinic acid (delta-ALA), which in itself may potentiate neurotoxicity. The objective of this study was to investigate the utility of urinary delta-ALA (delta-ALA-U) levels as BM of exposure and/or neurotoxic effects induced by this mixture. Five groups of Wistar rats were treated for 8 days with Pb (5mg/kg), As (60mg/L), Mn (10mg/kg), the 3-metal mixture (same doses of the single metals), and control group. Motor activity was evaluated and 24-h urine collected before and after the treatment. 24-hours (h) after the last dose, the rats were sacrificed and the brains removed for analyses. Delta-ALA and metal levels were determined in brain and urine. Co-treated rats showed a significant (p<0.05) correlation between increased Pb, As, Mn and delta-ALA levels in the brain and decreased motor activity. Delta-ALA-U concentrations were higher in the mixture-treated group than the sum of the delta-ALA-U levels in each single-treated groups and discriminated (p<0.05) between the mixture and untreated rats. Moreover, delta-ALA-U was correlated (p<0.05) with brain delta-ALA levels. These results establish that treatments with this metal mixture exacerbate behavioral dysfunction, increasing most prominently brain Pb levels. This study is the first to establish that delta-ALA-U levels represent a sensitive BM of exposure/neurotoxic effect to this metal mixture.

Morphological and functional differentiation in BE(2)-M17 human neuroblastoma cells by treatment with Trans-retinoic acid

Background

Immortalized neuronal cell lines can be induced to differentiate into more mature neurons by adding specific compounds or growth factors to the culture medium. This property makes neuronal cell lines attractive as in vitro cell models to study neuronal functions and neurotoxicity. The clonal human neuroblastoma BE(2)-M17 cell line is known to differentiate into a more prominent neuronal cell type by treatment with trans-retinoic acid. However, there is a lack of information on the morphological and functional aspects of these differentiated cells.

Results

We studied the effects of trans-retinoic acid treatment on (a) some differentiation marker proteins, (b) types of voltage-gated calcium (Ca²⁺) channels and (c) Ca²⁺-dependent neurotransmitter ([³H] glycine) release in cultured BE(2)-M17 cells. Cells treated with 10 μM trans-retinoic acid (RA) for 72 hrs exhibited marked changes in morphology to include neurite extensions; presence of P/Q, N and T-type voltage-gated Ca²⁺ channels; and expression of neuron specific enolase (NSE), synaptosomal-associated protein 25 (SNAP-25), nicotinic acetylcholine receptor α7 (nAChR-α7) and other neuronal markers. Moreover, retinoic acid treated cells had a significant increase in evoked Ca²⁺-dependent neurotransmitter release capacity. In toxicity studies of the toxic gas, phosgene (CG), that differentiation of M17 cells with RA was required to see the changes in intracellular free Ca²⁺ concentrations following exposure to CG.

Conclusion

Taken together, retinoic acid treated cells had improved morphological features as well as neuronal characteristics and functions; thus, these retinoic acid differentiated BE(2)-M17 cells may serve as a better neuronal model to study neurobiology and/or neurotoxicity.

Interactions between effects of environmental chemicals and natural stressors: a review

Ecotoxicological effect studies often expose test organisms under optimal environmental conditions. However, organisms in their natural settings rarely experience optimal conditions. On the contrary, during most of their lifetime they are forced to cope with sub-optimal conditions and occasionally with severe environmental stress. Interactions between the effects of a natural stressor and a toxicant can sometimes result in greater effects than expected from either of the stress types alone. The aim of the present review is to provide a synthesis of existing knowledge on the interactions between effects of "natural" and chemical (anthropogenic) stressors. More than 150 studies were evaluated covering stressors including heat, cold, desiccation, oxygen depletion, pathogens and immunomodulatory factors combined with a variety of environmental pollutants. This evaluation revealed that synergistic interactions between the effects of various natural stressors and toxicants are not uncommon phenomena. Thus, synergistic interactions were reported in more than 50% of the available studies on these interactions. Antagonistic interactions were also detected, but in fewer cases. Interestingly, about 70% of the tested chemicals were found to compromise the immune system of humans as judged from studies on human cell lines. The challenge for future studies will therefore be to include aspects of combined stressors in effect and risk assessment of chemicals in the environment.

GT1-7 cell-based cytoxicity screening assay on 96-well microplates as a platform for the safety assessment of genetically modified Gerbera hybrida extracts

In this investigation, a GT1-7 cell-based cytotoxicity screening assay in 96-well microplates was set up. The assay, using propidium iodide fluorescence, was proven to be reliable, with good quality (Z' = 0.51) and low plate-to-plate and day-to-day variations. Further on, a library containing extracts from 227 genetic modification (GM) Gerbera hybrida and 42 Gerbera varieties was screened; however, no differences between them were found. Based on these findings, we propose the use of the current assay within the first-tier screening studies of large collections. Also, these results provide valuable information for GM Gerbera risk-assessment purposes and offer a model for the toxicity cell-based screening of GM crops.

Stir bar sorptive extraction-thermal desorption-gas chromatography-mass spectrometry: an effective tool for determining persistent organic pollutants and nonylphenol in coastal waters in compliance with existing Directives

A multi-residual method based on stir bar sorptive extraction coupled with thermal desorption-gas chromatography-mass spectrometry (SBSE-TD-GC-MS) has been developed to measure 49 organic pollutants (organochlorine pesticides, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, polybrominated diphenyl ethers and nonylphenol) in seawater. Using 100ml of water, the method exhibited good linearity, with recoveries between 86% and 118% and relative standard deviation between 2% and 24% for almost all compounds. The method was applied to determine target contaminants in Catalonian seawater, including coastal areas, ports and desalination plant feed water. Overall individual compound levels oscillated between 0.16 and 597 ng l(-1); PAHs and nonylpenol were the compounds found at the highest concentrations. The method provided LODs between 0.011 and 2.5 ng l(-1), lower than the Environmental Quality Standards (EQS) fixed by Directive 2008/105/EC. In compliance with the directive, this method can be used as a tool to survey target compounds and is aimed at protecting coastal ecosystems from chemical pollution.

Twenty-First Century Challenges for In Vitro Neurotoxicity

During the last 40 years, studies incorporating in vitro methodologies have greatly advanced our understanding of human nerve cell biology. Attempts have been made to apply these to investigations of neurotoxicity. Due to the complexity of the nervous system, underpinned by an array of integrated interactions between a host of cell types, it is concluded that, at present, alternative neural models are most successful in determining the underlying mechanisms which can cause perturbation of normal functioning of the nervous system, both in adults and during the embryonic period. The use of tiered batteries of test models has been proposed in screening programmes for neurotoxicity, with the generation of much encouraging data in laboratories across the globe. This review aims to discuss the development of neural alternatives, considers the various model systems available, and highlights specific neuronal endpoints which can be tested, in addition to the cytotoxic evaluation of neuronal viability. Developments in molecular and stem cell biology, which are appropriate to neural tissue, and which offer the prospect of exciting advances for the next decade, are cited.

Interpreting epidemiologic studies of developmental neurotoxicity: conceptual and analytic issues

This paper discusses issues pertaining to the validity, precision, and interpretation of epidemiologic studies of neurotoxicity. With regard to validity, the critical issues pertain to the appropriate strategy for confounder adjustment, particularly when confounders are complex, multi-faceted constructs, and to the need for greater clarity and transparency in articulating the causal relationships implicit in the analytic approach applied. With regard to precision, the critical issue is a need to identify the contributors to the substantial variability observed in the effect estimates that describe dose-response and dose-effect relationships. In addition to methodological sources, such as imprecision in estimating dose at the critical organ site(s), true inter-individual differences in susceptibility to a neurotoxicant could also contribute to the variability. Variability might be reduced by taking full account of factors such as co-exposures or health co-morbidities, genetic polymorphisms, and the social ecology of exposure. With regard to interpretation, we need to do a better job as a field conveying to risk assessors and others the ecological significance of the types of performance deficits observed following neurotoxicant exposure, emphasizing the distinction between individual and population risk. A final issue discussed is the need to define standards for the conduct, analysis, and reporting of epidemiologic studies of neurotoxicity, similar to those developed for other fields.

Determination and occurrence of phthalates, alkylphenols, bisphenol A, PBDEs, PCBs and PAHs in an industrial sewage grid discharging to a Municipal Wastewater Treatment Plant

Industrial and urban discharges release organic contaminants which might affect the quality of receiving waters if not properly eliminated in Wastewater Treatment Plants (WWTP). This study is aimed to evaluate the source, transport and fate of contaminants of industrial origin in a sewage grid discharging to a WWTP and finally to the sea. The sampling network covered an industrial and urban area and wastewaters, influents and effluents of a WWTP were analyzed using a newly developed multiresidual method to capture a wide range contaminants (phthalates, alkylphenols, bisphenol A, PBDEs, PCBs and PAHs). Alkylphenols and phthalates followed by PAHs were the main compounds detected at levels between 0.01 to 698 microg l(-1) in the sewage pipelines. At the WWTP influent they were detected at concentrations up to 345 microg l(-1). The contaminant load was eliminated in a 64-92% during the primary and secondary treatment of the plant. However, alkylphenols, phthalates bisphenol A and traces of PAHs were discharged with the effluent, producing a total net input of 825 g d(-1) to the sea. The study of wastewaters herein proposed can be used to better predict the loads into WWTP to improve treatment conditions according to specific sewage inputs and to assess the risks associated with the continuous discharge of contaminants to receiving plants.