Neuron and glial cell marker proteins as indicators of heavy metal-induced neurotoxicity in neuroblastoma and glioma cell lines

Metal-organic frameworks: A promising option for the diagnosis and treatment of Alzheimer's disease

Beta-amyloid (Aβ) peptide is one of the main characteristic biomarkers of Alzheimer's disease (AD). Previous clinical investigations have proposed that unusual concentrations of this biomarker in cerebrospinal fluid, blood, and brain tissue are closely associated with the AD progression. Therefore, the critical point of early diagnosis, prevention, and treatment of AD is to monitor the levels of Aβ. In view of the potential of metal-organic frameworks (MOFs) for diagnosing and treating the AD, much attention has been focused in recent years. This review discusses the latest advances in the applications of MOFs for the early diagnosis of AD via fluorescence and electrochemiluminescence (ECL) detection of AD biomarkers, fluorescence detection of the main metal ions in the brain (Zn²⁺, Cu²⁺, Mn²⁺, Fe³⁺, and Al³⁺) in addition to magnetic resonance imaging (MRI) of the Aβ plaques. The current challenges and future strategies for translating the in vitro applications of MOFs into in vivo diagnosis of the AD are discussed.

Involvement of the synapse-specific zinc transporter ZnT3 in cadmium-induced hippocampal neurotoxicity

The present study examined the involvement of zinc (Zn)-transporters (ZnT3) in cadmium (Cd)-induced alterations of Zn homeostasis in rat hippocampal neurons. We treated primary rat hippocampal neurons for 24 or 48 hr with various concentrations of CdCl₂ (0, 0.5, 5, 10, 25, or 50 μM) and/or ZnCl ₂ (0, 10, 30, 50, 70, or 90 μM), using normal neuronal medium as control. By The CellTiter 96 ^® Aqueous One Solution Cell Proliferation Assay (MTS; Promega, Madison, WI) assay and immunohistochemistry for cell death markers, 10 and 25 μM of Cd were found to be noncytotoxic doses, and both 30 and 90 μM of Zn as the best concentrations for cell proliferation. We tested these selected doses. Cd, at concentrations of 10 or 25 μM (and depending on the absence or presence of Zn), decreased the percentage of surviving cells. Cd-induced neuronal death was either apoptotic or necrotic depending on dose, as indicated by 7-AAD and/or annexin V labeling. At the molecular level, Cd exposure induced a decrease in hippocampal brain-derived neurotrophic factor-tropomyosin receptor kinase B (BDNF-TrkB) and Erk1/2 signaling, a significant downregulation of the expression of learning- and memory-related receptors and synaptic proteins such as the NMDAR NR2A subunit and PSD-95, as well as the expression of the synapse-specific vesicular Zn transporter ZnT3 in cultured hippocampal neurons. Zn supplementation, especially at the 30 μM concentration, led to partial or total protection against Cd neurotoxicity both with respect to the number of apoptotic cells and the expression of several genes. Interestingly, after knockdown of ZnT3 by small interfering RNA transfection, we did not find the restoration of the expression of this gene following Zn supplementation at 30 μM concentration. These data indicate the involvement of ZnT3 in the mechanism of Cd-induced hippocampal neurotoxicity.

Evaluation of the cytotoxicity and genotoxicity of extracts of mussels originating from Moroccan Atlantic coast, in human colonic epithelial cells Caco-2

Industrial processing of phosphates generates chemical wastes which are, without any treatment, discharged directly into the Atlantic Ocean at Jorf Lasfar (JL), located 120 km south of Casablanca (Morocco) were shellfish are also collected by people without any control. Marine bivalves concentrate these pollutants by filtration and serve as vectors in human's exposure. The objective of this study was to test and compare in vitro on human intestinal cells (Caco-2) the cytotoxicity and genotoxicity of mussels (Mytilus galloprovincialis) extracts (either hydrophilic or lipophilic) collected at two coastal sites; JL (neighboring a phosphate processing plat-form) and Oualidia (OL) (a vegetable growing area) located 160 km south of Casablanca (i.e. 40 km south of JL). Using Caco-2 cells, the following end-points have been evaluated, cytotoxicity as measured by MTS test, inhibition of cellular macromolecules syntheses (DNA and protein) and genotoxicity evaluated by DNA fragmentation in agarose gel electrophoresis. The results indicated, that hydrophilic and lipophilic OL mussels extracts are cytotoxic and inhibit cellular macromolecules syntheses. Moreover these extracts damage the DNA in Caco-2 cells. The lipophilic JL mussels extract is cytotoxic, inhibits cellular macromolecules syntheses, and damages the DNA in Caco-2 cells whereas the hydrophilic extract of JL mussels fails to inhibit protein synthesis and does not damage the DNA. This extract rather enhances protein synthesis, suggesting possible metallothioneins induction by metal ions. Altogether these in vitro data indicate that mussels collected from OL could be more harmful than those from JL even though the later is closer to the pollution site than OL. Nevertheless consumption of mussels from all these areas may present a risk for humans. Epidemiological studies will be needed for global risk assessment in humans living in these areas especially those consuming see food regularly.

Cadmium-induced toxicity in rat primary mid-brain neuroglia cultures: role of oxidative stress from microglia

This study examined the role of oxidative stress in neurotoxic effects of cadmium chloride (Cd) in rat primary mid-brain neuron-glia cultures. Cd accumulated in neuron-glia cultures and produced cytotoxicity in a dose-dependent manner, with IC(50) of 2.5microM 24 h after exposure. (3)H-dopamine uptake into neuron-glia cultures was decreased 7 days after Cd exposure, with IC(50) of 0.9microM, indicative of the sensitivity of dopaminergic neurons to Cd toxicity. To investigate the role of microglia in Cd-induced toxicity to neurons, microglia-enriched cultures were prepared. Cd significantly increased intracellular reactive oxygen species production in microglia-enriched cultures, as evidenced by threefold increases in 2',7'-dichlorofluorescein signals. Using 5,5-dimethyl-1-pyrroline N-oxide as a spin-trapping agent, Cd increased electron spin resonance signals by 3.5-fold in microglia-enriched cultures. Cd-induced oxidative stress to microglia-enriched cultures was further evidenced by activation of redox-sensitive transcription factor nuclear factor kappa B and activator protein-1 (AP-1), and the increased expression of oxidative stress-related genes, such as metallothionein, heme oxygenase-1, glutathione S-transferase pi, and metal transport protein-1, as determined by gel-shift assays and real-time reverse transcription-PCR, respectively, in microglia-enriched cultures. In conclusion, Cd is toxic to neuron-glia cultures, and the oxidative stress from microglia may play important roles in Cd-induced damage to dopaminergic neurons.

Cerebrospinal Fluid S100B Increases Reversibly in Neonates of Methyl Mercury-Intoxicated Pregnant Rats

Methylmercury (MeHg), an organic methylated form of mercury, is one of the most hazardous environmental pollutants. MeHg is a potent neurotoxin, particularly during brain development. Neurotoxicity-induced by MeHg in prenatal age can cause mental disorders, cerebral palsy and seizures. We investigated cerebrospinal fluid (CSF) and brain tissue contents of S100B, a calcium binding protein produced and secreted by astrocytes, which has trophic and toxic activity on neurons depending on concentration. Pregnant rats were exposed to MeHg (5 mg/kg per day, on the 12th, 13th and 14th days of pregnancy). CSF and brain tissue (hippocampus, cerebral cortex and cerebellum) were obtained from neonate rats on 1, 15 and 30 days postnatal. MeHg accumulation was measured in brain tissue after birth and on the 30th postnatal day. An increase of CSF S100B was observed on the 15th, but not on the 30th postnatal day. Hippocampal tissue demonstrated increased S100B (and reduction in glial fibrillary acidic protein) immediately after birth, but not later. No changes in the S100B content were observed in cerebellum and cerebral cortex. No changes were observed in the spatial learning of these rats at adult age. These specific and reversible changes in the hippocampus could be related to the cognitive and epileptic disorders attributed to MeHg. Our results further indicate the glial involvement in the MeHg-induced neurotoxicity. The increment of CSF S100B in neonates exposed to MeHg reinforces the view that increased S100B is related to damage in the nervous system and that S100B could be a marker for MeHg-neurotoxicity. Although the cellular mechanism related to MeHg-induced increase in S100B content in CSF remains unknown, our results suggest the use of S100B as a peripheral marker of brain damage induced by MeHg.

Glutamine transport in C6 glioma cells: substrate specificity and modulation in a glutamine deprived culture medium

A previous study has shown that glutamine (Gln) uptake in C6 cells grown in a standard medium containing 2 mM Gln, is predominantly mediated by a sodium-dependent system that is inhibited by ASC system substrates alanine (Ala), serine (Ser), cysteine (Cys) and threonine (Thr), shows pH sensitivity and partial tolerance to substitution of Na+ by Li+, features compatible with system ASCT2 that is strongly expressed in cultured astrocytes. The uptake was not inhibited by the model system A substrate alpha-(methylamino)isobutyric acid (MeAiB), and glycine (Gly) or proline (Pro), indicating that the substrate-regulated system A as defined by routine criteria is relatively inactive in these cells (Dolinska et al., 2000). In this study we compared the uptake of radiolabeled Gln and a model ASC substrate -Thr in cells grown to the same density in Gln-containing and Gln-deprived media. Cells grown in the absence of Gln showed a reduced activity of system ASC-mediated Gln uptake, and the system lost tolerance for Li+ and became somewhat more resistant to lowering pH of the medium. In contrast to cultured astrocytes deprived of Gln, the overall Gln uptake activity in C6 cells adapted to grow in a medium without Gln was lower than in cells grown in a Gln containing medium, and the uptake by system A remained inactive. C6 cells cultured both in the presence and absence of Gln expressed ASCT2 mRNA, indicating that system ASCT2-mediated Gln uptake is modulated at a posttranscriptional level. In contrast to Gln uptake, Thr uptake was more active in cells cultured in the absence of Gln and showed neither pH dependence nor lithium tolerance in either medium, which is typical of an uptake mediated by the widespread ASCT1 isoform of system ASC. In C6 cells grown in the presence or absence of Gln alike, approximately 20% of the sodium-dependent Gln uptake was resistant to MeAiB+Thr, indicating contribution of system N. The N system-mediated uptake in C6 cells grown in the absence, but not in the presence of Gln was not inhibited by glutamate (Glu) that conforms to the characteristics of the glial N system variant, SN1.