Alterations in the glial fibrillary acidic protein content of primary astrocyte cultures for evaluation of glial cell toxicity

Amburana cearensis seed extract stimulates astrocyte glutamate homeostatic mechanisms in hippocampal brain slices and protects oligodendrocytes against ischemia

BACKGROUND

Stroke is a leading cause of death and disability worldwide. A major factor in brain damage following ischemia is excitotoxicity caused by elevated levels of the neurotransmitter glutamate. In the brain, glutamate homeostasis is a primary function of astrocytes. Amburana cearensis has long been used in folk medicine and seed extract obtained with dichloromethane (EDAC) have previously been shown to exhibit cytoprotective activity in vitro. The aim of the present study was to analyse the activity of EDAC in hippocampal brain slices.

METHODS

We prepared a dichloromethane extract (EDAC) from A. cearensis seeds and characterized the chemical constituents by 1H and 13C-NMR. Hippocampal slices from P6-8 or P90 Wistar rats were used for cell viability assay or glutamate uptake test. Hippocampal slices from P10-12 transgenic mice SOX10-EGFP and GFAP-EGFP and immunofluorescence for GS, GLAST and GLT1 were used to study oligodendrocytes and astrocytes.

RESULTS

Astrocytes play a critical role in glutamate homeostasis and we provide immunohistochemical evidence that in excitotoxicity EDAC increased expression of glutamate transporters and glutamine synthetase, which is essential for detoxifying glutamate. Next, we directly examined astrocytes using transgenic mice in which glial fibrillary acidic protein (GFAP) drives expression of enhanced green fluorescence protein (EGFP) and show that glutamate excitotoxicity caused a decrease in GFAP-EGFP and that EDAC protected against this loss. This was examined further in the oxygen-glucose deprivation (OGD) model of ischemia, where EDAC caused an increase in astrocytic process branching, resulting in an increase in GFAP-EGFP. Using SOX10-EGFP reporter mice, we show that the acute response of oligodendrocytes to OGD in hippocampal slices is a marked loss of their processes and EDAC protected oligodendrocytes against this damage.

CONCLUSION

This study provides evidence that EDAC is cytoprotective against ischemia and glutamate excitotoxicity by modulating astrocyte responses and stimulating their glutamate homeostatic mechanisms.

Conventional and PEGylated Liposomes as Vehicles of Copaifera sabulicola

Traditional medicine uses resin oils extracted from plants of the genus Copaifera for several purposes. Resin oils are being studied to understand and profile their pharmacological properties. The aim of this work was to prepare and to characterize conventional and pegylated liposomes incorporating resin oils or the hexanic extract obtained from Copaifera sabulicola (copaiba) leaves. The cytotoxic effect of these products was also investigated. Conventional and stealth liposomes with copaiba extract showed similar average diameters (around 126 nm), encapsulation efficiencies greater than 75% and were stable for 90 days. A cytotoxicity test was performed on murine glioma cells and the developed liposomes presented antiproliferative action against these cancer cells at the average concentration of 30 μg/mL. Phytochemicals encapsulated in PEGylated liposomes induced greater reduction in the viability of tumor cells. In addition, bioassay-s measured the cytotoxicity of copaiba resin oil (Copaifera sabulicola) in liposomes (conventional and PEGylated), which was also checked against pheochromocytoma PC12 cells. Its safety was verified in normal rat astrocytes. The results indicate that liposomes encapsulating copaiba oil showed cytotoxic activity against the studied tumor strains in a dose-dependent fashion, demonstrating their potential applications as a chemotherapeutic bioactive formulation.

Astrocyte Reaction to Catechol-Induced Cytotoxicity Relies on the Contact with Microglia Before Isolation

Astrocytes preserve the brain microenvironment homeostasis in order to protect other brain cells, mainly neurons, against damages. Glial cells have specific functions that are important in the context of neuronal survival in different models of central nervous system (CNS) diseases. Microglia are among these cells, secreting several molecules that can modulate astrocyte functions. Although 1,2-dihydroxybenzene (catechol) is a neurotoxic monoaromatic compound of exogenous origin, several endogenous molecules also present the catechol group. This study compared two methods to obtain astrocyte-enriched cultures from newborn Wistar rats of both sexes. In the first technique (P1), microglial cells began to be removed early 48 h after primary mixed glial cultures were plated. In the second one (P2), microglial cells were late removed 7 to 10 days after plating. Both cultures were exposed to catechol for 72 h. Catechol was more cytotoxic to P1 cultures than to P2, decreasing cellularity and changing the cell morphology. Microglial-conditioned medium (MCM) protected P1 cultures and inhibited the catechol autoxidation. P2 cultures, as well as P1 in the presence of 20% MCM, presented long, dense, and fibrillary processes positive for glial fibrillary acidic protein, which retracted the cytoplasm when exposed to catechol. The Ngf and Il1beta transcription increased in P1, meanwhile astrocytes expressed more Il10 in P2. Catechol decreased Bdnf and Il10 in P2 cultures, and it decreased the expression of Il1beta in both conditions. A prolonged contact with microglia before isolation of astrocyte-enriched cultures modifies astrocyte functions and morphology, protecting these cells against catechol-induced cytotoxicity.

In Vitro Methods as a Tool in Neurotoxicity Studies

— There are several hundred industrial chemicals with neurotoxic potential. The neurotoxic risks of most of these chemicals are unknown. Additional methods are needed to assess the risks more effectively and to elucidate the mechanisms of neurotoxicity more accurately than is possible with the conventional methods.

This paper deals with general tasks concerning the use of in vitro models in the evaluation of neurotoxic risks. It is based on our previous studies with various in vitro models and on recent literature. The induction of glial fibrillary acidic protein in astrocyte cultures after treatment with known neurotoxicants (mercury compounds and aluminium) is discussed in more detail as an important response which can be detected in vitro.

When used appropriately with in vivo tests and with previous toxicological data, in vitro neurotoxicity testing considerably improves risk assessment. The incorporation of in vitro tests into the early stages of risk evaluation can reduce the number of animals used in routine toxicity testing, by identifying chemicals with high neurotoxic potential.

A Comparison of the Acute and Chronic Effects of Antidepressants in Cultured C6 and 1321N1 Cells

The cytotoxicities of the antidepressants amitriptyline, imipramine (both tricyclic), fluoxetine (a selective serotonin re-uptake inhibitor) and tranylcypromine (a monoamine oxidase inhibitor) were compared in vitro in rat (C6) glioma and human (1321N1) astrocytoma cell lines. Differences in toxicity were determined after acute (24-hour) and chronic (7-day) administration and assessed by using the neutral red uptake (NRU) assay, the MTT assay, increased expression of glial fibrillary acidic protein (GFAp), and reactive morphology criteria. The relative toxicities (EC50 [concentration causing an effect in 50% of cells] value range) were fluoxetine > amitriptyline > imipramine > tranylcypromine for all the tests employed, in both cell lines and at both exposure times. There was a high and significant positive correlation between the different cell types, at both exposure times, with both the NRU and MTT assays. Increases in MTT reduction, NRU, and GFAp expression associated with cell activation were noted in C6 cells after exposure for 24 hours, but decreased after exposure for 7 days. For 1321N1 cells, increases in NRU were only observed after exposure for 24 hours. Reactive-type changes in morphology were seen after exposure to all the antidepressants, in both the C6 and 1321N1 cell lines. The data show that low concentrations of antidepressants induce metabolic changes in the astrocyte cell lines, with some significant differences in the patterns of toxicity of the tested substances.

Autophagy protects against neural cell death induced by piperidine alkaloids present in Prosopis juliflora (Mesquite)

Prosopis juliflora is a shrub that has been used to feed animals and humans. However, a synergistic action of piperidine alkaloids has been suggested to be responsible for neurotoxic damage observed in animals. We investigated the involvement of programmed cell death (PCD) and autophagy on the mechanism of cell death induced by a total extract (TAE) of alkaloids and fraction (F32) from P. juliflora leaves composed majoritary of juliprosopine in a model of neuron/glial cell co-culture. We saw that TAE (30 µg/mL) and F32 (7.5 µg/mL) induced reduction in ATP levels and changes in mitochondrial membrane potential at 12 h exposure. Moreover, TAE and F32 induced caspase-9 activation, nuclear condensation and neuronal death at 16 h exposure. After 4 h, they induced autophagy characterized by decreases of P62 protein level, increase of LC3II expression and increase in number of GFP-LC3 cells. Interestingly, we demonstrated that inhibition of autophagy by bafilomycin and vinblastine increased the cell death induced by TAE and autophagy induced by serum deprivation and rapamycin reduced cell death induced by F32 at 24 h. These results indicate that the mechanism neural cell death induced by these alkaloids involves PCD via caspase-9 activation and autophagy, which seems to be an important protective mechanism.

Neurotoxicity of Prosopis juliflora: from Natural Poisoning to Mechanism of Action of Its Piperidine Alkaloids

Prosopis juliflora was introduced in northeastern Brazil in the 1940s, and since then, it has been available as an alternative for animal nutrition. However, the consumption of P. juliflora as main or sole source of food causes an illness in animals known locally as "cara torta" disease. Cattle and goats experimentally intoxicated presents neurotoxic damage in the central nervous system. Histologic lesions were mainly characterized by vacuolation and loss of neurons in trigeminal motor nuclei. Furthermore, mitochondrial damage in neurons and gliosis was reported in trigeminal nuclei of intoxicated cattle. Studies, using neural cell cultures, have reproduced the main cellular alterations visualized in cara torta disease and contributed to understanding the mechanism of action piperidine alkaloids, the main neurotoxic compound in P. juliflora leaves and pods. Here, we will present aspects of the biological and toxicological properties of P. juliflora and its pharmacologically active compounds.

Nigella sativa Oil Reduces Extrapyramidal Symptoms (EPS)-Like Behavior in Haloperidol-Treated Rats

The symptoms of Parkinsonism and oral dyskinesia have been showing to be induced by neuroleptics that significantly affect its clinical use. In this study, we investigate whether Nigella sativa-oil (NS) (black cumin seeds)-a traditional medicine used for the seizure treatment in eastern country-may reduce the haloperidol (HAL)-induced extrapyramidal symptoms (EPS)-like behavior in rats. After combine treatment with HAL (1 mg/kg) on NS (0.2 ml/rat), rats displayed a significant decreased EPS-like behavior including movement disorders and oral dyskinesia as compared to controls. Immunohistochemical analysis indicates that NS reduced astrogliosis in caudate and accumbens nuclei. These results suggest that NS may consider as an adjunct to antipsychotics to reduce the EPS-like side effect.

A critical review of cell culture strategies for modelling intracortical brain implant material reactions

The capacity to predict in vivo responses to medical devices in humans currently relies greatly on implantation in animal models. Researchers have been striving to develop in vitro techniques that can overcome the limitations associated with in vivo approaches. This review focuses on a critical analysis of the major in vitro strategies being utilized in laboratories around the world to improve understanding of the biological performance of intracortical, brain-implanted microdevices. Of particular interest to the current review are in vitro models for studying cell responses to penetrating intracortical devices and their materials, such as electrode arrays used for brain computer interface (BCI) and deep brain stimulation electrode probes implanted through the cortex. A background on the neural interface challenge is presented, followed by discussion of relevant in vitro culture strategies and their advantages and disadvantages. Future development of 2D culture models that exhibit developmental changes capable of mimicking normal, postnatal development will form the basis for more complex accurate predictive models in the future. Although not within the scope of this review, innovations in 3D scaffold technologies and microfluidic constructs will further improve the utility of in vitro approaches.

Juliprosopine and juliprosine from prosopis juliflora leaves induce mitochondrial damage and cytoplasmic vacuolation on cocultured glial cells and neurons

Prosopis juliflora is a shrub largely used for animal and human consumption. However, ingestion has been shown to induce intoxication in animals, which is characterized by neuromuscular alterations induced by mechanisms that are not yet well understood. In this study, we investigated the cytotoxicity of a total alkaloid extract (TAE) and one alkaloid fraction (F32) obtained from P. juliflora leaves to rat cortical neurons and glial cells. Nuclear magnetic resonance characterization of F32 showed that this fraction is composed of a mixture of two piperidine alkaloids, juliprosopine (majority constituent) and juliprosine. TAE and F32 at concentrations between 0.3 and 45 μg/mL were tested for 24 h on neuron/glial cell primary cocultures. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide test revealed that TAE and F32 were cytotoxic to cocultures, and their IC50 values were 31.07 and 7.362 μg/mL, respectively. Exposure to a subtoxic concentration of TAE or F32 (0.3-3 μg/mL) induced vacuolation and disruption of the astrocyte monolayer and neurite network, ultrastructural changes, characterized by formation of double-membrane vacuoles, and mitochondrial damage, associated with changes in β-tubulin III and glial fibrillary acidic protein expression. Microglial proliferation was also observed in cultures exposed to TAE or F32, with increasing levels of OX-42-positive cells. Considering that F32 was more cytotoxic than TAE and that F32 reproduced in vitro the main morphologic and ultrastructural changes of "cara torta" disease, we can also suggest that piperidine alkaloids juliprosopine and juliprosine are primarily responsible for the neurotoxic damage observed in animals after they have consumed the plant.

The Role of Astrocytes in Metabolism and Neurotoxicity of the Pyrrolizidine Alkaloid Monocrotaline, the Main Toxin of Crotalaria retusa

The metabolic interactions and signaling between neurons and glial cells are necessary for the development and maintenance of brain functions and structures and for neuroprotection, which includes protection from chemical attack. Astrocytes are essential for cerebral detoxification and present an efficient and specific cytochrome P450 enzymatic system. Whilst Crotalaria (Fabaceae, Leguminosae) plants are used in popular medicine, they are considered toxic and can cause damage to livestock and human health problems. Studies in animals have shown cases of poisoning by plants from the genus Crotalaria, which induced damage to the central nervous system. This finding has been attributed to the toxic effects of the pyrrolizidine alkaloid (PA) monocrotaline (MCT). The involvement of P450 enzymatic systems in MCT hepatic and pulmonary metabolism and toxicity has been elucidated, but little is known about the pathways implicated in the bioactivation of these systems and the direct contribution of these systems to brain toxicity. This review will present the main toxicological aspects of the Crotalaria genus that are established in the literature and recent findings describing the mechanisms involved in the neurotoxic effects of MCT, which was extracted from Crotalaria retusa, and its interaction with neurons in isolated astrocytes.

Assessment of neurotoxicity of monocrotaline, an alkaloid extracted from Crotalaria retusa in astrocyte/neuron co-culture system

Studies have shown cases of poisoning with plants from the genus Crotalaria (Leguminosae) mainly in animals. They induce damages in the central nervous system (CNS), which has been attributed to toxic effects of the pyrrolizidine alkaloid (PA) monocrotaline (MCT). Previously we demonstrated that both MCT and dehydromonocrotaline (DHMC), its main active metabolite, induce changes in the levels and patterns of expression of the main protein from astrocyte cytoskeleton, glial fibrillary acidic protein (GFAP). In this study we investigated the effect of MCT on rat cortical astrocyte/neuron primary co-cultures. Primary cultures were exposed to 10 or 100 μM MCT. The MTT test and the measurement of LDH activity on the culture medium revealed that after 24h exposure MCT was not cytotoxic to neuron/astrocyte cells. However, the cell viability after 72 h treatment decreased in 10-20%, and the LDH levels in the culture medium increased at a rate of 12% and 23%, in cultures exposed to 10 or 100 μM MCT. Rosenfeld staining showed vacuolization and increase in cell body in astrocytes after MCT exposure. Immunocytochemistry and Western blot analyses revealed changes on pattern of GFAP and βIII-tubulin expression and steady state levels after MCT treatment, with a dose and time dependent intense down regulation and depolarization of neuronal βIII-tubulin. Moreover, treatment with 100 μM MCT for 12h induced GSH depletion, which was not seen when cytochrome P450 enzyme system was inhibited indicating that it is involved in MCT induced cytotoxicity in CNS cells.

Hormesis provides a generalized quantitative estimate of biological plasticity

Phenotypic plasticity represents an environmentally-based change in an organism's observable properties. Since biological plasticity is a fundamental adaptive feature, it has been extensively assessed with respect to its quantitative features and genetic foundations, especially within an ecological evolutionary framework. Toxicological investigations on the dose-response continuum (i.e., very broad dose range) that include documented evidence of the hormetic dose response zone (i.e., responses to doses below the toxicological threshold) can be employed to provide a quantitative estimate of phenotypic plasticity. The low dose hormetic stimulation is an adaptive response that reflects an environmentally-induced altered phenotype and provides a quantitative estimate of biological plasticity. Analysis of nearly 8,000 dose responses within the hormesis database indicates that quantitative features of phenotypic plasticity are highly generalizable, being independent of biological model, endpoint measured and chemical/physical stress inducing agent. The magnitude of phenotype changes indicative of plasticity is modest with maximum responses typically being approximately 30-60% greater than control values. The present findings provide the first quantitative estimates of biological plasticity and its capacity for generalization. Summary This article provides the first quantitative estimate of biological plasticity that may be generalized across plant, microbial, animal systems, and across all levels of biological organization. The quantitative features of plasticity are described by the hormesis dose response model. These findings have important biological, biomedical and evolutionary implications.

Vacuolar pathology in the median eminence of the hypothalamus after hyponatremia

The median eminence of the hypothalamus is an important conduit by which neurosecretory hormones from hypothalamic nuclei are delivered to the pars nervosa (neural lobe) of the pituitary en route to the bloodstream. Dilutional hyponatremia was produced in adult rats to determine the effect on the morphology of the median eminence of the hypothalamus. Hyponatremia was caused by reducing electrolyte and organic osmolyte reserves to block the excretion of water through delivery of the nephrotoxin mercuric chloride (HgCl2). Histological examination of the brain 1 day after a hyponatremic insult revealed vacuolation within the median eminence of the hypothalamus. No other lesions were found in other parts of the brain after hyponatremia. The hyponatremic lesion consisted of a band of closely packed vacuoles that crossed the floor of the third ventricle. Vacuoles associated with hyponatremia were predominantly in the subependymal, fiber, reticular, and palisade layers of the median eminence. Vacuolation was not observed in the tanycyte layer of the median eminence. This study indicates that the median eminence is a potentially vulnerable site in human hyponatremic conditions that should be evaluated further in relevant animal models.

Single-cell ELISA and flow cytometry as methods for highlighting potential neuronal and astrocytic toxicant specificity

The timeline imposed by recent worldwide chemical legislation is not amenable to conventional in vivo toxicity testing, requiring the development of rapid, economical in vitro screening strategies which have acceptable predictive capacities. When acquiring regulatory neurotoxicity data, distinction on whether a toxic agent affects neurons and/or astrocytes is essential. This study evaluated neurofilament (NF) and glial fibrillary acidic protein (GFAP) directed single-cell (S-C) ELISA and flow cytometry as methods for distinguishing cell-specific cytoskeletal responses, using the established human NT2 neuronal/astrocytic (NT2.N/A) co-culture model and a range of neurotoxic (acrylamide, atropine, caffeine, chloroquine, nicotine) and non-neurotoxic (chloramphenicol, rifampicin, verapamil) test chemicals. NF and GFAP directed flow cytometry was able to identify several of the test chemicals as being specifically neurotoxic (chloroquine, nicotine) or astrocytoxic (atropine, chloramphenicol) via quantification of cell death in the NT2.N/A model at cytotoxic concentrations using the resazurin cytotoxicity assay. Those neurotoxicants with low associated cytotoxicity are the most significant in terms of potential hazard to the human nervous system. The NF and GFAP directed S-C ELISA data predominantly demonstrated the known neurotoxicants only to affect the neuronal and/or astrocytic cytoskeleton in the NT2.N/A cell model at concentrations below those affecting cell viability. This report concluded that NF and GFAP directed S-C ELISA and flow cytometric methods may prove to be valuable additions to an in vitro screening strategy for differentiating cytotoxicity from specific neuronal and/or astrocytic toxicity. Further work using the NT2.N/A model and a broader array of toxicants is appropriate in order to confirm the applicability of these methods.

Further preliminary assessment of three human glioma cell lines as models of human astrocytic toxicity in vitro

Three human astroglioma lines U251-MG, U373-MG and CCF-STTG1 have been evaluated further as possible models for astrocytotoxicity (GFAP and IL-6 release). The effects of bacterial lipopolysaccharide, chloroquine diphosphate and acrylamide were studied on GFAP expression and LPS, chloroquine diphosphate, ethanol, trimethyltin chloride (TMTC) and acrylamide were examined on interleukin-6 (IL-6) release in the U373-MG line only. At 4-h LPS elevated GFAP (17.0±5.0% P<0.05) above control in the U251-MG cell line only. Chloroquine diphosphate over 4h in the U251-MG line resulted in an increase in GFAP-IR to 20.3±4.2% and 21.1±4.1% above control levels 0.1μM (P<0.05) and 1μM (P<0.05) respectively. CQD was associated with decreases in MTT turnover, particularly after 24h incubation. With the U373-MG line, LPS (0.5μg/ml) increased IL-6 expression 640% above control (P<0.001), whilst chloroquine diphosphate (100μM), ethanol (10mM) and TMTC chloride (1μM) also increased IL-6. It is possible that batteries of astrocytic human glioma cell lines may be applicable to the sensitive evaluation of toxicants on astrogliotic expression markers such as GFAP and IL-6.

Astrocytes: adaptive responses to low doses of neurotoxins

This article assesses how astrocytes respond to numerous endogenous agonists and a wide variety of chemical stressors, including well-known neurotoxic agents such as lead and methylmercury, and drugs, within the context of dose-response relationships. In general, astrocytes displayed biphasic dose-response relationships from exposure to neurotoxic agents with temporal and quantitative features similar to hormetic dose responses. While the low-dose stimulatory responses have been viewed as a manifestation of a toxic response, this perspective is being broadly reconsidered and in some cases reinterpreted as being an indicator of an adaptive/protective response. These dose-response patterns are likely to have significant implications in a wide range of conditions affecting normal developmental processes, tumor development, adaptive responses to numerous environmental neurotoxins, and strategies for drug development for the treatment of neurodegenerative conditions.

Assessment of the astrogliotic responses of three human astrocytoma cell lines to ethanol, trimethyltin chloride and acrylamide

The astrogliotic responses of the CCF-STTG1, U251-MG, and U373-MG human astrocytoma lines were determined after exposure to ethanol, trimethyltin chloride (TMTC), and acrylamide over 4, 16, and 24h. Basal glial fibrillary acidic protein (GFAP) expression in the U-251MG and U373-MG cells was 10-fold greater than the CCF-STGG1 line. Ethanol treatment over 24h, but not at 4 and 16h, resulted in significant increases in GFAP in all three glioma lines at sub-cytotoxic levels; the GFAP responses in the CCF-STTG1 line were the most sensitive, as concentrations of 0.1 and 1mM led to increases in GFAP expression compared with control of 56.8+/-15.7 and 58.9+/-11.5%, respectively (P<0.05). Treatment with TMTC (1 microM) over 4h showed elevated GFAP expression in the U251-MG cell line to 28.0+/-15.7% above control levels (P<0.01), but not in the other U373-MG or CCF-STTG1 cells. At 4h, MTT turnover was markedly increased compared with control, particularly in the U373-MG line at concentrations as low as 1 microM (17.1+/-2.3%; P<0.01). TMTC exposure over 16 and 24h resulted in reduction in GFAP expression in all three lines at concentrations; at 24h incubation, the reduction was >50% (P<0.01). There were no changes in GFAP expression or MTT turnover in response to acrylamide except at the highest concentration ranges of 10-100 mM. This study underlines the significance of period of exposure, as well as toxin concentration in astrocytoma cellular response to toxic pressure.

The flavonoid rutin induces astrocyte and microglia activation and regulates TNF-alpha and NO release in primary glial cell cultures

Astrocyte and microglia cells play an important role in the central nervous system (CNS). They react to various external aggressions by becoming reactive and releasing neurotrophic and/or neurotoxic factors. Rutin is a flavonoid found in many plants and has been shown to have some biological activities, but its direct effects on cells of the CNS have not been well studied. To investigate its potential effects on CNS glial cells, we used both astrocyte primary cultures and astrocyte/microglia mixed primary cell cultures derived from newborn rat cortical brain. The cultures were treated for 24 h with rutin (50 or 100 micromol/L) or vehicle (0.5% dimethyl sulfoxide). Mitochondrial function on glial cells was not evidenced by the MTT test. However, an increased lactate dehydrogenase activity was detected in the culture medium of both culture systems when treated with 100 micromol/L rutin, suggesting loss of cell membrane integrity. Astrocytes exposed to 50 micromol/L rutin became reactive as revealed by glial fibrillary acidic protein (GFAP) overexpression and showed a star-like phenotype revealed by Rosenfeld's staining. The number of activated microglia expressing OX-42 increased in the presence of rutin. A significant increase of nitric oxide (NO) was observed only in mixed cultures exposed to 100 micromol/L rutin. Enhanced TNFalpha release was observed in astrocyte primary cultures treated with 100 micromol/L rutin and in mixed primary cultures treated with 50 and 100 micromol/L, suggesting different sensitivity of both activated cell types. These results demonstrated that rutin affects astrocytes and microglial cells in culture and has the capacity to induce NO and TNFalpha production in these cells. Hence, the impact of these effects on neurons in vitro and in vivo needs to be studied.

Cytotoxic effect of ciprofloxacin in primary culture of rat astrocytes and protection by Vitamin E

The aim of this study was to investigate the possible cytotoxic and oxidative stress inducing effects of ciprofloxacin (CPFX) on primary cultures of rat astrocytes. The cultured cells were incubated with various concentrations of CPFX (0.5-300mg/l), and cytotoxicity was determined by neutral red (NR) and MTT assays. Survival profile of cells was biphasic in NR assay: CPFX did not cause any alteration at any concentration for 7h, whereas < or =50mg/l concentrations induced significant cell proliferation in incubation periods of 24, 48, 72, and 96h. However, cell proliferation gradually decreased at higher concentrations, and 200 and 300mg/l of CPFX exposure was found to be significantly (p<0.05) cytotoxic at all time periods. With MTT assay, no alteration was noted for incubation period of 7h, as observed with NR assay. But, cell viability decreased with approximately > or =50mg/l CPFX exposure in all other time periods. Cell proliferation was only seen in 24h of incubation with 0.5 and 5mg/l CPFX. Vitamin E pretreatment of cell cultures were found to be providing complete protection against cytotoxicity of 300mg/l CPFX in 96h incubation when measured with both NR and MTT assays. The SOD pretreatment was partially protective with NR assay, but no protection was noted when measured with MTT. A significant enhancement of lipid peroxidation was observed with the cytotoxic concentration of the drug, but total glutathione content and catalase activity of cells did not change. The data obtained in this study suggest that, in accordance with our previous results with fibroblast cells, CPFX-induced cytotoxicity is related to oxidative stress. And the biphasic effect of CPFX possibly resulted from the complex dose-dependent relationships between reactive oxygen species, cell proliferation, and cell viability.

Alkaloids from Prosopis juliflora leaves induce glial activation, cytotoxicity and stimulate NO production

Prosopis juliflora is used for feeding cattle and humans. Intoxication with the plant has been reported, and is characterized by neuromuscular alterations and gliosis. Total alkaloidal extract (TAE) was obtained using acid/basic-modified extraction and was fractionated. TAE and seven alkaloidal fractions, at concentrations ranging 0.03-30 microg/ml, were tested for 24h on astrocyte primary cultures derived from the cortex of newborn Wistar rats. The MTT test and the measure of LDH activity on the culture medium, revealed that TAE and fractions F29/30, F31/33, F32 and F34/35 were cytotoxic to astrocytes. The EC(50) values for the most toxic compounds, TAE, F31/33 and F32 were 2.87 2.82 and 3.01 microg/ml, respectively. Morphological changes and glial cells activation were investigated through Rosenfeld's staining, by immunocytochemistry for the protein OX-42, specific of activated microglia, by immunocytochemistry and western immunoblot for GFAP, the marker of reactive and mature astrocytes, and by the production of nitric oxide (NO). We observed that astrocytes exposed to 3 microg/ml TAE, F29/30 or F31/33 developed compact cell body with many processes overexpressing GFAP. Treatment with 30 microg/ml TAE and fractions, induced cytotoxicity characterized by a strong cell body contraction, very thin and long processes and condensed chromatin. We also observed that when compared with the control (+/-1.34%), the proportion of OX-42 positive cells was increased in cultures treated with 30 microg/ml TAE or F29/30, F31/33, F32 and F34/35, with values raging from 7.27% to 28.74%. Moreover, incubation with 3 microg/ml F32, 30 microg/ml TAE, F29/30, F31/33 or F34/35 induced accumulation of nitrite in culture medium indicating induction of NO production. Taken together these results show that TAE and fractionated alkaloids from P. juliflora act directly on glial cells, inducing activation and/or cytotoxicity, stimulating NO production, and may have an impact on neuronal damages observed on intoxicated animals.

Evaluation of neurotoxic potential by use of in vitro systems

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

The involvement of calcium in the protective and toxic (nonlinear) responses of rodent and human astroglial cells

The involvement of [Ca(2+)](i) in the reactive changes of astrocytes which accompany exposure to different chemicals were studied in cultures of C6 and 1321N1 cells. Cells were exposed to up to three serial pulses of the differentiating agent dBcAMP, which induces activation-type changes in the cells. Other cells, with or without the dBcAMP treatments, were treated with a range of concentrations of the antidepressants amitriptyline and fluoxetine and the glial toxicants acrylamide and chloroquine. In some experiments the L-type voltage calcium channel blocker Nifedipine was employed. [Ca(2+)](i) was measured in populations of the cells using Fura-2AM and a charge coupled device (CCD) camera attached to a fluorescence microscope. dBcAMP induced both dose- and time-dependent changes in [ Ca(2+)](i) with increases in both the [Ca(2+)](i) oscillations and mean [Ca(2+)](i) (e.g. in C6 cells at 18 min mean [Ca(2+)](i) was 318 +/- 20nM following the single differentiating dBcAMP pulses, 489 +/- 17nM (p < 0.001) following two serial pulses, and 275 +/- 30nM (not significant) following three pulses). Therapeutic doses of fluoxetine and amitriptyline caused increases in the calcium oscillations and the mean calcium concentrations ( maximum recorded mean increase was in the C6 cells at 10min by 0.02 muM fluoxetine when [Ca(2+)](i) was 411 +/- 35nM c.f. control 254 +/- 25nM, p = 0.01). Higher (non-therapeutic) doses of both antidepressants caused significant reductions. Chloroquine and acrylamide also caused dose-dependent bi-phasic types of alterations in [Ca(2+)](i), with significant reductions at lower, sub-cytotoxic doses followed by significant increases at higher concentrations, approaching those which cause cell damage. Nifedipine treatment caused some reductions in the dBcAMP, antidepressant or toxicant-induced calcium changes, but this substance also initiated cytotoxic alterations. The findings show that both the activation-type changes (which are frequently associated with increased protective capacities) and toxic responses of C6 and 1321N1 cells to different chemical agents are associated with dose-dependent alterations in [Ca(2+)](i).

Responses of Cultured Astrocytes, C6 Glioma and 1321NI Astrocytoma Cells to Amyloid beta-Peptide Fragments

The effect of amyloid beta-peptide (betaAP), which can have both neurotrophic or neurotoxic effects on neurons and has been implicated in the pathogenesis of Alzheimer's disease (AD), was studied on astrocytes using primary cultures and astrocyte cell lines (rat C6 glioma, human 1321NI astrocytoma cells). The cultures were exposed to 0.0005-50 mug/ml) betaAP fragments 1-40, 25-35, 31-35, or 40-41 (control) for 24 hr. Some of the fragments were maintained at 37 degrees C for 48 hr to induce aggregation and some of the cell cultures were pretreated with the differentiating agent dBcAMP before the experiments. The astrocyte responses were evaluated for lysosome activity (neutral red assay) and levels of structural proteins, glial fibrillary acidic protein, vimentin, and S-100, which are altered in the dystrophic plaques with associated astrogliosis in AD. The cells frequently responded with biphasic responses, with initial (low-dose) activation-type responses (i.e., increases of indicator compared to controls), before reductions with altered morphology (increased branching of cells) at higher concentrations. However, cell death (with EC(50) values) was not observed, even at the maximum concentrations of betaAP fragments. The findings suggest that the astrocytes have a relatively high resistance against the betaAP toxicity.

Sensor-based measurements of the role and interactions of free radicals in cellular systems

Direct real-time electrochemical measurements have offered new insight into the importance of free radical interplay in a number of cell culture and in vivo models of neurodegenerative processes. This review highlights investigations carried out in this laboratory of real-time superoxide and nitric oxide free radical generation, and presents evidence of complex inter-relationships between these species. These include: a novel function for astrocytic nitric oxide synthase in controlling neuronal nitric oxide availability; and the demonstration that extracellular superoxide flux can lead to the generation of NO by glial cells. The possible consequences of these interactions are discussed.

Superoxide-induced nitric oxide release from cultured glial cells

Nitric oxide (NO) has been implicated as a potential contributor to neural cell death in a variety of neurological conditions. Cultured glial cells were exposed to extracellular superoxide generated by the action of xanthine oxidase on xanthine. In this experimental paradigm, both C6 glioma cells and primary astrocytes from rat cerebral cortex produced a rapid release of nitric oxide, measured using an NO specific electrode, in response to the applied superoxide stimulus. Application of a superoxide scavenger, or over-expression of Cu/Zn superoxide dismutase decreased the observed NO release. Authenticity of the NO signal was confirmed by the addition of the NO scavenger 2-(carboxyphenyl)-4,4,5,5-tetramethyllimidazoline-1-oxyl 3-oxide (carboxy-PTIO), which abolished the observed NO release without affecting simultaneously measured superoxide. Therefore, we suggest that glial cells may produce NO under free radical stimulation, which may be relevant to several neurological disorders where superoxide radicals are generated in the vicinity of glia. This would be predicted to result in the release of NO, which may exert toxic effects on neighbouring cells.

Endocytosis in rat cultured astrocytes is inhibited by unconjugated bilirubin

Excessive hyperbilirubinemia can cause irreversible neurological damage in the neonatal period. However, the complete understanding of the pathogenesis of unconjugated bilirubin (UCB) encephalopathy remains a matter of debate. This study investigates whether UCB inhibits the endocytosis of cationized ferritin (CF) by cultured rat astrocytes. The relationship between endocytosis and MTT reduction, as well as changes on tubulin and glial fibrillary acidic protein (GFAP) assembly, were also evaluated. Inhibition of endocytosis was complete in the presence of 171 microM UCB, while a marked decrease of CF labeling was noticed for 86 microM UCB. In addition, MTT reduction was inhibited by 60 to 76% as UCB concentrations changed from 17 to 171 microM, while alterations on both GFAP and microtubule morphology were only achieved by cell exposure to 171 microM UCB. These findings indicate that inhibition of CF endocytosis in rat cortical astrocytes by UCB is a concentration-dependent process that appears to be primarily related to a direct effect on the cell membrane and not to any alteration of cytoskeletal microtubules and intermediate filaments.

Cultured glial cells are resistant to the effects of motor neurone disease-associated SOD1 mutations

Free radical damage has been implicated in the pathophysiology of motor neurone disease (MND); mutations have been identified in the gene encoding Cu/Zn superoxide dismutase (SOD1). There is evidence that glial cell dysfunction may contribute to motor neurone injury, but the exact role of glial cells in MND has yet to be established. The aim of this study was to determine whether expression of mutant SOD1 affects the response of glia to oxidative stress. Stable C6 glioma cells expressing mutant SOD1 and cortical astrocyte cultures from G93A-SOD1 transgenic mice were exposed to: xanthine/xanthine oxidase; hydrogen peroxide; A23187 and 3-morpholinosydonimine. Cell viability was measured using the 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Neither C6 glioma cells nor cortical astrocytes expressing mutant SOD1 were more susceptible to any of the free radical generating systems compared to control cells. These results suggest that astrocytes are resistant to the toxic effects of mutant SOD1 widely reported for neuronal cells.

Astrocyte phenotype and prevention against oxidative damage in neurotoxicity

Astrocytes possess a potent array of protective systems. These are chiefly targeted against oxidised products and radicals, which are frequently present in increased amounts following exposure of nervous tissue to a range of toxic insults. Following exposure to the toxic chemicals astrocytes commonly respond by alteration in phenotype with upregulation of a large number of molecules, including those controlling the protective systems. This article summarizes evidence, largely obtained from in vitro studies, which supports the concept that some of the changes in astrocyte phenotype are associated with increased protection against the cytotoxicity caused by the oxidative damage that results from exposure to range of neurotoxicants.

In vitro techniques for the assessment of neurotoxicity

Risk assessment is a process often divided into the following steps: a) hazard identification, b) dose-response assessment, c) exposure assessment, and d) risk characterization. Regulatory toxicity studies usually are aimed at providing data for the first two steps. Human case reports, environmental research, and in vitro studies may also be used to identify or to further characterize a toxic hazard. In this report the strengths and limitations of in vitro techniques are discussed in light of their usefulness to identify neurotoxic hazards, as well as for the subsequent dose-response assessment. Because of the complexity of the nervous system, multiple functions of individual cells, and our limited knowledge of biochemical processes involved in neurotoxicity, it is not known how well any in vitro system would recapitulate the in vivo system. Thus, it would be difficult to design an in vitro test battery to replace in vivo test systems. In vitro systems are well suited to the study of biological processes in a more isolated context and have been most successfully used to elucidate mechanisms of toxicity, identify target cells of neurotoxicity, and delineate the development and intricate cellular changes induced by neurotoxicants. Both biochemical and morphological end points can be used, but many of the end points used can be altered by pharmacological actions as well as toxicity. Therefore, for many of these end points it is difficult or impossible to set a criterion that allows one to differentiate between a pharmacological and a neurotoxic effect. For the process of risk assessment such a discrimination is central. Therefore, end points used to determine potential neurotoxicity of a compound have to be carefully selected and evaluated with respect to their potential to discriminate between an adverse neurotoxic effect and a pharmacologic effect. It is obvious that for in vitro neurotoxicity studies the primary end points that can be used are those affected through specific mechanisms of neurotoxicity. For example, in vitro systems may be useful for certain structurally defined compounds and mechanisms of toxicity, such as organophosphorus compounds and delayed neuropathy, for which target cells and the biochemical processes involved in the neurotoxicity are well known. For other compounds and the different types of neurotoxicity, a mechanism of toxicity needs to be identified first. Once identified, by either in vivo or in vitro methods, a system can be developed to detect and to evaluate predictive ability for the type of in vivo neurotoxicity produced. Therefore, in vitro tests have their greatest potential in providing information on basic mechanistic processes in order to refine specific experimental questions to be addressed in the whole animal.

An aluminum-induced increase in GFAP is attenuated by some chelators

Enhanced expression of glial fibrillary acidic protein (GFAP) has been shown to be associated with gliosis, a generic response of the CNS to neural injury. The effects of aluminum (Al) on regional GFAP concentrations were evaluated to determine potential sites of Al-induced neural injury. Rabbits received 20 Al (100 mumol/kg) or sodium lactate injections over 1 month. Frontal cortical GFAP increased (approximately twofold above control) in Al-loaded rabbits; whereas hippocampal and cerebellar GFAP concentrations were not affected. Frontal cortical synaptophysin, neurofilament 68, and myelin basic protein concentrations were then examined in an attempt to determine cell-specific targets of Al neurotoxicity. These proteins were not affected by Al. The ability of chelators to influence brain Al concentrations and the Al effect on GFAP were assessed. Desferrioxamine (DFO) and six 3-hydroxypyridin-4-ones (CPs) were given 12 times, over 1 month, to Al-loaded rabbits. CP24 significantly reduced brain Al. CP93, CP52, and CP24 significantly reduced frontal cortical GFAP. The data suggest an Al-induced gliosis consequent to subtle damage in the frontal cortex and a protective role of some chelators against this CNS injury.