Melatonin induces mechanisms of brain resilience against neurodegeneration.

Melatonin is an endogenous pleiotropic molecule which orchestrates regulatory functions and protective capacity against age-related ailments. The increase in circulating levels of melatonin through dietary supplements intensifies its health benefits. Investigations in animal models have shown that melatonin protects against Alzheimer's disease (AD)-like pathology, although clinical studies have not been conclusive. We hypothesized that melatonin induces changes in the brain that prevent or attenuate AD by increasing resilience. Therefore, we treated healthy nontransgenic (NoTg) and AD transgenic (3xTg-AD) 6-month-old mice with a daily dose of 10 mg/kg of melatonin until 12 months of age. As expected, melatonin reversed cognitive impairment and dementia-associated behaviors of anxiety and apathy and reduced amyloid and tau burden in 3xTg-AD mice. Remarkably, melatonin induced cognitive enhancement and higher wellness level-related behavior in NoTg mice. At the mechanism level, NF-κB and proinflammatory cytokine expressions were decreased in both NoTg and 3xTg-AD mice. The SIRT1 pathway of longevity and neuroprotection was also activated in both mouse strains after melatonin dosing. Furthermore, we explored new mechanisms and pathways not previously associated with melatonin treatment such as the ubiquitin-proteasome proteolytic system and the recently proposed neuroprotective Gas6/TAM pathway. The upregulation of proteasome activity and the modulation of Gas6 and its receptors by melatonin were similarly displayed by both NoTg and 3xTg-AD mice. Therefore, these results confirm the potential of melatonin treatment against AD pathology, by way of opening new pathways in its mechanisms of action, and demonstrating that melatonin induces cognitive enhancement and brain resilience against neurodegenerative processes.

New insights in animal models of neurotoxicity-induced neurodegeneration.

The high prevalence of neurodegenerative diseases is an unintended consequence of the high longevity of the population, together with the lack of effective preventive and therapeutic options. There is great pressure on preclinical research, and both old and new models of neurodegenerative diseases are required to increase the pipeline of new drugs for clinical testing. We review here the main models of neurotoxicity-based animal models leading to central neurodegeneration. Our main focus was on studying how changes in neurotransmission and neuroinflammation, mainly in rodent models, contribute to harmful processes linked to neurodegeneration. The majority of the models currently in use mimic Parkinson's disease (PD) and Alzheimer's disease (AD), which are the most common neurodegenerative conditions in older adults. AD is the most common age-related dementia, whereas PD is the most common movement disorder with also cases of dementia. Several natural toxins and xenobiotic agents induce dopaminergic neurodegeneration and can reproduce neuropathological traits of PD. The literature analysis of MPTP, 6-OH-dopamine, and rotenone models suggested the latter as a useful model when specific doses of rotenone were administrated systemically to C57BL/6 mice. Cholinergic neurodegeneration is mainly modelled with the toxin scopolamine, which is a useful rodent model for the screening of protective drugs against cognitive decline and AD. Several agents have been used to model neuroinflammation-based neurodegeneration and dementia in AD, including lipopolysaccharide (LPS), streptozotocin, and monomeric C-reactive protein. The bacterial agent LPS makes a useful rodent model for testing anti-inflammatory therapies to halt the development and severity of AD. However, neurotoxin models might be more useful than genetic models for drug discovery in PD but that is not the case in AD where they cannot beat the new developments in transgenic mouse models. Overall, we should work using all available models, either in vivo, in vitro, or in silico, considering the seriousness of the moment and urgency of developing effective drugs.

Resveratrol confers neuroprotection against high-fat diet in a mouse model of Alzheimer's disease via modulation of proteolytic mechanisms.

Cumulative evidence indicates that excessive consumption of calories from saturated fat contributes to the development of Alzheimer's disease (AD). Here, we assess the triggering and progression of AD pathology induced by a high-fat diet (HFD), and the effects of resveratrol, a polyphenol found in common dietary sources with pleiotropic neuroprotective activities. Over 16 weeks, male wild type (WT) and AD transgenic 5XFAD mice were fed a control diet, HFD (60% kcal from fat), or HFD supplemented with 0.1% resveratrol. Resveratrol protected against HFD-induced memory loss in WT mice and prevented memory loss in 5XFAD mice. Resveratrol also reduced the amyloid burden aggravated by HFD in 5XFAD, and protected against HFD-induced tau pathology in both WT and 5XFAD strains. At the mechanistic level, resveratrol inhibited the HFD-increased amyloidogenic processing of the amyloid precursor protein in both strains; it also restored abnormal high levels in the proteolytic activity of the ubiquitin-proteasome system induced by HFD, suggesting the presence of a compensatory mechanism to counteract the accumulation of aberrant proteins. Thus, our data suggest that resveratrol can correct the harmful effects of HFD in the brain and may be a potential therapeutic agent against obesity-related disorders and AD pathology.

Spatial distribution of Parkinson's disease mortality in Spain, 1989-1998, as a guide for focused aetiological research or health-care intervention.

BACKGROUND: Aetiologically, genetic and environmental factors having an uneven spatial distribution may underlie Parkinson's disease (PD). Undiagnosis of PD in selected regions might have limited access to treatment with levodopa and simultaneously, if present at death, determined PD underreporting at the death record. The purpose of this study was to describe and analyse municipal mortality due to PD in Spain in aetiological and interventional perspective. METHODS: PD mortality at a municipal level was modelled using the Besag-York- Molliè autoregressive spatial model, combining demographic information with cause-of-death diagnostic data (International Classification of Diseases 9th Revision (ICD-9) code 332.0). Municipal relative risks (RRs) were independently estimated for women, men and both sexes, and plotted on maps depicting smoothed RR estimates and the distribution of the posterior probability of RR>1. RESULTS: A south-north gradient, with large geographical areas suggesting clustered towns with high mortality, was seen in Asturias, the Basque Country, Balearic Islands and, particularly, in the Lower Ebro valley around Tarragona. Similarly, there was a suggestion that lowest mortality was clustered in the south-east and south-west. We identified some isolated or clustered municipalities with high mortality that were situated near industrial plants reported to be associated with environmental xenobiotic emissions. However, the same pattern was also observed for some cities with low mortality. CONCLUSION: Municipal PD mortality in Spain was unevenly distributed. Patterns were roughly similar to reported provincial PD mortality and use of levodopa. While the overall pattern appears to result from spatially selective PD undiagnosis, and can not be ascribed to industrial emissions, it can not be excluded that selected "hot spots" reflect genetic factors and/or environmental exposures inducing parkinsonism. A few municipal populations, located in low-mortality-risk areas in the vicinity of polluting plants or registering high excess PD mortality, might constitute a priority for conducting direct etiological studies. Additionally, interventions aimed to reduce potential PD undiagnosis might be most appropriate in the South.

Resveratrol Induces Brain Resilience Against Alzheimer Neurodegeneration Through Proteostasis Enhancement.

Resveratrol is a natural compound that mimics the antioxidant and antiaging effects of caloric restriction, mainly mediated through SIRT1, a deacetylase that induces longevity and neuroprotection. We aimed to analyze the effects of resveratrol on the brain status of control non-transgenic (NoTg) and AD transgenic (3xTg-AD) mice to discern the mechanisms involved in a potential inducement of resilience against age-related neurodegeneration and Alzheimer's disease (AD). Mice were fed with a diet supplemented with 100 mg/kg of resveratrol from 2 months of age during 10 months. Resveratrol administration induced complete protection against memory loss and brain pathology in 3xTg-AD mice, and also induced cognitive enhancement in healthy NoTg mice. Resveratrol improved exploration and reduced anxiety in both mouse strains, indicative of well-being. Resveratrol reduced the presence of Aß and p-tau pathology in the hippocampus of the 3xTg-AD mouse. Proteostasis analysis showed the following in both NoTg and 3xTg-AD mice: (i) increased levels of the amyloid-degrading enzyme neprilysin, (ii) reduction of the amyloidogenic secretase BACE1, and (iii) increase of proteasome protein levels and enhancement of proteasome activity. Resveratrol also increased AMPK protein levels, then upregulating the SIRT1 pathway, as shown by the activation of PGC-1α and CREB in both mice, resulting in further beneficial changes. Our data demonstrated that resveratrol induces cognitive enhancement and neuroprotection against amyloid and tau pathologies. Improvement of proteostasis by resveratrol, in both healthy and AD mice, suggests that it is a mechanism of brain resilience and defense against neurodegeneration caused by the accumulation of aberrant proteins.

Peripheral Maintenance of the Axis SIRT1-SIRT3 at Youth Level May Contribute to Brain Resilience in Middle-Aged Amateur Rugby Players.

Physical exercise performed regularly is known to improve health and to reduce the risk of age-related diseases. Furthermore, there is some evidence of cognitive improvement in physically active middle-aged and older adults. We hypothesized that long-term physically active middle-aged men may have developed brain resilience that can be detected with the analysis of peripheral blood markers. We aimed to analyze the activation of pathways potentially modulated by physical activity in a cohort of healthy amateur rugby players (n = 24) and control subjects with low physical activity (n = 25) aged 45-65 years. We had previously reported neuropsychological improvement in immediate memory responses in the player group compared to the controls. Here, we tested the expression of selected genes of longevity, inflammation, redox homeostasis, and trophic signaling in whole blood mRNA. Analyses were also performed on blood samples of young (aged 15-25 years) control subjects with low physical activity (n = 21). Physical activity and other lifestyle factors were thoroughly recorded with standardized questionnaires. Interestingly, middle-aged control subjects showed lower levels of expression of SIRT1, SIRT3, CAT, and SOD1 than the young controls, although rugby players maintained the expression levels of these genes at a young-like level. Middle-aged players showed lower levels of IL1B than the non-physically active groups. However, there was a tendency towards a decrease in trophic and transduction factors in middle-aged groups as compared to the young controls. A statistical study of Spearman's correlations supported a positive effect of sporting activity on memory and executive functions, and on peripheral gene expression of SIRT1, SIRT3 and downstream genes, in the middle-aged rugby players. Our results indicate that the SIRT1-SIRT3 axis, and associated neuroprotective signaling, may contribute to the anti-aging resilience of the brain mediated by physical exercise.

Neurotransmitter amines and antioxidant agents in neuronal protection against methylmercury-induced cytotoxicity in primary cultures of mice cortical neurons.

Methylmercury (MeHg) is an environmental toxicant with detrimental effects on the developing brain and adult nervous system. The main mechanisms identified include oxidative stress, changes in intracellular calcium, mitochondrial changes, inhibition of glutamate uptake, of protein synthesis and disruption of microtubules. However, little is known about mechanisms of protection against MeHg neurotoxicity. We found that resveratrol (10 µM) and ascorbic acid (200 µM) protected MeHg-induced cell death in primary cultures of cortical neurons. In this work, we aimed at finding additional targets that may be related to MeHg mode of action in cell toxicity with special emphasis in cell protection. We wonder whether neurotransmitters may affect the MeHg effects on neuronal death. Our findings show that neurons exposed to low MeHg concentrations exhibit less mortality if co-exposed to 10 µM dopamine (DA). However, DA metabolites, HVA (homovanillic acid) and DOPAC (3,4-dihydroxyphenylacetic acid) are not responsible for such protection. Furthermore, both DA D1 and D2 receptors agonists showed a protective effect against MeHg toxicity. It is striking though that DA receptor antagonists SKF83566 (10 µM) and haloperidol (10 µM) did not inhibit DA protection against MeHg. In addition, the protective effect of 10 µM DA against MeHg-induced toxicity was not affected by additional organochlorine pollutants exposure. Our results also demonstrate that cells exposed to MeHg in presence of 100 µM acetylcholine (ACh), show an increase in cell mortality at the "threshold value" of 100 nM MeHg. Finally, norepinephrine (10 µM) and serotonin (20 µM) also had an effect on cell protection. Altogether, we propose to further investigate the additional mechanisms that may be playing an important role in MeHg-induced cytotoxicity.

Cell viability and proteomic analysis in cultured neurons exposed to methylmercury.

Methylmercury is an environmental contaminant with special selectivity for cerebellar granule cells. The aim of this study was to determine the effect of long-term methylmercury exposure on cell viability and cellular proteome in cultured cerebellar granule cells. Primary cultures of mice cerebellar granule cells were treated with 0-300 nM methylmercury at 2 days in vitro (div) and afterwards the cells were harvested at 12 div. 100 nM methylmercury produced loss of cell viability, reduced intracellular glutamate content and increased lipid peroxidation. Glutamate transport was not modified by methylmercury treatment. Cell death induced by 300 nM methylmercury at 8 div was apoptotic without producing activation of caspase 3. Extracts of total protein were separated by 2D electrophoresis. Around 800 protein spots were visualized by silver staining in SDS-polyacrylamide gels. Gel images were digitized and protein patterns were analysed by image analysis. Several spots were identified through a combination of peptide mass fingerprinting and matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). The mitochondrial protein 3-ketoacid-coenzyme A transferase I was decreased up to 39% of controls at concentrations of methylmercury that did not produce cytotoxic effects, whereas the cytoplasmic proteins lactate dehydrogenase chain B and actin did not change.

Methylmercury-induced developmental toxicity is associated with oxidative stress and cofilin phosphorylation. Cellular and human studies.

Environmental exposure to methylmercury (MeHg) during development is of concern because it is easily incorporated in children's body both pre- and post-natal, it acts at several levels of neural pathways (mitochondria, cytoskeleton, neurotransmission) and it causes behavioral impairment in child. We evaluated the effects of prolonged exposure to 10-600nM MeHg on primary cultures of mouse cortical (CCN) and of cerebellar granule cells (CGC) during their differentiation period. In addition, it was studied if prenatal MeHg exposure correlated with altered antioxidant defenses and cofilin phosphorylation in human placentas (n=12) from the INMA cohort (Spain). Exposure to MeHg for 9days in vitro (DIV) resulted in protein carbonylation and in cell death at concentrations ≥200nM and ≥300nM, respectively. Exposure of CCN and CGC to non-cytotoxic MeHg concentrations for 5 DIV induced an early concentration-dependent decrease in cofilin phosphorylation. Furthermore, in both cell types actin was translocated from the cytosol to the mitochondria whereas cofilin translocation was found only in CGC. Translocation of cofilin and actin to mitochondria in CGC occurred from 30nM MeHg onwards. We also found an increased expression of cortactin and LIMK1 mRNA in CGC but not in CCN. All these effects were prevented by the antioxidant probucol. Cofilin phosphorylation was significantly decreased and a trend for decreased activity of glutathione reductase and glutathione peroxidase was found in the fetal side of human placental samples from the highest (20-40µg/L) MeHg-exposed group when compared with the low (<7µg/L) MeHg-exposed group. In summary, cofilin dephosphorylation and oxidative stress are hallmarks of MeHg exposure in both experimental and human systems.

Neurotoxicity of organomercurial compounds.

Mercury is a ubiquitous contaminant, and a range of chemical species is generated by human activity and natural environmental change. Elemental mercury and its inorganic and organic compounds have different toxic properties, but all them are considered hazardous in human exposure. In an equimolecular exposure basis, organomercurials with a short aliphatic chain are the most harmful compounds and they may cause irreversible damage to the nervous system. Methylmercury (CH(3)Hg(+)) is the most studied following the neurotoxic outbreaks identified as Minamata disease and the Iraq poisoning. The first description of the CNS pathology dates from 1954. Since then, the clinical neurology, the neuropathology and the mechanisms of neurotoxicity of organomercurials have been widely studied. The high thiol reactivity of CH(3)Hg(+), as well as all mercury compounds, has been suggested to be the basis of their harmful biological effects. However, there is clear selectivity of CH(3)Hg(+) for specific cell types and brain structures, which is not yet fully understood. The main mechanisms involved are inhibition of protein synthesis, microtubule disruption, increase of intracellular Ca(2+) with disturbance of neurotransmitter function, oxidative stress and triggering of excitotoxicity mechanisms. The effects are more damaging during CNS development, leading to alterations of the structure and functionality of the nervous system. The major source of CH(3)Hg(+) exposure is the consumption of fish and, therefore, its intake is practically unavoidable. The present concern is on the study of the effects of low level exposure to CH(3)Hg(+) on human neurodevelopment, with a view to establishing a safe daily intake. Recommendations are 0.4 micro g/kg body weight/day by the WHO and US FDA and, recently, 0.1 micro g/kg body weight/day by the US EPA. Unfortunately, these levels are easily attained with few meals of fish per week, depending on the source of the fish and its position in the food chain.

Influence of prenatal exposure to environmental pollutants on human cord blood levels of glutamate.

Some chemicals released into the environment, including mercury and some organochlorine compounds (OCs), are suspected to have a key role on subclinical brain dysfunction in childhood. Alteration of the glutamatergic system may be one mechanistic pathway. We aimed to determine whether mercury and seven OCs, including PCBs 138, 153, and 180, DDT and DDE, hexachlorobenzene (HCB), and beta-hexachlorocyclohexane (ß-HCH) influence the cord levels of two excitatory amino acids, glutamate and aspartate. Second, we evaluated if this association was mediated by glutamate uptake measured in human placental membranes. The study sample included 40 newborns from a Spanish cohort selected according to cord mercury levels. We determined the content of both amino acids in cord blood samples by means of HPLC and assessed their associations with the contaminants using linear regression analyses, and the effect of the contaminants on glutamate uptake by means of [(3)H]-aspartate binding in human placenta samples. PCB138, ß-HCH, and the sum of the three PCBs and seven OCs showed a significant negative association with glutamate levels (decrease of 51, 24, 56 and 54%, respectively, in glutamate levels for each 10-fold increase in the contaminant concentration). Mercury did not show a significant correlation neither with glutamate nor aspartate levels in cord blood, however a compensatory effect between T-Hg and both PCB138, and 4,4'-DDE was observed. The organo-metallic derivative methylmercury completely inhibited glutamate uptake in placenta while PCB138 and ß-HCH partially inhibited it (IC50 values: 4.9±0.8 µM, 14.2±1.2 nM and 6.9±2.9 nM, respectively). We conclude that some environmental toxicants may alter the glutamate content in the umbilical cord blood, which might underlie alterations in human development.

Differential estrogenic effects of the persistent organochlorine pesticides dieldrin, endosulfan, and lindane in primary neuronal cultures.

The organochlorine chemicals endosulfan, dieldrin, and γ-hexachlorocyclohexane (lindane) are persistent pesticides to which people are exposed mainly via diet. Their antagonism of the γ-aminobutyric acid-A (GABA(A)) receptor makes them convulsants. They are also endocrine disruptors because of their interaction with the estrogen receptor (ER). Here, we study the effects of dieldrin, endosulfan, and lindane on ERs in primary cultures of cortical neurons (CN) and cerebellar granule cells (CGC). All the compounds tested inhibited the binding of [(3)H]-estradiol to the ER in both CN and CGC, with dieldrin in CGC showing the highest affinity. We also determined the effects of the pesticides on protein kinase B (Akt) and extracellular-regulated kinase 1 and 2 (ERK1/2) phosphorylation. Dieldrin and endosulfan increased Akt phosphorylation in CN, which was inhibited by the ERß antagonist 4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol. Instead, Akt and ERK1/2 phosphorylation induced by dieldrin in CGC was mediated by multiple activation of ERα, ERß, and G protein-coupled receptor 30. Lindane did not activate these pathways, but it inhibited estradiol-mediated Akt and ERK1/2 activation. In CN, all the chemicals activated ERK1/2 through a mechanism involving GABA(A) and glutamate receptors. Long-term exposure to these pesticides reduced the levels of ERα, but not of ERß. Moreover, extracts of CN treated with endosulfan, dieldrin, or lindane induced cell proliferation in MCF-7 human breast cancer-derived cells, whereas only extracts of CGC treated with dieldrin induced MCF-7 cell proliferation. Overall, the observed alterations on ER-mediated signaling and ER levels in neurons might contribute to the neurotoxicity of these organochlorine pesticides.

GABAA receptor and cell membrane potential as functional endpoints in cultured neurons to evaluate chemicals for human acute toxicity.

Toxicity risk assessment for chemical-induced human health hazards relies mainly on data obtained from animal experimentation, human studies and epidemiology. In vitro testing for acute toxicity based on cytotoxicity assays predicts 70-80% of rodent and human toxicity. The nervous system is particularly vulnerable to chemical exposure which may result in different toxicity features. Acute human toxicity related to adverse neuronal function is usually a result of over-excitation or depression of the nervous system. The major molecular and cellular mechanisms involved in such reactions include GABAergic, glutamatergic and cholinergic neurotransmission, regulation of cell and mitochondrial membrane potential, and those critical for maintaining central nervous system functionality, such as controlling cell energy. In this work, a set of chemicals that are used in pharmacy, industry, biocide treatments or are often abused by drug users are tested for their effects on GABA(A) receptor activity, GABA and glutamate transport, cell membrane potential and cell viability in primary neuronal cultures. GABA(A) receptor function was inhibited by compounds for which seizures have been observed after severe human poisoning. Commonly abused drugs inhibit GABA uptake but not glutamate uptake. Most neurotoxins altered membrane potential. The GABA(A) receptor, GABA uptake and cell membrane potential assays were those that identified the highest number of chemicals as toxic at low concentrations. These results show that in vitro cell assays may identify compounds that produce acute neurotoxicity in humans, provided that in vitro models expressing neuronal targets relevant for acute neural dysfunctions are used.

Mercury compounds disrupt neuronal glutamate transport in cultured mouse cerebellar granule cells.

Cerebellar granule cells are targeted selectively by mercury compounds in vivo. Despite the affinity of mercury for thiol groups present in all cells, the molecular determinant(s) of selective cerebellar degeneration remain to be elucidated fully. We studied the effect of mercury compounds on neuronal glutamate transport in primary cultures of mouse cerebellar granule cells. Immunoblots probed with an antibody against the excitatory amino acid transporter (EAAT) neuronal glutamate transporter, EAAT3, revealed the presence of a specific band in control and mercury-treated cultures. Micromolar concentrations of both methylmercury and mercuric chloride increased the release of endogenous glutamate, inhibited glutamate uptake, reduced mitochondrial activity, and decreased ATP levels. All these effects were completely prevented by the nonpermeant reducing agent Tris-(2-carboxyethyl)phosphine (TCEP). Reduction of mitochondrial activity by mercuric chloride, but not by methylmercury, was inhibited significantly by 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS) and by reduced extracellular Cl- ion concentration. In addition, DIDS and low extracellular Cl- completely inhibited the release of glutamate induced by mercuric chloride, and produced a partial although significant reduction of that induced by methylmercury. We suggest that a direct inhibition of glutamate uptake triggers an imbalance in cell homeostasis, leading to neuronal failure and Cl(-)-regulated cellular glutamate efflux. Our results demonstrate that neuronal glutamate transport is a novel target to be taken into account when assessing mercury-induced neurotoxicity.

Evaluation of fluorescent dyes for measuring intracellular glutathione content in primary cultures of human neurons and neuroblastoma SH-SY5Y.

BACKGROUND: Reduced glutathione (GSH) protects cells against oxidative injury and maintains a range of vital functions. To study GSH content in human neuronal cell cultures, thiol-sensitive fluorescent techniques requiring a small number of cells may be of great value, but their GSH specificity has not been established in these cells. METHODS: We tested the efficiency of four currently available GSH fluorescent stains in human neurons and SH-SY5Y neuroblastoma cells, both cultured in microwells, by using a fluorescence plate reader. Cultures were treated with the inhibitor of the GSH synthesis, buthionine sulfoximine (BSO), and progressive GSH depletion was assayed with monochlorobimane (mBCl), monobromobimane (mBBr), 5-chloromethylfluorescein diacetate (CMFDA), and 7-amino-4-chloromethylcoumarin (CMAC). GSH was also determined by a biochemical method in cell homogenates to obtain quantitative reference values. RESULTS: Neurons and SH-SY5Y neuroblastoma had basal GSH contents of 27.1 +/- 3.2 and 14.5 +/- 1.7 nmol/mg protein (n = 5), respectively. An approximate 90% depletion of GSH was obtained after 3 days of exposure to 1,000 microM of BSO in neurons and after 1 day in SH-SY5Y cells. Cell death through an apoptotic pathway appeared 1-2 days after total GSH depletion. The assayed stains had different degrees of background fluorescence and sensitivity to GSH content, with similar results in both neuronal cell types. The probes mBCl and CMAC showed the lowest background, and the GSH-depletion curves were most similar to that of the reference method. CONCLUSIONS: Both mBCl and CMAC are useful fluorescent stains to determine semiquantitative GSH concentration in human neuronal cell cultures.

Down's syndrome astrocytes have greater antioxidant capacity than euploid astrocytes.

Down's syndrome (trisomy 21) brain tissue is considered to be susceptible to oxidative injury, mainly because its increased Cu/Zn-superoxide dismutase (SOD1) activity is not followed by an adaptive rise in hydrogen peroxide metabolizing enzymes. In vitro, trisomic neurons suffer oxidative stress and degenerate. We studied the response of trisomy 21 neuron and astrocyte cultures to hydrogen peroxide injury and found that they were, respectively, more and less vulnerable than their euploid counterparts. Differences were detected 24 h after exposures in the region of 50 microm and 500 microm hydrogen peroxide for neuron and astrocyte cultures, respectively. Cytotoxicity results were paralleled by a decrease in cellular glutathione. In addition, trisomic astrocytes showed a lower basal content of superoxide ion and a higher clearance of hydrogen peroxide from the culture medium. In the presence of hydrogen peroxide, trisomic astrocytes maintained their concentration of intracellular superoxide and hydroperoxides at a lower level than euploid astrocytes. Consistent with these results, trisomic astrocytes in neuron coculture were more neuroprotective than euploid astrocytes against hydrogen peroxide injury. We suggest that SOD1 overexpression has beneficial effects on astrocytes, as it does in other systems with similarly high disposal of hydroperoxides. In addition to a higher enzymatic activity of SOD1, cultures of trisomic astrocytes showed slightly higher glutathione reductase activity than euploid cultures. Thus, trisomy 21 astrocytes showed a greater antioxidant capacity against hydrogen peroxide than euploid astrocytes, and they partially counteracted the oxidative vulnerability of trisomic neurons in culture.