Coral Sanfeliu

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 (CH3Hg+) 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 CH3Hg+, as well as all mercury compounds, has been suggested to be the basis of their harmful biological effects. However, there is clear selectivity of CH3Hg+ 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 Ca2+ 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 CH3Hg+ 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 CH3Hg+ on human neurodevelopment, with a view to establishing a safe daily intake. Recommendations are 0.4 μg/kg body weight/day by the WHO and US FDA and, recently, 0.1 μg/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.

Physical exercise protects against alzheimer's disease in 3xTg-AD mice

Physical exercise is considered to exert a positive neurophysiological effect that helps to maintain normal brain activity in the elderly. Expectations that it could help to fight Alzheimers disease (AD) were recently raised. This study analyzed the effects of different patterns of physical exercise on the 3xTg-AD mouse. Male and female 3xTg-AD mice at an early pathological stage (4-month-old) have had free access to a running wheel for 1 month, whereas mice at a moderate pathological stage(7-month-old) have had access either during 1 or 6 months. The non-transgenic mouse strain was used as a control. Parallel animal groups were housed in conventional conditions. Cognitive loss and behavioral and psychological symptoms of dementia (BPSD)-like behaviors were present in the 3xTg-AD mice along with alteration in synaptic function and ong-term potentiation impairment in vivo. Brain tissue showed AD-pathology and oxidative-related changes. Disturbances were more severe at the older age tested. Oxidative stress was higher in males but other changes were similar or higher in females. Exercise treatment ameliorated cognitive deterioration and BPSD-like behaviors such as anxiety and the startle response. Synaptic changes were partially protected by exercise. Oxidative stress was reduced. The best neuroprotection was generally obtained after 6 months of exercise in 7-month-old 3xTg-AD mice. Improved sensorimotor function and brain tissue antioxidant defence were induced in both 3xTg-AD and NonTg mice. Therefore, the benefits of aerobic physical exercise on synapse, redox homeostasis, and general brain function demonstrated in the 3xTg-AD mouse further support the value of this healthy life-style against neurodegeneration.

Dietary resveratrol prevents Alzheimer’s markers and increases life span in SAMP8

Resveratrol is a polyphenol that is mainly found in grapes and red wine and has been reported to be a caloric restriction (CR) mimetic driven by Sirtuin 1 (SIRT1) activation. Resveratrol increases metabolic rate, insulin sensitivity, mitochondrial biogenesis and physical endurance, and reduces fat accumulation in mice. In addition, resveratrol may be a powerful agent to prevent age-associated neurodegeneration and to improve cognitive deficits in Alzheimer’s disease (AD). Moreover, different findings support the view that longevity in mice could be promoted by CR. In this study, we examined the role of dietary resveratrol in SAMP8 mice, a model of age-related AD. We found that resveratrol supplements increased mean life expectancy and maximal life span in SAMP8 and in their control, the related strain SAMR1. In addition, we examined the resveratrol-mediated neuroprotective effects on several specific hallmarks of AD. We found that long-term dietary resveratrol activates AMPK pathways and pro-survival routes such as SIRT1 in vivo. It also reduces cognitive impairment and has a neuroprotective role, decreasing the amyloid burden and reducing tau hyperphosphorylation.

Antioxidant compounds and Ca2+ pathway blockers differentially protect against methylmercury and mercuric chloride neurotoxicity

The effects of the environmental contaminants methylmercury (MeHg) and inorganic mercury (HgCl2) on cell viability, intracellular calcium concentration ([Ca2+]i), and reactive oxygen species (ROS) generation were studied in rat cerebellar granule neuron cultures using fluorescent methods. MeHg exhibited an LC50 (2.47 μM) tenfold lower than that of HgCl2 (26.40 μM). To study the involvement of oxidative stress and Ca2+ homeostasis disruption in mercury‐induced cytotoxicity, we tested the neuroprotective effects of several agents that selectively interfere with these mechanisms. After a 24 hr exposure, the cytotoxic effect of both mercury compounds was reduced by thapsigargin, an inhibitor of endoplasmic reticulum Ca2+‐ATPase; the Ca2+ channel blocker flunarizine; and the Na+/Ca2+ exchanger blocker benzamil. All these compounds decreased the mercury‐mediated [Ca2+]i rise. These results indicate that Ca2+ influx through Ca2+ channels and the Na+/Ca2+ exchanger and Ca2+ mobilization from the endoplasmic reticulum are involved in mercury‐mediated cytotoxicity. The antioxidants probucol and propyl gallate reduced the HgCl2 toxicity. Probucol and vitamin E partially inhibited the MeHg toxicity after a 24 hr period, whereas propyl gallate completely prevented this effect. Probucol slightly reduced ROS generation in methylmercury‐exposed cultures and decreased mercury‐mediated rise of [Ca2+]i. Propyl gallate abolished ROS generation and partially inhibited the increase of [Ca2+]i induced by both mercury compounds. Propyl gallate also protected human cerebral cortical neuron cultures from the MeHg effect even after 72 hr of MeHg exposure, thus showing a long‐lasting effect. Our data suggest that disruption of redox equilibrium and Ca2+ homeostasis contribute equally to HgCl2‐mediated toxicity, whereas oxidative stress is the main cause of MeHg neurotoxicity. J. Neurosci. Res. 66:135–145, 2001.

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

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.

Astrocytes aged in vitro show a decreased neuroprotective capacity

Alterations in astrocyte function that may affect neuronal viability occur with brain aging. In this study, we evaluate the neuroprotective capacity of astrocytes in an experimental model of in vitro aging. Changes in oxidative stress, glutamate uptake and protein expression were evaluated in rat cortical astrocytes cultured for 10 and 90 days in vitro (DIV). Levels of glial fibrillary acidic protein and S100β increased at 90 days when cells were positive for the senescence β‐galactosidase marker. In long‐term astrocyte cultures, the generation of reactive oxygen species was enhanced and mitochondrial activity decreased. Simultaneously, there was an increase in proteins that stained positively for nitrotyrosine. The expression of Cu/Zn‐superoxide dismutase (SOD‐1) and haeme oxygenase‐1 (HO‐1) proteins and inducible nitric oxide synthase (iNOS) increased in aged astrocytes. Glutamate uptake in 90‐DIV astrocytes was higher than in 10 DIV ones, and was more vulnerable to inhibition by H2O2 exposure. Enhanced glutamate uptake was probably because of up‐regulation of the glutamate/aspartate transporter protein. Aged astrocytes had a reduced ability to maintain neuronal survival. These findings indicate that astrocytes may partially loose their neuroprotective ability during aging. The results also suggest that aged astrocytes may contribute to exacerbating neuronal injury in age‐related neurodegenerative processes.

Melatonin plus physical exercise are highly neuroprotective in the 3xTg-AD mouse

Alzheimers disease (AD) is a devastating age-related neurodegenerative disease with no specific treatment at present. Several healthy lifestyle options and over-the-counter drugs that it has been suggested delay the onset of the disease are in an experimental phase, but it is unclear whether they will have any therapeutic value against AD. We assayed physical exercise and melatonin in 3xTg-AD male mice aged from 6 to 12 months, therefore from moderate to advanced phases of AD pathology. Analysis of behavior and brain tissue at termination showed differential patterns of neuroprotection for the 2 treatments. Both treatments decreased soluble amyloid β oligomers, whereas only melatonin decreased hyperphosphorylated tau. Melatonin was effective against the immunosenescence that 3xTg-AD mice present. Voluntary physical exercise protected against behavioral and psychological symptoms of dementia such as anxiety, a lack of exploration, and emotionality. Both treatments protected against cognitive impairment, brain oxidative stress, and a decrease in mitochondrial DNA (mtDNA). Interestingly, only the combined treatment of physical exercise plus melatonin was effective against the decrease of mitochondrial complexes. Therefore, melatonin plus physical exercise may exert complementary, additive, or even synergistic effects against a range of disturbances present in AD.

Expression of GDNF transgene in astrocytes improves cognitive deficits in aged rats

Glial cell line-derived neurotrophic factor (GDNF) was assayed for its neurotrophic effects against the neuronal atrophy that causes cognitive deficits in old age. Aged Fisher 344 rats with impairment in the Morris water maze received intrahippocampal injections at the dorsal CA1 area of either a lentiviral vector encoding human GDNF or the same vector encoding human green fluorescent protein as a control. Recombinant lentiviral vectors constructed with human cytomegalovirus promotor and pseudotyped with lyssavirus Mokola glycoprotein specifically transduced the astrocytes in vivo. Astrocyte-secreted GDNF enhanced neuron function as shown by local increases in synthesis of the neurotransmitters acetylcholine, dopamine and serotonin. This neurotrophic effect led to cognitive improvement of the rats as early as 2 weeks after gene transduction. Spatial learning and memory testing showed a significant gain in cognitive abilities due to GDNF exposure, whereas control-transduced rats kept their performance at the chance level. These results confirm the broad spectrum of the neurotrophic action of GDNF and open new gene therapy possibilities for reducing age-related neurodegeneration.

Physical exercise improves synaptic dysfunction and recovers the loss of survival factors in 3xTg-AD mouse brain.

Physical exercise has become a potentially beneficial therapy for reducing neurodegeneration symptoms in Alzheimers disease. Previous studies have shown that cognitive deterioration, anxiety and the startle response observed in 7-month-old 3xTg-AD mice were ameliorated after 6 months of free access to a running wheel. Also, alterations in synaptic response to paired-pulse stimulation were improved. The present study further investigated some molecular mechanisms underlying the beneficial effects of 6 months of voluntary exercise on synaptic plasticity in 7-month-old 3xTg-AD mice. Changes in binding parameters of [(3)H]-flunitrazepam to GABAA receptor and of [(3)H]-MK-801 to NMDA receptor in cerebral cortex of 3xTgAD mice were restored by voluntary exercise. In addition, reduced expression levels of NMDA receptor NR2B subunit were reestablished. The synaptic proteins synaptophysin and PSD-95 and the neuroprotective proteins GDNF and SIRT1 were downregulated in 3xTgAD mice and were recovered by exercise treatment. Overall, in this paper we highlight the fact that different interrelated mechanisms are involved in the beneficial effects of exercise on synaptic plasticity alterations in the 3xTg-AD mouse model.

Self-assembled multifunctional Fe/MgO nanospheres for magnetic resonance imaging and hyperthermia

UNLABELLED A one-step process for the production of nanoparticles presenting advanced magnetic properties can be achieved using vapor condensation. In this article, we report on the fabrication of Fe particles covered by a uniform MgO epitaxial shell. MgO has a lower surface energy than Fe, which results in a core-shell crystal formation. The particles satisfy a few of technical requirements for the practical use in real clinics, such as a high biocompatibility in living cells in-vitro, an injection through blood vessels without any clothing problems in murine model, a high absorption rate for magnetic hyperthermia at small particle concentration, and the potential to be used as contrast agent in the field of diagnostic magnetic imaging. They are also able to be used in drug delivery and magnetic-activated cell sorting. FROM THE CLINICAL EDITOR In this paper, the authors report on the synthesis of Fe particles covered by a uniform MgO epitaxial shell resulting in a core-shell crystal formation. The particles are proven to be useful as contrast agents for magnetic resonance imaging and have the potential to be useful as heating mediators for cancer therapy through hyperthermia. They also might be used in drug delivery and magnetic-activated cell sorting.