Zinc: the brain's dark horse

Glucose starvation stimulates Zn2+ toxicity in cultures of cerebellar granule neurons

Zinc chloride (0.02 mM, 3h) did not have any influence on the survival of cerebellar granule neurons (CGNs) incubated in balanced salt solution (BSS). However, in the absence of glucose ZnCl(2) caused severe neuronal damage, decreasing cell survival to 12±2%. Either the blockade of ionotropic glutamate NMDA-receptors with MK-801 or APV or supplementation the medium with ruthenium red (mitochondrial Ca(2+) uniporter blocker) almost entirely protected CGNs from the toxic effect of ZnCl(2) during glucose deprivation (GD). However, NBQX (AMPA/kainate glutamate receptor blocker) did not show protective effect. Measurements of intracellular calcium ions concentration using fluorescent probe (Fluo-4 AM) and zinc ions (FluoZin-3AM) demonstrated that 1.5h-exposure to GD induced intensive increase of Fluo-4 fluorescence and small increase of FluoZin-3 fluorescence in neurons. The supplementation of medium with ZnCl(2) caused equal increase of FluoZin-3 fluorescence at both GD and normoglycemia, whereas the potentiation of Fluo-4 fluorescence by zinc was observed only under GD and could be prevented by MK-801. However, neither MK-801 nor NBQX could influence [Zn(2+)](i) increase caused by zinc addition under GD, while ruthenium red did cause significant increase of [Zn(2+)](i). This data implies that zinc ions during GD induce an additional overload of CGNs with calcium ions that get transported through activated NMDA-channel. Zinc and calcium ions accumulate in mitochondria and amplify individual destructive action on these organelles leading to neuronal death.

Stimulation of kainate toxicity by zinc in cultured cerebellar granule neurons and the role of mitochondria in this process

Zinc chloride (0.01 mM kept for 3h) is not toxic to cultured cerebellar granule neurons (CGNs) while kainate (0.1mM kept for 3h) demonstrates some but very low toxicity towards these cells. Measurements of the relative intraneuronal zinc ion concentration showed that increase in [Zn(2+)](i) under the simultaneous action of ZnCl(2) and kainate was significantly stronger compared to their separate action. Simultaneous treatment of CGNs with kainate and zinc chloride caused the swelling of neuronal mitochondria and consequent intensive neuronal death, which was totally prevented by NBQX (an AMPA/kainate-receptors blocker) or ruthenium red (a mitochondrial Ca(2+) uniporter blocker). These data imply that Zn(2+) synergistically to kainate increase their separate toxic effects on mitochondria leading to rapid neuronal death.

Dithizone staining of intracellular zinc: an unexpected and versatile counterscreen for auxotrophic marker genes in Saccharomyces cerevisiae

Auxotrophic marker genes such as URA3, LEU2, and HIS3 in Saccharomyces cerevisiae have long been used to select cells that have been successfully transformed with recombinant DNA. A longstanding challenge in working with these genes is that counterselection procedures are often lacking. This paper describes the unexpected discovery of a simple plate assay that imparts a bright red stain to cells experiencing nutritional stress from the lack of a marker gene. The procedure specifically stains a zinc-rich vesicular compartment analogous to the zinc-rich secretory vesicles found in insulin-secreting pancreatic islet cells and glutamate-secreting neurons. Staining was greatly diminished in zap1 mutants, which lack a homeostatic activator of zinc uptake, and in cot1 zrc1 double mutants, which lack the two yeast homologs of mammalian vesicle-specific zinc export proteins. Only one of 93 strains with temperature-sensitive alleles of essential genes exhibited an increase in dithizone staining at its non-permissive temperature, indicating that staining is not simply a sign of growth-arrested or dying cells. Remarkably, the procedure works with most commonly used marker genes, highlights subtle defects, uses no reporter constructs or expensive reagents, requires only a few hours of incubation, yields visually striking results without any instrumentation, and is not toxic to the cells. Many potential applications exist for dithizone staining, both as a versatile counterscreen for auxotrophic marker genes and as a powerful new tool for the genetic analysis of a biomedically important vesicular organelle.

Selective, quantitative measurement of releasable synaptic zinc in human autopsy hippocampal brain tissue from Alzheimer's disease patients

Aberrant central nervous system zinc homeostasis has been reported in Alzheimer's disease (AD). However, there are conflicting reports describing zinc concentration either increased or decreased in the brain of AD patients. Such discrepancies may be due to differences in the brain area examined, zinc detection method, and/or tissue composition. Furthermore, detection and measurement of the releasable zinc pool in autopsy tissue is difficult and usually unreliable. Obtaining an adequate assessment of this releasable zinc pool is of particular significance in AD research in that zinc can coordinate with and stabilize toxic amyloid beta oligomers, which are believed to play a key role in AD neuropathology. In addition, zinc released into the synaptic cleft can interact with the postsynaptic neurons causing altered signaling and synaptic dysfunction, which is a well established event in AD. The method presented here combines two approaches, biochemical fractionation and atomic absorption spectrophotometry, to allow, in addition to extracellular zinc concentration, the reliable and quantitative measurement of zinc specifically localized in synaptic vesicles, which contain the majority of the neuronal releasable zinc. Using this methodology, we found that synaptic vesicle zinc concentrations were increased in AD hippocampi compared to age-matched controls and that this increase in releasable zinc matched increased concentration of zinc in the extracellular space.

Brain-Delivery of Zinc-Ions as Potential Treatment for Neurological Diseases: Mini Review

Homeostasis of metal ions such as Zn(2+) is essential for proper brain function. Moreover, the list of psychiatric and neurodegenerative disorders involving a dysregulation of brain Zn(2+)-levels is long and steadily growing, including Parkinson's and Alzheimer's disease as well as schizophrenia, attention deficit and hyperactivity disorder, depression, amyotrophic lateral sclerosis, Down's syndrome, multiple sclerosis, Wilson's disease and Pick's disease. Furthermore, alterations in Zn(2+)-levels are seen in transient forebrain ischemia, seizures, traumatic brain injury and alcoholism. Thus, the possibility of altering Zn(2+)-levels within the brain is emerging as a new target for the prevention and treatment of psychiatric and neurological diseases. Although the role of Zn(2+) in the brain has been extensively studied over the past decades, methods for controlled regulation and manipulation of Zn(2+) concentrations within the brain are still in their infancy. Since the use of dietary Zn(2+) supplementation and restriction has major limitations, new methods and alternative approaches are currently under investigation, such as the use of intracranial infusion of Zn(2+) chelators or nanoparticle technologies to elevate or decrease intracellular Zn(2+) levels. Therefore, this review briefly summarizes the role of Zn(2+) in psychiatric and neurodegenerative diseases and highlights key findings and impediments of brain Zn(2+)-level manipulation. Furthermore, some methods and compounds, such as metal ion chelation, redistribution and supplementation that are used to control brain Zn(2+)-levels in order to treat brain disorders are evaluated.

Micronutrients deficiency and associated sociodemographic factors in Chinese children

BACKGROUND

Although the prevalence of malnutrition has decreased, micronutrient deficiency still exists among children. While iron level has been studied, limited information on serum levels of zinc in Chinese children is available. This study aims to describe the status of micronutrients and its association with sociodemographic factors, and to assess associated risk factors.

METHODS

A cross-sectional study was performed on 1375 Chinese preschool children. Venous blood samples were collected and analyzed for zinc and iron by atomic absorption spectrophotometry. Sociodemographic information was obtained from self-administered questionnaires given to the parents.

RESULTS

The high prevalence of low serum zinc (38.2%) and iron (24.3%) was found. Children from rural preschools had the lowest zinc levels, whereas those from urban preschools had the lowest iron levels. Children living in small houses had the highest prevalence of low serum zinc (47.1%), and children from small families (≤3 persons) had a higher prevalence of low serum zinc than those from large families (41.8% vs. 34.1%).

CONCLUSIONS

Our findings in the recent socioeconomic development of China suggest the need for continuous monitoring of nutritional factors and highlight the importance of public health implication in preschool children even in developed regions.

Zinc signaling through glucocorticoid and glutamate signaling in stressful circumstances

Humans and animals are constantly exposed to environmental stress. The hypothalamic-pituitary-adrenal (HPA) axis responds to stress, followed by glucocorticoid secretion from the adrenal glands. This response serves to maintain homeostasis in the living body through energy mobilization or to restore it. The brain is an important target for glucocorticoids. The hippocampus participates in the regulation of the HPA axis. Stress activates glutamatergic neurons in the hippocampus, and serious stress induces dyshomeostasis of extracellular glutamate. This dyshomeostasis, which is potentiated by glucocorticoids, modifies cognitive and emotional behavior. On the other hand, zinc is necessary for glucocorticoid signaling and is released from glutamatergic (zincergic) neurons to modulate synaptic glutamate signaling. Stress also induces dyshomeostasis of extracellular zinc, which may be linked to dyshomeostasis of extracellular glutamate. Thus, glucocorticoid signaling might also contribute to dyshomeostasis of extracellular zinc. It is likely that zinc signaling participates in cognitive and emotional behavior through glucocorticoid and glutamate signaling under stressful circumstances. This Mini-Review analyzes the relationship among signals of glucocorticoid, glutamate, and zinc under stressful circumstances to elucidate the significance of the zinc signaling in response to stress.

TRPM channels modulate epileptic-like convulsions via systemic ion homeostasis

Neuronal networks operate over a wide range of activity levels, with both neuronal and nonneuronal cells contributing to the balance of excitation and inhibition. Activity imbalance within neuronal networks underlies many neurological diseases, such as epilepsy. The Caenorhabditis elegans locomotor circuit operates via coordinated activity of cholinergic excitatory and GABAergic inhibitory transmission. We have previously shown that a gain-of-function mutation in a neuronal acetylcholine receptor, acr-2(gf), causes an epileptic-like convulsion behavior. Here we report that the behavioral and physiological effects of acr-2(gf) require the activity of the TRPM channel GTL-2 in nonneuronal tissues. Loss of gtl-2 function does not affect baseline synaptic transmission but can compensate for the excitation-inhibition imbalance caused by acr-2(gf). The compensatory effects of removing gtl-2 are counterbalanced by another TRPM channel, GTL-1, and can be recapitulated by acute treatment with divalent cation chelators, including those specific for Zn(2+). Together, these data reveal an important role for ion homeostasis in the balance of neuronal network activity and a novel function of nonneuronal TRPM channels in the fine-tuning of this network activity.

Reactive oxygen species in the regulation of synaptic plasticity and memory

The brain is a metabolically active organ exhibiting high oxygen consumption and robust production of reactive oxygen species (ROS). The large amounts of ROS are kept in check by an elaborate network of antioxidants, which sometimes fail and lead to neuronal oxidative stress. Thus, ROS are typically categorized as neurotoxic molecules and typically exert their detrimental effects via oxidation of essential macromolecules such as enzymes and cytoskeletal proteins. Most importantly, excessive ROS are associated with decreased performance in cognitive function. However, at physiological concentrations, ROS are involved in functional changes necessary for synaptic plasticity and hence, for normal cognitive function. The fine line of role reversal of ROS from good molecules to bad molecules is far from being fully understood. This review focuses on identifying the multiple sources of ROS in the mammalian nervous system and on presenting evidence for the critical and essential role of ROS in synaptic plasticity and memory. The review also shows that the inability to restrain either age- or pathology-related increases in ROS levels leads to opposite, detrimental effects that are involved in impairments in synaptic plasticity and memory function.

Quantitative comparison of preparation methodologies for X-ray fluorescence microscopy of brain tissue

X-ray fluorescence microscopy (XFM) facilitates high-sensitivity quantitative imaging of trace metals at high spatial resolution over large sample areas and can be applied to a diverse range of biological samples. Accurate determination of elemental content from recorded spectra requires proper calibration of the XFM instrument under the relevant operating conditions. Here, we describe the manufacture, characterization, and utilization of multi-element thin-film reference foils for use in calibration of XFM measurements of biological and other specimens. We have used these internal standards to assess the two-dimensional distribution of trace metals in a thin tissue section of a rat hippocampus. The data used in this study was acquired at the XFM beamline of the Australian Synchrotron using a new 384-element array detector (Maia) and at beamline 2-ID-E at the Advanced Photon Source. Post-processing of samples by different fixation techniques was investigated, with the conclusion that differences in solvent type and sample handling can significantly alter elemental content. The present study highlights the quantitative capability, high statistical power, and versatility of the XFM technique for mapping trace metals in biological samples, e.g., brain tissue samples in order to help understand neurological processes, especially when implemented in conjunction with a high-performance detector such as Maia.

The role of zinc in neurodegenerative inflammatory pathways in depression

According to new hypothesis, depression is characterized by decreased neurogenesis and enhanced neurodegeneration which, in part, may be caused by inflammatory processes. There is much evidence indicating that depression, age-related changes often associated with impaired brain function and cognitive performances or neurodegenerative processes could be related to dysfunctions affecting the zinc ion availability. Clinical studies revealed that depression is accompanied by serum hypozincemia, which can be normalized by successful antidepressant treatment. In patients with major depression, a low zinc serum level was correlated with an increase in the activation of markers of the immune system, suggesting that this effect may result in part from a depression-related alteration in the immune-inflammatory system. Moreover, a preliminary clinical study demonstrated the benefit of zinc supplementation in antidepressant therapy in both treatment non-resistant and resistant patients. In the preclinical study, the antidepressant activity of zinc was observed in the majority of rodent tests and models of depression and revealed a causative role for zinc deficiency in the induction of depressive-like symptoms, the reduction of neurogenesis and neuronal survival or impaired learning and memory ability. This paper provides an overview of the clinical and experimental evidence that implicates the role of zinc in the pathophysiology and therapy of depression within the context of the inflammatory and neurodegenerative hypothesis of this disease.

Investigating the role of zinc in a rat model of epilepsy

AIMS

The aim of the present study was to investigate the role of zinc (Zn) in pilocarpine-induced seizures and its interrelation with an antiepileptic drug, namely, valproic acid.

METHODOLOGY

The study was carried out on 110 male Wistar albino rats that were divided into the following groups: Group I, control rats that received intraperitoneal (i.p.) saline vehicle; Groups II-V received Zn in a medium dose, Zn in a high dose, valproic acid in a therapeutic dose, as well as a combination of valproic acid with medium dose Zn, respectively, for 3 weeks before saline injection, Group VI received i.p. pilocarpine to induce seizures; Groups VII-XI received Zn in a medium dose, Zn in a high dose, valproic acid in a therapeutic dose, a combination of therapeutic dose of valproic acid with medium dose Zn, as well as a combination of subeffective dose of valproic acid with medium dose of Zn, respectively, for 3 weeks before pilocarpine injection. The seizure's latency and severity for each rat was recorded. Blood and brain hippocampal samples were collected for determination of serum neuron specific enolase (NSE), hippocampal Zn, interleukin-1 beta concentrations as well as hippocampal superoxide dismutase and caspase-3 activities.

RESULTS

The results of the current study demonstrated that pretreatment with high dose of Zn exacerbated pilocarpine-induced seizures. Whereas, a medium dose of Zn and valproic acid either alone or in combination reduced the severity of pilocarpine-induced limbic seizures and increased the latency to attain the forelimb clonus. Also both drugs, either alone or in combination, ameliorated all studied biochemical parameters with the exception of hippocampal Zn concentration, which was only significantly increased by pretreatment with Zn, either alone or in combination with valproic acid.

CONCLUSIONS

The present study highlights the antiepileptic role that could be played by Zn, when given in appropriate doses.

Prion protein expression level alters regional copper, iron and zinc content in the mouse brain

The central role of the prion protein (PrP) in a family of fatal neurodegenerate diseases has garnered considerable research interest over the past two decades. Moreover, the role of PrP in neuronal development, as well as its apparent role in metal homeostasis, is increasingly of interest. The host-encoded form of the prion protein (PrP(C)) binds multiple copper atoms via its N-terminal domain and can influence brain copper and iron levels. The importance of PrP(C) to the regulation of brain metal homeostasis and metal distribution, however, is not fully understood. We therefore employed synchrotron-based X-ray fluorescence imaging to map the level and distributions of several key metals in the brains of mice that express different levels of PrP(C). Brain sections from wild-type, prion gene knockout (Prnp(-/-)) and PrP(C) over-expressing mice revealed striking variation in the levels of iron, copper, and even zinc in specific brain regions as a function of PrP(C) expression. Our results indicate that one important function of PrP(C) may be to regulate the amount and distribution of specific metals within the central nervous system. This raises the possibility that PrP(C) levels, or its activity, might regulate the progression of diseases in which altered metal homeostasis is thought to play a pathogenic role such as Alzheimer's, Parkinson's and Wilson's diseases and disorders such as hemochromatosis.

Ethanol reduces zincosome formation in cultured astrocytes

AIMS

Zinc is an ion that participates in basic cellular and tissular functions. Zinc deficiency is present in many physiological and health problems affecting most body organs, including the brain. Among the circumstances involved in zinc deficiency, ethanol consumption is probably one of the most frequent. A dietary zinc supplement has been proposed as possibly being an efficient method to palliate zinc deficiency. Astrocytes form part of the hematoencephalic barrier, and they are apparently implicated in the homeostasis of the neuronal medium. In this work, we analyze the effect of ethanol on extracellular zinc management by rat astrocytes in culture.

METHODS

Intracellular levels of 'free zinc ions', in controls and 30 mM ethanol-treated astrocytes, were visualized by using the zinc fluorochrome TSQ. Cytoplasmic fluorescence and zincosome formation were measured after adding extracellular 50 µM ZnSO(4) to cell monolayers. Zincosomes were also observed at the electron microscopy level.

RESULTS

Exposure to ethanol for 7 days lowered the basal zinc levels of astrocytes by ∼30%. This difference was consistently maintained after the zinc pulse. Zinc ions were confined to bright fluorescent particles, the 'zincosomes', which appeared to be formed by the endocytic pathway. Zincosomes were less abundant in alcohol-treated cells, indicating a deficit in endocytoses as the origin of low zinc intake in astrocytes after ethanol treatment.

CONCLUSIONS

Ethanol reduces both intracellular ionic zinc levels and extracellular zinc uptake, resulting in poorer zincosome formation. Given the endocytic nature of zincosomes, the effect of ethanol on membrane trafficking is apparently the origin of this deficit.

pH-dependent toxicity of high aspect ratio ZnO nanowires in macrophages due to intracellular dissolution

High-aspect ratio ZnO nanowires have become one of the most promising products in the nanosciences within the past few years with a multitude of applications at the interface of optics and electronics. The interaction of zinc with cells and organisms is complex, with both deficiency and excess causing severe effects. The emerging significance of zinc for many cellular processes makes it imperative to investigate the biological safety of ZnO nanowires in order to guarantee their safe economic exploitation. In this study, ZnO nanowires were found to be toxic to human monocyte macrophages (HMMs) at similar concentrations as ZnCl(2). Confocal microscopy on live cells confirmed a rise in intracellular Zn(2+) concentrations prior to cell death. In vitro, ZnO nanowires dissolved very rapidly in a simulated body fluid of lysosomal pH, whereas they were comparatively stable at extracellular pH. Bright-field transmission electron microscopy (TEM) showed a rapid macrophage uptake of ZnO nanowire aggregates by phagocytosis. Nanowire dissolution occurred within membrane-bound compartments, triggered by the acidic pH of the lysosomes. ZnO nanowire dissolution was confirmed by scanning electron microscopy/energy-dispersive X-ray spectrometry. Deposition of electron-dense material throughout the ZnO nanowire structures observed by TEM could indicate adsorption of cellular components onto the wires or localized zinc-induced protein precipitation. Our study demonstrates that ZnO nanowire toxicity in HMMs is due to pH-triggered, intracellular release of ionic Zn(2+) rather than the high-aspect nature of the wires. Cell death had features of necrosis as well as apoptosis, with mitochondria displaying severe structural changes. The implications of these findings for the application of ZnO nanowires are discussed.

Correlation between dietary zinc intakes and its serum levels with depression scales in young female students

It has been suggested that mood disorders and depressive status may be accompanied by lowered zinc status in the body, and adequate consumption of zinc increases a general perceived well-being. The main objective of this study was to assess the correlation between serum zinc concentrations and dietary zinc intakes with depression scores in university female students. In the first phase, Beck's depression questionnaire was applied in a random sampling of 308 selected 20-25-year-old female students (one third of total students in Ahvaz Jondi-Shapour University of Medical Sciences Golestan dormitories) to assess the major depressive disorder (MDD) scales. Then, in the second phase, 23 students who identified as having moderate and severe depression were selected as the case group, and 23 healthy age matched were chosen as the controls. Each of them completed a 12-item semiquantitative food frequency questionnaire containing the main food sources of zinc in the usual dietary patterns and also a 24-h food recall questionnaire to assure the daily zinc intakes. Daily zinc intakes were obtained by multiplying each portion size by its zinc content using food tables. A 5-ml blood sample was taken for further serum zinc status using flame atomic absorption spectrophotometry technique. Pearson's r was used to show the correlation between quantitative variables. Both daily zinc intake and serum zinc concentrations of MDD group were about two thirds of healthy index (p < 0.01). Depressed individuals used to eat lower servings of red meats and chicken as the main food sources of zinc in students' usual diets (p < 0.001). Consumption of other foods as the sources of zinc was not significantly different in two groups. A linear significant correlation between dietary zinc intakes and its serum levels was seen in samples (r = 0.62; p < 0.001) and MDD students (r = 0.55; p < 0.001). There was a linear inverse correlation between Beck questionnaire scores and serum zinc concentrations in all of the investigated students(r = -0.65; p < 0.001) and MDD girls (r = -0.71; p < 0.001). Beck questionnaire scores and diatary zinc intakes were also inversly correlated (r = -0.58; p < 0.001). However, no statistical correlation was seen between these two variables in MDD cases. In depressed female students, dietary zinc intake is correlated to its serum concentrations; however, the serum zinc levels are inversely correlated to depression scales. Consumption of the main dietary sources of zinc such as red meats and chicken should be encouraged in young depressed girls.

Dose-related gene expression changes in forebrain following acute, low-level chlorpyrifos exposure in neonatal rats

Chlorpyrifos (CPF) is a widely used organophosphorus insecticide (OP) and putative developmental neurotoxicant in humans. The acute toxicity of CPF is elicited by acetylcholinesterase (AChE) inhibition. We characterized dose-related (0.1, 0.5, 1 and 2mg/kg) gene expression profiles and changes in cell signaling pathways 24h following acute CPF exposure in 7-day-old rats. Microarray experiments indicated that approximately 9% of the 44,000 genes were differentially expressed following either one of the four CPF dosages studied (546, 505, 522, and 3,066 genes with 0.1, 0.5, 1.0 and 2.0mg/kg CPF). Genes were grouped according to dose-related expression patterns using K-means clustering while gene networks and canonical pathways were evaluated using Ingenuity Pathway Analysis®. Twenty clusters were identified and differential expression of selected genes was verified by RT-PCR. The four largest clusters (each containing from 276 to 905 genes) constituted over 50% of all differentially expressed genes and exhibited up-regulation following exposure to the highest dosage (2mg/kg CPF). The total number of gene networks affected by CPF also rose sharply with the highest dosage of CPF (18, 16, 18 and 50 with 0.1, 0.5, 1 and 2mg/kg CPF). Forebrain cholinesterase (ChE) activity was significantly reduced (26%) only in the highest dosage group. Based on magnitude of dose-related changes in differentially expressed genes, relative numbers of gene clusters and signaling networks affected, and forebrain ChE inhibition only at 2mg/kg CPF, we focused subsequent analyses on this treatment group. Six canonical pathways were identified that were significantly affected by 2mg/kg CPF (MAPK, oxidative stress, NFΚB, mitochondrial dysfunction, arylhydrocarbon receptor and adrenergic receptor signaling). Evaluation of different cellular functions of the differentially expressed genes suggested changes related to olfactory receptors, cell adhesion/migration, synapse/synaptic transmission and transcription/translation. Nine genes were differentially affected in all four CPF dosing groups. We conclude that the most robust, consistent changes in differential gene expression in neonatal forebrain across a range of acute CPF dosages occurred at an exposure level associated with the classical marker of OP toxicity, AChE inhibition. Disruption of multiple cellular pathways, in particular cell adhesion, may contribute to the developmental neurotoxicity potential of this pesticide.

Differential effects of zinc influx via AMPA/kainate receptor activation on subsequent induction of hippocampal CA1 LTP components

Zinc potentiates the induction of NMDA receptor-dependent hippocampal CA1 long-term potentiation (LTP) at low micromolar concentrations, while excessive zinc attenuates it. Homeostasis of synaptic zinc is critical for LTP induction. In the present study, LTP at hippocampal CA1 synapses was analyzed focused on the timing and level of zinc influx into hippocampal cells in hippocampal slices from young rats. Zinc (100 microM) perfusion increased intracellular zinc level and subsequently attenuated CA1 LTP induced by tetanic stimuli at 100 Hz for 1s, which was completely inhibited in the presence of 50 microM APV, an NMDA receptor antagonist. When 10 microM CNQX, an AMPA/kainate receptor antagonist, which reduced zinc influx into hippocampal cells, was perfused prior to the zinc perfusion, the attenuation of CA1 LTP by the zinc perfusion was restored. These results suggest that facilitated zinc influx into hippocampal cells via AMPA/kainate receptor activation is an event to attenuate subsequent induction of NMDA receptor-dependent CA1 LTP. On the other hand, the zinc pre-perfusion also attenuated CA1 LTP induced by 200-Hz tetanus, but not NMDA receptor-independent CA1 LTP induced by 200-Hz tetanus in the presence of APV, suggesting that the induction of NMDA receptor-independent CA1 LTP is less susceptibility to the facilitated zinc influx into hippocampal CA1 cells. Zinc influx via AMPA/kainate receptor activation may differentially act on subsequent induction of CA1 LTP components.

NR2B-NMDA receptor-mediated increases in intracellular Ca2+ concentration regulate the tyrosine phosphatase, STEP, and ERK MAP kinase signaling

NMDA receptors regulate both the activation and inactivation of the extracellular signal-regulated kinase (ERK) signaling cascade, a key pathway involved in neuronal plasticity and survival. This bi-directional regulation of ERK activity by NMDA receptors has been attributed to opposing actions of NR2A- versus NR2B-containing NMDA receptors, but how this is implemented is not understood. Here, we show that glutamate-mediated intracellular Ca(2+) increases occur in two phases, a rapid initial increase followed by a delayed larger increase. Both phases of the Ca(2+) increase were blocked by MK-801, a non-selective NMDA receptor inhibitor. On the other hand, selective inhibition of NR2B-NMDA receptors by Ifenprodil or Ro 25-6981 blocked the delayed larger phase but had only a small effect on the rapid initial increase. The rapid initial increase in Ca(2+), presumably because of NR2A-NMDAR activation, was sufficient to activate ERK, whereas the large delayed increases in Ca(2+) mediated by NR2B-NMDARs were necessary for dephosphorylation and subsequent activation of striatal-enriched phosphatase, a neuron-specific tyrosine phosphatase that in turn mediates the dephosphorylation and inactivation of ERK. We conclude that the magnitude of Ca(2+) increases mediated through NR2B-NMDA receptors plays a critical role in the regulation of the serine/threonine and tyrosine kinases and phosphatases that are involved in the regulation of ERK activity.

Chemical blocking of zinc ions in CNS increases neuronal damage following traumatic brain injury (TBI) in mice

Background

Traumatic brain injury (TBI) is one of the leading causes of disability and death among young people. Although much is already known about secondary brain damage the full range of brain tissue responses to TBI remains to be elucidated. A population of neurons located in cerebral areas associated with higher cognitive functions harbours a vesicular zinc pool co-localized with glutamate. This zinc enriched pool of synaptic vesicles has been hypothesized to take part in the injurious signalling cascade that follows pathological conditions such as seizures, ischemia and traumatic brain injury. Pathological release of excess zinc ions from pre-synaptic vesicles has been suggested to mediate cell damage/death to postsynaptic neurons.

Methodology/Principal Findings

In order to substantiate the influence of vesicular zinc ions on TBI, we designed a study in which damage and zinc movements were analysed in several different ways. Twenty-four hours after TBI ZnT3-KO mice (mice without vesicular zinc) were compared to littermate Wild Type (WT) mice (mice with vesicular zinc) with regard to histopathology. Furthermore, in order to evaluate a possible neuro-protective dimension of chemical blocking of vesicular zinc, we treated lesioned mice with either DEDTC or selenite. Our study revealed that chemical blocking of vesicular zinc ions, either by chelation with DEDTC or accumulation in zinc-selenium nanocrystals, worsened the effects on the aftermath of TBI in the WT mice by increasing the number of necrotic and apoptotic cells within the first 24 hours after TBI, when compared to those of chemically untreated WT mice.

Conclusion/Significance

ZnT3-KO mice revealed more damage after TBI compared to WT controls. Following treatment with DEDTC or selenium an increase in the number of both dead and apoptotic cells were seen in the controls within the first 24 hours after TBI while the degree of damage in the ZnT3-KO mice remained largely unchanged. Further analyses revealed that the damage development in the two mouse strains was almost identical after either zinc chelation or zinc complexion therapy.

Classical maple syrup urine disease and brain development: principles of management and formula design

Branched-chain ketoacid dehydrogenase deficiency results in complex and volatile metabolic derangements that threaten brain development. Treatment for classical maple syrup urine disease (MSUD) should address this underlying physiology while also protecting children from nutrient deficiencies. Based on a 20-year experience managing 79 patients, we designed a study formula to (1) optimize transport of seven amino acids (Tyr, Trp, His, Met, Thr, Gln, Phe) that compete with branched-chain amino acids (BCAAs) for entry into the brain via a common transporter (LAT1), (2) compensate for episodic depletions of glutamine, glutamate, and alanine caused by reverse transamination, and (3) correct deficiencies of omega-3 essential fatty acids, zinc, and selenium widespread among MSUD patients. The formula was enriched with LAT1 amino acid substrates, glutamine, alanine, zinc, selenium, and alpha-linolenic acid (18:3n-3). Fifteen Old Order Mennonite children were started on study formula between birth and 34 months of age and seen at least monthly in the office. Amino acid levels were checked once weekly and more often during illnesses. All children grew and developed normally over a period of 14-33 months. Energy demand, leucine tolerance, and protein accretion were tightly linked during periods of normal growth. Rapid shifts to net protein degradation occurred during illnesses. At baseline, most LAT1 substrates varied inversely with plasma leucine, and their calculated rates of brain uptake were 20-68% below normal. Treatment with study formula increased plasma concentrations of LAT1 substrates and normalized their calculated uptakes into the nervous system. Red cell membrane omega-3 polyunsaturated fatty acids and serum zinc and selenium levels increased on study formula. However, selenium and docosahexaenoic acid (22:6n-3) levels remained below normal. During the study period, hospitalizations decreased from 0.35 to 0.14 per patient per year. There were 28 hospitalizations managed with MSUD hyperalimentation solution; 86% were precipitated by common infections, especially vomiting and gastroenteritis. The large majority of catabolic illnesses were managed successfully at home using 'sick-day' formula and frequent amino acid monitoring. We conclude that the study formula is safe and effective for the treatment of classical MSUD. In principle, dietary enrichment protects the brain against deficiency of amino acids used for protein accretion, neurotransmitter synthesis, and methyl group transfer. Although the pathophysiology of MSUD can be addressed through rational formula design, this does not replace the need for vigilant clinical monitoring, frequent measurement of the complete amino acid profile, and ongoing dietary adjustments that match nutritional intake to the metabolic demands of growth and illness.

The essential toxin: impact of zinc on human health

Compared to several other metal ions with similar chemical properties, zinc is relatively harmless. Only exposure to high doses has toxic effects, making acute zinc intoxication a rare event. In addition to acute intoxication, long-term, high-dose zinc supplementation interferes with the uptake of copper. Hence, many of its toxic effects are in fact due to copper deficiency. While systemic homeostasis and efficient regulatory mechanisms on the cellular level generally prevent the uptake of cytotoxic doses of exogenous zinc, endogenous zinc plays a significant role in cytotoxic events in single cells. Here, zinc influences apoptosis by acting on several molecular regulators of programmed cell death, including caspases and proteins from the Bcl and Bax families. One organ where zinc is prominently involved in cell death is the brain, and cytotoxicity in consequence of ischemia or trauma involves the accumulation of free zinc. Rather than being a toxic metal ion, zinc is an essential trace element. Whereas intoxication by excessive exposure is rare, zinc deficiency is widespread and has a detrimental impact on growth, neuronal development, and immunity, and in severe cases its consequences are lethal. Zinc deficiency caused by malnutrition and foods with low bioavailability, aging, certain diseases, or deregulated homeostasis is a far more common risk to human health than intoxication.

Zinc deficiency and neurodevelopment: the case of neurons

Zinc is essential for normal brain development. Gestational severe zinc deficiency can lead to overt fetal brain malformations. Although not teratogenic, suboptimal zinc nutrition during gestation can have long-term effects on the offspring's nervous system. This article will review current knowledge on the role of zinc in modulating neurogenesis and neuronal apoptosis as well as the proposed underlying mechanisms. A decrease in neuronal zinc causes cell cycle arrest, which in part involves a deregulation of select signals (ERK1/2, p53, and NF-kappaB). Zinc deficiency also induces apoptotic neuronal death through the intrinsic (mitochondrial) pathway, which can be triggered by the activation of the zinc-regulated enzyme caspase-3, and as a consequence of abnormal regulation of prosurvival signals (ERK1/2 and NF-kappaB). Alterations in the finely tuned processes of neurogenesis, neuronal migration, differentiation, and apoptosis, which involve the developmental shaping of the nervous system, could have a long-term impact on brain health. Zinc deficiency during gestation, even at the marginal levels observed in human populations, could increase the risk for behavioral/neurological disorders in infancy, adolescence, and adulthood.