Protective effect of zinc against ischemic neuronal injury in a middle cerebral artery occlusion model

A multimodal electrochemical approach to measure the effect of zinc on vesicular content and exocytosis in a single cell model of ischemia

Zinc ion is essential for normal brain function that modulates synaptic activity and neuronal plasticity and it is associated with memory formation. Zinc is considered to be a contributing factor to the pathogenesis of ischemia, but the association between zinc and ischemia on vesicular exocytosis is unclear. In this study, we used a combination of chemical analysis methods and a cell model of ischemia/reperfusion to investigate exocytotic release and vesicular content, as well as the effect of zinc alteration on vesicular exocytosis. Oxygen–glucose deprivation and reperfusion (OGDR) was used as an in vitro model of ischemia in a model cell line. Exocytotic release and vesicular storage of catecholamine content were increased following OGDR, resulting in a higher fraction of release during exocytosis. However, zinc eliminated these increases following OGDR and the fraction of release remained unchanged. Understanding the consequences of zinc accumulation on vesicular exocytosis at the early stage of OGDR should aid in the development of therapeutic strategies to reduce ischemic brain injury. As the fraction released has been suggested to be related to presynaptic plasticity, insights are gained towards deciphering ischemia related memory impairment.

Zinc Switch in Pig Heart Lipoamide Dehydrogenase: Steady-State and Transient Kinetic Studies of the Diaphorase Reaction

Elevation of intracellular Zn2+ following ischemia contributes to cell death by affecting mitochondrial function. Zn2+ is a differential regulator of the mitochondrial enzyme lipoamide dehydrogenase (LADH) at physiological concentrations (K_a = 0.1 µM free zinc), inhibiting lipoamide and accelerating NADH dehydrogenase activities. These differential effects have been attributed to coordination of Zn2+ by LADH active-site cysteines. A detailed kinetic mechanism has now been developed for the diaphorase (NADH-dehydrogenase) reaction catalyzed by pig heart LADH using 2,6-dichlorophenol-indophenol (DCPIP) as a model quinone electron acceptor. Anaerobic stopped-flow experiments show that two-electron reduced LADH is 15-25-fold less active towards DCPIP reduction than four-electron reduced enzyme, or Zn2+-modified reduced LADH (the corresponding values of the rate constants are (6.5 ± 1.5) × 10³ M^-1·s^-1, (9 ± 2) × 10⁴ M^-1·s^-1, and (1.6 ± 0.5) × 10⁵ M^-1·s^-1, respectively). Steady-state kinetic studies with different diaphorase substrates show that Zn2+ accelerates reaction rates exclusively for two-electron acceptors (duroquinone, DCPIP), but not for one-electron acceptors (benzoquinone, ubiquinone, ferricyanide). This implies that the two-electron reduced form of LADH, prevalent at low NADH levels, is a poor two-electron donor compared to the four-electron reduced or Zn2+-modified reduced LADH forms. These data suggest that zinc binding to the active-site thiols switches the enzyme from one- to two-electron donor mode. This zinc-activated switch has the potential to alter the ratio of superoxide and H2O2 generated by the LADH oxidase activity.

Increased Zinc Serum Level: New Clues in Babol Stroke Patients, Northern Iran

Background

Stroke is the second leading cause of death worldwide. The role of zinc as a new predictor of stroke was considered.

Methods

This prospective study was conducted in Ayatollah Rouhani Hospital within a year on 100 stroke and 100 control patients.

Findings

The difference in zinc serum level in two groups was significant (deficiency: 3 (3%) in patients versus 20 (20%) in control group, normal: 25 (25%) versus 54 (54%), and increased level: 72 (72%) versus 26 (26%); p < 0.001). Difference in zinc serum levels was statistically significant with ischemic heart disease (deficiency: 0 cases (0%), normal: 8 cases (24%), increased level: 24 cases (75%), p = 0.003). Increases in zinc serum level were significantly correlated with the frequency of hemorrhagic and ischemic patients (deficiency: 3 (3.3%) hemorrhagic versus 0 (0%) ischemic; normal: 19 (21%) versus 6 (60%), increased level: 68 (75.6%) versus 4 (40%); p = 0.025). Regression logistics showed that ischemic heart disease (p < 0.001; OR = 28.29, %95 CI: 5.53; 144.87), hyperlipidemia (p < 0.001; OR = 0.26, %95 CI: 0.12; 0.56), and zinc serum level (p < 0.001, OR = 15.53, %95 CI: 4.03; 59.83) each had a significant role.

Conclusions

Babol stroke patients are prone to increased zinc serum level as a new parameter. Ischemic heart disease, increased levels of zinc, and hyperlipidemia were found to be probable predictor factors for stroke in Babol.

Prophylactic Subacute Administration of Zinc Increases CCL2, CCR2, FGF2, and IGF-1 Expression and Prevents the Long-Term Memory Loss in a Rat Model of Cerebral Hypoxia-Ischemia

Prophylactic subacute administration of zinc decreases lipoperoxidation and cell death following a transient cerebral hypoxia-ischemia, thus suggesting neuroprotective and preconditioning effects. Chemokines and growth factors are also involved in the neuroprotective effect in hypoxia-ischemia. We explored whether zinc prevents the cerebral cortex-hippocampus injury through regulation of CCL2, CCR2, FGF2, and IGF-1 expression following a 10 min of common carotid artery occlusion (CCAO). Male rats were grouped as follows: (1) Zn96h, rats injected with ZnCl2 (one dose every 24 h during four days); (2) Zn96h + CCAO, rats treated with ZnCl2 before CCAO; (3) CCAO, rats with CCAO only; (4) Sham group, rats with mock CCAO; and (5) untreated rats. The cerebral cortex-hippocampus was dissected at different times before and after CCAO. CCL2/CCR2, FGF2, and IGF-1 expression was assessed by RT-PCR and ELISA. Learning in Morris Water Maze was achieved by daily training during 5 days. Long-term memory was evaluated on day 7 after learning. Subacute administration of zinc increased expression of CCL2, CCR2, FGF2, and IGF-1 in the early and late phases of postreperfusion and prevented the CCAO-induced memory loss in the rat. These results might be explained by the induction of neural plasticity because of the expression of CCL2 and growth factors.

Chelating intracellularly accumulated zinc decreased ischemic brain injury through reducing neuronal apoptotic death

BACKGROUND AND PURPOSE

Zinc has been reported to possess both neurotoxic and neuroprotective capabilities. The effects of elevated intracellular zinc accumulation following transient focal cerebral ischemia remain to be fully elucidated. Here, we investigated whether removing zinc with the membrane-permeable zinc chelator, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), would decrease the intracellular levels of zinc in the ischemic tissue, leading to reduced brain damage and improved neurological outcomes.

METHODS

Rats were pretreated with TPEN or vehicle before or after a 90-minute middle cerebral artery occlusion. Cerebral infarct volume, neurological functions, neuronal apoptosis, poly(ADP-ribose) polymerase activity, and cytosolic labile zinc were assessed after ischemia and reperfusion.

RESULTS

Cerebral ischemia caused a dramatic cytosolic labile zinc accumulation in the ischemic tissue, which was decreased markedly by TPEN (15 mg/kg) pretreatment. Chelating zinc lead to reduced infarct volume compared with vehicle-treated middle cerebral artery occlusion rats, accompanied by much improved neurological assessment and motor function, which were sustained for 14 days after reperfusion. We also determined that reducing zinc accumulation rescued neurons from ischemia-induced apoptotic death by reducing poly(ADP-ribose) polymerase-1 activation.

CONCLUSIONS

Ischemia-induced high accumulation of intracellular zinc significantly contributed to ischemic brain damage through promotion of neuronal apoptotic death. Removing zinc may be an effective and novel approach to reduce ischemic brain injury.

Subacute zinc administration and L-NAME caused an increase of NO, zinc, lipoperoxidation, and caspase-3 during a cerebral hypoxia-ischemia process in the rat

Zinc or L-NAME administration has been shown to be protector agents, decreasing oxidative stress and cell death. However, the treatment with zinc and L-NAME by intraperitoneal injection has not been studied. The aim of our work was to study the effect of zinc and L-NAME administration on nitrosative stress and cell death. Male Wistar rats were treated with ZnCl₂ (2.5 mg/kg each 24 h, for 4 days) and N-ω-nitro-L-arginine-methyl ester (L-NAME, 10 mg/kg) on the day 5 (1 hour before a common carotid-artery occlusion (CCAO)). The temporoparietal cortex and hippocampus were dissected, and zinc, nitrites, and lipoperoxidation were assayed at different times. Cell death was assayed by histopathology using hematoxylin-eosin staining and caspase-3 active by immunostaining. The subacute administration of zinc before CCAO decreases the levels of zinc, nitrites, lipoperoxidation, and cell death in the late phase of the ischemia. L-NAME administration in the rats treated with zinc showed an increase of zinc levels in the early phase and increase of zinc, nitrites, and lipoperoxidation levels, cell death by necrosis, and the apoptosis in the late phase. These results suggest that the use of these two therapeutic strategies increased the injury caused by the CCAO, unlike the alone administration of zinc.

Intracellular Zn2+ accumulation enhances suppression of synaptic activity following spreading depolarization

Spreading depolarization (SD) is a feed-forward wave that propagates slowly throughout brain tissue and recovery from SD involves substantial metabolic demand. Presynaptic Zn(2+) release and intracellular accumulation occurs with SD, and elevated intracellular Zn(2+) ([Zn(2+) ]i ) can impair cellular metabolism through multiple pathways. We tested here whether increased [Zn(2+) ]i could exacerbate the metabolic challenge of SD, induced by KCl, and delay recovery in acute murine hippocampal slices. [Zn(2+) ]i loading prior to SD, by transient ZnCl2 application with the Zn(2+) ionophore pyrithione (Zn/Pyr), delayed recovery of field excitatory post-synaptic potentials (fEPSPs) in a concentration-dependent manner, prolonged DC shifts, and significantly increased extracellular adenosine accumulation. These effects could be due to metabolic inhibition, occurring downstream of pyruvate utilization. Prolonged [Zn(2+) ]i accumulation prior to SD was required for effects on fEPSP recovery and consistent with this, endogenous synaptic Zn(2+) release during SD propagation did not delay recovery from SD. The effects of exogenous [Zn(2+) ]i loading were also lost in slices preconditioned with repetitive SDs, implying a rapid adaptation. Together, these results suggest that [Zn(2+) ]i loading prior to SD can provide significant additional challenge to brain tissue, and could contribute to deleterious effects of [Zn(2+) ]i accumulation in a range of brain injury models.

Regulation of zinc transporter 1 expression in dorsal horn of spinal cord after acute spinal cord injury of rats by dietary zinc

Zinc concentrations in the dorsal horn of spinal cord are important for wound healing, neurological function, and reproduction. However, the response of the spinal cord to alterations in dietary zinc is unknown in rats after spinal cord injury (SCI). The current study explored cellular zinc levels and zinc transporter 1 (ZnT1) expression in the dorsal horn of spinal cord with different dietary zinc after SCI. A hundred and forty-four male Wistar rats were randomly divided into four groups: sham-operated group (30 mg Zn/kg), zinc-high dietary SCI model group (ZH, 180 mg Zn/kg), zinc-adequate dietary SCI model group (30 mg Zn/kg), and marginal zinc-deficient dietary SCI model group (MZD, 5 mg Zn/kg). To test the hypothesis that dietary zinc may regulate role of ZnT1 expression in dorsal horn after acute SCI, we traced ZnT1 proteins and zinc ions with immunohistochemistry, western blot, and autometallography. Zinc and ZnT1 levels of the dorsal horn in ZH significantly increased after surgery (P < 0.05), reached peak level (P < 0.05) on the seventh day, and subsequently levels of their expression began to decrease. But zinc levels and ZnT1 expression of spinal cord in MZD dietary groups decreased (P < 0.05) in SCI. There was a positive correlation between ZnT1 protein and zinc content in spinal cord (R = 0.49880, P = 0.0492). We found that both zinc and ZnT1 expressions in spinal cord are regulated by dietary zinc. These results indicate that dietary zinc may regulate the expression of ZnT1 in the dorsal horn of spinal cord after SCI. ZnT1 may, at the same time, play a significant role in the maintenance of zinc homeostasis in SCI.

Synaptic release and extracellular actions of Zn2+ limit propagation of spreading depression and related events in vitro and in vivo

Cortical spreading depression (CSD) is a consequence of a slowly propagating wave of neuronal and glial depolarization (spreading depolarization; SD). Massive release of glutamate contributes to SD propagation, and it was recently shown that Zn(2+) is also released from synaptic vesicles during SD. The present study examined consequences of extracellular Zn(2+) accumulation on the propagation of SD. SD mechanisms were studied first in murine brain slices, using focal KCl applications as stimuli and making electrical and optical recordings in hippocampal area CA1. Elevating extracellular Zn(2+) concentrations with exogenous ZnCl(2) reduced SD propagation rates. Selective chelation of endogenous Zn(2+) (using TPEN or CaEDTA) increased SD propagation rates, and these effects appeared due to chelation of Zn(2+) derived from synaptic vesicles. Thus, in tissues where synaptic Zn(2+) release was absent [knockout (KO) of vesicular Zn(2+) transporter ZnT-3], SD propagation rates were increased, and no additional increase was observed following chelation of endogenous Zn(2+) in these tissues. The role of synaptic Zn(2+) was then examined on CSD in vivo. ZnT-3 KO animals had higher susceptibility to CSD than wild-type controls as evidenced by significantly higher propagation rates and frequencies. Studies of candidate mechanisms excluded changes in neuronal excitability, presynaptic release, and GABA receptors but left open a possible contribution of N-methyl-d-aspartate (NMDA) receptor inhibition. These results suggest the extracellular accumulation of synaptically released Zn(2+) can serve as an intrinsic inhibitor to limit SD events. The inhibitory action of extracellular Zn(2+) on SD may counteract to some extent the neurotoxic effects of intracellular Zn(2+) accumulation in acute brain injury models.

Zinc: new clues to diverse roles in brain ischemia

Cerebral ischemia is a leading cause of morbidity and mortality, reflecting the extraordinary sensitivity of the brain to a brief loss of blood flow. A significant goal has been to identify pathways of neuronal injury that are selectively activated after stroke and may be amenable to drug therapy. An important advance was made nearly 25 years ago when Ca(2+) overload was implicated as a critical link between glutamate excitotoxicity and ischemic neurodegeneration. However, early hope for effective therapies faded as glutamate-targeted trials repeatedly failed to demonstrate efficacy in humans. In a review in 2000 in this journal, we described new evidence linking a related cation, zinc (Zn(2+)), to neuronal injury, emphasizing sources and mechanisms of Zn(2+) toxicity. The current review highlights progress over the last decade, emphasizing mechanisms through which Zn(2+) ions (from multiple sources) participate together with Ca(2+) in different stages of cascades of ischemic injury.

Spreading depression and related events are significant sources of neuronal Zn2+ release and accumulation

Spreading depression (SD) involves coordinated depolarizations of neurons and glia that propagate through the brain tissue. Repetitive SD-like events are common following human ischemic strokes, and are believed to contribute to the enlargement of infarct volume. Accumulation of Zn(2+) is also implicated in ischemic neuronal injury. Synaptic glutamate release contributes to SD propagation, and because Zn(2+) is costored with glutamate in some synaptic vesicles, we examined whether Zn(2+) is released by SD and may therefore provide a significant source of Zn(2+) in the postischemic period. Spreading depression-like events were generated in acutely prepared murine hippocampal slices by deprivation of oxygen and glucose (OGD), and Zn(2+) release was detected extracellularly by a Zn(2+)-selective indicator FluoZin-3. Deprivation of oxygen and glucose-SD produced large FluoZin-3 increases that propagated with the event, and signals were abolished in tissues from ZnT3 knockout animals lacking synaptic Zn(2+). Synaptic Zn(2+) release was also maintained with repetitive SDs generated by microinjections of KCl under normoxic conditions. Intracellular Zn(2+) accumulation in CA1 neurons, assessed using microinjection of FluoZin-3, showed significant increases following SD that was attributed to synaptic Zn(2+) release. These results suggest that Zn(2+) is released during SDs and could provide a significant source of Zn(2+) that contributes to neurodegeneration in the postischemic period.

Clinical significance of serum zinc levels in cerebral ischemia

Background. Zinc mediates several vital physiological, enzymatic and cellular functions. The association between serum zinc and stroke outcome has not been previously evaluated. Methods. This single center retrospective study was conducted on consecutive stroke (n = 158) and TIA (n = 74) patients. We sought to determine whether serum zinc concentrations in patients with acute ischemic strokes were associated with stroke severity and poor functional status at discharge, respectively. Results. Overall, out of the 224 patients analyzed (mean age 67 years), 35.7% patients had low zinc levels (65 mcg/dL). Patients with stroke (n = 152) were more likely to have low zinc levels (OR = 2.62, CI 1.92–3.57, P < .003) compared to patients with TIA (n = 72). For patients with stroke (n = 152), multivariate analysis showed that low serum zinc levels (OR 2.82, CI 1.35–5.91, P = .035) and strokes with admission severe strokes (NIHSS > 8) (OR 2.68, CI 1.1–6.5, P = .03) were independently associated with poor functional status (MRS > 3) at discharge from the hospital. Conclusion. Low serum zinc concentrations are associated with more severe strokes on admission and poor functional status at discharge.

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.

Effects of zinc supplementation on the survival of patients who received concomitant chemotherapy and radiotherapy for advanced nasopharyngeal carcinoma: follow-up of a double-blind randomized study with subgroup analysis

OBJECTIVES/HYPOTHESIS

Dietary zinc has been reported to have positive effects on treating carcinoma. This study examined the effects of zinc supplementation on the improved survival of patients with advanced nasopharyngeal carcinoma receiving concomitant chemotherapy and radiotherapy (CCRT).

STUDY DESIGN

A double-blind, placebo-controlled clinical study with subgroup analysis.

METHODS

Thirty-four patients with stages III and IV nasopharyngeal carcinoma were selected from a double-blind, placebo-controlled clinical study. All the patients were randomized to receive a standard dose (75 mg/day for 2 months) of zinc supplements or placebo, in conjunction with CCRT. The overall local recurrence, metastasis, and disease-free survivals were defined as the period between the time of first treatment to the time of death, local recurrence, or distant metastases occurred.

RESULTS

Patients in the experimental group exhibited a higher 5-year overall local-free and disease-free survival rate than the patients in the placebo group (P = .044, P = .007, and P = .033, respectively). However, no significant differences were found between both patient groups for the 5-year metastases-free survival rate (P = .149).

CONCLUSIONS

Zinc supplementation prescribed in conjunction with CCRT effects attenuating local tumor recurrence and improves the overall survival of patients with advanced nasopharyngeal carcinoma. The failure to reduce distant metastasis survival might have been related in part to the more advanced disease stages in our patients.

Essential role for zinc-triggered p75NTR activation in preconditioning neuroprotection

Ischemic preconditioning (PC) of the brain is a phenomenon by which mild ischemic insults render neurons resistant to subsequent strong insults. Key steps in ischemic PC of the brain include caspase-3 activation and poly(ADP-ribose) polymerase-1 (PARP-1) cleavage, but upstream events have not been clearly elucidated. We have tested whether endogenous zinc is required for ischemic PC of the brain in rats. Mild, transient zinc accumulation was observed in certain neurons after ischemic PC. Moreover, intraventricular administration of CaEDTA during ischemic PC abrogated both zinc accumulation and the protective effect against subsequent full ischemia. To elucidate the mechanism of the zinc-triggered PC (Zn PC) effect, cortical cultures were exposed to sublethal levels of zinc, and 18 h later to lethal levels of zinc or NMDA. Zn PC exhibited the characteristic features of ischemic PC, including caspase-3 activation, PARP-1 cleavage, and HSP70 induction, all of which are crucial for subsequent neuroprotection against NMDA or zinc toxicity. HSP70 induction was necessary for protection, as it halted caspase-3 activation before apoptosis. Interestingly, in both Zn PC in vitro and ischemic PC in vivo, p75(NTR) was necessary for neuroprotection. These results suggest that caspase-3 activation during ischemic PC, a necessary event for subsequent neuroprotection, may result from mild zinc accumulation and the consequent p75(NTR) activation in neurons.

Propofol exerts greater neuroprotection with disodium edetate than without it

The main objective of this study, on mice, was to compare the neuroprotective effects of propofol with those of propofol plus disodium edetate (propofol EDTA). We also administered propofol EDTA (0.005% (w/v) EDTA) to mice intravenously, and measured the changes in zinc concentrations occurring after permanent middle cerebral artery occlusion. In the in vivo study, propofol EDTA displayed stronger neuroprotective effects than propofol alone. Furthermore, we examined the neuroprotective effects of EDTA administered alone, and found that EDTA Na significantly reduced the infarct volume. The number of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling-positive cells in the ischemic penumbra was reduced more by propofol EDTA than by propofol alone. We performed in the in vitro study in five groups (aerobic, vehicle (control), propofol, EDTA, and propofol plus EDTA). Propofol and EDTA each protected PC12 cells against oxygen-glucose deprivation-induced cell damage, and the effect of propofol was increased by adding EDTA. Because the chelating action of EDTA was a potential causal mechanism, we examined the effect of propofol EDTA on intracerebral zinc homeostasis. When propofol EDTA was given intravenously 10 mins before cerebral ischemia, the zinc concentration decreased significantly in the cortical area, but not in the subcortex. In conclusion, (a) propofol provides neuroprotection against both in vivo and in vitro ischemic damage, and its effects are enhanced when EDTA is added; and (b) EDTA itself protects against ischemic neuronal damage, possibly, owing to its zinc-chelating action.

5-Iodo-A-85380, a specific ligand for alpha 4 beta 2 nicotinic acetylcholine receptors, prevents glutamate neurotoxicity in rat cortical cultured neurons

5-iodo-3-(2(S)-azetidinylmethoxy)pyridine (5-iodo-A-85380, 5IA) has very high affinity and selectivity to nicotinic acetylcholine receptor (nAChR) alpha 4 beta 2 subtype, and a relative safe profile. To assess whether 5IA has neuroprotective properties, we examined the effect of 5IA on glutamate (Glu)-induced neurotoxicity using primary cultures of rat cortical neurons. A 10-min exposure of cultures to Glu followed by 2-h incubation with drug-free medium caused a marked loss of viability, as determined by trypan blue exclusion method. Glu-induced neurotoxicity was prevented by 5IA both in a time- and concentration-dependent manner. 5IA-induced neuroprotection required pretreatment of 5IA prior to Glu exposure with an optimal concentration of 10 nM and an optimal pretreatment time of 2 h. Treatment after Glu exposure could not rescue the cultured cells. The neuroprotective effect of 5IA was antagonized by mecamylamine, a nAChR antagonist, but not by scopolamine, a muscarinic acetylcholine receptor antagonist. Dihydro-beta-erythroidine, an alpha 4 beta 2 nAChR antagonist, completely inhibited 5IA-induced neuroprotection, whereas alpha-bungarotoxin, an alpha 7 nAChR antagonist, had no effect. Furthermore, 5IA did not show neuroprotective effects in the absence of extracellular Ca2+. These results suggest that the neuroprotective effects of 5IA are produced by activation of alpha 4 beta 2 nAChRs followed by the influx of extracellular Ca2+. In conclusion, 5IA is possibly not only useful for the treatment and prevention of glutamate neurotoxicity, but also as an available tool for elucidating the mechanism of neuroprotection associated with alpha 4 beta 2 nAChRs.

The role of zinc in cerebral ischemia

Ischemic stroke is one of the most pervasive life-threatening neurological conditions for which there currently exists limited therapeutic intervention beyond prevention. As calcium-focused neuroprotective strategies have met with limited clinical success, it is imperative that alternative therapeutic targets be considered in the attempt to antagonize ischemic-mediated injury. As such, zinc, which is able to function both as a signaling mediator and neurotoxin, has been implicated in cerebral ischemia. While zinc was first purported to have a role in cerebral ischemia nearly twenty years ago, our understanding of how zinc mediates ischemic injury is still in its relative infancy. Within this review, we examine some of the studies by which zinc has exerted either neuroprotective or neurotoxic effects during global and focal cerebral ischemia.

The role of zinc in cerebral ischemia

Ischemic stroke is one of the most pervasive life-threatening neurological conditions for which there currently exists limited therapeutic intervention beyond prevention. As calcium-focused neuroprotective strategies have met with limited clinical success, it is imperative that alternative therapeutic targets be considered in the attempt to antagonize ischemic-mediated injury. As such, zinc, which is able to function both as a signaling mediator and neurotoxin, has been implicated in cerebral ischemia. While zinc was first purported to have a role in cerebral ischemia nearly twenty years ago, our understanding of how zinc mediates ischemic injury is still in its relative infancy. Within this review, we examine some of the studies by which zinc has exerted either neuroprotective or neurotoxic effects during global and focal cerebral ischemia.

The organotellurium compound ammonium trichloro(dioxoethylene-0,0') tellurate enhances neuronal survival and improves functional outcome in an ischemic stroke model in mice

Ammonium trichloro(dioxoethylene-0,0') tellurate (AS101) is a non-toxic organotellurium compound with pleiotropic activities. It was recently shown to induce production of the neurotrophic factor glial cell line-derived neurotrophic factor and to rescue neuronal-like PC-12 cells from neurotrophic factor deprivation-induced apoptosis. In this study, we show that AS101 improves functional outcome and reduces brain damage in a mouse model of focal ischemic stroke. Both pre-stroke and post-stroke intraperitoneal treatments with AS101 reduced infarct size and edema and improved the neurological function of the animals. AS101 treatments reduced both apoptotic and inflammatory caspase activities, and also inhibited protein tyrosine nitration suggesting that AS101 suppresses oxidative stress. Studies of cultured neurons showed that AS101 confers protection against apoptosis induced by either glucose deprivation or the lipid peroxidation product 4-hydroxynonenal. Moreover, AS101 treatment reduced glutamate-induced intracellular calcium elevation, a major contributor to neuronal death in stroke. As AS101 has an excellent safety profile in humans, our pre-clinical data suggest a potential therapeutic benefit of AS101 in patients suffering from stroke and other neurodegenerative conditions.