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We examined the distribution of zinc in the periphery (erythrocytes and serum) in a large, well-characterised cohort, the Australian Imaging, Biomarkers and Lifestyle (AIBL) study, in order to determine if there is systemic perturbation in zinc homeostasis in Alzheimer's disease (AD). We observed an age dependent decrease in serum zinc of approximately 0.4% per year. When correcting for the age dependent decline in serum zinc no significant difference between healthy controls (HC), mildly cognitively impaired (MCI) or AD subjects was observed.

Metals often determine the chemical reactivity of the proteins to which they are bound. Each cell in the body tightly maintains a unique metalloproteomic profile, mostly dependent on function. This paper describes an analytical online flow injection quantitative size exclusion chromatography-inductively coupled plasma-mass spectrometry (SEC-ICP-MS) method, which was applied to profiling the metal-binding proteins found in primary cultures of neurons and astrocytes. This method can be conducted using similar amounts of sample to those used for Western blotting (20-150 μg protein), and has a turnaround time of <15 minutes. Metalloprotein standards for Fe (as ferritin), Cu and Zn (as superoxide dismutase-1) were used to construct multi-point calibration curves for online quantification of metalloproteins by SEC-ICP-MS. Homogenates of primary neuron and astrocyte cultures were analysed by SEC-ICP-MS. Online quantification by external calibration with metalloprotein standards determined the mass of metal eluting from the column relative to time (as pg s(-1)). Total on-column Fe, Cu and Zn detection limits ranged from 0.825 ± 0.005 ng to 13.6 ± 0.7 pg. Neurons and astrocytes exhibited distinct metalloprotein profiles, featuring both ubiquitous and unique metalloprotein species. Separation and detection by SEC-ICP-MS allows appraisal of these metalloproteins in their native state, and online quantification was achieved using this relatively simple external calibration process.

Three dimensional maps of iron (Fe), zinc (Zn), copper (Cu), manganese (Mn) and phosphorous (P) in a 6-hydroxydopamine (6-OHDA) lesioned mouse brain were constructed employing a novel quantitative laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) imaging method known as elemental bio-imaging. The 3D maps were produced by ablating serial consecutive sections taken from the same animal. Each section was quantified against tissue standards resulting in a three dimensional map that represents the variation of trace element concentrations of the mouse brain in the area surrounding the substantia nigra (SN). Damage caused by the needle or the toxin did not alter the distribution of Zn, and Cu but significantly altered Fe in and around the SN and both Mn and Fe around the needle track. A 20% increase in nigral Fe concentration was observed within the lesioned hemisphere. This technique clearly shows the natural heterogeneous distributions of these elements throughout the brain and the perturbations that occur following trauma or intoxication. The method may applied to three-dimensional modelling of trace elements in a wide range of tissue samples.

Abnormal interaction of beta-amyloid 42 (Abeta42) with copper, zinc and iron induce peptide aggregation and oxidation in Alzheimer's disease (AD). However, in health, Abeta degradation is mediated by extracellular metalloproteinases, neprilysin, insulin degrading enzyme (IDE) and matrix metalloproteinases. We investigated the relationship between levels of Abeta and biological metals in CSF. We assayed CSF copper, zinc, other metals and Abeta42 in ventricular autopsy samples of Japanese American men (N=131) from the population-based Honolulu Asia Aging Study. There was a significant inverse correlation of CSF Abeta42 with copper, zinc, iron, manganese and chromium. The association was particularly strong in the subgroup with high levels of both zinc and copper. Selenium and aluminum levels were not associated to CSF Abeta42. In vitro, the degradation of synthetic Abeta substrate added to CSF was markedly accelerated by low levels (2microM) of exogenous zinc and copper. While excessive interaction with copper and zinc may induce neocortical Abeta precipitation in AD, soluble Abeta degradation is normally promoted by physiological copper and zinc concentrations.

Copper and zinc play important roles in Alzheimer disease pathology with recent reports describing potential therapeutics based on modulation of metal bioavailability. We examined the ability of a range of metal bis(thiosemicarbazonato) complexes (MII(btsc), where M=CuII or ZnII) to increase intracellular metal levels in Chinese hamster ovary cells overexpressing amyloid precursor protein (APP-CHO) and the subsequent effect on extracellular levels of amyloid-beta peptide (Abeta). The CuII(btsc) complexes were engineered to be either stable to both a change in oxidation state and dissociation of metal or susceptible to intracellular reduction and dissociation of metal. Treatment of APP-CHO cells with stable complexes resulted in elevated levels of intracellular copper with no effect on the detected levels of Abeta. Treatment with complexes susceptible to intracellular reduction increased intracellular copper levels but also resulted in a dose-dependent reduction in the levels of monomeric Abeta. Treatment with less stable ZnII(btsc) complexes increased intracellular zinc levels with a subsequent dose-dependent depletion of monomeric Abeta levels. The increased levels of intracellular bioavailable copper and zinc initiated a signaling cascade involving activation of phosphoinositol 3-kinase and c-Jun N-terminal kinase. Inhibition of these enzymes prevented Abeta depletion induced by the MII(btsc) complexes. Inhibition of metalloproteases also partially restored Abeta levels, implicating metal-driven metalloprotease activation in the extracellular monomeric Abeta depletion. However, a role for alternative metal-induced Abeta metabolism has not been ruled out. These studies demonstrate that MII(btsc) complexes have potential for Alzheimer disease therapy.

Biometals have an important role in AD (Alzheimer's disease) and metal ligands have been investigated as potential therapeutic agents for treatment of AD. In recent studies the 8HQ (8-hydroxyquinoline) derivative CQ (clioquinol) has shown promising results in animal models and small clinical trials; however, the actual mode of action in vivo is still being investigated. We previously reported that CQ-metal complexes up-regulated MMP (matrix metalloprotease) activity in vitro by activating PI3K (phosphoinositide 3-kinase) and JNK (c-jun N-terminal kinase), and that the increased MMP activity resulted in enhanced degradation of secreted Abeta (amyloid beta) peptide. In the present study, we have further investigated the biochemical mechanisms by which metal ligands affect Abeta metabolism. To achieve this, we measured the effects of diverse metal ligands on cellular metal uptake and secreted Abeta levels in cell culture. We report that different classes of metal ligands including 8HQ and phenanthroline derivatives and the sulfur compound PDTC (pyrrolidine dithiocarbamate) elevated cellular metal levels (copper and zinc), and resulted in substantial loss of secreted Abeta. Generally, the ability to inhibit Abeta levels correlated with a higher lipid solubility of the ligands and their capacity to increase metal uptake. However, we also identified several ligands that potently inhibited Abeta levels while only inducing minimal change to cellular metal levels. Metal ligands that inhibited Abeta levels [e.g. CQ, 8HQ, NC (neocuproine), 1,10-phenanthroline and PDTC] induced metal-dependent activation of PI3K and JNK, resulting in JNK-mediated up-regulation of metalloprotease activity and subsequent loss of secreted Abeta. The findings in the present study show that diverse metal ligands with high lipid solubility can elevate cellular metal levels resulting in metalloprotease-dependent inhibition of Abeta. Given that a structurally diverse array of ligands was assessed, the results are consistent with the effects being due to metal transport rather than the chelating ligand interacting directly with a receptor.

Biometals play an important role in Alzheimer disease, and recent reports have described the development of potential therapeutic agents based on modulation of metal bioavailability. The metal ligand clioquinol (CQ) has shown promising results in animal models and small phase clinical trials; however, the actual mode of action in vivo has not been determined. We now report a novel effect of CQ on amyloid beta-peptide (Abeta) metabolism in cell culture. Treatment of Chinese hamster ovary cells overexpressing amyloid precursor protein with CQ and Cu(2+) or Zn(2+) resulted in an approximately 85-90% reduction of secreted Abeta-(1-40) and Abeta-(1-42) compared with untreated controls. Analogous effects were seen in amyloid precursor protein-overexpressing neuroblastoma cells. The secreted Abeta was rapidly degraded through up-regulation of matrix metalloprotease (MMP)-2 and MMP-3 after addition of CQ and Cu(2+). MMP activity was increased through activation of phosphoinositol 3-kinase and JNK. CQ and Cu(2+) also promoted phosphorylation of glycogen synthase kinase-3, and this potentiated activation of JNK and loss of Abeta-(1-40). Our findings identify an alternative mechanism of action for CQ in the reduction of Abeta deposition in the brains of CQ-treated animals and potentially in Alzheimer disease patients.

Neocortical beta-amyloid (Abeta) aggregates in Alzheimer's disease (AD) are enriched in transition metals that mediate assembly. Clioquinol (CQ) targets metal interaction with Abeta and inhibits amyloid pathology in transgenic mice. Here, we investigated the binding properties of radioiodinated CQ ([(125)I]CQ) to different in vitro and in vivo Alzheimer models. We observed saturable binding of [(125)I]CQ to synthetic Abeta precipitated by Zn(2+) (K(d)=0.45 and 1.40 nm for Abeta(1-42) and Abeta(1-40), respectively), which was fully displaced by free Zn(2+), Cu(2+), the chelator DTPA (diethylene triamine pentaacetic acid) and partially by Congo red. Sucrose density gradient of post-mortem AD brain indicated that [(125)I]CQ concentrated in a fraction enriched for both Abeta and Zn, which was modulated by exogenous addition of Zn(2+) or DTPA. APP transgenic (Tg2576) mice injected with [(125)I]CQ exhibited higher brain retention of tracer compared to non-Tg mice. Autoradiography of brain sections of these animals confirmed selective [(125)I]CQ enrichment in the neocortex. Histologically, both thioflavine-S (ThS)-positive and negative structures were labeled by [(125)I]CQ. A pilot SPECT study of [(123)I]CQ showed limited uptake of the tracer into the brain, which did however, appear to be more rapid in AD patients compared to age-matched controls. These data support metallated Abeta species as the neuropharmacological target of CQ and indicate that this drug class may have potential as in vivo imaging agents for Alzheimer neuropathology.

Cerebral amyloid angiopathy (CAA) is common in Alzheimer's disease (AD) and may contribute to dementia and cerebral hemorrhage. Parenchymal beta-amyloid deposition is dependent on the activity of zinc transporter 3 (ZnT3), a neocortical synaptic vesicle membrane protein that causes enrichment of exchangeable Zn2+ in the vesicle, which is externalized on neurotransmission. However, the contribution of zinc to vascular beta-amyloid deposition remains unclear. Here, we identify for the first time an exchangeable pool of Zn2+ in the cerebrovascular wall of normal mice. This histochemically reactive Zn2+ is enriched in CAA in a transgenic mouse model of AD (Tg2576), and a dramatic reduction of CAA occurs after targeted disruption of the Znt3 gene in these mice. Also, in Znt3 knock-out mice, the amount of exchangeable Zn2+ [detected by N-(6-methoxy-8-quinolyl)-p-carboxybenzoylsulphonamide (TFL-Zn)] in the perivascular space was significantly decreased in the neocortex but not in peripheral organs. ZnT3 was not detected in the cerebral vessel walls or in blood components of wild-type mice. Thus, synaptic ZnT3 activity may promote CAA by indirectly raising exchangeable Zn2+ concentrations in the perivascular spaces of the brain.

Previous studies suggest that female sex hormones modulate synaptic zinc levels, which may influence amyloid plaque formation and Alzheimer's disease progression. We examined the effects of ovariectomy and estrogen supplement on the levels of synaptic zinc and zinc transporter protein Znt3 in the brain. Ovariectomy was performed on 5-month-old mice, and 2 weeks later, pellets containing vehicle, low (0.18 mg/pellet), or high dose (0.72 mg) 17beta-estradiol were implanted. After 4 weeks, animals were decapitated, and blood and brain were collected for analysis. Blood analysis indicated that estrogen implants altered plasma estrogen levels in a dose-dependent manner. Analysis of brain tissue showed that ovariectomy raised hippocampal synaptic vesicle zinc levels, whereas estrogen replacement lowered these zinc levels. Western blots revealed that Znt3 levels in the brain were modulated in parallel with synaptic zinc levels, whereas no change was detected in the levels of Znt3 mRNA, as determined by Northern blot and reverse transcriptase-PCR analysis. However, mRNA levels of the delta subunit of adaptor protein complex (AP)-3, which modulates the level of Znt3 levels, were altered by estrogen depletion or replacement. These data demonstrate that estrogen alters the levels of Znt3 and synaptic vesicle zinc in female mice, probably through changing AP-3 delta expression. Since synaptic zinc may play a key role in neuronal death in acute brain injury as well as in plaque formation in Alzheimer's disease, and since estrogen may be beneficial in both conditions, our results may provide new insights into the effects of estrogen on the brain.

The loss of cognitive function is a pervasive and often debilitating feature of the aging process for which there are no effective therapeutics. We hypothesized that a novel metal chaperone (PBT2; Prana Biotechnology, Parkville, Victoria, Australia) would enhance cognition in aged rodents. We show here that PBT2 rapidly improves the performance of aged C57Bl/6 mice in the Morris water maze, concomitant with increases in dendritic spine density, hippocampal neuron number and markers of neurogenesis. There were also increased levels of specific glutamate receptors (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and N-methyl- d-aspartate), the glutamate transporter ( VGLUT1) and glutamate itself. Markers of synaptic plasticity [calmodulin-dependent protein kinase II (CaMKII) and phosphorylated CaMKII, CREB, synaptophysin] were also increased following PBT2 treatment. We also demonstrate that PBT2 treatment results in a subregion-specific increase in hippocampal zinc, which is increasingly recognized as a potent neuromodulator. These data demonstrate that metal chaperones are a novel approach to the treatment of age-related cognitive decline. [ABSTRACT FROM AUTHOR]

J. Neurochem. (2011) 119, 220-230. Abstract Impaired metal ion homeostasis causes synaptic dysfunction and treatments for Alzheimer's disease (AD) that target metal ions have therefore been developed. The leading compound in this class of therapeutic, PBT2, improved cognition in a clinical trial with AD patients. The aim of the present study was to examine the cellular mechanism of action for PBT2. We show PBT2 induces inhibitory phosphorylation of the α- and β-isoforms of glycogen synthase kinase 3 and that this activity is dependent on PBT2 translocating extracellular Zn and Cu into cells. This activity is supported when Aβ:Zn aggregates are the source of extracellular Zn and adding PBT2 to Aβ:Zn preparations promotes Aβ degradation by matrix metalloprotease 2. PBT2-induced glycogen synthase kinase 3 phosphorylation appears to involve inhibition of the phosphatase calcineurin. Consistent with this, PBT2 increased phosphorylation of other calcineurin substrates, including cAMP response element binding protein and Ca2+/calmodulin-dependent protein kinase. These data demonstrate PBT2 can decrease Aβ levels by sequestering the Zn that promotes extracellular formation of protease resistant Aβ:Zn aggregates, and that subsequent intracellular translocation of the Zn by PBT2 induces cellular responses with synapto-trophic potential. Intracellular translocation of Zn and Cu via the metal chaperone activity of PBT2 may be an important mechanism by which PBT2 improves cognitive function in people with AD. [ABSTRACT FROM AUTHOR]

Accumulation of neurotoxic amyloid-β (Aβ) is central to the pathology of Alzheimer’s disease (AD). Elucidating the mechanisms of Aβ accumulation will therefore expedite the development of Aβ-targeting AD therapeutics. We examined activity of an Aβ-degrading protease (matrix metalloprotease 2) to investigate whether biochemical factors consistent with conditions in the AD brain contribute to Aβ accumulation by altering Aβ sensitivity to proteolytic degradation. An Aβ amino acid mutation found in familial AD, Aβ interactions with zinc (Zn), and increased Aβ hydrophobicity all strongly prevented Aβ degradation. Consistent to all of these factors is the promotion of specific Aβ aggregates where the protease cleavage site, confirmed by mass spectrometry, is inaccessible within an amyloid structure. These data indicate decreased degradation due to amyloid formation initiates Aβ accumulation by preventing normal protease activity. Zn also prevented Aβ degradation by the proteases neprilysin and insulin degrading enzyme. Treating Zn-induced Aβ amyloid with the metal-protein attenuating compound clioquinol reversed amyloid formation and restored the peptide’s sensitivity to degradation by matrix metalloprotease 2. This provides new data indicating that therapeutic compounds designed to modulate Aβ-metal interactions can inhibit Aβ accumulation by restoring the catalytic potential of Aβ-degrading proteases. [ABSTRACT FROM AUTHOR]

Transgenic mice carrying mutant Cu/Zn superoxide dismutase (SOD1) recapitulate the motor impairment of human amyotrophic lateral sclerosis (ALS). The amyloid-β (Aβ) peptide associated with Alzheimer's disease is neurotoxic. To investigate the potential role of Aβ in ALS development, we generated a double transgenic mouse line that overexpresses SOD1G93A and amyloid precursor protein (APP)-C100. The transgenic mouse C100.SOD1G93A overexpresses Aβ and shows earlier onset of motor impairment but has the same lifespan as the single transgenic SOD1G93A mouse. To determine the mechanism associated with this early-onset phenotype, we measured copper and zinc levels in brain and spinal cord and found both significantly elevated in the single and double transgenic mice compared with their littermate control mice. Increased glial fibrillary acidic protein and decreased APP levels in the spinal cord of C100.SOD1G93A mice compared with the SOD1G93A mice agree with the neuronal damage observed by immunohistochemical analysis. In the spinal cords of C100.SOD1G93A double transgenic mice, soluble Aβ was elevated in mice at end-stage disease compared with the pre-symptomatic stage. Buffer-insoluble SOD1 aggregates were significantly elevated in the pre-symptomatic mice of C100.SOD1G93A compared with the age-matched SOD1G93A mice, correlating with the earlier onset of motor impairment in the C100.SOD1G93A mice. This study supports abnormal SOD1 protein aggregation as the pathogenic mechanism in ALS, and implicates a potential role for Aβ in the development of ALS by exacerbating SOD1G93A aggregation. [ABSTRACT FROM AUTHOR]

Neocortical β-amyloid (Aβ) aggregates in Alzheimer's disease (AD) are enriched in transition metals that mediate assembly. Clioquinol (CQ) targets metal interaction with Aβ and inhibits amyloid pathology in transgenic mice. Here, we investigated the binding properties of radioiodinated CQ ([125I]CQ) to different in vitro and in vivo Alzheimer models. We observed saturable binding of [125I]CQ to synthetic Aβ precipitated by Zn2+ (Kd = 0.45 and 1.40 nm for Aβ1-42 and Aβ1-40, respectively), which was fully displaced by free Zn2+, Cu2+, the chelator DTPA (diethylene triamine pentaacetic acid) and partially by Congo red. Sucrose density gradient of post-mortem AD brain indicated that [125I]CQ concentrated in a fraction enriched for both Aβ and Zn, which was modulated by exogenous addition of Zn2+ or DTPA. APP transgenic (Tg2576) mice injected with [125I]CQ exhibited higher brain retention of tracer compared to non-Tg mice. Autoradiography of brain sections of these animals confirmed selective [125I]CQ enrichment in the neocortex. Histologically, both thioflavine-S (ThS)-positive and negative structures were labeled by [125I]CQ. A pilot SPECT study of [123I]CQ showed limited uptake of the tracer into the brain, which did however, appear to be more rapid in AD patients compared to age-matched controls. These data support metallated Aβ species as the neuropharmacological target of CQ and indicate that this drug class may have potential as in vivo imaging agents for Alzheimer neuropathology. [ABSTRACT FROM AUTHOR]

Previous studies suggest that female sex hormones modulate synaptic zinc levels, which may influence amyloid plaque formation and Alzheimer’s disease progression. We examined the effects of ovariectomy and estrogen supplement on the levels of synaptic zinc and zinc transporter protein Znt3 in the brain. Ovariectomy was performed on 5-month-old mice, and 2 weeks later, pellets containing vehicle, low (0.18 mg/pellet), or high dose (0.72 mg) 17β-estradiol were implanted. After 4 weeks, animals were decapitated, and blood and brain were collected for analysis. Blood analysis indicated that estrogen implants altered plasma estrogen levels in a dose-dependent manner. Analysis of brain tissue showed that ovariectomy raised hippocampal synaptic vesicle zinc levels, whereas estrogen replacement lowered these zinc levels. Western blots revealed that Znt3 levels in the brain were modulated in parallel with synaptic zinc levels, whereas no change was detected in the levels of Znt3 mRNA, as determined by Northern blot and reverse transcriptase-PCR analysis. However, mRNA levels of the δ subunit of adaptor protein complex (AP)-3, which modulates the level of Znt3 levels, were altered by estrogen depletion or replacement. These data demonstrate that estrogen alters the levels of Znt3 and synaptic vesicle zinc in female mice, probably through changing AP-3 δ expression. Since synaptic zinc may play a key role in neuronal death in acute brain injury as well as in plaque formation in Alzheimer’s disease, and since estrogen may be beneficial in both conditions, our results may provide new insights into the effects of estrogen on the brain. [ABSTRACT FROM AUTHOR]