Increased amount of zinc in the hippocampus and amygdala of Alzheimer's diseased brains: a proton-induced X-ray emission spectroscopic analysis of cryostat sections from autopsy material

Zinc utilization by microglia in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia defined by two key pathological characteristics in the brain, amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau. Microglia, the primary innate immune cells of the central nervous system (CNS), provide neuroprotection through Aβ and tau clearance but may also be neurotoxic by promoting neuroinflammation to exacerbate Aβ and tau pathogenesis in AD. Recent studies have demonstrated the importance of microglial utilization of nutrients and trace metals in controlling their activation and effector functions. Trace metals, such as zinc, have essential roles in brain health and immunity, and zinc dyshomeostasis has been implicated in AD pathogenesis. As a result of these advances, the mechanisms by which zinc homeostasis influences microglial-mediated neuroinflammation in AD is a topic of continuing interest since new strategies to treat AD are needed. Here, we review the roles of zinc in AD, including zinc activation of microglia, the associated neuroinflammatory response, and the application of these findings in new therapeutic strategies.

Establishment of a nonradioactive DNA ligation assay and its applications in murine tissues

As final process of every DNA repair pathway, DNA ligation is crucial for maintaining genomic stability and preventing DNA strand breaks to accumulate. Therefore, a method reliably assessing DNA ligation capacity in protein extracts from murine tissues was aimed to establish. To optimize applicability, the use of radioactively labeled substrates was avoided and replaced by fluorescently labeled oligonucleotides. Briefly, tissue extracts were incubated with those complementary oligonucleotides so that in an ensuing gel electrophoresis ligated strands could be separated from unconnected molecules. Originally, the method was intended for use in cerebellum tissue to further elucidate possible mechanisms of neurodegenerative diseases. However, due to its inhomogeneous anatomy, DNA ligation efficiency varied strongly between different cerebellar areas, illuminating the established assay to be suitable only for homogenous organs. Thus, for murine liver tissue sufficient intra- and interday repeatability was shown during validation. In further experiments, the established assay was applied to an animal study comprising young and old (24 and 110 weeks) mice which showed that DNA ligation efficiency was affected by neither sex nor age. Finally, the impact of in vitro addition of the trace elements copper, iron, and zinc on DNA ligation in tissue extracts was investigated. While all three metals inhibited DNA ligation, variations in their potency became evident. In conclusion, the established method can be reliably used for investigation of DNA ligation efficiency in homogenous murine tissues.

Antioxidant, anti-inflammatory and epigenetic potential of curcumin in Alzheimer's disease

Alzheimer's disease (AD) constitutes a multifactorial neurodegenerative pathology characterized by cognitive deterioration, personality alterations, and behavioral shifts. The ongoing brain impairment process poses significant challenges for therapeutic interventions due to activating multiple neurotoxic pathways. Current pharmacological interventions have shown limited efficacy and are associated with significant side effects. Approaches focusing on the early interference with disease pathways, before activation of broad neurotoxic processes, could be promising to slow down symptomatic progression of the disease. Curcumin-an integral component of traditional medicine in numerous cultures worldwide-has garnered interest as a promising AD treatment. Current research indicates that curcumin may exhibit therapeutic potential in neurodegenerative pathologies, attributed to its potent anti-inflammatory and antioxidant properties. Additionally, curcumin and its derivatives have demonstrated an ability to modulate cellular pathways via epigenetic mechanisms. This article aims to raise awareness of the neuroprotective properties of curcuminoids that could provide therapeutic benefits in AD. The paper provides a comprehensive overview of the neuroprotective efficacy of curcumin against signaling pathways that could be involved in AD and summarizes recent evidence of the biological efficiency of curcumins in vivo.

Distribution of Copper, Iron, and Zinc in the Retina, Hippocampus, and Cortex of the Transgenic APP/PS1 Mouse Model of Alzheimer's Disease

A mis-metabolism of transition metals (i.e., copper, iron, and zinc) in the brain has been recognised as a precursor event for aggregation of Amyloid-β plaques, a pathological hallmark of Alzheimer's disease (AD). However, imaging cerebral transition metals in vivo can be extremely challenging. As the retina is a known accessible extension of the central nervous system, we examined whether changes in the hippocampus and cortex metal load are also mirrored in the retina. Laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to visualise and quantify the anatomical distribution and load of Cu, Fe, and Zn in the hippocampus, cortex, and retina of 9-month-old Amyloid Precursor Protein/Presenilin 1 (APP/PS1, n = 10) and Wild Type (WT, n = 10) mice. Our results show a similar metal load trend between the retina and the brain, with the WT mice displaying significantly higher concentrations of Cu, Fe, and Zn in the hippocampus (p < 0.05, p < 0.0001, p < 0.01), cortex (p < 0.05, p = 0.18, p < 0.0001) and the retina (p < 0.001, p = 0.01, p < 0.01) compared with the APP/PS1 mice. Our findings demonstrate that dysfunction of the cerebral transition metals in AD is also extended to the retina. This could lay the groundwork for future studies on the assessment of transition metal load in the retina in the context of early AD.

The metal ion hypothesis of Alzheimer's disease and the anti-neuroinflammatory effect of metal chelators

Alzheimer's disease (AD), characterized by the β-amyloid protein (Aβ) deposition and tau hyperphosphorylation, is the most common dementia with uncertain etiology. The clinical trials of Aβ monoclonal antibody drugs have almost failed, giving rise to great attention on the other etiologic hypothesis regarding AD such as metal ions dysmetabolism and chronic neuroinflammation. Mounting evidence revealed that the metal ions (iron, copper, and zinc) were dysregulated in the susceptible brain regions of AD patients, which was highly associated with Aβ deposition, tau hyperphosphorylation, neuronal loss, as well as neuroinflammation. Further studies uncovered that iron, copper and zinc could not only enhance the production of Aβ but also directly bind to Aβ and tau to promote their aggregations. In addition, the accumulation of iron and copper could respectively promote ferroptosis and cuproptosis. Therefore, the metal ion chelators were recognized as promising agents for treating AD. This review comprehensively summarized the effects of metal ions on the Aβ dynamics and tau phosphorylation in the progression of AD. Furthermore, taking chronic neuroinflammation contributes to the progression of AD, we also provided a summary of the mechanisms concerning metal ions on neuroinflammation and highlighted the metal ion chelators may be potential agents to alleviate neuroinflammation under the condition of AD. Nevertheless, more investigations regarding metal ions on neuroinflammation should be taken into practice, and the effects of metal ion chelators on neuroinflammation should gain more attention. Running title: Metal chelators against neuroinflammation.

Zinc in Regulating Protein Kinases and Phosphatases in Neurodegenerative Diseases

Zinc is essential for human growth and development. As a trace nutrient, zinc plays important roles in numerous signal transduction pathways involved in distinct physiologic or pathologic processes. Protein phosphorylation is a posttranslational modification which regulates protein activity, degradation, and interaction with other molecules. Protein kinases (PKs) and phosphatases (PPs), with their effects of adding phosphate to or removing phosphate from certain substrates, are master regulators in controlling the phosphorylation of proteins. In this review, we summarize the disturbance of zinc homeostasis and role of zinc disturbance in regulating protein kinases and protein phosphatases in neurodegenerative diseases, with the focus of that in Alzheimer’s disease, providing a new perspective for understanding the mechanisms of these neurologic diseases.

Trace element alterations in Alzheimer's disease: A review

Dyshomeostasis of trace elements have been implicated in the progression of Alzheimer's disease (AD), which is characterized by amyloid-β (Aβ) plaques. Trace elements are particularly associated with the Aβ plaques. Metal-protein attenuating compounds have been developed to inhibit metals from binding to Aβ proteins, which result in Aβ termination, in the hope of improving cognitive functioning. However, there are still some contradicting reports. This review aims to first establish which trace elements are increased or decreased in the brains of Alzheimer's patients, and secondly, to review the effectiveness of clinical trials with metal-protein attenuating compounds for AD. Studies have consistently reported unchanged or increased iron, contradicting reports for zinc, decreased copper, unchanged or decreased manganese, inconsistent results for calcium, and magnesium seems to be unaffected. However, varied results have been reported for all trace elements. Clinical trials using metal-protein attenuating compounds to treat AD have also reported varied results. Copper chelators have repeatedly been used in clinical trials, even though few studies report increased brain copper levels in AD patients. Homeostasis of copper levels is important since copper has a vital role in several enzymes, such as cytochrome c, Cu/Zn superoxide dismutase and ceruloplasmin. Dyshomeostasis of copper levels can lead to increased oxidative stress and neuronal loss. Future studies should assess a variety of trace element levels in moderately and severely affected AD patients since there are contradicting reports. This review thus provides some insight into trace element alterations in the brains of individuals with AD.

The Role of Natural Antioxidants in the Prevention of Dementia-Where Do We Stand and Future Perspectives

Dementia, and especially Alzheimer's disease (AD), puts significant burden on global healthcare expenditure through its increasing prevalence. Research has convincingly demonstrated the implication of oxidative stress in the pathogenesis of dementia as well as of the conditions which increase the risk of developing dementia. However, drugs which target single pathways have so far failed in providing significant neuroprotection. Natural antioxidants, due to their effects in multiple pathways through which oxidative stress leads to neurodegeneration and triggers neuroinflammation, could prove valuable weapons in our fight against dementia. Although efficient in vitro and in animal models of AD, natural antioxidants in human trials have many drawbacks related to the limited bioavailability, unknown optimal dose, or proper timing of the treatment. Nonetheless, trials evaluating several of these natural compounds are ongoing, as are attempts to modify these compounds to achieve improved bioavailability.

Effect of Human Immunodeficiency Virus on Trace Elements in the Brain

Comorbidities of human immunodeficiency virus (HIV) include HIV-associated neurocognitive disorder (HAND). Changes in the brain due to HIV include atrophy, hyperintensities, and diffusion changes. However, no research has focused on trace elements concentration changes in the brain due to HIV, as seen in other neurodegenerative diseases. Therefore, the aim of this study was to determine the concentration of several trace elements in the brains of individuals with and without HIV infection. Prior to formalin embalming, blood was drawn and tested in triplicate with Determine HIV-1/2 rapid tests and confirmed with a SD HIV Device 1/2 3.0 rapid HIV Kit. After embalming, tissue was sampled from the caudate nucleus and analyzed using inductively coupled plasma mass spectrometry. A Kruskal-Wallis test was used to determine statistically significant differences between the two groups (p < 0.05). Fifteen HIV-positive and 14 HIV-negative male cadavers were included (mean age 44, range 22 to 61). Cadmium was marginally decreased, possibly due to malnutrition or utilization by the HIV nucleocapsid. Nickel was marginally increased, perhaps due to a reduced capability to remove metals from the body. In conclusion, this article provides the first information on trace element levels in the brains from HIV-infected individuals and postulates that cadmium and nickel may play a role in the pathophysiology of HAND. This information can contribute to finding a treatment for HAND, other than the use of antiretroviral drugs. Future studies should asses the levels of cadmium and nickel in a larger cohort of HIV-infected individuals.

The essential elements of Alzheimer's disease

Treatments for Alzheimer’s disease (AD) directed against the prominent amyloid plaque neuropathology are yet to be proved effective despite many phase 3 clinical trials. There are several other neurochemical abnormalities that occur in the AD brain that warrant renewed emphasis as potential therapeutic targets for this disease. Among those are the elementomic signatures of iron, copper, zinc, and selenium. Here, we review these essential elements of AD for their broad potential to contribute to Alzheimer’s pathophysiology, and we also highlight more recent attempts to translate these findings into therapeutics. A reinspection of large bodies of discovery in the AD field, such as this, may inspire new thinking about pathogenesis and therapeutic targets.

Peroxidase activity of heme bound amyloid β peptides associated with Alzheimer's disease

The amyloid cascade hypothesis attributes the neurodegeneration observed in Alzheimer's disease (AD) to the deposition of the amyloid β (Aβ) peptide into plaques and fibrils in the AD brain. The metal ion hypothesis which implicates several metal ions, viz. Zn²⁺, Cu²⁺ and Fe³⁺, in the AD pathology on account of their abnormal accumulation in the Aβ plaques along with an overall dyshomeostasis of these metals in the AD brain was proposed a while back. Metal ion chelators and ionophores, put forward as possible drug candidates for AD, are yet to succeed in clinical trials. Heme, which is widely distributed in the mammalian body as the prosthetic group of several important proteins and enzymes, has been thought to be associated with AD by virtue of its colocalization in the Aβ plaques along with the similarity of several heme deficiency symptoms with those of AD and most importantly, due to its ability to bind Aβ. This feature article illustrates the active site environment of heme-Aβ which resembles those of peroxidases. It also discusses the peroxidase activity of heme-Aβ, its ability to effect oxidative degradation of neurotransmitters like serotonin and also the identification of the highly reactive high-valent intermediate, compound I. The effect of second sphere residues on the formation and peroxidase activity of heme-Aβ along with the generation and decay of compound I is highlighted throughout the article. The reactivities of heme bound Aβ peptides give an alternative theory to understand the possible cause of this disease.

Ruthenium(iii) complexes containing thiazole-based ligands that modulate amyloid-β aggregation

Alzheimer's Disease (AD) is a devastating neurodegenerative disorder where one of the commonly observed pathological hallmarks is extracellular deposits of the peptide amyloid-β (Aβ). These deposits contain a high concentration of metals and initially presented a promising target for therapy; however it has become increasingly evident that the soluble form of the peptide is neurotoxic, not the amyloidogenic species. Metal-based therapeutics are uniquely suited to target soluble Aβ and have shown considerable promise to prevent the aggregation and induced cytotoxicity of the peptide in vitro. Herein, we have prepared a small series of derivatives of two promising Ru(iii) complexes NAMI-A (imidazolium [trans-RuCl₄(1H-imidazole)(dimethyl sulfoxide-S)]) and PMRU20 (2-aminothiazolium [trans-RuCl₄(2-aminothiazole)₂]), to determine structure-activity relationships (SAR) for Ru(iii) therapeutics for AD. Using the three complementary methods of Thioflavin T fluorescence, dynamic light scattering (DLS), and transmission electron microscopy (TEM), it was determined that the symmetry around the metal center did not significantly impact the activity of the complexes, but rather the attached thiazole ligand(s) mitigated Aβ aggregation. Across both families of Ru(iii) complexes the determined SAR for the functional groups on the thiazole ligands to modulate Aβ aggregation were NH₂ > CH₃ > H. These results highlight the importance of secondary interactions between the metallotherapeutic and the Aβ peptide where hydrogen-bonding has the greatest impact on modulating Aβ aggregation.

Characterising the spatial and temporal brain metal profile in a mouse model of tauopathy

A dysregulation in the homeostasis of metals such as copper, iron and zinc is speculated to be involved in the pathogenesis of tauopathies, which includes Alzheimer's disease (AD). In particular, there is a growing body of evidence to support a role for iron in facilitating the hyperphosphorylation and aggregation of the tau protein into neurofibrillary tangles (NFTs) - a primary neuropathological hallmark of tauopathies. Therefore, the aim of this study was to characterize the spatial and temporal brain metallomic profile in a mouse model of tauopathy (rTg(tauP301L)4510), so as to provide some insight into the potential interaction between tau pathology and iron. Using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), our results revealed an age-dependent increase in brain iron levels in both WT and rTg(tauP301L)4510 mice. In addition, size exclusion chromatography-ICP-MS (SEC-ICP-MS) revealed significant age-related changes in iron bound to metalloproteins such as ferritin. The outcomes from this study may provide valuable insight into the inter-relationship between iron and tau in ageing and neurodegeneration.

Transmembrane 163 (TMEM163) protein effluxes zinc

Recent investigations of rodent Tmem163 suggest that it binds to and transports zinc as a dimer, and that alanine mutagenesis of its two species-conserved aspartate (D123A/D127A) residues proposed to bind zinc, perturbs protein function. Direct corroboration, however, is lacking whether it is an influx or efflux transporter in cells. We hypothesized that human TMEM163 is a zinc effluxer based on its predicted protein characteristics. We used cultured human cell lines that either stably or transiently expressed TMEM163, and pre-loaded the cells with zinc to determine transport activity. We found that TMEM163-expressing cells exhibited significant reduction of intracellular zinc levels as evidenced by two zinc-specific fluorescent dyes and radionuclide zinc-65. The specificity of the fluorescence signal was confirmed upon treatment with TPEN, a high-affinity zinc chelator. Multiple sequence alignment and phylogenetic analyses showed that TMEM163 is related to distinct members of the cation diffusion facilitator (CDF) protein family. To further characterize the efflux function of TMEM163, we substituted alanine in two homologous aspartate residues (D124A/D128A) and performed site-directed mutagenesis of several conserved amino acid residues identified as non-synonymous single nucleotide polymorphism (S61R, S95C, S193P, and E286K). We found a significant reduction of zinc efflux upon cellular expression of D124A/D128A or E286K protein variant when compared with wild-type, suggesting that these particular amino acids are important for normal protein function. Taken together, our findings demonstrate that TMEM163 effluxes zinc, and it should now be designated ZNT11 as a new member of the mammalian CDF family of zinc efflux transporters.

Aggravated effects of coexisting marginal thiamine deficits and zinc excess on SN56 neuronal cells

Objectives: Zinc excitotoxicity and thiamine pyrophosphate deficiency (TD) are known pathogenic signals contributing to mechanism of different encephalopathies through inhibition of enzymes responsible for energy metabolism such as pyruvate dehydrogenase, aconitase or ketoglutarate dehydrogenase. The aim of this work was to investigate whether subclinical Zn excess and TD, frequent in aging brain, may combine yielding overt neuronal impairment.Results: Clonal SN56 cholinergic neuronal cells of septal origin were used as the model of brain cholinergic neurons, which are particularly susceptible to neurodegeneration in the course of Alzheimer's disease, hypoxia and other dementia-linked brain pathologies. Neither subtoxic concentration of Zn (0.10 mM) nor mild 20-25% TD deficits alone caused significant negative changes in cultured cholinergic neurons viability and their acetyl-CoA/acetylcholine metabolism. However, cells with mild TD accumulated Zn in excess, which impaired their energy metabolism causing a loss of neurons viability and their function as neurotransmitters. These negative effects of Zn were aggravated by amprolium which is an inhibitor of thiamine intracellular transport.Conclusion: Our data indicate that TD may amplify otherwise non-harmful border-line Zn excitotoxic signals yielding progress of neurodegeneration.

Metal Ions in Alzheimer's Disease: A Key Role or Not?

Despite tremendous research efforts in universities and pharmaceutical companies, effective drugs are still lacking for the treatment of Alzheimer's disease (AD). The biochemical mechanisms of this devastating neurodegenerative disease have not yet been clearly understood. Besides a small percentage of cases with early onset disease having a genetic origin (<5%, familial AD), most cases develop in the elderly as a sporadic form due to multiple and complex parameters of aging. Consequently, AD is spreading in all countries with a long life expectancy. AD is characterized by deposition of senile plaques made of β-amyloid proteins (Aβ) and by hyperphosphorylation of tau proteins, which have been considered as the main drug targets up to now. However, antibodies targeting amyloid aggregates, as well as enzyme inhibitors aiming to modify the amyloid precursor protein processing, have failed to improve cognition in clinical trials. Thus, to set up effective drugs, it is urgent to enlarge the panel of drug targets. Evidence of the link between AD and redox metal dysregulation has also been supported by post-mortem analyses of amyloid plaques, which revealed accumulation of copper, iron, and zinc by 5.7, 2.8, and 3.1 times, respectively, the levels observed in normal brains. Copper-amyloid complexes, in the presence of endogenous reductants, are able to catalyze the reduction of dioxygen and to produce reduced, reactive oxygen species (ROS), leading to neuron death. The possibility of using metal chelators to regenerate normal trafficking of metal ions has been considered as a promising strategy in order to reduce the redox stress lethal for neurons. However, most attempts to use metal chelators as therapeutic agents have been limited to existing molecules available from the shelves. Very few chelators have resulted from a rational design aiming to create drugs with a safety profile and able to cross the blood-brain barrier after an oral administration. In the human body, metals are handled by a sophisticated protein network to strictly control their transport and reactivity. Abnormal concentrations of certain metals may lead to pathological events due to misaccumulation and irregular reactivity. Consequently, therapeutic attempts to restore metal homeostasis should carefully take into account the coordination chemistry specificities of the concerned redox-active metal ions. This Account is focused on the role of the main biologically redox-active transition metals, iron and copper. For iron, the recent debate on the possible role of magnetite in AD pathogenesis is presented. The section devoted to copper is focused on the design of specific copper chelators as drug candidates able to regulate copper homeostasis and to reduce the oxidative damage responsible for the neuron death observed in AD brains. A short survey on non-redox-active metal ions is also included at the beginning, such as aluminum and its controversial role in AD and zinc which is a key metal ion in the brain.

Metal Toxicity Links to Alzheimer's Disease and Neuroinflammation

As the median age of the population increases, the number of individuals with Alzheimer's disease (AD) and the associated socio-economic burden are predicted to worsen. While aging and inherent genetic predisposition play major roles in the onset of AD, lifestyle, physical fitness, medical condition, and social environment have emerged as relevant disease modifiers. These environmental risk factors can play a key role in accelerating or decelerating disease onset and progression. Among known environmental risk factors, chronic exposure to various metals has become more common among the public as the aggressive pace of anthropogenic activities releases excess amount of metals into the environment. As a result, we are exposed not only to essential metals, such as iron, copper, zinc and manganese, but also to toxic metals including lead, aluminum, and cadmium, which perturb metal homeostasis at the cellular and organismal levels. Herein, we review how these metals affect brain physiology and immunity, as well as their roles in the accumulation of toxic AD proteinaceous species (i.e., β-amyloid and tau). We also discuss studies that validate the disruption of immune-related pathways as an important mechanism of toxicity by which metals can contribute to AD. Our goal is to increase the awareness of metals as players in the onset and progression of AD.

Revealing brain mechanisms of mTOR-mediated translational regulation: Implications for chronic pain

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mTOR is a major regulator of protein translation.

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mTOR serves an important role in neural plasticity.

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mTOR signalling in the brain as a pathology for neurological disorder is known.

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mTOR signalling in the brain as a chronic pain mechanism is understudied.

In the spinal cord, altered protein transcription and translation have received a lot of recent attention for their role in neural plasticity, a major mechanism leading to the development of chronic pain. However, changes in brain plasticity are also associated with the maintenance of pain symptoms, but these cellular mechanisms remain less clear. The mechanistic/mammalian target of rapamycin (mTOR) is a master regulator of protein synthesis, and controls several neuronal functions, including neural plasticity. While aberrant changes in mTOR signaling are associated with sensitization of the pain pathway (sensory neurons and spinal cord), there are various nervous system diseases that have pain as a comorbidity and altered mTOR activity in the brain. Here, we provide a brief review of mTOR changes in the brain that are associated with some neurological disorders and focus on how these changes may be relevant to the pain of the underlying condition and chronic pain itself.

Oxidative Stress, Synaptic Dysfunction, and Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disorder without a cure. Most AD cases are sporadic where age represents the greatest risk factor. Lack of understanding of the disease mechanism hinders the development of efficacious therapeutic approaches. The loss of synapses in the affected brain regions correlates best with cognitive impairment in AD patients and has been considered as the early mechanism that precedes neuronal loss. Oxidative stress has been recognized as a contributing factor in aging and in the progression of multiple neurodegenerative diseases including AD. Increased production of reactive oxygen species (ROS) associated with age- and disease-dependent loss of mitochondrial function, altered metal homeostasis, and reduced antioxidant defense directly affect synaptic activity and neurotransmission in neurons leading to cognitive dysfunction. In addition, molecular targets affected by ROS include nuclear and mitochondrial DNA, lipids, proteins, calcium homeostasis, mitochondrial dynamics and function, cellular architecture, receptor trafficking and endocytosis, and energy homeostasis. Abnormal cellular metabolism in turn could affect the production and accumulation of amyloid-β (Aβ) and hyperphosphorylated Tau protein, which independently could exacerbate mitochondrial dysfunction and ROS production, thereby contributing to a vicious cycle. While mounting evidence implicates ROS in the AD etiology, clinical trials with antioxidant therapies have not produced consistent results. In this review, we will discuss the role of oxidative stress in synaptic dysfunction in AD, innovative therapeutic strategies evolved based on a better understanding of the complexity of molecular mechanisms of AD, and the dual role ROS play in health and disease.

Zinc Signal in Brain Diseases

The divalent cation zinc is an integral requirement for optimal cellular processes, whereby it contributes to the function of over 300 enzymes, regulates intracellular signal transduction, and contributes to efficient synaptic transmission in the central nervous system. Given the critical role of zinc in a breadth of cellular processes, its cellular distribution and local tissue level concentrations remain tightly regulated via a series of proteins, primarily including zinc transporter and zinc import proteins. A loss of function of these regulatory pathways, or dietary alterations that result in a change in zinc homeostasis in the brain, can all lead to a myriad of pathological conditions with both acute and chronic effects on function. This review aims to highlight the role of zinc signaling in the central nervous system, where it may precipitate or potentiate diverse issues such as age-related cognitive decline, depression, Alzheimer's disease or negative outcomes following brain injury.

Various ketogenic diets can differently support brain resistance against experimentally evoked seizures and seizure-induced elemental anomalies of hippocampal formation

In this paper the influence of two different ketogenic diets (KDs) on the seizure-evoked elemental anomalies of hippocampal formation was examined. To achieve this purpose normal and pilocarpine treated rats previously fed with one of the two high fat and carbohydrate restricted diets were compared with animals on standard laboratory diet. The ketogenic ratios of the examined KDs were equal to 5:1 (KD1) and 9:1 (KD2). KD1 and standard diet fed animals presented similar patterns of seizure-evoked elemental changes in hippocampal formation. Also the analysis of behavioral data recorded after pilocarpine injection did not show any significant differences in intensity and duration of seizures between KD1 and standard diet fed animals. Higher ketogenic ratio KD2 introduced in the normal hippocampal formation prolonged changes in the accumulation of P, K, Zn and Ca. Despite this, both the intensity and duration of seizures were significantly reduced in rats fed with KD2 which suggests that its saving action on the nerve tissue may protect brain from seizure propagation. Also seizure-evoked elemental anomalies in KD2 animals were different than those observed for rats both on KD1 and standard diets. The comparison of seizure experiencing and normal rats on KD2, did not show any statistically significant differences in elemental composition of CA1 and H hippocampal areas whilst in CA3 area only Zn level changed as a result of seizures. DG was the area mostly affected by seizures in KD2 fed rats but areal densities of all examined elements increased in this hippocampal region.

Chelation of hippocampal zinc enhances long-term potentiation and synaptic tagging/capture in CA1 pyramidal neurons of aged rats: implications to aging and memory

Aging is associated with decline in cognitive functions, prominently in the memory consolidation and association capabilities. Hippocampus plays a crucial role in the formation and maintenance of long‐term associative memories, and a significant body of evidence shows that impairments in hippocampal function correlate with aging‐related memory loss. A number of studies have implicated alterations in hippocampal synaptic plasticity, such as long‐term potentiation (LTP), in age‐related cognitive decline although exact mechanisms underlying are not completely clear. Zinc deficiency and the resultant adverse effects on cognition have been well studied. However, the role of excess of zinc in synaptic plasticity, especially in aging, is not addressed well. Here, we have investigated the hippocampal zinc levels and the impairments in synaptic plasticity, such as LTP and synaptic tagging and capture (STC), in the CA1 region of acute hippocampal slices from 82‐ to 84‐week‐old male Wistar rats. We report increased zinc levels in the hippocampus of aged rats and also deficits in the tetani‐induced and dopaminergic agonist‐induced late‐LTP and STC. The observed deficits in synaptic plasticity were restored upon chelation of zinc using a cell‐permeable chelator. These data suggest that functional plasticity and associativity can be successfully established in aged neural networks by chelating zinc with cell‐permeable chelating agents.

Visualizing Metal Content and Intracellular Distribution in Primary Hippocampal Neurons with Synchrotron X-Ray Fluorescence

Increasing evidence suggests that metal dyshomeostasis plays an important role in human neurodegenerative diseases. Although distinctive metal distributions are described for mature hippocampus and cortex, much less is known about metal levels and intracellular distribution in individual hippocampal neuronal somata. To solve this problem, we conducted quantitative metal analyses utilizing synchrotron radiation X-Ray fluorescence on frozen hydrated primary cultured neurons derived from rat embryonic cortex (CTX) and two regions of the hippocampus: dentate gyrus (DG) and CA1. Comparing average metal contents showed that the most abundant metals were calcium, iron, and zinc, whereas metals such as copper and manganese were less than 10% of zinc. Average metal contents were generally similar when compared across neurons cultured from CTX, DG, and CA1, except for manganese that was larger in CA1. However, each metal showed a characteristic spatial distribution in individual neuronal somata. Zinc was uniformly distributed throughout the cytosol, with no evidence for the existence of previously identified zinc-enriched organelles, zincosomes. Calcium showed a peri-nuclear distribution consistent with accumulation in endoplasmic reticulum and/or mitochondria. Iron showed 2-3 distinct highly concentrated puncta only in peri-nuclear locations. Notwithstanding the small sample size, these analyses demonstrate that primary cultured neurons show characteristic metal signatures. The iron puncta probably represent iron-accumulating organelles, siderosomes. Thus, the metal distributions observed in mature brain structures are likely the result of both intrinsic neuronal factors that control cellular metal content and extrinsic factors related to the synaptic organization, function, and contacts formed and maintained in each region.

Alzheimer's disease due to loss of function: A new synthesis of the available data

Alzheimer's Disease (AD) is a highly complex disease involving a broad range of clinical, cellular, and biochemical manifestations that are currently not understood in combination. This has led to many views of AD, e.g. the amyloid, tau, presenilin, oxidative stress, and metal hypotheses. The amyloid hypothesis has dominated the field with its assumption that buildup of pathogenic β-amyloid (Aβ) peptide causes disease. This paradigm has been criticized, yet most data suggest that Aβ plays a key role in the disease. Here, a new loss-of-function hypothesis is synthesized that accounts for the anomalies of the amyloid hypothesis, e.g. the curious pathogenicity of the Aβ42/Aβ40 ratio, the loss of Aβ caused by presenilin mutation, the mixed phenotypes of APP mutations, the poor clinical-biochemical correlations for genetic variant carriers, and the failure of Aβ reducing drugs. The amyloid-loss view accounts for recent findings on the structure and chemical features of Aβ variants and their coupling to human patient data. The lost normal function of APP/Aβ is argued to be metal transport across neuronal membranes, a view with no apparent anomalies and substantially more explanatory power than the gain-of-function amyloid hypothesis. In the loss-of-function scenario, the central event of Aβ aggregation is interpreted as a loss of soluble, functional monomer Aβ rather than toxic overload of oligomers. Accordingly, new research models and treatment strategies should focus on remediation of the functional amyloid balance, rather than strict containment of Aβ, which, for reasons rationalized in this review, has failed clinically.

Obesity and age-related alterations in the gene expression of zinc-transporter proteins in the human brain

The incidence of Alzheimer's disease (AD) is increasing. Major risk factors for AD are advancing age and diabetes. Lately, obesity has been associated with an increased risk of dementia. Obese and diabetic individuals are prone to decreased circulating levels of zinc, reducing the amount of zinc available for crucial intracellular processes. In the brain, zinc co-localizes with glutamate in synaptic vesicles, and modulates NMDA receptor activity. Intracellular zinc is involved in apoptosis and fluctuations in cytoplasmic Zn(2+) affect modulation of intracellular signaling. The ZNT and ZIP proteins participate in intracellular zinc homeostasis. Altered expression of zinc-regulatory proteins has been described in AD patients. Using microarray data from human frontal cortex (BrainCloud), this study investigates expression of the SCLA30A (ZNT) and SCLA39A (ZIP) families of genes in a Caucasian and African-American sample of 145 neurologically and psychiatrically normal individuals. Expression of ZNT3 and ZNT4 were significantly reduced with increasing age, whereas expression of ZIP1, ZIP9 and ZIP13 were significantly increased. Increasing body mass index (BMI) correlated with a significant reduction in ZNT1 expression similar to what is seen in the early stages of AD. Increasing BMI also correlated with reduced expression of ZNT6. In conclusion, we found that the expression of genes that regulate intracellular zinc homeostasis in the human frontal cortex is altered with increasing age and affected by increasing BMI. With the increasing rates of obesity throughout the world, these findings warrant continuous scrutiny of the long-term consequences of obesity on brain function and the development of neurodegenerative diseases.

Multi-Target Directed Donepezil-Like Ligands for Alzheimer's Disease

HIGHLIGHTS ASS234 is a MTDL compound containing a moiety from Donepezil and the propargyl group from the PF 9601N, a potent and selective MAO B inhibitor. This compound is the most advanced anti-Alzheimer agent for preclinical studies identified in our laboratory.Derived from ASS234 both multipotent donepezil-indolyl (MTDL-1) and donepezil-pyridyl hybrids (MTDL-2) were designed and evaluated as inhibitors of AChE/BuChE and both MAO isoforms. MTDL-2 showed more high affinity toward the four enzymes than MTDL-1.MTDL-3 and MTDL-4, were designed containing the N-benzylpiperidinium moiety from Donepezil, a metal- chelating 8-hydroxyquinoline group and linked to a N-propargyl core and they were pharmacologically evaluated.The presence of the cyano group in MTDL-3, enhanced binding to AChE, BuChE and MAO A. It showed antioxidant behavior and it was able to strongly complex Cu(II), Zn(II) and Fe(III).MTDL-4 showed higher affinity toward AChE, BuChE.MTDL-3 exhibited good brain penetration capacity (ADMET) and less toxicity than Donepezil. Memory deficits in scopolamine-lesioned animals were restored by MTDL-3.MTDL-3 particularly emerged as a ligand showing remarkable potential benefits for its use in AD therapy. Alzheimer's disease (AD), the most common form of adult onset dementia, is an age-related neurodegenerative disorder characterized by progressive memory loss, decline in language skills, and other cognitive impairments. Although its etiology is not completely known, several factors including deficits of acetylcholine, β-amyloid deposits, τ-protein phosphorylation, oxidative stress, and neuroinflammation are considered to play significant roles in the pathophysiology of this disease. For a long time, AD patients have been treated with acetylcholinesterase inhibitors such as donepezil (Aricept®) but with limited therapeutic success. This might be due to the complex multifactorial nature of AD, a fact that has prompted the design of new Multi-Target-Directed Ligands (MTDL) based on the "one molecule, multiple targets" paradigm. Thus, in this context, different series of novel multifunctional molecules with antioxidant, anti-amyloid, anti-inflammatory, and metal-chelating properties able to interact with multiple enzymes of therapeutic interest in AD pathology including acetylcholinesterase, butyrylcholinesterase, and monoamine oxidases A and B have been designed and assessed biologically. This review describes the multiple targets, the design rationale and an in-house MTDL library, bearing the N-benzylpiperidine motif present in donepezil, linked to different heterocyclic ring systems (indole, pyridine, or 8-hydroxyquinoline) with special emphasis on compound ASS234, an N-propargylindole derivative. The description of the in vitro biological properties of the compounds and discussion of the corresponding structure-activity-relationships allows us to highlight new issues for the identification of more efficient MTDL for use in AD therapy.

Ginkgo biloba extract (Egb761) attenuates zinc-induced tau phosphorylation at Ser262 by regulating GSK3β activity in rat primary cortical neurons

In the brain, an excessive amount of zinc promotes the deposition of β-amyloid proteins and the intraneuronal accumulation of neurofibrillary tangles composed of hyperphosphorylated tau proteins. These consequences are key neuropathological traits that reflect Alzheimer's disease. Egb761, a standardized Ginkgo biloba extract, is a powerful antioxidant known to exhibit neuroprotective actions. In this study, we investigated whether Egb761 can counteract the zinc-induced tau phosphorylation in rat primary cortical neurons. To determine the modification of tau phosphorylation by Egb761 treatment, we conducted Western blot analyses, MTT assay, ROS measurements and immunocytochemistry. We found that zinc-induced tau phosphorylation occurred at Ser262 in a time- and dose-dependent manner while other tau sites were not phosphorylated. Tau phosphorylation at Ser262 was increased 30 min after zinc treatment and peaked 3 h after zinc treatment (control: 100 ± 1.2%, 30 min: 253 ± 2.24%, 3 h: 373 ± 1.3%). Interestingly, Egb761 treatment attenuated the zinc-induced tau hyperphosphorylation at Ser262 in a concentration-dependent manner while the antioxidant N-acetylcysteine showed a similar effect. Furthermore, Egb761 prevented the zinc-induced activation of p38 MAPK and GSK3β, as well as the zinc-induced increase in ROS production and neuronal cell death. Lithium chloride also inhibited the zinc-induced tau phosphorylation but did not affect ROS levels. These results suggest the potential of Egb761 for inhibiting the zinc-induced tau phosphorylation at Ser262 through its anti-oxidative actions involving the regulation of GSK3β. Therefore, Egb761 may be a candidate for the treatment of tauopathy present in neurological disorders such as Alzheimer's disease.

A possible significant role of zinc and GPR39 zinc sensing receptor in Alzheimer disease and epilepsy

Zinc the essential trace element, plays a significant role in the brain development and in the proper brain functions at every stage of life. Misbalance of zinc (Zn(2+)) ions in the central nervous system is involved in the pathogenesis of numerous neurodegenerative disorders such as Alzheimer's disease, Depression, and Epilepsy. In brain, Zn(2+) has been identified as a ligand, capable of activating and inhibiting the receptors including the NMDA-type glutamate receptors (NMDARs), GABAA receptors, nicotinic acetylcholine receptors (nAChRs), glycine receptors (glyR) and serotonin receptors (5-HT3). Recently GPR39 has been identified as a zinc-specific receptor, widely expressed in brain tissues including the frontal cortex, amygdala, and hippocampus. GPR39, when binding with Zn(2+) has shown promising therapeutic potentials. This review presents current knowledge regarding the role of GPR39 zinc sensing receptor in brain, with a focus on Alzheimer's disease and Epilepsy. Although the results are encouraging, further research is needed to clarify zinc and GPR39 role in the treatment of Alzheimer's disease and Epilepsy.

Comparison of Metal Levels between Postmortem Brain and Ventricular Fluid in Alzheimer's Disease and Nondemented Elderly Controls

An essential metal hypothesis for neurodegenerative disease suggests an alteration in metal homeostasis contributing to the onset and progression of disease. Similar associations have been proposed for nonessential metals. To examine the relationship between metal levels in brain tissue and ventricular fluid (VF), postmortem samples of frontal cortex (FC) and VF from Alzheimer's disease (AD) cases and nondemented elderly subjects were analyzed for arsenic (As), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), mercury (Hg), nickel (Ni), tin (Sn), vanadium (V), and zinc (Zn) using inductively coupled plasma sector field mass spectrometry. All metals, with exception of equivalent Pb levels, were lower in the VF, compared to FC. Within-subject comparisons demonstrated that VF levels were not representative of levels within brain tissue. The essential metals Cu, Fe, and Zn were found highest in both compartments. Cd, Hg, and V levels in the VF were below the limit of quantification. In AD cases, FC levels of Fe were higher and As and Cd were lower than levels in controls, while levels of As in the VF were higher. Parameter estimates for FC metal levels indicated an association of Braak stage and higher Fe levels and an association of Braak stage and lower As, Mn, and Zn levels. The data showed no evidence of an accumulation of nonessential metals within the AD brain and, with the exception of As, showed no significant shift in the ratio of FC to VF levels to indicate differential clearance.

Sialic Acid Hydroxamate: A Potential Antioxidant and Inhibitor of Metal-Induced β-Amyloid Aggregates

Current methods for Alzheimer's treatment require a three-component system: metal chelators, antioxidants, and amyloid β (Aβ)-peptide-binding scaffolds. We report sialic acid (Sia) hydroxamate as a potential radical scavenger and metal chelator to inhibit Aβ aggregation. A cell viability assay revealed that Sia hydroxamate can protect HeLa and glioblastoma (LN229) cells from oxidative damage induced by the Fenton reaction. Sedimentation and turbidity assays showed profound protection of neuroblastoma SH-SY5Y cells from metal-induced Aβ aggregation and neural toxicity.

Biometals and their therapeutic implications in Alzheimer's disease

No disease modifying therapy exists for Alzheimer's disease (AD). The growing burden of this disease to our society necessitates continued investment in drug development. Over the last decade, multiple phase 3 clinical trials testing drugs that were designed to target established disease mechanisms of AD have all failed to benefit patients. There is, therefore, a need for new treatment strategies. Changes to the transition metals, zinc, copper, and iron, in AD impact on the molecular mechanisms of disease, and targeting these metals might be an alternative approach to treat the disease. Here we review how metals feature in molecular mechanisms of AD, and we describe preclinical and clinical data that demonstrate the potential for metal-based drug therapy.

Metal and complementary molecular bioimaging in Alzheimer's disease

Alzheimer's disease (AD) is the leading cause of dementia in the elderly, affecting over 27 million people worldwide. AD represents a complex neurological disorder which is best understood as the consequence of a number of interconnected genetic and lifestyle variables, which culminate in multiple changes to brain structure and function. These can be observed on a gross anatomical level in brain atrophy, microscopically in extracellular amyloid plaque and neurofibrillary tangle formation, and at a functional level as alterations of metabolic activity. At a molecular level, metal dyshomeostasis is frequently observed in AD due to anomalous binding of metals such as Iron (Fe), Copper (Cu), and Zinc (Zn), or impaired regulation of redox-active metals which can induce the formation of cytotoxic reactive oxygen species and neuronal damage. Metal chelators have been administered therapeutically in transgenic mice models for AD and in clinical human AD studies, with positive outcomes. As a result, neuroimaging of metals in a variety of intact brain cells and tissues is emerging as an important tool for increasing our understanding of the role of metal dysregulation in AD. Several imaging techniques have been used to study the cerebral metallo-architecture in biological specimens to obtain spatially resolved data on chemical elements present in a sample. Hyperspectral techniques, such as particle-induced X-ray emission (PIXE), energy dispersive X-ray spectroscopy (EDS), X-ray fluorescence microscopy (XFM), synchrotron X-ray fluorescence (SXRF), secondary ion mass spectrometry (SIMS), and laser ablation inductively coupled mass spectrometry (LA-ICPMS) can reveal relative intensities and even semi-quantitative concentrations of a large set of elements with differing spatial resolution and detection sensitivities. Other mass spectrometric and spectroscopy imaging techniques such as laser ablation electrospray ionization mass spectrometry (LA ESI-MS), MALDI imaging mass spectrometry (MALDI-IMS), and Fourier transform infrared spectroscopy (FTIR) can be used to correlate changes in elemental distribution with the underlying pathology in AD brain specimens. Taken together, these techniques provide new techniques to probe the pathobiology of AD and pave the way for identifying new therapeutic targets. The current review aims to discuss the advantages and challenges of using these emerging elemental and molecular imaging techniques, and highlight clinical achievements in AD research using bioimaging techniques.

Zinc: The Metal of Life

The importance of zinc was 1st reported for Aspergillus niger. It took over 75 y to realize that zinc is also an essential trace element for rats, and an additional 30 y went by before it was recognized that this was also true for humans. The adult body contains about 2 to 3 g of zinc. Zinc is found in organs, tissues, bones, fluids, and cells. It is essential for many physiological functions and plays a significant role in a number of enzyme actions in the living systems. Bioinformatics estimates report that 10% of the human proteome contains zinc-binding sites. Based on its role in such a plethora of cellular components, zinc has diverse biological functions from enzymatic catalysis to playing a crucial role in cellular neuronal systems. Thus, based on the various published studies and reports, it is pertinent to state that zinc is one of the most important essential trace metals in human nutrition and lifestyle. Its deficiency may severely affect the homeostasis of a biological system. This review compiles the role of zinc in prophylaxis/therapeutics and provides current information about its effect on living beings.

The role of intracellular zinc release in aging, oxidative stress, and Alzheimer's disease

Brain aging is marked by structural, chemical, and genetic changes leading to cognitive decline and impaired neural functioning. Further, aging itself is also a risk factor for a number of neurodegenerative disorders, most notably Alzheimer’s disease (AD). Many of the pathological changes associated with aging and aging-related disorders have been attributed in part to increased and unregulated production of reactive oxygen species (ROS) in the brain. ROS are produced as a physiological byproduct of various cellular processes, and are normally detoxified by enzymes and antioxidants to help maintain neuronal homeostasis. However, cellular injury can cause excessive ROS production, triggering a state of oxidative stress that can lead to neuronal cell death. ROS and intracellular zinc are intimately related, as ROS production can lead to oxidation of proteins that normally bind the metal, thereby causing the liberation of zinc in cytoplasmic compartments. Similarly, not only can zinc impair mitochondrial function, leading to excess ROS production, but it can also activate a variety of extra-mitochondrial ROS-generating signaling cascades. As such, numerous accounts of oxidative neuronal injury by ROS-producing sources appear to also require zinc. We suggest that zinc deregulation is a common, perhaps ubiquitous component of injurious oxidative processes in neurons. This review summarizes current findings on zinc dyshomeostasis-driven signaling cascades in oxidative stress and age-related neurodegeneration, with a focus on AD, in order to highlight the critical role of the intracellular liberation of the metal during oxidative neuronal injury.

Biological metals and metal-targeting compounds in major neurodegenerative diseases

Metals are functionally essential, but redistribute in neurodegenerative disease where they induce protein aggregates, catalyze radical formation, and lose bioavailability.

Decreased serum zinc is an effect of ageing and not Alzheimer's disease

Serum zinc decreases with age.

Metallostasis in Alzheimer's disease

2012 has been another year in which multiple large-scale clinical trials for Alzheimer's disease (AD) have failed to meet their clinical endpoints. With the social and financial burden of this disease increasing every year, the onus is now on the field of AD researchers to investigate alternative ideas to deliver outcomes for patients. Although several major clinical trials targeting Aβ have failed, three smaller clinical trials targeting metal interactions with Aβ have all shown benefit for patients. Here we review the genetic, pathological, biochemical, and pharmacological evidence that underlies the metal hypothesis of AD. The AD-affected brain suffers from metallostasis, or fatigue of metal trafficking, resulting in redistribution of metals into inappropriate compartments. The metal hypothesis is built upon a triad of transition elements: iron, copper, and zinc. The hypothesis has matured from early investigations showing amyloidogenic and oxidative stress consequences of these metals; recently, disease-related proteins, APP, tau, and presenilin, have been shown to have major roles in metal regulation, which provides insight into the pathway of neurodegeneration in AD and illuminates potential new therapeutic avenues.