Astrocyte functions in the copper homeostasis of the brain

Role of copper in central nervous system physiology and pathology

Copper is a transition metal and an essential element for the organism, as alterations in its homeostasis leading to metal accumulation or deficiency have pathological effects in several organs, including the central nervous system. Central copper dysregulations have been evidenced in two genetic disorders characterized by mutations in the copper-ATPases ATP7A and ATP7B, Menkes disease and Wilson's disease, respectively, and also in multifactorial neurological disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis. This review summarizes current knowledge about the role of copper in central nervous system physiology and pathology, reports about unbalances in copper levels and/or distribution under disease, describes relevant animal models for human disorders where copper metabolism genes are dysregulated, and discusses relevant therapeutic approaches modulating copper availability. Overall, alterations in copper metabolism may contribute to the etiology of central nervous system disorders and represent relevant therapeutic targets to restore tissue homeostasis.

The Role of Glia in Wilson's Disease: Clinical, Neuroimaging, Neuropathological and Molecular Perspectives

Wilson's disease (WD) is inherited in an autosomal recessive manner and is caused by pathogenic variants of the ATP7B gene, which are responsible for impaired copper transport in the cell, inhibition of copper binding to apoceruloplasmin, and biliary excretion. This leads to the accumulation of copper in the tissues. Copper accumulation in the CNS leads to the neurological and psychiatric symptoms of WD. Abnormalities of copper metabolism in WD are associated with impaired iron metabolism. Both of these elements are redox active and may contribute to neuropathology. It has long been assumed that among parenchymal cells, astrocytes have the greatest impact on copper and iron homeostasis in the brain. Capillary endothelial cells are separated from the neuropil by astrocyte terminal legs, putting astrocytes in an ideal position to regulate the transport of iron and copper to other brain cells and protect them if metals breach the blood-brain barrier. Astrocytes are responsible for, among other things, maintaining extracellular ion homeostasis, modulating synaptic transmission and plasticity, obtaining metabolites, and protecting the brain against oxidative stress and toxins. However, excess copper and/or iron causes an increase in the number of astrocytes and their morphological changes observed in neuropathological studies, as well as a loss of the copper/iron storage function leading to macromolecule peroxidation and neuronal loss through apoptosis, autophagy, or cuproptosis/ferroptosis. The molecular mechanisms explaining the possible role of glia in copper- and iron-induced neurodegeneration in WD are largely understood from studies of neuropathology in Parkinson's disease and Alzheimer's disease. Understanding the mechanisms of glial involvement in neuroprotection/neurotoxicity is important for explaining the pathomechanisms of neuronal death in WD and, in the future, perhaps for developing more effective diagnostic/treatment methods.

The Role of Copper Overload in Modulating Neuropsychiatric Symptoms

Copper is a transition metal essential for growth and development and indispensable for eukaryotic life. This metal is essential to neuronal function: its deficiency, as well as its overload have been associated with multiple neurodegenerative disorders such as Alzheimer's disease and Wilson's disease and psychiatric conditions such as schizophrenia, bipolar disorder, and major depressive disorders. Copper plays a fundamental role in the development and function of the human Central Nervous System (CNS), being a cofactor of multiple enzymes that play a key role in physiology during development. In this context, we thought it would be timely to summarize data on alterations in the metabolism of copper at the CNS level that might influence the development of neuropsychiatric symptoms. We present a non-systematic review with the study selection based on the authors' judgement to offer the reader a perspective on the most significant elements of neuropsychiatric symptoms in Wilson's disease. We highlight that Wilson's disease is characterized by marked heterogeneity in clinical presentation among patients with the same mutation. This should motivate more research efforts to disentangle the role of environmental factors in modulating the expression of genetic predisposition to this disorder.

Advanced nanoparticle strategies for optimizing RNA therapeutic delivery in neurodegenerative disorders

Neurodegenerative diseases affect many people worldwide, and as the population ages, the incidence of these conditions increases. Alzheimer's disease (AD) and Parkinson's disease (PD) are the most prevalent neurodegenerative disorders worldwide. Different medicines are being used to control symptoms related to these conditions, but no treatment has yet been approved. Both genetic and environmental factors are involved in disease pathogenesis, and research on the pathophysiological pathways is still ongoing. The role of subcellular pathways and dysregulation in RNA pathways has been highlighted in pathophysiological studies, and treatment strategies focused on these pathways can be a promising approach. Many experiments have been conducted on delivering RNA cargo to the CNS to modulate various pathways involved. Yet another challenge to be faced is the effective transport of desired molecules to targets, which can be greatly hindered by distinct barriers limiting transport to the CNS, most noticeably the blood-brain barrier (BBB). Nanotechnology and the use of different nano-carriers for the delivery of nucleotides, peptides, proteins, and drug molecules are currently of great interest as these carriers help with better delivery and protection and, as a result, improve the effectiveness of the cargo. Nanocarriers can protect susceptible RNA molecules from possible degradation or destruction and improve their ability to reach the brain by enhancing BBB penetration. Different mechanisms for this process have been hypothesized. This review will go through the therapeutic application of RNA molecules in the treatment of AD and PD and the role of nanocarriers in overcoming delivery challenges and enhancing efficacy.

Impact of aging on copper isotopic composition in the murine brain

Aging is the main risk factor for Alzheimer's disease (AD). AD is linked to alterations in metal homeostasis and changes in stable metal isotopic composition can occur, possibly allowing the latter to serve as relevant biomarkers for potential AD diagnosis. Copper stable isotopes are used to investigate changes in Cu homeostasis associated with various diseases. Prior work has shown that in AD mouse models, the accumulation of 63Cu in the brain is associated with the disease's progression. However, our understanding of how the normal aging process influences the brain's isotopic composition of copper remains limited. In order to determine the utility and predictive power of Cu isotopes in AD diagnostics, we aim-in this study-to develop a baseline trajectory of Cu isotopic composition in the normally aging mouse brain. We determined the copper concentration and isotopic composition in brains of 30 healthy mice (WT) ranging in age from 6 to 12 mo, and further incorporate prior data obtained for 3-mo-old healthy mice; this range approximately equates to 20-50 yr in human equivalency. A significant 65Cu enrichment has been observed in the 12-mo-old mice compared to the youngest group, concomitant with an increase in Cu concentration with age. Meanwhile, literature data for brains of AD mice display an enrichment in 63Cu isotope compared to WT. It is acutely important that this baseline enrichment in 65Cu is fully constrained and normalized against if any coherent diagnostic observations regarding 63Cu enrichment as a biomarker for AD are to be developed.

The Role of Astrocytic Mitochondria in the Pathogenesis of Brain Ischemia

The morbidity rate of ischemic stroke is increasing annually with the growing aging population in China. Astrocytes are ubiquitous glial cells in the brain and play a crucial role in supporting neuronal function and metabolism. Increasing evidence shows that the impairment or loss of astrocytes contributes to neuronal dysfunction during cerebral ischemic injury. The mitochondrion is increasingly recognized as a key player in regulating astrocyte function. Changes in astrocytic mitochondrial function appear to be closely linked to the homeostasis imbalance defects in glutamate metabolism, Ca2+ regulation, fatty acid metabolism, reactive oxygen species, inflammation, and copper regulation. Here, we discuss the role of astrocytic mitochondria in the pathogenesis of brain ischemic injury and their potential as a therapeutic target.

Evaluation of the theranostic potential of [64Cu]CuCl2 in glioblastoma spheroids

BACKGROUND

Glioblastoma is an extremely aggressive malignant tumor with a very poor prognosis. Due to the increased proliferation rate of glioblastoma, there is the development of hypoxic regions, characterized by an increased concentration of copper (Cu). Considering this, 64Cu has attracted attention as a possible theranostic radionuclide for glioblastoma. In particular, [64Cu]CuCl2 accumulates in glioblastoma, being considered a suitable agent for positron emission tomography. Here, we explore further the theranostic potential of [64Cu]CuCl2, by studying its therapeutic effects in advanced three-dimensional glioblastoma cellular models. First, we established spheroids from three glioblastoma (T98G, U373, and U87) and a non-tumoral astrocytic cell line. Then, we evaluated the therapeutic responses of spheroids to [64Cu]CuCl2 exposure by analyzing spheroids' growth, viability, and cells' proliferative capacity. Afterward, we studied possible mechanisms responsible for the therapeutic outcomes, including the uptake of 64Cu, the expression levels of a copper transporter (CTR1), the presence of a cancer stem cell population, and the production of reactive oxygen species (ROS).

RESULTS

Results revealed that [64Cu]CuCl2 is able to significantly reduce spheroids' growth and viability, while also affecting cells' proliferation capacity. The uptake of 64Cu, the presence of cancer stem-like cells and the production of ROS were in accordance with the therapeutic response. However, expression levels of CTR1 were not in agreement with uptake levels, revealing that other mechanisms could be involved in the uptake of 64Cu.

CONCLUSIONS

Overall, our results further support [64Cu]CuCl2 potential as a theranostic agent for glioblastoma, unveiling potential mechanisms that could be involved in the therapeutic response.

Trace metals and astrocytes physiology and pathophysiology

Several trace metals, including iron, copper, manganese and zinc are essential for normal function of the nervous system. Both deficiency and excessive accumulation of these metals trigger neuropathological developments. The central nervous system (CNS) is in possession of dedicated homeostatic system that removes, accumulates, stores and releases these metals to fulfil nervous tissue demand. This system is mainly associated with astrocytes that act as dynamic reservoirs for trace metals, these being a part of a global system of CNS ionostasis. Here we overview physiological and pathophysiological aspects of astrocyte-cantered trace metals regulation.

Association of Serum Concentrations of Copper, Selenium, and Zinc with Grip Strength Based on NHANES 2013-2014

Increasing evidence has found metals to be strongly associated with muscle strength, but the correlations between serum copper (Cu), selenium (Se), and zinc (Zn) with grip strength in adult populations have not yet been established. We examined the linear and non-linear associations between these three metals and grip strength via multiple linear regression and restricted cubic spline (RCS) regression using data from the National Health and Nutrition Examination Survey (NHANES) 2013-2014. A higher concentration of serum Cu was monotonically linked with lower grip strength [β = - 0.004 m2 (95% CI: - 0.005, - 0.002)], and serum Zn was positively associated with grip strength [β = 0.004 m2 (95% CI: 0.002, 0.006)]. We observed a positive association between serum Se and grip strength in the unadjusted model but not in covariate-adjusted models. Interestingly, the results of RCS regression showed that serum Cu had an L-shaped non-linear association with grip strength in all participants and subgroups. We further found a linear-increased trend between serum Zn and the grip strength in all participants. There were also non-linear associations that varied across different subgroups. Taken together, serum Cu and Zn were significantly associated with grip strength, while Se was not. This study offers new evidence to help formulate a reference concentration range for serum Cu and Zn.

Copper Metabolism and Cuproptosis: Molecular Mechanisms and Therapeutic Perspectives in Neurodegenerative Diseases

Copper is an essential trace element, and plays a vital role in numerous physiological processes within the human body. During normal metabolism, the human body maintains copper homeostasis. Copper deficiency or excess can adversely affect cellular function. Therefore, copper homeostasis is stringently regulated. Recent studies suggest that copper can trigger a specific form of cell death, namely, cuproptosis, which is triggered by excessive levels of intracellular copper. Cuproptosis induces the aggregation of mitochondrial lipoylated proteins, and the loss of iron-sulfur cluster proteins. In neurodegenerative diseases, the pathogenesis and progression of neurological disorders are linked to copper homeostasis. This review summarizes the advances in copper homeostasis and cuproptosis in the nervous system and neurodegenerative diseases. This offers research perspectives that provide new insights into the targeted treatment of neurodegenerative diseases based on cuproptosis.

Are high copper levels related to Alzheimer's and Parkinson's diseases? A systematic review and meta-analysis of articles published between 2011 and 2022

Copper performs an important role in the brain, but in high levels it can be neurotoxic. Further, some authors have described that copper dyshomeostasis could be related with neurodegenerative diseases. Thus, this review was performed to observe whether high copper levels are related to Alzheimer's and Parkinson's diseases (AD and PD), using the literature published recently. Articles that measured copper levels in AD or PD patients was included, as well as they that measured copper levels in models used to mimic these diseases. Also, results about high copper levels effects and its relationship with AD and PD observed in laboratory animals are considered. In summary, 38 and 24 articles with AD and PD patients were included, respectively. Despite of the heterogeneity between the studies in humans, meta-analysis has demonstrated that there is an increase in free and total copper levels in the blood of AD patients compared to controls, and a decrease in copper levels in PD patients. A decrease in the metal content in postmortem brain tissue was observed in AD and PD. In manuscripts using animal models that mimic AD and PD, it was included seven and three articles, respectively. Two of them have reported an increase in copper concentrations in AD model, and one in PD model. Finally, studies with laboratory animals have concluded that high copper levels are related to oxidative stress, neuroinflammation, mitochondrial dysfunction, changes in neurotransmitter levels, cell death, and reduced both cognitive and locomotor activity, which are also described in AD or PD.

Inflammation in Metal-Induced Neurological Disorders and Neurodegenerative Diseases

Essential metals play critical roles in maintaining human health as they participate in various physiological activities. Nonetheless, both excessive accumulation and deficiency of these metals may result in neurotoxicity secondary to neuroinflammation and the activation of microglia and astrocytes. Activation of these cells can promote the release of pro-inflammatory cytokines. It is well known that neuroinflammation plays a critical role in metal-induced neurotoxicity as well as the development of neurological disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). Initially seen as a defense mechanism, persistent inflammatory responses are now considered harmful. Astrocytes and microglia are key regulators of neuroinflammation in the central nervous system, and their excessive activation may induce sustained neuroinflammation. Therefore, in this review, we aim to emphasize the important role and molecular mechanisms underlying metal-induced neurotoxicity. Our objective is to raise the awareness on metal-induced neuroinflammation in neurological disorders. However, it is not only just neuroinflammation that different metals could induce; they can also cause harm to the nervous system through oxidative stress, apoptosis, and autophagy, to name a few. The primary pathophysiological mechanism by which these metals induce neurological disorders remains to be determined. In addition, given the various pathways through which individuals are exposed to metals, it is necessary to also consider the effects of co-exposure to multiple metals on neurological disorders.

Air pollution, glymphatic impairment, and Alzheimer's disease

Epidemiological evidence demonstrates a link between air pollution exposure and the onset and progression of cognitive impairment and Alzheimer's disease (AD). However, current understanding of the underlying pathophysiological mechanisms is limited. This opinion article examines the hypothesis that air pollution-induced impairment of glymphatic clearance represents a crucial etiological event in the development of AD. Exposure to airborne particulate matter (PM) leads to systemic inflammation and neuroinflammation, increased metal load, respiratory and cardiovascular dysfunction, and sleep abnormalities. All these factors are known to reduce the efficiency of glymphatic clearance. Rescuing glymphatic function by restricting the impact of causative agents, and improving sleep and cardiovascular system health, may increase the efficiency of waste metabolite clearance and subsequently slow the progression of AD. In sum, we introduce air pollution-mediated glymphatic impairment as an important mechanistic factor to be considered when interpreting the etiology and progression of AD as well as its responsiveness to therapeutic interventions.

Elemental Mapping in a Preclinical Animal Model Reveals White Matter Copper Elevation in the Acute Phase of Central Nervous System Trauma

Understanding the chemical events following trauma to the central nervous system could assist in identifying causative mechanisms and potential interventions to protect neural tissue. Here, we apply a partial optic nerve transection model of injury in rats and use synchrotron X-ray fluorescence microscopy (XFM) to perform elemental mapping of metals (K, Ca, Fe, Cu, Zn) and other related elements (P, S, Cl) in white matter tracts. The partial optic nerve injury model and spatial precision of microscopy allow us to obtain previously unattained resolution in mapping elemental changes in response to a primary injury and subsequent secondary effects. We observed significant elevation of Cu levels at multiple time points following the injury, both at the primary injury site and in neural tissue near the injury site vulnerable to secondary damage, as well as significant changes in Cl, K, P, S, and Ca. Our results suggest widespread metal dyshomeostasis in response to central nervous system trauma and that altered Cu homeostasis may be a specific secondary event in response to white matter injury. The findings highlight metal homeostasis as a potential point of intervention in limiting damage following nervous system injury.

Interaction mechanism of Cu+/Cu2+ on bovine serum albumin: Vitro simulation experiments by spectroscopic methods

Copper (Cu) is an essential trace element for organisms, while excessive concentration of Cu is toxic. In order to assess the toxicity risk of copper in different valences, FTIR, fluorescence, and UV-vis absorption techniques were conducted to study the interactions between either Cu⁺ or Cu²⁺ and bovine serum albumin (BSA) under vitro simulated physiological condition. The spectroscopic analysis demonstrated that the intrinsic fluorescence emitted by BSA could be quenched by Cu⁺/Cu²⁺ via static quenching with binding sites 0.88 and 1.12 for Cu⁺ and Cu²⁺, respectively. On the other hand, the constants of Cu⁺ and Cu²⁺ are 1.14 × 10³ L/mol and 2.08 × 10⁴ L/mol respectively. ΔH is negative whereas ΔS is positive, showing that the interaction between BSA and Cu⁺/Cu²⁺ was mainly driven by electrostatic force. In accordance with Föster's energy transfer theory, the binding distance r showed that the transition of energy from BSA to Cu⁺/Cu²⁺ is highly likely to happen. BSA conformation analyses indicated that the interactions between Cu⁺/Cu²⁺ and BSA could alter the secondary structure of proteins. Current study provides more information of the interaction between Cu⁺/Cu²⁺ and BSA, and reveals the potential toxicological effect of different speciation of copper at molecular level.

Lead exposure disturbs ATP7B-mediated copper export from brain barrier cells by inhibiting XIAP-regulated COMMD1 protein degradation

The brain barrier is an important structure for metal ion homeostasis. According to studies, lead (Pb) exposure disrupts the transportation of copper (Cu) through the brain barrier, which may cause impairment of the nervous system; however, the specific mechanism is unknown. The previous studies suggested the X-linked inhibitor of apoptosis (XIAP) is a sensor for cellular Cu level which mediate the degradation of the MURR1 domain-containing 1 (COMMD1) protein. XIAP/COMMD1 axis was thought to be an important regulator in Cu metabolism maintenance. In this study, the role of XIAP-regulated COMMD1 protein degradation in Pb-induced Cu disorders in brain barrier cells was investigated. Pb exposure significantly increased Cu levels in both cell types, according to atomic absorption technology testing. Western blotting and reverse transcription PCR (RT-PCR) showed that COMMD1 protein levels were significantly increased, whereas XIAP, ATP7A, and ATP7B protein levels were significantly decreased. However, there were no significant effects at the messenger RNA (mRNA) level (XIAP, ATP7A, and ATP7B). Pb-induced Cu accumulation and ATP7B expression were reduced when COMMD1 was knocked down by transient small interfering RNA (siRNA) transfection. In addition, transient plasmid transfection of XIAP before Pb exposure reduced Pb-induced Cu accumulation, increased COMMD1 protein levels, and decreased ATP7B levels. In conclusion, Pb exposure can reduce XIAP protein expression, increase COMMD1 protein levels, and specifically decrease ATP7B protein levels, resulting in Cu accumulation in brain barrier cells.

Nanoparticles as Powerful Tools for Crossing the Blood-brain Barrier

The blood-brain barrier (BBB) is considered an important protective barrier in the central nervous system (CNS). The barrier is mainly formed by endothelial cells (ECs) interconnected by various junctions such as tight junctions (TJs), gap junctions, and adherent junctions. They collectively constitute an intensive barrier to the transit of different substances into the brain, selectively permitting small molecules to pass through by passive movement but holding off large ones such as peptides and proteins to cross the brain. Hence some molecules selectively transfer across the BBB by active routes via transcytosis. The BBB also forms a barrier against neurotoxins as well as pathogenic agents. Although various CNS disorders like Alzheimer's disease (AD) and Parkinson's disease (PD) could hamper the integrity of the border. Nevertheless, the BBB acts as a barrier for CNS disorders treatment because it prevents the drugs from reaching their target in the CNS. In recent years, different strategies, including osmotic disruption of BBB or chemical modification of drugs, have been used to transfer the chemotherapeutic agents into brain substances. Nowadays, nanoparticles (NPs) have been used as an effective and non-invasive tool for drug delivery and diagnosis of CNS disorders. In this review, we discuss the structural characteristic of BBB, safe passageways to cross the BBB, and the relation of barrier lesions with different CNS disorders. In the end, we explore the progress in drug delivery, diagnosis, imaging, and treatment of CNS disorders using nanoparticles.

Exposure of metal toxicity in Alzheimer’s disease: An extensive review

Metals serve important roles in the human body, including the maintenance of cell structure and the regulation of gene expression, the antioxidant response, and neurotransmission. High metal uptake in the nervous system is harmful because it can cause oxidative stress, disrupt mitochondrial function, and impair the activity of various enzymes. Metal accumulation can cause lifelong deterioration, including severe neurological problems. There is a strong association between accidental metal exposure and various neurodegenerative disorders, including Alzheimer’s disease (AD), the most common form of dementia that causes degeneration in the aged. Chronic exposure to various metals is a well-known environmental risk factor that has become more widespread due to the rapid pace at which human activities are releasing large amounts of metals into the environment. Consequently, humans are exposed to both biometals and heavy metals, affecting metal homeostasis at molecular and biological levels. This review highlights how these metals affect brain physiology and immunity and their roles in creating harmful proteins such as β-amyloid and tau in AD. In addition, we address findings that confirm the disruption of immune-related pathways as a significant toxicity mechanism through which metals may contribute to AD.

In Vitro Models of Biological Barriers for Nanomedical Research

Nanoconstructs developed for biomedical purposes must overcome diverse biological barriers before reaching the target where playing their therapeutic or diagnostic function. In vivo models are very complex and unsuitable to distinguish the roles plaid by the multiple biological barriers on nanoparticle biodistribution and effect; in addition, they are costly, time-consuming and subject to strict ethical regulation. For these reasons, simplified in vitro models are preferred, at least for the earlier phases of the nanoconstruct development. Many in vitro models have therefore been set up. Each model has its own pros and cons: conventional 2D cell cultures are simple and cost-effective, but the information remains limited to single cells; cell monolayers allow the formation of cell–cell junctions and the assessment of nanoparticle translocation across structured barriers but they lack three-dimensionality; 3D cell culture systems are more appropriate to test in vitro nanoparticle biodistribution but they are static; finally, bioreactors and microfluidic devices can mimicking the physiological flow occurring in vivo thus providing in vitro biological barrier models suitable to reliably assess nanoparticles relocation. In this evolving context, the present review provides an overview of the most representative and performing in vitro models of biological barriers set up for nanomedical research.

Astrocytes: GABAceptive and GABAergic Cells in the Brain

Astrocytes, the most numerous glial cells in the brain, play an important role in preserving normal neural functions and mediating the pathogenesis of neurological disorders. Recent studies have shown that astrocytes are GABAceptive and GABAergic astrocytes express GABA_A receptors, GABA_B receptors, and GABA transporter proteins to capture and internalize GABA. GABAceptive astrocytes thus influence both inhibitory and excitatory neurotransmission by controlling the levels of extracellular GABA. Furthermore, astrocytes synthesize and release GABA to directly regulate brain functions. In this review, we highlight recent research progresses that support astrocytes as GABAceptive and GABAergic cells. We also summarize the roles of GABAceptive and GABAergic astrocytes that serve as an inhibitory node in the intercellular communication in the brain. Besides, we discuss future directions for further expanding our knowledge on the GABAceptive and GABAergic astrocyte signaling.

Do glutathione and copper interact to modify Alzheimer's disease pathogenesis?

Alzheimer's disease (AD) is a progressive neurodegenerative disorder first described in 1906 that is currently estimated to impact ∼40 million people worldwide. Extensive research activities have led to a wealth of information on the pathogenesis, hallmarks, and risk factors of AD; however, therapeutic options remain extremely limited. The large number of pathogenic factors that have been reported to potentially contribute to AD include copper dyshomeostasis as well as increased oxidative stress, which is related to alterations to molecular antioxidants like glutathione (GSH). While the individual roles of GSH and copper in AD have been studied by many research groups, their interactions have received relatively little attention, although they appear to interact and affect each other's regulation. Existing knowledge on how GSH-copper interactions may affect AD is sparse and lacks focus. This review first highlights the most relevant individual roles that GSH and copper play in physiology and AD, and then collects and assesses research concerning their interactions, in an effort to provide a more accessible and understandable picture of the role of GSH, copper, and their interactions in AD.

A review of the “metallome” within neurons and glia, as revealed by elemental mapping of brain tissue

It is now well established that transition metals, such as Iron (Fe), Copper (Cu), and Zinc (Zn) are necessary for healthy brain function. Although Fe, Cu, and Zn are essential to the brain, imbalances in the amount, distribution, or chemical form ("metallome") of these metals is linked to the pathology of numerous brain diseases or disorders. Despite the known importance of metal ions for both brain health and disease, the metallome that exists within specific types of brain cells is yet to be fully characterised. The aim of this mini-review is to present an overview of the current knowledge of the metallome found within specific brain cells (oligodendrocytes, astrocytes, microglia, and neurons), as revealed by direct elemental mapping techniques. It is hoped this review will foster continued research using direct elemental mapping techniques to fully characterise the brain cell metallome.

Essential Metals in the Brain and the Application of Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry for their Detection

Metals are natural component of the ecosystem present throughout the layers of atmosphere; their abundant expression in the brain indicates their importance in the central nervous system (CNS). Within the brain tissue, their distribution is highly compartmentalized, the pattern of which is determined by their primary roles. Bio-imaging of the brain to reveal spatial distribution of metals within specific regions has provided a unique understanding of brain biochemistry and architecture, linking both the structures and the functions through several metal mediated activities. Bioavailability of essential trace metal is needed for normal brain function. However, disrupted metal homeostasis can influence several biochemical pathways in different fields of metabolism and cause characteristic neurological disorders with a typical disease process usually linked with aberrant metal accumulations. In this review we give a brief overview of roles of key essential metals (Iron, Copper and Zinc) including their molecular mechanisms and bio-distribution in the brain as well as their possible involvement in the pathogenesis of related neurodegenerative diseases. In addition, we also reviewed recent applications of Laser Ablation Inductively Couple Plasma Mass Spectrophotometry (LA-ICP-MS) in the detection of both toxic and essential metal dyshomeostasis in neuroscience research and other related brain diseases.

Microglia and Astrocytes in Alzheimer's Disease in the Context of the Aberrant Copper Homeostasis Hypothesis

Evidence of copper's (Cu) involvement in Alzheimer's disease (AD) is available, but information on Cu involvement in microglia and astrocytes during the course of AD has yet to be structurally discussed. This review deals with this matter in an attempt to provide an updated discussion on the role of reactive glia challenged by excess labile Cu in a wide picture that embraces all the major processes identified as playing a role in toxicity induced by an imbalance of Cu in AD.

Linking Oxidative Stress and Proteinopathy in Alzheimer's Disease

Proteinopathy and excessive production of reactive oxygen species (ROS), which are the principal features observed in the Alzheimer’s disease (AD) brain, contribute to neuronal toxicity. β-amyloid and tau are the primary proteins responsible for the proteinopathy (amyloidopathy and tauopathy, respectively) in AD, which depends on ROS production; these aggregates can also generate ROS. These mechanisms work in concert and reinforce each other to drive the pathology observed in the aging brain, which primarily involves oxidative stress (OS). This, in turn, triggers neurodegeneration due to the subsequent loss of synapses and neurons. Understanding these interactions may thus aid in the identification of potential neuroprotective therapies that could be clinically useful. Here, we review the role of β-amyloid and tau in the activation of ROS production. We then further discuss how free radicals can influence structural changes in key toxic intermediates and describe the putative mechanisms by which OS and oligomers cause neuronal death.

Repeated oral administration of low doses of silver in mice: tissue distribution and effects on central nervous system

BACKGROUND

Widespread use of silver in its different forms raises concerns about potential adverse effects after ingestion, the main exposure route for humans. The aim of this study was to investigate in CD-1 (ICR) male mice the tissue distribution and in vivo effects of 4-week oral exposure to 0.25 and 1 mg Ag/kg bw 10 nm citrate coated silver nanoparticles (AgNPs) and 1 mg Ag/kg bw silver acetate (AgAc) at the end of treatment (EoT) and after 4 weeks of recovery.

RESULTS

There were no treatment-related clinical signs and mortality, and no significant effects on body and organ weights at the EoT and after recovery. Treatment-related changes in hematology and clinical chemistry were found after recovery, the most relevant being a dose-dependent lymphopenia and increased triglycerides in AgNP-treated mice, and increased levels of urea in all treated groups, associated with decreased albumin only in AgAc-treated mice. At the EoT the highest silver concentration determined by Triple Quadrupole ICP-MS analysis was found in the brain, followed by testis, liver, and spleen; much lower concentrations were present in the small intestine and kidney. Tissue silver concentrations were slightly higher after exposure to AgAc than AgNPs and dose dependent for AgNPs. After recovery silver was still present in the brain and testis, highlighting slow elimination. No histopathological changes and absence of silver staining by autometallography were observed in the organs of treated mice. At the EoT GFAP (astrocytes) immunoreactivity was significantly increased in the hippocampus of AgNP-treated mice in a dose-dependent manner and Iba1 (microglial cells) immunoreactivity was significantly increased in the cortex of 1 mg/kg bw AgNP-treated mice. After recovery, a significant reduction of Iba1 was observed in the cortex of all treated groups. TEM analysis of the hippocampus revealed splitting of basement membrane of the capillaries and swelling of astrocytic perivascular end-feet in 1 mg/kg bw AgNP- and AgAc-treated mice at the EoT.

CONCLUSIONS

Our study revealed accumulation and slow clearance of silver in the brain after oral administration of 10 nm AgNPs and AgAc at low doses in mice, associated with effects on glial cells and ultrastructural alterations of the Blood-Brain Barrier.

Superoxide Dismutase 1 in Health and Disease: How a Frontline Antioxidant Becomes Neurotoxic

Cu/Zn superoxide dismutase (SOD1) is a frontline antioxidant enzyme catalysing superoxide breakdown and is important for most forms of eukaryotic life. The evolution of aerobic respiration by mitochondria increased cellular production of superoxide, resulting in an increased reliance upon SOD1. Consistent with the importance of SOD1 for cellular health, many human diseases of the central nervous system involve perturbations in SOD1 biology. But far from providing a simple demonstration of how disease arises from SOD1 loss-of-function, attempts to elucidate pathways by which atypical SOD1 biology leads to neurodegeneration have revealed unexpectedly complex molecular characteristics delineating healthy, functional SOD1 protein from that which likely contributes to central nervous system disease. This review summarises current understanding of SOD1 biology from SOD1 genetics through to protein function and stability.

Markers of copper transport in the cingulum bundle in schizophrenia

Imaging and postmortem studies indicate that schizophrenia subjects exhibit abnormal connectivity in several white matter tracts, including the cingulum bundle. Copper chelators given to experimental animals damage myelin and myelin-producing oligodendrocytes, and the substantia nigra of schizophrenia subjects shows lower levels of copper, copper transporters, and copper-utilizing enzymes. This study aimed to elucidate the potential role of copper homeostasis in white matter pathology in schizophrenia. Protein levels of the copper transporters ATP7A and CTR1, and dysbindin-1, an upstream modulator of copper metabolism and schizophrenia susceptibility factor, were measured using Western blot analyses of the postmortem cingulum bundle of schizophrenia subjects (n=16) and matched controls (n=13). Additionally, the patient group was subdivided by treatment status: off- (n=8) or on-medication (n=8). Relationships between proteins from the current study were correlated among themselves and markers of axonal integrity previously measured in the same cohort. Schizophrenia subjects exhibited similar protein levels to controls, with no effect of antipsychotic treatment. The dysbindin-1A/1BC relationship was positive in controls and schizophrenia subjects; however, antipsychotic treatment appeared to reverse this relationship in a statistically different manner from that of controls and unmedicated subjects. The relationships between dysbindin-1A/neurofilament heavy and ATP7A/α-tubulin were positively correlated in the schizophrenia group that was significantly different from the lack of correlation in controls. Copper transporters and dysbindin-1 appear to be more significantly affected in the grey matter of schizophrenia subjects. However, the relationships among proteins in white matter may be more substantial and dependent on treatment status.

Copper Dyshomeostasis in Neurodegenerative Diseases-Therapeutic Implications

Copper is one of the most abundant basic transition metals in the human body. It takes part in oxygen metabolism, collagen synthesis, and skin pigmentation, maintaining the integrity of blood vessels, as well as in iron homeostasis, antioxidant defense, and neurotransmitter synthesis. It may also be involved in cell signaling and may participate in modulation of membrane receptor-ligand interactions, control of kinase and related phosphatase functions, as well as many cellular pathways. Its role is also important in controlling gene expression in the nucleus. In the nervous system in particular, copper is involved in myelination, and by modulating synaptic activity as well as excitotoxic cell death and signaling cascades induced by neurotrophic factors, copper is important for various neuronal functions. Current data suggest that both excess copper levels and copper deficiency can be harmful, and careful homeostatic control is important. This knowledge opens up an important new area for potential therapeutic interventions based on copper supplementation or removal in neurodegenerative diseases including Wilson's disease (WD), Menkes disease (MD), Alzheimer's disease (AD), Parkinson's disease (PD), and others. However, much remains to be discovered, in particular, how to regulate copper homeostasis to prevent neurodegeneration, when to chelate copper, and when to supplement it.

Chronic copper exposure leads to hippocampus oxidative stress and impaired learning and memory in male and female rats

Environmental and occupational exposures to copper (Cu) play a pivotal role in the etiology of some neurological diseases and reduced cognitive functions. However, the precise mechanisms of its effects on cognitive function have not been yet thoroughly established. In our study, we aimed to investigate the behavior and neurochemical alterations in hippocampus of male and female rats, chronically exposed to copper chloride (CuCl2) and the possible involvement of oxidative stress. Twenty-four rats, for each gender, were divided into control and three test groups (n = 6), and were injected intraperitoneally with saline (0.9% NaCl) or CuCl2 (0.25 mg/kg, 0.5 mg/kg and 1 mg/kg) for 8 weeks. After the treatment period, Y-maze test was used for the evaluation of spatial working memory and the Morris Water Maze (MWM) to test the spatial learning and memory. Biochemical determination of oxidative stress levels in hippocampus was performed. The main results of the present work are working memory impairment in spatial Y-maze which induced by higher Cu intake (1 mg/kg) in male and female rats. Also, In the MWM test, the spatial learning and memory were significantly impaired in rats treated with Cu at dose of 1 mg/kg. Additionally, markers of oxidative stress such as catalase, superoxide dismutase, lipid peroxidation products and nitric oxide levels were significantly altered following Cu treatments. These data propose that compromised behavior following Cu exposure is associated with increase in oxidative stress.

Self-Reporting Transposons Enable Simultaneous Readout of Gene Expression and Transcription Factor Binding in Single Cells

Cellular heterogeneity confounds in situ assays of transcription factor (TF) binding. Single-cell RNA sequencing (scRNA-seq) deconvolves cell types from gene expression, but no technology links cell identity to TF binding sites (TFBS) in those cell types. We present self-reporting transposons (SRTs) and use them in single-cell calling cards (scCC), a novel assay for simultaneously measuring gene expression and mapping TFBS in single cells. The genomic locations of SRTs are recovered from mRNA, and SRTs deposited by exogenous, TF-transposase fusions can be used to map TFBS. We then present scCC, which map SRTs from scRNA-seq libraries, simultaneously identifying cell types and TFBS in those same cells. We benchmark multiple TFs with this technique. Next, we use scCC to discover BRD4-mediated cell-state transitions in K562 cells. Finally, we map BRD4 binding sites in the mouse cortex at single-cell resolution, establishing a new method for studying TF biology in situ.

64Cu-ATSM/64Cu-Cl2 and their relationship to hypoxia in glioblastoma: a preclinical study

Background

Diacetyl-bis(N4-methylthiosemicarbazone), labeled with 64Cu (⁶⁴Cu-ATSM) has been suggested as a promising tracer for imaging hypoxia. However, various controversial studies highlighted potential pitfalls that may disable its use as a selective hypoxic marker. They also highlighted that the results may be tumor location dependent. Here, we first analyzed uptake of Cu-ATSM and its less lipophilic counterpart Cu-Cl₂ in the tumor over time in an orthotopic glioblastoma model. An in vitro study was also conducted to investigate the hypoxia-dependent copper uptake in tumor cells. We then further performed a comprehensive ex vivo study to compare ⁶⁴Cu uptake to hypoxic markers, specific cellular reactions, and also transporter expression.

Methods

μPET was performed 14 days (¹⁸F-FMISO), 15 days (⁶⁴Cu-ATSM and ⁶⁴Cu-Cl2), and 16 days (⁶⁴Cu-ATSM and ⁶⁴Cu-Cl₂) after C6 cell inoculation. Thereafter, the brains were withdrawn for further autoradiography and immunohistochemistry. C6 cells were also grown in hypoxic workstation to analyze cellular uptake of Cu complexes in different oxygen levels.

Results

In vivo results showed that Cu-ASTM and Cu-Cl2 accumulated in hypoxic areas of the tumors. Cu-ATSM also stained, to a lesser extent, non-hypoxic regions, such as regions of astrogliosis, with high expression of copper transporters and in particular DMT-1 and CTR1, and also characterized by the expression of elevated astrogliosis. In vitro results show that 64Cu-ATSM showed an increase in the uptake only in severe hypoxia at 0.5 and 0.2% of oxygen while for ⁶⁴Cu-Cl2, the cell retention was significantly increased at 5% and 1% of oxygen with no significant rise at lower oxygen percentages.

Conclusion

In the present study, we show that Cu-complexes undoubtedly accumulate in hypoxic areas of the tumors. This uptake may be the reflection of a direct dependency to a redox metabolism and also a reflection of hypoxic-induced overexpression of transporters. We also show that Cu-ATSM also stained non-hypoxic regions such as astrogliosis.

Multimodal Imaging Analyses of Brain Hippocampal Formation Reveal Reduced Cu and Lipid Content and Increased Lactate Content in Non-Insulin-Dependent Diabetic Mice

Non-insulin-dependent diabetes mellitus (NIDDM) is reported to increase the risk of cognitive impairment and dementia. However, the underlying mechanisms are not fully understood. While the brain homeostasis of metals and lipids is pivotal to maintaining energy metabolism and redox homeostasis for healthy brain function, no studies have reported hippocampal metal and biochemical changes in NIDDM. Therefore, we here utilized direct spectroscopic imaging to reveal the elemental distribution within the hippocampal subregions of an established murine model of NIDDM, db/db mice. In 26-week-old insulin resistant db/db mice, X-ray fluorescence microscopy revealed that the Cu content within the dentate gyrus and CA3 was significantly greater than that of the age-matched nondiabetic control mice. In addition, Fourier transform infrared (FTIR) spectroscopy analysis indicated a significant increase in the abundance of lactate within the corpus callosum (CC), dentate gyrus, CA1, and CA3 regions of diabetic db/db mice compared to that of the control, indicating altered energy metabolism. FTIR analysis also showed a significant decrease in the level of lipid methylene and ester within the CC of db/db mice. Furthermore, immunomicroscopy analyses demonstrated the increase in the level of glial fibrillary acidic protein expression and peri-vascular extravasation of IgG, indicating astrogliosis and blood-brain barrier dysfunction, respectively. These data suggest that astrogliosis-induced alterations in the supply of Cu, lipids, and energy substrates may be involved in the mechanisms of NIDDM-associated cognitive decline.

Low-dose oral copper treatment changes the hippocampal phosphoproteomic profile and perturbs mitochondrial function in a mouse model of Alzheimer's disease

Excessive copper can cause neurotoxicity and contribute to the development of some neurological diseases; however, copper neurotoxicity and the potential mechanisms remain poorly understood. We used proteomics and phosphoproteomics to quantify protein changes in the hippocampus of wild-type and 3xTg-AD mice, both of which were treated at 6 months of age with 2 months of drinking water with or without added copper chloride (0.13 ppm concentration). A total of 3960 unique phosphopeptides (5290 phosphorylation sites) from 1406 phosphoproteins was identified. Differentially expressed phosphoproteins involved neuronal and synaptic function, transcriptional regulation, energy metabolism and mitochondrial function. In addition, low-dose copper treatment of wild-type mice decreased hippocampal mitochondrial copy number, mitochondrial biogenesis and disrupted mitochondrial dynamics; these changes were associated with increased hydrogen peroxide production (H₂O₂), reduced cytochrome oxidase activity and decreased ATP content. In 3xTg-AD mice, identical low-dose oral copper treatment increased axonal degeneration, which was associated with altered phosphorylation of Camk2α at T286 and phosphorylation of mitogen-activated protein kinase (ERK1/2), which involved long-term potentiation (LTP) signaling. Mitochondrial dysfunction was mainly related to changes in phosphorylation levels of glycogen synthase kinase-3 beta (GSK3β) and serine/threonine-protein phosphatase 2B catalytic subunit alpha isoform (Ppp3ca), which involved mitochondrial biogenesis signaling. In sum, low-dose oral copper treatment changes the phosphorylation of key hippocampal proteins involved in mitochondrial, synaptic and axonal integrity. These data showing that excess of copper speeds some early events of AD changes observed suggest that excess circulating copper has the potential to perturb brain function of wild-type mice and exacerbate neurodegenerative changes in a mouse model of AD.

Analysis of Trace Elements in Human Brain: Its Aim, Methods, and Concentration Levels

Trace elements play a crucial role in many biochemical processes, mainly as components of vitamins and enzymes. Although small amounts of metal ions have protective properties, excess metal levels result in oxidative injury, which is why metal ion homeostasis is crucial for the proper functioning of the brain. The changes of their level in the brain have been proven to be a risk factor for Alzheimer's, Parkinson's, and Huntington's diseases, as well as amyotrophic lateral sclerosis. Therefore, it is currently an important application of various analytical methods. This review covers the most important of them: inductively coupled ground mass spectrometry (ICP-MS), flame-induced atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (GFAAS), optical emission spectrometry with excitation in inductively coupled plasma (ICP-OES), X-ray fluorescence spectrometry (XRF), and neutron activation analysis (NAA). Additionally, we present a summary of concentration values found by different research groups.

Copper signalling: causes and consequences

Copper-containing enzymes perform fundamental functions by activating dioxygen (O2) and therefore allowing chemical energy-transfer for aerobic metabolism. The copper-dependence of O2 transport, metabolism and production of signalling molecules are supported by molecular systems that regulate and preserve tightly-bound static and weakly-bound dynamic cellular copper pools. Disruption of the reducing intracellular environment, characterized by glutathione shortage and ambient Cu(II) abundance drives oxidative stress and interferes with the bidirectional, copper-dependent communication between neurons and astrocytes, eventually leading to various brain disease forms. A deeper understanding of of the regulatory effects of copper on neuro-glia coupling via polyamine metabolism may reveal novel copper signalling functions and new directions for therapeutic intervention in brain disorders associated with aberrant copper metabolism.

Copper chelators promote nonamyloidogenic processing of AβPP via MT1/2 /CREB-dependent signaling pathways in AβPP/PS1 transgenic mice

Copper is essential for the generation of reactive oxygen species (ROS), which are induced by amyloid-β (Aβ) aggregation; thus, the homeostasis of copper is believed to be a therapeutic target for Alzheimer's disease (AD). Although clinical trials of copper chelators show promise when applied in AD, the underlying mechanism is not fully understood. Here, we reported that copper chelators promoted nonamyloidogenic processing of AβPP through MT_1/2 /CREB-dependent signaling pathways. First, we found that the formation of Aβ plaques in the cortex was significantly reduced, and learning deficits were significantly improved in AβPP/PS1 transgenic mice by copper chelator tetrathiomolybdate (TM) administration. Second, TM and another copper chelator, bathocuproine sulfonate (BCS), promoted nonamyloidogenic processing of AβPP via inducing the expression of ADAM10 and the secretion of sAβPPα. Third, the inducible ADAM10 production caused by copper chelators can be blocked by a melatonin receptor (MT_1/2 ) antagonist (luzindole) and a MT₂ inhibitor (4-P-PDOT), suggesting that the expression of ADAM10 depends on the activation of MT_1/2 signaling pathways. Fourth, three of the MT_1/2 -downstream signaling pathways, Gq/PLC/MEK/ERK/CREB, Gs/cAMP/PKA/ERK/CREB and Gs/cAMP/PKA/CREB, were responsible for copper chelator-induced ADAM10 production. Based on these results, we conclude that copper chelators regulate the balance between amyloidogenic and nonamyloidogenic processing of AβPP via promoting ADAM10 expression through MT_1/2 /CREB-dependent signaling pathways.

Brain Nutrition: A Life Span Approach

Appraising success in meeting the world's nutritional needs has largely focused on infant mortality and anthropometric measurements with an emphasis on the first 1,000 days (conception to approximately age 2 years). This ignores the unique nutritional needs of the human brain. Although the intrauterine environment and the early postnatal years are important, equally critical periods follow during which the brain's intricate wiring is established for a lifetime of experience-driven remodeling. At the peak of this process during childhood, the human brain may account for 50% of the body's basal nutritional requirement. Thus, the consequences of proper nutritional management of the brain play out over a lifetime. Our motivation in preparing this review was to move the human brain into a more central position in the planning of nutritional programs. Here we review the macro- and micronutrient requirements of the human brain and how they are delivered, from conception to adulthood.

Neurotoxicity Linked to Dysfunctional Metal Ion Homeostasis and Xenobiotic Metal Exposure: Redox Signaling and Oxidative Stress

SIGNIFICANCE

Essential metals such as copper, iron, manganese, and zinc play a role as cofactors in the activity of a wide range of processes involved in cellular homeostasis and survival, as well as during organ and tissue development. Throughout our life span, humans are also exposed to xenobiotic metals from natural and anthropogenic sources, including aluminum, arsenic, cadmium, lead, and mercury. It is well recognized that alterations in the homeostasis of essential metals and an increased environmental/occupational exposure to xenobiotic metals are linked to several neurological disorders, including neurodegeneration and neurodevelopmental alterations. Recent Advances: The redox activity of essential metals is key for neuronal homeostasis and brain function. Alterations in redox homeostasis and signaling are central to the pathological consequences of dysfunctional metal ion homeostasis and increased exposure to xenobiotic metals. Both redox-active and redox-inactive metals trigger oxidative stress and damage in the central nervous system, and the exact mechanisms involved are starting to become delineated.

CRITICAL ISSUES

In this review, we aim to appraise the role of essential metals in determining the redox balance in the brain and the mechanisms by which alterations in the homeostasis of essential metals and exposure to xenobiotic metals disturb the cellular redox balance and signaling. We focus on recent literature regarding their transport, metabolism, and mechanisms of toxicity in neural systems.

FUTURE DIRECTIONS

Delineating the specific mechanisms by which metals alter redox homeostasis is key to understand the pathological processes that convey chronic neuronal dysfunction in neurodegenerative and neurodevelopmental disorders. Antioxid. Redox Signal. 28, 1669-1703.

A copper-deficient form of mutant Cu/Zn-superoxide dismutase as an early pathological species in amyotrophic lateral sclerosis

Dominant mutations in the gene encoding copper and zinc-binding superoxide dismutase (SOD1) cause amyotrophic lateral sclerosis (ALS). Abnormal accumulation of misfolded SOD1 proteins in spinal motoneurons is a major pathological hallmark in SOD1-related ALS. Dissociation of copper and/or zinc ions from SOD1 has been shown to trigger the protein aggregation/oligomerization in vitro, but the pathological contribution of such metal dissociation to the SOD1 misfolding still remains obscure. Here, we tested the relevance of the metal-deficient SOD1 in the misfolding in vivo by developing a novel antibody (anti-apoSOD), which exclusively recognized mutant SOD1 deficient in metal ions at its copper-binding site. Notably, anti-apoSOD-reactive species were detected specifically in the spinal cords of the ALS model mice only at their early pre-symptomatic stages but not at the end stage of the disease. The cerebrospinal fluid as well as the spinal cord homogenate of one SOD1-ALS patient also contained the anti-apoSOD-reactive species. Our results thus suggest that metal-deficiency in mutant SOD1 at its copper-binding site is one of the earliest pathological features in SOD1-ALS.

Redox metals homeostasis in multiple sclerosis and amyotrophic lateral sclerosis: a review

The effect of redox metals such as iron and copper on multiple sclerosis and amyotrophic lateral sclerosis has been intensively studied. However, the origin of these disorders remains uncertain. This review article critically describes the physiology of redox metals that produce oxidative stress, which in turn leads to cascades of immunomodulatory alteration of neurons in multiple sclerosis and amyotrophic lateral sclerosis. Iron and copper overload has been well established in motor neurons of these diseases’ lesions. On the other hand, the role of other metals like cadmium participating indirectly in the redox cascade of neurobiological mechanism is less studied. In the second part of this review, we focus on this less conspicuous correlation between cadmium as an inactive-redox metal and multiple sclerosis and amyotrophic lateral sclerosis, providing novel treatment modalities and approaches as future prospects.

Crossing the blood-brain barrier with nanoparticles

The blood-brain barrier (BBB) is one of the most essential protection mechanisms in the central nervous system (CNS). It selectively allows individual molecules such as small lipid-soluble molecules to pass through the capillary endothelial membrane while limiting the passage of pathogens or toxins. However, this protection mechanism is also a major obstacle during disease state since it dramatically hinders the drug delivery. In recent years, various tactics have been applied to assist drugs to cross the BBB including osmotic disruption of the BBB and chemical modification of prodrugs. Additionally, nanoparticles (NPs)-mediated drug delivery is emerging as an effective and non-invasive system to treat cerebral diseases. In this review, we will summarize and analyze the advances in the drug delivery across the BBB using various NPs in the last decade. The NPs will cover both traditional and novel nanocarriers. The traditional nanocarriers consist of poly(butylcyanoacrylate), poly(lactic-co-glycolic acid), poly(lactic acid) NPs, liposomes and inorganic systems. In the meanwhile, novel nanocarriers such as carbon quantum dots with their recent applications in drug delivery will also be introduced. In terms of significance, this review clearly depicts the BBB structure and comprehensively describes various NPs-mediated drug delivery systems according to different NPs species. Also, the BBB penetration mechanisms are concluded in general, emphasized and investigated in each drug delivery system.

Biometal Dyshomeostasis and Toxic Metal Accumulations in the Development of Alzheimer's Disease

Biometal dyshomeostasis and toxic metal accumulation are common features in many neurodegenerative disorders, including Alzheimer’s disease (AD), Parkinson’s disease, and Huntington’s disease. The neurotoxic effects of metal imbalance are generally associated with reduced enzymatic activities, elevated protein aggregation and oxidative stress in the central nervous system, in which a cascade of events lead to cell death and neurodegeneration. Although the links between biometal imbalance and neurodegenerative disorders remain elusive, a major class of endogenous proteins involved in metal transport has been receiving increasing attention over recent decades. The abnormal expression of these proteins has been linked to biometal imbalance and to the pathogenesis of AD. Here, we present a brief overview of the physiological roles of biometals including iron, zinc, copper, manganese, magnesium and calcium, and provide a detailed description of their transporters and their synergistic involvement in the development of AD. In addition, we also review the published data relating to neurotoxic metals in AD, including aluminum, lead, cadmium, and mercury.

Stratification of astrocytes in healthy and diseased brain

Astrocytes, a subtype of glial cells, come in variety of forms and functions. However, overarching role of these cell is in the homeostasis of the brain, be that regulation of ions, neurotransmitters, metabolism or neuronal synaptic networks. Loss of homeostasis represents the underlying cause of all brain disorders. Thus, astrocytes are likely involved in most if not all of the brain pathologies. We tabulate astroglial homeostatic functions along with pathological condition that arise from dysfunction of these glial cells. Classification of astrocytes is presented with the emphasis on evolutionary trails, morphological appearance and numerical preponderance. We note that, even though astrocytes from a variety of mammalian species share some common features, human astrocytes appear to be the largest and most complex of all astrocytes studied thus far. It is then an imperative to develop humanized models to study the role of astrocytes in brain pathologies, which is perhaps most abundantly clear in the case of glioblastoma multiforme.

Memory and Learning Dysfunction Following Copper Toxicity: Biochemical and Immunohistochemical Basis

The prototype disease of Cu toxicity in human is Wilson disease, and cognitive impairment is the presenting symptom of it. There is no study correlating Cu-induced excitotoxicity, apoptosis, and astrocytic reaction with memory dysfunction. We report excitotoxicity, apoptosis, and astrocytic reaction of the hippocampus and frontal cortex with memory dysfunction in rat model of Cu toxicity. Thirty-six rats were divided into group I (control) and group II (100 mg/kgBwt/day CuSO₄ orally). Y-maze was performed for memory and learning at 0, 30, 60, and 90 days. Frontal and hippocampal free Cu concentration, oxidative stress markers [glutathione (GSH), total antioxidant toxicity (TAC), and malondialdehyde (MDA)], and glutamate were measured by atomic absorption spectroscopy, spectrophotometry, and ELISA, respectively. N-methyl-D-aspartate receptors (NMDARs) NR1, NR2A, and NR2B were done by real-time polymerase chain reaction. Immunohistochemistry for caspase-3 and glial fibrillary acidic protein (GFAP) were done and quantified using the ImageJ software. The glutamate level in hippocampus was increased, and NMDAR expression was decreased at 30, 60, and 90 days in group II compared to group I. In the frontal cortex, glutamate was increased at 90 days, but NMDARs were not significantly different in group II compared to group I. Caspase-3 and GFAP expressions were also higher in group II compared to group I, and these changes were more marked in hippocampus than frontal cortex. These changes correlated with respective free tissue Cu, oxidative stress, and Y-maze attention score. Cu toxicity induces apoptosis and astrocytosis of the hippocampus and frontal cortex through direct or glutamate and oxidative stress pathways, and results in impaired memory and learning.

On the nature of the Cu-rich aggregates in brain astrocytes

Fulfilling a bevy of biological roles, copper is an essential metal for healthy brain function. Cu dyshomeostasis has been demonstrated to be involved in some neurological conditions including Menkes and Alzheimer's diseases. We have previously reported localized Cu-rich aggregates in astrocytes of the subventricular zone (SVZ) in rodent brains with Cu concentrations in the hundreds of millimolar. Metallothionein, a cysteine-rich protein critical to metal homeostasis and known to participate in a variety of neuroprotective and neuroregenerative processes, was proposed as a binding protein. Here, we present an analysis of metallothionein(1,2) knockout (MTKO) mice and age-matched controls using X-ray fluorescence microscopy. In large structures such as the corpus callosum, cortex, and striatum, there is no significant difference in Cu, Fe, or Zn concentrations in MTKO mice compared to age-matched controls. In the astrocyte-rich subventricular zone where Cu-rich aggregates reside, approximately 1/3 as many Cu-rich aggregates persist in MTKO mice resulting in a decrease in periventricular Cu concentration. Aggregates in both wild-type and MTKO mice show XANES spectra characteristic of CuxSy multimetallic clusters and have similar [S]/[Cu] ratios. Consistent with assignment as a CuxSy multimetallic cluster, the astrocyte-rich SVZ of both MTKO and wild-type mice exhibit autofluorescent bodies, though MTKO mice exhibit fewer. Furthermore, XRF imaging of Au-labeled lysosomes and ubiquitin demonstrates a lack of co-localization with Cu-rich aggregates suggesting they are not involved in a degradation pathway. Overall, these data suggest that Cu in aggregates is bound by either metallothionein-3 or a yet unknown protein similar to metallothionein.

Neurotoxicity of Copper

Copper is an essential trace metal that is required for several important biological processes, however, an excess of copper can be toxic to cells. Therefore, systemic and cellular copper homeostasis is tightly regulated, but dysregulation of copper homeostasis may occur in disease states, resulting either in copper deficiency or copper overload and toxicity. This chapter will give an overview on the biological roles of copper and of the mechanisms involved in copper uptake, storage, and distribution. In addition, we will describe potential mechanisms of the cellular toxicity of copper and copper oxide nanoparticles. Finally, we will summarize the current knowledge on the connection of copper toxicity with neurodegenerative diseases.