Metals in motor neuron diseases

FKBP52 in Neuronal Signaling and Neurodegenerative Diseases: A Microtubule Story

The FK506-binding protein 52 (FKBP52) belongs to a large family of ubiquitously expressed and highly conserved proteins (FKBPs) that share an FKBP domain and possess Peptidyl-Prolyl Isomerase (PPIase) activity. PPIase activity catalyzes the isomerization of Peptidyl-Prolyl bonds and therefore influences target protein folding and function. FKBP52 is particularly abundant in the nervous system and is partially associated with the microtubule network in different cell types suggesting its implication in microtubule function. Various studies have focused on FKBP52, highlighting its importance in several neuronal microtubule-dependent signaling pathways and its possible implication in neurodegenerative diseases such as tauopathies (i.e., Alzheimer disease) and alpha-synucleinopathies (i.e., Parkinson disease). This review summarizes our current understanding of FKBP52 actions in the microtubule environment, its implication in neuronal signaling and function, its interactions with other members of the FKBPs family and its involvement in neurodegenerative disease.

Metals in ALS TDP-43 Pathology

Amyotrophic lateral sclerosis (ALS), Alzheimer's disease, Parkinson's disease and similar neurodegenerative disorders take their toll on patients, caregivers and society. A common denominator for these disorders is the accumulation of aggregated proteins in nerve cells, yet the triggers for these aggregation processes are currently unknown. In ALS, protein aggregation has been described for the SOD1, C9orf72, FUS and TDP-43 proteins. The latter is a nuclear protein normally binding to both DNA and RNA, contributing to gene expression and mRNA life cycle regulation. TDP-43 seems to have a specific role in ALS pathogenesis, and ubiquitinated and hyperphosphorylated cytoplasmic inclusions of aggregated TDP-43 are present in nerve cells in almost all sporadic ALS cases. ALS pathology appears to include metal imbalances, and environmental metal exposure is a known risk factor in ALS. However, studies on metal-to-TDP-43 interactions are scarce, even though this protein seems to have the capacity to bind to metals. This review discusses the possible role of metals in TDP-43 aggregation, with respect to ALS pathology.

Amyotrophic Lateral Sclerosis After Exposure to Manganese from Traditional Medicine Procedures in Kenya

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by motor neuron loss and widespread muscular atrophy. Despite intensive investigations on genetic and environmental factors, the cause of ALS remains unknown. Recent data suggest a role for metal exposures in ALS causation. In this study we present a patient who developed ALS after a traditional medical procedure in Kenya. The procedure involved insertion of a black metal powder into several subcutaneous cuts in the lower back. Four months later, general muscle weakness developed. Clinical and electrophysiological examinations detected widespread denervation consistent with ALS. The patient died from respiratory failure less than a year after the procedure. Scanning electron microscopy and X-ray diffraction analyses identified the black powder as potassium permanganate (KMnO4). A causative relationship between the systemic exposure to KMnO4 and ALS development can be suspected, especially as manganese is a well-known neurotoxicant previously found to be elevated in cerebrospinal fluid from ALS patients. Manganese neurotoxicity and exposure routes conveying this toxicity deserve further attention.

Role of Oxidative Stress in the Pathogenesis of Amyotrophic Lateral Sclerosis: Antioxidant Metalloenzymes and Therapeutic Strategies

Amyotrophic lateral sclerosis (ALS) affects motor neurons in the cerebral cortex, brainstem and spinal cord and leads to death due to respiratory failure within three to five years. Although the clinical symptoms of this disease were first described in 1869 and it is the most common motor neuron disease and the most common neurodegenerative disease in middle-aged individuals, the exact etiopathogenesis of ALS remains unclear and it remains incurable. However, free oxygen radicals (i.e., molecules containing one or more free electrons) are known to contribute to the pathogenesis of this disease as they very readily bind intracellular structures, leading to functional impairment. Antioxidant enzymes, which are often metalloenzymes, inactivate free oxygen radicals by converting them into a less harmful substance. One of the most important antioxidant enzymes is Cu²⁺Zn²⁺ superoxide dismutase (SOD1), which is mutated in 20% of cases of the familial form of ALS (fALS) and up to 7% of sporadic ALS (sALS) cases. In addition, the proper functioning of catalase and glutathione peroxidase (GPx) is essential for antioxidant protection. In this review article, we focus on the mechanisms through which these enzymes are involved in the antioxidant response to oxidative stress and thus the pathogenesis of ALS and their potential as therapeutic targets.

AMPA receptor contribution to methylmercury-mediated alteration of intracellular Ca2+ concentration in human induced pluripotent stem cell motor neurons

α motor neurons (MNs) are a target of the environmental neurotoxicant methylmercury (MeHg), accumulating MeHg and subsequently degenerating. In mouse spinal cord MN cultures, MeHg increased intracellular Ca²⁺ [Ca²⁺]_i; the AMPA receptor (AMPAR) antagonist CNQX delayed the increase in [Ca²⁺]_i, implicating the role of AMPARs in this response. Here we used human induced pluripotent stem cell-derived MNs (hiPSC-MNs), to characterize the role of MN AMPARs in MeHg neurotoxicity. Acute exposure to MeHg (0.1, 0.2, 0.5, 1 and 1.5 μM), fura-2 microfluorimetry, and a standard cytotoxicity assay, were used to examine MN regulation of [Ca²⁺]_i, and cytotoxicity, respectively. Contribution of Ca²⁺-permeable and impermeable AMPARs was compared using either CNQX, or the Ca²⁺-permeable AMPAR antagonist N-acetyl spermine (NAS). MeHg-induced cytotoxicity was evaluated following a 24 h delay subsequent to 1 h exposure of hiPSC-MNs. MeHg caused a characteristic biphasic increase in [Ca²⁺]_i, the onset of which was concentration-dependent; higher MeHg concentrations hastened onset of both phases. CNQX significantly delayed MeHg's effect on onset time of both phases. In contrast, NAS significantly delayed only the 2nd phase increase in fura-2 fluorescence. Exposure to MeHg for 1 h followed by a 24 h recovery period caused a concentration-dependent incidence of cell death. These results demonstrate for the first time that hiPSC-derived MNs are highly sensitive to effects of MeHg on [Ca²⁺]_i, and cytotoxicity, and that both Ca²⁺-permeable and impermeable AMPARs contribute the elevations in [Ca²⁺]_i.

The molecular mechanisms of copper metabolism and its roles in human diseases

Copper is an essential element in cells; it can act as either a recipient or a donor of electrons, participating in various reactions. However, an excess of copper ions in cells is detrimental as these copper ions can generate free radicals and increase oxidative stress. In multicellular organisms, copper metabolism involves uptake, distribution, sequestration, and excretion, at both the cellular and systemic levels. Mammalian enterocytes take in bioavailable copper ions from the diet in a Ctr1-dependent manner. After incorporation, cuprous ions are delivered to ATP7A, which pumps Cu⁺ from enterocytes into the blood. Copper ions arrive at the liver through the portal vein and are incorporated into hepatocytes by Ctr1. Then, Cu⁺ can be secreted into the bile or the blood via the Atox1/ATP7B/ceruloplasmin route. In the bloodstream, this micronutrient can reach peripheral tissues and is again incorporated by Ctr1. In peripheral tissue cells, cuprous ions are either sequestrated by molecules such as metallothioneins or targeted to utilization pathways by chaperons such as Atox1, Cox17, and CCS. Copper metabolism must be tightly controlled in order to achieve homeostasis and avoid disorders. A hereditary or acquired copper unbalance, including deficiency, overload, or misdistribution, may cause or aggravate certain diseases such as Menkes disease, Wilson disease, neurodegenerative diseases, anemia, metabolic syndrome, cardiovascular diseases, and cancer. A full understanding of copper metabolism and its roles in diseases underlies the identification of novel effective therapies for such diseases.

The influence of metallothionein treatment and treadmill running exercise on disease onset and survival in SOD1G93A amyotrophic lateral sclerosis mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease, characterised by the degeneration of motor neurons innervating skeletal muscle. The mechanisms underlying neurodegeneration in ALS are not yet fully elucidated, and with current therapeutics only able to extend lifespan by a matter of months there is a clear need for novel therapies to increase lifespan and patient quality of life. Here, we evaluated whether moderate-intensity treadmill exercise and/or treatment with metallothionein-2 (MT2), a neuroprotective protein, could improve survival, behavioural or neuropathological outcomes in SOD1^G93A familial ALS mice. Six-week-old female SOD1^G93A mice were allocated to one of four treatment groups: MT2 injection, i.m.; moderate treadmill exercise; neither MT2 nor exercise; or both MT2 and exercise. MT2-treated mice survived around 3% longer than vehicle-treated mice, with this mild effect reaching statistical significance in Cox proportional hazards analysis once adjusted for potential confounders. Mixed model body weight trajectories over time indicated that MT2-treated mice, with or without exercise, reached maximum body weight at a later age, suggesting a delay in disease onset of around 4% compared to saline-treated mice. Exercise alone did not significantly increase survival or delay disease onset, and neither exercise nor MT2 substantially ameliorated gait abnormalities or muscle strength loss. We conclude that neither exercise nor MT2 treatment was detrimental in female SOD1^G93A mice, and further study could determine whether the mild effect of peripheral MT2 administration on disease onset and survival could be improved via direct administration of MT2 to the central nervous system.

Molecular Mechanisms of TDP-43 Misfolding and Pathology in Amyotrophic Lateral Sclerosis

TAR DNA binding protein 43 (TDP-43) is a versatile RNA/DNA binding protein involved in RNA-related metabolism. Hyper-phosphorylated and ubiquitinated TDP-43 deposits act as inclusion bodies in the brain and spinal cord of patients with the motor neuron diseases: amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). While the majority of ALS cases (90-95%) are sporadic (sALS), among familial ALS cases 5-10% involve the inheritance of mutations in the TARDBP gene and the remaining (90-95%) are due to mutations in other genes such as: C9ORF72, SOD1, FUS, and NEK1 etc. Strikingly however, the majority of sporadic ALS patients (up to 97%) also contain the TDP-43 protein deposited in the neuronal inclusions, which suggests of its pivotal role in the ALS pathology. Thus, unraveling the molecular mechanisms of the TDP-43 pathology seems central to the ALS therapeutics, hence, we comprehensively review the current understanding of the TDP-43's pathology in ALS. We discuss the roles of TDP-43's mutations, its cytoplasmic mis-localization and aberrant post-translational modifications in ALS. Also, we evaluate TDP-43's amyloid-like in vitro aggregation, its physiological vs. pathological oligomerization in vivo, liquid-liquid phase separation (LLPS), and potential prion-like propagation propensity of the TDP-43 inclusions. Finally, we describe the various evolving TDP-43-induced toxicity mechanisms, such as the impairment of endocytosis and mitotoxicity etc. and also discuss the emerging strategies toward TDP-43 disaggregation and ALS therapeutics.

Alterations to the Intestinal Microbiome and Metabolome of Pimephales promelas and Mus musculus Following Exposure to Dietary Methylmercury

Mercury is a global contaminant, which may be microbially transformed into methylmercury (MeHg), which bioaccumulates. This results in potentially toxic body burdens in high trophic level organisms in aquatic ecosystems and maternal transfer to offspring. We previously demonstrated effects on developing fish including hyperactivity, altered time-to-hatch, reduced survival, and dysregulation of the dopaminergic system. A link between gut microbiota and central nervous system function in teleosts has been established with implications for behavior. We sequenced gut microbiomes of fathead minnows exposed to dietary MeHg to determine microbiome effects. Dietary exposures were repeated with adult CD-1 mice. Metabolomics was used to screen for metabolome changes in mouse brain and larval fish, and results indicate effects on lipid metabolism and neurotransmission, supported by microbiome data. Findings suggest environmentally relevant exposure scenarios may cause xenobiotic-mediated dysbiosis of the gut microbiome, contributing to neurotoxicity. Furthermore, small-bodied teleosts may be a useful model species for studying certain types of neurodegenerative diseases, in lieu of higher vertebrates.

Ultrasonic energy enhanced the efficiency of advance extraction methodology for enrichment of trace level of copper in serum samples of patients having neurological disorders

An innovative dual dispersive ionic liquid based on ultrasound assisted microextraction (UDIL-μE), for the enrichment of trace levels of copper ion (Cu²⁺), in serum (blood) of patients suffering from different neurological disorders. The enriched metal ions were subjected to flame atomic absorption spectrometry (FAAS). In the UDIL-μE method, the extraction solvent, ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [C₄mim][PF₆], was dispersed into the aqueous samples using an ultrasonic bath. The(PAN) 1-(2-pyridylazo)-2-naphthol was used as ligand for the complexation of Cu ion in IL (as extracting solvent). The various variables such as sonication time, pH, concentration of complexing agent, time and rate of centrifugation, IL volume that affect the extraction process were optimized. The enhancement factor (EF) and detection limit (LOD) was found under favorable condition was 31 and 0.36μgL^-1, respectively. Reliability of the proposed method was checked by relative standard deviation (%RSD), which was found to be <5%. The accuracy of developed procedure was assured by using certified reference material (CRM) of blood serum. The developed procedure was applied successfully to the analysis of concentration of Cu ion in blood serum of different neurological disorders subjects and referents of same age group. It was observed that the levels of Cu ion was two folds higher in serum samples of neurological disorders patients as related to normal referents of same age group.

Effects of methylmercury on spinal cord afferents and efferents-A review

Methylmercury (MeHg) is an environmental neurotoxicant of public health concern. It readily accumulates in exposed humans, primarily in neuronal tissue. Exposure to MeHg, either acutely or chronically, causes severe neuronal dysfunction in the central nervous system and spinal neurons; dysfunction of susceptible neuronal populations results in neurodegeneration, at least in part through Ca2+-mediated pathways. Biochemical and morphologic changes in peripheral neurons precede those in central brain regions, despite the fact that MeHg readily crosses the blood-brain barrier. Consequently, it is suggested that unique characteristics of spinal cord afferents and efferents could heighten their susceptibility to MeHg toxicity. Transient receptor potential (TRP) ion channels are a class of Ca2+-permeable cation channels that are highly expressed in spinal afferents, among other sensory and visceral organs. These channels can be activated in numerous ways, including directly via chemical irritants or indirectly via Ca2+ release from intracellular storage organelles. Early studies demonstrated that MeHg interacts with heterologous TRP channels, though definitive mechanisms of MeHg toxicity on sensory neurons may involve more complex interaction with, and among, differentially-expressed TRP populations. In spinal efferents, glutamate receptors of the N-methyl-D-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and possibly kainic acid (KA) classes are thought to play a major role in MeHg-induced neurotoxicity. Specifically, the Ca2+-permeable AMPA receptors, which are abundant in motor neurons, have been identified as being involved in MeHg-induced neurotoxicity. In this review, we will describe the mechanisms that could contribute to MeHg-induced spinal cord afferent and efferent neuronal degeneration, including the possible mediators, such as uniquely expressed Ca2+-permeable ion channels.

Methylmercury can induce Parkinson's-like neurotoxicity similar to 1-methyl-4- phenylpyridinium: a genomic and proteomic analysis on MN9D dopaminergic neuron cells

Exposure to environmental chemicals has been implicated as a possible risk factor for the development of neurodegenerative diseases. Our previous study showed that methylmercury (MeHg) exposure can disrupt synthesis, uptake and metabolism of dopamine similar to 1-methyl-4-phenylpyridinium (MPP(+)). The objective of this study was to investigate the effects of MeHg exposure on gene and protein profiles in a dopaminergic MN9D cell line. MN9D cells were treated with MeHg (1-5 μM) and MPP(+) (10-40 μM) for 48 hr. Real-time PCR Parkinson's disease (PD) arrays and high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) were performed for the analysis. PD PCR array results showed that 19% genes were significantly changed in the 2.5 μM MeHg treated cells, and 39% genes were changed in the 5 μM MeHg treated cells. In comparison, MPP(+) treatment (40 µM) resulted in significant changes in 25% genes. A total of 15 common genes were altered by both MeHg and MPP(+), and dopaminergic signaling transduction was the most affected pathway. Proteomic analysis identified a total of 2496 proteins, of which 188, 233 and 395 proteins were differentially changed by 1 μM and 2.5 μM MeHg, and MPP(+) respectively. A total of 61 common proteins were changed by both MeHg and MPP(+) treatment. The changed proteins were mainly involved in energetic generation-related metabolism pathway (propanoate metabolism, pyruvate metabolism and fatty acid metabolism), oxidative phosphorylation, proteasome, PD and other neurodegenerative disorders. A total of 7 genes/proteins including Ube2l3 (Ubiquitin-conjugating enzyme E2 L3) and Th (Tyrosine 3-monooxygenase) were changed in both genomic and proteomic analysis. These results suggest that MeHg and MPP(+) share many similar signaling pathways leading to the pathogenesis of PD and other neurodegenerative diseases.

Metals and Neurodegeneration

Metals play important roles in the human body, maintaining cell structure and regulating gene expression, neurotransmission, and antioxidant response, to name a few. However, excessive metal accumulation in the nervous system may be toxic, inducing oxidative stress, disrupting mitochondrial function, and impairing the activity of numerous enzymes. Damage caused by metal accumulation may result in permanent injuries, including severe neurological disorders. Epidemiological and clinical studies have shown a strong correlation between aberrant metal exposure and a number of neurological diseases, including Alzheimer’s disease, amyotrophic lateral sclerosis, autism spectrum disorders, Guillain–Barré disease, Gulf War syndrome, Huntington’s disease, multiple sclerosis, Parkinson’s disease, and Wilson’s disease. Here, we briefly survey the literature relating to the role of metals in neurodegeneration.

A novel Schiff-base as a Cu(II) ion fluorescent sensor in aqueous solution

A new fluorescent Cu(II) sensor (L) obtained from the Schiff base of 5,5'-methylene-bis-salicylaldehyde with amidol (2,4-diaminophenol) was synthesized and characterized by FT-IR, MS, (1)H NMR, (13)C NMR techniques. In the presence of pH 6.5 (KHPO4-Na2HPO4) buffer solutions, copper reacted with L to form a stable 2:1 complex. Fluorescence spectroscopic study showed that Schiff base is highly sensitive towards Cu(II) over other metal ions (K(+), Na(+), Al(3+), Ni(2+), Co(2+), Fe(3+), Zn(2+), Pb(2+)) in DMSO/H2O (30%, v/v). The sensor L was successfully applied to the determination of copper in standard reference material. The structural properties and molecular orbitals of the complex formed between L and Cu(2+) ions were also investigated using quantum chemical computations.

Iron and copper in progressive demyelination--New lessons from Skogholt's disease

The pathophysiological mechanisms of progressive demyelinating disorders including multiple sclerosis are incompletely understood. Increasing evidence indicates a role for trace metals in the progression of several neurodegenerative disorders. The study of Skogholt disease, a recently discovered demyelinating disease affecting both the central and peripheral nervous system, might shed some light on the mechanisms underlying demyelination. Cerebrospinal fluid iron and copper concentrations are about four times higher in Skogholt patients than in controls. The transit into cerebrospinal fluid of these elements from blood probably occurs in protein bound form. We hypothesize that exchangeable fractions of iron and copper are further transferred from cerebrospinal fluid into myelin, thereby contributing to the pathogenesis of demyelination. Free or weakly bound iron and copper ions may exert their toxic action on myelin by catalyzing production of oxygen radicals. Similarities to demyelinating processes in multiple sclerosis and other myelinopathies are discussed.

Interaction of four low dose toxic metals with essential metals in brain, liver and kidneys of mice on sub-chronic exposure

This study reports on interactions between low dose toxic and essential metals. Low dose Pb (0.01mg/L), Hg (0.001mg/L), Cd (0.005mg/L) and As (0.01mg/L) were administered singly to four groups of 3-week old mice for 120 days. Pb exposure increased brain Mg and Cu by 55.5% and 266%, respectively. Increased brain Mg resulted from metabolic activity of brain to combat insults, whiles Cu overload was due to alteration and dysfunction of CTR1 and ATP7A molecules. Reduction of liver Ca by 56.0% and 31.6% (on exposure to As and Cd, respectively) resulted from inhibition of Ca-dependent ATPase in nuclei and endoplasmic reticulum through binding with thiol groups. Decreased kidney Mg, Ca and Fe was due to uptake of complexes of As and Cd with thiol groups from proximal tubular lumen. At considerably low doses, the study establishes that, toxic metals disturb the homeostasis of essential metals.

Studies on fate and toxicity of nanoalumina in male albino rats

The work aimed to evaluate the nanoalumina toxicity on the histological architecture, some haematological and biochemical aspects in male albino rats, during acute and sublethal experiments. Rats, in acute experiments, were injected with a single-acute dose of 3.9 g or 6.4 g or 8.5 g of aluminium oxide (Al2O3) kg−1, whereas those of sublethal were injected with 1.3 g of Al2O3 kg−1 2 days−1. One-way analysis of variance indicated that injected doses and the experimental periods were significantly affected by haemoglobin (Hb) content; haematocrit value (Hct); white blood cell (WBC) count; blood platelet (Plt) count; mean corpuscular volume (MCV); mean corpuscular Hb (MCH) and MCH concentration (MCHC). In acute experiments, Hct, WBC count, MCV and Plt were significantly higher than the corresponding controls, whereas Hb, MCH and MCHC markedly decreased. In comparison with the related controls after 1, 3 and 7 days post-injection, red blood cell count, Hb, Hct, WBC count, Plt and MCV were significantly increased, but begun to decrease after 14 or/and 28 days and were associated with a marked decrease in MCH and MCHC. In serum of rats injected with acute or sublethal dose, the concentrations of total protein (TP) and total lipid (TL) were significantly lesser than the corresponding controls, whereas the levels of urea, uric acid, creatinine and the activities of aspartate aminotransferase and alanine aminotransferase were markedly increased. The injected doses were directly proportional with all the studied biochemical parameter, except the TL and TP that exhibited a negative correlation. Histologically, the highest acute and sublethal doses of nanoalumina caused hepatic irregular disarray, necrosis to the hepatic and Kupffer cells that are associated with congested blood sinusoids. The renal tissues characterized by the appearance of inter-tubular congestion that is accompanied by the dilation of the vascular glomeruli that completely occupied Bowman’s capsule and accompanied with partial disappearance of the renal tubule’s brush border. The brain showed a progressive degeneration of neurons in both the experiments.

Protective efficacy of selenite against lead-induced neurotoxicity in Caenorhabditis elegans

Background

Selenium is an essential micronutrient that has a narrow exposure window between its beneficial and toxic effects. This study investigated the protective potential of selenite (IV) against lead (Pb(II))-induced neurotoxicity in Caenorhabditis elegans.

Principal Findings

The results showed that Se(IV) (0.01 µM) pretreatment ameliorated the decline of locomotion behaviors (frequencies of body bends, head thrashes, and reversal ) of C. elegans that are damaged by Pb(II) (100 µM) exposure. The intracellular ROS level of C. elegans induced by Pb(II) exposure was significantly lowered by Se(IV) supplementation prior to Pb(II) exposure. Finally, Se(IV) protects AFD sensory neurons from Pb(II)-induced toxicity.

Conclusions

Our study suggests that Se(IV) has protective activities against Pb(II)-induced neurotoxicity through its antioxidant property.

Metal concentrations in cerebrospinal fluid and blood plasma from patients with amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal degenerative disorder of motor neurons. The cause of this degeneration is unknown, and different causal hypotheses include genetic, viral, traumatic and environmental mechanisms. In this study, we have analyzed metal concentrations in cerebrospinal fluid (CSF) and blood plasma in a well-defined cohort (n = 17) of ALS patients diagnosed with quantitative electromyography. Metal analyses were performed with high-resolution inductively coupled plasma mass spectrometry. Statistically significant higher concentrations of manganese, aluminium, cadmium, cobalt, copper, zinc, lead, vanadium and uranium were found in ALS CSF compared to control CSF. We also report higher concentrations of these metals in ALS CSF than in ALS blood plasma, which indicate mechanisms of accumulation, e.g. inward directed transport. A pattern of multiple toxic metals is seen in ALS CSF. The results support the hypothesis that metals with neurotoxic effects are involved in the pathogenesis of ALS.

The relevance of metals in the pathophysiology of neurodegeneration, pathological considerations

Neurodegenerative disorders are featured by a variety of pathological conditions that share similar critical processes, such as oxidative stress, free radical activity, proteinaceous aggregations, mitochondrial dysfunctions, and energy failure. They are mediated or triggered by an imbalance of metal ions leading to changes of critical biological systems and initiating a cascade of events finally leading to neurodegeneration and cell death. Their causes are multifactorial, and although the source of the shift in oxidative homeostasis is still unclear, current evidence points to changes in the balance of redox transition metals, especially iron, copper, and other trace metals. They are present at elevated levels in Alzheimer disease, Parkinson disease, multisystem atrophy, etc., while in other neurodegenerative disorders, copper, zinc, aluminum, and manganese are involved. This chapter will review the recent advances of the role of metals in the pathogenesis and pathophysiology of major neurodegenerative diseases and discuss the use of chelating agents as potential therapies for metal-related disorders.

Interaction of heme proteins with anionic polyfluorene: insights into physiological effects, folding events, and inhibition activity

Because of the toxicity caused by the heme redox-active iron proteins, their elevated levels, localization, and accumulation in the brain, many forms of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, occur as a result of which the brain becomes vulnerable to oxidative stress, ultimately resulting in neuronal death. An anionic water-soluble conjugated polyfluorene derivative poly(9,9-bis(6-sulfate hexyl) fluorene-alt-1,4-phenylene) sodium salt (P1) that binds Fe³⁺ proteins with very high selectivity and sensitivity is reported here. The photophysical properties of P1 were modified by the interaction with ferric heme-containing proteins cytochrome c (Cc), methemoglobin (MetHb), and hemin. P1 was found to be highly sensitive toward Fe³⁺ heme proteins as compared to nonmetalloproteins. We observed that the respective activities of ferric heme proteins were inhibited and proteins were unfolded, due to modification in their heme microenvironment in the presence of the polymer P1. The observations reported in this article provide the first example for the use of a water-soluble conjugated polymer in applications, such as (1) to detect small quantities of iron proteins in aqueous medium/physiological condition with the highest K(sv) values of 2.27 × 10⁸ M⁻¹ for Cc, 3.81 × 10⁷ M⁻¹ for MetHb, and 5.31 × 10⁷ M⁻¹ for hemin; (2) to study the physiological effects of heme metalloproteins; (3) to visualize the folding events in real time; and (4) the inhibition activity of metalloproteins can be selectively studied using a conjugated polymer based assay system rapidly without interference from nonmetalloproteins at biological pH. All this is achieved by generating optical events, taking advantage of the bright fluorescence of anionic polyfluorene P1 in this case, that can be observed and monitored by modification in the absorption and emission color in real time.

Manganese in cerebrospinal fluid and blood plasma of patients with amyotrophic lateral sclerosis

Neurotoxic properties of manganese (Mn) are well documented. It is less known that Mn contributes to the development of neurodegenerative disorders in the general population. This study presents Mn data from patients with amyotrophic lateral sclerosis (ALS) in a well-defined cohort diagnosed by electrophysiological methods. Cerebrospinal fluid (CSF) and plasma were collected from patients and controls. Mn concentrations were analyzed by high-resolution inductively coupled plasma mass spectrometry. Concentrations of Mn were significantly higher in ALS CSF (median 5.67 μg/L) than in CSF from controls (median 2.08 μg/L). Also, ALS CSF Mn concentrations were higher than ALS plasma Mn concentrations (median 0.91 μg/L), suggesting transport of Mn into the central nervous system. The properties of barrier systems between blood and the brain are discussed and the possibility of Mn accumulation contributing to the relentless course of ALS is introduced.

Mercury in the spinal cord after inhalation of mercury

Amyotrophic lateral sclerosis (ALS) affects anterior horn cells of the spinal cord causing an indolent slow and steady deterioration of muscle strength leading inevitably to death in respiratory failure. ALS is a model condition for neurodegenerative disorders. Exposure to different agents dispersed in the environment has been suggested to cause neurodegeneration but no convincing evidence for such a link has yet been presented. Respiratory exposure to metallic mercury (Hg(0)) from different sources may be suspected. Body distribution of metallic mercury is fast and depends on solubility properties. Routes of transport, metabolism, excretion and biological half-life determine the overall toxic effects. Inhalation experiments were performed in 1984 where small marmoset monkeys (Callithrix jacchus) were exposed to (203) Hg(0 vapour) mixed into the breathing air (4-5 μg/l). After 1 hr of exposure, they were killed and whole body autoradiograms prepared to study the distribution of mercury within organs. Autoradiograms showed that Hg was deposited inside the spinal cord. Areas of enhanced accumulation anatomically corresponding to motor nuclei could be observed. This study describes a reinvestigation, with new emphasis on the spinal cord, of these classical metal exposure data in a primate, focusing on their relevance for the causation of neurodegenerative disorders. A comparison with more recent rodent experiments with similar findings is included. The hypothesis that long-time low-dose respiratory exposure to metals, for example, Hg, contributes to neurodegenerative disorders is forwarded and discussed.

Metallothioneins and copper metabolism are candidate therapeutic targets in Huntington's disease

HD (Huntington's disease) is caused by a polyQ (polyglutamine) expansion in the huntingtin protein, which leads to protein misfolding and aggregation of this protein. Abnormal copper accumulation in the HD brain was first reported more than 15 years ago. Recent findings show that copper-regulatory genes are induced during HD and copper binds to an N-terminal fragment of huntingtin, supporting the involvement of abnormal copper metabolism in HD. We have demonstrated that in vitro copper accelerates the fibrillization of an N-terminal fragment of huntingtin with an expanded polyQ stretch (httExon1). As we found that copper also increases polyQ aggregation and toxicity in mammalian cells expressing httExon1, we investigated further whether overexpression of genes involved in copper metabolism, notably MTs (metallothioneins) known to bind copper, protect against httExon1 toxicity. Using a yeast model of HD, we have shown that overexpression of several genes involved in copper metabolism reduces polyQ-mediated toxicity. Overexpression of MT-3 in mammalian cells significantly reduced polyQ aggregation and toxicity. We propose that copper-binding and/or -chaperoning proteins, especially MTs, are potential therapeutic targets for HD.

Exposure to lead and mercury in young larvae induces more severe deficits in neuronal survival and synaptic function than in adult nematodes

In the present study, we investigated the possibly neurotoxic effects of metal (Pb and Hg) exposure at different developmental stages on neuronal loss in the GABAergic nervous system and synaptic functions in the nematode Caenorhabditis elegans. Our data suggest that neuronal survival in GABAergic neurons and cholinergic transmission were relatively stable during development in nematodes. Moreover, neurodegeneration, as shown by the neuronal loss and dorsal/ventral cord gaps, was more severely induced by Pb and Hg exposure at the L1 through L3 larval stages than at the L4 larval and young-adult stages. Similarly, pre- and postsynaptic functions were more severely impaired by Pb and Hg exposure at the L1 through L3 larval stages than at the L4 larval and young-adult stages. Furthermore, both aldicarb and levamisole resistance were significantly correlated with neuronal loss, dorsal cord gap, and ventral cord gap in Pb- and Hg-exposed nematodes, suggesting that neuronal survival was noticeably correlated with synaptic function in metal-exposed nematodes during development. Therefore, younger (L1-L3) larvae show more sensitivity to neurotoxicity of neuronal survival and synaptic function than L4 larvae and young adult nematodes.

Pharmacotherapeutic targets in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder which is characterized by an increasing impairment in normal memory and cognitive processes that significantly diminishes a person's daily functioning. Despite decades of research and advances in our understanding of disease aetiology and pathogenesis, there are still no effective disease-modifying drugs available for the treatment of AD. However, numerous compounds are currently undergoing pre-clinical and clinical evaluations. These candidate pharma-cotherapeutics are aimed at various aspects of the disease, such as the microtubule-associated τ-protein, the amyloid-β (Aβ) peptide and metal ion dyshomeostasis – all of which are involved in the development and progression of AD. We will review the way these pharmacological strategies target the biochemical and clinical features of the disease and the investigational drugs for each category.

Role of copper in human neurological disorders

Copper is a trace element present in all tissues and is required for cellular respiration, peptide amidation, neurotransmitter biosynthesis, pigment formation, and connective tissue strength. Copper is a cofactor for numerous enzymes and plays an important role in central nervous system development; low concentrations of copper may result in incomplete development, whereas excess copper maybe injurious. Copper may be involved in free radical production, via the Haber-Weiss reaction, that results in mitochondrial damage, DNA breakage, and neuronal injury. Evidence of abnormal copper transport and aberrant copper-protein interactions in numerous human neurological disorders supports the critical importance of this trace metal for proper neurodevelopment and neurological function. The biochemical phenotypes of human disorders that involve copper homeostasis suggest possible biomarkers of copper status that may be applicable to general populations.

[Exogenous risk factors in sporadic ALS: a review of the literature]

The latest reviews of the literature devoted to the epidemiology of ALS all agree that exogenic risk factors play a role in sporadic ALS. Nevertheless, there is no convincing evidence demonstrating in a reproducible manner an association between an environmental risk factor and ALS. This discordance is mainly explained by methodological skews. Over the last ten years, exogenic factors have been analyzed within the framework of specific lifestyle factors such as place of residence, smoking or not, or certain eating practices. The most recent work suggests that interactions between genetic and environmental factors depend on the age at exposure and the duration of exposure. The objectives of this general review is: to analyze the principal case-control studies, historical cohort studies or mortality studies which looked at the associations between an environmental factor and ALS, to present main results of studies having analyzed lifestyles in relation to one or more exogenic factors, and to discuss the limitations of epidemiologic studies on ALS.

ALS and mercury intoxication: A relationship?

We report the case of an 81-year-old woman in whom clinical signs and features of electromyographic activity patterns were consistent with amyotrophic lateral sclerosis (ALS). Increased blood level and massive urinary excretion of mercury proved mercury intoxication. Despite a chelation treatment with Meso 2-3 dimercaptosuccininc acid (DMSA), she died after 17 months. The pathophysiology of sporadic ALS remains unclear. However, the role of environmental factors has been suggested. Among some environmental factors, exposure to heavy metals has been considered and ALS cases consecutive to occupational intoxication and accidental injection of mercury have been reported. Although no autopsy was performed, we discuss the role of mercury intoxication in the occurrence of ALS in our case, considering the results of experimental studies on the toxicity of mercury for motor neuron.

Separation of proteins including metallothionein in cerebrospinal fluid by size exclusion HPLC and determination of trace elements by HR-ICP-MS

A method to study the protein binding patterns of trace elements in human cerebrospinal fluid (CSF) is described. Proteins in CSF samples were separated by size exclusion chromatography combined with high performance liquid chromatography (SEC-HPLC). The column was calibrated to separate proteins in the molecular weight range 6-70 kDa. Fractions were then analyzed off-line for trace elements using high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). We were able to accurately determine more than 10 elements of clinical interest in the CSF fractions. Results are presented for Cd, Mn, Fe, Pb, Cu and Zn. The total concentrations of 16 trace elements in human plasma and CSF are also presented. The method was able to differentiate the relative contribution of metallothionein and other proteins towards metal binding in human CSF.