Motor Neuron Disease: A Chemical Perspective - Journal of Medicinal

Perspective pubs.acs.org/jmc

Motor Neuron Disease: A Chemical Perspective Laura K. Wood and Steven J. Langford* School of Chemistry, Monash University, Clayton, Victoria 3800, Australia ABSTRACT: This Perspective provides a background to the pathogenesis of neurodegenerative disease and specifically amyotrophic lateral sclerosis (ALS) and gives an overview of the many pathways, both genetically inheritable and sporadic, that may lead to the premature activation of apoptotic pathways in neurons, as well as current and proposed approaches toward interrupting these pathways.

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INTRODUCTION

Neurodegeneration is a condition that involves the progressive loss of neurological function caused by the degeneration of neurons. Many different types of diseases are neurodegenerative, for example, amyotrophic lateral sclerosis, Alzheimer’s disease, Huntington’s disease, and Parkinson’s disease.1,2 The most common form of motor neuron disease in humans is amyotrophic lateral sclerosis (ALS), also known generically as motor neuron disease (MND) and Lou Gehrig’s disease. MND is a neurodegenerative disorder that leads to the death of both the upper and lower motor neurons found in the brain and spinal cord.1,3−5 Discovered by French neurologist Jean-Martin Charcot in 1869, incidence of the disease occurs at roughly 1− 3 per 100 000 people, with a prevalence of about 4−6 per 100 000.3,4 ALS is typically an age-dependent condition, and most sufferers are afflicted in middle-adult life, leading to motor weakness in the extremities, spasticity, paralysis, and eventually death, typically within 3−5 years of the onset of symptoms with current therapies.6,7 Characteristic of ALS is the selective damage of motor neurons, particularly in the brain stem, cerebral cortex, and spinal cord, leaving cognitive function intact in a majority of cases, while muscle function associated with limb movement and breathing is greatly debilitated.1,3−5 Progression of the disease is usually accompanied by trouble with swallowing (dysphagia), talking and difficulty with breathing, and death is usually associated with respiratory failure.5 Cases of spontaneous recovery or improvement have been reported;8 however, they are exceptionally rare. Currently there is no cure or effective preventative treatment for ALS. The benzothiazole riluzole 1, a glutamate antagonist (Figure 1), is the only currently approved treatment for ALS and only extends survival by 2−3 months,9 usually with side effects.9,10 Thus, there is a need to examine alternative potential treatments for this debilitating and terminal condition. © XXXX American Chemical Society

Figure 1. Riluzole, a glutamate antagonist approved for the treatment of ALS.

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DETERMINING ALS One of the significant problems with developing a treatment for ALS is that the exact cause of the condition is often varied and difficult to determine. Amyotrophic lateral sclerosis can be classified into two major types: familial ALS (fALS), which is an inheritable form of ALS, and sporadic ALS (sALS), which appears to occur spontaneously, without familial history of ALS. While most cases of ALS are sporadic, suggesting environmental factors are involved such as heavy metals, pesticides, and excitotoxins such as β-N-methylamino-L-alanine (BMAA),6 fALS accounts for 5−10% of all ALS cases, the vast majority of which occur by autosomal dominant transmission,11 and is pathologically and clinically indistinguishable from sALS.4 Studies have shown links between about 20% of cases of the fALS form of neurodegeneration and mutation of the SOD1 gene,12 the gene that encodes the cytoplasmic human antioxidant enzyme copper/zinc superoxide dismutase (SOD1). It has been found that mutant SOD1 enzymes exhibit a toxic gain-of-function, which catalyze the oxidation of cellular substrates present in motor neurons, leading to neuron death.4−7 Various studies of ALS patients throughout the years have exposed a few notable differences between sALS and fALS, in particular the gender ratio of sufferers, age of symptom onset, and expected survival of patients after onset of the disease. While the Received: January 28, 2014

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dx.doi.org/10.1021/jm5001584 | J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry

Perspective

further converted to water by enzymes such as catalase and glutathione peroxidase.19 Thus, SOD1 converts free radicals into innocuous molecules in the process.

onset of ALS may occur anywhere from childhood to the late 1980s, the disease is considerably more common later in life. sALS is largely an age-dependent condition, with an average age of onset of 58−63 years,5 while the onset of fALS generally occurs at a lower age, with mean onset at 47−52 years,5 although juvenile cases are known.7 Mean age of onset is generally earlier in ALS arising from SOD1 mutations compared to non-SOD fALS cases,13 and onset age is generally a predictor of survival, with younger patients of both sALS and fALS surviving significantly longer than those who develop the disease at a later age.14 It has been suggested that the reason for longer survival in younger patients is due to greater neuronal reserves. In rare cases, patients have been known to live longer than 20 years with the disease,15 although the reasons for why some patients live much longer than others are largely unknown, likely to be due to the multifactorial nature of the disease. Overall, ALS is more common in men than in women, with an average male to female ratio between 2:1 and 1.5:1, which has been reported to be over 3:1 under the age of 40 and decreases with increasing age of onset, approaching 1:1 over the age of 70.14 While little is known about the mechanisms of sporadic ALS, population studies of fALS patients have provided some insight into the inheritance of the familial form of the disease (Figure 2).11−13,16 Familial ALS can be inherited as an autosomal

Scheme 1. Mechanism for SOD1 Conversion of Superoxide (O2−)

SOD1 exists as a homodimeric enzyme (Figure 3), present in virtually every cell type, although it is particularly abundant in

Figure 3. Secondary structure of human SOD1 showing the position of copper (red) and zinc (green) metal ions.

motor neurons, particularly in the spinal cord.18,19 Each monomer within the homodimeric structure binds one zinc ion, generally accepted to have a structural function, and one copper ion, which provides catalytic activity for the dismutation of superoxide.20 Mutation in SOD1. The SOD1 gene was the first gene conclusively associated with fALS, and this form of the disease is often specifically referred to as ALS1.6 Several other loci have been linked to fALS in recent years, but few have been attributed to specific genes, which code for a variety of difference cellular processes, including oxidation, DNA repair, axonal transport, and RNA processing; examples of ALS-linked genes include ALS2, TARDBP, VAPB, SETX, and ANG.5−7,21 Over 160 different mutations of SOD1 are currently known, a vast majority of which are dominantly inheritable.11 Located on chromosome 21, a majority of SOD1 mutations are point mutations, although mutations due to deletions, insertions, and truncations are also known. Surprisingly, some SOD1 mutations have specific geographic distribution; for instance, the A4V mutation is the most common mutation in the United States while D90A is a common adult-onset recessively inherited mutation in Europe.16 Mutations may present a wide variety of phenotypes, including varied onset age, duration, and clinical severity;13,22 for example, fALS patients with the A4V mutation, one of the most clinically severe SOD1 mutations, have a mean disease duration of around 1.4 years,21,26 compared to 2.5 years in other fALS patients,26 and much shorter than the average duration of 10.1 years in patients with the G93C mutation.16,23 The study of SOD1 mutants has uncovered interesting insights into the pathogenic pathways of neurodegeneration. As sALS and fALS patients are clinically indistinguishable,4 studies on the SOD1-linked form of the

Figure 2. Mechanisms implicated in motor neuron disease at the nucleus and within the cytosol of a neuron.

recessive or autosomal dominant trait, although transmission of fALS is nearly always autosomal dominant,11 while it is clinically and pathologically indistinguishable from sALS. Recessive forms of ALS, however, usually have juvenile onset.3 While roughly 10% of all ALS patients are referred to as fALS cases, this figure generally refers to only a dominant mode of inheritance with high penetrance, where a high proportion of individuals who carry the mutant gene express the disease phenotype.17 In reality, cases with dominant inheritance and low penetrance, recessive inheritance, or oligogenic inheritance may be misdiagnosed as sALS, as the complicated familial pattern of inheritance is not always understood.17

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IMPLICATION OF SOD1 IN fALS In 15−20% of cases of fALS, a relationship exists between a mutation of the gene that encodes the human antioxidant enzyme copper/zinc superoxide dismutase (SOD1) and the onset of the disease, caused by the production of ROS.12,18 Normally, SOD1 converts superoxide anions, formed as an undesirable byproduct of phosphorylation in mitochondria, to oxygen and hydrogen peroxide (H2O2) (Scheme 1), which is B



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standing of sporadic cases of ALS may be gained from fALS models, since the pathophysiology of both forms of the disease is largely unknown.26 Despite the aforementioned differences, SOD1 transgenic mouse and rat models have been highly valuable in conducting pharmacokinetic studies and testing efficacy of therapeutics, which is possibly due to the likely common pathways between the various forms of motor neuron degeneration.20,30 Gain-of-Function Model of SOD1. Studies have suggested that the pathogenic mechanism of ALS develops via SOD1 enzyme mutations through a gain-of-function mechanism independent of SOD1 activity, not a loss of function as originally proposed, meaning that the absence of the SOD1 gene does not lead to development of ALS and that progression of the disease does not correlate to the enzyme’s activity, rather the novel toxic properties acquired by mutation. This is supported by the autosomal dominant mode of transmission and the lack of correlation between clinical severity in ALS patients and enzyme activity levels,22 as well as evidence that mutant SOD1 transgenic mice develop severe and progressive motor neuron degeneration24 while mice overexpressing or lacking wild type SOD1 do not.32 There are currently two hypothesized SOD1 gain-offunction mechanisms by which neurodegeneration may progress: by the aggregation or oligomerization of misfolded SOD1 proteins; by oxidative damage caused by aberrant oxidative reactions. It is likely that the true pathological mode of action of mutant SOD1 is a mixture of both oxidative damage and protein aggregation, though the latter is not restricted to SOD. The SOD1 oxidative damage theory suggests that mutant SOD1 enzymes catalyze aberrant oxidative reactions that damage substrates essential for cell function and viability or may promote the oxidative damage of the enzyme itself. This is supported by evidence that mutant SOD1 genes increase cellular markers of oxidative damage compared to wild type SOD1, resulting in mitochondrial dysfunction and motor neuron death in cell cultures and transgenic mice.33,34 The gain-of-function hypothesis is supported by evidence that a normal level of SOD1 activity is observed in SOD1 transgenic mice that display neurodegeneration.25 Furthermore, it has been observed that superoxide levels are significantly lower in mutant SOD1 transgenic mice compared to controls while H2O2 and •OH levels are increased, indicating that increased reactive oxygen species (ROS) levels in transgenic mice are not due to decreased dismutase activity.34b Evidence suggests that an increased rate of the oxidation of substrates by hydrogen peroxide associated with A4V- and G93A-encoded mutant SOD1 enzymes may account for gain-of-function toxic property, and the effect is reduced in vitro by treatment with copper chelators.35 Further studies have suggested that the same mutant SOD1 enzymes exhibit enhanced free radical-generating function relative to the wild type enzyme, due to a small decrease in the Km for H2O2, as mutant and wild type SOD1 enzymes have the same H2O2 dismutation activity.36 Note that some SOD1 mutations affect the metal-binding capacity of the enzyme,37 putting the coppermediated oxidative stress hypothesis into question. Further evidence that other mechanisms must play a part in the gain-offunction action of mutant SOD1 is that copper knockout in SOD1 transgenic mice does not change the onset or progression of neurodegeneration.38 Intracellular protein aggregates and protein misfolding are frequently associated with neurodegenerative disorders and are present in all forms of ALS, particularly in spinal cord motor

disease may have the potential for revealing common mechanisms of the disease. Mouse Models. Knowledge of the link between SOD1 and ALS has led to the development of novel experimental methods involving transgenic species, in particular transgenic mice expressing the mutant gene SOD1G93A,24 the most widely used mouse model for ALS. These mice develop symptoms and pathology that mimic human ALS patients and have led to the generation of a series of other transgenic rodents that express a wide variety of SOD1 enzyme mutants and develop neurodegenerative pathophysiology similar to human ALS,24,25 used to extensively study the pathogenic mechanisms of neurodegeneration. Unfortunately, therapeutic success in transgenic mouse models has not always correlated with success in human trials.26 For example, creatine 2 (Figure 4) has been shown to have

Figure 4. Structure of creatine, a neuroprotective agent.

neuroprotective properties in SOD1G93A mice, with a significant extension in survival and improvement of motor function.27 While the neuroprotective effect of creatine has shown promise in human clinical trials for Parkinson’s disease and Huntington’s disease,28 human ALS clinical trials have been shown to exhibit limited beneficial effect.29 Despite the wealth of information provided about ALS mechanisms by transgenic rodent models, there appear to be a number of problems that may arise in the comparison of such models with human ALS patients. For example, not all features of human ALS are reproduced in mutant SOD1 rodents and different modes of delivery for drug administration may be necessary, exacerbated by metabolism differences.20,26,30 Moreover, differences in the apparent efficacy in rodent models and human clinical trials may arise because of the timing of drug administration; as drug candidates tend to be administered to transgenic rodents prior to clinical onset, efficacy results may appear to be different across species, as human ALS patients are only treated well into disease progression.30 This is highlighted by the fact that the efficacy of riluzole is greatest when administered to SOD1 transgenic mice early in disease progression, compared to human ALS patients, where a “probable” or “definite” ALS diagnosis is required before administration.31 A higher level of gene expression (approximately 10- to 30-fold increase) is necessary in transgenic rodent models to induce pathogenic phenotype compared to ALS patients, where only a single copy of the mutant gene is required to develop fALS.30 Furthermore, SOD1 transgenic models may not fully represent the entire ALS population, given that only 1− 2% of ALS patients experience motor neuron death due to mutant SOD1 enzymes and even less due to the popular G93A mutation.26,30 While it is possible that some therapies may target possible downstream pathways common to sALS, SOD1-fALS, and nonSOD1-fALS patients, it is also possible that limited underC



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Figure 5. Glutamate-induced Ca2+ excitotoxicity. Excess glutamate activates ligand-gates (top left) leads to an influx of intracellular Ca2+ (top right) which can result in an overproduction of toxic species (e.g., free radicals) and the initiation of cellular death pathways (bottom).

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MITOCHONDRIAL DYSFUNCTION, APOPTOSIS, AND NEURODEGENERATIVE DISEASE A common feature of a number of neurodegenerative diseases is mitochondrial dysfunction that can inevitably lead to cell death.19,41,42 Mitochondria are eukaryote organelles responsible for cell metabolism, with vital cellular functions including ATP production, regulation of apoptosis, participation in calcium signaling, and maintenance of calcium homeostasis in cells.41 Because of the potential for disruption of the electron transport chain, mitochondria are a major source of ROS.42 While it is established that mitochondrial dysfunction leads to a flux of cytoplasmic ROS by disruption of the mitochondrial respiratory chain,19,42 there is also considerable evidence to suggest that mitochondrial damage can be attributed to oxidative stress in both sALS and fALS cases, as mitochondria themselves are targets of ROS.43,44 This suggests a possible common oxidative mechanism of neuronal death between sALS and fALS. Furthermore, markers of oxidative damage to mitochondrial

neurons. While the association between the aggregates and onset of the disease is unclear, several hypotheses have been put forward to explain their formation and function. Protein misfolding may occur as a consequence of products of oxidative stress, namely, from the carbonylation, nitration, and other forms of modification of common proteins.20 Aggregate formation is a common, and possibly toxic, property of several investigated mutant SOD1 enzymes; insoluble SOD1 aggregates have been shown to form from mutant SOD1 enzymes in vitro, in vivo, and in human ALS patients, arising from abnormal folding.32a,37,39 In addition to the misfolding of mutant SOD1 species, evidence suggests that even wild type SOD1 (as well as mutant SOD1) can misfold and form aggregates, thereby providing a possible cell death pathway between sALS and fALS. The link between cell death pathways and formation of these intracellular aggregates is not yet fully understood; however, various theories involve the mechanical interference of such aggregates with intercellular and axonal transport, and the sequestration of proteins critical for cell viability, for example, the antiapoptotic protein Bcl-2.20,40 D



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DNA (mtDNA) have been demonstrated in SOD1 transgenic mice,45 while significantly higher levels of mutant mtDNA have been observed in the spinal cord of ALS patients compared to controls,46 supporting an established correlation between mtDNA mutation and neurodegeneration.42 Because mitochondria can be a large source of ROS and regulate apoptotic processes, mitochondrial dysfunction can lead to cell death by either energy failure or apoptosis.41,42 Although the mechanisms of motor neurodegeneration are mostly unclear, evidence suggests that mitochondrial-dependent apoptosis may play a part in motor neuron death in ALS.47,48 Apoptosis is initiated by a number of apoptogenic factors. Members of the Bcl-2 family may be either pro- or antiapoptotic and may initiate the release of cytochrome c from mitochondria, which plays a key part in the activation of cell-death pathways.47−49 Cytochrome c is an important part of the mitochondrial electron-transport chain, which is required for the generation of ATP, and it has been shown to display an antioxidant effect on ROS produced in the cell.47b When released from the mitochondria into the cytoplasm, it forms a cytoplasmic molecular complex called an apoptosome, which in turn activates members of the caspase family, a set of intracellular cysteine proteases capable of degrading vital cell proteins and activating the enzymatic degradation of other cellular constituents such as lipids and DNA.47−50 Caspases have been shown to play a role in the pathogenesis of neurodegenerative disease, as supported by mutant SOD1 transgenic mouse models and cell culture studies.50,51 Localization of Mutant SOD1 in Mitochondria. The SOD1 protein is mainly localized in the cytosol; however, it is also found in a number of organelles, including the mitochondria.12,42 Both the wild type and fALS-related human mutant SOD1 enzymes are found in brain and spinal cord mitochondria, localized in the matrix, inner/outer membranes, and particularly the intermembrane space of mitochondria.41,42 Mutant SOD1 enzymes appear to have a much greater association with motor neuron mitochondria than wild type SOD1 enzymes do, and it has been shown that their presence has a tendency to shift the redox potential of mitochondria and disrupt respiration because of mitochondrial membrane damage.52 This can lead to downstream consequences such as disrupted redox processes, impaired respiration and ATP production,82 as well as the disruption of calcium homeostasis54,66 and the activation of the apoptotic cascade, as observed in numerous SOD1 transgenic in vitro and in vivo models.52,53 Evidence of SOD1-induced damage to mitochondria has been found in transgenic mouse models of fALS,41,48 and death due to SOD1-induced mitochondrial dysfunction can be prevented by antioxidant administration in vitro and in vivo,34 as well as apoptosis inhibitors.51 Cell death is not observed when mutant SOD1 accumulates in the cytoplasm or other organelles, indicating that localization of mutant SOD1 within mitochondria is important in the pathogenesis of SOD1-related fALS.53 Non-SOD1 fALS. Although the SOD1 gene has provided the strongest link with motor neuron degeneration, because of the low prevalence of ALS, it has been difficult to determine other genes linked to the disease. To date, roughly 20 genes linked to ALS have been identified. One such gene is ALS2, located on chromosome 2, which codes for the protein alsin, mutants of which have been linked with ALS2, an autosomal recessive form of juvenile ALS.54 Other genes include SETX, which codes for the protein senataxin, associated with ALS4, a rare dominant juvenile onset disease with slow progression,55 and VAPB, which

codes for the vesicle associated membrane protein, linked with ALS8, a dominantly inherited adult onset form of the disease.56 Additionally, a link between ALS and the gene TARDBP, which codes for the TAR DNA-binding protein (TDP-43), has been found.57 Under normal conditions, TDP-43 regulates the gene expression process including transcription and splicing; however, the protein has been identified as a major component of ubiquitinated protein aggregates (intraneuronal inclusions) in ALS and dominant mutations of the gene have been linked to 3− 4% of fALS cases and 1−2% of sALS cases.57,58

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PROPOSED MODES OF ACTION OF NEURODEGENERATION Excitotoxicity. Studies have also shown that the production of radical species through excitotoxicity is a major factor in the degeneration of neurons, not only in the case of ALS but also for a number of other neurodegenerative disorders.59 Glutamate receptor stimulation and an influx of intracellular Ca2+ increase the production of free radicals by activating enzymes that produce free radical molecules, leading to cytotoxicity and oxidative stress, a condition that describes exposure to oxygen radicals beyond the threshold of natural antioxidant defense mechanisms (Figure 5).59

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CELLULAR IMPACT OF REACTIVE OXYGEN SPECIES There is a fine balance between the production of reactive oxygen species (ROS) during processes of oxidative metabolism in mitochondria and the ability of a biological system to protect itself by antioxidative processes from oxidative damage by reactive species in aerobic organisms. The disruption of this balance favoring the production of ROS leads to a condition of oxidative stress and can result in cellular injury.59 Several common neurological disorders are associated with oxidative stress, although it is not always established whether oxidative damage is a cause or consequence of neurodegeneration. Reactive oxygen species refer to that group of reactive, oxygencontaining molecules and ions that can have a large impact on cellular processes. Examples include hydroxyl (•OH), superoxide (•O2−), and nitric oxide (NO•) free radicals, as well as hydrogen peroxide (H2O2), singlet oxygen (1O2), hypochlorous acid (HOCl), and ozone (O3).59 ROS can be formed in the human body by deliberate pathways and by chemical side reactions and can be removed or tempered by naturally occurring enzymatic and nonenzymatic antioxidants. Molecular oxygen itself is a notable ROS and in its triplet state is a diradical with parallel spins of two lone electrons. Spin restriction does not allow acceptance of a pair of electrons of opposite spin, so O2 reacts slowly with nonradicals; however, it can react quickly with radical species. ROS can have a disastrous effect on biological tissue, causing a free radical chain reaction (Schemes 2 and 3), which Scheme 2. Free Radical Chain Reaction95,a

“LH” represents a general lipid molecule, typical of those found in cell membranes. NB: not exhaustive with respect to reactions possible at each step.

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membranes and react with iron or even copper ions to form more damaging ROS such as •OH. The hydroxyl radical itself may be produced by a number of processes, such as the homolytic fission of H2O2 by UV light or reaction of H2O2 with metal ions. It reacts very rapidly with many biological substrates, including DNA, proteins, and lipids, and can initiate lipid peroxidation, leading to a loss of membrane integrity, which can lead to other subsequent deleterious pathways. Fenton Chemistry. Redox-active transition metals, in particular copper and iron, can play a significant role in the production of ROS. Transition metals can undergo “redox cycling”, a process by which metals are alternately oxidized and reduced, which may lead to the generation of toxic ROS. Metals are usually stringently managed in living organisms, sequestered within complexes or bound to enzymes or metal carriers. Unbound transition metal ions have the ability to reduce H2O2 to generate highly reactive hydroxyl radicals, as shown in Scheme 4.

Scheme 3. Representation of Typical Lipid Peroxidation Pathways Applicable to Cell Membranes59a

leads to autoxidation, or lipid peroxidation when the reactant is a lipid, resulting in a decrease in the integrity of the cell.59 Because of the nature of the propagation step, many lipid molecules can be autoxidated from the product of a single free radical. Allylic hydrogens are susceptible to hydrogen abstraction by a radical species because of the weakened C−H bond energy arising from the adjacent carbon−carbon double bond. Bis-allylic hydrogens are particularly susceptible to hydrogen abstraction and are therefore a likely site of lipid radical formation. Carboncentered radicals formed from the abstraction of a bis-allylic hydrogen often undergo molecular rearrangement to form stable conjugated dienes, as shown in Scheme 3. ROS Targets. Principal targets of chain-carrying peroxyl radicals are polyunsaturated fatty acids and esters located within the cellular membranes, and thus as the purpose of these biomembranes is to separate the various biochemical environments into specific regions of the cell, degradation of these membranes has a drastic effect on the protection and function of biological cells.59a Lipid peroxidation has been observed in fALS mouse models, supporting the hypothesis of the role of oxidative stress in fALS.60 The central nervous system (CNS) is more susceptible to oxidative stress than other tissues, as neurons contain a high proportion of easily oxidized substituents, including polyunsaturated lipids in the membrane, have a high oxygen consumption rate and flux of ROS from respiratory processes, and are lacking in efficient endogenous antioxidant defenses. As motor neurons rely heavily on membrane integrity and energy supply, disruption of the mitochondrial function and damage to cell membranes can have dire consequences on the survival of the cell. Evidence of ROS and oxidative damage has been reported for years in both sALS and fALS patients, indicating that oxidative stress plays a role in the pathogenesis of ALS.61 Cellular markers of oxidative stress that have been observed in human ALS patients include nitrotyrosine, a stable oxidation product of peroxynitrite, lipid peroxidation byproducts malondialdehyde and 4-hydroxynonenal (found also in Alzheimer’s disease cases62), as well as protein carbonyls and oxidized DNA.61 ROS Production. During the normal process of the reduction of oxygen in mitochondria, low levels of potentially toxic ROS are produced. Around 2−3% of O2 reduced in mitochondria via the electron transport chain forms •O2−.59a Superoxide itself is not a very reactive radical; however, it does react rapidly with other radical species, such as nitric oxide (NO•). Superoxide is converted to H2O2 and O2 by superoxide dismutases SOD1 (in cytoplasm) and SOD2 (in mitochondria). In addition to superoxide, other ROS such as hydrogen peroxide and hydroxyl radicals can be formed during normal respiratory processes, as well as from the abnormal leakage of electrons from mitochondria.47b Like superoxide, H2O2 has limited chemical reactivity, although they both have the ability to generate more reactive species in vivo. Hydrogen peroxide may cross cell

Scheme 4. Disproportionation of Hydrogen Peroxide by Iron95

Iron, while playing an important role in many biochemical processes, also has the potential for toxicity in most organisms. The disproportionation of hydrogen peroxide by iron, as shown in Scheme 4, is often loosely referred to as Fenton chemistry.63 It involves a catalytic process by which ferrous and ferric ions are alternately oxidized and reduced respectively by hydrogen peroxide, forming hydroxyl radicals, hydroxyl anions, peroxyl radicals, and protons in the process.59 Evidence suggests that iron may play a part in the pathogenesis of sALS;64 an increase in iron levels in the spinal cord has been observed in sALS patients.108 Studies have also shown an increased incidence of mutations in the Hfe gene (associated with the iron-overload disease hemochromatosis) in patients with sALS, indicating some involvement of iron handling in the pathogenesis of the disease.65 Furthermore, an up-regulation of ferritin in end-stage SOD1 transgenic mice indicates an excessive accumulation of iron.66 Implication of Copper. The involvement of copper in the mechanisms of SOD1-fALS motor neuron degeneration has been supported by various studies, both in vitro and in vivo.34a,67 Copper chelators have been shown to delay disease onset and increase survival in SOD1 transgenic mice67 and prevent cell death in SOD1-fALS cell models,68 supporting the toxic gain-offunction hypothesis of SOD1 mutations. Furthermore, SOD1 transgenic mice genetically bred for a spinal cord copper deficiency had a significant delay in motor neuron degeneration and prolonged survival.69 It is known that many mutant SOD1 proteins do not bind copper effectively,70 and the inadequate buffering of Cu can lead to aberrant oxidative chemistry, inducing oxidative stress and subsequent cell death.71 F



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dysfunction of both glutamate transporters and Ca2+-permeable receptors influence the pathogenic pathways of neuronal death.78 Glutamate Transporters and Excitotoxicity. Glutamate exists almost entirely intracellularly because of the activity of high-affinity glutamate transporters. It is usually found at low concentrations (≤1 μM) in extracellular fluid,79 significantly lower than in cells, where glutamate concentration is ∼10 mM.80 Extracellular glutamate levels are regulated by the rapid uptake of the amino acid by glutamate transporters, preventing overstimulation of excitatory amino acid receptors and resulting excitotoxic neuronal damage that readily occurs at concentrations above 10 μM.81 Five different subtypes of high-affinity glutamate or excitatory amino acid transporters (EAATs), located in the plasma membranes of both neurons and astrocytes, have been identified.81 Immunocytochemistry has shown that glutamate transporter subtypes are distributed differently within cell types and across regions of the brain and the CNS; EAAT1 (GLAST in rodents) and EAAT2 (GLT-1 in rodents) are located primarily in astrocytes, while EAAT3 (EAAC1 in rodents), EAAT4, and EAAT5 are expressed by neurons in the brain.81 Antisense knockdown experiments and biochemical studies have indicated that astrocyte transporter EAAT2/GLT-1, located within the brain and spinal cord, is the predominant glutamate transporter subtype in buffering extracellular glutamate at an appropriate level in the CNS and protecting neurons from excitotoxicity.82 The first demonstration that ALS patients present reduced glutamate transport function in the spinal cord and regions of the brain, compared to healthy subjects and patients with Alzheimer’s disease and Huntington’s disease, was made in 1992.83 Studies have since shown that the decreased transport function is primarily due to a significant decrease of EAAT2 levels in ALS patients.81,84 The loss of functional glutamate transport could account for significantly increased levels of glutamate in the CSF of some ALS patients compared to controls. Several in vitro and in vivo studies have supported the involvement of impaired glutamate transport function in motor neuron degeneration; however, the extent to which transporter dysfunction contributes to neurodegeneration has been difficult to assess.72 A decrease of EAAT2/GLT-1 has been observed in the spinal cord of SOD1 transgenic rats at the onset of neuron degeneration and in SOD1G93A mice at advanced stages of the disease.85 It has been demonstrated that decreases in transporter levels are specifically localized to regions of neuron loss in the CNS, such as the motor cortex and spinal cord, and do not occur in areas of no neuronal degeneration. In vitro inhibition of glutamate transporters has been shown to lead to an increase in extracellular glutamate and the slow degeneration of motor neurons; toxicity was prevented by non-NMDA receptor antagonists (although not NMDA receptor antagonists), supporting the hypothesis that progressive motor neuron degeneration in ALS may be due in part to defective glutamate transport.86 In SOD1G93A mice, a lack of change in GLT-1 levels at the presymptomatic stage of the disease indicates that the loss of transport function is not a primary event in the neurodegenerative cascade; rather changes in transporter and glutamate levels merely contribute to the disease progression.85 This hypothesis is supported by observations in SOD1G93A mice bred to overexpress GLT-1, where increase in the transporter did not delay disease onset or increase survival but did delay motor neuron loss and grip-strength decline.87 While a lot of data suggest at least some involvement of glutamate transport deficiency in motor neuron degeneration, one study demon-

EXCITOTOXIC MECHANISMS AND NEURODEGENERATION Implication of Glutamate. Glutamate 3 is the primary excitatory neurotransmitter in the central nervous system, responsible for a number of neurologic functions such as learning, memory, and movement (Figure 6).72 Excitotoxicity, a

Figure 6. Glutamate, the primary excitatory neurotransmitter.

pathological process by which neurons die from overactivation of glutamate receptors at the synaptic cleft caused by an excess of glutamate, is strongly implicated as a major contributing factor in the pathogenesis of neuronal death.72,73 The link between glutamate-mediated excitotoxicity and ALS is well established, with early studies indicating that many ALS patients exhibit a significant increase in glutamate in cerebrospinal fluid (CSF).74 One of the causes of neuronal death appears to be the disruption of calcium homeostasis via activation of Ca2+ channels, release of Ca2+ from intracellular stores, and production of free radicals by Ca2+-dependent enzymes.72,73 Excess Ca2+ influx in neurons can result from an overstimulation of glutamate receptors, such as the N-methyl-D-aspartate (NMDA) receptor and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor, leading to cytotoxic effects, especially in mitochondria (Figure 5).73,75 Calcium is an important secondary messenger in the CNS, important in signaling pathways vital for cell survival; however, an excess of intracellular Ca2+ can have disastrous effects, as studies have demonstrated a correlation between the disruption of Ca2+ homeostasis and neurodegeneration.72,73 Evidence has shown that high levels of cytosolic free Ca2+ are not necessarily toxic to neurons; however, potential-driven uptake of Ca2+ into mitochondria triggers glutamate-induced neuronal death.76 Numerous toxic pathways may be activated by glutamateinduced Ca2+ influx. In a number of neurodegenerative disorders, the increase in Ca2+ levels in the neuron results in activation of Ca2+-dependent proteins and enzymes (Figure 5), which can lead to nuclear and membrane damage, as well as an increase of ROS.75,77 In particular, Ca2+ uptake from glutamate receptor stimulation results in increased ROS production from mitochondrial electron transport chain processes.77 It is thought that the process of neuronal death due to oxidative stress may be self-sustaining, since hydroxyl radicals may be released from mitochondria as the organelle wall integrity is compromised, electron transport chain may be altered, mtDNA may be oxidized, and membrane degradation may lead to the disruption of Ca2+ homeostasis. There may be a number of mechanisms by which the overstimulation of glutamate receptors is initiated: increased synaptic glutamate due to uncontrolled release of glutamate from presynaptic neurons; increased synaptic glutamate due to deficient glutamate transport function; altered expression or sensitivity of glutamate receptors, leading to increased Ca2+ influx in neurons at normal glutamate levels.72−78 In the case of motor neuron disease, there is significant evidence to suggest that the G



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that the increased Ca2+ permeability of AMPA receptors in ALS patients may be due to either a significant decrease in posttranscriptional editing of GRIA2,95 reduced GRIA2 expression,96 or a combination of both factors.169 Various in vivo studies support the theory that a high proportion of Ca2+-permeable AMPA receptors in motor neurons may cause the cells to be highly susceptible to excitotoxicity from Ca2+ influx.91 In SOD1 transgenic mice, deficiency or overexpression of GluA2 can either accelerate or ameliorate motor neuron degeneration, respectively,97 which supports evidence that the SOD1G93A mutation causes changes in the expression and function of AMPA receptors, increasing vulnerability of motor neurons to excitotoxicity.98 Treatment with AMPA receptor antagonists has also been shown to slow disease progression and extend survival of SOD1 transgenic mice.99 While a decrease in permeability-regulating GluA2 has been observed in spinal cords of fALS SOD1G93A mice before the onset of neurodegenerative symptoms, a modest up-regulation of Ca2+permeable GluA3 has been shown to occur concomitantly, indicating a possible deleterious involvement of GluA3 in the excitotoxic mechanisms of ALS (Figure 8).99 Supporting these

strated that in vivo administration of glutamate transport blockers significantly elevated extracellular glutamate in rats; however, despite this, no motor neuron degeneration, gliosis, or motor activity deficits were observed.88 Evidence has shown that glutamate transporters can be rendered inactive because of oxidative stress.89 Of the glutamate transporters found in humans and rodents, GLT-1/EAAT2 is particularly susceptible to oxidative damage.90 GLT-1/EAAT2 function has been demonstrated to be reduced by mutant (but not wild type) SOD1 in vitro and in mice and rats. A mechanism of inhibition by oxidation is supported by a similar pattern of GLT-1 inactivation observed when the transporter was exposed to peroxidation by H2O2 under Fenton conditions, and the restoration of transport function after treatment with the antioxidant MnIIITBAP.90 This supports the hypothesis that SOD1-linked fALS occurs via an excitotoxic mechanism caused by the toxic properties of SOD1 mutants. Glutamate Receptors and Excitotoxicity. Glutamate secreted from glutamatergic vesicles stimulates ionotropic (ligand-gated) glutamate receptors such as the NMDA receptors, AMPA receptors and kainite (KA) receptors, and metabotropic receptors (Figure 5), all of which regulate the influx of ions such as K+, Na+, and Ca2+ into the neuron.91 Overstimulation of these receptors can lead to an increase in cytosolic free Ca2+ levels. In vitro studies have shown that motor neurons are particularly sensitive to glutamate excitotoxicity resulting from AMPA receptor activation.92 AMPA receptors are predominantly heteromeric, tetrameric, ligand-gated channels, consisting of four subunits, GluA1−4 (previously referred to as GluR1−4), of which the subunit GluA2 is functionally dominant in determining Ca2+ permeability (Figure 7).93 Calcium permeability of AMPA receptors depends

Figure 8. Immunohistochemical analysis of GluA3 expression in the ventral and dorsal horn reveals qualitatively increased expression in spinal motor neurons.101

observations, treatment of SOD1G93A mice with peptide nucleic acids antisense to GluA3 mRNA has been shown to significantly extend disease onset and mouse survival.100 This evidence suggests that GluA3 may act as an ideal candidate as a therapeutic target for the treatment of neurodegeneration. There is also promise in the development of specific AMPA receptor antagonists for treatment of glutamate-induced neurodegenerative disorders.

Figure 7. The presence or absence of an edited GluA2 (GluR2) subunit determines the Ca2+ permeability of AMPA receptors.

on their GluA subunit composition; AMPA receptors lacking the GluA2 subunit are permeable to Ca2+ (Figure 7), an influx of which can lead to excitotoxicity.91c The functional dominance of the GluA2 subunit results from post-transcriptional mRNA (mRNA) editing, which involves the replacement of a neutral glutamine (Q) residue (found in GluA1, 3, and 4) with a positively charged arginine (R) residue at what is known as the “Q/R site” in the second transmembrane region of GluA2.94 In the nondiseased state, virtually all GluA2 subunits are impermeable to Ca2+ because of editing of effectively 100% of GRIA2, the gene that encodes GluA2. Evidence has suggested

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SMALL MOLECULE APPROACHES TO TREATING ALS Riluzole. Marketed as Rilutek, riluzole (Figure 1) is often administered in 50 mg doses, usually twice a day,102 and although it can increase life expectancy by an average of 2−3 months, there are a number of common side effects of the drug, include nausea, vomiting, asthenia, anorexia, diarrhea, dizziness, gastrointestinal disorders, and liver dysfunction.9,10 The action of riluzole has not H



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yet been extensively determined; however, it is proposed that it interrupts glutamatergic neurotransmission, through both the blockage of voltage-gated sodium channels, which inhibits glutamate release, and the indirect antagonism of glutamate receptors.103 A survival benefit of greater than 6 months has been suggested; however, an increase in the quality of care of ALS patients may affect this figure.104 The drug has been found to be well tolerated by patients for up to 7 years.105 The benefit of riluzole has been shown to be more significant in patients with bulbar onset, compared to limb onset.106 Because of riluzole’s limited efficacy, concern over adverse side effects, and the prohibitive cost of the drug, there is a requirement for alternative treatments of ALS on the market. Antioxidants. Vitamin E and vitamin C have been shown to act synergistically in vitro, with vitamin E acting as the primary antioxidant, of which the resulting phenoxyl radical is regenerated to vitamin E on reaction with vitamin C.107,108 This interaction is believed to occur at the membrane interface, thus effectively transporting the potentially damaging radical from the membrane to the aqueous phase, as vitamin E acts as the better antioxidant in the lipid phase, whereas vitamin C is an excellent inhibitor of peroxidation in the aqueous phase.109 The resulting vitamin C radical may then be enzymatically reduced back to vitamin C by endogenous antioxidants, for example, NADH (Scheme 5).

Figure 9. Selection of compounds used in clinical trials for MND.

clinical studies are ongoing in the United States and Canada. AMPA receptor antagonists have also been shown to have a beneficial effect in transgenic mice,99 while a phase II clinical trial of talampanel 6122 (Figure 9) has been terminated because of conclusively negative results in humans. Dexpramipexole 7, a low molecular weight and orally bioactive compound that is renally excreted, was identified as a candidate for the treatment of ALS in 2010 in phase II clinical trials on over 100 patients.123 The phase III study using 7 failed to meet primary end points but was reported to succeed on several secondary end points. A Multifunctional Approach. Ideally, a candidate for the treatment of neurodegeneration would perform multiple specific functions. Studies have indicated that if a drug candidate could simultaneously target multiple specific factors that lead to neuron death, the efficacy of the drug in combating neurodegeneration could be increased. Combinatorial therapies that incorporate drugs that target multiple pathways or cell types may play a role in neurodegeneration and have been of recent interest. However, the large expense of such trials means that they are not readily approved by regulatory agencies and thus are rarely attempted.124 A number of combinatorial therapies have shown promising results in transgenic models and even exhibited synergistic effects.30 Of particular interest is the combination of creatine 2 and minocycline 4, an apoptosis inhibitor (Figure 9).125 When administered separately, both agents have been shown to improve motor performance and extend survival in transgenic mice, although when administered together, they exhibit an additive neuroprotective effect in delaying disease onset and increasing survival in the ALS model. Other combinatorial treatments shown to exhibit an additive effect on motor function and survival in ALS mouse models include the combination of minocycline, riluzole, and nimodipine 8, a voltage-gated calcium channel antagonist (Figure 9),126 as well as the concurrent administration of Neu2000 9, a potent antioxidant and NMDA agonist, and lithium carbonate, a mood stabilizer that prevents apoptosis.127 Gene Approaches. As well as pharmacological approaches, therapies that target gene translation and transcription are

Scheme 5. Antioxidant Action of Vitamin E and Subsequent Regeneration by Vitamin C and NADH

While treatment with vitamin E has been shown to have a beneficial effect in SOD1 transgenic mice,110 to date, there has been limited success in human ALS patients;111 however, longterm regular users of vitamin E supplements have less than half the risk of dying of ALS than nonusers.112 Treatment of ALS patients with other antioxidants has been met with limited success. Despite evidence that antioxidants such as Gingko biloba extract,113 spin-trapping molecule DMPO, and antioxidant porphyrins AEOL10150114 and FeTCPP115 protect against oxidative damage, delay paralysis, and extend survival in SOD1 transgenic mice, there is little evidence of their efficacy in human ALS patients. Overall, clinical trials of antioxidant therapies have shown little therapeutic effect on patients to date.116 Other Therapeutic Approaches. A number of other pharmacological treatments for motor neuron degeneration have been examined (Figure 9).117 Administration of minocycline 4, an antibiotic agent, delays disease onset and extends survival in SOD1G93A mice by inhibiting cytochrome c release from mitochondria;118 however, phase III clinical trials of minocycline failed in human patients.119 Various therapeutic agents targeting excitotoxic pathways have also been studied. Ceftriaxone 5, a β-lactam antibiotic (Figure 9) that stimulates the transcription of glutamate transporter GLT-1/EAAT2, has been shown to delay neurodegeneration and increase survival in SOD1 transgenic mice,120 although early clinical trials have shown limited evidence of clinical efficacy.121 Despite this, phase III I



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have multiple pharmacological effects on both neurons and glial cells. However, it is anticipated that these general effects can be overcome with the design of multifunctional drug candidates that incorporate two or more desired modes of action. In the case of treating motor neuron degeneration, it is possible that incorporating both antioxidant function and Ca2+-buffering capability in the one molecule may prove to be favorable in targeting known cell death pathways (Figure 10), or a

possible candidates in the treatment of motor neuron degeneration. RNA silencing may be achieved using small interfering RNAs (siRNAs), double-stranded RNA duplexes of 21−23 nucleotides, which promote degradation of selected target mRNAs, thus decreasing protein expression levels of a single gene.128 While siRNA designed to selectively target mutant alleles have been shown to be effective in the treatment of SOD1-linked fALS models in vitro and in vivo,129 targeting individual point mutations would not be a feasible strategy in the treatment of such a multifactorial disease such as ALS, where a number of point mutations have been linked to the disease. Interfering RNA broadly targeting all alleles of the SOD1 gene has been shown to reduce gene expression in SOD1G93A transgenic mice, resulting in improved motor performance, significant delay in disease onset, and increase of survival.130 Administration of antisense oligonucleotides to SOD1 mRNA has been shown to reduce both SOD1 protein and mRNA levels in the brain and spinal cord of transgenic rats, slowing disease progression significantly.131 Similarly, treatment with antisense peptide nucleic acid (PNA) oligomers directed against GluA3 showed neuroprotection against an AMPA agonist in vitro and extended survival in a SOD1G93A transgenic mouse model. Likewise, treatment of SOD1G93A mice with antisense PNA oligomers targeting p75NTR, a neurotrophin receptor implicated in the pathogenesis of mutant SOD1-mediated neuronal death, has been demonstrated to delay motor impairment and increase mouse survival.132 Growth Factors. Several clinical trials have been attempted with insulin-like growth factors such as rh-IGF-1, a protein that in humans is encoded by the IGF-1 gene, with inconsistent results. One study demonstrated a clear benefit to patients and remains the only clinical program in ALS where a decrease in disease progression was observed and recognized by FDA. A second European study of 330 patients failed to confirm the disease progression effect, and subsequently any further trials was abandoned.133

Figure 10. Proposed generic structure and function of the potential drug candidate, incorporating both a antioxidant (FRS) and Ca2+-buffering component.

combination of antioxidant and gene therapy will be required. Such an approach may be wishful thinking or at best lead to serendipitous discovery, from a rational drug design perspective. However, given the complexity of MND and the unusual nature of neurons, their metabolism and size, this approach may bear fruit, since hitherto approaches have fallen short. And while nature’s secrets to this disease are yet to be unlocked, a stronger push for a cure should be demanded, for nature is not in a hurry but all patients afflicted by ALS are.

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AUTHOR INFORMATION

Corresponding Author

*Phone: +613 99054569. E-mail: [email protected].

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Notes

The authors declare no competing financial interest.

CONCLUDING REMARKS While the specific causes for motor neuron disease are still unknown, there is no doubt given the breadth of both fALS and sALS cases that this is an extremely complex disease. The severity of the disease and the rapid degeneration that occurs from the onset of symptoms make it one of the most aggressive diseases known. For us, as for those impacted by the disease (including carers, family, and friends) this is also a very tragic disease in that patients remain alert with normal brain function throughout its progression, since only motor neurons are affected. In this Perspective, we have tried to provide an understanding of the pathology of motor neuron disease as seen specifically through amyotrophic lateral sclerosis as well as current thinking in terms of therapeutic approaches from both a small molecule and gene approach. Some evidence is clear; the implication of SOD1 and glutamate transporters mean they are likely targets that will continue to be explored. It is likely that combinatorial therapies will provide the best solution for effective management of MND alongside early and accurate diagnosis, particularly since the disease continues to be aggressive. These combinations may include approaches that look at nerve cell growth and communication above and beyond simple repair and impeding degeneration. One well-known problem of combinatorial therapies is the possibility of unfavorable interactions between therapeutic agents or mode of action in different places along the disease pathway;37 for example, both creatine and minocycline

Biographies Laura K. Wood studied at Monash University (Australia), where she received her B.Sc. (Hons.) degree in 2005 and her Ph.D. in 2012, working on novel therapeutic treatments for motor neuron disease. In 2010 she joined Biota Pharmaceuticals in Clayton working in a project development role. Steven J. Langford is Professor of Organic Chemistry and Head of School of Chemistry at Monash University, Australia. He received his B.Sc. (Hons. I) and Ph.D. from the University of Sydney, Australia, in 1994. After postdoctoral work in the U.K. under the auspices of a Ramsay Memorial Fellowship with Sir J. Fraser Stoddart FRS investigating the formation of topologically interesting molecular assemblies for molecular device development and at the University of UNSW, Australia, as an ARC Postdoctoral Fellow investigating electron transfer processes in giant multichromophoric systems, he joined the School of Chemistry at Monash University in 1998. Here, his interests in diverse areas such as nanoscaled devices, photosynthetic mimicry, and motor neuron disease were developed.

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ACKNOWLEDGMENTS We thank Professor Surindar Cheema for inspirational perspective and collaboration, which awoke our interest in this field. We wish to thank Dr Elisse Browne for help in generating Figure 3. J



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(12) Rosen, D. R.; Siddique, T.; D, P.; Figlewicz, D. A.; Sapp, P.; Hentati, A.; Donaldson, D.; Goto, J.; O’Regan, J. P.; Deng, H. X. Mutations in Cu/Zn Superoxide Dismutase Gene are Associated with Familial Amyotrophic Lateral Sclerosis. Nature 1993, 362, 59−62. (13) Cudkowicz, M. E.; McKenna-Yasek, D.; Sapp, P. E.; Chin, W.; Geller, B.; Hayden, D. L.; Schoenfeld, D. A.; Hosler, B. A.; Horvitz, H. R.; Brown, R. H. Epidemiology of Mutations in Superoxide Dismutase in Amyotrophic Lateral Sclerosis. Ann. Neurol. 1997, 41, 210−221. (14) (a) Eisen, A.; Schulzer, M.; MacNeil, M.; Pant, B.; Mak, E. Duration of Amyotrophic Lateral Sclerosis is Age Dependent. Muscle Nerve 1993, 16, 27−32. (b) Haverkamp, L. J.; Appel, V.; Appel, S. H. Natural History of Amyotrophic Lateral Sclerosis in a Database Population: Validation of a Scoring System and a Model for Survival Prediction. Brain 1995, 118, 707−719. (15) Grohme, K.; v. Maravic, M.; Gasser, T.; Borasio, G. D. A Case of Amyotrophic Lateral Sclerosis with a Very Slow Progression Over 44 years. Neuromuscular Disord. 2001, 11, 414−416. (16) (a) Andersen, P. M.; Forsgren, L.; Binzer, M.; Nilsson, P.; AlaHurula, V.; Keranen, M.-L.; Bergmark, L.; Saarinen, A.; Haltia, T.; Tarvainen, I.; Kinnunen, E.; Udd, B.; Marklund, S. L. Autosomal Recessive Adult-Onset Amyotrophic Lateral Sclerosis Associated with Homozygosity for Asp90Ala CuZn-superoxide Dismutase Mutation: A Clinical and Genealogical Study of 36 Patients. Brain 1996, 119, 1153− 1172. (b) Rosen, D. R.; Bowling, A. C.; Patterson, D.; Usdin, T. B.; Sapp, P.; Mezey, E.; McKenna-Yasek, D.; O’Regan, J.; Rahmani, Z.; Ferrante, R. J.; Brownstein, M. J.; Kowall, N. W.; Beal, M. F.; Horvitz, H. R.; Brown, R. H. A Frequent Ala 4 to Val Superoxide Dismutase-1 Mutation Is Associated with a Rapidly Progressive Familial Amyotrophic Lateral Sclerosis. Hum. Mol. Genet. 1994, 3, 981−987. (17) Andersen, P. M.; Borasio, G. D.; Dengler, R.; Hardiman, O.; Kollewe, K.; Leigh, P. N.; Pradat, P.-F.; Silani, V.; Tomik, B. EFNS Task Force on Management of Amyotrophic Lateral Sclerosis: Guidelines for Diagnosing and Clinical Care of Patients and Relatives. Eur. J. Neurol. 2005, 12, 921−938. (18) (a) Deng, H.-X.; Hentati, A.; Tainer, J. A.; Iqbal, Z.; Cayabyab, A.; Hung, W.-Y.; Getzoff, E. D.; Hu, P.; Herzfeldt, B.; Roos, R. P.; Warner, C.; Deng, G.; Soriano, E.; Smyth, C.; Parge, H. E.; Ahmed, A.; Roses, A. D.; Hallewell, R. A.; Pericak-Vance, M. A.; Siddique, T. Amyotrophic Lateral Sclerosis and Structural Defects in Cu,Zn Superoxide Dismutase. Science 1993, 261, 1047−1051. (b) Milani, P.; Gagliardi, S.; Cova, E.; Cereda, C. SOD1 Transcriptional and Posttranscriptional Regulation and Its Potential Implications in ALS. Neurol. Res. Int. 2011, 1−9. (19) (a) Duffy, L. M.; Chapman, A. L.; Shaw, P. J.; Grierson, A. J. The Role of Mitochondria in the Pathogenesis of Amyotrophic Lateral Sclerosis. Neuropathol. Appl. Neurobiol. 2011, 37, 336−352. (b) Faes, L.; Callewaert, G. Itochondrial Dysfunction in Familial Amyotrophic Lateral Sclerosis. J. Bioenerg. Biomembr. 2011, 43, 587−592. (c) Reddy, P. H.; Reddy, T. P. Mitochondria as a Therapeutic Target for Aging and Neurodegenerative Diseases. Curr. Alzheimer Res. 2011, 8, 393−409. (d) McCord, J. M.; Fridovich, I. Superoxide Dismutase: An Enzymic Function for Erythrocuprein (Hemocuprein). J. Biol. Chem. 1969, 244, 6049−6055. (20) Cozzolino, M.; Ferri, A.; Carrì, M. T. Amyotrophic Lateral Sclerosis: From Current Developments in the Laboratory to Clinical Implications. Antioxid. Redox Signaling 2008, 10, 405−444. (21) Sreedharan, J. Neuronal Death in Amyotrophic Lateral Sclerosis (ALS): What Can We Learn from Genetics? CNS Neurol. Disord.: Drug Targets 2010, 9, 259−267. (22) Shibata, N. Transgenic Mouse Model for Familial Amyotrophic Lateral Lclerosis with Superoxide Dismutase-1 Mutation. Neuropathology 2001, 21, 82−92. (23) It is important to note that some SOD1 mutations may have diminished penetrance and therefore may be recorded as apparent cases of sALS. (24) Gurney, M. E.; Pu, H.; Chiu, A. Y.; Canto, M. C. D.; Polchow, C. Y.; Alexander, D. D.; Caliendo, J.; Hentati, A.; Kwon, Y. W.; Deng, H.X.; Chen, W.; Zhai, P.; Sufit, R. L.; Siddique, T. Motor Neuron Degeneration in Mice That Express a Human Cu,Zn Superoxide Dismutase Mutation. Science 1994, 264, 1772−1775.

ABBREVIATIONS USED ALS, amyotrophic lateral sclerosis; AMPA, α-amino-3-hydroxy5-methyl-4-isoxazolepropionic acid; ATP, adenosine triphosphate; CNS, central nervous system; CSF, cerebrospinal fluid; DMPO, 5,5-dimethyl-1-pyrroline N-oxide; EAAT, excitatory amino acid transporter; fALS, familial amyotrophic lateral sclerosis; GluA1−4, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunits; GLT, glutamate transporter; MND, motor neuron disease; mtDNA, mitochondrial DNA; NMDA, N-methyl-D-aspartate; PNA, peptide nucleic acid; ROS, reactive oxygen species; ppm, parts per million; sALS, sporadic amyotrophic lateral sclerosis; SETX, protein senataxin; siRNA, small interfering RNA; SOD1, copper/zinc superoxide dismutase; TARDBP, TAR DNA binding protein; TCPP, tetrakis(carboxphenyl)porphyrin; VAPB, vessicle associated membrane protein

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REFERENCES

(1) Shukla, V.; Mishra, S. K.; Pant, H. C. Oxidative Stress in Neurodegeneration. Adv. Pharmacol. Sci. 2011, No. 572634. (2) Cui, H.; Kong, Y.; Zhang, H. Oxidative Stress, Mitochondrial Dysfunction, and Aging. J. Signal Transduction 2012, No. 646354. (3) Ferraiuolo, L.; Kirby, J.; Grierson, A. J.; Sendtner, M.; Shaw, P. J. Molecular Pathways of Motor Neuron Injury in Amyotrophic Lateral Sclerosis. Nat. Rev. Neurol. 2011, 7, 616−630. (4) Contestabile, A. Amyotrophic Lateral Sclerosis: From Research to Therapeutic Attempts and Therapeutic Perspectives. Curr. Med. Chem. 2011, 18, 5655−5665. (5) Kiernan, M. C.; Vucic, S.; Cheah, B. C.; Turner, M. R.; Eisen, A.; Hardiman, O.; Burrell, J. R.; Zoing, M. C. Amyotrophic Lateral Sclerosis. Lancet 2011, 377, 942−955. (6) (a) Joyce, P.; Fratta, P.; Fisher, E.; Acevedo-Arozena, A. SODI and TDP-43 Animal Models of Amyotrophic Lateral Sclerosis: Recent Advances in Understanding Disease Toward the Development of Clinical Treatments. Mamm. Genome 2011, 22, 420−448. (b) RoelofsIverson, R. A.; Mulder, D. W.; Elveback, L. R.; Kurland, L. T.; Molgaard, C. A. Neurology 1984, 34, 393−395. (c) Pablo, J.; Banack, S. A.; Cox, P. A.; Johnson, T. E.; Papapetropoulos, S.; Bradley, W. G.; Buck, A.; Mash, D. C. Acta Neurol. Scand. 2009, 120, 216−225. (7) Swarup, V.; Julien, J.-P. ALS Pathogenesis: Recent Insights from Genetics and Mouse Models. Prog. Neuropsychopharmacol. Biol. Psychiatry 2011, 35, 363−369. (8) (a) Tucker, T.; Layzer, R. B.; Miller, R. G.; Chad, D. Subacute, Reversible Motor Neuron Disease. Neurology 1991, 41, 1541−1544. (b) Tsai, C. P.; Ho, H. H.; Yen, D. J.; Wang, V.; Lin, K. P.; Liao, K. K.; Wu, Z. A. Reversible Motor Neuron Disease. Eur. Neurol. 1993, 33, 387−389. (9) (a) Bensimon, G.; Lacomblez, L.; Meininger, V.; ALS/Riluzole Study Group.. A Controlled Trial of Riluzole in Amyotrophic Lateral Sclerosis. N. Engl. J. Med. 1994, 330, 585−591. (b) Lacomblez, L.; Bensimon, G.; Meininger, V.; Leigh, P. N.; Guillet, P. Dose-Ranging Study of Riluzole in Amyotrophic Lateral Sclerosis. Lancet 1996, 347, 1425−1431. (c) Miller, R. G.; Mitchell, J. D.; Lyon, M.; Moore, D. H. Riluzole for Amyotrophic Lateral Sclerosis (ALS)/Motor Neuron Disease (MND). Amyotrophic Lateral Scler. 2003, 4, 191−206. (10) (a) Kiernan, M. C. Riluzole: A Glimmer of Hope in the Treatment of Motor Neurone Disease. Med. J. Aust. 2005, 182, 319−320. (b) Bensimon, G.; Doble, A. The Tolerability of Riluzole in the Treatment of Patients with Amyotrophic Lateral Sclerosis. Expert Opin. Drug Saf. 2004, 3, 525−534. (c) Bensimon, G.; Lacomblez, L.; Delumeau, J. C.; Bejuit, R.; Truffinet, P.; Meininger, V.; ALS Study Group II.. A Study of Riluzole in the Treatment of Advanced Stage or Elderly Patients with Amyotrophic Lateral Sclerosis. J. Neurol. 2002, 249, 609−615. (11) Strong, M. J.; Hudson, A. J.; Alvord, W. G. Familial Amyotrophic Lateral Sclerosis; 1850−1989. Can. J. Neurol. Sci. 1991, 18, 45−58. K



Perspective

(25) (a) Wong, P. C.; Pardo, C. A.; Borchelt, D. R.; Lee, M. K.; Copeland, N. G.; Jenkins, N. A.; Sisodia, S. S.; Cleveland, D. W.; Price, D. L. An Adverse Property of a Familial ALS-Linked SOD1 Mutation Causes Motor Neuron Disease Characterized by Vacuolar Degeneration of mitochondria. Neuron 1995, 14, 1105−1116. (b) Ripps, M. E.; Huntley, G. W.; Hof, P. R.; Morrison, J. H.; Gordon, J. W. Proc. Natl. Acad. Sci. U.S.A. 1995, 92, 689−693. (c) Bruijn, L. I.; Becher, M. W.; Lee, M. K.; Anderson, K. L.; Jenkins, N. A.; Copeland, N. G.; Sisodia, S. S.; Rothstein, J. D.; Borchelt, D. R.; Price, D. L.; Cleveland, D. W. ALSLinked SOD1 Mutant G85R Mediates Damage to Astrocytes and Promotes Rapidly Progressive Disease with SOD1-Containing Inclusions. Neuron 1997, 18, 327−338. (26) Benatar, M. Treatment Trials in the SOD1 Mouse and in Human ALS. Neurobiol. Dis. 2007, 26, 1−13. (27) Klivenyi, P.; Ferrante, R. J.; Matthews, R. T.; Bogdanov, M. B.; Klein, A. M.; Andreassen, O. A.; Mueller, G.; Wermer, M.; KaddurahDaouk, R.; Beal, M. F. Neuroprotective Effects of Creatine in a Transgenic Animal Model of Amyotrophic Lateral Sclerosis. Nat. Med. 1999, 5, 347−350. (28) Beal, M. Neuroprotective Effects of Creatine. Amino Acids 2011, 40, 1305−1313. (29) Groeneveld, G. J.; Veldink, J. H.; Tweel, I. v. d.; Kalmijn, S.; Beijer, C.; Visser, M. d.; Wokke, J. H. J.; Franssen, H.; Berg, L. H. v. d. A Randomized Sequential Trial of Creatine in Amyotrophic Lateral Sclerosis. Ann. Neurol. 2003, 53, 437−445. (30) Carrì, M. T.; Grignaschi, G.; Bendotti, C. Targets in ALS: designing multidrug therapies. Trends Pharmacol. Sci. 2006, 27, 267− 273. (31) Gurney, M. E.; Fleck, T. J.; Himes, C. S.; Hall, E. D. Riluzole Preserves Motor Function in a Transgenic Model of Familial Amyotrophic Lateral Sclerosis. Neurology 1998, 50, 62−66. (32) (a) Bruijn, L. I.; Houseweart, M. K.; Kato, S.; Anderson, K. L.; Anderson, S. D.; Ohama, E.; Reaume, A. G.; Scott, R. W.; Cleveland, D. W. Aggregation and Motor Neuron Toxicity of an ALS-Linked SOD1 Mutant Independent from Wild-Type SOD1. Science 1998, 281, 1851− 1854. (b) Reaume, A. G.; Elliott, J. L.; Hoffman, E. K.; Kowall, N. W.; Ferrante, R. J.; Siwek, D. R.; Wilcox, H. M.; Flood, D. G.; Beal, M. F.; Brown, R. H.; Scott, R. W.; Snider, W. D. Motor Neurons in Cu/Zn Superoxide Dismutase-Deficient Mice Develop Normally but Exhibit Enhanced Cell Death after Axonal Injury. Nat. Genet. 1996, 13, 43−47. (33) (a) Liu, R.; Althaus, J. S.; Ellerbrock, B. R.; Becker, D. A.; Gurney, M. E. Enhanced Oxygen Radical Production in a Transgenic Mouse Model of Familial Amyotrophic Lateral Sclerosis. Ann. Neurol. 1998, 44, 763−770. (b) Kruman, I. I.; Pedersen, W. A.; Springer, J. E.; Mattson, M. P. ALS-Linked Cu/Zn-SOD Mutation Increases Vulnerability of Motor Neurons to Excitotoxicity by a Mechanism Involving Increased Oxidative Stress and Perturbed Calcium Homeostasis. Exp. Neurol. 1999, 160, 28−39. (34) (a) Ghadge, G. D.; Lee, J. P.; Bindokas, V. P.; Jordan, J.; Ma, L.; Miller, R. J.; Roos, R. P. Mutant Superoxide Dismutase-1-Linked Familial Amyotrophic Lateral Sclerosis: Molecular Mechanisms of Neuronal Death and Protection. J. Neurosci. 1997, 17, 8756−8766. (b) Liu, D.; Wen, J.; Liu, J.; Li, L. The Roles of Free Radicals in Amyotrophic Lateral Sclerosis: Reactive Oxygen Species and Elevated Oxidation of Protein, DNA, and Membrane Phospholipids. FASEB J. 1999, 13, 2318−2328. (c) Liu, R.; Li, B.; Flanagan, S. W.; Oberley, L. W.; Gozal, D.; Qiu, M. Increased Mitochondrial Antioxidative Activity or Decreased Oxygen Free Radical Propagation Prevent Mutant SOD1Mediated Motor Neuron Cell Death and Increase Amyotrophic Lateral Sclerosis-like Transgenic Mouse Survival. J. Neurochem. 2002, 80, 488− 500. (35) Wiedau-Pazos, M.; Goto, J. J.; Rabizadeh, S.; Gralla, E. B.; Roe, J. A.; Lee, M. K.; Valentine, J. S.; Bredesen, D. E. Altered Reactivity of Superoxide Dismutase in Familial Amyotrophic Lateral Sclerosis. Science 1996, 271, 515−518. (36) (a) Yim, H.-S.; Kang, J.-H.; Chock, P. B.; Stadtman, E. R.; Yim, M. B. A Familial Amyotrophic Lateral Sclerosis-Associated A4V Cu,ZnSuperoxide Dismutase Mutant Has a Lower Km for Hydrogen Peroxide. J. Biol. Chem. 1997, 272, 8861−8863. (b) Yim, M. B.; Kang, J. H.; Yim,

H. S.; Kwak, H. S.; Chock, P. B.; Stadtman, E. R. A Gain-of-Function of an Amyotrophic Lateral Sclerosis-Associated Cu,Zn-Superoxide Dismutase Mutant: An Enhancement of Free Radical Formation Due to a Decrease in Km for Hydrogen Peroxide. Proc. Natl. Acad. Sci. U.S.A. 1996, 93, 5709−5714. (37) Wang, J.; Slunt, H.; Gonzales, V.; Fromholt, D.; Coonfield, M.; Copeland, N. G.; Jenkins, N. A.; Borchelt, D. R. Copper-Binding-SiteNull SOD1 Causes ALS in Transgenic Mice: Aggregates of Non-Native SOD1 Delineate a Common Feature. Hum. Mol. Genet. 2003, 12, 2753− 2764. (38) Subramaniam, J. R.; Lyons, W. E.; Liu, J.; Bartnikas, T. B.; Rothstein, J.; Price, D. L.; Cleveland, D. W.; Gitlin, J. D.; Wong, P. C. Mutant SOD1 Causes Motor Neuron Disease Independent of Copper Chaperone-Mediated Copper Loading. Nat. Neurosci. 2002, 5, 301− 307. (39) (a) Johnston, J. A.; Dalton, M. J.; Gurney, M. E.; Ron, R. K. Formation of High Molecular Weight Complexes of Mutant Cu,ZnSuperoxide Dismutase in a Mouse Model for Familial Amyotrophic Lateral Sclerosis. Proc. Natl. Acad. Sci. U.S.A. 2000, 97, 12571−12576. (b) Rakhit, R.; Cunningham, P.; Furtos-Matei, A.; Dahan, S.; Qi, X.-F.; Crow, J. P.; Cashman, N. R.; Kondejewski, L. H.; Chakrabartty, A. Oxidation-Induced Misfolding and Aggregation of Superoxide Dismutase and Its Implications for Amyotrophic Lateral Sclerosis. J. Biol. Chem. 2002, 277, 47551−47556. (40) Pasinelli, P.; Belford, M. E.; Lennon, N.; Bacskai, B. J.; Hyman, B. T.; Trotti, D.; Brown, R. H., Jr. Amyotrophic Lateral SclerosisAssociated SOD1 Mutant Proteins Bind and Aggregate with Bcl-2 in Spinal Cord Mitochondria. Neuron 2004, 43, 19−30. (41) (a) Carrì, M.; Cozzolino, M. SOD1 and Mitochondria in ALS: A Dangerous Liaison. J. Bioenerg. Biomembr. 2011, 43, 593−599. (b) Shi, P.; Gal, J.; Kwinter, D. M.; Liu, X.; Zhu, H. Mitochondrial Dysfunction in Amyotrophic Lateral Sclerosis. Biochim. Biophys. Acta 2010, 1802, 45−51. (42) Filosto, M.; Scarpelli, M.; Cotelli, M.; Vielmi, V.; Todeschini, A.; Gregorelli, V.; Tonin, P.; Tomelleri, G.; Padovani, A. The Role of Mitochondria in Neurodegenerative Diseases. J. Neurol. 2011, 258, 1763−1774. (43) Kirkinezos, I. G.; Bacman, S. R.; Hernandez, D.; Oca-Cossio, J.; Arias, L. J.; Perez-Pinzon, M. A.; Bradley, W. G.; Moraes, C. T. Cytochrome c Association with the Inner Mitochondrial Membrane Is Impaired in the CNS of G93A-SOD1 Mice. J. Neurosci. 2005, 25, 164− 172. (44) Mattiazzi, M.; D’Aurelio, M.; Gajewski, C. D.; Martushova, K.; Kiaei, M.; Beal, M. F.; Manfredi, G. Mutated Human SOD1 Causes Dysfunction of Oxidative Phosphorylation in Mitochondria of Transgenic Mice. J. Biol. Chem. 2002, 277, 29626−29633. (45) Warita, H.; Hayashi, T.; Murakami, T.; Manabe, Y.; Abe, K. Oxidative Damage to Mitochondrial DNA in Spinal Motoneurons of Transgenic ALS Mice. Mol. Brain Res. 2001, 89, 147−152. (46) Wiedemann, F. R.; Manfredi, G.; Mawrin, C.; Beal, M. F.; Schon, E. A. Mitochondrial DNA and Respiratory Chain Function in Spinal Cords of ALS Patients. J. Neurochem. 2002, 80, 616−625. (47) (a) Holcik, M., LaCasse, E., MacKenzie, A., Korneluk, R., Eds. Apoptosis in Health and Disease: Clinical and Therapeutic Aspects, 1st ed.; Cambridge University Press: Cambridge, U.K., 2005. (b) Caroppi, P.; Sinibaldi, F.; Fiorucci, L.; Santucci, R. Apoptosis and Human Diseases: Mitochondrion Damage and Lethal Role of Released Cytochrome c as Proapoptotic Protein. Curr. Med. Chem. 2009, 16, 4058−4065. (48) Guégan, C.; Vila, M.; Rosoklija, G.; Hays, A. P.; Przedborski, S. Recruitment of the Mitochondrial-Dependent Apoptotic Pathway in Amyotrophic Lateral Sclerosis. J. Neurosci. 2001, 21, 6569−6576. (49) (a) Naoi, M.; Maruyama, W.; Yi, H.; Inaba, K.; Akao, Y.; ShamotoNagai, M. Mitochondria in Neurodegenerative Disorders: Regulation of the Redox State and Death Signaling Leading to Neuronal Death and Survival. J. Neural Transm. 2009, 116, 1371−1381. (b) Ribe, E. M.; Serrano-saiz, E.; Akpan, N.; Troy, C. M. Mechanisms of Neuronal Death in Disease: Defining the Models and the Players. Biochem. J. 2008, 415, 165−182. (c) Manfredi, G.; Xu, Z. Mitochondrial Dysfunction and Its L



Perspective

Role in Motor Neuron Degeneration in ALS. Mitochondrion 2005, 5, 77−87. (50) (a) Bossy-Wetzel, E.; Newmeyer, D. D.; Green, D. R. Mitochondrial Cytochrome c Release in Apoptosis Occurs Upstream of DEVD-Specific Caspase Activation and Independently of Mitochondrial Transmembrane Depolarization. EMBO J. 1998, 17, 37−49. (b) Pasinelli, P.; Houseweart, M. K.; Brown, R. H., Jr.; Don, W. C. Caspase-1 and -3 Are Sequentially Activated in Motor Neuron Death in Cu,Zn Superoxide Dismutase-Mediated Familial Amyotrophic Lateral Sclerosis. Proc. Natl. Acad. Sci. U.S.A. 2000, 97, 13901−13906. (51) (a) Li, M.; Ona, V. O.; Guégan, C.; Chen, M.; Jackson-Lewis, V.; Andrews, L. J.; Olszewski, A. J.; Stieg, P. E.; Lee, J.-P.; Przedborski, S.; Friedlander, R. M. Functional Role of Caspase-1 and Caspase-3 in an ALS Transgenic Mouse Model. Science 2000, 288, 335−339. (b) Friedlander, R. M.; Brown, R. H.; Gagliardini, V.; Wang, J.; Yuan, J. Inhibition of ICE Slows ALS in Mice. Nature 1997, 388, 31−32. (52) Ferri, A.; Cozzolino, M.; Crosio, C.; Nencini, M.; Casciati, A.; Gralla, E. B.; Rotilio, G.; Valentine, J. S.; Carrì, M. T. Familial ALSSuperoxide Dismutases Associate with Mitochondria and Shift their Redox Potentials. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 13860−13865. (53) Takeuchi, H.; Kobayashi, Y.; Ishigaki, S.; Doyu, M.; Sobue, G. Mitochondrial Localization of Mutant Superoxide Dismutase 1 Triggers Caspase-Dependent Cell Death in a Cellular Model of Familial Amyotrophic Lateral Sclerosis. J. Biol. Chem. 2002, 277, 50966−50972. (54) (a) Yang, Y.; Hentati, A.; Deng, H.-X.; Dabbagh, O.; Sasaki, T.; Hirano, M.; Hung, W.-Y.; Ouahchi, K.; Yan, J.; Azim, A. C.; Cole, N.; Gascon, G.; Yagmour, A.; Ben-Hamida, M.; Pericak-Vance, M.; Hentati, F. The Gene Encoding Alsin, a Protein with Three Guanine-Nucleotide Exchange Factor Domains, Is Mutated in a Form of Recessive Amyotrophic Lateral Sclerosis. Nat. Genet. 2001, 29, 160−165. (b) Hadano, S.; Hand, C. K.; Osuga, H.; Yanagisawa, Y.; Otomo, A.; Devon, R. S.; Miyamoto, N.; Showguchi-Miyata, J.; Okada, Y.; Singaraja, R.; Figlewicz, D. A.; Kwiatkowski, T.; Hosler, B. A.; Sagie, T. A Gene Encoding a Putative GTPase Regulator Is Mutated in Familial Amyotrophic Lateral Sclerosis. Nat. Genet. 2001, 29, 166−173. (55) Chen, Y.-Z.; Bennett, C. L.; Huynh, H. M.; Blair, I. P.; Puls, I.; Irobi, J.; Dierick, I.; Abel, A.; Kennerson, M. L.; Rabin, B. A.; Nicholson, G. A.; Auer-Grumbach, M.; Wagner, K.; De Jonghe, P.; Griffin, J. W.; Fischbeck, K. H.; Timmerman, V.; Cornblath, D. R.; Chance, P. F. DNA/RNA Helicase Gene Mutations in a Form of Juvenile Amyotrophic Lateral Sclerosis (ALS4). Am. J. Hum. Genet. 2004, 74, 1128−1135. (56) Nishimura, A. L.; Mitne-Neto, M.; Silva, H. C. A.; Richieri-Costa, A.; Middleton, S.; Cascio, D.; Kok, F.; Oliveira, J. R. M.; Gillingwater, T.; Webb, J.; Skehel, P.; Zatz, M. A Mutation in the Vesicle-Trafficking Protein VAPB Causes Late-Onset Spinal Muscular Atrophy and Amyotrophic Lateral Sclerosis. Am. J. Hum. Genet. 2004, 75, 822−831. (57) Neumann, M.; Sampathu, D. M.; Kwong, L. K.; Truax, A. C.; Micsenyi, M. C.; Chou, T. T.; Bruce, J.; Schuck, T.; Grossman, M.; Clark, C. M.; McCluskey, L. F.; Miller, B. L.; Masliah, E.; Mackenzie, I. R.; Feldman, H.; Feiden, W.; Kretzschmar, H. A.; Trojanowski, J. Q.; Lee, V. M.-Y. Ubiquitinated TDP-43 in Frontotemporal Lombar Degeneration and Amyotrophic Lateral Sclerosis. Science 2006, 314, 130−133. (58) (a) Mackenzie, I. R. A.; Bigio, E. H.; Ince, P. G.; Geser, F.; Neumann, M.; Cairns, N. J.; Kwong, L. K.; Forman, M. S.; Ravits, J.; Stewart, H.; Eisen, A.; McClusky, L.; Kretzschmar, H. A.; Monoranu, C. M.; Highley, J. R.; Kirby, J.; Siddique, T.; Shaw, P. J.; Lee, V. M. Y.; Trojanowski, J. Q. Pathological TDP-43 Distinguishes Sporadic Amyotrophic Lateral Sclerosis from Amyotrophic Lateral Sclerosis with SOD1 Mutations. Ann. Neurol. 2007, 61, 427−434. (b) Sreedharan, J.; Blair, I. P.; Tripathi, V. B.; Hu, X.; Vance, C.; Rogelj, B.; Ackerley, S.; Durnall, J. C.; Williams, K. L.; Buratti, E.; Baralle, F.; de Belleroche, J.; Mitchell, J. D.; Leigh, P. N.; Al-Chalabi, A.; Miller, C. C.; Nicholson, G.; Shaw, C. E. TDP-43 Mutations in Familial and Sporadic Amyotrophic Lateral Sclerosis. Science 2008, 319, 1668−1672. (c) Tan, C.-F.; Eguchi, H.; Tagawa, A.; Onodera, O.; Iwasaki, T.; Tsujino, A.; Nishizawa, M.; Kakita, A.; Takahashi, H. TDP-43 Immunoreactivity in Neuronal

Inclusions in Familial Amyotrophic Lateral Sclerosis with or without SOD1 Gene Mutation. Acta Neuropathol. 2007, 113, 535−542. (59) (a) Halliwell, B.; Gutteridge, J. M. C. Free Radicals in Biology and Medicine, 4th ed.; Oxford University Press: Oxford, U.K., 2007. (b) Adibhatla, R. M.; Hatcher, J. F. Lipid Oxidation and Peroxidation in CNS Health and Disease: From Molecular Mechanisms to Therapeutic Opportunities. Antioxid. Redox Signaling 2010, 12, 125− 169. (60) Hall, E. D.; Andrus, P. K.; Oostveen, J. A.; Fleck, T. J.; Gurney, M. E. Relationship of Oxygen Radical-Induced Lipid Peroxidative Damage to Disease Onset and Progression in a Transgenic Model of Familial ALS. J. Neurosci. Res. 1998, 53, 66−77. (61) (a) Ferrante, R. J.; Browne, S. E.; Shinobu, L. A.; Bowling, A. C.; Baik, M. J.; MacGarvey, U.; Kowall, N. W.; Brown, R. H., Jr.; Beal, M. F. Evidence of Increased Oxidative Damage in Both Sporadic and Familial Amyotrophic Lateral Sclerosis. J. Neurochem. 1997, 69, 2064−2074. (b) Beal, M. F.; Ferrante, R. J.; Browne, S. E.; Matthews, R. T.; Kowall, N. W.; Brown, R. H., Jr. Increased 3-Nitrotyrosine in Both Sporadic and Familial Amyotrophic Lateral Sclerosis. Ann. Neurol. 1997, 42, 644−654. (c) Ferrante, R. J.; Shinobu, L. A.; Schulz, J. B.; Matthews, R. T.; Thomas, C. E.; Kowall, N. W.; Gurney, M. E.; Beal, M. F. Increased 3Nitrotyrosine and Oxidative Damage in Mice with a Human Copper/ Zinc Superoxide Dismutase Mutation. Ann. Neurol. 1997, 42, 326−334. (d) Pedersen, W. A.; Fu, W.; Keller, J. N.; Markesbery, W. R.; Appel, S.; Smith, R. G.; Kasarskis, E.; Mattson, M. P. Protein Modification by the Lipid Peroxidation Product 4-Hydroxynonenal in the Spinal Cords of Amyotrophic Lateral Sclerosis Patients. Ann. Neurol. 1998, 44, 819− 824. (e) Tohgi, H.; Abe, T.; Yamazaki, K.; Murata, T.; Ishizaki, E.; Isobe, C. Remarkable Increase in Cerebrospinal Fluid 3-Nitrotyrosine in Patients with Sporadic Amyotrophic Lateral Sclerosis. Ann. Neurol. 1999, 46, 129−131. (62) Markesbery, W. R.; Lovell, M. A. Four-hydroxynonenal, a Product of Lipid Peroxidation, Is Increased in the Brain in Alzheimer’s Disease. Neurobiol. Aging 1998, 19, 33−36. (63) Fenton, H. J. H. Oxidation of Tartaric Acid in Presence of Iron. J. Chem. Soc. 1894, 65, 899−903. (64) (a) Leveugle, B.; Spik, G.; Perl, D. P.; Bouras, C.; Fillit, H. M.; Hof, P. R. The Iron-Binding Protein Lactotransferrin Is Present in Pathologic Lesions in a Variety of Neurodegenerative Disorders: A Comparative Immunohistochemical Analysis. Brain Res. 1994, 650, 20− 31. (b) Kasarskis, E. J.; Tandon, L.; Lovell, M. A.; Ehmann, W. D. Aluminum, Calcium, and Iron in the Spinal Cord of Patients with Sporadic Amyotrophic Lateral Sclerosis Using Laser Microprobe Mass Spectroscopy: A Preliminary Study. J. Neurol. Sci. 1995, 130, 203−208. (65) (a) Wang, X.-S.; Lee, S.; Simmons, Z.; Boyer, P.; Scott, K.; Liu, W.; Connor, J. Increased Incidence of the Hfe Mutation in Amyotrophic Lateral Sclerosis and Related Cellular Consequences. J. Neurol. Sci. 2004, 227, 27−33. (b) Goodall, E. F.; Greenway, M. J.; van Marion, I.; Carroll, C. B.; Hardiman, O.; Morrison, K. E. Association of the H63D Polymorphism in the Hemochromatosis Gene with Sporadic ALS. Neurology 2005, 65, 934−937. (66) Olsen, M. K.; Roberds, S. L.; Ellerbrock, B. R.; Fleck, T. J.; McKinley, D. K.; Gurney, M. E. Disease Mechanisms Revealed by Transcription Profiling in SOD1-G93A Transgenic Mouse Spinal Cord. Ann. Neurol. 2001, 50, 730−740. (67) Hottinger, A. F.; Fine, E. G.; Gurney, M. E.; Zurn, A. D.; Aebischer, P. The Copper Chelator D-Penicillamine Delays Onset of Disease and Extends Survival in a Transgenic Mouse Model of Familial Amyotrophic Lateral Sclerosis. Eur. J. Neurosci. 1997, 9, 1548−1551. (68) Azzouz, M.; Poindron, P.; Guettier, S.; Leclerc, N.; Andres, C.; Warter, J.-M.; Borg, J. Prevention of Mutant SOD1 Motor Neuron Degeneration by Copper Chelators in Vitro. J. Neurobiol. 2000, 42, 49− 55. (69) Kiaei, M.; Bush, A. I.; Morrison, B. M.; Morrison, J. H.; Cherny, R. A.; Volitakis, I.; Beal, M. F.; Gordon, J. W. Genetically Decreased Spinal Cord Copper Concentration Prolongs Life in a Transgenic Mouse Model of Amyotrophic Lateral Sclerosis. J. Neurosci. 2004, 24, 7945− 7950. M



Perspective

(70) Hayward, L. J.; Rodriguez, J. A.; Kim, J. W.; Tiwari, A.; Goto, J. J.; Cabelli, D. E.; Valentine, J. S.; Brown, R. H. Decreased Metallation and Activity in Subsets of Mutant Superoxide Dismutases Associated with Familial Amyotrophic Lateral Sclerosis. J. Biol. Chem. 2002, 277, 15923−15931. (71) (a) Gabbianelli, R.; Ferri, A.; Rotilio, G.; Carrì, M. T. Aberrant Copper Chemistry as a Major Mediator of Oxidative Stress in a Human Cellular Model of Amyotrophic Lateral Sclerosis. J. Neurochem. 1999, 73, 1175−1180. (b) Corson, L. B.; Strain, J. J.; Culotta, V. C.; Cleveland, D. W. Chaperone-Facilitated Copper Binding Is a Property Common to Several Classes of Familial Amyotrophic Lateral Sclerosis-Linked Superoxide Dismutase Mutants. Proc. Natl. Acad. Sci. U.S.A. 1998, 95, 6361−6366. (72) (a) Lau, A.; Tymianski, M. Glutamate Receptors, Neurotoxicity and Neurodegeneration. Pfluegers Arch. 2010, 460, 525−542. (b) Le Verche, V.; Ikiz, B.; Jacquier, A. Glutamate Pathway Implication in Amyotrophic Lateral Sclerosis: What Is the Signal in the Noise? J. Recept., Ligand Channel Res. 2011, 4, 1−22. (73) Grosskreutz, J.; Van Den Bosch, L.; Keller, B. U. Calcium Dysregulation in Amyotrophic Lateral Sclerosis. Cell Calcium 2010, 47, 165−174. (74) Rothstein, J. D.; Tsai, G.; Kuncl, R. W.; Clawson, L.; Cornblath, D. R.; Drachman, D. B.; Pestronk, A.; Stauch, B. L.; Coyle, J. T. Abnormal Excitatory Amino Acid Metabolism in Amyotrophic Lateral Sclerosis. Ann. Neurol. 1990, 28, 18−25. (75) (a) Lafon-Cazal, M.; Pietri, S.; Culcasi, M.; Bockaert, J. NMDADependent Superoxide Production and Neurotoxicity. Nature 1993, 364, 535−537. (b) Reynolds, I.; Hastings, T. Glutamate Induces the Production of Reactive Oxygen Species in Cultured Forebrain Neurons Following NMDA Receptor Activation. J. Neurosci. 1995, 15, 3318− 3327. (c) Dugan, L.; Sensi, S.; Canzoniero, L.; Handran, S.; Rothman, S.; Lin, T.; Goldberg, M.; Choi, D. Mitochondrial Production of Reactive Oxygen Species in Cortical Neurons Following Exposure to N-MethylD-aspartate. J. Neurosci. 1995, 15, 6377−6388. (d) Stout, A. K.; Raphael, H. M.; Kanterewicz, B. I.; Klann, E.; Reynolds, I. J. Glutamate-Induced Neuron Death Requires Mitochondrial Calcium Uptake. Nat. Neurosci. 1998, 1, 366−373. (76) Zhu, L. P.; Yu, X. D.; Ling, S.; Brown, R. A.; Kuo, T. H. Mitochondrial Ca2+ Homeostasis in the Regulation of Apoptotic and Necrotic Cell Deaths. Cell Calcium 2000, 28, 107−117. (77) Dykens, J. A. Isolated Cerebral and Cerebellar Mitochondria Produce Free Radicals when Exposed to Elevated Ca2+ and Na+: Implications for Neurodegeneration. J. Neurochem. 1994, 63, 584−591. (78) Rattray, M.; Bendotti, C. Does Excitotoxic Cell Death of Motor Neurons in ALS Arise from Glutamate Transporter and Glutamate Receptor Abnormalities? Exp. Neurol. 2006, 201, 15−23. (79) Bouvier, M.; Szatkowski, M.; Amato, A.; Attwell, D. The Glial Cell Glutamate Uptake Carrier Countertransports pH-Changing Anions. Nature 1992, 360, 471−474. (80) Kvamme, E.; Schousboe, A.; Hertz, L.; Torgner, I. A.; Svenneby, G. Developmental Change of Endogenous Glutamate and GammaGlutamyl Transferase in Cultured Cerebral Cortical Interneurons and Cerebellar Cranule Cells, and in Mouse Cerebral Cortex and Cerebellum in Vivo. Neurochem. Res. 1985, 10, 993−1008. (81) (a) Shaw, P. J.; Forrest, V.; Ince, P. G.; Richardson, J. P.; Wastell, H. J. CSF and Plasma Amino Acid Levels in Motor Neuron Disease: Elevation of CSF Glutamate in a Subset of Patients. Neurodegeneration 1995, 4, 209−216. (b) Rothstein, J. D.; Martin, L.; Levey, A. I.; DykesHoberg, M.; Jin, L.; Wu, D.; Nash, N.; Kuncl, R. W. Localization of Neuronal and Glial Glutamate Transporters. Neuron 1994, 13, 713− 725. (c) Lehre, K.; Levy, L.; Ottersen, O.; Storm-Mathisen, J.; Danbolt, N. Differential Expression of Two Glial Glutamate Transporters in the Rat Brain: Quantitative and Immunocytochemical Observations. J. Neurosci. 1995, 15, 1835−1853. (82) (a) Tanaka, K.; Watase, K.; Manabe, T.; Yamada, K.; Watanabe, M.; Takahashi, K.; Iwama, H.; Nishikawa, T.; Ichihara, N.; Kikuchi, T.; Okuyama, S.; Kawashima, N.; Hori, S.; Takimoto, M.; Wada, K. Epilepsy and Exacerbation of Brain Injury in Mice Lacking the Glutamate Transporter GLT-1. Science 1997, 276, 1699−1702. (b) Howland, D. S.;

Liu, J.; She, Y.; Goad, B.; Maragakis, N. J.; Kim, B.; Erickson, J.; Kulik, J.; DeVito, L.; Psaltis, G.; DeGennaro, L. J.; Cleveland, D. W.; Rothstein, J. D. Focal Loss of the Glutamate Transporter EAAT2 in a Transgenic Rat Model of SOD1 Mutant-Mediated Amyotrophic Lateral Sclerosis (ALS). Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 1604−1609. (c) Haugeto, Ø.; Ullensvang, K.; Levy, L. M.; Chaudhry, F. A.; Honoré, T.; Nielsen, M.; Lehre, K. P.; Danbolt, N. C. Brain Glutamate Transporter Proteins Form Homomultimers. J. Biol. Chem. 1996, 271, 27715−27722. (d) Lehre, K. P.; Danbolt, N. C. The Number of Glutamate Transporter Subtype Molecules at Glutamatergic Synapses: Chemical and Stereological Quantification in Young Adult Rat Brain. J. Neurosci. 1998, 18, 8751−8757. (e) Rothstein, J. D.; Dykes-Hoberg, M.; Pardo, C. A.; Bristol, L. A.; Jin, L.; Kuncl, R. W.; Kanai, Y.; Hediger, M. A.; Wang, Y.; Schielke, J. P.; Welty, D. F. Knockout of Glutamate Transporters Reveals a Major Role for Astroglial Transport in Excitotoxicity and Clearance of Glutamate. Neuron 1996, 16, 675−686. (83) Rothstein, J. D.; Martin, L. J.; Kuncl, R. W. Decreased Glutamate Transport by the Brain and Spinal Cord in Amyotrophic Lateral Sclerosis. N. Engl. J. Med. 1992, 326, 1464−1468. (84) (a) Maragakis, N. J.; Dykes-Hoberg, M.; Rothstein, J. D. Altered Expression of the Glutamate Transporter EAAT2b in Neurological Disease. Ann. Neurol. 2004, 55, 469−477. (b) Lin, C.-L. G.; Bristol, L. A.; Jin, L.; Dykes-Hoberg, M.; Crawford, T.; Clawson, L.; Rothstein, J. D. Aberrant RNA Processing in a Neurodegenerative Disease: The Cause for Absent EAAT2, a Glutamate Transporter, in Amyotrophic Lateral Sclerosis. Neuron 1998, 20, 589−602. (c) Rothstein, J. D.; Kammen, M. V.; Levey, A. I.; Martin, L. J.; Kuncl, R. W. Selective Loss of Glial Glutamate Transporter GLT-1 in Amyotrophic Lateral Sclerosis. Ann. Neurol. 1995, 38, 73−84. (d) Bristol, L. A.; Rothstein, J. D. Glutamate Transporter Gene Expression in Amyotrophic Lateral Sclerosis Motor Cortex. Ann. Neurol. 1996, 39, 676−679. (85) Bendotti, C.; Tortarolo, M.; Suchak, S. K.; Calvaresi, N.; Carvelli, L.; Bastone, A.; Rizzi, M.; Rattray, M.; Mennini, T. Transgenic SOD1 G93A Mice Develop Reduced GLT-1 in Spinal Cord without Alterations in Cerebrospinal Fluid Glutamate Levels. J. Neurochem. 2001, 79, 737−746. (86) Rothstein, J. D.; Jin, L.; Dykes-Hoberg, M.; Kuncl, R. W. Chronic Inhibition of Glutamate Uptake Produces a Model of Slow Neurotoxicity. Proc. Natl. Acad. Sci. U.S.A. 1993, 90, 6591−6595. (87) Guo, H.; Lai, L.; Butchbach, M. E. R.; Stockinger, M. P.; Shan, X.; Bishop, G. A.; Lin, C.-l. G. Increased Expression of the Glial Glutamate Transporter EAAT2 Modulates Excitotoxicity and Delays the Onset but Not the Outcome of ALS in Mice. Hum. Mol. Genet. 2003, 12, 2519− 2532. (88) Tovar-y-Romo, L. B.; Santa-Cruz, L. D.; Zepeda, A.; Tapia, R. Chronic Elevation of Extracellular Glutamate Due to Transport Blockade Is Innocuous for Spinal Motoneurons in Vivo. Neurochem. Int. 2009, 54, 186−191. (89) Volterra, A.; Trotti, D.; Tromba, C.; Floridi, S.; Racagni, G. Glutamate Uptake Inhibition by Oxygen Free Radicals in Rat Cortical Astrocytes. J. Neurosci. 1994, 14, 2924−2932. (90) Trotti, D.; Rolfs, A.; Danbolt, N. C.; Brown, R. H.; Hediger, M. A. SOD1 Mutants Linked to Amyotrophic Lateral Sclerosis Selectively Inactivate a Glial Glutamate Transporter. Nat. Neurosci. 1999, 2, 427− 433. (91) (a) MacDermott, A. B.; Mayer, M. L.; Westbrook, G. L.; Smith, S. J.; Barker, J. L. NMDA-receptor Activation Increases Cytoplasmic Calcium Concentration in Cultured Spinal Cord Neurones. Nature 1986, 321, 519−522. (b) Weiss, J. H. Ca2+ Permeable AMPA Channels in Diseases of the Nervous System. Front. Mol. Neurosci. 2011, 4, 1−7. (c) Hollmann, M.; Hartley, M.; Heinemann, S. Ca2+ Permeability of KAAMPA-Gated Glutamate Receptor Channels Depends on Subunit Composition. Science 1991, 252, 851−853. (92) Carriedo, S. G.; Yin, H. Z.; Weiss, J. H. Motor Neurons Are Selectively Vulnerable to AMPA/Kainate Receptor-Mediated Injury in Vitro. J. Neurosci. 1996, 16, 4069−4079. (93) (a) Greger, I. H.; Ziff, E. B.; Penn, A. C. Molecular Determinants of AMPA Receptor Subunit Assembly. Trends Neurosci. 2007, 30, 407− N



Perspective

416. (b) Mayer, M. L. Glutamate Receptor Ion Channels. Curr. Opin. Neurobiol. 2005, 15, 282−288. (94) (a) Kawahara, Y.; Ito, K.; Sun, H.; Aizawa, H.; Kanazawa, I.; Kwak, S. Glutamate Receptors: RNA Editing and Death of Motor Neurons. Nature 2004, 427, 801. (b) Burnashev, N.; Monyer, H.; Seeburg, P. H.; Sakmann, B. Divalent Ion Permeability of AMPA Receptor Channels Is Dominated by the Edited Form of a Single Subunit. Neuron 1992, 8, 189−198. (95) Kawahara, Y.; Kwak, S.; Sun, H.; Ito, K.; Hashida, H.; Aizawa, H.; Jeong, S.-Y.; Kanazawa, I. Human Spinal Motoneurons Express Low Relative Abundance of GluR2 mRNA: An Implication for Excitotoxicity in ALS. J. Neurochem. 2003, 85, 680−689. (96) Pellegrini-Giampietro, D. E.; Gorter, J. A.; Bennett, M. V. L; Zukin, R. S. The GluR2 (GluR-B) Hypothesis: Ca2+-Permeable AMPA Receptors in Neurological Disorders. Trends Neurosci. 1997, 20, 464− 470. (97) (a) Van Damme, P.; Braeken, D.; Callewaert, G.; Robberecht, W.; Van Den Bosch, L. GluR2 Deficiency Accelerates Motor Neuron Degeneration in a Mouse Model of Amyotrophic Lateral Sclerosis. J. Neuropathol. Exp. Neurol. 2005, 64, 605−612. (b) Tateno, M.; Sadakata, H.; Tanaka, M.; Itohara, S.; Shin, R.-M.; Miura, M.; Masuda, M.; Aosaki, T.; Urushitani, M.; Misawa, H.; Takahashi, R. Calcium-Permeable AMPA Receptors Promote Misfolding of Mutant SOD1 Protein and Development of Amyotrophic Lateral Sclerosis in a Transgenic Mouse Model. Hum. Mol. Genet. 2004, 13, 2183−2196. (98) Spalloni, A.; Albo, F.; Ferrari, F.; Mercuri, N.; Bernardi, G.; Zona, C.; Longone, P. Cu/Zn-Superoxide Dismutase (GLY93–>ALA) Mutation Alters AMPA Receptor Subunit Expression and Function and Potentiates Kainate-Mediated Toxicity in Motor Neurons in Culture. Neurobiol. Dis. 2004, 15, 340−350. (99) (a) Tortarolo, M.; Grignaschi, G.; Calvaresi, N.; Zennaro, E.; Spaltro, G.; Colovic, M.; Fracasso, C.; Guiso, G.; Elger, B.; Schneider, H.; Seilheimer, B.; Caccia, S.; Bendotti, C. Glutamate AMPA Receptors Change in Motor Neurons of SOD1G93A Transgenic Mice and Their Inhibition by a Noncompetitive Antagonist Ameliorates the Progression of Amytrophic Lateral Sclerosis-like Disease. J. Neurosci. Res. 2006, 83, 134−146. (b) Van Damme, P.; Leyssen, M.; Callewaert, G.; Robberecht, W.; Van Den Bosch, L. The AMPA Receptor Antagonist NBQX Prolongs Survival in a Transgenic Mouse Model of Amyotrophic Lateral Sclerosis. Neurosci. Lett. 2003, 343, 81−84. (c) Canton, T.; Böhme, G. A.; Boireau, A.; Bordier, F.; Mignani, S.; Jimonet, P.; Jahn, G.; Alavijeh, M.; Stygall, J.; Roberts, S.; Brealey, C.; Vuilhorgne, M.; Debono, M.-W.; Le Guern, S.; Laville, M.; Briet, D.; Roux, M.; Stutzmann, J.-M.; Pratt, J. RPR 119990, a Novel α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid Antagonist: Synthesis, Pharmacological Properties, and Activity in an Animal Model of Amyotrophic Lateral Sclerosis. J. Pharmacol. Exp. Ther. 2001, 299, 314−322. (100) Rembach, A.; Turner, B. J.; Bruce, S.; Cheah, I. K.; Scott, R. L.; Lopes, E. C.; Zagami, C. J.; Beart, P. M.; Cheung, N. S.; Langford, S. J.; Cheema, S. S. Antisense Peptide Nucleic Acid Targeting GluR3 Delays Disease Onset and Progression in the SOD1 G93A Mouse Model of Familial ALS. J. Neurosci. Res. 2004, 77, 573−582. (101) Langford, S. J.; Cheema, S. S. Unpublished results. (102) Francis, K.; Bach, J. R.; DeLisa, J. A. Evaluation and Rehabilitation of Patients with Adult Motor Neuron Disease. Arch. Phys. Med. Rehabil. 1999, 80, 951−963. (103) (a) Cheah, B. C.; Vucic, S.; Krishnan, A. V.; Kiernan, M. C. Riluzole, Neuroprotection and Amyotrophic Lateral Sclerosis. Curr. Med. Chem. 2010, 17, 1942−1959. (b) Bellingham, M. C. A Review of the Neural Mechanisms of Action and Clinical Efficiency of Riluzole in Treating Amyotrophic Lateral Sclerosis: What Have We Learned in the Last Decade? CNS Neurosci. Ther. 2011, 17, 4−31. (104) Traynor, B. J.; Alexander, M.; Corr, B.; Frost, E.; Hardiman, O. Effect of a Multidisciplinary Amyotrophic Lateral Sclerosis (ALS) Clinic on ALS Survival: A Population Based Study, 1996−2000. J. Neurol. Neurosurg. Psychiatry 2003, 74, 1258−1261. (105) Lacomblez, L.; Bensimon, G.; Leigh, P.; Debove, C.; Bejuit, R.; Truffinet, P.; Meininger, V. Long-Term Safety of Riluzole in

Amyotrophic Lateral Sclerosis. Amyotrophic Lateral Scler. 2002, 3, 23− 29. (106) Traynor, B. J.; Alexander, M.; Corr, B.; Frost, E.; Hardiman, O. An Outcome Study of Riluzole in Amyotrophic Lateral Sclerosis. J. Neurol. 2003, 250, 473−479. (107) Packer, J. E.; Slater, T. F.; Willson, R. L. Direct Observation of a Free Radical Interaction between Vitamin E and Vitamin C. Nature 1979, 278, 737−738. (108) Doba, T.; Burton, G. W.; Ingold, K. U. Antioxidant and CoAntioxidant Activity of Vitamin C. The Effect of Vitamin C, Either Alone or in the Presence of Vitamin E or a Water-Soluble Vitamin E Analogue, upon the Peroxidation of Aqueous Multilamellar Phospholipid Liposomes. Biochim. Biophys. Acta 1985, 835, 298−303. (109) Frei, B.; England, L.; Ames, B. N. Ascorbate Is an Outstanding Antioxidant in Human Blood Plasma. Proc. Natl. Acad. Sci. U.S.A. 1989, 86, 6377−6381. (110) Gurney, M. E.; Cutting, F. B.; Zhai, P.; Doble, A.; Taylor, C. P.; Andrus, P. K.; Hall, E. D. Benefit of Vitamin E, Riluzole, and Gababapentin in a Transgenic Model of Familial Amyotrophic Lateral Sclerosis. Ann. Neurol. 1996, 39, 147−157. (111) (a) Orrell, R. W.; Lane, R. J. M.; Ross, M. Antioxidant Treatment for Amyotrophic Lateral Sclerosis or Motor Neuron Disease. Cochrane Database Syst. Rev. 2007, 1−30. (b) Galbussera, A.; Tremolizzo, L.; Brighina, L.; Testa, D.; Lovati, R.; Ferrarese, C.; Cavaletti, G.; Filippin, G. Vitamin E Intake and Quality of Life in Amyotrophic Lateral Sclerosis Patients: A Follow-Up Case Series Study. Neurol. Sci. 2006, 27, 190− 193. (112) Ascherio, A.; Weisskopf, M. G.; O’Reilly, E. J.; Jacobs, E. J.; McCullough, M. L.; Calle, E. E.; Cudkowicz, M.; Thun, M. J. Vitamin E Intake and Risk of Amyotrophic Lateral Sclerosis. Ann. Neurol. 2005, 57, 104−110. (113) Ferrante, R.; Klein, A.; Dedeoglu, A.; Flint Beal, M. Therapeutic Efficacy of EGb761 (Gingko biloba Extract) in a Transgenic Mouse Model of Amyotrophic Lateral Sclerosis. J. Mol. Neurosci. 2001, 17, 89− 96. (114) Crow, J. P.; Calingasan, N. Y.; Chen, J.; Hill, J. L.; Beal, M. F. Manganese Porphyrin Given at Symptom Onset Markedly Extends Survival of ALS Mice. Ann. Neurol. 2005, 58, 258−265. (115) Wu, A. S.; Kiaei, M.; Aguirre, N.; Crow, J. P.; Calingasan, N. Y.; Browne, S. E.; Beal, M. F. Iron Porphyrin Treatment Extends Survival in a Transgenic Animal Model of Amyotrophic Lateral Sclerosis. J. Neurochem. 2003, 85, 142−150. (116) Barber, S. C.; Mead, R. J.; Shaw, P. J. Oxidative Stress in ALS: A Mechanism of Neurodegeneration and a Therapeutic Target. Biochim. Biophys. Acta 2006, 1762, 1051−1067. (117) Traynor, B. J.; Bruijn, L.; Conwit, R.; Beal, F.; O’Neill, G.; Fagan, S. C.; Cudkowicz, M. E. Neuroprotective Agents for Clinical Trials in ALS: A Systematic Assessment. Neurology 2006, 67, 20−27. (118) (a) Kriz, J.; Nguyen, M. D.; Julien, J.-P. Minocycline Slows Disease Progression in a Mouse Model of Amyotrophic Lateral Sclerosis. Neurobiol. Dis. 2002, 10, 268−278. (b) Zhu, S.; Stavrovskaya, I. G.; Drozda, M.; Kim, B. Y. S.; Ona, V.; Li, M.; Sarang, S.; Liu, A. S.; Hartley, D. M.; Wu, D. C.; Gullans, S.; Ferrante, R. J.; Przedborski, S.; Kristal, B. S.; Friedlander, R. M. Minocycline Inhibits Cytochrome c Release and Delays Progression of Amyotrophic Lateral Sclerosis in Mice. Nature 2002, 417, 74−78. (119) Gordon, P. H.; Moore, D. H.; Miller, R. G.; Florence, J. M.; Verheijde, J. L.; Doorish, C.; Hilton, J. F.; Spitalny, G. M.; MacArthur, R. B.; Mitsumoto, H.; Neville, H. E.; Boylan, K.; Mozaffar, T.; Belsh, J. M.; Ravits, J.; Bedlack, R. S.; Graves, M. C.; McCluskey, L. F.; Barohn, R. J.; Tandan, R. Efficacy of Minocycline in Patients with Amyotrophic Lateral Sclerosis: A Phase III Randomised Trial. Lancet Neurol. 2007, 6, 1045−1053. (120) Rothstein, J. D.; Patel, S.; Regan, M. R.; Haenggeli, C.; Huang, Y. H.; Bergles, D. E.; Jin, L.; Dykes Hoberg, M.; Vidensky, S.; Chung, D. S.; Toan, S. V.; Bruijn, L. I.; Su, Z.-z.; Gupta, P.; Fisher, P. B. β-Lactam Antibiotics Offer Neuroprotection by Increasing Glutamate Transporter Expression. Nature 2005, 433, 73−77. O



Perspective

(121) Beghi, E.; Bendotti, C.; Mennini, T.; Miller, T.; Cleveland, D. Merits of a New Drug Trial for ALS? Science 2005, 308, 632b−633b. (122) Pascuzzi, R. M.; Shefner, J.; Chappell, A. S.; Bjerke, J. S.; Tamura, R.; Chaudhry, V.; Clawson, L.; Haas, L.; Rothstein, J. D. A Phase II Trial of Talampanel in Subjects with Amyotrophic Lateral Sclerosis. Amyotrophic Lateral Scler. 2010, 11, 266−271. (123) Robinson, R. New ALS Drug Shows Dose-Dependent Efficacy in Phase 2 Trial. Neurol. Today 2010, 10, 33−34. (124) McGeer, E. G.; McGeer, P. L. Pharmacologic Approaches to the Treatment of Amyotrophic Lateral Sclerosis. BioDrugs 2005, 19, 31−37. (125) Zhang, W.; Narayanan, M.; Friedlander, R. M. Additive Neuroprotective Effects of Minocycline with Creatine in a Mouse Model of ALS. Ann. Neurol. 2003, 53, 267−270. (126) Kriz, J.; Gowing, G.; Julien, J.-P. Efficient Three-Drug Cocktail for Disease Induced by Mutant Superoxide Dismutase. Ann. Neurol. 2003, 53, 429−436. (127) Shin, J. H.; Cho, S. I.; Lim, H. R.; Lee, J. K.; Lee, Y. A.; Noh, J. S.; Joo, I. S.; Kim, K.-W.; Gwag, B. J. Concurrent Administration of Neu2000 and Lithium Produces Marked Improvement of Motor Neuron Survival, Motor Function, and Mortality in a Mouse Model of Amyotrophic Lateral Sclerosis. Mol. Pharmacol. 2007, 71, 965−975. (128) Dykxhoorn, D. M.; Novina, C. D.; Sharp, P. A. Killing the Messenger: Short RNAs that Silence Gene Expression. Nat. Rev. Mol. Cell Biol. 2003, 4, 457−467. (129) Ding, H.; Schwarz, D. S.; Keene, A.; Affar, E. B.; Fenton, L.; Xia, X.; Shi, Y.; Zamore, P. D.; Xu, Z. Selective Silencing by RNAi of a Dominant Allele That Causes Amyotrophic Lateral Sclerosis. Aging Cell 2003, 2, 209−217. (130) (a) Raoul, C.; Abbas-Terki, T.; Bensadoun, J.-C.; Guillot, S.; Haase, G.; Szulc, J.; Henderson, C. E.; Aebischer, P. Lentiviral-Mediated Silencing of SOD1 through RNA Interference Retards Disease Onset and Progression in a Mouse Model of ALS. Nat. Med. 2005, 11, 423− 428. (b) Ralph, G. S.; Radcliffe, P. A.; Day, D. M.; Carthy, J. M.; Leroux, M. A.; Lee, D. C. P.; Wong, L.-F.; Bilsland, L. G.; Greensmith, L.; Kingsman, S. M.; Mitrophanous, K. A.; Mazarakis, N. D.; Azzouz, M. Silencing Mutant SOD1 Using RNAi Protects against Neurodegeneration and Extends Survival in an ALS Model. Nat. Med. 2005, 11, 429− 433. (131) Smith, R. A.; Miller, T. M.; Yamanaka, K.; Monia, B. P.; Condon, T. P.; Hung, G.; Lobsiger, C. S.; Ward, C. M.; McAlonis-Downes, M.; Wei, H.; Wancewicz, E. V.; Bennett, C. F.; Cleveland, D. W. Antisense Oligonucleotide Therapy for Neurodegenerative Disease. J. Clin. Invest. 2006, 116, 2290−2296. (132) 2urner, B. J.; Cheah, I. K.; Macfarlane, K. J.; Lopes, E. C.; Petratos, S.; Langford, S. J.; Cheema, S. S. Antisense Peptide Nucleic Acid-Mediated Knockdown of the p75 Neurotrophin Receptor Delays Motor Neuron Disease in Mutant SOD1 Transgenic Mice. J. Neurochem. 2003, 87, 752−763. (133) (a) Nagano, I.; Shiote, M.; Murakami, T.; Kamada, H.; Hamakawa, Y.; Matsubara, E.; Yokoyama, M.; Moritaz, K.; Shoji, M.; Abe, K. Beneficial Effects of Intrathecal IGF-1 Administration in Patients with Amyotrophic Lateral Sclerosis. Neurol. Res. 2005, 27, 768− 772. (b) Sakowski, S. A.; Schuyler, A. D.; Feldman, E. L. Insulin-like Growth Factor-I for the Treatment of Amyotrophic Lateral Sclerosis. Amyotrophic Lateral Scler. 2009, 10, 63−73. (c) Sorenson, E. J.; Windbank, A. J.; Mandrekar, J. N.; Bamlet, W. R.; Appel, S. H.; Armon, C.; Barkhaus, P. E.; Bosch, P.; Boylan, K.; David, W. S.; Feldman, E.; Glass, J.; Gutmann, L.; Katz, J.; King, W.; Luciano, C. A.; McCluskey, L. F.; Nash, S.; Newman, D. S.; Pascuzzi, R. M.; Pioro, E.; Sams, L. J.; Scelsa, S.; Simpson, E. P.; Subramony, S. H.; Tiryaki, E.; Thornton, C. A. Subcutaneous IGF-1 Is Not Beneficial in 2-Year ALS Trial. Neurology 2008, 71, 1770−1775.

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