Oxidative stress and motor neurone disease

Discovery of molecular mechanisms of neuroprotection using cell-based bioassays and oligonucleotide arrays

Oxidative injury and the resulting death of neurons is a major pathological factor involved in numerous neurodegenerative diseases. However, the development of drugs that target this mechanism remains limited. The goal of this study was to test a compound library of approved Food and Drug Administration drugs against a hydrogen peroxide-induced oxidant injury model in neuroblastoma cells. We identified 26 neuroprotective compounds, of which megestrol, meclizine, verapamil, methazolamide, sulindac, and retinol were examined in greater detail. Using large-scale oligonucleotide microarray analysis, we identified genes modulated by these drugs that might underlie the cytoprotection. Five key genes were either uniformly upregulated or downregulated by all six drug treatments, namely, tissue inhibitor of matrix metalloproteinase (TIMP1), ret-proto-oncogene, clusterin, galanin, and growth associated protein (GAP43). Exogenous addition of the neuropeptide galanin alone conferred survival to oxidant-stressed cells, comparable to that seen with the drugs. Our approach, which we term "interventional profiling," represents a general and powerful strategy for identifying new bioactive agents for any biological process, as well as identifying key downstream genes and pathways that are involved.

Antioxidants as treatment for neurodegenerative disorders

Oxidative stress is a ubiquitously observed hallmark of neurodegenerative disorders. Neuronal cell dysfunction and cell death due to oxidative stress may causally contribute to the pathogenesis of progressive neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease, as well as acute syndromes of neurodegeneration, such as ischaemic and haemorrhagic stroke. Neuroprotective antioxidants are considered a promising approach to slowing the progression and limiting the extent of neuronal cell loss in these disorders. The clinical evidence demonstrating that antioxidant compounds can act as protective drugs in neurodegenerative disease, however, is still relatively scarce. In the following review, the available data from clinical, animal and cell biological studies regarding the role of antioxidant neuroprotection in progressive neurodegenerative disease will be summarised, focussing particularly on Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis. The general complications in developing potent neuroprotective antioxidant drugs directed against these long-term degenerative conditions will also be discussed. The major challenges for drug development are the slow kinetics of disease progression, the unsolved mechanistic questions concerning the final causalities of cell death, the necessity to attain an effective permeation of the blood-brain barrier and the need to reduce the high concentrations currently required to evoke protective effects in cellular and animal model systems. Finally, an outlook as to which direction antioxidant drug development and clinical practice may be leading to in the near future will be provided.

Update on the glutamatergic neurotransmitter system and the role of excitotoxicity in amyotrophic lateral sclerosis

Excitotoxicity may play a role in certain disorders of the motor system thought to be caused by environmentally acquired toxins, including lathyrism and domoic acid poisoning. Motor neurons appear to be particularly susceptible to toxicity mediated via alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-kainate receptors. There is a body of evidence implicating glutamatergic toxicity as a contributory factor in the selective neuronal injury occurring in amyotrophic lateral sclerosis (ALS). Interference with glutamate-mediated toxicity is so far the only neuroprotective therapeutic strategy that has shown benefit in terms of slowing disease progression in ALS patients. Biochemical studies have shown decreased glutamate levels in central nervous system (CNS) tissue and increased levels in the cerebrospinal fluid (CSF) of ALS patients. CSF from ALS patients is toxic to neurons in culture, apparently via a mechanism involving AMPA receptor activation. There is evidence for altered expression and function of glial glutamate transporters in ALS, particularly excitatory amino acid transporter 2 (EAAT2). Abnormal splice variants of EAAT2 have been detected in human CNS. Mitochondrial dysfunction may contribute to excitotoxicity in ALS. Induction of neuronal nitric oxide synthase and cyclooxygenase 2 in ALS may also lead to significant interactions with regulation of the glutamate transmitter system. Certain features of motor neurons may predispose them to the neurodegenerative process in ALS, such as the cell size, mitochondrial activity, neurofilament content, and relative lack of certain calcium-binding proteins and molecular chaperones. Motor neurons appear vulnerable to toxicity mediated by calcium-permeable AMPA receptors. The relatively low expression of the glutamate receptor 2 (GluR2) AMPA receptor subunit and the high current density caused by the large number and density of cell surface AMPA receptors are potentially important factors that may predispose to such toxicity.

Elevated levels of neurotrophins in human biceps brachii tissue of amyotrophic lateral sclerosis

Previous studies suggest that neurotrophins support regeneration and survival of injured motoneurons. Based on these findings, brain-derived neurotrophic factor (BDNF) has been clinically investigated for its therapeutic potential in amyotrophic lateral sclerosis (ALS), a rapidly progressing and fatal motoneuronal disease. We questioned whether imbalances of neurotrophic levels are indeed involved in the pathology of ALS. Therefore the expression of nerve growth factor (NGF), BDNF, neurotrophin-3 (NT-3), and neurotrophin-4/5 (NT-4/5) was investigated in postmortem muscle tissue of the biceps from 15 patients with neuropathologically confirmed sporadic ALS and 15 age-matched controls. Using mRNA analysis techniques and quantitative protein measurements, we have demonstrated that both mRNA and protein levels of all four neurotrophins are increased in muscle tissue of ALS patients. The production levels displayed a disease duration dependency and different expression patterns emerged for the four neurotrophins. Whereas the early phase of the disease was characterized by a strong upregulation of BDNF, levels of NGF, NT-3, and NT-4/5 gradually increased in the course of the disorder, peaking at later stages. We conclude that decreased neurotrophic support from muscle tissue is most likely not the cause of motoneuron degeneration in ALS. On the contrary, our results suggest that degenerating motoneurons in ALS are exposed to elevated levels of muscle-derived neurotrophins.

Hydroxyl radical as a strong electrophilic species

In order to clarify an index which could be used as proof of the presence of hydroxyl radical, a new standard isomer distribution ratio of phenols formed from aromatic hydroxylation with [(4-bromophenyl)diazenyl](phenyl)methyl hydroperoxide 4, which is a stable source of hydroxyl radical, under a new appropriate photolysis condition in the presence or absence of benzoquinones is reported. We also demonstrated the strong electrophilic properties of hydroxyl radical in reference to earlier results of electron density calculations.

Environmental exposure to trace elements and risk of amyotrophic lateral sclerosis: a population-based case-control study

We analyzed the association between the environmental exposure to trace elements and the risk of sporadic amyotrophic lateral sclerosis (ALS) in a population-based case-control study in the Emilia-Romagna region in northern Italy. We evaluated exposure to selected trace elements by measuring toenail concentrations of the same by means of inductively coupled plasma optical spectrometry and instrumental neutron activation analysis. The final number enrolled in the study was 22 patients and 40 controls. Disease progression, assessed through a clinical score, was generally unassociated with toenail trace element levels, with the exception of an inverse relation with zinc and selenium content and a direct correlation with copper concentration. In logistic regression analysis, we found no evidence of an association between ALS risk and toenail content of cadmium, lead, copper, zinc, manganese, selenium, chromium, cobalt, iron, and aluminum. This investigation does not suggest a major role in sporadic ALS etiology of environmental exposure to these trace elements, though results for zinc, selenium, and copper should be evaluated with caution due to the potential limitations of toenails as biomarkers of chronic exposure in patients.

Early onset of severe familial amyotrophic lateral sclerosis with a SOD-1 mutation: potential impact of CNTF as a candidate modifier gene

Mutations in the copper/zinc superoxide dismutase 1 (SOD-1) gene are found in approximately 20% of patients with familial amyotrophic lateral sclerosis (FALS), or amyotrophic lateral sclerosis 1. Here we describe a 25-year-old male patient who died from FALS after a rapid disease course of 11 mo. Sequencing of the SOD-1 gene revealed a heterozygous T-->G exchange at position 1513 within exon 5, coding for a V-->G substitution at position 148 of the mature protein. Genetic analysis of this family revealed the same mutation in both his healthy 35-year-old sister and his mother, who did not develop the disease before age 54 years. Screening for candidate modifier genes that might be responsible for the early onset and severe course of the disease in the 25-year-old patient revealed an additional homozygous mutation of the CNTF gene not found in his yet unaffected sister. hSOD-1G93A mice were crossbred with CNTF(-/-) mice and were investigated with respect to disease onset and duration, to test the hypothesis that CNTF acts as a candidate modifier gene in FALS with mutations in the SOD-1 gene. Such hSOD-1G93A/CNTF-deficient mice develop motoneuron disease at a significantly earlier stage than hSOD-1G93A/CNTF-wild-type mice. Linkage analysis revealed that the SOD-1 gene was solely responsible for the disease. However, disease onset as a quantitative trait was regulated by the allelic constitution at the CNTF locus. In addition, patients with sporadic amyotrophic lateral sclerosis who had a homozygous CNTF gene defect showed significantly earlier disease onset but did not show a significant difference in disease duration. Thus, we conclude that CNTF acts as a modifier gene that leads to early onset of disease in patients with FALS who have SOD-1 mutations, in patients with sporadic amyotrophic lateral sclerosis, and in the hSOD-1G93A mouse model.

Hypothesis: proteasomal dysfunction: a primary event in neurogeneration that leads to nitrative and oxidative stress and subsequent cell death

It is proposed that a primary mechanism leading to neuronal cell death in common neurodegenerative diseases is interference with proteasome function. This can involve genetic defects, direct inactivation of the proteasome (e.g., by reactive oxygen species), or overloading with proteins. The latter can be caused by excessive production of normal proteins or by the formation of poorly degradable proteins as a result of genetic mutations, faulty posttranslational modification, or protein modification by reactive oxygen or nitrogen species. Blockage of the proteasome leads to increased oxidative and nitrative stress, the latter apparently due to upregulation of nitric oxide synthase. Thus, agents that increase proteasome function may be generally neuroprotective, as may be NOS inhibitors. Proteasome inhibitors should be used with caution as therapeutic agents.

Methionine oxidation inhibits fibrillation of human alpha-synuclein in vitro

We examined the effect of methionine oxidation of human recombinant alpha-synuclein on its structural properties and propensity to fibrillate. Both oxidized and non-oxidized alpha-synucleins were natively unfolded under conditions of neutral pH, with the oxidized protein being slightly more disordered. Both proteins adopted identical partially folded conformations under conditions of acidic pH. The fibrillation of alpha-synuclein at neutral pH was completely inhibited by methionine oxidation. This inhibitory effect was eliminated at low pH. The addition of oxidized alpha-synuclein to the unoxidized form led to a substantial inhibition of alpha-synuclein fibrillation.

Role of free radicals in the neurodegenerative diseases: therapeutic implications for antioxidant treatment

Free radicals and other so-called 'reactive species' are constantly produced in the brain in vivo. Some arise by 'accidents of chemistry', an example of which may be the leakage of electrons from the mitochondrial electron transport chain to generate superoxide radical (O2*-). Others are generated for useful purposes, such as the role of nitric oxide in neurotransmission and the production of O2*- by activated microglia. Because of its high ATP demand, the brain consumes O2 rapidly, and is thus susceptible to interference with mitochondrial function, which can in turn lead to increased O2*- formation. The brain contains multiple antioxidant defences, of which the mitochondrial manganese-containing superoxide dismutase and reduced glutathione seem especially important. Iron is a powerful promoter of free radical damage, able to catalyse generation of highly reactive hydroxyl, alkoxyl and peroxyl radicals from hydrogen peroxide and lipid peroxides, respectively. Although most iron in the brain is stored in ferritin, 'catalytic' iron is readily mobilised from injured brain tissue. Increased levels of oxidative damage to DNA, lipids and proteins have been detected by a range of assays in post-mortem tissues from patients with Parkinson's disease, Alzheimer's disease and amyotrophic lateral sclerosis, and at least some of these changes may occur early in disease progression. The accumulation and precipitation of proteins that occur in these diseases may be aggravated by oxidative damage, and may in turn cause more oxidative damage by interfering with the function of the proteasome. Indeed, it has been shown that proteasomal inhibition increases levels of oxidative damage not only to proteins but also to other biomolecules. Hence, there are many attempts to develop antioxidants that can cross the blood-brain barrier and decrease oxidative damage. Natural antioxidants such as vitamin E (tocopherol), carotenoids and flavonoids do not readily enter the brain in the adult, and the lazaroid antioxidant tirilazad (U-74006F) appears to localise in the blood-brain barrier. Other antioxidants under development include modified spin traps and low molecular mass scavengers of O2*-. One possible source of lead compounds is the use of traditional remedies claimed to improve brain function. Little is known about the impact of dietary antioxidants upon the development and progression of neurodegenerative diseases, especially Alzheimer's disease. Several agents already in therapeutic use might exert some of their effects by antioxidant action, including selegiline (deprenyl), apomorphine and nitecapone.

Oxidative damage to nucleic acids in human prion disease

Recently, several studies proposed a physiological role for the cellular prion protein (PrP(c)) in defense against oxidative stress. Since the pathogenesis of prion disease necessarily involves a disturbance of PrP(c) homeostasis, we hypothesized that such diseases would be associated with concomitant disturbances in oxidative balance. In support of such a notion, in this study we show increased oxidative damage to nucleic acids in affected brains of patients with Creutzfeldt-Jakob disease. These data suggest that damage by free radicals is a likely cause for neurodegeneration in human prion disease, and antioxidants are a potential therapy for these disorders. Further, our data support the hypothesis that loss of the anti-oxidant function of PrP(c) plays a key role in the pathogenesis of these disorders.

Emerging strategies for drug development in motor neuron disease

Until recently, attempts to identify disease-modifying treatments in motor neuron disease have largely failed. This was due to a lack of understanding of the disease pathogenesis and poor clinical trial design. Recent advances in the genetics of motor neuron disease and the maturation of tissue culture techniques have increased our understanding of the mechanisms of cell death in motor neuron disease. This has in turn led to better in vitro and transgenic animal models, allowing for a more systematic study of the disease process and analysis of potential therapeutic agents. With the advent of these models, motor neuron disease drug research has entered a new era. It is now possible to pursue mass screening of compounds in the in vitro models. Successful compounds in vitro can be advanced to the transgenic animal models. Once toxicity and potential therapeutic effects in animals are known, agents which remain promising can be taken to Phase I, II and III clinical trials. This will increase the likelihood of success and is more desirable than methods previously utilised. A hierarchical approach such as this will be even more important as multi-drug regimens are to be studied. The number of combinations for these multi-drug regimens becomes prohibitive without a screening method.

Cell death in the peripheral nervous system: potential rescue strategies

Neuronal death occurs in many diseases of the peripheral nervous system including genetic, developmental, metabolic, degenerative, and toxic disorders. Specific diseases are mediated by one or several interlinked death-initiating pathways. These may involve oxidative stress, excitotoxicity, membrane disruption, loss of calcium homeostasis, DNA damage, trophic factor loss, or aberrant entry into the cell cycle. The death initiators activate two major final common pathways that lead to cell death. Necrosis is a catastrophic loss of ionic integrity caused by membrane disruption or loss of energy supply. Apoptosis is an endogenous programmed cell death pathway normally active in development and tissue homeostasis. It leads to orderly disassembly of the cell. Advances in understanding of the pathways from specific disease to neuronal death are leading to new strategies designed to prevent death and treat diseases of the nervous system.

Zinc status in athletes: relation to diet and exercise

Zinc is involved in the biochemical processes supporting life, such as cellular respiration, DNA reproduction, maintenance of cell membrane integrity and free radical scavenging. Zinc is required for the activity of more than 300 enzymes, covering all 6 classes of enzyme activity. Zinc binding sites in proteins are often of distorted tetrahedral or trigonal bipyramidal geometry, made up of the sulphur of cysteine, the nitrogen of histidine or the oxygen of aspartate and glutamate, or a combination. Zinc in proteins can either participate directly in chemical catalysis or be important for maintaining protein structure and stability. The nutritional habits of elite athletes during training and competition are quite different from the recommended diet in the majority of the population. Endurance athletes often adopt an unusual diet in an attempt to enhance performance: an excessive increase in carbohydrates and low intake of proteins and fat may lead to suboptimal zinc intake in 90% of athletes. Mild zinc deficiency is difficult to detect because of the lack of definitive indicators of zinc status. In athletes, zinc deficiency can lead to anorexia, significant loss in bodyweight, latent fatigue with decreased endurance and a risk of osteoporosis.

Clinical neurophysiology of ALS

The neurophysiology of amyotrophic lateral sclerosis is important not only in relation to diagnosis, but also in the development of methods to follow progress, and the effects of putative therapies, in the disease. Quantitative techniques can be applied to the measurement of reinnervation using needle electromyogram. The methodology of motor unit number estimation may be useful in measuring loss of functioning motor units in groups of patients but variability in the measurement using current methods limits its sensitivity in the evaluation of individual patients. Conventional neurophysiological measurements, expressed as a multimetric index, may be useful in assessing progress. The cortical and upper motor neuron system can be assessed using transcortical magnetic stimulation protocols, and cortical excitability may be measured by the peristimulus histogram method. In this review the advantages, limitations and promise of these various methods is discussed, in order to indicate the direction for further neurophysiological studies in this disorder.

Protective activity of aromatic amines and imines against oxidative nerve cell death

Oxidative stress is a widespread phenomenon in the pathology of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Neuronal cell death due to oxidative stress may causally contribute to the pathogeneses of these diseases. Therefore, neuroprotective antioxidants are considered to be a promising approach to slow down disease progression. We have investigated different aromatic amine and imine compounds for neuroprotective antioxidant functions in cell culture, and found that these compounds possess excellent cytoprotective potential in diverse paradigms of oxidative neuronal cell death, including clonal cell lines, primary cerebellar neurons, and organotypic hippocampal slice cultures. Aromatic amines and imines are effective against oxidative glutamate toxicity, glutathione depletion, and hydrogen peroxide toxicity. Their mode of action as direct antioxidants was experimentally confirmed by electron spin resonance spectroscopy, cell-free brain lipid peroxidation assays, and intracellular peroxide measurements. With half-maximal effective concentrations of 20-75 nM in different neuroprotection experiments, the aromatic imines phenothiazine, phenoxazine, and iminostilbene proved to be about two orders of magnitude more effective than common phenolic antioxidants. This remarkable efficacy could be directly correlated to calculated properties of the compounds by means of a novel, quantitative structure-activity relationship model. We conclude that bridged bisarylimines with a single free NH-bond, such as iminostilbene, are superior neuroprotective antioxidants, and may be promising lead structures for rational drug development.

Glutamine synthetase activity and expression are not affected by the development of motor neuronopathy in the G93A SOD-1/ALS mouse

The expression and activity of the enzyme glutamine synthetase (GS) were examined in the G93A/SOD-1 transgenic mouse model of progressive motor neuronopathy to investigate the mechanisms underlying degeneration of the motor neurones. Clinical signs appeared in G93A/SOD-1 mice at around 90 days, with severe spasticity and loss of self-righting reflex from 120 to 150 days of age. GS expression was examined using western blotting in primary astrocyte cultures derived from newborn (P1-2) G93A/SOD-1 mice and their non-transgenic littermates and in lower spinal cord from animals at 30, 60 and 90 days of age and disease end-stage (120-150 days). There were no differences in the levels of GS expression in the transgenic mice compared to the unaffected littermates at any of the disease stages examined. GS activity was measured spectrophotometrically in spinal cord extracts at these disease stages. There was a decrease in V(max) at 60 days compared to 30 days in both groups of mice (3.48+/-0.58 cf. 6.43+/-1.83 mmol/h/mg protein; non-transgenic littermates), with GS activity highest at end-stage (9.38+/-0.71 mmol/h/mg protein cf. 7.64+/-0.42 mmol/h/mg protein in littermates). Conversely, K(m) was transiently increased at 60 days (2.53+/-0.26 mM cf. 1.32+/-0.20 in littermates), remaining within the range of 30 day measurements from 90 days onwards. There were no differences in V(max) or K(m) values between the G93A/SOD-1 mice and their unaffected non-transgenic littermates at any of the disease stages examined. We conclude that there is no evidence that a change in glutamine synthetase activity or expression contributes to the progressive neurodegeneration observed in the G93A/SOD-1 mice.

Apoptotic morphology does not always require caspase activity in rat cerebellar granule neurons

The death of a cell via apoptosis is characterized by morphological changes including cell shrinkage and nuclear condensation. Intracellularly, proteases, including caspases, are activated. In the present article we have compared the ability of three different neurotoxic agents to induce caspase activity in cerebellar granule cells (CGC). These compounds are the microtubule-disrupting agent colchicine and the oxidative stress-inducing agents hydrogen peroxide and methylmercury (MeHg). We have previously shown that each of these agents causes nuclear changes that are consistent with apoptosis, i.e., induction of chromatin condensation and DNA cleavage into fragments of regular size (700, 300 and 50 kbp). However, only colchicine causes a large increase in caspase activity, as monitored by the ability of whole cell extracts to cleave the synthetic caspase substrate DEVD-MCA. In contrast, MeHg and hydrogen peroxide do not induce any significant increase of DEVDase activity as compared to control cells. Immunocytochemistry confirms that active caspase-3 is abundant only in colchicine-exposed cells. In agreement with these findings, the pan-caspase inhibitor, z-VAD-fmk, is efficient in protecting CGC against colchicine, but not against hydrogen peroxide or MeHg. These data suggest that in CGC the activation of caspases is not always required to induce morphological changes and pattern of DNA fragmentation consistent with apoptosis.

Glial cells of the spinal cord and subcortical white matter up-regulate neuronal nitric oxide synthase in sporadic amyotrophic lateral sclerosis

Several studies have suggested that excessive generation of nitric oxide (NO) may contribute to the pathogenesis of amyotrophic lateral sclerosis (ALS). Recently, a selective induction of the neuronal isoform of nitric oxide synthase (nNOS) in glial cells has been reported in an animal model of familial ALS. We therefore examined in postmortem tissue the expression of nNOS in patients with sporadic ALS and patients without any history of neurological disease. Using immunohistochemistry, we found an up-regulation of nNOS in glial cells of the spinal cord and subcortical white matter in ALS patients compared to controls. The enhanced glial nNOS expression seen in ALS patients could conceivably contribute to motoneuronal degeneration through NO-mediated cytotoxic effects.

Genetic inroads in familial ALS

Amyotrophic lateral sclerosis (ALS) is a common neurodegenerative disease causing cell death of motor neurons and progressive muscle weakness. The disease is familial in ten percent of cases, of which one-fifth are due to mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1). Two papers in this issue of Nature Genetics describe homozygous mutations in a new gene on chromosome 2q33 in 4 families of Arabian origin with a rare form of juvenile onset ALS (ALS2). The predicted protein structure has domains homologous to GTPase regulatory proteins, and both the types of mutation and the pattern of inheritance suggest that motor neuron degeneration is the result of a loss of function. Further work will determine the relevance of this breakthrough to other, more common forms of ALS.

Immunosuppressant FK506 does not exert beneficial effects in symptomatic G93A superoxide dismutase-1 transgenic mice

The immunosuppressant drug FK506 has been shown to exert neuroprotective effects in various model systems via inhibition of the protein phosphatase calcineurin (CN). The enzyme Cu/Zn-superoxide dismutase (SOD1), which is mutated in a familial form of amyotrophic lateral sclerosis (ALS), is an endogenous regulator of CN. Altered function of CN may therefore be involved in the pathogenesis of ALS. We tested FK506 in a transgenic mouse model expressing mutated SOD1 for potential beneficial effects. This treatment, initiated after onset of symptoms, did not cause a reduction in the decline of motor function nor did it prolong survival. These results argue against a crucial role of CN in the process leading to motoneuronal degeneration in SOD1-mutated mice.

Superoxide-induced nitric oxide release from cultured glial cells

Nitric oxide (NO) has been implicated as a potential contributor to neural cell death in a variety of neurological conditions. Cultured glial cells were exposed to extracellular superoxide generated by the action of xanthine oxidase on xanthine. In this experimental paradigm, both C6 glioma cells and primary astrocytes from rat cerebral cortex produced a rapid release of nitric oxide, measured using an NO specific electrode, in response to the applied superoxide stimulus. Application of a superoxide scavenger, or over-expression of Cu/Zn superoxide dismutase decreased the observed NO release. Authenticity of the NO signal was confirmed by the addition of the NO scavenger 2-(carboxyphenyl)-4,4,5,5-tetramethyllimidazoline-1-oxyl 3-oxide (carboxy-PTIO), which abolished the observed NO release without affecting simultaneously measured superoxide. Therefore, we suggest that glial cells may produce NO under free radical stimulation, which may be relevant to several neurological disorders where superoxide radicals are generated in the vicinity of glia. This would be predicted to result in the release of NO, which may exert toxic effects on neighbouring cells.

Mutation screening of manganese superoxide dismutase in amyotrophic lateral sclerosis

Seventy-seven cases of ALS were screened for mutations in the manganese superoxide dismutase gene (SOD2). DNA was extracted from CNS tissue and screened using single stranded conformation polymorphism and heteroduplex analysis. No mutations were identified in the entire coding region of the SOD2 gene. The known polymorphism in the mitochondrial targeting sequence was identified. No association was found between this polymorphism and ALS. A further polymorphism was detected in the intronic sequence upstream of exon 4, though no association with ALS was demonstrated. We therefore conclude that mutations in SOD2 do not appear to cause ALS.

Glutamate uptake

Brain tissue has a remarkable ability to accumulate glutamate. This ability is due to glutamate transporter proteins present in the plasma membranes of both glial cells and neurons. The transporter proteins represent the only (significant) mechanism for removal of glutamate from the extracellular fluid and their importance for the long-term maintenance of low and non-toxic concentrations of glutamate is now well documented. In addition to this simple, but essential glutamate removal role, the glutamate transporters appear to have more sophisticated functions in the modulation of neurotransmission. They may modify the time course of synaptic events, the extent and pattern of activation and desensitization of receptors outside the synaptic cleft and at neighboring synapses (intersynaptic cross-talk). Further, the glutamate transporters provide glutamate for synthesis of e.g. GABA, glutathione and protein, and for energy production. They also play roles in peripheral organs and tissues (e.g. bone, heart, intestine, kidneys, pancreas and placenta). Glutamate uptake appears to be modulated on virtually all possible levels, i.e. DNA transcription, mRNA splicing and degradation, protein synthesis and targeting, and actual amino acid transport activity and associated ion channel activities. A variety of soluble compounds (e.g. glutamate, cytokines and growth factors) influence glutamate transporter expression and activities. Neither the normal functioning of glutamatergic synapses nor the pathogenesis of major neurological diseases (e.g. cerebral ischemia, hypoglycemia, amyotrophic lateral sclerosis, Alzheimer's disease, traumatic brain injury, epilepsy and schizophrenia) as well as non-neurological diseases (e.g. osteoporosis) can be properly understood unless more is learned about these transporter proteins. Like glutamate itself, glutamate transporters are somehow involved in almost all aspects of normal and abnormal brain activity.

Apoptosis in amyotrophic lateral sclerosis: a review of the evidence

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease primarily affecting the upper and lower motor neurones of the central nervous system. Recently, a lot of interest has been generated by the possibility that a mechanism of programmed cell death, termed apoptosis, is responsible for the motor neurone degeneration in this condition. Apoptosis is regulated through a variety of different pathways which interact and eventually lead to controlled cell death. Apart from genetic regulation, factors involved in the control of apoptosis include death receptors, caspases, Bcl-2 family of oncoproteins, inhibitor of apoptosis proteins (IAPs), inhibitors of IAPs, the p53 tumour suppressor protein and apoptosis-related molecules. The first part of this article will give an overview of the current knowledge of apoptosis. In the second part of this review, we will examine in detail the evidence for and against the contribution of apoptosis in motor neurone cell death in ALS, looking at cellular-, animal- and human post-mortem tissue-based models. In a chronic neurodegenerative disease such as ALS, conclusive evidence of apoptosis is likely to be difficult to detect, given the rapidity of the apoptotic cell death process in relation to the relatively slow time course of the disease. Although a complete picture of motor neurone death in ALS has not been fully elucidated, there is good and compelling evidence that a programmed cell death pathway operates in this disorder. The strongest body of evidence supporting this comes from the findings that, in ALS, changes in the levels of members of the Bcl-2 family of oncoproteins results in a predisposition towards apoptosis, there is increased expression or activation of caspases-1 and -3, and the dying motor neurones in human cases exhibit morphological features reminiscent of apoptosis. Further supporting evidence comes from the detection of apoptosis-related molecules and anti-Fas receptor antibodies in human cases of ALS. However, the role of the p53 protein in cell death in ALS is at present unclear. An understanding of the mechanism of programmed cell death in ALS may provide important clues for areas of potential therapeutic intervention for neuroprotection in this devastating condition.

Protective effects of Debo on zinc-induced apoptosis of C6 glial cells via modulation of intracellular antioxidant, reduced glutathione

In the present study, the mechanical basis of a traditional herbal prescription, Debo. on cytotoxic damage of the brain cells including C6 glial and PC12 cells has been studied. Traditionally, Debo has been employed for the purpose of preventing responses to trauma, ischemia, and other diseases in the nervous system. C6 glial cells were exposed to oxidative stress through the imployment of ZnCl2, and generates H2O2 and hydroxyl radicals by fenton reaction. ZnCl2-induced death of C6 glial cells, which was revealed as apoptosis by chromatin condensation as well as DNA fragmentation. Pretreatment of Debo significantly prevented apoptotic death of C6 glial cells via inhibition of H2O, generation as well as the recovering of an antioxidant, reduced glutathione (GSH). Also, deprivation of serum and glucose, found in ischemia, deceased the viability of PC12 cells up to 60% via generation of H2O2. However, Debo significantly protected cells from ischemic damage through decrease in H2O, generation. Furthermore, Debo markedly inhibited the transcriptional activation of NF-kappaB by ZnCI, in C6 glial cells. These results suggest that Debo may function as an antioxidant system against free radicals and be applicable to protect brain cells against oxidative or ischemic stresses.

Effect of overexpression of wild-type and mutant Cu/Zn-superoxide dismutases on oxidative stress and cell death induced by hydrogen peroxide, 4-hydroxynonenal or serum deprivation: potentiation of injury by ALS-related mutant superoxide dismutases and protection by Bcl-2

Mutations in Cu/Zn-superoxide dismutase (SOD1) are associated with some cases of familial amyotrophic lateral sclerosis (ALS). We overexpressed Bcl-2, wild-type SOD1 or mutant SOD1s (G37R and G85R) in NT-2 and SK-N-MC cells. Overexpression of Bcl-2 rendered cells more resistant to apoptosis induced by serum withdrawal, H2O2 or 4-hydroxy-2-trans-nonenal (HNE). Overexpression of Bcl-2 had little effect on levels of protein carbonyls, lipid peroxidation, 8-hydroxyguanine (8-OHG) or 3-nitrotyrosine. Serum withdrawal or H2O2 raised levels of protein carbonyls, lipid peroxidation, 8-OHG and 3-nitrotyrosine, changes that were attenuated in cells overexpressing Bcl-2. Overexpression of either SOD1 mutant tended to increase levels of lipid peroxidation, protein carbonyls, and 3-nitrotyrosine and accelerated viability loss induced by serum withdrawal, H2O2 or HNE, accompanied by greater rises in oxidative damage parameters. The effects of mutant SOD1s were attenuated by Bcl-2. By contrast, expression of wild-type SOD1 rendered cells more resistant to loss of viability induced by serum deprivation, HNE or H2O2. The levels of lipid peroxidation in wild-type SOD1 transfectants were elevated. Overexpression of mutant SOD1s makes cells more predisposed to undergo apoptosis in response to several insults. Our cellular systems appear to mimic events in patients with ALS or transgenic mice overexpressing mutant SOD1.

Neurodegeneration in the animal model of Menkes' disease involves Bcl-2-linked apoptosis

Copper plays a key role in brain development, function and survival. Alteration of its homeostasis is suggested to be an aetiological factor in several neurodegenerative diseases. However, the molecular mechanisms relating copper to neurodegeneration are still unknown. In the present report, using morphological analyses of brain sections of mottled/brindled mutant (Mo(br/y)) mice, the animal model of the human genetic copper deficiency associated with neurodegeneration (Menkes' disease), we demonstrated that a high degree of apoptotic cells is present in the neocortex and in the hippocampus. Biochemical characterisation revealed decreased levels of copper content and of the activity of the mitochondrial copper-dependent enzyme cytochrome c oxidase. Copper, zinc-superoxide dismutase activity also shows a slight decrease, while no change was observed for glutathione content. Lower levels of ATP were also found, indicative of a copper-dependent impairment of energy metabolism. Changes appear to be specific for the brain, since no alterations in the activity of liver enzymes were found, although the level of copper was strongly decreased. We also tested biochemical factors involved in cell commitment to apoptosis. The expression of the anti-apoptotic protein Bcl-2, which plays a fundamental role in brain development and morphogenesis, was dramatically decreased and the levels of cytochrome c released from mitochondria into the cytosol were significantly increased. On the basis of these findings, we propose that down-regulation of Bcl-2 can cause neurodegeneration triggered by mitochondrial damage due to copper depletion during brain development in Mo(br/y) mice.

Cultured glial cells are resistant to the effects of motor neurone disease-associated SOD1 mutations

Free radical damage has been implicated in the pathophysiology of motor neurone disease (MND); mutations have been identified in the gene encoding Cu/Zn superoxide dismutase (SOD1). There is evidence that glial cell dysfunction may contribute to motor neurone injury, but the exact role of glial cells in MND has yet to be established. The aim of this study was to determine whether expression of mutant SOD1 affects the response of glia to oxidative stress. Stable C6 glioma cells expressing mutant SOD1 and cortical astrocyte cultures from G93A-SOD1 transgenic mice were exposed to: xanthine/xanthine oxidase; hydrogen peroxide; A23187 and 3-morpholinosydonimine. Cell viability was measured using the 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Neither C6 glioma cells nor cortical astrocytes expressing mutant SOD1 were more susceptible to any of the free radical generating systems compared to control cells. These results suggest that astrocytes are resistant to the toxic effects of mutant SOD1 widely reported for neuronal cells.

Programmed cell death induced by glutathione depletion in PC 12 cells is blocked by inhibitors of 12 lipoxygenase, but does not appear to be mediated through the formation of 12 HETE derivatives

Lipoxygenase metabolites have been postulated to be involved in the degenerative events provoked by oxidative stress in neuronal and nonneuronal targets, but their roles remain controversial. In the present work, we investigated the putative role of 12 lipoxygenase metabolites in the programmed cell death induced by glutathione depletion in PC 12 cells. Determinations of 12 lipoxygenase expression and activity reveal the presence of the enzyme in PC 12 cells, but the formation of arachidonate metabolites appears rather low and is not influenced by glutathione depletion. In addition, although the death induced by buthionine sulfoximine (BSO) treatment is abolished by known inhibitors of lipoxygenase enzymes, dexamethasone, a potent steroidal inhibitor of both cyclooxygenase and lipoxygenase pathways, fails to protect the cells from BSO-induced degeneration. Finally, incubation of the cells for 24 h in the presence of exogenous 12 HETE did not induce any significant decrease in cell viability. Our results indicate that 12 lipoxygenase is unlikely to play a major role in the process of cell degeneration provoked by glutathione depletion.

Mechanisms of Peroxynitrite Decomposition Catalyzed by FeTMPS, a Bioactive Sulfonated Iron Porphyrin

Peroxynitrite is a known cytotoxic agent that plays a role in many pathological conditions. Various peroxynitrite decomposition catalysts and pathways are being explored to develop efficient therapeutic agents that can safely remove peroxynitrite from cells and tissues. Water-soluble porphyrins, such as iron(III) meso-tetra(2,4,6-trimethyl-3,5-disulfonato)porphine chloride (FeTMPS) and iron(III) meso-tetra(N-methyl4-pyridyl)porphine chloride (FeTMPyP), have been shown to react catalytically with peroxynitrite (ONOO-). However, their mechanisms are yet to be fully understood. In this study, we have explored the reactivity of FeTMPS in the catalytic decomposition of peroxynitrite. The mechanism of this complex process has been determined. According to this mechanism, Fe(III)TMPS is oxidized by peroxynitrite to produce oxoFe(lV)TMPS and NO2 (k1 = 1.3 x 10(5) M(-1)(s(-1). The porphyrin is then reduced back to Fe(III)TMPS by nitrite, but this rate (k2 = 1.4 x 10(4) M(-1)s(-1)) is not sufficient to maintain the catalytic process at the observed rate. The overall rate of peroxynitrite decomposition catalysis, kcat, was determined to be 6 x 10(4) M(-1)s(-1), under typical conditions. We have postulated that an additional reduction pathway must exist. Kinetic simulations showed that a reaction of oxoFe(IV)TMPS with NO2 (k3 = 1.7 x 10(7) M((-1)s(-1)) could explain the behavior of this system and account for the fast reduction of oxoFe(IV)TMPS to Fe(III). Using the kinetic simulation analysis, we have also shown that two other rearrangement reactions, involving FeTMPS and peroxynitrite, are plausible pathways for peroxynitrite decay. A "cage-return" reaction between the generated oxoFe(IV)TMPS and NO2 (k8 = 5.4 x 10(4) M(-1)s(-1)), affording Fe(III)TMPS and nitrate, and a reaction between oxoFe(IV)TMPS and peroxynitrite (k7 = 2.4 x 10(4) M(-1)s(-1)) that affords oxoFe(IV)TMPS and nitrate are presented. The mechanism of FeTMPS-catalyzed peroxynitrite decay differs markedly from that of FeTMPyP, providing some insight into the reactivity of metal centers with peroxynitrite and biologically important radicals such as NO2.

Therapeutic potential of dietary phase 2 enzyme inducers in ameliorating diseases that have an underlying inflammatory component

Many diseases associated with ageing have an underlying oxidative stress and accompanying inflammatory component, for example, Alzheimer's disease or atherosclerosis. Reviewed in this manuscript are: the role of oxidative stress in activating the transcription factor nuclear factor kappa B (NFκB), the role of NFκB in activating pro-inflammatory gene transcription, strong oxidants produced by cells, anti-oxidant defense systems, the central role of phase 2 enzymes in the anti-oxidant defense, dietary phase 2 enzyme inducers and evidence that dietary phase 2 enzymes decrease oxidative stress. It is likely that a diet containing phase 2 enzyme inducers may ameliorate or even prevent diseases that have a prominent inflammatory component to them. Research should be directed into the potential therapeutic effects of dietary phase 2 enzyme inducers in ameliorating diseases with an underlying oxidative stress and inflammatory component to them.Key words: Alzheimer's disease, atherosclerosis, diet, glutathione, inflammation, stroke.

Molecular evolution of aerobic energy metabolism in primates

As part of our goal to reconstruct human evolution at the DNA level, we have been examining changes in the biochemical machinery for aerobic energy metabolism. We find that protein subunits of two of the electron transfer complexes, complex III and complex IV, and cytochrome c, the protein carrier that connects them, have all undergone a period of rapid protein evolution in the anthropoid lineage that ultimately led to humans. Indeed, subunit IV of cytochrome c oxidase (COX; complex IV) provides one of the best examples of positively selected changes of any protein studied. The rate of subunit IV evolution accelerated in our catarrhine ancestors in the period between 40 to 18 million years ago and then decelerated in the descendant hominid lineages, a pattern of rate changes indicative of positive selection of adaptive changes followed by purifying selection acting against further changes. Besides clear evidence that adaptive evolution occurred for cytochrome c and subunits of complexes III (e.g., cytochrome c(1)) and IV (e.g., COX2 and COX4), modest rate accelerations in the lineage that led to humans are seen for other subunits of both complexes. In addition the contractile muscle-specific isoform of COX subunit VIII became a pseudogene in an anthropoid ancestor of humans but appears to be a functional gene in the nonanthropoid primates. These changes in the aerobic energy complexes coincide with the expansion of the energy-dependent neocortex during the emergence of the higher primates. Discovering the biochemical adaptations suggested by molecular evolutionary analysis will be an exciting challenge.

Human brain thioltransferase: constitutive expression and localization by fluorescence in situ hybridization

Thioltransferase (glutaredoxin) is a member of the family of thiol-disulfide oxido-reductases that maintain the sulfhydryl homeostasis in cells by catalyzing thiol-disulfide interchange reactions. One of the major consequences of oxidative stress in brain is formation of protein-glutathione mixed disulfide (through oxidation of protein thiols) which can be reversed by thioltransferase during recovery of brain from oxidative stress. Here we have visualized the location of thioltransferase in brain regions from seven human tissues obtained at autopsy. Constitutively expressed thioltransferase activity was detectable in all human brains examined although inter-individual variations were seen. The enzyme activity was significantly higher in hippocampus and cerebellum as compared to other regions. Constitutive expression of thioltransferase mRNA was detectable by Northern blot analysis. Localization of thioltransferase mRNA by fluorescence in situ hybridization revealed its presence predominantly in neurons in the cerebral cortex, Purkinje and granule cell layers of the cerebellum, granule cell layer of the dentate gyrus and in the pyramidal neurons of CA1, CA2 and CA3 subfields of hippocampus. These discrete neuronal concentrations of thioltransferase would be consistent with an essential role in modulating recovery of protein thiols from mixed disulfides formed during oxidative stress.

Prenatal exposure to high levels of glucocorticoids increases the susceptibility of cerebellar granule cells to oxidative stress-induced cell death

There is growing concern that prenatal exposure to excessive glucocorticoids may have deleterious effects on the development of various organs, including the nervous system. This study aimed at evaluating whether prenatal exposure to high levels of glucocorticoids might produce long-term effects on neuronal cell survival. Pregnant rats were injected i.p. with 0.1 mg/kg dexamethasone (DEX) from day 14 postconception, and cerebellar granule cells (CGC) were prepared from 1-week-old rats from DEX-treated and control dams. After 7 days in culture, cells were exposed to H(2)O(2), methylmercury, or colchicine at concentrations known to induce apoptotic cell death. After exposure to H(2)O(2) or methylmercury, both inducing oxidative stress, the number of apoptotic cells was significantly higher in DEX- than in control-CGC. Because mitochondria play a key role in apoptosis, mitochondrial function was investigated, and a decrease in the threshold level of Ca(2+) necessary for induction of mitochondrial permeability transition, in Ca(2+) accumulation rate, and in oxygen consumption was detected in DEX-CGC. Moreover, the activity of the antioxidant enzyme catalase was significantly decreased in DEX-CGC. A similar decrease in catalase activity was observed in cerebellar homogenate from newborn and 40-day-old DEX-rats. In conclusion, these results indicate that prenatal exposure to high levels of glucocorticoids induces long-lasting changes in CGC rendering them more sensitive to oxidative stress. With the increasing use of multiple doses of glucocorticoids in preterm infants, the possibility that prenatal exposure to excess glucocorticoids may lead to long-term neurological consequences becomes a relevant issue.

Metabolism and functions of glutathione in brain

The tripeptide glutathione is the thiol compound present in the highest concentration in cells of all organs. Glutathione has many physiological functions including its involvement in the defense against reactive oxygen species. The cells of the human brain consume about 20% of the oxygen utilized by the body but constitute only 2% of the body weight. Consequently, reactive oxygen species which are continuously generated during oxidative metabolism will be generated in high rates within the brain. Therefore, the detoxification of reactive oxygen species is an essential task within the brain and the involvement of the antioxidant glutathione in such processes is very important. The main focus of this review article will be recent results on glutathione metabolism of different brain cell types in culture. The glutathione content of brain cells depends strongly on the availability of precursors for glutathione. Different types of brain cells prefer different extracellular glutathione precursors. Glutathione is involved in the disposal of peroxides by brain cells and in the protection against reactive oxygen species. In coculture astroglial cells protect other neural cell types against the toxicity of various compounds. One mechanism for this interaction is the supply by astroglial cells of glutathione precursors to neighboring cells. Recent results confirm the prominent role of astrocytes in glutathione metabolism and the defense against reactive oxygen species in brain. These results also suggest an involvement of a compromised astroglial glutathione system in the oxidative stress reported for neurological disorders.

Oxidative damage linked to neurodegeneration by selective alpha-synuclein nitration in synucleinopathy lesions

Aggregated alpha-synuclein proteins form brain lesions that are hallmarks of neurodegenerative synucleinopathies, and oxidative stress has been implicated in the pathogenesis of some of these disorders. Using antibodies to specific nitrated tyrosine residues in alpha-synuclein, we demonstrate extensive and widespread accumulations of nitrated alpha-synuclein in the signature inclusions of Parkinson's disease, dementia with Lewy bodies, the Lewy body variant of Alzheimer's disease, and multiple system atrophy brains. We also show that nitrated alpha-synuclein is present in the major filamentous building blocks of these inclusions, as well as in the insoluble fractions of affected brain regions of synucleinopathies. The selective and specific nitration of alpha-synuclein in these disorders provides evidence to directly link oxidative and nitrative damage to the onset and progression of neurodegenerative synucleinopathies.

Apoptosis in neurodegenerative disorders

Neuronal death underlies the symptoms of many human neurological disorders, including Alzheimer's, Parkinson's and Huntington's diseases, stroke, and amyotrophic lateral sclerosis. The identification of specific genetic and environmental factors responsible for these diseases has bolstered evidence for a shared pathway of neuronal death--apoptosis--involving oxidative stress, perturbed calcium homeostasis, mitochondrial dysfunction and activation of cysteine proteases called caspases. These death cascades are counteracted by survival signals, which suppress oxyradicals and stabilize calcium homeostasis and mitochondrial function. With the identification of mechanisms that either promote or prevent neuronal apoptosis come new approaches for preventing and treating neurodegenerative disorders.

Widespread nitration of pathological inclusions in neurodegenerative synucleinopathies

Reactive nitrogen species may play a mechanistic role in neurodegenerative diseases by posttranslationally altering normal brain proteins. In support of this hypothesis, we demonstrate that an anti-3-nitrotyrosine polyclonal antibody stains all of the major hallmark lesions of synucleinopathies including Lewy bodies, Lewy neurites and neuraxonal spheroids in dementia with Lewy bodies, the Lewy body variant of Alzheimer's disease, and neurodegeneration with brain iron accumulation type 1, as well as glial and neuronal cytoplasmic inclusions in multiple system atrophy. This antibody predominantly recognized nitrated alpha-synuclein when compared to other in vitro nitrated constituents of these pathological lesions, such as neurofilament subunits and microtubules. Collectively, these findings imply that alpha-synuclein is nitrated in pathological lesions. The widespread presence of nitrated alpha-synuclein in diverse intracellular inclusions suggests that oxidation/nitration is involved in the onset and/or progression of neurodegenerative diseases.

Motor neuron disease in vitro: the use of cultured motor neurons to study amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a lethal neurodegenerative disease in which motor neurons in the nervous system die. The cause is unknown, and no effective treatment exists. Mutations in the gene for superoxide dismutase found in a subpopulation have led to an animal model, but research with these mice has not produced complete insight into the disease mechanism. Studies with isolated motor neurons may produce important information. This review discusses approaches to culture motor neurons - single cells, cocultured with other cells, and in intact preparations, such as the spinal or cortical slice. Motor neurons in monoculture are suitable for acute but not for chronic studies, whereas cocultures and slices survive up to months and are used for chronic studies. Results with toxic substances believed to play a role in the disease, such as oxidants and glutamate, and of studies where the energy status of the cells is manipulated, are presented.

Blood oxidative stress in amyotrophic lateral sclerosis

It has been suggested that amyotrophic lateral sclerosis (ALS), a neurodegenerative disorder resulting in motor neuron death, is associated with oxidative damage induced by free radicals. Our study aimed to get an assessment of the blood oxidative stress status in a population of 167 ALS patients (aged 59+/-13 years), treated or not with riluzole, compared with 62 age-matched healthy control subjects (aged 60+/-11 years) simultaneously included in the study. We determined the level of plasma lipid peroxidation (thiobarbituric acid-reactive substances, TBARS); the status of the major lipophilic plasma antioxidant defenses (vitamin E, vitamin A and beta-carotene); the activities of erythrocyte Cu,Zn-superoxide dismutase (Cu,Zn-SOD) and of plasma and erythrocyte glutathione peroxidase (GSH-Px). Plasma selenium was also determined as a trace element essential to the activity of the GSH-Px. In comparison with controls, we observed in ALS patients (mean+/-S.D.) significantly higher TBARS values (ALS=1.34+/-0.28 micromol/l; controls=1.11+/-0. 20 micromol/l) and a significant enhancement of the erythrocyte SOD activity (ALS=710+/-114 U/g Hb; controls=667+/-93 U/g Hb). No differences were observed for selenium level, GSH-Px activity, plasma vitamin E, beta-carotene and vitamin A concentrations. These data confirm the presence of an oxidative stress in blood of ALS patients. The elevated plasma TBARS, without any deficiency in plasma lipophilic antioxidants such as vitamin E, vitamin A and beta-carotene, suggest an enhancement in the production of free radicals. No correlation was found in our study between the level of any of the blood oxidative stress markers and the disease duration. Comparison between patients treated or not with riluzole did not display any modification of the plasma TBARS concentration, but we observed a slight decrease of erythrocyte SOD activity in treated patients (treated=705+/-113 U/g Hb; not treated=725+/-118 U/g Hb), suggesting a possible activity of riluzole on the oxygenated free radical production.

Evidence for oxidative stress in experimental prion disease

Oxidative stress has been shown to be important in several neurodegenerative disorders. Previous in vitro studies have already demonstrated the ability of a prion protein fragment to induce oxidative stress in cultured cells. By immunohistochemistry for nitrotyrosine (NT) and heme oxygenase-1 as markers for oxidative stress, we found widespread neuronal labeling for NT in scrapie-infected mouse brains, in agreement with peroxynitrite mediated neuronal degeneration. Damage by free radicals is a likely cause for neurodegeneration in prion disease, and antioxidants are a potential therapy of these disorders.

Development and characterisation of a glutamate-sensitive motor neurone cell line

Modification of the growth conditions of NSC-34 mouse neuroblastoma x motor neurone cells by serum depletion promotes the expression of functional glutamate receptors as the cells mature into a form that bears the phenotypic characterisation of motor neurones. Immunocytochemical studies demonstrated the presence of the glutamate receptor proteins NMDAR1, NMDAR2A/B, GluR1, GluR2, GluR2/3, GluR4, GluR6/7, and KA2. Toxicity assays using cell counting techniques demonstrated a mild but significant cell death (approximately 30%, p < 0.01) following a 24-h exposure to 1 mM glutamate that could be prevented by the presence of the glutamate receptor antagonists (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (10 microM) and 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulphonamide (1 microM). As an indication of glutamate receptor functional activity a novel approach was used to detect the production of free radicals following stimulation with glutamate receptor agonists. The release of superoxide free radicals was detected using a micro-electrochemical sensor following addition of glutamate receptor agonists to the cell bathing solution. Alterations in intracellular calcium concentrations were examined using fura-2 imaging. Exposure of the differentiated NSC-34 cells to glutamate leads to an increase in intracellular calcium concentrations that is prevented by the presence of glutamate receptor antagonists. The motor neurone origin of these cells makes them particularly useful for investigating the potential role of glutamatergic toxicity in motor neurone degeneration.

Mitochondrial enzyme activity in amyotrophic lateral sclerosis: implications for the role of mitochondria in neuronal cell death

The mechanism of selective loss of motor neurons in amyotrophic lateral sclerosis (ALS) has not been clarified. Mitochondrial pathology is present in central nervous system tissue from ALS cases and occurs as an early event in a mouse model of ALS. We demonstrate that, in sporadic ALS, there is a selective decrease in the activity of the mitochondrial DNA-encoded enzyme cytochrome c oxidase in human spinal cord motor neurons. We propose that this may not only be important in neuronal cell death but could well be caused by oxidative damage to mitochondrial DNA leading to the accumulation of mitochondrial DNA mutations.

Poly(ADP-ribose) polymerase is found in both the nucleus and cytoplasm of human CNS neurons

There is evidence that inhibitors of poly(ADP-ribose) polymerase (PARP) may be therapeutically useful in neurodegenerative diseases. Using immunocytochemistry, we have investigated the distribution of PARP in the human CNS. Some neuronal groups showed cytoplasmic staining in addition to the expected staining of nuclei. Considerable variation between different neuronal groups was noted: motor neurons in the spinal cord showed greatest cytoplasmic staining, whereas staining was virtually absent in other neurons, notably in the hippocampus. These results indicate that PARP can be associated with sub-cellular components other than the nucleus, and may indicate additional roles for this enzyme.