Pathogenesis of amyotrophic lateral sclerosis: a critical review

Amyotrophic lateral sclerosis-like presentation in a HIV-positive patient

There has been several reports of an MND like syndrome in HIV-1 infection, however the data is still sparse. Furthermore, HIV-associated amyotrophic lateral sclerosis (ALS) syndrome differs from the classical ALS in some key aspects.. A 44-year-old male presented with a history of insidious onset and gradually progressive asymmetric weakness of lower limbs. He also complained of thinning in both legs, the left leg more than the right since 1 year along with spontaneous twitching of muscles in both the thighs. On neurological examination, the assessment of higher mental functions was normal. There were no cranial nerve deficits. Motor power was grade 5/5 (Medical Research Council scale) in both the upper limbs and 4+ at hips and knees bilaterally, 5 at right ankle, and 4+ at left ankle. All the deep tendon reflexes were brisk with extensor planter responses. There were no cerebellar signs or sensory deficits. HIV-1 was reactive in enzyme-linked immunosorbent assay. Electrophysiological studies were conducted per the MND protocol.None of the nerves studied showed an abnormal drop in compound muscle action potential amplitude with proximal stimulation. There was evidence of diffuse spontaneous activity, which manifests as fibrillation and fasciculation potentials in most muscles tested . Overall there seems to be sufficient evidence to implicate HIV as a potential cause of an ALS-like disorder, but one must also consider the possibility of coincidental HIV infection in patients who have sporadic ALS.

Minocycline and riluzole brain disposition: interactions with p-glycoprotein at the blood-brain barrier

Amyotrophic lateral sclerosis is a neurodegenerative fatal disease. The only drug recognized to increase the survival time is riluzole(RLZ). In animal models, minocycline (MNC) delayed the onset of the disease and increased the survival time (in combination with RLZ). The objective of our work was to study the interactions between RLZ, MNC and the efflux pump p-glycoprotein (p-gp) at the blood-brain barrier. We investigated these two drugs as: (i) p-gp substrates by comparing their brain uptake in CF1 mdr1a (-/-) and mdr1a (+/+) mice, (ii) p-gp modulators by studying their effect on the cerebral uptake of digoxin. mdr1a (-/-) mice showed higher brain uptake of MNC and RLZ than mdr1a (+/+) (in a 1.6- and 1.4-fold, respectively); and in mdr1a (+/+) mice pre-treated with repeated doses of MNC, brain uptake of digoxin was increased. When both drugs were administrated to mdr1a (+/+) mice, MNC increased the brain uptake of RLZ in a 2.1-fold. In conclusion, MNC and RLZ are both p-gp substrates. MNC is also a p-gp inhibitor and increases the brain diffusion of RLZ. In vitro experiments with the GPNT cell line confirmed these results. These interactions should be taken into account in the design of future clinical trials.

Catalytic antioxidants to treat amyotropic lateral sclerosis

Catalytic antioxidants are comprised of specialised classes of organometallic complexes that can catalyse the decomposition of injurious biological oxidants. These complexes have been shown to prevent the formation of several oxidative markers in spinal cord of G93A amyotropic lateral sclerosis mice and markedly extend survival, even when administered at symptom onset; however, it is now clear that some complexes lacking in antioxidant activity are also protective. New proteomics data suggest that these complexes also induce a broad spectrum of endogenous cellular defense mechanisms. The combination of antioxidant and adaptive resistance effects may explain the remarkable potency of these compounds and may also suggest wide applicability for them in a number of neurodegenerative diseases.

RNAi knockdown of Par-4 inhibits neurosynaptic degeneration in ALS-linked mice

Evidence from human amyotrophic lateral sclerosis (ALS) patients and ALS-linked Cu/Zn superoxide dismutase (Cu/Zn-SOD) transgenic mice bearing the mutation of glycine to alanine at position 93 (G93A) suggests that the pro-apoptotic protein prostate apoptosis response-4 (Par-4) might be a critical link in the chain of events leading to motor neuron degeneration. We now report that Par-4 is enriched in synaptosomes and post-synaptic density from the ventral horn of the spinal cord. Levels of Par-4 in synaptic compartments increased significantly during rapid and slow declining stages of muscle strength in hSOD1 G93A mutant mice. In the pre-muscle weakness stage, hSOD1 G93A mutation sensitized synaptosomes from the ventral horn of the spinal cord to increased levels of Par-4 expression following excitotoxic and apoptotic insults. In ventral spinal synaptosomes, Par-4-mediated production of pro-apoptotic cytosolic factor(s) was significantly enhanced by the hSOD1 G93A mutation. RNA interference (RNAi) knockdown of Par-4 inhibited mitochondrial dysfunction and caspase-3 activation induced by G93A mutation in synaptosomes from the ventral horn of the spinal cord, and protected spinal motor neurons from apoptosis. These results identify the synapse as a crucial cellular site for the cell death promoting actions of Par-4 in motor neurons, and suggest that targeted inhibition of Par-4 by RNAi may prove to be a neuroprotective strategy for motor neuron degeneration.

Differential expression of voltage-activated calcium channels in III and XII motoneurones during development in the rat

To further our understanding of the role that voltage-activated Ca2+ channels play in the development, physiology and pathophysiology of motoneurones (MNs), we used whole-cell patch-clamp recording to compare voltage-activated Ca2+ currents in oculomotor (III) and hypoglossal (XII) MNs of neonatal [postnatal day (P)1-5] and juvenile (P14-19) rats. In contrast to III MNs that innervate extraocular muscles, XII MNs that innervate tongue muscles mature more rapidly, fire bursts of low frequency action potentials and are vulnerable to degeneration in amyotrophic lateral sclerosis. In neonates, low voltage-activated (LVA) Ca2+ current densities are similar in XII and III MNs but high voltage-activated (HVA) Ca2+ current densities are twofold higher in XII MNs. The HVA Ca2+ channel antagonists (nimodipine and nifedipine for L-type, omega-agatoxin-TK for P/Q-type and omega-conotoxin-GVIA for N-type) revealed that, while N- and P/Q-type HVA Ca2+ channels are present in both MN pools, a 3.5-fold greater P/Q-type Ca2+ current in XII MNs accounts for their greater HVA Ca2+ currents. Developmentally, LVA and HVA Ca2+ current densities decrease in III MNs but remain unchanged in XII MNs. Thus, the differences between these MN pools increase developmentally so that, in juveniles, the LVA Ca2+ current density is twofold greater and the HVA Ca2+ current density is threefold greater in XII compared with III MNs. We propose that this differential expression of LVA and HVA Ca2+ channels in XII and III MNs during development contributes to their distinct physiology and may also be a factor contributing to the greater susceptibility of XII MNs to degeneration as seen in amyotrophic lateral sclerosis.

Analysis of neurological disease in four dimensions: insight from ALS-PDC epidemiology and animal models

The causal factor(s) responsible for sporadic neurological diseases are unknown and the stages of disease progression remain undefined and poorly understood. We have developed an animal model of amyotrophic lateral sclerosis-parkinsonism dementia complex which mimics all the essential features of the disease with the initial neurological insult arising from neurotoxins contained in washed cycad seeds. Animals fed washed cycad develop deficits in motor, cognitive, and sensory behaviors that correlate with the loss of neurons in specific regions of the central nervous system. The ability to recreate the disease by exposure to cycad allows us to extend the model in multiple dimensions by analyzing behavioral, cellular, and biochemical changes over time. In addition, the ability to induce toxin-based neurodegeneration allows us to probe the interactions between genetic and epigenetic factors. Our results show that the impact of both genetic causal and susceptibility factors with the cycad neurotoxins are complex. The article describes the features of the model and suggests ways that our understanding of cycad-induced neurodegeneration can be used to decipher and identify the early events in various human neurological diseases.

Folding of Cu, Zn Superoxide Dismutase and Familial Amyotrophic Lateral Sclerosis

Cu, Zn superoxide dismutase (SOD1) has been implicated in the familial form of the neurodegenerative disease amyotrophic lateral sclerosis (ALS). It has been suggested that mutant mediated SOD1 misfolding/aggregation is an integral part of the pathology of ALS. We study the folding thermodynamics and kinetics of SOD1 using a hybrid molecular dynamics approach. We reproduce the experimentally observed SOD1 folding thermodynamics and find that the residues which contribute the most to SOD1 thermal stability are also crucial for apparent two-state folding kinetics. Surprisingly, we find that these residues are located on the surface of the protein and not in the hydrophobic core. Mutations in some of the identified residues are found in patients with the disease. We argue that the identified residues may play an important role in aggregation. To further characterize the folding of SOD1, we study the role of cysteine residues in folding and find that non-native disulfide bond formation may significantly alter SOD1 folding dynamics and aggregation propensity.

Amyotrophic lateral sclerosis: enteral nutrition provision--endoscopic or radiologic gastrostomy?

PURPOSE

To retrospectively evaluate gastrostomy placement in patients with amyotrophic lateral sclerosis (ALS) to determine the insertion method of choice.

MATERIALS AND METHODS

During 3(1/2) years, 36 patients with ALS (19 men, 17 women; mean age, 54 years; age range, 37-69 years) underwent gastrostomy. Twenty patients were primarily referred for percutaneous endoscopic gastrostomy (PEG) and 16 for percutaneous radiologic gastrostomy (PRG). Gastrostomy method, success rate of each technique, and reason for procedure failure were reviewed in each patient. Forced vital capacity (FVC) prior to gastrostomy was recorded. PEG was performed with a pull-through technique after transillumination of the abdominal wall. PRG was performed with fluoroscopic guidance and T-fastener gastropexy. A log-rank test was used to compare survival rates after PRG and PEG, and a Wilcoxon rank sum test was used to evaluate the influence of declining FVC on PEG success. The Kaplan-Meier product limit method was used to estimate survival probabilities.

RESULTS

Of the 20 patients referred for PEG, 11 had successful results. The nine failures (45%) resulted from failure to transilluminate the abdominal wall. All 16 patients primarily referred for PRG underwent successful gastrostomy. The nine patients in whom PEG failed underwent subsequent successful PRG. In patients with diaphragmatic palsy and a high subcostal stomach, an angled subcostal approach (n = 6) or intercostal approach (n = 2) was required at PRG. One death occurred in the PEG group (9%) because of procedure-related aspiration, and a second patient from the PEG group required laparotomy for postprocedural peritonitis. One death occurred in the PRG group (4%) because of inadvertent placement of the feeding tube in the peritoneal cavity. There was no significant difference between PEG and PRG in patient survival. FVC did not have a statistically significant influence on PEG failure.

CONCLUSION

Results show PRG to be the method of choice.

S100A6 overexpression within astrocytes associated with impaired axons from both ALS mouse model and human patients

Astrogliosis is one of the earliest pathological changes observed in neurodegenerative diseases in general and in amyotrophic lateral sclerosis (ALS) in particular. ALS is characterized by selective degeneration of motoneurons. There are 2 forms of the disease: sporadic ALS (SALS), comprising 90%-95% of cases, and familial ALS (FALS), comprising 5%-10% of cases. FALS is an age-dependent autosomal dominant disorder in which mutations in the homodimeric enzyme Cu/ Zn superoxide dismutase 1 (SOD1) is linked to the disease. The animal model for this disease is a transgenic mouse expressing the mutated human SOD1(G93A) gene. Here we show by immunohistochemistry and double immunofluorescence that astrocytes located near impaired axons of motoneurons that were selectively programmed to die overexpressed S100A6, a Ca2+/Zn2+ binding protein able to translocate into the nucleus. Transgenic mice overexpressing the mutated human SOD1 gene and patients suffering from SALS showed this selective astrocytic S100A6 expression. For instance, the pyramidal tract could be macroscopically detected on S100A6-labeled spinal cord and brainstem sections from SALS patients. Transgenic mice overexpressing the non-mutated SOD1 gene did not overexpress S100A6, although glial fibrillary associated protein astrogliosis was seen. Although these results do not give any clue about the beneficial or detrimental role played by S100A6, its induction may be assumed to appropriately serve some function(s).

Visual and auditory event-related potentials in sporadic amyotrophic lateral sclerosis

OBJECTIVES

To investigate the relationship between amyotrophic lateral sclerosis (ALS) and cognitive function by means of oddball event-related potentials (ERPs) and to determine the usefulness of this methodology in the cognitive status assessment of physically disabled patients.

METHODS

Visual and auditory oddball ERPs were recorded in 16 consecutive sporadic ALS patients. A comprehensive battery of neuropsychological (NP) tests assessed intelligence, executive functions, attention, memory, word fluency, visuo-motor and visual-constructive skills.

RESULTS

All patients performed visual and auditory ERPs and 75% of cases showed abnormal N200 and/or P300 waves. Ten patients (62.5%) carried out the entire psychometric evaluation with significant impairment on tests of executive function and attention. A significant correlation between delayed visual (P<0.04) and auditory (P<0.04) P300 latency and impaired NP tests was found.

CONCLUSIONS

In agreement with literature data, our findings confirm the hypothesis of cognitive impairment in ALS patients especially on attention and executive functions suggesting a more extensive degeneration beyond the motor areas. ALS causes severe physical disabilities and such a condition may interfere with NP testing. Thus, the P300 seems to be a useful tool for the assessment of cognition and attention when severe physical deficits are present.

Placental morphogenesis in pregnancies with Down's syndrome might provide a clue to pre-eclampsia

Insufficient perfusion of placenta in pre-eclampsia is commonly associated with oxidative stress leading to increased superoxide formation and reduced invasion of uterine spiral arteries by differentiated migratory cytotrophoblasts. The superoxide dismutase (SOD) level, responsible for eliminating toxic superoxides, drops significantly in pre-eclampsia. On the contrary, the SOD synthesis increases dramatically, compared to that of normal placenta, in pregnancies with trisomy 21 (T21) fetus. However, despite a low level of placental hypoplasia, the overall perfusion of T21 placentae is comparable to that of normal pregnancy. In the light of recent reports on alternative modes of SOD function and factors regulating pathways of cytotrophoblast differentiation, here we have attempted to reconcile the two seemingly disparate pregnancy conditions and suggest that trisomy 21 pregnancies might provide new insight into our understanding of placental morphogenesis in pre-eclampsia.

Association of APOE epsilon4 allele with survival in amyotrophic lateral sclerosis

APOE epsilon4 allele is associated with poorer outcome in degenerative neurological diseases. Its role in amyotrophic lateral sclerosis (ALS) is still unclear. The aim of the present study was to further analyze the association of APOE epsilon4 allele with progression and survival of ALS. One hundred consecutive ALS patients (53 males) and 133 controls were genotyped for the APOE epsilon4 allele. The association of this allele with survival to death or tracheostomy was analyzed by Kaplan-Meier survival analysis. The frequency of the APOE epsilon4 allele in ALS patients was slightly higher (15.1%) than in the control group (10.9%). Patients with or without an APOE epsilon4 allele had a similar age of onset and frequency of bulbar onset. There was a significant shortening of the 50% probability of survival (by 32 months) in patients carrying the APOE epsilon4 allele (p=0.03). In conclusion, carrying an APOE epsilon4 allele is a poor prognostic factor in ALS. This is compatible with a role of apolipoprotein on neuronal survival and repair.

Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter causes motor neuron degeneration

Hypoxia stimulates angiogenesis through the binding of hypoxia-inducible factors to the hypoxia-response element in the vascular endothelial growth factor (Vegf) promotor. Here, we report that deletion of the hypoxia-response element in the Vegf promotor reduced hypoxic Vegf expression in the spinal cord and caused adult-onset progressive motor neuron degeneration, reminiscent of amyotrophic lateral sclerosis. The neurodegeneration seemed to be due to reduced neural vascular perfusion. In addition, Vegf165 promoted survival of motor neurons during hypoxia through binding to Vegf receptor 2 and neuropilin 1. Acute ischemia is known to cause nonselective neuronal death. Our results indicate that chronic vascular insufficiency and, possibly, insufficient Vegf-dependent neuroprotection lead to the select degeneration of motor neurons.

Nitrotyrosination contributes minimally to toxicity of mutant SOD1 associated with ALS

Enhanced production of nitrotyrosine and subsequent protein nitration has been proposed as the mechanism by which mutant SOD1 causes death of motor neurons in a familial form of amyotrophic lateral sclerosis (FALS-1). We have tested this hypothesis in a primary culture model in which mutant human SOD1 was expressed in motor neurons of dissociated spinal cord cultures. Preventing formation of nitrotyrosine by inhibiting nitric oxide synthase rescued cultured motor neurons from excitotoxic death induced by adding glutamate to the culture medium, but failed to significantly delay death of motor neurons expressing the G93A mutant SOD1. The results do not support generation of nitrotyrosine being the predominant lethal gain of function conferred by mutations in SOD1.

Mutant Cu/Zn-superoxide dismutase proteins have altered solubility and interact with heat shock/stress proteins in models of amyotrophic lateral sclerosis

Mutations in the Cu/Zn-superoxide dismutase (SOD-1) gene are responsible for a familial form of amyotrophic lateral sclerosis. In humans and experimental models, death of motor neurons is preceded by formation of cytoplasmic aggregates containing mutant SOD-1 protein. In our previous studies, heat shock protein 70 (HSP70) prolonged viability of cultured motor neurons expressing mutant human SOD-1 and reduced formation of aggregates. In this paper, we report that mutant SOD-1 proteins have altered solubility in cells relative to wild-type SOD-1 and can form a direct association with HSP70 and other stress proteins. Whereas wild-type human and endogenous mouse SOD-1 were detergent-soluble, a portion of mutant SOD-1 was detergent-insoluble in protein extracts of NIH3T3 transfected with SOD-1 gene constructs, spinal cord cultures established from G93A SOD-1 transgenic mouse embryos, and lumbar spinal cord from adult G93A transgenic mice. A direct association of HSP70, HSP40, and alphaB-crystallin with mutant SOD-1 (G93A or G41S), but not wild-type or endogenous mouse SOD-1, was demonstrated by coimmunoprecipitation. Mutant SOD-1.HSP70 complexes were predominantly in the detergent-insoluble fraction. However, only a small percentage of total cellular mutant SOD-1 was detergent-insoluble, suggesting that mutation-induced alteration of protein conformation may not in itself be sufficient for direct interaction with heat shock proteins.

Novel drug development for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) has become an increasingly attractive area for the pharmaceutical industry, the most experimentally tractable of the neurodegenerative diseases. Mechanisms underlying cell death in ALS are likely to be important in more common but more complex disorders. Riluzole, the only drug launched for treatment ALS is currently undergoing industrial trials for Alzheimer's, Parkinson's, Huntington disease, stroke and head injury. Other compounds in Phase III testing for ALS (mecamserin, xaliproden, gabapentin) are also in trials for other neurodegenerative disorders. Mechanisms of action of these advanced compounds are limited to glutamate antagonism, direct or indirect growth factor activity, as well as GABA agonism and interaction with calcium channels. A broader range of mechanisms is represented by compounds in Phase I trials: glutamate antagonism (dextramethorphan/p450 inhibitor; talampanel), growth factors (leukemia inhibiting factor; IL-1 receptor; encapsulated cells secreting CNTF) and antioxidants (TR500, a glutathione-repleting agent; recombinant superoxide dismutase; procysteine.) An even broader range of mechanisms is being explored in preclinical discovery programs. Recognition of the difficulties associated with delivery of protein therapeutics to the CNS has led to development of small molecules interacting either with neurotrophin receptors or with downstream intracellular signalling pathways. Other novel drug targets include caspaces, protein kinases and other molecules influencing apoptosis. High-throughput screens of large libraries of small molecules yield lead compounds that are subsequently optimized by chemists, screened for toxicity, and validated before a candidate is selected for clinical trials. The net is cast wide in early discovery efforts, only about 1% of which result in useful drugs at the end of a decade-long process. Successful discovery and development of novel drugs will increasingly depend on collaborative efforts between the academy and industry.