Amyotrophic Lateral Sclerosis: New Developments in Diagnostic Markers

From reactive species to disease development: Effect of oxidants and antioxidants on the cellular biomarkers

The influence of modern lifestyle, diet, exposure to chemicals such as phytosanitary substances, together with sedentary lifestyles and lack of exercise play an important role in inducing reactive stress (RS) and disease. The imbalance in the production and scavenging of free radicals and the induction of RS (oxidative, nitrosative, and halogenative) plays an essential role in the etiology of various chronic pathologies, such as cardiovascular diseases, diabetes, neurodegenerative diseases, and cancer. The implication of free radicals and reactive species injury in metabolic disturbances and the onset of many diseases have been accumulating for several decades, and are now accepted as a major cause of many chronic diseases. Exposure to elevated levels of free radicals can cause molecular structural impact on proteins, lipids, and DNA, as well as functional alteration of enzyme homeostasis, leading to aberrations in gene expression. Endogenous depletion of antioxidant enzymes can be mitigated using exogenous antioxidants. The current interest in the use of exogenous antioxidants as adjunctive agents for the treatment of human diseases allows a better understanding of these diseases, facilitating the development of new therapeutic agents with antioxidant activity to improve the treatment of various diseases. Here we examine the role that RS play in the initiation of disease and in the reactivity of free radicals and RS in organic and inorganic cellular components.

Impact of Reactive Species on Amino Acids-Biological Relevance in Proteins and Induced Pathologies

This review examines the impact of reactive species RS (of oxygen ROS, nitrogen RNS and halogens RHS) on various amino acids, analyzed from a reactive point of view of how during these reactions, the molecules are hydroxylated, nitrated, or halogenated such that they can lose their capacity to form part of the proteins or peptides, and can lose their function. The reactions of the RS with several amino acids are described, and an attempt was made to review and explain the chemical mechanisms of the formation of the hydroxylated, nitrated, and halogenated derivatives. One aim of this work is to provide a theoretical analysis of the amino acids and derivatives compounds in the possible positions. Tyrosine, methionine, cysteine, and tryptophan can react with the harmful peroxynitrite or ^•OH and ^•NO₂ radicals and glycine, serine, alanine, valine, arginine, lysine, tyrosine, histidine, cysteine, methionine, cystine, tryptophan, glutamine and asparagine can react with hypochlorous acid HOCl. These theoretical results may help to explain the loss of function of proteins subjected to these three types of reactive stresses. We hope that this work can help to assess the potential damage that reactive species can cause to free amino acids or the corresponding residues when they are part of peptides and proteins.

Emerging Evidence Highlighting the Importance of Redox Dysregulation in the Pathogenesis of Amyotrophic Lateral Sclerosis (ALS)

The cellular redox state, or balance between cellular oxidation and reduction reactions, serves as a vital antioxidant defence system that is linked to all important cellular activities. Redox regulation is therefore a fundamental cellular process for aerobic organisms. Whilst oxidative stress is well described in neurodegenerative disorders including amyotrophic lateral sclerosis (ALS), other aspects of redox dysfunction and their contributions to pathophysiology are only just emerging. ALS is a fatal neurodegenerative disease affecting motor neurons, with few useful treatments. Hence there is an urgent need to develop more effective therapeutics in the future. Here, we discuss the increasing evidence for redox dysregulation as an important and primary contributor to ALS pathogenesis, which is associated with multiple disease mechanisms. Understanding the connection between redox homeostasis, proteins that mediate redox regulation, and disease pathophysiology in ALS, may facilitate a better understanding of disease mechanisms, and lead to the design of better therapeutic strategies.

Lessons of ALS imaging: Pitfalls and future directions - A critical review

Background

While neuroimaging in ALS has gained unprecedented momentum in recent years, little progress has been made in the development of viable diagnostic, prognostic and monitoring markers.

Objectives

To identify and discuss the common pitfalls in ALS imaging studies and to reflect on optimal study designs based on pioneering studies.

Methods

A “PubMed”-based literature search on ALS was performed based on neuroimaging-related keywords. Study limitations were systematically reviewed and classified so that stereotypical trends could be identified.

Results

Common shortcomings, such as relatively small sample sizes, statistically underpowered study designs, lack of disease controls, poorly characterised patient cohorts and a large number of conflicting studies, remain a significant challenge to the field. Imaging data of ALS continue to be interpreted at a group-level, as opposed to meaningful individual-patient inferences.

Conclusions

A systematic, critical review of ALS imaging has identified stereotypical shortcomings, the lessons of which should be considered in the design of future prospective MRI studies. At a time when large multicentre studies are underway a candid discussion of these factors is particularly timely.

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Stereotypical shortcomings can be identified in ALS neuroimaging studies.

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A systematic discussion of ALS study limitations is particularly timely.

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Individual patient data meta-analyses and multicentre studies are urgently required.

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The gaps identified in ALS imaging indicate exciting research opportunities.

Proteome analysis of body fluids for amyotrophic lateral sclerosis biomarker discovery

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder of motor neurons leading to death of the patients, mostly within 2-5 years after disease onset. The pathomechanism of motor neuron degeneration is only partially understood and therapeutic strategies based on mechanistic insights are largely ineffective. The discovery of reliable biomarkers of disease diagnosis and progression is the sine qua non of both the revelation of insights into the ALS pathomechanism and the assessment of treatment efficacies. Proteomic approaches are an important pillar in ALS biomarker discovery. Cerebrospinal fluid is the most promising body fluid for differential proteome analyses, followed by blood (serum, plasma), and even urine and saliva. The present study provides an overview about reported peptide/protein biomarker candidates that showed significantly altered levels in certain body fluids of ALS patients. These findings have to be discussed according to proposed pathomechanisms to identify modifiers of disease progression and to pave the way for the development of potential therapeutic strategies. Furthermore, limitations and advantages of proteomic approaches for ALS biomarker discovery in different body fluids and reliable validation of biomarker candidates have been addressed.

G-CSF prevents the progression of structural disintegration of white matter tracts in amyotrophic lateral sclerosis: a pilot trial

Background

The hematopoietic protein Granulocyte-colony stimulating factor (G-CSF) has neuroprotective and -regenerative properties. The G-CSF receptor is expressed by motoneurons, and G-CSF protects cultured motoneuronal cells from apoptosis. It therefore appears as an attractive and feasible drug candidate for the treatment of amyotrophic lateral sclerosis (ALS). The current pilot study was performed to determine whether treatment with G-CSF in ALS patients is feasible.

Methods

Ten patients with definite ALS were entered into a double-blind, placebo-controlled, randomized trial. Patients received either 10 µg/kg BW G-CSF or placebo subcutaneously for the first 10 days and from day 20 to 25 of the study. Clinical outcome was assessed by changes in the ALS functional rating scale (ALSFRS), a comprehensive neuropsychological test battery, and by examining hand activities of daily living over the course of the study (100 days). The total number of adverse events (AE) and treatment-related AEs, discontinuation due to treatment-related AEs, laboratory parameters including leukocyte, erythrocyte, and platelet count, as well as vital signs were examined as safety endpoints.

Furthermore, we explored potential effects of G-CSF on structural cerebral abnormalities on the basis of voxel-wise statistics of Diffusion Tensor Imaging (DTI), brain volumetry, and voxel-based morphometry.

Results

Treatment was well-tolerated. No significant differences were found between groups in clinical tests and brain volumetry from baseline to day 100. However, DTI analysis revealed significant reductions of fractional anisotropy (FA) encompassing diffuse areas of the brain when patients were compared to controls. On longitudinal analysis, the placebo group showed significant greater and more widespread decline in FA than the ALS patients treated with G-CSF.

Conclusions

Subcutaneous G-CSF treatment in ALS patients appears as feasible approach. Although exploratory analysis of clinical data showed no significant effect, DTI measurements suggest that the widespread and progressive microstructural neural damage in ALS can be modulated by G-CSF treatment. These findings may carry significant implications for further clinical trials on ALS using growth factors.

Trial Registration

ClinicalTrials.gov NCT00298597

Noninvasive detection of brainstem and spinal cord axonal degeneration in an amyotrophic lateral sclerosis mouse model

Degeneration of motor neurons and their associated axons is a hallmark of amyotrophic lateral sclerosis, but reliable noninvasive lesion detection is lacking. In vivo diffusion tensor imaging was performed to evaluate neurodegeneration in the brainstem and cervical spinal cord of wild-type and G93A-SOD1 transgenic mice, an animal model of amyotrophic lateral sclerosis. A statistically significant reduction in the apparent diffusion coefficient was observed in the motor nuclei VII and XII of G93A-SOD1 transgenic mice relative to wild-type mice. No significant difference in diffusion anisotropy was observed in dorsal white or gray matter in cervical and lumbar segments of the spinal cord. In contrast, statistically significant decreases in axial diffusivity (diffusivity parallel to the axis of the spinal cord) and apparent diffusion coefficient were found in the ventrolateral white matter of G93A-SOD1 mice in both the cervical and lumbar spinal cord. The reduction in axial diffusivity, suggestive of axonal injury, in the white matter of the spinal cord of G93A-SOD1 mice was verified by immunostaining with nonphosphorylated neurofilament. The present study demonstrates that in vivo diffusion tensor imaging-derived axial diffusivity may be used to accurately evaluate axonal degeneration in an animal model of amyotrophic lateral sclerosis.

Emerging functions of myelin-associated proteins during development, neuronal plasticity, and neurodegeneration

Adult mammalian central nervous system (CNS) axons have a limited regrowth capacity following injury. Myelin-associated inhibitors (MAIs) limit axonal outgrowth, and their blockage improves the regeneration of damaged fiber tracts. Three of these proteins, Nogo-A, MAG, and OMgp, share two common neuronal receptors: NgR1, together with its coreceptors [p75(NTR), TROY, and Lingo-1]; and the recently described paired immunoglobulin-like receptor B (PirB). These proteins impair neuronal regeneration by limiting axonal sprouting. Some of the elements involved in the myelin inhibitory pathways may still be unknown, but the discovery that blocking both PirB and NgR1 activities leads to near-complete release from myelin inhibition, sheds light on one of the most competitive and intense fields of neuroregeneration study in recent decades. In parallel with the identification and characterization of the roles and functions of these inhibitory molecules in axonal regeneration, data gathered in the field strongly suggest that most of these proteins have roles other than axonal growth inhibition. The discovery of a new group of interacting partners for myelin-associated receptors and ligands, as well as functional studies within or outside the CNS environment, highlights the potential new physiological roles for these proteins in processes, such as development, neuronal homeostasis, plasticity, and neurodegeneration.

Diagnostic problems and delay of diagnosis in amyotrophic lateral sclerosis

OBJECTIVE

Initial symptoms of amyotrophic lateral sclerosis (ALS) mimic several neurological syndromes that may decelerate a correct diagnosis. The aim of our study was to investigate if diagnostic and therapeutic parameters have influence on the time of diagnosis.

METHODS

We retrospectively reviewed the medical records of 100 consecutive ALS patients focusing on clinical and diagnostic data, the timing of diagnosis and treatments attributed to the onset of symptoms of ALS.

RESULTS

Among 100 consecutive patients with ALS, 12% underwent surgery due to symptoms retrospectively attributable to ALS. The comparison of duration from first symptoms to correct diagnosis showed a significant difference between operated and non-operated patients. 35% of all ALS patients had bulbar onset symptoms. The mean time from first symptoms to diagnosis was 9 months in this group. In patients without bulbar onset it was 16.4 months which also represents a significant difference. In 44% of patients other diagnoses were considered and medically treated previous to correct diagnosis, but there was no significant delay of diagnosis.

CONCLUSION

Our study confirms that diagnosis of ALS is still a common clinical problem and shows the need of sensitive and specific diagnostic tests.

Proteomics of brain extracellular fluid (ECF) and cerebrospinal fluid (CSF)

Mass spectrometry has become the gold standard for the identification of proteins in proteomics. In this review, I will discuss the available literature on proteomic experiments that analyze human cerebrospinal fluid (CSF) and brain extracellular fluid (ECF), mostly obtained by cerebral microdialysis. Both materials are of high diagnostic value in clinical neurology, for example, in cerebrovascular disorders like stroke, neurodegenerative diseases like Alzheimer's Disease, Parkinson's Disease, amyotrophic lateral sclerosis (ALS), traumatic brain injury and cerebral infectious and inflammatory disease, such as multiple sclerosis. Moreover, there are standard procedures for sampling. In a number of studies in recent years, biomarkers have been proposed in CSF and ECF for improved diagnosis or to control therapy, based on proteomics and mass spectrometry. I will also discuss the needs for a transition of research-based experimental screening with mass spectrometry to fast and reliable diagnostic instrumentation for clinical use.

Assessing and minimizing the effects of noise and motion in clinical DTI at 3 T

Compared with conventional MRI, diffusion tensor imaging (DTI) is more prone to thermal noise and motion. Optimized sampling schemes have been proposed that reduce the propagation of noise. At 3 T, however, motion may play a more dominant role than noise. Although the effects of noise at 3 T are less compared with 1.5 T because of the higher signal-to-noise ratio, motion is independent of field strength and will persist. To improve the reliability of clinical DTI at 3 T, it is important to know to what extent noise and motion contribute to the uncertainties of the DTI indices. In this study, the effects of noise- and motion-related signal uncertainties are disentangled using in vivo measurements and computer simulations. For six clinically standard available sampling schemes, the reproducibility was assessed in vivo, with and without motion correction applied. Additionally, motion and noise simulations were performed to determine the relative contributions of motion and noise to the uncertainties of the mean diffusivity (MD) and fractional anisotropy (FA). It is shown that the contributions of noise and motion are of the same order of magnitude at 3 T. Similar to the propagation of noise, the propagation of motion-related signal perturbations is also influenced by the choice of sampling scheme. Sampling schemes with only six diffusion directions demonstrated a lower reproducibility compared with schemes with 15 and 32 directions and feature a positive bias for the FA in relatively isotropic tissue. Motion correction helps improving the precision and accuracy of DTI indices.

Reliability of fiber tracking measurements in diffusion tensor imaging for longitudinal study

The statistical reliability of diffusion property measurements was evaluated in ten healthy subjects using deterministic fiber tracking to localize tracts affected in motor neuron disease: corticospinal tract (CST), uncinate fasciculus (UNC), and the corpus callosum in its entirety (CC), and its genu (GE), motor (CCM), and splenium (SP) fibers separately. Measurements of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (lambda(1)), transverse diffusivity (lambda( perpendicular)), and volume of voxels containing fibers (VV) were obtained within each tract. To assess intra-rater and inter-rater reliability, two raters carried out fiber tracking five times on each scan. Scan-rescan and longitudinal reliability were assessed in a subset of four subjects who had six scans, with two sets of three scans separated by 1 year. The statistical reliability of repeated measurements was evaluated using intraclass correlation coefficients (ICC) and coefficients of variation (CV). Spatial agreement of tract shape was assessed using the kappa (kappa) statistic.

RESULTS

Repeated same-scan fiber tracking evaluations showed good geometric alignment (intra-rater kappa >0.90, inter-rater kappa >0.76) and reliable diffusion property measurements (intra-rater ICC >0.92, inter-rater ICC >0.77). FA, MD, and lambda( perpendicular) were highly reliable with repeated scans on different days, up to a year apart (ICC >0.8). VV also exhibited good reliability, but with higher CVs. We were unable to demonstrate reproducibility of lambda(1). Longitudinal reliability after one year was improved by averaging measurements from multiple scans at each time point. Fiber tracking provides a reliable tool for the longitudinal evaluation of white matter diffusion properties.

Redox modifier genes and pathways in amyotrophic lateral sclerosis

Enhanced redox-stress caused by neuroinflammation, mitochondria, and NADPH oxidases has been hypothesized to play critical roles in disease progression of amyotrophic lateral sclerosis (ALS). However, distinguishing whether the redox-stress observed in ALS is due to a primary defect in cellular reactive oxygen species metabolism/catabolism, or is a secondary consequence of neuroinflammation, has been difficult and the issue remains a matter of debate. Emerging evidence suggests that defects in genes that regulate NADPH oxidases may account for at least some forms of ALS. NADPH oxidases are key signaling complexes that influence cellular responses to growth factors and cytokines. In this context, NADPH oxidase-derived reactive oxygen species exert spatial control over the redox-dependent activation of certain pro-inflammatory receptors. Understanding the biology of how NADPH oxidases control cell signaling may help to clarify how genetic determinants of ALS lead to dysregulated pro-inflammatory signaling. This review provides a framework for understanding endosomal signaling through NADPH oxidases and potential mechanisms whereby gene defects in various forms of ALS may influence this cellular process and lead to motor neuron degeneration. Lastly, this review discusses past and current efforts to treat ALS using antioxidant therapies, as well as the limitations and advantages of each of these approaches.

Mapping genetic influences on the corticospinal motor system in humans

It is becoming increasingly clear that genetic variations account for a certain amount of variance in the acquisition and maintenance of different skills. Until now, several levels of genetic influences were examined, ranging from global heritability estimates down to the analysis of the contribution of single nucleotide polymorphisms (SNP) and variable number tandem repeats. In humans, the corticospinal motor system is essential to the acquisition of fine manual motor skills which require a finely tuned coordination of activity in distal forelimb muscles. Here we review recent brain mapping studies that have begun to explore the influence of functional genetic variation as well as mutations on function and structure of the human corticospinal motor system, and also the clinical implications of these studies. Transcranial magnetic stimulation of the primary motor hand area revealed a modulatory role of the common val66met polymorphism in the BDNF gene on corticospinal plasticity. Diffusion-sensitive magnetic resonance imaging has been employed to pinpoint subtle structural changes in corticospinal motor projections in individuals carrying a mutation in genes associated with motor neuron degeneration. These studies underscore the potential of non-invasive brain mapping techniques to characterize the genetic influence on the human corticospinal motor system.

Highly selective artificial gel antibodies for detection and quantification of biomarkers in clinical samples. II. Albumin in body fluids of patients with neurological disorders

We have previously used the molecular-imprinting method for the synthesis of artificial gel antibodies, highly selective for various proteins. In the present work, we have synthesized artificial gel antibodies against human albumin with the aim to develop a simple and rapid procedure to measure the concentration of this protein in samples of clinical interest. The procedure, based on the design of a standard curve (see the preceding paper), was applied on a quantitative analysis of albumin in human plasma and cerebrospinal fluid (CSF). We found that our technique permitted detection of albumin in these body fluids with high precision and that the concentration of this protein was significantly enhanced in CSF from patients with amyotrophic lateral sclerosis (ALS), compared to control samples. This finding is in agreement with results from earlier studies, which confirms the validity of our analysis technique and suggests that the barrier permeability may be affected in ALS, perhaps also for other proteins. No enhancement in plasma levels of albumin was seen in patients with ALS, but rather a decrease. The results further indicate that our approach might also apply well to other biomarkers for the actual neurological disease and other disorders.

Glial cells in ALS: the missing link?

Amyotrophic lateral sclerosis (ALS) was initially known as Charcot's sclerosis, named after the French neurobiologist and physician Jean-Martin Charcot who first described this type of muscular atrophy in the early nineteenth century. In the United States, ALS became widely known as Lou Gehrig's disease after the famous baseball player who succumbed to the disease in the late 1930s. Currently, ALS is the most common motor neuron disease, with a worldwide incidence of 8 cases per 100,000 population per year. Familial forms constitute approximately 5% to 10% of all cases. Onset increases with age, with a peak in the seventh decade and a slight preponderance (relative risk, 1.3-1.5) among men compared with women. Rapid progression of motor neuron loss leads to death an average of 3 to 5 years after symptom onset. The cause of ALS remains unknown and there is still no curative therapy.

Nogo-A and Nogo-66 receptor in amyotrophic lateral sclerosis

Nogo/reticulon (RTN)-4 has been strongly implicated as a disease marker for the motor neuron disease amyotrophic lateral sclerosis (ALS). Nogo isoforms, including Nogo-A, are ectopically expressed in the skeletal muscle of ALS mouse models and patients and their levels correlate with the disease severity. The notion of a direct involvement of Nogo-A in ALS aetiology is supported by the findings that Nogo-A deletion in mice reduces muscle denervation and prolongs survival, whereas overexpression of Nogo-A destabilizes motor nerve terminals and promotes denervation. Another intriguing, and somewhat paradoxical, recent finding revealed that binding of the Nogo-66 receptor (NgR) by either agonistic or antagonistic Nogo-66-derived peptides protects against p75 neurotrophin receptor (p75(NTR))-dependent motor neuron death. Ligand binding by NgR could result in subsequent engagement of p75(NTR), and this association could preclude pro-apoptotic signalling by the latter. Understanding the intricate interplay among Nogo isoforms, NgR and p75(NTR) in ALS disease progression may provide important, therapeutically exploitable information.

Clinical perspectives of high-resolution mass spectrometry-based proteomics in neuroscience: exemplified in amyotrophic lateral sclerosis biomarker discovery research

Biomarker discovery is a central application in today's proteomic research. There is an urgent need for valid biomarkers to improve diagnostic tools and treatment in many disorders, such as the rapidly progressing neurodegenerative disorder amyotrophic lateral sclerosis (ALS) that has a fatal outcome in about 3 years and yet no curative treatment. Screening for clinically relevant biomarkers puts high demands on high-throughput, rapid and precise proteomic techniques. There is a large variety in the methods of choice involving mainly gel-based approaches as well as chromatographic techniques for multi-dimensional protein and peptide separations followed by mass spectrometry (MS) analysis. This special feature article will discuss some important aspects of MS-based clinical proteomics and biomarker discovery in the field of neurodegenerative diseases and ALS research respectively, with the aim to provide a prospective view on current and future research aspects in the field. Furthermore, examples for application of high-resolution MS-based proteomic strategies for ALS biomarker discovery will be demonstrated with two studies previously reported by our group. These studies include among others, utilization of capillary liquid chromatography-Fourier transform ion cyclotron resonance mass spectrometry (LC-FTICR-MS) for advanced protein pattern classification in cerebrospinal fluid (CSF) samples of ALS patients as well as highly sensitive protein identification in minimal amounts of postmortem spinal cord tissue and laser micro-dissected motor neurons using FT-ICR-MS in conjunction with nanoflow LC coupled to matrix-assisted laser desorption ionization time-of-flight tandem mass spectrometry (LC-MALDI-TOF-TOF-MS).