Motor neuronal protection by L-arginine prolongs survival of mutant SOD1 (G93A) ALS mice

Hydrolyzed Chicken Meat Extract and Its Bioactive Cyclopeptides Protect Neural Function by Attenuating Inflammation and Apoptosis via PI3K/AKT and AMPK Pathways

Cognitive decline is inevitable with age, and due to the lack of well-established pharmacotherapies for neurodegenerative disorders, dietary supplements have become important alternatives to ameliorate brain deterioration. Hydrolyzed chicken meat extract (HCE) and its bioactive components were previously found to improve neuroinflammation and cognitive decline by regulating microglia polarization. However, the effects and mechanisms of these bioactives on neurons remain unclear. Here, the most potent bioactive component on neural function in HCE was screened out, and the detailed mechanism was clarified through in vivo and in vitro experiments. We found that HCE, cyclo(Val-Pro), cyclo(Phe-Phe), cyclo(His-Pro), cyclo(Leu-Lys), and arginine exerted stronger anti-inflammatory and antioxidant effects among the 12 bioactives in amyloid β (Aβ)-treated HT-22 cells. Further transcriptome sequencing and polymerase chain reaction (PCR) array analysis showed that these bioactives participated in different signaling pathways, and cyclo(Val-Pro) was identified as the most potent cyclic dipeptide. In addition, the antiapoptotic and neuroprotective effect of cyclo(Val-Pro) was partly regulated by the activation of PI3K/AKT and AMPK pathways, and the inhibition of these pathways abolished the effect of cyclo(Val-Pro). Moreover, cyclo(Val-Pro) enhanced cognitive function and neurogenesis and alleviated neuroinflammation and oxidative stress in middle-aged mice, with an effect similar to HCE. Hippocampal transcriptome analysis further revealed that HCE and cyclo(Val-Pro) significantly enriched the neuroactive ligand-receptor interaction pathway, verified by enhanced neurotransmitter levels and upregulated neurotransmitter receptor-related gene expression. Therefore, the mechanism of cyclo(Val-Pro) on neural function might be associated with PI3K/AKT and AMPK pathway-mediated antiapoptotic effect and neurogenesis and the activation of the neurotransmitter-receptor pathway.

Effect of Various Pathological Conditions on Nitric Oxide Level and L-Citrulline Uptake in Motor Neuron-Like (NSC-34) Cell Lines

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disorder that causes progressive paralysis. L-Citrulline is a non-essential neutral amino acid produced by L-arginine via nitric oxide synthase (NOS). According to previous studies, the pathogenesis of ALS entails glutamate toxicity, oxidative stress, protein misfolding, and neurofilament disruption. In addition, L-citrulline prevents neuronal cell death in brain ischemia; therefore, we investigated the change in the transport of L-citrulline under various pathological conditions in a cell line model of ALS. We examined the uptake of [14C]L-citrulline in wild-type (hSOD1wt/WT) and mutant NSC-34/ SOD1G93A (MT) cell lines. The cell viability was determined via MTT assay. A transport study was performed to determine the uptake of [14C]L-citrulline. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis was performed to determine the expression levels of rat large neutral amino acid transported 1 (rLAT1) in ALS cell lines. Nitric oxide (NO) assay was performed using Griess reagent. L-Citrulline had a restorative effect on glutamate induced cell death, and increased [14C]L-citrulline uptake and mRNA levels of the large neutral amino acid transporter (LAT1) in the glutamate-treated ALS disease model (MT). NO levels increased significantly when MT cells were pretreated with glutamate for 24 h and restored by co-treatment with L-citrulline. Co-treatment of MT cells with L-arginine, an NO donor, increased NO levels. NSC-34 cells exposed to high glucose conditions showed a significant increase in [14C]L-citrulline uptake and LAT1 mRNA expression levels, which were restored to normal levels upon co-treatment with unlabeled L-citrulline. In contrast, exposure of the MT cell line to tumor necrosis factor alpha, lipopolysaccharides, and hypertonic condition decreased the uptake significantly which was restored to the normal level by co-treating with unlabeled L-citrulline. L-Citrulline can restore NO levels and cellular uptake in ALS-affected cells with glutamate cytotoxicity, pro-inflammatory cytokines, or other pathological states, suggesting that L-citrulline supplementation in ALS may play a key role in providing neuroprotection.

Fecal microbiota transplantation significantly improved respiratory failure of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that leads to respiratory failure, and eventually death. However, there is a lack of effective treatments for ALS. Here we report the results of fecal microbiota transplantation (FMT) in two patients with late-onset classic ALS with a Japan ALS severity classification of grade 5 who required tracheostomy and mechanical ventilation. In both patients, significant improvements in respiratory function were observed following two rounds of FMT, leading to weaning off mechanical ventilation. Their muscle strength improved, allowing for assisted standing and mobility. Other notable treatment responses included improved swallowing function and reduced muscle fasciculations. Metagenomic and metabolomic analysis revealed an increase in beneficial Bacteroides species (Bacteroides stercoris, Bacteroides uniformis, Bacteroides vulgatus), and Faecalibacterium prausnitzii after FMT, as well as elevated levels of metabolites involved in arginine biosynthesis and decreased levels of metabolites involved in branched-chain amino acid biosynthesis. These findings offer a potential rescue therapy for ALS with respiratory failure and provide new insights into ALS in general.

Neurobiochemical characteristics of arginine-rich peptides explain their potential therapeutic efficacy in neurodegenerative diseases

Neurodegenerative diseases, including Alzheimer̕ s disease (AD), Parkinson̕ s disease (PD), Huntington̕ s disease (HD), and Amyotrophic Lateral Sclerosis (ALS) require special attention to find new potential treatment methods. This review aims to summarize the current knowledge of the relationship between the biochemical properties of arginine-rich peptides (ARPs) and their neuroprotective effects to deal with the harmful effects of risk factors. It seems that ARPs have portrayed a promising and fantastic landscape for treating neurodegeneration-associated disorders. With multimodal mechanisms of action, ARPs play various unprecedented roles, including as the novel delivery platforms for entering the central nervous system (CNS), the potent antagonists for calcium influx, the invader molecules for targeting mitochondria, and the protein stabilizers. Interestingly, these peptides inhibit the proteolytic enzymes and block protein aggregation to induce pro-survival signaling pathways. ARPs also serve as the scavengers of toxic molecules and the reducers of oxidative stress agents. They also have anti-inflammatory, antimicrobial, and anti-cancer properties. Moreover, by providing an efficient nucleic acid delivery system, ARPs can play an essential role in developing various fields, including gene vaccines, gene therapy, gene editing, and imaging. ARP agents and ARP/cargo therapeutics can be raised as an emergent class of neurotherapeutics for neurodegeneration. Part of the aim of this review is to present recent advances in treating neurodegenerative diseases using ARPs as an emerging and powerful therapeutic tool. The applications and progress of ARPs-based nucleic acid delivery systems have also been discussed to highlight their usefulness as a broad-acting class of drugs.

Swimming and L-arginine loaded chitosan nanoparticles ameliorates aging-induced neuron atrophy, autophagy marker LC3, GABA and BDNF-TrkB pathway in the spinal cord of rats

Aging is associated with muscle atrophy, and erosion and destruction of neuronal pathways in the spinal cord. The study aim was to assess the effect of swimming training (Sw) and L-arginine loaded chitosan nanoparticles (LA-CNPs) on the sensory and motor neuron population, autophagy marker LC3, total oxidant status/total antioxidant capacity, behavioural test, GABA and BDNF-TrkB pathway in the spinal cord of aging rats. The rats were randomized to five groups: young (8-weeks) control (n = 7), old control (n = 7), old Sw (n = 7), old LA-CNPs (n = 7) and old Sw + LA-CNPs (n = 7). Groups under LA-CNPs supplementation received 500 mg/kg/day. Sw groups performed a swimming exercise programme 5 days per week for 6 weeks. Upon the completion of the interventions the rats were euthanized and the spinal cord was fixed and frozen for histological assessment, IHC, and gene expression analysis. The old group had more atrophy in the spinal cord with higher changes in LC3 as an indicator of autophagy in the spinal cord compared to the young group (p < 0.0001). The old Sw + LA-CNPs group increased (improved) spinal cord GABA (p = 0.0187), BDNF (p = 0.0003), TrkB (p < 0.0001) gene expression, decreased autophagy marker LC3 protein (p < 0.0001), nerve atrophy and jumping/licking latency (p < 0.0001), improved sciatic functional index score and total oxidant status/total antioxidant capacity compared to the old group (p < 0.0001). In conclusion, swimming and LA-CNPs seems to ameliorate aging-induced neuron atrophy, autophagy marker LC3, oxidant-antioxidant status, functional restoration, GABA and BDNF-TrkB pathway in the spinal cord of aging rats. Our study provides experimental evidence for a possible positive role of swimming and L-arginine loaded chitosan nanoparticles to decrease complications of aging.

A Glutamate Scavenging Protocol Combined with Deanna Protocol in SOD1-G93A Mouse Model of ALS

Amyotrophic lateral sclerosis (ALS) is a progressive disease of neuronal degeneration in the motor cortex, brainstem, and spinal cord, resulting in impaired motor function and premature demise as a result of insufficient respiratory drive. ALS is associated with dysfunctions in neurons, neuroglia, muscle cells, energy metabolism, and glutamate balance. Currently, there is not a widely accepted, effective treatment for this condition. Prior work from our lab has demonstrated the efficacy of supplemental nutrition with the Deanna Protocol (DP). In the present study, we tested the effects of three different treatments in a mouse model of ALS. These treatments were the DP alone, a glutamate scavenging protocol (GSP) alone, and a combination of the two treatments. Outcome measures included body weight, food intake, behavioral assessments, neurological score, and lifespan. Compared to the control group, DP had a significantly slower decline in neurological score, strength, endurance, and coordination, with a trend toward increased lifespan despite a greater loss of weight. GSP had a significantly slower decline in neurological score, strength, endurance, and coordination, with a trend toward increased lifespan. DP+GSP had a significantly slower decline in neurological score with a trend toward increased lifespan, despite a greater loss of weight. While each of the treatment groups fared better than the control group, the combination of the DP+GSP was not better than either of the individual treatments. We conclude that the beneficial effects of the DP and the GSP in this ALS mouse model are distinct, and appear to offer no additional benefit when combined.

Modulation of histone H3K4 dimethylation by spermidine ameliorates motor neuron survival and neuropathology in a mouse model of ALS

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by progressive paralysis due to motor neuron degeneration. It has been proposed that epigenetic modification and transcriptional dysregulation may contribute to motor neuron death. In this study, we investigate the basis for therapeutic approaches to target lysine-specific histone demethylase 1 (LSD1) and elucidate the mechanistic role of LSD1-histone H3K4 signaling pathway in ALS pathogenesis.

METHODS

In order to examine the role of spermidine (SD), we administered SD to an animal model of ALS (G93A) and performed neuropathological analysis, body weight, and survival evaluation.

RESULTS

Herein, we found that LSD1 activity is increased while levels of H3K4me2, a substrate of LSD1, is decreased in cellular and animal models of ALS. SD administration modulated the LSD1 activity and restored H3K4me2 levels in ChAT-positive motor neurons in the lumbar spinal cord of ALS mice. SD prevented cellular damage by improving the number and size of motor neurons in ALS mice. SD administration also reduced GFAP-positive astrogliogenesis in the white and gray matter of the lumbar spinal cord, improving the neuropathology of ALS mice. Moreover, SD administration improved the rotarod performance and gait analysis of ALS mice. Finally, SD administration delayed disease onset and prolonged the lifespan of ALS (G93A) transgenic mice.

CONCLUSION

Together, modulating epigenetic targets such as LSD1 by small compounds may be a useful therapeutic strategy for treating ALS.

Blood-Brain Barrier Solute Carrier Transporters and Motor Neuron Disease

Defective solute carrier (SLC) transporters are responsible for neurotransmitter dysregulation, resulting in neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS). We provided the role and kinetic parameters of transporters such as ASCTs, Taut, LAT1, CAT1, MCTs, OCTNs, CHT, and CTL1, which are mainly responsible for the transport of essential nutrients, acidic, and basic drugs in blood-brain barrier (BBB) and motor neuron disease. The affinity for LAT1 was higher in the BBB than in the ALS model cell line, whereas the capacity was higher in the NSC-34 cell lines than in the BBB. Affinity for MCTs was lower in the BBB than in the NSC-34 cell lines. CHT in BBB showed two affinity sites, whereas no expression was observed in ALS cell lines. CTL1 was the main transporter for choline in ALS cell lines. The half maximal inhibitory concentration (IC50) analysis of [3H]choline uptake indicated that choline is sensitive in TR-BBB cells, whereas amiloride is most sensitive in ALS cell lines. Knowledge of the transport systems in the BBB and motor neurons will help to deliver drugs to the brain and develop the therapeutic strategy for treating CNS and neurological diseases.

Antioxidant and Neuroprotective Effects of Paeonol against Oxidative Stress and Altered Carrier-Mediated Transport System on NSC-34 Cell Lines

Paeonol is a naturally occurring phenolic agent that attenuates neurotoxicity in neurodegenerative diseases. We aimed to investigate the antioxidant and protective effects of paeonol and determine its transport mechanism in wild-type (WT; NSC-34/hSOD1^WT) and mutant-type (MT; NSC-34/hSOD1^G93A) motor neuron-like amyotrophic lateral sclerosis (ALS) cell lines. Cytotoxicity induced by glutamate, lipopolysaccharides, and H₂O₂ reduced viability of cell; however, the addition of paeonol improved cell viability against neurotoxicity. The [³H]paeonol uptake was increased in the presence of H₂O₂ in both cell lines. Paeonol recovered ALS model cell lines by reducing mitochondrial oxidative stress induced by glutamate. The transport of paeonol was time-, concentration-, and pH-dependent in both NSC-34 cell lines. Kinetic parameters showed two transport sites with altered affinity and capacity in the MT cell line compared to the WT cell line. [³H]Paeonol uptake increased in the MT cell line transfected with organic anion transporter1 (Oat1)/Slc22a6 small interfering RNA compared to that in the control. Plasma membrane monoamine transporter (Pmat) was also involved in the uptake of paeonol by ALS model cell lines. Overall, paeonol exhibits neuroprotective activity via a carrier-mediated transport system and may be a beneficial therapy for preventing motor neuronal damage under ALS-like conditions.

Preclinical investigation of Pegylated arginase 1 as a treatment for retina and brain injury

Arginase 1 (A1) is the enzyme that hydrolyzes the amino acid, L-arginine, to ornithine and urea. We have previously shown that A1 deletion worsens retinal ischemic injury, suggesting a protective role of A1. In this translational study, we aimed to study the utility of systemic pegylated A1 (PEG-A1, recombinant human arginase linked to polyethylene glycol) treatment in mouse models of acute retinal and brain injury. Cohorts of WT mice were subjected to retinal ischemia-reperfusion (IR) injury, traumatic optic neuropathy (TON) or brain cerebral ischemia via middle cerebral artery occlusion (MCAO) and treated with intraperitoneal injections of PEG-A1 or vehicle (PEG only). Drug penetration into retina and brain tissues was measured by western blotting and immunolabeling for PEG. Neuroprotection was measured in a blinded fashion by quantitation of NeuN (neuronal marker) immunolabeling of retina flat-mounts and brain infarct area using triphenyl tetrazolium chloride (TTC) staining. Furthermore, ex vivo retina explants and in vitro retina neuron cultures were subjected to oxygen-glucose deprivation (OGD) followed by reoxygenation (R) and treated with PEG-A1. PEG-A1 given systemically did not cross the intact blood-retina/brain barriers in sham controls but reached the retina and brain after injury. PEG-A1 provided neuroprotection after retinal IR injury, TON and cerebral ischemia. PEG-A1 treatment was also neuroprotective in retina explants subjected to OGD/R but did not improve survival in retinal neuronal cultures exposed to OGD/R. In summary, systemic PEG-A1 administration is neuroprotective and provides an excellent route to deliver the drug to the retina and the brain after acute injury.

Differences of Transport Activity of Arginine and Regulation on Neuronal Nitric Oxide Synthase and Oxidative Stress in Amyotrophic Lateral Sclerosis Model Cell Lines

L-Arginine, a semi-essential amino acid, was shown to delay dysfunction of motor neurons and to prolong the lifespan, upon analysis of transgenic mouse models of amyotrophic lateral sclerosis (ALS). We investigated the transport function of arginine and neuronal nitric oxide synthase (nNOS) expression after pretreatment with L-arginine in NSC-34 hSOD1^WT (wild-type, WT) and hSOD1^G93A (mutant-type, MT) cell lines. [³H]L-Arginine uptake was concentration-dependent, voltage-sensitive, and sodium-independent in both cell lines. Among the cationic amino acid transporters family, including system y+, b^0,+, B^0,+, and y⁺L, system y⁺ is mainly involved in [³H]L-arginine transport in ALS cell lines. System b^0,+ accounted for 23% of the transport in both cell lines. System B^0,+ was found only in MT, and whereas, system y⁺L was found only in WT. Lysine competitively inhibited [³H]L-arginine uptake in both cell lines. The nNOS mRNA expression was significantly lower in MT than in WT. Pretreatment with arginine elevated nNOS mRNA levels in MT. Oxidizing stressor, H₂O₂, significantly decreased their uptake; however, pretreatment with arginine restored the transport activity in both cell lines. In conclusion, arginine transport is associated with system y⁺, and neuroprotection by L-arginine may provide an edge as a possible therapeutic target in the treatment of ALS.

Untargeted metabolomics yields insight into ALS disease mechanisms

OBJECTIVE

To identify dysregulated metabolic pathways in amyotrophic lateral sclerosis (ALS) versus control participants through untargeted metabolomics.

METHODS

Untargeted metabolomics was performed on plasma from ALS participants (n=125) around 6.8 months after diagnosis and healthy controls (n=71). Individual differential metabolites in ALS cases versus controls were assessed by Wilcoxon rank-sum tests, adjusted logistic regression and partial least squares-discriminant analysis (PLS-DA), while group lasso explored sub-pathway-level differences. Adjustment parameters included sex, age and body mass index (BMI). Metabolomics pathway enrichment analysis was performed on metabolites selected by the above methods. Finally, machine learning classification algorithms applied to group lasso-selected metabolites were evaluated for classifying case status.

RESULTS

There were no group differences in sex, age and BMI. Significant metabolites selected were 303 by Wilcoxon, 300 by logistic regression, 295 by PLS-DA and 259 by group lasso, corresponding to 11, 13, 12 and 22 enriched sub-pathways, respectively. 'Benzoate metabolism', 'ceramides', 'creatine metabolism', 'fatty acid metabolism (acyl carnitine, polyunsaturated)' and 'hexosylceramides' sub-pathways were enriched by all methods, and 'sphingomyelins' by all but Wilcoxon, indicating these pathways significantly associate with ALS. Finally, machine learning prediction of ALS cases using group lasso-selected metabolites achieved the best performance by regularised logistic regression with elastic net regularisation, with an area under the curve of 0.98 and specificity of 83%.

CONCLUSION

In our analysis, ALS led to significant metabolic pathway alterations, which had correlations to known ALS pathomechanisms in the basic and clinical literature, and may represent important targets for future ALS therapeutics.

Protein aggregation as a consequence of non-enzymatic glycation: Therapeutic intervention using aspartic acid and arginine

Non-enzymatic glycation tempted AGEs of proteins are currently at the heart of a number of pathological conditions. Production of chemically stable AGEs can permanently alter the protein structure and function, concomitantly leading to dilapidated situations. Keeping in perspective, present study aims to report the glycation induced structural and functional modification of a cystatin type isolated from rai mustard seeds, using RSC-glucose and RSC-ribose as model system. Among the sugars studied, ribose was found to be most potent glycating agent as evident from different biophysical assays. During the course of incubation, RSC was observed to pass through a series of structural intermediates as revealed by circular dichroism, altered intrinsic fluorescence and high ANS binding. RSC incubation with ribose post day 36 revealed the possible buildup of β structures as observed in CD spectral analysis, hinting towards the generation of aggregated structures in RSC. High thioflavin T fluorescence and increased Congo red absorbance together with enhanced turbidity of the modified form confirmed the aggregation of RSC. The study further revealed anti-glycation and anti-aggregation potential of amino acids; aspartic acid and arginine as they prevented and/or slowed down the process of AGEs and β structure buildup in a concentration dependent manner with arginine proving to be the most effective one.

L-Citrulline Level and Transporter Activity Are Altered in Experimental Models of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron disease caused by the death of the neurons regulating the voluntary muscles which leads to the progressive paralysis. We investigated the difference of transport function of L-citrulline in ALS disease model (NSC-34/hSOD1^G93A, MT) and a control model (NSC-34/hSOD1^wt, WT). The [¹⁴C]L-citrulline uptake was significantly reduced in MT cells as compared with that of control. The Michaelis-Menten constant (K_m) for MT cells was 0.67 ± 0.05 mM, whereas it was 1.48 ± 0.21 mM for control. On the other hand, the V_max values for MT and control were 10.9 ± 0.8 nmol/mg protein/min and 18.3 ± 2.9 nmol/mg protein/min, respectively. The K_m and V_max values showed the high affinity and low capacity for MT as compared with control. Moreover, the uptake of [¹⁴C]L-citrulline was significantly inhibited by 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH) and harmaline which is the inhibitor of the large neutral amino acid transporter1 (LAT1) in NSC-34 cell lines. Furthermore, [¹⁴C]L-citrulline uptakes took place in Na⁺-independent manner. It was also inhibited by the neutral amino acids such as citrulline and phenylalanine. Likewise, L-dopa, gabapentin, and riluzole significantly inhibited the [¹⁴C]L-citrulline uptake. It shows the competitive inhibition for L-dopa in ALS cell lines. On the other hand, [¹⁴C]L-citrulline uptake in the presence of riluzole showed competitive inhibition in WT cells, whereas it was uncompetitive for MT cells. The small interfering RNA experiments showed that LAT1 is involved in the [¹⁴C]L-citrulline uptake in NSC-34 cell lines. On the other hand, in the examination of the alteration in the expression level of LAT1, it was significantly lower in MT cells as compared with that of control. Similarly, in the spinal cord of ALS, transgenic mice revealed a slight but significant decrease in LAT1 immunoreactivity in motor neurons of ALS mice compared with control. However, the LAT1 immunoreactivity in non-motor neurons and in astrocytes was relatively increased in the spinal cord gray matter of ALS mice. The experimental evidences of our results suggest that the change of transport activity of [¹⁴C]L-citrulline may be partially responsible for the pathological alteration in ALS.

Small Molecules Attenuate the Interplay between Conformational Fluctuations, Early Oligomerization and Amyloidosis of Alpha Synuclein

Aggregation of alpha synuclein has strong implications in Parkinson’s disease. The heterogeneity of folding/aggregation landscape and transient nature of the early intermediates result in difficulty in developing a successful therapeutic intervention. Here we used fluorescence measurements at ensemble and single molecule resolution to study how the late and early events of alpha synuclein aggregation modulate each other. In-vitro aggregation data was complemented using measurements inside live neuroblastoma cells by employing a small molecule labeling technique. An inhibitor molecule (arginine), which delayed the late event of amyloidosis, was found to bind to the protein, shifting the early conformational fluctuations towards a compact state. In contrast, a facilitator of late aggregation (glutamate), was found to be excluded from the protein surface. The presence of glutamate was found to speed up the oligomer formation at the early stage. We found that the effects of the inhibitor and facilitator were additive and as a result they maintained a ratio at which they cancelled each other’s influence on different stages of alpha synuclein aggregation.

Astrocytes and Microglia as Non-cell Autonomous Players in the Pathogenesis of ALS

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder that leads to a progressive muscle wasting and paralysis. The pathological phenotypes are featured by severe motor neuron death and glial activation in the lumbar spinal cord. Proposed ALS pathogenic mechanisms include glutamate cytotoxicity, inflammatory pathway, oxidative stress, and protein aggregation. However, the exact mechanisms of ALS pathogenesis are not fully understood yet. Recently, a growing body of evidence provides a novel insight on the importance of glial cells in relation to the motor neuronal damage via the non-cell autonomous pathway. Accordingly, the aim of the current paper is to overview the role of astrocytes and microglia in the pathogenesis of ALS and to better understand the disease mechanism of ALS.

A retrospective review of the progress in amyotrophic lateral sclerosis drug discovery over the last decade and a look at the latest strategies

INTRODUCTION

Drug discovery for amyotrophic lateral sclerosis (ALS) has experienced a surge in clinical studies and remarkable preclinical milestones utilizing a variety of mutant superoxide dismutase 1 model systems. Of the drugs that were tested and showed positive preclinical effects, none demonstrated therapeutic benefits to ALS patients in clinical settings.

AREAS COVERED

This review discusses the advances made in drug discovery for ALS and highlights why drug development is proving to be so difficult. It also discusses how a closer look at both preclinical and clinical studies could uncover the reasons why these preclinical successes have yet to result in the availability of an effective drug for clinical use.

EXPERT OPINION

Valuable lessons from the numerous preclinical and clinical studies supply the biggest advantage in the monumental task of finding a cure for ALS. Obviously, a single design type for ALS clinical trials has not yielded success. The authors suggest a two-pronged approach that may prove essential to achieve clinical efficacy in the identification of novel targets and preclinical testing in multiple models to identify biomarkers that can function in diagnostic, predictive and prognostic roles, and changes to clinical trial design and patient recruitment criteria. The advancement of technology and invention of more powerful tools will further enhance the above. This will give rise to more sophisticated clinical trials with consideration of a range of criteria from: optimum dose, route of delivery, specific biomarkers, pharmacokinetics, pharmacodynamics and toxicology to biomarkers, timing for trial and patients' clinical status.

A(a)LS: Ammonia-induced amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a dreadful, devastating and incurable motor neuron disease. Aetiologically, it is a multigenic, multifactorial and multiorgan disease. Despite intense research, ALS pathology remains unexplained. Following extensive literature review, this paper posits a new integrative explanation. This framework proposes that ammonia neurotoxicity is a main player in ALS pathogenesis. According to this explanation, a combination of impaired ammonia removal- mainly because of impaired hepatic urea cycle dysfunction-and increased ammoniagenesis- mainly because of impaired glycolytic metabolism in fast twitch skeletal muscle-causes chronic hyperammonia in ALS. In the absence of neuroprotective calcium binding proteins (calbindin, calreticulin and parvalbumin), elevated ammonia-a neurotoxin-damages motor neurons. Ammonia-induced motor neuron damage occurs through multiple mechanisms such as macroautophagy-endolysosomal impairment, endoplasmic reticulum (ER) stress, CDK5 activation, oxidative/nitrosative stress, neuronal hyperexcitability and neuroinflammation. Furthermore, the regional pattern of calcium binding proteins' loss, owing to either ER stress and/or impaired oxidative metabolism, determines clinical variability of ALS. Most importantly, this new framework can be generalised to explain other neurodegenerative disorders such as Huntington's disease and Parkinsonism.

ABC transporter-driven pharmacoresistance in Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a slowly progressing neurodegenerative disease that affects motor neurons of the nervous system. Despite the identification of many potential therapeutics targeting pathogenic mechanisms in in vitro models, there has been limited progress in translating them into a successful pharmacotherapy in the animal model of ALS. Further, efforts to translate any promising results from preclinical trials to effective pharmacotherapies for patients have been unsuccessful, with the exception of riluzole, the only FDA-approved medication, which only modestly extends survival both in the animal model and in patients. Thus, it is essential to reconsider the strategies for developing ALS pharmacotherapies. Growing evidence suggests that problems identifying highly effective ALS treatments may result from an underestimated issue of drug bioavailability and disease-driven pharmacoresistance, mediated by the ATP-binding cassette (ABC) drug efflux transporters. ABC transporters are predominately localized to the lumen of endothelial cells of the blood-brain and blood-spinal cord barriers (BBB, BSCB) where they limit the entry into the central nervous system (CNS) of a wide range of neurotoxicants and xenobiotics, but also therapeutics. In ALS, expression and function of ABC transporters is increased at the BBB/BSCB and their expression has been detected on neurons and glia in the CNS parenchyma, which may further reduce therapeutic action in target cells. Understanding and accounting for the contribution of these transporters to ALS pharmacoresistance could both improve the modest effects of riluzole and set in motion a re-evaluation of previous ALS drug disappointments. In addition, identifying pathogenic mechanisms regulating ABC transporter expression and function in ALS may lead to the development of new therapeutic strategies. It is likely that novel pharmacological approaches require counteracting pharmacoresistance to improve therapeutic efficacy. This article is part of a Special Issue entitled ALS complex pathogenesis.

Regulation of CuZnSOD and its redox signaling potential: implications for amyotrophic lateral sclerosis

SIGNIFICANCE

Molecular oxygen is a Janus-faced electron acceptor for biological systems, serving as a reductant for respiration, or as the genesis for oxygen-derived free radicals that damage macromolecules. Superoxide is well known to perturb nonheme iron proteins, including Fe/S proteins such as aconitase and succinate dehydrogenase, as well as other enzymes containing labile iron such as the prolyl hydroxylase domain-containing family of enzymes; whereas hydrogen peroxide is more specific for two-electron reactions with thiols on glutathione, glutaredoxin, thioredoxin, and the peroxiredoxins.

RECENT ADVANCES

Over the past two decades, familial cases of amyotrophic lateral sclerosis (ALS) have been shown to have an association with commonly altered superoxide dismutase 1 (SOD1) activity, expression, and protein structure. This has led to speculation that an altered redox balance may have a role in creating the ALS phenotype.

CRITICAL ISSUES

While SOD1 alterations in familial ALS are manifold, they generally create perturbations in the flux of electrons. The nexus of SOD1 between one- and two-electron signaling processes places it at a key signaling regulatory checkpoint for governing cellular responses to physiological and environmental cues.

FUTURE DIRECTIONS

The manner in which ALS-associated mutations adjust SOD1's role in controlling the flow of electrons between one- and two-electron signaling processes remains obscure. Here, we discuss the ways in which SOD1 mutations influence the form and function of copper zinc SOD, the consequences of these alterations on free radical biology, and how these alterations might influence cell signaling during the onset of ALS.

Microglia and motor neurons during disease progression in the SOD1G93A mouse model of amyotrophic lateral sclerosis: changes in arginase1 and inducible nitric oxide synthase

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting the motor system. Although the etiology of the disease is not fully understood, microglial activation and neuroinflammation are thought to play a role in disease progression.

METHODS

We examined the immunohistochemical expression of two markers of microglial phenotype, the arginine-metabolizing enzymes inducible nitric oxide synthase (iNOS) and arginase1 (Arg1), in the spinal cord of a mouse model carrying an ALS-linked mutant human superoxide dismutase transgene (SOD1(G93A)) and in non-transgenic wild-type (WT) mice. Immunolabeling for iNOS and Arg1 was evaluated throughout disease progression (6 to 25 weeks), and correlated with body weight, stride pattern, wire hang duration and ubiquitin pathology. For microglia and motor neuron counts at each time point, SOD1(G93A) and WT animals were compared using an independent samples t-test. A Welch t-test correction was applied if Levene's test showed that the variance in WT and SOD1G93A measurements was substantially different.

RESULTS

Disease onset, measured as the earliest change in functional parameters compared to non-transgenic WT mice, occurred at 14 weeks of age in SOD1(G93A) mice. The ventral horn of the SOD1(G93A) spinal cord contained more microglia than WT from 14 weeks onwards. In SOD1(G93A) mice, Arg1-positive and iNOS-positive microglia increased 18-fold and 7-fold, respectively, between 10 and 25 weeks of age (endpoint) in the lumbar spinal cord, while no increase was observed in WT mice. An increasing trend of Arg1- and iNOS-expressing microglia was observed in the cervical spinal cords of SOD1(G93A) mice. Additionally, Arg1-negative motor neurons appeared to selectively decline in the spinal cord of SOD1(G93A) mice, suggesting that Arg1 may have a neuroprotective function.

CONCLUSIONS

This study suggests that the increase in spinal cord microglia occurs around and after disease onset and is preceded by cellular pathology. The results show that Arg1 and iNOS, thought to have opposing inflammatory properties, are upregulated in microglia during disease progression and that Arg1 in motor neurons may confer protection from disease processes. Further understanding of the neuroinflammatory response, and the Arg1/iNOS balance in motor neurons, may provide suitable therapeutic targets for ALS.

Rodent models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterised by the degeneration of upper and lower motor neurons. Recent advances in our understanding of some of the genetic causes of ALS, such as mutations in SOD1, TARDBP, FUS and VCP have led to the generation of rodent models of the disease, as a strategy to help our understanding of the pathophysiology of ALS and to assist in the development of therapeutic strategies. This review provides detailed descriptions of TDP-43, FUS and VCP models of ALS, and summarises potential therapeutics which have been recently trialled in rodent models of the disease. This article is part of a Special Issue entitled: Animal Models of Disease.

Expression of taurine transporter (TauT) is modulated by heat shock factor 1 (HSF1) in motor neurons of ALS

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disorder characterized by progressive paralysis caused by the degeneration of motor neurons throughout the central nervous system. Mutations of the free radical scavenging enzyme Cu/Zn superoxide dismutase 1 (SOD1) are a cause of familial ALS. In the present study, we demonstrated an age-dependent increase in taurine transporter (TauT) immunoreactivity in spinal cord motor neurons of ALS transgenic mice (mutant SOD1 (G93A)) and a similar increase in TauT in spinal motor neurons of patients with ALS. Chromatin immunoprecipitation analysis verified that heat shock factor 1 (HSF1) preferentially occupies the HSF1 binding element in the promoter of TauT under oxidative stress conditions. Knockdown of HSF1 by small interfering RNA reduced the transcriptional activity of TauT. Using [(3)H] taurine, we confirmed that an elevated expression of TauT directly contributes to increased taurine uptake in ALS motor neurons. In addition, we showed that taurine plays an antioxidant role and may prevent motor neuron loss due to oxidative stress in ALS. Our findings suggest that HSF1-induced TauT expression partially protects motor neurons by compensating for constitutive oxidative stress, which is thought to be a key mechanism contributing to the pathogenesis of ALS. Taken together, our results suggest that TauT is a novel pathological marker for stressed motor neurons in ALS and that modulation of TauT and taurine may slow neuronal degeneration in ALS.

One universal common endpoint in mouse models of amyotrophic lateral sclerosis

There is no consensus among research laboratories around the world on the criteria that define endpoint in studies involving rodent models of amyotrophic lateral sclerosis (ALS). Data from 4 nutrition intervention studies using 162 G93A mice, a model of ALS, were analyzed to determine if differences exist between the following endpoint criteria: CS 4 (functional paralysis of both hindlimbs), CS 4+ (CS 4 in addition to the earliest age of body weight loss, body condition deterioration or righting reflex), and CS 5 (CS 4 plus righting reflex >20 s). The age (d; mean ± SD) at which mice reached endpoint was recorded as the unit of measurement. Mice reached CS 4 at 123.9±10.3 d, CS 4+ at 126.6±9.8 d and CS 5 at 127.6±9.8 d, all significantly different from each other (P<0.001). There was a significant positive correlation between CS 4 and CS 5 (r = 0.95, P<0.001), CS 4 and CS 4+ (r = 0.96, P<0.001), and CS 4+ and CS 5 (r = 0.98, P<0.001), with the Bland-Altman plot showing an acceptable bias between all endpoints. Logrank tests showed that mice reached CS 4 24% and 34% faster than CS 4+ (P = 0.046) and CS 5 (P = 0.006), respectively. Adopting CS 4 as endpoint would spare a mouse an average of 4 days (P<0.001) from further neuromuscular disability and poor quality of life compared to CS 5. Alternatively, CS 5 provides information regarding proprioception and severe motor neuron death, both could be important parameters in establishing the efficacy of specific treatments. Converging ethics and discovery, would adopting CS 4 as endpoint compromise the acquisition of insight about the effects of interventions in animal models of ALS?

Differential expression of c-Ret in motor neurons versus non-neuronal cells is linked to the pathogenesis of ALS

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disorder characterized by selective degeneration of motor neurons throughout the central nervous systems. Non-cell autonomous damage induced by glial cells is linked to the selective susceptibility of motor neurons in ALS, but the mechanisms underlying this phenomenon are not known. We found that the expression of non-phosphorylated and phosphorylated forms (tyrosine (Tyr) residue 905, 1016, and 1062) of c-Ret, a member of the glial cell line-derived neurotrophic factor (GDNF) receptor, are altered in motor neurons of the lumbar spinal cord in ALS transgenic (G93A) mice and ALS (G93A) cell line models. Phosphorylated forms of c-Ret were colocalized with neurofilament aggregates in motor neurons of ALS mice. Consistent with the in vivo data, levels of non-phosphorylated and phosphorylated c-Ret (Tyr 905, 1016, and 1062) were decreased by oxidative stress in motor neuronal cells (NSC-34). Non-phosphorylated and phosphorylated forms of c-Ret immunoreactivity were markedly elevated in active microglia of ALS mice. Our findings suggest that constitutive oxidative stress modulates c-Ret function, thereby reducing GDNF signaling in motor neurons. Furthermore, the induction of c-Ret expression in microglia may contribute to non-cell autonomous cell death of motor neurons by available GDNF in ALS.

New animal models of progressive neurodegeneration: tools for identifying targets in predictive diagnostics and presymptomatic treatment

Mental and neurological disorders are increasingly prevalent and constitute a major societal and economic burden worldwide. Many of these diseases and disorders are characterized by progressive deterioration over time, that ultimately results in identifiable symptoms that in turn dictate therapy. Disease-specific symptoms, however, often occur late in the degenerative process. A better understanding of presymptomatic events could allow for the development of new diagnostics and earlier interventions that could slow or stop the disease process. Such studies of progressive neurodegeneration require the use of animal models that are characterized by delayed or slowly developing disease phenotype(s). This brief review describes several examples of such animal models that have recently been developed with relevance to various neurological diseases and disorders, and delineates the potential of such models to aid in predictive diagnosis, early intervention and disease prevention.

Differential regulation of neuronal and inducible nitric oxide synthase (NOS) in the spinal cord of mutant SOD1 (G93A) ALS mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disorder characterized by degeneration of motor neurons throughout the central nervous system. Mutations of the free radical scavenging enzyme superoxide dismutase-1 (SOD1) are a cause of familial ALS but it is not known how mutations lead to cell death. Free radicals such as nitric oxide (NO) are thought to play a key pathogenic role. NO is synthesized by NO synthases (NOSs) from arginine, which is a rate-limiting factor for NO production. We found that neuronal NOS (nNOS)-positive motor neurons were depleted while inducible NOS (iNOS)-positive activated glial cells were increased in transgenic mtSOD1 (G93A) ALS mice. iNOS expression was up regulated consistent with the increases of motor neuron loss and glial activation and citrulline and NO levels while nNOS expression was decreased in G93A ALS mice. Administration of l-arginine to G93A mice reduced the severity of motor neuron depletion and glial activation. In treated animals, nNOS expression was preserved while citrulline and NO were reduced, possibly due to reduced activation of glia expressing iNOS. Our findings show that high concentrations of NO correlate with iNOS expression rather than nNOS expression in G93A ALS mice. This suggests that therapy focused on iNOS inhibition might be a fruitful direction for future ALS therapeutic trials.

Current and emerging treatments for amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a relatively rare neurodegenerative disorder of both upper and lower motoneurons. Currently, the management of ALS is essentially symptoms-based, and riluzole, an antiglutamatergic agent, is the only drug for the treatment of ALS approved by the food and drug administration.

OBJECTIVE

We reviewed current literature concerning emerging treatments for amyotrophic lateral sclerosis.

METHODS

A Medline literature search was performed to identify all studies on ALS treatment published from January 1st, 1986 through August 31st, 2009. We selected papers concerning only disease-modifying therapy.

RESULTS

Forty-eight compounds were identified and reviewed in this study.

CONCLUSIONS

Riluzole is the only compound that demonstrated a beneficial effect on ALS patients, but with only modest increase in survival. Although several drugs showed effective results in the animal models for ALS, none of them significantly prolonged survival or improved quality of life of ALS patients. Several factors have been implicated in explaining the predominantly negative results of numerous randomized clinical trials in ALS, including methodological problems in the use of animal-drug screening, the lack of assessment of pharmacokinetic profile of the drugs, and methodological pitfalls of clinical trials in ALS patients.