A review of the neural mechanisms of action and clinical efficiency of riluzole in treating amyotrophic lateral sclerosis: what have we learned in the last decade?

Efficacy of riluzole in the treatment of spinal cord injury: a systematic review of the literature

OBJECTIVERiluzole is a glutamatergic modulator that has recently shown potential for neuroprotection after spinal cord injury (SCI). While the effects of riluzole are extensively documented in animal models of SCI, there remains heterogeneity in findings. Moreover, there is a paucity of data on the pharmacology of riluzole and its effects in humans. For the present study, the authors systematically reviewed the literature to provide a comprehensive understanding of the effects of riluzole in SCI.METHODSThe PubMed database was queried from 1996 to September 2018 to identify animal studies and clinical trials involving riluzole administration for SCI. Once articles were identified, they were processed for year of publication, study design, subject type, injury model, number of subjects in experimental and control groups, dose, timing/route of administration, and outcomes.RESULTSA total of 37 studies were included in this study. Three placebo-controlled clinical trials were included with a total of 73 patients with a mean age of 39.1 years (range 18-70 years). For the clinical trials included within this study, the American Spinal Injury Association Impairment Scale distributions for SCI were 42.6% grade A, 25% grade B, 26.6% grade C, and 6.2% grade D. Key findings from studies in humans included decreased nociception, improved motor function, and attenuated spastic reflexes. Twenty-six animal studies (24 in vivo, 1 in vitro, and 1 including both in vivo and in vitro) were included. A total of 520 animals/in vitro specimens were exposed to riluzole and 515 animals/in vitro specimens underwent other treatment for comparison. The average dose of riluzole for intraperitoneal, in vivo studies was 6.5 mg/kg (range 1-10 mg/kg). Key findings from animal studies included behavioral improvement, histopathological tissue sparing, and modified electrophysiology after SCI. Eight studies examined the pharmacology of riluzole in SCI. Key findings from pharmacological studies included riluzole dose-dependent effects on glutamate uptake and its modified bioavailability after SCI in both animal and clinical models.CONCLUSIONSSCI has many negative sequelae requiring neuroprotective intervention. While still relatively new in its applications for SCI, both animal and human studies demonstrate riluzole to be a promising pharmacological intervention to attenuate the devastating effects of this condition.

Altered calcium dynamics and glutamate receptor properties in iPSC-derived motor neurons from ALS patients with C9orf72, FUS, SOD1 or TDP43 mutations

The fatal neurodegenerative disease amyotrophic lateral sclerosis (ALS) is characterized by a profound loss of motor neurons (MNs). Until now only riluzole minimally extends life expectancy in ALS, presumably by inhibiting glutamatergic neurotransmission and calcium overload of MNs. Therefore, the aim of this study was to investigate the glutamate receptor properties and key aspects of intracellular calcium dynamics in induced pluripotent stem cell (iPSC)-derived MNs from ALS patients with C9orf72 (n = 4 cell lines), fused in sarcoma (FUS) (n = 9), superoxide dismutase 1 (SOD1) (n = 3) or transactive response DNA-binding protein 43 (TDP43) (n = 3) mutations as well as healthy (n = 7 cell lines) and isogenic controls (n = 3). Using calcium imaging, we most frequently observed spontaneous transients in mutant C9orf72 MNs. Basal intracellular calcium levels and α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-induced signal amplitudes were elevated in mutant TDP43 MNs. Besides, a majority of mutant TDP43 MNs responded to 3.5-dihydroxyphenylglycine as metabotropic glutamate receptor agonist. Quantitative real-time PCR demonstrated significantly increased expression levels of AMPA and kainate receptors in mutant FUS cells compared to healthy and isogenic controls. Furthermore, the expression of kainate receptors and voltage gated calcium channels in mutant C9orf72 MNs as well as metabotropic glutamate receptors in mutant SOD1 cells was markedly elevated compared to controls. Our data of iPSC-derived MNs from familial ALS patients revealed several mutation-specific alterations in glutamate receptor properties and calcium dynamics that could play a role in ALS pathogenesis and may lead to future translational strategies with individual stratification of neuroprotective ALS treatments.

TRPC channels: Structure, function, regulation and recent advances in small molecular probes

Transient receptor potential canonical (TRPC) channels constitute a group of receptor-operated calcium-permeable nonselective cation channels of the TRP superfamily. The seven mammalian TRPC members, which can be further divided into four subgroups (TRPC1, TRPC2, TRPC4/5, and TRPC3/6/7) based on their amino acid sequences and functional similarities, contribute to a broad spectrum of cellular functions and physiological roles. Studies have revealed complexity of their regulation involving several components of the phospholipase C pathway, G_i and G_o proteins, and internal Ca²⁺ stores. Recent advances in cryogenic electron microscopy have provided several high-resolution structures of TRPC channels. Growing evidence demonstrates the involvement of TRPC channels in diseases, particularly the link between genetic mutations of TRPC6 and familial focal segmental glomerulosclerosis. Because TRPCs were discovered by the molecular identity first, their pharmacology had lagged behind. This is rapidly changing in recent years owning to great efforts from both academia and industry. A number of potent tool compounds from both synthetic and natural products that selective target different subtypes of TRPC channels have been discovered, including some preclinical drug candidates. This review will cover recent advancements in the understanding of TRPC channel regulation, structure, and discovery of novel TRPC small molecular probes over the past few years, with the goal of facilitating drug discovery for the study of TRPCs and therapeutic development.

Efficacy of three neuroprotective drugs in secondary progressive multiple sclerosis (MS-SMART): a phase 2b, multiarm, double-blind, randomised placebo-controlled trial

Background

Neurodegeneration is the pathological substrate that causes major disability in secondary progressive multiple sclerosis. A synthesis of preclinical and clinical research identified three neuroprotective drugs acting on different axonal pathobiologies. We aimed to test the efficacy of these drugs in an efficient manner with respect to time, cost, and patient resource.

Methods

We did a phase 2b, multiarm, parallel group, double-blind, randomised placebo-controlled trial at 13 clinical neuroscience centres in the UK. We recruited patients (aged 25–65 years) with secondary progressive multiple sclerosis who were not on disease-modifying treatment and who had an Expanded Disability Status Scale (EDSS) score of 4·0–6·5. Participants were randomly assigned (1:1:1:1) at baseline, by a research nurse using a centralised web-based service, to receive twice-daily oral treatment of either amiloride 5 mg, fluoxetine 20 mg, riluzole 50 mg, or placebo for 96 weeks. The randomisation procedure included minimisation based on sex, age, EDSS score at randomisation, and trial site. Capsules were identical in appearance to achieve masking. Patients, investigators, and MRI readers were unaware of treatment allocation. The primary outcome measure was volumetric MRI percentage brain volume change (PBVC) from baseline to 96 weeks, analysed using multiple regression, adjusting for baseline normalised brain volume and minimisation criteria. The primary analysis was a complete-case analysis based on the intention-to-treat population (all patients with data at week 96). This trial is registered with ClinicalTrials.gov, NCT01910259.

Findings

Between Jan 29, 2015, and June 22, 2016, 445 patients were randomly allocated amiloride (n=111), fluoxetine (n=111), riluzole (n=111), or placebo (n=112). The primary analysis included 393 patients who were allocated amiloride (n=99), fluoxetine (n=96), riluzole (n=99), and placebo (n=99). No difference was noted between any active treatment and placebo in PBVC (amiloride vs placebo, 0·0% [95% CI −0·4 to 0·5; p=0·99]; fluoxetine vs placebo −0·1% [–0·5 to 0·3; p=0·86]; riluzole vs placebo −0·1% [–0·6 to 0·3; p=0·77]). No emergent safety issues were reported. The incidence of serious adverse events was low and similar across study groups (ten [9%] patients in the amiloride group, seven [6%] in the fluoxetine group, 12 [11%] in the riluzole group, and 13 [12%] in the placebo group). The most common serious adverse events were infections and infestations. Three patients died during the study, from causes judged unrelated to active treatment; one patient assigned amiloride died from metastatic lung cancer, one patient assigned riluzole died from ischaemic heart disease and coronary artery thrombosis, and one patient assigned fluoxetine had a sudden death (primary cause) with multiple sclerosis and obesity listed as secondary causes.

Interpretation

The absence of evidence for neuroprotection in this adequately powered trial indicates that exclusively targeting these aspects of axonal pathobiology in patients with secondary progressive multiple sclerosis is insufficient to mitigate neuroaxonal loss. These findings argue for investigation of different mechanistic targets and future consideration of combination treatment trials. This trial provides a template for future simultaneous testing of multiple disease-modifying medicines in neurological medicine.

Funding

Efficacy and Mechanism Evaluation (EME) Programme, an MRC and NIHR partnership, UK Multiple Sclerosis Society, and US National Multiple Sclerosis Society.

Endothelial Transient Receptor Potential Channels and Vascular Remodeling: Extracellular Ca2 + Entry for Angiogenesis, Arteriogenesis and Vasculogenesis

Vasculogenesis, angiogenesis and arteriogenesis represent three crucial mechanisms involved in the formation and maintenance of the vascular network in embryonal and post-natal life. It has long been known that endothelial Ca²⁺ signals are key players in vascular remodeling; indeed, multiple pro-angiogenic factors, including vascular endothelial growth factor, regulate endothelial cell fate through an increase in intracellular Ca²⁺ concentration. Transient Receptor Potential (TRP) channel consist in a superfamily of non-selective cation channels that are widely expressed within vascular endothelial cells. In addition, TRP channels are present in the two main endothelial progenitor cell (EPC) populations, i.e., myeloid angiogenic cells (MACs) and endothelial colony forming cells (ECFCs). TRP channels are polymodal channels that can assemble in homo- and heteromeric complexes and may be sensitive to both pro-angiogenic cues and subtle changes in local microenvironment. These features render TRP channels the most versatile Ca²⁺ entry pathway in vascular endothelial cells and in EPCs. Herein, we describe how endothelial TRP channels stimulate vascular remodeling by promoting angiogenesis, arteriogenesis and vasculogenesis through the integration of multiple environmental, e.g., extracellular growth factors and chemokines, and intracellular, e.g., reactive oxygen species, a decrease in Mg²⁺ levels, or hypercholesterolemia, stimuli. In addition, we illustrate how endothelial TRP channels induce neovascularization in response to synthetic agonists and small molecule drugs. We focus the attention on TRPC1, TRPC3, TRPC4, TRPC5, TRPC6, TRPV1, TRPV4, TRPM2, TRPM4, TRPM7, TRPA1, that were shown to be involved in angiogenesis, arteriogenesis and vasculogenesis. Finally, we discuss the role of endothelial TRP channels in aberrant tumor vascularization by focusing on TRPC1, TRPC3, TRPV2, TRPV4, TRPM8, and TRPA1. These observations suggest that endothelial TRP channels represent potential therapeutic targets in multiple disorders featured by abnormal vascularization, including cancer, ischemic disorders, retinal degeneration and neurodegeneration.

Soluble iron accumulation induces microglial glutamate release in the spinal cord of sporadic amyotrophic lateral sclerosis

Previous studies on sporadic amyotrophic lateral sclerosis (SALS) demonstrated iron accumulation in the spinal cord and increased glutamate concentration in the cerebrospinal fluid. To clarify the relationship between the two phenomena, we first performed quantitative and morphological analyses of substances related to iron and glutamate metabolism using spinal cords obtained at autopsy from 12 SALS patients and 12 age-matched control subjects. Soluble iron content determined by the Ferrozine method as well as ferritin (Ft) and glutaminase C (GLS-C) expression levels on Western blots were significantly higher in the SALS group than in the control group, while ferroportin (FPN) levels on Western blots were significantly reduced in the SALS group as compared to the control group. There was no significant difference in aconitase 1 (ACO1) and tumor necrosis factor-alpha (TNFα)-converting enzyme (TACE) levels on Western blots between the two groups. Immunohistochemically, Ft, ACO1, TACE, TNFα, and GLS-C were proven to be selectively expressed in microglia. Immunoreactivities for FPN and hepcidin were localized in neuronal and glial cells. Based on these observations, it is predicted that soluble iron may stimulate microglial glutamate release. To address this issue, cell culture experiments were carried out on a microglial cell line (BV-2). Treatment of BV-2 cells with ferric ammonium citrate (FAC) brought about significant increases in intracellular soluble iron and Ft expression levels and conditioned medium glutamate and TNFα concentrations. Glutamate concentration was also significantly increased in conditioned media of TNFα-treated BV-2 cells. While the FAC-driven increases in glutamate and TNFα release were completely canceled by pretreatment with ACO1 and TACE inhibitors, respectively, the TNFα-driven increase in glutamate release was completely canceled by GLS-C inhibitor pretreatment. Moreover, treatment of BV-2 cells with hepcidin resulted in a significant reduction in FPN expression levels on Western blots of the intracellular total protein extracts. The present results provide in vivo and in vitro evidence that microglial glutamate release in SALS spinal cords is enhanced by intracellular soluble iron accumulation-induced activation of ACO1 and TACE and by increased extracellular TNFα-stimulated GLS-C upregulation, and suggest a positive feedback mechanism to maintain increased intracellular soluble iron levels, involving TNFα, hepcidin, and FPN.

ALS Genetics, Mechanisms, and Therapeutics: Where Are We Now?

The scientific landscape surrounding amyotrophic lateral sclerosis (ALS) continues to shift as the number of genes associated with the disease risk and pathogenesis, and the cellular processes involved, continues to grow. Despite decades of intense research and over 50 potentially causative or disease-modifying genes identified, etiology remains unexplained and treatment options remain limited for the majority of ALS patients. Various factors have contributed to the slow progress in understanding and developing therapeutics for this disease. Here, we review the genetic basis of ALS, highlighting factors that have contributed to the elusiveness of genetic heritability. The most commonly mutated ALS-linked genes are reviewed with an emphasis on disease-causing mechanisms. The cellular processes involved in ALS pathogenesis are discussed, with evidence implicating their involvement in ALS summarized. Past and present therapeutic strategies and the benefits and limitations of the model systems available to ALS researchers are discussed with future directions for research that may lead to effective treatment strategies outlined.

Modeling cell-autonomous motor neuron phenotypes in ALS using iPSCs

Amyotrophic lateral sclerosis (ALS) is an aggressive and uniformly fatal degenerative disease of the motor nervous system. In order to understand underlying disease mechanisms, researchers leverage a host of in vivo and in vitro models, including yeast, worms, flies, zebrafish, mice, and more recently, human induced pluripotent stem cells (iPSCs) derived from ALS patients. While mouse models have been the main workhorse of preclinical ALS research, the development of iPSCs provides a new opportunity to explore molecular phenotypes of ALS within human cells. Importantly, this technology enables modeling of both familial and sporadic ALS in the relevant human genetic backgrounds, as well as a personalized or targeted approach to therapy development. Harnessing these powerful tools requires addressing numerous challenges, including different variance components associated with iPSCs and motor neurons as well as concomitant limits of reductionist approaches. In order to overcome these obstacles, optimization of protocols and assays, confirmation of phenotype robustness at scale, and validation of findings in human tissue and genetics will cement the role for iPSC models as a valuable complement to animal models in ALS and more broadly among neurodegenerative diseases.

Fascaplysin Derivatives Are Potent Multitarget Agents against Alzheimer's Disease: in Vitro and in Vivo Evidence

Alzheimer's disease (AD) is characterized by progressive neurodegeneration and impaired cognitive functions. Fascaplysin is a β-carboline alkaloid isolated from marine sponge Fascaplysinopsis bergquist in 1988. Previous studies have shown that fascaplysin might act on acetylcholinesterase and β-amyloid (Aβ) to produce anti-AD properties. In this study, a series of fascaplysin derivatives were synthesized. The cholinesterase inhibition activities, the neuronal protective effects, and the toxicities of these compounds were evaluated in vitro. Compounds 2a and 2b, the two most powerful compounds in vitro, were further selected to evaluate their cognitive-enhancing effects in animals. Both 2a and 2b could ameliorate cognitive dysfunction induced by scopolamine or Aβ oligomers without affecting locomotor functions in mice. We also found that 2a and 2b could prevent cholinergic dysfunctions, decrease pro-inflammatory cytokine expression, and inhibit Aβ-induced tau hyperphosphorylation in vivo. Most importantly, pharmacodynamics studies suggested that 2b could penetrate the blood-brain barrier and be retained in the central nervous system. All these results suggested that fascaplysin derivatives are potent multitarget agents against AD and might be clinical useful for AD treatment.

A Pharmacokinetic Bioequivalence Study Comparing Sublingual Riluzole (BHV-0223) and Oral Tablet Formulation of Riluzole in Healthy Volunteers

Orally administered riluzole extends survival in patients with amyotrophic lateral sclerosis, although it has significant shortcomings (eg, adverse events, dysphagic patients) that limit its utility. BHV-0223 is a Zydis-based orally disintegrating formulation of riluzole designed for sublingual administration that addresses the limitations of conventional tablets. This study assessed the bioequivalence between 40-mg BHV-0223 and standard 50-mg oral riluzole tablets, and the food effect on BHV-0223 pharmacokinetics in healthy volunteers. Overall, 133 healthy subjects received BHV-0223 and riluzole tablets under fasted conditions. Geometric mean ratios for the area under the plasma concentration-time curve (AUC) from time zero to time of last nonzero concentration (AUC_0-t ) (89.9%; confidence interval [CI], 87.3%-92.5%), AUC from time zero to infinity (AUC_0-∞ ) (89.8%; CI, 87.3%-92.4%), and maximum observed concentration (112.7%; CI, 105.5%-120.4%) all met bioequivalence criteria (80%-125%). Subsequently, 67 subjects received BHV-0223 under fed conditions. The geometric mean ratios of AUC_0-t (91.2%; CI, 88.1-94.3%), and AUC_0-∞ (92.0%; CI, 89.0-95.1%) were similar, but maximum observed concentration ratios were not within bioequivalence criteria. BHV-0223 was well tolerated. This study demonstrated that 40-mg sublingual BHV-0223 is bioequivalent to 50-mg oral riluzole tablets.

Size-Dependent Vulnerability of Lumbar Motor Neuron Dendritic Degeneration in SOD1G93A Mice

The motor neuron (MN) soma surface area is correlated with motor unit type. Larger MNs innervate fast fatigue-intermediate (FInt) or fast-fatiguable (FF) muscle fibers in type FInt and FF motor units, respectively. Smaller MNs innervate slow-twitch fatigue-resistant (S) or fast fatigue-resistant (FR) muscle fibers in type S and FR motor units, respectively. In amyotrophic lateral sclerosis (ALS), FInt and FF motor units are more vulnerable, with denervation and MN death occurring for these units before the more resilient S and FR units. Abnormal MN dendritic arbors have been observed in ALS in humans and rodent models. We used a Golgi-Cox impregnation protocol to examine soma size-dependent changes in the dendritic morphology of lumbar MNs in SOD1^G93A mice, a model of ALS, at pre-symptomatic, onset and mid-disease stages. In wildtype control mice, the relationship between MN soma surface area and dendritic length or dendritic spine number was highly linear (i.e., increased MN soma size correlated with increased dendritic length and spines). By contrast, in SOD1^G93A mice, this linear relationship was lost and dendritic length reduction and spine loss were observed in larger MNs, from pre-symptomatic stages onward. These changes correlated with the neuromotor symptoms of ALS in rodent models. At presymptomatic ages, changes were restricted to the larger MNs, likely to comprise vulnerable FInt and FF motor units. Our results suggest morphological changes of MN dendrites and dendritic spines are likely to contribute ALS pathogenesis, not compensate for it. Anat Rec, 303:1455-1471, 2020. © 2019 American Association for Anatomy.

Effects of persistent sodium current blockade in respiratory circuits depend on the pharmacological mechanism of action and network dynamics

The mechanism(s) of action of most commonly used pharmacological blockers of voltage-gated ion channels are well understood; however, this knowledge is rarely considered when interpreting experimental data. Effects of blockade are often assumed to be equivalent, regardless of the mechanism of the blocker involved. Using computer simulations, we demonstrate that this assumption may not always be correct. We simulate the blockade of a persistent sodium current (I_NaP), proposed to underlie rhythm generation in pre-Bötzinger complex (pre-BötC) respiratory neurons, via two distinct pharmacological mechanisms: (1) pore obstruction mediated by tetrodotoxin and (2) altered inactivation dynamics mediated by riluzole. The reported effects of experimental application of tetrodotoxin and riluzole in respiratory circuits are diverse and seemingly contradictory and have led to considerable debate within the field as to the specific role of I_NaP in respiratory circuits. The results of our simulations match a wide array of experimental data spanning from the level of isolated pre-BötC neurons to the level of the intact respiratory network and also generate a series of experimentally testable predictions. Specifically, in this study we: (1) provide a mechanistic explanation for seemingly contradictory experimental results from in vitro studies of I_NaP block, (2) show that the effects of I_NaP block in in vitro preparations are not necessarily equivalent to those in more intact preparations, (3) demonstrate and explain why riluzole application may fail to effectively block I_NaP in the intact respiratory network, and (4) derive the prediction that effective block of I_NaP by low concentration tetrodotoxin will stop respiratory rhythm generation in the intact respiratory network. These simulations support a critical role for I_NaP in respiratory rhythmogenesis in vivo and illustrate the importance of considering mechanism when interpreting and simulating data relating to pharmacological blockade.

The application of pharmacological agents that affect transmembrane ionic currents in neurons is a commonly used experimental technique. A simplistic interpretation of experiments involving these agents suggests that antagonist application removes the impacted current and that subsequently observed changes in activity are attributable to the loss of that current’s effects. The more complex reality, however, is that different drugs may have distinct mechanisms of action, some corresponding not to a removal of a current but rather to a changing of its properties. We use computational modeling to explore the implications of the distinct mechanisms associated with two drugs, riluzole and tetrodotoxin, that are often characterized as sodium channel blockers. Through this approach, we offer potential explanations for disparate findings observed in experiments on neural respiratory circuits and show that the experimental results are consistent with a key role for the persistent sodium current in respiratory rhythm generation.

Novel pharmacological targets in drug development for the treatment of anxiety and anxiety-related disorders

Current medication for anxiety disorders is suboptimal in terms of efficiency and tolerability, highlighting the need for improved drug treatments. In this review an overview of drugs being studied in different phases of clinical trials for their potential in the treatment of fear-, anxiety- and trauma-related disorders is presented. One strategy followed in drug development is refining and improving compounds interacting with existing anxiolytic drug targets, such as serotonergic and prototypical GABAergic benzodiazepines. A more innovative approach involves the search for compounds with novel mechanisms of anxiolytic action using the growing knowledge base concerning the relevant neurocircuitries and neurobiological mechanisms underlying pathological fear and anxiety. The target systems evaluated in clinical trials include glutamate, endocannabinoid and neuropeptide systems, as well as ion channels and targets derived from phytochemicals. Examples of promising novel candidates currently in clinical development for generalised anxiety disorder, social anxiety disorder, panic disorder, obsessive compulsive disorder or post-traumatic stress disorder include ketamine, riluzole, xenon with one common pharmacological action of modulation of glutamatergic neurotransmission, as well as the neurosteroid aloradine. Finally, compounds such as D-cycloserine, MDMA, L-DOPA and cannabinoids have shown efficacy in enhancing fear-extinction learning in humans. They are thus investigated in clinical trials as an augmentative strategy for speeding up and enhancing the long-term effectiveness of exposure-based psychotherapy, which could render chronic anxiolytic drug treatment dispensable for many patients. These efforts are indicative of a rekindled interest and renewed optimism in the anxiety drug discovery field, after decades of relative stagnation.

Altered glutamatergic response and functional connectivity in treatment resistant schizophrenia: the effect of riluzole and therapeutic implications

RATIONALE

Anterior cingulate cortex (ACC) glutamatergic abnormalities are reported in treatment-resistant schizophrenia (TRS) and implicated in functional dysconnectivity and psychopathology. Preclinical evidence indicates riluzole reduces synaptic glutamate. However, it is unknown whether riluzole can modulate glutamate metabolite levels and associated functional connectivity in TRS.

OBJECTIVES

To examine the relationship between glutamatergic function and cortical connectivity and determine if riluzole can modulate glutamate metabolite levels and cortical functional connectivity in TRS.

METHODS

Nineteen TRS patients and 18 healthy volunteers (HV) underwent magnetic resonance imaging consisting of MR spectroscopy measuring ACC glutamate plus glutamine (Glx), fMRI measuring resting ACC-functional connectivity, and arterial spin labelling measuring regional cerebral blood flow (rCBF), and clinical measures. They then received 50 mg riluzole twice daily for 2 days when imaging was repeated.

RESULTS

Baseline (pre-riluzole) Glx levels were correlated directly with negative symptom severity (r = 0.49; p = 0.03) and inversely with verbal learning in TRS (r = - 0.63; p = 0.002), but not HV (r = - 0.24; p = 0.41). Connectivity between the ACC and anterior prefrontal cortex (aPFC) was correlated with verbal learning in TRS (r = 0.49; p = 0.04), but not HV (r = 0.28; p = 0.33). There was a significant group × time interaction effect on Glx levels (p < 0.05) and on ACC connectivity to the aPFC (p < 0.05, FWE-corrected). Riluzole decreased Glx and increased ACC-aPFC connectivity in TRS relative to HV. Change in Glx correlated inversely with change in ACC-aPFC connectivity in TRS (r = - 0.52; p = 0.02) but not HV (r = 0.01; p = 0.98). Riluzole did not alter rCBF (p > 0.05), indicating absence of a non-specific blood flow effect.

CONCLUSION

Results indicate glutamatergic function and cortical connectivity are linked to symptoms and cognitive measures and that it is possible to pharmacologically modulate them in TRS.

Effects of cenobamate (YKP3089), a newly developed anti-epileptic drug, on voltage-gated sodium channels in rat hippocampal CA3 neurons

New, more effective pharmacologic treatments for epilepsy are needed, as a substantial portion of patients (>30%) are refractory to currently available anti-epileptic drugs. Cenobamate (YKP3089) is an investigational anti-epileptic drug in clinical development. Two completed adequate and well-controlled studies demonstrated a significant reduction in focal seizures with cenobamate in patients with epilepsy. In this study, we characterized the effects of cenobamate on voltage-gated Na⁺ channels in acutely isolated rat hippocampal CA3 neurons using a whole-cell patch-clamp technique. While cenobamate had little effect on the peak component of transient Na⁺ current (I_NaT) induced by brief depolarizing step pulses, it potently inhibited the non-inactivating persistent component of I_Na (I_NaP). In addition, cenobamate potently inhibited the current by slow voltage-ramp stimuli. Cenobamate significantly shifted the steady-state fast inactivation relationship toward a hyperpolarizing range, indicating that cenobamate binds to voltage-gated Na⁺ channels at the inactivated state with a higher affinity. Cenobamate also accelerated the development of inactivation and retarded recovery from inactivation of voltage-gated Na⁺ channels. In current clamp experiments, cenobamate hyperpolarized membrane potentials in a concentration-dependent manner, and these effects were mediated by inhibiting the I_NaP. Cenobamate also increased the threshold for generation of action potentials, and decreased the number of action potentials elicited by depolarizing current injection. Given that the I_NaP plays a pivotal role in the repetitive and/or burst generation of action potentials, the cenobamate-mediated preferential blockade of I_NaP might contribute to anti-epileptic activity.

Interstitial pneumonia and other adverse events in riluzole-administered amyotrophic lateral sclerosis patients: a retrospective observational study

Background

Riluzole is the only approved oral drug for amyotrophic lateral sclerosis (ALS). We performed a retrospective study including ALS patients treated with riluzole, focusing on adverse events.

Methods

Patients diagnosed with ALS according to the revised El Escorial criteria (World Federation of Neurology) in our center and who were administered 50 mg oral riluzole twice daily between January 2011 and September 2017 and followed up for at least 6 months from treatment initiation or until death were included. Data regarding sex, age, disease type, initial symptoms, biochemical analyses performed before and after riluzole administration, and medical history were collected. In case of withdrawal, cause of discontinuation and durations of disease and drug administration were recorded.

Results

A total of 92 cases were enrolled. Riluzole administration was discontinued in 20 cases (21.7%). The most frequent reason for discontinuation was elevated liver enzymes (n = 5, 5.4%), followed interstitial pneumonia (IP), nausea and appetite loss, dizziness, general malaise, tongue paresthesia, and urinary urgency. In two cases, administration was discontinued primarily because of progression of bulbar palsy. All adverse events occurred within 6 months from treatment initiation and improved soon after its discontinuation. Three IP cases developed severe respiratory failure and required steroid treatment.

Conclusion

Riluzole administration was discontinued in 20 cases among total of 92 cases. Careful follow-up is important for the first six months after the initiation of riluzole administration, including through interviews, chemical analyses, and chest X-rays, as required.

The Pathobiology of TDP-43 C-Terminal Fragments in ALS and FTLD

During neurodegenerative disease, the multifunctional RNA-binding protein TDP-43 undergoes a vast array of post-translational modifications, including phosphorylation, acetylation, and cleavage. Many of these alterations may directly contribute to the pathogenesis of TDP-43 proteinopathies, which include most forms of amyotrophic lateral sclerosis (ALS) and approximately half of all frontotemporal dementia, pathologically identified as frontotemporal lobar degeneration (FTLD) with TDP-43 pathology. However, the relative contributions of the various TDP-43 post-translational modifications to disease remain unclear, and indeed some may be secondary epiphenomena rather than disease-causative. It is therefore critical to determine the involvement of each modification in disease processes to allow the design of targeted treatments. In particular, TDP-43 C-terminal fragments (CTFs) accumulate in the brains of people with ALS and FTLD and are therefore described as a neuropathological signature of these diseases. Remarkably, these TDP-43 CTFs are rarely observed in the spinal cord, even in ALS which involves dramatic degeneration of spinal motor neurons. Therefore, TDP-43 CTFs are not produced non-specifically in the course of all forms of TDP-43-related neurodegeneration, but rather variably arise due to additional factors influenced by regional heterogeneity in the central nervous system. In this review, we summarize how TDP-43 CTFs are generated and degraded by cells, and critique evidence from studies of TDP-43 CTF pathology in human disease tissues, as well as cell and animal models, to analyze the pathophysiological relevance of TDP-43 CTFs to ALS and FTLD. Numerous studies now indicate that, although TDP-43 CTFs are prevalent in ALS and FTLD brains, disease-related pathology is only variably reproduced in TDP-43 CTF cell culture models. Furthermore, TDP-43 CTF expression in both transgenic and viral-mediated in vivo models largely fails to induce motor or behavioral dysfunction reminiscent of human disease. We therefore conclude that although TDP-43 CTFs are a hallmark of TDP-43-related neurodegeneration in the brain, they are not a primary cause of ALS or FTLD.

The Effects of Riluzole on Cisplatin-induced Ototoxicity

Introduction  Riluzole (2-amino-6-trifluoromethoxy benzothiazole) is known as a neuroprotective, antioxidant, antiapoptotic agent. It may have beneficial effects on neuronal cell death due to cisplatin-induced ototoxicity.

Objective  To evaluate the effect of riluzole on cisplatin-induced ototoxicity in guinea pigs.

Methods  Twenty-four guinea pigs, studied in three groups, underwent auditory brainstem response evaluation using click and 8 kHz tone burst stimuli. Subsequently, 5 mg/kg of cisplatin were administered to all animals for 3 days intraperitoneally (i.p.) to induce ototoxicity. Half an hour prior to cisplatin, groups 1, 2 and 3 received 2 ml of saline i.p., 6 mg/kg of riluzole hydrochloride i.p., and 8 mg/kg of riluzole hydrochloride i.p., respectively, for 3 days. The auditory brainstem responses were repeated 24 hours after the last drug administration. The cochleae were analyzed by transmission electron microscopy (TEM).

Results  After drug administiration, for 8,000 Hz stimulus, group 1 had significantly higher threshold shifts when compared with groups 2 ( p  < 0.05) and 3 ( p  < 0.05), and there was no significant difference in threshold shifts between groups 2 and 3 ( p  > 0.05). Transmission electron microscopy findings demonstrated the protective effect of riluzole on the hair cells and the stria vascularis, especially in the group treated with 8 mg/kg of riluzole hydrochloride.

Conclusion  We can say that riluzole may have a protective effect on cisplatin- induced ototoxicity. However, additional studies are needed to confirm these results and the mechanisms of action of riluzole.

Treatment with the glutamate modulator riluzole prevents early life stress-induced cognitive deficits and impairments in synaptic plasticity in APPswe/PS1dE9 mice

BACKGROUND

Environmental factors like stress affect age-related cognitive deficits and promote Alzheimer's disease (AD)-related pathology in mice. Excess glutamate has been proposed as a possible mediator underlying these effects in the hippocampus, a vulnerable brain region implicated in learning and memory.

METHODS

Here, we examined a) whether stress applied during a sensitive developmental period early in life affects later synaptic plasticity, learning and memory and plaque load in the APPswe/PS1dE9 mouse model for Alzheimer's disease and b) whether these effects could be rescued using long-term treatment with the glutamate modulator riluzole.

RESULTS

Our results demonstrate that ELS impairs synaptic plasticity in 6-month-old mice and increases plaque load in 12-month-old APPswe/PS1dE9 mice, while impairing flexible spatial learning in the Barnes maze at this age. Notably, spatial learning correlated well with hippocampal expression of the transporter EAAT2, which is important for extracellular glutamate uptake. The changes in LTP, plaque load and cognition after ELS were all prevented by riluzole treatment that started from post-weaning.

CONCLUSION

These results suggest that normalising glutamate signalling may be a viable therapeutic strategy for treating vulnerable individuals at risk of developing stress-aggravated AD, particularly in relation to adverse early life experiences.

Mechanisms of compensatory plasticity for respiratory motor neuron death

Respiratory motor neuron death arises from multiple neurodegenerative and traumatic neuromuscular disorders. Despite motor neuron death, compensatory mechanisms minimize its functional impact by harnessing intrinsic mechanisms of compensatory respiratory plasticity. However, the capacity for compensation eventually reaches limits and pathology ensues. Initially, challenges to the system such as increased metabolic demand reveal sub-clinical pathology. With greater motor neuron loss, the eventual result is de-compensation, ventilatory failure, ventilator dependence and then death. In this brief review, we discuss recent advances in our understanding of mechanisms giving rise to compensatory respiratory plasticity in response to respiratory motor neuron death including: 1) increased central respiratory drive, 2) plasticity in synapses on spared phrenic motor neurons, 3) enhanced neuromuscular transmission and 4) shifts in respiratory muscle utilization from more affected to less affected motor pools. Some of these compensatory mechanisms may prolong breathing function, but hasten the demise of surviving motor neurons. Improved understanding of these mechanisms and their impact on survival of spared motor neurons will guide future efforts to develop therapeutic interventions that preserve respiratory function with neuromuscular injury/disease.

Amyotrophic lateral sclerosis as a synaptopathy

The synapse is an incredibly specialized structure that allows for the coordinated communication of information from one neuron to another. When assembled into circuits, steady streams of excitatory and inhibitory synaptic activity shape neural outputs. At the organismal level, ensembles of neural networks underlie behavior, emotion and memory. Disorder or dysfunctions of synapses, a synaptopathy, may underlie a host of developmental and degenerative neurological conditions. There is a possibility that amyotrophic lateral sclerosis may be a result of a synaptopathy within the neuromotor system. To this end, particular attention has been trained on the excitatory glutamatergic synapses and their morphological proxy, the dendritic spine. The extensive detailing of these dysfunctions in vulnerable neuronal populations, including corticospinal neurons and motor neurons, has recently been the subject of original research in rodents and humans. If amyotrophic lateral sclerosis is indeed a synaptopathy, it is entirely consistent with other proposed pathogenic mechanisms – including glutamate excitotoxicity, accumulation of misfolded proteins and mitochondrial dysfunction at distal axon terminals (cortico-motor neuron and neuromuscular). Further, although the exact mechanism of disease spread from region to region is unknown, the synaptopathy hypothesis is consistent with emerging die-forward evidence and the prion-like propagation of misfolded protein aggregates to distant neuronal populations. Here in this mini-review, we focus on the timeline of synaptic observations in both cortical and spinal neurons from different rodent models, and provide a conceptual framework for assessing the synaptopathy hypothesis in amyotrophic lateral sclerosis.

Tandem pore TWIK-related potassium channels and neuroprotection

TWIK-related potassium channels (TREK) belong to a subfamily of the two-pore domain potassium channels family with three members, TREK1, TREK2 and TWIK-related arachidonic acid-activated potassium channels. The two-pore domain potassium channels is the last big family of channels being discovered, therefore it is not surprising that most of the information we know about TREK channels predominantly comes from the study of heterologously expressed channels. Notwithstanding, in this review we pay special attention to the limited amount of information available on native TREK-like channels and real neurons in relation to neuroprotection. Mainly we focus on the role of free fatty acids, lysophospholipids and other neuroprotective agents like riluzole in the modulation of TREK channels, emphasizing on how important this modulation may be for the development of new therapies against neuropathic pain, depression, schizophrenia, epilepsy, ischemia and cardiac complications.

Targeting Protein Kinase CK1δ with Riluzole: Could It Be One of the Possible Missing Bricks to Interpret Its Effect in the Treatment of ALS from a Molecular Point of View?

Riluzole, approved by the US Food and Drug Administration (FDA) in 1995, is the most widespread oral treatment for the fatal neurodegenerative disorder amyotrophic lateral sclerosis (ALS). The drug, whose mechanism of action is still obscure, mitigates progression of the illness, but unfortunately with only limited improvements. Herein we report the first demonstration, using a combination of computational and in vitro studies, that riluzole is an ATP-competitive inhibitor of the protein kinase CK1 isoform δ, with an IC₅₀ value of 16.1 μm. This allows us to rewrite its possible molecular mechanism of action in the treatment of ALS. The inhibition of CK1δ catalytic activity indeed links the two main pathological hallmarks of ALS: transactive response DNA-binding protein of 43 kDa (TDP-43) proteinopathy and glutamate excitotoxicity, exacerbated by the loss of expression of glial excitatory amino acid transporter-2 (EAAT2).

Modulation of tetrodotoxin-resistant Na+ channels by amitriptyline in dural afferent neurons

Migraine is characterized by recurrent and disabling headaches; therefore, several drugs have been widely prescribed to prevent acute migraine attacks. Amitriptyline, a tricyclic antidepressant, is among the most commonly administered. It is poorly known, however, whether amitriptyline modulates the excitability of dural afferent neurons that transmit pain signals from the dura mater. In this study, the effects of amitriptyline on tetrodotoxin-resistant (TTX-R) Na⁺ channels were examined in acutely isolated rat dural afferent neurons, which were identified by the fluorescent dye DiI. The TTX-R Na⁺ currents (I_Na) were recorded from medium-sized DiI-positive neurons using a whole-cell patch clamp technique. Amitriptyline (3 μM) slightly reduced the peak component of transient I_Na and induced a marked decrease in the steady-state component of transient TTX-R I_Na, as well as in the slow ramp-induced TTX-R I_Na. Our findings suggest that amitriptyline specifically inhibits persistent Na⁺ currents mediated by TTX-R Na⁺ channels. While amitriptyline had minor effects on voltage-activation/inactivation, it increased the extent of the use-dependent inhibition of TTX-R Na⁺ channels. Amitriptyline also affected the inactivation kinetics of TTX-R Na⁺ channels by significantly accelerating the inactivation of TTX-R Na⁺ channels and slowing the subsequent recovery. Amitriptyline decreased the number of action potentials by increasing the threshold for their generation. In conclusion, the amitriptyline-mediated diverse modulation of TTX-R Na⁺ channels would be, at least in part, responsible for its prophylactic efficacy for migraine attacks.

Riluzole induces LTD of spinal nociceptive signaling via postsynaptic GluR2 receptors

Purpose

Riluzole - a major therapeutic medicine for patients with amyotrophic lateral sclerosis - reportedly has anti-nociceptive and anti-allodynic efficacies in neuropathic pain models. However, little is known about its effect on neurotransmission in the spinal superficial dorsal horn (SDH). The present study aims to investigate the effects of riluzole on the synaptic transmission of SDH nociceptive pathways in both physiological and pathological conditions.

Materials and methods

Spinal nerve ligation was used to produce a neuropathic pain model. Mechanical allodynia behavior was assessed with Von Frey filaments. Riluzole's effects on nociceptive synaptic transmission under both physiological and pathological conditions were examined by patch-clamp recordings in rat SDH neurons.

Results

The principal findings of the present study are three-fold. First, we affirm that riluzole has a remarkable long-lasting analgesic effect on both in vitro and in vivo pathological pain models. Second, the prolonged inhibitory effects of riluzole on spinal nociceptive signaling are mediated by both presynaptic and postsynaptic mechanisms. Finally, endocytosis of post-synaptic GluR2 contributes to the riluzole-induced long-term depression (LTD) of the spinal nociceptive pathway.

Conclusion

The present study finds that riluzole induces LTD of nociceptive signaling in the SDH and produces long-lasting anti-allodynia effects in nerve injury-induced neuropathic pain conditions via postsynaptic AMPA receptors associated with the endocytosis of GluR2.

Choline and NMDG directly reduce outward currents: reduced outward current when these substances replace Na+ is alone not evidence of Na+-activated K+ currents

Choline chloride is often, and N-methyl-d-glucamine (NMDG) sometimes, used to replace sodium chloride in studies of sodium-activated potassium channels. Given the high concentrations used in sodium replacement protocols, it is essential to test that it is not the replacement substances themselves, as opposed to the lack of sodium, that cause any observed effects. We therefore compared, in lobster stomatogastric neurons and leech Retzius cells, the effects of applying salines in which choline chloride replaced sodium chloride, and in which choline hydroxide or sucrose was added to normal saline. We also tested, in stomatogastric neurons, the effect of adding NMDG to normal saline. These protocols allowed us to measure the direct effects (i.e., effects not due to changes in sodium concentration or saline osmolarity or ionic strength) of choline on stomatogastric and leech currents, and of NMDG on stomatogastric currents. Choline directly reduced transient and sustained depolarization-activated outward currents in both species, and NMDG directly reduced transient depolarization-activated outward currents in stomatogastric neurons. Experiments with lower choline concentrations showed that adding as little as 150 mM (stomatogastric) or 5 mM (leech) choline reduced at least some depolarization-activated outward currents. Reductions in outward current with choline chloride or NMDG replacement alone are thus not evidence of sodium-activated potassium currents. NEW & NOTEWORTHY We show that choline or N-methyl-d-glucamine (NMDG) directly (i.e., not due to changes in extracellular sodium) decrease outward currents. Prior work studying sodium-activated potassium channels in which sodium was replaced with choline or NMDG without an addition control may therefore be artifactual.

Genistein Ameliorates Scopolamine-Induced Amnesia in Mice Through the Regulation of the Cholinergic Neurotransmission, Antioxidant System and the ERK/CREB/BDNF Signaling

Genistein (GE) was reported to exert a wide spectrum of biological activities, including antioxidant, anti-inflammatory, anti-mutagenic, anticancer, and cardio-protective effects. In addition, both clinical and preclinical studies have recently suggested GE a potential neuroprotective and memory-enhancing drug against neurodegenerative diseases. The animal model of scopolamine (Scop)-induced amnesia is widely used to study underlying mechanisms and treatment of cognitive impairment in neurodegenerative diseases. However, there is no report about the effects of GE on Scop-induced amnesia in mice. Therefore, the present study was carried out to investigate the beneficial effects and potential mechanism of GE against Scop-induced deficits in mice. The mice were orally pretreated with either GE (10, 20, and 40 mg/kg) or donepezil (1.60 mg/kg) for 14 days. After the pretreatment, the open field test was conducted to assess the effect of GE on the locomotor activity of mice. Thereafter, mice were daily injected with Scop (0.75 mg/kg) intraperitoneally to induce memory deficits and subjected to the cognitive behavioral tests including the Object Location Recognition (OLR) experiment and Morris Water Maze (MWM) task. After the behavioral tests, biochemical parameter assay and western blot analysis were used to examine the underlying mechanisms of its action. The results showed that GE administration significantly improved the cognitive performance of Scop-treated mice in OLR and Morris water maze tests, exerting the memory-enhancing effects. Additionally, GE remarkably promoted the cholinergic neurotransmission and protected against the oxidative stress damage in the hippocampus of Scop-treated mice, as indicated by decreasing AChE activity, elevating ChAT activity and Ach level, increasing SOD activity, lowering the level of MDA and increasing GSH content. Furthermore, GE was found to significantly upregulate the expression levels of p-ERK, p-CREB and BDNF proteins in the hippocampus of Scop-treated mice. Taken together, these results for the first time found that GE exerts cognitive-improving effects in Scop-induced amnesia and suggested it may be a potential candidate compound for the treatment of some neurodegenerative diseases such as Alzheimer's Disease (AD).

Multiple Sclerosis-Secondary Progressive Multi-Arm Randomisation Trial (MS-SMART): a multiarm phase IIb randomised, double-blind, placebo-controlled clinical trial comparing the efficacy of three neuroprotective drugs in secondary progressive multiple sclerosis

INTRODUCTION

The major unmet need in multiple sclerosis (MS) is for neuroprotective therapies that can slow (or ideally stop) the rate of disease progression. The UK MS Society Clinical Trials Network (CTN) was initiated in 2007 with the purpose of developing a national, efficient, multiarm trial of repurposed drugs. Key underpinning work was commissioned by the CTN to inform the design, outcome selection and drug choice including animal models and a systematic review. This identified seven leading oral agents for repurposing as neuroprotective therapies in secondary progressive MS (SPMS). The purpose of the Multiple Sclerosis-Secondary Progressive Multi-Arm Randomisation Trial (MS-SMART) will be to evaluate the neuroprotective efficacy of three of these drugs, selected with distinct mechanistic actions and previous evidence of likely efficacy, against a common placebo arm. The interventions chosen were: amiloride (acid-sensing ion channel antagonist); fluoxetine (selective serotonin reuptake inhibitor) and riluzole (glutamate antagonist).

METHODS AND ANALYSIS

Patients with progressing SPMS will be randomised 1:1:1:1 to amiloride, fluoxetine, riluzole or matched placebo and followed for 96 weeks. The primary outcome will be the percentage brain volume change (PBVC) between baseline and 96 weeks, derived from structural MR brain imaging data using the Structural Image Evaluation, using Normalisation, of Atrophy method. With a sample size of 90 per arm, this will give 90% power to detect a 40% reduction in PBVC in any active arm compared with placebo and 80% power to detect a 35% reduction (analysing by analysis of covariance and with adjustment for multiple comparisons of three 1.67% two-sided tests), giving a 5% overall two-sided significance level. MS-SMART is not powered to detect differences between the three active treatment arms. Allowing for a 20% dropout rate, 110 patients per arm will be randomised. The study will take place at Neuroscience centres in England and Scotland.

ETHICS AND DISSEMINATION

MS-SMART was approved by the Scotland A Research Ethics Committee on 13 January 2013 (REC reference: 13/SS/0007). Results of the study will be submitted for publication in a peer-reviewed journal.

TRIAL REGISTRATION NUMBERS

NCT01910259; 2012-005394-31; ISRCTN28440672.

Persistent sodium current modulates axonal excitability in CA1 pyramidal neurons

Axonal excitability is an important determinant for the accuracy, direction, and velocity of neuronal signaling. The mechanisms underlying spike generation in the axonal initial segment and transmitter release from presynaptic terminals have been intensely studied and revealed a role for several specific ionic conductances, including the persistent sodium current (I_NaP ). Recent evidence indicates that action potentials can also be generated at remote locations along the axonal fiber, giving rise to ectopic action potentials during physiological states (e.g., fast network oscillations) or in pathological situations (e.g., following demyelination). Here, we investigated how ectopic axonal excitability of mouse hippocampal CA1 pyramidal neurons is regulated by I_NaP . Recordings of field potentials and intracellular voltage in brain slices revealed that electrically evoked antidromic spikes were readily suppressed by two different blockers of I_NaP , riluzole and phenytoin. The effect was mediated by a reduction of the probability of ectopic spike generation while latency was unaffected. Interestingly, the contribution of I_NaP to excitability was much more pronounced in axonal branches heading toward the entorhinal cortex compared with the opposite fiber direction toward fimbria. Thus, excitability of distal CA1 pyramidal cell axons is affected by persistent sodium currents in a direction-selective manner. This mechanism may be of importance for ectopic spike generation in oscillating network states as well as in pathological situations.

The efficacy and safety of riluzole for neurodegenerative movement disorders: a systematic review with meta-analysis

Neurodegenerative movement disorders mainly include Parkinson’s disease, atypical parkinsonisms, Huntington disease, and hereditary ataxia. Riluzole is the only drug approved by the US Food and Drug Administration for amyotrophic lateral sclerosis. The neuroprotective effects of riluzole have been observed in experimental models of neurodegenerative movement disorders. In this paper, we aimed to systematically analyze the efficacy and safety of riluzole for patients with neurodegenerative movement disorder. We searched the electronic databases such as PubMed, EMBASE, CINAHL, Cochrane Library and China National Knowledge Infrastructure until June 2017 for the eligible randomized controlled trials, as well as the unpublished and ongoing trials. For continuous data, we calculated standardized mean differences with 95% confidence intervals if studies did not use the same scales to measure outcomes. For dichotomous data, we calculated risk differences if a trial reported no adverse events or dropouts. We pooled the results using a random-effects model. We included nine studies with 1320 patients with neurodegenerative movement disorders, which compared riluzole with placebo. No significant difference was found in the number of participants with adverse events but with motor improvement in hereditary ataxia. There were only two studies focusing on neuroprotective effect. Riluzole is well-tolerated in the patients with neurodegenerative movement disorders. Riluzole seems to be promising for patients with hereditary ataxia in symptomatic effect, which needs to be further confirmed by well-designed studies in the future. Moreover, it makes sense to design long-term study focusing on neuroprotective effect of riluzole in disease-modifying.

Inspiratory-Activated Airway Vagal Preganglionic Neurones Excited by Thyrotropin-Releasing Hormone via Multiple Mechanisms in Neonatal Rats

The airway vagal preganglionic neurons (AVPNs) providing projections to intrinsic tracheobronchial ganglia are considered to be crucial to modulation of airway resistance in physiological and pathological states. AVPNs classified into inspiratory-activated AVPNs (IA-AVPNs) and inspiratory-inhibited AVPNs (II-AVPNs) are regulated by thyrotropin-releasing hormone (TRH)-containing terminals. TRH causes a direct excitatory current and attenuates the phasic inspiratory glycinergic inputs in II-AVPNs, however, whether and how TRH influences IA-AVPNs remains unknown. In current study, TRH regulation of IA-AVPNs and its mechanisms involved were investigated. Using retrogradely fluorescent labeling method and electrophysiology techniques to identify IA-AVPNs in brainstem slices with rhythmic inspiratory hypoglossal bursts recorded by a suction electrode, the modulation of TRH was observed with patch-clamp technique. The findings demonstrate that under voltage clamp configuration, TRH (100 nM) caused a slow excitatory inward current, augmented the excitatory synaptic inputs, progressively suppressed the inhibitory synaptic inputs and elicited a distinctive electrical oscillatory pattern (OP). Such a current and an OP was independent of presynaptic inputs. Carbenoxolone (100 μM), a widely used gap junction inhibitor, fully suppressed the OP with persistence of TRH-induced excitatory slow inward current and augment of the excitatory synaptic inputs. Both tetrodotoxin (1 μM) and riluzole (20 μM) functioned to block the majority of the slow excitatory inward current and prevent the OP, respectively. Under current clamp recording, TRH caused a slowly developing depolarization and continuously progressive oscillatory firing pattern sensitive to TTX. TRH increased the firing frequency in response to injection of a square-wave current. The results suggest that TRH excited IA-AVPNs via the following multiple mechanisms: (1) TRH enhances the excitatory and depresses the inhibitory inputs; (2) TRH induces an excitatory postsynaptic slow inward current; (3) TRH evokes a distinctive OP mediated by gap junction.

Activation of TREK currents by riluzole in three subgroups of cultured mouse nodose ganglion neurons

Two-pore domain potassium channels (K2P) constitute major candidates for the regulation of background potassium currents in mammalian cells. Channels of the TREK subfamily are also well positioned to play an important role in sensory transduction due to their sensitivity to a large number of physiological and physical stimuli (pH, mechanical, temperature). Following our previous report describing the molecular expression of different K2P channels in the vagal sensory system, here we confirm that TREK channels are functionally expressed in neurons from the mouse nodose ganglion (mNG). Neurons were subdivided into three groups (A, Ah and C) based on their response to tetrodotoxin and capsaicin. Application of the TREK subfamily activator riluzole to isolated mNG neurons evoked a concentration-dependent outward current in the majority of cells from all the three subtypes studied. Riluzole increased membrane conductance and hyperpolarized the membrane potential by approximately 10 mV when applied to resting neurons. The resting potential was similar in all three groups, but C cells were clearly less excitable and showed smaller hyperpolarization-activated currents at -100 mV and smaller sustained currents at -30 mV. Our results indicate that the TREK subfamily of K2P channels might play an important role in the maintenance of the resting membrane potential in sensory neurons of the autonomic nervous system, suggesting its participation in the modulation of vagal reflexes.

Acute Effects of Riluzole and Retigabine on Axonal Excitability in Patients With Amyotrophic Lateral Sclerosis: A Randomized, Double-Blind, Placebo-Controlled, Crossover Trial

Increased excitability of motor neurons in patients with amyotrophic lateral sclerosis (ALS) may be a relevant factor leading to motor neuron damage. This randomized, double-blind, three-way crossover, placebo-controlled study evaluated peripheral motor nerve excitability testing as a biomarker of hyperexcitability and assessed the effects of riluzole and retigabine in 18 patients with ALS. We performed excitability testing at baseline, and twice after participants had received a single dose of either 100 mg riluzole, 300 mg retigabine, or placebo. Between- and within-day repeatability was at least acceptable for 14 out of 18 recorded excitability variables. No effects of riluzole on excitability testing were observed, but retigabine significantly decreased strength-duration time-constant (9.2%) and refractoriness at 2 ms (10.2) compared to placebo. Excitability testing was shown to be a reliable biomarker in patients with ALS, and the acute reversal of previously abnormal variables by retigabine justifies long-term studies evaluating the impact on disease progression and survival.

Small conductance calcium activated potassium (SK) channel dependent and independent effects of riluzole on neuropathic pain-related amygdala activity and behaviors in rats

BACKGROUND AND PURPOSE

Chronic neuropathic pain is an important healthcare issue with significant emotional components. The amygdala is a brain region involved in pain and emotional-affective states and disorders. The central amygdala output nucleus (CeA) contains small-conductance calcium-activated potassium (SK) channels that can control neuronal activity. A clinically available therapeutic, riluzole can activate SK channels and may have antinociceptive effects through a supraspinal action. We tested the hypothesis that riluzole inhibits neuropathic pain behaviors by inhibiting pain-related changes in CeA neurons, in part at least through SK channel activation.

EXPERIMENTAL APPROACH

Brain slice physiology and behavioral assays were done in adult Sprague Dawley rats. Audible and ultrasonic vocalizations and von Frey thresholds were measured in sham and neuropathic rats 4 weeks after left L5 spinal nerve ligation (SNL model). Whole cell patch-clamp recordings of regular firing CeA neurons in brain slices were used to measure synaptic transmission and neuronal excitability.

KEY RESULTS

In brain slices, riluzole increased the SK channel-mediated afterhyperpolarization and synaptic inhibition, but inhibited neuronal excitability through an SK channel independent action. SNL rats had increased vocalizations and decreased withdrawal thresholds compared to sham rats, and intra-CeA administration of riluzole inhibited vocalizations and depression-like behaviors but did not affect withdrawal thresholds. Systemic riluzole administration also inhibited these changes, demonstrating the clinical utility of this strategy. SK channel blockade in the CeA attenuated the inhibitory effects of systemic riluzole on vocalizations, confirming SK channel involvement in these effects.

CONCLUSIONS AND IMPLICATIONS

The results suggest that riluzole has beneficial effects on neuropathic pain behaviors through SK channel dependent and independent mechanisms in the amygdala.

Driven to decay: Excitability and synaptic abnormalities in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron (MN) disease and is clinically characterised by the death of corticospinal motor neurons (CSMNs), spinal and brainstem MNs and the degeneration of the corticospinal tract. Degeneration of CSMNs and MNs leads inexorably to muscle wastage and weakness, progressing to eventual death within 3-5 years of diagnosis. The CSMNs, located within layer V of the primary motor cortex, project axons constituting the corticospinal tract, forming synaptic connections with brainstem and spinal cord interneurons and MNs. Clinical ALS may be divided into familial (∼10% of cases) or sporadic (∼90% of cases), based on apparent random incidence. The emergence of transgenic murine models, expressing different ALS-associated mutations has accelerated our understanding of ALS pathogenesis, although precise mechanisms remain elusive. Multiple avenues of investigation suggest that cortical electrical abnormalities have pre-eminence in the pathophysiology of ALS. In addition, glutamate-mediated functional and structural alterations in both CSMNs and MNs are present in both sporadic and familial forms of ALS. This review aims to promulgate debate in the field with regard to the common aetiology of sporadic and familial ALS. A specific focus on a nexus point in ALS pathogenesis, namely, the synaptic and intrinsic hyperexcitability of CSMNs and MNs and alterations to their structure are comprehensively detailed. The association of extramotor dysfunction with neuronal structural/functional alterations will be discussed. Finally, the implications of the latest research on the dying-forward and dying-back controversy are considered.

Remarkable Progress with Small-Molecule Modulation of TRPC1/4/5 Channels: Implications for Understanding the Channels in Health and Disease

Proteins of the TRPC family can form many homo- and heterotetrameric cation channels permeable to Na⁺, K⁺ and Ca2+. In this review, we focus on channels formed by the isoforms TRPC1, TRPC4 and TRPC5. We review evidence for the formation of different TRPC1/4/5 tetramers, give an overview of recently developed small-molecule TRPC1/4/5 activators and inhibitors, highlight examples of biological roles of TRPC1/4/5 channels in different tissues and pathologies, and discuss how high-quality chemical probes of TRPC1/4/5 modulators can be used to understand the involvement of TRPC1/4/5 channels in physiological and pathophysiological processes.

Verapamil and riluzole cocktail liposomes overcome pharmacoresistance by inhibiting P-glycoprotein in brain endothelial and astrocyte cells: A potent approach to treat amyotrophic lateral sclerosis

Riluzole is currently one of two approved medications for the treatment of amyotrophic lateral sclerosis (ALS). However, brain disposition of riluzole, as a substrate of P-glycoprotein (P-gp), is limited by the efflux transporters at the blood-brain barrier (BBB). We propose to develop a liposomal co-delivery system that could effectively transport riluzole to brain cells by reducing efflux pumps with a P-gp inhibitor, verapamil. Riluzole and verapamil cocktail liposomes were prepared by lipid film hydration. The average particle size of cocktail liposomes was 194.3 ± 6.0 nm and their polydispersity index (PDI) was 0.272 ± 0.017. The encapsulation efficiencies of verapamil and riluzole in the cocktail liposomes were 86.0 ± 1.4% and 85.6 ± 1.1%, respectively. The drug release from cocktail liposomes after 8 h in PBS at 37 °C was 78.4 ± 6.2% of riluzole and 76.7 ± 3.8% of verapamil. The average particle size of liposomes did not show significant changes at 4 °C after three months. Verapamil cocktail liposomes inhibited P-gp levels measured by western blotting in dose and time-dependent manners in brain endothelial bEND.3 cells. Increased drug efflux transporters were detected in bEND.3 and astrocytes C8D1A cells, promoted by tumor necrosis factor (TNF-α) or hydrogen peroxide (H₂O₂). Restored accumulations of riluzole and fluorescent dye rhodamine 123 were observed in bEND.3 cells after treatments with cocktail liposomes. It indicated that inhibitory potential of co-delivery liposome system towards P-gp could mediate the transport of both P-gp substrates. Verapamil and riluzole co-loaded liposomes may be used to overcome pharmacoresistance of riluzole for improving ALS therapy.

Exploiting ROS and metabolic differences to kill cisplatin resistant lung cancer

Cisplatin resistance remains a major problem in the treatment of lung cancer. We have discovered that cisplatin resistant (CR) lung cancer cells, regardless of the signaling pathway status, share the common parameter which is an increase in reactive oxygen species (ROS) and undergo metabolic reprogramming. CR cells were no longer addicted to the glycolytic pathway, but rather relied on oxidative metabolism. They took up twice as much glutamine and were highly sensitive to glutamine deprivation. Glutamine is hydrolyzed to glutamate for glutathione synthesis, an essential factor to abrogate high ROS via xCT antiporter. Thus, blocking glutamate flux using riluzole (an amyotropic lateral sclerosis approved drug) can selectively kill CR cells in vitro and in vivo. However, we discovered here that glutathione suppression is not the primary pathway in eradicating the CR cells. Riluzole can lead to further decrease in NAD+ (nicotinamide adenine dinucleotide) and lactate dehydrogenase-A (LDHA) expressions which in turn further heightened oxidative stress in CR cells. LDHA knocked-down cells became hypersensitive to riluzole treatments and possessed increased levels of ROS. Addition of NAD+ re-stabilized LDHA and reversed riluzole induced cell death. Thus far, no drugs are available which could overcome cisplatin resistance or kill cisplatin resistant cells. CR cells possess high levels of ROS and undergo metabolic reprogramming. These metabolic adaptations can be exploited and targeted by riluzole. Riluzole may serve as a dual-targeting agent by suppression LDHA and blocking xCT antiporter. Repurposing of riluzole should be considered for future treatment of cisplatin resistant lung cancer patients.

Animal Toxins as Therapeutic Tools to Treat Neurodegenerative Diseases

Neurodegenerative diseases affect millions of individuals worldwide. So far, no disease-modifying drug is available to treat patients, making the search for effective drugs an urgent need. Neurodegeneration is triggered by the activation of several cellular processes, including oxidative stress, mitochondrial impairment, neuroinflammation, aging, aggregate formation, glutamatergic excitotoxicity, and apoptosis. Therefore, many research groups aim to identify drugs that may inhibit one or more of these events leading to neuronal cell death. Venoms are fruitful natural sources of new molecules, which have been relentlessly enhanced by evolution through natural selection. Several studies indicate that venom components can exhibit selectivity and affinity for a wide variety of targets in mammalian systems. For instance, an expressive number of natural peptides identified in venoms from animals, such as snakes, scorpions, bees, and spiders, were shown to lessen inflammation, regulate glutamate release, modify neurotransmitter levels, block ion channel activation, decrease the number of protein aggregates, and increase the levels of neuroprotective factors. Thus, these venom components hold potential as therapeutic tools to slow or even halt neurodegeneration. However, there are many technological issues to overcome, as venom peptides are hard to obtain and characterize and the amount obtained from natural sources is insufficient to perform all the necessary experiments and tests. Fortunately, technological improvements regarding heterologous protein expression, as well as peptide chemical synthesis will help to provide enough quantities and allow chemical and pharmacological enhancements of these natural occurring compounds. Thus, the main focus of this review is to highlight the most promising studies evaluating animal toxins as therapeutic tools to treat a wide variety of neurodegenerative conditions, including Alzheimer's disease, Parkinson's disease, brain ischemia, glaucoma, amyotrophic lateral sclerosis, and multiple sclerosis.

Synaptic dysfunction and altered excitability in C9ORF72 ALS/FTD

Amyotrophic lateral sclerosis (ALS) is characterized by a progressive degeneration of upper and lower motor neurons, resulting in fatal paralysis due to denervation of the muscle. Due to genetic, pathological and symptomatic overlap, ALS is now considered a spectrum disease together with frontotemporal dementia (FTD), the second most common cause of dementia in individuals under the age of 65. Interestingly, in both diseases, there is a large prevalence of RNA binding proteins (RBPs) that are mutated and considered disease-causing, or whose dysfunction contribute to disease pathogenesis. The most common shared genetic mutation in ALS/FTD is a hexanucleuotide repeat expansion within intron 1 of C9ORF72 (C9). Three potentially overlapping, putative toxic mechanisms have been proposed: loss of function due to haploinsufficient expression of the C9ORF72 mRNA, gain of function of the repeat RNA aggregates, or RNA foci, and repeat-associated non-ATG-initiated translation (RAN) of the repeat RNA into toxic dipeptide repeats (DPRs). Regardless of the causative mechanism, disease symptoms are ultimately caused by a failure of neurotransmission in three regions: the brain, the spinal cord, and the neuromuscular junction. Here, we review C9 ALS/FTD-associated synaptic dysfunction and aberrant neuronal excitability in these three key regions, focusing on changes in morphology and synapse formation, excitability, and excitotoxicity in patients, animal models, and in vitro models. We compare these deficits to those seen in other forms of ALS and FTD in search of shared pathways, and discuss the potential targeting of synaptic dysfunctions for therapeutic intervention in ALS and FTD patients.

A Possible Role for Platelet-Activating Factor Receptor in Amyotrophic Lateral Sclerosis Treatment

Amyotrophic lateral sclerosis (ALS) is the third most prevalent neurodegenerative disease affecting upper and lower motor neurons. An important pathway that may lead to motor neuron degeneration is neuroinflammation. Cerebrospinal Fluids of ALS patients have increased levels of the inflammatory cytokine IL-18. Because IL-18 is produced by dendritic cells stimulated by the platelet-activating factor (PAF), a major neuroinflammatory mediator, it is expected that PAF is involved in ALS. Here we show pilot experimental data on amplification of PAF receptor (PAFR) mRNA by RT-PCR. PAFR is overexpressed, as compared to age matched controls, in the spinal cords of transgenic ALS SOD1-G93A mice, suggesting PAF mediation. Although anti-inflammatory drugs have been tested for ALS before, no clinical trial has been conducted using PAFR specific inhibitors. Therefore, we hypothesize that administration of PAFR inhibitors, such as Ginkgolide B, PCA 4248 and WEB 2086, have potential to function as a novel therapy for ALS, particularly in SOD1 familial ALS forms. Because currently there are only two approved drugs with modest effectiveness for ALS therapy, a search for novel drugs and targets is essential.

Effects of Benzothiazolamines on Voltage-Gated Sodium Channels

Benzothiazole is a versatile fused heterocycle that aroused much interest in drug discovery as anticonvulsant, neuroprotective, analgesic, anti-inflammatory, antimicrobial, and anticancer. Two benzothiazolamines, riluzole and lubeluzole, are known blockers of voltage-gated sodium (Na_v) channels. Riluzole is clinically used as a neuroprotectant in amyotrophic lateral sclerosis. Inhibition of Na_v channels by riluzole is voltage-dependent due to preferential binding to inactivated sodium channels. Yet the drug exerts little use-dependent block, probably because it lacks protonable amine. One important property is riluzole ability to inhibit persistent Na⁺ currents, which likely contributes to its neuroprotective activity. Lubeluzole showed promising neuroprotective effects in animal stroke models, but failed to show benefits in acute ischemic stroke in humans. One important concern is its propensity to prolong the cardiac QT interval, due to hERG K⁺ channel block. Lubeluzole very potently inhibits Na_v channels in a voltage- and use-dependent manner, due to its great preferential affinity for inactivated channels and the presence of a protonable amine group. Patch-clamp experiments suggest that the binding sites of both drugs overlap the local anesthetic receptor within the ion-conducting pathway. Riluzole and lubeluzole displayed very potent antimyotonic activity in a rat model of myotonia, a pathological skeletal muscle condition characterized by high-frequency runs of action potentials. Such results well support the repurposing of riluzole as an antimyotonic drug, allowing the launch of a pilot study in myotonic patients. Riluzole, lubeluzole, and new Na_v channel blockers built on the benzothiazolamine scaffold will certainly continue to be investigated for possible clinical applications.