Effect of Riluzole on serum amino acids in patients with amyotrophic lateral sclerosis

Extracellular Vesicles as Potential Biomarkers in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is described as a fatal and rapidly progressive neurodegenerative disorder caused by the degeneration of upper motor neurons in the primary motor cortex and lower motor neurons of the brainstem and spinal cord. Due to ALS's slowly progressive characteristic, which is often accompanied by other neurological comorbidities, its diagnosis remains challenging. Perturbations in vesicle-mediated transport and autophagy as well as cell-autonomous disease initiation in glutamatergic neurons have been revealed in ALS. The use of extracellular vesicles (EVs) may be key in accessing pathologically relevant tissues for ALS, as EVs can cross the blood-brain barrier and be isolated from the blood. The number and content of EVs may provide indications of the disease pathogenesis, its stage, and prognosis. In this review, we collected a recent study aiming at the identification of EVs as a biomarker of ALS with respect to the size, quantity, and content of EVs in the biological fluids of patients compared to controls.

Are Circulating Cytokines Reliable Biomarkers for Amyotrophic Lateral Sclerosis?

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that has no effective treatment. The lack of any specific biomarker that can help in the diagnosis or prognosis of ALS has made the identification of biomarkers an urgent challenge. Multiple panels have shown alterations in levels of numerous cytokines in ALS, supporting the contribution of neuroinflammation to the progressive motor neuron loss. However, none of them is fully sensitive and specific enough to become a universal biomarker for ALS. This review gathers the numerous circulating cytokines that have been found dysregulated in both ALS animal models and patients. Particularly, it highlights the opposing results found in the literature to date, and points out another potential application of inflammatory cytokines as therapeutic targets.

Biomarkers in Motor Neuron Disease: A State of the Art Review

Motor neuron disease can be viewed as an umbrella term describing a heterogeneous group of conditions, all of which are relentlessly progressive and ultimately fatal. The average life expectancy is 2 years, but with a broad range of months to decades. Biomarker research deepens disease understanding through exploration of pathophysiological mechanisms which, in turn, highlights targets for novel therapies. It also allows differentiation of the disease population into sub-groups, which serves two general purposes: (a) provides clinicians with information to better guide their patients in terms of disease progression, and (b) guides clinical trial design so that an intervention may be shown to be effective if population variation is controlled for. Biomarkers also have the potential to provide monitoring during clinical trials to ensure target engagement. This review highlights biomarkers that have emerged from the fields of systemic measurements including biochemistry (blood, cerebrospinal fluid, and urine analysis); imaging and electrophysiology, and gives examples of how a combinatorial approach may yield the best results. We emphasize the importance of systematic sample collection and analysis, and the need to correlate biomarker findings with detailed phenotype and genotype data.

Fluid-Based Biomarkers for Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a highly heterogeneous disease with no effective treatment. Drug development has been hampered by the lack of biomarkers that aid in early diagnosis, demonstrate target engagement, monitor disease progression, and can serve as surrogate endpoints to assess the efficacy of treatments. Fluid-based biomarkers may potentially address these issues. An ideal biomarker should exhibit high specificity and sensitivity for distinguishing ALS from control (appropriate disease mimics and other neurologic diseases) populations and monitor disease progression within individual patients. Significant progress has been made using cerebrospinal fluid, serum, and plasma in the search for ALS biomarkers, with urine and saliva biomarkers still in earlier stages of development. A few of these biomarker candidates have demonstrated use in patient stratification, predicting disease course (fast vs slow progression) and severity, or have been used in preclinical and clinical applications. However, while ALS biomarker discovery has seen tremendous advancements in the last decade, validating biomarkers and moving them towards the clinic remains more elusive. In this review, we highlight biomarkers that are moving towards clinical utility and the challenges that remain in order to implement biomarkers at all stages of the ALS drug development process.

ACTH (Acthar Gel) Reduces Toxic SOD1 Protein Linked to Amyotrophic Lateral Sclerosis in Transgenic Mice: A Novel Observation

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease with a complex etiology and pathology that makes the development of new therapies difficult. ACTH has neurotrophic and myotrophic effects, but has not been tested in an ALS mouse model. The G93A-SOD1 mouse model of ALS was used to test the ability of this drug to delay ALS-like symptoms. We showed that within a specific dose range, ACTH significantly postponed the disease onset and paralysis in the mouse model. To our surprise and of greater significance is that ACTH significantly reduced the levels of soluble SOD1 in the spinal cord and CNS tissues of G93A-SOD1 treated mice as well as cultured fibroblasts.

Berberine Inhibits the Release of Glutamate in Nerve Terminals from Rat Cerebral Cortex

Berberine, an isoquinoline plant alkaloid, protects neurons against neurotoxicity. An excessive release of glutamate is considered to be one of the molecular mechanisms of neuronal damage in several neurological diseases. In this study, we investigated whether berberine could affect endogenous glutamate release in nerve terminals of rat cerebral cortex (synaptosomes) and explored the possible mechanism. Berberine inhibited the release of glutamate evoked by the K⁺ channel blocker 4-aminopyridine (4-AP), and this phenomenon was prevented by the chelating extracellular Ca²⁺ ions and the vesicular transporter inhibitor bafilomycin A1, but was insensitive to the glutamate transporter inhibitor DL-threo-beta-benzyl-oxyaspartate. Inhibition of glutamate release by berberine was not due to it decreasing synaptosomal excitability, because berberine did not alter 4-AP-mediated depolarization. The inhibitory effect of berberine on glutamate release was associated with a reduction in the depolarization-induced increase in cytosolic free Ca²⁺ concentration. Involvement of the Ca_v2.1 (P/Q-type) channels in the berberine action was confirmed by blockade of the berberine-mediated inhibition of glutamate release by the Ca_v2.1 (P/Q-type) channel blocker ω-agatoxin IVA. In addition, the inhibitory effect of berberine on evoked glutamate release was prevented by the mitogen-activated/extracellular signal-regulated kinase kinase (MEK) inhibitors. Berberine decreased the 4-AP-induced phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and synapsin I, the main presynaptic target of ERK; this decrease was also blocked by the MEK inhibition. Moreover, the inhibitory effect of berberine on evoked glutamate release was prevented in nerve terminals from mice lacking synapsin I. Together, these results indicated that berberine inhibits glutamate release from rats cortical synaptosomes, through the suppression of presynaptic Cav2.1 channels and ERK/synapsin I signaling cascade. This finding may provide further understanding of the mode of berberine action in the brain and highlights the therapeutic potential of this compound in the treatment of a wide range of neurological disorders.

Tanshinone IIA, a constituent of Danshen, inhibits the release of glutamate in rat cerebrocortical nerve terminals

ETHNOPHARMACOLOGICAL RELEVANCE

Danshen is a commonly used traditional Chinese medicine and has received considerable attention due to their beneficial effects on the health, including prevention of cardiovascular disease, and cancer. Tanshinone IIA, a major active constituent of Danshen, has been reported to have a neuroprotective profile.

AIM OF THE STUDY

An excessive release of glutamate is considered to be related to neuropathology of several neurological diseases. In this study, we investigated whether tanshinone IIA could affect endogenous glutamate release and explored the possible mechanism.

MATERIALS AND METHODS

The experimental model was the isolated nerve terminals (synaptosomes) purified from the rat cerebral cortex. The release of glutamate was evoked by the K(+) channel blocker 4-aminopyridine (4-AP) and measured by one-line enzyme-coupled fluorometric assay. We also used a membrane potential-sensitive dye to assay nerve terminal excitability and depolarization, and a Ca(2+) indicator, Fura-2-acetoxymethyl ester, to monitor cytosolic Ca(2+) concentrations ([Ca(2+)]C).

RESULTS

Tanshinone IIA inhibited the release of glutamate evoked by 4-AP in a concentration-dependent manner. Inhibition of glutamate release by tanshinone IIA was prevented by the chelating the extracellular Ca(2+) ions, and by the vesicular transporter inhibitor bafilomycin A1. However, the glutamate transporter inhibitor DL-threo-beta-benzyl-oxyaspartate did not have any effect on the action of tanshinone IIA. Tanshinone IIA decreased the depolarization-induced increase in [Ca(2+)]C, whereas it did not alter the resting synaptosomal membrane potential or 4-AP-mediated depolarization. Furthermore, the effect of tanshinone IIA on evoked glutamate release was prevented by the Cav2.2 (N-type) and Cav2.1 (P/Q-type) channel blocker ω-conotoxin MVIIC, but not by the ryanodine receptor blocker dantrolene or the mitochondrial Na(+)/Ca(2+) exchanger blocker CGP37157. Mitogen-activated protein kinase (MEK) inhibition also prevented the inhibitory effect of tanshinone IIA on evoked glutamate release.

CONCLUSION

These results show that tanshinone IIA inhibits glutamate release from cortical synaptosomes in rats through the suppression of presynaptic voltage-dependent Ca(2+) entry and MEK signaling cascade.

Ferulic acid suppresses glutamate release through inhibition of voltage-dependent calcium entry in rat cerebrocortical nerve terminals

This study investigated the effects and possible mechanism of ferulic acid, a naturally occurring phenolic compound, on endogenous glutamate release in the nerve terminals of the cerebral cortex in rats. Results show that ferulic acid inhibited the release of glutamate evoked by the K⁺ channel blocker 4-aminopyridine (4-AP). The effect of ferulic acid on the evoked glutamate release was prevented by chelating the extracellular Ca²⁺ ions, but was insensitive to the glutamate transporter inhibitor DL-threo-beta-benzyl-oxyaspartate. Ferulic acid suppressed the depolarization-induced increase in a cytosolic-free Ca²⁺ concentration, but did not alter 4-AP-mediated depolarization. Furthermore, the effect of ferulic acid on evoked glutamate release was abolished by blocking the Ca(v)2.2 (N-type) and Ca(v)2.1 (P/Q-type) channels, but not by blocking ryanodine receptors or mitochondrial Na⁺/Ca²⁺ exchange. These results show that ferulic acid inhibits glutamate release from cortical synaptosomes in rats through the suppression of presynaptic voltage-dependent Ca²⁺ entry.

Coenzyme Q10 inhibits the release of glutamate in rat cerebrocortical nerve terminals by suppression of voltage-dependent calcium influx and mitogen-activated protein kinase signaling pathway

This study investigates the effects and possible mechanism of coenzyme Q10 (CoQ10) on endogenous glutamate release in the cerebral cortex nerve terminals of rats. CoQ10 inhibited the release of glutamate evoked by the K+ channel blocker 4-aminopyridine (4-AP). CoQ10 reduced the depolarization-induced increase in cytosolic [Ca2+]c but did not alter the 4-AP-mediated depolarization. The effect of CoQ10 on evoked glutamate release was abolished by blocking the Cav2.2 (N-type) and Cav2.1 (P/Q-type) Ca2+ channels and mitogen-activated protein kinase kinase (MEK). In addition, CoQ10 decreased the 4-AP-induced phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and synaptic vesicle-associated protein synapsin I, a major presynaptic substrate for ERK. Moreover, the inhibition of glutamate release by CoQ10 was strongly attenuated in mice without synapsin I. These results suggest that CoQ10 inhibits glutamate release from cortical synaptosomes in rats through the suppression of the presynaptic voltage-dependent Ca2+ entry and ERK/synapsin I signaling pathway.

New therapeutic targets for amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is one of the most devastating neurological disorders, affecting approximately half a million people worldwide. Currently there is no cure or prevention for ALS. Although ALS is a rare condition, it places a tremendous socioeconomic burden on patients, family members, caregivers and health systems.

AREAS COVERED

The review examines the mechanisms that may contribute to motor neuron degeneration in ALS, among which oxidative damage, glutatamate excitoxicity, mitochondrial dysfunction, impaired axonal transport, apoptotic cell death, growth factor deficiency, glial cell pathology and abnormal RNA metabolism are potential targets for ALS treatment. The article provides an overview of clinical trials performed to date in attempts to treat ALS with regard to molecular mechanisms and pathways they act on. It also discusses new trials based on recently developed molecular biology techniques.

EXPERT OPINION

Despite significant effectiveness of several potential therapeutics observed in preclinical trials, the results were not translatable to patients with ALS. The development of effective treatments of ALS strictly depends on understanding the primary cause of the disease. This goal will only be achieved when we identify the trigger point for motor neuron death in ALS.

Glutamate transporters and the excitotoxic path to motor neuron degeneration in amyotrophic lateral sclerosis

Responsible for the majority of excitatory activity in the central nervous system (CNS), glutamate interacts with a range of specific receptor and transporter systems to establish a functional synapse. Excessive stimulation of glutamate receptors causes excitotoxicity, a phenomenon implicated in both acute and chronic neurodegenerative diseases [e.g., ischemia, Huntington's disease, and amyotrophic lateral sclerosis (ALS)]. In physiology, excitotoxicity is prevented by rapid binding and clearance of synaptic released glutamate by high-affinity, Na(+)-dependent glutamate transporters and amplified by defects to the glutamate transporter and receptor systems. ALS pathogenetic mechanisms are not completely understood and characterized, but excitotoxicity has been regarded as one firm mechanism implicated in the disease because of data obtained from ALS patients and animal and cellular models as well as inferred by the documented efficacy of riluzole, a generic antiglutamatergic drug, has in patients. In this article, we critically review the several lines of evidence supporting a role for glutamate-mediated excitotoxicity in the death of motor neurons occurring in ALS, putting a particular emphasis on the impairment of the glutamate-transport system.

Survey of ALS-associated factors potentially promoting Ca2+ overload of motor neurons

The deleterious consequences of Ca(2+) overload are thought to be a probable cause of motoneuronal death in ALS, although the overloading mechanism is currently unclear. In this paper some ALS-linked factors are analysed with regard to their influence on Ca(2+ )influx into neurons. Intensive cortex activity can render motor neurons susceptible to stimulation of calcium-permeable glutamate NMDA-receptors; increase in CSF concentrations of glutamate, glycine, and norepinephrine supposedly can intensify these receptors' activity. Elevated CSF levels of GABA and reduced levels of serotonin can promote Ca(2+ )influx through glutamate AMPA-receptors and voltage-gated channels of L-, N-, and P-type. Additionally, brain ischaemia can contribute to Ca(2+ )overload of motor neurons. Thus, ALS is characterized by the unique combination of factors potentially able to promote the overload of motor neurons with calcium.

Plasma glutamate and glycine levels in patients with amyotrophic lateral sclerosis: the effect of riluzole treatment

OBJECTIVES

Defective glutamate (glu) metabolism and excitotoxicity have been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). Moreover, glycine (gly) has been shown to potentiate excitatory transmission. The "antiglutamatergic" agent riluzole has been shown to prolong survival in ALS. The aim of the study was to investigate a possible effect of riluzole on plasma glu and gly levels, correlating with clinical response to treatment.

PATIENTS AND METHODS

Plasma concentrations of glu and gly were measured in 20 healthy volunteers and 22 ALS patients before treatment and after 6 months on riluzole.

RESULTS

At baseline, increased plasma glu correlated with spinal onset and male gender whereas gly levels did not differ between patients and controls. No significant change was observed for both amino acids post-treatment, despite a lower rate of disease progression.

CONCLUSION

These results suggest that riluzole may affect disease progression without a significant impact on plasma glu and gly levels, possibly indicating different mechanisms of drug action.

Strategic approaches to developing drug treatments for ALS

Significant progress in understanding the cellular mechanisms of motor neuron degeneration in amyotrophic lateral sclerosis (ALS) has not been matched with the development of therapeutic strategies to prevent disease progression. The multiple potential causes and relative rarity of the disease are two significant factors that make drug development and assessment in clinical trials extremely difficult. We review recent progress in promoting therapeutics into clinical trials and highlight the value of moderate throughput screening for the acceleration and improvement of drug design.

Considerations on intervention goal and efficacy evaluation of traditional Chinese medicine in the treatment of neurological diseases

In the last several years, traditional Chinese medicine (TCM) has made much progress in the treatment of neurological diseases. The living space of TCM in neurological diseases lies in refractory diseases, aging and chronic diseases caused by multiple factors as well as sub-health state and chronic fatigue state. The effect model of TCM mainly consists of whole effect, self-organization, self-stable model, holographic effect and butterfly effect. The effective point of TCM in neurological diseases lies mainly in end-points and health-related events. Moreover, TCM has advantages in the evaluation of symptoms, syndrome and quality of life (QOL). Some key indexes should be included when evaluating the efficacy of TCM in neurological diseases. Meanwhile, the advantages of TCM such as end-points, health-related events and QOL should be highlighted. Multi-subject researching methods could be adopted to make a comprehensive evaluation of subjective and objective indexes. The clinical evidence on the TCM efficacy evaluation may come from RCTs, and other types of designs can also be considered.

Serum amino acids as indicators of cerebrospinal neuronal activity in patients with micturition disorders

OBJECTIVE

Our previous study showed that the spinal glycine level in rats was changed by spinal injury or bladder outlet obstruction, and this change was reflected by serum glycine levels. Therefore, we measured the serum glutamate and glycine levels in healthy volunteers and patients with cerebrospinal damage or benign prostatic hyperplasia (BPH) to confirm whether the change of serum amino acid levels was obtained from these patients as well as the animal experiment.

METHODS

We measured the serum glutamate and glycine levels in 170 healthy controls, 57 patients with cerebrovascular disease (CVD), 68 patients with spinal cord injury (SCI), and 70 patients with BPH. Amino acid levels were compared between the controls and patients, according to gender, level of spinal injury and the type of bladder activity.

RESULTS

In the healthy controls, glutamate levels were higher and glycine levels were lower in men than in women. On group comparison of each gender, there were no differences of glutamate levels. However, glycine levels were lower in male and female SCI patients and BPH patients than in controls. According to the level of spinal injury or the pattern of bladder activity and amino acid levels, there were no relationships among them.

CONCLUSIONS

Serum glutamate and glycine levels were not related to the spinal injury level or bladder activity. However, serum glycine levels changed in patients with SCI or BPH patients, so it may be possible to use it as an indicator of spinal glycinergic neuronal activity.

Add-on lamotrigine treatment and plasma glutamate levels in epilepsy: Relation to treatment response

We investigated the effects of add-on lamotrigine treatment on plasma glutamate (Glu) levels, in 29 epileptic patients. Plasma Glu levels were determined by high-performance liquid chromatography at baseline and at 1 and 3 months post-treatment. In patients with a seizure reduction of > or = 66% a decrease of Glu at month 1 was noted, followed by return to baseline levels at month 3. In the remaining patients a gradual increase of Glu was noted throughout the 3 months of the study. The above findings indicate that an excellent clinical response to add-on lamotrigine may be characterized by a statistically significant, yet transient decrease of plasma Glu levels, while increasing Glu levels may accompany a response that is moderate at best. The combination of lamotrigine with valproate was more frequent in patients with excellent clinical response and tended to result in glutamate decrease.

IGF-I prevents glutamate-induced motor neuron programmed cell death

Insulin-like growth factor I (IGF-I) is currently in clinical trials for treatment of amyotrophic lateral sclerosis (ALS), but little is known about how it promotes the survival of motor neurons. In the current study, we examined IGF-I-mediated neuroprotection in an in vitro model of ALS utilizing enriched cultures of embryonic rat spinal cord motor neurons. IGF-I binds to the IGF-I receptor (IGF-IR) in motor neurons and activates MAPK and the downstream effector of phosphatidylinositol 3-kinase (PI-3K) signaling, Akt. IGF-I:IGF-IR signaling involves phosphorylation of IRS-1 and Shc, but not IRS-2. Glutamate, which is elevated in the cerebrospinal fluid of ALS patients, induced DNA fragmentation and caspase-3 cleavage in the spinal cord motor neurons. These effects of glutamate were blocked by co-treatment with IGF-I. However, a delay of IGF-I treatment for as little as 30 min eliminated its neuroprotective effect. Finally, alone, neither the MAPK pathway inhibitor PD98059 nor the PI-3K inhibitor LY294002 blocked the neuroprotective effect of IGF-I, but both inhibitors together were effective in this regard. These results suggest that the dose and timing of IGF-I administration are critical for producing a neuroprotective effect, and also suggest that both the MAPK and PI-3K/Akt pathways can promote the survival of motor neurons. We discuss our results in terms of novel strategies for ALS therapy.