Efficacy of Glutamate Modulators in Tic Suppression: A Double-Blind, Randomized Control Trial of D-serine and Riluzole in Tourette Syndrome

Tourette syndrome and obsessive-compulsive disorder: A comprehensive review of structural alterations and neurological mechanisms

Currently, it is possible to study the pathogenesis of Tourette's syndrome (TS) in more detail, due to more advanced methods of neuroimaging. However, medical and surgical treatment options are limited by a lack of understanding of the nature of the disorder and its relationship to some psychiatric disorders, the most common of which is obsessive-compulsive disorder (OCD). It is believed that the origin of chronic tic disorders is based on an imbalance of excitatory and inhibitory influences in the Cortico-Striato-Thalamo-Cortical circuits (CSTC). The main CSTCs involved in the pathological process have been identified by studying structural and neurotransmitter disturbances in the interaction between the cortex and the basal ganglia. A neurotransmitter deficiency in CSTC has been demonstrated by immunohistochemical and genetic methods, but it is still not known whether it arises as a consequence of genetically determined disturbances of neuronal migration during ontogenesis or as a consequence of altered production of proteins involved in neurotransmitter production. The aim of this review is to describe current ideas about the comorbidity of TS with OCD, the involvement of CSTC in the pathogenesis of both disorders and the background of structural and neurotransmitter changes in CSTC that may serve as targets for drug and neuromodulatory treatments.

D-Serine: A Cross Species Review of Safety

Background:D-Serine, a direct, full agonist at the D-serine/glycine modulatory site of the N-methyl-D-aspartate-type glutamate receptors (NMDAR), has been assessed as a treatment for multiple psychiatric and neurological conditions. Based on studies in rats, concerns of nephrotoxicity have limited D-serine research in humans, particularly using high doses. A review of D-serine's safety is timely and pertinent, as D-serine remains under active study for schizophrenia, both directly (R61 MH116093) and indirectly through D-amino acid oxidase (DAAO) inhibitors. The principal focus is on nephrotoxicity, but safety in other physiologic and pathophysiologic systems are also reviewed. Methods: Using the search terms "D-serine," "D-serine and schizophrenia," "D-serine and safety," "D-serine and nephrotoxicity" in PubMed, we conducted a systematic review on D-serine safety. D-serine physiology, dose-response and efficacy in clinical studies and dAAO inhibitor safety is also discussed. Results: When D-serine doses >500 mg/kg are used in rats, nephrotoxicity, manifesting as an acute tubular necrosis syndrome, seen within hours of administration is highly common, if not universal. In other species, however, D-serine induced nephrotoxicity has not been reported, even in other rodent species such as mice and rabbits. Even in rats, D--serine related toxicity is dose dependent and reversible; and does not appear to be present in rats at doses producing an acute Cmax of <2,000 nmol/mL. For comparison, the Cmax of D-serine 120 mg/kg, the highest dose tested in humans, is ~500 nmol/mL in acute dosing. Across all published human studies, only one subject has been reported to have abnormal renal values related to D-serine treatment. This abnormality did not clearly map on to the acute tubular necrosis syndrome seen in rats, and fully resolved within a few days of stopping treatment. DAAO inhibitors may be nephroprotective. D-Serine may have a physiologic role in metabolic, extra-pyramidal, cardiac and other systems, but no other clinically significant safety concerns are revealed in the literature. Conclusions: Even before considering human to rat differences in renal physiology, using current FDA guided monitoring paradigms, D-serine appears safe at currently studied maximal doses, with potential safety in combination with DAAO inhibitors.

Optimizing behavior therapy for youth with Tourette's disorder

Tourette's Disorder (TD) is characterized by tics that cause distress and impairment. While treatment guidelines recommend behavior therapy as a first-line intervention, patients with TD may exhibit limited therapeutic response. Given the need to improve treatment outcomes, this study examined the efficacy of augmenting behavior therapy with D-cycloserine (DCS) to reduce tic severity in a placebo-controlled quick-win/fast-fail trial. Twenty youth with TD completed a baseline assessment to characterize tic severity, premonitory urges, medical history, and psychiatric comorbidity. Youth were randomly assigned to receive a single session of habit reversal training (HRT) augmented by either 50 mg of DCS or placebo. Two bothersome tics on the Hopkins Motor/Vocal Tic Scale (HM/VTS) were targeted for treatment during HRT. One week after the HRT session, youth completed a posttreatment assessment to evaluate change in the severity of bothersome tics. All assessments were completed by independent evaluators masked to treatment group. There was a Treatment Group by Time Interaction in favor of DCS-augmented HRT (p < 0.01), controlling for baseline tic severity, tic medication, and attention deficit hyperactivity disorder. Follow-up comparisons revealed small group differences at the treatment visit (d = 0.27), with the DCS group exhibiting slightly greater severity for targeted tics. There was a large group difference at posttreatment, in which the DCS group exhibited lower severity for targeted tics (d = 1.30, p < 0.001) relative to the placebo group. Findings demonstrate the preliminary enhancement of tic severity reductions by augmenting HRT with DCS compared with placebo augmentation.

N-Methyl-D-Aspartate (NMDA) receptor modulators: a patent review (2015-present)

INTRODUCTION

- The NMDA receptor is implicated in various diseases including neurodegenerative, neurodevelopmental and mood disorders. However, only a limited number of clinically approved NMDA receptor modulators are available. Today, apparent NMDA receptor drug development strategies entail 1) exploring the unknown chemical space to identify novel scaffolds; 2) using the clinically available NMDA receptor modulators to expand the therapeutic indication space; 3) and to trace physiological functions of the NMDA receptor.

AREAS COVERED

- The current review reflects on the functional and pharmacological facets of NMDA receptors and the current clinical status quo of NMDA receptor modulators. Patent literature covering 2015 till April 2020 is discussed with emphasis on new indications.

EXPERT OPINION

- Supporting evidence shows that subtype-selective NMDA receptor antagonists show an improved safety profile compared to broad-spectrum channel blockers. Although GluN2B-selective antagonists are by far the most extensively investigated subtype-selective modulators, they have shown only modest clinical efficacy so far. To overcome the limitations that have hampered the clinical development of previous subtype-selective NMDA receptor antagonists, future studies with improved animal models that better reflect human NMDA receptor pathophysiology are warranted. The increased availability of subtype-selective probes will allow target engagement studies and proper dose finding in future clinical trials.

The Pathophysiology of Tics; An Evolving Story

Background:

Tics, defined as quick, rapid, sudden, recurrent, non-rhythmic motor movements or vocalizations are required components of Tourette Syndrome (TS) - a complex disorder characterized by the presence of fluctuating, chronic motor and vocal tics, and the presence of co-existing neuropsychological problems. Despite many advances, the underlying pathophysiology of tics/TS remains unknown.

Objective:

To address a variety of controversies surrounding the pathophysiology of TS. More specifically: 1) the configuration of circuits likely involved; 2) the role of inhibitory influences on motor control; 3) the classification of tics as either goal-directed or habitual behaviors; 4) the potential anatomical site of origin, e.g. cortex, striatum, thalamus, cerebellum, or other(s); and 5) the role of specific neurotransmitters (dopamine, glutamate, GABA, and others) as possible mechanisms (Abstract figure).

Methods:

Existing evidence from current clinical, basic science, and animal model studies are reviewed to provide: 1) an expanded understanding of individual components and the complex integration of the Cortico-Basal Ganglia-Thalamo-Cortical (CBGTC) circuit - the pathway involved with motor control; and 2) scientific data directly addressing each of the aforementioned controversies regarding pathways, inhibition, classification, anatomy, and neurotransmitters.

Conclusion:

Until a definitive pathophysiological mechanism is identified, one functional approach is to consider that a disruption anywhere within CBGTC circuitry, or a brain region inputting to the motor circuit, can lead to an aberrant message arriving at the primary motor cortex and enabling a tic. Pharmacologic modulation may be therapeutically beneficial, even though it might not be directed toward the primary abnormality.

Comprehensive systematic review summary: Treatment of tics in people with Tourette syndrome and chronic tic disorders

OBJECTIVE

To systematically evaluate the efficacy of treatments for tics and the risks associated with their use.

METHODS

This project followed the methodologies outlined in the 2011 edition of the American Academy of Neurology's guideline development process manual. We included systematic reviews and randomized controlled trials on the treatment of tics that included at least 20 participants (10 participants if a crossover trial), except for neurostimulation trials, for which no minimum sample size was required. To obtain additional information on drug safety, we included cohort studies or case series that specifically evaluated adverse drug effects in individuals with tics.

RESULTS

There was high confidence that the Comprehensive Behavioral Intervention for Tics was more likely than psychoeducation and supportive therapy to reduce tics. There was moderate confidence that haloperidol, risperidone, aripiprazole, tiapride, clonidine, onabotulinumtoxinA injections, 5-ling granule, Ningdong granule, and deep brain stimulation of the globus pallidus were probably more likely than placebo to reduce tics. There was low confidence that pimozide, ziprasidone, metoclopramide, guanfacine, topiramate, and tetrahydrocannabinol were possibly more likely than placebo to reduce tics. Evidence of harm associated with various treatments was also demonstrated, including weight gain, drug-induced movement disorders, elevated prolactin levels, sedation, and effects on heart rate, blood pressure, and ECGs.

CONCLUSIONS

There is evidence to support the efficacy of various medical, behavioral, and neurostimulation interventions for the treatment of tics. Both the efficacy and harms associated with interventions must be considered in making treatment recommendations.

Efficacy and tolerability of riluzole in psychiatric disorders: A systematic review and preliminary meta-analysis

There is a pressing need for better pharmacological treatment strategies for psychiatric disorders as current treatment often results in partial symptom remission and unwanted side effects. A point of entry may be the glutamatergic system since glutamatergic dysregulation contributes to multiple psychiatric disorders. We evaluated the evidence from randomized controlled trials (RCTs) regarding the use of the glutamatergic drug riluzole in mental illnesses; and conducted preliminary meta-analyses of its effectiveness in treating obsessive-compulsive disorder (OCD) and depression. A systematic search was performed using PubMed (Medline), Embase, Cochrane Database of Systematic Reviews and PsycINFO. Meta-analyses were performed using Comprehensive Meta-Analysis software. Twenty-three RCTs were included for qualitative analysis and showed positive effects of adjunctive/monotherapy riluzole in patients with OCD, depression, autism, substance abuse and schizophrenia. Seven studies were also used for quantitative analysis, which revealed positive but non-significant effects on OCD and depression. Riluzole was generally well tolerated with few serious adverse events. The studies included in this systematic review were highly heterogeneous and the number of studies was limited per diagnostic condition. Moreover, few studies have examined riluzole as a single treatment. We suggest carrying out further work to provide definitive evidence for the benefit of riluzole in psychiatric illness.

Evidence-based treatment of Tourette's disorder and chronic tic disorders

Introduction: Chronic Tic Disorders and Tourette's Disorder (collectively referred to as TD) are characterized by sudden, rapid, and repetitive motor movements or vocalizations called tics. Children, adolescents, and adults with TD often experience co-occurring psychiatric symptoms and impairments in multiple domains. As a result of tics and other symptoms, patients with TD can develop negative self-views, require considerable accommodations, and experience a poor quality of life. Therefore, the efficient and effective management of TD bears considerable importance. Areas covered: This expert review evaluated the empirical support for behavioral and pharmacological interventions based on the results of randomized controlled trials (RCTs). Behavioral interventions evaluated include habit reversal training (HRT), comprehensive behavioral intervention for tics (CBIT), and exposure response prevention (ERP). Reviewed pharmacological interventions included alpha-2 agonists, antipsychotics, and anticonvulsants. Expert opinion: This review identified several efficacious behavioral and pharmacological interventions for TD. However, several gaps in the management of TD include: (1) the access/availability of behavioral interventions, (2) novel and more efficacious treatment approaches, and (3) the development of more comprehensive interventions to manage TD. In order to advance the treatment of TD, additional research is necessary to efficiently, effectively, and comprehensively develop and evaluate new treatments for patients with TD.

Merging the Pathophysiology and Pharmacotherapy of Tics

Background

Anatomically, cortical-basal ganglia-thalamo-cortical (CBGTC) circuits have an essential role in the expression of tics. At the biochemical level, the proper conveyance of messages through these circuits requires several functionally integrated neurotransmitter systems. In this manuscript, evidence supporting proposed pathophysiological abnormalities, both anatomical and chemical is reviewed. In addition, the results of standard and emerging tic-suppressing therapies affecting nine separate neurotransmitter systems are discussed. The goal of this review is to integrate our current understanding of the pathophysiology of Tourette syndrome (TS) with present and proposed pharmacotherapies for tic suppression.

Methods

For this manuscript, literature searches were conducted for both current basic science and clinical information in PubMed, Google-Scholar, and other scholarly journals to September 2018.

Results

The precise primary site of abnormality for tics remains undetermined. Although many pathophysiologic hypotheses favor a specific abnormality of the cortex, striatum, or globus pallidus, others recognize essential influences from regions such as the thalamus, cerebellum, brainstem, and ventral striatum. Some prefer an alteration within direct and indirect pathways, whereas others believe this fails to recognize the multiple interactions within and between CBGTC circuits. Although research and clinical evidence supports involvement of the dopaminergic system, additional data emphasizes the potential roles for several other neurotransmitter systems.

Discussion

A greater understanding of the primary neurochemical defect in TS would be extremely valuable for the development of new tic-suppressing therapies. Nevertheless, recognizing the varied and complex interactions that exist in a multi-neurotransmitter system, successful therapy may not require direct targeting of the primary abnormality.

Transcranial Magnetic Stimulation in Tourette Syndrome: A Historical Perspective, Its Current Use and the Influence of Comorbidities in Treatment Response

Background. Tourette syndrome (TS) is a childhood-onset neuropsychiatric disorder consisting of impairing motor and vocal tics which often persists adolescent and adult years. In this older refractory group, standard treatments such as pharmacotherapy and psychotherapeutic interventions may only have limited effects. Based on electrical cortical dysregulation in individuals with TS, a novel approach has employed brain stimulation strategies to modulate the putative aberrant neural electrical activity in pathways that may underlie tics, such as insula-supplementary motor area (SMA) connectivity. Methods. This review will examine all published clinical trials employing transcranial magnetic stimulation (TMS) to ameliorate tics, and discuss a framework for the pathophysiology of TS in relation to electrical brain activity. A framework for future research in tic disorders using TMS and imaging targeting neuroplasticity will be discussed. Results. Therapeutic electrical brain activity modulation with TMS has been carried out in stroke neuro-rehabilitation and neuropsychiatry, including trials in TS. Eleven trials document the use of TMS in TS targeting several brain areas, a positive effect is seen for those trials targeting the SMA. In particular, it appears that younger individuals with concurrent attention-deficit hyperactivity disorder (ADHD) benefit the most. Conclusions. TMS can be used as an effective tool to explore the psychophysiology of TS and potentially provide a therapeutic option. Ultimately, translational research using TMS in TS needs to explore connectivity differences pre- and post-treatment in individuals with TS that are linked to improvement in tic symptoms, with an emphasis on approaches using functional neuroimaging as well as other probes of neuroplasticity.

Pharmacotherapies to tics: a systematic review

The efficacy of all pharmacotherapies for patients suffering from tics were unclear. Literatures were searched from Medline, Embase, The Cochrane Library, and four Chinese databases. The primary efficacy outcome scale was defined as the Yale Global Tic Severity Scale (YGTSS). Overall estimates of pooled weighted mean difference (WMD) with 95% confidence interval (CI) were calculated for each outcome measure. A total of 53 trials were included. Meta-analysis suggested that alpha-2 adrenergic agonist agents and atypical antipsychotic agents were effective in improving tics, which included the maximum number of trials. Typical antipsychotic agents were associated with severer side-effects than alpha-2 adrenergic agonist agents. Besides, Traditional Chinese Medicine showed positive effects in YGTSS (NingDong Granule: WMD=-7.100, 95% CI, -10.430- -3.770; 5-Ling Granule: WMD=-11.300, 95% CI, -14.208- -8.392), while glutamate modulators (D-serine, N-Acetylcysteine and riluzole) might not be working. In summary, alpha-2 adrenergic agonist agents were associated with the optimal weigh between efficacy and safety. However, the significant factor of limited trials and sample sizes discounted these findings. Further better studies are necessary to ascertain them.

Altered dopaminergic regulation of the dorsal striatum is able to induce tic-like movements in juvenile rats

Motor tics are sudden, repetitive, involuntary movements representing the hallmark behaviors of the neurodevelopmental disease Tourette’s syndrome (TS). The primary cause of TS remains unclear. The initial observation that dopaminergic antagonists alleviate tics led to the development of a dopaminergic theory of TS etiology which is supported by post mortem and in vivo studies indicating that non-physiological activation of the striatum could generate tics. The striatum controls movement execution through the balanced activity of dopamine receptor D1 and D2-expressing medium spiny neurons of the direct and indirect pathway, respectively. Different neurotransmitters can activate or repress striatal activity and among them, dopamine plays a major role. In this study we introduced a chronic dopaminergic alteration in juvenile rats, in order to modify the delicate balance between direct and indirect pathway. This manipulation was done in the dorsal striatum, that had been associated with tic-like movements generation in animal models. The results were movements resembling tics, which were categorized and scored according to a newly developed rating scale and were reduced by clonidine and riluzole treatment. Finally, post mortem analyses revealed altered RNA expression of dopaminergic receptors D1 and D2, suggesting an imbalanced dopaminergic regulation of medium spiny neuron activity as being causally related to the observed phenotype.

GABA and glutamate in children with Tourette syndrome: A 1H MR spectroscopy study at 7T

Tourette syndrome (TS) is characterized by presence of chronic, fluctuating motor and phonic tics. The underlying neurobiological basis for these movements is hypothesized to involve cortical-striatal-thalamo-cortical (CSTC) pathways. Two major neurotransmitters within these circuits are γ-aminobutyric acid (GABA) and glutamate. Seventy-five participants (32 with TS, 43 controls) ages 5-12 years completed ¹H MRS at 7T. GABA and glutamate were measured in dorsolateral prefrontal cortex (DLPFC), ventromedial prefrontal cortex (VMPFC), premotor cortex (PMC), and striatum, and metabolites quantified using LCModel. Participants also completed neuropsychological assessment emphasizing inhibitory control. Scans were well tolerated by participants. Across ROIs combined, glutamate was significantly higher in the TS group, compared to controls, with no significant group differences in GABA observed. ROI analyses revealed significantly increased PMC glutamate in the TS group. Among children with TS, increased PMC glutamate was associated with improved selective motor inhibition; however, no significant associations were identified between levels of glutamate or GABA and tic severity. The dopaminergic system has long been considered to have a dominant role in TS. Accumulating evidence, however, suggests involvement of other neurotransmitter systems. Data obtained using ¹H MRS at 7T supports alteration of glutamate within habitual behavior-related CSTC pathways of children with TS.

Tourette syndrome and other chronic tic disorders: an update on clinical management

INTRODUCTION

The management of Tourette syndrome (TS) and other chronic tic disorders occurs in multiple stages and begins with comprehensive assessment and complex psychoeducation. Behavioral and pharmacological interventions (second stage) are needed when tics cause physical or psychosocial impairment. Deep brain stimulation surgery or experimental therapies represent the third stage. Areas covered: Discussed are recent advances in assessment and therapy of chronic tic disorders, encompassing the three stages of intervention, with the addition of experimental, non-invasive brain stimulation strategies. A PubMed search was performed using as keywords: 'tic disorders', 'Tourette syndrome', 'assessment', 'rating scales', 'behavioral treatment', 'pharmacological treatment', 'deep brain stimulation', 'transcranial magnetic (or current) stimulation', and 'transcranial current stimulation'. More than 300 peer-reviewed articles were evaluated. The studies discussed have been selected on the basis of novelty and impact. Expert commentary: Comprehensive assessment of tic disorders and psychoeducation are crucial to a correct active management approach. Behavioral treatments represent first line of active interventions, with increasing potential offered by telehealth. Antipsychotics and alpha agonists remain first line pharmacological interventions for tics, although VMAT-2 inhibitors appear promising. Deep brain stimulation is a potential option for medically refractory, severely disabled patients with tics, but age and target selection require further investigation.

Aripiprazole and Riluzole treatment alters behavior and neurometabolites in young ADHD rats: a longitudinal 1H-NMR spectroscopy study at 11.7T

Attention deficit hyperactivity disorder (ADHD), Tourette syndrome (TS) as well as obsessive compulsive disorder (OCD) are co-occurring neurodevelopmental diseases that share alterations of frontocortical neurometabolites. In this longitudinal study we investigated the behavioral and neurochemical effects of aripiprazole and riluzole treatment in juvenile spontaneously hypertensive rats (SHR), a model for ADHD. For neurochemical analysis we employed in vivo magnetic resonance spectroscopy (MRS). Spectra from voxels located at the central striatum and prefrontal cortex were acquired postnatally from day 35 to 50. In the SHR strain only, treatments reduced repetitive grooming and climbing behavior. The absolute quantification of cerebral metabolites in vivo using localized ¹H-MRS at 11.7T showed significant alterations in SHR rats compared to controls (including glutamine, aspartate and total NAA). In addition, drug treatment reduced the majority of the detected metabolites (glutamate and glutamine) in the SHR brain. Our results indicate that the drug treatments might influence the hypothesized 'hyperactive' state of the cortico-striatal-thalamo-cortical circuitries of the SHR strain. Furthermore, we could show that behavioral changes correlate with brain region-specific alterations in neurometabolite levels in vivo. These findings should serve as reference for animal studies and for the analysis of neurometabolites in selected human brain regions to further define neurochemical alterations in neuropsychiatric diseases.

Glycinergic signaling in the human nervous system: An overview of therapeutic drug targets and clinical effects

Glycine and related endogenous compounds (d-serine, d-alanine, sarcosine) serve critical roles in both excitatory and inhibitory neurotransmission and are influenced by a multitude of enzymes and transporters, including glycine transporter 1 and 2 (GlyT1 and GlyT2), d-amino acid oxidase (DAAO), serine racemase (SRR), alanine-serine-cysteine transporter 1 (Asc-1), and kynurenine aminotransferase (KAT). MEDLINE, Web of Science, and PsychINFO were searched for relevant human trials of compounds. Many studies utilizing exogenous administration of small molecule agonists of the glycineB site of n-methyl-d-aspartate receptor have been studied as have a growing number of glycine transporter type 1 (GlyT1) inhibitors. The clinical effects of these compounds are reviewed as are the potential effects of newer novel compounds.

Treatment-refractory Tourette Syndrome

Tourette Syndrome (TS) is a complex neurodevelopmental condition marked by tics and frequently associated with psychiatric comorbidities. While most cases are mild and improve with age, some are treatment-refractory. Here, we review strategies for the management of this population. We begin by examining the diagnosis of TS and routine management strategies. We then consider emerging treatments for refractory cases, including deep brain stimulation (DBS), electroconvulsive therapy (ECT), repetitive transcranial magnetic stimulation (rTMS), and novel pharmacological approaches such as new vesicular monoamine transporter type 2 inhibitors, cannabinoids, and anti-glutamatergic drugs.

Tourette syndrome research highlights 2015

We present selected highlights from research that appeared during 2015 on Tourette syndrome and other tic disorders. Topics include phenomenology, comorbidities, developmental course, genetics, animal models, neuroimaging, electrophysiology, pharmacology, and treatment. We briefly summarize articles whose results we believe may lead to new treatments, additional research or modifications in current models of TS.