Vesicular Monoamine Transporter-2 Inhibitor Research Articles

The impact of diagnosing provider type on longitudinal care for patients with newly diagnosed Huntington’s Disease

Aims This study evaluated the association between provider types for patients with newly diagnosed Huntington’s disease (HD) and healthcare resource utilization (HCRU), costs, and treatment patterns. Materials and methods This retrospective analysis used MarketScan® databases (1/1/2017-12/31/21) to identify provider type who diagnosed and managed US adult patients with HD. Patients with continuous enrollment 6 months pre- and 12 months post-diagnosis were included. Outcomes evaluated over 12 months post-diagnosis included hospitalizations, outpatient visits, antipsychotic or vesicular monoamine transporter 2 (VMAT2) inhibitor use, and total healthcare costs. Results 340 eligible patients had a mean age at diagnosis of 49 years. 56.5% were female; 71.5% had a Charlson Comorbidity Index of 0. Patients were diagnosed by neurologists (48.5%), primary care providers (PCP) (35.6%), psychiatrists (3.5%), or other providers (12.4%). Patients diagnosed by PCPs or neurologists received significantly more follow-ups by the same diagnosing provider type (P < 0.05). All-cause and HD-related outpatient visits at 12-month follow-up had more patients diagnosed by PCPs (23.9, 5.1) than neurologists (18.0, 2.4), psychiatrists (16.7, 1.67), or others (15.3, 2.4). HD-related mean costs totaled $2,489 ($1,179 inpatient and $1,310 outpatient). Patients diagnosed by neurologists had significantly lower HD-related total non-medication costs vs those diagnosed by PCPs (−$2,256; P < 0.05). Among patients diagnosed by neurologists vs PCPs, similar proportions received antipsychotics within the first year (55% vs 52%, respectively); more patients managed by neurologists received VMAT2 inhibitors (12% vs 7%, respectively). Limitations Our study includes limitations inherent to retrospective claims studies. Conclusions Patients with HD are most often diagnosed by neurologists or PCPs; the same diagnosing provider type typically manages follow-up. Patients diagnosed by neurologists had significantly fewer HD-related outpatient visits, lower HD-related non-drug costs, and more frequently received VMAT2 inhibitors vs those diagnosed by PCPs. Our findings show an integrated care team may provide evidence-based, personalized care for patients with HD.

Gastrodin relieves Parkinson's disease-related motor deficits by facilitating the MEK-dependent VMAT2 to maintain dopamine homeostasis

BackgroundDysfunction of dopamine homeostasis (DAH), which is regulated by vesicular monoamine transporter 2 (VMAT2), is a vital cause of dopamine (DA) neurotoxicity and motor deficits in Parkinson's disease (PD). Gastrodin (4-hydroxybenzyl alcohol 4-O-β-D-glucoside; GTD), a natural active compound derived from Gastrodia elata Blume, can be used to treat multiple neurological disorders, including PD. However, whether GTD regulates VMAT2-mediated DAH dysfunction in PD models remains unclear. PurposeTo explore whether GTD confers dopaminergic neuroprotection by facilitating DA vesicle storage and maintaining DAH in PD models. MethodsMice were treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and PC12 cells with 1-methyl-4-phenyl-pyridinium (MPP+) to induce PD characteristics. Multiple behavioural tests were performed to evaluate the motor functions of the mice. HPLC was used to measure DA and 3,4-dihydroxyphenylacetic acid (DOPAC) levels. Transmission electron microscopy was used to observe synaptic vesicles. Molecular docking and molecular dynamics were used to determine the binding affinity of GTD to the target protein. Reserpine (Res, a VMAT2 inhibitor) and PD0325901 (901, a MEK inhibitor) were employed to investigate the mechanism of GTD. Western blotting and immunohistochemistry were used to assess the expression of the target proteins. ResultsGTD attenuated motor deficits and dopaminergic neuronal injury, reversed the imbalance of DAH, and increased VMAT2 levels and vesicle volume in MPTP-induced mice. GTD ameliorated cell damage, ROS release, and dysfunction of DAH in MPP+-induced PC12 cells. Moreover, the neuroprotective effects of GTD were reversed by Res in vitro and in vivo. Furthermore, GTD can activate the MEK/ERK/CREB pathway to upregulate VMAT2 in vitro and in vivo. Interestingly, 901 reversed the effects of GTD on VMAT2 and dopaminergic neuronal impairment. ConclusionGTD relieved PD-related motor deficits and dopaminergic neuronal impairment by facilitating MEK-depended VMAT2 to regulate DAH, which offers new insights into its therapeutic potential.

Risk of VMAT2 inhibitors on suicidality and parkinsonism: report utilizing the United States Food and Drug Administration adverse event reporting system.

Prescription of vesicular monoamine transporter 2 (VMAT2) inhibitors, valbenazine, deutetrabenazine, and tetrabenazine, is becoming increasingly common in persons treated with antipsychotics. Reported suicidality and parkinsonism are safety concerns with VMAT2 inhibitors. Herein, we aim to evaluate the aforementioned safety outcomes using the FDA Adverse Event Reporting System. Reporting odds ratios (RORs) and lower limits of 95% confidence intervals of information components (IC025) were calculated to quantify VMAT2 inhibitor-associated adverse events. Acetaminophen was the reference agent. Suicidal ideation was significantly associated with VMAT2 inhibitors, with RORs ranging from 2.38 to 10.67 and IC025 ranging from 0.73 to 2.39. Increased odds of suicidal behavior was observed with tetrabenazine (ROR 3.011, IC025 0.0087), but not deutetrabenazine or valbenazine. Decreased odds of suicide attempts and completed suicide were observed with VMAT2 inhibitors, with RORs ranging from 0.011 to 0.10 (all IC025 < 0). Increased odds of parkinsonism were reported for all VMAT2 inhibitors, with RORs and IC025 ranging from 19.49 to 25.37 and 1.66 to 2.93, respectively. The mixed results with VMAT2 inhibitor-associated suicidality and parkinsonism do not establish causal relationships. The parameters of suicidality may be explained by underlying psychiatric disorders.

Vesicular monoamine transporter-2 inhibitor JPC-141 prevents methamphetamine-induced dopamine toxicity and blocks methamphetamine self-administration in rats

Previous research has demonstrated therapeutic potential for VMAT2 inhibitors in rat models of methamphetamine use disorder. Here, we report on the neurochemical and behavioral effects of 1-(2-methoxyphenethyl)-4-phenethypiperazine (JPC-141), a novel analog of lobelane. JPC-141 potently inhibited (Ki = 52 nM) [3H]dopamine uptake by VMAT2 in striatal vesicles with 50 to 250-fold greater selectivity for VMAT2 over dopamine, norepinephrine and serotonin plasmalemma transporters. Also, JPC-141 was 57-fold more selective for inhibiting VMAT2 over [3H]dofetilide binding to hERG channels expressed by HEK293, suggesting relatively low potential for cardiotoxicity. When administered in vivo to rats, JPC-141 prevented the METH-induced reduction in striatal dopamine content when given either prior to or after a high dose of METH, suggesting a reduction in METH-induced dopaminergic neurotoxicity. In behavioral assays, JPC-141 decreased METH-stimulated locomotor activity in METH-sensitized rats at doses of JPC-141 which did not alter locomotor activity in the saline control group. Moreover, JPC-141 specifically decreased iv METH self-administration at doses that had no effect on food-maintained responding. These findings support the further development of VMAT2 inhibitors as pharmacotherapies for individuals with methamphetamine use disorder.

Transport and inhibition mechanism for VMAT2-mediated synaptic vesicle loading of monoamines.

Monoamine neurotransmitters such as serotonin and dopamine are loaded by vesicular monoamine transporter 2 (VMAT2) into synaptic vesicles for storage and subsequent release in neurons. Impaired VMAT2 function underlies various neuropsychiatric diseases. VMAT2 inhibitors reserpine and tetrabenazine are used to treat hypertension, movement disorders associated with Huntington's Disease and Tardive Dyskinesia. Despite its physiological and pharmacological significance, the structural basis underlying VMAT2 substrate recognition and its inhibition by various inhibitors remains unknown. Here we present cryo-EM structures of human apo VMAT2 in addition to states bound to serotonin, tetrabenazine, and reserpine. These structures collectively capture three states, namely the lumen-facing, occluded, and cytosol-facing conformations. Notably, tetrabenazine induces a substantial rearrangement of TM2 and TM7, extending beyond the typical rocker-switch movement. These functionally dynamic snapshots, complemented by biochemical analysis, unveil the essential components responsible for ligand recognition, elucidate the proton-driven exchange cycle, and provide a framework to design improved pharmaceutics targeting VMAT2.

Exploring real-world symptom impact and improvement in well-being domains for tardive dyskinesia in VMAT2 inhibitor-treated patients via clinician survey and chart review.

Two vesicular monoamine transporter 2 (VMAT2) inhibitors are approved in the United States (US) for the treatment of tardive dyskinesia (TD). There is a paucity of information on the impact of VMAT2 inhibitor treatment on patient social and physical well-being. The study objective was to elucidate clinician-reported improvement in symptoms and any noticeable changes in social or physical well-being in patients receiving VMAT2 inhibitors. A web-based survey was offered to physicians, nurse practitioners, and physician assistants based in the US who prescribed valbenazine for TD within the past 24 months. Clinicians reported data from the charts of patients who met the inclusion criteria and were allowed to recall missing information. Respondents included 163 clinicians who reviewed charts of 601 VMAT2-treated patients with TD: 47% had TD symptoms in ≥2 body regions, with the most common being in the head or face and upper extremities. Prior to treatment, 93% of patients showed impairment in ≥1 social domain, and 88% were impaired in ≥1 physical domain. Following treatment, among those with improvement in TD symptoms (n = 540), 80% to 95% showed improvement in social domains, 90% to 95% showed improvement in physical domains, and 73% showed improvement in their primary psychiatric condition. In VMAT2-treated patients with TD symptom improvement, clinicians reported concomitant improvement in psychiatric disorder symptoms and in social and physical well-being. Regular assessment of TD impact on these types of domains should occur simultaneously with movement disorder ratings when evaluating the value of VMAT2 inhibitor therapy.

Valbenazine promotes body growth via growth hormone signaling during zebrafish embryonic development

Vesicular monoamine transporter 2 (VMAT-2) functions by uptake of cytoplasmic monoamines into vesicles for storage. Valbenazine (VBZ) is a newly FDA-approved oral VMAT-2 inhibitor used for the treatment of movement disorders such as tardive dyskinesia (TD), and Tourette syndrome (TS). Clinical data shows that VBZ is a relatively safe drug with no cardiotoxicity or hepatotoxicity. However, the effect of VBZ on embryonic development remains unknown. Here, we use zebrafish larvae as an animal model to demonstrate that VBZ exposure causes premature hatching and increased body size and hyperactivity-like behaviors in zebrafish larvae. In addition, VBZ exposure leads to increased dopamine (DA) and Glutamate (Glu) levels. Moreover, an increase of growth hormone (gh) and enriched PI3K/AKT signaling were found in VBZ-exposed zebrafish larvae, which may explain their accelerated development. In summary, VBZ exposure may be developmentally toxic in zebrafish larvae.

Real-world experience with VMAT2 inhibitors in Tourette syndrome.

We aimed to review our "real-world" experience with the vesicular monoamine transporter 2 (VMAT2) inhibitors tetrabenazine, deutetrabenazine, and valbenazine for treatment of Tourette syndrome, focusing on therapeutic benefits, side effect profile, and accessibility for the off-label use of these drugs. We performed a retrospective chart review, supplemented with a telephone survey, of all our patients treated for their tics with VMAT2 inhibitors over a period of 4years from January 2017 until January 2021. We identified 164 patients treated with the various VMAT2 inhibitors (tetrabenazine, n = 135; deutetrabenazine, n = 71; valbenazine, n = 20). Data on the mean treatment duration and daily dosages were collected. The response to VMAT2 inhibitors was assessed by a Likert scale by comparing the symptom severity before initiation and while on treatment. Side effects were mild and mostly consisted of depression as the major side effect but there was no suicidality reported. VMAT2 inhibitors are effective and safe in the treatment of tics associated with Tourette syndrome but are not readily accessible by patients in the United States, partly because of lack of approval by the Food and Drug Administration.

Historical developments, hotspots, and trends in tardive dyskinesia research: a scientometric analysis of 54 years of publications.

Since being recognized as an important drug-induced clinical entity during the 1960s, tardive dyskinesia (TD) has generated an extensive body of research seeking to understand its clinical characteristics, epidemiology, pathophysiology and management. Modern scientometric approaches allow interactive visualization of large bodies of literature to identify trends and hotspots within knowledge domains. This study thus aimed to provide a comprehensive scientometric review of the TD literature. Web of Science was searched for articles, reviews, editorials and letters with the term "tardive dyskinesia" in the title, abstract, or keywords through 12/31/2021. A total of 5,228 publications and 182,052 citations were included. Annual research output, prominent research areas, authors, affiliations and countries were summarized. VOSViewer and CiteSpace were used for bibliometric mapping and co-citation analysis. Structural and temporal metrics were used to identify key publications in the network. TD-related publications peaked in the 1990s, gradually declined after 2004, and showed a further small increase after 2015. The most prolific authors were Kane JM, Lieberman JA, and Jeste DV overall (1968-2021), and Zhang XY, Correll CU and Remington G in the last decade (2012-2021). The most prolific journal was the Journal of Clinical Psychiatry overall, and the Journal of Psychopharmacology in the last decade. Knowledge clusters in the 1960-1970s dealt with clinical and pharmacological characterization of TD. In the 1980s, epidemiology, clinical TD assessment, cognitive dysfunction and animal models predominated. During the 1990s, research diverged into pathophysiological studies, especially oxidative stress, and clinical trials on atypical antipsychotics, with a focus on clozapine and bipolar disorder. In the 1990-2000s, pharmacogenetics emerged. More recent clusters include serotonergic receptors, dopamine-supersensitivity psychosis, primary motor abnormalities of schizophrenia, epidemiology/meta-analyses, and advances in TD treatment, particularly vesicular monoamine transporter-2 inhibitors since 2017. This scientometric review visualized the evolution of scientific knowledge on TD over more than five decades. These findings will be useful for researchers to find relevant literature when writing scientific articles, choosing appropriate journals, finding collaborators or mentors for research, and to understand the historical developments and emerging trends in TD research.

Baseline Characteristics and Treatment Patterns of a Global Huntington Disease Population Stratified by Chorea Severity (P2-11.011)

<h3>Objective:</h3> To describe baseline characteristics and treatment patterns in Huntington Disease-associated chorea by chorea severity. <h3>Background:</h3> Though multiple treatment options exist for HD-associated chorea, there are little real-world data on treatment patterns, especially across disease trajectory and variation by severity of chorea. <h3>Design/Methods:</h3> Participants were adults from “Enroll-HD”, a global observational registry for patients with HD and their families (data cut 2013 – 31 October, 2020). Data on age, sex, Total Maximal Chorea (TMC) score, vesicular monoamine transporter 2 (VMAT2) inhibitors, and antipsychotic agents (APs; typical, atypical, and other [lithium]) were collected at the baseline visit. Participants were grouped by chorea severity (TMC score categories) recorded at baseline (0–7, 8–14, 15–21, 22–28). <h3>Results:</h3> There were 10,903 participants (TMC 0–7, n=5055; TMC 8–14, n=4374; TMC 15–21, n=1310; TMC 22–28, n=164). 51% were female (51.2%, 51.5%, 51.4%, and 53.1%, respectively) and the mean age at baseline was 53.0 years (50.8, 54.5, 55.9, 54.4, respectively). Overall, VMAT2i use at baseline was 14.9% and increased with chorea severity (10.8%, 16.4%, 23.9%, 29.3%, respectively). The proportion of patients using APs at baseline was 34.5% overall and increased with chorea severity (29.9%, 35.1%, 47.8%, 57.3%, respectively). Overall, 5.8% of patients used VMAT2 inhibitors combined with APs, and combined use increased with chorea severity (3.9%, 5.8%, 11.5%, 15.9%, respectively). <h3>Conclusions:</h3> Use of medications to treat chorea was low across the spectrum of chorea severities but increased incrementally in patients with greater chorea severity. Use of a combination of VMAT2 inhibitors and APs at baseline was low but increased as chorea severity increased. These data suggest that HD-associated chorea may be under treated globally. More data are needed to understand chorea treatment considerations and the utility of VMAT2 inhibitors and APs for treating HD-associated chorea and comorbidities. <b>Disclosure:</b> Dr. Sung has received personal compensation in the range of $5,000-$9,999 for serving as a Consultant for Teva Neuroscience. Dr. Sung has received personal compensation in the range of $5,000-$9,999 for serving as a Consultant for Genentech. Dr. Furr-Stimming has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Teva Pharmaceuticals. Dr. Furr-Stimming has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Michael J. Fox Foundation. Dr. Furr-Stimming has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Teva Pharmaceuticals. The institution of Dr. Furr-Stimming has received research support from Cures within Reach. The institution of Dr. Furr-Stimming has received research support from Huntington’s Disease Society of America. The institution of Dr. Furr-Stimming has received research support from Roche/Genetech. The institution of Dr. Furr-Stimming has received research support from Uniqure. The institution of Dr. Furr-Stimming has received research support from CHDI. The institution of Dr. Furr-Stimming has received research support from Huntington Study Group/Neurocrine. The institution of Dr. Furr-Stimming has received research support from NIH/University of Iowa. The institution of Dr. Furr-Stimming has received research support from Sage Therapeutics. Dr. Furr-Stimming has received publishing royalties from a publication relating to health care. Dr. Reshef has received personal compensation for serving as an employee of Teva. Ms. Willock has received personal compensation for serving as an employee of HCD Economics. Rinat Ribalov has received personal compensation for serving as an employee of TEVA. Miss Brighton has nothing to disclose. Dr. Leo has received personal compensation for serving as an employee of Teva Pharmaceutical Industries.

Anticholinergics Should Not Be Used to Treat Tardive Dyskinesia: Insights From an Expert Panel of Psychiatry and Neurology Healthcare Professionals

AbstractIntroductionTardive dyskinesia (TD) is a persistent and often disabling hyperkinetic movement disorder associated with prolonged exposure to dopamine receptor blocking agents (e.g., antipsychotics, antiemetics). The use of anticholinergics for the treatment of movement disorders including TD is a common practice, despite a lack of supportive evidence and the potential to worsen TD. Moreover, there are now FDA-approved medications specifically indicated for TD. Two virtual meetings were held with movement disorder experts from neurology and psychiatry to better understand the real-world use of anticholinergics for TD.MethodsIn November 2020, a panel of eight experts was convened to gather insights on the challenges of differentiating TD from other drug-induced movement disorders (DIMDs) and to discuss appropriate treatments for TD and other DIMDs. A follow-up meeting was held in June 2021 to consolidate these insights. Key recommendations based on the panel discussions are presented.ResultsThe panel emphasized that while anticholinergics can help with managing some DIMDs, current evidence indicates that they are not effective in TD and may even worsen symptoms. Therefore, FDA-approved vesicular monoamine transporter 2 (VMAT2) inhibitors like valbenazine were recommended by the panel as first-line TD therapies. The panel noted that TD is often grouped under the term “extrapyramidal symptoms,” which leads to difficulty in differentiating TD from other DIMDs and the inappropriate treatment of TD with anticholinergics. The panel agreed that prophylaxis with anticholinergics is only appropriate in patients at high risk of acute dystonia. However, chronic anticholinergic use should be avoided whenever possible due to potentially serious adverse effects (e.g., cognitive difficulties) and anticholinergic burden, particularly in older patients. The potential for abuse, addiction, and diversion should also be considered when prescribing anticholinergics. Abrupt anticholinergic discontinuation can result in cholinergic rebound, which is characterized by sleep disturbances, gastrointestinal problems, urinary urgency, and manifestations of DIMDs. Thus, when used appropriately (e.g., for acute dystonia), anticholinergics should be prescribed at minimally effective doses and slowly tapered for successful discontinuation.ConclusionsThese findings align with the current TD treatment guidelines, including the lack of evidence for anticholinergic use and recommended first-line treatment with approved VMAT2 inhibitors. Conclusions from this panel highlight educational needs across HCPs on the phenomenology of DIMDs, the inappropriate use of anticholinergics for TD, TD risks and assessment, and treatment strategies for TD.FundingNeurocrine Biosciences, Inc.

Pharmacokinetic and Pharmacologic Characterization of the Dihydrotetrabenazine Isomers of Deutetrabenazine and Valbenazine.

Valbenazine and deutetrabenazine are vesicular monoamine transporter 2 (VMAT2) inhibitors approved for tardive dyskinesia. The clinical activity of valbenazine is primarily attributed to its only dihydrotetrabenazine (HTBZ) metabolite, [+]-α-HTBZ. Deutetrabenazine is a deuterated form of tetrabenazine and is metabolized to four deuterated HTBZ metabolites: [+]-α-deuHTBZ, [+]-β-deuHTBZ, [-]-α-deuHTBZ, and [-]-β-deuHTBZ. An open-label, crossover study characterized the pharmacokinetic profiles of the individual deuHBTZ metabolites, which have not been previously reported. VMAT2 inhibition and off-target interactions of the deuHTBZ metabolites were evaluated using radioligand binding. The only valbenazine HTBZ metabolite, [+]-α-HTBZ, was a potent VMAT2 inhibitor, with negligible affinity for off-target dopamine, serotonin, and adrenergic receptors. Following deutetrabenazine administration, [-]-α-deuHTBZ represented 66% of circulating deuHTBZ metabolites and was a relatively weak VMAT2 inhibitor with appreciable affinity for dopamine (D2S , D3 ) and serotonin (5-HT1A , 5-HT2B , 5-HT7 ) receptors. [+]-β-deuHTBZ was the most abundant deuHTBZ metabolite that potently inhibited VMAT2, but it represented only 29% of total circulating deuHTBZ metabolites. The mean half-life of [+]-α-HTBZ (22.2hours) was ∼3× longer than that of [+]-β-deuHTBZ (7.7hours). These findings are similar to studies with tetrabenazine, in that deutetrabenazine is metabolized to four deuHTBZ stereoisomers, the most abundant of which has negligible interaction with VMAT2 in vitro and appreciable affinity for several off-target receptors. In contrast, valbenazine's single HTBZ metabolite is a potent VMAT2 inhibitor in vitro with no discernible off-target activity. Determination of the effects of intrinsic/extrinsic variables on deutetrabenazine's safety/efficacy profile should incorporate assessment of the effects on all deuHTBZ metabolites.

Inhibition of VMAT2 by β2-adrenergic agonists, antagonists, and the atypical antipsychotic ziprasidone

Vesicular monoamine transporter 2 (VMAT2) is responsible for packing monoamine neurotransmitters into synaptic vesicles for storage and subsequent neurotransmission. VMAT2 inhibitors are approved for symptomatic treatment of tardive dyskinesia and Huntington’s chorea, but despite being much-studied inhibitors their exact binding site and mechanism behind binding and inhibition of monoamine transport are not known. Here we report the identification of several approved drugs, notably β2-adrenergic agonists salmeterol, vilanterol and formoterol, β2-adrenergic antagonist carvedilol and the atypical antipsychotic ziprasidone as inhibitors of rat VMAT2. Further, plausible binding modes of the established VMAT2 inhibitors reserpine and tetrabenazine and hit compounds salmeterol and ziprasidone were identified using molecular dynamics simulations and functional assays using VMAT2 wild-type and mutants. Our findings show VMAT2 as a potential off-target of treatments with several approved drugs in use today and can also provide important first steps in both drug repurposing and therapy development targeting VMAT2 function.

β-N-methylamino-l-alanine is a non-competitive inhibitor of vesicular monoamine transporter 2

The neurotoxic, non-proteinogenic amino acid β-N-methylamino-l-alanine (BMAA) has been implicated in the development of neurodegenerative diseases; however, the mechanism(s) and mode(s) of toxicity remain unclear. Similarities in the neuropathology and behavioural deficits of neonatal rats exposed to either BMAA or reserpine, a known vesicular monoamine transporter 2 (VMAT2) inhibitor, suggest a similar mode of action. The aims of this study were therefore to determine if BMAA could prevent the uptake of serotonin into dense granules via inhibition of VMAT2, and, if so, the type of inhibition caused by BMAA. Exposing platelet dense granules to BMAA resulted in a concentration-dependent reduction in serotonin uptake. The inhibition of VMAT2 was non-competitive. The findings from this study support previous reports that BMAA-associated neuropathologies in a neonatal rat model may be due to VMAT2 inhibition during critical periods of neurogenesis.

A new era in the diagnosis and treatment of tardive dyskinesia.

Tardive dyskinesia (TD) is a heterogeneous, hyperkinetic movement disorder induced by dopamine-receptor blocking agents that presents a unique challenge in the treatment of psychosis. Although acceptance of TD as a serious consequence of antipsychotic treatment was resisted initially, subsequent research by many investigators in psychopharmacology contributed to a rich store of knowledge on many aspects of the disorder. While basic neuroscience investigations continue to deepen our understanding of underlying motor circuitry, past trials of potential treatments of TD focusing on a range of theoretical targets were often inconclusive. Development of newer antipsychotics promised to reduce the risk of TD compared to older drugs, but their improved tolerability unexpectedly enabled an expanding market that paradoxically both increased the absolute number of patients at risk and diminished attention to TD which was relegated to legacy status. Fortunately, development and approval of novel vesicular monoamine transporter inhibitors offered evidence-based symptomatic treatment of TD for the first time and rekindled interest in the disorder. Despite recent progress, many questions remain for future research including the mechanisms underlying TD, genetic predisposition, phenomenological diversity, whether new cases are reversible, how to implement best practices to prevent and treat TD, and whether the development of novel antipsychotics free of the risk of TD is attainable. We owe our patients the aspirational goal of striving for zero prevalence of persistent symptoms of TD in anyone treated for psychosis.

9-Cyclopropylmethoxy-dihydrotetrabenazine and its stereoisomers as vesicular monoamine transporter-2 inhibitors.

Aim: To separate and evaluate 9-cyclopropylmethoxy-dihydrotetrabenazine (13a) and its stereoisomers for their high affinity for vesicular monoamine transporter-2 (VMAT2). Method: Stereoisomers of 13a were separated and configurations were ascertained by chiral chromatography and crystal diffraction combined with 1H-1H NOESY assay. Possible binding modes of eight stereoisomers and VMAT2 were explored by molecular docking assays. TheVMAT2 affinity of thestereoisomers, inhibition in vivoand pharmacokinetics in rats were evaluated. Results: Three stereoisomers were obtained: P1, P2and P3, and all had similar VMAT2 binding modes. P2 [(2R, 3R, 11bR)-13a] showed the highest potential VMAT2 binding activity (Ki=0.75 nM), decreased locomotor activity in ratsand had anoral absolute bioavailability of 92.0%. Conclusion: P2 has good efficacy and pharmacokinetic properties and warrants further development to treat tardive dyskinesia.

Using complex behavior to understand brain mechanisms in health and disease.

Using complex behavior to understand brain mechanisms in health and disease.

Efficacy of Vesicular Monoamine Transporter 2 Inhibition and Synergy with Antipsychotics in Animal Models of Schizophrenia.

Antipsychotic medications function by blocking postsynaptic dopaminergic signaling in the central nervous system. Dopamine transmission can also be modulated presynaptically by inhibitors of vesicular monoamine transporter 2 (VMAT2), which inhibit loading of dopamine into presynaptic vesicles. Here we investigated the combination of these mechanisms in animal models of schizophrenia and weight gain (a primary side effect of antipsychotics). When dosed alone, the highly selective VMAT2 inhibitor RRR-dihydrotetrabenazine (RRR-DHTBZ, also known as [+]-α-HTBZ) elicited efficacy comparable to conventional antipsychotics in prepulse inhibition and conditioned avoidance models without eliciting weight gain. In combination experiments, synergy was observed: subthreshold doses of RRR-DHTBZ and risperidone or olanzapine produced robust efficacy, and in dose response experiments, RRR-DHTBZ increased the antipsychotic potency in the efficacy models but did not affect weight gain. The combinations did not affect plasma compound concentrations. The synergy is consistent with VMAT2 inhibition blocking the counterproductive presynaptic stimulation of dopamine by antipsychotics. These results suggest a therapeutic strategy of adding a VMAT2 inhibitor to lower the antipsychotic dose and reduce the side effect burden of the antipsychotic while maintaining and potentially enhancing its therapeutic effects. SIGNIFICANCE STATEMENT: Antipsychotics are often necessary and life-changing medications that reduce psychotic symptoms; however, these benefits come with a high side effect burden. This study shows that combining these postsynaptic dopaminergic modulators with a presynaptic dopamine modulator (vesicular monoamine transporter 2 [VMAT2] inhibitor) potentiates efficacy synergistically in animal models of schizophrenia without potentiating weight gain. Our data suggest that adding a VMAT2 inhibitor may be a viable therapeutic strategy for reducing antipsychotic side effects by lowering antipsychotic dose while maintaining therapeutic efficacy.

Pathophysiology, prognosis and treatment of tardive dyskinesia.

Tardive dyskinesia (TD), a movement disorder associated with antipsychotics, most frequently affects the lower face and jaw muscles, but can also affect walking, breathing and use of the hands and limbs. Knowledge of TD among physicians may be limited, and the pathophysiology of TD is poorly understood. We conducted this review to summarise the current knowledge surrounding the pathophysiology of TD and present recommendations for prevention and treatment based on a literature search and roundtable discussion attended by psychiatrists in Japan. It has been suggested that dopamine hypersensitivity, damaged gamma-aminobutyric acidergic neurons and/or increased production of reactive oxygen species may contribute to development of TD. Symptoms can profoundly affect everyday life; patients who develop TD have poorer prognoses, worse health-related quality of life, greater social withdrawal and higher mortality than patients without TD. Traditional treatment options include dietary supplements, although evidence for their effectiveness is low. Among pharmaceutical interventions, there is moderate evidence that switching to the second-generation antipsychotic clozapine, which has a lower affinity for dopamine D2 receptors than other antipsychotics, may improve symptoms. Vesicular monoamine transporter 2 (VMAT-2) inhibitors, which oppose the increased dopaminergic activity associated with prolonged antipsychotic use by interfering with dopamine uptake and storage, have the strongest evidence for efficacy. VMAT-2 inhibitors are approved in the United States for the treatment of TD, and the first VMAT-2 inhibitor was approved in Japan for this indication in March 2022. Most guidelines recommend treating TD by first reducing the dose of antipsychotics or switching to clozapine or other second-generation antipsychotics, which have a lower association with TD than first-generation antipsychotics. We recommend focusing on prevention and monitoring for TD when prescribing antipsychotics, given that TD is often irreversible. Physicians should treat with antipsychotics only when necessary and at the lowest effective dose, and frequently monitor for TD symptoms.Plain Language Summary Plain Language Summary (In Japanese) Visual Summary Visual Summary (In Japanese)

Synthesis and analysis of dihydrotetrabenazine derivatives as novel vesicular monoamine transporter 2 inhibitors.

Vesicular monoamine transporter 2 (VMAT2) is essential for synaptic transmission of all biogenic amines in the brain including serotonin, norepinephrine, histamine, and dopamine (DA). Given its crucial role in the neurophysiology and pharmacology of the central nervous system, VMAT2 is recognized as an important therapeutic target for various neurological disorders such as tardive dyskinesia (TD). Here, a novel series of dihydrotetrabenazine derivative analogs were designed and synthesized to evaluate their effects on [3H]dihydrotetrabenazine (DTBZ) binding and [3H]DA uptake at VMAT2. Of these analogs, compound 13e showed a high binding affinity for VMAT2 (IC50=5.13±0.16nM) with excellent inhibition of [3H]DA uptake (IC50=6.04±0.03nM) in striatal synaptosomes. In human liver microsomes, 13e was more stable (T1/2=161.2min) than other reported VMAT2 inhibitors such as DTBZ (T1/2=119.5min). In addition, 13e effectively inhibited the spontaneous locomotor activity (percent inhibition at 3μmol/kg=64.7%) in Sprague-Dawley rats. Taken together, our results indicate that 13e might be a promising lead compound for the development of novel treatments of TD.