Vesicular Monoamine Transporter Research Articles

Anterior pituitary gland synthesises dopamine from l-3,4-dihydroxyphenylalanine (l-dopa).

Prolactin (PRL) is a hormone principally secreted by lactotrophs of the anterior pituitary gland. Although the synthesis and exocytosis of this hormone are mainly under the regulation of hypothalamic dopamine (DA), the possibility that the anterior pituitary synthesises this catecholamine remains unclear. The present study aimed to determine if the anterior pituitary produces DA from the precursor l-3,4-dihydroxyphenylalanine (l-dopa). Accordingly, we investigated the expression of aromatic l-amino acid decarboxylase (AADC) enzyme and the transporter vesicular monoamine transporter 2 (VMAT2) in the anterior pituitary, AtT20 and GH3 cells by immunofluorescence and western blotting. Moreover, we investigated the production of DA from l-dopa and its release in vitro. Then, we explored the effects of l-dopa with respect to the secretion of PRL from anterior pituitary fragments. We observed that the anterior pituitary, AtT20 and GH3 cells express both AADC and VMAT2. Next, we detected an increase in DA content after anterior pituitary fragments were incubated with l-dopa. Also, the presence of l-dopa increased DA levels in incubation media and reduced PRL secretion. Likewise, the content of cellular DA increased after AtT20 cells were incubated with l-dopa. In addition, l-dopa reduced corticotrophin-releasing hormone-stimulated adrenocorticotrophic hormone release from these cells after AADC activity was inhibited by NSD-1015. Moreover, DA formation from l-dopa increased apoptosis and decreased proliferation. However, in the presence of NSD-1015, l-dopa decreased apoptosis and increased proliferation rates. These results suggest that the anterior pituitary synthesises DA from l-dopa by AADC and this catecholamine can be released from this gland contributing to the control of PRL secretion. In addition, our results suggest that l-dopa exerts direct actions independently from its metabolisation to DA.

The dopamine depleting agent tetrabenazine alters effort-related decision making as assessed by mouse touchscreen procedures.

Effort-based decision-making tasks allow animals to choose between preferred reinforcers that require high effort to obtain vs. low-effort/low reward options. Mesolimbic dopamine (DA) and related neural systems regulate effort-based choice. Tetrabenazine (TBZ) is a vesicular monoamine transport type-2 inhibitor that blocks DA storage and depletes DA. In humans, TBZ induces motivational dysfunction and depression. TBZ has been shown reliably to induce a low-effort bias in rats, but there are fewer mouse studies. The present studies used touchscreen operant procedures (Bussey-Saksida chambers) to assess the effects of TBZ on effort-based choice in mice. C57BL6 mice were trained to press an elevated lit panel on the touchscreen on a fixed ratio 1 schedule reinforced by strawberry milkshake, vs. approaching and consuming a concurrently available but less preferred food pellets (Bio-serv). TBZ (2.0-8.0 mg/kg IP) shifted choice, producing a dose-related decrease in panel pressing but an increase in pellet intake. In contrast, reinforcer devaluation by pre-feeding substantially decreased both panel pressing and pellet intake. In free-feeding choice tests, mice strongly preferred the milkshake vs. the pellets, and TBZ had no effect on milkshake intake or preference, indicating that the TBZ-induced low-effort bias was not due to changes in primary food motivation or preference. TBZ significantly decreased tissue levels of nucleus accumbens DA. The DA depleting agent TBZ induced an effort-related motivational dysfunction in mice, which may have clinical relevance for assessing novel drug targets for their potential use as therapeutic agents in patients with motivation impairments.

Fentanyl but not Morphine Interacts with Nonopioid Recombinant Human Neurotransmitter Receptors and Transporters.

Synthetic opioids, including fentanyl and its analogs, have therapeutic efficacy in analgesia and anesthesia. However, their illicit use in the United States has increased and contributed to the number one cause of death for adults 18-50 years old. Fentanyl and the heroin metabolite morphine induce respiratory depression that can be treated with the μ opioid receptor (MOR) antagonist naloxone. With higher or more rapid dosing, fentanyl, more than morphine, causes chest wall rigidity and can also induce rapid onset laryngospasm. Because non-MORs could mediate differing clinical manifestations, we examined the interactions of fentanyl and morphine at recombinant human neurotransmitter transporters, G protein-coupled receptors, and the N-methyl-D-aspartate glutamate receptor. Both drugs were agonists at MOR, κ, and δ opioid receptors. Morphine had little or no affinity at other human receptors and transporters (K i or IC50 value >100 µM). However, fentanyl had K i values of 1407 and 1100 nM at α 1A and α 1B adrenoceptor subtypes, respectively, and K i values of 1049 and 1670 nM at dopamine D4.4 and D1 receptor subtypes, respectively; it also blocked [3H]neurotransmitter uptake by the vesicular monoamine transporter 2 (IC50 = 911 nM). Pharmacokinetic models indicate that these Ki and IC50 values are pharmacologically relevant. Fentanyl had little affinity for other receptors or transporters. Thus, noradrenergic disposition at specific receptor subtypes in relevant organs may play a role in respiratory and cardiothoracic effects of fentanyl. Data suggest that less selective fentanyl receptor pharmacology could play a role in the different clinical effects of morphine compared with fentanyl, including fentanyl-induced deaths after illicit use. SIGNIFICANCE STATEMENT: The synthetic opioid fentanyl induces different clinical effects, including rapid onset muscular rigidity, vocal cord closure, and rapid death, than the heroin metabolite morphine. Our data indicate for the first time that the two drugs have very different effects at recombinant human neurotransmitter receptors and transporters that might explain those clinical differences.

Risk of Neuroleptic Malignant Syndrome with Vesicular Monoamine Transporter Inhibitors.

ObjectiveVesicular monoamine transporter-2 (VMAT2) inhibitors have been proven to be effective for the treatment of tardive dyskinesia and their use is likely to increase. The evidence base of published clinical reports was reviewed to evaluate the possible risk of neuroleptic malignant syndrome (NMS) with these drugs.MethodsPubmed, Embase, Web of Science and PsycINFO databases were queried for all years using terms for “neuroleptic malignant syndrome”, “hyperthermia” AND “vesicular monoamine transporter inhibitors”, “reserpine”, “tetrabenazine”, “valbenazine” or “deutetrabenazine”ResultsThirteen clinical cases, ten of which involved tetrabenazine, were identified in which VMAT2 inhibitors were prescribed in patients with current or past NMS episodes. In most cases, the association was confounded by limited reporting of clinical data, variable temporal correlation with VMAT2 inhibitors, polypharmacy with antipsychotics, and uncertain differential diagnoses.ConclusionWhile rare cases of NMS meeting consensus criteria have been reported primarily with tetrabenazine, the risk with recently developed VMAT2 inhibitors may be even less. Evidence of causality of NMS with VMAT2 inhibitors is confounded by concomitant treatment with antipsychotics and diagnostic uncertainties in patients susceptible to basal ganglia dysfunction. Nevertheless, clinicians should remain vigilant for early signs of NMS in all patients treated with any drugs that affect brain dopamine activity.

11C]dihydrotetrabenazine Positron Emission Tomography in Manganese-Exposed Workers.

To understand the neurotoxic effects of manganese (Mn) exposure on monoaminergic function, utilizing [C]dihydrotetrabenazine (DTBZ) positron emission tomography (PET) to measure vesicular monoamine transporter 2 (VMAT2). Basal ganglia and thalamic DTBZ binding potentials (BPND) were calculated on 56 PETs from 41 Mn-exposed workers. Associations between cumulative Mn exposure, regional BPND, and parkinsonism were examined by mixed linear regression. Thalamic DTBZ BPND was inversely associated with exposure in workers with less than 3 mg Mn/m-yrs, but subsequently remained stable. Pallidal DTBZ binding increased in workers with less than 2 mg Mn/m-yrs of exposure, but decreased thereafter. Thalamic DTBZ binding was inversely associated with parkinsonism (P = 0.003). Mn-dose-dependent associations with thalamic and pallidal DTBZ binding indicate direct effects on monoaminergic VMAT2. Thalamic DTBZ binding was also associated with parkinsonism, suggesting potential as an early biomarker of Mn neurotoxicity.

Pharmacologic Treatment of Tardive Dyskinesia

To examine the efficacy of pharmacologic treatments for tardive dyskinesia (TD). PubMed was searched on December 12, 2017, for randomized, placebo-controlled trials examining the treatment of TD using the search terms (drug-induced dyskinesia OR tardive dyskinesia) AND (psychotic disorders OR schizophrenia). Studies were included if they examined tardive dyskinesia treatment as the primary outcome and were randomized and placebo-controlled trials. The effect size (standard mean difference) of improvement (compared to placebo) stratified by medication class is reported for each of the trials included in this systematic review. A meta-analysis was conducted utilizing a fixed-effects model. Vitamin E was associated with significantly greater reduction in TD symptoms compared to placebo (standardized mean difference [SMD] = 0.31 ± 0.08; 95% CI, 0.16 to 0.46; z = 4.1; P < .001). There was significant evidence of publication bias in vitamin E studies (Egger test: P = .02). Shorter duration of treatment and lower dose of vitamin E were significantly associated with greater measured treatment benefit. Vitamin B₆ was associated with significantly greater reduction in TD symptoms compared to placebo (SMD = 1.41 ± 0.22; 95% CI, 0.98 to 1.85; z = 6.4; P < .001) in 2 trials conducted by the same research group. Vesicular monoamine transporter 2 (VMAT2) inhibitors demonstrated significant benefit on tardive dyskinesia symptoms compared to placebo (SMD = 0.63 ± 0.11; 95% CI, 0.41 to 0.85; z = 5.58; P < .005). Amantadine was associated with significantly greater score reduction compared to placebo (SMD = 0.46 ± 0.21; 95% CI, 0.05 to 0.87; z = 2.20; P < .05). Calcium channel blockers were not associated with significantly greater score reduction compared to placebo (SMD = 0.31 ± 0.33; 95% CI, -0.34 to 0.96; z = 0.93; P = .35). Data from multiple trials suggests that VMAT2 inhibitors, vitamin E, vitamin B₆, and amantadine may be effective for the treatment of TD. Evidence of publication bias and a significant negative association of dose and duration of treatment with measured efficacy suggest that the benefits of vitamin E in TD may be overstated. Head-to-head trials are needed to compare the efficacy and cost-effectiveness of pharmacologic agents for TD.

3,4-Methylenedioxypyrovalerone: Neuropharmacological Impact of a Designer Stimulant of Abuse on Monoamine Transporters.

Methylenedioxypyrovalerone (MDPV) is an abused synthetic cathinone, commonly referred to as a "bath salt." Because the dopamine (DA) transporter (DAT) and vesicular monoamine transporter-2 (VMAT-2) are key regulators of both the abuse and neurotoxic potential of structurally and behaviorally related agents, the impact of MDPV on these transporters was investigated. Results revealed that a single in vivo MDPV administration rapidly (within 1 hour) and reversibly increased both rat striatal DAT and VMAT-2 activity, as assessed via [3H]DA uptake in synaptosomes and synaptic vesicles, respectively, prepared from treated rats. There was no evidence of an MDPV-induced increase in plasmalemmal membrane DAT surface expression. Plasma concentrations of MDPV increased dose-dependently as assessed 1 hour after 2.5 and 5.0 mg/kg (s.c.) administration and returned to levels less than 10 ng/ml by 18 hours after 2.5 mg/kg (s.c.). Neither pretreatment with a D1 receptor (SCH23390), a D2 receptor (eticlopride), nor a nicotinic receptor (mecamylamine) antagonist attenuated the MDPV-induced increase in DAT activity. In contrast, eticlopride pretreatment attenuated both the MDPV-induced increase in VMAT-2-mediated DA uptake and an associated increase in cytoplasmic-associated vesicle VMAT-2 immunoreactivity. SCH23390 did not attenuate the MDPV-induced increase in VMAT-2 activity. Repeated MDPV injections did not cause persistent DAergic deficits, as assessed 7 to 8 days later. The impact of MDPV on striatal and hippocampal serotonergic assessments was minimal. Taken together, these data contribute to a growing pharmacological rubric for evaluating the ever-growing list of designer cathinone-related stimulants. The profile of MDPV compared with related psychostimulants is discussed. SIGNIFICANCE STATEMENT: Pharmacological characterization of the synthetic cathinone, 3,4-methylenedioxypyrovalerone (MDPV; commonly referred to as a "bath salt"), is critical for understanding the abuse liability and neurotoxic potential of this and related agents. Accordingly, the impact of MDPV on monoaminergic neurons is described and compared with that of related psychostimulants.

Chronic Neuroleptic-Induced Parkinsonism Examined With Positron Emission Tomography.

Neuroleptic drug-induced parkinsonism (NIP) is a leading cause of parkinsonism, particularly in aging. Based on abnormal dopamine transporter scan results, individuals displaying chronic NIP are often diagnosed with Lewy-body Parkinson's disease (PD), but this assumption needs further substantiation. To quantitate the profile of striatal dopaminergic nerve terminal density in NIP relative to PD. We used the positron emission tomography ligand [11 C](+)-dihydrotetrabenazine targeting vesicular monoamine transporter type 2 (VMAT2) binding sites and collected various clinical parameters (motor ratings, olfaction, polysomnography to document rapid eye movement sleep muscle activity, quantitative sensory testing for pain thresholds) possibly predicting binding results in patients older than age 50 living with schizophrenia spectrum disorders under long-term stable antipsychotic drug treatment, with (N = 11) or without (N = 11) chart documention of chronic NIP, and compared them to healthy volunteers (N = 11) and others medicated for PD (N = 12). Striatal VMAT2 binding was dichotomous in the NIP group between those with spared (N = 5) or low (N = 6) PD-like values. Striatal binding reduction in the low VMAT2-NIP group was asymmetric without the gradient of maximal involvement in the posterior putamen typical of PD. Anosmia was the only nonmotor parameter measured matching the abnormal striatal VMAT2 binding status. These preliminary observations suggest that striatal VMAT2 binding is abnormal in a fraction of chronic NIP cases and differs in spatial distribution from PD. The possibility of a drug-induced axonopathy and resultant synaptopathy, as well as the evolution of the binding deficit, warrant further longitudinal studies in a large cohort. © 2020 International Parkinson and Movement Disorder Society.

Alterations of the Motor and Olfactory Functions Related to Parkinson's Disease in Transgenic Mice With a VMAT2-Deficiency in Dopaminergic Neurons.

Parkinson’s disease (PD) is one of the most common neurodegenerative diseases, with approximately six million people affected worldwide. Vesicular monoamine transporter 2 (VMAT2) dysfunction has recently become a hot topic in the pathophysiology of PD, and the advent of transgenic mice has also accelerated the development of behavioral studies in animal models. However, there are only a few systematic behavioral tests that embrace abundant motor and non-motor performance in a unique mutant mouse model which correspond to the varied symptoms observed in human PD. The aim of this study is to evaluate the responsibility of the unique reduction of dopamine in the varied motor and non-motor symptoms of PD via a transgenic mice model. We analyzed neurotransmitter concentrations in the brain tissue of 18-month-old mutant mice, with selective inactivation of one allele of Vmat2 in dopaminergic neurons (VMAT2DATcre-HET) to confirm the selective reduction of dopamine, and then examined behavioral functions. Neurochemical tests showed lower dopamine concentrations in specific brain regions of VMAT2DATcre-HET mice, especially the ventral tegmental area/substantia nigra and striatum, together with relatively unchanging concentrations of norepinephrine and serotonin, demonstrating the dopaminergic specificity of this mouse model. Behavioral tasks showed impairments in several motor functions and major defects in olfactory abilities in the VMAT2DATcre-HET mice. However, no significant changes were found in the majority of non-motor tests, such as emotional performance and sleep patterns. We concluded from this study that the selective inactivation of one allele of the Vmat2 gene in dopaminergic neurons was related to dopamine reduction, resulting in phenotypes resembling some of the major deficits in PD, especially those of motor symptoms and olfactory functions.

Exploring the anti-stress effects of imatinib and tetrabenazine in cold-water immersion-induced acute stress in mice.

The aim of the present study was to explore the ameliorative role of imatinib and tetrabenazine in acute stress-induced behavioural and biochemical changes in mice. Cold-water immersion (5min duration) was employed to induce acute stress and the resulting changes in the locomotor activity, exploratory behaviour, motor activity and social behaviour were assessed using the actophotometer, the hole board, the open field and the social interaction tests. The biochemical alterations were assessed by measuring the plasma corticosterone levels using ELISA kit. Cold-water immersion-induced acute stress diminished the locomotor activity, exploratory behaviour, motor activity and social behaviour along with increase in the plasma corticosterone levels. Administration of imatinib (50 and 100mg/kg, i.p.), a tyrosine kinase inhibitor, significantly attenuated the cold-water immersion-induced behavioural alterations with normalization of the plasma corticosterone levels in a dose-dependent manner. Moreover, administration of tetrabenazine (1 and 2mg/kg, i.p.), a vesicular monoamine transporter 2 (VMAT2) inhibitor, also abolished the acute stress-induced behavioural and biochemical changes in a dose-dependent manner. The beneficial effects of imatinib and tetrabenazine in normalizing acute stress-induced biochemical and behavioural changes make them promising therapeutic agents in the treatment of acute stress-related problems.

Current Treatment Options and Emerging Agents for Schizophrenia.

The currently available antipsychotics mostly treat the positive symptoms of schizophrenia and have at least one adverse effect as a potential liability. Encouraging data suggest potential efficacy for a variety of new agents for the treatment of total symptoms and/or specific symptom domains of schizophrenia. Mechanisms of action that are under investigation include dopamine D3 antagonism/serotonin 5-HT1A partial agonism; combined dopamine, serotonin, and glutamate modulation; phosphodiesterase 10A inhibition; trace amine-associated receptor-1 (TAAR1) agonism plus 5-HT1A agonism; 5-HT2A inverse agonism; sigma-2/5-HT2A antagonism; D-amino acid oxidase (DAAO) inhibition; glycine transporter-1 inhibition; vesicular monoamine transporter-2 antagonism; mu opioid antagonism added to olanzapine; and novel long-acting injectable antipsychotic formulations. It is hoped that ongoing and recently completed trials for agents with known and/or novel mechanisms of action will lead to approved treatments that effectively target the various symptom domains of schizophrenia, minimize the risk for a broad range of clinically relevant adverse effects, and improve functional outcomes for patients. Some novel treatments have already received approval for use in patients with schizophrenia. This brief report discusses recently approved novel agents and potential new treatment options for schizophrenia that are being investigated.

123 Long-Term Outcomes with Valbenazine 40 mg/day in Adults With Tardive Dyskinesia

Tardive dyskinesia (TD), a persistent and potentially disabling movement disorder, is associated with prolonged exposure to antipsychotics and other dopamine receptor blocking agents. Valbenazine (VBZ) is a novel and highly selective vesicular monoamine transporter 2 (VMAT2) inhibitor approved for the treatment of TD in adults. Using data from two long-term phase 3 studies (KINECT 3 [K3], NCT02274558; KINECT 4 [K4], NCT02405091) and a rollover study (1506, NCT02736955), the long-term outcomes of once-daily VBZ on TD were examined in participants who received 40mg or had a dose reduction from 80 to 40mg. The effects of VBZ 40mg (as well as VBZ 80mg) were evaluated in the following studies: the pivotal K3 study (6 weeks double-blind, placebo controlled), the extension phase of K3 (42 additional weeks of VBZ, 4 week discontinuation), and the open-label K4 study (48 weeks of VBZ, 4 week discontinuation). Completers from K3 extension and K4 were invited to participate in 1506 (up to 72 additional weeks of VBZ or until commercial availability of VBZ). Few participants reached Week 60 (n=4) or Week 72 (n=0) in the 1506 study before termination. Analyses focused on VBZ 40mg in two populations: pooled K3/K4 (participants who received VBZ 40mg throughout K3 or K4 or who had a dose reduction [80/40mg] during K3 or K4); and 1506 (participants who received VBZ 40mg from beginning of K3 or K4 to last visit in 1506 or who had a dose reduction [80/40mg] at any time). Outcomes for the K3/K4 population included mean change from baseline (CFB) in Abnormal Involuntary Movement Scale (AIMS) total score (sum of items 1-7) and AIMS response (≥50% total score improvement from baseline) at Week 48 of K3 or K4. Outcomes for the 1506 population included a Clinical Global Impression of Severity-Tardive Dyskinesia (CGIS-TD) score ≤2 ("normal, not at all ill" or "borderline ill"). In the K3/K4 population, AIMS CFB to Week 48 indicated mean TD improvements in participants who received 40mg continuously (40mg, -5.7 [n=54]) and in those who had a dose reduction to 40mg (80/40mg, -6.2 [n=13]). In addition, a majority of these participants had an AIMS response after 48 weeks of treatment (40mg, 53.7%; 80/40mg, 53.8%). In the 1506 population, the percentage of participants who had a CGIS-TD score ≤2 (rating of "normal, not at all ill" or "borderline ill") at Week 12 was 63.6% (7/11) in the 40mg group and 30.8% (4/13) in the 80/40mg group. Data from Weeks 24 to 60 of 1506 were limited by the small sample sizes (<10 participants each in 40mg or 80/40mg group at each of these visits). Based on these analyses and results from published studies, VBZ 40mg may be an effective long-term option for some TD patients. Dose reductions from 80 to 40mg, if necessary, did not appear to compromise long-term benefit. This study was sponsored by Neurocrine Biosciences, Inc.

152 Development of Deutetrabenazine as a Potential New Non-Antipsychotic Treatment for Tourette Syndrome in Children and Adolescents

Tourette syndrome (TS) is a neurodevelopmental disorder characterized by the hyperkinetic movements of motor and phonic tics manifested in young age. Currently approved treatments in the United States are antipsychotics: haloperidol, pimozide, and aripiprazole, which are associated with serious side effects, including tardive dyskinesia (TD). Deutetrabenazine, a vesicular monoamine transporter type 2 (VMAT2) inhibitor, was approved in 2017 by the US FDA for the treatment of chorea associated with Huntington's disease and TD. Three ongoing studies (Alternatives for Reducing Tics in TS [ARTISTS]) are evaluating the efficacy, safety, and tolerability of deutetrabenazine in reducing tics in TS in children and adolescents (age 6-16 years). ARTISTS 1, a phase 2/3, response-driven, dose-titration, placebo-controlled study, randomizes patients (N=116) 1:1 to deutetrabenazine or placebo for 12 weeks. ARTISTS 2, a phase 3, fixed-dose study, randomizes patients (N=150) 1:1:1 to deutetrabenazine high or low dose, or placebo for 8 weeks. The primary efficacy outcome in these pivotal studies is change from baseline to end of treatment in the Total Tic Score (TTS) of the Yale Global Tic Severity Scale (YGTSS). Additional efficacy endpoints and safety/tolerability are also evaluated. ARTISTS is a 56-week, open-label, single-arm, long-term safety/tolerability study in patients who have successfully completed either ARTISTS 1 or ARTISTS 2. Not available yet. TS can have potentially long-term life impact, and there remains unmet medical need for effective and well-tolerated treatments. Three ARTISTS studies will evaluate the efficacy, safety, and tolerability of deutetrabenazine in patients with tics in TS. The studies are sponsored by Teva Pharmaceuticals and operationalized by Teva's development partner, Nuvelution TS Pharma INC.

EFFECTS OF LONG-TERM VALBENAZINE IN KINECT 4: POST HOC RESPONSE AND SHIFT ANALYSES IN YOUNGER AND OLDER ADULTS WITH TARDIVE DYSKINESIA

Introduction Tardive dyskinesia (TD) is a persistent and potentially disabling movement disorder associated with prolonged antipsychotic exposure. Compared to younger patients, older patients have a higher risk of TD and may develop symptoms earlier during antipsychotic treatment. Valbenazine, a novel and highly selective vesicular monoamine transporter 2 (VMAT2) inhibitor, is approved to treat TD in adults of all ages, with no dose adjustment required for older patients. The long-term effects of valbenazine on TD were evaluated in KINECT 4 (NCT02405091), an open-label study in which participants received up to 48 weeks of once-daily treatment with valbenazine. Abnormal Involuntary Movement Scale (AIMS) data from this study were analyzed post hoc to evaluate treatment responses in older (≥55 to 85 years) and younger (18 to Methods KINECT 4 included participants who met the following criteria: ages 18 to 85 years; DSM-IV diagnosis of schizophrenia, schizoaffective disorder, or mood disorder; neuroleptic-induced TD for ≥3 months prior to screening; stable psychiatric status (Brief Psychiatric Rating Scale score Results Of 163 participants in the safety/efficacy population, 103 (63.2%) had an available AIMS assessment at Week 48. At Week 48, the percentages of patients who met the criteria for minimal response (≥10% AIMS total score improvement from baseline) or clinically meaningful (≥30% improvement) response were similar between the older and younger subgroups (≥55 years; Conclusions After 48 weeks of treatment with once-daily valbenazine, >95% of all KINECT 4 participants (older and younger) had a minimal AIMS total score response (≥10% improvement), >90% had a clinically meaningful response (≥30% improvement), and >80% had a robust response (≥50% improvement). Older patients seemed more likely than younger patients to achieve a maximal response, including 100% improvement, although these results may be limited by smaller sample sizes. Shift analyses based on AIMS item scores were supportive of AIMS total score responses. Together, the results presented in this post hoc analysis suggest that valbenazine is an appropriate long-term treatment for both older and younger adults with TD. This research was funded by: This study was sponsored by Neurocrine Biosciences, Inc.

Synthesis of Tetrabenazine and Its Derivatives, Pursuing Efficiency and Selectivity.

Tetrabenazine is a US Food and Drug Administration (FDA)-approved drug that exhibits a dopamine depleting effect and is used for the treatment of chorea in Huntington’s disease. Mechanistically, tetrabenazine binds and inhibits vesicular monoamine transporter type 2, which is responsible for importing neurotransmitters from the cytosol to the vesicles in neuronal cells. This transportation contributes to the release of neurotransmitters inside the cell to the synaptic cleft, resulting in dopaminergic signal transmission. The highly potent inhibitory activity of tetrabenazine has led to its advanced applications and in-depth investigation of prodrug design and metabolite drug discovery. In addition, the synthesis of enantiomerically pure tetrabenazine has been pursued. After a series of research studies, tetrabenazine derivatives such as valbenazine and deutetrabenazine have been approved by the US FDA. In addition, radioisotopically labeled tetrabenazine permits the early diagnosis of Parkinson’s disease, which is difficult to treat during the later stages of this disease. These applications were made possible by the synthetic efforts aimed toward the efficient and asymmetric synthesis of tetrabenazine. In this review, various syntheses of tetrabenazine and its derivatives have been summarized.

In vitro binding affinity vs. in vivo site occupancy: A PET study of four diastereomers of dihydrotetrabenazine (DTBZ) in monkey brain

IntroductionIn vivo imaging methods such as Positron Emission Tomography (PET) can be used to examine the relationship between in vitro binding affinity and in vivo occupancy of binding sites in the brain for new drug candidates. In this study, PET imaging in monkey brain was used to evaluate that correlation for a set of four diastereomers of the compound dihydrotetrabenazine (DTBZ), the pharmacologically active metabolite of the drug tetrabenazine. MethodsPET studies of DTBZ diastereomers were completed in a single monkey brain. In vivo occupancies (ED50) were estimated using multiple drug doses and the vesicular monoamine transporter 2 specific radioligand (+)-α-[11C] DTBZ, employing a test-retest sequence of control PET scan, drug administration and a second PET scan completed on a single day. ResultsDTBZ has three chiral carbon centers and eight possible stereoisomers, and in vivo occupancy of the target site VMAT2 was observed only for the four diastereomers of DTBZ having the 11bR absolute configuration. The estimated in vivo occupancies (ED50 values from 0.023 to >3.15 mg/kg) correlated well (R2 = 0.95) with the in vitro binding affinities (Ki values of 4 to 600 nM for the VMAT2), and an even better correlation (R2 = 0.99) was found for the three isomers with in vitro binding affinities <100 nM. ConclusionsIf the physiochemical (MW, log P, pKa) or physiological (metabolism, transport, protein binding) properties of a set of drug stereoisomers are considered similar, the binding affinities determined from in vitro assays may predict the in vivo occupancies of the target binding site in the monkey brain.

Effects of NBI-98782, a selective vesicular monoamine transporter 2 (VMAT2) inhibitor, on neurotransmitter efflux and phencyclidine-induced locomotor activity: Relevance to tardive dyskinesia and antipsychotic action

Valbenazine, a vesicular monoamine transporter 2 (VMAT2, SLC18A2) inhibitor, is a newly approved treatment for tardive dyskinesia. VMAT2 is present in the membrane of secretory vesicles and transports dopamine (DA), norepinephrine (NE), serotonin (5-HT), histamine, glutamate (Glu), and GABA into vesicles for presynaptic release. We utilized microdialysis in awake, freely moving mice to determine the effect of NBI-98782, the active metabolite of valbenazine, alone, or in combination with several antipsychotic drugs (APDs), to influence neurotransmitter efflux in the medial prefrontal cortex (mPFC), dorsal striatum (dSTR), hippocampus and nucleus accumbens (NAC); we also compared it with tetrabenazine, the prototypical VMAT2 inhibitor. Acute NBI-98782 and tetrabenazine decreased mPFC, dSTR, hippocampus, and NAC DA, 5-HT, and NE efflux, while increasing that of DOPAC, HVA, and 5-HIAA. Sub-chronic NBI-98782 (7 days) decreased baseline DA and 5-HT efflux in both mPFC and dSTR. NBI-98782 elicited similar effects on neurotransmitter efflux in sub-chronic NBI-98782-treated mice but also enhanced ACh and GABA; the decrease in DA efflux in mPFC and dSTR was not significant in the sc-treated animals. NBI-98782 suppressed clozapine-, olanzapine- and risperidone-induced DA efflux in both mPFC and dSTR, and ACh efflux in mPFC. NBI-98782 suppressed the haloperidol-induced DA efflux in dSTR, with minimal effect on GABA efflux. NBI-98782 attenuated PCP-induced DA, 5-HT, NE and Glu efflux, and AMPH-induced DA and NE efflux, in both mPFC and dSTR, as well as PCP- and AMPH-induced hyperlocomotion, suggesting possible beneficial antipsychotic effects.

Postnatal zinc or paraquat administration increases paraquat or zinc-induced loss of dopaminergic neurons: insight into augmented neurodegeneration.

Epidemiological evidences have shown an association of exposure to pesticides or heavy metals with increased incidences of Parkinson's disease (PD) in humans. Exposure to pesticides or metals during the decisive period of the brain development increases the susceptibility of dopaminergic neurons upon re-exposure in adult rodents. However, the effect of early life exposure to pesticide on the heavy metal-induced neurodegeneration or heavy metal on pesticide-induced neurodegeneration is not yet explored. The current study explored the effect of developmental exposure to zinc (Zn), a metal or paraquat (PQ), a pesticide on the nigrostriatal dopaminergic neurons of rats challenged to Zn or PQ during adulthood. Exposure of Zn or PQ during adulthood alone exhibited marked reduction in motor activities, striatal dopamine and metabolites, glutathione content and number of dopaminergic neurons. However, the levels of lipid peroxidation, protein carbonyls, superoxide dismutase activity, pro-inflammatory cytokines and 4-hydroxynonenal-protein adducts were increased. While the expression of vesicular monoamine transporter-2 and tyrosine hydroxylase were attenuated, dopamine transporter and microglial marker Iba-1 expression, activated microglia, nuclear factor-kappa B activation, mitochondrial cytochrome c release and caspase-3/9 activation were augmented following Zn or PQ exposure. Albeit postnatal alone exposure did not alter any of the studied parameters, the developmental administration of Zn/PQ in re-challenged adult rats produced more pronounced changes in the aforementioned variables as compared with adulthood Zn or PQ alone intoxicated animals. The results demonstrate that postnatal Zn/PQ intoxication dents the oxidative stress, inflammation, cell death and dopamine metabolism and storage regulating machineries, which speed up the toxicant-induced degeneration during adulthood.

Increased endogenous dopamine prevents myopia in mice

Experimental evidence suggests that dopamine (DA) modulates refractive eye growth. We evaluated whether increasing endogenous DA activity using pharmacological or genetic approaches decreased myopia susceptibility in mice. First, we assessed the effects of systemic L-3,4-dihydroxyphenylalanine (L-DOPA) injections on form deprivation myopia (FDM) in C57BL/6 J (WTC57) mice. WTC57 mice received daily systemic injections of L-DOPA (n = 11), L-DOPA + ascorbic acid (AA, n = 22), AA (n = 20), or Saline (n = 16). Second, we tested transgenic mice with increased or decreased expression of vesicular monoamine transporter 2 (VMAT2HI, n = 22; WTHI, n = 18; VMAT2LO, n = 18; or WTLO, n = 9) under normal and form deprivation conditions. VMAT2 packages DA into vesicles, affecting DA release. At post-natal day 28 (P28), monocular FD was induced in each genotype. Weekly measurements of refractive error, corneal curvature, and ocular biometry were performed until P42 or P49. WTC57 mice exposed to FD developed a significant myopic shift (treated-contralateral eye) in AA (−3.27 ± 0.73D) or saline (−3.71 ± 0.80D) treated groups that was significantly attenuated by L-DOPA (−0.73 ± 0.90D, p = 0.0002) or L-DOPA + AA (−0.11 ± 0.46D, p = 0.0103). The VMAT2LO mice, with under-expression of VMAT2, were most susceptible to FDM. VMAT2LO mice developed significant myopic shifts to FD after one week compared to VMAT2HI and WT mice (VMAT2LO: −5.48 ± 0.54D; VMAT2HI: −0.52 ± 0.92D, p < 0.05; WT: −2.13 ± 0.78D, p < 0.05; ungoggled control: −0.22 ± 0.24D, p < 0.001). These results indicate that endogenously increasing DA synthesis and release by genetic and pharmacological methods prevents FDM in mice.

Complete transcriptome assembly and annotation of a critically important amphipod species in freshwater ecotoxicological risk assessment: Gammarus fossarum

Because of their crucial role in ecotoxicological risk assessment, amphipods (Crustacea) are commonly employed as model species in a wide range of studies. However, despite their ecological importance, their genome has not yet been completely annotated and molecular mechanisms underlying key pathways, such as the serotonin pathway, in development of ecotoxicological biomarkers of exposure to neuroactive pharmaceuticals are still poorly understood. Furthermore, genetic similarities and discrepancies with other model arthropods (e.g., Drosophila melanogaster) have not been completely clarified. In this report, we present a new transcriptome assembly of Gammarus fossarum, an important amphipod species, widespread in Central Europe. RNA-Seq with Illumina HiSeq technology was used to analyse samples extracted from total internal tissues. We used the Trinity and Trinotate software suites for transcriptome assembly and annotation, respectively. The quality of this assembly and the affiliated targeted homology searches greatly enrich the molecular knowledge on this species. Because of the lack of publicly available molecular information on the serotonin pathway, we also highlighted sequence homologies and divergences of the genes encoding the serotonin pathway components of the well-annotated arthropod D. melanogaster, and Crustacea with the corresponding genes of our assembly. An inferior number of hits was found when running a BLAST analysis of both D. melanogaster and Crustacea mRNA sequences encoding serotonin receptors available in GenBank against the total assembly, compared to other serotonin pathway components. A lack of information on important components for serotonin biosynthesis and vesicle endocytosis (i.e., tryptophan hydroxylase and vesicular monoamine transporter) in Crustacea was also brought to light. Our results will provide an extensive transcriptional resource for this important species in ecotoxicological risk assessment and highlight the need for a more detailed categorization of neuronal pathways components in invertebrates.