Tetrabenazine Research Articles

A Chimeric Vesicular Monoamine Transporter Dissociates Sensitivity to Tetrabenazine and Unsubstituted Aromatic Amines

Publisher Summary Two isoforms of the human vesicular monoamine transporter (hVMAT1 and hVMAT2) have recently been cloned and shown to differ with respect to their tissue distribution, substrate affinity, and sensitivity toward various inhibitors, including neurotoxic and psychoactive compounds. Functional chimeras have been constructed between hVMATl and hVMAT2 to identify domains responsible for the observed pharmacologic differences between these proteins. Tetrabenazine (TBZ) and two unsubstituted aromatic amines—amphetamine and histamine—have been evaluated because of the marked differences in their interaction with hVMAT1 and hVMAT2. The ability of these compounds to inhibit or compete with [ 3 H]serotonin (SHT) for uptake by hVMAT1 or hVMAT2 was measured after expression in digitonin-permeabilized fibroblastic (CV-1) cells. The affinity of hVMAT2 and hVMAT1 for [ 3 H]SHT was similiar. The specific interactions of substrates, inhibitors, neurotoxins, and psychoactive substances with VMAT1 and VMAT2 may facilitate a basic understanding of the molecular mechanisms of vesicular H + /monoamine antiport. Conserved Asp residues are predicted to lie within putative transmembrane domain (TMD) I, VI, X, and XI. It is likely that these putative TMDs, and perhaps others, participate in the formation of a gated pore through which protonated substrates and H + ions are exchanged.

TJS-010, a new prescription of oriental medicine, antagonizes tetrabenazine-induced supression of spontaneous locomotor activity in rats

1. 1.The authors have determined the effect of TJS-010, a new prescription of oriental medicine, on the locomotor activity in rats. 2. 2.Tetrabenazine(TBZ) decreased the spontaneous locomotion in rats, and attenuated the contents of amines and increased their metabolism in various regions in rat brain. 3. 3.TJS-010 inhibited the locomotor suppression induced by TBZ: however, neither amine contents nor their metabolism was not altered, which suggested that TJS-010 postsynaptically modulated the transmission or transduction. 4. 4.Imipramine also inhibited the decrease in locomotion induced by TBZ. 5. 5.Thcse results suggest a possibility that TJS-010 has an antidepressive effect.

Amino- and amido-tetrabenazine derivatives: Synthesis and evaluation as potential ligands for the vesicular monoamine transporter

Tetrabenazine (TBZ) and dihydrotetrabenazine are well known inhibitors of the CNS vesicular monoamine transporter (VMAT), which is responsible for the packaging of monoamine neurotransmitters in presynaptic vesicles. Amino and amido derivatives of tetrabenazine were prepared as potential ligands for the vesicular monoamine transporter. Ultimately, organotin derivatives of promising ligands were prepared for radiolabeling with 125I. The compounds were evaluated for their ability to inhibit the specific binding of a selective radioligand to the transporter in rat striatal homogenates. Of the compounds evaluated, three amine derivatives of TBZ (primary, secondary and tertiary) were found to have modest to high affinity for the transporter, while two amides exhibited low to undectable affinity. The secondary propargyl amine was found to possess the highest affinity ( K i = 7.6 nM) and was chosen for further evaluation. The organotin derivative of this compound was synthesized in order to prepare the corresponding radioiodinated ligand. However, our inability to synthesize and characterize the iodinated amine precluded its evaluation as a potential radioiodinated ligand for the transporter. Alternative approaches for decreasing the lipophilicity of TBZ analogs while maintaining high binding affinity are currently being explored.

Binding of 125I-iodovinyltetrabenazine to CNS vesicular monoamine transport sites.

Binding characteristics of a novel radioiodinated tetrabenazine (TBZ) analog (iodovinyltetrabenazine; 125I-TBZ-Fraction I) were evaluated. In rat striatal homogenates, 125I-TBZ-I displayed a pharmacological profile consistent with specific binding to vesicular monoamine transport (VMAT) sites. In vitro autoradiographic studies using rat brain sections further demonstrated that 125I-TBZ-I labeled the regions rich in VMAT sites, and it may be a useful marker for these sites. This novel radioiodinated ligand, with high specific activity and high binding affinity, may provide a powerful tool for the in vitro assessment of neuronal loss in various neurodegenerative diseases.

The Human Platelet Dense Granule: Serotonin Uptake, Tetrabenazine Binding, Phospholipid and Ganglioside Profiles

The functioning and composition of human platelet dense granules were studied using granules purified by Percoll fractionation. Reserpine-blockable serotonin (5-HT) uptake by the dense granule fraction was characterized and also demonstrated in the crude membrane fraction. Tetrabenazine (TBZ)-displaceable [ 3H]ketan-serin binding was used to label the granular 5-HT transporter. Scatchard analyses, Hill plots, displacement curves, and binding kinetics indicated that TBZ-displaceable [ 3H]ketanserin binding labeled a site similar to that previously reported for chromaffin granules and synaptic vesicles. Analysis of phospholipid profiles in platelet fractions revealed that most platelet lysolecithin was associated with the dense granule fraction. Ganglioside analysis indicated that the predominant platelet ganglioside, GM 3, was highly enriched in the dense granule fraction. The data lend further support to the idea that the 5-HT transporter complex is similar in platelet dense granules, chromaffin granules, and synaptic vesicles. However, the ganglioside and phospholipid findings clearly distinguish the types of storage sites and raise questions concerning the functional roles of dense granule GM 3 and lysolecithin.

Synthesis of [ 11C]tetrabenazine, a vesicular monoamine uptake inhibitor, for PET imaging studies

Tetrabenazine (TBZ), a high affinity and specific inhibitor of the vesicular monoamine transporter, has been labeled with carbon-11 as a potential probe for in vivo positron emission tomographic imaging of monoaminergic neuronal losses in neurodegenerative diseases. [ 11C]TBZ was synthesized by O-[ 11C]methylation of the 9- O-desmethylTBZ using [ 11C]methyl iodide in the presence of tetrabutyl-ammonium hydroxide. The radiochemical yields were 35–55% (decay corrected) and the synthesis time 32–37 min from EOB. [ 11C]TBZ was obtained with specific activities of 2000–2500 Ci/mmol (EOS) and radiochemical and chemical purities were >95%. [ 11C]Tetrabenazine is a promising new radioligand for the in vivo study of monoaminergic neurons using PET.

The correlated blanching of synaptic bodies and reduction in afferent firing rates caused by transmitter-depleting agents in the frog semicircular canal

Synaptic bodies (SBs) associated with rings of synaptic vesicles and well-defined, pre-and post-synaptic membrane structures are indicators of maturity in most hair cell-afferent nerve junctions. The role of the SBs remains elusive despite several experiments showing that they may be involved in storage of neurotransmitter. Our results demonstrate that SBs of the adult posterior semicircular canal (SCC) cristae hair cells become less electron dense following incubation of the SCC with the transmitter-depleting drug tetrabenazine (TBZ). Objective quantification and comparison of the densities of the SBs in untreated and TBZ-treated frog SCC demonstrated that TBZ significantly decreased the electron density of SBs. This reduction in electron density was accompanied by a reduction in firing rates of afferent fibers innervating the posterior SCC. A second transmitter-depleting drug, guanethidine, previously shown to reduce the electron density of hair cell SBs, also reduced the firing rates of afferent fibers innervating the posterior SCC. In contrast, the electron density of dense granules (DG), similar in size and shape to synaptic bodies (SB) in hair cells, did not change after incubation in TBZ, thus indicating that granules and SBs are not similar in regard to their electron density. The role of SBs in synaptic transmission and the transmitter, if any, stored in the SBs remain unknown. Nonetheless, the association of the lessening of electron density with a reduction in afferent firing rate provides impetus for the further investigation of the SB's role in neurotransmission.

An in vivo alpha-2 assay reversal of opioid-induced muscular rigidity and neuroleptic-induced ptosis

A method is described to detect selective α-2 adrenergic agonists in vivo. Palpebral ptosis is induced in rats by the neuroleptic agent haloperidol (Hal), or by tetrabenazine (TBZ) methanesulfonate. Twenty minutes later, test compounds are injected, and ptosis is scored. In a separate test, muscular rigidity is induced by the opioid, fentanyl, and subsequently, test compounds are assessed for their ability to reverse muscular rigidity. Results indicate that only α-2 agonists reliably reverse neuroleptic-induced and TBZ-induced ptosis, as well as opioid-induced rigidity. An α-1 antagonist reversed only rigidity, whereas, α-2 antagonists and β-agonists were generally ineffective in all tests. Therefore, the ability to reverse neuroleptic and TBZ-induced ptosis along with the ability to reverse opioid-induced muscular rigidity is a characteristic unique to α-2 agonists.

Serotonergic effects on carbonic anhydrase activity in the choroid plexus

The carbonic anhydrase (CA) activities in the choroid plexus of dogs were investigated by electron microscopy, and the effects of 5-hydroxytryptophan (5-HTP) on them were examined to elucidate the participation of serotonin in the production of cerebrospinal fluid. The reaction products yielded by the method employed proved to be CA activity by elimination tests using acetazolamide (Diamox). Following administration of 5-HTP, the CA activities fell to 43.3% of the control value, that is, approximately 56% of the CA activities in the choroid plexus were affected by serotonin. When tetrabenazine (TBZ) was administered, the CA activities in the choroid plexus decreased to 22.4% of the control value. These results suggest that the CA activity in the choroid plexus is remarkably suppressed when nervous control of the choroid plexus is disturbed by the administration of a monoamine denervator such as TBZ. The present data indicate that the serotonergic inhibitory effect on the CA activity in the choroid plexus may be less predominant than that of TBZ and acetazolamide.

125I]MIBG uptake and release in different regions of the rat brain

Radioiodinated m-iodobenzylguanidine ([ 125I]MIBG) and tritiated norepinephrine ([ 3H]NE]) uptake and release were compared, in different regions of the brain of the rat. The classification of the regions according to uptake was the same for both tracers: striatum > hypothalamus > hippocampus > cortex > brainstem. Tetrabenazine (TBZ), a granular monoamine uptake inhibitor reduced the uptake in the different regions. The inhibition rate was higher for [ 3H]NE uptake than for [ 125I]MIBG. The spontaneous release was the same for [ 125I]MIBG and [ 3H]NE and was the lowest in the striatum. The K + stimulated release of [ 3H]NE was more complete than the release of [ 125I]MIBG and was the most important in the striatum. From these results, it is inferred that MIBG enters the brain tissue via NE uptake mechanisms. It appears that MIBG is stored in the chromaffin granules, as NE, but also in the cytoplasm. A modified molecule derived from MIBG which would cross the blood-brain barrier, would then appear as a potential scintigraphic marker of monoamine uptake, storage and release.

Reserpine binding to chromaffin granules suggests the existence of two conformations of the monoamine transporter

The binding of [3H]reserpine ([3H]RES) to purified bovine chromaffin granule membranes has been studied at low membrane concentration. Saturation isotherms indicated a dissociation equilibrium constant KD of 30 pM and a density of binding sites of 8 pmol/mg of protein at 30 degrees C. The association rate constant was 4.0 X 10(5) M-1 s-1, and the calculated dissociation rate constant was 1.2 X 10(-5) s-1, corresponding to a half-lifetime of about 16 h. Although this dissociation was too low to be measured directly, [3H]RES binding was indeed reversible since it was lost after addition of the detergent Triton X-100. Dihydrotetrabenazine (TBZOH) inhibited [3H]RES binding in a time-dependent manner, EC50 varying from 37 nM after a 1-h incubation to 600 nM after 16 h. On the contrary, [3H]RES binding inhibition by the substrate noradrenaline was time independent. It is proposed that the transporter exists in two different conformations which bind exclusively either tetrabenazine (TBZ) or RES and which are in equilibrium. The effects of detergents were consistent with this two-conformation model. The transporter solubilized by cholate bound [3H]TBZOH, but not [3H]RES. On the other hand, addition of cholate to membrane-bound [3H]RES solubilized the membrane without releasing the ligand from its binding site. It is proposed that the TBZ-binding conformation is obtained by solubilization with cholate and that RES stabilizes the RES-binding conformation, allowing its solubilization by this detergent.

Pharmacologie moléculaire du transporteur des catécholamines des granules chromaffines de la médullo-surrénale bovine

Tetrabenazine (TBZ) and reserpine are two inhibitors of the catecholamine uptake system of the chromaffin granule membrane. They are structural analogs of the substrates dopamine and serotonin and they inhibit the monoamine transporter, which catalyzes a H+/neutral amine antiport. [3H]Dihydrotetrabenazine ([3H]TBZOH) is bound by chromaffin granule membranes on one class of site (T sites, KD = 3 nM); [3H]reserpine is bound on T sites and a second class of site (R1 sites, KD = 0.7 nM). The two sites are involved in monoamine translocation. The substrates displace the ligands with different efficiency: noradrenaline (Km = 10 microM) displaces reserpine efficiently (EC50 = 30 microM), but TBZOH poorly (EC50 = 2000 microM); m-iodobenzylguanidine, which has recently been shown to be a substrate of the monoamine uptake system (Km = 5 microM), displaces TBZOH efficiently (EC50 = 25 microM), but reserpine inefficiently (EC50 = 300 microM). Since both substrates are translocated by the same transporter, this result confirms the existence of two sites with different properties. T sites are characterized by a linear relationship between the reciprocal of the dissociation constants of various drugs displacing [3H]TBZOH and their partition coefficient in octanol/H2O mixtures. This relationship, which indicates a hydrophobic environment of T sites, does not exist for R1 sites. T sites have been identified by covalent labeling with a derivative of TBZ coupled to an arylazido group. The labeled sites are borne by a 65,000 dalton protein. The kinetics of reserpine binding are accelerated in the presence of ATP.(ABSTRACT TRUNCATED AT 250 WORDS)

ChemInform Abstract: STRUCTURE‐ACTIVITY STUDIES ON ANTIDEPRESSANT 2,2‐DIARYLETHYLAMINES

AbstractDie nach bekannten Methoden synthetisierten Amine (I) werden auf antidegressive Wirkung untersucht.

P2B0105) - The comparison between the effects of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) and L-erythro-DOPS on tetrabenazine (TBZ)-induced ptosis in mice.

P2B0105) - The comparison between the effects of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) and L-erythro-DOPS on tetrabenazine (TBZ)-induced ptosis in mice.

Cerebromicrocirculatory defects in animal model of depression

In the tetrabenazine (TBZ) model of depression, the cerebromicrocirculation was discovered to respond abnormally to metabolic demand as mimicked by the administration of CO2. Altered responsivity of cerebral blood flow and effective permeability of the blood--brain barrier to changes in PaCO2 were found. These physiologic defects coincided temporally with TBZ-induced depletion of central norepinephrine and dopamine and with the development of the behavioral effects of TBZ (the end points used to test the antidepressant potential of experimental drugs). Pretreatment with amitriptyline (a standard antidepressant and amine reuptake inhibitor) prevented the development of these TBZ-induced abnormalities in the cerebromicrocirculation, just as it prevented the behavioral effects.

Structure-activity studies on antidepressant 2,2-diarylethylamines.

A series of 2,2-diarylethylamine derivatives has been examined for potential antidepressant activity in the tetrabenazine (TBZ) test. Diethanolamine 4 (McN-4187) was one of the more potent compounds despite its polar alcohol functionalities [ED50 values of 15 mg/kg (exploratory activity) and 1.5 mg/kg (ptosis)]. Structure-activity relationships are described. Minor structural modifications of 4 were sufficient to strongly attenuate activity. For example, changing one phenyl group to a 2-thienyl, cyclohexyl, or 3,4-dimethoxyphenyl group greatly reduced activity. Replacing both phenyl groups by 4-chlorophenyl groups also dissipated activity. The bisethanol functionality was not essential for activity (q.v. 17-19 in Table I). Although 17-19 compared well with 4 in the TBZ assay, only 19 (like 4) showed a satisfactory profile in the maximal electroshock seizure threshold test.

Tetrabenazine-induced depletion of brain monoamines: Characterization and interaction with selected antidepressants

The peripheral administration of tetrabenazine (TBZ) induces rapid depletion of brain regional concentrations of norepinephrine (NE), dopamine (DA) and serotonin (5-HT). With respect to both dosage and time, striatal DA was most sensitive to the effects of TBZ while hypothalamic NE was least affected. Pretreatment with the monoamine oxidase (MAO)-inhibitor, clorgyline (1–6 mg/kg) dose-dependently prevented the reduction of all three monoamines for up to 60 min after TBZ (3 mg/kg). The TBZ-induced depletion of cortical NE was also significantly antagonized by desmethylimipramine (DMI) but was of shorter duration (up to 30 min after TBZ). DMI, however, did not influence the effect of TBZ on striatal DA or hypothalamic 5-HT. The protective effects of both clorgyline and DMI were also evident under the conditions of the behavioral TBZ test utilizing high doses of TBZ (20 mg/kg).

Tetrabenazine-induced depletion of brain monoamines: Mechanism by which desmethylimipramine protects cortical norepinephrine

Pretreatment of rats with desmethylimipramine (DMI) (5 mg/kg) significantly antagonized the tetrabenazine (TBZ)-induced (3 mg/kg) depletion of cortical norepinephrine (NE) in rats. This protective effect of DMI was fully blocked by the specific α 2-adrenergic antagonist, RX 781094. The doses of DMI which antagonized the depleting effects of TBZ caused rapid, maximal reductions in cortical dihydroxyphenylalanine (DOPA) accumulation, effects which were also blocked by RX 781094. Like DMI, the α 2-adrenergic agonist, clonidine (50 μg/kg) decreased cortical DOPA accumulation and rapidly prevented the TBZ-evoked loss of NE in this brain region. On the other hand, doses of RX 781094 (0.5-2.0 mg/kg) which accelerated cortical DOPA synthesis, enhanced significantly the depleting effects of a threshold dose of TBZ (0.6 mg/kg). These findings suggest that DMI reduces the rate of TBZ-induced depletion of cortical NE by lowering NE turnover through the indirect stimulation of α 2-adrenoceptors.

Alpha methylparatyrosine and tetrabenazine in movement disorders.

Clinical and experimental evidence suggests that alpha methylparatyrosine (AMPT), an inhibitor of tyrosine hydroxylase, can potentiate the effects of other dopamine antagonists. We therefore treated patients having various forms of dystonia and chorea with tetrabenazine (TBZ), and then added AMPT to determine if further improvement could be obtained. Side effects of both drugs were common, and they often necessitated withdrawal of the drug. Patients with Huntington's chorea and tardive dyskinesia were improved by TBZ. They obtained additional benefit from the combination of AMPT and TBZ. The results in the dystonia patients were disappointing with both drugs. Although a small number of patients did improve, and short- and long-term remissions occurred in a few, most patients with dystonia were not benefited by either drug.

EFFECTS OF TRICYCLIC ANTIDEPRESSANTS ON TETRABENAZINE-INDUCED DEPLETION OF BRAIN MONOAMINES IN RATS. 2. DOPAMINE

AbstractWe studied the effects of tricyclic antidepressants on the tetra-benazine (TB)-induced depletion of brain dopamine (DA) using rats. The test drugs were generally administered orally 3 hours before sacrifice and 2 mg/kg of TB or reserpine (RES) was administered subcutaneously 2 hours before sacrifice. The TB-induced DA depletion was enhanced by pretreatment with desmethylimipramine (DMI, 12.5–100 mg/kg), Imipramine (12.5–100 mg/kg), chlorimipramine (25–100 mg/kg), ami-triptyrine (100 mg/kg), maprotyrine (50 mg/kg) and chlorpromazine (5–20 mg/kg i.p.), while these drugs did not enhance RES-induced depletion. Observations to elucidate the action mechanism of antidepressant-induced enhancement were as follows. After TB administration, brain DA content was at the minimal level at 30 min after and on the way to recovery at 2 hours, but it approached the minimal level at 2 hours after RES administration. DMI pretreatment did not enhance the DA depletion at 0.5 hours after TB administration. In pargyline-pretreated rats, TB produced a decrease of brain DA with an increase of 3-methoxy-tyramine (3-MT), while RES showed only a slight effect on DA and 3-MT up to 2 hours. Amphetamine sulfate (20 mg/kg i.p.) slightly increased, while combinations with DMI decreased brain DA. These results suggest that tricyclic antidepressants inhibit DA reuptake from the synaptic cleft in vivo.