Tesofensine, a novel triple monoamine re-uptake inhibitor with anti-obesity effects: dopamine transporter occupancy as measured by PET

Tesofensine (TE) is a novel triple monoamine re-uptake inhibitor inducing a potent inhibition of the re-uptake process in the synaptic cleft of the neurotransmitters dopamine, norepinephrine, and serotonin. In recent preclinical and clinical evaluations TE showed a robust anti-obesity effect, but the specific mechanism of this triple monoamine re-uptake inhibitor still needs to be further elucidated. This positron emission tomography (PET) study, using [¹¹C]βCIT-FE, aimed to assess the degree of the dopamine transporter (DAT) occupancy, at constant TE plasma levels, following different oral, multiple doses of TE during totally 8-12 days. In addition, the relationships between DAT occupancy and TE plasma concentrations, or doses, were investigated to enable assessment of DAT occupancies in subsequent clinical trials. The results demonstrated that TE induced a dose-dependent blockade of DAT following multiple doses of 0.125-1 mg TE at anticipated steady-state conditions. The mean striatal DAT occupancy varied dose-dependently between 18% and 77%. A sigmoid E(max) model well described the relationship between striatal DAT occupancy and TE plasma concentrations or doses. It was estimated that the maximum achievable DAT occupancy was about 80% and that half of this effect was accomplished by approximately 0.25 mg TE and a plasma drug concentration of 4 ng/ml. The results indicated an important mechanism of action of TE on DAT. Further, these results suggest that the previously reported dose-dependent weight loss, in TE treated subjects, was in part mediated by an up-regulation of dopaminergic pathways due to enhanced amounts of synaptic dopamine after blockade of DAT.

Anti-hypertensive treatment preserves appetite suppression while preventing cardiovascular adverse effects of tesofensine in rats

OBJECTIVE

Tesofensine is a novel triple monoamine reuptake inhibitor which is in development for the treatment of obesity. Preclinical and clinical data suggest that appetite suppression is an important mechanism by which tesofensine exerts its robust weight reducing effect. Notably, the strong hypophagic response to tesofensine treatment is demonstrated to be linked to central stimulation of noradrenergic and dopaminergic neurotransmission. The sympathomimetic mode of action of tesofensine may also associate with the elevated heart rate and blood pressure observed in clinical settings, and we therefore sought experimentally to address this issue.

DESIGN AND METHODS

The anorexigenic and cardiovascular effects of tesofensine were studied simultaneously in telemetrized conscious rats in a combined real-time food intake and cardiovascular telemetry monitoring system.

RESULTS

Acute administration of tesofensine caused a dose-dependent hypophagic effect as well as increased heart rate and blood pressure. Interestingly, combined treatment with metoprolol (b1 adrenoceptor blocker, 10-20 mg/kg, p.o.) fully prevented the cardiovascular sympathetic effects of tesofensine while leaving the robust inhibitory efficacy on food intake unaffected. Similarly, the angiotensin AT1 receptor antagonist telmisartan (1.0-3.0 mg/kg, p.o.) did not interfere with the anti-obesity effects of tesofensine, however, telmisartan only partially reversed the increase in systolic blood pressure and had no effect on the elevated heart rate induced by tesofensine.

CONCLUSION

These data suggests that tesofensine causes elevations in heart rate and blood pressure by increasing sympathetic activity, and that different adrenoceptor subtypes may be responsible for the anti-obesity and cardiovascular effects of tesofensine.

A water lick conflict paradigm using drug experienced rats

A modified water-lick conflict paradigm is described, using trained rats for up to 35 weekly test sessions under 48 h of water deprivation. The rats rapidly became maximally suppressed by the punishment. This suppression was attenuated by the anxiolytics lorazepam, diazepam, phenobarbital, and meprobamate. The potentially anxiolytic drug CL 218872 and the anticonvulsant drug valproate sodium were also active. The antiserotonin drugs methysergide, cyproheptadine, cinanserin and parachlorophenylalanine were all inactive, as were several several other distinct classes of psychotropic drugs including propranolol, clonidine, THIP, theophylline, chlorpromazine, paroxetine and ethanol. The paradigm proved reliable, reproducible and useful for large scale investigations. Furthermore, it may provide means for detailed neuropharmacological and anatomical studies.

Inhibition of apomorphine-induced climbing in mice by cholinergic drugs and neuroleptics

Apomorphine (ap) was administered subcutaneously to mice kept in individual cages. Ap elicited an abnormal vertical climbing behaviour. The muscarinomimetics physostigmine and oxotremorine as well as the neuroleptics clozapine and haloperidol inhibited the climbing produced by ap 1 mg/kg. A small inactive dose of physostigmine potentiated the effect of clozapine but not that of haloperidol. The anticholinergic atropine antagonized the effect of physostigmine, oxotremozine, clozapine and haloperidol. The climbing behaviour produced by ap is presumably due to stimulation of dopamine receptors and this effect can be antagonized either by blockade of dopamine receptors or by activation of muscarinic receptors. Some lines of evidence suggest that the ap-inhibitory effect of clozapine may be partly due to a muscarinomimetic effect.

Influence of the new 5-HT-uptake inhibitor paroxetine on hypermotility in rats produced by p-chloroamphetamine (PCA) and 4,alpha-dimethyl-7-tyramine (H 77/77)

Two different forms of hypermotility produced by the amphetamine derivatives PCA and H 77/77, 5 mg/kg of each, was studied in rats treated s.c. with the new 5-HT uptake inhibitor paroxetine. The substance inhibited the effect of PCA but did not influence that of H 77/77. The 5-HT-uptake inhibitors paroxetine, imipramine, and chlorimipramine were also administered p.o. at various times before PCA. The three substances inhibited PCA-induced hypermotility. Paroxetine 0.5-2 mg/kg, was active at intervals of 1-4 h and 4 mg/kg was active at 18-h interval. Imipramine and chlorimipramine 25-30 mg/kg showed PCA inhibition at treatment intervals of 1-2h, but 80-100 mg/kg or more was required to inhibit PCA at intervals of 4 and 18 h. Previous results have shown that PCA-induced hypermotility is antagonized by substances inhibiting 5-HT synthesis and uptake, whereas H 77/77-induced hypermotility is inhibited by substances blocking NA synthesis, uptake, and receptors. The previous and present results indicate that paroxetine is a selective 5-HT-uptake inhibitor. After oral administration paroxetine presumably produces a more potent and long-lasting 5-HT-uptake inhibition than imipramine and chlorimipramine.

Evidence for a noradrenergic mechanism in the grooming produced by (+)-amphetamine and 4, alpha-dimethyl-m-tyramine (H 77/77) in rats

Rats were kept on a 12-h light-dark cycle. One hour after the light was switched on, physiological saline, (+)-amphetamine 1 mg/kg, and H 77/77 5 mg/kg were injected s.c.; the number of groomings was counted 1-2 h after the treatments. (+)-Amphetamine and H 77/77 produced increased grooming which was antagonized by the tyrosine hydroxylase inhibitor H 44/68 (250 mg/kg), the dopamine-beta-hydroxylase inhibitor FLA 63 (40), the neuroleptics haloperidol (0.1 and 0.5), and clozapine (1 and 5). The (+)-amphetamine-induced grooming was also antagonized by the NA-receptor blocker aceperone (10) but not by the sedative phenothiazines mepazine (10) and diphenhydramine (20) nor diazepam (1). These results indicate that NA-release is involved in the mediation of (+)-amphetamine- and H 77/77-induced grooming. The inhibition of haloperidol and clozapine is presumably due to NA-receptor blockade.

Inhibition and potentiation of apomorphine-induced hypermotility in rats by neuroleptics

The effect of apomorphine (ap) was investigated in rats kept in a familiar cage; 0.25-5 mg/kg s.c. produced a short-lasting, abnormal hypermotility consisting mainly of locomotion and sniffing without grooming. Ap was administered to rate pretreated s.c. with various drugs. Ap hypermotility was antagonized by 12 neuroleptics from different chemical groups. The ap inhibitory effect of 5 neuroleptics was decreased when the interval between pretreatment and ap administration was increased from 0.5 to 4 hr. Clozapine was the only neuroleptic showing no inhibition but potentiation at 4 hr. Mepazine, a phenothiazine lacking antipsychotic effects, as well as the NA receptor blockers aceperone and phenoxybenzamine, did not inhibit ap hypermotility. Ap was also given 24 hr after haloperidol and clozapine. At this time both neuroleptics showed ap potentiation. The ap inhibition and potentiation after a single administration of the neuroleptics is presumable due to selective blockade and subsequent supersensitivity of some DA receptors.

Comparative studies of a new 5HT-uptake inhibitor and some tricyclic thymoleptics

The new 5HT-uptake inhibitor, FG 4963, and some tricyclic thymoleptics antagonized p-chloroamphetamine (PCA)-induced hypermotility in rats. FG 4963 was active in about the same s.c. and p.o. doses as chlorimipramine. FG 4963, imipramine and chlorimipramine potentiated hypermotility induced in mice by the 5HT precursor 5HTP, FG 4963 being slighly more active than chlorimipramine. In contrast to the tricyclic thymoleptics FG 4963 did not potentiate the heart rate increasing effect of NA in pithed rats. The peripheral anticholinergic effect of FG 4963 and of desipramine was almost identical while the other imipramine derivatives were more active. All tricyclic thymoleptics were strong peripheral antihistaminics, but FG 4963 was almost devoid of this action. Acute tests for ECG changes in guinea pigs and toxicity in mice and rats showed that FG 4963 and chlorimipramine were less toxic than imipramine and amitriptyline. FG 4963 is presumably a selective 5HT-uptake inhibitor producing much less potentiation of peripheral sympathetic mechanisms than do the tricyclic antidepressants.

Neurochemical and pharmacological studies on a new 5HT-uptake inhibitor, FG4963, with potential antidepressant properties

A new phenylpiperidine derivative, FG4963, and several tricyclic antidepressants were compared in various in vitro and in vivo tests for central 5HT- and NA-uptake inhibition. FG4963 was found to be a 5HT-pump blocker with activity similar to that of chlorimipramine. FG4963 inhibited NA-uptake less than the most potent tricyclic thymoleptics. In contrast to imipramine derivatives FG4963 was a weak inhibitor of peripheral NA-uptake. FG4963 seems to produce central 5HT-potentiation without affecting organ functions regulated by the autonomic nervous system as much as tricyclic antidepressants.

The inhibition of A and B forms of MAO in the production of a characteristic behabioural syndrome in rats after 1-tryptophan loading

1-Tryptophan was administered to rats pretreated with selective inhibitors of the A and B forms of MAO deprenyl, a selective inhibitor of MAO-B, produced minor changes in behaviour and in the concentrations of apparent 5-HT and 5-HAA in brain. High doses of clorgyline, a selective inhibitor MAO-A, produced a characteristic stereotyped syndrome of hypermotility and tremor as well as an increase in apparent 5-HT and a decrease in apparent 5-HIAA in brain. Small doses of deprenyl and clorgyline in combination, but not singly, produced maximal effects on behaviour as well as on the concentrations of apparent 5-HT and 5-HIAA in brain. Maximum behavioural and biors before the other. It is concluded that the syndrome may be dependent on the formation of an N-substituted derivative of 5-HT which is at least partly deaminated by MAO-B. Alternatively, the syndrome may be dependent on a sufficiently high concentration of 5-HT in a special compartment where it is partly deaminated by MAO-B.