Amineptine: its effect on the dopaminergic system of rats

Pharmacological Treatment of Methamphetamine/Amphetamine Dependence: A Systematic Review

BACKGROUND

Stimulant drugs are second only to cannabis as the most widely used class of illicit drug globally, accounting for 68 million past-year consumers. Dependence on amphetamines (AMPH) or methamphetamine (MA) is a growing global concern. Yet, there is no established pharmacotherapy for AMPH/MA dependence. A comprehensive assessment of the research literature on pharmacotherapy for AMPH/MA dependence may inform treatment guidelines and future research directions.

METHODS

We systematically reviewed the peer-reviewed literature via the electronic databases PubMed, EMBASE, CINAHL and SCOPUS for randomised controlled trials reported in the English language examining a pharmacological treatment for AMPH/MA dependence or use disorder. We included all studies published to 19 June 2019. The selected studies were evaluated for design; methodology; inclusion and exclusion criteria; sample size; pharmacological and (if included) psychosocial interventions; length of follow-up and follow-up schedules; outcome variables and measures; results; overall conclusions and risk of bias. Outcome measures were any reported impact of treatment related to AMPH/MA use.

RESULTS

Our search returned 43 studies that met our criteria, collectively enrolling 4065 participants and reporting on 23 individual pharmacotherapies, alone or in combination. Disparate outcomes and measures (n = 55 for the primary outcomes) across studies did not allow for meta-analyses. Some studies demonstrated mixed or weak positive signals (often in defined populations, e.g. men who have sex with men), with some variation in efficacy signals dependent on baseline frequency of AMPH/MA use. The most consistent positive findings have been demonstrated with stimulant agonist treatment (dexamphetamine and methylphenidate), naltrexone and topiramate. Less consistent benefits have been shown with the antidepressants bupropion and mirtazapine, the glutamatergic agent riluzole and the corticotropin releasing factor (CRF-1) antagonist pexacerfont; whilst in general, antidepressant medications (e.g. selective serotonin reuptake inhibitors [SSRIs], tricyclic antidepressants [TCAs]) have not been effective in reducing AMPH/MA use.

CONCLUSIONS

No pharmacotherapy yielded convincing results for the treatment of AMPH/MA dependence; mostly studies were underpowered and had low treatment completion rates. However, there were positive signals from several agents that warrant further investigation in larger scale studies; agonist therapies show promise. Common outcome measures should include change in use days. Future research must address the heterogeneity of AMPH/MA dependence (e.g. coexisting conditions, severity of disorder, differences between MA and AMPH dependence) and the role of psychosocial intervention.

Do antidepressants have any potential to cause addiction?

Addiction/dependence is a syndrome in which the hallmark is a compulsive pattern of drug use. Most authorities do not regard antidepressants as causing addiction but this has been challenged. This debate is explored drawing on case reports and related clinical and pharmacological data. An extensive literature review identified 21 English language case reports of antidepressant addiction (DSM-IV 'substance dependence' criteria) published since 1963. Sixteen involved tranylcypromine or amineptine and may reflect their dopaminergic and stimulant properties. Subject characteristics included male sex (14/21), personality problems (10/21) and prior substance misuse (14/21). Withdrawal or discontinuation symptoms have long been recognized with antidepressants but other features of addiction such as tolerance and compulsive use are exceptionally rare. Common clinical problems are patients taking subtherapeutic dosages and prematurely stopping antidepressants. The pharmacodynamic profiles of most antidepressants and the absence of acute 'desirable' effects make addiction theoretically unlikely. It is concluded that, with the exception of tranylcypromine and amineptine, antidepressants do not have a clinically significant liability to cause addiction. Tranylcypromine and amineptine should be avoided in those with a history of substance misuse. Patients prescribed other antidepressants should be told that they are not addictive.

Amphetamine withdrawal: II. A placebo-controlled, randomised, double-blind study of amineptine treatment

OBJECTIVE

The aim of this study was to examine the benefits of amineptine, a dopamine agonist antidepressant, in treating amphetamine withdrawal.

METHOD

Inpatients with amphetamine withdrawal were recruited to participate in this placebo-controlled, randomised, double-blind, parallel group, 2-week comparison of amineptine and placebo treatments. The treatment effects were evaluated by means of the self-administered Amphetamine Withdrawal Questionnaire (AWQ) and the interviewer-administered Clinical Global Impression (CGI) scale. An intention-to-treat analysis was applied to evaluate the therapeutic effects at the end of week 1 and week 2.

RESULTS

Twenty-two patients took part in each treatment group. The week-1 and week-2 intention-to-treat analyses showed that the mean AWQ reversed vegetative scores (combined scores of decreased energy, increased appetite and craving for sleep items) of the amineptine group were significantly lower than those of the placebo group. The general condition of the amineptine group assessed by CGI also significantly improved at the end of week 2. Although the discontinuation rate due to dissatisfaction with treatment of amineptine group (1/21) was much lower than that of placebo group (6/22), those rates were not significantly different (p = 0.09).

CONCLUSIONS

Amineptine is specifically effective for treating a major component of amphetamine withdrawal: a reversed vegetative syndrome. Although more than 2 weeks of amineptine treatment may contribute further benefits, both risks and benefits should be taken into account in doing so.

Amineptine, response timing, and time discrimination in the albino rat

Experiment 1 recorded the effects of single (doses of 1, 5, 10, and 20 mg/kg) and repeated intraperitoneal injections (10 mg/kg) of amineptine (a tricyclic antidepressant drug) on the performance of albino rats in differential reinforcement of low rate (DRL) of 30 s, fixed-interval (FI) of 60 s, and signalled continuous reinforcement (CRF-SD) schedules. In the second experiment, the effects of repeated (10 mg/kg) and single injections (20 mg/kg) were assessed on the discrimination of the duration of auditory stimuli (2 and 8 s). A dose-related increase in response rates was observed in FI and DRL, correlating with a dose-related impairment in the temporal regulation of performance. However, the drug remained without effect on duration discrimination. In other respects, decreases in response latency in CRF-SD or duration discrimination tended to indicate that the drug improved vigilance and reactivity to extraneous significant stimuli. Interpretations in terms of sensitization, tolerance, or dependency could be discarded. Our data support the hypothesis that drug effects on temporal regulation in FI and DRL are secondary to a nonspecific activation of motor activity. They question the plausibility of an antidepressant effect of the drug in humans via modulation of a timing mechanism.

Ascorbic acid and atypical antipsychotic drugs: modulation of amineptine-induced behavior in mice

To provide a detailed characterization of individual kinds of behavior produced by ascorbic acid in combination with typical (haloperidol) or atypical (clozapine, sulpiride and remoxipride) antipsychotic drugs, the 'open-field' test was selected. Amineptine, an indirect dopamine agonist, was used as an explicit model of dopaminergic activity. Results showed that amineptine (5-10-20 mg/kg i.p.), dose-dependently, increased ambulation and rearing. Ascorbic acid (62.5-125-250 mg/kg i.p.) markedly inhibited the behavior of mice as well as the amineptine-induced hyperactivity. A combination of each typical or atypical antipsychotic drug (except clozapine 2.5 mg/kg i.p.) with amineptine (20 mg/kg i.p.) induced a significant increase in ambulation and rearing over that seen with the antipsychotic drugs alone. The combination of antipsychotic drugs with ascorbic acid 250 mg/kg i.p. led to a decrease in open-field parameters when compared with controls. In conclusion, these data provide further in vivo support for the effect of ascorbic acid on dopaminergic system and demonstrate that the antidopaminergic effects of both typical and atypical antipsychotic drugs may be enhanced with concurrent administration of ascorbic acid.

Amineptine improves the performance of dogs in a complex temporal regulation schedule

Amineptine is a tricyclic antidepressant with activating properties, that stimulates spontaneous locomotor activity in rodents and elevates mood in humans. It mainly inhibits dopamine uptake and weakly increased dopamine release. Formulating the hypothesis that this drug would decrease waiting capacity, we decided to test amineptine in a Differential Reinforcement of Response Duration schedule (DRRD 9 s Limited Hold 1.5 s) in the dog. The drug was administered orally at 2.5, 5.0, 7.5, 10 and 20 mg/kg, 1 h before the experimental session. Between 2.5 and 10 mg/kg, amineptine improved the performance by increasing the response (nonsignificantly) and reinforcement (significantly) rates and by increasing the peak of correct responses (significantly). The inverse effect was measured for the reinforcement rate (nonsignificantly) and for the peak of correct responses (significantly) at the dose of 20 mg/kg. These results were compared to those obtained with other classes of drugs, like neuroleptics, barbiturates or anxiolytics, that disturbed the performance, and particularly with low doses of neuroleptics, which also increase the dopamine release. The positive effects of amineptine on performance (2.5-10 mg/kg) were related to its inhibitory effect on dopamine uptake and discussed in terms of improved vigilance and attention, increase of waiting capacity, improved anticipation, and cognitive enhancement.

Metabolism of amineptine in rat, dog and man

After oral administration of amineptine (7-[(10-11)-dihydro-5H-dibenzo(a,d)cycloheptane-5yl] amino heptanoic acid), an original tricyclic antidepressant, seven metabolites were isolated from urine and plasma of rat, dog and man. The metabolic pathways were similar for the three species studied. The two major pathways consisted of the beta-oxidation of the heptanoic side chain leading to pentanoic (first step) and propanoic (second step) side chain metabolites and the hydroxylation of the dibenzocycloheptyl ring on carbon atom 10 (C10) causing the formation of two diastereoisomers. Lactamization by internal dehydration of beta-oxidized metabolites appeared to be a minor route of biotransformation. Conjugation reactions were of minor importance in the rat, in contrast to findings for dog and man. Urinary elimination was the major route of excretion in man while in dog and in rat faecal excretion was predominant.

An open field study of antidepressant drugs

Eight psychotropic drugs, mainly acting on the catecholaminergic systems, were investigated in an open field setting. All drugs but one showed a significant reduction in overall activity over time. Only piribedil at 32 mg/kg showed an increase, while 2 mg/kg showed a decrease over time. Amineptine and nomifensine significantly increased and salbutamol significantly decreased both ambulation and rearing with dose. For viloxazine, metapramine, piribedil and piracetam no significant dose effects were revealed at the doses tested. It is concluded that no clear correlation between clinically reported antidepressant efficacy and the selected open field variables can be demonstrated. However, some of the dopaminergic drugs have substantial activating properties, which might render them dependence-producing properties.

Modulation of striatal dopamine metabolism by the activity of dorsal raphe serotonergic afferences

Serotonin (5-HT)-dopamine (DA) interaction was studied in the caudate nucleus after electrical stimulation of the dorsal raphe (DR), an area containing 5-HT cell bodies and sending afferences to nigrostriatal dopaminergic neurons. The DR was stimulated by means of a bipolar stainless steel electrode for 16 min (10 Hz, 0.6 ms, 200 microA). 5-HT and DA metabolism were monitored before, during and after stimulation by in vivo differential pulse voltammetry. This electrochemical technique uses carbon fiber electrodes implanted in brain areas to record oxidation peaks corresponding to extracellular 5-hydroxyindolacetic acid (5-HIAA) and dihydroxyphenylacetic acid (DOPAC). Changes in the concentrations of the metabolites were recorded every 2 min in freely moving rats. Both 5-HIAA and DOPAC increased in the first minutes after the beginning of stimulation, the rise lasting 30 min after the end. That DR was closely involved was borne out by the fact that stimulation in the surrounding areas had no effect on either metabolite. Classical biochemical determinations in tissue samples were also used to study the effect on DA release: 3-methoxytyramine (3-MT) levels, measured in basal conditions and after blockade of its degradation by pargyline, were not changed, indicating that DR stimulation, though increasing DA metabolism, does not affect release. However, modulation of DA transmission by 5-HT afferences seems possible in certain circumstances. This 5-HT-DA interaction appears to be presynaptic (on dopaminergic terminals or cell bodies) since it is not prevented by kainic acid degeneration of striatal neurons.

Differences in the effect of the antidepressant amineptine on striatal and limbic DOPAC measured by HPLC-ECD and in vivo voltammetry

The acute effect of the antidepressant amineptine was studied in two dopaminergic areas, the striatum and the limbic system, by in vivo voltammetry. This electrochemical technique uses carbon fibre electrodes implanted in brain areas of non-anaesthetized freely moving rats to measure DOPAC diffusing from the neurons. In vivo voltammetry recordings showed that amineptine induced a slight and transient decrease in DOPAC levels in the caudate nucleus but a persistent, clear-cut decrease in the nucleus accumbens. These results were confirmed by classical biochemical determination in tissue samples. The findings indicate the possible importance of the limbic area in the mechanism of action of amineptine.