The Differential Effects of Atypical Antipsychotics on Prolactin Elevation Are Explained by Their Differential Blood-Brain Disposition: A Pharmacological Analysis in Rats

Tardive dyskinesia (TD) may occur in never-medicated patients with psychotic illness, indicating the existence of non-medication, possibly disease-related, causes. We tested the hypothesis that, independent of the antipsychotic-induced rise in prolactin, the incidence of TD would be associated with the incidence of prolactin-related sexual disturbances (PRSD), which would be suggestive of a common pathology involving multiple dopamine tracts. Simple, global measures of TD and PRSD (loss of libido, amenorrhea, gynaecomastia, impotence, and galactorrhea) were rated in a prospective, observational European Health Outcomes Study (SOHO). New onset of TD and new onset of PRSD at 3, 6, and 12 months was analyzed in a risk set of 4263 patients using a Cox proportional hazard model yielding adjusted hazard ratios (aHR). Incidence of TD was significantly and linearly comorbid with the incidence of PRSD in both men and women. Compared to those with no PRSD, the risk for TD was 2.0 (95% CI: 1.1, 3.7) with one PRSD, 2.4 (95% CI: 1.3, 4.5) with two PRSD, and 3.6 (95% CI: 1.1, 11.8) with three PRSD. Associations were stronger in those who only had received prolactin-sparing medications (aHR per unit PRSD increase ¼ 2.0, 95% CI: 1.2, 3.3) than in those who only had received prolactin-raising medications (aHR ¼ 1.3, 95% CI: 0.9, 1.9). In people with schizophrenia, TD and PRSD show comorbidities that are independent of antipsychoticinduced alterations in plasma prolactin. This may suggest a shared, pandopaminergic pathological mechanism associated with schizophrenia itself, rather than only a medication effect.

Section: Discussionmentioning

confidence: 95%

Tardive Dyskinesia in Schizophrenia is Associated with Prolactin-Related Sexual Disturbances

Tenback

Harten²,

Slooff

et al. 2006

“…The other dissociation is that aripiprazole does not give rise to prolactin elevation despite very high D 2 RO. The first one probably is an issue of drugs or their active metabolites poorly crossing the blood-brain barrier, such that there is a preferential occupancy of peripheral (pituitary) vs central D 2 receptors (Kapur et al, 2002). In the case of aripiprazole, it is most likely its partial agonist effect (Inoue et al, 1996).…”

Section: Discussionmentioning

confidence: 99%

Dissociation between In Vivo Occupancy and Functional Antagonism of Dopamine D2 Receptors: Comparing Aripiprazole to Other Antipsychotics in Animal Models

Natesan

Reckless

Nóbrega

et al. 2005

176

115

The novel antipsychotic aripiprazole requires high (490%) striatal D 2 receptor occupancy (D 2 RO) to be clinically active, but despite its high D 2 RO it does not show extrapyramidal symptoms. While most antipsychotics are active at nearly 65% D 2 RO, they show motor side effects when D 2 RO exceeds 80%. We investigated this discrepancy between D 2 RO, 5HT 2 receptor occupancy (5-HT 2 RO) and in vivo functional activity of aripiprazole in comparison to haloperidol (typical) and risperidone (atypical) in animal models. All three drugs showed dose-dependent D 2 RO. While risperidone clearly showed higher 5-HT 2 RO than D 2 RO, aripiprazole and haloperidol showed higher D 2 RO than 5-HT 2 RO at all doses. Haloperidol and risperidone induced catalepsy at doses producing 480% D 2 RO, while aripiprazole despite higher D 2 RO (490%) induced no catalepsy. Haloperidol and risperidone's ED 50 values for inhibition of conditioned avoidance response (CAR) and amphetamine-induced locomotor activity (AIL) corresponded to B60% D 2 RO. In contrast, aripiprazole showed a significant dissociation; while it blocked AIL at similar D 2 RO, a 23-fold higher dose (86% D 2 RO) was required to inhibit CAR. FOS expression in shell region of the nucleus accumbens was significant for all drugs at D 2 ROs that were effective in CAR. However, in the core region of the nucleus accumbens and dorsolateral striatum, aripiprazole differed from the others in that despite high D 2 RO it induced low FOS. Haloperidol and risperidone showed dose/occupancy-dependent prolactin elevations, while aripiprazole did not. Across models, haloperidol and risperidone show similar occupancy-functional antagonism of the D 2 system, while aripiprazole shows a clear dissociation. Partial agonism of aripiprazole offers a good explanation for this dissociation and provides a framework for understanding occupancy-functional relationships of partial D 2 agonist antipsychotics.

“…Next, we compared them in models of functional dopamine antagonism and antipsychotic efficacy: amphetamine-induced locomotor activity (AIL), conditioned avoidance response (CAR), and Fos induction in the nucleus accumbens (shell region), along with markers of motor side effectsFcatalepsy (CAT) and Fos expression in the dorsolateral striatum (Deutch et al, 1992;Robertson et al, 1994;Arnt and Skarsfeldt, 1998). Plasma prolactin levels, which serve as an endocrine marker of D 2 receptor antagonism outside the blood-brain barrier, were also evaluated (Kapur et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Evaluation of N-Desmethylclozapine as a Potential Antipsychotic—Preclinical Studies

Natesan

Reckless

Barlow

et al. 2006

There is growing interest in N-desmethylclozapine (NDMC), the major metabolite of clozapine, as a unique antipsychotic because it acts in vitro as a 5-HT 2 antagonist and as a partial agonist to dopamine D 2 and muscarinic receptors. To explore this, we compared NDMC to a typical (haloperidol), atypical (clozapine), and partial-agonist atypical (aripiprazole) antipsychotic in preclinical models. The comparison was carried out using: brain D 2 and 5-HT 2 receptor occupancy; animal models predictive of antipsychotic efficacy (amphetamine-induced hyperlocomotion (AIL) and conditioned avoidance response (CAR) models); measures predictive of side effects (catalepsy and prolactin elevation); and molecular markers predictive of antipsychotic action (striatal Fos induction). NDMC (10-60 mg/kg/s.c.) showed high 5-HT 2 (64-79%), but minimal D 2 occupancy (o15% at 60 mg/kg) 1 h after administration. In contrast to other antipsychotics, NDMC was not very effective in reducing AIL or CAR and showed minimal induction of Fos in the nucleus accumbens. However, like atypical antipsychotics, it showed no catalepsy, prolactin elevation, and minimal Fos in the dorsolateral striatum. It seems unlikely that NDMC would show efficacy as a stand-alone antipsychotic, however, its freedom from catalepsy and prolactin elevation, and its unique pharmacological profile (muscarinic agonism) may make it feasible to use this drug as an adjunctive treatment to existing antipsychotic regimens.