Asenapine induces differential regional effects on serotonin receptor subtypes

A Postsynaptic Density Immediate Early Gene-Based Connectome Analysis of Acute NMDAR Blockade and Reversal Effect of Antipsychotic Administration

Although antipsychotics' mechanisms of action have been thoroughly investigated, they have not been fully elucidated at the network level. We tested the hypothesis that acute pre-treatment with ketamine (KET) and administration of asenapine (ASE) would modulate the functional connectivity of brain areas relevant to the pathophysiology of schizophrenia, based on transcript levels of Homer1a, an immediate early gene encoding a key molecule of the dendritic spine. Sprague-Dawley rats (n = 20) were assigned to KET (30 mg/kg) or vehicle (VEH). Each pre-treatment group (n = 10) was randomly split into two arms, receiving ASE (0.3 mg/kg), or VEH. Homer1a mRNA levels were evaluated by in situ hybridization in 33 regions of interest (ROIs). We computed all possible pairwise Pearson correlations and generated a network for each treatment group. Acute KET challenge was associated with negative correlations between the medial portion of cingulate cortex/indusium griseum and other ROIs, not detectable in other treatment groups. KET/ASE group showed significantly higher inter-correlations between medial cingulate cortex/indusium griseum and lateral putamen, the upper lip of the primary somatosensory cortex, septal area nuclei, and claustrum, in comparison to the KET/VEH network. ASE exposure was associated with changes in subcortical-cortical connectivity and an increase in centrality measures of the cingulate cortex and lateral septal nuclei. In conclusion, ASE was found to finely regulate brain connectivity by modelling the synaptic architecture and restoring a functional pattern of interregional co-activation.

Molecular targets of atypical antipsychotics: From mechanism of action to clinical differences

The introduction of atypical antipsychotics (AAPs) since the discovery of its prototypical drug clozapine has been a revolutionary pharmacological step for treating psychotic patients as these allow a significant recovery not only in terms of hospitalization and reduction in symptoms severity, but also in terms of safety, socialization and better rehabilitation in the society. Regarding the mechanism of action, AAPs are weak D₂ receptor antagonists and they act beyond D₂ antagonism, involving other receptor targets which regulate dopamine and other neurotransmitters. Consequently, AAPs present a significant reduction of deleterious side effects like parkinsonism, hyperprolactinemia, apathy and anhedonia, which are all linked to the strong blockade of D₂ receptors. This review revisits previous and current findings within the class of AAPs and highlights the differences in terms of receptor properties and clinical activities among them. Furthermore, we propose a continuum spectrum of "atypia" that begins with risperidone (the least atypical) to clozapine (the most atypical), while all the other AAPs fall within the extremes of this spectrum. Clozapine is still considered the gold standard in refractory schizophrenia and in psychoses present in Parkinson's disease, though it has been associated with adverse effects like agranulocytosis (0.7%) and weight gain, pushing the scientific community to find new drugs as effective as clozapine, but devoid of its side effects. To achieve this, it is therefore imperative to characterize and compare in depth the very complex molecular profile of AAPs. We also introduce relatively new concepts like biased agonism, receptor dimerization and neurogenesis to identify better the old and new hallmarks of "atypia". Finally, a detailed confrontation of clinical differences among the AAPs is presented, especially in relation to their molecular targets, and new means like therapeutic drug monitoring are also proposed to improve the effectiveness of AAPs in clinical practice.

The preclinical discovery and development of cariprazine for the treatment of schizophrenia

INTRODUCTION

Cariprazine is approved in the United States and Europe for the treatment of manic or mixed episodes associated with bipolar I disorder and for the treatment of schizophrenia in adult patients. It is typically administered orally once a day (a dose range 1.5 - 6 mg/day), does require titration, and may be given with or without food. It has a half-life of 2 - 4 days with an active metabolite that has a terminal half-life of 2 - 3 weeks. Areas covered: This review article focuses on the preclinical discovery of cariprazine providing details regarding its pharmacological, behavioral, and neurochemical mechanisms and its contribution to clinical therapeutic benefits. This article is based on the available literature with respect to the preclinical and clinical findings and product labels of cariprazine. Expert opinion: Cariprazine shows highest affinity toward D₃ receptors, followed by D₂, 5-HT_2B, and 5-HT_1A receptors. It also shows moderate affinity toward σ₁, 5-HT_2A, and histamine H₁ receptors. Long-term administration of cariprazine altered the abundance of dopamine, serotonin, and glutamate receptor subtypes in different brain regions. All these mechanisms of cariprazine may contribute toward its unique preclinical profile and its clinically observed benefits in the treatment of schizophrenia, bipolar mania, and possibly other psychiatric disorders.

Long-term effects of aripiprazole exposure on monoaminergic and glutamatergic receptor subtypes: comparison with cariprazine

OBJECTIVE

This study examined the chronic effects of aripiprazole and cariprazine on serotonin (5-HT1A and 5-HT2A) and glutamate (NMDA and AMPA) receptor subtypes. In addition, the effects of aripiprazole on D2 and D3 receptors were tested and compared with previously reported cariprazine data.

METHODS

Rats received vehicle, aripiprazole (2, 5, or 15 mg/kg), or cariprazine (0.06, 0.2, or 0.6 mg/kg) for 28 days. Receptor levels were quantified using autoradiographic assays on brain sections from the medial prefrontal cortex (MPC), dorsolateral frontal cortex (DFC), nucleus accumbens (NAc), caudate-putamen medial (CPu-M), caudate-putamen lateral (CPu-L), hippocampal CA1 (HIPP-CA1) and CA3 (HIPP-CA3) regions, and the entorhinal cortex (EC).

RESULTS

Similar to previous findings with cariprazine, aripiprazole upregulated D2 receptor levels in various regions; D3 receptor changes were less than those reported with cariprazine. All aripiprazole doses and higher cariprazine doses increased 5-HT1A receptors in the MPC and DFC. Higher aripiprazole and all cariprazine doses increased 5-HT1A receptors in HIPP-CA1 and HIPP-CA3. Aripiprazole decreased 5-HT2A receptors in the MPC, DFC, HIPP-CA1, and HIPP-CA3 regions. Both compounds decreased NMDA receptors and increased AMPA receptors in select brain regions.

CONCLUSIONS

Long-term administration of aripiprazole and cariprazine had similar effects on 5-HT1A, NMDA, and AMPA receptors. However, cariprazine more profoundly increased D3 receptors while aripiprazole selectively reduced 5-HT2A receptors. These results suggest that the unique actions of cariprazine on dopamine D3 receptors, combined with its effects on serotonin and glutamate receptor subtypes, may confer the clinical benefits, safety, and tolerability of this novel compound in schizophrenia and bipolar mania.

Repeated asenapine treatment does not participate in the mild stress induced FosB/ΔFosB expression in the rat hypothalamic paraventricular nucleus neurons

Effect of repeated asenapine (ASE) treatment on FosB/ΔFosB expression was studied in the hypothalamic paraventricular nucleus (PVN) of male rats exposed to chronic mild stress (CMS) for 21days. Our intention was to find out whether repeated ASE treatment for 14days may: 1) induce FosB/ΔFosB expression in the PVN; 2) activate selected PVN neuronal phenotypes, synthesizing oxytocin (OXY), vasopressin (AVP), corticoliberin (CRH) or tyrosine hydroxylase (TH); and 3) interfere with the impact of CMS. Control, ASE, CMS, and CMS+ASE treated groups were used. CMS included restraint, social isolation, crowding, swimming, and cold. From the 7th day of CMS, rats received ASE (0.3mg/kg) or saline (300μl/rat) subcutaneously, twice a day for 14days. They were sacrificed on the day 22nd (16-18h after last treatments). FosB/ΔFosB was visualized with avidin biotin peroxidase complex and OXY, AVP, CRH or TH antibodies by fluorescent dyes. Saline and ASE did not promote FosB/ΔFosB expression in the PVN. CMS and CMS+ASE elicited FosB/ΔFosB-expression in the PVN, whereas, ASE did not augment or attenuate FosB/ΔFosB induction elicited by CMS. FosB/ΔFosB-CRH occurred after CMS and CMS+ASE treatments in the PVN middle sector, while FosB/ΔFosB-AVP and FosB/ΔFosB-OXY after CMS and CMS+ASE treatments in the PVN posterior sector. FosB/ΔFosB-TH colocalization was rare. Larger FosB/ΔFosB profiles, running above the PVN, did not show any colocalizations. The study provides an anatomical/functional knowledge about an unaccented nature of prolonged ASE treatment at the level of PVN and excludes its positive or negative interplay with CMS effect. Data indicate that long-lasting ASE treatment might not act as a stressor acting at the PVN level.

Impact of repeated asenapine treatment on FosB/ΔFosB expression in the forebrain structures under normal conditions and mild stress preconditioning in the rat

Long-term effect of asenapine (ASE), an atypical antipsychotic drug, on FosB/ΔFosB quantitative variations in the striatum, septum, nucleus accumbens, and prefrontal cortex, was light microscopically evaluated in normal rats and rats preconditioned with chronic unpredictable mild stress (CMS). CMS included restraint, social isolation, crowding, swimming, and cold. The rats were exposed to CMS for 21 days. From the 7th day of CMS, the rats were injected subcutaneously with saline (300μl/rat) or ASE (0.3mg/kg b.w.), twice a day for 14 days. On the 22nd day, i.e. 16-18h after the last treatment, the animals were perfused with fixative and the brains cut into 30μm thick coronal sections. FosB/ΔFosB protein was immunohistochemically visualized by avidin-biotin peroxidase complex (ABC). Four groups of animals were investigated: control+vehicle, control+ASE, CMS+vehicle, and CMS+ASE. Repeated ASE treatment significantly increased the amount of FosB/ΔFosB immunostained cell nuclei in the dorsolateral and dorsomedial striatum and the shell of the nucleus accumbens, followed by strVM and coACC, as assessed by numerical analysis in both total (different size for each structure) and unified (equal size for each structure) brain sectors. The effect of ASE was significantly lowered by CMS preconditioning only in the dorsolateral striatum, dorsomedial striatum, and the shell of the nucleus accumbens, indicated by both total and unified calculations. Although, highest FosB/ΔFosB expression was seen in the prefrontal cortex and lowest in the dorsolateral and ventrolateral septum, no differences between the groups occurred. CMS itself did not affect FosB/ΔFosB expression level. These findings demonstrate for the first time that repeated administration of ASE may result in eliciting of long-lasting FosB/ΔFosB-like transcription factors that could mediate some of the persistent and region-specific changes in brain function, interconnected with chronic drug exposure. However, it cannot be excluded that the impact of repeated ASE exposure might be influenced by an ambient stressogen leverage.

An update of safety of clinically used atypical antipsychotics

INTRODUCTION

The atypical antipsychotic (APs) drugs have become the most widely used agents to treat a variety of psychoses because of their superiority with regard to safety and tolerability profile compared to conventional/'typical' APs.

AREAS COVERED

We aimed at providing a synthesis of most current evidence about the safety and tolerability profile of the most clinically used atypical APs so far marketed. Qualitative synthesis followed an electronic search made inquiring of the following databases: MEDLINE, Embase, PsycINFO and the Cochrane Library from inception until January 2016, combining free terms and MESH headings for the topics of psychiatric disorders and all atypical APs as following: ((safety OR adverse events OR side effects) AND (aripiprazole OR asenapine OR quetiapine OR olanzapine OR risperidone OR paliperidone OR ziprasidone OR lurasidone OR clozapine OR amisulpride OR iloperidone)).

EXPERT OPINION

A critical issue in the treatment with atypical APs is represented by their metabolic side effect profile (e.g. weight gain, lipid and glycaemic imbalance, risk of diabetes mellitus and diabetic ketoacidosis) which may limit their use in particular clinical samples. Electrolyte imbalance, ECG abnormalities and cardiovascular adverse effects may recommend a careful baseline and periodic assessments.

Asenapine: A Review in Schizophrenia

Asenapine (Saphris(®), Sycrest(®)) is an atypical antipsychotic that is administered sublingually twice daily and is approved for schizophrenia in the USA, Japan and other countries, but not in the EU. This article reviews the pharmacology, clinical efficacy and tolerability profile of asenapine in the treatment of adults with schizophrenia. Clinical trials with asenapine have demonstrated efficacy in terms of both positive and negative symptoms of schizophrenia, although findings have not always been consistent. Across three short-term (6-week) studies in acute schizophrenia (including one in Asian patients), asenapine was generally superior to placebo and had broadly similar efficacy to active controls in improving total scores on the Positive and Negative Syndrome Scale. A meta-analysis of four short-term trials with asenapine (that also included a negative study and a failed trial) also showed significant benefit with asenapine over placebo. In longer-term trials and extensions (up to ≈3 years' duration), asenapine was effective relative to placebo in preventing relapse in schizophrenia, but was less effective than olanzapine in patients with schizophrenia or schizoaffective disorder (according to intent-to-treat LOCF analysis). However, in two trials in patients with persistent negative symptoms of schizophrenia, asenapine and olanzapine were similarly effective in reducing negative symptoms at week 26, with asenapine providing better results than olanzapine at week 52 in one of the extensions. The most frequently reported adverse events with asenapine are somnolence, akathisia and oral hypoesthesia. Although potentially associated with more extrapyramidal symptoms, asenapine appears to have less weight gain and metabolic effects than some other antipsychotic agents, such as olanzapine.

Effects of repeated asenapine in a battery of tests for anxiety-like behaviours in mice

OBJECTIVE

A number of atypical antipsychotic drugs were demonstrated to have anxiolytic effects in patients and in animal models. These effects were mostly suggested to be the consequence of the drugs' affinity to the serotonin system and its receptors. Asenapine is a relatively new atypical antipsychotic that is prescribed for schizophrenia and for bipolar mania. Asenapine has a broad pharmacological profile with significant effects on serotonergic receptors, hence it is reasonable to expect that asenapine may have some anxiolytic effects. The present study was therefore designed to examine possible effects of asenapine on anxiety-like behaviour of mice.

METHOD

Male ICR mice were repeatedly treated with 0.1 or 0.3 mg/kg injections of asenapine and then tested in a battery of behavioural tests related to anxiety including the open-field test, elevated plus-maze (EPM), defensive marble burying and hyponeophagia tests. In an adjunct experiment, we tested the effects of acute diazepam in the same test battery.

RESULTS

The results show that diazepam reduced anxiety-like behaviour in the EPM, the defensive marble burying test and the hyponeophagia test but not in the open field. Asenapine has anxiolytic-like effects in the EPM and the defensive marble burying tests but had no effects in the open-field or the hyponeophagia tests. Asenapine had no effects on locomotor activity.

CONCLUSION

The results suggest that asenapine may have anxiolytic-like properties and recommends that clinical trials examining such effects should be performed.

Stress alters asenapine-induced Fos expression in the Meynert's nucleus: response of adjacent hypocretin and melanin-concentrating hormone neurons in rat

OBJECTIVE

Asenapine (ASE), an atypical antipsychotic drug used in the treatment of schizophrenia, induces Fos expression in forebrain. Effect of ASE on activity of basal nucleus of Meynert (NBM) cells, a part of the striatal-cortical circuits, was studied. We were also interested to reveal whether a chronic unpredictable variable mild stress (CMS) preconditioning might affect the ASE impact.

METHODS

Rats were divided into as follows: controls-vehicle, controls-ASE, stressed-vehicle and stressed-ASE groups. CMS included restrain, social isolation, crowding, swimming and cold applied for 21 days. On the 22nd day, rats were subcutaneously injected with ASE (0.3 mg/kg) or vehicle (saline 300 μl/rat), 90 min prior euthanizing. After transcardial fixation, brains were cut into 30 μm thick coronal sections. Fos protein presence, as indicator of cell activity, was detected by ABC immunohistochemistry. Hypocretin (Hcrt) and melanin-concentrating hormone (MCH) containing cells were visualized with fluorescent dyes.

RESULTS

ASE induced significant increase in Fos expression in NBM in both controls and CMS preconditioned rats in comparison with the related vehicle-treated controls. CMS preconditioning, however, significantly lowered the Fos response to ASE in NBM. From Hrct and MCH cells, only Hcrt ones displayed Fos presence in response to ASE.

DISCUSSION

This study demonstrates for the first time that ASE may target a special group of cells occupying NBM, which effect can be modulated by CMS preconditioning. This finding extends a view that ASE impact may extend beyond the classical forebrain target areas common for the action of all antipsychotics and might be helpful in the identification of sites and side effects of its therapeutic actions.

Progressive recruitment of cortical and striatal regions by inducible postsynaptic density transcripts after increasing doses of antipsychotics with different receptor profiles: insights for psychosis treatment

Antipsychotics may modulate the transcription of multiple gene programs, including those belonging to postsynaptic density (PSD) network, within cortical and subcortical brain regions. Understanding which brain region is activated progressively by increasing doses of antipsychotics and how their different receptor profiles may impact such an activation could be relevant to better correlate the mechanism of action of antipsychotics both with their efficacy and side effects. We analyzed the differential topography of PSD transcripts by incremental doses of two antipsychotics: haloperidol, the prototypical first generation antipsychotic with prevalent dopamine D2 receptors antagonism, and asenapine, a second generation antipsychotic characterized by multiple receptors occupancy. We investigated the expression of PSD genes involved in synaptic plasticity and previously demonstrated to be modulated by antipsychotics: Homer1a, and its related interacting constitutive genes Homer1b/c and PSD95, as well as Arc, C-fos and Zif-268, also known to be induced by antipsychotics administration. We found that increasing acute doses of haloperidol induced immediate-early genes (IEGs) expression in different striatal areas, which were progressively recruited by incremental doses with a dorsal-to-ventral gradient of expression. Conversely, increasing acute asenapine doses progressively de-recruited IEGs expression in cortical areas and increased striatal genes signal intensity. These effects were mirrored by a progressive reduction in locomotor animal activity by haloperidol, and an opposite increase by asenapine. Thus, we demonstrated for the first time that antipsychotics may progressively recruit PSD-related IEGs expression in cortical and subcortical areas when administered at incremental doses and these effects may reflect a fine-tuned dose-dependent modulation of the PSD.

Effect of acute asenapine treatment on Fos expression in the forebrain structures under normal conditions and mild stress preconditioning in the rat

Asenapine (ASE) is a novel atypical antipsychotic drug approved for the treatment of schizophrenia and bipolar disorder. Stress is an inseparable part of the human life, which may interfere with the therapeutic effect of different drugs. The aim of the present study was: (1) to delineate the quantitative and qualitative profiles of the ASE effect on Fos expression in the striatum, septum, nucleus accumbens, and the prefrontal cortex and (2) to find out whether a chronic unpredictable variable mild stress (CMS) preconditioning may modify the effect of acute ASE treatment. Stress paradigms included restrain, social isolation, crowding, swimming, and cold. The animals were exposed to CMS for 21 days and on the 22nd day received an injection of vehicle (saline 300 μl/rat s.c.) or ASE (0.3mg/kg s.c.). They were sacrificed 90 min after the treatments. Fos protein was visualized by avidin biotin peroxidase (ABC). Four groups of animals were investigated: controls+vehicle, controls+ASE, CMS+vehicle, and CMS+ASE. The number of Fos labeled neurons was calculated per total investigated area, which was selective for each structure, and also recalculated per unified sector. ASE treatment induced significant and very similar increase of the Fos expression in both ASE control and ASE CMS animals in comparison with saline control and CMS ones. Moreover, ASE induced regional differences in the number of Fos-positive neurons. In both ASE groups most pronounced response in the number of Fos profiles occurred in the dorsolateral striatum, ventrolateral septum, shell of the nucleus accumbens, and the medial prefrontal cortex. Mild Fos response was seen in the dorsomedial and ventromedial striatum and core of the nucleus accumbens. No response was seen in the dorsolateral septum. The present paper demonstrates for the first time the character of the Fos distribution in the forebrain structures induced by acute ASE treatment as well as ASE response to 21 days CMS preconditioning. The study provides an important comparative background that may help in the further understanding of the effect of ASE on the brain activation as well as its responsiveness to CMS challenges.

Asenapine sensitization from adolescence to adulthood and its potential molecular basis

Asenapine is a new antipsychotic drug that induces a long-lasting behavioral sensitization in adult rats. The present study investigated the developmental impacts of adolescent asenapine treatment on drug sensitivity and on 3 proteins implicated in the action of antipsychotic drugs (i.e. brain-derived neurotrophic factor (BDNF), dopamine D2 receptor, and ΔFosB) in adulthood. Male adolescent Sprague-Dawley rats (postnatal days, P 43-48) were first treated with asenapine (0.05, 0.10 or 0.20mg/kg, sc) and tested in the conditioned avoidance or PCP (2.0mg/kg, sc)-induced hyperlocomotion tasks for 5 days. After they became adults (∼P 76), asenapine sensitization was assessed in a single avoidance or PCP-induced hyperlocomotion challenge test with all rats being injected with asenapine (0.10mg/kg, sc). Rats were then sacrificed 1 day later and BDNF, D2 and ΔFosB in the prefrontal cortex, striatum and hippocampus were examined using Western blotting. In adolescence, repeated asenapine treatment produced a persistent and dose-dependent inhibition of avoidance response, spontaneous motor activity and PCP-induced hyperlocomotion. In the asenapine challenge test, adult rats treated with asenapine (0.10 and 0.20mg/kg) in adolescence made significantly fewer avoidance responses and showed a stronger inhibition of spontaneous motor activity than those previously treated with saline. However, no group difference in the levels of BDNF, D2 and ΔFosB expression was found. These findings suggest that although adolescent asenapine treatment for a short period of time induces a robust behavioral sensitization that persists into adulthood, such a long-term effect is not likely to be mediated by BDNF, D2 and ΔFosB.

Long-term effects of cariprazine exposure on dopamine receptor subtypes

INTRODUCTION

All clinically effective antipsychotics are known to act on the dopaminergic system, and previous studies have demonstrated that repeated treatment with antipsychotics produced region-specific changes in dopamine receptor levels. Cariprazine is a dopamine D₃ and D₂ receptor partial agonist with preferential binding to D₃ receptors. We examined the effects of chronic cariprazine administration on dopamine receptor levels.

METHODS

Rats were administered either vehicle or cariprazine (0.06, 0.2, or 0.6 mg/kg) for 28 days. Dopamine receptor levels were quantitated using autoradiographic assays on brain tissue sections from the medial prefrontal cortex (mPFC), nucleus accumbens (NAc), caudate putamen (CPu), hippocampus (HIPP), olfactory tubercle (OT), and islands of Calleja (ICj).

RESULTS

Chronic treatment with cariprazine did not alter D₁ receptor levels in any brain region tested. Cariprazine increased D₂ receptor levels in mPFC (27%-43%), NAc (40%-45%), medial (41%-53%) and lateral (52%-63%) CPu, and HIPP (38%). Cariprazine dose-dependently upregulated D₃ receptor levels in ICj (32%-57%), OT (27%-67%), and NAc shell (31%-48%). Repeated cariprazine treatment increased D₄ receptor in NAc (53%-82%), medial (54%-98%) and lateral (58%-74%) CPu, and HIPP (38%-98%).

CONCLUSION

Similar to other antipsychotics, cariprazine upregulated D₂ and D₄ receptor levels in various brain regions. Cariprazine was unique among antipsychotics in increasing D₃ receptor levels, which may support its unique psychopharmacologic properties.

Time-dependence of risperidone and asenapine sensitization and associated D2 receptor mechanism

When an antipsychotic drug is given repeatedly and intermittently, there is often a long-term increase in its behavioral efficacy, termed antipsychotic sensitization. With the passage of time, the magnitude of antipsychotic sensitization may increase or decrease based on the principle of time-dependent sensitization (TDS) or memory decay, respectively. In the present study, we examined the time-dependent feature and possible dopamine D2 receptor mechanism of sensitization induced by risperidone and asenapine in the conditioned avoidance response test. Well-trained male adult Sprague-Dawley rats were first repeatedly treated with risperidone (1.0mg/kg) or asenapine (0.2mg/kg) and tested for avoidance response daily for 5 consecutive days. Eight, 18 or 38 days after the 5th drug treatment, all rats were retested drug-free to assess the long-term impact of prior risperidone or asenapine treatment. Drug-pretreated rats had significantly lower avoidance than vehicle-pretreated ones on this test, and the group differences increased with the passage of time. In the subsequent drug challenge test at 10, 20 or 40 days after the 5th drug treatment, all rats were injected with a low dose of risperidone (0.3mg/kg) or asenapine (0.1mg/kg). Drug-pretreated rats again made significantly fewer avoidances than controls, confirming the antipsychotic sensitization effect. Finally, in the quinpirole (a D2/3 receptor agonist, 1.0mg/kg, sc)-induced hyperlocomotion test, risperidone-pretreated rats exhibited a significantly higher level of motor activity than the vehicle-pretreated ones. These findings suggest that risperidone and asenapine sensitization is long-lasting, follows the TDS principle, and is likely mediated by D2 receptor supersensitivity.

Repeated asenapine treatment produces a sensitization effect in two preclinical tests of antipsychotic activity

Among several commonly used atypical antipsychotic drugs, olanzapine and risperidone cause a sensitization effect in the conditioned avoidance response (CAR) and phencyclidine (PCP)-induced hyperlocomotion paradigms--two well established animal tests of antipsychotic drugs, whereas clozapine causes a tolerance effect. Asenapine is a novel antipsychotic drug recently approved for the treatment of schizophrenia and manic disorders. It shares several receptor binding sites and behavioral features with other atypical antipsychotic drugs. However, it is not clear what type of repeated effect (sensitization or tolerance) asenapine would induce, and whether such an effect is transferrable to other atypicals. In this study, male adult Sprague-Dawley rats were first repeatedly tested with asenapine (0.05, 0.10 or 0.20 mg/kg, sc) for avoidance response or PCP (3.20 mg/kg, sc)-induced hyperlocomotion daily for 5 consecutive days. After 2-3 days of retraining/drug-free recovery, they were then challenged with asenapine (0.10 mg/kg, sc), followed by olanzapine (0.50 mg/kg, sc) and clozapine (2.50 mg/kg, sc). During the 5-day drug test period (the induction phase), repeated asenapine treatment progressively increased its inhibition of avoidance response and PCP-induced hyperlocomotion in a dose-dependent fashion. On the asenapine and olanzapine challenge tests (the expression phase), rats previously treated with asenapine still showed significantly lower avoidance response and lower PCP-induced hyperlocomotion than those previously treated with vehicle. An increased reactivity to clozapine challenge in prior asenapine-treated rats was also found in the PCP-induced hyperlocomotion test. These findings suggest that asenapine is capable of inducing a sensitization effect and a cross-sensitization to olanzapine and clozapine (to a lesser extent). Because the behavioral profile of asenapine in both tests is similar to that of olanzapine, but different from that of clozapine, we suggest that asenapine resembles olanzapine to a greater extent than clozapine in its therapeutic and side effect profiles.

Asenapine for the treatment of manic and mixed episodes associated with bipolar I disorder: from clinical research to clinical practice

INTRODUCTION

Asenapine is a sublingually administered second-generation antipsychotic with proven efficacy for the treatment of moderate to severe manic episodes associated with bipolar I disorder in adults. Its relatively favorable weight and metabolic profile, as well as the lack of appreciable activity at muscarinic cholinergic receptors and the sublingual administration are of clinical interest.

AREAS COVERED

This paper comprises a review and commentary regarding the use of sublingual asenapine in the treatment of acute manic and mixed episodes of bipolar disorder. Basic principles in dosing, switching, management of side effects and co-administration with other medications are provided.

EXPERT OPINION

Asenapine displays quick and reliable effects on manic symptoms, very low risk of depressive switches, efficacy on depressive symptoms during manic and mixed episodes, usually good tolerability and continued longer-term efficacy on residual and subthreshold symptoms. The fast-dissolving sublingual route of administration may favor those who have difficulties in swallowing medications. Also, the sublingual administration reduces the risk of overdose when more than the prescribed tablets are swallowed. The relatively low metabolic risk and the lack of anticholinergic side effects contribute to making this medication a useful tool for the treatment of patients with bipolar disorder.

Iloperidone, asenapine and lurasidone: a primer on their current status

INTRODUCTION

Three newer atypical antipsychotic drugs were FDA-approved in 2009 and 2010 in the following order: iloperidone, asenapine and lurasidone. The three drugs are indicated for the treatment of acute schizophrenia. Asenapine is also approved for treatment of manic or mixed episodes associated with bipolar I disorder, for the maintenance treatment of schizophrenia and as an adjunctive therapy with lithium or valproate for the acute treatment of manic or mixed episodes associated with bipolar I disorder in adults.

AREAS COVERED

This review compares and contrasts the current preclinical, clinical, safety and tolerability profiles of the three newer drugs, as reported in published preclinical and clinical studies, product labels, poster presentations and press releases.

EXPERT OPINION

Preclinical studies have reported that the three drugs have variable affinities for a wide range of neurotransmitter receptors, and are active in animal models predictive of antipsychotic activity. Asenapine is the first antipsychotic to be administered sublingually, whereas iloperidone requires titration to minimize orthostatic hypotension. Asenapine and lurasidone are associated with dose-related akathisia, whereas iloperidone is not. The three drugs appear to have relatively benign metabolic profiles. The availability of the three novel antipsychotics should provide additional options for improved treatment of schizophrenia and other psychotic disorders.

Receptor mechanisms of antipsychotic drug action in bipolar disorder - focus on asenapine

The atypical antipsychotic drugs are considered a first-line treatment for mania in bipolar disorder with many having a proven superiority to the classical mood stabilisers. This review addresses the pharmacological mechanisms underlying this therapeutic efficacy, as well as those mechanisms considered responsible for the adverse effects of antipsychotic drugs, with a particular focus on the recently introduced asenapine. The high efficacy in bipolar mania of haloperidol, a relatively selective dopamine D2-like receptor antagonist, indicates that the one common receptor mechanism underlying antipsychotic effects on mania is antagonism at the D2 receptor. Serotonin receptors are implicated in antidepressant response, and relief of depressed mood in mixed states is likely to involve drug effects at one, or more likely several interacting, serotonin receptors. Asenapine shows a unique breadth of action at these sites, with potential effects at clinical doses at 5HT1A, 1B, 2A, 2C, 6 and 7 receptors. Antagonism at alpha2 adrenoceptors may also be involved. Adverse effects include those classically associated with dopamine D2 receptor blockade, the extrapyramidal side effects (EPS), and which are relatively diminished in the atypical (in comparison with the conventional) antipsychotics. A variety of protective mechanisms against EPS associated with different drugs include low D2 affinity, D2 partial agonism, high 5-HT2A and 2C antagonism. Similar effects at the D2 and 5-HT2C receptors may underlie the low propensity for hyperprolactinaemia of the atypicals, although the strong prolactin-elevating effect of risperidone reflects its relatively high blood/brain concentration ratio, a consequence of it being a substrate for the p-glycoprotein pump. Weight gain is a further concern of antipsychotic treatment of bipolar disorder which is particularly severe with olanzapine. Histamine H1, alpha1 adrenergic and particularly 5-HT2C receptors are implicated in this effect, although the lower propensity for weight gain shown by asenapine which, like olanzapine, binds to these receptors, indicates that other protective receptor mechanisms, or subtle differences in the 5-HT2C receptor-mediated effects, may be important. Of other peripheral and central effects, the pharmacological basis of sedation (H1 receptors) and postural hypotension (alpha1 adrenoceptors) are rather better understood. The relative benefits of atypical antipsychotics like asenapine can be understood from their receptor pharmacology, and this understanding is key to the future development of improved treatment for bipolar disorder.

Attenuation of chronic mild stress-induced 'anhedonia' by asenapine is not associated with a 'hedonic' profile in intracranial self-stimulation

Chronic mild stress (CMS)-induced 'anhedonia' is a predictive model of antidepressant activity. We assessed the reversal of CMS-induced behavioral changes by asenapine, the antidepressant imipramine, and the atypical antipsychotics olanzapine and risperidone. Secondarily, the ability of these agents to facilitate intracranial self-stimulation (ICSS) was assessed to ensure that any attenuation of CMS-induced anhedonia was not associated with an overt hedonic profile. After 2 weeks of CMS, male Wistar rats were administered asenapine (0.06-0.6 mg/kg), olanzapine (2 mg/kg), risperidone (0.5 mg/kg), or imipramine (10 mg/kg) by intraperitoneal injection over 5 weeks to examine their ability to reverse CMS-induced reductions in the intake of a sucrose solution. For the ICSS study, rats were trained to deliver an electrical stimulus to the ventral tegmental area. The effects of acute doses of subcutaneous asenapine (0.01-0.3 mg/kg), olanzapine (0.3 and 1 mg/kg), risperidone (0.1 and 0.3 mg/kg), and intraperitoneal imipramine (3-30 mg/kg), cocaine (5.0 mg/kg), or amphetamine (1.0 mg/kg) on ICSS were then examined. CMS significantly reduced sucrose intake (P < 0.001). All active agents (0.6 mg/kg asenapine, 2 mg/kg olanzapine, 0.5 mg/kg risperidone, and 10 mg/kg imipramine) reversed the effect of CMS (all P < 0.001). In the ICSS protocol, asenapine (0.01 and 0.03 mg/kg), olanzapine (1 mg/kg), and risperidone (0.3 mg/kg) impaired ICSS performance, whereas positive controls (5 mg/kg cocaine, 1 mg/kg amphetamine) facilitated ICSS. Asenapine reversed CMS-induced anhedonia without facilitating ICSS, providing support for a role of asenapine in treating bipolar disorder and aspects of negative and/or affective symptoms in schizophrenia.

The role of serotonin receptors in the action of atypical antipsychotic drugs

The main class of atypical antipsychotic drugs (APDs) in current use includes the protypical atypical APD, clozapine, as well as aripiprazole, asenapine, iloperidone, lurasidone, olanzapine, quetiapine, risperidone, and ziprasidone. At clinically effective doses, these agents produce extensive blockade of serotonin (5-HT)(2A) receptors, direct or indirect stimulation of 5-HT(1A) receptors, and to a lesser extent, reduction in dopamine (DA) D(2) receptor-mediated neurotransmission. This contrasts with typical APDs, for example haloperidol and perphenazine, which are mainly DA D(2/)D(3) receptor antagonists and have weaker, if any, potency as 5-HT(2A) receptor antagonists. Some, but not all, atypical APDs are also effective 5-HT(2C) receptor inverse agonists or neutral antagonists, 5-HT(6) or 5-HT(7) receptor antagonists. This diverse action on 5-HT receptors may contribute to significant differences in efficacy and tolerability among the atypical APDs. There is considerable preclinical and some clinical evidence that effects on 5-HT receptors contribute to the low risk of producing extrapyramidal side effects, which is the defining characteristic of an atypical APD, the lack of elevation in plasma prolactin levels (with risperidone and 9-hydroxyrisperidone being exceptions), antipsychotic action, and ability to improve some domains of cognition in patients with schizophrenia. The serotonergic actions of the atypical APDs, especially 5-HT(2A) receptor antagonism, are particularly important to the differential effects of typical and atypical APDs to overcome the effects of acute or subchronic administration of N-methyl-d-aspartate (NMDA) receptor antagonists, such as phencyclidine, ketamine, and dizocipline (MK-801). 5-HT(1A) receptor stimulation and 5-HT(6) and 5-HT(7) receptor antagonism may contribute to beneficial effects of these agents on cognition. In particular, 5-HT(7) receptor antagonism may be the basis for the pro-cognitive effects of the atypical APD, amisulpride, a D(2)/D(3) receptor antagonist, which has no effect on other 5-HT receptor. 5-HT(2C) receptor antagonism appears to contribute to the weight gain produced by some atypical APDs and may also affect cognition and psychosis via its influence on cortical and limbic dopaminergic activity.

Asenapine: a review of its use in the management of mania in adults with bipolar I disorder

Asenapine is an atypical antipsychotic agent available in sublingual formulations (5 or 10 mg) and indicated in the US (Saphris) for the acute treatment, as monotherapy or adjunctive therapy, of manic and mixed episodes and in the EU (Sycrest) for the treatment of moderate to severe manic episodes, in adult patients with bipolar I disorder. In two large (both n = 480), well designed, 3-week trials in adult patients with bipolar I disorder, asenapine monotherapy was significantly more effective than placebo at improving mania symptoms, as assessed using the Young Mania Rating Scale total score (YMRS; primary endpoint), with significant differences between the asenapine and placebo groups occurring after 2 days of treatment. In both trials, Clinical Global Impression for Bipolar Disorder (CGI-BP) scale mania severity scores exceeded those of placebo. In one trial, response and remission rates exceeded those of placebo. In a 9-week extension study that recruited completers from the monotherapy trials, there were no significant differences between asenapine and olanzapine groups in terms in Montgomery-Åsberg Depression Rating Scale (MADRS) scores, CGI-BP mania severity scores, YMRS response rates or YMRS remission rates during the extension phase. In the extension study, the efficacy of asenapine monotherapy appeared to be maintained over 40 weeks (total treatment duration of 52 weeks). In a 12-week trial of asenapine as adjunctive therapy to lithium or valproate, asenapine was more effective than placebo in improving manic symptoms, based on the difference between groups in the YMRS total score at week 3 (primary endpoint). Most adverse events associated with asenapine were of mild to moderate severity, with <7% of asenapine recipients experiencing serious adverse events (vs 7% with placebo). In a pooled analysis of the monotherapy trials, the most common adverse events (occurring in ≥ 5% of patients and at twice the incidence of placebo) reported during acute phase asenapine monotherapy for bipolar mania were somnolence, dizziness, extrapyramidal symptoms (EPS, other than akathisia) and increased bodyweight, which were similar in nature to those occurring during longer-term monotherapy with asenapine. EPS did not worsen in severity during longer-term asenapine monotherapy. Asenapine had minimal effects on plasma glucose, lipid and prolactin levels over both short- and longer-term treatment periods, and had little pro-arrhythmogenic potential. Further active comparator trials and longer-term tolerability and safety data are required. In the meantime, asenapine is a further option for the management of manic and/or mixed symptoms in patients with bipolar I disorder and may be of particular value for patients who are at high risk for metabolic abnormalities.