Affinity For Dopamine D2 Receptors Research Articles

In vitro characterization of [125I]HY-3-24, a selective ligand for the dopamine D3 receptor.

Dopamine D3 receptor (D3R) ligands have been studied for the possible treatment of neurological and neuropsychiatric disorders. However, selective D3R radioligands for in vitro binding studies have been challenging to identify due to the high structural similarity between the D2R and D3R. In a prior study, we reported a new conformationally-flexible benzamide scaffold having a high affinity for D3R and excellent selectivity vs. D2R. In the current study, we characterized the in vitro binding properties of a new radioiodinated ligand, [125I]HY-3-24. In vitro binding studies were conducted in cell lines expressing D3 receptors, rat striatal homogenates, and rat and non-human primate (NHP) brain tissues to measure regional brain distribution of this radioligand. HY-3-24 showed high potency at D3R (Ki = 0.67 ± 0.11 nM, IC50 = 1.5 ± 0.58 nM) compared to other D2-like dopamine receptor subtypes (D2R Ki = 86.7 ± 11.9 nM and D4R Ki > 1,000). The Kd (0.34 ± 0.22 nM) and Bmax (38.91 ± 2.39 fmol/mg) values of [125I]HY-3-24 were determined. In vitro binding studies in rat striatal homogenates using selective D2R and D3R antagonists confirmed the D3R selectivity of [125I]HY-3-24. Autoradiography results demonstrated that [125I]HY-3-24 specifically binds to D3Rs in the nucleus accumbens, islands of Calleja, and caudate putamen in rat and NHP brain sections. These results suggest that [125I]HY-3-24 appears to be a novel radioligand that exhibits high affinity binding at D3R, with low binding to other D2-like dopamine receptors. It is anticipated that [125I]HY-3-24 can be used as the specific D3R radioligand.

Withdrawal syndrome after antipsychotics discontinuation: an analysis of the WHO database of spontaneous reports (Vigibase) between 2000 and 2022.

Withdrawal syndrome (WDS) has been described after discontinuation of antipsychotics. WDS could be the consequence of an over-activation of the dopaminergic pathway. Antipsychotics with a higher affinity for dopamine D2 receptors could be associated with a higher risk of WDS. This study aims to address this statement and evaluate the risk difference for withdrawal syndrome between antipsychotics based on pharmacovigilance data. We collected individual reports registered in Vigibase® between 01/01/2000 and 31/12/2022 of patients treated with antipsychotics and who had presented WDS. A disproportionality analysis was performed to evaluate the risk of reporting WDS with each antipsychotic compared to all other antipsychotics. We performed a correlation analysis to assess the correlation between the risk of reporting WDS for each antipsychotic in relation with their pKi for D2 and 5HT2A receptors. The most frequent psychiatric withdrawal symptoms after antipsychotic discontinuation were insomnia, anxiety and depression. Tremor, headache and dizziness were among the most frequently reported neurologic withdrawal symptoms. Tiotixene had the highest risk of reporting WDS (ROR 7.08; 95%CI 3.49 - 14.35) followed by pimozide (ROR 4.35; 95%CI 1.93 - 9.77), quetiapine (ROR 4.24; 95%CI 3.87 - 4.64), thioridazine (ROR 4.17; 95%CI 2.50-6.98) and ziprasidone (ROR 2.98; 95%CI 2.41-3.67). We found a poor correlation between D2/5HT2A binding affinity and the risk of reporting withdrawal syndrome (R2 = 0,094). Our results suggest that there might be a risk difference for WDS between antipsychotics. Tiotixene, pimozide and quetiapine were associated with a higher risk of reporting a WDS whereas this risk was lower with chlorpromazine, clozapine and fluphenazine. We could not address the issue of withdrawal psychosis, withdrawal dyskinesia, rebound psychosis or supersensitivity psychosis due to the lack of specific WHO medDRA coded terms to identify potential cases.

Relationship between antipsychotic medication and aggressive events in patients with a psychotic disorder hospitalized for treatment

BackgroundDisruptive and aggressive behavior is frequent in patients with a psychotic disorder; furthermore, it is a recurrent reason for compulsory admission. Even during treatment, many patients continue to show aggressive behavior. Antipsychotic medication is posed to have anti-aggressive properties; its prescription is a common strategy for the treatment (and prevention) of violent behavior. The present study aims to investigate the relation between the antipsychotic class, according to the dopamine D2-Receptor binding affinity (i.e., “loose” – “tight binding”), and aggressive events perpetrated by hospitalized patients with a psychotic disorder.MethodsWe conducted a four-year retrospective analysis of legally liable aggressive incidents perpetrated by patients during hospitalization. We extracted patients’ basic demographic and clinical data from electronic health records. We used the Staff Observation Aggression Scale (SOAS-R) to grade the severity of an event. Differences between patients with a “loose” or “tight-binding” antipsychotic were analyzed.ResultsIn the observation period, there were 17,901 direct admissions; and 61 severe aggressive events (an incidence of 0.85 for every 1,000 admissions year). Patients with a psychotic disorder perpetrated 51 events (incidence of 2.90 for every 1,000 admission year), with an OR of 15.85 (CI: 8.04–31.25) compared to non-psychotic patients. We could identify 46 events conducted by patients with a psychotic disorder under medication. The mean SOAS-R total score was 17.02 (2.74). The majority of victims in the “loose-binding” group were staff members (73.1%, n = 19), while the majority of victims in the “tight-binding” group were fellow patients (65.0%, n = 13); (X2(3,46) = 19.687; p < 0.001). There were no demographic or clinical differences between the groups and no differences regarding dose equivalents or other prescribed medication.ConclusionsIn aggressive behaviors conducted by patients with a psychotic disorder under antipsychotic medication, the dopamine D2-Receptor affinity seems to have a high impact on the target of aggression. However, more studies are needed to investigate the anti-aggressive effects of individual antipsychotic agents.

Potential Mechanisms for Why Not All Antipsychotics Are Able to Occupy Dopamine D3 Receptors in the Brain in vivo.

Dysfunctions of the dopaminergic system are believed to play a major role in the core symptoms of schizophrenia such as positive, negative, and cognitive symptoms. The first line of treatment of schizophrenia are antipsychotics, a class of medications that targets several neurotransmitter receptors in the brain, including dopaminergic, serotonergic, adrenergic and/or muscarinic receptors, depending on the given agent. Although the currently used antipsychotics display in vitro activity at several receptors, majority of them share the common property of having high/moderate in vitro affinity for dopamine D2 receptors (D2Rs) and D3 receptors (D3Rs). In terms of mode of action, these antipsychotics are either antagonist or partial agonist at the above-mentioned receptors. Although D2Rs and D3Rs possess high degree of homology in their molecular structure, have common signaling pathways and similar in vitro pharmacology, they have different in vivo pharmacology and therefore behavioral roles. The aim of this review, with summarizing preclinical and clinical evidence is to demonstrate that while currently used antipsychotics display substantial in vitro affinity for both D3Rs and D2Rs, only very few can significantly occupy D3Rs in vivo. The relative importance of the level of endogenous extracellular dopamine in the brain and the degree of in vitro D3Rs receptor affinity and selectivity as determinant factors for in vivo D3Rs occupancy by antipsychotics, are also discussed.

Synthesis and biological evaluation of 18F-labelled dopamine D3 receptor selective ligands

The dopamine D3 receptor (D3R) is highly expressed in the limbic regions of the brain and closely related to a variety of neurological disorders including Parkinson's disease, schizophrenia and drug-seeking behavior. In vivo imaging of D3R with radio-labelled tracers and positron emission tomography (PET) has become a powerful technique in related disorders. In this study, we synthesized three novel aromatically 18F-labelled phenylpiperazine-like D3R selective radioactive ligands ([18F]5b, [18F]8b and [18F]11b) and developed a simple, rapid and efficient 18F-labelling method by condition optimization. Radiosynthesis of [18F]5b, [18F]8b and [18F]11b was achieved by 18F-fluorination from nitroarene precursors. Final radiochemical purities of [18F]5b, [18F]8b and [18F]11b solution were > 99% and remained good stability (> 98% for up to 6 h) in PBS and FBS. PET imaging and cellular binding studies revealed that [18F]8b had a higher D3R affinity than [18F]5b and [18F]11b. Autoradiography and biodistribution studies of the brain showed that [18F]8b had medium intensity specific accumulation in the striatum and cortex. Meanwhile, the low skeletal uptake of [18F]8b revealed a good in vivo stability with negligible defluorination. These results indicated that [18F]8b might be a potential 18F-labelled D3R PET imaging agent.

Pathophysiology, prognosis and treatment of tardive dyskinesia.

Tardive dyskinesia (TD), a movement disorder associated with antipsychotics, most frequently affects the lower face and jaw muscles, but can also affect walking, breathing and use of the hands and limbs. Knowledge of TD among physicians may be limited, and the pathophysiology of TD is poorly understood. We conducted this review to summarise the current knowledge surrounding the pathophysiology of TD and present recommendations for prevention and treatment based on a literature search and roundtable discussion attended by psychiatrists in Japan. It has been suggested that dopamine hypersensitivity, damaged gamma-aminobutyric acidergic neurons and/or increased production of reactive oxygen species may contribute to development of TD. Symptoms can profoundly affect everyday life; patients who develop TD have poorer prognoses, worse health-related quality of life, greater social withdrawal and higher mortality than patients without TD. Traditional treatment options include dietary supplements, although evidence for their effectiveness is low. Among pharmaceutical interventions, there is moderate evidence that switching to the second-generation antipsychotic clozapine, which has a lower affinity for dopamine D2 receptors than other antipsychotics, may improve symptoms. Vesicular monoamine transporter 2 (VMAT-2) inhibitors, which oppose the increased dopaminergic activity associated with prolonged antipsychotic use by interfering with dopamine uptake and storage, have the strongest evidence for efficacy. VMAT-2 inhibitors are approved in the United States for the treatment of TD, and the first VMAT-2 inhibitor was approved in Japan for this indication in March 2022. Most guidelines recommend treating TD by first reducing the dose of antipsychotics or switching to clozapine or other second-generation antipsychotics, which have a lower association with TD than first-generation antipsychotics. We recommend focusing on prevention and monitoring for TD when prescribing antipsychotics, given that TD is often irreversible. Physicians should treat with antipsychotics only when necessary and at the lowest effective dose, and frequently monitor for TD symptoms.Plain Language Summary Plain Language Summary (In Japanese) Visual Summary Visual Summary (In Japanese)

ERK1/2 kinases and dopamine D2 receptors participate in the anticonvulsant effects of a new derivative of benzoylpyridine oxime and valproic acid

Inhibition of the activity of extracellular signal-regulated kinases (ERK1/2) induced by the activation of the dopamine D2 receptor signalling cascade may be a promising pharmacological target. The aim of this work was to study the involvement of ERK1/2 and dopamine D2 receptor in the mechanism of the anticonvulsant action of valproic acid (VA) and a new benzoylpyridine oxime derivative (GIZH-298), which showed antiepileptic activity in different models of epilepsy. We showed that subchronic exposure to maximal electroshock seizures (MES) for 5 days reduced the density of dopamine D2 receptors in the striatum of mice. GIZH-298 counteracted the decrease in the number of dopamine D2 receptors associated with MES and increased the number of ligand binding sites of dopamine D2 receptors in mice without MES. The affinity of dopamine D2 receptors to the ligand was not changed by GIZH-298. MES caused an increase in ERK1/2 and synapsin I phosphorylation in the striatum while GIZH-298, similar to VA, reduced the levels of both phospho-ERK1/2 and phosphosynapsin I after MES, which correlated with the decrease in the intensity of seizure in mice. In addition, GIZH-298 suppressed ERK1/2 phosphorylation in SH-SY5Y human neuroblastoma cells at therapeutic concentrations, while VA inhibited ERK1/2 phosphorylation in vivo but not in vitro. The data obtained expand the understanding of the mechanisms of action of VA and GIZH-298, which involve regulating the activity of ERK1/2 kinases, probably by modulating dopamine D2 receptors in limbic structures, as well as (in the case of GIZH-298) directly inhibiting of the ERK1/2 cascade.

Pimavanserin exhibits serotonin 5-HT2A receptor inverse agonism for Gαi1- and neutral antagonism for Gαq/11-proteins in human brain cortex

Pimavanserin is claimed as the first antipsychotic drug that shows selectivity for serotonin 5-HT2 receptors (5-HT2Rs) and lacks of affinity for dopamine D2 receptors (D2Rs). Cell-based functional assays suggest that pimavanserin and antipsychotics with D2R/5-HT2R affinity could act as inverse agonists of 5-HT2ARs. However, there is not evidence of such pharmacological profile in native brain tissue. 5-HT2ARs are able to engage both canonical Gαq/11- and non-canonical Gαi1-proteins. In the present study, the response to pimavanserin of the 5-HT2AR coupling to Gαq/11- and Gαi1-proteins was measured in membranes of postmortem human prefrontal cortex by antibody-capture [35S]GTPγS binding scintillation proximity assays. Pimavanserin promoted a concentration-dependant inhibition of the 5-HT2AR coupling to Gαi1-proteins whereas the response of Gαq/11-proteins was unaltered, suggesting inverse agonism and neutral antagonism properties, respectively. The inhibition was abolished in the presence of the selective 5-HT2AR antagonist MDL-11,939 and was absent in brain cortex of 5-HT2AR knock-out mice when compared to respective 5-HT2AR wild-type animals. In conclusion, the results demonstrate the existence of constitutive 5-HT2AR activity in human brain for the signalling pathway mediated by Gαi1-proteins. Pimavanserin demonstrates 5-HT2AR functional selectivity and exhibits inverse agonist profile towards Gαi1-proteins, which is considered the effector pathway promoting hallucinogenic responses. In contrast, pimavanserin behaves as neutral antagonist on the 5-HT2AR coupling to the canonical Gαq/11-protein pathway. The results strengthen the relevance of inverse agonism as potential mechanism of antipsychotic activity. Moreover, the existence of functional selectivity of 5-HT2ARs for different Gα-proteins could contribute to better design of 5-HT2AR-related antipsychotic drugs.

Cariprazine for bipolar depression: What is the number needed to treat, number needed to harm and likelihood to be helped or harmed?

Cariprazine is an oral antipsychotic approved in the US for the treatment of schizophrenia, acute bipolar mania, and most recently, bipolar depression. The aim of this systematic review is to describe the efficacy, tolerability and safety of cariprazine for the treatment of depressive episodes associated with bipolar I disorder (bipolar depression) in adults. The pivotal registration trials were accessed by querying http://www.ncbi.nlm.nih.gov/pubmed/ and http://www.clinicaltrials.gov, for the search terms "cariprazine" AND "bipolar" AND "depression," and by also querying the Web of Science commercial database for clinical poster abstracts, and by asking the manufacturer for copies of posters presented at congresses. Product labelling provided additional information. Double-blind placebo-controlled studies in adults with bipolar depression. Descriptions of the principal results and calculation of number needed to treat (NNT) and number needed to harm (NNH) for relevant dichotomous outcomes were calculated from the available study reports and other sources of information. Cariprazine differs from other antipsychotics in that it has a 10-fold higher affinity for dopamine D3 receptors than for D2 receptors. Cariprazine's principal active metabolite, didesmethyl-cariprazine (DDCAR), has a half-life of 1-3weeks and at steady state DDCAR is the predominant circulating moiety. Four double-blind placebo-controlled studies of cariprazine for bipolar depression were found of which three were considered positive and provided data on efficacy; all four studies were used to assess tolerability. Rates of treatment response, defined by a ≥50% reduction from baseline on the Montgomery-Asburg Depression Ratting Scale (MADRS) total score at study endpoint, for the approved doses of 1.5 and 3.0mg/d (pooled) vs placebo were 46.3% vs 35.9% (NNT 10, 95% CI 7-21). Corresponding rates for remission (defined as MADRS total score ≤10 at endpoint) were 30.2% vs 20.9% (NNT 11, 95% CI 8-22). Discontinuation rates because of an adverse event (AE) were 6.7% for cariprazine (all doses pooled) vs 4.8% for placebo (NNH 51, ns). Product labelling lists the most common AEs as nausea, akathisia, restlessness and extrapyramidal symptoms. Patients receiving cariprazine 3.0 vs 1.5mg/d were more likely to experience AEs and discontinue the trials because of an AE. Cariprazine is the fourth agent approved for bipolar depression in the US. The likelihood to experience a benefit (response or remission) is substantially greater than the likelihood to encounter a discontinuation because of an AE. Direct, head-to-head comparisons with the other approved choices for bipolar depression in the "real world" are needed.

Leveraging a Low-Affinity Diazaspiro Orthosteric Fragment to Reduce Dopamine D3 Receptor (D3R) Ligand Promiscuity across Highly Conserved Aminergic G-Protein-Coupled Receptors (GPCRs).

Previously, we reported a 3-(2-methoxyphenyl)-9-(3-((4-methyl-5-phenyl-4 H-1,2,4-triazol-3-yl)thio)propyl)-3,9-diazaspiro[5.5]undecane (1) compound with excellent dopamine D3 receptor (D3R) affinity (D3R Ki = 12.0 nM) and selectivity (D2R/D3R ratio = 905). Herein, we present derivatives of 1 with comparable D3R affinity (32, D3R Ki = 3.2 nM, D2R/D3R ratio = 60) and selectivity (30, D3R Ki = 21.0 nM, D2R/D3R ratio = 934). Fragmentation of 1 revealed orthosteric fragment 5a to express an unusually low D3R affinity ( Ki = 2.7 μM). Compared to piperazine congener 31, which retains a high-affinity orthosteric fragment (5d, D3R Ki = 23.9 nM), 1 was found to be more selective for the D3R among D1- and D2-like receptors and exhibited negligible off-target interactions at serotoninergic and adrenergic G-protein-coupled receptors (GPCRs), common off-target sites for piperazine-containing D3R scaffolds. This study provides a unique rationale for implementing weakly potent orthosteric fragments into D3R ligand systems to minimize drug promiscuity at other aminergic GPCR sites.

Novel sumanirole bivalent analogues as potent dopamine D2 receptor Go‐protein biased agonists

The dopamine D2 receptor (D2R) is a major target for therapeutic development of treatments for neuropsychiatric disorders. In particular, D2R agonists have been used for neurological disorders such as restless leg syndrome and Parkinson's Disease. However, current D2R agonist pharmacotherapies have drawbacks including the development of tolerance and other adverse side‐effects. To potentially improve D2R agonist‐based medications, we have designed bivalent ligands that have two pharmacophores tethered by a link. This strategy aims to improve selectivity, affinity, and cell signaling activation bias. Indeed, it has been demonstrated that the secondary pharmacophore plays a key role in inducing activation bias towards either G protein, or β‐arrestin pathways.Here we characterized a series of bivalent orthosteric‐arthosteric heteroaryl pharmacophores with assorted linkers and compared them with the potent orthosteric D2R‐selective agonist, sumanirole. Several bivalent analogues demonstrated modest increases in D2R affinity compared to sumanirole. D2R functional assays using bioluminescence resonance energy transfer (BRET) showed improved efficacy and potency for G protein coupling, but substantially diminished efficacy and potency for β‐arrestin recruitment. Analysis using an operational model of bias revealed significant G‐protein activation bias (&gt;1000‐fold). Further, several compounds exhibited a G protein subtype (GoA over Gi1) activation bias. Finally, D2R‐mediated, G protein‐coupled inwardly‐rectifying potassium channel (GIRK) activity was measured in midbrain slices using electrophysiology. Recordings from D2R‐expressing dopaminergic cells in the ventral tegmental area confirmed prolonged GIRK activation by the biased bivalent compounds, compared to dopamine or sumanirole.Our novel sumanirole bivalent analogues demonstrate a proof of concept for G protein activation bias and thus may lead to D2R agonist therapeutics with reduced tolerance and improved efficacy. With these novel tools, the preferential targeting and activation of Go‐proteins, the most predominant Gi‐like protein family in the brain, are now conceivable in animal models. This advance may aid in treatments of basal ganglia disorders with reductions in untoward side‐effects in humans.Support or Funding InformationWork was supported by the Intramural funds of the National Institute on Drug AbuseThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Novel and Potent Dopamine D2 Receptor Go-Protein Biased Agonists.

The discovery of functionally biased and physiologically beneficial ligands directed toward G-protein coupled receptors (GPCRs) has provided the impetus to design dopamine D2 receptor (D2R) targeted molecules that may be therapeutically advantageous for the treatment of certain neuropsychiatric or basal ganglia related disorders. Here we describe the synthesis of a novel series of D2R agonists linking the D2R unbiased agonist sumanirole with privileged secondary molecular fragments. The resulting ligands demonstrate improved D2R affinity and selectivity over sumanirole. Extensive in vitro functional studies and bias factor analysis led to the identification of a novel class of highly potent Go-protein biased full D2R agonists with more than 10-fold and 1000-fold bias selectivity toward activation of specific G-protein subtypes and β-arrestin, respectively. Intracellular electrophysiological recordings from midbrain dopamine neurons demonstrated that Go-protein selective agonists can elicit prolonged ligand-induced GIRK activity via D2Rs, which may be beneficial in the treatment of dyskinesias associated with dopamine system dysfunction.

O-methyl-11C]N-(4-(4-(3-Chloro-2-methoxyphenyl)-piperazin-1-yl)butyl)-1H-indole-2-carboxamide ([11C]BAK4-51) Is an Efflux Transporter Substrate and Ineffective for PET Imaging of Brain D₃ Receptors in Rodents and Monkey.

Selective high-affinity antagonists for the dopamine D3 receptor (D3R) are sought for treating substance use disorders. Positron emission tomography (PET) with an effective D3R radioligand could be a useful tool for the development of such therapeutics by elucidating pharmacological specificity and target engagement in vivo. Currently, a D3R-selective radioligand does not exist. The D3R ligand, N-(4-(4-(3-chloro-2-methoxyphenyl)piperazin-1-yl)butyl)-1H-indole-2-carboxamide (BAK4-51, 1), has attractive properties for PET radioligand development, including full antagonist activity, very high D3R affinity, D3R selectivity, and moderate lipophilicity. We labeled 1 with the positron-emitter carbon-11 (t1/2 = 20.4 min) in the methoxy group for evaluation as a radioligand in animals with PET. However, [11C]1 was found to be an avid substrate for brain efflux transporters and lacked D3R-specific signal in rodent and monkey brain in vivo.

Antipsychotic-induced motor symptoms in schizophrenic psychoses-Part1 : Dystonia, akathisia und parkinsonism

Acute antipsychotic-induced movement disorders (AIMD) are clinically relevant since they are frequently associated with high subjective distress, and since over the long-term they can negatively impact treatment adherence of patients with schizophrenic psychoses. This review article summarizes the relevant studies on the prevalence, risk factors, prevention and treatment options and instruments for early prediction of acute AIMD in schizophrenic psychoses. The current evidence and treatment recommendations are divided into three main areas: acute dystonia, akathisia, and parkinsonism. For the treatment of acute dystonia trihexyphenidyl and biperiden have shown their efficacy. Considering pharmacological treatment of akathisia, there is some preliminary evidence for medication with lipophilic beta-receptor blockers (propranolol and pindolol), clonidine, benzodiazepines, mianserin, mirtazapine und trazodone. The treatment options for drug-induced parkinsonism include reduction or switching from one antipsychotic to another with alower affinity for dopamine D2 receptors, amantadine or in the regular administration of anticholinergic drugs. In conclusion, acute AIMD is easily to recognize but is not always effectively and durably treated. Early recognition and treatment of acute AIMD could be associated with improved treatment outcomes.

O4.3. INCREASED CEREBRAL BLOOD FLOW AFTER SINGLE DOSE OF ANTIPSYCHOTICS IN HEALTHY SUBJECTS DEPENDS ON DOPAMINE D2 RECEPTOR DENSITY PROFILES EVALUATED WITH PET AND MRNA EXPRESSION DATA.

BackgroundPrevious studies measuring cerebral blood flow (CBF) with magnetic resonance sequences like Arterial Spin Labelling (ASL) showed that patients with schizophrenia (SCZ) have increased CBF in basal ganglia and reduced blood flow in cortical areas like the prefrontal cortex. It is still not clear whether these abnormalities are related to antipsychotic treatment or rather they reflect a disease trait independent from medication. Interestingly, administration of single dose of antipsychotics in healthy volunteers produce marked functional effects that are in the same region reported as altered in SCZ. These effects are thought to depend on dopamine D2 receptor (D2R) blockade, although their relationship with antipsychotic pharmacodynamics has not been fully established yet. In fact, the haemodynamic nature of CBF measures makes difficult to interpret drug effects in terms of altered neurotransmission function. Here, we tested whether CBF changes induced by different antipsychotics mirror receptor distribution profiles of D2R. We evaluated the correlation of CBF variation with receptor density as measured with PET and brain mRNA expression extracted from the Allen Human Brain Atlas (ABA).MethodsForty-two healthy male subjects were enrolled in a double blind, randomized, placebo-controlled, crossover study. Participants were randomized in two equal parallel groups to receive a single dose of antipsychotic/placebo in three separate sessions. In Group 1 placebo, olanzapine 7.5mg (OLA) or haloperidol 3mg (HAL) were administered before the MRI scan. In Group 2 participants received placebo, 0.5mg (lowRIS) or 2mg (highRIS) of risperidone. Regional CBF was assessed with pseudo-continuous ASL (pCASL) sequence. For each antipsychotic, a paired T-test was performed in SPM12 with global CBF values as covariate of no interest.A template image of dopamine D2 receptor density was derived from 6 PET scans in healthy volunteers using the high affinity D2/D3 antagonist ligand [18F]-Fallypride. Brain mRNA expression values for DRD2 gene (coding for D2R) were extracted from the ABA dataset by using the MENGA toolbox. CBF contrast images and the [18F]Fallypride BPND template were segmented into 83 ROIs by using the Desikan-Killiany Atlas. The regional changes in CBF against placebo (∆CBF) were compared with regional BPND values and gene expression maps using multivariate correlations.ResultsFor all antipsychotics, CBF changes in each ROI were directly proportional to [18F]Fallypride non displaceable binding potential (BPND) values (OLA R2= 0.24, HAL R2= 0.61, lowRIS R2= 0.54, highRIS R2= 0.52, all p<0.001) and DRD2 mRNA expression levels (OLA R2= 0.04, HAL R2= 0.15, lowRIS R2= 0.19, highRIS R2= 0.20, all chance likelihood <2%).DiscussionIn the present study, we were able to show that the CBF increase induced by antipsychotic is directly proportional to D2R concentration in the brain, as indexed by PET BPND maps and mRNA expression levels. Interestingly, the association strength between ∆CBF and brain receptor distribution profiles mirrored differential D2R affinity between the tested drugs. Overall, these results indicate that CBF increases after administration of a single dose of antipsychotics actually reflect known pharmacodynamics profile of these compounds. In addition, these results further reinforce previous evidence suggesting the role of D2R blockade as a mechanism behind increased CBF induced by antipsychotics. Finally, CBF is ultimately a functional marker and this work is important in bridging the considerable gap between the pharmacokinetic and pharmacodynamic effects of compounds with unclear brain functional effects like antipsychotics.

Immediate-Early Genes Modulation by Antipsychotics: Translational Implications for a Putative Gateway to Drug-Induced Long-Term Brain Changes.

An increasing amount of research aims at recognizing the molecular mechanisms involved in long-lasting brain architectural changes induced by antipsychotic treatments. Although both structural and functional modifications have been identified following acute antipsychotic administration in humans, currently there is scarce knowledge on the enduring consequences of these acute changes. New insights in immediate-early genes (IEGs) modulation following acute or chronic antipsychotic administration may help to fill the gap between primary molecular response and putative long-term changes. Moreover, a critical appraisal of the spatial and temporal patterns of IEGs expression may shed light on the functional “signature” of antipsychotics, such as the propensity to induce motor side effects, the potential neurobiological mechanisms underlying the differences between antipsychotics beyond D2 dopamine receptor affinity, as well as the relevant effects of brain region-specificity in their mechanisms of action. The interest for brain IEGs modulation after antipsychotic treatments has been revitalized by breakthrough findings such as the role of early genes in schizophrenia pathophysiology, the involvement of IEGs in epigenetic mechanisms relevant for cognition, and in neuronal mapping by means of IEGs expression profiling. Here we critically review the evidence on the differential modulation of IEGs by antipsychotics, highlighting the association between IEGs expression and neuroplasticity changes in brain regions impacted by antipsychotics, trying to elucidate the molecular mechanisms underpinning the effects of this class of drugs on psychotic, cognitive and behavioral symptoms.

Dropped Head Syndrome after Minor Trauma in a Patient with Levosulpiride-Aggravated Vascular Parkinsonism.

Dropped Head Syndrome after Minor Trauma in a Patient with Levosulpiride-Aggravated Vascular Parkinsonism.

The fast-off hypothesis revisited: A functional kinetic study of antipsychotic antagonism of the dopamine D2 receptor

Newer, “atypical” antipsychotics carry a lower risk of motor side-effects than older, “typical” compounds. It has been proposed that a ~100-fold faster dissociation from the dopamine D2 receptor (D2R) distinguishes atypical from typical antipsychotics. Furthermore, differing antipsychotic D2R affinities have been suggested to reflect differences in dissociation rate constants (koff), while association rate constants (kon) were assumed to be similar. However, it was recently demonstrated that lipophilic accumulation of ligand in the cell interior and/or membrane can cause underestimation of koff, and as high-affinity D2R antagonists are frequently lipophilic, this may have been a confounding factor in previous studies. In the present work, a functional electrophysiology assay was used to measure the recovery of dopamine-mediated D2R responsivity from antipsychotic antagonism, using elevated concentrations of dopamine to prevent the potential bias of re-binding of lipophilic ligands. The variability of antipsychotic kon was also reexamined, capitalizing on the temporal resolution of the assay. kon was estimated from the experimental recordings using a simple mathematical model assumed to describe the binding process. The time course of recovery from haloperidol (typical antipsychotic) was only 6.4- to 2.5-fold slower than that of the atypical antipsychotics, amisulpride, clozapine, and quetiapine, while antipsychotic kons were found to vary more widely than previously suggested. Finally, affinities calculated using our kon and koff estimates correlated well with functional potency and with affinities reported from radioligand binding studies. In light of these findings, it appears unlikely that typical and atypical antipsychotics are primarily distinguished by their D2R binding kinetics.

Impact of antipsychotic medication on transcranial direct current stimulation (tDCS) effects in schizophrenia patients

Transcranial direct current stimulation (tDCS) has generated interest as a treatment modality for schizophrenia. Dopamine, a critical pathogenetic link in schizophrenia, is also known to influence tDCS effects. We evaluated the influence of antipsychotic drug type (as defined by dopamine D2 receptor affinity) on the impact of tDCS in schizophrenia. DSM-IV-TR-diagnosed schizophrenia patients [N=36] with persistent auditory hallucinations despite adequate antipsychotic treatment were administered add-on tDCS. Patients were divided into three groups based on the antipsychotic’s affinity to D2 receptors. An auditory hallucinations score (AHS) was measured using the auditory hallucinations subscale of the Psychotic Symptom Rating Scales (PSYRATS). Add-on tDCS resulted in a significant reduction inAHS. Antipsychotic drug type had a significant effect on AHS reduction. Patients treated with high affinity antipsychotics showed significantly lesser improvement compared to patients on low affinity antipsychotics or a mixture of the two. Furthermore, a significant sex-by-group interaction occurred; type of medication had an impact on tDCS effects only in women. Improvement differences could be due to the larger availability of the dopamine receptor system in patients taking antipsychotics with low D2 affinity. Sex-specific differences suggest potential estrogen-mediated effects. This study reports a first-time observation on the clinical utility of antipsychotic drug type in predicting tDCS effects in schizophrenia.

Can quetiapine extended release (ER) induce labial edema in a female patient with treatment-resistant major depressive episode?

Major depressive episode (MDE) is a clinical condition affecting about 350 million people worldwide, and leading a high morbidity and mortality. There are a large proportion of patients who still do not always respond to currently available and conventional pharmacological treatments (antidepressant medication). Rates of treatment-resistant depression (TRD) range from 2–3 to 30 %, vary according to the threshold of unsuccessful trials: it remains, however, a significant clinical challenge [1]. Quetiapine extended release (ER) is classified as an atypical antipsychotic that is commonly prescribed for a broad range of psychiatric conditions, also in off label use (such as sleep disturbances in dementia, anxiety and personality disorders). It has been approved and proven to be effective in the treatment of schizophrenia, bipolar disorder (acute phases and long-term treatment) and, recently, as an adjunctive agent in patients with partial or no response to a conventional treatment [2]. It is mainly metabolized in the liver via cytochrome P450 isoenzyme CYP3A4 and it is characterized by the weakest affinity for dopamine D2 receptors of all the antipsychotics: this drug certainly binds D2 receptors, but rapidly dissociates from them. It exhibits a strong affinity for antagonism at histamine H1-receptors, similar to that of diphenhydramine, amitriptyline, mirtazapine, and has a moderate affinity for serotonin type 2A (5-HT2A) receptors. Other neurotransmitter systems are involved such as serotoninergic (5-HT2C, 5-HT6, 5-HT7), adrenergic (a1, a2), muscarinic (M1, M3) receptors, and a partial agonist to serotonin 5HT1A receptors. Case reports reporting peripheral edema induced by quetiapine are described in literature [3] but no case report exists reporting labial edema.