The antipsychotic drug sertindole is a specific inhibitor of alpha1A-adrenoceptors in rat mesenteric small arteries

A Concise and Useful Guide to Understand How Alpha1 Adrenoceptor Antagonists Work

Adrenoceptors are the receptors for the catecholamines, adrenaline and noradrenaline. They are divided in α (α1 and α2) and β (β1, β2 and β3). α1-Adrenoceptors are subdivided in α1A, α1B and α1D. Most tissues express mixtures of α1-adrenoceptors subtypes, which appear to coexist in different densities and ratios, and in most cases their responses are probably due to the activation of more than one type. The three subtypes of α1-adrenoceptors are G-protein-coupled receptors (GPCR), specifically coupled to Gq/11. Additionally, the activation of these receptors may activate other signaling pathways or different components of these pathways, which leads to a great variety of possible cellular effects. The first clinically used α1 antagonist was Prazosin, for Systemic Arterial Hypertension (SAH). It was followed by its congeners, Terazosin and Doxazosin. Nowadays, there are many classes of α-adrenergic antagonists with different selectivity profiles. In addition to SAH, the α1-adrenoceptors are used for the treatment of Benign Prostatic Hyperplasia (BPH) and urolithiasis. This antagonism may be part of the mechanism of action of tricyclic antidepressants. Moreover, the activation of these receptors may lead to adverse effects such as orthostatic hypotension, similar to what happens with the antidepressants and with some antipsychotic. Structure-activity relationships can explain, in part, how antagonists work and how selective they can be for each one of the subtypes. However, it is necessary to develop new molecules which antagonize the α1-adrenoceptors or make chemical modifications in these molecules to improve the selectivity, pharmacokinetic profile and/or reduce the adverse effects of known drugs.

The selectivity of α-adrenoceptor agonists for the human α1A, α1B, and α1D-adrenoceptors

Highly selective drugs offer a way to minimize side-effects. For agonist ligands, this could be through highly selective affinity or highly selective efficacy, but this requires careful measurements of intrinsic efficacy. The α1-adrenoceptors are important clinical targets, and α1-agonists are used to manage hypotension, sedation, attention deficit hypersensitivity disorder (ADHD), and nasal decongestion. With 100 years of drug development, there are many structurally different compounds with which to study agonist selectivity. This study examined 62 α-agonists at the three human α1-adrenoceptor (α1A, α1B, and α1D) stably expressed in CHO cells. Affinity was measured using whole-cell 3 H-prazosin binding, while functional responses were measured for calcium mobilization, ERK1/2-phosphorylation, and cAMP accumulation. Efficacy ratios were used to rank compounds in order of intrinsic efficacy. Adrenaline, noradrenaline, and phenylephrine were highly efficacious α1-agonists at all three receptor subtypes. A61603 was the most selective agonist and its very high α1A-selectivity was due to selective α1A-affinity (>660-fold). There was no evidence of Gq-calcium versus ERK-phosphorylation biased signaling at the α1A, α1B, or α1D-adrenoceptors. There was little evidence for α1A calcium versus cAMP biased signaling, although there were suggestions of calcium versus cAMP bias the α1B-adrenoceptor. Comparisons of the rank order of ligand intrinsic efficacy suggest little evidence for selective intrinsic efficacy between the compounds, with perhaps the exception of dobutamine which may have some α1D-selective efficacy. There seems plenty of scope to develop affinity selective and intrinsic efficacy selective drugs for the α1-adrenoceptors in future.

The affinity and selectivity of α-adrenoceptor antagonists, antidepressants, and antipsychotics for the human α1A, α1B, and α1D-adrenoceptors

α1-adrenoceptor antagonists are widely used for hypertension (eg, doxazosin) and benign prostatic hypertrophy (BPH, eg, tamsulosin). Some antidepressants and antipsychotics have been reported to have α1 affinity. This study examined 101 clinical drugs and laboratory compounds to build a comprehensive understanding of α1-adrenoceptor subtype affinity and selectivity. [3H]prazosin whole-cell binding was conducted in CHO cells stably expressing either the full-length human α1A, α1B, or α1D-adrenoceptor. As expected, doxazosin was a high-affinity nonselective α1-antagonist although other compounds (eg, cyclazosin, 3-MPPI, and ARC239) had higher affinities. Several highly α1A-selective antagonists were confirmed (SNAP5089 had over 1700-fold α1A selectivity). Despite all compounds demonstrating α1 affinity, only BMY7378 had α1D selectivity and no α1B-selective compounds were identified. Phenoxybenzamine (used in pheochromocytoma) and dibenamine had two-component-binding inhibition curves at all three receptors. Incubation with sodium thiosulfate abolished the high-affinity component suggesting this part is receptor mediated. Drugs used for hypertension and BPH had very similar α1A/α1B/α1D-adrenoceptor pharmacological profiles. Selective serotonin reuptake inhibitors (antidepressants) had poor α1-adrenoceptor affinity. Several tricyclic antidepressants (eg, amitriptyline) and antipsychotics (eg, chlorpromazine and risperidone) had high α1-adrenoceptor affinities, similar to, or higher than, α blockers prescribed for hypertension and BPH, whereas others had poor α1 affinity (eg, protriptyline, sulpiride, amisulpiride, and olanzapine). The addition of α blockers for the management of hypertension or BPH in people already taking tricyclic antidepressants and certain antipsychotics may not be beneficial. Awareness of the α-blocking potential of different antipsychotics may affect the choice of drug for those with delirium where additional hypotension (eg, in sepsis) may be detrimental.

A systematic review of genetic variants associated with metabolic syndrome in patients with schizophrenia

Metabolic syndrome (MetS) is a cluster of factors that increases the risk of cardiovascular disease (CVD), one of the leading causes of mortality in patients with schizophrenia. Incidence rates of MetS are significantly higher in patients with schizophrenia compared to the general population. Several factors contribute to this high comorbidity. This systematic review focuses on genetic factors and interrogates data from association studies of genes implicated in the development of MetS in patients with schizophrenia. We aimed to identify variants that potentially contribute to the high comorbidity between these disorders. PubMed, Web of Science and Scopus databases were accessed and a systematic review of published studies was conducted. Several genes showed strong evidence for an association with MetS in patients with schizophrenia, including the fat mass and obesity associated gene (FTO), leptin and leptin receptor genes (LEP, LEPR), methylenetetrahydrofolate reductase (MTHFR) gene and the serotonin receptor 2C gene (HTR2C). Genetic association studies in complex disorders are convoluted by the multifactorial nature of these disorders, further complicating investigations of comorbidity. Recommendations for future studies include assessment of larger samples, inclusion of healthy controls, longitudinal rather than cross-sectional study designs, detailed capturing of data on confounding variables for both disorders and verification of significant findings in other populations. In future, big genomic datasets may allow for the calculation of polygenic risk scores in risk prediction of MetS in patients with schizophrenia. This could ultimately facilitate early, precise, and patient-specific pharmacological and non-pharmacological interventions to minimise CVD associated morbidity and mortality.

Clinical significance of pharmacogenomic studies in tardive dyskinesia associated with patients with psychiatric disorders

Pharmacogenomics is the study of the effects of genetic polymorphisms on medication pharmacokinetics and pharmacodynamics. It offers advantages in predicting drug efficacy and/or toxicity and has already changed clinical practice in many fields of medicine. Tardive dyskinesia (TD) is a movement disorder that rarely remits and poses significant social stigma and physical discomfort for the patient. Pharmacokinetic studies show an association between cytochrome P450 enzyme-determined poor metabolizer status and elevated serum antipsychotic and metabolite levels. However, few prospective studies have shown this to correlate with the occurrence of TD. Many retrospective, case-control and cross-sectional studies have examined the association of cytochrome P450 enzyme, dopamine (receptor, metabolizer and transporter), serotonin (receptor and transporter), and oxidative stress enzyme gene polymorphisms with the occurrence and severity of TD. These studies have produced conflicting and confusing results secondary to heterogeneous inclusion criteria and other patient characteristics that also act as confounding factors. This paper aims to review and summarize the pharmacogenetic findings in antipsychotic-associated TD and assess its clinical significance for psychiatry patients. In addition, we hope to provide insight into areas that need further research.

Frequencies of polymorphisms in cytokines, neurotransmitters and adrenergic receptors in patients with complex regional pain syndrome type I after distal radial fracture

OBJECTIVES

The complex regional pain syndrome type I (CRPS I) is one of the main complications after a fracture of the distal radius. The underlying pathology is not fully understood. Different theories have been put forward to explain the pathogenesis of this disease, some including genetic models. The aim of this study was to find a possible genetic involvement in the occurrence of CRPS I.

METHODS

We tested for known single nucleotide polymorphisms in cytokines, adrenergic receptors, and inflammatory neuropeptides in a cohort of patients at risk to develop CRPS I after a distal radius fracture. Subjective pain and functional parameters were recorded during the course of 1 year after trauma.

RESULTS

Fifteen of 163 patients with fractures of the distal radius were diagnosed with CRPS I according to the International Association for the Study of Pain research criteria. A significant association was detected for the rs1048101 polymorphism of the alpha1a-adrenoceptor. All other tested variants were not associated with CRPS I. Patients with CRPS I fared worse in all functional tests compared with the control group.

DISCUSSION

This study suggests the rs1048101 single nucleotide polymorphism within the alpha1a-adrenoceptor as one risk factor for the development of CRPS I after the distal radius fracture.

Pharmacogenetic of response efficacy to antipsychotics in schizophrenia: pharmacodynamic aspects. Review and implications for clinical research

Pharmacogenetics constitutes a new and growing therapeutic approach in the identification of the predictive factors of the response to antipsychotic treatment. This review aims to summarize recent finding into pharmacodynamic approach of pharmacogenetics of antipsychotics and particularly second generation. Studies were identified in the MEDLINE database from 1993 to July 2008 by combining the following Medical Subject Heading search terms: genetic, polymorphism, single nucleotide polymorphism, pharmacogenetics, antipsychotics, and response to treatment as well as individual antipsychotics names. Only pharmacodynamics studies were analyzed and we focused on efficacy studies. We also reviewed the references of ll identified articles. Most studies follow a polymorphism-by-polymorphism approach, and concern polymorphisms of genes coding for dopamine and serotonin receptors. Haplotypic approach has been considered in some studies. Few have studied the combinations of polymorphisms of several genes as a predictive factor of the response to antipsychotics. We present this gene-by-gene approach while detailing the features of the polymorphisms being studied (functionality, linkage disequilibrium) and the features of the studies (studied treatment(s), prospective/retrospective study, pharmacological dosage). We discuss the heterogeneity of the results and their potential clinical implications and extract methodological suggestions for the future concerning phenotype characterization, genotypes variants studied and methodological and statistical approach.

Association of the α2A adrenergic receptor -1291C/G polymorphism and antipsychotic-induced weight gain in European–Americans

Aims: To investigate the -1291 C/G promoter polymorphism (rs1800544) of the adrenergic α-2A receptor (ADRA2A) with clozapine-/olanzapine-induced weight gain in European–Americans and African–Americans. The α-adrenergic receptors inhibit lipolysis in the adipose tissue and are involved in weight gain regulation. Moreover, two previous studies indicated an association with antipsychotic-induced weight gain with the same polymorphism in Asian populations. Materials & methods: We analyzed a relatively large (n = 129) and well-characterized group of patients and monitored them for a period of 6–14 weeks. Our refined sample consisted of 60 European–Americans and 39 African–Americans on clozapine or olanzapine, prospectively. Results: In European–Americans, we observed a significant difference in weight gain across the genotypic categories (p = 0.046). The carriers of the C allele gained more weight compared with the subjects homozygous for the GG allele (CC + CG vs GG; 3.73 ± 4.13 kg vs 0.23 ± 2.92 kg; p = 0.013). We did not find a significant association in African–Americans, although the sample size was probably too small. Conclusion: Our observations suggest a possible role of ADRA2A polymorphisms in clozapine-/olanzpaine-induced weight gain in subjects of European descent.

Orthostatic hypotensive effect of antipsychotic drugs in Wistar rats by in vivo and in vitro studies of alpha1-adrenoceptor function

RATIONALE

Many antipsychotics cause orthostatic hypotension possibly due to antagonist action on resistance vessel alpha1A-adrenoceptors (alpha1A-AR).

OBJECTIVE

We have tested this possibility by determining in Wistar rats how the orthostatic hypotensive effect of several antipsychotic drugs compares with their affinity for adrenoceptors in mesenteric small arteries (MSA with mainly alpha1A-AR) and aorta (mainly alpha1D-AR).

MATERIALS AND METHODS

Using a tilt setup, orthostatic hypotension was measured in anaesthetized rats for prazosin and the antipsychotics haloperidol, sertindole, risperidone, clozapine, ziprasidone, domperidone, olanzapine, and aripiprazole. For in vitro studies, segments of MSA and aorta were mounted on a wire myograph for isometric tension recording. Cumulative concentration-response curves were constructed to phenylephrine (PE) in the absence and presence of the drugs. Apparent affinity (pA2) was calculated by Schild analysis.

RESULTS

Prazosin antagonized tilt-induced and PE responses in both studies (threshold 4 ng/ml, pA2 9.52 MSA, 10.1 aorta). The rank order of the potency of the antipsychotics in the tilt experiments correlated (r2 = 0.69, P = 0.01) with the pA2-values in MSA: Risperidone and sertindole had the highest potency in the tilt test (threshold 159 and 97 ng/ml) and the highest apparent affinity in MSA (pA2 8.92 and 8.78), in contrast with aripiprazole and domperidone, which had the lowest in each case (threshold 4.1 and 3.0 microg/ml, pA2 7.17 and 6.99). In aorta, the pA2 values did not correlate with the in vivo potencies; in particular, sertindole had no functional affinity in aorta.

CONCLUSION

We conclude that the orthostatic hypotensive effect in rats of the antipsychotic drugs investigated is mediated through alpha1A-ARs.

An investigation of the alpha1A-adrenergic receptor gene and antipsychotic-induced side-effects

Antipsychotic treatment is hampered by the induction of side-effects such as tardive dyskinesia (TD), weight gain, sedation and extrapyramidal side-effects (EPS). Identification of the factors related to their development would facilitate their avoidance and the improvement of antipsychotic treatment. It has been hypothesised that genetic variants in drug targeted receptors may contribute to the development of side-effects. In this study, we have investigated the possible influence of genetic variants (-563-C/T, -4155-G/C and -4884-A/G) of the alpha(1A)-adrenergic receptor, an important target of atypical antipsychotic drugs, and development of side-effects after antipsychotic medication in a sample of N = 427 US Caucasian patients. We found several marginal associations (p < 0.05) between alpha(1A)-adrenergic genetic variants and antipsychotic-induced side-effects which did not reach statistical significance after corrections for multiple analyses. These results do not support a major role of alpha(1A)-adrenergic genetic variants in obesity and other side-effects observed after prolonged treatment with antipsychotic medications.

Alpha1-adrenergic receptors mediate the locomotor response to systemic administration of (+/-)-3,4-methylenedioxymethamphetamine (MDMA) in rats

The recreational drug 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) increases locomotor activity when administered to rats. Although the published pharmacology of MDMA has focused almost exclusively on the roles of serotonin and dopamine, in vitro studies indicate that MDMA induces serotonin and norepinephrine release with equal potency. The present experiments tested the hypothesis that blockade of alpha(1)-adrenoceptors with systemic or local administration of the antagonist prazosin would attenuate the locomotor response to systemic administration of (+/-)-MDMA. Pretreatment with systemic prazosin (0.5 mg/kg) or microinjections into either the prefrontal cortex or ventral tegmental area completely blocked the locomotor stimulant effects of 5 mg/kg (+/-)-MDMA, assessed using a computerized Behavioral Pattern Monitor. Prazosin was more potent in blocking the locomotor stimulant effects of (+/-)-MDMA than a 2 mg/kg dose of (+)-amphetamine that produced a similar locomotor activity increase. These results indicate that activation of alpha(1)-adrenoceptors in both the prefrontal cortex and ventral tegmental areas modulates the locomotor response to MDMA.

Myocardium distribution of sertindole and its metabolite dehydrosertindole in guinea-pigs

Sertindole, like other atypical antipsychotics, has been shown to increase the action potential duration and QT interval in a concentration dependent manner, in in vitro electrophysiological studies. However, this does not always translate into increased duration of the QT interval, increased risk of torsade de pointes or sudden death in clinical practice. The reasons for these apparent discrepancies are unclear and many studies have underscored the importance of the interpretation of in vitro electrophysiological data in the context of other pharmacodynamic (e.g. cardiac ion channels target, receptor affinity) and pharmacokinetic parameters (total plasma drug concentration and drug distribution). To address the possible relevance of the concentrations used in experimental studies, the myocardium distribution of sertindole and its metabolite was determined after single and repeated intraperitoneal administration to guinea-pigs. The data suggest that the plasma concentration appears to predict the concentration in the myocardium and that the myocardium concentrations of sertindole are 3.1 times higher than plasma concentrations. Using these data, the relevance of in vitro electrophysiological studies to clinical plasma concentrations has been appraised.

Evidence for involvement of alpha1D-adrenoceptors in contraction of femoral resistance arteries using knockout mice

The role of alpha(1D)-adrenoceptors in vasoconstrictor responses to noradrenaline in mouse femoral resistance arteries was investigated using wire myography in alpha(1D)-adrenoceptor knockout (alpha(1D)-KO) and wild-type (WT) mice of the same genetic background.alpha(1D)-KO mice were 2.5-fold less sensitive than WTs to exogenous noradrenaline and BMY 7378 was significantly less potent against noradrenaline in alpha(1D)-KO mice than in WTs, showing a minor contribution of alpha(1D)-adrenoceptors in response to noradrenaline. Prazosin and 5-methyl-urapidil were equally effective against noradrenaline in alpha(1D)-KO and WT mice. Chloroethylclonidine produced a significantly greater attenuation of the response to noradrenaline in alpha(1D)-KO mice than in WTs. Responses to electrical field stimulation (EFS), at 2-20 Hz for 10 s and 0.09 ms pulse width were significantly smaller overall in alpha(1D)-KOs than in WTs although no significant differences were seen at the different frequencies.BMY 7378 produced significantly greater inhibition of responses at 2 and 5 Hz than at higher frequencies in WTs. In alpha(1D)-KOs, this greater sensitivity to BMY 7378 at lower frequencies was not apparent, confirming that the effect of BMY 7378 was due to blockade of alpha(1D)-adrenoceptors. Prazosin and 5-methyl-urapidil had similar inhibitory effects on responses to EFS in alpha(1D)-KO and WT mice. Chloroethylclonidine inhibited responses to EFS to a significantly greater extent in alpha(1D)-KO mice. The present study with alpha(1D)-KO mice shows that alpha(1D)-adrenoceptors contribute to vasoconstrictor responses to exogenous and neurally released noradrenaline in femoral resistance arteries.

Correlation between mRNA levels and functional role of alpha1-adrenoceptor subtypes in arteries: evidence of alpha1L as a functional isoform of the alpha1A-adrenoceptor

The mRNA levels for the three alpha1-adrenoceptor subtypes, alpha1A, alpha1B, and alpha1D, were quantified by real-time RT-PCR in arteries from Wistar rats. The alpha1D-adrenoceptor was prominent in both aorta (79.0%) and mesenteric artery (68.7%), alpha1A predominated in tail (61.7%) and small mesenteric artery (73.3%), and both alpha1A- and alpha1D-subtypes were expressed at similar levels in iliac artery. The mRNA levels of the alpha1B-subtype were a minority in all vessels (1.7-11.1%). Concentration-response curves of contraction in response to phenylephrine or relaxation in response to alpha1-adrenoceptor antagonists on maximal sustained contraction induced by phenylephrine were constructed from control vessels and vessels pretreated with 100 micromol/l chloroethylclonidine (CEC) for 30 min. The significant decrease in the phenylephrine potency observed after CEC treatment together with the inhibitory potency displayed by 8-{2-[4-(2-methoxyphenyl)-1-piperazinyl]-8-azaspiro (4,5) decane-7-dionedihydrochloride} (BMY-7378, an alpha1D-adrenoceptor antagonist) confirm the relevant role of alpha1D-adrenoceptors in aorta and iliac and proximal mesenteric arteries. The potency of 5-methylurapidil (an alpha1A-adrenoceptor antagonist) and the changes in the potency of both BMY-7378 and 5-methylurapidil after CEC treatment provided evidence of a mixed population of alpha1A- and alpha1D-adrenoceptors in iliac and distal mesenteric arteries. The low potency of prazosin (pIC50 < 9) as well as the high 5-methylurapidil potency in tail and small mesenteric arteries suggest the main role of alpha1A/alpha1L-adrenoceptors with minor participation of the alpha1D-subtype. The mRNA levels and CEC treatment corroborated this pattern and confirmed that the alpha1L-adrenoceptor could be a functional isoform of the alpha1A-subtype.

Antipsychotics lack alpha 1A/B adrenoceptor subtype selectivity in the rat

The alpha1A- and alpha1B-adrenoceptor affinity of the typical (chlorpromazine, haloperidol, pimozide, thioridazine and trifluoperazine) and atypical (clozapine, olanzapine, quetiapine, risperidone and sertindole) antipsychotics was determined by competition binding at alpha1A- and alpha1B-adrenoceptors in rat submaxillary gland and liver. Although all antipsychotics bound to both subtypes with relatively high affinity (K(i)s<74 nM), none were selective (>10-fold). Comparison with published dopamine D2 receptor affinities suggests that antipsychotic blockade of alpha1A- and/or alpha1B-adrenoceptors may contribute to the antipsychotic activity of all the atypical and several of the typical antipsychotics examined.

Alpha1-adrenoceptor subtypes involved in vasoconstrictor responses to exogenous and neurally released noradrenaline in rat femoral resistance arteries

1. The alpha(1)-adrenoceptor subtypes involved in responses to exogenous and neurally released noradrenaline in rat femoral resistance arteries were characterised using a small vessel myograph, with antagonists prazosin (nonsubtype selective), 5-methyl-urapidil (alpha(1A)-selective), BMY 7378 (alpha(1D)-selective) and the alkylating agent chloroethylclonidine (preferential for alpha(1B)-). 2. Prazosin and 5-methyl-urapidil produced rightward shifts of the exogenous noradrenaline concentration - response curve (CRC) with pA(2) values of 9.2 and 9.1 respectively, in agreement with the presence of alpha(1A)-adrenoceptors. BMY 7378 (1 microm) shifted the noradrenaline CRC with an apparent pK(B) of 6.7, in agreement with the presence of alpha(1A)-, but not alpha(1D)-, adrenoceptors. Chloroethylclonidine at 1 microm had no effect and at 10 microm produced only a small reduction (c. 20%) in the maximum response to noradrenaline, indicating little, if any, contribution from alpha(1B)-adrenoceptors. 3. Responses of the rat femoral resistance arteries to electrical field stimulation (EFS) at 5-30 Hz for 10 s and 0.05 ms pulse width were principally due to alpha(1)-adrenoceptor stimulation. Prazosin and 5-methyl-urapidil inhibited EFS-mediated responses with pIC(50)s of 9.3 and 8.2, respectively, consistent with the alpha(1A)-adrenoceptor being the predominant subtype. Responses to EFS at 10-30 Hz were relatively insensitive to BMY 7378 (pIC(50), 6.5-6.7), while responses to 5 Hz were inhibited with a significantly higher pIC(50) of 8.02, suggesting the contribution of alpha(1D)-adrenoceptors. Chloroethylclonidine had no effect on responses to EFS, ruling out the contribution of an alpha(1B)-subtype. In the presence of cocaine, the predominant subtype involved in responses to EFS was the alpha(1A)-adrenoceptor, with a contribution from alpha(1D)-adrenoceptors at low frequency, as seen in the absence of cocaine. However, there was also a significant increase in the sensitivity to BMY 7378 at higher frequencies, suggesting that a further small alpha(1D)-adrenoceptor component may be uncovered in the presence of cocaine. 5. The present study has shown a predominant role of the alpha(1A)-adrenoceptor in contractions due to exogenous noradrenaline and to neurally released noradrenaline in rat femoral resistance arteries. alpha(1D)-Adrenoceptors are not involved in responses to exogenous noradrenaline but appear to be activated by neurally released noradrenaline at a low frequency of stimulation and at higher frequencies in the presence of neuronal-uptake blockade.

Electrophysiological safety of sertindole in dogs with normal and remodeled hearts

Inhibition of the potassium current IKr and QT prolongation are associated with drug-induced torsades de pointes arrhythmias (TdP) and sudden cardiac death. We investigated the cardiac electrophysiological effects of sertindole, an antipsychotic drug reported to prolong the QT interval in schizophrenic patients. In cell cultures, sertindole seemed to be a selective blocker of IHERG over other ion currents. For IHERG, the IC50 value was 64 +/- 7 nM, whereas ISCN5A, ICa,L, ICa,T, IKCNQ1/KCNE1, and IKv4.3 were blocked in the micromolar range. In canine ventricular myocytes, the IC50 value for IKr inhibition by sertindole was 107 +/- 21 nM. Action potentials in these cells prolonged in a reverse rate- and concentration-dependent manner at 10 to 300 nM sertindole. In vivo, sertindole was administered to anesthetized dogs at clinically relevant (0.05-0.20 mg/kg) and high doses (1.0-2.0 mg/kg) i.v. At 0.05 to 0.20 mg/kg sertindole (plasma concentrations 30-157 nM), QTc was prolonged by 1 to 5% in normal dogs and by 9 to 20% in dogs with remodeled hearts due to chronic atrioventricular block (CAVB). TdP was not induced at these doses in normal dogs or in CAVB dogs with reproducible induction of TdP by dofetilide in previous experiments. At 1.0 to 2.0 mg/kg sertindole (plasma concentrations 0.5-3.1 microM), QTc prolonged by 6 to 11% in normal dogs and by 22% in dofetilide-sensitive CAVB dogs. TdP occurred in three of five animals in the latter group. Thus, at high i.v. doses sertindole can pose a serious proarrhythmic risk when electrical remodeling of the ventricles is present. At clinically relevant doses, however, sertindole does not cause TdP in anesthetized dogs with normal or remodeled hearts.

Alpha(1) adrenoceptor subtype selectivity. 3D-QSAR models for a new class of alpha(1) adrenoceptor antagonists derived from the novel antipsychotic sertindole

Receptor-binding affinities for the alpha(1) adrenoceptor subtypes alpha(1a), alpha(1b) and alpha(1d) for a series of 39 alpha(1) adrenoceptor antagonists derived from the antipsychotic sertindole are reported. The SAR of the compounds with respect to affinity for the alpha(1a), alpha(1b) and alpha(1d) adrenoceptor subtypes as well as affinity obtained by an alpha(1) assay (rat brain membranes) were investigated using a 3D-QSAR approach based on the GRID/GOLPE methodology. Good statistics (r(2)=0.91-0.96; q(2)=0.65-0.73) were obtained with the combination of the water (OH2) and methyl (C3) probes. The combination of steric repulsion and electrostatic attractions explain the affinities of the included molecules. The adrenergic alpha(1a) receptor seems to be more tolerant to large substituents in the area between the indole 5- and 6-positions compared to the adrenergic alpha(1b) and alpha(1d) receptor subtypes. There seems to be minor differences in the position of areas in the alpha(1b) receptor compared to alpha(1a) and alpha(1d) receptors where electrostatic interaction between the molecules and the receptor (OH2 probe) contribute to increased affinity. These observations may be used in the design of new subtype selective compounds. In addition, the model based on biological data from an alpha(1) assay (rat brain membranes) resembles the model for the alpha(1b) adrenoceptor subtype.

Synthesis and structure-affinity relationship investigations of 5-aminomethyl and 5-carbamoyl analogues of the antipsychotic sertindole. A new class of selective alpha1 adrenoceptor antagonists

A new class of selective alpha(1) adrenoceptor antagonists derived from the antipsychotic drug sertindole is described. The most potent and selective compound 1-(2-(4-[5-aminomethyl-1-(4-fluorophenyl)-1H-indol-3-yl]-1-piperidinyl)ethyl)-2-imidazolidinone (11) binds with 0.50 nM affinity for alpha(1) adrenergic receptors and with more than 44 times lower affinity for dopamine D(2),D(3), D(4) and serotonin 5-HT(1A), 5-HT(1B), 5-HT(2A) and 5-HT(2C) receptors. The molecular features providing high affinity for adrenergic alpha(1) receptors and high selectivity towards dopamine D(2) and serotonin 5-HT(2A) and 5-HT(2C) receptors are discussed.

Synthesis and structure-affinity relationship investigations of 5-heteroaryl-substituted analogues of the antipsychotic sertindole. A new class of highly selective alpha(1) adrenoceptor antagonists

A new class of 5-heteroaryl-substituted 1-(4-fluorophenyl)-3-(4-piperidinyl)-1H-indoles as highly selective and potentially CNS-active alpha 1-adrenoceptor antagonists is described. The compounds are derived from the antipsychotic sertindole. The structure-affinity relationships of the 5-heteroaryl substituents, and the substituents on the piperidine nitrogen atom were optimized with respect to affinity for alpha 1 adrenoceptors and selectivity in respect to dopamine (D(1-4)) and serotonin (5-HT(1A-1B) and 5-HT(2A,2C)) receptors. The most selective compound obtained, 3-[4-[1-(4-fluorophenyl)-5-(1-methyl-1,2,4-triazol-3-yl)-1H-indol-3-yl]-1-piperidinyl]propionitrile (15c), has affinities of 0.99, 3.2, and 9.0 nM for the alpha(1a), alpha(1b), and alpha(1d) adrenoceptor subtypes, respectively, and a selectivity for adrenergic alpha(1a) receptors in respect to dopamine D2, D3, and D4 and serotonin 5-HT(2A) and 5-HT(2C) higher than 900, comparable to the selectivity of prazosin. In addition, the compound is more than 150-fold selective in respect to serotonin 5-HT(1A) and 5-HT(1B) receptors. A new basic pharmacophore for alpha 1-adrenoceptor antagonists based on a previously reported pharmacophore model for dopamine D2 antagonist is suggested.

Electrophysiologic characterization of the antipsychotic drug sertindole in a rabbit heart model of torsade de pointes: low torsadogenic potential despite QT prolongation

There is growing concern that antipsychotic drugs that prolong the QT interval almost always increase the risk for patients to develop life-threatening ventricular tachyarrhythmias (VTs) of the torsade de pointes type. We therefore sought to compare the electrophysiologic effects of the psychotropic agent sertindole, which prolongs cardiac repolarization by inhibiting the rapid component of the delayed rectifier potassium current (I(Kr)) but has a low torsadogenic potential to the antiarrhythmic agent dl-sotalol. In 18 Langendorff-perfused rabbit hearts, sotalol (10 microM, n = 8) and sertindole (0.5, 1.0, and 1.5 microM; n = 10) led to significant and comparable QT prolongation. In the presence of sotalol, torsade de pointes reproducibly occurred in atrioventricular node-blocked hearts after lowering the potassium concentration to 1.5 mM. High doses of sertindole (1.5 microM) only caused monomorphic VT (n = 4) and nonsustained polymorphic VT (n = 2) in the presence of QRS prolongation. Multiple simultaneous epi- and endocardial monophasic action potentials and a volume-conducted ECG demonstrated widening of the T/U wave, early afterdepolarizations, and increased dispersion of repolarization in the presence of dl-sotalol. In contrast to sotalol, QT and monophasic action potential prolongation were cycle length-independent in the presence of sertindole. Sertindole had no significant effect on transmural or interventricular dispersion of repolarization. Early afterdepolarizations did not occur. Despite comparable QT prolongation, sertindole did not display the proarrhythmic profile typical of other blockers of I(Kr) such as dl-sotalol. It is likely that a different mode of interaction between sertindole and the channel and/or additional pharmacological effects of sertindole, e.g., its ability to inhibit I(Na) and/or its ability to block alpha(1)-receptors, play a role.

No influence of adrenergic receptor polymorphisms on schizophrenia and antipsychotic response

The adrenergic system plays an important role in psychiatric disorders such as depression and schizophrenia. Antagonism of the adrenergic receptor subtypes alpha1A and alpha2A has been found to have an antipsychotic effect. Genetic mutations in these receptors could be related to the alterations in the adrenergic system observed in psychiatric patients and to failure to respond to drug antagonism. We have studied one polymorphism in the alpha1A-adrenergic receptor (Arg492Cys) and two polymorphisms in the promoter region of the alpha2A-adrenergic receptor (-1291-C/G and -261-G/A) in a sample of clozapine-treated schizophrenic patients and controls. No clear differences were observed between the different groups suggesting that these polymorphisms did not play an important role in the aetiology of the disorder or in determining antipsychotic response.

Analysis of alpha 1L-adrenoceptor pharmacology in rat small mesenteric artery

1. To illuminate the controversy on alpha 1A- or alpha 1L-adrenoceptor involvement in noradrenaline-mediated contractions of rat small mesenteric artery (SMA), we have studied the effects of subtype-selective alpha 1-adrenoceptor agonists and antagonists under different experimental conditions. 2. The agonist potency order in rat SMA was: A61603 >> SKF89748-A > cirazoline > noradrenaline > ST-587 > methoxamine. Prazosin antagonized all agonists with a low potency (pA2: 8.29-8.80) indicating the involvement of alpha 1L-rather than alpha 1A-adrenoceptors. 3. The putative alpha 1L-adrenoceptor antagonist JTH-601, but not the alpha 1B-adrenoceptor antagonist chloroethylclonidine (10 microM) antagonized noradrenaline-induced contractions of SMA. The potency of the selective alpha 1D-adrenoceptor antagonist BMY 7378 against noradrenaline (pA2 = 6.16 +/- 0.13) and of the selective alpha 1A-adrenoceptor antagonist RS-17053 against noradrenaline (pKB = 8.35 +/- 0.10) and against the selective alpha 1A-adrenoceptor agonist A-61603 (pKB = 8.40 +/- 0.09) were too low to account for alpha 1D- and alpha 1A-adrenoceptor involvement. 4. The potency of RS-17053 (pKB/pA2's = 7.72-8.46) was not affected by lowering temperature, changing experimental protocol or inducing myogenic tone via KCl or U46619. 5. Selective protection of a putative alpha 1A-adrenoceptor population against the irreversible action of phenoxybenzamine also failed to increase the potency of RS-17053 (pA2 = 8.25 +/- 0.06 against A61603). 6. Combined concentration-ratio analysis demonstrated that tamsulosin, which does not discriminate between alpha 1A- and alpha 1L-adrenoceptors, and RS-17053 competed for binding at the same site in the SMA. 7. In summary, data obtained in our experiments in rat SMA indicate that the alpha 1-adrenoceptor mediating noradrenaline-induced contraction displays a distinct alpha 1L-adrenoceptor pharmacology. This study does not provide evidence for the hypothesis that alpha 1L-adrenoceptors represent an affinity state of the alpha 1A-adrenoceptor in functional assays. Furthermore, there is no co-existing alpha 1A-adrenoceptor in the SMA.

Mechanisms involved in the vasorelaxant effect of (-)-stepholidine in rat mesenteric small arteries

The purpose of the present investigation was to clarify whether the hypotensive action of the protoberberine alkaloid, and dopamine receptor antagonist, (-)-stepholidine, can be ascribed to an effect on peripheral small arteries. For this purpose isolated mesenteric small arteries were suspended in microvascular myographs for isometric tension recording. Relaxations mediated by dopamine D1 receptors were antagonized by (-)-stepholidine. (-)-Stepholidine inhibited in a concentration-dependent manner the contractile responses evoked by noradrenaline (10(-6) M), but not the contractile responses evoked by depolarizing solution (KCl, 60 mM) or 9,11-dideoxy-11alpha,9alpha-epoxymethano prostaglandin F2alpha (U46619, 10(-7) M). Mechanical endothelial cell removal, blockade of K+ channels, muscarinic receptors or adrenoceptors did not influence the inhibitory effect of (-)-stepholidine on the contractile response evoked with noradrenaline in the segments. (-)-Stepholidine caused rightward shifts of the concentration-response curves for noradrenaline and phenylephrine. The pA2 values for (-)-stepholidine were 6.05 and 5.94 against noradrenaline and phenylephrine, respectively. Electrical field stimulation induced prazosin-sensitive frequency-dependent contractions in mesenteric small arteries. These contractions were significantly inhibited by 10(-6) and 10(-5) M (-)-stepholidine. In membranes from the rat cerebral cortex labelled with [3H]prazosin, (-)-stepholidine (10(-7)-10(-4) M) completely inhibited the specific binding of the ligand with a pKi of 5.6. The present investigation suggests the inhibitory effect of (-)-stepholidine on the alpha1-adrenoceptor-mediated contractions induced by exogenously added and nerve-released noradrenaline in peripheral small arteries might contribute to a hypotensive effect of the drug.