Carolina Muguruza

Identification of Three Residues Essential for 5-Hydroxytryptamine 2A-Metabotropic Glutamate 2 (5-HT2A·mGlu2) Receptor Heteromerization and Its Psychoactive Behavioral Function

Background: The 5-HT2A·mGlu2 receptor heterocomplex is involved in psychosis. Results: Substitution of Ala-6774.40, Ala-6814.44, and Ala-6854.48 in mGlu2 abolishes the behavioral effects of hallucinogenic 5-HT2A agonists. Conclusion: Three residues at transmembrane domain 4 of mGlu2 are necessary to form the 5-HT2A·mGlu2 receptor heterocomplex. Significance: These results provide insight into the structure and behavioral function of the 5-HT2A·mGlu2 receptor heterocomplex. Serotonin and glutamate G protein-coupled receptor (GPCR) neurotransmission affects cognition and perception in humans and rodents. GPCRs are capable of forming heteromeric complexes that differentially alter cell signaling, but the role of this structural arrangement in modulating behavior remains unknown. Here, we identified three residues located at the intracellular end of transmembrane domain four that are necessary for the metabotropic glutamate 2 (mGlu2) receptor to be assembled as a GPCR heteromer with the serotonin 5-hydroxytryptamine 2A (5-HT2A) receptor in the mouse frontal cortex. Substitution of these residues (Ala-6774.40, Ala-6814.44, and Ala-6854.48) leads to absence of 5-HT2A·mGlu2 receptor complex formation, an effect that is associated with a decrease in their heteromeric ligand binding interaction. Disruption of heteromeric expression with mGlu2 attenuates the psychosis-like effects induced in mice by hallucinogenic 5-HT2A agonists. Furthermore, the ligand binding interaction between the components of the 5-HT2A·mGlu2 receptor heterocomplex is up-regulated in the frontal cortex of schizophrenic subjects as compared with controls. Together, these findings provide structural evidence for the unique behavioral function of a GPCR heteromer.

Dysregulated 5-HT2A receptor binding in postmortem frontal cortex of schizophrenic subjects

Previous postmortem and neuroimaging studies have repeatedly suggested alterations in serotonin 5-HT(2A) receptor (5-HT(2A)R) binding associated with the pathophysiology of schizophrenia. These studies were performed with ligands, such as ketanserin, altanserin and LSD, that may bind with high-affinity to different structural or functional conformations of the 5-HT(2A)R. Interpretation of results may also be confounded by chronic antipsychotic treatment and suicidal behavior in the schizophrenia group. We quantified 5-HT(2A)R density by radioligand binding assays in postmortem prefrontal cortex of antipsychotic-free (n=29) and antipsychotic-treated (n=16) schizophrenics, suicide victims with other psychiatric diagnoses (n=13), and individually matched controls. [³H]Ketanserin binding, and its displacement by altanserin or the LSD-like agonist DOI, was assayed. Results indicate that the number of [³H]ketanserin binding sites to the 5-HT(2A)R was increased in antipsychotic-free (128 ± 11%), but not in antipsychotic-treated (92 ± 12%), schizophrenic subjects. In suicide victims, [³H]ketanserin binding did not differ as compared to controls. Aging correlated negatively with [³H]ketanserin binding in schizophrenia, suicide victims and controls. The fraction of high-affinity sites of DOI displacing [³H]ketanserin binding to the 5-HT(2A)R was increased in antipsychotic-free schizophrenic subjects. Functional uncoupling of heterotrimeric G proteins led to increased fraction of high-affinity sites of altanserin displacing [³H]ketanserin binding to the 5-HT(2A)R in schizophrenic subjects, but not in controls. Together, these results suggest that the active conformation of the 5-HT(2A)R is up-regulated in prefrontal cortex of antipsychotic-free schizophrenic subjects, and may provide a pharmacological explanation for discordant findings previously obtained.

Antidepressant-like properties of three new α2-adrenoceptor antagonists.

Evidence suggests that depression is associated with an increase in the high-affinity conformation of the α2-adrenoceptors in human brain. Such enhanced α2-adrenoceptor activity could explain the deficit in central noradrenergic transmission described in the aetiology of depression. Thus, administration of α2-adrenoceptor antagonists augments noradrenaline levels and provides an effective therapeutic approach for the treatment of depressive disorders. In previous studies, we have characterized three new synthesized guanidine and 2-aminoimidazoline aromatic derivatives (8b, 17b and 20b) as α2-adrenoceptor antagonists that are able to increase extracellular concentration of noradrenaline in rat brain. The purpose of the present study was to evaluate the in vivo antidepressant-like properties of these three new α2-adrenoceptor antagonists. For that aim, compounds were tested on the tail suspension test (TST) and forced swim test (FST), two classically widely-used behavioural paradigms for the evaluation of antidepressant-like activity. Compound 8b significantly reduced the immobility time at 10, 20 and 40 mg/kg doses in both TST and FST. Compound 17b reduced the immobility time at 40 mg/kg in both TST and FST. Compound 20b showed a significant decrease in the immobility time at 20 mg/kg in the TST. As drugs of reference, fluoxetine induced a significant antidepressant-like effect in both TST and FST, while mirtazapine induced a significant antidepressant-like effect only in the FST. Additionally, none of the tested compounds increased locomotor activity or displayed anxiolytic-like properties. These results suggest that these new synthesized α2-adrenoceptor antagonists may be useful as potential antidepressant drugs.

α2-adrenoceptor antagonists: synthesis, pharmacological evaluation, and molecular modeling investigation of pyridinoguanidine, pyridino-2-aminoimidazoline and their derivatives.

We have previously identified phenylguanidine and phenyl-2-aminoimidazoline compounds as high affinity ligands with conflicting functional activity at the α2-adrenoceptor, a G-protein-coupled receptor with relevance in several neuropsychiatric conditions. In this paper we describe the design, synthesis, and pharmacological evaluation of a new series of pyridine derivatives [para substituted 2- and 3-guanidino and 2- and 3-(2-aminoimidazolino)pyridines, disubstituted 2-guanidinopyridines and N-substituted-2-amino-1,4-dihydroquinazolines] that were found to be antagonists/inverse agonists of the α2-adrenoceptor. Furthermore, the compounds exert their effects at the α2-adrenoceptor both in vitro in human prefrontal cortex tissue and in vivo in rat brain as shown by microdialysis experiments. We also provide a docking study at the α2A- and α2C-adrenoceptor subtypes demonstrating the structural features required for high affinity binding to the receptor.

Antipsychotic-induced Hdac2 transcription via NF-κB leads to synaptic and cognitive side effects

Antipsychotic drugs remain the standard for schizophrenia treatment. Despite their effectiveness in treating hallucinations and delusions, prolonged exposure to antipsychotic medications leads to cognitive deficits in both schizophrenia patients and animal models. The molecular mechanisms underlying these negative effects on cognition remain to be elucidated. Here we demonstrate that chronic antipsychotic drug exposure increases nuclear translocation of NF-κB in both mouse and human frontal cortex, a trafficking event triggered via 5-HT2A-receptor-dependent downregulation of the NF-κB repressor IκBα. This upregulation of NF-κB activity led to its increased binding at the Hdac2 promoter, thereby augmenting Hdac2 transcription. Deletion of HDAC2 in forebrain pyramidal neurons prevented the negative effects of antipsychotic treatment on synaptic remodeling and cognition. Conversely, virally mediated activation of NF-κB signaling decreased cortical synaptic plasticity via HDAC2. Together, these observations may aid in developing therapeutic strategies to improve the outcome of schizophrenia treatment.

Group II Metabotropic Glutamate Receptors as Targets for Novel Antipsychotic Drugs

Schizophrenia is a chronic psychiatric disorder which substantially impairs patients’ quality of life. Despite the extensive research in this field, the pathophysiology and etiology of schizophrenia remain unknown. Different neurotransmitter systems and functional networks have been found to be affected in the brain of patients with schizophrenia. In this context, postmortem brain studies as well as genetic assays have suggested alterations in Group II metabotropic glutamate receptors (mGluRs) in schizophrenia. Despite many years of drug research, several needs in the treatment of schizophrenia have not been addressed sufficiently. In fact, only 5–10% of patients with schizophrenia successfully achieve a full recovery after treatment. In recent years mGluRs have turned up as novel targets for the design of new antipsychotic medications for schizophrenia. Concretely, Group II mGluRs are of particular interest due to their regulatory role in neurotransmission modulating glutamatergic activity in brain synapses. Preclinical studies have demonstrated that orthosteric Group II mGluR agonists exhibit antipsychotic-like properties in animal models of schizophrenia. However, when these compounds have been tested in human clinical studies with schizophrenic patients results have been inconclusive. Nevertheless, it has been recently suggested that this apparent lack of efficacy in schizophrenic patients may be related to previous exposure to atypical antipsychotics. Moreover, the role of the functional heterocomplex formed by 5-HT2A and mGlu2 receptors in the clinical response to Group II mGluR agonists is currently under study.

Guanidine-based α2-adrenoceptor ligands: Towards selective antagonist activity.

Depression has been linked to a selective increase in the high affinity conformation of the α2-adrenergic autoreceptors (α2-ARs) in the human brain as well as to an overexpression of α2-ARs in the hippocampus and cerebral cortex. Thus, the development of novel α2-AR antagonists represents an attractive source of new antidepressants. This paper describes the design, synthesis and pharmacological evaluation of 30 new guanidinium and 2-iminoimidazolidinium as potential α2-AR antagonists. In order to design this new series of α2-AR antagonists, a pharmacophore model was developed using the GALAHAD software. This study suggested that increased substitution in the space surrounding the cationic guanidine moiety might lead selectively to antagonist activity. Following the preparation of compounds incorporating this feature and competitive radioligand binding, [(35)S]GTPγS functional assays revealed that this structural modification affords exclusively α2-AR antagonists, in contrast with the analogous unsubstituted compounds in which a mixture of antagonist/agonist activities was previously observed.

The endocannabinoid system in mental disorders: Evidence from human brain studies

Graphical abstract Figure. No Caption available. ABSTRACT Mental disorders have a high prevalence compared with many other health conditions and are the leading cause of disability worldwide. Several studies performed in the last years support the involvement of the endocannabinoid system in the etiopathogenesis of different mental disorders. The present review will summarize the latest information on the role of the endocannabinoid system in psychiatric disorders, specifically depression, anxiety, and schizophrenia. We will focus on the findings from human brain studies regarding alterations in endocannabinoid levels, cannabinoid receptors and endocannabinoid metabolizing enzymes in patients suffering mental disorders. Studies carried out in humans have consistently demonstrated that the endocannabinoid system is fundamental for emotional homeostasis and cognitive function. Thus, deregulation of the different elements that are part of the endocannabinoid system may contribute to the pathophysiology of several mental disorders. However, the results reported are controversial. In this sense, different alterations in gene and/or protein expression of CB1 receptors have been shown depending on the technical approach used or the brain region studied. Despite the current discrepancies regarding cannabinoid receptors changes in depression and schizophrenia, present findings point to the endocannabinoid system as a pivotal neuromodulatory pathway relevant in the pathophysiology of mental disorders.