Targeting Serotonin 5-HT(2A) Receptors to Better Treat Schizophrenia: Rationale and Current Approaches

Negative Symptoms in Schizophrenia: An Update on Research Assessment and the Current and Upcoming Treatment Landscape

The negative symptoms of schizophrenia include diminished emotional expression, avolition, alogia, anhedonia, and asociality, and due to their low responsiveness to available treatments, are a primary driver of functional disability in schizophrenia. This narrative review has the aim of providing a comprehensive overview of the current research developments in the treatment of negative symptoms in schizophrenia, and begins by introducing the concepts of primary, secondary, prominent, predominant, and broadly defined negative symptoms. We then compare and contrast commonly used research assessment scales for negative symptoms and review the evidence for the specific utility of widely available off-label and investigational treatments that have been studied for negative symptoms. Mechanism of action/putative treatments included are antipsychotics (D2R antagonists), N-methyl-D-aspartate receptor (NMDAR) and other glutamatergic modulators, serotonin receptor (5-HTR) modulators, anti-inflammatory agents, antidepressants, pro-dopaminergic modulators (non-D2R antagonists), acetylcholine modulators, oxytocin, and phosphodiesterase (PDE) inhibitors. With the caveat that no compounds are definitively proven as gold-standard treatments for broadly defined negative symptoms, the evidence base supports several potentially beneficial off-label and investigational medications for treating negative symptoms in schizophrenia, such as monotherapy with cariprazine, olanzapine, clozapine, and amisulpride, or adjunctive use of memantine, setrons such as ondansetron, minocycline, and antidepressants. These medications are widely available worldwide, generally tolerable and could be considered for an off-label, time-limited trial for a predesignated period of time, after which a decision to switch or stay can be made based on clinical response. Among investigational medications, NMDAR agonists, muscarinic agonists, and LB-102 remain under study. Suggestions for future research include reducing placebo effects by designing studies with a smaller number of high-quality study sites, potentially increasing the use of more precise rating scales for negative symptoms, and focused studies in people with predominant negative symptoms.

Brain metabolic profiling of schizophrenia: a path towards a better understanding of the neuropathogenesis of psychosis

Schizophrenia (SCZ) is a complex psychotic syndrome whose pathogenesis involves countless protagonists, none of which, to date, can fully explain how this disorder develops. In this narrative review, an overview of the biochemical impairment is offered according to several perspectives. Indeed, the metabolic framework behind SCZ dopaminergic hypotheses, glutamate - gamma-amynobutyric acid dysregulation, norepinephrine and serotonin, calcium channel dysfunction is addressed together with the energetic impairment, involving glucose and lipids in SCZ etiopathogenesis, in order to highlight the multilevel pathways affected in this neuropsychiatric disorder. Furthermore, neuroinflammation is analyzed, by virtue of its important role, widely investigated in recent years, in neurodegeneration. Tracing the neurotransmitter activity at the brain level by assessing the metabolic network behind the abovementioned molecules puts into light as unavoidable the need for future studies to adopt an integrate approach to address SCZ pathological and clinical picture. The combination of all these factors, essential in acquiring an overview on the complexity of SCZ pathophysiology represents a crucial step in the development of a more targeted management of SCZ patients.

Role of ruscogenin extracted from Radix Ophiopogon Japonicus in antagonizing 5-hydroxytryptamine and dopamine receptors through computational screening

The 5-hydroxytryptamine (5-HT) and dopamine (DA) receptors have emerged as significant targets for therapeutic intervention in psychiatric disorders. Currently, the efficacy of psychiatric drugs is limited by challenges in achieving desired outcomes, the occurrence of adverse effects, dependence, and withdrawal reactions. Consequently, there is a pressing need for the development of safe and effective therapeutic agents for psychiatric disorders. To explore the potential effects of natural product extracts as therapeutic agents for psychiatric disorders, 73 active ingredients from natural medicine extracts were screened to identify potential inhibitors of the serotonin 2A receptor (5-HT2AR) and dopamine D2 receptor (DRD2) using computerized virtual molecular docking. The most effective inhibitor of 5-HT2AR and DRD2 among these natural extracts was then evaluated for its drug-like properties using ADMET analysis, and its mechanisms of antagonism on DRD2 and 5-HT2AR were studied through molecular dynamics simulation. Risperidone was used as a positive control drug. The results showed that ruscogenin (RUS) was the most effective inhibitor of 5-HT2AR and DRD2, possessing favorable drug-like properties (most values of ADMET analysis were within the optimal range). When compared to risperidone, RUS exhibited more stable root mean square deviation (RMSD) plots, lower root mean square fluctuation (RMSF) values from residues 50 to 260, stronger hydrogen bonding interactions, higher compactness, a smaller solvent-accessible surface area (SASA) value, and lower binding free energy (-43.81 kcal/mol vs. -35.68 kcal/mol). RUS also demonstrated inhibitory effects on DRD2, as indicated by stable RMSD plots, low RMSF values from residues 50 to 250, strong hydrogen bonding interactions, high compactness, a small SASA value, and low binding free energy (-35.00 kcal/mol). Consequently, this research suggests that RUS, a natural pharmaceutical extract, is a promising candidate for further validation through clinical studies, representing a potential development of a therapeutic agent targeting psychiatric disorders.

DSP-6745, a novel 5-hydroxytryptamine modulator with rapid antidepressant, anxiolytic, antipsychotic and procognitive effects

BACKGROUND

Current treatment of major depressive disorder is facing challenges, including a low remission rate, late onset of efficacy, and worsening severity due to comorbid symptoms such as psychosis and cognitive dysfunction. Serotonin (5-HT) neurotransmission is involved in a wide variety of psychiatric diseases and its potential as a drug target continues to attract attention.

OBJECTIVES

The present study elucidates the effects of a novel 5-HT modulator, DSP-6745, on depression and its comorbid symptoms.

RESULTS

In vitro radioligand binding and functional assays showed that DSP-6745 is a potent inhibitor of 5-HT transporter and 5-HT2A, 5-HT2C, and 5-HT7 receptors. In vivo, DSP-6745 (6.4 and 19.1 mg/kg as free base, p.o.) increased the release of not only 5-HT, norepinephrine, and dopamine, but also glutamate in the medial prefrontal cortex. The results of in vivo mouse phenotypic screening by SmartCube® suggested that DSP-6745 has a behavioral signature combined with antidepressant-, anxiolytic-, and antipsychotic-like signals. A single oral dose of DSP-6745 (6.4 and 19.1 mg/kg) showed rapid antidepressant-like efficacy in the rat forced swim test, even at 24 h post-dosing, and anxiolytic activity in the rat social interaction test. Moreover, DSP-6745 (12.7 mg/kg, p.o.) led to an improvement in the apomorphine-induced prepulse inhibition deficit in rats. In the marmoset object retrieval with detour task, which is used to assess cognitive functions such as attention and behavioral inhibition, DSP-6745 (7.8 mg/kg, p.o.) enhanced cognition.

CONCLUSIONS

These data suggest that DSP-6745 is a multimodal 5-HT receptor antagonist and a 5-HT transporter inhibitor and has the potential to be a rapid acting antidepressant with efficacies in mitigating the comorbid symptoms of depression.

Bridging the gap: Prenatal nutrition, myelination, and schizophrenia etiopathogenesis

Schizophrenia (SZ) is a complex mental illness characterized by disturbances in thinking, emotionality, and behavior, significantly impacting the quality of life for individuals affected and those around them. The etiology of SZ involves intricate interactions between genetic and environmental factors, although the precise mechanisms remain incompletely understood. Genetic predisposition, neurotransmitter dysregulation (particularly involving dopamine and serotonin), and structural brain abnormalities, including impaired prefrontal cortex function, have been implicated in SZ development. However, increasing evidence reveals the role of environmental factors, such as nutrition, during critical periods like pregnancy and lactation. Epidemiological studies suggest that early malnutrition significantly increases the risk of SZ symptoms manifesting in late adolescence, a crucial period coinciding with peak myelination and brain maturation. Prenatal undernutrition may disrupt myelin formation, rendering individuals more susceptible to SZ pathology. This review explores the potential relationship between prenatal undernutrition, myelin alterations, and susceptibility to SZ. By delineating the etiopathogenesis, examining genetic and environmental factors associated with SZ, and reviewing the relationship between SZ and myelination disorders, alongside the impact of malnutrition on myelination, we aim to examine how malnutrition might be linked to SZ by altering myelination processes, which contribute to increasing the understanding of SZ etiology and help identify targets for intervention and management.

Pharmacodynamic properties of lumateperone and its efficacy in acute bipolar depression: a mechanistic hypothesis based on data

The treatment of bipolar depression is one of the most challenging needs in contemporary psychiatry. Currently, only quetiapine, olanzapine-fluoxetine combination, lurasidone, cariprazine, and recently lumateperone have been FDA-approved to treat this condition. The neurobiology of bipolar depression and the possible mechanistic targets of bipolar antidepressant therapy remain elusive. The current study investigated whether the pharmacodynamic properties of lumateperone fit into a previously developed model which was the first to be derived based on the strict combination of clinical and preclinical data. The authors performed a systematic review of the literature to identify the pharmacodynamic properties of lumateperone. The original model suggests that a constellation of effects on different receptors is necessary, but refinements, including the present study, suggest that the inhibition of the serotonin reuptake at the first level, the 5HT-2A blockade at the second level, and the norepinephrine alpha-1 receptors blockade at a third level in combination with D1 blockade contribute to the antidepressant effect in acute bipolar depression. The D2 blockade acts as a protective mechanism and reduces the risk of switching to mania/hypomania.

Synthesis, In Vitro Biological Evaluation and Molecular Modeling of Benzimidazole-Based Pyrrole/Piperidine Hybrids Derivatives as Potential Anti-Alzheimer Agents

Benzimidazole-based pyrrole/piperidine analogs (1-26) were synthesized and then screened for their acetylcholinesterase and butyrylcholinesterase activities. All the analogs showed good to moderate cholinesterase activities. Synthesized compounds (1-13) were screened in cholinesterase enzyme inhibition assays and showed AChE activities in the range of IC50 = 19.44 ± 0.60 µM to 36.05 ± 0.4 µM against allanzanthane (IC50 = 16.11 ± 0.33 µM) and galantamine (IC50 = 19.34 ± 0.62 µM) and varied BuChE inhibitory activities, with IC50 values in the range of 21.57 ± 0.61 µM to 39.55 ± 0.03 µM as compared with standard allanzanthane (IC50 = 18.14 ± 0.05 µM) and galantamine (IC50 = 21.45 ± 0.21 µM). Similarly, synthesized compounds (14-26) were also subjected to tests to determine their in vitro AChE inhibitory activities, and the results obtained corroborated that all the compounds showed varied activities in the range of IC50 = 22.07 ± 0.13 to 42.01 ± 0.02 µM as compared to allanzanthane (IC50 = 20.01 ± 0.12 µM) and galantamine (IC50 = 18.05 ± 0.31 µM) and varied BuChE inhibitory activities, with IC50 values in the range of 26.32 ± 0.13 to 47.03 ± 0.15 µM as compared to standard allanzanthane (IC50 = 18.14 ± 0.05 µM) and galantamine (IC50 = 21.45 ± 0.21 µM). Binding interactions of the most potent analogs were confirmed through molecular docking studies. The active analogs 2, 4, 10 and 13 established numerous interactions with the active sites of targeted enzymes, with docking scores of -10.50, -9.3, -7.73 and -7.8 for AChE and -8.97, -8.2, -8.20 and -7.6 for BuChE, respectively.

Serotonin 2A Receptor (5-HT2AR) Agonists: Psychedelics and Non-Hallucinogenic Analogues as Emerging Antidepressants

Psychedelics make up a group of psychoactive compounds that induce hallucinogenic effects by activating the serotonin 2A receptor (5-HT2AR). Clinical trials have demonstrated the traditional psychedelic substances like psilocybin as a class of rapid-acting and long-lasting antidepressants. However, there is a pressing need for rationally designed 5-HT2AR agonists that possess optimal pharmacological profiles in order to fully reveal the therapeutic potential of these agonists and identify safer drug candidates devoid of hallucinogenic effects. This Perspective provides an overview of the structure-activity relationships of existing 5-HT2AR agonists based on their chemical classifications and discusses recent advancements in understanding their molecular pharmacology at a structural level. The encouraging clinical outcomes of psychedelics in depression treatment have sparked drug discovery endeavors aimed at developing novel 5-HT2AR agonists with improved subtype selectivity and signaling bias properties, which could serve as safer and potentially nonhallucinogenic antidepressants. These efforts can be significantly expedited through the utilization of structure-based methods and functional selectivity-directed screening.

Psychedelics action and schizophrenia

Psychedelics are compounds acting by serotonin 5-hydroxytryptamine (5-HT)2A receptor activation and induce several behavioral responses. They are of special interest because of their positive effects on neuropsychiatric disorders (depression and posttraumatic stress disorder). However, several findings revealed that some psychedelic actions are similar to symptoms observed in schizophrenia (psychosis, sensorimotor gating impairments, attention, and working memory deficits) which might limit their clinical applications. Psychedelics activate some neurotransmitters, i.e., serotonergic, and glutamatergic, that are also impaired in schizophrenia. Therefore, the neurobiological background of psychedelics and schizophrenia is partially similar. Another important aspect to discuss is the perspective of using psychedelics in schizophrenia therapy. Postmortem studies showed a loss of synapses in schizophrenia, and the positive effects of psychedelics on neuroplasticity (synaptogenesis, neurogenesis, and neuritogenesis) might be essential in the context of schizophrenia therapy. However, because of psychedelics' psychotic action, the recommended doses of psychedelics in schizophrenia treatment are not established, and subpsychedelic dosing or microdosing are considered. Exploratory studies are needed to determine the tolerability of treatment and appropriate dosing regimen. Another therapeutic option is using non-hallucinogenic psychedelic analogs that also induce neuroplastic outcomes but do not have psychotogenic effects. Further preclinical and clinical studies are needed to recognize the potential effectiveness of 5-HT2A agonists in schizophrenia therapy.

Ulotaront: review of preliminary evidence for the efficacy and safety of a TAAR1 agonist in schizophrenia

Ulotaront is a trace amine-associated receptor 1 (TAAR1) agonist in Phase 3 clinical development for the treatment of schizophrenia. Ulotaront was discovered through a unique, target-agnostic approach optimized to identify drug candidates lacking D2 and 5-HT2A receptor antagonism, while demonstrating an antipsychotic-like phenotypic profile in vivo. The mechanism of action (MOA) of ulotaront is thought to be mediated by agonism at TAAR1 and serotonin 5-HT1A receptors. Ulotaront has completed two Phase 2 trials (4-week acute study and 26-week open-label extension) which led to Breakthrough Therapy Designation from the US Food and Drug Administration for the treatment of schizophrenia. In the double-blind, placebo-controlled, acute study, ulotaront was associated with significant (p < 0.001) improvement in Positive and Negative Syndrome Scale (PANSS) total score (effect size [ES]: 0.45), with improvements vs. placebo also observed across secondary endpoints. Post-hoc analyses of the acute trial revealed additional evidence to support the effect of ulotaront on negative symptoms. In the 4-week study, ulotaront was well-tolerated, with an incidence of adverse events (AEs) numerically lower compared to placebo (45.8% vs. 50.4%; with a number needed to harm [NNH] for individual ulotaront AEs all > 40). The open-label extension demonstrated further improvement across schizophrenia symptoms and confirmed the tolerability of ulotaront, with a 6-month completion rate of 67%. Based on current data, ulotaront shows potential to be a first-in-class TAAR1 agonist for the treatment of schizophrenia with a safety and efficacy profile distinct from current antipsychotics.

Lateral Septal Circuits Govern Schizophrenia-Like Effects of Ketamine on Social Behavior

Schizophrenia is marked by poor social functioning that can have a severe impact on quality of life and independence, but the underlying neural circuity is not well understood. Here we used a translational model of subanesthetic ketamine in mice to delineate neural pathways in the brain linked to social deficits in schizophrenia. Mice treated with chronic ketamine (30 mg/kg/day for 10 days) exhibit profound social and sensorimotor deficits as previously reported. Using three- dimensional c-Fos immunolabeling and volume imaging (iDISCO), we show that ketamine treatment resulted in hypoactivation of the lateral septum (LS) in response to social stimuli. Chemogenetic activation of the LS rescued social deficits after ketamine treatment, while chemogenetic inhibition of previously active populations in the LS (i.e. social engram neurons) recapitulated social deficits in ketamine-naïve mice. We then examined the translatome of LS social engram neurons and found that ketamine treatment dysregulated genes implicated in neuronal excitability and apoptosis, which may contribute to LS hypoactivation. We also identified 38 differentially expressed genes (DEGs) in common with human schizophrenia, including those involved in mitochondrial function, apoptosis, and neuroinflammatory pathways. Chemogenetic activation of LS social engram neurons induced downstream activity in the ventral part of the basolateral amygdala, subparafascicular nucleus of the thalamus, intercalated amygdalar nucleus, olfactory areas, and dentate gyrus, and it also reduces connectivity of the LS with the piriform cortex and caudate-putamen. In sum, schizophrenia-like social deficits may emerge via changes in the intrinsic excitability of a discrete subpopulation of LS neurons that serve as a central hub to coordinate social behavior via downstream projections to reward, fear extinction, motor and sensory processing regions of the brain.

Ligand-Free Signaling of G-Protein-Coupled Receptors: Physiology, Pharmacology, and Genetics

G-protein-coupled receptors (GPCRs) are ubiquitous sensors and regulators of cellular functions. Each GPCR exists in complex aggregates with multiple resting and active conformations. Designed to detect weak stimuli, GPCRs can also activate spontaneously, resulting in basal ligand-free signaling. Agonists trigger a cascade of events leading to an activated agonist-receptor G-protein complex with high agonist affinity. However, the ensuing signaling process can further remodel the receptor complex to reduce agonist affinity, causing rapid ligand dissociation. The acutely activated ligand-free receptor can continue signaling, as proposed for rhodopsin and μ opioid receptors, resulting in robust receptor activation at low agonist occupancy with enhanced agonist potency. Continued receptor stimulation can further modify the receptor complex, regulating sustained ligand-free signaling-proposed to play a role in opioid dependence. Basal, acutely agonist-triggered, and sustained elevated ligand-free signaling could each have distinct functions, reflecting multi-state conformations of GPCRs. This review addresses basal and stimulus-activated ligand-free signaling, its regulation, genetic factors, and pharmacological implications, focusing on opioid and serotonin receptors, and the growth hormone secretagogue receptor (GHSR). The hypothesis is proposed that ligand-free signaling of 5-HT2A receptors mediate therapeutic effects of psychedelic drugs. Research avenues are suggested to close the gaps in our knowledge of ligand-free GPCR signaling.

Towards Novel Potential Molecular Targets for Antidepressant and Antipsychotic Pharmacotherapies

Depression and schizophrenia are two highly prevalent and severely debilitating neuropsychiatric disorders. Both conventional antidepressant and antipsychotic pharmacotherapies are often inefficient clinically, causing multiple side effects and serious patient compliance problems. Collectively, this calls for the development of novel drug targets for treating depressed and schizophrenic patients. Here, we discuss recent translational advances, research tools and approaches, aiming to facilitate innovative drug discovery in this field. Providing a comprehensive overview of current antidepressants and antipsychotic drugs, we also outline potential novel molecular targets for treating depression and schizophrenia. We also critically evaluate multiple translational challenges and summarize various open questions, in order to foster further integrative cross-discipline research into antidepressant and antipsychotic drug development.

Piperidine Derivatives: Recent Advances in Synthesis and Pharmacological Applications

Piperidines are among the most important synthetic fragments for designing drugs and play a significant role in the pharmaceutical industry. Their derivatives are present in more than twenty classes of pharmaceuticals, as well as alkaloids. The current review summarizes recent scientific literature on intra- and intermolecular reactions leading to the formation of various piperidine derivatives: substituted piperidines, spiropiperidines, condensed piperidines, and piperidinones. Moreover, the pharmaceutical applications of synthetic and natural piperidines were covered, as well as the latest scientific advances in the discovery and biological evaluation of potential drugs containing piperidine moiety. This review is designed to help both novice researchers taking their first steps in this field and experienced scientists looking for suitable substrates for the synthesis of biologically active piperidines.

Disclosing common biological signatures and predicting new therapeutic targets in schizophrenia and obsessive-compulsive disorder by integrated bioinformatics analysis

Schizophrenia (SCZ) is a severe mental illness mainly characterized by a number of psychiatric symptoms. Obsessive-compulsive disorder (OCD) is a long-lasting and devastating mental disorder. SCZ has high co-occurrence with OCD resulting in the emergence of a concept entitled "schizo-obsessive disorder" as a new specific clinical entity with more severe psychiatric symptoms. Many studies have been done on SCZ and OCD, but the common pathogenesis between them is not clear yet. Therefore, this study aimed to identify shared genetic basis, potential biomarkers and therapeutic targets between these two disorders. Gene sets were extracted from the Geneweaver and Harmonizome databases for each disorder. Interestingly, the combination of both sets revealed 89 common genes between SCZ and OCD, the most important of which were BDNF, SLC6A4, GAD1, HTR2A, GRIN2B, DRD2, SLC6A3, COMT, TH and DLG4. Then, we conducted a comprehensive bioinformatics analysis of the common genes. Receptor activity as the molecular functions, neuron projection and synapse as the cellular components as well as serotonergic synapse, dopaminergic synapse and alcoholism as the pathways were the most significant commonalities in enrichment analyses. In addition, transcription factor (TFs) analysis predicted significant TFs such as HMGA1, MAPK14, HINFP and TEAD2. Hsa-miR-3121-3p and hsa-miR-495-3p were the most important microRNAs (miRNAs) associated with both disorders. Finally, our study predicted 19 existing drugs (importantly, Haloperidol, Fluoxetine and Melatonin) that may have a potential influence on this co-occurrence. To summarize, this study may help us to better understand and handle the co-occurrence of SCZ and OCD by identifying potential biomarkers and therapeutic targets.

A New Treatment Paradigm: Targeting Trace Amine-Associated Receptor 1 (TAAR1) in Schizophrenia

This continuing education supplement is jointly provided by Medical Education Resources and CMEology. The supplement is supported by an independent educational grant from Sunovion Pharmaceuticals Inc. It was edited and peer reviewed by the Journal of Clinical Psychopharmacology.After reviewing the learning objectives and reading the supplement, please complete the Activity Evaluation/Credit Request form online at https://www.cmesurvey.site/TAAR1.

ABSTRACT

All currently available antipsychotics work via essentially the same mechanism: by antagonizing the dopamine D2 receptor. However, schizophrenia is an extremely heterogeneous condition, and antipsychotics do not adequately control symptoms for all patients. Negative and cognitive symptoms are especially difficult to manage with existing medications. Therefore, antipsychotic agents with novel mechanisms of action are urgently needed. Recently, a phase 2 clinical trial and extension study demonstrated that, relative to placebo, the trace amine-associated receptor 1 (TAAR1) agonist ulotaront was effective at controlling the positive, negative, and cognitive symptoms of schizophrenia. In addition, ulotaront seems to lack the weight gain, metabolic issues, and extrapyramidal symptoms associated with traditional antipsychotics. This agent is currently undergoing multiple phase 3 trials for the treatment of schizophrenia. Another TAAR1 agonist, ralmitaront, is being investigated for the treatment of schizophrenia and schizoaffective disorders. Two phase 2 clinical trials are underway, evaluating ralmitaront both as a monotherapy and an add-on therapy to traditional antipsychotics. In this supplement, we review the biologic, preclinical, and clinical data available for TAAR1 agonists, so that if and when they are approved for the treatment of schizophrenia, psychiatry specialists will be ready to use them to optimize patient outcomes. We also briefly review other emerging therapies in late-stage development for the treatment of schizophrenia.

Challenges and Strategies for the Recruitment of Patients With Schizophrenia in a Research Setting

BACKGROUND

With numerous potentially novel targets and pharmacodynamic biomarkers for schizophrenia entering late-stage testing, the next decade will bring an urgent need for well-conducted clinical trials. A critically important step for the successful execution of clinical research trials is timely and appropriate recruitment of participants. Patients with schizophrenia can be especially challenging to recruit because of the disability inherent in psychotic spectrum disorders. Research on how best to recruit for clinical trials is understudied. Clearly defining a model for recruitment procedures would be valuable for researchers and, by extension, the patient populations that may benefit from the insight gained by future clinical research.

METHODS

This article aims to offer suggestions for recruitment based on years of experience at the Columbia Schizophrenia Research Clinic (CSRC), a hub for clinical trials focusing on the etiology and treatment of various psychotic disorders.

RESULTS

The present report provides practical, step-by-step recommendations for implementing the highly effective CSRC recruitment model, including the benefits of 2 recruitment initiatives that were instituted in 2018: hiring a dedicated recruiter and targeted chart reviews at affiliated clinics. Other topics discussed include our umbrella protocol and database, advertising, and tips for collaborating with external sites.

CONCLUSIONS

Despite ongoing complications from coronavirus disease 2019, these strategies have been successful, increasing the rate of both consents and study enrollments by approximately 40% and enabling the CSRC to conduct multiple studies simultaneously.

Psilocybin—Mediated Attenuation of Gamma Band Auditory Steady-State Responses (ASSR) Is Driven by the Intensity of Cognitive and Emotional Domains of Psychedelic Experience

Psilocybin is a classical serotoninergic psychedelic that induces cognitive disruptions similar to psychosis. Gamma activity is affected in psychosis and is tightly related to cognitive processing. The 40 Hz auditory steady-state responses (ASSR) are frequently used as indicators to test the ability to generate gamma activity. Based on previous literature, we studied the impact of psilocybin on 40 Hz ASSR in healthy volunteers. The study was double blind and placebo controlled with a crossover design. A sample of 20 healthy subjects (10M/10F) received psilocybin orally 0.26 mg/kg or placebo. Participants were measured four times in total, one time before ingestion of psilocybin/placebo and one time after ingestion, during the peak of intoxication. A series of 500 ms click trains were used for stimulation. Psilocybin induced a psychedelic effect and decreased 40 Hz ASSR phase-locking index compared to placebo. The extent of the attenuation was related to Cognition and Affect on the Hallucinogen Rating Scale. The current study shows that psilocybin lowers the synchronization level and the amplitude of 40 Hz auditory steady-state responses, which yields further support for the role of gamma oscillations in cognitive processing and its disturbance.

A neurobiological perspective on social influence: Serotonin and social adaptation

Humans are inherently social beings. Being suggestible to each other's expectations enables pro-social skills that are crucial for social learning and adaptation. Despite its high relevance for psychiatry, the neurobiological mechanisms underlying social adaptation are still not well understood. This review therefore provides a conceptual framework covering various distinct mechanisms underlying social adaptation and explores the neuropharmacology - in particular the role of the serotonin (5-HT) system - modulating these mechanisms. This article therefore reviews empirical results on social influence processing and reconciles them with recent findings from psychedelic research on social processing to elucidate neurobiological and neuropharmacological underpinnings of social adaptation. Various computational, neurobiological, and neurochemical processes are involved in distinct mechanisms underlying social adaptation such as the multisensory process of social information integration that is crucial for the forming of self-representation and representations of social norms. This is again associated with self- and other-perception during social interactions as well as value-based decision making that guides our behaviour in daily interactions. We highlight the critical role of 5-HT in these processes and suggest that 5-HT can facilitate social learning and may represent an important target for treating psychiatric disorders characterized by impairments in social functioning. This framework also has important implications for psychedelic-assisted therapy as well as for the development of novel treatment approaches and future research directions.

Maternal Metabolic State and Fetal Sex and Genotype Modulate Methylation of the Serotonin Receptor Type 2A Gene (HTR2A) in the Human Placenta

The serotonin receptor 2A gene (HTR2A) is a strong candidate for the fetal programming of future behavior and metabolism. Maternal obesity and gestational diabetes mellitus (GDM) have been associated with an increased risk of metabolic and psychological problems in offspring. We tested the hypothesis that maternal metabolic status affects methylation of HTR2A in the placenta. The prospective study included 199 pairs of mothers and healthy full-term newborns. Genomic DNA was extracted from feto-placental samples and analyzed for genotypes of two polymorphisms (rs6311, rs6306) and methylation of four cytosine residues (−1665, −1439, −1421, −1224) in the HTR2A promoter region. Placental HTR2A promoter methylation was higher in male than female placentas and depended on both rs6311 and rs6306 genotypes. A higher maternal pre-gestational body mass index (pBMI) and, to a lesser extent, diagnosis of GDM were associated with reduced HTR2A promoter methylation in female but not male placentas. Higher pBMI was associated with reduced methylation both directly and indirectly through increased GDM incidence. Tobacco use during pregnancy was associated with reduced HTR2A promoter methylation in male but not female placentas. The obtained results suggest that HTR2A is a sexually dimorphic epigenetic target of intrauterine exposures. The findings may contribute to a better understanding of the early developmental origins of neurobehavioral and metabolic disorders associated with altered HTR2A function.

Mismatch negativity as an index of target engagement for excitation/inhibition-based treatment development: a double-blind, placebo-controlled, randomized, single-dose cross-over study of the serotonin type-3 receptor antagonist CVN058

Serotonin type-3 receptor (5-HT₃R) antagonists show potential as a treatment for cognitive deficits in schizophrenia. CVN058, a brain-penetrant, potent and selective 5-HT₃R antagonist, shows efficacy in rodent models of cognition and was well-tolerated in Phase-1 studies. We evaluated the target engagement of CVN058 using mismatch negativity (MMN) in a randomized, double-blind, placebo-controlled, cross-over study. Subjects were stable outpatients with schizophrenia or schizoaffective disorder treated with antipsychotics. Subjects were not permitted to use other 5-HT₃R modulators or serotonin reuptake inhibitors. Each subject received a high (150 mg) and low (15 mg or 75 mg) oral dose of CVN058 and placebo in a randomized order across 3 single-day treatment visits separated by at least 1 week. The primary pre-registered outcome was amplitude of duration MMN. Amplitude of other MMN deviants (frequency, intensity, frequency modulation, and location), P50, P300 and auditory steady-state response (ASSR) were exploratory endpoints. 19 of 22 randomized subjects (86.4%) completed the study. Baseline PANSS scores indicated moderate impairment. CVN058 150 mg led to significant improvement vs. placebo on the primary outcome of duration MMN (p = 0.02, Cohen's d = 0.48). A significant treatment effect was also seen in a combined analysis across all MMN deviants (p < 0.001, d = 0.57). Effects on location MMN were independently significant (p < 0.007, d = 0.46). No other significant effects were seen for other deviants, doses or EEG measures. There were no clinically significant treatment related adverse effects. These results show MMN to be a sensitive target engagement biomarker for 5-HT₃R, and support the potential utility of CVN058 in correcting the excitatory/inhibitory imbalance in schizophrenia.

Progress and Pitfalls in Developing Agents to Treat Neurocognitive Deficits Associated with Schizophrenia

Cognitive impairments associated with schizophrenia (CIAS) represent a central element of the symptomatology of this severe mental disorder. CIAS substantially determine the disease prognosis and hardly, if at all, respond to treatment with currently available antipsychotics. Remarkably, all drugs presently approved for the treatment of schizophrenia are, to varying degrees, dopamine D₂/D₃ receptor blockers. In turn, rapidly growing evidence suggests the immense significance of systems other than the dopaminergic system in the genesis of CIAS. Accordingly, current efforts addressing the unmet needs of patients with schizophrenia are primarily based on interventions in other non-dopaminergic systems. In this review article, we provide a brief overview of the available evidence on the importance of specific systems in the development of CIAS. In addition, we describe the promising targets for the development of new drugs that have been used so far. In doing so, we present the most important candidates that have been investigated in the field of the specific systems in recent years and present a summary of the results available at the time of drafting this review (May 2022), as well as the currently ongoing studies.

Trace Amine-Associated Receptor 1 as a Target for the Development of New Antipsychotics: Current Status of Research and Future Directions

Schizophrenia is a mental illness associated with an array of symptoms that often result in disability. The primary treatments for schizophrenia are termed antipsychotics. Although antipsychotics modulate a number of different receptor types and subtypes, all currently regulatory agency-approved antipsychotics share in common direct or functional antagonism at the dopamine type 2 receptor (D₂R). The majority of people with schizophrenia do not achieve full resolution of their symptoms with antipsychotics, suggesting the need for alternative or complementary approaches. The primary focus of this review is to assess the evidence for the role of the trace amine-associated receptor 1 (TAAR-1) in schizophrenia and the role of TAAR-1 modulators as novel-mechanism antipsychotics. Topics include an overview of TAAR-1 physiology and pathophysiology in schizophrenia, interaction with other neurotransmitter systems, including the dopaminergic, glutamatergic and serotonergic system, and finally, a review of investigational TAAR-1 compounds that have reached Phase II clinical studies in schizophrenia: SEP-363856 (ulotaront) and RO6889450 (ralmitaront). Thus far, results are publicly available only for ulotaront in a relatively young (18-40 years) and acutely exacerbated cohort. These results showed positive effects for overall schizophrenia symptoms without significant tolerability concerns. An ongoing study of ralmitaront will assess specific efficacy in patients with persistent negative symptoms. If trials of TAAR-1 modulators, and other novel-mechanism targets for schizophrenia that are under active study, continue to show positive results, the definition of an antipsychotic may need to be expanded beyond the D₂R target in the near future.

Novel approaches in schizophrenia-from risk factors and hypotheses to novel drug targets

Schizophrenia is a severe psychiatric disorder characterized by emotional, behavioral and cognitive disturbances, and the treatment of schizophrenia is often complicated by noncompliance and pharmacoresistance. The search for the pathophysiological mechanisms underlying schizophrenia has resulted in the proposal of several hypotheses to explain the impacts of environmental, genetic, neurodevelopmental, immune and inflammatory factors on disease onset and progression. This review discusses the newest insights into the pathophysiology of and risk factors for schizophrenia and notes novel approaches in antipsychotic treatment and potential diagnostic and theranostic biomarkers. The current hypotheses focusing on neuromediators (dopamine, glutamate, and serotonin), neuroinflammation, the cannabinoid hypothesis, the gut-brain axis model, and oxidative stress are summarized. Key genetic features, including small nucleotide polymorphisms, copy number variations, microdeletions, mutations and epigenetic changes, are highlighted. Current pharmacotherapy of schizophrenia relies mostly on dopaminergic and serotonergic antagonists/partial agonists, but new findings in the pathophysiology of schizophrenia have allowed the expansion of novel approaches in pharmacotherapy and the establishment of more reliable biomarkers. Substances with promising results in preclinical and clinical studies include lumateperone, pimavanserin, xanomeline, roluperidone, agonists of trace amine-associated receptor 1, inhibitors of glycine transporters, AMPA allosteric modulators, mGLUR_2-3 agonists, D-amino acid oxidase inhibitors and cannabidiol. The use of anti-inflammatory agents as an add-on therapy is mentioned.

Pharmacological Treatment for Social Cognition: Current Evidence

Cognitive impairment is currently considered a core feature of schizophrenia (SZ) and is gaining attention as a fundamental therapeutic target. Standard treatment for SZ involves the use of antipsychotics that are successfully used to control positive symptoms and disorganized behaviour. However, it is still unclear whether they are effective on social cognition (SC) impairment. Furthermore, different medications are currently being studied to improve SC in patients with SZ. A literature search on this topic was conducted using the PubMed database. All kinds of publications (i.e., reviews, original contributions and case reports) written in English and published in the last 15 years were included. The aim of our literature review is to draw a picture of the current state of the pharmacological treatment of SC impairment in SZ.

Discovery of a new class of multi-target heterocycle piperidine derivatives as potential antipsychotics with pro-cognitive effect

A series of benzoisoxazoleylpiperidine derivatives were synthesized by using the multi-target strategies and their potent affinities for dopamine (DA), serotonin (5-HT) and human histamine H₃ receptors have been evaluated. Of these compounds, the promising candidate 4w displayed high affinities for D₂, D₃, 5-HT_1A, 5-HT_2A and H₃, a moderate affinity for 5-HT₆, negligible effects on the human ether-a-go-go-related gene (hERG) channel, low affinities for off-target receptors (5-HT_2C, adrenergic α₁ and H₁). In addition, the animal behavioral study revealed that, compared to risperidone, compound 4w significantly inhibited apomorphine-induced climbing and MK-801-induced movement behaviors with a high threshold for catalepsy and low liabilities for weight gain and hyperprolactinemia. Results from the conditioned avoidance response test and novel object recognition task demonstrated that 4w had pro-cognitive effects. Thus, the antipsychotic drug-like activities of 4w indicate that it may be a potential polypharmacological antipsychotic candidate drug.

Behavioral and Psychological Symptoms in Dementia (BPSD) and the Use of Antipsychotics

Dementia affects about 47 million people worldwide, number expected to exponentially increase within 30 years. Alzheimer’s disease (AD) is the most common dementia type, accounting on its own for almost 70% of all dementia cases. Behavioral and psychological symptoms (BPSD) frequently occur during the disease progression; to treat agitation, aggressiveness, delusions and hallucinations, the use of antipsychotic drugs should be limited, due to their safety issues. In this literature review regarding the use of antipsychotics for treating BPSD in dementia, the advantages and limitation of antipsychotic drugs have been evaluated. The available medications for the management of behavioral and psychological symptoms are the antipsychotics, classed into typical and atypical, depending on their action on dopamine and serotonin receptors. First generation, or typical, antipsychotics exhibit lack of tolerability and display a broad range of side effects such as sedation, anticholinergic effects and extrapyramidal symptoms. Atypical, or second generation, antipsychotics bind more selectively to dopamine receptors and simultaneously block serotonin receptors, resulting in higher tolerability. High attention should be paid to the management of therapy interruption or switch between antipsychotics, to limit the possible rebound effect. Several switching strategies may be adopted, and clinicians should “tailor” therapies, accounting for patients’ symptoms, comorbidities, polytherapies and frailty.

Towards personalized pharmacology: Antipsychotics and schizophrenia

Since the discovery of the first antipsychotic in 1952, many antipsychotic drugs have been developed, each with different pharmacokinetic and pharmacodynamic properties. The pharmacological heterogeneity of antipsychotic drugs should allow a personalized drug prescription adapted to the different clinical picture of schizophrenia. Schizophrenia is a chronic disease, during which 3 stages of pharmacological intervention can be identified: the first episode psychotic (FEP), the phase of therapeutic stabilization that can progress to situations of resistance, and the question of long-term prescription. During FEP, the choice of the first antipsychotic treatment seems to be underpinned by its safety profile in relation to the patient for whom it is prescribed, according to the adage start low and go-slow. The therapeutic stabilization phase is based on treatment optimization through a rigorous evaluation of the benefits-harm balance, with the use of tools such as personalized therapeutic drug monitoring and pharmacogenetics. Generally speaking, while some antipsychotic drugs seem to present a more favorable efficacy profile in certain situations, the differences are small, whereas the differences in safety are more important and should be considered in the first line. Individual factors such as the presence of co-morbidities, as well as previously experienced treatments must also be taken into account. Finally, the question of maintaining the prescription of antipsychotic drugs over the long term arises in view of the iatrogenic risk with controversial current data. Overall, the personalized prescription of antipsychotic drugs in schizophrenia remains limited by a lack of data in the literature, justifying the development of clinical studies in this field. But at present, the dogma remains that of primum non nocere.