Evaluating the role of the alpha-7 nicotinic acetylcholine receptor in the pathophysiology and treatment of schizophrenia

Amphetamine increases motivation of humans and mice as measured by breakpoint, but does not affect an Electroencephalographic biomarker

Translation of drug targets from preclinical studies to clinical trials has been aided by cross-species behavioral tasks, but evidence for brain-based engagement during task performance is still required. Cross-species progressive ratio breakpoint tasks (PRBTs) measure motivation-related behavior and are pharmacologically and clinically sensitive. We recently advanced elevated parietal alpha power as a cross-species electroencephalographic (EEG) biomarker of PRBT engagement. Given that amphetamine increases breakpoint in mice, we tested its effects on breakpoint and parietal alpha power in both humans and mice. Twenty-three healthy participants performed the PRBT with EEG after amphetamine or placebo in a double-blind design. C57BL/6J mice were trained on PRBT with EEG (n = 24) and were treated with amphetamine or vehicle. A second cohort of mice was trained on PRBT without EEG (n = 40) and was treated with amphetamine or vehicle. In humans, amphetamine increased breakpoint. In mice, during concomitant EEG, 1 mg/kg of amphetamine significantly decreased breakpoint. In cohort 2, however, 0.3 mg/kg of amphetamine increased breakpoint consistent with human findings. Increased alpha power was observed in both species as they reached breakpoint, replicating previous findings. Amphetamine did not affect alpha power in either species. Amphetamine increased effort in humans and mice. Consistent with previous reports, elevated parietal alpha power was observed in humans and mice as they performed the PRBT. Amphetamine did not affect this EEG biomarker of effort. Hence, these findings support the pharmacological predictive validity of the PRBT to measure effort in humans and mice and suggest that this EEG biomarker is not directly reflective of amphetamine-induced changes in effort.

Effects of varenicline on the serum levels of olanzapine in male patients with Schizophrenia: a randomized controlled trial

Background

Smoking in patients with Schizophrenia is more common than in the general population. Varenicline, a partial agonist at α4β2 nicotinic acetylcholine receptors, is an effective smoking cessation pharmacotherapy in patients with Schizophrenia. However, its effects on the serum levels of antipsychotics in Schizophrenia are understudied. This study investigated the impact of smoking cessation with varenicline on the serum concentration of olanzapine in patients with Schizophrenia.

Methods

Adult smokers with Schizophrenia were enrolled in a 12-week course of varenicline and placebo for smoking cessation. The serum concentration of olanzapine was measured at baseline and weeks 1, 2, 4, 8, and 12. Data were analyzed with the generalized additive mixed model.

Results

During the 12-week study, the results indicated that olanzapine concentrations increased nonlinearly in the varenicline and placebo groups. Threshold effect analysis suggested that the olanzapine concentrations increased over time until the turning point (week 4). However, there was no significant difference between the two treatment groups.

Conclusion

Varenicline showed safety and efficacy in smoking cessation in people with Schizophrenia.

Deletion induced splicing in RIC3 drives nicotinic acetylcholine receptor regulation with implications for endoplasmic reticulum stress in human astrocytes

Nicotinic acetylcholine receptor (nAChR) dysregulation in astrocytes is reported in neurodegenerative disorders. Modulation of nAChRs through agonists confers protection to astrocytes from stress but regulation of chaperones involved in proteostasis with pathological implications is unclear. Resistance to inhibitors of cholinesterase 3 (RIC3), a potential chaperone of nAChRs is poorly studied in humans. We characterized RIC3 in astrocytes derived from an isogenic wild-type and Cas9 edited "del" human iPSC line harboring a 25 bp homozygous deletion in exon2. Altered RIC3 transcript ratio due to deletion induced splicing and an unexpected gain of α7nAChR expression were observed in "del" astrocytes. Transcriptome analysis showed higher expression of neurotransmitter/G-protein coupled receptors mediated by cAMP and calcium/calmodulin-dependent kinase signaling with increased cytokines/glutamate secretion. Functional implications examined using tunicamycin induced ER stress in wild-type astrocyte stress model showed cell cycle arrest, RIC3 upregulation, reduction in α7nAChR membrane levels but increased α4nAChR membrane expression. Conversely, tunicamycin-treated "del" astrocytes showed a comparatively higher α4nAChR membrane expression and upsurged cAMP signaling. Furthermore, reduced expression of stress markers CHOP, phospho-PERK and lowered XBP1 splicing in western blot and qPCR, validated by proteome-based pathway analysis indicated lowered disease severity. Findings indicate (i) a complex RNA regulatory mechanism via exonic deletion induced splicing; (ii) RIC-3 as a disordered protein having contrasting effects on co-expressed nAChR subtypes under basal/stress conditions; and (iii) RIC3 as a potential drug target against ER stress in astrocytes for neurodegenerative/nicotine-related brain disorders. Cellular rescue mechanism through deletion induced exon skipping may encourage ASO-based therapies for tauopathies.

Nicotinic acetylcholine receptors: Key targets for attenuating neurodegenerative diseases

Nicotinic acetylcholine receptors (nAChRs) are master regulators of immune functions via the cholinergic anti-inflammatory pathway and are expressed in microglia, the brain's resident immune cells. There is an extensive dialogue between the neurons and the glial cells around them from which microglia are tasked with monitoring, nurturing, and defending their microenvironment. Dysregulation of any of these processes can have devastating and long-lasting consequences involving microglia-mediated neuroinflammation associated with neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, amongst others. Disease-associated microglia acquire a distinguishing phenotype that emphasizes scavenging and defence functions while nurturing and repairing functions become muted. Attempts to resolve this critical imbalance remain a key focus of research. Furthermore, cholinergic modulation of neuroinflammation represents a promising avenue for treatment.

An α7 nAChR approach for the baseline-dependent modulation of deviance detection in schizophrenia: A pilot study assessing the combined effect of CDP-choline and galantamine

BACKGROUND

Cognitive operations including pre-attentive sensory processing are markedly impaired in patients with schizophrenia (SCZ) but evidence significant interindividual heterogeneity, which moderates treatment response with nicotinic acetylcholine receptor (nAChR) agonists. Previous studies in healthy volunteers have shown baseline-dependency effects of the α7 nAChR agonist cytidine 5'-diphosphocholine (CDP-choline) administered alone and in combination with a nicotinic allosteric modulator (galantamine) on auditory deviance detection measured with the mismatch negativity (MMN) event-related potential (ERP).

AIM

The objective of this pilot study was to assess the acute effect of this combined α7 nAChR-targeted treatment (CDP-choline/galantamine) on speech MMN in patients with SCZ (N = 24) stratified by baseline MMN responses into low, medium, and high baseline auditory deviance detection subgroups.

METHODS

Patients with a stable diagnosis of SCZ attended two randomized, double-blind, placebo-controlled and counter-balanced testing sessions where they received a placebo or a CDP-choline (500 mg) and galantamine (16 mg) treatment. MMN ERPs were recorded during the presentation of a fast multi-feature speech MMN paradigm including five speech deviants. Clinical measures were acquired before and after treatment administration.

RESULTS

While no main treatment effect was observed, CDP-choline/galantamine significantly increased MMN amplitudes to frequency, duration, and vowel speech deviants in low group individuals. Individuals with higher positive and negative symptom scale negative, general, and total scores expressed the greatest MMN amplitude improvement following CDP-choline/galantamine.

CONCLUSIONS

These baseline-dependent nicotinic effects on early auditory information processing warrant different dosage and repeated administration assessments in patients with low baseline deviance detection levels.

Schizophrenia Hypothesis: Autonomic Nervous System Dysregulation of Fetal and Adult Immune Tolerance

The autonomic nervous system can control immune cell activation via both sympathetic adrenergic and parasympathetic cholinergic nerve release of norepinephrine and acetylcholine. The hypothesis put forward in this paper suggests that autonomic nervous system dysfunction leads to dysregulation of immune tolerance mechanisms in brain-resident and peripheral immune cells leading to excessive production of pro-inflammatory cytokines such as Tumor Necrosis Factor alpha (TNF-α). Inactivation of Glycogen Synthase Kinase-3β (GSK3β) is a process that takes place in macrophages and microglia when a toll-like receptor 4 (TLR4) ligand binds to the TLR4 receptor. When Damage-Associated Molecular Patterns (DAMPS) and Pathogen-Associated Molecular Patterns (PAMPS) bind to TLR4s, the phosphatidylinositol-3-kinase (PI3K)-protein kinase B (Akt) pathway should be activated, leading to inactivation of GSK3β. This switches the macrophage from producing pro-inflammatory cytokines to anti-inflammatory cytokines. Acetylcholine activation of the α7 subunit of the nicotinic acetylcholine receptor (α7 nAChR) on the cell surface of immune cells leads to PI3K/Akt pathway activation and can control immune cell polarization. Dysregulation of this pathway due to dysfunction of the prenatal autonomic nervous system could lead to impaired fetal immune tolerance mechanisms and a greater vulnerability to Maternal Immune Activation (MIA) resulting in neurodevelopmental abnormalities. It could also lead to the adult schizophrenia patient’s immune system being more vulnerable to chronic stress-induced DAMP release. If a schizophrenia patient experiences chronic stress, an increased production of pro-inflammatory cytokines such as TNF-α could cause significant damage. TNF-α could increase the permeability of the intestinal and blood brain barrier, resulting in lipopolysaccharide (LPS) and TNF-α translocation to the brain and consequent increases in glutamate release. MIA has been found to reduce Glutamic Acid Decarboxylase mRNA expression, resulting in reduced Gamma-aminobutyric acid (GABA) synthesis, which combined with an increase of glutamate release could result in an imbalance of glutamate and GABA neurotransmitters. Schizophrenia could be a “two-hit” illness comprised of a genetic “hit” of autonomic nervous system dysfunction and an environmental hit of MIA. This combination of factors could lead to neurotransmitter imbalance and the development of psychotic symptoms.

Cross-species evidence that nicotine widens the attentional window

RATIONALE

The ability to spread attention over items or locations is as important for everyday functioning as the ability to focus narrowly. Little is known about neuronal processes involved in broad monitoring, but indirect evidence suggests a role of nicotinic acetylcholine receptors (nAChRs).

OBJECTIVE

The present study tested whether the prototypical nAChR agonist nicotine enhances the ability of humans and rodents to maintain a broad attentional window.

METHODS

Fifty-three never-smokers wearing a nicotine (7 mg/24 h) or placebo patch performed an attention task requiring detection of stimuli presented randomly in one of four peripheral locations, with a central cue predicting the target location or indicating the need to spread attention over all locations. Nineteen rats performed the 5-choice serial reaction time task requiring detection of stimuli presented randomly in a horizontal array of five locations. Performance after nicotine (0.1 and 0.2 mg/kg) or vehicle administration was analyzed as a function of target location eccentricity.

RESULTS

In human subjects, nicotine caused greater reaction time reduction when all locations were monitored than when a single location was cued. In rats, nicotine attenuated the decline in stimulus detections and the increase in omission errors with greater target location eccentricity.

CONCLUSIONS

The findings represent cross-species evidence that nAChR agonism facilitates the ability to spread attention broadly. This suggests that nAChR hypofunction may be central to broad monitoring deficits as seen, for example, in schizophrenia. The homology of findings between the rodent and the human paradigm contributes to validating a translational strategy for treatment development.

Regulation of membrane NMDA receptors by dynamics and protein interactions

Understanding neurotransmitter system crosstalk in the brain is a major challenge in neurobiology. Several intracellular and genomic cascades have been identified in this crosstalk. However, the discovery that neurotransmitter receptors are highly diffusive in the plasma membrane of neurons, where they form heterocomplexes with other proteins, has profoundly changed our view of neurotransmitter signaling. Here, we review new insights into neurotransmitter crosstalk at the plasma membrane. We focus on the membrane organization and interactome of the ionotropic glutamate N-methyl-D-aspartate receptor (NMDAR) that plays a central role in excitatory synaptic and network physiology and is involved in the etiology of several major neuropsychiatric disorders. The nanoscale organization and dynamics of NMDAR is a key regulatory process for glutamate synapse transmission, plasticity, and crosstalk with other neurotransmitter systems, such as the monoaminergic ones. The plasma membrane appears to be a prime regulatory compartment for spatial and temporal crosstalk between neurotransmitter systems in the healthy and diseased brain. Understanding the molecular mechanisms regulating membrane neurotransmitter receptor crosstalk will likely open research avenues for innovative therapeutical strategies.

Prefrontal α7nAChR Signaling Differentially Modulates Afferent Drive and Trace Fear Conditioning Behavior in Adolescent and Adult Rats

Increased level of kynurenic acid is thought to contribute to the development of cognitive deficits in schizophrenia through an α7nAChR-mediated mechanism in the prefrontal cortex (PFC). However, it remains unclear to what extent disruption of PFC α7nAChR signaling impacts afferent transmission and its modulation of behavior. Using male rats, we found that PFC infusion of methyllycaconitine (MLA; α7nAChR antagonist) shifts ventral hippocampal-induced local field potential (LFP) suppression to LFP facilitation, an effect only observed in adults. Hippocampal stimulation can also elicit a GluN2B-mediated LFP potentiation (when PFC GABA_AR is blocked) that is insensitive to MLA. Conversely, PFC infusion of MLA diminished the gain of amygdalar transmission, which is already enabled by postnatal day (P)30. Behaviorally, the impact of prefrontal MLA on trace fear-conditioning and extinction was also age related. While freezing behavior during conditioning was reduced by MLA only in adults, it elicited opposite effects in adolescent and adult rats during extinction as revealed by the level of reduced and increased freezing response, respectively. We next asked whether the late-adolescent onset of α7nAChR modulation of hippocampal inputs contributes to the age-dependent effect of MLA during extinction. Data revealed that the increased freezing behavior elicited by MLA in adult rats could be driven by a dysregulation of the GluN2B transmission in the PFC. Collectively, these results indicate that distinct neural circuits are recruited during the extinction of trace fear memory in adolescents and adults, likely because of the late-adolescent maturation of the ventral hippocampal-PFC functional connectivity and its modulation by α7nAChR signaling.SIGNIFICANCE STATEMENT Abnormal elevation of the astrocyte-derived metabolite kynurenic acid in the prefrontal cortex (PFC) is thought to impair cognitive functions in schizophrenia through an α7nAChR-mediated mechanism. Here, we found that prefrontal α7nAChR signaling is recruited to control the gain of hippocampal and amygdalar afferent transmission in an input-specific, age-related manner during the adolescent transition to adulthood. Behaviorally, prefrontal α7nAChR modulation of trace fear memory was also age-related, likely because of the late-adolescent maturation of the ventral hippocampal pathway and its recruitment of PFC GABAergic transmission enabled by local α7nAChR signaling. Collectively, these results reveal that distinct α7nAChR-sensitive neural circuits contribute to regulate behavior responses in adolescents and adults, particularly those requiring proper integration of hippocampal and amygdalar inputs by the PFC.

LL-00066471, a novel positive allosteric modulator of α7 nicotinic acetylcholine receptor ameliorates cognitive and sensorimotor gating deficits in animal models: Discovery and preclinical characterization

α7 nicotinic acetylcholine receptor (α7 nAChR) is an extensively validated target for several neurological and psychiatric conditions namely, dementia and schizophrenia, owing to its vital roles in cognition and sensorimotor gating. Positive allosteric modulation (PAM) of α7 nAChR represents an innovative approach to amplify endogenous cholinergic signaling in a temporally restricted manner in learning and memory centers of brain. α7 nAChR PAMs are anticipated to side-step burgeoning issues observed with several clinical-stage orthosteric α7 nAChR agonists, related to selectivity, tolerance/tachyphylaxis, thus providing a novel dimension in therapeutic strategy and pharmacology of α7 nAChR ion-channel. Here we describe a novel α7 nAChR PAM, LL-00066471, which potently amplified agonist-induced Ca2+ fluxes in neuronal IMR-32 neuroblastoma cells in a α-bungarotoxin (α-BTX) sensitive manner. LL-00066471 showed excellent oral bioavailability across species (mouse, rat and dog), low clearance and good brain penetration (B/P ratio > 1). In vivo, LL-00066471 robustly attenuated cognitive deficits in both procognitive and antiamnesic paradigms of short-term episodic and recognition memory in novel object recognition task (NORT) and social recognition task (SRT), respectively. Additionally, LL-00066471 mitigated apomorphine-induced sensorimotor gating deficits in acoustic startle reflex (ASR) and enhanced antipsychotic efficacy of olanzapine in conditioned avoidance response (CAR) task. Further, LL-00066471 corrected redox-imbalances and reduced cortico-striatal infarcts in stroke model. These finding together suggest that LL-00066471 has potential to symptomatically alleviate cognitive deficits associated with dementias, attenuate sensorimotor gating deficits in schizophrenia and correct redox-imbalances in cerebrovascular disorders. Therefore, LL-00066471 presents potential for management of cognitive impairments associated with neurological and psychiatric conditions.

The role of nicotinic cholinergic neurotransmission in delusional thinking

Delusions are a difficult-to-treat and intellectually fascinating aspect of many psychiatric illnesses. Although scientific progress on this complex topic has been challenging, some recent advances focus on dysfunction in neural circuits, specifically in those involving dopaminergic and glutamatergic neurotransmission. Here we review the role of cholinergic neurotransmission in delusions, with a focus on nicotinic receptors, which are known to play a part in some illnesses where these symptoms appear, including delirium, schizophrenia spectrum disorders, bipolar disorder, Parkinson, Huntington, and Alzheimer diseases. Beginning with what we know about the emergence of delusions in these illnesses, we advance a hypothesis of cholinergic disturbance in the dorsal striatum where nicotinic receptors are operative. Striosomes are proposed to play a central role in the formation of delusions. This hypothesis is consistent with our current knowledge about the mechanism of action of cholinergic drugs and with our abstract models of basic cognitive mechanisms at the molecular and circuit levels. We conclude by pointing out the need for further research both at the clinical and translational levels.

α7 nicotinic acetylcholine receptors as therapeutic targets in schizophrenia: Update on animal and clinical studies and strategies for the future

Schizophrenia is a devastating mental illness and its effective treatment is among the most challenging issues in psychiatry. The symptoms of schizophrenia are heterogeneous ranging from positive symptoms (e.g., delusions, hallucinations) to negative symptoms (e.g., anhedonia, social withdrawal) to cognitive dysfunction. Antipsychotics are effective at ameliorating positive symptoms in some patients; however, they are not reliably effective at improving the negative symptoms or cognitive impairments. The inability to address the cognitive impairments is a particular concern since they have the greatest long-term impact on functional outcomes. While decades of research have been devoted to the development of pro-cognitive agents for schizophrenia, to date, no drug has been approved for clinical use. Converging behavioral, neurobiological, and genetic evidence led to the identification of the α7-nicotinic acetylcholine receptor (α7-nAChR) as a therapeutic target several years ago and there is now extensive preclinical evidence that α7-nAChR ligands have pro-cognitive effects and other properties that should be beneficial to schizophrenia patients. However, like the other pro-cognitive strategies, no α7-nAChR ligand has been approved for clinical use in schizophrenia thus far. In this review, several topics are discussed that may impact the success of α7-nAChR ligands as pro-cognitive agents for schizophrenia including the translational value of the animal models used, clinical trial design limitations, confounding effects of polypharmacy, dose-effect relationships, and chronic versus intermittent dosing considerations. Determining the most optimal pharmacologic strategy at α7-nAChRs: agonist, positive allosteric modulator, or potentially even receptor antagonist is also discussed. article is part of the special issue on 'Contemporary Advances in Nicotine Neuropharmacology'.

Convergent neural substrates of inattention in bipolar disorder patients and dopamine transporter-deficient mice using the 5-choice CPT

OBJECTIVES

Bipolar disorder (BD) is a debilitating psychiatric illness affecting 2%-5% of the population. Although mania is the cardinal feature of BD, inattention and related cognitive dysfunction are observed across all stages. Since cognitive dysfunction confers poor functional outcome in patients, understanding the relevant neural mechanisms remains key to developing novel-targeted therapeutics.

METHODS

The 5-choice continuous performance test (5C-CPT) is a mouse and fMRI-compatible human attentional task, requiring responding to target stimuli while inhibiting responding to nontarget stimuli, as in clinical CPTs. This task was used to delineate systems-level neural deficits in BD contributing to inattentive performance in human subjects with BD as well as mouse models with either parietal cortex (PC) lesions or reduced dopamine transporter (DAT) expression.

RESULTS

Mania BD participants exhibited severe 5C-CPT impairment. Euthymic BD patients exhibited modestly impaired 5C-CPT. High impulsivity BD subjects exhibited reduced PC activation during target and nontarget responding compared with healthy participants. In mice, bilateral PC lesions impaired both target and nontarget responding. In the DAT knockdown mouse model of BD mania, knockdown mice exhibited severely impaired 5C-CPT performance versus wildtype littermates.

CONCLUSIONS

These data support the role of the PC in inattention in BD-specifically regarding identifying the appropriate response to target vs nontarget stimuli. Moreover, the findings indicate that severely reduced DAT function/hyperdopaminergia recreates the attentional deficits observed in BD mania patients. Determining the contribution of DAT in the PC to attention may provide a future target for treatment development.

Radioiodinated 9-fluorenone derivatives for imaging α7-nicotinic acetylcholine receptors

A series of 9H-fluoren-9-one substituents were synthesized and evaluated for imaging cerebral α7-nAChRs. Meta-iodine substituted 9-fluorenone 5 with high binding affinity (K _i = 9.3 nM) and selectivity was radiolabeled with ¹²⁵I. Fully in vitro and in vivo studies of [¹²⁵I]5 have been performed. [¹²⁵I]5 exhibited well brain uptake with a peak concentration of 7.5 ± 0.9% ID/g in mice brains. Moreover, ex vivo autoradiography studies and micro single-photon emission computed tomography (micro-SPECT/CT) dynamic imaging in mice confirmed its in vivo imaging properties. Besides, molecular docking and MD studies were also performed to interpret the binding mechanisms of the two series of ligands towards α7-nAChRs. To conclude, the meta-iodine substituted 9-fluorenone [¹²⁵I]5 could be a promising tracer for imaging α7-nAChRs.

Ribbon α-Conotoxin KTM Exhibits Potent Inhibition of Nicotinic Acetylcholine Receptors

KTM is a 16 amino acid peptide with the sequence WCCSYPGCYWSSSKWC. Here, we present the nuclear magnetic resonance (NMR) structure and bioactivity of this rationally designed α-conotoxin (α-CTx) that demonstrates potent inhibition of rat α3β2-nicotinic acetylcholine receptors (rα3β2-nAChRs). Two bioassays were used to test the efficacy of KTM. First, a qualitative PC12 cell-based assay confirmed that KTM acts as a nAChR antagonist. Second, bioactivity evaluation by two-electrode voltage clamp electrophysiology was used to measure the inhibition of rα3β2-nAChRs by KTM (IC50 = 0.19 ± 0.02 nM), and inhibition of the same nAChR isoform by α-CTx MII (IC50 = 0.35 ± 0.8 nM). The three-dimensional structure of KTM was determined by NMR spectroscopy, and the final set of 20 structures derived from 32 distance restraints, four dihedral angle constraints, and two disulfide bond constraints overlapped with a mean global backbone root-mean-square deviation (RMSD) of 1.7 ± 0.5 Å. The structure of KTM did not adopt the disulfide fold of α-CTx MII for which it was designed, but instead adopted a flexible ribbon backbone and disulfide connectivity of C2-C16 and C3-C8 with an estimated 12.5% α-helical content. In contrast, α-CTx MII, which has a native fold of C2-C8 and C3-C16, has an estimated 38.1% α-helical secondary structure. KTM is the first reported instance of a Framework I (CC-C-C) α-CTx with ribbon connectivity to display sub-nanomolar inhibitory potency of rα3β2-nAChR subtypes.

Qualitative Assay to Detect Dopamine Release by Ligand Action on Nicotinic Acetylcholine Receptors

A pheochromocytoma of the rat adrenal medulla derived (a.k.a. PC12) cell-based assay for dopamine measurement by luminescence detection was customized for the qualitative evaluation of agonists and antagonists of nicotinic acetylcholine receptors (nAChRs). The assay mechanism begins with ligand binding to transmembrane nAChRs, altering ion flow into the cell and inducing dopamine release from the cell. Following release, dopamine is oxidized by monoamine oxidase generating hydrogen peroxide that catalyzes a chemiluminescence reaction involving luminol and horseradish peroxidase, thus producing a detectable response. Results are presented for the action of nAChR agonists (acetylcholine, nicotine, and cytisine), and antagonists (α-conotoxins (α-CTxs) MII, ImI, LvIA, and PeIA) that demonstrate a luminescence response correlating to the increase or decrease of dopamine release. A survey of cell growth and treatment conditions, including nerve growth factor, nicotine, ethanol, and temperature, led to optimal assay requirements to achieve maximal signal intensity and consistent response to ligand treatment. It was determined that PC12 cells treated with a combination of nerve growth factor and nicotine, and incubated at 37 °C, provided favorable results for a reduction in luminescence signal upon treatment of cells with α-CTxs. The PC12 assay is intended for use as a fast, efficient, and economic qualitative method to assess the bioactivity of molecules that act on nAChRs, in which testing of ligand-nAChR binding hypotheses and computational predictions can be validated. As a screening method for nAChR bioactivity, lead compounds can be assessed for their likelihood of exhibiting desired bioactivity prior to being subjected to more complex quantitative methods, such as electrophysiology or live animal studies.

Kynurenines and the Endocannabinoid System in Schizophrenia: Common Points and Potential Interactions

Schizophrenia, which affects around 1% of the world’s population, has been described as a complex set of symptoms triggered by multiple factors. However, the exact background mechanisms remain to be explored, whereas therapeutic agents with excellent effectivity and safety profiles have yet to be developed. Kynurenines and the endocannabinoid system (ECS) play significant roles in both the development and manifestation of schizophrenia, which have been extensively studied and reviewed previously. Accordingly, kynurenines and the ECS share multiple features and mechanisms in schizophrenia, which have yet to be reviewed. Thus, the present study focuses on the main common points and potential interactions between kynurenines and the ECS in schizophrenia, which include (i) the regulation of glutamatergic/dopaminergic/γ-aminobutyric acidergic neurotransmission, (ii) their presence in astrocytes, and (iii) their role in inflammatory mechanisms. Additionally, promising pharmaceutical approaches involving the kynurenine pathway and the ECS will be reviewed herein.

Auditory Sensory Gating and the Big Five Personality Factors

Abstract. Sensory gating allows an individual to filter out irrelevant sensory information from the environment, potentially freeing attentional resources for more complex tasks. Some work has demonstrated a relationship between auditory sensory gating and cognitive skills such as executive function, although the functional significance is not well understood. The relationship between sensory gating and personality dimensions has not been adequately explored. Participants completed a paired-tone sensory gating event-related potential (ERP) paradigm and the Big Five Inventory to assess personality characteristics. Participants with more robust P50 sensory gating reported a significantly greater degree of conscientiousness; conscientiousness (but not the other Big Five factors) predicted sensory gating ability. Longer ERP latencies were associated with participants being more conscientious (P50 component), more agreeable, and less neurotic (N100 component). A better understanding of the behavioral correlates of sensory gating will help elucidate the functional consequences of reduced sensory gating both in typical adults and clinical groups.

Dysregulation of auditory neuroplasticity in schizophrenia

Schizophrenia is a complex brain syndrome characterized by an array of positive symptoms (delusions, hallucinations, disorganized speech), negative symptoms (alogia, apathy, avolition) and cognitive impairments (memory, executive functions). Although investigations of the cognitive deficits in schizophrenia have primarily concentrated on disturbances affecting higher-order cognitive processes, there is an increasing realization that schizophrenia also affects early sensory processing, which might, in fact, play a significant role in the development of higher-order cognitive impairments. Recent evidence suggests that many of these early sensory processing impairments possibly arise from a dysregulation of plasticity regulators in schizophrenia, resulting in either reduced plasticity or excessive unregulated plasticity. The purpose of the present manuscript is to provide a concise overview of how the dysregulation of cortical plasticity mechanisms contributes to schizophrenia symptoms with an emphasis on auditory dysplasticity and to discuss its relevance for treatment outcomes. The idea that plasticity mechanisms are not constrained only within sensitive periods suggests that many functional properties of sensory neurons can be altered throughout the lifetime.

Drug Discovery on Natural Products: From Ion Channels to nAChRs, from Nature to Libraries, from Analytics to Assays

Natural extracts are complex mixtures that may be rich in useful bioactive compounds and therefore are attractive sources for new leads in drug discovery. This review describes drug discovery from natural products and in explaining this process puts the focus on ion-channel drug discovery. In particular, the identification of bioactives from natural products targeting nicotinic acetylcholine receptors (nAChRs) and serotonin type 3 receptors (5-HT3Rs) is discussed. The review is divided into three parts: "Targets," "Sources," and "Approaches." The "Targets" part will discuss the importance of ion-channel drug targets in general, and the α7-nAChR and 5-HT3Rs in particular. The "Sources" part will discuss the relevance for drug discovery of finding bioactive compounds from various natural sources such as venoms and plant extracts. The "Approaches" part will give an overview of classical and new analytical approaches that are used for the identification of new bioactive compounds with the focus on targeting ion channels. In addition, a selected overview is given of traditional venom-based drug discovery approaches and of diverse hyphenated analytical systems used for screening complex bioactive mixtures including venoms.

Novel Approach for the Search for Chemical Scaffolds with Dual Activity with Acetylcholinesterase and the α7 Nicotinic Acetylcholine Receptor-A Perspective for the Treatment of Neurodegenerative Disorders

Neurodegenerative disorders, including Alzheimer’s disease, belong to the group of the most difficult and challenging conditions with very limited treatment options. Attempts to find new drugs in most cases fail at the clinical stage. New tactics to develop better drug candidates to manage these diseases are urgently needed. It is evident that better understanding of the neurodegeneration process is required and targeting multiple receptors may be essential. Herein, we present a novel approach, searching for dual active compounds interacting with acetylcholinesterase (AChE) and the α7 nicotinic acetylcholine receptor (nAChR) using computational chemistry methods including homology modelling and high throughput virtual screening. Activities of identified hits were evaluated at the two targets using the colorimetric method of Ellman and two-electrode voltage-clamp electrophysiology, respectively. Out of 87,250 compounds from a ZINC database of natural products and their derivatives, we identified two compounds, 8 and 9, with dual activity and balanced IC₅₀ values of 10 and 5 µM at AChE, and 34 and 14 µM at α7 nAChR, respectively. This is the first report presenting successful use of virtual screening in finding compounds with dual mode of action inhibiting both the AChE enzyme and the α7 nAChR and shows that computational methods can be a valuable tool in the early lead discovery process.

Clinical Trials and Therapeutic Rationale for Drug Repurposing in Schizophrenia

There is a paucity of efficacious novel drugs to address high rates of treatment resistance and refractory symptoms in schizophrenia. The identification of novel therapeutic indications for approved drugs-drug repurposing-has the potential to expedite clinical trials and reduce the costly risk of failure which currently limits central nervous system drug discovery efforts. In the present Review we discuss the historical role of drug repurposing in schizophrenia drug discovery and review the main classes of repurposing candidates currently in clinical trials for schizophrenia in terms of their therapeutic rationale, mechanisms of action, and preliminary results from clinical trials. Subsequently we outline the challenges and limitations which face the clinical repurposing pipeline and how novel technologies might serve to address these.

Genetic variation in CHRNA7 and CHRFAM7A is associated with nicotine dependence and response to varenicline treatment

The role of nicotinic acetylcholine receptors (nAChR) in nicotine dependence (ND) is well established; CHRNA7, encoding the α7 subunit, has a still uncertain role in ND, although it is implicated in a wide range of neuropsychiatric conditions. CHRFAM7A, a hybrid gene containing a partial duplication of CHRNA7, is possibly involved in modulating α7 nAChR function. The aim of this study was to investigate the role of CHRNA7 and CHRFAM7A genetic variants in ND and to test the hypothesis that α7 nAChR variation may modulate the efficacy of varenicline treatment in smoking cessation. We assessed CHRNA7 and CHRFAM7A copy number, CHRFAM7A exon 6 ∆2 bp polymorphism, and sequence variants in the CHRNA7 proximal promoter in an Italian sample of 408 treatment-seeking smokers. We conducted case-control and quantitative association analyses using two smoking measures (cigarettes per day, CPD, and Fagerström Test for Nicotine Dependence, FTND). Next, driven by the hypothesis that varenicline may exert some of its therapeutic effects through activation of α7 nAChRs, we restricted the analysis to a subgroup of 142 smokers who received varenicline treatment. The CHRNA7 promoter variant rs28531779 showed association with both smoking quantitative measures (FNTD p = 0.026, β = 0.89, 95% CI 0.11-1.67; CPD p = 0.006, β = 4.82 95% CI 1.42-8.22). Moreover, in the varenicline-treated subgroup we observed association of CHRFAM7A copy number with 6 months smoking abstinence (p = 0.035, OR = 3.18, 95% CI = 1.09-9.30). Thus, our study points to a possible role of genetic variation in CHRNA7 and CHRFAM7A in tobacco addiction mechanisms and response to varenicline treatment.

Smokin' hot: adolescent smoking and the risk of psychosis

OBJECTIVE

Daily smoking has been associated with a greater risk of psychosis. However, we are still lacking studies to adjust for baseline psychotic experiences and other substance use. We examined associations between daily smoking and psychosis risk in a 15-year follow-up while accounting for these covariates in a prospective sample (N = 6081) from the Northern Finland Birth Cohort 1986.

METHODS

Self-report questionnaires on psychotic experiences (PROD-screen), tobacco smoking and other substance use were completed when the cohort members were 15-16 years old. Tobacco smoking was categorized into three groups (non-smokers, 1-9 cigarettes and ≥10 cigarettes/day). Psychosis diagnoses were obtained from national registers until the age of 30 years.

RESULTS

Subjects in heaviest smoking category were at increased risk of subsequent psychosis (unadjusted HR = 3.15; 95% CI 1.94-5.13). When adjusted for baseline psychotic experiences the association persisted (HR = 2.87; 1.76-4.68) and remained significant even after adjustments for multiple known risk factors such as cannabis use, frequent alcohol use, other illicit substance use, parental substance abuse, and psychosis. Furthermore, number of smoked cigarettes increased psychosis risk in a dose-response manner (adjusted OR = 1.05; 1.01-1.08).

CONCLUSION

Heavy tobacco smoking in adolescence was associated with a greater risk for psychosis even after adjustment for confounders.

α7 Nicotinic receptor-modulating agents reverse the hyperdopaminergic tone in the MAM model of schizophrenia

Recent evidence has emerged supporting a role for the cholinergic system in schizophrenia, including the potential of α7 modulators as a treatment strategy. However, preclinical studies to date have relied on studies in normal systems rather than on a validated developmental model of schizophrenia. Furthermore, there have been only few studies on whether orthosteric and allosteric modulators have differential impacts in such models. Thus, we investigated the effects of α7 agonists and positive allosteric modulators (PAMs) on dopamine (DA) neuron activity in the ventral tegmental area (VTA) in the methylazoxymethanol acetate (MAM) developmental disruption model of schizophrenia. Four different drugs were evaluated: PNU282987 (full agonist), SSR180711 (partial agonist) NS1738 (PAM type I) and PNU120596 (PAM type II). PNU120596 increased the number of spontaneously active VTA DA neurons in normal rats. In contrast, PNU282987 and SSR180711 reduced the hyperdopaminergic tone in MAM rats. This appeared to be due to effects on DA afferent regulation, in that PNU282987 or SSR180711 infusion into the ventral hippocampus of MAM rats replicated the decrease in the number of spontaneously active VTA DA neurons. In contrast, infusion of the same drugs into the basolateral amygdala increased the number of spontaneously active VTA DA neurons in normal rats without impacting MAM rats. These data suggest that α7 receptors may represent a promising target in the development of new pharmacological therapies for schizophrenia.

In vivo imaging of Α7 nicotinic receptors as a novel method to monitor neuroinflammation after cerebral ischemia

In vivo positron emission tomography (PET) imaging of nicotinic acetylcholine receptors (nAChRs) is a promising tool for the imaging evaluation of neurologic and neurodegenerative diseases. However, the role of α7 nAChRs after brain diseases such as cerebral ischemia and its involvement in inflammatory reaction is still largely unknown. In vivo and ex vivo evaluation of α7 nAChRs expression after transient middle cerebral artery occlusion (MCAO) was carried out using PET imaging with [¹¹ C]NS14492 and immunohistochemistry (IHC). Pharmacological activation of α7 receptors was evaluated with magnetic resonance imaging (MRI), [¹⁸ F]DPA-714 PET, IHC, real time polymerase chain reaction (qPCR) and neurofunctional studies. In the ischemic territory, [¹¹ C]NS14492 signal and IHC showed an expression increase of α7 receptors in microglia and astrocytes after cerebral ischemia. The role played by α7 receptors on neuroinflammation was supported by the decrease of [¹⁸ F]DPA-714 binding in ischemic rats treated with the α7 agonist PHA 568487 at day 7 after MCAO. Moreover, compared with non-treated MCAO rats, PHA-treated ischemic rats showed a significant reduction of the cerebral infarct volumes and an improvement of the neurologic outcome. PHA treatment significantly reduced the expression of leukocyte infiltration molecules in MCAO rats and in endothelial cells after in vitro ischemia. Despite that, the activation of α7 nAChR had no influence to the blood brain barrier (BBB) permeability measured by MRI. Taken together, these results suggest that the nicotinic α7 nAChRs play a key role in the inflammatory reaction and the leukocyte recruitment following cerebral ischemia in rats.

Brain PET Imaging of α7-nAChR with [18F]ASEM: Reproducibility, Occupancy, Receptor Density, and Changes in Schizophrenia

BACKGROUND

The α7 nicotinic acetylcholine receptor increasingly has been implicated in normal brain physiology, as well as in neuropsychiatric disorders. The highly cortical distribution of α7 nicotinic acetylcholine receptor suggests a role in cognition.

METHODS

We expanded the first-in-human PET imaging of α7 nicotinic acetylcholine receptor with [18F]ASEM from 5 to 21 healthy nonsmoking volunteers and added a feasibility study in 6 male patients with schizophrenia. Study aims included: (1) confirmation of test-retest reproducibility of [18F]ASEM binding, (2) demonstration of specificity by competition with DMXB-A, an α7 nicotinic acetylcholine receptor partial agonist, (3) estimation of [18F]ASEM binding potentials and α7 nicotinic acetylcholine receptor density in vivo in humans, and (4) demonstrating the feasibility of studying α7 nicotinic acetylcholine receptor as a target for schizophrenia.

RESULTS

Test-retest PET confirmed reproducibility (>90%) (variability ≤7%) of [18F]ASEM volume of distribution (VT) estimates in healthy volunteers. Repeated sessions of PET in 5 healthy subjects included baseline and effect of inhibition after oral administration of 150 mg DMXB-A. From reduction of binding potentials, we estimated the dose-dependent occupancy of α7 nicotinic acetylcholine receptor by DMXB-A at 17% to 49% for plasma concentrations at 60 to 200 nM DMXB-A. In agreement with evidence postmortem, α7 nicotinic acetylcholine receptor density averaged 0.67 to 0.82 nM and inhibitor affinity constant averaged 170 to 385 nM. Median VT in a feasibility study of 6 patients with schizophrenia was lower than in healthy volunteers in cingulate cortex, frontal cortex, and hippocampus (P = 0.02, corrected for multiple comparions, Mann-Whitney test).

CONCLUSIONS

The current results confirm the reproducibility of [18F]ASEM VT estimates and the specificity of the tracer for α7 nicotinic acetylcholine receptor. Preliminary findings from our feasibility study of [18F]ASEM binding in patients with schizophrenia are suggestive and provide guidance for future studies with more subjects.

Prenatal kynurenine treatment in rats causes schizophrenia-like broad monitoring deficits in adulthood

RATIONALE

Elevated brain kynurenic acid (KYNA) levels are implicated in the pathology and neurodevelopmental pathogenesis of schizophrenia. In rats, embryonic treatment with kynurenine (EKyn) causes elevated brain KYNA levels in adulthood and cognitive deficits reminiscent of schizophrenia.

OBJECTIVES

Growing evidence suggests that people with schizophrenia have a narrowed attentional focus, and we aimed at establishing whether these abnormalities may be related to KYNA dysregulation.

METHODS

To test whether EKyn rats display broad monitoring deficits, kynurenine was added to the chow of pregnant Wistar dams on embryonic days 15-22. As adults, 20 EKyn and 20 control rats were trained to stable performance on the five-choice serial reaction time task, requiring the localization of 1-s light stimuli presented randomly across five apertures horizontally arranged along a curved wall, equating the locomotor demands of reaching each hole.

RESULTS

EKyn rats displayed elevated omission errors and reduced anticipatory responses relative to control rats, indicative of a lower response rate, and showed reduced locomotor activity. The ability to spread attention broadly was measured by parsing performance by stimulus location. Both groups displayed poorer stimulus detection with greater target location eccentricity, but this effect was significantly more pronounced in the EKyn group. Specifically, the groups differed in the spatial distribution of correct but not incorrect responses. This pattern cannot be explained by differences in response rate and is indicative of a narrowed attentional focus.

CONCLUSIONS

The findings suggest a potential etiology of broad monitoring deficits in schizophrenia, which may constitute a core cognitive deficit.

Acute administration of roflumilast enhances sensory gating in healthy young humans in a randomized trial

INTRODUCTION

Sensory gating is a process involved in early information processing which prevents overstimulation of higher cortical areas by filtering sensory information. Research has shown that the process of sensory gating is disrupted in patients suffering from clinical disorders including attention deficit hyper activity disorder, schizophrenia, and Alzheimer's disease. Phosphodiesterase (PDE) inhibitors have received an increased interest as a tool to improve cognitive performance in both animals and man, including sensory gating.

METHODS

The current study investigated the effects of the PDE4 inhibitor roflumilast in a sensory gating paradigm in 20 healthy young human volunteers (age range 18-30 years). We applied a placebo-controlled randomized cross-over design and tested three doses (100, 300, 1000 μg).

RESULTS

Results show that roflumilast improves sensory gating in healthy young human volunteers only at the 100-μg dose. The effective dose of 100 μg is five times lower than the clinically approved dose for the treatment of acute exacerbations in chronic obstructive pulmonary disease (COPD). No side-effects, such as nausea and emesis, were observed at this dose. This means roflumilast shows a beneficial effect on gating at a dose that had no adverse effects reported following single-dose administration in the present study.

CONCLUSION

The PDE4 inhibitor roflumilast has a favorable side-effect profile at a cognitively effective dose and could be considered as a treatment in disorders affected by disrupted sensory gating.

Astrocytic Regulation of Glutamate Transmission in Schizophrenia

According to the glutamate hypothesis of schizophrenia, the abnormality of glutamate transmission induced by hypofunction of NMDA receptors (NMDARs) is causally associated with the positive and negative symptoms of schizophrenia. However, the underlying mechanisms responsible for the changes in glutamate transmission in schizophrenia are not fully understood. Astrocytes, the major regulatory glia in the brain, modulate not only glutamate metabolism but also glutamate transmission. Here we review the recent progress in understanding the role of astrocytes in schizophrenia. We focus on the astrocytic mechanisms of (i) glutamate synthesis via the glutamate-glutamine cycle, (ii) glutamate clearance by excitatory amino acid transporters (EAATs), (iii) D-serine release to activate NMDARs, and (iv) glutamatergic target engagement biomarkers. Abnormality in these processes is highly correlated with schizophrenia phenotypes. These findings will shed light upon further investigation of pathogenesis as well as improvement of biomarkers and therapies for schizophrenia.

Recombinant Newcastle disease virus rL-RVG enhances the apoptosis and inhibits the migration of A549 lung adenocarcinoma cells via regulating alpha 7 nicotinic acetylcholine receptors in vitro

BACKGROUND

The aim of this study were to investigate the possible pro-apoptotic mechanisms of the recombinant Newcastle disease virus (NDV) strain rL-RVG, which expresses the rabies virus glycoprotein, in A549 lung adenocarcinoma cells via the regulation of alpha 7 nicotinic acetylcholine receptors (α7 nAChRs) and to analyze the relationships between α7 nAChR expression in lung cancer and the clinical pathological features.

METHODS

α7 nAChR expression in A549, LΑ795, and small-cell lung carcinoma (SCLC) cells, among others, was detected using reverse transcription polymerase chain reaction (RT-PCR). The optimal α7 nAChR antagonist and agonist concentrations for affecting A549 lung adenocarcinoma cells were detected using MTT assays. The α7 nAChR expression in A549 cells after various treatments was assessed by Western blot, immunofluorescence and RT-PCR analyses. Apoptosis in the various groups was also monitored by Western blot and TUNEL assays, followed by the detection of cell migration via transwell and scratch tests. Furthermore, α7 nAChR expression was examined by immunohistochemistry in lung cancer tissue samples from 130 patients and 40 pericancerous tissue samples, and the apoptotis in lung adenocarcinoma tissue was detected by Tunel assay, Then, the expression levels and clinicopathological characteristics were analyzed.

RESULTS

Of the A549, LΑ795, SCLC and U251 cell lines, the A549 cells exhibited the highest α7 nAChR expression. The cells infected with rL-RVG exhibited high RVG gene and protein expression. The rL-RVG group exhibited weaker α7 nAChR expression compared with the methyllycaconitine citrate hydrate (MLA, an α7 nAChR antagonist) and NDV groups. At the same time, the MLA and rL-RVG treatments significantly inhibited proliferation and migration and promoted apoptosis in the lung cancer cells (P < 0.05). The expression of α7 nAChR was upregulated in lung cancer tissue compared with pericancerous tissue (P = 0.000) and was significantly related to smoking, clinical tumor-node-metastases stage, and histological differentiation (P < 0.05). The AI in lung adenocarcinoma tissue in high-medium differentiation group was lower than that in low differentiation group (p < 0.01).

CONCLUSIONS

An antagonist of α7 nAChR may be used as a molecular target for lung adenocarcinoma therapy. Recombinant NDV rL-RVG enhances the apoptosis and inhibits the migration of A549 lung adenocarcinoma cells by regulating α7 nAChR signaling pathways.

Effects of haloperidol, olanzapine, ziprasidone, and PHA-543613 on spatial learning and memory in the Morris water maze test in naïve and MK-801-treated mice

INTRODUCTION

Cognitive impairment is the core symptom of schizophrenia, significantly impacting the functional outcome. Improvement of cognitive function has been an important aspect of the treatment of schizophrenia. Therefore, this study is to demonstrate the effects of first-generation antipsychotic haloperidol, second-generation antipsychotic olanzapine and ziprasidone, and alpha-7 nicotinic acetylcholine receptor agonist PHA-543613 on spatial learning and memory.

MATERIAL AND METHODS

C57BL/6 mice received intraperitoneal injections of haloperidol (2 mg/kg), olanzapine (2.5 mg/kg), ziprasidone (2 mg/kg), and PHA-543613 (1 mg/kg), and cognitive dysfunctions were induced by MK-801 (0.1 mg/kg). Morris water maze was used for investigating the effects of all agents.

RESULTS

Mk-801 significantly increased the mean escape latency to the platform and decreased the number of platform area crossings. Ziprasidone had no effect on the mean escape latency to platform and the number of platform area crossings in naïve mice, but haloperidol, olanzapine, and PHA-543613 did not. Haloperidol and olanzapine significantly increased the mean escape latency to platform and decreased the number of platform area crossings, while ziprasidone and PHA-543613 did not. All the agents had no effect on swimming speed.

CONCLUSIONS

Ziprasidone and alpha-7 nicotinic acetylcholine receptor agonist PHA-543613 might be helpful in the treatment of CIAS.

Oxidative stress-driven parvalbumin interneuron impairment as a common mechanism in models of schizophrenia

Parvalbumin inhibitory interneurons (PVIs) are crucial for maintaining proper excitatory/inhibitory balance and high-frequency neuronal synchronization. Their activity supports critical developmental trajectories, sensory and cognitive processing, and social behavior. Despite heterogeneity in the etiology across schizophrenia and autism spectrum disorder, PVI circuits are altered in these psychiatric disorders. Identifying mechanism(s) underlying PVI deficits is essential to establish treatments targeting in particular cognition. On the basis of published and new data, we propose oxidative stress as a common pathological mechanism leading to PVI impairment in schizophrenia and some forms of autism. A series of animal models carrying genetic and/or environmental risks relevant to diverse etiological aspects of these disorders show PVI deficits to be all accompanied by oxidative stress in the anterior cingulate cortex. Specifically, oxidative stress is negatively correlated with the integrity of PVIs and the extracellular perineuronal net enwrapping these interneurons. Oxidative stress may result from dysregulation of systems typically affected in schizophrenia, including glutamatergic, dopaminergic, immune and antioxidant signaling. As convergent end point, redox dysregulation has successfully been targeted to protect PVIs with antioxidants/redox regulators across several animal models. This opens up new perspectives for the use of antioxidant treatments to be applied to at-risk individuals, in close temporal proximity to environmental impacts known to induce oxidative stress.

Classics in Chemical Neuroscience: Aripiprazole

Aripiprazole was the first antipsychotic developed to possess agonist properties at dopamine D₂ autoreceptors, a groundbreaking strategy that presented a new vista for schizophrenia drug discovery. The dopamine D₂ receptor is the crucial target of all extant antipsychotics, and all developed prior to aripiprazole were D₂ receptor antagonists. Extensive blockade of these receptors, however, typically produces extrapyramidal (movement) side effects, which plagued first-generation antipsychotics, such as haloperidol. Second-generation antipsychotics, such as clozapine, with unique polypharmacology and D₂ receptor binding kinetics, have significantly lower risk of movement side effects but can cause myriad additional ones, such as severe weight gain and metabolic dysfunction. Aripiprazole's polypharmacology, characterized by its unique agonist activity at dopamine D₂ and D₃ and serotonin 5-HT_1A receptors, as well as antagonist activity at serotonin 5-HT_2A receptors, translates to successful reduction of positive, negative, and cognitive symptoms of schizophrenia, while also mitigating risk of weight gain and movement side effects. New observations, however, link aripiprazole to compulsive behaviors in a small group of patients, an unusual side effect for antipsychotics. In this review, we discuss the chemical synthesis, pharmacology, pharmacogenomics, drug metabolism, and adverse events of aripiprazole, and we present a current understanding of aripiprazole's neurotherapeutic mechanisms, as well as the history and importance of aripiprazole to neuroscience.

Partial agonism at the α7 nicotinic acetylcholine receptor improves attention, impulsive action and vigilance in low attentive rats

Inattention is a disabling symptom in conditions such as schizophrenia and attention deficit/hyperactivity disorder. Nicotine can improve attention and vigilance, but is unsuitable for clinical use due to abuse liability. Genetic knockout of the α7 nicotinic acetylcholine receptor (nAChR) induces attention deficits therefore selective agonism may improve attention, without the abuse liability associated with nicotine. The α7 nAChR partial agonist encenicline (formerly EVP-6124) enhances memory in rodents and humans. Here we investigate, for the first time, efficacy of encenicline to improve attention and vigilance in animals behaviourally grouped for low attentive traits in the 5 choice-continuous performance task (5C-CPT). Female Lister Hooded rats were trained to perform the 5C-CPT with a variable stimulus duration (SD). Animals were then grouped based on performance into upper and lower quartiles of d' (vigilance) and accuracy (selective attention), producing high-attentive (HA) and low-attentive (LA) groups. LA animals showed an increase in selective attention and vigilance at 0.3mg/kg encenicline, a reduction in impulsive action (probability of false alarms) and increase in vigilance following 1mg/kg at 0.75sSD. At 1mg/kg, HA animals had reduced selective attention at 0.75sSD and reduced vigilance at 0.75 and 1.25sSD. Improvement of attention, vigilance and impulsive action in LA animals demonstrates that encenicline has pro-attentive properties dependent on baseline levels of performance. Our work suggests that α7 nAChR partial agonism may improve attention particularly in conditions with low attention.

BMS-933043, a Selective α7 nAChR Partial Agonist for the Treatment of Cognitive Deficits Associated with Schizophrenia

The therapeutic treatment of negative symptoms and cognitive dysfunction associated with schizophrenia is a significant unmet medical need. Preclinical literature indicates that α7 neuronal nicotinic acetylcholine (nACh) receptor agonists may provide an effective approach to treating cognitive dysfunction in schizophrenia. We report herein the discovery and evaluation of 1c (BMS-933043), a novel and potent α7 nACh receptor partial agonist with high selectivity against other nicotinic acetylcholine receptor subtypes (>100-fold) and the 5-HT_3A receptor (>300-fold). In vivo activity was demonstrated in a preclinical model of cognitive impairment, mouse novel object recognition. BMS-933043 has completed Phase I clinical trials.

Stimulation of nicotinic acetylcholine alpha7 receptors rescue schizophrenia-like cognitive impairments in rats

Alpha7 nicotinic acetylcholine receptor (α7 nAChR) dysfunction plays an important role in schizophrenia. Positive allosteric modulators of α7 nAChR have emerged as a promising therapeutic approach to manage cognitive deficits that are inadequately treated in schizophrenic patients. The aim of the present study was to evaluate the ability of type I (CCMI) and type II (PNU120596) α7 nAChR positive allosteric modulators to counteract MK-801-induced cognitive and sensorimotor gating deficits. The activity of these compounds was compared with the action of the α7 nAChR agonist A582941. CCMI, PNU120596 and A582941 reversed the sensorimotor gating impairment evoked by MK-801 based on the prepulse inhibition of the startle response. Additionally, no MK-801-evoked working memory deficits were observed with α7 nAChR ligand pretreatment as assessed in a discrete paired-trial delayed alternation task. However, these compounds did not affect the rats' attentional performances in the five-choice serial reaction time test. The α7 nAChR agents demonstrated a beneficial effect on sensorimotor gating and some aspects of cognition tested in a rat model of schizophrenia. Therefore, these results support the use of α7 nAChR positive allosteric modulators as a potential treatment strategy in schizophrenia.

B-973, a novel piperazine positive allosteric modulator of the α7 nicotinic acetylcholine receptor

The alpha7 (α7) nicotinic acetylcholine receptor is a therapeutic target for cognitive disorders. Here we describe 3-(3,4-difluorophenyl)-N-(1-(6-(4-(pyridin-2-yl)piperazin-1-yl)pyrazin-2-yl)ethyl)propanamide (B-973), a novel piperazine-containing molecule that acts as a positive allosteric modulator of the α7 receptor. We characterize the action of B-973 on the α7 receptor using electrophysiology and radioligand binding. At 0.1mM acetylcholine, 1μM B-973 potentiated peak acetylcholine-induced currents 6-fold relative to maximal acetylcholine (3mM) and slowed channel desensitization, resulting in a 6900-fold increase in charge transfer. The EC₅₀ of B-973 was approximately 0.3μM at acetylcholine concentrations ranging from 0.03 to 3mM. At a concentration of 1μM, B-973 shifted the acetylcholine EC₅₀ of peak currents from 0.30mM in control to 0.007mM. B-973 slowed channel deactivation upon acetylcholine removal (τ=50s) and increased the affinity of the α7 agonist [³H]A-585539. In the absence of exogenously added acetylcholine, application of B-973 at concentrations >1μM induced large methyllycaconitine-sensitive currents, suggesting B-973 can function as an Ago-PAM at high concentrations. B-973 will be a useful probe for investigating the biological consequences of increasing α7 receptor activity through allosteric modulation.

Design and synthesis of a novel series of 4-heteroarylamino-1'-azaspiro[oxazole-5,3'-bicyclo[2.2.2]octanes as α7 nicotinic receptor agonists 2. Development of 4-heteroaryl SAR

Quinuclidine-containing spirooxazolines, as described in the previous report in this series, were demonstrated to have utility as α7 nicotinic acetylcholine receptor (α7 nAChR) partial agonists. In this work, the SAR of this chemotype was expanded to include an array of diazine heterocyclic substitutions. Many of the heterocyclic analogs were potent partial agonists of the α7 receptor, selective against other nicotinic receptors and the serotinergic 5HT_3A receptor. (1'S,3'R,4'S)-N-(6-phenylpyrimidin-4-yl)-4H-1'-azaspiro[oxazole-5,3'-bicyclo[2.2.2]octan]-2-amine, a potent and selective α7 nAChR partial agonist, was demonstrated to improve cognition in the mouse novel object recognition (NOR) model of episodic memory.

Discovery, synthesis, biological evaluation and structure-based optimization of novel piperidine derivatives as acetylcholine-binding protein ligands

The homomeric α7 nicotinic receptor (α7 nAChR) is widely expressed in the human brain that could be activated to suppress neuroinflammation, oxidative stress and neuropathic pain. Consequently, a number of α7 nAChR agonists have entered clinical trials as anti-Alzheimer's or anti-psychotic therapies. However, high-resolution crystal structure of the full-length α7 receptor is thus far unavailable. Since acetylcholine-binding protein (AChBP) from Lymnaea stagnalis is most closely related to the α-subunit of nAChRs, it has been used as a template for the N-terminal domain of α-subunit of nAChR to study the molecular recognition process of nAChR-ligand interactions, and to identify ligands with potential nAChR-like activities.Here we report the discovery and optimization of novel acetylcholine-binding protein ligands through screening, structure-activity relationships and structure-based design. We manually screened in-house CNS-biased compound library in vitro and identified compound 1, a piperidine derivative, as an initial hit with moderate binding affinity against AChBP (17.2% inhibition at 100 nmol/L). During the 1st round of optimization, with compound 2 (21.5% inhibition at 100 nmol/L) as the starting point, 13 piperidine derivatives with different aryl substitutions were synthesized and assayed in vitro. No apparent correlation was demonstrated between the binding affinities and the steric or electrostatic effects of aryl substitutions for most compounds, but compound 14 showed a higher affinity (K_i=105.6 nmol/L) than nicotine (K_i=777 nmol/L). During the 2nd round of optimization, we performed molecular modeling of the putative complex of compound 14 with AChBP, and compared it with the epibatidine-AChBP complex. The results suggested that a different piperidinyl substitution might confer a better fit for epibatidine as the reference compound. Thus, compound 15 was designed and identified as a highly affinitive acetylcholine-binding protein ligand. In this study, through two rounds of optimization, compound 15 (K_i=2.8 nmol/L) has been identified as a novel, piperidine-based acetylcholine-binding protein ligand with a high affinity.

Repurposing Drugs for Cognition in Schizophrenia

Currently approved treatments for schizophrenia only minimally affect the cognitive features of the illness that are the most closely related to disability. Hence, there is now considerable effort to repurpose drugs for schizophrenia, and to seek agents that can improve cognition by targeting receptor systems other than the dopaminergic system. The results of these studies have been mixed thus far; however, this continues to be a high-priority area of schizophrenia research and an important unmet need.