Functional magnetic resonance imaging of effects of a nicotinic agonist in schizophrenia

Cholinergic Functioning, Cognition, and Anticholinergic Medication Burden in Schizophrenia

Acetylcholine (ACh) signaling is critical for central nervous function and is known to be abnormal in schizophrenia (SZ), a chronic neuropsychiatric disorder in which cognitive deficits persist, despite treatment. This review provides a summary of the clinical evidence linking ACh abnormalities to SZ-associated cognitive deficits, an overview of ACh-based pro-cognitive strategies attempted in SZ, and a survey of recent studies that describe the impact of anticholinergic medication burden on cognitive outcomes in SZ. Methodological challenges that currently limit more substantial investigation of ACh in SZ patients and future directions are also discussed.

Role of Brain Imaging in Drug Development for Psychiatry

Background:

Over the last decades, many brain imaging studies have contributed to new insights in the pathogenesis of psychiatric disease. However, in spite of these developments, progress in the development of novel therapeutic drugs for prevalent psychiatric health conditions has been limited.

Objective:

In this review, we discuss translational, diagnostic and methodological issues that have hampered drug development in CNS disorders with a particular focus on psychiatry. The role of preclinical models is critically reviewed and opportunities for brain imaging in early stages of drug development using PET and fMRI are discussed. The role of PET and fMRI in drug development is reviewed emphasizing the need to engage in collaborations between industry, academia and phase I units.

Conclusion:

Brain imaging technology has revolutionized the study of psychiatric illnesses, and during the last decade, neuroimaging has provided valuable insights at different levels of analysis and brain organization, such as effective connectivity (anatomical), functional connectivity patterns and neurochemical information that may support both preclinical and clinical drug development. Since there is no unifying pathophysiological theory of individual psychiatric syndromes and since many symptoms cut across diagnostic boundaries, a new theoretical framework has been proposed that may help in defining new targets for treatment and thus enhance drug development in CNS diseases. In addition, it is argued that new proposals for data-mining and mathematical modelling as well as freely available databanks for neural network and neurochemical models of rodents combined with revised psychiatric classification will lead to new validated targets for drug development.

The Recent Development of Piperazine and Piperidine Derivatives as Antipsychotic Agents

Schizophrenia is a chronic neuropsychiatric disorder that affects nearly 1% of the global population. There are various anti-psychotic drugs available for the treatment of schizophrenia, but they have certain side effects; therefore, there is a need to explore and develop novel potential lead compounds against schizophrenia. The currently available drugs e.g. typical and atypical antipsychotics act on different dopamine and serotonin receptors and as per literature reports, various piperidine and piperazine derivatives have shown promising activity against these receptors. When different heterocyclic groups are attached to basic piperidine and piperazine rings, the antipsychotic activity is greatly potentiated. In this direction, various antipsychotic drugs have been synthesized at the laboratory level, and few are under clinical trial studies, such as Lu AE58054, PF-04802540, ORG25935, DMXB-A, Bitopertin, and ABT-126. In the present review, we include the studies related to the effect of different substituents on piperidine/piperazine derivatives and their anti-psychotic activity. Various series of synthesized compounds by other researchers with piperidine/piperazine nucleus have been reviewed and diagrammatically represented in the form of SAR (structure-activity relationships), which will help the scientists for the development of potential lead compounds.

Cholinergic Receptors and Addiction

Human behavior can be controlled by physical or psychological dependencies associated with addiction. One of the most insidious addictions in our society is the use of tobacco products which contain nicotine. This addiction can be associated with specific receptors in the brain that respond to the natural neurotransmitter acetylcholine. These nicotinic acetylcholine receptors (nAChR) are ligand-gated ion channels formed by the assembly of one or multiple types of nAChR receptor subunits. In this paper, we review the structure and diversity of nAChR subunits and our understanding for how different nAChR subtypes play specific roles in the phenomenon of nicotine addiction. We focus on receptors containing β2 and/or α6 subunits and the special significance of α5-containing receptors. These subtypes all have roles in regulating dopamine-mediated neurotransmission in the mesolimbic reward pathways of the brain. We also discuss the unique roles of homomeric α7 nAChR in behavioral responses to nicotine and how our knowledge of nAChR functional diversity may help guide pharmacotherapeutic approaches for treating nicotine addiction. While nicotine addiction is a truly global problem, the use of areca nut (betel) products is also a serious addiction associated with public health issues across most of South Asia, impacting as many as 600 million people. We discuss how cholinergic receptors of the brain are also involved with areca addiction and the unique challenges for dealing with addiction to this substance.

Alpha7 Nicotinic Receptors as Therapeutic Targets in Schizophrenia

While current treatments for schizophrenia often provide much relief for positive symptoms such as hallucinations, other symptoms, particularly cognitive deficits, persist and contribute to substantial suffering and reduced quality of life for patients. In searching for novel therapeutic avenues to treat cognitive deficits in schizophrenia, recent work is exploring nicotinic receptor neurobiology. Supported by a large body of evidence, with contributions from studies of smoking behaviors, genetics, receptor distribution and function, animal models and nicotinic effects on illness symptoms, the alpha7 nicotinic receptor has emerged as a potential therapeutic target. Despite promise in early clinical trials, however, no drug targeting nicotinic systems has succeeded in larger phase 3 trials. Following a brief review of nicotinic receptor biology and the evidence that has led to pursuit of alpha7 nicotinic agonism as a therapeutic strategy, this review will provide an update on the status of recent trials, discuss potential issues that may have contributed to negative outcomes, and point to new directions and promising advances in developing alpha7 nicotinic receptor-based treatment for cognitive symptoms in schizophrenia.

IMPLICATIONS

By examining alpha7 nicotinic receptor biology and recent efforts to target the receptor in clinical trials, it is hoped that investigators will be motivated to explore novel, promising directions focusing on the receptor as a strategy to treat cognitive symptoms in schizophrenia.

Discovery of Novel, Potent, Brain-Permeable, and Orally Efficacious Positive Allosteric Modulator of α7 Nicotinic Acetylcholine Receptor [4-(5-(4-Chlorophenyl)-4-methyl-2-propionylthiophen-3-yl)benzenesulfonamide]: Structure-Activity Relationship and Preclinical Characterization

The discovery of a series of thiophenephenylsulfonamides as positive allosteric modulators (PAM) of α7 nicotinic acetylcholine receptor (α7 nAChR) is described. Optimization of this series led to identification of compound 28, a novel PAM of α7 nicotinic acetylcholine receptor (α7 nAChR). Compound 28 showed good in vitro potency, with pharmacokinetic profile across species with excellent brain penetration and residence time. Compound 28 robustly reversed the cognitive deficits in episodic/working memory in both time-delay and scopolamine-induced amnesia paradigms in the novel object and social recognition tasks, at very low dose levels. Additionally, compound 28 has shown excellent safety profile in phase 1 clinical trials and is being evaluated for efficacy and safety as monotherapy in patients with mild to moderate Alzheimer's disease.

Effects of nicotine on smooth pursuit eye movements in healthy non-smokers

RATIONALE

The non-selective nicotinic acetylcholine receptor (nAChR) agonist nicotine has been argued to improve attention via enhanced filtering of irrelevant stimuli. Here, we tested this hypothesis in the context of smooth pursuit eye movements (SPEMs), an oculomotor function previously shown to improve with nicotine in some but not all studies.

OBJECTIVES

In order to test whether nicotine improves performance particularly when the inhibition of distracting stimuli is required, SPEM was elicited in conditions with or without peripheral distractors. Additionally, different target frequencies were employed in order to parametrically vary general processing demands on the SPEM system.

METHODS

Healthy adult non-smokers (N = 18 females, N = 13 males) completed a horizontal sinusoidal SPEM task at different target frequencies (0.2 Hz, 0.4 Hz, 0.6 Hz) in the presence or absence of peripheral distractors in a double-blind, placebo-controlled, cross-over design using a 2 mg nicotine gum.

RESULTS

Nicotine increased peak pursuit gain relative to placebo (p < .001), but an interaction with distractor condition (p = .001) indicated that this effect was most pronounced in the presence of distractors. Catch-up saccade frequency was reduced by nicotine (p = .01), particularly at higher target frequencies (two-way interaction, p = .04). However, a three-way interaction (p = .006) indicated that the reduction with nicotine was strongest at the highest target frequency (0.6 Hz) only without distractors, whereas in the presence of distractors, it was strongest at 0.4-Hz target frequency. There were no effects of nicotine on subjective state measures.

CONCLUSIONS

Together, these findings support a role of both distractor inhibition and general processing load in the effects of nicotine on smooth pursuit.

Sex differences in the nicotinic excitation of principal neurons within the developing hippocampal formation

The hippocampal formation (HF) plays an important role to facilitate higher order cognitive functions. Cholinergic activation of heteromeric nicotinic acetylcholine receptors (nAChRs) within the HF is critical for the normal development of principal neurons within this brain region. However, previous research investigating the expression and function of heteromeric nAChRs in principal neurons of the HF is limited to males or does not differentiate between the sexes. We used whole-cell electrophysiology to show that principal neurons in the CA1 region of the female mouse HF are excited by heteromeric nAChRs throughout postnatal development, with the greatest response occurring during the first two weeks of postnatal life. Excitability responses to heteromeric nAChR stimulation were also found in principal neurons in the CA3, dentate gyrus, subiculum, and entorhinal cortex layer VI (ECVI) of young postnatal female HF. A direct comparison between male and female mice found that principal neurons in ECVI display greater heteromeric nicotinic passive and active excitability responses in females. This sex difference is likely influenced by the generally more excitable nature of ECVI neurons from female mice, which display a higher resting membrane potential, greater input resistance, and smaller afterhyperpolarization potential of medium duration (mAHP). These findings demonstrate that heteromeric nicotinic excitation of ECVI neurons differs between male and female mice during a period of major circuitry development within the HF, which may have mechanistic implications for known sex differences in the development and function of this cognitive brain region.

Bidirectional Regulation of Aggression in Mice by Hippocampal Alpha-7 Nicotinic Acetylcholine Receptors

Humans with 15q13.3 microdeletion syndrome (15q13.3DS) are typically hemizygous for CHRNA7, the gene coding for the α7 nicotinic acetylcholine receptor (nAChR), and manifest a variable neuropsychiatric phenotype that frequently includes persistent aggression. In mice, nAChR activation by nicotine is anti-aggressive, or 'serenic,' an effect which requires α7 nAChRs and is recapitulated by GTS-21, an α7 nAChR partial agonist. Pharmacotherapies potentiating α7 nAChR signaling have also been shown to reduce aggression in human 15q13.3DS. These findings identify the α7 nAChR as an important regulator of aggressive behavior, but the underlying neurobiological substrates remain to be determined. We therefore investigated the brain regions and potential neural circuits in which α7 nAChRs regulate aggressive behavior in male mice. As in 15q13.3DS, mice heterozygous for Chrna7 were significantly more aggressive compared to wild-type controls in the resident-intruder test. We subsequently examined the hippocampus, where α7 nAChRs are highly expressed, particularly in GABAergic interneurons. Resident-intruder interactions strongly activated granule cells in the dentate gyrus (DG). In contrast, GTS-21, which reduces aggression in mice, reduced DG granule cell activity during resident-intruder interactions. Short hairpin RNA knockdown of Chrna7 in the DG enhanced baseline aggression and eliminated the serenic effects of both nicotine and GTS-21 on attack latency. These data further implicate α7 nAChRs in regulation of aggression, and demonstrate that hippocampal α7 nAChR signaling is necessary and sufficient to limit aggression. These findings suggest that nAChR-mediated regulation of hippocampal excitatory-inhibitory balance could be a promising therapeutic intervention for aggression arising in certain forms of neuropsychiatric disease.

Similar nicotinic excitability responses across the developing hippocampal formation are regulated by small-conductance calcium-activated potassium channels

The hippocampal formation forms a cognitive circuit that is critical for learning and memory. Cholinergic input to nicotinic acetylcholine receptors plays an important role in the normal development of principal neurons within the hippocampal formation. However, the ability of nicotinic receptors to stimulate principal neurons across all regions of the developing hippocampal formation has not been determined. We show in this study that heteromeric nicotinic receptors mediate direct inward current and depolarization responses in principal neurons across the hippocampal formation of the young postnatal mouse. These responses were found in principal neurons of the CA1, CA3, dentate gyrus, subiculum, and entorhinal cortex layer VI, and they varied in magnitude across regions with the greatest responses occurring in the subiculum and entorhinal cortex. Despite this regional variation in the magnitude of passive responses, heteromeric nicotinic receptor stimulation increased the excitability of active principal neurons by a similar amount in all regions. Pharmacological experiments found this similar excitability response to be regulated by small-conductance calcium-activated potassium (SK) channels, which exhibited regional differences in their influence on neuron activity that offset the observed regional differences in passive nicotinic responses. These findings demonstrate that SK channels play a role to coordinate the magnitude of heteromeric nicotinic excitability responses across the hippocampal formation at a time when nicotinic signaling drives the development of this cognitive brain region. This coordinated input may contribute to the normal development, synchrony, and maturation of the hippocampal formation learning and memory network. NEW & NOTEWORTHY This study demonstrates that small-conductance calcium-activated potassium channels regulate similar-magnitude excitability responses to heteromeric nicotinic acetylcholine receptor stimulation in active principal neurons across multiple regions of the developing mouse hippocampal formation. Given the importance of nicotinic neurotransmission for the development of principal neurons within the hippocampal formation, this coordinated excitability response is positioned to influence the normal development, synchrony, and maturation of the hippocampal formation learning and memory network.

Targeting Functional Biomarkers in Schizophrenia with Neuroimaging

Many of the most debilitating symptoms for psychiatric disorders such as schizophrenia remain poorly treated. As such, the development of novel treatments is urgently needed. Unfortunately, the costs associated with high failure rates for investigational compounds as they enter clinical trials has led to pharmaceutical companies downsizing or eliminating research programs needed to develop these drugs. One way of increasing the probability of success for investigational compounds is to incorporate alternative methods of identifying biological targets in order to more effectively screen new drugs. A promising method of accomplishing this goal for psychiatric drugs is to use functional magnetic resonance imaging (fMRI). fMRI investigates neural circuits, shedding light on the biology that generates symptoms such as hallucinations. Once identified, relevant neural circuits can be targeted with pharmacologic interventions and the response to these drugs measured with fMRI. This review describes the early use of fMRI in this context, and discusses the alpha7 nicotinic receptor agonist 3-(2,4-dimethoxybenzylidene) anabaseine (DMXB-A), as an example of the potential value of fMRI for psychiatric drug development.

Targeting neuronal dysfunction in schizophrenia with nicotine: Evidence from neurophysiology to neuroimaging

Patients with schizophrenia self-administer nicotine at rates higher than is self-administered for any other psychiatric illness. Although the reasons are unclear, one hypothesis suggests that nicotine is a form of 'self-medication' in order to restore normal levels of nicotinic signaling and target abnormalities in neuronal function associated with cognitive processes. This brief review discusses evidence from neurophysiological and neuroimaging studies in schizophrenia patients that nicotinic agonists may effectively target dysfunctional neuronal circuits in the illness. Evidence suggests that nicotine significantly modulates a number of these circuits, although relatively few studies have used modern neuroimaging techniques (e.g. functional magnetic resonance imaging (fMRI)) to examine the effects of nicotinic drugs on disease-related neurobiology. The neuronal effects of nicotine and other nicotinic agonists in schizophrenia remain a priority for psychiatry research.

Modulatory effects of α7 nAChRs on the immune system and its relevance for CNS disorders

The clinical development of selective alpha-7 nicotinic acetylcholine receptor (α7 nAChR) agonists has hitherto been focused on disorders characterized by cognitive deficits (e.g., Alzheimer's disease, schizophrenia). However, α7 nAChRs are also widely expressed by cells of the immune system and by cells with a secondary role in pathogen defense. Activation of α7 nAChRs leads to an anti-inflammatory effect. Since sterile inflammation is a frequently observed phenomenon in both psychiatric disorders (e.g., schizophrenia, melancholic and bipolar depression) and neurological disorders (e.g., Alzheimer's disease, Parkinson's disease, and multiple sclerosis), α7 nAChR agonists might show beneficial effects in these central nervous system disorders. In the current review, we summarize information on receptor expression, the intracellular signaling pathways they modulate and reasons for receptor dysfunction. Information from tobacco smoking, vagus nerve stimulation, and cholinesterase inhibition is used to evaluate the therapeutic potential of selective α7 nAChR agonists in these inflammation-related disorders.

Nicotine restores functional connectivity of the ventral attention network in schizophrenia

While previous work has suggested that nicotine may transiently improve attention deficits in schizophrenia, the neuronal mechanisms are poorly understood. This study is the first to examine the effects of nicotine on connectivity within the ventral attention network (VAN) during a selective attention task in schizophrenia. Using a crossover design, 17 nonsmoking patients with schizophrenia and 20 age/gender-matched nonsmoking healthy controls performed a go/no-go task with environmental noise distractors during application of a 7 mg nicotine or placebo patch. Psychophysiological interaction analysis was performed to analyze task-associated changes in connectivity between a ventral parietal cortex (VPC) seed and the inferior frontal gyrus (IFG), key components of the human VAN. Effects of nicotine on resting state VAN connectivity were also examined. A significant diagnosis × drug interaction was observed on task-associated connectivity between the VPC seed and the left IFG (F(1,35) = 8.03, p < 0.01). This effect was driven by decreased connectivity after placebo in patients and greater connectivity after nicotine. Resting state connectivity analysis showed a significant main effect of diagnosis between the seed and right IFG (F = 4.25, p = 0.023) due to increased connectivity in patients during placebo, but no drug × diagnosis interactions or main effects of drug. This study is the first to demonstrate that 1) the VAN is disconnected in schizophrenia during selective attention, and 2) nicotine may normalize this pathological state.

Effect of Pharmacological Interventions on the Fronto-Cingulo-Parietal Cognitive Control Network in Psychiatric Disorders: A Transdiagnostic Systematic Review of fMRI Studies

Executive function deficits, such as working memory, decision-making, and attention problems, are a common feature of several psychiatric disorders for which no satisfactory treatment exists. Here, we transdiagnostically investigate the effects of pharmacological interventions (other than methylphenidate) on the fronto-cingulo-parietal cognitive control network, in order to identify functional brain markers for future procognitive pharmacological interventions. Twenty-nine manuscripts investigated the effect of pharmacological treatment on executive function-related brain correlates in psychotic disorders (n = 11), depression (n = 4), bipolar disorder (n = 4), ADHD (n = 4), OCD (n = 2), smoking dependence (n = 2), alcohol dependence (n = 1), and pathological gambling (n = 1). In terms of impact on the fronto-cingulo-parietal network, the preliminary evidence for catechol-O-methyl-transferase inhibitors, nicotinic receptor agonists, and atomoxetine was relatively consistent, the data for atypical antipsychotics and anticonvulsants moderate, and interpretation of the data for antidepressants was hampered by the employed study designs. Increased activity in task-relevant areas and decreased activity in task-irrelevant areas were the most common transdiagnostic effects of pharmacological treatment. These markers showed good positive and moderate negative predictive value. It is concluded that fronto-cingulo-parietal activity changes can serve as a marker for future procognitive interventions. Future recommendations include the use of randomized double-blind designs and selective cholinergic and glutamatergic compounds.

Neuronal effects of nicotine during auditory selective attention in schizophrenia

Although nicotine has been shown to improve attention deficits in schizophrenia, the neurobiological mechanisms underlying this effect are poorly understood. We hypothesized that nicotine would modulate attention-associated neuronal response in schizophrenia patients in the ventral parietal cortex (VPC), hippocampus, and anterior cingulate based on previous findings in control subjects. To test this hypothesis, the present study examined response in these regions in a cohort of nonsmoking patients and healthy control subjects using an auditory selective attention task with environmental noise distractors during placebo and nicotine administration. In agreement with our hypothesis, significant diagnosis (Control vs. Patient) X drug (Placebo vs. Nicotine) interactions were observed in the VPC and hippocampus. The interaction was driven by task-associated hyperactivity in patients (relative to healthy controls) during placebo administration, and decreased hyperactivity in patients after nicotine administration (relative to placebo). No significant interaction was observed in the anterior cingulate. Task-associated hyperactivity of the VPC predicted poor task performance in patients during placebo. Poor task performance also predicted symptoms in patients as measured by the Brief Psychiatric Rating Scale. These results are the first to suggest that nicotine may modulate brain activity in a selective attention-dependent manner in schizophrenia.

Targeting of α7 Nicotinic Acetylcholine Receptors in the Treatment of Schizophrenia and the Use of Auditory Sensory Gating as a Translational Biomarker

Accumulating evidence suggests that the α7 subtype of nicotinic acetylcholine receptors (nAChRs) plays a key role in inflammatory processes, thought to be involved in the pathophysiology of neuropsychiatric diseases, such as schizophrenia and Alzheimer's disease. Preclinical and clinical studies showed that the diminished suppression of P50 auditory evoked potentials in patients with schizophrenia may be associated with a decreased density of α7 nAChRs in the brain. This points to a role for auditory sensory gating (P50) as a translational biomarker. A number of agonists and positive allosteric modulators (PAMs) for α7 nAChR promoted beneficial effects in animal models with sensory gating and cognitive deficits. Additionally, several clinical studies showed that α7 nAChR agonists could improve suppression in auditory P50 evoked potentials, as well as cognitive deficits, and negative symptoms in patients with schizophrenia. Taken together, α7 nAChR presents as an extremely attractive therapeutic target for schizophrenia. In this article, the author discusses recent findings on α7 nAChR agonists such as DMXB-A, RG3487, TC-5619, tropisetron, EVP-6124 (encenicline), ABT-126, AQW051 and α7 nAChR PAMs such as JNJ-39393406, PNU- 120596 and AVL-3288 (also known as UCI-4083), and their potential as therapeutic drugs for neuropsychiatric diseases, such as schizophrenia.

Nicotinic receptors and attention

Facilitation of different attentional functions by nicotinic acetylcholine receptor (nAChR) agonists may be of therapeutic potential in disease conditions such as Alzheimer's disease or schizophrenia. For this reason, the neuronal mechanisms underlying these effects have been the focus of research in humans and in preclinical models. Attention-enhancing effects of the nonselective nAChR agonist nicotine can be observed in human nonsmokers and in laboratory animals, suggesting that benefits go beyond a reversal of withdrawal deficits in smokers. The ultimate aim is to develop compounds acting with greater selectivity than nicotine at a subset of nAChRs, with an effects profile narrowly matching the targeted cognitive deficits and minimizing unwanted effects. To date, compounds tested clinically target the nAChR subtypes most abundant in the brain. To help pinpoint more selectively expressed subtypes critical for attention, studies have aimed at identifying the secondary neurotransmitter systems whose stimulation mediates the attention-enhancing properties of nicotine. Evidence indicates that noradrenaline and glutamate, but not dopamine release, are critical mediators. Thus, attention-enhancing nAChR agents could spare the system central to nicotine dependence. Neuroimaging studies suggest that nAChR agonists act on a variety of brain systems by enhancing activation, reducing activation, and enhancing deactivation by attention tasks. This supports the notion that effects on different attentional functions may be mediated by distinct central mechanisms, consistent with the fact that nAChRs interact with a multitude of brain sites and neurotransmitter systems. The challenge will be to achieve the optimal tone at the right subset of nAChR subtypes to modulate specific attentional functions, employing not just direct agonist properties, but also positive allosteric modulation and low-dose antagonism.

Pharmacodynamics, pharmacokinetics, safety, and tolerability of encenicline, a selective α7 nicotinic receptor partial agonist, in single ascending-dose and bioavailability studies

PURPOSE

Encenicline (EVP-6124) is a selective α7 nicotinic acetylcholine receptor partial agonist being developed for cognitive impairment in Alzheimer's disease and schizophrenia. We report on 2 single-dose studies to assess the relative bioavailability, pharmacokinetic profile, tolerability, and cognitive effects of encenicline in healthy volunteers.

METHODS

A single ascending-dose study assessed the safety, tolerability, pharmacokinetic, and pharmacodynamic profiles of encenicline in healthy male volunteers. Subjects received a single 1-, 3.5-, 7-, 20-, 60-, or 180-mg oral solution dose of encenicline or placebo. A second single-dose, randomized, open-label, 3-period, crossover study in healthy male and female subjects compared the relative bioavailability of a 1-mg oral capsule versus a 1-mg oral solution dose of encenicline and evaluated the effects of food and sex on encenicline pharmacokinetic profile.

FINDINGS

In the first study, encenicline was well tolerated and dose-proportional increases in C(max) (mean range 0.59-100 ng/mL) and AUC0-∞ (mean range 45.6-8890 ng·h/mL) were observed over a 1- to 180-mg dose range. Procognitive effects on the Digit Symbol Substitution Test were maximal at the 20-mg dose. In the second study, encenicline 1-mg oral capsules and oral solution were bioequivalent and there was no observed food effect on encenicline pharmacokinetic profile with the 90% confidence intervals of the treatment ratios for both comparisons (ie, capsule to solution and fed to fasted) for Cmax and AUC being within 80% to 125%. A 30% to 40% higher encenicline exposure in female subjects than respective values in male subjects was consistent with a 33% higher weight of the male subjects. No clinically relevant safety profile or tolerability effects of encenicline were observed.

IMPLICATIONS

Encenicline was well tolerated at single doses up to 180 mg, and doses as low as 1 mg had dose- and time-dependent pharmacodynamic effects on the central nervous system. Oral capsule and solution were bioequivalent and were not affected by food. Although a sex effect on pharmacokinetic profile was observed, it was attributable to weight differences. Clinical Trial Registration at EudraCT: 2006-005623-42 and EudracT: 2008-000029-20.

Neuroimaging biomarkers for early drug development in schizophrenia

Given the relative inability of currently available antipsychotic treatments to adequately provide sustained recovery and improve quality of life for patients with schizophrenia, new treatment strategies are urgently needed. One way to improve the therapeutic development process may be an increased use of biomarkers in early clinical trials. Reliable biomarkers that reflect aspects of disease pathophysiology can be used to determine if potential treatment strategies are engaging their desired biological targets. This review evaluates three potential neuroimaging biomarkers: hippocampal hyperactivity, gamma-band deficits, and default network abnormalities. These deficits have been widely replicated in the illness, correlate with measures of positive symptoms, are consistent with models of disease pathology, and have shown initial promise as biomarkers of biological response in early studies of potential treatment strategies. Two key features of these deficits, and a guiding rationale for the focus of this review, are that the deficits are not dependent upon patients' performance of specific cognitive tasks and they have analogues in animal models of schizophrenia, greatly increasing their appeal for use as biomarkers. Using neuroimaging biomarkers such as those proposed here to establish early in the therapeutic development process if treatment strategies are having their intended biological effect in humans may facilitate development of new treatments for schizophrenia.

Merging old and new perspectives on nicotinic acetylcholine receptors

This review covers history underlying the discovery of the molecular mediators of nicotine's effects in the brain and the diversity of the nicotinic acetylcholine receptor (nAChR) subtypes. Models are presented for both their structure and their function as mediators of signal transduction, with special consideration of the differences between the two main subtypes: heteromeric receptors, which are specialized for rapid electrochemical signal transduction, and homomeric α7 receptors, which have come to be implicated in both ionotropic and metabotropic signaling. This review presents perspectives on the pharmacology and therapeutic targeting of nAChRs for the treatment of nicotine dependence or disease.

Evidence for gamma and beta sensory gating deficits as translational endophenotypes for schizophrenia

Thorough analysis of translational endophenotypes is needed to improve therapeutic development in schizophrenia. Abnormal sensory gating, one such endophenotype, is associated with reduced expression of the α7 nicotinic receptor. However, typical gating measures such as the P50 evoked response are often low-pass filtered, and it is unclear how α7 expression affects gating at higher frequencies. Therefore, this study used time-frequency analysis to compare sensory gating at the beta and gamma frequencies between human patients and healthy controls as well as between α7 heterozygote mutant mice and wild-type. Gating of total beta (15-26Hz) and gamma (30-50Hz) power during paired clicks was assessed from mouse in vivo hippocampal CA3 recordings. Gating was also assessed in schizophrenia patients and healthy controls using electroencephalography. Relative to wild-type, α7 heterozygote mice showed impaired gating of total beta and gamma power. Similarly, relative to controls, patients showed impaired gating of total beta and gamma power. Poor beta gating was associated with negative symptoms. These results demonstrate that schizophrenia patients and α7 heterozygote mice show similar deficits in gating high frequency power. Time-frequency analysis of beta and gamma gating may thus be a translational method of assessing the genetic basis of gating deficits in schizophrenia.

The clinical importance of the anti-inflammatory vagovagal reflex

Excessive activation of the immune system is prevented by anti-inflammatory mediators such as corticosteroids and anti-inflammatory cytokines. Recently, it became clear that the brain not only senses peripheral inflammation through vagal afferent nerve fibers, but also provides an integrated response dampening the immune system through vagal efferents. This so-called anti-inflammatory pathway has been introduced as a third system by which the immune system is modulated. In sepsis, the anti-inflammatory effect is mediated by modulation of splenic macrophages, whereas in the gut, vagal nerve fibers synapse with enteric cholinergic neurons interacting with resident intestinal macrophages. In this chapter, the preclinical data underscoring the importance of this pathway are summarized, and its clinical significance is reviewed. Finally, the current data supporting its relevance to human disease and its therapeutic potential will be discussed. Insight in the mechanisms underlying these crucial properties will lead to better understanding of immune-mediated diseases and ultimately to improved anti-inflammatory therapies.

Pharmacological treatment of schizophrenia: a critical review of the pharmacology and clinical effects of current and future therapeutic agents

Since the introduction of chlorpromazine and throughout the development of the new-generation antipsychotic drugs (APDs) beginning with clozapine, the D(2) receptor has been the target for the development of APDs. Pharmacologic actions to reduce neurotransmission through the D(2) receptor have been the only proven therapeutic mechanism for psychoses. A number of novel non-D(2) mechanisms of action of APDs have been explored over the past 40 years but none has definitively been proven effective. At the same time, the effectiveness of treatments and range of outcomes for patients are far from satisfactory. The relative success of antipsychotics in treating positive symptoms is limited by the fact that a substantial number of patients are refractory to current medications and by their lack of efficacy for negative and cognitive symptoms, which often determine the level of functional impairment. In addition, while the newer antipsychotics produce fewer motor side effects, safety and tolerability concerns about weight gain and endocrinopathies have emerged. Consequently, there is an urgent need for more effective and better-tolerated antipsychotic agents, and to identify new molecular targets and develop mechanistically novel compounds that can address the various symptom dimensions of schizophrenia. In recent years, a variety of new experimental pharmacological approaches have emerged, including compounds acting on targets other than the dopamine D(2) receptor. However, there is still an ongoing debate as to whether drugs selective for singe molecular targets (that is, 'magic bullets') or drugs selectively non-selective for several molecular targets (that is, 'magic shotguns', 'multifunctional drugs' or 'intramolecular polypharmacy') will lead to more effective new medications for schizophrenia. In this context, current and future drug development strategies can be seen to fall into three categories: (1) refinement of precedented mechanisms of action to provide drugs of comparable or superior efficacy and side-effect profiles to existing APDs; (2) development of novel (and presumably non-D(2)) mechanism APDs; (3) development of compounds to be used as adjuncts to APDs to augment efficacy by targeting specific symptom dimensions of schizophrenia and particularly those not responsive to traditional APD treatment. In addition, efforts are being made to determine if the products of susceptibility genes in schizophrenia, identified by genetic linkage and association studies, may be viable targets for drug development. Finally, a focus on early detection and early intervention aimed at halting or reversing progressive pathophysiological processes in schizophrenia has gained great influence. This has encouraged future drug development and therapeutic strategies that are neuroprotective. This article provides an update and critical review of the pharmacology and clinical profiles of current APDs and drugs acting on novel targets with potential to be therapeutic agents in the future.

Nicotine effects on anterior cingulate cortex in schizophrenia and healthy smokers as revealed by EEG-informed fMRI

Nicotine can have beneficial effects on attention performance and corresponding brain function in both schizophrenia patients and healthy controls, but it remains controversial whether nicotine affects brain function differentially in patients vs. controls. The effects of nicotine on brain activity elicited by attention-requiring oddball-type tasks have not been studied in schizophrenia patients. In this study we sought to investigate the impact of nicotine on the p300 evoked potential component and corresponding fMRI (functional magnetic resonance imaging) activation measures in schizophrenia patients and controls. Applying a double-blind, placebo-controlled cross-over design, the effects of 1mg nasal nicotine on brain activity elicited by a visual oddball-type task in N=14 schizophrenia and N=15 control smokers were studied with simultaneous EEG-fMRI. EEG single trial amplitudes were used to inform the fMRI analysis. We found a nicotine-associated increase in P300-informed fMRI activation in schizophrenia patients and controls, mainly in the anterior cingulate and adjacent medial frontal cortex. No group differences in the response to nicotine were found. Remarkably, averaged EEG and fMRI activation measures considered in isolation were largely unaffected by nicotine. Taken together, the effects of nicotine on P300 amplitude-associated brain activation do not seem to be fundamentally different in schizophrenic smokers and healthy controls.

The possible role of the Akt signaling pathway in schizophrenia

Serine/threonine protein kinase v-akt murine thymoma viral oncogene homolog (Akt) is one of the survival kinases with multiple biological functions in the brain and throughout the body. Schizophrenia is one of the most devastating psychiatric disorders. Accumulating evidence has indicated the involvement of the Akt signaling pathway in the pathogenesis of this disorder. Genetic linkage and association studies have identified Akt-1 as a candidate susceptibility gene related for schizophrenia. The level of Akt-1 protein and its kinase activity decreased significantly both in white blood cells from schizophrenic patients and in postmortem brain tissue of schizophrenic patients. Consistent with these findings, alterations in the upstream and downstream pathways of Akt have also been found in many psychiatric disorders. Furthermore, both typical and atypical antipsychotic drugs modify the Akt signaling pathway in a variety of conditions relative to schizophrenia. In addition as a survival kinase, Akt participates in neurodevelopment, synaptic plasticity, protein synthesis and neurotransmission in the central nervous system. It is thought that reduced activity of phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway could at least partially explain the cognitive impairment, synaptic morphologic abnormality, neuronal atrophy and dysfunction of neurotransmitter signaling in schizophrenia. In addition, reduced levels of Akt may increase the effects of risk factors on neurodevelopment, attenuate the effects of growth factors on neurodevelopment and reduce the response of patients to antipsychotic agents. More recently, the role of Akt signaling in the functions of schizophrenia susceptibility genes such as disrupted-in-schizophrenia 1 (DISC-1), neuregulin-1 (NRG-1) and dysbindin-1 has been reported. Thus, Akt deficiency may create a context permissive for the expression of risk-gene effects in neuronal morphology and function. This paper reviews the role of Akt in the pathophysiology of schizophrenia and as a potential therapeutic strategy targeting Akt.

3-(2,4-dimethoxybenzylidene)-anabaseine: a promising candidate drug for Alzheimer's disease?

3-(2,4-dimethoxybenzylidene)-anabaseine is an analog of the paralytic alkaloid, anabaseine, from the ribbon worms Amphiporus sp., that shows numerous properties, in particular an agonist activity on alpha 7 nicotinic acetylcholine receptors. This article reviews these properties and explains to what extent they could be valuable to control symptomatology and/or neurodegeneration in Alzheimer's disease.

Cognitive dysfunction in psychiatric disorders: characteristics, causes and the quest for improved therapy

Studies of psychiatric disorders have traditionally focused on emotional symptoms such as depression, anxiety and hallucinations. However, poorly controlled cognitive deficits are equally prominent and severely compromise quality of life, including social and professional integration. Consequently, intensive efforts are being made to characterize the cellular and cerebral circuits underpinning cognitive function, define the nature and causes of cognitive impairment in psychiatric disorders and identify more effective treatments. Successful development will depend on rigorous validation in animal models as well as in patients, including measures of real-world cognitive functioning. This article critically discusses these issues, highlighting the challenges and opportunities for improving cognition in individuals suffering from psychiatric disorders.

Muscarinic and nicotinic acetylcholine receptor agonists and allosteric modulators for the treatment of schizophrenia

Muscarinic and nicotinic acetylcholine (ACh) receptors (mAChRs and nAChRs) are emerging as important targets for the development of novel treatments for the symptoms associated with schizophrenia. Preclinical and early proof-of-concept clinical studies have provided strong evidence that activators of specific mAChR (M(1) and M(4)) and nAChR (α(7) and α(2)β(4)) subtypes are effective in animal models of antipsychotic-like activity and/or cognitive enhancement, and in the treatment of positive and cognitive symptoms in patients with schizophrenia. While early attempts to develop selective mAChR and nAChR agonists provided important preliminary findings, these compounds have ultimately failed in clinical development due to a lack of true subtype selectivity and subsequent dose-limiting adverse effects. In recent years, there have been major advances in the discovery of highly selective activators for the different mAChR and nAChR subtypes with suitable properties for optimization as potential candidates for clinical trials. One novel strategy has been to identify ligands that activate a specific receptor subtype through actions at sites that are distinct from the highly conserved ACh-binding site, termed allosteric sites. These allosteric activators, both allosteric agonists and positive allosteric modulators, of mAChR and nAChR subtypes demonstrate unique mechanisms of action and high selectivity in vivo, and may provide innovative treatment strategies for schizophrenia.

Nicotinic mechanisms in the treatment of psychotic disorders: a focus on the α7 nicotinic receptor

Nicotine is heavily abused by persons with schizophrenia. Nicotine better enables people with schizophrenia to filter out extraneous auditory stimuli. Nicotine also improves prepulse inhibition when compared to placebo. Nicotine similarly increases the amplitude of patients' duration mismatch negativity. The 15q13-14 region of the genome coding for the α7 nicotinic receptor is linked to schizophrenia. Multiple single nucleotide polymorphisms have been identified in this 15q13-14 gene promoter region that are more frequently present in people with schizophrenia than in normal controls. Abnormalities in expression and regulation of central nicotinic cholinoceptors with decreased α7 binding in multiple brain regions are also present. Nicotine enhances cognition in schizophrenia. Alternative agents that activate the nicotinic receptor have been tested including 3-[2,4-dimethoxybenzylidene]anabaseine (DMXB-A). This compound improved attention, working memory, and negative symptoms in an add-on study in nonsmoking patients with schizophrenia. There are multiple other nicotinic agents, including positive allosteric modulators, in the preclinical stages of development. Finally, the effects of varenicline and clozapine and their relation to smoking cessation are discussed.

Functional brain imaging of nicotinic effects on higher cognitive processes

Significant advances in human functional brain imaging offer new opportunities for direct observation of the effects of nicotine, novel nicotinic agonists and nicotinic antagonists on human cognitive and behavioral performance. Careful research over the last decade has enabled investigators to explore the role of nicotinic systems on the functional neuroanatomy and neural circuitry of cognitive tasks in domains such as selective attention, working memory, episodic memory, cognitive control, and emotional processing. In addition, recent progress in understanding functional connectivity between brain regions utilized during cognitive and emotional processes offers new opportunities for examining drug effects on network-related activity. This review will critically summarize available nicotinic functional brain imaging studies focusing on the specific cognitive domains of attention, memory, behavioral control, and emotional processing. Generally speaking, nicotine appears to increase task-related activity in non-smokers and deprived smokers, but not active smokers. By contrast, nicotine or nicotinic stimulation decreases the activity of structures associated with the default mode network. These particular patterns of activation and/or deactivation may be useful for early drug development and may be an efficient and cost-effective method of screening potential nicotinic agents. Further studies will have to be done to clarify whether such activity changes correlate with cognitive or affective outcomes that are clinically relevant. The use of functional brain imaging will be a key tool for probing pathologic changes related to brain illness and for nicotinic drug development.

Effects of adjunct galantamine to risperidone, or haloperidol, in animal models of antipsychotic activity and extrapyramidal side-effect liability: involvement of the cholinergic muscarinic receptor

The acetylcholine esterase inhibitor/cholinergic nicotinic receptor (nAChR) allosteric modulator galantamine (Gal) is used against cognitive impairment in Alzheimer's disease. Negative/cognitive and psychotic symptom improvement in schizophrenia by adjunct Gal to antipsychotic drugs (APDs) has been reported. Cognitive symptoms in schizophrenia may involve brain prefrontal hypo-dopaminergia. Experimental data by others indicate nAChR involvement in animal pro-cognitive effects of Gal. The role of nAChRs in antipsychotic effects by Gal has, however, not been elucidated. Using the conditioned avoidance response (CAR) and the catalepsy tests for antipsychotic activity and extrapyramidal side-effect (EPS) liability, respectively, we here investigated the effects of adjunct Gal (1.25 mg/kg) to the typical APD haloperidol (Hal) (0.05 mg/kg), or the atypical APD risperidone (Ris) (0.2 mg/kg), in rats. Adjunct Gal significantly enhanced APD-like effects by low doses of Hal or Ris, but showed a safe EPS liability profile only in combination with Ris. Pretreatment with the muscarinic receptor (mAChR) antagonist scopolamine, but not the nAChR antagonist mecamylamine, completely reversed the enhancing effects of adjunct Gal to Hal treatment, in the CAR test. While the nAChR-modulating properties of Gal probably contribute to pro-cognitive activity, as shown by others, the present data suggest that any contribution to antipsychotic activity by Gal is mediated primarily via mAChRs. This property combination of Gal may offer a unique, favourable therapeutic profile for schizophrenia treatment.

A procedural framework for good imaging practice in pharmacological fMRI studies applied to drug development #1: processes and requirements

There is increasing interest in the application of quantitative magnetic resonance imaging (MRI) methods to drug development, but as yet little standardization or best practice guidelines for its use in this context. Pharmaceutical trials are subject to regulatory constraints and sponsor company processes, including site qualification and expectations around study oversight, blinding, quality assurance and quality control (QA/QC), analysis and reporting of results. In this article, we review the processes on the sponsor side and also the procedures involved in data acquisition at the imaging site. We then propose summary recommendations to help guide appropriate imaging site qualification, as part of a framework of 'good imaging practice' for functional (f)MRI studies applied to drug development.

Cerebellar hyperactivity during smooth pursuit eye movements in bipolar disorder

INTRODUCTION

Smooth pursuit eye movements (SPEM) are abnormal in individuals with schizophrenia and individuals with bipolar disorder. Functional imaging methods have revealed greater hippocampal activity and less frontotemporal, visual, and posterior cerebellar activity in individuals with schizophrenia when performing a SPEM task. The underlying neurobiology of SPEM deficits in bipolar disorder is unknown.

METHODS

Functional magnetic resonance imaging at 3T was performed on fourteen subjects with bipolar disorder and 14 subjects without psychiatric illness during a block design SPEM task. Clinical measures were assessed on the day of testing and related to imaging measures.

RESULTS

Subjects with bipolar disorder had greater hemodynamic response than control subjects in cerebellar vermis. Responses were associated with levels of depressive symptoms on the day of study.

DISCUSSION

Increased cerebellar vermis activity during the smooth pursuit eye movement task in individuals with bipolar disorder further implicates cerebellar involvement in bipolar disorder. Increased hemodynamic response within the hippocampus was not seen in these individuals and may be a finding specific to schizophrenia.

Effects of an alpha 7-nicotinic agonist on default network activity in schizophrenia

BACKGROUND

3-(2,4-dimethoxybenzylidene)-anabaseine (DMXB-A) is a partial agonist at α7 nicotinic acetylcholine receptors that has been evaluated clinically for treatment of schizophrenia. This study examined the effects of DMXB-A on default network activity as a biomarker for drug effects on pathologic brain function associated with schizophrenia.

METHODS

Placebo and two doses of DMXB-A were administered in a random, double-blind crossover design during a Phase 2 study of DMXB-A. Functional magnetic resonance imaging was performed on 16 nonsmoking patients with schizophrenia while they performed a simple eye movement task. Independent component analysis was used to identify the default network component. Default network changes were evaluated in the context of a polymorphism in CHRNA7, the α7-nicotinic acetylcholine receptor subunit gene, which was previously found to be associated with schizophrenia.

RESULTS

Compared with placebo, both 150 and 75 mg twice daily DMXB-A altered default network activity, including a reduction in posterior cingulate, inferior parietal cortex, and medial frontal gyrus activity and an increase in precuneus activity. The most robust difference, posterior cingulate activity reduction, was affected by CHRNA7 genotype.

CONCLUSIONS

The observed DMXB-A-related changes are consistent with improved default network function in schizophrenia. Pharmacogenetic analysis indicates mediation of the effect through the α7-nicotinic receptor. These results further implicate nicotinic cholinergic dysfunction in the disease and suggest that default network activity may be a useful indicator of biological effects of novel therapeutic agents.

How human electrophysiology informs psychopharmacology: from bottom-up driven processing to top-down control

This review surveys human event-related brain potential (ERP) and event-related magnetic field (ERF) approaches to psychopharmacology and psychopathology, and the way in which they complement behavioral studies and other neuroimaging modalities. The major paradigms involving ERP/ERF are P50 suppression, loudness-dependent auditory evoked potential (LDAEP), mismatch negativity (MMN), P300, mental chronometry, inhibitory control, and conflict processing (eg, error-related negativity (ERN)). Together these paradigms cover a range of more bottom-up driven to more top-down controlled processes. A number of relationships between the major neurotransmitter systems and electrocortical mechanisms are highlighted. These include the role of dopamine in conflict processing, and perceptual processing vs motor preparation; the role of serotonin in P50 suppression, LDAEP, and MMN; glutamate/NMDA and MMN; and the role of acetylcholine in P300 generation and memory-related processes. A preliminary taxonomy for these relationships is provided, which should be helpful in attuning possible new treatments or new applications of existing treatments to various disorders.

Beyond the dopamine receptor: novel therapeutic targets for treating schizophrenia

All current drugs approved to treat schizophrenia appear to exert their antipsychotic effects through blocking the dopamine D2 receptor. Recent meta-analyses and comparative efficacy studies indicate marginal differences in efficacy of newer atypical antipsychotics and the older drugs, and little effects on negative and cognitive symptoms. This review integrates findings from postmortem, imaging, and drug-challenge studies to elucidate a corticolimbic “pathologic circuit” in schizophrenia that may be particularly relevant to the negative symptoms and cognitive impairments of schizophrenia. Potential sites for pharmacologic intervention targeting glutatatergic, GABAergic, and cholinergic neurotransmission to treat these symptoms of schizophrenia are discussed.

Continuous administration of a selective alpha7 nicotinic partial agonist, DMXBA, improves sensory inhibition without causing tachyphylaxis or receptor upregulation in DBA/2 mice

Stimulation of nicotinic receptors, specifically the alpha7 subtype, improves sensory inhibition and cognitive function in receptor deficient humans and rodents. However, stimulation with a full agonist, such as nicotine, produces rapid tachyphylaxis of the P20N40-measured sensory inhibition process. 3-(2,4-dimethoxybenzylidine) anabaseine (DMXBA, also GTS-21) selectively activates the alpha7 nicotinic receptor, and in acute administration studies, has been shown to improve deficient sensory inhibition in both humans and rodents with repeated dosing. Unlike nicotine, this partial agonist acted without inducing tachyphylaxis. Here, we assessed the ability of DMXBA to improve sensory inhibition in DBA/2 mice after 7 days of continuous administration via a subcutaneously implanted osmotic minipump. When assessed on day 8, mice receiving saline showed the characteristic deficient sensory inhibition seen with untreated DBA/2 mice. The 25- and 50-mg/ml infusion concentrations of DMXBA, but not the 100-mg/ml, produced significantly improved sensory inhibition in the mice, exclusively through a decrease in test amplitude. No concentration significantly upregulated hippocampal alpha7 receptor levels. DMXBA levels in the brain were higher than plasma at 2 of the 3 concentrations infused. These data suggest that continuous exposure to DMXBA does not significantly affect the underlying responsiveness of the sensory inhibition pathway to this partial agonist, nor cause receptor upregulation, at these relatively low brain concentrations. The ability of DMXBA to maintain its effectiveness during constant administration conditions may be due to an ability to activate alpha7 receptors at low concentrations, and consequently low fractional occupancy of the five possible binding sites on this homomeric receptor.