Effects of the CCK(B) antagonist CI-988 on responses to mCPP in generalized anxiety disorder

Peripheral Biomarkers in DSM-5 Anxiety Disorders: An Updated Overview

Anxiety disorders are prevalent and highly disabling mental disorders. In recent years, intensive efforts focused on the search for potential neuroimaging, genetic, and peripheral biomarkers in order to better understand the pathophysiology of these disorders, support their diagnosis, and characterize the treatment response. Of note, peripheral blood biomarkers, as surrogates for the central nervous system, represent a promising instrument to characterize psychiatric disorders, although their role has not been extensively applied to clinical practice. In this report, the state of the art on peripheral biomarkers of DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, 5th edition) Anxiety Disorders is presented, in order to examine their role in the pathogenesis of these conditions and their potential application for diagnosis and treatment. Available data on the cerebrospinal fluid and blood-based biomarkers related to neurotransmitters, neuropeptides, the hypothalamic-pituitary-adrenal axis, neurotrophic factors, and the inflammation and immune system are reviewed. Despite the wide scientific literature and the promising results in the field, only a few of the proposed peripheral biomarkers have been defined as a specific diagnostic instrument or have been identified as a guide in the treatment response to DSM-5 Anxiety Disorders. Therefore, further investigations are needed to provide new biological insights into the pathogenesis of anxiety disorders, to help in their diagnosis, and to tailor a treatment.

Developing small molecule nonpeptidergic drugs for the treatment of anxiety disorders: is the challenge still ahead?

Neuropeptide systems have been considered a major opportunity for the development of novel treatment approaches for anxiety disorders based on preclinical evidence and neurochemical alterations seen in anxiety disorders. This excitement was further facilitated by the fact that drugs acting at these systems, such as CRF1 antagonists, NK1 antagonists, NK3 antagonists or CCK2 antagonists, may have unique properties not seen with drugs affecting more classical mechanisms involved in anxiety. Consequently, there have been major efforts to develop such small-molecule, nonpeptide receptor ligands. A number of these molecules have been tested in the clinic, either in trials where levels of anxiety served as a secondary measure, or in a few studies with patients suffering from anxiety disorders. But unfortunately, and despite all the efforts of the field as a whole, we still lack convincing clinical proof-of-concept for any of the neuropeptidergic approaches in patients. It must, therefore, be concluded that neuropeptide targets remain a promising approach for the development of the next generation drugs to treat anxiety disorders, but that they continue to be high-risk targets for drug development.

The CCK-system mediates adaptation to novelty-induced stress in the rat: a pharmacological evidence

Brain cholecystokinin (CCK) and its receptor CCK(2) have been implicated in the etiology of anxiety. CCK(2) antagonists, however, fail to ameliorate anxiety in humans. In this study, a role for CCK in adaptation to stress is investigated by testing carry-over effects of Ly225.910, a potent CCK(2) antagonist, in a rat model of individual differences in novelty-induced emotionality. Novelty-seeking behavior in the rat is thought to model some aspects of sensation-seeking, a personality trait closely associated with risk activities including substance abuse. Animals were categorized as high-responders (HR) and low-responders (LR) based on the activity response to an inescapable novel environment. High-responders exhibit increased exploration and proactive behavior while low-responders are less exploratory and deemed to behave more anxiously. We analyzed the effects of the CCK(2) antagonist Ly225.910 (0.1 mg/kg or 0.5 mg/kg, i.p.) on the anxiety displayed by HR and LR rats in the light-dark (LD) box test (Day 1). Treatment and phenotype effects were not acutely evident. LD-experienced rats were then re-exposed to drug-free LD-box (Days 4 and 11) and elevated plus-maze (EPM) test (Day 14). Drug-naïve HR rats behaved less anxiously than drug-naïve LR rats while exploring the open arms. Previous exposure to the antagonist curtailed these differences. The emotional responses in drug-naïve HR and LR rats to the EPM test could reflect different degrees of adaptation to anxiety-like training. Long-term effects of Ly225.910 on EPM-induced risk assessment in HR and LR rats suggest that CCK-system may be involved in modulating preparedness to arousing environmental changes.

Role of CCK/gastrin receptors in gastrointestinal/metabolic diseases and results of human studies using gastrin/CCK receptor agonists/antagonists in these diseases

In this paper, the established and possible roles of CCK1 and CCK2 receptors in gastrointestinal (GI) and metabolic diseases are reviewed and available results from human agonist/antagonist studies are discussed. While there is evidence for the involvement of CCK1R in numerous diseases including pancreatic disorders, motility disorders, tumor growth, regulation of satiety and a number of CCK-deficient states, the role of CCK1R in these conditions is not clearly defined. There are encouraging data from several clinical studies of CCK1R antagonists in some of these conditions, but their role as therapeutic agents remains unclear. The role of CCK2R in physiological (atrophic gastritis, pernicious anemia) and pathological (Zollinger-Ellison syndrome) hypergastrinemic states, its effects on the gastric mucosa (ECL cell hyperplasia, carcinoids, parietal cell mass) and its role in acid-peptic disorders are clearly defined. Furthermore, recent studies point to a possible role for CCK2R in a number of GI malignancies. Current data from human studies of CCK2R antagonists are presented and their potential role in the treatment of these conditions reviewed. Furthermore, the role of CCK2 receptors as targets for medical imaging is discussed.

Cholecystokinin antagonists: pharmacological and therapeutic potential

Cholecystokinin (CCK) is a regulatory peptide hormone, predominantly found in the gastrointestinal tract, and a neurotransmitter present throughout the nervous system. In the gastrointestinal system CCK regulates motility, pancreatic enzyme secretion, gastric emptying, and gastric acid secretion. In the nervous system CCK is involved in anxiogenesis, satiety, nociception, and memory and learning processes. Moreover, CCK interacts with other neurotransmitters in some areas of the CNS. The biological effects of CCK are mediated by two specific G protein coupled receptor subtypes, termed CCK(1) and CCK(2). Over the past fifteen years the search of CCK receptor ligands has evolved from the initial CCK structure derived peptides towards peptidomimetic or non-peptide agonists and antagonists with improved pharmacokinetic profile. This research has provided a broad assortment of potent and selective CCK(1) and CCK(2) antagonists of diverse chemical structure. These antagonists have been discovered through optimization programs of lead compounds which were designed based on the structures of the C-terminal tetrapeptide, CCK-4, or the non-peptide natural compound, asperlicin, or derived from random screening programs. This review covers the main pharmacological and therapeutic aspects of these CCK(1) and CCK(2) antagonist. CCK(1) antagonists might have therapeutic potential for the treatment of pancreatic disorders and as prokinetics for the treatment of gastroesophageal reflux disease, bowel disorders, and gastroparesis. On the other hand, CCK(2) antagonists might have application for the treatment of gastric acid secretion and anxiety disorders.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Effects of cholecystokinin tetrapeptide (CCK(4)) and anxiolytic drugs on the electrically evoked [(3)H]5-hydroxytryptamine outflow from rat cortical slices

The outflow of [(3)H]5-hydroxytryptamine ([(3)H]5-HT) from electrically stimulated rat cortical slices was measured to ascertain the modulatory role of endogenous cholecystokinin (CCK) on the amine outflow and to test the hypothesis that different anxiolytic compounds inhibit 5-HT secretion. The [(3)H]5-HT outflow evoked at 10 Hz was increased up to +30% by CCK(4) 300-1000 nM, the effect being prevented by the CCK(B) receptor antagonist GV 150013, 3 nM. The limited sensitivity to CCK(4) seemed to depend on 5-HT auto-receptor feedback because pre-treatment with 100 nM methiothepin enhanced the [(3)H]5-HT outflow and lowered the CCK(4) threshold concentration from 300 to 30 nM. In addition, pre-treatment with 1 microM bacitracin to inhibit CCK metabolism increased [(3)H]5-HT efflux. This effect was concentration-dependently counteracted by GV150013 suggesting the presence of an endogenous CCK positive modulation. GV150013 30 nM, the 5-HT(1A) partial agonist buspirone 300 nM and the GABA(A) receptor modulator diazepam 10 nM, known to have anxiolytic properties, all significantly reduced the [(3)H] amine outflow from cortical slices by about 20%. This inhibition depended on their interaction with their respective receptors, which seemed to restrain the activity of functionally interconnected glutamatergic interneurones. In fact, APV (50 microM) and NBQX (10 microM) prevented the effect of the anxiolytic compounds. Thus, anxiolytic drugs with different receptor targets can reduce 5-HT outflow by dampening the glutamatergic signal, and in turn, the secretory process of the serotonergic nerve ending.

Neurobiology of generalized anxiety disorder

On reviewing the literature on GAD and trying to summarize the various developments in the field of neurobiology of GAD, we see that a range of hypotheses try to explore and integrate the observations found into potentially meaningful theories. Abnormal serotonergic and GABAergic function occur in many patients with GAD. Functional imaging data have shown increased cortical activity and decreased basal ganglia activity in patients with GAD, which reverses with treatment, but it is apparent that no one theory is sufficiently comprehensive to propose a unitary hypothesis for the development of GAD and other anxiety disorders. GAD is a relatively new diagnosable condition, first introduced into the classification system of psychiatric disorders in 1980, and since then has undergone a series of changes in its conceptualization, with some investigators questioning the existence of the condition as a distinct entity. Any inferences that may be drawn from various studies must be guarded, and it is appropriate to compare studies using the same diagnostic criteria. Significant research has been done and may lead to exciting new discoveries in the treatment of anxiety disorders in general and GAD in particular. Gray's model of behavioral inhibition, in which the septohippocampal system acts by assessing stimuli for the presence of danger and, when that is detected, activates the behavioral-inhibition circuit, provides a neuroanatomic conceptualization that has been expanded by preclinical research. Some exciting work has been done on CRF and the concept of development, vulnerability, and kindling and some investigators have contributed to this area of interest. This concept supports the hypothesis that a genetic predisposition, coupled with early stress, in the crucial phases of development may result in a phenotype that is neurobiologically vulnerable to stress and may lower an individual's threshold for developing anxiety or depression on additional stress exposure. The pharmaceutical industry is exploring treatment options using CRF antagonists, and research on other neuropeptides, especially NPY, will be of interest. Research on neurosteroids also may bring the opportunity for pharmacologic treatment approaches. Future research on the startle reflex and on the NMDA and the metabotropic glutamate receptors is important. Future studies of a more homogenous patient population and using more sophisticated techniques, such as molecular genetic strategies and better imaging techniques, may answer some of the outstanding questions.