Current Pharmaceutical Design - Volume 14, Issue 33, 2008

Anxiety disorders are highly prevalent and disabling disorders, which are commonly treated using pharmacotherapeutic and psychotherapeutic approaches. Benzodiazepines are widely used in the treatment of acute anxiety states whereas both serotonergic acting antidepressants and gamma-aminobutyric acid (GABA) ergic substances represent standard treatments on the long term. Due to the dependence potential of the first mentioned pharmacological group and the slow onset of action and the specific side effect profile of the latter groups, there is need for new pharmacologic anxiolytic treatment strategies. In this issue of CPD, new insights in pathophysiological mechanisms of anxiety disorders together with information about actual available and novel anxiolytic acting drugs are provided.

Anxiety disorders are common in community settings and in primary and secondary medical care. The associated societal burden is considerable, but many of those who might benefit from pharmacological or psychological treatment are not recognised or treated. By contrast, some patients receive unnecessary or inappropriate interventions. Recent evidence-based guidelines for pharmacological management of patients with anxiety disorders recommend initial treatment with either a selective serotonin reuptake inhibitor or a serotonin-norepinephrine reuptake inhibitor. However, there is considerable room for improvement in both the efficacy and tolerability of pharmacological treatment. For example, response rates to initial treatment can be disappointing and it is still not possible to predict reliably which patients will respond well and which will show only a limited response to treatment. Furthermore, many patients fear or experience unwanted and distressing adverse effects and this limits the effectiveness of pharmacological treatments in clinical practice. Because of the relative lack of longitudinal studies of clinical outcomes in anxiety disorders and the small number of placebo- controlled relapse prevention studies, the optimal duration of treatment after a satisfactory response to acute treatment is still uncertain. There have been comparatively few studies of the further management of patients who do not respond to initial treatment and there is a clear need for further randomised controlled trials of augmentation treatment, in patients who do not respond to a selective serotonin reuptake inhibitor, serotonin-norepinephrine reuptake inhibitor or other initial pharmacological approaches. Future treatment guidelines will be influenced by emerging data with both established and novel pharmacological interventions and through better identification of patient sub-groups that are likely to respond preferentially to particular interventions.

Pharmacological magnetic resonance imaging (phMRI) is a method to study effects of psychopharmacological agents on neural activation. Changes of the blood oxygen level dependent (BOLD), the basis of functional MRI (fMRI), are typically obtained at relatively high sampling frequencies. This has more recently been exploited in the field of fMRI by applying independent component analysis (ICA), an explorative data analysis method decomposing activation into distinct neural networks. While already successfully used to investigate resting network and task-induced activity, its use in phMRI is new. Further extension of this method to tensorial probabilistic ICA (tensor PICA) allows to group similar brain activation across the anatomical, temporal, subject or session domain. This approach is useful for pharmacological experiments when no pharmacokinetic model exists. We exemplify this method using data from a placebo-controlled cholecystokinine- 4 (CCK-4) injection experiment performed on 16 neuropsychiatrically and medically healthy males (age 25.6 ± 4.2 years). Tensor PICA identified strong increases in activity in 12 networks. Comparison with results gained from the standard approach (voxelwise regression analysis) revealed good reproduction of areas previously associated with CCK-4 action, such as the anterior cingulate, orbitofrontal cortex, cerebellum, temporolateral, left parietal and insular areas, striatum, and precuneus. Several other components such as the dorsal anterior cingulate and medial prefrontal cortex were identified, suggesting higher sensitivity of the method. Exploration of the time courses of each activated network revealed differences, that might be lost when a fixed time course is modeled, e. g. neuronal responses to an acoustic warning signal prior to injection. Comparison of placebo and CCK-4 runs further showed that a proportion of networks are newly elicited by CCK-4 whereas other components are significantly active in the placebo conditions but further enhanced by CCK-4. In conclusion, group ICA is a promising tool for phMRI studies that allows quantifying and visualizing the modulation of neural networks by pharmacological interventions.

With a lifetime prevalence of up to 25% anxiety disorders are among the most frequently occurring psychiatric disorders. The etiology of anxiety is considered to be multifactorial with an interaction of neurobiological, psychological and environmental factors. With regard to neurobiological factors, several neurochemical systems and neuroanatomical circuits have been discussed to be involved. In particular, anxiety might be a result of insufficient inhibitory control, pointing towards a major role of the gamma-amino-butyric acid (GABA) system in these disorders. Preclinical and clinical studies discuss a decreased GABAergic inhibition in anxiety and patients with anxiety disorders. In view of these findings it is intriguing that benzodiazepines, which currently represent the most potent and powerful anxiolytic agents, act through an enhancement of GABAergic inhibition targeting the GABAA receptor. Thus, it has been suggested that the GABAergic system might represent a promising future target for new pharmacologic strategies for the treatment of anxiety. Closely linked to the GABAergic system is the endocannabinoid system, which might also play an important role in this group of disorders. The endocannabinoid system has particularly been involved in extinction learning, suggesting a key role of this system in the process of fear extinction. In this paper, both the GABAergic and the endocannabinoid system will be reviewed with regard to their role in anxiety and anxiety disorders in humans with particular attention to findings from genetic and neuroimaging studies. Moreover, both systems will be discussed as potential therapeutic targets.

Introduction: Data on basal hypothalamo-pituitary-adrenomedullary (HPA) function over controlled treatment trials with serotonergic drugs in anxiety disorders are still rare. Methods: 29 patients with panic disorder participating in a 10 week randomized, controlled trial (paroxetine vs. placebo with exercise or relaxation; N=60) collected urine for cortisol excretion over 3 consecutive nights before start and before termination of the treatment episode. Urinary cortisol was measured by radioimmunoassay. Efficacy measures were the Clinical Global Impression Scale (CGI) and the Panic and Agoraphobia Scale (P&A). 83% were female (p<.05 vs. males). 55% received additional aerobic exercise, and 45% relaxation. 55% received paroxetine treatment, and 45% placebo. Significantly fewer males received placebo treatment (p<.05). Results: All subjects improved significantly. Cortisol excretion did not differ between treatment groups or at pre-/post measurements. Females showed a significantly higher variability of cortisol excretion compared to males, at pre-(p<.005) and post (p=.015) assessments. Males displayed a trend to lower basal HPA function at end of treatment (p=.08). HPA variability after treatment showed a trend to be higher in the paroxetine (p=.052) -who clinically improved significantly better- compared to the placebo group. No relationship between HPA activity and treatment response or with exercise was detected. Discussion: HPA function shows significant gender differences, with females having a higher HPA function variability. Future studies on HPA function in treatment trials should address gender and medication effects.

In the past decades considerable evidence has emerged that certain so called neuroactive steroids not only act as transcription factors in the regulation of gene expression but may also alter neuronal excitability through interaction with specific neurotransmitter receptors such as γ-aminobutyric acid type A (GABAA), N-methyl-D-aspartate (NMDA) and glutamate receptors. There is growing evidence that neuroactive steroids play an important role as endogenous modulators of neuronal function and behavioural processes and that alterations of endogenous neuroactive steroid concentrations may contribute to the pathophysiology of affective disorders. In view of their positive allosteric potential at GABAA-receptors, especially 3α-reduced neuroactive steroids have been suggested to play a major role in the pathophysiology of anxiety disorders. In panic disorder patients a dysequilibrium of neuroactive steroid composition has been observed, which may represent counterregulatory mechanisms against the occurrence of spontaneous panic attacks. Therefore, attenuation of neuroactive steroid concentrations either by synthetic derivates of neuroactive steroids or by modulation of endogenous neurosteroid synthesis might constitute a promising novel strategy for the treatment of anxiety disorders. In conclusion, neuroactive steroids are important endogenous modulators of depression and anxiety and may provide a basis for development of novel therapeutic agents in the treatment of affective disorders.

Anxiety disorders are common and disabling conditions. Current drug treatment methods have limitations including resistance, delayed efficacy and side effects. The advent of sophisticated imaging techniques and the production of highly selective receptor ligands have increased our knowledge of the biological mechanisms underpinning anxiety. Our aim is to review recent discoveries in important neurological systems to provide an understanding of important current anxiolytic targets. Some of these systems, such as GABA, have been implicated in anxiety disorders for decades, but a recent greater understanding is enabling more sophisticated targeting of treatments. In other systems, including the neuropeptides, we have now developed the pharmacological tools in human subjects to begin exploring their relationship to anxiety disorders. We review GABA, serotonin, glutamate, noradrenaline, dopamine and some neuropeptides herein.

Interest in neuroimmunology and the actions of cytokines in the brain has grown exponentially over the last decade. Cytokines represent a large and rapidly growing group of polypeptides that comprises the interleukins, chemokines, tumor necrosis factors, interferons, and growth and cell stimulating factors [1]. The functions and actions of many of these cytokines in the brain remain to be elucidated, but probably include both beneficial and detrimental effects.. During the course of brain ischemia, inflammatory mechanisms both intrinsic to brain as well as blood are among the important mediators of focal cerebral injury, nevertheless ischemic stroke is a heterogeneous disease, and inflammatory pathways may have different impacts depending on underlying pathophysiological processes [2] . Inflammatory cells such as neutrophils and macrophages infiltrate into the ischemic brain in various animal models of ischemic stroke and in patients with cerebral ischemia [3]. In addition, inherent cells such as astrocytes, microglia, or endothelia have been found to be activated by cerebral injuries including ischemic stroke. These cells then become immunologically reactive and interact with each other by producing substances including cytokines and adhesion molecules. These molecules appear to be responsible for the accumulation of inflammatory cells in the injured brain, and the resulting immunologic-inflammatory cascade produces an environment that may affect the survival of neurons subjected to ischemic injury. Several aspects of this immunologic-inflammatory cascade will be presented in this issue of Current Pharmaceutical Design, in order to put in a better perspective of the inflammatory mechianisms of neuronal damage mechanism, the role of proinflammatory cytokines in acute ischemic stroke, the linkage between proinflammatory genes polymorphism and ischemic stroke and the role of inflammation markers as possible target for a neuroprotective treatment of acute ischemic stroke. TNF-a is activated in experimental ischemia at both the mRNA and protein levels. Furthermore, increased levels of cytokines such as interleukin IL-1β, tumor necrosis factor-α (TNF-α), and IL-6, as well as adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1), have been observed after experimental brain ischemia [4]. Clinical studies [5-7] have reported increased levels of proinflammatory cytokines and adhesion molecules in the peripheral blood and cerebrospinal fluid (CSF) of patients with ischemic stroke. Among cytokines involved in pathogenesis of ischemic stroke, high IL-6 concentrations in CSF and plasma have been associated with larger infarct size, neurological deterioration, and poor outcome independently of the stroke subtype [8]. Castellanos [9] et al. showed that in patients with lacunar infarction, high concentrations of inflammatory markers in blood are associated with early neurological deterioration (END) and poor functional outcome in lacunar infarctions. So, cerebral ischemia and inflammation are closely interrelated: ischemia is a robust stimulus for potentially damaging inflammation, and infection and its associated inflammation is a known risk factor for ischemic stroke [10] and inflammation also contributes to ischemic events through the promotion of atherosclerosis [11]. Moreover, functional polymorphisms of inflammatory genes may thereby influence the incidence and outcome of ischemic stroke and recent studies explored the role of IL-6 gene polymorphism [12-14] and of TNF-α polymorphism [15-17] both in acute stroke setting and in subjects with a history of ischemic stroke. On this basis, in acute ischemic stroke setting, cytokines and other markers of inflammation may represent, owing to their pathogenetic and predictive role, a possible therapeutic target and although there are no current clinical ‘anti-cytokine’ treatment studies for stroke, experimental studies modulating IL-1 and TNF-alpha have shown neuroprotection, [18,19] but further studies are needed to confirm this issue, which could open new future therapeutic avenues in the treatment of brain ischemia.

Ischemic stroke is the most frequent cause of persistent neurologic disability in modern Western societies. Albeit it is still not clear whether inflammation is merely an epiphenomenon or rather has a disease-promoting function, accumulating evidence implicates inflammation in many forms of acute neurodegenerative disorders including ischemia. The immune cell influx during a neuropathological event is thought to be elicited by glial cells, especially microglia. This article reviews the cellular and molecular pathways involved in stroke-induced inflammatory response in the CNS. We focused on how CNS innate immune cells including microglia and macrophages play integral roles in receiving and propagating inflammatory signals, and how activated microglia secrete a wide range of factors. We present the relevance of the expression of adhesion molecules after ischemia including selectin, immunoglobulin superfamily, integrins, and the role of inflammatory mediators such as cytokines, chemokines and matrix metalloproteinases. Further, we explore the role of transcription factors in inflammation, and the function of immunomodulation and innate and adaptive immunity in brain ischemia, focusing on immunosupression therapies for acute stroke. Although several approaches for anti-inflammatory treatment have proven effective in animal models, clinical trials of immune system modulation therapy after stroke have not yet proved successful. There is still much to be done in order to translate interesting findings into therapies, but undoubtedly studying the cellular and molecular pathways may not only improve our understanding of inflammatory mechanism but also serve as a basis for designing effective therapies.

Knowledge of the molecular mechanisms that underlie neuron death following stroke is important to allow the development of effective neuroprotective strategies. Since studies in human stroke are extremely limited due to the inability of collecting post mortem tissue at time points after the onset of stroke where neuronal death occurs, brain ischemia research focuses on information derived from animal models of ischemic injury. The two principal models for human stroke are induced in rodents either by global or focal ischemia. In both cases, blood flow disruptions limit the delivery of oxygen and glucose to neurons causing ATP reduction and energy depletion, initiating excitotoxic mechanisms that are deleterious for neurons. These include activation of glutamate receptors and release of excess glutamate in the extracellular space inducing neuron depolarisation and dramatic increase of intracellular calcium that in turn activates multiple intracellular death pathways. The notion that excitotoxicity leads only to neuron necrosis has been abandoned, as ultrastructural and biochemical analysis have shown signs of apoptotic and autophagic cell death in ischemic neurons and this has been further confirmed in neurons subjected to in vitro ischemia models. Both in vitro and in vivo studies, targeting a single death mechanism either by the inhibition of death-inducing molecules or the overexpression of antiapoptotic components in neurons, have shown tremendous neuroprotective potential. Despite their effectiveness in preclinical studies, a large number of neuroprotectants have failed in clinical trials for stroke suggesting that we still lack essential knowledge on the triggers and mediators of ischemic neuron death. In this review evidence will be presented on how ischemic injury occurs, what death mechanisms are activated and how these can be manipulated to induce neuroprotection.

Three major cytokines, namely, tumor necrosis factor (TNF-α), interleukin (IL)-1, and IL-6 are produced by cultured brain cells after various stimuli such as ischemia. Neurones, astrocytes, microglia and oligodendrocytes can produce inflammatory mediators, and cytokine receptors are expressed constitutionally throughout the Central Nervous System (CNS), albeit at low levels. Cytokines are involved in virtually every facet of stroke and they have numerous proinflammatory and pro-coagulant effects on endothelium. TNF-α expression after stroke stimulates expression of tissue factor and adhesion molecules for leukocytes, release of interleukin-1 (IL-1), nitric oxide, factor VIII/von Willebrand factor, platelet-activating factor and endothelin, suppression of the thrombomodulin-protein C-protein S system, reduction of tissue-plasminogen activator and release of plasminogen activator inhibitor-1. Research into the actions of IL-1β in the brain initially focused on its role in host defence responses to systemic disease. IL-1β can also elicit an array of responses which could either inhibit, exacerbate or induce neuronal damage and death. IL-6 can be induced by a variety of molecules including IL-1, TNF-α, transforming growth factor-β and prostaglandins (PGs), and many other mediators such as b-amyloid, interferon-g (IFNg) and IL-4 can potentiate these primary inducers, highlighting the complex nature of IL-6 modulation. Several studies reported that plasma levels of TNF-α and IL-6 are associated with prognosis after ischemic stroke and our group showed that plasma levels of cytokines such as TNF-α, IL-1β are different in every diagnostic subtype of ischemic stroke, and how plasma levels of some immunoinflammatory markers and thrombotic-phybrinolitic markers are predictive of acute ischemic stroke diagnosis in the acute setting.

Despite recent advances in acute stroke therapy, stroke remains the leading cause of severe disability and the third leading cause of death, after heart disease and cancer, in Western countries and Japan. The identification of biomarkers of stroke risk is thus important both for risk prediction and for intervention to avert future events. Although genetic linkage analyses of families and sib-pairs as well as candidate gene and genome-wide association studies have implicated several loci and candidate genes in predisposition to ischemic or hemorrhagic stroke, the genes that contribute to genetic susceptibility to these conditions remain to be identified definitively. Given that vascular inflammation has been recognized as an important mechanism of atherosclerotic disease, proinflammatory genes may play pivotal roles in the pathogenesis of ischemic stroke. In this review, we summarize candidate genes that have been implicated in common forms of ischemic stroke by linkage analyses and association studies. We also review in more detail studies that have revealed an association of ischemic stroke with polymorphisms of proinflammatory genes of particular interest (LTA, IL6, and ALOX5AP) as well as with polymorphisms at chromosomal region 9p21.3, which has recently been identified as a susceptibility locus for coronary heart disease. Such studies may provide insight into the function of implicated genes as well as into the role of genetic factors in the development of ischemic stroke.