Effect of acute and chronic benzodiazepines on plasma GABA in anxious patients and controls

Treatment Response Biomarkers in Anxiety Disorders: From Neuroimaging to Neuronally-Derived Extracellular Vesicles and Beyond

Multiple and diverse psychotherapeutic or psychopharmacologic treatments effectively reduce symptoms for many patients with anxiety disorders, but the trajectory and magnitude of response vary considerably. This heterogeneity of treatment response has invigorated the search for biomarkers of treatment response in anxiety disorders, across the lifespan. In this review, we summarize evidence for biomarkers of treatment response in children, adolescents and adults with generalized, separation and social anxiety disorders as well as panic disorder. We then discuss the relationship between these biomarkers of treatment response and the pathophysiology of anxiety disorders. Finally, we provide context for treatment response biomarkers of the future, including neuronally-derived extracellular vesicles in anxiety disorders and discuss challenges that must be overcome prior to the debut of treatment response biomarkers in the clinic. A number of promising treatment response biomarkers have been identified, although there is an urgent need to replicate findings and to identify which biomarkers might guide clinicians in selecting from available treatments rather than just simply identifying patients who may be less likely to respond to a given intervention.

Development of psychopathology in deployed armed forces in relation to plasma GABA levels

The GABA system is pivotal for an adequate response to a stressful environment but has remained largely unexplored in this context. The present study investigated the relationship of prospectively measured plasma GABA levels with psychopathology symptoms in military deployed to Afghanistan at risk for developing psychopathology following trauma exposure during deployment, including posttraumatic stress disorder (PTSD) and major depressive disorder (MDD). Plasma GABA levels were measured in military personnel (N=731) one month prior to deployment (T0), and one (T1) and six months (T2) after deployment using ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS). Mental health problems and depressive symptoms were measured with the Dutch revised Symptom Checklist (SCL-90) and PTSD symptoms with the Dutch Self-Rating Inventory for PTSD (SRIP). Six months after deployment increases in GABA concentrations were present in individuals who had developed mental health problems (T2: β=0.06, p=1.6×10^-2, T1: β=4.7×10^-2, p=0.13), depressive symptoms (T2: β=0.29, p=7.9×10^-3, T1: β=0.23, p=0.072) and PTSD symptoms at T2 (T2: β=0.12, p=4.3×10^-2, T1: β=0.11, p=0.13). Plasma GABA levels prior to and one month after deployment poorly predicted a high level of psychopathology symptoms either one or six months after deployment. The number of previous deployments, trauma experienced during deployment, childhood trauma, age and sex were not significantly associated with plasma GABA levels over time. Exclusion of subjects who either started or stopped smoking, alcohol or medication use between the three time points rendered the association of increasing GABA levels with the emergence of psychopathology symptoms more pronounced (mental health problems at T2: β=0.09, p=4.2×10^-3; depressive symptoms at T2: β=0.35, p=3.5×10^-3, PTSD symptoms at T2: β=0.17, p=1.7×10^-2). To our knowledge, this is the first study to provide prospective evidence that the development of psychopathology after military deployment is associated with increasing plasma GABA levels. Our finding that plasma GABA rises after the emergence of psychopathology symptoms suggests that GABA increase may constitute a compensatory mechanism and warrants further exploration of the GABA system as a potential target for treatment.

Epigenetic signature of panic disorder: a role of glutamate decarboxylase 1 (GAD1) DNA hypomethylation?

Glutamate decarboxylases (GAD67/65; GAD1/GAD2) are crucially involved in gamma-aminobutyric acid (GABA) synthesis and thus were repeatedly suggested to play an important role in the pathogenesis of anxiety disorders. In the present study, DNA methylation patterns in the GAD1 and GAD2 promoter and GAD1 intron 2 regions were investigated for association with panic disorder, with particular attention to possible effects of environmental factors. Sixty-five patients with panic disorder (f=44, m=21) and 65 matched healthy controls were analyzed for DNA methylation status at 38 GAD1 promoter/intron2 and 10 GAD2 promoter CpG sites via direct sequencing of sodium bisulfate treated DNA extracted from blood cells. Recent positive and negative life events were ascertained. Patients and controls were genotyped for GAD1 rs3762556, rs3791878 and rs3762555, all of which are located in the analyzed promoter region. Patients with panic disorder exhibited significantly lower average GAD1 methylation than healthy controls (p<0.001), particularly at three CpG sites in the promoter as well as in intron 2. The occurrence of negative life events was correlated with relatively decreased average methylation mainly in the female subsample (p=0.01). GAD1 SNP rs3762555 conferred a significantly lower methylation at three GAD1 intron 2 CpG sites (p<0.001). No differential methylation was observed in the GAD2 gene. The present pilot data suggest a potentially compensatory role of GAD1 gene hypomethylation in panic disorder possibly mediating the influence of negative life events and depending on genetic variation. Future studies are warranted to replicate the present finding in independent samples, preferably in a longitudinal design.

Elevated plasma γ-aminobutyrate/glutamate ratio and responses to risperidone antipsychotic treatment in schizophrenia

BACKGROUND

γ-aminobutyrate (GABA) and Glutamate (Glu) are respectively two major inhibitory and excitatory neurotransmitters in the central nervous system and recent theories propose that both of their signaling complexes are compromised in patients with schizophrenia.

METHODS

The changes in plasma GABA, Glu and GABA/Glu ratio in schizophrenia have been studied and may be potential clinical markers. Here, we examined if plasma GABA, Glu and GABA/Glu ratio are altered in 32 schizophrenics, including a comprehensive investigation of their involvements with clinical course of a 6-week risperidone antipsychotic treatment.

RESULTS

Plasma levels of GABA and Glu were significantly lower in patients than in controls, while plasma GABA/Glu ratio was significantly elevated. During treatment, a non-significant further decrease of plasma GABA, a significant increase of plasma Glu and a significant reduction of plasma GABA/Glu ratio were observed. The ratio returned to the control level at week 6 even though concentrations of GABA and Glu were still distant from normal. After the Bonferroni correction, partial correlation analyses showed that plasma GABA and GABA/Glu ratio were positively correlated with the dose of risperidone and plasma concentration of 9-hydroxyrisperidone. The reduction of plasma GABA/Glu ratio was positively correlated with the improvement of activation symptom cluster.

CONCLUSIONS

The elevated plasma GABA/Glu ratio reinforces the idea of an abnormal GABA-Glu interaction in schizophrenia. The ratio may be a good peripheral state-like marker in schizophrenia research.

Corticotropin-Releasing Hormone, Glutamate, and γ-Aminobutyric Acid in Depression

Stress response and depression have a significant impact on modern society. Although the symptoms are well characterized, the molecular mechanisms underlying depression are largely unknown. The monoamine hypothesis, which postulates dysfunctional noradrenergic and serotonergic systems as the underlying primary cause of depression, has been valuable for the development of conventional antidepressants, which can reverse these dysfunctional states to some degree. However, recent data from various neuroscience disciplines have questioned the major role of amines in the pathogenesis of depression. A considerable amount of evidence has accumulated that suggests that normalization of the hypothalamo—pituitary—adrenal (HPA) system might be the final step necessary for a remission of depression. In addition, an increasing body of clinical and postmortem evidence is pointing to a role played by γ-aminobutyric acid (GABA) and glutamate in the etiology of depression. This review examines the evidence, mainly obtained from clinical studies or from postmortem brain material, for a major role of the HPA axis, glutamatergic, and GABAergic systems in the pathogenesis of major and bipolar depression. The authors hope that these insights will stimulate further studies with the final aim of developing new types of antidepressants that combine increased efficacy with a shorter delay of the onset of action and reduced side-effect profiles.

Baseline plasma GABA: its relationship to the adverse effects of acute lorazepam administration on cognition in the elderly

The GABA system is an active target for drugs to treat a variety of disorders and the availability of an indirect measure of central GABA activity would not only enhance psychiatric research, but also permit assessment of the pharmacodynamic effects of drugs designed to act on this system. The relationships between plasma baseline pre-drug GABA concentrations and cognitive impairments induced by an acute oral dose of lorazepam (0.5 and 1.0 mg) were investigated in 22 healthy elderly individuals. Partial correlations controlling for plasma lorazepam concentrations revealed no significant relationship between baseline plasma GABA levels and lorazepam-induced impairments on tests of cognitive functioning. Plasma GABA concentration does not appear to be a useful marker of susceptibility to benzodiazepine-induced cognitive toxicity in the elderly. Other approaches to estimating central GABA activity should be pursued.

GABAergic dysfunction in mood disorders

The authors review the available literature on the preclinical and clinical studies involving GABAergic neurotransmission in mood disorders. Gamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter present almost exclusively in the central nervous system (CNS), distributed across almost all brain regions, and expressed in interneurons modulating local circuits. The role of GABAergic dysfunction in mood disorders was first proposed 20 years ago. Preclinical studies have suggested that GABA levels may be decreased in animal models of depression, and clinical studies reported low plasma and CSF GABA levels in mood disorder patients. Also, antidepressants, mood stabilizers, electroconvulsive therapy, and GABA agonists have been shown to reverse the depression-like behavior in animal models and to be effective in unipolar and bipolar patients by increasing brain GABAergic activity. The hypothesis of reduced GABAergic activity in mood disorders may complement the monoaminergic and serotonergic theories, proposing that the balance between multiple neurotransmitter systems may be altered in these disorders. However, low GABAergic cortical function may probably be a feature of a subset of mood disorder patients, representing a genetic susceptibility. In this paper, we discuss the status of GABAergic hypothesis of mood disorders and suggest possible directions for future preclinical and clinical research in this area.

Molecular targets in the treatment of anxiety

Although the cathecholamine systems have long been the focus of drug therapy in anxiety and depression, the development of novel drugs specifically aimed at new targets within these traditional neurotransmitter systems and at targets outside of these systems is now propelling the field of drug development in anxiety. A greater understanding of regional brain networks implicated in stress, anxiety, and anxious behaviors has provided localized targets for anxiolytics. Within the serotonin and norepinephrine systems, increased understanding of postsynaptic receptor regulation with chronic treatment and cross-system effects of drug therapy have been critical in furthering our understanding of effective pharmacological interventions. Receptors within the glutamate, gamma-aminobutyric acid, and neuropeptide systems provide a rich diversity of drug targets, both in localization and function. While acknowledging significant clinical and biological differences between the various anxiety disorders, an important aspect of modern neurobiological research is to look for similarities among these disorders, given that they are highly comorbid with each other and often respond to the same spectrum of treatments. Here we review current views on both traditional and new molecular targets in the treatment of anxiety, realizing that the ultimate challenge in effective anxiolytic drug development may be achieving specificity in brain regions important in generating and sustaining anxiety.

Common effects of chronically administered antipanic drugs on brainstem GABA(A) receptor subunit gene expression

Panic disorder is an anxiety disorder that can be treated by long-term administration of tricyclic antidepressants such as imipramine, monoamine oxidase inhibitors such as phenelzine, or the selective serotonin reuptake inhibitor (SSRI) antidepressants. Clinical data also indicate that some benzodiazepines, such as alprazolam, are effective antipanic agents, and that their therapeutic onset is faster than that of antidepressants. Benzodiazepines are well known for their action at GABA(A) receptors, and preclinical data indicate that imipramine and phenelzine also interfere with the GABAergic system. In addition some clinical data lend support to decreased benzodiazepine-sensitive receptor function in panic disorder patients. Using imipramine, phenelzine and alprazolam, we investigated, in rats, the possibility that the therapeutic efficacy of antipanic agents stems from the remodeling of GABAergic transmission in the pons-medulla region. Of the 12 GABA(A) receptor subunit (alpha 1--6, beta 1--3, gamma 1--3) steady-state mRNA levels investigated, we observed an increase in the levels of the alpha 3-, beta 1- and gamma 2-subunit transcripts with all three antipanic agents tested. The effects of imipramine and phenelzine on these subunits occurred after 21 days of treatment, while alprazolam effects were observed after 3 days of administration. Histochemical data suggest that the alpha 3 beta 1 gamma 2 subunits comprise a receptor subtype in the pons-medulla region. Therefore, we conclude that these molecular events parallel the therapeutic profile of the drugs examined. We further propose that these events may correspond to a remodeling of the GABA(A) receptor population, and may be useful markers for investigation of the antipanic properties of drugs.

Differences in pharmacodynamics but not pharmacokinetics between subjects with panic disorder and healthy subjects after treatment with a single dose of alprazolam

The pharmacokinetics and pharmacodynamics of the benzodiazepine alprazolam (1 mg, administered orally) were compared between eight patients with panic disorder and eight age- and sex-matched healthy volunteers. Subjects received orally administered placebo and alprazolam in a randomized, double-blind, single-dose crossover study. The elimination half-life, time of maximum plasma concentration, maximum concentration, volume of distribution, and clearance of alprazolam were similar for both groups. For each cohort, alprazolam treatment (vs. placebo) produced significant changes in typical benzodiazepine agonist effects, such as increased sedation and impaired cognitive performance on the digit-symbol substitution test. For the panic disorder group only, there was a significant increase in the subjective rating of"contented" and a reduction in the rating of "easily irritated." For the healthy volunteer group, alprazolam produced increases in ratings of "fatigued" and "slowed thinking," but also increases in ratings of "relaxed." In each group, alprazolam significantly increased the electroencephalographic (EEG) measure of relative beta amplitude (range, 13-30 Hz) compared with placebo. Concentration-EEG response curves fit a sigmoid E(max) model, and there was greater sensitivity to EEG effects, as measured by a 28% reduction in the EC50 value, in the panic disorder group compared with healthy control subjects. After alprazolam treatment, there was increased sensitivity to EEG and mood effects and fewer aversive effects in the panic disorder group compared with healthy subjects. There were no differences in the pharmacodynamic measures of sedation and cognition or differences in pharmacokinetics between the two groups.

Plasma levels of gamma-aminobutyric acid and panic disorder

Low levels of gamma-aminobutyric acid (GABA) in plasma have been associated with the presence of mood disorders in patients with major depressive disorder. We examined plasma GABA in patients with panic disorder, a disorder that is often comorbid with major depression, and in a group of control subjects. Patients with panic disorder had plasma GABA levels that did not differ significantly from levels in controls subjects. These data support the specificity of low plasma GABA as a marker for mood disorders.

Effect of diazepam on plasma gamma-aminobutyric acid in sons of alcoholic fathers

A subgroup of abstinent alcoholics, display low levels of plasma gamma-aminobutyric acid (GABA). Two previous studies of plasma GABA in sons of alcoholic fathers (SOAs) have yielded conflicting results. The aim of the current study was to measure plasma GABA both at baseline and after challenge with diazepam, a GABAA receptor agonist, in a group of SOAs already shown to display decreased eye movement, memory, and sedative effects of diazepam. Twenty-seven SOAs and 23 male control subjects received four logarithmically increasing doses of diazepam or placebo in randomized order on 2 days at least 1 week apart. Plasma GABA was measured at baseline and after the last dose. There were no significant differences between SOAs and controls in baseline plasma GABA levels. In the whole sample, there were significant correlations between baseline plasma GABA and both high novelty-seeking and low-harm avoidance scores on the Tridimensional Personality Questionnaire. Both SOAs and controls displayed decreases in plasma GABA over time on both testing days, but there was no effect of diazepam on plasma GABA and no significant difference between groups in plasma GABA response to diazepam. These results suggest that neither low plasma GABA at baseline nor altered plasma GABA response to diazepam is associated with increased genetic risk for alcoholism.

Plasma GABA predicts acute response to divalproex in mania

Bipolar I, manic phase inpatients were treated with divalproex sodium, lithium, or placebo in a previously reported parallel group multicenter, double-blind, randomized, controlled acute phase treatment trial. Plasma concentrations of gamma aminobutyric acid (GABA) were measured before and after treatment. Higher pretreatment plasma GABA levels were significantly (p = .04) related to a better clinical response to divalproex (n = 19). Pretreatment plasma GABA levels did not correlate with response to either lithium (n = 13) or placebo (n = 31). Following treatment with divalproex sodium, plasma GABA levels decreased significantly (p < .05), compared to placebo. Pretreatment plasma GABA levels were not related to overall severity of manic symptoms. Plasma GABA may predict response to pharmacologic agents acting on the GABA system.

GABA and mood disorders: a brief review and hypothesis

Considerable evidence implicates the neurotransmitter gamma-aminobutyric acid (GABA) in the biochemical pathophysiology of mood disorders. Animal models of depression show regional brain GABA deficits and GABA agonists have antidepressant activity in these models. Somatic treatments for depression and mania upregulate the GABAB receptor, similar to the effect of GABA agonists. Clinical data indicate that decreased GABA function accompanies depressed or manic mood states. GABA agonists are effective antidepressant and antimanic agents. Low GABA levels are found in brain, cerebrospinal fluid and plasma of patients with depression and in plasma of patients with mania. Plasma GABA levels, which reflect brain GABA, are not normalized with treatment and clinical remission in depression, suggesting low GABA is not a marker for mood state. Some somatic treatments, including valproic acid and electroconvulsive shock, reduced plasma GABA and response to these correlates with higher levels of baseline plasma GABA. From these data, a GABA hypothesis for mood disorders is formulated. Low GABA function is proposed to be an inherited biological marker of vulnerability for development of mood disorders. Environmental factors, including stress and excessive alcohol use, may increase GABA, causing symptoms of depression or mania. Treatment, or the passage of time, then returns GABA to its presymptomatic baseline as the symptoms remit. This hypothesis, applicable to a subset of mood disordered persons, is testable.