Platelet serotonin levels in panic 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.

Platelet serotonin binding and plasma cortisol in panic disorder before and after alprazolam plus behavioral guidance treatment

In 32 patients with panic disorder with or without agoraphobia, Bmax measures of 5-HT binding in platelets did not differ from normal controls at baseline. Plasmatic cortisol levels were significantly higher than controls in the morning and in the evening measures as well as in post-dexamethasone assays. Following an 8-week treatment period with alprazolam plus behavioral guidance encouraging exposure, Bmax values did not alter but cortisol measures diminished significantly. Measures of phobic avoidance were negatively correlated with 5-HT Bmax values. Plasmatic cortisol correlated positively with the number of situational panic attacks in the month before treatment. There were no correlations between cortisol and 5-HT Bmax measures. A possible link between serotonin function and phobic avoidance is discussed. Cortisol changes were interpreted as being related to the global severity of the anxious state.

Biological markers for anxiety disorders, OCD and PTSD: A consensus statement. Part II: Neurochemistry, neurophysiology and neurocognition

OBJECTIVE

Biomarkers are defined as anatomical, biochemical or physiological traits that are specific to certain disorders or syndromes. The objective of this paper is to summarise the current knowledge of biomarkers for anxiety disorders, obsessive-compulsive disorder (OCD) and posttraumatic stress disorder (PTSD).

METHODS

Findings in biomarker research were reviewed by a task force of international experts in the field, consisting of members of the World Federation of Societies for Biological Psychiatry Task Force on Biological Markers and of the European College of Neuropsychopharmacology Anxiety Disorders Research Network.

RESULTS

The present article (Part II) summarises findings on potential biomarkers in neurochemistry (neurotransmitters such as serotonin, norepinephrine, dopamine or GABA, neuropeptides such as cholecystokinin, neurokinins, atrial natriuretic peptide, or oxytocin, the HPA axis, neurotrophic factors such as NGF and BDNF, immunology and CO2 hypersensitivity), neurophysiology (EEG, heart rate variability) and neurocognition. The accompanying paper (Part I) focuses on neuroimaging and genetics.

CONCLUSIONS

Although at present, none of the putative biomarkers is sufficient and specific as a diagnostic tool, an abundance of high quality research has accumulated that should improve our understanding of the neurobiological causes of anxiety disorders, OCD and PTSD.

Platelet studies in panic disorder: A review

Objective: The blood platelet has been proposed as a model of central neurons and may therefore be used as a peripheral marker of psychiatric illness. One method of investigating serotonin function in panic disorder has relied on the use of the platelet as a model of serotonergic neurons. This article reviews the studies of platelet function in panic disorder.

Method: A literature search and review of relevant papers was undertaken.

Result: Studies examining platelet serotonin uptake and concentration in panic disorder patients have to date yielded conflicting results, with some investigators reporting increased serotonin uptake, others reduced uptake. Similarly studies of platelet 3H-imipramine binding have also yielded conflicting results. Two studies of platelet 3H-paroxetine binding have shown a reduction in the density of binding sites (Bmax) in patients with panic disorder. Platelet monoamine oxidase activity in anxiety disorders has been reported to be increased by some investigators but decreased by others. Methodological considerations may have been responsible for these differences. Finally, studies of α2 adrenoceptor density have also produced contrasting findings.

Conclusion: The findings of these studies indicate that platelet function is altered in panic disorder. Such changes may allow an insight into the biochemical aetiology of the illness. Further studies are required to delineate the role of serotonin and non-adrenaline in panic disorder.

Neuroanatomical circuits modulating fear and anxiety behaviors

OBJECTIVE

Our understanding of the neurobiology of anxiety disorders, although not complete, has advanced significantly with the development and application of genetic, neuroimaging and neurochemical approaches.

METHOD

The neuroanatomical basis of anxiety disorders is reviewed with particular focus on the amygdala and the temporal and prefrontal cortex. The functional anatomical correlates of anxiety disorders such as panic disorder, specific phobias and post-traumatic stress disorder are also discussed.

RESULTS

Functional neuroimaging studies in patients with anxiety disorders have shown neurophysiological abnormalities during symptom provocation tests, implicating the limbic, paralimbic and sensory association regions. The involvement of neurotransmitters such as serotonin and norepinephrine in depressive disorders is well established. Antidepressants that affect these neurotransmitter systems have also been shown to be useful in the treatment and management of patients with anxiety disorders. The role of serotonin and norepinephrine in the pathophysiology of anxiety disorders is reviewed. In addition, the involvement of the stress hormone corticotropin-releasing hormone, the peptide cholecystokinin and the amino acid transmitter gamma-amino butyric acid in anxiety disorders is reviewed.

CONCLUSION

The inconsistency in the results of biologic investigations of anxiety disorders highlights the importance of addressing the neurobiologic heterogeneity inherent within criteria-based, psychiatric diagnoses. Understanding of this heterogeneity will be facilitated by the continued development and application of genetic, neuroimaging and neurochemical approaches that can refine anxiety disorder phenotypes and elucidate the genotypes associated with these disorders. Application of these experimental approaches will also facilitate research aimed at clarifying the mechanisms of anti-anxiety therapies.

The genes encoding the 5HT1D alpha and 5HT1D beta receptors are unchanged in patients with panic disorder

To determine the serotonergic function in panic disorder, sequencing of the genes encoding the 5HT1D alpha and 5HT1D beta receptors was carried out. The genes for the 5HT1D alpha and 5HT1D beta receptors were amplified by polymerase chain reaction and sequenced by the dideoxy method. Some patients have both nucleotides C and T at position 1080 in 5HT1D alpha receptor gene; however, both of them code the same amino acid, asparagine. The 5HT1D beta receptor gene had a substitution from GCA276 to GCG276, not only panic disorder but also in controls; however, this substitution does not change the corresponding amino acid, alanine92.

Panic disorder. Pathophysiology and drug treatment

Advances over the past 2 decades in our understanding of the biology of panic disorder have paralleled a remarkable increase in the development of new pharmacological agents with antipanic effects. Although we can not presently use biological tests to help with our choice of therapeutic agent for individual patients, we can use this biological understanding in the development of overall pharmaco-therapeutic strategies. Current evidence does not support the hypothesis that panic disorder is associated with a primary disorder in one neurotransmitter system. Rather, the data suggest that the biological aetiology of panic disorder is related to abnormalities in the function of a variety of neurotransmitters including serotonin (5-hydroxytyrptamine; 5-HT), noradrenaline (norepinephrine), gamma-aminobutyric acid (GABA), dopamine, and cholecystokinin. It is likely, however, that panic disorder is a biologically heterogeneous condition and that biological subtypes may exist in which the primary abnormality may involve one or a few neurotransmitter systems. Currently, the data best support the hypothesis that pharmacotherapeutic agents with primary action at sites within the GABA and serotonin systems are the most effective in the treatment of panic disorder. Nevertheless, some patients will respond well to drugs with predominant activity in other systems, or may require pharmacotherapy designed to affect the function of more than 1 neurotransmitter. As our understanding of the biological aetiology of panic disorder evolves, the pharmacotherapeutic agents and strategies used in the treatment of this disorder will continue to evolve as well.

The Galway Study of Panic Disorder. II: Changes in some peripheral markers of noradrenergic and serotonergic function in DSM III-R panic disorder

Sixty six patients with panic disorders, fulfilling the DSM III criteria for panic attack, together with a group of age and sex matched controls, were studied for changes in their peripheral noradrenergic and serotonergic status before treatment and during six months treatment with either clomipramine or lofepramine. The results of this study suggest that, despite clinical improvement, the peripheral markers of both adrenergic (platelet aggregation to noradrenaline, platelet alpha 2 receptor density and lymphocyte beta receptor density) and serotonergic (platelet aggregation to serotonin, 3H-ketanserin binding to platelet 5HT2 receptors and 3H-5HT uptake into platelets) function largely remained abnormal. It is concluded that such abnormalities are trait markers of biogenic amine function in patients with panic attack. Further studies are needed to determine whether or not these parameters eventually normalize in those patients showing prolonged remission of symptoms.

Platelet serotonin decrease in panic disorder with obsessive compulsive symptoms

Platelet 5-HT levels were determined by fluorescent orthophthaldehyde assay in 33 panic disorder patients with and without obsessive compulsive symptoms (PD + OCS: n = 16; PD-OCS: n = 17) according to DSM III-R criteria, and compared With those of 38 healthy controls. Mean platelet levels were significantly lower in PD + OCS than in PD-OCS patients. The results are discussed in relation to serotonergic dysfunction linked to PD and OCS comorbidity.

Comparison of panic symptom sequences and pathophysiologic models

In an attempt to assess which of the proposed etiologic models best accounts for the symptomatology seen in panic attacks, 21 patients with panic attacks were asked to describe the symptom sequence during an attack. Using the Kolmogorov-Smirnov test, the Runs test, and Friedman's 2-way ANOVA, the degree of agreement between their attacks, and the proposed models was assessed. All three analyses suggest that, at the 0.1, 0.025, and 0.05 levels of significance respectively, the autonomic dysfunction model best accounts for the sequence of symptoms in panic attacks.

Platelet monoamine oxidase activity and 5-hydroxytryptamine uptake in agoraphobic patients

Platelet MAO activity and platelet serotonin uptake were determined in 20 agoraphobic and 16 neurotic depressive out-patients, and 19 healthy volunteers. Agoraphobic patients were characterised by significantly higher mean values of platelet MAO activity compared with the other two groups, while neurotic depressive patients exhibited significantly higher maximum platelet serotonin uptake velocity. These findings are compatible with an abnormality in the uptake and metabolism of serotonin.

Platelet serotonin uptake in panic disorder patients: a replication study

Platelet serotonin uptake was measured in 29 patients with DSM-III panic disorder or agoraphobia with panic attacks and compared to values obtained in 23 controls. Both the affinity constant (Km) and the maximal rate of uptake (Vmax) were determined in a buffered medium using 14C-serotonin. Patients and controls did not differ significantly with respect to age or Km values. A statistically significant difference was observed for Vmax (mean +/- SD = 65 +/- 22 pmol/10(8) platelet/min in patients vs. 44 +/- 13 pmol/10(8) platelets/min in controls). This finding suggests an overactivity of peripheral serotonergic function in panic disorder, which may also imply a similar dysfunction centrally.

Platelet serotonin uptake in panic disorder: comparison with normal controls and the effect of treatment

Platelet serotonin uptake was measured in 59 patients with panic attacks and compared to 26 controls. Scatchard analysis of the data showed that the maximal rate of uptake (Vmax) of serotonin was significantly higher in patients than controls. The affinity constant (Km) was not different. In a sub-group of 24 patients, benzodiazepine treatment did not alter the kinetics of platelet serotonin uptake. These findings suggest an abnormality in serotonergic function in patients with panic attacks. Insofar as the platelet is a model of central neuronal function they support serotonergic hyperactivity as a biochemical basis of panic attacks.

Systemic hormonal and physiological abnormalities in anxiety disorders

Among the studies of systemic hormonal and physiological abnormalities associated with anxiety disorders, the most consistent and extensive findings suggest (a) peripheral adrenergic hyperactivity (including increases in norepinephrine but not epinephrine) and functional dysregulation, (b) increased incidence of mitral valve prolapse in panic patients, and (c) normal suppressibility of the hypothalamic-pituitary-adrenal cortical endocrine system with dexamethasone in panic patients. Other less-certain findings include (a) increased circulating concentrations of plasma ACTH and/or cortisol, and prolactin, in panic patients, (b) increased platelet monoamine oxidase activity in generalized anxiety and/or panic patients, (c) decreased gonadal axis activity in some anxious individuals, (d) decreased nighttime melatonin plasma concentrations in panic patients, and (e) peripheral alpha 2 and beta-adrenoreceptor down-regulation, with normal serotonin binding parameters. These findings, taken together, provide tentative support for dysfunction in adrenergic and GABAergic central nervous system mechanisms in people with anxiety disorders. Abnormal anxiety and normal stress both show evidence of adrenergic hyperactivity; however, there appear to be differences in hormonal profiles, especially the apparent lack of increase of epinephrine during panic attacks, as well as differences in the reactivity of the system, and in the "trigger" mechanisms which determine when the response occurs.