Platelet serotonin uptake and 3H-imipramine binding 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.

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.

The platelet as a peripheral marker in psychiatric illness

The identification of peripheral markers of psychiatric illness is important if an improvement in the diagnosis and treatment of various diseases with overlapping symptomatology is desired. There are many disorders that not only have overlapping symptomatology, but also have similar biological disturbances. The functional capability of the neurons involved in the disease processes may be at the crux of the underlying pathology. The platelet intracellular calcium response to neurotransmitter stimulation has previously been used as a peripheral marker of psychiatric illness. This review discusses evidence in support of the extended use of the platelet as a peripheral marker. The use of the platelet intracellular calcium response to neurotransmitter stimulation as a state or trait marker in major depression, the specificity and selectivity of this response, and the possible use of the platelet as a peripheral marker in psychotic disorders such as schizophrenia, mania and psychotic depression are shown. Finally, a proposed mechanism for the association between certain psychiatric disorders and cardiovascular disease is discussed. Copyright 2001 John Wiley & Sons, Ltd.

Modification of 35% carbon dioxide hypersensitivity across one week of treatment with clomipramine and fluvoxamine: a double-blind, randomized, placebo-controlled study

The effects of short treatments (7 days) with clomipramine and fluvoxamine on the reactivity to inhalations of 35% CO2/65% O2 were compared in 39 panic patients who had positive responses to 35% CO2 inhalations. A double-blind, randomized, placebo-controlled design was applied. Each patient was given the 35% CO2 challenge on days 0 (before starting treatment), 3, and 7. Patients on placebo did not report any significant changes in their reactivity to 35% CO2 across the three sessions, whereas patients on clomipramine and fluvoxamine reported a significant attenuation of the reactivity on day 7. These results indicate that treatments with clomipramine and fluvoxamine decrease hypersensitivity to 35% CO2 after a few days, suggesting a relevant role of the modulation of CO2 sensitivity by the serotonergic system in antipanic properties of these compounds.

Pharmacologic effect of imipramine, paroxetine, and sertraline on 35% carbon dioxide hypersensitivity in panic patients: a double-blind, random, placebo-controlled study

The effects of short treatment (7 days) with the tricyclic antidepressant imipramine and the two selective serotonin reuptake inhibitors paroxetine and sertraline on the reactivity to inhalation of 35% CO2/65% O2 were compared in 70 panic patients who had positive responses to 35% CO2 inhalations. A double-blind, random, placebo-controlled design was applied. Each patient was given the 35% CO2 challenge on days 0 (before starting the treatment), 3, and 7. In the placebo group, there were no significant changes in the reactivity to 35% CO2 in the three sessions whereas there were significant similar reductions of reactivity to 35% CO2 in all three drug-treated groups. These results confirm the good reproducibility of 35% CO2 reactivity and the negligible effects of placebo on reactivity to CO2 and suggest that short treatments with imipramine, paroxetine, and sertraline decrease reactivity to 35% CO2, possibly as an expression of their antipanic properties.

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.

Platelet markers in suicide attempters

1. The authors measured 3H-imipramine (3H-IMI) binding and serotonin (5HT) uptake parameters as well as sulphotransferase activity in platelets of suicide attempters. 2. Platelet 3H-IMI binding sites and 5HT uptake are related to similar sites and processes present in the brain, and sulphotransferase (ST) is an enzyme involved in the catabolism of cathecholamines. 3. The results showed the presence of a decreased density of both 3H-IMI binding and of 5HT uptake sites, with no change in ST activity in suicide attempters, as compared with healthy controls. 4. The reduced 3H-IMI binding and 5HT uptake may be related to a hypofunction of presynaptic serotonergic mechanisms which might be altered in suicidal behavior.

Platelet [3H]paroxetine binding in panic disorder

Platelet [3H]paroxetine binding was measured in 20 patients (14 females, six males) with panic disorder and 20 normal controls (14 females, six males). For patients with panic disorder, Bmax was 1987 +/- 1135 fmol/mg protein (mean +/- SD) compared with control Bmax values of 1626 +/- 611 fmol/mg protein. The mean Kd value for the patients was 0.076 +/- 0.056 nM and for the controls was 0.083 +/- 0.033 nM. ANCOVA indicated no significant effect of sex, diagnosis (panic disorder vs. normal controls) or season of sampling on either Kd or Bmax. The data provide no evidence for an abnormality of the platelet uptake mechanism in panic disorder.

Effectiveness of an intensive partial hospitalization program for treatment of anxiety disorders

This study evaluates the effectiveness of a partial hospitalization program for the treatment of anxiety disorders. The 5-week program was based on an integration of biological, cognitive, and behavioral theories. Neuman's systems theory provided the framework for the study. The 32 participants were tested pre- and posttreatment. All three hypotheses were supported; "fear of fear," severity of impairment, and general emotional distress were all significantly lower posttreatment than pretreatment. The limitations, including the lack of a comparison group, possible sample bias, and the lack of long-term follow-up, are addressed.

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.