Altered [3H]imipramine and 5-HT2 but not [3H]paroxetine binding sites in platelets from depressed patients

Is there a relationship between morphological and functional platelet changes and depressive disorder?

BACKGROUND

Blood platelets, due to shared biochemical and functional properties with presynaptic serotonergic neurons, constituted, over the years, an attractive peripheral biomarker of neuronal activity. Therefore, the literature strongly focused on the investigation of eventual structural and functional platelet abnormalities in neuropsychiatric disorders, particularly in depressive disorder. Given their impact in biological psychiatry, the goal of the present paper was to review and critically analyze studies exploring platelet activity, functionality, and morpho-structure in subjects with depressive disorder.

METHODS

According to the PRISMA guidelines, we performed a systematic review through the PubMed database up to March 2020 with the search terms: (1) platelets in depression [Title/Abstract]"; (2) "(platelets[Title]) AND depressive disorder[Title/Abstract]"; (3) "(Platelet[Title]) AND major depressive disorder[Title]"; (4) (platelets[Title]) AND depressed[Title]"; (5) (platelets[Title]) AND depressive episode[Title]"; (6) (platelets[Title]) AND major depression[Title]"; (7) platelet activation in depression[All fields]"; and (8) platelet reactivity in depression[All fields]."

RESULTS

After a detailed screening analysis and the application of specific selection criteria, we included in our review a total of 106 for qualitative synthesis. The studies were classified into various subparagraphs according to platelet characteristics analyzed: serotonergic system (5-HT2A receptors, SERT activity, and 5-HT content), adrenergic system, MAO activity, biomarkers of activation, responsivity, morphological changes, and other molecular pathways.

CONCLUSIONS

Despite the large amount of the literature examined, nonunivocal and, occasionally, conflicting results emerged. However, the findings on structural and metabolic alterations, modifications in the expression of specific proteins, changes in the aggregability, or in the responsivity to different pro-activating stimuli, may be suggestive of potential platelet dysfunctions in depressed subjects, which would result in a kind of hyperreactive state. This condition could potentially lead to an increased cardiovascular risk. In line with this hypothesis, we speculated that antidepressant treatments would seem to reduce this hyperreactivity while representing a potential tool for reducing cardiovascular risk in depressed patients and, maybe, in other neuropsychiatric conditions. However, the problem of the specificity of platelet biomarkers is still at issue and would deserve to be deepened in future studies.

Inflammatory cytokine-associated depression

Inflammatory cytokines can sometimes trigger depression in humans, are often associated with depression, and can elicit some behaviors in animals that are homologous to major depression. Moreover, these cytokines can affect monoaminergic and glutamatergic systems, supporting an overlapping pathoetiology with major depression. This suggests that there could be a specific major depression subtype, inflammatory cytokine-associated depression (ICAD), which may require different therapeutic approaches. However, most people do not develop depression, even when exposed to sustained elevations in inflammatory cytokines. Thus several vulnerabilities and sources of resilience to inflammation-associated depression have been identified. These range from genetic differences in neurotrophic and serotonergic systems to sleep quality and omega-3 fatty acid levels. Replicating these sources of resilience as treatments could be one approach for preventing "ICAD". This article is part of a Special Issue entitled SI: Neuroimmunology in Health And Disease.

Major depression during interferon-alpha treatment: vulnerability and prevention

Major Depressive Disorder (MDD) during interferons (IFN-α) treatment can occur within a few months of therapy, and shares many homologies with other forms of MDD, Most patients are resilient to the side effect ofinterferon-induced depression (IFN-MDD), but 15% to 40% are vulnerable. Several studies have employed antidepressants to prevent the incidence of an IFN-MDD episode, and the results suggest that prophylactic antidepressants may be specifically useful in those with pre-existing subthreshold depressive symptoms andlor a history of prior MDD episodes. Several other potential markers of vulnerability for IFN-MDD have been implicated in assessments of nondepressed patients before they start IFN-α These include poor sleep quality, premorbid elevations in inflammatory cytokines, genetic polymorphisms in the serotonin system, personality, and social support. The interplay of these factors strongly predicts who is at risk for IFN-MDD, and indicates several potentially modifiable targets for the personalized prevention of IFN-MDD,

Clinical and serotonergic predictors of non-affective acute remitting psychosis in patients with a first-episode psychosis

OBJECTIVE

The study aimed to establish clinical predictors of non-affective acute remitting psychosis (NARP) and assess whether these patients showed a distinct serotonergic profile.

METHOD

First-episode never treated psychotic patients diagnosed of paranoid schizophrenia (n=35; 21 men and 14 women) or NARP (n=28; 15 men and 13 women) were included.

RESULTS

NARP patients showed significantly lower negative symptomatology, better premorbid adjustment, shorter duration of untreated psychosis, more depressive symptomatology and a lower number of 5-HT2A receptors than the paranoid schizophrenia patients. In the logistic regression, the four variables associated with the presence of NARP were: low number of 5-HT2A receptors; good premorbid adjustment; low score in the item 'hallucinatory behaviour' and reduced duration of untreated psychosis.

CONCLUSION

Our findings support the view that NARP is a highly distinctive condition different from either affective psychosis or other non-affective psychosis such as schizophrenia, and highlight the need for its validation.

Enhanced serotonin transporter function during depression in seasonal affective disorder

Decreased synaptic serotonin during depressive episodes is a central element of the monoamine hypothesis of depression. The serotonin transporter (5-HTT, SERT) is a key molecule for the control of synaptic serotonin levels. Here we aimed to detect state-related alterations in the efficiency of 5-HTT-mediated inward and outward transport in platelets of drug-free depressed patients suffering from seasonal affective disorder (SAD). 5-HTT turnover rate, a measure for the number of inward transport events per minute, and tyramine-induced, 5-HTT-mediated outward transport were assessed at baseline, after 4 weeks of bright light therapy, and in summer using a case-control design in a consecutive sample of 73 drug-free depressed patients with SAD and 70 nonseasonal healthy controls. Patients were drug-naive or medication-free for at least 6 months prior to study inclusion, females patients were studied in the follicular phase of the menstrual cycle. All participants were genotyped for a 5-HTT-promoter polymorphism (5-HTTLPR) to assess the influence of this polymorphism on 5-HTT parameters. Efficiency of 5-HTT-mediated inward (p=0.014) and outward (p=0.003) transport was enhanced in depressed patients. Both measures normalized toward control levels after therapy and in natural summer remission. Changes in outward transport showed a clear correlation with treatment response (rho=0.421, p=0.001). Changes in inward transport were mediated by changes in 5-HTT transport efficiency rather than affinity or density. 5-HTTLPR was not associated with any of the 5-HTT parameters. In sum, we conclude that the 5-HTT is in a hyperfunctional state during depression in SAD and normalizes after light therapy and in natural summer remission.

In vivo effect of antidepressants on [3H]paroxetine binding to serotonin transporters in rat brain

Amine transporters are major target for development of various pharmacological agents to treat behavioral disorders. Serotonin transporters (SERT) have been implicated in the etiology of depression and drugs acting on SERT can be effective in treating depression. The aim of the present study was to study the in vivo effect of various antidepressants on [(3)H]paroxetine binding to SERT in regions of rat brain. Rats were treated with tricyclic antidepressant (TCAs) such as amitriptyline (AMI), serotonin/norepinephrine reuptake inhibitor (SNRIs) such as clomipramine (CMI), and selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine (FLX) and citalopram (CIT) (10 mg/kg body wt.) for 30 days. Density of SERT was measured in cortex and hippocampus using [(3)H]paroxetine (0.03-1.0 nM) in presence and absence of 10 muM fluoxetine as displacer. It was observed that the density of cortical SERT was significantly decreased with CMI (68%, P < 0.0001), FLX (67%, P < 0.0001), CIT (54%, P < 0.0001), and AMI (52%, P < 0.0001) treatment, when compared to the density of 120.7 +/- 4.0 fmol/mg protein in control rats, without altering the affinity (Kd) of [(3)H]paroxetine to the transporters. The density of SERT in hippocampus was also significantly decreased with FLX (65%, P < 0.0001), CMI (54%, P < 0.0001), CIT (52%, P < 0.0001) and AMI (46%, P < 0.0001) treatment, when compared to the density of 74.0 +/- 2.6 fmol/mg protein in control rats, without altering the affinity of [(3)H]paroxetine to the transporters. Displacement study showed high affinity for CMI > CIT > FLX. The results suggest that chronic antidepressant treatment significantly down-regulates both cortical and hippocampal SERT in rat brain and SSRIs have high affinity for SERT than TCAs.

Tandem regulation of phosphoinositide signaling and acute behavioral effects induced by antidepressant agents in rats

RATIONALE

Antidepressants increase synaptic monoamine concentrations, but the subsequent signaling events that produce the beneficial clinical effects remain unclear. Diverse antidepressants increase CDP-diacylglycerol, a crucial step in phosphoinositide signaling. Serotonin 5HT(2) receptors, implicated in depression or the actions of some antidepressants, signal through phosphoinositide hydrolysis. Thus, cross talk between antidepressant-induced CDP-diacylglycerol and 5HT(2) signaling could contribute to the antidepressant mechanism.

OBJECTIVE

The objective of the study was to test the hypotheses that antidepressants enhance net signaling via 5HT(2) receptors by augmenting the supply of phosphoinositide substrates and that this action contributes to the behavioral effects of the drugs.

MATERIALS AND METHODS

Brain slices pre-labeled with [(3)H]inositol in the presence of various antidepressant concentrations were washed and incubated with the 5HT(2) agonist, alpha-methylserotonin, followed by measuring phosphoinositide synthesis and inositol phosphate accumulation. Further, rats administered antidepressants after pretreatment with neomycin to inhibit metabolic utilization of phosphoinositides were behaviorally evaluated in the forced swim test.

RESULTS

Diverse antidepressants significantly enhanced phosphoinositide synthesis. While alpha-methylserotonin increased inositol phosphate accumulation, this effect was significantly accentuated in hippocampal or cortical tissues pre-incubated in the presence of imipramine, desipramine, fluoxetine, paroxetine, or maprotiline. Drug-induced behavioral antidepressant effects were reversed by neomycin pretreatment, whereas neomycin alone did not alter basal immobility times.

CONCLUSIONS

Antidepressants probably exert tandem neurochemical effects by increasing synaptic monoamine concentrations and by producing phosphoinositides used in 5HT(2) receptor signaling. This combination of actions may constitute the mechanism of at least the acute behavioral effects of the drugs and could implicate aberrant neurolipid signaling in the pathophysiology of depression.

Polymorphisms in the regulatory region of the human serotonin 5-HT2A receptor gene (HTR2A) influence gene expression

BACKGROUND

Genomic variation in the regulatory region of the serotonin (5-HT) 2A receptor gene (HTR2A) may contribute to altered levels of 5-HT2A receptor and to psychiatric disease.

METHODS

Frequency and linkage disequilibrium (LD) were determined for promoter single nucleotide polymorphisms (SNPs) -1438A/G, -1420C/T, and -783A/G in 156 subjects. Functional relevance of -1438A/G and -783A/G was assayed in vitro using a luciferase reporter assay and ex vivo using quantitative real time polymerase chain reaction in a set of human fibroblast cell lines.

RESULTS

Significant LD was observed between SNPs -1438A/G and -783A/G. In vitro assays showed no significant differences in promoter activity between the A- and G-allele of -1438 locus when expressed with the major alleles at -1420C/T and -783A/G; however, when the minor allele G at -783 was expressed with G-allele at -1438, promoter activity was significantly decreased. 5-HT2A receptor mRNA expression in human fibroblast cell lines confirmed that -783A/G polymorphism significantly modified the effects of -1438A/G SNP.

CONCLUSIONS

Our results demonstrate that SNP -783A/G modifies the effects of the major SNP -1438A/G. Future studies examining the association of -1438A/G polymorphism with diseases and 5-HT2A receptor expression analyses should account for this epistasis.

Peripheral serotonergic markers in acutely suicidal patients. 1. Comparison of serotonergic platelet measures between suicidal individuals, nonsuicidal patients with major depression and healthy subjects

BACKGROUND

A robust association between "suicidality" and deficits of the serotoninergic neurotransmission has been claimed in the past. However, many studies having investigated the relationship between suicidality and peripheral indicators of serotoninergic neurotransmission suffer from considering only one or a very small number of potentially useful serotoninergic parameters, whereas a synoptic multidimensional approach appears to be more appropriate. Furthermore, the psychiatric context within which suicidal behaviour occurs should be considered when interpreting biochemical findings of patients with suicidal ideation and suicide attempts.

METHODS

In the present study 5 peripheral serotonergic markers, (platelet 5HT concentration, 5HT uptake activity, 5HT(2A) receptor binding characteristics, MAO-B activity and tryptophan concentration in plasma) were assessed simultaneously. Of the 60 acutely suicidal inpatients (ICD-10: F43.xx, n = 52; F31/32/33, n = 8), 45 were suicide attempters. Data of 28 nonsuicidal patients with major depression (F31, n = 4; F32, n = 14; F33, n = 10) and 123 healthy volunteers represented the control groups.

RESULTS

Mean platelet 5HT concentration was significantly lower in suicidal inpatients when compared to nonsuicidal depressed patients, but did not differ from the figure in healthy subjects. Nonsuicidal depressed patients showed significantly higher mean platelet-5HT concentration than healthy controls. Mean V(max) of 5HT uptake in washed platelets, but not in platelet-rich plasma, was significantly higher in suicidal patients than in healthy controls, not, however, when compared to nonsuicidal depressed patients. Mean K(D) for the platelet 5HT(2A) receptor and MAO-B activity were significantly lower in suicidal patients as compared to nonsuicidal depressed patients and healthy controls. The observed differences in peripheral serotonergic markers between groups are partially due to a significant gender effect. A lower MAO-B activity was observed only in suicidal females, while the higher V(max) of 5HT uptake in washed platelets of suicidal patients was due to suicidal males.

CONCLUSIONS

In view of conflicting observations made by other authors and the present findings on suicidal patients with adjustment disorder it remains doubtful whether and if so to which extent platelet studies can provide valid information on serotonergic mechanisms related to suicidal behaviour.

Impaired platelet [3H]paroxetine binding in female patients with borderline personality disorder

RATIONALE

There have been few studies of platelet paroxetine binding in borderline personality disorder (BPD).

OBJECTIVE

Our aim was to determine whether female BPD subjects show abnormalities in platelet paroxetine binding.

METHODS

Twenty-one female BPD subjects and 16 age- and gender-matched normal control subjects were assessed using the following: (1) Diagnostic Interview for Borderlines, Revised, (2) Diagnostic Assessment for Personality Pathology: Brief Questionnaire, and (3) Barratt Impulsivity Scale. Platelets were collected and assayed for platelet paroxetine binding.

RESULTS

Bmax was lower in the BPD group (p < 0.0001), but differences in Kd only reached a trend level. There were no associations with trait dimensions independent of diagnosis.

CONCLUSIONS

Reduced platelet paroxetine binding in female BPD patients may reflect presynaptic serotonin dysfunction.

Increased cerebral serotonin-2A receptor binding in depressed patients with myocardial infarction

Serotonin (5-HT) has been implicated in the pathophysiology of depression. It is not known whether depression in post-myocardial infarction (MI) patients is also serotonin-mediated. In somatically healthy depressed persons, increased brain 5-HT(2A) receptor binding has been reported in some studies. In animal studies, decreased serotonin activity was found after induction of MI. In the present study, it was hypothesized that depressed post-MI patients would exhibit increased brain 5-HT(2A) receptor binding compared with non-depressed post-MI patients. Single photon emission computed tomography (SPECT) with the radioligand 123I-5-I-R91150, a 5-HT(2A) receptor antagonist, was used to study 5-HT(2A) receptor binding. SPECT scans were performed in nine depressed post-MI patients, 10 non-depressed post-MI patients and 10 healthy control subjects. Results were analysed using statistical parametric mapping. Depressed post-MI patients showed increased 5-HT(2A) receptor binding compared with non-depressed post-MI patients, and MI patients showed decreased 5-HT(2A) receptor binding compared with control persons. Both post-MI depression and MI seem to be associated with changes in 5-HT(2A) receptor binding.

Decreased serotonin 5-HT2A receptor-stimulated phosphoinositide signaling in fibroblasts from melancholic depressed patients

Abnormalities in serotonin (5-HT) receptors and 5-HT receptor-mediated signal transduction systems have been widely reported in mood disorders. This study was intended to evaluate 5-HT(2A) receptor-coupled activation of phosphatidylinositol (PI) hydrolysis in subtypes of depression. Samples for fibroblast culture were obtained from patients with major depression with or without melancholia, and normal controls. Dose response curves were determined for 5-HT-induced PI hydrolysis. PI response was determined for bradykinin and l-alpha-lysophosphatidic acid (LPA), alternative Gq-coupled receptor agonists. [125I]LSD binding for 5-HT(2A) also was conducted. Finally, Western blot analysis was performed for phospholipase Cbeta1 (PLCbeta1) and Galpha(q/11) proteins. The maximum PI response observed with 5-HT was significantly lower in melancholics but not nonmelancholic patients relative to controls. Activation of PI hydrolysis by bradykinin and LPA was not reduced in melancholic vs melancholics and controls; responses to both agonists actually were increased in the melancholic group. [125I]LSD binding, PLCbeta1, and Galpha(q/11) protein levels did not differ between groups. The data raise the possibility that the reduced 5-HT(2A) receptor-induced PI hydrolysis is intrinsic to the receptor itself or its coupling to Gq protein, and is not related to altered availability of the 5-HT(2A) receptor, Gq or PLC.

Serotonergic platelet markers of suicidal behavior--do they really exist?

BACKGROUND

Abnormal changes in platelets used as peripheral markers of central serotonergic functions are said to be associated with suicidality and depression, but this association has not been supported by consistent findings.

AIM

This review based on selected, often quoted publications in this area focuses firstly, on obviously contradictory findings and, secondly, on potential methodological flaws explaining these discrepancies.

RESULTS

The platelet 5-HT transporter has been found to have an inconsistent association with suicidality; furthermore, the specificity of imipramine for the 5-HT transporter is most likely low, since the number of platelet impramine binding sites has not been reliably associated with platelet serotonin uptake (Vmax). Significant changes of platelet serotonin content in suicidal individuals, as described in various studies, are most likely due to washout periods that are too short to eliminate the effects of a previous drug intake, or, in violent suicide attempters, due to blood loss and dilution. Similar methodological shortcomings might account for an often-reported elevated number of platelet 5-HT(2) receptor binding sites in suicidal individuals. In many studies, the results have not been sufficiently controlled for drug effects on platelet 5-HT(2) receptors, and associations of platelet 5-HT(2) binding with selective classifications of suicidal behavior are often generalized as further evidence for an association of platelet 5-HT(2) receptors with 'suicidality'. Finally, changes in platelet MAO-B-activity in suicidal patients have not been reproducibly found, and the impact of smoking on MAO-B activity has not been controlled in any studies.

CONCLUSIONS

Methodological flaws such as small sample sizes, insufficient matching criteria for controls, use of inadequate ligands in binding experiments, nonconsideration of comorbidity etc. and considerable methodological differences between studies limit their validity and comparability. It does not seem possible, at present, to integrate published findings and concepts into a plausible biological model of suicidality.

Combined use of platelet serotonergic markers and psychopathological scales as diagnostic screening of a psychotic versus a depressive disorder

A single case of a patient suffering from a first psychotic episode and the differential diagnoses between affective and psychosis is performed throughout the combined use of peripheral serotonergic markers and clinical psychopathological scales during a 6-months follow-up. The results suggest the need of performing further studies combining biological and clinical markers of psychiatric disorders.

Increased coronary events in depressed cardiovascular patients: 5-HT2A receptor as missing link?

OBJECTIVE

Major depressive disorder and depressive symptoms have been identified as independent risk factors for cardiac morbidity and mortality in patients with ischemic heart disease. Increased susceptibility to platelet activation has been proposed as one of the mechanisms by which depression acts as a significant risk factor for thrombotic events. In this review, data on platelet activation and platelet aggregation measures in depressed patients with or without concomitant cardiovascular disease are given. Data on the influence of antidepressants on parameters of platelet activation are summarized.

METHODS

A literature search was done by checking MEDLINE Advanced and PsycInfo from 1990 to 2003 and through checking the bibliographies of these sources. The following key words were used for this search: platelet activation, platelet aggregation, depression, depressive disorder, ischemic heart disease, calcium, and serotonin.

RESULTS

There is an indication of enhanced platelet activation and aggregation in depressed patients. Next, patients with a depressive disorder show signs of a hyperactive platelet 5-HT2A receptor signal transduction system as measured by increased platelet calcium mobilization after stimulation of platelets with serotonin.

CONCLUSIONS

Depression appears to be associated with an increased susceptibility for serotonin-mediated platelet activation. Upregulation and/or increased sensitivity of 5-HT2A/1B receptors and downregulated 5-HT transporter receptors in the periphery may contribute to increased risk of thromboembolic events in patients with depression and cardiovascular disease. Increased platelet reactivity based on a hyperreactive 5-HT2A receptor signaling system might be influenced by antidepressive medication that antagonizes platelet 5-HT2A receptors.

The effects of paroxetine and tianeptine on peripheral biochemical markers in major depression

Depression is related to the alterations of the central serotonergic system and some antidepressants achieve their therapeutic effects through alteration of serotonin (5-HT) (re)uptake. Peripheral biochemical markers, platelet and serum 5-HT concentrations, platelet monoamine oxidase (MAO) activity, plasma levels of cortisol and prolactin (PRL), were investigated in patients with major depression before and after 4 weeks of treatment with paroxetine (an inhibitor of 5-HT uptake) or tianeptine (a stimulator of 5-HT uptake). Study was open, single center and included female depressed patients, 21 treated with tianeptine (37.5 mg/day) and 15 treated with paroxetine (20 mg/day), and 11 drug-free healthy women (controls). Before treatment, depressed patients as a group had significantly higher serum 5-HT and cortisol concentrations than healthy controls. There were no differences in the other biochemical markers. Response to antidepressant treatment was estimated according to the 50% fall in the initial scores of Hamilton Depression Rating Scale (HAMD) after 4 weeks of treatment. Good therapeutic response was observed in 47% and 45% patients treated with paroxetine and tianeptine, respectively. Paroxetine treatment induced significant decrease in platelet 5-HT concentrations in both responders and nonresponders, while no alterations in platelet 5-HT values were found in tianeptine-treated patients. There was a subgroup of depressed patients in paroxetine-treated group with high pretreatment platelet 5-HT concentration and later poor therapeutic response to paroxetine treatment. Serum 5-HT values, platelet MAO activity or plasma cortisol or PRL levels were unchanged after both treatments. The results suggest that pretreatment platelet 5-HT levels, but not other peripheral biochemical markers, might predict therapeutic outcome at least in paroxetine-treated patients.

Loss of the circadian variation of platelet [3H]imipramine binding in delusional compared with non-delusional endogenously depressed patients

BACKGROUND

The circadian variations of the serotonin reuptake sites were studied in 16 patients meeting DSM-IV criteria for major depression with melancholia, either with (n=8) or without (n=8) psychotic symptomatology.

METHOD

The [3H]imipramine binding sites were measured in platelet samples.

RESULTS

While no statistically significant difference was found between the morning (09:00 h) and evening (21:00 h) [3H]imipramine B(max) values in the control group, both the non-delusional and delusional melancholic patients showed higher evening than morning B(max) values, which were only statistically significant in the former. When both diagnostic groups were compared, the delusional patients showed significantly lower [3H]imipramine binding values than the non-delusional patients both in the morning and evening samples. Within the non-delusional depressed patients, those individuals with mood circadian variation, assessed by the 18th item of the HDRS, showed significantly lower B(max) values than those without mood variation. Lowest morning and evening B(max) values were noted in the delusional depressed group without mood variations.

CONCLUSIONS

These results suggest that delusional depressions might have a different neurobiological substrate with loss of chronobiological rhythms.

Depression is associated with an increase in the expression of the platelet adhesion receptor glycoprotein Ib

There is a significant association between cardiovascular disease and depression. Previous studies have documented changes in platelets in depression. It is unknown if depression causes functional changes in platelet surface receptors. Therefore, we analyzed (1) the surface expression of glycoprotein (GP)Ib and the integrin receptor alpha(IIb)beta(IIIa), receptors involved in platelet adhesion and aggregation, (2) CD62 (P-selectin) and CD63, integral granule proteins translocated during platelet activation, (3) platelet aggregation in response to ADP and (4) plasma levels of glycocalicin and von Willebrand factor (vWF), in depressed patients compared to healthy volunteers. Fifteen depressed patients with a Hamilton depression score of at least 22 and fifteen control subjects were studied. Platelets were assessed for surface expression levels of GPIb, alpha(IIb)beta(IIIa), CD62 and CD63 by flow cytometry. Genomic DNA was isolated to investigate a recently described polymorphism in the 5' untranslated region of the GPIbalpha gene. The number of GPIb receptors was significantly increased on the surface of platelets from patients with depression compared to control subjects. Surface expression of CD62 was also significantly increased in the depressed patients versus control subjects. There was no significant difference between depressed patients and healthy volunteers in the surface expression of alpha(IIb)beta(IIIa) or CD63, or in glycocalicin or vWF plasma concentration, or ADP-induced aggregation. There was no difference in allele frequency of the Kozak region polymorphism of the GPIbalpha gene, which can affect GPIb expression. The results of this study demonstrate that the number of GPIb receptors on platelets are increased in depression and suggest a novel risk factor for thrombosis in patients with depression.

Platelet serotonin transporters and the transporter gene in control subjects, unipolar patients and bipolar patients

OBJECTIVE

The purpose of the present study was to relate the number of platelet serotonin transporters in unipolar and bipolar patients and in control subjects to two polymorphisms in the serotonin transporter gene: a VNTR in intron 2 and a deletion/insertion in the promoter region.

METHOD

Density of platelet serotonin transporters was determined by radioligand binding analysis. Genotyping was performed by PCR amplification of polymorphic regions followed by size determination of the obtained fragments.

RESULTS

The control subjects and the two groups of patients were similar with respect to the genotype and allele distribution belonging to the two polymorphisms in the serotonin transporter gene for. An interaction between status (control, unipolar- or bipolar patient) and VNTR genotype regarding the number of platelet serotonin transporters was observed; unipolar patients with the genotype 12/10 had more platelet serotonin transporters than bipolar patients and controls with this genotype. No association related to the polymorphism was found in the promoter region of the serotonin transporter gene.

CONCLUSION

An association was observed between the polymorphism in intron 2 of the serotonin transporter gene and the number of platelet serotonin transporters. Unipolar patients with a particular genotype had more platelet serotonin transporters than the corresponding controls and bipolar patients.

Altered 5-HT(2A) binding sites and second messenger inositol trisphosphate (IP(3)) levels in hippocampus but not in frontal cortex from depressed suicide victims

The binding parameters of 5-HT(2A) and levels of its second messenger, 1,4,5-trisphosphate (IP(3)), were simultaneously studied in frontal cortex and hippocampus from the brains of 18 control subjects and 18 depressed suicide victims. All suicides met DSM-III-R criteria for depressive symptoms, suffered a violent death and had not taken any antidepressant drugs for at least 6 months prior to death. A significant decrease in the number of 5-HT(2A) binding sites (154+/-22 vs. 254+/-36 fmol/mg), together with a significantly lower apparent affinity constant (1.02+/- 0.08 vs. 1. 36+/-0.09 nM), was detected in hippocampus but not in frontal cortex from the depressed suicides compared to the control subjects. Furthermore, IP(3) concentrations were significantly increased in hippocampus (3.2+/-0.3 vs. 2.1+/-0.3 pmol/g) but not in frontal cortex (1.3+/-0.3 vs. 2.7+/-0.5 pmol/g) from the suicide victims. The reported results may indicate a significant hypersensitivity of the 5-HT(2A) postsynaptic receptor located in the hippocampus from depressed suicide victims, giving rise to an enhancement of its intracellular signaling system with higher IP(3) production.

The current status of the platelet 5-HT(2A) receptor in depression

The author reviews the current status of the platelet serotonin (5-HT)(2A) receptor in depression. Considered are studies of receptor binding, and 5-HT-induced platelet activation and aggregation. 5-HT(2A) receptor density tends to increase in depression, although this more clearly relates to suicidality than depression per se. Indeed, data are consistent with the hypothesis that increased density of platelet 5-HT(2A) receptors may be a marker for increased risk of suicide. 5-HT-induced calcium mobilization is enhanced in unipolar depression; however, unlike in bipolar depression, baseline calcium levels are not. Despite inconsistencies, 5-HT-induced aggregation appears inhibited in depression. This may manifest as a relative inhibition, i.e. no change in aggregation response despite a higher density of 5-HT(2A) receptors. The inhibited aggregation response is state dependent, and acute phase proteins or components of the stress response may be factors. It is unclear if differences between depressed and normal subjects in disposition of 5-HT(2A) receptors are generally indicative of traits or states. Nonetheless, there is little evidence that the degree of departure from normal density or activity of platelet of 5-HT(2A) receptors reflects severity of depression.