Platelet alpha-2 adrenoceptor-mediated primary aggregation and adenylate cyclase inhibition in 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.

Evaluation of peripheral serotonin content and α2-adrenergic receptor function as potential markers for life-long recurrent depressive disorder by using methodological improvements

OBJECTIVE

We aimed to evaluate the role and the relations between peripheral platelet serotonin content, blood plasma serotonin concentration and the function of platelet α₂-adrenergic receptors (α₂-AR) as potential state or trait biomarkers for recurrent depressive disorder (RDD).

METHODS

26 drug-free patients with life-long RDD and 31 healthy controls were included in the study. Several methodological improvements in blood collection and platelet isolation were implemented following the present standards in Haematology and Light transmission aggregometry.

RESULTS

Our results have shown lower platelet serotonin content, higher plasma serotonin concentration and desensitization of platelet α₂-AR in patients with RDD. The variables were found heterogeneous and mainly influenced by the clinical characteristics of the current episode. High amplitude of the α₂-AR correlated with severe anxious symptoms and high platelet serotonin content (as well as low plasma serotonin levels) were associated with psychotic symptoms.

CONCLUSIONS

The evaluated peripheral markers reflect only state (but not trait) abnormalities in patients with current severe episode of RDD. The observed peripheral α₂-AR and serotonin abnormalities are mutually not related and they are probably triggered by different mechanisms.

SSRI-reduced platelet reactivity in non-responding patients with life-long Recurrent Depressive Disorder: Detection and involved mechanisms

INTRODUCTION

Adverse effects with bleeding disorders are often associated with the administration of SSRI in depression, although the exact mechanisms remain contradicting. This study is aimed at detecting and exploring the mechanisms of SSRI-induced changes in platelet reactivity in non-responding patients with Recurrent Depressive Disorder (RDD) and life-long exposure to antidepressants.

MATERIALS AND METHODS

Thirty-one patients and thirty-one healthy controls were included in the study. A comprehensive approach which includes evaluation of peripheral markers and microscopic analyses of platelet morphology changes has been used.

RESULTS

RDD SSRI patients have shown blunted aggregatory responses towards collagen and epinephrine. Evident differences in the microscopic evaluation of platelet morphology were observed between the groups, with inherent absence of micro-aggregates and platelet shape changes within the patients; after quantification, the sensitivity and specificity of this method were assessed as high. The abnormalities were found in association with lower platelet serotonin content and high fluctuations of free plasma serotonin levels. Changes in the levels of CRP, fibrinogen and nitric oxide were not observed. Macroplatelets were also detected within RDD SSRI patients via increased MPV, PDW and P-LCR, which were associated with discoid shape and without procoagulant activity.

CONCLUSIONS

The microscopic evaluation might be useful as a simple method for detection of SSRI-reduced platelet function for research purposes or systematic correlations with other biochemical parameters. The mechanisms involved in SSRI-reduced platelet function in non-responding RDD patients are complex, including combined effects of lower platelet serotonin content, high fluctuations in plasma serotonin concentration and abnormal α-AR function.

[Correlation of depression with stroke. Pathophysiological mechanisms]

Stroke is the third leading cause of death, just after heart disease and cancer. Its incidence will probably increase dramatically in the coming decades. For prevention it is urgently necessary to gain fundamental knowledge about the risk factors and pathophysiological mechanisms. It is now widely accepted that depression and stroke are correlated with each other. There is little knowledge, however, about the links that might connect both diseases. This review discusses different mechanisms that lead to an increased stroke risk and can be influenced by depression as well thus possibly linking depression and stroke.

Platelet hyperactivity in clinical depression and the beneficial effect of antidepressant drug treatment: how strong is the evidence?

OBJECTIVE

Platelet hyperactivity is thought to contribute to the increased coronary artery disease (CAD) risk in depression. This study reviewed the evidence for hyperactive platelets and for effects of antidepressant drug treatment on platelet 'stickiness' in clinical depression.

METHOD

By means of PubMed electronic library search, 34 studies in English were identified (1983-2003) and critically reviewed.

RESULTS

In depression, flow cytometry studies allowing detection of subtle platelet activation states consistently found at least one platelet activation marker to be increased, while the bulk of platelet aggregation studies did not suggest increased platelet aggregability. Platelets seem to be more activated in depressed patients with CAD than in depressed individuals without CAD. The selective serotonin reuptake inhibitors normalized platelet hyperactivity in four studies.

CONCLUSION

Data on platelet activity in depression are inconclusive. To resolve this issue and its clinical implications, studies in larger sample sizes controlling for confounders of platelet functioning and prospectively designed are needed.

Stress, norepinephrine and depression

Experimental and clinical evidence implicates stress as a major predisposing factor in depression and other severe psychiatric disorders. In this review, evidence is presented to show how the impact of stress on the central sympathetic system leads to changes in the endocrine, immune and neurotransmitter axes which underlie the main clinical symptoms of depression. Thus it can be shown that the noradrenergic system is dysfunctional in depression, a situation which reflects the chronic hypersecretion of glucocorticoids and inflammatory mediators within the brain in addition to an enhanced activity of the locus ceruleus. With regard to the actions of antidepressants in modulating the stress response and alleviating depression it is now evident that, irrespective of the presumed specificity of the antidepressants for the noradrenergic or serotonergic systems, they all normalize noradrenergic function. This action is due partly to the regulation of tyrosine hydroxylase activity in the locus ceruleus but also enhances neuronal sprouting which counteracts the neurodegenerative effects of chronic stress.