Adrenaline-induced platelet aggregation in depressed patients and control subjects

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.

Platelet function in patients with major depression

Depression, ischaemic heart disease and cerebrovascular disease are important causes of morbidity and are among the leading contributors to global health burden. These conditions often occur in the same patient, resulting in considerably greater effect on health than combinations of chronic diseases without depression. The frequent occurrence of these conditions in the same patient raises the possibility of a common genetic predisposition, similar risk factors or a pathophysiological link. Serotoninergic and adrenergic signalling play important roles in causing major depression and also in platelet activation and aggregation, which underlies vascular disease. This review discusses the potential pathophysiological link between major depression and conditions in which platelet activation plays an important role and also provides evidence linking the use of the most commonly used antidepressant drugs (i.e. the selective serotonin re-uptake inhibitors) to increased risk of bleeding.

Platelet inhibition beyond conventional antiplatelet agents: expanding role of angiotensin receptor blockers, statins and selective serotonin reuptake inhibitors

Aspirin, dipyridamole, cilostazol, thienopyridines and glycoprotein IIb/IIIa inhibitors represent the classical examples of the established antiplatelet agents commonly used for the secondary prevention in patients after vascular events. Obviously, the era of expanding antiplatelet regimens and indications may require new agents as the substitutes, or additions to the available strategies. However, recent results of the majority of antiplatelet trials strongly suggest boarder line advantages in clinical outcomes, and higher associated bleeding risks with the novel antiplatelet agents or/and regimens. Moreover, unexpected failures, such as lack of efficacy of clopidogrel and aspirin combination for ischaemic stroke prevention (MATCH), or use of the same antiplatelet regimen for the primary vascular prevention (CHARISMA) raise legitimate concerns that the concept 'the more the better' may not be valid. Broad use of statins, angiotensin receptor blockers and selective serotonin reuptake inhibitors may be in part responsible for the lack of impressive results with the antiplatelet therapy because each of these drug classes per se inhibits platelets. In this review, we discuss the available evidence and potential clinical significance of these findings.

Escitalopram, but not its major metabolites, exhibits antiplatelet activity in humans

BACKGROUND

Clinical depression has been identified as an independent risk factor for increased mortality during follow-up in patients suffered from acute coronary events, whereas increased platelet activity has been proposed as one of the mechanisms for this association. Some evidence suggests that selective serotonin reuptake inhibitors and/or their metabolites exhibit potent antiplatelet properties.

METHODS

We assessed the in vitro effects of preincubation with escalating (50-200 nmol/L) concentrations of escitalopram (ESC) S-desmethyl-citalopram (S-DCT), and S-di-desmethyl-citalopram, (S-DCT) on platelet aggregation through the expression of major surface receptors using flow cytometry and quantitatively using platelet function analyzers in 20 healthy volunteers.

RESULTS

Pretreatment of blood samples with ESC with ESC resulted in a significant inhibition of platelet aggregation induced by ADP (P = 0.0001) and by collagen with the highest dose (P = 0.001). Surface platelet expressions of glycoprotein Ib (CD42) (P = 0.04), lysosome associated membrane protein-3 (CD63) (P = 0.02), and GP37 (CD165) (P = 0.03) was decreased in the ESC-pretreated samples. Closure time by the Platelet Function Analyzer-100 analyzer was prolonged for the 200 nmol/L dose (P = 0.02), indicating platelet inhibition under high shear conditions. Two major metabolites of ESC, namely S-DCT and S-DDCT, did not affect platelet activity.

CONCLUSION

Escitalopram, but not its metabolites, exhibited selective inhibition of human platelet properties. The direct antiplatelet effect of ESC requires further prospective or ex vivo testing to determine the possible clinical advantage of this finding.

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.

Circulating neurotransmitters during the different wake-sleep stages in normal subjects

We investigated the changes of circulating neurotransmitters during the wake-sleep cycle in order to find possible correlations with the activity of central neurocircuitry functioning. Noradrenaline (NA), adrenaline (Ad), dopamine (DA), platelet serotonin (p-5HT), plasma serotonin (f-5HT) and plasma tryptophan (TRP) were assessed during the morning (supine resting + 1-min orthostasis + 5-min exercise) and at night (supine resting + slow wave sleep (SWS) + REM sleep). Only NA increased in the plasma during short-lasting (1-min) orthostasis morning waking period. Both NA and Ad rose during moderate exercise. The nocturnal results demonstrated that whereas Ad dropped during the supine resting, NA did not fall until SWS period. Although DA did not show significant changes during the nocturnal test, the NA/DA ratio showed significant reduction. The analysis of correlations supports the postulation that this finding reflects the DA modulatory role on neural sympathetic activity. Both f-5HT and p-5HT values were lower during sleep cycle than wake periods. However, they showed progressive rises during sleep stages. Conversely, the f-5HT/p-5HT ratio showed significantly greater values during the SWS period than during supine resting and REM periods. These findings are consistent with the postulation that f-5HT/p-5HT ratio is positively associated with parasympathetic activity during the sleep-cycle. We concluded that the profile of sleep-cycle circulating neurotransmitters differs from that obtained during waking periods. According to the above, we attempted to correlate the profile of circulating neurotransmitters with the very well-known central neurocircuitry functioning during wake-sleep cycle, in experimental mammals.

Platelet inhibition by sertraline and N-desmethylsertraline: a possible missing link between depression, coronary events, and mortality benefits of selective serotonin reuptake inhibitors

Recently, clinical depression has been identified as an independent risk factor for increased mortality in patients following acute coronary events. Although the underlying mechanisms of this link remain uncertain, increased platelet activity has been suggested but never proven as the mechanism responsible for this association. Sertraline hydrochloride is a selective serotonin reuptake inhibitor (SSRI), and is an effective antidepressant agent. Its major liver metabolite, N-desmethylsertraline (NDMS), is known to be neurologically inactive. We assessed the in vitro effects of escalating concentrations of sertraline and NDMS on human platelets by aggregometry in plasma and whole blood, by expression of major surface receptors with flow cytometry in washed cells and in the whole blood, and quantitatively by various platelet function analysers in healthy volunteers and patients with coronary artery disease. Pretreatment of blood samples with sertraline and NDMS resulted in a dose-dependent inhibition of platelet-rich plasma aggregation induced by 5 microM ADP (P =, 0.002), by 10 microM ADP (P = 0.0017), by collagen (P = 0.008), and by thrombin (P = 0.026). Whole blood platelet aggregability was also significantly reduced when induced by 20 microM ADP (P = 0.006), and by collagen (P = 0.01). Surface expression of CD9 (P = 0.004), GP Ib (P = 0.0001), GP IIb/IIIa (P = 0.007), VLA-2 (P = 0.01), P-selectin (P = 0.02), and PECAM-1 (P = 0.01), but not the vitronectin receptor, was also reduced in sertraline and NDMS pretreated washed platelets. Whole blood flow cytometry revealed significant inhibition of GP IIb/IIIa (P = 0.008), and P-selectin expression (P = 0.0001) in NDMS treated samples. Closure time was delayed for the collagen-ADP cartridge (P = 0.009), and for the collagen-epinephrin cartridge (P = 0.01), indicating platelet inhibition in whole blood under high shear conditions. Rapid platelet-function assay revealed a decreased (P = 0.002) ability of platelets to agglutinate fibrinogen-coated beads, suggesting GP IIb/IIIa inhibition. Both sertraline, and its neurologically inactive metabolite NDMS, exhibited significant dose-dependent inhibition of human platelets. The documented anti-platelet effects of sertraline and NDMS may be directly related to the mortality benefits of SSRIs after ischemic events including myocardial infarction and stroke.

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.

Blood coagulation and platelet aggregation in major depression

Recently, it was found that the plasma of depressed patients significantly reduced the primary and secondary platelet aggregation to aggregating agents, such as ADP and collagen, in platelet rich plasma (PRP) of normal volunteers. Other authors found significantly decreased maximum amplitudes of adrenaline-induced platelet aggregation in major depressed patients versus normal controls. The aim of the present study was to examine platelet aggregation and blood coagulation in depression. Toward this end, the authors have measured secondary platelet aggregation to ADP and collagen, and the activated partial thromboplastin time (APTT) and prothrombin time (PT) in 16 normal volunteers, 16 minor, 40 simple major and 23 melancholic subjects. There were no significant differences in ADP- or collagen-induced platelet aggregability, APTT or PT between normal controls, minor, simple major or melancholic depressed patients. There were no significant relationships between severity of depression and APTT, PT or platelet aggregability to ADP or collagen. It is concluded that blood coagulation and platelet aggregability to ADP and collagen are probably not disordered in major depression.