Platelet cytosolic calcium responses to serotonin in depressed patients and controls: relationship to symptomatology and medication

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.

The antidepressant 5-HT2A receptor antagonists pizotifen and cyproheptadine inhibit serotonin-enhanced platelet function

There is considerable interest in defining new agents or targets for antithrombotic purposes. The 5-HT_2A receptor is a G-protein coupled receptor (GPCR) expressed on many cell types, and a known therapeutic target for many disease states. This serotonin receptor is also known to regulate platelet function. Thus, in our FDA-approved drug repurposing efforts, we investigated the antiplatelet activity of cyproheptadine and pizotifen, two antidepressant 5-HT_2A Receptor antagonists. Our results revealed that cyproheptadine and pizotifen reversed serotonin-enhanced ADP-induced platelet aggregation in vitro and ex vivo. And the inhibitory effects of these two agents were found to be similar to that of EMD 281014, a 5-HT_2A Receptor antagonist under development. In separate experiments, our studies revealed that these 5-HT_2A receptor antagonists have the capacity to reduce serotonin-enhanced ADP-induced elevation in intracellular calcium levels and tyrosine phosphorylation. Using flow cytometry, we also observed that cyproheptadine, pizotifen, and EMD 281014 inhibited serotonin-enhanced ADP-induced phosphatidylserine (PS) exposure, P-selectin expression, and glycoprotein IIb-IIIa activation. Furthermore, using a carotid artery thrombosis model, these agents prolonged the time for thrombotic occlusion in mice in vivo. Finally, the tail-bleeding time was investigated to assess the effect of cyproheptadine and pizotifen on hemostasis. Our findings indicated prolonged bleeding time in both cyproheptadine- and pizotifen-treated mice. Notably, the increases in occlusion and bleeding times associated with these two agents were comparable to that of EMD 281014, and to clopidogrel, a commonly used antiplatelet drug, again, in a fashion comparable to clopidogrel and EMD 281014. Collectively, our data indicate that the antidepressant 5-HT_2A antagonists, cyproheptadine and pizotifen do exert antiplatelet and thromboprotective effects, but similar to clopidogrel and EMD 281014, their use may interfere with normal hemostasis.

Association of depressed mood and mortality in older adults with and without cognitive impairment in a prospective naturalistic study

OBJECTIVE

The authors examined predictors of mortality in individuals age 50 or older with or without cognitive impairment in a 12-year prospective naturalistic study of subcortical ischemic vascular disease focusing on symptoms of depressed mood, apathy, anhedonia, or anergia.

METHOD

A total of 498 participants were recruited from the community and from memory clinics into a multicenter longitudinal study of subcortical ischemic vascular disease. For baseline cognitive status, 36% of participants were assessed as cognitively intact, 31% as cognitively impaired, and 33% as demented. All participants underwent a research protocol MRI, and 41% were classified as having subcortical lacunes. Depressed mood, anhedonia, anergia, and apathy were assessed at baseline using a structured behavioral assessment. Cox regression models were used to investigate the associations between neuropsychiatric symptoms and mortality, controlling for age, gender, race, education level, cognitive status, presence of vascular lacunes, and vascular risk factors.

RESULTS

Of 498 participants, 175 (35%) died over the follow-up period, with a median survival time of 5.6 years. In the multivariate analyses, cognitive impairment, age, male gender, depressed mood, and the presence of lacunes predicted higher mortality. Participants with both lacunes and depressed mood had the shortest survival among all cognitive groups. The mortality hazard ratio for participants with depressed mood was 2.2 (95% CI=1.5-3.2) after adjustment for cognitive status, age, gender, education level, race, lacunes, and all vascular conditions.

CONCLUSIONS

These findings suggest the importance of detecting depressed mood in individuals with cerebrovascular disease and of developing more aggressive treatment and preventive interventions for this vulnerable population.

PI-PLC signal pathway: a possible pathogenesis link post-myocardial infarction to depression

Depressive disorder in the post-myocardial infarction (MI) period has been associated with increased cardiac morbidity and mortality. The most prominent findings are the increased mortality in patients with depression after myocardial infarction. Despite the extensive studies, the possible pathophysiologic mechanisms behind this association have not been clear. More recently, the data have suggested that both depression and post-MI have been associated with an increased activation status of the platelet. And increased sensitivity to platelet activation has been postulated as one of the mechanisms that may underlie increased vulnerability of depressed post-MI patients to cardiac events, suggesting a pathophysiologic cross-talk between the heart and the brain. Considering the similar changes in serotonin(5-HT) and platelet activation through phosphoinositide (PI)-phospholipase C(PLC) pathway, we guess that PI-PLC signal transduction pathway is a common pathogenesis between depression and post-MI, which mediated by 5-HT resulting in the platelet activation. The article introduces the hypothesis that proposes one possibility. This common mechanism of signal pathway may develop other current theories which are beneficial to future therapies to reduce post-MI depression.

Serotonin-induced decrease of intracellular Ca(2+) release in platelets of bulimic patients normalizes during treatment

Numerous symptoms related to eating disorders have been shown to be influenced by serotonergic (5-HT) functioning, with the 5-HT(2A) receptor subtype being one of the most relevant involved in the pathophysiology of bulimia nervosa (BN). In line with this, Ca(2+) mobilization as mediated by 5-HT(2) receptors in platelets was shown to serve as a peripheral model for central nervous 5-HT functioning. Here, the 5-HT-induced intracellular Ca(2+) mobilization in platelets was measured in 13 female normal weight bulimic patients (14-18 years) upon admission and at the end of inpatient treatment. Findings were compared to 21 age-matched healthy female adolescents. 5-HT-induced Ca(2+) release was significantly decreased in bulimic patients upon admission and normalized during inpatient treatment. Antidepressive medication caused a significant improvement. The data provide further evidence that altered 5-HT(2) receptor functioning is involved in the pathophysiological underpinnings in BN.

Modulation of phosphoinositide-protein kinase C signal transduction by omega-3 fatty acids: implications for the pathophysiology and treatment of recurrent neuropsychiatric illness

The phosphoinositide (PI)-protein kinase C (PKC) signal transduction pathway is initiated by pre- and postsynaptic Galphaq-coupled receptors, and regulates several clinically relevant neurochemical events, including neurotransmitter release efficacy, monoamine receptor function and trafficking, monoamine transporter function and trafficking, axonal myelination, and gene expression. Mounting evidence for PI-PKC signaling hyperactivity in the peripheral (platelets) and central (premortem and postmortem brain) tissues of patients with schizophrenia, bipolar disorder, and major depressive disorder, coupled with evidence that PI-PKC signal transduction is down-regulated in rat brain following chronic, but not acute, treatment with antipsychotic, mood-stabilizer, and antidepressant medications, suggest that PI-PKC hyperactivity is central to an underlying pathophysiology. Evidence that membrane omega-3 fatty acids act as endogenous antagonists of the PI-PKC signal transduction pathway, coupled with evidence that omega-3 fatty acid deficiency is observed in peripheral and central tissues of patients with schizophrenia, bipolar disorder, and major depressive disorder, support the hypothesis that omega-3 fatty acid deficiency may contribute to elevated PI-PKC activity in these illnesses. The data reviewed in this paper outline a potential molecular mechanism by which omega-3 fatty acids could contribute to the pathophysiology and treatment of recurrent neuropsychiatric illness.

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.

Psychosocial factors and cardiovascular diseases

Rapidly accruing evidence from a diversity of disciplines supports the hypothesis that psychosocial factors are related to morbidity and mortality due to cardiovascular diseases. We review relevant literature on (a) negative emotional states, including depression, anger and hostility, and anxiety; (b) chronic and acute psychosocial stressors; and (c) social ties, social support, and social conflict. All three of these psychosocial domains have been significantly associated with increased risk of cardiovascular morbidity and mortality. We also discuss critical pathophysiological mechanisms and pathways that likely operate in a synergistic and integrative way to promote atherogenesis and related clinical manifestations. We conclude by discussing some of the important challenges and opportunities for future investigations.

Whole blood serotonin and platelet activation in depressed post-myocardial infarction patients

Depression is an independent risk factor for post myocardial infarction (MI) mortality. Abnormalities in platelet function have been proposed as one of the mechanisms involved in increased cardiovascular risk among patients with depression post-MI. Depression in somatically healthy patients has been associated with increased platelet activation. Some but not all studies showed changes in blood serotonin level. Increased platelet activation and blood serotonin level have been associated with increased risk of cardiac events in patients with MI. The goal of this study was to investigate whether 1) depressed post-MI patients have higher markers of platelet activation as measured by plasma levels of beta-thromboglobulin (betaTG), platelet factor 4 (PF4) and soluble CD40 ligand (sCD40L) and higher serotonin (5-HT) levels than non-depressed post-MI patients and 2) treatment with the antidepressant mirtazapine decreases platelet activation. In this study, 25 depressed post-MI patients were asked for blood collection before start as well as after 8 weeks treatment with mirtazapine or placebo. The control group (n=22) consisted of non-depressed post-MI patients, matched for age, gender and time elapsed since MI. Plasma levels of betaTG, PF4 and sCD40L were not statistically different between the groups, but 5-HT levels were significantly higher in depressed patients. Treatment with mirtazapine resulted in a non-significant decrease in betaTG and PF4 and platelet 5-HT levels. Platelet and whole blood 5-HT, but not platelet activation was significantly increased in depressed post-MI patients. Treatment with mirtazapine showed a non-significant decrease in platelet activation and platelet 5-HT.

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.

SSRI Treatment—Associated Stroke: Causality Assessment in Two Cases

OBJECTIVE:

To assess the probability of cerebrovascular adverse drug reactions (CV-ADRs) due to treatment with selective serotonin-reuptake inhibitors (SSRIs) using 2 causality methods.

CASE SUMMARIES:

Two patients with the possibility of SSRI-related stroke were referred for causality assessment. Causality assessment was performed using an adverse drug reaction probability scale, as well as clinical and radiologic parameters. A 31–year-old white man, who had been receiving paroxetine 200 mg/day over a period of 3 years, developed ischemic stroke involving left middle cerebral artery. The second patient was a 46–year-old white woman with a history of recurrent depression who developed delirium and ischemic stroke while she was taking a combination of paroxetine 50 mg/day, trazodone 200 mg/day, and bupropion 150 mg/day.

DISCUSSION:

Carotid and cardiothromboembolism were found to be the major etiological factors for ischemic stroke. Accounting for the temporal relation, prior reports of SSRI treatment—associated CV-ADRs, and the pharmacologic action of serotonin on coagulation and the vascular system, the possible contribution of SSRIs to stroke in these patients was considered. An objective causality assessment using the Naranjo probability scale revealed that a CV-ADR was possible. However, the nature of the stroke, plus clinical and radiologic findings, were inconsistent with known pathophysiologic mechanisms linking SSRIs and stroke in these patients.

CONCLUSIONS:

Causality assessment may improve unbiased recognition, management, and voluntary reporting of infrequent adverse effects such as SSRI treatment—related cerebrovascular accident.

The platelet window: examining receptor regulated second messenger processes in psychosis and depression

Peripheral markers of psychiatric illness provide a potentially important window into the pathophysiology of a number of psychiatric illnesses. Direct access to pathophysiological processes is fraught with difficulty. However, receptor-regulated second messenger-mediated calcium shifts are an accessible and practical method by which to examine changes in a clinical population. This is possible because platelets and neurons share some physiological features. The platelet intracellular calcium response to receptor stimulation has previously been used as a peripheral marker of psychiatric illness across a range of neurotransmitters, including serotonin, dopamine and glutamate. This review considers the specificity and selectivity of this response and its use in psychotic and mood 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.

Platelet 5-HT2A-receptor-mediated induction of aggregation is not altered in major depression

BACKGROUND

Studies of the 5-HT(2A) receptor subtype in major depression have focused on the density of these receptors in neuronal cells and platelets, showing an up-regulation secondary to a deficit in serotonergic activity in major depression. However, their functional state has often been disregarded. The aim of the study was to investigate whether depressed patients show abnormalities in the function of the 5-HT(2A) receptor pathway in platelets.

METHOD

The percentage of serotonin-amplified platelet aggregation to adenosine diphosphate (ADP) was assessed in 30 untreated patients with major depressive disorder and in 15 controls. Since 5-HT(2A) platelet receptors mediate the serotonin-induced platelet aggregation response, this index was used as a measure of the functional status of the platelet 5-HT(2A) receptor pathway.

RESULTS

There was no significant difference in the percentage of serotonin-amplified platelet aggregation to ADP between depressed patients and controls. No correlation with the severity of depression, as assessed by the Hamilton scale, was found.

CONCLUSION

The results showed no consistent changes in the platelet aggregating responses to serotonin in the depressed patients. Therefore this study does not support the hypothesis of an alteration of the functional status of platelet 5-HT(2A) receptors in major depression.

Selective serotonin reuptake inhibitors and myocardial infarction

BACKGROUND

Depression is an independent risk factor for myocardial infarction (MI). Selective serotonin reuptake inhibitors (SSRIs) may reduce this risk through attenuation of serotonin-mediated platelet activation in addition to treatment of depression itself.

METHODS AND RESULTS

case-control study of first MI in smokers 30 to 65 years of age was conducted among all 68 hospitals in an 8-county area during a 28-month period. Cases were patients hospitalized with a first MI. Approximately 4 community control subjects per case were randomly selected from the same geographic area using random digit dialing. Detailed information regarding use of antidepressant medication as well as other clinical and demographic data were obtained by telephone interview. A total of 653 cases of first MI and 2990 control subjects participated. After adjustment, using multivariable logistic regression, for age, sex, race, education, exercise, quantity smoked per day, body mass index, aspirin use, family history of MI, number of physician encounters, and history of coronary disease, diabetes, hypertension, or hypercholesterolemia, the odds ratio for MI among current SSRI users compared with nonusers was 0.35 (95% CI 0.18, 0.68; P<0.01). Non-SSRI antidepressant users had a nonsignificant reduction in MI risk with wide confidence intervals (adjusted odds ratio 0.48, CI 0.17, 1.32; P=0.15). However, analysis of this group was limited by the small number of exposed subjects.

CONCLUSIONS

The use of SSRIs may confer a protective effect against MI. This could be attributable to the inhibitory effect SSRIs have on serotonin-mediated platelet activation or possibly amelioration of other factors associated with increased risk for MI in depression.

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.

Depression after myocardial infarction

Depression is an independent risk factor for increased postmyocardial infarction morbidity and mortality, even after controlling for the extent of coronary artery disease, infarct size, and the severity of left ventricular dysfunction. This risk factor takes on added significance when one considers that almost half of patients recovering from a myocardial infarction have major or minor depression and that major depression alone occurs in about one in five of these individuals. Despite the well-documented risk of depression, questions remain about the mechanism of the relationship between mood disturbance and adverse outcome. The link may be explained by an association with lower levels of social support, poor adherence to recommended medical therapy and lifestyle changes intended to reduce the risk of subsequent cardiac events, disturbances in autonomic tone, enhanced platelet activation and aggregation, and systemic immune activation. Unfortunately, questions about the pathophysiologic mechanism of depression in this setting are paralleled by uncertainties about the optimal treatment of depression for patients recovering from a myocardial infarction and by a lack of knowledge about whether treating depression lowers the associated increased mortality risk. Ongoing research studies will help to determine the benefits of psychosocial interventions and of antidepressant therapy for patients soon after myocardial infarction. Although the identification of depression as a risk factor may by itself be a reason to incorporate a comprehensive psychological evaluation into the routine care of patients with myocardial infarction, this practice should certainly become standard if studies show that treating depression reduces the increased mortality risk of these patients.

Protein kinase A and Rap1 levels in platelets of untreated patients with major depression

We have recently reported altered levels of protein kinase A and Rap1 in patients with bipolar disorder. The purpose of the current investigation was to assess the levels of these proteins in platelets from untreated euthymic and depressed patients with major unipolar depression. Platelets were collected from 45 drug-free unipolar patients (13 euthymic and 32 depressed) and 45 healthy subjects. The levels of protein kinase A and Rap1 were assessed by Western blot analysis, immunostaining and computer-assisted imaging. The immunolabeling of the regulatory subunit type II of protein kinase A and that of Rap1 was significantly lower in untreated depressed patients compared with untreated euthymic patients and healthy subjects. No significant differences were found in the immunolabeling of both the regulatory type I and the catalytic subunits of protein kinase A among groups. Levels of the regulatory subunit type II of protein kinase A and Rap1 are altered in platelets of unipolar depressive patients. These findings may provide new insight about the relationship between components of cAMP signaling and affective disorders.

Depression and ischemic heart disease

Major depression is a common comorbidity associated with ischemic heart disease (IHD). There is growing evidence that psychological stress in general and depression in particular predispose to cardiovascular disease. Persons who have mental stress during daily life are at twice the risk of myocardial ischemia, and patients with post-myocardial infarction depression have higher mortality rates than nondepressed controls. These data suggest a psychophysiologic mechanism underlying the vulnerability of depressed patients to IHD. Clinical studies have demonstrated that depression is associated with a much higher risk of both cardiovascular morbidity and mortality, which could be caused by platelet activation. Physicians should maintain a heightened level of clinical suspicion for depression and depressive disorders in persons with IHD, particularly those individuals who are recovering from an acute ischemic event, such as myocardial infarction. Furthermore, depression may complicate the recovery of IHD, but in most cases depression can be effectively treated with antidepressant agents.

Association between depressive symptoms and mortality in medical inpatients

The authors interviewed a consecutive series of medical inpatients (N = 241) using the Schedule for Affective Disorders and Schizophrenia to determine which depressive symptoms are associated with in-hospital mortality. Fifteen depressive symptoms, pain, and physical discomfort were assessed along with medical comorbidity. Twenty patients died in-hospital (8.3%). Logistic regression showed that anhedonia, hopelessness, worthlessness, indecisiveness, and insomnia predicted in-hospital death after adjusting for physical comorbidity and age. Clinicians should be aware that these depressive symptoms may predict mortality in medical inpatients. Future studies should address which treatment modalities lead to better outcomes.

Platelet supersensitivity to thrombin stimulation in depression: a possible mechanism for the association with cardiovascular mortality

The mortality risk associated with cardiovascular disease is significantly increased in patients with major depression and panic disorder. The mechanism of this phenomenon is unclear. Thrombin is responsible for platelet aggregation and shape change, and it plays a significant role in the development of thromboembolic events. In this study, we examined the platelet second messenger intracellular calcium response to thrombin stimulation in patients with major depression (n = 13), major depression after response to electroconvulsive therapy (ECT; n = 13), subsyndromal depression (n = 16), schizophrenia (n = 15), and control subjects (n = 65). Patients with major depression had significantly higher intracellular calcium responses to thrombin stimulation than control subjects, patients with subsyndromal depression, and patients with schizophrenia (p < 0.05). Electroconvulsive therapy did not significantly change this supersensitivity. This suggests that the platelet response to activation in patients with major depression is supersensitive. This study suggests a possible mechanism for the increased risk of cardiovascular disease that is seen in these two psychiatric disorders. The lack of difference between the control and subsyndromal depression groups appears to validate current diagnostic thresholds in depression. The failure of nonpharmacologic treatment to alter this marker suggests that it may be a trait marker of depression.

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.

Platelet cytosolic calcium hyperresponsivity to serotonin in patients with hypertension and depressive symptoms

BACKGROUND

Data from recent studies indicate that the presence of depression is an independent risk factor for cardiovascular and cerebrovascular events. The mechanism by which depression increases the morbidity and mortality risks in patients with comorbid vascular disease is currently the object of considerable research interest. Platelets may be involved in this pathological process. Although many investigators have extensively evaluated platelet biochemistry in depressed patients, there currently exists very little information regarding how the biochemical alterations might relate to an increased risk of cardiovascular events. In this study, we examined the responsivity of platelet cytosolic calcium concentrations ([Ca++]i) to serotonin stimulation in populations of hypertensive patients with or without comorbid depressive symptoms.

METHODS

We utilized Fura-2 loaded platelets to compare changes in intracellular calcium levels (delta [Ca++]i) following serotonin stimulation among 48 patients with hypertension and varying degrees of depressive symptomatology.

RESULTS

We found that those patients with higher scores on standardized depression rating scales showed significantly greater [Ca++]i (82.82 +/- 15.88 mmol/L) increase compared with [Ca++]i (60.10 +/- 22.65 mmol/L) patients with lower depression scores.

CONCLUSIONS

The results of this study support the hypothesis that the enhanced platelet reactivity seen in patients with depressive symptoms may mediate the deleterious effects of depression on cardiovascular disease.