Decreased platelet [3H]paroxetine binding sites in suicide attempters

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 complex interactions among serotonin, insulin, leptin, and glycolipid metabolic parameters in human obesity

OBJECTIVE

To provide evidence to the link between serotonin (5-HT), energy metabolism, and the human obese phenotype, the present study investigated the binding and function of the platelet 5-HT transporter (SERT), in relation to circulating insulin, leptin, and glycolipid metabolic parameters.

METHODS

Seventy-four drug-free subjects were recruited on the basis of divergent body mass index (BMIs) (16.5-54.8 Kg/m2). All subjects were tested for their blood glycolipid profile together with platelet [3H]-paroxetine ([3H]-Par) binding and [3H]-5-HT reuptake measurements from April 1st to June 30th, 2019.

RESULTS

The [3H]-Par Bmax (fmol/mg proteins) was progressively reduced with increasing BMIs (P < .001), without changes in affinity. Moreover, Bmax was negatively correlated with BMI, waist/hip circumferences (W/HC), triglycerides (TD), glucose, insulin, and leptin, while positively with high-density lipoprotein (HDL) cholesterol (P < .01). The reduction of 5-HT uptake rate (Vmax, pmol/min/109 platelets) among BMI groups was not statistically significant, but Vmax negatively correlated with leptin and uptake affinity values (P < .05). Besides, [3H]-Par affinity values positively correlated with glycemia and TD, while [3H]-5-HT reuptake affinity with glycemia only (P < .05). Finally, these correlations were specific of obese subjects, while, from multiple linear-regression analysis conducted on all subjects, insulin (P = .006) resulting negatively related to Bmax independently from BMI.

CONCLUSIONS

Present findings suggest the presence of a possible alteration of insulin/5-HT/leptin axis in obesity, differentially impinging the density, function, and/or affinity of the platelet SERT, as a result of complex appetite/reward-related interactions between the brain, gut, pancreatic islets, and adipose tissue. Furthermore, they support the foremost cooperation of peptides and 5-HT in maintaining energy homeostasis.

Research on potential biomarker correlates for suicidal behavior: A review

Suicide is a world health priority. Studies over the last few decades have revealed the complexity underlying the neurobiological mechanisms of suicide. Researchers have found dysregulations in the serotonergic system, the stress system, neural plasticity, lipid metabolism, and cell signaling pathways in relation to suicidal behaviors. These findings have provided more insight into the final path leading to suicide, at which medical intervention should be applied to prevent the action. However, because these molecular mechanisms have been implicated in both depression and suicide, the specificity of the mechanisms has been obscured. In this review, we summarize the main findings of studies on molecular mechanisms of suicidal behavior from the last 2 decades, with particular emphasis on the potential, independent role of each mechanism that is not contingent upon an underlying psychopathology, such as depression. The act of suicide is multifactorial; no single molecular mechanism is sufficient to fully account for the act. Knowledge of the reciprocal interactions among these molecular mechanisms and studying them in the context of brain circuitry by using neuroimaging techniques will provide a better understanding of the neurobiology of suicide.

The mechanism of antidepressant-like effects of piroxicam in rats

Objective:

To investigate the antidepressant-like effect of piroxicam with a focus on serotonergic neurotransmission.

Materials and Methods:

Rats were randomly distributed into the following groups: 0.9% saline control; 3 mg/kg pizotifen; 10 mg/kg sertraline; 10 mg/kg piroxicam; 10 mg/kg sertraline + 10 mg/kg piroxicam; 10 mg/kg sertraline + 3 mg/kg pizotifen; and 10 mg/kg piroxicam + 3 mg/kg pizotifen. All the drugs were dissolved in 0.9% saline. Three administrations of the drugs (piroxicam and sertraline) were performed 1, 5 and 24 h before testing the animals in the open field followed by the forced swim test (FST). Piroxicam and sertraline were administered orally by gavage and pizotifen was administered intraperitoneally 30 min before gavage. Immediately after the FST, the hippocampi were rapidly dissected for neurochemical analysis in high-performance liquid chromatography.

Results:

Acute treatment with piroxicam promoted an antidepressant-like effect in the FST, which was associated with an increase in serotonin levels in the hippocampus. This effect was potentiated in the piroxicam + sertraline group but counteracted by administration of the non-selective serotonin receptor antagonist pizotifen.

Conclusion:

These results suggest that the antidepressant-like effect of piroxicam in the FST is mediated by the serotonin system; however, by different mechanisms from those of sertraline.

A link between oxytocin and serotonin in humans: supporting evidence from peripheral markers

Pharmacological studies indicate a functional interaction between the serotonergic and oxytocinergic systems. In particular, some selective serotonin (5-HT) reuptake inhibitors, such as citalopram and fluvoxamine, seem to exert part of their antidepressant effects through oxytocin (OT) release. Further, the administration of fenfluramine, a serotonergic agonist, to healthy subjects increases plasma OT levels. Interestingly, immunocytochemical and double-immunofluorescent techniques revealed a high degree of overlap between 5-HT transporter (SERT)-labeled fibers and OT-containing cells in the paraventricular and supraoptic nuclei of primate hypothalamus. These findings suggest that the influence of 5-HT on OT system might be mediated by SERT. In this study, we explored the possible existence of a link between OT and SERT in human subjects, by means of two peripheral markers, the platelet SERT, as measured by [³H]-paroxetine ([³H]-Par) binding, and plasma OT levels. As far as [³H]-Par binding parameters are concerned, the Bmax (mean ± SD, fmol/mg protein) was 1155 + 130 and the Kd (mean ± SD, nM) was 1.31 ± 0.61. The OT plasma levels (mean ± SD, pg/ml) were 1.14 ± 1.07. A significant and positive correlation was found between plasma OT levels and Kd values (correlation coefficient: r: 0.466, p = .038). This result represents the first evidence of an interaction between OT and SERT, as measured by [³H]-Par binding, at peripheral levels in humans. Given the several activities mediated by both OT and 5-HT, such a relationship might provide new perspectives and insights into psychiatric disorders and/or social relationship disturbances, as well as novel treatment strategies overcoming and/or integrating the serotonergic paradigm.

Serotonin transporter (SERT) and translocator protein (TSPO) expression in the obese ob/ob mouse

Background

An ever growing body of evidences is emerging concerning metabolism hormones, neurotransmitters or stress-related biomarkers as effective modulators of eating behavior and body weight in mammals. The present study sought at examining the density and affinity of two proteins related to neurotransmission and cell metabolism, the serotonin transporter SERT and the cholesterol import-benzodiazepine site TSPO (translocator protein), in a rodent leptin-lacking mutant, the obese ob/ob mouse. Binding studies were thus carried out in brain or peripheral tissues, blood platelets (SERT) and kidneys (TSPO), of ob/ob and WT mice supplied with a standard diet, using the selective radiochemical ligands [³H]-paroxetine and [³H]-PK11195.

Results

We observed comparable SERT number or affinity in brain and platelets of ob/ob and WT mice, whilst a significantly higher [³H]-PK11195 density was reported in the brain of ob/ob animals. TSPO binding parameters were similar in the kidneys of all tested mice. By [³H]-PK11195 autoradiography of coronal hypothalamic-hippocampal sections, an increased TSPO signal was detected in the dentate gyrus (hippocampus) and choroids plexus of ob/ob mice, without appreciable changes in the cortex or hypothalamic-thalamic regions.

Conclusions

These findings show that TSPO expression is up-regulated in cerebral regions of ob/ob leptin-deficient mice, suggesting a role of the translocator protein in leptin-dependent CNS trophism and metabolism. Unchanged SERT in mutant mice is discussed herein in the context of previous literature as the forerunner to a deeper biochemical investigation.

Alteration of serotonin transporter density and activity in fibromyalgia

The aim of the study was to evaluate the kinetic parameters of a specific serotonin transporter (SERT) and serotonin uptake in a mentally healthy subset of patients with fibromyalgia. Platelets were obtained from 40 patients and 38 healthy controls. SERT expression and functionality were evaluated through the measurement of [³H]paroxetine binding and the [³H]serotonin uptake itself. The values of maximal membrane binding capacity (B_max) were statistically lower in the patients than in the healthy volunteers, whereas the dissociation constant (K_d) did not show any statistically significant variations. Moreover, a decrease in the maximal uptake rate of SERT (V_max) was demonstrated in the platelets of patients, whereas the Michaelis constant (K_m) did not show any statistically significant variations. Symptom severity score (tiredness, tender points index and Fibromyalgia Impact Questionnaire) were negatively correlated with B_max and with V_max, and positively correlated with K_m. A change in SERT seems to occur in fibromyalgic patients, and it seems to be related to the severity of fibromyalgic symptoms.

No evidence for an association between serum cholesterol and the course of depression and suicidality

In a number of previous reports, an association of altered, in most cases lower, serum cholesterol levels with depression, suicidal ideation and current or past suicidal behavior has been suggested. In this investigation, the course of serum cholesterol concentrations was measured in depressed patients during treatment. Ninety-two inpatients with a major depressive episode were included. Serum lipid concentrations were assessed at admission, after 1 week and after 4 weeks of antidepressant treatment. Degrees of depression and suicidality were measured with the Hamilton Depression Rating Scale. Although there was a significant reduction in depression and suicidality scores, neither a significant change in serum cholesterol levels nor a correlation between cholesterol levels and clinical improvement was found. Further, there were no significant differences in lipid levels between patients with and without a history of attempted suicide. In patients who had used a violent method, there was a trend for lower total cholesterol levels compared to those who had poisoned themselves. The results of this study do not support the hypothesis of an association of serum cholesterol with the course of depression and suicidal ideation. Cholesterol levels do not appear to be an appropriate biological marker for suicidality during the first 4 weeks of treatment in patients with a major depressive episode.