Platelet-5HT uptake and gastrointestinal symptoms in patients suffering from major depression

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.

Enteric Microbiota-Mediated Serotonergic Signaling in Pathogenesis of Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a chronic functional disorder that affects the gastrointestinal tract. Details regarding the pathogenesis of IBS remain largely unknown, though the dysfunction of the brain-gut-microbiome (BGM) axis is a major etiological factor, in which neurotransmitters serve as a key communication tool between enteric microbiota and the brain. One of the most important neurotransmitters in the pathology of IBS is serotonin (5-HT), as it influences gastrointestinal motility, pain sensation, mucosal inflammation, immune responses, and brain activity, all of which shape IBS features. Genome-wide association studies discovered susceptible genes for IBS in serotonergic signaling pathways. In clinical practice, treatment strategies targeting 5-HT were effective for a certain portion of IBS cases. The synthesis of 5-HT in intestinal enterochromaffin cells and host serotonergic signaling is regulated by enteric resident microbiota. Dysbiosis can trigger IBS development, potentially through aberrant 5-HT signaling in the BGM axis; thus, the manipulation of the gut microbiota may be an alternative treatment strategy. However, precise information regarding the mechanisms underlying the microbiota-mediated intestinal serotonergic pathway related to the pathogenesis of IBS remains unclear. The present review summarizes current knowledge and recent progress in understanding microbiome–serotonin interaction in IBS cases.

The 5-HTTLPR polymorphism, platelet serotonin transporter activity and platelet serotonin content in underweight and weight-recovered females with anorexia nervosa

Serotonin (5-HT) pathways play an important role in the pathophysiology of anorexia nervosa (AN). In this study, we investigated functional characteristics of the platelet 5-HT transporter and platelet 5-HT content in AN patients at various stages of their illness in comparison to healthy control woman (HCW) controlling for the 5-HTTLPR deletion/insertion polymorphism and other confounding variables. Fasting blood samples of 58 acutely underweight AN patients (acAN, BMI = 15.2 ± 1.4), 26 AN patients of the initial acAN sample after short-term/partial weight restoration (BMI = 17.3 ± 0.9), 36 weight-recovered AN patients (recAN, BMI = 20.7 ± 2.2) and 58 HCW (BMI = 21.6 ± 2.0) were assessed for kinetic characteristics of platelet 5-HT uptake (V (max), K (m)) and platelet 5-HT content. Plasma leptin served as an indicator of malnutrition. Mean V (max) and K (m) values were significantly higher in recAN subjects in comparison to HCW (2.05 ± 0.62 vs. 1.66 ± 0.40 nmol 5-HT/10(9) platelets min and 432 ± 215 vs. 315 ± 136 nmol, respectively) but there were no differences in platelet 5-HT content (464.8 ± 210.6 vs. 472.0 ± 162.2 ng 5-HT/10(9) platelets). 5-HT parameters in acAN patients and HCW were similar. 5-HTTLPR variants were not related to 5-HT platelet variables. In the longitudinal part of the study we found significantly increased 5-HT content but unchanged 5-HT uptake in AN patients after short-term/partial weight restoration. Our results highlight the importance of malnutrition for the interpretation of abnormalities in neurotransmitter systems in AN. Changes in platelet 5-HT transporter activity were related to the stage of the illness but not to 5-HTTLPR genotype. Increased V (max) and K (m) in recovered AN patients might mirror adaptive modulations of the 5-HT system.

Serotonin transporter activity and serotonin concentration in platelets of patients with irritable bowel syndrome: effect of gender

BACKGROUND

In the past decade, a strong argument has been built for the role of serotonin (5HT) and the serotonin transporter (SERT) in irritable bowel syndrome (IBS). However, it is still not clear how SERT contributes to this clinically heterogeneous disease. The present study addressed this issue by implementing platelet (plt) markers of SERT activity in the assessment protocol.

METHODS

Fasting blood samples of 149 (51 male/98 female) subjects with Rome II and III defined IBS subtypes, and 163 healthy control subjects (CSs; 75 male/88 female) were analyzed for platelet 5HT concentration and 5HT uptake activity [maximum uptake rate (V (max)) and affinity constant (K (m))].

RESULTS

Gender had a significant impact on platelet markers of SERT activity. Male IBS patients showed significantly lower median V (max) and K (m) values than the male CS (V (max) 1.706 vs. 2.148 nmol/10(9) plts x min, P < 0.001; K (m) 346 vs. 410 nmol, P = 0.008) without any significant reduction in platelet 5HT concentration (362 vs. 394 ng/10(9) plts). On the other hand, V (max) values were not different between female IBS patients and female CS (1.642 vs. 1.741 nmol/10(9) plts x min), but platelet 5HT concentration was significantly lower in females with diarrhea-predominant IBS (363 vs. 435 ng/10(9) plts, P < 0.05).

CONCLUSION

Although an absolute extrapolation from platelets to the gastrointestinal tissue does not appear to be justified, our findings demonstrated that the contribution of disturbed SERT activity to IBS is not uniform and is possibly gender-specific. The results suggest that an assessment of SERT function in platelets may help to elucidate the differences between IBS patients in response to drugs affecting the 5HT system.

Platelet serotonin uptake in drug-naïve depressive patients before and after treatment with citalopram

We investigated the kinetic parameters of serotonin (5-HT) uptake into platelets in a group of 26 drug-naïve patients suffering from major depression before and after 3-7 weeks of treatment with citalopram. The degree of depression was rated using the Hamilton Depression Rating Scale (HDRS). The 5-HT uptake characteristics in untreated depressive patients were not significantly different from those of normal subjects. The apparent Michaelis constant (K(M)) was significantly increased, the apparent maximal velocity (V(max)) was not different from baseline, and the uptake efficiency (V(max)/K(M)) was significantly decreased after citalopram treatment. A significantly positive correlation between K(M) and V(max) was found in all groups. There was a significantly lower V(max) and V(max)/K(M) in the female compared with the male depressed patients before citalopram treatment; a hypothesis was supported that lowered 5-HT uptake may reflect a gender-linked vulnerability to a serotonin-related depression. A significant negative correlation between 5-HT uptake efficiency and the initial HDRS score suggests that platelet 5-HT uptake can be used as a marker of effective depressive disorder pharmacotherapy. The initial severity of depression was significantly negatively correlated with V(max), which supported a hypothesis that the initial severity of depressive disorder could be related to the lower V(max).

Meta-analysis: a functional polymorphism in the gene encoding for activity of the serotonin transporter protein is not associated with the irritable bowel syndrome

BACKGROUND

Serotonin is associated with symptoms of the irritable bowel syndrome, its action is terminated by the serotonin transporter protein.

AIM

To assess the association between a functional polymorphism in the gene encoding for activity of the serotonin transporter protein and the irritable bowel syndrome.

METHODS

Meta-analysis of studies identified through a Medline, PubMed and Web of Science search, describing the prevalence of a polymorphism in the serotonin transporter gene creating long and short alleles.

RESULTS

Eight eligible studies described a total of 1034 patients with the irritable bowel syndrome, and 1377 healthy controls. Presence of the short allele is not associated with an increased risk for the irritable bowel syndrome: OR 1.0; 95% CI: 0.7-1.4 for homozygous subjects, and OR 1.0; 95% CI: 0.8-1.2 for homozygous subjects and heterozygotes together. Although Caucasians and Asians had diverging genotypic frequencies, no association with the shot allele and irritable bowel syndrome was observed in subgroups: Asians OR 1.2; 95% CI: 0.9-1.6 and OR 1.1; 95% CI: 0.2-5.9; Caucasians OR 0.9; 95% CI: 0.5-1.7 and OR 0.9; 95% CI: 0.7-1.2, respectively, for homozygous subjects alone and for homozygous subjects and heterozygotes together.

CONCLUSION

A genetic polymorphism in the gene encoding for activity of the serotonin transporter protein is not associated with the irritable bowel.

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.

Brain and platelet serotonin transporter in humans-correlation between [123I]-ADAM SPECT and serotonergic measurements in platelets

Blood platelets are thought to be a useful peripheral model for investigating the central serotoninergic mechanisms associated with the serotonin transporter (SERT). On the other hand, an in vivo investigation of SERT in the human brain has been made possible by the development of several promising SPECT radioligands, such as [123I]-ADAM. The aim of the present study was to investigate the possible correlation between the SERT measurements in the brain and those in platelets. Forty-four subjects (14 healthy subjects and 30 patients with the diagnosis of major depression or schizoaffective disorder) were examined. The [123I]-ADAM binding was assessed 4h after injection using MR-guided regions of interest (ROIs) in the midbrain and cerebellum. In a parallel investigation, serotonin (5HT) concentration and kinetic characteristics of 5HT uptake activity (Vmax and Km) were determined in platelet-rich plasma. Overall, there was no significant correlation between the V(max) of 5HT uptake in platelets and the specific to nonspecific partition coefficient of [123I]-ADAM (V''3) in the midbrain. However, low but significant Pearson correlation coefficients were found for V(max) and normalised activities measured in the midbrain (r=0.310, p=0.043). The correlation was stronger and significant in females (n=20, r=0.629, p=0.003) but low and non-significant in the 24 males (r=0.104). Although confirmation is necessary, it seems that the relationship between different indices of [123I]-ADAM binding in the brain and 5HT uptake characteristics in platelets is complex, nonuniform, and possibly gender-specific.