Platelet Serotonin Transporter Research Articles

Platelet Activity In Elevated Plasma Seretonin Level

The serotonin transporter (SERT) on the platelet surface is the major mechanism for the uptake of plasma serotonin (5‐hydroxytryptamine; 5HT), which subsequently is stored in platelet dense granules. The 5HT uptake capacity of the platelets depends on the number of SERT molecules on the plasma membrane.Our earlier studies demonstrated the presence of a dynamic relationship between plasma 5HT elevation, loss of surface SERT, and depletion of platelet 5HT. However it is not clear whether decreased SERT density on the platelet plasma membrane is a cause or consequence of increased plasma 5HT levels.In the current study, we addressed this issue by using two model systems: (a) 5HT‐pretreated platelets isolated from untreated C57BL/6J mice, and (b) platelets isolated from C57BL/6J mice in which plasma 5HT was elevated chronically by osmotic minipump. Our data in both model systems show a profound loss of surface SERT expression in platelets, depletion of platelet 5HT content and enhanced aggregation response to fibrillar collagen, demonstrating that 5HT‐depleted platelets appear to aggregate more readily. Furthermore, the aggregation rate of platelet is rescued by blocking the uptake ability of platelet SERT with serotonin reuptake inhibitor (SSRI), SERT blocker. These studies explicitly indicated that SERT down‐regulation by high extracellular 5HT in isolated platelets occurs in vivo and impacts platelet function against further aggregation in a protective feedback mechanism.Overall, these studies addressed that the intracellular 5HT concentration has a significant role in promoting hypercoagulation than the plasma 5HT‐level. The importance of understanding the structure, function, and regulation of SERT is underscored by the observations that plasma 5HT is elevated in the plasma, either locally or globally, during atherosclerosis, hypertension, stroke, and other cardiovascular diseases.

Serotonin in the gastrointestinal tract

To assess the role of serotonin and its control in the manifestations and treatment of lower functional gastrointestinal disorders. Recent literature has explored several novel concepts in the association of serotonin and symptoms, alterations in tissue levels of serotonin and its reuptake protein, aspects of the genetic determinants of serotonergic function (particularly 5-HTTLPR) and its relationship to gastrointestinal motor and sensory functions, and novel serotonergic agents used in therapy of lower functional gastrointestinal disorders. The most consistent findings are the increase in plasma 5-hydroxytryptamine (5-HT) in diarrheal diseases and reduction in constipation. The serotonin transporter in platelets has an impact on the circulating level of 5-HT. Meta-analysis shows that 5-HTTLPR genotype is not significantly associated with irritable bowel syndrome in Whites or Asians. New 5-HT3 antagonists and 5-HT4 agonists are efficacious and promise to provide relief for patients if they can pass regulatory hurdles. Although the most relevant implication for clinical practice remains the evidence that serotonergic agents are efficacious in the treatment of chronic constipation, chronic diarrhea and irritable bowel syndrome, the role of genetic control of 5-HT and its receptors is the subject of ongoing research, and is likely to enhance understanding of the mechanisms and treatment of these diseases.

Corrigendum

Journal of NeurochemistryVolume 107, Issue 1 p. 302-302 Free Access Corrigendum This article corrects the following: Plasma serotonin levels and the platelet serotonin transporter B. Brenner, J. T. Harney, B. A. Ahmed, B. C. Jeffus, R. Unal, J. L. Mehta, F. Kilic, Volume 102Issue 1Journal of Neurochemistry pages: 206-215 First Published online: February 28, 2007 First published: 16 September 2008 https://doi.org/10.1111/j.1471-4159.2008.05634.xAboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat In Brenner et al. (2007), the first paragraph of the Subjects section in Materials and methods should have read as follows: Twenty-five adult men between the ages of 45 and 50 years with high blood pressure (Table 1) were recruited for this study. The blood samples were collected from these subjects during the hypertension, and after the blood pressure returned to normal values. Our study was carried out after approval from University of Arkansas for Medical Sciences (UAMS) IRB. The subjects provided written informed consent before the blood sample was drawn. Reference Brenner B., Harney J. T., Ahmed B. A., Jeffus B. C., Unal R., Mehta J. L. and Kilic F. (2007) Plasma serotonin levels and the platelet serotonin transporter. J. Neurochem. 102, 206– 215. Wiley Online LibraryCASPubMedWeb of Science®Google Scholar Volume107, Issue1October 2008Pages 302-302 ReferencesRelatedInformation

Decreased Density of the Platelet Serotonin Transporter in Pathological Gamblers

Background/Aims: The aim of this study was to investigate the serotonin transporter (SERT), by means of the ³H-paroxetine ([³H]-Par) binding to platelet membranes, in patients affected by pathological gambling (PG), as compared with a similar group of healthy control subjects. Methods: Seventeen PG patients were selected amongst those who were drug-free and at the first psychiatric interview in a Department of Addiction. The diagnosis was assessed according to DSM-IV criteria and PG severity was measured by means of the South Oaks Gambling Screen. The platelet [³H]-Par binding was carried out according to a standardized method. The binding parameters, the maximum binding capacity (B_max) and the dissociation constant (K_d), were obtained by means of the Scatchard analysis. Results: The B_max values of PG patients were significantly lower than that of healthy subjects, while the K_d values were not different in the two groups. No significant effect of age, sex or psychiatric comorbidity on B_max or K_d was observed; there were also no correlations between clinical and biological variables. Conclusions: PG patients showed a dysfunction at the level of the platelet SERT that would suggest the involvement of the 5-HT system in this condition.

293 Increased Intraepithelial Lymphocytes and Mast Cells with Depressed Serotonin Transporter in Duodenal Biopsies and Platelets of Patients with IBS and Diarrhoea (IBS-D): Correlation with Bowel Frequency

INTRODUCTION: Several groups report increased mucosal inflammation and increased circulating cytokines, which both cell and animal studies show to depress SERT, in IBS. We therefore assessed mucosal and platelet SERT function together with 5HT & Mast Cell tryptase release (MCT) from duodenal biopsies which were also assessed for mast cells (MC), intra-epithelial lymphocytes (IEL) & 5HT-containing enterochromaffin cells (EC) compared to coeliac patients who are known to have mucosal inflammation with depressed SERT mRNA. AIMS & METHODS: 28 healthy volunteers, 20 patients with IBS-D & 20 with untreated coeliac disease (CD) completed bowel symptom questionnaires and underwent duodenal biopsy. 5HT & MCT release was assayed after 6 hour incubation. MC, IELs & ECs were identified by immuno-histochemistry. SERT and cytokeratin 20(CK20) mRNA were assessed by Taqman qRT-PCR. Platelet SERT function was assayed by H3-5HT uptake. Project supported by Novartis Pharma AG. RESULTS: IBS-D showed increase IELs, mast cell numbers and increased mast cell tryptase release (see Table). DIBS also showed depressed SERT/CK20(arbitrary units) at 0.19(0.1-0.43) versus 0.96(0.14-1.40) for HV, p<0.02. Platelet uptake of H3-5HT was also depressed at 12.8(8.3-23.2) versus 45.2(27.7-69.3)pmol/min/ mg protein for HV, p<0.01. CD had intermediate values, difference NS v HV. Mast cell numbers correlated (r=0.56, p=0.02) with stool frequency in IBS patients but not in coeliacs nor HV. IELs, in HV and IBS, correlated positively with mast cell numbers r=0.45 , p=0.001 and with EC count r=0.39, p=0.006 but negatively with SERT r=-0.37 ,p=0.01 and platelet 5HT uptake -0.53, p=0.001. CONCLUSIONS: IBS-D is characterised by increased duodenal IELs and mast cells associated with increased mast cell tryptase release. The depressed SERT in mucosa and platelets correlates with mucosal IELs and may be secondary to increased inflammatory mediators. Depressed SERT may contribute to increased 5HT availability and diarrhoeal symptoms. Mast cell numbers correlate with stool frequency suggesting mast cell products also play a part in symptoms.

Catatonic Features in Major Depression Relieved by Electroconvulsive Treatment: Parallel Evaluation of the Status of Platelet Serotonin Transporter

The aim of this research was to follow parallelly the clinical status of a patient and the dynamics of the serotonin transporter (SERT), a likely player in the effect of electroconvulsive treatment (ECT), a powerful tool against deep depression.A patient affected by major depression with catatonic features, not responding to pharmacological therapy, underwent ECT. Evaluations of the binding of labelled paroxetine to venous blood platelet SERT were parallel to the assessments of clinical improvements.The density of platelet SERT, starting from a low level before ECT, displayed an initial steep increase peaking the day after the third electroconvulsive session (5 days after the start of ECT). This was followed by a rapid decrease, which seemed to precede the process of clinical recovery.These results were found in a case of unavoidable ECT treatment. If generalizable, they suggest interesting ideas about the still mysterious mechanism of ECT antidepressant action.

Serotonin (5-HT) Transport in Human Platelets is Modulated by Src-Catalysed Tyr-Phosphorylation of the Plasma Membrane Transporter SERT

Background/Aim: platelets possess tightly regulated systems for serotonin (5-HT) transport. This study analysed whether the 5-HT transport mediated by the plasma-membrane transporter SERT is regulated by its Tyr-phosphorylation. Methods: 5-HT transport was determined by filtration techniques, while immunoblotting procedures were adopted for detecting the Tyr-phosphorylation of SERT in human platelet fractions. Results: 5-HT accumulation in platelets pre-treated with reserpine, which prevents the neurotransmitter transport into the dense granules, decreased upon cellular exposure to PP2 and SU6656, two structurally unrelated inhibitors of Src-kinases. By contrast, the protein Tyr-phosphatase inhibitor pervanadate increased the 5-HT accumulation. Anti-SERT immunostaining of the platelet fractions showed a major band displaying an apparent molecular mass of 50 κDa, indicating that, during the analytical procedure, SERT underwent proteolysis, which was counteracted by addition of 4 M urea in the cellular disrupting medium. The Tyr-phosphorylation degree of SERT immunoprecipitated from membrane extracts decreased by platelet treatment with SU6656 or PP2, and enhanced upon pervanadate treatment. The anti-SERT immunoprecipitates displayed anti-Src immunostaining and in vitro kinase activity towards a Src-specific peptide-substrate. Platelet treatment with PP2 or SU6656 also caused a decrease in the imipramine binding to platelets. It was concluded that the Src-mediated SERT Tyr-phosphorylation regulates the 5-HT transport by affecting the neurotransmitter binding sites.

Blood Pressure in Mutant Rats Lacking the 5-Hydroxytryptamine Transporter

To the Editor: Although 5-HT uptake inhibitors are widely used as antidepressants, the role of 5-HT in the control of systemic blood pressure is far from clear.1 In a recent issue of Hypertension , Ni et al reported that 5-hydroxytryptamine (5-HT) transporter (SERT) expression was increased, whereas SERT function was decreased in aorta of rats with DOCA salt and Nω-nitro-L-arginine (L-NNA)-induced hypertension.2 We have observed that several 5-HT receptors are induced in leukocytes of hypertensive patients.3 These 2 observations could point at a functional response of the serotonin system …

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 4 h 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 ( V max and K m) 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.

Low density and high affinity of platelet [ 3H]paroxetine binding in women with bulimia nervosa

Impaired serotonin transmission has been suggested to be implicated in the pathophysiology of bulimia nervosa. As an indirect measure of brain serotonergic activity, the binding of tritiated ligands to platelet serotonin transporters has been studied in bulimia nervosa as well as in other putatively serotonin-related psychiatric disorders. In this study, the density and affinity of platelet serotonin transporters were assessed in 20 women meeting the DSM-IV criteria for bulimia nervosa and in 14 controls without previous or ongoing eating disorder using [ 3H]paroxetine as a ligand. In comparison to controls, women with bulimia nervosa had a significantly reduced number of platelet binding sites ( B max = 721 ± 313 vs. 1145 ± 293 fmol/mg protein) and an increase in the affinity for the ligand demonstrated by a lower dissociaton constant ( K d = 33 ± 10 vs. 44 ± 10 pM). A significant correlation between B max and K d values was found in patients but not in controls. Our results support the notion that bulimia nervosa is associated with a reduction in platelet serotonin transporter density. In addition, our study is the first to report that this reduced transporter density in women with bulimia nervosa is accompanied by an increase in the affinity of the transporter for the ligand.

Successful Treatment of Epilepsy with Serotonin Reuptake Inhibitors: Proposed Mechanism

The widely used antidepressants Specific Serotonin Reuptake Inhibitors (SSRI) have been tried with success as anticonvulsants in cases of nonsymptomatic epilepsy. This attempt was performed on the basis of experimental data suggesting the involvement of impairments of the serotonin system in the genesis of epilepsy. This overview summarizes the clinical data and presents biochemical and neurochemical evidences suggesting the mechanism of the therapeutic effects of SSRI in nonsymptomatic epilepsy. In particular, studies on blood-borne neutral amino acids and platelet serotonin transporter (SERT) in epileptics suggest: (a) That a decreased brain availability of tryptophan may be related to some types of epilepsy. (b) That reduction of the density of SERT may be a homeostatic reaction in the brain following epileptic seizures.

Characterization of the serotonin transporter in lymphocytes and platelets of schizophrenia patients treated with atypical or typical antipsychotics compared to healthy individuals

A rapidly growing body of data suggests that abnormalities in serotonergic function might be involved in the pathophysiology of schizophrenia and that serotonergic mechanisms play a role in the therapeutic effects of antipsychotics. The activity of the serotonin transporter (5-HTT), as determined by [ 3H]5-HT uptake to blood lymphocytes, was measured in 38 medicated schizophrenia patients (15 of them treated with typical antipsychotics and 23 treated with atypical antipsychotics) and 15 healthy control subjects. In addition, the pharmacodynamic characteristics of platelet 5-HTT were assessed by [ 3H]citalopram binding. There were no significant differences in the density ( B max) of platelet [ 3H]citalopram binding sites between the three groups. Similarly, the dissociation constant ( K d) values were indistinguishable. There were no significant differences in the maximal uptake velocity ( V max) of [ 3H]5-HT to fresh lymphocytes between the three groups. The affinity ( K m) values of 5-HT to the 5-HTT were significantly higher in schizophrenia patients treated with typical antipsychotics compared with control subjects. The K m values in schizophrenia patients treated with atypical antipsychotics were significantly lower compared with those observed in the group of schizophrenia patients treated with typical antipsychotics; however, they were comparable to values in the control group. The high values of K m associated with typical antipsychotic treatment may be relevant to the high risk of developing extrapyramidal side effects (EPS). The role of the various components of the serotonergic system in the etiopathology of schizophrenia and the mechanisms by which antipsychotics achieve their therapeutic effects need to be further evaluated.

Common Alterations in the Serotonin Transporter in Platelets and Lymphocytes of Psychotic Patients

Given the controversial data concerning the role of the serotonin (5-HT) transporter in psychosis, our study was aimed to investigate this structure by means of the measurements of the re-uptake kinetics and of the protein density, in both platelets and lymphocytes of 25 out- and inpatients with different psychotic disorders. Diagnoses, according to DSM-IV criteria, were bipolar 1 disorders with mood incongruent psychotic features (14), mixed states (7) and schizophrenia (4). Twenty-five matched healthy subjects were also selected as the control group. Platelet and lymphocyte membranes were prepared according to standardized protocols, as were the [3H]5HT re-uptake and [3H]paroxetine ([3H]Par) binding. The results of this study showed a decreased density of the [3H]Par binding sites coupled with a reduced velocity of [3H]5-HT re-uptake in both platelets and lymphocytes of psychotic patients, as compared with healthy control subjects. These findings would suggest a general abnormality of the 5-HT system in psychotic patients, probably not confined only to the brain.

Is the Platelet Serotonin Transporter Different in Venous vs. Arterial Blood?

The binding of labelled paroxetine to the serotonin transporter (SERT) of platelet membranes has been studied in both venous and mixed venous/arterial blood of the rat. In addition, we studied the inhibition of paroxetine binding to SERT by quipazine and N-methyl-quipazine (NMQ). The results indicate differences in affinity for the two test drugs, quipazine and NMQ, in venous vs. mixed venous/arterial blood. This suggests different post-translational modifications of SERT in platelets of arterial vs. venous blood.

Seasonal variations in [3H]citalopram platelet binding between healthy controls and violent offenders in Finland

Monthly binding densities (B(max)) of [3H]citalopram to the platelet serotonin transporter (SERT) was measured longitudinally over 1 year in a control group of 18 healthy Finnish male volunteers. Single platelet samples were also analysed from 33 men who were incarcerated for violent crimes during the same calendar year. A statistically significant seasonal variation in SERT B(max) was observed in both data sets, and bi-monthly floating averages for SERT B(max) were calculated and then fit to an annual sinusoidal curve for both groups. The B(max) for platelet [3H]citalopram binding showed a statistically significant (p = 0.001) seasonal variance between a winter (January-February) maximum of 1590 fmol/mg protein and a summer (July-August) minimum of 1216 fmol/mg protein for the control group, with an R2 of 70% for the annual sinusoidal curve fit. A statistically significant (p = 0.007) seasonal variance was also observed between a winter (January-February) maximum of 1980 fmol/mg protein and an autumnal (August-September) minimum of 1234 fmol/mg protein for the violent offenders, again with an R2 of 70% for the annual sinusoidal curve fit. This observation lends additional support to the idea that violent human behavior and impulsivity may be directly linked to values of SERT B(max), which can be affected by various psychoactive drugs and also varies with the natural change of seasons.

Western blot analysis of human and rat serotonin transporter in platelets and brain using site-specific antibodies: Evidence that transporter undergoes endoproteolytic cleavage

Background Serotonin transporter (SERT) is important target molecule for many antidepressive drugs and substances of abuse and is implicated in psychiatric disorders. We performed immunoblotting analysis of human and rat SERT in platelets and brain using the panel of eight site-specific SERT monoclonal and polyclonal antibodies (mAbs and pAbs). Methods SDS-PAGE/Western blotting was conducted using peroxidase-labeled DEAE and affinity purified SERT antibodies under conditions preventing SERT post-extraction degradation. Results Immunoreactive polypeptides of 14, 22, 32, 35, 37, 56, 68, and ∼150–200 kDa were revealed in human platelet extracts using N-terminal and C-terminal SERT antibodies. In rat brain, C-terminal mAbs detected 68, 56, and 37 kDa proteins, in postmortem human brain predominated 35–37 kDa proteins. The immunoreactivity was abolished after antibody preadsorption with antigens. N-terminal pAbs recognized the 68 kDa protein, affinity purified on C-terminal mAbs, confirming its identity as full-size human SERT (the predicted size ∼70.5 kDa). Conclusions The explanation of the results of immunoblotting most likely is a site-specific SERT endoproteolytic cleavage and a marked difference in glycosylation rather than nonspecific protein degradation, cross-reactivity with other epitopes or SERT alternative splicing.

Serotonin transport kinetics correlated between human platelets and brain synaptosomes

Blood platelets have been used extensively as a model system for investigating the role of the serotonin transporter (SERT) in various psychiatric disorders, especially depression. However, to date, it is not known whether platelet serotonin (5-HT) transport would be related to that in brain. We examined 5-HT transport kinetics simultaneously in human blood platelets and human cortical brain synaptosomes to determine whether they were correlated. Blood platelets and synaptosomes were obtained from 25 patients undergoing epileptic surgery. Synaptosomes were obtained from normal margins of surgical neuropathology specimens of anterotemporal cortex. Platelet SERT V(max) was significantly correlated with brain SERT V(max) on linear regression (r=0.58, p<0.005), after controlling for the confounding effects of gender (t=-2.4, p=0.025) and time of day (t=2.1, p<0.05). Consistent with previous observations, there was a negative correlation between the maximum velocity (V(max)) of platelet 5-HT transport and pO2 (r=-0.52, p<0.01). Females had a significantly higher pO2 than males (F=4.9, p<0.05). After accounting for gender differences, addition of pO2 did not add further strength to the regression, given the aforementioned gender differences in pO2. The correlation between unadjusted values for platelet vs brain SERT V(max) was r=0.3, p=0.06. These results suggest that a relationship may exist between 5-HT transport in platelets and cortical synaptosomes, when appropriate controls for confounding factors are employed.

Serotonin transporter kinetics in rats selected for extreme values of platelet serotonin level

By selective breeding of Wistar rats for the extreme values of platelet serotonin (5HT) level (PSL), we have developed earlier two sublines of animals differing markedly in this parameter. Further studies, performed on the protein and mRNA levels, revealed platelet serotonin transporter (5HTt) as parameter underlying mentioned differences in PSL between sublines. In this work, we have performed full-kinetic analysis of platelet serotonin uptake (PSU) in animals from the genetically selected sublines. The results demonstrated marked differences in maximal velocity (V max) of the 5HT transporter, as contrasted to the lack of any difference in the Michaelis constant (K m). High correlation between PSL and V max of PSU was demonstrated, revealing that the number of membrane 5HT transporter sites is under genetic control and responsible for marked differences in PSL between high- and low-5HT sublines. These results enabled further selective breeeding of animals for the extremes of V max of platelet 5HT transporter, and so the development of more specific model “Wistar-Zagreb 5HT rats”.

Relationships between serotonin transporter promoter polymorphism, platelet serotonin transporter binding and clinical phenotype in suicidal and non-suicidal adolescent inpatients

Relationships between the serotonin transporter promoter polymorphism (5-HTTLPR), platelet serotonin transporter (SERT) binding and clinical phenotype were examined in 32 suicidal and 28 non-suicidal Ashkenazi Israeli adolescent psychiatric inpatients. The 5-HTTLPR polymorphism was not associated with transporter binding or with suicidality or other clinical phenotypes. However, in the suicidal group, a significant positive correlation between platelet SERT density and anger scores (n=32, r=.40; p=.027) and a negative correlation between platelet count and trait anxiety (n=32, r=-.42; p=.034) were observed.

P.3.138 Complex alterations of the serotonin transporter in platelets and lymphocytes of psychotic patients

P.3.138 Complex alterations of the serotonin transporter in platelets and lymphocytes of psychotic patients