Platelet [H]paroxetine binding in patients with OCD-related disorders

The recently introduced notion of clinical conditions being related one to another, the spectrum concept, permits the testing of the involvement of serotonergic systems in a broad range of disorders tentatively linked to obsessive–compulsive disorder (OCD) for which no pathophysiological hypotheses yet exist. We therefore compared the binding of [³H]paroxetine ([³H]Par), a ligand that specifically labels the serotonin (5-HT) transporter, in platelets of drug-free outpatients suffering from various OCD-related disorders with binding in platelets of OCD patients and healthy subjects. Diagnoses were made according to DSM-IV criteria. The most frequent diagnosis was that of body dysmorphic disorder, followed by impulse control disorder, kleptomania, Tourette’s syndrome and trichotillomania. Platelet membranes and [³H]Par binding were studied according to standardized protocols. The results, showing a similarly decreased density of [³H]Par binding sites in both patient groups as compared with healthy subjects, suggest the presence of a shared abnormality at the level of the presynaptic 5-HT transporter, probably linked to a common dimension yet to be identified.     

Common alterations in the serotonin transporter in platelets and lymphocytes of psychotic patients

INTRODUCTION: 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. METHODS: 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. RESULTS: 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. CONCLUSION: These findings would suggest a general abnormality of the 5-HT system in psychotic patients, probably not confined only to the brain.     

Increased density of the platelet serotonin transporter in autism

BACKGROUND: Various data have shown the involvement of serotonin (5-HT) in autism. The presence of the 5-HT transporter in platelets, similar to the same structure located in presynaptic serotonergic neurons, has produced a series of studies aimed at assessing its functionality in this disorder, but the ensuing findings are quite controversial. For this reason, we investigated the 5-HT transporter by means of the specific binding of [3H]-Paroxetine ([3H]-Par), which is currently considered the first-choice ligand for labeling it, in platelets of 20 autistic children and adolescents, as compared with healthy control subjects. METHODS: Twenty children and adolescents of both sexes suffering from autism according to DSM IV criteria were included in the study and compared with a similar group of healthy control subjects. Platelet membranes and the binding of [3H]-Par were carried out according to standardized protocols. RESULTS: The results showed a significantly higher density of [3H]-Par binding sites in autistic children than in healthy control subjects. CONCLUSIONS: These findings support the presence of a serotonergic dysfunction in autism and would suggest that the 5-HT transporter may have a specific role in this disorder, also in the light of its recently proposed role in brain development.     

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

Research to date would suggest the possible involvement of the serotonin (5-HT) system in the pathophysiology of suicide. With this study, we aimed to investigate the platelet 5-HT transporter, by means of the specific binding of tritiated paroxetine ([3H]Par), in a sample of 20 suicide attempters recruited at a first-aid service, as compared with healthy control subjects and psychiatric patients with no current or previous history of suicide attempt. The results, showing a decreased number of [3H]Par binding sites in suicide attempters, would suggest the involvement of the presynaptic 5-HT transporter in self-aggressive behavior.     

Decreased lymphocyte 3H-paroxetine binding in obsessive-compulsive disorder

The pathophysiology of obsessive-compulsive disorder (OCD) is mainly focused on the serotonin (5-HT) system and transporter. The presence of this structure in blood lymphocytes prompted us to investigate it, by means of the specific binding of (3)H-paroxetine ((3)H-PAR), in a group of drug-free OCD patients as compared with healthy control subjects matched for sex and age. Lymphocyte membranes and (3)H-PAR binding were carried out according to standard protocols. The results showed that the patients had a statistically significant lower density of (3)H-PAR-binding sites than the control subjects. On one hand, this finding confirms previous data of an abnormal platelet 5-HT transporter in OCD, on the other it provides the possibility to explore the regulation of this structure in this and other disorders, since lymphocytes are nucleate cells.     

Decreased platelet imipramine binding in Tourette syndrome children with obsessive-compulsive disorder.

[3H]Imipramine binding to blood platelets was assessed in eight untreated Tourette syndrome (TS) children, nine drug-free TS children with obsessive-compulsive disorder (OCD), and nine age-matched and gender-matched control subjects. The density of [3H]imipramine binding sites in TS + OCD patients was significantly lower compared with TS-OCD patients (28%) as well as when compared with controls (31%). This alteration was not accompanied by differences in the affinity of the binding site to the ligand. The decreased density of the platelet serotonin "transporter" might implicate the involvement of the serotonergic system in the pathophysiology of OCD in TS patients, but not in TS per se.     

Changes in [3H]5-HT uptake and [3H]imipramine binding in platelets after chlorimipramine in healthy volunteers. Comparison with maprotiline and amineptine

In the platelets of normal healthy volunteers (n = 8) taking chlorimipramine (50 mg/day) for 1 week, the saturable uptake of [3H]5-hydroxytryptamine (5-HT) was fully inhibited at the end of the week, but returned to control values after 2 weeks washout. The Bmax of [3H]imipramine binding was decreased by 63% at the end of the treatment and remained significantly decreased below control values after 1 week washout, whereas the Kd values were increased at the end of the treatment, but had returned to baseline values after 1 week washout. The time course of recovery following the administration of chlorimipramine showed some variation between subjects, but it was necessary to wait up to 4 weeks of washout before the Bmax of [3H]imipramine returned to baseline levels. In contrast, neither 1-week treatment with maprotiline (50 mg/day) nor with amineptine (100 mg/day) changed the parameters of [3H]5-HT uptake or [3H]imipramine binding in platelets from healthy volunteers. These results support the following conclusions. (1) [3H]Imipramine binding in platelets can be down-regulated by relatively low, subtherapeutic doses of chlorimipramine. (2) It is possible to dissociate [3H]imipramine binding parameters from [3H]5-HT uptake because the time course of recovery was clearly different, indicating that [3H]imipramine labels a site linked with, but different from, the 5-HT recognition site in the transporter complex. (3) A washout of antidepressants of 4 weeks may be needed when studying the parameters of [3H]imipramine binding in platelets from depressed patients if the previous medication involved chlorimipramine. For antidepressants like maprotiline or amineptine, that act through mechanisms other than inhibition of 5-HT uptake, the time of washout appears to be less critical, although it is not possible to rule out the existence of some secondary modifications influencing the 5-HT transporter complex.     

Regulation of the platelet serotonin transporter by protein kinase C in the young and elderly.

BACKGROUND: Some data show that different factors may influence the serotonin (5-HT) uptake rate. Our study aimed at evaluating the possible role of a protein kinase C (PKC) activator, i.e., 4-beta-12-tetradecanoylphorbol-13-acetate (beta-TPA) on the platelet 5-HT uptake of young and elderly subjects, through the measurement of the 5-HT uptake itself and 3H-paroxetine ([3H]PAR) binding sites, which correspond to the transporter protein. METHODS: Human platelets and 5-HT uptake were evaluated according to the method of Arora and Meltzer, while [3H]PAR binding was performed following the Marazziti et al method. RESULTS: The results showed that beta-TPA reduced significantly the maximal velocity (Vmax) of 5-HT uptake, with no change in the Michaelis constant or in [3H]PAR binding parameters, in platelets of both young and elderly subjects. Although this last group of subjects had a significantly lower Vmax than the other, the degree of inhibition was almost the same (75%) in both. CONCLUSIONS: These findings indicate that PKC decreases the 5-HT uptake rate by modifying the phosphorylation state of the transporter and with no change in the number of [3H]PAR binding sites. The responsiveness of this pathway is identical in both young and elderly subjects.     

Elevated brain serotonin transporter availability in patients with obsessive-compulsive disorder.

BACKGROUND: A central serotonergic dysfunction is considered to be involved in the pathophysiology of obsessive-compulsive disorder (OCD). The aim of this study was to investigate the serotonin transporter availability in patients with OCD as an in vivo marker of the central serotonergic system. METHODS: Nine unmedicated (7 drug-naive) patients with OCD and 10 healthy control subjects were included and received single photon emission computed tomography (SPECT) 20.75 +/- 1.51 hours after injection of a mean 147.20 +/- 6.74 MBq [(123)I]-2beta-carbomethoxy-3beta-(4-iodophenyl)tropane ([(123)I]beta-CIT). As a measure of brain serotonin transporter availability, a ratio of specific-to-nonspecific [(123)I]beta-CIT binding for the midbrain-pons (V(3)" = [midbrain/pons-occipital]/occipital) was used. RESULTS: Mean specific-to-nonspecific ratios showed a 25% higher midbrain-pons [(123)I]beta-CIT binding in the patients as compared with healthy controls (2.26 +/-.37 vs. 1.81 +/-.23, p <.01). The difference remained significant after adjustment for clinical variables and controlling for age and gender. Stratification of the patients according to onset of the disorder revealed significant differences between controls and patients with early (childhood, adolescence) but not late (adult) onset of OCD. CONCLUSIONS: The study provides evidence of a serotonergic dysfunction in patients with OCD and suggests a serotonergic component in the pathophysiology of the disorder.     

Increased inhibitory activity of protein kinase C on the serotonin transporter in OCD

Different observations show a reduced functionality of the serotonin (5-HT) transporter in obsessive-compulsive disorder (OCD) that might be due to a disturbance of its regulation at intracellular level. Protein kinase C (PKC) has been reported to provoke a decrease in the number of the 5-HT transporter proteins. Therefore, we investigated whether OCD patients differed from control subjects in the effect of PKC upon the 5-HT transporter, after stimulation of this enzyme with 4beta-12-tetradecanoylphorbol 13-acetate (beta-TPA). Fifteen patients affected by OCD, according to DSM-IV criteria, were compared with a similar group of healthy subjects. The determination of 5-HT uptake was carried out according to the method of Arora and Meltzer with slight modifications. At baseline, OCD patients showed a significant decrease in the maximal velocity (V(max)) of 5-HT uptake, as compared with control subjects, with no change in the Michaelis-Menten constant (K(m)). The activation of PKC with beta-TPA provoked a significant decrease in V(max) values in both groups, but the effect was significantly more robust in OCD patients who, in turn, also showed also an increase in K(m) values. These findings could indicate the presence of hyperactivity of PKC in OCD that could be the result of increased activity of the phosphatidylinositol pathway. In addition, this suggests new potential therapeutic targets in OCD.     

No correlation between aggression and platelet (3)H-paroxetine binding in obsessive-compulsive disorder patients

Different findings suggest that the serotonin (5-HT) system may be involved in both the regulation of aggression and the pathophysiology of obsessive-compulsive disorder (OCD). Our study aimed to evaluate the aggressive features of a group of OCD patients and to explore possible correlations with a serotonergic marker, namely platelet 5-HT transporter. Psychopathological and biological patterns were compared with those of a group of healthy controls and those of patients with major depression. Twenty-one patients affected by OCD, 21 by depression and 21 healthy controls were included in the study. Aggressive features were measured by means of the Buss and Durkee Hostility Inventory (BDHI). The platelet 5-HT transporter was evaluated by means of the (3)H-paroxetine binding parameters (maximum binding capacity, B(max) and dissociation constant, K(d)). The OCD patients showed a total score on the BDHI not significantly different from that of healthy controls and lower than that of depressed patients. The factor profile was similar in the 3 groups, but higher in the depressed patients. The irritability, resentment, guilt, negativism and suspiciousness factors were significantly more pronounced in depressed patients. Some sex-related difference in single factors were also observed. The B(max) of (3)H-paroxetine binding was lower in OCD patients than in depressives or healthy controls. OCD patients were more similar to healthy controls than to depressed patients with regard to aggressive features measured by means of the BDHI. This suggests that aggression in OCD is a complex phenomenon that probably requires specific instruments of evaluation.     

Serotonergic markers in platelets of patients with major depression: upregulation of 5-HT2 receptors.

The uptake of [3H]5-HT and the density (Bmax) as well as affinity (Kd) of 5-HT uptake sites labelled with [3H]paroxetine and of 5-HT2 receptors labelled by [3H]LSD were determined in platelets from 25 medication-free patients with major depression and 20 normal controls. The density (Bmax) of 5-HT2 receptors was found to be significantly increased (by 52%) in platelets from depressed patients, particularly females. No changes were found in the affinity (Kd) of 5-HT2 receptors and in 5-HT uptake or [3H]paroxetine binding parameters. Density of 5-HT2 receptors positively correlated with that of [3H]paroxetine sites in control but not in depressed subjects. No correlation was found between the HAMD scores and Bmax of [3H]LSD binding. The results suggest that upregulation of platelet 5-HT2 receptors is a useful biological marker in major depression, particularly in females.     

Platelet serotonin uptake and paroxetine binding among allelic genotypes of the serotonin transporter in alcoholics

Expression rates of long (L) and short (S) alleles of the serotonin (5-HT) transporter (5-HTT) gene have been shown to differ under various circumstances. We compared 5-HTT uptake (function) level and paroxetine binding (density) in platelets of alcoholics as indices of 5-HTT expression rate among LL, LS, and SS genotypes. Concentration curves of [3H]5-HT and [3H]paroxetine were used to quantify the equilibrium constant (Km) and maximum 5-HT uptake rate (Vmax) for 5-HTT uptake into intact platelets and the dissociation constant (Kd) and maximum specific binding density (Bmax) for paroxetine binding to platelet membranes, respectively. Genotypes were determined using electrophoresis with fluorescent markers. Vmax for 5-HTT uptake did not correlate with Bmax for paroxetine binding (r=-0.095, P=0.415). Means of Vmax and Bmax did not differ in a statistically significant manner among LL, LS, and SS genotypes in these alcoholic subjects. However, Vmax for LL and SS appeared to have a bimodal distribution, so the percentage of subjects with Vmax <200 fmol/min-10(7) platelets was statistically significantly higher in LL than in SS (51.5% vs. 22.7%, respectively), with an odds ratio of 3.6 (P<0.05). The percentage of Vmax <200 fmol/min-10(7) platelets for LS was 39.3% (not significant vs. LL or SS). Previous studies of healthy human controls have shown that 5-HTT density in raphe nuclei and 5-HTT uptake in platelets are higher in the LL genotype than in S carriers. Our findings in currently drinking alcoholics support the hypothesis that those with the LL genotype of the 5'-HTTLPR region of the 5-HTT gene have reduced 5-HTT function.     

Platelet serotonin functions in untreated major depression

The uptake of [14C]5-HT, [3H]paroxetine and [3H]LSD binding was determined in platelets from 30 untreated patients with major depression and compared with corresponding variables from 30 healthy age-, sex- and season-matched control subjects. The maximum velocity (Vmax) for the 5-HT uptake was significantly decreased in patients (P = 0.014) compared to control subjects. Depressed women had significantly lower Vmax than female control subjects. In men, Vmax did not differ between patients and control subjects. Vmax was significantly lower in male inpatients compared with male outpatients (P = 0.05). The density (Bmax) of 5-HT uptake sites was found to be significantly increased in patients (P < 0.05) compared to control subjects and male patients had significantly higher Bmax than male control subjects, but there was no difference between female control subjects and female patients. No significant difference was found in Bmax of 5-HT2-receptors between patients and control subjects. A positive correlation was found between Bmax of 5-HT2-uptake sites and the degree of anxiety and between Bmax of 5-HT2 receptors and MADRS scores. Bmax of 5-HT2-receptors was positively correlated with the degree of suicidality. The results in the present study indicate that there may be a gender difference in serotonergic dysfunction in depression.     

Serotonin function in obsessive-compulsive disorder. A comparison of the effects of tryptophan and m-chlorophenylpiperazine in patients and healthy subjects

To evaluate the role of serotonin (5-HT) function in obsessive-compulsive disorder (OCD), behavioral and biochemical responses to the 5-HT receptor agonist m-chlorophenylpiperazine (MCPP) and the 5-HT precursor tryptophan were examined in healthy subjects and patients with OCD. Baseline prolactin levels and the prolactin rise following MCPP were significantly reduced in female patients compared with female healthy subjects. In contrast, the increase in prolactin level following tryptophan administration was not significantly different between male or female patients with OCD and the respective sex-matched healthy subjects. The prolactin responses to MCPP and tryptophan were both significantly higher in female patients and healthy subjects than in their male counterparts. The cortisol and growth hormone responses to MCPP and tryptophan were similar in the patients and healthy subjects and were not related to gender. The behavioral responses to MCPP or tryptophan were not consistently different between patients and healthy subjects, and neither MCPP nor tryptophan had effects on obsessive or compulsive symptoms. These results lend only partial support to the hypothesis that 5-HT dysfunction may be linked to the pathophysiology of OCD and point to the need for the evaluation of other neurotransmitter systems in future investigations of OCD.     

Influence of menstrual cycle on platelet serotonin uptake site and serotonin2A receptor binding

Depression and anxiety are common health problems affecting women, particularly during the reproductive years. Major depression is two to three times as common in women than in men. Neuroendocrine factors are likely to contribute to this overall increased risk for developing mood disorders in women, and the neuroendocrine influence is most obviously seen in women with premenstrual dysphoric disorder (PMDD) as these women experience depressed mood and anxiety premenstrually only during ovulatory cycles. Moreover, dysfunction of serotonergic transmission has been regarded as an important mechanism in several psychiatric disorders and ovarian steroids have been shown to profoundly influence the activity of the serotonergic system. Given these facts, the purpose of this study was to examine whether binding of [3H]paroxetine to the platelet serotonin transporter or binding of [3H]lysergic acid diethylamide ([3H]LSD) to the platelet 5-HT2A receptor are influenced by the cyclical changes in circulating estradiol and progesterone that occur during the menstrual cycle. We examined 28 healthy women, without oral contraceptives and with regular menstrual cycles. In the late follicular phase, Bmax for [3H]paroxetine binding was significantly higher than in the ovulatory (p<0.01), early luteal phase (p<0.05) and mid-luteal phase (p<0.01). Bmax for [3H]LSD binding was significantly higher in the early follicular phase and the early luteal phase compared to the mid-luteal phase (p<0.001 and p<0.05, respectively). In the early follicular phase and the ovulatory phase, significant correlations between estradiol serum concentrations and Kd for [3H]paroxetine were obtained (p<0.001, respectively). In the luteal phase, significant inverse correlations between progesterone as well as estradiol serum concentrations and Kd for [3H]LSD binding were found (p<0.05, respectively).     

The 5-HT(2A) receptor and serotonin transporter in Asperger's disorder: A PET study with [¹¹C]MDL 100907 and [¹¹C]DASB

Evidence from biochemical, imaging, and treatment studies suggest abnormalities of the serotonin system in autism spectrum disorders, in particular in frontolimbic areas of the brain. We used the radiotracers [(11)C]MDL 100907 and [(11)C]DASB to characterize the 5-HT(2A) receptor and serotonin transporter in Asperger's Disorder. Seventeen individuals with Asperger's Disorder (age=34.3 ± 11.1 years) and 17 healthy controls (age=33.0 ± 9.6 years) were scanned with [(11)C]MDL 100907. Of the 17 patients, eight (age=29.7 ± 7.0 years) were also scanned with [11C]DASB, as were eight healthy controls (age=28.7 ± 7.0 years). Patients with Asperger's Disorder and healthy control subjects were matched for age, gender, and ethnicity, and all had normal intelligence. Metabolite-corrected arterial plasma inputs were collected and data analyzed by two-tissue compartment modeling. The primary outcome measure was regional binding potential BP(ND). Neither regional [11C]MDL 100907 BP(ND) nor [11C]DASB BP(ND) was statistically different between the Asperger's and healthy subjects. This study failed to find significant alterations in binding parameters of 5-HT(2A) receptors and serotonin transporters in adult subjects with Asperger's disorder.     

Activation of human platelets by 2-arachidonoylglycerol is enhanced by serotonin

The endocannabinoid 2-arachidonoylglycerol (2-AG) has been shown to activate human platelets in platelet-rich plasma, by binding to a "platelet-type" cannabinoid receptor (CB(PT)). Here, washed human platelets were used to characterize the binding of [(3)H]2-AG to CB(PT), showing a dissociation constant (Kd) of 140 +/- 31 nM and a maximum binding (Bmax) of 122 +/- 10 pmol.mg protein(-1). Selective antagonists of both CB1 and CB2 cannabinoid receptors inhibited this binding, which was enhanced up to approximately 230% over the controls by 1 micro M serotonin (5-hydroxytryptamine, 5-HT). Human platelets were also able to bind [(3)H]5-HT (Kd = 79 +/- 17 nM, Bmax = 14.6 +/- 1.3 pmol.mg protein(-1)), and 1 micro M 2-AG enhanced this binding up to approximately 150%. Moreover, they were able to take up [(3)H]5-HT through a high affinity transporter (Michaelis-Menten constant = 22 +/- 2 nM, maximum velocity = 344 +/- 15 pmol.min(-1).mg protein(-1)), which was not affected by 2-AG. Interestingly, 5-HT did not affect the activity of the 2-AG transporter of human platelets. Treatment of washed platelets with 1 micro M 2-AG led to increased intracellular inositol-1,4,5-trisphosphate (up to approximately 300%) and decreased cyclic AMP (down to approximately 50%). Furthermore, treatment of pre-loaded platelets with 1 micro M 2-AG induced a approximately 300% increase in [(3)H]2-AG release, according to a CBPT-dependent mechanism. Also, 1 micro M 5-HT enhanced the effect of 2-AG on inositol-1,4,5-trisphosphate ( approximately 500% of the controls), cyclic AMP ( approximately 20%) and [(3)H]2-AG release ( approximately 570%), and the latter process was shown to be partly ( approximately 50%) involved in the 5-HT-dependent platelet activation. Taken together, reported findings represent the first demonstration that 2-AG and 5-HT can mutually reinforce their receptor binding on platelet surface, which might have therapeutic implications.     

The relationship of obsessive-compulsive disorder to putative spectrum disorders: results from an Indian study

The relationship between obsessive-compulsive disorder (OCD) and putative obsessive-compulsive (OC) spectrum disorders is unclear. This study investigates the prevalence of putative OC spectrum disorders in OCD subjects in a controlled clinical design. The putative OC spectrum disorders studied included somatoform disorders (body dysmorphic disorder [BDD] and hypochondriasis), eating disorders, tic disorders (e.g., Tourette's syndrome [TS]), and impulse control disorders (e.g., trichotillomania). Only those disorders that are commonly noted to be possibly related to OCD are studied. Included in this study were 231 subjects with a diagnosis of OCD according to DSM-IV criteria and 200 controls who were not screened for psychiatric morbidity. The subjects and controls were assessed in detail by extensive clinical and semistructured interviews by expert clinical psychiatrists. The lifetime diagnoses were made by consensus of two psychiatrists. Prevalence of tic disorders, hypochondriasis, BDD, and trichotillomania was significantly greater in OCD subjects compared to controls. However, the prevalence of sexual compulsions, pathological gambling, eating disorders, and depersonalization disorder was not greater in the OCD subjects compared to controls. The findings of this comorbidity study suggest that tic disorders, hypochondriasis, BDD, and trichotillomania are perhaps part of the OC spectrum disorders. There is a need to evaluate evidence from other sources such as epidemiological, neurobiological, and family studies to further our understanding of the concept of OC spectrum disorders.     

High-affinity imipramine binding and serotonin uptake in platelets of eight adolescent and ten adult obsessive-compulsive patients

The authors evaluated high-affinity [3H]imipramine binding and [3H]serotonin uptake to platelets in eight adolescent and 10 adult patients who met DSM-III criteria for obsessive-compulsive disorder in comparison with those of normal control subjects of similar ages. The maximal binding of [3H]imipramine was significantly lower in adults and adolescents with obsessive-compulsive disorder than in the control subjects. No differences between groups in the affinity of [3H]imipramine to its binding sites or in serotonin uptake kinetic measures were detected. The lower density of [3H]imipramine binding sites in platelet membrane in patients with obsessive-compulsive disorder might implicate involvement of the serotonergic system or might represent an adaptive response to a chronic disease.