Reduction of Blood Platelet Serotonin Levels in Manic and Depressed Patients

Blood platelet serotonin levels were measured in unmedicated 12 manic and 74 depressive patients with 118 normal control subjects employed. Blood platelets were separated by multiple centrifugation in the medium of Naz-EDTA solution, and the loss of serotonin during collecting procedures was about 11%). The mean value of blood platelet serotonin levels in depressed patients was 594±288 ng/mg platelet protein (±S.D.), which was significantly lower than that for normal controls, 780±253 ng/mg protein (p<0.001). Age does not account for the reduction of serotonin levels both in depressed and in normal population. Unipolar and involutional depressed patients exhibited to have the most pronounced reduced levels of serotonin of various subtypes of depression, while bipolar depressed patients, neurotic and chronic characterological depressed patients as well as patients with first-episode depression had the values which were comparable with those in normal controls. Manic patients did not show enhancement but did reduction of serotonin levels, the mean being 5802±152 ng/mg protein, which made a contrast with their clinical manifestations of exhilaration and hyperactivity. Changes in blood platelet serotonin levels were determined before, during and after administration of L-5–HTP with a maintenance dose of 300 mg daily in nine depressed patients. Serotonin levels in all subjects were lifted to normal levels during the L-5–HTP treatment, while clinical symptoms were not improved with the treatment. Reduction of blood platelet serotonin levels in depressed patients may be due to their psychobiological distinction, which involves abnormal biogenic amine metabolism in the brain.     

Monoamine Oxidase Activity in Blood Platelets in Alcoholism

A newly developed assay for monoamine oxidase (MAO) activity in blood platelets was applied in 50 alcoholic patients. The assay is the direct measurement of serotonin oxidation by MAO employing a double microcolumn technique on Sephadex G-10 and Amberlite CG-50 for separating 5–HIAA formed, which is measured fluori-metrically. Rebound of MAO activity levels after withdrawal of alcohol was observed to be more pronounced in the patients with delirium tremens than those who exhibited no outstanding abstinent symptomatology. MAO activity levels measured in the 1st week of alcohol withdrawal were 3.49±1.15 (Mean±S.D.) nmol/mg protein/hour in the alcoholic patients with delirium tremens, a value significantly lower than that in the subjects without (p<0.01) and that in the male normal subjects (p<0.001). Four weeks after withdrawal of alcohol, the reduced MAO activity levels in the alcoholic population were restored to normal levels. These data demonstrate that physical dependency for alcohol occurred evidently in the alcoholic patients examined. Delirium tremens and other psychotic symptoms in alcoholism may be manifested as impaired serotonin metabolism in the brain, which may be due to MAO inhibition caused by excessive alcohol intake.     

Reduction of blood platelet serotonin levels in manic and depressed patients.

Blood platelet serotonin levels were measured in unmedicated 12 manic and 74 depressive patients with 118 normal control subjects employed. Blood platelets were separated by multiple centrifugation in the medium of Na2-EDTA solution, and the loss of serotonin during collecting procedures was about 11%. The mean value of blood platelet serotonin levels in depressed patients was 594 +/- 288 ng/mg platelet protein (+/- S.D.), which was significantly lower than that for normal controls, 780 +/- 253 ng/mg protein (p less than 0.001). Age does not account for the reduction of serotonin levels both in depressed and in normal population. Unipolar and involutional depressed patients exhibited to have the most pronounced reduced levels of serotonin of various subtypes of depression, while bipolar depressed patients, neurotic and chronic characterological depressed patients as well as patients with first-episode depression had the values which were comparable with those in normal controls. Manic patients did not show enhancement but did reduction of serotonin levels, the mean being 580 +/- 152 ng/mg protein, which made a contrast with their clinical manifestations of exhilaration and hyperactivity. Changes in blood platelet serotonin levels were determined before, during and after administration of L-5-HTP with a maintenance dose of 300 mg daily in nine depressed patients. Serotonin levels in all subjects were lifted to normal levels during the L-5-HTP treatment, while clinical symptoms were not improved with the treatment. Reduction of blood platelet serotonin levels in depressed patients may be due to their psychobiological distinction, which involves abnormal biogenic amine metabolism in the brain.     

Monoamine Oxidase Activity in Blood-Platelets From Autistic Children

In order to evaluate the possible abnormality in monoamine oxidase (MAO) activity in early infantile autism, blood platelet samples were obtained from 20 autistic children, aged 2–12 years. MAO activity, measured fluorometrically using serotonin as substrate, was 5.24 ± 1.65 (Mean ± Standard Deviation) nM/mg protein/hour in these autistic children. This value was not significantly different from either that in 30 age-matched normal children or that in 39 nonautistic children with various psychiatric and neurological disorders, although autistic children had higher platelet serotonin concentrations than these nonautistic individuals.     

Platelet MAO deamination of serotonin in depressed patients. Changes after imipramine treatment and clinical correlations

Monoamine oxidase (MAO) in blood platelets has been used as a model to study MAO in the central nervous system, where disorders in serotonergic systems are thought to occur in depression. Inconsistent changes in platelet MAO of depressed patients have been reported when several substrates other than serotonin (5-HT) have been used. To correlate changes in platelet MAO activity with the enzyme activity in central serotonergic systems, the platelet MAO activity of depressed patients (first unmedicated and then after 3 weeks and 2 months of imipramine treatment) and normal controls was measured using 5-HT as substrate. The results showed that there is a steady, measurable platelet MAO activity with that substrate. This activity was significantly higher in unmedicated depressed patients than in controls, and it decreased progressively with imipramine treatment, reaching a normal level when the patients were clinically recovered from depression after 2 months of therapy.     

Monoamine oxidase activity in blood platelets in alcoholism.

A newly developed assay form monoamine oxidase (MAO) activity in blood platelets was applied in 50 alcoholic patients. The assay is the direct measurement of serotonin oxidation by MAO employing a double microcolumn technique on Sephadex G-10 and Amberlite CG-50 for separating 5-HIAA formed, which is measured flourimetrically. Rebound of MAO activity levels after withdrawal of alcohol was observed to be more pronounced in the patients with delirium tremens than those who exhibited no outstanding abstinent symptomatolgy. MAO ACTIVITY LEVELS MEASURED IN THE 1ST WEEK OF ALCOHOL WITHDRAWAL WERE 3.49+/-1.15 (Mean+/-S.D.) nmol/mg protein/hour in the alcoholic patients with delirium tremens, a value significantly lower than that in the subjects without (p less than 0.001) and that in the male normal subjects (p less than 0.001). Four weeks after withdrawal of alcohol, the reduced MAO activity levels in the alcoholic population were restored to normal levels. These data demonstrate that physical dependency for alchol occurred evidently in the alcoholic patients examined. Delirium tremens and other psychotic symptoms in alcoholism may be manifested as impaired serotonin metabolism in the brain, which may be due to MAO inhibition caused by excessive alcohol intake.     

THE LEVEL AND DIURNAL RHYTHM OF SERUM SEROTONIN IN MANIC-DEPPESSIVE PATIENTS

The serum levels and diurnal rhythm of serotonin before and during treatment were investigated in 65 manic-depressive patients, comparing with those in 34 normal controls and 13 schizophrenics. 1. The serum serotonin level in 40 newly admitted depressive patients who had not been medicated (127±58 ng/ml) was significantly lower than that in normal controls (221±96ng/ml). 2. The serum serotonin level in 24 recovering patients with depression had the tendency to return to normal while under treatment with imipramine type antidepressants (281±189 ng/ml). 3. The serum serotonin level in 10 manic patients (365±85 ng/ml) was significantly higher than that in normal controls. 4. After the injection of imipramine to depressive patients, serum serotonin level tended to increase (1.5 times). 5. Electroconvulsive shock did not appear to alter the serum serotonin level in depressive patients and normal dogs. 6. As for the diurnal rhythm of serum serotonin of depressive patients, the serotonin level in the morning was the lowest, which seemed to be related to the worst depressed mood in the morning. In the manic patients, the serotonin level at 20.00 hours was the highest. This pattern of rhythm resembled that of normal controls. 7. The significance of serum serotonin levels in manic-depressive patients was discussed.     

Increased membrane-associated protein kinase C activity and translocation in blood platelets from bipolar affective disorder patients

BACKGROUND: recent investigations have suggested that the phosphoinositide (PI) signal transduction system may be involved in the pathophysiology of bipolar affective disorders. Earlier studies in our laboratory have implicated altered PKC-mediated phosphorylation in bipolar affective disorder and in the clinical action of lithium. In the present study, we compared PKC activity and its translocation in platelets from subjects with bipolar affective disorder and three other groups. METHODS: subjects included 44 with bipolar disorder (acute manic episode), 25 with acute major depression, 23 with schizophrenia in acute exacerbation and 43 controls free of personal or family history of an Axis I disorder. Blood platelet membrane and cytosol PKC activity was measured before and after in vitro stimulation with serotonin (5-HT), thrombin and the direct PKC activator, PMA. In addition, we examined 5-HT-, thrombin- and PMA-elicited translocations of PKC isozymes from cytosol to the membrane in platelets of control subjects. RESULTS: in the basal state, manic subjects demonstrated higher membrane PKC activity than depressive and control subjects. The ratio of membrane to cytosol PKC activity was significantly higher in manic (1.10), as compared to control (0.84), depressed (0.93) or schizophrenic (0.93) subjects. Stimulation of platelets with 5-HT in vitro, resulted in greater membrane to cytosol ratio in the manic subjects compared to the three other groups. The responsiveness of platelets to PMA and thrombin was greater for manic subjects than for depressed and schizophrenic subjects, but not greater than the controls. In this measure both the schizophrenic and depressive groups were less active than controls. The results also demonstrate that platelets contain alpha-, beta-, delta- and zeta-PKC isozymes. While alpha- and beta-PKC isoforms were translocated from cytosol to membrane in response to serotonin, PMA and thrombin, serotonin also elicited the redistribution of delta-PKC and thrombin also activated zeta-PKC. CONCLUSION: the results demonstrate that a heightened PKC-mediated signal transduction is associated with acute mania and suggest a decreased transduction in patients with unipolar depression or schizophrenia.     

Reduction of blood platelet monoamine oxidase activity in schizophrenic patients on phenothiazines.

A newly developed assay for monoamine oxidase (MAO) activity in blood platelets (serotonin used as substrate) was applied for the measurement of the enzyme activity in 76 schizophrenic patients. No significant reduction was found in the blood platelet MAO activity in a group of 33 untreated schizophrenic patients, as compared to that in the normal controls. Male patients revealed to have lower enzyme activity than females in the schizophrenic group, as we described previously in the normal subjects. Treatment with phenothiazines caused significant reduction of blood platelet MAO activity, while platelet serotonin content and platelet count appeared to be not affected by the drug treatment. The authors suggest that blood platelet MAO activity may be related to hormonal factors but not to psychiatric diagnosis of schizophrenia or constitution liable to schizophrenic illnesses.     

Measurement of Platelet Monoamine Oxidase Using Three Different Substrates in Patients with Alcoholism and Schizophrenia

Abstract: The platelet monoamine oxidase (MAO) activities in alcoholism and schizophrenia were investigated by means of the simultaneous determination, using β-phenyl-ethylamine, tryptamine and serotonin as substrates. No significant difference was found between the MAO levels in the alcoholic and schizophrenic groups, when tryptamine was used as a substrate, but both groups showed lower values than the controls. On the other hand, β-phenylethylamine, a specific substrate for MAO B used as a substrate, showed no significant difference between the alcoholic and control groups in the activities. These two groups showed higher values in MAO activity than the schizophrenic group, whereas when MAO activity was estimated using serotonin, platelet enzyme was found to be inhibited significantly in alcoholism, and the level of activities in the schizophrenics was similar to that of the controls. Moreover, the β-phenylethylamine inhibition curve obtained serotonin as the substrate in the pooled platelets of 50 normal human subjects, and the MAO activity could not be inhibited by higher concentrations than the Km value of serotonin. These findings suggested that there might be two interacting catabolic sites having different substrate affinities in blood platelet MAO. Thus, it could be speculated that serotonergic catabolic sites of MAO in the platelets are disturbed in the alcoholics, while β-phenylethylaminergic catabolic sites of platelet MAO are inherently vulnerable in schizophrenia.     

The influence of selective serotonin reuptake inhibitors on human platelet serotonin

Clinical depression has been proposed to be an independent risk factor for cardiovascular disease. While it is suggested that selective serotonin reuptake inhibitors (SSRIs) reduce the risk of acute cardiovascular problems of depressed patients, the effect of SSRIs on platelets, the only blood cells committed to serotonin (5-HT) transport, remains largely unknown.The goal of this pilot study was to measure the 5-HT levels in platelets of untreated and SSRI-treated depressed patients and normal subjects and to determine whether the interaction of SSRIs with platelets can explain their possible cardiovascular benefit in patients with depression. Platelet 5-HT was determined by an immunocytochemical assay and high-pressure liquid chromatography with electrochemical detection (HPLC-ECD). In normal control subjects without cardiovascular disease, 78 +/- 8% of platelets were 5-HT-positive (n = 14). Depression caused a significant reduction in platelet 5-HT to 46 +/- 21% in untreated patients (n = 13) and 22 +/- 13% in SSRI-treated patients (n = 14). As a class, all selective serotonin reuptake inhibitors significantly reduced the 5-HT concentration in patient platelets. An inverse relationship of 5-HT level and dose of medication might be suggested.These results correlated well with 5-HT data from HPLC (r = 0.8509, p < 0.001). SSRIs did not affect platelet aggregation and dense granule release in response to thrombin, but significantly reduced ADP-induced platelet aggregation and dense granule release in both patient and normal control samples. The active inhibition of platelet aggregation by SSRIs might explain their cardiovascular benefit.     

Increased platelet intracellular calcium concentration in patients with bipolar affective disorders

Using the fluorescent indicator Fura 2, we measured the free intracellular calcium ion concentration in blood platelets of patients with untreated mania, bipolar depression, and unipolar depression; patients who had recovered from bipolar depression or mania; and age- and sex-matched controls. The baseline intracellular calcium ion concentration was significantly increased in platelets from patients with mania compared with controls. The free intracellular calcium ion concentration after stimulation with platelet-activating factor and thrombin was significantly higher in platelets of manic and bipolar depressed patients than in all other groups. The degree to which intracellular calcium ion concentration increased over baseline after stimulation was significantly lower in unipolar than in bipolar patients. These findings suggest that platelets of manic and depressed bipolar patients have a similar enhancement of intracellular calcium ion activity that is distinctly different from the decreased ability of platelets of unipolar patients to mobilize intracellular calcium in response to stimulation.     

Monoamine oxidase activity in blood platelets from autistic children

In order to evaluate the possible abnormality in monoamine oxidase (MAO) activity in early infantile autism, blood platelet samples were obtained from 20 autistic children, aged 2--12 years. MAO activity, measured fluorometrically using serotonin as substrate, was 5.24 +/- 1.65 (Mean +/- Standard Deviation) nM/MG protein/hour in these autistic children. This value was not significantly different from either that in 30 age-matched normal children or that in 39 nonautistic children with various psychiatric and neurological disorders, although autistic children had higher platelet serotonin concentration than these nonautistic individuals.     

Reduced inhibitory effect of imipramine on radiolabeled serotonin uptake into platelets in geriatric depression

Tritiated imipramine binding, uptake of radiolabeled serotonin, and inhibition of uptake by imipramine in vitro were studied in platelets obtained from four groups of subjects: (1) normal controls 50 years of age or younger, (2) patients with major depression 50 years of age or younger, (3) normal controls 60 years of age or older, and (4) patients with major depression 60 years of age or older. Depression in both age groups was associated with a substantial decrease in the number of [3H]imipramine binding sites; the elderly depressed patients exhibited a small but significant (p less than 0.05) reduction in platelet [3H]serotonin uptake. However, the inhibition of serotonin uptake into platelets by imipramine was markedly reduced only in the elderly depressed patients. This reduced sensitivity to imipramine may explain the reduced responsiveness of patients with geriatric depression to the therapeutic effects of imipramine and other tricyclic antidepressants.     

Calcium function in affective disorders and healthy controls

Calcium metabolism has been reported to be disturbed in some forms of affective disorder. We studied concurrently a battery of calcium measures in 29 unipolar, 14 bipolar depressed, 11 manic, and 10 healthy control subjects. In addition to measures of extracellular calcium, we studied intracellular calcium concentration in platelets and measures that reflect cellular capability to maintain a low intracellular Ca++ concentration in red blood cells (RBCs) and platelets. Plasma calcium was lower in unipolar and manic patients than in control subjects. Platelet calcium concentration was lower in unipolar than bipolar depressed patients. RBC Ca++ adenosine triphosphatase (ATPase) was lower in unipolar and control subjects than in bipolar depressed and manic patients. Platelet Ca++ ATPase and Ca++ uptake were inversely correlated with severity of illness in unipolar patients. In bipolar depressed patients, RBC Ca++ ATPase and platelet Ca++ uptake were inversely correlated with severity. In addition to indicating abnormalities in calcium activity in affective disorders, the data suggest that unipolar and bipolar patients differ in several measures and may have different pathophysiological disturbances in calcium metabolism.     

Lithium and valproic acid treatments reduce PKC activation and receptor-G protein coupling in platelets of bipolar manic patients

Dysregulated protein kinase C (PKC) distribution and activation, and abnormal receptor-G protein coupling, have been implicated in the pathophysiology of bipolar affective disorder (BD). The therapeutic effectiveness of lithium has also been correlated with its ability to reduce PKC activation and G protein-mediated signaling. We examine the cellular distribution and activation of PKC and receptor-G protein coupling in blood platelets from normal controls, patients with BD mania or schizophrenia during treatment-free state, and after lithium or valproic acid administration. PKC activity was measured under basal and 50 nM phorbol 12-myristate, 13-acetate (PMA), 1 microM serotonin or 0.5 U/ml thrombin-stimulated conditions. The coupling of G proteins to serotonin or thrombin receptors were assessed by serotonin or thrombin-mediated [35S]GTPgammaS binding to membrane Galpha proteins. The results demonstrate that membrane-associated PKC activity and stimulus-induced PKC translocation are increased in BD manic, whereas stimulus-elicited PKC translocation is attenuated in schizophrenic patients. Lithium and valproic acid treatments attenuated the stimulus-induced PKC translocations to a similar degree and decreased PKC activity in both cytosolic and membranous fractions after two weeks of drug administration. An increase in 5-HT or thrombin stimulated [35S]GTPgammaS binding to Galpha proteins was detected in BD manic but not in schizophrenic patients although basal [35S]GTPgammaS binding was not different across the diagnostic groups. Lithium and valproic acid treatments similarly reduced receptor-G protein coupling with comparable time courses. Thus, increased membrane-associated PKC, cytosol to membrane PKC translocation and receptor-G protein coupling in platelets of BD manic patients were alleviated by lithium or valproic acid treatments.     

Effect of 5-hydroxytryptophan on serum cortisol levels in major affective disorders. I. Enhanced response in depression and mania

The serum cortisol concentration following administration of 5-hydroxytryptophan (5-HTP), 200 mg orally, a precursor of serotonin (5-HT), was significantly greater in unmedicated depressed and manic patients than in normal controls. Increases in serum cortisol levels greater than 5 micrograms/dL were significantly more frequent in both unmedicated depressed and manic patients than in the normal controls. There was significant test-retest reliability. Baseline serum cortisol concentration correlated negatively with the cortisol response to 5-HTP in normal controls. These results suggest increased 5-HT receptor sensitivity may be present, possibly in the hypothalamus or pituitary, in some patients with affective disorders. These results are consistent with the hypothesis that decreased serotonergic activity, which would be expected to produce increased 5-HT receptor sensitivity, may be present in both depression and mania.     

Long-term sertraline treatment and peripheral biochemical markers in female depressed patients

Serotonergic system is implicated in the pathogenesis of depression. Peripheral biochemical markers, platelet serotonin (5-HT) and platelet monoamine oxidase (MAO) activity were determined spectrofluorimetrically at baseline and after 4 and 24 weeks of sertraline (a selective serotonin reuptake inhibitor (SSRI)) treatment in 15 female nonsuicidal, nonpsychotic patients with major depression and compared with 15 drug-free healthy women. The aim of the study was to determine the effects of 4 and 24 weeks of sertraline treatment on platelet 5-HT concentration and platelet MAO activity in depressed patients subdivided according to the treatment response into remitters, responders and nonresponders after 4 and 24 weeks of sertraline treatment based on the 70%, 50-69% and <49% reductions in baseline Montgomery-Asperg Depression Rating Scale (MADRS) scores, respectively. Platelet 5-HT concentration was significantly lower in all depressed patients at baseline than in healthy subjects. Among patients, platelet 5-HT concentration or platelet MAO activity did not differ before treatment. There was no significant correlation between MADRS scores and peripheral biochemical markers. The limitation of the study was in a small number of patients, but its advantage was in a long-term (24 weeks) follow-up of both patients and healthy controls. Our results show that long-term sertraline treatment induced remission and response in 87% patients, decreased platelet 5-HT concentration after 4 and 24 weeks of treatment and decreased platelet MAO activity after 24 weeks and suggest that pretreatment values of platelet 5-HT and platelet MAO might not predict therapeutic outcome to sertraline treatment in female depressed patients.     

Measurement of platelet monoamine oxidase using three different substrates in patients with alcoholism and schizophrenia

The platelet monoamine oxidase (MAO) activities in alcoholism and schizophrenia were investigated by means of simultaneous determination, using beta-phenyl-ethylamine, tryptamine and serotonin as substrates. No significant difference was found between the MAO levels in the alcoholic and schizophrenic groups, when tryptamine was used as a substrate, but both groups showed lower values than the controls. On the other hand, beta-phenylethylamine, a specific substrate for MAO B used as a substrate, showed no significant difference between the alcoholic and control groups in the activities. These two groups showed higher values in MAO activity than the schizophrenic group, whereas when MAO activity was estimated using serotonin, platelet enzyme was found to be inhibited significantly in alcoholism, and the level of activities in the schizophrenics was similar to that of the controls. Moreover, the beta-phenylethylamine inhibition curve obtained serotonin as the substrate in the pooled platelets of 50 normal human subjects, and the MAO activity could not be inhibited by higher concentrations than the Km value of serotonin. These findings suggested that there might be two interacting catabolic sites having different substrate affinities in blood platelet MAO. Thus, it could be speculated that serotonergic catabolic sites of MAO in the platelets are disturbed in the alcoholics, while beta-phenylethylaminergic catabolic sites of platelet MAO are inherently vulnerable in schizophrenia.     

Longitudinal effect of amitriptyline and fluoxetine treatment on plasma phenylacetic acid concentrations in depression

Unconjugated (U-PAA), conjugated (C-PAA), and total phenylacetic acid (T-PAA) concentrations in blood plasma and monoamine oxidase (MAO) activity in platelets towards phenylethylamine (PE) were determined in 40 drug-free, depressed patients (23 melancholic, 17 nonmelancholic) from five psychiatric treatment centers, and in 34 normal healthy volunteers. No significant differences were found between controls and all depressed patients or between melancholic and nonmelancholic depressed patients. Treatment of the depressed patients with amitriptyline or fluoxetine over a 6-week period resulted in clinical improvement and in a significant increase in plasma PAA concentrations. A decline in the Beck and Hamilton rating scores during treatment correlated significantly with increases in the concentrations of unconjugated, conjugated, and total phenylacetic acid but not with MAO activity, which did not change during treatment. At each of the three assessment times, however, plasma PAA concentrations and psychiatric rating scores were not significantly correlated. Except for higher end-of-study T-PAA concentrations in the amitriptyline-treated subjects, no significant differences were found between the effects of the two drugs with regard to plasma phenylacetic acid levels, MAO activity, or rating scores.