[3H]spiroperidol binding on lymphocytes: changes in two different groups of schizophrenic patients and effect of neuroleptic treatment

Dopamine receptors in human lymphocytes: radioligand binding and quantitative RT-PCR assays

Analysis of dopamine receptors (DR) in lymphocytes of the human peripheral blood mononuclear cell (PBMC) fraction is an attractive tool for evaluation of functional properties of dopaminergic function underlying variation in complex psychological/psychopathological traits. Receptor binding assays (RBAs) with selective radioligands, which are widely used in CNS studies, have not produced consistent results when applied to isolated PBMC. We tested the assay conditions that could be essential for detection of DR in human PBMC and their membrane preparations. Using [(3)H]SCH23390, a dopamine D1-like receptor antagonist, we demonstrated the presence of two binding sites in PBMC-derived membrane fraction. One of them is characterized by the K(d) value consistent with that reported for D5 dopamine receptors in human lymphocytes, whereas the other K(d) value possibly corresponds to serotonin receptor(s). Although D5 receptor binding sites in PBMC membranes could be characterized by binding assays, the low protein expression and the large volume of blood needed for membrane preparation render the binding method impracticable for individual phenotyping. In contrast, real-time RT-PCR may be used for this purpose, contingent on the relationship between DR expression in the brain and in lymphocytes. The expression of the DRD2-DRD5 genes, as detected by this method, varied widely among samples, whereas the DRD1 expression was not detected. The expression levels were comparable with those in the brain for DRD3 and DRD4, and were significantly lower for DRD2 and DRD5.

Specific binding of 3H-spiperone to peripheral blood cells: relevance for the interpretation of binding studies in psychiatric disorders

1. There is an ongoing discussion regarding the elevated binding of 3H-spiperone to lymphocytes of schizophrenic patients. Several authors described an atypical binding pattern with a saturable high-affinity and a nonsaturable binding site both displaceable by (+)-butaclamol. Recent findings are still controversial (Fartacek et al., 1997; Wodarz et al., 1996), possibly due to methodological differences. The authors investigated 3H-spiperone binding to different peripheral blood cells including B- and T-lymphoblastoids. 2. B-lymphocytes (KD = 0.081 nM; Bmax = 0.46 x 10(-15) mol/10(6) cells) and macrophages (KD = 0.1-1 nM, Bmax = 2.44 x 10(-15) mol/10(6) cells) are characterized by a minor but saturable binding of 3H-spiperone in a concentration range between 0.5 and 1 nM. Above 1 nM, only non-saturable binding was measurable. Interestingly, Epstein-Barr virus (EBV) transformed lymphoblastoids (KD = 0.13 nM) have nearly the same affinity for 3H-spiperone as native B-cells, but an increased number of binding sites (Bmax = 1.76 x 10(-15) mol/10(6) cells). 3. Membranes from B-lymphoblastoids displayed a saturable binding in a concentration between 0 and 1.8 nM of 3H-spiperone (KD = 0.5 nM and Bmax = 1.72 x 10(-15) mol/mg protein). Extraction with 1% digitonin resulted in a similar binding characteristic (KD = 0.17 nM and Bmax = 1.97 x 10(-15) mol/mg protein). 4. T-cells, granulocytes and MOLT-3-cells did not show is a saturable binding even not at high concentrations of 3H-spiperone. 5. The pharmacological profile of the high-affinity 3H-spiperone binding site is clearly different from the dopamine D2 and D4, serotonin 5-HT2 histamine H1 and noradrenergic alpha1 and alpha2 receptor, respectively. 6. In summary, the results suggest that spiperone binding studies to enriched lymphocytes of psychiatric patients should be interpreted cautiously. Variable amounts of leucocytes might result in a higher proportion of nonsaturable, butaclamol displaceable spiperone binding with relevance for the calculation of KD and Bmax of the saturable high-affinity site. Interestingly, homogenous B-lymphoblastoid cell lines have the same binding characteristics as native B-lymphocytes and therefore should be recommended for characterization of 3H-spiperone binding sites.

Dopamine D4 receptor in human peripheral blood lymphocytes: a radioligand binding assay study

The expression of dopamine D4 receptor was investigated in human peripheral blood lymphocytes with a radioligand binding assay technique, using [3H]clozapine as radioligand. [3H]Clozapine was specifically bound to human peripheral blood lymphocytes. The binding was time-, temperature-, and concentration-dependent and of high affinity, with a dissociation constant (K(d)) value of 0.34 +/- 0.02 nM and a maximum density of binding sites (B(max)) value of 27 +/- 1.4 fmol/10(6) cells. The pharmacological profile of [3H]clozapine binding to human peripheral blood lymphocytes was similar to that found in Chinese hamster ovary (CHO) cells transfected with the D4 clone (D4.2 variant). The above results are consistent with molecular biology studies demonstrating the expression of a dopamine D4 receptor in immune cells and in human peripheral blood lymphocytes. The availability of a rapid and sensitive radioligand binding assay technique for the dopamine D4 receptor in human peripheral blood lymphocytes may contribute to better define the role of this dopamine receptor subtype in neurological and psychiatric disorders.

Identification of dopamine D4 receptor mRNA in circulating human lymphocytes using nested polymerase chain reaction

There is a long standing controversy if dopamine receptors are present on human lymphocytes. In recent years the expression of dopamine D3 and D5 receptors was demonstrated with molecular biological methods. Using reverse transcription and polymerase chain reaction (RT-PCR) we were able to demonstrate the expression of the dopamine D4 receptor (DRD4) mRNA in human circulating lymphocytes. Direct sequencing of the RT-PCR product assured that it corresponds to the human DRD4 sequence. However, because of the unusual high G/C content of the DRD4, several precautions have to be applied for reliable results.

3H-spiperone binding to peripheral mononuclear cells in psychiatric in-patients

1. There is an ongoing controversy, if increased binding of 3H-spiperone to lymphocytes might discriminate between schizophrenia and other psychiatric diseases or even be a genetic vulnerability marker for schizophrenia, or predict the response to neuroleptic treatment. 2. Some critical methodological details which might contribute to this controversy are described. 3. 3H-spiperone binding was evaluated in 31 patients with schizophrenia, 7 patients with schizoaffective disorder, bipolar type, 6 patients with a manic episode and 6 patients with a depressive episode of bipolar major affective disorder (DSM-III-R criteria), and in 19 healthy subjects. 4. There were no significant differences in characteristic binding parameters (KD, Bmax) between all groups of psychiatric in-patients and in comparison to healthy subjects. Moreover, there was no relation of binding parameters to any of the subtypes of schizopherenia or to the course of illness according to DSM-III-R-criteria. 5. Neuroleptic treatment or clinical response to treatment had no consistent effect on binding parameters intra-individually. 6. In summary, 3H-spiperone binding to lymphocytes failed to differentiate between the diagnostic subgroups (DSM-III-R) and between treatment responders and non-responders in our sample of patients.

Evaluation of cyclic AMP accumulation in EBV-transformed human B-lymphocytes: effects of dopamine agonists, isoproterenol, prostaglandin E1, cholera toxin, forskolin, and phorbol 12-myristate-13 acetate

1. Phorbol 12-myristate-13-acetate (PMA), a protein kinase C activator, elevated cyclic AMP accumulation in EBV-transformed human B-lymphocytes, and potentiated isoproterenol-, prostaglandin- (PGE1), cholera toxin-, and forskolin-stimulated cyclic AMP accumulation. 2. The dopamine D1 receptor agonist, SKF38393 (10(-7) to 10(-5) MH, had no effect on cyclic AMP accumulation in transformed human B-lymphocytes. 3. The dopamine D2 receptor agonist, quinpirole (10(-7) to 10(-5) MH did not inhibit cyclic AMP accumulation even when cyclic AMP accumulation was maximized by the addition of PMA and forskolin. 4. These data suggest that dopamine D1- and D2-receptor coupling to a cyclic AMP generating system is not present at detectable levels in transformed human B-lymphocytes.

Radioligand binding characterization of putative dopamine D3 receptor in human peripheral blood lymphocytes with [3H]7-OH-DPAT

The presence and the pharmacological profile of dopamine D3 receptor have been investigated in human peripheral blood lymphocytes using radioligand binding techniques and the selective dopamine D3 receptor agonist [3H]7-hydroxy-N,N-di-n-pro-pyl-2-aminotetralin ([3H]7-OH-DPAT) as a ligand. [3H]7-OH-DPAT binding to human peripheral blood lymphocytes was time-, temperature-, and concentration-dependent and of high affinity with a dissociation constant value (Kd) of 0.27 +/- 0.05 nM and a maximum binding density (Bmax) of 14.7 +/- 0.06 fmol/2 x 10(6) cells. Binding was also reversible. The rank order of potency of displacers of [3H]7-OH-DPAT binding to human peripheral blood lymphocytes resembled that found for dopamine D3 receptor in rat brain homogenates or in rat or human cell lines. Our findings, which are consistent with those of other authors performed with molecular biology techniques, suggest that human peripheral blood lymphocytes express dopamine D3 receptor. In the brain, dopamine D3 receptor probably mediates the anti-psychotic effect of neuroleptics. The availability of a rapid and reproducible technique for its assay may contribute to evaluate its status in brain disorders characterized by impaired dopaminergic neurotransmission.

Dopamine D5 receptors in human peripheral blood lymphocytes: a radioligand binding study

In the present study we have investigated, using radioligand binding techniques and the dopamine receptor antagonist [3H]SCH 23390 as a ligand, the existence of specific dopamine D1-like receptors in human peripheral blood lymphocytes. [3H]SCH 23390 binding to human peripheral blood lymphocytes was time-, temperature-, concentration-dependent and of high affinity with a dissociation constant value (Kd) of 0.58 +/- 0.05 nM and a maximum binding density (Bmax) of 11.02 +/- 0.3 fmol/5 x 10(6) cells. The binding was also reversible. Pharmacological analysis displacement curves of [3H]SCH 23390 binding with dopamine competing with the radioligand in the submicromolar range suggests that peripheral blood lymphocytes express dopamine D5 receptors rather than dopamine D1 receptors. These results, which are consistent with studies performed with molecular biology techniques, suggest that dopamine may modulate peripheral blood lymphocyte activity. Radioligand binding techniques, applied to lymphocyte receptor studies for their feasibility and flexibility may be used to investigate the possible relationship between the immune and dopaminergic systems. Moreover, they could be employed as a tool in Parkinson's disease, migraine, schizophrenia and hypertension research.

Pharmacological characterization and autoradiographic localization of dopamine D1-like receptors in the thymus

The present study was designed to identify the pharmacological profile and the anatomical localisation of dopamine D1-like receptor sites in the rat thymus using [3H]SCH 23390 as a ligand. [3H]SCH 23390 was specifically bound to sections of the thymus. Binding was time, temperature and concentration-dependent belonging in the range of concentrations of radioligand used to a single class of high affinity sites. The dissociation constant was 1.6 nM and the maximal density of binding sites averaged to 170 fmol/mg tissue. The pharmacological profile of [3H]SCH 23390 binding to sections of the rat thymus is consistent with the labelling of dopamine D1-like sites. Dopamine was able to compete with [3H]SCH 23390 binding to sections of rat thymus in the range of nanomolar concentrations. This suggests the labelling of dopamine D5 receptor sites. Light microscope autoradiography revealed the localisation of [3H]SCH 23390 binding sites primarily in the cortex of the thymus and in lesser amounts at the level of thymic corpuscles. The possible functional significance of dopamine D1-like receptors in the rat thymus is discussed.

3H-spiroperidol binding to peripheral mononuclear cells in schizophrenic and healthy subjects

3H-spiroperidol binding to peripheral blood mononuclear cells was measured in 28 patients, who fulfilled DSM-III-R-criteria for schizophrenia and 17 healthy subjects. There were no significant differences in characteristic binding parameters (Kd, Bmax) between schizophrenic and healthy subjects. Moreover, there was no relation of binding parameters to any of the subtypes of schizophrenia or to the course of illness according to DSM-III-R-criteria. However, some patients exhibited higher Bmax values without having a unique clinical symptomatology according to known diagnostic criteria. Neuroleptic treatment had no consistent effect on binding parameters intraindividually. Kd and Bmax values were not related to age or gender. In conclusion, despite our previously reported improved methodology, we were not able to corroborate the clinical importance of this "peripheral marker" as a tool for diagnosing schizophrenia or for predicting the response to neuroleptic treatment in our sample of schizophrenic patients.

3H-spiroperidol binding to human peripheral mononuclear cells: methodological aspects

3H-spiroperidol binding to lymphocytes has been proposed as a vulnerability marker for schizophrenia. However, the biological significance and even existence of this "binding site" are still in controversy. Therefore, the present study reevaluated methodological details using a filtration binding assay. The results indicated that some well-known, but obviously uncontrolled pitfalls might contribute to this controversy [e.g., unspecific filter binding, which increased in the presence of (+)-butaclamol, or a variable amount of contaminating granulocytes). Moreover, due to an atypically shaped saturation curve, different mathematical methods to analyze the data were used and compared. The present data should help us to understand the biological relevance of this marker, as viewed in different laboratories.

The sequestration of [3H]spiperone by lymphocytes in schizophrenics and their first-degree relatives: a limited vulnerability marker?

The sequestration of [3H]spiperone by lymphocytes was studied in preserved cells obtained from 22 schizophrenic subjects and 40 of their relatives, and the results were compared with those obtained from 25 healthy control subjects. Mean displaceable sequestration values, obtained from measurements made at a single radioligand concentration (1nM) which optimised the relative contribution of "high affinity" sequestration, were found to be similar for all groups of subjects. Furthermore, displaceable spiperone sequestration was abnormally high in only a small proportion of the schizophrenics (13.6%) and their relatives (5%). There was no evidence that either exposure to neuroleptic medication or duration of illness had an effect on sequestration values. The results suggest that, at least until the required experimental conditions are better established, [3H]spiperone sequestration by lymphocytes does not offer a useful vulnerability marker for schizophrenia.

3H-spiperone labels sigma receptors, not dopamine D2 receptors, in rat and human lymphocytes

3H-Spiperone binds to dopamine D2 receptors in striatum and, under the assumption that it labels the same receptors in lymphocytes, this binding site has been suggested as a biological marker for schizophrenia. Recent studies, however, have raised questions about the existence of dopamine receptor changes in drug-free schizophrenic patients, as well as on the presence and/or dopaminergic nature of lymphocytic 3H-spiperone binding sites. In the present study we have conducted an investigation of the binding of 3H-spiperone to rat and human lymphocytes. We found that 3H-spiperone binds in a specific, saturable and reversible manner to a site in lymphocytes; however, its dissociation constant Kd (9 nM) is about 40-fold higher than in striatum. An extensive investigation of the 3H-spiperone sites indicated that their pharmacological profile was not that of a dopamine D2 site, but rather that of sigma receptors, a novel class of non-dopaminergic, non-opioid receptors which bind with high affinity antipsychotic drugs. Sigma receptors were also identified in lymphocytes using the specific ligand 3H-DTG (1,3-di-o-tolyl-guanidine), whose binding characteristics were comparable to those of sigma receptors in rat brain. Receptor density and the pharmacological profile of 3H-spiperone and 3H-DTG were similar. Both compounds also labelled a higher number of sites in B cells than in T cells and a good correlation was found between the lymphocytic binding of both ligands in a group of 58 people. These findings indicate that sigma receptors are present in lymphocytes and suggest that 3H-spiperone binding in these cells occurs to sigma sites and not to dopamine D2 sites.

Methodology of 3H-spiperone binding to lymphocytes

Alterations in lymphocyte binding capacity for the dopamine antagonist 3H-spiperone may be of great interest in psychiatric and neurological disorders: an increase in capacity noted in lymphocytes of schizophrenic patients and their families may well turn out to be a phenotypic vulnerability marker. Since the 3H-spiperone binding assay with lymphocytes does not fulfill common receptor-binding assay criteria and depends more on crucial analytical conditions, shortcomings in binding assay might possibly lead to irreproducible results. A detailed methodological description of the binding assay and subsequent calculations has therefore been given in this paper.

Binding of 3H-spiperone to human peripheral lymphocytes: absence of stereospecific high-affinity binding

The binding of 3H-spiperone to human peripheral lymphocytes (PBL) was characterized. The (+)-butaclamol displaceable binding of 3H-spiperone was not saturable, and both (+) and (-)-butaclamol were equally potent in displacing 3H-spiperone binding. We did not find evidence for the existence of a high-affinity specific binding site of 3H-spiperone on human PBL.

Uptake of 3H-spiperone by lymphocytes in schizophrenia

Uptake of 3H-spiperone into lymphocytes obtained from control subjects (N = 22), chronic schizophrenics (N = 20), relatives with psychiatric disorder (N = 11) and unaffected relatives (N = 17) was studied. No differences were observed in spiperone uptake among any of the groups examined. Although previous investigations reported marked differences in 3H-spiperone uptake between schizophrenic and control subjects, we were unable to replicate their findings: the failure to replicate those of Bondy and colleagues may well be due to our inability to duplicate in our laboratory the exact biochemical methodology described by these investigators. Saturation curves could not be determined for most subjects. In addition, chronicity of illness and long-term exposure to neuroleptic medication among the schizophrenic subjects may partially account for the contradictory results reported by different investigators.

Cyclic adenosine 3',5'-monophosphate response to dopamine in mouse lymphoid cells and cell lines

Cyclic adenosine 3',5'-monophosphate responses to dopamine and isoproterenol were studied in mouse and rat spleen, thymus, lymph nodes and Peyer's patches lymphocytes and in 7 mouse cell lines of T- and B-lymphoid derivation. The responses of normal cells to dopamine were moderate, of the same extent, but selective to spleen and thymus in mouse, and to spleen and lymph nodes in rat. The YAC-1 T lymphoma cell line was sensitive to dopamine with a higher magnitude than normal lymphoid cells. Dopamine was less potent than isoproterenol in all cells, and whereas dopamine-sensitive and isoproterenol-sensitive cells, or dopamine-insensitive and isoproterenol-insensitive cells were found, no cell type was dopamine-sensitive and isoproterenol-insensitive. Altogether, these results suggest that only a small subset of lymphocytes is susceptible to the cAMP-elevating action of dopamine.

Dopamine receptors and the dopamine hypothesis of schizophrenia

The discovery of neuroleptic drugs in 1952 provided a new strategy for seeking a biological basis of schizophrenia. This entailed a search for a primary site of neuroleptic action. The Parkinsonian effects caused by neuroleptics suggested that dopamine transmission may be disrupted by these drugs. In 1963 it was proposed that neuroleptics blocked "monoamine receptors" or impeded the release of monoamine metabolites. The neuroleptic concentration in plasma water or cerebrospinal fluid was of the order of 2 nM for haloperidol in clinical therapy. A systematic research was made between 1963 and 1974 for a primary site of neuroleptic action which would be sensitive to 2 nM haloperidol and stereoselective for (+)-butaclamol. Direct evidence that neuroleptics selectively blocked dopamine receptors occurred in 1974 with the finding that nanomolar concentrations of these drugs stereoselectively inhibited the binding of [3H]-dopamine or [3H]-haloperidol. These binding sites, now termed D2 dopamine receptors (which inhibit adenylate cyclase), are blocked by neuroleptics in direct relation to the antipsychotic potencies of the neuroleptics. No such correlation exists for D1 receptors (which stimulate adenylate cyclase). Based on the fact that dopamine-mimetic drugs elicited hallucinations, and that neuroleptics caused rigidity, Van Rossum in 1966 had suggested a hypothesis that dopamine pathways may be overactive in schizophrenia. The D2-selective blockade by all neuroleptics (except the monoamine-depleting reserpine) provided strong support for the dopamine hypothesis. Further support now comes from postmortem data and in vivo positron tomographic data, both of which indicate that the density of D2 receptors are elevated in the schizophrenic brain. The postmortem data indicate a bimodal pattern with half the schizophrenics having striatal D2 densities of 14 pmol/g (control is 13 pmol/g) and the other half having 26 pmol/g. Current positron tomographic data indicate D2 densities of 14 pmol/g in control subjects, but values of 34 pmol/g in drug-naive schizophrenics. Future tests of the dopamine hypothesis of schizophrenia may entail an examination of the amino acid composition and genes for D2 receptors in schizophrenic tissue, an examination of the ability of the D2 receptor to become phosphorylated and to desensitize into the low-affinity state, and an examination of the interaction of D2 receptors with D1 receptors or other neurotransmitters.

3H-spiperone binding sites in lymphocytes as possible vulnerability marker in schizophrenia

The binding parameters for the dopamine antagonist 3H-spiperone to lymphocytes were investigated in nonmedicated schizophrenics (N = 43), in medicated schizophrenics (N = 25), as well as in 38 first- and second-degree relatives of schizophrenics, in a psychiatric control group (N = 27) and in normal, healthy controls (N = 40). The density of lymphocyte 3H-spiperone binding sites (Bmax) was significantly increased in all acute and chronic schizophrenic patients and in patients undergoing neuroleptic treatment for 2 weeks to several months and remained on a constant level during a drug-free remission period, suggesting that Bmax is a state independent variable. Elevated binding seems to be associated with schizophrenia; it could not be found in other psychiatric patients. In pedigree and family studies it became obvious that all relatives with one or more previous episodes of schizophrenia had similar increased binding capacity. But even in some well-state relatives elevated spiperone binding could be found, although they never had symptoms of the disease. Among these relatives of schizophrenics, there was an association between increased spiperone binding and the transmission of the disease. Although conclusive data about the precise genetic control obtainable in twin studies are still missing, we would suggest that elevated lymphocyte spiperone binding may be a marker of susceptibility to schizophrenia.

Binding of 3H-spiperone to human lymphocytes: a biological marker in schizophrenia?

The specific binding of the dopamine antagonist 3H-spiperone to lymphocytes from a healthy control group (n = 40), a group of acute, unmedicated schizophrenic patients (n = 27), and a psychiatric control group (n = 16) was investigated. There were no differences in binding parameters between the healthy controls (Bmax 2.6 +/- 0.7 fmoles/10(6) cells; Kd 0.17 +/- 0.07 nM) and the psychiatric control group. Binding capacity of 3H-spiperone was significantly increased in lymphocytes from the schizophrenic patients (Bmax 14.4 +/- 9.3 fmoles/10(6) cells). Moreover, a slight decrease in affinity was observed (Kd 0.44 +/- 0.21 nM). Because the increase in binding appeared only in schizophrenic patients, this peripheral model could prove valuable as a diagnostic criterion.

Reduced binding of 3H-spiroperidol to lymphocyte in Wilson's disease

Biochemical studies of CSF from patients with Wilson's disease (WD) have increased that alterations in the state of dopaminergic and serotoninergic systems are similar to those manifested in Parkinson's disease. Recently, the density of dopaminergic receptors on lymphocytes has been found to be diminished in Parkinson's disease. In the present study, 3H-spiroperidol binding was evaluated in lymphocytes acquired from 12 patients suffering from WD, as compared to blood donors. A significant decrease in the number of binding sites (Bmax) was observed in the lymphocytes of the WD patients. There was no clear relationship between clinical status, age and duration of the disease and the alterations in receptor density. The mechanism underlying the decrease in lymphocyte 3H-spiroperidol binding sites in WD demands clarification.

Lymphocyte 3H-spiroperidol binding in schizophrenia: preliminary findings

Binding of 3H-spiroperidol was determined in ten (10) unmedicated recently admitted and four (4) drug holiday schizophrenic patients to determine whether it could serve as a peripheral marker of central dopaminergic hyperactivity. Preliminary results indicate significantly increased binding but there is considerable intersubject variability. Displacement studies, the lack of stereospecificity and the necessity of having an intact lymphocyte do not indicate that this is binding to a dopamine receptor but rather an uptake phenomenon.