Dopamine D2-like receptors on human peripheral blood lymphocytes: a radioligand binding assay and immunocytochemical study

The role of dopamine receptors in lymphocytes and their changes in schizophrenia

Dopamine and its 5 receptors, which are grouped into two families (D1-like and D2-like), modulate functions at a systemic level in both the central nervous system and periphery. The central nervous system and the immune system are the main adaptive systems, which participate in a continuous and functional crosstalk to guarantee homeostasis. On binding to its 5 dopamine receptors, dopamine acts as a co-regulator of the immune system, contributing to the interaction of the central nervous system and inflammatory events and as a source of communication between the different immune cells. Dopaminergic perturbations in the central nervous system are observed in several neurological and psychiatric disorders. Schizophrenia is one of the most common mental disorders with a poorly understood pathoaetiology that includes genetic and environmental components that promote alterations in the dopaminergic system. Interestingly, abnormalities in dopamine receptors expression in lymphocytes of schizophrenia patients have been reported, often significantly correlating with the severity of the psychotic illness. Here, we review the current literature regarding the dopaminergic system in human lymphocytes and its alterations in schizophrenia.

1.

The existence of DA in the bloodstream suggests the presence of dopaminergic components that modulate functions at a systemic level; therefore, its effects are not limited to the CNS and the signalling in the neuronal dopaminergic system should be independent from that of the peripheral systems.

2.

The effects by DA-mediated activation of different DRs on immune cells show different sensitivities to DA, but binding profiles of DA on T cells are similar to those in neuronal membranes, suggesting receptors act similarly to those found in neurons.

3.

All DRs are expressed on the LYM membrane. However, more detailed information is required on the expression patterns of DR in immune cells in healthy conditions and in pathologies.

4.

DA has been observed to influence LYM functions acting in a variety of important processes, like cytokine secretion, cell adhesion, chemotaxis, and cytotoxicity.

5.

In human LYM, DA on D1-like receptors decreases oxidative metabolism and apoptosis, activates the selective secretion of IL-10 and TNFα, and facilitates NK cells. In contrast, most of the immunostimulatory DA effects on LYM depend on stimulation of D2-like receptors including activation, proliferation, differentiation, and suppression of NK cells.

6.

To date, an altered expression or signalling of neurotransmitter receptors is observed in immune cells during psychiatric disorders and, consequently, these cells also markedly respond to antipsychotics.

7.

Numerous technologies have been used in search of biomarkers for SCZ. However, after a century of studying SCZ their application in psychiatry remains rare and there are currently no validated biomarkers for the diagnosis and prognosis of patients with SCZ or the prediction of treatment efficacy.

Transplantation with Lewis bone marrow induces the reinstatement of cocaine-seeking behavior in male F344 resistant rats

One of the main challenges to understand drug addiction is defining the biological mechanisms that underlie individual differences in recidivism. Studies of these mechanisms have mainly focused on the brain, yet we demonstrate here a significant influence of the peripheral immune system on this phenomenon. Lewis (LEW) and Fischer 344 (F344) rats have different immunological profiles and they display a distinct vulnerability to the reinforcing effects of cocaine, with F344 more resistant to reinstate cocaine-seeking behavior. Bone marrow from male LEW and F344 rats was transferred to male F344 rats (F344/LEW-BM and F344/F344-BM, respectively), and these rats were trained to self-administer cocaine over 21 days. Following extinction, these animals received a sub-threshold primer dose of cocaine to evaluate reinstatement. F344/LEW-BM but not F344/F344-BM rats reinstated cocaine-seeking behavior, in conjunction with changes in their peripheral immune cell populations to a profile that corresponded to that of the LEW donors. After cocaine exposure, higher CD4⁺ T-cells and lower CD4⁺CD25⁺ T-cells levels were observed in F344/LEW-BM rats referred to control, and the splenic expression of Il-17a, Tgf-β, Tlr-2, Tlr-4 and Il-1β was altered in both groups. We propose that peripheral T-cells respond to cocaine, with CD4⁺ T-cells in particular undergoing Th17 polarization and generating long-term memory, these cells releasing mediators that trigger central mechanisms to induce reinstatement after a second encounter. This immune response may explain the high rates of recidivism observed despite long periods of detoxification, shedding light on the mechanisms underlying the vulnerability and resilience of specific individuals, and opening new perspectives for personalized medicine in the treatment of relapse.

Pro-inflammatory dopamine-2 receptor-specific T cells in paediatric movement and psychiatric disorders

Objectives

A dysregulated inflammatory response against the dopamine‐2 receptor (D2R) has been implicated in movement and psychiatric disorders. D2R antibodies were previously reported in a subset of these patients; however, the role of T cells in these disorders remains unknown. Our objective was to identify and characterise pro‐inflammatory D2R‐specific T cells in movement and psychiatric disorders.

Methods

Blood from paediatric patients with movement and psychiatric disorders of suspected autoimmune and neurodevelopmental aetiology (n = 24) and controls (n = 16) was cultured in vitro with a human D2R peptide library, and D2R‐specific T cells were identified by flow cytometric quantification of CD4⁺CD25⁺CD134⁺ T cells. Cytokine secretion was analysed using a cytometric bead array and ELISA. HLA genotypes were examined in D2R‐specific T‐cell‐positive patients. D2R antibody seropositivity was determined using a flow cytometry live cell‐based assay.

Results

Three immunodominant regions of D2R, amino acid (aa)121–131, aa171–181 and aa396–416, specifically activated CD4⁺ T cells in 8/24 patients. Peptides corresponding to these regions were predicted to bind with high affinity to the HLA of the eight positive patients and had also elicited the secretion of pro‐inflammatory cytokines IL‐2, IFN‐ γ, TNF, IL‐6, IL‐17A and IL‐17F. All eight patients were seronegative for D2R antibodies.

Conclusion

Autoreactive D2R‐specific T cells and a pro‐inflammatory Th1 and Th17 cytokine profile characterise a subset of paediatric patients with movement and psychiatric disorders, further underpinning the theory of immune dysregulation in these disorders. These findings offer new perspectives into the neuroinflammatory mechanisms of movement and psychiatric disorders and can influence patient diagnosis and treatment.

Influence of chronic L-DOPA treatment on immune response following allogeneic and xenogeneic graft in a rat model of Parkinson's disease

Although intrastriatal transplantation of fetal cells for the treatment of Parkinson's disease had shown encouraging results in initial open-label clinical trials, subsequent double-blind studies reported more debatable outcomes. These studies highlighted the need for greater preclinical analysis of the parameters that may influence the success of cell therapy. While much of this has focused on the cells and location of the transplants, few have attempted to replicate potentially critical patient centered factors. Of particular relevance is that patients will be under continued L-DOPA treatment prior to and following transplantation, and that typically the grafts will not be immunologically compatible with the host. The aim of this study was therefore to determine the effect of chronic L-DOPA administered during different phases of the transplantation process on the survival and function of grafts with differing degrees of immunological compatibility. To that end, unilaterally 6-OHDA lesioned rats received sham surgery, allogeneic or xenogeneic transplants, while being treated with L-DOPA before and/or after transplantation. Irrespective of the L-DOPA treatment, dopaminergic grafts improved function and reduced the onset of L-DOPA induced dyskinesia. Importantly, although L-DOPA administered post transplantation was found to have no detrimental effect on graft survival, it did significantly promote the immune response around xenogeneic transplants, despite the administration of immunosuppressive treatment (cyclosporine). This study is the first to systematically examine the effect of L-DOPA on graft tolerance, which is dependent on the donor-host compatibility. These findings emphasize the importance of using animal models that adequately represent the patient paradigm.

Immunomodulatory Effects Mediated by Dopamine

Dopamine (DA), a neurotransmitter in the central nervous system (CNS), has modulatory functions at the systemic level. The peripheral and central nervous systems have independent dopaminergic system (DAS) that share mechanisms and molecular machinery. In the past century, experimental evidence has accumulated on the proteins knowledge that is involved in the synthesis, reuptake, and transportation of DA in leukocytes and the differential expression of the D1-like (D1R and D5R) and D2-like receptors (D2R, D3R, and D4R). The expression of these components depends on the state of cellular activation and the concentration and time of exposure to DA. Receptors that are expressed in leukocytes are linked to signaling pathways that are mediated by changes in cAMP concentration, which in turn triggers changes in phenotype and cellular function. According to the leukocyte lineage, the effects of DA are associated with such processes as respiratory burst, cytokine and antibody secretion, chemotaxis, apoptosis, and cytotoxicity. In clinical conditions such as schizophrenia, Parkinson disease, Tourette syndrome, and multiple sclerosis (MS), there are evident alterations during immune responses in leukocytes, in which changes in DA receptor density have been observed. Several groups have proposed that these findings are useful in establishing clinical status and clinical markers.

The cross-talk of HIV-1 Tat and methamphetamine in HIV-associated neurocognitive disorders

Antiretroviral therapy has dramatically improved the lives of human immunodeficiency virus 1 (HIV-1) infected individuals. Nonetheless, HIV-associated neurocognitive disorders (HAND), which range from undetectable neurocognitive impairments to severe dementia, still affect approximately 50% of the infected population, hampering their quality of life. The persistence of HAND is promoted by several factors, including longer life expectancies, the residual levels of virus in the central nervous system (CNS) and the continued presence of HIV-1 regulatory proteins such as the transactivator of transcription (Tat) in the brain. Tat is a secreted viral protein that crosses the blood–brain barrier into the CNS, where it has the ability to directly act on neurons and non-neuronal cells alike. These actions result in the release of soluble factors involved in inflammation, oxidative stress and excitotoxicity, ultimately resulting in neuronal damage. The percentage of methamphetamine (MA) abusers is high among the HIV-1-positive population compared to the general population. On the other hand, MA abuse is correlated with increased viral replication, enhanced Tat-mediated neurotoxicity and neurocognitive impairments. Although several strategies have been investigated to reduce HAND and MA use, no clinically approved treatment is currently available. Here, we review the latest findings of the effects of Tat and MA in HAND and discuss a few promising potential therapeutic developments.

Expression of dopaminergic receptors on human CD4+ T lymphocytes: flow cytometric analysis of naive and memory subsets and relevance for the neuroimmunology of neurodegenerative disease

Dopamine (DA) is a crucial transmitter in the neuroimmune network, where it contributes to the nervous system-immune system interplay as well as in the communication among immune cells. DA acts through five different dopaminergic receptors (DR) grouped into two families: the D1-like (D1 and D5) and the D2-like (D2, D3 and D4). By use of 5-color flow cytometric analysis, we examined the expression of DR on human CD4+ naive T lymphocytes (CD3+CD4+CD45RA+CCR7+), central memory (TCM, CD3+CD4+CD45RA-CCR7+) and effector memory T cells (TEM, CD3+CD4+CD45RA-CCR7-). In addition, in cultured CD4+ T cells we investigated the changes in DR expression induced by stimulation with antiCD3/antiCD28 antibodies. Results showed that CD4+ T cells always expressed all the five DR: D1-like DR were identified on average on 11.6-13.1 % and D2-like DR on 3.1-8.1 % of the cells. DR on CD4+ naive T cells, TCM, and TEM had distinct expression patterns: naive T cells expressed more D1-like than D2-like DR, which on the contrary were increased in TCM and TEM cells. In cultured CD4+ T cells stimulation with anti-CD3/anti-CD28 antibodies increased the expression of D1-like DR by 71-84 % and of D2-like DR by 55-97 %. The frequency of DR was higher in apoptotic cells in comparison to viable cells, however stimulation increased all DR on viable cells, without affecting their expression on apoptotic cells. The present results contribute to unravel the complexity of dopaminergic pathways in human CD4+ T lymphocytes, suggesting their involvement in memory functions as well as in apoptotic processes. In view of the role of CD4+ memory T cells in neuroinflammation and neurodegeneration during Parkinson's disease, the relevance of these findings must be assessed in the clinical setting.

Methamphetamine toxicity and its implications during HIV-1 infection

Over the past two decades methamphetamine (MA) abuse has seen a dramatic increase. The abuse of MA is particularly high in groups that are at higher risk for HIV-1 infection, especially men who have sex with men (MSM). This review is focused on MA toxicity in the CNS as well as in the periphery. In the CNS, MA toxicity is comprised of numerous effects, including, but not limited to, oxidative stress produced by dysregulation of the dopaminergic system, hyperthermia, apoptosis, and neuroinflammation. Multiple lines of evidence demonstrate that these effects exacerbate the neurodegenerative damage caused by CNS infection of HIV perhaps because both MA and HIV target the frontostriatal regions of the brain. MA has also been demonstrated to increase viral load in the CNS of SIV-infected macaques. Using transgenic animal models, as well as cultured cells, the HIV proteins Tat and gp120 have been demonstrated to have neurotoxic properties that are aggravated by MA. In addition, MA has been shown to exhibit detrimental effects on the blood-brain barrier (BBB) that have the potential to increase the probability of CNS infection by HIV. Although the effects of MA in the periphery have not been as extensively studied as have the effects on the CNS, recent reports demonstrate the potential effects of MA on HIV infection in the periphery including increased expression of HIV co-receptors and increased expression of inflammatory cytokines.

Alterations of the dopamine transporter in resting lymphocytes of patients with different psychotic disorders

The aim of our study was to investigate and compare the dopamine (DA) transporter (DAT) in resting lymphocytes of 20 psychotic patients and 20 healthy control subjects, by means of both the binding parameters (Bmax and Kd) of 3H-WIN 35,428, and the reuptake parameters (Vmax and Km) of 3H-DA. The results showed that both the Bmax of 3H-WIN 35,428 binding and the Vmax of 3H-DA reuptake of the patients were significantly lower than those of healthy subjects, while the Kd or Km did not show any change. These findings, while indicating a reduced density of the lymphocyte DAT proteins, provide further support of the role of DA in psychoses and suggest that DA alterations may not be limited to brain structures.

Effects of insulin-like growth factor-1 on rotenone-induced apoptosis in human lymphocyte cells

Human peripheral blood lymphocytes have been useful as a putative model of oxidative stress-induced apoptosis for Parkinson's disease. The present work shows that rotenone, a mitochondrial complex I inhibitor, induced time- and concentration-dependent apoptosis in lymphocytes which was mediated by anion superoxide radicals (O(2)*(-))/hydrogen peroxide, depolarization of mitochondria, caspase-3 activation, concomitantly with the nuclear translocation of transcription factors such as NF-kappaB, p53, c-Jun and nuclei fragmentation. Since insulin-like growth factor-1 (IGF-1) interferes with a cell's apoptotic machinery when subjected to several stressful conditions, it is demonstrated here for the first time that IGF-1 effectively protects lymphocytes against rotenone through PI-3K/Akt activation, down-regulation of p53 and maintenance of mitochondrial membrane potential independently of ROS generation. These data might contribute to understanding the role played by IGF-1 against oxidative stress stimuli.

Dopamine transporter immunoreactivity in peripheral blood lymphocytes in multiple system atrophy

Previous studies showed the reduction of dopamine transporter immunoreactivity (DAT-IR) in peripheral blood lymphocytes (PBL) in Parkinson's disease. Here we report the reduction of DAT-IR in PBL in the extrapyramidal variant of multiple system atrophy. These results suggest the reduction of DAT-IR in PBL in a variety of neurodegenerative disorders, provided the presence of damage of the central dopaminergic systems. The reduction of DAT-IR in PBL in these disorders may represent a compensatory phenomenon aimed at reducing intracellular dopamine influx and, consequently, dopamine-mediated aggravation of oxidative stress in these cells.

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.

Neural control of the velum in larvae of the gastropod, Ilyanassa obsoleta

Larval molluscs commonly use ciliated vela to swim and feed. In this study we used immunohistochemistry to demonstrate innervation of velar cilia and muscles by monoaminergic and peptidergic fibres in the caenogastropod, Ilyanassa obsoleta. Photoelectric recordings from pre-oral cilia on isolated pieces of velum revealed that serotonin increased, whereas catecholamines (dopamine and norepinephrine) decreased beat frequency at concentrations of 10(-6) to 10(-9) mol l(-1). Catecholamines also increased the frequency of momentary, isolated arrests of pre-oral cilia, but failed to suppress beating of the post-oral cilia at these concentrations. The neuropeptides, FMRFamide and Leu-enkephalin, did not affect the frequency of ciliary beating or of isolated ciliary arrests, but did induce numerous muscular contractions, which were accompanied by sustained ciliary arrests. In terms of whole animal behaviour, serotonin caused larvae to concentrate toward the top of a water column and to increase feeding, whereas catecholamines caused larvae to concentrate toward the bottom of a water column and decrease feeding. Monoamine analogues which facilitated or opposed the effects of synthetic transmitters on larval behaviour, further suggested that these transmitters are released endogenously to control velar function. Finally, applications of peptides to whole larvae caused increased frequency of locomotory arrests. Together these findings demonstrate several potential roles for the nervous system in controlling larval behaviour in gastropods.

Reactions between beta-casomorphins-7 and 5-HT2-serotonin receptors

Radioreceptor analysis showed that human beta-casomorphin-7 displaced 3H-spiperone from 5-HT2-serotonin receptors of the rat cerebral frontal cortex: EC50 8 +/- 1 microM. Human and bovine beta-casomorphin-7 dose-dependently blocked serotonin-induced human platelet aggregation: IC50 5 +/- 1 and 20 +/- 4 microM, respectively. It was proved that beta-casomorphins-7 act as 5-HT2-serotonin receptor antagonists; one of the mechanisms of their biological effects is presumably associated with modulation of the serotoninergic system.

Insulin-like growth factor-1 prevents Abeta[25-35]/(H2O2)- induced apoptosis in lymphocytes by reciprocal NF-kappaB activation and p53 inhibition via PI3K-dependent pathway

The role of insulin-like growth factor (IGF-1) as neural survival factor for the treatment of Alzheimer's disease has recently gained attention. The present study shows that IGF-1 protects lymphocytes from (10, 30 microM) Abeta[(25-35)] and (25, 50, 100 microM) H(2)O(2)-induced apoptosis through NF-kappaB activation and p53 down regulation involving the phosphoinositide 3-kinase (PI-3K)-dependent pathway as demonstrated by using either (25 microM) LY294002 (PI-3K inhibitor), (10 nM) ammonium pyrrolidinedithiocarbamate (PDTC; NF-kappaB inhibitor), 50 nM pifithrin-alpha (PFT; p53 inhibitor) or by using immunocytochemistry detection of NF-kappaB and p53 transcription factors activation. Importantly, IGF-1, PDTC and PFT were able to protect and rescue lymphocytes pre-exposed to 10 muM Abeta[(25-35)], even when the three compounds were added up-to 12 h post- Abeta[(25-35)] exposure. Altogether these results suggest that survival/rescue of lymphocytes from Abeta[(25-35)] toxicity is determined by p53 inactivation via IGF-1/ PI-3K pathway.

Changes in innate and acquired immune responses in mice with targeted deletion of the dopamine transporter gene

The dopamine transporter (DAT) is responsible for the re-uptake of dopamine into presynaptic nerve terminals and thereby controls dopaminergic neurotransmission. Deletion of DAT results in a hyperdopaminergic phenotype and DAT(-/-) mice are characterized by pituitary hypoplasia, impaired maternal behavior, and increased locomotion. From earlier studies, we have evidence that the activity of the central dopaminergic system may play a role in determining immune reactivity and disease susceptibility. To further explore the functional relation between the dopaminergic system and the immune system, we investigated the activity of the immune system in DAT(-/-) mice. We show that in vitro, splenocytes from DAT(-/-) mice displayed reduced natural killer cell activity and reduced mitogen-induced cytokine responses. In contrast, LPS-induced cytokine production by macrophages was enhanced. In vivo, the cellular response to immunization with ovalbumine (OVA-induced delayed type hypersensitivity response) was significantly reduced. Interestingly, the OVA-induced humoral response (anti-OVA IgG) was increased in DAT(-/-) mice compared to wild-type animals. Plasma levels of catecholamines and corticosterone did not differ significantly between DAT(-/-) and wild-type animals. In conclusion, we show in the present study that interfering with the dopaminergic system has major consequences for both the acquired and the innate immune response.

Dopamine exerts no acute effects on Kv1.3 in activated encephalitogenic T cells

Apart from a central function in the extrapyramidal motor system, dopamine has been suggested to play a role in neuroimmune interactions. Particularly in diseases of the central nervous system, such as multiple sclerosis, alterations in dopamine homeostasis might have immunological consequences. We investigated potential effects of dopamine stabilized by ascorbic acid on specifically activated encephalitogenic T cells at the peak of activation. Those cells exhibited an upregulation of voltage-sensitive K+ channels which play a role in many neurotransmitter responses of lymphocytes and fulfilled a prerequisite to respond to dopamine, i.e. stable expression of mRNA for dopamine receptors DRD1, DRD2 and DRD3. However, whole-cell and perforated whole-cell recordings revealed no change in voltage-sensitive K+ currents. Moreover, T cell proliferation was not changed in the presence of dopamine. Previously reported dopamine effects on T cells may be explained by a comparatively lower activation of the cells under investigation, suggesting an activation dependence of dopamine effects that may not be mediated by K+ channels. Alternatively, the occurrence of dopamine degradation products under unprotected conditions may account for the changes reported. Nevertheless, care should be taken when using the dopamine-protecting anti-oxidant ascorbic acid, since we found that it markedly inhibited both K+ currents and lymphocyte proliferation at higher concentrations.

Exploration of neuroendocrine and immune gene expression in peripheral blood mononuclear cells

As pathways of communication between the nervous, endocrine, and immune systems are identified, the importance of the interplay of these systems for health and well-being is increasingly recognized. In this study, we created a comprehensive database of 1622 genes likely to be involved in synthetic, biochemical, and regulatory psycho-neuroendocrine-immune (PNI) pathways. Expression of 1058 of these genes was detected in the peripheral blood by querying both a peripheral blood-specific expressed sequence tag (EST) database and a peripheral blood database generated from microarray evaluation of 30,000 genes. Several neural and endocrine genes were expressed in the peripheral blood including hormone receptors, a hormone-responsive transcription factor, and neurotransmitter receptors. These findings document the expression of nervous and endocrine genes in the peripheral blood that have previously only been characterized in the respective system tissues, and indicate that the blood is a rich source of information that should help in deciphering the communication between the mind and the body.

The effect of citalopram on gene expression profile of Alzheimer lymphocytes

Antidepressants are widely used in the treatment of mood disorders associated with dementia, however little information is available on their effect at the molecular level. In certain neurodegenerative disorders, such as in Alzheimer's disease, lymphocytes have been used to assess mirror changes that thought to occur in the brain. Gene expression profiles of lymphocytes from Alzheimer patients have been shown to differ from that seen with controls. To address this issue in light of antidepressant treatment, we used lymphocytes derived from Alzheimer's disease patients and control individuals to assess the impact of the selective serotonine reuptake inhibitor citalopram on gene expression using a cDNA microarray representing 3200 distinct human genes. Sequences that are differentially regulated after treatment with citalopram were identified and categorized based on similarities in biological functions. This analysis revealed that the overexpression of genes in control and Alzheimer white blood cells by citalopram are implicated in cell survival. Apart from this, citalopram did not markedly alter genes involved in other molecular functions in control cells. In contrast, alteration of genes implicated in ionic currents, cell-adhesion, immune mechanism, and adrenergic functions, were also observed in Alzheimer lymphocytes. The expression of genes of Alzheimer lymphocytes by citalopram is modulated differently which may correlate with the pathology.

Dopaminergic D1-like receptor-dependent inhibition of tyrosine hydroxylase mRNA expression and catecholamine production in human lymphocytes

Activation of human peripheral blood mononuclear cells (PBMC) triggers endogenous production of catecholamines (CA) through protein kinase (PK) C-dependent induction of tyrosine hydroxylase (TH; EC 1.14.16.2), the first and rate-limiting enzyme in the synthesis of CA. Since CA themselves are major mediators of the neural input to the immune system, we have examined their ability to affect PKC-induced TH mRNA expression and CA production in human isolated PBMC. In T- and B-lymphocytes (but not in monocytes) the PKC activator 12-O-tetradecanoylphorbol-13-acetate (TPA) (but not its inactive analogue 4alpha-phorbol-12,13-didecanoate) induced TH mRNA expression which was followed by an increase in the amount of intracellular CA. Coincubation of human PBMC with dopamine (DA) (but not with norepinephrine or epinephrine) inhibited TPA-induced TH mRNA expression. The effect of DA was concentration-dependent and was mimicked by the dopaminergic D1-like receptor agonist SKF-38393 but not by the D2-like receptor agonist bromocriptine. The D1-like antagonist SCH-23390 shifted to the right the concentration-response curves of both DA and SKF-38393, while neither the D2-like antagonist domperidone, nor the alpha1-adrenoceptor antagonist prazosin, the alpha2-adrenoceptor antagonist yohimbine, or the beta-adrenoceptor antagonist propranolol affected to any significant extent the inhibitory effect of DA. SKF-38393 also significantly reduced TPA-induced increase of intracellular CA, an effect which was antagonized by SCH-23390. It is thus suggested that in human T- and B-lymphocytes PKC activation leads to TH mRNA expression and subsequent increase of intracellular CA, which can be inhibited by D1-like receptor activation. Inhibition of intracellular CA production in human PBMC promotes cell survival through reduction of activation-induced apoptosis, and dopaminergic modulation of TH expression and intracellular CA content may thus represent a novel mechanism in the cross-talk between the nervous and the immune system as well as among immune system cells.

Potential clozapine target sites on peripheral hematopoietic cells and stromal cells of the bone marrow

The antipsychotic drug clozapine, acts via interaction with selective neurotransmitter receptor systems. Its use however, is associated with life-threatening agranulocytosis. The mechanism by which this occurs and its possible relationship with the drug's atypicality remain unclear. As a first step in identifying mechanistic pathways involved, profiling of neurotransmitter receptors on human neutrophils, mononuclear and bone marrow stromal cells as putative targets for clozapine-mediated toxicity was undertaken. Expression of mRNA encoding dopaminergic d2, d3, d4; serotonergic 5ht2a, 5ht2c, 5ht3, 5ht6, 5ht7; adrenergic alpha1a, alpha2; histaminergic h1 and muscarinic m1, m2, m3, m4, m5 receptors was analyzed by reverse transcription-polymerase chain reaction methods. While 5ht2c, 5ht6, m1 and m2 mRNA were undetected, the presence of the other receptors indicates sites at which clozapine could bind and induce toxicity of neutrophils and stromal components which regulate granulopoiesis. The functional significance of differential receptor expression while unknown, may argue for neural regulation of hematopoiesis.

Pharmacological hyperprolactinemia attenuates hydrocortisone-induced expression of CD11b on human CD8+ cells in vivo

OBJECTIVE

To study the short-term influences of pharmacologic hyperprolactinemia on hydrocortisone (HC)-induced effects on selected immune parameters.

METHODS

A single dose of HC (40 mg per os) was administered to eleven healthy female volunteers 1 h after domperidone (10 mg per os) or placebo administration. Immune cell subsets and expression of adhesion molecules was assessed by flow cytometry at baseline and 4 and 6 h after HC administration. Intracellular staining of interleukin-4 (IL-4) and interferon-gamma (IFN-gamma) production in CD4+ lymphocytes after phorbol myristate acetate and ionomycin stimulation was performed at the same time points.

RESULTS

HC administration was followed by a significant increase in cortisol levels, numbers of leukocytes and granulocytes and the percentage of CD16+, CD19+, CD11a+, CD11a+CD8+, CD11b+ and CD11b+CD8+ cells. The number of lymphocytes and monocytes and the percentage of CD3+, CD4+, CD4+/CD8+ ratio, CD62L+, CD54+ and CD54+CD16+ cells decreased, while the percentage of CD8+ cells was unaffected. Domperidone administration resulted in a significant increase in prolactin (PRL) concentrations. During hyperprolactinemia, the HC-induced increase in CD11b+CD8+ cells was significantly (p < 0.05) attenuated at 4 h. HC-induced changes in other immune parameters remained unaffected. No significant changes in the intracellular production of IL-4 and IFN-gamma in CD4+ lymphocytes were observed after a single dose of HC alone or during hyperprolactinemia.

CONCLUSIONS

This study shows an attenuated HC-induced increase in CD11b+CD8+ cells in the peripheral blood of healthy females during hyperprolactinemia. Our in vivo observations suggest that short-term interactions occur between PRL and glucocorticoids, affecting selected immune functions. Further studies are needed for confirmation of these results.

The enhancement of T cell proliferation by l-dopa is mediated peripherally and does not involve interleukin-2

Although several recent studies suggest that dopamine may have a significant role in the regulation of immune cell function, the mechanisms involved remain unclear. We undertook this study to clarify the actions of dopamine in vivo on lymphocyte proliferation and to determine whether such effects are mediated by alterations in interleukin-2 (IL-2) production and/or IL-2 receptor (IL-2R) expression. Administration of the dopamine precursor, L-dopa, for 5 days to BALB/c mice significantly increased Concanavalin A (ConA)-induced proliferation of lymphocytes. This effect was blocked by treatment with dopamine receptor antagonists as well as a peripheral dopamine synthesis inhibitor, suggesting a peripheral action of dopamine. L-dopa treatment had no effect on IL-2 production or IL-2R expression, indicating that the effects of dopamine on lymphocyte proliferation are not indirectly mediated by alterations in the IL-2 system.

Dopamine receptor expression on human T- and B-lymphocytes, monocytes, neutrophils, eosinophils and NK cells: a flow cytometric study

This study documents expression of dopamine (DA) receptors on leukocyte subpopulations using flow cytometric techniques to identify dopamine receptors with subtype-specific antibodies. Of the D1-like receptor family (D(1) and D(5)), only D(5) was detected, and of the D2-like receptor family (D(2), D(3) and D(4)), all dopamine receptors were detected. T-lymphocytes and monocytes had low expression of dopamine receptors, whereas neutrophils and eosinophils had moderate expression. B cells and NK cells had higher and more consistent expression. Dopamine receptors D(3) and D(5) were found in most individuals whereas D(2) and D(4) had more variable expression. D(1) was never found.

Serotonin, 5-hydroxyindoleacetic acid and serotonin transporter in blood peripheral lymphocytes of patients with generalized anxiety disorder

Several immune system modifications have been reported in pathological anxiety, such as generalized anxiety, panic and obsessive-compulsive disorders. Since serotonin transporter is a marker of peripheral blood lymphocytes and it is modified in major depression, the aim of the present work was to evaluate this transporter by the binding of [3H]paroxetine to membrane preparations of blood peripheral lymphocytes from control subjects and patients with generalized anxiety disorder. The number of transporters and the affinity for the ligand did not differ among the two groups. Serotonin and 5-hydroxyindoleacetic acid (5HIAA) were determined in platelet-rich and -poor plasma, and in lymphocytes. Nonsignificant changes were found in the patients as compared to controls. However, there was a significant positive correlation between serotonin concentration in platelet-poor plasma and in lymphocytes in the patients, but not in the controls. This finding might be an indication of a poor regulation of the transporter function by which serotonin plasma concentration might influence lymphocyte serotonin concentration. Previous results indicate that serotonin transporter is reduced in these cells in major depression disorder; however, in generalized anxiety disorder, the number of transporters was not modified, although the functional efficiency of serotonin transporter might be altered.

Postnatal development of dopamine receptor expression in rat peripheral blood lymphocytes

Postnatal development in the expression of dopamine D1-like and D2-like receptors was investigated in peripheral blood lymphocytes of male Wistar rats aged 1, 3, 4, 8, 12 and 16 weeks of age by radioligand binding assay techniques. Sample of frontal cortex, striatum and hippocampus were also investigated as reference tissues. The dopamine D1-like receptor antagonist [3H]SCH 23390 and the dopamine D2-like receptor agonist [3H]7-OH-DPAT were used as radioligands. The affinity (K(d)) of [3H]SCH 23390 or of [3H]7-OH-DPAT binding was unchanged in lymphocytes of rats of different age groups. The density (B(max)) of [3H]SCH 23390 binding sites increased from the 1st to the 3rd week of age, remained constant from the 3rd to the 8th week of age, and then increased slightly at 12 and 16 weeks of age. The B(max) value of [3H]7-OH-DPAT binding to lymphocytes increased from the 1st to the 3rd week of age, remained constant from the 3rd to the 4th week, increased again until the 12th week and then plateaued. Dopamine D1-like and D2-like receptor maturation in frontal cortex, hippocampus and striatum revealed an increased receptor density until the 4th week of age and a relative stabilization of receptor density values between the 4th to the 12th week depending on the area considered. Comparatively postnatal maturation of lymphocyte dopamine D1-like receptors displayed a pattern different from that of brain areas investigated, whereas maturation of D2-like receptors displayed a pattern similar to that of striatum. The quantitative and/or qualitative dissimilarities between development of lymphocyte and brain dopamine receptors suggest that from a developmental point of view lymphocyte dopamine receptors probably cannot be considered as a marker of homologous brain receptors.

Monoamine neurotoxins-induced apoptosis in lymphocytes by a common oxidative stress mechanism: involvement of hydrogen peroxide (H(2)O(2)), caspase-3, and nuclear factor kappa-B (NF-kappaB), p53, c-Jun transcription factors

The destruction of dopaminergic and serotonergic nerve cells by selective 6-hydroxydopamine (6-OHDA), 5,6-dihydroxytryptamine (5,6-DHT) and 5,7-dihydroxytryptamine (5,7-DHT), respectively, is a commonly used tool to investigate the mapping of neuronal pathways, elucidation of function and to mimic human neurodegenerative disease such as Parkinson's and Alzheimer's diseases. Despite intense investigations, a complete picture of the precise molecular cascade leading to cell death in a single cellular model is still lacking. In this study, we provide evidence that 6-OHDA, 5,6- and 5,7-DHT toxins-induced apoptosis in peripheral blood lymphocytes cells in a concentration-dependent fashion by a common oxidative mechanism involving: (1) the oxidation of toxins into quinones and production of the by-product hydrogen peroxide, reflected by desipramine-a monoamine uptake blocker-and antioxidants inhibition, (2) activation and/or translocation of nuclear factor-kappaB, p53 and c-Jun transcription factors, showed by immunocytochemical diaminobenzidine-positive stained nuclei, (3) caspase-3 activation, reflected by caspase Ac-DEVD-CHO inhibition, (4) mRNA and protein synthesis de novo according to cycloheximide and actinomycin D cell death inhibition. These results are consistent with the notion that uptake and intracellular autoxidation of those toxins precede the apoptotic process and that once H(2)O(2) is generated, it is able to trigger a specific cell death signalisation. Thus, taken together these results, we present an ordered cascade of the major molecular events leading peripheral blood lymphocytes to apoptosis. These results may contribute to explain the importance of H(2)O(2) as a second messenger of death signal in some degenerative diseases linked to oxidative stress stimuli.

Identification of dopamine plasma membrane and vesicular transporters in human peripheral blood lymphocytes

Plasma membrane dopamine transporter (DAT), vesicular monoamine transporters (VMAT) type-1 and -2 and the expression of the dopaminergic markers dopamine and tyrosine hydroxylase were assessed in membranes and/or in cytospin centrifuged human peripheral blood lymphocytes. The radiolabeled DAT ligand [3H]GBR12935 was bound to peripheral lymphocytes in a manner consistent with the specific binding to a dopamine uptake system, with a dissociation constant similar to that found in striatum, but with a lower density of binding sites. On the other hand, no specific binding occurred in cerebellum used as a test tissue not expressing DAT. Western blot analysis using antibodies raised against amino or carboxy terminus of DAT or against VMAT-1 or VMAT-2 revealed labeling of single bands of approximately 76, 55 or 68 KDa, respectively, displaying similar migration characteristics in lymphocytes and test tissues used for comparison. Immunofluorescence revealed that anti-dopamine, anti-tyrosine hydroxylase, anti-DAT, anti-VMAT-1 and anti-VMAT-2 antibodies labeled the total population of cytospin-centrifuged lymphocytes mounted on microscope slides. Confocal laser microscopy demonstrated that dopamine and VMAT-2 immunoreactivity was developed mainly in cytoplasmic punctiform areas likely corresponding to vesicles and to a lower extent was associated to plasma membrane. Tyrosine hydroxylase immunoreactivity was diffused to cytoplasm and to plasma membrane of lymphocytes, whereas DAT and VMAT-1 immunoreactivity were located almost exclusively in lymphocyte plasma membrane and cytoplasm, respectively. Lymphocyte DAT characterized in this study has probably functional relevance as [3H]dopamine was taken up by intact lymphocytes and uptake was inhibited specifically by compounds known to affect dopamine transport. These findings indicate that human peripheral blood lymphocytes possess DAT plasma membrane and VMAT-1 and VMAT-2 transporters. Increasing evidence indicates that dopamine transporter changes may be related to neuronal injury. In view of this assessment of lymphocyte DAT and VMAT transporters can be considered for identifying pathologies characterized by impaired dopaminergic neurotransmission.

Reduced density of dopamine D2-like receptors on peripheral blood lymphocytes in Alzheimer's disease

Clinical and pathological evidence points to an involvement of dopamine in Alzheimer's disease (AD). The present study was designed to assay dopamine D1-like and D2-like receptors on peripheral blood lymphocytes (PBL) in 20 patients with AD and in 25 healthy controls by radioligand binding assay techniques with [3H][R]-(+)-(-)chloro-2,3,4,5 tetrahydro-5-phenyl-1H-3-benzazepin-al-hemimaleate (SCH 23390) and [3H]7-hydroxy-N,N-di-n-propyl-2-aminotetraline (7OH-DPAT) as radioligands. The density of dopamine D1-like receptors and the affinity of [3H]SCH 23390 and [3H]7OH-DPAT binding to PBL were similar in both groups investigated. AD patients revealed a lower density of dopamine D2-like receptors on PBL than controls (P=0. 0016). The pharmacological profile of [3H]SCH 23390 and [3H]7OH-DPAT binding to PBL was consistent with the labeling of dopamine D5 and D3 receptor subtypes, respectively. The reduced density of dopamine D2-like receptors on PBL is consistent with the observation of changes in the expression of D2-like receptors in dopaminergic brain areas in AD. Our findings support the hypothesis of an involvement of dopamine in AD, even in those patients with no evidence of Parkinsonism, behavioral abnormalities or psychosis.

The dopamine D(4) receptor: one decade of research

Dopamine is an important neurotransmitter involved in motor control, endocrine function, reward, cognition and emotion. Dopamine receptors belong to the superfamily of G protein-coupled receptors and play a crucial role in mediating the diverse effects of dopamine in the central nervous system (CNS). The dopaminergic system is implicated in disorders such as Parkinson's disease and addiction, and is the major target for antipsychotic medication in the treatment of schizophrenia. Molecular cloning studies a decade ago revealed the existence of five different dopamine receptor subtypes in mammalian species. While the presence of the abundantly expressed dopamine D(1) and D(2) receptors was predicted from biochemical and pharmacological work, the cloning of the less abundant dopamine D(3), D(4) and D(5) receptors was not anticipated. The identification of these novel dopamine receptor family members posed a challenge with respect to determining their precise physiological roles and identifying their potential as therapeutic targets for dopamine-related disorders. This review is focused on the accomplishments of one decade of research on the dopamine D(4) receptor. New insights into the biochemistry of the dopamine D(4) receptor include the discovery that this G protein-coupled receptor can directly interact with SH3 domains. At the physiological level, converging evidence from transgenic mouse work and human genetic studies suggests that this receptor has a role in exploratory behavior and as a genetic susceptibility factor for attention deficit hyperactivity disorder.

17 beta-estradiol protects lymphocytes against dopamine and iron-induced apoptosis by a genomic-independent mechanism. Implication in Parkinson's disease

Dopamine (DA) in combination with iron (Fe(2+)) has been demonstrated to induce apoptosis in neuronal-like PC12 cells by an oxidative stress mechanism. To get a better insight of cell death and protective mechanisms in DA/Fe(2+)-induced toxicity, we investigated the effects of DA/Fe(2+) and the antioxidant action of 17 beta-estradiol (E2) in peripheral blood lymphocytes (PBL). We found that DA/Fe(2+)-induces apoptosis in PBL via a hydrogen peroxide (H(2)O(2))-mediated oxidative mechanism, which in turn triggers a cascade of molecular events requiring RNA and de novo protein synthesis. We have also demonstrated that E2 prevents significantly DA/Fe(2+)-induced apoptosis in PBL by directly inhibiting the intracellular accumulation of peroxides generated by DA/Fe(2+)-reaction. This protective activity is independent of the presence or activation of the estrogen receptors (ERs). These data further support and validate our previous hypothesis that DA/Fe(2+)/H(2)O(2) could be a general mediator of oxidative stress through a common cell death mechanism in both neuronal and nonneuronal cells. These findings may be particularly relevant to the potential approaches to rescue and prolong the survival of neurons by estrogens in patients with Parkinson's disease (PD).