Dopamine D1-like receptor subtypes in human peripheral blood lymphocytes

Dopamine promotes the progression of AML via activating NLRP3 inflammasome and IL-1β

Mental stress has been shown to activate sympathetic adrenergic system to produce dopamine and finally promote the progression of cancer. Dopamine can also regulate the immune system through secreting kinds of cytokines. However, what role does dopamine play in acute myeloid leukemia (AML) remains unclear. Here, we investigated the effects and mechanisms of dopamine in NLRP3 inflammasome activation and cellular viability of acute myeloid leukemia U937 cells. Our results showed that dopamine enhanced the viability of U937 cells and activated the NLRP3 inflammasome in U937 cells. To further explore the mechanism of dopamine on U937 cells, we examined the expression level of dopamine receptors (DRs). We found that the mRNA expression level of DR5 in U937 cells was significantly higher than other dopamine receptors. Furthermore, we treated U937 cells with DR1/2/3/5 antagonist before dopamine, and it manifestly reversed the NLRP3 inflammasome activation and the viability-enhancing effect in U937 cells induced by dopamine. Anti-IL-1β antibody also could partly reversed the viability-enhancing effect by dopamine. We concluded that dopamine could enhance the viability of U937 cells through DR1/5 receptor pathway and activate NLRP3 inflammasome.

Transcriptomic signatures of schizophrenia revealed by dopamine perturbation in an ex vivo model

The dopaminergic hypothesis of schizophrenia (SZ) postulates that dopaminergic over activity causes psychosis, a central feature of SZ, based on the observation that blocking dopamine (DA) improves psychotic symptoms. DA is known to have both receptor- and non-receptor-mediated effects, including oxidative mechanisms that lead to apoptosis. The role of DA-mediated oxidative processes in SZ has been little studied. Here, we have used a cell perturbation approach and measured transcriptomic profiles by RNAseq to study the effect of DA exposure on transcription in B-cell transformed lymphoblastoid cell lines (LCLs) from 514 SZ cases and 690 controls. We found that DA had widespread effects on both cell growth and gene expression in LCLs. Overall, 1455 genes showed statistically significant differential DA response in SZ cases and controls. This set of differentially expressed genes is enriched for brain expression and for functions related to immune processes and apoptosis, suggesting that DA may play a role in SZ pathogenesis through modulating those systems. Moreover, we observed a non-significant enrichment of genes near genome-wide significant SZ loci and with genes spanned by SZ-associated copy number variants (CNVs), which suggests convergent pathogenic mechanisms detected by both genetic association and gene expression. The study suggests a novel role of DA in the biological processes of immune and apoptosis that may be relevant to SZ pathogenesis. Furthermore, our results show the utility of pathophysiologically relevant perturbation experiments to investigate the biology of complex mental disorders.

The role of dopaminergic immune cell signalling in poststroke inflammation

Upon ischaemic stroke, brain-resident and peripheral immune cells accumulate in the central nervous system (CNS). Interestingly, these cells express pattern specific to neurotransmitter receptors and, therefore, seem to be susceptible to neurotransmitter stimulation, potentially modulating their properties and functions. One of the principal neurotransmitters in the CNS, dopamine, is involved in the regulation of processes of brain development, motor control and higher brain functions. It is constantly released in the brain and there is experimental and clinical evidence that dopaminergic signalling is involved in recovery of lost neurological function after stroke. Independent studies have revealed specific but different patterns of dopamine receptor subtypes on different populations of immune cells. Those patterns are dependent on the activation status of cells. Generally, exposure to dopamine or dopamine receptor agonists decreases detrimental actions of immune cells. In contrast, a reduction of dopaminergic inputs perpetuates a pro-inflammatory state associated with increased release of pro-inflammatory molecules. In addition, subsets of immune cells have been identified to synthesize and release dopamine, suggesting autoregulatory mechanisms. Evidence supports that inflammatory processes activated following ischaemic stroke are modulated by dopaminergic signalling.

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.

Dopamine and T cells: dopamine receptors and potent effects on T cells, dopamine production in T cells, and abnormalities in the dopaminergic system in T cells in autoimmune, neurological and psychiatric diseases

Dopamine, a principal neurotransmitter, deserves upgrading to 'NeuroImmunotransmitter' thanks to its multiple, direct and powerful effects on most/all immune cells. Dopamine by itself is a potent activator of resting effector T cells (Teffs), via two independent ways: direct Teffs activation, and indirect Teffs activation by suppression of regulatory T cells (Tregs). The review covers the following findings: (i) T cells express functional dopamine receptors (DRs) D1R-D5R, but their level and function are dynamic and context-sensitive, (ii) DR membranal protein levels do not necessarily correlate with DR mRNA levels, (iii) different T cell types/subtypes have different DR levels and composition and different responses to dopamine, (iv) autoimmune and pro-inflammatory T cells and T cell leukaemia/lymphoma also express functional DRs, (v) dopamine (~10(-8) M) activates resting/naive Teffs (CD8(+) >>>CD4(+) ), (vi) dopamine affects Th1/Th2/Th17 differentiation, (vii) dopamine inhibits already activated Teffs (i.e. T cells that have been already activated by either antigen, mitogen, anti-CD3 antibodies cytokines or other molecules), (viii) dopamine inhibits activated Tregs in an autocrine/paracrine manner. Thus, dopamine 'suppresses the suppressors' and releases the inhibition they exert on Teffs, (ix) dopamine affects intracellular signalling molecules and cascades in T cells (e.g. ERK, Lck, Fyn, NF-κB, KLF2), (x) T cells produce dopamine (Tregs>>>Teffs), can release dopamine, mainly after activation (by antigen, mitogen, anti-CD3 antibodies, PKC activators or other), uptake extracellular dopamine, and most probably need dopamine, (xi) dopamine is important for antigen-specific interactions between T cells and dendritic cells, (xii) in few autoimmune diseases (e.g. multiple sclerosis/SLE/rheumatoid arthritis), and neurological/psychiatric diseases (e.g. Parkinson disease, Alzheimer's disease, Schizophrenia and Tourette), patient's T cells seem to have abnormal DRs expression and/or responses to dopamine or production of dopamine, (xiii) drugs that affect the dopaminergic system have potent effects on T cells (e.g. dopamine=Intropin, L-dopa, bromocriptine, haloperidol, quinpirole, reserpine, pergolide, ecopipam, pimozide, amantadine, tetrabenazine, nomifensine, butaclamol). Dopamine-induced activation of resting Teffs and suppression of Tregs seem beneficial for health and may also be used for immunotherapy of cancer and infectious diseases. Independently, suppression of DRs in autoimmune and pro-inflammatory T cells, and also in cancerous T cells, may be advantageous. The review is relevant to Immunologists, Neurologists, Neuroimmunologists, Hematologists, Psychiatrists, Psychologists and Pharmacologists.

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.

Dopamine controls systemic inflammation through inhibition of NLRP3 inflammasome

Inflammasomes are involved in diverse inflammatory diseases, so the activation of inflammasomes needs to be tightly controlled to prevent excessive inflammation. However, the endogenous regulatory mechanisms of inflammasome activation are still unclear. Here, we report that the neurotransmitter dopamine (DA) inhibits NLRP3 inflammasome activation via dopamine D1 receptor (DRD1). DRD1 signaling negatively regulates NLRP3 inflammasome via a second messenger cyclic adenosine monophosphate (cAMP), which binds to NLRP3 and promotes its ubiquitination and degradation via the E3 ubiquitin ligase MARCH7. Importantly, in vivo data show that DA and DRD1 signaling prevent NLRP3 inflammasome-dependent inflammation, including neurotoxin-induced neuroinflammation, LPS-induced systemic inflammation, and monosodium urate crystal (MSU)-induced peritoneal inflammation. Taken together, our results reveal an endogenous mechanism of inflammasome regulation and suggest DRD1 as a potential target for the treatment of NLRP3 inflammasome-driven diseases.

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.

Dopamine receptor D3 expressed on CD4+ T cells favors neurodegeneration of dopaminergic neurons during Parkinson's disease

Emerging evidence has demonstrated that CD4(+) T cells infiltrate into the substantia nigra (SN) in Parkinson's disease (PD) patients and in animal models of PD. SN-infiltrated CD4(+) T cells bearing inflammatory phenotypes promote microglial activation and strongly contribute to neurodegeneration of dopaminergic neurons. Importantly, altered expression of dopamine receptor D3 (D3R) in PBLs from PD patients has been correlated with disease severity. Moreover, pharmacological evidence has suggested that D3R is involved in IFN-γ production by human CD4(+) T cells. In this study, we examined the role of D3R expressed on CD4(+) T cells in neurodegeneration of dopaminergic neurons in the SN using a mouse model of PD. Our results show that D3R-deficient mice are strongly protected against loss of dopaminergic neurons and microglial activation during 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD. Notably, D3R-deficient mice become susceptible to MPTP-induced neurodegeneration and microglial activation upon transfer of wild-type (WT) CD4(+) T cells. Furthermore, RAG1 knockout mice, which are devoid of T cells and are resistant to MPTP-induced neurodegeneration, become susceptible to MPTP-induced loss of dopaminergic neurons when reconstituted with WT CD4(+) T cells but not when transferred with D3R-deficient CD4(+) T cells. In agreement, experiments analyzing activation and differentiation of CD4(+) T cells revealed that D3R favors both T cell activation and acquisition of the Th1 inflammatory phenotype. These findings indicate that D3R expressed on CD4(+) T cells plays a fundamental role in the physiopathology of MPTP-induced PD in a mouse model.

Self-regulation therapy to reproduce drug effects: a suggestion technique to change personality and the DRD3 gene expression

This study proposes a strategy, based on self-regulation therapy, to change personality and its biological substrate, the DRD3 gene expression. It has been demonstrated that acute doses of stimulating drugs, like methylphenidate, are able to change personality and the expression of certain genes in the short term. On the other hand, self-regulation therapy has been proven to reproduce the effects of drugs. Thus, it is feasible to hope that self-regulation therapy is equally effective as methylphenidate in changing personality and the gene expression. This is a preliminary study with a single-case experimental design with replication in which 2 subjects participated. The results and potential implications for research and psychotherapy are discussed.

Distorted expression of dopamine receptor genes in systemic lupus erythematosus

Several observations suggest that alterations in the neurotransmitter dopamine and/or its receptors could be associated with the pathophysiology of lupus. We therefore assessed expression of the five dopamine receptor genes in a cohort of patients. We found that all receptors are expressed in lupus peripheral blood cells. We also discovered that dopamine receptor 2 gene (DR2) was underexpressed, and that DR4 was overexpressed in lupus patients, as compared to controls. Cell sorting of peripheral T- and B-lymphocytes disclosed that the altered DR2 and DR4 expressions were borne by T-cells. These distorted expressions of DR2 and DR4 could influence immune functions in lupus through several mechanisms. Since DR2 can be effective in regulating the activation and differentiation of naive CD4⁺ cells by promoting polarization toward regulatory T-cells, the underexpression of DR2 we have observed may account, at least in part, for the reduction of regulatory T-cell function and/or numbers in lupus. In addition to providing novel insight into disease pathogenesis, our findings may have therapeutic implications. Because DR4 can be effective in triggering T-cell quiescence, its overexpression on lupus T cells suggests that inducing quiescence using DR4-specific agonists may represent a useful strategy in the treatment of lupus.

The dopaminergic system in peripheral blood lymphocytes: from physiology to pharmacology and potential applications to neuropsychiatric disorders

Besides its action on the nervous system, dopamine (DA) plays a role on neural-immune interactions. Here we review the current evidence on the dopaminergic system in human peripheral blood lymphocytes (PBL). PBL synthesize DA through the tyrosine-hydroxylase/DOPA-decarboxylase pathway, and express DA receptors and DA transporter (DAT) on their plasma membrane. Stimulation of DA receptors on PBL membrane contributes to modulate the development and initiation of immune responses under physiological conditions and in immune system pathologies such as autoimmunity or immunodeficiency.

The characterization of DA system in PBL gave rise to a further line of research investigating the feasibility of PBL as a cellular model for studying DA derangement in neuropsychiatric disorders. Several reports showed changes of the expression of DAT and/or DA receptors in PBL from patients suffering from several neuropsychiatric disorders, in particular parkinsonian syndromes, schizophrenia and drug- or alcohol-abuse. Despite some methodological and theoretical limitations, these findings suggest that PBL may prove a cellular tool with which to identify the derangement of DA transmission in neuropsychiatric diseases, as well as to monitor the effects of pharmacological treatments.

Dopamine receptors in human adipocytes: expression and functions

Introduction

Dopamine (DA) binds to five receptors (DAR), classified by their ability to increase (D1R-like) or decrease (D2R-like) cAMP. In humans, most DA circulates as dopamine sulfate (DA-S), which can be de-conjugated to bioactive DA by arylsulfatase A (ARSA). The objective was to examine expression of DAR and ARSA in human adipose tissue and determine whether DA regulates prolactin (PRL) and adipokine expression and release.

Methods

DAR were analyzed by RT-PCR and Western blotting in explants, primary adipocytes and two human adipocyte cell lines, LS14 and SW872. ARSA expression and activity were determined by qPCR and enzymatic assay. PRL expression and release were determined by luciferase reporter and Nb2 bioassay. Analysis of cAMP, cGMP, leptin, adiponectin and interleukin 6 (IL-6) was done by ELISA. Activation of MAPK and PI3 kinase/Akt was determined by Western blotting.

Results

DAR are variably expressed at the mRNA and protein levels in adipose tissue and adipocytes during adipogenesis. ARSA activity in adipocyte increases after differentiation. DA at nM concentrations suppresses cAMP, stimulates cGMP, and activates MAPK in adipocytes. Acting via D2R-like receptors, DA and DA-S inhibit PRL gene expression and release. Acting via D1R/D5R receptors, DA suppresses leptin and stimulates adiponectin and IL-6 release.

Conclusions

This is the first report that human adipocytes express functional DAR and ARSA, suggesting a regulatory role for peripheral DA in adipose functions. We speculate that the propensity of some DAR-activating antipsychotics to increase weight and alter metabolic homeostasis is due, in part, to their direct action on adipose tissue.

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.

Dopamine D1-like receptor antagonist attenuates Th17-mediated immune response and ovalbumin antigen-induced neutrophilic airway inflammation

Allergic airway inflammation is generally considered a Th2-type immune response. Recent studies, however, demonstrated that Th17-type immune responses also play important roles in this process, especially in the pathogenesis of neutrophilic airway inflammation, a hallmark of severe asthma. We previously reported that dendritic cells release dopamine to naive CD4(+) T cells in Ag-specific cell-cell interaction, in turn inducing Th17 differentiation through dopamine D1-like receptor (D1-like-R). D1-like-R antagonist attenuates Th17-mediated diseases such as experimental autoimmune encephalomyelitis and autoimmune diabetes. However, the effect of antagonizing D1-like-R on Th17-mediated airway inflammation has yet to be studied. In this study, we examined whether D1-like-R antagonist suppresses OVA-induced neutrophilic airway inflammation in OVA TCR-transgenic DO11.10 mice and then elucidated the mechanism of action. DO11.10 mice were nebulized with OVA or PBS, and some mice received D1-like-R antagonist orally before OVA nebulization. D1-like-R antagonist significantly suppressed OVA-induced neutrophilic airway inflammation in DO11.10 mice. It also inhibited the production of IL-17 and infiltration of Th17 cells in the lung. Further, D1-like-R antagonist suppressed the production of IL-23 by lung CD11c(+) APCs. In contrast, D1-like-R antagonist did not increase Foxp3(+) regulatory T cells in the lung. D1-like-R antagonist neither suppressed nonspecific LPS-induced neutrophilic airway inflammation nor OVA-induced eosinophilic airway inflammation. These results indicate that D1-like-R antagonist could suppress Th17-mediated neutrophilic airway inflammation, raising the possibility that antagonizing D1-like-R serves as a promising new strategy for treating neutrophil-dominant severe asthma.

Dopamine induces IL-6-dependent IL-17 production via D1-like receptor on CD4 naive T cells and D1-like receptor antagonist SCH-23390 inhibits cartilage destruction in a human rheumatoid arthritis/SCID mouse chimera model

A major neurotransmitter dopamine transmits signals via five different seven-transmembrane G protein-coupled receptors termed D1-D5. Several studies have shown that dopamine not only mediates interactions into the nervous system, but can contribute to the modulation of immunity via receptors expressed on immune cells. We have previously shown an autocrine/paracrine release of dopamine by dendritic cells (DCs) during Ag presentation to naive CD4(+) T cells and found efficacious results of a D1-like receptor antagonist SCH-23390 in the experimental autoimmune encephalomyelitis mouse model of multiple sclerosis and in the NOD mouse model of type I diabetes, with inhibition of Th17 response. This study aimed to assess the role of dopaminergic signaling in Th17-mediated immune responses and in the pathogenesis of rheumatoid arthritis (RA). In human naive CD4(+) T cells, dopamine increased IL-6-dependent IL-17 production via D1-like receptors, in response to anti-CD3 plus anti-CD28 mAb. Furthermore, dopamine was localized with DCs in the synovial tissue of RA patients and significantly increased in RA synovial fluid. In the RA synovial/SCID mouse chimera model, although a selective D2-like receptor antagonist haloperidol significantly induced accumulation of IL-6(+) and IL-17(+) T cells with exacerbated cartilage destruction, SCH-23390 strongly suppressed these responses. Taken together, these findings indicate that dopamine released by DCs induces IL-6-Th17 axis and causes aggravation of synovial inflammation of RA, which is the first time, to our knowledge, that actual evidence has shown the pathological relevance of dopaminergic signaling with RA.

Is the dopamine D3 receptor mRNA on blood lymphocytes help to for identification and subtyping of schizophrenia?

Schizophrenia is one of the neuropathological disorders, which are associated with dopamine and its receptors. In recent years, it has been shown that mRNA of D3, D4 and D5 dopamine receptor (DRD3, DRD4, DRD5) subtypes is expressed in human peripheral blood lymphocytes (PBL). A total 55 schizophrenic patients and 51 healthy subjects were included in the study to investigate the levels of DRD3 mRNA in PBL of schizophrenic patients and whether DRD3 mRNA level in PBL can serve as peripheral marker for schizophrenia. RNA was isolated from lymphocytes of both groups and reverse transcriptase polymerase chain reaction (RT-PCR) was performed for DRD3 mRNA. We found a significant difference in PBL DRD3 mRNA levels among schizophrenia subtypes (P=0.030) while no difference was detected between control subjects and schizophrenics. We concluded that the levels of DRD3 mRNA can help understanding and severity of clinical manifestations in schizophrenia.

Calcium homeostasis is dysregulated in parkinsonian patients with L-DOPA-induced dyskinesias

Long-term treatment of Parkinson disease (PD) is frequently associated with l-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesias (LIDs). L-DOPA-induced dyskinesias are likely due to changes in the signal transduction pathways, at the striatal level, related to pulsatile stimulation of dopamine receptors. We investigated whether markers of this phenomenon can also be detected peripherally. We analyzed mRNA expression for D5 (D1-like) and D3 (D2-like) receptors and levels of second messengers, such as cAMP and free intracellular Ca2+ ([Ca2+]i), in peripheral blood lymphocytes of PD patients with (LID+) or without LIDs (LID-). Patients with PD showed depressed [Ca2+]i rise in response to mitogen-induced activation. The defect was more pronounced in LID+ (-33% with respect to healthy controls) than in LID- patients (-20%). Peripheral blood lymphocyte levels of cAMP were decreased in both LID+ (3.8 +/- 2.9 pmol/10 cells) and LID- patients (4.2 +/- 2.4 pmol/10(6) cells), with respect to controls (6 +/- 2.6 pmol/10(6) cells). No differences were found in dopamine receptor mRNA expression. Our results demonstrate that second messenger levels are altered in the peripheral blood lymphocytes of PD patients treated with dopaminergic agents and that patients with LIDs show further alterations in the regulation of [Ca2+]i homeostasis. This may represent a distinctive trait of patients prone to develop dyskinetic movements.

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.

Dopaminergic receptor D5 mRNA expression is increased in circulating lymphocytes of Tourette syndrome patients

Tourette syndrome (TS) is a neuropsychiatric disorder in which dopaminergic dysfunction and immune system abnormalities seem to coexist. Using real-time PCR, we determined mRNA expression of dopamine receptors (DRs) D1-5 in peripheral blood lymphocytes (PBLs) from 15 TS patients and 15 sex- and age-matched healthy controls (HCs). DRD5 mRNA levels in cells from TS were higher than in cells from HCs. In TS patients with obsessive-compulsive disorder, DRD5 mRNA levels in PBLs showed a highly positive correlation with the severity of compulsive symptoms. DRD5 mRNA upregulation in PBLs from TS patients may represent a peripheral marker of dopaminergic dysfunction and supports the involvement of the immune system in TS.

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.

Dopamine D2 receptor polymorphisms in inflammatory bowel disease and the refractory response to treatment

Dopamine and its receptors may be involved in inflammatory reaction. The availability of this molecule depends on its receptors. The DRD2 gene, which codifies for the D2 dopamine receptor, has several polymorphisms. In this study, the DRD2 TaqIA polymorphism, which confers a decreased receptor density, was evaluated in 313 individuals including 220 inflammatory bowel disease patients (143 patients with Crohn's disease and 77 with ulcerative colitis) and in 93 healthy blood donors. The analysis was carried out by PCR-RFLP techniques. The frequencies of A (1) A (1) and A (2) A (2) genotypes were similar among Crohn's disease, ulcerative colitis patients, and health controls. Also, the genotype frequency was similar in different groups of disease localization, behavior, and age of disease onset. However, the Crohn's disease patients carriers of A (2) A (2) genotype showed a lower risk for development refractory Crohn's disease (37 out 65) than A (1) A (1) and A (1) A (2) carriers (28 out of 65) [(OR=0.4, 95% CI 0.21-0.87; p=0.02)]. Our results support an involvement of the dopamine receptor in inflammatory bowel disease and suggest a new potential target for therapy in refractory Crohn's disease patients.

Dopamine plasma membrane transporter (DAT) in rat thymus and spleen: an immunochemical and immunohistochemical study

The expression of the dopamine plasma membrane transporter (DAT) was investigated in rat thymus and spleen by immunochemical and immunohistochemical techniques. Antibodies raised against a peptide mapping near the amino terminus of DAT were bound to a single band of approximately 76 kDa in thymus and spleen membranes as well as in striatal and kidney membranes which were used as dopaminergic reference tissues. Reverse transcription-polymerase chain reaction analysis revealed that both thymus and spleen expressed DAT mRNA. Immunohistochemistry revealed in rat thymus a DAT immune reaction in the wall of arteries located in septa of connective tissue as well as in the medulla, with a reticular localization and an apparent negative reaction of thymocytes. In the spleen, DAT immunoreactivity was located primarily in the red-white pulp marginal zone, within small cells, likely corresponding to lymphocytes and in the wall of white pulp arteries. The presence of a dopamine transporter suggests that dopamine released in the lymphoid microenvironment may contribute to neuroimmune modulation. It cannot be excluded a different activity of dopamine in primary and secondary immune organs, such as maturation and selection of lymphocytes and activation of immune responses in the spleen.

Oxidative stress in peripheral blood mononuclear cells from patients with Parkinson's disease: negative correlation with levodopa dosage

Oxidative stress, resulting from the imbalance between reactive oxygen species (ROS) formation and antioxidant defenses, plays a major role in the pathogenesis of Parkinson's disease (PD). However, the contribution of levodopa (LD) therapy to oxidative damage is still debated. We investigated oxidative stress in peripheral blood mononuclear cells (PBMCs) from LD-treated PD patients and healthy subjects. Increased ROS production associated with unaltered glutathione reductase activity was detected in PBMC from PD patients. LD daily dosage appeared to be inversely correlated with ROS levels and positively associated with GR activity, suggesting a protective role for LD on PBMCs redox status. Our data support the view of systemic oxidative stress involvement in PD and give further rationale for using PBMCs as an easily accessible ex-vivo dopaminergic model for exploring the biological effects of LD therapy.

Dopamine selectively induces migration and homing of naive CD8+ T cells via dopamine receptor D3

The nervous systems affect immune functions by releasing neurohormones and neurotransmitters. A neurotransmitter dopamine signals via five different seven-transmembrane G protein-coupled receptors termed D1 to D5. The secondary lymphoid tissues are highly innervated by sympathetic nerve fibers that store dopamine at high contents. Lymphocytes also produce dopamine. In this study, we examined expression and function of dopamine receptors in lymphocytes. We found that D3 was the predominant subtype of dopamine receptors in the secondary lymphoid tissues and selectively expressed by naive CD8+ T cells of both humans and mice. Dopamine induced calcium flux and chemotaxis in mouse L1.2 cells stably expressing human D3. These responses were almost completely inhibited by pertussis toxin, indicating that D3 was coupled with the Galphai class of G proteins. Consistently, dopamine selectively induced chemotactic responses in naive CD8+ T cells of both humans and mice in a manner sensitive to pertussis toxin and D3 antagonists. Dopamine was highly synergistic with CCL19, CCL21, and CXCL12 in induction of chemotaxis in naive CD8+ T cells. Dopamine selectively induced adhesion of naive CD8+ T cells to fibronectin and ICAM-1 through activation of integrins. Intraperitoneal injection of mice with dopamine selectively attracted naive CD8+ T cells into the peritoneal cavity. Treatment of mice with a D3 antagonist U-99194A selectively reduced homing of naive CD8+ T cells into lymph nodes. Collectively, naive CD8+ T cells selectively express D3 in both humans and mice, and dopamine plays a significant role in migration and homing of naive CD8+ T cells via D3.

D3 dopamine receptor mRNA is elevated in T cells of schizophrenic patients whereas D4 dopamine receptor mRNA is reduced in CD4+ -T cells

The expression of dopamine receptors was examined in purified human neutrophils, monocytes, B cells, natural killer cells and CD4+ - and CD8+ -T lymphocytes by RT-PCR. In healthy subjects, D1 and D2 receptors were not expressed in leukocytes. Real Time PCR for dopamine receptors D3 and D4 disclosed that D3 receptors are expressed in T cells and natural killer cells and D4 receptors in CD4+ -T cells. The comparison of schizophrenic patients with sex- and age-matched controls revealed a significantly higher expression of D3 receptor mRNA in T cells of schizophrenic patients, whereas D4 receptor mRNA in CD4+ -T cells was downregulated.

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 receptor D3 mRNA expression in human lymphocytes is negatively correlated with the personality trait of persistence

It has been proposed that neurotransmitter receptor expression in peripheral immune cells reflects expression of these receptors in the brain. To test this "peripheral marker hypothesis", we compared mRNA expression of the dopamine receptors D3 (DRD3) and D4 (DRD4) in peripheral blood lymphocytes (PBL) to personality traits assessed with the Temperament and Character Inventory (TCI) in 50 healthy and unmedicated Caucasian individuals. A shared variance of at least 17% (p=0.016) between DRD3 mRNA expression in PBL and the personality trait of persistence was found. As personality traits have been generally assumed polygenic with a single gene accounting for rarely more than 1-2% of observed variance in a trait, this result lends further support to the peripheral marker hypothesis for DRD3 mRNA expression in PBL. It may also suggest a significant role for the DRD3 in the neurobiology of persistence and point to an interesting link between personality and functioning of the immune system.

Dopaminergic regulation of immune cells via D 3 dopamine receptor: a pathway mediated by activated T cells

Neuro-immune interactions enable mutual regulation of the nervous and immune systems. To date, evidence exists for manipulations of immune cells by neurotransmitters in the periphery. In this study, we suggest the existence of a pathway by which the brain affects immune cells. The pathway we describe here is mediated by dopamine receptors expressed on activated T cells, termed blasts. Blasts can cross the blood brain barrier regardless of antigen specificity and can therefore encounter neurotransmitters in the brain. We show that blasts have a unique response to dopaminergic activation, which has no counterpart in resting T cells. Dopaminergic activation of blasts induces a Th1 bias in their cytokine profile and causes changes in surface marker expression. We further suggest that these changes can subsequently be transferred to peripheral T cells. We have tested this pathway in two in vivo systems: in rats exogenously administered with L-dopa, and in schizophrenia, which is characterized by a central nervous system-restricted increase in dopamine. In both models, peripheral T cells exhibit similar features to those of dopaminergically activated blasts. The existence of such a pathway by which the brain can regulate immune cells opens a conceptually new direction in neuro-immune interactions.

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.

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.

Circulating dopamine level, in lung carcinoma patients, inhibits proliferation and cytotoxicity of CD4+ and CD8+ T cells by D1 dopamine receptors: an in vitro analysis

Besides cardiovascular and renal functions, the role of dopamine in periphery as an endogenous regulator of immune functions is in the limelight. In human malignancy, depression of T cell functions is known. Interestingly, recent evidences indicate significant elevation of plasma dopamine in malignancy due to stress of the disease process. Therefore, this study evaluates whether this increased plasma dopamine exerts any influence on the proliferation and cytotoxicity of CD4+ and CD8+ T cells. Patients with lung carcinoma were selected for this study due to the high prevalence rate of this kind of cancer in developing countries and also due to strong positive biochemical and psychological criteria of stress in most of the patients. Results showed significant elevation of plasma dopamine (48.6 +/- 5.1 pg/ml) in lung cancer patients than normal controls (10.2 +/- 0.9 pg/ml). In vitro dopamine concentration, simulating the plasma concentration of the patients, significantly inhibited the proliferation and cytotoxicity of T cells of these patients and also of the normal volunteers, in presence of their respective serum. The mechanism has been attributed to be D1 class of dopamine receptor mediated elevation of intracellular cAMP in these cell populations. The results may be of significance in understanding the role of peripheral dopamine as an immunomodulator in human health and diseases.

Therapeutic use of dopamine and beta-blockers modulates plasma interleukin-6 levels in patients with congestive heart failure

We previously reported that the spillover of interleukin-6 (IL-6) into the peripheral circulation increases with the severity of congestive heart failure (CHF), and that the increase is mainly associated with activation of the endogenous sympathetic nervous system. However, the role of the sympathetic nervous system in the increase of IL-6 in CHF patients is not yet fully understood. To address this question, we measured plasma IL-6 levels before and after therapeutic administration of dopamine and betablockers in patients with CHF. After more than 24 h (mean, 34 h) of treatment with a low dose of intravenous dopamine (mean, 2.4 microg/kg/min) in 1 patients with dilated cardiomyopathy and deterioration of CHF, the plasma IL-6 level was increased significantly (30.8 vs. 16.6 pg/ml; p = 0.003) despite the improved hemodynamics. After 377 days of beta-blocker therapy in 24 patients with dilated cardiomyopathy, the plasma IL-6 level was decreased significantly (2.04 vs. 3.11 pg/ml; p = 0.01) along with the improvement of symptoms, left ventricular ejection fraction, and neurohumoral factors. Dopamine increases and beta-blockers decrease the plasma IL-6 level in patients with CHF, suggesting that drugs modulating the sympathetic nervous system may alter IL-6 in these patients.

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.

Dopamine, a neurotransmitter, influences the immune system

Dopamine (DA) is a monoamine neurotransmitter of both central and peripheral nervous system. Its role in the neural-immune communication has been discussed in the present review. Results reveal that in vivo damage or stimulation of specific central dopaminergic system suppresses or enhances functional activities of the immune effector cells. The possible influences of other immunomodulators of the brain by altering brain DA may be the underlying mechanism. Direct effects of DA on the immune effector cells are also contradictory, it is suppressive in vitro, while in pharmacological doses, it is mostly stimulatory in vivo. The possible mechanisms have been discussed. Lastly, future areas of relevance on DA and immunity have been highlighted to advance our knowledge regarding DA as an immune regulator.