Influence of dopamine receptor gene polymorphisms on circulating T lymphocytes: A pilot study in healthy subjects

Polymorphisms in the Dopaminergic Receptor D3 Gene Correlate with Disease Progression Rate in Relapsing-Remitting Multiple Sclerosis Patients

BACKGROUND

Multiple sclerosis (MS) is a common chronic autoimmune disease of the central nervous system. In MS, disability progresses unpredictably. Dopamine (DA) is a modulator of immune functions, and compelling evidence supports its involvement in both pathogenesis and treatment of MS. Although single nucleotide polymorphisms (SNPs) in dopaminergic receptor (DR) genes have been extensively studied, their role in MS progression remains unexplored. Therefore, the aim of this explorative study is to investigate the potential association between functional SNPs in DR genes and MS progression.

METHODS

Caucasian patients with relapsing-remitting (RR) MS were enrolled, and disease progression assessed by the Multiple Sclerosis Severity Score (MSSS).

RESULTS

Out of the 59 RRMS patients enrolled, those with the G/G genotype for rs6280 and rs1800828 SNPs in DRD3 showed significantly higher MSSSs compared to those with ancestral and heterozygous genotypes.

CONCLUSIONS

If confirmed in a larger prospective study, the reported findings could contribute to a better understanding of MS pathophysiological mechanisms, opening the way for the identification of marker(s) for assessing MS progression as well as novel therapeutic strategies. A personalized approach to MS management has the potential to improve the overall well-being of MS patients and alleviate the burden on their caregivers.

Dopaminergic regulation of inflammation and immunity in Parkinson's disease: friend or foe?

Parkinson's disease (PD) is a neurodegenerative disease affecting 7-10 million people worldwide. Currently, there is no treatment available to prevent or delay PD progression, partially due to the limited understanding of the pathological events which lead to the death of dopaminergic neurons in the substantia nigra in the brain, which is known to be the cause of PD symptoms. The current available treatments aim at compensating dopamine (DA) deficiency in the brain using its precursor levodopa, dopaminergic agonists and some indirect dopaminergic agents. The immune system is emerging as a critical player in PD. Therefore, immune-based approaches have recently been proposed to be used as potential antiparkinsonian agents. It has been well-known that dopaminergic pathways play a significant role in regulating immune responses in the brain. Although dopaminergic agents are the primary antiparkinsonian treatments, their immune regulatory effect has yet to be fully understood. The present review summarises the current available evidence of the immune regulatory effects of DA and its mimics and discusses dopaminergic agents as antiparkinsonian drugs. Based on the current understanding of their involvement in the regulation of neuroinflammation in PD, we propose that targeting immune pathways involved in PD pathology could offer a better treatment outcome for PD patients.

Regulatory T cells mediate insomnia-related psychotic symptoms and cognitive impairment in chronic schizophrenia patients

Insomnia occurs frequently in schizophrenia patients and is often accompanied with severe psychotic symptoms and cognition impairment. Moreover, chronic insomnia is associated with immune alterations. This study explored the correlations between insomnia and clinical manifestations of schizophrenia and analyzed mediation effects of regulatory T cells (Tregs) on these correlations. In a total of 655 chronic schizophrenia patients, 70 persons (10.69%) had an ISI (Insomnia Severity Index) score >7 and were referred to as Insomnia group. Compared to non-Insomnia group, Insomnia group presented more severe psychotic symptoms (assessed by PANSS) and cognitive impairment (assessed by RBANS). The total effect of ISI on PANSS/RBANS total score was not significant due to the mediation effects by Tregs, in which Tregs strongly mediated the effect of ISI on PANSS total score in negative direction but mediated the effect of ISI on RBANS total score in positive direction. Pearson Correlation Coefficient revealed negative correlations between Tregs and PANSS total score or disorganization subscale of PANSS. Positive correlations existed between Tregs and RBANS total score, between Tregs and the subscales of attention, delayed memory, or language of RBANS. These mediation effects of Tregs on insomnia-related psychotic symptoms and cognitive impairment in chronic schizophrenia patients point to a potential therapeutic strategy of modulating Tregs for the patients.

Intravenous haloperidol and cocaine alter the distribution of T CD3+ CD4+ , non-T/NK and NKT cells in rats

The modulation of dopamine transmission evokes strong behavioural effects that can be achieved by commonly used psychoactive drugs such as haloperidol or cocaine. Cocaine non-specifically increases dopamine transmission by blocking dopamine active transporter (DAT) and evokes behavioural arousal, whereas haloperidol is a non-specific D2-like dopamine receptor antagonist with sedative effects. Interestingly, dopamine has been found to affect immune cells in addition to its action in the central nervous system. Here, we address the possible interactions between haloperidol and cocaine and their effects on both immune cells and behaviour in freely moving rats. We use an intravenous model of haloperidol and binge cocaine administration to evaluate the drugs' impact on the distribution of lymphocyte subsets in both the peripheral blood and the spleen. We assess the drugs' behavioural effects by measuring locomotor activity. Cocaine evoked a pronounced locomotor response and stereotypic behaviours, both of which were completely blocked after pretreatment with haloperidol. The results suggest that blood lymphopenia, which was induced by haloperidol and cocaine (except for natural killer T cells), is independent of D2-like dopaminergic activity and most likely results from the massive secretion of corticosterone. Haloperidol pretreatment prevented the cocaine-induced decrease in NKT cell numbers. Moreover, the increased systemic D2-like dopaminergic activity after cocaine administration is a significant factor in retaining T CD3⁺ CD4⁺ lymphocytes and non-T/NK CD45RA⁺ cells in the spleen.

The Immune System as a Therapeutic Target for Old and New Drugs in Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disease characterized by loss of dopaminergic neurons and intraneuronal accumulation of protein aggregates. The exact mechanisms leading to neuronal death in PD are not fully understood, but several different molecular pathways are involved, leading to the concept that molecular subtypes may coexist in the nosological spectrum of PD. To this respect, immune system activation, both in the periphery and inside the central nervous system, was detected as a common trait of several pathogenic pathways of PD. The current working hypothesis implies that immune cells shift towards a proinflammatory phenotype and trigger the production of neurotoxic cytokines, ultimately contributing to neurodegeneration. While it is very important to understand how commonly used antiparkinson drugs interact with such changes, the search for treatments that may directly or indirectly modulate immune function is a great opportunity for disease modification.

Dopamine, Immunity, and Disease

The neurotransmitter dopamine is a key factor in central nervous system (CNS) function, regulating many processes including reward, movement, and cognition. Dopamine also regulates critical functions in peripheral organs, such as blood pressure, renal activity, and intestinal motility. Beyond these functions, a growing body of evidence indicates that dopamine is an important immunoregulatory factor. Most types of immune cells express dopamine receptors and other dopaminergic proteins, and many immune cells take up, produce, store, and/or release dopamine, suggesting that dopaminergic immunomodulation is important for immune function. Targeting these pathways could be a promising avenue for the treatment of inflammation and disease, but despite increasing research in this area, data on the specific effects of dopamine on many immune cells and disease processes remain inconsistent and poorly understood. Therefore, this review integrates the current knowledge of the role of dopamine in immune cell function and inflammatory signaling across systems. We also discuss the current understanding of dopaminergic regulation of immune signaling in the CNS and peripheral tissues, highlighting the role of dopaminergic immunomodulation in diseases such as Parkinson's disease, several neuropsychiatric conditions, neurologic human immunodeficiency virus, inflammatory bowel disease, rheumatoid arthritis, and others. Careful consideration is given to the influence of experimental design on results, and we note a number of areas in need of further research. Overall, this review integrates our knowledge of dopaminergic immunology at the cellular, tissue, and disease level and prompts the development of therapeutics and strategies targeted toward ameliorating disease through dopaminergic regulation of immunity. SIGNIFICANCE STATEMENT: Canonically, dopamine is recognized as a neurotransmitter involved in the regulation of movement, cognition, and reward. However, dopamine also acts as an immune modulator in the central nervous system and periphery. This review comprehensively assesses the current knowledge of dopaminergic immunomodulation and the role of dopamine in disease pathogenesis at the cellular and tissue level. This will provide broad access to this information across fields, identify areas in need of further investigation, and drive the development of dopaminergic therapeutic strategies.

Dopamine and dopamine receptor D1 as a novel favourable biomarker for hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) remains one of the most common malignant tumours worldwide. Therefore, the identification and development of sensitivity- genes as novel diagnostic markers and effective therapeutic targets is urgently needed. Dopamine and dopamine receptor D1 (DRD1) are reported to be involved in the progression of various cancers. However, the crucial role of DRD1 in HCC malignant activities remains unclear.

Methods

We enrolled 371 patients with liver hepatocellular carcinoma (LIHC) from The Cancer Genome Atlas (TCGA) to detect the expression and functions of DRD1. The Tumour Immune Estimation Resource (TIMER), UALCAN database, Kaplan–Meier plotter, cBioPortal database, and LinkedOmics database were utilized for the systematic investigation of DRD1 expression and related clinical features, coexpressed genes, functional pathways, mutations, and immune infiltrates in HCC.

Results

In this study, we determined that DRD1 expression was decreased in HCC tumour tissues versus normal tissues and that low DRD1 expression indicated a poor prognosis. The significance of DRD1 expression varied among different tumour samples. The somatic mutation frequency of DRD1 in the LIHC cohort was 0.3%. The biological functions of DRD1 were detected and validated, and DRD1 was shown to be involved in various functional activities, including metabolism, oxidation, mitochondrial matrix-related processes and other related signaling pathways. In addition, out study indicated that DRD1 had significant correlations with the infiltration of macrophages, B cells and CD+ T cells in HCC.

Conclusions

These findings demonstrated the rationality of the potential application of DRD1 function as a novel biomarker for HCC diagnosis and a therapeutic target for HCC treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02298-9.

The Role and Function of Regulatory T Cells in Toxoplasma gondii-Induced Adverse Pregnancy Outcomes

Infection with Toxoplasma gondii (T. gondii) during the pregnant period and its potentially miserable outcomes for the fetus, newborn, and even adult offspring continuously occur worldwide. People acquire infection through the consumption of infected and undercooked meat or contaminated food or water. T. gondii infection in pregnant women primarily during the gestation causes microcephaly, mental and psychomotor retardation, or death. Abnormal pregnancy outcomes are mainly associated with regulatory T cell (Treg) dysfunction. Tregs, a special subpopulation of T cells, function as a vital regulator in maintaining immune homeostasis. Tregs exert a critical effect on forming and maintaining maternal-fetal tolerance and promoting fetal development during the pregnancy period. Forkhead box P3 (Foxp3), a significant functional factor of Tregs, determines the status of Tregs. In this review, we summarize the effects of T. gondii infection on host Tregs and its critical transcriptional factor, Foxp3.

Polymorphisms of Dopamine Receptor Genes and Parkinson's Disease: Clinical Relevance and Future Perspectives

Parkinson’s disease (PD) is a neurodegenerative disease caused by loss of dopaminergic neurons in the midbrain. PD is clinically characterized by a variety of motor and nonmotor symptoms, and treatment relies on dopaminergic replacement. Beyond a common pathological hallmark, PD patients may present differences in both clinical progression and response to drug therapy that are partly affected by genetic factors. Despite extensive knowledge on genetic variability of dopaminergic receptors (DR), few studies have addressed their relevance as possible influencers of clinical heterogeneity in PD patients. In this review, we summarized available evidence regarding the role of genetic polymorphisms in DR as possible determinants of PD development, progression and treatment response. Moreover, we examined the role of DR in the modulation of peripheral immunity, in light of the emerging role of the peripheral immune system in PD pathophysiology. A better understanding of all these aspects represents an important step towards the development of precise and personalized disease-modifying therapies for PD.

Involvement of dopaminergic signaling in the cross talk between the renin-angiotensin system and inflammation

The renin-angiotensin system (RAS) is a fundamental regulator of blood pressure and has emerged as an important player in the control of inflammatory processes. Accordingly, imbalance on RAS components either systemically or locally might trigger the development of inflammatory disorders by affecting immune cells. At the same time, alterations in the dopaminergic system have been consistently involved in the physiopathology of inflammatory disorders. Accordingly, the interaction between the RAS and the dopaminergic system has been studied in the context of inflammation of the central nervous system (CNS), kidney, and intestine, where they exert antagonistic actions in the regulation of the immune system. In this review, we summarized, integrated, and discussed the cross talk of the dopaminergic system and the RAS in the regulation of inflammatory pathologies, including neurodegenerative disorders, such as Parkinson’s disease. We analyzed the molecular mechanisms underlying the interaction between both systems in the CNS and in systemic pathologies. Moreover, we also analyzed the impact of the commensal microbiota in the regulation of RAS and dopaminergic system and how it is involved in inflammatory disorders. Furthermore, we summarized the therapeutic approaches that have yielded positive results in preclinical or clinical studies regarding the use of drugs targeting the RAS and dopaminergic system for the treatment of inflammatory conditions. Further understanding of the molecular and cellular regulation of the RAS-dopaminergic cross talk should allow the formulation of new therapies consisting of novel drugs and/or repurposing already existing drugs, alone or in combination, for the treatment of inflammatory disorders.

Reduced regulatory T cells with increased proinflammatory response in patients with schizophrenia

AIM

To investigate whether circulating T cells including regulatory T cells (Treg) and derived cytokines contribute to the immune imbalance observed in schizophrenia.

METHODS

Forty patients with schizophrenia and 40 age, sex, body mass index, education, and smoking status-matched healthy controls (HC) are included in the study. We stained cells with anti-CD14, anti-CD3, anti-CD4, anti-CD8, anti-CD19, anti-CD20, and anti-CD16/56. Peripheral blood mononuclear cells (PBMCs) were isolated and stained with the human FoxP3 kit containing anti-CD4/anti-CD25 and intracellular anti-Foxp3. PBMCs were cultured for 72 h and stimulated with anti-CD3/anti-CD28. Cytokines (IL-2, IL-4, IL-6, IL-10, IFN-γ, TNF-α, and IL-17A) were measured from the culture supernatant and plasma using the Th1/Th2/Th17 cytokine bead array kit.

RESULTS

In comparison with HC, Treg percentages in schizophrenia were higher (1.17 ± 0.63 vs 0.81 ± 0.53, P = 0.005) in unstimulated but lower in the stimulated condition (0.73 ± 0.69 vs 0.97 ± 0.55, P = 0.011). Activated T cell percentages were higher in schizophrenia than HC in unstimulated (2.22 ± 0.78 vs 1.64 ± 0.89, P = 0.001) and stimulated (2.25 ± 1.01 vs 1.72 ± 1.00, P = 0.010) conditions. The culture supernatant levels of IL-6 (7505.17 ± 5170.07 vs 1787.81 ± 1363.32, P < 0.001), IL-17A (191.73 ± 212.49 vs 46.43 ± 23.99, P < 0.001), TNF-α (1557 ± 1059.69 vs 426.57 ± 174.62, P = 0.023), and IFN-γ (3204.13 ± 1397.06 vs 447.79 ± 270.13, P < 0.001); and plasma levels of IL-6 (3.83 ± 3.41vs 1.89 ± 1.14, P = 0.003) and IL-17A (1.20 ± 0.84 vs 0.83 ± 0.53, P = 0.033) were higher in patients with schizophrenia than HC.

CONCLUSION

Our explorative study shows reduced level of Foxp3 expressing Treg in a stimulated condition with induced levels of proinflammatory cytokines in patients with schizophrenia.

Targeting the Dopaminergic System in Autoimmunity

Dopamine has emerged as a fundamental regulator of inflammation. In this regard, it has been shown that dopaminergic signalling pathways are key players promoting homeostasis between the central nervous system and the immune system. Dysregulation in the dopaminergic system affects both innate and adaptive immunity, contributing to the development of numerous autoimmune and inflammatory pathologies. This makes dopamine receptors interesting therapeutic targets for either the development of new treatments or repurposing of already available pharmacological drugs. Dopamine receptors are broadly expressed on different immune cells with multifunctional effects depending on the dopamine concentration available and the pattern of expression of five dopamine receptors displaying different affinities for dopamine. Thus, impaired dopaminergic signalling through different dopamine receptors may result in altered behaviour of immunity, contributing to the development and progression of autoimmune pathologies. In this review we discuss the current evidence involving the dopaminergic system in inflammatory bowel disease, multiple sclerosis and Parkinson's disease. In addition, we summarise and analyse the therapeutic approaches designed to attenuate disease development and progression by targeting the dopaminergic system. Graphical Abstract Targetting the dopaminergic system in autoimmunity. Effector T-cells (Teff) orchestrate inflamamtion involved in autoimmunity, whilst regulatory T-cells (Tregs) suppress Teff activity promoting tolerance to self-constituents. Dopamine has emerged as a key regulator of Teff and Tregs function, thereby dopamine receptors have becoming important therapeutic targets in autoimmune disorders, especially in those affecting the brain and the gut, where dopamine levels strongly change with inflammation.

Dopamine Alters Lipopolysaccharide-Induced Nitric Oxide Production in Microglial Cells via Activation of D1-Like Receptors

Dopamine (DA) is important in the maintenance of normal nervous system function. DA is the target of multiple drugs, and it induces critical alterations in immune cells. However, these impacts are controversial, and the mechanism remains unclear. In the present study, we treated BV-2 microglial cells and primary microglia with DA and measured the changes in cytokines. We also identified the expression of DA receptors (DRs) using confocal and immunofluorescent microscopy. Specific agonists and antagonists of D1-like DRs (D1DR and D5DR) were used to observe alterations in cytokines. Western blot and siRNA interference were performed to investigate the involvement of the downstream signaling molecules of DRs. We also measured changes in mitogen-activated protein kinases (MAPKs) and the nuclear factor-kappa B (NF-κB) signaling pathway and assessed their involvement using inhibitors. We found that DA alone produced no effects on IL-6, TNF-α or nitric oxide (NO) production, and it inhibited lipopolysaccharide (LPS)-induced NO in microglial cells. Microglia expressed a high abundance of D1-like DRs (D1DR and D5DR). The agonists inhibited NO production, and antagonists reversed the DA-induced suppression of NO. Adenylatec cyclase (AC), cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA) mediated DA function, and cAMP-response element binding protein (CREB) was not involved. ERK1/2 and NF-κB, but not p-38 or JNK, played roles in DA-suppressed NO generation via altering inducible nitric oxide synthase (iNOS) transcription. These data illustrate that DA modulates LPS-induced NO production via the AC/cAMP-PKA-ERK1/2-NF-κB-iNOS axis in mouse microglia, and D1-like DRs are involved. The present study provides functional evidence for an essential role of DA in immunoregulation.

Dopamine and its receptors play a role in the modulation of CCR5 expression in innate immune cells following exposure to Methamphetamine: Implications to HIV infection

The Human Immunodeficiency Virus (HIV) infects cells in the Central Nervous System (CNS), where the access of antiretrovirals and antibodies that can kill the virus may be challenging. As a result of the early HIV entry in the brain, infected individuals develop inflammation and neurological deficits at various levels, which are aggravated by drugs of abuse. In the non-human primate model of HIV, we have previously shown that drugs of abuse such as Methamphetamine (Meth) increase brain viral load in correlation with a higher number of CCR5-expressing myeloid cells. CCR5 is a chemokine receptor that may be involved in increasing inflammation, but also, it is a co-receptor for viral entry into target cells. CCR5-expressing myeloid cells are the main targets of HIV in the CNS. Thus, the identification of factors and mechanisms that impact the expression of CCR5 in the brain is critical, as changes in CCR5 levels may affect the infection in the brain. Using a well-characterized in vitro system, with the THP1 human macrophage cell line, we have investigated the hypothesis that the expression of CCR5 is acutely affected by Meth, and examined pathways by which this effect could happen. We found that Meth plays a direct role by regulating the abundance and nuclear translocation of transcription factors with binding sites in the CCR5 promoter. However, we found that the main factor that modifies the CCR5 gene promoter at the epigenetic level towards transcription is Dopamine (DA), a neurotransmitter that is produced primarily in brain regions that are rich in dopaminergic neurons. In THP1 cells, the effect of DA on innate immune CCR5 transcription was mediated by DA receptors (DRDs), mainly DRD4. We also identified a role for DRD1 in suppressing CCR5 expression in this myeloid cell system, with potential implications for therapy. The effect of DA on innate immune CCR5 expression was also detectable on the cell surface during acute time-points, using low doses. In addition, HIV Tat acted by enhancing the surface expression of CCR5, in spite of its poor effect on transcription. Overall, our data suggests that the exposure of myeloid cells to Meth in the context of presence of HIV peptides such as Tat, may affect the number of HIV targets by modulating CCR5 expression, through a combination of DA-dependent and–independent mechanisms. Other drugs that increase DA may affect similar mechanisms. The implications of these epigenetic and translational mechanisms in enhancing HIV infection in the brain and elsewhere are demonstrated.

β2 -Adrenoceptors inhibit neutrophil extracellular traps in human polymorphonuclear leukocytes

This study tests the hypothesis that in isolated human polymorphonuclear leukocytes (PMN) adrenergic ligands can affect neutrophil extracellular trap (NET) formation. We have previously shown that, in PMN, adrenaline (A), through the activation of adrenergic receptors (AR), reduces stimulus-dependent cell activation; we have, therefore, planned to investigate if AR are involved in NET production. PMN were obtained from venous blood of healthy subject. The ability of adrenergic ligands to affect reactive oxygen species (ROS) production, NET production, and cell migration was investigated in cells cultured under resting conditions or after activation with N-formyl-methionyl-leucyl-phenylalanine (fMLP), LPS, or IL-8. Stimuli-induced NET production measured as ROS, microscopic evaluation, and elastase production was reverted by A and this effect was blocked by the selective β₂ -AR antagonist ICI-118,551. The stimulus-induced ROS generation and migration was prevented by A and by isoprenaline (ISO), and these effects were counteracted only by ICI-118,551 and not by the other two selective ligands for the β₁ and β₃ -AR. Finally, the presence of the β-ARs on PMN was confirmed, by means of microscopy and flow cytometry. The data of the present study suggest that adrenergic compounds, through the interaction of mainly β₂ -AR, are able to affect neutrophil functions. These data are suggestive of a possible therapeutic role of β₂ -AR ligands (in addition to their classical use), promoting the possible therapeutic relevance of adrenergic system in the modulation of innate immunity proposing their possible use as anti-inflammatory drugs.

Interaction of childhood urbanicity and variation in dopamine genes alters adult prefrontal function as measured by functional magnetic resonance imaging (fMRI)

Brain phenotypes showing environmental influence may help clarify unexplained associations between urban exposure and psychiatric risk. Heritable prefrontal fMRI activation during working memory (WM) is such a phenotype. We hypothesized that urban upbringing (childhood urbanicity) would alter this phenotype and interact with dopamine genes that regulate prefrontal function during WM. Further, dopamine has been hypothesized to mediate urban-associated factors like social stress. WM-related prefrontal function was tested for main effects of urbanicity, main effects of three dopamine genes-catechol-O-methyltransferase (COMT), dopamine receptor D1 (DRD1), and dopamine receptor D2 (DRD2)-and, importantly, dopamine gene-by-urbanicity interactions. For COMT, three independent human samples were recruited (total n = 487). We also studied 253 subjects genotyped for DRD1 and DRD2. 3T fMRI activation during the N-back WM task was the dependent variable, while childhood urbanicity, dopamine genotype, and urbanicity-dopamine interactions were independent variables. Main effects of dopamine genes and of urbanicity were found. Individuals raised in an urban environment showed altered prefrontal activation relative to those raised in rural or town settings. For each gene, dopamine genotype-by-urbanicity interactions were shown in prefrontal cortex-COMT replicated twice in two independent samples. An urban childhood upbringing altered prefrontal function and interacted with each gene to alter genotype-phenotype relationships. Gene-environment interactions between multiple dopamine genes and urban upbringing suggest that neural effects of developmental environmental exposure could mediate, at least partially, increased risk for psychiatric illness in urban environments via dopamine genes expressed into adulthood.

cAMP levels in lymphocytes and CD4+ regulatory T-cell functions are affected by dopamine receptor gene polymorphisms

The neurotransmitter dopamine (DA) has prominent effects in the immune system and between the immune cells, CD4⁺ regulatory T (Treg) lymphocytes, a specialized T-cell subset crucial for the control of immune homeostasis, are especially sensitive to DA. Dopaminergic receptors (DR) are grouped into two families according to their pharmacological profile and main second messenger coupling: the D₁ -like (D₁ and D₅ ), which activate adenylate cyclase, and the D₂ -like (D₂ , D₃ and D₄ ), which inhibit adenylate cyclase and exist in several variants that have been associated to clinical conditions such as schizophrenia, bipolar disorder, substance abuse and addiction. We aimed to examine, in venous blood samples from healthy volunteers, the relationship between the arbitrary DR score and DR functional responses in human lymphocytes. All the samples were genotyped for selected DR gene variants (DRD1: rs4532 and rs686; DRD2: rs1800497 and rs6277; DRD3: rs6280; DRD4: rs747302 and seven 48-base pair variable number tandem repeat (VNTR)) and a DR score was attributed to each participant. We have also tested whether DR gene polymorphisms might affect Treg cell ability to suppress effector T-cell function. To our knowledge, this is the first study showing a correlation between DR gene variants and human T lymphocyte function. The main results are that both D₁ -like and D₂ -like DR are functionally active in human lymphocytes, although the D₁ -like DR stimulation results in stronger effects in comparison to the D₂ -like DR stimulation. In addition, it seems that the DR genetic profile may affect the ability of lymphocytes to respond to dopaminergic agents. More investigations are needed about the possible clinical relevance of such findings.

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.

Polymorphisms of dopamine receptor genes and risk of visual hallucinations in Parkinson's patients

BACKGROUND

Visual hallucinations (VHs) are frequent non-motor complication of Parkinson's disease (PD), associated to a negative prognosis. Previous studies showed an association between dopamine receptor (DR) gene (DR) variants and psychosis in Alzheimer's disease, addictions, schizophrenia, and bipolar disorder. However, there are only a few studies on DR variants and VHs in PD, which did not provide conclusive results.

OBJECTIVES

The present study aimed to determine whether genetic differences of DR are associated with visual hallucinations (VHs) in a cohort of Parkinson's disease (PD) patients.

METHODS

A case-control study of 84 PD subjects, 42 with and 42 without VHs,that were matched for age, gender, disease duration, and dopaminergic medication was conducted. Polymerase chain reaction for SNPs in both D1-like (DRD1A-48G [rs4532] and C62T [rs686], DRD5T798C [rs6283]) and D2-like DR (DRD2G2137A [rs1800497] and C957T [rs6277], DRD3G25A [rs6280] and G712C [rs1800828], DRD4C616G [rs747302] and nR VNTR 48bp) analyzed genomic DNA.

RESULTS

Patients carrying allele T at DRD1C62T had an increased risk of VHs, expressed as OR (95 % CI, p value), of 10.7 (2.9-40, p = 0.0001). Moreover, patients with DRD1-48 GG and 62TT genotype displayed shorter time to VHs, whereas a longer time to VHs was found in subjects carrying the DRD4 CG alleles.

CONCLUSIONS

PD patients with VHs display higher frequency of DR SNPs associated with increased D1-like activity and decreased D2-like activity. Our data are in line with associations reported in other neurodegenerative and psychiatric conditions. Results likely provide valuable information for personalizing pharmacological therapy in PD patients.