Macrophage Fcgamma receptors expression is altered by treatment with dopaminergic drugs

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.

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.

Immunomodulatory Effects of Dopamine in Inflammatory Diseases

Dopamine (DA) receptor, a significant G protein-coupled receptor, is classified into two families: D1-like (D1 and D5) and D2-like (D2, D3, and D4) receptor families, with further formation of homodimers, heteromers, and receptor mosaic. Increasing evidence suggests that the immune system can be affected by the nervous system and neurotransmitters, such as dopamine. Recently, the role of the DA receptor in inflammation has been widely studied, mainly focusing on NLRP3 inflammasome, NF-κB pathway, and immune cells. This article provides a brief review of the structures, functions, and signaling pathways of DA receptors and their relationships with inflammation. With detailed descriptions of their roles in Parkinson disease, inflammatory bowel disease, rheumatoid arthritis, systemic lupus erythematosus, and multiple sclerosis, this article provides a theoretical basis for drug development targeting DA receptors in inflammatory diseases.

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.

Dopaminergic Regulation of Innate Immunity: a Review

Dopamine (DA) is a neurotransmitter in the central nervous system as well as in peripheral tissues. Emerging evidence however points to DA also as a key transmitter between the nervous system and the immune system as well as a mediator produced and released by immune cells themselves. Dopaminergic pathways have received so far extensive attention in the adaptive branch of the immune system, where they play a role in health and disease such as multiple sclerosis, rheumatoid arthritis, cancer, and Parkinson's disease. Comparatively little is known about DA and the innate immune response, although DA may affect innate immune system cells such as dendritic cells, macrophages, microglia, and neutrophils. The present review aims at providing a complete and exhaustive summary of currently available evidence about DA and innate immunity, and to become a reference for anyone potentially interested in the fields of immunology, neurosciences and pharmacology. A wide array of dopaminergic drugs is used in therapeutics for non-immune indications, such as Parkinson's disease, hyperprolactinemia, shock, hypertension, with a usually favorable therapeutic index, and they might be relatively easily repurposed for immune-mediated disease, thus leading to innovative treatments at low price, with benefit for patients as well as for the healthcare systems.

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.

Drug induced increases in CNS dopamine alter monocyte, macrophage and T cell functions: implications for HAND

Central nervous system (CNS) complications resulting from HIV infection remain a major public health problem as individuals live longer due to the success of combined antiretroviral therapy (cART). As many as 70 % of HIV infected people have HIV associated neurocognitive disorders (HAND). Many HIV infected individuals abuse drugs, such as cocaine, heroin or methamphetamine, that may be important cofactors in the development of HIV CNS disease. Despite different mechanisms of action, all drugs of abuse increase extracellular dopamine in the CNS. The effects of dopamine on HIV neuropathogenesis are not well understood, and drug induced increases in CNS dopamine may be a common mechanism by which different types of drugs of abuse impact the development of HAND. Monocytes and macrophages are central to HIV infection of the CNS and to HAND. While T cells have not been shown to be a major factor in HIV-associated neuropathogenesis, studies indicate that T cells may play a larger role in the development of HAND in HIV infected drug abusers. Drug induced increases in CNS dopamine may dysregulate functions of, or increase HIV infection in, monocytes, macrophages and T cells in the brain. Thus, characterizing the effects of dopamine on these cells is important for understanding the mechanisms that mediate the development of HAND in drug abusers.

Mast cells express tyrosine hydroxylase and store dopamine in a serglycin-dependent manner

Here we show that mast cells contain dopamine and that mast cell activation causes dopamine depletion, indicating its presence within secretory granules. Dopamine storage increased during mast cell maturation from bone marrow precursors, and was dependent on the presence of serglycin. Moreover, the expression of tyrosine hydroxylase, the key enzyme in dopamine biosynthesis, was induced during mast cell maturation; histidine decarboxylase and tryptophan hydroxylase 1 were also induced. Mast cell activation caused a robust induction of histidine decarboxylase, but no stimulation of tyrosine hydroxylase or tryptophan hydroxylase 1 expression. The present study points toward a possible role of dopamine in mast cell function.

Dopamine and renal function and blood pressure regulation

Dopamine is an important regulator of systemic blood pressure via multiple mechanisms. It affects fluid and electrolyte balance by its actions on renal hemodynamics and epithelial ion and water transport and by regulation of hormones and humoral agents. The kidney synthesizes dopamine from circulating or filtered L-DOPA independently from innervation. The major determinants of the renal tubular synthesis/release of dopamine are probably sodium intake and intracellular sodium. Dopamine exerts its actions via two families of cell surface receptors, D1-like receptors comprising D1R and D5R, and D2-like receptors comprising D2R, D3R, and D4R, and by interactions with other G protein-coupled receptors. D1-like receptors are linked to vasodilation, while the effect of D2-like receptors on the vasculature is variable and probably dependent upon the state of nerve activity. Dopamine secreted into the tubular lumen acts mainly via D1-like receptors in an autocrine/paracrine manner to regulate ion transport in the proximal and distal nephron. These effects are mediated mainly by tubular mechanisms and augmented by hemodynamic mechanisms. The natriuretic effect of D1-like receptors is caused by inhibition of ion transport in the apical and basolateral membranes. D2-like receptors participate in the inhibition of ion transport during conditions of euvolemia and moderate volume expansion. Dopamine also controls ion transport and blood pressure by regulating the production of reactive oxygen species and the inflammatory response. Essential hypertension is associated with abnormalities in dopamine production, receptor number, and/or posttranslational modification.

Human immunodeficiency virus (HIV) infection of human macrophages is increased by dopamine: a bridge between HIV-associated neurologic disorders and drug abuse

The prevalence of human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) that result from HIV infection of the central nervous system is increasing. Macrophages, the primary target for HIV within the central nervous system, play a central role in HIV-induced neuropathogenesis. Drug abuse exacerbates HAND, but the mechanism(s) by which this increased neuropathology results in more severe forms of HAND in HIV-infected drug abusers is unclear. The addictive and reinforcing effects of many drugs of abuse, such as cocaine and methamphetamine, are mediated by increased extracellular dopamine in the brain. We propose a novel mechanism by which drugs of abuse intensify HIV neuropathogenesis through direct effects of the neurotransmitter dopamine on HIV infection of macrophages. We found that macrophages express dopamine receptors 1 and 2, and dopamine activates macrophages by increasing ERK 1 phosphorylation. Our results demonstrate for the first time that dopamine increases HIV replication in human macrophages and that the mechanism by which dopamine mediates this change is by increasing the total number of HIV-infected macrophages. This increase in HIV replication is mediated by activation of dopamine receptor 2. These findings suggest a common mechanism by which drugs of abuse enhance HIV replication in macrophages and indicate that the drug abuse-heightened levels of central nervous system dopamine could increase viral replication, thereby accelerating the development of HAND.

Dual mode of catecholamine action on splenic macrophage phagocytosis in wall lizard, Hemidactylus flaviviridis

In the present study, in vitro concentration-related effect of catecholamines, dopamine (DA), norepinephrine (NE), and epinephrine (E) was observed on phagocytic activity of splenic macrophages to understand the impact of sympatho-adrenal-medullary (SAM) activation on innate immunity in wall lizard Hemidactylus flaviviridis under stress condition. Restraint stress for 1 h resulted in marked suppression of macrophage phagocytosis, suggesting that supra-physiological level of catecholamines in response to SAM activation under stress suppressed phagocytosis. This interpretation was reinforced since all the catecholamines considerably reduced phagocytosis at high concentrations ranging from 10(-7) to 10(-5)M. On the contrary, DA, NE, and E at low concentrations considerably stimulated phagocytosis, which increased with the decrease of concentrations ranging from 10(-11) to 10(-15)M. Further, effect of NE and E was blocked by beta-adrenergic blocker suggesting the beta-adrenoceptor-dependent regulating mechanism of NE and E. DA acts through both beta-adrenoceptor-dependent and D1/D2 class receptor-dependent mechanism, since beta-adrenergic blocker could partially block the DA effect. beta-Adrenoceptor-linked adenylate cyclase-mediated cAMP action in modulation of phagocytic activity was evident as 3-isobutyl-1-methyl-xanthine suppressed phagocytosis. Further, to delineate the mode of dual effect of catecholamines through beta-adrenergic receptors, in vitro concentration-related effect of cAMP was investigated on macrophage phagocytosis. cAMP depending on concentration had opposite effect on phagocytosis, and its stimulatory effect at low concentrations was reversed by actinomycin D and cycloheximide, whereas these transcription and translation inhibitors, respectively, failed to alter the inhibitory effect of cAMP at high concentrations. This suggests the concentration-related two different pathways of catecholamine action, classical non-genomic at high concentration while genomic pathway at low concentration.

Therapeutic strategies in common variable immunodeficiency

The treatment of common variable immunodeficiency (CVID) is currently based on the early recognition of the condition and replacement immunoglobulin combined with prompt treatment of infections and complications. The route of administration, dose and frequency of administration of immunoglobulin still vary between centres and countries. Other interventions aimed at overcoming the immunological defects in CVID such as interleukin-2 therapy are being studied but there is as yet insufficient evidence to support their routine use. The treatment of complications such as suppurative lung disease uses principles broadly similar to those used for cystic fibrosis, whereas the granulomatous complications involving the lungs and other organ systems are in need of much more research to define optimum therapies.

Enhancement of splenic-macrophage Fcgamma receptor expression by treatment with estrogens

Splenic-macrophage Fcgamma receptors (FcgammaRs) participate in the pathophysiologies of immune-complex diseases and in host defense against infection. Modulation of macrophage FcgammaR expression is an immuno-therapeutic target. Glucocorticoids, sex steroids, and dopaminergic drugs modulate macrophage FcgammaR expression. Previous data indicate that estradiol increases macrophage FcgammaR expression. Nevertheless, the effects of clinically used estrogens upon macrophage FcgammaR expression are unknown. We assessed the effects of treatment with commonly used estrogens on the expression of macrophage FcgammaRs using a guinea pig experimental model. Six estrogens have been studied: ethynylestradiol (Et), mestranol (M), chlortianisene (Ct), promestriene, 17-epiestriol, and 17beta-estradiol. Following in vivo treatment of guinea pigs, we determined the clearance of immunoglobulin G (IgG)-sensitized erythrocytes in vivo, the binding of IgG-sensitized erythrocytes by isolated splenic macrophages, and splenic-macrophage FcgammaR cell surface expression. Estrogens enhance the clearance of IgG-sensitized erythrocytes by increasing splenic-macrophage FcgammaR expression. Et, M, and Ct were more effective than the other estrogens. Flow cytometry and fluorescence microscopy with monoclonal antibodies demonstrated that estrogens increase the cell surface expression of FcgammaR1 and -2 more than that of FcgammaR2. These data indicate that treatment with commonly used estrogens enhances the clearance of IgG-sensitized cells by improving splenic-macrophage FcgammaR expression.

Effects of androgen treatment on expression of macrophage Fcgamma receptors

Macrophage Fcgamma receptors (FcgammaRs) play an important role in the host defense against infection and in the pathophysiology of immune cytopenias. Modulation of macrophage FcgammaR expression is a potential therapeutic approach to immune disorders. Glucocorticoids and progesterones decrease macrophage FcgammaR expression. We assessed the effect of treatment with androgens and antiandrogens on the expression of macrophage FcgammaRs using an experimental guinea pig model. Four androgens (testosterone, dihydrotestosterone, mesterolone, and danazol) and five antiandrogens (flutamide, nilutamide, cyproterone acetate, spironolactone, and finasteride) were studied. Following in vivo treatment of guinea pigs, we determined the clearance of immunoglobulin G (IgG)-sensitized erythrocytes in vivo, the binding of IgG-sensitized erythrocytes by isolated splenic macrophages, and splenic macrophage FcgammaR cell surface expression. All of the androgens impaired the clearance of IgG-sensitized erythrocytes by decreasing splenic macrophage FcgammaR expression. Dihydrotestosterone and mesterolone were more effective than testosterone or dihydrotestosterone. Flow cytometry and fluorescence microscopy with monoclonal antibodies demonstrated that the androgens decreased the cell surface expression of FcgammaR1,2 more than that of FcgammaR2. Antiandrogens did not significantly alter macrophage FcgammaR expression. Nevertheless, antiandrogens counteracted the effects of androgens on macrophage FcgammaR expression. These data indicate that androgens impair the clearance of IgG-coated cells by decreasing splenic macrophage FcgammaR expression. Thus, androgens other than danazol are candidate drugs for the treatment of immune disorders.

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.