Therapeutic effect of the D2-dopamine agonist bromocriptine on acute and relapsing experimental allergic encephalomyelitis

Dopaminergic stimulation leads B-cell infiltration into the central nervous system upon autoimmunity

BACKGROUND

Recent evidence has shown dopamine as a major regulator of inflammation. Accordingly, dopaminergic regulation of immune cells plays an important role in the physiopathology of inflammatory disorders. Multiple sclerosis (MS) is an inflammatory disease involving a CD4⁺ T-cell-driven autoimmune response to central nervous system (CNS) derived antigens. Evidence from animal models has suggested that B cells play a fundamental role as antigen-presenting cells (APC) re-stimulating CD4⁺ T cells in the CNS as well as regulating T-cell response by mean of inflammatory or anti-inflammatory cytokines. Here, we addressed the role of the dopamine receptor D3 (DRD3), which displays the highest affinity for dopamine, in B cells in animal models of MS.

METHODS

Mice harbouring Drd3-deficient or Drd3-sufficient B cells were generated by bone marrow transplantation into recipient mice devoid of B cells. In these mice, we compared the development of experimental autoimmune encephalomyelitis (EAE) induced by immunization with a myelin oligodendrocyte glycoprotein (MOG)-derived peptide (pMOG), a model that leads to CNS-autoimmunity irrespective of the APC-function of B cells, or by immunization with full-length human MOG protein (huMOG), a model in which antigen-specific activated B cells display a fundamental APC-function in the CNS. APC-function was assessed in vitro by pulsing B cells with huMOG-coated beads and then co-culturing with MOG-specific T cells.

RESULTS

Our data show that the selective Drd3 deficiency in B cells abolishes the disease development in the huMOG-induced EAE model. Mechanistic analysis indicates that although DRD3-signalling did not affect the APC-function of B cells, DRD3 favours the CNS-tropism in a subset of pro-inflammatory B cells in the huMOG-induced EAE model, an effect that was associated with higher CXCR3 expression. Conversely, the results show that the selective Drd3 deficiency in B cells exacerbates the disease severity in the pMOG-induced EAE model. Further analysis shows that DRD3-stimulation increased the expression of the CNS-homing molecule CD49d in a B-cell subset with anti-inflammatory features, thus attenuating EAE manifestation in the pMOG-induced EAE model.

CONCLUSIONS

Our findings demonstrate that DRD3 in B cells exerts a dual role in CNS-autoimmunity, favouring CNS-tropism of pro-inflammatory B cells with APC-function and promoting CNS-homing of B cells with anti-inflammatory features. Thus, these results show DRD3-signalling in B cells as a critical regulator of CNS-autoimmunity.

Dopaminergic Receptors as Neuroimmune Mediators in Experimental Autoimmune Encephalomyelitis

The dopaminergic system plays an essential role in maintaining homeostasis between the central nervous system (CNS) and the immune system. Previous studies have associated imbalances in the dopaminergic system to the pathogenesis of multiple sclerosis (MS). Here, we examined the protein levels of dopaminergic receptors (D1R and D2R) in different phases of the experimental autoimmune encephalomyelitis (EAE) model. We also investigated if the treatment with pramipexole (PPX)-a dopamine D2/D3 receptor-preferring agonist-would be able to prevent EAE-induced motor and mood dysfunction, as well as its underlying mechanisms of action. We report that D2R immunocontent is upregulated in the spinal cord of EAE mice 14 days post-induction. Moreover, D1R and D2R immunocontents in lymph nodes and the oxidative damage in the spinal cord and striatum of EAE animals were significantly increased during the chronic phase. Also, during the pre-symptomatic phase, axonal damage in the spinal cord of EAE mice could already be found. Surprisingly, therapeutic treatment with PPX failed to inhibit the progression of EAE. Of note, PPX treatment inhibited EAE-induced depressive-like while failed to inhibit anhedonic-like behaviors. We observed that PPX treatment downregulated IL-1β levels and increased BNDF content in the spinal cord after EAE induction. Herein, we show that a D2/D3 receptor-preferred agonist mitigated EAE-induced depressive-like behavior, which could serve as a new possibility for further clinical trials on treating depressive symptoms in MS patients. Thus, we infer that D2R participates in the crosstalk between CNS and immune system during autoimmune and neuroinflammatory response induced by EAE, mainly in the acute and chronic phase of the disease.

[Blockade of D1-like dopaminergic receptors suppresses Th17-cell function in multiple sclerosis]

OBJECTIVE

To investigate the direct effect of D₁-like dopaminergic receptors antagonist on Th17-cells function in multiple sclerosis (MS) in vitro.

MATERIAL AND METHODS

Forty-one relapsing-remitting MS patients and twenty-five healthy subjects were examined. The functional activity of Th17-cells was assessed by the ability to produce IL-17 and IFN-γ by peripheral blood mononuclear cells (PBMCs) and CD4⁺ T cells, stimulated with microbeads coated with anti-CD3/anti-CD28-antibodies. To study the involvement of D₁-like dopaminergic receptors in modulation of Th17-cell function, the samples of PBMCs or CD4⁺ T-cells were cultured in the presence of dopamine and/or specific D₁-like dopaminergic receptors antagonist (SCH23390). Cytokine levels in cell culture supernatants were measured by ELISA.

RESULTS

The production of IL-17 and IFN-γ by stimulated PBMCs were higher in MS patients during relapse than in MS patients during clinical remission or in healthy subjects. The production of cytokines by stimulated PBMCs or CD4⁺ T-cells in MS patients during clinical remission and healthy subjects was comparable. Dopamine reduced the production of cytokines by PBMCs and CD4⁺ T-cells in all groups. Blockade of D₁-like dopaminergic receptors did not affect the dopamine-mediated cytokine suppression in MS patients and healthy subjects. Blockade of D₁-like dopaminergic receptors directly suppressed cytokine production by PBMCs and CD4⁺ T-cells in MS patients and healthy subjects.

CONCLUSIONS

Dopamine and blockade of D₁-like dopaminergic receptors have an inhibitory effect on Th17-cell function in MS. The activation of D₂-like dopaminergic receptors could mediate the inhibitory effect of dopamine on Th17-cells.

Hormones in experimental autoimmune encephalomyelitis (EAE) animal models

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) in which activated immune cells attack the CNS and cause inflammation and demyelination. While the etiology of MS is still largely unknown, the interaction between hormones and the immune system plays a role in disease progression, but the mechanisms by which this occurs are incompletely understood. Several in vitro and in vivo experimental, but also clinical studies, have addressed the possible role of the endocrine system in susceptibility and severity of autoimmune diseases. Although there are several demyelinating models, experimental autoimmune encephalomyelitis (EAE) is the oldest and most commonly used model for MS in laboratory animals which enables researchers to translate their findings from EAE into human. Evidences imply that there is great heterogeneity in the susceptibility to the induction, the method of induction, and the response to various immunological or pharmacological interventions, which led to conflicting results on the role of specific hormones in the EAE model. In this review, we address the role of endocrine system in EAE model to provide a comprehensive view and a better understanding of the interactions between the endocrine and the immune systems in various models of EAE, to open up a ground for further detailed studies in this field by considering and comparing the results and models used in previous studies.

The distinct roles of monoamines in multiple sclerosis: A bridge between the immune and nervous systems?

The monoaminergic neurotransmitters dopamine, noradrenaline, and serotonin are pivotal actors of the interplay between the nervous and the immune system due to their ability of binding to cell-receptors of both systems, crucially regulating their function within the central nervous system and the periphery. As monoamines are dysfunctional in many neurological and psychiatric diseases, they have been successfully used as pharmacological targets. Multiple sclerosis (MS) is one of the best examples of neurological disease caused by an altered interaction between the nervous and immune system and emerging evidence supports a dysregulation of monoaminergic systems in the pathogenesis of MS, secondary to both inflammation-induced reduction of monoamines' synthesis and structural damage to monoaminergic pathways within the brain. Here we review the evidence for monoamines being key mediators of neuroimmune interaction, affecting MS pathogenesis and course. Moreover, we discuss how the reduction/dysfunction of monoamines in MS may contribute to some clinical features typical of the disease, particularly fatigue and depression. Finally, we summarize different drugs targeting monoamines that are currently under evaluation for their potential efficacy to treat MS, as well as to alleviate fatigue and depression in MS.

[The prospect of dopaminergic therapy in multiple sclerosis]

Dopamine is a direct mediator of neuroimmune interactions. Recent studies show that by acting on the dopaminergic receptors, it is possible to modulate Th17-immune response, which play a crucial role in the pathogenesis of multiple sclerosis. Dopamine can modulate Th17 cells function as well as dendritic cell-mediated Th17-immune response that allows considering dopaminergic receptors as a new therapeutic target in multiple sclerosis. In this short communication, the prospects of using dopaminergic therapy as a pathogenetic treatment for multiple sclerosis are discussed.

Localisation of clozapine during experimental autoimmune encephalomyelitis and its impact on dopamine and its receptors

Multiple sclerosis is a disease characterised by axonal demyelination in the central nervous system (CNS). The atypical antipsychotic drug clozapine attenuates experimental autoimmune encephalomyelitis (EAE), a mouse model used to study multiple sclerosis, but the precise mechanism is unknown and could include both peripheral and CNS-mediated effects. To better understand where clozapine exerts its protective effects, we investigated the tissue distribution and localisation of clozapine using matrix-assisted laser desorption ionization imaging mass spectrometry and liquid chromatography-mass spectrometry. We found that clozapine was detectable in the brain and enriched in specific brain regions (cortex, thalamus and olfactory bulb), but the distribution was not altered by EAE. Furthermore, although not altered in other organs, clozapine levels were significantly elevated in serum during EAE. Because clozapine antagonises dopamine receptors, we analysed dopamine levels in serum and brain as well as dopamine receptor expression on brain-resident and infiltrating immune cells. While neither clozapine nor EAE significantly affected dopamine levels, we observed a significant downregulation of dopamine receptors 1 and 5 and up-regulation of dopamine receptor 2 on microglia and CD4+-infiltrating T cells during EAE. Together these findings provide insight into how neuroinflammation, as modelled by EAE, alters the distribution and downstream effects of clozapine.

Pregnancy, postpartum and parity: Resilience and vulnerability in brain health and disease

Risk and resilience in brain health and disease can be influenced by a variety of factors. While there is a growing appreciation to consider sex as one of these factors, far less attention has been paid to sex-specific variables that may differentially impact females such as pregnancy and reproductive history. In this review, we focus on nervous system disorders which show a female bias and for which there is data from basic research and clinical studies pointing to modification in disease risk and progression during pregnancy, postpartum and/or as a result of parity: multiple sclerosis (MS), depression, stroke, and Alzheimer's disease (AD). In doing so, we join others (Shors, 2016; Galea et al., 2018a) in aiming to illustrate the importance of looking beyond sex in neuroscience research.

Prolactin and autoimmunity: The hormone as an inflammatory cytokine

Nowadays, more than 80 autoimmune disorders are recognized, in which an aberrant immune response against different organs and tissues plays a crucial role. Hormonal homeostasis has great influence in achieving competent and healthy immune system function. Prolactin has a bioactive function acting as a hormone and a cytokine. It influences the immune system modulation, mainly inhibiting the negative selection of autoreactive B lymphocytes. Hyperprolactinemia has been detected in many patients with different autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, Sjögren syndrome, multiple sclerosis, autoimmune thyroid disease, systemic sclerosis, among others, and its believed to play a crucial role in disease pathogenesis. A direct correlation between prolactin levels and disease activity was not clear. Genetic factors may have a role in humans as in animal models. Dopamine agonists have proven to offer clinical benefits among autoimmune patients and represent a promising therapy to be explored. In this review, the authors attempt to provide a critical overview on the role of prolactin in the immune system, exploring its contribution to the development of autoimmune diseases.

Extrapituitary prolactin promotes generation of Eomes-positive helper T cells mediating neuroinflammation

We have previously demonstrated that induction of pathogenic eomesodermin-positive CD4⁺ T cells (Eomes⁺ T helper [Th] cells) is associated with transition from an acute stage to a later stage of experimental autoimmune encephalomyelitis (EAE). In the late phase of EAE, B cells and non-B cell antigen-presenting cells (APCs) recruited to the central nervous system strikingly up-regulate prolactin (PRL). The PRL-producing APCs have the potential to promote generation of Eomes⁺ Th cells from naïve T cells in an MHC class II-restricted manner, and therapies inhibitory for PRL production suppress the induction of Eomes⁺ Th cells and ameliorate clinical signs of EAE. Our study highlights the unexpected role of extrapituitary PRL in the development of persistent neuroinflammation.

Induction of eomesodermin-positive CD4⁺ T cells (Eomes⁺ T helper [Th] cells) has recently been correlated with the transition from an acute stage to a later stage of experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. Moreover, these cells’ pathogenic role has been experimentally proven in EAE. While exploring how the pathogenic Eomes⁺ Th cells are generated during the course of EAE, we unexpectedly found that B cells and MHC class II⁺ myeloid cells isolated from the late EAE lesions strikingly up-regulated the expression of prolactin (PRL). We demonstrate that such PRL-producing cells have a unique potential to induce Eomes⁺ Th cells from naïve T cells ex vivo, and that anti-MHC class II antibody could block this process. Furthermore, PRL levels in the cerebrospinal fluid were significantly increased in the late phase of EAE, and blocking the production of PRL by bromocriptine or Zbtb20-specific siRNA significantly reduced the numbers of Eomes⁺ Th cells in the central nervous system (CNS) and ameliorated clinical signs in the later phase of EAE. The PRL dependency of Eomes⁺ Th cells was confirmed in a series of in vitro and ex vivo experiments. Collectively, these results indicate that extrapituitary PRL plays a crucial role in the CNS inflammation mediated by pathogenic Eomes⁺ Th cells. Cellular interactions involving PRL-producing immune cells could be considered as a therapeutic target for the prevention of chronic neuroinflammation.

Dopaminergic Therapeutics in Multiple Sclerosis: Focus on Th17-Cell Functions

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS) with an autoimmune mechanism of development. Currently, one of the most promising directions in the study of MS pathogenesis are the neuroimmune interactions. Dopamine is one of the key neurotransmitters in CNS. Furthermore, dopamine is a direct mediator of interactions between the immune and nervous systems and can influence MS pathogenesis by modulating immune cells activity and cytokine production. Recent studies have shown that dopamine can enhance or inhibit the functions of innate and adaptive immune system, depending on the activation of different dopaminergic receptors, and can therefore influence the course of experimental autoimmune encephalomyelitis (EAE) and MS. In this review, we discuss putative dopaminergic therapeutics in EAE and MS with focus on Th17-cells, which are thought to play crucial role in MS pathogenesis. We suggest that targeting dopaminergic receptors could be explored as a new kind of disease-modifying treatment of MS. Graphical Abstract.

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.

Prolactin: Friend or Foe in Central Nervous System Autoimmune Inflammation?

The higher prevalence of multiple sclerosis (MS) in females, along with the modulation of disease activity observed during pregnancy and the post-partum period, has suggested a hormonal influence in MS. Even if prolactin (PRL) does not belong to the sex hormones family, its crucial role in female reproduction and lactation has prompted great efforts to understand if PRL could represent a gender factor in the pathogenesis of MS and experimental autoimmune encephalomyelitis (EAE), the animal model for this disease. Extensive literature has documented a remarkable immune-stimulating potential for this hormone, indicating PRL as a disease-promoting factor in MS and EAE. However, recent work has pointed out that PRL is endowed with important neuroprotective and remyelinating properties and has encouraged a reinterpretation of the involvement of this hormone in MS. In this review we summarize both the protective functions that PRL exerts in central nervous system tissue as well as the inflammatory activity of this hormone in the context of autoimmune responses against myelin. Last, we draw future lines of research that might help to better clarify the impact of PRL on MS pathology.

Pramipexole, a Dopamine D2/D3 Receptor-Preferring Agonist, Prevents Experimental Autoimmune Encephalomyelitis Development in Mice

Experimental autoimmune encephalomyelitis (EAE) is the most used animal model of multiple sclerosis (MS) for the development of new therapies. Dopamine receptors can modulate EAE and MS development, thus highlighting the potential use of dopaminergic agonists in the treatment of MS, which has been poorly explored. Herein, we hypothesized that pramipexole (PPX), a dopamine D2/D3 receptor-preferring agonist commonly used to treat Parkinson's disease (PD), would be a suitable therapeutic drug for EAE. Thus, we report the effects and the underlying mechanisms of action of PPX in the prevention of EAE. PPX (0.1 and 1 mg/kg) was administered intraperitoneally (i.p.) from day 0 to 40 post-immunization (p.i.). Our results showed that PPX 1 mg/kg prevented EAE development, abolishing EAE signs by blocking neuroinflammatory response, demyelination, and astroglial activation in spinal cord. Moreover, PPX inhibited the production of inflammatory cytokines, such as IL-17, IL-1β, and TNF-α in peripheral lymphoid tissue. PPX was also able to restore basal levels of a number of EAE-induced effects in spinal cord and striatum, such as reactive oxygen species, glutathione peroxidase, parkin, and α-synuclein (α-syn). Thus, our findings highlight the usefulness of PPX in preventing EAE-induced motor symptoms, possibly by modulating immune cell responses, such as those found in MS and other T helper cell-mediated inflammatory diseases.

Neuroprotective arylpiperazine dopaminergic/serotonergic ligands suppress experimental autoimmune encephalomyelitis in rats

Arylpiperazine-based dopaminergic/serotonergic ligands exert neuroprotective activity. We examined the effect of arylpiperazine D2 /5-HT1A ligands, N-{4-[2-(4-phenyl-piperazin-1-yl)-ethyl}-phenyl]-picolinamide (6a) and N-{3-[2-(4-phenyl-piperazin-1-yl)-ethyl]-phenyl}-picolinamide (6b), in experimental autoimmune encephalomyelitis (EAE), a model of neuroinflammation. Both compounds (10 mg/kg i.p.) reduced EAE clinical signs in spinal cord homogenate-immunized Dark Agouti rats. Compound 6b was more efficient in delaying the disease onset and reducing the maximal clinical score, which correlated with its higher affinity for D2 and 5-HT1A receptors. The protection was retained if treatment was limited to the effector (from day 8 onwards), but not the induction phase (day 0-7) of EAE. Compound 6b reduced CNS immune infiltration and expression of mRNA encoding the proinflammatory cytokines tumor necrosis factor, IL-6, IL-1, and GM-CSF, TH 1 cytokine IFN-γ, TH 17 cytokine IL-17, as well as the signature transcription factors of TH 1 (T-bet) and TH 17 (RORγt) cells. Arylpiperazine treatment reduced apoptosis and increased the activation of anti-apoptotic mediators Akt and p70S6 kinase in the CNS of EAE animals. The in vitro treatment with 6b protected oligodendrocyte cell line OLN-93 and neuronal cell line PC12 from mitogen-activated normal T cells or myelin basic protein-activated encephalitogenic T cells. In conclusion, arylpiperazine dopaminergic/serotonergic ligands suppress EAE through a direct neuroprotective action and decrease in CNS inflammation. Arylpiperazine dopaminergic/serotonergic ligands reduce neurological symptoms of acute autoimmune encephalomyelitis in rats without affecting the activation of autoreactive immune response, through mechanisms involving a decrease in CNS immune infiltration, as well as direct protection of CNS from immune-mediated damage. These data indicate potential usefulness of arylpiperazine-based compounds in the treatment of neuroinflammatory disorders such as multiple sclerosis.

Prolactin in combination with interferon-β reduces disease severity in an animal model of multiple sclerosis

Previous work has demonstrated that the hormone prolactin promotes oligodendrocyte precursor proliferation and remyelination following lysolecithin-induced demyelination of the mouse spinal cord. Prolactin, however, can elicit pro-inflammatory responses, and its use in the prototypical demyelinating and inflammatory condition, multiple sclerosis (MS), should thus be approached cautiously. Here, we sought to determine whether recombinant prolactin could alter the course of experimental autoimmune encephalomyelitis (EAE), an inflammatory animal model of MS. Consistent with previous literature, we found that prolactin activated leukocytes in vitro. Daily treatment with prolactin from around the time of onset of clinical signs, for 9 (days 9 to 17) or 25 (days 9 to 33) days did not increase clinical or histological signs of EAE over that of vehicle-treated mice. Instead, the combination of prolactin and a suboptimal dose of recombinant murine interferon-β resulted in (days 9 to 17 group) or trended towards (days 9 to 33 group), a greater amelioration of clinical signs of EAE, compared to either treatment alone or to vehicle controls. Histological analyses corroborated the clinical EAE data. These results suggest that prolactin may be beneficial when administered in combination with interferon-β in MS.

The dopamine imbalance hypothesis of fatigue in multiple sclerosis and other neurological disorders

Fatigue is one of the most pervasive symptoms of multiple sclerosis (MS), and has engendered hundreds of investigations on the topic. While there is a growing literature using various methods to study fatigue, a unified theory of fatigue in MS is yet to emerge. In the current review, we synthesize findings from neuroimaging, pharmacological, neuropsychological, and immunological studies of fatigue in MS, which point to a specific hypothesis of fatigue in MS: the dopamine imbalance hypothesis. The communication between the striatum and prefrontal cortex is reliant on dopamine, a modulatory neurotransmitter. Neuroimaging findings suggest that fatigue results from the disruption of communication between these regions. Supporting the dopamine imbalance hypothesis, structural and functional neuroimaging studies show abnormalities in the frontal and striatal regions that are heavily innervated by dopamine neurons. Further, dopaminergic psychostimulant medication has been shown to alleviate fatigue in individuals with traumatic brain injury, chronic fatigue syndrome, and in cancer patients, also indicating that dopamine might play an important role in fatigue perception. This paper reviews the structural and functional neuroimaging evidence as well as pharmacological studies that suggest that dopamine plays a critical role in the phenomenon of fatigue. We conclude with how specific aspects of the dopamine imbalance hypothesis can be tested in future research.

Treatment with the antipsychotic agent, risperidone, reduces disease severity in experimental autoimmune encephalomyelitis

Recent studies have demonstrated that atypical antipsychotic agents, which are known to antagonize dopamine D2 and serotonin 5-HT_2a receptors, have immunomodulatory properties. Given the potential of these drugs to modulate the immune system both peripherally and within the central nervous system, we investigated the ability of the atypical anti-psychotic agent, risperidone, to modify disease in the animal model of multiple sclerosis (MS)⁴, experimental autoimune encephalomyelitis (EAE). We found that chronic oral administration of risperidone dose-dependently reduced the severity of disease and decreased both the size and number of spinal cord lesions. Furthermore, risperidone treatment substantially reduced antigen-specific interleukin (IL)-17a, IL-2, and IL-4 but not interferon (IFN)-γ production by splenocytes at peak disease and using an in vitro model, we show that treatment of macrophages with risperidone alters their ability to bias naïve T cells. Another atypical antipsychotic agent, clozapine, showed a similar ability to modify macrophages in vitro and to reduce disease in the EAE model but this effect was not due to antagonism of the type 1 or type 2 dopamine receptors alone. Finally, we found that while risperidone treatment had little effect on the in vivo activation of splenic macrophages during EAE, it significantly reduced the activation of microglia and macrophages in the central nervous system. Together these studies indicate that atypical antipsychotic agents like risperidone are effective immunomodulatory agents with the potential to treat immune-mediated diseases such as MS.

Neuroendocrine immunoregulation in multiple sclerosis

Currently, it is generally accepted that multiple sclerosis (MS) is a complex multifactorial disease involving genetic and environmental factors affecting the autoreactive immune responses that lead to damage of myelin. In this respect, intrinsic or extrinsic factors such as emotional, psychological, traumatic, or inflammatory stress as well as a variety of other lifestyle interventions can influence the neuroendocrine system. On its turn, it has been demonstrated that the neuroendocrine system has immunomodulatory potential. Moreover, the neuroendocrine and immune systems communicate bidirectionally via shared receptors and shared messenger molecules, variously called hormones, neurotransmitters, or cytokines. Discrepancies at any level can therefore lead to changes in susceptibility and to severity of several autoimmune and inflammatory diseases. Here we provide an overview of the complex system of crosstalk between the neuroendocrine and immune system as well as reported dysfunctions involved in the pathogenesis of autoimmunity, including MS. Finally, possible strategies to intervene with the neuroendocrine-immune system for MS patient management will be discussed. Ultimately, a better understanding of the interactions between the neuroendocrine system and the immune system can open up new therapeutic approaches for the treatment of MS as well as other autoimmune diseases.

Prolactin is not required for the development of severe chronic experimental autoimmune encephalomyelitis

Predominance of multiple sclerosis (MS) in women, reductions of disease flares during pregnancy, and their increase in the postpartum period have suggested a hormonal influence on MS activity. The hormone prolactin (PRL) has long been debated as a potential immune-stimulating factor in several autoimmune disorders, including MS and its animal model experimental autoimmune encephalomyelitis (EAE). However, to date, no data clearly ascribe a pathogenic role to PRL in these diseases. Using PRL receptor-deficient (Prlr(-/-)) and PRL-deficient (Prl(-/-)) mice, we show that PRL plays a redundant role in the development of chronic EAE. In Prlr(-/-) and Prl(-/-) mice, EAE developed with a delayed onset compared with littermate control mice, but with full clinical severity. In line with the clinical outcome, T cell proliferation and production of IFN-γ, IL-17A, and IL-6 induced by myelin Ag were delayed in Prlr(-/-) and Prl(-/-) mice. Ag-specific IgG Ab responses were not affected by PRLR or PRL deficiency. We also show that mouse lymph node cells and purified CD4(+) T cells express transcript for Prlr, but not for Prl. These results reveal that PRL does not play a central role in the development of chronic EAE and optimal Th1 and Th17 responses against myelin. Moreover, they also rule out a possible contribution of PRL secreted by immune cells to the modulation of autoreactive T cell response in this model.

Adrenergic and dopaminergic modulation of immunity in multiple sclerosis: teaching old drugs new tricks?

Multiple sclerosis (MS) is an autoimmune disorder of the CNS characterized by inflammation, demyelination and axonal loss. Classical evidence in experimental allergic encephalomyelitis, the animal model of MS, support the relevance of sympatoadrenergic as well as of dopaminergic mechanisms. In MS patients, dysregulation of adrenergic and dopaminergic pathways contribute to the disease in immune system cells as well as in glial cells. Available evidence is summarized and discussed also in the light of the novel role of dopamine, noradrenaline and adrenaline as transmitters in immune cells, providing a conceptual frame to exploit the potential of several dopaminergic and adrenergic agents, already in clinical use for non-immune indications and with a usually favourable risk-benefit profile, as add-on drugs to conventional immunomodulating therapies in MS.

G protein-coupled receptors as therapeutic targets for multiple sclerosis

G protein-coupled receptors (GPCRs) mediate most of our physiological responses to hormones, neurotransmitters and environmental stimulants. They are considered as the most successful therapeutic targets for a broad spectrum of diseases. Multiple sclerosis (MS) is an inflammatory disease that is characterized by immune-mediated demyelination and degeneration of the central nervous system (CNS). It is the leading cause of non-traumatic disability in young adults. Great progress has been made over the past few decades in understanding the pathogenesis of MS. Numerous data from animal and clinical studies indicate that many GPCRs are critically involved in various aspects of MS pathogenesis, including antigen presentation, cytokine production, T-cell differentiation, T-cell proliferation, T-cell invasion, etc. In this review, we summarize the recent findings regarding the expression or functional changes of GPCRs in MS patients or animal models, and the influences of GPCRs on disease severity upon genetic or pharmacological manipulations. Hopefully some of these findings will lead to the development of novel therapies for MS in the near future.

Experimental autoimmune encephalomyelitis (EAE) as a model for multiple sclerosis (MS)

Experimental autoimmune encephalomyelitis (EAE) is the most commonly used experimental model for the human inflammatory demyelinating disease, multiple sclerosis (MS). EAE is a complex condition in which the interaction between a variety of immunopathological and neuropathological mechanisms leads to an approximation of the key pathological features of MS: inflammation, demyelination, axonal loss and gliosis. The counter-regulatory mechanisms of resolution of inflammation and remyelination also occur in EAE, which, therefore can also serve as a model for these processes. Moreover, EAE is often used as a model of cell-mediated organ-specific autoimmune conditions in general. EAE has a complex neuropharmacology, and many of the drugs that are in current or imminent use in MS have been developed, tested or validated on the basis of EAE studies. There is great heterogeneity in the susceptibility to the induction, the method of induction and the response to various immunological or neuropharmacological interventions, many of which are reviewed here. This makes EAE a very versatile system to use in translational neuro- and immunopharmacology, but the model needs to be tailored to the scientific question being asked. While creating difficulties and underscoring the inherent weaknesses of this model of MS in straightforward translation from EAE to the human disease, this variability also creates an opportunity to explore multiple facets of the immune and neural mechanisms of immune-mediated neuroinflammation and demyelination as well as intrinsic protective mechanisms. This allows the eventual development and preclinical testing of a wide range of potential therapeutic interventions.

Serum prolactin level in patients with relapsing-remitting multiple sclerosis during relapse

It has been hypothesized that hyperprolactinemia may contribute to the pathogenesis of multiple sclerosis (MS). In a case-control study, 58 patients with definite relapsing-remitting MS (RRMS) during relapse and 58 sex-matched and age-matched healthy controls were assessed for serum prolactin (PRL) concentration. Mean serum PRL levels (± standard deviation) were significantly higher in patients with MS (501.3 ± 232.6 mIU/L) than in healthy control patients (233.3 ± 142.7 mIU/L; p < 0.0001). Furthermore, these differences were consistent in each sex: females with MS (704.4 ± 119.6 mIU/L) compared to female controls (305.5 ± 156.9 mIU/L p < 0.001); and in males with MS (358.0 ± 180.0 mIU/L) compared to male controls (182.3 ± 107.5 mIU/L; p < 0.001). Our findings provided more evidence to support the hypothesis that patients with RRMS, regardless of gender, are in a hyperprolactinemic state.

Prolactin alters the mechanisms of B cell tolerance induction

OBJECTIVE

Autoimmune diseases predominantly affect women, suggesting that female sex hormones may play a role in the pathogenesis of such diseases. We have previously shown that persistent mild-to-moderate elevations in serum prolactin levels induce a break in self tolerance in mice with a BALB/c genetic background. The aim of this study was to evaluate the effects of hyperprolactinemia on the mechanisms of B cell tolerance induction.

METHODS

Effects of prolactin on splenic B cell subsets were studied in female BALB/c mice. B cell receptor (BCR)-mediated apoptosis and proliferation of transitional B cells were analyzed by flow cytometry. Expression of apoptotic genes was examined by microarrays and real-time polymerase chain reaction analysis. B cells coexpressing kappa/lambda light chains were assessed by flow cytometry and immunohistochemistry. Activation status of transitional type 3 (T3) B cells was evaluated by BCR-induced calcium influx studies.

RESULTS

BCR-mediated apoptosis of the T1 B cell subset, a major checkpoint for negative selection of autoreactive specificities, was decreased in prolactin-treated mice. Microarray studies indicated that this event may be mediated by the prolactin-induced up-regulation of the antiapoptotic gene interferon-gamma receptor type II and down-regulation of the proapoptotic gene Trp63. Prolactin treatment also altered the amount of receptor editing, as indicated by the increased number of transitional B cells coexpressing kappa/lambda light chains. Additionally, hyperprolactinemia modified the level of B cell anergy by increasing the degree of BCR-induced calcium influx in the T3 B cells.

CONCLUSION

Persistently elevated serum prolactin levels interfere with B cell tolerance induction by impairing BCR-mediated clonal deletion, deregulating receptor editing, and decreasing the threshold for activation of anergic B cells, thereby promoting autoreactivity.

Chemokine receptor antagonists: overcoming developmental hurdles

Chemokine receptors have a key role in the pathogenesis of autoimmune diseases, inflammation and viral infection. However, with the exception of selective CCR5 antagonists for HIV, the promise of obtaining new therapeutics related to chemokine receptors has not yet been realized. This article highlights some of the recent failures in the clinical trials of chemokine receptor antagonists and explores possible reasons as to why this might have occurred. Such reasons include the lack of predictability of animal models and redundancy of the target. A potential solution could be to develop drugs that target more than one receptor--known as polypharmacology--which could be a novel way to generate effective therapeutics.

Therapy with interferon-beta modulates endogenous catecholamines in lymphocytes of patients with multiple sclerosis

OBJECTIVE

To investigate the endogenous dopaminergic/adrenergic system of lymphocytes in multiple sclerosis (MS) patients during treatment with interferon (IFN)-beta.

METHODS

Patients with relapsing-remitting MS undergoing IFN-beta treatment were prospectively studied during the first year of treatment. Circulating lymphocytes were obtained at baseline and after 1, 3, 6 and 12 months of treatment and assayed for catecholamine (CA) production and mRNA expression of tyrosine hydroxylase (TH, the rate-limiting enzyme in the synthesis of CA), beta(2)-adrenoceptors (AR) and D2, D3 and D5 dopaminergic receptors (DR).

RESULTS

In cells from patients treated with IFN-beta for 12 months the production of CA hugely increased and was less sensitive to IFN-gamma-induced inhibition. Expression of mRNA for TH, beta(2)-AR and DRD5 was already enhanced after 1 month and further increased up to 6-12 months of treatment. On the contrary, DRD2 mRNA progressively decreased and DRD3 mRNA did not significantly change over the whole study period.

CONCLUSIONS

In MS patients IFN-beta treatment enhances the ability of lymphocytes to produce CA, and induces extensive modifications of both beta(2)-AR and DR-operated pathways. The clinical relevance of these effects deserves consideration.

Hormonal influences in multiple sclerosis

The function of hormones has expanded to include immunomodulation and neuroprotection in addition to their classic roles. The story of how hormones influence inflammation and neuron and glial function is being slowly unraveled. There is increasing evidence that estrogen, progesterone, and testosterone contain immune responses and influence damage repair in the nervous system. Hormones such as prolactin and vitamin D are being explored as immunomodulators and may influence diseases such as multiple sclerosis (MS) or may be used therapeutically to modulate the immune response. More recently identified hormones, such as leptin and gherlin, may also influence the course of disease. This chapter reviews some of the evidence that supports a role for hormones in MS.

Hyperprolactinemia and autoimmune diseases

The autoimmune diseases are more common in females. The sex hormones have an important role in this gender bias, mainly estrogen and prolactin (PRL) which modulate the immune response. PRL is secreted from the pituitary gland and other organs and cells mainly the lymphocytes. PRL has an immunostimulatory effect and promotes autoimmunity: PRL impairs the negative selection of autoreactive B lymphocytes occurring during B cell maturation into fully functional B cells. PRL has an anti-apoptotic effect, enhances proliferative response to antigens and mitogens and enhances the production of immunoglobulins and autoantibodies. Hyperprolactinemia (HPRL) is observed in multi-organ and organ specific autoimmune diseases like systemic lupus erythematosus (SLE) rheumatoid arthritis (RA), Sjogren's syndrome (SS), Hashimoto's thyroiditis (HT) and multiple sclerosis (MS). There is no consistent correlation between PRL levels and disease activity. Murine models and small studies in SLE patients suggest some role of dopamine agonists in the therapy of those diseases. The genetic factor may have a role in humans as in animal models. The PRL isoform has an important effect on the bioactivity on prolactin receptors (PRL-Rs).

Experimental allergic encephalomyelitis in pituitary-grafted Lewis rats

Treatment of susceptible rats with dopaminergic agonists that reduce prolactin release decreases both severity and duration of clinical signs of experimental allergic encephalomyelitis (EAE). To assess to what extent the presence of an ectopic pituitary (that produces an increase in plasma prolactin levels mainly derived from the ectopic gland) affects EAE, 39 male Lewis rats were submitted to pituitary grafting from littermate donors. Another group of 38 rats was sham-operated by implanting a muscle fragment similar in size to the pituitary graft. All rats received subcutaneous (s.c.) injections of complete Freund's adjuvant (CFA) plus spinal cord homogenate (SCH) and were monitored daily for clinical signs of EAE. Animals were killed by decapitation on days 1, 4, 7, 11 or 15 after immunization and plasma was collected for prolactin RIA. In a second experiment, 48 rats were immunized by s.c. injection of a mixture of SCH and CFA, and then received daily s.c. injections of bromocriptine (1 mg/kg) or saline. Groups of 8 animals were killed on days 8, 11 or 15 after immunization and plasma prolactin was measured. Only sham-operated rats exhibited clinical signs of the disease when assessed on day 15 after immunization. A progressive decrease in plasma prolactin levels was observed in pituitary-grafted rats, attaining a minimum 15 days after immunization, whereas plasma prolactin levels were increased during the course of the disease in sham-operated rats. Plasma prolactin levels were higher in pituitary-grafted rats than in sham-operated rats 1 day after immunization, but lower on days 7, 11 and 15 after immunogen injection. Further supporting a correlation of suppressed prolactin levels with absence of clinical signs of EAE, rats that were administered the dopaminergic agonist bromocriptine showed very low plasma prolactin levels and did not exhibit any clinical sign of EAE. These results indicate that low circulating prolactin levels coincide with absence of clinical signs of EAE in Lewis rats.

Prolactin regulation of the expression of TNF-α, IFN-γ and IL-10 by splenocytes in murine multiple low dose streptozotocin diabetes

Previously, the hormone prolactin (PRL) has been found to protect against development of type 1 diabetes induced by multiple injections of streptozotocin (STZ) in mice. To further investigate this effect of PRL, C57BL/Ks mice were injected intraperitoneally with STZ (40 mg/kg body weight) or NaCl for 5 days and PRL (4 mg/kg body weight) or NaCl for 14 days. On day 15, splenocytes were isolated from the in vivo treated mice. Spleen cell preparations depleted in erythrocytes and macrophages were stained for cytoplasmic TNF-alpha, IFN-gamma and IL-10 and analyzed with flow cytometry. Isolated spleen cells were also cultured (RPMI 1640+10% fetal bovine serum) for 24 h. Thereafter, cytokine mRNA expression by the spleen cells was measured by real-time PCR and cytokine secretion determined by enzyme linked immunosorbent assay (ELISA). Freshly isolated spleen cell preparations from PRL and STZ+PRL treated animals seemed to have an increased frequency of IL-10 positive cells compared to controls. In cultured spleen cells isolated from STZ treated mice, IFN-gamma and IL-10 mRNA expression was up-regulated. PRL treatment down-regulated the mRNA expression of these cytokines and also TNF-alpha in the splenocytes obtained from animals treated with STZ. The accumulation of these cytokines in the cultures of the explanted splenocytes showed only minor differences between the experimental groups. Overall, the data seems to favor the view that PRL enhanced a Th2 response, which may reflect the preventive effect of PRL against development of multiple low dose STZ diabetes in mice.

Dopamine fails to regulate activation of peripheral blood lymphocytes from multiple sclerosis patients: effects of IFN-beta

The neurotransmitter dopamine counteracts T cell functions through its specific receptor subtype D5R but favors T cell proliferation and adhesion when acting on D3R. We found diminished mRNA and protein levels of D5R, but not of D3R, in peripheral blood mononuclear cells (PBMCs) from untreated multiple sclerosis (MS) patients. Dopamine reduced T cell proliferation, secretion of interferon-gamma (IFN-gamma), and production of matrix metalloproteinase-9 (MMP-9) mRNA in PBMCs from controls but not from MS patients. By contrast, reduced levels of D3R and renewed dopamine-associated regulatory functions were found in PBMCs from IFN-beta treated MS patients. Failure of the dopaminergic system of lymphocytes may lessen the threshold of T cell activation and sustain the pathogenic cascade of MS.

Experimental allergic encephalomyelitis in male Lewis rats subjected to calorie restriction

This work analyzes the effect of calorie restriction on the development of experimental allergic encephalomyelitis (EAE) in Lewis rats. Plasma levels of ACTH, corticosterone, prolactin and growth hormone (GH) and mitogenic responses in submaxillary lymph nodes were measured. Male Lewis rats (6 weeks-old) were submitted to a calorie restriction equivalent to 66% of food restriction or to a normal diet. Fifteen days later, rats were injected with complete Freund's adjuvant plus spinal chord homogenate (SCH) or with complete Freund's adjuvant alone. Rats were monitored daily for clinical signs of EAE and were killed on day 15 after immunization. Only rats subjected to normal diet exhibited clinical signs of the disease. The increase in plasma ACTH and corticosterone found after SCH immunization in controls was not detectable in calorie restricted rats. Likewise, the correlation between circulating ACTH and corticosterone was no longer found after calorie restriction. Generally, calorie restriction by itself augmented plasma ACTH or corticosterone and this increase was not further amplified by SCH immunization. Only calorie restricted rats exhibited augmented plasma prolactin levels after SCH immunization, and decreased plasma GH levels regardless of immunization. Calorie restriction depressed the mitogenic response of lymphoid cells to concanavalin A but not to lipopolysaccharide. Calorie restricted rats did not exhibit augmented mitogenic response to concanavalin A following SCH immunization as those found in controls. The results are compatible with the view that the course of EAE can be significantly modified by caloric restriction.

Interferon-gamma and interferon-beta affect endogenous catecholamines in human peripheral blood mononuclear cells: implications for multiple sclerosis

Interferon (IFN)-gamma plays a pivotal role in the pathogenesis of multiple sclerosis (MS), while IFN-beta may be able to modify the clinical course of the disease, eventually also by counterbalancing IFN-gamma-mediated effects. Catecholamines (CA) exert important effects on the immune response, both as transmitters between the nervous and the immune system, as well as autocrine/paracrine mediators in immune cells, and several lines of evidence support their involvement in MS. In particular, dysregulated production of CA seems to occur in peripheral blood mononuclear cells (PBMCs) of MS patients. We assessed the effects of IFN-beta and IFN-gamma on endogenous CA in PBMCs. In cultured PBMCs stimulated with phytohaemagglutinin (PHA), IFN-beta increased CA production and induced CA release in the culture medium, while IFN-gamma decreased both CA production and the expression of mRNA for the CA-synthesizing enzyme tyrosine hydroxylase. Coincubation with both IFNs prevented the inhibitory effect of IFN-gamma, as well as the stimulatory effect of IFN-beta. IFNs are the first physiological compounds shown to affect endogenous CA in PBMCs: in view of the role of CA-dependent mechanisms in the immune response, these findings may help to better understand the mechanisms of action of IFN-beta as an immunomodulatory drug in MS.

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

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

Dopaminergic modulation of oxidative stress and apoptosis in human peripheral blood lymphocytes: evidence for a D1-like receptor-dependent protective effect

Dopamine (DA) is a neurotransmitter in the central and peripheral nervous system, which can be either cytotoxic or cytoprotective under selected conditions. Such effects involve oxidative mechanisms and are likely to play a role in neurodegenerative disorders. Because increasing evidence points to peripheral blood lymphocytes (PBL) as a feasible model for studying DA-related mechanisms of cell death and survival, we have explored in these cells the effects of DA on oxidative metabolism and apoptosis. Our results show that, whereas DA 100-500 microM resulted in increased intracellular reactive oxygen species (ROS) levels and apoptotic cell death through oxidative stress, DA 0.1-5 microM decreased ROS levels and apoptosis. DA (both 1 and 500 microM) partially counteracted the decrease in Cu/Zn superoxide dismutase levels observed in untreated PBL. However, whereas the effect of the low dose lasted for the whole incubation period (24 h), the effect of DA 500 microM was transient. DA-dependent reduction of ROS levels and apoptosis was prevented by D1-like (but not D2-like) receptor antagonism. The present findings add knowledge about the sensitivity of PBL to DA and strengthen the rationale for exploiting these cells as an easily accessible peripheral model for the ex vivo investigation of oxidative stress-related dopaminergic mechanisms underlying human neurodegenerative diseases.

Catecholamine production and tyrosine hydroxylase expression in peripheral blood mononuclear cells from multiple sclerosis patients: effect of cell stimulation and possible relevance for activation-induced apoptosis

Sympathoadrenergic mechanisms may play a role in multiple sclerosis (MS). We examined catecholamine (CA) levels and production and tyrosine hydroxylase (TH) expression in peripheral blood mononuclear cells (PBMCs) from MS patients, and the correlation between CA production and apoptosis in PBMCs. PBMCs from MS patients had increased norepinephrine (NE) levels. However, phytohaemagglutinin (PHA)-stimulated PBMCs from MS patients with active disease synthesized less dopamine (DA) than cells from both healthy controls and patients with inactive disease. PBMCs from patients with inactive disease showed lower expression of TH. Pharmacological inhibition of TH in cultured PBMCs stimulated with PHA reduced the percentage of apoptotic cells. Since a failure of activation-induced apoptosis in immune cells may be involved in MS, it is suggested that altered CA production by PBMCs may be implicated in such dysregulation.

Bromocriptine treatment of systemic lupus erythematosus

Prolactin, a peptide hormone, acts as a cytokine. It has been hypothesized that bromocriptine, a dopamine analog that suppresses pituitary secretion of prolactin, suppresses circulating prolactin and, through this mechanism, has the potential to suppress autoimmune disease. This rationale has been applied to the treatment of systemic lupus erythematosus (SLE), a prototype autoimmune illness that occurs spontaneously in animal models such as the F1 hybrid NZBxNZW mouse, and in humans. Treatment with bromocriptine was effective in treating some induced and spontaneous autoimmune disease in experimental models. Bromocriptine did slow the course of SLE in NZBxNZW mice when treatment was started before the appearance of clinical disease. In addition, bromocriptine was effective in treating established disease in this model. In three separate clinical trials, bromocriptine showed evidence that it had a therapeutic effect in treating human lupus. Bromocriptine is currently considered an unproven therapy for SLE. Its use is entirely experimental. The fact that bromocriptine was effective in treating NZBxNZW mice, the beneficial therapeutic effects in human trials, and the low toxicity of the drug form a solid rationale for undertaking further therapeutic trials.

Prolactin stimulation in multiple sclerosis--an indicator of disease subtypes and activity?

Prolactin (PRL) belongs to the growth and lactogenic hormone family and has potent immunomodulating properties. Mild hyperprolactinemia has been found to enhance several autoimmune diseases and increased PRL plasma levels have been described in the experimental multiple sclerosis (MS) model while the PRL antagonist bromocriptine was able to suppress the disease. As studies of PRL serum levels in MS have led to conflicting results we investigated further the question of prolactin alterations in MS. We correlated PRL baseline values in a large sample of 132 MS patients with disease course and activity. Furthermore, inhibitory (bromocriptine) and stimulatory (metoclopramide) tests were performed in a subsample (n = 39) to gain functional information. We found no correlation of baseline values with disease course or activity. Nevertheless in the regression analysis of stimulatory test results, 14% of the variance was attributable to disease activity. In conclusion PRL does not seem to be relevant as an activity marker in the whole MS population.

Bromocriptine in rheumatic and autoimmune diseases

BACKGROUND AND OBJECTIVES

Multiple lines of evidence support the concept that the anterior pituitary hormone prolactin has a pathogenic role in rheumatic and autoimmune diseases including, but not limited to, rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), Reiter's syndrome, psoriatic arthritis, and uveitis. Conversely, the dopaminergic agonist bromocriptine appears to have therapeutic effects through suppression of pituitary prolactin secretion and, perhaps, through actions on peripheral dopamine receptors. This article reviews the experimental and clinical data supporting the therapeutic use of bromocriptine as a nonstandard or adjunctive therapy in rheumatic and autoimmune diseases.

METHODS

Data addressing the potential therapeutic role of bromocriptine in rheumatic and autoimmune diseases, as well as frequently associated comorbidities, was accumulated from the author's work, online literature search of the National Library of Medicine, and references from these identified publications.

RESULTS

There have been a number of clinical therapeutic trials using 2.5 to 30 mg of bromocriptine per day in a single or divided dose, which have shown efficacy with minimal side effects in the treatment of rheumatic and autoimmune diseases. In RA, bromocriptine administration has induced immunosuppression of several immune parameters and has been associated with improvements in morning stiffness, grip strength, numbers of swollen/painful joints, and the Health Assessment Questionnaire disability index. In two blinded studies, bromocriptine reduced the number of SLE flares and was as effective as hydroxychloroquine in reducing lupus disease activity indices, respectively. In case reports, bromocriptine has been used successfully in the treatment of Reiter's syndrome enthesopathy and psoriatic arthritis. The potential efficacy of bromocriptine in the treatment of uveitis and multiple sclerosis is suggested but remains to be verified.

CONCLUSIONS

Double-blind, placebo-controlled studies are limited, but clinical observations and trials support the use of bromocriptine as a nonstandard primary or adjunctive therapy in the treatment of recalcitrant RA, SLE, Reiter's syndrome, and psoriatic arthritis and associated conditions unresponsive to traditional approaches. Additional investigation is needed to verify this conclusion and extend preliminary results.

RELEVANCE

In patients with rheumatic and autoimmune diseases, bromocriptine may be a relatively safe and efficacious alternative therapy. Semin Arthritis Rheum 31:21-32.

Estrogen, prolactin, and autoimmunity: actions and interactions

Estrogen and prolactin have a reciprocal endocrinologic relationship and both hormones have pleiotropic effects on the immune system. Despite the presence of a number of confounding variables, these hormones modulate autoimmunity; however, mechanisms by which this modulation occurs remain obscure. Estrogen appears to suppress cell-mediated and augment humoral-based immunity. Prolactin appears to stimulate both cell and humoral-based immunity. Both hormones have been shown to modulate IFN gamma secretion. Similar evidence in experimental models, human autoimmune disease, and during pregnancy in autoimmune disease patients suggests disparate effects of estrogen and prolactin on autoimmune responses and disease pathogenesis. In the NZB x NZW F1 mouse model of lupus, prolactin accelerates disease expression, whereas estrogen, devoid of its prolactin stimulating properties, is immunosuppressive and inhibits IL-2 production. Estrogen, because of its endocrinologic and immune effects, may directly or indirectly stimulate or inhibit immune responses. These dichotomous effects have limited its successful pharmacologic manipulation in human autoimmune disease with estrogen compounds, tamoxifen, oral contraceptives, antigonadotropic agents, or ovulation induction regimens. In contrast, reduction of immunostimulatory concentrations of prolactin with bromocriptine has successfully suppressed development or expression of murine and human autoimmune disease. Further investigation into actions and interactions of estrogen and prolactin with autoimmunity will provide a better understanding of the female preponderance of autoimmunity and facilitate a more rational approach to hormonal immunotherapy.