Dopamine in vivo inhibits VEGF-induced phosphorylation of VEGFR-2, MAPK, and focal adhesion kinase in endothelial cells

Involvement of neuronal factors in tumor angiogenesis and the shaping of the cancer microenvironment

Emerging evidence suggests that nerves within the tumor microenvironment play a crucial role in regulating angiogenesis. Neurotransmitters and neuropeptides released by nerves can interact with nearby blood vessels and tumor cells, influencing their behavior and modulating the angiogenic response. Moreover, nerve-derived signals may activate signaling pathways that enhance the production of pro-angiogenic factors within the tumor microenvironment, further supporting blood vessel growth around tumors. The intricate network of communication between neural constituents and the vascular system accentuates the potential of therapeutically targeting neural-mediated pathways as an innovative strategy to modulate tumor angiogenesis and, consequently, neoplastic proliferation. Hereby, we review studies that evaluate the precise molecular interplay and the potential clinical ramifications of manipulating neural elements for the purpose of anti-angiogenic therapeutics within the scope of cancer treatment.

Dopamine signaling from ganglion cells directs layer-specific angiogenesis in the retina

During central nervous system (CNS) development, a precisely patterned vasculature emerges to support CNS function. How neurons control angiogenesis is not well understood. Here, we show that the neuromodulator dopamine restricts vascular development in the retina via temporally limited production by an unexpected neuron subset. Our genetic and pharmacological experiments demonstrate that elevating dopamine levels inhibits tip-cell sprouting and vessel growth, whereas reducing dopamine production by all retina neurons increases growth. Dopamine production by canonical dopaminergic amacrine interneurons is dispensable for these events. Instead, we found that temporally restricted dopamine production by retinal ganglion cells (RGCs) modulates vascular development. RGCs produce dopamine precisely during angiogenic periods. Genetically limiting dopamine production by ganglion cells, but not amacrines, decreases angiogenesis. Conversely, elevating ganglion-cell-derived dopamine production inhibits early vessel growth. These vasculature outcomes occur downstream of vascular endothelial growth factor receptor (VEGFR) activation and Notch-Jagged1 signaling. Jagged1 is increased and subsequently inhibits Notch signaling when ganglion cell dopamine production is reduced. Our findings demonstrate that dopaminergic neural activity from a small neuron subset functions upstream of VEGFR to serve as developmental timing cue that regulates vessel growth.

Antiangiogenic Effect of Dopamine and Dopaminergic Agonists as an Adjuvant Therapeutic Option in the Treatment of Cancer, Endometriosis, and Osteoarthritis

Dopamine (DA) and dopamine agonists (DA-Ag) have shown antiangiogenic potential through the vascular endothelial growth factor (VEGF) pathway. They inhibit VEGF and VEGF receptor 2 (VEGFR 2) functions through the dopamine receptor D2 (D2R), preventing important angiogenesis-related processes such as proliferation, migration, and vascular permeability. However, few studies have demonstrated the antiangiogenic mechanism and efficacy of DA and DA-Ag in diseases such as cancer, endometriosis, and osteoarthritis (OA). Therefore, the objective of this review was to describe the mechanisms of the antiangiogenic action of the DA-D2R/VEGF-VEGFR 2 system and to compile related findings from experimental studies and clinical trials on cancer, endometriosis, and OA. Advanced searches were performed in PubMed, Web of Science, SciFinder, ProQuest, EBSCO, Scopus, Science Direct, Google Scholar, PubChem, NCBI Bookshelf, DrugBank, livertox, and Clinical Trials. Articles explaining the antiangiogenic effect of DA and DA-Ag in research articles, meta-analyses, books, reviews, databases, and clinical trials were considered. DA and DA-Ag have an antiangiogenic effect that could reinforce the treatment of diseases that do not yet have a fully curative treatment, such as cancer, endometriosis, and OA. In addition, DA and DA-Ag could present advantages over other angiogenic inhibitors, such as monoclonal antibodies.

Dopamine Receptors in Breast Cancer: Prevalence, Signaling, and Therapeutic Applications

Breast cancer (BC) is the most common malignancy among women, with over one million cases occurring annually worldwide. Although therapies against estrogen receptors and HER2 have improved response rate and survival, patients with advanced disease, who are resistant to anti-hormonal therapy and/or to chemotherapy, have limited treatment options for reducing morbidity and mortality. These limitations provide major incentives for developing new, effective, and personalized therapeutic interventions. This review presents evidence on the involvement of dopamine (DA) and its type 1 receptors (D1R) in BC. DA is produced in multiple peripheral organs and is present in the systemic circulation in significant amounts. D1R is overexpressed in ~ 30% of BC cases and is associated with advanced disease and shortened patient survival. Activation of D1R, which signals via the cGMP/PKG pathway, results in apoptosis, inhibition of cell invasion, and increased chemosensitivity in multiple BC cell lines. Fenoldopam, a peripheral D1R agonist that does not penetrate the brain, dramatically suppressed tumor growth in mouse models with D1R-expressing BC xenografts. It is proposed that D1R should serve as a novel diagnostic/prognostic factor through the use of currently available D1R detection methods. Fenoldopam, which is FDA-approved to treat renal hypertension, could be repurposed as an effective therapeutic agent for patients with D1R-expressing tumors. Several drugs that interfere with the cGMP/PKG pathway and are approved for treating other diseases should also be considered as potential treatments for BC.

Nerves in gastrointestinal cancer: from mechanism to modulations

Maintenance of gastrointestinal health is challenging as it requires balancing multifaceted processes within the highly complex and dynamic ecosystem of the gastrointestinal tract. Disturbances within this vibrant environment can have detrimental consequences, including the onset of gastrointestinal cancers. Globally, gastrointestinal cancers account for ~19% of all cancer cases and ~22.5% of all cancer-related deaths. Developing new ways to more readily detect and more efficiently target these malignancies are urgently needed. Whereas members of the tumour microenvironment, such as immune cells and fibroblasts, have already been in the spotlight as key players of cancer initiation and progression, the importance of the nervous system in gastrointestinal cancers has only been highlighted in the past few years. Although extrinsic innervations modulate gastrointestinal cancers, cells and signals from the gut's intrinsic innervation also have the ability to do so. Here, we shed light on this thriving field and discuss neural influences during gastrointestinal carcinogenesis. We focus on the interactions between neurons and components of the gastrointestinal tract and tumour microenvironment, on the neural signalling pathways involved, and how these factors affect the cancer hallmarks, and discuss the neural signatures in gastrointestinal cancers. Finally, we highlight neural-related therapies that have potential for the management of gastrointestinal cancers.

Advances in understanding cancer-associated neurogenesis and its implications on the neuroimmune axis in cancer

Nerves and immunologic mediators play pivotal roles in body homeostasis by interacting with each other through diverse mechanisms. The spread of nerves in the tumor microenvironment increases tumor cell proliferation and disease progression, and this correlates with poor patient outcomes. The effects of sympathetic and parasympathetic nerves on cancer regulation are being investigated. Recent findings demonstrate the possibility of developing therapeutic strategies that target the tumor microenvironment and its components such as immune cells, neurotransmitters, and extracellular vesicles. Therefore, examining and understanding the mechanisms and pathways associated with the sympathetic and parasympathetic nervous systems, neurotransmitters, cancer-derived mediators and their interactions with the immune system in the tumor microenvironment may lead to the development of new cancer treatments. This review discusses the effects of nerve cells, immune cells, and cancer cells have on each other that regulate neurogenesis, cancer progression, and dissemination.

The Inhibitory Effect of Selected D2 Dopaminergic Receptor Agonists on VEGF-Dependent Neovascularization in Zebrafish Larvae: Potential New Therapy in Ophthalmic Diseases

Pathological angiogenesis is correlated with many ophthalmic diseases. The most common are exudative age-related macular degeneration and proliferative diabetic retinopathy. The current treatment for these diseases is based on regularly administered anti-VEGF antibodies injections. In the study, we investigated selected D₂ dopaminergic receptor agonists, namely bromocriptine, cabergoline and pergolide, on hypoxia-induced neovascularization. We used the zebrafish laboratory model, specifically three-day post fertilization (dpf) Tg(fli-1: EGFP) zebrafish larvae. To induce abnormal angiogenesis of hyaloid-retinal vessels (HRVs) and intersegmental vessels (ISVs), the larvae were treated with cobalt chloride (II) (CoCl₂) (a hypoxia-inducing agent) from 24 h post fertilization. The inhibitory role of D₂ dopaminergic receptor agonists was investigated using confocal microscopy and qPCR. Additionally, the results were compared to those obtained in the group treated with CoCl₂ followed by bevacizumab, the well-known antiangiogenic agent. Confocal microscopy analyses revealed severe deformation of vessels in the CoCl₂ treated group, while co-incubation with bromocriptine, cabergoline, pergolide and bevacizumab, respectively, significantly inhibited abnormalities of angiogenesis. The qPCR analyses supported the protective role of the chosen dopaminergic agonists by demonstrating their influence on CoCl₂-derived upregulation of vegfaa expression. The present results suggest that the D₂ receptor agonists can be considered as a new direction in research for antiangiogenic therapy.

Sulpiride-induced hyperprolactinaemia increases retinal vasoinhibin and protects against diabetic retinopathy in rats

Excessive vasopermeability and angiogenesis compromise vision in diabetic macular oedema (DME) and diabetic retinopathy (DR). Vasoinhibin is a fragment of the hormone prolactin (PRL) that inhibits diabetes-induced retinal hypervasopermeability and ischaemia-induced retinal angiogenesis in rodents. Hyperprolactinaemia generated by the dopamine D2 receptor antagonist, levosulpiride, is associated with higher levels of vasoinhibin in the vitreous of patients with DR, implying a beneficial outcome due to vasoinhibin-mediated inhibition of retinal vascular alterations. Here, we tested whether hyperprolactinaemia induced by racemic sulpiride increases intraocular vasoinhibin levels and inhibits retinal hypervasopermeability in diabetic rats. Diabetes was generated with streptozotocin and, 4 weeks later, rats were treated for 2 weeks with sulpiride or osmotic minipumps delivering PRL. ELISA, Western blot, and Evans blue assay were used to evaluate serum PRL, retinal vasoinhibin, and retinal vasopermeability, respectively. Hyperprolactinaemia in response to sulpiride or exogenous PRL was associated with increased levels of vasoinhibin in the retina and reduced retinal hypervasopermeability. Furthermore, sulpiride decreased retinal haemorrhages in response to the intravitreal administration of vascular endothelial growth factor (VEGF). Neither sulpiride nor exogenous PRL modified blood glucose levels or bodyweight. We conclude that sulpiride-induced hyperprolactinaemia inhibits the diabetes- and VEGF-mediated increase in retinal vasopermeability by promoting the intraocular conversion of endogenous PRL to vasoinhibin. These findings support the therapeutic potential of sulpiride and its levorotatory enantiomer, levosulpiride, against DME and DR.

Depletion of Retinal Dopaminergic Activity in a Mouse Model of Rod Dysfunction Exacerbates Experimental Autoimmune Uveoretinitis: A Role for the Gateway Reflex

The gateway reflex is a mechanism by which neural inputs regulate chemokine expression at endothelial cell barriers, thereby establishing gateways for the invasion of autoreactive T cells into barrier-protected tissues. In this study, we hypothesized that rod photoreceptor dysfunction causes remodeling of retinal neural activity, which influences the blood–retinal barrier and the development of retinal inflammation. We evaluated this hypothesis using Gnat1^rd17 mice, a model of night blindness with late-onset rod-cone dystrophy, and experimental autoimmune uveoretinitis (EAU). Retinal remodeling and its effect on EAU development were investigated by transcriptome profiling, target identification, and functional validation. We showed that Gnat1^rd17 mice primarily underwent alterations in their retinal dopaminergic system, triggering the development of an exacerbated EAU, which was counteracted by dopamine replacement with L-DOPA administered either systemically or locally. Remarkably, dopamine acted on retinal endothelial cells to inhibit NF-κB and STAT3 activity and the expression of downstream target genes such as chemokines involved in T cell recruitment. These results suggest that rod-mediated dopamine release functions in a gateway reflex manner in the homeostatic control of immune cell entry into the retina, and the loss of retinal dopaminergic activity in conditions associated with rod dysfunction increases the susceptibility to autoimmune uveitis.

A Reassessment of the Therapeutic Potential of a Dopamine Receptor 2 Agonist (D2-AG) in Endometriosis by Comparison against a Standardized Antiangiogenic Treatment

Dopamine receptor 2 agonists (D2-ags) have been shown to reduce the size of tumors by targeting aberrant angiogenesis in pathological tissue. Because of this, the use of a D2-ag was inferred for endometriosis treatment. When assayed in mouse models however, D2-ags have been shown to cause a shift of the immature vessels towards a more mature phenotype but not a significant reduction in the amount of vascularization and size of lesions. These has raised concerns on whether the antiangiogenic effects of these compounds confer a therapeutic value for endometriosis. In the belief that antiangiogenic effects of D2-ags in endometriosis were masked due to non-optimal timing of pharmacological interventions, herein we aimed to reassess the antiangiogenic therapeutic potential of D2-ags in vivo by administering compounds at a timeframe in which vessels in the lesions are expected to be more sensitive to antiangiogenic stimuli. To prove our point, immunodeficient (NU/NU) mice were given a D2-ag (cabergoline), anti-VEGF (CBO-P11) or vehicle (saline) compounds (n = 8 per group) starting 5 days after implantation of a fluorescently labeled human lesion. The effects on the size of the implants was estimated by monitoring the extent of fluorescence emitted by the lesion during the three-week treatment period. Subsequently mice were sacrificed and lesions excised and fixed for quantitative immunohistochemical/immunofluorescent analysis of angiogenic parameters. Lesion size, vascular density and innervation were comparable in D2-ag and anti-VEGF groups and significantly decreased when compared to control. These data suggest that D2-ags are as powerful as standard antiangiogenic compounds in interfering with angiogenesis and lesion size. Our preliminary study opens the way to further exploration of the mechanisms beneath the antiangiogenic effects of D2-ags for endometriosis treatment in humans.

Catecholamines in the regulation of angiogenesis in cutaneous wound healing

Angiogenesis involves the formation of new blood vessels from preexisting ones, and it is an essential step during cutaneous wound healing, which supports cells at the wound site with nutrition and oxygen. Impaired angiogenesis in the wound tissues results in delayed wound closure and healing. Among the regulators of angiogenesis, the role of catecholamines (epinephrine, norepinephrine, and dopamine) is of interest due to their diverse roles in the process of wound healing. While both norepinephrine and epinephrine mostly inhibit the angiogenic process in cutaneous wounds, dopamine, the other member of the catecholamine family, has interesting and contradictory roles in the regulation of angiogenesis in the wound beds, depending on the type of dopamine receptor involved. The stimulation of dopamine D2 receptors negatively regulates the angiogenic process in normal dermal wounds and thereby delays healing, whereas the stimulation of dopamine D1 receptors promotes angiogenesis and expedites healing in diabetic wounds. Importantly, catecholamines also play important roles in other pathological conditions, and specific agonists and antagonists of catecholamines are available for the treatment of some disorders. Therefore, such drugs may be utilized for the management of angiogenesis to promote the healing of dermal wounds. This review provides a broad overview of the angiogenic process during cutaneous wound healing and the regulatory roles played by catecholamines during the process.

Blockade of Dopamine D2 Receptors as a Novel Approach to Stimulation of Notch1+ Endothelial Progenitor Cells and Angiogenesis in C57BL/6 Mice with Pulmonary Emphysema Induced by Proteases and Deficiency of α1-Antitrypsin

We studied the effects of spiperone, a selective blocker of dopamine D2 receptors, on the model of pulmonary emphysema provoked by administration of elastase and D-galactosamine hydrochloride to female C57BL/6 mice and characterized by activation of proteases in the lungs and systemic deficiency of its inhibitor α1-antitrypsin. In this model, spiperone prevented the development of inflammatory reaction and reduced the area of emphysematous expanded alveolar tissue. The expression of angiogenic marker CD31 in the lungs increased under these conditions. Regeneration of the damaged microvascular bed under the action of spiperone resulted from recruiting of Notch1⁺ endothelial progenitor cells (CD45^-CD31⁺CD34⁺) into the lungs and blockade of the inhibitory effect of dopamine on phosphorylation of VEGF-2 receptors in endothelial cells of different maturity. In addition, spiperone produced a protective effect on hepatocytes and restored the production and secretion of α1-antitrypsin by these cells.

Vascular tone and angiogenesis modulation by catecholamine coordinated to ruthenium

Catecholamines participate in angiogenesis, an important tumor development process. However, the way catecholamines interact with their receptors has not been completely elucidated, and doubts still remain as to whether these interactions occur between catechol and/or amine sites and particular amino acid residues on the catecholamine receptors. To evaluate how catechol and amine groups contribute to angiogenesis, we immobilized the catechol site through ruthenium ion (Ru) coordination, to obtain species with the general formula [Ru(NH₃)₄(catecholamine-R)]Cl. We then assessed the angiogenic activity of the complexes in a chorioallantoic membrane model (CAM) and examined vascular reactivity and calcium mobilization in rat aortas and vascular cells. [Ru(NH₃)₄(catecholamine-R)]Cl acted as partial agonists and/or antagonists of their respective receptors and induced calcium mobilization. [Ru(NH₃)₄(isoproterenol)]⁺ [Ru(NH₃)₄(noradrenaline)]⁺, and [Ru(NH₃)₄(adrenaline)]⁺ behaved as antiangiogenic complexes, whereas [Ru(NH₃)₄(dopamine)]⁺ proved to be a proangiogenic complex. In conclusion, catecholamines and [Ru(NH₃)₄(catecholamine-R)]Cl can modulate angiogenesis, and catechol group availability can modify the way these complexes impact the vascular tone, suggesting that catecholamines and their receptors interact differently after catecholamine coordination to ruthenium.

Neuroendocrine Factors and Head and Neck Squamous Cell Carcinoma: An Affair to Remember

Head and neck squamous cell carcinoma (HNSCC) is one of the most aggressive malignancies. Therefore, the major goal of cancer treatment is inhibition of tumor cell growth and of metastasis development. In order to choose the best management option for HNSCC patients, we need to identify reliable prognostic factors and to develop new molecular techniques in order to obtain a better understanding of therapy resistance. By acting as neurohormones, neurotransmitters, or neuromodulators, the neuroendocrine factors are able to signal the maintenance of physiological homeostasis or progression to malignant disease. Certain neuropeptides possess strong antitumor properties acting as tumor suppressors and immunomodulators, providing additional benefits for future potential therapeutic strategies. In light of the current understanding, cancer starts as a localized disease that can be effectively treated if discovered on proper time. Unfortunately, more than often cancer cells migrate to the surrounding tissues generating distant metastases, thus making the prognosis and survival in this stage much worse. As cellular migration is mandatory for tumor invasion and metastasis development, searching for alternate controllers of these processes, such as the neuroendocrine factors, it is an active tremendous task.

A Concise Review of the Conflicting Roles of Dopamine-1 versus Dopamine-2 Receptors in Wound Healing

Catecholamines play an important regulatory role in cutaneous wound healing. The exact role of dopamine in human epidermis has yet to be fully elucidated. Current published evidence describes its differential effects on two separate families of G protein coupled receptors: D1-like and D2-like dopamine receptors. Dopamine may enhance angiogenesis and wound healing through its action on dopamine D1 receptors, while impairing wound healing when activating D2 receptors. This review summarizes the evidence for the role of dopamine in wound healing and describes potential mechanisms behind its action on D1 versus D2-like receptors in the skin.

The potential roles of dopamine in malignant glioma

Despite the numerous promising discoveries in contemporary cancer research and the emerging innovative cancer treatment strategies, the global burden of malignant glioma is expected to increase, partially due to its poor prognosis and human aging. Dopamine, a monoamine catecholamine neurotransmitter, is currently regarded as an important endogenous regulator of tumor growth. Dopamine may be an important treatment for brain tumors and could impact the pathogenesis of glioma by regulating tumor angiogenesis and vasculogenesis. Additionally, dopamine might exert an anti-glioma, cytotoxic effect by modulating apoptosis and autophagy. Dopamine and its receptors are also known to influence the immune system, as it is related to the pathogenesis of glioma. Dopamine may also increase the efficacy of anti-cancer drugs. Here, we review the potential roles of dopamine in malignant glioma and further identify the previously unknown function of dopamine as a potent regulator in the pathogenesis of glioma. Currently, the precise mechanisms regarding the protective effect of dopamine on glioma are poorly understood. However, our experimental results strongly emphasize the importance of this topic in future investigations.

Dopamine Increases CD14+CD16+ Monocyte Transmigration across the Blood Brain Barrier: Implications for Substance Abuse and HIV Neuropathogenesis

In human immunodeficiency virus-1 (HIV) infected individuals, substance abuse may accelerate the development and/or increase the severity of HIV associated neurocognitive disorders (HAND). It is proposed that CD14⁺CD16⁺ monocytes mediate HIV entry into the central nervous system (CNS) and that uninfected and infected CD14⁺CD16⁺ monocyte transmigration across the blood brain barrier (BBB) contributes to the establishment and propagation of CNS HIV viral reservoirs and chronic neuroinflammation, important factors in the development of HAND. The effects of substance abuse on the frequency of CD14⁺CD16⁺ monocytes in the peripheral circulation and on the entry of these cells into the CNS during HIV neuropathogenesis are not known. PBMC from HIV infected individuals were analyzed by flow cytometry and we demonstrate that the frequency of peripheral blood CD14⁺CD16⁺ monocytes in HIV infected substance abusers is increased when compared to those without active substance use. Since drug use elevates extracellular dopamine concentrations in the CNS, we examined the effects of dopamine on CD14⁺CD16⁺ monocyte transmigration across our in vitro model of the human BBB. The transmigration of this monocyte subpopulation is increased by dopamine and the dopamine receptor agonist, SKF 38393, implicating D1-like dopamine receptors in the increase in transmigration elicited by this neurotransmitter. Thus, elevated extracellular CNS dopamine may be a novel common mechanism by which active substance use increases uninfected and HIV infected CD14⁺CD16⁺ monocyte transmigration across the BBB. The influx of these cells into the CNS may increase viral seeding and neuroinflammation, contributing to the development of HIV associated neurocognitive impairments.

Immunomodulatory Effects Mediated by Dopamine

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

Dopamine D2 receptor suppresses gastric cancer cell invasion and migration via inhibition of EGFR/AKT/MMP-13 pathway

Dopamine (DA), an important neurotransmitter, has been reported to play a negative role in tumor progression. DA acts its role via dopamine receptors (DRs), which can be divided into five receptor subtypes (D1R-D5R). Among these receptor subtypes, D2R has been found to inhibit IGF-I-induced gastric cancer cell growth. However, the functions of D2R in gastric cancer cell invasion remain elusive. Here, we found that D2R expression was decreased in gastric cancer cells. DA treatment dose-dependently inhibited EGF-mediated gastric cancer cell invasion and migration via D2R. Furthermore, D2R decreased EGF-mediated MMP-13 production, and attenuated EGFR and AKT activation. Together with the results that EGF promoted gastric cancer cell invasion and migration via EGFR/AKT pathway, these data indicate that DA treatment, acting via D2R, suppresses gastric cancer cell invasion and migration via inhibition of EGFR/AKT/MMP-13 pathway. Thus, our findings suggest that use of D2R agonist may have a potential therapeutic effect on gastric cancer.

Activation of Dopamine D1 Receptors in Dermal Fibroblasts Restores Vascular Endothelial Growth Factor-A Production by These Cells and Subsequent Angiogenesis in Diabetic Cutaneous Wound Tissues

In wound beds, fibroblasts are rich sources of vascular endothelial growth factor A, a cytokine necessary for promoting angiogenesis and thereby the healing of wound tissues. However, in diabetes mellitus, these cells are functionally impaired and produce reduced amounts of vascular endothelial growth factor A, resulting in deficient angiogenesis and delayed wound healing. We here for the first time demonstrate that stimulation of D1 dopamine receptors present in dermal fibroblasts restores vascular endothelial growth factor A production by these cells, resulting in adequate angiogenesis and subsequent healing of cutaneous wounds in both type 1 and type 2 diabetic mice. This action of D1 dopamine receptors was mediated through the protein kinase A pathway. As delayed wound healing or chronic wounds are one of the major health problems in diabetic patients, D1 dopamine receptor agonists, which are already in clinical use for the treatment of other disorders, may be of translational value in the treatment of chronic, nonhealing diabetic wounds.

Relationship between Oxidative Stress, Circadian Rhythms, and AMD

This work reviews concepts regarding oxidative stress and the mechanisms by which endogenous and exogenous factors produce reactive oxygen species (ROS). It also surveys the relationships between oxidative stress, circadian rhythms, and retinal damage in humans, particularly those related to light and photodamage. In the first section, the production of ROS by different cell organelles and biomolecules and the antioxidant mechanisms that antagonize this damage are reviewed. The second section includes a brief review of circadian clocks and their relationship with the cellular redox state. In the third part of this work, the relationship between retinal damage and ROS is described. The last part of this work focuses on retinal degenerative pathology, age-related macular degeneration, and the relationships between this pathology, ROS, and light. Finally, the possible interactions between the retinal pigment epithelium (RPE), circadian rhythms, and this pathology are discussed.

Expression and therapeutic targeting of dopamine receptor-1 (D1R) in breast cancer

Patients with advanced breast cancer often fail to respond to treatment, creating a need to develop novel biomarkers and effective therapeutics. Dopamine (DA) is a catecholamine that binds to five G protein-coupled receptors. We discovered expression of DA type-1 receptors (D1Rs) in breast cancer, thereby identifying these receptors as novel therapeutic targets in this disease. Strong to moderate immunoreactive D1R expression was found in 30% of 751 primary breast carcinomas, and was associated with larger tumors, higher tumor grades, node metastasis and shorter patient survival. DA and D1R agonists, signaling through the cGMP/protein kinase G (PKG) pathway, suppressed cell viability, inhibited invasion and induced apoptosis in multiple breast cancer cell lines. Fenoldopam, a peripheral D1R agonist that does not penetrate the brain, dramatically suppressed tumor growth in two mouse models with D1R-expressing xenografts by increasing both necrosis and apoptosis. D1R-expressing primary tumors and metastases in mice were detected by fluorescence imaging. In conclusion, D1R overexpression is associated with advanced breast cancer and poor prognosis. Activation of the D1R/cGMP/PKG pathway induces apoptosis in vitro and causes tumor shrinkage in vivo. Fenoldopam, which is FDA (Food and Drug Administration) approved to treat renal hypertension, could be repurposed as a novel therapeutic agent for patients with D1R-expressing tumors.

Dopamine agonist inhibits vascular endothelial growth factor protein production and secretion in granulosa cells

BACKGROUND

Dopamine receptor 2 agonists (D2-ags) inhibit vascular endothelial growth factor (VEGF) secretion in luteinized granulosa cells (LGCs) both in vitro and in vivo. However, the mechanism of D2 regulation of the VEGF/VEGF Receptor 2 (VEGFR-2) pathway remains to be elucidated. We sought to determine the effects of D2 signaling on VEGF transcription and translation in LGCs, with the expectation of identifying potential D2-ag-based therapies for ovarian hyperstimulation syndrome (OHSS).

FINDINGS

LGCs from egg donors were cultured with chorionic gonadotropin (hCG) in the presence of Actinomycin-D (ActD) or Brefeldin-A (BFA) to evaluate the effects of a D2-ag, cabergoline (Cb2), on VEGF secretion. The contribution of the conventional Gi/Go, Gz and AKT/β-Arrestin pathways in the VEGF regulation was assessed by adding pertussis toxin (PTX), phorbol 12-myristate 13-acetate (PMA), or wortmannin (WT). While Cb2 inhibited VEGF secretion by interfering with VEGF peptide translation and secretion, inhibition of conventional D2 transduction pathways did not reverse Cb2-mediated inhibition of VEGF secretion.

CONCLUSIONS

The effects of D2-ag on VEGF translation and secretion are mediated by D2 signaling pathways that have yet to be described. We found that D2-ag inhibits VEGF secretion at the post-transcriptional level, suggesting that D2-ag treatment should be combined with therapies that inhibit VEGF transcription, such as the employment of LH or GnRH for triggering ovulation, to improve the efficacy of OHSS prevention.

Renal dopaminergic system: Pathophysiological implications and clinical perspectives

Fluid homeostasis, blood pressure and redox balance in the kidney are regulated by an intricate interaction between local and systemic anti-natriuretic and natriuretic systems. Intrarenal dopamine plays a central role on this interactive network. By activating specific receptors, dopamine promotes sodium excretion and stimulates anti-oxidant and anti-inflammatory pathways. Different pathological scenarios where renal sodium excretion is dysregulated, as in nephrotic syndrome, hypertension and renal inflammation, can be associated with impaired action of renal dopamine including alteration in biosynthesis, dopamine receptor expression and signal transduction. Given its properties on the regulation of renal blood flow and sodium excretion, exogenous dopamine has been postulated as a potential therapeutic strategy to prevent renal failure in critically ill patients. The aim of this review is to update and discuss on the most recent findings about renal dopaminergic system and its role in several diseases involving the kidneys and the potential use of dopamine as a nephroprotective agent.

Dopamine and serotonin regulate tumor behavior by affecting angiogenesis

The biogenic amines dopamine and serotonin are neurotransmitters and hormones, which are mainly produced in the central nervous system and in the gastro-intestinal tract. They execute local and systemic functions such as intestinal motility and tissue repair. Dopamine and serotonin are primarily stored in and transported by platelets. This review focuses on the recently recognized role of dopamine and serotonin in the regulation of tumor behavior by affecting angiogenesis and tumor cell proliferation. Preclinical studies demonstrate that dopamine inhibits tumor growth via activation of dopamine receptor D2 on endothelial and tumor cells. Serotonin stimulates tumor growth via activation of serotonin receptor 2B on endothelial cells and serotonin receptors on tumor cells. Drugs that stimulate dopamine receptor D2 or inhibit serotonin receptors are available and therefore clinical intervention studies for cancer patients are within reach.

Kinase insert domain receptor/vascular endothelial growth factor receptor 2 (KDR) genetic variation is associated with ovarian hyperstimulation syndrome

BACKGROUND

The objective of this investigation was to determine if kinase insert domain/vascular endothelial growth factor receptor 2 (KDR/VEGFR2) genetic variation was associated with the development of ovarian hyperstimulation syndrome (OHSS) in patients undergoing controlled ovarian hyperstimulation (COH).

METHODS

This was a case-control study of 174 patients who underwent controlled ovarian stimulation. Patient blood samples were genotyped for single nucleotide polymorphisms (SNPs) spanning the KDR locus. OHSS development, clinical outcome variables, SNP and haplotype frequencies were compared between control (n = 155) and OHSS (n = 19) groups.

RESULTS

Patients who developed OHSS had significantly higher response markers (estradiol levels of the day of hCG administration, number of follicles developed, number of eggs retrieved) than control patients. When adjusted for age and self-identified race, the rs2305945 G/T genotype was associated (P = 0.027) with a decreased risk (OR = 0.30; 95% CI = 0.10, 0.93) of developing OHSS using an overdominant model. The rs2305945 G/T variant was also associated with decreased COH response (number of follicles, number of eggs retrieved) in an overdominant model. The rs2305948, rs1870378, rs2305945 (C-T-G) haplotype was associated with both decreased COH response and OHSS risk (unadjusted OR = 0.10; 95% CI = 0.01, 0.80, P = 0.031).

CONCLUSIONS

The KDR receptor is believed to play a central role OHSS development and is a target for pharmacological prevention of OHSS. These results indicate that genetic variation in the KDR gene may impact individual risk of developing OHSS from COH. In addition, the rs2305948 SNP and C-T-G haplotype might serve as potential biomarkers for poor ovarian response to COH.

Role of D2 dopamine receptor in adrenal cortical cell proliferation and aldosterone-producing adenoma tumorigenesis

Aldosterone-producing adenoma (APA) and bilateral adrenal hyperplasia are the two characteristic types of primary aldosteronism. Dysregulation of adrenal cortical cell proliferation contributes to both diseases. We previously demonstrated that APA expressed less dopamine D2 receptor than the respective non-tumor tissue and might contribute to the overproduction of aldosterone. As activation of D2 receptor inhibits the proliferation of various cells, downregulation of D2 receptor in APA may play a role in the tumorigenesis of APA. In this study, we demonstrate that D2 receptor plays a role in angiotensin II (AII)-stimulated adrenal cortical cell proliferation. The D2 receptor agonist, bromocriptine, inhibited AII-stimulated cell proliferation in primary cultures of the normal human adrenal cortex and APA through attenuating AII-induced phosphorylation of PK-stimulated cyclin D1 protein expression and cell proliferation. D2 receptor also inhibited AII-induced ERK1/2 phosphorylation. Our results demonstrate that, in addition to inhibiting aldosterone synthesis/production, D2 receptor exerts an anti-proliferative effect in adrenal cortical and APA cells by attenuating PKCμ and ERK phosphorylation. The lower level of expression of D2 receptor in APA may augment cell proliferation and plays a crucial role in the tumorigenesis of APA. Our novel finding suggests a new therapeutic target for primary aldosteronism.

Epigenetic repression of the dopamine receptor D4 in pediatric tumors of the central nervous system

Epigenetic alterations are common events in cancer. Using a genome wide methylation screen (Restriction Landmark Genomic Scanning-RLGS) we identified the gene for the dopamine receptor D4 (DRD4) as tumor-specific methylated. As DRD4 is involved in early brain development and may thus be involved in developmentally dependent tumors of the CNS in children epigenetic deregulation of DRD4 and its functional consequences were analyzed in vitro. CpG methylation of DRD4 was detected in 18/24 medulloblastomas, 23/29 ependymomas, 6/6 high-grade gliomas, 7/10 CNS PNET and 8/8 cell lines by qCOBRA and bisulfite sequencing. Real-time RT-PCR demonstrated a significantly inferior expression of DRD4 in primary tumors compared to cell lines and non-malignant control tissues. Epigenetic deregulation of DRD4 was analyzed in reexpression experiments and restoration of DRD4 was observed in medulloblastoma (MB) cells treated with 5-Aza-CdR. Reexpression was not accompanied by demethylation of the DRD4 promoter but by a significant decrease of H3K27me3 and of bound enhancer of zeste homologue 2 (EZH2). Knockdown of EZH2 demonstrated DRD4 as a direct target for inhibition by EZH2. Stimulation of reexpressed DRD4 resulted in an activation of ERK1/2. Our analyses thus disclose that DRD4 is epigenetically repressed in CNS tumors of childhood. DRD4 is a direct target of EZH2 in MB cell lines. EZH2 appears to dominate over aberrant DNA methylation in the epigenetic inhibition of DRD4, which eventually leads to inhibition of a DRD4-mediated stimulation of the ERK1/2 kinase pathway.

Cabergoline as treatment of ovarian hyperstimulation syndrome: a review

One of the most serious complications of assisted reproduction techniques is ovarian hyperstimulation syndrome (OHSS). OHSS not only increases morbidity and mortality in IFV cycles, but also causes significant other problems, as cancelled in vitro fertilization (IVF) cycles, prolonged hospitalization, causing emotional and sociofinancial consequences. Several treatments for OHSS have been proposed and among these Cabergoline (Cb2). Despite the above-mentioned beneficial effect, Cb2 has not been widely used in everyday's clinical practice. With our study, we try to review all studies with strong evidence examining Cb2 use for OHSS prevention.

Neurotransmitters as regulators of tumor angiogenesis and immunity: the role of catecholamines

The growing tumor employs various strategies to establish its growth, progression and spread in the host. Angiogenesis or formation of new blood vessels from existing ones and escape from immune surveillance are the two critical steps that ensure proper establishment and growth of the newly formed tumor. Thus understanding the novel pathways associated with tumor angiogenesis and immunity may lead to the development of newer therapeutic strategies using the regulators of these pathways to improve patient outcomes. These two pivotal steps in the process of tumorigenesis are governed by plethora of endogenous factors. The neuroendocrine molecules, which include the catecholamine neurotransmitters, dopamine, norepinephrine and epinephrine are of growing interest considering their varied and diverse regulatory roles both in the process of tumor angiogenesis and tumor immunity. This review focuses on the emerging roles of catecholamines in modulating tumor angiogenesis and immunity, and also discusses the probable molecular mechanisms of their actions. Understanding of this new group of endogenous regulators of tumor growth may lead to the development of newer therapeutic approaches for the treatment of cancer.

Dopamine regulates mobilization of mesenchymal stem cells during wound angiogenesis

Angiogenesis is an important step in the complex biological and molecular events leading to successful healing of dermal wounds. Among the different cellular effectors of wound angiogenesis, the role of mesenchymal stem cells (MSCs) is of current interest due to their transdifferentiation and proangiogenic potentials. Skin is richly innervated by sympathetic nerves which secrete dopamine (DA) and we have recently shown that concentration of DA present in synaptic cleft can significantly inhibit wound tissue neovascularization. As recent reports indicate that MSCs by mobilizing into wound bed play an important role in promoting wound angiogenesis, we therefore investigated the effect of DA on the migration of MSCs in wound tissues. DA acted through its D(2) receptors present in the MSCs to inhibit their mobilization to the wound beds by suppressing Akt phosphorylation and actin polymerization. In contrast, this inhibitory effect of DA was reversed after treatment with specific DA D(2) receptor antagonist. Increased mobilization of MSCs was demonstrated in the wound site following blockade of DA D(2) receptor mediated actions, and this in turn was associated with significantly more angiogenesis in wound tissues. This study is of translational value and indicates use of DA D(2) receptor antagonists to stimulate mobilization of these stem cells for faster regeneration of damaged tissues.

Dopamine inhibits pulmonary edema through the VEGF-VEGFR2 axis in a murine model of acute lung injury

The neurotransmitter dopamine and its dopamine receptor D2 (D2DR) agonists are known to inhibit vascular permeability factor/vascular endothelial growth factor (VEGF)-mediated angiogenesis and vascular permeability. Lung injury is a clinical syndrome associated with increased microvascular permeability. However, the effects of dopamine on pulmonary edema, a phenomenon critical to the pathophysiology of both acute and chronic lung injuries, have yet to be established. Therefore, we sought to determine the potential therapeutic effects of dopamine in a murine model of lipopolysaccharide (LPS)-induced acute lung injury (ALI). Compared with sham-treated controls, pretreatment with dopamine (50 mg/kg body wt) ameliorated LPS-mediated edema formation and lowered myeloperoxidase activity, a measure of neutrophil infiltration. Moreover, dopamine significantly increased survival rates of LPS-treated mice, from 0-75%. Mechanistically, we found that dopamine acts through the VEGF-VEGFR2 axis to reduce pulmonary edema, as dopamine pretreatment in LPS-treated mice resulted in decreased serum VEGF, VEGFR2 phosphorylation, and endothelial nitric oxide synthase phosphorylation. We used D2DR knockout mice to confirm that dopamine acts through D2DR to block vascular permeability in our lung injury model. As expected, a D2DR agonist failed to reduce pulmonary edema in D2DR(-/-) mice. Taken together, our results suggest that dopamine acts through D2DR to inhibit pulmonary edema-associated vascular permeability, which is mediated through VEGF-VEGFR2 signaling and conveys protective effects in an ALI model.

Dopamine regulates angiogenesis in normal dermal wound tissues

Cutaneous wound healing is a normal physiological process and comprises different phases. Among these phases, angiogenesis or new blood vessel formation in wound tissue plays an important role. Skin is richly supplied by sympathetic nerves and evidences indicate the significant role of the sympathetic nervous system in cutaneous wound healing. Dopamine (DA) is an important catecholamine neurotransmitter released by the sympathetic nerve endings and recent studies have demonstrated the potent anti-angiogenic action of DA, which is mediated through its D₂ DA receptors. We therefore postulate that this endogenous catecholamine neurotransmitter may have a role in the neovascularization of dermal wound tissues and subsequently in the process of wound healing. In the present study, the therapeutic efficacy of D₂ DA receptor antagonist has been investigated for faster wound healing in a murine model of full thickness dermal wound. Our results indicate that treatment with specific D₂ DA receptor antagonist significantly expedites the process of full thickness normal dermal wound healing in mice by inducing angiogenesis in wound tissues. The underlined mechanisms have been attributed to the up-regulation of homeobox transcription factor HoxD3 and its target α5β1 integrin, which play a pivotal role in wound angiogenesis. Since D₂ DA receptor antagonists are already in clinical use for other disorders, these results have significant translational value from the bench to the bedside for efficient wound management along with other conventional treatment modalities.

Vascular endothelial growth factor is upregulated by L-dopa in the parkinsonian brain: implications for the development of dyskinesia

Angiogenesis and increased permeability of the blood-brain barrier have been reported to occur in animal models of Parkinson's disease and l-dopa-induced dyskinesia, but the significance of these phenomena has remained unclear. Using a validated rat model of l-dopa-induced dyskinesia, this study demonstrates that chronic treatment with l-dopa dose dependently induces the expression of vascular endothelial growth factor in the basal ganglia nuclei. Vascular endothelial growth factor was abundantly expressed in astrocytes and astrocytic processes in the proximity of blood vessels. When co-administered with l-dopa, a small molecule inhibitor of vascular endothelial growth factor signalling significantly attenuated the development of dyskinesia and completely blocked the angiogenic response and associated increase in blood-brain barrier permeability induced by the treatment. The occurrence of angiogenesis and vascular endothelial growth factor upregulation was verified in post-mortem basal ganglia tissue from patients with Parkinson's disease with a history of dyskinesia, who exhibited increased microvascular density, microvascular nestin expression and an upregulation of vascular endothelial growth factor messenger ribonucleic acid. These congruent findings in the rat model and human patients indicate that vascular endothelial growth factor is implicated in the pathophysiology of l-dopa-induced dyskinesia and emphasize an involvement of the microvascular compartment in the adverse effects of l-dopa pharmacotherapy in Parkinson's disease.

Synthesis and biological evaluation of a polyglutamic acid-dopamine conjugate: a new antiangiogenic agent

Dopamine has previously been shown to inhibit angiogenesis in vitro and in vivo, but its clinical applications in this context are severely limited by its short half-life. Here we report the synthesis of a polyglutamic acid-dopamine conjugate and show that conjugation significantly extends (from 1 to 24 h) dopamine's antiangiogenic activity in vitro and in vivo. These findings form the basis for the development of a new class of agents for the treatment of angiogenesis-dependent diseases.

Dopamine blocks stress-mediated ovarian carcinoma growth

PURPOSE

Increased adrenergic activity in response to chronic stress is known to promote tumor growth by stimulating the tumor microenvironment. The focus of the current study was to determine whether dopamine, an inhibitory catecholamine, could block the effects of chronic stress on tumor growth.

EXPERIMENTAL DESIGN

Expression of dopamine receptors (DR1-DR5) was analyzed by reverse transcriptase-PCR and by Western blotting. In vitro effects of dopamine on cell viability, apoptosis, and migration were examined. For in vivo therapy, murine and human DR2-siRNAs were incorporated into chitosan nanoparticles (CH-NP).

RESULTS

In this model of chronic stress, tumoral norepinephrine levels remained elevated whereas dopamine levels were significantly decreased compared with nonstressed animals. Daily restraint stress resulted in significantly increased tumor growth in both immunodeficient (SKOV3ip1 and HeyA8) and immunocompetent (ID8) ovarian cancer models. This increase was completely blocked with daily dopamine treatment. Dopamine treatment also blocked the stress-induced increase in angiogenesis. Endothelial and ovarian cancer cells expressed all dopamine receptors except for the lack of DR3 expression in ovarian cancer cells. DR2 was responsible for the inhibitory effects of dopamine on tumor growth and microvessel density as well as the stimulatory effect on apoptosis, as the DR2 antagonist eticlopride reversed these effects. Dopamine significantly inhibited cell viability and stimulated apoptosis in vitro. Moreover, dopamine reduced cyclic AMP levels and inhibited norepinephrine and vascular permeability factor/VEGF-induced Src kinase activation.

CONCLUSIONS

Dopamine depletion under chronic stress conditions creates a permissive microenvironment for tumor growth that can be reversed by dopamine replacement.

Biogenic amines serotonin and dopamine regulate cholangiocyte hyperplastic and neoplastic growth

Biogenic amines, such as serotonin and dopamine, regulate a multitude of cellular responses. A great deal of effort has been invested into understanding the effects of these molecules and their corresponding receptor systems on cholangiocyte and cholangiocarcinoma secretion, apoptosis and growth. This review summarizes the results of these efforts and highlights the importance of these regulatory molecules on the physiology and pathophysiology of cholangiocytes. Specifically we have focused on the recent findings into the effects of serotonin and dopamine on cholangiocyte hyperplasia and neoplastic growth.

Sympathetic Neurotransmitters and Tumor Angiogenesis-Link between Stress and Cancer Progression

Recent evidence supports a longstanding hypothesis that chronic stress can influence tumor growth and progression. It has been shown that sympathetic neurotransmitters, such as catecholamines and neuropeptides, can affect both cancer cell growth and tumor vascularization. Depending on neurotransmitter and type of tumor, these effects can be both stimulatory and inhibitory. Norepinephrine (NE) and epinephrine (E) are potent stimulators of vascularization, acting both by inducing the release of angiogenic factors from tumor cells and directly on endothelial cell (EC) functions. As a result, activation of the adrenergic system increases growth of various types of tumors and has been shown to mediate stress-induced augmentation of tumor progression. Dopamine (DA), on the other hand, interferes with VEGF signaling in endothelial cells, blocks its angiogenic functions and inhibits tumor growth. Another sympathetic neurotransmitter coreleased with NE, neuropeptide Y (NPY), directly stimulates angiogenesis. However, proangiogenic actions of NPY can be altered by its direct effect on tumor cell proliferation and survival. In consequence, NPY can either stimulate or inhibit tumor growth, depending on tumor type. Hence, sympathetic neurotransmitters are powerful modulators of tumor growth and can become new targets in cancer therapy.

Increased local dopamine secretion has growth-promoting effects in cholangiocarcinoma

Cholangiocarcinoma is a devastating cancer of biliary origin with limited treatment options. Symptoms are usually evident after blockage of the bile duct by the tumor, and at this late stage, they are relatively resistant to chemotherapy and radiation therapy. Therefore, it is imperative that alternative treatment options are explored. We have previously shown that serotonin metabolism is dysregulated in cholangiocarcinoma leading to an increased secretion of serotonin, which has growth-promoting effects. Because serotonin and dopamine share the degradation machinery, we evaluated the secretion of dopamine from cholangiocarcinoma and its effects on cell proliferation. Using 4 cholangiocarcinoma cell lines and human biopsy samples, we demonstrated that there was an increase in mRNA and protein expression of the dopamine synthesis enzymes tyrosine hydroxylase and dopa decarboxylase in cholangiocarcinoma. There was increased dopamine secretion from cholangiocarcinoma cell lines compared to H69 and HIBEC cholangiocytes and increased dopamine immunoreactivity in human biopsy samples. Furthermore, administration of dopamine to all cholangiocarcinoma cell lines studied increased proliferation by up to 30%, which could be blocked by the pretreatment of the D2 and D4 dopamine receptor antagonists, whereas blocking dopamine production by alpha-methyldopa administration suppressed growth by up to 25%. Administration of alpha-methyldopa to nude mice also suppressed cholangiocarcinoma tumor growth. The data presented here represent the first evidence that dopamine metabolism is dysregulated in cholangiocarcinoma and that modulation of dopamine synthesis may represent an alternative target for the development of therapeutic strategies.

Differential involvement of D1 and D2 dopamine receptors in L-DOPA-induced angiogenic activity in a rat model of Parkinson's disease

Angiogenesis occurs in the brains of Parkinson's disease patients, but the effects of dopamine replacement therapy on this process have not been examined. Using rats with 6-hydroxydopamine lesions, we have compared angiogenic responses induced in the basal ganglia by chronic treatment with either L-DOPA, or bromocriptine, or a selective D1 receptor agonist (SKF38393). Moreover, we have asked whether L-DOPA-induced angiogenesis can be blocked by co-treatment with either a D1- or a D2 receptor antagonist (SCH23390 and eticlopride, respectively), or by an inhibitor of extracellular signal-regulated kinases 1 and 2 (ERK1/2) (SL327). L-DOPA, but not bromocriptine, induced dyskinesia, which was associated with endothelial proliferation, upregulation of immature endothelial markers (nestin) and downregulation of endothelial barrier antigen in the striatum and its output structures. At a dose inducing dyskinesia (1.5 mg/kg/day), SKF38393 elicited angiogenic changes similar to L-DOPA. Antagonism of D1- but not D2 class receptors completely suppressed both the development of dyskinesia and the upregulation of angiogenesis markers. In fact, L-DOPA-induced endothelial proliferation was markedly exacerbated by low-dose D2 antagonism (0.01 mg/kg eticlopride). Inhibition of ERK1/2 by SL327 attenuated L-DOPA-induced dyskinesia and completely inhibited all markers of angiogenesis. These results highlight the specific link between treatment-induced dyskinesias and microvascular remodeling in the dopamine-denervated brain. L-DOPA-induced angiogenesis requires stimulation of D1 receptors and activation of ERK1/2, whereas the stimulation of D2 receptors seems to oppose this response.

Dopamine regulates phosphorylation of VEGF receptor 2 by engaging Src-homology-2-domain-containing protein tyrosine phosphatase 2

Vascular endothelial growth factor (VEGF)-induced receptor phosphorylation is the crucial step for initiating downstream signaling pathways that lead to angiogenesis or related pathophysiological outcomes. Our previous studies have shown that the neurotransmitter dopamine could inhibit VEGF-induced phosphorylation of VEGF receptor 2 (VEGFR-2), endothelial cell proliferation, migration, microvascular permeability, and thus, angiogenesis. In this study, we address the mechanism by which VEGFR-2 phosphorylation is regulated by dopamine. Here, we demonstrate that D2 dopamine receptor (D2DR) colocalizes with VEGFR-2 at the cell surface. Dopamine pretreatment increases the translocation and colocalization of Src-homology-2-domain-containing protein tyrosine phosphatase (SHP-2) with D2DR at the cell surface. Dopamine administration leads to increased VEGF-induced phosphorylation of SHP-2 and this increased phosphorylation parallels the increased phosphatase activity of SHP-2. Active SHP-2 then dephosphorylates VEGFR-2 at Y951, Y996 and Y1059, but not Y1175. We also observe that SHP-2 knockdown impairs the dopamine-regulated inhibition of VEGF-induced phosphorylation of VEGFR-2 and, subsequently, Src phosphorylation and migration. Our data establish a novel role for SHP-2 phosphatase in the dopamine-mediated regulation of VEGFR-2 phosphorylation.

High dose cabergoline in management of ovarian hyperstimulation syndrome

OBJECTIVE

To describe a case of moderate ovarian hyperstimulation syndrome (OHSS) that was treated with high dose cabergoline.

DESIGN

Case report.

SETTING

Private assisted reproduction center.

PATIENT(S)

A 29-year-old woman who developed early moderate OHSS despite preventive cabergoline administration (0.5 mg/day) following controlled ovarian hyperstimulation for IVF treatment.

INTERVENTION(S)

Cabergoline dose was increased to 1 mg/day upon diagnosis of OHSS on the second day after oocyte collection and embryo transfer was postponed to the fifth day after oocyte collection.

MAIN OUTCOME MEASURE(S)

Resolution of OHSS and achievement of healthy live birth.

RESULT(S)

OHSS resolved rapidly despite occurrence of pregnancy and patient delivered a healthy boy at term.

CONCLUSION(S)

The higher cabergoline dose might have prevented an increase in the severity of OHSS and its prolongation following occurrence of pregnancy. Randomized controlled trials assessing the efficacy and safety of different doses and durations of cabergoline administration in both prophylactic and therapeutic settings are required.