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

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.

Common key-signals in learning and neurodegeneration: focus on excito-amino acids, beta-amyloid peptides and alpha-synuclein

In this paper a hypothesis that some special signals ("key-signals" excito-amino acids, beta-amyloid peptides and alpha-synuclein) are not only involved in information handling by the neuronal circuits, but also trigger out substantial structural and/or functional changes in the Central Nervous System (CNS) is introduced. This forces the neuronal circuits to move from one stable state towards a new state, but in doing so these signals became potentially dangerous. Several mechanisms are put in action to protect neurons and glial cells from these potentially harmful signals. However, in agreement with the Red Queen Theory of Ageing (Agnati et al. in Acta Physiol Scand 145:301-309, 1992), it is proposed that during ageing these neuroprotective processes become less effective while, in the meantime, a shortage of brain plasticity occurs together with an increased need of plasticity for repairing the wear and tear of the CNS. The paper presents findings supporting the concept that such key-signals in instances such as ageing may favour neurodegenerative processes in an attempt of maximizing neuronal plasticity.

Dopamine D2 receptor stimulation inhibits angiotensin II-induced hypertrophy in cultured neonatal rat ventricular myocytes

1. Myocardial hypertrophy is a common pathological change that accompanies cardiovascular disease. Dopamine D2 receptors have been demonstrated in cardiovascular tissues. However, the pathophysiological involvement of D2 receptors in myocardial hypertrophy is unclear. Therefore, the effects of the D2 receptor agonist bromocriptine and the D2 receptor antagonist haloperidol on angiotensin (Ang) II- or endothelin (ET)-1-induced hypertrophy of cultured neonatal rat ventricular myocytes were investigated in the present study. 2. Protein content and protein synthesis, determined by examining [(3)H]-leucine uptake, were used as estimates of cardiomyocyte hypertrophy. The expression of D2 receptor protein in neonatal rat ventricular myocytes was determined using western blotting. Changes in [Ca(2+)](i) in cardiomyocytes were observed by laser scanning confocal microscopy. 3. Angiotensin II and ET-1, both at 10 nmol/L, induced myocyte hypertrophy, as demonstrated by increased protein content and synthesis, [Ca(2+)](i) levels, protein kinase C (PKC) activity and phosphorylation of extracellular signal-regulated kinase, c-Jun N-terminal kinase and mitogen-activated protein kinase (MAPK) p38 (p38). Concomitant treatment of cells with 10 nmol/L AngII plus 10 micromol/L bromocriptine significantly inhibited cardiomyocyte hypertrophy, MAPK phosphorylation and PKC activity in the membrane, as well as [Ca(2+)](i) signalling pathways, compared with the effects of AngII alone. In addition, 10 micromol/L bromocriptine significantly inhibited cardiomyocyte hypertrophy induced by 10 nmol/L ET-1. However, pretreatment with haloperidol (10 micromol/L) had no significant effects on cardiomyocyte hypertrophy induced by either AngII or ET-1. 4. In conclusion, D2 receptor stimulation inhibits AngII-induced hypertrophy of cultured neonatal rat ventricular myocytes via inhibition of MAPK, PKC and [Ca(2+)](i) signalling pathways.

The neurotransmitter dopamine modulates vascular permeability in the endothelium

BACKGROUND

Vascular permeability factor/Vascular endothelial growth factor (VPF/VEGF), a multifunctional cytokine, is a potent inducer of vascular permeability, an important early step in angiogenesis. It is known that the neurotransmitter dopamine can inhibit VPF/VEGF mediated angiogenesis, in particular microvascular permeability, but the effectors of this action remain unclear.

RESULTS

Here, we define the signaling pathway modulated by dopamine that inhibits VPF/VEGF induced vascular permeability in endothelial cells. Signals from VPF/VEGF lead to changes in the phosphorylation of tight junction protein zonula occludens (ZO-1) and adherens junction proteins like VE-cadherin and associated catenins, thus weakening endothelial cell-cell adhesion and increasing vascular permeability. We found VEGF receptor-2 (VEGFR-2) to be part of a multi-protein complex involving ZO-1, VE-cadherin and beta-catenin. VPF/VEGF induced phosphorylations of VE-cadherin, beta-catenin and ZO-1 were inhibited by dopamine treatment. Association of occludin with ZO-1 and ZO-1 with VE-cadherin were significantly inhibited by dopamine in VEGF treated cells. Furthermore, we identified Src as an important target for dopamine-mediated inhibition of VPF/VEGF induced permeability.

CONCLUSION

Taken together, our results provide molecular insights of dopamine function in the vascular endothelium and suggest a central role of Src in regulating key molecules that control vascular permeability.

Dopamine increases the efficacy of anticancer drugs in breast and colon cancer preclinical models

PURPOSE

Because neurotransmitter dopamine inhibits vascular permeability factor/vascular endothelial growth factor (VEGF)-induced angiogenesis and as anti-VEGF agents act synergistically with anticancer drugs, we therefore investigated whether dopamine can increase the efficacies of these drugs.

EXPERIMENTAL DESIGN

The effect of dopamine was investigated in human breast cancer-(MCF-7) and colon (HT29) cancer-bearing mice. Experimental groups received either dopamine or doxorubicin or dopamine plus doxorubicin in MCF-7 tumor-bearing mice, and either dopamine or 5-fluorouracil or dopamine plus 5-fluorouracil in HT29-bearing mice. Thereafter, tumor growth, angiogenesis, tumor cell apoptosis, life span, and the effect of dopamine on the growth and survival of tumor cells in vitro were determined. Finally, the effects of dopamine on tumor vascular permeability; on VEGF receptor-2, mitogen-activated protein kinase, and focal adhesion kinase phosphorylation; and also on the proliferation and migration of tumor endothelial cells were investigated.

RESULTS

Dopamine, in combination with anticancer drugs, significantly inhibited tumor growth and increased the life span when compared with treatment with dopamine or anticancer drugs alone. Dopamine had no direct effects on the growth and survival of tumor cells. The antiangiogenic action of dopamine was mediated by inhibiting proliferation and migration of tumor endothelial cells through suppression of VEGF receptor-2, mitogen-activated protein kinase, and focal adhesion kinase phosphorylation.

CONCLUSION

Our study shows that dopamine significantly enhances the efficacies of commonly used anticancer drugs and also indicates that an inexpensive drug like dopamine, which is being extensively used in the clinics, might have a role as an antiangiogenic agent for the treatment of breast and colon cancer.

Dopamine regulates endothelial progenitor cell mobilization from mouse bone marrow in tumor vascularization

Mobilization of endothelial progenitor cells (EPCs) from the bone marrow and their subsequent participation in neovessel formation are implicated in tumor growth and neovascularization. As the neurotransmitter dopamine (DA) modulates adult endothelial cell function, we hypothesized that DA might have a regulatory role in mobilization of EPCs from the bone marrow niche. We show that there was a significant decrease in bone marrow DA content and an increase in EPC mobilization in tumor-bearing mice associated with tumor neovascularization. DA treatment of tumor-bearing mice inhibited EPC mobilization and tumor growth through its D2 receptors, as DA treatment failed to inhibit EPC mobilization in tumor-bearing mice treated with a specific DA D2 receptor antagonist and in tumor-bearing mice lacking the D2 receptor. In addition, we found that DA, through D2 receptors, exerted its inhibitory effect on EPC mobilization through suppression of VEGFA-induced ERK1/ERK2 phosphorylation and MMP-9 synthesis. These findings reveal a new link between DA and EPC mobilization and suggest a novel use for DA and D2 agents in the treatment of cancer and other diseases involving neovessel formation.

Low-dose dopamine agonist administration blocks vascular endothelial growth factor (VEGF)-mediated vascular hyperpermeability without altering VEGF receptor 2-dependent luteal angiogenesis in a rat ovarian hyperstimulation model

No specific treatment is available for ovarian hyperstimulation syndrome (OHSS), the most important complication in infertile women treated with gonadotropins. OHSS is caused by increased vascular permeability (VP) through ovarian hypersecretion of vascular endothelial growth factor (VEGF)-activating VEGF receptor 2 (VEGFR-2). We previously demonstrated in an OHSS rodent model that increased VP was prevented by inactivating VEGFR-2 with a receptor antagonist (SU5416). However, due to its toxicity (thromboembolism) and disruption of VEGFR-2-dependent angiogenic processes critical for pregnancy, this kind of compound cannot be used clinically to prevent OHSS. Dopamine receptor 2 (Dp-r2) agonists, used in the treatment of human hyperprolactinemia including pregnancy, inhibit VEGFR-2-dependent VP and angiogenesis when administered at high doses in animal cancer models. To test whether VEGFR-2-dependent VP and angiogenesis could be segregated in a dose-dependent fashion with the Dp-r2 agonist cabergoline, a well-established OHSS rat model supplemented with prolactin was used. A 100 microg/kg low-dose Dp-r2 agonist cabergoline reversed VEGFR-2-dependent VP without affecting luteal angiogenesis through partial inhibition of ovarian VEGFR-2 phosphorylation levels. No luteolytic effects (serum progesterone levels and luteal apoptosis unaffected) were observed. Cabergoline administration also did not affect VEGF/VEGFR-2 ovarian mRNA levels. Results in the animal model and the safe clinical profile of Dp-r2 agonists encouraged us to administer cabergoline to oocyte donors at high risk for developing the syndrome. Prophylactic administration of cabergoline (5-10 microg/kg x d) decreased the occurrence of OHSS from 65% (controls) to 25% (treatment). Therefore, a specific, safe treatment for OHSS is now available.

Dopamine modulates von Willebrand factor secretion in endothelial cells via D2-D4 receptors

OBJECTIVE

von Willebrand factor (VWF) is acutely released from endothelial cells in response to numerous calcium-raising agents (e.g. thrombin, histamine) and cAMP-raising agents (e.g. epinephrine, adenosine, vasopressin). In contrast, very few inhibitors of endothelial VWF secretion have been described. The neurotransmitter dopamine is a modulator of exocytosis in several endocrine cells, and is possibly involved in the regulation of several endothelial cell functions. We therefore investigated the effect of dopamine on endothelial VWF secretion.

RESULTS

Dopamine, D2/D3- and D4-specific agonists inhibited histamine- but not thrombin-induced VWF secretion. Expression of dopamine D2, D3 and D4 receptors was demonstrated by reverse transcription polymerase chain reaction (RT-PCR) in both human aortic (HAEC) and umbilical vein (HUVEC) endothelial cells. D2-D4 agonists did not inhibit histamine-induced rise in [Ca(2+)](i): they inhibited histamine-induced secretion even in the absence of extracellular calcium. Thus, the dopamine effects are not mediated by [Ca(2+)](i)-dependent signalling. D2/D3- and D4-specific agonists inhibited neither the rise in cAMP nor VWF secretion in response to epinephrine and adenosine, arguing against an effect on cAMP-mediated signalling. D1 and D5 receptors were not detected in HAEC or HUVEC by RT-PCR, and the D1/D5-specific agonist SKF 38 393 failed to modulate VWF secretion, arguing against a role for these receptors in endothelial exocytosis.

CONCLUSIONS

Dopamine inhibits histamine-induced endothelial exocytosis by activating D2-D4 receptor, via a mechanism distinct from [Ca(2+)](i)-or cAMP-mediated signaling. In contrast, D1 and D5 receptors are not functionally expressed in cultured endothelial cells. Dopamine agonists may be useful as inhibitors of endothelial activation in inflammation and cardiovascular disease.