Endothelins

Blockade of endothelin-1 with a novel series of 1,3,6-trisubstituted-2-carboxy-quinol-4-ones controls infection-associated preterm birth

Preterm birth (PTB) currently accounts for 13% of all births in the United States, with the leading cause of PTB being maternal infection. Endothelin-1, an extremely potent vasoconstrictor capable of increasing myometrial smooth muscle tone, has been shown to be up-regulated in the setting of infection in pregnancy, ultimately leading to PTB. In previous work, we have shown that infection-associated PTB is controlled in our murine model by using phospharamidon, an endothelin-converting enzyme-1 inhibitor; knocking down endothelin-converting enzyme-1 mRNA; or blocking the binding of endothelin-1 to the endothelin-A (ET(A)) receptor with either BQ-123 or with HJP-272, the 6-OH compound of our series of novel synthetic (ET(A)) receptor antagonists. In the current study, we show that HJP-272, a highly selective ET(A) receptor antagonist with an IC(50) of 70.1 nmol/L, binds in a noncompetitive manner to the ET(A) receptor. Additionally, we introduce n-propyl (HJP-286) and n-butyl (HJP-278) analogs of HJP-272. We find that the LD(50) of HJP-272, the analog in the series most effective in controlling preterm birth, is more than 20-fold higher than its therapeutic dose. Acute exposure to high doses of these compounds produces no histological changes in any organ, while chronic exposure produces only a rare hepatotoxic effect. These findings may be of clinical significance, as there is currently no FDA-approved therapy for women presenting with threatened preterm delivery.

High level of plasma endothelin-1 predicts development of hypertension in normotensive subjects

BACKGROUND

Endothelin-1 (ET-1) is a potent vasoconstrictor derived from the endothelium. However, most large scale cross-sectional studies in humans have indicated no relationship between plasma ET-1 levels and hypertension. The present study was designed to determine whether high plasma ET-1 levels predict the development of hypertension.

METHODS

A total of 1,492 subjects received a health examination in the Japanese cohort of Seven Countries Study in 1999, when, we examined blood pressure (BP), body mass index (BMI), and blood chemistries. Data on fasting ET-1 were obtained from 1,451 individuals. Seven years later, 1,261 subjects (494 males and 767 females) were re-examined (follow-up rate = 87%).

RESULTS

Of 814 normotensives (BP <140/90 mm Hg without antihypertensive medications) at baseline, 222 subjects developed hypertension. We divided the baseline plasma ET-1 levels into quartiles. The odds ratio for the development of hypertension after 7 years was 1.79 (95% confidence interval (CI): 1.08-2.96) in the highest quartile vs. the lowest quartile of ET-1 level after adjustment for confounding factors.

CONCLUSION

A high level of plasma ET-1 predicted the development of hypertension in normotensive subjects.

Zibotentan for the treatment of castrate-resistant prostate cancer

IMPORTANCE OF THE FIELD

Patients with prostate cancer who have progression of their disease while on androgen deprivation therapy have limited therapeutic options. Docetaxel is currently the only agent that increases overall survival in patients with metastatic, castration-resistant prostate cancer; additional agents are needed.

AREAS COVERED IN THIS REVIEW

This review will describe the importance of endothelin-1 (ET-1) for growth of prostate cancer cells, development of bone metastases, and pain responses; the preclinical data for zibotentan, a specific inhibitor of the ET(A) receptor; and the clinical development of atrasentan, a first-generation ET receptor inhibitor, and zibotentan, a more selective inhibitor of the ET(A) receptor.

WHAT THE READER WILL GAIN

Readers will understand the importance of ET-1 as a novel pathway to target for patients with castration-resistant prostate cancer due to its association with prostate cancer growth, metastases to bone, and pain. Readers will learn about the preclinical and clinical development of zibotentan, including the promising Phase II results that have resulted in an extensive Phase III clinical trials program.

TAKE HOME MESSAGE

Modulating the activity of ET-1 through the ET(A) receptor is a novel target for treating patients with metastatic, castration-resistant prostate cancer. There are currently three ongoing Phase III trials with zibotentan, a selective ET(A) inhibitor, to determine the effect of this agent on overall survival in these patients.

Evaluation of salivary endothelin-1 levels in oral squamous cell carcinoma and oral leukoplakia

Oral squamous cell carcinoma (OSCC) is the most frequent malignant neoplasia of the oral cavity, which largely compromises the patient's life quality. Therefore, the identification of biomarkers for this kind of cancer is essential to provide a better diagnosis and prognosis for patients. Endothelin-1 is a peptide produced mainly by endothelial cells, and might be found in several body fluids, such as saliva, milk, urine, cerebrospinal fluid and plasma. It has been demonstrated that expression of this peptide is increased in a great number of neoplasias, including oral carcinoma. The identification of salivary biomarkers would be a useful tool for scanning and monitoring patients with risk of developing OSCC, as well to early detect recurrence, or the formation of a new primary tumor. In the present study, we have analyzed the levels of endothelin-1 in saliva obtained from patients with OSCC or oral leukoplakia, in comparison to healthy control patients. This study also evaluated the salivary ET-1 levels in patients with complete remission of OSCC. The results revealed no statistical difference in salivary endothelin-1 levels, neither in OSCC nor in oral leukoplakia, even when conditions such as elderly, sex and hypertension were taken into consideration. Although, ET-1 might display an important role in OSCC, its levels in saliva do not seem to be a good marker of neoplasias grade or malignant transformation.

The matrix metalloproteases and endothelin-1 in infection-associated preterm birth

Preterm birth (PTB) is clinically defined as any delivery which occurs before the completion of 37 weeks of gestation, and is currently the most important problem in obstetrics. In the United States, PTB accounts for 12-13% of all live births, and, with the exception of fetuses suffering from anomalies, is the primary cause of perinatal mortality. While the risk factors for PTB are numerous, the single most common cause is intrauterine infection. As there is currently no FDA-approved therapy for infection-associated PTB, understanding the pathogenesis of preterm labor (PTL) and delivery should be given high priority. The matrix metalloproteinases (MMPs) are a family of enzymes that have been implicated in normal parturition as well as infection-triggered rupture of membranes and preterm birth. Several lines of evidence also suggest a role for endothelin-1 (ET-1) in infection-associated preterm delivery. This paper focuses on the evidence that the MMPs and ET-1 act in the same molecular pathway in preterm birth.

Endothelins and their receptors as biological markers for oral cancer

Oral squamous cell carcinoma (OSCC) is one of the most common malignancies recognized nowadays, and represents a public health problem. Its early detection is the better alternative to provide a good quality of life for the patients. During the last years, several studies have identified potential biomarkers of OSCC progression and prognosis. Endothelins and their receptors are involved in several pathophysiological conditions and in various cancer types. The present review article discusses whether the endothelin system would represent a biomarker for OSCC.

Luminal platelet aggregates in functional deficits in parenchymal vessels after subarachnoid hemorrhage

The pathophysiology of early ischemic injury after aneurysmal subarachnoid hemorrhage (SAH) is not understood. This study examined the acute effect of endovascular puncture-induced SAH on parenchymal vessel function in rat, using intravascular fluorescent tracers to assess flow and vascular permeability and immunostaining to assess structural integrity and to visualize platelet aggregates. In sham-operated animals, vessels were well filled with tracer administered 10s before sacrifice, and parenchymal escape of tracer was rare. At ten minutes and three hours after hemorrhage, patches of poor vascular filling were distributed throughout the forebrain. Close examination of these regions revealed short segments of narrowed diameter along many profiles. Most vascular profiles with reduced perfusion contained platelet aggregates and in addition showed focal loss of collagen IV, a principal component of basal lamina. In contrast, vessels were well filled at 24h post-hemorrhage, indicating that vascular perfusion had recovered. Parenchymal escape of intravascular tracer was detected at 10 min post-hemorrhage and later as plumes of fluorescence emanating into parenchyma from restricted microvascular foci. These data demonstrate that parenchymal microvessels are compromised in function by 10 min after SAH and identify focal microvascular constriction and local accumulation of luminal platelet aggregates as potential initiators of that compromise.

Endothelin-1 inhibits prolyl hydroxylase domain 2 to activate hypoxia-inducible factor-1alpha in melanoma cells

BACKGROUND

The endothelin B receptor (ET(B)R) promotes tumorigenesis and melanoma progression through activation by endothelin (ET)-1, thus representing a promising therapeutic target. The stability of hypoxia-inducible factor (HIF)-1alpha is essential for melanomagenesis and progression, and is controlled by site-specific hydroxylation carried out by HIF-prolyl hydroxylase domain (PHD) and subsequent proteosomal degradation.

PRINCIPAL FINDINGS

Here we found that in melanoma cells ET-1, ET-2, and ET-3 through ET(B)R, enhance the expression and activity of HIF-1alpha and HIF-2alpha that in turn regulate the expression of vascular endothelial growth factor (VEGF) in response to ETs or hypoxia. Under normoxic conditions, ET-1 controls HIF-alpha stability by inhibiting its degradation, as determined by impaired degradation of a reporter gene containing the HIF-1alpha oxygen-dependent degradation domain encompassing the PHD-targeted prolines. In particular, ETs through ET(B)R markedly decrease PHD2 mRNA and protein levels and promoter activity. In addition, activation of phosphatidylinositol 3-kinase (PI3K)-dependent integrin linked kinase (ILK)-AKT-mammalian target of rapamycin (mTOR) pathway is required for ET(B)R-mediated PHD2 inhibition, HIF-1alpha, HIF-2alpha, and VEGF expression. At functional level, PHD2 knockdown does not further increase ETs-induced in vitro tube formation of endothelial cells and melanoma cell invasiveness, demonstrating that these processes are regulated in a PHD2-dependent manner. In human primary and metastatic melanoma tissues as well as in cell lines, that express high levels of HIF-1alpha, ET(B)R expression is associated with low PHD2 levels. In melanoma xenografts, ET(B)R blockade by ET(B)R antagonist results in a concomitant reduction of tumor growth, angiogenesis, HIF-1alpha, and HIF-2alpha expression, and an increase in PHD2 levels.

CONCLUSIONS

In this study we identified the underlying mechanism by which ET-1, through the regulation of PHD2, controls HIF-1alpha stability and thereby regulates angiogenesis and melanoma cell invasion. These results further indicate that targeting ET(B)R may represent a potential therapeutic treatment of melanoma by impairing HIF-1alpha stability.

Anti-endothelin drugs in solid tumors

IMPORTANCE OF THE FIELD

The endothelin (ET) axis, which includes the biological functions of ETs and their receptors, has played a physiological role in normal tissue, acting as a modulator of vasomotor tone, tissue differentiation and development, cell proliferation and hormone production. Interestingly, it also functions in the growth and progression of various tumors. Several researchers have identified the blockade of the ET-1 receptor as a promising therapeutic approach.

AREAS COVERED IN THIS REVIEW

The clinical investigation of an orally bioavailable ET antagonist, atrasentan, in prostate cancer, is encouraging. In this neoplasia, it has shown antitumor activity, bone metastasis control and amelioration of cancer-related pain but improvement in time to progression and overall survival has still not been demonstrated. The clinical trials of other ET antagonists are reported. Literature research was performed by Pubmed and Pharmaprojects.

WHAT THE READER WILL GAIN

A comprehensive view about the use of atrasentan in the treatment of castration-resistant prostate cancer (CRPC) is provided together with the scientific rationale based on the function of ET and its receptor in various cancer development mechanisms.

TAKE HOME MESSAGE

Atrasentan seems to be active in CRPC, although strong scientific evidence is still to be found. Interesting clinical findings regard zibotentan.

Identification of a novel role for endothelins within the oviduct

Endothelins were first identified as potent vasoactive peptides; however, diversity in the biological function of these hormones is now evident. We have identified a novel role for endothelins: a requirement for these peptides within the oviduct during fertilization and/or early embryo development. In vivo, treatment after ovulation with a dual endothelin receptor antagonist (tezosentan) decreased the number of two-cell embryos that could be collected from within the oviducts. In vitro fertilization experiments showed that gamete viability and their ability to fertilize were not affected by treatment with this antagonist, suggesting that the effect observed in vivo was mediated by the oviduct itself. Expression of mRNA for all three isoforms of the endothelins and both receptor subtypes was detectable within the oviduct. Expression of mRNA for endothelin-3 was regulated by gonadotropins in epithelial cells of the oviduct and increased specifically within the isthmus of this structure. Immunostaining revealed localization of both endothelin receptors A and B to the columnar epithelial cells within the oviduct, suggestive of a local role for endothelins in the regulation of epithelial function and ultimately oviductal secretions. A microarray analysis revealed three likely endothelin-regulated protein networks for future analysis: the TGFbeta, IL-10, and CCAAT/enhancer-binding protein superfamilies. Overall, these results suggest a novel and requisite role for endothelins within the oviduct during fertilization and/or early embryo development.

Endothelin--biology and disease

Endothelins are important mediators of physiological and pathophysiologic processes including cardiovascular disorders, pulmonary disease, renal diseases and many others. Additionally, endothelins are involved in many other important processes such as development, cancer biology, wound healing, and even neurotransmission. Here, we review the cell and molecular biology as well as the prominent pathophysiological aspects of the endothelin system.

Endothelin-1 enhances cell migration via matrix metalloproteinase-9 up-regulation in brain astrocytes

The bioactivity of endothelin-1 (ET-1) has been suggested in the development of CNS diseases, including disturbance of water homeostasis and blood-brain barrier integrity. Recent studies suggest that hypoxic/ischemic injury of the brain induces release of ET-1, behaving through a G-protein coupled ET receptor family. The deleterious effects of ET-1 on astrocytes may aggravate brain inflammation. Increased plasma levels of matrix metalloproteinases (MMPs), in particular MMP-9, have been observed in patients with neuroinflammatory disorders. However, the detailed mechanisms underlying ET-1-induced MMP-9 expression remain unknown. In this study, the data obtained with zymographic, western blotting, real-time PCR, and immunofluorescent staining analyses showed that ET-1-induced MMP-9 expression was mediated through an ET(B)-dependent transcriptional activation. Engagement of G(i/o)- and G(q)-coupled ET(B) receptor by ET-1 led to activation of p42/p44 MAPK and then activated transcription factors including Ets-like kinase, nuclear factor-kappa B, and activator protein-1 (c-Jun/c-Fos). These activated transcription factors translocated into nucleus and bound to their corresponding binding sites in MMP-9 promoter, thereby turning on MMP-9 gene transcription. Eventually, up-regulation of MMP-9 by ET-1 enhanced the migration of astrocytes. Taken together, these results suggested that in astrocytes, activation of Ets-like kinase, nuclear factor-kappa B, and activator protein-1 by ET(B)-dependent p42/p44 MAPK signaling is necessary for ET-1-induced MMP-9 gene up-regulation. Understanding the mechanisms of MMP-9 expression and functional changes regulated by ET-1/ET(B) system on astrocytes may provide rational therapeutic interventions for brain injury associated with increased MMP-9 expression.

Genetic polymorphisms in endothelin-receptor-subtype-a-gene as susceptibility factor for obstructive sleep apnea syndrome

INTRODUCTION

Traits of obstructive sleep apnea syndrome (OSAS) such as impaired ventilatory control, craniofacial abnormalities, and concomitant cardiovascular diseases are associated with modified endothelin-1 gene (EDN-1) or endothelin-receptor-subtype-a (EDNRA) gene. The endothelin system regulates the cardiovascular homeostasis. EDN-1 interacts mainly with EDNRA for signal transduction. In our study we investigate associations of EDNRA-polymorphisms (four frequent polymorphisms with an allele frequency >5%) and OSAS severity.

METHODS

Three hundred ninety-three patients older than 18years, of Caucasian origin and with OSAS (AHI>5/h and daytime sleepiness) were investigated by cardiorespiratory polysomnography. In addition 58 control subjects with healthy sleep were recruited from nearly 300 volunteers. We analysed the EDNRA-polymorphisms E335E, H323H, G-231A and G+70C by polymerase-chain-reaction, restriction-fragment-length-polymorphism and real-time-PCR.

RESULTS

Carrier of the mutant G-231A allele had a significantly lower AHI (p=0.03, OR 0.53, 95% CI 0.3-0.94) when comparing patients and controls. When comparing OSAS severity groups without controls we could not detect significant correlations for the four investigated EDNRA-polymorphisms. Our data confirm that BMI (p<0.001) and male gender (p=0.02) are significantly associated with AHI. The allele frequencies were similar.

DISCUSSION

The genetic investigation of OSA remains important. Our control group was relatively small and we investigated 4 reasonable candidates out of more than 100 EDNRA-polymorphisms. The detected protective effect of the mutant G-231A allele needs further confirmation. Gene based research in OSAS should use genome wide scan and should still consider the endothelin system.

Cardiovascular responses to cold exposure

The prevalence of hypertension is increased in winter and in cold regions of the world. Cold temperatures make hypertension worse and trigger cardiovascular complications (stroke, myocardial infarction, heart failure, etc.). Chronic or intermittent exposure to cold causes hypertension and cardiac hypertrophy in animals. The purpose of this review is to provide the recent advances in the mechanistic investigation of cold-induced hypertension (CIH). Cold temperatures increase the activities of the sympathetic nervous system (SNS) and the renin-angiotensin system (RAS). The SNS initiates CIH via the RAS. Cold exposure suppresses the expression of eNOS and formation of NO, increases the production of endothelin-1 (ET-1), up-regulates ETA receptors, but down-regulates ETB receptors. The roles of these factors and their relations in CIH will be reviewed.

Endothelin B receptor antagonists block proliferation and induce apoptosis in glioma cells

The proliferative and antiapoptotic actions of endothelin (ET)-1 in cancer cells have been documented and ET receptor antagonists have been exploited as potential anticancer drugs. Glioblastoma cell lines express both ETA and ETB receptors and previous works have shown that ETB receptors are involved in the proliferation of different cancer cell types. In this study we have investigated the effects of two structurally unrelated ETB receptor antagonists, BQ788 and A192621, on cell survival, proliferation and apoptosis in 1321-N1, U87 and IPDDCA2 glioma cell lines. BQ788 and A192621 reduced glioma cells viability and proliferation assessed by BrdU incorporation and cell cycle analysis by flow cytometry, while in contrast the ETA receptor antagonist BQ123 had no effect on cell survival. TUNEL assay and immunocytochemical experiments showed that BQ788 and A192621 trigger apoptotic processes mainly via activation of the intrinsic mitochondrial pathway involving caspase-9 activation, AIF release and cytochrome c translocation. Furthermore, treatment with ETB antagonists downregulates ERK- and p38MAPK-dependent pathways but does not affect VEGF mRNA levels. Our findings support the hypothesis that ETB antagonists represent a new promising therapeutic strategy for the treatment of high grade gliomas.

The human prostacyclin receptor from structure function to disease

Thirty years have passed since Vane and colleagues first described a substance, prostanoid X, from microsomal fractions (later called prostacyclin) that relaxed rather than contracted mesenteric arteries. The critical role of prostacyclin in many pathophysiological conditions, such as atherothrombosis, has only recently become appreciated (through receptor knockout mice studies, selective cyclooxygenase-2 inhibition clinical trials, and the discovery of dysfunctional prostacyclin receptor genetic variants). Additionally, important roles in such diverse areas as pain and inflammation, and parturition are being uncovered. Prostacyclin-based therapies, currently used for pulmonary hypertension, are accordingly emerging as possible treatments for such diseases, fueling interests in structure function studies for the receptor and signal transduction pathways in native cells. The coming decade is likely to yield many further exciting advances.

Differential endothelin receptor expression and function in rat myometrial cells and leiomyoma ELT3 cells

Uterine leiomyoma are the most common benign tumors of the myometrium. We previously identified endothelin (ET)-1 as a proliferative and antiapoptotic factor in Eker rat-derived leiomyoma (ELT3) cells. A major role of ETB receptor in the prosurvival effect was revealed. Here we investigated, in ELT3 and myometrial cells, the respective contribution of ETA and ETB in the proliferative effect of ET-1. In myometrial cells, binding experiments show that ETA is almost exclusively expressed and stimulates phospholipase C (PLC) activity and ERK1/2 phosphorylation and proliferation. In ELT3 cells, ETB is expressed at about the same level as ETA, and the two receptors are differently coupled to Gi protein. The ETB agonist, sarafotoxin S6c, stimulates PLC activity 60% less than ET-1 but is as potent as ET-1 to increase ERK1/2 phosphorylation and induce proliferation. However, the ability of ETA to activate ERK1/2 is observed after ETB desensitization. Although ETA and ETB antagonists partially reduce ET-1 stimulated PLC activity, they are without effect on ET-1-induced ERK1/2 phosphorylation and proliferation. Only the simultaneous use of ETA and ETB antagonists reduces ET-1-triggered ERK1/2 activation. These unconventional properties of ETRs may reveal the existence of functional ETA-ETB heterodimers. Finally, treatment of ELT3 cells with ETB but not ETA-directed small interfering RNA reduces the proliferative effect of ET-1. All the data obtained in ELT3 cells strengthen the relation between ETB overexpression, which decreases the ETA to ETB ratio, and the ability of leiomyoma cells to highly proliferate and resist apoptosis.

Contribution of Endothelin 1 to the Vascular Effects of Diesel Exhaust Inhalation in Humans

Diesel exhaust inhalation impairs vascular function, and, although the underlying mechanism remains unclear, endothelin (ET) 1 and NO are potential mediators. The aim of this study was to identify whether diesel exhaust inhalation affects the vascular actions of ET-1 in humans. In a randomized, double-blind crossover study, 13 healthy male volunteers were exposed to either filtered air or dilute diesel exhaust (331±13 μg/m 3 ). Plasma concentrations of ET-1 and big-ET-1 were determined at baseline and throughout the 24-hour study period. Bilateral forearm blood flow was measured 2 hours after the exposure during infusion of either ET-1 (5 pmol/min) or the ET A receptor antagonist, BQ-123 (10 nmol/min) alone and in combination with the ET B receptor antagonist, BQ-788 (1 nmol/min). Diesel exhaust exposure had no effect on plasma ET-1 and big-ET-1 concentrations ( P >0.05 for both) or 24-hour mean blood pressure or heart rate ( P >0.05 for all). ET-1 infusion increased plasma ET-1 concentrations by 58% ( P <0.01) but caused vasoconstriction only after diesel exhaust exposure (−17% versus 2% after air; P <0.001). In contrast, diesel exhaust exposure reduced vasodilatation to isolated BQ-123 infusion (20% versus 59% after air; P <0.001) but had no effect on vasodilatation to combined BQ-123 and BQ-788 administration ( P >0.05). Diesel exhaust inhalation increases vascular sensitivity to ET-1 and reduces vasodilatation to ET A receptor antagonism despite unchanged plasma ET-1 concentrations. Given the tonic interaction between the ET and NO systems, we conclude that diesel exhaust inhalation alters vascular reactivity to ET-1 probably through its effects on NO bioavailability.

A phase I study of zibotentan (ZD4054) in patients with metastatic, castrate-resistant prostate cancer

PURPOSE

To assess the maximum well-tolerated dose (MWTD), dose limiting toxicity (DLT), pharmacokinetics (PK) and pharmacodynamics of zibotentan, a novel specific endothelin-A receptor antagonist, in patients with metastatic prostate cancer.

METHODS

Patients with metastatic, castrate-resistant prostate cancer (CRPC) were treated with escalating doses of oral zibotentan (ZD4054) 10-200 mg once daily. The initial cohort received 28 daily doses (Period 1). Patients who had evidence of clinical benefit and who had not met any of the criteria for withdrawal were allowed to receive zibotentan at their current dose level until they no longer derived clinical benefit (Period 2). PK of zibotentan and changes in prostate-specific antigen and bone markers were also assessed.

RESULTS

Sixteen patients were evaluable for the safety and single-dose PK analyses. Eleven patients completed Period 1, and nine patients proceeded to Period 2. DLTs were encountered at 22.5 mg; one patient had grade 3 dyspnea and peripheral edema and a second patient had grade 3 headache and intraventricular hemorrhage. Enrollment was expanded at the 15 mg dose level to further determine the safety and tolerability of zibotentan. No DLTs were seen at 15 mg, and the most frequent adverse events were headache, peripheral edema, fatigue, nasal congestion and nausea.

CONCLUSIONS

The MWTD for zibotentan was 15 mg orally daily. The predominant adverse events observed were consistent with those reported for this class of drugs, and prolonged stable disease was noted in some patients. Phase III studies with zibotentan in men with metastatic CRPC are ongoing.

Stromal endothelin B receptor-deficiency inhibits breast cancer growth and metastasis

The endothelin (ET) axis, often deregulated in cancers, is a promising target for anticancer strategies. Whereas previous investigations have focused mostly on ET action in malignant cells, we chose a model allowing separate assessment of the effects of ETs and their receptors ET(A)R and ET(B)R in the tumor cells and the stromal compartment, which is increasingly recognized as a key player in cancer progression. In homozygous spotting lethal rats (sl/sl), a model of constitutive ET(B)R deficiency, we showed significant reduction of growth and metastasis of MAT B III rat mammary adenocarcinoma cells overexpressing ET(A)R and ET-1 but negative for ET(B)R. Lack of stromal ET(B)R expression did not influence angiogenesis. However, it was correlated with diminished infiltration by tumor-associated macrophages and with reduced production of tumor necrosis factor-alpha, both known as powerful promoters of tumor progression. These effects were almost completely abolished in transgenic sl/sl rats, wherein ET(B)R function is restored by expression of an intact ET(B)R transgene. This shows that tumor growth and metastasis are critically dependent on ET(B)R function in cells of the microenvironment and suggests that successful ETR antagonist therapy should also target the stromal component of ET signaling

Effects of insulin resistance on endothelial progenitor cells and vascular repair

Insulin resistance, a key feature of obesity, the metabolic syndrome and Type 2 diabetes mellitus, results in an array of metabolic and vascular phenomena which ultimately promote the development of atherosclerosis. Endothelial dysfunction is intricately related to insulin resistance through the parallel stimulatory effects of insulin on glucose disposal in metabolic tissues and NO production in the endothelium. Perturbations characteristic of insulin resistance, including dyslipidaemia, inflammation and oxidative stress, may jeopardize the structural or functional integrity of the endothelium. Recent evidence suggests that endothelial damage is mitigated by endogenous reparative processes which mediate endothelial regeneration. EPCs (endothelial progenitor cells) are circulating cells which have been identified as mediators of endothelial repair. Several of the abnormalities associated with insulin resistance, including reduced NO bioavailability, increased production of ROS (reactive oxygen species) and down-regulation of intracellular signalling pathways, have the potential to disrupt EPC function. Improvement in the number and function of EPCs may contribute to the protective actions of evidence-based therapies to reduce cardiometabolic risk. In the present article, we review the putative effects of insulin resistance on EPCs, discuss the underlying mechanisms and highlight potential therapeutic manoeuvres which could improve vascular repair in individuals with insulin resistance.

Positive association between two polymorphic sites (+134 insA/delA and G198T) of the endothelin-1 gene and chronic obstructive pulmonary disease. A case-control study

Endothelin-1 (ET-1) has been implicated in the pathogenesis of Chronic Obstructive Pulmonary Disease (COPD) for establishing an inflammatory loop in the respiratory mucosa that could become independent from the initial irritant factor. Common causes of COPD exacerbations are associated with elevated ET-1 sputum concentrations. Genetic variants of the ET-1 gene, that lead to elevated ET-1 peptide levels, have not been investigated in COPD. We performed a case control, genetic study to assess possible associations of two polymorphisms of the ET-1 gene, an adenine insertion (+134 insA/delA) and a guanine to thymine transversion (G198T) with the COPD phenotype and disease severity. The genotypes of 209 subjects, 107 COPD smokers (patients) and 102 non-COPD smokers (controls) were examined. Statistical analysis revealed that the 3A/4A and 4A/4A genotypes were more common (P<0.01) in patients. Moreover, a protective effect against COPD of the TT genotype (G198T) was exhibited. COPD smokers were carrying more frequently the GG genotype and less frequently the TT genotype (P=0.047). Diplotypic analysis revealed that subjects carrying the 3A3A;TT genotype had a lower risk of COPD development (P=0.027). Within the COPD patient group carriers of the GT genotype had more often mild or moderate COPD compared to patients carrying the GG genotype (P=0.004). Haplotypic distribution revealed that carriers of the 4A:T and 4A:G haplotypes were in increased risk of COPD development. Additionally, patients with the 3A:G haplotype were in increased risk of developing severe COPD, whereas patients with the 3A:T and 4A:T had most probably mild-moderate COPD.

Hemifacial microsomia: from gestation to childhood

Hemifacial microsomia (HFM) is a variable, complex malformation involving asymmetric hypoplasia of the face and ear. Little is known about the risk factors for or consequences of HFM. In this study, we describe 3 studies that have been or are currently being conducted to further our understanding of this malformation. The first completed study examined whether HFM risk is related to maternal exposures that may affect blood flow. In that case-control study, interview data from 230 mothers of children in the case group and 678 mothers of children in the control group suggested that maternal use of vasoactive medications in the first trimester, particularly in combination with cigarette smoking, was associated with increased risks of HFM. The second study is currently underway, in which we are evaluating whether HFM risk is related to genetic variation in pathways associated with vasculogenesis and hemostasis, using DNA collected in the first study. The third ongoing study observes children with HFM to identify psychosocial, cognitive, dental, and medical sequelae. When the children from the original case-control study are 6 or 7 years of age, mothers and teachers complete self-administered questionnaires that cover a wide range of psychosocial development domains. Preliminary analyses of 115 case and 314 control children suggest that children with HFM may have worse teacher-reported academic performance and possibly higher levels of internalizing behavior problems than control children. When data on the full study sample are available, further analyses will determine whether the preliminary findings remain and if they vary by HFM phenotype, parenting style, or indicators of social risk.

[Endothelin system function in diabetic nephropathy]

Diabetic Nephropathy (DN) is a major chronic complication of diabetes mellitus (DM), and one of the main causes of new cases for dialysis, being associated with increasing mortality. The main risk factors for DN are hypertension, hyperglycemia, dyslipidemia, and genetic susceptibility. The renin-angiotensin system (RAS) plays an important role in genesis and progression of DN and there is evidence of an interrelationship between this system and the endothelins. Endothelins are powerful vasoconstrictor peptides and act as modulators of vasomotor tone, cell proliferation, and hormone production. These peptides act through two types of receptors (ET-A and ET-B) and are expressed on endothelial cells and vascular smooth-muscle cells. Activation of this receptor in renal cells leads to a complex signaling cascade resulting in stimulation of mesangial cell hypertrophy, proliferation, contraction, and extracellular matrix accumulation. These hemodynamic renal alterations are associated with the onset and progress of renal disease in DM. Elevated endothelin-1 (ET-1) levels have been reported in patients with DM. There is evidence suggesting that an increase in the production of ET-1 leads to glomerular damage. The use of ET receptor antagonists has been reported as renoprotective, correcting the early hemodynamic abnormalities in experimental DM, reinforcing the importance of this system in DN.

Involvement of NADPH oxidase and protein kinase C in endothelin-1-induced superoxide production in retinal microvessels

Redox signaling has been implicated in pathophysiological changes in the vascular system. We examined whether endothelin-1 (ET-1) increases the formation of superoxide anions in retinal microvessels. Freshly isolated retinal microvessels from rats were exposed to ET-1 (100 nM), and the intracellular superoxide formation in the retinal pericytes was assessed semi-quantitatively by time-lapse fluorometric analyses using hydroethidine. The receptor mechanisms were determined by BQ-123 and BQ-788, receptor antagonists for ET(A) and ET(B) receptors, respectively, and also by IRL-1620, a selective agonist for ET(B) receptors. In addition, the changes induced by adding apocynin (10 microM), myr-PKC (1.0 microM), allopurinol (100 microM), rotenone (10 microM), or L-NAME (100 microM) with ET-1 were evaluated. Microvessels were incubated with phorbol 12-myristate 13-acetate (PMA, 10nM), a protein kinase C (PKC) activator. Fluorometric analyses showed ethidium fluorescence-positive regions that coincided well with the location of retinal pericytes. The intracellular superoxide levels were significantly increased after addition of ET-1 (100 nM), and this elevation was suppressed by apocynin or myr-PKC. Other enzyme inhibitors including L-NAME had no effect. The ET-1-induced increase of superoxide was significantly suppressed by BQ-123 (1.0 microM), while effects of adding BQ-788 (1.0 microM) were insignificant. IRL-1620 (100 nM) did not increase superoxide formation significantly. PMA (10nM) mimicked the effect of ET-1. These results suggest that ET-1 increases the formation of superoxides in the retinal microvascular pericytes most likely by activating NADPH oxidase through ET(A) receptors. The activation of PKC may be involved in the mechanism. Thus, ET-1 may augment its vasoconstrictive effects through the formation of superoxide, which may impair the bioavailability of nitric oxide in the retinal microvasculature.

Leptin and endothelin-1 mediated increased extracellular matrix protein production and cardiomyocyte hypertrophy in diabetic heart disease

BACKGROUND

We investigated the role of leptin and its interaction with endothelin 1 (ET-1) in fibronectin (FN) synthesis and cardiomyocyte hypertrophy, two characteristic features of diabetic cardiomyopathy.

METHODS

Endothelial cells [human umbilical vein endothelial cells (HUVECs)] were examined for FN production and neonatal rat cardiomyocytes for hypertrophy, following incubation with glucose, ET-1, leptin and specific blockers. FN, ET-1, leptin and leptin receptors mRNA expression and FN protein were measured. Myocytes were also morphometrically examined. Furthermore, hearts from streptozotocin-diabetic rats were analysed.

RESULTS

Glucose caused increased FN mRNA and protein expression in HUVECs and cardiomyocytes hypertrophy along with upregulation of ET-1 mRNA, leptin mRNA and protein. Glucosemimetic effects were seen with leptin and ET-1. Leptin receptor antagonist (leptin quadruple mutant) and dual endothelin A endothelin B (ETA/ETB) receptor blocker bosentan normalized such abnormalities. Hearts from the diabetic animals showed hypertrophy and similar mRNA changes.

CONCLUSION

These data indicate that in diabetes increased FN production and cardiomyocyte hypertrophy may be mediated through leptin with its interaction with ET-1.

Elevated level of endothelin-1 in cerebrospinal fluid and lack of nitric oxide in basilar arterial plasma associated with cerebral vasospasm after subarachnoid haemorrhage in rabbits

BACKGROUND

The role of endothelin-1 (ET-1) and nitric oxide (NO) as two important mediators in the development of cerebral vasospasm (CVS) after subarachnoid haemorrhage (SAH) is controversial. The objective of this study was to determine whether local levels of ET-1 and NO in cerebral arterial plasma and/or in cerebrospinal fluid (CSF) are associated with the occurrence of CVS after SAH.

METHODS

CVS was induced using the one-haemorrhage rabbit model and confirmed by digital subtraction angiography of the rabbits' basilar artery on day 5. Prior to sacrifice, local CSF and basilar arterial plasma samples were obtained by a transclival approach to the basilar artery. Systemic arterial plasma samples were obtained. ET-1 levels were determined by immunometric technique (pg/ml +/- SEM) and total nitrate/nitrite level spectrophotometrically (micromol/l +/- SEM).

FINDINGS

Angiographic CVS was documented after SAH induction (n = 12, P < 0.05). The ET-1 level in CSF was significantly elevated by 27.3% to 0.84 +/- 0.08 pg/ml in SAH animals (n = 7) in comparison to controls (0.66 +/- 0.04 pg/ml, n = 7, P < 0.05). There was no significant difference in ET-1 levels in systemic and basilar arterial plasma samples of SAH animals compared to controls. A significant lack of local NO metabolites was documented in basilar arterial plasma after SAH (36.8 +/- 3.1 micromol/l, n = 6) compared to controls (61.8 +/- 6.2 micromol/l, n = 6, P < 0.01).

CONCLUSION

This study demonstrates that an elevated ET-1 level in CSF and local lack of NO in the basilar arterial plasma samples are associated with CVS after experimental SAH.

Frequent loss of endothelin-3 (EDN3) expression due to epigenetic inactivation in human breast cancer

Introduction

Endothelin (EDN) signalling plays a crucial role in cell differentiation, proliferation and migration processes. There is compelling evidence that altered EDN signalling is involved in carcinogenesis by modulating cell survival and promoting invasiveness. To date, most reports have focused on the oncogenic potential of EDN1 and EDN2, both of which are overexpressed in various tumour entities. Here, we aimed at a first comprehensive analysis on EDN3 expression and its implication in human breast cancer.

Methods

EDN3 mRNA expression was assessed by Northern blotting in normal human tissues (n = 9) as well as in matched pairs of normal and tumourous tissues from breast specimens (n = 50). EDN3 mRNA expression in breast cancer was further validated by real-time polymerase chain reaction (PCR) (n = 77). A tissue microarray was used to study EDN3 protein expression in breast carcinoma (n = 150) and normal breast epithelium (n = 44). EDN3 promoter methylation was analysed by methylation-specific PCR in breast cell lines (n = 6) before and after demethylating treatment, normal breast tissues (n = 17) and primary breast carcinomas (n = 128). EDN3 expression and methylation data were statistically correlated with clinical patient characteristics and patient outcome.

Results

Loss of EDN3 mRNA expression in breast cancer, as initially detected by array-based expression profiling, could be confirmed by Northern blot analysis (> 2-fold loss in 96%) and real-time PCR (> 2-fold loss in 78%). Attenuated EDN3 expression in breast carcinoma was also evident at the protein level (45%) in association with adverse patient outcome in univariate (P = 0.022) and multivariate (hazard ratio 2.0; P = 0.025) analyses. Hypermethylation of the EDN3 promoter could be identified as the predominant mechanism leading to gene silencing. Reversion of the epigenetic lock by 5-aza-2'-deoxycytidine and trichostatin A resulted in EDN3 mRNA re-expression in vitro. Furthermore, EDN3 promoter hypermethylation was detected in 70% of primary breast carcinomas with significant association to loss of EDN3 mRNA expression (P = 0.005), whilst normal matched breast tissues revealed no EDN3 promoter methylation.

Conclusions

EDN3 is a frequent target of epigenetic inactivation in human breast cancer, potentially contributing to imbalanced EDN signalling commonly found in this disease. The clinical implication supports the view that EDN3, in contrast to EDN1 and EDN2, may act as natural tumour suppressor in the human mammary gland.

Endothelin receptor selectivity: evidence from in vitro and pre-clinical models of scleroderma

Scleroderma [systemic sclerosis (SSc)] is a spectrum of connective tissue diseases characterized by micro- and macro-vasculopathy, inflammation and autoimmunity and tissue remodelling that often leads to excessive scarring and fibrosis in both interstitial and vascular compartments. Pre-clinical investigations and gene association studies have led to improved understanding of the cell and molecular mechanisms underlying disease pathogenesis and to the identification of key molecular candidates that may represent potentially useful disease biomarkers and effective therapeutic targets. Studies on the endothelin (ET) system, pre-dominantly ET-1 and the cell surface receptors [type A (ET(A))] and type B (ET(B))], have provided evidence for an important role of this system in the vascular and fibrotic pathologies in SSc. To date, promising clinical results, utilizing dual/mixed ET receptor antagonism have been obtained in two of the vascular complications associated with SSc, ischaemic digital ulceration and pulmonary arterial hypertension. Evidence suggests that ET-1 is able to activate and re-program the functional phenotypes of vascular smooth muscle cells, microvascular pericytes and tissue fibroblasts into pro-fibrogenic cell populations with myofibroblasts-like properties. The impact of receptor-selective, over mixed-receptor, antagonism has also been studied in vitro with respect to cell differentiation and proliferation, extracellular matrix synthesis, production and deposition and in pathological cellular contraction. However, the complexity of the ET system, potential for receptor cross-talk, interactions with down-stream signal transduction cascades, as well as the potent inter-relationships with other important ligand-receptor pathways have made in vivo studies difficult to unravel. Moreover, little information is available on the role of the ET system and receptor selectivity in the recruitment and activation of mesenchymal progenitor cells in tissue remodelling and fibrosis or on the early inflammatory response. Here, we discuss the available pre-clinical evidence for the role of the ET system in tissue repair, scarring and fibrosis, using the connective tissue diseases SSc and model systems of fibrogenesis.

Preclinical anticancer activity of the specific endothelin A receptor antagonist ZD4054

Endothelins are a family of small peptides (ET-1, ET-2, and ET-3) that mediate various physiological processes of mitogenesis, repair, and tissue differentiation by binding to endothelin A (ETA) and endothelin B (ETB) cell surface receptors. Activation of the ETA receptor by ET-1 has emerged as an important factor promoting tumor cell proliferation, survival, angiogenesis, migration, invasion, and metastasis in several tumor types including prostate, ovary, colon, cervix, breast, and lung. As activation of the ETB receptor has an opposing effect, inducing cell death by apoptosis, a rationale exists for specific antagonism of the ETA receptor as a treatment strategy for cancer. ZD4054 is a specific ETA receptor antagonist currently being evaluated in hormone-resistant prostate cancer in phase III clinical trials. In vitro, ZD4054 reversed ET-1-mediated inhibition of apoptosis in serum-deprived rat A10 and human VLTR-16 cells in a concentration-dependent manner. ZD4054 inhibited ET-1-mediated survival signaling pathways and decreased proliferation in ovarian OVCA 433 and HEY cells and in prostate PPC-1 and LAPC-4 cells. In A673 rhabdomyosarcoma cells, ET-1-induced phosphorylation of FAK, FAK, and paxillin was reversed with ZD4054, inhibiting the invasive phenotype mediated by these adhesion factors. In vivo, ZD4054 led to a significant reduction in tumor growth in animals bearing ovarian tumor xenografts, and significantly inhibited tumor angiogenesis. Pretreatment with ZD4054 also significantly delayed the onset of metastatic events after intracardiac injection of bladder TSU-Pr1-B1 cells in mice. These preclinical data show the potential anticancer effects of the specific blockade of the ETA receptor with ZD4054, supporting a program of clinical investigation.

Transcriptional control of human adipose tissue blood flow

Adipose tissue is highly vascularized and expresses several genes involved in vasodilatory and vasoconstrictive regulation. We took a transcriptional approach to study the relationships between adipose tissue blood flow (ATBF) and genes involved in vasoactive processes. As ATBF is impaired in obesity, we tested whether body weight interfered with the transcriptional regulation of ATBF. The mRNA content (real-time PCR) of 26 genes was quantified in subcutaneous adipose tissue biopsies from 28 healthy men with a wide range of BMI. ATBF was measured by 133Xe washout. None of the transcripts was related to fasting ATBF (ATBFF). However, the expression levels of two transcripts involved in vasodilation (natriuretic peptide receptor A/guanylate cyclase A (NPRA) and endothelial nitric oxide synthase (eNOS)) were positively associated with postprandial ATBF (r = 0.53 and r = 0.55, P < 0.01, respectively). Although BMI was negatively related to the mRNA content of NPRA and eNOS (r = -0.78 and r = -0.63, P < 0.01, respectively), the strong associations found between postprandial ATBF and the two transcripts were not affected by obesity. Several genes were subject to coordinated regulation of expression. This study demonstrates for the first time that ATBF responsiveness to nutrient intake is related to the transcription of two genes expressed in adipose tissue and directly involved in vasodilatory actions (eNOS and NPRA), suggesting that part of the regulation of ATBF is at a transcriptional level. Interestingly, these associations were not secondary to changes in BMI. We also found that certain genes involved in the regulation of ATBF are subject to coordinate regulation of expression suggesting physiological autoregulation.

Diabetic macular edema: pathogenesis and treatment

Diabetic macular edema is a major cause of visual impairment. The pathogenesis of macular edema appears to be multifactorial. Laser photocoagulation is the standard of care for macular edema. However, there are cases that are not responsive to laser therapy. Several therapeutic options have been proposed for the treatment of this condition. In this review we discuss several factors and mechanisms implicated in the etiology of macular edema (vasoactive factors, biochemical pathways, anatomical abnormalities). It seems that combined pharmacologic and surgical therapy may be the best approach for the management of macular edema in diabetic patients.

Pharmacogenetic effect of an endothelin-1 haplotype on response to bucindolol therapy in chronic heart failure

BACKGROUND

Beta-blocker therapy has become a mainstay therapy for the over 5 million patients with chronic heart failure in the United States. Variation in clinical response to beta-blockers is a well-known phenomenon and may be because of genetic differences between patients. We hypothesized that variation in genes of the endothelin system mediate the clinical response to beta-blockers in heart failure.

METHODS

Single nucleotide polymorphisms (SNPs) in six endothelin system genes were genotyped in 309 heart failure patients in a randomized trial of bucindolol versus placebo therapy. We adjusted for multiple comparisons and tested for association between genotype and time to two prospective endpoints.

RESULTS

Nine SNPs were sufficiently common to undergo statistical analysis. The SNPs had no significant effect on prospective outcomes in the placebo group, or on the primary endpoint of time to death in either arm. Two SNPs (IVS-4 G/A and Lys198Asn) in the endothelin-1 gene, however, predicted time to the combined endpoint of heart failure hospitalization or all-cause death in bucindolol-treated patients. The alleles at these SNPs were in tight linkage disequilibrium appearing on either of two complementary haplotypes. A 'dose-response' trend was observed, with participants carrying the rarer haplotype having the highest hazard ratios as compared to the relative 'protective' effect of the common haplotype.

CONCLUSION

A common endothelin-1 gene haplotype may be a pharmacogenetic predictor of a favorable clinical response to beta-blocker therapy in heart failure patients. The existence of a less common 'high-risk' haplotype could identify a subpopulation of heart failure patients destined to respond poorly to beta-blocker therapies.

Ambrisentan for the treatment of pulmonary arterial hypertension

Ambrisentan is an endothelin receptor antagonist (ERA) that was recently approved for treatment of pulmonary arterial hypertension (PAH). Endothelin (ET) is a potent vasoconstrictor with mitogenic, hypertrophic and pro-inflammatory properties that is upregulated in pulmonary hypertensive diseases. The biologic effects of ET are mediated by 2 cell surface receptors termed ET_A and ET_B. ET_A mediates the vasoconstrictor effect of ET on vascular smooth muscle, whereas ET_B is expressed primarily on vascular endothelial cells where it induces nitric oxide synthesis and acts to clear ET from the circulation. Ambrisentan is the first ET_A selective ERA approved for use in the US. Recently published clinical trials in patients with PAH demonstrate improvement in functional capacity and pulmonary hemodynamics similar to other ET_A selective and non-selective ERAs. Its once daily dosing and lower incidence of serum aminotransferase elevation offer potential advantages over other ERAs, but further experience with this agent is needed to fully understand its long-term efficacy and safety. This review discusses the endothelin family of proteins and receptors and their role in the pathophysiology of pulmonary hypertensive diseases. It also examines the development process, safety profile and clinical trials that have resulted in ambrisentan being approved for treatment of PAH.

Fibrinogen-induced endothelin-1 production from endothelial cells

We previously demonstrated that fibrinogen (Fg) binding to the vascular endothelial intercellular adhesion molecule-1 (ICAM-1) leads to microvascular constriction in vivo and in vitro. Although a role of endothelin-1 (ET-1) in this Fg-induced vasoconstriction was suggested, the mechanism of action was not clear. In the current study, we tested the hypothesis that Fg-induced vasoconstriction results from ET-1 production by vascular endothelial cells (EC) and is mediated by activation of extracellular signal-regulated kinase -1/2 (ERK-1/2). Confluent, rat heart microvascular endothelial cells (RHMECs) were treated with one of the following: Fg (2 or 4 mg/ml), Fg (4 mg/ml) with ERK-1/2 kinase inhibitors (PD-98059 or U-0126), Fg (4 mg/ml) with an antibody against ICAM-1, or medium alone for 45 min. The amount of ET-1 formed and the concentration of released von Willebrand factor (vWF) in the cell culture medium were measured by ELISAs. Fg-induced exocytosis of Weibel-Palade bodies (WPBs) was assessed by immunocytochemistry. Phosphorylation of ERK-1/2 was detected by Western blot analysis. Fg caused a dose-dependent increase in ET-1 formation and release of vWF from the RHMECs. This Fg-induced increase in ET-1 production was inhibited by specific ERK-1/2 kinase inhibitors and by anti-ICAM-1 antibody. Immunocytochemical staining showed that an increase in Fg concentration enhanced exocytosis of WPBs in ECs. A specific endothelin type B receptor blocker, BQ-788, attenuated the enhanced phosphorylation of ERK-1/2 in ECs caused by increased Fg content in the culture medium. The presence of an endothelin converting enzyme inhibitor, SM-19712, slightly decreased Fg-induced phosphorylation of ERK-1/2, but inhibited production of Fg-induced ET-1 production. These results suggest that Fg-induced vasoconstriction may be mediated, in part, by activation of ERK-1/2 signaling and increased production of ET-1 that further increases EC ERK-1/2 signaling. Thus, an increased content of Fg may enhance vasoconstriction through increased production of ET-1.

Endothelin-1 enhances the expression of the androgen receptor via activation of the c-myc pathway in prostate cancer cells

Increasing evidence suggests that androgen independent prostate cancer (PC) maintains a functional androgen receptor (AR) pathway despite the low levels of circulating androgen following androgen withdrawal, the molecular mechanisms of which are not well defined yet. To address this question, we investigated the effects of endothelin-1 (ET-1) on AR expression. Western analysis and RT-PCR revealed that in the presence of ET-1, levels of AR significantly increased in a time- and dose-dependent manner in LNCaP cells. Pretreatments with inhibitors of Src and phosphoinositide kinase 3 (PI-3K) suppressed ET-1-induced AR expression. As ET-1 was reported to cause a transient increase in c-myc mRNA levels, we examined the involvement of c-myc in ET-1-mediated AR expression. Transient transfection of c-myc siRNA neutralized ET-1-induced AR expression, suggesting that AR induction by ET-1 is c-myc dependent. AR can regulate the transcription of its own gene via a mechanism in which c-myc plays a crucial role. Therefore, we assessed if ET-1-induced-c-myc leads to the enhancement of AR transcription. Reporter gene assays using the previously identified AR gene enhancer containing a c-myc binding site were conducted in LNCaP cells. We found that ET-1 induced reporter gene activity from the construct containing the wild-type but not mutant c-myc binding site. Chromatin immunoprecipitation assays confirmed that ET-1 increased interaction between c-myc and c-myc binding sites in AR enhancer, suggesting that ET-1-induced AR transcription occurs via c-myc-mediated AR transcription. Together, these data support the notion that ET-1, via Src/PI-3K signaling, augments c-myc expression leading to enhanced AR expression in PC.

Paracrine regulation of the resumption of oocyte meiosis by endothelin-1

Mammalian oocytes remain dormant in the diplotene stage of prophase I until the resumption of meiosis characterized by germinal vesicle breakdown (GVBD) following the preovulatory gonadotropin stimulation. Based on genome-wide analysis of peri-ovulatory DNA microarray to identify paracrine hormone-receptor pairs, we found increases in ovarian transcripts for endothelin-1 and endothelin receptor type A (EDNRA) in response to the preovulatory luteinizing hormone (LH)/human chorionic gonadotropin (hCG) stimulation. Immunohistochemical analyses demonstrated localization of EDNRA in granulosa and cumulus cells. In cultured preovulatory follicles, treatment with endothelin-1 promoted oocyte GVBD. The stimulatory effect of endothelin-1 was blocked by cotreatment with antagonists for the type A, but not related type B, receptor. The stimulatory effect of hCG on GVBD was partially blocked by the same antagonist. The endothelin-1 promotion of GVBD was found to be mediated by the MAPK/ERK pathway but not by the inhibitory G protein. Studies using cumulus-oocyte complexes and denuded oocytes demonstrated that the endothelin-1 actions are mediated by cumulus cells. Furthermore, intrabursal administration with endothelin-1 induced oocyte GVBD in preovulatory follicles. Our findings demonstrate a paracrine role of endothelin-1 in the induction of the resumption of meiosis and provide further understanding on the molecular mechanisms underlying the nuclear maturation of oocytes induced by the preovulatory LH surge.

Clazosentan, an endothelin receptor antagonist, prevents early hypoperfusion during the acute phase of massive experimental subarachnoid hemorrhage: a laser Doppler flowmetry study in rats

Object

Acute cerebral hypoperfusion and early disturbances in cerebral autoregulation after subarachnoid hemorrhage (SAH) have been demonstrated repeatedly and have been shown to contribute significantly to acute and secondary brain injury. Acute vasoconstriction has been identified as a major contributing factor. Although increasing evidence implicates endothelin (ET)–1 in the development of cerebral vasospasm, its role in the acute phase after SAH has not yet been investigated. The purpose of this study was to further determine the role of ET in the first minutes to hours after massive experimental SAH induced by prophylactic treatment with the ET receptor antagonist clazosentan.

Methods

Subarachnoid hemorrhage was induced in 22 anesthetized rats by injection of 0.5-ml arterial, nonheparinized blood into the cisterna magna over the course of 60 seconds. In addition to monitoring intracranial pressure (ICP) and mean arterial blood pressure, laser Doppler flowmetry (LDF) probes were placed stereotactically over the cranial windows to allow online recording of cerebral blood flow (CBF) starting 30 minutes prior to SAH and continuing for 3 hours after SAH. The control group (Group A, 11 rats) received vehicle saline solution via a femoral catheter before SAH, and a second group (Group B, 11 rats) was treated prophylactically with clazosentan, an ETA receptor antagonist. Treatment was started 30 minutes prior to bolus injection (1 mg/kg body weight), immediately followed by a continuous infusion of 1 mg/kg body weight/hr until the end of the experiment.

Results

Induction of SAH in the rats caused an immediate increase in ICP, which led to an acute decrease in cerebral perfusion pressure (CPP). Perfusion, as measured with LDF, was found to have decreased relative to baseline by 30 ±20% in the control group and 20 ±9% in the clazosentan-treated group. Intracranial pressure and CPP recovered comparably in both groups thereafter within minutes. Control animals demonstrated prolonged hypoperfusion with a loss of autoregulation independent of CPP changes, finally approaching 80% of baseline values toward the end of the experiment. The authors observed that clazosentan did not influence peracute CPP-dependent hypoperfusion, but prevented continuous CBF reduction. Laser Doppler flowmetry perfusion readings remained depressed in control animals at 73 ±19% of baseline in comparison with 106 ±25% of baseline in clazosentan-treated animals (p = 0.001).

Conclusions

The first hours after a massive experimental SAH can be characterized by a CPP-independent compromise in cerebral perfusion. Prophylactic treatment with the ET receptor antagonist clazosentan prevented hypoperfusion. It is known that in the first days after SAH, a reduction in CBF correlates clinically to high-grade SAH. Although research currently focuses on delayed vasospasm, administration of vasoactive drugs in the acute phase of SAH may reverse perfusion deficits and improve patient recovery.

Endothelin receptor B antagonists decrease glioma cell viability independently of their cognate receptor

BACKGROUND

Endothelin receptor antagonists inhibit the progression of many cancers, but research into their influence on glioma has been limited.

METHODS

We treated glioma cell lines, LN-229 and SW1088, and melanoma cell lines, A375 and WM35, with two endothelin receptor type B (ETRB)-specific antagonists, A-192621 and BQ788, and quantified viable cells by the capacity of their intracellular esterases to convert non-fluorescent calcein AM into green-fluorescent calcein. We assessed cell proliferation by labeling cells with carboxyfluorescein diacetate succinimidyl ester and quantifying the fluorescence by FACS analysis. We also examined the cell cycle status using BrdU/propidium iodide double staining and FACS analysis. We evaluated changes in gene expression by microarray analysis following treatment with A-192621 in glioma cells. We examined the role of ETRB by reducing its expression level using small interfering RNA (siRNA).

RESULTS

We report that two ETRB-specific antagonists, A-192621 and BQ788, reduce the number of viable cells in two glioma cell lines in a dose- and time-dependent manner. We describe similar results for two melanoma cell lines. The more potent of the two antagonists, A-192621, decreases the mean number of cell divisions at least in part by inducing a G2/M arrest and apoptosis. Microarray analysis of the effects of A-192621 treatment reveals up-regulation of several DNA damage-inducible genes. These results were confirmed by real-time RT-PCR. Importantly, reducing expression of ETRB with siRNAs does not abrogate the effects of either A-192621 or BQ788 in glioma or melanoma cells. Furthermore, BQ123, an endothelin receptor type A (ETRA)-specific antagonist, has no effect on cell viability in any of these cell lines, indicating that the ETRB-independent effects on cell viability exhibited by A-192621 and BQ788 are not a result of ETRA inhibition.

CONCLUSION

While ETRB antagonists reduce the viability of glioma cells in vitro, it appears unlikely that this effect is mediated by ETRB inhibition or cross-reaction with ETRA. Instead, we present evidence that A-192621 affects glioma and melanoma viability by activating stress/DNA damage response pathways, which leads to cell cycle arrest and apoptosis. This is the first evidence linking ETRB antagonist treatment to enhanced expression of DNA damage-inducible genes.