The Human Preproendothelin-1 Gene

The Lack of Relationship between an Endothelin-1 Gene Polymorphism (Ala288Ser) and Incidence of Hypertension: A Retrospective Cohort Study among Japanese Workers

BACKGROUND

Some case-control association studies revealed the relationship between some endothelin-1 (ET-1) gene polymorphisms and blood pressure. Because no report was available about the relationship between any ET-1 gene polymorphism and incidence of hypertension, we examined the relationship between novel ET-1 gene polymorphism (G862T / Ala288Ser in exon 5) and incidence of hypertension by a retrospective cohort study.

METHODS

The subjects were Japanese workers at a company in Shimane Prefecture in Japan. The polymorphism with genome DNA extracted from the blood of the workers was analyzed using the polymerase chain reaction confronting two pair primers method. According to the results of two regular health checkups with a 6-year interval, the study population was divided into two groups by blood pressure and antihypertensive treatment in 1998, after excluding people who had hypertension in 1992.

RESULTS

There were 133 (93 males and 40 females) incidences of hypertension observed among the study population of 922 (540 males and 382 females). In the univariate analysis, odds ratios of Ala/Ser and Ser/Ser against Ala/Ala were 0.98 (95% confidence interval [CI]): 0.7-1.4) and 0.79 (95% CI: 0.4-1.6), respectively. In the multivariate analysis adjusted for sex, age, body mass index, serum total cholesterol, fasting blood sugar, and smoking and drinking habits, odds ratios for Ala/Ser and Ser/Ser against Ala/Ala were 0.97 (95% CI: 0.7-1.4) and 0.75 (95% CI: 0.4-1.5), respectively.

CONCLUSIONS

The ET-1 gene polymorphism in this study did not seem to be associated with the incidence of hypertension among the Japanese workers.

Comparative Sequences of Canine and Feline Endothelin-1

BACKGROUND

Endothelin-1 (ET-1, "mature ET-1") is a potent vasoconstrictor peptide that is made along with "big ET-1" from its precursor, preproET-1. Increased plasma concentrations of ET-1 and big ET-1 occur with various forms of cardiovascular disease in humans. Our laboratory is investigating plasma endothelins as diagnostic tests of cardiovascular disease in dogs and cats; however, commercial immunoassays designed specifically for use in dogs and cats are limited.

OBJECTIVE

Amino acid sequences of feline and canine big ET-1 were obtained and used to predict antibody cross-reactivity with immunoassay test kits from other species.

METHODS

Genomic DNA was extracted from peripheral blood and total RNA was extracted from canine and feline left ventricles for reverse transcription polymerase chain reaction (PCR) and PCR amplification of segments of the canine and feline preprohormone containing the big ET-1 sequences. The derived amino acid sequences were compared with known big ET-1 and ET-1 sequences of several other species, including human, mouse, and rat.

RESULTS

Feline and canine big ET-1 had 87-97% and 89-100% homology, respectively, with that of other mammalian species. Canine ET-1 was identical to human, mouse, and rat ET-1. In contrast, the amino acid sequence of feline ET-1 was unique owing to a leucine for methionine substitution at position 7.

CONCLUSIONS

It is highly likely that anti-human and anti-rodent ET-1 antibodies will cross-react with mature canine ET-1. In contrast, antibodies to mature ET-1 intended for use with feline tissues and antibodies to big ET-1 in either dogs or cats may have partial or no cross-reactivity depending on the peptide sequences used to produce the antibodies.

Mechanisms of 17beta-estradiol on the production of ET-1 in ovariectomized rats

In order to clarify the mechanism underlying the possible preventive effect of estrogen on atherogenesis, we investigated the role of 17beta-estradiol (E2) in the regulation of endothelin-1 (ET-1) production in ovariectomized rats, which may contribute to atherogenesis. Female Spragure-Dawly rats were randomly divided into three groups: sham-operated group (sham), ovariectomized group (OVX) and 17beta-estradiol replacement group (OVX + E2, 20 microg(-1).kg.d(-1),s.c.). 4 weeks after operation, the plasma concentration of ET-1, clearance of ET-1, functional ECE activity and preproET-1 mRNA expression in aorta were measured. Concentration of plasma ET-1 change from 107.8 +/- 18.3 pg/ml (sham) and 135.5 +/- 27.6 pg/ml (OVX + E2) to 190.7 +/- 25.5 pg/ml (OVX ) (n = 8, p < 0.05). There was no significant difference in the clearance of 125IET-1 among three groups (p > 0.05). Functional ECE activity was increased in OVX group in comparison to that in sham group (p < 0.05). The OVX increased the preproET-1 mRNA expression in sham, whereas treatment with estrogen reversed these changes (p < 0.05). The present study have shown that estrogen down-regulates plasma ET-1 levels by inhibiting the preproET-1 mRNA expression and functional ECE activity. Clearance of ET-1 was not affected. Inhibition of ET-1 production mediated by modulating ECE activity may be one of the novel mechanisms of the protective of estrogens on the cardiovascular system.

Role for nuclear factor-kappaB and signal transducer and activator of transcription 1/interferon regulatory factor-1 in cytokine-induced endothelin-1 release in human vascular smooth muscle cells

Endothelin-1 (ET-1) is a potent vasoconstrictor and growth-promoting mediator that is involved in the maintenance of vascular tone within the healthy circulation. However, a pathogenic role has been implicated by its overproduction in a number of cardiovascular diseases, which include pulmonary hypertension, congestive heart failure, atherosclerosis, and coronary vasospasm. ET-1 mRNA expression and peptide production in human vascular smooth muscle cells (HVSMCs) are markedly increased by exposure to tumor necrosis factor-alpha and interferon-gamma. The intracellular signaling mechanism involved in this pathway is not known. Because the transcription factors nuclear factor-kappaB (NF-kappaB), signal transducer and activator of transcription 1 (STAT1), and interferon regulatory factor-1 (IRF-1) often mediate the effects of cytokines in target cells the aim of this study was to determine whether the production of ET-1 after exposure of HVSMCs to cytokines depends upon synergism between NF-kappaB and STAT1/IRF-1. Immunoblotting showed that cytokine-stimulation of ET-1 release in VSMCs involves nuclear translocation of NF-kappaB and STAT1. Cytokines also induced an increase in IRF-1 protein expression. Antisense oligonucleotides to NF-kappaB, STAT1, and IRF-1 significantly inhibited cytokine induced ET-1 release. In conclusion, NF-kappaB, STAT1, and IRF-1 activation are involved in the stimulation by cytokines of ET-1 release from HVSMCs. However, nuclear run-on assays would provide definitive proof that ET-1 is regulated transcriptionally by cytokines. Because up-regulated production of ET-1 within VSMCs may underlie the causative role of ET-1 in a number of disease states, this finding indicates that NF-kappaB, STAT1, and IRF-1 within HVSMCs could be central to a number of vascular pathologies and that inhibition of this pathway could be of therapeutic benefit.

Intravenous vasodilator therapy in congestive heart failure

The prevalence of congestive heart failure (CHF) is increasing in the US and worldwide, partly because patients are living longer. Treatment of CHF is mostly on an outpatient basis, but inpatient care is required for decompensated CHF, acute CHF or poor response to outpatient treatment. Control of symptoms is usually achieved by diuresis. Intravenous (IV) vasodilators are an important adjunct to the inpatient treatment of CHF. They work mainly by reducing the afterload on the myocardium although preload reduction also occurs. After clinical stabilisation, the goal is to switch to a maintenance oral regimen to be continued as outpatient therapy. The range of IV vasodilators available for inpatient treatment of CHF includes nitrates, phosphodiesterase inhibitors, dobutamine, morphine, ACE inhibitors, B-type natriuretic peptides and endothelin receptor antagonists. As each agent may have a different mechanism or site of action, each agent may affect preload, contractility or afterload to a different extent and it may be desirable to choose one over the other in a particular clinical setting. Examples of standard therapy include dobutamine, milrinone and nitroglycerin. Nesiritide, a B-type natriuretic peptide, is a newer vasodilator and US FDA approved for use in acute CHF. However, most studies with this agent have been in small numbers of patients with anecdotal findings. Larger studies are warranted to pinpoint the efficacy and adverse effects of this agent. It is primarily used to reduce the acuity of decompensated CHF on admission to hospital.Endothelin receptor antagonists show promise in the management of acute CHF, but continue to be investigational. Long-term data on their efficacy and safety are limited. None of the endothelin receptor antagonists are FDA approved for use in patients with CHF.

Pharmacologic Blockade of the Renin-Angiotensin System: Vascular Benefits Beyond Commonly Understood Pharmacologic Actions

Angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs) are recognized primarily for their use in hypertension, in heart failure, and after myocardial infarction. New evidence, particularly with ACE inhibitors, has shown their ability to reduce acute coronary events associated with atherosclerosis in patients without a history of the aforementioned cardiac conditions. This is likely due to inhibitory effects on the renin-angiotensin system--a system that adversely influences fibrinolytic balance, vascular endothelial function, and vascular inflammation, all key components of atherosclerotic progression and adverse coronary outcomes. Results of various studies suggest favorable effects of ACE inhibitors and ARBs on markers of these components, including effects on plasminogen activator inhibitor-1, endothelin-1, and nitric oxide by ACE inhibitors, and effects on vascular cell adhesion molecule-1 and C-reactive protein by ARBs. Although early evidence suggests that ACE inhibitors may provide a greater beneficial effect on some of these markers compared with ARBs, and that certain ACE inhibitors may provide greater vascular benefits than others, further investigation is required to verify such findings. Overall, understanding the distinct coronary vascular benefits of these agents will emphasize the importance of using them, particularly ACE inhibitors, to improve outcomes in patients with coronary atherosclerotic disease.

A role for increased mRNA stability in the induction of endothelin-1 synthesis by lipopolysaccharide

An association exists between infection and cardiovascular diseases, including atherosclerosis, stroke and myocardial infarction. This may involve endothelin-1 (ET-1) which has been implicated in these and other vascular pathologies. ET-1 synthesis is controlled primarily by the level of its mRNA and numerous stimuli, including infection, lead to elevated ET-1 levels. Here, we have investigated the regulation of ET-1 release and preproET-1 (ppET-1) mRNA in bovine aortic endothelial cells by lipopolysaccharide (LPS). ET-1 release from bovine aortic endothelial cells was stimulated by LPS and reporter gene assays implicated LPS-induced ppET-1 transcription. However, changes in transcription were modest compared to increases in ET-1 synthesis. Therefore, ppET-1 mRNA levels were measured by real-time reverse transcription-polymerase chain reaction. The effect of LPS on ppET-1 mRNA levels was more marked than on transcription (1.2-fold increase in transcription vs. 5.5-fold increase in ppET-1 mRNA). Analysis of ppET-1 mRNA stability by real-time reverse transcription-polymerase chain reaction showed that LPS increased its half-life by approximately 2-fold. Thus, upregulated ppET-1 mRNA and hence increased ET-1 synthesis may be due to both increased transcription and reduced mRNA degradation. These effects of LPS on mRNA stability may be a key mechanism in vascular pathologies through which many proteins are induced in response to infection.

Functional significance of a hereditary adenine insertion variant in the 5'-UTR of the endothelin-1 gene

Endothelin-1 (ET-1) is known as a potent vasoconstrictor peptide and stimulator of cell proliferation. The human preproendothelin-1 mRNA contains a frequent adenine insertion polymorphism (allele frequency = 0.28) within the 5'-untranslated region (5'-UTR), 138 bp downstream of the transcription start site, which was assumed to be related to hypertension. This 5'-UTR variant could putatively influence the mRNA secondary structure and stability, efficacy of translation initiation, or binding of sequence-specific mRNA-binding proteins. By cloning the entire ET-1 gene 5'-UTR in a pGL3 vector and transfection of two cell lines, we studied the effects on luciferase expression in vitro. Luciferase activity was significantly increased in the insertion variant (I) compared to the wild-type (D) variant for both COS1 (2.97 +/- 0.12 versus 2.17 +/- 0.10; P = 0.002) and HepG2 cells (5.42 +/- 0.90 versus 3.68 +/- 0.37; P = 0.002). Investigations performed ex vivo using human umbilical vein endothelial cells were performed to examine the influence of genotypes on the formation of mRNA and protein. Preproendothelin-1-mRNA was quantified in relation to GAPDH by a realtime polymerase chain reaction. Homozygous I-carriers showed significant elevated mRNA levels compared to I/D and I/I-carriers (I/I 9.03 +/- 1.86, I/D 2.07 +/- 1.15, D/D 2.33 +/- 0.99; P = 0.001). ET-1 protein expression, determined by enzyme-linked immunosorbent assay, was increased among I-carriers (I/I 814 +/- 144, I/D 528 +/- 103, D/D 556 +/- 75 pg/ml; P = 0.001). The observed effects may be due to an enhanced mRNA stability because the half-life of mRNA consisting of the I-variant was prolonged (35.4 +/- 7.9 versus 19.9 +/- 4.5 min). We were able to show that the +138 I/D polymorphism is of functional importance for ET-1 expression, and this may have consequences for vessel tonus regulation.

Suppression of cytokine-induced expression of adrenomedullin and endothelin-1 by dexamethasone in T98G human glioblastoma cells

There is accumulating evidence showing that glial cells and gliomas secrete some neuropeptides and vasoactive peptides, such as adrenomedullin and endothelin-1. We have previously shown that expression of these two peptides is induced by inflammatory cytokines in T98G human glioblastoma cells. Glucocorticoids are frequently used for the treatment of inflammatory diseases and glioblastomas. We therefore studied effects of dexamethasone on expression of adrenomedullin and endothelin-1 in T98G human glioblastoma cells. Dexamethasone dose-dependently increased adrenomedullin mRNA levels and immunoreactive-adrenomedullin levels in the medium in T98G cells, whereas it decreased immunoreactive-endothelin levels in the medium. A combination of three cytokines, interferon-gamma (100 U/ml), tumor necrosis factor-alpha (20 ng/ml) and interleukin-1beta (10 ng/ml) induced expression of adrenomedullin and endothelin-1 in T98G cells. Dexamethasone (10(-8) mol/l) suppressed increases in expression of both adrenomedullin and endothelin-1 induced by these three cytokines. Thus, dexamethasone alone increased adrenomedullin expression whereas it suppressed the cytokine-induced expression of adrenomedullin in T98G cells. These findings raised the possibility that effects of dexamethasone on brain inflammation and glioblastomas may be partly mediated or modulated by its effects on expression of adrenomedullin and endothelin-1.

Functional cooperation between Smad proteins and activator protein-1 regulates transforming growth factor-beta-mediated induction of endothelin-1 expression

Endothelin-1 (ET-1) is a 21-amino-acid potent vasoconstrictor peptide that is mainly produced by vascular endothelial cells. Expression of the ET-1 gene is subject to complex regulation by numerous factors, among which transforming growth factor-beta (TGF-beta) is one of the most important. It has been widely documented that TGF-beta increases ET-1 mRNA and peptide levels. We have explored the mechanism by which TGF-beta upregulates ET-1 expression in endothelial cells. Transcriptional activation of the ET-1 promoter accounted for the TGF-beta-induced increase in ET-1 mRNA levels. We have identified within the ET-1 promoter two DNA elements indispensable for TGF-beta-mediated induction of ET-1: an activator protein-1 (AP-1) site at -108/-102, known to be important for constitutive and induced expression, and a novel regulatory sequence located at -193/-171, which constitutes a specific binding site for Smad transcription factors. Mutation of both elements abolished TGF-beta responsiveness. Binding of Smad3/Smad4 and c-Jun to their corresponding DNA elements was evidenced by electrophoretic mobility shift assays. Furthermore, the coactivator CREB-binding protein (CBP)/p300 was found to play an essential role in the induction of the gene. The simultaneous requirement for two distinct and independent DNA elements suggests that Smads and activator protein-1 functionally cooperate through CBP/p300 to mediate TGF-beta-induced transcriptional activation of the ET-1 gene.

Endothelin-1 activity in pregnancy

Plasma endothelin-1 activity was measured by radioimmunoassay in 24 normotensive non-pregnant women and in 24 normotensive pregnant, 24-aproteinuric hypertensive and 24 pre-eclamptic women. Endothelin-1 activity was increased in the pre-eclamptic group (2.7 +/- 06 pg/ml) compared to the normotensive non-pregnant (1.0 +/- 0.8 pg/ml; P < 0.0001), normotensive pregnant (1.2 +/- 0.4 pg/ml; P < 0.0001) group and the aproteinuric hypertensive group (1.4 +/- 0.7 pg/ml; P < 0.0001). There was no difference in endothelin-1 activity between the normotensive non-pregnant and normotensive pregnant group (1.0 +/- 0.8 vs. 1.2 +/- 0.4 pg/ml; P = 0.3). However, there was a difference between the aproteinuric hypertensive group (1.4 +/- 0.7 pg/ml) and both the normotensive nonpregnant (1.0 +/- 0.8 pg/ml; P < 0.01) and the normotensive pregnant group (1.2 +/- 0.4 pg/ml; P < 0.06). The birth weight in the pre-eclamptic group (2.48 +/- 0.61 kg) was significantly lower than that of the normotensive pregnant group (2.85 +/- 0.33 kg; P < 0.001) and the aproteinuric hypertensive group (2.99 +/- 0.46 kg; P < 0.001). In addition, there was no difference in birth weight between the normotensive pregnant group and aproteinuric hypertensive group (2.85 +/- 0.33 vs. 2.99 +/- 0.46 kg; P = 0.3). A significant Pearson's correlation of plasma endothelin-l versus birth weight in the pre-eclamptic group was obtained (r = 0.64; P < 0.0001). Endothelin-1 activity is increased with pre-eclampsia in black African women with pre-eclampsia. The results of our study also suggests an ethnic difference in plasma endothelin-1 activity when compared to result of studies carried out in Caucasian women with hypertensive disorders of pregnancy.

Vasoactive and natriuretic mediators in umbilical cord blood: a report of our observation and review of the literature

BACKGROUND

The relative potency and interrelationship among vasoactive and natriuretic mediators are thought to be important in the transition from fetal to neonatal life. However, little is known about their potential roles in the perinatal setting.

AIM

The aim of this study was to evaluate further the potential roles of vasoactive and natriuretic mediators in the perinatal setting.

STUDY DESIGN

We measured umbilical venous levels of arginine vasopressin, endothelin-1, adrenomedullin, natriuretic peptides and NO(2)(-)/NO(3)(-) in 24 vaginally delivered newborns and examined their possible functions.

RESULTS

Cord levels of vasopressin, endothelin-1 and adrenomedullin were considerably higher compared with normal adult values; the concentrations were more than 10-fold higher for vasopressin, and more than threefold higher for endothelin-1 and adrenomedullin. The levels of natriuretic peptides and NO(2)(-)/NO(3)(-) were almost comparable to those of normal adults. Among the mediators, there was a significant correlation between endothelin-1 and adrenomedullin.

CONCLUSIONS

It appears from other studies that the postnatal fall in vasopressin and endothelin-1 levels is associated with increased levels of natriuretic peptides and NO(2)(-)/NO(3)(-). Based on these observations, we consider that these mediators may play active roles in the initiation, maintenance or both of the transition from fetal to neonatal life.

Homocysteine decreases endothelin-1 expression by interfering with the AP-1 signaling pathway

The increased cardiovascular risk associated with hyperhomocysteinemia has been linked to homocysteine-induced endothelial cell (EC) dysfunction. Endothelin-1 is a vasoactive peptide, synthesized mainly by vascular ECs. We have previously shown that homocysteine decreases endothelin-1 biosynthesis. Here we addressed the molecular mechanism of endothelin-1 regulation by homocysteine. Experiments with the transcription inhibitor actinomycin D indicated that the decrease in preproendothelin-1 mRNA content in homocysteine-treated cells did not result from transcript destabilization. Transient transfection assays demonstrated that homocysteine downregulated endothelin-1 at the transcriptional level by decreasing preproendothelin-1 promoter activity. Mutation of the activator protein-1 (AP-1) site of the promoter eliminated the repression induced by homocysteine. Western blot analysis showed that the homocysteine-induced decrease in promoter activity was not associated with reduced expression of the AP-1 components c-Fos and c-Jun. The inhibitory action of homocysteine on preproendothelin-1 mRNA expression was not prevented by cycloheximide. Electrophoretic mobility shift assays demonstrated that homocysteine reduced the binding activity of ECs nuclear extracts to an AP-1 consensus site. These results indicate that homocysteine downregulates endothelin-1 synthesis by inhibiting AP-1 activity, and that the AP-1 signaling pathway may be of major importance in homocysteine-induced endothelial dysfunction.

Endothelin and endothelin receptor antagonists in heart failure

Endothelin (ET) is a recently discovered 21-amino acid peptide that has potent physiologic and pathophysiologic effects that appear to be involved in the development of heart failure. These include effects on arterial smooth muscle cells that cause intense peripheral vasoconstriction and stimulation of cardiac myocytes and fibroblasts. The latter promotes phenotypic changes in these cells that are consistent with cardiac remodeling. The effects of ET are mediated through interaction with two classes of cell surface receptors. The type A receptor (ET-A) has been associated with vasoconstriction and cell growth while the type B receptor (ET-B) has been associated with endothelial-cell mediated vasodilation and with the release of other neurohormones, such as aldosterone. This review summarizes evidence supporting the potential role of ET in the pathogenesis of heart failure and the available information concerning the use of ET receptor antagonists in treating this condition.

Endothelin antagonism with bosentan: current status and future perspectives

Endothelin receptor antagonists have been proposed for the treatment of a variety of disorders in which the endothelins may act as pathogenic mediators, such as hypertension, congestive heart failure, and cerebral vasospasm. Bosentan is a nonpeptide competitive antagonist, which can be a good tool for studying the endothelin system. It is specific for the endothelin system and blocks the actions of endothelin at both mammalian receptors (A and B). Bosentan has recently moved into Phase III clinical trial. This review will attempt to overview the experimental and clinical effects of bosentan.

Leptin induces endothelin-1 in endothelial cells in vitro

Leptin, a protein encoded by the obese gene, is produced by adipocytes and released into the bloodstream. In obese humans, serum leptin levels are increased and correlate with the individual's body mass index and blood pressure. Elevated serum concentrations of endothelin-1 (ET-1), a potent vasoconstrictor and mitogen, were also observed in obese subjects. The pathomechanisms underlying this ET-1 increase in obesity are poorly understood. In the present study, we investigated the influence of the ob gene product leptin on the expression of ET-1 in human umbilical vein endothelial cells (HUVECs). Binding studies using (125)I-radiolabeled leptin revealed high- and low-affinity leptin binding sites on HUVECs (Kd1=13.1+/-3.1 nmol/L and Kd2=1390+/-198 nmol/L, respectively), mediating a time- and dose-dependent increase of ET-1 mRNA expression and protein secretion after incubation of HUVECs with leptin. This leptin-induced ET-1 expression was inhibited by preincubation of HUVECs with 0.75 micromol/L antisense phosphorothioate oligonucleotides directed against the leptin receptor Ob-Rb. Furthermore, after incubation with leptin, increased nuclear staining of c-fos and c-jun, the major components of the transcription factor AP-1, and increased AP-1 DNA binding were observed. Transient transfection studies with ET-1 promoter constructs showed that leptin-induced promoter activity was abolished in the absence of AP-1 binding sites or by cotransfection with a plasmid overexpressing a mutated jun, which is able to bind c-fos but not DNA. Thus, leptin upregulates ET-1 production in HUVECs via a mechanism potentially involving jun binding members of the bZIP family.

Role of endothelin in cardiovascular disease

Endothelins are a family of peptides, which comprises endothelin-1 (ET-1), endothelin-2 (ET-2) and endothelin-3 (ET-3), each containing 21 amino-acids. ET-1 is a peptide secreted mostly by vascular endothelial cells, the predominant isoform expressed in vasculature and the most potent vasoconstrictor currently known. ET-1 also has inotropic, chemotactic and mitogenic properties. In addition, it influences salt and water homeostasis through its effects on the renin-angiotensin-aldosterone system (RAAS), vasopressin and atrial natriuretic peptide and stimulates the sympathetic nervous system. The overall action of endothelin is to increase blood pressure and vascular tone. Therefore, endothelin antagonists may play an important role in the treatment of cardiac, vascular and renal diseases associated with regional or systemic vasoconstriction and cell proliferation, such as essential hypertension, pulmonary hypertension, chronic heart failure and chronic renal failure. Long-term anti-endothelin therapy may improve symptoms and favourably alter the progression of heart failure. Endothelin appears to participate in induction and progression of sclerotic renal changes, leading to progression to end-stage renal disease. Anti-endothelin therapy might offer additional benefits in the prevention of progression of chronic renal failure in addition to the known benefits of RAAS inhibition. Clinical trials have demonstrated potentially important benefits of endothelin antagonists for patients with essential hypertension, pulmonary hypertension and heart failure. Further studies are necessary to determine the role of anti-endothelin therapy in the treatment of cardiovascular diseases and determine the different roles of selective receptor antagonism vs. mixed ET(A/B)-receptor antagonism in human diseases.

Attenuation of SAH-induced cerebral vasospasm by a selective ECE inhibitor

CGS 26303, a dual inhibitor of endothelin-converting enzyme-1 (ECE-1) and neutral endopeptidase 24.11, was previously shown to prevent and reverse vasospasm in an experimental model of subarachnoid hemorrhage (SAH). However, reversal of the vasospastic response was not very efficacious. This study was designed to examine the effects of a highly selective ECE-1 inhibitor, CGS 35066, on SAH-induced cerbrovasospasm. Experimental SAH was induced in New Zealand white rabbits by injecting autogenous blood into cisterna magna and CGS 35066 was injected i.v. twice daily, either at 1 h (prevention protocol) or 24 h (reversal protocol) after SAH. Treatment with CGS 35066 significantly attenuated basilar arterial narrowing at a dose of 1 mg/kg in both protocols. These findings provide support for the use of selective ECE-1 inhibitors for the treatment of SAH-induced vasospasm even after the process of arterial narrowing has begun.

Endothelin antagonists and heart failure

Chronic heart failure (CHF) is characterized by impaired left ventricular function, increased peripheral and pulmonary vascular resistance, reduced exercise tolerance, and dyspnea. Despite considerable progress in the treatment of CHF, especially in targeting activated neurohumoral systems, mortality in these patients remains high. Therefore, new treatment approaches are warranted. Endothelin-1 (ET-1) plasma levels are elevated in CHF and correlate with both hemodynamic severity and symptoms. Plasma levels of ET-1 are strong independent predictors of mortality in CHF. Combined ET(A/B) selective ET(A) receptor antagonists have been evaluated in patients with CHF showing impressive hemodynamic improvements. These results indicate that ET receptor antagonists indeed have a potential to improve hemodynamics, symptoms, and potentially prognosis in patients with CHF, which still carries a high mortality.

Timing of nitric oxide donor supplementation determines endothelin-1 regulation and quality of lung preservation for transplantation

Nitroglycerin (NTG) given to donor lungs improves lung preservation for transplantation, but the mechanism(s) underlying this therapeutic benefit remain incompletely understood. Furthermore, it is not known whether the therapeutic window of opportunity for NTG administration is temporally-restricted. Because endothelin-1 (ET-1), a potent vasoconstrictor, and nitric oxide (NO) are reciprocally regulated in vitro, we hypothesized that early administration of the NO donor NTG may suppress ET-1 and thereby improve lung preservation. Using an isogeneic rat left lung transplantation model, four groups were studied (n = 12 transplant/group): (1) NTG given during flush/ preservation (Early NTG); (2) NTG given in the ex vivo flush (Late NTG); (3) No NTG; and (4) a nonselective ET-receptor antagonist (PD156252) given during flush/preservation. Early NTG decreased vascular tone in lung grafts measured ex vivo as well as in vivo following lung transplantation, and resulted in improved survival (100%) and gas exchange (pO2 209 +/- 19 mm Hg) compared with Late (17%, 62 +/- 16 mm Hg) or No NTG (25%, 59 +/- 9 mm Hg) (P < 0.05 for Early NTG versus all other groups for both survival and pO2). PD156252 was associated with an intermediate level of survival (50%) and function (104 +/- 23 mm Hg). Transplanted lung graft ET-1 mRNA, measured by Northern blotting and in situ hybridization, and protein, measured by Western blotting and immunohistochemistry, were suppressed only with Early NTG (P < 0.05 versus all other groups). Post-transplantation benefits of NTG are restricted to lung grafts which received NTG during the early harvest and immersion periods, and are coincident with suppression of graft ET-1 expression. When viewed in the context of improved graft survival and function with ET-1 receptor blockade, these data suggest that early administration of NTG to donor lungs improves primary graft function, in part, by suppressing graft ET-1 expression.

Vascular effects of newer cardiovascular drugs: focus on nebivolol and ACE-inhibitors

Alterations in the function and structure of the blood vessel wall account for most clinical events in the coronary and cerebrovascular circulation such as myocardial infarction and stroke. Cardiovascular drugs may exert beneficial effects on the vascular wall both at the level of the endothelium and vascular smooth muscle cells. Therefore, endothelial mediators, in particular nitric oxide (NO) and endothelin (ET), are of special interest. Drugs can modulate the expression and actions of NO, a vasodilator with antiproliferative and antithrombotic properties, and of ET, a potent vasoconstrictor and proliferative mitogenic agent. The most successful drugs in this context are statins and angiotensin-converting enzyme (ACE)-inhibitors. While statins increase the expression of NO synthase. ACE-inhibitors increase the release of NO via bradykinin-mediated mechanisms. Antioxidant properties of drugs are also important, as oxidative stress is crucial in atherosclerotic vascular disease. These properties may explain part of the effects of calcium antagonists and ACE-inhibitors. Indeed, angiotensin II stimulates NAD(P)H oxidases responsible for the formation of superoxide, which inactivates NO. ACE-Inhibitors thus increase the bioavailability of NO. Newer cardiovascular drugs such as nebivolol are able to directly stimulate NO release from the endothelium both in isolated arteries and in the human forearm circulation. ET receptor antagonists may exert beneficial effects in the vessel wall by preventing the effects of ET at its receptors and by reducing ET production. In summary, cardiovascular drugs have important effects on the vessel wall, which may be clinically relevant for the prevention and treatment of cardiovascular disease.

Retinoic acid suppresses endothelin-1 gene expression at the transcription level in endothelial cells

Retinoids have been shown to inhibit cell growth, which can result in an anti-atherosclerotic action in the vasculature. Endothelin-1 (ET-1), a potent vasoconstrictor peptide produced in endothelial cells, plays an important role in inducing proliferation of vascular smooth muscle cells. In this study, we investigated the effect of retinoids on the mRNA expression and transcriptional activity of the ET-1 gene in endothelial cells. All-trans retinoic acid (ATRA) suppressed ET-1 mRNA expression in cultured endothelial cells. Synthetic retinoids, Ch55 and Am580 (retinoic acid receptor (RAR) agonists) markedly enhanced this effect, and an RAR antagonist, LE540, blocked this inhibitory effect on ET-1 gene expression. ATRA did not change ET-1 mRNA half-life. Transfection experiments using 5 kb of the ET-1 promoter-reporter gene construct which contains 5 kb of the preproET-1 promoter revealed that ATRA and Ch55 suppressed ET-1 promoter activity, resulting in down-regulation of ET-1 gene transcription. Taken together, retinoids may be another modulator of endothelial cell function through regulation of vasoactive substances at the transcription level.

Rapid quantification of murine endothelin-1 and vasoactive intestinal contractor gene expression levels by a real-time PCR system

A rapid quantitative analysis method for murine endothelin-1 (ET-1) and vasoactive intestinal contractor (VIC) gene expression levels was established using a real-time polymerase chain reaction (PCR). We designed primer pairs and TaqMan probes specific for murine prepro-ET-1 (PPET-1) and prepro-VIC (PPVIC) genes, based on the cDNA sequence region common to both mouse and rat. The dynamic range for detection in this system spanned 100000-fold of the starting molecule. The gene expression levels of PPET-1 and PPVIC were estimated as gene expression rates normalized by the expression of the house-keeping gene, glyceraldehyde-3-phosphate dehydrogenase. To examine the reproducibility of this assay system, we calculated the intra-assay and interassay coefficients of variation of the gene expression rate, which ranged from 16.2 to 55.0% and from 24.2 to 56. 5%, respectively. Using this system, we examined gene expression levels of PPET-1 and PPVIC in mouse tissues. PPET-1 gene expression was found in all tissues at relatively high levels, whereas high levels of PPVIC gene expression were observed only in stomach, intestine, uterus, and ovary. The gene expression patterns agreed well with those determined by RNase protection assay and conventional PCR. These results show that this new rapid method is accurate and reproducible.

Induction of endothelin-1 expression by oxidative stress in vascular smooth muscle cells

Atherosclerosis is based on endothelial dysfunction leading to impaired vasomotor function. This is partially due to nitric oxide (NO) depletion caused by oxidative stress. Since the vasoconstrictor endothelin-1 (ET-1) might also be involved in endothelial dysfunction, we investigated whether oxidative stress regulates ET-1 expression in vascular smooth muscle cells (VSMC). Human aortic VSMC were treated with H(2)O(2) (200 microM) for up to 8 h. mRNA expression of preproendothelin (prepro-ET) was analyzed by RT-PCR. ET-1 protein and the marker for oxidative stress, 8-isoprostane, were determined by ELISA. Activity of cytosolic phospholipase A2 (cPLA(2)) as an indicator of ET-1 autocrine activity was measured photometrically. Stimulation of VSMC with H(2)O(2) resulted in increased expression of prepro-ET mRNA after 1 h with a maximum after 6 h (fourfold), similar to treatment with angiotensin II. ET-1 protein was significantly increased by H(2)O(2) treatment with a maximum after 8 h (P<.05). This effect was inhibited by the antioxidants resveratrol (100 microM) and quercetin (50 microM). In quiesced VSMC, incubation with H(2)O(2)-conditioned medium resulted in increased cPLA(2) activity compared to the controls (P<.05). This activity was partially inhibited by the ET(A)-receptor antagonist, PD 142893 (10 microM), indicating functional ET-1 in the conditioned medium. The presence of oxidative stress in H(2)O(2)-treated VSMC was associated by significantly increased formation of 8-isoprostane (P<.05). The data indicate for the first time that oxidative stress increases ET-1 generation and autocrine ET-1 activity in VSMC, a mechanism that might contribute to endothelial dysfunction in atherosclerosis.

Association between the endothelin-1 gene Lys198Asn polymorphism blood pressure and plasma endothelin-1 levels in normal and pre-eclamptic pregnancy

OBJECTIVE

This study examined the frequency of the Lys198Asn polymorphism in the endothelin-1 (ET-1) gene in women with pre-eclampsia and normal pregnancy; and its contribution to levels of plasma ET-1 and blood pressure.

DESIGN AND METHODS

This was a retrospective study examining the frequency of the ET-1 Lys198Asn polymorphism in 72 proteinuric pre-eclamptics and 81 normal pregnant women. Height, weight, blood pressure and plasma ET-1 were measured antenatally and at 6 weeks post-partum. Using specific mutagenic primers, the frequency of the G/G (normal), G/T heterozygote and T/T (mutant) genotypes of the Lys198Asn polymorphism were examined.

RESULTS

The polymorphism was not associated with pre-eclampsia. However, in the combined pregnant groups after correction for BMI and group, a significant effect of the T-allele (T/T,G/T) on systolic blood pressure was found (121 +/- 1.5 mmHg compared with 116 +/- 1.3 mmHg in the G/G homozygotes). A significant interaction was found between the T-allele and pregnancy in determining systolic blood pressure, so that the effect was no longer seen post-partum. Pregnant women with the T/T genotype had significantly elevated plasma ET-1 levels 5.8 pg/ml [confidence interval (CI) 3.7-9.1] compared with 3.1 pg/ml (CI 2.6-3.8) in the G/T heterozygotes and 3.6 pg/ml (CI 3.0-4.1) in the normal G/G homozygotes.

CONCLUSION

The Lys198Asn polymorphism does not directly contribute to the incidence of pre-eclampsia. However, the association of the T-allele with raised blood pressure and the T/T genotype with increased plasma ET-1 levels suggest that this polymorphism may interact with other genes or environmental factors to sensitize pregnant women to develop pre-eclampsia.

Coordinate regulation of endothelin and adrenomedullin secretion by oxidative stress in endothelial cells

To elucidate the significance of oxidative stress in the modulation of endothelial functions, we examined the effects of H(2)O(2) on the expression of two endothelium-derived vasoactive peptides, endothelin (ET) and adrenomedullin (Am), and their interaction. H(2)O(2) dose dependently suppressed ET secretion and ET-1 mRNA expression in bovine carotid endothelial cells (ECs). Menadion sodium bisulfate, a redox cycling drug, also decreased ET secretion in a dose-dependent manner. Catalase, a H(2)O(2) reductase, and dl-alpha-tocopherol (vitamin E) significantly inhibited H(2)O(2)-induced suppression of ET secretion. Downregulation of ET-1 mRNA under oxidative stress was regulated at the transcriptional level. In contrast, H(2)O(2) increased Am secretion (and its mRNA expression) accompanied by the augmentation of cAMP production. Am, as well as 8-bromo-cAMP and forskolin decreased ET secretion in a dose-dependent fashion. Furthermore, an anti-Am monoclonal antibody that we developed abolished H(2)O(2)-induced suppression of ET secretion at 6-24 h after the addition of H(2)O(2). H(2)O(2) increased the intracellular Ca(2+) concentration ([Ca(2+)](i)). Moreover, treatment with ionomycin, a Ca(2+) ionophore, and thapsigargin, an inhibitor of endoplasmic reticulum ATPase, decreased ET secretion dose dependently for 3 h. These results suggest that the production of ET was decreased via activation of the Am-cAMP pathway and by the elevation of [Ca(2+)](i) under oxidative stress. These findings elucidate the coordinate expression of two local vascular hormones, ET and Am, under oxidative stress, which may protect against vascular diseases.

Continuous intravenous infusion of CGS 26303, an endothelin-converting enzyme inhibitor, prevents and reverses cerebral vasospasm after experimental subarachnoid hemorrhage

OBJECTIVE

Endothelin-mediated vasoconstriction has been implicated in the pathophysiology of cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH). Endothelin-1, the most potent vasoconstrictor peptide of the endothelin family, is synthesized initially as a large prepropeptide that requires multiple steps of post-translational processing for activation. The final step of this processing involves the proteolytic cleavage of a relatively inactive precursor, big endothelin-1, by the metalloprotease endothelin-converting enzyme. Previous findings have demonstrated that intravenous bolus injections of an endothelin-converting enzyme inhibitor (CGS 26303) administered twice daily can prevent and reverse arterial narrowing in a rabbit model of SAH. However, attenuation of vasospastic response was incomplete and required relatively high doses to be effective in reversing vasospasm. Therefore, the present study evaluated an alternative protocol for administration of CGS 26303 to optimize the antispastic influence of this compound.

METHODS

Continuous intravenous infusion of CGS 26303 at doses of 2.4, 8.0, or 24.0 mg/kg/d was initiated either 1 hour (prevention paradigm) or 24 hours (reversal paradigm) after experimental SAH in New Zealand White rabbits. All animals were killed by perfusion-fixation 48 hours after SAH. Basilar arteries were then removed and sectioned, and their cross-sectional areas were measured by use of computer-assisted video microscopy.

RESULTS

Continuous intravenous infusion of CGS 26303 attenuated SAH-induced cerebral vasospasm in a dose-dependent manner in both the prevention and the reversal groups. These effects achieved statistical significance at all doses as compared with the SAH-only or SAH-plus-vehicle groups. Furthermore, the attenuation of vasospasm after continuous infusion of CGS 26303 was more efficacious than that obtained with bolus injections.

CONCLUSION

These findings provide further support for the use of endothelin-converting enzyme inhibition as a therapeutic strategy for reduction of cerebral vasospasm, and they also support the effectiveness of this strategy even when initiated after arterial narrowing has been established. The findings also indicate that continuous intravenous infusion of CGS 26303 is a more effective approach for attenuation of vasospasm than bolus intravenous administration.

Oxidative stress increases endothelin-1 synthesis in human coronary artery smooth muscle cells

Endothelins, nitric oxide, and oxygen-derived free radicals decisively regulate vascular tone. An imbalance in the biosynthesis of these substances in pathophysiologic conditions may trigger vasospasm and promote the development of atherosclerosis. Previous studies have shown that oxygen-derived free radicals can increase the synthesis of endothelin-1 in cultured endothelial cells. Interestingly, conditions of increased oxidative stress within smooth muscle cells as induced by angiotensin II infusion or hypercholesterolemia have been shown to be associated with increased autocrine synthesis of endothelin-1. Because endothelin-1 formed in smooth muscle cells can trigger hypersensitivity to vasoconstrictors, we tested whether oxidative stress per se may affect endothelin expression in vascular smooth muscle cells. Cultured human coronary artery smooth muscle cells were exposed to oxidative stress generated by the xanthine/xanthine oxidase reaction or by hydrogen peroxide. Preproendothelin-1 mRNA content was quantitated by means of quantitative polymerase chain reaction and endothelin-1 protein was measured by radioimmunoassay. Incubation with xanthine/xanthine oxidase significantly increased preproendothelin-1 mRNA synthesis, whereas GAPDH remained unchanged. Likewise, xanthine/xanthine oxidase also led to a dose-dependent increase of intracellular endothelin-1. The increase in ET-1 expression induced by xanthine/xanthine oxidase was significantly inhibited by superoxide dismutase but not by catalase. We conclude that oxygen-derived free radicals can stimulate the synthesis of endothelin-1 in endothelial and vascular smooth muscle cells by increasing preproendothelin-1 mRNA content and that this effect is mediated predominantly by superoxide anions. We therefore have identified a new mechanism in the interaction of oxidative stress and endothelin-1 expression in smooth muscle cells that may have important implications in diseases such as atherosclerosis and hypertension.

Endogenously released endothelin-1 from human pulmonary artery smooth muscle promotes cellular proliferation: relevance to pathogenesis of pulmonary hypertension and vascular remodeling

Endothelin (ET)-1 is a potent vasoconstrictor and comitogen/ proliferation factor for vascular smooth muscle (VSM). As such, it has been implicated in the vascular wall remodeling observed in pulmonary hypertension (PH). Although the endothelium is considered the main source of ET-1, it can be released by other cells including VSM and may mediate proliferation in an autocrine manner. We investigated this possibility using human pulmonary artery smooth-muscle (HPASM) cells. Serum stimulated the release of ET-1 from HPASM cells in a concentration-dependent fashion and caused proliferation as determined by [(3)H]thymidine uptake and increase in cell number. Addition of an ET-A receptor antagonist (BQ123) or an inhibitor of ET-1 synthesis (phosphoramidon) reduced the proliferation induced by serum, confirming an autocrine role for ET-1. In addition, treatment of HPASM cells with two drug types used in the management of PH-cicaprost, a stable prostacyclin-mimetic; or diltiazem, a calcium-channel blocker-reduced ET-1 release from these cells. We conclude that ET-1 released from HPASM cells has an autocrine function in serum-induced proliferation, with important implications for the pathogenesis of human vascular remodeling. Drugs used in the treatment of PH may act, at least in part, by inhibiting this autocrine loop.

PreproEndothelin-1 Expression in Human Mesangial Cells: Evidence for a p38 Mitogen-Activated Protein Kinase/Protein Kinases-C—Dependent Mechanism

Abstract. Endothelin-1 (ET-1) has been implicated in the pathogenesis of renal inflammation. This study investigated the mechanisms underlying the synergistic upregulation of preproET-1 gene expression in human mesangial cells after co-stimulation with thrombin and tumor necrosis factor α (TNFα). Whereas thrombin induced a moderate upregulation of preproET-1 mRNA, co-stimulation with TNFα resulted in a strong and protracted upregulation of this mRNA species. Thrombin+TNFα-induced upregulation of preproET-1 expression was found to require p38 mitogen-activated protein kinase and protein kinases C, whereas activation of extracellular signal-regulated kinase, c-Jun-N-terminal kinase, or intracellular Ca2+ release were not required. Actinomycin D chase experiments suggested that enhanced stability of preproET-1 mRNA did not account for the increase in transcript levels. PreproET-1 promoter analysis demonstrated that the 5′-flanking region of preproET-1 encompassed positive regulatory elements engaged by thrombin. Negative modulation of thrombin-induced activation exerted by the distal 5′ portion of preproET-1 promoter (-4.4 kbp to 204 bp) was overcome by co-stimulation with TNFα, providing a possible mechanism underlying the synergistic upregulation of preproET-1 expression by these two agonists. In conclusion, human mesangial cell expression of preproET-1 may be increased potently in the presence of two common proinflammatory mediators, thereby providing a potential mechanism for ET-1 production in inflammatory renal disease.

Gene expression of endothelin-1 (ET-1) and release of mature peptide by activated human neutrophils

Polymorphonuclear neutrophils (PMNs) are only regarded as being involved in the cleavage of exogenous big endothelin-1 (ET-1) to the active peptide. The aims of the present study were to investigate whether PMNs may themselves express mRNA for prepro-ET-1 (pp-ET-1, a long precursor of 212 amino acids) and to determine the capacity of several PMN stimulants to modulate mRNA expression and the release of ET-1 in culture medium. PMNs, isolated from seven healthy adult volunteers, were stimulated with lipopolysaccharide (LPS, 0.25-10 microg/ml), or LPS (1 microg/ml) + phorbol myristate acetate (PMA, 10 ng/ml) or N-formyl-L-methionyl-L-leucyl-L-phenylalanine (f-MLP, 10(-5) M) or tumour necrosis factor-alpha (TNF-alpha, 50 IU/ml). They were found to express pp-ET-1 mRNA by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Enzyme immunoassay (EIA) revealed low levels of ET-1 in the culture supernatants of PMNs stimulated for 3 h with LPS (10 microg/ml) and with LPS + PMA. Control unstimulated PMNs did not express pp-ET-1 mRNA. The local production of ET-1 by PMNs in vivo has significant implications in inflammatory diseases.

Endothelin as a therapeutic target in the treatment of cardiovascular disease

Endothelins, a family of peptides derived from the vascular endothelium and smooth muscle cells possess vasoconstrictor and mitogenic properties. By acting predominantly in a paracrine fashion, these peptides activate specific receptors and have protean effects in normal and diseased organ systems. The wide distribution of these receptors in various tissues mediate the multiplicity of physiologic actions attributed to endothelins. Much of our understanding about endothelins has come from the development of an array of receptor-specific and mixed receptor antagonists. Based on the promising results from animal studies, active research and drug development programs are under way to investigate the clinical potential of endothelin antagonism for treatment of cardiovascular disease.

Endothelin receptor antagonists in congestive heart failure: a new therapeutic principle for the future?

Congestive heart failure (CHF) is characterized by impaired left ventricular function, increased peripheral and pulmonary vascular resistance and reduced exercise tolerance and dyspnea. Thus, mediators involved in the control of myocardial function and vascular tone may be involved in its pathophysiology. The family of endothelins (ET) consists of four closely related peptides, ET-1, ET-2, ET-3 and ET-4, which cause vasoconstriction, cell proliferation and myocardial effects through activation of ETA receptors. In contrast, endothelial ETB receptors mediate vasodilation via release of nitric oxide and prostacyclin. In addition, ETB receptors in the lung are a major pathway for the clearance of ET-1 from plasma. Thus, infusion of an ETA-receptor antagonist into the brachial artery in healthy humans leads to vasodilation, whereas infusion of an ETB-receptor antagonist causes vasoconstriction. Endothelin-1 plasma levels are elevated in CHF and correlate both with hemodynamic severity and symptoms. Plasma levels of ET-1 and its precursor, big ET-1, are strong independent predictors of death after myocardial infarction as well as in CHF. Endothelin-1 contributes to increased systemic and pulmonary vascular resistance, vascular dysfunction, myocardial ischemia and renal impairment in CHF. Selective ETA, as well as combined ETA/B-receptor antagonists, have been studied in patients with CHF, and their use has shown impressive hemodynamic improvement (i.e., reduced peripheral vascular and pulmonary resistance as well as increased cardiac output). These results indicate that ET-receptor antagonists, indeed, have a potential to improve hemodynamics, symptoms and, potentially, prognosis in patients with CHF, which still carries a high mortality.

Molecular regulation of the endothelin-1 gene by hypoxia. Contributions of hypoxia-inducible factor-1, activator protein-1, GATA-2, AND p300/CBP

Endothelin-1 (ET-1) is a peptide hormone with potent vasoconstrictor properties which is synthesized and secreted predominantly by vascular endothelial cells. Its production is regulated by numerous stimuli including ischemia and hypoxia, and the enhanced levels that occur during myocardial ischemia may contribute to the progression of heart failure. We reported previously a preliminary characterization of a hypoxia-inducible factor-1 (HIF-1) binding site in the human ET-1 promoter which contributed to the activation of ET-1 expression in endothelial cells. We report here that the HIF-1 binding site alone is not sufficient for the response to hypoxia but requires an additional 50 base pairs of flanking sequence that includes binding sites for the factors activator protein-1 (AP-1), GATA-2, and CAAT-binding factor (NF-1). Mutation of any one of these sites or the HIF-1 site eliminated induction by hypoxia. Mutations of the AP-1 and GATA-2 sites, but not the HIF-1 site, were complemented by overexpressing AP-1, GATA-2, HIF-1alpha, or the activator protein p300/CBP, restoring the response to hypoxia. Binding studies in vitro confirmed physical associations among GATA-2, AP-1, and HIF-1 factors. Overexpression or depletion of p300/CBP modulated the level of ET-1 promoter expression as well as the endogenous ET-1 transcript but did not change the fold induction by hypoxia in either case. Regulation of the ET-1 promoter by hypoxia in non-endothelial cells required overexpression of GATA-2 and HIF-1alpha. The results support essential roles for AP-1, GATA-2, and NF-1 in stabilizing the binding of HIF-1 and promoting recruitment of p300/CBP to the ET-1 hypoxia response complex.

Vascular protective effects of angiotensin converting enzyme inhibitors and their relation to clinical events

Endothelial cells are a rich source of a variety of vasoactive substances, which either cause vasodilation or vasoconstriction. Important endothelium-derived vasodilators are prostacyclin, bradykinin, nitric oxide and endothelium-derived hyperpolarizing factor. In particular, nitric oxide inhibits cellular growth and migration. In concert with prostacyclin. nitric oxide exerts potent anti-atherogenic and thromboresistant properties by preventing platelet aggregation and cell adhesion. Endothelium-derived contracting factors include the 21 amino acid peptide endothelin (ET). vasoconstrictor prostanoids such as thromboxane A2 and prostaglandin H2, as well as free radicals and components of the renin angiotensin system. In hypertension, elevated blood pressure transmits into cardiovascular disease by causing endothelial dysfunction. Hence, modem therapeutic strategies in human hypertension focus on preserving or restoring endothelial integrity. Angiotensin converting enzyme (ACE) inhibitors are a primary candidate for that concept as they inhibit the circulating and local renin angiotensin system. Angiotensin converting enzyme is an endothelial enzyme which converts angiotensin-I (A-I) into angiotensin-II (A-II). This effect of the ACE inhibitor prevents direct effects of angiotensin-II such as vasoconstriction and proliferation in the vessel wall but also prevents activation of the ET system and of plasminogen activator inhibitor. Furthermore, inhibition of ACE prolongs the half-life of bradykinin and stabilizes bradykinin receptors linked to the formation of nitric oxide and prostacyclin. In isolated arteries ACE inhibitors prevent the contractions induced by angiotensin II and enhance relaxation induced by bradykinin. Chronic treatment of experimental hypertension with ACE inhibitors normalizes endothelium-dependent relaxation to acetylcholine and other agonists. In addition, the dilator effects of exogenous nitric oxide donors are enhanced, at least in certain models of hypertension. In humans with essential hypertension ACE inhibitors augment endothelium-dependent relaxation to bradykinin, while those to acetylcholine remain unaffected, at least in the time frame of the published studies, i.e. 3-6 months. In patients with coronary artery disease, however, paradoxical vasoconstriction to acetylcholine is markedly reduced after 6 months of ACE inhibition. After myocardial infarction ACE inhibitors reduce the development of overt heart failure, the occurrence of reinfarction and cardiovascular death in hypertensive patients. These effects have also been demonstrated in a subgroup analysis of the SOLVD (Studies of Left Ventricular Dysfunction) trial. Thus, in summary, ACE inhibitors are an important class of drugs providing cardiovascular protection in patients with increased cardiovascular risk.

Inhibition of endothelin-converting enzyme activity in the rabbit basilar artery

OBJECTIVE

Endothelin (ET)-1 may be involved in the regulation of cerebrovascular resistance under pathological conditions, most notably during the development of vasospasm after subarachnoid hemorrhage. Blocking ET-converting enzyme activity may be a promising approach to the prevention of cerebral vasospasm after subarachnoid hemorrhage.

METHODS

In this study, the effects of several putative ET-converting enzyme inhibitors were investigated after intracisternal application in rabbits, to inhibit basilar artery contractions induced by big ET-1 (2 x 10(-6) mol/L).

RESULTS

In the group pretreated with [D-Val22]big ET-1[16-38] (2 x 10(-5) mol/L) (n = 8), the angiographically measured diameter of the basilar artery changed from 0.63 +/- 0.12 mm to 0.66 +/- 0.12 mm. In the control group (n = 8), the diameter of the basilar artery decreased from 0.71 +/- 0.13 mm to 0.57 +/- 0.15 mm. These results corresponded to an increase in vessel diameter of 5 +/- 10% in the treatment group and a decrease in vessel diameter of 20 +/- 16% in the control group (P = 0.014). In the group pretreated with captopril (2 x 10(-4) mol/L) (n = 8), the angiographically measured diameter of the basilar artery changed from 0.64 +/- 0.11 mm to 0.71 +/- 0.10 mm. These results corresponded to an increase in vessel diameter of 14 +/- 19% in the treatment group, compared with a decrease in vessel diameter of 20 +/- 16% in the control group (P = 0.014).

CONCLUSION

These results demonstrate that [D-Val22]big ET-1[16-38] and captopril act as highly potent ET-converting enzyme inhibitors, affecting big ET-1-induced contraction of the rabbit basilar artery.

The role of protein kinase C in the development of the complications of diabetes

Diabetes mellitus produces a state of chronic hyperglycemia which in turn leads to the development of severe complications including retinopathy, nephropathy, neuropathy, and atherosclerosis. Many different mechanisms have been put forward to attempt to explain how glucose elevations can damage these various organ systems. Protein kinase C activation is one of the sequelae of hyperglycemia and is thought to play a role in the development of diabetic complications. There are multiple mechanisms for its activation in the diabetic state and multiple downstream effects attributable to that activation. The role of protein kinase C activation in the development of the above-mentioned complications of diabetes is discussed in this chapter. In addition, the potential use of isoform-specific inhibitors of protein kinase C for the treatment of diabetic complications is proposed.

The role of endothelins and their receptors in heart failure

Endothelin (ET) is a peptide composed of 21 amino acids, derived from a larger precursor, the big-endothelin, by action of the endothelin-converting enzyme (ECE) family; three isoforms of endothelin, named ET-1, ET-2 and ET-3, have been identified. Endothelin-1 is generated mainly by vascular endothelial cells and exerts various important biological actions, mediated by two receptor subtypes, ET-A and ET-B, belonging to the G protein-coupled family that have been identified in various human tissues such as the cardiac tissue. Endothelin-1 is a potent vasoconstrictive agent, has inotropic and mitogenic actions, modulates salt and water homeostasis and plays an important role in the maintenance of vascular tone and blood pressure in healthy subjects. Endothelin-1, as well as ET-A and ECE-1, also has an important role in cardiovascular development, as observed by the variety of abnormalities related to neural crest-derived tissues in mouse embryos deficient of a member of the ET-1/ECE-1/ET-A pathway. Various evidence indicates that endogenous endothelin-1 may contribute to the pathophysiology of conditions associated with sustained vasoconstriction, such as heart failure. In heart failure, elevated circulating levels of both endothelin-1 and big-endothelin-1 are observed; in failing hearts an activation of the endothelin system is found: tissue level of ET-1 is increased with respect to non-failing hearts as well as receptor density, due mainly to an upregulation of the ET-A subtype, the prevalent receptor subclass in cardiac tissue. Finally, studies in both humans and animal models of cardiovascular disease show that inhibition of the endothelin function (anti-endothelin strategy) is associated with an improvement of haemodynamic conditions; these observations indicate that endothelin receptor antagonists or endothelin-converting enzyme inhibitors may constitute a novel and potentially important class of agents for the treatment of this disease.

Therapeutic potential for endothelin receptor antagonists in cardiovascular disorders

The endothelins are synthesized in vascular endothelial and smooth muscle cells, as well as in neural, renal, pulmonal, and inflammatory cells. These peptides are converted by endothelin-converting enzymes (ECE-1 and -2) from 'big endothelins' originating from large preproendothelin peptides cleaved by endopeptidases. Endothelin (ET)-1 has major influence on the function and structure of the vasculature as it favors vasoconstriction and cell proliferation through activation of specific ET(A) and ET(B) receptors on vascular smooth muscle cells. In contrast, ET(B )receptors on endothelial cells cause vasodilation via release of nitric oxide (NO) and prostacyclin. Additionally, ET(B) receptors in the lung are a major pathway for the clearance of ET-1 from plasma. Indeed, ET-1 contributes to the pathogenesis of important disorders as arterial hypertension, atherosclerosis, and heart failure. In patients with atherosclerotic vascular disease (as well as in many other disease states), ET-1 levels are elevated and correlate with the number of involved sites. In patients with acute myocardial infarction, they correlate with 1-year prognosis. ET receptor antagonists have been widely studied in experimental models of cardiovascular disease. In arterial hypertension, they prevent vascular and myocardial hypertrophy. Experimentally, ET receptor blockade also prevents endothelial dysfunction and structural vascular changes in atherosclerosis due to hypercholesterolemia. In experimental myocardial ischemia, treatment with an ET receptor antagonist reduced infarct size and prevented left ventricular remodeling after myocardial infarction. Most impressively, treatment with the selective ET(A) receptor antagonist BQ123 significantly improved survival in an experimental model of heart failure. In many clinical conditions, such as congestive heart failure, both mixed ET(A/B )as well as selective ET(A) receptor antagonism ameliorates the clinical status of patients, i.e. symptoms and hemodynamics. A randomized clinical trial showed that a mixed ET(A/B) receptor antagonist effectively lowered arterial blood pressure in patients with arterial hypertension. In patients with primary pulmonary hypertension or pulmonary hypertension related to scleroderma, treatment with a mixed ET(A/B) receptor antagonist resulted in an improvement in exercise capacity. ET receptor blockers thus hold the potential to improve the outcome in patients with various cardiovascular disorders. Randomized clinical trials are under way to evaluate the effects of ET receptor antagonism on morbidity and mortality.

Endothelin-1 in subarachnoid hemorrhage: An acute-phase reactant produced by cerebrospinal fluid leukocytes

BACKGROUND AND PURPOSE

The most potent vasoconstrictor known, endothelin-1, is currently considered to mediate cerebral vasospasm in subarachnoid hemorrhage (SAH), which can cause delayed cerebral ischemia. In our study, we performed clinical and in vitro experiments to investigate the origin and the mechanisms of the secretion of endothelin-1 in SAH.

METHODS

Endothelin-1 and markers of inflammatory host response (interleukin [IL]-1ss, IL-6, and tumor necrosis factor-alpha) were comparatively quantified in the cerebrospinal fluid (CSF) of SAH patients and control subjects, and concentrations were related to clinical characteristics. Furthermore, mononuclear leukocytes isolated from the CSF of SAH patients and control subjects were analyzed regarding their mRNA expression of endothelin-1 and inflammatory cytokines. Finally, complementary in vitro experiments were performed to investigate whether coincubation of blood and CSF can trigger leukocytic mRNA expression and release of these factors.

RESULTS

Activated mononuclear leukocytes in the CSF of SAH patients synthesize and release endothelin-1 in parallel with known acute-phase reactants (IL-1ss, IL-6, and tumor necrosis factor-alpha). Complementary in vitro experiments not only further confirmed this leukocytic origin of endothelin-1 but also showed that aging and subsequent hemolysis of blood is sufficient to induce such endothelin-1 production.

CONCLUSIONS

The demonstration that endothelin-1 is produced by activated CSF mononuclear leukocytes suggests that subarachnoid inflammation may represent a therapeutic target to prevent vasospasm and delayed cerebral ischemia after SAH.

Endothelins and endothelin receptor antagonists: therapeutic considerations for a novel class of cardiovascular drugs

The 21-amino acid peptide endothelin-1 (ET-1) is the predominant isoform of the endothelin peptide family, which includes ET-2, ET-3, and ET-4. It exerts various biological effects, including vasoconstriction and the stimulation of cell proliferation in tissues both within and outside of the cardiovascular system. ET-1 is synthesized by endothelin-converting enzymes (ECE), chymases, and non-ECE metalloproteases; it is regulated in an autocrine fashion in vascular and nonvascular cells. ET-1 acts through the activation of G(i)-protein-coupled receptors. ET(A) receptors mediate vasoconstriction and cell proliferation, whereas ET(B) receptors are important for the clearance of ET-1, endothelial cell survival, the release of nitric oxide and prostacyclin, and the inhibition of ECE-1. ET is activated in hypertension, atherosclerosis, restenosis, heart failure, idiopathic cardiomyopathy, and renal failure. Tissue concentrations more reliably reflect the activation of the ET system because increased vascular ET-1 levels occur in the absence of changes in plasma. Experimental studies using molecular and pharmacological inhibition of the ET system and the first clinical trials have demonstrated that ET-1 takes part in normal cardiovascular homeostasis. Thus, ET-1 plays a major role in the functional and structural changes observed in arterial and pulmonary hypertension, glomerulosclerosis, atherosclerosis, and heart failure, mainly through pressure-independent mechanisms. ET antagonists are promising new agents in the treatment of cardiovascular diseases.

Endothelin-1, endothelin receptors and ecNOS gene transcription in vital organs during traumatic shock in rats

Endothelin-1 (ET-1) is a vasoconstrictor peptide that may play an important role in the pathophysiology of severe trauma. We examined ET-1 gene expression in vital organs (i.e., heart, lungs, kidneys, liver and small intestine) during murine traumatic shock using ribonuclease protection assays. Our data show that ET-1 mRNA was significantly increased in the lungs two hours after trauma when compared with control anesthetized rats. There was also a significant increase in ET-1 transcripts occurring in the kidneys, heart and liver. During these experimental conditions, we also observed statistically significant increased endothelin type B (ET(B)) receptor mRNA expression in the lung, heart, liver, kidney and small intestine. Expression of endothelial constitutive nitric oxide synthase (ecNOS) gene, which is functionally coupled to ET(B) receptor, also was increased in vital organs during traumatic shock. Endothelin type A (ET(A)) receptor gene expression was slightly decreased in the lung, liver and small intestine. These results suggest that ET-1 and ET(B) mRNA expression are mainly increased in the lung and other vital organs and may play a functional role in the pathophysiology of murine traumatic shock.

Superoxide regulation of endothelin-converting enzyme

Reactive oxygen species (ROS) act as signaling molecules in the cardiovascular system, regulating cellular proliferation and migration. However, an excess of ROS can damage cells and alter endothelial cell function. We hypothesized that endogenous mechanisms protect the vasculature from excess levels of ROS. We now show that superoxide can inhibit endothelin-converting enzyme activity (ECE) and decrease endothelin-1 synthesis. Superoxide inhibits ECE but hydrogen peroxide and nitric oxide do not. Superoxide inhibits ECE by ejecting zinc from the enzyme, and the addition of exogenous zinc restores enzymatic activity. Superoxide may inhibit other zinc metalloproteinases by a similar mechanism and may thus play an important role in regulating the biology of blood vessels.

Oxidative stress increases synthesis of big endothelin-1 by activation of the endothelin-1 promoter

Modulation of the biosynthesis of the vasoconstrictor peptide endothelin-1 by oxygen-derived free radicals generated by xanthine oxidase or hydrogen peroxide was studied in cultured endothelial cells. Endothelin-1 metabolism was investigated at the level of endothelin-1 promoter, preproendothelin-1 mRNA and intracellular big endothelin-1. Endothelin-1 mRNA, as characterized by Northern blotting, was increased both time- and dose-dependently by xanthine oxidase to up to 500% above baseline. Analysis of endothelin-1 promoter activity using a construct containing 1329 bp of the endothelin-1 promoter revealed that promoter activity was increased up to eight-fold by incubation with xanthine oxidase. Specificity was ascertained by co-incubation with superoxide dismutase and catalase leading to inhibition of the effect of xanthine oxidase. A significant contribution of nitric oxide was ruled out, since NOS III-mRNA transcription remained unchanged and l -NAME did not significantly alter endothelin-1 promoter activity. Synthesis of intracellular big endothelin-1 protein was increased dose-dependently by xanthine oxidase. Our results indicate that oxidative stress leads to increased endothelial synthesis of big endothelin-1, which is a previously unknown mechanism and may help to understand the detrimental association of increased oxidative stress and elevated endothelin-1 levels in pathophysiological conditions promoting atherosclerosis.

Differential transcriptional regulation of endothelin-1 by immunosuppressants FK506 and cyclosporin A

Calcineurin antagonists FK506 and CsA, administered to treat organ allograft rejection, exert specific effects on renal vasoconstriction and nephrotoxicity, possibly due to endogenous vasoconstrictor release such as ET-1. We investigated contribution of FK506 and CsA on regulation of prepro ET-1 gene transcription in HUVEC. To conclude on transcriptional regulation, ET-1 mRNA levels were quantified by Northern blot analysis upon stimulation with calcineurin antagonists, and newly transcribed luciferase gene, placed under the control of the rat ET-1 promoter, was quantified by reporter gene assays, where luciferase activity reflects ET-1 promoter activation. Calcium fluorometry was employed to examine calcium dependency of ET-1 promoter-dependent gene transcription. Northern blot analysis shows differential induction of prepro ET-1 mRNA in favour of CsA over FK506. Likewise, luciferase assays demonstrate stronger ET-1 promoter-dependent stimulation of the reporter gene by CsA than by FK506. Transcription of prepro ET-1 gene upon stimulation with both calcineurin antagonists is regulated by intracellular calcium levels. Lack of extra- or intracellular calcium prevents ET-1 promoter-dependent gene transcription and ET-1 mRNA induction. These observations demonstrate that calcineurin antagonists FK506 and CsA differ in quality to induce transcription of prepro ET-1 in HUVEC via calcium-dependent nuclear signalling events. To examine the contribution of ET-1 in nephrotoxicity upon CsA and FK506 immunosuppression the availability of endothelin receptor antagonists or endothelin converting enzyme inhibitors is required.

Endothelium-derived factors as paracrine mediators of prostate cancer progression

BACKGROUND

Vascular endothelium represents a complex network of cells producing a large number of active substrates affecting physiologic, metabolic, and immunologic properties of the whole organism, as well as particular organs or tissues. The potential influence of endothelium-derived paracrine factors on prostate cancer progression has only begun to be examined.

METHODS

This review summarizes recent literature on endothelium-derived factors, including vasoactive agents, peptide growth factors, cytokines, and colony-stimulating factors, involved in the development and progression of prostate cancer.

RESULTS

Endothelial cells produce an array of active substrates, many of which have been shown to influence prostate cancer growth. Available data demonstrate the positive impact of such molecules as endothelin-1, basic FGF, TGF-beta, IL-6, and IL-8 on prostate cancer progression. Many other endothelium-derived factors NO, IGF, PDGF, IL-1, G-CSF, and GM-CSF (Nitric Oxide, Insulin-Like Growth Factor, Platelet-Derived Growth Factor, Interleukin-1, Granulocyte Colony Stimulating Factor, and Granulocyte-Macrophage Colony Stimulating Factor) are, at best, implicated in prostate cancer growth, and in most cases support cancer progression.

CONCLUSIONS

A better understanding of endothelium-derived factors, as paracrine mediators of prostate carcinogenesis and progression, should aid in the development of novel therapeutic strategies.