Regulation of endothelin-1 biosynthesis

The role of endothelin-1 in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare but debilitating disease, which if left untreated rapidly progresses to right ventricular failure and eventually death. In the quest to understand the pathogenesis of this disease differences in the profile, expression and action of vasoactive substances released by the endothelium have been identified in patients with PAH. Of these, endothelin-1 (ET-1) is of particular interest since it is known to be an extremely powerful vasoconstrictor and also involved in vascular remodelling. Identification of ET-1 as a target for pharmacological intervention has lead to the discovery of a number of compounds that can block the receptors via which ET-1 mediates its effects. This review sets out the evidence in support of a role for ET-1 in the onset and progression of the disease and reviews the data from the various clinical trials of ET-1 receptor antagonists for the treatment of PAH.

Renal, retinal and cardiac changes in type 2 diabetes are attenuated by macitentan, a dual endothelin receptor antagonist

AIMS

Diabetes is known to cause alteration of the endothelin (ET) system. We have previously demonstrated that ETs regulate augmented production of extracellular matrix proteins causing structural alterations in type 1 diabetes. Here we investigated the effects of macitentan, an orally-active, tissue-targeting dual ET receptor antagonist on chronic complications in type 2 diabetes.

MAIN METHODS

db/db mice and their age- and sex-matched controls were examined after 2 and 4 months of diabetes. Groups of diabetic animals were treated with oral macitentan (25mg/kg/day). The animals were monitored with respect to body weight and blood glucose. Urine analyses were performed for albumin. Cardiac hemodynamic studies were carried out. Renal, cardiac and retinal tissues were analyzed for ET-1, transforming growth factor-β1 (TGF-β1), vascular endothelial growth factor (VEGF), fibronectin (FN), extradomain B containing FN (EDB(+)FN) and collagen α-I (IV) mRNA. Cardiac atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were measured. Protein expressions were measured by ELISA and Western blot. Microscopic analyses were performed in the kidneys.

KEY FINDINGS

Diabetic animals showed hyperglycemia, increased urinary albumin and augmented serum creatinine levels. Diabetes caused increased renal, cardiac and retinal ET-1, TGF-β1, VEGF, FN, EDB(+)FN, collagen α-I(IV) mRNA expression along with increased FN and collagen protein and NF-κB activation. Diabetic mice also demonstrated mesangial expansion, cardiac dysfunction and increased expression of ANP and BNP. Treatment with macitentan attenuated such abnormalities.

SIGNIFICANCE

These experiments confirmed that ET system plays a significant role in the pathogenesis of chronic complications in type 2 diabetes. Such diabetes induced changes can be reduced macitentan therapy.

Endothelin-1 and nitric oxide in patients on chronic hemodialysis

AIM

To establish the role of endothelin-1 and nitric oxide in the pathogenesis of hypertension in patients on chronic hemodialysis by correlating endothelin-1 and NO plasma concentrations to the level of arterial hypertension with respect to angiotensin-converting enzyme (ACE) inhibitor therapy.

METHODS

We determined plasma concentrations of endothelin-1 and NO in patients on chronic hemodialysis (CHD) before and after hemodialysis treatment. The study included 30 CHD patients and 20 healthy participants as controls. Correlation to blood pressure was determined, as well as the effect of ACE inhibitors on the relationship between both endothelin-1 and NO in correlation with arterial hypertension.

MAIN FINDINGS

Endothelin-1 plasma concentration was significantly higher in CHD patients before hemodialysis treatment than in healthy controls. Endothelin-1 plasma concentration was also significantly higher in CHD patients after hemodialysis than in healthy controls. There was a significant decrease in endothelin-1 plasma concentration after hemodialysis in comparison with its values before hemodialysis. In CHD patients, a positive correlation was found between endothelin-1 plasma concentration and systolic blood pressure after hemodialysis, irrespective of ACE inhibitors therapy. In CHD patients taking ACE inhibitors, systolic blood pressure increased with increasing endothelin-1 plasma concentration before as well as after hemodialysis. In patients taking ACE inhibitors, there was a tendency for diastolic blood pressure to increase with an increase in endothelin-1 plasma concentration after hemodialysis and to decrease with an increase in NO plasma concentration.

CONCLUSION

NO and endothelin-1 play a significant role in etiology of the hemodynamic changes of blood pressure during the dialysis.

Low-Dose Ionizing Radiation Stimulates Transcription and Production of Endothelin by Human Vein Endothelial Cells

A transient increase of EDN1 mRNA accumulation is observed in human vein endothelial cells (HUVECs) after a low dose of ionizing radiation. The kinetics of this mRNA accumulation parallels that of other AP1-regulated transcripts, showing a sharp peak 2 h after irradiation. This accumulation is followed by a net increase of endothelin 1 and big endothelin 1 in the cytoplasm that reaches a peak 4 h after irradiation. We followed the kinetics of endothelin 1 secretion in cell culture medium and did not find a detectable increase in the rate of secretion by the irradiated cells compared to sham-irradiated cells. We conclude that in HUVEC monolayers, an increase in endothelin production does not automatically correspond to an increase in secretion. These findings suggest that endothelin is an important component in the response of endothelial cells to ionizing radiation and that it could be used as a biomarker for low-dose irradiation of endothelial tissues.

Heparin Regulates Transcription of Endothelin-1 Gene in Endothelial Cells

Heparin, which is widely used as an anticoagulant, has been shown to have antiatherosclerotic and antihypertensive effects in animals and humans. These effects are mediated by the inhibition of endothelin-1 (ET-1) production in endothelial cells. To clarify the mechanism of this inhibition, we investigated the effect of heparin on transcriptional regulation of the ET-1 gene in bovine aortic endothelial cells (BAEC) cultured in fetal calf serum. ET-1 mRNA expression was significantly suppressed by heparin in a dose-dependent manner. Promoter analysis revealed that the minimum ET-1 promoter containing only the GATA and AP-1 sequences as positive cis-acting sites in the ET-1 promoter is sufficient for this suppression. Gel mobility shift assays using oligonucleotides encoding the ET-1 AP-1 and ET-1 GATA sites confirmed that both AP-1 and GATA binding activities in BAEC nuclear extract were markedly inhibited by heparin. Western blot analyses indicated that heparin completely blocked extracellular signal-regulated kinase (ERK) activation, and inhibiting ERK activity resulted in loss of heparin-dependent inhibition of the ET-1 gene. These data indicate that the ET-1 mRNA level is negatively regulated by heparin at the transcription level, through modification of AP-1 and GATA protein binding activities, which direct the ET-1 promoter in BAEC. This effect may be mediated, at least in part, through inhibition of ERK activity.

Role of endogenous endothelin-1 in transplant obliterative airway disease in the rat

Endothelin-1 (ET-1) expression is increased after lung transplantation in association with ischemia reperfusion injury and acute rejection. However, little is known of the role of ET-1 during the development of obliterative bronchiolitis. In this study, we investigated the biological significance of ET-1 in obliterative airway disease development using a rat tracheal allograft model. Immunoreactivity of ET-1 and its receptors ET-RA and ET-RB was increased four-fold in allografts compared with syngrafts and localized to mononuclear cells and smooth muscle cells of the myofibroproliferative lesion and airway wall, indicating that ET-1 may mediate its effects in both a paracrine and autocrine manner in smooth muscle cells. Inhibition of ET-1 action by a nonselective ET-1 receptor antagonist, bosentan, significantly decreased tracheal occlusion, which was linked to delayed epithelial necrosis, suppressed smooth muscle cell proliferation, and a marked reduction in the number of interleukin-1beta and interleukin-2 immunoreactive cells. Our findings show that endogenous ET-1 activation is associated with obliteration of the airway wall, and blocking signaling downstream of ET-1 receptors leads to attenuation of obliterative airway disease. The results suggest that ET-1 has a proproliferative and proinflammatory role in the development of obliterative bronchiolitis.

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.

Endothelins in chronic diabetic complications

Endothelins are widely distributed in the body and perform several vascular and nonvascular functions. Experimental data indicate abnormalities of the endothelin system in several organs affected in chronic diabetic complications. In support of this notion, it has been shown that endothelin-receptor antagonists prevent structural and functional abnormalities in target organs of diabetic complications in animal models. Alterations of plasma endothelin levels have also been demonstrated in human diabetes. This review discusses the role of endothelins in the pathogenesis of chronic diabetic complications. The current experimental evidence suggests that endothelin-receptor antagonism may potentially be an adjuvant therapeutic tool in the treatment of chronic diabetic complications.

Effect of endothelin-1 on intracellular glutathione and lipid peroxide availability and on the secretion of vasoactive substances by human umbilical vein endothelial cells

BACKGROUND

The major pathophysiologic changes observed in preeclampsia suggest that endothelial cell dysfunction plays an important role in this disorder. The pathway mediating endothelial cell layer dysfunction is unknown. The concentration of endothelin-1 (ET-1), a potent mammalian vasoconstrictor peptide produced by the vascular endothelium, has been observed to be significantly increased in preeclampsia. In this study, we determined the in vitro effect of endothelin-1 on glutathione and lipid peroxide levels and on the secretion of vasoactive substances by human umbilical vein endothelial cells (HUVECs).

METHODS

Human umbilical vein endothelial cells were incubated for 24 h in the presence of different concentrations of ET-1 (0-1000 pmol L(-1)), which were shown in an earlier experiment to have no effects on vitality and proliferation rate of HUVECs. The levels of glutathione (GSH) and lipid peroxides (LPO) were measured in endothelial cell lysates. For the measurement of vasoactive substances, levels of nitric oxide (NO), prostacyclin (PGI2) and thromboxane A2 (TXA2) were measured in endothelial cell supernatants.

RESULTS

At lower concentrations (5-50 pmol L(-1)), ET-1 increases the intracellular content of LPO, stimulates the secretion of TXA2, but inhibits the secretion of PGI2 in endothelial cells compared with control cells. At higher concentrations (100-1000 pmol L(-1)), ET-1 increases the intracellular content of GSH, but results in a decrease of LPO, and increase of PGI2, back to control levels. ET-1 has no effect on NO secretion.

CONCLUSION

These findings demonstrate that at concentrations corresponding to values in plasma from preeclamptic women, ET-1 induces oxidative stress and results in altered secretion of vasoactive substances in human endothelial cells. We conclude that ET-1 may participate in the pathway leading to endothelial cell dysfunction seen in preeclampsia.

Therapeutic potential of endothelin receptor antagonists and nitric oxide donors in pulmonary hypertension

Pulmonary hypertension can occur idiopathically as a primary disorder of the pulmonary circulation or more commonly, it can exist as a haemodynamic manifestation of a wide variety of pulmonary and cardiovascular diseases, including acute lung injury, chronic obstructive lung disease, congenital heart disease, mitral stenosis, chronic left-sided congestive heart failure and connective tissue diseases such as scleroderma. Pulmonary hypertension is associated with changes in vascular tone as well as vascular structure, with the relative contribution of each dependent upon the aetiology of the increased pulmonary vascular resistance. Most currently available treatments utilise anticoagulants as well as vasodilator drugs that only attenuate the vasoconstrictive component of the disease. The latter category includes oral calcium channel blockers, iv. and aerosolised prostacyclin analogues and inhaled nitric oxide but all three classes of vasodilators have disadvantages and limitations. Treatment with vasodilators is often ineffective in patients with longstanding pulmonary hypertension in which structural changes contribute significantly to the pulmonary hypertension, blood flow obstruction and right heart failure. In view of the immense clinical need, new therapies are being developed by pharmaceutical companies to treat pulmonary hypertension. This update will focus on the current development status of endothelin receptor antagonists and nitric oxide donors for the treatment of pulmonary hypertension.

Endothelins: vasoactive modulators of renal function in health and disease

Vasoactive autocoids with directly opposing actions on the renal vasculature, glomerular function, and in salt and water homeostasis have been demonstrated in the kidney. In the renal cortex, endothelin (ET)-1 and angiotensin-II cause vasoconstriction, decreasing renal blood flow, and glomerular filtration rate, whereas bradykinin and atrial natriuretic peptide cause vasodilation and increase glomerular capillary permeability. ET-1 causes vasoconstriction of the afferent and efferent arteries and outer medullary descending vasa recta, thereby decreasing vasa recta and papillary blood flow, while bradykinin has the opposite effect. ET-1 stimulates cell proliferation, increasing the expression of several genes, including collagenase, prostaglandin endoperoxidase synthase, and platelet-derived growth factor. ET-1 promotes natriuresis via the ET-B receptor, causing down-regulation of the epithelial Na(+) channel in the renal tubule. Thus, ETs affect three major aspects of renal physiology: vascular and mesangial tone, Na(+) and water excretion, and cell proliferation and matrix formation.

Pregnancy, vascular tone, and maternal hemodynamics: a crucial adaptation

The adaptation of vascular tone in early pregnancy precedes and probably triggers blood volume and cardiac output increase. Because the endothelium is known to regulate vascular smooth muscle action, the role of nitric oxide (NO) in the setting up of adequate uteroplacental and renal blood flow during normal pregnancy was investigated. The persistence of abnormally high uteroplacental resistance is a strong predisposing factor for intrauterine growth retardation and preeclampsia and can be screened by second trimester Doppler assessment of the uterine arteries. Current hypotheses suggested by experimental and clinical data concerning preeclampsia confirm the crucial role played by the endothelium and vascular tone adaptation. The analysis of these data leads to consider apart early-onset preeclampsia affecting pregnancies with growth retarded fetuses and associated with high vascular resistance. Lastly, NO donors seem to significantly decrease the impedance in the uteroplacental circulation and to improve fetoplacental hemodynamics assessed by Doppler measurements, and their therapeutic use in some forms of preeclampsia might be promising.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians

LEARNING OBJECTIVES

After completion of this article, the reader will be able to summarize the events that regulate vascular tone in pregnancy, specifically the role of nitric oxide and other vasoactive prostaglandins in the regulation of vascular tone and to describe the various hypotheses concerning the mechanism and the mediators responsible for initiating endothelial damage in the various disorders of vascular tone in pregnancy.

Endothelin and the central and peripheral nervous systems: a decade of endothelin research

1. During the past decade, extensive investigation of the endothelin (ET) system, primarily characterized by its potent vasoactive peptide element ET-1, has suggested a prominent role for this humoral agent and its isopeptides in cardiovascular and neural regulation. 2. Major elements of this system, including its peptide isoforms, converting enzymes involved in their formation and metabolism, as well as multiple receptor subtypes, have been localized within various components of the cardiovascular system and the central and peripheral nervous systems. 3. An understanding of the possible roles for the ET system in neural regulation and development has progressed over the past several years; most notable is the influence of ET on the central control of cardiovascular function and sympathetic tone. 4. The present concentrated review of ET and the central and peripheral nervous systems is presented to introduce the other papers within this symposium by briefly describing the presence and influence of components of this unique peptide system within pertinent physiological structures involved in cardiovascular, adrenal, sympathetic and enteric developmental function.

Stobadine is a potent modulator of endogenous endothelin-1 in human fibroblasts

Binding of endothelin (ET) peptides to their respective receptors with resulting proliferation of vascular smooth muscle has been implicated in the pathogenesis of arterial hypertension and atherosclerosis. Recently it was hypothesized that endothelin- (ET-1) bound to its two membrane receptors (ET(A) and ET(B)) continues to activate signal transducing proteins in cells. It was also shown that pyridoindole stobadine stabilized lysosomal membranes in myocardium in early ischemia. Therefore we decided to study the effects of stobadine on specific, subtype-selective binding and subsequent degradation of human, synthetic [125I]-ET-1 in human fibroblasts (HF). Our results indicate that stobadine significantly potentiated ET-1 binding by reductive ET(B) selective degradation of ET-1 in HF. Hence, it is very plausible that stobadine may modulate endogenous endothelin and its intracellular mitogenic and chemotactic factors, principally by affecting two presumably related processes, participating in the proliferative and mitogenic response, (1) potentiation of signal trasduction from ET(A) receptors, and (2) subtype-ET(B) selective intracellular processing.

Postischemic hyperemia in subjects with lower limbs obstructive arteriopathy: role of PGI2 and endothelin

The physiological basis of postischemic hyperemia is not yet fully understood. The present study investigated the effects of pharmacologic manipulation of the prostaglandin system on local hemodynamics. Strain-gauge plethysmography was used to study 8 normal subjects and 9 patients with obliterating arterial disease of the lower limbs. Hemodynamic evaluations were performed before treatment, after seven days of low-dose acetylsalicylic acid (100 mg/day) to inhibit platelet thromboxane synthesis, and after acute infusion of 1 g of acetylsalicylic acid to inhibit endothelial prostacyclin synthesis. In patients with arterial disease, the hemodynamic study was also carried out after infusion of iloprost, a synthetic prostacyclin analogue. Acute infusion of acetylsalicylic acid significantly reduced basal blood flow in normal subjects, but not in patients with arterial disease. In the latter group, iloprost affected neither basal nor maximal postischemic flow. The study also evaluated the role of endothelin in musculocutaneous hemodynamic regulation, both in physiological conditions and in atherosclerosis. This part of the study addressed the possibility that the hemodynamic effects of vasodilator prostanoids like prostacyclin might affect endothelin release in vivo. During reactive hyperemia, plasma endothelin was reduced in normal subjects (-1.02 pg/mL, 95% CI: -2.23, 0.08), but not in patients with atherosclerosis (-0.35 pg/mL, 95% CI: -1.45, 0.75). In both groups, plasma endothelin was not affected by aspirin. These findings confirm the role of prostacyclin in local hemodynamic regulation. In the normal subject, musculocutaneous blood flow seems to depend at least in part on the action of vasodilator prostanoids and endothelin. This is not the case in patients with arterial disease, in whom plasma endothelin does not seem to be affected by postischemic changes in blood flow. A possible explanation for this difference could be alteration of the endothelial function in patients with arterial disease, related to the functional and structural characteristics of the artery wall in atherosclerosis.

The endothelin system and its potential as a therapeutic target in cardiovascular disease

Endothelin (ET)-1, an endothelium-derived peptide, is the most potent vasoconstrictor agent described to date. ET-1 also has positive inotropic and chronotropic effects in the heart and is a co-mitogen in both cardiac and vascular myocytes. The major elements of the system involved in formation of ET-1 and its isopeptides, as well as the receptors mediating their effects, have been cloned and characterised. Antagonists of the ET receptors are now available, and selective inhibitors of the ET-converting enzymes are being developed. Early studies using receptor antagonists support the involvement of ET-1 in the pathophysiology of several cardiovascular diseases. The relative merits of ET-converting enzyme inhibitors and receptor antagonists for the treatment of cardiovascular disease are discussed.

Modifications of plasma levels of tissue factor pathway inhibitor and endothelin-1 induced by a reverse Trendelenburg position: influence of elastic compression--preliminary results

PURPOSE

The purpose of this study was to assess the effects of the passive 45-degree reverse Trendelenburg position and graduated compression stockings (GCS) on plasma tissue factor pathway inhibitor (TFPI) and endothelin-1 levels in a group of volunteers.

METHODS

Ten healthy subjects lay on an examining table for 30 minutes while baseline measurements were made. The table was then tilted to a 45-degree upright position for 60 minutes, and measurements were repeated. On a different day, subjects were tilted again, but on this occasion they wore thigh-length GCS. Blood was drawn before and 60 minutes after tilting during both sessions, and plasma TFPI and endothelin-1 were obtained. Cross-sectional areas of the calf medial gastrocnemius vein, before and after tilting, were measured by a duplex scanner.

RESULTS

Upright tilting induced a significant dilation of the medial gastrocnemius veins that was partially corrected by the use of elastic stockings. Similarly, endothelin-1 levels significantly increased after tilting. The use of GCS did not modify these differences. On the other hand, although TFPI levels were not affected by tilting without stockings, they were significantly elevated after tilting when GCS were used.

CONCLUSIONS

Upright passive tilting induces significant dilation of the deep calf veins and is associated with a significant increase in plasma levels of endothelin-1, whereas TFPI levels remain unchanged. The use of elastic stockings reduces the degree of calf distention but does not prevent an increase in endothelin-1. TFPI levels are significantly increased after tilting when GCS are used. This might represent a previously unknown mechanism of action of elastic stockings with interesting potential for deep vein thrombosis prophylaxis. More studies are warranted in a larger series to confirm these results.