Clinical significance of endothelin in cardiovascular disease

Does Preoperative Plasma Endothelin-1 Level Influences the Postoperative Events in Patients Undergoing Coronary Artery Bypass Grafting (CABG)? Revisiting Endothelin-1 Molecule in CABG Patients

Endothelin-1 (ET-1) is a powerful physiological vasoconstrictor release in response to endothelial injury. Increased synthesis of endothelin is associated with myocardial ischemia and reperfusion injury. The normal level varies between 0.2 and 18.5 pg/mL that maintains normal vascular homeostasis. We hypothesized that there exists a correlation between ET-1 and clinical outcome in patient undergoing elective coronary artery bypass grafting (CABG) surgery under cardiopulmonary bypass.

Fifty-eight patients undergoing elective on-pump CABG were enrolled in the study. Blood sample for plasma ET-1 was taken before anesthesia induction. The median ET-1 level was 5 pg/mL (range: 0.6–30.33 pg/mL). The inotropic and intraaortic balloon pump requirement was significantly higher among patients having baseline ET-1 level more than 14.24pg/mL (p = 0.001in each case). A similar finding was observed in the duration of mechanical ventilation, intensive care unit stay, and duration of hospital stay (r = 0.68, p = 0.000; r = 0.58, p = 0.000; and r = 0.61, p = 0.000 respectively). The occurrence of complications was also more in individuals with higher baseline ET-1 level. The p-value was significant for occurrence infection, arrhythmia, renal and respiratory problems as observed in postoperative period by using Mann–Whitney U test.

This study concludes that higher level of preoperative ET-1 levels correlates well to adverse clinical outcome in patients undergoing on-pump CABG surgery, so herein it can be used as a single independent parameter to predict postoperative outcome.

The cold effects on circulatory inflammation, thrombosis and vasoconstriction in type 2 diabetic patients

Short-term associations between temperature variation and adverse cardiovascular outcomes have been well documented. However, it remains unclear whether these temperature-related cardiovascular effects are reflected in circulating biomarkers. We aimed to examine the associations between ambient temperature and circulating biomarkers of inflammation, coagulation and vasoconstriction. We collected 207 blood samples from a panel of 35 type 2 diabetes mellitus patients. Sixteen biomarkers of inflammation, coagulation and vasoconstriction were repeatedly measured over six follow-ups. The short-term associations between air temperature and these biomarkers were assessed by mixed-effect models with controls of demographic characteristics and main air pollutants. We found significant and acute effects of temperature on circulatory biomarkers occurred as early as 3h after exposure, peaked at 25-48h and lasted until 72h after exposure. For example, a 1°C decrease in the 25-48h average of air temperature was associated with 2.2%-15.1% increases in biomarkers of inflammation, 1.4%-24.5% of coagulation and 8.2% of vasoconstriction. Our results provided significant evidence that a temperature decline results in a response in biomarkers of inflammation, coagulation and vasoconstriction biomarkers, suggesting them to be the potential biologic mechanisms underlying the cardiovascular effects of temperature variation, and may have implications for disease prevention.

Impaired endothelial function in siblings of patients with diabetic mellitus type 2

Background

Endothelial dysfunction is considered as a risk factor for cardiovascular disease, which is a consistent finding in diabetic mellitus type 2 (DMT2). First-degree relatives of DMT2 patients have a higher risk of developing DMT2 later on the life. We aimed to investigate whether impaired endothelial function exists in siblings of DMT2 patients.

Methods

As endothelial function markers, plasma E-selectin, soluble inter-cellular adhesion molecule-1 (sICAM-1), and endothelin-1 (ET-1) were measured on 27 DMT2 patients (9 m/18f; mean age: 48.48 ± 6.75 years), 28 siblings of DMT2 patients (14 m/14f; mean age: 44.54 ± 7.10 years), and 30 control subjects (18 m/12f; mean age: 44.72± 7.56 years) without any family history of diabetes. All the groups were matched by gender, age, and body mass index (BMI).

Results

Plasma levels of ET-1, sICAM-1, and E-selectin were significantly higher in the DMT2 group compared to the control group (ET-1:0.79 ± 1.63 pg/ml vs. 0.33 ± 0.08 pg/ml; P_CD = 0.049, sICAM-1: 71.15 ± 27.20 ng/ml vs. 34.57 ± 22.56 ng/ml; P_CD = 0.001, E-selectin: 22.45 ± 11.57 ng/ml vs. 16.28 ± 7.50 ng/ml; P_CD =0.026). There was a significant difference in sICAM-1 levels between siblings (62.08 ± 26.37 ng/ml) and controls (P_CS = 0.002), but not between siblings and DMT2 patients (P_SD = 0.411). Moreover, a significant difference was observed in ET-1 levels between siblings (0.75 ± 1.26 pg/ml) and controls (P_CS = 0.031), but not between siblings and DMT2 patients (P_SD = 0.751). There was also a significant difference in E-selectin levels between DMT2 patients and siblings (16.56 ± 8.71 ng/ml; P_SD =0.028); however, the difference in E-selectin levels was not statistically significant between siblings and controls (P_CS = 0.919).

Conclusion

Endothelial function markers in the siblings of DMT2 patients are increased in comparision to the control group Therefore; family history in the DMT2 patients seems to be a risk factor for endothelial function. Furthermore, endothelial dysfunction is available very early in the DMT2 patients, even before overt hyperglycemia ensues (in siblings), and may play a key role in the etiopathology of the vasculopathy associated with DMT2.

Ontogeny of endothelin receptors in the brain, heart, and kidneys of neonatal rats

BACKGROUND

Endothelin (ET) plays an important role in many physiological functions. It has been demonstrated that endogenous ET-1 concentration in the central nervous system (CNS) changes with age; however the ontogeny of ETA and ETB receptors in the brain, heart, and kidneys during postnatal development has not been studied.

METHODS

Brains, hearts and kidneys of rats at postnatal days 1, 7, 14 and 28 were evaluated for the expression of ETA and ETB receptors via Western blot. ETB receptors within the developing brain were further accessed via immunofluorescence.

RESULTS

The mean organ and body weights increased proportionally with advancing age demonstrating normal growth. The expression of ETA receptors in the brain, heart, and kidneys and ETB receptor expression in the heart and kidneys was similar in these rats at postnatal ages 1, 7, 14 and 28days. However, brain ETB receptor expression significantly (P<0.001) decreased by 72% on day 28 compared to the levels on postnatal day 1. Upon immunofluorescent analysis, the intensity of ETB staining in the cerebral cortex and subventricular zones of the developing rat brain decreased significantly from day 1 to day 7 (P<0.001) and from day 7 to day 14 (P<0.0001). There was no further decrease in ETB intensity noted in the cerebral cortex and subventricular zones between day 14 and day 28 of postnatal age. The intensity of ETB receptor staining within the cerebrovasculature, on the other hand, increased significantly (P<0.05) from days 1 and 7 to day 14.

CONCLUSIONS

These results demonstrate that expression of ETA receptors does not change with postnatal development. On the other hand ETB receptors in the cerebral cortex and subventricular zones of the brain decrease with age, while ETB receptors in the cerebrovasculature increase with age, implicating ETB receptor involvement in the structural maturity and development of the CNS.

Circulating endothelial cells and chronic kidney disease

Endothelial dysfunction may play a crucial role in initiation of the pathogenesis of vascular disease and atherosclerosis. The identification and quantification of circulating endothelial cells (CEC) have been developed as a novel marker of endothelial function. We describe, in great detail, mechanisms of endothelial dysfunction and CEC detachment. We also review the relationship between numbers of CEC and disease severity and response to treatment. In addition, we describe the possible clinical use of CEC in chronic kidney disease (CKD) and kidney transplantation. In summary, CEC have been developed as a novel approach to assess the endothelial damage. Measurement of the CEC level would provide an important diagnostic and prognostic value on the endothelium status and the long-term outcome of vascular dysfunction.

Isolated Heart Function after Ischemia and Reperfusion in Sucrose-Fed Rats: Influence of Gender and Treatment

Sucrose-fed rats (HTG) develop hypertension, hypertriglyceridemia, and other features of the metabolic syndrome. This condition, nowadays a world epidemic, is more prevalent in males and increases the risk of cardiovascular diseases. Weanling male and female rats were given either tap water in control (C) or 30% sucrose solution in HTG groups and commercial rat chow for 3, 5, or 8 months. We studied possible variations in cardiac function, due to gender and length of treatment, in isolated heart after ischemia-reperfusion, since an impaired performance may be more easily detected under stress. Together, sucrose treatment and age affected all cardiac variables. Gender had significant effect on coronary vascular resistance and postischemic levels of the enzyme CK-MB; the percentages of retained cardiac enzymes after ischemia were higher in C and HTG females. C and HTG males had a higher incidence of arrhythmias than females, but only HTG males suffered lethal ventricular fibrillation.

Natriuretic peptides in cardiovascular diseases

The natriuretic peptide family comprises atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), dendroaspis natriuretic peptide (DNP), and urodilatin. The activities of natriuretic peptides and endothelins are strictly associated with each other. ANP and BNP inhibit endothelin-1 (ET-1) production. ET-1 stimulates natriuretic peptide synthesis. All natriuretic peptides are synthesized from polypeptide precursors. Changes in natriuretic peptides and endothelin release were observed in many cardiovascular diseases: e.g. chronic heart failure, left ventricular dysfunction and coronary artery disease.

Enhanced oxidative stress and endothelial dysfunction in streptozotocin-diabetic rats exposed to fine particles

The association between ambient particulate matter (PM) and cardiovascular diseases has been demonstrated in epidemiological studies. Recent studies suggest that diabetic patients are at greater risk for PM-associated cardiovascular events. Although diabetes and PM exposure individually have been reported to be associated with increased oxidative stress, inflammation, and endothelial dysfunction, it is not clear whether PM may induce synergistic interaction effects on these parameters in diabetics. Strepotozotocin-induced diabetic (n=4) and healthy (n=4) rats were intratracheally administered with PM2.5 collected from a busy traffic area in a dose of 200 microg suspended in 0.5 mL phosphate-buffered saline (PBS). The same number of rats was exposed to PBS as controls. Cell and differential counts and protein and lactate dehydrogenase activity were determined in bronchoalveolar lavage. Markers of 8-hydroxydeoxy-guanosine (8-OHdG), endothelin-1 (ET-1), and [nitrate+nitrite], an indicator of nitric oxide (NO) production, in addition to C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) in peripheral blood were also determined. Our results showed that diabetic rats were associated with increased 8-OHdG, IL-6, and ET-1 decreased [nitrate+nitrite]. In nondiabetic rats PM exposure was also associated with increased 8-OHdG, IL-6, TNF-alpha, and CRP but decreased [nitrate+nitrite]. Interestingly, increases of 8-OHdG and ET-1 after PM exposure were more prominent in diabetic rats than in nondiabetic rats. The general linear model further indicated that there were interactions between diabetes and PM on 8-OHdG (P<0.01) and ET-1 (P=0.08). We suggest that PM exposure may enhance the risk of cardiovascular diseases through interaction between PM and diabetes on excess reactive oxygen species generation and endothelial dysfunction. These findings provide further support for previous epidemiological studies.

Disruptions and detours in the myocardial matrix highway and heart failure

Myocardial remodeling invariably occurs in congestive heart failure (CHF) and is a response to a prolonged cardiovascular stress, which is characterized by a cascade of compensatory structural events. Remodeling of the myocardial interstitium occurs in CHF and likely contributes to the progression of the remodeling process. The myocardial matrix can be considered a biological highway in which a large amount of signaling proteins and structural proteins are being moved within the interstitium, entering and exiting the interstitial space, and docking to cellular components. The rates at which these events occur can accelerate and decelerate depending on the particular cardiac disease state and thereby can alter the course of myocardial remodeling. Once considered merely a scaffolding to align cells, the matrix plays a complex and divergent role in influencing cell behavior. For example, the matrix has a functional role in cell migration, proliferation, adhesion, and cell-to-cell signaling. In light of this, the myocardial matrix should not be regarded as merely a static structure, but rather, as a complex system of dynamic interactions between matrix molecules, signaling proteins, and transmembrane proteins. Specific strategies that are targeted at modifying activity along this matrix highway will likely alter the course of myocardial remodeling and heart failure.

Positron emission tomography using 18F-labelled endothelin-1 reveals prevention of binding to cardiac receptors owing to tissue-specific clearance by ET B receptors in vivo

Our aim was to synthesise an (18)F analogue of endothelin-1 (ET-1), to dynamically image ET receptors in vivo by positron emission tomography (PET) and to elucidate the function of the ET(B) subtype as a clearing receptor in organs expressing high densities including kidney and lung.[(18)F]-ET-1 was characterised in vitro and bound with a single subnanomolar affinity (K(D)=0.43+/-0.05 nM, B(max)=27.8+/-2.1 fmol mg(-1) protein) to human left ventricle (n=4). The in vivo distribution of [(18)F]-ET-1 in anaesthetised rats was measured using a dedicated small animal PET scanner (microPET) and ex vivo analysis. Dynamic PET data demonstrated that high levels of radioligand accumulated rapidly in the lung, kidney and liver, consistent with receptor binding. The in vivo distribution correlated with the anatomical localisation of receptors detected in vitro using [(125)I]-ET-1. However, the receptor density visualised in the heart was unexpectedly low compared with that predicted from the in vitro measurements.[(18)F]-ET-1 binding in lungs could not be displaced by the ET(B) selective antagonist BQ788, in agreement with the proposed internalisation of ET-1 by ET(B) receptors. In contrast, infusion of BQ788 prior to injecting [(18)F]-ET-1 significantly reduce the amount of radioligand visualised in the ET(B) rich lung and kidney by 85% (P< 0.05, n=3) and 55% (P<0.05, n=3), respectively. Under conditions of ET(B) receptor blockade, the heart could be visualised by microPET imaging.These results suggest that clearance by ET(B) receptors in the lung and kidney prevents binding of ET-1 to receptors in the heart.

In-vivo interaction of nitric oxide and endothelin

OBJECTIVE AND METHODS

Endothelin-1 (ET-1) was initially characterized as a potent vasoconstrictor. However, the expected role of ET-1 as a major blood pressure controlling peptide could not be clearly established. Moreover, ET-1 transgenic mice are not hypertensive. We assume that counter-regulating mechanisms such as the nitric oxide (NO) system or an altered expression of endothelin receptors might cause this finding.

RESULTS

An intravenous (i.v.) bolus injection of N(omega)-nitro-L-arginine methyl ester (L-NAME) resulted in a significantly higher blood pressure increase in ET-1 transgenic mice, as compared to non-transgenic littermates. On the other hand, blood pressure increased similarly after an i.v. injection of ET-1 in ET-1 transgenic mice and non-transgenic littermates. Pretreatment with dexamethasone abolished the higher blood pressure increase after L-NAME in ET-1 transgenic mice. Urinary excretion of NO metabolites was elevated in ET-1 transgenic mice and decreased significantly after dexamethasone treatment. Immunohistochemistry revealed that the inducible NO synthase (iNOS) was highly expressed in intrarenal arteries in these mice. Dexamethasone pretreatment abolished vascular iNOS expression. No vascular iNOS expression was detectable in non-transgenic littermates. Furthermore, immunohistochemistry revealed that ET-1 transgenic mice are characterized by an increased tissue density of CD4-positive lymphocytes and macrophages. Analysis of endothelin receptor expression and function revealed that the endothelin subtype A (ETA) receptor was not differently expressed in ET-1 transgenic mice as compared to age-matched littermates. The blood pressure response to an ETA receptor antagonist was likewise similar in ET-1 transgenic mice and age-matched littermates. The endothelin subtype B (ETB) receptor density was decreased in ET-1 transgenic mice. Treatment with an ETB receptor antagonist led to a non-significant slightly higher blood pressure increase in ET-1 transgenic mice as compared to controls.

CONCLUSION

The endothelin receptor expression pattern and the blood pressure responses to ETA and ETB receptor antagonists could not explain the lack of hypertension in ET-1 transgenic mice. Overexpression of the human ET-1 gene causes chronic kidney inflammation with an induction of vascular iNOS expression. The induction of iNOS expression might cause a new local balance between vascular ET-1 and nitric oxide, resulting in no alterations of blood pressure.

Endothelin B receptor deficient transgenic rescue rats: a rescue phenomenon in the brain

Homozygous endothelin B receptor deficiency leads to congenital aganglionosis of the gut in rats and mice, equivalent to human Hirschsprung disease. Homozygous endothelin B receptor deficient rats (spotting lethal rats, sl/sl) are characterized not only by this developmental disorder of the enteric nervous system, which limits their life span to 3-4 weeks, but exhibit an increased rate of apoptosis in the dentate gyrus compared to wildtype (+/+) rats. Recently, endothelin B receptor deficient transgenic rescue rats (sl/sl, tg/tg) were created to further investigate the role of the endothelin B receptor in mature animals. Linkage of the human dopamine-beta-hydroxylase promoter to the rat endothelin B receptor gene and expression of this transgenic construct results in normal development of the enteric nervous system. We investigated the expression pattern of this transgenic construct in the brain by using reverse transcriptase polymerase chain reaction. Unexpectedly, transgene mRNA expression was not restricted to the brain stem where adrenergic and noradrenergic nuclei are known to be present but, in addition, was also detectable in hippocampus and cortex. Using in situ tailing technique, cleaved caspase-3 immunohistochemistry and analysis of hematoxylin-eosin-stained serial sections, we found that all studied transgenic animals were rescued from the increased rate of apoptosis in the dentate gyrus characteristic for non-transgenic sl/sl rats. This finding supports our previous observation that the endothelin B receptor might be an important regulatory element supporting cellular survival in the hippocampus during postnatal development. The endothelin B receptor deficient transgenic rescue rats used here are rescued from developmental disorders both in the gut and in the brain.

Significance of recently identified peptides in hypertension: endothelin, natriuretic peptides, adrenomedullin, leptin

Arterial hypertension is one of the major risk factors in cardiovascular and renal disease. Advances in the study of pathophysiologic mechanisms and the relationship between several regulatory systems provide the basis for development of more selective therapeutic strategies. The increasing understanding of the role played by ETs, natriuretic peptides, AM, and leptin opens new frontiers in the care of hypertension and its complications, coronary artery disease and heart failure and other forms of cardiovascular disease.

Role of endothelins in animal models of hypertension: focus on cardiovascular protection

Investigation of the regulation of vascular function by endothelium-derived factors has been a prominent topic of research in the field of hypertension during the last decade. Of the different endothelial factors, endothelins, which play an important role in vasodilatation-vasoconstriction balance, have been the subject of great interest and an impressive number of publications. This peptide, a very potent vasoconstrictor, triggers as well events involved in growth, proliferation, matrix production and local inflammation. In parallel, its role in hypertension has evolved from a simple vasoconstrictor to a central local regulator of vascular homeostasis contributing not only to the elevation of blood pressure, but also to the complications of hypertension. This review summarizes research on endothelins and its receptor antagonists in experimental hypertension, with special emphasis on vascular remodeling and target-organ protection.

Role of endothelin in human hypertension

Endothelin-1 (ET-1) is a pleiotropic hormone produced primarily by the endothelium. Synthesis of ET-1 is stimulated by the major signals of cardiovascular stress, such as vasoactive agents (angiotensin II, norepinephrine, vasopressin, and bradykinin), cytokines (e.g., tumor necrosis factor alpha and transforming growth factor beta), and other factors, including thrombin and mechanical stress. ET-1 induces vasoconstriction, is proinflammatory, promotes fibrosis, and has mitogenic potential, important factors in the regulation of vascular tone, arterial remodeling, and vascular injury. These effects are mediated via two receptor types, ETA and ETB. The role ET-1 plays in normal cardiovascular homeostasis and in mild essential hypertension in humans is unclear. However, certain groups of essential hypertensive patients may have ET-1-dependent hypertension, including blacks (subjects of African descent), salt-sensitive hypertensives, patients with low renin hypertension, and those with obesity and insulin resistance. ET-1 has also been implicated in severe hypertension, heart failure, atherosclerosis, and pulmonary hypertension. In all of these conditions, plasma immunoreactive ET levels are elevated and tissue ET-1 expression is increased. Accordingly, it is becoming increasingly apparent that ET-1 plays an important role in cardiovascular disease and in some forms of hypertension in humans. Data from clinical trials using combined ETA-ETB receptor blockers have already demonstrated significant blood-pressure-lowering effects. Thus, targeting the endothelin system may have important therapeutic potential in the treatment of hypertension, particularly by contributing to the prevention of target organ damage and the management of cardiovascular disease.

Physiological and pathophysiological roles of ATP-sensitive K+ channels

ATP-sensitive potassium (K(ATP)) channels are present in many tissues, including pancreatic islet cells, heart, skeletal muscle, vascular smooth muscle, and brain, in which they couple the cell metabolic state to its membrane potential, playing a crucial role in various cellular functions. The K(ATP) channel is a hetero-octamer comprising two subunits: the pore-forming subunit Kir6.x (Kir6.1 or Kir6.2) and the regulatory subunit sulfonylurea receptor SUR (SUR1 or SUR2). Kir6.x belongs to the inward rectifier K(+) channel family; SUR belongs to the ATP-binding cassette protein superfamily. Heterologous expression of differing combinations of Kir6.1 or Kir6.2 and SUR1 or SUR2 variant (SUR2A or SUR2B) reconstitute different types of K(ATP) channels with distinct electrophysiological properties and nucleotide and pharmacological sensitivities corresponding to the various K(ATP) channels in native tissues. The physiological and pathophysiological roles of K(ATP) channels have been studied primarily using K(ATP) channel blockers and K(+) channel openers, but there is no direct evidence on the role of the K(ATP) channels in many important cellular responses. In addition to the analyses of naturally occurring mutations of the genes in humans, determination of the phenotypes of mice generated by genetic manipulation has been successful in clarifying the function of various gene products. Recently, various genetically engineered mice, including mice lacking K(ATP) channels (knockout mice) and mice expressing various mutant K(ATP) channels (transgenic mice), have been generated. In this review, we focus on the physiological and pathophysiological roles of K(ATP) channels learned from genetic manipulation of mice and naturally occurring mutations in humans.

Lysophosphatidylcholine is a major contributor to the synergistic effect of mildly oxidized low-density lipoprotein with endothelin-1 on vascular smooth muscle cell proliferation

Endothelin-1 (ET-1) and oxidized low-density lipoprotein (ox-LDL) are associated with atherosclerosis and essential hypertension. We assessed the effect of mildly oxidized LDL (mox-LDL) and ox-LDL and their major oxidative components, i.e., reactive oxygen species (ROS), lysophosphatidylcholine (LPC), and 4-hydroxy-2-nonenal (HNE) and their interaction with ET-1 on vascular smooth muscle cell (VSMC) proliferation. Growth-arrested VSMCs isolated from the rabbit aorta were incubated with different concentrations of LDL, mox-LDL, ox-LDL, hydrogen peroxide (H(2)O(2)) (a donor of ROS), LPC, or HNE with or without ET-1. DNA synthesis in VSMCs was measured by [(3)H] thymidine incorporation. Mox-LDL, ox-LDL, H(2)O(2), LPC, HNE, or ET-1 stimulated DNA synthesis in a dose-dependent manner. Maximal effect was observed at 5 microg/ml for mox-LDL (162%) or ox-LDL (154%), 15 microM LPC (156%), 5 microM H2O2 (177%), 1 microM HNE (144%), and 0.1 microM ET-1 (195%). By contrast, LDL was without any significant effect. When added together, there was no synergistic effect of LDL, H2O2, or HNE with ET-1 on DNA synthesis. However, the effect of mox-LDL (0.1 microg/ml), ox-LDL (0.5 microg/ml), or LPC (10 microM) was potentiated by ET-1 (114%-338%, 133%-425%, 118%-333%, respectively). The mitogenic effect of mox-LDL, ox-LDL, or LPC and their interaction with ET-1 were inhibited by defatted albumin (10 microg/ml), antioxidant N-acetylcysteine (400 microM), the reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor diphenylene iodonium (1 microM). The ET(A/B) receptor antagonist TAK044 (1 microM) or the MAPK kinase inhibitor PD098059 (10 microM) inhibited the mitogenic effect of ET-1 and its interaction with mox-LDL, ox-LDL, or LPC. The synergistic interaction of mox-LDL, ox-LDL, or LPC with ET-1 was completely reversed by the combined use of N-acetylcysteine and TAK044. Our results suggest that mox-LDL, ox-LDL, and their major phospholipid component LPC act synergistically with ET-1 in inducing VSMC proliferation by way of the activation of redox-sensitive and MAPK pathways.

Endothelin-1 and atherosclerosis: potential complications associated with endothelin-receptor blockade

Atherosclerotic vascular disease remains the single most prevalent cause of death and morbidity in the western world. Endothelin-1 (ET-1) is a potent vasoconstrictor peptide that also possesses mitogenic activity on many cell types, including vascular smooth muscle cells. Raised plasma and tissue levels of ET-1 have been described in atherosclerosis in animal models and in man, suggesting that this peptide plays a pathophysiological role in this condition. Two main ET-1 receptors have been cloned (ET(A) and ET(B)). Mixed ET(A/B) and receptor subtype selective antagonists are now available. Since ET-1 is generally believed to be a 'pathophysiological peptide', we discuss the therapeutic potential of ET-1 antagonists in atherosclerosis and consider whether, at certain sites in this process, ET-1 may play a beneficial role. In such situations ET antagonism may be undesirable.

Six-month outcomes of percutaneous transluminal coronary angioplasty in hypertensive patients: results from the ROSETTA registry. Routine Versus Selective Exercise Treadmill Testing After Angioplasty

PURPOSE

Hypertension is an important risk factor for coronary artery disease. However, the impact of hypertension on the outcomes of patients undergoing percutaneous transluminal coronary angioplasty (PTCA) is unknown. Our purpose was to evaluate the association between hypertension and adverse outcomes and repeat cardiac procedures during the 6-month period after PTCA.

METHODS

We studied 791 patients who were enrolled in the Routine Versus Selective Exercise Treadmill Testing After Angioplasty (ROSETTA) registry. This registry is a prospective multicenter study examining the use of functional testing after a successful PTCA.

RESULTS

We compared 411 hypertensive patients (mean age 60.1 +/- 10 years, 31.1% female) with 380 normotensive patients (mean age 59.1 +/- 12 years, 16.2% female). Patients with hypertension had a higher 6-month rate of composite clinical events (unstable angina, myocardial infarction, death) than did normotensive patients (16.5% vs 10.5%, P =.017). In addition, there was a trend for hypertensive patients to have higher rates of cardiac procedures (angiography, repeat PTCA, coronary artery bypass graft surgery) compared with normotensive patients (19.8% vs 14.9%, P =.074). However, functional testing after PTCA was lower among hypertensive subjects (44.4% vs 54.0%, P =.008). Among the 411 hypertensive patients, a regression analysis showed that several variables were independently associated with increased 6-month adverse event rates, including pre-PTCA Killip class III-IV (odds ratio [OR] 5.7, 95% CI 1.7-19.0), Canadian Cardiovascular Society angina class III-IV (OR 2.1, 95% CI 1.1-4.2), unstable angina as the reason for PTCA (OR 2.3, 95% CI 1.2-4.3), peripheral vascular disease (OR 3.2, 95% CI 1.5-6.4), PTCA of a bypass graft (OR 3.1, 95% CI 1.2-7.6), and calcium antagonist usage at admission for the index PTCA (OR 1.9, 95% CI 1.1-3.4).

CONCLUSIONS

During the 6-month period after a successful PTCA, patients with hypertension have significantly higher adverse event rates than do those without hypertension. Several clinical variables may help identify which hypertensive patients are at higher risk for clinical events.

Endothelin receptor subtype A blockade selectively reduces pulmonary pressure after cardiopulmonary bypass

BACKGROUND

The bioactive peptide endothelin-1 is elevated during and after cardiopulmonary bypass and exerts cardiovascular effects through its 2 receptor subtypes, endothelin-1A and endothelin-1B. Increased endothelin-1A receptor stimulation after cardiopulmonary bypass can cause increased pulmonary vascular resistance and modulate myocardial contractility. However, whether and to what degree selective endothelin-1A blockade influences these parameters in the postbypass setting is not completely understood.

OBJECTIVES

Our objective was to measure left ventricular function and hemodynamics in a porcine model of cardiopulmonary bypass after selective blockade of endothelin-1A.

METHODS

Adult pigs (n = 23) underwent 90 minutes of cardiopulmonary bypass and were randomized 30 minutes after bypass to receive a selective endothelin-1A antagonist (TBC 11251, 10 mg/kg; n = 13) or saline vehicle (n = 10).

RESULTS

After bypass and before randomization, pulmonary vascular resistance rose nearly 4-fold, and left ventricular preload recruitable stroke work fell to one third of baseline values (both P <.05). In the vehicle group pulmonary vascular resistance continued to rise, and preload recruitable stroke work remained reduced. However, after endothelin-1A blockade, the rise in pulmonary vascular resistance was significantly blunted compared with that in the vehicle group. Moreover, the reduction in pulmonary vascular resistance with endothelin-1A blockade was achieved without a significant change in systemic perfusion pressures.

CONCLUSIONS

The present study demonstrated that increased activity of the endothelin-1A receptor likely contributes to alterations in pulmonary vascular resistance in the postbypass setting. Selective endothelin-1A blockade may provide a means to selectively decrease pulmonary vascular resistance without significant effects on systemic hemodynamics.

beta-Adrenergic and endothelin receptor interaction in dilated human cardiomyopathic myocardium

BACKGROUND

Although end-stage dilated cardiomyopathy (DCM) is characterized by defects in beta-adrenergic receptor (beta-AR) activity and increased endothelin-1 (ET-1), possible interactions between these 2 systems remain to be defined. Accordingly, the goal of this study was to determine the effects of ET receptor activation on beta-AR signaling through measurement of cyclic adenosine monophosphate (cAMP) in normal and DCM myocardium.

METHODS AND RESULTS

Myocardial sarcolemmal preparations were prepared from normal human (n = 6), dilated cardiomyopathic (n = 10), and ischemic cardiomyopathic (ICM, n = 10) tissue. Basal cAMP production was measured in the presence of ET-1 alone (10(-6) to 0(-9) mol/L) as well as after (-)isoproterenol (10(-6) to 10(-2) mol/L) or forskolin (0.05 to 30.0 micromol/L) stimulation. beta-AR and ET receptor profiles were determined by radiolabeled ligand assays. ET-1 inhibited basal cAMP production in all preparations in a concentration-dependent manner. However, beta-AR-stimulated cAMP production by either isoproterenol or forskolin was not significantly affected by ET-1. beta-AR receptor density was reduced, and a selective reduction of the ET(B) receptor occurred in both forms of DCM.

CONCLUSIONS

Under basal conditions, ET receptor stimulation reduced cAMP levels, which may influence contractility, particularly with DCM.

Angiotensin II and serotonin potentiate endothelin-1-induced vascular smooth muscle cell proliferation

BACKGROUND

Vascular smooth muscle cell (VSMC) proliferation induced by various growth factors has been implicated in a wide variety of pathological processes, including hypertension, atherosclerosis and restenosis after angioplasty.

OBJECTIVES

To investigate the interactions among well-known potent vasoconstrictor substances, endothelin-1 (ET-1), angiotensin II (Ang II), and serotonin (5-HT), on VSMC proliferation.

METHODS

Growth-arrested rabbit VSMCs were incubated with different concentrations of ET-1 in the absence or presence of Ang II, 5-HT, or both. VSMC proliferation was examined by increases in incorporation of [3H]thymidine into DNA and in cell number.

RESULTS

ET-1, Ang II and 5-HT stimulated DNA synthesis in a dose-dependent manner. ET-1 had a maximal effect at a concentration of 0.5 micromol/l (259% of control), Ang II at 1 micromol/l (173%), and 5-HT at 50 micromol/l (205%). When added together, ET-1 (0.1 micromol/l) and Ang II (1 micromol/l) synergistically induced DNA synthesis (341%). When the vasoconstrictors were tested in combination, even non-mitogenic concentrations of ET-1 (0.01 nmol/l) potentiated 5-HT (5 micromol/l)-induced DNA synthesis (404%). Co-incubation of ET-1 (0.01 micromol/l) with Ang II (1 micromol/l) and 5-HT (5 micromol/l) synergistically induced DNA synthesis (566%). These effects on DNA synthesis were paralleled by an increase in cell number. The ETA/B non-selective receptor antagonist, TAK044 (1 micromol/l) and the ETA receptor antagonist, BQ123 (1 micromol/l), but not the ETB receptor antagonist, BQ788 (1 micromol/l), inhibited the mitogenic effect of ET-1 and its interaction with Ang II or 5-HT. In addition, TAK044 (1 micromol/l) or BQ123 (1 micromol/l) along with the angiotensin II type 1 (AT1) receptor antagonist, candesartan (1 micromol/l), the 5-HT2A receptor antagonist, sarpogrelate (10 micromol/l), or both, inhibited the interactions of ET-1 with Ang II or 5-HT.

CONCLUSIONS

Our results suggest that Ang II and 5-HT could potentiate ET-1-induced VSMC proliferation. Inhibition of ETA, AT1, and 5-HT2A may be effective in the treatment of VSMC proliferative disorders associated with hypertension, atherosclerosis and restenosis after angioplasty.

Endothelin: role in experimental hypertension

The role of endothelins (ET) in blood pressure elevation remains controversial. Data supporting involvement of the ET system in different forms of genetic and experimental hypertension in the rat has appeared in the literature in recent years. Production of endothelin (ET)-1 may be enhanced in several experimental rat models of hypertension. Examples of these exhibiting increased preproendothelin-1 mRNA or peptide in the vasculature include salt-sensitive forms like deoxycorticosterone (DOCA)-salt hypertension, DOCA-salt treated spontaneously hypertensive rat (SHR) and Dahl salt-sensitive rats, and other models like stroke-prone SHR, angiotensin II-infused rats and fructose-fed rats, and possibly 1-kidney 1 clip (1-K 1C) Goldblatt hypertensive rats. SHR, 2-kidney 1 clip (2-K 1C) Goldblatt hypertensive rats and chronic N(omega)-nitro-L-arginine methyl ester (L-NAME)-treated hypertensive rats do not appear to exhibit an ET-1 component. Significant vascular growth, and a hypotensive response and regression of vascular growth after treatment with an ET antagonist demonstrate the endothelin-dependency present in some hypertensive models. Severity of high blood pressure elevation, salt-sensitivity and insulin resistance may be common denominators of involvement of the ET system in hypertension. ET antagonism in hypertension may result in regression of vascular damage, prevention of stroke and renal failure and improvement of heart failure. Whether the same is true in human hypertension remains to be established.

Decoy oligodeoxynucleotide characterization of transcription factors controlling endothelin-B receptor expression in vascular smooth muscle cells

Endothelin-1 is not only a powerful vasoconstrictor but also a potent mitogen for vascular smooth muscle cells (SMC), acting through both the endothelin-A and endothelin-B receptor (ET(B)-R). Although vascular SMC are known to express the ET(B)-R, its transcriptional regulation has not been studied thus far. Here we demonstrate that the potent inhibitor of nuclear factor kappaB activation, pyrrolidine dithiocarbamate (PDTC; 30-100 microM), induces de novo ET(B)-R expression in rat aortic and mesenteric cultured SMC. Electrophoretic mobility shift analyses revealed that besides inhibition of nuclear factor kappaB, PDTC enhances activator protein-1 (AP-1), CCAAT/enhancer-binding protein (C/EBP), and GATA-2 activity in these cells. Preincubation of PDTC-stimulated cells with appropriate decoy oligodeoxynucleotides confirmed the involvement of these three transcription factors, namely that of AP-1, in ET(B)-R expression. The stimulatory effect of PDTC on ET(B)-R expression was also confirmed functionally by monitoring an enhanced ET-1-induced apoptosis in PDTC-treated cells that was sensitive to the ET(B)-R antagonist, BQ788. Taken together, these findings demonstrate that C/EBP, GATA-2, and in particular AP-1 can control ET(B)-R expression in vascular SMC. They further support the notion that ET(B)-R expression in these cells may play an important role in cardiovascular complications, such as restenosis following angioplasty that in the early phase is characterized by prominent SMC apoptosis.

Temporal endothelin dynamics of the myocardial interstitium and systemic circulation in cardiopulmonary bypass

OBJECTIVE

Increased systemic levels of the bioactive peptide endothelin 1 during and after cardioplegic arrest and cardiopulmonary bypass have been well documented. However, endothelin 1 is synthesized locally, and therefore myocardial endothelin 1 production during and after cardiopulmonary bypass remains unknown.

METHODS

Pigs (n = 11) were instrumented for cardiopulmonary bypass, and cardioplegic arrest was initiated. Myocardial interstitial and systemic arterial levels of endothelin 1 were measured before cardiopulmonary bypass, throughout bypass and cardioplegic arrest (90 minutes), and up to 90 minutes after separation from bypass. Myocardial interstitial endothelin 1 was determined by microdialysis and radioimmunoassay.

RESULTS

Baseline myocardial endothelin 1 levels were higher than systemic endothelin 1 levels (25.6 +/- 6.7 vs 8.3 +/- 1.1 fmol/mL, P <.05). With the onset of bypass, myocardial endothelin 1 increased by 327% +/- 92% from baseline (P <.05), which preceded the increase in systemic endothelin 1 levels.

CONCLUSION

Myocardial compartmentalization of endothelin 1 exists in vivo. Cardiopulmonary bypass and cardioplegic arrest induce temporal differences in endothelin 1 levels within the myocardial interstitium and systemic circulation, which, in turn, may influence left ventricular function in the postbypass period.

Endothelin-receptor antagonists: current and future perspectives

Despite much effort over recent years to design and develop endothelin-receptor antagonists, these compounds are far from becoming new drug entities. This article will review preclinical data on select endothelin-receptor antagonists as well as clinical data on bosentan, the only molecule currently in Phase III clinical trials. Though efficacious, bosentan is less potent than the angiotensin converting enzyme (ACE) inhibitor, enalapril, in patients with hypertension. We will therefore discuss the possible reason(s) for this low potency, the consequences thereof, and a few therapeutic areas where endothelin-receptor antagonists could find better use.

Endothelin-induced cardiac myocyte hypertrophy: role for focal adhesion kinase

Endothelin-1 (ET) produces neonatal rat ventricular myocyte (NRVM) hypertrophy and activates focal adhesion kinase (FAK) in other cell types. In the present study, we examined whether ET activated FAK in NRVM and whether FAK was necessary and/or sufficient for ET-induced NRVM hypertrophy. Chronic ET-1 stimulation (100 nM, 48 h) increased protein-to-DNA and myosin heavy chain (MHC)-to-DNA ratios and stimulated the assembly of newly synthesized MHC into sarcomeres. ET-1 also induced the assembly of focal adhesions and costameres, as evidenced by increased phosphotyrosine, FAK, and paxillin immunostaining. Acutely, ET treatment rapidly increased tyrosine phosphorylation of FAK and paxillin. FAK was also activated by phorbol 12-myristate 13-acetate (2 microM, 5 min). Pretreatment with chelerythrine (5 microM) or rottlerin (10 microM) completely blocked ET-induced FAK phosphorylation, indicating that protein kinase C activation was upstream of ET-induced FAK activation. In contrast, ET-induced FAK activation was not affected by blocking calcium influx via L-type voltage-gated calcium channels. Adenoviruses (Adv) containing FAK and FAK-related nonkinase (FRNK) were used to specifically define the role of FAK in ET-induced hypertrophy. ET stimulation failed to increase total protein-to-DNA or MHC-to-DNA ratios or to stimulate sarcomeric assembly in myocytes infected with Adv-FRNK. However, Adv-FAK alone did not increase total protein-to-DNA or MHC-to-DNA ratios and failed to increase the number or size of myofibrils as evidenced by double immunofluorescence labeling for MHC and FAK. Thus, although FAK is necessary for ET-induced NRVM hypertrophy, other ET-generated signals are also required to elicit the hypertrophic phenotype.

Cor Pulmonale

The goals of treatment of cor pulmonale are 1) to reduce pulmonary arterial hypertension; 2) to optimize gas-exchange efficiency; and 3) to improve survival. These goals are achieved through long-term oxygen therapy, bronchodilator and vasodilator therapy, aggressive treatment of pulmonary infection, and anticoagulation. Selected patients may benefit from available surgical options.

Elevated perfusion pressure upregulates endothelin-1 and endothelin B receptor expression in the rabbit carotid artery

To investigate the hypothesis that high blood pressure activates the endothelin system in the vessel wall, isolated segments of the rabbit carotid artery were subjected to different levels of perfusion pressure. Both preproendothelin-1 (ppET-1) mRNA abundance and intravascular ET-1 peptide content were strongly upregulated on raising the intraluminal pressure from 90 to 160 mm Hg for 3 to 12 hours, and this increase in ppET-1 mRNA occurred predominantly in the endothelial cells. Endothelin-converting enzyme-1 and endothelin A receptor (ET(A)-R) expression were pressure-insensitive, whereas that of the ET(B)-R in the smooth muscle cells was also significantly enhanced. Both the pressure-induced increase in ppET-1 and ET(B)-R expression required RNA synthesis because they were abolished by actinomycin D. The nuclear signaling mechanisms involved therein, however, appeared to be different. Thus, the pressure-induced expression of ppET-1 and activation of CCAAT-enhancer binding proteins beta and delta were blocked by the tyrosine kinase inhibitor herbimycin A, whereas ET(B)-R expression and the nuclear translocation of activator protein-1 were abolished by the protein kinase C inhibitor Ro 31-8220. One consequence of these presumably deformation-induced changes in gene expression was an increased rate of apoptosis of the smooth muscle cells in the media that if transferable to the situation in human blood vessels may contribute to hypertension-induced arterial remodeling.

Pressure-induced upregulation of preproendothelin-1 and endothelin B receptor expression in rabbit jugular vein in situ : implications for vein graft failure?

Upregulation of endothelin-1 (ET-1) synthesis in venous bypass grafts in response to arterial levels of blood pressure may play a major role in graft failure. To investigate this hypothesis, isolated segments of the rabbit jugular vein were perfused at physiological (0 to 5 mm Hg) and nonphysiological (20 mm Hg) levels of intraluminal pressure. As judged by reverse transcription-polymerase chain reaction analysis (mRNA level), neither endothelin-converting enzyme nor endothelin A receptor expression appeared to be pressure sensitive. In contrast, there was a profound and time-dependent increase in endothelial prepro-ET-1 mRNA and intravascular ET-1 abundance (by ELISA) as well as in smooth muscle endothelin B receptor mRNA and functional protein (by superfusion bioassay) on raising the perfusion pressure from 5 to 20 mm Hg, but not from 0 to 5 mm Hg, for up to 12 hours. Video microscopy analysis revealed that the segments were distended by 75% at 5 mm Hg and near maximally at 20 mm Hg compared with the resting diameter at 0 to 1 mm Hg. Treatment of the segments with actinomycin D (1 micromol/L), the specific protein kinase C inhibitor, Ro 31-8220 (0.1 micromol/L), or the c-Src family-specific tyrosine kinase inhibitor, herbimycin A (0.1 micromol/L), demonstrated that the pressure-induced expression of these gene products occurs at the level of transcription and requires activation of protein kinase C, but not c-Src. In venous bypass grafts such deformation-induced changes in gene expression may contribute not only to acute graft failure through ET-1-induced vasospasm but also to endothelin A receptor- and/or endothelin B receptor-mediated smooth muscle cell hyperplasia and graft occlusion.

Cardiac microvasculature in DOCA-salt hypertensive rats : effect of endothelin ET(A) receptor antagonism

The cardiac abnormalities associated with hypertension include left ventricular hypertrophy and vascular changes. The latter may affect the cardiac microvasculature and predispose to myocardial ischemia. To test the hypothesis that endothelin-1 contributes to changes in the microcirculation of the heart, we studied cardiac microvessels of the deoxycorticosterone acetate-salt (DOCA-salt) model of hypertension in the rat, in which the endothelin system is activated, and the effect of the endothelin-A (ET(A)) subtype-selective endothelin receptor antagonist A-127722. A-127722 (30 mg x kg(-1) x d(-1)) was administered for 4 weeks. Arterioles (</=20 microm in lumen diameter) were identified in the myocardium by use of immunolabeling with an anti-smooth muscle alpha-actin antibody, and capillaries with an anti-laminin antibody with nuclear counterstaining by nuclear fast red. Systolic blood pressure was 103+/-1.6 mm Hg in unilaterally nephrectomized rats (UniNx), 202+/-3.2 mm Hg in DOCA-salt (P<0.01 versus UniNx), and 182+/-3.1 mm Hg in ET(A) antagonist-treated DOCA-salt (P<0.01 versus DOCA-salt or UniNx). Arteriolar and capillary densities were altered significantly in the subendocardial myocardium but not in the subepicardial myocardium of the left ventricle. Arteriolar density per square millimeter was 18.1+/-1.48 in UniNx, 31.9+/-3.26 in DOCA-salt (P<0.01 versus UniNx), and 24.2+/-1.36 in ET(A) antagonist-treated DOCA-salt (P<0.05 versus DOCA-salt or UniNx). Capillary density per square millimeter was 2395+/-148 in UniNx, 1576+/-107 in DOCA-salt (P<0.01 versus UniNx), and 1982+/-31 in ET(A) antagonist-treated DOCA-salt (P<0.01 versus DOCA-salt or UniNx). In conclusion, in DOCA-salt hypertensive rats, subendocardial arteriolar growth and capillary rarefaction were observed in the left ventricular myocardium, and both were partially corrected by ET(A) receptor antagonism. This suggests a role for endothelin-1 in cardiac arteriolar growth and capillary rarefaction, which may have pathophysiological implications by contributing to myocardial ischemia in hypertension.

State-of-the-Art lecture. Role of endothelin-1 in hypertension

Endothelin-1 (ET-1) is overexpressed in the vascular wall in certain models of experimental hypertension: deoxycorticosterone acetate salt-treated rats, deoxycorticosterone acetate salt-treated spontaneously hypertensive rats (SHR), stroke-prone SHR, Dahl salt-sensitive rats, angiotensin II-infused rats, and 1-kidney 1 clip Goldblatt rats; it is not overexpressed in SHR, 2-kidney 1-clip hypertensive rats, or L-NAME-treated rats. In hypertensive rats without generalized vascular overexpression, however, expression of ET-1 was often enhanced in intramyocardial coronary arteries, suggesting a role of endothelin in myocardial ischemia in hypertension. In rats overexpressing ET-1, ET(A/B) and ET(A)-selective receptor antagonists lowered blood pressure and reduced vascular growth, particularly in small arteries, beyond what could be attributed to blood pressure lowering, suggesting a direct effect of ET-1 on growth. Hypertensive rats treated with endothelin antagonists are protected from stroke and renal injury. The ET(A/B) antagonist bosentan induced blood-pressure reductions in mildly hypertensive patients similar to those achieved with an angiotensin-converting enzyme inhibitor. Moderately to severely hypertensive patients presented with enhanced expression of prepro-ET-1 mRNA in the endothelium of subcutaneous resistance arteries, suggesting that these stages of hypertension may respond particularly well to endothelin antagonism. Hypertensive patients with coronary artery disease have increased arterial expression of ET-1, and increased plasma levels of immunoreactive endothelin have been described in black patients. ET-1 plays an important role in atherosclerosis, for which hypertension is an important risk factor. Thus, ET-1 may be involved in experimental and human hypertension. Endothelin antagonists may prove effective as disease-modifying agents if they are shown clinically, as they are experimentally, to offer target organ protection and reduce long-term complications of hypertension. This remains to be demonstrated in humans.

Insulin-induced endothelin release and vasoreactivity in hypertriglyceridemic and hypertensive rats

Insulin-elicited endothelin release in hypertriglyceridemic, hypertensive, hyperinsulinemic (HTG) rats was shown. Weanling male Wistar rats were given 30% sucrose in their drinking water for 20-24 wk. In vitro contractions of aorta and femoral arteries were elicited with 40 mM KCl. Endothelin release induced with KCl plus 50 microU/ml insulin resulted in increases in contractile responses: 41 +/- 5.9 and 57 +/- 6% for control and 65.5 +/- 6 and 95 +/- 9% for HTG aortas and femoral arteries, respectively. The endothelin ET(B)-receptor blocker BQ-788 decreased responses to KCl + insulin by 39 +/- 8 and 53 +/- 5% in control and 48 +/- 13 and 79 +/- 3.5% in HTG aortas and femoral arteries, respectively. The ET(A)-receptor antagonist PD-151242 inhibited these responses by 12 +/- 10 and 1 +/- 9% in control and by 51.5 +/- 9 and 58.5 +/- 1% in HTG aortas and femoral arteries, respectively. These results suggest that endothelin may contribute to the hypertension in this model.

Endothelin system-dependent cardiac remodeling in renovascular hypertension

The aim of the present study was to analyze whether the cardiac endothelin system contributes to cardiac remodeling in rats with 2-kidney, 1 clip (2K1C) renovascular hypertension. The endothelin system seems to be a promising candidate for cardiac remodeling because endothelin (ET)-1 promotes growth of cardiomyocytes in vitro and induces cardiac collagen synthesis. The activity of the cardiac endothelin system was analyzed by measuring cardiac tissue big ET-1 and ET-1 concentrations as well as by estimating the cardiac expression of the ETA and ETB receptors 10 days, 4 weeks, and 12 weeks after the renal artery was clipped. The effects of long-term treatment with ETA, ETB, and combined ETA/ETB receptor antagonists on cardiac hypertrophy, media/lumen ratio of intracardiac arteries, and left ventricular fibrosis were also analyzed. This study demonstrated that the overall left ventricular cardiac endothelin system has a similar activity in the early, middle, and late stages of 2K1C renovascular hypertension compared with sham-operated controls. Fibrosis of the left ventricle and hypertrophy of intracardiac arteries, however, were markedly altered after long-term treatment with endothelin receptor antagonists in a blood pressure-independent manner. These 2 effects are mediated by different subtypes of endothelin receptors. ETA receptor blockade completely normalized the hypertrophy of intracardiac arteries (P<0. 01 compared with 2K1C without treatment) in renovascular hypertension, whereas the ETB antagonist reduced cardiac fibrosis of the left ventricle (P<0.001 compared with 2K1C without treatment) to baseline values. This study demonstrates that the cardiac endothelin system plays an important role in the development of cardiac fibrosis as well as in hypertrophy of intracardiac arteries in 2K1C renovascular hypertensive rats.

Hypertension-induced end-organ damage : A new transgenic approach to an old problem

Angiotensin (Ang) II-induced organ damage has fascinated students of hypertension since the work of Wilson and Byrom. We are investigating a double transgenic rat (dTGR) model, in which rats transgenic for the human angiotensinogen and renin genes are crossed. These rats develop moderately severe hypertension but die of end-organ cardiac and renal damage by week 7. The heart shows necrosis and fibrosis, whereas the kidneys resemble the hemolytic-uremic syndrome vasculopathy. Surface adhesion molecules (ICAM-1 and VCAM-1) are expressed early on the endothelium, while the corresponding ligands are found on circulating leukocytes. Leukocyte infiltration in the vascular wall accompanies PAI-1, MCP-1, and VEGF expression. The expression of TGF-beta and deposition of extracellular matrix proteins follows, which is accompanied by fibrinoid vasculitis in small vessels of the heart and kidneys. Angiotensin-converting enzyme inhibitors and AT1 receptor blockers each lowered blood pressure and shifted pressure natriuresis partially leftward by different mechanisms. When combined, they normalized blood pressure, pressure natriuresis, and protected from vasculopathy completely. Renin inhibition lowered blood pressure partially, but protected from vasculopathy completely. Endothelin receptor blockade had no influence on blood pressure but protected from vasculopathy and improved survival. We show evidence that Ang II stimulates oxidative stress directly or indirectly via endothelin 1 and that NFkappaB is upregulated in this model. We speculate that the transcription factors NFkappaB and AP-1 are involved with initiating chemokine and cytokine expression, leading to the above cascade. The unique model and our pharmacological probes will enable us to test these hypotheses.

Endothelin and endothelin antagonists in hypertension

The endothelins (ET) are potent 21-amino-acid vasoconstrictor peptides produced in many different tissues, particularly in the endothelium of blood vessels. ET-1 is the main endothelin secreted by the endothelium, and acts in a paracrine or autocrine fashion on blood vessels by interacting with ETA or ETB receptors on smooth muscle to stimulate contraction or on ETB receptors on endothelial cells to induce the release of vasorelaxants (nitric oxide and prostacyclin). Production of ET-1 is enhanced in several experimental models of hypertension in the rat, such as sodium-sensitive forms, e.g. deoxycorticosterone acetate (DOCA)-salt hypertensive, DOCA-salt-treated spontaneously hypertensive rats (SHR) and Dahl salt-sensitive rats, as well as other models such as stroke-prone SHR, angiotensin II-infused rats and fructose-fed rats, and possibly 1-K 1C Goldblatt hypertensive rats. In contrast, SHR, 2-K 1C Goldblatt hypertensive rats and nitric oxide-deficient (L-NAME-treated) hypertensive rats do not exhibit an ET-1 component. Endothelin dependency is manifested by excessive vascular growth, particularly in small arteries, and blood pressure lowering and regression of vascular growth after treatment with endothelin antagonists. The latter may be combined ETA/ETB or selective ETA antagonists, of which several are orally active and already in clinical development. In humans, endothelin-dependent vascular tone has been shown in studies of forearm blood flow. Enhanced expression of ET-1 mRNA has been demonstrated in the endothelium of small arteries of patients with moderate to severe hypertension. In a 4-week trial the combined ETA/ETB antagonist bosentan reduced the blood pressure of essential hypertensive patients equally to enalapril. Bosentan improved hemodynamics in patients with heart failure in acute and 2-week-long studies. Endothelin antagonists also offer promise in a rapidly fatal condition, primary pulmonary hypertension. Thus, the endothelin system appears to be involved in different forms of cardiovascular disease in experimental animals and humans, and its interruption offers great promise as a new therapeutic intervention in hypertension, heart failure and other diseases.

Neurohormonal markers of clinical outcome in cardiovascular disease: is endothelin the best one?

Endothelin-1 (ET-1) is the most potent vasoconstrictor yet described. The active 21-amino-acid peptide is derived from the conversion of the inactive precursor "Big ET-1" by an enzyme called endothelin-converting enzyme. In addition to its potent action as a vasoconstrictor, endothelin promotes growth and proliferation of smooth muscle and myocardial hypertrophy. ET-1 levels are elevated in acute myocardial infarction (MI), atherosclerosis, renal failure, diabetes, pulmonary hypertension, and congestive heart failure (CHF). ET-1 levels correlate extremely well with the seriousness of the pathophysiologic condition. ET-1 levels at 72 h post MI accurately predict long-term survival. In patients with heart failure, ET-1 levels also predict long-term outcome, with the prognosis being severely compromised in patients with elevated ET-1 levels. Levels of plasma big ET-1 have been demonstrated to predict 1-year mortality and have been shown to be a better predictor of 1-year outcome than plasma atrial natriuretic peptide and norepinephrine, NYHA class, age, and echocardiographic left ventricular parameters. Although a small number of studies have reported beneficial effects of ACE inhibitors on ET-1 levels in animal models, most reports in humans have not found an effect of ACE inhibitors on ET-1 levels. Only one ACE inhibitor, fosinopril, has been shown to be effective in normalizing ET-1 levels in clinically relevant situations, such as the long-term study of patients with CHF. This observation may point to a superior role of fosinopril compared with other ACE inhibitors in CHF patients and may indicate beneficial effects of fosinopril beyond blood pressure control.

The role of endothelin in hypertension

The endothelins are 21-amino-acid peptides which may play a role in the pathogenesis of hypertension. There is increasing evidence that the endothelins have a central function in mediating end-organ damage in hypertension, and that important effects of endothelin in the pathogenesis of hypertension may be based on the interactions of the endothelins and the renin-angiotensin and the nitric oxide systems.