Circulating and tissue endothelin immunoreactivity in hypercholesterolemic pigs

Endothelin-1 in Health and Disease

Discovered almost 40 years ago, the potent vasoconstrictor peptide endothelin-1 (ET-1) has a wide range of roles both physiologically and pathologically. In recent years, there has been a focus on the contribution of ET-1 to disease. This has led to the development of various ET receptor antagonists, some of which are approved for the treatment of pulmonary arterial hypertension, while clinical trials for other diseases have been numerous yet, for the most part, unsuccessful. However, given the vast physiological impact of ET-1, it is both surprising and disappointing that therapeutics targeting the ET-1 pathway remain limited. Strategies aimed at the pathways influencing the synthesis and release of ET-1 could provide new therapeutic avenues, yet research using cultured cells in vitro has had little follow up in intact ex vivo and in vivo preparations. This article summarises what is currently known about the synthesis, storage and release of ET-1 as well as the role of ET-1 in several diseases including cardiovascular diseases, COVID-19 and chronic pain. Unravelling the ET-1 pathway and identifying therapeutic targets has the potential to treat many diseases whether through disease prevention, slowing disease progression or reversing pathology.

The Causal Relationship between Endothelin-1 and Hypertension: Focusing on Endothelial Dysfunction, Arterial Stiffness, Vascular Remodeling, and Blood Pressure Regulation

Hypertension (HTN) is one of the most prevalent diseases worldwide and is among the most important risk factors for cardiovascular and cerebrovascular complications. It is currently thought to be the result of disturbances in a number of neural, renal, hormonal, and vascular mechanisms regulating blood pressure (BP), so crucial importance is given to the imbalance of a number of vasoactive factors produced by the endothelium. Decreased nitric oxide production and increased production of endothelin-1 (ET-1) in the vascular wall may promote oxidative stress and low-grade inflammation, with the development of endothelial dysfunction (ED) and increased vasoconstrictor activity. Increased ET-1 production can contribute to arterial aging and the development of atherosclerotic changes, which are associated with increased arterial stiffness and manifestation of isolated systolic HTN. In addition, ET-1 is involved in the complex regulation of BP through synergistic interactions with angiotensin II, regulates the production of catecholamines and sympathetic activity, affects renal hemodynamics and water–salt balance, and regulates baroreceptor activity and myocardial contractility. This review focuses on the relationship between ET-1 and HTN and in particular on the key role of ET-1 in the pathogenesis of ED, arterial structural changes, and impaired vascular regulation of BP. The information presented includes basic concepts on the role of ET-1 in the pathogenesis of HTN without going into detailed analyses, which allows it to be used by a wide range of specialists. Also, the main pathological processes and mechanisms are richly illustrated for better understanding.

Assessment of vascular function in complete glycaemic spectrum

Purpose: The present study was conceived to delineate the point of vascular dysfunction along the glycemic spectrum (normoglycemic individuals with no family history of diabetes, normoglycemic individuals with family history of diabetes, prediabetic individuals, and diabetic individuals).Materials and Methods: In this cross-sectional comparative study, we enrolled 252 participants of both gender in the age group of 30-50 years. They were classified based on their family history of diabetes and glycemic status into four groups along the glycemic spectrum as mentioned above. We measured flow-mediated dilation (FMD) from brachial artery and vascular function biomarkers such as enthothelin-1 (ET-1), von Willbrand Factor (vWF), Vascular Endothelial Growth Factor (VEGF) to assess the vascular function. The comparison of data between groups were done using One Way ANOVA/Kruskal-Wallis followed by post-hoc analysis using LSD/Mann-Whitney U Test depending on the normality of the data. Spearman correlation was done between vascular function and plasma glucose levels to identify its relationship. Linear regression was carried out to identify the factors influencing the FMD across the glycemic spectrum.Results: We observed that vascular function negatively correlated with blood glucose levels. However, endothelin-1 and vWF derangement was there even in normoglycemic first degree relatives of diabetes (FDRD) and the derangement increased in prediabetes and diabetes. Physiological dysfunction in terms of decreased flow-mediated dilation starts from prediabetes only. VEGF derangement is found only in diabetic individuals.Conclusion: Vascular dysfunction is found even in normoglycemic FDRD and the derangement increased and compounded with the advancement of disease.

The Reducing Effects of Pyrogallol-Phloroglucinol-6,6-Bieckol on High-Fat Diet-Induced Pyroptosis in Endothelial and Vascular Smooth Muscle Cells of Mice Aortas

In hyperlipidemia, pyroptosis in endothelial cells (ECs) induces atherosclerosis via the toll-like receptor 4 (TLR4) pathway. We evaluated the effects of Ecklonia cava extract (ECE) and pyrogallol-phloroglucinol-6,6-bieckol (PPB) on pyroptosis of ECs and vascular smooth muscle cells (VSMCs), which leads to attenuation of these cells and dysfunction of the aorta in high-fat-diet (HFD)-fed mice and in palmitate-treated ECs and VSMCs. The expression of TLR4 and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), which induce formation of NOD-LRR-and pyrin domain-containing protein 3 (NLRP3) inflammasomes, were increased by HFD and were decreased by ECE and PPB. The TLR4/NF-κB pathway was upregulated in palmitate-treated ECs and VSMCs and was decreased by ECE and PPB. The expressions of NLRP3/apoptosis-associated speck like protein containing a caspase recruitment domain, caspase-1, interleukin (IL)-1β, and IL-18 were increased by HFD and were decreased by ECE and PPB. Pyroptotic cells were increased by HFD and decreased by ECE and PPB. The expressions of the adhesion molecules, intercellular adhesion molecule and vascular cell adhesion molecule, and endothelin-1 were increased by HFD and were decreased by ECE and PPB. ECE and PPB decreased pyroptosis in the ECs and VSMCs, which was induced by HFD in the mouse aorta, and attenuated EC and VSMC dysfunction, an initiation factor of atherosclerosis.

Endothelial deficiency of insulin-like growth factor-1 receptor reduces endothelial barrier function and promotes atherosclerosis in Apoe-deficient mice

Insulin-like growth factor-1 (IGF-1) decreases atherosclerosis in apolipoprotein E (Apoe)-deficient mice when administered systemically. However, mechanisms for its atheroprotective effect are not fully understood. We generated endothelium-specific IGF-1 receptor (IGF1R)-deficient mice on an Apoe-deficient background to assess effects of IGF-1 on the endothelium in the context of hyperlipidemia-induced atherosclerosis. Endothelial deficiency of IGF1R promoted atherosclerotic burden, when animals were fed on a high-fat diet for 12 wk or normal chow for 12 mo. Under the normal chow feeding condition, the vascular relaxation response to acetylcholine was increased in the endothelial IGF1R-deficient aorta; however, feeding of a high-fat diet substantially attenuated the relaxation response, and there was no difference between endothelial IGF1R-deficient and control mice. The endothelium and its intercellular junctions provide a barrier function to the vasculature. In human aortic endothelial cells, IGF-1 upregulated occludin, claudin 5, VE-cadherin, JAM-A, and CD31 expression levels, and vice versa, specific IGF1R inhibitor, picropodophyllin, an IGF1R-neutralizing antibody (αIR3), or siRNA to IGF1R abolished the IGF-1 effects on junction and adherens proteins, suggesting that IGF-1 promoted endothelial barrier function. Moreover, endothelial transwell permeability assays indicated that inhibition of IGF-1 signaling elevated solute permeability through the monolayer of human aortic endothelial cells. In summary, endothelial IGF1R deficiency increases atherosclerosis, and IGF-1 positively regulates tight junction protein and adherens junction protein levels and endothelial barrier function. Our findings suggest that the elevation of the endothelial junction protein level is, at least in part, the mechanism for antiatherogenic effects of IGF-1.NEW & NOTEWORTHY Endothelial insulin-like growth factor-1 (IGF-1) receptor deficiency significantly elevated atherosclerotic burden in apolipoprotein E-deficient mice, mediated at least in part by downregulation of intercellular junction proteins and, thus, elevated endothelial permeability. This study revealed a novel role for IGF-1 in supporting endothelial barrier function. These findings suggest that IGF-1's ability to promote endothelial barrier function may offer a novel therapeutic strategy for vascular diseases such as atherosclerosis.

Quality of life of patients with central serous chorioretinopathy - a major cause of vision threat among middle-aged individuals

INTRODUCTION

The 25-item National Eye Institute Visual Function Questionnaire (NEI VFQ-25) was designed to measure the vision-related quality of life (QoL). We aimed to assess the effect of disease duration, disease type (i.e., acute vs. chronic and unilateral vs. bilateral), and selected sociodemographic data on the QoL of patients with central serous chorioretinopathy (CSC).

MATERIAL AND METHODS

The study included 79 patients diagnosed with CSC. The QoL was assessed using the NEI VFQ-25. The statistical analysis was performed using IBM SPSS Statistics 24.

RESULTS

A significant positive correlation was found between deterioration in peripheral vision as assessed by the NEI VFQ-25 and duration of CSC (r = -0.22, p = 0.046). Compared with women, men obtained higher scores on the scales assessing general health, mental health, ocular pain and role limitations (p = 0.018, p = 0.027, p = 0.009 and p = 0.007, respectively). Patients with acute CSC reported higher levels of social functioning as compared with those with chronic CSC (p = 0.04). There were no differences in any of the scales between patients with unilateral and bilateral CSC. Elderly patients obtained lower scores on 9 of the 12 analyzed scales, as compared with younger patients (p < 0.05).

CONCLUSIONS

Patients with CSC do not assess their QoL in negative terms, which may be related to the fact that the disease presents with transient symptoms. However, the QoL deteriorated with longer disease duration. Men with CSC have better vision-related QoL than women.

Role of Orai1 and L-type CaV1.2 channels in Endothelin-1 mediated coronary contraction under ischemia and reperfusion

Ischemia and Reperfusion (I/R) injuries are associated with coronary artery hypercontracture. They are mainly originated by an exacerbated response to agonists released by endothelium such as Endothelin (ET-1), involving the alteration in intracellular calcium handling. Recent evidences have highlighted the implication of Store-Operated Calcium Channels (SOCC) in intracellular calcium homeostasis in coronary artery. However, little is known about the role of SOCC in the regulation of coronary vascular tone under I/R. The aim of this study was to evaluate the role of SOCC and l-type Ca²⁺ channels (LTCC) in coronary artery vasoconstriction originated by ET-1 in I/R. We used Left Anterior Descendent coronary artery (LAD) rings, isolated from Wistar rats, to study the contractility and intracellular Ca²⁺ concentration ([Ca²⁺]_i) under a simulated I/R protocol. We observed that responses to high-KCL induced depolarization and caffeine-induced Ca²⁺ release are attenuated in coronary artery under I/R. Furthermore, ET-1 addition in ischemia promotes transient and small rise of [Ca²⁺]_i and coronary vascular tone. Meanwhile, these effects are significantly potentiated during reperfusion. The resulting ET-1-induced vasoconstrictions and [Ca²⁺]_i increase were abolished by; GSK-7975A and gadolinium, inhibitors of SOCC; and nifedipine a widely used inhibitor of LTCC. Interestingly, using in situ Proximity Ligation Assay (PLA) in isolated coronary smooth muscle cells we found significant colocalization of LTCC Ca_V1.2 isoform with Orai1, the pore forming subunit of SOCC, and TRPC1 under I/R. Our data suggest that hypercontraction of coronary artery induced by ET-1 after I/R involves the co-activation of LTCC and SOCC, which colocalize significantly in the sarcolemma of coronary smooth muscle cells.

The association of endothelin-1 gene polymorphism and its plasma levels with hypertension and coronary atherosclerosis

INTRODUCTION

Endothelin-1 (ET-1) is the most potent among all vasoconstrictors, and its association with cardiovascular diseases has been reported before. Our aim was to investigate the association of ET-1 plasma level and its gene polymorphisms (rs5370 and rs10478694) with hypertension and coronary atherosclerosis (CA).

MATERIAL AND METHODS

This study was carried out on 128 women and 132 men, who were divided into 4 groups: hypertensive without atherosclerosis (H+A-); hypertensive with atherosclerosis (H+A+); non-hypertensive with atherosclerosis (H-A+); and non-hypertensive without atherosclerosis (control group). Endothelin-1 plasma levels were measured by ELISA, and gene polymorphisms were detected by polymerase chain reaction - restriction fragment length polymorphism (PCR-RFLP) methods. Coronary artery diseases (CAD) were then defined based on angiography data.

RESULTS

The ET-1 plasma level was significantly higher in the H+A+ group in comparison with the other groups, especially H+A-. Comparing people with CA and those without it, the highest frequency level of the T allele of rs5370 was found in people with CA. Significantly higher frequencies of the 3A allele were detected in hypertensive patients in comparison with non-hypertensive individuals, when analyzing rs10478694.

CONCLUSIONS

Endothelin-1 plasma level shows a direct association with the risk of CA development. The T allele of rs5370 can be regarded as a risk factor for CA development. The 3A allele of rs10478694 can be associated with the risk of hypertension; therefore, it can be concluded that ET-1 and its gene polymorphisms play an important role in CA development and hypertension observed in the south-eastern populations of Iran.

Association between circulating big endothelin-1 and noncalcified or mixed coronary atherosclerotic plaques

Background

Noncalcified plaques (NCPs) and mixed plaques (MPs) are considered as the high-risk coronary plaques. Endothelin-1 (ET-1) is a vasoactive peptide and shows a high expression in vulnerable plaque. The aim of this study is to investigate the relationship between the bigET-1, the precursor of ET-1, and NCPs/MPs in a Chinese population.

Methods and results

A total of 513 patients with chest pain and suspected coronary artery disease were collected and divided into three groups with no plaques, calcified plaques, or NCPs/MPs according to the characteristics of all the plaques. It demonstrated that NCPs/MPs were associated with elevated bigET-1 (P < 0.001). Moreover, the proportion of NCPs/MPs was significantly increased from 43.3% in bigET-1 tertile 1 to 61.0% in tertile 3 group (P = 0.001). Multiple logistic regression analysis further showed that bigET-1 was an independent predictor for the presence of NCPs/MPs (odds ratio = 1.858; 95% confidence interval: 1.017–3.394; P = 0.044).

Conclusion

The bigET-1 could be an independent predictor for the presence of NCPs/MPs.

Noncalcified plaques (NCPs) and mixed plaques (MPs) are considered as the high risk coronary plaques. Endothelin- 1(ET-1) is a vasoactive peptide and shows a high expression in vulnerable plaque. However, the relationship between circulating ET-1 and NCPs/MPs is still an unanswered question. In the present study, we found that NCPs and MPs were associated with elevated plasma bigET-1, the precursor of ET-1. The patients with NCPs and MPs had significantly elevated bigET-1, compared to those without coronary plaque or those have calcified plaques. Multiple logistic regression analysis further showed that bigET-1 was an independent predictor for the presence of NCPs/MPs. The finding highlights the potential value of this assay in predicting the characteristics of plaques in patients with suspected or known coronary artery disease.

The Value of Big Endothelin-1 in the Assessment of the Severity of Coronary Artery Calcification

Progression of coronary artery calcification (CAC) was significantly associated with all-cause mortality, and high coronary artery calcium score (CACS) portends a particularly high risk of cardiovascular events. But how often one should rescan is still an unanswered question. Preliminary screening by testing circulating biomarker may be an alternative before repeat computed tomography (CT) scan. The aim of this study was to investigate the value of big endothelin-1 (bigET-1), the precursor of endothelin-1 (ET-1), in predicting the severity of CAC. A total of 428 consecutively patients who performed coronary computed tomography angiography (CCTA) due to chest pain in Fuwai Hospital were included in the study. The clinical characteristics, CACS, and laboratory data were collected, and plasma bigET-1 was detected by enzyme-linked immunosorbent assay (ELISA). The bigET-1 was positively correlated with the CACS (r = .232, P < .001), and the prevalence of CACS >400 increased significantly in the highest bigET-1 tertile than the lowest tertile. Multivariate analysis showed that bigET-1was the independent predictor of the presence of CACS >400 (odds ratio [OR] = 1.721, 95% confidence interval [CI], 1.002-2.956, P = .049). The receiver operating characteristic (ROC) curve analysis showed that the optimal cutoff value of bigET-1 for predicting CACS >400 was 0.38 pmol/L, with a sensitivity of 59% and specificity of 68% (area under curve [AUC] = 0.65, 95% CI, 0.58-0.72, P < .001). The present study demonstrated that the circulating bigET-1 was valuable in the assessment of the severity of CAC.

Reduced contribution of endothelin to the regulation of systemic and pulmonary vascular tone in severe familial hypercholesterolaemia

Vascular dysfunction has been associated with familial hypercholesterolaemia (FH), a severe form of hyperlipidaemia. We recently demonstrated that swine with FH exhibit reduced exercise-induced systemic, but not pulmonary, vasodilatation involving reduced nitric oxide (NO) bioavailability. Since NO normally limits endothelin (ET) action, we examined the hypothesis that reduced systemic vasodilatation during exercise in FH swine results from increased ET-mediated vasoconstriction. Systemic and pulmonary vascular responses to exercise were examined in chronically instrumented normal and FH swine in the absence and presence of the ETA/B receptor antagonist tezosentan. Intrinsic reactivity to ET was further assessed in skeletal muscle arterioles. FH swine exhibited ∼9-fold elevation in total plasma cholesterol versus normal swine. Similar to our recent findings, systemic, not pulmonary, vasodilatation during exercise was reduced in FH swine. Blockade of ET receptors caused marked systemic vasodilatation at rest and during exercise in normal swine that was significantly reduced in FH swine. The reduced role of ET in FH swine in vivo was not the result of decreased arteriolar ET responsiveness, as responsiveness was increased in isolated arterioles. Smooth muscle ET receptor protein content was unaltered by FH. However, circulating plasma ET levels were reduced in FH swine. ET receptor antagonism caused pulmonary vasodilatation at rest and during exercise in normal, but not FH, swine. Therefore, contrary to our hypothesis, FH swine exhibit a generalised reduction in the role of ET in regulating vascular tone in vivo probably resulting from reduced ET production. This may represent a unique vascular consequence of severe familial hypercholesterolaemia.

Pathological Importance of the Endothelin-1/ET(B) Receptor System on Vascular Diseases

Activation of the endothelin (ET)-1/ET receptor system is involved in the development of vascular diseases such as atherosclerosis, vascular hypertrophy, and restenosis. Some issues still remain unresolved including whether ET receptor antagonists are expected to become the new therapeutic tools for the treatment of vascular diseases. One of the unresolved critical points is the functional role of ET receptor subtypes on each vascular disease, in particular the pathophysiological roles of the ET_B receptor. We recently demonstrated that selective inhibition of the ET_B receptor system showed harmful effects in the development of neointimal formation after vascular injury. However, there was no apparent difference in the therapeutic effects between a nonselective ET_A/ET_B receptor antagonist and selective ET_A receptor antagonist. These findings indicate that antagonism of the ET_A receptor system is essential for suppressing vascular remodeling, irrespective of the presence of ET_B-receptor-mediated actions, although the selective ET_B receptor antagonist worsens vascular remodeling. In addition, we found that ET receptor systems contribute to sex differences in the severity of vascular disease, thereby suggesting that the efficacy of ET receptor antagonists for vascular diseases may differ between sexes. In this paper, we outline the roles of the ET-1/ET_B receptor system on vascular diseases and its sex differences.

New perspectives on endothelin-1 in atherosclerosis and diabetes mellitus

Endothelin-1 (ET-1) is a vasoconstrictor, proinflammatory and proliferative endothelial cell-derived peptide that is of significant importance in the regulation of vascular function. It is involved in the development of endothelial dysfunction including important interactions with nitric oxide. The expression and functional effects of ET-1 and its receptors are markedly altered during development of cardiovascular disease. Increased production of ET-1 and its receptors mediate many pathophysiological events contributing to the development of atherosclerosis and vascular complications in diabetes mellitus. The present review focuses on the pathophysiological role of ET-1 and the potential importance of ET receptors as a therapeutic target for treatment of these conditions.

Endothelin-1 and diabetic complications: focus on the vasculature

Diabetes is not only an endocrine but also a vascular disease. Cardiovascular complications are the leading cause of morbidity and mortality associated with diabetes. Diabetes affects both large and small vessels and hence diabetic complications are broadly classified as microvascular (retinopathy, nephropathy and neuropathy) and macrovascular (heart disease, stroke and peripheral arterial disease) complications. Endothelial dysfunction, defined as an imbalance of endothelium-derived vasoconstrictor and vasodilator substances, is a common denominator in the pathogenesis and progression of both macro and microvascular complications. While the pathophysiology of diabetic complications is complex, endothelin-1 (ET-1), a potent vasoconstrictor with proliferative, profibrotic, and proinflammatory properties, may contribute to many facets of diabetic vascular disease. This review will focus on the effects of ET-1 on function and structure of microvessels (retina, skin and mesenteric arteries) and macrovessels (coronary and cerebral arteries) and also discuss the relative role(s) of endothelin A (ET(A)) and ET(B) receptors in mediating ET-1 actions.

Long-term administration of endothelin receptor antagonist improves coronary endothelial function in patients with early atherosclerosis

BACKGROUND

Endothelin (ET-1) is one of the most potent vasoconstrictors and plays a seminal role in the pathogenesis of atherosclerosis. The present study was designed to test the hypothesis that long-term treatment with an endothelin-A (ET(A)) receptor antagonist improves coronary endothelial function in patients with early coronary atherosclerosis.

METHODS AND RESULTS

Forty-seven patients with multiple cardiovascular risk factors, nonobstructive coronary artery disease, and coronary endothelial dysfunction were randomized in a double-blind manner to either the ET(A) receptor antagonist atrasentan (10 mg) or placebo for 6 months. Coronary endothelium-dependent vasodilation was examined by infusing acetylcholine (10(-6) to 10(-4) mol/L) in the left anterior descending coronary artery. N(G)-monomethyl-l-arginine was administered to a subgroup of patients. Endothelium-independent coronary flow reserve was examined by use of intracoronary adenosine and nitroglycerin. Baseline characteristics and incidence of adverse effects were similar between the 2 groups. There was a significant improvement in percent change of coronary blood flow in response to acetylcholine at 6 months from baseline in the atrasentan group compared with the placebo group (39.67%, 95% confidence interval 23.23% to 68.21%, versus -2.22%, 95% confidence interval -27.37% to 15.28%; P<0.001). No significant difference in the percent change of coronary artery diameter or change in coronary flow reserve was demonstrated. Coronary blood flow, coronary artery diameter, and the effect of N(G)-monomethyl-l-arginine were similar between the groups at baseline and at 6 months.

CONCLUSIONS

This study demonstrates that 6-month treatment with atrasentan improves coronary microvascular endothelial function and supports the role of the endogenous endothelin system in the regulation of endothelial function in early atherosclerosis in humans. Clinical Trial Registration Information- URL: http://www.clinicaltrials.gov. Unique identifier: NCT00271492.

Tendency to angry rumination predicts stress-provoked endothelin-1 increase in patients with coronary artery disease

OBJECTIVE

To determine whether a tendency to angry rumination predicts anger recall (AR) stress-provoked increase in endothelin (ET)-1 among patients with coronary heart disease (CHD).

METHODS

Patients with chronic stable CHD (n = 105) completed a five-item measure of tendency to angry rumination (DAB-VR) and underwent a laboratory AR stress protocol (15-minute resting baseline [BL], 8-minute AR). Blood samples drawn at end of BL and AR were assayed for ET-1. Change in ET-1 from BL to AR (increase versus decrease/no change) was treated dichotomously in multivariate logistic regression models, including DAB-VR score and potential confounders, to evaluate the contribution of DAB-VR to the prediction of change in ET-1.

RESULTS

In the multivariate model, DAB-VR score significantly predicted ET-1 increase (odds ratio, 1.34; 95% confidence interval, 1.10-1.1.63; p = .004), controlling for age, history of diabetes, hypercholesterolemia, rate pressure product, use of beta blockers, and statins.

CONCLUSIONS

A tendency to angry rumination independently predicted AR stress-provoked ET-1 increase among patients with CHD. Given the involvement of ET-1 in plaque rupture, anger rumination tendency may identify vulnerability to anger-triggered acute coronary syndrome through prolongation of initial anger mobilization. The contribution of ruminative thinking to sustained poststress ET-1 elevation and the synergistic relationship of ET-1 during emotional stress with norepinephrine and nitric oxide remain to be explored.

Regulation of coronary vascular tone via redox modulation in the alpha1-adrenergic-angiotensin-endothelin axis of the myocardium

We hypothesized that alpha(1)-adrenoceptor stimulation of cardiac myocytes results in the production of an endothelin (ET)-releasing factor that stimulates the coronary vasculature to release ET and, by manipulating the redox state of cardiac and vascular cells, may influence the extent of alpha(1)-adrenergic-ET-1 vasoconstriction. Dihydroethidium (DHE) and dichlorodihydrofluorescein (DCF) intensities were increased by phenylephrine stimulation in isolated rat cardiac myocytes, which were enhanced by the mitochondrial electron transport chain complex I inhibitor rotenone (DHE: 20.4 +/- 1.2-fold and DCF: 25.2 +/- 0.9-fold, n = 8, P < 0.01, respectively) but not by the NADPH oxidase inhibitor apocynin. Olmesartan, an angiotensin II type 1 receptor antagonist, and enalaprilate did not change DHE and DCF intensities by phenylephrine. Next, we measured the vasoconstriction of isolated, pressurized rat coronary arterioles (diameter: 74 +/- 8 microm) in response to supernatant collected from isolated cardiac myocytes. The addition of supernatant from phenylephrine-stimulated myocytes to a 2-ml vessel bath (n = 8 each) caused volume-dependent vasoconstriction (500 microl: -14.8 +/- 2.2%). Olmesartan and TA0201, an ET type A receptor antagonist, converted vasoconstriction into vasodilation (8.5 +/- 1.2% and 10.5 +/- 0.5%, P < 0.01, respectively) in response to supernatant from phenylephrine-stimulated myocytes, which was eliminated with catalase. Vasoconstriction was weakened using supernatant from phenylephrine with rotenone-treated myocytes. Treatment of arterioles with apocynin to myocyte supernatant converted vasoconstriction into vasodilation (7.8 +/- 0.8%, P < 0.01). These results suggest that alpha(1)-adrenergic stimulation in cardiac myocytes produces angiotensin I and H(2)O(2) and that angiotensin releases ET-1 through NADPH oxidase in coronary arterioles. Thus, coronary vasoconstriction via the alpha-adrenergic-angiotensin-ET axis appears to require redox-mediated signaling in cardiac and vascular cells.

Endothelin-1 signalling in vascular smooth muscle: pathways controlling cellular functions associated with atherosclerosis

Atherosclerosis is the primary ischaemic vascular condition underlying a majority of cardiovascular disease related deaths. Endothelin-1 is a vasoactive peptide agent upregulated in atherosclerosis and in conjunction with its G protein-coupled receptors exerts diverse actions on all cells of the vasculature in particular vascular smooth muscle cells (VSMC). The effects of endothelin-1 include cell proliferation, migration and contraction, and the induction of extracellular matrix components and growth factors. VSMC as the major component of the neointima in atherosclerotic plaques accordingly play a key role in atherogenesis. In this review we examine classic and novel signalling pathways activated by endothelin-1 in VSMC (including phospholipase C, adenylate cyclase, Rho kinase, transactivation of receptor tyrosine kinases, mitogen activated protein kinase cascades and beta-arrestin) and their likely impact on the development and progression of atherosclerosis.

Endothelin-a receptor blockade improves renal microvascular architecture and function in experimental hypercholesterolemia

Hypercholesterolemia (HC) may trigger early renal injury, partly by impairing the function or the structure of renal microvessels (MV). The endothelin (ET) system is upregulated in HC and can have an impact on the renal microcirculation by regulating MV tone, growth factors, and remodeling. It was hypothesized that ET-A blockade would protect the HC kidney by improving the function and attenuating the damage of intrarenal MV. Single-kidney function and hemodynamic responses to endothelium-dependent challenge were assessed in pigs after 12 wk of experimental HC, HC and chronic supplementation with the ET receptor A blocker ABT-627 (HC+ET-A, 0.75 mg/kg per d), and normal controls. Renal MV architecture then was studied ex vivo using three-dimensional microcomputed tomography imaging, and growth factors and remodeling pathways were explored in renal tissue. The HC kidney showed increased MV density compared with normal (77.68 +/- 5.1 versus 62.9 +/- 4.8 vessels/cm(2); P = 0.04) but blunted endothelial function. Chronic ET-A blockade in HC upregulated renal vascular growth factors, further increased renal MV density (139.9 +/- 8.4 vessels/cm(2); P = 0.001 versus normal and HC), and decreased renal tissue and MV remodeling. Furthermore, ET-A blockade in HC decreased MV tortuosity and improved MV endothelial function, suggesting accelerated stabilization and maturation of neo-vessels. Modulation of renal MV architecture and function in HC is mediated partly by the endogenous ET system. Notably, ET-A blockade enhanced the proliferation and facilitated the maturation of renal MV in the HC kidney and improved renal MV remodeling and function. This study suggests novel renoprotective effects of ET-A blockers and supports further exploration of strategies that target the ET pathway in HC and atherosclerosis.

Regulation of stretch-induced JNK activation by stress fiber orientation

Cyclic mechanical stretch associated with pulsatile blood pressure can modulate cytoskeletal remodeling and intracellular signaling in vascular endothelial cells. The aim of this study was to evaluate the role of stretch-induced actin stress fiber orientation in intracellular signaling involving the activation of c-jun N-terminal kinase (JNK) in bovine aortic endothelial cells. A stretch device was designed with the capability of applying cyclic uniaxial and equibiaxial stretches to cultured endothelial cells, as well as changing the direction of cyclic uniaxial stretch. In response to 10% cyclic equibiaxial stretch, which did not result in stress fiber orientation, JNK activation was elevated for up to 6 h. In response to 10% cyclic uniaxial stretch, JNK activity was only transiently elevated, followed by a return to basal level as the actin stress fibers became oriented perpendicular to the direction of stretch. After the stress fibers had aligned perpendicularly and the JNK activity had subsided, a 90-degree change in the direction of cyclic uniaxial stretch reactivated JNK, and this activation again subsided as stress fibers became re-oriented perpendicular to the new direction of stretch. Disrupting actin filaments with cytochalasin D blocked the stress fiber orientation in response to cyclic uniaxial stretch and it also caused the uniaxial stretch-induced JNK activation to become sustained. These results suggest that stress fiber orientation perpendicular to the direction of stretch provides a mechanism for both structural and biochemical adaptation to cyclic mechanical stretch.

Dietary reversal of experimental hypercholesterolemia improves endothelial dysfunction of epicardial arteries but not of small coronary vessels in pigs

Endothelial dysfunction is characterized by impaired vasodilation, increase of oxidative stress and inflammation. The current study was designed to test the hypothesis that reversal of hypercholesterolemic diet alone does not normalize all the parameters of endothelial dysfunction. After 10 weeks on a high-cholesterol diet, female juvenile pigs were randomized to normal diet (n=5, "Reversals") or continued on the same diet (n=6, "HC") for another 6 weeks. A control group of 11 pigs received a normal diet ("C"). Coronary epicardial and arteriolar endothelial function was tested in vitro. NFkappaB and p47phox expression was analyzed in epicardial arteries and myocardium, respectively. P47phox localization in coronary arteries was demonstrated with immunohistochemistry. Lipid levels normalized in Reversal pigs. Epicardial arteries of Reversals showed a normalized relaxation and NFkappaB expression compared to HC (p<0.05). Small vessel relaxation remained attenuated, and expression of p47phox in myocardial tissue was elevated in Reversals compared to C (p<0.05). Dietary lowering of serum cholesterol and LDL improves vascular function of epicardial arteries but neither of small vessels nor vascular oxidative stress within this time frame. Hence, dietary normalization of serum lipid levels alone may not be synonymous to normalization of the components of endothelial dysfunction.

Responses to neither exogenous nor endogenous endothelin-1 are altered in patients with hypercholesterolemia

There is some controversy regarding whether vascular responses to endothelin are altered in hypercholesterolemia. Studies performed to date have been compromised by the use of endothelin antagonists at inappropriate concentrations. In the current study, we examine the role of endothelin-1 in hypercholesterolemic patients using lower, more selective doses of specific endothelin antagonists. Twenty-two patients with hypercholesterolemia (total plasma cholesterol > 6.0 mmol/l) and 17 healthy controls were recruited. Forearm vascular responses to endothelin-1 (5 pmol/min), the endothelin A antagonist BQ-123 (10 nmol/min), and the endothelin B antagonist BQ-788 (1 nmol/min) were obtained. Endothelin-1 caused a significant vasoconstriction in both hypercholesterolemic and control subjects, an effect that was not significantly different between the two groups (P = 0.784). BQ-123 caused a significant vasodilatation that was not significantly different between the two groups (P = 0.899). Similarly, responses to BQ-788 (P = 0.774) and mean plasma endothelin-1 levels were not different (control vs. hypercholesterolemia, 1.16 +/- 0.18 vs. 1.06 +/- 0.15 fmol/ml; P = 0.64). Responses to neither exogenous nor endogenous endothelin are influenced by plasma cholesterol levels in humans. It is thus unlikely that the endothelin system contributes to early vascular disease pathology in patients with hypercholesterolemia.

Plasma levels of endothelin-1, angiotensin II, nitric oxide and prostaglandin E2 in the venous and cavernosal blood of patients with erectile dysfunction

OBJECTIVES

To determine the alterations in the plasma levels of endothelin-1, angiotensin II, nitric oxide (NO) and prostaglandin E(2) (PGE(2)) in the venous and cavernosal blood of patients with organic and psychogenic erectile dysfunction (ED).

PATIENTS, SUBJECTS AND METHODS

The study included 32 patients complaining of ED; they were subdivided into two equal groups with either organic or psychogenic ED. Fifteen healthy potent age-matched male volunteers were enrolled as a control group. For each patient, venous and cavernosal blood samples were obtained, while venous blood was obtained from the controls.

RESULTS

There were significantly greater mean plasma levels of endothelin-1 and angiotensin II, and significantly lower mean plasma levels of NO and PGE(2), in the venous blood of patients with ED than in the controls. Patients with organic ED had significantly higher levels of endothelin-1 and significantly lower levels of NO in both venous and cavernosal blood than had those with psychogenic ED. There were significant positive correlations in both venous and cavernosal blood between endothelin-1 and angiotensin II, and between NO and PGE(2) in all patients with ED and the two subgroups. There were significant negative correlations between venous and cavernosal endothelin-1 and NO, endothelin-1 and PGE(2), angiotensin II and NO, and between angiotensin II and PGE(2).

CONCLUSION

The present results suggest that endothelin-1 could be a clinical marker of diffuse endothelial disease manifested by ED. As angiotensin-converting enzyme (ACE) activity controls angiotensin II there might be a rationale for the use of ACE inhibitors to prevent or treat ED. NO and PGE(2) may provide new strategies for the pharmacological treatment of ED.

Decrease of Endothelin Receptor Subtype ETB and Release of COX-Derived Products Contribute to Endothelial Dysfunction of Porcine Epicardial Coronary Arteries in Left Ventricular Hypertrophy

Alterations in the regulation of coronary circulation play a major role in the enhanced susceptibility to ischemic injury of the myocardium in left ventricular hypertrophy (LVH). The present study was designed to assess the role of endothelium-dependent contracting factors and endothelin receptors in the coronary endothelial dysfunction in LVH, occurring 2 months after aortic banding in a swine model. Hemodynamic and morphologic analyses were performed in LVH and control groups. Vascular reactivity studies were performed in rings from control and aortic banding groups to assess the contribution of endothelin (ET-1) receptor subtypes to the contraction induced by ET-1 and IRL-1620 (an ETB receptor agonist), with and without endothelium. The effects of cyclooxygenase (COX)-derived products induced by ET-1, serotonin (5-HT), and bradykinin (BK) were evaluated, with or without indomethacin (a COX antagonist). ET-1 receptor density was assessed by confocal microscopy and Western blot experiments. The wall-to-lumen ratio, determined in digital planimetry, was increased in the LVH group with no significant changes in coronary perfusion pressures. There was a significant increase in contractions to ET-1 in the LVH group, which were reduced by exposure to indomethacin and daltroban (thromboxane A2 [TXA2] receptor antagonist). Relaxations to 5-HT and BK were improved by indomethacin in the LVH group. There was no significant change in ETA receptor density (3.113 +/- 0.389 vs 3.594 +/- 0.314) but a decrease in ETB receptor density (6.435 +/- 0.265 vs 4.588 +/- 0.089; P < 0.001) in the LVH group. The coronary endothelial dysfunction of swine epicardial coronary arteries in LVH secondary to 2 months of aortic banding involves both relaxing and contracting factors. ETA receptors and COX-derived products are preferentially implicated in the increased contractions to ET-1. Strategies aimed at decreasing ET-1 effects with ET-1 antagonists selective for ETA receptors could improve the coronary endothelial dysfunction in LVH.

Effects of Proteasome Inhibition on the Kidney in Experimental Hypercholesterolemia

Hypercholesterolemia (HC) and atherosclerosis often accompany and aggravate renal disease. Proteasome inhibitors (PSI) can decrease proliferation and inflammation, likely by reducing activation of the proinflammatory NF-kappaB. However, chronic proteasome inhibition has never been demonstrated in the HC kidney. Four groups of pigs (n = 7 each) were studied after a 12-wk normal (N) or 2% HC diet alone or supplemented (N+PSI and HC+PSI) with MLN-273 (0.08 mg/kg subcutaneously twice weekly). Renal hemodynamics and function were quantified in vivo using electron-beam computed tomography at baseline and after vasodilator challenge using acetylcholine. Renal tissue was studied ex vivo using immunoblotting, PCR, and immunohistochemistry. Serum cholesterol was similarly elevated in HC and HC+PSI. Basal renal blood flow was similar among the groups, whereas GFR was decreased in both N+PSI and HC+PSI. The blunted renovascular and functional responses to acetylcholine in HC were normalized in HC+PSI (suggesting renal endothelial function improvement), which was accompanied by decreased renal endothelin, NF-kappaB, and augmented endothelial nitric oxide synthase expression. In parallel, HC+PSI animals also showed elevated NAD(P)H oxidase expression and circulating oxidized LDL, suggesting a potential for increased oxidative stress. This study shows that chronic PSI intervention in HC improves renal endothelial functional responses to challenge, possibly by modulating nitric oxide availability and endothelin. Furthermore, PSI may decrease intrarenal inflammation through modulation of the NF-kappaB pathway but may potentially increase oxidative stress, which warrants further investigation. This study may support a role for the ubiquitin/proteasome system in the kidney in HC and early atherosclerosis.

Effect of simvastatin on left ventricular mass in hypercholesterolemic rabbits

Epidemiological studies showed that hypercholesterolemia is associated with higher left ventricular mass. Endothelin signaling is activated in hyperlipidemic animals and may contribute to progressive ventricular hypertrophy. Simvastatin has been shown to inhibit endothelin-1. However, the behavior of simvastatin on ventricular hypertrophy in hyperlipidemic animals is not well understood. In this study, we evaluated the hemodynamic, biochemical, and morphological responses to simvastatin in cholesterol-fed (1%) rabbits. The left ventricular weight increased 8 wk after cholesterol feeding compared with that in normocholesterolemic rabbits. Simvastatin at a clinical therapeutic dose (1.2 mg x kg(-1) x day(-1)) significantly decreased left ventricular weight by 14% and left ventricular myocyte sizes by 14% as isolated by enzymatic dissociation. Hypercholesterolemia upregulated ventricular preproendothelin-1 mRNA as assessed by real-time quantitative RT-PCR and elevated production of cardiac endothelin-1 concentration. The increased endothelin-1 responses can be inhibited after simvastatin administration. Left ventricular mass indexed by body weight positively correlated with tissue endothelin-1 levels (P = 0.0003). In Langendorff-perfused rabbit hearts, hyperlipidemia led to significant QT prolongation compared with normocholesterolemia, which can be reversed by administering simvastatin. In contrast, simvastatin-induced beneficial effects were reversed by the addition of mevalonate. The addition of bosentan, a nonspecific endothelin receptor blocker, improved the response in hypercholesterolemic rabbits and did not have additional beneficial effects in simvastatin-treated rabbits. The results of the present study suggest that the antihypertropic and electrocardiographic effects of simvastatin at a clinical therapeutic dose are mediated through inhibition of tissue endothelin-1 expression, which is linked to mevalonate metabolism, and result in an amelioration of cardiomyocyte hypertrophy development by an atherogenic diet.

Endothelin-1 receptor blockade prevents renal injury in experimental hypercholesterolemia

BACKGROUND

The potent vasoconstrictor endothelin-1 is involved in regulation of renal function, and is up-regulated in hypercholesterolemia (HC), a risk factor for renal disease that increases oxidative stress and impairs renal hemodynamic responses. However, the involvement of endothelin (ET) in this disease process is yet unknown.

METHODS

Regional renal hemodynamics and function in vivo were quantified in pigs at baseline and during infusion of acetylcholine using electron beam computed tomography after a 12-week normal diet (N = 6), HC diet (N = 6), and HC diet orally supplemented (4 mg/kg/day) with the selective ET receptor-A (ET-A) blocker ABT-627 (HC+ET-A, N = 6). Plasma levels of 8-epi-PGF2-alpha-isoprostanes, markers of oxidative stress, were measured using enzyme immunoassay, and renal tissue was studied ex vivo using Western blotting, electrophoretic mobility shift assay, and immunohistochemistry.

RESULTS

Total and low-density lipoprotein (LDL) cholesterol were similarly increased, but isoprostanes were decreased in HC+ET-A compared to HC alone. Basal renal perfusion was similar among the groups, while glomerular filtration rate (GFR) increased in HC+ET-A compared to HC. Stimulated perfusion and GFR were blunted in HC, but normalized in HC+ET-A. Moreover, ET blockade increased expression of endothelial nitric oxide synthase, and decreased endothelial expression of the oxidized-LDL receptor LOX-1, as well as tubular immunoreactivity of inducible nitric oxide synthase, nitrotyrosine, nuclear factor-kappaB, transforming growth factor-beta, and tubulointerstitial and perivascular trichrome staining.

CONCLUSION

ET-A blockade improves renal hemodynamic and function in HC, and decreases oxidative stress, and renal vascular and tubulointerstitial inflammation and fibrosis. These findings support a role for the endogenous ET system in renal injury in HC and atherosclerosis.

Endothelin type A receptor antagonism restores myocardial perfusion response to adenosine in experimental hypercholesterolemia

Experimental hypercholesterolemia is characterized by increased endothelin-1 (ET-1) activity and is associated with an attenuated myocardial perfusion response and an inappropriate increase in coronary microvascular permeability during episodes of increased myocardial demand. This study was designed to determine the effect of chronic selective ET type A (ET(A)) receptor antagonism on coronary vascular response to simulated cardiac stress in experimental hypercholesterolemia. Twenty-one pigs were randomized to three groups: normal diet (N), high-cholesterol diet (HC), and HC diet plus ABT-627, a selective ET(A) receptor antagonist, (HC+ABT-627). After 12 weeks, cardiac electron beam computed tomography (EBCT) was performed before and during intravenous infusion of adenosine, and myocardial perfusion (ml/min per g) and coronary microvascular permeability index (arbitrary units) were calculated. Basal myocardial perfusion was similar in all groups (N: 0.91+/-0.10; HC: 0.95+/-0.08; HC+ABT-627: 1.03+/-0.09; P=0.64). Adenosine infusion led to a significant increase in myocardial perfusion in the N (1.32+/-0.15; P<0.001) but not in the HC (0.95+/-0.07) group. However, in the HC+ABT-627 group, adenosine also significantly increased myocardial perfusion (1.33+/-0.12; P=0.001). Basal permeability index did not differ between the groups (N: 1.56+/-0.13; HC: 1.34+/-0.19; HC+ABT-627: 1.62+/-0.10; P=0.38). Adenosine infusion significantly increased permeability index in HC pigs (2.29+/-0.22; P<0.001) but not in N (1.71+/-0.21) and HC+ABT-627 (1.82+/-0.08) pigs. We conclude that chronic selective ET(A) receptor antagonism preserves myocardial perfusion response and coronary microvascular integrity during episodes of increased myocardial demand in experimental hypercholesterolemia, indicating an important role for the endogenous endothelin system in this disorder.

Role of ET-1 in the regulation of coronary circulation

Given that circulating ET levels in heart failure, in particular, may reach physiological threshold for coronary constrictor responses, the primary objective of the present review is to consider coronary vessels as an important target for circulating and locally produced endothelin(s). In healthy vessels, ET-1 causes biphasic coronary responses characterized by a transient dilation of large and small arteries followed by a sustained constriction. ETB receptors are pivotal in the early dilation of resistance vessels, whereas dilation of conductance vessels may be a secondary phenomenon triggered by flow increases. Exogenous ET-1 causes coronary constriction almost exclusively through ETA receptor activation. Human and canine large epicardial coronary vessels display significant baseline ET-1 dependent tone in vitro and in vivo, an ETA-dependent process. In contrast, ETB receptors located on smooth muscle cells are apparently less important for producing constrictor responses. NO production may serve as an important counter-regulatory mechanism to limit ET-dependent effects on coronary vessels. Conversely, in a dysfunctional endothelium, the loss of NO may augment ET-1 production and activity. By lifting the ET-dependent burden from coronary vessels, ET receptor blockade should help to ensure a closer match between cardiac metabolic demand and coronary perfusion.

Increased endothelin-1 and endothelin receptor expression in myocytes of ischemic and reperfused rat hearts and ventricular myocytes exposed to ischemic conditions and its inhibition by nitric oxide generation

Endothelin-1 (ET-1) and nitric oxide (NO) exert opposite effects in the cardiovascular system, and there is evidence that the NO counters the potential deleterious effects of ET-1. We investigated whether NO affects the increased mRNA expression of ET-1 and endothelin receptors induced by (i) 30 min of ischemia with or without 30 min reperfusion in myocytes from isolated rat hearts or (ii) ischemic conditions (acidosis or hypoxia) in cultured rat neonatal ventricular myocytes. Ischemia with or without reperfusion produced more than a twofold increase in mRNA expression of ET-1 as well as the ET(A) and ET(B) receptor (P < 0.05), although these effects were completely blocked by the NO donor 3-morpholinosydnonimine (SIN-1; 1 microM). To assess the possible factors regulating ET expression, myocytes were exposed to acidosis (pH 6.8-6.2) or to hypoxic conditions in an anaerobic chamber for 24 h in the presence or absence of SIN-1. At all acidic pHs, ET-1 and ET(A) receptor mRNA expression was significantly (P < 0.05) elevated approximately threefold, although the magnitude of elevation was independent of the degree of acidosis. These effects were completely prevented by SIN-1. ET(B) receptor expression was unaffected by acidosis. Hypoxia increased ET-1 as well as ET(A) and ET(B) receptor expression threefold (P < 0.05), although this was unaffected by SIN-1. Our results demonstrate that myocardial ischemia and reperfusion upregulate the ET system, which is inhibited by NO. Although increased expression of the ET system can be mimicked by both acidosis and hypoxia, only the effects of the former are NO sensitive. NO may serve an endogenous inhibitory factor which regulates the expression of the ET system under pathological conditions.

Nitric oxide, atherosclerosis and the clinical relevance of endothelial dysfunction

The endothelium plays a key role in vascular homeostasis through the release of a variety of autocrine and paracrine substances, the best characterized being nitric oxide. A healthy endothelium acts to prevent atherosclerosis development and its complications through a complex and favorable effect on vasomotion, platelet and leukocyte adhesion and plaque stabilization. The assessment of endothelial function in humans has generally involved the description of vasomotor responses, but more widely includes physiological, biochemical and genetic markers that characterize the interaction of the endothelium with platelets, leukocytes and the coagulation system. Stable markers of inflammation such as high sensitivity C-reactive protein are indirect and potentially useful measures of endothelial function for example. Attenuation of the effect of nitric oxide accounts for the majority of what is described as endothelial dysfunction. This occurs in response to atherosclerosis or its risk factors. Much remains to be learned about the molecular and genetic pathophysiological mechanisms of endothelial cell abnormalities. However, pharmacological intervention with a growing list of medications can favorably modify endothelial function, paralleling beneficial effects on cardiovascular morbidity and mortality. In addition, several small studies have provided tantalizing evidence that measures of endothelial health might provide prognostic information about an individual patient's risk of subsequent events. As such, the sum of this evidence makes the clinical assessment of endothelial function an attractive surrogate marker of atherosclerosis disease activity. The review will focus on the role of nitric oxide in atherosclerosis and the clinical relevance of these findings.

Chronic endothelin receptor antagonism prevents coronary vasa vasorum neovascularization in experimental hypercholesterolemia

OBJECTIVES

The purpose of this study was to test the hypothesis that endothelin (ET) receptor antagonism reduces coronary vasa vasorum neovascularization in experimental hypercholesterolemia.

BACKGROUND

Experimental hypercholesterolemia is associated with increased expression of ET-1, an endothelium-derived peptide with vasoconstricting, mitogenic and angiogenic properties, in the coronary arterial wall as well as with vasa vasorum neovascularization. A pathomechanistic role of the endogenous ET system in vasa vasorum neovascularization in hypercholesterolemia has, however, remained uncertain so far.

METHODS

Female domestic pigs were placed on a normal diet (N; n = 7) or on a hypercholesterolemic diet without (HC; n = 6) or with ET-A receptor antagonism (ABT-627, 4 mg/kg/day; HC + ET-A; n = 6). After 12 weeks, coronary vasa vasorum structure was assessed by three-dimensional microscopic computed tomography, expression of vascular endothelial growth factor (VEGF) within the coronary arterial wall by Western blotting and immunostaining.

RESULTS

Compared with the N group, plasma concentrations of low-density lipoprotein cholesterol were higher in both the HC and HC + ET-A groups (36 +/- 3 mg/dl vs. 312 +/- 153 mg/dl and 303 +/- 113 mg/dl, p < 0.01). Vasa vasorum density was higher in the HC group compared with the N group (4.7 +/- 1.8 per mm(2) vs. 2.5 +/- 1.5 per mm(2); p < 0.05) and was preserved in the HC + ET-A group (3.2 +/- 0.7 per mm(2)). In parallel, increase in VEGF expression in the coronary arterial wall in the HC group was preserved in the HC + ET-A group.

CONCLUSIONS

The current study demonstrates that chronic endothelin receptor antagonism prevents the increase in VEGF expression and vasa vasorum density of coronary arteries in experimental hypercholesterolemia. These findings support a role for the endogenous ET system in vasa vasorum neovascularization in early coronary atherosclerosis.

Crosstalk between endothelin and nitric oxide in the control of vascular tone

Several lines of evidence indicate that nitric oxide (NO) impairs endothelin (ET) production/action in vitro. Acute pressor responses caused by the blockade of NO formation with arginine analogues in vivo are blunted by selective ET(A) or dual ET(A)/ET(B) receptor blockade whereas blockade of NO formation magnifies ET-induced constriction of various vascular territories. Given that ET receptor blockade has normally limited effects on mean arterial pressure, the reversal of pressor responses caused by the blockade of NO formation with ET receptor blockade most likely reflects a significant crosstalk between NO and ET. Suppression of NO formation also leads to significant increases in ET production caused by agents targeting the endothelium, such as acetylcholine and thrombin. In addition, the inhibitory effect of shear stress on endothelial cells ET production also involves NO as an intermediate.Paradoxically, chronic exposure to organic nitrates which causes nitrate tolerance leads to an augmented vascular ET content. An increased angiotensin II (AII) production is apparently pivotal in this process. This article reviews observations pointing to the importance of NO/ET interactions as a fundamental and common regulatory mechanism shared across species. As a consequence of this crosstalk between NO and ET, experimental strategies designed to assess endothelial NO-dependent activity by the blockade of NO formation may be mitigated by magnified ET-dependent influences.

Coronary artery endothelial protection after local delivery of 17beta-estradiol during balloon angioplasty in a porcine model: a potential new pharmacologic approach to improve endothelial function

OBJECTIVES

The goal of this research was to study the effect of locally delivered 17beta-estradiol (17beta-E) during angioplasty on endothelial function after percutaneous transluminal coronary angioplasty (PTCA) at four weeks.

BACKGROUND

The endothelium plays a major role in the structural and functional integrity of coronary arteries and is damaged by PTCA.

METHODS

Juvenile swine were subjected to PTCA, after which each artery was randomly-assigned to 600-microg 17beta-E delivered locally, an equal volume of vehicle (V) or PTCA alone. After four weeks, the improvement in endothelial function was assessed by angiography using intracoronary acetylcholine (Ach) infusion and by immunohistochemistry.

RESULTS

At 10(-5) mol/l and 10(-4) mol/l Ach, significant vasoconstriction was noted in arteries treated with PTCA alone (p < 0.01 and p < 0.0001, respectively) and with PTCA plus V (p < 0.02 and p < 0.001, respectively). No significant vasoconstrictive response to Ach was observed in arteries treated with PTCA plus 17beta-E. Immunohistochemistry of vessels four weeks after PTCA revealed enhanced re-endothelialization (p < 0.0005) and endothelial nitric-oxide synthase (eNOS) expression (p < 0.0005) in PTCA plus 17beta-E-treated arteries compared with the other two treatment groups. Arteries treated with 17beta-E showed significantly lower neointima formation, which correlated inversely with the extent of re-endothelialization and eNOS expression.

CONCLUSIONS

Locally delivered 17beta-E significantly enhances re-endothelialization and endothelial function after PTCA, possibly by improving the expression of eNOS. Since endothelial dysfunction can promote both restenosis and coronary spasm, local 17beta-E administration is a promising new approach to improve long-term results after PTCA.

Role of endogenous endothelin on coronary flow in health and disease

The role of the endothelium in the control of coronary flow has been demonstrated. Results of recent studies, both on animals and on humans, suggest that endogenous endothelin also plays an important role in basal coronary tone. Disease processes such as ischaemia-reperfusion injury, congestive heart failure, hypertension and atherosclerosis may be contributed to by an imbalance in, or excess of, release of endothelin. With the discovery of newer endothelin antagonists and endothelin converting enzyme inhibitors, especially with fewer hepatic side effects, there is the potential for much future research into novel therapeutic management of these common cardiovascular disorders.

Involvement of oxidation-sensitive mechanisms in the cardiovascular effects of hypercholesterolemia

Hypercholesterolemia is a common clinical metabolic and/or genetic disorder that promotes functional and structural vascular wall injury. The underlying mechanisms for these deleterious effects involve a local inflammatory response and release of cytokines and growth factors. Consequent activation of oxidation-sensitive mechanisms in the arterial wall, modulation of intracellular signaling pathways, increased oxidation of low-density lipoprotein cholesterol, and quenching of nitric oxide can all impair the functions controlled by the vascular wall and lead to the development of atherosclerosis. This cascade represents a common pathological mechanism activated by various cardiovascular risk factors and may partly underlie synergism among them as well as the early pathogenesis of atherosclerosis. Antioxidant intervention and restoration of the bioavailability of nitric oxide have been shown to mitigate functional and structural arterial alterations and improve cardiovascular outcomes. Elucidation of the precise nature and role of early transductional signaling pathways and transcriptional events activated in hypercholesterolemia in children and adults, including mothers during pregnancy, and understanding their downstream effects responsible for atherogenesis may help in directing preventive and interventional measures against atherogenesis and vascular dysfunction.

Coronary endothelial function in health and disease

The endothelium participates in the control of coronary vascular tone and growth through the release of vasodilating and growth-inhibiting factors such as nitric oxide (NO) and C-type natriuretic peptide (CNP), and vasoconstricting and growth-promoting substances such as endothelin-1 (ET-1). Abnormalities in NO and/or CNP generation or actions have been demonstrated in various cardiovascular pathophysiological states, specifically atherosclerosis, congestive heart failure, hypertension and hypercholesterolaemia. Moreover, an increase in plasma ET-1 levels has also been reported in these disease states. When these observations are considered together, these states may be characterised by an attenuated release or action of NO and/or CNP, together with an augmented release of ET-1. Thus, an imbalance between these opposing factors may contribute to the alteration in vascular tone and the vascular remodelling characteristics of cardiovascular disease. The following article summarises the present knowledge of endothelial control of the coronary circulation and derangements associated with coronary endothelial dysfunction.

Enhanced endothelin-converting enzyme immunoreactivity in early atherosclerosis

Endothelin-1 (ET-1) is a 21-amino-acid local and circulating factor whose plasma concentrations are increased in advanced atherosclerosis. ET-1 is cleaved from a prohormone (big ET-1) by endothelin-converting enzymes (ECEs) into the biologically active mature form which mediates vasoconstriction and cell proliferation. This study was designed to test by immunohistochemistry the hypothesis that ECE is present locally in the neointima of atherosclerotic vessels. Two groups of rabbits, control (n = 6) and cholesterol-fed (1% cholesterol diet for 8 weeks; n = 6) were sacrificed. Aortas were excised and divided for determination of tissue ET-1 concentration by RIA and immunohistochemical analysis of ECE. Vascular wall ET-1 was increased in the atherosclerotic aorta (6.1 +/- 0.8 vs. 9.8 +/- 0.9 pg/mg protein; p < 0.05), whereas circulating ET-1 concentrations were similar in the two groups (3.8 +/- 0.4 vs. 2.4 +/- 1.4 pg/ml). Immunostaining revealed the presence of ECE in endothelial and vascular smooth-muscle cells of the control group. Enhanced ECE immunoreactivity was present in atherosclerotic aortas, particularly in the neointimal macrophages and smooth-muscle cells. We conclude that local vascular wall, but not circulating ET-1, is increased in early atherosclerosis. In addition, ECE immunoreactivity is increased in early atherosclerosis and may therefore contribute to the generation of local ET-1 in early experimental atherosclerosis. These studies provide important insights into the regulation of ET-1 in early atherosclerosis, which may contribute to the elucidation of factors involved in the progression of atherosclerosis.

Treatment with endothelin-receptor antagonists increases NOS activity in hypercholesterolemia

In experimental hypercholesterolemia, endothelium-dependent relaxations decrease, as does endothelial immunoreactivity for nitric oxide (NO) synthase (NOS; eNOS) in coronary arteries. Systemic levels of NO also decrease with concomitant elevations in systemic circulating levels of endothelin (ET)-1. Chronic treatment of hypercholesterolemic pigs with ET-receptor antagonists increases circulating NO and improves endothelium-dependent relaxations. Mechanisms causing these increases are not known. Therefore, experiments were designed to test the hypothesis that chronic administration of ET-receptor antagonists to hypercholesterolemic pigs increases NO production through increases in NOS activity. Female juvenile pigs were fed a 2% cholesterol atherogenic diet and were randomly allocated to receive no treatment (controls), a selective ET(A)-receptor antagonist (ABT-624), or a combined ET(A) + ET(B)-receptor antagonist (RO-48-5695) daily for 12 wk. After 12 wk, endothelial cells from thoracic aorta were prepared for measurement of eNOS mRNA or eNOS activity. Total cholesterol, low-density-lipoprotein cholesterol, and concentrations of ET-1 were significantly higher in all three groups at 12 wk compared with baseline levels. Circulating plasma-oxidized products of NO (NOx) increased with ET-receptor blockade. NOS mRNA was similar among groups. Total and Ca-dependent NOS activity was significantly higher in aortic endothelial cells from the ET(A) + ET(B)-treated pigs compared with those treated with ET(A) antagonist alone. These results suggest that changes in systemic NOx after chronic inhibition of ET(A) + ET(B) receptors in hypercholesterolemia may result from posttranscriptional changes in NOS.

Endothelin in cardiovascular disease: from atherosclerosis to heart failure

Since the discovery of endothelin (ET) as a potent vasoconstrictor, increasing evidence supports the role of ET in the pathogenesis of cardiovascular diseases including coronary artery disease and congestive heart failure. This peptide not only alters vascular tone and cardiac hemodynamics, but also has a substantial role in the regulation of cellular proliferation and apoptosis, activation of monocytes and cellular matrix production. Thus, ET may play a role in the pathogenesis of cardiovascular diseases through multiple mechanisms. The development of ET receptor antagonists has lead to a greater understanding of the role of the endogenous ET system in both physiologic and pathophysiologic states. Endothelin receptor antagonists are becoming new therapeutic tools for the treatment of cardiovascular disease and their study will lead to a greater understanding of the role of ET in disease progression.

Increased activity of endogenous endothelin in patients with hypercholesterolemia

OBJECTIVE

We sought to assess the activity of endogenous endothelin-1 (ET-1) in hypercholesterolemic patients using antagonists of ET-1 receptors.

BACKGROUND

Endothelial dysfunction in hypercholesterolemic patients may contribute to their risk of premature atherosclerosis. Endothelin, a peptide released by endothelial cells, may be involved in this process by activating smooth muscle cell mitogenesis and leukocyte adhesion.

METHODS

Forearm blood flow (FBF) responses (strain-gauge plethysmography) to intra-arterial infusion of a selective blocker of ETA receptors (BQ-123) and, on a separate occasion, to ET-1 were measured in 12 hypercholesterolemic patients and 12 normal control subjects. In addition, on a different day, six hypercholesterolemic patients received co-infusion of BQ- 123 and BQ-788 (a selective blocker of ETB receptors).

RESULTS

In normal subjects, BQ-123 did not significantly modify FBF from baseline (p = 0.78); however, in hypercholesterolemic patients, BQ-123 administration resulted in a significant vasodilator response (p < 0.001). Administration of exogenous ET-1 resulted in similar vasoconstrictor responses in patients (37%) and control subjects (35%) (p = 0.83). In hypercholesterolemic patients, the vasodilator response to selective ETA blockade was reversed by nonselective blockade of ET-1 receptors obtained by co-infusion of BQ-123 and BQ-788.

CONCLUSIONS

The vascular activity of endogenous ET-1 is enhanced in hypercholesterolemic patients, whereas their sensitivity to exogenous ET-1 is unchanged. These findings suggest increased production of ET-1, which may participate in the pathophysiology of vascular disease characteristic of hypercholesterolemia.

Expression of endothelin-1 after endothelial denudation of thoracic aortas in experimental hypercholesterolemic rats

Although endothelin-1 (ET-1) is involved in balloon-induced neointima formation, the role of ET-1 in balloon-induced neointima formation in hypercholesterolemia is unclear. In addition, it remains to be determined whether ET-1 is produced by endothelial cells or vascular smooth muscle cells, or both. We investigated tissue immunoreactive ET-1 levels by immunoblot analysis, localization of ET-1 immunoreactivity by immunohistochemistry, and expression of preproET-1 mRNA by in situ hybridization in balloon-induced neointima formation in experimental hypercholesterolemic rats. Serum total cholesterol levels were significantly higher (p< 0.01) in the 5%cholesterol-diet group (194 +/- 17 mg/dl, n=20) than in the normal-diet group (64 +/- 2 mg/dl, n=20). Before and after endothelial denudation, plasma ET-1 levels and tissue immunoreactive ET-1 levels were significantly higher in cholesterol-diet rats. The expression of preproET-1 mRNA by in situ hybridization was observed in the nuclei of endothelial cells, but not medial smooth muscle cells in normal- or cholesterol diet rats. After endothelial denudation, plasma ET-1 levels and serum total cholesterol levels did not change in either the normal- or the cholesterol-diet rats. Tissue level of ET-1 tended to increase at 3 days after denudation in normal-diet rats (1.0 +/- 0.1 vs 2.6 +/- 0. 2 density ratio, p< 0.05), although endothelial cells had not yet regenerated. The expression of preproET-1 mRNA by in situ hybridization was not observed at 3 days after endothelial denudation in either endothelial or medial smooth muscle cells in normal-diet rats. Four weeks after denudation, regeneration of endothelial cells was almost complete, and an intimal hyperplasia was observed. Tissue ET-1 levels were significantly elevated 4 weeks after endothelial denudation in normal-diet rats (1.0 +/- 0.1 vs 7.6 +/- 0.2 density ratio, p< 0.05). The expression of preproET-1 mRNA by in situ hybridization was observed in the nuclei of regenerated endothelial cells after endothelial denudation, and in smooth muscle cells migrating into the intima, but was not observed in medial smooth muscle cells in normal-diet rats. A similar pattern was observed in cholesterol-diet rats. We concluded that ET-1 was involved in neointima formation and that ET-1 was produced by both endothelial and neointimal smooth muscle cells, but not medial smooth muscle cells after endothelial denudation in experimental hypercholesterolemic rats.

High level of cholesterol increases coronary vasomotor tone during exercise

BACKGROUND

Coronary vasomotor tone plays an important role in the regulation of myocardial perfusion and influences ischemic threshold significantly. Endothelial dysfunction occurs in the presence of coronary risk factors and is closely linked to the development of atherosclerosis affecting myocardial perfusion and decreasing ischemic threshold.

OBJECTIVE

To study the effect of hypercholesterolemia on coronary vasomotor tone in normal and stenotic coronary arteries at rest and during exercise.

PATIENTS AND METHODS

In total 48 patients were included in the present analysis. Patients were divided into two groups according to the actual levels of serum cholesterol: 18 patients had normal (mean 181 +/- 28 mg%; group 1) and 30 had elevated (mean 263 +/- 46 mg%; group 2) levels of serum cholesterol according to the 4S criteria with a cutoff level of 213 mg% (5.5 mmol/l). Coronary vasomotor tone at rest and during supine bicycle exercise was calculated by dividing mean aortic pressure by radius of coronary vessel obtained using biplanar quantitative coronary angiography. A normal as well as a stenotic vessel segment in each patient were studied.

RESULTS

Normal vessel segments in patients with normal levels of cholesterol (group 1) exhibited no exercise-induced change in coronary vascular tone (+3%, NS), whereas a significant increase in tone (+24%, P < 0.01 versus rest) occurred in those with high levels of cholesterol (group 2). In contrast, stenotic segments in members of both groups exhibited an increase in vascular tone irrespective of the actual level of serum cholesterol.

CONCLUSIONS

Hypercholesterolemia causes a pathologic increase in coronary vasomotor tone of angiographically normal vessel segments during exercise. A similar pathologic response occurs in stenotic arteries, but this is independent of the actual level of serum cholesterol. These findings suggest that hypercholesterolemia influences vasomotor tone of the nonstenosed coronary arteries in patients with coronary artery disease probably through the occurrence of endothelial dysfunction.