Efficacy and safety of atrasentan in patients with cardiovascular risk and early atherosclerosis

Targeting the endothelium by combining endothelin-1 antagonism and SGLT-2 inhibition: better together?

Endothelin A and B receptors, together with sodium-glucose cotransporter-2 (SGLT-2) channels are important targets in improving endothelial function and intervention with inhibitors has been the subject of multiple mechanistic and clinical outcome trials over recent years. Notable successes include the treatment of pulmonary hypertension with endothelin receptor antagonists, and the treatment of heart failure and chronic kidney disease with SGLT-2 inhibitors. With distinct and complementary mechanisms, in this review, we explore the logic of combination therapy for a number of diseases which have endothelial dysfunction at their heart.

Blood Pressure Control in Patients with Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the most common cause of end-stage kidney disease. Blood pressure (BP) control can reduce the risks of cardiovascular (CV) morbidity, mortality, and kidney disease progression. Recently, the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines have suggested the implementation of a more intensive BP control with a target systolic BP (SBP) of <120 mmHg based on the evidence that the CV benefits obtained is outweighed by the kidney injury risk associated with a lower BP target. However, an extremely low BP level may paradoxically aggravate renal function and CV outcomes. Herein, we aimed to review the existing literature regarding optimal BP control using medications for DKD.

Increased endothelin-1 levels in coronary artery disease with diabetes mellitus in an Indonesian population

Diabetes mellitus (DM) increases risk of coronary artery disease (CAD). Endothelin-1 (ET-1) is a potential biomarker of endothelial dysfunction. This study aimed to evaluate ET-1 level in CAD patients and its relationship with DM. The cross-sectional design included subjects with angiographically proven CAD and controls among Indonesian. DM was defined by medical history and anti-diabetics use. Serum ET-1 level was measured in both subject groups. We recruited 305 subjects, 183 CAD patients and 122 controls. CAD subjects had higher percentage of males, DM, hypertension, dyslipidemia, smoking, family history of cardiovascular disease, and obesity. ET-1 level was significantly higher in CAD than in controls (2.44 ± 1.49 pg/mL vs. 1.76 ± 0.83 pg/mL; p < 0.001). Increased ET-1 level was significantly associated with DM and dyslipidemia. The highest ET-1 level was observed in CAD with DM, followed by CAD non-DM (2.79 ± 1.63 pg/mL vs. 2.29 ± 1.40 pg/mL; p = 0.023). Among controls, ET-1 level was the lowest in non-DM subjects. Female CAD had higher proportion of DM; however, ET-1 level was similar to male CAD with DM. In conclusion, an increased ET-1 level was significantly associated with DM in patients with CAD. Further research should investigate the potential role of ET-1 receptor antagonists in the secondary prevention of CAD with DM.

Modulation by antenatal therapies of cardiovascular and renal programming in male and female offspring of preeclamptic rats

Morbidity and mortality risks are enhanced in preeclamptic (PE) mothers and their offspring. Here, we asked if sexual dimorphism exists in (i) cardiovascular and renal damage evolved in offspring of PE mothers, and (ii) offspring responsiveness to antenatal therapies. PE was induced by administering N^G-nitro-L-arginine methyl ester (L-NAME, 50 mg/kg/day, oral gavage) to pregnant rats for 7 days starting from gestational day 14. Three therapies were co-administered orally with L-NAME, atrasentan (endothelin ETA receptor antagonist), terutroban (thromboxane A2 receptor antagonist, TXA2), or α-methyldopa (α-MD, central sympatholytic drug). Cardiovascular and renal profiles were assessed in 3-month-old offspring. Compared with offspring of non-PE rats, PE offspring exhibited elevated systolic blood pressure and proteinuria and reduced heart rate and creatinine clearance (CrCl). Apart from a greater bradycardia in male offspring, similar PE effects were noted in male and female offspring. While terutroban, atrasentan, or α-MD partially and similarly blunted the PE-evoked changes in CrCl and proteinuria, terutroban was the only drug that virtually abolished PE hypertension. Rises in cardiorenal inflammatory (tumor necrosis factor alpha, TNFα) and oxidative (isoprostane) markers were mostly and equally eliminated by all therapies in the two sexes, except for a greater dampening action of atrasentan, compared with α-MD, on tissue TNFα in female offspring only. Histopathologically, antenatal terutroban or atrasentan was more effective than α-MD in rectifying cardiac structural damage, myofiber separation, and cytoplasmic alterations, in PE offspring. The repair by antenatal terutroban or atrasentan of cardiovascular and renal anomalies in PE offspring is mostly sex-independent and surpasses the protection offered by α-MD, the conventional PE therapy.

Blood pressure control in patients with chronic kidney disease

Uncontrolled blood pressure (BP) in patients with chronic kidney disease (CKD) can lead to serious adverse outcomes. To prevent the occurrence of cardiovascular events (CVEs), and end-stage kidney disease, achieving an optimal BP level is important. Recently, there has been a paradigm shift in the management of BP largely as a result of the Systolic Blood Pressure Intervention Trial (SPRINT), which showed a reduction in CVEs by lowering systolic BP to 120 mmHg. A lower systolic blood pressure (SBP) target has been accepted by the Kidney Disease: Improving Global Outcomes (KDIGO) 2021 guidelines. However, whether intensive control of SBP targeting < 120 mmHg is also effective in patients with CKD is controversial. Notably, this lower target SBP is associated with a higher risk of adverse kidney outcomes. Unfortunately, there have been no randomized controlled trials on this issue involving only patients with CKD, particularly those with advanced CKD. In this review, we discuss the optimal control of BP in patients with CKD in terms of reduction in death and CVEs as well as attenuation of CKD progression based on the evidence-based literature.

Endothelin: 30 Years From Discovery to Therapy

Discovered in 1987 as a potent endothelial cell-derived vasoconstrictor peptide, endothelin-1 (ET-1), the predominant member of the endothelin peptide family, is now recognized as a multifunctional peptide with cytokine-like activity contributing to almost all aspects of physiology and cell function. More than 30 000 scientific articles on endothelin were published over the past 3 decades, leading to the development and subsequent regulatory approval of a new class of therapeutics-the endothelin receptor antagonists (ERAs). This article reviews the history of the discovery of endothelin and its role in genetics, physiology, and disease. Here, we summarize the main clinical trials using ERAs and discuss the role of endothelin in cardiovascular diseases such as arterial hypertension, preecclampsia, coronary atherosclerosis, myocardial infarction in the absence of obstructive coronary artery disease (MINOCA) caused by spontaneous coronary artery dissection (SCAD), Takotsubo syndrome, and heart failure. We also discuss how endothelins contributes to diabetic kidney disease and focal segmental glomerulosclerosis, pulmonary arterial hypertension, as well as cancer, immune disorders, and allograft rejection (which all involve ET_A autoantibodies), and neurological diseases. The application of ERAs, dual endothelin receptor/angiotensin receptor antagonists (DARAs), selective ET_B agonists, novel biologics such as receptor-targeting antibodies, or immunization against ET_A receptors holds the potential to slow the progression or even reverse chronic noncommunicable diseases. Future clinical studies will show whether targeting endothelin receptors can prevent or reduce disability from disease and improve clinical outcome, quality of life, and survival in patients.

Endothelin Receptor Antagonism Improves Lipid Profiles and Lowers PCSK9 (Proprotein Convertase Subtilisin/Kexin Type 9) in Patients With Chronic Kidney Disease

Dyslipidemia is common in chronic kidney disease (CKD). Despite statins, many patients fail to adequately lower lipids and remain at increased risk of cardiovascular disease. Selective ET_A (endothelin-A) receptor antagonists reduce cardiovascular disease risk factors. Preclinical data suggest that ET_A antagonism has beneficial effects on circulating lipids. We assessed the effects of selective ET_A antagonism on circulating lipids and PCSK9 (proprotein convertase subtilisin/kexin type 9) in CKD. This was a secondary analysis of a fully randomized, double-blind, 3-phase crossover study. Twenty-seven subjects with predialysis CKD on optimal cardio- and renoprotective treatment were randomly assigned to receive 6 weeks dosing with placebo, the selective ET_A receptor antagonist, sitaxentan, or long-acting nifedipine. We measured circulating lipids and PCSK9 at baseline and then after 3 and 6 weeks. Baseline lipids and PCSK9 did not differ before each study phase. Whereas placebo and nifedipine had no effect on lipids, 6 weeks of ET_A antagonism significantly reduced total (-11±1%) and low-density lipoprotein-associated (-20±3%) cholesterol, lipoprotein (a) (-16±2%) and triglycerides (-20±4%); high-density lipoprotein-associated cholesterol increased (+14±2%), P<0.05 versus baseline for all. Additionally, ET_A receptor antagonism, but neither placebo nor nifedipine, reduced circulating PCSK9 (-19±2%; P<0.001 versus baseline; P<0.05 versus nifedipine and placebo). These effects were independent of statin use and changes in blood pressure or proteinuria. Selective ET_A antagonism improves lipid profiles in optimally-managed patients with CKD, effects that may occur through a reduction in circulating PCSK9. ET_A receptor antagonism offers a potentially novel strategy to reduce cardiovascular disease risk in CKD. Clinical Trial Registration- URL: http://www.clinicaltrials.gov . Unique identifier: NCT00810732.

Coronary endothelial function testing may improve long-term quality of life in subjects with microvascular coronary endothelial dysfunction

Aim

Angina pectoris in the absence of obstructive coronary artery disease (CAD) is common and is associated with poor quality of life (QOL). Coronary microvascular endothelial dysfunction is associated with myocardial ischaemia and is a common cause of angina. We hypothesise that evaluation of coronary endothelial function, its diagnosis and treatment will favourably impact QOL in patients with angina symptoms and non-obstructive CAD.

Methods and results

Follow-up was done on 457 patients with chest pain and non-obstructive coronary arteries who had undergone coronary vascular reactivity evaluation by administration of intracoronary acetylcholine at the time of diagnostic study. After a mean follow-up of 8.4±4.7 years, QOL was assessed by administration of the SF-36 QOL survey. Patients diagnosed and treated for microvascular endothelial dysfunction had a higher (better) overall mental composite score (44.8 vs 40.9, p=0.036) and mental health score (44.2 vs 40.7, p=0.047), and a trend towards higher vitality scores (39.1 vs 35.9, p=0.053) and role emotional scores (43.6 vs 40.4, p=0.073), compared with patients with normal endothelial function.

Conclusion

Among patients with chest pain and normal coronaries, diagnosis and treatment of coronary microvascular endothelial dysfunction in those with angina pectoris and non-obstructive CAD are associated with better QOL compared with patients with normal endothelial function.

Novel therapies for diabetic kidney disease

Over the past 30 years there have been many complementary therapies developed to achieve glycemic control and have an impact on cardiovascular outcomes, as well as reduce the risk of microvascular disease. The 2 most notable new entries have been the sodium-glucose cotransporter 2 (SGLT2) inhibitors and the glucagon-like peptide-1 (GLP-1) agonists. Both these classes of agents have demonstrated reductions in cardiovascular event rates as well as reductions in blood pressure and weight. Moreover, while both have demonstrated a benefit in slowing nephropathy progression, the SGLT2 inhibitors appear to have a significantly greater effect compared with the GLP-1 agents. There is an ongoing trial specifically powered for renal disease progression, CREDENCE (Evaluation of the Effects of Canagliflozin on Renal and Cardiovascular Outcomes in Participants With Diabetic Nephropathy). Additionally, there are 2 other classes of agents being tested to slow nephropathy progression, a selective endothelin-1 receptor antagonist, atrasantan, in the SONAR (Study of Diabetic Nephropathy With Atrasentan) trial and a nonsteroidal mineralocorticoid receptor antagonist, finerenone, in the FIDELIO (Efficacy and Safety of Finerenone in Subjects With Type 2 Diabetes Mellitus) trial. These and other studies are discussed.

Peri-interventional endothelin-A receptor blockade improves long-term outcome in patients with ST-elevation acute myocardial infarction

Endothelin (ET)-1 is a pro-fibrotic vasoconstrictive peptide causing microvascular dysfunction and cardiac remodelling after acute ST-elevation myocardial infarction (STEMI). It acts via two distinct receptors, ET-A and ET-B, and is involved in inflammation and atherogenesis. Patients with posterior-wall STEMI were randomly assigned to intravenous BQ-123 at 400 nmol/minute (min) or placebo over 60 min, starting immediately prior to primary percutaneous coronary intervention (n=54). Peripheral blood samples were drawn at baseline as well as after 24 hours and 30 days. Myeloperoxidase (MPO), as a marker of neutrophil activation and matrix metalloproteinase 9 (MMP-9), a marker of extracellular matrix degradation were measured in plasma. Clinical follow-up was conducted by an investigator blinded to treatment allocation over three years. During the median follow-up period of 3.6 years (interquartile range [IQR] 3.3–4.1) we observed a longer event-free survival in patients randomised to receive BQ-123 compared with patients randomised to placebo (mean 4.5 years (95% confidence interval: 3.9–5) versus mean 3 years (2.2–3.7), p=0.031). Patients randomised to ET-A receptor blockade demonstrated a greater reduction of MPO levels from baseline to 24 hours compared to placebo-treated patients (-177 ng/ml (IQR 103–274) vs –108 ng/ml (74–147), p=0.006). In addition, a pronounced drop in MMP-9 levels (-568 ng/ml (44–1157) vs –117 ng/ml (57–561), p=0.018) was observed. There was no significant difference in amino-terminal propetide of pro-collagen type III levels. In conclusion, short-term administration of BQ-123 leads to a reduction in MPO, as well as MMP-9 plasma levels and to a longer event-free survival in patients with STEMI.

ClinicalTrials.gov Identifier: NCT00502528

Association of oral endothelin receptor antagonists with risks of cardiovascular events and mortality: meta-analysis of randomized controlled trials

BACKGROUND

Endothelin receptor antagonists (ERAs) are widely used in a variety of disorders, including pulmonary artery hypertension, systemic sclerosis, diabetic and kidney diseases, and several tumors. However, reported adverse events, especially increased risks of cardiovascular disease (CVD) morbidity and mortality, have cast doubt on their potential clinical application. Therefore, we conducted this meta-analysis to confirm whether ERAs increased CVD risk and mortality.

METHODS

We systematically searched PubMed (1966-2015), EMBASE (1974-2015), ClinicalTrials.gov, and the Cochrane Controlled Clinical Trials Register Database for randomized controlled trials published between Jan 1, 1990 and Mar 18, 2015. Inclusion criteria included a study duration of more than 3 weeks, the use of a randomized control group receiving an oral ERA or placebo, and the availability of outcome data for cardiovascular events and all-cause death.

RESULTS

A total of 33 trials met the inclusion criteria. There were 8098 cases in the ERA group and 5074 cases in the placebo group. Compared with the control group, the risk ratio (RR) for all-cause death in the ERA group was 0.983 [95% confidence interval (CI), 0.883 to 1.094, P = 0.754]. The summary RR for cardiovascular events was 1.651 in the ERA group (95% CI, 1.164 to 2.34, P = 0.005). The pooled results showed that ERAs treatment could lead to more edema, anemia, and abnormal transaminase levels. Also, there was an increased proportion of discontinued therapy in the ERA treatment because of side effects (RR = 1.322, 95% CI, 1.036 to 1.686, P = 0.025). There were no significant differences in the experienced episodes of headache and dyspnea between the active therapy and control groups.

CONCLUSIONS

ERAs therapy is not significantly associated with increased all-cause death, but there are more cardiovascular events and edema or fluid retention, anemia, and liver enzymes disorder. Large clinical randomized controlled studies are needed to further confirm the safety of the clinical application of ERAs.

Microvascular endothelial dysfunction predicts the development of erectile dysfunction in men with coronary atherosclerosis without critical stenoses

BACKGROUND

Erectile dysfunction (ED) is associated with an increased risk for cardiovascular disease, stroke, and all-cause mortality, independent of conventional cardiovascular risk factors. Coronary endothelial dysfunction is independently associated with ED in men with early coronary atherosclerosis. We aimed to investigate whether coronary microvascular dysfunction predicts development of ED in patients presenting with coronary atherosclerosis without critical stenoses.

PATIENTS AND METHODS

Coronary microvascular function was evaluated in 130 men with coronary atherosclerosis without critical stenoses by administration of intracoronary acetylcholine at the time of diagnostic study. After a mean follow-up of 8.4 years, patients were assessed for the development of ED by administration of a questionnaire.

RESULTS

In all, 68 (50%) men had microvascular endothelial dysfunction at baseline; 35 (51%) men with microvascular endothelial dysfunction developed ED on follow-up compared with 19 (31%) men without microvascular endothelial dysfunction. Men who developed ED had a lower coronary blood flow response (% [INCREMENT]CBF) compared with men who did not develop ED, with mean±SD of 25.4±71.3 versus 81.7±120 (P=0.003). In univariate analysis, microvascular endothelial dysfunction was a predictor for the development of ED, with relative risk of 2.4 (1.2-4.9) (P=0.016). In multivariate logistic regression adjusting for traditional cardiovascular risk factors (age, hypertension, hyperlipidemia, diabetes, vascular disease, and family history of coronary artery disease), only microvascular endothelial dysfunction (P=0.027) and age (P=0.044) remained significant predictors of development of ED.

CONCLUSION

Coronary microvascular dysfunction is a predictor of the development of ED in men with coronary atherosclerosis without critical stenoses. This study underscores the systemic involvement of the endothelial function in vascular disease.

Endothelin A receptor antagonist, atrasentan, attenuates renal and cardiac dysfunction in Dahl salt-hypertensive rats in a blood pressure independent manner

Proteinuria is a hallmark of chronic kidney disease (CKD) and cardiovascular disease (CVD), and a good predictor of clinical outcome. Selective endothelin A (ET_A) receptor antagonist used with renin-angiotensin system (RAS) inhibitors prevents development of proteinuria in CKD. However, whether the improvement in proteinuria would have beneficial effects on CVD, independent of RAS inhibition, is not well understood. In this study, we investigated whether atrasentan, an ET_A receptor antagonist, has renal and cardiovascular effects independent of RAS inhibition. Male Dahl salt sensitive (DSS) rats, at six weeks of age, received water with or without different doses of atrasentan and/or enalapril under high salt (HS) diet or normal diet (ND) for 6 weeks. At the end of 12th week, atrasentan at a moderate dose significantly attenuated proteinuria and serum creatinine without reducing mean arterial pressure (MAP), thereby preventing cardiac hypertrophy and improving cardiac function. ACE inhibitor enalapril at a dose that did not significantly lowered BP, attenuated cardiac hypertrophy while moderately improving cardiac function without reducing proteinuria and serum creatinine level. Nonetheless, combined therapy of atrasentan and enalapril that does not altering BP exerted additional cardioprotective effect. Based on these findings, we conclude that BP independent monotherapy of ET_A receptor antagonist attenuates the progression of CKD and significantly mitigates CVD independent of RAS inhibition.

Endothelin ETA receptor antagonism in cardiovascular disease

Since the discovery of the endothelin system in 1988, it has been implicated in numerous physiological and pathological phenomena. In the cardiovascular system, endothelin-1 (ET-1) acts through intracellular pathways of two endothelin receptors (ETA and ETB) located mainly on smooth muscle and endothelial cells to regulate vascular tone and provoke mitogenic and proinflammatory reactions. The endothelin ETA receptor is believed to play a pivotal role in the pathogenesis of several cardiovascular disease including systemic hypertension, pulmonary arterial hypertension (PAH), dilated cardiomyopathy, and diabetic microvascular dysfunction. Growing evidence from recent experimental and clinical studies indicates that the blockade of endothelin receptors, particularly the ETA subtype, grasps promise in the treatment of major cardiovascular pathologies. The simultaneous blockade of endothelin ETB receptors might not be advantageous, leading possibly to vasoconstriction and salt and water retentions. This review summarizes the role of ET-1 in cardiovascular modulation and the therapeutic potential of endothelin receptor antagonism.

Random forest fishing: a novel approach to identifying organic group of risk factors in genome-wide association studies

Genome-wide association studies (GWAS) has brought methodological challenges in handling massive high-dimensional data and also real opportunities for studying the joint effect of many risk factors acting in concert as an organic group. The random forest (RF) methodology is recognized by many for its potential in examining interaction effects in large data sets. However, RF is not designed to directly handle GWAS data, which typically have hundreds of thousands of single-nucleotide polymorphisms as predictor variables. We propose and evaluate a novel extension of RF, called random forest fishing (RFF), for GWAS analysis. RFF repeatedly updates a relatively small set of predictors obtained by RF tests to find globally important groups predictive of the disease phenotype, using a novel search algorithm based on genetic programming and simulated annealing. A key improvement of RFF results from the use of guidance incorporating empirical test results of genome-wide pairwise interactions. Evaluated using simulated and real GWAS data sets, RFF is shown to be effective in identifying important predictors, particularly when both marginal effects and interactions exist, and is applicable to very large GWAS data sets.

Endothelin antagonists in hypertension and kidney disease

The endothelin (ET) system seems to play a pivotal role in hypertension and in proteinuric kidney disease, including the micro- and macro-vascular complications of diabetes. Endothelin-1 (ET-1) is a multifunctional peptide that primarily acts as a potent vasoconstrictor with direct effects on systemic vasculature and the kidney. ET-1 and ET receptors are expressed in the vascular smooth muscle cells, endothelial cells, fibroblasts and macrophages in systemic vasculature and arterioles of the kidney, and are associated with collagen accumulation, inflammation, extracellular matrix remodeling, and renal fibrosis. Experimental evidence and recent clinical studies suggest that endothelin receptor blockade, in particular selective ETAR blockade, holds promise in the treatment of hypertension, proteinuria, and diabetes. Concomitant blockade of the ETB receptor is not usually beneficial and may lead to vasoconstriction and salt and water retention. The side-effect profile of ET receptor antagonists and relatively poor antagonist selectivity for ETA receptor are limitations that need to be addressed. This review will discuss what is currently known about the endothelin system, the role of ET-1 in the pathogenesis of hypertension and kidney disease, and summarize literature on the therapeutic potential of endothelin system antagonism.

Long-term endothelin receptor antagonism attenuates coronary plaque progression in patients with early atherosclerosis

AIM

The purpose of the current study was to determine if long term treatment with an endothelin-A (ETA) receptor antagonist attenuates the progression of coronary plaques in patients with coronary endothelial dysfunction.

METHODS

Thirty-five patients with non-obstructive coronary disease and coronary endothelial dysfunction were randomized in a double blind manner to treatment with placebo or ETA receptor antagonist Atrasentan (10 mg) for six months. Endothelial function was assessed by the change in coronary blood flow and coronary artery diameter in response to intracoronary acetylcholine. Normalized mean total atheroma volume (TAVMEAN), percent atheroma volume (PAV) and changes of atheroma volume were assessed by intravascular ultrasound (IVUS) at baseline and 6-month follow-up.

RESULTS

In segments with coronary endothelial dysfunction, there was a significant decrease in normalized TAVMEAN and PAV at six months from baseline in the Atrasentan group compared to the placebo group median (IQR) -2.00 mm(3) (-7.28, 2.53.) vs 9.11 mm(3) (1.23, 14.05), p=0.0024 and 0.955% (-3.43, 1.70) vs 3.85% (-0.39, 14.59) p=0.010. There was no change in normalized TAV or PAV in the segments with normal endothelial function.

CONCLUSION

This study demonstrates that 6-month treatment with Atrasentan attenuates progression of coronary plaque in segments with endothelial dysfunction.

Endothelin-A receptor antagonism modifies cardiovascular risk factors in CKD

Arterial stiffness and impaired nitric oxide (NO) bioavailability contribute to the high risk for cardiovascular disease in CKD. Both asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO production, and endothelin-1 (ET-1) oppose the actions of NO, suggesting that ET-1 receptor antagonists may have a role in cardiovascular protection in CKD. We conducted a randomized, double-blind, three-way crossover study in 27 patients with proteinuric CKD to compare the effects of the ET(A) receptor antagonist sitaxentan, nifedipine, and placebo on proteinuria, BP, arterial stiffness, and various cardiovascular biomarkers. After 6 weeks of treatment, placebo and nifedipine did not affect plasma urate, ADMA, or urine ET-1/creatinine, which reflects renal ET-1 production; in contrast, sitaxentan led to statistically significant reductions in all three of these biomarkers. No treatment affected plasma ET-1. Reductions in proteinuria and BP after sitaxentan treatment was associated with increases in urine ET-1/creatinine, whereas reduction in pulse-wave velocity, a measure of arterial stiffness, was associated with a decrease in ADMA. Taken together, these data suggest that ET(A) receptor antagonism may modify risk factors for cardiovascular disease in CKD.

Clinical trials with endothelin receptor antagonists: what went wrong and where can we improve?

In the early 1990s, within three years of cloning of endothelin receptors, orally active endothelin receptor antagonists (ERAs) were tested in humans and the first clinical trial of ERA therapy in humans was published in 1995. ERAs were subsequently tested in clinical trials involving heart failure, pulmonary arterial hypertension, resistant arterial hypertension, stroke/subarachnoid hemorrhage and various forms of cancer. The results of most of these trials - except those for pulmonary arterial hypertension and scleroderma-related digital ulcers - were either negative or neutral. Problems with study design, patient selection, drug toxicity, and drug dosing have been used to explain or excuse failures. Currently, a number of pharmaceutical companies who had developed ERAs as drug candidates have discontinued clinical trials or further drug development. Given the problems with using ERAs in clinical medicine, at the Twelfth International Conference on Endothelin in Cambridge, UK, a panel discussion was held by clinicians actively involved in clinical development of ERA therapy in renal disease, systemic and pulmonary arterial hypertension, heart failure, and cancer. This article provides summaries from the panel discussion as well as personal perspectives of the panelists on how to proceed with further clinical testing of ERAs and guidance for researchers and decision makers in clinical drug development on where future research efforts might best be focused.

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.

Addition of atrasentan to renin-angiotensin system blockade reduces albuminuria in diabetic nephropathy

Although endothelin-receptor antagonists reduce albuminuria in diabetic nephropathy, fluid retention limits their use. Here, we examined the effect of atrasentan, a selective endothelin A receptor (ET(A)R) antagonist, on albuminuria in a randomized, double-blind, placebo-controlled trial of subjects with diabetic nephropathy already receiving stable doses of renin-angiotensin system (RAS) inhibitors. We randomly assigned 89 subjects with eGFR >20 ml/min per 1.73 m(2) and a urinary albumin-to-creatinine ratio (UACR) of 100 to 3000 mg/g to placebo or atrasentan (0.25, 0.75, or 1.75 mg daily) for 8 weeks. Compared with placebo, atrasentan significantly reduced UACR only in the 0.75- and 1.75-mg groups (P=0.001 and P=0.011, respectively). Compared with the 11% reduction in the geometric mean of the UACR from baseline to final observation in the placebo group during the study, the geometric mean of UACR decreased by 21, 42, and 35% in the 0.25-, 0.75-, and 1.75-mg atrasentan groups (P=0.291, P=0.023, and P=0.073, respectively). In the placebo group, 17% of subjects achieved ≥40% reduction in UACR from baseline compared with 30, 50, and 38% in the 0.25-, 0.75-, and 1.75-mg atrasentan groups, respectively (P=0.029 for 0.75 mg versus placebo). Peripheral edema occurred in 9% of subjects receiving placebo and in 14, 18, and 46% of those receiving 0.25, 0.5, and 1.75 mg atrasentan, respectively (P=0.007 for 1.75 mg versus placebo). In summary, atrasentan, at the doses tested, is generally safe and effective in reducing residual albuminuria and may ultimately improve renal outcomes in patients with type 2 diabetic nephropathy.

Resistant hypertension workup and approach to treatment

Resistant hypertension is defined as blood pressure above the patient's goal despite the use of 3 or more antihypertensive agents from different classes at optimal doses, one of which should ideally be a diuretic. Evaluation of patients with resistive hypertension should first confirm that they have true resistant hypertension by ruling out or correcting factors associated with pseudoresistance such as white coat hypertension, suboptimal blood pressure measurement technique, poor adherence to prescribed medication, suboptimal dosing of antihypertensive agents or inappropriate combinations, the white coat effect, and clinical inertia. Management includes lifestyle and dietary modification, elimination of medications contributing to resistance, and evaluation of potential secondary causes of hypertension. Pharmacological treatment should be tailored to the patient's profile and focus on the causative pathway of resistance. Patients with uncontrolled hypertension despite receiving an optimal therapy are candidates for newer interventional therapies such as carotid baroreceptor stimulation and renal denervation.

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.

Endothelial cell-derived endothelin-1 promotes cardiac fibrosis in diabetic hearts through stimulation of endothelial-to-mesenchymal transition

BACKGROUND

Persistently high plasma endothelin-1 (ET-1) levels in diabetic patients have been associated with the development of cardiac fibrosis, which results from the deposition of extracellular matrix and fibroblast recruitment from an as-yet unknown source. The underlying mechanism, however, remains elusive. Here, we hypothesize that ET-1 might contribute to the accumulation of cardiac fibroblasts through an endothelial-to-mesenchymal transition in diabetic hearts.

METHODS AND RESULTS

We induced diabetes mellitus in vascular endothelial cell-specific ET-1 knockout [ET-1(f/f);Tie2-Cre (+)] mice and their wild-type littermates using the toxin streptozotocin. Gene expression and histological and functional parameters were examined at 8, 24, and 36 weeks after the induction of diabetes mellitus. Diabetes mellitus increased cardiac ET-1 expression in wild-type mice, leading to mitochondrial disruption and myofibril disarray through the generation of superoxide. Diabetic mice also showed impairment of cardiac microvascularization and a decrease in cardiac vascular endothelial growth factor expression. ET-1 further promotes cardiac fibrosis and heart failure through the accumulation of fibroblasts via endothelial-to-mesenchymal transition. All of these features were abolished in ET-1(f/f);Tie2-Cre (+) hearts. Targeted ET-1 gene silencing by small interfering RNA in cultured human endothelial cells ameliorated high glucose-induced phenotypic transition and acquisition of a fibroblast marker through the inhibition of transforming growth factor-beta signaling activation and preservation of the endothelial cell-to-cell contact regulator VE-cadherin.

CONCLUSIONS

These results provide new insights suggesting that diabetes mellitus-induced cardiac fibrosis is associated with the emergence of fibroblasts from endothelial cells and that this endothelial-to-mesenchymal transition process is stimulated by ET-1. Targeting endothelial cell-derived ET-1 might be beneficial in the prevention of diabetic cardiomyopathy.

Endothelin, hypertension and chronic kidney disease: new insights

PURPOSE OF REVIEW

Endothelin is important in the development of cardiorenal disease. This review discusses recent developments in understanding endothelin's role in hypertension and chronic kidney disease (CKD).

RECENT FINDINGS

Endothelin-1 production is increased in hypertension and CKD. Endothelin-1 stimulates vasoconstriction, inflammation and fibrosis, thereby promoting hypertension, atherosclerosis and CKD. These effects are closely linked to angiotensin II and reactive oxygen species. In preclinical studies, endothelin receptor antagonists were effective in treating hypertension (particularly with endothelial dysfunction) and CKD. In preclinical studies, endothelin A-selective, as opposed to combined endothelin A and B, receptor blockers have generally been more efficacious. Few clinical trials have been conducted in hypertension and/or kidney disease, partly due to concerns over side effects of testicular toxicity and fluid retention. Endothelin blockade reduces blood pressure in patients with resistant hypertension, with additional beneficial metabolic effects. Endothelin antagonism improves proteinuria in CKD (diabetic or not), particularly in patients taking inhibitors of angiotensin II action.

SUMMARY

Endothelin is a promising target in the treatment of resistant hypertension and CKD, with additional potential benefits on atherosclerosis and the metabolic syndrome. The nature and mechanisms of drug side effects require elucidation before the potential of this new class of drugs can be fully realized.

Endothelin receptor antagonists as antihypertensives: the next frontier

The endothelin system is a pivotal player along the continuum of cardiovascular disease. There is convincing evidence that the system not only exerts a potent pressor effect but also promotes end-organ damage independent from blood pressure changes. The role of endothelin receptor antagonists (ERAs) in the treatment of hypertension is rapidly evolving. Recent studies demonstrate a formidable antihypertensive effect. Utility of ERAs is likely to be greatest in patients with resistant hypertension. Beyond blood pressure lowering, ERAs exert several properties that may confer additional protection, including effects on endothelial function, atherosclerosis, arterial stiffening, renal function and proteinuria. The full potential of this class will only be realized when the results of ongoing and future studies in hypertension, heart failure and other forms of cardiovascular disease are completed.