Regulation of plasma endothelin by salt in salt-sensitive hypertension

Endothelin System in Hypertension and Chronic Kidney Disease

ET (endothelin) is a powerful vasoconstrictor 21-amino acid peptide present in many tissues, which exerts many physiological functions across the body and participates as a mediator in many pathological conditions. ETs exert their effects through ETA and ETB receptors, which can be blocked by selective receptor antagonists. ETs were shown to play important roles among others, in systemic hypertension, particularly when resistant or difficult to control, and in pulmonary hypertension, atherosclerosis, cardiac hypertrophy, subarachnoid hemorrhage, chronic kidney disease, diabetic cardiovascular disease, scleroderma, some cancers, etc. To date, ET antagonists are only approved for the treatment of primary pulmonary hypertension and recently for IgA nephropathy and used in the treatment of digital ulcers in scleroderma. However, they may soon be approved for the treatment of patients with resistant hypertension and different types of nephropathy. Here, the role of ETs is reviewed with a special emphasis on participation in and treatment of hypertension and chronic kidney disease.

Dietary Salt Restriction and Adherence to the Mediterranean Diet: A Single Way to Reduce Cardiovascular Risk?

The dietary restriction of salt intake and the adhesion to Mediterranean dietary patterns are among the most recommended lifestyle modifications for the prevention of cardiovascular diseases. A large amount of evidence supports these recommendations; indeed, several studies show that a higher adherence to Mediterranean dietary patterns is associated with a reduced risk of cardiovascular disease. Likewise, findings from observational and clinical studies suggest a causal role of excess salt intake in blood pressure increase, cardiovascular organ damage, and the incidence of cardiovascular diseases. In this context, it is also conceivable that the beneficial effects of these two dietary patterns overlap because Mediterranean dietary patterns are typically characterized by a large consumption of plant-based foods with low sodium content. However, there is little data on this issue, and heterogeneous results are available on the relationship between adherence to salt restriction and to Mediterranean dietary patterns. Thus, this short review focuses on the epidemiological and clinical evidence of the relationship between the adherence to Mediterranean dietary patterns and dietary salt restriction in the context of cardiovascular risk.

Isolated systolic hypertension of the young and sodium intake

Isolated systolic hypertension is associated with higher risk of cardiovascular disease and all-cause mortality. Despite being the most common form of hypertension in the elderly, it is also detectable among young and middle-aged subjects. Dietary salt (sodium chloride) intake is an important determinant of blood pressure, and high salt intake is associated with greater risk of hypertension and cardiovascular events. In most countries, habitual salt intake at all age categories largely exceeds the international recommendations. Excess salt intake, often interacting with overweight and insulin resistance, may contribute to the development and maintenance of isolated systolic hypertension in young individuals by causing endothelial dysfunction and promoting arterial stiffness through a number of mechanisms, namely increase in the renin-angiotensin-aldosterone system activity, sympathetic tone and salt-sensitivity. This short review focused on the epidemiological and clinical evidence, the mechanistic pathways and the cluster of pathophysiological factors whereby excess salt intake may favor the development and maintenance of isolated systolic hypertension in young people.

Aprocitentan and the endothelin system in resistant hypertension

Endothelin has emerged as a target for therapeutic intervention in systemic hypertension. As a vasoconstrictor, co-mitogenic agent, linking pulse pressure and vascular remodeling, and mediator of aldosterone and catecholamine release, endothelin is a key player in hypertension and end-organ damage. In 10-20% of the hypertensive population, the high blood pressure is resistant to administration of antihypertensive drugs of different classes in combination. Because endothelin is not targeted by the current antihypertensive drugs this may suggest that this resistance is due, in part at least, to a dependence on endothelin. This hypothesis is supported by the observation that this form of hypertension is often salt-sensitive, and that the endothelin system is stimulated by salt. In addition, the endothelin system is activated in subjects at risk of developing resistant hypertension, such as African-Americans or patients with obesity or obstructive sleep apnea. Aprocitentan is a novel, potent, dual endothelin receptor antagonist (ERA) currently in phase 3 development for the treatment of difficult-to-treat hypertension. This article discusses the research which underpinned the discovery of this ERA and the choice of its first clinical indication for patients with forms of hypertension which cannot be well controlled with classical antihypertensive drugs.

MicroRNA-210-5p alleviates cardiac fibrosis via targeting transforming growth factor-beta type I receptor in rats on high sodium chloride (NaCl)-based diet

The present study was designed to explore whether high sodium chloride (NaCl)-based diet (HSD) caused cardiac fibrosis regardless of blood pressure in Sprague-Dawley (SD) rats, and to further determine the effects and the underlying mechanisms of microRNA (miR)-210-5p on HSD-induced cardiac fibrosis in rats or NaCl-induced cardiac fibroblast activation in neonatal rat cardiac fibroblasts (NRCFs). The SD rats received 8% HSD, and NRCFs were treated with NaCl. The levels of collagen I, alpha-smooth muscle actin (α-SMA) and transforming growth factor-beta 1 (TGF-β1) were increased in the heart of hypertension (HTN), hypertension-prone (HP) and hypertension-resistant (HR) rats on HSD in vivo. NaCl increased the levels of collagen I, α-SMA and TGF-β1 in NRCFs in vitro. The level of miR-210-5p was reduced in both NBD-induced rats' hearts and NaCl-treated NRCFs, which was consistent with the results of miR high-throughput sequencing in NRCFs. The HSD or NaCl-induced increases of collagen I, α-SMA and TGF-β1 were inhibited by miR-210-5p agomiR in vitro and in vivo, respectively. miR-210-5p antagomiR could mimic the pathological effects of NaCl in NRCFS. Bioinformatics analysis and luciferase reporter assays demonstrated that TGF-β type I receptor (TGFBR1) was a direct target gene of miR-210-5p. These results indicated that HSD resulted in cardiac fibrosis regardless of blood pressure. The upregulation of miR-210-5p could attenuate cardiac fibroblast activation in NRCFS via targeting TGFBR1. Thus, upregulating miR-210-5p might be a strategy for the treatment of cardiac fibrosis.

Biochemical interaction of salt sensitivity: a key player for the development of essential hypertension

Worldwide, more than 1 billion people have elevated blood pressure, with up to 45% of adults affected by the disease. In 2016 the global health study report on patients from 67 countries was released in Lancet, which identified hypertension as the world's leading cause for death and disability-adjusted years since 1990. This paper aims to analyze the pathophysiological connection between hemodynamic inflammatory reactions through sodium balance, salt sensitivity, and potential pathophysiological reactions. Besides, we explore how sodium consumption enhances the expression of transient receptor potential channel 3 (TrpC3) mRNA and facilitates the release of calcium inside immune cell groups, together with elevated blood pressure in essential hypertensive patients.

Effects and Mechanisms of Tea Regulating Blood Pressure: Evidences and Promises

Cardiovascular diseases have overtaken cancers as the number one cause of death. Hypertension is the most dangerous factor linked to deaths caused by cardiovascular diseases. Many researchers have reported that tea has anti-hypertensive effects in animals and humans. The aim of this review is to update the information on the anti-hypertensive effects of tea in human interventions and animal studies, and to summarize the underlying mechanisms, based on ex-vivo tissue and cell culture data. During recent years, an increasing number of human population studies have confirmed the beneficial effects of tea on hypertension. However, the optimal dose has not yet been established owing to differences in the extent of hypertension, and complicated social and genetic backgrounds of populations. Therefore, further large-scale investigations with longer terms of observation and tighter controls are needed to define optimal doses in subjects with varying degrees of hypertensive risk factors, and to determine differences in beneficial effects amongst diverse populations. Moreover, data from laboratory studies have shown that tea and its secondary metabolites have important roles in relaxing smooth muscle contraction, enhancing endothelial nitric oxide synthase activity, reducing vascular inflammation, inhibiting rennin activity, and anti-vascular oxidative stress. However, the exact molecular mechanisms of these activities remain to be elucidated.

Tauroursodeoxycholic acid (TUDCA) abolishes chronic high salt-induced renal injury and inflammation

AIM

Chronic high salt intake exaggerates renal injury and inflammation, especially with the loss of functional ET_B receptors. Tauroursodeoxycholic acid (TUDCA) is a chemical chaperone and bile salt that is approved for the treatment of hepatic diseases. Our aim was to determine whether TUDCA is reno-protective in a model of ET_B receptor deficiency with chronic high salt-induced renal injury and inflammation.

METHODS

ET_B -deficient and transgenic control rats were placed on normal (0.8% NaCl) or high salt (8% NaCl) diet for 3 weeks, receiving TUDCA (400 mg/kg/d; ip) or vehicle. Histological and biochemical markers of kidney injury, renal cell death and renal inflammation were assessed.

RESULTS

In ET_B -deficient rats, high salt diet significantly increased glomerular and proximal tubular histological injury, proteinuria, albuminuria, excretion of tubular injury markers KIM-1 and NGAL, renal cortical cell death and renal CD4⁺ T cell numbers. TUDCA treatment increased proximal tubule megalin expression as well as prevented high salt diet-induced glomerular and tubular damage in ET_B -deficient rats, as indicated by reduced kidney injury markers, decreased glomerular permeability and proximal tubule brush border restoration, as well as reduced renal inflammation. However, TUDCA had no significant effect on blood pressure.

CONCLUSIONS

TUDCA protects against the development of glomerular and proximal tubular damage, decreases renal cell death and inflammation in the renal cortex in rats with ET_B receptor dysfunction on a chronic high salt diet. These results highlight the potential use of TUDCA as a preventive tool against chronic high salt induced renal damage.

Pharmacological Characterization of Aprocitentan, a Dual Endothelin Receptor Antagonist, Alone and in Combination with Blockers of the Renin Angiotensin System, in Two Models of Experimental Hypertension

The endothelin (ET) system has emerged as a novel target for hypertension treatment where a medical need persists despite availability of several pharmacological classes, including renin angiotensin system (RAS) blockers. ET receptor antagonism has demonstrated efficacy in preclinical models of hypertension, especially under low-renin conditions and in hypertensive patients. We investigated the pharmacology of aprocitentan (N-[5-(4-bromophenyl)-6-[2-[(5-bromo-2-pyrimidinyl)oxy]ethoxy]-4-pyrimidinyl]-sulfamide), a potent dual ETA/ETB receptor antagonist, on blood pressure (BP) in two models of experimental hypertension: deoxycorticosterone acetate (DOCA)-salt rats (low-renin model) and spontaneously hypertensive rats [(SHR), normal renin model]. We also compared the effect of its combination with RAS blockers (valsartan and enalapril) with that of the combination of the mineraloreceptor antagonist spironolactone with the same RAS blockers on BP and renal function in hypertensive rats. Aprocitentan was more potent and efficacious in lowering BP in conscious DOCA-salt rats than in SHRs. In DOCA-salt rats, single oral doses of aprocitentan induced a dose-dependent and long-lasting BP decrease and 4-week administration of aprocitentan dose dependently decreased BP (statistically significant) and renal vascular resistance, and reduced left ventricle hypertrophy (nonsignificant). Aprocitentan was synergistic with valsartan and enalapril in decreasing BP in DOCA-salt rats and SHRs while spironolactone demonstrated additive effects with these RAS blockers. In hypertensive rats under sodium restriction and enalapril, addition of aprocitentan further decreased BP without causing renal impairment, in contrast to spironolactone. In conclusion, ETA/ETB receptor antagonism represents a promising therapeutic approach to hypertension, especially with low-renin characteristics, and could be used in combination with RAS blockers, without increasing the risk of renal impairment.

Endothelin-1 levels and cardiovascular events

Circulating plasma levels of endothelin-1 and related peptides generated during the synthesis of endothelin-1 from its precursor molecule pre-proendothelin-1 have been widely studied as potential risk markers for cardiovascular events. The associations of endothelin-1 with aging, blood pressure, lung function, and chronic kidney disease have been described, as have relations between endothelin-1 levels and evidence of cardiac remodeling, including increased left atrial diameter and increased left ventricular mass. Endothelin-1 has been studied as a predictor of and prognostic marker in coronary artery disease, myocardial infarction, and heart failure. The relationship of endothelin-1 levels to mortality in the general population has also been explored. This review examines the current state of knowledge of circulating endothelin-1 levels as they relate to cardiovascular events and prognosis, and explores future directions for research, including using endothelin-1 or related peptide levels to guide personalized treatment regimens and to select patients for primary prevention strategies.

High salt-induced hypertension in B2 knockout mice is corrected by the ETA antagonist, A127722

BACKGROUND AND PURPOSE

The contribution of endothelin-1 (ET-1) in a B2KO mouse model of a high salt-induced arterial hypertension was investigated.

EXPERIMENTAL APPROACH

Wild-type (WT) or B2KO mice receiving a normal diet (ND) or a high-salt diet (HSD) were monitored by radiotelemetry up to a maximum of 18 weeks. At the 12th week of diet, subgroups under ND or HSD received by gavage the ETA antagonist A127722 during 5 days. In addition, blood samples were collected and, following euthanasia, the lungs, heart and kidneys were extracted, homogenized and assayed for ET-1 by RIA. In a separate series of experiments, the ETA antagonist, BQ123 was tested against the pressor responses to a NOS inhibitor L-N(G)-nitroarginine methyl ester (L-NAME) in anaesthetized WT and B2KO mice.

KEY RESULTS

In B2KO, but not WT mice, 12 weeks of HSD triggered a maximal increase of the mean arterial pressure (MAP) of 19.1 ± 2.8 mmHg, which was corrected by A127722 to MAP levels found in B2KO mice under ND. Significant increases in immunoreactive ET-1 were detected only in the lungs of B2KO mice under HSD. On the other hand, metabolic studies showed that sodium urinary excretion was markedly reduced in B2KO compared with WT mice under ND. Finally, BQ123 (2 mg·kg(-1)) reduced by 50% the pressor response to L-NAME (2 mg·kg(-1)) in B2KO, but not WT mice under anaesthesia.

CONCLUSIONS AND IMPLICATIONS

Our results support the concept that functional B2 receptors oppose high salt-induced increments in MAP, which are corrected by an ETA receptor antagonist in this mouse model of experimental hypertension.

Salt loading and potassium supplementation: effects on ambulatory arterial stiffness index and endothelin-1 levels in normotensive and mild hypertensive patients

The authors investigated effects of excessive salt intake and potassium supplementation on ambulatory arterial stiffness index (AASI) and endothelin-1 (ET-1) in salt-sensitive and non-salt-sensitive individuals. AASI and symmetric AASI (s-AASI) were used as indicators of arterial stiffness. Plasma ET-1 levels were used as an index of endothelial function. Chronic salt-loading and potassium supplementation were studied in 155 normotensive to mild hypertensive patients from rural northern China. After 3 days of baseline investigation, participants were maintained sequentially for 7 days each on diets of low salt (51.3 mmol/d), high salt (307.7 mmol/d), and high salt+potassium (60 mmol/d). Ambulatory 24-hour blood pressure (BP) and plasma ET-1 were measured at baseline and on the last 2 days of each intervention. High-salt intervention significantly increased BP, AASI, s-AASI (all P<.001); potassium supplementation reversed increased plasma ET-1 levels. High-salt-induced changes in BP, s-AASI, and plasma ET-1 were greater in salt-sensitive individuals. Potassium supplementation decreased systolic BP and ET-1 to a significantly greater extent in salt-sensitive vs non-salt-sensitive individuals (P<.001). Significant correlations were identified between s-AASI and ET-1 change ratios in response to both high-salt intervention and potassium supplementation (P<.001). Reducing dietary salt and increasing daily potassium improves arterial compliance and ameliorates endothelial dysfunction.

Effects of peroxisome proliferator-activated receptor-β activation in endothelin-dependent hypertension

AIMS

We analysed the chronic effects of the peroxisome proliferator-activated receptor β/δ (PPAR-β) agonist GW0742 on the renin-independent hypertension induced by deoxycorticosterone acetate (DOCA)-salt.

METHODS AND RESULTS

Rats were treated for 5 weeks with: control-vehicle, control-GW0742 (5 or 20 mg kg(-1) day(-1)), DOCA-vehicle, DOCA-GW0742 (5 or 20 mg kg(-1) day(-1)), DOCA-GSK0660 (1 mg kg(-1) day(-1)), and DOCA-GSK0660-GW0742. Rats receiving DOCA-vehicle showed increased systolic blood pressure, left ventricular and kidney weight indices, endothelin-1 (ET-1), and malondialdehyde plasma levels, urinary iso-PGF2α excretion, impaired endothelium-dependent relaxation to acetylcholine, and contraction to ET-1 when compared with controls. Aortic reactive oxygen species content, NADPH oxidase activity, and p47(phox), p22(phox), NOX-4, glutathione peroxidase 1, hemeoxygenase-1, and preproET-1 expression were increased, whereas catalase and regulators of G protein-coupled signalling proteins (RGS)5 expression were decreased in the DOCA-vehicle group. GW0742 prevented the development of hypertension in a dose-dependent manner but the reduction of renal and cardiac hypertrophy, systemic and vascular oxidative stress markers, and improvement of endothelial dysfunction were only observed after the higher dose. GW0742, at 20 mg kg(-1) day(-1), attenuated ET-1 contraction by increasing RGS5 expression and restored the intracellular redox balance by reducing NADPH-oxidase activity, and by increasing the antioxidant genes expression. The PPAR-β antagonist GSK0660 prevented all vascular changes induced by GW0742 but not its antihypertensive effects.

CONCLUSION

Vascular protective effects of GW0742 operate via PPAR-β by interference with the ET-1 signalling as a result of increased expression of RGS5 and up-regulation of antioxidant genes and via PPAR-β-independent mechanisms to decrease blood pressure.

Epicatechin lowers blood pressure, restores endothelial function, and decreases oxidative stress and endothelin-1 and NADPH oxidase activity in DOCA-salt hypertension

Flavanol-rich diets have been reported to exert beneficial effects in preventing cardiovascular diseases, such as hypertension. We studied the effects of chronic treatment with epicatechin on blood pressure, endothelial function, and oxidative status in deoxycorticosterone acetate (DOCA)-salt-induced hypertension. Rats were treated for 5 weeks with (-)-epicatechin at 2 or 10 mg kg(-1)day(-1). The high dose of epicatechin prevented both the increase in systolic blood pressure and the proteinuria induced by DOCA-salt. Plasma endothelin-1 and malondialdehyde levels and urinary iso-prostaglandin F(2α) excretion were increased in animals of the DOCA-salt group and reduced by the epicatechin 10 mg kg(-1) treatment. Aortic superoxide levels were enhanced in the DOCA-salt group and abolished by both doses of epicatechin. However, only epicatechin at 10 mg kg(-1) reduced the rise in aortic nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity and p47(phox) and p22(phox) gene overexpression found in DOCA-salt animals. Epicatechin increased the transcription of nuclear factor-E2-related factor-2 (Nrf2) and Nrf2 target genes in aortas from control rats. Epicatechin also improved the impaired endothelium-dependent relaxation response to acetylcholine and increased the phosphorylation of both Akt and eNOS in aortic rings. In conclusion, epicatechin prevents hypertension, proteinuria, and vascular dysfunction. Epicatechin also induced a reduction in ET-1 release, systemic and vascular oxidative stress, and inhibition of NADPH oxidase activity.

Inflammation and therapy for hypertension

It is currently accepted that hypertension, atherosclerosis, and diabetes are disorders with subtle or overt activation of inflammatory mediators. Therefore, it has become increasingly important to ascertain whether current antihypertensive drug families have proinflammatory or anti-inflammatory actions that modify the outcomes of their hemodynamic effects on blood pressure. We review the current state of knowledge about the effects of the major classes of available antihypertensive agents on inflammation and speculate on the possible contribution of these effects to observations in clinical trials. We suggest that a strategy of drug development specifically addressing inflammation in hypertension may provide increased benefit in terms of target organ damage, and we describe some examples of these promising developments.

The interdependence of endothelin-1 and calcium: a review

The 21-amino-acid peptide ET-1 (endothelin-1) regulates a diverse array of physiological processes, including vasoconstriction, angiogenesis, nociception and cell proliferation. Most of the effects of ET-1 are associated with an increase in intracellular calcium concentration. The calcium influx and mobilization pathways activated by ET-1, however, vary immensely. The present review begins with the basics of calcium signalling and investigates the different ways intracellular calcium concentration can increase in response to a stimulus. The focus then shifts to ET-1, and discusses how ET receptors mobilize calcium. We also examine how disease alters calcium-dependent responses to ET-1 by discussing changes to ET-1-mediated calcium signalling in hypertension, as there is significant interest in the role of ET-1 in this important disease. A list of unanswered questions regarding ET-mediated calcium signals are also presented, as well as perspectives for future research of calcium mobilization by ET-1.

The effects of ethnic discrimination and socioeconomic status on endothelin-1 among blacks and whites

BACKGROUND

Ethnic disparities in cardiovascular disease (CVD) may partially reflect differences in chronic stress burden that vary by social class and exposure to ethnic discrimination. Stress is associated with increased endothelin-1 (ET-1). This study examined the relationship of ET-1 to socioeconomic status (SES) and to perceived ethnic discrimination among black (n = 51) and white (n = 65) adults (mean age 36.5).

METHODS

The Perceived Discrimination subscale of the Scale of Ethnic Experience measured exposure to discrimination and the Hollingshead Two-Factor Index of Social Position assessed SES. Plasma ET-1 was sampled upon awakening after an overnight admission.

RESULTS

SES and ET-1 levels were similar across ethnic groups, but mean discrimination scores were higher among blacks than whites (P < 0.001). Multiple regressions found that the SES x ethnicity interaction was associated with ET-1 (P < 0.05), after adjustment for gender, resting mean arterial pressure (MAP), body mass index (BMI), and exercise frequency. Regressions stratified by ethnicity revealed that lower SES correlated with higher ET-1 in whites (P < 0.001), but not blacks, and accounted for 21% of the variance. Another series of regressions revealed an interaction effect of ethnicity by discrimination on ET-1 (P < 0.05). Increased discrimination correlated with increased ET-1 among blacks (P < 0.05), but not whites, and explained 11% of the variance after adjustment for SES, gender, exercise frequency, and socially desirable response bias.

CONCLUSIONS

Thus, ET-1 levels increased in association with different psychosocial burdens in blacks and whites. Plasma ET-1 was higher among whites with lower SES and among blacks with higher levels of perceived ethnic discrimination, regardless of SES.

Polymorphisms of the endothelin-1 gene associate with hypertension in patients with rheumatoid arthritis

Rheumatoid arthritis (RA) associates with excess cardiovascular (CV) morbidity and mortality. Hypertension, a highly prevalent entity in RA, has been associated with the endothelin-1 (ET-1) gene locus (EDN1) in some groups, such as Afro-Caribbean, the obese, and in low-renin states, but not in the general population as a whole. High levels of plasma ET-1 have been observed in RA. This study evaluated the potential association of EDN1 gene locus and serum ET-1 levels with hypertension in patients with RA. Genomic DNA and serum samples were collected from 397 well-characterized RA patients; DNA was also available from 401 local general population controls without RA. To explore the overall relevance of EDN1, two suitable single-nucleotide polymorphisms (SNPs), rs1800541 and rs5370, were selected and haplotype analysis was performed. Both SNPs were identified using real-time polymerase chain reaction (PCR) and melting curve analysis. Genetic analysis was related to hypertension as dichotomous trait and to blood pressure indices as continuous variables. Serum endothelin levels were also assessed in the RA patients. No genotype or haplotype differences were observed between RA and control subjects. Within RA, logistic regression analysis of each SNP separately revealed a threefold increase in the adjusted odds of being hypertensive of rs5370 TT homozygotes compared to GG homozygotes (OR = 2.89, 95%CI: 1.02 to 8.19). After adjustment for multiple potential confounders, haplotype analysis revealed an additive effect of the rs1800541-rs5370 T-T haplotype on hypertension (OR = 2.96, 95%CI: 1.28 to 6.86; p = .011), systolic blood pressure (SBP) (beta = 6.75 +/- 2.57 mm Hg; p = .009), and pulse pressure (PP) (beta = 4.37 +/- 2.12 mm Hg; p = .040). There was an increased prevalence of raised ET-1 levels amongst hypertensive RA patients, whereas a similar trend was observed for T-T haplotype carriers. RA patients who carry the rs1800541-rs5370 T-T EDN1 haplotype appear more likely to be hypertensive with an increased SBP and PP. These findings, if replicated in future studies, could be used as a screening tool for RA patients at increased hypertension, and thus cardiovascular, risk.

Efficacy and safety of darusentan: a novel endothelin receptor antagonist

OBJECTIVE

To summarize the role of the endothelin system (ETS) in cardiovascular disease (CVD) and evaluate the potential usefulness of darusentan, a selective endothelin type A (ET(A)) receptor antagonist, in the treatment of hypertension and chronic heart failure (CHF).

DATA SOURCES

A literature search was conducted in MEDLINE (1966-February 2008), International Pharmaceutical Abstracts (1970-February 2008), and EMBASE (1990-February 2008) using the search terms endothelin, darusentan, LU 135252, hypertension, and heart failure.

STUDY SELECTION AND DATA EXTRACTION

Studies evaluating the role of the ETS in CVD and the pharmacology, pharmacokinetics, safety, and efficacy of darusentan for the treatment of hypertension and CHF were included.

DATA SYNTHESIS

Darusentan represents a novel treatment strategy for patients with resistant hypertension. Its safety and efficacy have been evaluated in the treatment of hypertension and CHF. Darusentan selectively blocks the ET(A) receptor, promoting vasodilatation and preventing several proliferative and inflammatory processes, while promoting the actions of the ET(B) receptor. Studies in patients with stage 2 or resistant hypertension concluded that darusentan safely and effectively lowers blood pressure. Darusentan's unique mechanism of action, dose-dependent blood pressure-lowering profile, once-daily dosing regimen, and sustained 24-hour blood pressure-lowering effect are valuable features. Darusentan is well tolerated, with only peripheral edema, headache, and nasal symptoms being reported more frequently than with placebo. Endothelin receptor antagonists, including darusentan, have been associated with a decrease in hemoglobin and hematocrit and are teratogens. Darusentan does not appear to cause hepatotoxicity. Additional studies in CHF are warranted to assess the safety and efficacy of darusentan, especially given its association with peripheral edema and decreased red blood cell count.

CONCLUSIONS

Given the important role of the ETS in hypertension and available data with darusentan, selective antagonism of the ET(A) receptor represents a promising approach to managing resistant hypertension. Darusentan's role will be more clearly elucidated by ongoing Phase 3 studies.

Endothelin-receptor antagonists in arterial hypertension: Further indications?

Endothelin-1 exerts vasoactive, pro-inflammatory, hypertrophic, and profibrotic properties on the heart, kidney, and blood vessels. Hence, endothelin-receptor antagonists hold the potential to reduce blood pressure and to prevent complications of hypertension, atherosclerosis, and diabetes through blood pressure-independent effects on cardiovascular growth, inflammation, and fibrosis. These potentially important effects of endothelin antagonism may contribute to its therapeutic potential in hypertension and other cardiovascular disorders, including chronic renal failure and diabetes. First clinical trial evidence demonstrates a moderate reduction in blood pressure in studies of patients with mild-to-moderate essential hypertension and patients with resistant hypertension. Future large-scale randomized clinical trials will provide more insight into whether the blood-pressure reduction and promising pleiotropic effects observed with several members of this novel class of drugs, which are already established therapy in pulmonary hypertension, will translate into clinical benefit in patients with arterial hypertension.

Role of Endothelins in Hypertension

There are three peptides of endothelial origin, called endothelins (ETs), having different receptors that mediate a potent vasoconstrictor effect and also a mild vasodilation. Their renal effects are characterized by natriuresis in spite of the renal vasoconstriction. This effect, along with the stimulation of ETs by high sodium intake, suggests that ETs may be responsible for maintaining sodium balance when the renin angiotensin system is depressed. ET is activated in deoxycorticosterone acetate (DOCA) salt hypertension models and salt-sensitive hypertension. In humans, the role of ET seems to be similar to that shown in experimental animals; in both, ET participates in the regulation of salt metabolism. Salt-sensitive patients exhibit a blunted renal ET-1 response during sodium load. The role of ETs in humans has been investigated with use of nonspecific ET receptor blockers that inhibit the vasoconstriction and vasodilator components of ET. However, the effects of ET blockade should be investigated with ETA receptor blockers that mediate vasoconstriction alone. Effects of ET blockade should also be evaluated with respect to stimulation of oxidative stress and tissue damage, important mechanisms responsible for tissue fibrosis.

The future of endothelin-receptor antagonism as treatment for systemic hypertension

Endothelin (ET) is an endogenous peptide secreted predominantly by endothelial cells that mediates its effects via vasoconstriction and hypertrophy of vascular smooth muscle. Because the role of ET has been described in multiple pathologic processes in cardiovascular disease, including hypertension, there has been a strong interest in the development of therapeutic agents that inhibit ET receptors. ET receptor antagonists have shown much promise in disease states such as pulmonary arterial hypertension, essential hypertension, and various forms of secondary hypertension. This review serves to summarize the current role of ET and ET receptor antagonists in both the pathophysiology and the treatment of hypertension.

The role of endothelin receptor antagonists in cardiovascular pharmacotherapy

Endothelin (ET) is a hormone produced predominantly by endothelial cells which has been recognised to play a significant role in the development of several cardiovascular disease states. In order to combat the deleterious effects of ET, several ET-receptor antagonists (ETRA) are currently in clinical development. The agents developed thus far inhibit the actions of ET through either selective inhibition of the ET(A) receptors or non-selective inhibition of both ET(A) and ET(B) receptors. However, due to the differing proportions of the two receptor subtypes in various tissues, animal models and pathologies, it remains a matter of debate whether receptor selective agents impart significant clinical benefits over non-selective agents. This paper seeks to briefly summarise the important preclinical and clinical effects that have been reported in the literature and will attempt to provide a rationale for the use of both types of ETRAs in the treatment of both systemic and pulmonary hypertension as well as chronic heart failure (CHF).

Circulating endothelin parallels arterial blood pressure during sleep in healthy subjects

OBJECTIVE

To characterize plasma endothelin 1 (ET-1) and arterial blood pressure (ABP) time courses during the first complete non-rapid eye movement (NREM)-REM sleep cycle in healthy subjects, together with plasma renin activity (PRA) and plasma atrial natriuretic peptide (ANP).

METHODS

Heart rate (HR), intra-arterial blood pressure and sleep electroencephalographic activity were recorded continuously during the night in eight healthy 20-28-year-old males. Blood was sampled every 10 min during their first complete sleep cycle for simultaneous measurements of plasma ET-1, PRA and ANP.

RESULTS

Circulating ET-1 demonstrated significant variations during the sleep cycle (p<0.0001) that paralleled those of ABP (p<0.05) and HR (p<0.005), with a minimum during NREM sleep and a maximum during REM sleep. ET-1 time course opposed that of PRA which increases during NREM sleep and decreases during REM sleep (p<0.0005). Plasma ANP did not demonstrate systematic variation in relation with the sleep cycle.

CONCLUSION

Circulating ET-1, which parallels variations of ABP, may participate in ABP regulation during sleep in healthy subjects, in association with the renin-angiotensin system.

Endothelin???aldosterone interaction and proteinuria in low-renin hypertension

OBJECTIVE

To investigate whether endothelin and aldosterone participate in the increased prevalence and severity of nephrosclerosis in human low-renin hypertension, analogous to observations in experimental hypertension.

DESIGN

Comparison of endothelin, aldosterone and their relationships with proteinuria, in hypertensive patients with high aldosterone : renin ratios (HARR group, n = 14) or normal aldosterone : renin ratios (NARR group, n = 15).

METHODS

Urine protein and radioimmunoassay measurements of plasma renin activity, endothelin and aldosterone were carried out in individuals taking their usual diet, and after salt loading and salt depletion.

RESULTS

Compared with the NARR group, patients in the HARR group had higher blood pressure, greater salt sensitivity of their blood pressure, significantly greater urine protein and lower serum potassium concentrations, lower renin activities [0.14 +/- 0.03 ng AngiotensinI (AI)/l per s compared with 0.76 +/- 0.16 ng AI/l per s; P < 0.005], blunted renin-aldosterone responses to salt loading and salt depletion, enhanced catecholamine responses to salt depletion, and increased plasma endothelin (5.1 +/- 0.5 fmol/ml compared with 3.7 +/- 0.3 fmol/ml; P < 0.03). In the HARR group, endothelin and aldosterone concentrations were highly correlated, and both correlated with blood pressure and urine protein. In contrast, in the NARR group, endothelin and aldosterone did not correlate between them or with blood pressure, and only endothelin, not aldosterone, correlated with urine protein. Multivariate regression confirmed that the interaction between aldosterone and endothelin was the major predictor of urine protein in the HARR group (r = 0.442), whereas endothelin, renin and their interaction were predictors in the NARR group (r = 0.467).

CONCLUSIONS

Our results concur with experimental evidence for participation of endothelin in renal damage of angiotensin-dependent hypertension and for that of an endothelin-aldosterone interaction in low-renin hypertension. We propose that combined pharmacological antagonism of endothelin and aldosterone may confer renal protection beyond blood pressure reduction in patients with low-renin hypertension, a population at high risk for hypertensive nephrosclerosis.

Role of endothelin in human hypertension

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

Participation of renal and circulating endothelin in salt-sensitive essential hypertension

Salt sensitivity of blood pressure is a cardiovascular risk factor, independent of and in addition to hypertension. In essential hypertension, a conglomerate of clinical and biochemical characteristics defines a salt-sensitive phenotype. Despite extensive research on multiple natriuretic and antinatriuretic systems, there is no definitive answer yet about the major causes of salt-sensitivity, probably reflecting the complexity of salt-balance regulation. The endothelins, ubiquitous peptides first described as potent vasoconstrictors, also have vasodilator, natriuretic and antinatriuretic actions, depending on their site of generation and binding to different receptors. We review the available data on endothelin in salt-sensitive essential hypertension and conclude that abnormalities of renal endothelin may play a primary role. More importantly, the salt-sensitive patient may have blood pressure-dependency on endothelin in all states of salt balance, thus predicting that endothelin receptor blockers will have a major therapeutic role in salt-sensitive essential hypertension.

Endothelin-1 and endothelin receptor antagonists as potential cardiovascular therapeutic agents

Endothelin (ET)-1 is an endothelium-derived peptide with potent vasoconstrictor and proliferative properties. The ET system is activated in several cardiovascular disease states associated with functional and structural vascular changes, including hypertension and heart failure. The two ET receptor subtypes are known as ET(A)R and ET(B)R. The former is located mainly on vascular smooth muscle cells and is responsible for mediating vasoconstriction and proliferation. The latter is present predominantly on endothelial cells and mediates vasorelaxation as well as ET-1 clearance. Activation of smooth muscle ET(B)R causes vasoconstriction. Selective ET(A)R antagonists as well as nonselective ET(A)R-ET(B)R antagonists have been developed. Studies with animal models and early-phase clinical trials provided strong evidence that these agents are effective in the treatment of heart failure, essential hypertension, pulmonary hypertension, and atherosclerosis. However, the complexity of biologic effects mediated by two different receptor subtypes complicates therapy with selective versus nonselective ET receptor antagonists. In addition to subtype selectivity and potency, changes in receptor subtype distribution under different pathologic conditions and different patient populations will play a crucial role in the evaluation of these potentially therapeutic drugs.

Salt intake, endothelial dysfunction, and salt-sensitive hypertension

Numerous epidemiologic and clinical studies have demonstrated a clear relationship between high salt intake and blood pressure. However, the mechanisms of a salt-induced increase in blood pressure--a phenomenon known as salt sensitivity--and the heterogeneity of this effect are far from being completely understood. Endothelial dysfunction, and especially the nitric oxide system, is implicated in both experimental and clinical hypertension. Animal studies indicate that endogenous nitric oxide plays an important role in renal hemodynamics and sodium homeostasis, inducing renal vasodilation and natriuresis. Studies of essential hypertensive patients have also suggested that both high salt intake and salt sensitivity are associated with impaired endothelial function. Although there are many hypotheses concerning the nature of salt sensitivity, clinical data indicate that salt-sensitive patients may be unable to up-regulate the production of nitric oxide in response to salt intake. This endothelial dysfunction, which is more frequent in salt-sensitive than in salt-resistant essential hypertensive patients, may partially explain the blood pressure increase in response to salt intake and may underlie the more pronounced target organ damage and cardiovascular risk in salt-sensitive patients.