Role of endothelin in human hypertension

Pattern of expression of inflammatory markers in adipose tissue of untreated hypertensive patients

OBJECTIVE

Adiposity contributes to the insulin resistance and endothelial dysfunction of the hypertensive state; the inflammatory network and the metalloprotease (MMP)/ tissue inhibitor of metalloprotease (TIMP) system modulate vascular structure and function.

METHODS

We measured interleukin-6 (IL-6); plasminogen activator inhibitor-1 (PAI-1); tumor necrosis factor-alpha; transforming growth factor-beta; MMP-2, MMP-9, TIMP-1, and TIMP-2 expression; MMP-2 and MMP-9 activity; and TIMP-1 and TIMP-2 protein in adipocytes isolated from paired samples of visceral and subcutaneous adipose tissue of 30 nonobese, untreated hypertensive patients and 20 normotensive controls.

RESULTS

Although expression of IL-6, PAI-1, tumor necrosis factor-alpha, and transforming growth factor-beta were generally higher in visceral adipocytes, IL-6, PAI-1, and tumor necrosis factor-alpha were overexpressed, and transforming growth factor-beta was underexpressed in hypertensive vs. controls (all P<0.0001). These changes were paralleled by higher circulating IL-6 and PAI-1 levels in hypertensive patients. MMP-2 and TIMP-2 expression - which were higher in subcutaneous than visceral cells - were reduced in hypertensive patients (all P<0.0001), whereas MMP-9 and TIMP-1 did not differ between the two groups. Both MMP-2 and MMP-9 activity were reduced in hypertensive patients (all P<0.0001). In the whole dataset, SBP and DBP were directly related to IL-6 and PAI-1 expression and inversely to MMP-2 and MMP-9 activity.

CONCLUSION

Adipocytes from both visceral and subcutaneous depots of untreated hypertensive patients show a pattern of expression of inflammatory and MMP/TIMP molecules that is compatible with the raised circulating levels of inflammatory markers, is quantitatively related to the height of blood pressure, and provides the cellular basis for the proinflammatory and prothrombotic predisposition of these patients.

O-GlcNAcylation: a novel pathway contributing to the effects of endothelin in the vasculature

Glycosylation with O-linked β-N-acetylglucosamine (O-GlcNAc) or O-GlcNAcylation on serine and threonine residues of nuclear and cytoplasmic proteins is a posttranslational modification that alters the function of numerous proteins important in vascular function, including kinases, phosphatases, transcription factors, and cytoskeletal proteins. O-GlcNAcylation is an innovative way to think about vascular signaling events both in physiological conditions and in disease states. This posttranslational modification interferes with vascular processes, mainly vascular reactivity, in conditions where endothelin-1 (ET-1) levels are augmented (e.g. salt-sensitive hypertension, ischemia/reperfusion, and stroke). ET-1 plays a crucial role in the vascular function of most organ systems, both in physiological and pathophysiological conditions. Recognition of ET-1 by the ET(A) and ET(B) receptors activates intracellular signaling pathways and cascades that result in rapid and long-term alterations in vascular activity and function. Components of these ET-1-activated signaling pathways (e.g., mitogen-activated protein kinases, protein kinase C, RhoA/Rho kinase) are also targets for O-GlcNAcylation. Recent experimental evidence suggests that ET-1 directly activates O-GlcNAcylation, and this posttranslational modification mediates important vascular effects of the peptide. This review focuses on ET-1-activated signaling pathways that can be modified by O-GlcNAcylation. A brief description of the O-GlcNAcylation biology is presented, and its role on vascular function is addressed. ET-1-induced O-GlcNAcylation and its implications for vascular function are then discussed. Finally, the interplay between O-GlcNAcylation and O-phosphorylation is addressed.

O-GlcNAcylation contributes to the vascular effects of ET-1 via activation of the RhoA/Rho-kinase pathway

AIMS

Glycosylation with β-N-acetylglucosamine (O-GlcNAcylation) is one of the most complex post-translational modifications. The cycling of O-GlcNAc is controlled by two enzymes: UDP-NAc transferase (OGT) and O-GlcNAcase (OGA). We recently reported that endothelin-1 (ET-1) augments vascular levels of O-GlcNAcylated proteins. Here we tested the hypothesis that O-GlcNAcylation contributes to the vascular effects of ET-1 via activation of the RhoA/Rho-kinase pathway.

METHODS AND RESULTS

Incubation of vascular smooth muscle cells (VSMCs) with ET-1 (0.1 μM) produces a time-dependent increase in O-GlcNAc levels. ET-1-induced O-GlcNAcylation is not observed when VSMCs are previously transfected with OGT siRNA, treated with ST045849 (OGT inhibitor) or atrasentan (ET(A) antagonist). ET-1 as well as PugNAc (OGA inhibitor) augmented contractions to phenylephrine in endothelium-denuded rat aortas, an effect that was abolished by the Rho kinase inhibitor Y-27632. Incubation of VSMCs with ET-1 increased expression of the phosphorylated forms of myosin phosphatase target subunit 1 (MYPT-1), protein kinase C-potentiated protein phosphatase 1 inhibitor protein (protein kinase C-potentiated phosphatase inhibitor-17), and myosin light chain (MLC) and RhoA expression and activity, and this effect was abolished by both OGT siRNA transfection or OGT inhibition and atrasentan. ET-1 also augmented expression of PDZ-Rho GEF (guanine nucleotide exchange factor) and p115-Rho GEF in VSMCs and this was prevented by OGT siRNA, ST045849, and atrasentan.

CONCLUSION

We suggest that ET-1 augments O-GlcNAcylation and this modification contributes to increased vascular contractile responses via activation of the RhoA/Rho-kinase pathway.

Niacin in the prevention of atherosclerosis: Significance of vasodilatation

There is a rising interest towards the old drug, nicotinic acid (niacin, vitamin B(3)), because at pharmacological concentrations it has a beneficial effect on HDL cholesterol. Its use, however, was limited due to its adverse effect, flushing. When the mechanism of flushing was solved, a combination of niacin and DP1 receptor antagonist or prostaglandin inhibitor is used, there has been a comeback of niacin with extensive clinical trials. This paper argues that the new strategy with niacin for the prevention of atherosclerosis should be re-evaluated, because vasodilatation of the peripheral vessels might be crucially important in the early primary prevention according to our "vasa vasorum hypoxia" hypothesis.

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.

Hypercholesterolaemia induces early renal lesions characterized by upregulation of MMP-9 and iNOS and ETAR: alleviated by a dual endothelin receptor antagonist CPU0213 and simvastatin

Objectives

We aimed to investigate hypercholesterolaemia-induced early renal lesions which result in abnormal expression of endothelin A receptor (ETAR), induced nitric oxide synthase (iNOS) and matrix metalloproteinase 9 (MMP-9). We hypothesized that this is due to an upregulated endothelin (ET) pathway consequent to hypercholesterolaemia and that CPU0213, a dual ET antagonist, could mitigate these changes.

Methods

Rats were randomly divided into four groups: (1), control; (2), high-fat diet for 60 days (HFD); HFD rats medicated in the last 15 days with either (3) CPU0213 (30 mg/kg daily, s.c.) or (4) simvastatin (4 mg/kg daily, p.o.).

Key findings

Body weight, serum triglycerides, total cholesterol and low-density-lipoprotein cholesterol were significantly increased, whereas high-density lipoprotein cholesterol decreased in the HFD group, relative to normal. Meanwhile, these changes were associated with upregulation of mRNA and protein of ETAR, iNOS and MMP-9 in the kidney. The lipid-lowering effect of simvastatin was predominant, lessening abnormal expression of these molecules in the kidney dramatically. Interestingly, CPU0213 significantly normalized expression of mRNA and protein of ETAR, iNOS and MMP-9, comparable with simvastatin, leaving no changes in hyperlipidaemia.

Conclusions

CPU0213 relieves renal lesions by blunting hypercholesterolaemia caused by the upregulated ET system, iNOS and MMP-9 in the kidney. This indicates that CPU0213 is promising in treating patients with end stage renal disease.

Sex differences in endothelin-1-mediated vasoconstrictor tone in middle-aged and older adults

The prevalence of cardiovascular disease is lower in middle-aged and older women than men. Increased endothelin-1-mediated vasoconstriction has been linked to the etiology of a number of cardiovascular diseases, including atherosclerosis, heart failure, and hypertension. It is unknown whether a sex difference in endothelin-1-mediated vasoconstrictor tone exists in middle-aged and older adults. Therefore, we tested the hypothesis that middle-aged and older men would demonstrate greater ET-1-mediated vasoconstrictor tone than age-matched women. Forearm blood flow in response to intra-arterial infusions of endothelin (ET)-1, BQ-123 (a selective ET(A) receptor antagonist), and BQ-788 (a selective ET(B) receptor antagonist) was assessed by venous occlusion plethysmography in 21 women (age: 58 + or - 1 yr; body mass index: 26.0 + or - 1.0 kg/m(2)) and 25 men (age: 57 + or - 2 yr; body mass index: 26.8 + or - 0.7 kg/m(2)). In response to BQ-123, the increase in forearm blood flow from baseline was significantly higher in the men than the women (24 + or - 5% vs. 9 + or - 5%; P < 0.05). In contrast, the increase in forearm blood flow in response to BQ-123 coinfused with BQ-788 was greater in the women than the men, such that the maximum vasodilation to dual endothelin receptor blockade was similar between men and women (approximately 25%). There was no difference in the vasoconstrictor response to ET-1 between the sexes. These results indicate that middle-aged and older men are under greater ET(A) receptor-mediated vasoconstrictor tone than age-matched women. Since the ET(A) receptor is the predominant receptor subtype in the coronary vasculature, this sex difference in vasoconstrictor tone may be a mechanism contributing to the sex difference in the prevalence of coronary heart disease in middle-aged and older adults.

Endothelin receptors: what's new and what do we need to know?

Receptors are at the heart of how a molecule transmits a signal to a cell. Two receptor classes for endothelin (ET) are recognized, the ET(A) and ET(B) receptors. Intriguing questions have arisen in the field of ET receptor pharmacology, physiology, and function. For example, a host of pharmacological studies support the interaction of the ET(A) and ET(B) receptor in tissues (veins, arteries, bronchus, arterioles, esophagus), but yet few have been able to demonstrate direct ET(A)/ET(B) receptor interaction. Have we modeled this interaction wrong? Do we have a truly selective ET(A) receptor agonist such that we could selectively stimulate this important receptor? What can we learn from the recent phylogenic studies of the ET receptor family? Have we adequately addressed the number of biological molecules with which ET can interact to exert a biological effect? Recent mass spectrometry studies in our laboratory suggest that ET-1 interacts with other hereto unrecognized proteins. Biased ligands (ligands at the same receptor that elicit distinct signaling responses) have been discovered for other receptors. Do these exist for ET receptors and can we take advantage of this possibility in drug design? These and other questions will be posed in this minireview on topics on ET receptors.

Inhibitory effect of ETB receptor on Na(+)-K(+) ATPase activity by extracellular Ca(2+) entry and Ca(2+) release from the endoplasmic reticulum in renal proximal tubule cells

The kidney is important in the long-term regulation of blood pressure and sodium homeostasis. Stimulation of ETB receptors in the kidney increases sodium excretion, in part, by decreasing sodium transport in the medullary thick ascending limb of Henle and in collecting duct. However, the role of ETB receptor on Na(+)-K(+) ATPase activity in renal proximal tubule (RPT) cells is not well defined. The purpose of this study is to test the hypothesis that ETB receptor inhibits Na(+)-K(+) ATPase activity in rat RPT cells, and investigate the mechanism(s) by which such an action is produced. In RPT cells from Wistar-Kyoto rats, stimulation of ETB receptors by the ETB receptor agonist, BQ3020, decreased Na(+)-K(+) ATPase activity, determined by ATP hydrolysis (control=0.38+/-0.02, BQ3020=0.26+/-0.03, BQ788=0.40+/-0.06, BQ3020+BQ788=0.37+/-0.04, n=5, P<0.01). The ETB receptor-mediated inhibition of Na(+)-K(+) ATPase activity was dependent on an increase in intracellular calcium, because this effect was abrogated by a chelator of intracellular-free calcium (BAPTA-AM; 5 x 10(-3) M 15 min(-1)), Ca(2+) channel blocker (10(-6) M 15 min(-1) nicardipine) and PI3 kinase inhibitor (10(-7) M per wortmannin). An inositol 1,4,5-trisphosphate (IP3) receptor blocker (2-aminoethyl diphenyl borate; 10(-4) M 15 min(-1)) also blocked the inhibitory effect of the ETB receptor on Na(+)-K(+)ATPase activity (control=0.39+/-0.06, BQ3020=0.25+/-0.01, 2-APB=0.35+/-0.05, BQ3020+ 2-APB=0.35+/-0.06, n=4, P<0.01). The calcium channel agonist (BAY-K8644; 10(-6) M 15 min(-1)) inhibited Na(+)-K(+) ATPase activity, an effect that was blocked by a phosphatidylinositol-3 kinase inhibitor (10(-7) M 15 min(-1) wortmannin). In rat RPT cells, activation of the ETB receptor inhibits Na(+)-K(+) ATPase activity by facilitating extracellular Ca(2+) entry and Ca(2+) release from endoplasmic reticulum.

Endothelial dysfunction in patients with noncomplicated and complicated hypertension

Endothelial dysfunction plays an important role in the pathogenesis of hypertension. Other risk factors of atherosclerosis also affect its development. The aim of the study was to assess nitric oxide metabolites concentration (nitrites and nitrates No(x)) and endothelin (ET-1) in plasma and cyclic 3,5-guanosine monophosphate (cGMP) in 24 h-urine collection in patients with noncomplicated hypertension without risk factors of atherosclerosis and in hypertensive patients with coronary artery disease (CAD). Sixty-eight subjects were included in the study (44 men, 24 women), aged 47 +/- 76 years, allotted into four groups: I - controls (18 clinically healthy subjects); II - 12 subjects with hypertension without risk factors of atherosclerosis; III - 16 subjects with hypertension and risk factors of atherosclerosis; and IV - 22 subjects with hypertension and CAD. Plasma NO(x) concentration was determined using the Greiss method, plasma ET-1 by ELISA, and urine cGMP using the immunoenzymatic method. Plasma NO(x) concentration was 14.00 +/- 6.88 micromol/L in group I, in group II - 18.62 +/- 5.84 micromol, in group III - 9.96 +/- 4.72 micromol/L, and in group IV - 8.78 +/- 3.72 micromol/L. Statistically significant differences were between groups I and III (p < 0.05) and I and IV (p < 0.04) and groups II and III (p < 0.01) and II and IV (p < 0.01). The concentration of cGMP in 24 h urine collection was in group I - 40 +/- 24 pmol/L; in group II - 54 +/- 41 pmol/L; in group III - 38 +/- 32 pmol/L; and in group IV - 42 +/- 36 pmol/L. There were no significant differences between the groups. Plasma ET-1 concentration was 3.86 +/- 0.52 pg/mL in group I, in group II - 4.05 +/- 0.71 pg/mL, in group III - 4.22 +/- 0.79 pg/mL and in group IV - 4.38 +/- 0.75 pg/mL. Statistically significant differences were between group I and III (p < 0.05), I and IV (p < 0.03), and between group II and IV (p < 0.04). Endothelial dysfunction was not found in hypertensive patients without a family history of cardiovascular diseases and without other risk factors of atherosclerosis. Deterioration of endothelial function was observed in patients with hypertension with risk factors of atherosclerosis. It was most pronounced in those with CAD.

Renal cell carcinoma and arterial hypertension

BACKGROUND

The association between renal cell carcinoma and arterial hypertension has been the subject of various studies. These studies have not been consistent in clarifying the relationship between the two. Some authors contend that arterial hypertension is a consequence of renal cell carcinoma, which secretes vasoactive peptides. Others claim that arterial hypertension is a risk factor for the development of renal cell carcinoma. The purpose of our study is to assess if there is a direct connection between arterial hypertension and renal cell carcinoma.

METHODS

Out of 16,755 patients who were examined by ultrasonography, 40 were diagnosed with renal tumors. Of the 40 patients, 29 had malignant renal tumors, and 11 had benign renal tumors. These diagnoses were confirmed by CT scan, renal biopsy, and histology. Most of the patients with renal cell carcinoma (79.3%) had arterial hypertension. The group with benign renal tumors served as a control group. Out of the 29 patients with malignant renal cell carcinoma, 24 patients were treated with total nephrectomy, one had a partial nephrectomy, and four patients were too unwell for surgical intervention. In the group of those with benign renal tumors, seven patients had partial nephrectomies for the removal of angiomyolipomas. The personal histories were taken at the initiation of the study, and vital signs were obtained before and after surgery. Statistical analyses were performed using the Statistical Package for Social Sciences, version 10.0.

RESULTS

In the malignant group, the systolic blood pressure (SBP) before surgery was 157.41 +/- 27.86 mmHg, and the diastolic blood pressure (DBP) was 97.24 +/- 15.33 mmHg, while in the benign group, SBP was 134.55 +/- 17.53 mmHg, and DBP was 88.18 +/- 14.01 mmHg. In the malignant group in those who had undergone nephrectomies, the mean systolic pressure was 136.82, and the diastolic pressure was 85.90. In the benign group, the systolic and diastolic blood pressures were normal before and after surgery.

CONCLUSION

In the group of patients with both renal cell carcinoma and arterial hypertension, their hypertension was resolved after they underwent nephrectomies. In conclusion, our data suggest that renal cell carcinomas may cause arterial hypertension.

Endothelin-1 stimulates human adipocyte lipolysis through the ET A receptor

OBJECTIVE

Levels of the vascular peptide endothelin-1 (ET-1) are significantly elevated in obesity. Adipose tissue-derived ET-1 attenuates insulin-mediated antilipolysis in human visceral adipocytes through the activation of the ET receptor B (ET(B)R), thereby linking ET-1 to insulin resistance. Whether ET-1 has direct effects on lipolysis in human adipocytes is not known.

RESEARCH DESIGN AND SUBJECTS

Endothelin-1 receptor (ETR) mRNA expression was determined by quantitative PCR in 130 non-obese and obese subjects. ET-1 mRNA in different adipose tissue regions was also assessed. ETR protein expression was analyzed by western blotting in 37 subjects. The effect of ET-1 on lipolysis was assessed in freshly isolated adipocytes and in vitro differentiated adipocytes from human donors.

RESULTS

Freshly isolated human adipocytes incubated with different concentrations of ET-1 showed no acute effect on lipolysis. In contrast, a 24 h incubation in primary cultures of human adipocytes resulted in a significant 50% increase in lipolysis. This effect was concentration dependent and could be mimicked by an agonist of the ET(A) receptor but not with a selective ET(B)R agonist. Adipocyte differentiation was not affected by any of the agonists. In subcutaneous (s.c.) adipose tissue from 19 non-obese and 18 obese subjects, the protein expression of ET(A)R was significantly higher in obese subjects whereas there was no difference in ET(B)R expression. Interestingly, the differences in protein expression were not observed at the mRNA level as ET(A)R expression was similar between lean and obese subjects.

CONCLUSION

Long-term but not acute incubation of human adipocytes with ET-1 results in a significant increase in lipolysis. This appears to be mediated through the activation of ET(A)R, demonstrating a yet another receptor-specific effect of ET-1. In addition, the protein expression of ET(A)R is increased in s.c. adipose tissue in obesity, possibly through post-transcriptional mechanisms. An increased effect of ET-1 could be a mechanism that contributes to increased basal lipolysis in human obesity.

Endothelin-1, aging and hypertension

PURPOSE OF REVIEW

Endothelin-1 system activation plays an important role in the etiology of atherosclerotic vascular disease. Aging and hypertension are two independent cardiovascular risk factors that have been shown to exhibit increased endothelin-1 system activation. This review focuses on the cardiovascular effects of the endothelin system, its relation to aging and hypertension, as well as potential treatment options.

RECENT FINDINGS

Many of the cardiovascular complications associated with both aging and hypertension are attributable, in part, to endothelial dysfunction, particularly vasomotor dysregulation. To date most studies have focused on the effects of aging and hypertension on endothelium-dependent nitric oxide-mediated vasodilation. However, endothelin-1-mediated vasoconstrictor tone increases with age and contributes to the pathogenesis of hypertension. Pharmacologic approaches to reduce endothelin-1 system activation have produced limited results and are largely disease-specific. In contrast, regular aerobic exercise has been shown to be extremely effective at reducing endothelin-1 system activity.

SUMMARY

Both aging and hypertension represent important cardiovascular disease risk factors that are characterized by increased endothelin-1-mediated vasoconstrictor tone. Future studies are needed to elucidate pharmacologic options for reducing endothelin-1 system activity especially in older hypertensive adults, though regular aerobic exercise must continue to be a point of emphasis for maintaining/improving vascular health.

Teleost fish osmoregulation: what have we learned since August Krogh, Homer Smith, and Ancel Keys

In the 1930s, August Krogh, Homer Smith, and Ancel Keys knew that teleost fishes were hyperosmotic to fresh water and hyposmotic to seawater, and, therefore, they were potentially salt depleted and dehydrated, respectively. Their seminal studies demonstrated that freshwater teleosts extract NaCl from the environment, while marine teleosts ingest seawater, absorb intestinal water by absorbing NaCl, and excrete the excess salt via gill transport mechanisms. During the past 70 years, their research descendents have used chemical, radioisotopic, pharmacological, cellular, and molecular techniques to further characterize the gill transport mechanisms and begin to study the signaling molecules that modulate these processes. The cellular site for these transport pathways was first described by Keys and is now known as the mitochondrion-rich cell (MRC). The model for NaCl secretion by the marine MRC is well supported, but the model for NaCl uptake by freshwater MRC is more unsettled. Importantly, these ionic uptake mechanisms also appear to be expressed in the marine gill MRC, for acid-base regulation. A large suite of potential endocrine control mechanisms have been identified, and recent evidence suggests that paracrines such as endothelin, nitric oxide, and prostaglandins might also control MRC function.

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.

Vascular peptide endothelin-1 links fat accumulation with alterations of visceral adipocyte lipolysis

OBJECTIVE

Visceral obesity increases risk of insulin resistance and type 2 diabetes. This may partly be due to a region-specific resistance to insulin's antilipolytic effect in visceral adipocytes. We investigated whether adipose tissue releases the vascular peptide endothelin-1 (ET-1) and whether ET-1 could account for regional differences in lipolysis.

RESEARCH DESIGN AND METHODS

One group consisted of eleven obese and eleven nonobese subjects in whom ET-1 levels were compared between abdominal subcutaneous and arterialized blood samples. A second group included subjects undergoing anti-obesity surgery. Abdominal subcutaneous and visceral adipose tissues were obtained to study the effect of ET-1 on differentiated adipocytes regarding lipolysis and gene and protein expression.

RESULTS

Adipose tissue had a marked net release of ET-1 in vivo, which was 2.5-fold increased in obesity. In adipocytes treated with ET-1, the antilipolytic effect of insulin was attenuated in visceral but not in subcutaneous adipocytes, which could not be explained by effects of ET-1 on adipocyte differentiation. ET-1 decreased the expression of insulin receptor, insulin receptor substrate-1 and phosphodiesterase-3B and increased the expression of endothelin receptor-B (ET(B)R) in visceral but not in subcutaneous adipocytes. These effects were mediated via ET(B)R with signals through protein kinase C and calmodulin pathways. The effect of ET-1 could be mimicked by knockdown of IRS-1.

CONCLUSIONS

ET-1 is released from human adipose tissue and links fat accumulation to insulin resistance. It selectively counteracts insulin inhibition of visceral adipocyte lipolysis via ET(B)R signaling pathways, which affect multiple steps in insulin signaling.

Endothelin, sex and hypertension

The ETs (endothelins) comprise a family of three 21-amino-acid peptides (ET-1, ET-2 and ET-3) and 31-amino-acid ETs (ET-1(1-31), ET-2(1-31) and ET-3(1-31)). ET-1 is synthesized from a biologically inactive precursor, big ET-1, by ECEs (ET-converting enzymes). The actions of ET-1 are mediated through activation of the G-protein-coupled ET(A) and ET(B) receptors, which are found in a variety of cells in the cardiovascular and renal systems. ET-1 has potent vasoconstrictor, mitogenic, pro-inflammatory and antinatriuretic properties, which have been implicated in the pathophysiology of a number of cardiovascular diseases. Overexpression of ET-1 has been consistently described in salt-sensitive models of hypertension and in models of renal failure, and has been associated with disease progression. Sex differences are observed in many aspects of mammalian cardiovascular function and pathology. Hypertension, as well as other cardiovascular diseases, is more common in men than in women of similar age. In experimental models of hypertension, males develop an earlier and more severe form of hypertension than do females. Although the reasons for these differences are not well established, the effects of gonadal hormones on arterial, neural and renal mechanisms that control blood pressure are considered contributing factors. Sex differences in the ET-1 pathway, with males displaying higher ET-1 levels, greater ET-1-mediated vasoconstrictor and enhanced pressor responses in comparison with females, are addressed in the present review. Sex-associated differences in the number and function of ET(B) receptors appear to be particularly important in the specific characteristics of hypertension between females and males. Although the gonadal hormones modulate some of the differences in the ET pathway in the cardiovascular system, a better understanding of the exact mechanisms involved in sex-related differences in this peptidergic system is needed. With further insights into these differences, we may learn that men and women could require different antihypertensive regimens.

Alcohol consumption, cardiovascular health, and endothelial function markers

Cardiovascular diseases are among the worldwide leading causes of shorter life expectancy and loss of quality of life. Thus, any influence of diet or life habits on the cardiovascular system may have important implications for public health. Most world populations consume alcoholic beverages. Since alcohol may have both protective and harmful effects on cardiovascular health, the identification of biochemical mechanisms that could explain such paradoxical effects is warranted. The vascular endothelium is the target of important mediating pathways of differential ethanol concentrations, such as oxidative stress, lipoproteins, and insulin resistance. Alcohol-induced endothelial damage or protection may be related to the synthesis or action of several markers, such as nitric oxide, cortisol, endothelin-1, adhesion molecules, tumor necrosis factor alpha, interleukin-6, C-reactive protein, and haemostatic factors. The expression of these markers is consistent with the J-shaped curve between alcohol consumption and cardiovascular health. However, there is genetic and phenotypic heterogeneity in alcohol response, and despite the apparent beneficial biochemical effects of low doses of ethanol, there is not enough clinical and epidemiological evidence to allow the recommendation to consume alcoholic beverages for abstemious individuals. Considering the potential for addiction of alcoholic beverage consumption and other negative consequences of alcohol, it would be worthwhile to identify substances able to mimic the beneficial effects of low doses of ethanol without its adverse effects.

Endothelin-1 blockade prevents COX2 induction and TXA2 production in the fructose hypertensive rat

Feeding rats with a high fructose diet results in insulin resistance and hypertension. Fructose-hypertensive rats (FHR) have increased vascular levels of endothelin-1 (ET-1) and thromboxane (TXA2). We have previously shown that chronic treatment with either the dual endothelin receptor blocker, bosentan, or the thromboxane synthase inhibitor, dazmegrel, prevented fructose-induced increases in blood pressure, suggesting that both ET-1 and TXA2 play important roles in the development of hyperinsulinemia/insulin resistance-associated hypertension. In this study, we investigated the potential interrelationship between ET-1 and TXA2 in the development of fructose-induced hypertension in vivo. Male Wistar rats were fed on a high fructose diet for 9 weeks. Either bosentan or dazmegrel treatment (daily by oral gavage) was initiated 3 weeks after the start of fructose feeding for a total duration of 6 weeks. At the end of drug treatment, blood and aorta were collected from each animal. Plasma thromboxane B2 (TXB2), a stable TXA2 metabolite, increased significantly in FHR and was reduced to control level by both chronic bosentan and dazmegrel treatment. Protein expression of cyclooxygenase 2 (COX2) was elevated significantly in FHR aortas and treatment with bosentan and dazmegrel corrected these changes. These results indicate that the actions of ET-1 in the aorta of FHR may be mediated through COX2-derived TXA2. Bosentan may prevent the development of hypertension in fructose-fed rats through inhibition of COX2 induction and subsequently the reduction in plasma TXA2.

Chronic Activation of Endothelin B Receptors

Endothelin (ET) exerts powerful pressor actions primarily through activation of the ET(A) receptor subtype. The ET(B) receptor (ET(B)R) subtype, on the other hand, is generally thought to initiate physiological actions that decrease arterial pressure. Such actions include clearing ET from the bloodstream, initiating endothelium-mediated vasodilation, and facilitating renal sodium and water excretion. The effect of long-term activation of the ET(B)R on arterial pressure, however, never has been directly tested. In this study we evaluated cardiovascular responses to chronic (5-day) activation of ET(B)R in male rats using continuous intravenous infusion of the selective agonist sarafotoxin 6c. Surprisingly, we found that sarafotoxin 6c caused a sustained increase in arterial pressure that rapidly reversed on termination of infusion. The hypertension was associated with increased renal excretion of sodium and water and decreased plasma volume. Alterations in daily sodium intake did not affect the magnitude of the hypertension. Hemodynamic studies revealed a decreased cardiac output and increased total peripheral resistance during sarafotoxin 6c infusion. Infusion of sarafotoxin 6c caused a small increase in plasma ET levels. Nevertheless, the hypertension was not affected by coadministration of a selective ET(A) receptor antagonist (atrasentan) but was completely prevented by treatment with a combined ET(A) receptor and ET(B)R antagonist (A186280). These experiments reveal for the first time that chronic activation of ET(B)R in rats causes sustained hypertension.

Endothelin-1 Vasoconstrictor Tone Increases With Age in Healthy Men But Can Be Reduced by Regular Aerobic Exercise

Increased endothelin-1–mediated vasoconstrictor tone has been linked to the etiology of a number of pathologies associated with human aging, including hypertension, congestive heart failure, and coronary artery disease. However, it is currently unclear whether aging, per se, is associated with enhanced endothelin-1 system activity. We hypothesized that endothelin-1 vasoconstrictor activity is greater in healthy older compared with young men and that regular aerobic exercise is an effective intervention for reducing endothelin-1 vasoconstrictor tone in older previously sedentary men. Forearm blood flow (plethysmography) responses to intra-arterial infusion of endothelin-1 (5 pmol/min; for 20 minutes) and selective (BQ-123; 100 nmol/min; for 60 minutes) and nonselective (BQ-123+BQ-788; 100 nmol/min; for 60 minutes) endothelin-1 receptor blockade were determined in 28 healthy, sedentary men: 13 younger (age: 27±1 years) and 15 older (age: 62±2 years). The vasoconstrictor response to endothelin-1 was significantly blunted (≈65%) in the older versus younger men. In response to BQ-123, resting forearm blood flow increased (≈20%; P <0.05) in the older but not in the younger men. The addition of BQ-788 to BQ-123 did not significantly affect the blood flow responses to BQ-123 in either group. Eight of the 15 older sedentary men completed a 3-month aerobic exercise intervention. After the intervention, the vasoconstrictor response to endothelin-1 was markedly increased (225%; P <0.05), whereas BQ-123 resulted in modest vasoconstriction in the previously sedentary older men. These results demonstrate that endothelin-1–mediated vasoconstrictor tone increases with age in healthy men but can be alleviated with regular aerobic exercise.

Effect of chronic IL-6 infusion on acute pressor responses to vasoconstrictors in mice

Interleukin (IL)-6 has been implicated as a contributing factor in the pathogenesis of hypertension, although the mechanisms involved are unclear. Studies conducted in vitro suggest that IL-6 may have a direct effect on vascular tone and may modulate constrictor responses to agonists. Whether this effect can be observed in vivo is unknown. Therefore, mice were treated with either IL-6 (16 ng/h sc) or vehicle for 14 days, and the acute blood pressure and heart rate responses to endothelin (ET)-1, angiotensin II (ANG II), and phenylephrine (PE) were assessed under isoflurane anesthesia. Blood pressure responses to ET-1 were identical in vehicle- and IL-6-infused mice, both in the presence and the absence of ganglion blockade with chlorisondamine. The fall in heart rate during ET-1 responses was significantly attenuated in IL-6-infused mice with autonomic reflexes intact (vehicle vs. IL-6, P < 0.05 at 1 and 3 nmol/kg of ET-1), but this difference was not observed after ganglionic blockade. Both blood pressure and heart rate responses to ANG II were indistinguishable between IL-6- and vehicle-infused mice, as were responses to PE except for a significant increase in the blood pressure response and decrease in the heart rate response in IL-6-infused mice observed only at the highest dose of PE (300 microg/kg; P < 0.05). These findings show that, despite what might be predicted from studies conducted in vitro, chronic exposure to elevated plasma IL-6 concentrations in itself does not predispose the mouse to enhanced responsiveness to vasoconstrictors in vivo.

Vasoactive peptides in cardiovascular (patho)physiology

Numerous vasoactive agents play an important physiological role in regulating vascular tone, reactivity and structure. In pathological conditions, alterations in the regulation of vasoactive peptides result in endothelial dysfunction, vascular remodeling and vascular inflammation, which are important processes underlying vascular damage in cardiovascular disease. Among the many vasoactive agents implicated in vascular (patho)biology, angiotensin II (Ang II), endothelin (ET), serotonin and natriuretic peptides appear to be particularly important because of their many pleiotropic actions and because they have been identified as potential therapeutic targets in cardiovascular disease. Ang II, ET-1, serotonin and natriuretic peptides mediate effects via specific receptors, which belong to the group of G-protein-coupled receptors. ET, serotonin and Ang II are primarily vasoconstrictors with growth-promoting actions, whereas natriuretic peptides, specifically atrial, brain and C-type natriuretic peptides, are vasodilators with natriuretic effects. Inhibition of vasoconstrictor actions with drugs that block peptide receptors, compounds that inhibit enzymes that generate vasoactive peptides or agents that increase levels of natriuretic peptides are potentially valuable therapeutic tools in the management of cardiovascular diseases. This review focuses on ET, natriuretic peptides and serotonin. The properties and distribution of these vasoactive agents and their receptors, mechanisms of action and implications in cardiovascular (patho)physiology will be discussed.

Endothelin 1, its Endothelin Type A Receptor, Connective Tissue Growth Factor, Platelet-Derived Growth Factor, and Adrenomedullin Expression in Lungs of Pulmonary Hypertensive and Nonhypertensive Chickens

Twenty-four 1-d-old broilers were distributed in 2 groups, pulmonary hypertensive broilers (PHB) and pulmonary nonhypertensive broilers (NPHB), to estimate possible differences between them in the expression of endothelin 1 (ET-1) and its type A receptor, connective tissue growth factor, platelet-derived growth factor, and adrenomedullin expression in the lungs. For this purpose, total RNA extraction and real-time PCR analysis were used. Endothelin 1 mRNA levels in the lungs of PHB were significantly higher than the corresponding level in NPHB (P < 0.001). In contrast, the opposite was true for ET-1 type A receptor mRNA levels (P < 0.001). Connective tissue growth factor mRNA levels in the lungs of PHB were significantly higher than in the lungs of NPHB (P < 0.01). However, no differences were encountered between the 2 groups of broilers in platelet-derived growth factor mRNA expression (P > 0.05). Adrenomedullin mRNA levels in the lungs of PHB were significantly higher than in NPHB (P < 0.01). It has been demonstrated for the first time that ET-1, connective tissue growth factor, and adrenomedullin are upregulated in the lungs of PHB. Furthermore, it is suggested that these peptides may play a major role in pulmonary hypertension pathophysiology. Present data might provide clues for future research directions such as genetic selection and therapeutic intervention to revert the process of pulmonary vasoconstriction and vascular remodeling. Major research goals could be to find endothelium-derived factors that probably trigger endothelial dysfunction, as well as possible interactions with already identified molecules which also intervene in the pulmonary response to hypoxia.

Activation of insulin-like growth factor type-1 receptor is required for H2O2-induced PKB phosphorylation in vascular smooth muscle cells

Evidence accumulated in recent years has revealed a potential role for reactive oxygen species (ROS) in the pathophysiology of cardiovascular diseases. However, the precise mechanisms by which ROS contribute to the development of these diseases are not fully established. Previous work from our laboratory has indicated that exogenous hydrogen peroxide (H2O2) activates several signaling protein kinases, such as extracellular signal-regulated kinase 1 and 2 (ERK1/2) and protein kinase B (PKB) in A10 vascular smooth muscle cells (VSMC). However, the upstream elements responsible for this activation remain unclear. Although a role for epidermal growth factor receptor (EGFR) protein tyrosine kinase (PTK) in H2O2-induced ERK1/2 signaling has been suggested, the contribution of this PTK or other receptor or nonreceptor PTKs to PKB activation is not well defined in VSMC. In this study, we used pharmacological inhibitors to investigate the role of receptor and Src-family-PTKs in H2O2-induced PKB phosphorylation. AG1478, a specific inhibitor of EGFR, failed to attenuate the H2O2-induced increase in PKB Ser473 phosphorylation, whereas AG1024, an inhibitor of insulin-like growth factor type1 receptor (IGF-1R)-PTK, almost completely blocked this response. H2O2 treatment also enhanced tyrosine phosphorylation of the IGF-1Rbeta subunit, which was significantly inhibited by AG1024 pretreatment of cells. Furthermore, pharmacological inhibition of Src by PP2 (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazole(3,4-d) pyrimidine) decreased PKB phosphorylation. Moreover, H2O2-induced PKB phosphorylation was associated with increased tyrosine phosphorylation of c-Src and Pyk2 in an AG1024- and PP2-inhibitable manner. In conclusion, these data provide evidence of the contribution of IGF-1R-PTK in initiating H2O2-evoked PKB phosphorylation in A10 VSMC, with an intermediary role for c-Src and Pyk2 in this process.

Endothelin induces functional hypertrophy of peritubular smooth muscle cells

When chronically stimulated with agonists of contraction, smooth muscle cells (SMCs) undergo cell hypertrophy, a process defined as increase in size and potentiation of the contractile phenotype in the absence of proliferation. Hypertrophic response has long been associated to a number of pathologies of the cardiovascular and respiratory systems. We have investigated the phenotypic and functional response of SMCs to long-term treatment with endothelin. Our model was primary cultures of peritubular smooth muscle cells (PSMC) a testicular cell type target of locally produced endothelin and characterized by an unusual phenotypic stability when cultured in simple medium in complete absence of serum. We report the following responses of PSMC to 4-day exposure to ET-1: (i) increased protein synthesis without induction of cell proliferation; (ii) increase in cell size (evaluated by means of flow cytometry) and increased expression of SM-alpha-actin, desmin, caldesmon and calponin, markers of the contractile phenotype. In experiments of selective stimulation of either ETA or ETB receptor subtypes, both proved to be involved in inducing the observed hypertrophic responses. The hypertrophic cells exhibit the ultrastructural features of differentiated SMCs and are capable of calcium mediated contractile response when acutely stimulated with ET-1 specifically through ETA and/or ETB receptors, as evaluated by calcium imaging and scanning electron microscopy. These observations demonstrate that engagement of ET receptors is capable of inducing potentiation of the contractile phenotype and functional hypertrophy of PSMC.

Review: Insulin and endothelin: an interplay contributing to hypertension development?

CONTEXT

The aim of this article was to review the existing data on the interactions among insulin, insulin resistance, and endothelin and how those contribute to the development of hypertension in insulin-resistant states.

EVIDENCE ACQUISITION

A literature search of MEDLINE database was performed to identify English-language articles published during the last 20 yr. Search terms used were endothelin, insulin, insulin resistance, and hyperinsulinemia in combination with blood pressure and hypertension. Reference lists of retrieved articles were also evaluated for relevant information.

EVIDENCE SYNTHESIS

Several mechanisms connect insulin resistance and compensatory hyperinsulinemia with blood pressure elevation in the context of the metabolic syndrome, i.e. sodium retention, sympathetic activation, and impairment of endothelial nitric oxide production. Accumulating evidence suggests that activation of the endothelin system seems to be another important, yet less discussed, mechanism. In vitro studies have shown that insulin stimulates both endothelin-1 production and action on the vascular wall. In vivo, high levels of insulin result in increase in circulating endothelin-1 in healthy individuals, and this effect is also seen in insulin-resistant subjects, a relationship not observed with nitric oxide production. Moreover, endothelin receptor antagonism effectively reduces blood pressure in animal models of insulin resistance and hypertension. On the other hand, elevation of endothelin-1 levels can further increase insulin resistance, forming possibly a deleterious circle.

CONCLUSIONS

Endothelin-1 may play a crucial role in the pathogenesis of hypertension in insulin-resistant states. Future research should examine the potential of endothelin receptor antagonism to help blood pressure control in patients with insulin resistance.

Pathophysiological role of endothelin in ectopic ossification of human spinal ligaments induced by mechanical stress

Ossification of the posterior longitudinal ligament (OPLL) of the spine is characterized by progressive ectopic bone formation in the spinal ligament. To identify the genes related to ossification affected by mechanical stress during OPLL, analyses using cDNA microarray were carried out using cultured human spinal ligament cells that had been subjected to uniaxial cyclic stretching. Samples were obtained from a total of 14 patients: seven cervical or thoracic OPLL patients and seven control patients. Spinal ligament cells derived from tissues of OPLL (OPLL cells) and control (non-OPLL cells) patients were subjected to uniaxial sinusoidal cyclic stretching (0.5 Hz, 20% stretch) for various time periods (0-9 hours). cDNA microarrays revealed that ranges of distribution of both up- and downregulated genes evoked by cyclic stretching were significantly wider in OPLL cells than in non-OPLL cells. Increases in the mRNA expression of endothelin-1 (ET-1) as well as various marker genes related to ossification were also observed. mRNA expression of ET-1 and alkaline phosphatase was increased by mechanical stress in a time-dependent manner, while addition of ET-1 to static cultures of OPLL cells increased mRNA expression of alkaline phosphatase in a dose-dependent manner. During 9 hours of cyclic stretching, ET-1 release increased to about sixfold the amount observed in nonstretched cells. In non-OPLL cells, neither cyclic stretching nor ET-1 induced any increase in alkaline phosphatase expression. These results suggest that mechanical stress promotes the progression of ossification in OPLL cells through autocrine and/or paracrine mechanisms of ET-1.

Embryonic lethality in Dear gene-deficient mice: new player in angiogenesis

The dual endothelin-1/angiotensin II receptor (Dear) binds endothelin-1 (ET-1) and angiotensin II (ANG II) with equal affinities in the Dahl S/JRHS rat strain. To elucidate its physiological significance within the context of multiple receptor isoforms and diverse ET-1 and ANG II functions spanning blood pressure regulation, tumor proliferation, and angiogenesis, we characterized mouse Dear and Dear-deficient mice. Unlike null mutant models of ET-1, ANG II, and all other ET-1 and ANG II receptors, Dear(-/-) deficiency results in impaired angiogenesis, dysregulated neuroepithelial development, and embryonic lethality by embryonic day 12.5. Interestingly, mouse Dear does not bind ANG II, similar to Dahl R/JRHS rat Dear, but binds ET-1 and vascular endothelial growth factor (VEGF) signal peptide (VEGFsp) with equal affinities, suggesting a putative novel multifunction for VEGFsp and a parsimonious mechanism for coordination of VEGF-induced and Dear-mediated pathways. Consistent with its developmental angiogenic role, Dear inhibition results in decreased tumor growth in B16-F10 melanoma cell-induced subcutaneous tumor in female Dear(+/-)/C57BL6BC10 mice, but not in males (age 3.5 mo), and in 127Cs radiation-induced orthotopic mammary tumors in Sprague-Dawley female rats (age range 3-6.5 mo). Altogether, the data identify Dear as a new player in angiogenesis during development downstream to, and nonredundant with, VEGF-mediated pathways, as well as a putative modulator of tumor angiogenesis acting within a gender-specific paradigm.

Effects of chronic cold exposure on the endothelin system

Cold temperatures have adverse effects on the human cardiovascular system. Endothelin (ET)-1 is a potent vasoconstrictor. We hypothesized that cold exposure increases ET-1 production and upregulates ET type A (ETA) receptors. The aim of this study was to determine the effect of cold exposure on regulation of the ET system. Four groups of rats (6–7 rats/group) were used: three groups were exposed to moderate cold (6.7 ± 2°C) for 1, 3, and 5 wk, respectively, and the remaining group was maintained at room temperature (25°C) and served as control. Cold exposure significantly increased ET-1 levels in the heart, mesenteric arteries, renal cortex, and renal medulla. Cold exposure increased ETA receptor protein expression in the heart and renal cortex. ET type B (ETB) receptor expression, however, was decreased significantly in the heart and renal medulla of cold-exposed rats. Cold exposure significantly increased the ratio of ETA to ETB receptors in the heart. An additional four groups of rats (3 rats/group) were used to localize changes in ETA and ETB receptors at 1, 3, and 5 wk of cold exposure. Immunohistochemical analysis showed an increase in ETA, but a decrease in ETB, receptor immunoreactivity in cardiomyocytes of cold-exposed rats. Increased ETA receptor immunoreactivity was also found in vascular smooth muscle cells of cold-exposed rats. Cold exposure increased ETA receptor immunoreactivity in tubule epithelial cells in the renal cortex but decreased ETB receptor immunoreactivity in tubule epithelial cells in the renal medulla. Therefore, cold exposure increased ET-1 production, upregulated ETA receptors, and downregulated ETB receptors.

Atrasentan: targeting the endothelin axis in prostate cancer

Endothelin axis deregulation triggers a series of events that lead to a profound deregulation in cancer cells, including key tumorigenic cellular events such as proliferation, invasion, escape from programmed cell death, new vessel formation, abnormal osteogenesis and the alteration of nociceptive stimuli. Atrasentan is a novel agent that effectively targets this pathway and is able to inhibit and/or reverse several of those events. Biological and clinical activity in patients with prostate cancer has been demonstrated in a Phase III clinical setting by the suppression of markers of biochemical and clinical prostate cancer progression, and by a delay in time to disease progression, especially in patients with bone disease.

Elastic fibres and vascular structure in hypertension

Blood vessels are dynamic structures composed of cells and extracellular matrix (ECM), which are in continuous cross-talk with each other. Thus, cellular changes in phenotype or in proliferation/death rate affect ECM synthesis. In turn, ECM elements not only provide the structural framework for vascular cells, but they also modulate cellular function through specific receptors. These ECM-cell interactions, together with neurotransmitters, hormones and the mechanical forces imposed by the heart, modulate the structural organization of the vascular wall. It is not surprising that pathological states related to alterations in the nervous, humoral or haemodynamic environment-such as hypertension-are associated with vascular wall remodeling, which, in the end, is deleterious for cardiovascular function. However, the question remains whether these structural alterations are simply a consequence of the disease or if there are early cellular or ECM alterations-determined either genetically or by environmental factors-that can predispose to vascular remodeling independent of hypertension. Elastic fibres might be key elements in the pathophysiology of hypertensive vascular remodeling. In addition to the well known effects of hypertension on elastic fibre fatigue and accelerated degradation, leading to loss of arterial wall resilience, recent investigations have highlighted new roles for individual components of elastic fibres and their degradation products. These elements can act as signal transducers and regulate cellular proliferation, migration, phenotype, and ECM degradation. In this paper, we review current knowledge regarding components of elastic fibres and discuss their possible pathomechanistic associations with vascular structural abnormalities and with hypertension development or progression.

Atrasentan: a novel and rationally designed therapeutic alternative in the management of cancer

Endothelin axis deregulation triggers a series of events that ultimately activate proliferation, invasion, escape from programmed cell death, new vessel formation, abnormal osteogenesis and alteration of nociceptive stimuli. Atrasentan is a novel agent that effectively targets this pathway and is able to inhibit and/or reverse several of those events. Biologic and clinical activity in patients with prostate cancer has been demonstrated in a Phase III, placebo-controlled setting by the suppression of markers of biochemical prostate cancer progression and a delay in time to disease progression. Atrasentan represents a new therapeutic option in the management of prostate cancer, especially in those patients with bone metastases. However, its precise role in other diseases such as ovarian cancer is yet to be defined.

Reversal of cardiac dysfunction by selective ET-A receptor antagonism

The effectiveness of a selective endothelin receptor-A (ET-A) antagonist, A-127722 (approximately 10 mg kg(-1) day(-1) as 200 mg kg(-1) powdered food), to reverse existing cardiac remodelling and prevent further remodelling was tested in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Uninephrectomised rats (UNX) administered DOCA (25 mg every fourth day s.c.) and 1% NaCl in drinking water for 28 days developed hypertension (systolic blood pressure (BP): UNX 128+/-6 mmHg, DOCA-salt 182+/-5* mmHg; *P<0.05 vs UNX), left ventricular hypertrophy (UNX 1.99+/-0.06 mg kg(-1) body wt, DOCA-salt 3.30+/-0.08* mg kg(-1) body wt), decreased left ventricular internal diameter (UNX 6.69+/-0.18 mm, DOCA-salt 5.51+/-0.37* mm), an increased left ventricular monocyte/macrophage infiltration together with an increased interstitial collagen from 2.7+/-0.3 to 11.7+/-1.3%, increased passive diastolic stiffness (UNX 21.1+/-0.5, DOCA-salt 30.1+/-1.3*), prolongation of the action potential duration at 20 and 90% of repolarisation (APD20-UNX 6.8+/-1.1, DOCA-salt 10.1+/-1.5* ms; APD90-UNX 34.4+/-3.5 ms, DOCA-salt 64.3+/-10.4* ms) and vascular dysfunctions (2.6-fold decrease in maximal contractile response to noradrenaline, 3.5-fold decrease in maximal relaxation response to acetylcholine). Administration of A-127722 for 14 days starting 14 days after surgery attenuated the increases in systolic BP (150+/-6** mmHg, **P<0.05 vs DOCA-salt), left ventricular wet weight (2.65+/-0.06** mg kg(-1) body wt) and internal diameter (6.39+/-0.31** mm), prevented left ventricular monocyte/macrophage accumulation, attenuated the increased left ventricular interstitial collagen (7.6+/-1.3%**), reversed the increased passive diastolic stiffness (22.1+/-1.2**), attenuated the action potential duration prolongation (APD20 - 7.6+/-1.4**, APD90 - 41.5+/-6.9** ms) and normalised changes in vascular function. ET-A receptor antagonism both reverses and prevents the cardiac and vascular remodelling in DOCA-salt hypertension and improves cardiovascular function.

Gene array profiling of large hypothalamic CNS regions in lactating and randomly cycling virgin mice

A dramatic example of neuronal and physiological plasticity in adult mammals occurs during the transition from a non-maternal to a maternal, lactating state. In this study, we compared gene expression within a large continuous region of the CNS involved in maternal behaviors (hypothalamus, preoptic regions, and nucleus accumbens) between lactating (L) (postpartum Day 7) and randomly cycling virgin (V) outbred mice. Using high-density oligonucleotide arrays representing 11,904 genes, two statistical algorithms were used to identify significant differences in gene expression: robust multiarray (P < 0.001) (n = 92 genes) and significance analysis of microarrays using a 10% false discover rate (n = 114 genes). 27 common genes were identified as significant using both techniques. A subset of genes (n = 5) were selected and examined by real-time PCR. Our findings were consistent with previous published work. For example, neuropeptide Y (NPY) and proenkephalin were elevated in L mice, whereas POMC was decreased. Increased levels of NPY Y2 receptor and polo-like kinase and decreased levels of endothelin receptor type b in L mice are examples of novel gene expression changes not previously identified. Expression differences occurred in broad classes. Together, our findings provide possible new material on gene expression changes that may support maternal behaviors. The advantages and drawbacks of sampling large CNS regions using arrays are discussed.

The vascular endothelin system in hypertension--recent patents and discoveries

The discovery of endothelin two decades ago has now evolved into an intricate vascular endothelin (ET) system. Several ET isoforms, receptors, signaling pathways, agonists, antagonists, and clinical applications have been identified and documented in first-rate patents. The role of ET as one of the most potent endothelium-derived vasoconstricting factors is now complemented by a newly discovered role in vascular relaxation. ET synthesis is initiated by the transcription of ET genes in endothelial cells and the generation of the gene products preproET and big ET, which are further cleaved by specific ET converting enzymes into ET-1, -2, -3 and -4 isoforms. ET isoforms bind with different affinities to ET(A) and ET(B2) receptors in vascular smooth muscle, and stimulate [Ca(2+)](i), protein kinase C, mitogen-activated protein kinase and other signaling mechanisms of smooth muscle contraction, growth and proliferation. ET also binds to endothelial ET(B1) receptors, which mediate the release of vasodilator substances such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor. Endothelial ET(B1) receptors may also function in ET re-uptake and clearance. Although the effects of ET on vascular function and growth are well-recognized, the role of ET and its receptors in the regulation of blood pressure and in the pathogenesis of hypertension is not clearly established. Salt-dependent hypertension in experimental animals and some forms of moderate to severe hypertension in human may show elevated levels of plasma or vascular ET; however, other forms of hypertension show normal ET levels. The currently available ET receptor antagonists reduce blood pressure in some forms of experimental hypertension. Careful examination of recent patents may identify more effective and specific modulators of the vascular ET system for clinical use in human hypertension.

Pharmacological efficacy of CPU 86017 on hypoxic pulmonary hypertension in rats: mediated by direct inhibition of calcium channels and antioxidant action, but indirect effects on the ET-1 pathway

Endothelin-1 (ET-1) plays a key role in the pathogenesis of pulmonary hypertension. The present study was conducted to examine the effects of a novel compound p-chlorobenzyltetrahydroberberine (CPU 86017) on endothelin-1 system of hypoxia-induced pulmonary hypertension in rats. SD male rats were divided into control, untreated pulmonary hypertension, nifedipine (10 mg/kg p.o.), and CPU 86017 (80, 40, and 20 mg/kg p.o.) groups. The pulmonary hypertension was established by housing the rats in a hypoxic (10 +/- 0.5% oxygen) chamber 8 hours per day for 4 weeks. Hemodynamic and morphologic assessment exhibited a significant increase in the central vein pressure (CVP), right ventricular systolic pressure (RVSP), and pulmonary arteriole remodeling in the pulmonary hypertensive rats, which were improved by CPU 86017 80 and 40 mg/kg administration (P < 0.01). The elevated pulmonary endothelin-1 level and the over-active preproET-1 and iNOS mRNA expression were also decreased significantly (P < 0.01) in CPU 86017 groups. The maladjustment of redox enzyme system in pulmonary hypertension rats was corrected after treatment. We concluded that CPU 86017 improves pulmonary hypertension mainly to suppress the endothelin-1 pathway at the upstream and downstream via calcium antagonism and antioxidative action, then, resulting in a relief in pathogenesis of the disease.

Angiotensin-II type 1 receptor-mediated hypertension in D4 dopamine receptor-deficient mice

Dopamine receptors are important in systemic blood pressure regulation. D4 receptors are expressed in the kidney and brain, but their role in cardiovascular regulation is unknown. In pentobarbital-anesthetized mice, systolic and diastolic blood pressures were elevated in sixth-generation D4 receptor-deficient (D4(-/-)) mice and in tenth-generation D4(-/-) mice compared with D4 wild-type (D4(+/+)) littermates. The conscious blood pressures measured via a chronic arterial (femoral) catheter or telemetry (carotid) were also higher in D4(-/-) mice than in D4 littermates. Basal renal and plasma renin concentrations were similar in the 2 mouse strains. The protein expression of angiotensin II type 1 receptor was increased in homogenates of kidney (330+/-53%, n=5) and brain (272+/-69%, n=5) of D4(-/-) mice relative to D4(+/+) mice (kidney: 100+/-12%, n=5; brain: 100+/-32%, n=5). The expression of the receptor in renal membrane was also increased in D4(-/-) mice (289+/-28%, n=8) relative to D4(+/+) mice (100+/-14%, n=10). In contrast, the expression in the heart was similar in the 2 strains. Bolus intravenous injection of angiotensin II type 1 receptor antagonist losartan initially decreased mean arterial pressures to a similar degree in D4(-/-) and D4(+/+) littermates. However, the hypotensive effect of losartan dissipated after 10 minutes in D4(+/+) mice, whereas the effect persisted for >45 minutes in D4(-/-) mice. We conclude that the absence of the D(4) receptor increases blood pressure, possibly via increased angiotensin II type 1 receptor expression.

Endothelin-1 in plasma, cisternal CSF and microdialysate following aneurysmal SAH

OBJECTIVE

Endothelin-1 (ET-1) is postulated to play an important role in the development of cerebral vasospasm (CVS) following SAH. This study was conducted to investigate the time course of ET-release in three different sources: CSF, plasma and microdialysate.

METHODS

In a prospective study ET-1-concentrations were measured in plasma, cisternal CSF and microdialysate in 20 patients with aneurysmal SAH for at least 8 days after hemorrhage.

RESULTS

ET-1 concentration in microdialysate was almost four times higher compared to CSF and plasma. (p<0.001) Only in CSF ET-1-release showed a significant increase over time with highest values on day 5 post ictus (p = 0.03). This was parallel to the increase of transcranial Doppler velocities. ET-1 in plasma and microdialysate did not change over time.

CONCLUSION

ET-1 may have a different biological function in different biological tissues. Only ET-1 in CSF seemed to be associated with CVS.

Aberrant ETB receptor regulation of AT1 receptors in immortalized renal proximal tubule cells of spontaneously hypertensive rats

BACKGROUND

The renin-angiotensin and endothelin systems interact to regulate blood pressure, in part, by affecting sodium transport in the kidney. Because angiotensin II type 1 (AT(1)) receptor activation increases ETB receptor expression in renal proximal tubule cells from Wistar-Kyoto (WKY) rat, we hypothesize that ETB receptor activation may also regulate AT(1) receptor expression. Furthermore, ETB receptor regulation of the AT(1) receptor may be different in the WKY and spontaneously hypertensive rat (SHR).

METHOD

AT(1) and ETB receptors were studied in immortalized renal proximal tubule cells from WKY and SHRs, using immunoblotting, confocal microscopic colocalization, and immunoprecipitation.

RESULTS

In WKY renal proximal tubule cells, an ETB receptor agonist, BQ3020, decreased AT(1) receptor protein in a time- and concentration-dependent manner [median effective concentration (EC(50)) = 3.2 x 10(-10) mol/L, t(1/2)= 15 hours]. The inhibitory effect of BQ3020 (10(-8) mol/L/24 hours) on AT(1) receptor protein was blocked by an ETB receptor antagonist (BQ788). However, BQ3020 (10(-8) mol/L/24 hours) increased ETB receptor protein in WKY renal proximal tubule cells. In contrast, in SHR renal proximal tubule cells, BQ3020 (10(-8) mol/L/24 hours) no longer affected AT(1) or ETB receptor protein. AT(1)/ETB receptors colocalized and coimmunoprecipitated in WKY and SHRs. BQ3020 (10(-8) mol/L/15 minutes) treatment had no effect on AT(1)/ETB coimmunoprecipitation in WKY but decreased it in SHRs. BQ3020 (10(-8) mol/L/15 minutes) treatment increased AT(1) receptor phosphorylation in WKY, but decreased it in SHRs.

CONCLUSION

ETB receptors regulate AT(1) receptors by direct physical receptor interaction and receptor expression. An impaired ETB receptor regulation of the AT(1) receptor may participate in the pathogenesis of high blood pressure in the SHR.

Endothelin A antagonist LU-135252 and trandolapril in the treatment of the Cohen-Rosenthal diabetic hypertensive rat

BACKGROUND

Hypertension and non-insulin-dependent diabetes mellitus (NIDDM) often occur simultaneously and the combination requires vigorous control of hypertension. This can generally be achieved by a combination of antihypertensive drugs. The present study examines the antihypertensive and possible hypoglycemic effects of combined therapy with endothelin A (ETA) receptor antagonist LU-135252 and angiotensin-converting enzyme (ACE) inhibitor trandolapril in male Cohen-Rosenthal Diabetic Hypertensive (CRDH) rats.

METHODS

Rats were divided into four groups as follows: group I served as control; group II--LU-135252 30 mg/kg/day; group III--trandolapril 0.1 mg/kg/day and group IV--both LU-135252 30 mg/kg/day and trandolapril 0.1 mg/kg/day. Systolic blood pressure (SBP) and plasma glucose levels were evaluated at the beginning of the experiment and after 2, 4 and 6 weeks.

RESULTS

SBP decreased significantly in all treated groups after 2, 4 and 6 weeks of treatment compared to baseline. Maximum decrease was in group IV (combination) from 174.8+/-3.7 to 136.1+/-2.4 mmHg (22%) (p<0.0001); in group III (trandolapril) from 165.8+/-2.7 to 137.5+/-2.9 mmHg (17%) (p=0.0002); and in group II (LU-135252) and from 169.1+/-3.1 to 147.8+/-2.5 mmHg (12%) (p=0.0004). Glucose levels in plasma decreased significantly after 6 weeks of treatment. Maximum decrease was in group IV: from 501.0+/-42.8 to 178.6+/-7.3 mg/dl (62%) (p<0.0001); in group III from 428.2+/-47.7 to 146.8+/-5.6 mg/dl (63%) (p<0.0001); and in group II from 491.2+/-39.3 to 272.2+/-28.3 mg/dl (42%) (p=0.0002).

CONCLUSION

The SBP decrease was additive when both drugs were given together. Thus, combination of ETA antagonist and ACE inhibitor appears to offer a rational fixed-dose antihypertensive therapy, which is superior to that of either drug alone. The decrease in glucose level, which was the least impressive while on LU-135252 alone, was more prominent during combination after 2 weeks, although without further decrease.

Vascular protection by dietary polyphenols

Consumption of polyphenol-rich foods, such as fruits and vegetables, and beverages derived from plants, such as cocoa, red wine and tea, may represent a beneficial diet in terms of cardiovascular protection. Indeed, epidemiological studies demonstrate a significant inverse correlation between polyphenol consumption and cardiovascular risk. Among the numerous plausible mechanisms by which polyphenols may confer cardiovascular protection, improvement of the endothelial function and inhibition of angiogenesis and cell migration and proliferation in blood vessels have been the focus of recent studies. These studies have indicated that, in addition to and independently from their antioxidant effects, plant polyphenols (1) enhance the production of vasodilating factors [nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF) and prostacyclin] and inhibit the synthesis of vasoconstrictor endothelin-1 in endothelial cells; and (2) inhibit the expression of two major pro-angiogenic factors, vascular endothelial growth factor (VEGF) and matrix metalloproteinase-2 (MMP-2) in smooth muscle cells. The mechanisms of these effects involve: (1) in endothelial cells, increased Ca(2+) level and redox-sensitive activation of the phosphoinositide 3 (PI3)-kinase/Akt pathway (leading to rapid and sustained activation of nitric oxide synthase and formation of EDHF) and enhanced expression of nitric oxide synthase; and (2) in smooth muscle cells, both redox-sensitive inhibition of the p38 mitogen-activated protein kinase (p38 MAPK) pathway activation (leading to inhibition of platelet-derived growth factor (PDGF)-induced VEGF gene expression) and redox-insensitive mechanisms (leading to inhibition of thrombin-induced MMP-2 formation). The current evidence suggests that all these mechanisms are triggered by polyphenols with specific structures, although the structural requirements may be different from one effect to the other, and that they all contribute to the vasoprotective, anti-angiogenic, anti-atherogenic, vasorelaxant and anti-hypertensive effects of acute or chronic administration of plant polyphenols found in vivo in animals and in patients.

Augmented Endothelin Vasoconstriction in Intermittent Hypoxia-Induced Hypertension

We reported previously that simulating sleep apnea in rats by exposing them 7 hours per day to intermittent hypoxia/hypercapnia (IH) elevates plasma endothelin-1 and causes hypertension, which is reversed by an endothelin-1 antagonist. We hypothesized that in this model of sleep apnea–induced hypertension, vascular sensitivity to endothelin-1 is increased in combination with the elevated plasma endothelin-1 to cause the endothelin-1–dependent hypertension. In small mesenteric arteries with endothelial function disabled by passing air through the lumen, diameter and vessel wall [Ca 2+ ] were recorded simultaneously. IH arteries demonstrated increased constrictor sensitivity to endothelin-1 (percentage max constriction 100±0% IH versus 80±10% Sham; P <0.05). This was accompanied by increased calcium sensitivity of IH arteries. In contrast, constrictor sensitivity and increases in vessel wall [Ca 2+ ] to KCl and phenylephrine were not different between IH and Sham arteries. We have shown previously that endothelin-1 constriction in mesenteric arteries is mediated by endothelin A receptors. In the current study, the selective increase in endothelin-1 constriction in IH resistance arteries was accompanied by increased expression of endothelin A receptor expression (densitometry units 271±23 IH versus 158±25 Sham; P <0.05). Thus, IH hypertension appears to cause alterations in signaling components unique to endothelin-1 at the receptor level and in postreceptor signaling that increases calcium sensitivity during endothelin A activation. Future studies will determine the specific changes in vascular smooth muscle signaling in IH hypertension causing this augmented contractile phenotype.