Selective Endothelin Research Articles

Change in pharmacological effect of endothelin receptor antagonists in rats with pulmonary hypertension: Role of ET B-receptor expression levels

Background and purpose The endothelin (ET) system is activated in pulmonary arterial hypertension (PAH). The therapeutic value of pharmacological blockade of ET receptors has been demonstrated in various animal models and led to the current approval and continued development of these drugs for the therapy of human PAH. However, we currently incompletely comprehend what local modifications of this system occur as a consequence of PAH, particularly in small resistance arteries, and how this could affect the pharmacological response to ET receptor antagonists with various selectivities for the receptor subtypes. Therefore, the purposes of this study were to evaluate potential modifications of the pharmacology of the ET system in rat pulmonary resistance arteries from monocrotaline (MCT)-induced pulmonary arterial hypertension. Experimental approach ET-1 levels were quantified by ELISA. PreproET-1, ET A and ET B receptor mRNA expressions were quantified in pulmonary resistance arteries using Q-PCR, while protein expression was evaluated by Western blots. Reactivity to ET-1 of isolated pulmonary resistance arteries was measured in the presence of ET A (A-147627), ET B (A-192621) and dual ET A/B (bosentan) receptor antagonists. Key results In rats with PAH, plasma ET-1 increased ( p < 0.001) while pulmonary levels were reduced ( p < 0.05). In PAH arteries, preproET-1 ( p < 0.05) and ET B receptor ( p < 0.001) gene expressions were reduced, as were ET B receptor protein levels ( p < 0.05). ET-1 induced similar vasoconstrictions in both groups. In arteries from sham animals, neither bosentan nor the ET A or the ET B receptor antagonists modified the response. In arteries from PAH rats, however, bosentan and the ET A receptor antagonist potently reduced the maximal contraction, while bosentan also reduced sensitivity ( p < 0.01). Conclusions and implications The effectiveness of both selective ET A and dual ET A/B receptor antagonists is markedly increased in PAH. Down-regulation of pulmonary resistance arteries ET B receptor may contribute to this finding.

ETA Receptor Blockade With Atrasentan Prevents Hypertension With the Multitargeted Tyrosine Kinase Inhibitor ABT-869 in Telemetry-instrumented Rats

ABT-869 is a novel multitargeted inhibitor of vascular endothelial growth factor and platelet-derived growth factor receptor tyrosine kinases (RTKs) with potent antiangiogenic properties that slow tumor progression. Vascular endothelial growth factor receptor blockade has been shown to produce hypertension. Atrasentan is a potent and selective endothelin (ETA) receptor antagonist that lowers blood pressure and affects tumor growth. To assess the utility of ETA receptor blockade in controlling hypertension with RTK inhibition, we evaluated the ability of atrasentan to block hypertension with ABT-869 in conscious, telemetry-instrumented rats. Changes in mean arterial pressure (MAP) and heart rate (HR) were evaluated using mean values and the area under the curve (AUC). Atrasentan (0.5, 1.5, and 5.0 mg kg(-1) d(-1) for 5 days) elicited dose-dependent decreases in MAP-AUC (-16.7 +/- 1.3, -20.94 +/- 3.68, and -30.12 +/- 3.57 mm Hg x day, respectively) compared with vehicle. ABT-869 (1, 3, 10, 30 mg kg(-1) d(-1) for 5 days) increased MAP compared with vehicle (MAP-AUC values of -5.52 +/- 3.75, 12.7 +/- 8.4, 37.5 +/- 4.4, and 63.8 +/- 3.3 mm Hg x day, respectively). Pretreatment with atrasentan (5 mg/kg for 5 days) prevented and abolished the hypertensive effects of ABT-869. Thus, ETA receptor blockade effectively alleviated hypertension with RTK inhibition and may serve a dual therapeutic role by preventing hypertension and slowing tumor progression.

Successful switch to sitaxsentan in a patient with HIV-related pulmonary arterial hypertension and late intolerance to nonselective endothelin receptor blockade

Pulmonary arterial hypertension [PAH] is a rare but well-known cardiovascular condition potentially associated with human immunodeficiency virus [HIV] infection and is currently recognized to be one of the most ominous noninfectious HIV complications. Although there is no clear evidence supporting the use of any medication for the treatment of HIV-related PAH, many of the currently available agents have been shown to exert some clinical benefits HIV-PAH patients. To date, no data are available regarding the potential effects of sitaxsentan, a selective endothelin type-A receptor antagonist, in this peculiar patient population. We report the case of a successful switch to sitaxsentan in a HIV-infected patient with PAH initially receiving bosentan who developed a late treatment-related side-effect.

Endothelin A Receptor Blockade Influences Apoptosis and Cellular Proliferation in the Developing Rat Kidney

Endothelin systems are believed to play important roles in the emergence and maintenance of functions of various organs during perinatal development, including the kidney. The present study was designed to investigate the roles of endothelin systems on physiologic renal growth and development. Newborn rat pups were treated with either Bristol-Myers Squibb-182874 (30 mg/kg/day), a selective endothelin A receptor (ETAR) antagonist, or vehicle for 7 days. To identify cellular changes, kidneys were examined for apoptotic cells by terminal deoxynucleotide transferase-mediated nick-end labeling stain and proliferating cell nuclear antigen (PCNA) by immunohistochemical (IHC) stain. To clarify the molecular control of these processes, immunoblots and reverse transcriptase-polymerase chain reaction for Clusterin, Bcl-2, Bcl-XL, Bax, and p53 were performed. ETAR antagonist treatment resulted in reduced kidney weights, decreased PCNA-positive proliferating cells, and increased apoptotic cells. The protein expressions of renal Bcl-XL and Bax in the ETAR antagonist-treated group were significantly decreased, whereas the mRNA expressions of these genes were not changed. There were no significant differences in the expressions of Clusterin, Bcl-2, and p53. In conclusion, inhibition of endogenous endothelins impairs renal growth, in which decreased cellular proliferation, increased apoptosis and decreased expressions of renal Bcl-XL and Bax are possibly implicated.

Endothelin antagonist for the treatment of resistant hypertension

Introduction: More aggressive lowering of blood pressure (BP) is widely considered an important strategy in reducing cardiovascular morbidity and mortality, yet despite increased awareness and extensive use of combination therapy, recommended BP goals are frequently not achieved. Resistant hypertension is defi ned as the failure to achieve guideline-recommended BP goals in patients who are adherent to an appropriate three-drug regimen including a diuretic. The prevalence of resistant hypertension, probably less than 5% in an unselected hypertensive population, may be as high as 50% in patients followed in specialty referral clinics. Thus additional therapeutic modalities are needed. Endothelin receptor antagonists (ERAs) have been shown to have modest antihypertensive effects in prior studies, particularly in patients with more severe hypertension. Darusentan, a selective endothelin type A receptor ERA, has been effective and well tolerated, and the authors hypothesized that, because it lowers BP by a different mechanism than other classes, it might be useful as add-on therapy in patients with resistant hypertension.

Chymase-Dependent Conversion of Big Endothelin-1 in the Mouse in Vivo

The aim of this study was to identify the role of chymase in the conversion of exogenously administered Big endothelin-1 in the mouse in vivo. Real-time polymerase chain reaction analysis detected mRNA of mucosal mast cell chymases 4 and 5, endothelin-converting enzyme 1a, and neutral endopeptidase 24.11 in pulmonary, cardiac, and aorta homogenates derived from C57BL/6J mice, with the latter tissue expressing the highest levels of both chymase isoforms. Furthermore, hydrolysis of a fluorogenic peptide substrate, Suc-Leu-Leu-Val-Tyr-7-amino-4-methylcoumarin, was sensitive to the chymase inhibitors Suc-Val-Pro-Phe(P)(OPh)(2) (200 microM) and chymostatin [(S)-1-carboxy-2-phenylethyl]-carbamoyl-alpha-[2-iminohexahydro-4(S)-pyrimidyl]-(S)-Gly-X-Phe-al, where X can be the amino acid Leu, Val, or Ile) (100 microM) in supernatants extracted from the same tissue homogenates. In anesthetized mice, Big endothelin-1, endothelin-1 (1-31), and endothelin-1 triggered pressor responses (ED(50)s, 0.67, 0.89, and 0.16 nmol/kg) that were all reduced or potentiated by selective endothelin ET(A) or ET(B) receptor antagonists, respectively, BQ-123 (cyclo[D-Asp-Pro-D-Val-Leu-D-Trp]) or BQ-788 (N-[N-[N-[(2,6-dimethyl-1-piperidinyl)carbonyl]-4-methyl-l-leucyl]-1-(methoxycarbonyl)-D-tryptophyl]-d-norleucine sodium salt), each at 1 mg/kg. The pressor responses to big endothelin-1 were significantly reduced by the neutral endopeptidase inhibitor thiorphan (dl-3-mercapto-2-benzylpropanoylglycine) (1 mg/kg) or the endothelin-converting enzyme inhibitor CGS 35066 [alpha-[(S)-(phosphonomethyl)amino]-3-dibenzofuranopropanoic acid] (0.1 mg/kg). In contrast, the responses to endothelin-1 (1-31) were abolished by thiorphan but unaffected by CGS 35066. In addition, Suc-Val-Pro-Phe(P)(OPh)(2) (20-40 mg/kg) reduced, by more than 60%, the hemodynamic response to big endothelin-1 but not to endothelin-1 (1-31) and endothelin-1. Finally, intravenous administration of big endothelin-1 induced Suc-Val-Pro-Phe(P)-(OPh)(2)-sensitive increases in plasma-immunoreactive levels of endothelin-1 (1-31) and endothelin-1. The present study suggests that chymase plays a pivotal role in the conversion and cardiovascular properties of big endothelin-1 in vivo.

Phase 3, randomized, controlled trial of atrasentan in patients with nonmetastatic, hormone‐refractory prostate cancer

Atrasentan is a potent, oral, selective endothelin-A (ET(A)) receptor antagonist that has clinical activity in patients with hormone-refractory prostate cancer (HRPC). In this article, the authors report the results from a phase 3, randomized, double-blind, placebo-controlled trial of atrasentan in patients with nonmetastatic HRPC. Of 941 patients who had adequate androgen suppression and no radiographic evidence of metastases but rising prostate-specific antigen (PSA) levels, 467 patients were randomized to receive atrasentan at a dose of 10 mg, and 474 patients were randomized to receive placebo daily. The primary endpoint was the time to disease progression (TTP), which was defined as the onset of metastases. Secondary endpoints were the time to PSA progression, change in bone alkaline phosphatase (BALP) levels, PSA doubling time, and overall survival. There was a 93-day delay in the median TTP with atrasentan, but the difference from placebo in TTP was not statistically significant (P= .288). Large geographic differences in the median TTP were noted: in the US: The difference was 81 days longer with placebo; whereas, in non-US sites, the difference was 180 days longer with atrasentan. Atrasentan lengthened the PSA doubling time (P= .031) and slowed the increase in BALP (P< .001). The median survival was 1477 days with atrasentan and 1403 days with placebo. The most common adverse events associated with atrasentan were peripheral edema, nasal congestion, and headache, consistent with the vasodilatory properties of ET(A) receptor antagonists. Although the primary endpoint was not achieved, large regional differences in TTP were noted, suggesting that trial conduct may have influenced the results. The biologic activity was consistent with findings from other clinical trials of atrasentan in HRPC.

The Endothelin-Converting Enzyme-1/Endothelin-1 Pathway Plays a Critical Role in Inflammation-Associated Premature Delivery in a Mouse Model

Premature delivery occurs in 12% of all births and accounts for nearly half of long-term morbidity. Current therapeutic approaches to preterm delivery are ineffective and present serious risks to both mother and fetus. The single most common cause of preterm birth is infection. Previous in vitro investigations have shown that endothelin-1 (ET-1) is induced by inflammatory cytokines and that it increases myometrial smooth muscle tone. Furthermore, we have previously shown that both the endothelin-converting enzyme-1 (ECE-1) inhibitor, phosphoramidon, as well as a novel ET-1 receptor A antagonist synthesized by our group, control premature delivery in a mouse model of inflammation-associated preterm delivery. In the current work, we show that levels of both ET-1 and ECE-1 are increased in gestational tissues in E16.5 mice induced to deliver prematurely after lipopolysaccharide administration. We also show that premature delivery is controlled by treatment with the selective endothelin receptor A antagonist BQ-123 in a dose-dependent manner. Finally, we show here for the first time that premature delivery can be controlled using RNA silencing, by hydrodynamic transfection of E15 mice with ECE-1 RNAi. Taken together, these data support a critical role for the ECE-1/ET-1 system in inflammation-associated premature delivery. The ability to control premature delivery by antagonizing or silencing the ECE-1/ET-1 system offers a novel approach to an unmet clinical need.

EXERCISE CAPACITY AND ECHOCARDIOGRAPHIC EVALUATION OF RIGHT HEART INDICES IN PATIENTS ON LONG-TERM AMBRISENTAN THERAPY FOR ESTABLISHED PULMONARY ARTERIAL HYPERTENSION

PURPOSE: Ambrisentan is a highly selective oral endothelin receptor antagonist (ERA) shown to improve exercise capacity and delay clinical worsening in pulmonary arterial hypertension (PAH). Little is known of its effects on right heart structure and function with long-term therapy. We evaluated right-sided cardiac variables from surveillance echocardiograms and 6-minute walk distance (6MWD) in patients on maximum therapy.

CONCOMITANT USE OF ACENOCOUMAROL AND SITAXSENTAN IN PATIENTS WITH PULMONARY ARTERIAL HYPERTENSION

PURPOSE: Sitaxsentan is a selective endothelin-A receptor antagonist approved for the treatment of pulmonary arterial hypertension (PAH). As an inhibitor of the cytochrome 2C9 enzyme, sitaxsentan inhibits the metabolism of warfarin, resulting in a need for routine measurement and adjustment of warfarin doses when both drugs are co-administered. In Mexico and other countries including Spain and Portugal, the vitamin K antagonist acenocoumarol is used in preference to warfarin. Here we report on the long-term effects on bleeding of acenocoumarol co-administered with sitaxsentan in a subset of patients enrolled in STRIDE-3.

Influence of food intake on the pharmacokinetics of avosentan in man

Avosentan is a potent, selective endothelin A receptor blocker. The effect of food intake on the pharmacokinetics of avosentan was investigated in healthy volunteers. In a randomized, open-label, 2-period oral crossover study, 12 healthy subjects (8 males and 4 females) received Treatments A and B. Treatment A consisted of a single dose of avosentan 50 mg after a high-fat, high-calorie breakfast. Treatment B consisted of a single dose of avosentan 50 mg administered in the fasted state. Plasma concentrations of avosentan and its hydroxymethyl metabolite Ro 68-5925 were measured by liquid chromatography-tandem mass spectrometry. The overall exposure to avosentan and its metabolite, as reflected by the area under the plasma concentration-time curve from time zero to infinity (AUC0-inf), was not affected by food intake. The ratios of least square means (90% confidence interval (CI)) of AUC0-inf for avosentan and Ro 68-5925 in the fed and fasted state were 1.06 (0.96, 1.17) and 1.05 (0.96, 1.15), respectively. The maximum plasma concentration (Cmax) of avosentan and its metabolite was increased by food intake, and their apparent terminal half-life (t1/2) was shortened. The ratios of least square means (90% CI) of pharmacokinetic parameters for avosentan and its metabolite in the fed and fasted state were Cmax 1.61 (1.37, 1.90) and 1.46 (1.27, 1.67), and t1/2; 0.80 (0.69, 0.92) and 0.61 (0.51, 0.74), respectively. Single oral doses of avosentan were well tolerated under fasted and fed conditions. Food intake does not influence the pharmacokinetics of avosentan to a clinically relevant extent.

HIV-related pulmonary arterial hypertension: clinical presentation and management

Pulmonary arterial hypertension (PAH) is a progressive albeit rare long-term complication of HIV infection, which has gained importance following the improved survival of HIV-infected patients with the use of HAART. The clinical and pathological findings in PAH associated with HIV infection (HIV-PAH) share many features with the idiopathic form of the disease. HIV-PAH is associated with a particularly poor prognosis and decreased survival compared with HIV-infected patients without this complication, and patients with HIV-PAH tend to die from the effects of PAH rather than as a result of their HIV infection. Prompt diagnosis and effective treatment of PAH in HIV-infected patients is therefore essential. There are currently only limited data regarding the efficacy of PAH therapies in HIV-PAH. Treatment with epoprostenol has been reported to provide benefit in some cases, but is associated with a range of problems linked to the need for continuous intravenous infusion. The dual endothelin receptor antagonist bosentan has proved to be effective in HIV-PAH without affecting the control of HIV infection, and has the benefit of oral administration. Other PAH therapies including prostacyclin analogs, phosphodiesterase type 5 inhibitors and selective endothelin receptor antagonists have yet to be trialed in this setting. Taking into account currently available data and clinical experience, a treatment algorithm for HIV-PAH based on that defined in treatment guidelines for other forms of PAH is suggested.

The effect and mechanism of endothelin-1-induced intracellular free calcium in human lung adenocarcinoma cells SPC-A1.

Endothelin-1 (ET-1) is a potent mitogen involved in cell growth in human lung adenocarcinoma cells SPC-A1. The increase in intracellular free calcium ([Ca(2+)]i) plays a great role in this process. The aim of this study is to investigate the ET-1-induced [Ca(2+)]i responses in SPC-A1 cells and to explore its cellular mechanism. [Ca(2+)]i was measured by Fura-2/AM fluorescent assay. Endothelin receptors antagonists, calcium channel blockers and intracellular signal transduction blockers were used to study the underlying mechanism of ET-1-induced [Ca(2+)]i responses in SPC-A1 cells. At the concentration of 1*10(-15) mol/L-1*10(-8) mol/L, ET-1 caused a dose-dependent increase of [Ca(2+)]i in SPC-A1 cells (P <0.05) in vitro . The ET-1-induced (1*10(-10) mol/L) increase of [Ca(2+)]i was blocked by BQ123 at 1*10(-7) mol/L (P <0.05), a highly selective endothelin receptor A (ETAR) antagonist, not by BQ788 at 10(-7) mol/L (P >0.05), a highly selective endothelin receptor B (ETBR) antagonist. Depletion of extracellular Ca(2+) with free Ca(2+) solution and 0.1mmol/L ethyleneglycol bis (2-aminoethyl ether) tetraacetic acid (EGTA) or blockade of voltage dependent calcium channel with nifedipine at 1*10(-6) mol/L significantly reduced the ET-1-induced increase of [Ca(2+)]i. The ET-1-induced (1*10(-10) mol/L) increase of [Ca(2+)]i was also significantly attenuated by U73122 at 1*10(-5) mol/L (P <0.05), a phospholipase C inhibitor, and by Ryanodine at 50*10(-6) mol/L. However, Staurosporine (2*10(-9) mol/L), a protein kinas C inhibitor, exerted no significant effect on the ET-1-induced (1*10(-10) mol/L) increase of [Ca(2+)]i. ET-1 elevates [Ca(2+)]i via activation of ETA receptor. Both phospholipase C/Ca(2+) pathway and Ca(2+) influx through voltage dependent Ca(2+) channel activate by ETAR contribute to this process.

Endothelin-3-dependent pulmonary vasoconstriction in monocrotaline-induced pulmonary arterial hypertension

Blockade of the endothelin (ET) system is beneficial in pulmonary arterial hypertension (PAH). The contribution of ET-3 and its interactions with ET receptors have never been evaluated in the monocrotaline (MCT)-induced model of PAH. Vasoreactivity of pulmonary arteries was investigated; ET-3 localization was determined by confocal imaging and gene expression of prepro-ET-3 quantified using RT-PCR. ET-3 plasma levels tended to increase in PAH. ET-3 localized in the media of pulmonary arteries, where gene expression of prepro-ET-3 was reduced in PAH. ET-3 induced similar pulmonary vasoconstrictions in sham and PAH rats. In sham rats, the ET A antagonist A-147627 (10 nmol/l) significantly reduced the maximal response to ET-3 ( E max 77 ± 1 to 46 ± 2%, mean ± S.E.M., P < 0.001), while the ET B antagonist A-192621 (1 μmol/l) reduced the sensitivity (EC 50 21 ± 7 to 59 ± 16 nmol/l, P < 0.05) without affecting E max. The combination of both antagonists completely abolished ET-3-induced pulmonary vasoconstriction. In PAH, the ET A antagonist further reduced the maximal response to ET-3 and shifted the EC 50 ( E max 23 ± 2%, P < 0.001, EC 50 104 ± 24 nmol/l, P < 0.05), while the ET B antagonist only shifted the EC 50 (123 ± 36 nmol/l, P < 0.05) without affecting the E max. In PAH, dual ET receptor inhibition did not further reduce constriction compared to selective ET A inhibition. ET-3 significantly contributes to pulmonary vasoconstriction by activating the ET B at low concentration, and the ET A at high concentration. The increased inhibitory effect of the ET A antagonist in PAH suggests that the contribution of ET B to ET-3-induced vasoconstriction is reduced. Although ET-3 is a potent pulmonary vasoconstrictor in PAH, its potential pathophysiologic contribution remains uncertain.

Efficacy and Safety of Atrasentan in Patients With Cardiovascular Risk and Early Atherosclerosis

Endothelin plays an important role in the pathogenesis of atherosclerosis. The aim of the study was to evaluate the safety and hemodynamic and metabolic responses to 6 months treatment with atrasentan, the selective endothelin-A receptor antagonist. Seventy-two patients with multiple cardiovascular risk factors and nonobstructive coronary artery disease on coronary angiogram were randomly assigned in a double-blind manner to atrasentan or placebo. Mean aortic blood pressure decreased from 92+/-10 to 80+/-10 mm Hg (P<0.001) in the atrasentan group and did not change in the placebo group (93+/-10 and 92+/-11 mm Hg; P=0.84). The difference between the groups was significant (P<0.001). No effect on heart rate was observed. In a subgroup of patients not treated with angiotensin-converting enzyme inhibitor, creatinine level decreased in the atrasentan versus the placebo group (P=0.011). Fasting glucose (P=0.026), glycosylated hemoglobin level (P=0.041), triglyceride l (P=0.013), lipoprotein-A (P=0.046), and uric acid levels (P=0.048) decreased significantly in the atrasentan group compared with the placebo group. No progression of angiographic coronary disease was observed. The most common adverse effects with atrasentan were nasal stuffiness, headache, and edema. In conclusion, 6 months of treatment with atrasentan results in a reduction of blood pressure and improvement in glucose and lipid metabolism. These findings suggest the beneficial role of atrasentan in the treatment of hypertension and metabolic syndrome.

Role of Endothelin-1 in Clinical Hypertension

Hypertension is the most common risk factor worldwide for cardiovascular morbidity and mortality.1,2 Currently it is estimated that a quarter of the world’s adult population is hypertensive, and this number is projected to increase to ≈30% by 2025.1 Although, there exist a number of drug therapies for hypertension, blood pressure (BP) control to target is still only achieved in ≈30% of patients.3 Over the last 20 years, novel licensed therapies have primarily focused on the renin-angiotensin-aldosterone system. Endothelin (ET) receptor antagonism represents an innovative, but as yet only partially explored, alternative approach in the management of hypertension. A review in Hypertension 10 years ago outlined the potential role that ET-1 may play in the development of hypertension,4 as proposed by Yanagisawa et al in their original Nature article in 1988.5 This largely focused on preclinical data because, at that time, there was only 1 published study of ET receptor antagonism in patients with essential hypertension.6 There were also few data that focused on the relative benefits of selective or mixed ET blockade. Finally, the lack of longer-term data on safety and tolerability for these drugs made their place in the antihypertensive armamentarium unclear. In this review we aim to answer many of these questions and outline some of the key findings in this field from the last decade. The ET family consists of three 21-amino acid peptides (ET-1, ET-2, and ET-3) with powerful vasoconstrictor and pressor properties.7 Of the 3 peptides, ET-1 is the major vascular isoform and of most importance in the cardiovascular system.8 The gene product is the 212-amino acid prepro-ET-1. This is cleaved to big ET-1, after which an ET-converting enzyme (ECE) catalyzes the generation of the biologically active ET-1 and a C-terminal fragment. ET-1 acts by binding to …

Phase I safety study of escalating doses of atrasentan in adults with recurrent malignant glioma

Atrasentan is an oral selective endothelin-A receptor antagonist that may inhibit cell proliferation and interfere with angiogenesis during glioma growth. We conducted a dose-finding study to assess atrasentan's safety and toxicity and to gather preliminary evidence of efficacy. Patients with recurrent malignant glioma received oral atrasentan at >or=10 mg/day. We increased the dose among cohorts until the maximum tolerated dose (MTD) was defined. Patients were evaluated for response every 8 weeks and remained on the study until the tumor progressed or toxicities occurred. Twenty-five patients were enrolled, with a median age of 53 years (range, 25-70) and a median KPS of 90% (range, 60-100%). Twenty-two patients had glioblastoma multiforme (GBM), 2 had anaplastic astrocytoma, and 1 had an anaplastic oliogodendroglioma; 24 patients had received one prior chemo therapy regimen before being enrolled in the study. The most common atrasentan-related toxicities were grade 1 or 2 rhinitis, fatigue, and edema. One patient developed grade 3 hypoxia and peripheral edema at a dose of 90 mg/day. We observed no dose-limiting toxicities in an expanded cohort of 10 patients at 70 mg/day, which was declared the MTD. Two partial responses (8%) were seen in patients with GBM at the 70- and 90-mg/day dose levels, and 4 patients had stable disease before progressing. Nineteen patients have died, and median survival was 6.0 months (95% confidence interval, 4.2-9.5 months). We conclude that the MTD of daily oral atrasentan in patients with recurrent malignant glioma is 70 mg/day. Further study of atrasentan with radiation therapy and temozolomide in newly diagnosed GBM is warranted to evaluate the efficacy of this novel agent.

Darusentan: a new perspective for treatment of resistant hypertension?

Despite multi-drug therapy, hypertension remains uncontrolled in a significant amount of patients, especially those with multiple cardiovascular risk factors. Endothelin-1 is a long lasting and very potent vasoconstrictor and plays a key role in cardiovascular hemostasis. Endothelin mediates its biological activity in humans through the endothelin A and B receptors. The selective endothelin – A receptor antagonist darusentan may be a new treatment option in patients with resistant hypertension. The objectives were that the clinical experience and the evidence for therapy with darusentan in resistant systemic hypertension were reviewed. The methods by the authors were that the leading journals which publish basic science and clinical research in the area of cardiovascular diseases and PubMed were scanned. In conclusion, early clinical results from Phase II studies suggest that darusentan may find a place in the treatment of resistant hypertension.

Role of endogenous endothelin-1 in post-ischemic cardiac dysfunction and norepinephrine overflow in rat hearts

Endothelin-1 and norepinephrine are involved in myocardial ischemia/reperfusion injury. The aim of this study was to investigate the role of endogenously generated endothelin-1 in ischemia/reperfusion-induced norepinephrine overflow and cardiac dysfunction using a nonselective prototype of endothelin-converting enzyme (ECE) inhibitor, phosphoramidon, and a selective ECE inhibitor, SM-19712 (4-chloro-N-[[(4-cyano-3-methyl-1-phenyl-1H-pyrazol-5-yl)amino]carbonyl]benzenesulfonamide, monosodium salt). According to the Langendorff technique, isolated Sprague–Dawley rat hearts were subjected to 40-min global ischemia followed by 30-min reperfusion. Phosphoramidon and SM-19712 were perfused 30 min before ischemia and during reperfusion. Endothelin-1 level in left ventricle was increased by ischemia/reperfusion. This increase in left ventricular endothelin-1 level was suppressed by treatment with SM-19712. SM-19712 significantly improved ischemia/reperfusion-induced cardiac dysfunction such as decreased left ventricular developed pressure and dP/dt max and increased left ventricular end diastolic pressure. In addition, this agent suppressed excessive norepinephrine overflow in the coronary effluent from the post-ischemic heart. In contrast, treatment with phosphoramidon further enhanced left ventricular endothelin-1 level and norepinephrine overflow, and significantly worsened cardiac dysfunction after ischemia/reperfusion. These responses such as exaggerated norepinephrine overflow and the cardiac dysfunction observed after ischemia/reperfusion were markedly suppressed in the presence of a selective endothelin ET A receptor antagonist, ABT-627 [2 R-(4-methoxyphenyl)-4 S-(1,3-benzodioxol-5-yl)-1-( N,N-di(n-butyl)aminocarbonyl-methyl)-pyrrolidine-3 R-carboxylic acid]. These findings indicate that cardiac endothelin-1 production is enhanced by ischemia/reperfusion, and this endogenously increased endothelin-1 is involved in post-ischemic norepinephrine overflow and cardiac dysfunction via the activation of endothelin ET A receptors.

The role of endothelin pathway in modulation of airway reactivity to methacholine in C57Bl/6 and BALB/c mice

Endothelin peptides have been shown to increase cholinergic neurotransmission in the airway. Genetic differences in airway responsiveness to methacholine where reported in mice. The present study compared the airway reactivity to methacholine in C57Bl/6 and BALB/c mice, the involvement of endothelin on this reactivity and endothelin levels in lung homogenates. Whole airway reactivity was analyzed by means of an isolated lung preparation where lungs were perfused through the trachea with warm gassed Krebs solution at 5 ml/min, and changes in perfusion pressure triggered by methacholine at increasing bolus doses (0.1–100 µg) were recorded. We found that the maximal airway response to methacholine was much greater in C57Bl/6 than in BALB/c (Emax 34 ± 2 vs 12 ± 1 cmH 2O, respectively). Bosentan (mixed endothelin A/B receptor antagonist; 10 mg/kg, i.p., 30 min before sacrifice) reduced lung responsiveness to methacholine in C57Bl/6 (58% at EC50 level) but had no effect in BALB/c mouse strain. This effect seems to be mediated by the endothelin ET A receptor since it was significantly reduced by the selective endothelin ET A receptor antagonist, BQ 123. Immunoreactive endothelin levels were higher in C57Bl/6 than in BALB/c lungs (43 ± 5 vs 19 ± 5 pg/g of tissue). In conclusion, airway reactivity to methacholine and lung endothelins content varies markedly between C57Bl/6 and BALB/c strains. Endothelins upregulate lung responsiveness to methacholine only in C57Bl/6, an effect achieved through the endothelin ET A receptor.