Efficacy and Adverse Effects of Atrasentan in Patients with Diabetic Nephropathy: A Meta-Analysis.

Background: About 30% of Type 1 diabetes (T1DM) patients and 40% of Type 2 diabetes (T2DM) patients were diagnosed with diabetic nephropathy, which has also greatly affected the global end-stage renal disease (ESRD) outcome. Atrasentan is a selective endothelin receptor type A (ETA) antagonist initially studied for the potential treatment of cancer. However, the role of Atrasentan was not sure in the DM. Methods: The machine searches eight databases to find studies examining the impact of Atrasentan in people with diabetic nephropathy both domestically and overseas. Type of Study Design RCTs have been published on Atrasentan's effects in patients with chronic kidney disease.Utilizing RevMan 5.3 software, data analysis was carried out following a thorough assessment of the quality of the literature. Results: This meta-analysis has included 4 papers for statistics. They were all regarded as being random controlled trials. According to 4 studies, the test group's urinary albumin/creatinine ratio (UACR) was significantly lower than the control group's (standardized mean difference (SMD): -222.47; 95% confidence interval (CI): -367.57, -77.38; P < .01), as were the test group's prevalence of cardiovascular disease (OR: 0.83; 95% CI: 0.73, 0.95; P < .01) and adverse reactions (OR: 1.00; 95% CI: 1.00). Conclusion: Atrasentan improves the UACR in individuals with chronic kidney disease as compared to the control category. However, these findings need to be confirmed by more high-quality research. Further studies could focus on the effect of the Atrasentan on the diabetic nephropathy management,which will shed light on the treatment of diabetic nephropathy.

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

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

Intracellular iron deficiency in pulmonary arterial smooth muscle cells induces pulmonary arterial hypertension in mice.

Iron deficiency augments hypoxic pulmonary arterial pressure in healthy individuals and exacerbates pulmonary arterial hypertension (PAH) in patients, even without anemia. Conversely, iron supplementation has been shown to be beneficial in both settings. The mechanisms underlying the effects of iron availability are not known, due to lack of understanding of how cells of the pulmonary vasculature respond to changes in iron levels. The iron export protein ferroportin (FPN) and its antagonist peptide hepcidin control systemic iron levels by regulating release from the gut and spleen, the sites of absorption and recycling, respectively. We found FPN to be present in pulmonary arterial smooth muscle cells (PASMCs) and regulated by hepcidin cell autonomously. To interrogate the importance of this regulation, we generated mice with smooth muscle-specific knock in of the hepcidin-resistant isoform fpn C326Y. While retaining normal systemic iron levels, this model developed PAH and right heart failure as a consequence of intracellular iron deficiency and increased expression of the vasoconstrictor endothelin-1 (ET-1) within PASMCs. PAH was prevented and reversed by i.v. iron and by the ET receptor antagonist BQ-123. The regulation of ET-1 by iron was also demonstrated in healthy humans exposed to hypoxia and in PASMCs from PAH patients with mutations in bone morphogenetic protein receptor type II. Such mutations were further associated with dysregulation of the HAMP/FPN axis in PASMCs. This study presents evidence that intracellular iron deficiency specifically within PASMCs alters pulmonary vascular function. It offers a mechanistic underpinning for the known effects of iron availability in humans.

Oleanolic Acid, a Novel Endothelin A Receptor Antagonist, Alleviated High Glucose-Induced Cardiomyocytes Injury.

Endothelin-1 (ET-1) and its receptor endothelin A receptor (ET[Formula: see text] have been shown to be upregulated in a high glucose environment, which increase the incidence of diabetes-related heart failure. Our previous study demonstrated that oleanolic acid (OA), a natural compound found in Chinese herbs had ET-1 antagonistic effects. We aimed to verify whether OA could ameliorate diabetes mellitus (DM)-induced injury in cardiomyocytes by reducing the antagonistic effects of the ET-1 pathway. For the induction of high glucose-related injury in cardiomyocytes, neonatal rat ventricular cardiomyocytes (NRVMs) were subjected to culture medium containing 25[Formula: see text]mM of glucose. Natriuretic peptide B (BNP), mitochondrial membrane potential (MMP) and cell surface area were measured to evaluate the severity of NRVMs injury. mRNA expression of ET-1 and ETA was determined using quantitative PCR. Moreover, a Ca[Formula: see text] influx assay was used to evaluate potential ETA antagonistic effects. Molecular docking of OA and ETA was performed using the Sulflex-Dock program. Human induced pluripotent stem cell (iPS-C)-derived cardiomyocytes and real time cell analysis system (RTCA) were used to verify the effect of OA on the ET-1 pathway. High glucose levels increased the expression of BNP at both mRNA and protein levels in cardiomyocytes. Moreover, cell surface area and MMP were also elevated in a high glucose environment. High glucose-induced injury in NRVMs was not reversible by hypoglycemic therapy. In addition, ETA was upregulated by high glucose treatment and levels could not be reduced by hypoglycemic treatment. The Ca[Formula: see text] influx assay on ETA/HEK293 cells showed that OA had a partial ETA antagonistic effect. Molecular docking approaches showed that OA was docked into the active site of ETA. Furthermore, functionality tests based on iPS-C and RTCA demonstrated that treatment with OA could reverse ET-1-induced alternation of beating rates and amplitude. Thus, OA could reverse high glucose-induced BNP upregulation, and increased both the cell area and MMP in NRVMs. High glucose-induced irreversible ETA upregulation is a major reason of continuous diabetes-related injury in cardiomyocytes. Treatment with OA had a protective effect on high glucose-induced injury in cardiomyocytes through a partial ETA antagonistic role.

[Prediction of ETA oligopeptides antagonists from Glycine max based on in silico proteolysis].

Oligopeptides are one of the the key pharmaceutical effective constituents of traditional Chinese medicine(TCM). Systematic study on composition and efficacy of TCM oligopeptides is essential for the analysis of material basis and mechanism of TCM. In this study, the potential anti-hypertensive oligopeptides from Glycine max and their endothelin receptor A (ETA) antagonistic activity were discovered and predicted based on in silico technologies.Main protein sequences of G. max were collected and oligopeptides were obtained using in silico gastrointestinal tract proteolysis. Then, the pharmacophore of ETA antagonistic peptides was constructed and included one hydrophobic feature, one ionizable negative feature, one ring aromatic feature and five excluded volumes. Meanwhile, three-dimensional structure of ETA was developed by homology modeling methods for further docking studies. According to docking analysis and consensus score, the key amino acid of GLN165 was identified for ETA antagonistic activity. And 27 oligopeptides from G. max were predicted as the potential ETA antagonists by pharmacophore and docking studies.In silico proteolysis could be used to analyze the protein sequences from TCM. According to combination of in silico proteolysis and molecular simulation, the biological activities of oligopeptides could be predicted rapidly based on the known TCM protein sequence. It might provide the methodology basis for rapidly and efficiently implementing the mechanism analysis of TCM oligopeptides.

Endothelin type A receptor blockade reduces vascular calcification and inflammation in rats with chronic kidney disease.

OBJECTIVE: Arterial stiffness and calcification are nontraditional cardiovascular risk factors in chronic kidney disease (CKD). Using a rat model of CKD with mineral imbalance, medial vascular calcification has been associated with inflammation and increased endothelin-1 (ET-1) production. We therefore hypothesized that ET-1, through the endothelin type A (ETA) receptor, induces vascular inflammation, calcification and stiffness in CKD. METHODS: CKD was induced in Wistar rats by renal mass ablation. To induce medial vascular calcification, mineral imbalance was established with a identified as calcium-rich/phosphate-rich diet and vitamin D supplementation (Ca/P/VitD). One group of CKD + Ca/P/VitD rats was given the ETA receptor antagonist atrasentan (10 mg/kg/day) for 6 weeks. Hemodynamic parameters including SBP, pulse pressure (PP) and pulse wave velocity (PWV) were determined. Vascular calcification, smooth muscle cells osteoblastic differentiation and expression of inflammatory markers such as inflammatory cytokines and calgranulins S100A8 and S100A9 were assessed in the thoracic aorta. RESULTS: As compared with CKD control rats, CKD + Ca/P/VitD rats developed medal vascular calcification that was associated with increased SBP, PP and PWV. These changes were also associated with increased macrophage infiltration and expression of IL-6, calgranulins and osteoblastic markers. Treatment of CKD + Ca/P/VitD rats with atrasentan reduced vascular calcification, SBP, PP and PWV, macrophage infiltration and expression of IL-1ß, IL-6, tumor necrosis factor, calgranulins and osteoblastic markers. CONCLUSION: This study shows that ETA receptor blockade reduced vascular inflammation, smooth muscle cells differentiation, calcification and stiffness indicating a pivotal role for ET-1 in medial vascular calcification in this rat remnant kidney model of CKD with mineral imbalance. Therefore, the endothelin system may be a potential therapeutic target for improving cardiovascular morbidity in patients with CKD.

Salvianolic Acid A, as a Novel ETA Receptor Antagonist, Shows Inhibitory Effects on Tumor in Vitro.

Endothelin-1 (ET-1) autocrine and paracrine signaling modulate cell proliferation of tumor cells by activating its receptors, endothelin A receptor (ETAR) and endothelin B receptor (ETBR). Dysregulation of ETAR activation promotes tumor development and progression. The potential of ETAR antagonists and the dual-ETAR and ETBR antagonists as therapeutic approaches are under preclinical and clinical studies. Salvianolic acid A (Sal A) is a hydrophilic polyphenolic derivative isolated from Salvia miltiorrhiza Bunge (Danshen), which has been reported as an anti-cancer and cardio-protective herbal medicine. In this study, we demonstrate that Sal A inhibits ETAR activation induced by ET-1 in both recombinant and endogenous ETAR expression cell lines. The IC50 values were determined as 5.7 µM in the HEK293/ETAR cell line and 3.14 µM in HeLa cells, respectively. Furthermore, our results showed that Sal A suppressed cell proliferation and extended the doubling times of multiple cancer cells, including HeLa, DU145, H1975, and A549 cell lines. In addition, Sal A inhibited proliferation of DU145 cell lines stimulated by exogenous ET-1 treatment. Moreover, the cytotoxicity and cardio-toxicity of Sal A were assessed in human umbilical vein endothelial cells (HUVEC) and Human-induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs), which proved that Sal A demonstrates no cytotoxicity or cardiotoxicity. Collectively, our findings indicate that Sal A is a novel anti-cancer candidate through targeting ETAR.

Discovery of Dual ETA/ETB Receptor Antagonists from Traditional Chinese Herbs through in Silico and in Vitro Screening.

Endothelin-1 receptors (ETAR and ETBR) act as a pivotal regulator in the biological effects of ET-1 and represent a potential drug target for the treatment of multiple cardiovascular diseases. The purpose of the study is to discover dual ETA/ETB receptor antagonists from traditional Chinese herbs. Ligand- and structure-based virtual screening was performed to screen an in-house database of traditional Chinese herbs, followed by a series of in vitro bioassay evaluation. Aristolochic acid A (AAA) was first confirmed to be a dual ETA/ETB receptor antagonist based intracellular calcium influx assay and impedance-based assay. Dose-response curves showed that AAA can block both ETAR and ETBR with IC50 of 7.91 and 7.40 µM, respectively. Target specificity and cytotoxicity bioassay proved that AAA is a selective dual ETA/ETB receptor antagonist and has no significant cytotoxicity on HEK293/ETAR and HEK293/ETBR cells within 24 h. It is a feasible and effective approach to discover bioactive compounds from traditional Chinese herbs using in silico screening combined with in vitro bioassay evaluation. The structural characteristic of AAA for its activity was especially interpreted, which could provide valuable reference for the further structural modification of AAA.

Plasma pro-endothelin-1 peptide concentrations rise in chronic kidney disease and following selective endothelin A receptor antagonism.

BACKGROUND: Endothelin 1 (ET-1) contributes to chronic kidney disease (CKD) development and progression, and endothelin receptor antagonists are being investigated as a novel therapy for CKD. The proET-1 peptides, endothelin-like domain peptide (ELDP) and C-terminal pro-ET-1 (CT-proET-1), are both potential biomarkers of CKD and response to therapy with endothelin antagonists. METHODS AND RESULTS: We assessed plasma and urine ELDP and plasma CT-proET-1 in CKD patients with minimal comorbidity. Next, in a randomized double-blind crossover study of 27 subjects with proteinuric CKD, we examined the effects of 6 weeks of treatment with placebo, sitaxentan (endothelin A antagonist), and nifedipine on these peptides alongside the primary end points of proteinuria, blood pressure, and arterial stiffness. Plasma ELDP and CT-proET-1 increased with CKD stage (both P<0.0001), correlating inversely with estimated glomerular filtration rate (both P<0.0001). Following intervention, placebo and nifedipine did not affect plasma and urine ELDP or plasma CT-proET-1. Sitaxentan increased both plasma ELDP and CT-proET-1 (baseline versus week 6±SEM: ELDP, 11.8±0.5 versus 13.4±0.6 fmol/mL; CT-proET-1, 20.5±1.2 versus 23.3±1.5 fmol/mL; both P<0.0001). Plasma ET-1 was unaffected by any treatment. Following sitaxentan, plasma ELDP and CT-proET-1 correlated negatively with 24-hour urinary sodium excretion. CONCLUSIONS: ELDP and CT-proET-1 increase in CKD and thus are potentially useful biomarkers of renal injury. Increases in response to endothelin A antagonism may reflect EDN1 upregulation, which may partly explain fluid retention with these agents. CLINICAL TRIAL REGISTRATION: URL: www.clinicalTrials.gov Unique identifier: NCT00810732.

Endothelin A receptor blocker atrasentan lowers blood pressure by the reduction of nifedipine-sensitive calcium influx in Ren-2 transgenic rats fed a high-salt diet.

BACKGROUND: Our previous experiments demonstrated that selective endothelin A (ETA) receptor blockade had antihypertensive effects in Ren-2 transgenic rats (TGRs), but the mechanisms responsible for this change of blood pressure (BP) have not been explored yet. METHOD: Four-week-old male heterozygous TGRs and their normotensive controls--Hannover Sprague-Dawley (HanSD) rats--were fed high-salt diet (2% NaCl) and were treated with selective ETA receptor blocker atrasentan (5 mg/kg per day) for 8 weeks. At the end of the study, the contribution of principle vasoactive systems was evaluated by the sequential blockade of the renin-angiotensin system (captopril), sympathetic nervous system (pentolinium) and nitric oxide synthase [N-nitro-L-arginine methyl ester (L-NAME)]. The role of calcium influx through L-type voltage-dependent calcium channels in BP maintenance was evaluated using nifedipine. In a separate group of animals, the efficiency of distinct vasodilator systems--prostanoids (blocked by nonselective cyclooxygenase inhibitor indomethacin) and Ca-activated K channels (inhibited by tetraethylammonium)--was also analyzed. RESULTS: Atrasentan attenuated the development of hypertension in heterozygous TGRs, but had no effects in Hannover Sprague-Dawley rats. Moreover, atrasentan moderately attenuated renin-angiotensin system-dependent vasoconstriction, whereas it had no effect on sympathetic vasoconstriction. The nifedipine-sensitive BP component was markedly decreased by atrasentan treatment. In contrast, vasodilatation mediated by nitric oxide, endogenous prostanoids or Ca-activated K channels was reduced in atrasentan-treated TGRs, indicating the absence of compensatory augmentation of endothelin B receptor-mediated vasodilation in these animals. CONCLUSION: BP-lowering effect of chronic atrasentan treatment in TGRs was mainly caused by reduced Ca influx through L-type voltage-dependent calcium channels due to missing ETA receptor-dependent vasoconstriction and attenuated angiotensin II-dependent vasoconstriction.

Efficacy of the specific endothelin a receptor antagonist zibotentan (ZD4054) in colorectal cancer: a preclinical study.

Endothelin 1 (ET-1) is overexpressed in cancer, contributing to disease progression. We previously showed that ET-1 stimulated proliferative, migratory, and contractile tumorigenic effects via the ET(A) receptor. Here, for the first time, we evaluate zibotentan, a specific ET(A) receptor antagonist, in the setting of colorectal cancer, in cellular models. Pharmacologic characteristics were further determined in patient tissues. Colorectal cancer lines (n = 4) and fibroblast strains (n = 6), isolated from uninvolved areas of colorectal cancer specimens, were exposed to ET-1 and/or ET(A)/(B) receptor antagonists. Proliferation (methylene blue), migration (scratch wounds), and contraction (gel lattices) were assessed. Receptor distribution and binding characteristics (K(d), B(max)) were determined using autoradiography on tissue sections and homogenates and cytospun cells, supported by immunohistochemistry. Proliferation was inhibited by ET(A) (zibotentan > BQ123; P < 0.05), migration by ET(B) > ET(A), and contraction by combined ET(A) and ET(B) antagonism. Intense ET-1 stromal binding correlated with fibroblasts and endothelial cells. Colorectal cancer lines and fibroblasts revealed high density and affinity ET-1 binding (B(max) = 2.435 fmol/1 × 10(6) cells, K(d) = 367.7 pmol/L; B(max) = 3.03 fmol/1 × 10(6) cells, K(d) = 213.6 pmol/L). In cancer tissues, ET(A) receptor antagonists (zibotentan; BQ123) reduced ET-1 binding more effectively (IC(50): 0.1-10 µmol/L) than ET(B) receptor antagonist BQ788 (∼IC(50), 1 mmol/L). ET-1 stimulated cancer-contributory processes. Its localization to tumor stroma, with greatest binding/affinity to fibroblasts, implicates these cells in tumor progression. ET(A) receptor upregulation in cancer tissues and its role in tumorigenic processes show the receptor's importance in therapeutic targeting. Zibotentan, the most specific ET(A) receptor antagonist available, showed the greatest inhibition of ET-1 binding. With its known safety profile, we provide evidence for zibotentan's potential role as adjuvant therapy in colorectal cancer.

Prunellae spica extract contains antagonists for human endothelin receptors.

Endothelin-1 (ET-1) is a powerful vasoconstrictor that contributes to blood pressure elevation. The biological effects of ETs are mediated by two receptors, namely, endothelin type A receptor (ET(A)R) and endothelin type B receptor (ET(B)R). Chinese herbal medicines (CHM) with antagonist activity for these two receptors were screened by establishing stable clones of CHO-K1 cells expressing high levels of human ET(A)R and ET(B)R, namely CHO-ET(A)R and CHO-ET(B)R.The aqueous extract of Prunellae Spica (P1) inhibited the binding of (125)I-ET-1 to ET(A)R and ET(B)R in CHO-ET(A)R and CHO-ET(B)R cells, respectively. P1 suppressed the ET-1-induced mobilization of intracellular Ca(2+) . Through the alcohol fractionation of P1, the antagonists of human ET(A)R and ET(B)R were found to belong to different, separable ingredients and the antagonist of ET(A)R is more soluble in alcohol. The two antagonists were also effective in the test on human primary cells, HASMC and HUVEC. P1 successfully prevented the development of ET-1-associated hypertension in rats without further purification. These results indicate the presence of anti-hypertensive ingredients in P. Spica extract, at least through the inactivation of ET(A)R and/or ET(B)R.

Effects of selenium supplementation on expression of endothelin-1 and its receptors in pulmonary microvascular endothelial cells from chick embryos.

The objective of this study was to evaluate the effects of supplemental selenium (Se) on expression of endothelin-1 (ET-1) and its receptors in cultured chick embryos pulmonary microvascular endothelial cells (PMVECs). To accomplish this, PMVECs were treated in Se-deficient or Se-supplement (12, 24, 50, 100 ng/ml) culture medium for 48 h. Low Se medium was achieved by reducing serum concentrations and the essential growth factors were added. After the incubation, the effects of supplemental Se on ET-1 and its receptors gene expression were assessed by quantitative real-time PCR (qRT-PCR). Compared with the control group, our results showed that among the different concentrations of Se supplement, the levels of ET-1 gene expression treated with both the moderate Se doses (24, 50 ng/ml, P < 0.01, P < 0.01, respectively) and the high doses (100 ng/ml, P < 0.05) were noticeably decreased, the low-dose group (12 ng/ml), which showed no changes. Meanwhile, Se supplement (24, 50, 100 ng/ml) was found to be effective in reducing the expression levels of ETA (P < 0.01, P < 0.05, P < 0.05, respectively) in cultured PMVECs grown in low Se medium. However, there were no significant changes (P > 0.05) in ETB mRNA levels during the cell proliferation. These observations indicated that Se may play both direct and indirect role in the regulation of ET-1 and its receptors gene expression and their production in avian PMVECs. Se supplement decreases in ET-1 and ETA production in Se-deficient PMVECs may partly explain the mechanism of the protective effects of the Se on the cardiovascular system.

Practical considerations for the pharmacotherapy of pulmonary arterial hypertension.

Pulmonary arterial hypertension is a devastating disease. Before the 1990s, when pharmacologic treatment was finally approved, only supportive therapy was available, consisting of anticoagulation, digoxin, diuretics, and supplemental oxygen. Calcium channel blocker therapy was also an option, but only a small percentage of patients respond to it. However, starting with epoprostenol in 1996, the number of drugs approved to treat pulmonary arterial hypertension increased. Three distinct classes of drugs were developed based on the pathophysiology of the disease: the prostanoids, endothelin-1 receptor antagonists, and phosphodiesterase type 5 inhibitors. The prostanoids are administered either parenterally or by inhalation to replace the lack of prostacyclin within the pulmonary arterial vasculature. The endothelin-1 receptor antagonists were the first class of oral drugs to be developed, but drug interactions and adverse effects are prominent with this class. The phosphodiesterase type 5 inhibitors increase the second messenger cyclic guanosine monophosphate (GMP) that is induced by nitric oxide stimulation. All of the drugs within these three classes are distinct in and of themselves, and their clinical use requires in-depth knowledge of pulmonary arterial hypertension and its pathophysiology. Because these drugs have different mechanisms of action, combination therapy has shown promise in patients with severe disease, although data are still lacking. This article should serve as a practical guide for clinicians who encounter patients with pulmonary arterial hypertension and the drugs used for the treatment of this devastating disease.

Selective endothelin-A receptor antagonism reduces proteinuria, blood pressure, and arterial stiffness in chronic proteinuric kidney disease.

Proteinuria is associated with adverse cardiovascular and renal outcomes that are not prevented by current treatments. Endothelin 1 promotes the development and progression of chronic kidney disease and associated cardiovascular disease. We, therefore, studied the effects of selective endothelin-A receptor antagonism in proteinuric chronic kidney disease patients, assessing proteinuria, blood pressure (BP), and arterial stiffness, key independent, surrogate markers of chronic kidney disease progression and cardiovascular disease risk. In a randomized, double-blind, 3-way crossover study, 27 subjects on recommended renoprotective treatment received 6 weeks of placebo, 100 mg once daily of sitaxsentan, and 30 mg once daily of nifedipine long acting. Twenty-four-hour proteinuria, protein:creatinine ratio, 24-hour ambulatory BP, and pulse wave velocity (as a measure of arterial stiffness) were measured at baseline and week 6 of each treatment. In 13 subjects, renal blood flow and glomerular filtration rate were assessed at baseline and week 6 of each period. Compared with placebo, sitaxsentan reduced 24-hour proteinuria (-0.56±0.20 g/d; P=0.0069), protein:creatinine ratio (-38±15 mg/mmol; P=0.0102), BP (-3.4±1.2 mm Hg; P=0.0069), and pulse wave velocity (-0.64±0.24 m/s; P=0.0052). Nifedipine matched the BP and pulse wave velocity reductions seen with sitaxsentan but did not reduce proteinuria. Sitaxsentan alone reduced both glomerular filtration rate and filtration fraction. It caused no clinically significant adverse effects. Endothelin-A receptor antagonism may provide additional cardiovascular and renal protection by reducing proteinuria, BP, and arterial stiffness in optimally treated chronic kidney disease subjects. The antiproteinuric effects of sitaxsentan likely relate to changes in BP and renal hemodynamics.

Endothelin receptor expression in idiopathic pulmonary arterial hypertension: effect of bosentan and epoprostenol treatment.

Endothelin receptor antagonists are used to treat idiopathic pulmonary arterial hypertension (IPAH), but human pulmonary arterial endothelin receptor expression is not well defined. We hypothesised that disease and treatment would modify normal receptor distribution in pulmonary resistance arteries of children. Using immunohistochemistry and semiquantitative analysis, we investigated endothelin receptor subtypes A and B (ET(A) and ET(B), respectively), and endothelial nitric oxide synthase (eNOS) expression in peripheral pulmonary arteries of tissue from untreated children with IPAH (n=7), following extended combined bosentan and epoprostenol therapy (n=5) and from normal subjects (n=5). Clinical, haemodynamic and pathological abnormalities were severe and advanced in all IPAH cases. ET(A) was detected in pulmonary arterial endothelial cells of all normal and diseased tissue and cultured cells. Endothelial ET(A), ET(B) and eNOS expression was reduced in patent, plexiform and dilatation lesions of untreated cases, but in treated cases, ET(A) and ET(B) were normal and eNOS increased. In smooth muscle, ET(A) expression was reduced in treated cases but ET(B) expression increased in all arteries of both treated and untreated cases. In summary, ET(A) is expressed on human pulmonary arterial endothelium. In IPAH, combination treatment with bosentan and epoprostenol had a more marked influence on endothelin receptor expression of endothelial than smooth muscle cells.

Acid retention during kidney failure induces endothelin and aldosterone production which lead to progressive GFR decline, a situation ameliorated by alkali diet.

Rats with 5/6 nephrectomy have metabolic acidosis with a progressive decline in the glomerular filtration rate (GFR) ameliorated by endothelin and aldosterone antagonists and by dietary alkali. Interestingly, rats with 2/3 nephrectomy have no metabolic acidosis yet have a progressive GFR decline induced by acid retention and ameliorated by dietary alkali. Because patients without metabolic acidosis but with a moderately reduced GFR have a progressive GFR decline, ameliorated by oral sodium bicarbonate, we used rats with 2/3 nephrectomy to model these patients. Kidney acid content, endothelin-1, and aldosterone (measured by microdialysis) were higher in the rats with 2/3 nephrectomy than those with a sham operation despite no differences in plasma acid-base parameters. The GFR of the former but not the latter was lower at 25 than at 1 week after nephrectomy. Endothelin and aldosterone antagonism improved the preservation of GFR; however, this remained lower at week 24 than at week 1. By contrast, the GFR at weeks 24 and 1 was not different if the rats were given dietary alkali to normalize the kidney acid content. Antagonist of endothelin and aldosterone yielded no added GFR benefit. Thus, our study shows that (1) the decline in GFR in 2/3 nephrectomy is mediated by acid retention-induced kidney endothelin and aldosterone production; (2) receptor antagonism and dietary alkali are not additive; and (3) dietary alkali better preserves GFR than both endothelin and aldosterone receptor antagonism.

Zibotentan for the treatment of castrate-resistant prostate cancer.

IMPORTANCE OF THE FIELD: Patients with prostate cancer who have progression of their disease while on androgen deprivation therapy have limited therapeutic options. Docetaxel is currently the only agent that increases overall survival in patients with metastatic, castration-resistant prostate cancer; additional agents are needed. AREAS COVERED IN THIS REVIEW: This review will describe the importance of endothelin-1 (ET-1) for growth of prostate cancer cells, development of bone metastases, and pain responses; the preclinical data for zibotentan, a specific inhibitor of the ET(A) receptor; and the clinical development of atrasentan, a first-generation ET receptor inhibitor, and zibotentan, a more selective inhibitor of the ET(A) receptor. WHAT THE READER WILL GAIN: Readers will understand the importance of ET-1 as a novel pathway to target for patients with castration-resistant prostate cancer due to its association with prostate cancer growth, metastases to bone, and pain. Readers will learn about the preclinical and clinical development of zibotentan, including the promising Phase II results that have resulted in an extensive Phase III clinical trials program. TAKE HOME MESSAGE: Modulating the activity of ET-1 through the ET(A) receptor is a novel target for treating patients with metastatic, castration-resistant prostate cancer. There are currently three ongoing Phase III trials with zibotentan, a selective ET(A) inhibitor, to determine the effect of this agent on overall survival in these patients.