Specific Endothelin Receptor Antagonist Research Articles

CT perfusion imaging of cerebral microcirculatory changes following subarachnoid hemorrhage in rabbits: Specific role of endothelin-1 receptor antagonist

BackgroundCerebral vasospasm may lead to delayed ischemic neurological deficits following subarachnoid hemorrhage (SAH). Endothelin (ET-1) is an important factor participating in cerebral vasospasm underlying SAH. We used a specific endothelin receptor antagonist, BQ123 to assess the specific role of endothelin-1 receptor antagonist in cerebral vasospasm in a rabbit model of SAH by examining plasma ET-1 levels and the principal CT perfusion (CTP) parameters pertinent to the hemodynamic status of microcirculation following SAH. Methods102 male New Zealand white rabbits were divided into control, SAH and SAH + BQ123 intervention group (BQ123 group). Rabbit SAH model was established by double hemorrhage injection of autologous blood into the cisterna magna; Aquilion ONE was used to collect cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) which were used to evaluate cerebral microcirculation hemodynamics; Elisa was used to assess plasma ET-1 levels. Data were collected on days 1, 4, 7 and 14 following SAH, respectively. ResultsCompared with the control group, the CBF in the SAH group was significantly lower, while the MTT was significantly higher. The CBF decreased on the 4th day and reached the lowest on the 7th day. The MTT began to rise on the 4th day and peaked on the 7th day. While in the BQ123 intervention group, the CBF significantly increased while the MTT significantly decreased on the 1st and the 4th days, respectively. Compared with SAH group, plasma ET-1 levels in BQ123 group significantly increased on the earlier (1st and 4th days) but not later days (between the 7th and 14th days). In addition, the inflammatory infiltration of brain tissues in rabbits treated with BQ123 post-SAH was significantly reduced compared with SAH group. ConclusionCTP can quantify the therapeutic effect of BQ123 after SAH; Selective blockade of ET-1 endothelin receptor, BQ123 significantly improved microcirculatory perfusion along with a reduction in resultant vasogenic inflammatory responses. The effect of BQ123 on the cerebral microcirculation was lobe dependent.

Hepatic Transaminase Abnormalities in Pulmonary Arterial Hypertension: A Report From the REVEAL Registry

PURPOSE: The Registry to EValuate Early And Long-term Pulmonary Arterial Hypertension (PAH) Disease Management (REVEAL), a 55-center observational, US study, examines current clinical practice in patients with PAH. We assessed aspartate transaminase/alanine transaminase (AST/ALT) elevation frequencies in patients by PAH-specific medication class, and by specific endothelin receptor antagonist (ERA) due to ERAs’ association with AST/ALT abnormalities.

Retracted Article: Pericyte-mediated vasoconstriction underlies TBI-induced hypoperfusion

Endothelin-1 is a 21-amino acid peptide that together with specific receptors, A (ETrA) and B (ETrB) is induced following traumatic brain injury (TBI) and has been closely linked to regulation of cerebral vasospasm, oxidative stress, and hypoperfusion. Specific endothelin receptor antagonists have been shown to ameliorate early evidence of neuronal cell injury, activation of microglial cells, and hypoperfusion following TBI. The exact mechanism involved in TBI-induced hypoperfusion is still unclear; however, it is thought that endothelin-1 engagement of ETrA is primarily responsible for changes in blood flow. In this study we question the role of the microvascular pericyte in endothelin-1-mediated pathophysiology in TBI. Pericyte expression of endothelin-1, ETrA, and ETrB was examined in primary culture and in sham and impacted rat brain. Adult male rats were also given intracerebroventricular injections of ETrA (BQ-123) before being subjected to TBI using a closed head acceleration impact model. Primary pericytes express both endothelin-1 and its receptors ETrA and ETrB. Following TBI, the number of alpha-smooth muscle actin (SMA) positive pericytes located in microvessels is significantly increased by 4 hours post-traumatic impact. Increases in pericyte expression of alpha-SMA correlated with evidence of a reduction in both arteriolar and capillary diameter. Capillary endothelin-1, ETrA, and ETrB transcript and protein was also increased. Increased endothelin-1 expression was seen by 2-4 hours post-impact. Upregulation of receptors was observed by 4-8 hours and maximum by 24 hours. ETrA antagonists decreased the number of alpha-SMA(+) pericytes as well as changes in microvascular diameter. These results suggest that decreased vasoconstriction following TBI may be due to an endothelin-1-induced pericyte-mediated regulation of microvessel blood flow following TBI. Furthermore, results suggest that ETrA antagonists ameliorate trauma induced hypoperfusion, in part, by inhibiting endothelin-1-mediated upregulation of alpha-SMA in pericytes.

Tezosentan Reduces the Renal Injury Induced by Abdominal Aortic Ischemia-Reperfusion in Rats

Renal injury induced by aortic ischemia-reperfusion (IR) is an important factor in the development of postoperative acute renal failure following abdominal aortic surgery. Endothelin (ET) is involved in the development of renal injury induced by aortic IR and tezosentan (R0 61-0612) is a specific ET receptor antagonist. The aim of this study was to examine the effect of tezosentan on renal injury induced by abdominal aortic IR in rats. Twenty-four Wistar-Albino rats were randomized into three groups (eight per group). Control group underwent laparotomy and dissection of the infrarenal abdominal aorta (IAA) without occlusion. The aortic IR group underwent laparotomy and clamping of the IAA for 120 min followed by 120 min of reperfusion. Aortic IR + tezosentan group underwent same aortic IR periods, and received a bolus intravenous injection of 10 mg/kg tezosentan before ischemia plus continuous intravenous infusion of 1 mg/kg/h tezosentan during 120 min ischemia and 120 min reperfusion. At the end of the experiment, blood and kidney tissue specimens were obtained for biochemical analysis. Histological evaluation of the rat kidney tissues was also done. Biochemical analysis showed that aortic IR significantly increased (P < 0.05 versus control) while tezosentan significantly decreased (P < 0.05 versus aortic IR) the tissue levels of malondialdehyde, superoxide dismutase, catalase and myeloperoxidase. Histological analyses showed that aortic IR significantly increased (P < 0.05 versus control) while tezosentan significantly decreased (P < 0.05 versus aortic IR) focal glomerular necrosis, dilatation of Bowman's capsule, degeneration of tubular epithelium, necrosis in tubular epithelium and tubular dilatation in the renal tissue samples. The results of this study indicate that tezosentan reduces renal injury induced by aortic IR in rats. We think that tezosentan exerted this beneficial effect via reducing oxidative stress and lipid peroxidation, inhibition of leukocyte infiltration into renal tissue and acting cytoprotective on renal tubular cells after aortic IR.

Endothelin is a downstream mediator of profibrotic responses to transforming growth factor β in human lung fibroblasts

Fibrosis is excessive scarring caused by the accumulation and contraction of extracellular matrix proteins and is a common end pathway in many chronic diseases, including scleroderma (systemic sclerosis [SSc]). Indeed, pulmonary fibrosis is a major cause of death in SSc. Transforming growth factor beta (TGFbeta) induces endothelin 1 (ET-1) in human lung fibroblasts by a Smad-independent, JNK-dependent mechanism. The goal of this study was to assess whether ET-1 is a downstream mediator of the profibrotic effects of TGFbeta in lung fibroblasts. We used a specific endothelin receptor antagonist to determine whether ET-1 is a downstream mediator of TGFbeta responses in lung fibroblasts, using microarray technology, real-time polymerase chain reaction, and Western blot analyses. The ability of TGFbeta to induce the expression of a cohort of profibrotic genes, including type I collagen, fibronectin, and CCN2, and to contract a collagen gel matrix, depends on ET-1. ET-1 contributes to the ability of TGFbeta to promote a profibrotic phenotype in human lung fibroblasts, consistent with the notion that endothelin receptor antagonism may be beneficial in controlling fibrogenic responses in lung fibroblasts.

Pharmacological and Functional Characterization of Endothelin Receptors in Bovine Trabecular Meshwork and Ciliary Muscle

To clarify the potential role of endothelin-1 (ET-1) in the pathogenesis of glaucoma, the endothelin receptors expressed in bovine trabecular meshwork (TM) and ciliary muscle (CM) were identified. TM and CM strips were subjected to ET-1 as well as to specific endothelin receptor antagonists. In both tissues BQ123, a specific ET-A receptor antagonist, substantially inhibited ET-1-induced contraction. BQ788, a specific ET-B receptor antagonist, showed only moderate effects. Both ET receptor types were detected in bovine TM and CM using Western blot analysis. ET-1 produced an increase in intracellular calcium in cultured TM cells. This effect was inhibited by BQ123, but not by BQ788. Thus, although both receptors are present, the ET-A receptor appears to play the predominant role in mediating contraction in both the TM and CM, while the ET-B receptor seems to contribute little to the overall ET-1 effect.

Endothelin Receptor A Blockade Ameliorates Hypothermic Ischemia–Reperfusion-Related Microhemodynamic Disturbances during Liver Transplantation in the Rat

Background. The objective of this study was to investigate the effect of graft treatment with specific endothelin receptor antagonists (ETA and ETB) on the microhemodynamic disturbances which occur following ischemia/reperfusion injury during orthotopic liver transplantation (OLT) in the rat.Materials and methods. OLT was performed in male Sprague–Dawley rats. An ETA receptor antagonist (BQ-610; 0.3 mg/kg) or ETB receptor antagonist IRL-1038 (20 nmol/kg) was administered intraportally into liver grafts in vitro at the beginning of 2- and 6-h cold storage (4°C) using physiological saline. Sham-operated animals served as controls (Cont). Seven groups were studied: Cont; vehicle—2 h (saline treated); ETB antagonist—2 h; ETA antagonist—2 h; vehicle—6 h; ETA antagonist—6 h; and ETB antagonist—6 h. At 1 h after graft implantation, the liver microcirculation was investigated by intravital fluorescence microscopy.Results. In vehicle-treated livers, the hepatic microcirculation was markedly impaired compared with the Cont as manifested by a reduced lobular perfusion index, increased incidence of sinusoidal nonperfusion, elevated leukocyte adhesion in sinusoids and terminal hepatic venules, and increased hepatic venous resistance (23-fold; 6-h group). In addition, plasma liver enzymes were significantly elevated in the vehicle treated groups. Alterations to all these parameters were markedly reduced in the ETA receptor antagonist-treated liver grafts although there was still evidence of hepatic injury. The ETB receptor antagonist had little effect on the I/R-induced changes to the hepatic microcirculation.Conclusions. Our results indicate that the ETA antagonism ameliorates hypothermic I/R-related microhemodynamic disturbances during OLT in the rat, suggesting that application of an ETA antagonist to liver grafts may have therapeutic potential in human liver transplantation.

Diagnostic and therapeutic potential of the endothelin system in patients with chronic heart failure.

There is now considerable evidence to support a role for the endothelin (ET) system in the pathogenesis and progression of chronic heart failure (CHF). As such, the potential exists for this system to be useful in both diagnosis (by measurement of peptide levels in plasma and other body fluids) and treatment (by pharmacological blockade) of this condition. Plasma levels of endothelin-1 (ET-1) are elevated in CHF and the magnitude of elevation correlates with disease severity. ET-1 levels in plasma predict subsequent mortality in patients with CHF. ET-1 may also contribute to symptoms associated with CHF, such as exercise intolerance. In the diagnosis of CHF, plasma levels of ET-1 appear to be a less powerful discriminator between patients with mild disease and control subjects with normal ventricular function on multivariate analyses, compared to brain natriuretic peptide (BNP), or its N-terminal fragment. ET-1 concentrations are also elevated in the saliva of patients with CHF and may represent an alternative approach to assessment of the status of the ET system in these patients. Specific ET receptor antagonists (both mixed and ET(A)-selective) have been developed. Studies with these agents in animal models of CHF have demonstrated beneficial effects via both haemodynamic and non-haemodynamic pathways. A number of short-term clinical studies have been performed demonstrating improvements in haemodynamic parameters without neurohormonal activation. Long-term clinical studies with ET receptor antagonists are currently underway to definitively test the impact of blockade of this system on mortality and major cardiovascular endpoints. Endothelin converting enzyme (ECE) inhibitors represent an alternative strategy of ET blockade, and early data from animal models suggest these agents may be of clinical utility, either alone or, more likely, in combination with other zinc metallopeptidases.

Inter-relationships between endothelin and prostaglandin F2alpha in corpus luteum function.

In cattle and other species, the corpus luteum plays a central role in the regulation of cyclicity and maintenance of pregnancy. In the absence of fertilization and implantation, the corpus luteum undergoes functional and morphological regression or luteolysis. Luteal regression is initiated in domestic ruminants by surges of prostaglandin F2alpha (PGF2alpha) from the uterus. Despite intensive investigation, the mechanisms by which PGF2alpha causes luteal regression remain undetermined. Recent studies from several laboratories have demonstrated that endothelial cells and their product, endothelin 1, are required for the manifestation of the luteolytic effects of PGF2alpha. Experimental evidence strongly supports the concept that luteal endothelin 1 inhibits luteal steroidogenesis and mediates the effects of PGF2alpha. Endothelin 1 caused a dose-dependent reduction in both basal and luteinizing hormone-stimulated biosynthesis of progesterone and prostacyclin, and an increase in PGF2alpha by ovine and bovine luteal cells. Specific receptors for endothelin 1 were identified on large and small bovine luteal cells, and the addition of specific endothelin receptor antagonists abolished the inhibitory effects of endothelin 1. Luteal endothelin 1 content increased as the cyclic corpus luteum aged, and the highest concentrations were observed during luteolysis. The amount of mRNA encoding endothelin 1 was greatly increased during the period of luteolysis. Gene expression for endothelin 1 was increased, in a time-dependent manner, in corpora lutea collected from heifers and ewes after exogenous administration of PGF2alpha. In heifers, exogenous PGF2alpha resulted in increased luteal output of endothelin 1. In ewes, the luteolytic effects of PGF2alpha were mitigated by pretreatment with a specific endothelin receptor antagonist. Administration of endothelin 1 or a sub-luteolytic dose of PGF2alpha to ewes reduced concentrations of jugular venous progesterone but did not shorten luteal lifespan. However, a combination of endothelin 1 and PGF2alpha acted synergistically to bring about complete luteolysis and reduced lifespan of the corpus luteum. In summary, endothelin 1 appears to have a direct effect on luteal cells in cattle and sheep, and it plays an essential role in mediating the luteolytic effects of PGF2alpha.

Inter-relationships between endothelin and prostaglandin F2alpha in corpus luteum function

In cattle and other species, the corpus luteum plays a central role in the regulation of cyclicity and maintenance of pregnancy. In the absence of fertilization and implantation, the corpus luteum undergoes functional and morphological regression or luteolysis. Luteal regression is initiated in domestic ruminants by surges of prostaglandin F2alpha (PGF2alpha) from the uterus. Despite intensive investigation, the mechanisms by which PGF2alpha causes luteal regression remain undetermined. Recent studies from several laboratories have demonstrated that endothelial cells and their product, endothelin 1, are required for the manifestation of the luteolytic effects of PGF2alpha. Experimental evidence strongly supports the concept that luteal endothelin 1 inhibits luteal steroidogenesis and mediates the effects of PGF2alpha. Endothelin 1 caused a dose-dependent reduction in both basal and luteinizing hormone-stimulated biosynthesis of progesterone and prostacyclin, and an increase in PGF2alpha by ovine and bovine luteal cells. Specific receptors for endothelin 1 were identified on large and small bovine luteal cells, and the addition of specific endothelin receptor antagonists abolished the inhibitory effects of endothelin 1. Luteal endothelin 1 content increased as the cyclic corpus luteum aged, and the highest concentrations were observed during luteolysis. The amount of mRNA encoding endothelin 1 was greatly increased during the period of luteolysis. Gene expression for endothelin 1 was increased, in a time-dependent manner, in corpora lutea collected from heifers and ewes after exogenous administration of PGF2alpha. In heifers, exogenous PGF2alpha resulted in increased luteal output of endothelin 1. In ewes, the luteolytic effects of PGF2alpha were mitigated by pretreatment with a specific endothelin receptor antagonist. Administration of endothelin 1 or a sub-luteolytic dose of PGF2alpha to ewes reduced concentrations of jugular venous progesterone but did not shorten luteal lifespan. However, a combination of endothelin 1 and PGF2alpha acted synergistically to bring about complete luteolysis and reduced lifespan of the corpus luteum. In summary, endothelin 1 appears to have a direct effect on luteal cells in cattle and sheep, and it plays an essential role in mediating the luteolytic effects of PGF2alpha.

Endothelin-1 increases the neuronal activity and augments the responses to glutamate in the NTS.

The aims of this study were to determine 1) whether endothelin (ET)-1 affects the neuronal activity of the NTS neurons, 2) whether specific ET receptor antagonists affect the neuronal activity of the NTS neurons, and 3) whether ET-1 or ET receptor antagonists modulate the responses of the nucleus of the solitary tract (NTS) neurons to L-glutamate (Glu). The single-unit discharge was extracellularly recorded with a fine electrode from medulla brain slice preparations of rats. ET-1 and Glu were iontophoretically applied to the recorded neuron. Both ET-1 and Glu increased the neuronal activity. The ETA receptor antagonist BQ-123 attenuated the basal neuronal activity. ET-1 augmented the magnitude of the increases in the neuronal activity evoked by Glu, and these responses were antagonized by BQ-123. These studies suggest the following conclusions: 1) ET-1 increases the neuronal activity of the NTS neurons via ETA receptors, 2) endogenous ET plays a controlling role of the neuronal activity of NTS neurons, and 3) ET-1 augments the responses evoked by Glu, believed to be the neurotransmitter from the solitary tract, via ETA receptors. These results suggest that ET-1 facilitates synaptic transmission in the NTS.

Defining the role of endothelins in renal pathophysiology on the basis of selective and unselective endothelin receptor antagonist studies.

The sensitivity of the renal vasculature to endothelin-1 together with the effect of the peptide on the kidney prompted investigators to study the role of endothelin-1 in renal pathophysiology. The kidney expresses both endothelinA and endothelinB receptors, which differ from species to species. Experiments employing specific endothelin receptor antagonists in experimental animals have suggested a role for endothelin-1 in ischaemia-induced acute renal failure and renal disease progression.