Regional haemodynamic effects of endothelin-1 in rat and man: unexpected adverse reaction

Endothelin-1 was infused into the non-dominant brachial artery in two male subjects. We then monitored intra-arterial mean blood pressure, right atrial pressure, the heart rate and forearm blood flow (by plethysmography). Endothelin-1 at a dose of 5 x 10(-14) to 5 x 10(-9) mol, infused over 5 min periods, elicited no major changes in mean arterial pressure, heart rate and right atrial pressure. We observed an initial increase in forearm blood flow, followed by dose-dependent decreases of 25, 34 and 42% at 5 x 10(-11) to 5 x 10(-9) mol. A higher dose of endothelin-1, 5 x 10(-8) mol, given to only one of the subjects, elicited sweating and vomiting. In this subject, mean arterial pressure, right atrial pressure and the heart rate did not change, while forearm blood flow increased transiently. A deep muscular pain developed in the forearm receiving the endothelin-1 infusion after 30 min (maximum 2 h, duration 10 h), and this pain was intensified by touch and muscle contractions. The force of muscle contractions in the forearm was markedly reduced and a visible oedema developed. In order to investigate the mechanisms of oedema formation, endothelin-1 (10(-10) to 5 x 10(-8) mol/l) was given intra-arterially in a rat hindquarter preparation which was perfused at a constant flow rate. In the rat, endothelin-1 increased both pre- and postcapillary resistance, leading to an increase in capillary hydrostatic pressure and a marked net transcapillary fluid transfer from the perfusate to tissue. There was no sign of increased vascular permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelin and myocardial ischemia

Endothelin is a potent vasoconstrictor with a wide range of effects on the heart. Changes in myocardial and circulating levels of endothelin have been described in various experimental models of myocardial ischemia, and in humans with acute myocardial infarction and different forms of angina pectoris. The role played by endothelin in the different states of myocardial ischemia is unclear. However, myocardial damage has been shown to be reduced in several experimental models of myocardial infarction by administering agents that block the action of endothelin. The aim of this review article is to present the current literature concerning the interaction between endothelin and the various forms of myocardial ischemia, and to explore the significance of such interactions.

Safety and Efficacy of Sovateltide (IRL-1620) in a Multicenter Randomized Controlled Clinical Trial in Patients with Acute Cerebral Ischemic Stroke

BACKGROUND

Sovateltide (IRL-1620, PMZ-1620), an endothelin-B receptor agonist, has been previously shown to increase cerebral blood flow, have anti-apoptotic activity and produce neurovascular remodeling when administered intravenously following acute cerebral ischemic stroke in rats. Its safety and tolerability were confirmed in healthy human volunteers (CTRI/2016/11/007509).

OBJECTIVE

Our objective was to determine the safety, tolerability and efficacy of sovateltide as an addition to standard of care (SOC) in patients with acute cerebral ischemic stroke.

METHODS

A prospective, multicentric, randomized, double-blind, placebo-controlled study was conducted to compare the safety (primary objective) and efficacy (secondary objective) of sovateltide in patients with acute cerebral ischemic stroke. Adult males or females aged 18-70 years who had experienced a radiologically confirmed ischemic stroke within the last 24 h were included in the study. Patients with intracranial hemorrhage and those receiving endovascular therapy were excluded. Patients randomized to the sovateltide group received three doses of sovateltide (each dose 0.3 µg/kg) administered as an intravenous bolus over 1 min at an interval of 3 ± 1 h on day 1, day 3 and day 6 (total dose of 0.9 µg/kg/day). Patients randomized to the placebo group received an equal volume of saline. Every patient in both groups received SOC for stroke. Efficacy was evaluated using neurological outcomes based on National Institute of Health Stroke Scale (NIHSS), modified Rankin Scale (mRS) and Barthel Index (BI) scores from day 1 through day 90. Quality of life was measured using the EuroQoL-5 Dimensions (EQ-5D) and Stroke-Specific Quality of Life (SSQoL) at 60 and 90 days of follow-up.

RESULTS

A total of 40 patients with acute cerebral ischemic stroke were enrolled in this study, of whom 36 completed the 90-day follow-up. Patients received saline (n = 18; 11 male and 7 female) or sovateltide (n = 18; 15 male and 3 female) within 24 h of onset of stroke. The number of patients receiving investigational drug within 20 h of onset of stroke was 14/18 in the saline group and 10/18 in the sovateltide group. The baseline characteristics and SOC in both cohorts was similar. Sovateltide was well-tolerated, and all patients received complete treatment with no incidence of drug-related adverse events. Hemodynamic, biochemical or hematological parameters were not affected by sovateltide. Sovateltide treatment resulted in improved mRS and BI scores on day 6 compared with day 1 (p < 0.0001), an effect not seen in the saline group. Sovateltide increased the frequency of favorable outcomes at 3 months. An improvement of ≥ 2 points on the mRS was observed in 60 and 40% of patients in the sovateltide and saline groups, respectively (p = 0.0519; odds ratio [OR] 5.25). An improvement on the BI of ≥ 40 points was seen in 64 and 36% of the sovateltide and saline groups, respectively (p = 0.0112; OR 12.44). An improvement of ≥6 points on the NIHSS was seen in 56% of patients in the sovateltide group versus 43% in the saline group (p = 0.2714; OR 2.275). The number of patients with complete recovery (defined as an NIHSS score of 0 and a BI of 100) was significantly greater (p < 0.05) in the sovateltide group than in the saline group. An assessment of complete recovery using an mRS score of 0 did not show a statistically significant difference between the treatment groups. Sovateltide treatment resulted in improved quality of life as measured by the EQ-5D and SSQoL on day 90.

CONCLUSION

Sovateltide was safe and well-tolerated and resulted in improved neurological outcomes in patients with acute cerebral ischemic stroke 90 days post-treatment.

TRIAL REGISTRATION

The study is registered at CTRI/2017/11/010654 and NCT04046484.

Role of endothelin in endotoxin-induced hepatic microvascular dysfunction in rats fed chronically with ethanol

BACKGROUND

We examined the role of endothelin in endotoxin-induced hepatic microcirculatory disturbance in pair-fed rats given a liquid diet containing ethanol or isocaloric control.

METHODS AND RESULTS

One lobe of the liver was observed with the use of an intravital microscope. Erythrocytes (RBCs) labeled with fluorescein isothiocyanate (FITC) were injected, and the flow velocity of the FITC-RBCs in the sinusoids was measured with an off-line velocimeter. The flow velocity decreased 30 min after 1 mg/kg of lipopolysaccharide (LPS) was administered to the controls, and portal pressure (PP) was increased at 60 min. In ethanol-fed rats, however, both the flow velocity and PP increased in the early phase (at 10 min), and in the late phase, flow velocity decreased and PP increased more than in the controls. The LPS-induced decrease in flow velocity was blunted, when BQ-123, an antagonist of endothelin receptor subtype A, was infused into ethanol-fed rats, and BQ-123 also attenuated the change in PP. The plasma endothelin levels in both systemic and portal blood of the ethanol-fed rats were higher than in the controls.

CONCLUSIONS

These results suggest that endothelin plays a role in the LPS-induced hepatic microcirculatory disturbance, especially in alcohol-fed animals.

Vasoactive effect of endothelin-1 on rat liver in vivo

The purpose of this study was to evaluate the role of endothelin-1 in modulating hepatic microcirculation and liver damage. Rats were infused with endothelin-1 at doses ranging from 30 to 1,000 pmol/kg over 1 min through an indwelling cannula placed in the portal vein. In control rats, saline solution was infused at the same rate. Alterations in hepatic microcirculation were measured with an in vivo microscopy system. Serum lactate dehydrogenase activity, an indicator of hepatic damage, was measured 1 hr after endothelin-1 infusion. Immediately after infusion of endothelin-1, we noted a rapid increase in portal pressure, which remained increased for up to 30 min after endothelin-1 infusion. In contrast, systemic blood pressure remained unchanged, even at 1,000 pmol/kg of endothelin-1. Sinusoidal width was reduced and sinusoidal erythrocyte velocity was diminished in a dose-dependent manner. Oxygen saturation of blood in sinusoids was decreased in a dose-dependent manner, reaching values around 40% of control with 1,000 pmol/kg endothelin-1. The degree of decrease in oxygen saturation of blood in sinusoids had an excellent correlation with the calculated blood flow in the liver tissue. Serum lactate dehydrogenase levels were three to four times control values when endothelin-1 was administered at 1,000 pmol/kg. Thus endothelin-1 decreased hepatic tissue oxygenation associated with sinusoidal vasoconstriction. At high concentrations of endothelin-1, this decrease results in hepatocellular damage.

Endothelin is a key modulator of progressive renal injury: experimental data and novel therapeutic strategies

1. Glomerulosclerosis and tubulointerstitial damage are common histological abnormalities of many renal diseases that progress to end-stage renal failure. 2. In some models of renal damage, glomerulosclerosis seems to be associated with increased glomerular capillary pressure. 3. Due to the positive correlation of glomerulosclerosis and proteinuria in both experimental models and in humans, abnormal permeability to macromolecules has also been considered a possible determinant of glomerulosclerosis. 4. Abnormally filtered macromolecules have an intrinsic toxicity to the kidney due to protein over-reabsorption, possibly leading to tubulointerstitial damage. 5. Endothelin-1 (ET-1) is a vasoconstrictor peptide that induces mitogenesis and the accumulation of matrix proteins by mesangial cells. 6. Evidence is available that ET-1 plays a role in progressive renal disease in different experimental models, including renal mass reduction, lupus nephritis, streptozotocin-induced diabetes and puromycin-induced nephrosis.

Subepicardial microischemia formation induced by epicardial application of endothelin-1

The effects of endothelin-1 (ET-1), applied topically on the epicardium, on the coronary microcirculation of the beating canine heart were investigated in situ. ET-1 (1, 10, 100, and 1,000 pmol) induced a dose-dependent elevation of the ST segment in the epicardial ECG (n = 5). After application of ET-1 (100 pmol), the beating hearts were rapidly cross-sectioned and freeze-clamped in 120 ms using a specially developed device (n = 6). By NADH fluorescence photography of the cross-sectioned frozen sample, an increased fluorescent area in the subepicardium was clearly observable. The fluorescent dye injected from the left atrium was negative in the NADH fluorescent area. It can be concluded that ET-1, when administered extravascularly, induces severe vasoconstriction and myocardial ischemia in the microcirculation of the beating canine heart.

Submucosal microinfusion of endothelin and adrenaline mobilizes ECL-cell histamine in rat stomach, and causes mucosal damage: a microdialysis study

Rat stomach ECL cells release histamine in response to gastrin. Submucosal microinfusion of endothelin or adrenaline, known to cause vasoconstriction and gastric lesions, mobilized striking amounts of histamine. While the histamine response to gastrin is sustainable for hours, that to endothelin and adrenaline was characteristically short-lasting (1-2 h). The aims of this study were to identify the cellular source of histamine mobilized by endothelin and adrenaline, and examine the differences between the histamine-mobilizing effects of gastrin, and of endothelin and adrenaline. Endothelin, adrenaline or gastrin were administered by submucosal microinfusion. Gastric histamine mobilization was monitored by microdialysis. Local pretreatment with the H1-receptor antagonist mepyramine and the H2-receptor antagonist ranitidine did not prevent endothelin- or adrenaline-induced mucosal damage. Submucosal microinfusion of histamine did not cause damage. Acid blockade by ranitidine or omeprazole prevented the damage, suggesting that acid back diffusion contributes. Gastrin raised histidine decarboxylase (HDC) activity close to the probe, without affecting the histamine concentration. Endothelin and adrenaline lowered histamine by 50-70%, without activating HDC. Histamine mobilization declined upon repeated administration. Endothelin reduced the number of histamine-immunoreactive ECL cells locally, and reduced the number of secretory vesicles. Thus, unlike gastrin, endothelin (and adrenaline) is capable of exhausting ECL-cell histamine. Microinfusion of alpha-fluoromethylhistidine (known to deplete ECL cells but not mast cells of histamine) reduced the histamine-mobilizing effect of endothelin by 80%, while 1-week pretreatment with omeprazole enhanced it, supporting the involvement of ECL cells. Somatostatin or the prostanoid misoprostol inhibited gastrin-, but not endothelin-stimulated histamine release, suggesting that endothelin and gastrin mobilize histamine via different mechanisms. While gastrin effectively mobilized histamine from ECL cells in primary culture, endothelin had no effect, and adrenaline, a modest effect. Hence, the striking effects of endothelin and adrenaline on ECL cells in situ are probably indirect, possibly a consequence of ischemia.

Eclampsia-like seizures and electroencephalographic changes in pregnant rabbits with endothelin-1 injections

To examine the possible role of endothelin and vasospasm in eclamptic seizures, we studied and analyzed the electroencephalograms (EEG) of endothelin-1 (ET-1)-treated pregnant, nonpregnant and sham control (dextrose-treated) rabbits. After multiple intravenous bolus injections of ET-1 (500 pmol/kg) or 5% dextrose in the rabbits, we recorded EEG directly from the brain cortex and analyzed by Fast Fourier Transform (FFT). Water content was measured in the brain of all groups (n = 7). Repeated seizures occurred in all of the pregnant and 2 of the nonpregnant rabbits by variable doses of ET-1. FFT analysis showed remarkable changes in frequency and power arrays characterized by mild to severe form of dysrhythmia, high-voltage spikes, high-voltage fast and slow waves after ET-1 injections. Water content was increased in brain mass in ET-1-treated rabbits (p = 0.001) suggesting an ET-1-induced edema. Histologically we confirmed that ET-1 caused ischemic changes in brain tissues. However, ET-1 induced more pronounced changes in behavior, EEG, brain edema or ischemia in pregnant than in nonpregnant groups. The injections of exogenous ET-1 into the brain substances were strongly suggested by immunohistochemical study with polyclonal antiendothelin antibody in brain tissue sections. Therefore, we assume that endothelin along with other vasoactive substances causes acute cerebral vasospasm and ischemia inducing EEG changes leading to ultimate clinical convulsions in eclampsia.

Profile of past and current clinical trials involving endothelin receptor antagonists: the novel "-sentan" class of drug

Since its initial characterization in 1988, over 18,236 papers, including 2,485 reviews, have been published in the endothelin (ET) field. Over this period, several generations of selective and mixed (dual) ET receptor antagonists (ERAs), from peptidic backbones to orally active potent (subnanomolar) small molecular compounds, have been developed. These agents have been studied in many experimental animal models of various pathological conditions (cardiovascular, respiratory, and neuro-immunological). Continued basic research has led to a better understanding of the complex interactions between the ET axis and other biologic systems in human pathophysiology. The first clinical trial involved patients with idiopathic pulmonary arterial hypertension and led to approval of bosentan (Tracleer) for use in the United States and Europe in 2002. Since then, bosentan, the only currently approved dual (mixed) ERA, has been used in numerous other clinical trials. In addition, more selective ET(A) receptor antagonists (ambrisentan, atrasentan, avosentan, clazosentan, darusentan, and sitaxsentan) are undergoing clinical trials. Here we outline the ERAs undergoing development and summarize the standing of completed and ongoing trials at the time of the Ninth International Conference on Endothelin and even thereafter. This review is intended to provide a useful reference for those interested in the current state of clinical trials involving ERAs, and to identify lessons that might apply to the design of future trials.

[Effects of vasoactive peptides on the development of restenosis]

OBJECTIVE

To investigate the effects of several vasoactive peptides on the development of restenosis.

METHODS

The model of balloon angioplasty to the rat aorta was prepared and used to study the changes of endothelin (ET), angiotensin II (A II), calcitonin gene-related peptide (CGRP) and adrenomedullin (Adm) in the plasma and aorta tissues, with radioimmuno-assay. (3)H-TdR incorporation and intima/media ratio of aortic tissue were measured after angioplasty. In cultured vascular smooth muscle cells, effects of these peptides on the proliferation of VSMC were evaluated with (3)H-TdR incorporation. Effects of these peptides on the expression of hypertension-related gene (HRG-1) in aorta tissue and cultured VSMC from SHR and WKY rats were studied by semi-quantitative RT-PCR.

RESULTS

After angioplasty, the levels of ET and A II in the plasma and/or aorta tissue were significantly increased, with VSMC proliferation. On day 10 after angioplasty, the levels of ET in the plasma and tissue were increased by 69% and 124% respectively, compared with the that in the control group (P < 0.01); and the levels of aortic A II were increased by 80% (P < 0.01). Antiserum against ET and angiotensin converting enzyme (ACE) inhibitors could obviously inhibit the proliferation of VSMC and neointima formation. Compared with the sham group on day 3 after angioplasty, the CGRP levels in plasma and aorta tissue were increased by 64% and 89% respectively (P < 0.01); the Adm levels in the plasma and aorta tissue were increased by 129% and 102% respectively (P < 0.01). On day 10, intravenous administration of CGRP significantly inhibited the proliferation of VSMC and neointima formation induced by balloon aortic injury with the inhibitory rate of 66% and 79%, respectively, (P < 0.01). ET and A II attenuated the expression of HRG-1 in the aorta, thus activating mitogen activated protein kinase (MAPK). CGRP and Adm potentiated the expression of HRG-1, thus inhibiting the activity of MAPK.

CONCLUSIONS

ET and A II stimulate the proliferation of injured intima, and CGRP and Adm have an anti-hyperplasia effects after angioplasty. That these peptides are suggested to be involved in the regulation of proliferation of VSMC and to affect the developing of vascular restenosis, by means of regulating the expression of HRG-1 and MAPK activities.

[Evaluation of bunazosin hydrochloride with a model of ocular circulation disturbance induced by endothelin-1]

We studied the effect of bunazosin hydrochloride, a selective alpha-1 blocker under development as an antiglaucomatous drug, on the circulation of the optic nerve head (ONH) in normal and endothelin-1 treated albino rabbit eyes. The effect was investigated by measurement of the capillary blood flow in the ONH, using a hydrogen gas clearance flowmeter (for 5 hours). The relative caliber of the retinal artery (the caliber of the retinal artery at the edge of the ONH/that of the ONH) was also measured, using fundus photography. Administration of bunazosin hydrochloride had no significant effect on the capillary blood flow in the ONH in normal eyes, but it inhibited the decrease of blood flow for at least 5 hours in the endothelin-1 treated eyes. The relative caliber of the retinal artery decreased in the endothelin-1 treated eyes (maximum at 5 hours), but previous administration of bunazosin hydrochloride inhibited the decrease. Thus, Bunazosin hydrochloride inhibits the disturbance of ONH circulation induced by endothelin-1 and promises to be useful also with regard to the ocular circulation.

[Effect of inhibition by 17beta-estradiol on endothelin-induced proliferation of vascular smooth muscle cells]

AIM AND METHODS

To determine the effect of 17 beta-estradiol on proliferation of cultured vascular smooth muscle cells (VSMC) and expression of ET(A) receptor mRNA stimulated by endothelin-1 (ET-1). The experimental models of proliferation in cultured rat aortic smooth muscle cells induced by ET-1 was established. The 3H-thymidine ([3H]-TdR) incorporation, cell counts and reverse transcription-polymerase chain reaction (RT-PCR) were used in this study.

RESULTS

BQ123, the selective ET(A) receptor antagonist, inhibited the increase of [3H]-TdR incorporation and cell number in response to ET-1 of VSMC.17 beta-estradiol may reverse the increase of [3H] TdR incorporation and cell number stimulated by ET-1. 17 beta-estradiol downregulated of ET(A) receptor mRNA expression, with the maximum at 12 hours, which was partially prevented by tamoxifen, an estrogen receptor antagonist.

CONCLUSION

The proliferation of VSMC stimulated by ET-1 was mainly through ET(A) receptor. 17 beta-estradiol inhibited the proliferation of VSMC stimulated by ET-1, which might be through downregulation of ET(A) receptor.

Basic research into the mechanisms responsible for postmenopausal hypertension

Women typically experience increased cardiovascular disease (CVD) following menopause. Major risk factors for CVD include hypertension and, after menopause, blood pressure increases in women. The mechanism(s) responsible for this increase are not determined. Changes in oestrogen/androgen ratios, possible activation of the renin-angiotensin system, and increases in endothelin and oxidative stress, are hallmarks in postmenopausal women. Obesity, type 2 diabetes and activation of the sympathetic nervous system may also play important roles. However, progress in clarifying the mechanisms responsible for postmenopausal hypertension has been hampered by lack of a suitable animal model. We have recently characterised the ageing female spontaneously hypertensive rat (SHR) as a model of postmenopausal hypertension, since this strain exhibits many of the humoral characteristics of postmenopausal women. This review discusses some of the mechanisms that could play a role in postmenopausal hypertension, as well as the characteristics of the ageing female SHR as a model.

Endothelin-1-induced oedema in rat and guinea-pig isolated perfused lungs

Endothelin-1 caused an increase in perfusion pressure, bronchial resistance, lung weight and tracheal effusion when infused through the pulmonary artery of rat and guinea-pig isolated lungs. In contrast to vasoconstriction, the effects of endothelin-1 on bronchial resistance, lung weight and tracheal effusion were not concentration-dependent. Recovery from vasoconstriction occurred within 15-30 min when the lung was further perfused with Krebs buffer. Increases in lung weight, bronchial resistance and tracheal effusion induced by endothelin-1 were irreversible when infused at concentrations above 10(-10) M. UK 38,485, a thromboxane A2 synthesis inhibitor, partly prevented the increase in lung weight and tracheal effusion without altering the vasoconstriction induced by endothelin-1. Such an antagonism was not seen in guinea-pig lung at the concentration used. Iloprost, a stable analogue of prostacyclin, antagonized the effects of endothelin-1 on perfusion pressure and lung weight without reducing tracheal effusion in both rat and guinea-pig lungs. Pretreatment with allopurinol did not alter the effects of endothelin-1. These results were taken as evidence for the potent lung oedema-producing effect of the peptide which seems to be partially mediated by the secondary release of thromboxane A2.