Endothelin and endothelin antagonists: pharmacology and clinical implications

Role of the COP9 Signalosome (CSN) in Cardiovascular Diseases

The constitutive photomorphogenesis 9 (COP9) signalosome (CSN) is an evolutionarily conserved multi-protein complex, consisting of eight subunits termed CSN1-CSN8. The main biochemical function of the CSN is the control of protein degradation via the ubiquitin-proteasome-system through regulation of cullin-RING E3-ligase (CRL) activity by deNEDDylation of cullins, but the CSN also serves as a docking platform for signaling proteins. The catalytic deNEDDylase (isopeptidase) activity of the complex is executed by CSN5, but only efficiently occurs in the three-dimensional architectural context of the complex. Due to its positioning in a central cellular pathway connected to cell responses such as cell-cycle, proliferation, and signaling, the CSN has been implicated in several human diseases, with most evidence available for a role in cancer. However, emerging evidence also suggests that the CSN is involved in inflammation and cardiovascular diseases. This is both due to its role in controlling CRLs, regulating components of key inflammatory pathways such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and complex-independent interactions of subunits such as CSN5 with inflammatory proteins. In this case, we summarize and discuss studies suggesting that the CSN may have a key role in cardiovascular diseases such as atherosclerosis and heart failure. We discuss the implicated molecular mechanisms ranging from inflammatory NF-κB signaling to proteotoxicity and necrosis, covering disease-relevant cell types such as myeloid and endothelial cells or cardiomyocytes. While the CSN is considered to be disease-exacerbating in most cancer entities, the cardiovascular studies suggest potent protective activities in the vasculature and heart. The underlying mechanisms and potential therapeutic avenues will be critically discussed.

Does sleep quality affects the immediate clinical outcome in patients undergoing coronary artery bypass grafting: A clinico-biochemical correlation

Objective:

Poor sleep quality is emerging as high prevalence among the patients suffering from cardiometabolic disturbances. The vascular polypeptide endothelin 1 (ET-1) is involved in many of the health disorders. However, its potential involvement in patients having poor sleep quality along with cardiovascular problem is limited. The present study was formulated to conduct a prospective analysis of the relationship between ET-1 and in hospital outcome in sleep disorder patients undergoing routine coronary artery bypass grafting (CABG).

Methods:

A total of 156 patients were enrolled and divided into two groups based on the Pittsburg Sleep Quality Index (PSQI) of ≤5 (Group I, n = 101) or >5 (Group II, n = 55). Blood sample was collected before anesthesia induction (ET-1a) and at 48 h (ET-1b) to analyze the plasma ET-1 and blood sugar level. The patients were monitored for any intraoperative adverse events and postoperative complications during their hospital stay.

Results:

Both groups were comparable in relation to age, sex, incidence of smoking and alcohol consumption. The distribution of comorbid conditions was also similar in both groups. The ET-1 level was higher in Group II than Group I before anesthesia induction as well as 48 h postoperatively (4.5 ± 1.75 vs. 10.61 ± 9.3, P = 0.001; 2.08 ± 1.3 vs. 8.3 ± 9.86, P = 0.0001, respectively). The Group II patients had a longer duration of mechanical ventilation (14.6 ± 12.05 vs. 10.1 ± 8.19, P = 0.001), Intensive Care Unit stay (2.08 ± 0.95 vs. 2.7 ± 1.45, P = 0016) and hospital stay (5.98 ± 1.73 vs. 7.8 ± 3.66, P = 0.0001, respectively). The high number of patients from Group II required inotrope and intra-aortic balloon pump support while compared with Group I (P ≤ 0.05 in each). The overall postoperative complication rate was significantly higher among patients with PSQI of >5 (Group II) except the rate of infection and neurological complications which was similar among both group of patients. The postoperative in hospital mortality was nil in Group I and 3.6% in Group II (P = 0.05). There was a strong relationship between PSQI and ET-1 at both the time points.

Conclusion:

Poor sleep quality associated with a higher incidence of adverse perioperative events in patients undergoing elective CABG. There exists a potential link between poor sleep quality and ET-1 in these groups of patients.

[Bosentan use in pulmonary arterial hypertension: Russian and foreign experience]

The results of evaluating the efficacy and safety of bosentan in patients with pulmonary arterial hypertension (PAH), as shown by the data of foreign randomized controlled trials and the authors' own experience, convincingly demonstrate that the introduction of the drug into clinical practice has led to a significant improvement of the possibilities of drug therapy in patients with this serious illness. Bosentan substantially improves physical activity in patients, reduces the severity of clinical symptoms, slows down the rates of disease progression, and prolongs survival in patients with different forms of PAH.

Pulmonary Hypertension in Preterm Infants with Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD), the chronic lung disease of prematurity, is a significant contributor to perinatal morbidity and mortality. Premature birth disrupts pulmonary vascular growth and initiates a cascade of events that result in impaired gas exchange, abnormal vasoreactivity, and pulmonary vascular remodeling that may ultimately lead to pulmonary hypertension (PH). Even infants who appear to have mild BPD suffer from varying degrees of pulmonary vascular disease (PVD). Although recent studies have enhanced our understanding of the pathobiology of PVD and PH in BPD, much remains unknown with respect to how PH should be properly defined, as well as the most accurate methods for the diagnosis and treatment of PH in infants with BPD. This article will provide neonatologists and primary care providers, as well as pediatric cardiologists and pulmonologists, with a review of the pathophysiology of PH in preterm infants with BPD and a summary of current clinical recommendations for managing PH in this population.

Endothelin antagonism as an active principle for glaucoma therapy

Endothelin, the most potent vasoactive peptide known to date, has been suggested to play a potential role in the pathogenesis of open-angle glaucoma. Open-angle glaucoma is the most common optic nerve head neuropathy and is associated with a loss of retinal ganglion cells and visual field damage. Although an increased intraocular pressure is a major risk factor for glaucomatous optic neuropathy, other factors such as a reduced ocular blood flow play an important role for appearance of the disease. Thus, treatment of glaucoma is focused on lowering of intraocular pressure and preventing the occurrence or progression of glaucomatous optic neuropathy. Endothelin participates in the regulation of intraocular pressure by an effect on trabecular outflow, the main route for aqueous humour outflow from the eye. Trabecular outflow is modulated by trabecular meshwork contractility which is affected by endothelin. In addition to the effects of endothelin in the anterior part of the eye, the vasoconstrictor causes a decrease in ocular blood flow followed by pathological changes in the retina and the optic nerve head which is assumed to contribute to the degeneration of retinal ganglion cells. In sum, inhibition of endothelin signalling leads to lowering of intraocular pressure and exerts neuroprotective effects. Thus, endothelin antagonism in the eye represents a promising approach for pharmacological treatment of glaucoma.

Endothelin-1 and vasopressin plasma levels are not associated with the insertion/deletion polymorphism of the human angiotensin I-converting enzyme gene in patients with coronary artery disease

The objective was to investigate whether the renin-angiotensin (RA) system and related peptides endothelin-1 (ET-1) and vasopressin (VP) influence the development of coronary artery disease (CAD). Angiotensin I-converting enzyme (ACE) insertion/deletion (I/D) gene polymorphism has been associated with the risk of CAD. The ACE I/D polymorphism determines ACE activity, but plasma levels of other RA system components remain unchanged. However, ET-1 and VP production could be increased by RA system-dependent stimulation, continually promoted by paracrine stimulation and sustained by neointimal growth. ET-1 and VP have not been associated with the ACE I/D polymorphism so far. The present study investigated the association of the ACE I/D polymorphism with plasma concentrations of ET-1 and VP, as well as with renin, angiotensin-II (AT-II) and ACE activity in 98 Caucasian individuals with CAD. ACE I/D polymorphism showed no association with plasma levels of VP, ET-1, AT-II or renin. These parameters were also not associated taking into consideration different patient variables, such as diabetes mellitus, hypertension or severity of CAD. Only plasma ACE activity was associated with the D allele. In conclusion, the ACE I/D polymorphism could not be related to plasma concentrations of VP, ET-1, renin or AT-II, but as previously demonstrated, it could only be related to ACE activity in patients with CAD. Differences in ACE activity between ACE I/D genotype subgroups are probably compensated within the RA system itself or within non-ACE pathways, so that plasma concentrations of the related peptides ET-1 and VP remain unaffected.

Effects of cerebrovascular challenges on plasma endothelin

Plasma endothelin elevations have been associated with cerebrovascular pathology. Mechanisms of stimulation, however, are unknown. Therefore, in healthy subjects a marked physiological cerebrovascular response was experimentally provoked by hypercapnia, hypocapnia, and alternating capneic conditions. During these challenges plasma immunoreactive-endothelin-1 (ir-ET-1) concentrations were determined using a radioimmunassay. Physiological effects were continuously recorded for pCO(2), cerebral blood flow velocity, pulse frequency, and arterial blood pressure. No alterations in plasma ET-1 levels were found upon any of the cerebrovascular stimuli. We conclude that massive cerebrovascular challenges in healthy individuals do not lead to high circulating ET-1 levels.

Role of endothelin ET(A)- and ET(B)-receptors in haemodynamic compensation following haemorrhage in anaesthetized rats

1. This study examined the role of endothelin ET(A) and ET(B) receptors on haemodynamic compensation following haemorrhage (-17.5 ml kg(-1)) in thiobutabarbitone-anaesthetized rats. Rats were divided into four groups (n=6 each): time-control, haemorrhage-control, haemorrhage after treatment with FR 139317 (ET(A)-receptor antagonist), and haemorrhage after treatment with BQ-788 (ET(B)-receptor antagonist). 2. In the time-control rats, there were no significant changes in any haemodynamics for the duration of the experiments. Relative to the time-control rats, rats given haemorrhage had reduced mean arterial pressure (MAP), cardiac output (CO) and mean circulatory filling pressure (MCFP), but increased systemic vascular resistance (R(SV)). Venous resistance (R(V)) was slightly (but insignificantly) reduced by haemorrhage. MAP, however, gradually returned towards baseline (-17+/-4 and -3+/-2 mmHg at 10 and 60 min after haemorrhage, respectively) as a result of a further increase in R(SV). 3. Pre-treatment with FR 139317 (i.v. 1 mg kg(-1), followed by 1 mg kg(-1) h(-1)) accentuated haemorrhage-induced hypotension through abolition of the increase in R(SV). FR 139317 did not modify haemorrhage-induced changes in CO, MCFP and R(V). 4. Pre-treatment of BQ-788 (3 mg kg(-1)) did not affect MAP or MCFP following haemorrhage; however, CO was lower, and R(SV) as well as R(V) were higher relative to the readings in the haemorrhaged-control rats. 5. These results show that following compensated haemorrhage, ET maintains arterial resistance and blood pressure via the activation of ET(A) but not ET(B) receptors.

Effects of L-749,329, an ET(A)/ET(B) endothelin receptor antagonist, in a porcine coronary artery injury model of vascular restenosis

BACKGROUND

Previous studies in animal models of angioplasty have suggested a role in neointimal hyperplasia for endothelins (ETs), potent vasoconstricting peptides that also exert growth-promoting effects. The present studies were undertaken to test the hypothesis that endothelin receptor blockade can reduce neointimal thickening in injured porcine coronary arteries.

METHODS AND RESULTS

An ET(A)/ET(B) antagonist, L-749,329, was evaluated as an inhibitor of intimal thickening in a porcine balloon/stent model of coronary artery injury. L-749,329 competitively inhibited [(125)I]ET-1 binding to porcine ET(A) (IC(50) approximately 0.3 nmol/L) or ET(B) (IC(50) approximately 20 nmol/L) receptors and inhibited ET-1-stimulated signaling in cell culture. In anesthetized pigs, big ET-1-stimulated increases in systemic blood pressure were totally inhibited after intravenous infusion of L-749,329 (>/=0.2 mg. kg(-1). h(-1)). In vascular injury studies, pigs were treated with vehicle or L-749,329 (1 mg. kg(-1). h(-1)) beginning 2 days before and continuing 28 days after experimental angioplasty. Left anterior descending, left circumflex, and/or right coronary arteries were injured by inflation of an angioplasty balloon wrapped with a coiled metallic stent. After 28 days, mean neointimal thickness in the L-749,329-treated group was reduced by 9.0% compared with vehicle-treated controls, but this effect was not statistically significant (P=0.13).

CONCLUSIONS

Blockade of endothelin receptors for 28 days with only a mixed ET(A)/ET(B) receptor antagonist is insufficient to substantially inhibit intimal hyperplasia after balloon/stent coronary artery injury in the pig, in contrast to results with a selective ET(A) antagonist. The effects of selective or mixed ET(A)/ET(B) antagonists in diseased vessels remain to be determined in this model.

Control of coronary blood flow by autacoids

Coronary flow and thus myocardial perfusion is regulated by myogenic, metabolic, humoral and neuro-hormonal factors which closely interact with local autacoids released from the endothelial lining of the coronary bed. In a number of disease states an impaired synthesis and release of autacoids decisively limit the overall capacity of coronary regulation and adaptation of myocardial perfusion to increased metabolic demands. The important factors for these control mechanisms are analyzed and reviewed in this article.