Role of endothelin-1 in myocardial failure

Endothelin: 20 years from discovery to therapy

Since its identification as an endothelial cell-derived vasoconstrictor peptide in 1988, endothelin-1, the predominant member of the endothelin peptide family, has received considerable interest in basic medical science and in clinical medicine, which is reflected by more than 20 000 scientific publications on endothelin research in the past 20 years. The story of endothelin is unique as the gene sequences of endothelin receptors and the first receptor antagonists became available within only 4 years of the identification of the peptide sequence. The first clinical study in patients with congestive heart failure was published only 3 years thereafter. Yet, despite convincing experimental evidence of a pathogenetic role for endothelin in development, cell function, and disease, many initial clinical studies on endothelin antagonism were negative. In many of these studies, study designs or patient selection were inadequate. Today, for diseases such as pulmonary hypertension, endothelin antagonist treatment has become reality in clinical medicine, and ongoing clinical studies are evaluating additional indications, such as renal disease and cancer. Twenty years after the discovery of endothelin, its inhibitors have finally arrived in the clinical arena and are now providing us with new options to treat disease and prolong the lives of patients. Possible future indications include resistant arterial hypertension, proteinuric renal disease, cancer, and connective tissue diseases.

Induction and detection of disturbed homeostasis in cardiopulmonary bypass

During cardiopulmonary bypass (CPB) haemodynamic alterations, haemostasis and the inflammatory response are the main causes of homeostatic disruption. Even with CPB procedures of short duration, the homeostasis of a patient is disrupted and, in many cases, requires intensive postoperative treatment to re-establish the physiological state of the patient. Although mortality is low, disruption of homeostasis may contribute to increased morbidity, particularly in high-risk patients. Over the past decades, considerable technical improvements in CPB equipment have been made to prevent the development of the systemic inflammatory response syndrome (SIRS). Despite all these improvements, only the inflammatory response, to some extent, has been reduced. The microcirculation is still impaired, as measured by tissue degradation products of various organs, indicating that CPB may still be considered as an unphysiological procedure. The question is, therefore, whether we can detect the pathophysiological consequences of CPB in each individual patient with valid bedside markers, and whether we can relate this to determinant factors in the CPB procedure in order to assist the perfusionist in improving the adequacy of CPB. The use of these markers could play a pivotal role in decision making by providing an immediate feedback on the determinant quality of perfusion. Therefore, we suggest validating the proposed markers in a nomogram to optimize not only the CPB procedure, but also the patient's safety.

Plasma neurohormone levels correlate with left ventricular functional and morphological improvement in LVAD patients1

OBJECTIVE

Brain natriuretic peptide (BNP) and endothelin-1 (ET-1) have been shown to be markers of left ventricular (LV) function. To determine the feasibility of using serial assays of these neurohormones in the assessment of cardiac status in the left ventricular assist device (LVAD) setting, we examined the relationship between LV function, myocardial morphology, and plasma levels of these hormones in LVAD recipients.

METHODS

Plasma BNP and ET-1 levels were serially assayed in 19 end-stage congestive heart failure (CHF) patients before and after LVAD implantation with various devices (i.e., MicroMed DeBakeyVAD/DVAD, Novacor/NVAD, TCI Heartmate/TCI, Thoratec/TVAD). Echocardiography performed correspondingly at the time points of the hormonal assays and immunohistochemical collagen staining of left ventricular tissue samples, derived from six non-failing hearts as well as from LVAD patients at the time of device insertion and removal, were then contrasted. Patients were grouped according to device used and etiology of heart disease (ischemic or dilated cardiomyopathy, ICM/DCM).

RESULTS

LVAD therapy significantly improved LV ejection fraction (EF%: 21 +/- 3.8% to 28.11 +/- 3.57%), cardiac output (CO: 3.49 +/- 1.3 to 7.3 +/- 0.2 l/m), and left ventricular end-diastolic diameter (LVEDD: 6.68 +/- 0.92 versus 4.79 +/- 1.54 cm, P < 0.0001) in all patients. Absolute BNP and ET-1 plasma levels remained significantly lower in all patients after LVAD implantation (both P < 0.001). The NVAD group exhibited the most BNP reduction and EF% increase (P < 0.0004 and P < 0.038, respectively). Average collagen levels were reduced in all patients (P < 0.0005). Among the devices, the NVAD group demonstrated the most evident change (P < 0.0036), while there was comparable reduction in the DCM and ICM groups (both P < 0.03). In general, postoperative BNP and ET-1 trends exhibited a notable parallelism with both manifesting bi-phasic tendencies and an inverse proportionality to corresponding EF% measurements.

CONCLUSIONS

Device selection appears to influence the cardiac morphological and neurohormonal expressive tendencies exhibited by recipients. Plasma BNP and ET-1 levels correlate with both LV function and myocardial morphological improvement. Alterations in the levels of these hormones during LVAD support may be real-time indicators of prevailing myocardial autocrine/paracrine activity and as such may be of potential use in future algorithms of cardiac assessment and therapeutic decision-making with regard to transplant urgency and/or possible device explantation.

Exhaled nitric oxide: a marker of pulmonary hemodynamics in heart failure

OBJECTIVES

We sought to test the hypothesis that patients with decompensated heart failure (HF) lose a compensatory process whereby nitric oxide (NO) maintains pulmonary vascular tone.

BACKGROUND

Exhaled nitric oxide (eNO) partially reflects vascular endothelial NO release. Levels of eNO are elevated in patients with compensated HF and correlate inversely with pulmonary artery pressures (PAP), reflecting pulmonary vasodilatory activity.

METHODS

We measured the mean mixed expired NO content of a vital-capacity breath using chemiluminescence in patients with compensated HF (n = 30), decompensated HF (n = 7) and in normal control subjects (n = 90). Pulmonary artery pressures were also measured in patients with HF. The eNO and PAP were determined sequentially during therapy with intravenous vasodilators in patients with decompensated HF (n = 7) and in an additional group of patients with HF (n = 13) before and during administration of milrinone.

RESULTS

The eNO was higher in patients with HF than in control subjects (9.9 +/- 1.1 ppb vs. 6.2 +/- 0.4 ppb, p = 0.002) and inversely correlated with PAP (r = -0.81, p < 0.00001). In marked contrast, patients with decompensated HF exhibited even higher levels of eNO (20.4 +/- 6.2 ppb) and PAP, but there was a loss of the inverse relationship between these two variables. During therapy (7.3 +/- 6 days) with sodium nitroprusside and diuresis, hemodynamics improved, eNO concentrations fell (11.2 +/- 1.2 ppb vs. before treatment, p < 0.05), and the relationship between eNO and PAP was restored. After milrinone, eNO rose proportionally with decreased PAP (p < 0.05).

CONCLUSIONS

Elevated eNO may reflect a compensatory circulatory mechanism in HF that is lost in patients with clinically decompensated HF. The eNO may be an easily obtainable and quantifiable measure of the response to therapy in advanced HF.

Mediators of chronic heart failure: how drugs work

OBJECTIVE

To critically review the pathophysiology of chronic heart failure at the neurohormonal level, and discuss the effect of present and future therapeutic options on these neurohormones.

DATA SOURCES

A MEDLINE search (1986-November 2000) was used to identify important primary literature and reviews. Additional references were obtained from these articles.

DATA SYNTHESIS

Chronic heart failure is a common, progressive disorder with high morbidity and mortality. Progression is due in large part to several redundant neurohormonal responses. The neurohormones include angiotensin II, norepinephrine, aldosterone, endothelin-1, arginine vasopressin, and tumor necrosis factor. These responses are initially adaptive, but become maladaptive in the long term, impairing the function of the heart, vasculature, and kidneys. Counter-regulatory hormones, such as bradykinin and natriuretic peptides, are insufficient to offset the adverse effects of the other neurohormones. Most drugs used to treat chronic heart failure, such as angiotensin-converting enzyme inhibitors, beta-adrenergic antagonists, and spironolactone, achieve their benefits through altering the neurohormonal pathways. New agents that affect more or different neurohormones may soon be available.

CONCLUSIONS

Multiple agents are required for treatment of chronic heart failure, as no single agent can counteract all of the various adverse pathways. The appropriate prescription and use of such inherently complex regimens require significant physician and patient education.

ET(A)-receptor blockade prevents matrix metalloproteinase activation late postmyocardial infarction in the rat

Endothelin (ET) A (ET(A)) receptors activate matrix metalloproteinases (MMP). Since endothelin-1 (ET) is increased in myocardium late postmyocardial infarction (MI), we hypothesized that stimulation of ET(A) receptors contributes to activation of myocardial MMPs late post-MI. Three days post-MI, rats were randomized to treatment with the ET(A)-selective receptor antagonist sitaxsentan (n = 12) or a control group (n = 12). Six weeks later, there were rightward shifts of the left ventricular (LV) end-diastolic and end-systolic pressure-volume relationships, as measured ex vivo by the isovolumic Langendorff technique. Both shifts were markedly attenuated by sitaxsentan. In LV myocardium remote from the infarct, the activities of MMP-1, MMP-2, and MMP-9 were increased in the post-MI group, and the increases were prevented by sitaxsentan treatment. Expression of tissue inhibitor of MMP-1 was decreased post-MI, and the decrease was prevented by sitaxsentan treatment. Chronic post-MI remodeling is associated with activation of MMPs in myocardium remote from the infarct. Inhibition of ET(A) receptors prevents MMP activation and LV dilation, suggesting that ET, acting via the ET(A) receptor, contributes to chronic post-MI remodeling by its effects on MMP activity.

The role of endothelins and their receptors in heart failure

Endothelin (ET) is a peptide composed of 21 amino acids, derived from a larger precursor, the big-endothelin, by action of the endothelin-converting enzyme (ECE) family; three isoforms of endothelin, named ET-1, ET-2 and ET-3, have been identified. Endothelin-1 is generated mainly by vascular endothelial cells and exerts various important biological actions, mediated by two receptor subtypes, ET-A and ET-B, belonging to the G protein-coupled family that have been identified in various human tissues such as the cardiac tissue. Endothelin-1 is a potent vasoconstrictive agent, has inotropic and mitogenic actions, modulates salt and water homeostasis and plays an important role in the maintenance of vascular tone and blood pressure in healthy subjects. Endothelin-1, as well as ET-A and ECE-1, also has an important role in cardiovascular development, as observed by the variety of abnormalities related to neural crest-derived tissues in mouse embryos deficient of a member of the ET-1/ECE-1/ET-A pathway. Various evidence indicates that endogenous endothelin-1 may contribute to the pathophysiology of conditions associated with sustained vasoconstriction, such as heart failure. In heart failure, elevated circulating levels of both endothelin-1 and big-endothelin-1 are observed; in failing hearts an activation of the endothelin system is found: tissue level of ET-1 is increased with respect to non-failing hearts as well as receptor density, due mainly to an upregulation of the ET-A subtype, the prevalent receptor subclass in cardiac tissue. Finally, studies in both humans and animal models of cardiovascular disease show that inhibition of the endothelin function (anti-endothelin strategy) is associated with an improvement of haemodynamic conditions; these observations indicate that endothelin receptor antagonists or endothelin-converting enzyme inhibitors may constitute a novel and potentially important class of agents for the treatment of this disease.