Endothelin blockers and renal protection: a new strategy to prevent end-organ damage in cardiovascular disease?

Endothelin-1, big endothelin-1, and nitric oxide in patients with chronic renal disease and hypertension

The complex pathogenesis of chronic renal disease (CRD) depends on endothelin (ET) axis (ETs and ET receptors) and nitric oxide (NO) because of their vasoactive effects and their role in general modulation of vascular homeostasis. Various renal cells synthesize ETs and NO that play a significant role in renal hemodynamics as well as in water and salt excretion via urine. ET-1 is a strong vasoconstrictor. Besides its vasoactive effects, ET-1 modulates mitosis and apoptosis in a cell type-dependent manner, and may play an important role in CRD pathogenesis. The aims of this study were to emphasize the role and interactions of ET-1, Big ET-1, and NO in CRD. Concentrations of these vasoactive molecules were measured in plasma/serum and/or urine of 57 patients with diabetic nephropathy (subgroup 1), arterial hypertension (subgroup 2) or CRD with chronic renal insufficiency (subgroup 3), and in healthy control subjects (n=18). In comparison with control group, urine concentration of Big ET-1 was significantly increased (13.13 pmol/L vs. 11.34 pmol/L; P<0.001) in CRD patients, whereas plasma and urine concentrations of ET-1 did not differ significantly. NO concentrations were also significantly increased in CRD patients (serum, 72.55 micromol/L; P<0.001, and urine 141.74 micromol/L; P<0.05) as compared to control group. Study results indicated that Big ET-1 and NO could be useful diagnostic parameters in CRD for their diagnostic sensitivity and diagnostic specificity (Big ET-1 in urine: 56.1 and 88.9%, and NO in serum: 66.7 and 83.3%, respectively). In addition, Big ET-1 may prove useful in the differential diagnosis of diabetic nephropathy (78.6% diagnostic sensitivity and 88.9% diagnostic specificity).

The cytoskeleton and related proteins in the human failing heart

In addition to functional alterations, heart failure has a structural basis as well. This concerns all components of the cardiac myocytes as well as the extracellular space. Proteins of the cardiomyocyte can be subdivided in 5 different categories: 1) Contractile proteins including myosin, actin, tropomyosin and the troponins. 2) Sarcomeric skeleton: titin, myosin binding protein C, alpha-actinin, myomesin, and M-protein. 3) True 'cytoskeletal' proteins: tubulin, desmin and actin. 4) Membrane-associated proteins: dystrophin, spectrin, talin, vinculin, ankyrin and others. 5) Proteins of the intercalated disc: desmosomes consisting of desmoplakin, desmocollin, desmoglein and desmin; adherens junctions with N-cadherin, the catenins and vinculin, and gap junctions with connexin. Failing myocardium obtained from patients undergoing cardiac transplantation exhibits ultrastuctural degeneration and an altered nucleus/cytoplasm relationship. The contractile proteins and those of the sarcomeric skeleton, especially titin, are downregulated, the cytoskeletal proteins desmin and tubulin and membrane-associated proteins such as vinculin and dystrophin are upregulated and those of the intercalated disc are irregularly arranged. Elevation of cytoskeletal proteins correlates well with diastolic and contractile dysfunction in these patients. The enlarged interstitial space contains fibrosis, i.e. accumulations of fibroblasts and extracellular matrix components, in addition to macrophages and microvascular elements. Loss of the contractile machinery and related proteins such as titin and alpha-actinin may be the first and decisive event initiating an adaptive increase in cytoskeleton and membrane associated components. Fibrosis may be stimulated by subcellular degeneration. The hypothesis is put forward that all proteins of the different myocardial compartments contribute to the deterioration of cardiac function in heart failure.

Ambrisentan for pulmonary arterial hypertension

Endothelin receptor antagonists (ERAs) are an important class of agents used for the treatment of pulmonary arterial hypertension (PAH). Ambrisentan is an oral, once-daily, endothelin type-A receptor (ETA)-selective, propanoic acid class ERA under clinical investigation for the treatment of PAH. In a Phase II study, ambrisentan improved 6-minute walk distance, Borg dyspnea index, World Health Organization Functional Class, and hemodynamics. Ambrisentan was well tolerated and adverse events were not dose related, including a low incidence and severity of liver function test abnormalities. There are no relevant interactions between ambrisentan and cytochrome P450 isoenzymes (metabolism, induction or inhibition) that might alter the activity of P450-metabolized drugs. Potential benefits of ambrisentan include oral, once-daily dosing, ETA-receptor selectivity, and the decreased risks of liver toxicity and adverse drug–drug interactions compared with other ERAs.

Role of endothelins in animal models of hypertension: focus on cardiovascular protection

Investigation of the regulation of vascular function by endothelium-derived factors has been a prominent topic of research in the field of hypertension during the last decade. Of the different endothelial factors, endothelins, which play an important role in vasodilatation-vasoconstriction balance, have been the subject of great interest and an impressive number of publications. This peptide, a very potent vasoconstrictor, triggers as well events involved in growth, proliferation, matrix production and local inflammation. In parallel, its role in hypertension has evolved from a simple vasoconstrictor to a central local regulator of vascular homeostasis contributing not only to the elevation of blood pressure, but also to the complications of hypertension. This review summarizes research on endothelins and its receptor antagonists in experimental hypertension, with special emphasis on vascular remodeling and target-organ protection.

New therapeutics that antagonize endothelin: promises and frustrations

The discovery of endothelin--a highly potent endogenous vasoconstrictor - in 1988 has led to considerable efforts to develop antagonists of endothelin receptors that could have therapeutic potential in disorders including hypertension, heart failure and renal diseases. However, in general, the results of trials in humans have not mirrored the highly promising effects in animal disease models. Here, we discuss preclinical and clinical results with endothelin antagonists, and consider possible approaches to fully realizing the potential of endothelin antagonism.