Endothelin and endothelin receptor antagonism in heart failure

Association of 18bp insertion/deletion polymorphism, at -2549 position of VEGF gene, with diabetic vascular complications in type 2 diabetes mellitus

PURPOSE

Diabetes mellitus type 2 (T2DM) and its vascular complications are a serious world health problem. For this reason it is important to look for new diabetes complication risk factors. The aim of this study was to determine whether 18-bp insertion/deletion (I/D) polymorphism at -2549 position of the vascular endothelial growth factor (VEGF) gene is associated with diabetic vascular complications (DVC).

MATERIAL AND METHODS

Caucasian subjects (n = 100) with T2DM were recruited for this study. Genotyping of the VEGF gene I/D polymorphism was done by the polymerase chain reaction (PCR) method. The results were correlated with laboratory and clinical data.

RESULTS

In our population heterozygous of the VEGF gene polymorphism was observed most frequently (57%). DVC were observed in 53 patients. Heterozygous T2DM patients significantly more often suffered from heart failure (HF) and stroke (p = 0.05). Amongst all the DVC, D allele of the VEGF polymorphism had a significantly increased risk of diabetic retinopathy (DR) (OR = 1.31; p = 0.033) irrespective of the duration of diabetes, BMI, the glycemia control expressed by HbA1c, renal function, lipid values or applied treatment. The studied polymorphism did not correlate with coronary heart disease, peripheral vascular disease, cardiovascular death, diabetic kidney disease or applied treatment.

CONCLUSIONS

The multivariate logistic regression analysis showed that the D allele in the promoter region of the VEGF gene is an independent risk factor of DR irrespective of other laboratory and clinical variables in T2DM patients. Our study suggests that I/D allele in the studied gene is associated with HF and strokes.

Effect of endothelins on the cardiovascular system

Endothelins (ETs) exert a persistent constrictor effect on the vessels via an increase in intracellular Ca2+ concentration due to the activation of Na+/H+ and Na+/Ca2+ exchangers of the vascular smooth muscle fibres. They also produce a transient dilator effect via the activation of endothelial nitric oxide synthase mediated by protein kinase B/Akt. ETA and ETB2 receptors are involved in vasoconstriction, whereas transient vasodilatation depends on the activation of ETB1 receptors. Depending on animal species and experimental conditions, ETs can also play a role in cardiac muscle contraction and induce either an increase or a decrease in contractility. It is likely that only ETA, and not ETB, receptors are involved in the ET-induced increase in myocardial contractility. As in the case of vasoconstriction, this inotropic effect depends on an increase in intracellular Ca2+ concentration induced by Na+/H+ and Na+/Ca2+ exchangers. Activation of the Na+/H+ exchanger is stimulated by protein kinase C, which is activated by diacylglycerol released in response to ET activity. It has also been proposed that the positive inotropic effect can occur without the contribution of the Na+/Ca2+ exchanger, if the cell alkalinisation produced by the Na/H exchanger improves myofibrillar Ca2+ sensitivity. A reduction in contractility has been attributed to the involvement of the Gi protein/protein kinase G pathway or to the activation of protein kinase C without an increase in intracellular Ca2+ concentration or in myofibrillar Ca2+ sensitivity. The chronic effect of ETs on the myocardium results in hypertrophy and prevention of apoptosis, two processes that are together responsible for the contradictory effect of ETs in heart failure.

Aldosterone breakthrough during ras blockade: A role for endothelins and their antagonists?

Activation of the renin-angiotensin system (RAS), with ensuing aldosterone excess, detrimentally affects outcome in patients with hypertension and heart failure (HF). RAS blockade with angiotensin (Ang) 1-converting enzyme inhibitors (ACEIs) or Ang II type 1 receptor blockers (ARBs) is beneficial in such conditions. However, aldosterone secretion can persist despite these treatments. Hence, mechanisms besides Ang II acquire the role of aldosterone secretagogue. The RALES and EPHESUS studies have shown that this aldosterone "escape" or "breakthrough" is an important factor, because it is a determinant of outcome in HF patients. Endothelin (ET)-1, which stimulates aldosterone secretion via both A (ETA) and B (ETB) receptor subtypes, and which is increased in HF, is a candidate for the "aldosterone breakthrough." Moreover, the novel ET peptide ET-1(1-31) is involved in adrenocortical growth. Therefore, findings suggesting a role for the ET-1 system as an aldosterone secretagogue, along with the potential usefulness of endothelin antagonists for the prevention of "aldosterone breakthrough," are discussed.

ET(B) receptor in renal medulla is enhanced by local sodium during low salt intake

Renal endothelin-1 participates in sodium and water handling, and its urinary excretion is increased in sodium-retentive states. We compared the cortical and medullary renal expression of prepro-endothelin-1, endothelin-converting enzyme-1, and endothelin type A and type B receptors in patients who underwent nephrectomy after normal (108 mmol/d NaCl; n=6) or low (20 mmol/d NaCl; n=6) sodium diet and investigated whether sodium exerts a direct role on endothelin receptor binding in vitro. With normal sodium diet prepro-endothelin-1 mRNA was 3-fold higher in renal medulla than in cortex (P<0.01), whereas endothelin-converting enzyme-1 mRNA was equally distributed. Endothelin-1 receptor density was 2-fold higher in renal medulla than in cortex (P<0.05). Type B was the main receptor subtype in both regions. In the renal cortex, low sodium diet caused a 194% increase in prepro-endothelin-1 mRNA (P<0.05), whereas endothelin-converting enzyme-1 type B and type A receptors remained unchanged. In contrast, in the renal medulla the increase in prepro-endothelin-1 mRNA (+30%, P<0.05) was associated with a selective increase in type B receptor for both mRNA expression (+37%, P<0.05) and binding density (+55%, P<0.05). Increasing in vitro sodium concentrations between 154 and 308 mmol/L significantly enhanced type B receptor density (P<0.05) and affinity (P<0.05). In conclusion, during low sodium diet, renal prepro-endothelin-1 synthesis increases mainly in the renal cortex (where no changes in receptors occur), whereas type B receptor is selectively enhanced in the renal medulla. The range of sodium concentrations that are physiologically present in vivo in the renal medulla selectively modulate type B receptor density and affinity.

Reciprocal regulation of endothelin-1 and nitric oxide: relevance in the physiology and pathology of the cardiovascular system

The endothelium plays a crucial role in the regulation of cardiovascular structure and function by releasing several mediators in response to biochemical and physical stimuli. These mediators are grouped into two classes: (1) endothelium-derived constricting factors (EDCFs) and (2) endothelium-derived relaxing factors (EDRFs), the roles of which are considered to be detrimental and beneficial, respectively. Endothelin-1 (ET-1) and nitric oxide (NO) are the prototypes of EDCFs and EDRFs, respectively, and their effects on the cardiovascular system have been studied in depth. Numerous conditions characterized by an impaired availability of NO have been found to be associated with enhanced synthesis of ET-1, and vice versa, thereby suggesting that these two factors have a reciprocal regulation. Experimental studies have provided evidence that ET-1 may exert a bidirectional effect by either enhancing NO production via ETB receptors located in endothelial cells or blunting it via ETA receptors prevalently located in the vascular smooth muscle cells. Conversely, NO was found to inhibit ET-1 synthesis in different cell types. In vitro and in vivo studies have started to unravel the molecular mechanisms involved in this complex interaction. It has been clarified that several factors affect in opposite directions the transcription of preproET-1 and NO-synthase genes, nuclear factor-KB and peroxisome proliferator-activated receptors playing a key role in these regulatory mechanisms. ET-1 and NO interplay seems to have a great relevance in the physiological regulation of vascular tone and blood pressure, as well as in vascular remodeling. Moreover, an imbalance between ET-1 and NO systems may underly the mechanisms involved in the pathogenesis of systemic and pulmonary hypertension and atherosclerosis.

Current limitations in treatment of heart failure: new avenues and treatment options

Chronic heart failure is one of the main causes of death in western countries. Despite state-of-the-art treatment including angiotensin-converting enzyme inhibitors, beta-blockers, and spironolactone, survival and relief from symptoms still are unacceptably poor in patients with chronic heart failure. The present article gives an overview of current limitations in the treatment of heart failure and points out possible treatment options in the future. It seems possible to reduce or at least delay progression of heart failure by adding drugs that interfere with novel pathophysiologic aspects in heart failure activation of the neuroendocrine system, including catecholamines, angiotensin II, cytokines, and endothelins, as well as alteration of calcium homeostasis and energy depletion.