ET(A) receptor antagonist ameliorates nephrosclerosis and left ventricular hypertrophy induced in rat by prolonged inhibition of nitric oxide synthesis

Endothelin Receptor Antagonists in Kidney Disease

Endothelin (ET) is found to be increased in kidney disease secondary to hyperglycaemia, hypertension, acidosis, and the presence of insulin or proinflammatory cytokines. In this context, ET, via the endothelin receptor type A (ET_A) activation, causes sustained vasoconstriction of the afferent arterioles that produces deleterious effects such as hyperfiltration, podocyte damage, proteinuria and, eventually, GFR decline. Therefore, endothelin receptor antagonists (ERAs) have been proposed as a therapeutic strategy to reduce proteinuria and slow the progression of kidney disease. Preclinical and clinical evidence has revealed that the administration of ERAs reduces kidney fibrosis, inflammation and proteinuria. Currently, the efficacy of many ERAs to treat kidney disease is being tested in randomized controlled trials; however, some of these, such as avosentan and atrasentan, were not commercialized due to the adverse events related to their use. Therefore, to take advantage of the protective properties of the ERAs, the use of ET_A receptor-specific antagonists and/or combining them with sodium-glucose cotransporter 2 inhibitors (SGLT2i) has been proposed to prevent oedemas, the main ERAs-related deleterious effect. The use of a dual angiotensin-II type 1/endothelin receptor blocker (sparsentan) is also being evaluated to treat kidney disease. Here, we reviewed the main ERAs developed and the preclinical and clinical evidence of their kidney-protective effects. Additionally, we provided an overview of new strategies that have been proposed to integrate ERAs in kidney disease treatment.

Upregulation of adrenomedullin and its receptor components during cardiomyocyte hypertrophy induced by chronic inhibition of nitric oxide synthesis in rats

Adrenomedullin may provide a compensatory mechanism to attenuate left ventricular hypertrophy (LVH). Nitric oxide synthase inhibition, induced by chronic administration of N(omega)-nitro-L-arginine methyl ester (L-NAME) to rats, induces cardiac hypertrophy in some, but not all cases; there are few reports of direct assessment of cardiomyocyte parameters. The objective was to characterize hypertrophic parameters in left (LV) and right ventricular (RV) cardiomyocytes after administration of L-NAME to rats for 8 wk and to determine whether adrenomedullin and its receptor components were upregulated. After treatment with L-NAME (20 and 50 mg x kg(-1) x day(-1)), compared with nontreated animals, 1) systolic blood pressure increased (by 34.2 and 104.9 mmHg), 2) heart weight-to-body wt ratio increased 24.1% at the higher dose (P < 0.05), 3) cardiomyocyte protein mass increased (P = NS), 4) cardiomyocyte protein synthesis ([14C]phenylalanine incorporation) increased (P < 0.05), 5) expression of skeletal alpha-actin, atrial natriuretic peptide, brain natriuretic peptide, and ET-1 mRNAs was enhanced (P < 0.05) in LV but not RV cardiomyocytes at 20 and 50 mg x kg(-1) x day(-1), respectively, and 6) expression of adrenomedullin, receptor activity-modifying protein 3 (RAMP3), and RAMP2 (but not calcitonin receptor-like receptor and RAMP1) mRNAs was increased by L-NAME (20 mg x kg(-1) x day(-1)) in LV. In conclusion, L-NAME enhanced protein synthesis in both LV and RV cardiomyocytes but elicited a hypertrophic phenotype accompanied by altered expression of the counterregulatory peptide adrenomedullin and receptor components (RAMP2, RAMP3) in LV only, indicating that the former is due to impaired nitric oxide synthesis, whereas the phenotypic changes are due to pressure overload.

Differential effects of antihypertensive drugs on renal and glomerular hemodynamics and injury in the chronic nitric-oxide-suppressed rat

BACKGROUND/AIMS

Prolonged nitric oxide synthase (NOS) inhibition with N(omega)-nitro-L-arginine methylester in normotensive and hypertensive rats has been demonstrated to produce severe systemic and glomerular hypertension with glomerular sclerosis, and these changes have become a useful experimental model of hypertensive nephrosclerosis. This review summarizes data from our serial studies as well as work of others who are also investigating the effects of the commonly used antihypertensive drugs (including calcium antagonist, angiotensin-converting enzyme inhibitor, angiotensin II type 1 receptor blocker, aldosterone antagonist and thiazide diuretic) on renal and glomerular hemodynamics, renal function and glomerular histopathology using this model.

METHODS

A Medline search was performed to identify the relevant literature describing renal effects of antihypertensive drugs in models of hypertension and nephrosclerosis produced or exacerbated by NOS inhibition.

RESULTS

Existing data have indicated that most of these drug classes have produced dramatic renoprotective effects, structurally or functionally, on nephrosclerosis induced by prolonged NOS inhibition.

CONCLUSION

This review of experimental studies has provided strong evidence supporting the clinical benefits of antihypertensive drugs for hypertensive patients with renal impairment particularly those with endothelial dysfunction associated with NOS deficiency.

Role of endothelin-1/endothelin receptor system in endotoxic shock rats

Endothelin (ET)-1, a potent vasoconstrictor peptide derived from the endothelium, is markedly increased in endotoxic shock, although the pathophysiological role of ET-1 under septic conditions remains obscure. To delineate the role of ET-1 and its receptor subtype in endotoxic shock, we here attempted to determine the changes of circulating levels of ET-1 and its biosynthetic intermediate big ET-1 in endotoxic shock rats, to evaluate the gene expression of ET-1 as well as the ET-1 receptor subtypes (ETA and ETB) in the heart, lung and liver, and to study the effects of ET receptor antagonists on systemic arterial blood pressure, heart rate and survival rate. Administration of bacterial lipopolysaccharide (LPS) caused profound hypotension, increased heart rate and death, and these effects were blocked by a nonselective ETA/ETB receptor antagonist (TAK044), but not by an ETA selective antagonist (BQ123). Administration of exogenous ET-1 caused a profound pressor response in control rats, but not in the LPS-pretreated rats. Injection of LPS caused marked elevation of plasma levels of both ET-1 and big ET-1, which were not affected by treatment with either ET receptor antagonist. Administration of LPS caused up-regulation of ET-1 and ETB receptor mRNA in the heart, whereas ETA receptor mRNA was markedly down-regulated in the heart, lung and liver. These data suggest differential gene regulation of ET-1 and its receptor subtypes in various organs from endotoxic shock rats, and that nonselective ETA/ETB receptor antagonist, but not ETA receptor antagonist, ameliorates endotoxin-induced hypotension and death.

Genetic analysis of nitric oxide and endothelin in end-stage renal disease

BACKGROUND

Genetic factors have been implicated in the development of the common aetiologies of end-stage renal disease (ESRD), including renal failure attributed to hypertension, diabetes mellitus, systemic lupus erythematosus and human immunodeficiency virus infection. Nitric oxide (NO) and endothelin are powerful vasoactive mediators involved in inflammation and regulation of vascular tone and blood pressure. We evaluated the role of the neuronal constitutive (NOS1) and endothelial constitutive (NOS3) nitric oxide synthase genes and the endothelin-1 (EDN-1) gene in predisposition to chronic renal failure in African-Americans.

METHODS

The study population for the linkage and association analyses in ESRD consisted of 361 individuals from 168 multiplex African-American families. These individuals comprised 207 unweighted sibling pairs concordant for all-cause ESRD. Microsatellite markers NOS1B (NOS1), D7S636 (NOS3) and CPHD1-1/2 (EDN-1) were genotyped in the sample. In addition, a mutation, Glu298Asp, in exon 7 of NOS3 and a 27 bp variable number tandem repeat (VNTR) marker in intron 4 of NOS3 were evaluated in the sibling pairs and in an additional 92 unrelated African-Americans with type 2 diabetes mellitus-associated ESRD (singletons). Association analyses utilized the relative predispositional effect method. Model independent linkage analyses were performed using GeneHunter-plus and MapMaker/SIBS (exclusion analysis) software.

RESULTS

Significant evidence for association with ESRD was detected for alleles 7 and 9 of the NOS1 gene (11.9 and 34.2%, respectively, in unrelated probands of ESRD families versus 6.5 and 27.5%, respectively, in race-matched controls, both P:<0.01). These associations were maintained when the unrelated first sibling from each family was used in a case-control comparison and was most pronounced in the non-diabetic ESRD cases. The NOS3 and EDN-1 markers failed to provide consistent evidence for association in the sibling pairs and the diabetic ESRD singletons, although we identified two novel endothelial constitutive NOS4 (ecNOS4) VNTR alleles in African-Americans. Significant evidence for linkage was not detected between the NOS genes or the EDN-1 gene in either all-cause ESRD or when the ESRD sibling pairs were stratified by aetiology (type 2 diabetic ESRD or non-diabetic aetiologies).

CONCLUSION

Based upon the consistent allelic associations, we believe that further evaluation of the NOS1 gene in ESRD susceptibility in African-Americans is warranted.

Endothelin and renal vascular fibrosis: of mice and men

The present review focuses on recent data regarding the role of endothelin as a mediator of renal vascular fibrosis. Following a brief description of the endothelin system, the question of whether endothelin is involved in hypertensive mechanisms is examined in experimental, genetic and transgenic animal models. Evidence is provided that implicates endothelin as an important factor of the development of tissue fibrosis and end-organ damage associated with hypertension, with particular emphasis on renal vascular fibrosis. Data indicating that endothelin interacts with other vasoconstrictor systems, such as angiotensin II, are also considered. Finally, results from preliminary clinical studies using endothelin receptor antagonists to treat cardiac and renal pathologies are briefly discussed.