Endothelin receptor antagonists in cardiology clinical trials

Midregional pro-atrial natriuretic peptide: a novel marker of myocardial fibrosis in patients with hypertrophic cardiomyopathy

We aimed to determine the diagnostic performance of biomarkers in predicting myocardial fibrosis assessed by late gadolinium enhancement (LGE) cardiovascular magnetic resonance imaging (CMR) in patients with hypertrophic cardiomyopathy (HCM). LGE CMR was performed in 40 consecutive patients with HCM. Left and right ventricular parameters, as well as the extent of LGE were determined and correlated to the plasma levels of midregional pro-atrial natriuretic peptide (MR-proANP), midregional pro-adrenomedullin (MR-proADM), carboxy-terminal pro-endothelin-1 (CT-proET-1), carboxy-terminal pro-vasopressin (CT-proAVP), matrix metalloproteinase-9 (MMP-9), tissue inhibitor of metalloproteinase-1 (TIMP-1) and interleukin-8 (IL-8). Myocardial fibrosis was assumed positive, if CMR indicated LGE. LGE was present in 26 of 40 patients with HCM (65%) with variable extent (mean: 14%, range: 1.3-42%). The extent of LGE was positively associated with MR-proANP (r = 0.4; P = 0.01). No correlations were found between LGE and MR-proADM (r = 0.1; P = 0.5), CT-proET-1 (r = 0.07; P = 0.66), CT-proAVP (r = 0.16; P = 0.3), MMP-9 (r = 0.01; P = 0.9), TIMP-1 (r = 0.02; P = 0.85), and IL-8 (r = 0.02; P = 0.89). After adjustment for confounding factors, MR-proANP was the only independent predictor associated with the presence of LGE (P = 0.007) in multivariate analysis. The area under the ROC curve (AUC) indicated good predictive performance (AUC = 0.882) of MR-proANP with respect to LGE. The odds ratio was 1.268 (95% confidence interval 1.066-1.508). The sensitivity of MR-proANP at a cut-off value of 207 pmol/L was 69%, the specificity 94%, the positive predictive value 90% and the negative predictive value 80%. The results imply that MR-proANP serves as a novel marker of myocardial fibrosis assessed by LGE CMR in patients with HCM.

Lack of association between endothelin-1 gene variants and myocardial infarction

AIM

Endothelin-1 (ET-1) promotes vasoconstriction and cell proliferation, and has been implicated in hypertension and coronary artery disease. Our aim was to analyse the role of the ET-1 gene (EDN1) in the risk for atherosclerosis/myocardial infarction (MI) in a population with smoking as the prevalent risk factor.

METHODS

The study included 316 patients with early onset MI (<55 years old). All were male with at least one diseased coronary vessel. Denaturing high performance liquid chromatography (DHPLC), single-strand conformation analysis (SSCA), and direct sequencing were used to search for DNA variants in the five EDN1 exons and the promoter region. To determine the association of EDN1 polymorphisms with MI, we genotyped the patients and controls (n=350) and compared the allele and genotype frequencies between groups.

RESULTS

We found six common nucleotide changes: -1394 (T/G) and -974 C/A (promoter), +120 ins/del A (exon 1, 5' UTR), 568 A/G (exon 3, E106E), 844 G/T (exon 5, K198N), and 1617 T/C (exon 5, 3' UTR). No rare EDN1-variants specific to the MIpatients were found. None of the EDN1 polymorphisms were significantly associated with early-onset MI in our population. The two promoter polymorphisms were in linkage disequilibrium with K198N, but no haplotype was associated with MI risk.

CONCLUSIONS

In our population, the EDN1 variation did not contribute to early-onset MI.

Up-regulation of endothelin type B receptors in the human internal mammary artery in culture is dependent on protein kinase C and mitogen-activated kinase signaling pathways

Background

Up-regulation of vascular endothelin type B (ET_B) receptors is implicated in the pathogenesis of cardiovascular disease. Culture of intact arteries has been shown to induce similar receptor alterations and has therefore been suggested as a suitable method for, ex vivo, in detail delineation of the regulation of endothelin receptors. We hypothesize that mitogen-activated kinases (MAPK) and protein kinase C (PKC) are involved in the regulation of endothelin ET_B receptors in human internal mammary arteries.

Methods

Human internal mammary arteries were obtained during coronary artery bypass graft surgery and were studied before and after 24 hours of organ culture, using in vitro pharmacology, real time PCR and Western blot techniques. Sarafotoxin 6c and endothelin-1 were used to examine the endothelin ET_A and ET_B receptor effects, respectively. The involvement of PKC and MAPK in the endothelin receptor regulation was examined by culture in the presence of antagonists.

Results

The endohtelin-1-induced contraction (after endothelin ET_B receptor desensitization) and the endothelin ET_A receptor mRNA expression levels were not altered by culture. The sarafotoxin 6c contraction, endothelin ET_B receptor protein and mRNA expression levels were increased after organ culture. This increase was antagonized by; (1) PKC inhibitors (10 μM bisindolylmaleimide I and 10 μM Ro-32-0432), and (2) inhibitors of the p38, extracellular signal related kinases 1 and 2 (ERK1/2) and C-jun terminal kinase (JNK) MAPK pathways (10 μM SB203580, 10 μM PD98059 and 10 μM SP600125, respectively).

Conclusion

In conclusion, PKC and MAPK seem to be involved in the up-regulation of endothelin ET_B receptor expression in human internal mammary arteries. Inhibiting these intracellular signal transduction pathways may provide a future therapeutic target for hindering the development of vascular endothelin ET_B receptor changes in cardiovascular disease.

Cardiovascular endothelins: essential regulators of cardiovascular homeostasis

The endothelin (ET) system consists of 3 ET isopeptides, several isoforms of activating peptidases, and 2 G-protein-coupled receptors, ETA and ETB, that are linked to multiple signaling pathways. In the cardiovascular system, the components of the ET family are expressed in several tissues, notably the vascular endothelium, smooth muscle cells, and cardiomyocytes. There is general agreement that ETs play important physiological roles in the regulation of normal cardiovascular function, and excessive generation of ET isopeptides has been linked to major cardiovascular pathologies, including hypertension and heart failure. However, several recent clinical trials with ET receptor antagonists were disappointing. In the present review, the authors take the stance that ETs are mainly and foremost essential regulators of cardiovascular function, hence that antagonizing normal ET actions, even in patients, will potentially do more harm than good. To support this notion, we describe the predominant roles of ETs in blood vessels, which are (indirect) vasodilatation and ET clearance from plasma and interstitial spaces, against the background of the subcellular mechanisms mediating these effects. Furthermore, important roles of ETs in regulating and adapting heart functions to different needs are addressed, including recent progress in understanding the effects of ETs on diastolic function, adaptations to changes in preload, and the interactions between endocardial-derived ET-1 and myocardial pump function. Finally, the potential dangers (and gains) resulting from the suppression of excessive generation or activity of ETs occurring in some cardiovascular pathological states, such as hypertension, myocardial ischemia, and heart failure, are discussed.

Novel Benzo[1,4]diazepin-2-one Derivatives as Endothelin Receptor Antagonists

Since its discovery in 1988 by Yanagisawa et al., endothelin (ET), a potent vasoconstrictor, has been widely implicated in the pathophysiology of cardiovascular, cerebrovascular, and renal diseases. Many research groups have embarked on the discovery and development of ET receptor antagonists for the treatment of such diseases. While several compounds, e.g., ambrisentan 2, are in late clinical trials for various indications, one compound (bosentan, Tracleer) is being marketed to treat pulmonary arterial hypertension. Inspired by the structure of ambrisentan 2, we designed a novel class of ET receptor antagonists based on a 1,3,4,5-tetrahydro-1H-benzo[e][1,4]diazepin-2-one scaffold. Here, we report on the preparation as well as the in vitro and in vivo structure-activity relationships of these derivatives. Potent dual ET(A)/ET(B) receptor antagonists with affinities in the low nanomolar range have been identified. In addition, several compounds efficiently reduced arterial blood pressure after oral administration to Dahl salt sensitive rats. In this animal model, the efficacy of the benzo[e][1,4]diazepin-2-one derivative rac-39au was superior to that of racemic ambrisentan, rac-2.

Ischemic heart disease induce upregulation of endothelin receptor mRNA in human coronary arteries

Endothelin has been implicated in the pathogenesis of ischemic heart disease and congestive heart failure. The aims were to quantify endothelin type A (ETA) and type B (ETB) receptor mRNA levels in human coronary arteries from patients with ischemic heart disease, congestive heart failure and controls using real-time polymerase chain reaction (real-time PCR). In addition, the suitability of organ culture as a model mimicking endothelin receptor changes in cardiovascular disease was evaluated by in vitro pharmacology and real-time PCR. Endothelin ETA and ETB receptor mRNA levels were significantly higher in arteries from patients with ischemic heart disease (0.23+/-0.04 and 0.35+/-0.06) as compared to congestive heart failure (0.09+/-0.02 and 0.07+/-0.01) and controls (0.08+/-0.02 and 0.08+/-0.01). After organ culture, the endothelin ETB receptor mRNA levels were elevated, and the sarafotoxin 6c-induced vasoconstriction was more efficacious. Increased endothelin receptor activity may contribute to the increased vascular tone and development of atherosclerotic disease in ischemic heart disease in man.