Comparison of the regulation of endothelin-2 and endothelin-converting enzyme-1 b [correction of beta] by forskolin and TNF-alpha in ACHN cells

Endothelin-2, the forgotten isoform: emerging role in the cardiovascular system, ovarian development, immunology and cancer

Endothelin-2 [ET-2; also known as vasoactive intestinal contractor (VIC), in rodents] differs from endothelin-1 (ET-1) by only two amino acids, and unlike the third isoform, endothelin-3 (ET-3), it has the same affinity as ET-1 for both ET(A) and ET(B) receptors. It is often assumed that ET-2 would mimic the actions of the more abundant ET-1 and current pharmacological interventions used to inhibit the ET system would also block the actions of ET-2. These assumptions have focused research on ET-1 with ET-2 studied in much less detail. Recent research suggests that our understanding of the ET family requires re-evaluation. Although ET-2 is very similar in structure as well as pharmacology to ET-1, and may co-exist in the same tissue compartments, there is converging evidence for an important and distinct ET-2 pathway. Specifically is has been demonstrated that ET-2 has a key role in ovarian physiology, with ET-2-mediated contraction proposed as a final signal facilitating ovulation. Furthermore, ET-2 may also have a pathophysiological role in heart failure, immunology and cancer. Comparison of ET-2 versus ET-1 mRNA expression suggests this may be accomplished at the level of gene expression but differences may also exist in peptide synthesis by enzymes such as endothelin converting enzymes (ECEs) and chymase, which may allow the two pathways to be distinguished pharmacologically and become separate drug targets. LINKED ARTICLES This article is part of a themed section on Endothelin. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.168.issue-1.

Endothelin converting enzyme-1 expression in endometrial adenocarcinomas

Endothelin-1 (ET-1) is a potent mitogen in various precursor tumor cells, including endometrial adenocarcinoma. It is proposed that ET-1 produced by endometrial adenocarcinoma may participate in the angiogenesis of this carcinoma in vivo. Endothelin converting enzyme-1 (ECE-1) is the key enzyme that synthesizes ET-1. In this study, we tried to demonstrate the expression of ECE-1 in endometrial carcinomas. Deparaffinized tissue sections from patients with endometrial adenocarcinoma were analyzed by immunohistochemistry for the presence of ECE-1. Our study showed that the expression of ECE-1 was markedly increased in 9 of 15 (60%) well-differentiated endometrial adenocarcinomas; in contrast, only 2 out of 10 (20%) control specimens showed a mild labeling. With new selective inhibitory molecules emerging, research is currently evaluating the possible inhibition of ECE-1 as an alternative approach for the treatment of endometrial as well as other carcinomas.

Regulation of the hepatic endothelin system in advanced biliary fibrosis in rats

The aim of the present study was to analyze the hepatic endothelin system and its regulation in liver cirrhosis due to bile duct obstruction. Wistar rats were subjected for 6 weeks to: 1) sham operation; 2) bile duct obstruction; 3) bile duct obstruction and the selective oral endothelin A receptor antagonist LU 135252; 4) bile duct obstruction and oral silymarin, a hepatoprotective and antifibrotic compound. We determined tissue concentrations of endothelin-1 and big-endothelin-1 by ELISA and the density of both endothelin receptor subtypes in plasma membrane fractions by Scatchard analysis. The hepatic endothelin system in liver cirrhosis due to chronic bile duct obstruction is characterized by a simultaneous up-regulation of both endothelin-1 tissue concentration (7.2 fold compared to sham operation; p<0.001) as well as the density of both endothelin receptor subtypes (ET(A) 7.4-fold, ET(B) 4.9-fold, p<0.001, respectively) suggesting a synergistic activation of the hepatic endothelin system in this rat model of non-inflammatory cirrhosis. Treatment with proven antifibrotic agents such as silymarin or a selective endothelin-A-receptor blocker (LU 135252) did not reduce the activity of the hepatic endothelin system, suggesting that the hepatic endothelin system is not activated by the fibrotic process itself.