The emerging role of endothelin-1 in the pathogenesis of pre-eclampsia

Abstract

Pre-eclampsia (PE) is the most frequently encountered medical complication during pregnancy. It is characterized by a rise in systemic vascular resistance with a relatively low cardiac output and hypovolemia, combined with severe proteinuria. Despite the hypovolemia, renin-angiotensin system (RAS) activity is suppressed and aldosterone levels are decreased to the same degree as renin. This suggests that the RAS is not the cause of the hypertension in PE, but rather that its suppression is the consequence of the rise in blood pressure. Abnormal placentation early in pregnancy is widely assumed to be an important initial event in the onset of PE. Eventually, this results in the release of anti-angiogenic factors [in particular, soluble Fms-like tyrosine kinase-1 (sFlt-1)] and cytokines, leading to generalized vascular dysfunction. Elevated sFlt-1 levels bind and inactivate vascular endothelial growth factor (VEGF). Of interest, VEGF inhibition with drugs like sunitinib, applied in cancer patients, results in a PE-like syndrome, characterized by hypertension, proteinuria and renal toxicity. Both in cancer patients treated with sunitinib and in pregnant women with PE, significant rises in endothelin-1 occur. Multiple regression analysis revealed that endothelin-1 is an independent determinant of the hypertension and proteinuria in PE, and additionally a renin suppressor. Moreover, studies in animal models representative of PE, have shown that endothelin receptor blockers prevent the development of this disease. Similarly, endothelin receptor blockers are protective during sunitinib treatment. Taken together, activation of the endothelin system emerges as an important pathway causing the clinical manifestations of PE. This paper critically addresses this concept, taking into consideration both clinical and preclinical data, and simultaneously discusses the therapeutic consequences of this observation.

Keywords: angiotensin; auto-antibody; cancer; endothelial growth factor; endothelin-1; nitric oxide; pre-eclampsia; soluble Fms-like tyrosine kinase 1; vascular endothelial growth factor.

Figure 1.

Endothelin (ET) synthesis and receptors in the vascular wall. ECE, endothelin-converting enzyme; ET_A, ET_B, endothelin type A and type B receptor. See text for explanation.

Figure 2.

Relationship between soluble Fms-like tyrosine kinase-1 (sFlt-1) and endothelin-1 (ET-1) in plasma obtained from healthy pregnant women and women with preeclampsia. Data have been modified from [Verdonk et al. 2015].

Figure 3.

Unifying model depicting the central role of endothelin-1 (ET-1) in pre-eclampsia. Decreased perfusion of the placenta results in placental hypoxia and soluble Fms-like tyrosine kinase-1 (sFlt-1) release. SFlt-1 binds free vascular endothelial growth factor (VEGF), thereby inactivating this factor and inducing endothelial dysfunction. As a consequence, ET-1 production is turned on, which not only induces hypertension and proteinuria but also suppresses renin release. Such suppression will also occur due to the rise in blood pressure. The renin suppression is accompanied by a parallel aldosterone suppression, illustrating that the latter is entirely due to diminished angiotensin generation. Diminished renin–angiotensin-aldosterone system activity combined with high blood pressure results in a reduced circulating volume, thereby further decreasing placental perfusion. In addition, ET-1 induces sFlt-1 release from the placenta, thereby generating a deleterious feed-forward mechanism.