Endothelins (ETs) are potent vasoactive peptides critical in the human body's various physiological and pathological processes. One of the most promising therapeutic strategies for treating pulmonary arterial hypertension (PAH) involves counteracting the effects of these endothelins using a class of drugs known as endothelin receptor antagonists.
ETs are synthesized through a complex sequence of enzymatic steps, primarily involving an enzyme referred to as endothelin-converting enzyme (ECE). Of particular interest is ECE-1, which acts as the rate-limiting step in synthesizing ET-1, the predominant form of endothelin within the body.
Upon synthesis, ET-1 interacts with two types of receptors — ETA and ETB. These interactions trigger biological responses within the body, including vasoconstriction and vasodilation, which can significantly impact blood pressure levels and contribute to conditions like PAH.
Currently, three main endothelin receptor antagonists are available for treating PAH: bosentan (Tracleer), macitentan (Opsumit), and ambrisentan (Letairis). All three drugs are administered orally and work by blocking the actions of ET-1 on its receptors. Bosentan and macitentan are non-selective antagonists, blocking both ETA and ETB receptors. This dual action helps alleviate PAH symptoms and slow disease progression. On the other hand, ambrisentan selectively inhibits the ETA receptor alone, providing a more targeted approach to treatment.
Like all medications, endothelin receptor antagonists come with potential side effects. Common ones include headaches, pulmonary edema (fluid accumulation in the lungs), and nasal congestion or pharyngitis. Additionally, these drugs can lead to elevated liver transaminases, an indicator of liver damage. As such, they should be avoided in patients with moderate-to-severe liver disease.
Pregnancy is another crucial consideration when prescribing these drugs. Due to their potential to cause harm to fetuses, endothelin antagonists should not be used during pregnancy. Women of childbearing age who are prescribed these medications should be advised to use effective contraception during treatment and afterward.
Endothelin receptor antagonists or ERAs counteract the effects of endothelins, or ETs, to treat pulmonary arterial hypertension or PAH.
ETs are produced through a sequence of steps involving endothelin-converting enzyme or ECE.
ECE-1, in particular, is the rate-limiting step in synthesizing ET-1, the predominant form of endothelin.
ET-1 interacts with receptors, ETA, and ETB and triggers both vasoconstriction and vasodilation in the pulmonary arteries.
Currently, three oral ERAs are available for PAH treatment.
Bosentan and macitentan block both ETA and ETB receptors, effectively reducing PAH progression and symptoms, while ambrisentan selectively inhibits ETA.
Common side effects of these drugs include headache, pulmonary edema, nasal congestion, and pharyngitis.
These drugs may elevate liver transaminases, rendering them unsuitable for patients with moderate-to-severe liver disease.
Importantly, due to potential harm to fetuses, endothelin antagonists must be avoided during pregnancy.
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