Healing Hearts: How Angiotensin 1-7 Could Revolutionize Cardiac Recovery After Heart Attacks
"Discover how the naturally occurring peptide Angiotensin 1-7 (Ang(1-7)) could promote cardiac repair and improve heart function post-infarction."
When a heart attack, or myocardial infarction (MI), strikes, the heart's battle to repair itself begins. This repair involves angiogenesis, the growth of new blood vessels, and inflammatory responses in the damaged heart tissue. This process helps maintain the heart's structural integrity and is vital for recovery. However, sometimes, the heart can remodel in ways that aren't helpful, leading to fibrosis (stiffening of tissue) and hypertrophy (enlargement) in the undamaged areas.
Scientists have been focusing on what controls this repair and remodeling. The renin-angiotensin system (RAS), a hormone system that regulates blood pressure and fluid balance, plays a significant role. Angiotensin II (AngII), a key player in the RAS, can stimulate processes that lead to repair but also remodeling. Recently, a new understanding of the RAS has emerged with the discovery of angiotensin-converting enzyme 2 (ACE2).
ACE2 generates Angiotensin (1-7) [Ang(1-7)], which interacts with Mas receptors to trigger protective cellular actions. Ang(1-7) has shown promise in countering issues such as apoptosis (cell death), fibrosis, and hypertrophy in the heart following an MI. In this article, we delve into how Ang(1-7) might regulate angiogenesis and improve heart function after a heart attack.
Angiotensin 1-7 and Cardiac Repair
Angiotensin-(1-7) has been reported to promote angiogenesis in infarcted rat hearts through the Mas receptor. The proposed mechanism involves increased expression of vascular endothelial growth factor D (VEGF-D) and matrix metalloproteinase-9 (MMP-9). The same research describes cardioprotective effects related to reduced fibrosis and hypertrophy.
How Angiogenesis Works
Angiogenesis is the formation of new blood vessels from existing ones or the creation of new capillaries from preexisting vessels. It requires coordinated extracellular-matrix degradation, increased vascular permeability, endothelial-cell proliferation, migration, invasion, and vessel formation. Chemical signals such as vascular endothelial growth factor (VEGF) help regulate this process, which occurs throughout life but must be carefully balanced because angiogenesis also supports cancer growth.
Ang(1-7): A Key to Cardiac Angiogenesis?
The study investigates whether Ang(1-7) regulates cardiac angiogenesis and contributes to cardiac repair. The research involved examining the expression of ACE2 and Mas receptors in rats post-MI, alongside administering a Mas receptor antagonist (A779) to assess Ang(1-7)'s role.
- Creating an MI Model: Left ventricular anterior transmural MI was induced in female Sprague Dawley rats through permanent ligation of the left coronary artery.
- Monitoring ACE2 and Mas Receptor Expression: The levels of ACE2 and Mas receptors in the heart tissue were tracked over time in both control and MI rats.
- Administering A779: Some MI rats were treated with A779, a Mas receptor antagonist, to block the effects of Ang(1-7).
- Assessing Vascular Density: The growth of new blood vessels in the infarcted area was quantified using CD31 staining, a marker for vascular endothelial cells.
- Evaluating Cardiac Function: Echocardiography was performed to assess heart function, including left ventricular dimensions and fraction shortening.
- Measuring Angiogenic Mediators: The expression of various factors involved in angiogenesis, such as VEGF-D and MMP-9, was measured using RT-PCR.
VEGF-D, MMP-9, and Mas Signaling
Reviews report that cardiac angiotensin-converting enzyme 2 produces angiotensin 1-7, which stimulates VEGF-D and MMP-9 expression in the heart and may promote angiogenesis, recovery, and improved ventricular function. Other cited research associates angiotensin 1-7 with vascular endothelial growth factor and MMP-9 expression, improved vascular endothelial function, and delayed heart-failure development after myocardial infarction. Experimental studies have also reported angiogenesis and tissue-healing effects in heart disease models.
Testing the Mas Receptor
Experimental work in myocardial-infarction rats has tested whether angiotensin 1-7 effects depend on the Mas receptor. In the reported design, one group of infarcted rats received the Mas receptor antagonist A779 at 1 mg/kg/day through a minipump for seven days, while another group did not receive the antagonist. This antagonist-based design reflects a test of receptor involvement rather than proof that angiotensin 1-7 will produce the same results in human cardiac recovery.
What the Study Tells Us
The study reveals that Ang(1-7) promotes angiogenesis in the infarcted myocardium by stimulating the expression of VEGF-D and MMP-9. Blocking Mas receptors with A779 reduced vascular density and impaired ventricular function, highlighting the importance of Ang(1-7) signaling in cardiac repair. This suggests that Ang(1-7) could be a therapeutic target for improving cardiac function post-MI. More research is needed to fully understand the potential of Ang(1-7) in cardiac care.
Mapping RAAS Pathways
Future research must account for the fact that both renin-angiotensin-aldosterone system pathways operate in the heart and lung. In the heart, the classic RAAS contributes to hemodynamics and tissue remodeling. These processes are associated with cardiomyocyte and endothelial dysfunction and can lead to progressive functional impairment.