The Relationship Between ACE/ACE2 And CHF Cardiac Remodeling

Background and ObjectiveThe prevention of chronic heart failure (CHF) has been a major subject in both basic science research and clinical research. Since mid-1990s, it has been recognized that cardiac remodeling constitutes the pathophysiological basis leading to the development of CHF. This has transformed the treatment strategy for CHF, from one focusing on increasing myocardial contractility to one emphasizing the prevention of cardiac remodeling. Clinical research has found that all treatment methods that can reverse cardiac remodeling are effective in improving prognosis and lowering mortality, as cardiac remodeling is a crucial factor determining both the morbility and mortality rates of CHF patients—regardless of the origin of the disease.Cardiac remodeling is a self-evolving process that is most closely related to renin-angiotensin system (RAS), and particularly localized RAS at the heart—which has much greater pathological significance than circular RAS. Traditionally it is believed that angiotensin converting enzyme (ACE) is one key element in RAS, as it is responsible for a catalysis that produces angiotensin II (Ang II)—a key effector of RAS. In 2000, Donoghue first discovered a homologue of ACE, which he named ACE2. As its major biological effect, ACE2 degenerates Ang II and produces Ang1-7. Ang1-7 functions in a way that is opposite to Ang II, as it can relax blood vessel, resist hyperplasy and inflammation, and protect failing hearts by inhibiting and reversing cardiac remodeling.Heart is not only an important target organ of RAS, but also a key venue for RAS synthesis, with most of the RAS components synthesized from cardiac tissues. For many years, ACE and Ang II had been put at the center stage of RAS studies, and the activation of RAS had been generally blamed for inducing cardiac remodeling and CHF. The discovery of ACE2 and Ang 1-7, however, has altered perceptions about RAS. As researchers have found, RAS plays dual roles of both inducing and inhibiting cardiac remodeling, with Ang II causing vasoconstriction and cell proliferation, while Ang 1-7 relaxing blood vessels and resisting cell proliferation. Such duel effects have emerged due to the existence of a pair of enzymes functioning in opposite ways.This study is based on research conducted on the three levels of clinical patients, animal model and cultured myocardial cell, all with respective drug intervention. We have looked into the relationship between ACE/ACE2 and CHF heart function/cardiac remodeling, and observed the treatment effect of ACE1 andβ-blocker.Methods1.We select CHF patients and normal people, RT-PCR and Western Blot were used to detect the ACE and ACE2 gene and protein expression; HE staining was used to decect the pathology changes of cardiac tissue; Immunohistochemistry was used to determine the position where ACE and ACE2 expressed; Masson trichrome stain was used to detect the deposition of cardiac collagen tissue.2.The rat heart failure model was induced by acute myocardial infarction (AMI) through ligating the left anterior descending coronary artery. One month after operation, rats were randomized to placebo, Benazapril, Carvedilol, and combination (Carvedilol with Benazapril) groups. Sham-operated rats were used as the control group. Then evaluate the following indexes at 8th week: (1) Hemodynamics; (2) Body mass and left ventricular mass index; (3) The circulate and cardiac level of angiotensin II; (4) ACE and ACE2 gene and protein expression using RT-PCR and Western Blot; (5) HE staining; (6) The position where ACE and ACE2 expressed using immunohistochemistry method; (7) The deposition of cardiac collagen tissue using Masson trichrome staining; (8) The ultramicrostructure changes of cardiac tissue using Electron microscope.3.Primary cultured neonatal rat cardiomyocytes were treated with placebo, angiotensin II or angiotensin1-7. Then evaluate the following indexes: (1) The diameter and surface area; (2) RT-PCR and Western Blot were used to detect the expression of ACE and ACE2 mRNA and protein in cardiomyocytes; (3) Laser confocal microscopy was used to detect where ACE and ACE2 expressed.Results1.The ACE and ACE2 mRNA and protein concentration of cardiac tissure in heart failure patients were significantly higher than normal people, especially in moderate to severe CHF patients. The ACE/ACE2 ratio was significantly decreased in mild CHF patients, but ACE/ACE2 ratio was significantly increased in moderate to severe patients.2.The cardiomyocytes of failing myocardium were disposed derangement, cardiomyocytes compensatory hypertrophy in earlier period, focal necrosis and interstitial collagen tissue hyperplasy and fibrosis also inflammatory cell infiltrate were detected in advanced stage.3.Immunohistochemistry showed that ACE and ACE2 mainly expressed in cardiomyocytes and vascular endothelial cells, positive staining of failing myocardium was obviously increased than normal myocardium.4.Positive staining of collagen tissue in failing myocardium was obviously increased, not only deposite aroud blood vessle but also in intercellular substance of cardiac tissue.5.The hemodynamics parameters of Benazapril, Carvedilol and combination groups improved significantly than CHF placebo group. The value of +dp/dtmax and -dp/dtmin and LVSP were increased significantly than CHF placebo group. The hemodynamics parameters were not different between Benazapril and Carvedilol group.6.Compared with sham-operation group, left ventricular mass index(LVMI) was obviously increased in CHF rats. The LVMI of Benazapril and combination group was decreased obviously compared with CHF placebo group, but not different obviously between Carvedilol and CHF placebo group.7.The cirlutation and cardiac angiotentin II level were decreased significantly in Benazapril and combination group than CHF placebo group. Carvedilol can not effected cirlulating angiotensinII level, but decreased cardiac angiotensinII level.8.The ACE mRNA and protein were significantly decreased in all treated groups, especially in combination group. The ACE2 mRNA and protein were increased in all treated groups.9.The failing myocardium showed chondriosome swelling and cristae disruption, endocytoplasmic reticulum dilation, interstitial edema and muscle fibril collapsion.10.The diameter and surface area of cardiomyocytes were increased significantly in antiotensin II group, but angiotensin1-7 can not infuence the diameter and surface area of cardiomyocytes.11.Compared with normal cardiomyocytes, antiotensin II and angiotensin1-7 had no effect on ACE mRNA and protein. ACE2 mRNA and protein were decreased in angiotensin II group, but increased in angiotensin1-7 group.12.Using laser confocal microscopy, we found ACE and ACE2 protein expressed restrictly on the membrane of cardiomyocytes, but not kytoplasm or nuclei.Conclusions1.The failing myocardium of rat and human showes cardiac remodeling and RAS activation, display cardiac angiotensin II level increases, ACE and ACE2 gene and protein increase, especially ACE, the ratio of ACE/ACE2 elevates.2.The cardiac ACE and ACE2 gene and protein increase in CHF patients, corelate with heart function.3.Benazapril and Carvedilol treatment can improve heart function of rats, especially the combination of the two drugs. Benazapril treatment can lighten cardiac remodeling, but not Carvedilol.4.Benazapril and Carvedilol can down regulate the expression of cardiac ACE, upregulate the expression of ACE2, the ratio of ACE/ACE2 decreases. It can inhibits angiotensin II production, promotes angiotensin II degradation, this is the new explanation of the mechanism of these two drugs.5.Angiotensin II can induces cardiomyocytes hypertrophy, inhibites ACE2 gene and protein expression of cardiomyocytes, and have no effect on ACE.6.Angiotensin1-7 have no effect on cardiomyocytes shape, it can stimulates ACE2 gene and protein expression of cardiomyocytes, and have no effect on ACE.