ACE is a zinc-containing metalloprotease, which mainly exists in the vasculature. ACE transforms inactive Ang I into vasoconstrictor Ang II [1]. The latter acts on AT1 to constrict blood vessels and stimulate aldosterone secretion, leading to increased blood pressure. At the same time, ACE can also hydrolyze bradykinin to make it Inactivation, and bradykinin can release N0, prostaglandin and other endothelial cytokines to relax blood vessels and inhibit the proliferation of vascular smooth muscle cells. In addition, ACE can also hydrolyze many other vasoactive peptides. Studies have shown that Ang II can cause the production of superoxide anion (02.), nitric oxide (N0.), and hydrogen peroxide (H202), produce a strong vasoconstrictor effect, induce a variety of inflammatory factors, and activate macrophages and monomers. Nuclear cells induce inflammation; at the same time, they induce and promote vascular smooth muscle proliferation and vascular remodeling, leading to vascular wall damage and promoting atherosclerosis. In addition, inflammatory response can activate reactive oxygen species and cause oxidative stress in tissues, and oxidative stress plays an important role in cardiovascular diseases [2-3], including atherosclerosis, hypertension, coronary heart disease, etc.; At the same time, reactive oxygen species can activate MMPs (matrix metalloproteinases). MMP.1, MMP.2, and MMP.9 have been confirmed in a number of experiments to be related to the occurrence of aortic dissection/aneurysm [4-5]. Therefore, AngII may promote the occurrence of aortic dissection [6], and studies have shown that the RAS system plays a role in the occurrence of abdominal aortic aneurysm [7]. Although experiments found that ACE activity in cardiovascular diseases such as heart failure, hypertension, and angina pectoris was significantly increased in the disease group [8-10], the detection of peripheral venous blood ACE concentration in this experiment showed contradictory results. The concentration of ACE in the aortic dissection group decreased and was statistically significant (P <0.05); while the concentration of ACE in the coronary heart disease group and the control group did not change significantly.
This change is consistent with the expression of ACE mRNA in the ascending aorta wall. The expression of ACE mRNA in the aortic dissection group is lower than that in the coronary heart disease group, and there is a statistical difference between the two groups (P <0.05). We speculate that the reasons for this phenomenon may be: (1) Changes in the body after aortic dissection lead to a decrease in ACE. ACE can be converted into AngII by acting on Ang I, and Ang II can also regulate ACE. Current studies have shown that AngII can up-regulate ACE through AT1. ERK (extracellular signal regulation) / p38 MAP (mitogen-activated protein) kinase pathway at the same time, ACE2 is reduced [11-12]. (2) Aortic dissection occurs after ACE decreases. ACE transforms AngI into AngII and produces vasoconstriction. When ACE is excessively reduced, the vasoconstriction effect on blood vessels decreases, which may lead to changes in the tension of the aortic wall, and this change in tension, may lead to aortic dissection to some extent However, the number of cases in this experiment is small, and further sample studies are needed to confirm whether this relationship exists. In addition, the patients in the aortic dissection group in this experiment are all acute aortic dissections. Whether there are similar results in chronic aortic dissection patients is not known, and further experimental verification is needed.
In the past, it was thought that only the ACE Ang II. AT1 axis existed in the RAs system, but in 2000 Donoghue [13] and Tipnis et al. [14] respectively confirmed that there is another homologous substance in ACE, that is, angiotensin-converting enzyme 2 (ACE2). It is found that there is another branch system in the RAS system: ACE2.Ang (1.7).Mas axis. Like ACE, ACE2 is also a zinc-containing metalloprotease. Studies have shown that the metal catalytic region of ACE2 is 42% identical to ACE [13]. The gene encoding ACE2 contains 18 exons and the gene encoding ACE contains The 17 exons are similar [14]. The distribution of ACE2 in the human body is not as widespread as that of ACE. It is mainly distributed in the heart, kidney, testis, lung, arteries, veins, brain and other tissues. Among them, the ileum is the most distributed, and it is also more distributed in the cardiac vascular endothelial cells and kidney tissues [15]. ACE2 can decompose AngII into Ang (l-7). In addition, ACE2 can also directly act on Ang-1I to decompose it into Ang (l-9). Ang (l.9) is then decomposed into Ang (l-9) under the action of ACE. L-7), meanwhile, the efficiency of ACE2 to decompose AngII is 400 times that of AngI [16]. The physiological functions of Ang (1-7) are mainly to relax blood vessels, lower blood pressure, improve coronary perfusion and endothelial function, inhibit the hypertrophy of myocardial cells, inhibit the proliferation of myocardial fibroblasts, and also have inhibitory effects on vascular smooth muscle cells. In vitro experiments have also confirmed that ACE2 can decompose other vasoactive peptide terminal amino acids, including exercise vasopressin, bradykinin desarginine, etc [17], and ACE2 can also catalyze the decomposition of the activities of aPelin.13 and apel16, and aPelin-13 can cause ionization. With the contraction of the coronary arteries, ACE2 can also stimulate the body to produce vasodilators such as NO, prostaglandins, and bradykinin[18]. Because the physiological effect of ACE2 is opposite to that of ACE, many domestic and foreign studies have suggested that ACE2 can stabilize atherosclerotic plaques, reduce platelet adhesion, anti-thrombosis, reduce inflammation, promote myocardial remodeling, and lower blood pressure, etc. [19] Therefore, the current literature generally believes that ACE2 plays a protective role in cardiovascular disease. In this experiment, the expression of ACE2 mRNA in the ascending aorta wall was observed. The expression of ACE in the aortic dissection group was lower, which confirmed that ACE2 may have a protective effect in the occurrence of aortic dissection. However, this experiment has no results of the expression of ACE and ACE2 in the ascending aorta wall of normal people, and its expression in normal people is still unknown. In addition, studies have shown that the imbalance of the ratio of ACE and ACE2 has a certain relationship with the occurrence of cardiovascular disease [8]. In this experiment, we also observed the difference between the ratio of ACE and ACE2 among the groups. The results showed that the ratio of ACE/ACE2 was in the aortic dissection. In the coronary heart disease group and the coronary heart disease group, they were (0.414 ± 0.449) and (0.811 ± 0.256). Statistical analysis showed that the difference in the proportion of the aortic dissection group and the coronary heart disease group was statistically significant (P <0.05), suggesting that the imbalance of the proportion of ACE and ACE2 may have a certain relationship with the occurrence of different diseases. In summary, this experiment showed that plasma ACE concentration, ACE and ACE2 gene expression were significantly reduced in aortic dissection, providing evidence for the role of the RAS system in the occurrence of aortic dissection. However, how the expression of ACE and ACE2 changes during the pathogenesis of aortic dissection is still unknown, and further studies are needed to confirm it.