Upregulation of Angiotensin (1-7)-Mediated Signaling Preserves Endothelial Function Through Reducing Oxidative Stress in Diabetes

Diminazene aceturate: an antibacterial agent for Shiga-toxin-producing Escherichia coli O157:H7

The aim of this study was to investigate the bacteriostatic and bactericidal effects of diminazene aceturate (DA) against five strains of pathogenic bacteria and two strains of nonpathogenic bacteria. The results showed that 5 μg/mL of DA suppressed the growth of pathogenic Escherichia coli by as much as 77% compared with the controls. Enterohemorrhagic E. coli EDL933 (an E. coli O157:H7 strain) was the most sensitive to DA with a minimum inhibitory concentration of 20 μg/mL. Additional investigations showed that DA induced the highest level of intracellular reactive oxygen species in EDL933. A positive correlation between the reactive oxygen species levels and DA concentration was demonstrated. DA (5 μg/mL) was also a potent uncoupler, inducing a stationary phase collapse (70%–75%) in both strains of E. coli O157:H7. Further investigation showed that the collapse was due to the NaCl:DA ratio in the broth and was potassium ion dependent. A protease screening assay was conducted to elucidate the underlying mechanism. It was found that at neutral pH, the hydrolysis of H-Asp-pNA increased by a factor of 2–3 in the presence of DA, implying that DA causes dysregulation of the proton motive force and a decrease in cellular pH. Finally, a commercial verotoxin test showed that DA did not significantly increase toxin production in EDL933 and was a suitable antibacterial agent for Shiga-toxin-producing E. coli.

ACE2 and Microbiota: Emerging Targets for Cardiopulmonary Disease Therapy

The health of the cardiovascular and pulmonary systems is inextricably linked to the renin-angiotensin system (RAS). Physiologically speaking, a balance between the vasodeleterious (Angiotensin-converting enzyme [ACE]/Angiotensin II [Ang II]/Ang II type 1 receptor [AT1R]) and vasoprotective (Angiotensin-converting enzyme 2 [ACE2]/Angiotensin-(1-7) [Ang-(1-7)]/Mas receptor [MasR]) components of the RAS is critical for cardiopulmonary homeostasis. Upregulation of the ACE/Ang II/AT1R axis shifts the system toward vasoconstriction, proliferation, hypertrophy, inflammation, and fibrosis, all factors that contribute to the development and progression of cardiopulmonary diseases. Conversely, stimulation of the vasoprotective ACE2/Ang-(1-7)/MasR axis produces a counter-regulatory response that promotes cardiovascular health. Current research is investigating novel strategies to augment actions of the vasoprotective RAS components, particularly ACE2, in order to treat various pathologies. Although multiple approaches to increase the activity of ACE2 have displayed beneficial effects against experimental disease models, the mechanisms behind its protective actions remain incompletely understood. Recent work demonstrating a non-catalytic role for ACE2 in amino acid transport in the gut has led us to speculate that the therapeutic effects of ACE2 can be mediated, in part, by its actions on the gastrointestinal tract and/or gut microbiome. This is consistent with emerging data which suggest that dysbiosis of the gut and lung microbiomes is associated with cardiopulmonary disease. This review highlights new developments in the protective actions of ACE2 against cardiopulmonary disorders, discusses innovative approaches to targeting ACE2 for therapy, and explores an evolving role for gut and lung microbiota in cardiopulmonary health.

Protective role of ACE2-Ang-(1-7)-Mas in myocardial fibrosis by downregulating KCa3.1 channel via ERK1/2 pathway

The intermediate-conductance Ca²⁺-activated K⁺ (K_Ca3.1) channel plays a vital role in myocardial fibrosis induced by angiotensin (Ang) II. However, as the antagonists of Ang II, the effect of angiotensin-converting enzyme 2 (ACE2)-angiotensin-(1-7)-Mas axis on K_Ca3.1 channel during myocardial fibrosis remains unknown. This study was designed to explore the function of K_Ca3.1 channel in the cardioprotective role of ACE2-Ang-(1-7)-Mas. Wild-type (WT) mice, hACE2 transgenic mice (Tg), and ACE2 deficiency mice (ACE2^-/-) were administrated with Ang II by osmotic mini-pumps. As the activator of ACE2, diminazene aceturate (DIZE) inhibited increase of blood pressure, collagen deposition, and K_Ca3.1 protein expression in myocardium of WT mice induced by Ang II. In Tg and ACE2^-/- mice, besides the elevation of blood pressure, Ang II induced transformation of cardiac fibroblast into myofibroblast and resulted in augmentation of hydroxyproline concentration and collagen deposition, as well as K_Ca3.1 protein expression, but the changes in ACE2^-/- mice were more obvious than those in Tg mice. Mas antagonist A779 reduced blood pressure, myocardium fibrosis, and myocardium K_Ca3.1 protein expression by Ang II in Tg mice, but activation of K_Ca3.1 with SKA-31 in Tg mice promoted the pro-fibrogenic effects of Ang II. Respectively, in ACE2^-/- mice, TRAM-34, the K_Ca3.1 blocker, and Ang-(1-7) inhibited increase of blood pressure, collagen deposition, and K_Ca3.1 protein expression by Ang II. Moreover, DIZE and Ang-(1-7) depressed p-ERK1/2/t-ERK increases by Ang II in WT mice, and after blockage of ERK1/2 pathway with PD98059, the K_Ca3.1 protein expression was reduced in WT mice. In conclusion, the present study demonstrates that ACE2-Ang-(1-7)-Mas protects the myocardium from hypertension-induced injury, which is related to its inhibiting effect on K_Ca3.1 channels through ERK1/2 pathway. Our results reveal that K_Ca3.1 channel is likely to be a critical target on the ACE2-Ang-(1-7)-Mas axis for its protective role in myocardial fibrosis and changes of K_Ca3.1 induced by homeostasis of ACE-Ang II-AT1 axis and ACE2-Ang-(1-7)-Mas axis may be a new therapeutic target in myocardial fibrosis.

Reactive Oxygen Species, Endoplasmic Reticulum Stress and Mitochondrial Dysfunction: The Link with Cardiac Arrhythmogenesis

BACKGROUND

Cardiac arrhythmias represent a significant problem globally, leading to cerebrovascular accidents, myocardial infarction, and sudden cardiac death. There is increasing evidence to suggest that increased oxidative stress from reactive oxygen species (ROS), which is elevated in conditions such as diabetes and hypertension, can lead to arrhythmogenesis.

METHOD

A literature review was undertaken to screen for articles that investigated the effects of ROS on cardiac ion channel function, remodeling and arrhythmogenesis.

RESULTS

Prolonged endoplasmic reticulum stress is observed in heart failure, leading to increased production of ROS. Mitochondrial ROS, which is elevated in diabetes and hypertension, can stimulate its own production in a positive feedback loop, termed ROS-induced ROS release. Together with activation of mitochondrial inner membrane anion channels, it leads to mitochondrial depolarization. Abnormal function of these organelles can then activate downstream signaling pathways, ultimately culminating in altered function or expression of cardiac ion channels responsible for generating the cardiac action potential (AP). Vascular and cardiac endothelial cells become dysfunctional, leading to altered paracrine signaling to influence the electrophysiology of adjacent cardiomyocytes. All of these changes can in turn produce abnormalities in AP repolarization or conduction, thereby increasing likelihood of triggered activity and reentry.

CONCLUSION

ROS plays a significant role in producing arrhythmic substrate. Therapeutic strategies targeting upstream events include production of a strong reducing environment or the use of pharmacological agents that target organelle-specific proteins and ion channels. These may relieve oxidative stress and in turn prevent arrhythmic complications in patients with diabetes, hypertension, and heart failure.

Electrophysiological Mechanisms of Bayés Syndrome: Insights from Clinical and Mouse Studies

Bayés syndrome is an under-recognized clinical condition characterized by inter-atrial block (IAB). This is defined electrocardiographically as P-wave duration > 120 ms and can be categorized into first, second and third degree IAB. It can be caused by inflammatory conditions such as systemic sclerosis and rheumatoid arthritis, abnormal protein deposition in cardiac amyloidosis, or neoplastic processes invading the inter-atrial conduction system, such as primary cardiac lymphoma. It may arise transiently during volume overload, autonomic dysfunction or electrolyte disturbances from vomiting. In other patients without an obvious cause, the predisposing factors are diabetes mellitus, hypertensive heart disease, and hypercholesterolemia. IAB has a strong association with atrial arrhythmogenesis, left atrial enlargement (LAE), and electro-mechanical discordance, increasing the risk of cerebrovascular accidents as well as myocardial and mesenteric ischemia. The aim of this review article is to synthesize experimental evidence on the pathogenesis of IAB and its underlying molecular mechanisms. Current medical therapies include anti-fibrotic, anti-arrhythmic and anti-coagulation agents, whereas interventional options include atrial resynchronization therapy by single or multisite pacing. Future studies will be needed to elucidate the significance of the link between IAB and atrial tachyarrhythmias in patients with different underlying etiologies and optimize the management options in these populations.

Vascular Actions of Angiotensin 1-7 in the Human Microcirculation: Novel Role for Telomerase

OBJECTIVE

This study examined vascular actions of angiotensin 1-7 (ANG 1-7) in human atrial and adipose arterioles.

APPROACH AND RESULTS

The endothelium-derived hyperpolarizing factor of flow-mediated dilation (FMD) switches from antiproliferative nitric oxide (NO) to proatherosclerotic hydrogen peroxide in arterioles from humans with coronary artery disease (CAD). Given the known vasoprotective properties of ANG 1-7, we tested the hypothesis that overnight ANG 1-7 treatment restores the NO component of FMD in arterioles from patients with CAD. Endothelial telomerase activity is essential for preserving the NO component of vasodilation in the human microcirculation; thus, we also tested whether telomerase activity was necessary for ANG 1-7-mediated vasoprotection by treating separate arterioles with ANG 1-7±the telomerase inhibitor 2-[[(2E)-3-(2-naphthalenyl)-1-oxo-2-butenyl1-yl]amino]benzoic acid. ANG 1-7 dilated arterioles from patients without CAD, whereas dilation was significantly reduced in arterioles from patients with CAD. In atrial arterioles from patients with CAD incubated with ANG 1-7 overnight, the NO synthase inhibitor NG-nitro-l-arginine methyl ester abolished FMD, whereas the hydrogen peroxide scavenger polyethylene glycol catalase had no effect. Conversely, in vessels incubated with ANG 1-7+2-[[(2E)-3-(2-naphthalenyl)-1-oxo-2-butenyl1-yl]amino]benzoic acid, NG-nitro-l-arginine methyl ester had no effect on FMD, but polyethylene glycol catalase abolished dilation. In cultured human coronary artery endothelial cells, ANG 1-7 significantly increased telomerase activity. These results indicate that ANG 1-7 dilates human microvessels, and dilation is abrogated in the presence of CAD. Furthermore, ANG 1-7 treatment is sufficient to restore the NO component of FMD in arterioles from patients with CAD in a telomerase-dependent manner.

CONCLUSIONS

ANG 1-7 exerts vasoprotection in the human microvasculature via modulation of telomerase activity.

Genetic Deletion of ACE2 Induces Vascular Dysfunction in C57BL/6 Mice: Role of Nitric Oxide Imbalance and Oxidative Stress

Accumulating evidence indicates that angiotensin-converting enzyme 2 (ACE2) plays a critical role in cardiovascular homeostasis, and its altered expression is associated with major cardiac and vascular disorders. The aim of this study was to evaluate the regulation of vascular function and assess the vascular redox balance in ACE2-deficient (ACE2^-/y) animals. Experiments were performed in 20–22 week-old C57BL/6 and ACE2^-/y male mice. Evaluation of endothelium-dependent and -independent relaxation revealed an impairment of in vitro and in vivo vascular function in ACE2^-/y mice. Drastic reduction in eNOS expression at both protein and mRNA levels, and a decrease in ^•NO concentrations were observed in aortas of ACE2^-/y mice in comparison to controls. Consistently, these mice presented a lower plasma and urine nitrite concentration, confirming reduced ^•NO availability in ACE2-deficient animals. Lipid peroxidation was significantly increased and superoxide dismutase activity was decreased in aorta homogenates of ACE2^-/y mice, indicating impaired antioxidant capacity. Taken together, our data indicate, that ACE2 regulates vascular function by modulating nitric oxide release and oxidative stress. In conclusion, we elucidate mechanisms by which ACE2 is involved in the maintenance of vascular homeostasis. Furthermore, these findings provide insights into the role of the renin-angiotensin system in both vascular and systemic redox balance.

RELATIONSHIP OF OXIDATIVE STRESS TO URINARY ANGIOTENSIN CONVERTING ENZYME 2 IN TYPE 2 DIABETES MELLITUS PATIENTS

CONTEXT

Angiotensin converting enzyme 2 (ACE2) is highly expressed in the kidney and cleaves angiotensin II to Angiotensin (1-7), annihilating the deleterious effects of angiotensin II which is known to be a strong activator of oxidative stress.

OBJECTIVE

We aimed to evaluate the relationship of oxidative stress to urinary ACE2 (uACE2) in type 2 diabetes mellitus (T2DM) patients.

DESIGN

We included consecutive normo or microalbuminuric T2DM patients in an observational transversal study. Routine laboratory investigations, plasma malondialdehyde (MDA, fluorimetric thiobarbituric method) as a marker of prooxidant capacity and superoxide dismutase (SOD, cytochrome reduction method) and catalase (CAT) activity (in erythrocyte lysate by the modification of absorbance method) as two measures of serum antioxidant capacity and uACE2 (ELISA method) were assessed.

RESULTS

MDA showed a negative correlation with SOD (r=-0.44, p=0.001), CAT (r=-0.37, p=0.006), uACE2 (r=-0.33, p=0.016) and a positive correlation with glycated haemoglobin (HbA1c) (r=0.49, p<0.001) and associated cardiovascular disease (r=0.42, p=0.001). CAT as also positively correlated to uACE2 (r=0.29, p=0.037). SOD was also negatively correlated with glycemia (r=-0.71, p<0.001) and HbA1c (r=-0.53, p<0.001). Patients with lower MDA (when divided according to median value of 3.88 nmol/mL) had higher uACE2 57.15(40.3-71.2) pg/mL compared to 38.5(31.8-45.95) pg/mL in patients with higher MDA (p<0.001). In multivariate logistic regression uACE2 was the only predictor for MDA above or below its median (OR=0.94, 95%CI[0.90-0.98], p=0.002).

CONCLUSION

Increased prooxidant serum capacity is associated with lower uACE2 levels in T2DM patients.

Angiotensin 1-7 Protects against Angiotensin II-Induced Endoplasmic Reticulum Stress and Endothelial Dysfunction via Mas Receptor

Angiotensin 1–7 (Ang 1–7) counter-regulates the cardiovascular actions of angiotensin II (Ang II). The present study investigated the protective effect of Ang 1–7 against Ang II-induced endoplasmic reticulum (ER) stress and endothelial dysfunction. Ex vivo treatment with Ang II (0.5 μM, 24 hours) impaired endothelium-dependent relaxation in mouse aortas; this harmful effect of Ang II was reversed by co-treatment with ER stress inhibitors, l4-phenylbutyric acid (PBA) and tauroursodeoxycholic acid (TUDCA) as well as Ang 1–7. The Mas receptor antagonist, A779, antagonized the effect of Ang 1–7. The elevated mRNA expression of CHOP, Grp78 and ATF4 or protein expression of p-eIF2α and ATF6 (ER stress markers) in Ang II-treated human umbilical vein endothelial cells (HUVECs) and mouse aortas were blunted by co-treatment with Ang 1–7 and the latter effect was reversed by A779. Furthermore, Ang II-induced reduction in both eNOS phosphorylation and NO production was inhibited by Ang 1–7. In addition, Ang 1–7 decreased the levels of ER stress markers and augmented NO production in HUVECs treated with ER stress inducer, tunicamycin. The present study provides new evidence for functional antagonism between the two arms of the renin-angiotensin system in endothelial cells by demonstrating that Ang 1–7 ameliorates Ang II-stimulated ER stress to raise NO bioavailability, and subsequently preserves endothelial function.

Some Aspects of the Renin-Angiotensin-System in Hemodialysis Patients

Understanding of the renin-angiotensin system (RAS) has changed remarkably over the past decade. Renin, angiotensin converting enzyme (ACE), angiotensin II (Ang II), and Ang II receptors are the main components of the RAS. Recent studies identified the ACE2/Ang 1–7/ Mas receptor axis, which counter-regulates the classical RAS. Many studies have examined the effects of the RAS on the progression of cardiovascular disease and chronic kidney disease (CKD). In addition, many studies have documented increased levels of ACE in hemodialysis (HD) patients, raising concerns about the negative effects of RAS activation on the progression of renal disease. Elevated ACE increases the level of Ang II, leading to vasoconstriction and cell proliferation. Ang II stimulation of the sympathetic system leads to renal and cardiovascular complications that are secondary to uncontrolled hypertension. This review provides an overview of the RAS, evaluates new research on the role of ACE2 in dialysis, and reviews the evidence for potentially better treatments for patients undergoing HD. Further understanding of the role of ACE and ACE2 in HD patients may aid the development of targeted therapies that slow the progression of CKD and cardiovascular disease.

Diminazene enhances stability of atherosclerotic plaques in ApoE-deficient mice

Angiotensin (Ang) II contributes to the development of atherosclerosis, while Ang-(1-7) has atheroprotective actions. Accordingly, angiotensin-converting enzyme 2 (ACE2), which breaks-down Ang II and forms Ang-(1-7), has been suggested as a target against atherosclerosis. Here we investigated the actions of diminazene, a recently developed ACE2 activator compound, in a model of vulnerable atherosclerotic plaque. Atherosclerotic plaque formation was induced in the carotid artery of ApoE-deficient mice by a shear stress (SS) modifier device. The animals were treated with diminazene (15mg/kg/day) or vehicle. ACE2 was strongly expressed in the aortic root and low SS-induced carotid plaques, but poorly expressed in the oscillatory SS-induced carotid plaques. Diminazene treatment did not change the lesion size, but ameliorated the composition of aortic root and low SS-induced carotid plaques by increasing collagen content and decreasing both MMP-9 expression and macrophage infiltration. Interestingly, these beneficial effects were not observed in the oscillatory SS-induced plaque. Additionally, diminazene treatment decreased intraplaque ICAM-1 and VCAM-1 expression, circulating cytokine and chemokine levels and serum triglycerides. In summary, ACE2 was distinctively expressed in atherosclerotic plaques, which depends on the local pattern of shear stress. Moreover, diminazene treatment enhances the stability of atherosclerotic plaques.