Effect of ACE2 and angiotensin-(1-7) in a mouse model of early chronic kidney disease

Urinary angiotensin-converting enzyme 2 and its activity in cats with chronic kidney disease

Introduction

Angiotensin-converting enzyme 2 (ACE2) played an important role in the renin-angiotensin-aldosterone system (RAAS) and it was proved to be renoprotective in renal disease. Urinary angiotensin-converting enzyme 2 (uACE2) has been shown to reflect renal injury in human and experimental studies, but its role in feline kidney disease remains unknown.

Aims

Our objectives involve comparing uACE2 concentrations and activities in cats across CKD stages with healthy controls, investigating the relationship between uACE2 concentrations, activities, and clinicopathological data in feline CKD patients, and assessing the predictive abilities of both for CKD progression.

Methods

A retrospective, case-control study. The concentration and activity of uACE2 were measured by commercial ELISA and fluorometric assay kits, respectively. The concentration was adjusted to give uACE2 concentration-to-creatinine ratios (UACCRs).

Results

In total, 67 cats consisting of 24 control and 43 chronic kidney disease (CKD), including 24 early-stage CKD and 19 late-stage CKD, were enrolled in this study. UACCR values were significantly higher in both early-stage (2.100 [1.142-4.242] x 10-6) and late-stage feline CKD (4.343 [2.992-5.0.71] x 10-6) compared to healthy controls (0.894 [0.610-1.076] x 10-6; p < 0.001), and there was also significant difference between-early stage group and late-stage group (p = 0.026). Urinary ACE2 activity (UAA) was significantly lower in CKD cats (1.338 [0.644-2.755] x pmol/min/ml) compared to the healthy cats (7.989 [3.711-15.903] x pmol/min/ml; p < 0.001). UACCR demonstrated an independent, positive correlation with BUN (p < 0.001), and UAA exhibited an independent, negative correlation with plasma creatinine (p < 0.001). Both UACCR and UAA did not yield significant results in predicting CKD progression based on the ROC curve analysis.

Conclusion and clinical importance

uACE2 concentration and activity exhibit varying changes as renal function declines, particularly in advanced CKD cats.

The antihypertensive action of C-phycocyanin is related to the prevention of angiotensin II-caused vascular dysfunction in chronic kidney disease

C-phycocyanin (CPC) is a photosynthetic protein found in Arthrospira maxima with a nephroprotective and antihypertensive activity that can prevent the development of hemodynamic alterations caused by chronic kidney disease (CKD). However, the complete nutraceutical activities are still unknown. This study aims to determine if the antihypertensive effect of CPC is associated with preventing the impairment of hemodynamic variables through delaying vascular dysfunction. Twenty-four normotensive male Wistar rats were divided into four groups: (1) sham + 4 mL/kg/d vehicle (100 mM of phosphate buffer, PBS) administered by oral gavage (og), (2) sham + 100 mg/kg/d og of CPC, (3) CKD induced by 5/6 nephrectomy (CKD) + vehicle, (4) CKD + CPC. One week after surgery, the CPC treatment began and was administrated daily for four weeks. At the end treatment, animals were euthanized, and their thoracic aorta was used to determine the vascular function and expression of AT1, AT2, and Mas receptors. CKD-induced systemic arterial hypertension (SAH) and vascular dysfunction by reducing the vasorelaxant response of angiotensin 1-7 and increasing the contractile response to angiotensin II. Also, CKD increased the expression of the AT1 and AT2 receptors and reduced the Mas receptor expression. Remarkably, the treatment with CPC prevented SAH, renal function impairment, and vascular dysfunction in the angiotensin system. In conclusion, the antihypertensive activity of CPC is associated with avoiding changes in the expression of AT1, AT2, and Mas receptors, preventing vascular dysfunction development and SAH in rats with CKD.

Diverse biological functions of the renin-angiotensin system

The renin-angiotensin system (RAS) has been widely known as a circulating endocrine system involved in the control of blood pressure. However, components of RAS have been found to be localized in rather unexpected sites in the body including the kidneys, brain, bone marrow, immune cells, and reproductive system. These discoveries have led to steady, growing evidence of the existence of independent tissue RAS specific to several parts of the body. It is important to understand how RAS regulates these systems for a variety of reasons: It gives a better overall picture of human physiology, helps to understand and mitigate the unintended consequences of RAS-inhibiting or activating drugs, and sets the stage for potential new therapies for a variety of ailments. This review fulfills the need for an updated overview of knowledge about local tissue RAS in several bodily systems, including their components, functions, and medical implications.

Increased Estimated GFR Is Negatively Associated With the Risk of SARS-CoV-2 Infection and Severe COVID-19 Within Normal to Mildly Decreased Levels: Nested Case-Control Study

BACKGROUND

While accumulating evidence indicates chronic kidney disease as a risk factor for coronavirus disease 2019 (COVID-19), the association between normal or mildly decreased kidney function and COVID-19 is unaddressed. Here, we have examined the association of an increase in estimated glomerular filtration rate (eGFR) with the incidence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and severe COVID-19 outcomes among patients within normal to mildly decreased kidney function.

METHODS

The patients who participated in both health screenings from period I (2017-2018) to II (2019-2020) were enrolled to our study. All participants were categorized into four groups according to the changes in eGFR stage from period I to II: 1) persistently stage G1, 2) from stage G2 to G1, 3) from stage G1 to G2, 4) persistently stage G2. In addition, the changes in eGFR value were defined by subtracting its value of period I from II. Patients were followed up for SARS-CoV-2 infection from January 1, 2021 to any diagnosis of COVID-19 or December 31, 2021, whichever happened first. In addition, those with SARS-CoV-2 infection were followed-up for one month after diagnosis to analyze severe COVID-19. Adjusted odds ratio (aOR) was calculated using multivariable-adjusted logistic regression.

RESULTS

We identified 159,427 patients with and 1,804,798 patients without SARS-CoV-2 infection. The risk of SARS-CoV-2 infection decreased when eGFR stage changed from G2 to G1 (aOR, 0.957; 95% confidence interval [CI], 0.938-0.977) and persistently maintained at G1 (aOR, 0.966; 95% CI, 0.943-0.990), compared with the persistently stage G2 group. In addition, the risk showed an inverse relationship with changes in eGFR value, which was depicted by restricted cubic spline curves. For the overall risk of severe COVID-19, the persistently stage G1 showed the lowest risk (aOR, 0.897; 95% CI, 0.827-0.972), followed by those from stage G1 to G2 (aOR, 0.900; 95% CI, 0.828-0.978) and those from stage G2 to G1 (aOR, 0.931; 95% CI, 0.871-0.995), compared with the persistently stage G2 group.

CONCLUSION

An increase in eGFR was negatively associated with the risk of SARS-CoV-2 infection and severe COVID-19 among normal or mildly decreased kidney function. For severe COVID-19, maintaining higher baseline eGFR may act as a protective factor against its risk.

Central angiotensin 1-7 triggers brown fat thermogenesis

We tested the hypothesis that third ventricular (3V) injections of angiotensin 1-7 (Ang 1-7) increases thermogenesis in brown adipose tissue (BAT), and whether the Mas receptor mediates this response. First, in male Siberian hamsters (n = 18), we evaluated the effect of Ang 1-7 in the interscapular BAT (IBAT) temperature and, using selective Mas receptor antagonist A-779, the role of Mas receptor in this response. Each animal received 3V injections (200 nL), with 48 h intervals: saline; Ang 1-7 (0.03, 0.3, 3, and 30 nmol); A-779 (3 nmol); and Ang 1-7 (0.3 nmol) + A-779 (3 nmol). IBAT temperature increased after 0.3 nmol Ang 1-7 compared with Ang 1-7 + A-779 at 20, 30, and 60 min. Also, 0.3 nmol Ang 1-7 increased IBAT temperature at 10 and 20 min, and decreased at 60 min compared with pretreatment. IBAT temperature decreased after A-779 at 60 min and after Ang 1-7 + A-779 at 30 and 60 min compared with the respective pretreatment. A-779 and Ang 1-7 + A-779 decreased core temperature at 60 min compared with 10 min. Then, we evaluated blood and tissue Ang 1-7 levels, and the expression of hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) in IBAT. Male Siberian hamsters (n = 36) were killed 10 min after one of the injections. No changes were observed in blood glucose, serum and IBAT Ang 1-7 levels, and ATGL. Ang 1-7 (0.3 nmol) increased p-HSL expression compared with A-779 and increased p-HSL/HSL ration compared with other injections. Ang 1-7 and Mas receptor immunoreactive cells were found in brain regions that coincide with the sympathetic nerves outflow to BAT. In conclusion, 3V injection of Ang 1-7 induced thermogenesis in IBAT in a Mas receptor-dependent manner.

Renal angiotensin I-converting enzyme-deficient mice are protected against aristolochic acid nephropathy

The renal renin-angiotensin system (RAS) is involved in the development of chronic kidney disease. Here, we investigated whether mice with reduced renal angiotensin I-converting enzyme (ACE^-/-) are protected against aristolochic acid nephropathy (AAN). To further elucidate potential molecular mechanisms, we assessed the renal abundances of several major RAS components. AAN was induced using aristolochic acid I (AAI). Glomerular filtration rate (GFR) was determined using inulin clearance and renal protein abundances of renin, angiotensinogen, angiotensin I-converting enzyme (ACE) 2, and Mas receptor (Mas) were determined in ACE^-/- and C57BL/6J control mice by Western blot analyses. Renal ACE activity was determined using a colorimetric assay and renal angiotensin (Ang) (1-7) concentration was determined by ELISA. GFR was similar in vehicle-treated mice of both strains. AAI decreased GFR in controls but not in ACE^-/- mice. Furthermore, AAI decreased renal ACE activity in controls but not in ACE^-/- mice. Vehicle-treated ACE^-/- mice had significantly higher renal ACE2 and Mas protein abundances than controls. AAI decreased renal ACE2 protein abundance in both strains. Furthermore, AAI increased renal Mas protein abundance, although the latter effect did not reach statistical significance in the ACE^-/- mice. Renal Ang(1-7) concentration was similar in vehicle-treated mice of both strains. AAI increased renal Ang(1-7) concentration in the ACE^-/- mice but not in the controls. Mice with reduced renal ACE are protected against AAN. Our data suggest that in the face of renal ACE deficiency, AAI may activate the ACE2/Ang(1-7)/Mas axis, which in turn may deploy its reno-protective effects.

Ginsenoside Re attenuates memory impairments in aged Klotho deficient mice via interactive modulations of angiotensin II AT1 receptor, Nrf2 and GPx-1 gene

Ginseng is known to possess anti-aging potential. Klotho mutant mice exhibit phenotypes that resemble the phenotype of the human aging process. Similar to Klotho deficient mice, patients with chronic kidney disease (CKD) suffer vascular damage and cognitive impairment, which might upregulate the angiotensin II AT1 receptor. Since AT1 receptor expression was more pronounced than endothelin ET-1 expression in the hippocampus of aged Klotho deficient (±) mice, we focused on the AT1 receptor in this study. Ginsenoside Re (GRe), but not ginsenoside Rb1 (GRb1), significantly attenuated the increase in AT1 receptor expression in aged Klotho deficient mice. Both GRe and the AT1 receptor antagonist losartan failed to attenuate the decrease in phosphorylation of JAK2/STAT3 in aged Klotho deficient (±) mice but significantly activated nuclear factor erythroid 2-related factor 2 (Nrf2)-mediated signaling. Both GRe and losartan attenuated the increased NADPH oxidase (NOX) activity and reactive oxygen species (ROS) in aged Klotho deficient mice. Furthermore, of all the antioxidant enzymes, GRe significantly increased glutathione peroxidase (GPx) activity. GRe significantly attenuated the reduced phosphorylation of ERK and CREB in GPx-1 knockout mice; however, genetic overexpression of GPx-1 did not significantly affect them in aged mice. Klotho-, Nrf2-, and GPx-1-immunoreactivities were co-localized in the same cells of the hippocampus in aged Klotho wild-type mice. Both the GPx inhibitor mercaptosuccinate and Nrf2 inhibitor brusatol counteracted the effects of GRe on all neurobehavioral impairments in aged Klotho deficient (±) mice. Our results suggest that GRe attenuates all alterations, such as AT1 receptor expression, NOX-, ROS-, and GPx-levels, and cognitive dysfunction in aged Klotho deficient (±) mice via upregulation of Nrf2/GPx-1/ERK/CREB signaling.

Mechanisms of SARS-CoV-2 Infection-Induced Kidney Injury: A Literature Review

The severe acute respiratory coronavirus 2 (SARS-CoV-2) has become a life-threatening pandemic. Clinical evidence suggests that kidney involvement is common and might lead to mild proteinuria and even advanced acute kidney injury (AKI). Moreover, AKI caused by coronavirus disease 2019 (COVID-19) has been reported in several countries and regions, resulting in high patient mortality. COVID-19-induced kidney injury is affected by several factors including direct kidney injury mediated by the combination of virus and angiotensin-converting enzyme 2, immune response dysregulation, cytokine storm driven by SARS-CoV-2 infection, organ interactions, hypercoagulable state, and endothelial dysfunction. In this review, we summarized the mechanism of AKI caused by SARS-CoV-2 infection through literature search and analysis.

Angiotensin-converting enzyme 2: a key enzyme in key organs

2020 marked the 20th anniversary of the discovery of the angiotensin-converting enzyme 2 (ACE2). This major event that changed the way we see the renin-angiotensin system today could have passed quietly. Instead, the discovery that ACE2 is a major player in the severe acute respiratory syndrome coronavirus 2 pandemic has blown up the literature regarding this enzyme. ACE2 connects the classical arm renin-angiotensin system, consisting mainly of angiotensin II peptide and its AT1 receptor, with a protective arm, consisting mainly of the angiotensin 1-7 peptide and its Mas receptor. In this brief article, we have reviewed the literature to describe how ACE2 is a key protective arm enzyme in the function of many organs, particularly in the context of brain and cardiovascular function, as well as in renal, pulmonary and digestive homeostasis. We also very briefly review and refer to recent literature to present an insight into the role of ACE2 in determining the course of coronavirus diseases 2019.

Tissue-specific expression of the SARS-CoV-2 receptor, angiotensin-converting enzyme 2, in mouse models of chronic kidney disease

Elevated angiotensin-converting enzyme 2 (ACE2) expression in organs that are potential targets of severe acute respiratory syndrome coronavirus 2 may increase the risk of coronavirus disease 2019 (COVID-19) infection. Previous reports show that ACE2 alter its tissue-specific expression patterns under various pathological conditions, including renal diseases. Here, we examined changes in pulmonary ACE2 expression in two mouse chronic kidney disease (CKD) models: adenine-induced (adenine mice) and aristolochic acid-induced (AA mice). We also investigated changes in pulmonary ACE2 expression due to renin-angiotensin system (RAS) blocker (olmesartan) treatment in these mice. Adenine mice showed significant renal functional decline and elevated blood pressure, compared with controls. AA mice also showed significant renal functional decline, compared with vehicles; blood pressure did not differ between groups. Renal ACE2 expression was significantly reduced in adenine mice and AA mice; pulmonary expression was unaffected. Olmesartan attenuated urinary albumin excretion in adenine mice, but did not affect renal or pulmonary ACE2 expression levels. The results suggest that the risk of COVID-19 infection may not be elevated in patients with CKD because of their stable pulmonary ACE2 expression. Moreover, RAS blockers can be used safely in treatment of COVID-19 patients with CKD.

Overexpression of angiotensin-converting enzyme 2 by renin-angiotensin system inhibitors. Truth or myth? A systematic review of animal studies

Angiotensin-converting enzyme 2 (ACE2) protects against organ damage in hypertension and cardiovascular diseases by counter regulating the renin-angiotensin system (RAS). ACE2 is also the receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Based on the claim that RAS inhibitors (RASIs) cause ACE2 overexpression in some animal experiments, concerns have arisen that RASIs may aggravate SARS-CoV-2 infection and coronavirus disease-2019 severity in RASI-treated patients. To achieve a comprehensive review, a systematic search of MEDLINE/PubMed was conducted regarding the effects of RASIs on tissue ACE2 mRNA/protein expression in healthy animals and animal models of human diseases. We identified 88 eligible articles involving 168 experiments in the heart, kidneys, lungs, and other organs. Three of 38 experiments involving healthy animals showed ACE2 expression greater than twice that of the control (overexpression). Among 102 disease models (130 experiments), baseline ACE2 was overexpressed in 16 models (18 experiments) and less than half the control level (repression) in 28 models (40 experiments). In 72 experiments, RASIs did not change ACE2 levels from the baseline levels of disease models. RASIs caused ACE2 overexpression compared to control levels in seven experiments, some of which were unsupported by other experiments under similar conditions. In 36 experiments, RASIs reversed or prevented disease-induced ACE2 repression, yielding no or marginal changes. Therefore, ACE2 overexpression appears to be a rare rather than common consequence of RASI treatment in healthy animals and disease models. Future studies should clarify the pathophysiological significance of RASI-induced reversal or prevention of ACE2 repression in disease models.

A comprehensive guide to the pharmacologic regulation of angiotensin converting enzyme 2 (ACE2), the SARS-CoV-2 entry receptor

The recent emergence of coronavirus disease-2019 (COVID-19) as a global pandemic has prompted scientists to address an urgent need for defining mechanisms of disease pathology and treatment. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent for COVID-19, employs angiotensin converting enzyme 2 (ACE2) as its primary target for cell surface attachment and likely entry into the host cell. Thus, understanding factors that may regulate the expression and function of ACE2 in the healthy and diseased body is critical for clinical intervention. Over 66% of all adults in the United States are currently using a prescription drug and while earlier findings have focused on possible upregulation of ACE2 expression through the use of renin angiotensin system (RAS) inhibitors, mounting evidence suggests that various other widely administered drugs used in the treatment of hypertension, heart failure, diabetes mellitus, hyperlipidemias, coagulation disorders, and pulmonary disease may also present a varied risk for COVID-19. Specifically, we summarize mechanisms on how heparin, statins, steroids and phytochemicals, besides their established therapeutic effects, may also interfere with SARS-CoV-2 viral entry into cells. We also describe evidence on the effect of several vitamins, phytochemicals, and naturally occurring compounds on ACE2 expression and activity in various tissues and disease models. This comprehensive review aims to provide a timely compendium on the potential impact of commonly prescribed drugs and pharmacologically active compounds on COVID-19 pathology and risk through regulation of ACE2 and RAS signaling.

Angiotensin-(1-7)-A Potential Remedy for AKI: Insights Derived from the COVID-19 Pandemic

Membrane-bound angiotensin converting enzyme (ACE) 2 serves as a receptor for the Sars-CoV-2 spike protein, permitting viral attachment to target host cells. The COVID-19 pandemic brought into light ACE2, its principal product angiotensin (Ang) 1-7, and the G protein-coupled receptor for the heptapeptide (MasR), which together form a still under-recognized arm of the renin–angiotensin system (RAS). This axis counteracts vasoconstriction, inflammation and fibrosis, generated by the more familiar deleterious arm of RAS, including ACE, Ang II and the ang II type 1 receptor (AT1R). The COVID-19 disease is characterized by the depletion of ACE2 and Ang-(1-7), conceivably playing a central role in the devastating cytokine storm that characterizes this disorder. ACE2 repletion and the administration of Ang-(1-7) constitute the therapeutic options currently tested in the management of severe COVID-19 disease cases. Based on their beneficial effects, both ACE2 and Ang-(1-7) have also been suggested to slow the progression of experimental diabetic and hypertensive chronic kidney disease (CKD). Herein, we report a further step undertaken recently, utilizing this type of intervention in the management of evolving acute kidney injury (AKI), with the expectation of renal vasodilation and the attenuation of oxidative stress, inflammation, renal parenchymal damage and subsequent fibrosis. Most outcomes indicate that triggering the ACE2/Ang-(1-7)/MasR axis may be renoprotective in the setup of AKI. Yet, there is contradicting evidence that under certain conditions it may accelerate renal damage in CKD and AKI. The nature of these conflicting outcomes requires further elucidation.

Angiotensin-Converting Enzyme 2 Activator Ameliorates Severe Pulmonary Hypertension in a Rat Model of Left Pneumonectomy Combined With VEGF Inhibition

Background: Pulmonary arterial hypertension (PAH) is a life-threatening and deteriorating disease with no promising therapy available currently due to its diversity and complexity. An imbalance between vasoconstriction and vasodilation has been proposed as the mechanism of PAH. Angiotensin-converting enzyme 2 (ACE2), which catalyzes the hydrolysis of the vasoconstrictor angiotensin (Ang) II into the vasodilator Ang-(1-7), has been shown to be an important regulator of blood pressure and cardiovascular diseases. Herein we hypothesized diminazene aceturate (DIZE), an ACE2 activator, could ameliorate the development of PAH and pulmonary vascular remodeling.

Methods: A murine model of PAH was established using left pneumonectomy (PNx) on day 0 followed by injection of a single dose of the VEGF receptor-2 inhibitor SU5416 (25 mg/kg) subcutaneously on day 1. All hemodynamic and biochemical measurements were done at the end of the study on day 42. Animals were divided into 4 groups (n = 6–8/group): (1) sham-operated group, (2) vehicle-treatment group (SuPNx₄₂), (3) early treatment group (SuPNx₄₂/DIZE₁₋₄₂) with DIZE at 15 mg/kg/day, subcutaneously from day 1 to day 42, and (4) late treatment group (SuPNx₄₂/DIZE₂₉₋₄₂) with DIZE from days 29–42.

Results: In both the early and late treatment groups, DIZE significantly attenuated the mean pulmonary artery pressure, pulmonary arteriolar remodeling, and right ventricle brain natriuretic peptide (BNP), as well as reversed the overexpression of ACE while up-regulating the expression of Ang-(1-7) when compared with the vehicle-treatment group. In addition, the early treatment group also significantly decreased plasma BNP and increased the expression of eNOS.

Conclusions: ACE2 activator has therapeutic potentials for preventing and attenuating the development of PAH in an animal model of left pneumonectomy combined with VEGF inhibition. Activation of ACE2 may thus be a useful therapeutic strategy for the treatment of human PAH.

Inflammation Triggered by SARS-CoV-2 and ACE2 Augment Drives Multiple Organ Failure of Severe COVID-19: Molecular Mechanisms and Implications

The widespread occurrence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to a pandemic of coronavirus disease 2019 (COVID-19). The S spike protein of SARS-CoV-2 binds with angiotensin-converting enzyme 2 (ACE2) as a functional "receptor" and then enters into host cells to replicate and damage host cells and organs. ACE2 plays a pivotal role in the inflammation, and its downregulation may aggravate COVID-19 via the renin-angiotensin system, including by promoting pathological changes in lung injury and involving inflammatory responses. Severe patients of COVID-19 often develop acute respiratory distress syndrome and multiple organ dysfunction/failure with high mortality that may be closely related to the hyper-proinflammatory status called the "cytokine storm." Massive cytokines including interleukin-6, nuclear factor kappa B (NFκB), and tumor necrosis factor alpha (TNFα) released from SARS-CoV-2-infected macrophages and monocytes lead inflammation-derived injurious cascades causing multi-organ injury/failure. This review summarizes the current evidence and understanding of the underlying mechanisms of SARS-CoV-2, ACE2 and inflammation co-mediated multi-organ injury or failure in COVID-19 patients.

Tubular Mas receptor mediates lipid-induced kidney injury

Obesity-related kidney diseases are becoming serious health problems worldwide, yet the mechanism by which obesity causes kidney injury is not fully understood. The purpose of current study was to investigate the role of Mas receptor in lipid-induced kidney injury. In mice fed with high-fat diet (HFD), the protein abundance of markers of autophagy, endoplasmic reticulum stress (ER stress) and apoptosis was dramatically increased in the kidney cortex, which was markedly prevented by Mas deletion (Mas^-/-) or Mas receptor antagonist A779. Palmitic acid (PA) induced persistently increased autophagy, ER stress, and apoptosis as well as mitochondrial injuries in primary cultured proximal tubular cells from wild type, but not from Mas^-/- mice. In human proximal tubular HK2 cells, PA-induced autophagy and ER stress was aggravated by Mas agonists Ang (1-7) or AVE0991, but attenuated by A779 or Mas knockdown. Stimulation of Mas resulted in elevated intracellular calcium levels [Ca²⁺]_i in HK2 cells treated with PA, whereas inhibition or knockdown of Mas decreased [Ca²⁺]_i. Mitochondrial outer membrane located voltage-dependent anion channel (VDAC1) was markedly upregulated in HK2 cells treated with PA, which was associated with impaired mitochondrial morphology and depolarization. These were enhanced by AVE0991 and suppressed by A779 or Mas knockdown. Mas knockdown in HK2 cells prevented impaired interactions among VDAC1, autophagy adaptor P62, and ubiquitin, induced by PA, leading to a potential ubiquitination of VDAC1. In conclusion, Mas receptor-mediated lipid-induced impaired autophagy and ER stress in the kidney, likely contributing to tubular injuries in obesity-related kidney diseases.

ACE2, the kidney and the emergence of COVID-19 two decades after ACE2 discovery

Angiotensin-converting enzyme II (ACE2) is a homologue of angiotensin-converting enzyme discovered in 2000. From the initial discovery, it was recognized that the kidneys were organs very rich on ACE2. Subsequent studies demonstrated the precise localization of ACE2 within the kidney and the importance of this enzyme in the metabolism of Angiotensin II and the formation of Angiotensin 1–7. With the recognition early in 2020 of ACE2 being the main receptor of severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2), the interest in this protein has dramatically increased. In this review, we will focus on kidney ACE2; its localization, its alterations in hypertension, diabetes, the effect of ACE inhibitors and angiotensin type 1 receptor blockers (ARBs) on ACE2 and the potential use of ACE2 recombinant proteins therapeutically for kidney disease.

We also describe the emerging kidney manifestations of COVID-19, namely the frequent development of acute kidney injury. The possibility that binding of SARS-CoV-2 to kidney ACE2 plays a role in the kidney manifestations is also briefly discussed.

An evaluation of renin-angiotensin system markers in youth with type 2 diabetes and associations with renal outcomes

AIMS/HYPOTHESIS

Youth with type 2 diabetes (T2D) have high rates of obesity, hypertension and suboptimal glycemic control. We hypothesized that renin-angiotensin system (RAS) activation is present in youth with T2D and associated with poor glycemic control and renal outcomes.

METHODS

Cross-sectional analysis of 183 youth with T2D and 100 controls from the Improving renal Complications in Adolescents with T2D through REsearch cohort. Diabetes youth stratified by urine albumin:creatinine ratio (ACR) < or ≥2 mg/mmol. RAS levels measured with enzyme-linked immunosorbent assay (ELISA) and enzyme activities by synthetic substrates. In T2D, levels log transformed and Tobit linear regressions evaluated for associations with hemoglobin A1c (HbA1c), mean arterial pressure (MAP), estimated glomerular filtration rate (eGFR), ACR.

RESULTS

Youth were 14 to 15 years, with diabetes duration 1.7 to 1.8 years; 21.3% albuminuria. Serum: differences in plasma renin activity (<0.0001), and angiotensin converting enzyme (ACE) activity (P = .003) in T2D vs controls. Urine: higher ACE activity and ACE2 protein/activity (all P < .0001) in T2D, higher levels in T2D with albuminuria. Multivariable regressions: higher serum ACE activity (ß = 0.03, SE 0.01;P < .01), urine ACE activity (ß = 0.44, SE 0.18;P < .01), ACE2 (ß = 0.51, SE 0.19;P < .01) positively associated with HbA1c; urine angiotensinogen (AGT) negatively associated (ß = -0.28 [SE 0.06;P < .01]). Higher serum aldosterone (ß = 0.11 [SE 0.04;P < .01]) and urine AGT (ß = 0.32 [SE 0.07;P < .01]) significantly associated with ACR and urine ACE2 (ß = 0.21 [SE 0.13;P < .03]). No associations between RAS markers and eGFR/MAP.

CONCLUSIONS/INTERPRETATION

RAS activation present in youth with T2D and associated with higher HbA1c. Higher serum aldosterone and urine AGT associated with albuminuria. The prognostic significance of the combined effect of glycemia and RAS activation on renal outcomes requires additional investigation.

Twenty years of progress in angiotensin converting enzyme 2 and its link to SARS-CoV-2 disease

The virulence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and the aggressive nature of the disease has transformed the universal pace of research in the desperate attempt to seek effective therapies to halt the morbidity and mortality of this pandemic. The rapid sequencing of the SARS-CoV-2 virus facilitated identification of the receptor for angiotensin converting enzyme 2 (ACE2) as the high affinity binding site that allows virus endocytosis. Parallel evidence that coronavirus disease 2019 (COVID-19) disease evolution shows greater lethality in patients with antecedent cardiovascular disease, diabetes, or even obesity questioned the potential unfavorable contribution of angiotensin converting enzyme (ACE) inhibitors or angiotensin II (Ang II) receptor blockers as facilitators of adverse outcomes due to the ability of these therapies to augment the transcription of Ace2 with consequent increase in protein formation and enzymatic activity. We review, here, the specific studies that support a role of these agents in altering the expression and activity of ACE2 and underscore that the robustness of the experimental data is associated with weak clinical long-term studies of the existence of a similar regulation of tissue or plasma ACE2 in human subjects.

Coronavirus Disease 2019 and Hypertension: The Role of Angiotensin-Converting Enzyme 2 and the Renin-Angiotensin System

Hypertension emerged from early reports as a potential risk factor for worse outcomes for persons with coronavirus disease 2019 (COVID-19). Among the putative links between hypertension and COVID-19 is a key counter-regulatory component of the renin-angiotensin system (RAS): angiotensin-converting enzyme 2 (ACE2). ACE2 facilitates entry of severe acute respiratory syndrome coronavirus 2, the virus responsible for COVID-19, into host cells. Because RAS inhibitors have been suggested to increase ACE2 expression, health-care providers and patients have grappled with the decision of whether to discontinue these medications during the COVID-19 pandemic. However, experimental models of analogous viral pneumonias suggest RAS inhibitors may exert protective effects against acute lung injury. We review how RAS and ACE2 biology may affect outcomes in COVID-19 through pulmonary and other systemic effects. In addition, we briefly detail the data for and against continuation of RAS inhibitors in persons with COVID-19 and summarize the current consensus recommendations from select specialty organizations.

Effects of exercise training on renal interstitial fibrosis and renin-angiotensin system in rats with chronic renal failure

OBJECTIVE

To clarify the mechanisms of the renal protective effects of exercise training, we examined the effects of exercise training on the renal interstitial fibrosis and renin-angiotensin system (RAS) in rats with chronic renal failure.

METHODS

Six-week-old male Sprague-Dawley rats were divided into three groups: sham operation; 5/6 nephrectomy + sedentary; 5/6 nephrectomy + exercise training. The 5/6 nephrectomy + exercise training group underwent treadmill running (20 m/min, 60 min/day, 5 days/week). After 12 weeks, renal function, histology and protein expression of collagen type I, transforming growth factor-β1 (TGF-β1), matrix metalloproteinase (MMP), tissue inhibitors of metalloproteinase (TIMP) and RAS components in the renal cortex were examined.

RESULTS

Exercise training ameliorated the 5/6 nephrectomy-induced hypertension, proteinuria, renal dysfunction, glomerular sclerosis and renal interstitial fibrosis. 5/6 Nephrectomy increased the expression of collagen type I, TGF-β1, MMP-2, MMP-9, TIMP-1, angiotensinogen, angiotensin-converting enzyme (ACE), (pro)renin receptor and angiotensin II type 1 receptor, and exercise training inhibited the 5/6 nephrectomy-increased expression of collagen type I, TGF-β1, TIMP-1, angiotensinogen and ACE expressions. 5/6 Nephrectomy decreased the expression of renin, ACE2, angiotensin II type 2 receptor and Mas receptor, and exercise training inhibited the 5/6 nephrectomy-decreased expressions.

CONCLUSION

These results indicated that exercise training attenuates the progression of glomerular sclerosis and renal interstitial fibrosis in chronic renal failure rats. The renal protective effects of exercise training may be mediated by ameliorating the renal collagen turnover and the exacerbation of renal RAS.

Involvement of sex hormones, oxidative stress, ACE and ACE2 activity in the impairment of renal function and remodelling in SHR

AIMS

Hypertension is a relevant sex and sex hormones-dependent risk factor where the cardiovascular and renal health of the population are concerned. Men experience greater losses of renal function (RF) than women, but the mechanisms remain somewhat unclear. Our goal was to evaluate the relationship between oxidative stress (OS), angiotensin-converting enzyme (ACE) and angiotensin-converting enzyme 2 (ACE2) activities and RF in male and female SHR.

MAIN METHODS

Twelve-week-old spontaneously hypertensive rats (SHR) were submitted to either castration or SHAM surgery and divided into 4 groups, SHAM or Castrated (CAST) males or females. After 51 days we evaluated RF (inulin and sodium para-aminohippurate), ACE and ACE2 activities (fluorimetry), OS (flow cytometry), collagen deposition (picrosirius red) and protein expression (western blot).

KEY FINDINGS

Males presented lower RF than females and castration impaired this parameter in both groups. Sexual dimorphism was not observed regarding OS and inflammation; however, castration increased this parameter more severely in males than in females. SHAM males exhibited higher collagen deposition than females, though castration increased it in both sexes, eliminating the difference. We found sexual dimorphism regarding renal ACE and ACE2 activities, which were lower in males than in females. Although castration did not alter ACE activity, it reduced ACE2 activity in females and increased it in males.

SIGNIFICANCE

These results indicate that sex hormones affect RF in SHR. As alterations in the oxidative system were capable of promoting podocyte injury, inflammation, and collagen deposition, we put forward that these effects are differently modulated by ACE and ACE2.

Refining the Mouse Subtotal Nephrectomy in Male 129S2/SV Mice for Consistent Modeling of Progressive Kidney Disease With Renal Inflammation and Cardiac Dysfunction

Chronic kidney disease (CKD) is prevalent worldwide and is associated with significant co-morbidities including cardiovascular disease (CVD). Traditionally, the subtotal nephrectomy (remnant kidney) experimental model has been performed in rats to model progressive renal disease. The model experimentally mimics CKD by reducing nephron number, resulting in renal insufficiency. Presently, there is a lack of translation of pre-clinical findings into successful clinical results. The pre-clinical nephrology field would benefit from reproducible progressive renal disease models in mice in order to avail of more widely available transgenics and experimental tools to dissect mechanisms of disease. Here we evaluate if a simplified single step subtotal nephrectomy (STNx) model performed in the 129S2/SV mouse can recapitulate the renal and cardiac changes observed in patients with CKD in a reproducible and robust way. The single step STNx surgery was well-tolerated and resulted in clinically relevant outcomes including hypertension, increased urinary albumin:creatinine ratio, and significantly increased serum creatinine, phosphate and urea. STNx mice developed significant left ventricular hypertrophy without reduced ejection fraction or cardiac fibrosis. Analysis of intra-renal inflammation revealed persistent recruitment of Ly6C^hi monocytes transitioning to pro-fibrotic inflammatory macrophages in STNx kidneys. Unlike 129S2/SV mice, C57BL/6 mice exhibited renal fibrosis without proteinuria, renal dysfunction, or cardiac pathology. Therefore, the 129S2/SV genetic background is susceptible to induction of progressive proteinuric renal disease and cardiac hypertrophy using our refined, single-step flank STNx method. This reproducible model could be used to study the systemic pathophysiological changes induced by CKD in the kidney and the heart, intra-renal inflammation and for testing new therapies for CKD.

Beneficial Effects of the Angiotensin-Converting Enzyme 2 Activator Dize in Renovascular Hypertension

BACKGROUND

Angiotensin Converting Enzyme (ACE) 2 is an important modulator of the Renin Angiotensin System (RAS) and the RAS plays a central role in renovascular hypertension. Very few studies investigated the role of components of the counterregulatory RAS axis (ACE2, Ang-(1-7) and Mas receptor) in renovascular hypertension and the results are controversial.

OBJECTIVE

The aim of this study was to investigate the effects of Diminazene Aceturate (DIZE) administration on renal function and renal inflammation parameters in 2K1C hypertensive rats.

METHODS

Male Wistar rats were divided into three experimental groups: sham-operated animals, 2K1C+saline and 2K1C+DIZE orally (1 mg/kg/day). At the end of the 30 days of treatment, renal function was analyzed and kidneys from all the groups were collected and processed separately for measurement of N-acetyl-beta-D-glucosaminidase (NAG) and Myeloperoxidase (MPO) activities, cytokines, chemokines and nitric oxide levels.

RESULTS

Oral DIZE administration for 4 weeks in hypertensive rats attenuated renal dysfunction and reduced the levels of MPO and NAG, cytokines and chemokines (IL1β, IL-6, TNF-α and MCP-1) and increased urinary nitrate/nitrite levels in 2K1C hypertensive rats.

CONCLUSION

Our findings showed that ACE2 activation may effectively improve renal alterations and inflammation induced by renovascular hypertension.

Decreased Renal Function Induced by High-Fat Diet in Wistar Rat: The Role of Plasma Angiotensin Converting Enzyme 2 (ACE2)

Researches on the effects of High Fat Diet (HFD) on decreased renal function with cystatin C (cysC) serum levels biomarker are few and show different findings. Renin Angiotensin System (RAS) plays a key role in controlling renal function and one of the integral components of the RAS is Angiotensin Converting Enzyme 2 (ACE2). Research on the relationship between plasma ACE2 levels with serum cysC levels in animals induced by HFD has not been done. We hypothesize that administration of HFD can cause a decline in early stage renal function through the role of ACE2. 30 male wistar rats aged 10-12 weeks (body weight between 170-220 grams) were randomly divided into 5 groups (6 rats/group): baseline, normal diet for 8 weeks (ND8), ND for 16 weeks (ND16), HFD for 8 weeks (HFD8) and HFD for 16 weeks (HFD16). Body weight and naso-anal length were measured to get the index value of obesity and body fat percentage. Obesity index measured are lee index, rohrer index and TM index. Blood samples obtained by intracardiac for examination of plasma ACE2 levels and serum cysC levels. After 8 and 16 weeks, HFD increases body weight, obesity index and body fat percentage. HFD also increases plasma ACE2 levels and serum cysC levels. Body weight, obesity index and body fat percentage have a positive correlation with plasma ACE2 levels. Plasma ACE2 levels were positively correlated with serum cysC levels. HFD causes a decrease of early stage renal function as evidenced by the increase in serum cysC levels. Plasma ACE2 levels play a role in the pathogenesis of the decline in early stage renal function induced by HFD.

Intrarenal Renin–Angiotensin System Involvement in the Pathogenesis of Chronic Progressive Nephropathy—Bridging the Informational Gap Between Disciplines

Chronic progressive nephropathy (CPN) is the most commonly encountered spontaneous background finding in laboratory rodents. Various theories on its pathogenesis have been proposed, but there is a paucity of data regarding specific mechanisms or physiologic pathways involved in early CPN development. The current CPN mechanism of action for tumorigenesis is largely based on its associated increase in tubular cell proliferation without regard to preceding subcellular degenerative changes. Combing through the published literature from multiple biology disciplines provided insight into the preceding cellular events. Mechanistic pathways involved in the progressive age-related decline in rodent kidney function and several key inflexion points have been identified. These critical pathway factors were then connected using data from renal models from multiple rodent strains, other species, and mechanistic work in humans to form a cohesive picture of pathways and protein interactions. Abundant data linked similar renal pathologies to local events involving hypoxia (hypoxia-inducible factor 1α), altered intrarenal renin–angiotensin system (RAS), oxidative stress (nitric oxide), and pro-inflammatory pathways (transforming growth factor β), with positive feedback loops and downstream effectors amplifying the injury and promoting scarring. Intrarenal RAS alterations seem to be central to all these events and may be critical to CPN development and progression.

Azilsartan causes natriuresis due to its sympatholytic action in kidney disease

The sympathoinhibitory mechanism of azilsartan was investigated in an adenine-induced chronic renal failure model. Azilsartan exerted an antihypertensive effect, though BP elevation induced by adenine was marginal. The creatinine value was significantly lower in the azilsartan group (AZ) than in the vehicle group (VEH); furthermore, proteinuria was suppressed, and sodium excretion was augmented in the AZ group. The low frequency (LF) of systolic BP was suppressed (VEH: 4.07 ± 2.67 mmHg² vs. AZ: 3.32 ± 1.93 mmHg² P < 0.001), and the spontaneous baroreflex gain (sBRG) was augmented (VEH: 1.04 ± 0.62ms/mmHg vs. AZ: 1.38 ± 0.69 ms/mmHg, P < 0.001) in AZ. There were no significant differences in ACE1 and ACE2 expression between the groups, which indicated that the action of azilsartan on these components of the intrarenal renin-angiotensin-aldosterone system was comparatively small. Although NHE3, NKCC, and ENaC expression was similar between the groups, NaCl cotransporter (NCC) expression was markedly suppressed by azilsartan (P < 0.05). Thus, in a mild chronic kidney disease (CKD) model with slight BP elevation, the sympatholytic effect of ARB might be expected, and azilsartan might exert its natriuretic effect by NCC suppression achieved by sympathoinhibitory activity.

Evidence for a role of angiotensin converting enzyme 2 in proteinuria of idiopathic nephrotic syndrome

Introduction: Renin angiotensin system (RAS) plays a role in idiopathic nephrotic syndrome (INS). Most studies investigated only the classical RAS axis. Therefore, the aims of the present study were to evaluate urinary levels of RAS molecules related to classical and to counter-regulatory axes in pediatric patients with INS, to compare the measurements with levels in healthy controls and to search for associations with inflammatory molecules, proteinuria and disease treatment. Subjects and methods: This cross-sectional study included 31 patients with INS and 19 healthy controls, matched for age and sex. Patients and controls were submitted to urine collection for measurement of RAS molecules [Ang II, Ang-(1-7), ACE and ACE2] by enzyme immunoassay and cytokines by Cytometric Bead Array. Findings in INS patients were compared according to proteinuria: absent (<150 mg/dl, n = 15) and present (≥150 mg/dl, n = 16). Results: In comparison to controls, INS patients had increased Ang II, Ang-(1-7) and ACE, levels while ACE2 was reduced. INS patients with proteinuria had lower levels of ACE2 than those without proteinuria. ACE2 levels were negatively correlated with 24-h-proteinuria. Urinary concentrations of MCP-1/CCL2 were significantly higher in INS patients, positively correlated with Ang II and negatively with Ang-(1-7). ACE2 concentrations were negatively correlated with IP-10/CXCL-10 levels, which, in turn, were positively correlated with 24-h-proteinuria. Conclusion: INS patients exhibited changes in RAS molecules and in chemokines. Proteinuria was associated with low levels of ACE2 and high levels of inflammatory molecules.

Modulation of leucocytic angiotensin-converting enzymes expression in patients maintained on high-permeable haemodialysis

Background

High mortality of haemodialysis patients is associated with systemic chronic inflammation and overactivation of the renin-angiotensin system (RAS). Insufficient elimination of pro-inflammatory immune mediators, especially in the molecular weight range of 15-45 kDa, may be one of the reasons for this. Employment of haemodialysis membranes with increased permeability was shown to ameliorate the inflammatory response and might modulate the effects of local RAS. In this study, we tested the impact of high cut-off (HCO), medium cut-off (MCO) and high-flux (HF) dialysis on leucocytic transcripts of angiotensin-converting enzymes (ACE and ACE2). Additionally, the impact of HCO, MCO and HF sera and dialysates on local ACEs and inflammation markers was tested in THP-1 monocytes.

Methods

Patients' leucocytes were obtained from our recent clinical studies comparing HCO and MCO dialysers with HF. The cells were subjected to quantitaive polymerase chain reaction (qPCR) analyses with TaqMan probes specific for ACE, ACE2 and angiotensin II (AngII) and Ang1-7 receptors. Sera and dialysates from the clinical trials as well as samples from in vitro dialysis were tested on THP-1 monocytic cells. The cells were subjected to qPCR analyses with TaqMan probes specific for ACE, ACE2, interleukin-6 and tumour necrosis factor α and immunocytochemistry with ACE and ACE2 antibodies.

Results

Leucocytes obtained from patients treated with HCO or MCO demonstrated decreased transcript expression of ACE, while ACE2 was significantly upregulated as compared with HF. Receptors for AngII and Ang1-7 remained unchanged. THP-1 monocytes preconditioned with HCO and MCO patients' or in vitro dialysis sera reflected the same expressional regulation of ACE and ACE2 as those observed in HCO and MCO leucocytes. As a complementary finding, treatment with HCO and MCO in vitro dialysates induced a pro-inflammatory response of the cells as demonstrated by elevated messenger RNA expression of tumour necrosis factor α and interleukin-6, as well as upregulation of ACE and decreased levels of ACE2.

Conclusions

Taken together, these data demonstrate that employment of membranes with high permeability eliminates a spectrum of mediators from circulation that affect the RAS components in leucocytes, especially ACE/ACE2.

Egg White-Derived Tripeptide IRW (Ile-Arg-Trp) Is an Activator of Angiotensin Converting Enzyme 2

Angiotensin converting enzyme 2 (ACE2) plays beneficial roles in the renin angiotensin aldosterone system. Our previous studies indicated that egg white-derived antihypertensive peptide IRW (Ile-Arg-Trp) could upregulate ACE2 mRNA level in mesenteric artery of spontaneously hypertensive rats (SHRs), suggesting the potential of IRW as an in vivo ACE2 activator. In this study, the effects of IRW on activity and protein expression of ACE2 were investigated. Results indicated that IRW activated human recombinant ACE2 with an EC₅₀ value of 7.24 × 10^-5 M. In rat aortic vascular smooth muscle cell line A7r5 cells, IRW treatment (50 μM) significantly increased the expression and activity of ACE2. Oral administration of IRW to SHRs upregulated ACE2 protein levels in kidney and aorta. Molecular docking study suggested that IRW might activate ACE2 through interaction with the subdomain I near the active site through hydrogen bonds. Overall, this study established IRW as the first food-derived ACE2 activating peptide.

The ACE2/Angiotensin-(1-7)/MAS Axis of the Renin-Angiotensin System: Focus on Angiotensin-(1-7)

The renin-angiotensin system (RAS) is a key player in the control of the cardiovascular system and hydroelectrolyte balance, with an influence on organs and functions throughout the body. The classical view of this system saw it as a sequence of many enzymatic steps that culminate in the production of a single biologically active metabolite, the octapeptide angiotensin (ANG) II, by the angiotensin converting enzyme (ACE). The past two decades have revealed new functions for some of the intermediate products, beyond their roles as substrates along the classical route. They may be processed in alternative ways by enzymes such as the ACE homolog ACE2. One effect is to establish a second axis through ACE2/ANG-(1-7)/MAS, whose end point is the metabolite ANG-(1-7). ACE2 and other enzymes can form ANG-(1-7) directly or indirectly from either the decapeptide ANG I or from ANG II. In many cases, this second axis appears to counteract or modulate the effects of the classical axis. ANG-(1-7) itself acts on the receptor MAS to influence a range of mechanisms in the heart, kidney, brain, and other tissues. This review highlights the current knowledge about the roles of ANG-(1-7) in physiology and disease, with particular emphasis on the brain.

The role of ACE2, angiotensin-(1-7) and Mas1 receptor axis in glucocorticoid-induced intrauterine growth restriction

BACKGROUND

Plasma and urine levels of the potent vasodilator Ang-(1-7) are elevated in mid and late pregnancy and are correlated with elevated placental angiogenesis, fetal blood flow, and rapid fetal growth. We hypothesized that Ang-(1-7), its receptor (Mas1) and the enzymes involved in Ang-(1-7) production (ACE2 and Membrane metallo-endopeptidase; MME) are down regulated in response to glucocorticoid administration contributing to IUGR.

METHODS

Pregnant female Sprague-Dawley rats were injected with dexamethasone (DEX; 0.4 mg/kg/day) starting from 14 day gestation (dg) till sacrifice at 19 or 21 dg while control groups were injected with saline (n = 6/group). The gene and protein expression of ACE2, MME, Ang-(1-7) and Mas1 receptor in the placental labyrinth (LZ) and basal zones (BZ) were studied.

RESULTS

DEX administration caused a reduction in LZ weight at 19 and 21 dg (p < 0.001). IUGR, as shown by decreased fetal weights, was evident in DEX treated rats at 21 dg (p < 0.01). ACE2 gene expression was elevated in the LZ of control placentas at 21 dg (p < 0.01) compared to 19 dg and DEX prevented this rise at both gene (p < 0.01) and protein levels (p < 0.05). In addition, Ang-(1-7) protein expression in LZ was significantly reduced in DEX treated rats at 21 dg (p < 0.05). On the other hand, Mas1 and MME were upregulated in LZ at 21 dg in both groups (p < 0.05 and p < 0.001, respectively).

CONCLUSION

The results of this study indicate that a reduced expression of ACE2 and Ang-(1-7) in the placenta by DEX treatment may be responsible for IUGR and consequent disease programming later in life.

P16 INK4a Deletion Ameliorated Renal Tubulointerstitial Injury in a Stress-induced Premature Senescence Model of Bmi-1 Deficiency

To determine whether p16 ^INK4a deletion ameliorated renal tubulointerstitial injury by inhibiting a senescence-associated secretory phenotype (SASP) in Bmi-1-deficient (Bmi-1 ^-/-) mice, renal phenotypes were compared among 5-week-old Bmi-1 and p16 ^INK4a double-knockout, and Bmi-1 ^-/- and wild-type mice. Fifth-passage renal interstitial fibroblasts (RIFs) from the three groups were analyzed for senescence and proliferation. The effect of Bmi-1 deficiency on epithelial-to-mesenchymal transition (EMT) was examined in Bmi-1-knockdown human renal proximal tubular epithelial (HK2) cells, which were treated with concentrated conditioned medium (CM) from the fifth-passage renal interstitial fibroblasts (RIFs) of above three group mice or with exogenous TGF-β1. Our results demonstrated that p16 ^INK4a deletion largely rescued renal aging phenotypes caused by Bmi-1 deficiency, including impaired renal structure and function, decreased proliferation, increased apoptosis, senescence and SASP, DNA damage, NF-κB and TGF-β1/Smad signal activation, inflammatory cell infiltration, and tubulointerstitial fibrosis and tubular atrophy. P16 ^INK4a deletion also promoted proliferation, reduced senescence and SASP of RIFs and subsequently inhibited EMT of Bmi-1-knockdown HK2 cells. TGF-β1 further induced the EMT of Bmi-1-knockdown HK2 cells. Thus, p16 ^INK4a positive senescent cells would be a therapeutic target for preventing renal tubulointerstitial injury.

Treatment with enalapril and not diltiazem ameliorated progression of chronic kidney disease in rats, and normalized renal AT1 receptor expression as measured with PET imaging

ACE inhibitors are considered first line of treatment in patients with many forms of chronic kidney disease (CKD). Other antihypertensives such as calcium channel blockers achieve similar therapeutic effectiveness in attenuating hypertension-related renal damage progression. Our objective was to explore the value of positron emission tomography (PET) imaging of renal AT1 receptor (AT1R) to guide therapy in the 5/6 subtotal-nephrectomy (Nx) rat model of CKD. Ten weeks after Nx, Sprague-Dawley rats were administered 10mg/kg/d enalapril (NxE), 30mg/kg/d diltiazem (NxD) or left untreated (Nx) for an additional 8-10 weeks. Kidney AT1R expression was assessed using in vivo [18F]fluoropyridine-losartan PET and in vitro autoradiography. Compared to shams, Nx rats exhibited higher systolic blood pressure that was reduced by both enalapril and diltiazem. At 18-20 weeks, plasma creatinine and albuminuria were significantly increased in Nx, reduced to sham levels in NxE, but enhanced in NxD rats. Enalapril treatment decreased kidney angiotensin II whereas diltiazem induced significant elevations in plasma and kidney levels. Reduced PET renal AT1R levels in Nx were normalized by enalapril but not diltiazem, and results were supported by autoradiography. Reduction of renal blood flow in Nx was restored by enalapril, while no difference was observed in myocardial blood flow amongst groups. Enhanced left ventricle mass in Nx was not reversed by enalapril but was augmented with diltiazem. Stroke volume was diminished in untreated Nx compared to shams and restored with both therapies. [18F]Fluoropyridine-Losartan PET allowed in vivo quantification of kidney AT1R changes associated with progression of CKD and with various pharmacotherapies.

Adverse cardiac effects of exogenous angiotensin 1-7 in rats with subtotal nephrectomy are prevented by ACE inhibition

We previously reported that exogenous angiotensin (Ang) 1–7 has adverse cardiac effects in experimental kidney failure due to its action to increase cardiac angiotensin converting enzyme (ACE) activity. This study investigated if the addition of an ACE inhibitor (ACEi) to Ang 1–7 infusion would unmask any beneficial effects of Ang 1–7 on the heart in experimental kidney failure. Male Sprague–Dawley rats underwent subtotal nephrectomy (STNx) and were treated with vehicle, the ACEi ramipril (oral 1mg/kg/day), Ang 1–7 (subcutaneous 24 μg/kg/h) or dual therapy (all groups, n = 12). A control group (n = 10) of sham-operated rats were also studied. STNx led to hypertension, renal impairment, cardiac hypertrophy and fibrosis, and increased both left ventricular ACE2 activity and ACE binding. STNx was not associated with changes in plasma levels of ACE, ACE2 or angiotensin peptides. Ramipril reduced blood pressure, improved cardiac hypertrophy and fibrosis and inhibited cardiac ACE. Ang 1–7 infusion increased blood pressure, cardiac interstitial fibrosis and cardiac ACE binding compared to untreated STNx rats. Although in STNx rats, the addition of ACEi to Ang 1–7 prevented any deleterious cardiac effects of Ang 1–7, a limitation of the study is that the large increase in plasma Ang 1–7 with ramipril may have masked any effect of infused Ang 1–7.

Angiotensin-(1-7) relieved renal injury induced by chronic intermittent hypoxia in rats by reducing inflammation, oxidative stress and fibrosis

We aimed to study the renal injury and hypertension induced by chronic intermittent hypoxia (CIH) and the protective effects mediated by angiotensin 1-7 [Ang(1-7)]. We randomly assigned 32 male Sprague-Dawley rats (body weight 180-200 g) to normoxia control, CIH, Ang(1-7)-treated normoxia, and Ang(1-7)-treated CIH groups. Systolic blood pressure (SBP) was monitored at the start and end of each week. Renal sympathetic nerve activity (RSNA) was recorded. CTGF and TGF-β were detected by immunohistochemistry and western blotting. Tissue parameters of oxidative stress were also determined. In addition, renal levels of interleukin-6, tumor necrosis factor-α, nitrotyrosine, and hypoxia-inducible factor-1α were determined by immunohistochemistry, immunoblotting, and ELISA. TUNEL assay results and cleaved caspase 3 and 12 were also determined. Ang(1-7) induced a reduction in SBP together with a restoration of RSNA in the rat model of CIH. Ang(1-7) treatment also suppressed the production of reactive oxygen species, reduced renal tissue inflammation, ameliorated mesangial expansion, and decreased renal fibrosis. Thus, Ang(1-7) treatment exerted renoprotective effects on CIH-induced renal injury and was associated with a reduction of oxidative stress, inflammation and fibrosis. Ang(1-7) might therefore represent a promising therapy for obstructive sleep apnea-related hypertension and renal injury.

Antenatal corticosteroids and the renin-angiotensin-aldosterone system in adolescents born preterm

BACKGROUND

Antenatal corticosteroid (ANCS) treatment hastens fetal lung maturity and improves survival of premature infants, but the long-term effects of ANCS are not well-described. Animal models suggest that ANCS increases the risk of cardiovascular disease through programmed changes in the renin-angiotensin (Ang)-aldosterone system (RAAS). We hypothesized that ANCS exposure alters the RAAS in adolescents born prematurely.

METHODS

A cohort of 173 adolescents born prematurely was evaluated, of whom 92 were exposed to ANCS. We measured plasma and urine Ang II and Ang-(1-7) and calculated Ang II/Ang-(1-7) ratios. We used general linear regression models to estimate the difference in the RAAS between the ANCS-exposed and unexposed groups, adjusting for confounding variables.

RESULTS

In unadjusted analyses, and after adjustment for sex, race, and maternal hypertension, ANCS exposure was associated with increased urinary Ang II/Ang-(1-7) (estimate 0.27 (95% CI 0.03, 0.5), P = 0.03), increased plasma Ang-(1-7) (0.66 (0.26, 1.07), P = 0.002), and decreased plasma Ang II/Ang-(1-7) (-0.48 (-0.91, -0.06), P = 0.03).

CONCLUSION

These alterations indicate an imbalance in the urinary RAAS, promoting the actions of Ang II at the expense of Ang-(1-7), which over time may increase the risk of renal inflammation and fibrosis and ultimately hypertension and renal disease.

Serum protease activity in chronic kidney disease patients: The GANI_MED renal cohort

Serum or plasma proteases have been associated with various diseases including cancer, inflammation, or reno-cardiovascular diseases. We aimed to investigate whether the enzymatic activities of serum proteases are associated with the estimated glomerular filtration rate (eGFR) in patients with different stages of chronic kidney disease (CKD). Our study population comprised 268 participants of the "Greifswald Approach to Individualized Medicine" (GANI_MED) cohort. Enzymatic activity of aminopeptidase A, aminopeptidase B, alanyl (membrane) aminopeptidase, insulin-regulated aminopeptidase, puromycin-sensitive aminopeptidase, leucine aminopeptidase 3, prolyl-endopeptidase (PEP), dipeptidyl peptidase 4 (DPP4), angiotensin I-converting enzyme, and angiotensin I-converting enzyme 2 (ACE2) proteases was measured in serum. Linear regression of the respective protease was performed on kidney function adjusted for age and sex. Kidney function was modeled either by the continuous Modification of Diet in Renal Disease (MDRD)-based eGFR or dichotomized by eGFR < 15 mL/min/1.73 m² or <45 mL/min/1.73 m², respectively. Results with a false discovery rate below 0.05 were deemed statistically significant. Among the 10 proteases investigated, only the activities of ACE2 and DPP4 were correlated with eGFR. Patients with lowest eGFR exhibited highest DPP4 and ACE2 activities. DPP4 and PEP were correlated with age, but all other serum protease activities showed no associations with age or sex. Our data indicate that ACE2 and DPP4 enzymatic activity are associated with the eGFR in patients with CKD. This finding distinguishes ACE2 and DPP4 from other serum peptidases analyzed and clearly indicates that further analyses are warranted to identify the precise role of these serum ectopeptidases in the pathogenesis of CKD and to fully elucidate underlying molecular mechanisms. Impact statement • Renal and cardiac diseases are very common and often occur concomitantly, resulting in increased morbidity and mortality. Understanding of molecular mechanisms linking both diseases is limited, available fragmentary data point to a role of the renin-angiotensin system (RAS) and, in particular, Ras-related peptidases. • Here, a comprehensive analysis of serum peptidase activities in patients with different stages of chronic kidney disease (CKD) is presented, with special emphasis given to RAS peptidases • The serum activities of the peptidases angiotensin I-converting enzyme 2 and dipeptidyl peptidase 4 were identified as closely associated with kidney function, specifically with the estimated glomerular filtration rate. The findings are discussed in the context of available data suggesting protective roles for both enzymes in reno-cardiac diseases. • The data add to our understanding of pathomechanisms underlying development and progression of CKD and indicate that both enzymes might represent potential pharmacological targets for the preservation of renal function.

Decreased renal AT1 receptor binding in rats after subtotal nephrectomy: PET study with [(18)F]FPyKYNE-losartan

Background

Significant renal mass reduction induced by 5/6 subtotal nephrectomy (Nx) is associated with a chain of events that culminates in hypertension and chronic kidney disease (CKD). Numerous studies have provided evidence for the role of angiotensin (Ang) II type 1 receptor (AT₁R) in the promotion and progression of the disease; however, conflicting results were reported on intrarenal AT₁R levels in CKD models.

Methods

Male Sprague-Dawley rats (n = 26) underwent Nx or sham operations. Animals were scanned at 8–10 weeks post-surgery with PET using the novel AT₁R radioligand [¹⁸F]FPyKYNE-losartan. Radioligand binding was quantified by kidney-to-blood ratio (KBR), standard uptake value (SUV), and distribution volume (DV). After sacrifice, plasma and kidney Ang II levels were measured. Western blot and ¹²⁵I-[Sar¹, Ile⁸]Ang II autoradiography were performed to assess AT₁R expression.

Results

At 8–10 weeks post-surgery, Nx rats developed hypertension, elevated plasma creatinine levels, left ventricle hypertrophy, increased myocardial blood flow (MBF), and reduced Ang II levels compared to shams. PET measurements displayed significant decrease in KBR (29 %), SUV (24 %), and DV (22 %) induced by Nx (p < 0.05), and these findings were confirmed by in vitro assays.

Conclusions

Reduced renal AT₁Rs in hypertensive rats measured with [¹⁸F]FPyKYNE-losartan PET at 8–10 weeks following Nx support further use of this non-invasive approach in longitudinal studies to better understand the AT₁R role in CKD progression.

ACE inhibition, ACE2 and angiotensin-(1-7) axis in kidney and cardiac inflammation and fibrosis

The Renin Angiotensin System (RAS) is a pivotal physiological regulator of heart and kidney homeostasis, but also plays an important role in the pathophysiology of heart and kidney diseases. Recently, new components of the RAS have been discovered, including angiotensin converting enzyme 2 (ACE2), Angiotensin(Ang)-(1-7), Mas receptor, Ang-(1-9) and Alamandine. These new components of RAS are formed by the hydrolysis of Ang I and Ang II and, in general, counteract the effects of Ang II. In experimental models of heart and renal diseases, Ang-(1-7), Ang-(1-9) and Alamandine produced vasodilation, inhibition of cell growth, anti-thrombotic, anti-inflammatory and anti-fibrotic effects. Recent pharmacological strategies have been proposed to potentiate the effects or to enhance the formation of Ang-(1-7) and Ang-(1-9), including ACE2 activators, Ang-(1-7) in hydroxypropyl β-cyclodextrin, cyclized form of Ang-(1-7) and nonpeptide synthetic Mas receptor agonists. Here, we review the role and effects of ACE2, ACE2 activators, Ang-(1-7) and synthetic Mas receptor agonists in the control of inflammation and fibrosis in cardiovascular and renal diseases and as counter-regulators of the ACE-Ang II-AT1 axis. We briefly comment on the therapeutic potential of the novel members of RAS, Ang-(1-9) and alamandine, and the interactions between classical RAS inhibitors and new players in heart and kidney diseases.

Angiotensin-(1-7) Attenuates Kidney Injury Due to Obstructive Nephropathy in Rats

Background

Angiotensin-(1–7) [Ang-(1–7)] counteracts many actions of the renin-angiotensin-aldosterone system. Despite its renoprotective effects, extensive controversy exists regarding the role of Ang-(1–7) in obstructive nephropathy, which is characterized by renal tubulointerstitial fibrosis and apoptosis.

Methods

To examine the effects of Ang-(1–7) in unilateral ureteral obstruction (UUO), male Sprague-Dawley rats were divided into three groups: control, UUO, and Ang-(1–7)-treated UUO rats. Ang-(1–7) was continuously infused (24 μg/[kg·h]) using osmotic pumps. We also treated NRK-52E cells in vitro with Ang II (1 μM) in the presence or absence of Ang-(1–7) (1 μM), Mas receptor antagonist A779 (1 μM), and Mas receptor siRNA (50 nM) to examine the effects of Ang-(1–7) treatment on Ang II-stimulated renal injury via Mas receptor.

Results

Angiotensin II (Ang II) and angiotensin type 1 receptor (AT₁R) protein expression was higher in UUO kidneys than in controls. Ang-(1–7) treatment also decreased proapoptotic protein expression in UUO kidneys. Ang-(1–7) also significantly ameliorated TUNEL positive cells in UUO kidneys. Additionally, Ang-(1–7) reduced profibrotic protein expression and decreased the increased tumor growth factor (TGF)-β1/Smad signaling present in UUO kidneys. In NRK-52E cells, Ang II induced the expression of TGF-β1/Smad signaling effectors and proapoptotic and fibrotic proteins, as well as cell cycle arrest, which were attenuated by Ang-(1–7) pretreatment. However, treatment with A779 and Mas receptor siRNA enhanced Ang II-induced apoptosis and fibrosis. Moreover, Ang II increased tumor necrosis factor-α converting enzyme (TACE) and decreased angiotensin-converting enzyme 2 (ACE2) expression in NRK-52E cells, while pretreatment with Ang-(1–7) or A779 significantly inhibited or enhanced these effects, respectively.

Conclusion

Ang-(1–7) prevents obstructive nephropathy by suppressing renal apoptosis and fibrosis, possibly by regulating TGF-β1/Smad signaling and cell cycle arrest via suppression of AT₁R expression. In addition, Ang-(1–7) increased and decreased ACE2 and TACE expression, respectively, which could potentially mediate a positive feedback mechanism via the Mas receptor.

Functional and molecular evidence for expression of the renin angiotensin system and ADAM17-mediated ACE2 shedding in COS7 cells

The renin angiotensin system (RAS) plays a vital role in the regulation of the cardiovascular and renal functions. COS7 is a robust and easily transfectable cell line derived from the kidney of the African green monkey, Cercopithecus aethiops. The aims of this study were to 1) demonstrate the presence of an endogenous and functional RAS in COS7, and 2) investigate the role of a disintegrin and metalloproteinase-17 (ADAM17) in the ectodomain shedding of angiotensin converting enzyme-2 (ACE2). Reverse transcription coupled to gene-specific polymerase chain reaction demonstrated expression of ACE, ACE2, angiotensin II type 1 receptor (AT1R), and renin at the transcript levels in total RNA cell extracts. Western blot and immunohistochemistry identified ACE (60 kDa), ACE2 (75 kDa), AT1R (43 kDa), renin (41 kDa), and ADAM17 (130 kDa) in COS7. At the functional level, a sensitive and selective mass spectrometric approach detected endogenous renin, ACE, and ACE2 activities. ANG-(1-7) formation (m/z 899) from the natural substrate ANG II (m/z 1,046) was detected in lysates and media. COS7 cells stably expressing shRNA constructs directed against endogenous ADAM17 showed reduced ACE2 shedding into the media. This is the first study demonstrating endogenous expression of the RAS and ADAM17 in the widely used COS7 cell line and its utility to study ectodomain shedding of ACE2 mediated by ADAM17 in vitro. The transfectable nature of this cell line makes it an attractive cell model for studying the molecular, functional, and pharmacological properties of the renal RAS.

Role of non-classical renin-angiotensin system axis in renal fibrosis

The renin–angiotensin system (RAS) is a major regulator of renal fibrosis. Besides the classical renin/Angiotensin-converting enzyme (ACE)/angiotensin II (Ang II)/AT1 and AT2 axis, multiple new axes have been recently described. The new members have added new dimensions to RAS, including the ACE2/Ang(1–7)/Mas receptor axis, the prorenin/(pro)renin receptor(PRR)/intracelluar pathway axis, and the Angiotensin A (Ang A), alamandine-Mas-related G protein coupled receptor D(MrgD) axis. This review summarized recent studies regarding role of the non-classical RAS axis in renal fibrosis, and its possible implications to the intervention of progression of chronic kidney disease.

Characterization of the intrarenal renin-angiotensin system in experimental alport syndrome

Blockade of the renin-angiotensin system attenuates the progression of experimental and clinical Alport syndrome (AS); however, the underlying mechanism(s) remains largely unknown. We evaluated the renin-angiotensin system in 4- and 7-week-old homozygous for collagen, type IV, α3 gene (Col4A3(-/-)) and wild-type mice, a model of AS characterized by proteinuria and progressive renal injury. Renal angiotensin (Ang) II levels increased, whereas renal Ang-(1-7) levels decreased in 7-week-old Col4a3(-/-) mice compared with age-matched controls; these changes were partially reversed by recombinant angiotensin-converting enzyme 2 (ACE2) treatment. The expression of both the angiotensinogen and renin protein increased in Col4a3(-/-) compared with wild-type mice. Consistent with the Ang-(1-7) levels, the expression and activity of kidney ACE2 decreased in 7-week-old Col4a3(-/-) mice. The urinary excretion rate of ACE2 paralleled the decline in tissue expression. Expression of an Ang II-induced gene, heme oxygenase-1, was up-regulated in the kidneys of 7-week-old Col4a3(-/-) mice compared with wild-type mice by microarray analysis. Heme oxygenase-1 (HO-1) protein expression was increased in kidneys of Col4a3(-/-) mice and normalized by treatment with ACE inhibitor. Urinary HO-1 excretion paralleled renal HO-1 expression. In conclusion, progressive kidney injury in AS is associated with changes in expression of intrarenal renin Ang system components and Ang peptides. HO-1 and ACE2 may represent novel markers of AS-associated kidney injury, whereas administration of recombinant ACE2 and/or Ang-(1-7) may represent novel therapeutic approaches in AS.

ACE and ACE2 in kidney disease

Renin angiotensin system (RAS) activation has a significant influence on renal disease progression. The classical angiotensin-converting enzyme (ACE)-angiotensin II (Ang II)-Ang II type 1 (AT1) axis is considered to control the effects of RAS activation on renal disease. However, since its discovery in 2000 ACE2 has also been demonstrated to have a significant impact on the RAS. The synthesis and catabolism of Ang II are regulated via a complex series of interactions, which involve ACE and ACE2. In the kidneys, ACE2 is expressed in the proximal tubules and less strongly in the glomeruli. The synthesis of inactive Ang 1-9 from Ang I and the catabolism of Ang II to produce Ang 1-7 are the main functions of ACE2. Ang 1-7 reduces vasoconstriction, water retention, salt intake, cell proliferation, and reactive oxygen stress, and also has a renoprotective effect. Thus, in the non-classical RAS the ACE2-Ang 1-7-Mas axis counteracts the ACE-Ang II-AT1 axis. This review examines recent human and animal studies about renal ACE and ACE2.

The effect of angiotensin-(1-7) in mouse unilateral ureteral obstruction

Angiotensin-(1-7) is a ligand for the Mas receptor and may protect against tissue injury associated with renin-angiotensin system activation. We determined the effects of endogenous or exogenous angiotensin-(1-7) in mice with unilateral ureteral obstruction (UUO). Mice with UUO were treated with or without the angiotensin-(1-7) antagonist A779 or with 6, 24, or 62 μg/kg per hour exogenous angiotensin-(1-7). After 10 days, kidneys were harvested for histology, immunoblots, and measurement of NADPH oxidase. Compared with controls, A779 treatment significantly increased fibronectin, transforming growth factor-β, and α-smooth muscle actin expression in obstructed kidneys and enhanced tubulointerstitial injury, apoptosis, and NADPH oxidase. Unexpectedly, administration of angiotensin-(1-7) to mice with UUO caused injury in obstructed kidneys compared with controls and increased macrophage infiltration. In obstructed kidneys from mice with gene deletion of Mas (Mas(-/-)), apoptosis and macrophage infiltration were increased compared with wild-type mice. Angiotensin-(1-7) (but not A779) further increased apoptosis and macrophage influx in obstructed kidneys from Mas(-/-) mice, compared with untreated Mas(-/-) mice. These data indicate that endogenous angiotensin-(1-7) protects against kidney injury in UUO. In mice with or without the Mas receptor, however, delivery of exogenous angiotensin-(1-7) worsens kidney damage. The results suggest dose-dependent effects of angiotensin-(1-7) in the kidney in UUO, with endogenous angiotensin-(1-7) promoting repair pathways via interaction with Mas and higher amounts exacerbating injury.

Receptor MAS protects mice against hypothermia and mortality induced by endotoxemia

The renin-angiotensin (Ang) system is involved in maintaining cardiovascular function by regulating blood pressure and electrolyte homeostasis. More recently, alternative pathways within the renin-angiotensin system have been described, such as the ACE-2/Ang-(1-7)/Mas axis, with opposite effects to the ones of the ACE/Ang-II/AT1 axis. Correspondingly, our previous work reported that Ang-(1-7) via its receptor Mas inhibits the mRNA expression of the proinflammatory cytokines interleukin 6 (IL-6) and tumor necrosis factor-α increased by lipopolysaccharide (LPS) in mouse peritoneal macrophages. These data led us to investigate the functional role of the Ang-(1-7)/Mas axis in an in vivo LPS model. In this work, we present evidence that Ang-(1-7) via Mas significantly reduced the LPS-increased production of circulating cytokines, such as IL-6, IL-12, and CXCL-1. This inhibitory effect was mediated by Mas because it was not detectable in Mas-deficient (Mas) mice. Accordingly, IL-6, CXCL-1, and CXCL-2 levels were higher after LPS treatment in the absence of Mas. Mas mice were less resistant to LPS-induced endotoxemia, their survival rate being 50% compared with 95% in wild-type mice. Telemetric analyses showed that Mas mice presented more pronounced LPS-induced hypothermia with a 3°C lower body temperature compared with wild-type mice. Altogether, our findings suggest that Ang-(1-7) and Mas inhibit LPS-induced cytokine production and hypothermia and thereby protect mice from the fatal consequences of endotoxemia.