Critical Role of Neprilysin in Kidney Angiotensin Metabolism

Pathogenesis of Focal Segmental Glomerulosclerosis and Minimal Change Disease: Insights from Glomerular Proteomics

Podocyte injury is a hallmark of both focal segmental glomerulosclerosis (FSGS) and minimal change disease (MCD), ultimately reflected in foot process effacement and proteinuria. Triggers and pathogenic pathways leading to podocyte cytoskeleton rearrangements are, however, incompletely explained. Here, we aimed to contribute to the understanding of these pathways using tissue bottom-up proteomic profiling of laser-capture microdissected glomeruli from MCD and FSGS. Forty-six differentially expressed proteins were identified between the two groups (p < 0.05, |FC| ≥ 1.2). Pathway analysis showed that 16 out of 46 proteins were associated with the immune system, with E2 ubiquitin-conjugating enzyme (UBE2K) and complement factor H-related protein-1 (CFHR1) yielding the highest fold change in FSGS compared to MCD. The two target proteins were further validated through immunohistochemistry, confirming the podocyte localization of UBE2K and endothelial staining of CFHR. Additionally, several other differentially expressed proteins were linked to the cytoskeleton structure and its regulation. Our results point to the possibility that complement dysregulation may be the source of cytoskeleton rearrangement in FSGS.

Angiotensin Dysregulation in Patients with Arterial Aneurysms

Besides playing a critical role in maintaining cardiovascular homeostasis, the renin-angiotensin-aldosterone system (RAS) has been strongly implicated in (aortic) aneurysm pathogenesis. This study aims to investigate systemic and local levels of angiotensin (Ang) and its metabolites in patients with arterial aneurysms, predominantly abdominal aortic aneurysms, using advanced biochemical profiling techniques to provide new insights into the involvement of RAS in aneurysm genesis. A prospective, single-center study was conducted between October 2023 and July 2024. Serum Ang metabolite levels were measured using RAS Fingerprint technology. Aortic tissue samples were analyzed for local RAS activity, including Ang levels and enzyme activity. Additionally, pre- and postoperative serum samples were obtained in a select group of patients. In total, 37 aneurysm patients and 56 controls were included. Aneurysm patients exhibited higher systemic levels of nearly all Ang metabolites compared to controls, with significant differences in Ang I (p = 0.002), Ang II (p = 0.047), Ang 1-5 (p = 0.004), and Renin (p = 0.014) in patients without pharmacological RAS interference. Aneurysm patients receiving ACE inhibitors showed lower serum concentrations in ACE2 activity (p = 0.042) and increased Ang IV levels (p = 0.049) compared to controls. Postoperative measurements indicated different dynamics regarding angiotensin metabolite changes in patients with or without ACE inhibition. This study provides the first comprehensive characterization of RAS profiles in aneurysm patients. These findings add to the body of evidence regarding associations between of RAS and the pathogenesis of arterial aneurysms.

The renin-angiotensin-aldosterone system in kidney diseases of cats and dogs

The renin-angiotensin-aldosterone system (RAAS) has a well-established key pathophysiologic role in kidney diseases, and pharmacotherapy targeting this system is a mainstay of treatment of affected human beings, cats, and dogs. Several studies have evaluated the circulating RAAS in animals with spontaneous or experimentally induced kidney diseases. Evidence supporting the activation of this system has been demonstrated in some - but not all - studies and individuals, and the interindividual variability in circulating RAAS markers is high. Advances over the last few decades have expanded our understanding of the system, which now includes the existence of a counterbalancing "alternative" RAAS and tissular renin-angiotensin systems (RASs), the latter regulated independently of the circulating endocrine RAAS. The local RAS in the kidney, termed the intrarenal RAS, is currently recognized as an important regulator of kidney function and mediator of kidney disease. In general, information on the intrarenal RAS is lacking in cats and dogs with kidney diseases; however, existing limited data suggest its activation. Despite the inconsistent evidence for circulating RAAS activation in chronic kidney diseases, RAAS inhibitors have proven effective for the treatment of its common comorbidities, systemic arterial hypertension and renal proteinuria, in both cats and dogs. Further research of the circulating RAAS, the intrarenal RAS, and the interplay between these systems in the context of kidney diseases in companion animals might contribute to the development or refinement of future treatment strategies.

Aerobic training increases renal antioxidant defence and reduces angiotensin II levels, mitigating the high mortality in SHR-STZ model

OBJECTVE

The purpose of the research was to investigate the effects of aerobic training on renal function, oxidative stress, intrarenal renin-angiotensin system, and mortality of hypertensive and diabetic (SHR-STZ) rats.

MATERIALS AND METHODS

Blood pressure, creatinine, urea levels, urinary glucose, urine volume, and protein excretion were reduced in trained SHR-STZ rats.

RESULTS

Aerobic training not only attenuated oxidative stress but also elevated the activity of antioxidant enzymes in the kid'ney of SHR-STZ rats. Training increased intrarenal levels of angiotensin-converting enzymes (ACE and ACE2) as well as the neprilysin (NEP) activity, along with decreased intrarenal angiotensin II (Ang II) levels. Aerobic training significantly improved the survival of STZ-SHR rats.

CONCLUSION

The protective role of aerobic training was associated with improvements in the renal antioxidative capacity, reduced urinary protein excretion along with reduced intrarenal Ang II and increased NEP activity. These findings might reflect a better survival under the combined pathological conditions, hypertension, and diabetes.

Losartan is more effective than angiotensin (1-7) in preventing thyroxine-induced renal injury in the rat

AIM

Studies have shown that renal hypertrophy seen in experimental hyperthyroidism induced by thyroxine (T4) is due to angiotensin (Ang) II. However, other renal effects of Ang II in experimental hyperthyroidism have not been investigated. In addition, Ang 1-7 is believed to be protective against renal injury, but its possible role in thyroxine-induced renal injury is not known. The aim of this study is to elaborate the role of Ang II in thyroxine-induced renal injury and the possible protective role of Ang 1-7. We hypothesize that Ang 1-7 will be as protective against thyroxine-induced renal injury as the use of an ACE inhibitor or an Ang II receptor blocker.

METHODS

Adult Sprague Dawley rats were used in this study and were divided into 5 groups: (1) Control (treated with vehicle), (2) Treated with thyroxine (T4, 100 µg/kg), (3) Treated with T4 and Ang 1-7 (500 µg/kg), (4) Treated with T4 and captopril (20 mg/kg), and (5) Treated with T4 and losartan (10 mg/kg). Parameters tested after fourteen days of treatment were creatinine clearance, protein excretion rate, glomerular volume, renal ACE1 and ACE2 protein expression. Data were compared using One-way-ANOVA followed by Tukey's HSD post hoc test.

RESULTS

Thyroxine caused glomerular hypertrophy and proteinuria but had no effect on glomerular filtration rate (GFR). Glomerular hypertrophy was prevented by losartan and captopril, but not by Ang 1-7. Captopril and losartan had no effect on GFR; however, Ang 1-7 caused an increase in GFR in T4-treated rats. The increase in protein excretion rate was prevented by losartan but not by captopril or Ang 1-7. Renal expression of ACE1 protein was not altered in any of the treatment groups except in captopril treated rats were ACE1 expression was increased. Renal ACE2 protein expression was only increased in T4-losartan-treated rats and not affected by any of the other treatments.

CONCLUSION

We conclude that losartan was more protective than captopril against thyroxine-induced renal changes while Ang 1-7 offered no protection.

Chymase Activity in Plasma and Urine Extracellular Vesicles in Primary Hypertension

Key Points

Background

Circulating extracellular vesicles (EVs) carry protected cargoes of nucleic acids, proteins, and metabolites. In this study, we identified and validated the surface proteins and enzymatic activity of chymase, angiotensin converting enzymes 1 (ACE) and 2 (ACE2), and neprilysin (NEP) in EVs isolated from the blood and urine of primary hypertensive patients.

Methods

Peripheral venous blood and spot urine from 34 hypertensive patients were processed to isolate plasma and urinary EVs. Immunogold labeling and transmission electron microscopy validated the presence of the exosomal marker protein CD63 on the surface of plasma and urinary EVs. Flow cytometry characterized plasma and urinary EVs for CD63, CD9, and CD81 surface markers. In addition, exosomal CD63, TSG101, and Alix were analyzed in urine by western blotting. Urinary EVs did not express the endoplasmic reticulum protein calnexin and Golgi protein GM130. Chymase, ACE, ACE2, and NEP activities on 125I substrates—angiotensin-(1–12) (Ang-[1–12]) and angiotensin II—(1 nmol/L each) were quantified by HPLC. Data were analyzed based on whether the patient's BP was controlled (group 1: <140/80 mm Hg) or noncontrolled (group 2: ≥140/80 mm Hg).

Results

Chymase activity on Ang-(1–12) was significantly higher in plasma and urinary EVs than in ACE, ACE2, and NEP. In addition, chymase activity in urine EVs was more than three-fold higher than in plasma EVs. Chymase activity increased in plasma and urine EVs retrieved from group 2 patients. No comparable differences were found in the enzymatic activities of ACE, ACE2, and NEP urinary EVs between group 1 and group 2.

Conclusions

These studies reveal a differential enzymatic activity of renin angiotensin system enzymes in plasma and urine EVs isolated from hypertensive patients. Demonstrating a comparatively high chymase enzymatic activity in EVs expands a previously documented finding of increased plasma Ang-(1–12) in hypertensive patients.

A molecular mechanism for angiotensin II receptor blocker-mediated slit membrane protection: Angiotensin II increases nephrin endocytosis via AT1-receptor-dependent ERK 1/2 activation

Albuminuria is characterized by a disruption of the glomerular filtration barrier, which is composed of the fenestrated endothelium, the glomerular basement membrane, and the slit diaphragm. Nephrin is a major component of the slit diaphragm. Apart from hemodynamic effects, Ang II enhances albuminuria by β-Arrestin2-mediated nephrin endocytosis. Blocking the AT1 receptor with candesartan and irbesartan reduces the Ang II-mediated nephrin-β-Arrestin2 interaction. The inhibition of MAPK ERK 1/2 blocks Ang II-enhanced nephrin-β-Arrestin2 binding. ERK 1/2 signaling, which follows AT1 receptor activation, is mediated by G-protein signaling, EGFR transactivation, and β-Arrestin2 recruitment. A mutant AT1 receptor defective in EGFR transactivation and β-Arrestin2 recruitment reduces the Ang II-mediated increase in nephrin β-Arrestin2 binding. The mutation of β-Arrestin2K11,K12, critical for AT1 receptor binding, completely abrogates the interaction with nephrin, independent of Ang II stimulation. β-Arrestin2K11R,K12R does not influence nephrin cell surface expression. The data presented here deepen our molecular understanding of a blood-pressure-independent molecular mechanism of AT-1 receptor blockers (ARBs) in reducing albuminuria.

Megalin is involved in angiotensinogen-induced, angiotensin II-mediated ERK1/2 signaling to activate Na + -H + exchanger 3 in proximal tubules

BACKGROUND

Kidney angiotensin (Ang) II is produced mainly from liver-derived, glomerular-filtered angiotensinogen (AGT). Podocyte injury has been reported to increase the kidney Ang II content and induce Na + retention depending on the function of megalin, a proximal tubular endocytosis receptor. However, how megalin regulates the renal content and action of Ang II remains elusive.

METHODS

We used a mass spectrometry-based, parallel reaction-monitoring assay to quantitate Ang II in plasma, urine, and kidney homogenate of kidney-specific conditional megalin knockout (MegKO) and control (Ctl) mice. We also evaluated the pathophysiological changes in both mouse genotypes under the basal condition and under the condition of increased glomerular filtration of AGT induced by administration of recombinant mouse AGT (rec-mAGT).

RESULTS

Under the basal condition, plasma and kidney Ang II levels were comparable in the two mouse groups. Ang II was detected abundantly in fresh spot urine in conditional MegKO mice. Megalin was also found to mediate the uptake of intravenously administered fluorescent Ang II by PTECs. Administration of rec-mAGT increased kidney Ang II, exerted renal extracellular signal-regulated kinase 1/2 (ERK1/2) signaling, activated proximal tubular Na + -H + exchanger 3 (NHE3), and decreased urinary Na + excretion in Ctl mice, whereas these changes were suppressed but urinary Ang II was increased in conditional MegKO mice.

CONCLUSION

Increased glomerular filtration of AGT is likely to augment Ang II production in the proximal tubular lumen. Thus, megalin-dependent Ang II uptake should be involved in the ERK1/2 signaling that activates proximal tubular NHE3 in vivo , thereby causing Na + retention.

Plasma Serotonin and Cardiovascular Outcomes in Chronic Kidney Disease

Background Platelet-poor plasma serotonin levels are associated with adverse cardiovascular outcomes. Although plasma serotonin levels increase in chronic kidney disease, the cardiovascular implications remain unknown. Methods and Results In 1114 participants from the prospective CRIC (Chronic Renal Insufficiency Cohort) Study, we evaluated the association between plasma serotonin, categorized as undetectable, intermediate, and high (≥20 ng/mL) levels, and cross-sectional findings on echocardiography, including left ventricular hypertrophy, left ventricular ejection fraction, and pulmonary hypertension. We also analyzed whether serotonin was associated with time-to-event cardiovascular outcomes, including heart failure hospitalization and atherosclerotic cardiovascular disease (ASCVD) events, in addition to mortality. Because selective serotonin reuptake inhibitors decrease plasma serotonin levels, we specifically evaluated the influence of selective serotonin reuptake inhibitor use in the relationship between serotonin and outcomes. Plasma serotonin level inversely correlated with estimated glomerular filtration rate and directly correlated with blood pressure. High plasma serotonin was associated with left ventricular hypertrophy (adjusted odds ratio, 2.74 [95% CI, 1.11-7.41]). In contrast, undetectable plasma serotonin level was associated with the highest risk of heart failure (adjusted hazard ratio [HR], 2.26 [95% CI, 1.40-3.66]) and ASCVD events (adjusted HR, 1.96 [95% CI, 1.15-3.32]). Conclusions In a large chronic kidney disease cohort, plasma serotonin levels correlated with blood pressure, and elevated serotonin levels were associated with left ventricular hypertrophy. In contrast, undetectable plasma serotonin was associated with the highest risk of heart failure and ASCVD events.

Is chymase 1 a therapeutic target in cardiovascular disease?

INTRODUCTION

Non-angiotensin converting enzyme mechanisms of angiotensin II production remain underappreciated in part due to the success of current therapies to ameliorate the impact of primary hypertension and atherosclerotic diseases of the heart and the blood vessels. This review scrutinize the current literature to highlight chymase role as a critical participant in the pathogenesis of cardiovascular disease and heart failure.

AREAS COVERED

We review the contemporaneous understanding of circulating and tissue biotransformation mechanisms of the angiotensins focusing on the role of chymase as an alternate tissue generating pathway for angiotensin II pathological mechanisms of action.

EXPERT OPINION

While robust literature documents the singularity of chymase as an angiotensin II-forming enzyme, particularly when angiotensin converting enzyme is inhibited, this knowledge has not been fully recognized to clinical medicine. This review discusses the limitations of clinical trials' that explored the benefits of chymase inhibition in accounting for the failure to duplicate in humans what has been demonstrated in experimental animals.

Sex differences in the renin-angiotensin-aldosterone system and its roles in hypertension, cardiovascular, and kidney diseases

Cardiovascular disease is a pathology that exhibits well-researched biological sex differences, making it possible for physicians to tailor preventative and therapeutic approaches for various diseases. Hypertension, which is defined as blood pressure greater than 130/80 mmHg, is the primary risk factor for developing coronary artery disease, stroke, and renal failure. Approximately 48% of American men and 43% of American women suffer from hypertension. Epidemiological data suggests that during reproductive years, women have much lower rates of hypertension than men. However, this protective effect disappears after the onset of menopause. Treatment-resistant hypertension affects approximately 10.3 million US adults and is unable to be controlled even after implementing ≥3 antihypertensives with complementary mechanisms. This indicates that other mechanisms responsible for modulating blood pressure are still unclear. Understanding the differences in genetic and hormonal mechanisms that lead to hypertension would allow for sex-specific treatment and an opportunity to improve patient outcomes. Therefore, this invited review will review and discuss recent advances in studying the sex-specific physiological mechanisms that affect the renin-angiotensin system and contribute to blood pressure control. It will also discuss research on sex differences in hypertension management, treatment, and outcomes.

The systemic and hepatic alternative renin-angiotensin system is activated in liver cirrhosis, linked to endothelial dysfunction and inflammation

We aimed to assess the systemic and hepatic renin-angiotensin-system (RAS) fingerprint in advanced chronic liver disease (ACLD). This prospective study included 13 compensated (cACLD) and 12 decompensated ACLD (dACLD) patients undergoing hepatic venous pressure gradient (HVPG) measurement. Plasma components (all patients) and liver-local enzymes (n = 5) of the RAS were analyzed using liquid chromatography-tandem mass spectrometry. Patients with dACLD had significantly higher angiotensin (Ang) I, Ang II and aldosterone plasma levels. Ang 1-7, a major mediator of the alternative RAS, was almost exclusively detectable in dACLD (n = 12/13; vs. n = 1/13 in cACLD). Also, dACLD patients had higher Ang 1-5 (33.5 pmol/L versus cACLD: 6.6 pmol/L, p < 0.001) and numerically higher Ang III and Ang IV levels. Ang 1-7 correlated with HVPG (ρ = 0.655; p < 0.001), von Willebrand Factor (ρ = 0.681; p < 0.001), MELD (ρ = 0.593; p = 0.002) and interleukin-6 (ρ = 0.418; p = 0.047). Considerable activity of ACE, chymase, ACE2, and neprilysin was detectable in all liver biopsies, with highest chymase and ACE2 activity in cACLD patients. While liver-local classical and alternative RAS activity was already observed in cACLD, systemic activation of alternative RAS components occurred only in dACLD. Increased Ang 1-7 was linked to severe liver disease, portal hypertension, endothelial dysfunction and inflammation.

Association between chronic kidney disease, obesity, cardiometabolic risk factors, and severe COVID-19 outcomes

Introduction

Chronic kidney disease (CKD) is a risk factor for acquiring severe Coronavirus disease 2019 (COVID-19) but underlying mechanisms are unknown. We aimed to study the risk associated with CKD for severe COVID-19-outcomes in relation to BMI and diabetes, since they are common risk factors both for CKD and severe COVID-19.

Methods

This nationwide case-control study with data from mandatory national registries included 4684 patients admitted to the intensive care units (ICUs) requiring mechanical ventilation (cases) and 46840 population-based controls matched by age, sex and district of residency. Logistic regression was used to calculate odds ratios (ORs) with 95% confidence intervals (CIs) for associations between severe COVID -19 and exposures with adjustment for confounders, in subgroups by BMI, and matched by type 2 diabetes.

Results

The median age was 64 years and 27.7% were female. CKD was observed in 5.4% of the cases and 1.5% of the controls whereas 1.9% and 0.3% had end-stage CKD, respectively. CKD was associated with severe COVID-19 (OR 2.20 [95% CI, 1.85-2.62]), continuous renal replacement therapy at ICU (OR 7.36 [95% CI 5.39-10.05]), and death any time after ICU admission (OR 2.51 [95% CI 1.96-3.22]). The risk associated with CKD for severe COVID-19 did not differ significantly by weight but was higher in non-diabetics (OR, 2.76 [95% CI 2.15-3.55]) than in diabetics (OR, 1.88 [95% CI 1.37-2.59]).

Conclusion

CKD, especially end-stage CKD, is an important risk factor for severe COVID-19 and death after ICU-admission also in patients with normal BMI and without type 2 diabetes.

Blood pressure-independent renoprotective effects of small interference RNA targeting liver angiotensinogen in experimental diabetes

BACKGROUND AND PURPOSE

Small interfering RNA (siRNA) targeting liver angiotensinogen lowers blood pressure, but its effects in hypertensive diabetes are unknown.

EXPERIMENTAL APPROACH

To address this, TGR (mRen2)27 rats (angiotensin II-dependent hypertension model) were made diabetic with streptozotocin over 18 weeks and treated with either vehicle, angiotensinogen siRNA, the AT₁ antagonist valsartan, the ACE inhibitor captopril, valsartan + siRNA or valsartan + captopril for the final 3 weeks. Mean arterial pressure (MAP) was measured via radiotelemetry.

KEY RESULTS

MAP before treatment was 153 ± 2 mmHg. Diabetes resulted in albuminuria, accompanied by glomerulosclerosis and podocyte effacement, without a change in glomerular filtration rate. All treatments lowered MAP and cardiac hypertrophy, and the largest drop in MAP was observed with siRNA + valsartan. Treatment with siRNA lowered circulating angiotensinogen by >99%, and the lowest circulating angiotensin II and aldosterone levels occurred in the dual treatment groups. Angiotensinogen siRNA did not affect renal angiotensinogen mRNA expression, confirming its liver-specificity. Furthermore, only siRNA with or without valsartan lowered renal angiotensin I. All treatments lowered renal angiotensin II and the reduction was largest (>95%) in the siRNA + valsartan group. All treatments identically lowered albuminuria, whereas only siRNA with or without valsartan restored podocyte foot processes and reduced glomerulosclerosis.

CONCLUSION AND IMPLICATIONS

Angiotensinogen siRNA exerts renoprotection in diabetic TGR (mRen2)27 rats and this relies, at least in part, on the suppression of renal angiotensin II formation from liver-derived angiotensinogen. Clinical trials should now address whether this is also beneficial in human diabetic kidney disease.

Osteopontin: An important protein in the formation of kidney stones

The incidence of kidney stones averages 10%, and the recurrence rate of kidney stones is approximately 10% at 1 year, 35% at 5 years, 50% at 10 years, and 75% at 20 years. However, there is currently a lack of good medicines for the prevention and treatment of kidney stones. Osteopontin (OPN) is an important protein in kidney stone formation, but its role is controversial, with some studies suggesting that it inhibits stone formation, while other studies suggest that it can promote stone formation. OPN is a highly phosphorylated protein, and with the deepening of research, there is growing evidence that it promotes stone formation, and the phosphorylated protein is believed to have adhesion effect, promote stone aggregation and nucleation. In addition, OPN is closely related to immune cell infiltration, such as OPN as a pro-inflammatory factor, which can activate mast cells (degranulate to release various inflammatory factors), macrophages (differentiated into M1 macrophages), and T cells (differentiated into T1 cells) etc., and these inflammatory cells play a role in kidney damage and stone formation. In short, OPN mainly exists in the phosphorylated form in kidney stones, plays an important role in the formation of stones, and may be an important target for drug therapy of kidney stones.

Actions of Novel Angiotensin Receptor Blocking Drugs, Bisartans, Relevant for COVID-19 Therapy: Biased Agonism at Angiotensin Receptors and the Beneficial Effects of Neprilysin in the Renin Angiotensin System

Angiotensin receptor blockers (ARBs) used in the treatment of hypertension and potentially in SARS-CoV-2 infection exhibit inverse agonist effects at angiotensin AR1 receptors, suggesting the receptor may have evolved to accommodate naturally occurring angiotensin ‘antipeptides’. Screening of the human genome has identified a peptide (EGVYVHPV) encoded by mRNA, complementary to that encoding ANG II itself, which is an inverse agonist. Thus, opposite strands of DNA encode peptides with opposite effects at AR1 receptors. Agonism and inverse agonism at AR1 receptors can be explained by a receptor ‘switching’ between an activated state invoking receptor dimerization/G protein coupling and an inverse agonist state mediated by an alternative/second messenger that is slow to reverse. Both receptor states appear to be driven by the formation of the ANG II charge-relay system involving TyrOH-His/imidazole-Carboxylate (analogous to serine proteases). In this system, tyrosinate species formed are essential for activating AT1 and AT2 receptors. ANGII is also known to bind to the zinc-coordinated metalloprotease angiotensin converting enzyme 2 (ACE2) used by the COVID-19 virus to enter cells. Here we report in silico results demonstrating the binding of a new class of anionic biphenyl-tetrazole sartans (‘Bisartans’) to the active site zinc atom of the endopeptidase Neprilysin (NEP) involved in regulating hypertension, by modulating humoral levels of beneficial vasoactive peptides in the RAS such as vasodilator angiotensin (1–7). In vivo and modeling evidence further suggest Bisartans can inhibit ANG II-induced pulmonary edema and may be useful in combatting SARS-CoV-2 infection by inhibiting ACE2-mediated viral entry to cells.

Kidney Angiotensin in Cardiovascular Disease: Formation and Drug Targeting

The concept of local formation of angiotensin II in the kidney has changed over the last 10-15 years. Local synthesis of angiotensinogen in the proximal tubule has been proposed, combined with prorenin synthesis in the collecting duct. Binding of prorenin via the so-called (pro)renin receptor has been introduced, as well as megalin-mediated uptake of filtered plasma-derived renin-angiotensin system (RAS) components. Moreover, angiotensin metabolites other than angiotensin II [notably angiotensin-(1-7)] exist, and angiotensins exert their effects via three different receptors, of which angiotensin II type 2 and Mas receptors are considered renoprotective, possibly in a sex-specific manner, whereas angiotensin II type 1 (AT1) receptors are believed to be deleterious. Additionally, internalized angiotensin II may stimulate intracellular receptors. Angiotensin-converting enzyme 2 (ACE2) not only generates angiotensin-(1-7) but also acts as coronavirus receptor. Multiple, if not all, cardiovascular diseases involve the kidney RAS, with renal AT1 receptors often being claimed to exert a crucial role. Urinary RAS component levels, depending on filtration, reabsorption, and local release, are believed to reflect renal RAS activity. Finally, both existing drugs (RAS inhibitors, cyclooxygenase inhibitors) and novel drugs (angiotensin receptor/neprilysin inhibitors, sodium-glucose cotransporter-2 inhibitors, soluble ACE2) affect renal angiotensin formation, thereby displaying cardiovascular efficacy. Particular in the case of the latter three, an important question is to what degree they induce renoprotection (e.g., in a renal RAS-dependent manner). This review provides a unifying view, explaining not only how kidney angiotensin formation occurs and how it is affected by drugs but also why drugs are renoprotective when altering the renal RAS. SIGNIFICANCE STATEMENT: Angiotensin formation in the kidney is widely accepted but little understood, and multiple, often contrasting concepts have been put forward over the last two decades. This paper offers a unifying view, simultaneously explaining how existing and novel drugs exert renoprotection by interfering with kidney angiotensin formation.

Combined sodium glucose co-transporter-2 inhibitor and angiotensin-converting enzyme inhibition upregulates the renin-angiotensin system in chronic kidney disease with type 2 diabetes: Results of a randomized, double-blind, placebo-controlled exploratory trial

AIM

Sodium glucose co-transporter-2 inhibitors (SGLT-2i) improve cardiorenal outcomes in patients with chronic kidney disease (CKD), with and without type 2 diabetes. The molecular mechanisms underlying these pleiotropic effects remain unclear, yet it is speculated that SGLT-2i elicit a neurohormonal modulation resulting in renin-angiotensin system (RAS) activation. We hypothesized that combined SGLT-2 and angiotensin-converting enzyme inhibition (ACEi) favours RAS regulation towards the beneficial angiotensin-(1-7)-driven axis.

MATERIALS AND METHODS

This randomized controlled prospective study investigated the effect of 12 weeks treatment with the SGLT-2i empagliflozin on top of ACEi on the molecular RAS dynamics in 24 diabetic and 24 non-diabetic patients with CKD. Systemic RAS peptides were quantified by mass spectrometry.

RESULTS

In patients with type 2 diabetes, combined SGLT-2i and ACEi significantly upregulated plasma renin activity [pre-treatment median and interquartile range 298.0 (43.0-672.0) pmol/L versus post-treatment 577.0 (95.0-1543.0) pmol/L; p = .037] and angiotensin I levels [pre-treatment 289.0 (42.0-668.0) pmol/L versus post-treatment 573.0 (93.0-1522.0) pmol/L; p = .037], together with a significant increase of angiotensin-(1-7) levels [pre-treatment 14.0 (2.1-19.0) pmol/L versus post-treatment 32.0 (5.7-99.0) pmol/L; p = .012]. Empagliflozin treatment resulted in a 1.5 to 2-fold increase in main RAS peptides in patients with diabetes compared with placebo. No significant effect of empagliflozin on top of ACEi on RAS peptides was found in patients with CKD without diabetes.

CONCLUSION

A distinct RAS modulation by SGLT-2i occurs in diabetic kidney disease reflected by enhancement of the beneficial angiotensin-(1-7) providing a molecular background for this renoprotective therapeutic approach.

The Nephrotoxin Puromycin Aminonucleoside Induces Injury in Kidney Organoids Differentiated from Induced Pluripotent Stem Cells

Kidney diseases, including acute kidney injury (AKI) and chronic kidney disease (CKD), which can progress to end stage renal disease (ESRD), are a worldwide health burden. Organ transplantation or kidney dialysis are the only effective available therapeutic tools. Therefore, in vitro models of kidney diseases and the development of prospective therapeutic options are urgently needed. Within the kidney, the glomeruli are involved in blood filtration and waste excretion and are easily affected by changing cellular conditions. Puromycin aminonucleoside (PAN) is a nephrotoxin, which can be employed to induce acute glomerular damage and to model glomerular disease. For this reason, we generated kidney organoids from three iPSC lines and treated these with PAN in order to induce kidney injury. Morphological observations revealed the disruption of glomerular and tubular structures within the kidney organoids upon PAN treatment, which were confirmed by transcriptome analyses. Subsequent analyses revealed an upregulation of immune response as well as inflammatory and cell-death-related processes. We conclude that the treatment of iPSC-derived kidney organoids with PAN induces kidney injury mediated by an intertwined network of inflammation, cytoskeletal re-arrangement, DNA damage, apoptosis and cell death. Furthermore, urine-stem-cell-derived kidney organoids can be used to model kidney-associated diseases and drug discovery.

Relevance of Neutrophil Neprilysin in Heart Failure

Significant expression of neprilysin (NEP) is found on neutrophils, which present the transmembrane integer form of the enzyme. This study aimed to investigate the relationship of neutrophil transmembrane neprilysin (mNEP) with disease severity, adverse remodeling, and outcome in HFrEF. In total, 228 HFrEF, 30 HFpEF patients, and 43 controls were enrolled. Neutrophil mNEP was measured by flow-cytometry. NEP activity in plasma and blood cells was determined for a subset of HFrEF patients using mass-spectrometry. Heart failure (HF) was characterized by reduced neutrophil mNEP compared to controls (p < 0.01). NEP activity on peripheral blood cells was almost 4-fold higher compared to plasma NEP activity (p = 0.031) and correlated with neutrophil mNEP (p = 0.006). Lower neutrophil mNEP was associated with increasing disease severity and markers of adverse remodeling. Higher neutrophil mNEP was associated with reduced risk for mortality, total cardiovascular hospitalizations, and the composite endpoint of both (p < 0.01 for all). This is the first report describing a significant role of neutrophil mNEP in HFrEF. The biological relevance of neutrophil mNEP and exact effects of angiotensin-converting-enzyme inhibitors (ARNi) at the neutrophil site have to be determined. However, the results may suggest early initiation of ARNi already in less severe HF disease, where effects of NEP inhibition may be more pronounced.

Ectodomain shedding by ADAM proteases as a central regulator in kidney physiology and disease

Besides its involvement in blood and bone physiology, the kidney's main function is to filter substances and thereby regulate the electrolyte composition of body fluids, acid-base balance and toxin removal. Depending on underlying conditions, the nephron must undergo remodeling and cellular adaptations. The proteolytic removal of cell surface proteins via ectodomain shedding by A Disintegrin and Metalloproteases (ADAMs) is of importance for the regulation of cell-cell and cell-matrix adhesion of renal cells. ADAM10 controls glomerular and tubule development in a Notch1 signaling-dependent manner and regulates brush border composition. ADAM17 regulates the renin angiotensin system and is together with ADAM10 involved in calcium phosphate homeostasis. In kidney disease ADAMs, especially ADAM17 contribute to inflammation through their involvement in IL-6 trans-signaling, Notch-, epithelial growth factor receptor-, and tumor necrosis factor α signaling. ADAMs are interesting drug targets to reduce the inflammatory burden, defective cell adhesion and impaired signaling pathways in kidney diseases.

ACE2, the Counter-Regulatory Renin-Angiotensin System Axis and COVID-19 Severity

Angiotensin (ANG)-converting enzyme (ACE2) is an entry receptor of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes coronavirus disease 2019 (COVID-19). ACE2 also contributes to a deviation of the lung renin-angiotensin system (RAS) towards its counter-regulatory axis, thus transforming harmful ANG II to protective ANG (1-7). Based on this purported ACE2 double function, it has been put forward that the benefit from ACE2 upregulation with renin-angiotensin-aldosterone system inhibitors (RAASi) counterbalances COVID-19 risks due to counter-regulatory RAS axis amplification. In this manuscript we discuss the relationship between ACE2 expression and function in the lungs and other organs and COVID-19 severity. Recent data suggested that the involvement of ACE2 in the lung counter-regulatory RAS axis is limited. In this setting, an augmentation of ACE2 expression and/or a dissociation of ACE2 from the ANG (1-7)/Mas pathways that leaves unopposed the ACE2 function, the SARS-CoV-2 entry receptor, predisposes to more severe disease and it appears to often occur in the relevant risk factors. Further, the effect of RAASi on ACE2 expression and on COVID-19 severity and the overall clinical implications are discussed.

Cyclotides Isolated From Violet Plants of Cameroon Are Inhibitors of Human Prolyl Oligopeptidase

Traditional medicine and the use of herbal remedies are well established in the African health care system. For instance, Violaceae plants are used for antimicrobial or anti-inflammatory applications in folk medicine. This study describes the phytochemical analysis and bioactivity screening of four species of the violet tribe Allexis found in Cameroon. Allexis cauliflora, Allexis obanensis, Allexis batangae and Allexis zygomorpha were evaluated for the expression of circular peptides (cyclotides) by mass spectrometry. The unique cyclic cystine-rich motif was identified in several peptides of all four species. Knowing that members of this peptide family are protease inhibitors, the plant extracts were evaluated for the inhibition of human prolyl oligopeptidase (POP). Since all four species inhibited POP activity, a bioactivity-guided fractionation approach was performed to isolate peptide inhibitors. These novel cyclotides, alca 1 and alca 2 exhibited IC50 values of 8.5 and 4.4 µM, respectively. To obtain their amino acid sequence information, combinatorial enzymatic proteolysis was performed. The proteolytic fragments were evaluated in MS/MS fragmentation experiments and the full-length amino acid sequences were obtained by de novo annotation of fragment ions. In summary, this study identified inhibitors of the human protease POP, which is a drug target for inflammatory or neurodegenerative disorders.

Mechanism of Radix Astragali and Radix Salviae Miltiorrhizae Ameliorates Hypertensive Renal Damage

Hypertensive-induced renal damage (HRD) is an important public health and socioeconomic problem worldwide. The herb pair Radix Astragali- (RA-) Radix Salviae Miltiorrhizae (RS) is a common prescribed herbal formula for the treatment of HRD. However, the underlying mechanisms are unclear. The purpose of our study is to explore the mechanism of combination of Radix Astragali (RA) and Radix Salviae Miltiorrhizae (RS) ameliorating HRD by regulation of the renal sympathetic nerve. Thirty 24-week-old spontaneously hypertensive rats (SHRs) as the experimental group were randomly divided into the RA group, the RS group, the RA+RS group, the valsartan group, and the SHR group and six age-matched Wistar Kyoto rats (WKY) as the control group. After 4 weeks of corresponding drug administration, venipuncture was done to collect blood and prepare serum for analysis. A color Doppler ultrasound diagnostic instrument was used to observe renal hemodynamics. Enzyme-linked immunosorbent assay was used to detect norepinephrine (NE), epinephrine (E), angiotensin II (Ang II), and B-type brain natriuretic peptide (BNP). Simultaneously, the kidneys were removed immediately and observed under a transmission electron microscope to observe the ultrastructural changes. And the concentration of transforming growth factor-β1 (TGF-β1), angiotensin type 1 receptor (AT1), and nitric oxide (NO) was detected by immunohistochemistry. Our results showed that renal ultrasonography of rats showed no significant difference in renal size among groups. The RA+RS group had obviously decreased vascular resistance index. The levels of NE, E, BNP, Ang II, AT1, and TGF-β1 were decreased (P < 0.05), and the density of NO was increased. Pathological damage of the kidney was alleviated. In conclusion, the results of the present study suggested sympathetic overexpression in the pathogenesis of HRD. The combination of RA and RS may inhibit the hyperexcitability of sympathetic nerves and maintain the normal physiological structure and function of kidney tissue and has a protective effect on the cardiovascular system.

Mast Cell Chymase and Kidney Disease

A sizable part (~2%) of the human genome encodes for proteases. They are involved in many physiological processes, such as development, reproduction and inflammation, but also play a role in pathology. Mast cells (MC) contain a variety of MC specific proteases, the expression of which may differ between various MC subtypes. Amongst these proteases, chymase represents up to 25% of the total proteins in the MC and is released from cytoplasmic granules upon activation. Once secreted, it cleaves the targets in the local tissue environment, but may also act in lymph nodes infiltrated by MC, or systemically, when reaching the circulation during an inflammatory response. MC have been recognized as important components in the development of kidney disease. Based on this observation, MC chymase has gained interest following the discovery that it contributes to the angiotensin-converting enzyme's independent generation of angiotensin II, an important inflammatory mediator in the development of kidney disease. Hence, progress regarding its role has been made based on studies using inhibitors but also on mice deficient in MC protease 4 (mMCP-4), the functional murine counterpart of human chymase. In this review, we discuss the role and actions of chymase in kidney disease. While initially believed to contribute to pathogenesis, the accumulated data favor a more subtle view, indicating that chymase may also have beneficial actions.