Urinary angiotensinogen as a novel biomarker of the intrarenal renin-angiotensin system status in hypertensive patients

JTT-654, an 11-beta hydroxysteroid dehydrogenase type 1 inhibitor, improves hypertension and diabetic kidney injury by suppressing angiotensinogen production

11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1) plays an important role in regulating the expression of glucocorticoid actions in target tissues. Overexpression of 11β-HSD1 in mouse adipose tissue causes a metabolic syndrome-like phenotype, leading to hypertension. Although, many 11β-HSD1 inhibitors have been studied, few have shown a clear ameliorative effect against hypertension. We investigated whether JTT-654, a novel 11β-HSD1 inhibitor, ameliorated hypertension and elucidated the underlying mechanisms. JTT-654 showed inhibitory effects on angiotensinogen production in cortisone-treated 3T3-L1 adipocytes and in a rat model. JTT-654 improved hypertension not only in cortisone-treated rats and spontaneously hypertensive rats (SHR), but also in SHR/NDmcr-cp rats. In the SHR study, JTT-654 and losartan showed the same degree of antihypertensive efficacy. In addition, JTT-654 ameliorated diabetic nephropathy by suppressing renal angiotensinogen production in SHR/NDmcr-cp rats. These effects of JTT-654 were independent of its insulin-sensitizing effects, and similar effects were not observed for pioglitazone, an insulin sensitizer. Moreover, JTT-654 did not affect normotension or hypothalamus-pituitary-adrenal (HPA) axis function in normal Sprague-Dawley rats. Our results indicate that JTT-654 ameliorates hypertension and diabetic nephropathy by inhibiting 11β-HSD1 in the adipose tissue, liver, and kidney.

Targeting Angiotensinogen With N-Acetylgalactosamine-Conjugated Small Interfering RNA to Reduce Blood Pressure

Blood pressure management involves antihypertensive therapies blocking the renin-angiotensin system (RAS). Yet, it might be inadequate due to poor patient adherence or the so-called RAS escape phenomenon, elicited by the compensatory renin elevation upon RAS blockade. Recently, evidence points toward targeting hepatic AGT (angiotensinogen) as a novel approach to block the RAS pathway that could circumvent the RAS escape phenomenon. Removing AGT, from which all angiotensins originate, should prevent further angiotensin generation, even when renin rises. Furthermore, by making use of a trivalent N-acetylgalactosamine ligand-conjugated small interfering RNA that specifically targets the degradation of hepatocyte-produced mRNAs in a highly potent and specific manner, it may be possible in the future to manage hypertension with therapy that is administered 1 to 2× per year, thereby supporting medication adherence. This review summarizes all current findings on AGT small interfering RNA in preclinical models, making a comparison versus classical RAS blockade with either ACE (angiotensin-converting enzyme) inhibitors or AT1 (angiotensin II type 1) receptor antagonists and AGT suppression with antisense oligonucleotides. It ends with discussing the first-in-human study with AGT small interfering RNA.

Predicting autosomal dominant polycystic kidney disease progression: review of promising Serum and urine biomarkers

Autosomal dominant polycystic kidney disease (ADPKD) is one of the leading causes of end-stage renal disease. In spite of the recent tremendous progress in the understanding of ADPKD pathogenesis, the molecular mechanisms of the disease remain incompletely understood. Considering emerging new targeted therapies for ADPKD, it has become crucial to disclose easily measurable and widely available biomarkers for identifying patients with future rapid disease progression. This review encompasses all the research with a shared goal of identifying promising serum or urine biomarkers for predicting ADPKD progression or response to therapy. The rate of the ADPKD progress varies significantly between patients. The phenotypic variability is only partly explained by the underlying genetic lesion diversity. Considering significant decline in kidney function in ADPKD is not usually evident until at least 50% of the parenchyma has been destroyed, conventional kidney function measures, such as glomerular filtration rate (GFR), are not suitable for monitoring disease progression in ADPKD, particularly in its early stages. Since polycystic kidney enlargement usually precedes the decline in GFR, height-adjusted total kidney volume (ht-TKV) has been accepted as an early biomarker for assessing disease severity in ADPKD patients. However, since measuring ht-TKV is time-consuming and observer-dependent, the identification of a sensitive and quickly measurable biomarker is of a great interest for everyday clinical practice. Throughout the last decade, due to development of proteomic and metabolomic techniques and the enlightenment of multiple molecular pathways involved in the ADPKD pathogenesis, a number of urine and serum protein biomarkers have been investigated in ADPKD patients, some of which seem worth of further exploring. These include copeptin, angiotensinogen, monocyte chemoattractant protein 1, kidney injury molecule-1 and urine-to-plasma urea ratio among many others. The aim of the current review is to provide an overview of all of the published evidence on potentially clinically valuable serum and urine biomarkers that could be used for predicting disease progression or response to therapy in patients with ADPKD. Hopefully, this review will encourage future longitudinal prospective clinical studies evaluating proposed biomarkers as prognostic tools to improve management and outcome of ADPKD patients in everyday clinical practice.

Elevated urinary angiotensinogen excretion links central and renal hemodynamic alterations

Inappropriate activation of intrarenal renin-angiotensin system (RAS) may contribute to the pathogenesis of cardio-renal syndrome (CRS). We aimed to examine the cross-sectional associations of urinary angiotensinogen (AGT) excretion, a biomarker of intrarenal RAS activity, with central (aortic) and renal hemodynamic parameters in middle-aged and older adults, including patients with chronic kidney disease. Aortic and renal hemodynamic parameters were measured using applanation tonometry and duplex ultrasonography in 282 participants. Urinary AGT, liver-type fatty acid-binding protein (L-FABP), and plasma N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels were measured for each participant. Multiple linear regression analyses demonstrated that urinary AGT levels were associated with aortic blood pressures, pulsatile measures of renal blood flow, plasma NT-proBNP and urinary L-FABP levels after adjusting for potential covariates, including age, sex, body mass index, estimated glomerular filtration rate (GFR), and medication use. Additionally, when classified based on GFR stages and urinary AGT levels, plasma NT-proBNP and urinary L-FABP levels increased in participants with lower GFR and higher AGT groups. Our findings suggest that urinary AGT excretion is a shared determinant of central (aortic) and renal hemodynamics in middle-aged and older adults, providing clinical evidence for the potential role of intrarenal RAS activity in the development of CRS.

Fetal growth restriction followed by very preterm birth is associated with smaller kidneys but preserved kidney function in adolescence

BACKGROUND

Preterm birth and fetal growth restriction (FGR) are associated with structural and functional kidney changes, increasing long-term risk for chronic kidney disease and hypertension. However, recent studies in preterm children are conflicting, indicating structural changes but normal kidney function. This study therefore assessed kidney structure and function in a cohort of adolescents born very preterm with and without verified FGR.

METHODS

Adolescents born very preterm with FGR and two groups with appropriate birthweight (AGA) were included; one matched for gestational week at birth and one born at term. Cortical and medullary kidney volumes and T1 and T2* mapping values were assessed by magnetic resonance imaging. Biochemical markers of kidney function and renin-angiotensin-aldosterone system (RAAS) activation were analyzed.

RESULTS

Sixty-four adolescents were included (13-16 years; 48% girls). Very preterm birth with FGR showed smaller total (66 vs. 75 ml/m²; p = 0.01) and medullary volume (19 vs. 24 ml/m²; p < 0.0001) compared to term AGA. Corticomedullary volume ratio decreased from preterm FGR (2.4) to preterm AGA (2.2) to term AGA (1.9; p = 0.004). There were no differences in T1 or T2* values (all p ≥ 0.34) or in biochemical markers (all p ≥ 0.12) between groups.

CONCLUSIONS

FGR with abnormal fetal blood flow followed by very preterm birth is associated with smaller total kidney and medullary kidney volumes, but not with markers of kidney dysfunction or RAAS activation in adolescence. Decreased total kidney and medullary volumes may still precede a long-term decrease in kidney function, and potentially be used as a prognostic marker. A higher resolution version of the Graphical abstract is available as Supplementary information.

Hepatic and proximal tubule angiotensinogen play distinct roles in kidney dysfunction, glomerular and tubular injury, and fibrosis progression

Components of the renin-angiotensin system, including angiotensinogen (AGT), are critical contributors to chronic kidney disease (CKD) development and progression. However, the specific role of tissue-derived AGTs in CKD has not been fully understood. To define the contribution of liver versus kidney AGT in the CKD development, we performed 5/6 nephrectomy (Nx), an established CKD model, in wild-type (WT), proximal tubule (PT)- or liver-specific AGT knockout (KO) mice. Nx significantly elevated intrarenal AGT expression and elevated blood pressure (BP) in WT mice. The increase of intrarenal AGT protein was completely blocked in liver-specific AGT KO mice with BP reduction, suggesting a crucial role for liver AGT in BP regulation during CKD. Nx-induced glomerular and kidney injury and dysfunction, as well as fibrosis, were all attenuated to a greater extent in liver-specific AGT KO mice compared with PT-specific AGT KO and WT mice. However, the suppression of interstitial fibrosis in PT- and liver-specific AGT KO mouse kidneys was comparable. Our findings demonstrate that liver AGT acts as a critical contributor in driving glomerular and tubular injury, renal dysfunction, and fibrosis progression, whereas the role of PT AGT was limited to interstitial fibrosis progression in chronic renal insufficiency. Our results provide new insights for the development of tissue-targeted renin-angiotensin system intervention in the treatment of CKD.NEW & NOTEWORTHY Chronic kidney disease (CKD) is a major unmet medical need with no effective treatment. Current findings demonstrate that hepatic and proximal tubule angiotensinogen have distinct roles in tubular and glomerular injury, fibrogenesis, and renal dysfunction during CKD development. As renin-angiotensin system components, including angiotensinogen, are important targets for treating CKD in the clinic, the results from our study may be applied to developing better tissue-targeted treatment strategies for CKD and other fibroproliferative diseases.

Urinary Angiotensinogen in Patients With Type 1 Diabetes With Microalbuminuria: Gender Differences and Effect of Intensive Insulin Therapy

Introduction

Angiotensinogen (AOG) is the precursor of peptides of the renin angiotensin system (RAS). Because insulin up-regulates transcriptional factors that normally repress kidney AOG synthesis, we evaluated urinary AOG (uAOG) in patients with type 1 diabetes (T1D) and microalbuminuria who are receiving either intensive or conventional insulin therapy.

Methods

Urine samples from participants of the Diabetes Control and Complications Trial (DCCT) were used for the following: (i) uAOG/creatinine measurements in 103 patients with microalbuminuria and 103 patients with normoalbuminuria, matched for age, gender, disease duration, and allocation to insulin therapy; and (ii) uAOG/creatinine measurements from patients with microalbuminuria allocated to intensive insulin therapy (n = 58) or conventional insulin therapy (n = 41) after 3 years on each modality.

Results

uAOG was higher in patients who started with microalbuminuria than in those with normoalbuminuria (6.65 vs. 4.0 ng/mg creatinine, P < 0.01). uAOG was higher in females than in males with microalbuminuria (11.7 vs. 5.4 ng/mg creatinine, P = 0.015). uAOG was lower in patients with microalbuminuria allocated to intensive insulin therapy than in conventional insulin therapy (3.98 vs. 7.42 ng/mg creatinine, P < 0.01). These differences in uAOG were observed though albumin excretion rate (AER) was not significantly different.

Conclusion

In patients with T1D and microalbuminuria, uAOG is increased and varies with gender and the type of insulin therapy independently of AER. This suggests that AOG production is increased in females and it is decreased by intensive insulin therapy. The reduction in uAOG with intensive insulin therapy, by kidney RAS downregulation, may contribute to the known renoprotective action associated with intensive insulin and improved glycemic control.

Interactions between the intrarenal dopaminergic and the renin-angiotensin systems in the control of systemic arterial pressure

Systemic arterial hypertension is one of the leading causes of morbidity and mortality in the general population, being a risk factor for many cardiovascular diseases. Although its pathogenesis is complex and still poorly understood, some systems appear to play major roles in its development. This review aims to update the current knowledge on the interaction of the intrarenal renin-angiotensin system (RAS) and dopaminergic system in the development of hypertension, focusing on recent scientific hallmarks in the field. The intrarenal RAS, composed of several peptides and receptors, has a critical role in the regulation of blood pressure (BP) and, consequently, the development of hypertension. The RAS is divided into two main intercommunicating axes: the classical axis, composed of angiotensin-converting enzyme, angiotensin II, and angiotensin type 1 receptor, and the ACE2/angiotensin-(1-7)/Mas axis, which appears to modulate the effects of the classical axis. Dopamine and its receptors are also increasingly showing an important role in the pathogenesis of hypertension, as abnormalities in the intrarenal dopaminergic system impair the regulation of renal sodium transport, regardless of the affected dopamine receptor subtype. There are five dopamine receptors, which are divided into two major subtypes: the D1-like (D1R and D5R) and D2-like (D2R, D3R, and D4R) receptors. Mice deficient in any of the five dopamine receptor subtypes have increased BP. Intrarenal RAS and the dopaminergic system have complex interactions. The balance between both systems is essential to regulate the BP homeostasis, as alterations in the control of both can lead to hypertension.

Low plasma renin activity is independently associated with kidney disease progression in patients with type 2 diabetes and overt nephropathy, including those with impaired kidney function: a 2-year prospective study

Plasma renin activity (PRA) is lower in patients with diabetic nephropathy (DN) than in healthy individuals. However, the association, if any, between PRA and renal outcomes in patients with DN remains uncertain. In a 2-year prospective observational study, we aimed to investigate the association of PRA with the decline in kidney function in patients with DN. We studied 97 patients with DN who were categorized according to tertile (T1-T3) of PRA. The annual changes in estimated glomerular filtration rate (eGFR) (mL/min/1.73 m²/year) were determined from the slope of the linear regression curve for eGFR. The secondary endpoint was defined as a composite of the doubling of serum creatinine or end-stage renal disease. Results showed that kidney function rapidly declined with lower tertiles of PRA (median value [interquartile range] of the annual eGFR changes: -8.8 [-18.5 to -4.2] for T1, -8.0 [-14.3 to -3.2] for T2, and -3.1 [-6.3 to -2.0] for T3; p for trend <0.01). Multivariable linear regression analyses showed that, compared with T3, T1 was associated with a larger annual change in eGFR (coefficient, -4.410; 95% confidence interval [CI], -7.910 to -0.909 for T1). Composite renal events occurred in 46 participants. In multivariable Cox analysis, the lower tertiles of PRA (T1 and T2) were associated with higher incidences of the composite renal outcome (T2: hazard ratio [HR], 4.78; 95% CI, 1.64-13.89; T1: HR, 4.85; 95% CI 1.61-14.65) than T3. In conclusion, low PRA is independently associated with poor renal outcomes in patients with DN.

Urinary Angiotensinogen-Melatonin Ratio in Gestational Diabetes and Preeclampsia

Background: A large research portfolio indicates that an activated renal renin-angiotensin system or a deficit on melatonin is associated with several cardiovascular pathologies. In this observational clinical study, we hypothesized that alterations in urinary melatonin or angiotensinogen levels may be altered in two common conditions, preeclampsia and gestational diabetes. Our study’s primary objective was to assess melatonin and angiotensinogen as novel disease biomarkers detectable and quantifiable in the urine of pregnant women with or without pregnancy complications.

Methods: This was a concurrent cohort study of pregnant women with selected obstetric pathologies (gestational diabetes, preeclampsia, hypertension and obesity with hypertension). A group of healthy controls was also included. Urinary 6-sulfatoxymelatonin and angiotensinogen were measured by sensitive and specific ELISAs in first morning void urine samples. The patients were included in the cohort consecutively, and the diagnosis was blinded at the level of urine collection. Urinary 6-sulfatoxymelatonin and angiotensinogen levels were investigated in the patients included in the cohort.

Results: Urinary levels of angiotensinogen were significantly higher in the gestational diabetes [angiotensinogen/creatinine ratio median (25th, 75th): 0.11 (0.07, 0.18)] and preeclampsia [0.08 (0.06, 0.18)] groups than in those with healthy pregnancy [0.05(0.04, 0.06]; 6-sulfatoxymelatonin levels were significantly lower in the gestational diabetes [ug/h: median (25th, 75th): 0.12(0.08, 0.17)] and preeclampsia [0.12 (0.09, 0.15)] groups than in those with healthy pregnancy [0.20 (0.15, 0.27]. Neither morning void protein/creatinine ratio nor 24-h urine protein estimate were significantly different between the study groups.

Conclusion: These results suggest that urinary angiotensinogen levels may indicate an intrarenal RAS activation while melatonin production appears to be defective in gestational diabetes or hypertension. An angiotensinogen/melatonin ratio is suggested as an early biomarker for identification of gestational diabetes or hypertension. This report provides a basis for the potential use of melatonin for the treatment of preeclampsia. A prospective study in a larger number of patients to determine the operative characteristics of these markers as potential diagnostic tests is justified.

The adaptive renal response for volume homeostasis during two weeks of dapagliflozin treatment in people with type 2 diabetes and preserved renal function on a sodium-controlled diet

Introduction

Proximal tubule sodium uptake is diminished following sodium glucose cotransporter 2 (SGLT2) inhibition. We previously showed that during SGLT2 inhibition, the kidneys adapt by increasing sodium uptake at distal tubular segments, thereby maintaining body sodium balance. Despite continuous glycosuria, we detected no increased urine volumes. We therefore assessed the adaptive renal responses to prevent excessive fluid loss.

Methods

We conducted a mechanistic open-label study in people with type 2 diabetes mellitus with preserved kidney function, who received a standardized sodium intake (150 mmol/d) to evaluate the effects of dapagliflozin on renin-angiotensin-aldosterone system (RAAS) hormones, volume-related biomarkers, urinary albumin-to-creatinine ratio (UACR), and estimated glomerular filtration rate (eGFR), at start of treatment (day 4), end of treatment (day 14), and follow-up (day 18).

Results

A total of 14 people were enrolled. Plasma renin and angiotensin II and urinary aldosterone and angiotensinogen were acutely and persistently increased during treatment with dapagliflozin. Plasma copeptin level was numerically increased after 4 days (21%). Similarly, fractional urea excretion was significantly decreased at start of treatment (−17%). Free water clearance was significantly decreased after 4 days (−74%) and 14 days (−41%). All changes reversed after dapagliflozin discontinuation.

Conclusion

Dapagliflozin-induced osmotic diuresis triggers kidney adaptive mechanisms to maintain volume and sodium balance in people with type 2 diabetes and preserved kidney function. ClinicalTrials.gov (identification: NCT03152084).

Angiotensinogen and Risk of Stroke Events in Patients with Type 2 Diabetes Mellitus

BACKGROUND

Activation of the renin-angiotensin system (RAS) in diabetic patients is a vital pathophysiological mechanism of cardiovascular complications.

AIM

We aimed to assess whether serum and urinary angiotensinogen levels could predict the risk of stroke events in patients with type 2 diabetes.

METHODS

An analysis of the relationships between serum and urinary angiotensinogen levels at baseline and the risk of stroke events was performed in a study consisting of 467 patients with type 2 diabetes with a follow-up of 5 years. Multivariate Cox regression models were built by controlling for a large range of related risk factors.

RESULTS

Kaplan-Meier analysis showed that patients with low estimated glomerular filtration rate (eGFR) <57 mL/min/1.73 m² had a significantly higher risk of stroke events than those with high eGFRs (≥57 mL/min/1.73 m², P=0.040). Our results suggested that urinary angiotensinogen levels (HR=2.74, 95% CI 1.50-5.88, P=<0.001), but not serum angiotensinogen levels (HR=1.42, 95% CI 0.95-2.65, P=0.071), were independent predictors of the risk of stroke events in patients with type 2 diabetes after adjusting for confounding factors. Similarly, sensitivity analysis also suggested that higher urinary angiotensinogen levels still contributed to an increased risk of stroke events (HR=2.71, 95% CI 1.48-5.82, P<0.001) but not serum angiotensinogen levels (HR=1.37, 95% CI 0.89-2.21, P=0.104). Importantly, we found that significant associations only existed in patients with eGFRs<60 mL/min/1.73 m² (HR=2.78, 95% CI 1.59-6.30, P<0.001) but not in patients with eGFRs≥60 mL/min/1.73 m² (HR=1.39, 95% CI 0.95-3.53, P=0.054).

CONCLUSION

The study suggested that elevated urinary angiotensinogen levels were correlated with a higher risk of stroke events in patients with type 2 diabetes mellitus.

Reduced urinary angiotensinogen excretion in preeclampsia

OBJECTIVE

This study evaluated urinary angiotensinogen in preeclampsia.

METHODS

Normal pregnant (n = 57) and preeclamptic patients (n = 31); Normal pregnant (n = 10) and preeclamptic rats (n = 10) were studied. Urinary angiotensinogen and plasma angiotensin II were assayed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Urinary angiotensinogen in preeclampsia patients (2.0 ± 1.1 ng/mg creatinine) was suppressed (*p < 0.05) compared to normal pregnant (2.7 ± 1.5 ng/mg creatinine). Plasma angiotensin II in preeclampsia patients (preeclampsia: 36.2 ± 7; normal pregnant: 48.1 ± 5 fmol/mL) was lower. The similar result was observed in preeclampsia rat model.

CONCLUSIONS

The reduced urinary excretion of angiotensinogen was both in human preeclampsia patients and rat model of preeclampsia.

Renin-Angiotensin System Induced Secondary Hypertension: The Alteration of Kidney Function and Structure

Long-term hypertension is known as a major risk factor for cardiovascular and chronic kidney disease (CKD). The Renin-angiotensin system (RAS) plays a key role in hypertension pathogenesis. Angiotensin II (Ang II) enhancement in Ang II-dependent hypertension leads to progressive CKD and kidney fibrosis. In the two-kidney one-clip model (2K1C), more renin is synthesized in the principal cells of the collecting duct than juxtaglomerular cells (JGCs). An increase of renal Ang I and Ang II levels and a decrease of renal cortical and medullary Ang 1–7 occur in both kidneys of the 2K1C hypertensive rat model. In addition, the activity of the angiotensin-converting enzyme (ACE) increases, while ACE2's activity decreases in the medullary region of both kidneys in the 2K1C hypertensive model. Also, the renal prolyl carboxypeptidase (PrCP) expression and its activity reduce in the clipped kidneys. The imbalance in the production of renal ACE, ACE2, and PrCP expression causes the progression of renal injury. Intrarenal angiotensinogen (AGT) expression and urine AGT (uAGT) excretion rates in the unclipped kidney are greater than the clipped kidney in the 2K1C hypertensive rat model. The enhancement of Ang II in the clipped kidney is related to renin secretion, while the elevation of intrarenal Ang II in the unclipped kidney is related to stimulation of AGT mRNA and protein in proximal tubule cells by a direct effect of systemic Ang II level. Ang II-dependent hypertension enhances macrophages and T-cell infiltration into the kidney which increases cytokines, and AGT synthesis in proximal tubules is stimulated via cytokines. Accumulation of inflammatory cells in the kidney aggravates hypertension and renal damage. Moreover, Ang II-dependent hypertension alters renal Ang II type 1 & 2 receptors (AT₁R & AT₂R) and Mas receptor (MasR) expression, and the renal interstitial fluid bradykinin, nitric oxide, and cGMP response to AT₁R, AT₂R, or BK B₂-receptor antagonists. Based on a variety of sources including PubMed, Google Scholar, Scopus, and Science-Direct, in the current review, we will discuss the role of RAS-induced secondary hypertension on the alteration of renal function.

Angiotensin II-induced renal angiotensinogen formation is enhanced in mice lacking tumor necrosis factor-alpha type 1 receptor

In hypertension induced by angiotensin II (AngII) administration with high salt (HS) intake, intrarenal angiotensinogen (AGT) and tumor necrosis factor-alpha (TNF-α) levels increase. However, TNF-α has been shown to suppress AGT formation in cultured renal proximal tubular cells. We examined the hypothesis that elevated AngII levels during HS intake reduces TNF-α receptor type 1 (TNFR1) activity in the kidneys, thus facilitating increased intrarenal AGT formation. The responses to HS diet (4% NaCl) with chronic infusion of AngII (25 ng/min) via implanted minipump for 4 weeks were assessed in wild-type (WT) and knockout (KO) mice lacking TNFR1 or TNFR2 receptors. Blood pressure was measured by tail-cuff plethysmography, and 24-h urine samples were collected using metabolic cages prior to start (0 day) and at the end of 2nd and 4th week periods. The urinary excretion rate of AGT (uAGT; marker for intrarenal AGT) was measured using ELISA. HS +AngII treatment for 4 weeks increased mean arterial pressure (MAP) in all strains of mice. However, the increase in MAP in TNFR1KO (77 ± 2 to 115 ± 3 mmHg; n = 7) was significantly greater (p < 0.01) than in WT (76 ± 1 to 102 ± 2 mmHg; n = 7) or in TNFR2KO (78 ± 2 to 99 ± 5 mmHg; n = 6). The increase in uAGT at 4th week was also greater (p < 0.05) in TNFR1KO mice (6 ± 2 to 167 ± 75 ng/24 h) than that in WT (6 ± 3 to 46 ± 16 ng/24 h) or in TNFR2KO mice (8 ± 7 to 65 ± 44 ng/24 h). The results indicate that TNFR1 exerts a protective role by mitigating intrarenal AGT formation induced by elevated AngII and HS intake.

Baseline Urinary Angiotensinogen Excretion Predicts Deterioration of the Kidney Function in Patients with Chronic Kidney Disease

Objective The intrarenal renin-angiotensin system (RAS) is activated in patients with chronic kidney disease (CKD), and urinary angiotensinogen (AGT) levels, a surrogate marker of the intrarenal RAS activation, are associated with blood pressure (BP) and urinary albumin excretion. In addition, it has been shown that changes in urinary AGT levels correlate with annual changes in the estimated glomerular filtration rate (eGFR) in patients with type 2 diabetes and that elevated levels of urinary AGT in type 2 diabetic patients with albuminuria are a high-risk factor for worsening renal and cardiovascular complications. However, whether or not baseline urinary AGT levels predict deterioration of the kidney function in all patients with CKD is unclear. Methods We recruited 62 patients with CKD whose eGFR was >15 mL/min/1.73 m². We performed 24-hour ambulatory BP monitoring at 30-min intervals and daily urinary collection to examine the urinary AGT levels and albumin excretion and measured the levels of plasma angiotensin II (Ang II), a surrogate marker of circulating RAS. In addition, annual changes in the eGFR were followed up for 3.4±1.5 years. Results Annual changes in the eGFR were significantly and negatively associated with urinary AGT levels (r=-0.31, p=0.015) as well as the age, systolic BP, and urinary albumin levels. In contrast, annual changes in the eGFR were not correlated with plasma Ang II levels. Furthermore, when dividing patients into quartiles according to urinary AGT levels, patients with the highest urinary AGT levels showed a progressive decline in the eGFR. Conclusion These results suggest that elevated baseline urinary AGT levels can predict renal dysfunction in patients with CKD.

Urinary chloride concentration and progression of chronic kidney disease: results from the KoreaN cohort study for Outcomes in patients With Chronic Kidney Disease

BACKGROUND

Urinary chloride is regulated by kidney transport channels, and high urinary chloride concentration in the distal tubules can trigger tubuloglomerular feedback. However, little attention has been paid to urinary chloride as a biomarker of clinical outcomes. Here, we studied the relationship between urinary chloride concentration and chronic kidney disease (CKD) progression.

METHODS

We included 2086 participants with CKD from the KoreaN cohort study for Outcomes in patients With Chronic Kidney Disease. Patients were categorized into three groups, according to baseline urinary chloride concentration tertiles. The study endpoint was a composite of ≥50% decrease in estimated glomerular filtration rate from baseline values, or end-stage kidney disease.

RESULTS

During a median follow-up period of 3.4 years (7452 person-years), 565 participants reached the primary endpoint. There was a higher rate of CKD progression events in the lowest and middle tertiles than in the highest tertile. Compared with the lowest tertile, the highest tertile was associated with 33% [95% confidence interval (CI) 0.49-0.90] lower risk for the primary outcome in a cause-specific hazard model after adjustment for confounding variables. In addition, for every 25 mEq/L increase in urinary chloride concentration, there was 11% (95% CI 0.83-0.96) lower risk for CKD progression. This association was consistent in a time-varying model. Urinary chloride concentration correlated well with tubule function and kidney injury markers, and its predictive performance for CKD progression was comparable to that of these markers.

CONCLUSIONS

In this hypothesis-generating study, low urinary chloride concentration was associated with a higher risk for CKD progression.

Novel roles of the renal angiotensin-converting enzyme

The observation that all components of the renin angiotensin system (RAS) are expressed in the kidney and the fact that intratubular angiotensin (Ang) II levels greatly exceed the plasma concentration suggest that the synthesis of renal Ang II occurs independently of the circulating RAS. One of the main components of this so-called intrarenal RAS is angiotensin-converting enzyme (ACE). Although the role of ACE in renal disease is demonstrated by the therapeutic effectiveness of ACE inhibitors in treating several conditions, the exact contribution of intrarenal versus systemic ACE in renal disease remains unknown. Using genetically modified mouse models, our group demonstrated that renal ACE plays a key role in the development of several forms of hypertension. Specifically, although ACE is expressed in different cell types within the kidney, its expression in renal proximal tubular cells is essential for the development of high blood pressure. Besides hypertension, ACE is involved in several other renal diseases such as diabetic kidney disease, or acute kidney injury even when blood pressure is normal. In addition, studies suggest that ACE might mediate at least part of its effect through mechanisms that are independent of the Ang I conversion into Ang II and involve other substrates such as N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP), Ang-(1-7), and bradykinin, among others. In this review, we summarize the recent advances in understanding the contribution of intrarenal ACE to different pathological conditions and provide insight into the many roles of ACE besides the well-known synthesis of Ang II.

Newly developed radioimmunoassay for Human Angiotensin-(1-12) measurements in plasma and urine

The dodecapeptide angiotensin-(1-12) [Ang-(1-12)] functions as an intracrine/paracrine substrate for local production of angiotensin II. We developed a reliable and specific radioimmunoassay (RIA) method for the measurement of Ang-(1-12) in human plasma and urine using an affinity purified antibody fraction directed towards the C-terminus of the human Ang-(1-12) sequence. The RIA method was applied to quantify the Ang-(1-12) in plasma and urine collected from thirty-four human subjects (29 treated with antihypertensive medicines and 5 untreated patients). Plasma Ang-(1-12) level was significantly higher (P < 0.05) in patients with systolic blood pressure ≥140 mm Hg (n = 10) compared to the group with systolic blood pressure <140 mm Hg (n = 24). No significant difference (P = 0.22) was found in spot urine between the groups. Our study also shows that the polyclonal antibody neutralizes the cleavage sites of the human Ang-(1-12) from recombinant human chymase (rhChymase) and serum angiotensin converting enzyme (ACE) mediated Ang II generating hydrolysis. Overall, this newly developed RIA method is reliable and applicable to accurately quantify the Ang-(1-12) level in clinical samples (plasma and urine). Further, our in vitro neutralization study suggests that the anti-Ang-(1-12)-antibody might be used as an in vivo therapeutic agent for preventing Ang-(1-12)/Ang II-mediated hypertension and organ damage.

Stronger Effect of Azilsartan on Reduction of Proteinuria Compared to Candesartan in Patients with CKD: A Randomized Crossover Trial

INTRODUCTION

Angiotensin receptor blockers (ARBs) are preferably used in hypertensive patients with CKD. Azilsartan is a strong antihypertensive ARB, but its antiproteinuric effects are not well understood. We compared the antiproteinuric effect of azilsartan and candesartan in CKD patients in an open-label, randomized, crossover trial.

METHODS

A total of 111 patients were treated with 20 mg of azilsartan daily for 2 months as a run-in period. After the run-in period, patients were randomized into 2 arms and received either 20 mg of azilsartan or 8 mg of candesartan daily for 3 months in a crossover trial. The primary outcome was the percent change in urinary protein-to-Cr ratio (UPCR).

RESULTS

Ninety-five patients completed the trial. The mean age was 64.3 years. The estimated glomerular filtration rate (eGFR) and UPCR were 41.5 mL/min/1.73 m2 and 1.8 g/gCr, respectively. The baseline systolic and diastolic blood pressures were 131.4 and 71.0 mm Hg, respectively. The mean percent change in the UPCR was -3.8% in the azilsartan group and 30.8% in the candesartan group at the 1st endpoint (p = 0.0004), and 6.1% in the azilsartan group and 25.8% in the candesartan group at the 2nd (final) endpoint (p = 0.029). The incidence of adverse events, including eGFR levels and serum potassium levels, was not significantly different between the groups.

CONCLUSION

A 20 mg azilsartan dose had potent antiproteinuric effects compared with an 8 mg candesartan dose, without an increase in adverse events. Azilsartan may provide renal protection in addition to antihypertensive effects in CKD patients.

Urinary excretion of renin and angiotensinogen in hypertensive children and adolescents

INTRODUCTION

In recent years hypertension has become an emerging condition in the young population. It has been proposed that the renin-angiotensin system plays an important role in regulation of blood pressure. We assessed whether activation of the intrarenal renin-angiotensin system occurs in hypertensive children and adolescents and what better reflects its activity: urine angiotensinogen (AGT) or urine renin (REN).

MATERIAL AND METHODS

The study was conducted on a sample of 58 subjects with primary hypertension (HT) and 29 normotensive children and adolescents. We measured urine REN and AGT excretion and assessed the values in relation to blood pressure (BP) and other clinical parameters. Both REN and AGT values were calculated by urine creatinine: REN/cr. and AGT/cr., respectively.

RESULTS

We observed higher urine REN/cr. values in hypertensive subjects in comparison to the reference group (6.99 vs. 2.93, p = 0.003). Hypertensive participants showed positive correlations between urine REN/cr. and diastolic 24-hour BP (r = 0.42, p = 0.002) as well as between urine REN/cr. and urine AGT/cr. (r = 0.266, p = 0.044, respectively).

CONCLUSIONS

Increased urine REN/cr. in hypertensive children and adolescents and its positive correlation with BP may indicate its important role in the pathogenesis of HT. Perhaps urine REN/cr. could be a marker of intrarenal renin-angiotensin system activity. Nevertheless, further research should be undertaken to confirm this observation.

Augmented transcripts of kidney injury markers and renin angiotensin system in urine samples of overweight young adults

Obesity has been firmly established as a major risk factor for common disease states including hypertension, type 2 diabetes mellitus, and chronic kidney disease. Increased body mass index (BMI) contributes to the activation of both the systemic and intra-tubular renin angiotensin systems (RAS), which are in turn associated with increased blood pressure (BP) and kidney damage. In this cross-sectional study, 43 subjects of normal or increased body weight were examined in order to determine the correlation of BMI or body fat mass (BFM) with blood pressure, fasting blood glucose (FBG), and urinary kidney injury markers such as interleukin-18 (IL-18), connective tissue growth factor (CTGF), neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1 (KIM-1). Our results showed that: (1) subjects with increased body weight showed significantly higher BP, BFM, total body water and metabolic age; (2) BMI was positively correlated to both systolic (R² = 0.1384, P = 0.01) and diastolic BP (R² = 0.2437, P = 0.0008); (3) BFM was positively correlated to DBP (R² = 0.1232, P = 0.02) and partially correlated to urine protein (R² = 0.047, P = 0.12) and FBG (R² = 0.07, P = 0.06); (4) overweight young adults had higher urinary mRNA levels of renin, angiotensinogen, IL-18 and CTGF. These suggest that BMI directly affects BP, kidney injury markers, and the activation of the intra-tubular RAS even in normotensive young adults. Given that BMI measurements and urine analyses are non-invasive, our findings may pave the way to developing a new and simple method of screening for the risk of chronic kidney disease in adults.

Oxidative Stress in ESRD Patients on Dialysis and the Risk of Cardiovascular Diseases

Chronic kidney disease is highly prevalent worldwide. The decline of renal function is associated with inadequate removal of a variety of uremic toxins that exert detrimental effects on cells functioning, thus affecting the cardiovascular system. The occurrence of cardiovascular aberrations in CKD is related to the impact of traditional risk factors and non-traditional CKD-associated risk factors, including anemia; inflammation; oxidative stress; the presence of some uremic toxins; and factors related to the type, frequency of dialysis and the composition of dialysis fluid. Cardiovascular diseases are the most frequent cause for the deaths of patients with all stages of renal failure. The kidney is one of the vital sources of antioxidant enzymes, therefore, the impairment of this organ is associated with decreased levels of these enzymes as well as increased levels of pro-oxidants. Uremic toxins have been shown to play a vital role in the onset of oxidative stress. Hemodialysis itself also enhances oxidative stress. Elevated oxidative stress has been demonstrated to be strictly related to kidney and cardiac damage as it aggravates kidney dysfunction and induces cardiac hypertrophy. Antioxidant therapies may prove to be beneficial since they can decrease oxidative stress, reduce uremic cardiovascular toxicity and improve survival.

Urinary angiotensinogen antedates the development of stage 3 CKD in patients with type 1 diabetes mellitus

We examined if urinary angiotensinogen (uAOG), a marker of intrarenal renin‐angiotensin system activity, antedates stage 3 chronic kidney disease (CKD) using samples from participants in the Diabetes Control and Complications Trial (DCCT) and later in the Epidemiology of Diabetes Intervention and Complications (EDIC) trial. In a nested case–control design, cases were matched at the outcome visit (eGFR less than 60, 21‐59 mL/min per 1.73 m²) on age, gender, and diabetes duration, with controls: eGFR (95, 75‐119, mL/min per 1.73 m².) Additionally, in an exploratory analysis progressive renal decline (PRD), defined as eGFR loss >3.5 mL/min per 1.73m²/year, was evaluated using only data from EDIC because no progressions were observed during DCCT. At the EDIC visit, which antedated the GFR outcome visit by 2 years (range 1–7years) the median uAOG/creatinine was markedly higher in cases than in controls (13.9 vs. 3.8 ng/mg P = 0.003) whereas at the DCCT visit, which antedated the GFR outcome by 17 to 20 years it was not (2.75 vs. 3.16 ng/mg, respectively). The Odds Ratio for uAOG and CKD stage 3 development was significant after adjusting for eGFR, HbA1c, and systolic blood pressure 1.82 (1.00–3.29) but no longer significant when Albumin Excretion Ratio (AER) was included 1.21 (0.65–2.24).In the PRD analysis, uAOG/creatinine was sixfold higher in participants who experienced PRD than in those who did not (26 vs. 4.0 ng/mg, P = 0.003). The Odds Ratio for uAOG and PRD was significant after adjusting for eGFR, HbA1c, and systolic blood pressure 2.48 (1.46–4.22) but no longer significant when AER was included 1.32 (0.76–2.30). In people with type1 diabetes, a robust increase in uAOG antedates the development of stage 3 CKD but is not superior to AER in predicting this renal outcome. Increased uAOG moreover is associated with PRD, an index of progression to End Stage Kidney Disease (ESKD).

Endogenous Activation of Glucagon-Like Peptide-1 Receptor Contributes to Blood Pressure Control: Role of Proximal Tubule Na+/H+ Exchanger Isoform 3, Renal Angiotensin II, and Insulin Sensitivity

The pharmacological administration of GLP-1R (glucagon-like peptide-1 receptor) agonists reduces blood pressure (BP) in type 2 diabetes mellitus and nondiabetic patients. This study tested the hypothesis that endogenous GLP-1R signaling influences the regulation of BP. To this end, SHRs (spontaneously hypertensive rats) and Wistar rats were treated with the GLP-1R antagonist Ex9 (exendin-9) or vehicle for 4 weeks. Rats receiving the GLP-1R agonist Ex4 (exenatide) were used as an additional control. We found that blockade of baseline GLP-1R signaling by Ex9 increased systolic BP in both SHR and Wistar rats, compared with vehicle-treated animals, while Ex4 only reduced systolic BP in SHR. Higher systolic BP induced by Ex9 was accompanied by reduced lithium clearance and lower levels of NHE3 (Na⁺/H⁺ exchanger isoform 3) phosphorylation at the serine 552, indicative of increased proximal tubule sodium reabsorption. Additionally, urinary AGT (angiotensinogen) and renal cortical concentration of Ang II (angiotensin II) were enhanced by Ex9. Conversely, Ex4 decreased both urinary AGT and cortical Ang II but exclusively in SHRs. Moreover, both SHR and Wistar rats treated with Ex9 displayed hyperinsulinemia as compared with vehicle-treated rats, whereas Ex4 reduced fasting insulin concentration in SHR. Collectively, these results suggest that endogenous GLP-1R signaling exerts a physiologically relevant effect on BP control, which may be attributable, in part, to its tonic actions on the proximal tubule NHE3-mediated sodium reabsorption, intrarenal renin-angiotensin system, and insulin sensitivity. The possible role of impaired GLP-1R signaling in the pathogenesis of hypertension warrants further investigation.

Reduction in urinary angiotensinogen levels and improvement of proteinuria by renin-angiotensin system blockade in pediatric chronic kidney disease patients with very low birth weight

BACKGROUND

Children with low birth weight (LBW) have an increased risk of developing chronic kidney disease (CKD), and no effective strategies have been established to prevent the progression of CKD in these patients. Urinary angiotensinogen (UAGT) may represent a useful marker of intrarenal renin-angiotensin system (RAS) activation, which has been suggested to play a critical role in the development of hypertension and CKD. Herein, we conducted a prospective study to determine whether RAS blockade is beneficial for suppressing the progression of CKD in children with LBW, using UAGT as a surrogate marker of renal impairment.

METHODS

Nine children with CKD (stages: 1-2) who had very low birth weight (VLBW; < 1500 g) were started on RAS blockade with candesartan. We measured blood pressure and laboratory parameters, including urinary concentrations of angiotensinogen, protein, albumin, creatinine (Cr), and estimated glomerular filtration rate (eGFR), before and after candesartan treatment.

RESULTS

Birth weight was 712 g (range, 536-800 g). Age at evaluation was 11.6 years (range, 10.3-15.6 years). After candesartan treatment for 47.6 ± 25.0 months, the UAGT to urinary Cr ratio decreased from 61.9 ± 44.7 to 16.8 ± 14.4 μg/g (p = 0.015). The urinary protein to Cr and albumin to Cr ratios also decreased (p = 0.008 and p = 0.012, respectively), whereas there was no significant change in eGFR.

CONCLUSIONS

RAS blockade reduced UAGT levels and improved proteinuria/albuminuria in children with CKD who had VLBW. Suppression of intrarenal RAS activity may slow the progression of CKD in children with LBW.

The emerging role of angiotensinogen in cardiovascular diseases

Angiotensinogen (AGT) is the unique precursor of all angiotensin peptides. Many of the basic understandings of AGT in cardiovascular diseases have come from research efforts to define its effects on blood pressure regulation. The development of novel techniques targeting AGT manipulation such as genetic animal models, adeno-associated viral approaches, and antisense oligonucleotides made it possible to deeply investigate the relationship between AGT and cardiovascular diseases. In this brief review, we provide contemporary insights into the emerging role of AGT in cardiovascular diseases. In light of the recent progress, we emphasize some newly recognized features and mechanisms of AGT in heart failure, hypertension, atherosclerosis, and cardiovascular risk factors.

Urinary angiotensinogen as a surrogate marker predicting the antiproteinuric effects of angiotensin receptor blockers in patients with overt proteinuria: a multicenter prospective study

BACKGROUND

Although urinary angiotensinogen (AGT) and renin reflect intrarenal renin-angiotensin system activity and are enhanced in proteinuric chronic kidney disease, the clinical value of urinary AGT and renin levels during antiproteinuric treatment has yet to be determined. We investigated the clinical usefulness of initial urinary AGT or renin to determine the antiproteinuric effects of angiotensin receptor blockers (ARBs).

METHODS

This multicenter, prospective, single-arm study included 205 patients with overt proteinuria (urinary protein/creatinine ratio [uPCR] ≥ 1 mg/mg) enrolled between April 2009 and December 2011. All patients were treated with valsartan. The urinary AGT/creatinine ratio (uAGT/Cr) was measured at the baseline and 24 weeks, and the renin/creatinine ratio (uR/Cr) was measured at the baseline. Fifty-six patients were followed-up for 5 years.

RESULTS

The mean age was 47.6 years and 51.2% were male. The mean uPCR was 2.32 mg/mg and the mean eGFR was 63.2 mL/min/1.73m². Natural logarithms (ln) (uAGT/Cr), ln(uR/Cr), and diabetes mellitus were associated with proteinuria decrement (decrease in uPCR ≥1 mg/mg). Ln(uAGT/Cr) was an independent predictor for proteinuria decrement (OR 1.372, 95% CI, 1.068-1.762, P = 0.013). Among the 56 patients followed-up for 5 years, Δln(uAGT/Cr) at 24 weeks was an independent predictor for uPCR < 1 mg/mg at 5 years (OR 0.379, 95% CI, 0.20-0.715, P = 0.003).

CONCLUSIONS

Our study demonstrates the potential role of both baseline urinary AGT and changes in urinary AGT during the initial 24 weeks as surrogate markers predicting the antiproteinuric effects of ARBs in patients with overt proteinuria.

Comparison of the effects of insulin and SGLT2 inhibitor on the Renal Renin-Angiotensin system in type 1 diabetes mice

AIMS

SGLT2 inhibitors have been proposed as an adjunct to insulin therapy for glycemic control in type 1 diabetes (T1D) patients. However, concern has been raised due to an increase in renin-angiotensin-system (RAS) activity reported in a clinical trial in which an SGLT2 inhibitor was added while insulin dose was reduced in T1D patients. We previously reported that insulin inhibits intrarenal angiotensinogen (Agt) gene transcription and RAS activation. We hypothesized that insulin, rather than SGLT2 inhibition might regulate the intrarenal RAS.

METHODS

We compared RAS activity in non-diabetic wild type mice, Akita mice (T1D model) and Akita mice treated with insulin or the SGLT2 inhibitor canagliflozin.

RESULTS

Treatment of Akita mice with insulin or canagliflozin produced similar reductions in blood glucose, whereas insulin, but not canagliflozin, reduced elevated systolic blood pressure. Akita mice exhibited increased renal Agt mRNA/protein expression, which was attenuated by insulin, but not by canagliflozin. Furthermore, insulin was more effective than canagliflozin in lowering kidney weight and albuminuria.

CONCLUSIONS

Insulin, but not canagliflozin, lowers intrarenal RAS activity in Akita mice. Our findings can be of potential clinical importance, especially for T1D patients who are not on RAS inhibitors at the time of adding SGLT2 inhibitors.

Urinary angiotensinogen increases in the absence of overt renal injury in high fat diet-induced type 2 diabetic mice

AIM OF THE STUDY

During type 2 diabetes (T2D) and hypertension there is stimulation of renal proximal tubule angiotensinogen (AGT), but whether urinary excretion of AGT (uAGT) is an indicator of glomerular damage or intrarenal RAS activation is unclear. We tested the hypothesis that elevations in uAGT can be detected in the absence of albuminuria in a mouse model of T2D.

METHODS

Male C57BL/6 mice (N = 10) were fed a high fat (HFD; 45% Kcal from fat) for 28 weeks, and the metabolic phenotype including body weight, blood pressures, glucose, insulin, ippGTT, HOMA-IR, and cholesterol was examined. In addition, kidney Ang II content and reactive oxygen species (ROS) was measured along with urinary albumin, creatinine, Ang II, and AGT.

RESULTS

All parameters consistent with T2D were present in mice after 12-14 weeks on the HFD. Systolic BP increased after 18 weeks in HFD but not NFD mice. Intrarenal ROS and Ang II concentrations were also increased in HFD mice. Remarkably, these changes paralleled the augmentation uAGT excretion (3.66 ± 0.50 vs. 0.92 ± 0.13 ng/mg by week 29; P < 0.01), which occurred in the absence of overt albuminuria.

CONCLUSIONS

In HFD-induced T2D mice, increases in uAGT occur in the absence of overt renal injury, indicating that this biomarker accurately detects early intrarenal RAS activation.

The Urinary Angiotensinogen to Urinary Albumin Ratio Reflects Whether the Renin-angiotensin System in the Kidney Is Activated due to Filtration of Plasma Angiotensinogen through the Damaged Glomeruli or the Production of Angiotensinogen in the Proximal Tubules

Objective Urinary angiotensinogen (AGT) is a surrogate marker for intrarenal renin-angiotensin system (RAS) activity that plays an important role in the development of renal damage. Urinary AGT levels are determined by the filtration of plasma AGT through the damaged glomeruli and production of AGT in the proximal tubules. However, the relative merits of the filtration and production of urinary AGT levels in chronic kidney diseases (CKD) have not been clarified. Therefore, we investigated them in CKD patients. Methods We recruited 41 biopsy-proven patients diagnosed with IgA nephropathy (IgAN) in 31, membranous nephropathy (MN) in 5, and tubulointerstitial nephritis (TIN) in 5. The patients taking RAS blockers were excluded. Results The urinary albumin levels in MN patients were significantly higher and those in TIN patients significantly lower than in IgAN patients, and the urinary AGT levels in the MN and TIN patients were significantly higher than those in IgAN patients. Conversely, the urinary AGT-to-urinary albumin (urinary AGT/Alb) ratios were the same for IgAN and MN patients, and those of TIN patients were significantly higher than those of IgAN and MN patients. A multiple linear regression analysis revealed that the urinary AGT/Alb ratios had a significant positive association with IgAN and TIN after adjustments (β=0.75, and p<0.01). Conclusion These data suggest that the origins of urinary AGT may differ according to the etiology of renal damage [i.e. glomerular damage (such as IgAN and MN) or tubulointerstitial damage (such as TIN)], and a higher urinary AGT/Alb ratio, as in TIN, may reflect AGT production in the kidney.

Chronotherapy with a Renin-angiotensin System Inhibitor Ameliorates Renal Damage by Suppressing Intrarenal Renin-angiotensin System Activation

Objective The intrarenal renin-angiotensin system (RAS) is activated in chronic kidney disease (CKD) patients and is not suppressed at night in CKD patients showing nocturnal hypertension, contributing to renal damage. Furthermore, changes in RAS inhibitor administration from morning to evening, namely chronotherapy, ameliorates renal damage at night. We attempted to clarify whether or not chronotherapy ameliorates renal damage by suppressing the intrarenal RAS activity. Methods We recruited 34 CKD patients with RAS inhibitors in the morning. We conducted ambulatory blood pressure (BP) monitoring and urine collection and evaluated urinary albumin (Alb) and angiotensinogen (AGT), which are surrogate markers for intrarenal RAS activity during the day and at night, respectively. The same experiments were conducted after changing the administration time. The ratio of values associated with morning versus evening dosing was defined as the morning to evening (M/E) ratio. Results The M/E ratio of urinary Alb had a significant and positive relationship with that of urinary AGT during the day and at night in all CKD patients. However, no significant relationships were found between the M/E ratios of urinary Alb and AGT using multiple linear regression analyses. Conversely, there was a significant and positive relationship between the M/E ratios of urinary Alb and AGT at night but not during the day in CKD patients whose estimated glomerular filtration rate was <45 mL/min/1.73 m² and whose night-to-day ratio of systolic BP was >0.90, even after adjustment. Conclusion This study indicated that chronotherapy with RAS inhibitors improved the renal damage via intrarenal RAS suppression, especially in CKD patients with an impaired renal function and nocturnal hypertension.

Time Course Changes in Urinary Angiotensinogen and Circulating N-Terminal Pro-B-Type Natriuretic Peptide in Patients Hospitalized with Acute Heart Failure

Objective Home care is important in patients with heart failure (HF) in order to maintain their quality of life. A biomarker that can be measured noninvasively is needed to optimize the home care of patients with HF. Urinary angiotensinogen (uAGT) is an indicator of the intrarenal renin-angiotensin system activity, which may be augmented in HF. We hypothesized that uAGT might be a urinary biomarker in HF. Methods We measured uAGT by an enzyme-linked immunosorbent assay and uAGT normalized by urinary creatinine (uCr)-designated uAGT/uCr-at admission and discharge in 45 patients hospitalized for HF. Results We found that both uAGT/uCr [median (interquartile range): 65.5 (17.1-127.7) μg/g Cr at admission; 12.1 (6.0-37.0) μg/g Cr at discharge; p<0.01] and N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels [5,422 (2,280-9,907) pg/mL at admission; 903 (510-1,729) pg/mL at discharge; p<0.01] significantly decreased between admission and discharge along with an improvement in patient's clinical status [New York Heart Association scores: 3 (3-4) at admission; 1 (1-1) at discharge; p<0.01]. The generalized least squares model revealed that the time course changes in uAGT/uCr also correlated with those in NT-proBNP levels between admission and readmission in five patients readmitted for HF. Conclusion The results indicated that the time course changes in uAGT/uCr correlated with those in the NT-proBNP levels in patients with HF who showed a clinical improvement. Further investigation and development of a kit for the rapid measurement of uAGT are needed to evaluate the clinical utility of uAGT as a biomarker in HF.

Potassium Intake Prevents the Induction of the Renin-Angiotensin System and Increases Medullary ACE2 and COX-2 in the Kidneys of Angiotensin II-Dependent Hypertensive Rats

In angiotensin II (Ang II)-dependent hypertensive rats there is an increased expression of proximal tubule angiotensinogen (AGT), collecting duct renin and angiotensin converting enzyme (ACE), which contributes to intratubular Ang II formation. Ang II acts on Ang II type 1 receptors promoting sodium retention and vasoconstriction. However concurrently, the ACE2-Ang-(1–7) axis and the expression of kallikrein and medullary prostaglandins counteract the effects of Ang II, promoting natriuresis and vasodilation. Human studies demonstrate that dietary potassium (K⁺) intake lowers blood pressure. In this report we evaluate the expression of AGT, ACE, medullary prorenin/renin, ACE2, kallikrein and cyclooxygenase-2 (COX-2) in Ang II-infused rats fed with high K⁺ diet (2%) for 14 days. Dietary K⁺ enhances diuresis in non-infused and in Ang II-infused rats. The rise in systolic blood pressure in Ang II-infused rats was attenuated by dietary K⁺. Ang II-infused rats showed increased renal protein levels of AGT, ACE and medullary prorenin and renin. This effect was attenuated in the Ang II + K⁺ group. Ang II infusion decreased ACE2 compared to the control group; however, K⁺ diet prevented this effect in the renal medulla. Furthermore, medullary COX-2 was dramatically induced by K⁺ diet in non-infused and in Ang II infused rats. Dietary K⁺ greatly increased kallikrein immunostaining in normotensive rats and in Ang II-hypertensive rats. These results indicate that a high K⁺ diet attenuates Ang II-dependent hypertension by preventing the induction of ACE, AGT and collecting duct renin and by enhancing medullary COX-2 and ACE2 protein expression in the kidney.

Relationship between intrarenal renin-angiotensin activity and re-hospitalization in patients with heart failure with reduced ejection fraction

OBJECTIVE

Heart failure (HF) is a clinical syndrome resulting from structural or functional damages. Although clinical trials have shown that the plasma renin-angiotensin system (RAS) activation decreases HF functional status and increases hospitalization for HF patients, the effect of intrarenal RAS activity is still unknown. In this study, we investigated the relationship between the New York Heart Association (NYHA) class, duration, and number of hospitalizations in the previous year and urinary angiotensinogen (UAGT) in patients with HF with reduced ejection fraction (HFrEF).

METHODS

This study included 85 patients who had an ejection fraction of <40% and were receiving optimal medical treatment. Among these, 22 were excluded from the study for various reasons. Demographically and biochemically, the remaining 63 patients were compared according to the NYHA functional classes and re-hospitalization status.

RESULTS

When the groups were compared in terms of N-terminal pro-B-type natriuretic peptide (NT-proBNP), UAGT, and high-sensitivity C-reactive protein (Hs-CRP), it was found that these parameters were significantly higher in patients who were hospitalized more than two times in the previous year [p<0.001; p=0.007; p<0.001, respectively]. There was a significant correlation between number of hospitalizations and NT-proBNP (r=0.507, p<0.001), Hs-CRP (r=0.511, p<0.001), hemoglobin (r=-0.419, p=0.001), serum sodium (r=-0.26, p=0.04), and systolic blood pressure (r=-0.283, p=0.02). When the independence of multiple correlations was assessed using multiple linear regression analysis, NT-proBNP, Hs-CRP, and hemoglobin levels were independent predictors of re-hospitalization, but this was not the same for UAGT.

CONCLUSION

Although UAGT levels are high in patients with poor NYHA functional class and repeated hospitalizations, this marker is not valuable for predicting repeated hospitalization in patients with HFrEF.

Effects of Sleeve Gastrectomy on Blood Pressure and the Renal Renin-Angiotensin System in Rats with Diet-Induced Obesity

OBJECTIVE

Sleeve gastrectomy (SG) has been reported to decrease blood pressure (BP), although the reason has not been revealed. The present study aimed to establish the reason why SG decreases BP.

METHODS

Male Sprague-Dawley rats were subjected to surgical (sham operation or SG) and dietary interventions (fed a normal diet or high-fat diet ad libitum or fed by pair-feeding [PF]). Systolic BP (SBP), urinary sodium excretion, and endocrine parameters were examined 4 weeks after surgery.

RESULTS

Both SG and PF rats had reduced body weight compared with SO rats fed normal diet or high-fat diet ad libitum. SG rats exhibited a reduction in SBP compared with PF, which was associated with a reduction in renal renin, angiotensin II, and catechol-O-methyltransferase levels (P < 0.01 for each). SG increased plasma cholecystokinin (CCK) levels compared with PF (P < 0.0001 for each), whereas glucagon-like peptide 1 and peptide YY were not changed in fasting. Exogenous administration of CCK reduced renal catechol-O-methyltransferase (P = 0.0233), renin (P < 0.0001), and angiotensin II (P < 0.0001) levels and SBP (P = 0.0053).

CONCLUSIONS

SG reduced SBP, at least in part, through suppression of sympathetic nerve action by elevation of CCK, which was followed by suppression of the intrarenal renin-angiotensin system.

Diagnostic Indicators of Superimposed Preeclampsia in Women With CKD

Introduction

Diagnosis of superimposed preeclampsia in women with chronic kidney disease (CKD) is complicated by the presence of hypertension and proteinuria due to renal disease. The aims of this study were to determine mechanistic links between superimposed preeclampsia and renin-angiotensin system activation, endothelial pathology, complement dysfunction, and tubular injury, and to explore the role of diagnostic indicators of superimposed preeclampsia.

Methods

Plasma and urinary biomarkers derived from the renin-angiotensin system (active renin, angiotensinogen), endothelial glycocalyx (hyaluronan, intercellular adhesion molecule, vascular cell adhesion molecule [VCAM], P-selectin, E-selectin), complement activation (C3a, C5a, complement factor H, C5b-9), and tubular injury (kidney injury molecule-1, urinary lipocalin-2) were quantified in 60 pregnant women with CKD including 15 women at the time of superimposed preeclampsia diagnosis and 45 women who did not develop superimposed preeclampsia, 18 women with preeclampsia, and 20 normal pregnancies. Correlation with placental growth factor was assessed.

Results

Plasma concentrations of hyaluronan (67.5 ng/ml vs. 27.5 ng/ml, P = 0.0017, receiver operating characteristic area 0.80) and VCAM (1132 ng/ml vs. 659 ng/ml, P < 0.0001, receiver operating characteristic area 0.86) distinguished women with CKD and superimposed preeclampsia from those without superimposed preeclampsia, and correlated with placental growth factor concentration. The diagnostic discrimination of markers of the renin-angiotensin system was reduced by adjustment for chronic hypertension, antihypertensive drug use, and black ethnicity. Other markers offered limited or no diagnostic discrimination for superimposed preeclampsia.

Conclusion

This study suggests that endothelial dysfunction contributes to the pathophysiology of superimposed preeclampsia and a diagnostic role for plasma hyaluronan and VCAM is hypothesized.

The Intrarenal Renin-angiotensin System Is Activated Immediately after Kidney Donation in Kidney Transplant Donors

Objective The intrarenal renin-angiotensin system (RAS) is activated in clinical settings, such as chronic kidney disease (CKD), as well as in CKD animal models, and kidney transplant donors have a greater risk of end-stage renal disease than healthy controls. However, whether or not the intrarenal RAS is activated immediately after kidney donation in kidney transplant donors is unclear, and the mechanism underlying intrarenal RAS activation is unknown. Methods We investigated 10 kidney transplant donors (4 men and 6 women, 58.6±9.0 years of age). Their blood pressure (BP), estimated glomerular filtration rate (eGFR), plasma angiotensinogen (AGT) and plasma angiotensin II (AngII) levels (which reflect circulating RAS activation), urinary albumin excretion, and urinary AGT excretion (which reflects intrarenal RAS activation) were evaluated before kidney donation (-1.2±0.40 days) and after kidney donation (7.5±1.7 days). Results The renal function after kidney donation was significantly lower than before donation. There were no significant differences in the BP during 24-h ambulatory BP monitoring, plasma AngII levels, or urinary albumin excretion after kidney donation. In contrast, the levels of plasma AGT and urinary AGT excretion were significantly increased after kidney donation. The urinary AGT excretion after kidney donation did not show a significant relationship with the systolic BP, plasma AGT, plasma AngII, or urinary albumin excretion. In addition, the percentage change in urinary AGT excretion after kidney donation was not associated with the percentage change in other clinical parameters. Conclusion The intrarenal RAS is activated in kidney transplant donors immediately after kidney donation, independent of the systemic BP and filtration of increased plasma AGT, due to augmented inflammation.

Electrolyte transport in the renal collecting duct and its regulation by the renin-angiotensin-aldosterone system

Distal nephron of the kidney plays key roles in fluid volume and electrolyte homeostasis by tightly regulating reabsorption and excretion of Na⁺, K⁺, and Cl^- Studies to date demonstrate the detailed electrolyte transport mechanisms in principal cells of the cortical collecting duct, and their regulation by renin-angiotensin-aldosterone system (RAAS). In recent years, however, accumulating data indicate that intercalated cells, another cell type that is present in the cortical collecting duct, also play active roles in the regulation of blood pressure. Notably, pendrin in β-intercalated cells not only controls acid/base homeostasis, but is also one of the key components controlling salt and K⁺ transport in distal nephron. We have recently shown that pendrin is regulated by the co-ordinated action of angiotensin II (AngII) and aldosterone, and at the downstream of AngII, mammalian target of rapamycin (mTOR) signaling regulates pendrin through inhibiting the kinase unc51-like-kinase 1 and promoting dephosphorylation of mineralocorticoid receptor (MR). In this review, we summarize recent advances in the current knowledge on the salt transport mechanisms in the cortical collecting duct, and their regulation by the RAAS.

The pivotal role of melatonin in ameliorating chronic kidney disease by suppression of the renin-angiotensin system in the kidney

Melatonin is a hormone produced by the pineal gland, predominantly at night, and plays a pivotal role in regulating the circadian rhythm as well as a variety of biological functions, including anti-inflammation, anti-oxidation, inhibition of sympathetic nerve activity, and preservation of endothelial cell function. The intrarenal renin-angiotensin system (RAS) is one of the most important contributors in the pathophysiology of chronic kidney disease (CKD) and hypertension, independent of the circulating RAS, due to sodium reabsorption and inflammation and fibrosis in the kidney. However, the relationship between melatonin secretion and intrarenal RAS activation has remained unknown. It has been recently shown that impaired nighttime melatonin secretion is associated with nighttime urinary angiotensinogen excretion, a surrogate marker of intrarenal RAS activation and renal damage in patients with CKD. Moreover, it has also been indicated that melatonin administered exogenously exercises antioxidant effects that ameliorate intrarenal RAS activation and renal injury in chronic progressive CKD animal models. As a result, the new roles of melatonin in suppressing RAS in the kidney via amelioration of reactive oxygen species have been clarified. Therefore, we review the relationship between melatonin and intrarenal RAS activation and indicate the possibility of a new strategy to suppress CKD, which is a risk factor for cardiovascular and end-stage renal diseases.

Serum and urinary SOD3 in patients with type 2 diabetes: comparison with early chronic kidney disease patients and association with development of diabetic nephropathy

Extracellular superoxide dismutase 3 (SOD3), one member of the antioxidant defense system and a superoxide scavenger, has been noted to be downregulated in the kidneys of diabetic mice and is characterized by a heparin-binding domain that can anchor the protein to the endothelium and extracellular matrix. The association of the serum and urinary SOD3 levels with diabetic nephropathy in different stages has never been evaluated. It remains unclear how urinary SOD3 changes in different renal diseases. We recruited 98 Taiwanese patients with type 2 diabetes and 10 patients with early chronic kidney disease (CKD) into this study. Biochemical analyses were performed, including evaluation of the serum SOD3, urinary SOD3, urinary albumin, urinary vascular endothelial growth factor (VEGF), and urinary angiotensinogen (ANG). The Kruskal-Wallis rank sum test was used to compare various parameters among the three groups of patients: early CKD, diabetes alone, and diabetes with CKD. Results showed that lower serum and urinary SOD3 levels were observed in the group of patients with diabetes alone. Higher serum and urinary SOD3 levels were observed in the group of patients with diabetes and CKD, which had higher albuminuria and serum creatinine levels. The serum SOD3 levels were significantly positively correlated with renal function, according to the serum creatinine level. The urinary levels of SOD3 were significantly correlated with other urinary biomarkers such as urinary ANG and VEGF. Furthermore, albuminuria can positively predict the serum SOD3 level for the ratio of urinary albumin to urinary creatinine (ACR) >1,190.769 mg/g and the urinary SOD3 level for ACR ≥300 mg/g.

Decreased Ang-(1-7) and Downregulated Intrarenal RAS May Contribute to the Direct Podocyte Injury With Proteinuria in Preeclampsia

The mechanisms of proteinuria development in preeclampsia (PE) are still enigmatic. Renin-angiotensin system (RAS) components may play a role. Maternal serum and urinary concentrations of angiotensin-(1-7) [Ang-(1-7)], angiotensin II (Ang II), and angiotensinogen in women with PE (n = 14), gestational hypertension (n = 14), and normal pregnancy were quantified. The alteration in these concentrations was used to evaluate their relationships with podocyturia and proteinuria in PE. In addition, the podocytes cultured in vitro were interfered in serum of preeclamptic and normotensive pregnant women, with or without Ang-(1-7). The morphologic change in podocyte was observed using a microscope. The changes in podocyte-specific proteins (nephrin, CD2-associated protein [CD2AP]), the cytoskeletal protein F-actin, the tight junction protein (ZO-1), and Mas receptor (MasR) were examined by immunofluorescence. Western blot was used to examine the expression and variation of MasR. We found that the concentrations of RAS components were associated with prepartal urinary podocyte number, random urine albumin/creatinine ratio, blood pressure, and renal function. The expression of nephrin, F-actin, ZO-1, and MasR on podocytes interfered in serum of PE was significantly decreased compared to normal control and normal pregnant serum group in vitro, yet their expression was significantly increased after coculture by 10^-6 mol/L Ang-(1-7) and the preeclamptic serum. The expression of CD2AP had no significant difference. We concluded that decreased Ang-(1-7) and downregulated intrarenal RAS contributed to the direct podocyte injury with proteinuria in PE.

Stratification and Risk Reduction of Perioperative Acute Kidney Injury: An Update

Perioperative acute kidney injury is associated with morbidity and mortality. Several definitions have been proposed, incorporating small changes of serum creatinine and urinary output reduction as diagnostic criteria. In the surgical patient, comorbidities, type and timing of surgery, and nephrotoxins are important. Patient comorbidities remain a significant risk factor. Urgent or emergent surgery and cardiac or transplantation procedures are associated with a higher risk of acute kidney injury. Nephrotoxic drugs, contrast dye, and diuretics worsen preexisting kidney dysfunction or act as an adjunctive insult to perioperative injury. This review includes preoperative, intraoperative, and postoperative issues that can be mitigated.

Urinary angiotensinogen as a biomarker for acute to chronic kidney injury transition - prognostic and mechanistic implications

Accurate biomarkers that both predict the progression to, and detect the early stages of chronic kidney disease (CKD) are lacking, resulting in difficulty in identifying individuals who could potentially benefit from targeted intervention. In a recent issue [Clinical Science (2018) 132, 2121-2133], Cui et al. examine the ability of urinary angiotensinogen (uAGT) to predict the progression of acute kidney injury (AKI) to CKD. They principally employ a murine ischaemia reperfusion injury model to study this and provide data from a small prospective study of patients with biopsy proven acute tubular necrosis. The authors suggest that uAGT is a dynamic marker of renal injury that could be used to predict the likelihood of structural recovery following AKI. Here we comment on their findings, exploring the clinical utility of uAGT as a biomarker to predict AKI to CKD transition and perhaps more controversially, to discuss whether the early renin-angiotensin system blockade following AKI represents a therapeutic target.

Oxidative Stress and Cardiovascular Complications in Chronic Kidney Disease, the Impact of Anaemia

Patients with chronic kidney disease (CKD) have significant cardiovascular morbidity and mortality as a result of risk factors such as left ventricular hypertrophy (LVH), oxidative stress, and inflammation. The presence of anaemia in CKD further increases the risk of LVH and oxidative stress, thereby magnifying the deleterious consequence in uraemic cardiomyopathy (UCM), and aggravating progression to failure and increasing the risk of sudden cardiac death. This short review highlights the specific cardio-renal oxidative stress in CKD and provides an understanding of the pathophysiology and impact of uraemic toxins, inflammation, and anaemia on oxidative stress.

Enzymatic sources and physio-pathological functions of soluble (pro)renin receptor

PURPOSE OF REVIEW

(Pro)renin receptor (PRR) belongs to type I transmembrane receptor family and binds both prorenin and renin, representing a potential regulator of the activity of the renin-angiotensin system. Soluble form of PRR (sPRR) is generated by intracellular protease-mediated cleavage of full-length PRR. The purpose of this review is to highlight recent advances in understanding the mechanisms of action and production of sPRR.

RECENT FINDINGS

It has recently been demonstrated that site-1-protease (S1P) plays a dominant role in the generation of sPRR. New evidence is also emerging to support a biological function of sPRR in the physiological regulation of fluid homeostasis as well as pathogenesis of chronic kidney disease.

SUMMARY

sPRR is a 28 kDa product of PRR cleavage via S1P-mediated protease activity. Not only does sPRR regulate renal tubular water transport, but it also mediates pathogenic responses to renal cellular injury. sPRR is likely involved in a wide range of physio-pathological processes.

Greater reductions in plasma aldosterone with aliskiren in hypertensive patients with higher soluble (Pro)renin receptor level

The (pro)renin receptor is important in the regulation of the tissue renin-angiotensin-aldosterone system. The benefits and safety of single-aliskiren treatment without other renin-angiotensin-aldosterone system inhibitors remain unclear. The serum level of the soluble form of the (pro)renin receptor is thought to be a biomarker reflecting the activity of the tissue renin-angiotensin-aldosterone system. We investigated the effects of single renin-angiotensin-aldosterone system blockade with aliskiren on renal and vascular functions and determined if serum level of the soluble (pro)renin receptor was a predictor of aliskiren efficacy in hypertensive patients with chronic kidney disease. Thirty-nine essential hypertensive patients with chronic kidney disease in our outpatient clinic were randomly assigned to receive either aliskiren or amlodipine. The parameters associated with renal and vascular functions and indices of renin-angiotensin-aldosterone system components, including serum levels of the soluble form, were evaluated before and after 12-week and 24-week treatment. Blood pressure was not significantly different between the groups. No significant changes in serum levels were observed in the soluble (pro)renin receptor in either group. Urinary albumin, protein excretion, and cardio-ankle vascular index significantly decreased in the aliskiren group. In the aliskiren group, there was a significant negative correlation between the basal level of the soluble (pro)renin receptor and the change in plasma aldosterone concentration. Single renin-angiotensin-aldosterone system blockade with aliskiren showed renal and vascular protective effects independent of blood pressure reduction. Serum levels of the soluble (pro)renin receptor may indicate aldosterone production via the (pro)renin receptor in the adrenal gland.