Urinary angiotensinogen as a potential biomarker of severity of chronic kidney diseases

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.

Obstructive sleep apnoea and lung function, and their association with nocturnal hypoxemia: results from the Swedish CArdioPulmonary bioimage Study (SCAPIS) - a cross-sectional study

Obstructive sleep apnoea (OSA) and its associations with lung function.

BACKGROUND

OSA is highly prevalent and characterised by abnormal respiration during sleep. This large, population-based study aimed to investigate the associations between OSA and lung function in subjects aged 50-64 years.

METHOD

The population-based Swedish CArdioPulmonary bioimage Study includes information on anthropometry, comorbidities and spirometry. The current analysis included data from three centres (Gothenburg, Umeå and Uppsala) on whole-night respiratory polygraphy as a meta-analysis examining the overall effect size of lung function on sleep apnoea severity, expressed as ß-coefficient after stratifying for sex and adjusting for age, waist circumference and smoking status.

RESULTS

Data from 9016 participants (54% women, age 58±4 years, body mass index 27±4 kg/m2 ) with sleep recordings of good quality were included in the final analysis. Forced expiratory volume during 1 s (FEV 1 ) (ß=-0.10 (95% CI -0.16 to -0.03)), forced vital capacity (FVC) (-0.15 (-0.21 to -0.10)) and diffusion capacity for carbon monoxide (DLCO ) (-0.08 (-0.10 to -0.05)) were all negatively associated with the oxygen desaturation index (ODI) and also with per cent of registration with nocturnal oxygen saturation <90% FVC (-0.44 (-0.87 to -0.01)), FEV 1 (-0.86 (-1.36 to -0.36)) and DL CO (-0.47 (-0.60 to -0.35)). Additionally, a positive association was observed between FEV 1 (0.13 (0.05 to 0.22)) and DL CO (0.07 (0.04 to 0.09)) with the mean nocturnal saturation. There was a negative association between DL CO and apnoea-hypopnoea index, AHI, (ß=-0.04 (95% CI-0.06 to -0.03)), while no associations were found between FEV 1 or FVC and AHI.

CONCLUSION

In OSA, lower lung function is more distinctly associated with the nocturnal hypoxic burden than AHI. Potential lung function impairment should be investigated in OSA patients with a high ODI relative to AHI.

Transcriptomic and Multi-scale Network Analyses Reveal Key Drivers of Cardiovascular Disease

Cardiovascular diseases (CVDs) and pathologies are often driven by changes in molecular signaling and communication, as well as in cellular and tissue components, particularly those involving the extracellular matrix (ECM), cytoskeleton, and immune response. The fine-wire vascular injury model is commonly used to study neointimal hyperplasia and vessel stiffening, but it is not typically considered a model for CVDs. In this paper, we hypothesize that vascular injury induces changes in gene expression, molecular communication, and biological processes similar to those observed in CVDs at both the transcriptome and protein levels. To investigate this, we analyzed gene expression in microarray datasets from injured and uninjured femoral arteries in mice two weeks post-injury, identifying 1,467 significantly and differentially expressed genes involved in several CVDs such as including vaso-occlusion, arrhythmia, and atherosclerosis. We further constructed a protein-protein interaction network with seven functionally distinct clusters, with notable enrichment in ECM, metabolic processes, actin-based process, and immune response. Significant molecular communications were observed between the clusters, most prominently among those involved in ECM and cytoskeleton organizations, inflammation, and cell cycle. Machine Learning Disease pathway analysis revealed that vascular injury-induced crosstalk between ECM remodeling and immune response clusters contributed to aortic aneurysm, neovascularization of choroid, and kidney failure. Additionally, we found that interactions between ECM and actin cytoskeletal reorganization clusters were linked to cardiac damage, carotid artery occlusion, and cardiac lesions. Overall, through multi-scale bioinformatic analyses, we demonstrated the robustness of the vascular injury model in eliciting transcriptomic and molecular network changes associated with CVDs, highlighting its potential for use in cardiovascular research.

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.

Prognostic impact of renal sinus fat accumulation in patients with chronic kidney disease

BACKGROUND

Obesity is associated with the development and progression of chronic kidney disease (CKD). In the general population, the amount of renal sinus fat was associated with hypertension and renal impairment. However, its impact upon those with CKD remains uncertain.

METHODS

We prospectively included CKD patients who underwent renal biopsy and simultaneously measured their renal sinus fat volume. The association between the percentage of renal sinus fat volume, which was adjusted by kidney volume, and renal outcomes was investigated.

RESULTS

A total of 56 patients (median 55 years old, 35 men) were included. Among baseline characteristics, age and visceral fat volume were positively correlated with the percentage of renal sinus fat volume (p < 0.05). The percentage of renal sinus fat volume was associated with hypertension (p < 0.01) and tended to be associated with max glomerular diameter (p = 0.078) and urine angiotensinogen creatinine ratio (p = 0.064) after adjustment with several clinical factors. The percentage of renal sinus fat volume was significantly associated with a future > 50% decline in estimated glomerular filtration rate (p < 0.05).

CONCLUSIONS

Among those with CKD who required renal biopsy, the amount of renal sinus fat was associated with poor renal outcomes accompanied by systemic hypertension.

View of the Renin-Angiotensin System in Acute Kidney Injury Induced by Renal Ischemia-Reperfusion Injury

Renal ischemia-reperfusion injury (RIRI) is a sequence of complicated events that is defined as a reduction of the blood supply followed by reperfusion. RIRI is the leading cause of acute kidney injury (AKI). Among the diverse mediators that take part in RIRI-induced AKI, the renin-angiotensin system (RAS) plays an important role via conventional (angiotensinogen, renin, angiotensin-converting enzyme (ACE), angiotensin (Ang) II, and Ang II type 1 receptor (AT1R)) and nonconventional (ACE2, Ang 1-7, Ang 1-9, AT2 receptor (AT2R), and Mas receptor (MasR)) axes. RIRI alters the balance of both axes so that RAS can affect RIRI-induced AKI. In overall, the alteration of Ang II/AT1R and AKI by RIRI is important to consider. This review has looked for the effects and interactions of RAS activities during RIRI conditions.

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.

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.

Effect of intrarenal renin-angiotensin-aldosterone system on renal function in patients after cardiac surgery

The aim of the study was to investigate the influence of intrarenal RAS on the decrease of renal function in patients undergoing cardiac surgery with cardiopulmonary bypass. This observational study investigated the activation of intrarenal RAS in 24 patients with AKI after cardiac surgery with cardiopulmonary bypass. The activation of intrarenal RAS was determined by urinary angiotensinogen (uAGT), which was measured at 12 hours before surgery, 0 and12 hours after surgery. The results were compared with those of 21 patients without AKI after cardiac surgery with cardiopulmonary bypass. Clinical and laboratory data were collected. Compared with baseline, all patients with cardiac surgery had activation of intrarenal RAS at 0 and 12 hours after surgery. The activation of intrarenal RAS was found significantly higher at both 0 and 12 hours after surgery in AKI group versus non AKI group (6.18 ± 1.93 ng/mL vs 3.49 ± 1.71 ng/mL, 16.38 ± 7.50 ng/mL vs 6.04 ± 2.59 ng/mL, respectively). There was a positive correlation between the activation of RAS at 0 hour after surgery and the decrease of renal function at 48 hours after surgery (r = 0.654, P = .001). These findings suggest that uAGT might be a suitable biomarker for prediction of the occurrence and severity of AKI after cardiac surgery. Inhibition of intrarenal RAS activation might be one the path of future treatment for this type of disease.

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.

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.

Coregulation Analysis of Mechanistic Biomarkers in Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary kidney disorder leading to deterioration of kidney function and end stage kidney disease (ESKD). A number of molecular processes are dysregulated in ADPKD but the exact mechanism of disease progression is not fully understood. We measured protein biomarkers being linked to ADPKD-associated molecular processes via ELISA in urine and serum in a cohort of ADPKD patients as well as age, gender and eGFR matched CKD patients and healthy controls. ANOVA and t-tests were used to determine differences between cohorts. Spearman correlation coefficient analysis was performed to assess coregulation patterns of individual biomarkers and renal function. Urinary epidermal growth factor (EGF) and serum apelin (APLN) levels were significantly downregulated in ADPKD patients. Serum vascular endothelial growth factor alpha (VEGFA) and urinary angiotensinogen (AGT) were significantly upregulated in ADPKD patients as compared with healthy controls. Arginine vasopressin (AVP) was significantly upregulated in ADPKD patients as compared with CKD patients. Serum VEGFA and VIM concentrations were positively correlated and urinary EGF levels were negatively correlated with urinary AGT levels. Urinary EGF and AGT levels were furthermore significantly associated with estimated glomerular filtration rate (eGFR) in ADPKD patients. In summary, altered protein concentrations in body fluids of ADPKD patients were found for the mechanistic markers EGF, APLN, VEGFA, AGT, AVP, and VIM. In particular, the connection between EGF and AGT during progression of ADPKD warrants further investigation.

Sudden death in individuals with obstructive sleep apnoea: a systematic review and meta-analysis

Objectives

Over 1 billion individuals worldwide experience some form of sleep apnoea, and this number is steadily rising. Obstructive sleep apnoea (OSA) can negatively influence one’s quality of life and potentially increase mortality risk. However, the association between OSA and mortality has not been reliably estimated. This meta-analysis estimates the risk of all-cause and cardiovascular mortality in individuals with OSA.

Design

Systematic review and meta-analysis.

Data sources

MEDLINE, Cochrane Library, Scopus and Joanna Briggs Institute Evidence-Based Practice databases were searched from inception through 1 January 2020.

Eligibility criteria for selecting studies

We included observational studies assessing the association of sudden deaths in individuals with and without OSA.

Data extraction and synthesis

Two independent reviewers (AES and ESH) extracted data and assessed the risk of bias using the Newcastle-Ottawa Scale quality assessment tool. Data were pooled using the random-effects models and reported as risk ratios (RRs) with 95% CIs. Heterogeneity was quantified with I² statistic.

Results

We identified 22 observational studies (n=42 099 participants). The mean age was 62 years and 64% were men. OSA was associated with all-cause sudden death (RR=1.74, 95% CI: 1.44 to 2.10, I²=72%) and cardiovascular mortality (RR=1.94, 95% CI: 1.39 to 2.70, I²=32%). A marginally significant dose–response relationship between severity of OSA and the risk of death was observed (p for interaction=0.05): mild OSA (RR=1.16, 95% CI: 0.70 to 1.93), moderate OSA (RR=1.72, 95% CI: 1.11 to 2.67) and severe OSA (RR=2.87, 95% CI: 1.70 to 4.85). Meta-regression analysis showed that older age was a significant contributing factor in the relationship between OSA and mortality. The median study methodological quality was considered high.

Conclusions

OSA is a significant risk factor for all-cause mortality and cardiac mortality. Prevention and treatment strategies to optimise survival and quality of life in individuals with OSA are urgently needed.

PROSPERO registration number

CRD42020164941.

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).

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.

Urinary angiotensinogen: an indicator of active antineutrophil cytoplasmic antibody-associated glomerulonephritis

BACKGROUND

One of the major challenges in improving the management of antineutrophil cytoplasmic antibody-associated glomerulonephritis (ANCA-GN) is the lack of a disease-specific indicator for histological lesions and disease activity. Here we tested the utility of urinary angiotensinogen (UAGT) as a biomarker of renal disease activity in ANCA-GN.

METHODS

A prospective, two-stage cohort study was performed in ANCA-GN patients. In Stage I, UAGT was measured at the time of renal biopsy in 69 patients from two centers (test set) and 25 patients from two other centers (validation set). In Stage II, UAGT was monitored in 50 subjects in the test set for 24 months.

RESULTS

In Stage I, UAGT significantly increased in ANCA-GN patients, correlating well with cellular crescents formation and active interstitial inflammation. Patients with crescentic ANCA-GN exhibited the highest UAGT compared with other histopathological classes of ANCA-GN. After multivariable adjustment, the highest quartile of UAGT, compared with the lowest quartile, associated with a 6-fold increased risk of crescentic ANCA-GN. For predicting crescentic ANCA-GN, UAGT [area under the receiver operating characteristics curve (AUC) = 0.88] outperformed albuminuria (AUC = 0.73) and estimated glomerular filtration rate (AUC = 0.69). UAGT improved the performance of those clinical markers in diagnosing crescentic ANCA-GN (P < 0.034), suggesting a role of UAGT in identifying active crescentic ANCA-GN. In Stage II, UAGT decreased after immunotherapy and increased at the time of renal relapse during the 2-year follow-up, suggesting the usefulness of UAGT to monitor disease activity over time.

CONCLUSIONS

These results suggest the potential use of UAGT for assessing disease activity and renal relapse in ANCA-GN.

Relationship of obstructive sleep apnoea severity and subclinical systemic atherosclerosis

Obstructive sleep apnoea (OSA) is a common form of sleep disordered breathing. Untreated OSA might accelerate atherosclerosis, potentially increasing the cardiovascular disease burden in patients. The present study aimed to evaluate the association between objectively measured OSA severity and the presence of subclinical systemic atherosclerosis using noninvasive measurements, including tomographic quantification of the calcium burden.A total of 2157 participants of the Korean Genome and Epidemiology Study, who were free of structural heart disease and underwent both in-home polysomnography and chest computed tomography, were cross-sectionally analysed. Participants were divided into three groups based on the severity of OSA: no OSA (apnoea-hypopnoea index (AHI) <5 events·h^-1, n=1096), mild OSA (AHI 5- <15 events·h^-1, n=700) and moderate-to-severe OSA (AHI ≥15 events·h^-1, n=361). Calcium deposits in the thoracic aorta and coronary arteries were measured by the Agatston score.Participants with moderate-to-severe OSA were 1.6 times (95% CI 1.18-2.15 times; p=0.002) more likely to have ascending thoracic aorta calcification (≥100 units) than those without OSA, after adjustment for cardiovascular risk factors. In addition, the association between moderate-to-severe OSA and ascending thoracic aorta calcification of subjects with higher epicardial fat volume was slightly stronger than that in patients without OSA and in the lowest epicardial fat volume tertile (OR 2.11, 95% CI 1.30-3.43).Severity of OSA in the general population was independently associated with subclinical systemic atherosclerosis. These findings highlight the potential importance of severe OSA, especially in subjects with higher epicardial fat, as a possible predictive factor for systemic atherosclerosis and cardiovascular disease.

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.

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.

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.

The elevated levels of urinary angiotensinogen are correlated with the severity of idiopathic membranous nephropathy

Background

Immunosuppressive treatment will predispose an idiopathic membranous nephropathy (iMN) patient to opportunistic infections. Disease severity is one of the main concerns for making the treatment decision. Urinary angiotensinogen (UAGT) level has been shown highly correlated with intrarenal renin-angiotensin system (RAS) activity and severity of chronic kidney diseases (CKD). We aimed to test the relationship between the UAGT level and the severity of iMN.

Methods

This cross-sectional study included a total of 48 biopsy-proven iMN patients, 46 minimal change disease (MCD) patients, and 44 healthy volunteers. The clinical and laboratory data and urine samples were collected from all subjects before the use of RAS inhibitors. We determined the UAGT levels with a method of enzyme-linked immunosorbent assay.

Results

The UAGT levels were not different between the iMN (277.05 ± 61.25, μg/g.Cr) and MCD patients (244.19 ± 40.24, μg/g.Cr), but both of them were significantly higher than those of healthy controls (6.85 ± 1.10, μg/g.Cr). UAGT levels were correlated negatively with serum albumin (r = − 0.393, p = 0.006) and estimated glomerular filtration rate (eGFR) (r = − 0.352, p = 0.014) and positively with 24-h proteinuria (r = 0.614, p < 0.001) in iMN patients but not in MCD patients. Multivariate linear regression analysis revealed that only proteinuria independently determinate the levels of UAGT (β = 0.649, p < 0.001) in iMN patients.

Conclusions

UAGT levels were correlated negatively with serum albumin and glomerular filtration rate and positively with proteinuria in iMN patients at the onset. This suggests that elevated levels of UAGT are associated with the severity of iMN. The UAGT level may be used as a cofactor for deciding immunosuppressive therapy in iMN patient.

Gut microbiota and inflammation in chronic kidney disease and their roles in the development of cardiovascular disease

The health and proper functioning of the cardiovascular and renal systems largely depend on crosstalk in the gut-kidney-heart/vessel triangle. Recent evidence suggests that the gut microbiota has an integral function in this crosstalk. Mounting evidence indicates that the development of chronic kidney and cardiovascular diseases follows chronic inflammatory processes that are affected by the gut microbiota via various immune, metabolic, endocrine, and neurologic pathways. Additionally, deterioration of the function of the cardiovascular and renal systems has been reported to disrupt the original gut microbiota composition, further contributing to the advancement of chronic cardiovascular and renal diseases. Considering the interaction between the gut microbiota and the renal and cardiovascular systems, we can infer that interventions for the gut microbiota through diet and possibly some medications can prevent/stop the vicious cycle between the gut microbiota and the cardiovascular/renal systems, leading to a decrease in chronic cardiovascular and renal diseases.

Angiotensin II Attenuates the Bioactivities of Human Endothelial Progenitor Cells via Downregulation of β2-Adrenergic Receptor

Cross talks between the renin-angiotensin system (RAS), sympathetic nervous system, and vascular homeostasis are tightly coordinated in hypertension. Angiotensin II (Ang II), a key factor in RAS, when abnormally activated, affects the number and bioactivity of circulating human endothelial progenitor cells (hEPCs) in hypertensive patients. In this study, we investigated how the augmentation of Ang II regulates adrenergic receptor-mediated signaling and angiogenic bioactivities of hEPCs. Interestingly, the short-term treatment of hEPCs with Ang II drastically attenuated the expression of beta-2 adrenergic receptor (ADRB2), but did not alter the expression of beta-1 adrenergic receptor (ADRB1) and Ang II type 1 receptor (AT1R). EPC functional assay clearly demonstrated that the treatment with ADRB2 agonists significantly increased EPC bioactivities including cell proliferation, migration, and tube formation abilities. However, EPC bioactivities were decreased dramatically when treated with Ang II. Importantly, the attenuation of EPC bioactivities by Ang II was restored by treatment with an AT1R antagonist (telmisartan; TERT). We found that AT1R binds to ADRB2 in physiological conditions, but this binding is significantly decreased in the presence of Ang II. Furthermore, TERT, an Ang II-AT1R interaction blocker, restored the interaction between AT1R and ADRB2, suggesting that Ang II might induce the dysfunction of EPCs via downregulation of ADRB2, and an AT1R blocker could prevent Ang II-mediated ADRB2 depletion in EPCs. Taken together, our report provides novel insights into potential therapeutic approaches for hypertension-related cardiovascular diseases.

Tailoring surgical interventions to treat obstructive sleep apnoea: one size does not fit all

While continuous positive airway pressure (CPAP) remains the gold standard treatment of choice in patients with moderate or severe obstructive sleep apnoea (OSA), surgery has been established as a means to improve compliance and facilitate the use of CPAP, both of which are potential pitfalls in the efficacy of this treatment modality. In a minority of cases, with obvious oropharyngeal anatomical obstruction, corrective surgery may completely alleviate the need for CPAP treatment. In this review, we summarise clinical assessment, surgical options, discuss potential new treatments, and outline the importance of investigating and addressing the multiple anatomical levels that can contribute to OSA. Research into effectiveness of these procedures is rapidly accumulating, and surgery can be an effective treatment. However, given the myriad of options available and multiple levels of anatomical pathology that can present, it is imperative that correctly selected patients are matched with the most appropriate treatment for the best outcomes.

KEY POINTS

OSA is an increasingly prevalent disorder which has significant systemic effects if left untreated.Anatomical abnormalities can be corrected surgically to good effect with a growing and robust evidence base.Drug-induced sleep endoscopy is a key tool in the otolaryngologist's armamentarium to tailor specific surgery to address specific anatomical concerns, and to facilitate appropriate patient selection.Multilevel surgical approaches are often indicated instead of a "one size fits all" model.

EDUCATIONAL AIMS

To discuss how to assess patients presenting with OSA in clinic, from an otorhinolaryngology perspective.To discuss the indications for intervention.To provide an overview of nonsurgical interventions for treating OSA, with evidence.To discuss the different surgical modalities available for treatment of OSA, with evidence.

Independent regulation of renin-angiotensin-aldosterone system in the kidney

Renin-angiotensin-aldosterone system (RAAS) plays important roles in regulating renal hemodynamics and functions, as well as in the pathophysiology of hypertension and renal disease. In the kidney, angiotensin II (Ang II) production is controlled by independent multiple mechanisms. Ang II is compartmentalized in the renal interstitial fluid with much higher concentrations than those existing in the circulation. Inappropriate activation of the intrarenal RAAS is an important contributor to the pathogenesis of hypertension and renal injury. It has been revealed that intrarenal Ang II levels are predominantly regulated by angiotensinogen and therefore, urinary angiotensinogen could be a biomarker for intrarenal Ang II generation. In addition, recent studies have demonstrated that aldosterone contributes to the progression of renal injury via direct actions on glomerular podocytes, mesangial cells, proximal tubular cells and tubulo-interstitial fibroblasts through the activation of locally expressed mineralocorticoid receptor. Thus, it now appears that intrarenal RAAS is independently regulated and its inappropriate activation contributes to the pathogenesis of the development of hypertension and renal disease. This short review article will focus on the independent regulation of the intrarenal RAAS with an emphasis on the specific role of angiotensinogen.

Reno-Cerebral Reflex Activates the Renin-Angiotensin System, Promoting Oxidative Stress and Renal Damage After Ischemia-Reperfusion Injury

AIMS

A kidney-brain interaction has been described in acute kidney injury, but the mechanisms are uncertain. Since we recently described a reno-cerebral reflex, we tested the hypothesis that renal ischemia-reperfusion injury (IRI) activates a sympathetic reflex that interlinks the renal and cerebral renin-angiotensin axis to promote oxidative stress and progression of the injury.

RESULTS

Bilateral ischemia-reperfusion activated the intrarenal and cerebral, but not the circulating, renin-angiotensin system (RAS), increased sympathetic activity in the kidney and the cerebral sympathetic regulatory regions, and induced brain inflammation and kidney injury. Selective renal afferent denervation with capsaicin or renal denervation significantly attenuated IRI-induced activation of central RAS and brain inflammation. Central blockade of RAS or oxidative stress by intracerebroventricular (ICV) losartan or tempol reduced the renal ischemic injury score by 65% or 58%, respectively, and selective renal afferent denervation or reduction of sympathetic tone by ICV clonidine decreased the score by 42% or 52%, respectively (all p < 0.05). Ischemia-reperfusion-induced renal damage and dysfunction persisted after controlling blood pressure with hydralazine.

INNOVATION

This study uncovered a novel reflex pathway between ischemic kidney and the brain that sustains renal oxidative stress and local RAS activation to promote ongoing renal damage.

CONCLUSIONS

These data suggest that the renal and cerebral renin-angiotensin axes are interlinked by a reno-cerebral sympathetic reflex that is activated by ischemia-reperfusion, which contributes to ischemia-reperfusion-induced brain inflammation and worsening of the acute renal injury. Antioxid. Redox Signal. 27, 415-432.

Urine RAS components in mice and people with type 1 diabetes and chronic kidney disease

The pathways implicated in diabetic kidney disease (DKD) are largely derived from animal models. To examine if alterations in renin-angiotensin system (RAS) in humans are concordant with those in rodent models, we measured concentration of angiotensinogen (AOG), cathepsin D (CTSD), angiotensin-converting enzyme (ACE), and ACE2 and enzymatic activities of ACE, ACE2, and aminopeptidase-A in FVB mice 13-20 wk after treatment with streptozotocin (n = 9) or vehicle (n = 15) and people with long-standing type 1 diabetes, with (n = 37) or without (n = 81) DKD. In streptozotocin-treated mice, urine AOG and CTSD were 10.4- and 3.0-fold higher than in controls, respectively (P < 0.001). Enzymatic activities of ACE, ACE2, and APA were 6.2-, 3.2-, and 18.8-fold higher, respectively, in diabetic animals (P < 0.001). Angiotensin II was 2.4-fold higher in diabetic animals (P = 0.017). Compared with people without DKD, those with DKD had higher urine AOG (170 vs. 15 μg/g) and CTSD (147 vs. 31 μg/g). In people with DKD, urine ACE concentration was 1.8-fold higher (1.4 vs. 0.8 μg/g in those without DKD), while its enzymatic activity was 0.6-fold lower (1.0 vs. 1.6 × 10⁹ RFU/g in those without DKD). Lower ACE activity, but not ACE protein concentration, was associated with ACE inhibitor (ACEI) treatment. After adjustment for clinical covariates, AOG, CTSD, ACE concentration, and ACE activity remained associated with DKD. In conclusion, in mice with streptozotocin-induced diabetes and in humans with DKD, urine concentrations and enzymatic activities of several RAS components are concordantly increased, consistent with enhanced RAS activity and greater angiotensin II formation. ACEI use was associated with a specific reduction in urine ACE activity, not ACE protein concentration, suggesting that it may be a marker of exposure to this widely-used therapy.

Angiotensinogen and Interleukin-18 as Markers of Chronic Kidney Damage in Children With a History of Hemolytic Uremic Syndrome

Hemolytic uremic syndrome (HUS) is a type of thrombotic microangiopathy, in the course of which some patients may develop chronic kidney disease (CKD). It is clinically important to investigate the markers of a poor prognosis. The levels of angiotensinogen (AGT) and interleukin-18 (IL-18) in serum and urine were evaluated. Study was conducted in 29 children with a history of HUS. Serum and urine AGT concentration was significantly higher in children after HUS as compared to the control group. No differences depending on the type of HUS and gender were noted. The serum concentration of IL-18 in children after HUS was significantly lower, whereas in urine did not differ significantly between the sick and healthy children. A negative correlation between the concentration of AGT in serum and albuminuria in patients after HUS was detected. The results indicate that the concentration of AGT in serum and urine in children after HUS increases, which may indicate the activation of the intrarenal renin-angiotensin-aldosterone system. The statement, that AGT may be a good biomarker of CKD after acute kidney injury due to HUS requires prospective studies with follow-up from the acute phase of the disease on a larger group of patients. Reduced IL-18 serum concentration in children after HUS with no difference in its urine concentration may indicate a loss of the protective effects of this cytokine on renal function due to previously occurred HUS.

Urinary Angiotensinogen and Renin Excretion are Associated with Chronic Kidney Disease

BACKGROUND/AIMS

Several studies sought to identify new biomarkers for chronic kidney disease (CKD). As the renal renin-angiotensin system is activated in CKD, urinary angiotensinogen or renin excretion may be suitable candidates. We tested whether urinary angiotensinogen or renin excretion is elevated in CKD and whether these parameters are associated with estimated glomerular filtration rate (eGFR). We further tested whether urinary angiotensinogen or renin excretion may convey additional information beyond that provided by albuminuria.

METHODS

We measured urinary and plasma angiotensinogen, renin, albumin and creatinine in 177 CKD patients from the Greifswald Approach to Individualized Medicine project and in 283 healthy controls from the Study of Health in Pomerania. The urinary excretion of specific proteins is given as protein-to-creatinine ratio. Receiver operating characteristic (ROC) curves, spearman correlation coefficients and linear regression models were calculated.

RESULTS

Urinary angiotensinogen [2,511 (196-31,909) vs. 18.6 (8.3-44.0) pmol/g, *P<0.01] and renin excretion [0.311 (0.135-1.155) vs. 0.069 (0.045-0.148) pmol/g, *P<0.01] were significantly higher in CKD patients than in healthy controls. The area under the ROC curve was significantly larger when urinary angiotensinogen, renin and albumin excretion were combined than with urinary albumin excretion alone. Urinary angiotensinogen (ß-coefficient -2.405, standard error 0.117, P<0.01) and renin excretion (ß-coefficient -0.793, standard error 0.061, P<0.01) were inversely associated with eGFR. Adjustment for albuminuria, age, sex, systolic blood pressure and body mass index did not significantly affect the results.

CONCLUSION

Urinary angiotensinogen and renin excretion are elevated in CKD patients. Both parameters are negatively associated with eGFR and these associations are independent of urinary albumin excretion. In CKD patients urinary angiotensinogen and renin excretion may convey additional information beyond that provided by albuminuria.

Comparative Effects of Direct Renin Inhibitor and Angiotensin Receptor Blocker on Albuminuria in Hypertensive Patients with Type 2 Diabetes. A Randomized Controlled Trial

BACKGROUND

In patients with diabetes, albuminuria is a risk marker of end-stage renal disease and cardiovascular events. An increased renin-angiotensin system activity has been reported to play an important role in the pathological processes in these conditions. We compared the effect of aliskiren, a direct renin inhibitor (DRI), with that of angiotensin receptor blockers (ARBs) on albuminuria and urinary excretion of angiotensinogen, a marker of intrarenal renin-angiotensin system activity.

METHODS

We randomly assigned 237 type 2 diabetic patients with high-normal albuminuria (10 to <30 mg/g of albumin-to-creatinine ratio) or microalbuminuria (30 to <300 mg/g) to the DRI group or ARB group (any ARB) with a target blood pressure of <130/80 mmHg. The primary endpoint was a reduction in albuminuria.

RESULTS

Twelve patients dropped out during the observation period, and a total of 225 patients were analyzed. During the study period, the systolic and diastolic blood pressures were not different between the groups. The changes in the urinary albumin-to-creatinine ratio from baseline to the end of the treatment period in the DRI and ARB groups were similar (-5.5% and -6.7%, respectively). In contrast, a significant reduction in the urinary excretion of angiotensinogen was observed in the ARB group but not in the DRI group. In the subgroup analysis, a significant reduction in the albuminuria was observed in the ARB group but not in the DRI group among high-normal albuminuria patients.

CONCLUSION

DRI and ARB reduced albuminuria in hypertensive patients with type 2 diabetes. In addition, ARB, but not DRI, reduced albuminuria even in patients with normal albuminuria. DRI is not superior to ARB in the reduction of urinary excretion of albumin and angiotensinogen.

Urinary Angiotensinogen Could Be a Prognostic Marker of the Renoprotection of Olmesartan in Metabolic Syndrome Patients

This study was performed to demonstrate urinary angiotensinogen as a potential prognostic marker of the albuminuria reduction effects of olmesartan in patients with metabolic syndrome. In 24 patients (eight women, 57.88 ± 2.00 years), 5-40 mg/day of olmesartan were given. Urinary concentrations of albumin and angiotensinogen (normalized by urinary concentrations of creatinine) and plasma renin activity were measured before and after the 12- and 24-week marks of olmesartan treatment. Olmesartan treatment increased plasma renin activity and decreased urinary albumin and urinary angiotensinogen significantly (p < 0.05). Based on the % change in urinary albumin, patients were divided into two groups, responders (<-50%) and non-responders (≥-50%), and a logistic analysis of urinary angiotensinogen before treatment showed the area under the curve as 0.694. When the cutoff value of urinary angiotensinogen before the treatment of 13.9 µg/g Cr was used, the maximum Youden index (0.500, specificity: 11/12 = 91.7% and sensitivity: 7/12 = 58.3%) was obtained. When all patients were re-divided into two groups, those with higher values of urinary angiotensinogen before the treatment (Group H, n = 16) and those with lower values, Group H showed significantly decreased urinary albumin (p < 0.05). Therefore, urinary angiotensinogen could be a prognostic marker of the albuminuria reduction effects of olmesartan in patients with metabolic syndrome.

Intrarenal renin-angiotensin system activity is augmented after initiation of dialysis

Circulating renin-angiotensin system (RAS) activation is maintained after renal function has deteriorated. The activation of the intrarenal RAS plays a critical role in the pathophysiology of chronic kidney disease (CKD), independently of the circulating RAS. However, the activation of intrarenal RAS and the chymase-dependent pathway after initiation of dialysis has not been clarified. We recruited 19 CKD patients (10 without dialysis and 9 with dialysis) who underwent a heminephrectomy. Circulating RAS was investigated before nephrectomy. The levels of intrarenal RAS components and chymase-positive cells were investigated using radioimmunoassay or immunoblot analysis on samples collected from the removed kidney. Renal damage was evaluated by the extent of tubulointerstitial fibrosis. No significant differences in circulating RAS between nondialysis and dialysis patients were found. However, intrarenal angiotensin II (AngII) and the extent of tubulointerstitial fibrosis in dialysis patients were significantly increased when compared with nondialysis patients. Prorenin and angiotensin-converting enzyme (ACE) levels were dramatically decreased in accordance with renal dysfunction. On the other hand, chymase-positive cells and AngII type 1 receptor (AT1R) expression was significantly increased in dialysis patients when compared with nondialysis patients. In multiple linear regression analyses, there were significant positive and negative relationships between the extent of interstitial fibrosis and angiotensinogen (β=0.45, P=0.042) and prorenin levels (β=-0.85, P<0.01), respectively. In summary, a decrease in prorenin and ACE expression and an increase in chymase, angiotensinogen and AT1R expression in the kidney may augment the intrarenal RAS activation and be associated with renal damage, even after initiation of dialysis.

Urine angiotensinogen and salt-sensitivity and potassium-sensitivity of blood pressure

OBJECTIVE

Urinary excretion of angiotensinogen [urine angiotensinogen (UAGT)] has been proposed as a biomarker of intrarenal renin-angiotensin system activity. We investigated the association between UAGT and salt-sensitivity and potassium-sensitivity of blood pressure (BP) among Genetic Epidemiology Network of Salt Sensitivity study participants.

METHODS

The intervention consisted of a 7-day low-sodium diet (51.3  mmol sodium/day), 7-day high-sodium diet (307.8  mmol sodium/day), and 7-day high-sodium diet with potassium supplementation (307.8  mmol sodium/day and 60  mmol potassium/day). Twenty-four-hour UAGT was estimated at baseline and at the end of each intervention for 100 randomly selected participants.

RESULTS

Median UAGT (μg/24  h) and UAGT-to-creatinine ratio (UAGT/Cr, μg/g) were significantly reduced during the low-sodium and potassium-supplementation interventions and increased during the high-sodium intervention (both P = 0.01). Baseline log-transformed UAGT and UAGT/Cr ratio were significantly positively associated with BP at baseline and at the end of each intervention. For example, one standard deviation higher log-UAGT/Cr ratio (1.2  μg/g) was associated with a 5.0-mmHg (95% confidence interval 2.3-7.8) higher SBP at the end of the high-sodium intervention, after adjusting for multiple covariates (P = 0.003). In addition, one standard deviation higher log-UAGT/Cr ratio was associated with a 1.6-mmHg increase in age-adjusted and sex-adjusted SBP from the low-sodium intervention to the high-sodium intervention (95% confidence interval 0.1-3.1, P = 0.04). This association was no longer statistically significant after multivariable adjustment.

CONCLUSION

These data indicate that elevated UAGT are associated with BP sodium sensitivity. Augmentation of intrarenal renin-angiotensin system activity may play an important role in developing salt-sensitive hypertension.

Augmented circadian rhythm of the intrarenal renin-angiotensin systems in anti-thymocyte serum nephritis rats

We report that disturbance to the circadian rhythm of urinary angiotensinogen (AGT) excretion may lead to renal damage, hypertension and diurnal blood pressure (BP) variations. We aim to clarify the circadian rhythm of the intrarenal renin-angiotensin system (RAS) and its contribution to renal damage, hypertension and BP variations, and to evaluate whether the administration of RAS blockers influences the circadian rhythms of intrarenal RAS components. Anti-thymocyte serum (ATS) nephritis rats were used as a chronic progressive glomerulonephritis model (group A) and compared with control rats (group C). Other rats with ATS nephritis received olmesartan medoxomil (an angiotensin II (AngII) type 1 receptor (AT1R) blocker; group AO) or hydralazine (a vasodilator; group AH). The levels of intrarenal RAS components were evaluated every 6 h. The expression levels of intrarenal AGT, AngII and AT1R were increased in group A and peaked at the same time as BP and urinary protein excretion during the rest phase. The amplitude of the circadian fluctuation of these proteins was more increased in group A than in group C. The circadian fluctuation of these proteins was reduced in groups AO and AH. However, renal function, proteinuria and augmentation of intrarenal RAS components were reduced only in group AO. Intrarenal RAS components, such as AGT, AngII and AT1R proteins, were increased and the amplitude of the oscillations of these proteins was augmented in ATS nephritis rats. Interestingly, renal damage may be linked to the activation of the intrarenal RAS independent of the amplitude of its oscillations and BP.

A local renal renin-angiotensin system activation via renal uptake of prorenin and angiotensinogen in diabetic rats

The mechanism of activation of local renal renin-angiotensin system (RAS) has not been clarified in diabetes mellitus (DM). We hypothesized that the local renal RAS will be activated via increased glomerular filtration and tubular uptake of prorenin and angiotensinogen in diabetic kidney with microalbuminuria. Streptozotocin (STZ)-induced DM and control rats were injected with human prorenin and subsequently with human angiotensinogen. Human prorenin uptake was increased in podocytes, proximal tubules, macula densa, and cortical collecting ducts of DM rats where prorenin receptor (PRR) was expressed. Co-immunoprecipitation of kidney homogenates in DM rats revealed binding of human prorenin to the PRR and to megalin. The renal uptake of human angiotensinogen was increased in DM rats at the same nephron sites as prorenin. Angiotensin-converting enzyme was increased in podocytes, but decreased in the proximal tubules in DM rats, which may have contributed to unchanged renal levels of angiotensin despite increased angiotensinogen. The systolic blood pressure increased more after the injection of 20 μg of angiotensinogen in DM rats than in controls, accompanied by an increased uptake of human angiotensinogen in the vascular endothelium. In conclusion, endocytic uptake of prorenin and angiotensinogen in the kidney and vasculature in DM rats was contributed to increased tissue RAS and their pressor response to angiotensinogen.

Urine matrix metalloproteinase-7 and risk of kidney disease progression and mortality in type 2 diabetes

AIMS

The renin-angiotensin-aldosterone system (RAAS), bone morphogenetic protein (BMP) and WNT pathways are dysregulated in diabetic kidney disease (DKD). Urine excretion of angiotensinogen, gremlin-1 and matrix metalloproteinase-7 (MMP-7), components of the RAAS, BMP and WNT pathways, respectively, is increased in DKD. We asked if this increase is associated with subsequent progression to end-stage renal disease (ESRD) or death.

METHODS

Using time-to-event analyses, we examined the association of baseline urine concentration of these proteins with progression to ESRD or death in a predominantly Mexican-American cohort with type 2 diabetes and proteinuric DKD (n=141).

RESULTS

Progression to ESRD occurred for 38 participants over a median follow-up of 3.0years; 39 participants died over a median follow-up of 3.6years. Urine MMP-7 and gremlin-1 were associated with increased risk of ESRD after adjustment for demographic and clinical covariates. Angiotensinogen showed a U-shaped relationship with ESRD, with the middle tertile associated with lowest risk of ESRD. After additional adjustment for glomerular filtration rate and albuminuria, all associations with ESRD lost significance. Only urine MMP-7 was associated with mortality, and this association remained robust in the fully adjusted model with a Hazard ratio of 3.59 (95% confidence interval 1.31 to 9.85) for highest vs. lowest tertile. Serum MMP-7 was not associated with mortality and did not attenuate the association of urine MMP-7 with mortality (HR 4.03 for highest vs. lowest urine MMP-7 tertile).

CONCLUSIONS

Among people with type 2 diabetes and proteinuric DKD, urine MMP-7 concentration was strongly associated with subsequent mortality.