Chronic renovascular hypertension is associated with elevated levels of neutrophil gelatinase-associated lipocalin

Kidney Intrinsic Mechanisms as Novel Targets in Renovascular Hypertension

Almost a hundred years have passed since obstruction of the renal artery has been recognized to raise blood pressure. By now chronic renovascular disease (RVD) due to renal artery stenosis is recognized as a major source of renovascular hypertension and renal disease. In some patients, RVD unaccompanied by noteworthy renal dysfunction or blood pressure elevation may be incidentally identified during peripheral angiography. Nevertheless, in others, RVD might present as a progressive disease associated with diffuse atherosclerosis, leading to loss of renal function, renovascular hypertension, hemodynamic compromise, and a magnified risk for cardiovascular morbidity and mortality. Atherosclerotic RVD leads to renal atrophy, inflammation, and hypoxia but represents a potentially treatable cause of chronic renal failure because until severe fibrosis sets in the ischemic kidney, it retains a robust potential for vascular and tubular regeneration. This remarkable recovery capacity of the kidney begs for early diagnosis and treatment. However, accumulating evidence from both animal studies and randomized clinical trials has convincingly established the inadequate efficacy of renal artery revascularization to fully restore renal function or blood pressure control and has illuminated the potential of therapies targeted to the ischemic renal parenchyma to instigate renal regeneration. Some of the injurious mechanisms identified as potential therapeutic targets included oxidative stress, microvascular disease, inflammation, mitochondrial injury, and cellular senescence. This review recapitulates the intrinsic mechanisms that orchestrate renal damage and recovery in RVD and can be harnessed to introduce remedial opportunities.

Interleukin-1β Disruption Protects Male Mice From Heart Failure With Preserved Ejection Fraction Pathogenesis

Background Heart failure with preserved ejection fraction (HFpEF) is a significant unmet need in cardiovascular medicine and remains an untreatable cardiovascular disease. The role and mechanism of interleukin-1β in HFpEF pathogenesis are poorly understood. Methods and Results C57/Bl6J and interleukin-1β-/- male mice were randomly divided into 4 groups. Groups 1 and 2: C57/Bl6J and interleukin-1β-/- mice were fed a regular diet for 4 months and considered controls. Groups 3 and 4: C57/Bl6 and interleukin-1β-/- mice were fed a high-fat diet with N[w]-nitro-l-arginine methyl ester (endothelial nitric oxide synthase inhibitor, 0.5 g/L) in the drinking water for 4 months. We measured body weight, blood pressure, diabetes status, cardiac function/hypertrophy/inflammation, fibrosis, vascular endothelial function, and signaling. C57/Bl6 fed a high-fat diet and N[w]-nitro-l-arginine methyl ester in the drinking water for 4 months developed HFpEF pathogenesis characterized by obesity, diabetes, hypertension, cardiac hypertrophy, lung edema, low running performance, macrovascular and microvascular endothelial dysfunction, and diastolic cardiac dysfunction but no change in cardiac ejection fraction compared with control mice. Interestingly, the genetic disruption of interleukin-1β protected mice from HFpEF pathogenesis through the modulation of the inflammation and endoplasmic reticulum stress mechanisms. Conclusions Our data suggest that interleukin-1β is a critical driver in the development of HFpEF pathogenesis, likely through regulating inflammation and endoplasmic reticulum stress pathways. Our findings provide a potential therapeutic target for HFpEF treatment.

The significance of fibroblast growth factor-2 and kidney injury molecule-1 as biomarker of interstitial renal fibrosis in glomerulonephritis

Background

Renal tubulointerstitial fibrosis is a structural marker and prominent pathological characteristic of chronic progressive kidney disease, fibroblast growth factor-2 (FGF2) is a key fibrogenic cytokine that is likely to be involved in the pathogenesis of renal fibrosis, kidney injury molecule-1 (KIM-1) is one of the most promising, early biomarkers of renal disease, either acute or chronic, due to its translatability between preclinical and clinical trials. It is believed that this molecule participates in the process of both kidney injury and healing.

Methods

We prospectively enrolled a cohort study of eighty adult patients who had glomerular diseases (with glomerular filtration rate (GFR) > 30 ml/min/m2); serum level of FGF-2 and KIM-1 was measured at the same time of renal biopsy and was correlated with the degree of interstitial renal fibrosis.

Results

We found a significant positive correlation between FGF-2 and KIM-1 and the degree of interstitial renal fibrosis, albumin, and creatinine (P≤ 0.001), and a negative significant correlation with GFR and proteinuria. there is a positive significant correlation between serum KIM-1 and FGF-2 and hypertension with a significant P value (<0.001) that serum KIM-1 has sensitivity 90% and specificity of 95% and serum FGF-2 has sensitivity 95% and specificity 95% for detection of interstitial renal fibrosis.

Conclusions

Serum FGF-2 and KIM-1 seem to be a non-invasive novel biomarker of interstitial renal fibrosis in glomerulonephritis patients. It may become a useful biomarker without the need for the invasive maneuver of the renal biopsy. FGF-2 and KIM-1 are expected to be therapeutic targets for kidney injury.

Emergent players in renovascular disease

Renovascular disease (RVD) remains a common etiology of secondary hypertension. Recent clinical trials revealed unsatisfactory therapeutic outcomes of renal revascularization, leading to extensive investigation to unravel key pathophysiological mechanisms underlying irreversible functional loss and structural damage in the chronically ischemic kidney. Research studies identified complex interactions among various players, including inflammation, fibrosis, mitochondrial injury, cellular senescence, and microvascular remodeling. This interplay resulted in a shift of our understanding of RVD from a mere hemodynamic disorder to a pro-inflammatory and pro-fibrotic pathology strongly influenced by systemic diseases like metabolic syndrome (MetS), hypertension, diabetes mellitus, and hyperlipidemia. Novel diagnostic approaches have been tested for early detection and follow-up of RVD progression, using new imaging techniques and biochemical markers of renal injury and dysfunction. Therapies targeting some of the pathological pathways governing the development of RVD have shown promising results in animal models, and a few have moved from bench to clinical research. This review summarizes evolving understanding in chronic ischemic kidney injury.

Toll-like receptor 4 mutation protects the kidney from Ang-II-induced hypertensive injury

Cellular autophagy is a protective mechanism where cells degrade damaged organelles to maintain intracellular homeostasis. Apoptosis, on the other hand, is considered as programmed cell death. Interestingly, autophagy inhibits apoptosis by degrading apoptosis regulators. In hypertension, an imbalance of autophagy and apoptosis regulators can lead to renal injury and dysfunction. Previously, we have reported that toll-like receptor 4 (TLR4) mutant mice are protective against renal damage, in part, due to reduced oxidative stress and inflammation. However, the detailed mechanism remained elusive. In this study, we tested the hypothesis of whether TLR4 mutation reduces Ang-II-induced renal injury by inciting autophagy and suppressing apoptosis in the hypertensive kidney. Male mice with normal TLR4 expression (TLR4N, C3H/HeOuJ) and mutant TLR4 (TLR4M, C3H/HeJLps-d) aged 10-12 weeks were infused with Ang-II (1000 ng/kg/d) for 4 weeks to create hypertension. Saline infused appropriate control were used. Blood pressure was increased along with increased TLR4 expression in TLR4N mice receiving Ang-II compared to TLR4N control. Autophagy was downregulated, and apoptosis was upregulated in TLR4N mice treated with Ang-II. Also, kidney injury markers plasma lipocalin-2 (LCN2) and kidney injury molecule 1 (KIM-1) were upregulated in TLR4N mice treated with Ang-II. Besides, increased nuclear translocation and activity of NF-kB were measured in Ang-II-treated TLR4N mice. TLR4M mice remained protected against all these insults in hypertension. Together, these results suggest that Ang-II-induced TLR4 activation suppresses autophagy, induces apoptosis and kidney injury through in part by activating NF-kB signaling, and TLR4 mutation protects the kidney from Ang-II-induced hypertensive injury.

Cell-based regenerative medicine for renovascular disease

Renal artery stenosis (RAS) elicits the development of hypertension and post-stenotic kidney damage, which may become irresponsive to restoration of arterial patency. Rather than mere losses of blood flow or oxygen supply, irreversible intrarenal microvascular rarefaction, tubular injury, and interstitial fibrosis are now attributed to intrinsic pathways activated within the kidney, focusing attention on the kidney parenchyma as a therapeutic target. Several regenerative approaches involving the delivery of reparative cells or products have achieved kidney repair in experimental models of RAS and the delivery of mesenchymal stem/stromal cells (MSCs) has already been translated to human subjects with RAS with promising results. The ongoing development of innovative approaches in kidney disease awaits application, validation, and acceptance as routine clinical treatment to avert kidney damage in RAS.

Inflammation and Oxidative Damage in Ischaemic Renal Disease

Ischaemic renal disease as result of atherosclerotic renovascular disease activates a complex biological response that ultimately leads to fibrosis and chronic kidney disease. Large randomised control trials have shown that renal revascularisation in patients with atherosclerotic renal artery disease does not confer any additional benefit to medical therapy alone. This is likely related to the activation of complex pathways of oxidative stress, inflammatory cytokines and fibrosis due to atherosclerotic disease and hypoxic injury due to reduced renal blood flow. New evidence from pre-clinical trials now indicates a role for specific targeted therapeutic interventions to counteract this complex pathogenesis. This evidence now suggests that the focus for those with atherosclerotic renovascular disease should be a combination of revascularisation and renoprotective therapies that target the renal tissue response to ischaemia, reduce the inflammatory infiltrate and prevent or reduce the fibrosis.

Magnetization Transfer Imaging Predicts Porcine Kidney Recovery After Revascularization of Renal Artery Stenosis

MATERIALS AND METHODS

Stenotic kidney (STK) and contralateral kidney magnetization transfer ratios (MTRs; Mt/M0) were measured at 3.0-T magnetic resonance imaging, at offset frequencies of 600 and 1000 Hz, before and 1 month post-PTRA in 7 RVD pigs. Stenotic kidney MTR was correlated to renal perfusion, renal blood flow (RBF), and glomerular filtration rate (GFR), determined using multidetector computed tomography and with ex vivo renal fibrosis (trichrome staining). Untreated RVD (n = 6) and normal pigs (n = 7) served as controls.

RESULTS

Renovascular disease induced hypertension and renal dysfunction. Blood pressure and renal perfusion were unchanged post-PTRA, but GFR and RBF increased. Baseline cortical STK-MTR predicted post-PTRA renal perfusion and RBF, and MTR changes associated inversely with changes in perfusion and normalized GFR. Stenotic kidney MTR at 600 Hz showed closer association with renal parameters, but both frequencies predicted post-PTRA cortical fibrosis.

CONCLUSIONS

Renal STK-MTR, particularly at 600 Hz offset, is sensitive to hemodynamic changes after PTRA in swine RVD and capable of noninvasively predicting post-PTRA kidney perfusion, RBF, and fibrosis. Therefore, STK-MTR may be a valuable tool to predict renal hemodynamic and functional recovery, as well as residual kidney fibrosis after revascularization in RVD.

Peristenotic Collateral Circulation in Atherosclerotic Renovascular Disease: Association With Kidney Function and Response to Treatment

The significance of peristenotic collateral circulation (PCC) development around a stenotic renal artery is unknown. We tested the hypothesis that PCC is linked to loss of kidney function and recovery potential in patients with atherosclerotic renovascular disease (ARVD). Thirty-four patients with ARVD were assigned to medical-therapy with or without revascularization based on clinical indications. The PCC was visualized using multidetector computed tomography and defined relative to segmental arteries in patients with essential hypertension. PCC number before and 3 months after treatment was correlated with various renal parameters. Thirty-four stenotic kidneys from 30 patients were analyzed. PCC number correlated inversely with kidney volume. ARVD-stenotic kidneys with baseline PCC (collateral ARVD [C-ARVD], n=13) associated with elevated 24-hour urine protein and stenotic kidney vein level of tumor necrosis factor-α, lower single-kidney volume and blood flow, and greater hypoxia than in stenotic kidneys with no PCC (no collateral ARVD [NC-ARVD], n=17). Revascularization (but not medical-therapy alone) improved stenotic kidney function and reduced inflammation in both NC-ARVD and C-ARVD. In C-ARVD, revascularization also increased stenotic kidney volume, blood flow, and oxygenation to levels comparable to NC-ARVD, and induced PCC regression. However, revascularization improved systolic blood pressure, plasma renin activity, and filtration fraction only in NC-ARVD. Therefore, patients with C-ARVD have greater kidney dysfunction, atrophy, hypoxia, and inflammation compared with patients with NC-ARVD, suggesting that PCC does not effectively protect the stenotic kidney in ARVD. Renal artery revascularization improved in C-ARVD stenotic kidney function, but not hypertension or renin-angiotensin system activation. These observations may help direct management of patients with ARVD.

Novel therapeutic strategies for renovascular disease

PURPOSE OF REVIEW

Renovascular disease (RVD) remains an important cause of hypertension and renal dysfunction. Given the failure of renal revascularization to provide consistent clinical benefit in the Cardiovascular Outcomes for Renal Artery Lesions trial among others, further research has underscored the need for mechanistically targeted interventions to improve renal outcomes in patients in RVD. This review discusses novel therapeutic approaches for RVD in the post-Cardiovascular Outcomes for Renal Artery Lesions era.

RECENT FINDINGS

Emerging evidence indicates that renal inflammation, microvascular remodeling, and mitochondrial damage accelerate progression of renal injury and are important determinants of the response to revascularization. Experimental studies have identified interventions capable of ameliorating renal inflammation (e.g., cytokine inhibitors, mesenchymal stem cells), microvascular remodeling (proangiogenic interventions), and mitochondrial injury (mito-protective drugs), alone or combined with renal revascularization, to preserve the structure and function of the poststenotic kidney. Recent prospective pilot studies in patients with atherosclerotic RVD demonstrate the safety and feasibility of some of such interventions to protect the kidney.

SUMMARY

Experimental studies and pilot clinical trials suggest that therapies targeting renal inflammation, microvascular remodeling, and mitochondrial damage have the potential to preserve the structure and function of the stenotic kidney. Further studies in larger cohorts are needed to confirm their renoprotective effects and clinical role in human RVD.

Mesenchymal Stem Cell-Derived Extracellular Vesicles Induce Regulatory T Cells to Ameliorate Chronic Kidney Injury

Metabolic syndrome (MetS) profoundly changes the contents of mesenchymal stem cells and mesenchymal stem cells-derived extracellular vesicles (EVs). The anti-inflammatory TGF-β (transforming growth factor-β) is selectively enriched in EVs from Lean but not from MetS pigs, but the functional impact of this endowment remains unknown. We hypothesized that Lean-EVs more effectively induce regulatory T cells in injured kidneys. Five groups of pigs (n=7 each) were studied after 16 weeks of diet-induced MetS and unilateral renal artery stenosis (RAS; MetS+RAS). Two groups of MetS+RAS were treated 4 weeks earlier with an intrarenal injection of either Lean-EVs or MetS-EVs. MetS+RAS had lower renal volume, renal blood flow, and glomerular filtration rate than MetS pigs. Compared with Lean-EVs, MetS-EVs were less effective in improving renal function and decreasing tubular injury and fibrosis in MetS+RAS. Lean-EVs upregulated TGF-β expression in stenotic kidney and increased regulatory T cells numbers more prominently. Furthermore, markedly upregulated anti-inflammatory M2 macrophages reduced proinflammatory M1 macrophages, and CD8⁺ T cells were detected in stenotic kidneys treated with Lean-EVs compared with MetS-EVs, and renal vein levels of interleukin-1β were reduced. In vitro, coculture of Lean-EVs with activated T cells led to greater TGF-β-dependent regulatory T cells induction than did MetS-EVs. Therefore, the beneficial effects of mesenchymal stem cells-derived EVs on injured kidneys might be partly mediated by their content of TGF-β signaling components, which permitting increased Treg preponderance. Modulating EV cargo and transforming their functionality might be useful for renal repair.

Renal Artery Stenosis Alters Gene Expression in Swine Scattered Tubular-Like Cells

Background: Scattered tubular-like cells (STCs) proliferate and differentiate to support neighboring injured renal tubular cells during recovery from insults. Renal artery stenosis (RAS) induces renal ischemia and hypertension and leads to loss of kidney function, but whether RAS alters renal endogenous repair mechanisms, such as STCs, remains unknown. We hypothesize that RAS in swine modifies the messenger RNA (mRNA) profile of STCs, blunting their in vitro reparative capacity. Methods: CD24+/CD133+ STCs were isolated from pig kidneys after 10-weeks of RAS or sham (n = 3 each) and their gene cargo analyzed using high-throughput mRNAseq. Expression profiles for upregulated and downregulated mRNAs in RAS-STCs were functionally interpreted by gene ontology analysis. STC activation was assessed by counting the total number of STCs in pig kidney sections using flow cytometry, whereas cell proliferation was assessed in vitro. Results: Of all expressed genes, 1430 genes were upregulated and 315 downregulated in RAS- versus Normal-STCs. Expression of selected candidate genes followed the same fold change directions as the mRNAseq findings. Genes upregulated in RAS-STCs were involved in cell adhesion, extracellular matrix remodeling, and kidney development, whereas those downregulated in RAS-STCs are related to cell cycle and cytoskeleton. The percentage of STCs from dissociated kidney cells was higher in RAS versus Normal pigs, but their proliferation rate was blunted. Conclusions: Renal ischemia and hypertension in swine induce changes in the mRNA profile of STCs, associated with increased STC activation and impaired proliferation. These observations suggest that RAS may alter the reparative capacity of STCs.

Senescent Kidney Cells in Hypertensive Patients Release Urinary Extracellular Vesicles

Background

Hypertension may be associated with renal cellular injury. Cells in distress release extracellular vesicles (EVs), and their numbers in urine may reflect renal injury. Cellular senescence, an irreversible growth arrest in response to a noxious milieu, is characterized by release of proinflammatory cytokines. We hypothesized that EVs released by senescent nephron cells can be identified in urine of patients with hypertension.

Methods and Results

We recruited patients with essential hypertension (EH) or renovascular hypertension and healthy volunteers (n=14 each). Renal oxygenation was assessed using magnetic resonance imaging and blood samples collected from both renal veins for cytokine‐level measurements. EVs isolated from urine samples were characterized by imaging flow cytometry based on specific markers, including p16 (senescence marker), calyxin (podocytes), urate transporter 1 (proximal tubules), uromodulin (ascending limb of Henle's loop), and prominin‐2 (distal tubules). Overall percentage of urinary p16+ EVs was elevated in EH and renovascular hypertension patients compared with healthy volunteers and correlated inversely with renal function and directly with renal vein cytokine levels. Urinary levels of p16⁺/urate transporter 1⁺ were elevated in all hypertensive subjects compared with healthy volunteers, whereas p16⁺/prominin‐2⁺ levels were elevated only in EH versus healthy volunteers and p16⁺/uromodulin⁺ in renovascular hypertension versus EH.

Conclusions

Levels of p16⁺EVs are elevated in urine of hypertensive patients and may reflect increased proximal tubular cellular senescence. In EH, EVs originate also from distal tubules and in renovascular hypertension from Henle's loop. Hence, urinary EVs levels may be useful to identify intrarenal sites of cellular senescence.

Association of novel biomarkers with major clinical outcomes in a cohort of patients with atherosclerotic renovascular disease

Introduction

In this study, we investigate whether the addition of biomarkers to a model based on traditional risk factors improves risk prediction and patient selection for revascularization in atherosclerotic renovascular disease.

Methods

Patients in the Salford Renovascular Study who had the following biomarkers analysed on a baseline sample were included in this study: FGF-23, Cystatin C, kidney injury molecule-1, myeloperoxidase, neutrophil gelatinase-associated lipocalin, N-terminal prohormone of brain natriuretic peptide (NT-proBNP), high-sensitivity Troponin T and anti-apolipoprotein A1 IgG. Cox proportional hazards models and net reclassification index were used to study the effects of either individual or a panel of biomarkers on predicting death, end-stage kidney disease and cardiovascular events.

Results

A total of 112 patients were followed up for a median 59.9 months (IQR 33.6–86.9). In total, 75 patients died, 21 reached end-stage kidney disease and 36 suffered a cardiovascular event. Only NT-proBNP maintained a statistically significant association with all end-points (death: HR 1.62 [95% CI 1.26–2.10], P < 0.0005; end-stage kidney disease: HR 1.51 [95% 1.19–1.91], P = 0.001; cardiovascular event: HR 1.56 [95% CI 1.23–1.97], P < 0.0005). Risk reclassification improved with addition of all biomarkers as a panel to the base model. Only patients with NT-proBNP concentrations above 300 ng/L gained benefit from revascularization with regard to all adverse end-points compared with medically managed patients.

Conclusions

NT-proBNP is independently associated with increased risk for all adverse events in atherosclerotic renovascular disease. Novel biomarkers may have an incremental risk predictive value when used in combination with traditional risk factors, and NT-proBNP may have value in patient selection for revascularization. Given the small size of this study, larger multicentre studies are required to validate these findings.

Magnetization Transfer Magnetic Resonance Imaging Noninvasively Detects Renal Fibrosis in Swine Atherosclerotic Renal Artery Stenosis at 3.0 T

OBJECTIVES

Renal fibrosis is a useful biomarker for diagnosis and evaluation of therapeutic interventions of renal diseases but often requires invasive testing. Magnetization transfer magnetic resonance imaging (MT-MRI), which evaluates the presence of macromolecules, offers a noninvasive tool to probe renal fibrosis in murine renal artery stenosis (RAS) at 16.4 T. In this study, we aimed to identify appropriate imaging parameters for collagen detection at 3.0 T MRI and to test the utility of MT-MRI in measuring renal fibrosis in a swine model of atherosclerotic RAS (ARAS).

MATERIALS AND METHODS

To select the appropriate offset frequency, an MT-MRI study was performed on a phantom containing 0% to 40% collagen I and III with offset frequencies from -1600 to +1600 Hz and other MT parameters empirically set as pulse width at 16 milliseconds and flip angle at 800 degrees. Then selected MT parameters were used in vivo on pigs 12 weeks after sham (n = 8) or RAS (n = 10) surgeries. The ARAS pigs were fed with high-cholesterol diet to induce atherosclerosis. The MT ratio (MTR) was compared with ex vivo renal fibrosis measured using Sirius-red staining.

RESULTS

Offset frequencies at 600 and 1000 Hz were selected for collagen detection without direct saturation of free water signal, and subsequently applied in vivo. The ARAS kidneys showed mild cortical and medullary fibrosis by Sirius-red staining. The cortical and medullary MTRs at 600 and 1000 Hz were both increased. Renal fibrosis measured ex vivo showed good linear correlations with MTR at 600 (cortex: Pearson correlation coefficient r = 0.87, P < 0.001; medulla: r = 0.70, P = 0.001) and 1000 Hz (cortex: r = 0.75, P < 0.001; medulla: r = 0.83, P < 0.001).

CONCLUSIONS

Magnetization transfer magnetic resonance imaging can noninvasively detect renal fibrosis in the stenotic swine kidney at 3.0 T. Therefore, MT-MRI may potentially be clinically applicable and useful for detection and monitoring of renal pathology in subjects with RAS.

Atherosclerotic Renal Artery Stenosis: Should we Intervene Earlier?

Purpose of Review

Randomized trials have failed to show clinical benefit in patients with atherosclerotic renal artery stenosis who were treated with angioplasty with or without stenting. However, these studies were done in patients with a high-grade stenosis. This paper examines whether there are arguments to consider patients with low-grade stenosis for angioplasty.

Recent Findings

Patients with low-grade (< 50%) atherosclerotic renal artery stenosis have an excess risk for cardiovascular and renal complications. This could be related to inflammatory factors being generated by the stenotic kidney. Moreover, even a kidney with low-grade stenosis clears less or produces more of the natural nitric oxide inhibitor ADMA.

Summary

Patients with low-grade atherosclerotic renal artery stenosis have an increased risk for a variety of complications. In addition, the abnormality is progressive. There is a case for setting up a prospective trial to examine whether angioplasty confers benefit in patients with low-grade renal artery stenosis.

Urinary Mitochondrial DNA Levels Identify Acute Kidney Injury in Surgical Critical Illness Patients

BACKGROUND

Recent studies showed that mitochondrial injury and mitochondrial DNA (mtDNA) damage are associated with the initiation and progression of acute kidney injury (AKI). However, practical limitations of existing assays of mitochondrial function have limited our ability to study the link between mitochondrial dysfunction and renal injury. Therefore, we evaluated urinary mtDNA (UmtDNA) as a biomarker of AKI in critical illness patients.

METHODS

DNA was isolated from urine samples in surgical intensive care unit (SICU) patients and quantified by quantitative polymerase chain reaction (PCR). Correlation analyses showed the relationships between the UmtDNA and several biomarkers of renal dysfunction. Moreover, we evaluated the predictive and diagnostic values of UmtDNA in newly developed AKI, renal replacement therapy (RRT), and hospital mortality using receiver operating characteristics curves.

RESULTS

MtDNA were expressed as PCR threshold cycle (Tc) number. Lower Tc indicated increased urinary mtDNA concentration. The baseline UmtDNA levels were elevated in SICU patients especially in AKI patients, compared with that in healthy controls. UmtDNA Tc number inversely correlated with serum creatine and urinary neutrophil gelatinase-associated lipocalin and directly with estimated glomerular filtration rate. Furthermore, baseline UmtDNA levels had high effectiveness in predicting development of AKI, initiation of RRT, and hospital mortality.

CONCLUSIONS

Elevated UmtDNA levels could identify newly developed AKI and predict RRT or hospital mortality in SICU patients. UmtDNA Tc number correlated with markers of renal injury and dysfunction, suggesting the involvement of mitochondrial injury in kidney damage among surgical critical illness patients.

Mitoprotection attenuates myocardial vascular impairment in porcine metabolic syndrome

Metabolic syndrome (MetS) leads to cardiac vascular injury, which may reflect in increased retention of endothelial progenitor cells (EPCs). Coronary endothelial cell (EC) mitochondria partly regulate vascular function and structure. We hypothesized that chronic mitoprotection would preserve EC mitochondria and attenuate coronary vascular injury and dysfunction in swine MetS. Pigs were studied after 16 wk of diet-induced MetS, MetS treated for the last 4 wk with the mitochondria-targeted peptide elamipretide (ELAM; 0.1 mg/kg sc once daily), and lean controls ( n = 6 each). Cardiac remodeling and function were assessed in vivo by multidetector-computed tomography (CT), and coronary artery and sinus blood samples were collected. EC mitochondrial density, apoptosis, oxidative stress, endothelial nitric oxide synthase immunoreactivity, myocardial microvascular density (three-dimensional microcomputed tomography), and coronary endothelial function (organ bath) were assessed ex vivo. The number and arteriovenous gradient of CD34⁺/KDR⁺ EPCs were calculated by FACS (a negative net gradient indicating EPC retention). MetS and MetS + ELAM pigs developed similar MetS (obesity, hyperlipidemia, insulin resistance, and hypertension). EC mitochondrial density decreased in MetS animals compared with lean animals but normalized in MetS + ELAM animals. ELAM also attenuated EC oxidative stress and apoptosis and improved subendocardial microvascular density. ELAM-induced vasculoprotection was reflected by decreased coronary retention of EPCs. ELAM also partly improved endothelial nitric oxide synthase immunoreactivity, coronary endothelial function, and vessel maturity, whereas myocardial perfusion was unaffected. Chronic mitoprotection improved coronary EC mitochondrial density and decreased vascular remodeling and dysfunction. However, additional mitochondria-independent mechanisms likely contribute to MetS-induced cardiac vascular injury. NEW & NOTEWORTHY The present study shows that chronic mitoprotection preserved coronary endothelial cell mitochondria and decreased vascular injury, subendocardial microvascular loss, coronary retention of endothelial progenitor cells, and release of markers of vascular injury. However, myocardial perfusion remained blunted, suggesting that additional mitochondria-independent mechanisms likely contribute to metabolic syndrome-induced cardiac vascular injury.

Glomerular Hyperfiltration in Obese African American Hypertensive Patients Is Associated With Elevated Urinary Mitochondrial-DNA Copy Number

BACKGROUND

Glomerular hyperfiltration may contribute to the high incidence of renal disease in Obese African Americans essential hypertensive (ObAAEH) patients, but the precise mechanisms responsible for renal injury have not been elucidated. Mitochondria are important determinants of renal injury in hypertension, and increased levels of mitochondrial DNA (mtDNA) in the urine may indicate renal mitochondrial injury. We hypothesized that urine mtDNA copy numbers would be higher in ObAAEH compared to Caucasian essential hypertensive (CEH) patients.

METHODS

We prospectively measured systemic, renal vein (RV), inferior vena cava (IVC), and urinary copy number of the mtDNA genes COX3 and ND1 by quantitative-PCR in CEH and ObAAEH patients during constant sodium intake and antihypertensive regimens, and compared them with healthy volunteers (HV) (n = 23 each).

RESULTS

Blood pressure was similarly elevated in CEH and ObAAEH, while glomerular filtration rate (GFR) was higher and age lower in ObAAEH. Urinary (but not plasma) COX3 and ND1 were higher in CEH compared to HV, and further elevated in ObAAEH patients. COX3 and ND1 renal gradients (RV-IVC) were higher in ObAAEH vs. CEH, and their urinary levels directly correlated with GFR. In multivariate analysis, GFR remained the only predictor of elevated urinary COX3 and ND1 levels.

CONCLUSIONS

Urinary fragments of the mitochondrial genome are elevated in ObAAEH patients and correlate with glomerular hyperfiltration. A positive gradient across the kidney in ObAAEH suggests selective renal release. These results are consistent with mitochondrial injury that may aggravate renal damage and accelerate hypertension-related morbidity/mortality rates in ObAAEH.

Autologous Mesenchymal Stem Cells Increase Cortical Perfusion in Renovascular Disease

Atherosclerotic renovascular disease (RVD) reduces renal blood flow (RBF) and GFR and accelerates poststenotic kidney (STK) tissue injury. Preclinical studies indicate that mesenchymal stem cells (MSCs) can stimulate angiogenesis and modify immune function in experimental RVD. We assessed the safety and efficacy of adding intra-arterial autologous adipose-derived MSCs into STK to standardized medical treatment in human subjects without revascularization. The intervention group (n=14) received a single infusion of MSC (1.0 × 10⁵ or 2.5 × 10⁵ cells/kg; n=7 each) plus standardized medical treatment; the medical treatment only group (n=14) included subjects matched for age, kidney function, and stenosis severity. We measured cortical and medullary volumes, perfusion, and RBF using multidetector computed tomography. We assessed tissue oxygenation by blood oxygen level-dependent MRI and GFR by iothalamate clearance. MSC infusions were well tolerated. Three months after infusion, cortical perfusion and RBF rose in the STK (151.8-185.5 ml/min, P=0.01); contralateral kidney RBF increased (212.7-271.8 ml/min, P=0.01); and STK renal hypoxia (percentage of the whole kidney with R2*>30/s) decreased (12.1% [interquartile range, 3.3%-17.8%] to 6.8% [interquartile range, 1.8%-12.9%], P=0.04). No changes in RBF occurred in medical treatment only subjects. Single-kidney GFR remained stable after MSC but fell in the medical treatment only group (-3% versus -24%, P=0.04). This first-in-man dose-escalation study provides evidence of safety of intra-arterial infusion of autologous MSCs in patients with RVD. MSC infusion without main renal artery revascularization associated with increased renal tissue oxygenation and cortical blood flow.

Mesenchymal stem cell-derived extracellular vesicles attenuate kidney inflammation

Mesenchymal stem/stromal cells (MSCs) have distinct capability for renal repair, but may have safety concerns. MSC-derived extracellular vesicles emerged as a novel noncellular alternative. Using a porcine model of metabolic syndrome and renal artery stenosis we tested whether extracellular vesicles attenuate renal inflammation, and if this capacity is mediated by their cargo of the anti-inflammatory cytokine interleukin (IL) 10. Pigs with metabolic syndrome were studied after 16 weeks of renal artery stenosis untreated or treated four weeks earlier with a single intrarenal delivery of extracellular vesicles harvested from adipose tissue-derived autologous MSCs. Lean and sham metabolic syndrome animals served as controls (seven each). Five additional pigs with metabolic syndrome and renal artery stenosis received extracellular vesicles with pre-silenced IL10 (IL10 knock-down). Single-kidney renal blood flow, glomerular filtration rate, and oxygenation were studied in vivo and renal injury pathways ex vivo. Retention of extracellular vesicles in the stenotic kidney peaked two days after delivery and decreased thereafter. Four weeks after injection, extracellular vesicle fragments colocalized with stenotic-kidney tubular cells and macrophages, indicating internalization or fusion. Extracellular vesicle delivery attenuated renal inflammation, and improved medullary oxygenation and fibrosis. Renal blood flow and glomerular filtration rate fell in metabolic syndrome and renal artery stenosis compared to metabolic syndrome, but was restored in pigs treated with extracellular vesicles. These renoprotective effects were blunted in pigs treated with IL10-depleted extracellular vesicles. Thus, extracellular vesicle-based regenerative strategies might be useful for patients with metabolic syndrome and renal artery stenosis.

NGAL as an Early Predictive Marker of Diabetic Nephropathy in Children and Young Adults with Type 1 Diabetes Mellitus

AIMS

Type 1 diabetes (T1D) is often associated with early microvascular complications. Previous studies demonstrated that increased systolic (SAP) and diastolic arterial blood pressures (DAP) are linked to microvascular morbidity in T1D. The aim of the study was to investigate the predictive role of neutrophil gelatinase-associated lipocalin (NGAL) in unravelling early cardio-renal dysfunction in T1D.

METHODS

Two T1D patient groups participating in two-centre prospective cohorts were studied. Group A consisted of 57 participants aged 13.9 years (SD: 3.1) and group B consisted of 59 patients aged 28.0 years (SD: 4.4). Forty-nine healthy children [age: 10.5 years (SD: 6.6)] and 18 healthy adults [age 27.7 years (SD: 4.2)] served as controls. Serum concentrations of NGAL (ELISA) were determined, and SAP and DAP were examined (SAP and DAP also expressed as z-scores in the younger group).

RESULTS

NGAL correlated positively with SAP in both patient groups (P = 0.020 and P = 0.031, resp.) and SAP z-score (P = 0.009) (group A) and negatively with eGFR in both groups (P < 0.001 and P < 0.001, resp.).

CONCLUSIONS

NGAL may be proposed as a biomarker of early renal dysfunction even in nonalbuminuric T1D patients, since it was strongly associated with renal function decline and increasing systolic arterial pressure even at prehypertensive range in people with T1D, in a broad age range.

Atherosclerotic renal artery stenosis is associated with elevated cell cycle arrest markers related to reduced renal blood flow and postcontrast hypoxia

BACKGROUND

Atherosclerotic renal artery stenosis (ARAS) reduces renal blood flow (RBF), ultimately leading to kidney hypoxia and inflammation. Insulin-like growth factor binding protein-7 (IGFBP-7) and tissue inhibitor of metalloproteinases-2 (TIMP-2) are biomarkers of cell cycle arrest, often increased in ischemic conditions and predictive of acute kidney injury (AKI). This study sought to examine the relationships between renal vein levels of IGFBP-7, TIMP-2, reductions in RBF and postcontrast hypoxia as measured by blood oxygen level-dependent (BOLD) magnetic resonance imaging.

METHODS

Renal vein levels of IGFBP-7 and TIMP-2 were obtained in an ARAS cohort (n= 29) scheduled for renal artery stenting and essential hypertensive (EH) healthy controls (n = 32). Cortical and medullary RBFs were measured by multidetector computed tomography (CT) immediately before renal artery stenting and 3 months later. BOLD imaging was performed before and 3 months after stenting in all patients, and a subgroup (N = 12) underwent repeat BOLD imaging 24 h after CT/stenting to examine postcontrast/procedure levels of hypoxia.

RESULTS

Preintervention IGFBP-7 and TIMP-2 levels were elevated in ARAS compared with EH (18.5 ± 2.0 versus 15.7 ± 1.5 and 97.4 ± 23.1 versus 62.7 ± 9.2 ng/mL, respectively; P< 0.0001); baseline IGFBP-7 correlated inversely with hypoxia developing 24 h after contrast injection (r = -0.73, P< 0.0001) and with prestent cortical blood flow (r = -0.59, P= 0.004).

CONCLUSION

These data demonstrate elevated IGFBP-7 and TIMP-2 levels in ARAS as a function of the degree of reduced RBF. Elevated baseline IGFBP-7 levels were associated with protection against postimaging hypoxia, consistent with 'ischemic preconditioning'. Despite contrast injection and stenting, AKI in these high-risk ARAS subjects with elevated IGFBP-7/TIMP-2 was rare and did not affect long-term kidney function.

Urinary Mitochondrial DNA Copy Number Identifies Chronic Renal Injury in Hypertensive Patients

Mitochondrial injury contributes to renal dysfunction in several models of renal disease, but its involvement in human hypertension remains unknown. Fragments of the mitochondrial genome released from dying cells are considered surrogate markers of mitochondrial injury. We hypothesized that hypertension would be associated with increased urine mitochondrial DNA (mtDNA) copy numbers. We prospectively measured systemic and urinary copy number of the mtDNA genes cytochrome-c oxidase-3 and NADH dehydrogenase subunit-1 by quantitative polymerase chain reaction in essential (n=25) and renovascular (RVH, n=34) hypertensive patients and compared them with healthy volunteers (n=22). Urinary kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin served as indices of renal injury. Renal blood flow and oxygenation were assessed by multidetector computed tomography and blood oxygen level-dependent magnetic resonance imaging. Blood pressure, urinary neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1 were similarly elevated in essential hypertension and RVH, and estimated glomerular filtration rate was lower in RVH versus healthy volunteers and essential hypertension. Renal blood flow was lower in RVH compared with essential hypertension. Urinary mtDNA copy number was higher in hypertension compared with healthy volunteers, directly correlated with urinary neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 and inversely with estimated glomerular filtration rate. In RVH, urinary mtDNA copy number correlated directly with intrarenal hypoxia. Furthermore, in an additional validation cohort, urinary mtDNA copy number was higher in RVH compared with healthy volunteers (n=10 each). The change in serum creatinine levels and estimated glomerular filtration rate 3 months after medical therapy without or with revascularization correlated with the change in urinary mtDNA. Therefore, elevated urinary mtDNA copy numbers in hypertensive patients correlated with markers of renal injury and dysfunction, implicating mitochondrial injury in kidney damage in human hypertension.

Chronic renal ischemia in humans: can cell therapy repair the kidney in occlusive renovascular disease?

Occlusive renovascular disease caused by atherosclerotic renal artery stenosis (ARAS) elicits complex biological responses that eventually lead to loss of kidney function. Recent studies indicate a complex interplay of oxidative stress, endothelial dysfunction, and activation of fibrogenic and inflammatory cytokines as a result of atherosclerosis, hypoxia, and renal hypoperfusion in this disorder. Human studies emphasize the limits of the kidney adaptation to reduced blood flow, eventually leading to renal hypoxia with activation of inflammatory and fibrogenic pathways. Several randomized prospective clinical trials show that stent revascularization alone in patients with atherosclerotic renal artery stenosis provides little additional benefit to medical therapy once these processes have developed and solidified. Experimental data now support developing adjunctive cell-based measures to support angiogenesis and anti-inflammatory renal repair mechanisms. These data encourage the study of endothelial progenitor cells and/or mesenchymal stem/stromal cells for the repair of damaged kidney tissue.

Differences in GFR and Tissue Oxygenation, and Interactions between Stenotic and Contralateral Kidneys in Unilateral Atherosclerotic Renovascular Disease

BACKGROUND AND OBJECTIVES

Atherosclerotic renal artery stenosis (ARAS) can reduce renal blood flow, tissue oxygenation, and GFR. In this study, we sought to examine associations between renal hemodynamics and tissue oxygenation with single-kidney function, pressor hormones, and inflammatory biomarkers in patients with unilateral ARAS undergoing medical therapy alone or stent revascularization.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Nonrandomized inpatient studies were performed in patients with unilateral ARAS (>60% occlusion) before and 3 months after revascularization (n=10) or medical therapy (n=20) or patients with essential hypertension (n=32) under identical conditions. The primary study outcome was change in single-kidney GFR. Individual kidney hemodynamics and volume were measured using multidetector computed tomography. Tissue oxygenation (using R(2)* as a measure of deoxyhemoglobin) was determined by blood oxygen level-dependent magnetic resonance imaging at 3 T. Renal vein neutrophil gelatinase-associated lipocalin (NGAL), monocyte chemoattractant protein-1 (MCP-1), and plasma renin activity were measured.

RESULTS

Total GFR did not change over 3 months in either group, but the stenotic kidney (STK) GFR rose over time in the stent compared with the medical group (+2.2[-1.8 to 10.5] versus -5.3[-7.3 to -0.3] ml/min; P=0.03). Contralateral kidney (CLK) GFR declined in the stent group (43.6±19.7 to 36.6±19.5 ml/min; P=0.03). Fractional tissue hypoxia fell in the STK (fraction R(2)* >30/s: 22.1%±20% versus 14.9%±18.3%; P<0.01) after stenting. Renal vein biomarkers correlated with the degree of hypoxia in the STK: NGAL(r=0.3; P=0.01) and MCP-1(r=0.3; P=0.02; more so after stenting). Renal vein NGAL was inversely related to renal blood flow in the STK (r=-0.65; P<0.001). Biomarkers were highly correlated between STK and CLK, NGAL (r=0.94; P<0.001), and MCP-1 (r=0.96; P<0.001).

CONCLUSIONS

These results showed changes over time in single-kidney GFR that were not evident in parameters of total GFR. Furthermore, they delineate the relationship of measurable tissue hypoxia within the STK and markers of inflammation in human ARAS. Renal vein NGAL and MCP-1 indicated persistent interactions between the ischemic kidney and both CLK and systemic levels of inflammatory cytokines.

Atherosclerotic renal artery stenosis: current status

Atherosclerotic renal artery stenosis (ARAS) remains a major cause of secondary hypertension and kidney failure. Randomized prospective trials show that medical treatment should constitute the main therapeutic approach in ARAS. Regardless of intensive treatment and adequate blood pressure control, however, renal and extrarenal complications are not uncommon. Yet, the precise mechanisms, accurate detection, and optimal treatment in ARAS remain elusive. Strategies oriented to early detection and targeting these pathogenic pathways might prevent development of clinical end points. Here, we review the results of recent clinical trials, current understanding of the pathogenic mechanisms, novel imaging techniques to assess kidney damage in ARAS, and treatment options.

Paradigm Shifts in Atherosclerotic Renovascular Disease: Where Are We Now?

Results of recent clinical trials and experimental studies indicate that whereas atherosclerotic renovascular disease can accelerate both systemic hypertension and tissue injury in the poststenotic kidney, restoring vessel patency alone is insufficient to recover kidney function for most subjects. Kidney injury in atherosclerotic renovascular disease reflects complex interactions among vascular rarefication, oxidative stress injury, and recruitment of inflammatory cellular elements that ultimately produce fibrosis. Classic paradigms for simply restoring blood flow are shifting to implementation of therapy targeting mitochondria and cell-based functions to allow regeneration of vascular, glomerular, and tubular structures sufficient to recover, or at least stabilize, renal function. These developments offer exciting possibilities of repair and regeneration of kidney tissue that may limit progressive CKD in atherosclerotic renovascular disease and may apply to other conditions in which inflammatory injury is a major common pathway.

Extrarenal atherosclerotic disease blunts renal recovery in patients with renovascular hypertension

BACKGROUND

Atherosclerotic renovascular disease (ARVD) is associated with high rates of coronary events and predicts mortality among patients with coronary artery disease (CAD). However, the impact of coronary atherosclerosis on renal outcomes after revascularization of ARVD is unclear. We hypothesized that CAD negatively impacts renal functional outcomes among patients with ARVD undergoing renal artery revascularization.

METHODS

Patients with ARVD who underwent echocardiography at Mayo Clinic, Rochester, Minnesota, USA between 2004 and 2012 were identified retrospectively and included if they had ejection fraction more than 50%. Renal and overall outcomes were compared among atherosclerotic renovascular disease patients with coronary artery disease (ARVD-C, n = 75) and without coronary artery disease (ARVD, n = 56), within 1 year from initial revascularization and included blood pressure control, renal function, and incident cardiovascular/cerebrovascular events.

RESULTS

Degree of renal artery stenosis was similar in both groups. ARVD-C had higher prevalence of diabetes, peripheral artery disease (PAD), and cerebrovascular disease, and lower baseline renal function. Risk of developing end-stage renal disease was higher in ARVD-C (11 vs. 2%, P = 0.05). Despite better control of blood pressure and cholesterol levels, renal function postrevascularization worsened in 15% of ARVD-C compared with 2% of ARVD (P = 0.01). Differences in clinical outcomes remained statistically significant after adjustment for covariables, including sex, baseline blood pressure, renal function, underlying diabetes, cholesterol levels, and medications. Similar differences in clinical outcomes were also associated with PAD and cerebrovascular disease.

CONCLUSION

CAD in patients with ARVD is a predictor of worse outcomes after renal revascularization, likely reflecting diffuse atherosclerotic disease. Further studies are needed to develop strategies to manage patients with vascular comorbidities and improve their outcomes.

From the 1990s to CORAL (Cardiovascular Outcomes in Renal Atherosclerotic Lesions) trial results and beyond: does stenting have a role in ischemic nephropathy?

The prevalence of atherosclerotic renal artery stenosis is high, ∼7% in individuals older than 65 years and ∼50% in patients with diffuse arterial disease, and it is increasingly frequent in an aging population. About 10% to 15% of atherosclerotic renal artery stenosis cases lead to the development of resistant hypertension and/or ischemic nephropathy. The management of ischemic nephropathy may include medical therapy and/or revascularization. In the past, revascularization required surgical bypass or endarterectomy, accompanied by the morbidity and mortality associated with a major surgical procedure. During the last few decades, less invasive endovascular procedures such as percutaneous transluminal renal artery angioplasty with stent placement have become available. At the same time, new antihypertensive and cardiovascular drugs have been developed, which may preclude revascularization, at least in some cases. The indications of each of these therapeutic options have changed over time. This review offers a temporal perspective on the course of technical and scientific advances and the accompanying change in clinical practice for the treatment of ischemic nephropathy. The latest randomized clinical trials, including the CORAL (Cardiovascular Outcomes in Renal Atherosclerotic Lesions) trial, the largest on the subject, as well as a meta-analysis of these studies, have indicated that the best approach is medical therapy alone. There is evidence that revascularization brings no additional benefit, at least in low-risk and stable atherosclerotic renal artery stenosis. High-risk patients, especially those with recurrent flash pulmonary edema, could benefit from percutaneous transluminal renal artery angioplasty and stent placement, but there is no definitive evidence and the treatment choice should take into account the risks and potential benefits of the procedure.

Circulating and renal vein levels of microRNAs in patients with renal artery stenosis

BACKGROUND

MicroRNAs (miRs) are small non-coding RNAs that are important regulators of gene expression and have been implicated in atherosclerosis. Kidney injury distal to atherosclerotic renal artery stenosis (ARAS) is aggravated by atherosclerosis. Therefore, this study tested the hypothesis that renal miR expression would be altered in patients with ARAS.

METHODS

Patients with essential hypertension (EH; n = 13) or ARAS (n = 13) underwent a 3-day protocol study under controlled conditions. For miR levels, blood samples were collected from EH and ARAS renal vein (RV) and inferior vena cava or peripheral vein of matched normotensive healthy volunteers (HV; n = 13) and patients with coronary atherosclerosis (CA; n = 11). Single-renal blood flow was measured in EH and ARAS using computer tomography to calculate renal gradients and release of miRs.

RESULTS

Glomerular filtration rate (GFR) was lower in ARAS compared with the other groups. Systemic levels of most miRs were elevated in CA. RV miR levels were lower than systemic levels in both ARAS and EH. GFR-adjusted RV levels of miR-21, 155 and 210 were reduced only in ARAS patients compared with systemic levels in HV, although cross-kidney gradients were not different from EH. RV levels of miR-21, 126, 155 and 210 correlated with GFR.

CONCLUSIONS

Levels of atherosclerosis-related miR-21, 126, 155 and 210 are decreased in the stenotic-kidney vein of ARAS compared with EH patients, likely due to decreased GFR. Yet, these miRs might be implicated in modulating renal injury in ARAS, and their RV level may be a marker reflecting their renal expression.

Clinical problems in renovascular disease and the role of nuclear medicine

Although renovascular disease remains defined as a stenosis of the main renal artery or its proximal branches (renal artery stenosis [RAS]), its clinical overview has changed dramatically over the last 15-20 years and its management is more controversial than ever before. The clinical problems, not only diagnosis and treatment but also the relative contribution of different pathophysiological mechanisms involved in the progression of kidney disease, have shifted dramatically. This presentation aims to emphasize the paradigm change revisiting the (recent) past focused on renovascular hypertension (RVH) to the current context of preservation or recovery of threatened renal function in patients with progressive atherosclerotic renovascular disease until its last stage of irreversible "ischemic nephropathy." In the past, the foreground was occupied by RVH, a very rare disease, where the activation of the renin-angiotensin-aldosterone system (RAAS) was supposed to play the major, if not only, role in RVH issues. The retrospective RVH diagnosis was established either on the improvement or, more rarely, on the cure of hypertension after revascularization by, most often, a percutaneous transluminal renal angioplasty with or without a stent placement. At this time, captoptril radionuclide renography was an efficient diagnostic tool, because it was a functional (angiotensin-converting enzyme inhibition), noninvasive test aiming to evidence both the RAAS activation and the lateralization (or asymmetry) of renin secretion by the kidney affected by a "hemodynamically significant" RAS. At present, even if captoptril radionuclide renography could be looked upon as the most efficient (and cost effective in selected high-risk patients) noninvasive, functional test to predict the improvement of hypertension after RAS correction, its clinical usefulness is questioned as the randomized, prospective trials failed to demonstrate any significant benefits (either on blood pressure control or on renal function protection) of the revascularization over current antihypertensive therapy. Today many patients with RVH remain undetected for years because they are treated successfully and at low expense with these new blockers of RAAS. In addition to its well-known role in hemodynamics, angiotensin II promotes activations of profibrogenic and inflammatory factors and cells and stimulates reactive oxygen species generation. The "atherosclerotic milieu" itself plays a role in the loss of renal microvessels and defective angiogenesis. After an "adaptative" phase, ischemia eventually develops and induces hypoxia, the substratum of ischemic nephropathy. Because blood oxygen level-dependent MRI may provide an index of oxygen content in vivo, it may be useful to predict renal function outcome after percutaneous transluminal renal angioplasty. New PET tracers, dedicated to assess RAAS receptors, inflammatory cell infiltrates, angiogenesis, and apoptose, would be tested in this context of atherosclerotic renovascular disease.

Management of atherosclerotic renovascular disease after Cardiovascular Outcomes in Renal Atherosclerotic Lesions (CORAL)

Many patients with occlusive atherosclerotic renovascular disease (ARVD) may be managed effectively with medical therapy for several years without endovascular stenting, as demonstrated by randomized, prospective trials including the Cardiovascular Outcomes in Renal Atherosclerotic Lesions (CORAL) trial, the Angioplasty and Stenting for Renal Artery Lesions (ASTRAL) trial and the Stent Placement and Blood Pressure and Lipid-Lowering for the Prevention of Progression of Renal Dysfunction Caused by Atherosclerotic Ostial Stenosis of the Renal Artery (STAR) and ASTRAL. These trials share the limitation of excluding subsets of patients with high-risk clinical presentations, including episodic pulmonary edema and rapidly progressing renal failure and hypertension. Although hemodynamically significant, ARVD can reduce renal blood flow and glomerular filtration rate; adaptive mechanisms preserve both cortical and medullary oxygenation over a wide range of vascular occlusion. Progression of ARVD to severe vascular compromise eventually produces cortical hypoxia, however, associated with active inflammatory cytokine release and cellular infiltration of the renal parenchyma. In such cases ARVD produces a loss of glomerular filtration rate that no longer is reversible simply by restoring vessel patency with technically successful renal revascularization. Each of these trials reported adverse renal functional outcomes ranging between 16 and 22% over periods of 2-5 years of follow-up. Blood pressure control and medication adjustment may become more difficult with declining renal function and may prevent the use of angiotensin receptor blocker and angiotensin-converting enzyme inhibitors. The objective of this review is to evaluate the current management of ARVD for clinical nephrologists in the context of recent randomized clinical trials and experimental research.

Cardiac function in renovascular hypertensive patients with and without renal dysfunction

BACKGROUND

Hypertension impairs left ventricular (LV) diastolic and systolic function, which might be aggravated by inflammation or neurohumoral activation. We hypothesized that LV diastolic dysfunction is more common in patients with renovascular hypertension (RVHT) compared with essential hypertension (EHT).

METHODS

Hypertensive patients who underwent both renal imaging to exclude RVHT and cardiac echocardiography within a 3-year period were identified retrospectively. Patients with significant renovascular disease were included in the RVHT group (n = 75); those without significant renovascular disease were included in the EHT group (n = 69). Cardiac function and structure were compared.

RESULTS

Baseline renal function was preserved (serum creatinine ≤ 2mg/dl) in EHT patients and impaired (serum creatinine > 2mg/dl) in only 9 RVHT patients. RVHT patients had higher systolic blood pressure, E/e' ratio, and greater prevalence of concentric hypertrophy but lower estimated glomerular-filtration-rate (eGFR) compared with EHT patients. Increased prevalence of LV diastolic dysfunction remained statistically significant in patients with RVHT after multivariable adjustment for age, sex, blood pressure, eGFR, diabetes, smoking, and statin use, with a relative risk (95% CI) for abnormal E/e' of 1.70 (95% confidence interval = 1.05-2.90; P = 0.03) compared with EHT. RVHT patients with severe renal dysfunction showed greater impairments in cardiac systolic and diastolic function compared with those in EHT patients or preserved renal function RVHT patients.

CONCLUSIONS

Among hypertensive patients undergoing echocardiography, cardiac structure and diastolic function are impaired in RVHT patients compared with EHT patients and remain different after adjustment for multiple significant covariables. When associated with significant renal dysfunction, RVHT aggravates LV hypertrophy and both systolic and diastolic dysfunction. Hence, identification of RVHT and renal dysfunction warrants development of targeted management strategies.

Darkness at the end of the tunnel: poststenotic kidney injury

Renal artery stenosis remains an important contributor to renal failure in the elderly population, but uncertainty continues to surround the mechanisms underlying progressive renal dysfunction. Here, we present the current understanding of the pathogenic mechanisms responsible for renal injury in these patients, with emphasis on those involved in disease progression.

Association of neutrophil gelatinase associated lipocalin and cystatin-C with kidney function in children with nephrotic syndrome

BACKGROUND

Nephrotic syndrome (NS) is a major clinical concern in human health, especially in children. Despite of the etiology, the prediction of remission in different treatment regimens based on suitable biomarkers is under development. The goal of this evaluation was the demonstration of correlation between serum level of Neutrophil gelatinase associated lipocalin (NGAL) and cystatin-C with kidney function in patients with NS.

METHODS

During the period between September 2008 and December 2011, 52 patients admitted to St. Al Zahra University Hospital were selected for evaluation. The measured parameters consisted of NGAL, cystatin-C, creatinine, albumin, blood urea nitrogen, urine protein, glomerular filtration rate. Demographic data were collected and considered in comparisons. Comparison between variables and their correlations were examined.

RESULTS

Means of serum NGAL and cystatin-C were significantly higher in case than the control group, P < 0.05. The mean of serum NGAL in patients without remission and who achieved remission were 23.09 (standard deviation [SD] ±10.11) and 36.26 (SD ± 20.10) ng/ml respectively; P < 0.05. Serum NGAL levels had a correlation with the following factors: Systolic blood pressure, diastolic blood pressure (DBP), cystatin-C, remission. Linear regression analysis showed a significant correlation between cystatin-C and systolic and DBP.

CONCLUSIONS

Based on the results, serum NGAL can be used as a prognostic marker for remission. In addition, NGAL and cystatin-C are biomarkers of kidney injury in NS.

Stent revascularization restores cortical blood flow and reverses tissue hypoxia in atherosclerotic renal artery stenosis but fails to reverse inflammatory pathways or glomerular filtration rate

BACKGROUND

Atherosclerotic renal artery stenosis (ARAS) is known to reduce renal blood flow, glomerular filtration rate (GFR) and amplify kidney hypoxia, but the relationships between these factors and tubulointerstitial injury in the poststenotic kidney are poorly understood. The purpose of this study was to examine the effect of renal revascularization in ARAS on renal tissue hypoxia and renal injury.

METHODS AND RESULTS

Inpatient studies were performed in patients with ARAS (n=17; >60% occlusion) before and 3 months after stent revascularization, or in patients with essential hypertension (n=32), during fixed Na(+) intake and angiotensin converting enzyme/angiotensin receptors blockers Rx. Single kidney cortical, medullary perfusion, and renal blood flow were measured using multidetector computed tomography, and GFR by iothalamate clearance. Tissue deoxyhemoglobin levels (R(2)*) were measured by blood oxygen level-dependent MRI at 3T, as was fractional kidney hypoxia (percentage of axial area with R(2)*>30/s). In addition, we measured renal vein levels of neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, and tumor necrosis factor-α. Pre-stent single kidney renal blood flow, perfusion, and GFR were reduced in the poststenotic kidney. Renal vein neutrophil gelatinase-associated lipocalin, tumor necrosis factor-α, monocyte chemoattractant protein-1, and fractional hypoxia were higher in untreated ARAS than in essential hypertension. After stent revascularization, fractional hypoxia fell (P<0.002) with increased cortical perfusion and blood flow, whereas GFR and neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, and tumor necrosis factor-α remained unchanged.

CONCLUSIONS

These data demonstrate that despite reversal of renal hypoxia and partial restoration of renal blood flow after revascularization, inflammatory cytokines and injury biomarkers remained elevated and GFR failed to recover in ARAS. Restoration of vessel patency alone failed to reverse tubulointerstitial damage and partly explains the limited clinical benefit of renal stenting. These results identify potential therapeutic targets for recovery of kidney function in renovascular disease.

Increased circulating inflammatory endothelial cells in blacks with essential hypertension

Morbidity and mortality attributable to hypertension are higher in black essential hypertensive (EH) compared with white EH patients, possibly related to differential effects on vascular injury and repair. Although circulating endothelial progenitor cells (EPCs) preserve endothelial integrity, inflammatory endothelial cells (IECs) detach from sites of injury and represent markers of vascular damage. We hypothesized that blood levels of IECs and inflammatory markers would be higher in black EH compared with white EH patients. Inferior vena cava and renal vein levels of CD34+/KDR+ (EPC) and VAP-1+ (IEC) cells were measured by fluorescence-activated cell sorting in white EH and black EH patients under fixed sodium intake and blockade of the renin-angiotensin system, and compared with systemic levels in normotensive control subjects (n=19 each). Renal vein and inferior vena cava levels of inflammatory cytokines and EPC homing factors were measured by Luminex. Blood pressure, serum creatinine, lipids, and antihypertensive medications did not differ between white and black EH patients, and EPC levels were decreased in both. Circulating IEC levels were elevated in black EH patients, and inversely correlated with EPC levels (R(2)=0.58; P=0.0001). Systemic levels of inflammatory cytokines and EPC homing factors were higher in black EH compared with white EH patients, and correlated directly with IECs. Renal vein inflammatory cytokines, EPCs, and IECs did not differ from their circulating levels. Most IECs expressed endothelial markers, fewer expressed progenitor cell markers, but none showed lymphocyte or phagocytic cell markers. Thus, increased release of cytokines and IECs in black EH patients may impair EPC reparative capacity and aggravate vascular damage, and accelerate hypertension-related complications.

Angiotensin receptor blockade has protective effects on the poststenotic porcine kidney

Angiotensin converting enzyme inhibitors (ACEI)/ angiotensin-II receptor blockers (ARBs) may induce an acute decrease of glomerular filtration rate (GFR) in the stenotic kidney in renal artery stenosis, but most patients tolerate these drugs well. We hypothesized that ACEI/ARBs stabilize stenotic kidney function during prolonged treatment by conferring protective effects. We tested this in control domestic pigs and pigs with renal artery stenosis untreated or treated with valsartan, or triple therapy (7 pigs in each group) for 4 weeks starting 6 weeks after stenosis induction. Renal function, oxygenation, tubular function, and microcirculation were assessed by multi-detector computed tomography (CT), blood-oxygen-level-dependent magnetic-resonance imaging, and micro-CT. Valsartan and triple therapy decreased blood pressure similarly, however, valsartan did not change the GFR of the stenotic kidney compared to renal artery stenosis and was similar to triple therapy. Both valsartan and triple therapy stimulated microvascular density, and improved tubular function. Valsartan also caused a greater increase of angiogenic factors and a decrease in oxidative stress, which were related to higher cortical perfusion and tubular response than triple therapy. Thus, valsartan did not decrease stenotic kidney GFR, but improved cortical perfusion and microcirculation. These beneficial effects may partly offset the hemodynamic GFR reduction in renal artery stenosis and preserve kidney function.

Urine NGAL and KIM-1 in children and adolescents with hyperuricemia

BACKGROUND

The aim of this study was to test the hypothesis that urine levels of neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) are enhanced in pediatric patients with hyperuricemia.

METHODS

The study included 88 children and adolescents (60 males, 28 females) with a median age of 16 (range 11-18.5) years who had been referred to our department to rule out or confirm hypertension. The subjects were divided into two groups: the hyperuricemic (HU) group comprising 59 subjects with hyperuricemia (defined as serum uric acid >4.8 and >5.5 mg/dl in girls and boys, respectively) and the reference group comprising 29 patients with normouricemia. Urine NGAL and KIM-1 levels were evaluated using a commercially available kit.

RESULTS

Concentrations of the examined biomarkers [urine NGAL, NGAL/creatinine (cr.) ratio, urine KIM-1, KIM-1/cr. ratio] were increased in the HU group compared with the reference group (p < 0.01). There were positive correlations between the serum uric acid and urine NGAL/cr. ratio (R = 0.67, p < 0.001) and the urine KIM-1/cr. ratio (R = 0.36, p < 0.001). In the multiple regression models, serum uric acid, systolic blood pressure and cholesterol accounted for more than 49 % of the variation in the NGAL/cr. ratio (R = 0.702, p < 0.001). In the second model, serum uric acid, gender, age and systolic blood pressure accounted for more than 36 % of the variation in the KIM-1/cr. ratio (R = 0.604, p < 0.001).

CONCLUSION

We demonstrated that male, obese, hypertensive adolescents with hyperuricemia have higher urine NGAL and KIM-1 levels relative to a reference group with normouricemia.

Serum Neutrophil Gelatinase-Associated Lipocalin versus Serum Creatinine for the Prediction of Acute Kidney Injury after Liver Transplantation

BACKGROUND

Acute kidney injury (AKI) is a common complication after liver transplantation (LT), and considerably increases the morbidity and mortality of the procedure. The gold standard of measuring the kidney function, the serum creatinine level (sCr), has poor specificity and sensitivity for the early diagnosis of AKI. Novel biomarkers for the prediction or early diagnosis of AKI, would potentially increase the opportunities for therapeutic interventions.

OBJECTIVE

To compare the diagnostic value of the standard renal marker, sCr and neutrophil gelatinase-associated lipocalin (NGAL) to predict AKI within 48 hours of LT.

METHODS

During a 9-month period from 2010 to 2011, NGAL was measured two times in 90 patients who underwent LT from deceased donors-after induction of anesthesia (NGAL1) and 2 hours after reperfusion of the liver graft (NGAL2). Patients were grouped according to the presence of risk factors for developing AKI according to the Acute Kidney Injury Network criteria (increase of ≥0.3 mg/dL in plasma creatinine above the baseline value within 48 hours).

RESULTS

60 men and 30 women with mean±SD age of 40.2±14.2 years were included in this study. The incidence of AKI was 34% (95% CI: 24%-44%). The difference between the NGAL1 and NGAL2 (ΔNGAL) and the baseline NGAL concentration was predictive of AKI in all patients. Receiver operating characteristic (ROC) curve and area under curves (AUCs) of ΔNGAL and sCr levels during the first 48 hours of LT were similar in predicting AKI. The AUCs of the ΔNGAL to predict AKI was 0.64 (95% CI: 0.52-0.76). The development of AKI was significantly correlated with the number of units of fresh frozen plasma transfused intra-operatively (p=0.017) and cold ischemic time (p=0.042).

CONCLUSION

Serum NGAL concentrations obtained during surgery is a predictor of AKI in patients undergoing LT.