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

Stem cells prevent long-term deterioration of renal function after renal artery revascularization in a renovascular hypertension model in rats

Partial stenosis of the renal artery causes renovascular hypertension (RVH) and is accompanied by chronic renal ischemia, resulting in irreversible kidney damage. Revascularization constitutes the most efficient therapy for normalizing blood pressure (BP) and has significant benefits for renal function; however, the tissue damage caused by chronic hypoxia is not fully reversed. Mesenchymal stem cells (MSCs) have produced discrete results in minimizing RVH and renal tissue and functional improvements since the obstruction persists. This study aimed to evaluate the effects of administration of MSCs in combination with renal artery revascularization in rats subjected to RVH. The following groups were evaluated: control (SHAM), hypertensive (2K-1C), hypertensive treated with MSCs (MSC), hypertensive subjected to revascularization (REV), and hypertensive subjected to revascularization and treatment with MSCs (REV + MSC). The animals were followed up for 10 weeks. The animals in the MSC group received cell infusions at the 3rd, 5th, 7th and 9th weeks. In the REV and REV + MSC groups, the clip was removed by the 6th week (revascularization), and in the REV + MSC group, MSCs infusion was performed at the 6th and 8th weeks. Tail systolic blood pressure (SBP) was measured weekly, and histological parameters and renal function were evaluated at the end of the protocol. The clipped animals developed RVH, deterioration of total renal function (50% decrease in creatinine clearance), and significant proteinuria (15x increase). Treatment with MSCs had no detectable beneficial effects on kidney function or SBP. REV resulted in normalization of BP and a significant but partial reduction in proteinuria (80% vs. 2K-1C), but areas with renal fibrosis persisted. The combination of the two treatments was effective at normalizing all renal parameters as well as reversing proteinuria, reducing the number of ischemic glomeruli and atrophic tubules, indicating an improvement of the renal parenchyma. The results suggest that therapy with MSCs associated with revascularization can potentially help in the full recovery of renal function in the long term in patients with RVH.

Selective venous sampling for secondary hypertension

Selective venous sampling (SVS), an invasive radiographic procedure that depends on contrast media, holds a unique role in diagnosing and guiding the treatment of certain types of secondary hypertension, particularly in patients who may be candidates for curative surgery. The adrenal venous sampling (AVS), in particular, is established as the gold standard for localizing and subtyping primary aldosteronism (PA). Throughout decades of clinical practice, AVS could be applied not only to PA but also to other endocrine diseases, such as adrenal Cushing syndrome (ACS) and Pheochromocytomas (PCCs). Notably, the application of AVS in ACS and PCCs remains less recognized compared to PA, with the low success rate of catheterization, the controversy of results interpretation, and the absence of a standardized protocol. Additionally, the AVS procedure necessitates enhancements to boost its success rate, with several helpful but imperfect methods emerging, yet continued exploration remains essential. We also observed renal venous sampling (RVS), an operation akin to AVS in principle, serves as an effective means of diagnosing renin-dependent hypertension, aiding in the identification of precise sources of renin excess and helping the selection of surgical candidates with renin angiotensin aldosterone system (RAAS) abnormal activation. Nonetheless, further basic and clinical research is needed. Selective venous sampling (SVS) can be used in identifying cases of secondary hypertension that are curable by surgical intervention. Adrenal venous sampling (AVS) and aldosterone measurement for classificatory diagnosis of primary aldosteronism (PA) are established worldwide. While its primary application is for PA, AVS also holds the potential for diagnosing other endocrine disorders, including adrenal Cushing's syndrome (ACS) and pheochromocytomas (PCCs) through the measurements of cortisol and catecholamine respectively. In addition, renal venous sampling and renin measurement can help to diagnose renovascular hypertension and reninoma.

Mechanisms of inflammation modulation by different immune cells in hypertensive nephropathy

Hypertensive nephropathy (HTN) is the second leading cause of end-stage renal disease (ESRD) and a chronic inflammatory disease. Persistent hypertension leads to lesions of intrarenal arterioles and arterioles, luminal stenosis, secondary ischemic renal parenchymal damage, and glomerulosclerosis, tubular atrophy, and interstitial fibrosis. Studying the pathogenesis of hypertensive nephropathy is a prerequisite for diagnosis and treatment. The main cause of HTN is poor long-term blood pressure control, but kidney damage is often accompanied by the occurrence of immune inflammation. Some studies have found that the activation of innate immunity, inflammation and acquired immunity is closely related to the pathogenesis of HTN, which can cause damage and dysfunction of target organs. There are more articles on the mechanism of diabetic nephropathy, while there are fewer studies related to immunity in hypertensive nephropathy. This article reviews the mechanisms by which several different immune cells and inflammatory cytokines regulate blood pressure and renal damage in HTN. It mainly focuses on immune cells, cytokines, and chemokines and inhibitors. However, further comprehensive and large-scale studies are needed to determine the role of these markers and provide effective protocols for clinical intervention and treatment.

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.

Efficacy of Human Embryonic Stem Cells Compared to Adipose Tissue-Derived Human Mesenchymal Stem/Stromal Cells for Repair of Murine Post-Stenotic Kidneys

Clinical translation of mesenchymal stem/stromal cell (MSC) therapy has been impeded by the heterogenous nature and limited replicative potential of adult-derived MSCs. Human embryonic stem cell-derived MSCs (hESC-MSCs) that differentiate from immortal cell lines are phenotypically uniform and have shown promise in-vitro and in many disease models. Similarly, adipose tissue-derived MSCs (MSC(AT)) possess potent reparative properties. How these two cell types compare in efficacy, however, remains unknown. We randomly assigned mice to six groups (n = 7-8 each) that underwent unilateral RAS or a sham procedure (3 groups each). Two weeks post-operation, each mouse was administered either vehicle, MSC(AT)s, or hESC-MSCs (5 × 105 cells) into the aorta. Mice were scanned with micro-MRI to determine renal hemodynamics two weeks later and kidneys then harvested. hESC-MSCs and MSC(AT)s were similarly effective at lowering systolic blood pressure. However, MSC(AT)s more robustly increased renal perfusion, oxygenation, and glomerular filtration rate in the post-stenotic kidney, and more effectively mitigated tubular injury, fibrosis, and vascular remodeling. These observations suggest that MSC(AT) are more effective than hESC-MSC in ameliorating kidney dysfunction and tissue injury distal to RAS. Our findings highlight the importance of tissue source in selection of MSCs for therapeutic purposes and underscore the utility of cell-based therapy for kidney disease.

Perfusion and oxygenation in allografts with transplant renal artery stenosis: Evaluation with functional magnetic resonance imaging

BACKGROUND

Transplant renal artery stenosis (TRAS) has been shown to reduce kidney perfusion leading to post-operative hypertension. We aimed to measure the perfusion and oxygenation changes in TRAS with arterial spin labeling (ASL) and blood oxygen level-dependent (BOLD) imaging, respectively.

METHODS

In this single-center prospective study, a total of seven patients with TRAS and seven age- and sex-matched normal kidney transplant recipients underwent both ASL and BOLD imaging. Moreover, measurements of ASL and BOLD were also performed in five patients after successful angioplasty for TRAS.

RESULTS

Allograft cortical perfusion as measured by ASL in the TRAS group was significantly decreased as compared with normal control group (129.9 ± 46.6 ml/100 g vs. 202.4 ± 47.7 ml/100 g, P = .01). Interestingly, allograft oxygenation as indicated by R2* derived from BOLD in both the cortex (16.42 ± 1.90 Hz vs. 18.25 ± 4.34 Hz, P = .33) and the medulla (30.34 ± 2.35 Hz vs. 30.43 ± 6.85 Hz, P = .97) showed no statistical difference between the TRAS and normal control group. In addition, both cortical and medullary oxygenation remained unchanged despite significantly improved cortical perfusion in those undergone successful angioplasty.

CONCLUSION

Cortical and medullary oxygenation were preserved in the presence of reduced allograft perfusion in clinically significant TRAS. Prospective larger studies are needed to conclusively establish perfusion and oxygenation changes in TRAS.

Dynamic changes of renal cortical blood perfusion before and after percutaneous transluminal renal artery stenting in patients with severe atherosclerotic renal artery stenosis

BACKGROUND

This study aims to observe the dynamic changes of renal artery (RA) disease and cortical blood perfusion (CBP) evaluated by contrast-enhanced ultrasound (CEUS) after percutaneous transluminal renal artery stenting (PTRAS) in patients with severe atherosclerotic renal artery stenosis (ARAS) and to analyze the relationship between CBP and prognosis.

METHODS

This was a single-center retrospective cohort study. A total of 98 patients with unilateral severe ARAS after successful PTRAS in Beijing Hospital from September 2017 to September 2020 were included. According to renal glomerular filtration rate (GFR) detected by radionuclide imaging at 12 months after PTRAS, all patients were divided into the poor prognosis group (n = 21, GFR decreased by ≥20% compared with baseline) and the control group (n = 77, GFR decreased by < 20% or improved compared with baseline). Renal artery stenosis was diagnosed by digital subtraction angiography, and renal CBP was evaluated by CEUS using TomTec Imaging Systems (Germany) before PTRAS, at 6 months and 12 months after discharge. The receiver operating characteristic (ROC) curve with area under the curve (AUC) was used to analyze the predictive value of CBP parameters, including area under ascending curve (AUC1), area under the descending curve (AUC2), rising time (RT), time to peak intensity (TTP), maximum intensity (IMAX), and mean transit time (MTT) for poor prognosis.

RESULTS

Among the 98 patients, there were 52 males (53.1%), aged 55-74 years old, with an average age of 62.1 ± 8.7 years, and an average artery stenosis of 82.3 ± 12.9%. The poor prognosis group was associated with significantly increased incidence of diabetes (76.2% vs. 41.6%), and lower levels of GFR of the stenotic kidney (21.8 mL/min vs. 25.0 mL/min) and total GFR (57.6 mL/min vs. 63.7 mL/min) (all P < 0.05), compared with the control group (P < 0.05). In addition, the rate of RA restenosis was significantly higher in the poor prognosis group than in the control group (9.5% vs. 0, χ2 = 9.462, P = 0.002). Compared with the control group, the poor prognosis group was associated with significantly decreased baseline AUC1 and AUC2, and extended duration of TTP and MTT (P < 0.05). At 6 months and 12 months of follow-up, patients in the control group were associated with markedly increased AUC1, AUC2, and IMAX, and shorter duration of RT and MTT (P < 0.05). The ROC curve showed that the predictive values of AUC1, AUC2, RT, TTP, IMAX, and MTT for poor prognosis were 0.812 (95% CI: 0.698-0.945), 0.752 (95% CI: 0.591-0.957), 0.724 (95% CI: 0.569-0.961), 0.720 (95% CI: 0.522-0.993), 0.693 (95% CI: 0.507-0.947), and 0.786 (95% CI: 0.631-0.979), respectively.

CONCLUSIONS

Preoperative renal CBP in severe ARAS patients with poor prognosis is significantly reduced, and does not show significant improvement after stent treatment over the first year of follow-up. The parameter AUC1 may be a good predictor for renal dysfunction after PTRAS in severe ARAS patients. Trial Registration: ChiCTR.org.cn, ChiCTR1800016252.

Prediction of Split Renal Function Improvement After Renal Artery Stenting by Blood Oxygen Level–Dependent Magnetic Resonance Imaging

Background

The discrepancy between the high technical success rate and the relatively low clinical response rate of renal artery stenting (RAS) raises the importance to identify atherosclerotic renal artery stenosis (ARAS) patients who are most likely to benefit from RAS. This study aimed to investigate the feasibility and accuracy of blood oxygen level-dependent magnetic resonance imaging (BOLD-MRI) in predicting split renal function (SRF) improvement after RAS in patients with ARAS.

Methods

Thirty patients with severe ARAS who were treated with RAS were enrolled. Baseline cortical and medullary R2* values of each kidney were measured by BOLD-MRI, and each patient’s SRF was evaluated by nuclear renal dynamic imaging at baseline and 1-month follow-up.

Results

In total, 35 severe stenotic renal arteries of the 30 patients were analyzed. At 1-month follow-up, 34 kidneys (97.1%) of severe ARAS had acquired SRF. SRF improved in 12 kidneys of 10 patients. The cortical R2* and medullary R2* values in the SRF improvement kidneys were higher than those in the non-improvement kidneys (P ≤ 0.001). The area under the curve of medullary R2* was 0.879 (95% confidence interval [CI] 0.736–1.000). A medullary R2* value ≥29.1 s^–1 was noted to provide good sensitivity (0.833, 95% CI 0.552–0.970) and specificity (0.864, 95% CI 0.667–0.953) in predicting SRF improvement. Medullary R2* value was the only independent predictor of SRF improvement in multivariable analysis (P = 0.034, OR 3.017, 95%CI 1.089–8.358).

Conclusion

This study showed that a BOLD-MRI medullary R2* value ≥29.1 s^–1 was an excellent predictor of SRF improvement in patients with severe ARAS who underwent renal artery stenting.

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.

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.

Stem Cell Therapy for Microvascular Injury Associated with Ischemic Nephropathy

Ischemic nephropathy reflects progressive loss of kidney function due to large vessel atherosclerotic occlusive disease. Recent studies indicate that this process is characterized by microvascular rarefaction, increased tissue hypoxia and activation of inflammatory processes of tissue injury. This review summarizes the rationale and application of functional MR imaging to evaluate tissue oxygenation in human subjects that defines the limits of renal adaptation to reduction in blood flow, development of increasingly severe tissue hypoxia and recruitment of inflammatory injury pathways in ischemic nephropathy. Human mesenchymal stromal/stem cells (MSC) are capable of modifying angiogenic pathways and immune responses, but the potency of these effects vary between individuals and various clinical characteristics including age and chronic kidney disease and levels of hypoxia. We summarize recently completed first-in-human studies applying intrarenal infusion of autologous adipose-derived MSC in human subjects with ischemic nephropathy that demonstrate a rise in blood flow and reduction in tissue hypoxia consistent with partial repair of microvascular injury, even without restoring main renal arterial blood flow. Inflammatory biomarkers in the renal vein of post-stenotic kidneys fell after MSC infusion. These changes were associated with modest but significant dose-related increments in kidney function. These data provide support a role for autologous MSC in repair of microvascular injury associated with tissue hypoxia.

Mesenchymal Stem/Stromal Cell-Derived Extracellular Vesicles Elicit Better Preservation of the Intra-Renal Microvasculature Than Renal Revascularization in Pigs with Renovascular Disease

Background: Percutaneous transluminal renal angioplasty (PTRA) confers clinical and mortality benefits in select ‘high-risk’ patients with renovascular disease (RVD). Intra-renal-delivered extracellular vesicles (EVs) released from mesenchymal stem/stromal cells (MSCs) protect the kidney in experimental RVD, but have not been compared side-by-side to clinically applied interventions, such as PTRA. We hypothesized that MSC-derived EVs can comparably protect the post-stenotic kidney via direct tissue effects. Methods: Five groups of pigs (n = 6 each) were studied after 16 weeks of RVD, RVD treated 4 weeks earlier with either PTRA or MSC-derived EVs, and normal controls. Single-kidney renal blood flow (RBF) and glomerular filtration rate (GFR) were assessed in vivo with multi-detector CT, and renal microvascular architecture (3D micro CT) and injury pathways ex vivo. Results: Despite sustained hypertension, EVs conferred greater improvement of intra-renal microvascular and peritubular capillary density compared to PTRA, associated with attenuation of renal inflammation, oxidative stress, and tubulo-interstitial fibrosis. Nevertheless, stenotic kidney RBF and GFR similarly rose in both PTRA- and EV-treated pigs compared RVD + Sham. mRNA sequencing reveled that EVs were enriched with pro-angiogenic, anti-inflammatory, and antioxidants genes. Conclusion: MSC-derived EVs elicit a better preservation of the stenotic kidney microvasculature and greater attenuation of renal injury and fibrosis compared to PTRA, possibly partly attributed to their cargo of vasculo-protective genes. Yet, both strategies similarly improve renal hemodynamics and function. These observations shed light on diverse mechanisms implicated in improvement of post-stenotic kidney function and position EVs as a promising therapeutic intervention in RVD.

Progress toward the Clinical Application of Mesenchymal Stromal Cells and Other Disease-Modulating Regenerative Therapies: Examples from the Field of Nephrology

Drawing from basic knowledge of stem-cell biology, embryonic development, wound healing, and aging, regenerative medicine seeks to develop therapeutic strategies that complement or replace conventional treatments by actively repairing diseased tissue or generating new organs and tissues. Among the various clinical-translational strategies within the field of regenerative medicine, several can be broadly described as promoting disease resolution indirectly through local or systemic interactions with a patient's cells, without permanently integrating or directly forming new primary tissue. In this review, we focus on such therapies, which we term disease-modulating regenerative therapies (DMRT), and on the extent to which they have been translated into the clinical arena in four distinct areas of nephrology: renovascular disease (RVD), sepsis-associated AKI (SA-AKI), diabetic kidney disease (DKD), and kidney transplantation (KTx). As we describe, the DMRT that has most consistently progressed to human clinical trials for these indications is mesenchymal stem/stromal cells (MSCs), which potently modulate ischemic, inflammatory, profibrotic, and immune-mediated tissue injury through diverse paracrine mechanisms. In KTx, several early-phase clinical trials have also tested the potential for ex vivo-expanded regulatory immune cell therapies to promote donor-specific tolerance and prevent or resolve allograft injury. Other promising DMRT, including adult stem/progenitor cells, stem cell-derived extracellular vesicles, and implantable hydrogels/biomaterials remain at varying preclinical stages of translation for these renal conditions. To date (2021), no DMRT has gained market approval for use in patients with RVD, SA-AKI, DKD, or KTx, and clinical trials demonstrating definitive, cost-effective patient benefits are needed. Nonetheless, exciting progress in understanding the disease-specific mechanisms of action of MSCs and other DMRT, coupled with increasing knowledge of the pathophysiologic basis for renal-tissue injury and the experience gained from pioneering early-phase clinical trials provide optimism that influential, regenerative treatments for diverse kidney diseases will emerge in the years ahead.

Efficiency of Percutaneous Stent Angioplasty in Renal Artery Stenosis - 15 Years of Experience at a Single Center

PURPOSE

 To determine the therapeutic efficiency of percutaneous revascularization in renal artery stenosis (RAS), as well as the role of comprehensive factors such as patient selection and degree of artery stenosis, on clinical outcome.

METHODS AND MATERIALS

 101 patients with hemodynamically relevant RAS underwent percutaneous angioplasty (PTA). 65.7 % were male (mean age: 64 years; range: 18-84). The clinical data was retrospectively analyzed. The serum creatinine (Cr), glomerular filtration rate (GFR), and blood pressure (BP) levels pre- and postprocedural, between 6 months and 1 year, were retrospectively collected and statistically analyzed.

RESULTS

 Follow-up data was available in 34 (33.7 %) and 28 patients (27.7 %) for Cr and MAP, respectively. A significant drop in mean arterial pressure (MAP) was observed on follow-up (mean -5.27 mmHg). Higher baseline Cr and MAP values showed a more pronounced drop in the follow-up (Cr: p 0.002; difference to baseline -0.25 mg/dL, 95 %CI:-0.36, -0.07 and BP p < 0.001; diff. to baseline -0.72 mmHg; 95 %CI: -1.4, -0.40). There was no association between comorbidities, gender, and degree of stenosis with renal and BP outcome. No significant improvement in renal function was observed on follow-up (mean Cr drop: -0.015 mg/dL). The age group 51-60 years showed a significant improvement in BP (p 0.030; diff. to baseline -19.2 mmHg; 95 %CI: -34, -4.3). There was a slight reduction in antihypertensive medication following angioplasty (0.2 fewer). Minor complications were recorded in five procedures (4.9 %).

CONCLUSION

 Percutaneous renal artery revascularization in the presence of atherosclerotic RAS is a safe procedure associated with a significant drop in post-procedural BP. No significant improvement in renal function was observed. Further prospective studies focused on patient selection are necessary.

KEY POINTS

  · Percutaneous stent angioplasty in renal artery stenosis is associated with a significant improvement in post-procedural blood pressure control.. · There is no improvement in renal function after percutaneous stent angioplasty for renal artery stenosis (RAS).. · Percutaneous stent angioplasty is a safe procedure..

CITATION FORMAT

· Guerreiro H, Avanesov M, Dinnies S et al. Efficiency of Percutaneous Stent Angioplasty in Renal Artery Stenosis - 15 Years of Experience at a Single Center. Fortschr Röntgenstr 2021; 193: 298 - 304.

The Role of Hypoxia in Ischemic Chronic Kidney Disease

A gradually developing reduction in renal blood flow from atherosclerotic renovascular disease results in loss of kidney volume and a decrease in glomerular filtration rate that eventually becomes irreversible. Whether this process fundamentally reflects tissue hypoxia has been difficult to establish. Studies of human renovascular disease have indicated that reductions in blood flow of up to 30% to 40% can be tolerated with preservation of normal oxygenation and structural integrity. These observations are consistent with remarkable stability of poststenotic kidney function during sustained medical antihypertensive drug therapy in moderate renovascular disease. With more severe and sustained reductions, however, cortical oxygenation decreases and the magnitude of medullary hypoxia expands. These changes are associated with increasing renal venous levels of inflammatory cytokines, angiogenic markers, and infiltration of inflammatory cells, including tissue macrophages and T cells. Although restoring large-vessel blood flow can improve oxygenation, some of these processes reflect microvascular rarefication, remain activated, and do not depend on hemodynamic factors alone. Elucidation of tissue injury pathways associated with hypoxia opens the possibility of adjunctive therapeutic measures beyond renal revascularization. These include cell-based regeneration, mitochondrial protection, and/or angiogenic cytokine therapy to restore or preserve renal function in ischemic nephropathy.

Improved renal outcomes after revascularization of the stenotic renal artery in pigs by prior treatment with low-energy extracorporeal shockwave therapy

BACKGROUND

Revascularization does not restore renal function in most patients with atherosclerotic renal artery stenosis (RAS), likely because of inflammation and fibrosis within the stenotic kidney. Low-energy shockwave therapy (LE-SWT) stimulates angiogenesis in the stenotic kidney, but its ability to improve renal function and structure after revascularization remains unexplored. We tested the hypothesis that a LE-SWT regimen before percutaneous transluminal renal angioplasty (PTRA) would enable PTRA to restore renal function in hypercholesterolemic pigs with RAS (HC+RAS), and that this would be associated with attenuation of renal inflammation and fibrosis.

METHODS AND RESULTS

Twenty-six pigs were studied after 16 weeks of HC+RAS, HC+RAS treated with PTRA with or without a preceding LE-SWT regimen (bi-weekly for 3 weeks), and controls. Single-kidney renal blood flow (RBF), glomerular filtration rate (GFR), and oxygenation were assessed in vivo using imaging 4 weeks after PTRA, and then inflammation and fibrosis ex vivo.Four weeks after successful PTRA, blood pressure fell similarly in both revascularized groups. Yet, stenotic-kidney GFR remained lower in HC+RAS and HC+RAS+PTRA (P < 0.01 vs. normal), but was improved in HC+RAS+PTRA+SW (P > 0.05 vs. normal). Furthermore, reduced inflammation, medullary fibrosis, and cortical hypoxia were only shown in swine stenotic kidneys pretreated with LE-SWT before PTRA 4 weeks later.

CONCLUSION

LE-SWT delivery before revascularization permitted PTRA to improve function and decrease cortical and medullary damage in the stenotic swine kidney. This study, therefore, supports the use of an adjunct SW pretreatment to enhance the success of PTRA in blunting loss of kidney function in experimental HC+RAS.

In a Phase 1a escalating clinical trial, autologous mesenchymal stem cell infusion for renovascular disease increases blood flow and the glomerular filtration rate while reducing inflammatory biomarkers and blood pressure

Atherosclerotic renovascular disease (ARVD) reduces tissue perfusion and eventually leads to loss of kidney function with limited therapeutic options. Here we describe results of Phase 1a escalating dose clinical trial of autologous mesenchymal stem cell infusion for ARVD. Thirty-nine patients with ARVD were studied on two occasions separated by three months. Autologous adipose-derived mesenchymal stem cells were infused through the renal artery in 21 patients at three different dose levels (1, 2.5 and 5.0 × 105 cells/kg) in seven patients each. We measured renal blood flow, glomerular filtration rate (GFR) (iothalamate and estimated GFR), renal vein cytokine levels, blood pressure, and tissue oxygenation before and three months after stem cell delivery. These indices were compared to those of 18 patients with ARVD matched for age, kidney function and blood pressure receiving medical therapy alone that underwent an identical study protocol. Cultured mesenchymal stem cells were also studied in vitro. For the entire stem cell treated-cohort, mean renal blood flow in the treated stenotic kidney significantly increased after stem cell infusion from (164 to 190 ml/min). Hypoxia, renal vein inflammatory cytokines, and angiogenic biomarkers significantly decreased following stem cell infusion. Mean systolic blood pressure significantly fell (144 to 136 mmHg) and the mean two-kidney GFR (Iothalamate) modestly but significantly increased from (53 to 56 ml/min). Changes in GFR and blood pressure were largest in the high dose stem cell treated individuals. No such changes were observed in the cohort receiving medical treatment alone. Thus, our data demonstrate the potential for autologous mesenchymal stem cell to increase blood flow, GFR and attenuate inflammatory injury in post-stenotic kidneys. The observation that some effects are dose-dependent and related to in-vitro properties of mesenchymal stem cell may direct efforts to maximize potential therapeutic efficacy.

Selective intrarenal delivery of mesenchymal stem cell-derived extracellular vesicles attenuates myocardial injury in experimental metabolic renovascular disease

Extracellular vesicles (EVs) deliver genes and proteins to recipient cells, and mediate paracrine actions of their parent cells. Intrarenal delivery of mesenchymal stem cell (MSC)-derived EVs preserves stenotic-kidney function and reduces release of pro-inflammatory cytokines in a swine model of coexisting metabolic syndrome (MetS) and renal artery stenosis (RAS). We hypothesized that this approach is also capable of blunting cardiac injury and dysfunction. Five groups of pigs were studied after 16 weeks of diet-induced MetS and RAS (MetS + RAS), MetS and MetS + RAS treated 4 weeks earlier with a single intrarenal delivery of EVs-rich fraction harvested from autologous adipose tissue-derived MSCs, and lean and MetS Shams. Cardiac structure, function, and myocardial oxygenation were assessed in vivo using imaging, and cardiac inflammation, senescence, and fibrosis ex vivo. Inflammatory cytokine levels were measured in circulating and renal vein blood. Intrarenal EV delivery improved stenotic-kidney glomerular filtration rate and renal blood flow, and decreased renal release of monocyte-chemoattractant protein-1 and interleukin-6. Furthermore, despite unchanged systemic hemodynamics, intrarenal EV delivery in MetS + RAS normalized cardiac diastolic function, attenuated left ventricular remodeling, cellular senescence and inflammation, and improved myocardial oxygenation and capillary density in MetS + RAS. Intrarenal delivery of MSC-derived EVs blunts myocardial injury in experimental MetS + RAS, possibly related to improvement in renal function and systemic inflammatory profile. These observations underscore the central role of inflammation in the crosstalk between the kidney and heart, and the important contribution of renal function to cardiac structural and functional integrity in coexisting MetS and RAS.

[Kidney disease care for the elderly]

In our aging population, kidney disease management needs to take into account the frailty of the elderly. Standardized geriatric assessments can be proposed to help clinicians apprehend this dimension in their daily practice. These tools allow to better identify frail patients and offer them more personalized and harmless treatments. This article aims to focus on the kidney diseases commonly observed in elderly patients and analyze their specific nephrogeriatric care modalities. It should be noticed that all known kidney diseases can be also observed in the elderly, most often with a quite similar clinical presentation. This review is thus focused on the diseases most frequently and most specifically observed in elderly patients (except for monoclonal gammopathy associated nephropathies, out of the scope of this work), as well as the peculiarities of old age nephrological care.

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.

Loss of Renal Peritubular Capillaries in Hypertensive Patients Is Detectable by Urinary Endothelial Microparticle Levels

Hypertension, an important cause of chronic kidney disease, is characterized by peritubular capillary (PTC) loss. Circulating levels of endothelial microparticles (EMPs) reflect systemic endothelial injury. We hypothesized that systemic and urinary PTC-EMPs levels would reflect renal microvascular injury in hypertensive patients. We prospectively measured by flow cytometry renal vein, inferior vena cava, and urinary levels of EMPs in essential (n=14) and renovascular (RVH; n=24) hypertensive patients and compared them with peripheral blood and urinary levels in healthy volunteers (n=14). PTC-EMPs were identified as urinary exosomes positive for the PTC marker plasmalemmal-vesicle-associated protein. In 7 RVH patients, PTC and fibrosis were also quantified in renal biopsy, and in 18 RVH patients, PTC-EMPs were measured again 3 months after continued medical therapy with or without stenting (n=9 each). Renal vein and systemic PTC-EMPs levels were not different among the groups, whereas their urinary levels were elevated in both RVH and essential hypertension versus healthy volunteers (56.8%±12.7% and 62.8%±10.7% versus 34.0%±17.8%; both P≤0.001). Urinary PTC-EMPs levels correlated directly with blood pressure and inversely with estimated glomerular filtration rate. Furthermore, in RVH, urinary PTC-EMPs levels correlated directly with stenotic kidney hypoxia, histological PTC count, and fibrosis and inversely with cortical perfusion. Three months after treatment, the change in urinary PTC-EMPs levels correlated inversely with a change in renal function ( r=-0.582; P=0.011). Therefore, urinary PTC-EMPs levels are increased in hypertensive patients and may reflect renal microcirculation injury, whereas systemic PTC-EMPs levels are unchanged. Urinary PTC-EMPs may be useful as novel biomarkers of intrarenal capillary loss.

Tissue hypoxia, inflammation, and loss of glomerular filtration rate in human atherosclerotic renovascular disease

The relationships between renal blood flow (RBF), tissue oxygenation, and inflammatory injury in atherosclerotic renovascular disease (ARVD) are poorly understood. We sought to correlate RBF and tissue hypoxia with glomerular filtration rate (GFR) in 48 kidneys from patients with ARVD stratified by single kidney iothalamate GFR (sGFR). Oxygenation was assessed by blood oxygenation level dependent magnetic resonance imaging (BOLD MRI), which provides an index for the levels of deoxyhemoglobin within a defined volume of tissue (R2*). sGFR correlated with RBF and with the severity of vascular stenosis as estimated by duplex velocities. Higher cortical R2* and fractional hypoxia and higher levels of renal vein neutrophil-gelatinase-associated-lipocalin (NGAL) and monocyte-chemoattractant protein-1 (MCP-1) were observed at lower GFR, with an abrupt inflection below 20 ml/min. Renal vein MCP-1 levels correlated with cortical R2* and with fractional hypoxia. Correlations between cortical R2* and RBF in the highest sGFR stratum (mean sGFR 51 ± 12 ml/min; R = -0.8) were degraded in the lowest sGFR stratum (mean sGFR 8 ± 3 ml/min; R = -0.1). Changes in fractional hypoxia after furosemide were also absent in the lowest sGFR stratum. These data demonstrate relative stability of renal oxygenation with moderate reductions in RBF and GFR but identify a transition to overt hypoxia and inflammatory cytokine release with severely reduced GFR. Tissue oxygenation and RBF were less correlated in the setting of reduced sGFR, consistent with variable oxygen consumption or a shift to alternative mechanisms of tissue injury. Identifying transitions in tissue oxygenation may facilitate targeted therapy in ARVD.

Kidney-resident macrophages promote a proangiogenic environment in the normal and chronically ischemic mouse kidney

Renal artery stenosis (RAS) caused by narrowing of arteries is characterized by microvascular damage. Macrophages are implicated in repair and injury, but the specific populations responsible for these divergent roles have not been identified. Here, we characterized murine kidney F4/80+CD64+ macrophages in three transcriptionally unique populations. Using fate-mapping and parabiosis studies, we demonstrate that CD11b/cint are long-lived kidney-resident (KRM) while CD11chiMϕ, CD11cloMϕ are monocyte-derived macrophages. In a murine model of RAS, KRM self-renewed, while CD11chiMϕ and CD11cloMϕ increased significantly, which was associated with loss of peritubular capillaries. Replacing the native KRM with monocyte-derived KRM using liposomal clodronate and bone marrow transplantation followed by RAS, amplified loss of peritubular capillaries. To further elucidate the nature of interactions between KRM and peritubular endothelial cells, we performed RNA-sequencing on flow-sorted macrophages from Sham and RAS kidneys. KRM showed a prominent activation pattern in RAS with significant enrichment in reparative pathways, like angiogenesis and wound healing. In culture, KRM increased proliferation of renal peritubular endothelial cells implying direct pro-angiogenic properties. Human homologs of KRM identified as CD11bintCD11cintCD68+ increased in post-stenotic kidney biopsies from RAS patients compared to healthy human kidneys, and inversely correlated to kidney function. Thus, KRM may play protective roles in stenotic kidney injury through expansion and upregulation of pro-angiogenic pathways.

Phase 2a Clinical Trial of Mitochondrial Protection (Elamipretide) During Stent Revascularization in Patients With Atherosclerotic Renal Artery Stenosis

BACKGROUND

Atherosclerotic renal artery stenosis reduces renal blood flow (RBF) and amplifies stenotic kidney hypoxia. Revascularization with percutaneous transluminal renal angioplasty (PTRA) and stenting often fails to recover renal function, possibly because of ischemia/reperfusion injury developing after PTRA. Elamipretide is a mitochondrial-targeted peptide that binds to cardiolipin and stabilizes mitochondrial function. We tested the hypothesis that elamipretide plus PTRA would improve renal function, oxygenation, and RBF in patients with atherosclerotic renal artery stenosis undergoing PTRA.

METHODS AND RESULTS

Inpatient studies were performed in patients with severe atherosclerotic renal artery stenosis scheduled for PTRA. Patients were treated before and during PTRA with elamipretide (0.05 mg/kg per hour intravenous infusion, n=6) or placebo (n=8). Stenotic kidney cortical/medullary perfusion and RBF were measured using contrast-enhanced multidetector CT, and renal oxygenation by 3-T blood oxygen level-dependent magnetic resonance imaging before and 3 months after PTRA. Age and basal glomerular filtration rate did not differ between groups. Blood oxygen level-dependent imaging demonstrated increased fractional hypoxia 24 hours after angiography and stenting in placebo (+47%) versus elamipretide (-6%). These were reverted to baseline 3 months later. Stenotic kidney RBF rose (202±29-262±115 mL/min; P=0.04) 3 months after PTRA in the elamipretide-treated group only. Over 3 months, systolic blood pressure decreased, and estimated glomerular filtration rate increased (P=0.003) more in the elamipretide group than in the placebo group (P=0.11).

CONCLUSIONS

Adjunctive elamipretide during PTRA was associated with attenuated postprocedural hypoxia, increased RBF, and improved kidney function in this pilot trial. These data support a role for targeted mitochondrial protection to minimize procedure-associated ischemic injury and to improve outcomes of revascularization for human atherosclerotic renal artery stenosis.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT01755858.

Renal hypoxia in kidney disease: Cause or consequence?

Tissue hypoxia has been proposed as an important factor in the pathophysiology of both chronic kidney disease (CKD) and acute kidney injury (AKI), initiating and propagating a vicious cycle of tubular injury, vascular rarefaction, and fibrosis and thus exacerbation of hypoxia. Here, we critically evaluate this proposition by systematically reviewing the literature relevant to the following six questions: (i) Is kidney disease always associated with tissue hypoxia? (ii) Does tissue hypoxia drive signalling cascades that lead to tissue damage and dysfunction? (iii) Does tissue hypoxia per se lead to kidney disease? (iv) Does tissue hypoxia precede pathology? (v) Does tissue hypoxia colocalize with pathology? (vi) Does prevention of tissue hypoxia prevent kidney disease? We conclude that tissue hypoxia is a common feature of both AKI and CKD. Furthermore, at least under in vitro conditions, renal tissue hypoxia drives signalling cascades that lead to tissue damage and dysfunction. Tissue hypoxia itself can lead to renal pathology, independent of other known risk factors for kidney disease. There is also some evidence that tissue hypoxia precedes renal pathology, at least in some forms of kidney disease. However, we have made relatively little progress in determining the spatial relationships between tissue hypoxia and pathological processes (i.e. colocalization) or whether therapies targeted to reduce tissue hypoxia can prevent or delay the progression of renal disease. Thus, the hypothesis that tissue hypoxia is a "common pathway" to both AKI and CKD still remains to be adequately tested.

Elevated urinary podocyte-derived extracellular microvesicles in renovascular hypertensive patients

BACKGROUND

An increased number of podocyte-derived extracellular vesicles (pEVs) may reflect podocyte injury in renal disease. Elevated glomerular pressure and other insults may injure podocytes, yet it remains unclear whether the numbers of pEVs are altered in hypertensive patients. We tested the hypothesis that urinary pEV levels would be elevated in patients with renovascular hypertension (RVH) compared with essential hypertension (EH) or healthy volunteers (HVs).

METHODS

We prospectively enrolled patients with EH ( n = 30) or RVH ( n = 31) to study renal blood flow (RBF) and cortical perfusion using multidetector computed tomography under controlled condition (regulated sodium intake and renin-angiotensin blockade). After isolation from urine samples, pEVs (nephrin and podocalyxin positive) were characterized by flow cytometry. Fourteen RVH patients were studied again 3 months after stenting or continued medical therapy. HVs ( n = 15) served as controls.

RESULTS

The fraction of pEV among urinary EVs was elevated in RVH compared with HVs and EH (11.4 ± 6.4, 6.8 ± 3.4 and 6.3 ± 3.7%, respectively; P < 0.001) and remained unchanged after 3 additional months of therapy and after controlling for clinical parameters. However, eGFR- and age-adjusted pEV levels did not correlate with any clinical or renal parameters.

CONCLUSIONS

In hypertensive patients under controlled conditions, urinary pEV levels are elevated in patients with RVH and low eGFR compared with patients with EH and relatively preserved renal function. These pEVs may reflect podocyte injury secondary to kidney damage, and their levels might represent a novel therapeutic target.

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.

Renal Arterial Disease and Hypertension

Renal artery disease produces a spectrum of progressive clinical manifestations ranging from minor degrees of hypertension to circulatory congestion and kidney failure. Moderate reductions in renal blood flow do not induce tissue hypoxia or damage, making medical therapy for renovascular hypertension feasible. Several prospective trials indicate that optimized medical therapy using agents that block the renin-angiotensin system should be the initial management. Evidence of progressive disease and/or treatment failure should allow recognition of high-risk subsets that benefit from renal revascularization. Severe reductions in kidney blood flow ultimately activate inflammatory pathways that do not reverse with restoring blood flow alone.

[Management of atherosclerotic renal-artery stenosis in 2016]

Endovascular revascularization as treatment of atherosclerotic renal-artery stenosis (aRAS) is controversial since 3 large and multicentric randomised trials (CORAL, ASTRAL, STAR) failed to prove the superiority of percutaneous transluminal renal-artery stenting (PTRAS) over medical treatment only (MT). However, considering the multiple bias of these trials, among which questionable inclusion criterias, these results must be extrapolated in clinical practice with caution. New pathophysiological data have been helping to understand why restoring blood flow does not necessarily lead to kidney function improvement. Today, the diagnostic approach must in one hand confirm the artery stenosis and on the other hand assess its severity and impact on the kidney. Therapeutic options still lie on the American guidelines published in 2006, since no study data can be reasonably used in everyday practice. However, particular sub-groups of patients who could benefit from revascularisation have been identified through recent cohort studies. Further prospective studies are needed in order to confirm the superiority of PTRAS in these populations. Meanwhile, multidisciplinary approach should be promoted, in order to provide the best treatment for each patient.

Renal artery stenosis: if and when to intervene

PURPOSE OF REVIEW

Atherosclerotic renovascular disease remains highly prevalent and presents an array of clinical syndromes. Recent prospective trials have dampened enthusiasm for revascularization generally, but clinicians recognize the need to identify patients likely to benefit from vascular intervention.

RECENT FINDINGS

This article highlights the inflammatory nature of vascular occlusive disease and the limits of the kidney to adapt to reduced blood flow. Although moderate reductions can be tolerated, severe impairment of renal perfusion leads to tissue hypoxia and activates inflammatory injury within the kidney. Hence, assessment of kidney viability and potential tools to modify mitochondrial and inflammatory damage may be important to identify patients for whom clinical intervention should be undertaken.

SUMMARY

Clinicians must recognize clinical syndromes that identify 'high-risk' groups and apply revascularization in those likely to benefit. Future efforts to protect the kidney (e.g., mitochondrial protection) or cell-based therapy may amplify clinical recovery when combined with restoring renal blood flow.

Approach to atherosclerotic renovascular disease: 2016

The management of atherosclerotic renal artery stenosis in patients with hypertension or impaired renal function remains a clinical dilemma. The current general consensus, supported by the results of the Angioplasty and Stenting for Renal Atherosclerotic Lesions and Cardiovascular Outcomes for Renal Artery Lesions trials, argues strongly against endovascular intervention in favor of optimal medical management. We discuss the limitations and implications of the contemporary clinical trials and present our approach and formulate clear recommendations to help with the management of patients with atherosclerotic narrowing of the renal artery.

Adipose-derived mesenchymal stem cells from patients with atherosclerotic renovascular disease have increased DNA damage and reduced angiogenesis that can be modified by hypoxia

BACKGROUND

Adipose-derived MSC (AMSCs) possess angiogenic and immunomodulatory properties that may modulate kidney regeneration. Whether these properties are retained in older patients with atherosclerotic vascular disease is poorly understood. Hypoxic conditions are known to modify properties and growth characteristics of AMSCs. We tested the hypothesis that AMSCs from older patients with atherosclerotic renovascular disease (RVD) differ from normal kidney donors, and whether hypoxia changes their functional and molecular properties to promote angiogenesis.

METHODS

AMSCs from 11 patients with RVD (mean age =74.5 years) and 10 healthy kidney donors (mean age = 51.2 years) were cultured under normoxia (20 % O2) and hypoxia (1 % O2) for 3-4 days until they reached 80 % confluency. We analyzed expression of genes and microRNAs using RNA sequencing and real-time quantitative rt-PCR. Protein expression of selected angiogenic factors (VEGF, IGF, HGF and EGF) were quantified in conditioned media using ELISAs. Apoptosis was tested using Annexin IV staining.

RESULTS

Normoxic AMSC from RVD patients grew normally, but exhibited increased DNA damage and reduced migration. VEGF protein secretion was significantly lower in the RVD AMSCs (0.08 vs 2.4 ng/mL/ cell, p <0.05) while HGF was higher. Both trends were reversed during growth under hypoxic conditions. Hypoxia upregulated pro-angiogenic mRNAs expression in AMSCs (VEGF, FGF, STC and ANGPTL4), and downregulated expression of many miRNAs (e.g., miR-15a, miR-16, miR-93, miR-424, 126, 132, 221) except miR-210.

CONCLUSIONS

Thus, although AMSC from patients with RVD had increased DNA damage and reduced migration, hypoxia stimulated pro-angiogenic responses via increased expression of angiogenic genes, VEGF secretion and induction of the hypoxia-inducible miR-210, while downregulating angiogenesis-related miRNAs.

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.

Hypercholesterolemia Impairs Nonstenotic Kidney Outcomes After Reversal of Experimental Renovascular Hypertension

BACKGROUND

Revascularization of a stenotic renal artery improves kidney function only in select patients with renovascular hypertension (HT) secondary to atherosclerosis. However, the effects of reversal of renovascular HT (RRHT) on the nonstenotic kidney are unclear. We hypothesized that concurrent hypercholesterolemia (HC) attenuates nonstenotic kidney recovery.

METHODS

Female domestic pigs were randomized as Normal, renovascular HT, HT+RRHT, HTC (renovascular HT and HC), and HTC+RHT (n = 7 each). RRHT or sham was performed after 6 weeks of HT. Nonstenotic renal blood flow, glomerular filtration rate, and injurious pathways were studied 4 weeks later.

RESULTS

Mean arterial pressure increased similarly in HT and HTC and decreased after RRHT. Oxidative stress increased in HT and HTC kidneys, and decreased in HT+RRHT, but remained elevated in HTC+RRHT. Renal interstitial fibrosis, glomerulosclerosis, and tubular injury were all attenuated in HT+RRHT, but not HTC+RRHT. Endothelin-1 signaling and PGF2α isoprostane levels were elevated in both HTC and HTC+RRHT pigs.

CONCLUSIONS

RRHT reverses nonstenotic kidney injury in experimental renovascular HT, but concurrent HC blunts regression of kidney injury, possibly due to predominant vasoconstrictors and oxidative stress. These findings reinforce the contribution of the nonstenotic kidney and of prevailing cardiovascular risk factors to irreversibility of kidney dysfunction after revascularization.

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.

Atherosclerotic Renal Artery Stenosis and Hypertension: Pragmatism, Pitfalls, and Perspectives

For many years and even decades, a diagnostic work-up to look for a secondary form of hypertension, particularly of renovascular origin, has been a central tenet in medicine. Atherosclerotic renal artery stenosis is considered the most common cause of renovascular hypertension. However, advances in understanding the complex pathophysiology of this condition and the recently documented futility of renal revascularization bring into question whether atherosclerotic renal artery stenosis truly causes "renovascular hypertension." From a clinical point of view, a clear distinction should be made between hypertension associated with atherosclerotic renal artery stenosis and hypertension caused by renal artery stenosis-induced activation of the renin-angiotensin-aldosterone system. Most patients with atherosclerotic renal artery stenosis do not have a form of hypertension that is remediable or improved by angioplasty; to expose them to the cost, inconvenience, and risk of a diagnostic work-up add up to little more than a wild goose chase. However, with very few exceptions, medical therapy with antihypertensives and statins remains the cornerstone for the management of patients with atherosclerotic renal artery stenosis and 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.

Effects of Restoration of Blood Flow on the Development of Aortic Atherosclerosis in ApoE-/- Mice With Unilateral Renal Artery Stenosis

Background

Chronic unilateral renal artery stenosis (RAS) causes accelerated atherosclerosis in apolipoprotein E–deficient (ApoE^−/−) mice, but effects of restoration of renal blood flow on aortic atherosclerosis are unknown.

Methods and Results

Male ApoE^−/− mice underwent sham surgery (n=16) or had partial ligation of the right renal artery (n=41) with the ligature being removed 4 days later (D4LR; n=6), 8 days later (D8LR; n=11), or left in place for 90 days (chronic RAS; n=24). Ligature removal at 4 or 8 days resulted in improved renal blood flow, decreased plasma angiotensin II levels, a return of systolic blood pressure to baseline, and increased plasma levels of neutrophil gelatinase associated lipocalin. Chronic RAS resulted in increased lipid staining in the aortic arch (33.2% [24.4, 47.5] vs 11.6% [6.1, 14.2]; P<0.05) and descending thoracic aorta (10.2% [6.4, 25.9] vs 4.9% [2.8, 7.8]; P<0.05), compared to sham surgery. There was an increased amount of aortic arch lipid staining in the D8LR group (22.7% [22.1, 32.7]), compared to sham‐surgery, but less than observed with chronic RAS. Lipid staining in the aortic arch was not increased in the D4LR group, and lipid staining in the descending aorta was not increased in either the D8LR or D4LR groups. There was less macrophage expression in infrarenal aortic atheroma in the D4LR and D8LR groups compared to the chronic RAS group.

Conclusions

Restoration of renal blood flow at either 4 or 8 days after unilateral RAS had a beneficial effect on systolic blood pressure, aortic lipid deposition, and atheroma inflammation.

Changes in inflammatory biomarkers after renal revascularization in atherosclerotic renal artery stenosis

BACKGROUND

Atherosclerotic renal artery stenosis (ARAS) activates oxidative stress and chronic inflammatory injury. Contrast imaging and endovascular stenting pose potential hazards for acute kidney injury, particularly when superimposed upon reduced kidney perfusion.

METHODS

We measured sequential early and long-term changes in circulating inflammatory and injury biomarkers in 12 ARAS subjects subjected to computed tomography imaging and stent revascularization compared with essential hypertensive (EH) subjects of similar age under fixed sodium intake and medication regimens in a clinical research unit.

RESULTS

NGAL, TIMP-2, IGFBP7, MCP-1 and TNF-α all were elevated before intervention. Post-stenotic kidney volume, perfusion, blood flow and glomerular filtration rate (GFR) were lower in ARAS than in EH subjects. TIMP-2 and IGFBP7 fell briefly, then rose over 18 h after contrast imaging and stent deployment. Circulating NGAL decreased and remained lower for 27 h. These biomarkers in ARAS returned to baseline after 3 months, while kidney volume, perfusion, blood flow and GFR increased, but remained lower than EH.

CONCLUSIONS

These divergent patterns of inflammatory signals are consistent with cell cycle arrest (TIMP-2, IGFBP7) and relative protection from acute kidney injury after imaging and stenting. Sustained basal elevation of circulating and renal venous inflammatory biomarkers support ongoing, possibly episodic, renal stress in ARAS that limits toxicity from stent revascularization.

Early atherosclerosis aggravates renal microvascular loss and fibrosis in swine renal artery stenosis

Renal function in patients with atherosclerosis and renal artery stenosis (ARAS) deteriorates more frequently than in nonatherosclerotic RAS. We hypothesized that ARAS aggravates stenotic-kidney micro vascular loss compared to RAS. Domestic pigs were randomized to normal, RAS, and ARAS (RAS fed a high-cholesterol diet) groups (n = 7 each). Ten weeks later stenotic-kidney oxygenation, renal blood flow, and glomerular filtration rate (GFR) were evaluated in vivo, and micro vascular density by micro-computed tomography. Blood pressure in both RAS and ARAS was elevated; and stenotic-kidney renal blood flow and GFR similarly decreased. RAS decreased the density of small-size cortical microvessels (<200 μm), whereas ARAS extended the decrease to medium-sized microvessels (200-300 μm). Cortical hypoxia and interstitial fibrosis increased in both RAS and ARAS but correlated inversely with micro vascular density only in RAS. Atherosclerosis aggravates loss of stenotic-kidney microvessels, yet additional determinants likely contribute to cortical hypoxia and fibrosis in swine ARAS.

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.