Pathophysiology of ischemic nephropathy

Autologous Extracellular Vesicles Attenuate Cardiac Injury in Experimental Atherosclerotic Renovascular Disease More Effectively Than Their Parent Mesenchymal Stem/Stromal Cells

Atherosclerotic renovascular disease (RVD) leads to hypertension, chronic kidney disease (CKD), and heart disease. Intrarenal delivery of mesenchymal stem cells (MSCs) and MSC-derived extracellular vesicles (EVs) attenuate renal injury and suppress release of inflammatory cytokines in porcine RVD. We hypothesized that this strategy would also be useful for cardioprotection. Pigs with renovascular hypertension and metabolic syndrome were studied 4 weeks after treatment with a single intrarenal infusion of autologous MSCs, EVs, or vehicle. Cardiac structure and function were assessed in vivo, and myocardial remodeling and expression of the pro-fibrotic factor growth factor receptor-bound protein-2 (Grb2) were measured ex-vivo. Inflammatory cytokine levels were measured in the systemic circulation and myocardial tissue. Blood pressure was elevated in all RVD groups, but serum creatinine increased in RVD and decreased in both RVD + MSCs and RVD + EVs. RVD-induced diastolic dysfunction (lower E/A ratio) was normalized in both MSCs- and EVs- treated pigs. Intrarenal delivery of MSCs and EVs also attenuated RVD-induced myocardial fibrosis, collagen deposition, and Grb2 expression, yet EVs restored capillary density and inflammation more effectively than MSCs. These observations suggest that autologous EVs attenuate cardiac injury in experimental RVD more effectively than their parent MSCs.

The Effect of Nerolidol Renal Dysfunction following Ischemia-Reperfusion Injury in the Rat

Efforts to decrease the deleterious effects of renal ischemia-reperfusion injury (IRI) are ongoing. Recently, there has been increasing interest in using natural phytochemical compounds as alternative remedies in several diseases. Nerolidol is a natural product extracted from plants with floral odors and has been proven to be effective for the treatment of some conditions. We investigated the effect of nerolidol in a rat model of renal IRI. Nerolidol was dissolved in a vehicle and administered orally as single daily dose of 200 mg/kg for 5 days prior to IRI and continued for 3 days post IRI. G-Sham (n = 10) underwent sham surgery, whereas G-IRI (n = 10) and G-IRI/NR (n = 10) underwent bilateral warm renal ischemia for 30 min and received the vehicle/nerolidol, respectively. Renal functions and histological changes were assessed before starting the medication, just prior to IRI and 3 days after IRI. Nerolidol significantly attenuated the alterations in serum creatinine and urea, creatinine clearance, urinary albumin and the urinary albumin-creatinine ratio. Nerolidol also significantly attenuated the alterations in markers of kidney injury; proinflammatory, profibrotic and apoptotic cytokines; oxidative stress markers; and histological changes. We conclude that nerolidol has a renoprotective effect on IRI-induced renal dysfunction. These findings might have clinical implications.

Renal artery stenosis

Renal artery stenosis is the most common secondary cause of hypertension and predominantly caused by atherosclerosis. In suspected patients, a non-invasive diagnosis with ultrasound is preferred. Asymptomatic, incidentally found RAS does not require revascularization. In symptomatic patients requiring revascularization, renal artery stenting is the preferred therapy. Selecting appropriate patients for revascularization requires careful consideration of lesion severity and is optimized with a multidisciplinary team. All patients with atherosclerotic RAS should be treated with guideline-directed medical therapy, including hypertension control, diabetes control, statins, antiplatelet therapy, smoking cessation and encouraging activity.

Renovascular Disease Induces Senescence in Renal Scattered Tubular-Like Cells and Impairs Their Reparative Potency

Scattered tubular-like cells (STCs), dedifferentiated renal tubular epithelial cells, contribute to renal self-healing, but severe injury might blunt their effectiveness. We hypothesized that ischemic renovascular disease (RVD) induces senescence in STC and impairs their reparative potency. CD24+/CD133+ STCs were isolated from swine kidneys after 16 weeks of RVD or healthy controls. To test their reparative capabilities in injured kidneys, control or RVD-STC (5×10⁵) were prelabeled and injected into the aorta of 2 kidneys, 1-clip (2k,1c) mice 2 weeks after surgery. Murine renal function and oxygenation were studied in vivo 2 weeks after injection using micro-magnetic resonance imaging, and fibrosis, tubulointerstitial injury, capillary density, and expression of profibrotic and inflammatory genes ex vivo. STC isolated from swine RVD kidneys showed increased gene expression of senescence and senescence-associated secretory phenotype markers and positive SA-β-gal staining. Delivery of normal pig STCs in 2k,1c mice improved murine renal perfusion, blood flow, and glomerular filtration rate, and downregulated profibrotic and inflammatory gene expression. These renoprotective effects were blunted using STC harvested from RVD kidneys, which also failed to attenuate hypoxia, fibrosis, tubular injury, and capillary loss in injured mouse 2k,1c kidneys. Hence, RVD may induce senescence in endogenous STC and impair their reparative capacity. These observations implicate cellular senescence in the pathophysiology of ischemic kidney disease and support senolytic therapy to permit self-healing of senescent kidneys.

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.

Extracellular vesicles released by adipose tissue-derived mesenchymal stromal/stem cells from obese pigs fail to repair the injured kidney

AIMS

Mesenchymal stromal/stem cell (MSC)-derived extracellular vesicles (EVs) shuttle select MSC contents and are endowed with an ability to repair ischemic tissues. We hypothesized that exposure to cardiovascular risk factors may alter the microRNA cargo of MSC-derived EVs, blunting their capacity to repair the post-stenotic kidney in pigs with metabolic syndrome (MetS) and renal artery stenosis (RAS).

METHODS

Porcine MSCs were harvested from abdominal fat after 16wks of Lean- or MetS-diet, and their EVs isolated and characterized using microRNA-sequencing. Lean- and MetS-EV protective effects were assessed in-vitro in human umbilical endothelial cells (HUVECs). To compare their in-vivo efficacy to repair ischemic tissues, allogeneic-EVs were intrarenally delivered in pigs after 6wks of MetS + RAS, and 4wks later, single-kidney renal blood flow (RBF) and glomerular filtration rate (GFR) were studied in-vivo, and microvascular architecture and injury ex-vivo. Lean-, MetS-, and MetS + RAS-sham served as controls (n = 6 each).

RESULTS

Ten microRNAs, capable of targeting several pro-angiogenic genes, were upregulated in MetS-EVs versus Lean-EVs. In vitro, MetS-EVs failed to increase tube number and length, and to boost HUVEC migration compared to Lean-EVs. Lean- and MetS-EVs were detected in the stenotic-kidney 4wks after injection in the vicinity of small vessels. RBF and GFR were lower in MetS + RAS versus MetS, and restored in MetS + RAS + Lean-EVs, but not in MetS + RAS + MetS-EVs. Furthermore, MetS-EVs failed to restore renal expression of angiogenic factors, improve microvascular density, or attenuate fibrosis.

CONCLUSIONS

MetS alters the microRNA cargo of MSC-derived EVs and impairs their functional potency, limiting the therapeutic efficacy of this endogenous cellular repair system.

Adjunctive mesenchymal stem/stromal cells augment microvascular function in poststenotic kidneys treated with low-energy shockwave therapy

Effective therapeutic strategies are needed to preserve renal function in patients with atherosclerotic renal artery stenosis (ARAS). Low-energy shockwave therapy (SW) and adipose tissue-derived mesenchymal stem/stromal cells (MSCs) both stimulate angiogenesis repair of stenotic kidney injury. This study tested the hypothesis that intrarenal delivery of adipose tissue-derived MSCs would enhance the capability of SW to preserve stenotic kidney function and structure. Twenty-two pigs were studied after 16 weeks of ARAS, ARAS treated with a SW regimen (bi-weekly for 3 weeks) with or without subsequent intrarenal delivery of adipose tissue-derived MSCs and controls. Four weeks after treatment, single-kidney renal blood flow (RBF) before and after infusion of acetylcholine, glomerular filtration rate (GFR), and oxygenation were assessed in vivo and the renal microcirculation, fibrosis, and oxidative stress ex vivo. Mean arterial pressure remained higher in ARAS, ARAS + SW, and ARAS + SW + MSC compared with normal. Both SW and SW + MSC similarly elevated the decreased stenotic kidney GFR and RBF observed in ARAS to normal levels. Yet, SW + MSC significantly improved RBF response to acetylcholine in ARAS, and attenuated capillary loss and oxidative stress more than SW alone. Density of larger microvessels was similarly increased by both interventions. Therefore, although significant changes in functional outcomes were not observed in a short period of time, adjunct MSCs enhanced pro-angiogenic effect of SW to improve renal microvascular outcomes, suggesting this as an effective stratege for long-term management of renovascular disease.

Mitochondrial Protection Partly Mitigates Kidney Cellular Senescence in Swine Atherosclerotic Renal Artery Stenosis

BACKGROUND/AIMS

Atherosclerotic renal artery stenosis (ARAS) may cause kidney injury and mitochondrial dysfunction, which is linked to cellular senescence. Elamipretide, a mitochondria-targeted peptide, improves renal function in ARAS, but whether it alleviates senescence is unknown. We hypothesized that elamipretide would reduce senescence stenotic kidney (STK) in ARAS.

METHODS

Domestic pigs were randomized to control and unilateral ARAS untreated or treated with subcutaneous elamipretide (5d/wk) for 4 weeks starting after 6 weeks of ARAS or sham (n=6 each). After completion of treatment, STK renal blood flow (RBF) and glomerular filtration rate (GFR) were assessed in-vivo using multi-detector computed-tomography. Renal fibrosis and oxidative stress were analyzed in trichrome- and dihydroethidium-stained slides, respectively. Mitochondrial markers involved in the electrontransport chain (COX4, ATP/ADP ratio), biogenesis (PGC1α, PPARα), dynamics (MFN2, DRP1), and mitophagy (parkin, p62) were measured in the kidney using ELISA, western-blot, and immunohistochemistry. Cellular senescence (senescence-associated β-galactosidase and heterochromatin foci, phosphorylated-H2AX, and p16/21/53) and senescence-associated secretory phenotype (SASP; PAI-1, MCP-1, TGFβ, and TNFα) markers were studied by microscopy, quantitative reverse transcription-polymerase chain reaction, and western-blot.

RESULTS

Blood pressure was elevated whereas STK-RBF and GFR were decreased in ARAS pigs, and tissue scarring was increased. ARAS induced STK cellular senescence and accumulated dysfunctional mitochondria, which were associated with cardiolipin loss, upregulated mitochondrial biogenesis, and defective mitophagy. Elamipretide normalized STK-RBF and GFR, alleviated fibrosis and oxidative stress, and restored mitochondrial cardiolipin, biogenesis, and mitophagy in ARAS, but did not change SASP markers, and attenuated only senescenceassociated β-galactosidase activity and p53 gene expression.

CONCLUSION

Mitochondrial protection improved renal function and fibrosis in the ARAS STK, but only partly mitigated cellular senescence. This finding suggests that mitochondrial dysfunction may not be a major determinant of cellular senescence in the early stage of ARAS.

Mesenchymal Stem Cell-Derived Extracellular Vesicles Improve the Renal Microvasculature in Metabolic Renovascular Disease in Swine

Background:

Extracellular vesicles (EVs) released from mesenchymal stem/stromal cells (MSCs) mediate their paracrine effect, but their efficacy to protect the microcirculation of the kidney is unknown. Using a novel swine model of unilateral renovascular disease (RVD) complicated by metabolic syndrome (MetS), we tested the hypothesis that EVs would attenuate renal microvascular loss.

Methods:

Four groups of pigs (n = 7 each) were studied after 16 weeks of diet-induced MetS and RVD (MetS+RVD), MetS+RVD treated 4 weeks earlier with a single intra-renal delivery of EVs harvested from autologous adipose tissue-derived MSCs, and Lean and MetS Sham controls. Stenotic-kidney renal blood flow (RBF) and glomerular filtration rate (GFR) were measured in-vivo (fast CT), whereas EV characteristics, renal microvascular architecture (micro-CT), and injury pathways were studied ex-vivo.

Results:

mRNA sequencing and proteomic analysis revealed that EVs are packed with several pro-angiogenic genes and proteins, such as vascular endothelial growth factor. Labeled EVs were detected in the stenotic kidney 4 weeks after injection internalized by tubular and endothelial cells. EVs restored renal expression of angiogenic factors and improved cortical microvascular and peritubular capillary density. Renal apoptosis, oxidative stress, tubular injury, and fibrosis were also attenuated in EV-treated pigs. RBF and GFR decreased in MetS+RVD compared with MetS, but normalized in MetS+RVD+EVs.

Conclusions:

Intra-renal delivery of MSC-derived EVs bearing pro-angiogenic properties restored the renal microcirculation and in turn hemodynamics and function in chronic experimental MetS+RVD. Our study suggests a novel therapeutic potential for MSC-derived EVs in restoring renal hemodynamics in experimental MetS+RVD.

Role of peroxisome proliferator-activated receptor-gamma activation on visfatin, advanced glycation end products, and renal oxidative stress in obesity-induced type 2 diabetes mellitus

The present study focused on the role of peroxisome proliferator-activated receptor-gamma (PPAR-γ) activation on renal oxidative damages, serum visfatin, and advanced glycation end products (AGEs) in high-fat diet (HFD)-induced type 2 diabetes mellitus. Following the institutional animal ethics committee guidelines, Wistar rats were categorized into five groups: group 1: fed on a normal rat diet; group 2: HFD-induced obese rats (HFD for 8 weeks); group 3: HFD-fed rats treated with rosiglitazone (RSG; 3 mg/kg orally for 7 days); group 4: T2DM rats induced by HFD and low dose of streptozotocin (i.p. 35 mg/kg); group 5: T2DM rats treated with RSG (3 mg/kg orally for 7 days). Serum levels of AGEs and visfatin, renal damage, and oxidative stress were analyzed. Results showed that HFD-induced obesity and T2DM caused an elevated blood glucose, serum AGEs, visfatin, insulin, urea, creatinine, and tissue malondialdehyde, whereas a decreased catalase and superoxide dismutase activity were observed. The PPAR-γ activation via agonist restored these changes. Our findings suggest that AGEs and visfatin possess an important role in the progression of renal oxidative stress, which can be reduced by the PPAR-γ agonist that impede deleterious effects of HFD and HFD-induced T2DM on renal damage.

Low-Energy Shockwave Therapy Improves Ischemic Kidney Microcirculation

Microvascular rarefaction distal to renal artery stenosis is linked to renal dysfunction and poor outcomes. Low-energy shockwave therapy stimulates angiogenesis, but the effect on the kidney microvasculature is unknown. We hypothesized that low-energy shockwave therapy would restore the microcirculation and alleviate renal dysfunction in renovascular disease. Normal pigs and pigs subjected to 3 weeks of renal artery stenosis were treated with six sessions of low-energy shockwave (biweekly for 3 consecutive weeks) or left untreated. We assessed BP, urinary protein, stenotic renal blood flow, GFR, microvascular structure, and oxygenation in vivo 4 weeks after completion of treatment, and then, we assessed expression of angiogenic factors and mechanotransducers (focal adhesion kinase and β1-integrin) ex vivo A 3-week low-energy shockwave regimen attenuated renovascular hypertension, normalized stenotic kidney microvascular density and oxygenation, stabilized function, and alleviated fibrosis in pigs subjected to renal artery stenosis. These effects associated with elevated renal expression of angiogenic factors and mechanotransducers, particularly in proximal tubular cells. In additional pigs with prolonged (6 weeks) renal artery stenosis, shockwave therapy also decreased BP and improved GFR, microvascular density, and oxygenation in the stenotic kidney. This shockwave regimen did not cause detectable kidney injury in normal pigs. In conclusion, low-energy shockwave therapy improves stenotic kidney function, likely in part by mechanotransduction-mediated expression of angiogenic factors in proximal tubular cells, and it may ameliorate renovascular hypertension. Low-energy shockwave therapy may serve as a novel noninvasive intervention in the management of renovascular disease.

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.

Ameliorative Effect of Recombinant Human Erythropoietin and Ischemic Preconditioning on Renal Ischemia Reperfusion Injury in Rats

Background:

Ischemia-reperfusion (IR) injury is one of the most common causes of renal dysfunction. There is increasing evidence about the role of the reactive oxygen species (ROS) in these injuries and endogenous antioxidants seem to have an important role in decreasing the renal tissue injury.

Objectives:

The aim of this study was to compare the effect of recombinant human erythropoietin (EPO) and ischemic preconditioning (IPC) on renal IR injury.

Materials and Methods:

Twenty four male Wistar rats were allocated into four experimental groups: sham-operated, IR, EPO + IR, and IPC + IR. Rats were underwent 50 minutes bilateral ischemia followed by 24 hours reperfusion. Erythropoietin (5000 IU/kg, i.p) was administered 30 minutes before onset of ischemia. Ischemic preconditioning was performed by three cycles of 3 minutes ischemia followed by 3 minutes reperfusion. Plasma concentrations of urea and creatinine were measured. Kidney samples were taken for reactive oxidative species (ROS) measurement including superoxide dismutase (SOD) activity, glutathione (GSH) contents, and malondialdehyde (MDA) levels.

Results:

Compared to the sham group, IR led to renal dysfunction as evidenced by significantly higher plasma urea and creatinine. Treatment with EPO or IPC decreased urea, creatinine, and renal MDA levels and increased SOD activity and GSH contents in the kidney.

Conclusions:

Pretreatment with EPO and application of IPC significantly ameliorated the renal injury induced by bilateral renal IR. However, both treatments attenuated renal dysfunction and oxidative stress in kidney tissues. There were no significant differences between pretreatment with EPO or application of IPC.

Angiotensin type 1 receptor mediates renal production and conversion of prostaglandins E2 to F2α in conscious diabetic rats

INTRODUCTION

Previous studies demonstrated that stimulation of angiotensin subtype 1 receptor (AT1R) led to increased renal generation of prostaglandins E2 (PGE2) and renal inflammation. In turn, PGE2 increases AT1R activity. The conversion of PGE2 to the less active metabolite prostaglandin F2α (PGF2α) via 9-ketoreductase interrupts this feedback loop. The effects of diabetes on the interface between AT1R, PGE2 and PGF2α are not well established. We hypothesized that in diabetes, an aberrant AT1R activity enhances the biosynthesis of PGE2 and impairs the activity of PGE 9-ketoreductase, leading to accumulation of PGE2.

MATERIALS AND METHODS

Using microdialysis technique, we monitored renal interstitial fluid levels of angiotensin II (Ang II), PGE2 and PGF2α in control and AT1R blocker, valsartan, treated diabetic rats (N=8 each). We utilized the PGF2α to PGE2 ratio as indirect measure of PGE 9-ketoreductase activity.

RESULTS

Diabetes increased renal interstitial fluid levels of Ang II, PGE2 and PGF2α. PGF2α/PGE2 ratio increased by the third week, but declined by the sixth week of diabetes. Valsartan reduced PGE2 and PGF2α levels and increased Ang II and the conversion of PGE2 to PGF2α.

CONCLUSION

Our results suggest that in diabetes, AT1R increases PGE2 generation and reduces conversion of PGE2 to PGF2α with the progression of diabetes.

[Ischemic renal disease and renal artery stenosis]

Severe renal artery stenosis may cause renovascular hypertension; in case of bilateral narrowing or in a stenotic solitary or transplant kidney, renal insufficiency (ischemic renal disease) or rarely pulmonary flash edema may occur. In most cases arteriosclerotic disease is the underlying cause; less prevalent are the various manifestations of fibromuscular disease. Renal artery stenosis may be treated by revasularization, using either percutaneous (balloon angioplasty, stenting) or rarely open surgical procedures, both with excellent primary patency rates. However, randomized trials of renal artery angioplasty or stenting in patients with arteriosclerotic lesions have failed to demonstrate a longer-term benefit with regard to hypertension control and renal dysfunction over medical management alone. Careful patient selection is essential to maximize the potential benefit (e.g., in patients with refractory hypertension, progressive renal failure or recurrent pulmonary flash edema).

Optimal medical management in patients with renovascular hypertension

Renovascular hypertension refers to the rise of arterial pressure due to reduced perfusion of the kidney caused by the stenotic renal artery/ies. The most common cause of stenotic renal artery is atherosclerosis. Atherosclerotic renal stenosis is usually part of a systemic syndrome that involves hypertension, intrinsic renal damage, and cardiovascular morbidity. So far, large trials have not proven the superiority of interventional therapies to medical management. As a result, renal artery stenosis should be treated mainly as a coronary artery disease equivalent focusing on rigorous management of hypertension, hyperglycemia, and hyperlipidemia. Antihypertensive treatment should include renin-angiotensin system blockade medication in most cases, while HMG-CoA reductase inhibitors (statins) can be used even in chronic kidney disease with safety. Lifestyle modifications, such as cessation of smoking, and antiplatelet therapy have reduced the risk of cardiovascular events in high-risk patients.

Endothelial outgrowth cells shift macrophage phenotype and improve kidney viability in swine renal artery stenosis

OBJECTIVE

Endothelial outgrowth cells (EOC) decrease inflammation and improve endothelial repair. Inflammation aggravates kidney injury in renal artery stenosis (RAS), and may account for its persistence upon revascularization. We hypothesized that EOC would decrease inflammatory (M1) macrophages and improve renal recovery in RAS.

APPROACH AND RESULTS

Pigs with 10 weeks of RAS were studied 4 weeks after percutaneous transluminal renal angioplasty (PTRA+stenting) or sham, with or without adjunct intrarenal delivery of autologous EOC (10×10(6)), and compared with similarly treated normal controls (n=7 each). Single-kidney function, microvascular and tissue remodeling, inflammation, oxidative stress, and fibrosis were evaluated. Four weeks after PTRA, EOC were engrafted in injected RAS-kidneys. Stenotic-kidney glomerular filtration rate was restored in RAS+EOC, RAS+PTRA, and RAS+PTRA+EOC pigs, whereas stenotic-kidney blood flow and angiogenesis were improved and fibrosis attenuated only in EOC-treated pigs. Furthermore, EOC increased cell proliferation and decreased the ratio of M1 (inflammatory)/M2 (reparative) macrophages, as well as circulating levels and stenotic-kidney release of inflammatory cytokines. Cultured-EOC released microvesicles in vitro and induced phenotypic switch (M1-to-M2) in cultured monocytes, which was inhibited by vascular endothelial growth factor blockade. Finally, a single intrarenal injection of rh-vascular endothelial growth factor (0.05 μg/kg) in 7 additional RAS pigs also restored M1/M2 ratio 4 weeks later.

CONCLUSIONS

Intrarenal infusion of EOC after PTRA induced a vascular endothelial growth factor-mediated attenuation in macrophages inflammatory phenotype, preserved microvascular architecture and function, and decreased inflammation and fibrosis in the stenotic kidney, suggesting a novel mechanism and therapeutic potential for adjunctive EOC delivery in experimental RAS to improve PTRA outcomes.

Changes in glomerular filtration rate after renal revascularization correlate with microvascular hemodynamics and inflammation in Swine renal artery stenosis

BACKGROUND

The selection of patients with renal artery stenosis (RAS) likely to improve glomerular filtration rate (GFR) after percutaneous transluminal renal angioplasty is difficult. We examined basal hemodynamic and inflammatory factors linked to improved stenotic kidney (STK) function after percutaneous transluminal renal angioplasty in swine RAS.

METHODS AND RESULTS

Fifteen pigs after 6 weeks of hemodynamically significant RAS were studied before and 4 weeks after technically successful percutaneous transluminal renal angioplasty+stenting. STK and contralateral kidney hemodynamics and function were evaluated by multidetector computed-tomography before and after acetylcholine challenge. Single-kidney deoxyhemoglobin (R2*, reciprocal to blood relaxation) and energy-dependent tubular function were assessed using blood-oxygen-level-dependent magnetic resonance imaging before and after furosemide. Baseline renal vein and inferior vena cava levels of inflammatory markers were measured and their gradient and net release calculated. Baseline parameters were compared with normal (n=7) and sham-RAS (n=7) pigs and correlated with the change in STK-GFR after revascularization (ΔGFR). Four weeks after percutaneous transluminal, renal angioplasty blood pressure was normalized in all animals, but STK-GFR improved in 10 of 15 (ΔGFR =+22.0±8.5 mL/min). ΔGFR correlated inversely with basal STK-GFR, renal release of inflammatory markers, and medullary R2* response to furosemide, but directly with GFR response to acetylcholine. Basal contralateral kidney GFR correlated directly with ΔGFR.

CONCLUSIONS

Low basal STK-GFR with preserved response to acetylcholine may predict benefit from revascularization in RAS, whereas renal inflammation and robust STK-R2* responses to furosemide (possibly reflecting avid tubular oxygen consumption) are associated with less favorable outcomes. These tools may be useful for identification of patients likely to improve renal function after revascularization.

Noninvasive In vivo assessment of renal tissue elasticity during graded renal ischemia using MR elastography

OBJECTIVES

: Magnetic resonance elastography (MRE) allows noninvasive assessment of tissue stiffness in vivo. Renal arterial stenosis (RAS), a narrowing of the renal artery, promotes irreversible tissue fibrosis that threatens kidney viability and may elevate tissue stiffness. However, kidney stiffness may also be affected by hemodynamic factors. This study tested the hypothesis that renal blood flow (RBF) is an important determinant of renal stiffness as measured by MRE.

MATERIAL AND METHODS

: In 6 anesthetized pigs MRE studies were performed to determine cortical and medullary elasticity during acute graded decreases in RBF (by 20%, 40%, 60%, 80%, and 100% of baseline) achieved by a vascular occluder. Three sham-operated swine served as time control. Additional pigs were studied with MRE 6 weeks after induction of chronic unilateral RAS (n = 6) or control (n = 3). Kidney fibrosis was subsequently evaluated histologically by trichrome staining.

RESULTS

: During acute RAS the stenotic cortex stiffness decreased (from 7.4 ± 0.3 to 4.8 ± 0.6 kPa, P = 0.02 vs. baseline) as RBF decreased. Furthermore, in pigs with chronic RAS (80% ± 5.4% stenosis) in which RBF was decreased by 60% ± 14% compared with controls, cortical stiffness was not significantly different from normal (7.4 ± 0.3 vs. 7.6 ± 0.3 kPa, P = 0.3), despite histologic evidence of renal tissue fibrosis.

CONCLUSION

: Hemodynamic variables modulate kidney stiffness measured by MRE and may mask the presence of fibrosis. These results suggest that kidney turgor should be considered during interpretation of elasticity assessments.

Persistent kidney dysfunction in swine renal artery stenosis correlates with outer cortical microvascular remodeling

Percutaneous transluminal renal stenting (PTRS) does not consistently improve renal function in patients with atherosclerotic renovascular disease, but the mechanisms underlying irreversible kidney injury have not been fully elucidated. We hypothesized that renal dysfunction after PTRS is linked to ongoing renal microvascular (MV) remodeling. Pigs were studied after 10 wk of atherosclerosis and renal artery stenosis (ARAS), ARAS treated with PTRS 4 wk earlier, and normal controls (n = 10 each). Renal blood flow (RBF) and glomerular filtration rate (GFR) were studied using multidetector computer tomography. Renal microvascular architecture (micro-CT), angiogenic activity, oxidative stress, and fibrosis were evaluated ex vivo. Four weeks after PTRS, blood pressure was normalized. However, GFR and RBF remained similarly decreased in untreated ARAS and ARAS+PTRS (P < 0.05 vs. normal). MV rarefaction was unaltered after revascularization, and the spatial density of outer cortical microvessels correlated with residual GFR. Interstitial fibrosis and altered expression of proangiogenic and profibrotic factors persisted after PTRS. Tubulointerstitial injury in ARAS persisted 4 wk after mechanically successful PTRS, and vessel loss correlated with residual renal dysfunction. MV loss and fibrosis in swine ARAS might account for persistent renal dysfunction after PTRS and underscore the need to assess renal parenchymal disease before revascularization.

Ischaemic nephropathy secondary to atherosclerotic renal artery stenosis: clinical and histopathological correlates

BACKGROUND

Advanced renal artery stenosis (RAS) may cause progressive deterioration in renal function. We correlated the histopathological findings and clinical characteristics in selected patients with atherosclerotic RAS who underwent nephrectomy of their small kidneys for resistant renovascular hypertension.

METHODS

We studied 62 patients who underwent nephrectomy of a small kidney for uncontrolled hypertension between 1990 and 2000.

RESULTS

The mean patient age was 65.4 ± 9.6 years; 28 (45%) were men. Significant tubulointerstitial atrophy with relative glomerular sparing was the predominant pattern of injury in 44 (71%) patients. In 14 (23%) patients, diffuse global glomerulosclerosis was present. The severity of tubulointerstitial atrophy and the extent of glomerulosclerosis were both associated with smaller kidney size (P = 0.002). Three patterns of vascular involvement were present: atheroembolic, atherosclerotic and hypertensive vascular changes, which were documented in 39, 98 and 52% of subjects, respectively. The presence and severity of these vascular changes positively correlated with both atherosclerotic risk factors, such as hypertension, dyslipidaemia and renal insufficiency, and cardiovascular morbidity, including abdominal aortic aneurysm and myocardial infarction. Patients on statin therapy were noted to have less evidence of renal fibrosis as measured by transforming growth factor-beta staining (P = 0.003).

CONCLUSION

The severity of renal histopathological findings in patients who underwent nephrectomy for resistant hypertension correlated with an increased prevalence of cardiovascular disease, a greater degree of renal dysfunction and more severe dyslipidaemia. Statin therapy may affect development of intra-renal injury by slowing the progression of fibrosis.

Hydrogen-rich saline solution attenuates renal ischemia-reperfusion injury

PURPOSE

Renal ischemia-reperfusion (I/R), an important cause of acute kidney injury, is unavoidable during various types of operations, including renal transplantation, surgical revascularization of the renal artery, partial nephrectomy, and treatment of suprarenal aortic aneurysms. Exacerbation of I/R injury is mediated by reactive oxygen species (ROS). A recent study has shown that hydrogen has antioxidant properties. In this study, we tested the hypothesis that a hydrogen-rich saline solution (HRSS) attenuates renal I/R injury in a rodent model.

METHODS

Rats were treated with an intravenous injection of HRSS or control saline solution followed by renal I/R. After 24 h of treatment, we performed a histological examination and transmission electron microscopy, and measured serum levels of 8-OHdG.

RESULTS

Histological analysis revealed a marked reduction of interstitial congestion, edema, inflammation, and hemorrhage in renal tissue harvested 24 h after HRSS treatment compared to saline administration. Renal I/R injury, which led to altered mitochondrial morphology, was also inhibited by HRSS. Furthermore, serum 8-OHdG levels were significantly lower in rats treated with HRSS and subjected to renal I/R.

CONCLUSIONS

These protective effects were likely due to the antioxidant properties of HRSS. These results suggest that HRSS is a potential therapeutic candidate for treating various I/R diseases.

Revascularization of swine renal artery stenosis improves renal function but not the changes in vascular structure

Renal revascularization by percutaneous transluminal angioplasty improves blood pressure and stenotic kidney function in selected groups of patients, but the reversibility of intrarenal and microvascular remodeling remains unknown. Here, we tested the hypothesis that renal angioplasty improves the function and structure of renal microcirculation in experimental chronic renal artery stenosis. Stenotic kidney function, hemodynamics, and endothelial function were assessed in vivo in pigs after 10 weeks of unilateral renal artery stenosis. Renal microvascular remodeling, angiogenic pathways, and fibrosis were measured ex vivo. Angioplasty and stenting carried out 4 weeks before measurement decreased blood pressure, improved glomerular filtration rate, and improved microvascular endothelial function. It also promoted the expression of angiogenic factors and decreased renal apoptosis due to stenosis, compared with a sham intervention. The spatial density of renal microvessels, however, was partially improved after angioplasty. Renal blood flow was incompletely restored compared with the kidneys of sham-treated animals, as was interstitial fibrosis. Renal microvascular media-to-lumen ratio remained unchanged by angioplasty. Thus, our study shows that revascularization of a stenotic renal artery restores the glomerular filtration rate and renal endothelial function 4 weeks later. Renal hemodynamics and structure, however, are incompletely resolved.

[Management of renal atrophy in hypertensive patients: experience in Lille]

INTRODUCTION

In the absence of specific treatment, patients with renal vascular disease develop renal atrophy. This population frequently has hypertension refractory to medical treatment. The patients who may respond to revascularization or at the worst to a nephrectomy must be identified to optimize their therapeutic management.

METHODS

We conducted an observational retrospective study of hypertensive patients with unilateral renal atrophy (renal height < 9 cm) followed at the Lille University Hospital Center from 1998 to 2006. Hypertension, renal clearance (by scintigraphy with MAG3), and hypersecretion of renin (segmental/selective venous renin samples) were studied. We subsequently classified the patients into 3 groups. Medical treatment was optimized for all.

RESULTS

The mean follow-up period was 1.3+/-0.2 years. Eight patients were treated medically (group 1). Endovascular revascularization was used to treat the subjects for which atrophic kidney function accounted for more than 10% of their total renal function and with stenosis of the renal artery (>70%) (group 2, n=19). Those with a small nonfunctional kidney (<10% of total renal function) and hypersecretion of renin (ratio>1.5 in relation to the contralateral kidney) underwent a nephrectomy (group 3, n=8). The reduction in systolic blood pressure (SBP) was 27 mm Hg and diastolic blood pressure (DBP) 14 mm Hg for the overall study population (p < 0.001), without any significant aggravation of renal function. In group 1, the reduction in blood pressure was lower, with medical treatment alone; SBP fell by 13 mm Hg and DBP by 4mm Hg (p=ns) ; this group had the lowest initial blood pressure. In group 2, revascularization made it possible to improve SBP by 26 mm Hg and DBP by 14 mm Hg (p < 0.01) without significant impairment of renal function. Group 3 showed the most spectacular improvement in blood pressure, with SBP dropping by 40 mm Hg and DBP by 19 mm Hg (p=0.016). But it was also in this group that we observed an aggravation in the rate of glomerular filtration with a nonsignificant reduction of 12.8 mL/min, nonetheless superior to that expected according to the preoperative scintigraphy.

CONCLUSION

The results of this work underline the importance of multidisciplinary management of patients with small ischemic kidneys. Preselection of patients in unstable clinical situations (refractory hypertension, progressive kidney failure, flash pulmonary edema) by isotopic and endocrinal renal evaluation provides a basis for deciding on treatment. The existence of a renin ratio >1.5 can identify the patients most likely to respond to nephrectomy. The reduction of renal function following nephrectomy must be considered in the discussion about treatment. The functional threshold initially defined at 10% may be lowered to 5%, to limit this postoperative reduction.

Melatonin improves cardiovascular function and ameliorates renal, cardiac and cerebral damage in rats with renovascular hypertension

The effect of melatonin was investigated in an angiotensin II-dependent renovascular hypertension model in Wistar albino rats by placing a renal artery clip (two-kidney, one-clip; 2K1C), while sham rats did not have clip placement. Starting either on the operation day or 3 wk after the operation, the rats received melatonin (10 mg/kg/day) or vehicle for the following 6 wk. At the end of the nineth week, after blood pressure (BP) and echocardiographic recordings were obtained, plasma samples were obtained to assay lactate dehydrogenase (LDH), creatine kinase (CK), antioxidant capacity (AOC), asymmetric dimethylarginine (ADMA), and nitric oxide (NOx) levels. In the kidney, heart and brain tissues, malondialdehyde (MDA) and glutathione (GSH) levels, superoxide dismutase (SOD), catalase (CAT), myeloperoxidase (MPO) and Na(+)-K(+) ATPase activities were determined. 2K1C caused an increase in BP and left ventricular (LV) dysfunction. In hypertensive animals LDH, CK, ADMA levels were increased in plasma with a concomitant reduction in AOC and NOx. Moreover, hypertension caused a significant decrease in tissue SOD, CAT, and Na(+), K(+)-ATPase activities and glutathione content, while MDA levels and MPO activity were increased in all studied tissues. On the other hand, both melatonin regimens significantly reduced BP, alleviated oxidative injury and improved LV function. In conclusion, melatonin protected against renovascular hypertension-induced tissue damage and improved cardiac function presumably due to both its direct antioxidant and receptor-dependent actions, suggesting that melatonin may be of therapeutic use in preventing oxidative stress due to hypertension.

Inhibition of renal rho kinase attenuates ischemia/reperfusion-induced injury

The Rho kinase pathway plays an important role in dedifferentiation of epithelial cells and infiltration of inflammatory cells. For testing of the hypothesis that blockade of this cascade within the kidneys might be beneficial in the treatment of renal injury the Rho kinase inhibitor, Y27632 was coupled to lysozyme, a low molecular weight protein that is filtered through the glomerulus and is reabsorbed in proximal tubular cells. Pharmacokinetic studies with Y27632-lysozyme confirmed that the conjugate rapidly and extensively accumulated in the kidney. Treatment with Y27632-lysozyme substantially inhibited ischemia/reperfusion-induced tubular damage, indicated by reduced staining of the dedifferentiation markers kidney injury molecule 1 and vimentin, and increased E-cadherin relative to controls. Rho kinase activation was inhibited by Y27632-lysozyme within tubular cells and the interstitium. Y27632-lysozyme also inhibited inflammation and fibrogenesis, indicated by a reduction in gene expression of monocyte chemoattractant protein 1, procollagen Ialpha1, TGF-beta1, tissue inhibitor of metalloproteinase 1, and alpha-smooth muscle actin. Immunohistochemistry revealed reduced macrophage infiltration and decreased expression of alpha-smooth muscle actin, collagen I, collagen III, and fibronectin. In contrast, unconjugated Y27632 did not have these beneficial effects but instead caused systemic adverse effects, such as leukopenia. Neither treatment improved renal function in the bilateral ischemia/reperfusion model. In conclusion, the renally targeted Y27632-lysozyme conjugate strongly inhibits tubular damage, inflammation, and fibrogenesis induced by ischemia/reperfusion injury.

Atherosclerotic renal artery stenosis: overtreated but underrated?

Despite evidence of only moderate clinical benefit, application of renal endovascular stent procedures has increased at least four-fold in the past decade. Medicare is reviewing national coverage regarding reimbursement, questioning whether outcome data warrant many of these procedures. Several prospective, randomized trials are now in progress to compare outcomes with optimized medical therapy with and without stenting. Current imaging methods establish primarily the presence and severity of vascular occlusive disease. Optimal treatment for individual patients remains in flux and is reviewed here. Most important, nephrologists await development of tools to predict reliably when renal parenchymal injury is beyond recovery and/or when revascularization can produce meaningful salvage of kidney function.

Antioxidant capacity of 55 medicinal herbs traditionally used to treat the urinary system: a comparison using a sequential three-solvent extraction process

BACKGROUND

The prevalence of chronic renal disease exceeds 10% in industrialized societies. Oxidative damage is thought to be one of the main mechanisms involved in nearly all chronic renal pathologies.

OBJECTIVE

We aimed to use the oxygen radical absorbance capacity (ORAC) method and a sequential multisolvent extraction process to compare the in vitro antioxidant capacity of 55 medicinal herbs and prioritize them for in vivo studies investigating the value of herbal therapies in the treatment of renal disorders.

METHODS

The herbs were chosen on the basis of their traditional use in kidney or urinary system disorders, or because they have attracted the attention of recent investigations into renal pathologies. The three solvents used for extraction were ethyl acetate, methanol, and 50% aqueous methanol. Silybum marianum (milk thistle) seed and Camellia sinensis (tea) leaf, both known to possess high antioxidant capacity, were included for comparison.

RESULTS

Twelve of the 55 herbs were comparable to or exceeded ORAC levels of milk thistle seed or tea leaf. The highest radical-scavenging activity was found in Olea europaea (olive leaf), Cimicifuga racemosa (black cohosh), Rheum palmatum (rhubarb), Glycyrrhiza glabra (licorice), and Scutellaria lateriflora (Virginia skullcap).

CONCLUSIONS

The antioxidant capacity of many of the herbs studied may, at least in part, be responsible for their reputation as being protective of organs of the urinary system. Overall, the combined ORAC values for the methanol and aqueous methanol extracts comprised 84% of the total ORAC value. Sequential extraction with solvents of different polarities may be necessary to fully extract the antioxidant principles from medicinal plants.

Combined type-1 plasminogen activator inhibitor and NOD2/CARD15 genotyping predicts complicated Crohn's disease behaviour

BACKGROUND

NOD2/CARD15 gene variants have not been universally associated with stricturing behaviour in Crohn's disease. Other behaviour modifying genes could explain these results.

AIM

To study the combined influence of NOD2/CARD15 variants and 4G/4G genotype of type-1 plasminogen activator inhibitor (PAI-1) gene on Crohn's disease behaviour.

METHODS

One hundred and seventy Crohn's disease patients were studied prospectively, with a mean follow-up of 7+/- 6 years. Disease behaviour was registered by using two criteria: the Vienna classification and a non-hierarchical classification based on the behavioural Vienna categories.

RESULTS

In the multivariate analysis for stricturing behaviour according to the Vienna categories, only absence of colonic disease (OR, 4.0; 95% CI: 1.49-11.1; P = 0.006) was an independent predictive factor. However, in the multivariate analysis for stricturing disease applying a non-hierarchical criteria, ileal disease (OR, 4.19; 95% CI: 1.30-13.5; P = 0.01), and carrying both NOD2/CARD15 variants and the 4G/4G PAI-1 genotype (OR, 5.02; 95% CI: 1.44-17.48; P = 0.01) were independent predictive factors. In the multivariate analysis for penetrating behaviour, the 4G/4G PAI-1 (OR, 3.10; 95% CI: 1.54-6.23; P = 0.001) and male sex (OR, 2.44; 95% CI: 1.30-4.60; P = 0.005) were independent predictive factors irrespective of criteria applied.

CONCLUSIONS

Combined PAI-1 and NOD2/CARD15 genotyping predict complicated Crohn's disease. Patients with these variants could benefit from early interventions.

Simvastatin promotes angiogenesis and prevents microvascular remodeling in chronic renal ischemia

We tested the hypothesis that statins would decrease renal injury in renal artery stenosis (RAS) by restoring angiogenesis and attenuating intrarenal microvascular (IMV) remodeling. Single-kidney hemodynamics and function were quantified using electron-beam-computed tomography (CT) in normocholesterolemic pigs after 12 wk of experimental RAS, RAS supplemented with simvastatin (RAS+simvastatin), and normal controls. Renal circulation was also studied in vivo using angiography and ex vivo using a unique 3D micro-CT imaging technique. Angiogenic and remodeling pathways were subsequently explored in renal tissue. Blood pressure and the degree of stenosis were similarly increased in RAS groups. Simvastatin in RAS enhanced both intrarenal angiogenesis and peri-stenosis arteriogenesis and increased the expression of angiogenic growth factors and hypoxia-inducible factor-1alpha. Furthermore, simvastatin decreased tissue-transglutaminase expression and IMV inward remodeling, restored IMV endothelial function, decreased fibrogenic activity, and improved renal function. Chronic simvastatin supplementation promoted angiogenesis in vivo, decreased ischemia-induced IMV remodeling, and improved IMV function in the stenotic kidney, independent of lipid lowering. These novel renoprotective effects suggest a role for simvastatin in preserving the ischemic kidney in chronic RAS.

Pathways of renal fibrosis and modulation of matrix turnover in experimental hypercholesterolemia

Dyslipidemia often accompanies and accelerates renal disease, partly by promoting fibrosis. However, the mechanisms mediating this effect are unclear. We hypothesized that hypercholesterolemia modulates several interlinked pathways that promote deposition and blunt degradation of extracellular matrix, and that these could be manipulated by reversal of hypercholesterolemia. Fourteen pigs were fed a 16-week 2% high-cholesterol diet (HC-HC; n=7) or normal diet (n=7), whereas in 7 others, a 10-week HC was followed by a 6-week normal diet (HC-N). Renal endothelial function was assessed in vivo with electron-beam computed tomography, and renal tissue was then studied ex vivo using Western blot, real-time quantitative polymerase chain reaction, gelatin zymography, and immunostaining. HC-HC kidneys showed endothelial dysfunction, accompanied by increased intrarenal oxidative stress, inflammation, activation of the endothelin and transforming-growth factor-beta systems, and decreased matrix metalloproteinase expression and activity. Accordingly, HC-HC kidneys showed increased collagen IV expression and fibrosis. A lipid-lowering dietary intervention reversed most of these changes. In conclusion, this study indicates that renal fibrosis in early atherosclerosis is a result of a simultaneous increase in extracellular matrix deposition and blunted matrix metalloproteinase-mediated degradation, overall promoting perivascular and tubulointerstitial fibrosis. Notably, many of these pathways may be reversible in hypercholesterolemia, and crucial targets could potentially be identified for early interventions to preserve the kidney.

Blood oxygen level-dependent measurement of acute intra-renal ischemia

BACKGROUND

Ischemic nephropathy is a common cause of end-stage renal disease. Exploration of the mechanisms of deterioration of renal function is limited due to lack of noninvasive techniques available to study the single kidney. The Blood Oxygen Level-Dependent (BOLD) MRI method can measure deoxyhemoglobin and therefore indirectly estimates renal oxygen content, but has never been evaluated in renal artery stenosis (RAS). This study was therefore designed to test if BOLD can detect the characteristic of renal hypoxia induced by RAS.

METHODS

RAS was induced in 8 pigs using an occluder placed around the right renal artery. Renal blood flow (RBF) was measured continuously with an ultrasound probe. BOLD signal was measured bilaterally in the cortex and medulla (as the slope of the logarithm of MR signal) at baseline and at the lower limit of RBF autoregulation. The measurements were then repeated during six sequential graded decreases in RBF (80 to 0% of baseline) and during recovery.

RESULTS

During the control period, BOLD signals were not significantly different between the right and the left kidneys. In the occluded kidney, BOLD signal of the cortex (19.3 +/- 1.9/s) and the medulla (17.3 +/- 2.0/s) increased during occlusion gradually and significantly (P < 0.0001) to a maximum (at total occlusion) of 33.8 +/- 2.0/s (+79%) and 29.8 +/- 2.3/s (+78%), respectively, and returned to baseline values during recovery.

CONCLUSION

This study shows that the BOLD technique can noninvasively detect change in intra-renal oxygenation during an acute reduction of RBF. This study provides a strong rationale for developing the BOLD method for the detection and evaluation of renal hypoxia induced by RAS, which may be potentially applicable in humans.

Beneficial effects of antioxidant vitamins on the stenotic kidney

Renal artery stenosis (RAS) may lead to renal injury, partly mediated through increased oxidative stress. However, the potential effects of chronic oral antioxidant intervention on the stenotic kidney remain unknown. This study was designed to test the hypothesis that chronic antioxidant vitamin supplementation in RAS would preserve renal function and structure. Single-kidney hemodynamics and function were quantified in vivo in pigs using electron-beam CT after 12 weeks of unilateral RAS (n=7), a similar degree of RAS orally supplemented with vitamins C (1 g) and E (100 IU/kg) (RAS+Vitamins, n=7), or controls (normal, n=7). Renal tissue was studied ex vivo using Western blotting and immunohistochemistry. Mean arterial pressure was similarly elevated in both RAS groups, while ischemic renal volume and glomerular filtration rate were similarly reduced. Renal blood flow was decreased in RAS compared with normal (326.5+/-99.9 versus 553.4+/-48.7 mL/min, respectively, P=0.01), but preserved in RAS+Vitamins (485.2+/-104.1 mL/min, P=0.3 versus normal). The marked increase in the expression of the NADPH-oxidase subunits p47phox and p67phox, nitrotyrosine, endothelial and inducible nitric oxide synthase, and nuclear factor-kappaB observed in RAS (P<0.05 versus normal) was normalized in RAS+Vitamins (P>0.1). Furthermore, trichrome staining and the expression of transforming growth factor-beta and tissue inhibitor of matrix-metalloproteinase-1 were also decreased in RAS+Vitamins. In conclusion, chronic blockade of the oxidative stress pathway in RAS using antioxidant vitamins improved renal hemodynamics and decreased oxidative stress, inflammation, and fibrosis in the ischemic kidney. These observations underscore the involvement of oxidative stress in renal injury in RAS and support a role for antioxidant vitamins in preserving the ischemic kidney.

Selective protection of renal tubular epithelial cells by heme oxygenase (HO)-1 during stress-induced injury

BACKGROUND

The renal pathology of human heme oxygenase (HO)-1 deficiency is characterized by advanced tubulointerstitial injury, whereas the glomerular structures are affected little. These facts suggest that the renal tubuli are dependent on intrinsic HO-1 production for their survival under oxidative stresses.

METHODS

We compared the patterns of HO-1 expression by primary cultured human mesangial cells (HMCs) and renal proximal tubular epithelial cells (HRPTECs) in vitro. Furthermore, the cytoprotective roles of HO-1 induced in these cells were evaluated by stress-induced cytotoxicity assays. HO-1 expressions in HRPTECs and HMCs were evaluated by immunoblotting, and by reverse transcriptase (RT) and/or real time polymerase chain reaction (PCR).

RESULTS

In HRPTECs, both HO-1 mRNA expression and protein production peaked at around 12 h and persisted until 24 h after hemin stimulation. In contrast, HO-1 mRNA expression and protein production by HMCs peaked at 4 h and 6 h respectively, and the levels declined rapidly, being undetectable at 24 h. The peak level of HO-1 expression was significantly higher in HRPTECs than in HMCs. Oxidative stress-induced cell injury in HRPTECs was significantly reduced when HO-1 production had been induced prior to the culture. In contrast, HO-1 induction had little cytoprotective effect on HMCs. Tin protoporphyrin (SnPP), an inhibitor of HO function, significantly reversed the cytoprotection by HO-1.

CONCLUSION

These data suggest that HRPTECs are more susceptible to oxidative stress and are significantly more dependent on HO-1 for protection against noxious stimuli than HMCs. Collectively, these results indicate that HO-1 is an important protective factor for kidney tissue, in particular, renal tubular epithelial cells.

Managing renal arterial disease and hypertension

Treating patients with renovascular disease is complex, particularly as imaging and medical techniques become more effective. Atherosclerotic renal artery disease is present in 7% of the general population above age 65 and in 20 to 45% of patients with coronary disease or aortoiliac disease. Most patients are treated medically, but when progressive hypertension, renal insufficiency, or circulatory congestion develops, revascularization should be considered. Endovascular procedures with arterial stents are now widely employed. These procedures sometimes offer major benefits in blood pressure control and stabilization of renal function. Stent procedures continue to entail hazards, including atheroemboli, arterial dissections, and thrombosis, in addition to restenosis rates of 14 to 20%. Small, randomized trials to date demonstrate no survival benefit to either endovascular or surgical revascularization as compared with medical management. Recognizing renal artery disease and directing revascularization procedures to those with the most benefit remains a premier challenge for the clinician.

Urological manifestations of vascular disease

We have detailed several of the urological manifestations of vascular disease. With the aging of the North American population, urologists will encounter the urological complications of vascular disease with ever-increasing frequency.

Pathophysiology of renovascular hypertension

Studies of the renin-angiotension system and the effects of pharmacologic blockade have enhanced our understanding of renovascular hypertension. A critical degree of arterial stenosis produces kidney ischemia sufficient to activate this hormonal system, whose actions include vasoconstriction and sodium retention. Accurate clinical evaluation may depend upon recognizing the differences in pathophysiology between "one-kidney" and "two-kidney" forms and the dynamic nature of this condition.