Single-kidney Renal Blood Flow Research Articles

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.

Percutaneous transluminal renal angioplasty attenuates poststenotic kidney mitochondrial damage in pigs with renal artery stenosis and metabolic syndrome.

Percutaneous transluminal renal angioplasty (PTRA) has been used to treat renovascular disease (RVD), a chronic condition characterized by renal ischemia and metabolic abnormalities. Mitochondrial injury has been implicated as a central pathogenic mechanism in RVD, but whether it can be reversed by PTRA remains uncertain. We hypothesized that PTRA attenuates mitochondrial damage, renal injury, and dysfunction in pigs with coexisting renal artery stenosis (RAS) and metabolic syndrome (MetS). Four groups of pigs (n = 6 each) were studied after 16 weeks of diet-induced MetS and RAS (MetS + RAS), MetS + RAS treated 4 weeks earlier with PTRA, and Lean and MetS Sham controls. Single-kidney renal blood flow (RBF) and glomerular filtration rate (GFR) were assessed in vivo with multidetector computed tomography, and renal tubular mitochondrial structure and function and renal injury ex vivo. PTRA successfully restored renal artery patency, but mean arterial pressure remained unchanged. Stenotic kidney RBF and GFR, which fell in MetS + RAS compared to MetS, rose after PTRA. PTRA attenuated MetS + RAS-induced mitochondrial structural abnormalities in tubular cells and peritubular capillary endothelial cells, decreased mitochondrial H2 02 production, and increased renal cytochrome-c oxidase-IV activity and ATP production. PTRA also improved cortical microvascular and peritubular capillary density and ameliorated tubular injury and tubulointerstitial fibrosis in the poststenotic kidney. Importantly, renal mitochondrial damage correlated with poststenotic injury and dysfunction. Renal revascularization attenuated mitochondrial injury and improved renal hemodynamics and function in swine poststenotic kidneys. This study suggests a novel mechanism by which PTRA might be relatively effective in ameliorating mitochondrial damage and improving renal function in coexisting MetS and 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.

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

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. 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. 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.

Coexisting renal artery stenosis and metabolic syndrome magnifies mitochondrial damage, aggravating poststenotic kidney injury in pigs.

Renovascular disease (RVD) produces chronic underperfusion of the renal parenchyma and progressive ischemic injury. Metabolic abnormalities often accompany renal ischemia, and are linked to poorer renal outcomes. However, the mechanisms of injury in kidneys exposed to the ischemic and metabolic components of RVD are incompletely understood. We hypothesized that coexisting renal artery stenosis (RAS) and metabolic syndrome (MetS) would exacerbate mitochondrial damage, aggravating poststenotic kidney injury in swine. Domestic pigs were studied after 16 weeks of either standard diet (Lean) or high-fat/high-fructose (MetS) with or without superimposed RAS (n = 6 each). Single-kidney renal blood flow (RBF) and glomerular filtration rate (GFR) were assessed in vivo with multidetector-CT, and renal tubular mitochondrial structure, homeostasis and function and renal injury ex vivo. Both RAS groups achieved significant stenosis. Single-kidney RBF and GFR were higher in MetS compared with Lean, but decreased in Lean+RAS and MetS+RAS vs. their respective controls. MetS and RAS further induced changes in mitochondrial structure, dynamics, and function, and their interaction (diet × ischemia) decreased matrix density, mitophagy, and ATP production, and lead to greater renal fibrosis. Coexisting RAS and MetS synergistically aggravate mitochondrial structural damage and dysfunction, which may contribute to structural injury and dysfunction in the poststenotic kidney. These observations suggest that mitochondrial damage precedes loss of renal function in experimental RVD, and position mitochondria as novel therapeutic targets in these patients.

The metabolic syndrome induces early changes in the swine renal medullary mitochondria

The metabolic syndrome (MetS) is associated with nutrient surplus and kidney hyperfiltration, accelerating chronic renal failure. Mitochondria can be overwhelmed by substrate excess, leading to inefficient energy production and thereby tissue hypoxia. Mitochondrial dysfunction is emerging as an important determinant of renal damage, but whether it contributes to MetS-induced renal injury remains unknown. We hypothesized that early MetS induces kidney mitochondrial abnormalities and dysfunction, which would be notable in the vulnerable renal medulla. Pigs were studied after 16weeks of diet-induced MetS, MetS treated for the last 4weeks with the mitochondria-targeted peptide elamipretide (0.1mg/kg SC q.d), and Lean controls (n=7 each). Single-kidney renal blood flow, glomerular filtration rate, and oxygenation were measured in-vivo, whereas cortical and medullary mitochondrial structure and function and renal injurious pathways were studied ex-vivo. Blood pressure was slightly elevated in MetS pigs, and their renal blood flow and glomerular filtration rate were elevated. Blood oxygen level-dependent magnetic resonance imaging demonstrated that this was associated with medullary hypoxia, whereas cortical oxygenation remained intact. MetS decreased renal content of the inner mitochondrial membrane cardiolipin, particularly the tetra-linoleoyl (C18:2) cardiolipin species, and altered mitochondrial morphology and function, particularly in the medullary thick ascending limb. MetS also increased renal cytochrome-c-induced apoptosis, oxidative stress, and tubular injury. Chronic mitoprotection restored mitochondrial structure, ATP synthesis, and antioxidant defenses and decreased mitochondrial oxidative stress, medullary hypoxia, and renal injury. These findings implicate medullary mitochondrial damage in renal injury in experimental MetS, and position the mitochondria as a therapeutic target.

Mesenchymal stem cell–derived extracellular vesicles attenuate kidney inflammation

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

Renal vein cytokine release as an index of renal parenchymal inflammation in chronic experimental renal artery stenosis

Renal parenchymal inflammation is a critical determinant of kidney injury in renal artery stenosis (RAS) but is difficult to assess in the single kidney without tissue samples. Whether renal vein (RV) levels of inflammatory markers reflect active parenchymal inflammation remains unknown. We evaluated the relationship between net RV cytokine release and tissue inflammation in the post-stenotic kidney. Pigs were studied after 10 weeks of RAS treated 4 weeks earlier with intra-renal vehicle or anti-inflammatory mesenchymal stem cells (MSCs) or normal control. Single-kidney renal blood flow was measured by fast computerized tomography. RV and inferior vena cava levels of tumor necrosis factor (TNF)-α, interferon (IF)-γ, monocyte chemoattractant protein (MCP-1) and interleukin (IL)-10 were measured by enzyme-linked immunosorbent assay, and their net release calculated. Renal expression of the same cytokines was correlated with their net release. Net release of TNF-α, IF-γ and MCP-1 was higher in RAS compared with normal and to the contralateral kidney (all P<0.05), decreased in MSC-treated pigs as was their tissue expression. Contrarily, the release of the anti-inflammatory IL-10 was lower in RAS and normalized in RAS+MSC. The net release of TNF-α, MCP-1 and IL-10 directly correlated with their tissue expression. The ratio of inflammatory-to-reparative macrophages directly correlated with the release of MCP-1, but inversely with the release of IL-10. In vitro cultured MSCs also induced a shift in the macrophage phenotype from inflammatory (M1) to reparative (M2). Our findings demonstrate that the release of inflammatory markers from the affected kidney provides an index of renal tissue inflammation in experimental RAS.

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

Atherosclerotic renal artery stenosis (ARAS) is known to reduce renal blood flow, glomerular filtration rate (GFR) and amplify kidney hypoxia, but the relationships between these factors and tubulointerstitial injury in the poststenotic kidney are poorly understood. The purpose of this study was to examine the effect of renal revascularization in ARAS on renal tissue hypoxia and renal injury. Inpatient studies were performed in patients with ARAS (n=17; >60% occlusion) before and 3 months after stent revascularization, or in patients with essential hypertension (n=32), during fixed Na(+) intake and angiotensin converting enzyme/angiotensin receptors blockers Rx. Single kidney cortical, medullary perfusion, and renal blood flow were measured using multidetector computed tomography, and GFR by iothalamate clearance. Tissue deoxyhemoglobin levels (R(2)*) were measured by blood oxygen level-dependent MRI at 3T, as was fractional kidney hypoxia (percentage of axial area with R(2)*>30/s). In addition, we measured renal vein levels of neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, and tumor necrosis factor-α. Pre-stent single kidney renal blood flow, perfusion, and GFR were reduced in the poststenotic kidney. Renal vein neutrophil gelatinase-associated lipocalin, tumor necrosis factor-α, monocyte chemoattractant protein-1, and fractional hypoxia were higher in untreated ARAS than in essential hypertension. After stent revascularization, fractional hypoxia fell (P<0.002) with increased cortical perfusion and blood flow, whereas GFR and neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, and tumor necrosis factor-α remained unchanged. These data demonstrate that despite reversal of renal hypoxia and partial restoration of renal blood flow after revascularization, inflammatory cytokines and injury biomarkers remained elevated and GFR failed to recover in ARAS. Restoration of vessel patency alone failed to reverse tubulointerstitial damage and partly explains the limited clinical benefit of renal stenting. These results identify potential therapeutic targets for recovery of kidney function in renovascular disease.

Obesity-metabolic derangement preserves hemodynamics but promotes intrarenal adiposity and macrophage infiltration in swine renovascular disease

Obesity-metabolic disorders (ObM) often accompany renal artery stenosis (RAS). We hypothesized that the coexistence of ObM and RAS magnifies inflammation and microvascular remodeling in the stenotic kidney (STK) and aggravates renal scarring. Twenty-eight obesity-prone Ossabaw pigs were studied after 16 wk of a high-fat/high-fructose diet or standard chow including ObM-sham, ObM-RAS, Lean-RAS, or Lean-sham (normal control) groups. Single-kidney renal blood flow (RBF) and glomerular filtration rate (GFR) were assessed by multidetector computed tomography (CT), renal oxygenation and tubular transport capability by blood-oxygen-level-dependent MRI, and microcirculation by micro-CT for vessel density, and Western blotting for protein expressions of angiogenic factors (VEGF/FLK-1). Renal vein and inferior vena cava levels of inflammatory cytokines were measured to evaluate systemic and kidney inflammation. Macrophage (MØ) infiltration and subpopulations, fat deposition in the kidney, and inflammation in perirenal and abdominal fat were also examined. GFR and RBF were decreased in Lean-STK but relatively preserved in ObM-STK. However, ObM-STK showed impaired tubular transport function, suppressed microcirculation, and stimulated glomerulosclerosis. ObM diet interacted with RAS to blunt angiogenesis in the STK, facilitated the release of inflammatory cytokines, and led to greater oxidative stress than Lean-STK. The ObM diet also induced fat deposition in the kidney and infiltration of proinflammatory M1-MØ, as also in perirenal and abdominal fat. Coexistence of ObM and RAS amplifies renal inflammation, aggravates microvascular remodeling, and accelerates glomerulosclerosis. Increased adiposity and MØ-accentuated inflammation induced by an ObM diet may contribute to structural injury in the post-STK kidney.

A Mitochondrial Permeability Transition Pore Inhibitor Improves Renal Outcomes After Revascularization in Experimental Atherosclerotic Renal Artery Stenosis

Revascularization improves blood pressure but not renal function in most patients with atherosclerotic renal artery stenosis (ARAS), possibly related to injury incurred during renal reperfusion. Bendavia, a novel tetrapeptide that inhibits mitochondrial permeability transition pore opening, reduces apoptosis, oxidative stress, and ischemia-reperfusion injury in experimental models. However, its potential for improving renal response to revascularization of chronic ARAS is unknown. We hypothesized that adjunct Bendavia would improve renal structure and function after percutaneous transluminal renal angioplasty (PTRA). Pigs were treated after 6 weeks of ARAS or control with PTRA+stenting (or sham), adjunct continuous 4-hour infusion of Bendavia (0.05 mg/kg IV) or vehicle (n=7 each) during PTRA. Single-kidney renal blood flow and glomerular filtration rate were studied 4 weeks later and renal mitochondrial biogenesis, microvascular architecture, and injurious pathways evaluated ex vivo. Monocyte chemoattractant protein-1 levels rose after PTRA, suggesting inflammatory injury. Bendavia did not immediately affect inflammatory cytokine levels, yet 4 weeks later, stenotic kidney renal blood flow and glomerular filtration rate both improved (44.00 ± 0.21% and 36.40 ± 10.21%, respectively) in ARAS+PTRA+Bendavia compared with ARAS+PTRA+vehicle. Renal mitochondrial biogenesis was restored after PTRA+Bendavia, and microvascular rarefaction, apoptosis, oxidative stress, tubular injury, and fibrosis decreased. Infusion of Bendavia during PTRA preserved mitochondrial biogenesis, renal hemodynamics, and function, and attenuated tissue injury in swine ARAS. Thus, functional mitochondrial injury during renal reperfusion may sustain renal inflammatory injury and limit kidney recovery after PTRA. Potent antiapoptotic and antioxidant effects provide Bendavia a novel therapeutic potential for improving kidney outcomes after PTRA in experimental ARAS.

Enhanced endothelial progenitor cell angiogenic potency, present in early experimental renovascular hypertension, deteriorates with disease duration

Endothelial progenitor cells (EPCs) augment neovascularization and repair of damaged tissues, but may undergo functional changes during exposure to cardiovascular risk factors. This study tested the hypothesis that early renovascular hypertension (RVH) modulates the temporal pattern of EPC function that deteriorates with disease duration. RVH was induced in domestic pigs by unilateral renal artery stenosis. EPCs were cultured after 3, 6, and 12 weeks of RVH or normal control to evaluate EPC function, growth factor, and homing receptor expression. Plasma renin activity (PRA), vascular endothelial growth factor (VEGF), and its soluble receptor-1 (sFlt-1) were measured in plasma. EPCs (10 × 10) isolated from 3-week RVH or from normal pigs were also injected into control kidneys (n = 6-7, each group), and 4 weeks later single-kidney renal blood flow (RBF) and glomerular filtration rate (GFR) were evaluated. Microvascular density was studied ex vivo using microcomputed tomography. Blood pressure peaked at 3 weeks and remained higher than normal throughout the study. Systemic PRA also peaked after 3 weeks of RVH and declined thereafter, whereas sFlt-1 showed a reciprocal pattern. In vivo, only RVH but not normal EPCs increased RBF, GFR, and microvascular density. RVH-EPCs showed in vitro enhanced proliferation, tube formation, VEGF, and homing receptor expression that peaked at 3 weeks, which were abolished by valsartan and returned to baseline levels after 12 weeks of RVH. EPC number remained unchanged throughout the study. A transient enhancement of EPC function, mediated by angiotensin II, may contribute to compensatory vascular adaptation in early RVH, but is lost as hypertension persists.

Endothelin-A receptor blockade slows the progression of renal injury in experimental renovascular disease

Endothelin (ET)-1, a potent renal vasoconstrictor with mitogenic properties, is upregulated by ischemia and has been shown to induce renal injury via the ET-A receptor. The potential role of ET-A blockade in chronic renovascular disease (RVD) has not, to our knowledge, been previously reported. We hypothesized that chronic ET-A receptor blockade would preserve renal hemodynamics and slow the progression of injury of the stenotic kidney in experimental RVD. Renal artery stenosis, a major cause of chronic RVD, was induced in 14 pigs and observed for 6 wk. In half of the pigs, chronic ET-A blockade was initiated (RVD+ET-A, 0.75 mg·kg(-1)·day(-1)) at the onset of RVD. Single-kidney renal blood flow, glomerular filtration rate, and perfusion were quantified in vivo after 6 wk using multidetector computer tomography. Renal microvascular density was quantified ex vivo using three-dimensional microcomputer tomography, and growth factors, inflammation, apoptosis, and fibrosis were determined in renal tissue. The degree of stenosis and increase in blood pressure were similar in RVD and RVD+ET-A pigs. Renal hemodynamics, function, and microvascular density were decreased in the stenotic kidney but preserved by ET-A blockade, accompanied by increased renal expression of vascular endothelial growth factor, hepatocyte growth factor, and downstream mediators such as phosphorilated-Akt, angiopoietins, and endothelial nitric oxide synthase. ET-A blockade also reduced renal apoptosis, inflammation, and glomerulosclerosis. This study shows that ET-A blockade slows the progression of renal injury in experimental RVD and preserves renal hemodynamics, function, and microvascular density in the stenotic kidney. These results support a role for ET-1/ET-A as a potential therapeutic target in chronic RVD.

Role of renal microcirculation in experimental renovascular disease

Renal artery stenosis (RAS) causes renal injury partly via microvascular (MV) endothelial dysfunction and damage. Vascular endothelial growth factor (VEGF) is crucial for preservation of microvasculature and promotes vascular proliferation and endothelial repair. We have previously shown that MV rarefaction is associated with decreased VEGF in the kidney exposed to chronic RAS, accompanied by deteriorated renal function and fibrosis. We hypothesized that preserving the renal microcirculation in the stenotic kidney will halt the progression of renal damage. Unilateral RAS was induced in 16 pigs. In eight, VEGF (0.05 micrograms/kg) was infused intra-renally at the onset of RAS. After 6 weeks, single-kidney haemodynamics and function were assessed using in vivo multi-detector computed tomography (CT). Renal microvessels, angiogenic pathways and morphology were investigated ex vivo using micro-CT, real-time PCR and histology. Blood pressure and degree of RAS was similar in RAS and RAS + VEGF pigs. Single-kidney renal blood flow (RBF) and glomerular filtration rate (GFR) were reduced in RAS compared to Normal (221.1 +/- 46.5 and 29.9 +/- 3.8 vs. 522.5 +/- 60.9 and 49.3 +/- 3.4 mL/min, respectively, P < 0.05), accompanied by decreased cortical MV density and increased renal fibrosis. Pre-emptive administration of VEGF preserved MV architecture, attenuated fibrosis and normalized RBF and GFR (510.8 +/- 50.9 and 39.9.1 +/- 4.1 mL/min, P = not significant vs. Normal). This study underscores the importance of the renal microcirculation in renovascular disease. Intra-renal administration of VEGF preserved renal MV architecture and function of the stenotic kidney, which in turn preserved renal haemodynamics and function and decreased renal fibrosis. These observations suggest that preventing renal MV loss may be a potential target for therapeutic approaches for patients with chronic renovascular disease.

Intrarenal Blood Oxygenation and Renal Function Measured by Magnetic Resonance Imaging During Long-Term Cyclosporine Treatment

Treatment with cyclosporine (CsA) markedly affects the renin-angiotensin-aldosterone system in parallel with an increase in the net tubular reabsorption or a decrease in secretion. Since tubular reabsorption is closely linked to medullary oxygen consumption, the aim of the present study was to investigate the intrarenal oxygenation and renal function in response to CsA. Six mini Göttingen pigs were treated with CsA (10 mg/kg/d) for 6 months. The intrarenal oxygenation was indirectly measured as R2* obtained with a multiecho gradient-echo magnetic resonance imaging (MRI) sequence. Single-kidney renal blood flow (skRBF) was measured by a velocity-sensitive gradient-echo MRI sequence. Relative single-kidney glomerular filtration rate (rskGFR) was derived from the MRI time-activity curve in response to an intravenous bolus of Gd-DTPA (0.05 mmol/kg). The present study showed that administration of CsA increased the medullary R2* (23.1 Hz vs 19.0 Hz, P = .002), whereas R2* was slightly increased in the renal cortex (13.3 Hz vs 12.3 Hz, P = .012). In parallel, rskGFR increased significantly (47.2 mL/min vs 19.8 mL/min, P = .005) but skRBF was unchanged (197.6 mL/min vs 202.5 mL/min, P > .05). The increased R2* in the renal medulla indicated that CsA augments the tubular reabsorption of water, leading to increased oxygen consumption. The supply of oxygen to the kidney was, however, maintained during treatment with CsA as suggested by an unchanged renal blood flow. The increased tubular reabsorption was compensated for by an elevated glomerular filtration rate.

Noninvasive measurement of concurrent single-kidney perfusion, glomerular filtration, and tubular function.

To assess the reliability of electron beam computed tomography (EBCT), measurements of single-kidney renal blood flow (RBF), glomerular filtration rate (GFR), and intratubular contrast medium concentration (ITC) of radiographic contrast media were quantified in anesthetized pigs before and after acetylcholine-induced vasodilation and diuresis. EBCT measurements were compared with those obtained with intravascular Doppler and inulin clearance. The capability of EBCT to detect chronic changes in single-kidney function was evaluated in pigs with unilateral renal artery stenosis, and their long-term reproducibility in normal pigs was studied repeatedly at 1-mo intervals. EBCT-RBF (ml/min) correlated with Doppler-RBF as RBF(EBCT) = 45 + 1.07 * RBF(Doppler), r = 0.81. EBCT-GFR (ml/min) correlated with inulin clearance as GFR(EBCT) = 11.7 + 1.02 * GFR(inulin), r = 0.80. During vasodilation, RBF and GFR increased, whereas ITC decreased along the nephron. In renal artery stenosis, single-kidney GFR decreased linearly with the degree of stenosis, and ITC increased along the nephron, indicating increased fluid reabsorption. EBCT-RBF, GFR, and ITC were similar among repeated measurements. This approach might be invaluable for simultaneous quantification of regional hemodynamics and function in the intact kidneys, in a manner potentially applicable to humans.

Short-term effects of intra-aortic balloon pumping on renal blood flow and renal oxygen consumption in cardiogenic shock

Intra-aortic balloon pumping is frequently used in patients with cardiogenic shock when oliguria persists despite maximal pharmacologic support. The objective of this study was to measure the effect of intra-aortic balloon pumping on renal blood flow, renal oxygen delivery, and renal oxygen consumption in such patients. Central hemodynamics, renal blood flow, and oxygen transport were measured in 10 patients in low cardiac output states. Measurements were made with and without intra-aortic balloon counterpulsation. Renal blood flow was measured by continuous renal vein thermodilution. Small improvements were observed in cardiac output (3.1 ± 0.8 vs 3.5 ± 0.8 L/min, P < .01) and pulmonary capillary wedge pressure (22 ± 5.6 vs 19 ± 5.3 mmHg, P < .05), but mean arterial blood pressure was unchanged (69 ± 11 vs 69 ± 5 mmHg, not significant). Baseline renal blood flow was reduced to approximately 37%, renal oxygen delivery to 31%, and renal oxygen consumption to 60% of normal values. No significant improvement was seen in single-kidney renal blood flow (184 ± 108 vs 193 ± 107 mL/min), renal oxygen delivery (28 ± 16 vs 30 ± 16 mL/min), or renal oxygen consumption (4.9 ± 2.0 vs 4.7 ± 2.5 mL/min) in response to 1:1 counterpulsation. In comparison with measurements made during short-term suspension of counterpulsation, 1:1 aortic balloon pumping failed to result in an increase in renal blood flow, oxygen delivery, or oxygen consumption from the low levels observed in these patients.