Endothelial progenitor cells restore renal function in chronic experimental renovascular disease

Indoxyl sulfate signals for rapid mRNA stabilization of Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2) and suppresses the expression of hypoxia-inducible genes in experimental CKD and uremia

Chronic hypoxia in the tubulointerstitium serves as a final common pathway in progressive renal disease. Circumstantial evidence suggests that hypoxia-inducible factor (HIF)-1 in the ischemic tubules may be functionally inhibited in a chronic kidney disease (CKD) milieu. In this study, we hypothesized that indoxyl sulfate (IS), a uremic toxin, impairs the cellular hypoxic response. In human kidney (HK-2) proximal tubular cells, IS reduced the hypoxic induction of HIF-1 target genes. This effect was not associated with quantitative changes in the HIF-1α protein, but with functional impairment of the HIF-1α C-terminal transactivation domain (CTAD). Among factors that impeded the recruitment of transcriptional coactivators to the HIF-1αCTAD, IS markedly up-regulated Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2) through a mechanism of post-transcriptional mRNA stabilization involving the extracellular signal-regulated kinase (ERK) 1/2 pathway. In vivo, disproportionate expression of HIF target genes was demonstrated in several CKD models, which was offset by an oral adsorbent, AST-120. Furthermore, administration of indole reduced the induction of angiogenic, hypoxia-inducible genes in rats with experimental heart failure. Results of these studies reveal a novel role of IS in modulating the transcriptional response of HIF-1 and provide insight into molecular mechanisms underlying progressive nephropathies as well as cardiovascular complications.

Bone morphogenetic protein-5 and early endothelial outgrowth cells (eEOCs) in acute ischemic kidney injury (AKI) and 5/6-chronic kidney disease

Early endothelial outgrowth cells (eEOCs) reproducibly have been shown to act protectively in acute ischemic kidney injury (AKI) and chronic kidney injury. Bone morphogenetic protein-5 (BMP-5) acted antifibrotically in human hypertensive nephropathy. The aim of the current study was to analyze effects of BMP-5 treatment in an eEOC-based therapy of murine AKI and 5/6-nephrectomy. Male C57/Bl6N mice were either subjected to unilateral renal artery clamping postuninephrectomy or to 5/6-nephrectomy. Untreated or BMP-5-pretreated murine eEOCs were injected into recipient animals at the time of reperfusion (AKI) or at 2 and 5 days after 5/6-nephrectomy. Analysis of renal function and morphology was performed at 48 h and at 6 wk (AKI) or at 8 wk (5/6 model). Cellular consequences of eEOC treatment were evaluated using different in vitro assays. AKI was mitigated significantly by injecting BMP-5-pretreated eEOCs. Renal function was improved at 48 h [corrected] after cell therapy. In 5/6-nephrectomy, the cells failed to act renoprotectively, [corrected] but proteinuria was reduced after administering untreated eEOCs." Next, the original version read as "BMP-5 acts as a potent eEOC agonist in murine AKI in the short [corrected] term. Cell effects in 5/6-nephrectomy are heterogenous, but untreated cells act antifibrotically [corrected] without any impact on EnMT.

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.

Angiotensin receptor blockade has protective effects on the poststenotic porcine kidney

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

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.

Angiogenesis and hypoxia in the kidney

Loss of glomerular function associated with the presence of tubulointerstitial lesions, which are characterized by peritubular capillary loss, is a common finding in progressive renal disorders. Dysregulated expression of angiogenic factors (such as vascular endothelial growth factor [VEGF] and angiopoietins) and endogenous angiogenic inhibitors (such as thrombospondin-1, angiostatin and endostatin) underlie these conditions and negatively influence the balance between capillary formation and regression, resulting in capillary rarefaction. Recent studies have provided unequivocal evidence for a pathogenic role of tubulointerstitial hypoxia and the involvement of hypoxia-inducible transcription factors in the advanced stages of chronic kidney disease. The mainstay of potential angiogenic therapies is the application of angiogenic factors with the primary aim of ameliorating reduced oxygenation in the ischaemic tubulointerstitium. However, this strategy is strongly associated with inflammation and changes in vascular permeability. For example, supraphysiological expression of VEGF results in glomerular expansion and proteinuria, whereas VEGF blockade using neutralizing antibodies can cause hypertension and thrombotic microangiopathy. These effects highlight the importance of tight regulation of angiogenic factors and inhibitors. Novel therapeutic approaches that target vascular maturation and normalization are now being developed to protect kidneys from capillary rarefaction and hypoxic injury.

Angiogenic cytokines in renovascular disease: do they have potential for therapeutic use?

Experimental and clinical studies suggest that the damage of the renal microvascular function and architecture may participate in the early steps of renal injury in chronic renal disease, irrespective of the cause. This supporting evidence has provided the impetus to targeting the renal microvasculature as an attempt to interfere with the progressive nature of the disease process. Chronic renovascular disease is often associated with renal microvascular dysfunction, damage, loss, and defective renal angiogenesis associated with progressive renal dysfunction and damage. It is possible that damage of the renal microvasculature in renovascular disease constitutes an initiating event for renal injury and contributes towards progressive and later on irreversible renal injury. Recent studies have suggested that protection of the renal microcirculation can slow or halt the progression of renal injury in this disease. This brief review will focus on the therapeutic potential and feasibility of using angiogenic cytokines to protect the kidney microvasculature in chronic renovascular disease. There is limited but provocative evidence showing that stimulation of vascular proliferation and repair using vascular endothelial growth factor or hepatocyte growth factor can slow the progression of renal damage, stabilize renal function, and protect the renal parenchyma. Such interventions may potentially constitute a sole strategy to preserve renal function and/or a co-adjuvant tool to improve the success of current therapeutic approaches in renovascular disease.

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.

Hemodynamic determinants of perivascular collateral development in swine renal artery stenosis

BACKGROUND

Renal artery stenosis (RAS) resulting in reduced renal blood flow (RBF) is a common cause of secondary hypertension and deterioration of renal function, which may lead to end-stage renal disease. Recruitment and formation of periarterial collateral vessels may serve to bypass RAS and restore distal blood supply. We hypothesized that development of collaterals around RAS may preserve kidney function.

METHODS

Collateral formation index (CI) was assessed using multidetector computed tomography as fractional vascular volume surrounding the stenosis in 31 pigs with unilateral RAS. Single kidney RBF and glomerular filtration rate (GFR) were also measured.

RESULTS

Of 25 pigs that developed significant stenosis (≥65%), 8 demonstrated minor collateral development (CI < 0.3), and 17 showed major collateral development (CI ≥ 0.3). The degree of RAS was significantly higher in pigs with major collaterals compared with pigs with minor collaterals, and poststenotic kidney cortical volume, perfusion, RBF, and GFR were significantly lower. In a subset of pigs matched for the degree of RAS, RBF and GFR remained lower in pigs with major collaterals.

CONCLUSIONS

We conclude that collaterals develop in animals with significant RAS in proportion to its severity and might be triggered by distal injury, such as decreases in cortical volume and perfusion. However, development of collaterals was unable to confer measurable benefits for stenotic kidney function distal to severe RAS.

TGF expression and macrophage accumulation in atherosclerotic renal artery stenosis

BACKGROUND AND OBJECTIVES

Atherosclerotic renal artery stenosis (ARAS) reduces renal blood flow and is a potential cause of chronic kidney injury, yet little is known regarding inflammatory pathways in this disorder in human participants. This study aimed to examine the hypothesis that reduced renal blood flow (RBF) in ARAS would be associated with tissue TGF-β activation and inflammatory cell accumulation.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This cross-sectional study of ARAS of varying severity compared transjugular biopsy specimens in patients with ARAS (n=12, recruited between 2008 and 2012) with tissue from healthy kidney donors (n=15) and nephrectomy specimens from individuals with total vascular occlusion (n=65). ARAS patients were studied under controlled conditions to measure RBF by multidetector computed tomography and tissue oxygenation by blood oxygen level-dependent magnetic resonance imaging.

RESULTS

Compared with the nonstenotic contralateral kidneys, RBF was reduced in poststenotic kidneys (242±149 versus 365+174 ml/min; P<0.01) as was single-kidney GFR (28±17 versus 41±19 ml/min; P<0.01), whereas cortical and medullary oxygenation were relatively preserved. Tissue TGF-β immunoreactivity was higher in ARAS patients compared with those with both normal kidneys and those with total occlusion (mean score 2.4±0.7 versus 1.5+1.1 in the nephrectomy group and versus 0±0 in donors; P<0.01). By contrast, the number of CD68+ macrophages was higher with greater disease severity (from 2.2±2.7 in normal to 22.4±18 cells/high-power field in nephrectomy samples; P<0.001).

CONCLUSIONS

The results of this study indicate robust stimulation of TGF-β associated with macrophage infiltration within the human kidney with vascular occlusive disease.

Nefropatia isquêmica

A doença renal isquêmica ou nefropatia isquêmica relacionada à doença renovascular pode evoluir de forma rápida e progressiva para a insuficiência renal crônica. É fundamental a identificação e o tratamento precoces desta condição clínica, prevenindo a ocorrência de doença renal em estágio terminal, com consequente necessidade de terapia de substituição renal. Há uma década, o controle da hipertensão renovascular era o objetivo primário no manejo de pacientes com doença renovascular. Atualmente, a meta está dirigida principalmente para a estabilização e a melhora da função renal, além do controle dos níveis pressóricos.

Percutaneous revascularization for ischemic nephropathy: the past, present, and future

Occlusion of the renal arteries can threaten the viability of the kidney when severe, in addition to accelerating hypertension and circulatory congestion. Renal artery stenting procedures have evolved from a treatment mainly for renovascular hypertension to a maneuver capable of recovering threatened renal function in patients with “ischemic nephropathy” and improving management of congestive heart failure. Improved catheter design and techniques have reduced, but not eliminated hazards associated with renovascular stenting. Expanded use of endovascular stent grafts to treat abdominal aortic aneurysms has introduced a new indication for renal artery stenting to protect the renal circulation when grafts cross the origins of the renal arteries. Although controversial, prospective randomized trials to evaluate the added benefit of revascularization to current medical therapy for atherosclerotic renal artery stenosis until now have failed to identify major benefits regarding either renal function or blood pressure control. These studies have been limited by selection bias and have been harshly criticized. While studies of tissue oxygenation using blood oxygen level dependent (BOLD) MR establish that kidneys can adapt to reduced blood flow to some degree, more severe occlusive disease leads to cortical hypoxia associated with microvascular rarefication, inflammatory injury and fibrosis. Current research is directed toward identifying pathways of irreversible kidney injury due to vascular occlusion and to increase the potential for renal repair after restoring renal artery patency. The role of nephrologists likely will focus upon recognizing the limits of renal adaptation to vascular disease and identifying kidneys truly at risk for ischemic injury at a time point when renal revascularization can still be of benefit to recovering kidney function.

Bone marrow cell therapies for endothelial repair and their relevance to kidney disease

Endothelial injury is a characteristic finding in chronic kidney disease and is associated with both markedly increased cardiovascular risk and chronic kidney disease progression. The past decade has seen a remarkable surge of interest in the role of bone marrow-derived cells for the protection, repair, and regeneration of injured endothelium. In particular, despite controversies regarding their mechanisms of action, endothelial progenitor cells have garnered considerable attention, with multiple reports suggesting that these cells exhibit remarkable pro-angiogenic effects. Recent advances in our understanding of how the bone marrow responds to endothelial injury now suggest that multiple bone marrow cell populations, including both endothelial progenitor cells and a novel group of cells called early outgrowth cells, promote endothelial repair and regeneration through different, yet complementary, mechanisms. Moreover, certain subsets of bone marrow-derived cells also appear to have novel, potent, angiogenesis-independent tissue-protective properties. The bone marrow should thus now be viewed not only as a hematopoiesis organ, but also as a rich reservoir of cells capable of protecting and even regenerating nonhematopoietic tissues such as the kidney. To harness the prognostic and therapeutic potential of the bone marrow, the renal community must be aware of recent advances in our understanding of the nature and therapeutic potential of these cells.

Adipose tissue-derived mesenchymal stem cells improve revascularization outcomes to restore renal function in swine atherosclerotic renal artery stenosis

Reno-protective strategies are needed to improve renal outcomes in patients with atherosclerotic renal artery stenosis (ARAS). Adipose tissue-derived mesenchymal stem cells (MSCs) can promote renal regeneration, but their potential for attenuating cellular injury and restoring kidney repair in ARAS has not been explored. We hypothesized that replenishment of MSC as an adjunct to percutaneous transluminal renal angioplasty (PTRA) would restore renal cellular integrity and improve renal function in ARAS pigs. Four groups of pigs (n = 7 each) were studied after 16 weeks of ARAS, ARAS 4 weeks after PTRA and stenting with or without adjunct intrarenal delivery of MSC (10 × 10(6) cells), and controls. Stenotic kidney blood flow (renal blood flow [RBF]) and glomerular filtration rate (GFR) were measured using multidetector computer tomography (CT). Renal microvascular architecture (micro-CT), fibrosis, inflammation, and oxidative stress were evaluated ex vivo. Four weeks after successful PTRA, mean arterial pressure fell to a similar level in all revascularized groups. Stenotic kidney GFR and RBF remained decreased in ARAS (p = .01 and p = .02) and ARAS + PTRA (p = .02 and p = .03) compared with normal but rose to normal levels in ARAS + PTRA + MSC (p = .34 and p = .46 vs. normal). Interstitial fibrosis, inflammation, microvascular rarefaction, and oxidative stress were attenuated only in PTRA + MSC-treated pigs. A single intrarenal delivery of MSC in conjunction with renal revascularization restored renal hemodynamics and function and decreased inflammation, apoptosis, oxidative stress, microvascular loss, and fibrosis. This study suggests a unique and novel therapeutic potential for MSC in restoring renal function when combined with PTRA in chronic experimental renovascular disease.

Current views on the management of atherosclerotic renovascular disease

Atherosclerotic renovascular disease (ARVD) is a common condition in both elderly patients and those with other vascular disease. No published randomized controlled trial has demonstrated an overall benefit of revascularization on any clinical or biochemical end-point, and optimal medical therapy in this condition is not clearly defined. In this review we consider the epidemiology of ARVD and discuss the evidence for current medical treatment. We also address the literature on revascularization, consider settings in which an interventional approach may still be considered, and touch upon on-going areas of research.

Addition of endothelial progenitor cells to renal revascularization restores medullary tubular oxygen consumption in swine renal artery stenosis

Renal artery stenosis (RAS) promotes microvascular rarefaction and fibrogenesis, which may eventuate in irreversible kidney injury. We have shown that percutaneous transluminal renal angioplasty (PTRA) or endothelial progenitor cells (EPC) improve renal cortical hemodynamics and function in the poststenotic kidney. The renal medulla is particularly sensitive to hypoxia, yet little is known about reversibility of medullary injury on restoration of renal blood flow. This study was designed to test the hypothesis that PTRA, with or without adjunct EPC delivery to the stenotic kidney, may improve medullary remodeling and tubular function. RAS was induced in 21 pigs using implantation of irritant coils, while another group served as normal controls (n = 7 each). Two RAS groups were then treated 6 wk later with PTRA or both PTRA and EPC. Four weeks later, medullary hemodynamics, microvascular architecture, and oxygen-dependent tubular function of the stenotic kidneys were examined using multidetector computed tomography, microcomputed tomography, and blood oxygenation level-dependent MRI, respectively. Medullary protein expression of vascular endothelial growth factor, endothelial nitric oxide synthase, hypoxia-inducible factor-1α, and NAD(P)H oxidase p47 were determined. All RAS groups showed decreased medullary vascular density and blood flow. However, in RAS+PTRA+EPC animals, EPC were engrafted in tubular structures, oxygen-dependent tubular function was normalized, and fibrosis attenuated, despite elevated expression of hypoxia-inducible factor-1α and sustained downregulation of vascular endothelial growth factor. In conclusion, EPC delivery, in addition to PTRA, restores medullary oxygen-dependent tubular function, despite impaired medullary blood and oxygen supply. These results support further development of cell-based therapy as an adjunct to revascularization of RAS.

Age-dependent renal cortical microvascular loss in female mice

Renal function and blood flow decline during aging in association with a decrease in the number of intrarenal vessels, but if loss of estrogen contributes to this microvascular, rarefaction remains unclear. We tested the hypothesis that the decreased renal microvascular density with age is aggravated by loss of estrogen. Six-month-old female C57/BL6 mice underwent ovariectomy (Ovx) or sham operation and then were allowed to age to 18-22 mo. Another comparable group was replenished with estrogen after Ovx (Ovx+E), while a 6-mo-old group served as young controls. Kidneys were then dissected for evaluation of microvascular density (by micro-computed tomography) and angiogenic and fibrogenic factors. Cortical density of small microvessels (20-200 μm) was decreased in all aged groups compared with young controls (30.3 ± 5.8 vessels/mm², P < 0.05), but tended to be lower in sham compared with Ovx and Ovx+E (9.9 ± 1.7 vs. 17.2 ± 4.2 and 18 ± 3.0 vessels/mm², P = 0.08 and P = 0.02, respectively). Cortical density of larger microvessels (200-500 μm) decreased only in aged sham (P = 0.04 vs. young control), and proangiogenic signaling was attenuated. On the other hand, renal fibrogenic mechanisms were aggravated in aged Ovx compared with aged sham, but blunted in Ovx+E, in association with downregulated transforming growth factor-β signaling and decreased oxidative stress in the kidney. Therefore, aging induced in female mice renal cortical microvascular loss, which was likely not mediated by loss of endogenous estrogen. However, estrogen may play a role in protecting the kidney by decreasing oxidative stress and attenuating mechanisms linked to renal interstitial fibrosis.

Restoring the renal microvasculature to treat chronic kidney disease

Chronic kidney disease is characterized by progressive loss of the renal microvasculature, which leads to local areas of hypoxia and induction of profibrotic responses, scarring and deterioration of renal function. Revascularization alone might be sufficient to restore kidney function and regenerate the structure of the diseased kidney. For revascularization to be successful, however, the underlying disease process needs to be halted or alleviated and there must remain a sufficient number of surviving nephron units that can serve as a scaffold for kidney regeneration. This Perspectives article describes how revascularization might be achieved using vascular growth factors or adoptive transfer of endothelial progenitor cells and provides a brief outline of the studies performed to date. An overview of how therapeutic strategies targeting the microvasculature could be enhanced in the future is also presented.

Blood oxygen level-dependent (BOLD) MRI in renovascular hypertension

Establishing whether large vessel occlusive disease threatens tissue oxygenation and viability in the post-stenotic kidney is difficult for clinicians. Development of blood oxygen level-dependent (BOLD) MRI methods can allow functional evaluation of regional differences in deoxyhemoglobin levels within the kidney without requiring contrast. The complex renal circulation normally provides a gradient of oxygenation from a highly vascular cortex to much reduced levels in the deep sections of medulla, dependent upon adjustments in renal afferent arterioles, oxygen consumption related to solute transport, and arteriovenous shunting related to the juxtaposition of descending and ascending vasa recta. Studies with BOLD imaging have identified adaptation to substantial reductions in renal blood flow, volume, and glomerular filtration rate in post-stenotic kidneys that preserves medullary and cortical oxygenation during medical therapy. However, extreme vascular compromise overwhelms these adaptive changes and leads to cortical hypoxia and microvascular injury.

In vitro reconstitution of human kidney structures for renal cell therapy

BACKGROUND

Recent advances in cell therapies have provided potential opportunities for the treatment of chronic kidney diseases (CKDs). We investigated whether human kidney structures could be preformed in vitro for subsequent implantation in vivo to maximize tissue-forming efficiency.

METHODS

Human renal cells were isolated from unused donor kidneys. Human renal cells were cultured and expanded. Migration was analyzed using growth factors. To form structures, cells were placed in a three-dimensional culture system. Cells were characterized by immunofluorescence, western blots and fluorescence-activated cell sorting using renal cell-specific markers for podocin, proximal and distal tubules and collecting ducts. An albumin uptake assay was used to analyze function. Three-dimensional cultures were implanted into athymic rat kidneys to evaluate survival.

RESULTS

Human renal cells were effectively expanded in culture and retained their phenotype, migration ability and albumin uptake functions. Human renal cell in three-dimensional culture-formed tubules, which stained positively for proximal, distal tubule and collecting duct markers, and this was confirmed by western blot. Polarity of the tubular cells was determined by the presence of E-cadherin, N-cadherin and Na-K ATPase. Colocalization of labeled albumin and proximal tubule markers proved functionality and specificity of the newly formed tubules. An in vivo study showed that cells survived in the kidney for up to 6 weeks.

CONCLUSIONS

These findings demonstrate that human renal cell grown in three-dimensional culture are able to generate kidney structures in vitro. This system may ultimately be developed into an efficient cell-based therapy for patients with CKD.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

VEGF: Potential therapy for renal regeneration

Vascular endothelial growth factor (VEGF) plays a central role in angiogenesis. A number of studies have focused on its role in health and disease and discussed the possibility of VEGF as both a therapeutic tool and target based on its specific actions on vascular proliferation and cell survival. On one side, anti-VEGF therapies are at the fore-front of treatment of many solid tumors, but blockade of VEGF carries collateral effects such as hypertension and renal damage largely due to abnormalities in the microvasculature. On the other hand, recent clinical and experimental evidence has shown the feasibility of using VEGF administration to protect ischemic tissues such as the myocardium or the kidney via stimulation of microvascular proliferation and repair. In this commentary, we discuss the possibility and potential mechanisms of using intra-renal administration of VEGF to preserve the renal microcirculation and, consequently, decrease progressive renal injury in chronic renovascular disease. Targeted administration of VEGF may constitute a novel stand-alone or co-adjuvant intervention with the potential to become a part of a comprehensive plan to protect renal function.

The association between renal atherosclerotic plaque characteristics and renal function before and after renal artery intervention

OBJECTIVE

To evaluate the effect of plaque composition on renal function after renal artery intervention (RAI).

PATIENTS AND METHODS

In 33 consecutive patients with atherosclerotic renal artery stenosis (enrolled between January 1, 2007, and April 30, 2009), renal angiography, pressure gradients across the lesion, and intravascular ultrasonography (IVUS) with virtual histology (VH)-derived plaque characteristics were assessed. In 25 patients who underwent RAI, estimated glomerular filtration rate (eGFR) was evaluated at baseline and at 3 months.

RESULTS

Mean pressure gradients across the lesion were poorly associated with baseline eGFR (r=-0.37; P=.07). In gray scale IVUS data, only remodeling index was significantly correlated with baseline eGFR (r=-0.38; P=.03). Plaque components classified by VH-IVUS had no correlation with baseline eGFR. During follow-up of 25 patients, the improvement in eGFR after RAI was observed in 9 patients, unchanged in 3, and deteriorated in 13. Overall, follow-up eGFR (median, 49.0 mL/min/1.73 m(2); interquartile range [IQR], 40.6-63.9 mL/min/1.73 m(2)) was unchanged compared with baseline eGFR (median, 53.8 mL/min/1.73 m(2); IQR, 41.4-63.4 mL/min/1.73 m(2); P=.38). The percent change in eGFR (median, -0.2%; IQR, -16.0% to 16.0%) after RAI had a significant negative correlation with the mean percentage of necrotic core classified by VH-IVUS (r=-0.47; P=.02), and the mean percentage of necrotic core was significantly larger in patients with deterioration of eGFR than in patients without deterioration of eGFR (median, 12.7%; IQR, 9.5%-19.5%; vs median, 8.3%; IQR, 5.5%-11.6%; P=.04).

CONCLUSION

In patients with atherosclerotic renal artery stenosis, the change in eGFR after RAI was related to plaque composition classified by VH-IVUS. The evaluation of plaque composition may provide more insights into the change in renal function after RAI.

Blood oxygen level-dependent magnetic resonance imaging identifies cortical hypoxia in severe renovascular disease

Atherosclerotic renal artery stenosis has a range of manifestations depending on the severity of vascular occlusion. The aim of this study was to examine whether exceeding the limits of adaptation to reduced blood flow ultimately leads to tissue hypoxia, as determined by blood oxygen level dependent MRI. We compared 3 groups of hypertensive patients, 24 with essential hypertension, 13 with "moderate" (Doppler velocities 200-384 cm/s), and 17 with "severe" atherosclerotic renal artery stenosis (ARAS; velocities >384 cm/s and loss of functional renal tissue). Cortical and medullary blood flows and volumes were determined by multidetector computed tomography. Poststenotic kidney size and blood flow were reduced with ARAS, and tissue perfusion fell in the most severe lesions. Tissue medullary deoxyhemoglobin, as reflected by R2* values, was higher as compared with the cortex for all of the groups and did not differ between subjects with renal artery lesions and essential hypertension. By contrast, cortical R2* levels were elevated for severe ARAS (21.6±9.4 per second) as compared with either essential hypertension (17.8±2.3 per second; P<0.01) or moderate ARAS (15.7±2.1 per second; P<0.01). Changes in medullary R2* after furosemide administration tended to be blunted in severe ARAS as compared with unaffected (contralateral) kidneys. These results demonstrate that severe vascular occlusion overwhelms the capacity of the kidney to adapt to reduced blood flow, manifest as overt cortical hypoxia as measured by blood oxygen level-dependent MRI. The level of cortical hypoxia is out of proportion to the medulla and may provide a marker to identify irreversible parenchymal injury.

Selective improvement in renal function preserved remote myocardial microvascular integrity and architecture in experimental renovascular disease

AIM

Atherosclerotic renovascular disease (ARVD) may impair renal function and increase cardiovascular morbidity and mortality, but the mechanism by which ARVD impacts cardiovascular function is unclear. We tested the hypothesis that preservation of renal function can reverse cardiac dysfunction in ARVD.

METHODS AND RESULTS

Endothelial progenitor cells (EPC) were injected intra-renally (ARVD+EPC) after 6 weeks of swine ARVD (concurrent hypercholesterolemia and renovascular hypertension), and single-kidney function and myocardial blood-flow and microvascular permeability (MP) responses to adenosine were assessed using CT 4 weeks later. Myocardial microvascular density was evaluated by micro-CT. Inflammation and oxidative-stress were assessed in kidney venous and systemic blood samples. Normal and untreated ARVD pigs served as controls. Blood pressure was similarly increased in ARVD and ARVD+EPC. Compared to normal, ARVD showed lower glomerular filtration rate, elevated renal vein and systemic oxidized LDL (ox-LDL), aldosterone, uric acid, isoprostanes, transforming growth factor (TGF)-β, and interleukine-6. Renal vein ox-LDL and TGF-β showed a positive gradient across the stenotic kidney, indicating increased renal oxidative stress and fibrogenic activity. Furthermore, ARVD impaired myocardial blood-flow and MP response to adenosine, decreased microvascular density, and induced myocardial fibrosis. Improvement of renal function in ARVD+EPC decreased systemic aldosterone, inflammation, and oxidative stress, and improved myocardial microvascular integrity and density.

CONCLUSION

Selective improvement in renal function, which reduced renal and systemic oxidative stress and inflammation, preserved remote myocardial microvascular function and architecture, despite enduring hypertension. These findings underscore functionally important cardiorenal crosstalk possibly mediated by renal injury signals.

Effect of darbepoetin alfa on endothelial progenitor cells and vascular reactivity in chronic kidney disease

Endothelial progenitor cells (EPCs) are thought to be important for maintaining normal vascular function. We conducted a prospective study evaluating the effect of the erythropoiesis-stimulating agent darbepoetin alfa on EPCs and vascular function in patients with chronic kidney disease (CKD), with or without diabetes. Thirty subjects with CKD (20 subjects with type II diabetes mellitus and 10 without diabetes mellitus) received weekly subcutaneous administration of darbepoetin alfa for 4 weeks. EPCs were measured at baseline and 2 and 4 weeks after drug administration. Vascular function was measured with brachial ultrasound and cell activity was measured with a cell proliferation assay. Cells expressing CD133, CD34, CD146 and CD146/31 were significantly elevated (all p < 0.05), flow-mediated vasodilatation increased 2.1%, 95% CI: (0.4%, 3.8%) and colony-forming units increased twofold, 95% CI: (1.7, 2.3) after 4 weeks of treatment with darbepoetin alfa. Subjects with diabetes exhibited an increase in a subset of EPCs (CD133( +) and 34(+), p < 0.01 and p = 0.06, respectively), vasodilatation and proliferation. In conclusion, the administration of darbepoetin alfa for 4 weeks increased a subset of EPCs, improved endothelial function and increased cell proliferation, including those with diabetes, which is consistent with a favorable improvement in vascular health.

[Slowing chronic kidney disease progression: hopes and disappointments. Vascular repair of chronic kidney]

In chronic kidney disease patients, inexorable renal function decline is reduced by renin-angiotensin system (RAS) blockers. ACE inhibitors and angiotensin receptor blockers decrease blood pressure and proteinuria. Guidelines recommend a reduction of blood pressure to less than 130/80 mmHg and urinary protein excretion below 0.5 g/d. The combined use of a diuretic increases anti-proteinuric effect and blood pressure control of RAS blockers. Drugs as mineralo-corticocoids receptor antagonist and endothelin receptor antagonists reduce further albuminuria in combination with RAS blocker, but side effects need to be precised. Both metabolic acidosis and hyperuricemia represent new therapeutic goals to slow renal function decline in CKD patients. Renal fibrosis treatment and regenerative medicine are stemming and will be important issues for kidney and other organs in the future.

Mononuclear cell therapy attenuates atherosclerosis in apoE KO mice

Background

Recent studies have highlighted the potential of cell therapy for atherosclerosis. The aim of this study was to evaluate the effects of mononuclear cell (MNC) therapy on the development of atherosclerotic lesions in the apolipoprotein E knockout (apoE KO) mouse.

Methods

We investigated vascular lipid deposition, vascular remodeling, oxidative stress, and endothelial nitric oxide synthase (eNOS) expression in apoE KO mice treated with spleen MNCs isolated from lacZ transgenic mice (apoE KO-MNC) for 8 weeks compared to untreated control mice (apoE KO).

Results

Histological analysis of aortas showed a significant reduction in the lipid deposition area in apoE KO-MNC mice compared to apoE KO mice (0.051 ± 0.004 vs 0.117 ± 0.016 mm², respectively, p < 0.01). In addition, vessel morphometry revealed that MNC therapy prevented the outward (positive) remodeling in apoE KO mice that is normally observed (apoE KO-MNC: 0.98 ± 0.07 vs apoE KO: 1.37 ± 0.09), using wild-type mice (C57BL/6J) as a reference. ApoE KO-MNC mice also have reduced production of superoxide anions and increased eNOS expression compared to apoE KO mice. Finally, immunohistochemistry analysis revealed a homing of endothelial progenitor cells (EPCs) in the aortas of apoE KO-MNC mice.

Conclusion

MNC therapy attenuates the progression of atherosclerosis in the aortas of apoE KO mice. Our data provide evidence that the mechanism by which this attenuation occurs includes the homing of EPCs, a decrease in oxidative stress and an upregulation of eNOS expression.

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.

Renovascular hypertension: screening and modern management

The diagnosis and management of patients with renovascular disease and hypertension continue to elude healthcare providers. The advent of novel imaging and interventional techniques, and increased understanding of the pathways leading to irreversible renal injury and renovascular hypertension, have ushered in commendable attempts to optimize and fine-tune strategies to preserve or restore renal function and control blood pressure. Large randomized clinical trials that compare different forms of therapy, and smaller trials that test novel experimental treatments, will hopefully help formulate innovative concepts and tools to manage the patient population with atherosclerotic renovascular disease.

The effects of magnetically labeled rat spleen-originated endothelial progenitor cells on growth of glioma in vivo an experimental study

RATIONALE AND OBJECTIVES

The aim of this study was to investigate the effects of exogenous endothelial progenitor cells (EPCs) on the growth and invasiveness of glioma in vivo to provide an experimental basis for the value and safety of using magnetically labeled EPCs as target vectors to detect early infiltration of glioma.

MATERIALS AND METHODS

EPCs were collected from the spleens of healthy Sprague-Dawley rats, made EPCs conditioned medium after identification. Four models of Sprague-Dawley rat glioma (60 rats in total) were established as a control and three experimental groups (group A, B, and C). In the control group, orthotopic transplantation of C6 glioma cells was performed. Compared to the control group, EPCs conditioned medium was added in group A and P7228-labeled EPCs were added in group B. In group C, P7228-labeled EPCs were transplanted via the tail vein. Magnetic resonance imaging and perfusion-weighted imaging were performed on several days. Tumor microvascular density and vascular endothelial growth factor expression were determined through immunohistochemistry.

RESULTS

In group C, hypointense areas were detected at the periphery of the tumor on the first day after transplantation of EPCs, and more hypointense areas were found inside the tumor over time. Tumor size in all four groups developed significantly with increasing time (P < .01), but there was no marked difference among these groups at the same time (P > .05). No remarkable differences in microvascular density and cells positive for vascular endothelial growth factor were found at the same time among the four groups (P > .05).

CONCLUSIONS

Both magnetic resonance imaging and immunohistochemical findings confirmed that exogenous EPCs could not affect the biologic behavior of C6 glioma cells in vivo through a paracrine effect or by direct cellular interaction. Therefore, exogenous EPCs could not exert significant promoting effects on glioma growth.

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.

Cord blood-circulating endothelial progenitors for treatment of vascular diseases

Adult peripheral blood (PB) endothelial progenitor cells (EPC) are produced in the bone marrow and are able to integrate vascular structures in sites of neoangiogenesis. EPCs thus represent a potential therapeutic tool for ischaemic diseases. However, use of autologous EPCs in cell therapy is limited by their rarity in adult PB. Cord blood (CB) contains more EPCs than PB, and they are functional after expansion. They form primary colonies that give rise to secondary colonies, each yielding more than 10(7) cells after few passages. The number of endothelial cells obtained from one unit of CB is compatible with potential clinical application. EPC colonies can be securely produced, expanded and cryopreserved in close culture devices and endothelial cells produced in these conditions are functional as shown in different in vitro and in vivo assays. As CB EPC-derived endothelial cells would be allogeneic to patients, it would be of interest to prepare them from ready-existing CB banks. We show that not all frozen CB units from a CB bank are able to generate EPC colonies in culture, and when they do so, number of colonies is lower than that obtained with fresh CB units. However, endothelial cells derived from frozen CB have the same phenotypical and functional properties than those derived from fresh CB. This indicates that CB cryopreservation should be improved to preserve integrity of stem cells other than haematopoietic ones. Feasibility of using CB for clinical applications will be validated in porcine models of ischaemia.

Capillary rarefaction, hypoxia, VEGF and angiogenesis in chronic renal disease

Tubulointerstitial hypoxia and peritubular capillary rarefaction are typical features of chronic progressive renal disease. In response to low oxygen supply, hypoxia-inducible factors (HIFs) are activated but until now, it is unclear if this increased expression leads to a stabilization of the disease process and thus is nephroprotective or contributes to interstitial fibrosis and/or tubular atrophy. This duality has also been described as far as vascular endothelial growth factor (VEGF), one of the major target genes of HIFs, is concerned. On the one hand, neoangiogenesis driven by VEGF, if intact, ameliorates hypoxia, on the other, VEGF is a potent pro-inflammatory mediator and neoangiogenesis, if defective because interference by other pathologies exaggerates injury. In summary, experimental data support the idea that dependent on timing and predominant pathology, hypoxia counter-regulatory factors exert beneficial or undesirable effects. Thus, before their therapeutic potential can be fully explored, a better way to characterize the clinical and pathophysiological situation in an individual patient is mandatory.

Renovascular disease, microcirculation, and the progression of renal injury: role of angiogenesis

Emerging evidence supports the pivotal role of renal microvascular disease as a determinant of tubulo-interstitial and glomerular fibrosis in chronic kidney disease. An intact microcirculation is vital to restore blood flow to the injured tissues, which is a crucial step to achieve a successful repair response. The purpose of this review is to discuss the impact and mechanisms of the functional and structural changes of the renal microvascular network, as well as the role of these changes in the progression and irreversibility of renal injury. Damage of the renal microcirculation and deterioration of the angiogenic response may constitute early steps in the complex pathways involved in progressive renal injury. There is limited but provocative evidence that stimulation of vascular proliferation and repair may stabilize renal function and slow the progression of renal disease. The feasibility of novel potential therapeutic interventions for stabilizing the renal microvasculature is also discussed. Targeted interventions to enhance endogenous renoprotective mechanisms focused on the microcirculation, such as cell-based therapy or the use of angiogenic cytokines have shown promising results in some experimental and clinical settings.

Endothelial progenitor cells in long-standing asymptomatic type 1 diabetic patients with or without diabetic nephropathy

A decrease in the number and dysfunction of endothelial progenitor cells (EPC) may increase the risk for progression of cardiovascular disease (CVD) in type 1 diabetic patients with diabetic nephropathy (DN). Our aim was to evaluate EPC numbers in asymptomatic CVD type 1 diabetic patients with or without DN and to study the effect of CVD and medication on EPC numbers.

METHODS

We examined EPC numbers in 37 type 1 diabetic patients with DN and 35 type 1 diabetic patients with long-standing normoalbuminuria. Patients were without symptoms of CVD and the prevalence of CVD was previously shown to be very low. EPC number was assessed in in vitro cultures by fluorescent staining of attached cells.

RESULTS

There was no difference in EPC numbers between patients with DN (mean ± SD 120 ± 49 cells/field) and normoalbuminuria (108 ± 41 cells/field; p = 0.25). Furthermore, EPC number was not associated with CVD (p > 0.05). Conventional risk factors were significantly higher in patients with DN and they received more CVD-preventive treatment. All patients receiving simvastatin or calcium-channel blockers had higher numbers of EPC compared to patients not treated with these drugs.

CONCLUSIONS

Asymptomatic patients with DN had EPC numbers similar to normoalbuminuric patients, which was related to aggressive CVD intervention therapy. This may have contributed to the low prevalence of CVD.

Conditioned medium from renal tubular epithelial cells stimulated by hypoxia influences rat bone marrow-derived endothelial progenitor cells

BACKGROUND AND AIMS

It has been well documented that endothelial progenitor cells (EPCs) participate in neovascularization in adults and that rarefaction of peritubular capillaries (PTCs) is closely associated with progressive kidney disease. Therefore, we investigated whether EPCs were influenced by conditioned medium (CM) of renal tubular epithelial cells (RTECs) stimulated by hypoxia, to provide evidence for EPCs transplantation in vivo in the future.

METHODS

Mononuclear cells of rat bone marrow were isolated by density gradient centrifugation and were cultured according to previously described techniques. RTECs were cultured primarily with routine tissue block adhering wall method. In addition, CM was harvested from RTECs cultivated for 48 h in 5% O(2). EPCs proliferation and migration were evaluated by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay and transwell. The protein and mRNA expression of stromal cell-derived factor (SDF-1), vascular endothelial growth factor (VEGF), angiogenin 1 (Ang-1), and C-X-C chemokine receptor 4 (CXCR4) was separately assessed by Western blot, enzyme-linked immunosorbent assay (ELISA), and reverse transcriptase-polymerase chain reaction (RT-PCR) methods.

RESULTS

We showed that hypoxia increased the expression of SDF-1 and VEGF in RTEC. In addition, hypoxic CM improved proliferation, migration, and expression of VEGF, Ang-1, and CXCR4 of EPCs.

CONCLUSIONS

These results suggest that hypoxic CM improves neovascularization of EPCs and may also be considered as therapeutic agents to supply the potent origin of reconstituion of PTCs of progressive kidney disease.

Early experimental hypertension preserves the myocardial microvasculature but aggravates cardiac injury distal to chronic coronary artery obstruction

Coronary artery disease is a leading cause of death. Hypertension (HT) increases the incidence of cardiac events, but its effect on cardiac adaptation to coexisting coronary artery stenosis (CAS) is unclear. We hypothesized that concurrent HT modulates microvascular function in chronic CAS and aggravates microvascular remodeling and myocardial injury. Four groups of pigs (n=6 each) were studied: normal, CAS, HT, and CAS+HT. CAS and HT were induced by placing local irritant coils in the left circumflex coronary artery and renal artery, respectively. Six weeks later multidetector computerized tomography (CT) was used to assess systolic and diastolic function, microvascular permeability, myocardial perfusion, and responses to adenosine in the "area at risk." Microvascular architecture, inflammation, and fibrosis were then explored in cardiac tissue. Basal myocardial perfusion was similarly decreased in CAS and CAS+HT, but its response to adenosine was significantly more attenuated in CAS. Microvascular permeability in CAS+HT was greater than in CAS and was accompanied by amplified myocardial inflammation, fibrosis, and microvascular remodeling, as well as cardiac systolic and diastolic dysfunction. On the other hand, compared with normal, micro-CT-derived microvascular (20-200 μm) transmural density decreased in CAS but not in HT or CAS+HT. We conclude that the coexistence of early renovascular HT exacerbated myocardial fibrosis and vascular remodeling distal to CAS. These changes were not mediated by loss of myocardial microvessels, which were relatively preserved, but possibly by exacerbated myocardial inflammation and fibrosis. HT modulates cardiac adaptive responses to CAS and bears cardiac functional consequences.

Renovascular hypertension and ischemic nephropathy

Renovascular disease remains among the most prevalent and important causes of secondary hypertension and renal dysfunction. Many lesions reduce perfusion pressure including fibromuscular diseases and renal infarction, but most are caused by atherosclerotic disease. Epidemiologic studies establish a strong association between atherosclerotic renal-artery stenosis (ARAS) and cardiovascular risk. Hypertension develops in patients with renovascular disease from a complex set of pressor signals, including activation of the renin-angiotensin system (RAS), recruitment of oxidative stress pathways, and sympathoadrenergic activation. Although the kidney maintains function over a broad range of autoregulation, sustained reduction in renal perfusion leads to disturbed microvascular function, vascular rarefaction, and ultimately development of interstitial fibrosis. Advances in antihypertensive drug therapy and intensive risk factor management including smoking cessation and statin therapy can provide excellent blood pressure control for many individuals. Despite extensive observational experience with renal revascularization in patients with renovascular hypertension, recent prospective randomized trials fail to establish compelling benefits either with endovascular stents or with surgery when added to effective medical therapy. These trials are limited and exclude many patients most likely to benefit from revascularization. Meaningful recovery of kidney function after revascularization is limited once fibrosis is established. Recent experimental studies indicate that mechanisms allowing repair and regeneration of parenchymal kidney tissue may lead to improved outcomes in the future. Until additional staging tools become available, clinicians will be forced to individualize therapy carefully to optimize the potential benefits regarding both blood pressure and renal function for such patients.

Coronary endothelial dysfunction in humans is associated with coronary retention of osteogenic endothelial progenitor cells

AIMS

Endothelial progenitor cells (EPC) may participate in the repair of injured coronary endothelium. We have recently identified EPC co-expressing the osteoblastic marker osteocalcin [OCN (+) EPC] and found that their numbers are increased in patients with early and late coronary atherosclerosis. The current study was designed to test the hypothesis that early coronary atherosclerosis is associated with the retention of osteogenic EPC within the coronary circulation.

METHODS AND RESULTS

Blood samples were taken simultaneously from the proximal aorta and the coronary sinus from 31 patients undergoing invasive coronary endothelial function testing. Using flow cytometry, peripheral blood mononuclear cells were analysed for EPC markers (CD133, CD34, KDR) and OCN. The net gradient of EPC was calculated by multiplying the coronary blood flow by the arteriovenous EPC gradient (a negative net gradient indicating retention of EPC). Similarly, serum samples were analysed for stromal cell-derived factor-1 alpha (SDF-1 alpha) and interleukin-8 (IL-8) and their net production calculated. Compared with controls (n = 17) patients with endothelial dysfunction (ED, n = 14) had a significant net retention of CD34+/CD133-/KDR+/OCN+ EPC [118.38 (0.00, 267.04) vs. -112.03 (838.36, 0.00), P = 0.004]. The retention of OCN (+) EPC correlated with the degree of ED. Patients with ED also showed a net retention of CD34+/CD133-/KDR+ EPC (P = 0.010). Net production of IL-8 was positive in ED [1540.80 (-300.40, 21744.10)pg/mL] but negative in controls [-3428.50 (-11225.00, 647.48), P = 0.025].

CONCLUSION

Our study demonstrates that patients with early coronary atherosclerosis are characterized by retention of OCN (+) EPC within the coronary circulation, potentially leading to progressive coronary calcification rather than normal repair.

Rapid anastomosis of endothelial progenitor cell-derived vessels with host vasculature is promoted by a high density of cotransplanted fibroblasts

To ensure survival of engineered implantable tissues thicker than approximately 2-3 mm, convection of nutrients and waste products to enhance the rate of transport will be required. Creating a network of vessels in vitro, before implantation (prevascularization), is one potential strategy to achieve this aim. In this study, we developed three-dimensional engineered vessel networks in vitro by coculture of endothelial cells (ECs) and fibroblasts in a fibrin gel for 7 days. Vessels formed by cord blood endothelial progenitor cell-derived ECs (EPC-ECs) in the presence of a high density of fibroblasts created an interconnected tubular network within 4 days, compared with 5-7 days in the presence of a low density of fibroblasts. Vessels derived from human umbilical vein ECs (HUVECs) in vitro showed similar kinetics. Implantation of the prevascularized tissues into immune-compromised mice, however, revealed a dramatic difference in the ability of EPC-ECs and HUVECs to form anastomoses with the host vasculature. Vascular beds derived from EPC-ECs were perfused within 1 day of implantation, whereas no HUVEC vessels were perfused at day 1. Further, while almost 90% of EPC-EC-derived vascular beds were perfused at day 3, only one-third of HUVEC-derived vascular beds were perfused. In both cases, a high density of fibroblasts accelerated anastomosis by 2-3 days. We conclude that both EPC-ECs and a high density of fibroblasts significantly accelerate the rate of functional anastomosis, and that prevascularizing an engineered tissue may be an effective strategy to enhance convective transport of nutrients in vivo.

Endothelial progenitor cells homing and renal repair in experimental renovascular disease

Tissue injury triggers reparative processes that often involve endothelial progenitor cells (EPCs) recruitment. We hypothesized that atherosclerotic renal artery stenosis (ARAS) activates homing signals that would be detectable in both the kidney and EPCs, and attenuated on renal repair using selective cell-based therapy. Pigs were treated with intrarenal autologous EPC after 6 weeks of ARAS. Four weeks later, expression of homing-related signals in EPC and kidney, single kidney function, microvascular (MV) density, and morphology were compared with untreated ARAS and normal control pigs (n = 7 each). Compared with normal EPC, EPC from ARAS pigs showed increased stromal cell-derived factor (SDF)-1, angiopoietin-1, Tie-2, and c-kit expression, but downregulation of erythropoietin (EPO) and its receptor. The ARAS kidney released the c-kit-ligand stem cell factor, uric acid, and EPO, and upregulated integrin beta2, suggesting activation of corresponding homing signaling. However, angiopoietin-1 and SDF-1/CXCR4 were not elevated. Administration of EPC into the stenotic kidney restored angiogenic activity, improved MV density, renal hemodynamics and function, decreased fibrosis and oxidative stress, and attenuated endogenous injury signals. The ARAS kidney releases specific homing signals corresponding to cognate receptors expressed by EPC. EPC show plasticity for organ-specific recruitment strategies, which are upregulated in early atherosclerosis. EPC are renoprotective as they attenuated renal dysfunction and damage in chronic ARAS, and consequently decreased the injury signals. Importantly, manipulation of homing signals may potentially allow therapeutic opportunities to increase endogenous EPC recruitment.