Emerging research has identified the endothelin (ET)-1 pathway as a potential target for novel renoprotective therapies. We recently showed that selective ET-A receptor antagonism in chronic renovascular disease (RVD) improves renal function and reduces renal injury. Although ET-A and -B have opposing roles, in some clinical situations they may induce similar effects. Thus, we hypothesized that simultaneous blockade of the ET-A and -B receptors would protect the kidney during RVD.
Unilateral RVD was induced in pigs. After 6 weeks, single-kidney function was quantified in vivo using multi-detector computer tomography. Pigs were subsequently divided into untreated (RVD, n = 7) or daily-treated with the dual ET-A/B receptor antagonist macitentan (RVD + macitentan, n = 6) for 4 weeks. At 10 weeks, in vivo studies were repeated, then pigs were euthanized and ex vivo studies performed in the stenotic kidney to quantify inflammation, fibrosis, microvascular density and remodeling.
Four weeks of macitentan therapy modestly improved renal blood flow (29%, P = 0.06 versus pre-treatment) and showed protective effects on the renal parenchyma by attenuating inflammation and glomerulosclerosis, reducing apoptosis and tubular casts and improving albuminuria and cortical microvessel density. No overt adverse effects were observed.
Possibly by inducing a pro-survival renal microenvironment, macitentan increased renal microvascular density, promoted cell survival and decreased injury, which in turn improved stenotic kidney hemodynamics in our model. Our results further support the safety of using macitentan in patients with concomitant chronic renal disease and supported the feasibility of a new strategy that may preserve the stenotic kidney in RVD.
endothelin; imaging microcirculation; inflammation; renal hemodynamics; renovascular disease
We hypothesized that chronic specific endothelin (ET)-A receptor blockade therapy would reverse renal dysfunction and injury in advanced experimental renovascular disease. To test this, unilateral renovascular disease was induced in 19 pigs and after 6 weeks, single-kidney hemodynamics and function was quantified in vivo using computed-tomography. All pigs with renovascular disease were divided such that 7 were untreated, 7 were treated with ET-A blockers, and 5 were treated with ET-B blockers. Four weeks later, all pigs were re-studied in vivo, then euthanized and ex vivo studies performed on the stenotic kidney to quantify microvascular density, remodeling, renal oxidative stress, inflammation, and fibrosis. RBF, GFR, and redox status were significantly improved in the stenotic kidney after ET-A but not ET-B blockade. Furthermore, only ET-A blockade therapy reversed renal microvascular rarefaction and diminished remodeling, which was accompanied by a marked decreased in renal inflammatory and fibrogenic activity. Thus, ET-A but not ET-B blockade ameliorated renal injury in pigs with advanced renovascular disease by stimulating microvascular proliferation and decreasing the progression of microvascular remodeling, renal inflammation and fibrosis in the stenotic kidney. These effects were functionally consequential since ET-A blockade improved single kidney microvascular endothelial function, RBF, and GFR, and decreased albuminuria.
kidney; hemodynamics; vascular regulation; renal artery stenosis; endothelin; microcirculation; imaging
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.
kidney; cytokines; angiogenesis; renovascular disease; microcirculation
Tissue injury triggers reparative processes that often involve endothelial progenitor cells (EPC) recruitment. We hypothesized that atherosclerotic renal artery stenosis (ARAS) activates homing signals that would be detectable in both the kidney and endothelial progenitor cells (EPC), and attenuated upon renal repair using selective cell-based therapy.
Pigs were treated with intra-renal autologous EPC after 6 weeks of ARAS. Four weeks later, expression of homing-related signals in EPC and kidney, single-kidney function, microvascular density, and morphology were compared to untreated ARAS and normal control pigs (n=7 each).
Compared to normal EPC, EPC from ARAS pigs showed increased stromal cell-derived factor (SDF)-1, angiopoietin-1, Tie-2, and ckit expression, but downregulation of erythropoietin and its receptor. The ARAS kidney released the ckit-ligand stem-cell factor (SCF), uric acid, and erythropoietin, and upregulated integrin β2, 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 microvascular 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.
endothelial progenitor cells; renal artery stenosis; homing factors
Obesity, an independent risk factor for chronic kidney disease, may induce renal injury by promoting inflammation. Inflammatory cytokines can induce neovascularization in different organs, including the kidneys. However, whether obesity triggers renal neovascularization and, if so, its effect on renal function has never been investigated.
Blood pressure, proteinuria and glomerular-filtration-rate (GFR) were measured in-vivo. Renal microvascular (MV) architecture was studied by 3D micro-CT in lean and obese Zucker rats (LZR and OZR, n=7/group) at 12, 22, and 32 weeks of age. Renal inflammation was assessed by quantifying interleukin (IL)-6, tumor-necrosis-factor (TNF)-alpha, and ED-1 expression, as renal fibrosis in trichrome-stained cross-sections.
Mild inflammation and lower GFR was only observed in younger OZR, without renal fibrosis or changes in MV density. Interestingly, renal MV density increased in OZR at 32 weeks of age, accompanied by pronounced increase in renal IL-6 and TNF-alpha, ED-1+ cells, proteinuria, decreased GFR, and fibrosis.
This study shows increased renal cortical vascularization in experimental obesity, suggesting neovascularization as an evolving process as obesity progresses. Increased renal vascularization, possibly triggered by inflammation, may reflect an initially compensatory mechanism in obesity. However, increased inflammation and inflammatory-induced neovascularization may further promote renal injury as obesity advances.
obesity; kidney; microcirculation; inflammation; fibrosis
Background. 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.
Methods. 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.
Results. 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).
Conclusions. 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.
computerized tomography; microcirculation; renal artery stenosis; renal haemodynamics; VEGF
Percutaneous trasluminal renal angioplasty (PTRA) is the most frequent therapeutic approach to resolve renal artery stenosis (RAS). However, renal function recovers in only 30% of the cases. The causes of these poor outcomes are still unknown. We hypothesize that preserving the renal microcirculation distal to RAS will improve the responses to PTRA.
Methods and Results
RAS was induced in 28 pigs. In 14, vascular endothelial growth factor (VEGF)-165 was infused intra-renally (RAS+VEGF, 0.05 µg/kg). Single-kidney function was assessed in all pigs in vivo using ultra-fast CT after 6 weeks. Half of the RAS/RAS+VEGF completed their observation, and the other half underwent PTRA, VEGF was repeated, and CT studies repeated 4 weeks later. Pigs were then euthanized, the stenotic kidney removed, renal microvascular (MV) architecture reconstructed ex-vivo using 3D micro-CT, and renal fibrosis quantified.
Degree of RAS and hypertension were similar in RAS and RAS+VEGF. Renal function and MV density were decreased in RAS but improved in RAS+VEGF. PTRA largely resolved RAS, but the improvements of hypertension and renal function were greater in RAS+VEGF+PTRA than in RAS+PTRA, accompanied by a 34% increase in MV density and decreased fibrosis.
Preservation of the MV architecture and function in the stenotic kidney improved the responses to PTRA, indicating that renal MV integrity plays a role in determining the responses to PTRA. This study indicates that damage and early loss of renal MV is an important determinant of the progression of renal injury in RAS and instigates often irreversible damage.
renal artery stenosis; revascularization; microcirculation; imaging; renal function
Purpose of review
The prevalence of chronic kidney disease has been growing consistently for the past decades. Renal failure is often associated with defective angiogenesis, and recognition of the contribution of the renal microcirculation to the progression of chronic renal disease may aid in the development of therapeutic interventions.
Intra-renal proliferation, remodeling, and/or rarefaction of microvessels in response to injury can all aggravate nephron damage, and experimental evidence suggests that they may constitute the early steps in the complex pathways involved in progressive renal injury. Recent studies showed the benefits of targeted interventions deemed to promote neovascularization (e.g. progenitor cells, growth factors) on the ischemic myocardium and brain and in a few models of renal disease.
Evidence of aberrant renal microvascular architecture in various forms of renal disease provides the impetus to attempt modulating the renal microcirculation to interfere with the disease process. Targeted interventions to preserve the renal microcirculation may not only decrease the evolving injury in renal vascular disease but also potentially constitute a coadjuvant intervention to become part of a comprehensive management plan to improve the success of parallel strategies to preserve renal function, such as revascularization.
angiogenesis; kidney; microcirculation; vascular rarefaction
C-peptide is renoprotective in type 1 diabetes, however, the mechanisms of its actions are not completely understood. We hypothesized that C-peptide attenuates diabetes-associated renal microvascular injury.
After 4 or 8 weeks of streptozotocin (STZ)-induced diabetes, rats received either vehicle or C-peptide in the presence of low or high doses of insulin. Urine albumin excretion (UAE) was measured prior to initiation of treatment (baseline) and 2 or 4 weeks after treatment (sacrifice). Glomerular hypertrophy, glomerular filtration rate (GFR) and renal microvascular density, quantified ex vivo by 3D micro-CT reconstruction, were measured at sacrifice.
In rats receiving low doses of insulin, treatment with C-peptide reduced HbA1c levels by 24%. In these rats, the 107% increase in UAE rate from baseline to sacrifice in vehicle-treated rats was largely prevented with C-peptide. C-peptide also reduced diabetes-associated glomerular hyperfiltration by 30%, glomerular hypertrophy by 22% and increased the density of microvessels between 0–500 μm in diameter by an average of 31% compared with vehicle-treated groups. Similar renoprotective effects of C-peptide were observed in rats treated with higher doses of daily insulin, despite no differences in HbA1c levels.
The study suggests that C-peptide is renoprotective by preserving the integrity of the renal microvasculature irrespective of glucose regulation.
diabetes; kidney; blood vessels; rarefaction
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 intra-renal delivery of autologous EOC (10×10^6), and compared to 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 engrafted in injected RAS-kidneys. Stenotic-kidney glomerular filtration rate was restored in RAS+EOC, RAS+PTRA, and RAS+PTRA+EOC pigs, while 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 VEGF blockade. Finally, a single intra-renal injection of rhVEGF (0.05 μg/kg) in 7 additional RAS pigs also restored M1/M2 ratio 4 weeks later.
Intra-renal infusion of EOC after PTRA induced a VEGF-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.
renal artery stenosis; progenitor cells; kidney hypertension; revascularization; macrophages
An intact microcirculation is vital for diffusion of oxygen and nutrients and for removal of toxins of every organ and system in the human body. The functional and/or anatomical loss of microvessels is known as rarefaction, which can compromise the normal organ function and have been suggested as a possible starting point of several diseases. The purpose of this overview is to discuss the potential underlying mechanisms leading to renal microvascular rarefaction, and the potential consequences on renal function and on the progression of renal damage. Although the kidney is a special organ that receives much more blood than its metabolic needs, experimental and clinical evidence indicates that renal microvascular rarefaction is associated to prevalent cardiovascular diseases such as diabetes, hypertension, and atherosclerosis, either as cause or consequence. On the other hand, emerging experimental evidence using progenitor cells or angiogenic cytokines supports the feasibility of therapeutic interventions capable of modifying the progressive nature of microvascular rarefaction in the kidney. This overview will also attempt to discuss the potential renoprotective mechanisms of the therapeutic targeting of the renal microcirculation.
Fetal growth restriction (FGR) greatly increases the risk of perinatal morbidity and mortality and is associated with increased uterine artery resistance and levels of oxidative stress. There are currently no available treatments for this condition. The hypothesis that the antioxidant 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (Tempol) would improve uterine artery function and rescue fetal growth was tested in a mouse model of FGR, using the endothelial nitric oxide synthase knockout mouse (Nos3−/−). Pregnant Nos3−/− and control C57BL/6J mice were treated with the superoxide dismutase-mimetic Tempol (1 mmol/L) or vehicle from Gestational Day 12.5 to 18.5. Tempol treatment significantly increased pup weight (P < 0.05) and crown–rump length (P < 0.01) in C57BL/6J and Nos3−/− mice. Uterine artery resistance was increased in Nos3−/− mice (P < 0.05); Tempol significantly increased end diastolic velocity in Nos3−/− mice (P < 0.05). Superoxide production in uterine arteries did not differ between C57BL/6J and Nos3−/− mice but was significantly increased in placentas from Nos3−/− mice (P < 0.05). This was not reduced by Tempol treatment. Placental System A activity was reduced in Nos3−/− mice (P < 0.01); this was not improved by treatment with Tempol. Treatment of Nos3−/− mice with Tempol, however, was associated with reduced vascular density in the placental bed (P < 0.05). This study demonstrated that treatment with the antioxidant Tempol is able to improve fetal growth in a mouse model of FGR. This was associated with an increase in uterine artery blood flow velocity but not an improvement in uterine artery function or placental System A activity.
Treatment with the antioxidant Tempol increases uterine artery blood velocity and improves fetal growth in a mouse model of fetal growth restriction.
intrauterine growth restriction; nitric oxide; oxidative stress; placental transport; pregnancy
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.
Hypertension and hypercholesterolemia might interfere with renal repair mechanisms. We hypothesized that simvastatin improves the survival of endothelial progenitor cells (EPC) in the renal microenvironment imposed by concurrent renovascular hypertension and dietary hypercholesterolemia (HTC).
Methods and results
Pigs were studied after 12 weeks of no intervention (n=6), HTC (n=6), or HTC + oral simvastatin supplementation (80 mg/d, n=5). EPCs were also isolated and studied in-vitro after exposure to the pro-apoptotic oxide-low density lipoprotein (ox-LDL) with or without co-incubation with simvastatin. Renal hemodynamics, function, and endothelial function were evaluated in-vivo, and the number of CD34+/KDR+ EPC, apoptosis, oxidative-stress, inflammation, and fibrosis in renal tissue studied ex-vivo. Compared to normal, the HTC kidney showed endothelial dysfunction, increased oxidative-stress, interstitial macrophage filtration, and fibrosis. The number of EPC in the kidney increased, as did their apoptosis (0.85±0.24 vs. 0.22±0.07%, p<0.05 vs. normal). Simvastatin did not affect blood pressure, cholesterol levels, basal renal function, or number of renal EPC in HTC, but improved endothelial function, blunted renal oxidative-stress, inflammation, fibrosis, and attenuated EPC apoptosis (to 0.37±0.09%, p<0.05 vs. HTC). Simvastatin also significantly decreased ox-LDL-induced EPC apoptosis in-vitro.
EPC are recruited but undergo apoptosis in the HTC kidney, likely due to a hostile microenvironment. Simvastatin rescues renal repair mechanisms in HTC and counteracts renal damage, which may account for its protective effects on the kidney during exposure to cardiovascular risk factors.
Hypertension; hypercholesterolemia; simvastatin; fibrosis; apoptosis
Monocyte chemoattractant proteins (MCPs) play an important role in mediating inflammatory processes. Hypertension (HTN) is associated with inflammation as well as impaired cardiac microcirculatory function and structure, but the contribution of MCPs to these alterations remained unclear. This study tested the hypothesis that MCPs regulate cardiac microvascular function and structure in an experimental HTN.
Methods and Results
Pigs (n=6/group) were studied after 10 weeks of normal, renovascular HTN, or renovascular HTN+ bindarit (MCPs inhibitor, 50 mg/kg/day PO). Left ventricular (LV) function, myocardial microvascular permeability, and fractional vascular volume were assessed by fast computed tomography before and after adenosine infusion (400 μg/kg/min). Myocardial fibrosis, inflammation, and microvascular remodeling were determined ex-vivo. Hypertension was not altered by bindarit, but LV hypertrophy and diastolic function were improved. In response to adenosine, myocardial microvascular permeability increased in HTN (from 0.0083±0.0009 to 0.0103±0.0011 AU, p=0.038 vs. baseline) and fractional vascular volume decreased, while both remained unchanged in normal and HTN+bindarit pigs. HTN upregulated endothelin-1 expression, myocardial inflammation and microvascular wall thickening, which were inhibited by bindarit.
MCPs partly mediate myocardial inflammation, fibrosis, vascular remodeling, and impaired vascular integrity induced by hypertension. Inhibition of MCPs could potentially be a therapeutic target in hypertensive cardiomyopathy.
MCPs; inflammation; hypertension; microvascular permeability; remodeling
Renal artery stenosis (RAS) causes renovascular hypertension and renal damage, which may result from tissue inflammation. We have previously shown that the kidney in RAS exhibits increased expression of monocyte chemoattractant protein (MCP)-1, but its contribution to renal injury remained unknown. This study tested the hypothesis that MCP-1 contributes to renal injury and dysfunction in the stenotic kidney.
Kidney hemodynamics, function, and endothelial function were quantified in pigs after 10 weeks of experimental RAS (n=7), RAS supplemented with the MCP-1 inhibitor bindarit (RAS+bindarit, 50mg/kg/day PO, n=6), and normal controls (n=8). Renal inflammation was assessed by the immunoreactivity of MCP-1, its receptor CCR2, and NFkB, and oxidative-stress by NADPH-oxidase expression and in-situ superoxide production. Renal microvascular density was evaluated by micro-CT, and fibrosis by trichrome staining, collagen-I immunostaining, and hydroxyproline content.
After 10 weeks of RAS, blood pressure was similarly elevated in RAS and RAS+bindarit. Compared with normal, stenotic RAS kidneys had decreased renal blood flow (5.4±1.6 vs. 11.4±1.0 mL/min/kg, p<0.05) and glomerular filtration rate, and impaired endothelial function, which were significantly improved in bindarit-treated RAS pigs (to 8.4±0.8 mL/min/kg, p<0.05 vs. RAS). Furthermore, bindarit markedly decreased tubulointerstitial (but not vascular) oxidative-stress, inflammation, and fibrosis, and slightly increased renal microvascular density. The impaired renovascular endothelial function, increased oxidative-stress, and fibrosis in the contralateral kidney were also improved by bindarit.
MCP-1 contributes to functional and structural impairment in the kidney in RAS, mainly in the tubulointerstitial compartment. Its inhibition confers renoprotective effects by blunting renal inflammation and thereby preserving the kidney in chronic RAS.
Monocyte chemoattractant protein-1; Bindarit; Renal artery stenosis; renovascular hypertension
Coronary collateral arteries (CCA) reduce cardiovascular events. We tested the hypothesis that new microvessels that proliferate in early atherosclerosis may be associated with myocardial protection during acute subtotal coronary artery obstruction (CAO).
Methods and results
Acute left anterior descending CAO was induced by a balloon catheter in pigs after 12 weeks of high-cholesterol (HC) diet, renovascular hypertension (HTN), or normal control. Cardiac structure, myocardial perfusion, and functional response to iv adenosine and CAO were studied in vivo using electron beam computed tomography (CT). The intra-myocardial microvessels were subsequently evaluated ex vivo using micro-CT, and myocardial expression of growth factors using immunoblotting. Basal myocardial perfusion and microvascular permeability were similar among the groups, whereas their responses to adenosine were attenuated in HC and HTN. A significant decline in myocardial perfusion in normal pigs during acute CAO was attenuated in HC and abolished in HTN. CAO also elicited an increase in normal anterior wall microvascular permeability (+202 ± 59%, P < 0.05), which was attenuated in HC and HTN (+55 ± 9 and +31 ± 8%, respectively, P < 0.05 vs. normal). Microvascular (<200 µm) spatial density was significantly elevated in HC and HTN, accompanied by increased myocardial growth factor expression.
This study demonstrates that early exposure to the cardiovascular risk factors HC and HTN protects the heart from decreases in myocardial perfusion during acute subtotal CAO. This protective effect is associated with and potentially mediated by pre-emptive development of intra-myocardial microvessels that might serve as recruitable CCA.
Risk factors; Coronary collateral circulation; Preconditioning
Endothelial progenitor cells (EPC) promote neovascularization and endothelial repair. Renal artery stenosis (RAS) may impair renal function by inducing intra-renal microvascular (MV) injury and remodeling. We investigated whether replenishment with EPC would protect the renal microcirculation in chronic experimental renovascular disease.
Methods and results
Single-kidney hemodynamics and function were assessed using multi-detector CT in-vivo in pigs with RAS, RAS 4 weeks after intra-renal infusion of autologous EPC, and controls. Renal MV remodeling and angiogenic pathways were investigated ex-vivo using micro-CT, histology, and Western-blotting. EPC increased renal expression of angiogenic factors, stimulated proliferation and maturation of new vessels, and attenuated renal MV remodeling and fibrosis in RAS. Furthermore, EPC normalized the blunted renal MV and filtration function.
The current study shows that a single intra-renal infusion of autologous EPC preserved MV architecture and function and decreased MV remodeling in experimental chronic RAS. Likely, restoration of the angiogenic cascade by autologous EPC involved not only generation of new vessels, but also acceleration of their maturation and stabilization. This contributed to preserving the blood supply, hemodynamics, and function of the RAS kidney, supporting EPC as a promising therapeutic intervention for preserving the kidney in renovascular disease.
kidney; progenitor cells; renal blood flow; renal artery stenosis
Studies have shown that some of statin's pleiotropic effects were achieved by either promotion or inhibition of angiogenesis, depending on the underlying disease. This study tested the hypothesis that the angiogenic potential of simvastatin is related to the microenvironmental conditions.
Human umbilical vein endothelial cells (HUVEC) were studied after exposure to hypoxia or the inflammatory factors tumor necrosis factor (TNF)-α, with or without co-incubation with simvastatin (1μmol/L) and mevalonate. HUVEC angiogenesis was evaluated by tube formation, migration, and proliferation assays. Hypoxia inducible factor (HIF)-1α, vascular endothelial growth factor (VEGF), Akt, endothelium nitric oxide synthase (e-NOS), and oxidative stress were evaluated.
HUVEC angiogenesis increased during hypoxia (tube length 14.7±0.5 vs. 7.8±0.6 mm, p<0.05) and further enhanced by simvastatin (19.3±1.1 mm, p<0.05 vs. hypoxia alone), which downregulated the expression of the HIF-1 inhibitor PHD2 and upregulated HIF-1α, VEGF, and Akt, without changing oxidative stress or eNOS. Incubation with TNF-α promoted HUVEC angiogenesis (7.4±0.2 vs. 6.5±0.2 mm, p<0.05) with increased oxidative stress. However, simvastatin inhibited this promotion (2.5±0.3 mm, p<0.001 vs. TNF-α alone) by decreasing oxidative stress, VEGF, Akt, and eNOS.
We conclude that at the same dosage, simvastatin can either promote or inhibit angiogenesis, possibly by activating upstream regulators of HIF-1α in hypoxia, but conversely interfering with angiogenic signaling downstream to inflammation. These opposing angiogenic effects should be considered in the therapeutic strategies with statins.
Simvastatin; hypoxia; angiogenesis; inflammation
Advanced hypertension (HT), associated with left ventricular hypertrophy (LVH), impairs myocardial microvascular function and structure and leads to increased myocardial hypoxia and growth factor activation. However, the effect of HT on microvascular architecture and its relation to microvascular function, prior to the development of LVH (early HT), remain unclear.
Pigs were studied after 12 weeks of renovascular HT (n=7) or control (n=7). Myocardial microvascular function (blood volume and blood flow at baseline and in response to adenosine) was assessed using electron beam computed-tomography (CT). Microvascular architecture was subsequently studied ex-vivo using micro-CT, and microvessels (diameter<500μm) counted in-situ in 3-D images (40μm on-a-side cubic voxels). Myocardial expression of vascular endothelial growth factor, basic fibroblast growth factor, and hypoxia inducible factor-1α were also measured.
Left ventricular muscle mass was similar between the groups. The blood volume response to intravenous adenosine was attenuated in HT compared to normal animals (+7.4±17.0 vs. +46.2±12.3 % compared to baseline, p=0.48 and p=0.01, respectively). Microvascular spatial density in HT was significantly elevated compared to normal (246±26 vs. 125±20 vessels/cm2, p<0.05) and correlated inversely with the blood volume response to adenosine. Growth factors expression was increased in HT compared to control.
Early HT elicits changes in myocardial microvascular architecture, which are associated with microvascular dysfunction and precede changes in muscle mass. These observations underscore the direct and early effects of HT on the myocardial vasculature.
hypertension; microcirculation; imaging; growth factors; micro-CT