Angiotensin receptor blockade has protective effects on the poststenotic porcine kidney
2013; Elsevier BV; Volume: 84; Issue: 4 Linguagem: Inglês
10.1038/ki.2013.144
ISSN1523-1755
AutoresXin Zhang, Alfonso Eirin, Zi-Lun Li, John A. Crane, James D. Krier, Behzad Ebrahimi, Aditya S. Pawar, Xiang-Yang Zhu, Hui Tang, Kyra L. Jordan, Amir Lerman, Stephen C. Textor, Lilach O. Lerman,
Tópico(s)Chronic Kidney Disease and Diabetes
ResumoAngiotensin-converting enzyme inhibitors/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 angiotensin-converting enzyme inhibitors/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 (seven 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 with 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. Angiotensin-converting enzyme inhibitors/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 angiotensin-converting enzyme inhibitors/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 (seven 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 with 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. The prevalence of renal artery stenosis (RAS) is fast-growing worldwide, especially in the elderly population. In addition to hypertension and progressive renal function decline, the incidence of cardiovascular morbidity and mortality is also on the rise.1.Colyer Jr., W.R. Cooper C.J. Cardiovascular morbidity and mortality and renal artery stenosis.Prog Cardiovasc Dis. 2009; 52: 238-242Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar These pathophysiological changes are accompanied by increased levels of angiotensin II (AngII), which is formed by the activated renin–angiotensin–aldosterone system in RAS. The application of angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers (ARBs), which block the effects of AngII by binding to its type I receptor (AT1), have conferred invaluable benefits not only in relieving renovascular hypertension but also in lowering the cardiovascular complications.2.Yusuf S. Sleight P. Pogue J. et al.Effects of an angiotensin-converting-enzyme inhibitor, ramipril, on cardiovascular events in high-risk patients. The Heart Outcomes Prevention Evaluation Study Investigators.N Engl J Med. 2000; 342: 145-153Crossref PubMed Scopus (8157) Google Scholar,3.Yusuf S. Teo K.K. Pogue J. et al.Telmisartan, ramipril, or both in patients at high risk for vascular events.N Engl J Med. 2008; 358: 1547-1559Crossref PubMed Scopus (3037) Google Scholar In the kidney, although the inhibition of renin–angiotensin–aldosterone system has been useful in alleviating proteinuria and slowing renal function decline, it might acutely reduce the stenotic kidney capillary hydrostatic pressure and, consequently, glomerular filtration rate (GFR).4.Dworkin L.D. Controversial treatment of atherosclerotic renal vascular disease: the cardiovascular outcomes in renal atherosclerotic lesions trial.Hypertension. 2006; 48: 350-356Crossref PubMed Scopus (25) Google Scholar,5.Onuigbo M.A. Onuigbo N.T. Worsening renal failure in older chronic kidney disease patients with renal artery stenosis concurrently on renin angiotensin aldosterone system blockade: a prospective 50-month Mayo-Health-System clinic analysis.QJM. 2008; 101: 519-527Crossref PubMed Scopus (26) Google Scholar However, abundant evidence has shown that in most patients these drugs are well tolerated.6.Chrysochou C. Foley R.N. Young J.F. et al.Dispelling the myth: the use of renin-angiotensin blockade in atheromatous renovascular disease.Nephrol Dial Transplant. 2012; 27: 1403-1409Crossref PubMed Scopus (76) Google Scholar Conceivably, chronic blockade of renin–angiotensin–aldosterone system might also blunt deleterious processes in the kidney, such as microvascular remodeling that characterizes ischemic kidney damage,7.Zhu X.Y. Chade A.R. Rodriguez-Porcel M. et al.Cortical microvascular remodeling in the stenotic kidney: role of increased oxidative stress.Arterioscler Thromb Vasc Biol. 2004; 24: 1854-1859Crossref PubMed Scopus (133) Google Scholar,8.Chade A.R. Zhu X. Mushin O.P. et al.Simvastatin promotes angiogenesis and prevents microvascular remodeling in chronic renal ischemia.FASEB J. 2006; 20: 1706-1708Crossref PubMed Scopus (116) Google Scholar and may modulate oxidative stress and inflammation as observed in other forms of chronic kidney disease.9.Onozato M.L. Tojo A. Goto A. et al.Oxidative stress and nitric oxide synthase in rat diabetic nephropathy: effects of ACEI and ARB.Kidney Int. 2002; 61: 186-194Abstract Full Text Full Text PDF PubMed Scopus (346) Google Scholar,10.Esteban V. Lorenzo O. Ruperez M. et al.Angiotensin II, via AT1 and AT2 receptors and NF-kappaB pathway, regulates the inflammatory response in unilateral ureteral obstruction.J Am Soc Nephrol. 2004; 15: 1514-1529Crossref PubMed Scopus (203) Google Scholar However, the potential effects of long-term ARBs on the microvasculature within the stenotic kidney remain unclear. This study tested the hypothesis that chronic treatment with the ARB Valsartan would preserve stenotic kidney function in a unilateral RAS swine model, similar to a conventional antihypertensive regimen, by decreasing tissue injury that may offset the hemodynamic reduction of GFR. At 10 weeks, there were no differences in body weight and the degree of stenosis among the groups (Table 1), including Normal, unilateral RAS, RAS+Valsartan, or RAS+triple therapy (TT, reserpine+hydralazine+hydrochlorothiazide). Blood pressure changes of the study groups during the observation are shown in Figure 1a. Mean arterial pressure increased at 1 week after RAS induction and remained similarly elevated at 6 weeks (P=0.29 among three groups), suggesting hemodynamically significant RAS. Mean arterial pressure continued to increase in untreated RAS at 10 weeks (P<0.05 vs. 6 weeks), but was lowered by both Valsartan and TT groups to the same level, although neither reduced mean arterial pressure to normal (P=0.02 and 0.04 vs. Normal, respectively). Urine protein was increased in all three RAS groups, but was alleviated only by Valsartan (P=0.040 vs. RAS; P=0.053 vs. Normal, Table 1). Valsartan also decreased urinary levels of the kidney injury marker neutrophil gelatinase–associated lipocalin that was elevated in RAS. Creatinine level was increased in all RAS groups, and was unaffected by either treatment. Serum potassium in the RAS+Valsartan group did not differ from Normal and RAS groups, whereas TT induced a slight decrease. Serum sodium was comparable among the groups.Table 1Animal systemic characteristics in normal, unilateral RAS, and Valsartan or TT–treated RAS for 4 weeksCharacteristicsNormal (n=7)RAS (n=7)RAS+Valsartan (n=7)RAS+TT (n=7)Body weight (kg)49.4±0.850.8±2.148.3±1.947.8±0.9Degree of stenosis (%)—78±776±478±5MAP (mmHg)106.0±4.1173.4±5.0*P <0.05 versus Normal.134.0±6.3*P <0.05 versus Normal.,$P <0.05 versus RAS.130.9±11.2*P <0.05 versus Normal.,$P <0.05 versus RAS.Urine protein (µg/ml)13.2±1.340.2±5.6*P <0.05 versus Normal.23.8±4.4$P <0.05 versus RAS.29.7±5.0*P <0.05 versus Normal.Urine NGAL (ng/ml)6.08±0.268.32±0.71*P <0.05 versus Normal.6.62±0.21$P <0.05 versus RAS.7.21±0.47Serum creatinine (mg/dl)1.23±0.041.60±0.08*P <0.05 versus Normal.1.52±0.05*P <0.05 versus Normal.1.73±0.03*P <0.05 versus Normal.Serum K (mmol/l)3.78±0.113.75±0.143.57±0.193.38±0.10*P <0.05 versus Normal.Serum Na (mg/dl)138.8±0.9136.0±2.0137.7±5.1139.8±0.8Abbreviations: MAP, mean arterial pressure; NGAL, neutrophil gelatinase–associated lipocalin; RAS, renal artery stenosis; TT, triple therapy.Data were expressed as mean±SEM. *P <0.05 versus Normal.P<0.05 versus Normal. $P <0.05 versus RAS.P<0.05 versus RAS.* P <0.05 versus Normal.$ P <0.05 versus RAS. Open table in a new tab Abbreviations: MAP, mean arterial pressure; NGAL, neutrophil gelatinase–associated lipocalin; RAS, renal artery stenosis; TT, triple therapy. Data were expressed as mean±SEM. *P <0.05 versus Normal.P<0.05 versus Normal. $P <0.05 versus RAS.P<0.05 versus RAS. Stenotic-kidney GFR was decreased in all RAS groups, as were renal blood flow and cortical renal perfusion (Figure 1b (A–C)). Neither Valsartan nor TT increased renal blood flow or GFR, yet cortical perfusion was slightly but significantly increased in the RAS+Valsartan group compared with the RAS group. Basal medullary R2*, an index of the concentration of deoxyhemoglobin in the kidney,11.Warner L. Glockner J.F. Woollard J. et al.Determinations of renal cortical and medullary oxygenation using blood oxygen level-dependent magnetic resonance imaging and selective diuretics.Invest Radiol. 2011; 46: 41-47Crossref PubMed Scopus (74) Google Scholar,12.Ebrahimi B. Gloviczki M. Woollard J.R. et al.Compartmental analysis of renal BOLD MRI data: introduction and validation.Invest Radiol. 2012; 47: 175-182PubMed Google Scholar in both the RAS+Valsartan and RAS+TT groups was higher than the Normal group (Figure 1c (B)), suggesting lower medullary oxygenation. The tubular response to furosemide, which decreases R2* by increasing medulla oxygenation via the inhibition of solute transport and thereby of oxygen consumption,12.Ebrahimi B. Gloviczki M. Woollard J.R. et al.Compartmental analysis of renal BOLD MRI data: introduction and validation.Invest Radiol. 2012; 47: 175-182PubMed Google Scholar was abolished in RAS, but was improved by TT and to a slightly greater extent by Valsartan (Figure 1c (C)), indicating recovery of viability of medullar tubules. Cortical R2* value was slightly lower in the RAS+Valsartan group than in the RAS group, consistent with lower levels of cortical deoxyhemoglobin (Figure 1c (A)). RAS decreased the density of both small and medium-sized microvessels through the inner and outer cortex (Figure 2a (A–F)). Valsartan normalized outer cortical small-vessel density and improved that of medium-sized vessels (P=0.01 vs. RAS). In contrast, TT improved only small-vessel density. Microvascular density in the inner cortex remained unchanged by either drug. Consistent with the microvascular density changes, Valsartan increased the expression of basic fibroblast growth factor and vascular endothelial growth factor (VEGF), and normalized the expression of its receptor-2 (FLK-1) that was suppressed in RAS (Figure 2b (A)). TT only increased the receptor FLK-1 expression (P=0.01 vs. Normal). Expression of endothelial nitric oxide synthase remained unchanged among the groups. Valsartan also enhanced the expression of the neovessel maturation/stability modulators13.Yuan H.T. Suri C. Yancopoulos G.D. et al.Expression of angiopoietin-1, angiopoietin-2, and the Tie-2 receptor tyrosine kinase during mouse kidney maturation.J Am Soc Nephrol. 1999; 10: 1722-1736PubMed Google Scholar angiopoietin-1 and its receptor Tie-2, which was downregulated in RAS. TT also improved the expression of Tie-2, but to a lesser extent than Valsartan. Therefore, Valsartan promoted both angiogenic factors and their receptors, but TT mainly activated their receptors. Notably, TT but not Valsartan increased thrombospondin-1 (P=0.01 vs. Normal), which inhibits neovascularization. Hence, both Valsartan and TT improved microvascular density, but Valsartan tended to exert greater angiogenic impact. Hypoxia-inducible factor (HIF)-1-α, closely linked to neovascularization in tissue ischemia, was downregulated in RAS, as previously reported in our RAS model,14.Chade A.R. Zhu X. Lavi R. et al.Endothelial progenitor cells restore renal function in chronic experimental renovascular disease.Circulation. 2009; 119: 547-557Crossref PubMed Scopus (193) Google Scholar but normalized by both medication regimens (Figure 2b (B)) Dihydroethidium staining indicated increased oxidative stress in RAS that was attenuated by Valsartan (P=0.01 vs. RAS) but not by TT (P=0.07 vs. Normal). This was consistent with NAD(P)H oxidase P47 expression, which was increased in RAS but was decreased only by Valsartan (Figure 3a). Tumor necrosis factor-α expression in RAS kidneys was enhanced in renal tubules and interstitium, but was attenuated to a similar extent by Valsartan and TT (Figure 3b). Trichrome staining showed that fibrosis was blunted to the same extent by both Valsartan and TT compared with RAS (Figure 3c). In line with trichrome staining, both Valsartan and TT normalized elevated matrix metalloproteinase-2 expression in RAS and downregulated the tissue inhibitor of metalloproteinase-1. TT also induced a greater decrease in transforming growth factor-β compared with Valsartan (P=0.03). Neither medication decreased connective tissue growth factor (Figure 3d). AT1R was upregulated in RAS, and Valsartan further enhanced its expression, possibly as a feedback to its blockade. AT2R was similarly elevated in all RAS groups (Figure 4). Our study shows that for the same level of blood pressure control a 4-week chronic treatment with the ARB Valsartan achieved similar renal function and did not decrease the stenotic kidney GFR compared with a conventional antihypertensive regimen. In addition, Valsartan elicited a slightly better preservation of intrarenal perfusion, microvascular density, and medullary tubular function, although overall kidney function was similar to that achieved with TT. Nevertheless, our data suggest that the safety and efficacy of Valsartan in the management of renovascular hypertension in RAS might be mediated by a novel protective effect on the intrarenal microvasculature. An important mechanism contributing to intrarenal damage distal to RAS, microvascular remodeling and regression characterize the pathophysiologic alteration caused by prolonged vasoconstriction, oxidative stress, and fibrosis.7.Zhu X.Y. Chade A.R. Rodriguez-Porcel M. et al.Cortical microvascular remodeling in the stenotic kidney: role of increased oxidative stress.Arterioscler Thromb Vasc Biol. 2004; 24: 1854-1859Crossref PubMed Scopus (133) Google Scholar, 8.Chade A.R. Zhu X. Mushin O.P. et al.Simvastatin promotes angiogenesis and prevents microvascular remodeling in chronic renal ischemia.FASEB J. 2006; 20: 1706-1708Crossref PubMed Scopus (116) Google Scholar, 15.Lerman L.O. Textor S.C. Grande J.P. Mechanisms of tissue injury in renal artery stenosis: ischemia and beyond.Prog Cardiovasc Dis. 2009; 52: 196-203Abstract Full Text Full Text PDF PubMed Scopus (102) Google Scholar A physiological acute decrease in oxygen supply upregulates the expression of HIF-1-α, a primary defense mechanism in the adaptive response to ischemia, and in turn the expression of VEGF, which induces new vessel formation. However, this compensatory capability can be impaired in chronic ischemia by amplified oxidative stress and inflammation in RAS (reflected in our study by increased dihydroethidium staining, P47 expression, and tumor necrosis factor-α), which destabilize HIF-1-α and degrade VEGF protein, thus interfering with tissue repair by compensatory angiogenesis.7.Zhu X.Y. Chade A.R. Rodriguez-Porcel M. et al.Cortical microvascular remodeling in the stenotic kidney: role of increased oxidative stress.Arterioscler Thromb Vasc Biol. 2004; 24: 1854-1859Crossref PubMed Scopus (133) Google Scholar, 8.Chade A.R. Zhu X. Mushin O.P. et al.Simvastatin promotes angiogenesis and prevents microvascular remodeling in chronic renal ischemia.FASEB J. 2006; 20: 1706-1708Crossref PubMed Scopus (116) Google Scholar, 14.Chade A.R. Zhu X. Lavi R. et al.Endothelial progenitor cells restore renal function in chronic experimental renovascular disease.Circulation. 2009; 119: 547-557Crossref PubMed Scopus (193) Google Scholar Accordingly, the present study demonstrated that HIF-1-α was suppressed in RAS, along with downregulated FLK-1 and VEGF, which failed to increase. The unchanged level of VEGF could be a result of its dynamic temporal expression pattern in ischemia.16.Favreau F. Zhu X.Y. Krier J.D. et al.Revascularization of swine renal artery stenosis improves renal function but not the changes in vascular structure.Kidney Int. 2010; 78: 1110-1118Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar,17.Chade A.R. Kelsen S. Reversal of renal dysfunction by targeted administration of VEGF into the stenotic kidney: a novel potential therapeutic approach.Am J Physiol Renal Physiol. 2012; 302: F1342-F1350Crossref PubMed Scopus (59) Google Scholar Interestingly, our data show that Valsartan activates multiple angiogenic factors in the stenotic kidneys, including basic fibroblast growth factor, VEGF/FLK-1, and HIF-1-α, possibly by alleviating oxidative stress and inflammation (tumor necrosis factor-α), as observed in other chronic kidney diseases.9.Onozato M.L. Tojo A. Goto A. et al.Oxidative stress and nitric oxide synthase in rat diabetic nephropathy: effects of ACEI and ARB.Kidney Int. 2002; 61: 186-194Abstract Full Text Full Text PDF PubMed Scopus (346) Google Scholar, 10.Esteban V. Lorenzo O. Ruperez M. et al.Angiotensin II, via AT1 and AT2 receptors and NF-kappaB pathway, regulates the inflammatory response in unilateral ureteral obstruction.J Am Soc Nephrol. 2004; 15: 1514-1529Crossref PubMed Scopus (203) Google Scholar, 18.Ruiz-Ortega M. Ruperez M. Lorenzo O. et al.Angiotensin II regulates the synthesis of proinflammatory cytokines and chemokines in the kidney.Kidney Int Suppl. 2002; 82: S12-S22Abstract Full Text Full Text PDF PubMed Scopus (338) Google Scholar Furthermore, Valsartan upregulated the key modulators of vessel stability and maturation: angiopoietin-1 and Tie-2. Collectively, these effects may account for the slightly greater improvement of intrarenal microvascular density than that achieved by conventional TT, although both drug regimens improved cortical microvascular density. Such benefits are probably functionally consequential, because we have previously shown that the loss of small outer cortical microvessels correlates with persistent kidney dysfunction after renal artery revascularization.19.Eirin A. Zhu X.Y. Urbieta-Caceres V.H. et al.Persistent kidney dysfunction in swine renal artery stenosis correlates with outer cortical microvascular remodeling.Am J Physiol Renal Physiol. 2011; 300: F1394-F1401Crossref PubMed Scopus (68) Google Scholar However, although TT increased the expression of the receptors FLK-1 and Tie-2, and restored HIF-1-α, these might have been offset by the parallel upregulation of thrombospondin-1. Therefore, some of the beneficial effects of Valsartan on the kidney might be mediated by a microvascular protective effect, which appears to be independent of blood pressure. The drugs used for TT decrease blood pressure by direct vasodilation, diuresis, or by depleting central monoamine, and are considered to have few effects on inflammation, oxygenation, and the microvasculature. Importantly, in this study, we observed minor but significant renal protective effects, which might be attributed to vasodilation of intrarenal vessels, because blood pressure reduction per se might further decrease renal perfusion distal to the stenosis. Indeed, hydralazine has also been linked to antioxidative and anti-inflammatory effects.20.Echols M.R. Yancy C.W. Isosorbide dinitrate-hydralazine combination therapy in African Americans with heart failure.Vasc Health Risk Manag. 2006; 2: 423-431Crossref PubMed Scopus (13) Google Scholar,21.Xu B. Thornton C. Makris A. et al.Anti-hypertensive drugs alter cytokine production from preeclamptic placentas and peripheral blood mononuclear cells.Hypertens Pregnancy. 2007; 26: 343-356Crossref PubMed Scopus (13) Google Scholar In addition, hydrochlorothiazide might sustain GFR by increasing efferent arteriolar resistance.22.Komatsu K. Numabe A. Ono Y. et al.Hydrochlorothiazide increases efferent glomerular arteriolar resistance in spontaneously hypertensive rats.J Cardiovasc Pharmacol Ther. 1996; 1: 57-64Crossref PubMed Scopus (18) Google Scholar A protective effect of TT has been observed in other models, yet is often ascribed to antihypertensive properties.23.Velasquez M.T. Striffler J.S. Abraham A.A. et al.Perindopril ameliorates glomerular and renal tubulointerstitial injury in the SHR/N-corpulent rat.Hypertension. 1997; 30: 1232-1237Crossref PubMed Scopus (25) Google Scholar We have previously shown that basal R2* in poststenotic human kidneys increases in severe,24.Gloviczki M.L. Glockner J.F. Crane J.A. et al.Blood oxygen level-dependent magnetic resonance imaging identifies cortical hypoxia in severe renovascular disease.Hypertension. 2011; 58: 1066-1072Crossref PubMed Scopus (87) Google Scholar but not moderate, ischemia,25.Gloviczki M.L. Glockner J.F. Lerman L.O. et al.Preserved oxygenation despite reduced blood flow in poststenotic kidneys in human atherosclerotic renal artery stenosis.Hypertension. 2010; 55: 961-966Crossref PubMed Scopus (117) Google Scholar whereas medullary response to furosemide is blunted in the latter, as observed in RAS pig kidneys in the current study. Presumably, decreased tubular injury and resumed transport activity, reflected by an increase of delta-R2* in response to furosemide, might have contributed to the increase in basal R2* in RAS+Valsartan and RAS+TT kidneys.26.Ebrahimi B. Li Z. Eirin A. et al.Addition of endothelial progenitor cells to renal revascularization restores medullary tubular oxygen consumption in swine renal artery stenosis.Am J Physiol Renal Physiol. 2012; 302: F1478-F1485Crossref PubMed Scopus (33) Google Scholar Hence, our data reinforce the notion of a parallel decrease in oxygen-dependent tubular transport and subsequently oxygen consumption as a possible primary mechanism to minimize hypoxia and preserve tubular cells.26.Ebrahimi B. Li Z. Eirin A. et al.Addition of endothelial progenitor cells to renal revascularization restores medullary tubular oxygen consumption in swine renal artery stenosis.Am J Physiol Renal Physiol. 2012; 302: F1478-F1485Crossref PubMed Scopus (33) Google Scholar Indeed, in parallel to the increase in basal R2* value in our study, HIF-1-α that was inhibited in RAS was also increased by Valsartan and TT. The long-term effects of increased tubular work in the face of unchanged renal blood flow warrant further studies, although evidently both approaches ultimately decrease renal fibrosis in our model. ARBs exert their beneficial effects by blocking the binding of AngII to the AT1R, thereby allowing it to bind to the AT2R.27.Wolf G. Ritz E. Combination therapy with ACE inhibitors and angiotensin II receptor blockers to halt progression of chronic renal disease: pathophysiology and indications.Kidney Int. 2005; 67: 799-812Abstract Full Text Full Text PDF PubMed Scopus (256) Google Scholar Both the AT1R and AT2R were upregulated in RAS, as previously shown,28.Matavelli L.C. Huang J. Siragy H.M. Angiotensin AT(2) receptor stimulation inhibits early renal inflammation in renovascular hypertension.Hypertension. 2011; 57: 308-313Crossref PubMed Scopus (127) Google Scholar and we also found that AT1R expression was further increased by Valsartan, probably a feedback secondary to receptor blockade. Notably, this may also affect the microvascular remodeling observed in our study. Although microvascular rarefaction induced by oxidative stress, inflammation, and fibrosis dominates kidney remodeling in RAS, direct proangiogenic effects of AngII include upregulating angiogenic factors, such as VEGF, basic fibroblast growth factor, endothelial nitric oxide synthase, and Ang-1/Tie-2, and are mediated by binding to either the AT1R or AT2R.29.Rizkalla B. Forbes J.M. Cooper M.E. et al.Increased renal vascular endothelial growth factor and angiopoietins by angiotensin II infusion is mediated by both AT1 and AT2 receptors.J Am Soc Nephrol. 2003; 14: 3061-3071Crossref PubMed Scopus (73) Google Scholar However, the expression pattern of AT1R and AT2R differs greatly by tissue, and may affect the involvement of AngII in neovascularization.30.Willis L.M. El-Remessy A.B. Somanath P.R. et al.Angiotensin receptor blockers and angiogenesis: clinical and experimental evidence.Clin Sci (Lond). 2011; 120: 307-319Crossref PubMed Scopus (57) Google Scholar Although AT1R is abundant in a number of adult tissues,31.Gallinat S. Busche S. Raizada M.K. et al.The angiotensin II type 2 receptor: an enigma with multiple variations.Am J Physiol Endocrinol Metab. 2000; 278: E357-E374PubMed Google Scholar the AT2R, in general, is restricted in adults to organs, such as the kidney, brain, and adrenal gland. Hence, the influence of ARB on angiogenesis may possibly be affected by the type of tissue.30.Willis L.M. El-Remessy A.B. Somanath P.R. et al.Angiotensin receptor blockers and angiogenesis: clinical and experimental evidence.Clin Sci (Lond). 2011; 120: 307-319Crossref PubMed Scopus (57) Google Scholar Indeed, in our study, the improvement of microvascular density after AT1R blockade by Valsartan could be attributed to binding of AngII to the upregulated AT2R, possibly stimulated by kidney injury.31.Gallinat S. Busche S. Raizada M.K. et al.The angiotensin II type 2 receptor: an enigma with multiple variations.Am J Physiol Endocrinol Metab. 2000; 278: E357-E374PubMed Google Scholar,32.Ozono R. Wang Z.Q. Moore A.F. et al.Expression of the subtype 2 angiotensin (AT2) receptor protein in rat kidney.Hypertension. 1997; 30: 1238-1246Crossref PubMed Scopus (281) Google Scholar This stipulation is supported by the observation that chronic treatment with Lorsartan for 2 weeks increased microvessel density in the brain, where AT2 receptor is also richly expressed.33.Munzenmaier D.H. Greene A.S. Chronic angiotensin II AT1 receptor blockade increases cerebral cortical microvessel density.Am J Physiol Heart Circ Physiol. 2006; 290: H512-H516Crossref PubMed Scopus (37) Google Scholar Our study is limited by the use of relatively young animals and short duration of the disease, yet renal structure and function in our swine model are similar to that of human kidneys. The long-term effect of ARB on stenotic kidney function, and the contribution of microvascular protection to the improvement of renal function, warrant further studies. The blockade of the renin–angiotensin–aldosterone system in our study was incomplete, as suggested by the partial blood pressure response, indicating the need for dose adjustments in pigs. Nevertheless, the comparable decrease in blood pressure relative to TT implies that any observed effects of Valsartan compared with TT were independent of blood pressure. As TT can increase renin release and AngII, its influence on AngII and its link to microvascular change or other mechanisms of ischemic kidney injury should also be further explored. In summary, our study demonstrated that a 4-week regimen of ARB after 10 weeks of swine unilateral RAS did not impair hemodynamics or function in the stenotic kidney, as compared with untreated RAS or with conventional antihypertensive treatment eliciting a comparable blood pressure decrease. We also observed improved renal microvascular density and decreased tubulointerstitial fibrosis in the stenotic kidney of pigs treated with TT. In addition, Valsartan seems to offer slightly greater gains in cortical microvascular density and function (perfusion), and in medullary tubular function, possibly by upregulating the expression of several growth factors and suppressing oxidative stress and inflammation. Although the measureable differences between Valsartan and TT were not striking, they were associated with a greater decrease in urinary protein and neutrophil gelatinase–associated lipocalin levels, and may partly offset a hemodynamic ARB-induced reduction in GFR in the ischemic kidney. Therefore, our data imply that chronic use of ARB may not only be safe in unilateral RAS but may also provide renoprotective benefit.
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