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      Role of the Intrarenal Renin-Angiotensin-Aldosterone System in Chronic Kidney Disease

      review-article
      ,
      American Journal of Nephrology
      S. Karger AG
      Direct renin inhibition, Aliskiren, Kidney disease, Angiotensin

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          Abstract

          The existence of local or tissue-based renin-angiotensin-aldosterone systems (RAAS) is well documented and has been implicated as a key player in the pathogenesis of cardiovascular and renal diseases. The kidney contains all elements of the RAAS, and intrarenal formation of angiotensin II not only controls glomerular hemodynamics and tubule sodium transport, but also activates a number of inflammatory and fibrotic pathways. Experimental and clinical studies have shown that the intrarenal RAAS is activated early in diabetic nephropathy, the leading cause of chronic kidney disease (CKD). Although angiotensin-converting enzyme inhibitors and angiotensin receptor blockers decrease the rate of decline in kidney function in patients with diabetic and non-diabetic nephropathy, many patients still progress to end-stage renal disease or die from cardiovascular events. There is still a clear need for additional strategies to block the RAAS more effectively to reduce progression of CKD. The focus of this paper is to review the importance of the intrarenal RAAS in CKD and recent findings in renin-angiotensin biology pertinent to the kidney. We also discuss additional strategies to inhibit the RAAS more effectively and the potential impact of direct renin inhibition on the prevention and management of CKD.

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          Most cited references38

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          The intrarenal renin-angiotensin system: from physiology to the pathobiology of hypertension and kidney disease.

          In recent years, the focus of interest on the role of the renin-angiotensin system (RAS) in the pathophysiology of hypertension and organ injury has changed to a major emphasis on the role of the local RAS in specific tissues. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by independent multiple mechanisms. Proximal tubular angiotensinogen, collecting duct renin, and tubular angiotensin II type 1 (AT1) receptors are positively augmented by intrarenal Ang II. In addition to the classic RAS pathways, prorenin receptors and chymase are also involved in local Ang II formation in the kidney. Moreover, circulating Ang II is actively internalized into proximal tubular cells by AT1 receptor-dependent mechanisms. Consequently, Ang II is compartmentalized in the renal interstitial fluid and the proximal tubular compartments with much higher concentrations than those existing in the circulation. Recent evidence has also revealed that inappropriate activation of the intrarenal RAS is an important contributor to the pathogenesis of hypertension and renal injury. Thus, it is necessary to understand the mechanisms responsible for independent regulation of the intrarenal RAS. In this review, we will briefly summarize our current understanding of independent regulation of the intrarenal RAS and discuss how inappropriate activation of this system contributes to the development and maintenance of hypertension and renal injury. We will also discuss the impact of antihypertensive agents in preventing the progressive increases in the intrarenal RAS during the development of hypertension and renal injury.
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            Aliskiren combined with losartan in type 2 diabetes and nephropathy.

            Diabetic nephropathy is the leading cause of end-stage renal disease in developed countries. We evaluated the renoprotective effects of dual blockade of the renin-angiotensin-aldosterone system by adding treatment with aliskiren, an oral direct renin inhibitor, to treatment with the maximal recommended dose of losartan (100 mg daily) and optimal antihypertensive therapy in patients who had hypertension and type 2 diabetes with nephropathy. We enrolled 599 patients in this multinational, randomized, double-blind study. After a 3-month, open-label, run-in period during which patients received 100 mg of losartan daily, patients were randomly assigned to receive 6 months of treatment with aliskiren (150 mg daily for 3 months, followed by an increase in dosage to 300 mg daily for another 3 months) or placebo, in addition to losartan. The primary outcome was a reduction in the ratio of albumin to creatinine, as measured in an early-morning urine sample, at 6 months. The baseline characteristics of the two groups were similar. Treatment with 300 mg of aliskiren daily, as compared with placebo, reduced the mean urinary albumin-to-creatinine ratio by 20% (95% confidence interval, 9 to 30; P<0.001), with a reduction of 50% or more in 24.7% of the patients who received aliskiren as compared with 12.5% of those who received placebo (P<0.001). A small difference in blood pressure was seen between the treatment groups by the end of the study period (systolic, 2 mm Hg lower [P=0.07] and diastolic, 1 mm Hg lower [P=0.08] in the aliskiren group). The total numbers of adverse and serious adverse events were similar in the groups. Aliskiren may have renoprotective effects that are independent of its blood-pressure-lowering effect in patients with hypertension, type 2 diabetes, and nephropathy who are receiving the recommended renoprotective treatment. (ClinicalTrials.gov number, NCT00097955 [ClinicalTrials.gov].). Copyright 2008 Massachusetts Medical Society.
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              Renin-angiotensin-aldosterone system and progression of renal disease.

              Inhibition of the renin-angiotensin-aldosterone system (RAAS) is one of the most powerful maneuvers to slow progression of renal disease. Angiotensin II (AngII) has emerged in the past decade as a multifunctional cytokine that exhibits many nonhemodynamic properties, such as acting as a growth factor and profibrogenic cytokine, and even having proinflammatory properties. Many of these deleterious functions are mediated by other factors, such as TGF-beta and chemoattractants that are induced in the kidney by AngII. Moreover, understanding of the RAAS has become much more complex in recent years with the identification of novel peptides (e.g., AngIV) that could bind to specific receptors, elucidating deleterious effects, and non-angiotensin-converting enzyme (ACE)-mediated generation of AngII. The ability of renal cells to produce AngII in a concentration that is much higher than what is found in the systemic circulation and the observation that aldosterone may be engaged directly in profibrogenic processes independent of hypertension have added to the complexity of the RAAS. Even renin has now been identified to have a "life on its own" and mediates profibrotic effects via binding to specific receptors. Finally, drugs that are used to block the RAAS, such as ACE inhibitors or certain AngII type 1 receptor antagonists, may have properties on cells independent of AngII (ACE inhibitor-mediated outside-inside signaling and peroxisome proliferator-activated receptor-gamma stimulatory effects of certain sartanes). Although blockade of the RAAS with ACE inhibitors, AngII type 1 receptor antagonists, or the combination of both should be part of every strategy to slow progression of renal disease, a better understanding of the novel aspects of the RAAS should contribute to the development of innovative strategies not only to completely halt progression but also to induce regression of human renal disease.
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                Author and article information

                Journal
                AJN
                Am J Nephrol
                10.1159/issn.0250-8095
                American Journal of Nephrology
                S. Karger AG
                0250-8095
                1421-9670
                2010
                June 2010
                18 May 2010
                : 31
                : 6
                : 541-550
                Affiliations
                Division of Endocrinology and Metabolism, Department of Medicine, University of Virginia Health System, Charlottesville, Va., USA
                Author notes
                *Helmy M. Siragy, MD, Department of Medicine, University of Virginia Health System, PO Box 801409, Charlottesville, VA 22908 (USA), Tel. +1 434 924 5629, Fax +1 434 982 3626, E-Mail hms7a@virginia.edu
                Article
                313363 PMC3202956 Am J Nephrol 2010;31:541–550
                10.1159/000313363
                PMC3202956
                20484892
                716c2170-79bd-427d-b7ed-e022c23db2fe
                © 2010 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                History
                : 26 January 2010
                : 09 April 2010
                Page count
                Figures: 2, Tables: 2, References: 60, Pages: 10
                Categories
                In-Depth Topic Review

                Cardiovascular Medicine,Nephrology
                Aliskiren,Direct renin inhibition,Angiotensin,Kidney disease
                Cardiovascular Medicine, Nephrology
                Aliskiren, Direct renin inhibition, Angiotensin, Kidney disease

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