Diabetic Nephropathy: The Proteinuria Hypothesis

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Abstract

Background/Aims: Proteinuria, nearly a universal finding in progressive kidney disease, has been the subject of frequent recent analyses in the renal literature. Proteinuria is a hallmark of diabetic nephropathy: microalbuminuria is the principal early predictor for progression of diabetic glomerulopathy, and proteinuria may be viewed as a measure of the severity and promoter of progression of nephropathy. Methods: This article critically reviews for the first time the full scope of diabetic proteinuria – complex molecular mechanisms, natural history, and analysis of treatment trials – in order to address the validity of ‘the proteinuria hypothesis’, i.e., that diabetic proteinuria is a modifiable determinant of renal progression. This hypothesis is analyzed in detail, including recent studies on the primary therapy of diabetic nephropathy, renin-angiotensin blockade. Results: As fully developed, this hypothesis consists of three postulates: that higher amounts of proteinuria predict progressive loss of function, that proteinuria reduction correlates with slowing progression, and that proteinuria is a surrogate endpoint for clinical trials. The latter postulate has not before been adequately linked to growing information about the first two postulates as they apply to diabetic kidney disease. Conclusion: While diabetic nephropathy is a disease model for the potential use of proteinuria as a surrogate marker for renal progression, this shift in perspective will require prospective data from additional clinical trials, particularly of non-renin-angiotensin blocking drugs, to be complete.

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Effects of candesartan in patients with chronic heart failure and reduced left-ventricular systolic function taking angiotensin-converting-enzyme inhibitors: the CHARM-Added trial.

John J V McMurray, Jan Östergren, Karl Swedberg … (2003)

Angiotensin II type 1 receptor blockers have favourable effects on haemodynamic measurements, neurohumoral activity, and left-ventricular remodelling when added to angiotensin-converting-enzyme (ACE) inhibitors in patients with chronic heart failure (CHF). We aimed to find out whether these drugs improve clinical outcome. Between March, 1999, and November, 1999, we enrolled 2548 patients with New York Heart Association functional class II-IV CHF and left-ventricular ejection fraction 40% or lower, and who were being treated with ACE inhibitors. We randomly assigned patients candesartan (n=1276, target dose 32 mg once daily) or placebo (n=1272). At baseline, 55% of patients were also treated with beta blockers and 17% with spironolactone. The primary outcome of the study was the composite of cardiovascular death or hospital admission for CHF. Analysis was done by intention to treat. The median follow-up was 41 months. 483 (38%) patients in the candesartan group and 538 (42%) in the placebo group experienced the primary outcome (unadjusted hazard ratio 0.85 [95% CI 0.75-0.96], p=0.011; covariate adjusted p=0.010). Candesartan reduced each of the components of the primary outcome significantly, as well as the total number of hospital admissions for CHF. The benefits of candesartan were similar in all predefined subgroups, including patients receiving baseline beta blocker treatment. The addition of candesartan to ACE inhibitor and other treatment leads to a further clinically important reduction in relevant cardiovascular events in patients with CHF and reduced left-ventricular ejection fraction.

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Sustained effect of intensive treatment of type 1 diabetes mellitus on development and progression of diabetic nephropathy: the Epidemiology of Diabetes Interventions and Complications (EDIC) study.

(2003)

The Diabetes Control and Complications Trial (DCCT) demonstrated the benefits of intensive treatment of diabetes in reducing glycemic levels and slowing the progression of diabetic nephropathy. The DCCT cohort has been examined annually for another 8 years as part of the follow-up Epidemiology of Diabetes Interventions and Complications (EDIC) study. During the EDIC study, glycemic levels no longer differed substantially between the 2 original treatment groups. To determine the long-term effects of intensive vs conventional diabetes treatment during the DCCT on kidney function during the EDIC study. Observational study begun in 1993 (following DCCT closeout) in 28 medical centers in the United States and Canada. Participants were 1349 (of 1375) EDIC volunteers who had kidney evaluation at years 7 or 8. Development of microalbuminuria, clinical-grade albuminuria, hypertension, or increase in serum creatinine level. Results were analyzed by intention-to-treat analyses, comparing the 2 original DCCT treatment groups. New cases of microalbuminuria occurred during the EDIC study in 39 (6.8%) of the participants originally assigned to the intensive-treatment group vs 87 (15.8%) of those assigned to the conventional-treatment group, for a 59% (95% confidence interval [CI], 39%-73%) reduction in odds, adjusted for baseline values, compared with a 59% (95% CI, 36%-74%) reduction at the end of the DCCT (P<.001 for both comparisons). New cases of clinical albuminuria occurred in 9 (1.4%) of the participants in the original intensive-treatment group vs 59 (9.4%) of those in the original conventional-treatment group, representing an 84% reduction in odds (95% CI, 67%-92%), compared with a reduction of 57% (95% CI, -1% to +81%) at the end of the DCCT. Fewer cases of hypertension (prevalence at year 8, 29.9% vs 40.3%; P<.001) developed in the original intensive-treatment group. Significantly fewer participants reached a serum creatinine level of 2 mg/dL or greater in the intensive-treatment vs the conventional-treatment group (5 vs 19, P =.004), but there were no differences in mean log clearance values. Although small numbers of patients required dialysis and/or transplantation, fewer patients experienced either of these outcomes in the intensive group (4 vs 7, P =.36). The persistent beneficial effects on albumin excretion and the reduced incidence of hypertension 7 to 8 years after the end of the DCCT suggest that previous intensive treatment of diabetes with near-normal glycemia during the DCCT has an extended benefit in delaying progression of diabetic nephropathy.

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Proteinuria, a target for renoprotection in patients with type 2 diabetic nephropathy: lessons from RENAAL.

Dick de Zeeuw, Giuseppe Remuzzi, Hans-Henrik Parving … (2004)

Proteinuria or albuminuria is an established risk marker for progressive renal function loss. Albuminuria can be effectively lowered with antihypertensive drugs that interrupt the renin-angiotensin system (RAS). We investigated whether albuminuria could not only serve as a marker of renal disease, but also function as a monitor of the renoprotective efficacy of RAS intervention by the angiotensin II (Ang II) antagonist, losartan, in patients with diabetic nephropathy. The data from the RENAAL (Reduction in End Points in Noninsulin-Dependent Diabetes Mellitus with the Angiotensin II Antagonist Losartan) study, a double-blind, randomized trial, were used to examine the effects of losartan on the renal outcome [i.e., the primary composite end point of doubling of serum creatinine, end-stage renal disease (ESRD) or death] in 1513 type 2 diabetic patients with nephropathy. We examined the effect of the degree of albuminuria at baseline, initial antiproteinuric response to therapy, and the degree of remaining (residual) albuminuria on renal outcome (either the primary composite end point of RENAAL or ESRD). We also evaluated the contribution to renal protection of the antiproteinuric effect of losartan independently of changes in blood pressure. Baseline albuminuria is almost linearly related to renal outcome, and is the strongest predictor among all measured well-known baseline risk parameters. After adjusting for baseline risk markers of age, gender, race, weight, smoking, sitting diastolic blood pressure, sitting systolic blood pressure, total cholesterol, serum creatinine, albuminuria, hemoglobin, and hemoglobin A(1c) (HbA(1c)) patients with high baseline albuminuria (> or =3.0 g/g creatinine) showed a 5.2-fold (95% CI 4.3-6.3) increased risk for reaching a renal end point, and a 8.1-fold (95% CI 6.1-10.8) increased risk for progressing to ESRD, compared to the low albuminuria group (<1.5 g/g). The changes in albuminuria in the first 6 months of therapy are roughly linearly related to the degree of long-term renal protection: every 50% reduction in albuminuria in the first 6 months was associated with a reduction in risk of 36% for renal end point and 45% for ESRD during later follow-up. Albuminuria at month 6, designated residual albuminuria, showed a linear relationship with renal outcome, almost identical to the relationship between baseline albuminuria and renal risk. Losartan reduced albuminuria by 28% (95% CI -25% to -36%), while placebo increased albuminuria by 4% (95% CI +8% to -1%) in the first 6 months of therapy. The specific (beyond blood pressure lowering) renoprotective effect of the Ang II antagonist, losartan, in this study is for the major part explained by its antialbuminuric effect (approximately 100% for the renal end point, and 50% for ESRD end point). Albuminuria is the predominant renal risk marker in patients with type 2 diabetic nephropathy on conventional treatment; the higher the albuminuria, the greater the renal risk. Reduction in albuminuria is associated with a proportional effect on renal protection, the greater the reduction the greater the renal protection. The residual albuminuria on therapy (month 6) is as strong a marker of renal outcome as is baseline albuminuria. The antiproteinuric effect of losartan explains a major component of its specific renoprotective effect. In conclusion, albuminuria should be considered a risk marker for progressive loss of renal function in type 2 diabetes with nephropathy, as well as a target for therapy. Reduction of residual albuminuria to the lowest achievable level should be viewed as a goal for future renoprotective treatments.

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Author and article information

Journal

Journal ID (publisher-id): AJN

Journal ID (nlm-ta): Am J Nephrol

Journal ID (doi): 10.1159/issn.0250-8095

Title: American Journal of Nephrology

Publisher: S. Karger AG

ISSN (Print): 0250-8095

ISSN (Electronic): 1421-9670

Publication date Subscription-year: 2005

Publication date (Print): April 2005

Publication date (Electronic): 18 May 2005

Volume: 25

Issue: 2

Pages: 77-94

Affiliations

Joslin Diabetes Center, Harvard Medical School, Boston, Mass., USA

Article

Publisher ID: 84286 Other ID: Am J Nephrol 2005;25:77–94

DOI: 10.1159/000084286

PubMed ID: 15746541

SO-VID: 46e29ac9-e565-450e-b80c-ab9bb85ed86c

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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

Date received : 17 November 2004

Date accepted : 14 January 2005

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Figures: 5, Tables: 3, References: 186, Pages: 18

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Diabetic Nephropathy: The Proteinuria Hypothesis

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Abstract

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Karger: Nephrology

Most cited references 121

Effects of candesartan in patients with chronic heart failure and reduced left-ventricular systolic function taking angiotensin-converting-enzyme inhibitors: the CHARM-Added trial.

Sustained effect of intensive treatment of type 1 diabetes mellitus on development and progression of diabetic nephropathy: the Epidemiology of Diabetes Interventions and Complications (EDIC) study.

Proteinuria, a target for renoprotection in patients with type 2 diabetic nephropathy: lessons from RENAAL.

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Cited by 35

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