Albuminuria: a Great Risk Marker, but an Underestimated Target in Diabetes
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SECTION II Albuminuria: A Great Risk Marker, but an Underestimated Target in Diabetes 1 DICK DE ZEEUW, MD and cardiovascular disease progression in 2 ITAMAR RAZ, MD advanced diabetes, increased urinary al- bumin levels have their separate predic- tive power for risk of organ failure (3). iabetes is a growing disease with a the very early stages of the disease. More- An increased renal and cardiovascu- potentially devastating outcome. over, new antihypertensive therapies not lar risk profile is also observed even when D Diabetic patients run a great risk of only lower blood pressure, but also re- smaller amounts of albumin are present in developing multiple organ dysfunction duce albuminuria. We will address the the urine (microalbuminuria: 30–300 and ultimately organ failure. The current need of not only measuring the risk mg/day). Microalbuminuria heralds dia- approach of patients with diabetes is first marker, but also targeting therapies to betic nephropathy as well as cardiovascu- to assess their risk profile by measuring lower albuminuria. Finally, the individual lar risk (4,5). Although other risk factors risk factors such as glucose level, systemic response to such therapies appears to be (mainly increased blood pressure) already blood pressure, blood lipids, body highly variable, offering us opportunities play a major role in this stage, microalbu- weight, and smoking. Second, to reduce to optimize organ protection by individ- minuria also has important independent the risk, the patient is advised to make a ualizing therapies with the goal to over- value in estimating the cardiovascular and lifestyle change (lose weight and stop come therapy resistance. renal risk of a diabetic patient. smoking) and to take medication that reg- Clearly, diabetes constitutes a multi- Despite the clear power of using the ulates glucose and lowers blood pressure factorial disease in its organ damage (and level of albumin for marking renal and and cholesterol. This approach has in- maybe even in its cause). This forms a cardiovascular risk, the measurement if deed resulted in a slowing of progressive sound reason to look for multiple targets still markedly underused in worldwide organ dysfunction and has substantially (next to optimization of treating existing practice (6). One of the reasons for this prolonged life. targets). under use may be the fact that there is not However, the residual risk of diabetic yet a specific therapy that lowers albu- patients, despite “optimal” treatment of ALBUMINURIA AS A RISK minuria specifically. For other risk these risk factors, is still extremely high, MARKER — Large amounts of albu- factors, such as high glucose and hyper- and the number of patients is dramatically min in the urine (Ͼ300 mg/day) indicate tension, drugs are available to lower these growing. This has urged the medical pro- a late stage of diabetic renal disease and risk markers, with associated reduction of fession to improve risk profiling and de- indicate, next to loss of filtration rate, the risk. Currently, increased levels of albu- sign new therapeutic strategies to further degree of kidney damage. In addition, min are reduced by antihypertensive reduce existing risk. In addition, the however, the degree of increased albumin drugs that intervene in the renin- search for early disease markers was in- loss also heralds an increased chance of angiotensin-aldosterone system (RAAS) tensified with the goal to apply preventive losing kidney function. In fact, the more (7,8). Because such drugs are the recom- therapeutic measures in early stages of albumin is lost in the urine, the more mended therapy in diabetes, most doctors disease, instead of waiting until the dis- chance the individual has on reaching thus see no additive value in measuring ease had fully developed. end-stage renal disease (1). Intriguingly, urine albumin. The following paragraphs The next paragraphs will address the this predictive power of increased albu- will give reasons for measuring urine al- status of a “new” cardiovascular and renal min excretion does not only predict renal bumin in all individuals with diabetes. risk marker: increased levels of albumin progressive disease, but it also predicts an in the urine. This so-called albuminuria increased risk for cardiovascular disease ORGAN-PROTECTIVE not only marks risk in advanced stages of (2). Although classical risk factors such as PROPERTIES OF diabetic disease, but also indicates risk in hypertension play a major role in renal ALBUMINURIA LOWERING —As ●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●● mentioned above, intervention in the RAAS using antihypertensive drugs like From the 1Department of Clinical Pharmacology, University Medical Center Groningen, University of Gro- 2 ACE inhibitors or angiotensin II receptor ningen, Groningen, the Netherlands; and the Diabetes Unit, Department of Medicine, Hadassah University blockers (ARBs) are proven to be associ- Hospital, Ein-Karem, Jerusalem, Israel. ϳ Address correspondence and reprint requests to D. de Zeeuw, Department of Clinical Pharmacology, ated with substantial reductions of 50% University Medical Center Groningen, Sector F, PO Box 169, 9700 AD Groningen, the Netherlands. E-mail: in albuminuria both in microalbuminuric [email protected]. and macroalbuminuric patients. Several D.d.Z. has been a paid consultant for Novartis Pharmaceuticals, Abbott Laboratories, Keryx Biopharma- studies have demonstrated that this low- ceuticals, Inc., and AstraZeneca Pharmaceuticals; I.R. has been a paid consultant for Pfizer, Johnson & Johnson, sanofi-aventis, Keryx Biopharmaceuticals, Inc., Andromeda, and Merck Sharp & Dohme. ering of albuminuria is associated with re- This article is based on a presentation at the 1st World Congress of Controversies in Diabetes, Obesity and duction of renal risk, independent of the Hypertension (CODHy). The Congress and the publication of this article were made possible by unrestricted blood pressure–lowering effect of these educational grants from MSD, Roche, sanofi-aventis, Novo Nordisk, Medtronic, LifeScan, World Wide, Eli drugs (9,10). Recently, three important Lilly, Keryx, Abbott, Novartis, Pfizer, Generx Biotechnology, Schering, and Johnson & Johnson. Abbreviations: ARB, angiotensin II receptor blocker; RAAS, renin-angiotensin-aldosterone system. large trials were published that specifi- DOI: 10.2337/dc08-s248 cally targeted renal risk in type 2 diabetic © 2008 by the American Diabetes Association. patients using ARBs. The results of these S190 DIABETES CARE, VOLUME 31, SUPPLEMENT 2, FEBRUARY 2008 de Zeeuw and Raz trials showed that ARBs are indeed effec- tive in lowering blood pressure as well as albuminuria. In the long term, ARB treat- ment resulted in renal protection both in advanced diabetic nephropathy (11,12) and early diabetic renal disease (13). This renal protection goes beyond the blood pressure–lowering capacity of ARBs, since the blood pressure in the compara- tor arms of these trials (using conven- tional antihypertensive drugs) was the same as in the ARB arms. Intriguingly, al- buminuria was only lowered in the ARB arms of these trials. Although these clini- cal trials cannot give an answer to the question whether this lowering of albu- minuria is the “cause” of the renoprotec- tive effect of ARBs, post hoc analysis of both the Irbesartan Diabetic Nephropa- thy Trial and the Reduction of Endpoints Figure 1—The individual degree of proteinuria lowering (after several weeks of therapy) is a in NIDDM with the Angiotensin II Antag- predictor for long-term (years) renal protection: the more proteinuria is lowered, the less the onist Losartan (RENAAL) trial clearly glomerular filtration rate (GFR) will decline during follow-up, both in diabetic (15) and non- diabetic renal (16) disease patients. showed that the more one reduces albu- minuria, the more patients are protected against progressive renal disease (1,14). against cardiovascular and renal disease tients who had a drop in albuminuria in This appears not only to be applicable to progression. the first months of therapy showed a clear renal protection, but also to cardiovascu- The above findings with albuminuria renal protection during follow-up despite lar protection, since the level of albumin- constitute sound reason to measure albu- a rise in the blood pressure. In other uria reduction was also associated with minuria in each diabetic individual to words, monitoring therapy-induced the level of cardiovascular risk (2). monitor the effectiveness of RAAS inter- changes in albumin in individual patients Thus, albuminuria is not only a good vention therapy. However, the current is important independent of blood pres- risk marker, but the therapy-induced fall guideline tells us that antihypertensive sure changes, since it predicts the effec- of albuminuria is also predictive of renal therapy like RAAS intervention is targeted tiveness of renal protection. and cardiovascular protection. toward high blood pressure (and not to high albumin). In fact, one could argue FUTURE THERAPIES FOR INDIVIDUAL VARIABILITY that the variability in albuminuria reduc- (FURTHER) ALBUMINURIA IN THERAPY RESPONSE — Al- tion is likely paralleled by a similar vari- REDUCTION — Despite the fact that though RAAS intervention is clearly effec- ability in blood pressure–lowering we are able to reduce renal (and cardio- tive in lowering albuminuria, with an response. If true, than one would not vascular) risk in diabetic patients with average reduction around 50%, the indi- need to measure albuminuria,