Urinary Proteome Analysis Enables Assessment of Renoprotective Treatment in Type 2 Diabetic Patients with Microalbuminuria

Sten Andersen; Harald Mischak; Petra Zürbig; Hans-Henrik Parving; Peter Rossing

Disclosures

BMC Nephrology. 2010;11 

In This Article

Background

At present more than 170 million people worldwide have diabetes and the number is expected to double within the next 20 years mainly due to an epidemic increase in the prevalence of type 2 diabetes.[1] Type 2 diabetes is associated with an increased occurrence of cardiovascular disease and approximately 40% of all diabetic patients are at risk of developing diabetic nephropathy which has become the leading cause of end-stage renal disease (ESRD) in the Western world.[2] Therefore, the early identification and subsequent end-organ protective treatment of all patients at risk for ESRD is of outmost importance. Patients with persistent microalbuminuria [urinary albumin excretion (UAE) between 30 and 300 mg/24 hours] have a 10 to 20 times increased risk of developing diabetic nephropathy as compared to patients with normoalbuminuria.[2] In addition, the occurrence of microalbuminuria is associated with an increased risk of premature death due to cardiovascular disease.[3]

Reduction of UAE by blockade of the renin-angiotensin-aldosterone system (RAAS) has emerged as a key treatment goal for both reno- and cardiovascular protection.[4,5] Data from the large clinical "Irbesartan in Patients with type 2 diabetes and Microalbuminuria" (IRMA2) study[6] firmly demonstrated that treatment with the angiotensin II receptor blocker (ARB) Irbesartan, 300 mg once daily, reduces UAE and the risk of progression to overt diabetic nephropathy in hypertensive patients with type 2 diabetes and persistent microalbuminuria. Furthermore, in type 2 diabetic patients with more advanced renal disease, ARBs have been shown to reduce the risk of reaching the combined renal end point of doubling in serum creatinine, ESRD, or death.[5,7] Since 2002, ARBs have consequently been recommended as first-line therapy in hypertensive type 2 diabetic patients with microalbuminuria or overt diabetic nephropathy according to guidelines from the American Diabetes Association.[8]

Recently, we and others demonstrated that diabetic nephropathy and chronic renal disease in general are reflected by specific peptides and proteins in urine,[9–24] and the human urinary proteome has been extensively investigated to gain insight about disease processes affecting the kidney and the urogenital tract.[12,25–28] Urinary proteins and peptides originate not only from glomerular filtration, but also from tubular secretion, epithelial cells shed from the kidney and urinary tract, secreted exosomes,[29] and seminal secretions.[30–32] Thus, in principle, urine is a rich source of biomarkers for a wide range of diseases due to specific changes in its proteome.[33–36] Urine is a preferred body fluid for proteome analysis, as it is quite stable, probably due to the fact that it is "stored" for hours in the bladder, hence proteolytic degradation by endogenous proteases, a major obstacle in proteomics studies focusing on blood,[37] may be essentially complete by the time of voiding.[38,39] This also enabled the establishment of human urine reference standard samples.[40] In pilot studies aiming toward differential diagnosis of certain types of CKD we could show that several peptides are differentially excreted in the urine of patients with different chronic kidney diseases compared to healthy individuals.[41,42] An optimized protocol for sample preparation and analysis has been developed, that includes removal of proteins above 25 kDa without significant loss of low-molecular-weight urinary components.[43] Using this protocol, urinary biomarkers enabling differential diagnosis of specific single chronic renal diseases (IgA nephropathy, diabetic nephropathy, and ANCA-associated vasculitis) with good sensitivity and specificity in blinded data-sets could be identified.[13,19,21,44] Employing previously established biomarkers and biomarker patterns as classifiers,[19,20] we investigated if a therapeutic benefit of Irbesartan in microalbuminuric type 2 diabetes patients can by displayed by proteomic changes in urine. In addition, we aimed at identifying those peptides that show significant changes upon Irbesartan treatment, as these may reveal further insights into the pathophysiology of disease, and allow assessment of therapeutic efficacy.

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