Presence of Protein Fragments in Urine of Critically Ill Patients with Acute Renal Failure: A Nephrologic Enigma

Abstract

Predicting complications in intensive care units (ICUs) is an important step in the care of critically ill patients. Intensive care specialists have developed numerous prognostication tools for patients admitted to the ICU; however, although useful, many of these tools are not applicable in a clinical setting, and multiple severity-of-illness scores often underestimate hospital mortality in several conditions (1, 2 ).Many acute pathologic states, such as burns, trauma, bleeding, and sepsis, are associated with the induction of a "systemic inflammatory response", which is characterized by the release of pro-inflammatory mediators and the activation of different types of cellular elements (3-6 ). This response primarily involves endothelial cells and leukocytes (7)(8)(9). It is possible to use renal function as an early marker for systemic illness because kidney involvement is a recognized complication of several systemic diseases. Acute renal failure (ARF), usually attributable to intrarenal hemodynamic changes, often complicates the clinical course of critically ill patients (10 -12 ). Microalbuminuria has been proposed as a marker of capillary leak severity in the ICU (13,14 ). It has previously been demonstrated that urinary albumin degrades into multiple fragments in meningococcal sepsis and that the quantity of degraded albumin is associated with severity (15 ).Since April 2003, we have analyzed untimed urine samples from critically ill patients with ARF in ICUs: dipstick test and urine sediment analysis were performed on all samples, and none showed massive leukocyturia. The proteinuria is typed by quantitative (nephelometry) (16, 17 ) and qualitative (immunofixation) (18 ) immunologic techniques and by sodium dodecyl sulfate-agarose gel electrophoresis (SDS-AGE) (19 ), with retinol-binding protein (21 kDa) and ␣ 1 -microglobulin (31 kDa) considered as markers of tubular damage; albumin (67 kDa), transferrin (80 kDa), and IgG (150 kDa) as markers of glomerular injury; and ␣ 2 -macroglobulin (725 kDa) as a marker of postrenal proteinuria. In addition, we measure total urinary proteins by the biuret (20 ) and pyrogallol red assays. All samples were stored at 4°C after centrifugation (400g for 5 min) and were analyzed within 3-24 h. Storage in a refrigerator (4°C) did not change the results.Here we report on 10 cases (9 males and 1 female; age range, 40 -79 years; 18.1% of all screened patients) with ARF in whom we found evidence of urinary protein degradation. All patients had a prerenal cause of ARF; only one patient was not oliguric and did not need renal replacement therapy. Five patients died, and five had renal function recovery.SDS-AGE performed at the time of the nephrologic visit and diagnosis revealed a smeared band of proteins and protein fragments, covering the molecular mass range between 10 and 300 kDa, and an absence of the typical bands for the single proteins.The SDS-AGE migration patterns of one of these patients on 3 consecutive days are shown in Fig. 1; after 24 and 48 h, the bands for albu...

Measurement of Protein Glycation, Glycated Peptides, and Glycation Free Adducts

“…From quantitative LC-MS/MS analysis, we have been able to detect AGE (and oxidation adduct) enrichment on low molecular mass peptides in vivo only in portal venous plasma of human subjects and not in peripheral venous plasma (18,33). Peptides from incomplete proteolysis are found in vivo (34,35) but our LC-MS/MS analysis indicates that, except in portal venous plasma, they are not enriched with glycation, oxidation, or nitration adduct residues. Some glycation free adducts have been detected previously: for example, plasma pentosidine in uremia as an indicator of dialysis efficiency (36).…”

Human Serum Low Molecular Mass Prostate-Specific Antigen as Biomarker

“…It can produce many distinct low molecular mass species from a particular higher molecular mass protein. The fragmentation pattern may reflect different pathogenic processes, and protein fragments have already been recognized as diagnostic and prognostic biomarkers in different types of cancer, renal and connective tissue diseases, etc (34, 39, 40). Bearing in mind many limitations of this study regarding selection of fPSA-immunoreactive fragments as well as sample heterogeneity in distinct groups, the results obtained add new value to low molecular mass PSA-immunoreactive species in sera.…”