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Proteinuria is an important sign of kidney diseases. Different protein patterns in urine associated with glomerular, tubular and overload proteinuria may be differentiated using the immunochemical detection of indicator proteins or via urinary proteins electrophoresis. Our aim was to characterize sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE) using commercially available 4–20% gradient gels as a method to detect and differentiate proteinuria. Our laboratory-based study used excess urine samples collected for routine diagnostic purposes from adult patients of a tertiary-care hospital, including patients with albumin/creatinine < 30 mg/g and patients with dipstick proteinuria. The limit of albumin detection was estimated to be 3 mg/L. In 93 samples with albumin/creatinine < 30 mg/g, an albumin fraction was detected in 87% of samples with a minimum albumin concentration of 2.11 mg/L. The separation of 300 urine samples of patients with proteinuria revealed distinct protein patterns differentiated using the molecular weights of the detected proteins: glomerular (albumin and higher molecular weights) and two types of tubular proteinuria ("upper" ≥20 kDa and "lower" with lower molecular weights). These patterns were associated with different values of the glomerular filtration rate (median 66, 71 and 31 mL/min/1.72 m2, respectively, p = 0.004) and different proportions of multiple myeloma and nephrological diagnoses. As confirmed using tandem mass spectrometry and western blot, the SDS-PAGE protein fractions contained indicator proteins including immunoglobulin G, transferrin (glomerular proteinuria), α1-microglobulin, retinol-binding protein, neutrophil gelatinase-associated lipocalin, cystatin C, and β2-microglobulin (tubular), immunoglobulin light chain, myoglobin, and lysozyme (overflow). SDS-PAGE separation of urine proteins on commercially available 4–20% gradient gels is a reliable technique to diagnose proteinuria and differentiate between its main clinically relevant types. [ABSTRACT FROM AUTHOR]

Proteinuria is an important sign of kidney diseases. Different protein patterns in urine associated with glomerular, tubular and overload proteinuria may be differentiated using the immunochemical detection of indicator proteins or via urinary proteins electrophoresis. Our aim was to characterize sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE) using commercially available 4–20% gradient gels as a method to detect and differentiate proteinuria. Our laboratory-based study used excess urine samples collected for routine diagnostic purposes from adult patients of a tertiary-care hospital, including patients with albumin/creatinine < 30 mg/g and patients with dipstick proteinuria. The limit of albumin detection was estimated to be 3 mg/L. In 93 samples with albumin/creatinine < 30 mg/g, an albumin fraction was detected in 87% of samples with a minimum albumin concentration of 2.11 mg/L. The separation of 300 urine samples of patients with proteinuria revealed distinct protein patterns differentiated using the molecular weights of the detected proteins: glomerular (albumin and higher molecular weights) and two types of tubular proteinuria (“upper” ≥20 kDa and “lower” with lower molecular weights). These patterns were associated with different values of the glomerular filtration rate (median 66, 71 and 31 mL/min/1.72 m2, respectively, p = 0.004) and different proportions of multiple myeloma and nephrological diagnoses. As confirmed using tandem mass spectrometry and western blot, the SDS-PAGE protein fractions contained indicator proteins including immunoglobulin G, transferrin (glomerular proteinuria), α1-microglobulin, retinol-binding protein, neutrophil gelatinase-associated lipocalin, cystatin C, and β2-microglobulin (tubular), immunoglobulin light chain, myoglobin, and lysozyme (overflow). SDS-PAGE separation of urine proteins on commercially available 4–20% gradient gels is a reliable technique to diagnose proteinuria and differentiate between its main clinically relevant types.

Urine protein electrophoresis is often required for diagnosis and monitoring of urological or renal diseases and lymphoid hemopathies. We here report an uncommon urine protein electrophoresis result. The test was performed using agarose gel electrophoresis and capillary electrophoresis. It was a monoclonal peak of unknown significance migrating with gammaglobulins. Scientific literature and the tests performed demonstrated that it was myoglobin. In fact, myoglobin (17 kDa) is freely filtered by the glomerulus and normally reabsorbed by the tubules. If tubule capacity for reabsorption is exceeded, its presence results in overcharging proteinuria. Myoglobinuria helped diagnose rhabdomyolysis in our patient. Thus, the analysis of unknown peaks, can provide information on symptoms but also underlying pathologies, which may be of clinical interest. [ABSTRACT FROM AUTHOR]

Injury of the renal tubulointerstitial compartment is recognized to play an important role in hypertension. Its damage may in turn, impair the activity of vasodepressor systems, like the kallikrein–kinin, in blood pressure regulation. The overload proteinuria model induces tubulointerstitial injury with activation of the renin–angiotensin system, but renal kallikrein and the development of hypertension have not received special attention. Sprague–Dawley rats received seven intraperitoneal doses of bovine serum albumin (BSA) 2 g/day under normosodic diet and were hydrated ad libitum. A second group received a high potassium diet to stimulate kallikrein production during the previous four weeks and while under BSA administration. A third one received potassium and BSA in the same schedule, but with the kinin B2 receptor antagonist, HOE140, added during the protein load phase. A control group received seven saline injections. Kallikrein protein was detected by immune labeling on renal sections and enzymatic activity in the urine. The BSA group showed massive proteinuria followed by intense tubulointerstitial damage. Blood pressure increased after the third dose in BSA animals, remaining elevated throughout the experiment, associated with significant reductions in renal expression and urinary activity of kallikrein, compared with controls. An inverse correlation was found between blood pressure and immunohistochemistry and urinary activity of kallikrein. Potassium induced a significant increase in both urinary activity and renal kallikrein expression, associated with significant reduction in blood pressure. The HOE140 antagonist blunted the antihypertensive effect of kallikrein stimulation in proteinuric rats. Loss of renal kallikrein, produced by tubulointerstitial injury, may participate in the pathogenesis of the hypertension observed in this model.Kidney International (2006) 69, 53–59 doi:10.1038/sj.ki.5000005 [ABSTRACT FROM AUTHOR]

Objective: To examine the role of renal processing in the turnover of circulating albumin in the model of reversible overload proteinuria. Specifically, this study determines whether proteinuria due to hyperalbuminemia may be attributed to saturation of renal cell processing of albumin or alterations in diffusive/convective transport of albumin across the glomerular capillary wall. Methods: Overload proteinuria was induced in male Wistar rats by daily intraperitoneal injections of 1.5 g bovine serum albumin (BSA; endotoxin free) for 3 days. Plasma concentration and urinary excretion of total protein and rat serum albumin (RSA) were determined by the biuret assay and radioimmunoassay, respectively. Glomerular size selectivity was assessed by examining the fractional clearance (FC) of neutral [³H]Ficoll using a short-term, steady-state approach. Cellular processing was examined by size exclusion chromatography analysis of urinary [14C] albumin and [14C] transferrin structural integrity. Results: Total protein excretion (n = 4-15) increased 7-fold in BSA-treated rats (58 ± 26 mg/24 h at baseline vs. 417 ± 259 mg/24 h at day 3), while intact RSA excretion (n = 4-6) increased 200-fold (0.27 ± 0.15 mg/24 h vs. 53 ± 26 mg/24 h) despite a significant decrease in its plasma concentration. Total protein and albumin excretion returned to basal levels by day 7 (82 ± 16 mg/24 h and 0.93 ± 0.42 mg/24 h, respectively). FC of [³H}] Ficoll of equivalent size to albumin did not change in BSA- treated rats as compared to vehicle controls. Tubular lysosomal processing of proteins was altered at peak proteinuria, as determined by changes in the structural integrity of urinary [14C] albumin, as well as [14C]transferrin, but returned to normal by day 7. Conclusions: This study demonstrates the lack of proportionality between changes in plasma concentration and urinary excretion of albumin, as well as the lack of change in the glomerular size selectivity to albumin. The profound but reversible changes in the amount and integrity of excreted protein suggest that cell-mediated processes are saturated by albumin concentrations, leading to the development of proteinuria in this model. [ABSTRACT FROM AUTHOR]