SDS Electrophoresis on Gradient Polyacrylamide Gels as a Semiquantitative Tool for the Evaluation of Proteinuria

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 m(2), 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), alpha 1-microglobulin, retinol-binding protein, neutrophil gelatinase-associated lipocalin, cystatin C, and beta 2-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.

Automated summary

Proteinuria, an important sign of kidney diseases, can be differentiated using immunochemical detection or urinary proteins electrophoresis. The study aims to use SDS-PAGE with commercially available 4-20% gradient gels to detect and differentiate proteinuria. The results showed distinct protein patterns associated with glomerular and tubular proteinuria, and these patterns were related to different clinical characteristics. The SDS-PAGE separation is a reliable technique to diagnose proteinuria and differentiate its types.