Renal function, protein excretion, and pathology of Balkan endemic nephropathy. II. Protein excretion.

The urinary proteins of 40 patients with Balkan endemic nephropathy from the Tuzla region were examined using ultrathin-layer SDS pore-gradient polyacrylamide gel electrophoresis in combination with silver staining. The typical urinary protein spectrum contained immunoglobulin G, Tamm-Horsfall protein, transferrin, albumin, beta 2-microglobulin (beta 2m), immunoglobulin light chains, retinol-binding protein, and alpha 1-microglobulin (alpha 1m). Densitometric measurements were used to derive glomerular tubular protein ratios (GTPR) and to characterize protein excretion patterns in the 28 patients who excreted more than 150 mg/liter of protein. Results showed that proteinuria of Balkan nephropathy is predominantly tubular, consisting of low-molecular-weight species. The most commonly identified proteins were alpha 1m, light chains, retinol binding protein, and beta 2m. The pattern of proteinuria based on GTPR did not correlate with the underlying histology or the degree of renal failure. These findings, using the ultrathin-layer SDS pore-gradient method of protein separation, more accurately demonstrates the low-molecular-weight proteinuria characteristic for the early stages of BEN.