A simple method to detect an albumin permeability factor in the idiopathic nephrotic syndrome

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Several investigators have detected an albumin permeability factor in the serum of patients with the idiopathic nephrotic syndrome (INS), that is, minimal change disease (MCD) or focal segmental glomerulosclerosis (FSGS), but the methods used have been complex. We describe here a simpler method using cultured rat glomerular epithelial cell monolayers grown to confluence on Millicell filters, which allow sampling of apical and basolateral media. 125I-labeled human serum albumin (125I-HSA) was added to the basolateral compartment, and its leakage across the epithelial cell monolayer into the apical compartment was measured. In untreated cells (negative control), the albumin leakage reached 5.3% at 18 hours. Cell monolayers fixed with 95% ethanol (positive control) showed 62% leakage. Sera from three out of four patients with MCD and three out of four with FSGS resulted in considerable albumin leakage, whereas sera from nine patients with other types of nephrotic renal disease and five normal subjects caused no leakage. This study shows that the Millicell system provides a simple and useful method to screen for permeability factors in the INS.