Urinary liver-type fatty acid-binding protein levels for differential diagnosis of idiopathic focal glomerulosclerosis and minor glomerular abnormalities and effect of low-density lipoprotein apheresis

Aims: Focal glomerulosclerosis (FGS) and minor glomerular abnormalities are kidney diseases characterized by massive proteinuria. Urinary liver-type fatty acid-binding protein (L-FABP), an intracellular carrier protein of free fatty acids, is expressed in proximal tubules of the human kidney. Patients with FGS show significant improvement with low-density lipoprotein (LDL) apheresis. The aim of the present study was to determine whether urinary L-FABP levels differ between patients with FGS and those with minor glomerular abnormalities and whether levels are altered by LDL apheresis. Patients and methods: There were 24 patients with minor glomerular abnormalities (nephrotic stage, n = 14, remission stage, n = 10), 17 patients with FGS, and 20 healthy age-matched subjects were included in the present study. Urinary L-FABP levels were measured by enzyme-linked immunosorbent assay and compared. All patients with minor glomerular abnormalities at the nephrotic stage received prednisolone for 6 months, and all FGS patients received some form of immunosuppression therapy with prednisolone, cyclophosphamide or mizoribine for 12 months. LDL apheresis was performed in eight FGS patients with drug-resistant nephrotic syndrome. Results: Urinary L-FABP levels were significantly higher in the 17 FGS patients (82.0 ± 44.4 μg/g.Cr) than in the 24 patients with minor glomerular abnormalities (10.2 ± 8.4 μg/g.Cr) (p < 0.01) and in the 20 healthy subjects (7.4 ± 4.2 μg/g.Cr) (p < 0.01). Urinary L-FABP levels differed little between nephrotic stage and remission stage in patients with minor glomerular abnormalities. Urinary L-FABP levels were significantly higher in the eight drug-resistant FGS patients (122.6 ± 78.4 μg/g.Cr) than in the nine drug-sensitive FGS patients (45.9 ± 32.0 μg/g.Cr). Urinary L-FABP levels did not correlate with levels of other clinical markers including serum creatinine, urinary protein, and urinary N-acetyl-β-D- glucosaminidase. In the eight drug-resistant FGS patients, LDL-apheresis significantly reduced urinary protein excretion (p < 0.01) and urinary L-FABP levels (p < 0.01). Conclusions: Urinary L-FABP may be a useful diagnostic indicator for differentiation between FGS and minor glomerular abnormalities. LDL apheresis may be effective in ameliorating tubulointerstitial lesions associated with FGS.