The basic mechanism for idiopathic FSGS still is obscure. Indirect evidence in humans and generation of FSGS by
oxidants in experimental models suggest a role of
free radicals. In vitro studies demonstrate a main role of
plasma albumin as
antioxidant, its modification representing a chemical marker of oxidative stress. With the use of complementary liquid chromatography electron spray ionization tandem mass spectrometry (LC-ESI-MS/MS) and biochemical methods,
plasma albumin was characterized in 34 patients with FSGS; 18 had received a renal transplant, and 17 had
IgM mesangial deposition. Patients with FSGS that was in remission or without recurrence after
transplantation had normal
plasma albumin, and the same occurred in patients with primary and secondary nephrites and with
chronic renal failure. In contrast, patients with active FSGS or with posttransplantation recurrence had oxidized
plasma albumin. This finding was based on the characterization of
albumin Cys 34 with an mass-to-charge ratio of 511.71 in triple charge that was consistent with the formation of a
cysteic acid carrying a sulfonic group (alb-SO(3)(-)). The exact mass of
albumin was increased accordingly (+48 Da) for incorporation of three
oxygen radicals. Direct titration of the free sulfhydryl group 34 of
plasma albumin and electrophoretic titration curves confirmed loss of free sulfhydryl group and formation of a fast-moving
isoform in all cases with disease activity. This is the first demonstration of in vivo
plasma albumin oxidation that was obtained with an adequate structural approach.
Albumin oxidation seems to be specific for FSGS, suggesting some pathogenetic implications.
Free radical involvement in FSGS may lead to specific therapeutic interventions.