Rationale

Albumin is the most important antioxidant substance in plasma and performs many physiological functions. Furthermore, albumin is the major carrier of endogenous molecules and exogenous ligands.

The goal of this study was to detect modification in the expression of albumin and/or posttranslational modifications of their structure in patients with end stage renal disease and fragments thereof in patients with renal disease.

Patients and Methods

Serum samples from 19 adult patients treated by maintenance hemodialysis (MHD) were analyzed using sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and two-dimensional electrophoresis (2DE). Spots of interest were identified by mass spectrometry analysis. In addition, the 2DE maps were incubated with a human anti-albumin polyclonal antibody.

Results

SDS-PAGE gels, 2DE maps and matrix-assisted laser desorption/ionization time of flight analysis indicated over-expression of low-molecular weight proteins (LMWP) in sera from patients.

Unexpectedly, another 15 spots with estimated M r of 12.5–29 kDa from the 2DE maps of six patients were identified as fragments of albumin [Fig.1]. 2D immunoblotting of sera from 12 other patients detected numerous albumin fragments.

It is reasonable to hypothesize that proteolytic fragmentation of serum albumin is due to a higher susceptibility to proteases, induced by oxidative stress. These modifications could affect some physiological functions of albumin and have a patho-physiological role in uremic syndrome. The clinical relevance of the fragmentation of albumin has not yet been established.

Conclusions

Uremia appears to facilitate the fragmentation of albumin and/or the retention of albumin fragments in blood. Proteomic analysis of serum allows the identification of over-expressed proteins and can detect post-translational modifications of serum proteins, hitherto hidden, using standard laboratory techniques.