The aim of this study is to detect eventual modification in the expression of plasma proteins and/or post-translational modifications of their structure in end-stage renal disease.
Patients and Methods
Serum samples from 19 adult patients treated by maintenance hemodialysis were analyzed by using SDS-PAGE and two-dimensional electrophoresis (2DE). Spots of interest were identified by mass spectrometry analysis. Moreover, the 2DE maps were incubated with a human antialbumin polyclonal antibody.
SDS-PAGE gels, 2DE maps and MALDI-TOF analysis indicated the over-expression, in sera from patients, of low-molecular weight proteins (LMWP). Unexpectedly, other 15 spots with estimated Mr 12.5-29 kDa from 2DE maps of 6 patients were identified as fragments of albumin. 2-D immunoblotting of sera from 12 other patients detected numerous albumin fragments. Oxidative stress and inflammation are markedly increased in ESRD patients. Oxidative stress can affect the structure of albumin and increase the susceptibility of the molecule to the activity of proteolytic enzymes, thus justifying the presence of albumin fragments in the serum of ESRD patients. The clinical significance of albumin fragmentation in the pathogenesis of uremic syndrome remains uncertain. However, it is possible that antioxidant capacity, binding and transport functions of albumin be affected by post-translational modifications of the molecule. It is important to note that proteomic techniques allowed to highlight these post-translational modifications of albumin, which remained undetected hitherto hidden, using standard laboratory techniques.
A relevant amount of fragments of albumin is detectable in the serum of maintenance hemodialysis patients. Uremia seems to facilitate the fragmentation of albumin and/or the retention in the blood of albumin fragments.