Human serum albumin cysteinylation is increased in end stage renal disease patients and reduced by hemodialysis: mass spectrometry studies

The aim of the present work was to monitor the covalent modifications of human serum albumin (HSA) in end stage renal diseases (ESRD) non-diabetic patients, before and after hemodialysis (HD), by direct infusion electrospray mass spectrometry (ESI-MS). Human serum samples were collected from healthy subjects (n = 10, 20-60 yr) and age-matched ESRD patients (n = 8) before and after HD, purified by affinity chromatography and analyzed by a triple-quadrupole mass spectrometer. The deconvoluted spectra from healthy subjects were all characterized by three peaks attributed to non-glycated mercaptoalbumin (HSA-SH) and to the corresponding adducts with cysteine (HSA-Cys) and glucose (HSA-Glc); relative contents: mercaptoalbumin in both glycated and non-glycated form, HSA-SHt (74 + 6%), HSA-Cys (26 +/- 5%) and HSA-Glc (24 +/- 3%). HSA isolated from ESRD patients before HD was characterized by a significant reduction of HSA-SHt (42 +/- 7%), and by a concomitant increase of the HSA-Cys adduct (58 +/- 7%). Hemodialysis significantly reduced the cysteinylated form (37 +/- 7%) and restored HSA-SHt (63 + 8%) in all the ESRD patients. The mechanism of thiol oxidation and cysteinylation was then studied by mass spectrometry, using LQQCPF as a model peptide and H2O2 as an oxidizing agent.