Genomics and proteomics have been useful in many different areas of medicine and health science as an aid to discover new biomarker for disease diagnosis or staging and as a tool to predict or monitor treatment response or toxicity. Human serum albumin (HSA) exists in both reduced and oxidized forms, and the percentage of oxidized albumin increases in several diseases. However, little is known regarding the pathological and physiological significance of oxidation due to poor characterization of the precise structural and functional properties of oxidized HSA. Here, we characterize both the structural and functional differences between reduced and oxidized HSA. Using LC-ESI TOF MS and FT MS analysis, we determined that the major structural change in oxidized HSA in healthy human plasma is a disulfide-bonded cysteine at the thiol of Cys34 of reduced HSA. Based on this structural information, we prepared standard samples of purified HSA, e.g. non-oxidized (intact purified HSA which mainly exists in reduced form), mildly oxidized and highly oxidized HSA. Using these standards, we demonstrated several differences in functional properties of HSA including protease susceptibility, ligand-binding affinity and antioxidant activity. From these observations, we conclude that an increased level of oxidized HSA may impair HSA function in a number of pathological conditions. In addition, we determined blood and plasma sampling conditions for the accurate measurement of the oxidized albumin ratio in plasma by using EST-TOF MS screening.
