Proteins continually undergo spontaneous oxidation reactions, which lead to changes in structure and function. The quantitative assessment of protein oxidation adducts provides information on the level of exposure to reactive precursor compounds with a high oxidizing potential and reactive oxygen species (ROS). In the present work, we introduce N6-(2-hydroxyethyl)lysine as a novel marker based on the ratio of glycolaldehyde and its oxidized form glyoxal. The high analytical potential was proven with a first set of patients undergoing hemodialysis versus healthy controls, in comparison with well-established parameters for oxidative stress. In vitro experiments with N1- t-BOC-lysine and N1- t-BOC-arginine enlightened the mechanistic relationship of glycolaldehyde and glyoxal. Oxidation was strongly dependent on the catalytic action of the ε-amino moiety of lysine. Investigations on the formation of N6-carboxymethyl lysine revealed glycolaldehyde-imine as the more reactive precursor, even though an additional oxidative step is required. As a result, a novel and very effective alternative mechanism was unraveled.
Keywords: Maillard reaction; carbohydrate chemistry; carboxymethyl lysine; glycolaldehyde; glyoxal; hemodialysis; high-performance liquid chromatography; hydroxyethyl lysine; mass spectrometry; oxidative stress; plasma.